Analysis Of Front Wheel Shimmy And It's Affected Factors Of A Coach

Front wheel shimmy is the phenomenon that steering wheels vibrate around king-Pin axis when the vehicle travels in a straight road. It performs negative influence on Power Performance, fuel economy performance, vehicle handling stability, riding comfort and driving safety. There are two forms of front wheel shimmy: forced vibration and self-excited vibration. As the self-excited vibration is the vibration of nonlinear dynamic system-specific phenomena, a steering wheel shimmy model of a coach with five degrees of freedom is constructed which include nonlinear elements, such as dry friction, clearance and so on. Studied the mechanism of the occurrence of shimmy and explore effective measurements to reduce the shimmy. Details are:1. Taking a coach of domestic for the study, the establishment. A shimmy system dynamics model of the coach with five degrees of freedom is established. Elaborated that how to deal with these nonlinear elements of dry friction, clearance and so on, which included in the model.2. Applying nonlinear dynamical system theories, Elaborated that Steering wheel self-excited shimmy is a phenomenon of stable limit cycle vibration when the shimmy system occurred Hopf bifurcation. Determine shimmy system stability under different speeds According to Routh-Hurwitz criterion. Determine the coach shimmy system at the self-excited shimmy of the Hopf bifurcation point, and further to determine the stability of limit cycles.3. Through MATLAB&Simulink software, a steering wheel shimmy simulative model of the coach is constructed. Check the theoretic analysis results using simulative results, and obtain the characteristics of Steering wheel occurring forced shimmy, self-excited shimmy, coupled shimmy. Obtain the curves concerning the relationship between velocity, steering gear parameters, tie-rod parameters, center of mass location, kingpin caster angle and amplitude of the steering wheel self-excited shimmy. Find out the sensitive parameters and its suitable range which affect shimmy can effectively reduce or eliminate self-excited shimmy of the coach.4. The thesis focuses on analysis the influence of horizontal pulling lever clearance, kingpin dry friction on the self-excited shimmy of the speed range, swing amplitude effects. Studies have shown that clearance can increase the self-excited shimmy of the speed range, limit cycle amplitude; dry friction to a certain extent, can inhibit the occurrence of self-excited shimmy.