Rear Drive Unit Clutch Packs

The wet multiplate Rear Drive Unit (RDU) clutch packs are electro-mechanically operated by the clutch motors. The clutch motors are connected to the All Wheel Drive Control Module (AWDCM) and the AWDBCM through a hardwired connection.

The AWDCM and AWDBCM is connected to the Body Control Module/Gateway Module (BCM/GWM) through a FlexRay connection.

The BCM/GWM receives information from the following modules:

• Anti-lock Brake System (ABS) control module - FlexRay
  • Wheel speeds, ABS status, Dynamic Stability Control (DSC) status, Hill Descent Control (HDC) status and vehicle speed inputs.
• Restraints Control Module (RCM) - High Speed (HS) Controller Area Network (CAN) chassis systems bus
  • Lateral acceleration inputs.
• Steering Angle Sensor Module (SASM) in the Steering Wheel Module (SWM) - HS CAN chassis systems bus
  • Steering angle input.
• Electric Park Brake Control Module (EPBCM) - FlexRay
  • Electric park brake applied or released input.
• Terrain Response (TR) - HS CAN comfort systems bus
  • Selected 'Auto2® selection input.
• Powertrain Control Module (PCM) - FlexRay
  • Engine torque, Accelerator Pedal Position (APP), ambient temperature, RDU clutch temperature calculation.
• Transmission Control Switch (TCS) - HS CAN powertrain systems bus
  • Gear position.
• Transmission Control Module (TCM) - FlexRay
  • Transmission status.

The AWDCM and AWDBCM is connected by hardwired connection to the RDU. The AWDCM provides a Pulse Width Modulation (PWM) output to the left clutch motor and receives 3 inputs from the motor position sensors. The AWDBCM provides a PWM output to the right clutch motor and receives 3 inputs from the motor position sensors.

The AWDCM automatically connects the Power Transfer Unit (PTU) dog clutch and operates the left and right RDU clutches. The clutches connect and operate when the vehicle speed is less than 20 km/h (12 mph). This provides improved traction when the vehicle is pulling away from a standstill in a straight line. The system disconnects the driveline at speeds above 25 km/h (15 mph) to improve efficiency.

The AWDCM evaluates the received inputs and can predict when AWD is required. Typical inputs for the evaluation are received from the following:

• Accelerator Pedal Position (APP) sensor.
• Engine torque request from TCM.
• Steering angle from the SASM.
• Lateral acceleration from the RCM

Loss of traction is detected from inputs from the ABS control module:

• Wheel spin
• ABS activity
• DSC activity
• Yaw signals.

Evaluation of these inputs cause the AWDCM to connect the driveline.

The AWDCM automatically connects the PTU dog clutch and operate the RDU clutches to provide improved traction when:

• The vehicle is pulling away from a standstill in a straight line.
• Driving forward at speeds below 20 km/h (12 mph).
• In REVERSE (R) gear.

The AWDCM operates the driveline in AWD when the driver has selected a TR Auto2® mode that requires AWD. AWD is also activate when Hill Descent Control (HDC) is requested.

When ambient temperatures are below -10°C (14°F), the AWDCM keeps the driveline connected. When the vehicle is stationary and the engine is stopped, the driveline remains connected.

The RDU clutches can be fully or partially applied on each driveshaft individually to provide active torque biasing. The AWDCM and AWDBCM can determine the clutch torque required for each halfshaft based on inputs for acceleration, yaw and oversteer or understeer. This allows the RDU to be locked to perform in a similar manner to a Limited Slip Differential (LSD).