Active Return-to-Center Control Based on Torque and Angle Sensors for Electric Power Steering Systems

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.

Active Return Control Strategy of Electric Power Steering System Based on Disturbance Observer

“…In view of the problems of EPS systems in terms of high-speed vibration and steering feel, Ma et al proposed an active anti-disturbance EPS torque control method, developed an EPS variable-pattern controller, and verified the effectiveness of an active immune algorithm via bench test [14]. Du et al used a non-disturbance state switching logical algorithm to establish a complete active return control strategy and effectively solved the sudden change problem of the output torque of the drive motor under frequent switching between assistant steering state and RTC state [15]. By using a permanent magnet synchronous motor as the control object, Lin, F.J. et al proposed an intelligent second-order sliding-mode control (ISOSMC) algorithm based on the wavelet fuzzy neural network of asymmetrical membership function and verified the application effectiveness of the proposed ISOSMC in EPS systems through an experiment [16].…”

Study on Low-Speed Steering Resistance Torque of Vehicles Considering Friction between Tire and Pavement

“…The assist effort of EPS can vary with vehicle speed, which is conducive to improving handling stability. In addition, the motor in EPS provide steering assist effort directly, thus EPS hardly consumes electric energy under no-steering conditions, which is more energy saving [3,4]. Nevertheless, EPS is not suitable for heavy-duty commercial vehicles due to a large steering resistance torque and the power limitation of existing power supply systems in heavy-duty commercial vehicles, especially under the condition of pivot or low-speed steering [5].…”