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Click the above picture for high-res image.

All-wheel-drive systems are becoming an increasingly popular feature for large sedans. They allow for more exciting driving dynamics than pure front-wheel-drive, but also provide for increased fair weather traction over pure rear-wheel-drive. Acura revealed their all-wheel drive system dubbed Super Handling All-Wheel-Drive (SH-AWD) in the 2005 RL. Since then, the system has been adapted to the MDX and RDX vehicles as well. It is a system with a name only a Japanese company could get away with, after all there is a Honda powered Formula 1 team named Super Best Friends. Acura is proud of their technological development. Their 2007 Los Angeles Auto Show booth featured a SH-AWD display front and center. We used the opportunity to snap some pictures of the complex unit in order to illustrate its unique features. Follow the jump to read more.

Acura's SH-AWD system for the RL is like any other system in that it distributes torque between the front and rear wheels. However, unlike other systems it can also distribute torque between both rear wheels. The front transfercase sends a maximum of 70-percent of the total torque output to the front wheels. This occurs in situations like straight-line cruising and low throttle cornering. Full-throttle straight-line acceleration sends a maximum of 40-percent of the total torque to the rear wheels. Hard cornering situations can see up to 70-percent of the total torque reach the rear wheels. This percentage of total torque can also be split between the two rear wheels, even sending all 70-percent to the outside wheel. The rear wheels can even be overdriven to spin up to five-percent faster than the front.

A rear view of the Acura RL underside and drivetrain. The rear differential is situated in the center, between the rear axles. Click the image for a high-res view.

The SH-AWD system's rear differential case houses three sets of planetary gear and clutch sets in a T configuration. The first set, coupled to the drive-shaft, is known as the Acceleration Device. This is the device that overdrives the rear wheels by spinning the output shaft at higher rpms than the input shaft. The other two sets are known as Direct Electromagnetic Clutch Systems. There is one for each of the rear wheels. They function as limited slip differentials, adjusting clutch plate pressure to control the amount of torque that reaches each wheel. To determine the clutch pressures for the rear differentials the engine ECU provides engine rpm, intake manifold pressure and transmission gear data and the traction control ECU provides lateral g, yaw rate, wheel speed and steering angle information to the SH-AWD ECU. The SH-AWD ECU then controls electronic solenoids that adjust hydraulic actuators to change torque split as necessary.

A close-up view of the rear SH-AWD differential case. The driver's side Direct Electromagnetic Clutch system can be seen through the acrylic cover on the left side of the photo. Click the image for a high-res view.

Acura's all-wheel-drive system is a design that actively fights understeer. The Acceleration Device can increase the wheel speed of the rear wheels so that they do not drag behind in cornering. This is because the rear wheels take a larger arc when cornering than the front wheels. For the front and rear wheels to complete an arc simultaneously the rear wheels need to be traveling at a faster rate. The Electromagnetic Clutch System allows for the SH-AWD system to also compensate for the different arcs the inside and outside wheels must take in a corner. The inside wheels take a shorter arc than the outside wheels, thus the rear outside wheel must spin the fastest to keep up. SH-AWD lets the outside rear wheel receive all rear torque in cornering conditions and it can turn at a higher rate of rotation than the other wheels, thus increasing vehicle stability.

Rumor has it that Acura will employ SH-AWD in the next generation NSX. However, it must be noted that the NSX has been a mid-engine, rear-wheel-drive package and the SH-AWD system is designed for a front-engine vehicle with a front-wheel-drive bias. The entire system is also extremely heavy. The current vehicles offering the system weight in at over 3,900 lbs, 4,000 lbs and 4,500 lbs for the RDX, RL and MDX respectively. It is apparent that every ounce of weight savings in the package is key, as the RL employs the use of a carbon fiber reinforced driveshaft. When the system shows up in the NSX design hopefully it will have the strength to operate 100-percent rear-wheel-drive with the SH-AWD components located in positions that make for the best front-rear weight distribution. It could create a package with the potential to give Nissan and its GT-R's ATTESA all-wheel-drive system a run for its money.

The above picture shows the lightweight carbon fiber reinforced driveshaft used on the Acura RL. Click the image for a high-res view.

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    • 1 Second Ago
      • 7 Years Ago
      This was pretty nifty when I saw it at Detroit last year.
      • 7 Years Ago
      As a racer, I can appreciate the technology, but as a consumer, I sure don't want to know what this might cost to service out-of-warranty. Personally, I think the auto industry went past the point of diminishing returns on benefit vs. complexity long ago...
      • 7 Years Ago
      Neat system.

      But I sure wouldn't want to own one that's gone out of warranty. Even Honda's high quality can't keep it from eventually just plain wearing out - at enormous expense.
      • 7 Years Ago
      The technology has been used by Honda for a while with good results. I used to own a 1997 Prelude Type SH, which had a similar setup (except only driving the front wheels). In any case, the units proved very reliable over the years (I just sold the car this past summer, so the unit was good for at least ten years).
      • 7 Years Ago
      Would someone please ban this guy?
      • 7 Years Ago
      And it will only cost you $$$$$$$$.
      If Honda would just turn their engines 90 deg., put a differential in the back like with the S2000( you know they can)market a two door coupe,.....blah, blah
      Nope. Nobodys going to do that!!!
      • 7 Years Ago
      This is the design of the future, just as with the Nissan GT-R, this layout creates the best possible weight distribution in an all-wheel-drive vehicle. The next logical step will be a hybrid vehicle that locates the electric motor in the rear, and batteries in the center between the engine and transaxle helping to further spread the weight evenly and centralize the mass. I'm sure we'll see every car manufacturer adopt similar approaches to their new designs.
        • 7 Years Ago
        XWD is nothing special. It isn't anything but 4th generation haldex + the rear 'eLSD'
        There is still an open front differential, and the rear differential can not fully lock up.

        The RL weight distribution is 58/42. That sucks.
      • 7 Years Ago
      The F1 team is actually called "Super Aguri F1". "Super Best Friends" is a joke coined by the Speed Channel commentators.
        • 7 Years Ago
        Yes, it came from a South Park episode and rather escaladed from there. Otherwise Aguri is just a Japanese name. Regardless all of it is a play on the overuse of the word super in Japan.
        • 7 Years Ago
        Yep, whoever wrote this article is a super F1 noob
      • 7 Years Ago
      As an Audi owner I think thats kinda neat from what I see that Honda took it the next step forward in AWD technology.

      I know with the Quattro that I have that I am able to nudge my car safely around corners pushing the envelope, so id be curious to see what the effect is of having wheels in the rear that literally push you around the corner just as fast as the Audi if not faster yet with better rear end balance and less stepping from the bumps. (I live in he Detroit area and roads are bumpy here)
      • 7 Years Ago
      OH REALLY??? No way, could it be yours??? Nahhhh

      Gonna have to try a little harder than that, james.
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