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This paper presents a new motor current control strategy for Electric Power Steering (EPS) to reduce current fluctuation. Such current fluctuation may cause undesirable steering torque ripple and acoustic noise, if an inexpensive microprocessor is used. Using a DC-motor, current fluctuation associated with change in the battery voltage, etc., may occur. We have developed a new current control strategy which effectively alleviates current fluctuations of the motor without using higher performance microprocessors. The new controller is based on the estimation of disturbance voltage and compensation for this disturbance voltage. We have bench-tested the performance of this control strategy and confirmed that current fluctuation is reduced below that using conventional PI controller. The PI gain for the proposed controller is the same as that for the conventional controller.

This paper proposes a new Electric Power Steering (EPS) control strategy that enables improvement to steering-wheel returnability. Using a conventional EPS controller, frictional loss torque in the steering mechanism reduces steering-wheel returnability, which drivers occasionally perceive as unpleasant. This phenomena occurs in any EPS system regardless of motor type or mounting location. To improve steering-wheel returnability for EPS-equipped vehicles, we developed a new control strategy based on estimation of alignment torque generated by tires and road surfaces. This proposed control strategy requires no supplemental sensors like steering-wheel angle or motor-angle sensors. We experimented with this proposed control algorithm using a test vehicle and confirmed that it enables improved steering wheel returnability and also better on-center feeling.

This paper proposes a new Electric Power Steering (EPS) control strategy that enables remarkable progress on steering maneuverability for stationary vehicles. Using a conventional controller, undesirable steering vibration prevented us from reducing steering torque. To eliminate this vibration, we developed a new control strategy based on damping for specified frequency using a motor angular-velocity estimator. We experimented with this proposed control algorithm using a test vehicle and confirmed that it enables reduced steering torque without any perceived vibration for drivers. Concerning the gradient of the assist-map, the proposed control strategy enabled more than three times higher compared with that of the same type vehicles on the market as the test vehicle. This proposed control strategy requires only the torque sensor signal, supply voltage and current to the motor, which are used in the conventional EPS systems, so no supplemental sensors are required.