Road condition estimation for traction control in electric vehicle

The target of our project is to realise a novel traction control system for an electric vehicle with four independently controlled in-wheel-motors. In each in-wheel-motor, the optimal slip ratio control is implemented beforehand to prevent wheel slip for vehicle stability control. The optimal slip ratio control is achieved by maintaining the slip ratio to the value to give the maximum road friction. This means that the driving force of the vehicle is fixed at its maximum level. As the driving force is affected by highly nonlinear adhesion characteristics between tire and road surface, real-time generation of the optimal slip ratio is necessary while the vehicle is moving. To estimate the adhesion characteristics, only the estimation of the slope of road friction curve is enough. To this aim, in this paper, the driving-force observer is newly designed to detect the road friction coefficient and the fixed-trace algorithm is applied to the slope estimation. The effectiveness of the proposed method is confirmed by simulation and experimental data obtained by laboratory-made electric vehicle "UOT Electric March".