Shock absorbers


In recent years, advances in the development of modern vehicles and increasing engine performance and speed in particular have brought about sharp focus on chassis technology as an area of development. The shock absorber is an important component of the chassis. In actual fact, the term "shock absorber", which is customary in the trade, is misleading. Shock absorbers do not absorb shock. Their job is to reduce and decelerate the vibrations of vehicle springs. Together, the springs and the shock absorbers provide the link between wheel suspension and car body, working as a team to compensate uneven road surfaces. The frequency of vibrations emanating from the wheel is approximately ten times higher than the vibrations of the car body – sprung mass, to use the technical term. The shock absorber is the means via which these vibrations are dampened. In technical terms, this component is not a shock absorber then, but a vibration absorber.

Energy converter
In principle, the vibration absorber is an energy converter. It transforms the kinetic energy of the springs into heat by means of fluid friction. This transformation takes place when a damper piston moves up and down in a cylinder filled with oil. During this process, precisely defined valve passages in the damper piston and/or a base valve decelerate the movement of the damper piston so sharply that the spring vibration is nipped in the bud.

The spring is needed most when driving over an obstacle. It must not be hindered by the compression of the damper, which is being squeezed at this point (compression). Once the spring has compensated for the obstacle, the shock absorber must decelerate the motion of the spring, which is rebounding with significant force. During this process, the spring is uncompressed (rebound). The damping force of the vibration damper is higher during rebound than it is during compression. Depending on the condition of the road, the speed at which the vehicle is being driven and the outside temperature, this damping effort can result in the damper heating up to a temperature as high as 120 °C. Reliable vibration dampers are designed to withstand this type of thermal load.

Gas-filled shock absorbers
The introduction of complex chassis systems requires fine-tuned vibration dampers. As coil springs have slight internal friction, the ability of the dampers to reduce friction is of decisive importance for road safety. Today, cars produced in mass production feature gas-filled shock absorbers (either the more basic twin-tube design or the more complex mono-tube design).

Previously, cars were fitted with oil-filled shock absorbers as standard. This type of shock absorber had an inherent system flaw: a tendency for cavitation (oil foaming) occurring during the actual damping process. In damper oil, approx. 10% of the gas content is locked in a molecular bond. The movement of the damper piston in the oil creates pressure differences above and below the piston. This releases gas from the liquid and tiny bubbles form. When travelling long distances, the foaming of the oil reaches such an extent that the damping force measurably drops. On long journeys on highways or motorways, loss of damping force of up to 35% is possible. In other words, although there was full damping power at the start of the journey, this drops back slowly as the load exerted on the damper increases. As a consequence, there is a reduction in the road grip of the wheels. When the vehicle is stopped or at rest for a long period, the full damping force is restored as oil foaming decreases.

These constant changes in damping force do not occur with gas-filled shock absorbers. The gas (nitrogen) inside the damper with the oil keeps the oil pressurised, thereby preventing the gas molecules bound in the damper oil from being released. Gas-filled shock absorbers can be relied upon to exclude the risk of oil foaming during driving. As spring and damper characteristics remain constant even on long journeys and under maximum load, with gas-filled shock absorbers it is possible to precisely adjust the chassis. For chassis tuning in particular (low-slung vehicles), precision vibration damping during residual spring deflection is important.


Suspension spring


Suspension springs are the link between wheels and car body. Their primary task is to compensate uneven road surfaces and thus provide an assurance of high levels of ride comfort. Secondly, they must ensure that the wheels always have safe contact with the road regardless of its condition. Reliable transmission of drive, braking and transverse forces relies on these requirements being met. As such, suspension springs are one of the most safety-critical components of modern vehicles. They affect handling, roadholding and braking performance.

From the point of view of design, there are suspension springs with linear and progressive spring rate. With linear springs, the spring force increases in proportion with the extent to which they are squeezed together. Progressive springs start with a soft characteristic curve and become harder the further they travel. Depending on the vehicle manufacturer's specification, suspension springs are manufactured from constant wire (same wire diameter across entire spring length) or inconstant wire (varying wire diameter across spring length).

Where inconstant wire springs are concerned, it is said that there are two springs in one: one soft and the other strong. Progressive mini-block springs, for example, offer high levels of ride comfort at low vehicle load and low compression at full load. The spring is therefore "soft" at low vehicle load and "strong" at full load.

The following types of spring are primarily used in today's cars:

Cylindrical suspension springs
These are conventional cylindrical suspension springs with a linear spring rate.

Inconstant wire suspension springs
With this type of spring, the diameter of the wire used decreases towards the end of the suspension spring. Assuming normal road conditions and normal load, the soft ends of the spring can be relied upon for very comfortable ride properties. As well as improving ride comfort, this relieves the load on the wheel suspension as a whole and all steering components.

Mini-block springs
Mini-block springs are barrel-shaped. They are manufactured from tapered wire. This means that they generate a progressive spring rate. The design of the ends of the springs avoids direct contact from winding to winding. The main feature of the mini-block springs, which were developed from inconstant wire during the 1970, is that when under load, the windings of the ends intertwine without touching. When the ends of the mini-block springs are squeezed together and lie flat on the spring cups (which usually consist of a rubber block), the number of active windings drops and the spring rate increases.

Banana-shaped side load springs
This type of spring controls force distribution for the entire wheel suspension, reducing the friction between the shock absorber piston rod and its gasket. This helps to improve shock absorber response characteristics.


Exhaust system

Exhaust system


The exhaust system collects the exhaust gases from the cylinders, removes harmful substances, reduces the level of noise and discharges the purified exhaust gases at a suitable point of the vehicle away from its occupants. The exhaust system can consist of one or two channels depending on the engine. The flow resistance must be selected so that the exhaust backpressure affects engine performance as little as possible. To ensure that the exhaust system functions perfectly, it must be viewed as a whole and developed accordingly. This means that its components must be coordinated by the design engineers in line with the specific vehicle and engine.

Every internal combustion engine produces "exhaust noise" due to the pulsating emission of gases from the cylinders. This noise has to be silenced by reducing the sound energy of the exhaust gas flow. There are two basic options here: Absorption and reflection of the sound in the silencer. These two principles are generally combined in a single silencer. Exhaust chambers and exhaust flaps are other sound-absorbing and sound-modifying elements that can be used to eliminate especially undesirable frequencies from the outlet noise.Catalytic converters also have a sound-absorbing effect.

The exhaust system is itself a system subject to vibration, it produces noise itself through natural frequencies and vibration which are transmitted to the car body. Careful coordination of the entire system is therefore necessary here. This includes design and positioning of the individual elements of the exhaust system and their flexible mountings.

In addition to all the complex functions which the exhaust system has to perform, it is also subject to extreme stresses. The fuel-air mixture in the cylinders is abruptly heated to temperatures up to 2,400 °C. This causes it to expand greatly before escaping into the exhaust system at supersonic speed. This noise level resembles the crack of an explosion and must be reduced by approx. 50 dB(A) as it travels from the engine exhaust valve to the end of the exhaust system. Apart from temperature and pressure stresses, the exhaust system must also cope with vibrations from the engine and bodywork as well as vibrations and jolting from the carriageway. The exhaust system additionally has to resist corrosion attacking from the inside caused by hot gases and acid, and from the outside in the form of moisture, splashed water and salt water. There is also the risk that the catalyst may be poisoned through sulphur or lead present in the fuel.


Structure of an exhaust system

Today's exhaust systems have very little in common with the simple exhausts used in the past. In more modern cars, they basically consist of a front section with the exhaust manifold, the purification system and the connecting pipes, together with a rear section with the silencer system and pipes. The entire system is connected to the floor pan by means of flexible mounting elements. The number of catalytic converters and silencers depends on the type of engine, engine performance and the required emission values.

In Vee engines, each of the two cylinder banks has its own exhaust channel. The exhaust channels either remain separate up to the tailpipes or are brought together beforehand – for example, in a common end silencer. If the exhaust system consisted only of rigid pipes, the rear silencer would vibrate violently – with the risk of subsequent breakage. For this reason, modern exhaust systems are built with mass dampers and decoupling elements. They prevent major deflections of the exhaust system and also prevent smaller vibrations being passed from the engine to the exhaust system and entering the interior as acoustic pulses. Mass dampers and decoupling elements thus improve ride comfort while increasing the service life of the exhaust system.


Hydraulic shock absorber


The hydraulic shock absorber mostly comprises of a cylinder filled with hydraulic oil and a piston, which moves with every vertical movement of the wheel. This piston glides up and down when the spring is compressed and extended during the journey. During compression (pressure stage), the oil beneath the piston must flow through a narrow valve opening. This process generates friction that converts the kinetic energy from the oil into heat, brakes the movement of the piston and therefore damps the vibration in the car body. The compressed oil flows to a reserve pipe via valves in the base. The damping resistance varies depending on the speed at which the piston is moving, the volume of oil and the number and size of valves. In general, the faster the piston rod moves, the higher the force acting on the piston and more resistance is created. When the spring is extended (pull phase), the oil flows through an even narrower valve back down through the piston, achieving a stronger damping that when the spring is compressed. This is required so that the spring can relax in a controlled way and so that the wheels do not lose contact with the ground.

Exhaust system

Mounting technology


Modern exhaust systems consist of several individual components which have been precisely coordinated. The assembly/mounting technology is designed to connect the components of the exhaust system to each other and secure the entire system to the underbody of the vehicle. The requirements in terms of assembly technology are extremely high: They range from a long service life, through high gas tightness to optimised vibration behaviour.

Pipe connectors and clamps

The key function of making the exhaust system gas-tight is ensured by pipe connectors and clamps. A distinction is made here between single and double clamps.

A single clamp is mainly used for assembly of the end silencer. Here the pipe of the silencer is generally slid over the upstream intermediate pipe and bolted in place with positive locking using a single clamp.

A double clamp is used to connect two pipe diameters of identical size. This is why they are also called pipe connectors. Besides making the system gas-tight, the double clamp is designed to compensate for length differences up to 125 mm.

Pipe connectors and clamps are exposed to aggressive condensates, dirt, splashed water and salt water. This is why they should ideally be made of ferritic steel 1.4509 (stainless steel). They must offer a gas tightness with a leakage rate of 20 l/min at temperatures ranging from -40 °C to 450 °C .

Compensation elements

With today's growing demands for service life and comfort, particularly with modern engine weights, compensation vibration elements are used with transverse engines. These decoupling elements eliminate vibrations resulting from an unfavourable mass distribution, offer tolerances for assembly and compensate for thermal expansion.


Hose joints (flexible parts) are used as decoupling elements. It consists of an external corrugated tube, which ensures gas tightness while allowing the component to move. Both single and multi-layer versions are available, depending on the requirements. The corrugated tube is covered by an outer steel braid. This is designed to protect the corrugated tube (bellows) and limit tensile forces.

Internally, the hose joint consists of a gas-tight flexible pipe (spiral-wound metallic hose). Its main function is to control the flow of the exhaust gases. This design of this component, which is also known as an inliner, has a major impact on the damping effect of the exhaust system. The necessary long service life is ensured by extensive testing.

Exhaust system

Diesel particulate filter


Diesel particulate filters are designed to trap particles of soot in the flow of exhaust gases from diesel vehicles and convert them into CO2 during the regeneration phase. This helps to keep the air clean. Different systems are possible here, depending on the application and conditions of use. "Closed" particulate filter systems are used as original equipment in cars or when retrofitting heavy goods vehicles. "Open" particulate filter systems are generally used when retrofitting cars, vans or mobile homes. Diesel particulate filters are self-cleaning, i.e. they continuously burn off the soot deposits. They are normally maintenance-free and last the entire life of a vehicle.Retrofitted systems do not require the assistance of engine management computers, sensors and electronics or additives to control soot levels effectively and continuously burn off soot.

Particulate filters are made of different materials depending on the manufacturer: codierite, silicon carbide, aluminium titanate or sintered metal. The hot exhaust gases containing soot particles from the engine are fed to the relevant filter materials in the filter housing. The gaseous components of the exhaust flow through the microscopic pores of the filter pockets. They trap the soot including ultra-fine particles on the surface and deposit them into the individual filter pockets.

Filter regeneration

Regeneration (cleaning) of the filter starts when the exhaust gas temperature reaches roughly 200 °C. Nitrogen dioxide (NO2) formed by the oxidation catalytic converter comes into contact with the soot deposited in the filter pockets. The soot particles are oxidised and broken down, with the NO2 being reduced to nitrogen monoxide (NO). This chemical process is constantly repeated and allows the particulate filter to continuously clean itself. This means it does not require any further aid with regeneration, for example assistance from an engine management system.

Combi system

Combination systems are equipped with an integral or upstream oxidation catalytic converter or an efficient catalytic layer. This ensures optimum regeneration when the necessary exhaust gas temperature is reached.

Exhaust system

Catalytic converter


Catalytic converters (CAT) are designed to turn harmful constituents of exhaust emitted by internal combustion engines into harmless gases by means of a chemical reaction. A catalytic converter is therefore an important part of modern emission purification systems for SI and diesel engines.

A catalytic converter consists of a stainless-steel casing that houses a metallic (metalith) or ceramic (monolith) substrate. This substrate has a very large number of fine channels running through it along its length. The aim here is to create the greatest possible surface area to optimise the catalytic effect. The surface of the substrate is coated with a highly porous layer (washcoat) to which precious metals (platinum, palladium and/or rhodium) are added in suspension. It is these precious metals that are the actual catalysts initiating the chemical reactions required to purity the exhaust gases.

Three-way catalytic converter

The three-way catalytic converter is designed for SI engines. At operating temperature it converts unburnt hydrocarbons (HC) into CO2 and water vapour (H2O), carbon monoxide (CO) into carbon dioxide (CO2) and nitric/nitrogen oxide (NO/NO2) into nitrogen (N2) and oxygen (O2). These processes take place simultaneously in the CAT, which is the reason why it is called the three-way catalytic converter.

A three-way catalytic converter depends on a specific exhaust gas composition to achieve its full effectiveness. The process must release exactly the right amount of oxygen as required to oxidise the hydrocarbons and carbon monoxide. This is the case when one part of fuel is mixed with 14.7 parts of air and then burnt in the engine. Here we speak of a stoichiometric mixture (lambda = 1). To produce this mixture, the residual oxygen content in the exhaust gases is measured by the Oxygen sensor positioned between the engine and the catalytic converter. The result is processed by the engine management system, which outputs control pulses ensuring an optimum air-fuel ratio.


Replacement catalytic converters for Euro 3 and Euro 4 vehicles with European On-Board Diagnostics (EOBD) are known as EOBD-capable catalytic converters. Electronic On-Board Diagnosis is mainly found in recent vehicle models. This function monitors all emissions-relevant components and sensors while the vehicle is on the road. It registers any malfunctions and warns the driver, for example with an indicator light (MIL). The latest generations of diesel vehicles are generally equipped with the EOBD function.

Oxidation catalytic converter

Diesel engines usually function with a large amount of excess air, so that the exhaust gases contain high levels of oxygen. Catalytic converters for diesel engines oxidises carbon monoxide (CO) to carbon dioxide (CO2) and hydrocarbons (HC) to carbon dioxide (CO2) and water vapour (H2O). 

Exhaust system

Oxygen sensor


The oxygen sensor is an instrument for managing the exhaust emissions of petrol, diesel and gas engines. It is an oxygen concentration sensor which measures the residual oxygen content of the exhaust gases and then transmits a signal to the engine management system in the form of an electric voltage. The oxygen sensor voltage allows the control unit to detect whether the mixture is too lean or rich. The control unit reduces the quantity of fuel in the A/F ratio if it is too rich, and increases it if it is too lean.

The value measured by the oxygen sensor allows the control unit to adjust the amount of fuel injected to attain an optimum mixture. This creates ideal conditions for treatment of the exhaust gases in the catalytic converter. This also takes account of the engine load. There may also be a second oxygen sensor, the diagnostic sensor (downstream of the catalytic converter). This detects whether the control sensor (upstream of the CAT) is functioning to optimum effect. The control unit can then calculate how to compensate for this.

Configuration in exhaust system

More recent engines have an exhaust system with oxygen sensors upstream and downstream of the catalytic converter. The exhaust gases flow over the electrode side of the sensor element, while the other is in contact with the outside air. The outside air acts as a reference here for measurement of the residual oxygen content. The system has been simplified by the latest generation of oxygen sensors, in which the reference value measured against the outside air is replaced by a reference voltage.

Types of oxygen sensors

Today there are basically two different types of sensor: the binary and the universal exhaust gas oxygen (UEGO) sensor. When at operating temperature (from 350 °C), the binary sensor generates a change in electric voltage depending on the oxygen level in the exhaust. It compares the residual oxygen content in the exhaust with the oxygen level of the ambient air and identifies the transition from a rich mixture (lack of air) to a lean mixture (excess air) and vice versa.

The universal exhaust gas oxygen sensor is extremely accurate when measuring both a rich and lean air/fuel ratio. It has a greater measuring range and is also suitable for use in diesel and gas engines.

Nowadays heated oxygen sensors are used to ensure the oxygen sensors attain operating temperature more quickly and can thus intervene earlier in the emission control process. Heated HEGO sensors no longer need to be installed so close to the engine.

Structure of the oxygen sensor

Finger-type sensor

The core of the finger-type sensor consists of a finger-shaped ceramic element. It is heated by a heater incorporated in the sensor as control is possible only at a minimum operating temperature of 350 °C. The exhaust gases flow over the electrode side of the sensor element, while the other is in contact with the outside air. The outside air here acts as a reference for measurement of the residual oxygen content. To protect the sensor element from combustion residues and condensate in the exhaust gas, the sensor housing is fitted with a protection tube at the exhaust gas end.

Planar sensor

The planar oxygen sensor is manufactured using thick-film-technology. The shape of the sensor element resembles an elongated plate. Both the measuring cell and the heating element are integrated in this plate, so allowing the sensor to attain its operating state more quickly. Here too suitable protection tubes are used to protect the sensor element from combustion residues and condensate in the exhaust.

Drive train

Drive shaft


The function of the drive shaft is to transfer the engine torque from the gearbox or differential to the wheels. It must also compensate for all variations in angle or length resulting from manoeuvring and deflection for perfect synchronisation between joints.

Drive shafts for cars with front wheel drive consist of the outboard fixed joint, the inboard constant velocity joint and the connecting shaft. They also include elements such as the anti-lock system ring and the torsion damper. The basic design of the outboard fixed ball joint, the constant velocity joint, dates from the 1930s.

In most cases the inboard CVJ takes the form of a slip joint to allow the drive shaft to follow the movements of the wheel suspension. At the front axle (leading axle) the outboard joint must transfer the torque effectively through a large angle (up to 52 degrees). At the rear axle the angles of the outboard joints are considerably smaller.

Constant velocity drive shafts are exposed to maximum stress all the time that the vehicle is in operation. Alongside the extremely significant displacement angles and translational movement, the joints and bellows must be able to withstand temperatures of between minus 40 and plus 120 °C as well as speeds of up to 2800 rpm. In order to transmit the required torque in all engine speed and velocity ranges with reliable constancy (ideally throughout the entire service life of the vehicle), all components must be maintenance-free.

Drive train



The clutch is a separate connection in the transmission, linking the engine to the gearbox. It thus enables starting away from rest and changing gear.

The clutch is operated via the clutch pedal and the clutch release system. When the clutch is not in operation, the disc spring in the clutch automatically presses the clutch disc against the flywheel via the pressure plate. This establishes a positive connection, allowing the engine torque to be transmitted to the gearbox.

When the driver of the car activates the clutch release system via the clutch pedal, the pressure plate is pulled away from clutch plate against the spring force. The positive connection is broken and no engine torque is transmitted to the gearbox.

As the clutch disc wears, the force which must be applied to the pedal to operate the clutch increases. It is for this reason that SACs (Self-Adjusting Clutches) are fitted to modern passenger vehicles. Automatic wear adjustment in the clutch pressure plate ensures that pedal forces remain constant throughout the service life of the clutch.

The dual clutch is another type of clutch. It combines two multi-plate clutches in an oil bath or two dry single-plate clutches in a single module. Dual clutches are installed in dual-clutch gearboxes, with one clutch being used for the even gears and the other for the odd gears. This allows gears to be changed quickly without interruption of the tractive torque.


Drive train

Longitudinal shaft


The longitudinal shaft or cardan shaft is a very important component for rear-wheel drive and all-wheel drive.

Its task is to transmit the torque from the engine/gearbox unit to the axle differential. In some cases, long distances have to be bridged between the units. Therefore, longitudinal shafts can have not just one but two or three sections.

Longitudinal shafts can be manufactured from aluminium, fibre composites or steel. Universal joints (or cardan joints, as they are also known), flexible couplings or high-sped constant velocity joints provide the requisite connections. Strictly speaking, cardan joints are not constant velocity joints. As such they can only be used in applications with low bending angles. Depending on the vehicle model, automotive manufacturers use single-section, two-section or three-section longitudinal shafts with different options for intermediate bearings, sliders, impact optimisation, vibration damping and adjusting capacity.

Here are some examples:

- Single-section front longitudinal shafts are usually used for all – wheel drive vehicles (light commercial vehicles and SUVs in particular); they transmit the torque from the transfer box to the front axle differential.

- Two-section shafts are the most frequent configuration for vehicles with rear-wheel or all-wheel drive. The longitudinal shaft is supported by an intermediate bearing in the centre. With regard to their longitudinal and angular variability and their vibrational and noise characteristics, the three joints used in this shaft are matched specifically to the vehicle and its crash performance.

- Three-section longitudinal shafts are increasingly being used in vehicles with rear-wheel and all-wheel drive, where outstanding vibrational and noise characteristics are required and the longitudinal shaft must fit into a complex vehicle underbody. Three-section shafts have two intermediate bearings attaching them to the vehicle floor and four high-speed joints.

Due to the relative movements between the axles and the gearbox and high shock loads when driving off-road, the shaft joints and couplings must be able to withstand high levels of stress. Dividing the longitudinal shaft increases bending stiffness and thus rigidity at high speeds.

Drive train

Dual-mass flywheel


Modern engines can be driven at extremely low speeds. The trend is towards increasingly higher engine torques. Furthermore, bodies are getting quieter and many components getting lighter and lighter in order to reduce weight and thus save fuel. Other measures designed to find the optimum technical solution are resulting in more sources of noise but less natural damping. The principle of the reciprocating piston engine is still with us. Its periodic combustion processes induce torsional vibration in the drive train, with the unpleasant consequences of rattling gearboxes and roaring bodies. The dual-mass flywheel (DMF) effectively isolates engine vibrations from the gearbox and the drive train, offsetting such disadvantages.

