Influencing factors:
Intake system noise is one of the main noise sources of automobiles, and it is of great significance to control and optimize it. The intake noise is caused by the pressure fluctuations caused by the periodic opening and closing of the intake valve and the high-speed airflow flowing through the intake valve passage during the intake process. Depending on the generation mechanism, the intake noise mainly includes the following: periodic pressure pulsation noise, eddy current noise, Helmholtz resonance noise of the cylinder and air column resonance noise of the intake pipe; air filter and Helmholtz muffler noise The wall plate is very thin, and it is easy to be excited and cause radiated noise when high-speed airflow passes through it. The acoustic performance of the intake system is affected by factors such as the volume of noise reduction, the cross-sectional area of the pipe, and the position of the intake nozzle.
Noise reduction measures for the intake system:
The methods for dealing with gas flow noise and structure noise are relatively simple, and they are often not the main noise of the intake system. This paper mainly discusses the noise reduction measures of low frequency noise.
(1) Reasonably design the air filter. Generally speaking, the larger the muffling volume, the better the muffling effect, but it is also necessary to comprehensively consider the layout space, the weight of the parts and the cost of the parts. Under normal circumstances, the volume of the air filter can reach more than 3 times the volume of the engine, and a good noise reduction effect can be achieved.
(2) Determine the diameter and length of the inlet and outlet pipes of the air filter. Reducing the diameter of the inlet and outlet pipes of the air filter and increasing the expansion ratio is conducive to reducing noise, but it will increase the resistance of the intake system, reduce the intake air volume of the engine, and affect the performance of the engine. The effective muffling frequency of the air filter is related to the length of the trachea. If the length of the intake pipe is increased, the effective muffling frequency of the air filter will move to the low frequency. Therefore, it is also necessary to reasonably design the length of the inlet and outlet pipes.
(3) Reasonable design of muffler components. Commonly used muffling components include resonant cavity, 1/4 wavelength tube, porous tube and braided tube. The resonant cavity is generally aimed at low frequencies, the 1/4 wavelength tube is generally used to eliminate medium and high frequency noise, and the porous tube and braided tube are mainly used to eliminate noise with a relatively wide frequency band.
