ASR V Function Summary

General
The speeds of all wheels are recorded and processed in the ASR control module (N47-1).
If the ASR control module (N47-2) recognizes from the speed signals that one or both drive wheels are tending to spin, the ASR control mode begins.

This involves the following processes

Brake Moment Control Circuit
The spinning drive wheel is braked by the associated wheel brake until the calculated drive slip is attained.
As a result the other wheel can transmit optimum traction force (locking differential effect).
To brake the spinning wheel, the brake fluid pressure is led into the brake caliper (pressure build-up) via a pressure system in the hydraulic unit.
The brake moment is controlled by pressure build-up, pressure holding and pressure reduction via solenoid valves in the ASR/ETS hydraulic unit (A7/3).

Drive Moment Control Circuit - ASR Control
In order to reduce an excessive drive moment for optimum traction (with spinning wheels), the drive moment is reduced via the connection between the ASR control module and the respective engine control module EA, MI-SFI, HFM-SFI/MFI or LH/SFI and DI/KSS (on gasoline engines) and DFI or IFI (on diesel engines).

^ Gasoline engine with electronic accelerator:
The throttle valve position is reduced by an actuator in relation to the accelerator pedal position specified by the driver and the ignition point is retarded.

^ Gasoline engine with fuel shut-off:
The fuel supply is shut-off.

^ Diesel engine:
The fuel quantity is reduced.

Checks are continuously carried out in the ASR control module as to whether, for example, as a result of a sudden improvement in road adhesion, the control functions can be cancelled in order to once again permit the drive moment specified by the driver via the accelerator pedal as soon as possible.

A distinction is made between three control ranges in ASR control mode:

A. Control mode for a spinning drive wheel and at speeds of 40 or less km/h.

Here the slip threshold of drive moment control is higher than that of brake moment control. The brake moment control is therefore activated first during a control. Consequently priority is given to traction. if the drive wheel spins quicker nevertheless, drive moment control is also activated.

B. Control mode when both drive wheels spin or at a speed greater than 40 km/h.

In this case the slip threshold of brake moment control is above that of drive moment control. Initially an intervention on the engine side is carried out during a control. If the wheels spin quicker nevertheless, brake moment control is also activated.
Consequently priority is given to maximum directional stability.

C. Control mode when cornering at speeds between approx. 20 km/h and 120 km/h

In this mode drive moment control comes into force even sooner than for control mode "B", depending on the lateral acceleration. As a result the directional stability increases when cornering.

An ASR warning lamp (Ale2l) warns the driver when a wheel speed does not correspond to the vehicle speed. it also provides information on the ASR control mode and ASR shut-off.

Drive Moment Control Circuit EBR Control
(Not On Gasoline Engine With Fuel Shut-Off)

If slip occurs at the drive wheels when the throttle is closed, this is also recognized in the ASR control module. The signal (throttle valve or fuel quantity increase) is also transmitted to the FA or ME-SFI control module via the serial data bus. Using this information the drive moment can be varied so that no slip occurs at the drive wheels (engine braking regulation = EBR) and consequently the directional control of the vehicle stabilizes. This process takes place without informing the driver (ASR warning lamp). EBR can also be active if there is excessive slip at the rear axle.