# Estimation of Vehicle Body Side-slip Angle for Vehicle Dynamics Control Applications

Samuel Alfredsson ; Gabriel Trönnberg
Göteborg : Chalmers tekniska högskola, 2008. 64 s. Diploma work - Department of Applied Mechanics, Chalmers University of Technology, Göteborg, Sweden, ISSN 1652-8557, 2008.

The aim of an electronic stability control system in a passenger car is to assist the driver in order to avoid accidents by preventing unstable/uncontrollable behaviour of the vehicle. Most electronic stability control systems in cars of today are designed to minimize the difference between the measured yaw rate of the vehicle and the by the driver desired counterpart. This approach definitely affects the vehicle safety in a positive manner although the function and accuracy of the electronic stability control system can be extensively improved if the vehicle body side-slip angle is known. However, to measure the vehicle body side-slip angle is a complex task and requires expensive sensors why estimation of this angle is the only realistic option for use in production vehicles at this time. The objective of this work is to estimate the vehicle body side-slip angle, preferably without extending the sensor technology available in a modern vehicle. The estimation algorithm should be based on a linear model-based observer and validated against real vehicle test data. In this work a planar case is assumed, i.e. the road bank and slope angles are equal to zero. Furthermore, it is assumed that a linear vehicle model describes the vehicle dynamics with sufficient accuracy for this application. Since a linear vehicle model (especially a linear tire model) does not have the ability to perfectly describe the lateral dynamics of the vehicle an algorithm for continuously updating the cornering stiffness used in the tire model is developed. Furthermore, it is realized that a single observer tuned for a specific road surface friction does not produce an estimate of the vehicle body side-slip angle that is accurate enough on roads with a wide variety of surface friction. Therefore, the solution consists of three observers tuned for three different surfaces run in parallel, resulting in three estimates of the vehicle side-slip angle. Due to this the final component of the estimation algorithm is a system that estimates the current surface friction and based on this knowledge arbitrates between the three estimates produced by the observers in order to obtain the final estimate of the vehicle body side-slip angle. The estimation algorithm is validated against real test data presenting results that indicate that the algorithm works in a satisfactory way. Implementing this estimation algorithm in an ESC system could improve its ability to maintain vehicle stability.