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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.

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 improves steering maneuverability especially on slippery roads. In a conventional steering system (including mechanical and hydraulic ones), poor steering wheel returnability associated with reduced alignment torque from the road may lead to awkward handling on slippery roads. In experiments with a test driver, we found that this phenomenon occurs because of the delay in the driver turning the steering wheel to avoid spinning the vehicle. This delay comes from a lower steering wheel returnability than driver expected. Increasing the steering wheel returnability will be effective in avoiding this problem. This can be realized by using the steering angle feedback or the estimated alignment torque feedback. However, the simple feedback of such values will provide drivers with poor road information when the road is slippery.

This paper presents a new control strategy for Electric Power Steering (EPS) to reduce steering vibration associated with disturbance from road wheels. Disturbance from road wheels may cause undesirable steering vibration if drivers run on an unpaved road or road wheels are not well balanced. For drivers, road information generated by alignment torque is essential to steer a vehicle easily. However drivers are unpleasant for steering vibration associated with disturbance from road wheels. In the steering system, both of them are transmitted to the driver through steering mechanism. We have developed a new EPS control strategy that reduces steering vibration associated with disturbance from road wheels without influencing road information generated by alignment torque considering the difference in frequency. The new EPS controller is constructed based on damping for specified frequency using the motor angular- velocity.

We have developed a driving simulator for Electric Power Steering (EPS), which can be used to evaluate steering maneuverability on low μ roads. The simulator calculates an 11 DOF (degrees of freedom) vehicle motion based on the steering wheel angle, the accelerator pedal position and the brake pedal position which are operated by the driver. A reaction torque corresponding to the alignment torque is applied to the steering shaft using motors. A 3D CG reproducing the view from the cockpit is displayed on a forward screen. The simulator also includes column type EPS, which generates the assist torque. Consequently, the driver feels the steering torque with good reality. The tire model we used is non-linear and it enables us to simulate the vehicle dynamics also on slippery roads. We compared driver behavior in vehicle and simulator tests and found the simulator could evaluate the relationship between steering maneuverability and EPS control strategy even when the road was slippery.