Improving Steering Feel in Electric Power Steering Systems: A Model Reference Feedback Controller Approach

Jose Velazquez Alcantar

The introduction of electric power steering (EPS) systems has allowed automotive OEM’s to increase fuel efficiency and develop a myriad of driver assist functions such as park assist and active lane keeping. However, one of the biggest complaints about EPS systems is the lack of good steering “feel”. This paper introduces a model reference feedback control system aimed at improving steering feel. Detailed nonlinear models of column-mounted and rack-mounted EPS systems are derived using bond graphs to analyze the dynamics of the system. Reduced order linear model of the EPS systems are then derived for control development. A torque feedback controller is developed that allows engineers to quickly and easily tune the “feel” of the steering system via four tuning parameters on a reference model. A return-to-center controller is also developed to center the steering wheel whenever the driver releases it from an off center position. The two control systems are integrated together using fuzzy logic so as to determine when to use the return-to-center controller. It is shown through simulation studies that the final control system gives great tracking performance and that the use of fuzzy inference system allows the controllers to switch smoothly and appropriately thus showing potential to improve steering feel.

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