JP3701800B2 - Electronic silencer system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electronic silencing system and a silencing method that can reliably silence noise even when the exhaust flow is fast.
[0002]
[Prior art]
FIG. 5 schematically shows a configuration of a general electronic silencing system, in which a reference microphone and an error microphone are arranged along an exhaust duct across a secondary sound source that generates a sound wave for silencing. The sound wave having a phase opposite to that of the sound is emitted from the secondary sound source into the duct to cancel the noise. In the figure, an exhaust duct 1 having one end connected to the noise source 2 is arranged in order from the side closer to the noise source 2 in the direction Y of the exhaust gas flowing in the exhaust duct 1, that is, from upstream to downstream. The reference microphone 3, the secondary sound source 4 and the error microphone 5 are arranged, and the output signals of the reference microphone 3 and the error microphone 5 are processed by the processing unit 6 and then given to the secondary sound source 4.
[0003]
In the processing unit 6, an analog signal representing a sound wave received by the reference microphone 3 is converted into a digital signal, then processed by the adaptive filter 6, converted into an analog signal, and given to the secondary sound source 4. Then, the sound is emitted into the exhaust duct 1 as a sound wave for silencing.
[0004]
A signal obtained by converting the output signal of the reference microphone 3 into a digital signal is also applied to the controller 62, and the controller 62 receives a signal obtained by digitally converting the analog output signal from the error microphone 5 as an error signal. The controller 62 determines the filter coefficient of the adaptive filter 61 so that the error signal is minimized.
[0005]
However, in such an electronic silencing system, when a sound is detected by making a hole in the exhaust duct wall, if the flow rate of the exhaust gas in the exhaust duct 1 increases, the sound other than the silencing target frequency increases. However, there is a problem that the S / N ratio is deteriorated and the silencing effect is deteriorated. In order to solve this problem, conventionally, as shown in FIG. 6A, a bullet type or streamlined nose in which either or one of the reference microphone 3 and the error microphone 5 is arranged in the exhaust gas is used. As shown in FIG. 6 (B), a sound is passed through the wall of the exhaust duct 1 at either or both of the reference microphone 3 and the error microphone 5 as shown in FIG. The reference microphone 3 or the error microphone 5 is installed on the surface 11 parallel to the exhaust duct 1 of the protrusion 10 by providing a protrusion 10 having a space 9 surrounding the slit 8.
[0006]
However, when the nose cone 7 and the protrusion 10 shown in FIGS. 6A and 6B are installed, the structure of the silencer itself becomes complicated, and the exhaust gas reaches 400 ° C. However, there is a problem that it is difficult to make a structure that can withstand such exhaust gas.
[0007]
[Problems to be solved by the invention]
The present invention has been made to solve the various problems described above, and the present invention reliably provides a silencing effect even when the exhaust flow speed is high or the exhaust flow temperature is high. An object of the present invention is to provide an electronic silencing system capable of
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides:
A reference microphone, a secondary sound source, and an error microphone are installed in this order in the direction of the exhaust gas flow from the noise source to the exhaust duct connected at one end to the noise source, and the sound waves received by the reference microphone and the error microphone are An electronic muffler system for processing and generating a sound wave for muffling from the secondary sound source,
An electronic silencing system, characterized in that a slow speed means for slowing the flow rate of the exhaust gas is installed on the noise source side of at least one of the reference microphone and the error microphone;
I will provide a.
[0009]
In one embodiment of the present invention, the slow speed means is a wedge-shaped wall having a triangular cross section along the flow of the exhaust gas, or a square wall having a cross section along the flow of the exhaust gas.
[0010]
The wall is preferably arranged such that a distance between the reference microphone or the error microphone and a side surface of the wall perpendicular to the flow of the exhaust gas is smaller than ½ of the height of the wall surface.
[0011]
[Action]
Since the slow speed means locally slows the exhaust gas flow velocity at the location where the reference microphone or the error microphone is installed, even if the exhaust gas flow velocity is large, deterioration of the noise reduction effect due to the deterioration of the SN ratio is prevented. Is done.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, one embodiment of an electronic silencing system according to the present invention will be described with reference to FIGS. 1 and 2, the same or similar components as those shown in FIGS. 5 and 6 are indicated by the same reference numerals.
