Estimation of Tire Grip Margin Using Electric Power Steering System

This paper develops an estimation method of tire grip margin from sensor signals of an electric power steering system and vehicle stability control system. Tire grip margin is defined as a ratio of tire force margin to maximum tire force that corresponds to friction characteristics between tire and road. In this paper, SAT (Self Aligning Torque) can be described as a function of the lateral and longitudinal forces of the tire and the tire grip margin, and an estimation method of the tire grip margin is proposed. The estimation method is based on a brush model, so that the robustness of the estimation is verified by applying the method to a magic formula tire model. Furthermore, on line identification algorithm, which adapts to change of tire characteristics such as inflation pressure and types of tires, is applied to estimation method of tire grip margin for practical use. The estimation method is evaluated by experiment on a proving ground that has a constant friction coefficient between tire and road.