Research On Prediction Of Radiating Noise Of Engine Shell Part

With the increasingly strict of vehicle noise regulations in our country, as the main noise source of motor vehicles, the problem of engine noise has become more and more serious. The noise controlling of shell parts vibration, as the main radiated noise source, has become an urgent problem. In order to satisfy the low level of vibration and noise of shield part, corresponding measures must be adopted right away to analyze and predict engine surface sound field characteristic property. Those methods not only can provide rational theory basis and effectual designing scheme for reducing the body surface radiation noise, but also can reduce the mould development cycle and cost, save labors'power and material resources, reduce product design cost, and raise product economy and marketplace competition.In this paper, the engine of a four-wheel motorcycle is taken as the research object. The surface radiation noises of the right transmission cover are further studied; the sound field characteristics of surface radiation noises are forecasted, and effectively controlled measures are proposed.Firstly, in the sound intensity tests of the engine surface near field, by identified and analyzed the main noise source for a four-wheel motorcycle, it is found that the right gear shift cover of this motorcycle radiate large amount of noise outside, and the radiated noise is one of the main noise sources. To solve this problem, the finite element software MSC.PATRAN/NASTRAN is used to establish the finite element model of the structure and analyze the theoretical modal. Compared with the experimental results and theoretical analysis results, it shows that the two results are basically consistent. The results proved that the analysis modal is rational, it can effect reflect the dynamic characteristics of the shell parts structure. Secondly, the frequency response of the cover is researched, and the surface vibration response is analyzed. At last, the vibration -acoustics software SYSNOISE is used to prediction analysis the noise radiation. The results of noise prediction and sound intensity experiment are show to be consistent; they proved that the analysis theory and method are correct and credible. Based on the above researches, the related factors which affect the structural noise are found; a reasonable improve scheme of the shell structure is proposed, and the noise radiation prediction analyzing of the improved structure is done.The results of the modal analysis, the frequency response analysis and the noise radiation prediction analysis, which before and after improvement, show that by adding rib reinforcements, increasing structure basic thickness, and increasing structure damp in suitable position of engine shell parts, the dynamic characteristics of the shell structure are effectively improved and the structure noises are obviously controlled and improved.