Estimation of tire-road contact for integrated control applications in current vehicles

Current vehicle control strategies aim at the integration of several actuator algorithms of the vehicle. This means a combination of the available actuators according to multiple optimization criteria due to several targets. One goal is the comfort of the driver for cruising, another objective of the optimization is the agility and stability of the vehicle during cornering. Both targets require different setups of the vehicle and different tunings of the actuators that can be achieved by an integrated control system. Such an integrated control system requires a complete knowledge of the vehicle state. This includes the estimation of the longitudinal and lateral motion of the vehicle as well as the estimation of rotation (yaw, roll, pitch) and vertical movements of body and wheels. All this information is included in a vehicle state estimator (VSE) and it builds one basis of the integrated control approach. An important parameter of the VSE is the estimation of the tire-road contact, because the contact from tires to the road provides the stabilizing forces for traction and lateral movements of the vehicle. The friction coefficient varies from 1 to 0.1 and this means drastic changes in the forces that the vehicle is able to build up in the tire-road contact patch. This paper aims at the estimation of this important friction coefficient that is included in the estimation and in the control algorithms of the vehicle