Research On Crankshaft Vibration Mechanism Of The High-speed Diesel Engine Based On Virtual Engine Module

The vibration of shafting is one of the main vibrations of internal combustion engine. The crankshaft vibrations include torsional vibration, bending and axial vibration. For a long period, much of past work has been devoted to study on the torsional vibration of crankshaft and has been made significant advances, such as calculation and experiment, vibration absorber, etc. Until recently, many researches are only focus on one or two kinds of vibrations. There is less research on engine's bending and axial vibration. In this thesis, a comprehensive analysis is given which is devoted to the three-dimensional vibration and the vibration control of V6 high-speed diesel engine through theory analysis, simulation and experiment.Firstly, based on the engine crankshaft excitation, the status of dynamics and the balance of the high-speed V6 diesel's crankshaft system are estimated by using conventional method, especially the influence of the firing order and the balance mass.The result indicates that the V690°diesel engine in two different firing order is better balanced and 70% crankshaft balance weight is appropriate for the V690°diesel engine.Secondly, free and foeced torsional vibration of the high-speed V690°diesel engine are studied by a discrete system model and Transfer Matrix Method(TMM). Coupled with modern design method, the inertia moment and the flexibility of the crankshaft and the torsional vibration characteristic of the high-speed diesel engine are calculated. The results show that the natural frequcy of V6 diesel engine crankshaft is about 600 Hz and the non-main harmonious resonance have a great effect on torsional vibration, such as the 4.5th and the 7.5th order.The key point of this thesis is the analysis of the three-dimensional vibration. Firstly the theory of Hybrid Multi Body Dynamics (HMBD) based on a two-level dynamic substructure technique is expatiated. The three-dimensional vibration coupling with the engine block is analyzed by using HMBD including a flexible crankshaft, flexible main bearing wall and flexible connecting-rod. Then the status of the torsional vibration, bending and longitudinal vibration of the V6 diesel engine is studied based on the mechanism of the three-dimensional vibration. At last, the characteristic of the three-dimensional crankshaft vibration is analysed by measuring the torsional/bending/axial vibration of V6 diesel engine crankshaft system. The results show that the torsional/bending/axial vibration of V6 diesel engine crankshaft is large in the 4.5th order and the axial vibration is excited by the same frequency tosional and bending vibration, which is validated by test results.In order to control the vibrations of crankshaft, the dissertation investigate the three-dimensional vibration of V6 engine crankshaft in different firing order in detail by simulation. The results indicate that the torsional/bending/axial vibration of V6 diesel crankshaft in the 4.5th order can be reduced by changing engine firing order. Then the design method of the damper and dynamic-damper absorbers is given. The rubber torsional absorber and silicone fluid torsional absorber of V6 diesel is designed. The theoretical calculations indicate that the torsional vibration could be decreased effectively by these two methods.