The SH-AWD (Super-Handling All-Wheel-Drive) 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 provides incredibly neutral steering and outstanding vehicle stability.
Honda’s SH-AWD system is unique in the industry. It does not have any center differential or any limited-slip differential. All the mechanicals is mounted at the rear axle. The drive from propeller shaft is sent to an accelerator first. The latter uses planetary gears to step up the rotation speed, creating a speed difference between the input and output shaft. By applying electromagnetic clutches, the speed difference can transfer driving torque to the rear axle.
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 manoeuvrability.
The rear differential is also equipped with a built-in acceleration device, yet another world’s first. 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 manevrability.
The SH-AWD system uses torque not only for propulsion, but also to increase cornering precision and dramatically enhance vehicle maneuverability. During cornering the speed of the outside rear wheel is greater than the average of both front wheels. This prevents the efficient transfer of torque to the outside rear wheel. 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.
At Honda, driving pleasure is regarded as one of the most important factors in vehicle development. The new SH-AWD system features "feed-forward" control, which utilises the degree of driver input to determine appropriate torque distribution. This results in a super-neutral steering feel that responds with optimal faithfulness to the driver’s handling of the steering wheel, realising outstanding driving comfort and stability.
Sensors - ECU
* The input of steering angle, lateral g, yaw rate, wheel speed and other sensors monitor driver input, vehicle demeanour, and driving conditions such that the SH-AWD ECU can calculate ideal torque distribution.
* World’s first direct electromagnetic clutch
* An electromagnetic coil (electromagnet) attracts a magnetic body which, in turn, presses on the multi-plate clutch to facilitate torque transmission.
* A compact clutch unit, equipped with a planetary gear step-up mechanism to increase torque, permits transmission of substantial amounts of torque. A built-in search coil monitors the gap between the electromagnetic coil and the magnetic body. Current flow in the electromagnetic clutch is then adjusted to achieve highly precise torque regulation.
Deceleration 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
* During straight-ahead driving, the twin-pinion planetary carrier spins in synchronisation 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 synchronisation 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.
* 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.
Torque Distribution Regulation
* Acceleration 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 centre of gravity.
Advantage:Can vary torque between rear wheels to correct oversteer / understeer