JPH0816174A - Active type silencer - Google Patents

Abstract

PURPOSE:To surely prevent the generation of howling of an active type silencer constituted to positively silence noises of exhaust gases, etc., by a secondary sound source. CONSTITUTION:This active type silencer is constituted by inserting a flow pipe 49 in which gases flow into a silencing chamber 45 formed at a silencer body 41, forming through-holes 51 in the part of this flow pipe 49 existing in the silencing chamber 45 and arranging the secondary sound source 55 which radiates sound waves toward the silencing chamber 45 within a secondary sound source chamber 47 formed adjacently via a partition wall 43 in the silencing chamber 45. The active silencer described above has a communicating hole 64 which is disposed on the upstream side of the secondary sound source 55 of the partition wall 43 or in proximity to the secondary sound source and the secondary sound source chamber 47, a microphone 65 which is arranged in this communicating hole 64 or near this hole and an inverting means 75 which inverts the electric signal from this microphone 65 and outputs the electric signal to the secondary sound source 55.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention eliminates noise such as exhaust gas
The present invention relates to an active silencer that actively silences sound by a secondary sound source.

[0002]

2. Description of the Related Art Conventionally, as an active silencer that actively suppresses noise of exhaust gas by a secondary sound source,
For example, the one disclosed in Japanese Utility Model Publication No. 6-14424 is known.

FIGS. 3 and 4 show an active silencer of this type. In the drawings, reference numeral 11 denotes a silencer body having a rectangular cross section. This silencer body 11
Is divided into three by a partition wall 13 arranged at a predetermined interval, a muffling chamber 15 is formed in the center, and speaker chambers 17 are formed on both sides of the muffling chamber 15.

An exhaust pipe 19 that circulates the exhaust gas G is inserted into the muffler chamber 15. The exhaust pipe 19
In the interior of the muffling chamber 15, a large number of small holes 21 are formed.

An opening 23 is formed in the pair of partition walls 13 at a position facing each other around the exhaust pipe 19, and a speaker 25 as a secondary sound source is arranged in the opening 23.
A protective plate 27 for protecting the speaker 25 is arranged in the opening 23 of the partition wall 13, and a large number of small holes 29 are formed in the protective plate 27.

A sound absorbing material 31 made of, for example, glass wool is housed in the muffling room 15 and the speaker room 17. In addition, a microphone 33 is arranged in the muffling chamber 15, and the microphone 33 and the speaker 25 are connected via an inverting circuit 37 and a power amplifier 39.

In such an active silencer, noise of the exhaust gas G is detected by the microphone 33, and a erasing sound having a phase opposite to the detected noise is radiated from the speaker 25, whereby so-called active muffling is performed. Done.

[0008]

However, in such a conventional active silencer, the sound radiated from the speaker 25 is detected again by the microphone 33, so that the radiated sound from the speaker 25 passes through the closed circuit. However, there is a problem in that howling is likely to occur and therefore a sufficient silencing effect cannot always be obtained.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to provide an active silencer capable of reliably preventing howling from occurring.

[0010]

An active silencer according to a first aspect of the present invention has a silencer chamber formed in a silencer body, in which a gas flow passage is inserted, and the gas passage is located in the silencer chamber. An active silencer in which a secondary sound source that emits sound waves toward the silencing chamber is disposed in a secondary sound source chamber that is formed adjacent to the silencing chamber through a partition wall and has a through hole formed in the portion. In the upstream of the secondary sound source of the partition wall, or in the vicinity of the secondary sound source, a communication hole for communicating the silencing chamber and the secondary sound source chamber, and the microphone arranged in the communication hole or in the vicinity thereof. And an inverting means for inverting the electric signal from the microphone and outputting the inverted signal to the secondary sound source.

According to a second aspect of the present invention, in the active silencer according to the first aspect, the pressure receiving surface of the microphone is covered with a sound wave transmitting member. The active silencer of claim 3 is
In Claim 1 or 2, the said gas is exhaust gas from an engine.

An active silencer according to a fourth aspect of the present invention is the active silencer according to the first or second aspect, wherein the gas is intake gas from the engine.

[0013]

In the active silencer according to the first aspect of the present invention, a communication hole is formed on the upstream side of the secondary sound source of the partition wall to connect the muffler room and the secondary sound source room, and the microphone is arranged in this communication hole. In the microphone, gas noise and sound emitted from the front surface of the diaphragm of the secondary sound source are emitted from the side of the secondary sound source,
Radiated sound from the rear surface of the diaphragm of the secondary sound source arrives and is detected.

However, since the sound emitted from the front surface of the diaphragm of the secondary sound source and the sound emitted from the rear surface have opposite phases,
The electrical signals of the microphones cancel each other out,
The electric signal output from the microphone becomes a signal of only gas noise, and since only this electric signal is inverted by the inverting means and output to the secondary sound source, the radiated sound from the secondary sound source passes through the closed circuit. There is almost no formation.

In the active silencer of the second aspect, since the pressure receiving surface of the microphone is covered with the sound wave transmitting member, unnecessary high frequency sound waves are attenuated by the sound wave transmitting member, and heat is cut off. Foreign matter is prevented from adhering to the surface.

In the active silencer of the third aspect, the noise in the exhaust gas is silenced. In the active silencer of the fourth aspect, the noise in the intake gas is silenced.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an embodiment in which the active silencer of the present invention is applied to an engine exhaust system. In the figure, reference numeral 41 indicates a silencer body having a rectangular cross section.

