A sliding mode observer for tyre friction estimation during braking

This paper describes a new model based scheme for estimating the coefficient of road surface adhesion (mu) based only on wheel speed measurements. A sliding mode observer is proposed based on a LuGre friction model and a simple representation of the vehicle. The observer is driven by measurements of the wheel speed and the applied brake pressure. The observer is designed in such a way that the output of the observer tracks the measured wheel speed perfectly i.e. a sliding motion is obtained on the output estimation error. It is demonstrated that the nonlinear output error injection signal necessary to maintain a sliding motion gives information about the coefficient of adhesion