Study On The Acoustic Attenuation Characteristics Of Automotive Engine Air Cleaner

Induction noise is one of the major automotive noise sources. This paper introduced the situation and methods of intake system noise study, explained the source characteristics and generation mechanisms as well as the control method of intake noise. In view of the fact that the air cleaner may act as an effective intake silencer, the present paper investigated the acoustic attenuation characteristics of air cleaner in detail.Filter paper is a good absorbing material, and its effect on the acoustic attenuation characteristics of air cleaner should be considered. The acoustic characteristics of absorptive materials calculated by SYSNOISE were validated by comparing the experimental results with the calculated results. The effect caused by utilizing absorptive material on muffler had also been studied.The methods of measuring the acoustic characteristic parameters of air cleaner and absorbing material had been studied for the case without mean flow. According to the principle of Two-Load method, the simple expansion chamber was used to verify the methods of measuring the transmission loss of muffler carried out by impedance tube, and the fiber glass was used to verify the methods of measuring the acoustic characteristic parameters of absorptive material combined with the subroutine coded by MATLAB. The characteristic impedance and complex wavenumber of filter paper had also been measured.The finite element models of air cleaner were created based on the physical model of Jetta car and the acoustic characteristic parameters of filter paper were imported to software SYSNOISE for modedling the property of filter paper. The transmission loss of air cleaner had been calculated and compared with the measured results. The results indicated that the model created for air cleaner was reasonable. A simplified model based on the physical model of air cleaner was also created; the acoustic attenuation characteristics of the air cleaner had been studied with the position and thickness of filter paper fixed, the extended length of inlet pipe invariable, the extended length of outlet pipe variable. The results indicated that the desired acoustic attenuation performance of air cleaner can be obtained by accommodating the length of extended pipes.