Drive slip control

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The traction control (ASR), also known as automatic slip control, active slip control or traction control , ensures that the wheels do not spin when the vehicle starts up. The traction control is intended to prevent one or more wheels from spinning and the vehicle from spinning sideways when starting off with a lot of gas (" cavalier start ") or on bad surfaces such as ice, snow, gravel, wet cobblestones (little static friction ). The counterpart is the engine drag torque control (MSR), which is intended to reduce vehicle instability when the accelerator is suddenly released.

The system has different names for many manufacturers:

  • Audi : (ASR)
  • BMW : Automatic Stability Control [sic!] ( ASC in cars and motorcycles) or Dynamic Traction Control (DTC in motorcycles)
  • Fiat : (ASR)
  • Ford : Traction Control System (TCS)
  • Hyundai : (TSC)
  • Land Rover : (ETC)
  • Mazda : Traction Control System (TCS)
  • Mercedes : (ASR)
  • Mitsubishi : Traction Control System (TCS)
  • Nissan : Traction Control System (TCS)
  • Opel / GM : Traction Control Support System (TCSS)
  • Peugeot : (ASR)
  • Piaggio : traction control (ASR)
  • Porsche : ASR as part of Porsche Stability Management (PSM)
  • Saab : Traction Control System (TCS)
  • Renault : (ASR)
  • Seat : (ASR)
  • Škoda : (ASR)
  • Suzuki : (ASR)
  • Toyota : Traction Control (TRC)
  • Volkswagen : (ASR)
  • Volvo : Traction Control System (TRACS)


ASR intervenes when the wheels start to spin when a vehicle starts, i.e. they have little or no grip on the road. If there is a threat of excessive slip of the drive wheels, the drive torque is reduced through targeted braking and / or engine management intervention. The control system, which receives its information from the anti-lock braking system wheel speed sensors, among other things , improves traction and driving stability during the acceleration phase, both on straight roads and when cornering. Fully trained ASR systems come very close to the electronic stability program in their traditional operating areas , but do not replace it. The system only applies the brakes at low speed. Engine intervention generally brings driving stability over the entire speed range. Because the control system intervenes somewhat roughly with some manufacturers and also loads the brake, such systems are usually switched off at higher speeds. Within narrow limits (starting up), ASR can take over the function of a limited slip differential .

It was the first driver assistance system that built up brake pressure independently of the driver. This ensured adequate driving stability in critical driving situations.


While driving, the speed sensors, together with the control unit, monitor the slip behavior of the drive wheels (whether front, rear or all-wheel drive). If the driver accelerates more, the torque and consequently also the drive torque on the wheels, the wheel slip increases. With a wheel slip of around 10 to 20%, the coefficient of adhesion on dry roads reaches a maximum, and the circumferential forces that can be transmitted by the tire reach their maximum.

If the drive torque is increased further, the coefficient of adhesion drops, the transmittable torque decreases and at least one wheel tends to spin. Depending on the road surface and slip rate, both wheels can also be affected. The loss of cornering potential associated with excessive circumferential slip can also make driving behavior unstable. ASR is now active and regulates the drive torque on the wheels with several measures.

Some ASR systems also take the steering angle into account.

Drive slip control through brake intervention

Simple ASR systems usually only have access to the brake. Since the mechanical components are already present in the anti-lock braking system (ABS), the ASR is a software and hardware extension of the ABS and can brake each drive wheel individually. Such an intervention is only required for the wheels that are being driven. The wheel that is too fast is braked and the other wheel receives more of the drive torque. The braking intervention takes place without the driver's involvement. For this purpose, the ABS is switched from normal braking mode to ASR mode with an additional switch valve and an intake valve. The ABS return pump draws in brake fluid from the master brake cylinder via the suction valve and generates the ASR system pressure.

Active ASR control has a disadvantageous effect on longer journeys, especially in the off-road sector: the brake discs or drums can get very hot without you having ever braked yourself.

