Transfer Box - Description

Description

General
The NV225 Transfer Box is a full time, permanent four wheel drive, torque splitting transmission with equal torque distribution to the front and rear propeller shafts. The transfer box has the following features:
^ Permanent four wheel drive with 50/50 torque split
^ Two speed. fully synchronized "shift on the move" system with electronic control and operation
^ High range direct drive and low range via epicyclic gearset
^ Torsion (R) Type B torque sensing and torque biasing center differential
^ Self lubricating oil pump system.

The transfer box is located under the vehicle in a subframe, behind the transmission. The units used on both the Td6 and V8 variants are identical, with the exception of the large mounting bush. The transfer box is manufactured by New Venture Gear in Roitzsch, Germany.

The transfer box receives an input from the transmission output shaft which is passed through the unit to two outputs for the front end rear propeller shafts.

The transfer box provides full time four wheel drive via a 50/50 torque sensing Torsion (R) differential. The unit design allows "shift on the move" from high to low range and visa versa. A planetary gearset with helical planetary pinion gears provides low range operation. When in low range, the planetary gearset provides a ratio of 2.69:1 which gives the vehicle an extremely low, low range crawl speed. High range is a direct drive from the transmission output shaft and provides a 1:1 ratio.

The transfer box has electronic control, via a PWM actuator (DC motor), on the shift from high to low range. The actuator is controlled by a transfer box ECU, which is located behind the battery in the engine compartment.

Transfer Box - Sectional View

Part 1:

Part 2:

The major components of the transfer box are; the front casing assembly, the rear casing assembly, the planetary gearset, the Torsion (R) differential, the fork and rail assembly and the actuator assembly.
The front and rear casing assemblies are manufactured from cast aluminum. Fins are cast into the front casing to aid heat dissipation. Both casing assemblies are bolted together end provide the bearing locations for the main shaft, the Torsion (R) differential and the planetary gearset. The rear casing provides the attachment location for the actuator assembly.
An oil pump assembly is located in the rear casing and is driven by a splined coupling on the main shaft. The pump has an oil tube to the bottom of the two casings with a filter screen to collect particulate matter. A magnet is located below the filter screen to collect any metallic particulate matter. The oil pump provides a pressurized supply to a drilling in the center of the main shaft. Cross-drillings in the main shaft provide lubrication for the bearings and rotary components.

Planetary Gearset
The planetary gearset comprises a front and rear carrier half, an input shaft, four planet pinion gears, four planet pinion shafts and one hundred and forty four needle rollers.

The input shaft is located through the planetary carriers and is driven by the output shaft from the transmission. The sun gear is located on splines on the input shaft and rotates at the same speed. Rotation of the sun gear is transferred to the four pinion planet gears which in turn rotate around an annulus gear located in the front casing and secured with a retaining ring.

The rotation of the planetary pinion gears causes the front and rear carriers to rotate. The rear carrier has gear teeth which mesh with the teeth in the sleeve. To smooth the transition of the gear teeth of the sleeve and the rear carrier, an inner and outer blocker ring and a cone are fitted. When the fork moves the sleeve, the three detents in the hub are pushed, which in turn push the inner and outer blocker rings and the cone together. These items mesh together at an angle and operate as a synchromesh to provide smooth engagement of the gear teeth and the transition into low range.

The input shaft also has an outer blocker ring and a cone between the shaft and the hub. When the fork moves the sleeve, the three detents in the hub are pushed, which in turn push the outer blocker ring and the cone together. These items also mesh together at an angle and operate as a synchromesh to provide smooth engagement of the gear teeth of the hub and the input shaft and the transition into high range.

Fork and Rail Assembly
The fork and rail assembly is the main component for changing from high to low ratio and is driven by the actuator assembly and the lead screw. The actuator rotates the lead screw, via the gearbox, which in turn moves the fork and rail assembly linearly in plain bearings in the front and rear casings. The fork is positively located in a stepped ring on the outer diameter of the synchronizer sleeve. Therefore, linear movement of the fork is transferred to the sleeve which initiates the range change.

Motor and Gearbox Assembly

Part 1:

Part 2:

The actuator and gearbox is located on the rear casing and secured with three bolts. The purpose of the actuator and gearbox is to electrically change the ratio of the transfer box from low to high and visa versa.

The actuator is a DC four brush motor which is controlled by PWM signals from the transfer box ECU. The wires from the ECU are large diameter and are twisted to minimize electrical interference. The motor has an internal four pin integral connector which, when installed in the housing, mates with a female connector located in the housing. The motor housing contains the magnets which, along with the armature and brush assembly, operate the motor. The housing is located on the armature and brush assembly mounting plate which in turn is secured with screws into the main housing. The shaft of the armature and brush assembly locates in a pressed plain bearing in the housing and is adjusted for end float with shims. The opposite end of the shaft has a toothed gear which mates with the reduction gearbox.

