Description
Transfer box control schematic
1. Automatic transmission and transfer box selector
2. Speed sensor
3. Ratio control motor
4. Transfer Box ECU
5. ECM (NAS vehicles only)
6. EAT ECU (Automatic transmission only)
7. Neutral switch (Manual transmission only)
8. High/Low fascia switch (Manual transmission only)
9. BeCM Fuse 4 Battery supply to Transfer Box ECU and ratio control motor
10. BeCM Fuse 6 Ignition supply to Transfer Box ECU
11. BeCM
12. Diagnostic socket
13. Instrument pack
General
All models are fitted with a Borg Warner transfer box. The transfer box is a four wheel drive, two speed ratio reducing gearbox with high and low range outputs selected electrically by the driver.
A differential is fitted between the front and rear output shafts to allow the propeller shafts to rotate at different speeds when the vehicle is cornering. Drive to the front propeller shaft is through a viscous coupling, which eliminates the requirement for a differential lock.
The high and low ranges are selected by the driver. On manual transmission vehicles a switch is located on the fascia and when pressed selects low range. On automatic transmission vehicles high and low ranges are selected by moving the auto transmission selector lever across the H-gate to the required position.
On all vehicles, when the transfer box has changed to high range, 'HIGH' is displayed momentarily in the instrument pack message center. On automatic transmission vehicles, if low range is selected, the message center momentarily displays 'LOW' and then permanently displays 'L'. On manual transmission vehicles the message center permanently displays 'LOW'.
The high and low range selection is performed by a ratio control motor located on the transfer box. The motor is controlled by a Transfer Box ECU located below the LH front seat. The ECU is connected electrically to other ECU's to ensure that all conditions for a successful range change are correct. The transfer box ECU receives inputs and provides outputs to/from the following ECU's:
^ Body electrical Control Module (BeCM)
^ Electronic Automatic Transmission (EAT) ECU
^ Engine Control Module (ECM) (NAS only).
High/low range selection - Automatic transmission vehicles
On automatic transmission vehicles, high and low range selection is performed using the transmission selector lever. The selector lever assembly consists of a lever and a cover attached to a cast base. The base is located on a gasket and secured to the transmission tunnel.
The base has an 'H' pattern for the lever to move in. The lever is hinged to the base and is moved across the 'H' pattern to select Hi or LO range operating a micro switch located in the base. The driver's side of the 'H' pattern is the high range selection in all markets.
The cover incorporates LED lever position indicators for high and low range gear selection. Operation of the LED indicators are controlled by the BeCM. The selected range is displayed by the LED's being illuminated brightly, with the unused range LED's dimmed. An electrical connector at the rear of the cover connects the selector lever assembly to the vehicle wiring.
High/low range selection - Manual transmission vehicles
On manual transmission vehicles, high and low range selection is performed using a latching push button switch on the fascia. The switch has an indicator lamp, which flashes when the transfer box is changing range and is permanently illuminated in low range.
Transfer Box
The transfer box comprises:
^ a front and rear casing
^ an epicyclic gear set
^ a viscous coupling
^ a differential unit
^ a ratio control motor
^ a lubrication pump.
The epicyclic gear set is located in the front casing and comprises a sun gear and four planet gears. The sun gear receives the drive from the gearbox output shaft and transfers the drive directly to a reduction hub. The reduction hub is located on a splined intermediate shaft, which rotates at the same speed.
The reduction hub is moved along the intermediate shaft by the selector spool and the ratio control motor to one of three positions; high, low and neutral.
In the high position, the reduction hub is driven directly from the sun gear and rotates the intermediate shaft at the same speed as the gearbox output shaft.
In the low position, the reduction hub is engaged with the planet carrier and rotates at a lower speed than the gearbox output shaft.
In the neutral position, the reduction hub is not engaged with either the sun gear or the planet carrier and no drive is passed from the gearbox output shaft to the intermediate shaft.
Differential unit
Drive from the intermediate shaft is transferred by a morse chain to the differential unit. The differential unit comprises sun and planet gears. The rear output passes through the differential unit sun gear shaft and engages with the planet carrier. The splined forward end of the rear output shaft provides location for the viscous coupling unit inner spline. The outer diameter of the sun gear shaft engages with the outer splines of the viscous coupling unit.
Viscous coupling unit
The viscous coupling operates in conjunction with the differential unit to control the proportion of drive torque transferred to the front and rear drive shafts. The viscous coupling is a sealed unit filled with a silicon jelly, which surrounds discs within the unit. The silicon jelly has properties, which increase its viscosity and resistance to flow when agitated and heated.
During normal driving conditions, slight variations in the relative speed of each drive shaft is insufficient to increase the viscosity of the silicon jelly. Therefore the resistance within the viscous coupling is low.