The dual-mass flywheel is a flywheel complete with a torsional vibration damper. It prevents torsional vibration from the reciprocating piston engine being transmitted to the drive train. The DMF uses a spring damping system to decouple the primary flywheel mass on the engine side and the inbound secondary flywheel mass. The spring damping system absorbs virtually all of the torsional vibration and the resulting noises in the drive train. Vehicles with DMF benefit from increased noise and ride comfort. Furthermore, as the mass to be synchronised is less on vehicles with DMF, the gearbox can be shifted more easily and synchronisation wear is reduced.

Car care

Car care


Washing and caring for the car will help it to maintain its value. The car must be washed thoroughly before other work such as care of painted or plastic surfaces can commence. The car is washed thoroughly and carefully with plenty of water and special car shampoo. Unlike harsh household cleaning agents, a high-quality car shampoo will not damage paint preservers made from hard wax. Modern maintained car wash facilities provide a means of washing cars thoroughly and in a way that is not harmful to the environment. Washing brushes with soft bristles and textile brushes are particularly kind to painted surfaces.

Here is our list of top tips for various car care applications:


Tree resin

Tree resin causes dark brown and yellow stains; it must be removed quickly to avoid permanent damage to paint finishes. We recommend using a soft cloth and a gentle cleaning agent designed specifically for painted surfaces, glass panels, chrome surfaces and plastic surfaces.


Convertible top care

To avoid damaging soft or hard convertible tops, only suitable cleaning agents should be used. Cleaning agents that are too harsh can damage the protective coating on the convertible top. It is vital to follow the manufacturer's instructions for use! Depending on the type of cleaning agent used, convertibles can even be cleaned using mains-powered or battery-powered units featuring textile brushes or at self-service "SB boxes". However, automatic car washes are not suitable for convertible tops. Hot wax must not be used. If you use a mains-powered or battery-powered unit to wash a car with a convertible top, compliance with the manufacturer's instructions for use is just as vital!


Cleaning wheel rims

Today's cleaners for wheel rims gently remove all traces of the most stubborn road grime and brake dust that has become sticky due to mixing with oil. Aggressive cleaners can cause wheel bolts and other metallic surfaces to corrode. Therefore, we recommend using a cleaning agent that does not contain acid. The best way to proceed is to spray the wheel rim with the cleaning agent and then use a soft brush or a sponge to remove stubborn dirt. Finally, rinse the wheels thoroughly with water.


Sealing wheel rims

Sealing wheel rims is certainly to be recommended – the conventional method is to use hard wax or a special nano-based wheel rim sealer. This will reduce the incidence of stubborn dirt on the wheel rims – making cleaning much easier.


Frost protection

At cold times of the year, only a winter washer fluid with frost protection will be able to remove oil, grime, salt and other typical seasonal soiling with just a few squirts of fluid and wipes of the blades. Check that the product you choose will stop the nozzles icing over and the washer fluid freezing on the window glass, and that it is suitable for fan nozzles. Important: Poor quality products can cause stress cracks in paint and headlight lenses.


Odour neutralisation

Unpleasant odours (household pets or nicotine, for example) can be encapsulated and neutralised with chemical substances. We recommend using a spray that not only disguises but also neutralises unpleasant odours and is slightly perfumed to create a pleasant and fresh smell that lasts. Companies specialising in this field can also provide ozone treatment to get rid of odours.


Glass cleaners

Car windows should be cleaned thoroughly on a regular basis for a clear view. A streak-free cleaning agent that will quickly rid windows and headlights of all traces of insects, dirt, exhaust residue and nicotine is the best solution. The inside of windows and the mirror should also be cleaned regularly to remove nicotine deposits and layers of grease.


Rubber care

Regular cleaning of rubber strips or door seals will stop them becoming brittle and unsightly. Door rubbers will freeze in winter if they are not given special treatment. A good rubber cleaner will clean and protect all rubber parts of a car, keep them flexible, prolong their service life and refresh their colour. Even tyres and floor mats can be cleaned with ease with a good rubber cleaner and their fresh appearance restored.


Hard wax

Hard wax is the best way to preserve paint finishes and restore their shine. The latest generation of products is based on a recipe using super-fine nano particles. The fine wax particles, which are approximately 1000 times smaller than human hair, are very easy to work into the paint pores of all colour and metallic paint finishes. The fine structure of the wax particles means that the product can even be worked into the very densely meshed surface of scratch-resistant paints with relatively little effort.


Hot wax

The shelf life of the hot wax used in most car washes to preserve paint finishes is very short. A better solution is to use an active hard wax sealer after washing for long-term protection and a shiny appearance.


Cavity sealant

Rust from the inside can be prevented by using a special preservation product. Above all, the product selected must have an outstanding ability to penetrate so that it can get into even the tightest of angles, eliminate moisture and thus provide the best possible protection for narrow gaps, rebates and weld seams. To protect the environment, products that do not contain bitumen and are wax-based, for example, should be favoured.



Insect residue will damage paint finishes. Serious damage to paint finishes can be caused especially in sunlight if insect residue is not removed within a short period of time. A suitable insect remover will rid glass, paint, chrome and plastic of residue quickly and easily. Good flow properties are important, so that even dried-on stains can be broken down without damaging the surface. Products of this nature will remove residue quickly and gently.


Corrosion protection

The underbody and cavities in particular need to be well protected against damp, salt and aggressive influences. The right underbody protection will provide long-term protection for vehicle underbodies, the undersides of wings, wheel wells, car doors, edges and seams against rust and corrosion. As well as being abrasion-proof, the protection should remain flexible and be resistant to cold, heat, salt and spray water.


Paint care

Paintwork is constantly exposed to the damaging influences present in the environment. Sunlight, exhaust gases, acid rain, road salt and pollen are just some of the factors that can contribute to vehicle paintwork starting to look "old". Regular care and protection of paintwork will delay this ageing process so that the vehicle will once again "shine like a new pin".


Polishing paintwork

Depending on its condition, paintwork might have to be treated with products that contain hard wax for protection and shine or buffing ingredients for a glossy surface finish. According to requirements, care products are available for both paintwork that is in mint condition and paintwork that has undergone thorough cleaning. Other products can make paintwork that has lost its original sheen look as good as new. For paintwork that is very weather-beaten, a care product that will hide fogging and fine scratches is recommended.


Paintwork protection

There is no better protection for paintwork than hard wax. The latest generation of products is based on a recipe using super-fine nano particles. The fine wax particles, which are approximately 1000 times smaller than human hair, are very easy to work into the paint pores of all colour and metallic paint finishes. The fine structure of the wax particles means that the product can even be worked into the very densely meshed surface of scratch-resistant paints with relatively little effort. The shelf life of the hot wax used in most car washes to preserve paint finishes is very short. If wax from a car wash has to be used, an active hard wax sealer is a better solution, as it provides long-term protection and will lend the car a shiny appearance.


Leather care

Regular care and cleaning of all leather parts in the vehicle will prolong service life. As car seats in particular are subject to high levels of stress, it is important not only to clean the leather but also to use an appropriate care product to keep it supple. A care product that contains beeswax for long-term protection, for example, is also to be recommended. Make sure that the foam is suitable for vehicles with heated seats and perforated leather surfaces.


Engine cleaning

Oil and grease stains can be removed quickly and easily by spraying with an engine cleaner or cold cleaner. Thanks to its excellent ability to penetrate, the cleaner can even reach areas which are difficult to access.


Cleaning of upholstery and Alcantara

A cleaning agent which will both gently remove stains and neutralise unpleasant odours is recommended for Alcantara and upholstery covers.


Glass cleaning

Car windows should be cleaned thoroughly on a regular basis for a clear view. A streak-free cleaning agent that will quickly rid windows and headlights of all traces of dirt and exhaust residue is the best solution. The specific properties required of the cleaning agent will vary depending on the time of year. Between spring and autumn it is important that the cleaning agent is good at removing insects. In winter, the primary consideration is frost protection so that even at temperatures below zero, oil, grime, salt and other typical seasonal soiling can be removed with just a few wipes of the blades. Check that the product you choose will stop the nozzles icing over and the washer fluid freezing on the window glass, and that it is suitable for fan nozzles. Important: Poor quality products can cause stress cracks in paint and headlight lenses.


The inside of windows and the mirror should also be cleaned regularly to remove nicotine deposits and layers of grease.


Rapid protection

High-quality carnauba wax, for example, is capable of lightning-fast sealing of new paintwork and paintwork that is in mint condition. It will lend a glossy appearance and provide protection lasting many weeks. The ease with which it can be applied is a real delight, as there is no need to wear yourself out polishing the paintwork! Carnauba wax can also be used for the care of plastic and rubber parts.


Damage caused by stone chips

Damage caused by stone chips compromises protection of the car body and creates weak points for the formation of rust. A matching colour pen (available in a variety of colours) can be used to cover stone chips and deep scratches in paintwork with coloured wax pigments. A perfectly matched wax combination provides effective protection for the car body against rust. Damage caused by stone chips can be rectified by patching up the paintwork (spot coating, for example).


Carpet cleaning

When cleaning carpets, a stiff brush should be used to loosen and remove deep-seated dirt. For basic (deep) cleaning, the use of an interior car cleaner is recommended (the use of plenty of water will ensure that even deep-seated stains are removed). After this the carpets are wiped dry and should be allowed to air so that moisture does not remain inside the vehicle. A wet-and-dry vacuum cleaner is the ideal tool for this type of task.



Plastic and rubber parts in the vehicle can be cleaned, cared for and protected with high-quality care emulsions. The care emulsion penetrates deep into the surface and takes effect from within. Some products also have an anti-static effect, freshen up the colour and create a pleasant odour.


Underbody protection

The underbody and cavities in particular need to be well protected against damp, salt and aggressive influences. The right underbody protection will provide long-term protection for vehicle underbodies, the undersides of wings, wheel wells, car doors, edges and seams against rust and corrosion. As well as being abrasion-proof, the protection should remain flexible and be resistant to cold, heat, salt and spray water.


Bird droppings

Bird droppings damage paintwork. The surface swells up and cracks form. For this reason, soiling caused by bird droppings should always be removed as quickly as possible. We recommend using a soft cloth and a gentle cleaning agent designed specifically for painted surfaces, glass panels, chrome surfaces and plastic surfaces.


Wax deposits on window glass

Residue from hot wax sealing in car washes can smear window glass. We recommend using a cleaning cloth for window class to clean window glass and wiper blades.


Winter care

In winter, the weather is your car's most dangerous enemy. Washing your car regularly to remove salt residue and other sources of soiling is therefore recommended. At this time of the year, it is particularly important that paintwork is sealed to prevent moisture and aggressive substances causing damage to the car body. Furthermore, window washer systems must be in perfect working order for clear view of the road. They should be filled with winter washer fluid.





The primary task of headlights on cars is to illuminate the roadway and facilitate fatigue-free and safe driving. Headlights and their light sources are thus vehicle components that are relevant to safety. They require official approval and must not be tampered with. The nature and location of light functions on a vehicle and their design, light sources, colours and photometric values are regulated by law.

Today's cars feature the following headlight systems:

Halogen headlights

Headlights with H3, HB3, H7 and H9 bulbs have traditionally been used in vehicle illumination. They still enjoy great popularity today. Advances in halogen technology have resulted in a very good price/performance ratio for halogen headlights as original equipment.

Xenon headlights

Xenon light has two decisive advantages over the light emitted by conventional halogen bulbs: Firstly, a Xenon bulb supplies more than twice the light of a modern H7 bulb but needs only 2/3 of the electrical power to do this. Secondly, the light colour of a Xenon bulb is similar to daylight. This additional light makes the road lighter and brighter. Dangers at the edge of the road and even on the road are detected sooner. The improved illumination of the road and the daylight quality of the Xenon light accommodate the natural viewing habits of the human eye – drivers do not get tired as quickly and adopt a more relaxed driving style. With Xenon technology, instead of the coiled filament in a conventional bulb, the light in the bulb is generated by an intensive light arc. The high voltage of 20,000 V required to light up the Xenon bulb is supplied by an electronic ballast.

Full LED headlights

Energy-efficient and cost-effective, LEDs (light-emitting diodes) are becoming increasingly popular in all areas of the vehicle industry. Leading component manufacturers have succeeded in expanding the spectrum of possible applications for vehicles of all types at a rapid pace. Reliability, cost-effectiveness and design variety are the convincing arguments in favour of using LEDs in common applications.



Headlight bulb


Since the introduction of the H1 bulb in 1960, halogen bulbs have been an integral component of headlight illumination. Although in the intervening years Xenon technology, which has much higher light intensity, has captured an increasingly large share of the upper and middle vehicle segment, the vast majority of drivers on the road are using halogen bulbs.

As good illumination is an essential aspect of safety, manufacturers of halogen bulbs are also still continuing to strive for advances in development and improvements. A great deal of work is being done in particular on bulbs for the after-sales market which illuminate the road better than the standard bulbs used in original equipment.

As the amount of light for each type of bulb is precisely defined in ECE regulations and must not exceed the permissible tolerance limits, an increase in light intensity must be achieved by other means. Bulbs that cast more light on the road have a more compact but brighter coiled filament than a standard bulb. As a result, the headlight is able to direct the available amount of light more effectively and more selectively into the vital area of the road in front of or behind the vehicle.

The best halogen bulbs on the market today are capable of light intensity up to 100% higher in the area between 50 and 75 metres from the vehicle on the right-hand side of the carriageway. Bulbs with a blueish coating which generate bright white light similar to that produced by a Xenon light are also available, along with special long-life bulbs, which are used if the coiled filament is exposed to a particularly high load due to increased on-board voltage in the vehicle.



Daytime driving lights


Daytime driving lights offer impressive benefits: they make vehicles easier to see on the road, thereby decisively improving daytime safety. Furthermore, as they consume significantly less power, they avoid the disadvantages of low-beam headlights where consumption is concerned. Daytime driving lights are available in a variety of designs: designs using LEDs are doubtless the most modern and slick options; conversely, those featuring conventional bulbs are cheaper to buy than but not as energy-efficient as LEDs.

With daytime driving lights, a vehicle can be detected earlier and more effectively, giving other road users that additional reaction time that can often prove crucial. Whilst low-beam headlights are designed to act as an active visual aid when driving at night, daytime driving lights are designed to function as passive signalling lights. Daytime driving lights are switched on automatically via a relay as soon as the ignition is switched on. When the driver switches on the normal driving lights, the daytime driving lights are switched off again automatically.

Retrofit daytime driving lights (upright or suspended) can be fitted at any time if required. They can be screw-mounted, snapped on, installed on a mounting plate or even fitted with a universal bracket included in the scope of supply.


Additional headlights


Additional headlights supplement standard lighting and provide the ideal means of improving lighting performance in poor light and poor weather conditions. Whilst additional headlights are the right choice for drivers who frequently have to travel in poor ambient light conditions, additional fog lights improve safety in fog. Additional headlights can be retrofitted; they come on when the standard headlights are switched on. Additional fog lights are activated via a switch connected to the rear fog light. 


Anti-lock brake system (ABS)


If the wheels lock when the brakes are fully applied, the ability to steer is lost and the vehicle can become uncontrollable. The task of the anti-lock brake system (ABS) is to permanently and effectively stop the wheels from locking, thereby stabilising braking. This is achieved by repeatedly and intelligently reducing and increasing the brake pressure, a procedure known as pressure modulation.

The German road traffic registration ordinance (StVZO) also uses the abbreviation ABV, which stands for anti-lock braking system.

Anti-slip control
When the driver presses hard on the brake pedal, the tyres initially switch from their normal rolling motion to what is known as the brake slip range. The rolling circumference of the tyre is less than the distance the vehicle is covering. If the driver presses the brake pedal even harder, the wheel will lock. This is referred to as 100% brake slip.

With modern tyres and "standard road surfaces", optimum braking deceleration is reached at a brake slip of between approximately 8 and 25%. Even experienced drivers will find it difficult to reach this narrow, optimum range; they will not be able to reach it at all in extreme circumstances. The intelligent ABS system regulates the brake force so that the slip at each wheel remains within the optimum range and individual wheels do not lock at the same time.

Different systems
In the past, three-channel anti-lock systems were the most popular. Systems of this type control the front wheels separately and the rear wheels are jointly. Most of today's vehicles feature four-channel ABS systems, which enable the brake pressure to be controlled separately at each wheel. On vehicles with anti-lock systems, each wheel has a wheel speed sensor.

The sensor tells the electronic control unit the current speed of all wheels at any given time. If an individual wheel is decelerated more sharply during braking, exceeding the target slip range, the brake pressure of this wheel is maintained or reduced. This rule applies above a minimum velocity of 6 km/h. As long as the driver continues to press the brake pedal, the velocity of the vehicle will be permanently matched to the velocity at which the individual wheels are travelling. As a result, the break pressure is continuously modulated.


The anti-lock system comprises the following components:

  • Wheel speed sensors. Wheel speed sensors must capture the current wheel speed and report it to the electronic control unit in the form of an electrical signal.
  • "HECU" control unit. The HECU control unit must evaluate the signals. It comprises the hydraulic unit (hydraulic block with valves, integrated pump with electric motor and low pressure accumulator) and the electronics unit (coil carrier with electronic control unit).
  • Wheel brake. The wheel brake converts the braking effect at the wheels, each of which is controlled separately.


Brake shoes


Brake shoes are a vital component of a drum brake. Essentially, they comprise the brake drum, the brake shoes, the wheel brake cylinder and the adjustment mechanism. The brake drum is fixed to the wheel and turns with it. When the brakes are applied, the wheel brake cylinder forces apart the fixed brake shoes and presses them against the brake drum, inducing braking.

The brake shoes are also the carrier of the friction material. During braking, there is natural wear of the friction material. The decreasing thickness of the friction material is compensated by a mechanical adjustment mechanism. However, it can only be compensated if there is sufficient friction material. When the wear limit is reached, the entire brake shoe must be replaced. 



Brake pad


The task of vehicle brakes is to decelerate the vehicle safely and comfortably, bringing it to a standstill if necessary. This is done by means of converting the kinetic energy due to friction between the brake pads and the brake discs or drums into thermal energy. In this way the speed of the vehicle is reduced as required by the driver. The brake pads (also known as friction lining) have a very important role to play here. If that the friction linings are to achieve optimum braking results under varying operating conditions, a complex material manufactured from a range of very different components (composite material) is the order of the day. This material must not fail under any circumstances. With high levels of safety in mind, brake pads must combine a constant friction value (friction coefficient) with high mechanical strength and temperature resistance. New brake pads require a specific "running-in period" before they are able to achieve their full braking power. During this phase, the surface of the pad adapts to the surfaces of the discs/drums. It is only after this period that an optimum connection is established between the friction pairs (brake pad/disc, brake pad/drum) so that maximum deceleration can be achieved when braking.

Structure of a disc brake pad
Brake pads have a sandwich-type construction (see Figure 1). 

The brake pad plate (shown in blue) forms the basis of the brake pad.
It must hold the brake pad in the brake calliper and pass the temperature to the neighbouring components. Most brake pads feature damping (shown in black) on the reverse side in the form of springs, foils, sheet steel or paint/varnish, designed to reduce the noise generated during braking. An intermediate layer (shown in green, also known as the underlayer and approx. 2 to 4 mm thick) and the actual friction material are pressed onto the brake pad plate between the brake pad and the brake disc. An adhesive layer just a few µm thick is applied between the brake pad plate and the underlayer. This ensures a secure connection between the plate and the intermediate layer/friction material. Expanded metal, Sinterrauhgrund, a "combed plate" or pin-type anchors can be used as alternative to the intermediate layer or as an additional measure to increase the mechanical strength of the plate connection.


Brake lubricant


Disc and drum brakes can only offer optimum performance if the brake pads/brake shoes are mounted with a certain amount of movement. To achieve this and thus safeguard performance in the long term, garages use non-conductive permanent lubricants when repairing disc and drum brakes. When repairing disc brakes, the guides and contact points for the brake pads, for example, or, depending on the type of brake calliper, its guides too, are lubricated with a permanent lubricant. In the case of drum brakes, permanent lubricant is applied where the brake shoes make contact with the brake anchor plate and the shoe mount, for example.

Permanent brake lubricants are designed not only to provide long-term protection against corrosion for the moving parts of disc and drum brakes and to ensure that they retain freedom of movement. They also prevent noise generation during braking.

However, lubricants containing copper must not be used when repairing brakes. Their electric conductivity encourages electrochemical corrosion. Depending on external influences, this can result in brake components becoming sluggish after a relatively short period. Corrosion and pasting hinder the return travel of the brake pads when the brake is released, leading to noise and increased wear. Furthermore, lubricants containing copper can cause resonant vibration, also resulting in noise generation during braking.

High-quality brake lubricants have numerous benefits for noise-free and safe braking over a long service life. They are characterised by electrical neutrality, extremely low oil separation, low tendency for pasting, high erosion resistance and insensitivity to heat and cold.

Metal-free permanent lubricants from well-known manufacturers can be used for steel and aluminium brake callipers as well as for vehicles with ABS. Permanent lubricants are also suitable for other applications (mounting and protection of compressors, central lubricating systems, seat rails, guides for sliding/tilting sunroofs, retaining straps, battery poles and axle bearings, for example).



Brake fluid


The brake fluid must transmit the pedal force applied by the driver of a car to the wheel brakes. As soon as the driver presses the brake pedal, the force from his foot is exerted on the brake servo the via the pedal. The master brake cylinder converts the amplified foot force into hydraulic pressure. This hydraulic pressure is then transmitted to the wheel brakes via brake lines and brake hoses. The brake fluid acts as a transmission medium in this process. It must meet strict requirements. For example, it must not damage rubber seals. It must protect the components of the brake system against corrosion and wear and, above all, it must be temperature-resistant. This is because some of the heat generated during braking is transferred to the brake fluid. This results in high temperatures which, in extreme cases, can cause the brake fluid to boil. However, when the brake fluid starts to boil, the brake pedal slackens and the braking power drops significantly. When brake fluid boils, vapour locks are produced that can be compressed. Brake pulses are no longer sent to the wheel brakes, the brake pedal goes all the way to the floor and that dreaded moment when nothing happens at all occurs.

It is for this reason that the boiling point of a brake fluid is so important. We speak in terms of the dry boiling point and the wet boiling point. The dry boiling point describes the property of a new brake fluid that is still in its sealed container. It is usually between 240°C and 280°C.

On account of its composition, brake fluid has hygroscopic properties. This means that it draws in moisture from its surroundings, primarily through the brake hoses. As a consequence, the water content of the brake fluid increases over time and the boiling point drops. The temperature known as the wet boiling point is reached at a water content level of 3.5%. Once this point in time has been reached, the brake fluid must be changed.

The actual boiling point of the brake fluid can be determined in a garage using a test device. This test should be carried out annually. To safeguard the function of the brake system, the quality of the brake fluid must meet the specifications defined by the vehicle manufacturer. Furthermore, the prescribed intervals for changing the brake fluid must be observed.