The reduction gearbox comprises an annulus housing, eight planetary gears and a sun gear and carrier plate. The annulus housing has a shaft and a planet gear carrier plate. The planet gear carrier plate is attached to the shaft inside the annulus housing. A bevel gear is attached to the opposite end of the shaft on the outside of the housing. The planet gear carrier plate has four pins which provide the attachment and pivot points for four planes gears. The sun gear and carrier plate is located in the annulus housing with the sun gear locating between the four planetary gears. The carrier plate has four pins which provide for the location and pivot points for four further planetary gears. The toothed gear on the armature and brush assembly shaft locates between these four gears and provides the drive input into the reduction gearbox.

The housing is manufactured from cast aluminum and is machined to accept the reduction gear box and the drive shaft and bevel gear assembly. Three bosses with holes provide for the attachment of the housing to the transfer box rear casing assembly. An east aluminum cover is sealed to the housing with two "O" section gaskets end secured with six screws. The housing has a machined hole which is fitted with a plain brass bush to accept the drive shaft and bevel gear assembly. An oil seal is fitted behind the bush to provide a seal between the drive shaft and the transfer box rear casing half.

A hole in a boss on the housing allows for the fitment of the ten pin electrical connector to the ECU. The connector is secured in the housing with a spring clip and lip seal. A machined slot in the housing provides location for a second connector with four female pins. This connector mates with a similar male connector which is an integral part of the armature and brush assembly mounting plate and supplies power feed and ground connections for the motor.

The drive shaft and bevel gear assembly comprises a machined shaft, bevel gear and a mounting plate. The drive shaft has internal splines at one end. The splines have a missing tooth to act as a keyway which mates with the lead screw, providing the correct timing for the lead screw to the motor position. The bevel gear is an interference fit and is pressed onto the drive shaft. The opposite end of the shaft accepts the mounting plate and has a machined groove to provide a positive drive for the rotary potentiometer.

The mounting plate is located on the shaft and is secured in the housing with three screws and retains the drive shaft laterally. An external hexagonal boss on the mounting plate mates with a hexagonal moulding on the potentiometer. This provides a positive location for the potentiometer, preventing the potentiometer housing from rotating and providing the correct orientation for the potentiometer connector.

A third connector the housing has three female pins which mate with similar male pins on the potentiometer. These pins supply a 5V reference supply, en output signal end ground for the potentiometer. The connector is connected the pins of the ten pin electrical connector.
If the actuator and gearbox assembly is to be removed, the synchronizer sleeve position must be set to high range using TestBook/T4 before the assembly is removed.

Torsion(R) Differential





The Torsion(R) Type B traction differential unit is an integral part of the transfer box and is produced by Zexel Torsion of Belgium. The unit is a full time torque sensing and biasing system using parallel gearing for increased life and quiet operation.

During normal driving conditions, the Torsion (R) unit supplies a nominal 50:50 torque output to the front and rear drive shafts via the transfer box main shaft and the drive sprocket assembly.

The torque biasing capability consists of the ability to "bias" the torque from the transmission to the axle and wheels with the higher grip. This must be achieved without causing wheel slip to the wheels of the axle with the lower grip within the biasing range of approximately 35/65 to 65/35 front to rear.





The torque biasing capability is instantaneous and operates as a preventative system. The unit does not need wheel slip and speed differentiation to be activated. The unit senses, via torque saturation within the unit, that one propeller shaft has the intention to rotate faster than the other one. The unit then biases the torque away from that propeller shaft and applies it to the other propeller shaft. Conventional systems require the wheel slip to occur first before initiating the torque biasing action. Because the Torsion (R) unit reacts before the slip occurs, the driving action is very smooth which results in enhanced grip for the road wheels.

The Torsion (R) unit comprises a housing, two side gears, six pinion gears, thrust and friction washers and a cover plate.

The housing is a machined casting which contains all the differential components. Six machined pockets accept the pinion gears. The base of each pocket has a cast recess which retains oil to lubricate the pinion gear ends. The closed end of the housing has a roller bearing pressed into a hole. The transfer box main shaft is located through the bearing which provides support between the housing and the shaft. The main shaft has cross drillings which supply lubricating oil from the oil pump to the internal components of the differential.

Three threaded holes are located equally around the open end of the housing and provide for the attachment of the cover plate with bolts. The outer circumference of the housing has cast and machined teeth which mesh with corresponding teeth in the transfer box synchronizer sleeve. Rotational input from the transmission is passed, via the transfer box input shaft, directly to the synchronizer sleeve for high range or indirectly to the synchronizer sleeve via the planetary gear set for low range. The teeth on the housing allow for the sliding motion of the synchronizer sleeve when the transfer box range is changed.

