Four-Wheel Drive Systems (G427457)

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The DD295 transfer box is full time, permanent four-wheel-drive unit, with 50/50 torque distribution to the front and rear driveshafts. Magna Steyr Powertrain manufactures the unit, which is identical for all engine derivatives and supports the following features:

• Permanent four-wheel-drive with a bevel gear centre differential, providing a 50:50 torque split
• Selectable high and low range for optimum on-road and off-road performance
• Two-speed, fully synchronized 'shift-on-the-move' system allows the driver to change the range without having to stop the vehicle
• Electronically controlled multi-plate clutch providing a centre differential lock and torque biasing function to give improved traction performance and vehicle dynamic stability.

A strategy, to electronically control the centre differential multi plate clutch assembly, has been developed to provide;

• a pre-loading function, increasing locking torque with increased driving torque
• a slip controller to increase locking torque under off-road conditions and decrease locking torque for optimum comfort, e.g. parking.

The unit is located under the vehicle and is mounted on the cross-member, behind the transmission.

The transfer box receives a torque input from the transmission output shaft, which is passed through the unit to two outputs for the front and rear drive shafts.

The input torque is equally distributed via a bevel gear type differential. In order to provide an optimal torque distribution to each wheel in all driving conditions, the unit is equipped with an electronically controlled locking and torque-biasing device. This device detects wheel slip via various vehicle system inputs to the transfer box control module and locks the differential accordingly. The locking torque is applied through a multi-plate clutch assembly.

A planetary gear set, located in the differential assembly, allows the driver to select high or low range whilst driving, this is known as 'shift on the move'. When in low range, the planetary gear set provides a ratio of 2.93:1, which gives the vehicle an extremely low crawl speed for off road driving and trailer towing. High range is a direct drive from the transmission output shaft and provides a 1:1 ratio.

Both the centre differential locking and biasing and the 'shift on the move' features are actuated via a DC transfer box motor, which is controlled by the transfer box control module, via a Pulse Width Modulation (PWM) signal.

Input torque from the transmission is transferred to the input shaft of the transfer box and then onto the planetary sun gear and planetary pinion gears. The planetary pinion gears are held in place by the planet 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 carriers, which are connected to the outputs of the transfer box. The rear carrier is connected directly to the rear output flange; the front carrier is connected to the sprocket and therefore to the chain drive, which provides front output flange rotation.

The front and rear casing assemblies are manufactured from cast aluminium.

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 box breather pipe. The breather pipe allows an equalisation between atmospheric and internal transfer box pressure.

Rear Casing Assembly

The rear casing assembly provides the location for the rear output flange bearing, the transfer box motor and the oil fill and drain plug. Fins are cast into the rear casing assembly to improve heat dissipation. The unit number is also stamped into the rear housing.

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.

The chain-drive transfers drive from the centre differential to the front output flange. A 3/8" pitch chain connects the sprocket on the transfer box input shaft with the sprocket on the front output flange. As both sprockets have the same number of teeth, the rotational speed of both sprockets is identical.

One motor operates both the high/low range change and the differential locking and torque-biasing device (multi-plate clutch). The motor solenoid switches between the two functions, while the motor provides the rotational movement for both operations.

Transfer Box Motor Position For Clutch Control Mode

To actuate the multi-plate clutch, the transfer box control module energizes the solenoid (3). The solenoid pin pivots the solenoid shift fork (2), which engages the shifting sleeve (5) into the dogteeth on the clutch control disc (4). The rotational movement of the motor shaft (1) is then linked to the clutch control disc via the shifting sleeve.

This is the normal operating mode of the transfer box. In this position, the range change function is disengaged and mechanically locked.

Transfer Box Motor Position For High/Low Range Mode

To actuate the high/low range change, the transfer box control module de-energizes the solenoid (3). A spring in the solenoid retracts the solenoid pin and rotates the solenoid shift fork (2). This engages the shifting sleeve (4) to the dogteeth on the high/low actuation cam (5). The rotational movement of the motor shaft (1) is then linked to the cam.

In this position, the multi-plate clutch is open, the differential cannot be locked and torque cannot be biased. Once the range change is complete the system returns to clutch control mode. In the event of an electrical failure, the motor will default to this position.

The center differential assembly is the primary feature of the transfer box. 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 centre differential assembly.

