Abstract
This paper presents a complete control strategy of the active return-to-center (RTC) control for electric power steering (EPS) systems. We first establish the mathematical model of the EPS system and analyze the source and influence of the self-aligning torque (SAT). Second, based on the feedback signals of steering column torque and steering wheel angle, we give the trigger conditions of a state switch between the steering assist state and the RTC state. In order to avoid the sudden change of the output torque for the driving motor when the state switches frequently between the steering assist state and the RTC state, we design an undisturbed state switching logic algorithm. This state switching logic algorithm ensures that the output value of the RTC controller is set to an initial value and increases in given steps up to a maximum value after entering the RTC state, and the output value of the RTC controller will reduce in given steps down to zero when exiting the RTC state. This therefore ensures smooth switch control between the two states and improves the driver’s steering feeling. Third, we design the RTC controller, which depends upon the feedback signals of the steering wheel angle and the angular velocity. In addition, the controller increases the auxiliary control function of the RTC torque based on vehicle speed. The experimental results show that the active RTC control method does not affect the basic assist characteristics, which effectively reduces the residual angle of the steering wheel at low vehicle speed and improves the RTC performance of the vehicle.
Highlights
Electric power steering (EPS) systems have the advantages of safety, energy saving, and environmental protection
For EPS systems with a steering wheel angle sensor installed, since the absolute position of the steering wheel can be obtained in real-time, the research on this kind of system mainly focuses on the realization method of RTC control
This paper considers the deficiency of current RTC control for EPS systems, and a method based on steering wheel angle signal is proposed to accurately determine the RTC state of the vehicle
Summary
Electric power steering (EPS) systems have the advantages of safety, energy saving, and environmental protection. For EPS systems with a steering wheel angle sensor installed, since the absolute position of the steering wheel can be obtained in real-time, the research on this kind of system mainly focuses on the realization method of RTC control. When the assist state and the RTC state are switching because the direction of the assist torque and the RTC torque are opposite one another, if they are not connected properly, the steering process will result in a sense of frustration and affect the feel for the driver It is important for RTC control, but to the best of the authors’ knowledge, no literature has been published in this regard. This paper considers the deficiency of current RTC control for EPS systems, and a method based on steering wheel angle signal is proposed to accurately determine the RTC state of the vehicle. An RTC control strategy for the EPS system is designed to ensure uniformly smooth transition of the torque for the steering wheel to avoid affecting the feel for the driver
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