Analysis The Influence Of Rotor-Step Skewing On Vibration Characteristics Of Electric Drive System

In order to achieve the goal of carbon peaking and carbon neutrality,our country has formulated a development route for energy saving and new energy vehicles.Therefore,the reliability and comfort of electric vehicles have received much attention.Electric drive system is the power core of electric vehicle,and its vibration characteristics on the reliability of electric vehicle and ride comfort has a non-negligible impact.As an effective measure to improve vibration characteristics of permanent magnet synchronous motor(PMSM),rotor-step skewing has been applied in vehicle electric drive system in recent years.The rotor-step skewing directly affects the electromagnetic force and torque ripple of the motor,and the torque ripple of the motor has a direct effect on the dynamic characteristics of the gear transmission system in the electric drive system.Therefore,aiming at a vehicle electric drive system,the influence of rotor-step skewing on electromagnetic excitation of PMSM,gear drive system excitation and electric drive system vibration characteristics was systematically studied by combining theoretical analysis,numerical simulation and test.Firstly,Maxwell tensor method is used to analyze the radial/tangential electromagnetic force density,slot torque and torque ripple that considering the rotor-step skewing,and the results are verified by finite element method.The weakening laws of the radial/tangential electromagnetic force density,slot torque and torque ripple induced by rotor-step skewing(different rotor skew angles and step numbers)of the I-rotor and V-rotor were analyzed.Taking motor torque ripple as the excitation of gear transmission system,the dynamic analysis model of gear transmission system was established.Through dynamic analysis,it is found that the torque ripple has a significant effect on the transmission error of gear pair,and it is more obvious under the condition of high torque and low speed;The rotor-step skewing has obvious influence on the transmission error harmonics of gear pairs,and the dynamic characteristics of gear transmission system can be improved by adjusting the mode of rotor-step skewing.Free mode test is carried out step by step on stator,motor stator assembly and electric drive system housing assembly.Based on the modal test results,the finite element model of the stator,the motor stator assembly and the electric drive system shell assembly were established and modified step by step.Finally,the finite element model of the electric drive system shell assembly was obtained.The vibration analysis model of the electric drive system was established by using the electromagnetic force and the dynamic force of the bearing seat as excitation and loading into the finite element model of the shell assembly of the electric drive system,and The validity of vibration analysis model of electric drive system is verified by vibration test.The vibration analysis shows that the vibration of the electric drive system is mainly caused by the motor rippple torque and the transmission error of the first gear pair,and the vibration caused by the torque ripple can be improved by adjusting the rotor-step skewing mode.In order to solve the vibration problem of the electric drive system,genetic algorithm was used to optimize the rotor-step skewing mode and the micro-modification of the first gear pair.The optimization scheme of vibration characteristics of the electric drive system is obtained,and the effectiveness of the optimization scheme is analyzed.