The viscosity of the brake fluid is also very important. It is viscosity which safeguards the function of various brake systems. In modern control systems such as ABS or ESP®, very low viscosity is a prerequisite for absolutely reliable control processes in fractions of seconds. The hydraulic units in these systems have numerous small bores and channels, some of which are smaller than the diameter of a human hair. Selecting a brake fluid with the wrong viscosity can have fatal consequences for the function of modern brake systems.

Minimum requirements for brake fluids have been defined by the United States Department of Transportation (DOT) based on FMVSS 116 (FMVSS stands for Federal Motor Vehicle Safety Standard). The classes in the standard are differentiated on the basis of dry and wet boiling point, as well as viscosity.

Boiling points to DOT standard:





 in °C

 in °C

in mm²/sec









DOT 5.1





The following brake fluids are widely available on the market:

DOT 3 brake fluids are often found in older vehicles. Mixing DOT 3 fluids with other brake fluids is not recommended.

DOT 4 brake fluids have a higher boiling point; they are usually used in the latest vehicle models. For vehicles with electronically controlled brake systems such as ABS or ESP®, some manufacturers supply brake fluids based on DOT 4 but with lower viscosity. They are sold under such names as "DOT4 Plus", "DOT4 Pro" or "DOT4 HP". DOT 5 brake fluid is a silicone-based fluid which is typical of the American market. It must not be confused with DOT 5.1, which is manufactured based on minerals (glycol-based).

DOT 5.1 brake fluid is compatible with the DOT 3 and DOT 4 types. Its outstanding water-holding capacity means that the drop in the boiling point is minimal. This fluid is ideal for extreme operating conditions and drivers who are fans of motor racing.

The mineral-based hydraulic fluids used by some vehicle manufacturers (e.g. Citroen) are not usually categorised as brake fluids. They must not be mixed with DOT brake fluids. DOT brake fluids can be recognised by their fluorescent green/yellow colour.


Single-tube gas-filled shock absorbers


Single-tube gas-filled shock absorbers work along the same principle as a conventional hydraulic shock absorber, but also have a gas cushion that be compressed, therefore creating space for the compressed oil. A floating piston separates oil and gas, thus preventing them from mixing. If the oil is displaced when the spring is compressed, the piston compresses the gas cushion. When the spring then extends, the gas pushes the oil back, similar to a spring. The gas pressure is very high and ensures that even the smallest movements are damped.


Braking force regulator


When the brakes on a vehicle are applied, the vehicle weight shifts from the rear axle to the front axle. This is known as dynamic axle load transfer. The load on the rear wheels is relieved and their road grip is reduced. Too high a brake pressure at the rear axle can cause the rear wheels to lock. As a result they lose their cornering force and the entire vehicle may start to skid.

It is for this reason that braking force regulators, which reduce the brake pressure at the rear wheels, are used in brake systems. Different types of braking force regulator are in use:

  • Braking force limiters only permit a specific set brake pressure to be exerted at the rear wheels. They are usually mounted directly on the master brake cylinder.
  • Load-dependent braking force regulators are used in vehicles in which weight distribution varies significantly based on the number of occupants or the load. They control the brake pressure exerted at the rear wheels based on vehicle load. This prevents locking of the rear wheels and thus avoids the risk of skidding.

In the case of vehicles with diagonal force braking distribution, either two separate braking force regulators or one regulator with two control units are required for the rear wheel brakes. Load-dependent twin regulators accommodate two identical control units which work independently and in parallel in a single housing. If one circuit fails, the brake circuit that remains intact can continue working unaffected.

Electronic brake systems feature integrated electronic brake force distribution as standard. The brake pressure on the rear wheels is limited as soon as a defined pressure is exceeded. No additional components are required in the brake circuit.


Brake lines


When the driver presses the brake pedal, hydraulic pressure is generated in the master brake cylinder. So that a braking force can be produced from this, the hydraulic pressure must be transmitted to the wheel brakes with the assistance of the brake fluid. In motor vehicles, this happens via the brake lines. Brake lines are categorised as brake pipes or brake hoses on the basis of their design.

Brake pipes are rigid they are made from steel. They are installed in the engine compartment, underneath the car body or in the wheel arches, i.e. anywhere where movements of brake lines are not to be expected. Depending on the application, brake pipes vary in shape, length, diameter and connection fittings. A plastic or zinc coating provides protection against corrosion.

Brake hoses create a flexible connection between brake pipes and wheel brakes. They transmit the hydraulic pressure to the wheel cylinders and brake callipers. Brake hoses are usually made form a special inner and outer rubber with a multi-layer fabric insert in between. There are also brake hoses that are sheathed in steel braiding (braided stainless steel brake hoses). These types of brake hose have a particularly long service life. As braided stainless steel brake hoses also expand less even at increased brake pressure, the pressure point at the brake pedal is also more exact and braking can be dosed more precisely.



Brake calliper


The brake calliper is an essential part of the disc brake system. It must hold and guide the brake pads. With the assistance of one or a number of pistons, it also converts the hydraulic pressure in the brake system into a mechanical force which presses the brake pads against the brake disc. Brake callipers are located near to the wheels – on the left and right of the front axle. Vehicles with disc brakes at the rear axle too also have brake callipers there.

When the driver presses the brake pedal, overpressure relative to the atmospheric pressure is created in the hydraulic system. This pressure is transmitted to the brake callipers via the brake lines and hoses. When it reaches the callipers, it causes the brake calliper pistons to push the brake pads against the brake disc. As a result, the friction at the brake increases, causing the moving vehicle to slow down or stop completely. When the brake pedal is released, the overpressure in the brake system drops back. The rubber seal on the piston pushes the piston back to its original position. The brake disc can then turn freely again.

In most cases, the brake callipers are equipped with one or two pistons. Up to four pistons per brake calliper can be installed in high-performance or very heavy vehicles. In very few cases, there are even designs where two complete brake callipers are used for each wheel.

Alongside the service brake, which is needed to slow down a moving vehicle, the brake calliper can also take over the function of the parking brake. The parking brake must secure a stationary vehicle against rolling away. When the parking brake is applied, a force is applied mechanically to the brake piston and thus to the brake pad. This is sufficient to hold the stationary vehicle even on an incline. The parking brake can be applied purely mechanically by means of a lever system (traditional handbrake lever inside the vehicle) or with electrical assistance in the form of an electric motor and a gearbox or a cable (electromechanical parking brake).


By far the most widely used design in motor vehicles is the floating calliper. In this design, the pistons only press on the inner brake pad, pushing it onto the brake disc. The outer brake pad is pushed onto the brake disc with the same force by the reaction force of the floating brake calliper.

The fixed calliper is another design. It is used primarily on the rear axle. With a fixed calliper, there is a hydraulic piston on each side of the brake disc.



Brake disc



The brake disc is an important component of the brake system. If the brake system is to be able to decelerate the vehicle in safety and comfort at all times – bringing it to a complete stop if necessary – the brake disc must combine with the brake pads to generate a brake torque (a brake force). This torque is transmitted to the wheel hub and from there to the wheel rim. During braking, the vehicle's kinetic energy is converted into thermal energy due to friction between the brake pads and the brake disc, thereby enabling a reduction in speed to be achieved.

The disc brake was originally developed for motor sport. Having enjoyed considerable success in that field, it rapidly established itself in the front wheels of passenger cars in the 1960s. The drum brake that had been used prior to this time had numerous weak points brought about by its design, including temperature problems, distortion and fading, oscillating friction values, poor dosing, high wear and noise generation (squealing). For many years after this, the disc brake was only seen very rarely at the rear wheels, where thermal load is lower.


90% of the heat generated during braking penetrates the brake disc initially, where it is buffered. After this it is passed on to the ambient air. The brake disc thus functions like a heat exchanger. However, its ability to absorb heat is limited. Therefore, the heat must be dissipated to the ambient air quickly if damage due to overheating is to be avoided.

During downhill driving, the friction ring can reach temperatures of up to 700°C (red heat). For this reason, ventilated brake discs are very often used for better cooling – primarily at the front axle. Their surface area is much larger and better suited for heat exchange. Compared with ventilated brake discs, solid brake discs can only dissipate heat to the environment more slowly.

The friction rings on ventilated brake discs are interconnected by means of webs in the shape of ribs or domes. The rotation of the brake disc generates air suction which draws air out from the inside of the brake disc through a ventilating duct. The tiny particles of air that this causes to come into contact with the surface of the brake disc absorb the thermal energy and transport it outwards.

Even more effective cooling can be achieved with perforated or grooved brake discs. These types of disc also benefit from being less sensitive to wet. However, they are more expensive and can in some circumstances generate much more noise during braking.

Friction rings on brake discs generally have a tendency to deform when heated up. This can lead to unpleasant noise generation and vibrations during braking (brake judder). It is for this reason that well-known brake manufacturers are striving to find ways of adapting the design of brake discs in order to prevent deformation.

However, in some cases, brake judder is unavoidable, as vibrations or play in wheel bearings can bring brake pads into repeated contact with the brake disc even when no active braking is taking place. The resulting localised flatting of the brake disc, which after a certain period of time will lead to pulsating braking, then becomes apparent to the driver in the form of judder.

Brake disc material

Brake disc material must meet strict requirements. It must be able to withstand mechanical stress applied as a result of pressure and tensile forces during braking, centrifugal forces at high wheel speeds and thermal loads.

Most brake discs are made from a special grey cast iron (pearlitic grey cast iron). Alloys with chrome and molybdenum increase resistance to wear and improve the material's hot crack characteristics. Furthermore, a high carbon content increases heat absorption rates.

Ceramic materials (carbon fibre ceramic or carbon ceramic) are also increasingly being used to manufacture brake discs. The benefits of these brake discs are high dimensional stability in all temperature ranges, low own weight, good brake response, extremely long service life and very good fading characteristics. Their disadvantages include poor heat conductivity (which then requires special materials for the brake pads) and very high price. The latter doubtless explains why ceramic brake discs are currently only used as special equipment on high-power premium class vehicles.


Brake drum


Brake drums are an essential component of drum brakes. Together with the brake shoe, a brake drum forms a friction pair, which decelerates the rotation of the wheel. The brake drum also has the job of absorbing and discharging the heat generated during braking. This is particularly important because the friction effect between brake drum and brake shoe lining lessens as temperatures rise. This can lead to what is known as fading, i.e. the waning of the braking effect at high temperatures.

In order to ensure sufficient braking effect regardless of load, the brake drum must be dimensioned with adequate stability. Its diameter must not expand beyond a permissible limit under load and at high temperatures. Optimum surface roughness of the friction surface, good thermal conductivity and narrow form and positional tolerances are further guarantees of stable friction values and thus reliable and safe braking.

Brake drums are constantly exposed to spray water and road grime and, in the winter, to aggressive substances such as road salt. To stop them rusting too quickly, many well-known suppliers now feature brake drums with anti-corrosion coatings in their product portfolios. Anti-corrosion coatings ensure that brake drums will continue to look good following replacement.

Many vehicle models feature wheel bearings which are integrated into the brake drums. For safety reasons, the wheel bearing must always be replaced at the same time as the brake drum. It is for this reason that well-known manufacturers offer brake drums with ready-integrated wheel bearings. These complete kits speed up garage repair work and thus cut repair costs.


Wheel sensors


The wheel sensor has the task of recording the speed of the wheels and communicating this information to the driving safety systems in the form of an electrical signal. All modern vehicles are equipped with wheel sensors. This is because the ABS Anti-lock Braking System is now a standard feature of all new vehicles in Europe. The Electronic Stability Program (ESP®) is not far behind. The quick and precise recording of speeds, movements and physical forces applied to the vehicle is crucial for the functioning of electronic driving safety systems.

The very first ABS systems featured the use of what are known as passive wheel speed sensors. Working on the basis of the principle of induction, they supply an analogue output signal in the form of an alternating voltage. The signal from the passive sensor can only be evaluated meaningfully by the control unit from a speed of around 7 km/h. The passive wheel speed sensor is characterised by the fact that it picks up its signal from a sensor toothed wheel. This is usually pressed onto the brake disc or brake drum, the axle or the wheel hub.

Due to the expansion of the ABS with the addition of functions such as ESP® or anti-slip control (ASC), wheel sensors that are able to emit a useful signal at a standstill are now the order of the day. Active wheel sensors are able to meet this requirement. They work in accordance with the magneto-resistive principle, are supplied with voltage and pick up their signal from what is known as an encoder wheel. The latter is a magnetic ring with a precisely defined number of north and south poles. The active wheel speed sensors can also detect the wheel's direction of rotation and are considerably less mechanically sensitive than passive wheel sensors. This means that they are resistant to corrosion and that changes to the distance between the sensor and the encoder wheel (e.g. as a result of a "tilting" brake disc) do not affect the sensor signal. As such, they can function in the presence of a large air gap between the sensor and the encoder and in a wide temperature range between -40 and +150°C.

A further advantage of active wheel sensors is the fact that they supply a digital output signal. This can be used by the control unit directly, without the need for conversion. Active wheel sensors also supply more precise speed information, which can be used by other vehicle electrical systems, such as navigation devices.



Wheel cylinders


A wheel cylinder is a component of a hydraulic drum brake.

It comprises a housing made from made from grey cast iron or – in the case of newer models – aluminium, which is more lightweight. Other components of a wheel cylinder are one or two pistons, sleeves, compression springs, gaskets, protective caps and the bleeder valve.

The wheel cylinder must force apart the brake shoes and press them against the brake drum. This generates friction and the wheel is decelerated. This happens every time the driver presses on the brake pedal. Pressing on the brake pedal generates a hydraulic pressure in the master brake cylinder which is transmitted to the wheel cylinder in the brake fluid via the brake lines. In the wheel cylinder, the hydraulic pressure acts on the pistons, which then exert mechanical pressure on the brake shoes. 


Drum brake


The drum brake is almost as old as the car itself! It is still installed in modern cars today, although naturally in a modified and more developed format. It is primarily used at the rear axle of small cars and vehicles in the compact class.

Essentially, the drum brake comprises the brake drum, brake shoe, wheel cylinder, armature plate, adjusting mechanism, return springs and various attachments and actuators. The brake drum is fixed to the wheel and turns with it. During braking, the wheel cylinder forces the fixed brake shoes apart and presses them onto the brake drum, which is decelerated as a result. When the brake is released, the return springs return the brake shoe to its original position.

The drum brake continues to offer interesting advantages:

- Resistant to dirt through a closed system

- Easy integration of the parking brake possible

- Braking force due to self-reinforcement

- High durability and longevity

- Cheap

As well as being less expensive than disc brake pads, drum brake pads do not tend to "glaze" as quickly. "Glazing" is a hardening of the pad material caused by a combination of low levels of stress, frequent short journeys and low speeds. Pressing down hard on the brakes usually wears away the "glazed" coating and the pad returns to performing at full capacity. Another advantage of the drum brake is an automatic boost to braking force. Less force has to be exerted to apply the brake.

Furthermore, unlike the disc brake, the drum brake features an enclosed, cylinder-shaped design (hence its name). One advantage of the encapsulated design is that brake dust is unable to escape to the outside. Another is that the wheel brake is afforded better protection against the ingress of moisture and dirt from the outside, thus making it less sensitive to the effects of the environment. In addition, it is easier to use a drum brake system for the hand brake.

Like all technical developments, the drum brake also has its disadvantages.

 - For example, low thermal load and high sensitivity to variance in friction values mean that they can only be used at the rear axle.

 - High temperatures can significantly impair braking performance and wear repairs take longer compared with a disc brake.




Computer-assisted electronics account for most of the inner workings of modern motor vehicles. The number of control units installed in a vehicle, networked via a data bus and communicating with one another is very often in double figures.

Over time, almost all mechanical control components have been replaced by equivalent electronic circuits. Powerful electronic control unit open up whole new possibilities where safety and comfort are concerned. Complex systems (ABS, ESP, parking assistants and ACC, for example) can be implemented relatively easily.

This development has completely changed how garage mechanics work. Gone are the times in which troubleshooting relied solely on specialist knowledge, an open-end spanner and a screwdriver. Today, in-depth system knowledge, the latest garage software and a powerful control unit diagnosis system provide the basis for repairing modern vehicles. Control unit diagnosis is facilitated by communication with the vehicle electronics. This enables faults to be located more quickly in the garage or other service functions to be activated, for example.

Options supported by control unit diagnosis

A garage mechanic using the control unit diagnosis system can read out the fault memory of the systems installed in the vehicle, for example. If the fault memory contains error code entries, the expert mechanic must interpret them correctly. (Just because a fault code has been entered for an electronic component, this does not necessarily mean that the component is faulty.) Before a garage mechanic replaces a component, they must use conventional test methods (a signal generator, a multimeter or an oscilloscope, for example) to identify the exact cause of the fault. Powerful diagnosis devices can be used for vehicle-specific guided troubleshooting in such cases. The garage mechanic works through preconfigured test steps and is assisted by images and nominal values. Once the repair work is complete, the fault memory can be deleted with the diagnosis system.

For many vehicles, a diagnosis system has become essential even for standard tasks such as resetting service intervals, brake repairs or oil and battery changes.


The range of diagnosis systems is comprehensive, extending from diagnosis modules which are connected to a PC to touchscreen and handheld devices and even tablet PCs. Many devices are equipped with a Bluetooth interface for wireless data transmission.

The control unit diagnosis system is completed by a powerful garage software package which contains the control unit diagnosis software, service information, troubleshooting instructions, nominal values, job values, technical vehicle data for petrol and diesel vehicles, circuit diagrams for all important areas of convenience electronics and information about adapter plug requirements.

The latest generation control unit diagnosis systems feature a built-in camera to take photographs of anything out of the ordinary on the vehicle or parts that need to be replaced.

Control unit reprogramming to Euro 5

Going forward, the technical requirements for type approval will apply universally for the entire EU. According to these requirements, automotive manufacturers have an obligation to make technical repair information available on their online portals to independent garages also, and to provide independent garages with the necessary means to reprogramme control units. Only diagnosis systems with Euro 5 approval may be used in this context. These are devices which already feature what is known as a "Pass-Thru" interface. This interface is a communications driver which is used when reprogramming control units. These control unit diagnosis systems can install the latest software version from the manufacturer's online portal in a vehicle's control unit if this is required.





Combustion engines in motor vehicles need starting assistance in order to run independently. The starter is one of the most important components of the starter system. As well as the starter, the system includes switching devices and control units, cables and the starter battery.

To reach the speed required for the engine to run independently with as small as possible a starter motor, the significantly higher speed of the starter is adapted to the engine speed by means of a ratio between starter pinion and engine ring gear.

Starter design

The starter comprises the following assemblies:

– Electric motor
– Engagement system
– Freewheel
– Pinion and possibly countershaft transmission

During starting, the engagement relay engages the starter pinion in the gear ring. The starter motor is linked to the starter pinion either directly or via a countershaft transmission which sets back the speed of the DC motor. The starter pinion drives the combustion engine via the motor gear ring until it is running independently.

Once started, the combustion engine can accelerate quickly to high speeds. Even after just a few power strokes, the engine speed is higher than it was during starting. To protect the starter against speeds that are too high and thus against mechanical damage, the starter pinion is fitted with a freewheel which isolates power transmission between pinion and armature. When the ignition key is released, the starter relay drops out and the disengagement spring releases the pinion from the gear ring.



In addition to conventional starters, various manufacturers offer starters for use in fuel-efficient start/stop systems. These start/stop systems enable reductions of up to 8% to be achieved in CO2 emissions and fuel consumption during urban driving (ECE15 test cycle). In real urban driving situations, savings can be even higher.

The principle of operation of the start/stop system is as easy as it is efficient: When the vehicle is at standstill and the battery charge is sufficient, the combustion engine is switched off. To resume travel, simply press the accelerator to restart the engine. So, when the vehicle is stationary in traffic (in a traffic jam or at a red light, for example), no fuel is consumed and no CO2 is emitted. What's more, noise emissions are reduced to zero.

Starters for passenger cars must be lightweight, small, powerful and economical. The latest models impress with their lightweight, compact design, as lower weight reduces both fuel consumption and emissions. Furthermore, small starters create more room for design during vehicle development.

The aim of future development work will continue to be to reduce frame size and weight whilst maintaining or increasing power and performance.





The battery stores electrical energy and supplies power to the vehicle electrical system. In modern vehicles, the battery is not just needed to start the engine. It must also supply power to a large number of different electrical consumers. Convenience elements in particular (the air conditioning system, for example) but also safety systems such as the ABS and ESP have additional energy requirements which are not supported by the output of the alternator alone. This is particularly relevant given that standing traffic is an increasingly common sight in city centres, reducing the output of the alternator as a result.

New drive systems such as start/stop and hybrid vehicles are also placing new requirements on the performance and reliability of a modern starter battery. Similarly, starter batteries for trucks and HGVs have to meet specific requirements. They need to demonstrate particularly high vibration and cycle resistance. With these considerations in mind, modern AGM (Absorbent Glass Mat) batteries are at a significant advantage. In this type of battery, the electrolyte is bound in an absorbent glass fleece. This technology prevents acid layering and ensures very high vibration and cycle resistance at maximum output.

Design and technology

In order for a lead-acid battery to emit current, the positive mass (lead dioxide) and the negative mass (lead) must be in direct contact with diluted sulphuric acid. The cell is the smallest unit in a battery. It contains positive and negative plates which are divided by what are known as separators (isolators). The more plate volume the cell has, the larger its capacity (in other words, the larger the plate volume, the more electricity the cell can emit). The cell also contains diluted sulphuric acid. This acid penetrates the plates and separators, filling the cavities so that lead-oxide or lead particles are constantly in direct contact with acid. Therefore, some of the acid poured into the cell is to be found in the plates and separators and some of it outside the plates. The acid outside the plates acts as reserve acid and of course also helps to conduct the current inside the cell.

The battery in use

When the battery is connected to a load, a current flows, discharging the battery. The electrons move from the negative plate to the positive plate. This is offset by sulphate ions moving from the electrolyte to the negative plate, where they combine with the lead to form lead sulphate. Lead sulphate – with formation of water – is also produced from the lead dioxide at the positive plate when sulphate and hydrogen ions are consumed.

For charging, the battery is connected to a DC voltage source. The electrons flow from the positive plate to the negative plate. At the negative plate, the flow of electrons reduces the lead sulphate. At the positive plate, a process involving the release of electrons and the absorption of oxygen atoms turns the lead sulphate into lead dioxide. Sulphuric acid forms in the fluid and the amount of water is reduced.





The alternator is relied upon to supply power to the vehicle electrical network regardless of operating conditions. This power supply is needed not only by the engine but also by numerous safety and convenience systems. The alternator must also supply enough current to reliably charge the battery.

The alternator is driven by the engine via a V-belt drive or a V-ribbed belt drive and operates according to the principle of electro-magnetic induction. Accordingly: When an electrical conductor moves through a magnetic field, an electrical voltage is induced in the conductor. It does not matter whether the magnetic field or the conductor is moving. The main components of an alternator are the stator winding, the rotor, the regulator and the rectifier.

