Construction of Ideal Electric Power-Steering Characteristics by Inverse Dynamic Analysis Method

Currently, the control strategies of electric power-steering (EPS) systems mainly focus on power-steering torque control. There is no direct relationship between steering torque and steering motion intensity, which makes steering wheel adjustment difficult and does not easily meet the driver’s expectations. This paper proposes a method to represent the driver’s steering intention (steering torque) in the form of steering motion intensity based on the analysis of the dynamic characteristics of the EPS system and vehicle motion dynamics. This method establishes the optimal relationship between steering torque and motion intensity according to Stevens’s law of psychology, providing a theoretical basis for optimizing the driving feel. The study uses lateral acceleration and steering wheel steering angles as intermediate variables to connect the driver’s input information with vehicle dynamics and calculates the steering torque through the inverse dynamics of the steering system and the inverse dynamics of vehicle motion. The nonlinear relationship of steering assistance torque with vehicle speed and steering torque is analyzed into three functional modules. A new comprehensive model is proposed to analyze the characteristics of EPS steering assist based on a “comfortable driving style”, “sporty driving style”, and “multi-level driving style—comfortable driving style at low speed, sporty at medium speed, and heavy at high speed”, corresponding to three different power-steering characteristic maps.