All-wheel control

The all-wheel control function is governed by the Dynamic Stability Control. During active control the DSC control unit responds to both driver input and the vehicle's instantaneous dynamic status. The input parameters for this process are:

• Accelerator pedal angle
• Actual engine torque
• Gear engaged
• Steering angle
• Wheelspeeds and vehicle speed
• Longitudinal acceleration, lateral acceleration and yaw rate

The determining output signal for controlling the all-wheel drive is the torque that the drivetrain must transfer to the rear final-drive unit. The DSC control unit must engage the all-wheel drive clutch to the degree required to transmit the desired level of torque to the rear axle. An actuator with electrical connection to the DSC control unit contains a solenoid as its actuator. The output stages (driver circuits) integrated in the DSC control unit generate electrical power to actuate the solenoid. Progressively higher levels of control current correlate with proportionately higher levels of torque transfer to the rear axle.

The all-wheel drive clutch does not include any sensors. The DSC control unit measures the solenoid's control current. The transferred torque is determined using calculations. The temperature within the mutiple-disc clutch assembly is not monitored directly; instead, the DSC control unit calculates it using a temperature model. The maximum approved operating temperature for the all-wheel drive clutch is 150 °C. When the temperature model recognizes a violation of the temperature limit the multiple-disc clutch is disengaged to prevent damage.