Honda/Acura all wheel drive explained

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Honda/Acura

CR-V, HR-V 1996-... - Automatic all wheel drive. Honda's Real Time Four Wheel Drive System. Normally front wheel drive vehicle. Torque transfer to rear axle via multi-plate clutch. Dual pump system is used to apply pressure to the clutch. It also disengages the clutch when braking to allow ABS work smoothly.

Figure: Honda's rear differential with dual pump system and multi-plate clutch.

Figure: Honda's dual pump system

Figure: Honda CR-V rear differential

Figure: Honda CR-V

Figure: Honda HR-V

How Honda's Dual Pump 4WD works

For most of the time, only the HR-V’s front wheels are driven; it’s only when they begin to lose grip that the Dual Pump system starts to send power to the rear wheels. This is achieved by a hydraulic torque-split system, consisting of a conventional front-wheel drive arrangement, complete with transfer case, a propeller shaft running the length of the vehicle and a Dual Pump system integrated with the rear differential. This is the heart of the system and comprises two hydraulic pumps, one driven by the front wheels via the prop shaft, the other by the rear wheels via the rear differential.
During normal levels of grip the front and rear wheels, and their respective pumps, turn at the same speed; hydraulic pressure circulates between the two pumps, but no pressure is generated. If the front wheels begin to lose traction and start to spin faster than those at the rear, the two pumps turn at different rates; hydraulic pressure proportional to the difference in their speeds is generated, which in turn opens a valve body and activates a mechanical, multi-plate clutch.
This clutch then connects the front prop shaft to the rear diff, which feeds precisely the correct amount of torque to the rear wheels to re-establish overall traction. The more the front wheels slip, the greater the torque fed to the rear wheels.
The Dual Pump arrangement weighs less than a conventional four-wheel drive system and demands little maintenance – just a fluid change at 72,000 miles and thereafter every 36,000 miles. Further advantage of this design is that it automatically disengages under braking, thereby allowing the ABS to operate.

Source: www.theaa.com

(Honda Legend 2004-...) - Torque-Vectoring full-time all wheel drive. Super Handling All-Wheel-Drive system (SH-AWD).

Honda's SH-AWD all wheel drive system

By monitoring driver input and driving conditions, the SH-AWD system determines the optimum front-rear and lateral (left-right) torque distribution. This information is then conveyed to the rear differential, where direct electromagnetic clutches continuously regulate and vary front-rear torque distribution between ratios of 30:70 and 70:30, and lateral torque distribution in the rear wheels between ratios of 100:0 and 0:100. Torque is used not only for propulsion, but for cornering as well, resulting in a significant enhancement in vehicle maneuverability. SH-AWD system monitors vehicle speed, wheel speed, gear position, steering angle, yaw rate, lateral G forces and other inputs, while automatically adding torque to the outside rear wheel in corners to make the car turn quicker

How front-to-rear torque is distributed:

Straight-line driving front-rear torque distribution is regulated for optimum performance in accordance with the amount of torque produced. During rapid acceleration the load on the front wheels is reduced; conversely, rear-wheel load is reduced during cruising. The result is stable driving at all times.

How left-to-right torque is distributed on the rear wheels:

During cornering, torque to the rear wheels is continuously varied to supply up to 100% to the outside wheel and 0% to the inside wheel. This creates an inward yaw moment, significantly improving vehicle handling. Yaw moment is turning torque relative to the vertical axis running through the vehicle’s center of gravity.

When decelerating during cornering (throttle closed), torque to the outside rear wheel is freely varied to change from an inward to an outward yaw moment, ensuring vehicle stability at all times.

How does acceleration device works:

The rear differential is also equipped with a built-in acceleration device. During cornering, the track of the outside rear wheel normally falls outside the average of the tracks of the front wheels. The outside rear wheel does not rotate fast enough to keep up with the front wheels, preventing efficient transmission of torque. To counteract this problem, the SH-AWD acceleration device alters the gearing to speed up the outside rear wheel’s rotation relative to the front wheels. This reduces torque transmission losses and significantly improves vehicle maneuverability. During straight-ahead driving, the twin-pinion planetary carrier spins in synchronization with the propeller shaft, causing the front and rear wheels to turn at the same speed. When the vehicle enters a curve, however, the planetary carrier is locked to the case, releasing the device from synchronization with the propeller shaft and accelerating the rotation speed of the rear wheels. A hydraulic actuator which turns the clutches on and off, and a one-way clutch are included in this compact configuration.

Figure: Honda Legend SH-AWD rear differential.

Figure: Acura RDX SH-AWD rear differential

Source: http://world.honda.com/news/2004/4040401.html

Watch Honda's video about SH-AWD: http://world.honda.com/HDTV/news/2004-4040401a/

About SH-AWD (in German): http://www.hondaoldies.de/Korbmacher-Archiv/Technik/sh4wd.htm

Last updated: 2010-05-21 22:15

There are 2 comments

George

January 11, 2010 - 02:23

Subject:

Don't forget Honda's 'VTM-4' system: eliminates this dual pump nonsense, eliminates the rear differential. Each 'half-shaft' [axleshaft] is now independently coupled to the front via an electro-magnetically controlled wet clutch pack.
www.ridgelineownersclub.com
mypage.siu.edu

and the Acura 'SH-awd' system. How do you get a front wheel drive car to drive like a rear drive car? Easy, shunt as much power to the outer rear wheel during cornering, while not powering the inner rear-3 wheel drive.
world.honda.com
Synthetic Handling would be a better name.

gasar-magnus

December 31, 2009 - 15:39

Subject:

System updated 2005 with a 2 stage setting with quicker locking (1/8 wheel rotation) a simple ball �n stop then the rest remains as above