Research On Vibration Analysis And Noise Assessment Of Internal Combustion Engine Block Based On Finite Element Method

As the frame work of internal combustion engine, the cylinder block is the mainnoise radiation surface. Most of exciting forces of internal combustion engine istransported to the accessories by the cylinder block,so the vibration of the block willdirectly affect the vibration and noise of internal combustion engine. With the rapidprogress of computer technology, FEM is widely used in the field of vibrationanalysis and noise assessment of internal combustion engine. However, the predictionof vibration and noise of engine block in design stage is only limited to modalanalysis for such complicated structures and complex exciting forces of cylinderblock. And predicting the vibration and noise of a cylinder block by using finiteelement transient dynamic analysis just begins. The method is discussed in detail inthis article by analysis of the cylinder block of 4102BZQ. An FEM model of the cylinder block is built for simulating the dynamiccharacteristics of the real structure by powerful 3D soft PRO/E. The method ofsimplification of the cylinder block's simulation is described. The FEM modalanalysis of the cylinder block both at free-free condition and at real constraintcondition is performed by universal FEM soft ANSYS. The first ten order modes andfrequencies of the cylinder block are obtained. The inherent relation between theconstraints and the natural frequencies of the cylinder block is analyzed. Byincreasing the thickness of cylinder block skirt, reinforced ribs and main boring plates,the stiffness of the block skirt is improved, and the natural frequencies are increased.In order to perform transient FEM analysis of the cylinder block, the loads andconstraints are accurately calculated. The exciting forces are appropriately applied onthe cylinder block by making command flow programs according to the FEM rulesand principles. Then the time-history displacement of the nodes on the cylinder blockand the stress status of the cylinder block at any time are obtained by performingtransient dynamic FEM analysis to the cylinder block.After the time-history post-processing of the results of the analysis, the vibrationstatus of the surfaces of the cylinder block can be obtained. The influences on thevibration of the cylinder block caused by the exciting forces are studied in the article.Meanwhile, by using the theories of mechanical vibration principles, the frequencydomain analysis on the vibration velocity of the cylinder block is illustrated.Furthermore, the vibration strength of engine is predicted on base of the result ofFEM analysis of the cylinder block according to GB7184-87.By studying the basic acoustic theories, a simple and appropriate method ofpredicting the surface radiant noise of the cylinder block is developed according to theresult of transient FEM analysis of the cylinder block. The comparison between thepredicted result with that of test validate that is feasible to predict the noise of internalcombustion engine if the exciting forces and constraints are accurately simulated.