| Vibration is a familiar phenomenon in our life, which will have main influence on many aspects, such as life and performance of machine, the destroy of construction, etc. With the development of science and machine of higher power and speed being used, vibration is focused on more and more in modern industry.Environment protection, harshness and endurance in operation are concerned with vibration and noise in vehicle. Vehicle vibration will result in forepart fatigue in some parts, and drivers and passengers will feel uncomfortable in some frequency range. Driveline is an important part in automotive system, which transfers the power of engine to car, at the same time, transfers vibration of itself to car. Rigid modes in low frequencies directly influence comfort of car; however, the elastic vibration between 30Hz and 200Hz will give rise to the structure's resonance. Especially, the first-mode bending vibration will influence the using life of powerplant, even whole car. The familiar problem is premature crack in flywheel casing between engine and transmission. Therefore, with enhancement in demands for alleviating vibration, prelonging operation life and improving comfort, it is very indispensable to study the characteristics of powertrain system, especially of bending vibration.With the development of the computer in recent years, the CAE technology has become more and more useful in the design of automobile products. Before the components and entire vehicle are made, their strength, reliability and the other characteristics can be computed and analyzed, even experimented by CAE. Finite element analysis is one of important methods in the CAE. FEM has fully developed in the field of mechanics, so it has been broadly used in dynamic analysis of automotive parts.Experiment Modal Analysis (EMA) with calculating modal analysis is an important method for solving the dynamic characteristic design of complex structure. The complex structure may be simplified when the system response is calculated with this method. Therefore, the mathematics operation can be also simplified. In order to solve the cracking problem of flywheel casing due to powerplant bending resonance, the dynamic characteristic of powerplant needs to be obtained first. In this paper, the structure vibration of powerplant was simulated. First, the FEM models of every part in the powerplant were set up based on the preprocessor of ANSYS software. Then the Block Lanczos Method was used to have a completing modal analysis and some dynamic parameters of every part were got, such as inherent frequency, vibration shape and so on. The error between the measurement results and calculating results was less than 10%. It could be satisfied for the engineering calculation request. After that, every part was assembled through ideal bolted joints, then the powerplant model was obtained. It could set up a base for the latter dynamic analysis.The vibration characteristic of poweplant was obtained with modal analysis. The former eight modes was extracted。 The former six modes were rigid modes, the seventh mode was the first horizontal bending mode and the eighth mode was the first vertical bending mode. As the nodes in seventh mode shape appeared at the clapboard between the forth and the fifth cylinder and the front of transmission, flywheel casing crack may be mainly caused by the bending vibration at this frequency, the main force is double centripetal force of imbalance mass in driveshaft. Then a harmonic analysis was done on the original powerplant. The results showed that there is a large stress on the top of flywheel casing, and the safe coefficient is less than 1.5. So the flywheel casing is easy to break.After the mount disposal changed, in order to study the influence on the stress which appears on the top of flywheel casing, modal analysis and harmonic analysis were done. The result showed that mount disposal had a little influence on the inherent frequency of bending vibration. And the bending response was alleviated when the latte...
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