Active Rear Wheel Steer Systems Analysis - An Actuator Requirements Approach

Abstract

The purpose of this Master’s Thesis project is to analyze active rear wheel steer (RWS) systems from a vehicle handling and stability point of view, with focus on small rear wheel angles. The main objectives are to develop an active RWS system and specify requirements for the RWS actuators, such as maximum rear wheel angle, maximum actuator speed and maximum wheel forces, in order for the system to work satisfactory. The active RWS system is based on a linear vehicle dynamics model, which generates the desired vehicle dynamics. The RWS control has two components, one feedforward and one feedback control component. The feed-forward control is a function of the front wheel angle, whereas the feedback component is based on linear control theory. The RWS system is implemented in MATLAB/Simulink and its performance is evaluated in a number of driving scenarios, using a vehicle model with 50 degrees of freedom. The simulations show that the active RWS system improves vehicle stability in all of the performed driving scenarios. The maximum speed of the RWS actuators should be at least 25 degrees per second, the maximum rear wheel angle should be at least 1.5 degrees and the force that the RWS actuators should be able to withstand is about 4.0 kN.