Transfer Case - System Operation And Component Description (G1520699): Operation

WARNING: This page does not describe the selected car, but rather 16 other vehicles, including the 2015 Jaguar XFR-S, 2015 Jaguar XFR, 2015 Jaguar XF, 2014 Jaguar XFR-S, and 2014 Jaguar XFR. However, it is still accessible from the selected car via links, so may be relevant.

The Transfer Case Control Module (TCCM) receives inputs from the following sensors and other control modules:

Engine Control Module (ECM) - Accelerator Pedal Position (APP) sensor input for driver demand, engine torque
Anti-lock Brake System (ABS) control module - wheel speed, brake pressure input, steering angle
JaguarDrive Control (JDC) switch inputs.

The system is fully automatic and the driver has no direct control over the system. However, the driver can change the TCCM operation of the transfer case indirectly by changing the JDC mode.

Front to rear wheel torque distribution is constantly adjusted 'on-demand', with the system defaulting to Rear Wheel Drive (RWD) and only applying torque to the front wheels when required.

Torque is distributed to the front wheels in one of three ways:

Pre-load torque - The TCCM applies this torque to the transfer case coupling to assist in a smooth and safe drive off from stationary.
Feedforward - governed by the transmission output torque, requested flywheel torque and gear selection
Feedback - governed by the difference in speed between the wheels on the front and rear axles to determine wheel slip. Compensation is made when cornering and also the radius of the wheels.

Torque distribution between front and rear wheels can be 100% RWD or AWD, although the system is continuously variable dependent on signal inputs and road surface conditions.

DCS on/off or TracDSC On setting affect vehicle stability control only. Driver selections (Winter/Normal/Dynamic mode) using JDC affect the TCCM control in the following ways:

JDC SELECTION	TCCM INTERVENTION	DSC ON	TRAC DSC ON	DSC OFF
Winter	Highest locking torque for AWD. Preload torque applied to maintain drive off from stationary. Front to rear torque distribution is continuously variable depending on driving conditions.	Optimized for driving in snow/slippery conditions.	Not available	DSC off. ABS, EBD and EDC function only.
Normal	High locking torque for AWD. Preload torque applied to maintain drive off from stationary. Front to rear torque distribution is continuously variable depending on driving conditions but priority given to handling and steering feel over ultimate traction.	General setting for normal driving.	Optimized to allow fast driving with increased slip/yaw thresholds.
Dynamic		General setting for normal driving.

Input from the transmission rotates the input shaft which directly rotates the rear driveshaft output flange. When AWD is required, the TCCM operates the 12V actuator with a PWM (pulse width modulation) output which rotates a worm drive gear. The worm drive rotates a gear to rotate a ball ramp which applies locking torque (frictional pressure) to the multiplate clutch. Depending on the amount the ball ramp is rotated, determines the amount of locking torque applied to the multiplate clutch and the amount drive passed through the clutch plates to the front drive gear. The front drive gear rotates the intermediate gear which passes the rotation to the gear attached to the front output shaft.