The Research Of Vehicle Front Wheel Shimmy With Clearance In Steering System

Front wheel shimmy is the phenomenon that steering wheels vibrate around king-pin axis with a certain amplitude and frequency when the vehicle travels in a straight road. It performs negative influence on power performance, fuel economy performance, vehicle handling stability, ride comfort and driving safety.Many factors contribute to steering wheel shimmy of the vehicle, including nonlinear elements, such as clearance of the joints of steering mechanisms. Steering trapezoid mechanism, which is the important part of mechanism of steering, can be modeled as a four-bar linkage mechanism. For this reason, this dissertation has focused on the influence of clearance on the four-bar mechanism and steering wheel shimmy of the vehicle. The influences of other factors on shimmy are also analyzed, and several effective measurements for shimmy attenuation are discussed. The research work is mainly as follows:1. The dynamic model of a four-bar mechanism with clearance is established. The influence of clearance on the response and stability of the system is analyzed. The analysis shows that the movement state of the system partly depends on the clearance.2. The mechanism of steering wheel shimmy of the vehicle is analyzed from the standpoint of mathematics. Based on the nonlinear dynamic model of the four-bar linkage mechanism, the six-degree dynamic model of vehicle steering wheel shimmy with clearance and dynamic model of the tire with consideration of side fore are established.3. Based on the mathematic model of vehicle steering wheel shimmy, the simulation model of vehicle steering wheel shimmy is constituted with MATLAB&Simulink. The simulation results show that clearance is a key factor that contributes to chaos of the system. Moreover, driving speed, steering gear stiffness, steering gear damping and related parameters of tire are critical parameters for shimmy. And appropriate ranges for the value of these parameters are presented, which provide an effective method for attenuation of the shimmy.