Part 2
Four-Wheel Drive Systems - 4.2L/4.4L (Part 2)TRANSFER BOX MOTOR
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
Transfer Box Motor Position For Clutch Control Mode (Part 1):
Transfer Box Motor Position For Clutch Control Mode (Part 2):
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
Transfer Box Motor Position For High/Low Range Mode (Part 1):
Transfer Box Motor Position For High/Low Range Mode (Part 2):
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.
CENTER DIFFERENTIAL ASSEMBLY
CENTER DIFFERENTIAL ASSEMBLY (PART 1):
CENTER DIFFERENTIAL ASSEMBLY (PART 2):
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 center differential assembly.
The assembly comprises 3 differential pinion gears (4) and shafts (5), which are equally spaced within the center 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 center 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 synchronization 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 synchronization 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
High range actuation sequence (Part 1):
High range actuation sequence (Part 2):
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 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
Low range actuation sequence (Part 1):
Low range actuation sequence (Part 2):
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 center differential assembly via the high/low shifting fork (2) into low range position.
After the synchronization 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.
MULTI-PLATE CLUTCH ASSEMBLY
MULTI-PLATE CLUTCH ASSEMBLY (PART 1):
MULTI-PLATE CLUTCH ASSEMBLY (PART 2):
The multi-plate clutch assembly for both center and rear differentials act in a similar way. The aim of the multi-plate 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 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 center differential and optimizes 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 center differential housing.
Multi-plate Clutch Actuation
Transfer box motor levers in initial position, multi-plate clutch open condition:
Transfer box motor in end position, multi-plate clutch closed condition (Part 1):
Transfer box motor in end position, multi-plate clutch closed condition (Part 2):
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.