Control System Operation

Average Moving Current Control
The control unit monitors the average moving current of the motor to protect the system. When the average moving current exceeds a given value, the control unit lowers the current to change steering angle of the rear wheels gradually (approximately 6 degrees/3O seconds). When the average moving current to the motor is below the given value, the rear wheels return to the designated steering angle slowly (approximately 6 degrees/2 minutes).


Over-Voltage Control
An increase in battery voltage (due to a voltage regulator failure, for example) could cause excessive actuation of the motor and erratic control of the rear wheels. To prevent this, the control unit monitors the voltage. If it exceeds a given value, the control unit slowly returns the rear wheels to the straight-ahead position by reducing voltage to the motor and turns the 4WS indicator light ON.


Fail-Safe Function:
When the control unit senses a failure in the system, it switches to fail-safe mode. In this mode, it powers the fail-safe and damper relays. The fail-safe relay cuts power to the rear steering motor, while the damper relay slows the motor's return to neutral. As a result, the rear wheels return slowly to the straight-ahead position and then remain there. The car then drives like conventional 2WS.





When the control unit switches to fail-safe mode, it stores an problem code and turns on the 4WS indicator light to notify the driver of a problem. This error code can be read by connecting the maintenance connector terminals with a jumper wire under the dash. The error code is read as blinks of the 4WS indicator light.


Damper Control:
When the system goes into fail-safe mode, it cuts power to the motor by powering the fail-safe relay. Without some type of damping, the returns springs would turn the rear wheels to the straight-ahead position too rapidly, adversely affecting the car's handling.


To counteract this, the control unit also powers the damper relay. The armature of the now deactivated motor is spun by the movement of the steering shaft. This causes the motor to act as a generator. The voltage generated by this action is applied back to the motor through the damper relay. This causes the motor to resist the force of the return springs, allowing the rear wheels to go back to the straight-ahead position slowly.


Electronic Neutral Position
For the 4WS system to work correctly, it must be in electronic alignment as well as mechanical alignment. In other words, the system's front and rear sensors must signal that the wheels are pointed straight-ahead when the wheels are mechanically pointed straight ahead. The technician can test for "electronic straight-ahead" by connecting the maintenance connector terminals with a jumper wire and turning the front and rear wheels.