Research On Prediction And Optimization Of Radiation Noise Of Electric Vehicle Reducer

With the continuous development of the electric vehicles,the market for electric vehicles will be gradually expanded.It means that the attention of consumers to the electric vehicles' performances will be persistently increasing,and also means more rigorousness of regulations.As the core component of the electric vehicle transmission system,the reducer's performance not only affects the power and economy performances of the vehicle,but also affects the NVH performance.Its vibration and noise levels have a tremendous contribution to the overall noise level of the vehicle.Therefore,it is of great significance to research on vibration and noise characteristics of the reducer for the whole NVH performance control.This paper selects a reducer of an electric vehicle as the research object.Focus on the noise radiation prediction problem with the boundary element method,analyze its vibration and noise characteristics,and reduce its vibration and noise levels through the structural damping vibration mitigation technology and constraint damping treatment method.The main contents are as follows,(1)Based on SIMPACK software,a rigid-flexible coupling multi-body dynamic model is established,which consists of the two pairs of rigid gears,flexible transmission shafts,a flexible differential case and a flexible reducer case.Next,bearing forces are simulated under the maximum torque steady conditions,and provided the incentive condition for the subsequent research.(2)First,the finite element model of the reducer case is meshed,and the free boundary modal analysis and constraint boundary modal analysis are performed,so modal frequencies and mode shapes under the two boundary conditions are obtained.Second,in order to guide the modal test below,modal pre-test analysis is conducted and the locations and numbers of the test points are determined.Third,free modal test is performed and the accuracy of it is verified.Final,the validity of the finite element model is verified by the experimental versus finite element modality method.(3)To start with,the vibration response of the case is simulated using the bearing forces above.Next,the boundary element model and acoustic field mesh are established.What's more,the acoustic radiation response is simulated based on modal acoustic transfer vector(MATV)method,and the results,including acoustic power frequency response,pressure contour and field acoustic pressure frequency response,are analyzed.More important,the areas with more acoustic energy and the frequencies needed to be optimized are diagnosed through the application of panel contribution analysis.This provided a theoretical basis for subsequent optimizations and improvements.(4)Two optimization plans are identified,one of which is a local reinforcement scheme and the other is the combination of local reinforcement with structural damping vibration mitigation technology.Then the viscoelastic material is determined as the damping material.And then,the two optimization plans are conducted.Afterwards,the modal damping ratio of plan 2 is obtained using the modal damping identification technique.Finally,the differences between modal frequencies and mode shapes,vibration response and acoustic response of the origin and the optimizations are analyzed.The conclusion is that plan 2 has more significant effects than plan 1 on vibration and noise reduction.The RMS sound power level of plan 2 decreased by 2.32dB(A),and the RMS sound pressure levels at the three acoustic field mesh nodes decreased by 2.72 dB(A),2.19 dB(A)and 1.92 dB(A),respectively.