The assembly comprises 3 differential pinion gears (4) and shafts (5), which are equally spaced within the centre differential carrier (3). The differential shafts have a rigid connection to the differential carrier. Located between the pinion gears are 3 planetary pinion gears (6) and shafts (7). The planetary sun gear (8) and two differential side gears (10) are located in the centre line of the carrier.

The planetary ring gear (2) is supported in both directions by the differential casing and the differential cover (9). The planetary ring gear is connected to a shifting sleeve, which is engaged in either high or low range.

The multi-plate clutch basket (11), which is welded to the differential casing, supports the friction plates, the dogteeth (12) for high range engagement and the synchronisation cup and spring (1) for the 'shift-on-the-move' function.

When high range is engaged, the shifting sleeve (4) connects to the differential carrier via dogteeth (1). The planetary ring gear (3), via the shifting sleeve, and the planetary pinion gears (5), via the planetary shafts, which 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 (4) in the direction of the low range dogteeth (5). The low range dogteeth, with the synchronisation cup and spring, are fixed to the rear carrier assembly (6). When the shifting sleeve is engaged with the low range dogteeth, the planetary ring gear (3), via the shifting sleeve, is stationary and the planetary pinion gears (2), via the planetary bolts, turn the differential side gears with 2.93: 1 ratio.

High range actuation sequence

The rotational movement of the motor shaft turns the shifting cam (3) to high range position. The shifting cam then moves the shifting sleeve (1), via the high/low shifting fork (2), into the high range position. After the synchronisation 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

The rotational movement of the motor shaft (4) turns the shifting cam (3) into low range position. The shifting cam then moves the shifting sleeve (1) of the centre differential assembly via the high/low shifting fork (2) into low range position. After the synchronisation sequence, the planetary ring gear is connected to the low range dogteeth, via the shifting sleeve, on the rear carrier assembly. The output speed is then reduced to a ratio of 2.93:1.

The multi-plate clutch assembly for both centre and rear differentials act in a similar way. The aim of the multi-plate clutch assembly is to prevent excessive differential slip and therefore maximise 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 Braking System (ABS). The transfer box control module monitors the driver's demands through primary vehicle controls and automatically sets the slip torque at the differentials. The system is completely automatic and does not require any special driver input.

The multi-plate clutch assembly actively controls the torque flow through the centre differential and optimises the torque distribution in the driveline. The clutch assembly biases the torque from the transmission to the axle and wheels with the higher grip and prevents the wheels with the lower grip from spinning.

The multi-plate clutch assembly comprises the sprocket (7), which is connected to the front differential side gear, the motor levers (5) with the ball ramp mechanism (6), the clutch hub (1) as support for the clutch plates (3), the clutch piston (4) to generate friction between the clutch plates, and a pack of cup springs (2) 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 multi-plate clutch basket, which is welded to the centre differential housing.

Multi-plate Clutch Actuation

By turning the clutch control disc (3), via the motor shaft (2), the motor levers (4) are rotated relative to each other. This relative movement acts on 5 balls (5) in a ramp mechanism between the two levers and give a defined axial movement. The movement forces the clutch piston (1) to induce friction between the plates supported by the clutch hub and the plates supported by the clutch basket on the differential carrier. This frictional force inhibits the differential rotation; the differential carrier and front differential side gear are locked together.

The transfer box control module controls the high/low 'shift-on-the-move' actuation and the multi-plate clutch actuation. The control module is located in the E-box, next to the Engine Control Module (ECM), behind the battery in the engine compartment. The position of the control module changes with LH and RH drive vehicles.

The control module is connected to the Controller Area Network (CAN) bus and controls transfer box operation using CAN messages from other control modules on the network.

The control module memorises the position of the transfer box motor when the ignition is switched off.

The transfer box control module uses the same actuator to control both range change function and application of centre differential locking torque. The module uses position feed back from the actuator to provide smooth range changing capability and graduated application of locking torque appropriate for the current driving conditions. Range change can be carried out while moving providing the transmission is in neutral and the vehicle is below the speed necessary for the requested range change.

The control module uses three connectors for all inputs and outputs. It receives a permanent power supply via a 30A fusible link located in the Battery Junction Box (BJB), and an ignition supply via fuse 24 in the Central Junction Box (CJB).

The control module uses a series of programmed shift maps to control the synchronisation speed and ensure that a maximum shift time of approximately one second is achieved.

If the control module is replaced, T4 must be connected to the vehicle and the transfer box control module self-calibration procedure must be performed. This procedure must also be performed if the transfer box motor assembly is replaced.

