The Semi-active Muffler Device Research Of Controlling The Exhaust Pipe’s Low-frequency Noise

This topic put forward a new kind of semi-active muffler device which can control exhaust pipe low-frequency noise. It has solved both the traditional problem of poor performance of muffler in the low frequency noise elimination, and solved the technical problem which is caused by the semi-active muffler device based on existing HQ tube cannot adjust the matching Path difference accurately and rapidly as the incident frequency noise which leads to the noise reduction result limited.This semi-active muffler device proposed in this topic includes the main line, telescopic by-pass pipe equipment, fixed by- pass branch pipe, the electromagnetic valve that is used to change the through path of noise and the control system which is used to detect noise frequency and control magnetic valve and stepper motor. When noise passes through the main line, in the intersection made by the by-pass pipe and the main pipe, part of the noise would go into the by-pass pipe, and the other noise went on moving forward along the main line. By setting the microphone at the entrance of the noise and detect the frequency of the noise and calculate the matching path difference of by-pass pipe and the main pipe and by controlling the solenoid valve closed position and adjusting the length of the telescopic by-pass pipe achieved this path difference, which could make two columns noise waves that travel in different paths in the by-pass pipe and main line in the second intersection phase opposite, so as to occur destructive interference, then achieve the aim of noise elimination.In this article, by using the Matlab software it conducted the simulation research to the control system of this semi-active muffler device, which shows that the digital signal processing system established in this paper could extract the fundamental frequency accurately and can effectively control the step motor and the electromagnetic valve obtain and the matching path difference with the fundamental frequency noise frequency. This article also conducted the simulation research to the property of the semi-active muffler device through the ANSYS software, which can be seen from the results of the analysis, the semi-active muffler device, in low frequency band, has a good noise elimination performance, especially in the 150 Hz or lower frequency range, the average noise elimination is at about 35 dB.In this paper, It also obtained the noise elimination graph of this semi--active muffler device, from 30 Hz to 465 Hzfrequency range through experiments and respectively put it make a contrast with the finite element simulation results and the traditional resistance muffler attenuation curves. Compared with the simulation results indicate that, in the low frequency of 150 Hz, the result of the experiment and simulation was consistent, in more than 150 Hz frequency, silencing quantity is lower than the simulation value of the experiment. Compared with the traditional resistance muffler, in a 150 Hz or lower frequencies, the semi-active silencer muffler performance is much better than the resistance muffler;In the 350 Hz frequency range, the semi-active muffler noise elimination performance is superior to the resistance muffler;In more than 350 Hz frequency, the semi-active muffler noise elimination performance is more poor compared to the resistance muffler.Based on the above analysis, we can conclude that for low frequency noise below 350 Hz, adopting the semi-active muffler device researched by this topic to control is effective.