Road condition estimation and longitudinal control for electric vehicles

This paper presents a road condition estimator based on the wheel acceleration and a torque controller for a vehicle equipped with an electric motor. In the first step, the instantaneous friction coefficient and the maximum friction coefficient between the wheel and the road are estimated, without knowing a priori the road conditions. Next, a longitudinal controller is set up to ensure the two main functions : braking with anti-skidding function and traction control using the electric motor torque as a unique actuator. Unlike the torque generated by classic internal combustion engines, the torque of electric motors is available almost instantaneously. In addition, it can be measured on-line which means that advanced control techniques can be applied. The approach presented in this paper relies on recent algebraic techniques for numerical differentiation and diagnosis, and a feedback sliding mode control scheme to ensure the vehicle is operated at the maximum friction zone in both acceleration and braking phases, along with a given reference speed to track.