Study On Nonlinear Dynamic Characteristics Of Gear System For Electric Vehicle's Transmission

The gear transmission is used widely in automotive powertrain system.Due to the existence of the gap and the time-varying meshing stiffness,the system is of strong nonlinear characteristics like vibration.The vibration has great impact on shifting performance of the automotive transmission,and lead to noise and shock etc..This research focuses on 2-shift AMT(Automated Mechanical Transmission)system on electric vehicle.The main factors,such as time-varying meshing stiffness and tooth backlash,which influence the shifting operation of gear system,are taken into consideration.The nonlinear dynamics model of the gear system is established.The model is simulated in MATLAB.And bifurcation diagrams,phase diagram,temporal characteristic,Poincare maps and FFT spectrum are accomplished.Numerical simulation and theoretical study are combined to research effection of different parameters on the characteristic of bifurcation and vibration of the system.The research results show that,the dynamics behavior of nonlinear system occurs with the variation of the excitation frequency such as hopping and chaos.When the damping ratio is small,the system is in chaos state;with the increase of damping ratio,the system is placed into periodic state gradually.When the load is small,the system is in chaos state;with the increase of external load,hopping phenomenon occurs and the system tends to be in periodic state.When vehicle driving,one pair of cogwheels are engaged with the other idling.Because both gear pairs are supported on the same shaft,the states of them will be mutual coupling.In order to reveal the nonlinear characters of the gears system with the coupling impact,which is generated in the operating process,the coupling impact is analyzed by mode superposition method and the five dimension degree model of AMT has been built.The bifurcation diagrams about rotation rate of the system is accomplished through simulation.When the rotation rate is small,the system is in periodic state.As the speed increases,disorder of the system begins to increase.And then,the system enters into the state of chaos.In the shifting process based on motor active synchronizing without clutch andsynchronizer,in order to study the influence of nonlinear characteristics of the gear system on shifting,the dynamic equations of the unloading and motor active synchronizing two processes are established respectively based on the nonlinear dynamic model of the motor and gear system.The simulation analysis is finished.In the process of power interrupting,dimensionless torsional vibration speed and FFT spectrum of every gear.In the process of motor active synchronizing,the simulation results of two models,with or without the gear system consideration,are compared and show the impact of gear system on shifting process.