Differential Assembly: Description and Operation
Rear Drive Axle and Differential
COMPONENT LOCATION
Open Differential
Electronic Differential
INTRODUCTION
The differential converts the 'angle of drive' through 90° and distributes drive, via the rear drive halfshafts, to the rear wheels.
Two types of differential are installed on 5.0L vehicles. An open differential on naturally aspirated vehicles and an electronic differential on SC (supercharger) vehicles. Both types of differential are attached to the rear subframe at four mounting points. Each mounting point incorporates an insulator to reduce NVH (noise, vibration and harshness). The insulators in the forward mounting points are installed in the differential. The insulators in the rear mounting points are installed in the rear subframe.
OPEN DIFFERENTIAL
The open differential is a conventional design using a hypoid gear layout. The final drive ratio is 3.31:1.
The outer casing comprises two parts; a cover and a carrier. The carrier provides locations for all the internal components. Nine bolts attach the cover to the carrier. The cover and carrier have cast fins, which assist rigidity and cooling. A breather is fitted to the top of the carrier.
Exploded View of Open Differential
The open differential comprises a pinion shaft with a hypoid gear, and a crown wheel drive gear attached to a differential case. The differential case houses two planet gears and two sun gears.
An input flange is installed on the externally splined outer end of the pinion shaft and retained by a pinion nut. The input flange has six threaded holes for the driveshaft attachment bolts. An oil slinger and oil seal are installed in the carrier to seal the input flange. The hypoid gear of the pinion shaft mates with the drive gear.
Ten bolts attach the drive gear to the differential case. The differential case is mounted on taper roller bearings located in machined bores in the carrier and the cover. Shims are installed behind the bearing cups to apply the correct bearing preload and hypoid backlash.
The differential case has a through hole, which provides location for a shaft. Two planet gears are installed on the shaft, with thrust washers between the planet gears and the differential case. A roll pin locks the shaft to the differential case.
Two sun gears are located in pockets in the differential case and mesh with the planet gears. Spacers are fitted between the sun gears and the differential case to give the correct mesh contact between the planet gears and the sun gears. Each sun gear has a machined bore with internal splines and a machined groove. The splines transfer drive to the rear drive halfshafts. The groove provides positive location for the snap ring fitted to the inboard end of the rear drive halfshafts.
Oil seals are installed in the carrier and the cover to seal the rear drive halfshafts.
The open differential contains a quantity of oil for splash lubrication of the internal components. A magnetic drain plug is installed in the bottom of the carrier and a filler/level plug is installed in the cover.
ELECTRONIC DIFFERENTIAL
The electronic differential has the same functionality as the open differential, but it also incorporates a locking and torque biasing function to give improved traction performance and vehicle dynamic stability.
The basic construction of the electronic differential is similar to the open differential. However, the electronic differential also has the following:
- Two additional planet gears in the differential case, to cater for the higher torque of the SC (supercharger) engine.
- A multi-plate clutch and actuator assembly installed on the LH (left-hand) sun gear.
- A motor and reduction gearbox, attached to the cover.
- A temperature sensor installed in the cover.
The DLM (differential locking module) operates the motor of the electronic differential under the control of the ADCM (adaptive damping control module).
Exploded View of Electronic Differential
The multi-plate clutch is contained in a clutch basket attached to the differential case with the drive gear securing bolts. Alternate plates of the clutch pack are keyed to the clutch basket and the LH (left-hand) sun gear. A pressure disc is installed on the outer end of the clutch pack and keyed to the clutch basket. A thrust plate on the end of the clutch basket incorporates lugs which extend through the clutch basket onto the pressure disc.
The actuator assembly is mounted on bearings on the outboard end of the clutch basket, against the thrust race. The actuator assembly consists of input and output actuators separated by five ball bearings. A locking pin in the cover engages with a slot in the output actuator to prevent it turning, but allow it to move axially. The input actuator engages with the reduction gearbox and is free to rotate relative to the cover. Ball bearings locate in curved grooves in the mating faces of the input and output actuators. The bottom surface of each groove incorporates a ramp. Rotation of the input actuator forces the ball bearings up the ramps in the grooves and induces an axial movement in the output actuator. The thrust race and pressure disc transfer the axial movement from the output actuator to the clutch pack.
