Motion of a Four-Wheel-Steering Vehicle Subjected to Nonlinear Lateral Tyre Forces

摘要

Turning of a vehicle cannot be well controlled by only steering the front wheels due to the large yaw rate and sideslip angle of a vehicle body moving in high speed. The four-wheel-steering (4WS) technique is thus developed over the past decade. Various vibration models and control strategies for 4WS vehicles were reported[l-3]. However, few publications in current literature dealt with the dynamics of the 4WS vehicle/driver closed-loop system with nonlinearity of the lateral tyre forces taken into account. A new methodology of modelling for the 4WS system is developed in the present work, with the consideration of the nonlinear tyre forces and steering mechanism. Based on the model established, the steady state motion of the vehicle is determined. The stability of a typical steady state motion is further analysed by the bifurcation theory in order to assess the dynamical behavior of the vehicle before and after a loss of stability. The Hopf bifurcation of the steady state motion is evident.