The rotor must generate the magnetic field. The intensity of the magnetic field is determined by the current flowing through the rotor. This is controlled by the regulator. As soon as the rotor turns, it generates an alternating voltage in the stator windings. Before it reaches the vehicle electrical system, this voltage is converted into a direct voltage by the rectifier diodes.



Alternator regulator


A fully charged car battery is essential if a vehicle is to function trouble-free. The alternator regulator must monitor and control the process to charge the battery. It must also ensure that all power loads in the vehicle have sufficient energy to function. The alternator control is usually a component of the alternator. Due to the different power ratings of alternators and the large number of alternator manufacturers, there are now several hundred different types of regulator.

The current flowing through the rotating solenoid (rotor) is the decisive factor for regulating the output generated by the alternator. This current is used to alter the magnetic field. It is controlled by the alternator regulator based on the battery voltage, which has been measured in advance. This measurement process is repeated up to several hundred times a second so that a change in charge at the battery can be compensated very quickly. The voltage generated by the alternator must be higher than the battery voltage. Depending on the vehicle manufacturer's specifications, the alternator will have a control voltage of between 14 and 15 V for passenger cars and between 28 and 29 V for trucks and HGVs.

Rather than varying the current in the rotor in the same way, the regulator uses a process of switching the current on and off for different lengths of time (duty cycle). So, if the current is switched on for a prolonged period and is off only for a short time during a control phase, the alternator will supply a high output. Conversely, the output from the alternator will be low if the regulator only switches the current on for a short time and leaves it off for a prolonged period. The alternator regulator also automatically adapts the battery charge to the ambient temperature. This is necessary because the charge characteristics of the car battery are not the same at -20 °C, for example, as they are at +30 °C. The regulator takes care of the need to adapt the battery charge automatically with a charging curve which is specified in the data sheets as a temperature coefficient.

Additional functions going beyond the charging of the battery were first added to the remit of alternator regulators around 15 years ago. For example, the alternator remains switched off initially when the engine starts up. Only once the engine is running is the output from the alternator increased.This process takes between 2 and 10 seconds to complete and follows a slowly ascending charging curve. This helps starting at cold temperatures in particular or if the battery charge is low.

The regulator also minimises the mechanical stress placed on the drive belts, the bearings and the tensioning pulley of the alternator Mechanical stress occurs when there is a change in load due to loads in the vehicle being switched on or off (e.g. the headlights, heated seats, etc.). Every time there is a change in load, the alternator regulator regulates the alternator output to the setpoint following a slowly ascending or descending charging curve. Without this function, the entire output requirement would change within a tenth of a second.

A trend has developed recently whereby in many vehicles, it is not the alternator regulator which monitors the battery voltage but the engine control unit. The engine control unit is connected to the alternator regulator either with a separate cable or via the bus system. It controls the regulator using many different factors. In cases like these the regulator simply functions as a straightforward on/off switch.




Actuators are an essential part of electronic control systems in passenger cars and commercial vehicles. It is their job to convert the electrical signals from the control unit into an action. Most actuators are electric motors or electro-magnetic valves. They adjust flaps, for example, regulate the flow of fluids or actuate pumps to build up pressure (e.g. in brake and steering systems).

In the engine control system, actuators regulate the idle speed, control air flaps for torque and power optimisation and meter fuel for optimum combustion. In convenience systems they are used to lock and unlock car doors, for example, or for the remote control of fuel filler flaps, boot lids, engine bonnets and storage compartments.



Throttle valve


In general terms, the throttle valve must regulate the air or mixture supply for the combustion engine. Depending on the engine concept, this serves different purposes. In the case of petrol engines, speed and power output are regulated by means of fresh air or mixture dosing. Diesel engines generally do not need a throttle valve. However, in modern diesel cars, throttling the amount of intake air facilitates precision control for exhaust gas recirculation and stops the engine from shaking when the ignition is switched off.

The throttle valve is installed in the intake air system of the combustion engine. The opening angle of the valve determines how much fresh air or air/fuel mixture flows into the cylinders (carburettor engines, for example). In older generation engines, the throttle valve is connected directly to the accelerator pedal and operated mechanically via a cable. For newer vehicles there are various principles of operation:


Electromotive throttle actuators:
With electromotive throttle actuators, the position of the throttle valve is regulated mechanically via the accelerator Bowden cable. The throttle valve electronics forward the position of the throttle valve to the engine control unit as an electrical signal. This information is compared with other up-to-date data from a variety of engine management sensors. The engine control unit permanently calculates the optimum throttle position for consumption and exhaust gas emissions and sends this information back to the throttle valve as an electrical control signal. The position of the throttle valve is then fine-tuned with the assistance of a servomotor.


Electronic throttle actuators:
With electronic throttle actuators, there is no direct connection to the accelerator pedal. The driver's desired load is captured by an electronic accelerator pedal (electromotive throttle actuator). The engine management permanently matches this signal to all other available data from the engine sensors, using the information obtained to calculated the optimum throttle position for the prevailing situation. The electronic throttle actuator is controlled exclusively using the control signal from the engine management and with the assistance of a servomotor.


Air management valves:
If throttle valves are used in diesel engines, they are generally referred to as air management valves. Air management valves can be with or without integrated control electronics. As indicated above, air management valves throttle the intake air in the intake air system of diesel engines via electromotive means in order to achieve precision controlled exhaust gas recirculation and prevent the inconvenient shaking that would otherwise occur when the engine is switched off.


Air flap servomotors:
Air flap servomotors are electrical actuators with integrated position sensor and optional integrated electronics. They facilitate the continuous adjustment of intake pipe flaps or turbocharger guide vanes, for example, and, by means of more precise control, are able to replace conventional pneumatic drives which are no longer sufficient for the advanced requirements that have to be met.





Throttle valve sensor


Throttle valve sensors are attached to the throttle valve axle. They capture the opening angle of the throttle valve and forward this information to the engine control unit as an electrical signal. The engine electronics uses this value to calculate the fuel quantity injected on the basis of other factors such as engine temperature, air pressure, speed, etc. Throttle valve sensors are available in a variety of designs:

Throttle switches

There are two switches inside a throttle switch. Each is actuated via a shift gate. The engine electronics uses the two switches to detect the two load conditions idling and full load. During idling the throttle valve and the idling switch are closed. At and above a fixed opening angle, the full load range starts and the full load switch is closed. When the full load switch is closed, the fuel injection quantity is increased to optimise performance.

Throttle potentiometer

With the throttle potentiometer, the opening angle of the throttle valve is captured with the assistance of a variable resistance. As there is a set ratio between the opening angle and the resistance value, the engine electronics can detect the angle of the throttle valve at all times. The angular velocity (i.e. the time in which the changes are made to the angle of the throttle valve) is captured at the same time. In the event of a rapid change (if the driver presses the accelerator pedal down quickly), the engine electronics will inject more fuel to achieve good acceleration.


Oxygen sensor


The oxygen sensor is an instrument for controlling the exhaust emissions of petrol, diesel and gas engines. It is an oxygen concentration sensor which measures the residual oxygen content of the exhaust gas and then transmits a signal to the engine control unit in the form of an electric voltage. The oxygen sensor voltage allows the control unit to detect whether the mixture is too lean or rich. If the mixture is too rich, the control unit reduces the quantity of fuel in the A/F ratio and increases it if the mixture is too lean.

The value measured by the oxygen sensor allows the control unit to adjust the amount of fuel injected to obtain an optimum mixture. This creates ideal conditions for treatment of the exhaust gases in the catalytic converter Is the engine load taken into account here. There may also be a second oxygen sensor, the diagnostic sensor (downstream of the catalytic converter). This detects whether the control sensor (upstream of the cat) is functioning to optimum effect. The control unit can then calculate how to compensate for this.

Configuration in the exhaust gas system

In more recent engines, the exhaust system has an oxygen sensor upstream and downstream of the catalytic converter. The exhaust gases flow over the electrode side of the sensor element, while the other is in contact with the outside air. The outside air acts as a reference here for measurement of the residual oxygen content. The system has been simplified by the latest generation of oxygen sensors, in which the reference value measured against the outside air is replaced by a reference voltage.

Types of oxygen sensor

Today there are basically two different types of sensor: the binary and the universal exhaust gas oxygen (UEGO) sensor. When at operating temperature (from 350 °C), the binary sensor generates a change in electric voltage depending on the oxygen level in the exhaust. It compares the residual oxygen content in the exhaust with the oxygen level of the ambient air and identifies the transition from a rich mixture (lack of air) to a lean mixture (excess air) and vice versa.

The universal exhaust gas oxygen sensor is extremely accurate when measuring both a rich and lean air/fuel ratio. It has a greater measuring range and is also suitable for use in diesel and gas engines.

Nowadays heated oxygen sensors are used to ensure the oxygen sensors reach operating temperature more quickly and can thus intervene earlier in the emission control process. Heated HEGO sensors no longer always have to be installed close to the engine.

Structure of the oxygen sensor

Finger-type sensor

The core of the finger-type sensor consists of a finger-shaped ceramic element. It is heated by a heater incorporated in the sensor as control is only possible with a minimum operating temperature of 350 °C. The exhaust gases flow over the electrode side of the sensor element, while the other is in contact with the outside air. The outside air acts as a reference here for measurement of the residual oxygen content. To protect the sensor element from combustion residues and condensate in the exhaust gas, the sensor housing is fitted with a protection tube on the exhaust gas end.

Planar sensor

The planar oxygen sensor is manufactured using thick-film-technology. The shape of the sensor element resembles an elongated plate. Both the measuring cell and the heating element are integrated in this plate, so allowing the sensor to attain its operating state more quickly. Here too suitable protection tubes are used to protect the sensor element from combustion residues and condensate in the exhaust.


Wheel sensors


Today, the anti-lock brake system (ABS) is a standard feature of all new vehicles in Europe. ESP® is not far behind. To function reliably, electronic driving safety systems need information about the speed of the wheels, the dynamic behaviour of the vehicle and the forces that are acting on the car. Wheel speed sensors (also known as wheel sensors) must detect the speed of the wheels and supply this information to the ABS or ESP control unit in the form of an electrical signal. The latest wheel sensors are also able to detect the direction of rotation of the wheels. The ABS control unit uses this data to detect individual wheels locking during emergency braking and take countervailing measures to stabilise the vehicle. The EPS does the same thing as soon as it detects a critical situation on the basis of the wheel speed data and other sensor information.

Passive wheel sensors

The very first ABS systems featured the use of what are known as passive wheel sensors. Working on the basis of the principle of induction, they supply an analogue signal in the form of an alternating voltage to the electronic control unit. The passive sensor is characterised by the fact that it picks up its signal from a sensor toothed wheel which is usually pressed onto the brake disc or drum, the axle or the wheel hub. Passive wheel sensors are able to supply useful signals at and above approx. 7 km/h.

Active wheel sensors

Due to the expansion of the ABS with the addition of sensors such as ESP® or anti-slip control (ASC), sensor systems that are able to emit a useful signal at very low speeds (virtually as low as standstill) are now the order of the day. Active sensors are able to meet this requirement. They work in accordance with the magneto-resistive principle, are supplied with voltage and pick up their signal from what is known as an encoder wheel (magnetic pulse sensor). As well as being able to detect wheel speed up to vehicle standstill, active wheel sensors are also able to detect the direction of rotation. Also, from a mechanical point of view, they are much less sensitive than passive sensors. This is evident for example in their corrosion resistance, as well as in the fact that the sensor signal is not affected by varying sensor distances (caused by a "tilting" brake disc, for example).

Furthermore, the ability of active wheel sensors to function can also be relied upon in a temperature range from -40 to +150°C. Another of their advantages is that they supply a digital output signal; this does not require downstream conversion and can thus be evaluated directly by the control unit.  Thanks to the far greater precision of the available speed information, the signals of active wheel sensors can even be used by other vehicle systems such as engine and transmission control, or even the navigation system. 






In a way, sensors are the sensory organs of the vehicle. A fundamental component of electronic control systems, they must record physical or chemical variables and convert them into electrical signals. In recent years, there has been an explosion in the number of different types of sensor. Many new types of sensor have been seen in particular in the area of safety and convenience electronics. Essentially, sensors can be categorised as follows:

Position sensors (distance/angle sensors)

... are used to capture the position of the throttle valve, of the accelerator or brake pedal, of the distance and angular positions in diesel injection pumps, of the fill level in the fuel tank, of the steering angle, of the angle of tilt, etc. The ultrasonic and radar sensors used to determine distances from obstacles for modern driver assist systems also belong in this category.

Speed and velocity sensors

... are used to determine the speed of crankshafts, camshafts and diesel injection pumps or wheel speeds. Yaw rate sensors also belong in this category. They detect the rotational movement of the vehicle about its own axis and are needed for ESP.

Acceleration sensors

... record the acceleration of the car body and are used in passive safety systems (airbags, seat belt tensioners, roll bars) and driving stability systems such as ABS and ESP, as well as in chassis control.

Pressure sensors

... are used to capture a wide variety of pressures including suction or charging pressure, fuel pressure, brake pressure, tyre pressure, hydraulic reservoir pressure (for ABS and power steering), refrigerant pressure (air conditioning system), modulation pressure (automatic transmission) and so on.

Temperature sensors

... are used to capture temperatures, e.g. in the context of measuring suction or charge air temperature, ambient and interior temperatures, evaporator temperature (air conditioning system), coolant temperature, engine oil temperature, tyre air temperature and so on.

Force and torque sensors

... are used to measure forces such as pedal force, drive, brake and steering torque forces or the weight of the occupants of a vehicle (for adaptive restraint systems).


... are used to capture the fuel requirement and the amount of air drawn in by the engine.

Gas sensors

... capture the composition of the exhaust gas (oxygen sensor, NOx sensor) or detect hazardous substances in the fresh air supply.

Examples of sensors for engine control:

Pulse sensor, crankshaft

The crankshaft sensor captures the engine speed and the position of the crankshaft. The control unit uses these values to calculate the injection pulse and the ignition pulse.

Camshaft position

The camshaft sensor is located at the cylinder head and scans a ring gear at the camshaft. This information is used, for example, for the start of injection, for the signal to activate the solenoid valve for the pump/nozzle injection system and for cylinder-specific knock control.

Air mass meter

The air mass meter is installed between the air filter housing and the intake manifold. It measures the air mass drawn in by the engine. This variable provides the basis for calculating the fuel quantity that must be supplied to the engine.

Intake air temperature/Outside temperature/Interior temperature

Air temperature sensors capture the temperature of the ambient air. The values measured are used to control various systems (e.g. the air conditioning system) or as correction values for the injection system. The installation location is determined by the air temperature to be measured. The sensor for the intake air temperature, for example, is located in the air duct for the intake air.

Coolant temperature

The coolant temperature sensor is screw-mounted in the cooling system. The gauge tip protrudes into the coolant and records its temperature. The control unit uses this value to adapt the amount of fuel injected to the engine temperature.

Throttle position

Throttle valve sensors are attached to the throttle valve axle. They monitor the opening angle of the throttle valve. From the values, the engine electronics calculates the fuel quantity which is injected based on other factors.

Knock sensors

Knocking is an uncontrolled form of combustion in a petrol engine. As continuous knocking can damage the engine, it must be checked and regulated. The engine control unit evaluates the voltage signals received from the knock sensor and regulates the ignition point in a range just below what is known as the knock limit. Knock sensors are permanently monitored by the control unit.

Intake pipe pressure

The intake pipe pressure sensor measures the intake pipe vacuum downstream of the throttle valve and forwards this value to the engine control unit as an electrical signal. This is combined with the value of the air temperature sensor so that the air mass drawn in can be calculated.

Oxygen sensors

The oxygen sensor measures the residual oxygen content in the exhaust gas in order to ensure an optimum combustion mixture at all times. Depending on the type of sensor, a chemical element (titanium dioxide/zirconium dioxide) and the residual oxygen content of the exhaust gas bias a voltage, which is then used by the control unit as a measured variable.

Examples of sensors from car body electronics:

Wheel speed

The wheel speed is used by driving safety systems such as ABS and ASR as a speed value as well as by GPS systems to calculate distance travelled. A fault will cause these systems to fail, significantly impairing safety.

Speed, transmission

The transmission sensor captures the transmission speed. The speed signal is used by the control unit for precision control of the shift pressure during shifting and to decide which gear should be engaged when.

Speed, distances travelled

Distance sensors are used to capture driving speed. They are mounted on the transmission or rear axle. They information obtained is required for the speedometer, cruise control and converter slip control.

Engine oil level/Coolant level

For reasons of operational safety and for increased comfort, levels such as engine oil, coolant and washer fluid are monitored with level sensors. The level sensors send a signal to the engine control unit which activates an indicator lamp.

Brake lining wear

The brake wear sensors are located on the brake linings and are subject to the same wear. A visual signal tells the driver that the wear limit has been reached.



Spring strut support bearings


Spring strut support bearings (also known as tower bearings) are part of the spring damping system, acting as the interface between spring strut and car body. As an important construction element of the axle suspension, they contribute to optimum contact between tyres and road surface and increase comfort by isolating tyre noise and road noise from the car body. They must also facilitate precision low-friction rotation of the spring struts on the front axle about the longitudinal axis. This provides the basis for accurate and smooth steering and/or resetting of the wheels.

Where areas of application are concerned, a distinction is made between spring strut support bearings for the front axle and those for the rear axle. As the requirements of these areas of application are not the same, spring strut support bearings for the front axle are designed and built differently to those for the rear axle.

Spring strut support bearings for the front axle
Modern cars overwhelmingly use McPherson spring struts. They are supported on the car body by spring strut support bearings which contain a ball bearing. The ball bearing is able to absorb high forces yet allows the spring strut to rotate smoothly. Over time, the design of the spring strut support bearing has been adapted to meet market requirements.

Spring strut support bearings for the rear axle
Spring strut support bearings for the rear axle do not contain a ball bearing, as spring struts for the rear axle are usually mounted rigidly. In most cases, a rubber/metal design is used. Spring strut support bearings for the rear axle can usually be replaced without special tools.



Wheel suspension


The wheel suspension is part of the chassis. The chassis comprises the following components: wheels, wheel carrier, wheel bearing, brake, wheel suspension, axle support, suspension (including anti-roll bar), damping, steering gear, steering column, unit mount (e.g. engine and transmission bearings), side shafts, axle drive and suspension control systems. In a mid-class vehicle, these components account for 20% of total weight.

On the one hand, the function groups listed are self-enclosed systems. On the other hand, they must be precisely co-ordinated in order to optimise the functionality of the chassis as a whole.

Within the chassis, the role of the wheel suspension is to optimise wheel control. As such it represents the link between the wheel contact face and the vehicle body and transmits all forces and movements from the wheel carrier to the body. For safety purposes, this process must take place quickly and without delay. This is achieved with hinged links inside the wheel suspension.

The links take over both the tasks associated with wheel guidance and also frequently the transmission of spring, damping and anti-roll bar forces. They are made from steel (forged, cast, sheet) or aluminium (forged, die-cast). Design requirements determine whether two, three, or four-point links are used. The points are the number of connecting points a link has.

Links with ball joints are always used for connecting the wheel carrier to the body at the front axle (FA). They allow the freedom of movement required to steer the wheel. At least three links are required for wheel control: a lower link, an upper link and the track rod. For axles built with spring struts, two links and the damper are sufficient for wheel control. However, there are also axles where up to five links are used. In the case of these special designs, the applied forces are distributed across the links.

Ball joints are not absolutely necessary at the rear axle (RA). Therefore, rubber mounts or bushing links are usually used. For optimum rear axle control, five joints and five two-point links are required.

Types of link
Links are differentiated based on mounting direction:

  • Wishbones. Wishbones are positioned diagonally to the wheel plane.
  • Trailing arms. Trailing arms are installed in the direction of travel.
  • Twist-beam link. A twist-beam link involves two trailing arms which are connected with a wishbone.

Links are divided into three categories based on the function they are to perform:

  • Control arms. Control arms guide the wheel without supporting the weight of the vehicle. The forces applied at the joints of control arms are primarily horizontal.
  • Carrier arms. This category includes links with additional force application points for spring and damper forces which act vertically and are greater than the horizontal forces. The joints (also known as carrier joints) are thus larger and more stable than the control joints. In principle, any control arm can be used as a carrier arm subject to appropriate design where force application points and reinforcement are concerned.
  • Auxiliary links. Auxiliary links facilitate connections between control arms and carrier arms or, in the case of special axle designs, with the wheel carrier.


The joints of the links
Every link has at least two joints. The joints on the body side of the car use rubber bearings that are pressed into the designated bore holes in the link. Movement takes place in the rubber. Neither the outer ring nor the inner sleeve of the rubber bearing may move. This requires a perfect connection between the rubber (elastomer body) and the metal. With these joints, rotation is restricted to an angle of approx. ±20 degrees and horizontal/vertical movement is restricted to a distance of ±1 mm. The advantages of this type of joint are to be found primarily in the ability of the rubber to dampen vibration and sound.

Joints on the wheel side connect the link to the wheel carrier using ball joints which are riveted or screwed to the link or pressed into a barrel casing. Flange-mounted ball joints can be replaced without replacing the link, thus reducing repair costs. Built-in ball joints are integrated into links and must therefore be completely replaced when a link is replaced. The advantage of this design is that it is lighter in weight, takes up less installation space and is more reliable as there are no interfaces. ?Ball joints at the front axle enable the wheel to move freely upwards and downwards and all the castor to be changed.

Tensile forces, compressive forces and transverse forces can thus be absorbed and transmitted to the links. As ball joints have to absorb all occurring wheel forces (but not drive and brake forces) they must meet the most exacting of requirements.

These are:

-    Constant torques
-    Zero play (play leads to "clattering")
-    Maintenance-free?-    Transmission of high forces
-    Compact, small, lightweight
-    Compliance with safety requirements
-    Ability to withstand environmental factors, i.e. temperatures from approx.
-    40°C to +80°C, dirt, salt, stone chips and rust


Wheel bearings


Wheel bearings guide and support shafts and axles. They are part of the chassis, guide the wheels and absorb axial and radial forces. Radial forces are longitudinal forces produced as a result of rotation. They are applied to the wheel bearing at a right angle to the longitudinal axis. Axial forces, on the other hand, are forces that act on the wheel bearing in the direction of the longitudinal axis. They are produced during cornering, for example. The axial forces produced during cornering expose wheel bearings to particular stress.

Types of wheel bearing
In modern passenger cars, two types of wheel bearing are used in accordance with requirements: taper roller bearings and ball bearings. The versions of these bearings that are used vary according to application and load.

Essentially, wheel bearings consist of an outer ring and an inner ring, the rolling elements and a ball cage enclosing the rolling elements. Depending on the design of the bearing, the rolling elements ball or roll-shaped. They roll back and forth on the raceways of the two rings.Their task is to transfer the force acting on the bearing from one bearing ring to the other.

