Theoretical Modeling Of Complex Stator Structure Of Electric Vehicle Motor Based On Shell Theory

The NVH problem of electric vehicles has a long history.The high-frequency whistle caused by electromagnetic vibration seriously reduces the ride comfort of vehicles.Modeling research of motor stator is an important part in the analysis of motor vibration and noise.But at present,researchers only use finite element method to model motor stator.From the point of view of structure analysis,according to the geometric size and shape of stator,the stator winding is neglected and regarded as a cylindrical shell structure with longitudinal stiffening inside.The analytical modeling theory of stator structure is carried out.A preliminary study was carried out.The details are as follows:Firstly,three kinds of common differential equations of cylindrical shell vibration were deduced by the "standard" method,and the elastic constitutive relation of cylindrical shell was explained.The Schimit-Gram orthogonal method for constructing displacement admissible field function and the common simple boundary conditions of this kind of structure were briefly introduced and combed.Taking an elastic straight beam as an example,the frequency equation of the beam was deduced in detail by using the energy principle.This method can also be used to study the vibration characteristics of complex cylindrical shells,which only increases the complexity of derivation.The above analysis laid a theoretical foundation for the follow-up modeling work.Then,aiming at the problem of free vibration of thin-walled cylindrical shells strengthened with longitudinal ribs with arbitrary cross-section under complex boundary conditions,the Schimit-Gram orthogonal method was used to construct the axial vibration mode function of the shell under elastic constraints,and the compatibility between the shear center of the rib and the displacement of the middle surface of the shell was derived.Based on the accurate energy functional expression of the substructure,the Rayleigh-Ritz method was used to establish the unification of free vibration of the cylindrical shells with Analyze the model.The accuracy and convergence of the computational model were verified and analyzed.Three classical boundary conditions were simulated by changing the restrained stiffness of the spring at both ends of the shell.The effects of the stiffening mode,the number of ribs and the eccentricity of ribs on the natural frequencies of the structure were discussed.Compared with previous studies,this model is no longer restricted by boundary conditions and longitudinal rib section types.At the same time,because the energy functional of cylindrical shell and longitudinal rib structure are both exact forms,more accurate natural frequencies can be obtained for thin-walled cylindrical shells with longitudinal ribs with different thickness-diameter ratio and length-diameter ratio.On the basis of the above research,the specific geometric dimensions of different stator models were calculated,and a more accurate theory of medium-thick cylindrical shells for solving the vibration characteristics of stator structures was determined.In order to simplify the calculation difficulty and limit the radial displacement of the end face of the stator structure,the boundary conditions at both ends are simply supported constraints.The inner teeth of the stator core were regarded as longitudinal ribs attached to the cylindrical shell along the axis.Considering the inertial motion and torsional deformation in each direction,the displacement of the middle face of the shell was expressed in the form of Fourier series superposition,and the structure was deduced by energy method combined with Rayligh-Ritz technology.Frequency equation of free vibration.The natural frequencies of the smooth cylindrical shell model were calculated by the equation obtained in this paper.Then,considering the effect of additional longitudinal ribs,the finite element model of the complex structure of the inner stiffened medium-thick cylindrical shell was established.The results of this paper were compared with the calculated values of the finite element method.At the same time,the accuracy and the effectiveness of the model were proved by comparing with the experimental modal frequencies of the motor stator.Finally,the related theory and experimental steps of the cylindrical shell modal test were introduced in detail.A test bench for the cylindrical shell modal test and a test system for obtaining the response signal were built.The vibration characteristics of the open end cylindrical shell were tested by force hammer,and the experimental results were compared with the finite element results.The factors and errors affecting the accuracy of the test were listed and analyzed.