Transfer Case Power Flow
Output torque from the transmission is transferred to the input shaft of the transfer case and then onto the planetary sun gear and planetary pinion gears. The planetary pinion gears are held in place by the planetary pinion shafts, which are connected to the differential carrier, and drive the differential pinion gears. The torque is then distributed to both the front and rear differential side gear, which are connected to the outputs of the transfer case. The rear differential side gear is connected directly to the rear output flange. The front differential side gear is connected to the chain drive sprocket and therefore to the chain drive, which provides front output flange rotation.
Front Casing Assembly
The front casing assembly provides the location for the input shaft bearing, the front output flange bearing and the oil pump. It is also equipped with threaded holes to mount the chassis mounting bush, two lifting eyes and a breather cartridge for the transfer case breather pipe. The breather pipe allows equalization between atmospheric and internal transfer case pressure.
The front casing has two snubbers, one on drive side of the chain and one on the coast side, which are secured with two screws. The snubbers are suppressing chain vibrations which can occur under medium acceleration conditions, therefore improving Noise, Vibration and Harshness (NVH) issues. During normal operation the drive chain does not contact the snubbers.
Oil Pump
An oil pump assembly is located in the front casing to provide lubrication for the bearings and rotary components through cross-drillings in the input shaft. A flat-sectioned coupling on the input shaft drives the rotor of the pump, the stator is fixed to the front housing assembly. A tube is attached to the pump, which leads into a calm suction area at the bottom of the two casing assemblies. The collector magnet in the suction area of the pump collects any metallic debris.
Rear Casing Assembly
The rear casing assembly provides the location for the rear output flange bearing, the transfer case motor and the oil filler and drain plug. Fins are cast into the rear casing assembly to improve heat dissipation. The part number and serial number are printed on a bar code label, which is bonded to the rear casing assembly.
Chain Drive
The chain-drive transfers drive from the center differential to the front output flange. The drive chain connects the drive chain sprocket on the transfer case input shaft with the drive chain sprocket on the front output flange. As both sprockets have the same number of teeth, the rotational speed of both sprockets is identical.
Center Differential
| ITEM | DESCRIPTION |
|---|---|
| 1 | Drum clutch |
| 2 | Plate clutch pack |
| 3 | Synchronization cup |
| 4 | Synchronization spring |
| 5 | Differential carrier |
| 6 | Planetary pinion gear shaft (3 off) |
| 7 | Planetary pinion gear (3 off) |
| 8 | Pinion gear shaft (3 off) |
| 9 | Pinion gear (3 off) |
| 10 | Shifting sleeve |
| 11 | Multiplate clutch basket |
| 12 | Bolts (6 off) |
| 13 | Synchronizer sleeve |
| 14 | Planetary sun gear |
| 15 | Differential side gear (2 off) |
The center differential assembly is the primary feature of the twin speed transfer case. Torque is transmitted through the center differential carrier and distributed to the differential gears and the front and rear output flanges. The planetary gear set, for the high/low range change function, is also an integral part of the center differential assembly.
The assembly comprises three differential pinion gears and shafts, which are equally spaced within the center differential carrier. The differential shafts have a rigid connection to the differential carrier. Three planetary pinion gears and shafts are located between the pinion gears. The planetary sun gear and two differential side gears are located in the centerline of the differential carrier.
The planetary ring gear is supported in both directions by the differential casing and the differential cover. The planetary ring gear is connected to a shifting sleeve, which is engaged in either high or low range.
The multiplate clutch basket, which is welded to the differential casing, supports the friction plates. The dogteeth, synchronization cup and synchronization spring supports high range engagement for the range change function.
| ITEM | DESCRIPTION |
|---|---|
| A | High range position |
| B | Low range position |
| 1 | Dogteeth |
| 2 | Planetary pinion gears |
| 3 | Planetary ring gear |
| 4 | Shifting sleeve |
| 5 | Low range dogteeth |
| 6 | Rear carrier assembly |
When high range is engaged, the shifting sleeve connects to the differential carrier via dogteeth. The planetary ring gear, via the shifting sleeve, and the planetary pinion gears, via the planetary shafts are also attached to the differential carrier. The planetary gear set rotates as one unit and therefore turns the differential side gear with a 1:1 ratio.
In low range, the motor moves the shifting sleeve in the direction of the low range dogteeth. The low range dogteeth is fixed to the rear carrier assembly. When the shifting sleeve is engaged with the low range dogteeth, the planetary ring gear, via the shifting sleeve, is stationary and the planetary pinion gears, via the planetary bolts, turn the differential side gears with 2.93: 1 ratio.
Multiplate Clutch Assembly
| ITEM | DESCRIPTION |
|---|---|
| 1 | Drive chain sprocket |
| 2 | Ball ramp mechanism |
| 3 | Clutch plates |
| 4 | Cup springs |
| 5 | Clutch piston |
| 6 | Clutch lever |
The aim of the multiplate clutch assembly is to prevent excessive differential slip and therefore maximize the traction performance of the vehicle. This is fundamentally different from the 'braked' traction control, 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 Anti-lock Brake System (ABS). The Transfer Case Control Module (TCCM) monitors the drivers demands through the primary vehicle controls and automatically sets the slip torque at the differential. The system is completely automatic and does not require any special driver input.
