Road friction estimation using adaptive observer with periodical σ-modification

We propose an adaptive observer for estimation of a road friction coefficient, which is important for vehicle control. The observer needs the driving torque and wheel speeds of the driven and non-driven wheels as inputs. The road friction coefficient is assumed to be represented by a product of a known function and an unknown parameter to be estimated by an adaptive law. It is shown that non-robust adaptive law can obtain the true value, if there are no disturbances. However, it diverges when disturbances are added. Periodical σ-modification is proposed here as a robust adaptive law. The estimation robustness against disturbances can be improved with the law. Numerical simulation results are presented to show the effectiveness of the adaptive law