Transfer Case

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

The transfer case is an on-demand All Wheel Drive (AWD) system with compact chain and sprocket arrangement which provides a compact and low weight design.

The transfer case is mounted on the rear of the automatic transmission housing and includes a multiplate clutch with a electric hydraulic pump. The electric hydraulic pump is controlled by the Transfer Case Control Module (TCCM) which controls the amount of torque being transmitted to the rear and front differentials.

The TCCM has a wiring harness connector for the following:

• Power supply via a relay located in the Engine Junction Box (EJB).
• A wake-up ignition signal from the Body Control Module/Gateway Module (BCM/GWM) assembly.
• A High Speed (HS) Controller Area Network (CAN) chassis systems bus (quantity 2).
• The chassis ground.

The TCCM monitors inputs from other control modules on the HS CAN chassis systems bus. Inputs include:

• Wheel speed from the Anti-lock Brake System (ABS) control module.
  • For additional information, Refer to: ANTI-LOCK CONTROL - STABILITY ASSIST - PROJECT 8 .
• Steering wheel angle from the Steering Angle Sensor Module (SASM). The SASM transmits the steering wheel angle to the Steering Wheel Module (SWM) via a hardwired connection. The SWM then transmits the steering wheel angle to the TCCM on the HS CAN chassis systems bus.
• Yaw rate from the Restraints Control Module (RCM).
  • For additional information, Refer to: AIRBAG SUPPLEMENTARY RESTRAINT SYSTEM
• Position of the acceleration pedal from the Accelerator Pedal Position (APP) sensor.

• For additional information, Refer to: ELECTRONIC ENGINE CONTROLS

The data from the Powertrain Control Module (PCM) and the ABS control module is sent by FlexRay to the Body Control Module/Gateway Module (BCM/GWM). The BCM/GWM sends the data to the TCCM via the HS CAN chassis systems bus.

Using these inputs the TCCM calculates and delivers an output to the electric hydraulic pump. The electric hydraulic pump in turn, provides pressure to the multiplate clutch to distribute the required torque between the front and rear differentials.

The system provides continuously variable response within 165 milliseconds.

The transfer case also improves fuel economy by providing only the requested amount of torque to the front differential. If necessary, full locking torque is available at any given time and vehicle speed, depending on road conditions and vehicle load distribution.

The lubrication system in the transfer case does not use a lubrication pump. The lubrication system comprises a lower transmission fluid reservoir and an upper transmission fluid reservoir. The transmission fluid is moved from the lower transmission fluid reservoir to the upper transmission reservoir by the drive chain. The drive chain is coated in transmission fluid as it moves through the transmission fluid in the lower transmission fluid reservoir. This transmission fluid is then moved to the upper transmission fluid reservoir. The transmission fluid on the drive chain is deposited in the upper transmission fluid reservoir as it goes around the multiplate clutch sprocket.

The drive chain that transfers torque to the front differential and also transfers transmission fluid from the lower transmission fluid reservoir to upper transmission fluid reservoir. The transmission fluid in the upper transmission fluid reservoir lubricates the multiple clutch, bearing and upper seal. Excess transmission fluid from the upper transmission fluid reservoir is returned by gravity to the lower transmission fluid reservoir.

Transfer Case Internals 

Courtesy of JAGUAR LAND ROVER NORTH AMERICA, LLC

Multiplate Clutch 

The multiplate clutch comprises an inner drive hub, a clutch basket and a set of drive/reaction plates and friction plates.

The friction plates are located on splines on the input shaft and rotate when the input shaft rotates. The drive/reaction plates are located on splines in the clutch basket which is positively attached to the front drive gear.

The front drive sprocket and clutch basket are located on bearings to allow speed difference relative to the input shaft when no locking torque is applied.

When the vehicle is moving, the following components rotate:

• Front driveshaft
• Front driveshaft output flange
• Output drive gear
• Front drive gear
• Clutch basket.

Torque is not applied to the front driveshaft until the Transfer Case Control Module (TCCM) engages the multiplate clutch. The multiplate clutch is engaged by applying hydraulic pressure to the multiplate clutch piston to clamp the multiplate clutch. This allows the torque to be applied to the front driveshaft. The front drive gear is attached to the front output shaft by the drive chain.