Overview
This document contains information on:
General
Function requirements
Function
General
The traction control systems consist of acceleration slip regulation (ASR) and the electronic traction system (ETS). ASR is responsible for controlling the drive torque and the ETS for controlling the braking torque. Traction control prevents the drive wheels from spinning while driving. In addition, traction control improves driving stability with increased traction over the entire vehicle speed range.
Traction control prevents the following:
One-sided spinning of the drive wheels when starting off and accelerating
Momentary spinning of the drive wheels on both sides when cornering
Function requirements
Drive train operational
Engine in operation
Brake and traction system functional
Function
Spinning of the drive wheels is detected on a wheel-specific basis by the ESP® control unit using the signals from the rotational speed sensors. If the drive wheels spin, the drive torque is reduced by the engine management.
If the ESP® control unit detects spinning wheels from the wheel speed signals, the necessary brake pressure is built up automatically at the spinning wheel by the traction system hydraulic unit. The spinning wheels are thus braked. At the same time, the resulting locking differential effect causes the drive torque to shift to the non-spinning wheels.
To attain a controllable driving state, the torque is reduced by the combustion engine control unit parallel to the wheel-specific intervention by the brake system. To prevent any downshifting, the combustion engine control unit sends the ESP® intervention status to the fully integrated transmission control unit.
If a wheel speed does not match the vehicle speed, this is indicated by the ESP® warning lamp in the instrument cluster. The ESP® warning lamp informs the driver that he is approaching the physical driving limits of his vehicle.
A check is continuously performed to establish whether the drive torque specified by the driver via the accelerator pedal sensor can be permitted again, e.g. due to an improvement in road surface adhesion.
Control units | |||
Combustion engine control unit, basic function | Model all (CAR) | ||
Electronic Stability Program control unit, basic function | Model all (CAR) | ||
Components | |||
Fully integrated transmission control electrohydraulic controller unit, basic function | Model all with transmission 724.0/1 | ||
Accelerator pedal sensor, basic function | Model all (CAR) | ||
Wheel speed sensors, basic function | Model all (CAR) |