Module, Drivetrain Control: Operation: Operation

Fig 1: Identifying AWD Components

Courtesy of CHRYSLER GROUP, LLC

• The All Wheel Drive (AWD) system requires no driver input or control.
• Under most driving conditions, it is passive and power is transmitted to the front wheels alone.

The system functions to optimize traction and handling:

• Anticipates slip by responding to pedal position.
• The system requires no front-to-rear slippage for activation.
• Allows the system to transfer torque in response to accelerator pedal position.
• Once a demand for power is signaled, the system immediately starts clamping the Rear Drive Unit (RDU) and transferring a high percentage of power to the rear wheels.
• Modulates torque to optimize traction on slippery surfaces.
• Avoids front wheel slippage, as power to propel the car is transmitted through all four tires.
• The mode of operation is called open-loop operation in that there is no feedback to affect the torque transfer.
• A second, closed loop, operating mode uses feedback from the wheel-speed sensors to determine the appropriate torque transfer.
• When the front wheels slip, the Drivetrain Control Module (DTCM) tells the RDU to start clamping, sending power to the rear wheels.
• With the front wheels on ice and the rear wheels on dry pavement, the RDU sends even more torque to the rear wheels to minimize slippage and launch the vehicle.
• Both modes are always active and the maximum of the two is chosen.
• Influences handling at moderate speeds.
• The AWD system is used to influence vehicle dynamics.
• Additional Powertrain Control Module (PCM) calibration controls torque to the rear wheels for improved handling.
• The control strategy provides minimal torque to the rear wheels under normal driving conditions to aid fuel economy.
• The system utilizes torque to the rear wheels during cornering with the throttle open to make the handling more neutral.
• The AWD system uses the Electric Power Steering (ESP) steering angle sensor to determine when the vehicle is turning in a tight circle.
• Prevents binding during low-speed turns. DTCM to reduce amount of torque to the rear wheels to prevent binding in the driveline. The DTCM is always checking for this condition
• The DTCM also interfaces with the ESP and traction control systems.
• The interface allows the ESP system to use the RDU to help gain control of the vehicle.
• Torque transmitted to the rear wheels by the RDU can be reduced.
• Power to the rear wheels is modulated during loss of traction while traveling at freeway speeds such as, hydroplaning on a puddle of water, will send very little power to the rear wheels.
• The AWD system is not traction control and only works on situations where front-to-rear traction varies.
• AWD does not aid side-to-side traction the ESP does that through brake intervention.