Study On Shaft Dynamics Characteristics Of Hybrid Excavator Power System

Study in shaft dynamics characteristics of power system is one of important contents in hybrid excavator technology. Shaft dynamics characteristics of power system in hybrid excavator have strong impacts on engine-motor coupling efficiency. With unfavorable dynamics characteristics, tosional oscillations and bending vibrations would be happened in principal shaft, and it will lead to fatigue stress in shaft and Affect the service life. in severe case it may make shafts broken and unrepairable troubles. In the863Program Key projects which is named’The key technologies, systems development and demonstration of applications of the new type hybrid construction machinery’, accidents of shaft broken were happened twice, it requires a necessary research in dynamics characteristics of hybrid excavator power system.In this paper, structure of power system in coaxial parallel-type hybrid excavator, excitation and Deformation are Considered, and based finite element method a number of studies on dynamics characteristics of power system in hybrid excavator are made. Main results and conclusions are shown as following.1. The finite element models of crankshaft and motor rotor, which make up of principal shaft of power system in coaxial parallel-type hybrid excavator with flexible connection, are built, and the finite element model of principal shaft of hybrid power system with rigid connection are also built. Based on these models, modal analysis are made, it works out that vibration are likely to occur on the shaft part of the motor rotor near to coupling, and the main shaking types are tosional oscillations and bending vibrations.2. Dynamics model of diesel engine is built. With Simulation and analysis, it worked out that vibrations with high amplitude are happened in the interval of0～2.5times as rotation frequency, and the highest tosional oscillation occurs in the frequency as2times as rotation frequency, and the highest bending vibration occurs in the frequency as1times as rotation frequency.3. Dynamics models of shaft of power system in coaxial parallel-type hybrid excavator with flexible connection and rigid connection are built. The simulation results of two models are compared, it works out that instead of rigid connection, using flexible connection can make dynamics characteristics of power system in coaxial parallel-type hybrid excavator more better. 4. A further simulation and analysis are finished to the power system in coaxial parallel-type hybrid excavator with flexible connection. It worked out that tosional oscillations in the section of easily broken shaft part with high amplitude are happened on the frequency as1times as rotation frequency, in the interval of0-250Hz, there is natural frequency for tosional oscillation, and its value is41.73Hz. the radial vibrations in the section of easily broken shaft part with high amplitude are happened in the interval of0.5-2.5times as rotation frequency, in the interval of0-250Hz, there is natural frequency for radial vibrations to y-direction, and its value is41.73Hz.5. An experimental platform to study the dynamics characteristics of the power system in the coaxial parallel-type hybrid excavator is designed and made, and with this platform tosional oscillations in the section of easily broken shaft part are measured. The Analysis results of measured dates show that on the frequency as1time as rotation frequency, the high amplitudes in the section of easily broken shaft occur, and amplitudes value are concerned with rotate speed of shaft. Trends of Amplitude value with frequency are unrelated with rotate speed. There is natural frequency as nearly1time as rotation frequency. These conclusions are the same as the simulation results. The experimental natural frequency value is33Hz, which is smaller than the simulation one, because torsional rigidity of section in experiments is smaller than the one in simulation.