Anticipating a continued rise in the rate of all-wheel-drive demand in the luxury and premium vehicle segments over the next five years, John Mendel, senior vice president, Automotive Operations, American Honda Motor Co., said that the company will continue to implement the Super Handling-All Wheel Drive (SH-AWD) system that was first installed on the ’05 Acura RL sedan, and was subsequently deployed on the RDX and MDX sport utility vehicles. Although Mendel is reticent to discuss any specific future product plans, he did acknowledge that SH-AWD will be “one of the core technologies” on the NSX replacement. He was on safe ground doing so because it was acknowledged at the ’07 North American International Auto Show in Detroit by Takeo Fukui, president & CEO of Honda Motor Co., Ltd., when the “Advanced Sports Car Concept” was unveiled. That car features a V10 engine and a rear-wheel drive version of SH-AWD. Fukui stated, “As we advance toward building a car like this, I can tell you it will feature advanced technology matching our passion for performance,” undoubtedly referencing, in part, SH-AWD.
Shiyouji Tokushima, chief engineer, Powertrain, at Honda R&D Americas, who recently moved to Ohio from Japan, was involved in the development of SH-AWD. He said that as they began the development program they wanted to overcome some of the challenges that they saw inherent in many AWD systems based on multiple open or locking differentials, including:
- Understeer during cornering
- Heavy system weight
- Low mechanical efficiency
- High noise, vibration and harshness
He said they set out to achieve “direct yaw control,” or “torque vectoring,” for improved cornering. They began research on this in 1988 and it made its production debut on the 1997 Honda Prelude, the “Super Handling Prelude,” which had what was called the “Active Torque Transfer System” (ATTS). A parallel development was on a lightweight electromechanical clutch control AWD system, called “Variable Torque Management-4” (VTM-4) which appeared on the 2001 Acura MDX. “Adding the principle of ATTS to Acura’s VTM-4 system led us to the development of the first SH-AWD system for the 2005 RL.”
Unlike other available systems—and they make comparisons with the Audi Q7 quattro, BMW X3 X-Drive, Lexus GS350 AWD, and the Mercedes-Benz E350 4-Matic—the SH-AWD system uses a single differential. This helps contribute to weight savings, as well as reduced complexity. Sensor input is provided regarding yaw rate, wheel speed, steering angle, throttle position, lateral g forces, and front/rear g forces, as well as the engine rpms, intake pressure, and transmission gear ratio. In operation, torque transfer is proportional to load transfer in response to driver input. There are two electromechanical clutches at the rear (the whole system is electrical; there is no hydraulic actuation) that allow the torque sent to the rear (up to 70% of the total available torque) to be apportioned to the wheels, with up to 100% to either.
The application of torque to specific wheels is more effective—and faster—than the use of brake torque, according to Ted Klaus, chief engineer, Vehicle Research, Honda R&D Americas. Klaus notes that the SH-AWD system works in cooperation with Honda’s Vehicle Stability Assist (VSA) system, which modulates the throttle and applies brakes; the systems communicate (along with the engine ECU) via a CAN bus.—GSV