Brief description of components
xDrive consists of the following components
- Transfer case with multi-plate clutch The electronically controlled multi-plate clutch is housed in the transfer case. The multi-plate clutch distributes the drive torque smoothly and as required between the front and rear axles.
- VTG actuator motor with incremental sensor and classification resistor The VTG actuator motor (VTG: transfer case) opens and closes the multi-plate clutch. The location of the actuator motor shaft and the adjustment rate are detected by the incremental sensor. The classification resistor ensures that mechanical tolerances in the transfer case are considered. Optimum function is thus ensured.
- Actuator lever The actuator lever converts the rotational motion of the VTG actuator motor into an axial motion.
- VTG control unit The VTG control unit regulates the locking torque at the multi-plate clutch in the transfer case in response to the following factors: Demand for required locking torque (comes from the DSC control unit) Condition of the transmission oil (calculated in the VTG control unit) Multi-plate clutch wear (calculated in the VTG control unit) Load on VTG actuator motor (calculated in the VTG control unit) Transmission oil temperature (calculated in the VTG control unit) The VTG control unit supplies the following information to the DSC control unit: The locking torque currently set All calculated data The locking torque is limited whenever needed in order to reduce the frictional work. > E53, E83 > E70
- DSC: Dynamic Stability Control With xDrive, DSC includes the following functions: All-wheel control Automatic Differential Brake (ADB-X) Hill Descent Control (HDC)
Emergency operation
Driving dynamic control and the ADB-X function are not possible in emergency operation.
The VTG control unit has an integral regulator for emergency control. The regulator provides redundancy for controlling the multi-plate clutch in the DSC control units.
The regulator is used to attempt to maintain all-wheel drive for as long as possible when the DSC control unit malfunctions or important sensor signals drop out.
Substitute values are calculated when individual sensor signals drop out. Functions are operated by using the substitute values until it is no longer possible to control the all-wheel drive effectively. This can lead to the complete loss of all-wheel drive.