Vehicle state and friction force estimation using nonlinear observer strategies

Approaches to estimate friction forces and vehicle states are presented in this paper. Firstly, based on the dynamical equations of the wheels, the estimates of the longitudinal friction forces are achieved by means of sliding mode unknown input estimation technique. Secondly, using the longitudinal friction forces estimated and the nonlinear relation between lateral and longitudinal friction force of the tire, a new nonlinear vehicle dynamic model is established. Then, based on this model, nonlinear observers for estimation of longitudinal and lateral velocities are modified and extended to work for different road surface conditions and in critical driving maneuvers. The input-to-state stability results are given. The friction forces and vehicle states estimated are compared to those of the simulator veDYNA. The results show the effectiveness of the proposed approaches.