Estimation of road friction for enhanced active safety systems: Dynamic approach

Frictional coefficient between tire and road is difficult to detect but crucial for vehicle active safety systems. Several approaches for friction coefficient estimation were developed based on various vehicle dynamic phenomena. This paper suggests nonlinear state observers that use vehicle dynamics, steering system dynamics, and tire force dynamics as a viable approach. The stability of the observer highly relies on observer gains. We present two different ways to select the gains and discuss the stability of the observer. Furthermore, we introduce a hybrid estimator which uses a nonlinear observer and a nonlinear least square method which provides enhanced performances. These estimators are verified using the commercial software, Carsim, under various scenarios.