Dynamic Characteristics Analysis Of Electric Vehicle Reducer Under Internal And External Excitation

With the transformation and upgrading of the global automotive industry,the development of high-performance electric vehicles has become a hot spot in the automotive industry.The car’s NVH(Noise,Vibration and Harshness)performance is one of the important indicators for evaluating car driving comfort.After years of continuous research and innovation,the car’s NVH technology has developed to an unprecedented level.In electric vehicles,the electric drive assembly replaces the engine of the traditional car,without the acoustic mask of the engine,the noise of the electric drive assembly has become the main noise source.At the same time,with the gradual increase in the application scenarios of electric vehicles,the electric drive assembly is developing in the direction of high speed,light weight and integration.As one of the core components of the power transmission system of electric vehicles,the NVH performance of the reducer is facing a new challenge.To this end,this article aimed to analyze the dynamic characteristics and evaluate the NVH performance of a certain type of electric vehicle reducer,and mainly completed the following tasks:(1)The time-varying meshing stiffness of the two-stage gear pair was calculated based on the potential energy method;An analytical model of the static transmission error of the gear pair of the reducer was established based on the slicing method,and the static transmission error of the two-stage gear pair with considering time-varying meshing stiffness and average meshing stiffness was compared,it was found that the two results differed significantly,and transmission error analytical model considering the time-varying meshing stiffness could better reflect the actual meshing state of the gear pair,and the result was of practical significance.(2)The static transmission error test of the reducer was completed.The static transmission error and shell deformation of the reducer were measured.It was found that the shell deformation had an obvious effect on the static transmission error,and a correction model of the static transmission error of the reducer was proposed through the regression analysis of the static transfer error analysis results and the test results.The model took into account the influence of shell deformation and manufacturing errors,and had higher accuracy.(3)The dynamic model of the vehicle power transmission system with the reducer was established.The key parameters of mass,inertia,connection stiffness and damping,bearing support stiffness and damping,time-varying meshing stiffness and meshing damping,and static transmission error of each component in the model were calculated.Finally,the equation of motion was solved by Runge-Kutta method to obtain the dynamic meshing force of each gear pair.(4)The vibration analysis model of the reducer was established,the dynamic meshing force was used as the excitation and loading condition of the vibration response analysis,and the vibration response of the measuring points on the surface of the reducer shell was simulated with the aid of finite element tools.At the same time,the NVH test of the reducer was completed.By comparing the test and the simulated vibration acceleration data,it was found that the two were in good agreement.The model was valid.(5)Based on the verified dynamic model of the vehicle power transmission system,the inherent characteristics of the system and the dynamic transmission errors under multiple working conditions were solved,and the spectral characteristics of the dynamic transmission error under each working condition were analyzed and discussed.The analysis results showed that under steady-state conditions,the maximum amplitude at the second mode frequency was 12 μm in the spectrum of dynamic transmission error.The torsional vibration of the wheel had a significant effect on the dynamic transmission error.the torsional vibration of the wheel would have a significant impact on the dynamic transmission error when the torsional damping between the units was not considered or the torsional damping was small.It was necessary to analyze the dynamic characteristics of the reducer under the model.The amplitude at the fundamental frequency of the meshing frequency of the first stage gear pair had a great contribution to the spectrum of the first and second stage dynamic transmission errors under the condition of uniform speed and power-off taxiing,and the meshing excitation of the first stage gear pair was the main source of vibration and noise problems;The fluctuation of the driving motor speed would stimulate the amplitude of the higher-order meshing frequency,and the side frequency appeared in the frequency spectrum,which made the possibility of resonance greater.Therefore,the fluctuation of the driving motor speed should be reduced.