Application Of Noise Source Identification For The Engine With Beamforming And NAH Techniques

According to the survey of the professional organization on the automotive market,the consumers complained about the engine noise constantly,because it affects the ride comfort.In addition,the government is discussing to reduce the level of noise emitted by accelerating motor vehicles.According to the draft for noise emitted by accelerating motor vehicles,the new noise level should be reduced by 1 to 4 d B(A),which sets higher requirements on the vehicle's noise.A large number of studies have shown that engine noise is an important source of the vehicle noise.Based on the market and national regulation,the engine noise level was put forward higher requirements.An effective way to reduce engine noise is to find the main engine noise source and improve it in order to achieve less duplication of effort.However,based on the complexity of engine noise field,the traditional methods of noise source identification cannot meet the requirements.Therefore,it is necessary to develop a method that can quickly and accurately identify the noise source.In order to cope with the defects of traditional noise source identification techniques,the visual noise source identification techniques were developed.As a practical engineering study,this paper discusses two visual noise source identification techniques including beamforming and nearfield acoustic holography,and applies them to identify engine noise.In this paper,two kinds of visual noise source identification techniques(beamforming and nearfield acoustic holography)are studied theoretically.Three methods of beamforming(delay-sum beamforming based on plane wave assumption,delay-sum beamforming based on spherical wave assumption and cross-spectral beamforming method with exclusion of autospectra)and three methods of nearfield acoustic holography(two-dimensional spatial Fourier transformation method,boundary element method,Helmholtz equation least-squares method)are introduced.Also their features are studied.Based on the features of the beamforming and nearfield acoustic holography,a variety of experimental research on these two kinds of visual noise source identification techniques are carried out.The low frequency and high frequency sounds emitted by a pair of speake rs are used as the noise source.The visual noise source identification experiments established that the nearfield acoustic holography method in low frequency region and beamforming method in the high frequency region have a good ability for identifying noise source.Finally,two visual noise source identification techniques(beamforming and nearfield acoustic holography)are applied in the practical engineering.The nearfield acoustic holography method is used to identify the front end noise of the engine.The beamforming method is used to identify the noise of the engine exhaust side and the powertrain system.The visual noise source identification techniques can provide the improvement direction for reducing noise level of the engine.The research results show that the two kinds of visual noise source identification techniques(beamforming and nearfield acoustic holography)can not only identify the noise source of th e engine,but also can identify the noise of other parts of the vehicle.The application prospect of the two visual noise source identification techniques is very broad.