Tire Modeling and Friction Estimation

Sammanfattning: New system technologies are continuously improving the performance of vehicles regarding comfort, stability, environmental stresses, and safety. Novel sensors are developed and used together with advanced control algorithms and faster and more accurate actuators to help the driver to maneuver the vehicle in a safer way. The physical traction limit set by the friction between the tires and the road can, however, not be overridden. The behavior of tires is, therefore, an important issue since it determines the possibilities to control the vehicle. One essential task for the vehicle control system is to be able to fully utilize these limits. Another is to assist the driver to choose an adequate driving style, adapted to the actual conditions. A method to derive the tire forces for simultaneous braking, cornering and camber, by combining empirical models for the pure behavior of each of respective action is presented in the thesis. The method is based on the physical foundation brought by the simple, but well-suited brush model theory. The pure-slip tire models can be given as empirical models or as raw tabular data. The implementation is verified to be well-working and computationally sound and good results are obtained in validation with the available empirical data. A new type of on board brush-model based friction-estimator using the local measurements on the vehicle is also proposed. A major invention is the way of collecting the measurements into bins, such that the available data used for optimization is evenly weighted along the force and slip axis. Experimental data has been collected and evaluated to ensure the validity of the brush model during certain conditions. The estimator has been implemented and validated on a personal car. The wheel speed signal is an essential signal in many system applications. Based on problems observed during performed measurements, a few ways to reduce the noise on the signal, without adding any phase shift or time delay, are discussed in the thesis.