The pinion gears are parallel, helical gears which locate in the machined pockets in the housing. The lands of the helical teeth are ground with a radius which matches the internal diameter of the housing pockets. This creates frictional forces between the pinion gears and the housing and contributes to the operation of the unit. Each pinion gear has a machined section with no teeth. The pinions are fitted in the housing in opposite pairs. When fitted, one pinion gear of each pair meshes with one of the side gears, with the machined section of that gear preventing meshing with the other side gear.

The side gears have helical teeth machined on their outer circumference. The inner diameter of the side gears are different sizes and both have machined splines. The side gear with the smeller diameter bore locates on mating splines on the main shaft and provides output drive to the rear propeller shaft. The remaining side gear locates on mating splines on the drive sprocket and, via the chain and the front output shaft, provides output drive to the front propeller shaft. The side gears are located in the housing, supported laterally by the pinion gears. Transverse location is provided by the main shaft and three pairs of friction washers.

The friction washers comprise one washer with two ground faces. The second washer has one ground face and the opposite face has a sintered friction material. Axial thrust applied to the side gears from the pinion gears, forces the side gears into contact with two of the three pairs of thrust washers, causing a locking of the side and pinion gears under certain circumstances.

The cover plate is located on the open end of the housing and is secured with three bolts. The cover plate provides location for the ends of the pinion gears. A cast recess for each pinion gear retains oil to lubricate the pinion gear ends.

Transfer Box ECU





The transfer box ECU is located behind the battery, on the bulkhead. The position of the ECU changes with LH and RH drive vehicles.
The transfer box ECU is the main unit for controlling the operation of the transfer box. The ECU software was designed in conjunction with Land Rover, Siemens and New Venture Gear. The ECU is connected on the CAN bus and controls the transfer box operation using CAN messages from other ECU's on the network.

The transfer box ECU uses three connectors for all inputs and outputs. The ECU receives one permanent power supply via a 50A fusible link located on the bulkhead, behind the battery, and an ignition supply via fuse 33 in the passenger compartment fusebox. A second feed via the ignition switch position I and fuse 37 in the passenger compartment fusebox, activates the neutral selection function.

The ECU memorizes the position of the actuator when the ignition is switched off. When the ignition is subsequently switched on, the ECU powers the actuator until the lead screw drives the fork and rail assembly against the end stop for the previous range. The ECU then calibrates itself to this position and confirms that the selected range is correct.

The ECU controls the closed loop position sensing system within the actuator end regulates the power supply to the motor to ensure the optimum shift quality is achieved. Using a series of specific software algorithms, the ECU is capable of adjusting the performance of the synchronizer system to produce smooth and effortless shifting, regardless of temperature and vehicle speed, providing the neutral and speed parameters are achieved.

The ECU uses a series of programmed shift maps to control the synchronization speed and ensure that a maximum shift time of 1.2 seconds is achieved.

If the ECU is replaced, TestBook/T4 must be connected to the vehicle and the transfer box ECU self-calibration procedure must be performed. This procedure must also be performed if the actuator and gearbox assembly is replaced.

Default/Limp Home Strategy
If a fault occurs with the transfer box, the transfer box ECU or one of the required input signals, i.e.; road speed signal, the ECU records an error code and the transfer box low range "mountain" symbol in the instrument pack flashes permanently.

As a default setting, the ECU will attempt to engage high or low range in order to allow the vehicle to be driven to a Land Rover dealer for repair. To ensure a range is engaged, the ignition must be switched off and then on again (timed shift performs this without ignition cycling). This causes the ECU to power the actuator and engage the previously selected range.

Diagnostics
The transfer box ECU can store fault codes which can be retrieved using TestBook/T4 or a diagnostic tool using KW2000* protocol.





Diagnostic Socket

The information is communicated via a diagnostic socket which is located in the fascia, in the driver's side stowage tray. The socket is secured in the fascia panel and protected by a hinged cover.
The diagnostic socket allows the exchange of information between the various ECU's on the bus systems and TestBook/T4 or another suitable diagnostic tool. The information is communicated to the socket via a diagnostic ISOg141 K Line. This allows the retrieval of diagnostic information and programming of certain functions using TestBook/T4 or another suitable diagnostic tool.
The transfer box ECU uses Diagnostic Trouble Codes (DTC) which relate to transfer box electrical faults.

Controller Area Network (CAN) Bus
The CAN bus is a high speed broadcast network connected between various vehicle ECUs.
The CAN allows the fast exchange of data between ECU's every few microseconds. The bus comprises two wires which are identified as CAN high (H) and CAN low (L). The two wires are colored yellow/black (H) and yellow/brown (L) and are twisted together to minimize electromagnetic interference (noise) produced by the CAN messages.
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 pack low range warning lamp inoperative
^ Instrument pack transfer box messages in message center inoperative.