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 vehicle. The observer is driven by measurement 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.