Center Differential and Transfer

1. Transfer

The location of the center differential is different for the viscous coupling type and the mechanical locking type. The center differential is separated from the front differential. The front differential is located inside the ring gear mounting case. It can rotate freely inside the case. Also, the hydraulic multi-plate clutch, which is used to limit the differential action of the center differential, is housed in this case. There is no switching button in newer models, and differential limitation is controlled automatically at all times. Because hydraulic pressure is controlled by the Engine & ECT ECU.

2. Power transmission

(1) During straight-ahead driving

The power is divided in two at the center differential. One part of the power is transmitted to the rear differential via the center differential right side gear. The other part of the power is transmitted to the front drive shafts via the front differential.

(2) During cornering

When a difference in the rotational speed of the front and rear wheels arises, the center differential operates, creating a difference in rotational speed between the ring gear mounting and front differential case. When this occurs, hydraulic pressure is applied to the hydraulic multi-plate clutch, with fluid, which therefore operates to reduce this difference. The friction generated to reduce this rotational difference differs depending on the vehicle driving conditions and optimum driving force always distributed to the front differential and rear differential. (2/4)

3. Center differential

(1) Construction The center differential gear is the bevel gear type and the center differential limit control mechanism is the hydraulic multi-plate type. This type of center differential uses a hydraulic multiplate clutch as the differential limiting mechanism. The hydraulic multi-plate clutch consists of the inner side clutch discs, the outer side clutch plates and pushing pistons. The clutch is located beside the front differential.

(2) Principle of operation When hydraulic pressure is applied to the pistons, the clutch discs and plates are pushed tightly together, limiting the difference in rotational speed between the ring gear mounting case on the clutch plate side and the front differential case on the clutch disc side. If the front wheels get stuck in a mudhole and spin, the differential action of the center differential is limited by the clutch, so power is transmitted to the rear wheels, making it easy for the vehicle to get out of the mudhole. During normal driving in the “D” range, since the differential limit force is weak, driving is smooth when cornering at low speeds or when parking, etc., and the tight corner braking phenomenon does not occur. In the “L” and “R” ranges, since a higher differential limiting force is obtained the power obtained at the tires is effective in freeing the vehicle when it gets stuck.

(3) Features Excellent control of the differential action limit force is achieved in accordance with the automatic shift lever position, the throttle opening angle, and the vehicle’s speed. Newer models, a computer controls the differential limiting force in accordance with vehicle speed and with differences in front and rear wheel rotational speed, to ensure smooth driving under any conditions, whether on muddy roads, when cornering or when traveling straight ahead.

HINT: Older models had a center differential control switch. When driving in the “Off” mode, the condition is the same as when the mechanical locking type is run with the differential lock switch OFF.

Center Differential and Transfer

1. Transfer

The layout of the center differential, front differential, transfer drive gear and transfer driven gear is almost the same as with the center differential mechanical locking type, but viscous coupling is built into the transfer block to limit the differential action of the center differential. The center differential assembly consists mainly of the center differential right case, center differential intermediate case, center differential left case, center differential pinion gears, and center differential right side gear.

2. Power transmission

(1) During straight-ahead driving The transmission of engine power from the center differential drive gear to the center differential right and left side gears is the same as that in the center differential mechanical locking type. The power from the center differential right side gear is transmitted via the transaxle mode select sleeve to the transfer drive gear, transfer driven gear and rear propeller shaft. It is also transmitted to the viscous coupling outer plate. Since the No.2 intermediate shaft is inserted into the center differential left side gear, power is also transmitted to the viscous coupling inner plate.

