Principles of Operation

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Principles of Operation
The vehicle is equipped with a four wheel drive (4WD) system, also referred to as intelligent torque controlled 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), 4WD control module, rear axle and a solenoid actuated active torque coupling 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 active torque coupling device located inside the rear axle.

The 4WD 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 active torque coupling is not repairable. If a new component is required, the active torque coupling 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.

NOTE: PTU repair is limited to seals. If any of the geared components, bearings, case cover or internal shafts fail, a new PTU must be installed.

The PTU is sealed from the transaxle and has its own oil sump. The PTU uses 355 ml (12 oz) of Motorcraft SAE 75W-140 gear lubricant.

The active, on-demand AWD system uses data from other systems as inputs to the 4WD control module. The 4WD control module uses the inputs to determine the appropriate amount of current to send to the active torque coupling that delivers the desired torque to the rear wheels. Specific inputs to the 4WD control module are:
- accelerator pedal position.
- transaxle range from the transmission control module (TCM).
- brake system status from the anti-lock brake system (ABS).
- wheel speed from all 4 wheels (from the ABS).
4WD control module outputs are:
- solid-state clutch (pulse-width modulated signal) to the active torque coupling.
- percent of torque transfer commanded signal to the PCM.
- torque request available signal to the ABS.

Heat Protection Mode
During very extreme off-road operation, the AWD system utilizes a heat protection mode to protect the active torque coupling 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 4WD control module disables the active torque coupling. Allow the system to cool down at least 10 minutes with the ignition switch in the ON position.