Vibration Analysis And Optimization Of Steering System Of A Car Under Idling State

The NVH performance of vehicle, namely noise,vibration and harshness, is an important evaluation index of ride comfort. And it also affect the other performance of the vehicle. Many enterprises which in order to maintain the competitiveness of the market will give a lot of investment to improve the NVH performance. So there is no doubt about the importance of vehicle NVH performance.In the process of NVH subjective evaluation of a car, after the calibration of the mount system, the vibration of the steering wheel was found to be still overlarge under the idle condition when the air conditioning(AC) was switched on, which severely affected the cosiness of the vehicle. To solve the problem, Test investigation on the reason of the steering wheel vibration, and optimized the steering system structure through CAE, and verification via experimental to decrease the shake of steering wheel.The main research contents as follow:First of all, the mechanism of steering wheel vibration at idle speed was introduced, based on which the vibration test of steering wheel with LMS TEST.Lab was done to solve the problem. It was concluded that the rotating speed frequency of the cooling fan had a great impact on the steering wheel vibration. By using experimental modal analysis theory and method to search the excitation source, the main transfer path and the response points, it was observed that modal parameter of condenser-radiator-fan module(CRFM) and steering wheel were identical with cooling fan’s rotation frequency, which were the main cause of steering system vibration at the idle.Secondly, establishing the finite element simulation model of steering system constrained in the half of body-in-white(BIW). The front and back swing and left and right swing modal frequency of steering wheel and several order natural frequencies of CRFM were calculated. The accuracy of the finite element model was verified by comparing simulation modal results with corresponding test modal results. Based on this model, cooling fan excitation was applied to the CRFM by LMS Virtual.Lab, the frequency response of the steering system was analyzed, which would providetheoretical basis for the subsequent optimization of steering system.Then, modal sensitivity analysis and optimization design of steering wheel were carried out. The front and back swing and left and right swing modal frequency of steering wheel which were difference of 5.4Hz were to avoid cooling fan’s rotation frequency. The feasibility of the scheme was verified via the vibration test of steering wheel. But the objective test value of the steering wheel vibration was still slightly larger, it still need to continue to improve.Finally, after changing the isolator’s construction of CRFM, the yaw modal frequency of CRFM was to avoid the cooling fan’s rotation frequency through CAE modal analysis. Comparing simulation modal with test modal after improvement verified the feasibility of the scheme.The amplitude acceleration and RMS acceleration of steering wheel’s X and Y were significantly reduced. The steering wheel vibration problem was resolved.The research showed that the combination of test analysis and the CAE analysis method had better practicality and feasibility in solving the steering wheel vibration, it provided a reference for the future of the NVH engineering design and optimization of the steering system.