The multiplate clutch assembly actively controls the torque flow through the center differential and optimizes the torque distribution in the driveline. The multiplate clutch assembly biases the torque from the transmission to the front differential or rear differential and wheels with the higher grip. This torque biasing prevents the wheels with the lower grip from spinning.
The multiplate clutch assembly comprises:
- A drive chain sprocket, which is connected to the front differential side gear
- Clutch levers with the ball ramp mechanism
- Clutch hub as support for the clutch plates
- Clutch piston to generate friction between the clutch plates
- Pack of cup springs to return the clutch piston into its original position.
One set of friction plates are connected to the clutch hub, the other set of friction plates are connected to the multiplate clutch basket, which is welded to the center differential housing.
Multiplate Clutch Actuation
| ITEM | DESCRIPTION |
|---|---|
| 1 | Shifting fork - High/Low range |
| 2 | Fixed lever |
| 3 | Clutch lever |
| 4 | Clutch control disc |
| 5 | Transfer case motor shaft |
| 6 | Gear |
| 7 | Actuation shaft |
Transfer Case Motor Position For Clutch Control Mode
| ITEM | DESCRIPTION |
|---|---|
| 1 | Shifting fork - High/Low range |
| 2 | Fixed lever |
| 3 | Clutch lever |
| 4 | Clutch control disc |
| 5 | Motor shaft |
| 6 | Gear |
| 7 | Actuation shaft |
During range change operation, when the multiplate clutch is open, the center differential cannot be locked and the torque cannot be biased. Once the range change is complete the system returns to clutch control mode.
High Range Actuation Sequence
| ITEM | DESCRIPTION |
|---|---|
| 1 | Shifting fork - High/Low range |
| 2 | Transfer Case Control Module (TCCM) |
| 3 | Gear |
| 4 | Actuation shaft |
The rotational movement of the actuation shaft moves the shifting fork - High/Low range to the high range position. The shifting fork - High/Low range then moves the shifting sleeve into the high range position. After the synchronization sequence, the planetary ring gear is connected to the high range dogteeth, via the shifting sleeve, on the differential carrier. In this position the input speed equals the output speed, which equates to a high range ratio of 1:1.
Low Range Actuation Sequence
| ITEM | DESCRIPTION |
|---|---|
| 1 | Shifting fork - High/Low range |
| 2 | Transfer Case Control Module (TCCM) |
| 3 | Gear |
| 4 | Actuation shaft |
The rotational movement of the actuation shaft moves the shifting fork - High/Low range to low range position. The shifting fork - High/Low range then moves the shifting sleeve into the low range position. The planetary ring gear is then connected to the low range dogteeth, via the shifting sleeve, on the rear carrier assembly. The output speed is then reduced by a ratio of 2.93:1.
Transfer Case Control Module with Integrated Actuator
Transfer Case Control Module (TCCM) comprises an integrated control module and a brushless Direct Current (DC) motor. The TCCM is fitted to the twin speed transfer case. The integrated transfer case motor is controlled by the TCCM to operate both the high/low range change and the torque-biasing device (multiplate clutch).
The TCCM detects wheel slip and other vehicle conditions via various inputs from other control modules. The TCCM controls the multiplate clutch based on these inputs to provide optimal torque distribution to the front differential and rear differential. It also receives range change requests from the range change selection switch and controls high/low gear change. The multiple clutch control and range change actuation are achieved by the integrated transfer case motor via a worm gear which drives an actuation shaft. The TCCM monitors the rotational position of the integrated transfer case motor by a Hall effect sensor fitted within TCCM.
The actuation shaft rotational movement is monitored by a high/low range position sensor fitted in the transfer case. The electrical power and ground to the high/low range position sensor is provided by TCCM. The high/low range position sensor sends a Pulse Width Modulation (PWM) signal to the TCCM via hardwired connection.
The TCCM is connected to the FlexRay bus and controls transfer case operation. The TCCM receives a power supply via a relay from:
- A 40A fuse link located in the Engine Junction Box (EJB)
- The power supply relay is controlled by the relay - extended ignition which is controlled by Body Control Module/Gateway Module (BCM/GWM) assembly.
If the TCCM is replaced, the Land Rover approved diagnostic system must be connected to the vehicle and the "New Module Replacement" procedure must be completed. For additional information, refer to: TRANSFER CASE .
Range Status Indication
The range change selection switch has a Light Emitting Diode (LED), this LED operates in three ways:
- The LED illuminates when the twin speed transfer case is in low range.
- The LED is switched off when the twin speed transfer case is in high range.
- The LED is flashing when range change operation is in progress.
There will also be a message displayed in the Instrument Cluster (IC) message center, which can also inform the driver of any faults with the twin speed transfer case.
