Principles of Operation

Principles of Operation
The vehicle is equipped with a four wheel drive (4WD) system, also referred to as active torque control coupling (ATCC) or intelligent torque control coupling (ITCC), that is always active and requires no driver input. The system has no mode select switch. The system combines transparent all surface operation with all wheel drive (AWD), and is capable of handling all road conditions, including street and highway driving as well as off-road and winter driving.

The system continuously monitors vehicle conditions and automatically adjusts the torque distribution between the front and rear wheels. During normal operation, most of the torque is sent to the front wheels. If wheel slip between the front and rear wheels is detected, or if the vehicle is under heavy acceleration (high throttle position), the AWD system increases torque to the rear wheels to prevent or control wheel slip.

The system consists of a power transfer unit (PTU), 4X4 control module, rear axle and a solenoid actuated ATCC device. The module varies the torque sent to the rear wheels by sending a duty cycle based on the amount of current sent to the clutch to the ATCC device located inside the rear axle.

The 4X4 control module also provides the brake system with its current clutch duty cycle and whether or not the brake system may take command of the clutch duty cycle.

NOTE: The ATCC solenoid is not repairable. If a new component is required, the ATCC solenoid and rear axle are installed as an assembly.

The PTU is a gearbox that attaches to the transaxle. The RH halfshaft passes through the transfer case and engages the differential side gear as in normal front wheel drive (FWD) applications. The transaxle differential drives the PTU. The PTU then drives the driveshaft at all times. The driveshaft drives one half of the rear axle clutch pack. The other half of the rear axle clutch pack drives the rear axle ring and pinion.

The active, on-demand AWD system uses data from other systems as inputs to the 4X4 control module. The 4X4 control module uses the inputs to determine the appropriate amount of current to send to the ATCC solenoid that delivers the desired torque to the rear wheels. Specific inputs to the 4X4 control module are:
^ Accelerator pedal position via the high-speed controller area network (HS-CAN)
^ Transaxle range from the transmission control module (TCM) via the HS-CAN
^ Brake system status from the ABS module via the HS-CAN
^ Wheel speed from all 4 wheels from the ABS module via the HS-CAN

4X4 control module outputs are:
^ Solid-state clutch (pulse-width modulated signal) to the ATCC solenoid
^ Percent of torque transfer commanded signal to the ABS module via the HS-CAN
^ Torque request available signal to the ABS module via the HS-CAN

Heat Protection Mode
During very extreme off-road operation, the AWD system utilizes a heat protection mode to protect the active torque control coupling (ATCC) solenoid (part of rear axle) from damage. If the system detects an overheat condition, it enters a locked mode. If the heat in the system continues to rise once in the locked mode, the 4X4 control module disables the ATCC solenoid. Allow the system to cool down at least 10 minutes with the ignition switch in the ON position.