Power Transfer Unit Case Description and Operation: General Description
The GKN model 761 power transfer unit (PTU) is positioned in the right side of the vehicle and in model dependent applications is bolted to the transmission via an adapter plate. The primary function of the power transfer unit is to receive power from the transmission and transfer it through the propeller shaft to the rear differential using helical and hypoid gear sets. The power transfer unit housing, cover, extension housing, and rear output shaft housing are a cast aluminum design. Gear tooth clearances and bearing preloads are maintained by shims located behind the bearing races. The housings, internal gears, and bearings are not serviceable components. If housing, gear set, or bearing damage occurs, the assembly must be replaced.
The power transfer unit fluid is fill-for-life with no maintenance fluid change intervals required.
The disconnect-design power transfer unit has the ability to internally engage and send power and torque to the rear propeller shaft, activating AWD mode. Shifting is performed by a PTU mounted actuator motor, internal linear and rotary cams, and shift collar. The actuator motor operates as-directed by the rear differential clutch control module to perform the shifting operations.
During normal driving situations, the power transfer unit operates in FWD mode with no rotation of the rear propeller shaft. The rear differential clutch control module monitors wheel slip based on the inputs from the wheel speed sensors and/or vehicle speed sensor. When the vehicle experiences a wheel slip condition, the control module sends a pulse width modulated (PWM) signal to the PTU actuator motor. The actuator motor rotates the worm gear and rotary cam, moving the shift collar to engage AWD and propeller shaft rotation. AWD mode will remain active until the slip condition has stopped. The process would repeat if wheel slip is detected again.