Default/Limp-home Strategy

If a fault occurs with the transfer box, the transfer box control module or one of the required input signals i.e. road speed signal, the control module records an error code and will respond appropriately to provide the highest level of system capability under the specific fault conditions. The following fault states are possible:

If a driveline over temperature condition has occurred, after the driveline has been allowed to cool, clutch control will be re-enabled and the warnings will disappear. There is no need to seek service assistance following an over temperature event.

If clutch control or range change is not possible due to a permanent fault the driver must seek service assistance at the earliest opportunity.

If the system suffers a fault, which causes the transfer box to fail in neutral, the control module is designed to continue attempting to engage the requested range or return to its original range for a fixed number of attempts. If this has not been successful and the low range lamp is still flashing the driver should bring the vehicle to a halt and attempt the range change again while stationary. If this does not work after a number of attempts, key off for 30 seconds, restart engine and request range change again while stationary. The driver must seek service assistance at the earliest opportunity.

Transfer Box Control Module Pin Out Details

Connector C1319

Connector C1854

Connector C1855

The transfer box control module receives the following inputs:

• Range change selection switch
• High/low position sensor
• Transfer box actuator motor temperature
• Transfer box actuator motor position sensor
• CAN bus messages.

CAN Bus Messages

The CAN bus is a high speed broadcast network connected between various vehicle control modules. The CAN network carries an extensive list of messages between the different control modules enabling more sophisticated control with reduced complexity. Data on the network is packaged for efficient communication and prioritised according the urgency and importance of the messages. The bus comprises two wires, which are twisted together to minimise electromagnetic interference (noise) produced by the CAN messages. For additional information, refer to: Communications Network (418-00 Module Communications Network, Description and Operation).

The transfer box control module is connected on the CAN bus and controls transfer box operation using CAN messages from other control units on the network. Wheel speed, vehicle acceleration, engine torque and speed, gear information, from the transmission, temperature information, car configuration, axle ratios and Terrain Response mode inputs, are some of the main signals received by the control module.

In the event of a CAN bus failure the following symptoms may be observed:

• Shift from high to low or low to high inoperative
• Instrument cluster low range warning lamp inoperative
• Warning messages or lamps displayed in instrument cluster.

Range Change Selection Switch

The range change selection switch is located behind the main transmission selection lever, in the centre console. The switch is a 3-position momentary action centre sprung device. The driver pushes the lever forward to select high range and back to select low range.

The switch comprises a housing, which provides the location for a sliding contact. When the switch is moved to the high or low position, it completes a momentary connection to 12V with one of two micro-switches located at each end of the range change selection switch. These micro-switches correspond to the high or low range positions.

The transfer box control module receives this momentary signal and selects the requested range.

In this position, a spring will move the selector lever to the centre position when released.

High/Low Position Sensor

The high/low position sensor converts the pivotal movement of the high/low fork into a PWM signal on the input. The PWM signal of the position sensor differs between high range and low range. The control module checks this signal and informs the driver, via the instrument cluster and the range change selection switch LED's, if a range change is in progress or has been completed.

The high/low position sensor is connected to the transfer box control module via a three-pin connector.

The transfer box control module sends the following outputs:

• CAN bus messages
• Key interlock solenoid
• High/low range change LED
• Transfer box motor
• Solenoid.

CAN Bus Messages

The control module also sends messages via the CAN bus to tell other control modules on the network, the status of the transfer box. The high/low status, clutch torque and default mode status are some of the main signals sent out by the transfer box control module.

Key Interlock Solenoid

The transfer box control module is able to send a signal to the key interlock solenoid. This signal locks the key in the ignition barrel to prevent it from being removed if the transmission is not in the 'Park' position.

High/Low Range Change LED

The control module is responsible for illuminating the 2 'high/low' range change LED's adjacent to the range change lever. One LED indicates high range and the other indicates low range.

One LED will be on continuously when in the corresponding range.

When changing range, the current range LED will remain on until the new range status has been achieved.

The new range LED will start flashing only when the range change has commenced (i.e. speed and neutral conditions have been met). The new range LED will be illuminated continuously at the same instant that the current range (now the old range) LED turns off.

The flash rate is 2 Hz with a 50% duty cycle.

The LED's have 2 levels of intensity, high when the vehicle lights are switch off and low when they are switched on.

