Ford Escape: Power Transfer Unit / Description and Operation - Power Transfer Unit - Overview

Power Transfer Unit

The Power Transfer Unit (PTU) is a gearbox that attaches to the transmission. The PTU directs power from the transmission differential case through a dog clutch to a hypoid ring gear. A hypoid pinion gear is meshed to the ring gear and splined to the output flange. A dog clutch is used to transfer drive torque from the input shaft to the ring gear. When the dog clutch is released, no torque is transferred through the ring gear and pinion to the rear driveshaft. When the dog clutch is engaged, normal AWD function is achieved by directing torque to the rear wheels as needed to prevent or control wheel slip and improve handling

Power Transfer Unit (PTU) External Components

Power Transfer Unit (PTU) Intermediate Shaft

Power Transfer Unit (PTU) Components

Power Transfer Unit (PTU) Actuator Motor

Power Transfer Unit (PTU) Internal Components

Rear Seal Kit

RH Halfshaft Kit

Case Seal Kit

Actuator Seal Kit

Input Shaft Seal Kit

Power Transfer Unit (PTU) Operation

The PTU has four (4) distinct modes of operation: Connected, Connecting, Disconnected, and Disconnecting. Each mode is commanded by the AWD module. The PTU 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. PTU Position sensor A monitors the position of the actuator cam. PTU Position sensor B monitors the position of the shift fork.

Connected Mode

Connected Mode is the default mode for the PTU. 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 PTU. The dog clutch is engaged. The driveshaft is rotating at an overdrive ratio compared to the front axle shafts. Torque is available at the RDU .

Connecting Mode

To connect the PTU, 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 PTU gear ratio. The actuator motor will energize and rotate the gear reduction drive and the actuator cam against the actuator fork. When the dog clutch teeth line up, the cam pushes the actuator fork into position and the clutch engages. It can take approximately 100 - 150 ms 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 PTU. The dog clutch is disengaged.

Disconnecting Mode

To disengage the PTU, no torque can be routed through the dog clutch. That is, the RDU must be completely disengaged. Depending on vehicle conditions, the AWD module may keep the PTU engaged for the remainder of the key cycle. The actuator motor will energize and rotate the gear reduction drive and pull the actuator cam away from the actuator fork. When the dog clutch collar has moved far enough to the LH or transmission side, the dog clutch teeth disengage.