Research On Low Frequency Structural Road Noise Control Based On Damping Characteristics

The NVH(Noise,Vibration and Harshness)performance of passenger vehicles is one of the main factors affecting the comfort of the vehicle,so vibration and noise reduction is an eternal theme in automotive engineering.Damping material is one of the most widely used non-metallic materials in automobile body,it is often used in areas such as floors,car roofs,firewalls,spare tire cabins,etc.,and has the effect of damping structural vibration and reducing interior noise.However,in the existing mass production vehicles,the ineffective area of damping material layout is large,which does not conform to the lightweight principle under the optimal NVH performance.Therefore,it is of great significance to guide the research on the layout and optimization methods of vehicle body damping layers.In this thesis,the method of numerical simulation and experimental testing was combined.Firstly,the simulation prediction method for the surface damping treatment of thin panels was studied,which provides a simulation basis for the vehicle body damping treatment.Secondly,taking a pure electric vehicle as the research object,the transmission path of low-frequency structural road noise was analyzed,and the vehicle body panels that contributed a lot to the low-frequency structural road noise in the vehicle were diagnosed.Finally,the method of optimizing the layout of the body damping layer was studied,and the vehicle body floor was used as an example to optimize the placement position of the vehicle body floor damping layer.The optimized body damping layer not only improves the NVH performance of the vehicle body,but also reduces the amount of damping material used to meet the lightweight requirements of the body.The main research contents are as follows:(1)The construction of the finite element model of the research object and its modeling accuracy verification.A fixture finite element model holding a damped composite panel and a vehicle body-in-white finite element model were established,and the accuracy of the model establishment was verified by experimental modal analysis,avoiding large calculation errors caused by too low modeling accuracy.(2)Performance testing of viscoelastic damping materials and fine modeling of free damping structures.The dynamic characteristics of the viscoelastic damping material were expatiated,and the parameter of a vehicle viscoelastic damping material were identified by means of test,which provides parameter input for the subsequent finite element modeling of damping composite panels.The finite element modeling technology and dynamic characteristics analysis method of free damping structure were studied.The vibration and acoustic vibration tests of the damped composite panel based on fixture were designed.The accuracy of the simulation prediction method of the surface damping treatment of the thin panel was verified by comparing the simulation calculation results with the test results.(3)Identification of body panels with a large contribution of low-frequency structural road noise in a pure electric vehicle.Taking a pure electric engineering sample vehicle as the research object,the noise level in the vehicle was tested through experiments,and it was found that the low-frequency structural road noise in the vehicle was serious under the conditions of medium and high constant speed.The transmission path of low-frequency structure road noise was analyzed,and the dynamic stiffness characteristics and NTF(Noise Transfer Function)of the installation point of the body absorber shock absorber were tested.The test results show that the original dynamic stiffness of the shock absorber does not meet the requirements at certain frequencies.The NTF of the right rear shock absorber also has problem frequencies.The calculation and analysis of the contribution of the NTF of the right rear shock absorber installation point to the vehicle body panels at the frequency exceeding the standard,and the vehicle body panels that have a greater contribution to the interior noise at the frequency exceeding the standard were obtained.The damping materials laid on these vehicle body panels can effectively increase the NVH level of the vehicle body.(4)Optimization of the placement position of the vehicle body damping layer and verification of the optimization effect.Taking the body-in-white floor as the research object,based on the calculation result of the equivalent radiated sound power and the cloud diagram of the node acoustic contribution at the peak points,the vehicle body damping laying position was optimized.The excitation was applied to the four shock absorber installation points of the Trimmed Body,and the NTF of the vehicle body floor under no damping,full damping and damping optimization were calculated respectively,and the effects of damping and noise reduction after the optimization of damping were verified.