Robust estimation of road friction coefficient using lateral and longitudinal vehicle dynamics

Vehicle active safety systems stabilise the vehicle by controlling tyre forces. They work well only when the tyre forces commanded by the safety systems are within the friction limit. Therefore, knowledge of the tyre/road friction coefficient can improve the performance of vehicle active safety systems. This study presents four methods to estimate the friction coefficient based on four different excitation conditions: medium lateral excitation, large lateral excitation, small longitudinal excitation, and large longitudinal excitation. For the lateral excitation cases, the estimation is based on vehicle lateral/yaw dynamics and Brush tyre model, whereas for the longitudinal excitation cases, the estimation basis is the relationship between the tyre longitudinal slip and traction force. These four methods are then integrated to increase the working range of the estimator and to improve robustness. The performance of the integrated estimation algorithm is verified through experimental data collected on several surface conditions.