| Under the situation of increasingly tight energy supply and urgent need to improve the environment,developing energy-saving and new energy vehicles is an effective way to solve energy and environmental problems.As the key assembly of new energy vehicles,the electric drive system,composed of drive motors and transmission devices,directly affects the driving comfort of vehicles.In order to improve system efficiency,power density and reliability,the electric drive system is developing towards structural integration and control integration,but it also brings new problems and challenges.NVH is one of these important issues that needs to be resolved.In order to realize the improved performance and quality of the integrated electric drive system in terms of NVH,addressing the current basic scientific problems such as the unclear vibration mechanism and characteristic representation under the electromechanical coupling of the integrated electric drive system,and the key technical issues such as the complication of electromechanical coupling vibration caused by the coaxial motor rotor and gear,and the wide range of excitation frequency,the denser mode shape,and the increased possibility of resonance caused by the high-speed and integration of the electric drive system,combined with the National Key Research and Development Program of China,fine modeling and vibration characteristics research are carried out for high-performance precision integrated electric drive systems.The main research content includes the following five aspects:(1)Internal excitation modeling of electric drive system.Based on the electromagnetic field theory,the analytic model of the unbalanced magnetic pulling force under the eccentricity of the motor rotor is derived.Based on the Hertzian contact theory and the quasi-static model of deep groove ball bearings,the stiffness model of deep groove ball bearings is deduced,and the influence of load on the stiffness of the bearing is analyzed.Based on the meshing transmission mechanism of helical gears,the time-varying meshing line length model of helical gears is deduced,and the effect of helix angle and tooth width on the meshing length of helical gears is studied.Based on the energy method,a universal universal model of gear time-varying meshing stiffness with tooth profile error is derived,and the accuracy of the proposed model is verified by comparison with an existing literature.(2)Dynamic modeling of electric drive system.Based on the generalized finite element methods,the electric drive system is modularized,and the rotor dynamics theory is used to discretize the motor rotor into a multi-disk rotor system.The motor rotor dynamics model is derived,and the degree of discretization of the rotor is determined by the natural frequency convergence analysis.The finite element model of the drive shaft of the electric drive system is established based on the Timoshenko beam theory.Considering the different rotation directions and rotation directions of the driving wheel,a 12 freedoms of bending-torsion-shaft-swing meshing dynamic model of the helical gear is established.Based on the sub-model established above,considering the anisotropy of bearing support stiffness,a dynamic model of mechanical-electromagnetic coupling for the integrated electric drive system is built.(3)Inherent characteristic research,model verification and analysis of the influence of geometric parameters on vibration response.Using complex modal theory,the modal analysis of the multi-degree-of-freedom system considering damping and gyro effects is performed,the critical speed of the system is calculated,the modal characteristics of the system are studied.From the perspective of transient and steady-state conditions,the theoretical models were verified separately.According to the structural characteristics of the electric drive system,the influence of geometric parameters such as shaft azimuth angle,gear arrangement scheme,and deflection angle of counter shaft gears on the vibration response of the system is studied.It provides theoretical basis for an electric drive system structure design and optimization based on vibration control.(4)Research on the influence of internal excitation on the vibration characteristics of the electric drive system.From the perspective of internal excitation,the influence of electromagnetic stiffness on the natural frequency of the system is studied,and find that the natural frequency of each order of the system increases to different degrees under the influence of electromagnetic stiffness.The effect of the unbalanced magnetic tension,the eccentricity of the motor rotor and the combined two on the vibration response of the electric drive system is studied.The influence of the tooth modification position and the maximum modification amount on the time-varying meshing stiffness of helical gears and the vibration characteristics of the electric drive system are studied,separately.And it can provide theoretical support for the vibration control of the electric drive system.(5)Research on vibration test of electric drive system.Based on the public control platform of the automobile transmission system,a test bench for the vibration and noise of the electric drive system is built,and the vibration acceleration is analyzed under the two working conditions of uniform speed and uniform acceleration.According to the analysis results of the approach noise,the main noise level is determined.Then,the Vold-kalman method is used to extract the vibration acceleration signal of the corresponding order and analyze its transient change characteristics.The research results provide a relatively complete foundation for the dynamic behavior prediction and vibration mechanism analysis of the electric drive system of new energy vehicles,provide theoretical support for the optimal design of the electric drive system,and have important theoretical significance for promoting the development of independent intellectual property software and broad engineering application value. |
PDF Full Text Request