The low range status warning indicator in the IC has the following logic:
- The warning indicator illuminates when the twin speed transfer case is in low range.
- The warning indicator is switched off when the twin speed transfer case is in high range.
- The warning indicator is flashing when range change is pending or range change is in progress.
The following table shows the messages that can be displayed in the message center relating to the transfer case:
| MESSAGE | DESCRIPTION | CHIME |
|---|---|---|
| 'Low range selected' | Low range is engaged after a range change request. | None |
| Low Range Requested: Available when stationary | Low range is requested while vehicle speed is less than 2km/h (1.25 mph). Change to Low range is available when vehicle is stationary. | None |
| Low Range Requested: Select Neutral for Range Change | Low range is requested while vehicle is stationary and Transmission Control Switch (TCS) is not in Neutral (N). Change to Low range starts when N is selected on the TCS. | None |
| 'High range selected' | High range is engaged after a range change request. | None |
| High Range Requested: Available below 60 km/h (37mph) | High range is requested while driving in low range with vehicle speed above 60 km/h (37 mph). Range change will start when vehicle speed is lower than 60 km/h (37 mph). | None |
| None | ||
| High Range Requested: Select Neutral for Range Change | High range is requested while vehicle speed is below 60 km/h (37 mph) and TCS position is not in N. Change to High range starts when N is selected on the TCS. | None |
| Range Change Not Available | Range change is requested but not available due to: | None |
| A fault in the system | ||
| The supply voltage to the Transfer Case Control Module (TCCM) is below 10.5V | ||
| The oil temperature in the transfer case is below -30°C (-22°F). | ||
| Traction reduced | Center differential locking torque is not available due to a fault in system or lost communications between Instrument Cluster (IC) and Transfer Case Control Module (TCCM). Rear differential locking torque is not available due to a fault in system or lost communications between the IC and Rear Differential Control Module (RDCM) (if equipped). | None |
| Loss of Drive | Twin speed transfer case not in gear, no drive to wheels. | Yes |
Transfer Case Control Module Inputs/Outputs
- Power supply via a relay controlled by Body Control Module/Gateway Module (BCM/GWM) assembly
- Primary battery ground
- High/Low range position sensor ground.
The Transfer Case Control Module (TCCM) receives the following inputs:
- High/Low range position sensor signal
- FlexRay bus messages.
The TCCM sends the following outputs:
- High/Low range position signal power supply
- FlexRay bus messages.
Range Change Selection Switch
| ITEM | DESCRIPTION |
|---|---|
| 1 | Terrain Response (TR) switchpack |
| 2 | Range change selection switch |
The range change selection switch is a momentary switch and located in the Terrain Response (TR) switchpack, in the floor console.
When the range change selection switch is operated, the TR switchpack sends a message to the Body Control Module/Gateway Module (BCM/GWM) assembly on the High Speed (HS) Controller Area Network (CAN) chassis systems bus. The BCM/GWM assembly transmits this message to the Transfer Case Control Module (TCCM) via FlexRay bus.
A single press of the range change selection switch will initiate range change if all the required conditions for range change are met. The range change request is delayed for 1 minute if the vehicle speed or the Transmission Control Switch (TCS) position are out of operating condition. When the request is delayed, a corresponding warning message is displayed in the Instrument Cluster (IC) message center.
If all the required conditions are met a single press of the range change selection switch will initiate range change in the twin speed transfer case.
The range change selection request is delayed for 1 minute, if:
- The vehicle speed for range change is above 60 km/h (37 mph)
- TCS not in the requested position.
While the request is delayed, driver can cancel the request by pressing the range change selection switch.
If the vehicle speed condition or the TCS position condition is not in the requested operating range within 1 minute, the range change request is cancelled.
Range change is available only when engine is running.
High/Low Range Change Light Emitting Diode
The high/low range change Light Emitting Diode (LED) is connected to the Terrain Response (TR) switchpack. Transfer Case Control Module (TCCM) sends the range change status by a FlexRay bus to the Body Control Module/Gateway Module (BCM/GWM) assembly. The BCM/GWM assembly transmits this signal through a High Speed (HS) Controller Area Network (CAN) chassis systems bus connection to the TR. TR illuminates the high/low range change LED depending on the range change status from TCCM.
When the transfer case is in high range, the switch LED is not illuminated.
While range change is in progress, the LED will flash on until the new range status has been achieved.
High/Low Range Position Sensor
The high/low range position sensor detects the rotational angle of the actuation shaft. The actuation shaft angle position is correlated to the high/low fork shift position and the clutch torque control position. The high/low range position sensor output controls the actuation shaft position with a Pulse Width Modulation (PWM) signal to the Transfer Case Control Module (TCCM). The high/low range position sensor output controls the actuation shaft whether the transfer case is in high or low range, or during range change. The high/low range position sensor output also controls the clutch torque control position while the system is in high or low range.
The TCCM check the actuation shaft position when TCCM wakes up and engine starts. The high/low range position sensor is connected to the TCCM via a 3-pin connector.