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For active front steering control systems that intervene in driver's operation to assist in the control of the vehicle's motion, the effect of the man-machine interface is much larger than for other conventional control systems. This paper focuses on human factors. The results of analysis regarding control effects and system design concerns are also described. The user benefits of this control system are improved vehicle stability and reduced driving workload. Both theoretical and experimental evaluations are described. Regarding the man-machine interface, the influence of the oversteer characteristic when braking and turning on driver's steering operation, the influence of driver reaction in system failure and steering wheel reaction torque when driving with the actuator are also analyzed.

Rear steering system can improve vehicle stability using active control of the rear wheel angles. For designing the rear steering system, environmental conditions, performance deterioration due to aging and component variation as a result of manufacturing tolerance under mass production must be taken into consideration. We have applied two-degree-of-freedom (2DOF) feedback control with feedforward control for the motor servo control so that the rear steering actuator can track the target rear steering angle accurately and stably. The control system is designed based upon a nominal mathematical model and its variation range. As a result, the rear steering actuator can be controlled with excellent performance and high reliability. This paper describes the mathematical model construction in the frequency domain and a robust motor servo controller design based on 2DOF feedback control with feedforward control.