Functional Description

FUNCTIONAL DESCRIPTION:

General Block Diagram:

Operating Principle:

Automatic stability control (ASC) is a control system to increase active vehicle safety which prevents slip of the power wheels on roads which offer insufficient adhesion (prevents wheel spin).

The control system operates in conjunction with the electronic throttle control and the digital motor electronics.

The sensors of the antilock brake system (ABS) are used to detect the speed of the individual wheels.

The ASC is combined with the ABS in one control unit although it is a completely independent system.

While the antilock brake system (ABS) utilizes the maximum frictional force during braking, with the ASC system this is achieved during acceleration.

As soon as the driven wheels turn 0.25 km/h faster than the non-driven wheels, the ASC regulates the position of the throttle valve in conjunction with the EML system. In order to achieve fast control, the ignition angle (timing) is reduced step-by-step via the DME or the ignition is faded out. To protect the engine and the catalytic converter, the injection signal is correspondingly adapted at the same time with the DME system.

The ASC is combined with an engine drag torque control system (MSR) which prevents the power wheels from sliding during sudden engine thrust.

Engine Drag Torque Control (MSR):

Also by way of the wheel speed sensors, the ASC detects the speed difference between the driven (braked by the engine) and non-driven (not braked) wheels. The ASC deactivates the deceleration fuel cut-out if the slip drops below the slip thresholds.

Failure of the MSR is indicated in the same way as a failure of the ASC in the display unit of the instrument cluster with "ASC defective".

Overvoltage Protection Relay K10:

The ABS overvoltage protection relay K1O is no longer installed as of model year 1989. The voltage for the ABS/ASC control unit in the 7 and 5 Series is then supplied via the DME relay 2 or DDE pole protection relay (542td).

Important! The ABS/ASC control unit installed in conjunction with the overvoltage protection relay must not be Installed in vehicles without an overvoltage protection relay.