Tokyo 2011: Acura’s Super Handling All-Wheel Drive Evolves into a Hybrid Powertrain

The next generation of Acura’s Super Handling All-Wheel Drive trades torque-vectoring differentials for electric motors, creating a gas/electric hybrid powertrain that is capable of pure electric driving and distributing torque between the right and left rear wheels. The electric SH-AWD system’s hardware includes three electric motors, a V-6 gas engine, a lithium-ion battery, and a seven-speed dual-clutch transmission. Honda will announce the first car that will receive electric SH-AWD sometime in 2012.

Two 27-hp electric motors on the rear axle take the place of the current system’s electronically controlled differential to meter torque between the left and right wheels. By sending more torque to the outside rear wheel in a turn, the vehicle creates a yaw moment that encourages the car to rotate. While the SH-AWD system used today can only apportion torque when the driver is applying throttle, electric SH-AWD also vectors torque while the vehicle is slowing down. Under deceleration, the electric motor connected to the inside rear wheel uses regenerative braking to produce a negative torque and simultaneously generate electricity to charge the battery. The system can power a car up to 25 mph using electricity, but hard acceleration will cause the engine to fire up earlier.

The heart of the powertain is still a gas engine, specifically a 3.5-liter V-6 making more than 300 hp. The engine is mated to a seven-speed dual clutch automatic transmission that has been developed in-house by Honda engineers. A 40-hp electric motor connected to the transmission’s output shaft can send power to the front wheels or generate electricity to charge the battery.

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At a technical briefing prior to the Tokyo auto show, we scored a one-lap test drive of a Honda Accord mule packing electric SH-AWD hardware under its sheet-metal skin. The effectiveness of the torque vectoring rear motors is immediately apparent at turn in, rotating the car much more aggressively than the clutch-based system currently used in the TL, RL, MDX, and ZDX. It creates the sensation of being pushed rather than pulled through the turn. The handling is convincingly sporty but possibly too foreign for drivers heading to their local Whole Foods market. Aggressive driving would also benefit from steering that’s more accurate than the light, imprecise feel found in our mule.

Honda says the system delivers V-8 performance and four-cylinder fuel economy. While we had no way of verifying the efficiency, our internal accelerometer warns that claims of eight-cylinder acceleration are a stretch. Downshifts ordered from the wheel-mounted paddle shifters also weren’t quite ready for prime time, feeling slow and abrupt with no sign of rev matching. We have to note, though, that the car we drove was merely a mule, far from finalized in its calibration. We won’t know just how sporty Acura wants the electric SH-AWD system to be until we hear what car it will land in. Until then, electric SH-AWD is an interesting approach to all-wheel drive that offers much more than all-weather security, namely tangible fuel economy and handling benefits.

For the complete story on the 2011 Tokyo Motor Show, be sure to click over to Automobile’s Tokyo Motor Show home page, with all the latest photos, information, and much more on all things Tokyo.

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