A sliding mode observer of road condition estimation for four-wheel-independent-drive electric vehicles

A new strategy for the electric vehicle (EV) with individual four-wheel drive acquiring maximum acceleration while avoiding tire skid is proposed in this paper. The vehicle longitudinal dynamic model based on the LuGre friction dynamic was built. A sliding mode observer (SMO), which is based on the vehicle dynamic model, was proposed to estimate the slip of tires and vehicle speed under unknown road conditions by measuring electromagnetic torques and the angular velocity of four motors. Due to the slip estimation, the vehicle velocity sensor is not needed. The maximum torque of each motor can be determined in real time, thus the vehicle can acquire maximum acceleration without slipping. Finally, the control strategy proposed in this paper is verified by simulation of an electric vehicle model under different road conditions.