Analysis Method On Noise Radiated From Shell-typr Driving Motor Of Electric Vehicle

The main structure of the electric vehicle driving motor that radiates noise to the outside environment is the motor housing,which consists of a cylindrical shell with an irregular cross-section.It is difficult to solve the radiated noise by the analytical method,while the methods of finite element analysis and boundary element analysis have drawbacks like the difficulties of modeling and popularization.In this thesis,the motor housing of a certain shell-type driving motor used in electric vehicle and its equivalent model is taken as the research object.Through modal simulation and experiments,as well as acoustic radiation simulation and experiments,the radiated noise problems of the motor housing are investigated.The main conclusions of this study tasks are as follows:Firstly,the finite element model of an equivalent cylindrical shell of the motor housing is established,and modal simulation analysis is performed to determine the equivalent cylindrical shell model,which is similar to the modals of the motor housing.According to the weighted average method,the weighted average of the thickness of the motor housing,namely the "weighted thickness",is calculated.Establish multiple equivalent cylindrical shell models of motor housing with different thicknesses.Modal simulation calculation analysis show that the modal characteristics of the equivalent cylindrical shell model based on the "weighted thickness" are close to that of the motor housing.Secondly,a boundary element model of the equivalent cylindrical shell of the motor housing is established,and the vibration and acoustic radiation simulation analysis is carried out to determine an equivalent cylindrical shell model that is similar to the motor housing ?s.By comparing the acoustic radiation response of the motor housing and its equivalent cylindrical shell model in different frequency bands,it is found that the radiation sound power and acoustic radiation efficiency curves of the equivalent cylindrical shell model with a thickness value of the "weighted thickness" is similar to that of the motor housing.It indicates that the vibration sound radiation response of the equivalent cylindrical shell model based on "weighted thickness" is close to that of the motor housing.Then,modal experiments and acoustic radiation experiments are implemented on the motor housing and the "optimal" equivalent cylindrical shell model based on "weighted thickness",to verify the accuracy of the "optimal" equivalent cylindrical shell model.The results of free mode experiment and acoustic radiation experiment show that the two structures have high mode shape coincidence,close natural frequency,good consistency of sound pressure level curve,close RMS value of sound pressure level and good consistency of overall results..It is demonstrated that the motor housing can be equivalent to a cylindrical shell model based on the "weighted thickness" when calculating the vibration sound radiation,and the feasibility of the establishment of the equivalent cylindrical shell model of the motor housing using weighted average method is also verified.Finally,various thin shell theories are applied to calculate the circumferential natural frequencies of the "optimal" equivalent cylindrical shell model based on "weighted thickness".Comparing and analyzing the results with experiments,it is found that the Flügge theory is more suitable for this cylindrical shell.Based on the theory of Flügge,the influences of length,thickness and radius of the cylindrical shell on its circumferential modal frequencies are analyzed.The results show that the circumferential natural frequencies of cylindrical shells with different thicknesses are approximately linearly proportional to the thickness,and the circumferential natural frequencies of cylindrical shells with different radius are approximately inversely proportional to the square of the radius.In this thesis,the electric vehicle motor housing is taken as the research object,and a cylindrical shell model suitable for solving the vibration and acoustic radiation of the motor housing is established according to the weighted average method,and the cylindrical shell theory proper to the cylindrical shell model is determined.The studies provide certain theoretical guidance to the analysis of noise radiation characteristics of motor housing parts.