Experimental Research On Pass-by Noise Control Of The Car

Noise emitted by automobiles has become the major element of urban traffic acoustical noise. It pollutes the urban environment severely and affects people's work and life. Therefore, at present, controlling the automobiles'noise, especially pass-by noise, is an important research subject in the automotive industry.Based on the summing-up and analysis for the mechanism and transmission of the automobile pass-by noise, and connecting the current condition of a car, code X121, in this paper we initially obtain the magnitude of noise radiated from the main vibrating components and its percentage of the whole car radiating noise by the comprehensive use of noise source spotting methods, such as expurgation method, frequency spectrum analysis, and so on. We are sure that engine noise and exhaust noise are very heavy and they are the main noise sources. Adopting method of sound intensity measurement for the engine, we find that from the 3-D color map of sound intensity, radiating noise of oil sump tank ,cowl hood and belt pulley are the strongest, they are the main radiating noise sources of the engine。According to the noise source spotting analysis, we work out ways for controlling the main noise sources and carry it out. Because the volume of the original exhaust muffler is too small to eliminate the low-frequency and mid-frequency noise, the exhaust muffler of the car is improved. The experiment has proved that it makes the noise abatement efficiency improved by 2~4dB(A). Based on the controlling methods of sound absorption, sound insulation and damp, we take rational use of some materials to control the radiating noise from the engine room, engine cover, and oil sump tank and so on. This method can reduce the radiating noise of engine effectively.The application to the car, code X121, has presented the practicability and the validity of the noise controlling method. In the experiment, the A-weighted sound pressure level of the pass-by noise decreases from 75.5dB to 73.1dB. It has satisfied the condition of the Ultimate Value in GB1495-2002.