Study On The Bifurcation And Chaotic Characteristics Of Four-wheel Steering Vehicle Handing System

As a new automotive technology, Four-wheel steering technology can improve vehicle stability at high speeds and improve steering sensitivity at low speeds.The paper is focused on the lateral dynamics of Four-wheel steering vehicle. In order to provide a more reliable theoretical basis for the vehicle stability control, this paper explore the automotive steering instability mechanism at the point of nonlinear dynamics.In order to study the lateral instability mechanism from the perspective of nonlinear dynamics, a two degrees of 4WS vehicl car car model was established. Magic formulas was selected to describe the mechanical characteristics of the tire, ignoring the impact of the steering system, and a sine curve was selected as the input stimulus of front-wheel angle. The paper established a Matlab simulation model based on the differential equation of 4WS vehicle 2-DOF system. Using Fourth Order Runge-Kutta method, I got the global bifurcation diagram of the sideslip angle with the front corner frequency. Using Lyapunove ’clone’ method, the paper analysised the way in which the stable periodic motion toward Chaos in the process.Considering the relationship between body roll and planar motion, a 3-DOF model of 4WS vehicle was established. The square formula considering load transfer was selected to describe the mechanical characteristics of the tire. Using center manifold theory to reduce the dimension of the system to determine whether the system has a saddle- node bifurcation. The paper studied the way in which the saddle-node bifurcation toward instability to judge whether the 4WS can improve the stability of the system in critical situations compared with traditional 2WS.The dynamic equation of 4WS vehicle considering body roll and load transfer was established to analysis the stability region and bifurcation characteristics and analysis the Effect of different parameter.In a word, my research on 4WS lateral dynamics exploring the automotive steering instability mechanism at the point of nonlinear dynamics can provide a good support for further research of 4WS technology.