Outline
The Real-time 4WD-Dual Pump System model has a hydraulic clutch and a differential mechanism in the rear differential assembly. Under normal conditions, the vehicle is driven by the front wheels. However, depending on the driving force of the front wheels and the road conditions, the system instantly transmits appropriate driving force to the rear wheels without requiring the driver to switch between 2WD (front wheel drive) and 4WD (four wheel drive). The switching mechanism between 2WD and 4WD is integrated into the rear differential assembly to make the system light and compact.
In addition, the dual pump system switches off the rear-wheel-drive force when braking in a forward direction. This allows the braking system to work properly on models equipped with an vehicle stability assist (VSA).
Construction
The rear differential assembly consists of the torque control differential case assembly and the rear differential carrier assembly. The torque control differential case assembly consists of the differential clutch assembly, the companion flange, and the oil pump body assembly. The rear differential carrier assembly consists of the differential mechanism.
The differential clutch assembly consists of the clutch guide, the clutch hub, the clutch plate, the clutch disc, the return spring, and the pilot clutch.
The oil pump body assembly consists of the front oil pump, the rear oil pump, the hydraulic control mechanism, and the clutch piston. The clutch piston has a disc spring that constantly provides the differential clutch assembly with a preset torque to prevent abnormal sound.
The clutch guide in the differential clutch assembly is connected to the propeller shaft via the companion flange, and it receives the driving force from the transfer assembly. The clutch guide rotates the clutch plate and the front oil pump in the oil pump body assembly.
The clutch hub in the differential clutch assembly has clutch discs that are splined with the hypoid drive pinion gear. The hypoid drive gear drives the rear oil pump.
The front and rear oil pumps are trochoidal pumps. The rear oil pump capacity is 2.5 percent larger than the front oil pump to handle the rotation difference between the front and rear wheels caused by worn front tires and tight corner braking. The oil pumps are designed so the fluid intake works as a fluid discharge when the oil pumps rotate in reverse. Honda Dual Pump Fluid is used instead of differential fluid.
Forward Start and Acceleration (4WD)
During a forward start and forward acceleration, the dual pump system can engage four wheel drive.
If the front wheels spin faster than the rear wheels, the front oil pump spins faster than the rear oil pump. The front pump draws fluid through check valve B and discharges it. Some of the discharged fluid is drawn in by the rear oil pump. The remaining fluid will pass through check valve E into the clutch piston. There, hydraulic pressure is regulated by two orifices.
The regulated hydraulic pressure at the clutch piston pushes the plates and discs of the clutch together to form a connection. The engaged clutch then passes driving force from the transfer assembly to the rear wheels, producing 4WD.
Scheme 49
Forward Driving at Constant Speed (2WD)
When driving forward at a constant speed (cruising), the dual pump system functions in two wheel drive mode. The rotation speed of the front and rear wheels is the same, so the speed of the front and rear pumps is also the same. Fluid discharged by the front oil pump is drawn in by the rear oil pump and is circulated through the system. Because there is no pressure built up at the clutch piston, the clutch does not engage, and the vehicle remains in 2WD (front wheel drive).
Scheme 50
Forward Deceleration (2WD)
During forward deceleration, the dual pump system functions in two wheel drive mode.
Because of braking characteristics, the speed of the rear wheels may exceed the speed of the front wheels during deceleration. If so, the rear oil pump spins faster than the front oil pump.
Fluid discharged by the rear oil pump is simply drawn in again by the rear pump and recirculated. Because there is no pressure built up at the clutch piston, the clutch piston does not engage, and the vehicle remains in 2WD (front wheel drive).
Scheme 51
Reverse Start and Acceleration (4WD)
During reverse start and reverse acceleration, the dual pump system can engage four wheel drive.
If the front wheels spin faster than the rear wheels, the front oil pump spins faster than the rear oil pump. The front oil pump draws in fluid through check valve A and discharges it. (Note that in reverse, the direction of the pumps is the opposite of that during forward driving.)
Some of the fluid that is discharged by the front oil pump is drawn in by the rear oil pump. The remaining fluid passes through check valve F into the cylinder of the clutch piston, where it is regulated by two orifices.
The regulated hydraulic pressure at the clutch piston may force the plates and discs of the clutch together to form a connection. The engaged clutch passes driving force from the transfer assembly to the rear wheels, producing 4WD.
Scheme 52
Reverse Driving at Constant Speed (2WD)
When driving in reverse at a constant speed, the dual pump system functions in two wheel drive mode.
The rotation speed of the front and rear wheels is the same, so the speed of the front and rear pumps is also the same. Fluid discharged by the front oil pump is drawn in by the rear oil pump and is circulated through the system. But, because there is a difference in the capacity between the two pumps, fluid flows through check valve E, and then through orifices. This fluid lubricates and cools the clutch assembly and bearings.
