System is First To Distribute Torque Front to Rear and Between Left and Right Rear Wheels

TORRANCE, Calif., April 1, 2004 - The Acura RL Prototype, which will make its world debut at the New York International Auto Show, features a revolutionary new all-wheel-drive system called SH-AWD^TM. The SH-AWD system is the first and only all-wheel-drive platform that distributes the optimum amount of torque not only between the front and rear wheels but also between the left and right rear wheels. The result is precise cornering performance that reduces torque steer and provides outstanding vehicle stability.

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 vary the torque by up to 70 percent in either direction ¡V front or rear. Rear torque can also be proportioned between the left and right rear tires by up to 100 percent on either side.

The SH-AWD system is composed of an ECU, sensors that detect steering angle, lateral g-force, and other vehicle information, and a rear differential. The direct electromagnetic clutches inside the rear differential, another industry first, employ electromagnets to maintain precise control over the multi-plate clutches.

The SH-AWD system uses torque not only for propulsion, but also to increase cornering precision and dramatically enhance vehicle maneuverability. During cornering, the track of the outside rear wheel normally falls outside the track of the front wheels. Because of this, the outside rear wheel does not rotate fast enough to keep up with the front wheels, preventing efficient transmission of torque. To counteract this condition, the SH-AWD system¡¦s rear differential is equipped with a built-in acceleration device that can overdrive the outside rear wheel. This acceleration device, which is another industry first, uses a planetary gear to speed up the outside rear wheel¡¦s rotation relative to the front wheels. The result is a significant enhancement in vehicle maneuverability during cornering.

SH-AWD system torque regulation

• Acceleration while cornering: Torque to the rear wheels is continuously varied to supply up to 100 percent to the outside wheel. This creates an inward yaw moment, significantly improving vehicle handling precision.
• Deceleration (throttle closed) while cornering Torque to the outside rear wheel is varied to change from an inward to an outward yaw moment, helping vehicle stability at all times.
• Straight-line driving Front-rear torque distribution is modulated for optimum performance. During rapid acceleration, torque is redistributed from the front wheels to the rear wheels. Conversely, during cruising, torque is concentrated in the front wheels. The result is additional driving stability.