System Overview

Outline





The electronically controlled power assisted 4WS system consists of the hydraulic power steering system that steers the front wheels, the rear actuator that steers the rear wheels, the 4WS control unit, and the sensors that detect the car's speed and other steering conditions. The front steering gearbox and the rear actuator are connected by a wire harness. The rear steering angle is controlled electrically, allowing the rear wheels to be set at any designated steering angle.


System Operation





The 4WS control unit receives input from the vehicle speed sensor, front main steering angle sensor, and the front sub steering angle sensor. The control unit calculates the vehicle speed, steering turning angle, steering speed and steering direction to determine the best angle to steer the rear wheels.





The rear wheels are turned by a motor built into the rear steering actuator. The motor is activated by the power circuit in the control unit. The actual steering angle of the rear wheels is detected by the rear main steering angle sensor, and the rear sub steering angle sensor. The control unit adjusts the angle according to the difference between the sensed steering angle of the rear wheels and the targeted steering angle of the rear wheels.


Features Of Rear Wheel Steering:





The electronically controlled power assisted 4WS sets the rear wheels at the best steering angle for the car's speed, steering rotation speed, steering wheel angle, etc.


^ Car speed
When the car is traveling at low speed, the 4WS system turns the rear wheels in the reverse direction of the front wheels in proportion to the rotation angle of the steering wheel. When the car is traveling a higher speed, the system increases the steering angle of the rear wheels in the same direction as the front wheels.
Changing the steering angle performance of the rear wheels in relation to the car's speed gives the car improved handling characteristics.


^ Steering speed 30km/h (18 mph) or above
The rear wheel steering angle varies with how rapidly the steering wheel is rotated. See graph.