Control Research Of Vehicle Door Abnormal Vibration Based On The Transfer Path Analysis

Severe vibration problem of vehicle door in driving condition has large influence on evaluation of the vehicle quality from customers.Reducing the door vibration response is of great importance to design h igh quality door system and improve the ride comfortableness of the vehicle.The core technique of the door low vibration response design lies in the accurate prediction of door vibration response and optimization of the key design parameters.In the present thesis,the SUV door abnormal vibration problem which occurs when driving on the washboard pavement was taken as the research target.Based on the experimental and simulational techeniques,the causes of the door abnormal vibration problem were analyzed.And eventually the critical components of door vibration transfer process were recognized,namely chassis rubber bushing,door seal strip and door structure system.The dynamic stiffness calculation method of rubber bushing,the equivalent modelling of the door seal strip,and sequential optimization reliability analysis method base on maximum entropy were studied.These methods were used i n the door low vibration level design and the door abnormal vibration problem was solved.The main research contents and conclusions are as follows:(1)The door modal experiment and road test of door abnormal vibration problem were conducted.The finite element(FE)model of full vehcle was established and verified by the experimental results of door modal experiment and road test.Based on the experimental and simulational results,the three reasons of door abnormal vibration problem were identified.The first one is that the road excitation from washboard pavement generates the full vehicle vibration,which belongs to the forced vibration.The second reason is that the chasis structure is unsymmetric results in the the door vibration levels on the right and left side are different.The last one is that the modal frequency of door structure and frequency of road excitation are close,which leads to the door structre resonance.(2)The overlay model of rubber material was investigated and FE model of rubber bushing was established.The influence of excitation frequency,amplitude and preload on the dynamic stiffness of rubber bushing were analyzed.Based on the phenomenon that the dynamic stiffness curves of rubber bushing under different preload and excitation amplitude are parallel,a modified dynamic stiffness calculation method of rubber isolator considering frequency,amplitude and preload dependency was proposed.The proposed dynamic stiffness calculation method was utilized in the door vibration transfer path analysis.Through comparing the simulational and experimental door measured point accelerations,the correctness of the proposed method is verified.The results of transfer path contribution analysis show that in condition of excitation frequency at 26.5 Hz,the main cause of door severe vibration problem is the excessive transmitted forces at the rear stabilizer bar bushing in the x-direction and z-direction.In order to reduce the transmitted forces,a bushing stiffness softening(decreasing by20%)solution was adopted.The simulational result shows than it can reduce door acceleration by 20.1% compared to the innital value.(3)Based on the overlay model of rubber material,a door seal strip FE model was built,and the effect of excitation frequency,amplitude and compression on dynamic stiffness on seal strip was analyzed.An equivalent model was proposed,which can be used to accurately characterize the dynamics stiffness of seal strip.The proposed model was validated by comparing the simulated mode and vibration transfer function results with experimental ones.Based on the equivalent model,the effect of seal strip parameters on vibration transfer function of door was investigated.The r esults show that hyperelastic parameter,section height,section width and compression of seal strip have great effect on the vibration transfer function of door.In order to tackle the door abnormal vibration problem,a solution was proposed in which the compression of seal strip was changed from 4 mm to 6 mm.It can reduce the peak value of vibration transfer function by 39.9% compared to the innital value.(4)The sequential optimization reliability analysis method base on maximum entropy were studied.A numerical model of reliability based optimization and design was established,in which the thickness of door components were taken as the r andom design variants;reliability of the door stiffness,door modal frequency in trimed body strate,side impact intrusion and weight were regarded as constrints;minimizing the peak value of the door vibration transfer function were served as optimization objective.Sequential quadratic programming method was utilized to obtain the optimum.The results show that,the maximum entropy based sequential optimization reliability analysis method is more efficient that the traditional method.Optimum from the reliability method can ensure the reliability index of door stiffness,modal frequency,side impact intrusion and weight,and at the same time obtain 9.2% vibration suppression effect compared to the initial value.(5)In order to find the best solution for the door abnormal vibration problem,different combinations of optimizational measures were proposed.Adopting the simulational technique,the vibration reduction effects of different combinations were compared.Based on the comparasion results,the combinations of the rear stabilizer bar bushing stiffness softening(decreasing by 20%)and redesign of compression of seal strip from 4 mm to 6 mm was chose as a final solution.The road test shows that this solution can reduce the door accelearion peak value by 43.4% compared to the initial value,which prove to be an excellent sulotion for this door abnormal vibration problem.