The ABS/DSC control unit features interfaces to the electronic throttle control (EML), digital motor electronics (DME) and to the adaptive transmission control (AGS).
The electronic throttle control system and digital motor electronics reduce the drive torque while the adaptive transmission control required information from the ABS/DSC control unit to detect various driving and ambient conditions.
Data exchange between these control units takes place not as in earlier models via a large number of individual wires but rather via a serial bus system, the so-called CAN-bus (Controller Area Network). This bus system consists of two data links (CAN_L and CAN_H) and a shield (CAN_S) to protect from external spurious signals.
All users in this bus system have equal rights, i.e. each control unit can both transmit as well as receive. In the event of one user failing, the bus still remains available for the remaining users.
Note
All control units connected to the bus must feature the same bus index. This index is indicated in the diagnosis program on the first page of the control unit identification.
On request by the ABS/DSC control unit, the electronic throttle control system reduces or increases the torque at the power axle by changing the throttle position corresponding to the request. This intervention is the first yet relatively slow measure in reducing the drive torque in a DSC control procedure.
The electronic throttle control replaces the mechanical link between the accelerator pedal and throttle valve. The position of the accelerator pedal is converted into an electrical signal by a pedal position sensor and then converted in the EML control unit into a control voltage for an electrical actuator motor which in turn operates the throttle valve.
On request by the ABS/DSC control unit, the digital motor electronics varies the ignition timing (ignition angle) or blanks out the ignition as injection pulses:
Intervention |
Effect |
|---|---|
Ignition timing set towards "retard" |
Fast reduction of drive torque |
Blanking out ignition/injection pulses |
Fast reduction of drive torque |
The adaptive transmission control permanently receives the four wheel speed signals as well as the message "DSC passive" or "DSC active".
The AGS control unit detects cornering and winter driving by way of the wheel speed signals.
The "DSC passive" message prevents selection of the winter driving program.