Drive slip control via intervention in the engine control

An intervention in the engine management takes place here. By reducing the engine torque, the spinning of a driven wheel or the entire drive axle is counteracted. This is possible if the engine either has no mechanical connection from the accelerator pedal to the throttle valve ( gasoline engine ) or injection pump ( diesel engine ) or a second throttle valve is installed for the ASR in the gasoline engine.

In the first case, the task of power reduction is taken over by an electronic accelerator pedal . This e-gas function deals with commands from the ASR primarily before the driver's request. If ASR registers excessive drive slip, the engine control unit adjusts the throttle valve and the ignition angle in the gasoline engine and masks out individual injection and ignition signals in the injection system. In the case of the diesel engine, either the adjustment lever of the injection pump or, in the case of engines with common rail, the engine control unit reduces the amount of fuel at the request of the ASR with the aid of a torque interface via the CAN data bus . In both cases, this reduces the excess motor and drive torque.

Combined scheme

Interventions are carried out here via the brake system as well as via the engine management.


The Mercedes-Benz T 80 , built in 1939 under the leadership of Ferdinand Porsche , was equipped with a device to prevent wheel slip. As a mass product, this system was further developed to ASR after the introduction of ABS .

With the advent of ESP , ASR has become an integral part of vehicle control. ASR is the basis for the following ESP systems, which also contribute to vehicle stabilization via sensors and braking intervention on the non-driven wheels. With the increasing complexity of such electronic systems, it can be expected that maintenance and servicing will become a legal obligation, as has long been the case with aircraft.

The names of the ASR vary depending on the manufacturer. In addition, a distinction is often made between individual ASR systems, e.g. B.

  • at BMW: Automatic Stability Control (ASC) = sole intervention in engine management; ASC + T = combined control
  • at Mercedes: Electronic Traction System (ETS) = sole intervention via the braking system; ASR = combined regulation

Launch of passenger cars

In 1971 the Buick Division of General Motors introduced a traction control system called "MaxTrac". It was equipped with appropriate sensors and a computer system that could detect spinning wheels and distribute the power accordingly on the rear axle. “MaxTrac” was available as an accessory for all full-size Buick models ( Riviera , Estate Wagon , Electra 225 , Centurion and LeSabre ). The "Traction Monitoring System" (TMS) from Cadillac , which was offered in 1979 for the Eldorado , was less successful . Criticism aroused a long response time and a high susceptibility to errors. The aforementioned systems, however, are not traction control from today's point of view, but only an electronically controlled limited-slip differential .

In 1986 Mercedes brought the first traction control according to today's perspective in models of the W 126 series with V8 engines (S-Class) on the market; In 1978, the electronically controlled ABS was introduced in the previous model, the W 116 .

Launch of motorcycle

In 1992, Honda introduced traction control to its Pan European model for the first time . Current (November 2010) are the BMW R 1200 GS , BMW S 1000 RR , Ducati 1198 S , Kawasaki 1400 GTR , Kawasaki Z1000sx , MV Agusta Brutale 1090 , Yamaha XT 1200 Z Super Ténéré and Aprilia RSV4 Factory APRC and, since 2015, the Piaggio MP3 equipped with it. The systems are based on different principles. Either by measuring the rear wheel speed increase (MV Agusta), wheel speed comparison of the front and rear wheel (BMW, Ducati, Kawasaki, Yamaha) or wheel speed comparison and lean angle sensors (BMW S 1000 RR), the electronics react with an intervention on the throttle valve and engine management. The response times of the system are between 0.05 and 0.16 seconds, or half a wheel revolution.


  • Hans Jörg Leyhausen: The master craftsman's examination in the automotive trade 1. 1. 12 edition, Vogel Buchverlag, Würzburg, 1991, ISBN 3-8023-0857-3
  • Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3

Individual evidence

  2. Automatic Stability Control (ASC)
  3. [1]
  4. Jan P. Norbye, Jim Dunne: The Truth about limited-slip differentials. In: Popular Science ( ISSN  0032-4647 ), Vol. 195, H. 5, November 1969, pp. 118-123.
  5. bikers journal: Honda ST 1100 Pan European ( Memento from July 18, 2011 in the Internet Archive )
  6. MOTORRAD No. 23 of October 29, 2010, page 30 ff