In off-road conditions, when the wheels lose grip on loose or muddy surfaces, a greater difference in the rotational speeds of the front and rear drive shafts exists. The slippage, due to the difference in rotational speeds of the drive shafts, within the viscous coupling agitates the silicon jelly causing heat, which increases the viscosity. The increased viscosity increases the drag between the discs forcing both sets of discs to rotate at similar speeds, reducing axle slippage and increasing traction. The viscous coupling removes the need for a manually controlled differential lock.
Selector mechanism
The selector mechanism comprises a selector fork and an interlock spool. The selector fork is mounted on a shaft between the front and rear casings. The interlock spool is mounted on a spindle through the rear casing and is positively connected to the ratio control motor. The selector fork is engaged in a cam track on the spool. When the ratio control motor rotates the spool, the rotational movement of the spool is converted to linear movement of the selector along the shaft.
The selector is engaged with the reduction hub. The linear movement of the selector moves the reduction hub in the epicyclic gear set changing the ratio between high, low or neutral.
Lubrication
Lubrication is provided by a low geroter plunger type oil pump, which is driven from the epicyclic gear set. The oil pump passes oil through oil ways in the components to lubricate the epicyclic gear set. The differential unit and morse chain are partially immersed in oil and are lubricated as the components rotate.
Transfer Box Electrical Components
Ratio control motor
The ratio control motor is located on the rear casing of the transfer box and secured with four bolts. The motor comprises a conventional single speed permanent magnet type motor. The motor spindle has a worm, which engages with a worm wheel in a housing at the end of the motor. The worm wheel is attached to the spindle of the selector interlock spool inside the transfer box.
The worm wheel also drives a motor encoder, which comprises four position switches. The transfer box ECU provides a 5 V signal to each switch and interprets the transfer box range by monitoring the condition of each switch.
The transfer box ECU reads the motor position in the form of a binary code with each switch either open or closed circuit. The ECU measures between the switches and an encoder ground on connector pin 19.
By using the combinations of the switches, the transfer box ECU can calculate the transfer box position and how the motor should operate to select the desired range. If the transfer box should move to a position outside the normal condition, i.e. left of high range, the ECU can move the motor to the correct position.
The table provided shows the motor switch states and the corresponding motor position for each state.
Speed sensor
The speed sensor is located in the rear casing and secured with a screw. A toothed reluctor ring is integrated on the rear output shaft. The inductive speed sensor senses the reluctor ring and produces a sine wave, impulse type signal as each tooth on the reluctor ring passes the sensor.
The transfer box ECU processes the signal from the speed sensor and compares this to a stored speed value in the memory to determine if a range change is allowed.
NOTE: The speed sensor is dedicated to the transfer box ECU to determine if a range change can be permitted.
Temperature sensor
The temperature sensor is screwed into the rear casing. The sensor has two Lucar connectors. One connector is attached to an earth eyelet connector, the other is connected to the BeCM.
When the transfer box oil reaches a temperature of between 140 and 150°C (284 and 302°F), contacts in the switch close, completing an earth path to the BeCM. The BeCM uses the completed earth path as a signal to generate a 'TRANSFER OVERHEAT' message in the message center. The 'TRANSFER OVERHEAT' message is displayed alternately with a 'REFER HANDBOOK' message. When the transfer box oil cools to between 126 and 134°C (258 and 273°F), the switch contacts open and the 'TRANSFER OVERHEAT' message is extinguished.
Transfer box ECU
The transfer box ECU is located below the front LH seat and is identified from the other ECU's located under the seat by its single 36 pin harness connector. The connector supplies power, earth, signal and sensor information to/from the ECU and other ECU's for transmission operation.
The BeCM, located below the right hand front seat, contains its own integral fusebox. The transfer box ECU receives a battery power supply from the BeCM via fuse number 4. An ignition on signal is also supplied from the BeCM via fuse 6. The ignition on signal is supplied to different ECU connector pins for manual and automatic transmission vehicles.
On NAS only vehicles, if a fault occurs which prevents the transfer box moving from low to high range, the transfer box ECU outputs a signal to the ECM, which is interpreted as an OBDII fault flag.
The transfer box ECU provides feed and return paths to the ratio control motor to operate the motor in the required direction. Two pins are used to supply power to the motor in each direction. The feed is supplied from two pins to avoid overload and heat generation, which would occur if one pin was used. A 5 V signal current is supplied to the four motor encoder switches, which are used by the ratio control motor to determine motor position.
Speed signals from the transfer box speed sensor are received as an input to the transfer box ECU which calculates whether the speed is below the threshold to allow a range change.
Range change request signals are received from the H-gate selector switch on automatic transmission vehicles or the high/low switch on manual vehicles.
On automatic transmission vehicles, a park/neutral signal is transmitted from the BeCM to the transfer box ECU. On manual transmission vehicles, a neutral switch located in the transmission provides an earth signal, which is used by the ECU and BeCM to determine that the transmission is in neutral. The park/neutral and neutral signal are used by the ECU to allow a range change only when the transmission is in neutral.
Outputs are provided by the transfer box ECU to the BeCM for high and low range status. The BeCM uses the signals for instrument pack message center display of range status.