Functional Description - Power Transfer Unit (PTU)

The smart actuator mounted on the Power Transfer Unit (PTU) communicates with the Drivetrain Control Module (DTCM) over a Private CAN bus circuit. The smart actuator is supplied with a Fused B(+), Ignition Supply and Ground circuit. The Ignition Supply circuit is used to wake up the internal electronics of the smart actuator. The Fused B(+) circuit provides power for the operation of the shift fork(s). The PTU can be a 1-Speed or 2-Speed system depending on the vehicle and All Wheel Drive (AWD) system being used. The DTCM sends messages to the smart actuator over the Private CAN bus commanding the desired operation.

1-SPEED PTU:  On the 1-Speed PTU, the smart actuator controls the operation of a shift fork to move a collar engaging and disengaging splines on concentric shafts inside the PTU to shift between Front Wheel Drive (FWD) and AWD modes. The helical gears between the output shaft and Propeller shaft are constantly meshed. For AWD operation the PTU shifts the collar to lock the front axle shaft and output shaft to connect to the propeller shaft. This only happens after the Rear Drive Module (RDM) is applied to bring the propeller shaft up to speed. The collar may not immediately engage when the motor is energized and rotated if splines are not aligned. A spring applies pressure to the fork which will move the fork and collar when the splines are aligned. For FWD operation the PTU shifts the collar to unlock the shafts, disconnecting from the propeller shaft.

• The actuator motor has two internal position sensors to monitor the PTU actuator motor position as it is energized and rotates. There is also a position sensor that monitors the position of the shift fork. The smart actuator monitors both to determine that both the motor and fork are at the commanded position.
• The actuator motor has an internal temperature sensor to monitor the motor temperature. The motor temperature can be affected by the overall internal temperature of the PTU.

2-SPEED SYSTEM (KL ONLY):  On the 2-Speed system, the PTU smart actuator has two shift forks. The first is used to switch between FWD and AWD the same as on the 1-Speed system. The second fork is used to control engagement of 4WD Low Range or AWD Neutral for towing when selected.

• The actuator motor and shift forks internal position and temperature sensors operate the same as on the 1-Speed system.

The smart actuator monitors the shift fork actuator(s) internal position sensors and temperature sensor signals. The smart actuator communicates this information to the DTCM over the Private CAN bus. When the smart actuator detects a fault it sends a fault flag to the DTCM. The system faults are stored in the DTCM memory. If the smart actuator detects an overheat condition in an actuator motor, the motor will be commanded off and the PTU is disengaged until the internal temperature returns to a normal threshold. The motor can heat up due to an electrical or mechanical issue with the motor, or due to an issue in the PTU causing the PTU assembly temperature and internal components to increase.