Research On Dynamic Modeling And Dynamic Characteristic Of The Planetary Transmission System For Electric Driving Axle

As one of the key components of electric vehicles,electric drive axle is a new electric drive assembly integrating axle,permanent magnet synchronous motor(PMSM)and reducer.With the continuous improvement of assembly integration and lightweight design requirements,electric drive axles are gradually developing towards permanent magnetization,high speed and miniaturization,which requires the transmission ratio to be large,and the load capacity and the efficiency to be high.Additionally,the reliability and the NVH performance of the transmission system should not be low.Physically,the PMSM is integrated with the transmission system,and the number of transmission chain components is numerous.The entire system presents a series of complex dynamic characteristics such as multi-source excitation,strong coupling and nonlinearity.The dynamic performance design of the system puts forward higher requirements.How to complete the dynamic performance design while satisfying the functional design of the transmission system is one of the key points and difficulties of the current electric drive bridge design work.This thesis takes the coaxial electric drive axle planetary transmission system as the research object.Through establishing the dynamics model of the transmission system,the dynamic characteristics of the transmission system are studied under complex multi-source excitation,strong coupling and nonlinear conditions which theoretically and technically provides guidance for the dynamic performance design of the electric drive axle.The main research contents of the thesis include:Research on analytical calculation method of time-varying meshing stiffness of spur gears.Considering the defect of the existing analytical method,namely,the flexibility of the gear body is not appropriately considered.Based on Euler-Bernoulli beam theory and complex function method,analytical formulas for the gear body induced tooth deflections are proposed.Based on the proposed formulas,a pure analytical model for mesh stiffness is established based on the semi-analytical model we proposed,which shows an obvious advatages over the traditional analytical method.The research indicates that the structural coupling effect does exist.The traditional analytical method can not consider this phenomenon,and the calculation error can be up to about 57%.The proposed method can consider the tooth coupling phenomenon and the calculation error is greatly reduced.Theoretical study on dynamics modeling of single degree of freedom gear system.By establishing different gear static meshing models,the static meshing process of gears under load and error conditions is studied.The evolution of gear meshing stiffness and transmission error under load and error conditions is revealed,and the dynamics of single-degree-of-freedom gear system is combined.The correctness of the proposed model is proved by comparing the theoretical model and experimental results.Result shows that the influence of tooth compliance should not be neglected in the static meshing analysis of gear pair.The proposed IFGB model takes into account the influence of tooth compliance,so the calculation results are more accurate,and the static meshing model is established.The gear dynamics model is different due to the introduction of gear meshing stiffness and transmission error,and the predicted dynamic response is also different.Dynamic modeling and intrinsic characteristic analysis of electric axle planetary transmission system.Combined with the structural characteristics of the two-stage planetary gear system,the dynamic model of the double-stage planetary gear system of the electric drive axle considering the influence of centrifugal force and coriolis force is established.The inherent characteristics of the system including the mode shape and the mode natural frequency are obtained.The characteristics reveal the influence of electromagnetic torsional stiffness,load level and running speed on the inherent characteristics of the system.The research shows that there are four typical modes in the transmission system.The electromagnetic field forms a restraining effect on the transmission system,eliminating the rigid body mode,while the stiffness time,load and running speed have less influence on the lower-order modes,while the higher-order modes are more affected.Research on dynamic load sharing performance of electric drive axle planetary transmission system.Based on the principle of equivalent transmission error,the dynamic model of two-stage planetary gear system considering the influence of tooth profile error,gear eccentricity error and component assembly error is established.Combined with numerical calculation method,the sensitivity of system load factor to different kinds of errors is analyzed.The extent reveals the evolution of the load-carrying characteristics of the two-stage planetary gear system under error conditions.The research shows that manufacturing errors and assembly errors of the first-stage planetary gear system have a great influence on the load sharing performance of the system.In particular,the system load sensitivity coefficient of the first-stage planetary gears caused by the tangential assembly error reaches 30.5.From the perspective of load sharing,it is necessary to improve the manufacturing assembly accuracy of the firststage planetary gear system.Research on vibration and dynamic load characteristics of electric drive axle planetary transmission system.Based on the dynamic model of the two-stage planetary gear system,the influence of the component modeling method,the rotor of the motor,the operating parameters of the system on the time-frequency characteristics of the vibration response of the component and the dynamic load of the transmission system is further revealed,and the flexibility of the planetary pin shaft is realized.The design and gear tooth profile modification discussed the system vibration reduction and load reduction method.Finally,the correctness of the theoretical model was proved from the side with relevant experiments.Research shows that the modeling method of the coupling components and the motor have a significant impact on the vibration of the transmission system and the time-frequency characteristics of the dynamic load.The flexible design of the planetary pin and the gear profile modification can significantly reduce the dynamic load of the gear system.