JPS6235008A - Temperature control type adaptive noise suppressor - Google Patents

Abstract

PURPOSE:To improve the noise suppressing property in wide frequency range by adjusting the temperature of a resonator in proportion to the number of revolution of a rotary machine as a sound source, and thereby making a resonance frequency follow a prevailing frequency to be suppressed. CONSTITUTION:A heater 8 is provided on a resonator composed of a resonance pipe 2 and resonance chamber 3 which are mounted to the duct 1 of a rotary machine 4 as a sound source. The number of revolution of the rotary machine 4 is detected by a tachometer 5 and the number of revolution (n) is exchanged to a temperature command signal (t) by a converting device 6 so as to control the heater 8 by a temperature adjusting part 7. Therefore, the resonance frequency of the resonator is made to follow a prevailing frequency, thereby it is possible to remarkably reduce the noise in a duct.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a device for significantly silencing the exhaust noise of an internal combustion engine and the periodic noise in a duct generated from rotating equipment such as a blower or a ventilation fan.

Prior art and its problems Resonance-type silencers are effective in attenuating low-frequency sounds without increasing their size, so they are used alone or in combination with cavity-type silencers. . The amount of attenuation is determined by the resonance frequency fr, where C: speed of sound S: cross-sectional area of the resonance tube l: length of the resonance tube V: volume of the resonance chamber, theoretically it is infinite, and it can be made extremely large in practice. . Therefore, if the resonant frequency of the resonator is set to the predominant frequency of the sound source, the silencing effect is extremely large. However, this resonant muffler has the disadvantage that it cannot attenuate almost any sound at frequencies other than the resonant frequency. Therefore, when a resonant silencer is applied to an internal combustion engine or the like where the rotational speed constantly fluctuates, the noise reduction effect cannot be achieved as is. Therefore, there has been an invention to attenuate frequencies other than the resonance frequency to some extent by increasing the number of resonance tubes in a resonance type muffler or changing their shape (Japanese Patent Publication No. 59-5764). However, this comes at the expense of a very large damping effect at the resonant frequency, so a pure resonator has the disadvantage that no sound damping effect can be expected. There is also a method (Japanese Patent Laid-Open No. 59-250969) in which the volume of the resonance chamber is changed to adaptively make the resonance frequency follow the dominant frequency of the sound source. However, mechanically changing the volume, etc. in this way not only complicates the mechanism, but also has the drawback of making maintenance management difficult.

OBJECTS OF THE INVENTION In order to solve these drawbacks, the present invention provides an automobile whose rotational speed constantly changes, in which the resonant frequency of the resonator adaptively follows the dominant frequency of the sound source by adjusting the temperature of the resonator section. It is intended to be used to significantly attenuate engine exhaust noise and factory noise coming out through ventilation fans.

Structure of the Invention The present invention provides a resonant silencer for muffling sounds in a duct, which includes a tachometer unit that measures the rotational speed of a rotating device serving as a sound source, or a frequency analysis of a sound wave from the sound source side in the duct.
A detection section that detects the frequency of a prominent component among them, a conversion section that makes the rotation speed and predominant frequency proportional to the resonant frequency of the resonator, and a resonant frequency that can be adjusted by adjusting the temperature of the resonator. It consists of a temperature control section and is configured to make the resonance frequency of the resonator follow the rotational speed and dominant frequency.

The operation of the present invention will be explained in more detail using the operation diagram of the invention. 1st
The figure is a diagram of the principle of the present invention. In this Figure 1, 4
is a noise source generated by the rotation of an automobile engine, blower, ventilation fan, etc., and indicates that the sound generated by this is emitted into the duct 1. The length of the duct is 11
A Helmholtz resonator consisting of a resonance tube 2 with a cross-sectional area S and a resonance chamber 3 with a volume V is attached. Generally, sound generated from rotating equipment has a periodic waveform that is synchronized with rotation. As can be seen by Fourier transformation, the periodic waveform (,t) has a fundamental frequency and frequency components that are integral multiples of the fundamental frequency.

That is, the frequency characteristics are as shown in FIG. 2. The predominant frequency fo among them is fo=kn (2), where n is the rotational speed of the rotating equipment and k is the proportionality constant.

On the other hand, if the temperature inside the resonance chamber is t°C, the velocity C is c =
(332+0.6t) tn/s. Therefore, the resonance frequency in equation (1) is expressed by the following equation, where h is the proportionality constant.

fr = h (332+0.6t) −(3
) To match fo in equation (2) and f in equation (3), use t-1,67((k/h) n-332)
−(4) may be used. That is, the converter 6 is
The rotational speed n measured by the tachometer 5 is converted to L using equation (4). The temperature controller 7 heats a heater provided around the resonance chamber to maintain the temperature of the resonance chamber at t°C.

In this way, fo = fr · (5), and the resonant frequency of the resonator can be matched with the dominant frequency to be muted. Since the resonator can significantly damp the resonant frequency components, the noise from the rotor is significantly reduced at the outlet of the duct. Also, even if the rotation speed of the rotating equipment changes, if it is configured as shown in Figure 1,
Since the resonant frequency always matches the predominant frequency of the sound source, the silencing ability of the resonator can be utilized to the fullest.

Example If the rotation speed cannot be measured or if the sound source is a non-rotating device, detect the noise from the sound source 4' with the microphone 9 from a point near the sound source in the duct as shown in Figure 3. Frequency analysis is performed to detect the dominant frequency fr, and the temperature is adjusted through the converter 6 and the temperature controller 7 so that fo=fr, and the resonant frequency of the resonator is made to follow the dominant frequency.

Furthermore, if it is desired to mute the components 2fo and 3to other than the dominant frequency fO, a plurality of resonators as described above may be installed in the duct.

As described above, according to the present invention, the resonant frequency is adaptively adjusted so that the high silencing ability of the resonant silencer can always be exhibited, so that the number of dominant layers'e constantly fluctuates. It also has an extremely strong silencing effect when it comes to noise. Furthermore, since no mechanical mechanism is used to change the resonance frequency, the mechanism and maintenance are easy, and there is no problem of sound leakage. Furthermore, since one resonator can accommodate all frequencies, there is no need to use many resonators with different resonance frequencies. Therefore, there is an effect that the device can be made smaller.

[Brief explanation of drawings]

FIG. 1 shows a diagram of the principle of the present invention. FIG. 2 is an example of frequency characteristics of periodic noise having a dominant frequency fO. FIG. 3 shows another embodiment of the invention. In the figure, 1 is a duct, 2 is a resonance tube, 3 is a resonance chamber,
4 is a sound source accompanied by rotation, 4' is a general sound source, 5 is a tachometer, 6 is a conversion section, 7 is a temperature adjustment section, 8 is a heater, 9 is a microphone, and 10 is a dominant frequency detection section. 10th

Claims (1)

[Claims] A resonant silencer for eliminating sound in a duct includes a tachometer unit that measures the rotation speed of a rotating device that is a sound source, or a detection unit that detects the predominant frequency of the sound source, and a resonator that detects the rotation speed or predominant frequency. a conversion unit that makes the resonance frequency proportional to the resonance frequency of the
A temperature-controlled adaptive silencer is characterized by comprising a temperature control section that can heat and cool a resonator in order to change the resonance frequency, and making the resonance frequency of the resonator follow the rotational speed and dominant frequency.