RESEARCH ON Sound Insulation Theory And Experiment Based On Surface Radiation Noise Of I.C.Engine

Contraposing the state of the study on engine noise and vibration control, taking an engine used for vehicle as an example, this paper deeply studies its characteristic about noise. Due to the exciting force caused by combustion and mechanically drive transfer to the outer surface through each part of the engine, it causes the vibration response of the outer surface. The vibration of the surface stimulates the air particle to vibrate and thus radiate sound wave to outer space. So a direct method to reduce the engine noise is to insulate the exterior radiation noise. Insulating the exterior radiation noise mainly involves two methods: the general and local insulation. But the general insulation has some disadvantages ,such as taking up more space than the local one and difficult to be serviced etc. So in this paper the local insulation is studied. After literature indexing, research on local insulation is rare whether on theory or on experiment, and usually various experimental formulae are used. So one-dimensional elastic wave and plate vibration response theory are mainly applied to study the structure and experiments are made to verify the validity of the theory.Firstly, to get the best insulation result, the insulation structure mainly consists of outer insulation panel, porous materials, damping materials. On this basis, it is important to set up an entity model which meets the engineering demand and takes advantage of building mathematical model. So on the premise of satisfying the practical engineering demand, a simplified model is set up.Secondly, through analyzing the model, the noise radiated by outer insulation panel is considered to be composed of two parts: 1. on the assumption of no linked bolts, the noise comes from sound wave radiated by engine surfaces that stimulate outer insulation panel to vibrate through medium. One-dimensional elastic wave theory is adopted to solve this problem.2. on the assumption that there are linked bolts but no air space between engine surface and insulation panel, plate vibration response theory is adopted to solve the problem.Finally, the validity of theory depends on experimental results. In a reverberation chamber, experiments were made to measure the near-field sound pressure level and sound intensity level on the valve chamber cover of ZH1110 diesel engine which is a single cylinder and horizontal engine. Because the sound intensity level is a vector , it isn't affected by environment, but the sound pressure level is not. After analyzing, the mistake of the sound pressure level is rather big. The result is affected by the condition of the reverberation chamber . In a semi-anechoic room, experiments were made on YC6108 diesel sump whose material is replaced by composite damping steel plate and WD615 diesel crankcase skirt which is insulated by composite damping steel plate, the results are very good and prove that the theory are very practical and the foreground of the composite damping steel plate is broad.