[0013]
In FIG. 1, a through hole is formed in a wall surface at an appropriate location of the exhaust duct 1, and the sound detection unit 12 is attached to the through hole so that the exhaust gas in the exhaust duct 1 does not leak. The sound detection unit 12 is configured by a tube in which a cavity that is continuous from one end to the other end is formed so that the sound in the exhaust duct 1 can be transmitted, and a reference microphone 3 is attached to the other end of the sound detection unit 12. It is done.
[0014]
A wall 13 is installed on the upstream side of the sound detection unit 12, that is, on the noise source 2 side. 2A is a top view of the wall 13, FIG. 2B is a front view thereof, and FIG. 2C is a side view thereof. As shown in FIGS. 1 and 2 (A) to (C), the wall 13 has a wedge shape with a sharp tip, and the upper surface 14 of the wall 13 is an isosceles triangle. The rear surface 16 toward the inner wall, that is, the surface positioned at a right angle to the downstream side of the exhaust gas flow direction Y and the inner wall of the exhaust duct 1 forms a desired angle, for example, an angle of about 90 degrees. The cross section 15 along the direction Y of the exhaust gas flow on the wall 13 has a triangular shape. The bottom surface of the wall 13 forms an arc having the same curvature as that of the inner wall so that a cross section perpendicular to the flow direction Y of the exhaust gas is joined to the inner wall of the exhaust duct 1 without a gap.
[0015]
The material of the wall 13 is preferably the same as that of the exhaust duct 1 and is, for example, iron or stainless steel, but is not limited thereto. Further, the main surface 17 may be a quadrilateral instead of an isosceles triangle.
[0016]
The wall 13 is located on the upstream side of the sound detection unit 12 and has a wedge shape that gradually increases in height along the flow direction Y of the exhaust gas, so that the sound detection unit 12 communicates with the exhaust duct 1. There is an effect of locally reducing the flow rate of the exhaust gas. Therefore, even if the flow rate of the exhaust gas is large in the exhaust duct 1, the flow rate of the exhaust gas is locally reduced at the position where the sound detection unit 12 communicates with the exhaust duct 1, so that the silencing effect due to the deterioration of the SN ratio is achieved. No deterioration occurs.
[0017]
As shown in FIGS. 1 and 2 (A), (B), and (C), the width, length, and height of the wall 13 are W, L, and H, respectively, and the rear surface 16 of the wall 13 and the sound detection unit 12. If the distance from the center line is X, for example, W = 800 (mm), L = 1000 (mm), and H = 100 (mm). It has been experimentally confirmed that it is desirable to provide the wall 13 at a position satisfying X ≦ H / 2. Furthermore, when the inner diameter of the exhaust duct 1 is D (mm), if the height H of the wall 13 is about 1/18 of D, the wall 13 does not affect the flow of exhaust gas, and It has also been experimentally confirmed that the flow rate of the exhaust gas can be locally reduced at the portion where the sound detection unit 12 is located.
[0018]
3A and 3B show the frequency characteristics of the intensity of sound output from the detection microphone installed at the output of the exhaust duct 1 in order to detect the silencing effect on the sound propagating in the exhaust duct 1. It is a graph to show, (A) has shown the frequency characteristic when the wall 13 is not installed, (B) has shown the frequency characteristic when the wall 13 is installed, and the part which gave the oblique line is 50-100 Hz This is the frequency to be silenced, that is, the frequency to be silenced. In fact, it has been found that suppressing the noise level in the vicinity of the silencing target frequency leads to improvement in silencing efficiency. Therefore, looking at the periphery of the muffling target frequency, in the graph of FIG. 3A, the level around the muffling target frequency is high, and only a part of the muffling target frequency can be detected. The effect is inferior. On the other hand, in the graph of FIG. 3B, since the level around the silencing frequency is lowered, the entire silencing target frequency can be well detected and the silencing effect is improved.
