Analysis And Control Of Vibration And Noise Of A Passenger Car Body Structure

With the continuous improvement of people's living conditions and the increasing strength of automobile research and development in China,the demand for comfort of automobile consumers is becoming higher and higher,which compels enterprises to pay more and more attention to the noise and vibration performance(NVH)of automobile.Based on the NVH development process and the body NVH target system,the CAE analysis and structural optimization of the NVH performance of the Body in Prime(BIP)and the Trimmed body are carried out in combination with the NVH development project.The performance of the body NVH is effectively controlled in the CAE stage.The main research work of this paper is as follows:First of all,the NVH characteristics are analyzed based on BIP.According to the finite element modeling specification,the BIP model is established and the structural modal analysis is carried out.The first order torsional modal frequency of the BIP is 33.5Hz and the first order bending modal frequency is 49.1Hz.The similarity degree of the model is more than 95% and the model reaches the design target value.The finite element model is available.The finite element model is proved to be available.According to the basic principle and method of the key joint extraction of the BIP,the torsional stiffness of the eight joints was studied.The results showed that there was a problem of insufficient torsional stiffness in some joints.The torsional stiffness of the rear end of the joint on the B column was 46.11% weaker than that of the standard car.The mechanical properties of twelve key sections were studied.The section extraction and the calculation method of mechanical properties were focused on the front door hinge beam L2.The equivalent dynamic stiffness of the main installation points of the BIP is analyzed.The results show that the left suspension Y direction is 5568N/mm,the right suspension Y direction is3255N/mm,the 3#Z direction is 291N/mm,which is not reached the target value,and the structure optimization is needed in the later period.Then,the NVH characteristic is analyzed based on the Trimmed body.The acoustic finite element model is established and the acoustic modal analysis is carried out to determine the sound pressure distribution and frequency of the sound chamber in the cab.The model of the Trimmed body is established and the transfer function analysis is carried out.The results of the noise transfer function analysis show that the acoustic pressureresponse of the rear damper,the suspension arm and the exhaust hook exceed the target value.The most serious problem is the 3# hook,the peak sound pressure is 72 dB,exceeding the development target 12 dB.The vibration transfer function analysis results show that the acceleration responses of all excitation points satisfy the target values.Finally,based on the development goal of NVH,the optimization design of NVH performance is carried out.Modal is the focus of vibration development of vehicle body structure,and the main method of modal optimization is summarized.The NVH analysis item,which is not qualified,is optimized one by one.Three optimization schemes are proposed for the problem of the left suspension Y direction of dynamic stiffness.The comparison results show that the dynamic stiffness of the third schemes is 6302N/mm and basically reaches the standard.A comprehensive analysis of the reason that the noise transfer function is not up to standard under the 3# excitation of the exhaust system is analyzed,and three optimization schemes are proposed.The first one reduces the maximum peak sound pressure by 8dB to 64 dB,and the effect is obvious.Using the analysis method of panel acoustic contribution,the frequency of the peak sound pressure and the sound pressure contribution of each plate are determined by the partition of the plate parts around the sound cavity.In the later stage,the sample vehicle is contributing the larger plate to suppress the plate vibration to reduce the sound pressure.The optimization schemes are verified on the final model.The NVH analysis items reach the standard rate of over 90%,and the NVH performance development of the vehicle body is effectively controlled in the CAE stage.The research method and process are instructive and referenced for NVH performance development of vehicle body.