Dynamic Modeling And Analysis Of Independent Suspension Vehicle Shimmy With Consideration Of Clearances In Steering System Movement Pairs

McPherson independent suspension and rack and pinion steering mechanism are widely used in passenger cars, but the shimmy research on this type of vehicle is not deep enough. In engineering practice, vehicle shimmy due to wearing of the movement pairs in steering system is very common. Such a vehicle with McPherson independent suspension and rack and pinion steering mechanism should be as a research object, exploring the mechanism of occurrence of shimmy and study the sensitive factors that influence shimmy system.The structural features of this type of independent suspension automotive is using rack and pinion steering diverter, "five-linkage " type of steering transmission mechanism, disconnect front axles and wobble kingpin axis. According to the statements above, considering the influence of clearances in movement pairs in steering mechanism, an 8-DOF dynamic model of independent suspension vehicle shimmy system was established with Lagrange equations. The model is valid by comparison between simulation results by Rosenbrock algorithm with experimental data and empirical data from former researchers. Based on nonlinear dynamics analysis method, the effect of vehicle structural parameters to the response of shimmy system is analyzed, such as the clearance factor, the tire factor and the suspension factor. The studies shown that the size of clearance, the contact stiffness of clearance, the tire relaxation length, the unsprung mass, the caster angle have significant impact on the shimmy, the relevant conclusions can provide theoretical support for engineering practice.Mechanism of self-excited shimmy is analyzed in the end of the thesis. The power from the aligning torque to the swing angle because of the irregular phase difference between swing angle and sideslip angle is proved. And the severity of shimmy is directly determined by the energy input. As the internal force, the clearance contact force also exist energy input to the system, it is understood that the negative damping trend of the system is became larger by the clearance and the occurrence of self-excited shimmy is promoted.