Four Wheel Drive (4WD) Systems

The four wheel drive (4WD) 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 4WD system increases torque to the rear wheels to prevent or control wheel slip.

The 4WD control module varies the torque sent to the rear wheels by varying a pulse-width modulated (PWM) current to the clutch in the rear axle. The 4WD control module also provides the brake system with its current clutch duty cycle and determines whether or not the brake system may take command of the clutch duty cycle.

The 4WD system consists of the following:

• Power take off unit (PTU)
• Rear driveshaft
• Coupling device control module (4WD control module)
• Rear axle with coupling device