In this condition, only a low pressure is built up at the clutch piston. Therefore the clutch does not engage, and the vehicle remains in 2WD (front wheel drive).
Scheme 53
Reverse Deceleration (4WD)
During reverse deceleration, the dual pump system can engage four wheel drive.
When decelerating in reverse direction, the speed of the rear wheels may exceed the speed of the front wheels (due to engine braking). In this condition, the rear oil pump draws fluid through check valves B and C. Fluid discharged from the rear oil pump then flows through check valve E to the clutch piston. There, pressure is regulated by two orifices. The regulated hydraulic pressure at the clutch piston may force the plates and discs of the clutch together to form a connection. The engaged clutch passes driving force from the transfer assembly to the rear wheels, producing 4WD.
Scheme 54
Starting and Accelerating In Forward Gears (4WD Mode)
Note. Do not test repeatedly or the fluid will overheat.
- Raise the vehicle so all four wheels are off the ground (see «LIFT AND SUPPORT POINTS»(ref-290856-S03262290762008072200000) ).
- Start the engine, and let it idle until the radiator fan comes on at least twice.
- With the engine at idle, shift into 1st gear, and release the clutch pedal.
- Firmly apply the parking brake to lock the rear wheels. If the engine stalls, the 4WD system is normal. If the engine continues running, there is a problem in the 4WD system. Check the differential fluid. If the differential fluid is normal, replace the torque control differential (TCD) case kit.
Starting and Accelerating In Reverse Gear (4WD Mode)
Note. Do not test repeatedly or the fluid will overheat.
- Raise the vehicle so all four wheels are off the ground (see «LIFT AND SUPPORT POINTS»(ref-290856-S03262290762008072200000) ).
- Start the engine, and let it idle until the radiator fan comes on at least twice.
- With the engine at idle, shift into reverse gear, and release the clutch pedal.
- Firmly apply the parking brake to lock the rear wheels. If the engine stalls, the 4WD system is normal. If the engine continues running, there is a problem in the 4WD system. Check the differential fluid. If the differential fluid is normal, replace the torque control differential (TCD) case kit.
Starting and Accelerating In Forward Positions (4WD Mode)
Note. Do not test repeatedly or the fluid will overheat.
Scheme 55
- Raise the vehicle so all four wheels are off the ground (see «LIFT AND SUPPORT POINTS»(ref-290856-S03262290762008072200000) ).
- Make a mark (A) on either No. 1 or No. 2 propeller shaft (B).
- Start the engine, and let it idle until the radiator fan comes on at least twice.
- With the engine at idle, shift to the 1 position.
- Firmly apply the parking brake to lock the rear wheels, and measure the time it takes the propeller shaft to rotate 10 times. If the time is 10 seconds or more, the 4WD system is normal. If the time is less than 10 seconds, there is a problem in the 4WD system. Check the differential fluid. If the differential fluid is normal, replace the torque control differential (TCD) case kit.
Starting and Accelerating In the R position (4WD mode)
Note. Do not test repeatedly or the fluid will overheat.
Scheme 56
- Raise the vehicle so all four wheels are off the ground (see «LIFT AND SUPPORT POINTS»(ref-290856-S03262290762008072200000) ).
- Make a mark (A) on either No. 1 or No. 2 propeller shaft (B).
- Start the engine, and let it idle until the radiator fan comes on at least twice.
- With the engine at idle, shift to the R position.
- Firmly apply the parking brake to lock the rear wheels, and measure the time it takes the propeller shaft to rotate 10 times. If the time is 10 seconds or more, the 4WD system is normal. If the time is less than 10 seconds, there is a problem in the 4WD system. Check the differential fluid. If the differential fluid is normal, replace the torque control differential (TCD) case kit.
Scheme 57
Scheme 58
- Block the front wheels (A), raise the left rear wheel, and support it with a safety stand (B) as shown below.
- Hold the tire, and turn it counterclockwise continuously for more than one rotation. If the rotation of the wheel does not gradually feel heavy while rotating, the 2WD system when decelerating in a forward gear is normal. If the rotation of the wheel gradually feels heavy while rotating, there is a problem in the 2WD system. Check the differential fluid. If the fluid is normal, replace the torque control differential (TCD) case kit.
Scheme 59
Scheme 60
- Block the front wheels (A), raise the left rear wheel, and support it with a safety stand (B) as shown below.
- Hold the tire, and turn it clockwise continuously for more than one rotation. If the rotation of the wheel gradually feels heavy while rotating, the 4WD system when decelerating in reverse is normal. If the rotation of the wheel does not gradually feel heavy while rotating, there is a problem in the 4WD system. Check the differential fluid. If the fluid is normal, replace the torque control differential (TCD) case kit.