(2) During cornering Since the viscous coupling acts to reduce the difference in the number of revolutions between the center differential right and left side gears, the differential action of the center differential is limited. The differential limiting function is not so strong as to obstruct smooth turning. (2/4)

3. Center differential (viscous coupling)

(1) Construction The center differential gear is the bevel gear type and the center differential limit control mechanism is the viscous coupling type. The viscous coupling is built into the transfer ring gear mounting. The inner plates of the viscous coupling are joined to the center differential left side gear and the front differential case, while the outer plates of the viscous coupling are joined to the ring gear mount case and the center differential right side gear. Since the viscous coupling is built into the transfer ring gear mounting case the construction has been changed from the three-axis center differential shaft, based on the mechanical locking transaxle, to the four-axis type. A viscous coupling is a kind of fluid clutch which transmits torque by the viscous resistance of oil. It uses this viscous resistance to control the operation of the center differential, creating an effect in the center differential like that created by an LSD (Limited Slip Differential).

(2) Operation The center differential with viscous coupling operates when rotational speed differences between the inner plates (front) and outer plates (rear) of the viscous coupling occur, transmitting power and limiting the differential action of the center differential. Torque is transmitted by the viscous resistance of the silicone oil.

<1>When plates rotate at identical speeds No viscous resistance is generated.

<2>When plates rotate at different speeds When the plates begin to turn at different speeds, the silicone oil particles are pulled away from each other and a resistance is generated. This resistance reduces the difference in speed between the two plates.

<3>Transmitted torque characteristics

During normal operation The amount of viscous resistance due to differences in the rotational speeds of the outer and inner plates increases or decreases in proportion to the extent of the difference in speed.

During humping In the viscous coupling continues to operate with the outer and inner plates rotating at large different speeds, the temperature and internal pressure inside the viscous coupling increases. The inner plate, which can move in an axial direction, is pulled toward the side where pressure is lower. As a result, the inner plate contacts the outer plate directly to create a large resistance. This condition is called humping. Since there exists no speed difference between the inner and outer plates during humping, the temperature and internal pressure inside the viscous coupling decreases. The compressed bubbles expand again and separate the inner plate from the outer plate.

Center Differential and Transfer

1. Transfer

This transfer is a two-speed (Low- High) type. This transfer is a compact and lightweight. Its main feature is the adoption of the torque sensing type center differential with mechanical locking type. In this transfer, a planetary gear train is used in the reduction mechanism and a silent chain is used to reduce noise for the front drive. The method for switching the modes of this transfer involves the operation of a 4WD control switch to actuate the two shift motors. Thus, the transfer shift lever has been discontinued and the ease of operation has been improved.

Transfer shift actuator

The transfer shift actuator, which contains “H”-”L” shift motor limit switch, center differential lock shift motor, “H”-”L” shift motor limit switch, center differential lock shift motor limit switch and center differential lock detection switch, cannot be disassembled. (1/3)

2. Power transmission

(1) “H” position The splines at the rear of the transfer input shaft mesh with the internal gear teeth of the high and low clutch sleeve. Also, the high and low clutch sleeve is meshed to the differential case. Thus, the rotation of the input shaft is transmitted to the high and low clutch sleeve, the differential case.

(2) “L” position The external teeth of the high and low clutch sleeve are meshed with the planetary spline piece, and the planetary ring gear is fixed. Thus, the rotation of the input shaft is transmitted in a reduce from to the planetary sun gear, planetary pinion gear, planetary pinion gear shaft, planetary carrier, planetary spline piece, high and low clutch sleeve, high and low clutch hub, and differential case.

3. Center differential

(1) Construction Torque sensing type center differential with mechanical locking type consists of a differential case, coupling, ring gear, 8 pinion gears, sun gear, and carrier.

(2) Principle of operation 1. Normal driving (front wheel speed = rear wheel speed) The driving force that is input by the differential case is transmitted by front: 40, rear: 60. When a rotational difference exists between front wheel and rear wheel, the torque distribution of the driving force (torque) that is input by differential case changes instantly by the pinion gear and clutch plate operation before the torque is transmitted. 2. Front wheel skid driving (front wheel speed > rear wheel speed) The center differential distributes more torque to the rear wheels.

4. Rear wheel skid driving (front wheel speed = rear wheel speed)

The center differential distributes more torque to the rear wheels.

Center differential lock mechanism

When the center differential lock switch is ON, the center differential lock shift motor within the transfer shift actuator operates. This slides the center differential lock shift fork and locks the center differential.