Basic Provisions
On models with Real-Time 4WD-Dual Pump System (4 wheel drive with two pumps) the rear differential includes a hydraulic clutch and differential mechanism. Under normal conditions, the vehicle is driven by the front wheels. However, depending on the traction force of the front wheels and the road conditions, the system instantly transfers traction force to the rear wheels, eliminating the need for the driver to switch between 2WD mode (front wheel drive) and 4WD mode (four wheel drive). 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 disconnects traction from the rear wheels when braking in forward gear. This allows the braking system to function properly on models equipped with anti-lock braking system (ABS).
Design
The rear differential consists of a differential housing-torque distributor and a rear differential cup. The differential torque distributor housing includes the differential clutch, connecting flange and oil pump housing. The rear differential cup contains the differential mechanism. The driven and driving gears of the differential are hypoid gears.
The oil pump body consists of a front oil pump, a rear oil pump, a hydraulic control mechanism and a clutch piston. The clutch piston contains a disc spring, which constantly supplies the differential clutch with a given torque to avoid loud noise.
The clutch guide in the differential clutch is connected to the cardan shaft via a connecting flange and serves to transmit the traction force received from the transfer case. The clutch guide rotates the clutch drive disc 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 connected by splines to the leading hypoid gear. The leading hypoid gear drives the rear oil pump.
Front and rear oil pumps are trochoid type. The rear oil pump has a 2.5% higher output than the front pump, allowing it to cope with the difference in rotation between the front and rear wheels due to front tire wear and braking on sharp turns. Oil pumps are designed so that the suction of fluid is equal to the discharge of fluid when the pumps rotate in the opposite direction. Honda DPSF fluid is used instead of differential fluid (Dual Pump System Fluid).
Operating principle
When there is a difference in the speed of rotation of the front (guide coupling) and rear (driven hypoid gear) wheels, under the action of hydraulic pressure from the front and rear oil pumps, the differential clutch is activated and transmits traction force from the transfer case to the rear wheels.
When the vehicle starts moving 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 slowing down) 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 slowing down) the mechanism switches to 2WD mode.
To ensure system protection in both 4WD and 2WD modes, the differential clutch is lubricated by hydraulic pressure generated by oil pumps. In addition, when the differential fluid temperature rises above normal, the thermal relay releases hydraulic pressure on the clutch piston and cancels the 4WD mode.