Block Vibration Analysis Of F168 Gasoline Engine

Engine is widely applied in the national economy. With the increasing request of the comfort, the vibration-reduction analysis of engine block becomes more and more important.This paper takes a F168 engine as an example, systematically describing the computer simulation course of the engine block vibration. It aims at identifying the source of the block vibration of this engine, and coming up with some ideas of cutting down the block vibration and radiate noise, and meanwhile supplying a feasible and reliable approach for the block vibration analysis of the engine.It is known that the engine structure is rather complicated, which can be considered as a vibration system with a large number of degrees of freedom. The exciting force has a certain relationship with structural response, which can be calculated through the finite element method. And the natural frequencies and main vibration mode of the engine are essential for the block vibration control. An effective measure is to change the modal natural frequency, damping, stiffness or quality distribution, shifting the natural frequency to make the structure difficult to vibrate. Moreover the modal analysis not only verifies the correctness of the finite element model but also offers a reliable basis for structure modification later. Therefore, the modal analysis of the engine block is indispensable to the whole simulation.Through Finite element method, structure is divided into lots of elements with mass and stiffness. But too many dispersed units of the finite element model in a complete engine will increase the calculating amount significantly. And calculation could even be limited by computer hardware. Fortunately, the matrix condense method in dynamics are adopted. During the course of matrix condense, the choice of the main nodes of degree of freedom determines the calculating accuracy. Through matrix condense, the calculating degree of freedom is reduced largely and the calculating time is slashed.The vibration of engine is mainly caused by gas eruption pressure, the beat between cylinder liner and piston and the machinery collision of sport pieces and crankshaft. In order to be close to actual operating situation of engine, this paper considers the influence of crankshaft, bearing and oil film damping. Therefore, the vibration analysis of the engine is also a multi-body dynamics problem. Considering the non-linear factor between the structures, the multi-body dynamics method combined with the classical finite element method is applied to analyze the engine dynamic response.The velocity level of the engine block surface vibration has been mainly worked out. Consequently, the source and distribution of vibration energy is clearly acquired. As we know, the velocity level of vibration has certain convertible relation with the sound pressure grade. So noise strength in a certain position of engine can be indirectly but well illustrated by the velocity level. And increasing the stiffness or damping at these places, such as introducing ribs, is an effective way of reducing the vibration noise. Besides, it is also feasible to change the outlines of large flat thin walls.