As the rotation of the wheel bearing produces high friction, the rolling elements must be lubricated. Lubricants such as lubricating grease or lubricating oil are used for this purpose. Without lubrication, the bearing cannot function. Most wheel bearings used in modern passenger cars are designed to be totally maintenance-free. This is because they are filled with grease which will provide sufficient lubrication for the rolling elements for the entire service life of the wheel bearing. Elaborately designed seals ensure that neither water nor dirt can get into the wheel bearing. Seals for modern wheel bearings often feature integrated magnetic pulse generators which generate the speed signal for the ABS system in the wheel speed sensor.



Passenger compartment filters


In recent years, the concentration of harmful substances on our roads (dirt particles, dust, tyre debris, soot and pollen, nitrous gases, ozone, hydrocarbons or sulphur dioxide to name but a few) has increased significantly. Levels inside the vehicle can be significantly higher again than they are in ambient air. This is because the fans for the fresh air supply or in the air conditioning system suck in polluted air like a vacuum and distribute it inside the vehicle. To avoid this, modern vehicles are fitted with passenger compartment filters. These filters remove all harmful substances from the ambient air, supplying the interior with clean air. Passenger compartment filters must be capable of performing effectively and creating the conditions for comfortable travel even in extreme weather conditions (winter or summer), when pollen counts are high, in heavy traffic, in tunnels, on sections of road where work is taking place or in traffic jams.

However, the performance of a passenger compartment filter declines over time. The higher the levels of dust, the more clogged the filter becomes. A "filter cake" forms between the individual pleats, preventing air from flowing through. Therefore, it is important to replace passenger compartment filters regularly – ideally every 15,000 kilometres but at least once a year.

There are two types of passenger compartment filter design, particle filters and combination filters.

Particle filters

Particle filters are designed to absorb particulate impurities from road air so that the air flowing into the vehicle is clean. Air-borne particulate impurities vary in size and come from numerous sources. They occur as liquids and solids, e.g. in the form of pollen, road dust, debris from brakes, tyres or the clutch, as soot or industrial dust.

In a particle filter, the filter medium (sometimes also referred to as filter paper) is folded to form a zigzag shape. It is made from high-performance synthetic fleece which is usually electrostatically charged. Separation is either mechanical or electrostatic. Mechanical separation is achieved by means of the multi-layer fleece structure, which resembles a cobweb. The particles from the air stick to the fine fibres of the structure when the air flows through the filter.

With electrostatic charging, even the tiniest particles (< 5 µm) can be separated. The functional principle is similar to that of a magnet. The static pull of the fibres separates small particles from the air. High-quality particle filters use this technique to filter almost 100% of dust and particles out of the air.

Combined filters

Combined filters benefit from of the performance features of particle filters plus an active carbon layer. As such, in addition to dust and particles, combined filters are even able to filter odours and harmful gases such as benzene or ozone out of the ambient air. The open-pore surface of the special active carbon absorbs odour and gas molecules from the air like a sponge and stores them in labyrinth-like channels. A teaspoonful of active carbon will cover an area equivalent to the size of a football field. The combined filter is thus able to filter a significant amount of air. However, this capacity will reach its limits at some point. For optimum performance, combined filters should be replaced at recommended intervals.


Fuel filters


Although high standards of fuel quality can now be taken as read in western Europe, there is still a risk of dirt particles and water getting into fuel tanks. However, fuel injection systems for modern engines and the carburettors in order cars need fuel that is absolutely clean if they are to be relied up on to function effectively. Dirt particles cause wear and block the bore holes in fuel preparation systems, some of which are very small. Water in the injection system can cause corrosion and also lead to the failure of components, resulting in engine standstill.

It is for this reason that every combustion engine is fitted with a fuel filter. The fuel filter must filter dirt particles out of the fuel (some fuel filters are designed to also filter out water). In so doing, it makes an important contribution to the operational reliability of the engine.

The fuel filters in modern injection systems must meet very exacting requirements. Fuel filters for common rail or pump-nozzle diesel injection systems must provide an assurance of particularly high levels of fuel cleanliness, for example. As a consequence of the high injection pressures (up to 2000 bar and in some cases even higher), the injection system components have very low tolerances. Even the tiniest dirt particles can cause these systems to malfunction or even fail completely. Innovative filter systems that are able to meet these requirements are the order of the day.

The filter media must also be resistant to modern fuels (which contain high levels of ethanol or biodiesel, etc.) and provide an assurance that flow rates and filter performance will remain at consistently high levels across a wide temperature range (between -40 °C and 100 °C). Furthermore, fuel filters must be able to tolerate mechanical loads, in particular if they are mounted on vehicle underbodies.

Fuel filters are available in a variety of designs:
Fuel filter elements: They can be replaced and are located in a separate housing integrated in the engine.

Spin-on filters: They form a single unit comprising housing and filter element and are replaced as a single unit during service and maintenance. Depending on the application, these designs will feature additional functions such as a water drain plug and connecting branches for a fuel heating unit and the water level indicator.

Inline fuel filters: These filters are installed in the fuel line. The housing and the filter element form a single unit which is replaced during service and maintenance. Inline fuel filters can be made from steel, aluminium and plastic according to manufacturer requirements.



Air filters


Depending on displacement, at full load, the engine will draw in between 200 m³ and 500 m³ of air per hour. This air is loaded with dirt and dust particles. The level of pollution is determined by various factors: the time of year, weather conditions, the nature of the road surface or ambient conditions. Levels of pollution in the air are usually much higher in towns and cities than they are in the country. If these impurities are not filtered out effectively, they will act like sandpaper on the engine, leading to premature wear of mechanical components. Dirt and dust particles will also damage other components mounted in the air intake channel (the air mass meter or the turbocharger, for example).

Therefore, the engine air filter and the associated air filter elements are essential components of any combustion engine. They must supply the engine with the cleaned air that is necessary for fault-free combustion. The air filter must also dampen suction noise emanating from the engine.

Where air management in the vehicle is concerned, engine air filters perform a whole range of functions:
– Filtration of engine intake air
– Improved air flow for optimum combustion and engine acoustics (e.g. damping of suction noises)
– Integration of various components such as air mass meters, charge air lines or raw and clean air lines
– Protection of downstream engine parts such as a turbocharger or particle acceleration.

Important quality criteria for the filter element include high filtration performance (i.e. the separation of large and small particles) and sufficiently high dust absorption capacity. If the filter element does not let enough air pass through, the engine cannot achieve maximum performance. Modern filter media must be able to last at least 20,000 km or one year before needing to be replaced.

Thanks to intensive research and development work, original equipment manufacturers have been able to continuously improve the quality and composition of filter media. As a result, the mileage that can be covered before media need to be replaced is constantly on the rise. Distances of up to 50,000 km are by no means unusual.



Oil filters


Modern combustion engines required first-class lubrication for seamless operation. As engine performance increases and service intervals get longer, it is not only engine oils that need to meet ever more stringent requirements. Above all, the quality of the oil filters used plays a central role in avoiding damage caused by dirt particles, soot or unburned fuel in oil.

During the combustion process, both dirt particles and combustion residue such as dust, metal debris, oil carbons or soot get into the oil, soiling and thickening it. This impairs oil supply and results in increased fuel consumption and premature wear. In the worst-case scenario there is a risk of damage to the engine. Consistent engine performance can only be assured if oil is absolutely clean. Therefore, the oil filter is assigned the task of constantly and reliably cleaning the engine oil throughout its service life. Increasing engine performance combined with decreasing fuel consumption, high-performance lubricating oils and new challenges all the time in car manufacture are placing additional requirements on oil filters.

Development trends are increasingly moving towards compact oil filters which are integrated into the engine and perform a range of other tasks in addition to filtration. These filters feature the use of metal-free oil filter elements made from the very latest filter media which can be relied upon to achieve maximum performance values consistently even in the case of long intervals between changes.

In terms of function, oil filters can be divided into two groups:
Full-flow filters and combined full-flow/bypass filters. Full-flow filters are installed in the oil circuit in such a way that all of the oil to be cleaned flows through the filter during each cycle. With combined full-flow/bypass filters, approximately 90 to 95% of the oil flows through the paper star of the full-flow filter, whilst approximately 5 to 10% flows through the bypass filter or the bypass centrifuge. Bypass filters are fitted with finer filter media and are thus capable of continuous super-fine filtration. As the areas of application for oil filters and the requirements they are expected to meet vary, these filters are available in a variety of designs:

Spin-on oil filters (screw-on oil filters)

Thanks to efficient filter performance, reliability and ease of installation, the screw-on oil filter has been an important component in oil filtration for many years. Screw-on oil filters can be used in both full-flow filtration and bypass filtration.

Compact oil filter modules

Both the cleanliness and the temperature of lubricants play an important role in the reliability and service life of modern engines. Compact oil filters which can take care not only of filtration but also of the cooling function are increasingly being used for permanent monitoring of these two factors. Oil filter systems of this type are adapted to meet the needs of the prevailing engine environment and can also take over a range of other tasks. The elements permanently integrated in these modules include a bypass valve, a return check valve, a ribbed oil cooler, an electrically controlled coolant thermostat, the preparation for alternator cooling, a filler neck for topping up oil or an oil pressure switch.

Thanks to the use of high-performance plastics, the compact design of these modules saves installation space and reduces weight as well as helping to lower fuel consumption. The design of the module requires that filter manufacturers work in close collaboration with engine design engineers in order to optimise the integration of the filter into the engine block.

Replaceable oil filter elements

Replaceable oil filter elements are the actual interchangeable part in an oil filter module. Whilst the module and its attachments are fixed permanently to the engine block, where they remain for the entire service life of the vehicle, the filter element is replaced at the prescribed intervals. The filter element is particularly environmentally friendly as the element itself can be fully thermally recycled. Unlike the screw-on oil filter with metal housing, it can be burned without leaving behind any residue.

Specific designs

There are specific designs for special applications such as transmission oil coolers.


Mixture preparation

Exhaust gas recirculation


Exhaust gas recirculation (EGR) is a tried and tested method of reducing harmful substances. A defined quantity of exhaust gas is removed at the exhaust manifold and mixed back in with the intake air. This reduces the amount of oxygen in the fuel/air mixture, thereby reducing the combustion temperature in the cylinders. As hazardous nitrogen dioxide (NOx) is produced primarily at high temperatures and pressures, exhaust gas recirculation provides a means of reducing the levels of NOx concentration emitted to the environment by up to 50%.

In diesel engines, exhaust gas recirculation also reduces the formation of soot particles by approx. 10%.

The amount of exhaust gas recirculated is calculated by the engine control unit and regulated as appropriate for the design and dimensioning of the system by means of various actuators. These include:

- The EGR valve
The EGR valve is responsible for dosing the quantity of exhaust gas recirculated. It is mounted either on the exhaust manifold or in the intake area. In some engines, it is located inside a heat-resistant exhaust gas line which connects the exhaust manifold to the intake area. EGR valves in diesel vehicles have large opening cross-sections due to the high recirculation rates. The cross-sections of EGR valves in petrol engines are much smaller. Pneumatic and electromotive EGR valves are used in passenger car applications.

Pneumatic EGR valves are actuated via electro-magnetic valves under negative pressure. The negative pressure to control the valves is tapped from the intake pipe or generated with a vacuum pump. Electric or electromotive EGR valves are controlled directly by the control unit; they do not required negative pressure or a solenoid valve.

- The butterfly valve (diesel)
Since in diesel engines the pressure difference between the exhaust gas side and the intake side is not sufficient for high exhaust gas recirculation rates, "butterfly valves" are used in the intake pipe to generate the necessary negative pressure.

- Electric changeover valve
In simple systems with an electric changeover valve, the EGR valve simply has an open/close function. The negative pressure required to control the valve is tapped from the intake pipe or generated with a vacuum pump.

- Electropneumatic converter
In systems with electropneumatic converters, the EGR valve is infinitely variable. The negative pressure required to control the valve is tapped from the intake pipe or generated with a vacuum pump.

- EGR lines
EGR lines are also a component of exhaust gas recirculation. They connect all of the components for exhaust gas recirculation from the exhaust gas extraction point to the intake area, running via the EGR radiator and the EGR valve. As space is at a premium inside the engine compartment, connection routes often have to be complicated. Both flexible and rigid EGR lines are available.

Modern EGR lines must meet strict requirements. They have to be able to equalise not only different and varying temperature levels at mounting points but also the mounting tolerances of the components involved, for example, in addition to being resistant to temperature, exhaust gas and corrosion.

Unfavourable operating conditions such as frequent short trips, non-compliance with service intervals or combustion problems affecting the engine can in some cases lead to EGR lines in which deposits have accumulated deteriorating or coking. EGR valves are at risk of the same problem. This reduces the exhaust gas recirculation rate, in turn creating other problems that can impair optimum engine running. If an EGR valve has to be changed because of clogging or coking, the EGR line connected to it must always be checked and replaced if necessary.

Mixture preparation

Diesel injection system


Modern diesel engines must meet strict requirements. Drivers expect high power and torque values, low fuel consumption and quiet engine running. Furthermore, diesel engines must meet the strict emission values of current and future exhaust gas standards. A good mixture preparation is a prerequisite for full and efficient fuel combustion in a diesel engine. To achieve this, the fuel must be injected in the right quantity, at the right time and at the highest possible pressure. This is the task of the diesel injection system. Over time, the common rail system (CRS) has established itself as the best technological solution.

CRS2 with 1,600 to 2,000 bar and solenoid valve injectors

Rising fuel prices and increasingly strict exhaust gas limit values are making modern, economic and environmentally-friendly diesel engines the drive solution of choice. CRS2 series common rail systems are a cost-effective and performance-optimised solution for further reducing fuel consumption and thus vehicle running costs.

Each system comprises a high-pressure pump, the high-pressure rail, an injector for each cylinder and the electronic control unit. Electronic diesel control (EDC) regulates not only the overall injection process but also the charging pressure and exhaust gas recirculation.

At the heart of these systems are their rapid-switching solenoid valve injectors which make for short injection distances. The powerful second-generation solenoid valve injectors offer engine design engineers high levels of freedom when setting up the injection process. Up to eight separate injections per operating cycle are covered in a narrow time window. Multiple fuel injection helps to further reduce fuel consumption and CO2 emissions as well as harmful substance and noise emissions from the engine.

The solenoid valve injectors for the CRS2 are available in various designs. The optimised ferromagnetic core of the CRI2-16 injector, for example, achieves high forces when the solenoid valve opens. The second armature module increases dynamic performance during actuation of the nozzle needle and minimises intervals between injections. The injector in the CRS2-18 system has a pressure-compensated solenoid valve. This enables the system pressure to be increased still further. The CRI2-20 with pressure-compensated solenoid valve has an integrated additional rail volume which reduces pressure oscillations. A reduction in return flow volume increases hydraulic efficiency.

The CRS2 series is suitable for diesel engines with up to eight cylinders and a wide power and torque spectrum. The modular systems can be adapted to a wide variety of engine types. The increased pressure of these systems and technical modifications enable current and future emissions targets to be met. Moreover, higher injection pressures are giving engine manufacturers more freedom where the design of the basic engine and exhaust re-treatment are concerned. The CRS2 is available in variants for light commercial vehicles and customised for off-road vehicles (agricultural and construction machinery).

CRS3 with 1,800 to 2,000 bar and piezo injectors

Fuel consumption is an important factor for the cost-effectiveness and thus the market success of a vehicle, in particular where high mileages are concerned. Other important factors are emissions, running noise and the power output of the engine. The piezo injectors of modern CRS3-18 and CRS3-20 common rail systems with 1,800 bar and 2,000 bar system pressure respectively are enabling the design and construction of engines with ideal property profiles.

Each system comprises a high-pressure pump, the high-pressure rail, an injector for each cylinder and the electronic control unit. With their increased switching speed, pre-injection quantities are very low with CRS3-18/-20 piezo injectors. The reduction in hydraulic power loss results in a lower fuel temperature, rendering additional fuel cooling unnecessary. CRS3-18 and CRS3-2 common rail systems are used in top performance passenger cars and light commercial vehicles.

Variations in fuel quality are a challenge for every injection system. With their robust piezo actuator, CRS3-18/-20 injectors are fully equipped to rise to this challenge. A piezo actuator is capable of approximately ten times the power of a solenoid valve and is thus less sensitive to small impurities in fuel. With minimum pre-injection quantity, rapid injection processes and volume stability over time, CRI3-18 and -20 piezo injectors lead the field for multiple fuel injection.

As the piezo actuator is integrated in the housing, the piezo injectors are slim and take up much less installation space than injectors with a solenoid valve. The piezo injector supports multiple fuel injection at minimum intervals. As the actuator triggers the nozzle needle directly (no hydraulic control circuit), response times are short. Optimised injector characteristics mean that quantities can be corrected throughout the service life. Teach-in functions stored as software in the electronic control unit are used for this purpose.

Mixture preparation

Secondary air system


In petrol engine vehicles, secondary air injection is a proven method of reducing harmful substance emissions during cold starting. A petrol engine needs a "rich mixture" for reliable cold starting. This means that the fuel/air mixture contains excess fuel. As a result, high quantities of carbon monoxide and unburned hydrocarbons are produced during cold starting. Since the oxygen sensor emissions control and the catalytic converter have not yet reached their operating temperature at the time of this phase, these harmful exhaust gas components can escape into the environment if not re-treated.

To avoid this and reduce harmful substances during cold starting, ambient air containing high levels of oxygen ("secondary air") is injected into the exhaust gas manifold directly downstream of the exhaust valves using the secondary air system. This causes post-oxidation ("post-combustion") of the harmful substances, creating harmless carbon dioxide and water. The heat generated as a result of this process also heats the catalytic converter and reduces the time taken for the oxygen sensor emissions control to commence operation. The secondary air system comprises the secondary air pump and the secondary air valves.

Secondary air pump

The secondary air pump must draw in ambient air and inject it into the exhaust gas manifold downstream of the exhaust valves. If the air is drawn not from the intake area but directly from the engine compartment, a separate air filter is built into the secondary air pump.

Secondary air valve

The secondary air valves are installed between the secondary air pump and the exhaust gas manifold. They are available in various designs. The secondary air non-return valve, for example, stops exhaust gas, condensation or pressure peaks in the exhaust tract (caused by misfiring, for example) causing damage to the secondary air pump. The secondary air shut-off valve, on the other hand, ensures that the secondary air is only supplied to the exhaust gas manifold during the cold start phase.

Secondary air valves are actuated in various ways – either by means of negative pressure controlled by an electric changeover valve or by opening due to the pressure generated by the secondary air pump. In later generation secondary air valves, the shut-off and non-return functions are combined in a "shut-off non-return valve". Electric secondary air valves are a very recent development. They have shorter opening and closing times than pneumatically controlled valves. Thanks to higher actuating forces, they are more resistant to sticking caused by soot or dirt. For monitoring by on-board diagnostics (OBD), electric secondary air valves can be fitted with a pressure sensor.


Air conditioning


The air conditioning in a vehicle must cool the passenger compartment and draw moisture out of the fresh air supply. As such it provides an assurance of pleasant passenger compartment temperatures even in strong sunlight and condensation-free windows when humidity levels are high.

The most important components of vehicle air conditioning systems are the compressor, the capacitor, the dryer, the expansion valve and the evaporator. The individual components are interconnected via hose lines to form an enclosed system known as the refrigerant circuit. The refrigerant circulates in the refrigerant circuit. It is driven by the compressor.

The refrigerant circuit is divided into two sides:

- The part between the compressor and the expansion valve is called the high-pressure side.

- The area between the expansion valve and the compressor is the low-pressure side.

The gaseous refrigerant is compressed in the compressor and heated to a very high temperature. Finally, it is pressed through the capacitor at high pressure. The capacitor is usually located near to the radiator. In the capacitor, heat is drawn from the very hot refrigerant, causing it to condense, i.e. change from a gas to a liquid. In the dryer (the next station), impurities and air pockets are separated out of the liquid refrigerant. This safeguards the effectiveness of the system and protects the components against damage caused by impurities.

After the dryer, the liquid refrigerant travels to the expansion valve. The function of the expansion valve is similar to that of a weir. Upstream of the weir, it ensures that constant pressure is maintained. Downstream of the weir, on the other hand, decompression can occur as a result of volume expansion. As the expansion valve is positioned directly upstream of the evaporator, the refrigerant decompresses into the evaporator. During this process, its physical condition changes from liquid to gas.

As part of this physical process, the refrigerant draws heat from the atmosphere; this is perceived as evaporation chill. Like the capacitor, the evaporator is a heat exchanger. It has a huge surface area across which it emits evaporation chill into the atmosphere. The chill emitted is then injected into the passenger compartment by the ventilation system, where it is responsible for making passengers feel comfortable.

On the low pressure side, the refrigerant, which has now turned back into a gas, is fed back to the compressor, where the circuit starts again. In modern vehicles, air conditioning is part of thermal management. This includes both engine temperature control in all operating conditions and heating/cooling the passenger compartment. Accordingly, a modern thermal management system comprises components for engine cooling, vehicle heating and air conditioning. Components of these assemblies interact and often form a single unit. The vehicle air conditioning system is thus a combination of car heating and refrigerant circuit. This combined approach enables the desired climate conditions to be established regardless of the conditions outside the vehicle.


Thermal management


Thermal management: The engine cooling system

As we all know, engine compartments have got much smaller, resulting in an enormous build-up of heat that must be dissipated. Much is being asked of modern cooling systems where cooling down the engine compartment is concerned. In response, significant progress has been made recently in the field of cooling.

A cooling system must meet the following requirements:

– Shorter warm-up phase
– Faster passenger compartment heating
– Low fuel consumption
– Longer service life of components

The following components provide the basis for all engine cooling systems:

– Radiator
– Thermostat
– Coolant pump (mechanical or electric)
– Expansion tank
– Lines
– Engine fan (driven by a V-belt or Visco®)
– Temperature sensor (engine control/display)


Radiators are installed in the air flow at the vehicle's front end. It is their job to release the heat generated as a result of combustion in the engine and absorbed by the coolant to the outside air.

Coolant pump

The coolant pump has a mechanical or electric drive; it conveys the coolant through the coolant circuit.

Radiator fan

One or more radiator fans driven mechanically or electrically support the coolant cooling process. The fans are located upstream or downstream of the radiator and can be electronically regulated.


The coolant thermostat, which is mechanically or electronically regulated, is located in the refrigerant circuit. It regulates the temperature of the coolant.

Heat exchanger

The heating valve, which is controlled mechanically, pneumatically or electrically, opens and closes the cooling circuit to the heat exchanger. 

Heat exchanger valve (optional)

The air drawn from the passenger compartment fan is routed through the heat exchanger, being heated during this process.

Air-cooled or water-cooled after coolers must cool down the air compressed by the turbocharger in order to improve the efficiency of the engine. After coolers must be replaced following a mechanical fault affecting the turbocharger.