If both lights are flashing at 0.5 Hz, this would indicate a transfer box fault or that the transfer box is in undefined range and may require calibration.

Transfer Box Motor

The transfer box motor provides the necessary movement to perform the high/low range change and the multi-plate clutch actuation. The motor is located on the rear casing assembly and secured with four bolts.

The motor is a PWM controlled, DC motor with an integrated worm gear reduction drive. It is connected to the transfer box control module with an eight-pin connector; the power supply of the motor is maintained through two large diameter cables on the motor connector. An internal position sensor checks the rotational movement of the motor.

There is a temperature sensor located within the motor housing.

Solenoid

The solenoid switches the power flow on the actuation system between high/low range change mode and clutch control mode. When the solenoid is energized, the solenoid pin deploys and activates the clutch control mode. When the solenoid is de-energized, the internal spring rejects the solenoid pin and activates the high/low range change mode.

The solenoid is connected to the transfer box control module with a two-pin connector.

Status Indication

The low range status indicator will take the form of a mountain symbol and has the following logic:

• Lamp on = low range
• Lamp off = high range
• Lamp flashing = range change in progress/range undefined/range fault.

There will also be a message displayed in the message centre, which will inform the driver of any faults with the transfer box.

The following table shows the messages that can be displayed in the message centre relating to the transfer box:

The transfer box weighs 40.30 kg without oil and 41.55 kg with oil. The unit requires 1500 ml ± 2% of oil from empty (dry).

The oil used in the transfer box is Shell TF 0753, which has been specially developed by Magna Steyr and Shell. The oil contains unique additives, which enhance the transfer box operation. No other oil must be used in the transfer box.

There is a unique type of grease, Weicon anti-seize montagepaste grau TL 7391, that needs to be applied to the units input shaft spline when installing or reinstalling the transfer box.

The transfer box control module can store fault codes, which can be retrieved using T4 or a diagnostic tool using KW2000* protocol.

The information is communicated via a diagnostic socket.

The diagnostic socket allows the exchange of information between the various control modules on the bus systems and T4 or another suitable diagnostic tool. The information is communicated to the socket via the CAN bus. This allows the retrieval of diagnostic information and programming of certain functions using T4 or another suitable diagnostic tool.

The transfer box control module uses Diagnostic Trouble Codes (DTC), which relate to transfer box electrical faults.

Clutch and Range Change Mechanism Calibration

In order for the range change mechanism to function correctly, the transfer box control module must be calibrated to the mechanical dimensions of the transfer box that it is connected to.

This procedure will need to be followed if one of the following occurs:

• The vehicle is first assembled
• The switch is changed
• The transfer box control module is changed
• The transfer box or range position sensor is changed
• Vehicle or transfer box control module fault has caused the transfer box to revert to an undefined range.

Calibration can be carried out using the service tool or by following this procedure:

1. Switch ignition to position II without the engine running
2. Select neutral
3. Depress the throttle pedal fully
4. Press and hold the range change switch for 5 or more seconds to allow calibration to start
5. When the calibration is heard to start, the switch and throttle pedal can be released
6. Upon adopting high range, start the engine and wait 30 seconds while the first calibration of the clutch in high range is done. While this calibration process is in progress, no shifting is accepted
7. Switch ignition off and wait 15 seconds
8. Start engine
9. Perform a range change to low range. Wait 30 seconds while the first calibration of the clutch in low range is done. While this calibration process is in progress, no shifting is accepted
10. Switch ignition off and wait 15 seconds
11. Range and clutch calibration is now complete.

The selection of high/low range is achieved by using a switch located behind the main transmission selection lever in the centre console. A range change can only be performed when the transmission selector lever is in neutral (position 'N'). The accelerator pedal must not be depressed when a range change is in progress.

If high or low range is requested and the transmission selector lever is in a position other than 'N' or 'P', the instrument cluster message center will display 'SELECT NEUTRAL'.

When low range is selected, the low range 'mountain' symbol will flash when the range change is taking place and then remain illuminated when the range change is complete. The instrument cluster message centre will display 'LOW RANGE' for approximately 3 seconds followed by a chime from the instrument cluster to confirm that the range change has been completed. Only 'D' and 'Manual mode' are available, the 'Sport mode' selection is not available.

When high range is selected, the low range 'mountain' symbol will flash when the range change is taking place and then extinguish when the range change is complete. The instrument cluster message centre will display 'HIGH RANGE' for approximately 3 seconds followed by a chime from the instrument cluster to confirm that the range change has been completed.

