Linear Analysis of a Vehicle with Four-Wheel Steering

Linear anaylsis is a frequently used tool to aid in the understanding of directional response. Understeer gradient, characteristic or critical speed, and yaw rate and lateral acceleration response times have been particularly helpful.

This paper studies the use of these measures in the context of vehicles with four-wheel steering. The paper shows that, with only a slight change in SAE definitions, the understeer gradient retains its traditional meaning, but the characteristic speed will depend on the steering system if the steady state part of the steering control algorithm is speed sensitive. The paper also discusses testing for the understeer gradient, and the anticipated changes in response time due to four-wheel steering.