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This article discusses a vehicle stability improvement control method that utilizes an electric power steering system (EPS) with blushless motor. The purpose is to improve the vehicle stability by increasing the steering return torque in a region where the alignment torque is saturated due to the driver's excessive steering maneuver on a slippery road. In this study, a factor analysis was performed for the alignment torque on a slippery road and the basic control to improve the vehicle dynamics stability is studied by using a linear m1odel. Next, a new control algorithm was developed based on these studies. Finally, the new control algorithm was verified to be effective through an on-vehicle test. The proposed strategy can be realized only by adding a steering wheel angle sensor signal to a conventional EPS. That can be easily obtained from electronic stability control system.

In this paper, we suggest a novel algorithm to distinguish semi-steady states from various steering patterns and to estimate the stability factor. The algorithm also estimates each stability factor in left and right turns because there could be a case where they differ based on uneven tire wear and so on. The stability factor, which is the turning characteristic of a vehicle, has been treated as constant for most vehicle control systems. However, in fact, it may change in some situations, for example when a vehicle is overloaded. So there is a chance that a driver may be aware of an unusual sensation when vehicle control is designed based on a constant stability factor. We have succeeded in developing an algorithm to estimate the stability factor accurately enough to be able to compensate for it and have confirmed the effectiveness of the algorithm by simulation and vehicle testing as well.

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.

This paper proposes a vehicle state detection method for improving the stability of vehicles equipped with electric power steering (EPS) and electronic stability control (ESC) systems. ESC is an effective vehicle stability control system that operates within a vehicle's stability limitations. Generally ESC uses a vehicle state signal such as yaw rate. To enhance the ESC function so that it can alleviate understeer, a process that is capable of detecting understeer is required. This concept motivated us to develop a vehicle state detection algorithm based on estimated self-aligning torque using EPS. It is well known that maximum self-aligning torque occurs before maximum cornering force is reached. We have confirmed that the proposed algorithm can detect understeer earlier than conventional means based on vehicle yaw rate.

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.