Study On Torsional Vibration Characteristic Of Engine And ISG Motor Integrated Assembly

Shafting of hybrid system is the core component of a hybrid car.Its dynamic characteristics directly affect the durability and reliability of hybrid system.During the working process,vibration of the shafting system appears unavoidably,but excessive vibration of the axis will cause fatigue stress,and shorten the service life of the axis,even lead to shafting fracture.At the background of spline shaft fracture problem of a certain type bus,this thesis model the shafting of hybrid system,use modal analysis to find the natural frequency and understand the intrinsic characteristics of shafting system;use frequency response analysis to simulate the resonance;experiments to study the specific reason for the spline shaft fracture and compare with the simulation results;finally introduce road random excitation,discuss dynamic response of shafting system under road random excitation.(1)Considering response characteristics of system with single degree of freedom and multi degree of freedom under the free vibration and forced vibration,study the theoretical modeling of shafting and discuss the influence of shating system parameters on its inherent vibration characteristics.Discuss the calculation method of engine incentive.Use ISG motor shaft axis as the main body to establish finite element model of a hybrid system.Divide the grid,after contrast of different units and grid density.Analysis modal of the model under unconstrained and constrained conditions.The results show that constraint condition is closer to actual situation and stresses at the joint of torsional vibration damper and the joint of ISG motor rotor and clutch are larger.The main mode of vibration are torsional vibration and bending vibration.(2)Combined with the results of simulation analysis,use experiments to analysis shafting vibration and dispose the experimental data from time domain and frequency domain.The time domain analysis result that spline resonance take place respectively at the stage of the bus sart and stop,when clutch is in the state of separation.The frequency domain analysis result that in the process of start and stop of bus,resonance phenomenon happen when inherent frequency of the spline shaft meet the ISG motor excitation frequency.(3)Finally explore the vibration response of shafting system under the road random excitations.Apply frequency domain model of road random excitation and road roughness coefficients in government standard to calculate discrete road random excitation displacement power spectral density and acceleration power spectrum density.According to the principle,70% incentive load is carried out on the shafting system.Simulation results show that the maximum response of the axis stress is larger under gravel road random excitation.The maximum stress doesn’t reach the allowable standard of material,but it is easy to cause the tiredness of the shafting system.The maximum stress is located in the joint of torsional vibration damper,which is accordant with the modal analysis results.