Section Through Multi-plate Clutch
The motor is a 12 Vdc motor that adjusts the frictional loading of the multi-plate clutch, via the reduction gearbox and the actuator assembly, under the control of the DLM. Adjusting the frictional loading of the multi-plate clutch adjusts the locking torque between the crown wheel drive gear and the sun gear.
Four bolts attach the motor to the reduction gearbox, which is located in position on the cover with two dowels, and secured with four bolts. An O-ring seals the joint between the motor and the reduction gearbox.
The motor is driven by a 12 V PWM (pulse width modulated) feed from the DLM. The motor also incorporates the following connections with the DLM:
- A motor temperature sensor, to prevent excessive use from damaging the motor.
- Two Hall effect motor position sensors, to enable closed loop control of the motor.
The temperature sensor provides a differential oil temperature signal to the DLM, to prevent excessive use from damaging the multi-plate clutch.
Differential Locking Module
The DLM controls the operation of the motor on the electronic differential. The DLM is attached to a bracket located on the LH (left-hand) side of the luggage compartment, immediately forward of the tail lamp, behind the trim.
The DLM receives three battery feeds from the AJB (auxiliary junction box) and an ignition feed from the CJB (central junction box). A connection with the high speed CAN (controller area network) bus allows the DLM to communicate with the ADCM.
CONTROL DIAGRAM - ELECTRONIC DIFFERENTIAL
NOTE:
A = Hardwired; D = High speed CAN (controller area network) bus
PRINCIPLES OF OPERATION
Open Differential
Rotational input from the drive shaft is passed via the input flange to the pinion shaft and pinion gear. The angles of the pinion gear to the drive gear moves the rotational direction through 90°.
The transferred rotational motion is now passed to the drive gear, which in turn rotates the differential case. The planet gears rotate with the differential case and transfer rotational motion to the LH (left-hand) and RH (right-hand) sun gears, which rotate the rear drive halfshafts.
When the vehicle is moving in a forward direction, the torque applied through the differential to each sun gear is equal. In this condition both rear drive halfshafts rotate at the same speed. The planet gears do not rotate and effectively lock the sun gears to the differential case.
If the vehicle is turning, the outer wheel will be forced to rotate faster than the inner wheel by having a greater distance to travel. The differential senses the torque difference between the sun gears. The planet gears rotate on their shaft to allow the outer wheel to rotate faster than the inner one.
Electronic Differential
The multi-plate clutch prevents excessive differential slip and therefore maximizes the traction performance of the vehicle. This is fundamentally different from 'braked' traction control systems, which can only counteract differential slip when it occurs.
A certain amount of differential slip is required to allow the vehicle to turn corners and to remain stable under control of the ABS (anti-lock brake system). The ADCM monitors the driver's demands through primary vehicle controls and automatically sets the slip torque in the differential. The system is completely automatic and does not require any special driver input.
The multi-plate clutch actively controls the torque flow through the differential and optimizes the torque distribution in the driveline. The clutch biases the torque from the differential to the wheel with the higher grip and prevents the wheel with the lower grip from spinning.
The differential strategy in the ADCM includes:
- A pre-loading function, increasing locking torque with increased driving torque.
- A slip controller to decrease locking torque for optimum comfort, e.g. parking.
The ADCM memorizes the position of the motor when the ignition is switched off.
CAN (controller area network) bus messages used by the ADCM include wheel speed, steering angle, automatic transmission speed, temperature information, car configuration, axle ratios and mode inputs.
The ADCM also sends messages via the CAN (controller area network) bus to tell other control modules on the network the status of the electronic differential. The clutch torque and default mode status are some of the main signals sent out by the ADCM.
If the DLM or ADCM are replaced, a Jaguar approved diagnostic system must be connected to the vehicle and the differential self-calibration procedure must be performed. This procedure must also be performed if the motor or electronic differential is replaced.
If a fault occurs with the electronic differential, the ADCM, the DLM, or one of the required input signals, the ADCM records an error code and displays a warning in the message center.
The following messages can be displayed:
