Analysis Of Vibration Modal Factors And Structural Resonance Control Of Automobile Steering Motor

With the continuous development of the automotive industry,the application of steering motors is becoming more and more extensive,and the type of motor often used in automotive steering motors is permanent magnet brushless DC motor(BLDC).BLDC has the characteristics of high power density,sensitive start and stop,energy saving and environmental protection.BLDC is very different from the traditional engine,although the sound pressure level of BLDC noise is small,but the noise frequency is distributed in the 1 ～5k Hz frequency band that human hearing is more sensitive,and its high-frequency characteristics make the quality of the sound worse,which will cause people’s disgust.Therefore,the improvement of electromagnetic vibration and noise is of great significance for the sound quality of the car and the improvement of the comfort of the whole vehicle.In this thesis,the causes of large vibration of a certain type of BLDC during operation were studied and resonance control was carried out.The main research contents were as follows:(1)According to the mechanism of electromagnetic vibration of steering motor,the analytical expressions of air gap magnetic flux and electromagnetic force were obtained.The three-dimensional model of the motor was established,and the modal shapes and frequencies of each part and the whole motor were obtained according to the modal simulation analysis.Through electromagnetic simulation analysis,the radial electromagnetic force frequency distribution and corresponding amplitude were obtained.According to the analysis of the harmonic response,the acceleration amplitude of the motor vibration and the frequency range of the resonance were obtained.According to the acoustic simulation,the noise generated by the motor vibration was obtained.According to the simulation results,it was preliminarily concluded that the motor structural mode had resonance with the radial electromagnetic force.(2)In order to verify the accuracy of the established model,electromagnetic simulation,harmonic response analysis and acoustic simulation,an acoustic experiment was set up.A three-way acceleration sensor and an acoustic microphone sensor were used to obtain the vibration and noise generated during rated operation of the motor.At the same time,it was proved that the frequency of the maximum value of vibration and noise generated was within the overlapping range of the second order natural frequency of the steering motor and the frequency of the eleventh order radial electromagnetic force distribution.It was proved that the relatively large vibration and noise generated by the steering motor during operation was indeed the result of the resonance of these two factors.(3)The radial electromagnetic force generated by the resonance of the steering motor was applied to the stator core tooth surface,and the influences of winding and end winding length,end cover and end cover thickness on the natural frequency of the stator core of the steering motor were studied and analyzed in detail.At the same time,the material parameters of the stator core and the complex structure of the stator tooth groove were considered.The influence law of slot size parameters on the natural frequency of stator core was obtained.The obtained law can be used to improve the natural frequency of stator core and avoid resonance.(4)Because the steering motor has generated resonance,the topological optimization and multi-parameter target response surface optimization were carried out for the stator core structure.By raising the second order natural frequency of the stator core,and avoiding large resonance with the frequency of the eleventh order radial electromagnetic force,the vibration and noise of the motor were reduced while the use of the stator core material was reduced,and the structure was lightweight.The electromagnetic performance of the motor was improved,and the optimization effect of vibration reduction and noise reduction was obvious.