Vehicle climate control


The compressor is driven by the vehicle engine via a V-belt. It compresses the gaseous refrigerant drawn in before forwarding it to the capacitor.


The capacitor is located upstream of the radiator. It cools the refrigerant coming from the compressor so that it leaves the capacitor as a liquid.

Filter dryer

The filter dryer removes impurities and moisture from the liquid refrigerant. It also acts as a refrigerant store. Inside the housing there is a granulate filter pad which can only absorb a certain amount of moisture.

Expansion valve

The expansion valve is the point separating the high pressure and low pressure areas. It regulates the flow of refrigerant depending on temperature, by injecting more or less liquid refrigerant into the evaporator. At the same time it passes the gas refrigerant from the evaporator on to the compressor.





The thermostat is an important component in liquid cooling. It ensures that the combustion engine reaches its ideal operating temperature as quickly as possible and then maintains this temperature in all operating conditions. This is an important prerequisite allowing the combustion engine to achieve optimum performance under all load conditions and emit low levels of harmful substances.


Depending on the application and technology of the combustion engine, thermostats have to exhibit different functional characteristics and ways of functioning. The following designs are used:

– Cartridge thermostats (wax thermostats)

Cartridge thermostats are individual components inside a housing. They regulate the temperature precisely, are hard-wearing, maintenance-free and have been proving their worth for decades.

– Housing thermostats (wax thermostats)

Housing thermostats comprise the cartridge and the housing. These modules are fully integrated into the engine.

– Electrically heated thermostats (map thermostats)

The cooling power in performance-optimised modern passenger car combustion engines requires thermostats with a wider working range than that of conventional wax thermostats. The electrically heated thermostat was developed to meet this requirement. Electrically heated thermostats are characterised by a wider working range.

Thanks to additional control via the engine management, the engine temperature can be adjusted more effectively and in response to demand. This improves consumption values and reduces harmful substance emissions.


– Cartridge thermostats and housing thermostats (wax thermostats)

The work element is the linchpin of the wax thermostat. It is a pressure-resistant housing which is filled with a special wax. After the engine starts up, the coolant heats up the work element. When a predefined temperature is reached, the wax in the work element liquefies. It expands and acts on a pin in the housing which functions as a working piston. The working piston is pushed out of the housing and opens the flow of coolant to the radiator via a poppet valve so that the engine can be kept in the ideal temperature range. If the coolant falls back below the predefined opening temperature, a spring pushes the poppet and the pin back to their original position. The flow of coolant to the radiator is thus interrupted.

– Electrically heated thermostats (map thermostats)

In an electrically heated thermostat, the wax in the work element is heated up both by the coolant and by means of electric heating. Thanks to this combination, the engine temperature can be regulated specifically according to load requirement. The electrical heating of the work element is controlled using various parameters from the electronic engine management.

The electrical heating of the thermostat causes the premature opening of the coolant circuit in situations where increased performance is required. Depending on the default setting, the engine can thus run in the partial load range at approx. 100°C – 110°C, for example, i.e. hotter than has previously been usual. This reduces consumption by between 1 and 2%. At full load, the temperature is reduced to approx. 80°C, allowing the power and specifically the torque to increase measurably by between 2 and 3%.

Almost as a side-effect, the change in the temperature of the coolant enables the air conditioning to operate in a more favourable temperature range, thus improving climate control in the passenger compartment.



Window lifters


Most modern vehicles feature electric window lifters (power windows) alongside manual lifters. Electric window lifters are controlled using buttons in door trim panels. For central control, there is usually a panel featuring buttons for all electric window lifters in the vehicle in the driver's door. Occasionally there are also controls located in the centre console.

Window lifters work according to four functional principles:

1. Cable window lifters

This technology is the most commonly used. A cable drum is moved powered by an electric motor with a worm gear/spur gear. Two ends of a steel cable are fastened to this drum so that when the drum rotates one end is wound in and the other end is let out. The pull cable pulls the window fastening, which runs in a guide rail, up or down via a Bowden cable and a deflection roller. The end of the cable without pull is wound back onto the drum in parallel.

2. Dual-cable window lifters

The operating principle is the same as that of cable window lifters but this system is fitted with a second guide rail. The dual-cable window lifter is the latest and most innovative technology.

3. Scissor system

With this principle, the window is moved by two lifting arms arranged like scissors which are powered by servomotors. When the scissor arms are "closed", the window is pushed to the highest position. When the "scissors" open, the window slides down.

4. Cable system

This system is primarily used for industrial vehicles and reverse windows. A single cable moved by a central motor sets the position of the window.

Electric window lifters on more recent vehicles are fitted with what are known as convenience functions. These include:

  • Automatic full up or down of the window lifter when the switch is pressed once

  • Linking of the window lifter function to the central locking so that when the car is locked, all of the windows that were previously open close automatically.

  • Safety functions such as "anti-trap protection"


Gas pressure springs and dampers


Gas pressure springs facilitate the effortless and convenient opening and closing of luggage compartment lids/tailgates and engine hoods.?With the assistance of gas pressure springs, the tailgate and engine hood can be operated with one hand. When the hood or lid is open, the gas pressure spring holds it safely in the end position. During closing, the gas pressure spring gently dampens the movement so that the hood or lid drops smoothly into the lock.

The benefits of gas pressure springs are as follows:

  • Compact design
  • Ease of installation
  • Definable speed
  • Convenient power assistance for easy opening
  • Smooth and steady functional sequence
  • Definable spring characteristic
  • Damping of movement


Gas pressure springs are also used as dampers elsewhere in motor vehicles, as steering dampers or engine dampers, for example.




The steering system must steer the vehicle in the direction the driver wants it to go. It must be responsive and support precision driving. The steering is part of the frame of vehicle, or the chassis, to be more precise. Apart from the steering, the chassis comprises wheel suspension, suspension, brake, damping, wheel carrier and subframe. It is its job to establish the requisite conditions for directional stability and dynamic driving, at the same time damping impacts from the road.

The movements of the steering wheel are transmitted via the steering gear, the steering linkage and the steering arm to the steering stub and thus to the front wheels, where they manipulate the steering angle. In turn, the angle determines the direction in which the vehicle travels. However, the steering behaviour of the vehicle is not determined by the position of the steering wheel alone. Drive and brake forces or compression when driving over bumps in the road can affect the direction in which the driver wishes to travel. To minimise the resulting interference, vehicle manufacturers working in collaboration with the components industry have developed ingenious axle designs which help to ensure that even in poor road and weather conditions, modern vehicles can be steered safely regardless of whether the driver is accelerating or applying the brakes.





Additives are substances that are added to engine oil, transmission oil and coolant to improve their properties. Additives are even added to fuels and oils in refineries. Without additives, neither fuel nor oil would be able to deliver the required power. If modern vehicles were filled with fuel without additives, they would hardly get anywhere. Engine oil without additives would struggle to withstand the stresses and strains of modern engines and may even cause them irreparable damage. As such, additives are not just well tolerated – they are actually of vital importance to cars. Every driver uses them all the time, even if they are not aware of it.

Lots to do!

Additives perform many different roles: they must have a cleaning effect, care for mechanical components and protect them against wear. They also contribute to improving quality, to protecting against corrosion, to minimising foaming and to increasing power. Additives for engine oils are adapted specifically to the prevailing requirements resulting from the engine concept and the requirements of the automobile manufacturer.

Essentially there are two different types of additive. The first type are added to fuels and oils even before they leave the refinery. Drivers have no control over this process. However, additives which can be purchased from specialist retailers for mixing in with engine oil or fuel following the instructions issued by the corresponding supplier are a different story. These additives lend operating fluids additional properties which in many cases solve problems and can prevent expensive repairs.

So additional additives can help to save money. The benefits of additives can quickly be seen and felt by drivers in the form of fuel consumption falling or engines running more smoothly, for example. Their indirect benefits are even more important: when the engine, the oil system and the fuel system are cleaned, cared for and preserved with additives, the car becomes more reliable, expensive repairs are more likely to be avoided and the service life of the vehicle is extended. Several thousand euros can thus easily be saved over the lifetime of a vehicle.

Additional additives are useful accessories but not a miracle cure. Although they do of course provide assistance (they can help to reduce fuel consumption, for example), promises like "cuts fuel consumption by a third" are dubious and physically impossible. Reputable manufacturers will never be heard to make statements of this nature. They can make reference to tests carried out with recognised and well-known test institutes which have confirmed the effectiveness of additives in trials.

Super E10 fuel

E10 fuel has been available at pumps since the start of 2011. This special "super fuel" contains 10% ethanol. For the time being, standard commercial petrol containing 5% ethanol will remain on sale. For technical reasons, not all vehicles can run on E10 fuels. Using E10 can lead to the following problems, some of which can be prevented with additional additives:

– Corrosion of light-metal components made of materials like aluminium. The alcohol in the fuel causes acidification over time, resulting in corrosion of aluminium and magnesium. Additives such as petrol stabilisers can counter these phenomena (prevent corrosion).

– Lack of compatibility with some gaskets. In older vehicles, there may be a lack of compatibility with old sealing material when using E10 fuels. At the current time, there is no fuel additive that can solve this problem. Therefore, vehicles that have not been approved for E10 cannot be made compatible with the new fuel by mixing in fuel additives.

– Increased deposits on intake valves, injection nozzles and in the combustion chamber. The increased alcohol content in the fuel results in more deposits on intake valves, injection nozzles and in the combustion chamber. Special cleaning additives will remove deposits that have accumulated in these areas. Residue and deposits can be avoided by choosing to use the right additives preventively from the very start. This will safeguard the reliability and smooth running of the engine.


Engine oil


In combustion engines, engine oil fulfils a number of purposes. One of the most important of these is to lubricate mechanical components. Lubrication reduces friction between moving parts and keeps wear to a minimum. Engine oil also has to cool, clean, provide protection against corrosion and seal combustion chambers. Last but not least, it is used for power transmission in hydraulic engine systems (chain tensioners, camshaft adjustment, etc.).

Depending on their type and performance, modern engine oils are based on different base oils or base oil compounds. Additives are also used which perform a variety of tasks. A high-performance engine oil can only be achieved with a balanced formula (base oil and additive components).

The composition of a typical engine oil is as follows:
– 78% base oil
– 10% viscosity improvement additive (to improve flow)
– 3% detergent (detergent substances which clean the engine)
– 5% dispersant (for the suspension of dirt particles)
– 1% wear protection
– 3% other components


Viscosity is one of the most important properties of engine oil. The viscosity of an oil is always marked on its barrel. Viscosity is measure of a fluid's resistance to flow. It is determined by the internal friction which resists the flow of adjacent particles in the fluid. As long ago as 1911, viscosity provided the basis for the first engine oil classification system and was defined in the Society of Automotive Engineers (SAE) classification system. Most of the oils used today are multi-grade oils. SAE 5W30 is an example of a viscosity designation of a multi-grade oil.

Measures of viscosity are based on two variables:
- Dynamic viscosity. This describes the engine oil's resistance to flow at low temperatures. Oils are divided into the winter viscosity classes 0W, 5W, 10W, 15W, 20W, 25W. The smaller the number in front of the W, the lower the viscosity of the oil at cold temperatures. Dynamic viscosity affects the starter speed when the engine is cold, for example. The lower the cold viscosity index, the easier the cold engine will turn over on starting.

- Kinematic viscosity. Kinematic viscosity describes the ratio between dynamic viscosity and the thickness of the engine oil at a certain temperature. SAE summer viscosity classes are classified at a test temperature of 100°C. Typical viscosity classes are 20, 30, 40, 50 and 60. The larger the number in front of the W, the higher the viscosity of the oil at 100°C.


The viscosity classes referred to above (winter and summer) are supplemented by what is known as HTHS viscosity. HTHS stands for High Temperature High Shear. It describes dynamic viscosity measured at 150°C and under higher shear forces. It is expressed in millipascal seconds (mPas). HTHS limit values are defined to ensure that even in bearings (where both shear forces and oil temperatures are high), engine oils can be relied upon to provide the necessary lubrication.

The limit value for engine oils with specification ACEA A2/A3 and ACEA B2/B3 is to be found at an HTHS of 3.5 mPas. Engine oil qualities in category ACEA A1/B1 have a reduced HTHS of up to 2.9 mPas. Fuel consumption should be lower as a result of the reduced HTHS index.

Engine oil mixability

As a general rule, engine oils can be mixed together regardless of whether they are synthetic-based or mineral-oil-based. Mixing is even encouraged by motor companies.

However, engine oils of different brands or compositions should only be mixed if the requirement for topping up cannot be met in any other way. Accordingly, it is not recommended to mix synthetic or semi-synthetic engine oils with mineral-oil-based engine oils as this will lower the higher quality standard of synthetic oils. The quality rating is only as good as the weakest link in the chain.

Extensions to the intervals for changing lubricants mean that oils have to meet increasingly tough requirements. For example, modern engine oils have to maintain constant performance throughout their service life as well as exhibiting high thermal and oxidative stability for a long service life and optimised friction characteristics to reduce energy losses.

Special tool

Special tool


Approved garages know very well that their mechanics can only work safely, quickly and accurately if they have good quality tools at their disposal. Good quality tools are essential if an expert is to complete professional repair work quickly.

Drivers save money and can rely on the quality of the repairs carried out.
Without good quality special tools which are designed specifically for the task at hand, it is virtually impossible for garages to carry out work in the correct and proper way. As well as working in a highly professional way, garages make use of many different high-quality tools, garage vehicles and fixtures which complement and supplement the skills and abilities of their mechanics.

High-quality work relies as much on the installation of high-quality spare parts as it does on the use of top-quality tools that can be relied upon at all times. Unceasing advancements in technology over the years, which have seen vehicles become ever more sophisticated, require the use of numerous special tools which can function as the "right problem-solver" for the task at hand. These tools provide motor mechanics with the means to get to and get into installation locations where angles are tight and space is at an absolute premium, so that screw joints can be disconnected and components can be removed and subsequently re-assembled correctly. Special tools thus save valuable time and thus directly reduce the prices garage customers have to pay for repair or inspection work.

80% of all screw joints in modern cars have precisely defined torque specifications. Consequently, torque accuracy is more important than ever. Professional garages can no longer get by with a traditional hammer, pliers or "knocking". In an age of certified DIN/ISO garages, torque wrenches are high-precision measuring instruments. Regular calibration of these instruments means that they can be relied upon by the user when tightening screw joints. As a result, from a technical point of view, drivers have the assurance of "good and safe driving" on the road.

Leading tool designers and manufacturers working in the automotive industry are often involved in the design and development of new vehicles. They are thus able to develop special tools for possible repair work at a very early stage. Component manufacturers too are aware of the significance of high-quality tools and are working very closely with tool manufacturers in the field of complex repairs in particular, where special tools are the order of the day.

Garages must continuously invest in good quality professional tools and regular CPD for their mechanics in all of the different areas of car repair and maintenance. There is also a need for investment in ongoing training in the latest repair methods. Modern mechatronics engineers are thus becoming "car surgeons" with whom you can be sure your car will always be "in the best hands".





Horns and multi-tone horns are a requirement in every motor vehicle. This is regulated in Section 55 of Germany's Road Traffic Licensing Regulations. Horns provide drivers with a means of informing or warning other road users of the position and movement of their vehicle in hazardous situations. Various types of horn are available for motor vehicles.

They include standard volume horns, high volume horns and electropneumatic multi-tone horns, as well as compressed air and compressor multi-tone horns.



Central locking system


The locking system in a vehicle must grant access only to authorised persons. It is the means via which the vehicle doors and boot lid are locked and unlocked and the engine is started.The locking system is operated with a key or remote control.

In years gone by, purely mechanical locking systems were the norm. Each door or lid had an independent mechanism which could be operated from the outside with a key or from the inside with a knob. Central locking systems, for which pneumatic drives were used originally, brought about significant improvements in comfort and convenience. These systems feature a built-in vacuum reservoir which triggers the locks on all doors when the key is turned in a lock.

Electric locking systems are commonplace in today's vehicles. Most of these combine a key with infrared or wireless remote control. This means that they can be triggered remotely, i.e. without contact between key and vehicle. Today, most vehicle manufacturers only fit a lock which can be operated with a key in one door, so the car can be unlocked in an emergency. The very latest systems enable entirely keyless vehicle access. Drivers only need to have the transmitter in their pockets, for example. The doors are then unlocked when the driver touches a door handle which has a built-in contact point.


The locking system comprises the following components:


Start/stop system

Traditionally, a vehicle key was needed to unlock the steering lock and to start the engine. Subsequently, the vehicle key was enhanced with the addition of a transponder-based release mechanism for the electronic immobiliser. Today, keyless systems are increasingly being used to start engines. In a keyless system, a transmitter – which usually also houses the controller for the central locking – is inserted into a reader in the vehicle and the engine is then started by pressing a button. A more recent development has seen the use of systems that work without any contact at all. Here, it is sufficient to simply "take along" the transmitter (carrying it in a trouser pocket, for example) and press the pedals before starting the engine by pressing a button.


Steering lock

Steering locks have been a mandatory requirement set by insurance companies since 1969. They provide protection against theft. They are the means by which the steering column is unlocked and the engine is started – either electrically or in by conventional mechanical means.


Lock barrel unit

The lock barrel is a component which activates the locking system. It will only work if an appropriate object (such as a key or key card) is used with it. Lock barrels are used in doors, boot lids, clasps, etc. As such they are one of the basic security components of a vehicle.



The basic function of keys and remote controls is the locking and unlocking of doors, luggage compartments, fuel filler caps, etc. they are also used to control the interior lighting and electronic immobiliser, the alarm system and the window lifters. The keys comprise two units: the milled, toothed key blade and the key bow. The latter is home to an increasing number of electronic functions such as the remote control for the central locking system or the boot lid.


Remote control

Remote controls are being used with increasing frequency in small cars, replacing the functions of a conventional key to all intents and purposes.  A signal transmitter sends a signal or a coded order instruction to a receiver inside the vehicle, which usually controls a number of functions. Infrared remote controls have a range of up to 15 m. They rely on direct "visual" contact between transmitter and receiver. Today, infrared remote controls are only used rarely as they have been overtaken by other technologies. Wireless remote controls transmit on radio frequencies and have a range of up to approximately 100 m.



The transponder is usually integrated inside the key bow. It is the means by which the electronic immobiliser identifies that the correct key is being used. The transponder's code is read out as the key nears the ignition lock. If the code is correct, the electronic immobiliser sends the start enable to the engine.


Door handle/Handle strip

The door handle is the traditional means by which a vehicle is opened and closed from inside or outside. The external door strip usually houses the door lock. Door strips are increasingly used as design elements in modern cars. They can be chrome-plated or paint-finished in the same colour as the vehicle.


Door lock/Actuator

The latching mechanism in a vehicle is installed directly in its doors. It contains both a latch and an electric motor (actuator) which controls the central locking. The latch opens or closes the doors, whereas the door lock locks or unlocks the vehicle. Today, all door latches are powered by electric drives.


Fuel filler cap

The fuel filler cap must securely seal the fuel tank. Some fuel filler caps have locks, others do not. Fuel filler caps with locks are usually found on vehicles which have either a fuel filler flap which does not lock or no fuel filler flap at all. Fuel filler caps without locks are found on vehicles whose fuel filler flap is locked automatically via the central locking system.


Wiper blades


The wiper blades in a vehicle must meet the legal requirement for sufficient all-round vision at all times, thereby providing an assurance of road safety in the various situations drivers encounter. This means that wiper blades must meet the following requirements:

– They must clean rain, snow and dirt from the windscreen. The wiper range must be dimensioned sufficiently and meet legal requirements in order to ensure that the driver has a sufficient view of road signs and traffic lights extending to the edge of the road.

– The wiper quality must ensure that stray light from oncoming vehicles and the blinding effect associated with it are avoided as far as possible.

These are very challenging requirements given that in addition to mechanical stresses and strains, wiper blades are exposed to the most extreme environmental factors (heat, cold, chemicals and salt spray, for example). Therefore, only high-quality brand-name products can be used if good wiper performance and long-term reliability are to be achieved.

The current development trend is indisputably towards jointless wiper blades. With jointless wiper blades, instead of the claws of the wiper blade clips, two pre-bent spring strips adapted specifically to the curve of the windscreen distribute the force to the rubber of the wiper blade. They ensure that the pressure exerted on the windscreen by the edges of the wipers is distributed even more evenly. This both minimises wear of the wiper edges and improves wiper quality. The omission of the clip system also means that joint wear no longer occurs and installation heights can be much lower. Furthermore, moving away from using a metal clip protects the wiper blade more effectively against icing up, making it ideal for use during the winter months. Many manufacturers supply a universal adapter for wiper blade attachment which is able to replace up to four different original adapters.

The most important element of a wiper blade is the wiper rubber. Its micro double edge, which makes contact with the windscreen, is just 0.01 to 0.015 mm wide. The wiper is designed so that all the way through the wiper range, the micro double edge is pulled across the windscreen at an angle of approximately 45°. Special wipers with a two-component synthetic wiper rubber have a particularly hard abrasion-resistant wiper edge which produces super-soft wiper movements. This softness ensures optimum movement and smooth running at any temperature.



Glow plug


Function Diesel engines are compression-ignition engines. In other words: The fuel injected does not require an ignition spark to ignite. The power stroke is triggered in three steps:

1. First, pure air is drawn in.

2. The air drawn in is compressed to 30 to 55 bar, heating up to between 700 and 900°C as part of this process.

3. Diesel fuel is injected into the combustion chamber. The high temperature of the compressed air triggers combustion ignition. The internal pressure rises sharply and power is deployed to the engine.

Compared with petrol engines, combustion-ignition engines require more complex injection systems and engine designs. The first diesel engines did not provide a particularly comfortable or pleasurable ride. The harsh combustion process meant that they were very loud when cold. They were characterised by a higher power-to-weight ratio, low power output per litre and poor acceleration. Unceasing development of the injection technology and glow plugs has succeeded in overcoming all of these disadvantages. Today, diesel as a drive source is considered to be of equivalent if not higher quality.

The function of glow plugs in order for a diesel engine to reliably start at low outside temperatures and run with low noise and low emissions during the warm-up phase, glow plugs are fitted which protrude into the cylinder. The glow plugs must very quickly make a high temperature available to assist the ignition process, subsequently maintaining this temperature regardless of boundary conditions or even adapting it to suit them. During pre-heating, a high current initially flows via the connecting bolts and the regulator coil to the heater coil. The heater coil quickly heats up, causing the heater zone of the glow plug to glow. The glowing spreads rapidly. After between two and five seconds, the heater rod is glowing virtually right up to the plug body. This causes a further increase in the temperature of the regulator coil, which has already been heated by the current. As a result, the electrical resistance of the regulator coil rises and the current is reduced to a level that ensures that the glow rod is not at risk of damage. This prevents the glow plug from overheating. If the engine does not start, the glow plug is switched off by the glow time control unit after a certain stand-by time. Older style vehicles are usually fitted with glow plugs which only glow before and during the start phase.

