The Design And Testing Of A Microprocessor Controlled Four Wheel Steer Concept Car

The addition of four wheel steering to a vehicle improves transitional stability at highway speeds. This is accomplished by allowing additional control of the lateral forces generated by the rear tires. The strategies used to control the rear steer angle are classified as open loop or closed loop. The open loop control measures inputs to the vehicle including the steering wheel angle and the vehicle forward velocity to determine the rear steer angle. Closed loop control uses these inputs and also measures the resultant vehicle response. The error between a desired and actual vehicle response determines the rear steer angle. The closed loop strategies give reductions of undesirable responses to external inputs, such as wind gusts or rough roads.

This paper details the design and testing of a 4WS concept vehicle with both open loop and closed loop control. The vehicle used a computer controlled servo actuator with a self contained hydraulic circuit to steer the rear wheels. Different control algorithms using open loop, closed loop, and a combination of the two were implemented. One closed loop strategy measured the vehicle yaw rate, compared it to the desired rate and used the difference in an updated PID controller to determine the rear steer angle. This strategy demonstrated improved stability during simulation testing.