Study On Steering Wheel Shimmy Of The Hydraulic Power Steering System

Steering wheel shimmy is a complex vibration phenomenon occurred in a vehiclesteering system. It is the phenomenon that steering wheels vibrate around king-pinaxis when the vehicle travels in a straight road. As the existence of shimmy seriouslyaffects the handing stability, comfort and driving safety of vehicle, studying thesteering wheel shimmy has great practical value.Tyre imperfections caused by variations in manufacturing process take animportant role in affecting the steering wheel shimmy, although there are many factorsthat can influence steering wheel shimmy. Based on the theory, this paper analyzes thesteering wheel shimmy of the mechanical and hydraulic power steering system, andcarries a contrast between the two different steering systems. Firstly, by usingsimulation package ADAMS/car and FTire, this paper analyzes the effect of differenttyre imperfections on the steering wheel shimmy mechanism, such as static imbalance,dynamic imbalance, radial stiffness variation and tangential stiffness variation.According to the results, different type of tyre imperfection has different effects onshimmy vibration. Meanwhile, same type of tyre imperfections but different inmagnitude and location also have different effects on shimmy vibrations. Secondly, asthe suspension could transfer excitation energy, its vibration modal has certaininfluence on the steering wheel shimmy. In this paper, modal analysis of the frontsuspension has been conducted in ADAMS/Car to assess the modal frequencies andmodal shapes. Finally, based on comparative analysis of steering wheel shimmy in thetwo different types of steering system, we found that: due to the effect of spring damp-ing of the hydraulic cylinder, the hydraulic power steering system could control theshimmy at certain velocity interval. As a result, to a certain extent, the driver feelcould be optimized, the car driving comfort and stability could be improved.