The design of the transfer box allows range changes when the vehicle is moving, within set limitations as follows:

• High to Low – at speeds not exceeding 25 mph (40 km/h)
• Low to High – at speeds not exceeding 37 mph (60 km/h).

If the vehicle speed is higher than the parameters given, the instrument cluster message centre will display 'SLOW DOWN'. When the correct speed range is reached, the message will be deleted and the range change will commence.

The transfer box control module interprets a road speed of less than 2 mph (3 km/h) as a static shift (vehicle not moving). In this instance, the driver must use the shift lock procedure of operating the brake pedal to allow the selector lever to be moved from 'N' to 'D' after the range change has been performed.

High range should be used for all normal road driving and also for off-road driving across dry, level terrain. Low range should only be required where low speed manoeuvring is necessary, such as reversing a trailer, negotiating steep slippery surfaces or boulder-strewn terrain. Low range should also be used for extreme off-road conditions where progress in high range cannot be maintained. Low range should never be used for normal road driving.

Terrain Response

The Terrain Response system allows the driver to select a program, which will provide the optimum settings for traction and performance for the prevailing terrain conditions.

The system is controlled by a rotary control located on the centre console. The rotary control allows the selection of one of the following five programs:

• Special programs off (general driving conditions)
• Grass/Gravel/Snow
• Mud/Ruts
• Sand
• Rock crawl.

The Terrain Response system uses a combination of vehicle subsystems to achieve the required vehicle characteristics for the terrain selected. The following subsystems form the Terrain Response system:

• Engine management system
• Transmission
• Transfer box
• Rear locking differential (if fitted)
• Brake system
• Air suspension.

Each subsystem control module provides a feedback for the selected program so that the Terrain Response control module can check that all systems are controlling the system correctly. For additional information, refer to: Ride and Handling Optimization (204-06 Ride and Handling Optimization, Description and Operation).

In high range, the torque input from the transmission is passed to the transfer box input shaft. The position of the synchronizer sleeve couples the shaft directly to the differential housing. The differential splits the torque between the two side gears. One side gear is connected by splines and passes the torque to the rear output flange. The second side gear is connected to the chain drive sprocket and passes the torque, via the chain, to the front output flange.

In low range, the torque input from the transmission is passed to the transfer box input shaft. The synchroniser sleeve is moved and connects the planetary carrier to the differential housing. The torque from the transmission is now directed through the sun gear of the epicyclic gearset and, via the pinion gears and pinion gear shafts, into the planetary carrier. The annulus gear of the epicyclic gearset is secured inside the casing and generates the low range ratio of 2.93:1. The torque is then passed, via the synchroniser sleeve, to the differential housing where it is split between the two side gears. One side gear is connected by splines and passes the torque to the rear output flange. The second side gear is connected to the chain drive sprocket and passes the torque, via the chain, to the front output flange.

The driver is able to change between high and low range gears while the vehicle is moving, or if the vehicle is stationary.

Pushing the range change lever makes a range change requests. This lever is located on the centre console behind and to one side of the main transmission lever.

The driver requests a high to low range change by pushing the range change lever towards the rear of the vehicle and, conversely, a low to high request by pushing the lever towards the front of the vehicle. The range change lever is centre sprung and therefore does not latch in the forward or rear positions.

The driver is informed of the range status via a green lamp (mountain symbol) in the instrument cluster and LED's next to the range change lever. The lamp will not be illuminated in high range, illuminated in low range and flashes during a range change. There are two LED's on the range change lever one for high and one for low. During a range change the new range LED will flash.

The vehicle will remain in the selected range unless the driver requests a change, i.e. it will not automatically revert to high range following a key off/key on sequence.

Neutral must be selected on the main transmission before requesting a range change and then select the appropriate gear following completion of the range change. During the range change the main transmission will be locked in neutral.

If neutral is not selected when a range change is requested then the request is denied and the driver will be advised to select neutral via the instrument cluster message centre.

The range change process can take up to one second to complete following a request being accepted.

There is a limit set on the maximum speed at which a range change can be achieved. The maximum speed for a high to low range change is 25 mph (40 km/h). The maximum speed for a low to high range change is 37 mph (60 km/h). If the vehicle speed is over the limit when a range change is selected then the request is denied and the instrument cluster message centre will display a 'SLOW DOWN' message.