Research On Motor Noise Tracing And Suppression Method Of Electronic Power Steering System

Electronic power steering system(EPS)is more and more widely used in cars,C-EPS system power motor installed on the steering column,close to the driver,the vibration and noise in the process of operation will not only have a great impact on the experience of drivers and passengers will also affect the performance and life of the steering system.Therefore,the research on motor noise of electronic power steering system has certain practical value.The electronic power steering system uses brushless DC motor as the power motor,which has the advantages of easy start,low loss and convenient control.For brushless DC motor,electromagnetic noise is the main source of noise.Therefore,this thesis takes brushless DC motor as the main research object,combines structural dynamics and acoustics to trace and suppress electromagnetic noise of motor.Firstly,the air gap magnetic density and electromagnetic force of the motor are derived and calculated by the analytical method,and the two-dimensional electromagnetic distribution of the motor model is simulated and analyzed by the finite element simulation software,and the waveform of the time domain and frequency domain is obtained.The main concentration frequency of motor noise caused by radial electromagnetic force is determined.The stator free mode of the motor is calculated by electromechanical analogy method and verified by finite element simulation method.The noise frequency caused by the radial electromagnetic force and the resonance of the first order free mode of the motor is calculated.The characteristic frequency of motor noise caused by torque ripple is calculated by analytical method.The calculated characteristic frequency is defined as the noise characteristic frequency set.Then in the environment of semi-anechoic chamber,the four-point method stipulated by the national standard is adopted to collect the motor noise signal.The EMD-KR-FP motor noise tracing and emission method is proposed,and the empirical mode decomposition(EMD)method is used to decompose the time domain signal of motor noise.Then,according to the spectral kurtosis theory,the intrinsic mode function(IMF)component is screened for signal reconstruction,and the reconstructed signal is Fourier transform.Peak location algorithm is used to extract the peak frequency of several peaks with the largest contribution on the spectrum and compare with the frequency of characteristic frequency set,so as to determine the cause of electromagnetic noise of the motor.Then,according to the main causes of motor noise determined in the previous step,make targeted treatment.For the noise caused by torque ripple,improve the permanent magnet by optimizing the magnetic pole eccentricity,reduce the tangential electromagnetic force acting on the stator tooth surface,and realize the suppression of torque ripple.For the electromagnetic noise caused by radial electromagnetic force,stator chute is used to suppress the radial electromagnetic force of each order.For the noise caused by the radial electromagnetic force and the resonance of the motor,the stator yoke is thickened to increase the first-order natural frequency of the stator,so that the resonance band moves back and the resonance noise is suppressed.Finally,the suppression scheme proposed in the previous step is verified by finite element simulation.The simulation results show that the motor noise decreases from 59.96 d B to 53.16 d B after the optimization scheme is adopted comprehensively.The simulation results show that the three noise reduction schemes are effective.It provides reference for further exploration of vibration and noise of electric power steering system.