xDrive: Four-wheel drive

The VTG control unit employs the servomotor and the multiple-disc clutch assembly in the VTG for infinitely-variable distribution of drive torque. This process distributes the drive torque between the front and rear axles according to their respective requirements. The rear axle is always powered. This means that all of the drive torque is applied to the rear axle when the multidisc clutch is separated. The drive torque is distributed as follows in normal driving with four-wheel drive:

• 40 % to the front axle
• 60 % to the rear axle

Dynamic Stability Control (DSC) specifies the setpoint value for xDrive all-wheel control. The setpoint value varies according to the vehicle's instantaneous tendency toward oversteer or understeer and the wheel-slip rates. The setpoint value is transmitted to the VTG control unit.

The VTG control unit regulates the lockup torque of the multiple-disk clutch assembly in the transfer case.