Post-glowing glow plugs

Modern diesel passenger cars usually leave the production line with post-glowing glow plugs.

This means that they glow:

  • Before starting
  • During the start phase
  • After starting
  • Whilst the engine is in operation (in coasting mode)

The electronically controlled pre-heating phase starts when the ignition lock is turned. It lasts between approximately two and five seconds at normal outside temperatures, after which time the engine is ready to start. Post-glowing lasts for up to three minutes after the engine has started to minimise harmful substance and noise emissions. The operating state of the engine is identified by measuring the coolant temperature, for example. Post-glowing lasts until the coolant temperature reaches 70°C or it is stopped once a time set in the characteristic map has expired. Post-glowing does not usually take place if the coolant temperature is above 70°C prior to the engine starting up.

Protection against overheating

Self-regulating rod glow plugs protect themselves against overheating by limiting the current from the battery to the plug as the temperature increases. However, when the engine is running, the voltage increases to such a level that glow plugs which are not designed for the very latest technology can burn out. Furthermore, the energised plugs are exposed to high combustion temperatures following starting and are thus heated up from inside and out. Post-glowing rod glow plugs are able to function at full alternator voltage. Although their temperature rises quickly, a new regulator coil establishes a steady-state temperature which is lower than that of plugs which do not support post-heating.

Quick start in two seconds

With post-glowing glow plugs, it has been possible to reduce the glow time to between two and five seconds. To achieve this, design engineers have reduced the diameter of the heater rod at its front end. As a result, the heater rod starts to glow very quickly in this zone. At a temperature of 0°C, it takes just 2 seconds to achieve readiness for starting. At lower temperatures, glow time regulation enables the system to adapt to requirements and increase the glow time accordingly (at –5 °C to approximately 5 s and at –10 °C to around 7 s).



Spark plug


If we consider the basic construction of the spark plug, there have been no profound changes over the past 50 years. As ever, the spark plug comprises a metal core which is housed in a ceramic insulator. This, in turn, is surrounded by a metal casing which has a thread that is screwed in to the cylinder head and normally has a hexagonal section on the top which accommodates the spark plug socket and allows spark plugs to be installed or removed with a spark plug spanner.

The main purpose of the construction lies in ensuring that the electrical circuit at high voltage on the spark plug is closed with a spark, which jumps from the middle electrode to the earth electrode.

Inflammation (ignition)

The spark plug plays an important role in petrol engines. It is responsible for igniting the fuel/air mixture. The quality of this ignition influences several factors which are of great importance for both driving and the environment. They include smooth running, engine performance and efficiency as well as pollutant emissions. If we consider that a spark plug must ignite between 500 and 3,500 times per minute, it becomes clear how great the contribution of modern spark plug technology is to adherence to current emissions standards and the reduction of fuel consumption.


The connection is designed as an SAE connection or a 4 mm thread. The ignition cableor a rod coil is plugged into the connection. In both cases a high voltage coupled here must be transported to the other end of the spark plug. The ceramic insulator has two tasks. Its primary purpose is insulation, whereby it prevents flashover of the high voltage to the vehicle mass (= minus), and conducts combustion heat to the cylinder head. The wave-shaped leakage current barriers on the outside of the insulator prevent voltage leaking to the vehicle mass. In doing so, they extend the path to be travelled and increase the electrical resistance, thereby ensuring that the energy takes the path of least resistance - the path through the middle electrode. In order to ensure the electromagnetic compatibility (EMC) and thus the fault-free operation of the on-board electronics, a glass melt is used inside the spark plug as interference suppression. The middle electrode of a standard spark plug is comprised mostly of a nickel alloy. The spark must jump from the end of this electrode over to the earth electrode. The metal housing is firmly attached to the cylinder head via a thread and thus plays an important role in heat dissipation, discharging the bulk of the heat generated during combustion via this connection. The seal ring prevents combustion gas from emerging past the spark plug even at high combustion pressures. In so doing, it prevents pressure losses. Moreover, it conducts heat to the cylinder head and evens out the different expansion properties of the cylinder head and spark plug housing. The inner seals create a gas-tight connection between the insulator and the metal housing, providing an assurance of optimum sealing. The earth electrode of a standard spark plug is made of a nickel alloy. It represents the opposite pole of the middle electrode in normal function.

Temperature and heat flow

An up-to-date spark plug must be tailored individually to meet the requirements of different engine designs and driving conditions. Therefore, there cannot be one spark plug which will function without any difficulty in all engines. Due to the variations in temperature development in the respective combustion chambers in different engines, spark plugs with different heat ratings are needed. This heat rating is expressed using what is known as the heat rating number. These heat ratings represent an average temperature measured at electrodes and insulators, corresponding to the engine load in each case.

Spark plugs require a special temperature window in order to perform at their best. The lower threshold of this window is a spark plug temperature of 450°C, known as the self-cleaning temperature. Starting from this temperature threshold, the carbon particles which have collected on the insulator tip are burned off. If the operating temperature continuously lies below this point, electrically conductive carbon particles can collect, forming deposits until the ignition voltage flows over the carbon layer to the vehicle mass instead of forming a spark. At a spark plug temperature of 850°C or higher, the insulator heats up so much that uncontrolled ignitions can occur on its surface known as glow ignitions. Such uncontrolled, abnormal combustion can lead to engine damage.

Heat development varies greatly from engine to engine. For example, turbocharged engines run significantly hotter than engines which are not charged. Therefore, there is a spark plug for each engine which can conduct a precisely defined measure of heat to the cylinder head and ensures that the optimal temperature window is maintained. The heat rating provides information about the thermal endurance of a spark plug. Every spark plug manufacturer has its own way of expressing the heat rating.

Nearly 60% of the heat is dissipated via the spark plug case and thread. The seal ring conducts slightly less than 40% to the cylinder head. The small remaining percentage (making up 100%) flows out through the middle electrode. The insulator absorbs the heat in the combustion chamber and conducts it to the interior of the spark plug. Anywhere that it comes into contact with the case, heat is conducted. By increasing or decreasing the size of this contact surface area, it is possible to determine whether the spark plug is conducting more or less heat through the case.

The contact surface area is larger for spark plugs with higher thermal endurance. For spark plugs with lower thermal endurance it is smaller.


Brake servo


The brake servo supports the force the driver exerts on the master brake cylinder when he/she presses the brake pedal. This significantly reduces the effort required when braking. Together with the master brake cylinder, it is a component of most braking systems in cars.

The two most common designs are

Vacuum brake servo:
Most brake systems in cars have a vacuum brake servo. They use the vacuum that is produced in petrol engines by the air intake system in the engine's intake pipe or via a vacuum pump (0.5...0.9 bar) in diesel engines.

Hydraulic brake servo:
These types of servo use the pressure created by a hydraulic pump, which is driven by the engine. Hydraulic brake servos are used in vehicles which have hydraulic energy supply (e.g. power steering) and vehicles whose engine has low vacuum pressure in the intake pipe (e.g. turbo engines). Hydraulic brake servos are smaller than vacuum brake servos and require a higher pilot pressure.

There is a membrane inside the brake servo, which divides the servo into two chambers. When the brake is not being operated, there is a vacuum in both chambers, which is generated by the engine. When the brake is operated, both of these chambers are sealed off from one another. At the same time, a valve opens which allows atmospheric pressure to flow in on the pedal side. Now there is atmospheric pressure on one side of the membrane (pedal side) and on the other side a vacuum (master cylinder side), which pulls the membrane connected to the push rod towards the master cylinder and augmenting the force from the pedal.

When the brake pedal is released, both chambers are reconnected with each other via a valve opening whilst the valve, which was previously allowing atmospheric pressure to flow in, now closes. There is now a vacuum in both chambers. 

The brake servo only works when the engine is running. If the engine is switched off, e.g. when the vehicle is being towed, the brake force must be applied solely via the pedal.



Ignition wires (ignition cables)


Ignition wires must conduct the necessary voltage (U) to the spark plug with minimum possible losses. Depending on how the vehicle is designed, this is achieved using:

– A mechanical spark distributor and distributor cap
– A fully electronic ignition module
– A fully electronic semi-direct ignition or double spark ignition coil

Since the ignition voltage (U) of up to 36,000 volts is in the high-voltage range, the ignition cables have to be protected accordingly against overvoltage. The ignition voltage must never permeate the insulation and flow to ground, since this could cause misfiring. Although the fundamental aim is low-loss conduction, resistors are used in all ignition wire systems. Looking into the electrical technology, it is clear that this is not necessarily a contradiction. All electrically-operated devices create electromagnetic fields of greater or lesser strength. In most cases they are only negligible, but under some circumstances they are undesired (e.g. interference with radio reception). The ignition system requires optimal low-pass interference attenuation in order to ensure interference-free operation of radios, communications equipment and control units for engines or gearboxes. The assumption that resistors reduce ignition energy and thus engine performance has been proved to be mistaken. The resistors which are used are dimensioned so that they are hardly noticeable. The ignition cable systems offered by brand manufacturers combine the best interference suppression with optimum ignition performance. The unit of measurement for resistance (R) is the ohm. For ignition cables this value lies in the range of a few thousand ohm or "kiloohm". The purpose of this resistance, as already described, is to reduce electromagnetic radiation. This is achieved by limiting the current (I) through the ignition wire and simultaneously ensuring that the spark plug also receives the necessary voltage (U). The mathematical formula for this is U = R * I.

In simple terms, low-pass interference attenuation can be presented as follows: The ignition system consists of a coil and capacitors, referred to in electrical engineering terms as an "oscillating circuit". Interference suppressors (at least 1-5 kOhm) integrated into the ignition circuit reduce these electromagnetic fluctuations and safeguard the fault-free interplay of the various items of equipment. This is called "electromagnetic compatibility" (EMC). Ignition wires with inductive resistor have a special feature: with this design the resistance changes considerably depending on the ignition frequency (engine speed). In this case, a greater (inductive) resistance is built up due to the coil. Wherever electric current flows, electromagnetic fields are formed, such as with mobile phones and radio waves. Such electromagnetic fields also occur during ignition. They increase considerably in intensity at the time of each "spark breakaway" on the centre electrodes of the spark plug – resulting in strong voltage peaks along the cable. However, since strong electromagnetic fields can cause malfunctions in electronic equipment - e.g. radios, the ABS, they must be kept within a harmless range. For this purpose, ignition cables are equipped with electrical resistors. These limit the voltage peaks during the spark breakaway and during the discharge of the ignition coil. In the process, the energy from existing voltage and current strength is applied in a different energy-time relationship.




Ignition modules


In order for a petrol engine to function, an ignition spark must be generated between the electrodes of the spark plug at the correct point in time in order to ignite the petrol/air mixture compressed by the piston. This ignition spark must have sufficiently high energy. Depending on requirements, voltages between approx. 28,000 V and approx. 35,000 V are necessary to generate sparking between the spark plug electrodes. However, as the battery in a passenger car only has a voltage of 12 V, the high voltage required must be generated by means of transformation. This function of transformation from 12 V to the necessary high voltage is performed in the vehicle by an ignition coil /an ignition transformer.

An ignition module, for example, is needed to control this process.

Function of the ignition module
The function is relatively straightforward. The ignition coil has a primary winding (small number of turns) and a secondary winding (lots of turns). The turn ratio between primary and secondary winding determines the level of the voltage generated at the output. If the primary winding of the ignition coil is connected to the in-car 12 V battery voltage via a switch, a current will flow through the primary winding, creating a magnetic field in the ignition coil that acts on the secondary winding. If the switch is opened again at this point, no more current can flow via the primary winding. The energy (which is now stored inside the ignition coil as a magnetic field) looks for a balancing element and generates a high voltage in the secondary winding which is high enough to overcome the air gap between the spark plug electrodes. The energy can thus flow via the spark plug, generating a spark (the spark being generated when the switch is opened). In older vehicles, this switch was a mechanical contact activated via a "nose" on the camshaft (break contact). The function of this break contact was subsequently replaced by ignition modules (igniters). 
One of the components inside an ignition module is a transistor, which takes over the function of the switch. Effectively, this transistor replaces the switch > it still switches the current through the primary winding on and off, just more quickly/more precisely.

The advantages are clear to see:

  • No mechanical wear
  • No contact problems when damp
  • More precise control of ignition points

Furthermore, most ignition modules have automatic current limiting to prevent the ignition coil becoming overloaded and suffering irreparable damage as a result. When using an ignition module, the point in time at which switching is to take place is of course also determined by the processes in the engine, or more precisely by the position of the pistons inside the cylinders. For this purpose the ignition module requires a control signal. This is supplied by a sensor.
There are various different sensors:

Inductive sensor (pick-up):
Inside this sensor there is a small coil past which a permanent magnet moves (movement generated by the rotation of the camshaft). This generates an electric pulse in the coil which is forwarded to and controls the ignition module.

Hall sensor:
This sensor contains an electronic switch which reacts to magnetic fields. With this type of sensor, a permanent magnet is mounted in a fixed position relative to the sensor.

A slotted disc made from iron rotates between sensor and permanent magnet. The slotted disc either lets the magnetic field of the permanent magnet through to the sensor or blocks it. A precise square-wave signal is thus generated at the sensor. This signal is used to control the ignition module. Temporal sequences can be controlled much more precisely with a hall sensor than they can be with a pick-up.

Ignition timing/Ignition timing adjustment


Ignition coil


The ignition coil must transform the relatively low 12 V on-board vehicle voltage to the high ignition voltage required and supply the energy stored in that voltage to the spark plug. The functional principle of the ignition coil is relatively simple. It has a primary winding (small number of turns) and a secondary winding (lots of turns). The turn ratio between the number of primary and secondary winding turns determines the level of the voltage generated at the output. When on-board voltage is connected to the primary winding of the ignition coil, a current flows through the primary winding, generating a magnetic field in the ignition coil. Interrupting the current flow in the primary winding takes away the magnetic field suddenly, simultaneously generating the high voltage required for ignition sparking in the secondary winding. How the high voltage generated by the ignition coil is transferred to the spark plug will vary depending on the ignition system, the vehicle generation and the vehicle model. In older vehicles, a mechanical ignition distributor distributes the high voltage to the spark plugs. The ignition distributor was replaced when fully electronic ignition with direct connection between ignition coil and spark plug was introduced.

Over recent decades, the ignition system has undergone continuous development. The following ignition systems can be considered as milestones:

Conventional coil ignition SZ-ROV (rotating high voltage distribution)

In this type of system, a rotating distributor finger located inside the ignition distributor distributes the high voltage to the spark plugs. The ignition distributor required for ROV conversion consists of numerous components including a mechanically actuated and thus high-wear break contact. On account of the mechanics (and the associated inertia), the capacity of the switching operations is limited and switching does not always occur at exactly the right time. This ignition system is only to be found in classic cars and modern classics.

Transistor ignition TZ-ROV (rotating high voltage distribution)

The introduction of contact-controlled transistor ignition initially saw the susceptibility to wear of the mechanical break contact significantly reduced. Later, the brake contact was replaced by a transistor igniter (ignition module). The transistor igniter was usually controlled by a hall sensor or an induction sensor located inside the ignition distributor.

Electronic ignition EZ-ROV

With this ignition system, high voltage distribution is still implemented using mechanical means. However, mechanical ignition timing adjustment is replaced by electronic control, meaning that the ignition distributor no longer requires a vacuum unit. The necessary parameters (speed and load, for example) are captured electronically and compared with an ignition timing map stored in the system. The ignition coil is controlled with an igniter.

Fully electronic ignition VZ-RUV

Fully electronic ignition does not require an ignition distributor. Voltage is distributed fully electronically in an igniter ("static high voltage distribution"). This ignition system is the system of choice in most modern vehicles.

Different types of ignition coil are used depending on the ignition system. An overview of these appears below:

Cylinder ignition coils

Cylinder ignition coils are used primarily in older vehicle models. They are much safer due to the dry and thus fail-safe insulation between coil winding and cylinder housing. The cylinder coils made by budget providers are often filled with oil, which can leak out in the event of a fault or an accident and cause a vehicle fire.

Distributor ignition coils

Distributor ignition coils have a high-voltage dome which is connected to the ignition distributor via a high-voltage cable. They are primarily used in vehicles with rotating high-voltage distribution.

Block ignition coils

A block ignition coil combines several ignition coils which control several spark plugs via ignition wires. Block ignition coils are available with and without integrated output stage and in both single-spark and double-spark technology.

Pencil coils/Coil-on plugs

Pencil coils or coil-on plugs (with single-spark and double-spark technology) are plugged directly into the spark plug. This means that the ignition energy can be transferred directly to the spark plug with virtually zero power loss. Another advantage is that the existing spark shaft can provide the mounting base for the ignition coil depending on design. Pencil coils or coil-on plugs are used in vehicles with fully electronic ignition. Examples include models by BMW, Fiat, Mercedes-Benz, Porsche, Renault or VW.

Ignition coil strips

An ignition coil strip combines several single-spark ignition coils. These coils are plugged directly into the spark plug. So that misfiring and knocking combustion can be detected at an early stage, the coils can also be equipped with integrated ion current measurement. Ion current measurement monitors the mixture combustion and provides the basis for an ignition control circuit. These types of ignition coil are used in models by VW, Opel, Peugoet, Citroen and Skoda, for example.



Exhaust turbocharger


The exhaust turbocharger compresses the air supplied to the engine. Compared with naturally aspirated engines, cylinder filling is much better. Engine performance is increased whilst at the same time consumption is reduced and emission values are improved.

During exhaust gas turbocharging, exhaust gas energy which would otherwise escape into the environment unused is used to drive a turbine. A compressor is mounted on the shaft of the turbocharger opposite the turbine. The compressor draws in the combustion air, directing it to the engine in compressed form. There is no mechanical connection to the engine.

The exhaust turbocharger comprises a turbine and a compressor between which there is a fixed mechanical connection established via a common shaft. The turbine is driven by the exhaust gases from the engine and supplies the drive energy for the compressor. In most cases, centripetal turbines and centrifugal compressors are used for turbochargers.

Centrifugal compressor

A centrifugal compressor essentially comprises compressor wheel, diffuser and spiral housing. When the compressor wheel turns, it draws in air axially (in the direction of the longitudinal axis) and accelerates the air to a high velocity. The air exits the compressor wheel in the radial direction. In the diffuser, the velocity of the air is reduced, mostly without losses. As a consequence, both pressure and temperature rise. The diffuser is formed from the rear wall of the compressor and a part of the spiral housing. The air is collected inside the spiral housing and the velocity continues to be reduced until the air exits the compressor.

On the drive side, only centrifugal turbines (also known as centripetal turbines) are used in exhaust turobochargers for passenger cars, commercial vehicles and industrial engines. They convert the pressure of the exhaust gas into kinetic energy inside the spiral housing and feed the gas to the turbine wheel at constant velocity. In the turbine wheel, the kinetic energy of the exhaust gas is converted into rotation energy of the shaft. The turbine wheel is designed so that virtually all of the kinetic energy is converted on exiting the wheel.

Charging pressure regulation

If the turbo engine is to reach optimum performance levels, the charging pressure of the exhaust turbocharger must be matched to the engine load and the engine speed. Bypass on the turbine side (bypass channel) is the simplest form of charging pressure regulation. The turbine is small enough to meet the requirements for torque response at low speeds and ensure that the engine drives well. In such a design, shortly before the maximum torque is reached, more exhaust gas is supplied to the turbine than is necessary to generate the charging pressure. Therefore, once the required charging pressure has been reached, some of the exhaust gas is diverted around the turbine through a bypass. The charging pressure control valve, which opens and closes the bypass, is controlled by a spring-loaded membrane on the basis of the charging pressure.

In modern passenger car diesel engines, variable turbine geometry (VTG) with rotating guide vanes has established itself as the state of the art. With VTG, the flow cross-section of the turbine can be adjusted based on the engine operating point. All of the exhaust gas energy is used and the setting of the flow cross-section of the turbine can be optimised for any operating point, thereby improving the efficiency of the turbocharger and as a result that of the engine compared with bypass control. Constantly adapting the turbine cross-section to the prevailing driving conditions of the engine also reduces fuel consumption and emissions. The engine torque, which is already high even at low speeds, along with a carefully adapted control strategy, enable a perceptible improvement in driving dynamics to be achieved.


Accessory drive


Function The accessory drive is responsible for driving ancillary components such as the alternator, the power steering pump, the water pump or the air conditioning compressor. V-belts or a V-ribbed belts are used to transmit the drive energy from the crankshaft to the relevant accessories. The demand for increasing convenience in today's vehicles has led to a significant increase in electronic components and demand for electrical energy. As a result, a V-belt is often no longer sufficient to drive the more powerful alternators and other ancillary components such as air conditioning compressors or power steering pumps. Therefore, V-ribbed belts are being used, as they support smaller contact radii and higher transmission ratios. Furthermore, ancillary components arranged in the tightest of spaces can be driven by the front and back of the V-ribbed belt.

Tensioning pulleys and deflection rollers

Other components of the accessory drive include the tensioning pulleys and deflection rollers. The tensioning pulleys ensure that the belt is at constant tension and transmit the force from the belt tensioner to the belt. Deflection rollers vary the path of the belt based on which ancillary components are in use and often act as stabilising rollers to stop the belt from flapping.


Overrunning belt pulleys


Function unlike electric motors, combustion engines exhibit non-uniform rotation. The four-stroke principle dictates that the crankshaft is continuously accelerated and decelerated. These oscillations are transmitted to the accessory drive, having a negative effect on noise characteristics and the service life of the drive belt. It is for this reason that the alternators in modern vehicles are fitted with an overrunning belt pulley (also known as an alternator freewheel). The overrunning belt pulley is mounted on the alternator's drive shaft. It transmits the drive force in one direction only. In so doing, it decouples the alternator from the oscillations of the crankshaft. Thanks to this technical trick, the belt drive runs more smoothly and more quietly, and the service life of the drive belt is extended.




Plain bearings


Function Plain bearings support and guide moving components inside the engine. Their primary purpose is to facilitate the virtually wear-free rotation of these components. Plain bearings comprise one or two bearing shells which are locked firmly in place in the bearing seat. The bearing shells wrap around the rotating shaft at the bearing journals. Engine oil is pushed into the plain bearing through a bore hole. During normal operation of the engine, the shaft virtually guides above the film of oil without touching the bearing shell.

Plain bearings absorb the axial and radial forces, redirecting them to the bearing housing. Plain bearings are used both for rotating shafts (the crankshaft, camshaft, rocker arm shaft and counterbalance shaft, for example) and in the connecting rod. They also have the important task of absorbing and embedding abrasion. This abrasion occurs during normal operation of the engine. It takes the form of tiny particles of metal that are too small to be trapped by the oil filter but big enough to cause increased wear if they are not embedded. This key function of the plain bearing for smooth running and low-wear operation of the engine requires a specific design.



