Center Differential and 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.