Principles of Operation

WARNING: This page is about a different variant/trim than selected.

Power Transfer Unit (PTU) Operation

The PTU has four (4) modes of operation: Connected, Connecting, Disconnected, and Disconnecting. Each mode is commanded by the AWD module. The power transfer unit contains a reversible DC motor and two hall effect position sensors. The motor moves the shift fork which connects or disconnects the dog clutch collar. power transfer unit position sensor A monitors the position of the actuator cam. power transfer unit position sensor B monitors the position of the shift fork. Some power transfer unit models are equipped with an oil temperature sensor.

Connected Mode

Connected mode is the default mode for the power transfer unit. The AWD module will command Connected mode at the beginning of each key cycle. In connected mode, the fork and dog clutch collar are positioned towards the RH side of the power transfer unit and the dog clutch is engaged. The driveshaft will then rotate at an overdrive ratio compared to the front axle shafts. Torque will be available at the RDU.

Connecting Mode

To connect the power transfer unit, the two halves of the Dog clutch must be within 40 RPM of each other. The AWD module calculates the speed differential based on transmission OSS, RDU Driveshaft Speed, and power transfer unit gear ratio. The actuator motor will energize and rotate the gear reduction drive and the actuator cam against the shift fork. When the dog clutch teeth line up, the cam pushes the shift fork into position and the clutch engages. It can take approximately 100 - 150ms for the dog clutch to engage after the command is sent.

Disconnected Mode

The AWD module will command disconnected mode based on vehicle conditions. The purpose of the disconnected mode is to reduce drag losses from spinning the driveshaft when conditions indicate AWD will probably not be needed in the near future. In disconnected mode, the fork and dog clutch collar are positioned towards the LH or transmission side of the power transfer unit. The dog clutch is disengaged.

Disconnecting Mode

To allow disengagement of the RDU, no torque is routed through the power transfer unit, with the dog clutch being disconnected during this mode. Depending on vehicle operating conditions, the AWD module may keep the power transfer unit engaged for the remainder of the key cycle. The AWD module will send a duty cycle command to the power transfer unit actuator motor to disengage the dog clutch.