| Along with the rapid expansion of automobile industry, people are getting more and more strict concerns on automobile's comfortableness and noise reduction. According to the informations, 70-80 percent urban noise originates from the traffic noise, and the traffic noise is mainly the noise from automobile. It is polluting the urban environment, and affecting people's life, working and the health seriously. So the noise control relates not only the comfortableness, but also environmental protection.In 2007 our company had purchased the CDK6120CAR city bus, which uses CNG as the fuel. In using, its external noise surpassed the noise standards and affected the rest of partial residents. Aiming at this situation, our company organized the related companies to measure the noise of city bus on the spot. There was disparity between the measuring results and the national standard, and the disparity is bigger compared with the foreign noise limiting value. Therefore, our company and the related supporting factories organize the technical personnel to research immediately to reduce the noise and meet the demands of nationalnoise emission standard.The acoustics elementary knowledge, the noise production reason as well as the measures of noise control were introduced, and then the basic parameters and the equipment of CDK6120CAR, the noise test situation and so on were described. Finally, using the noise frequency spectrum curve measured, combining with the operation of engine and according to the production reason of noise, it concluded that the cooling fan noise and engine's exhaust noise were the noise source, and noise reduction measures were proposed and implemented. Through the National Automobile Product Examination unit testing, it showed that noise outside of car reduced from 89.1dB(A) to 82.8 dB(A), and reached the demand of the national standard GB1495-2002. It also showed that the analysis on the noise source was correct and the noise reduction measures proposed was effective.
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