Study On Torsional Vibration Characteristics Of Shaft System Of ISG Hybrid Power System

Vigorously developing new energy vehicles is one of the effective means to alleviate the energy crisis and reduce environmental pollution.The power system structure of hybrid electric vehicles is complex,and its torsional vibration has an important impact on the vibration and noise of the whole vehicle.Therefore,it is of great practical significance to study the torsional vibration characteristics of hybrid electric systems to further improve the NVH performance of the whole vehicle.Taking the shafting of an ISG hybrid power system as the research object,this paper studies its torsional vibration natural characteristics and response characteristics.This paper analyzes the structure and working principle of ISG hybrid power system,establishes the lumped parameter equivalent model of ISG hybrid power system shafting,and analyzes the determination methods of mechanical and electromagnetic parameters in the equivalent model.Based on the above model,the torsional vibration natural characteristics of ISG hybrid power system shafting are calculated and analyzed by using MATLAB software.The calculation results show that the torsional angle amplitude of the front end of the shafting is the largest and that of the ISG motor rotor is the smallest.With the increase of the order,the vibration form of the natural vibration mode becomes more and more intense.The main and driven ends of the coupling are the nodes of each order of natural vibration mode,where the stress is large and easy to be damaged.The electromagnetic stiffness changes the original natural frequency of 0Hz,and its transformation range is0-6.85hz;The external excitation torque characteristics of the shafting are analyzed,and the critical speed of the shafting of ISG hybrid power system in the common working speed range is determined.The exciting torque of ISG Hybrid Power System shafting is analyzed,and its simple harmonic analysis is carried out.The steady-state torsional vibration response characteristics of the shaft system of ISG Hybrid power system are analyzed by using the system matrix method.The results show that the torsional vibration characteristics of the front end of the shaft system and the rotor of ISG motor are mainly dominated by2 harmonics,and the fluctuation frequency of the additional torque in the fifth shaft section is mainly dominated by 4 harmonics;The front end of the shafting is more susceptible to resonance than the rotor of ISG motor.The shafting resonance is the largest when the critical speed is 1798.6 rpm;The torsional vibration characteristics of steady-state power generation are mainly dominated by 2 and 4 harmonics.Electromagnetic damping reduces the torsional angle amplitude of 2,4,6 and 8harmonics of ISG motor rotor,which has a certain damping function;Electromagnetic damping has the greatest influence on the torsional angle amplitude of the second harmonic at the front end of the shafting and increases it.Based on Newmark-β With the help of MATLAB software,the transient torsional vibration response characteristics of the shafting of ISG Hybrid power system are calculated and analyzed.The results show that there are obvious sudden changes in the front end of the shafting,the angular acceleration of the ISG motor rotor and the additional torque of the fifth shaft section during acceleration,which speeds up the fatigue failure of the shafting,and the sudden change of the front end of the shafting is greater than that of the ISG motor rotor.The vibration characteristics of ISG Hybrid Power System during start-up are analyzed.The analysis results show that the gas action torque generated by compressed air of each cylinder is the main resistance torque of shafting during start-up.There are frequency components similar to the natural frequency of the system in gas action torque and reciprocating inertia torque,so resonance occurs,resulting in large vibration during start-up.