Glow time relays


Glow plugs as ignition aids

Diesel engines are compression-ignition engines. This means that an additional heat source is not needed to ignite the mixture in the cylinder. In the cylinder, the air/diesel mixture is highly compressed. This results in a temperature that is so high that the mixture ignites itself, producing an explosion. However, if the engine is not hot, this process can be beset by problems. At cold temperatures, the air/diesel mixture will not ignite so easily. To safeguard combustion when the engine is cold, glow plugs (one per cylinder) are used as ignition aids. The glow plug increases the temperature in the cylinder's combustion chamber prior to the engine starting. At its peak, the temperature of the glow plug can reach up to 1,000°C. This ensures that the air/diesel mixture will explode even at low temperatures. The time required for "pre-heating" will vary depending on the glow plug used. Fast glow plugs only need a pre-heating time of just a few seconds. Other glow plugs must pre-heat for up to 15 seconds at low ambient temperatures. The glow time relay is responsible for switching the current for the glow plugs on and off as well as taking care of timing.

Glow time control unit switches known as power relays are built into the glow time relay (glow time control unit) to switch the current for the glow plugs on and off. If they are already hot, glow plus need a current of approx. 10 A. However, during the ON phase (when the glow coil is cold), the current is much higher. In the case of a 4-cylinder engine, the power relays must be able to switch currents of up to 80 A. This figure is even higher in the case of 6-cylinder and 8-cylinder engines. Therefore, the glow plugs to be controlled are often distributed across two circuits. Accordingly, there are then two power relays in the glow time relay.

Phases to be taken into account for timing

1. The pre-heating time.

The pre-heating time is determined by the type of engine, the glow plugs used and the ambient temperature measured with the assistance of a sensor. Depending on the type of relay, the temperature sensors can be located in the relay itself or externally (in the refrigerant circuit, for example). In winter, at temperatures below zero, the pre-heating time is much longer than it is in summer at temperatures of +30°C, for example. During the pre-heating time, the pre-heating indicator lamp on the dashboard lights up. In some vehicles, the pre-heating time starts when the driver opens the driver's door.

2. The stand-by time.

This starts immediately after the pre-heating time. The indicator lamp goes out but the glow plugs remain switched on for a few more seconds. During this time the engine should be started by the driver.

3. The post-heating time.

The post-heating time was introduced in more recent vehicles. This was necessary due to increasingly strict exhaust gas standards and the optimisation of combustion processes required as a result. The glow plugs remain switched on during the post-heating time even if the engine is running. The length of the post-heating time is determined by the type of engine and the engine temperature. Only special "post-heating" glow plugs are used for this function.

Variants even if the underlying technical function is not always the same, there are many different variants of glow time relay. There are different housing dimensions, connector plugs and types of attachment. There are more than 100 different types of relay for vehicles manufactured in Europe alone. There are also pre-heating systems in which the engine control unit takes over the timing function. The glow time relay then simply has to switch the high currents required for the glow plugs. 

Fully electronic glow time relay

It is an entirely different story with these modern types of glow time relay. They support diagnostics and are connected to On-Board Diagnostics (OBD). Fully electronic glow time relays are control units which are connected to the engine control unit via a data bus. The commands for switching on and off come from the engine control unit. It also measures whether there is actually a high enough current flowing after a glow plug has been switched on. This is then fed back to the engine control unit in the form of an acknowledgement signal. If too high a current is detected (in the event of a short-circuit in the cable or glow plug, for example), the corresponding current branch is shut down in order to avoid the electronics being damaged beyond repair.

Another particular feature of fully electronic glow time relays is the use of power transistors (electronic switches) rather than relays for switching on and off. Power transistors not only support switching glow plugs on and off, they also allow current levels to be varied. This is achieved by means of a variable duty cycle. In other words, the current is switched on and off at very short intervals during the current control phase. If the ON time is longer than the  OFF time, the glow plug receives more power and becomes hotter. Conversely, the glow plug is heated less if the ON times are shorter than the OFF times.

Glow time relays are installed in various locations in the vehicle. Plug-in relays are primarily located in the central relay box. Relays which have screw-on cable shoes for the supply line to the glow plugs instead of plug-in contacts are located in the engine compartment. These relays are screwed directly onto the splash panel or to the car body (in the latter case via the intermediary of special attachment brackets).


Master brake cylinder


The master cylinder, also known as the master brake cylinder, converts the pressure on the brake pedal to hydraulic pressure by feeding brake fluid into the brake circuit and controlling this according to the mechanical force. Master brake cylinders are used both in disc brakes and drum brakes.

Due to statutory provisions, a car must be equipped with two separate brake circuits. So-called tandem master cylinders generate the hydraulic pressure for the two separate brake circuits. In the event of one brake circuit failing, the brake pressure builds in the other brake circuit still intact.

When the driver presses the brake pedal, the power from his/her foot on the pedal is transmitted to the pressure piston. The piston is pushed towards the brake line.  

In master cylinders in older vehicle models, the piston collar passes over the compensating bore, the pressure chamber is closed and braking force is generated. When the driver now releases the brake pedal, the pressure piston,  supported by a spring, is returned to its original position. Brake fluid then flows into the main cylinder, so that if the pedal is pressed again immediately, the brake pressure is increased.

Master brake cylinders in newer vehicles

Newer vehicles with ESP® do not have compensating bores and replenishment ports.These components' tasks are assumed by the central valves.

When the master brake cylinder is in the neutral position, the central valve is open. The volume compensation between the brake fluid reservoir and the wheel brake is achieved via the replenishment port and the bores in the piston.

When the brake is operated, the central valve is closed, interrupting the connection between the brake fluid reservoir and the wheel brake. The pressure can now begin to build. Closing the central valve is the equivalent of the primary collar passing over the compensating bore in a master brake cylinder with such a bore.

Releasing the wheel brakes

After the brake pedal is released, pressure in the circuit falls and the wheel brakes are released. The piston returning to its neutral position can create a vacuum, which opens the central valve and therefore ensures that brake fluid is replenished. After the release procedure is complete, the neutral position is achieved and the central valve stays open.


Hybrid drive


The hybrid drive combines the combustion engine with an electric motor. Readiness for start of production of the first vehicles with hybrid drive is the result of the perfect combination of the very latest technologies. Thanks to the interplay of the very latest system components, it has been possible to integrate the hybrid drive into production vehicles for everyday use with impressive distance coverage and high efficiency.

A hybrid vehicle usually comprises the following components:

  • Electric machine
  • Inverter
  • Cooperative regenerative braking system
  • High-voltage battery

The electric machine

The electric machine is the linchpin of a modern vehicle with hybrid drive. It has two functions. As a motor, it provides the electric drive for the vehicle. As a generator, it helps to convert kinetic energy from the braking process into electrical energy.


The power electronics, also known as the inverter, provides the link between the battery and the electric machine. It converts the direct voltage from the high-voltage battery into an alternating voltage needed to run the electric machine.

Cooperative regenerative braking system

With conventional brakes, the kinetic energy from the vehicle generated from the fuel upstream is converted into heat and lost. The cooperative regenerative braking system ensures that as much braking energy as possible is recovered and stored as electrical energy. The generator is used to decelerate the vehicle. The conventional wheel brakes are only applied if the braking requirement exceeds the deceleration potential of the generator.  As such the cooperative regenerative braking system meets the same safety requirements as conventional braking systems.

High-voltage battery

The high-voltage battery supplies electrical energy to the electric machine during electric driving. When driving with the combustion engine and during regenerative braking, the battery is charged by the electric machine. Safe, powerful and high-quality lithium-ion batteries with a battery management system are used.

Types of system

Hybrid drives are often designated as follows based on performance dimensions:

  • Mild hybrid: uses the combined power of combustion engine and electric drive as a "boost function". In other words, the electric machine assists the combustion engine when accelerating, for example. Pure electric driving is not possible with this hybrid variant.

  • Strong hybrid: Pure electric driving is possible for short distances.

  • Plug-in hybrid: Electric driving is possible even for long distances.

Types of drive

Several drive type options are available for hybrid drive vehicles. The possible drive types at a glance:

Serial drive

The combustion engine drives a generator. The electric motor uses the electrical energy from the generator to drive the vehicle. The power flows in series (combustion engine, generator, engine).

Parallel drive

Both the combustion engine and the electric motor drive the drive wheels. Power addition of the drive units takes place. Power flows in parallel from combustion engine and/or electric motor.

Split-power drive

A split-power drive combines serial and parallel concepts. The drive can either be provided solely by an electric motor (serial energy conversion by means of combustion engine and generator) or by the electric motor with a combustion engine in parallel.

The range extender as a valuable option

The use of a range extender is another option supported by hybrid technology. In vehicles with range extender, the electric drive is even more powerful and supports pure electric driving. The range is big enough to cover the average daily need for mobility. If necessary, electrical energy can be generated on-board by the range extender (small combustion engine). The range covered by pure electric driving is approximately 80 km. Over longer distances, the range extender increases the range by recharging the battery.

The components for electric vehicles with range extender are:

  • Electric axle drive
  • Inverter
  • Charger
  • Cooperative regenerative braking system
  • High-voltage battery
  • Range extender (combustion engine – often dimensioned as a rotary engine)

The range extender offers the following benefits to customers:

  • Reduction in fuel consumption of up to 90%
  • Reduction in CO2 emissions of up to 90%
  • Mobility guarantee from the range extender
  • More driving pleasure thanks to the boost effect of the electric motor
  • Braking energy recovery
  • No noise emissions




The V-belt acts as a transmission belt. Connecting the V-belt pulleys, it transmits the force from the engine to the ancillary components including the alternator, the hydraulic pump for the power steering, the air conditioning compressor, the fan and the water pump

In a combustion engine, the combustion of the air/fuel mixture drives pistons. Via connecting rods, the movement of these pistons in a straight line is converted into the rotation of the crankshaft. The V-belt uses the force from the rotation (torque) of the crankshaft and drives additional units via V-belt pulleys. As such it is responsible for the correct operation of the engine and high levels of ride comfort. A V-belt can drive one or two additional units.


V-ribbed belts


The V-ribbed belt is a further development of the V-belt and works according to the same principle: It acts as a transmission belt, connects the V-belt pulleys and transmits the force from the engine to the ancillary components including the alternator, the hydraulic pump for the power steering, the air conditioning compressor, the fan and the water pump.

In a combustion engine, the combustion of the air/fuel mixture drives pistons. Via connecting rods, the movement of these pistons in a straight line is converted into the rotation of the crankshaft. The V-belt uses the force from the rotation (torque) of the crankshaft and drives additional units via V-ribbed belt pulleys. As such it is responsible for the correct operation of the engine and high levels of ride comfort. The V-ribbed belt has an advantage over the V-belt in that it is able to transmit the torque from the engine to several units at the same time.


Chain drive


The chain drive in combustion engines must transmit the rotation of the crankshaft to the camshafts, thus ensuring that the valves open and close reliably and at exactly the right time. A chain is used as the transmission medium. It is also known as a timing chain.

Timing chains have been a standard feature of combustion engines since the start of the 20th century. Since the 1980s, the toothed belt has increasingly been establishing itself as a more cost-effective alternative. Some manufacturers including Mercedes and BMW remain faithful to the traditional chain drive. Timing chains are frequently also used by other manufacturers to drive camshafts, in particular in large-volume engines.

Depending on the requirements of the automobile manufacturer, timing chains can take the form of simplex or duplex roller chains as well as inverted toothed chains. Compared with belt drives, timing chains have the advantage that they are able to bridge long distances between components and support the transmission of forces.

However, timing chains can stretch over time and must be re-tensioned after prolonged operation. To avoid this, they are pre-stretched in production before leaving the factory. Timing chains are also louder than toothed belt drives, but the higher noise emissions can be mitigated by using slide rails and chain tensioners.

Furthermore, chain drives are heavier than toothed belt drives and take more time and effort to install when components are replaced. The chain drive is exposed to high levels of stress and strain during normal operation. Typical wear parts of the chain drive are the timing chains, slide rails and tensioning rails, the chain tensioner and the chain wheels. The quality and processing of these components is decisive for the safety and longevity of the chain drive.




During the operating cycle of a combustion engine, the energy bound in the fuel is converted into heat and pressure in the cylinder in a very short space of time. This process is explosive in nature. It causes the temperature and pressure values in the cylinder to rise very significantly in fractions of a second.

The piston is a moving part of the combustion chamber. It is responsible for converting the energy released during the combustion process into mechanical work. The piston also performs a number of other important tasks. It seals the combustion chamber, guides the connecting rod (in trunk piston engines) and dissipates the heat generated in the combustion chamber. It also supports gas exchange (by means of gas suction and emission) and mixture preparation with a special piston surface design on the combustion chamber side which is known as the piston crown. It also houses the sealing elements (piston rings).

In terms of its basic structure, the piston is a hollow cylinder which is sealed on one side. It consists of the following areas: Piston crown with ring belt, piston hub and shaft. The piston crown transmits the compression forces generated during the combustion of the fuel/air mixture to the crankshaft via the piston hub, the piston crown and the connecting rod.

The piston is exposed to various forces. When the engine is running, it moves up and down constantly in the cylinder. At each reversing point it is braked sharply and then accelerated again.This generates mass inertia forces which act on the piston. Together with the forces generated from the gas pressure, they form the piston force.

The piston force is transmitted to connecting rod and the crankshaft. However, the connecting rod is only precisely vertical at the upper and lower reversing points (known as dead centre). The inclination of the connecting rod pushes the piston to the side, i.e. against the cylinder wall. The extent of this force (also known as lateral force or normal force) changes direction several times during an operating cycle. It is determined by the piston force and the angle of the piston crown in relation to the connecting rod axis. The lateral force can be derived from the parallelogram of forces.

Every piston is fitted with piston rings. The piston rings must seal off the combustion chamber and the working space from the crankcase and strip the oil from the cylinder walls, thereby regulating oil consumption. They must also dissipate the heat absorbed by the piston during combustion to the cooled cylinder barrel.



Cooling (engine cooling)


In a combustion engine, the bulk of the energy contained in the fuel is converted into heat. If this heat is not effectively dissipated to the outside, the engine overheats and serious damage is caused to the engine mechanics. The engine cooling system must therefore cool the engine by dissipating excess heat to the outside air. Some of the heat transported by the cooling system can be used to heat the passenger compartment if required.

The most important components of the cooling system are the water pump, the thermostat, the radiator and the expansion tank. Some of the individual components of the cooling circuit are installed in the engine block and interconnected via hose lines to form an enclosed system. The coolant circulates inside the system driven by a mechanical or electrical pump.

The combustion heat from the fuel first travels to the components of the engine before being released to the coolant. The heat is transported to the radiator by means of the circulation of the coolant. Having reached the radiator, it is discharged to the outside air. The cooling process of the coolant is assisted by one or more fans (driven mechanically or electrically) which can be located upstream or downstream of the radiator. This occurs in particular when the vehicle is travelling slowly or at standstill with the engine running. To shorten the warm-up phase of the engine and keep the temperature of the coolant and the engine relatively constant, the coolant flow is controlled by a thermostat.


Engine sealing technology


Gaskets are highly technical and complex engine components. They are used in many different forms and material compositions in modern combustion engines and assemblies (gearboxes, axles, etc.).

The engine gasket is a key component. It contributes to efficient, safe and cost-effective engine running. 

The primary task of gaskets is to seal off the various media in the engine (including gases, water and oil) from both one another and the outside world. However, gaskets also function as power transmission links. For example, the cylinder head gasket between the engine block and the cylinder head has a significant impact on power distribution within the entire tensioning system and the resulting component deformations.

Modern high-performance sealing systems are very reliable. Engine designers and component manufacturers have spent a great deal of time and effort developing product solutions which can be relied upon for safe operation even under critical boundary conditions. Accordingly, modern sealing systems are able to withstand aggressive media, high pressures and equally high temperatures throughout the lifetime of a car.

Drivers usually only notice components of the engine sealing system that they cannot see in the event of a leak. However, in such cases, the failure of the seal is not the cause of the leak. In most cases, it is damage to surrounding components that exposes the sealing element to excess stress and strain. The engine overheating, for example, can trigger a gasket fault. Depending on the load to which the engine is exposed, a leak can occur immediately following upstream damage to the sealing element or may take some time to manifest itself.


Engine control


Four-stroke engines rely on sophisticated gas exchange to run safely, efficiently and with low emissions. This means that during the intake stroke as much fresh air or fuel/air mixture as possible must be able to get into the cylinder. In the exhaust stroke, the exhaust gases must be discharged as quickly as possible. In four-stroke engines, the valves have the task of controlling gas exchange. They are in turn actuated by the camshaft, which is driven by the crankshaft.

The full set of components involved in controlling the inflow of fresh gases and the outflow of exhaust gases is known as the engine control.

The engine control must open and close the valves at a precisely defined point in time so that in each operating state the prevailing power and torque requirements are met and fuel consumption and harmful substances emissions are minimised at the same time.

The history of the car has seen numerous design solutions used for engine control, with toothed wheels and the vertical shaft being just two examples. In today's engines, only overhead camshafts are used, driven either by a timing chain or a toothed belt.

Depending on the design of the engine, other ancillary components such as the oil pump or the water pump are integrated into the engine control. Engine control components are exposed to high levels of stress and strain. Typical wear parts in this context are camshafts, oil pumps,belt drive components or valves.


Belt drive components


Belt drives can be found in every modern engine. They must transmit the rotation of the crankshaft to and drive the engine control or ancillary components.

The use of toothed belts to drive camshafts is widespread in modern engines. They are lighter and quieter than timing chains. The components of a toothed belt drive are the toothed belt itself, a belt tensioner, tensioning pulleys and deflection rollers as well as the toothed wheels at the crankshaft, the camshaft and the ancillary components. Toothed belts are made from synthetic rubber compounds and embedded glass tension cords. Force is transmitted via the teeth without slip. Over time, a variety of tooth designs have established themselves.

Alongside toothed belts, V-belts and V-ribbed belts are used in modern engines to drive ancillary components such as fans, alternators, compressors or hydraulic pumps. V-ribbed belts are exposed to high levels of stress and strain by the torques to be transmitted, dynamic loads and changing temperatures.

Belt drive components in all vehicles are expected to meet maximum performance requirements. Ancillary components will only function perfectly if belt drive components are achieving optimum levels of performance.


Vibration dampers


Four-stroke piston engines exhibit non-uniform rotation. The separate strokes (suction, compression, power, exhaust) combined with the firing order of the individual cylinders dictate that the crankshaft is continuously accelerated and decelerated. Torsional vibration dampers, or rotation vibration dampers , as they are also known, must damp these rotational irregularities and vibrations of the crankshaft so that they are not passed on to the belt drive system. They are screw-mounted directly on the crankshaft and fitted with a special damping device (inertia ring, plain bearing, rubber bearing). It is via the damping device that the connection to the V-ribbed belt pulley is established to drive the ancillary components (alternator, hydraulic pump for the power steering, air conditioning compressor, fan, water pump).



Tensioning pulleys and deflection rollers


In modern engines, the vast majority of ancillary components such as alternators, power steering pumps, water pumps and air conditioning compressors are driven by V-ribbed belts. Toothed belts are used for the timing drive in the bulk of engines. These belt drives need tensioning pulleys and deflection rollers in order to function reliably and quietly. They must guide and deflect the belt, as well as safeguarding the belt tension required for optimum operation.


Timing drive


The timing drive must drive the camshafts and thus control the opening and closing of the valves. The timing drive can be implemented with a belt drive, a timing chain or spur gears. These timing options all have one thing in common: they transmit the rotation of the crankshaft to the camshaft(s) at a ratio of 2:1. In so doing the timing drive coordinates the timed interplay (timings) between piston and valve movements. Belt drive timing drives need tensioning pulleys and deflection rollers. The tensioning pulleys ensure that the toothed belt is at constant tension and transmit the force from the toothed belt tensioner to the toothed belt itself. Deflection rollers vary the path of the toothed belt based on the arrangement of the shafts to be driven and often act as stabilising rollers to stop the toothed belt from flapping.





Valves seal off the combustion chamber and optimise gas exchange. As they are constantly in motion - and this under difficult tribological conditions and under the effect of aggressive gases or exhaust gases - they are subject to natural wear. This can be accelerated due to extreme conditions such as mechanical or thermal overloads. Valves must therefore generally be replaced when any sign of damage is noticeable.

The up and down motion of the valve opens and closes the engine's combustion chamber. Intake valves open and close the fresh air intake (or air/fuel mixture intake, depending on the engine). Exhaust valves open and close the outlet for exhaust gases. The valves are actuated via the camshaft, which is in turn driven by the crankshaft and thus opens and closes the valves in synchronism with the motion of the piston. Combustion temperatures are emitted via the valves to the cylinder head and thus to the coolant circuit.



Water pump


So that the cooling system can release the heat generated by the engine in the best possible way, the coolant must circulate in the system. The water pump must drive the coolant and safeguard the circulation required for heat exchange. As such, within the heating and cooling system, it helps the engine to reach optimum operating temperature quickly, to stay at this temperature and to avoid overheating.
Depending on the engine concept, water pumps with mechanical or electric drives are used in modern cars. Water pumps with mechanical drives are integrated in either the toothed belt drive or the V-ribbed belt drive. The transmission ratio between crankshaft drive and water pump impeller results in fixed link between its speed and the speed of the engine. Water pumps with electric drives run independently of the speed of the engine.

Their performance can be adapted to cooling requirements. This means that operating temperature can be reached more quickly. As they are more efficient, electric water pumps also help to reduce fuel consumption.



Toothed belt


The toothed belt controls the precision combustion process in the engine. It is driven by the crankshaft and controls the camshaft, which actuates the valves. The valves must be opened and closed at the correct time. The air/fuel mixture which, when combusted, drives the engine's pistons, is supplied to the combustion chamber via the valves. As the pistons in the engine move up and down, the correct control of the valves must be ensured in order to prevent a collision between pistons and valves inside the narrow combustion chamber. Toothed belts can also be used to drive injection pumps and counterbalance shafts or water pumps. As well as toothed belts, timing chains are also used in passenger cars. Spur gears or vertical shafts are seldom used. Unlike V-belt and V-ribbed belt drives, toothed belts transmit force via their teeth. In other words, they are positive-locking drive elements.




In combination with the piston and the cylinder head, the cylinders of a combustion engine form the working space and combustion chamber. The cylinders are also charged with the task of guiding the pistons as they move up and down and directing the heat generated during the combustion process to the cooling system.
Depending on their design, cylinders can be made from grey cast iron or aluminium, each with many different alloys. Determined by the design and build of the engine, the cylinders either have direct contact with the coolant, metallic contact with the engine block or are cast fast in the engine block. Appropriate materials are selected to safeguard good heat transfer to the engine block or coolant.

When the engine is running, the cylinder wall is wetted with oil. This ensures that the pistons and piston rings moving up and down inside the cylinder are sufficiently lubricated.


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