Analysis Of Three-Dimensional Coupling Vibration Characteristics Of Crankshaft Of High Power Density Diesel Engine

With the dynamic demand of diesel engine,the develops toward the direction of high power density.It is imperative to study the crankshaft vibration caused by high explosive pressure and high rotational speed.Crankshaft is one of the key parts of diesel engine,it's torsion,bending and axial vibration is more worse,and the coupling effects between them seriously affects the durability and stability of diesel engine.In this thesis,a 12 V high power density diesel engine is taken as the research object.A method to study the coupling vibration in time domain and frequency domain is proposed,and a crankshaft vibration control scheme considering the lubrication characteristics and the coupling vibration is proposed,which provides a reference for the optimization design of diesel engine.Based on multi-body dynamics and finite element theory,the model of shafting was established with the AVL EXCITE PU software.The stress and free vibration characteristics of crankshaft are calculated,and the natural frequency,mode and critical speed of the crankshaft are obtained.It is found that the crankshaft will resonate under several harmonics in the operating speed range.Using this model,the forced vibration characteristics of crankshaft are calculated.It is found that in the time domain,the three dimensional vibration trend of each axis segment is consistent,and there is an obvious coupling phenomenon.Then the three dimensional vibration of the free end of the crankshaft under each harmonic degree is calculated in the frequency domain.Torsional vibration has strong resonance under 1.5,3 and 4.5 harmonics.The vibration trends of horizontal bending,axial direction and torsional vibration amplitude are consistent with each harmonic degree,and there is a large coupling effect.The torsional and bending vibration under multiple harmonics will cause the axial vibration of same frequency or multiple frequencies.The vertical bending vibration is mainly in the higher harmonic degree,and in a wide range of frequencies.To control three dimensional vibration of crankshaft,it is calculated and analyzed from two aspects of shafting structure parameters and vibration reduction device.The radius clearance of the main bearing,the diameter of the spindle neck and the moment of inertia of the flywheel have great influence on the three dimensional vibration of the crankshaft.The installation of thrust bearings can significantly reduce axial vibration,and the influence law of three dimensional vibration caused by installing thrust bearings in different spindle neck positions is obtained.Installing the torsional damper can reduce the torsional vibration about 43.9%,and the improvement of vertical bending and axial vibration are obvious,but the peak of horizontal bending vibration increases.In the matching process of the torsional damper,the selection of the moment of inertia has a great influence on the three-dimensional vibration,while the influence of the tuning ratio is less.