Analysis And Control Of Light Duty Truck Exterior Noise

With the rapid development of automotive industry and the rapid increase of the number of the cars in the city, the problem of automotive noise pollution is becoming more and more serious. In order to control and reduce the motor vehicles noise, many countries have legislated to limit the vehicle noise. In 2002,our government constituted and enacted a new National Standard GB1495-2002 "Limits and measurement methods for noise emitted by accelerating motor vehicles". The standard is constituted on the basis of the original standard on limits for automotive noise GB1495-1979 "Limits for noise emitted by motor vehicles"and the practical situation of our automotive products. According to the statistic data, more than half of the trucks produced in our country can't meet the requirement of the second phase limits of the standard which has been carried into execution in January 1, 2005. This paper is carried out on the basis of the project "Analysis and control of light duty truck exterior noise"supported by the domestic auto manufacturer. In order to reduce the noise emitted by accelerating motor vehicles of the light duty truck, the main exterior noise sources of the light duty truck are firstly identified with the method of sound intensity measurement in this paper. After the noise emitted from the bottom of the engine is confirmed as the main exterior noise source of the light duty truck, some acoustic materials are chosen on the basis of the frequency characteristic of the noise emitted by the engine, and the material is used to absorb and insulate the noise. As a result, the noise emitted by accelerating motor vehicles of the light duty truck is reduced 3.8dB(A). The main research works completed in this paper are as follows: In order to get a sufficient cognition of the exterior noise of the light duty truck, the noise emitted by accelerating motor vehicles of the truck is measured according to GB1495-2002. The measurement result indicates that the noise emitted by accelerating motor vehicles of the light duty truck is 84.0dB(A), it is 4dB(A) above the first phase limits of the criteria GB1495-2002 "Limits and measurement methods for noise emitted by accelerating motor vehicles"and 6dB(A) above the second phase limits of the criteria. After comparing several methods of noise source identification, the method of sound intensity measurement is chose to identify the exterior noise source of the light duty truck, because this method has good measurement precision and the measurement result is intuitionistic. On the basis of analyzing the causes of the errors that exist in sound intensity measurement, some methods are brought forward according to the analysis results. The methods can be used to decrease the errors in the practical measurement. After choosing the apparatus and framing the measurement step, the main exterior noise source of the light duty truck is identified by the method of sound intensity measurement, and the noise emitted from the bottom of the engine is confirmed as the main exterior noise source of the light duty truck. During identifying the exterior noise source of the light duty truck by the method of sound intensity measurement, a shortcoming of the B&K 3560C sound intensity measurement system is found, and the shortcoming is that this system can only measure the sound intensity of the plane on which the distance between the measurement points is equal. In order to make up this shortcoming, a set of sound intensity data processing software is designed with the tool of MATLAB GUI in this paper. When the software is combinedwith B&K 3560C portable data gather system and 3599 sound intensity probe, the sound intensity of the plane on which the distance between the measurement points is not equal can be measured. In order to choose the proper material to shelter the noise, a set of material acoustic performance measurement system based on the method of impedance tube is devised. The system is devised on the basis of GB/T18696.2-2002 "Determination of sound absorption coefficient and impedance in impedance tubes-Part 2:Transfer function method"and some related theory on transmission loss measurement. The system can be used to measure not only the sound absorption coefficient of the material but also its transmission loss. The sound absorption coefficient and transmission loss of about twenty kinds of material are measured in the material acoustic performance measurement system. According to the measurement result and the frequency characteristic of the noise emitted by the engine of the light duty truck, some material is chose and used to shelter the noise. After the noise reduction measure is carried out, in order to validate the validity and the effect of the measure, the exterior noise source of the light duty truck is identified by the method of sound intensity measurement again, and the noise emitted by accelerating motor vehicles of the light duty truck is also measured. After analyzing and comparing the results of the two experiments of the noise source identification and the measurement of the noise emitted by accelerating motor vehicles, some conclusions are drawn: after the noise reduction measure is carried out, the noise emitted by accelerating motor vehicles of the light duty truck is reduced from 84.0 dB(A) to 80.2dB(A), and meets the requirement of the first phase limits of 80 dB(A) of the criteria GB1495-2002 "Limits and measurement methods for noise emitted by accelerating motor vehicles"on the whole, but it is still about 2dB(A) above the second phase limits of 78dB(A) of the criteria. In order to make the noise emitted by accelerating motor vehicles of the light...