Engine Vibration Characteristic Research And Low Noise Design

In recent years, as people begin to show more emphasis on the harm of noiseand higher requirement on vehicle riding comfort. The research on engine vibrationand noise has become an important direction in the field of engine study. In the paper,the vibration and noise characteristic of engine is studied; noise source identificationon engine start motor’s side is investigated and the structure of some enginecomponents are optimized.The geometric model of the engine body, cylinder head and cylinder head coverare built by CATIA and the finite element model is meshed. Then, their first tennatural frequencies and corresponding modes are obtained from modal analysis. Andthe modal shapes of the engine body are analyzed in detail, which provide the basisfor the subsequent structure optimization.The valve train assembly with a flexible camshaft model of engine is built up.Then, the dynamic simulation for the model is made. The loads of valve seats and thecamshaft bearings are obtained. The loads of valve seats are studied. These simulationresults provide load boundary conditions for dynamic response analysis of engine.Based on the established integrating finite model, nonlinear contact boundaryconditions were employed by using finite element analysis software Abaqus. Thecylinder pressure, bearing forces and the piston knocking forces are computed, theboundary conditions are also defined. The vibration response of the assembly underthe rated speed was calculated and then the computed results were compared with thetest results. It shows that the finite model is rational. The deformation of cylinderblock, cylinder head fire surface and cylinder hole was analyzed under the case ofmaximum firing pressure. The results show that the stiffness of cylinder body skirt issmall; the deformation of the central area of cylinder head fire surface is large, thestress in the connection region between cylinder head fire surface and cylinder head islarge; the deformation of cylinder hole is small and within the engineering allowance.Noise source identification on engine start motor’s side is investigated by usingthe method of surface vibration technique and microphone array, the oil pan isidentified as the major noise source. Finally, we optimized the structure of oil pan by placing ribs on the proper surfaces and connected5independent bearing covers. TheFEM results show that the stiffness of oil pan and cylinder body skirt has beenimproved. Thus the noise radiated by the oil pan can be reduced and so as that of thewhole engine.