[0019]
In the description so far, the wall 13 has a pointed wedge shape as shown in FIG. 2, but the shape of the wall 13 is not limited to this, and for example, FIG. The shape shown in (B) can also be taken. The wall 13 shown in FIG. 4A is formed by bending a single plate. (A) is a perspective view thereof, (B) is a top view thereof, (C) is a front view, and (D) is a front view. It is a side view. As shown in the figure, the wall 13 has a quadrilateral main surface 17 parallel to the flow direction Y of the exhaust gas, a slope 18 provided obliquely with respect to the main surface 17, and approximately 90 degrees with respect to the main surface 17. And a rear surface 16 provided on the same side as the inclined surface 18. Also in this example, the end portions in contact with the inner wall of the exhaust duct 1 on the slope 18 and the rear surface 16 form an arc having the same curvature as the curvature of the inner wall so as to be joined to the inner wall of the exhaust duct 1 without a gap. Note that the wall 13 shown in FIG. 4A is not limited to one formed by bending a single plate, and the cross section along the flow of the exhaust gas may be a rectangle.
[0020]
FIG. 4B shows the shape of the wall 13 to be installed in a portion where the inner wall of the exhaust duct 1 is a plane, (A) is a top view thereof, (B) is a front view, and (C). Is a side view. As shown in the figure, the upper surface 14 is a quadrilateral, the cross section along the flow direction Y of the exhaust gas is a triangle, for example, a right triangle, the rear surface 16 is a quadrilateral, and each surface is formed by a plate. Yes.
[0021]
Furthermore, although the case where the wall 13 is arranged upstream of the reference microphone 3 has been described so far, the wall 13 is arranged upstream of the reference microphone 3 and the error microphone 5 in order to obtain a desired silencing effect. can do. In some cases, the wall 13 may be arranged on the upstream side of only one of the reference microphone 3 and the error microphone 5.
[0022]
【The invention's effect】
As described above, as is apparent from the description of one embodiment of the electronic silencing system according to the present invention, the sound detector 12 communicates with the exhaust duct 1 even when the flow rate of the exhaust gas is high. Since the exhaust gas flow velocity is locally reduced at the position where the noise is applied, the noise reduction effect caused by the deterioration of the SN ratio is not deteriorated.
[0023]
Further, since the slow speed means can be a wedge-shaped wall, manufacture is simple.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing one embodiment of an electronic silencing system according to the present invention.
2A, 2B, and 2C are a top view, a front view, and a side view of the wall of FIG. 1, respectively.
FIGS. 3A and 3B are diagrams for explaining a silencing effect by providing a wall, where FIG. 3A shows frequency characteristics when no wall is provided, and FIG. 3B shows frequency characteristics when a wall is provided.
4A and 4B are diagrams showing modifications of the wall 13, respectively.
FIG. 5 is a diagram schematically showing a configuration of a conventional electronic silencing system.
FIG. 6 is a diagram showing a conventional microphone arrangement when the exhaust gas flow rate is high.
[Explanation of symbols]
1: exhaust duct, 3: reference microphone, 5: error microphone,
12: Sound detection unit, 13: Wall

Claims (4)

A reference microphone, a secondary sound source, and an error microphone are installed in this order in the direction of the exhaust gas flow from the noise source in a duct connected at one end to the noise source, and the sound waves received by the reference microphone and the error microphone are processed. An electronic silencing system for generating a sound wave for silencing from the secondary sound source, and a slow speed means for slowing the flow rate of the exhaust gas toward the noise source side of at least one of the reference microphone and the error microphone An electronic silencer system characterized by the installation of 2. The electronic muffler system according to claim 1, wherein the slow speed means is a wedge-shaped wall having a triangular cross section along the flow of the exhaust gas. 2. The electronic muffler system according to claim 1, wherein the slow speed means has a quadrangular wall in a cross section along the flow of the exhaust gas. The wall is arranged such that a distance between the reference microphone or the error microphone and a side surface of the wall perpendicular to the flow of the exhaust gas is smaller than half of the height of the wall surface. Electronic silencer system of 2 or 3.

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