Key points
On models with Real-Time 4WD-Dual Pump System (4 wheel drive with two pumps) the rear differential has a hydraulic clutch and a differential mechanism. Under normal conditions, the vehicle is driven from the front wheels. However, depending on front wheel traction and road conditions, the system instantly transfers traction to the rear wheels, eliminating the need for the driver to switch between 2WD (front wheel drive) and 4WD mode (four wheel drive). In order to reduce the weight and dimensions of the system, the mechanism for switching between these two modes is built into the rear differential.
In addition, the dual pump system cuts off traction from the rear wheels when braking in forward gear. This allows the brake system to work normally on models equipped with an anti-lock system (ABS).
Design
The rear differential consists of a torque distribution differential housing and a rear differential cup. The differential torque distributor housing includes a differential clutch, a connecting flange and an oil pump housing. The rear differential cup includes a differential mechanism. The driven and driving gears of the differential are hypoid gears.
The oil pump body is composed of front oil pump, rear oil pump, hydraulic control mechanism and clutch piston. The clutch piston contains a belleville spring which constantly supplies the differential clutch with the set torque to avoid excessive noise. The clutch guide in the differential clutch is connected to the cardan shaft through a connecting flange and serves to transmit the traction force received from the transfer case. The clutch guide drives the clutch drive plate and the front oil pump in the oil pump housing.
On the clutch hub in the differential clutch there is a driven disk, which is splined to the hypoid drive gear. The hypoid drive gear drives the rear oil pump.
The front and rear oil pumps are of the trochoidal type. The capacity of the rear oil pump is 2.5% higher than the front, allowing it to cope with the difference in rotation between the front and rear wheels due to front tire wear and braking in tight corners. Oil pumps are designed so that liquid suction is equal to liquid emptying when the pumps rotate in the reverse direction. Genuine Honda ATF PREMIUM is used instead of differential fluid (Automatic Transmission Flu-id-PREMIUM).
Operating principle
When there is a difference in the speed of rotation of the front (guide sleeve) and rear (hypoid driven gear) wheels, under the action of hydraulic pressure from the front and rear oil pumps, the differential clutch is activated and transfers the traction force from the transfer case to the rear wheels.
When the vehicle starts abruptly or accelerates in forward or reverse gear (causing the front and rear wheels to rotate at different speeds) or when braking in reverse gear (when decelerating) the hydraulic pressure control mechanism in the oil pump housing selects the 4WD mode. When the vehicle is moving at a constant speed in forward or reverse gear (when there is no difference in the speed of rotation of the front and rear wheels) or when braking in forward gear (when decelerating) the mechanism switches to 2WD mode.
To protect the system in both 4WD and 2WD modes, the differential clutch is lubricated by hydraulic pressure generated by oil pumps. In addition, when the temperature of the differential fluid rises above normal, the thermal switch relieves hydraulic pressure on the clutch piston and cancels the 4WD mode.
Rear differential assembly: 1. coupling guide; 2. differential clutch assembly; 3. oil pump housing; 4. crankcase differential-distributor of torque; 5. hypoid drive gear; 6. differential cup; 7. differential; 8. hypoid ring gear; 9. differential housing; 10. rear oil pump; 11. front oil pump; 12. clutch driven disc; 13. drive disc of the clutch; 14. coupling hub; 15. connecting flange