The muffler body 41 is divided into three by a pair of partition walls 43 arranged at a predetermined interval, a muffling chamber 45 is formed in the center, and speaker chambers 47 are formed on both sides of the muffling chamber 45. There is.

An exhaust pipe 49 which circulates the exhaust gas G is inserted into the muffler chamber 45, and a large number of small holes 51 are formed in a portion of the exhaust pipe 49 located inside the muffler chamber 45. There is.

An opening 53 is formed in the pair of partition walls 43 at a position facing each other around the exhaust pipe 49. In this embodiment, the center of the opening 53 is located at the downstream end of the silencer body 41. Is located at a distance of 1/3 of the total length of the silencer body 41.

A speaker 55, which is a secondary sound source, such as a round speaker, is arranged in the opening 53. A protective plate 57 for protecting the speaker 55 is arranged in the opening 53 of the partition wall 43, and a large number of small holes 59 are formed in the protective plate 57.

A sound absorbing material 61 made of, for example, glass wool is housed in the muffling room 45 and the speaker room 47. Then, in this embodiment, the speaker 5 of the partition wall 43 is
A communication hole 64 that connects the muffling chamber 45 and the speaker chamber 47 is formed on the upstream side of 5.

The microphone 6 is inserted in the communication hole 64.
5 are arranged. As shown in FIG. 2, the microphone 65 has a bracket 6 at the end opposite to the pressure receiving surface 65a.
It is fixed to the partition wall 43 via 7.

A sound wave transmitting member 69, which covers the pressure receiving surface 65a of the microphone 65, is inserted and fixed in the communication hole 64. The sound wave transmitting member 69 is formed of a porous body made of ceramic or the like, or a heat resistant fiber made of glass wool or the like.

A hole 69a into which the pressure receiving surface 65a of the microphone 65 is inserted is formed on the microphone 65 side of the sound wave transmitting member 69, and a groove 69b into which the partition wall 43 is fitted is formed on the other side. .

The microphone 65 is connected to the filter 71. The filter 71 suppresses frequency components other than exhaust noise in the electric signal from the microphone 65.

The filter 71 is connected to the inverting circuit 75 via the power amplifier 73. The power amplifier 73 is
The electric signal from the filter 71 is amplified. Inversion circuit 75
Outputs the signal inverted from the power amplifier 73 to the speaker 55.

In the above-described active silencer, in the microphone 65, the exhaust noise from the silencer chamber 45 side and the sound emitted from the front surface of the diaphragm 63 of the speaker 55 are generated in the speaker chamber 4.
Radiated sound from the rear surface of the diaphragm 63 of the speaker 55 arrives from the 7 side and is detected.

However, the diaphragm 63 of the speaker 55 is
Since the radiated sound from the front surface and the radiated sound from the rear surface have opposite phases, the electric signals of the microphones 65 cancel each other out, and the electric signals output from the microphone 65 are substantially exhaust noise only signals. , The phase of only this electric signal is inverted by the inverting circuit 75, and the speaker 55
Is emitted to the speaker 55, and a erasing sound having a phase opposite to that of the noise of the exhaust gas is emitted from the speaker 55, so-called active muffling is performed.

The filter 71 suppresses frequency components other than exhaust noise in the signal of the microphone 65. In the above-described active silencer, however, the sound emitted from the front surface of the diaphragm 63 of the speaker 55 and the sound emitted from the rear surface thereof have opposite phases, so that the electric signals of the microphones 65 cancel each other and the microphones cancel each other. The electrical signal output from 65 becomes a signal of only exhaust noise, and only this electrical signal is inverted by the inverting circuit 75 and output to the speaker 55, so that the radiated sound from the speaker 55 forms a closed circuit. The occurrence of howling can be reliably prevented.

Further, since the muffler chamber 45 and the speaker chamber 47 are communicated with each other by the communication hole 64, the diaphragm 6 of the speaker 55 is connected.
A sufficient balance of static pressure before and after 3 can be secured. In the pressure receiving surface 65a of the microphone 65,
When the sound pressures of the sound emitted from the front surface and the sound emitted from the rear surface of the diaphragm 63 of the speaker 55 are different, in order to keep the sound pressure at the same level, the muffling chamber 45 or the speaker chamber 47.
It is desirable to adjust the density and the like of the sound absorbing material 61 inside.

Further, in the above-described active silencer, since the pressure receiving surface 65a of the microphone 65 is covered with the sound wave transmitting member 69, unnecessary high frequency sound waves can be effectively attenuated by the sound wave transmitting member 69.

Furthermore, since the high temperature exhaust gas can be blocked by the sound wave transmitting member 69, the microphone 6
It is possible to reduce the heat load on 5. Further, the sound wave transmitting member 69 can prevent foreign matters such as carbon and water drops from adhering to the pressure receiving surface 65 a of the microphone 65.

Furthermore, since the time constant of the static pressure balance before and after the diaphragm 63 of the speaker 55 can be lengthened by the sound wave transmitting member 69, the speaker which has been limited to the suction end and the exhaust end of the conventional pipeline system. The mounting position of 55 can be freely selected.

As a result, the speaker 55 can be mounted at an acoustically advantageous position, for example, in the center of the conduit.
In the embodiment described above, the microphone 65 is provided on the partition wall 43 of one of the pair of speakers 55.
And a pair of loudspeakers 55 are provided by signals from these.
However, the present invention is not limited to such an embodiment. For example, a similar control system may be provided to the other speaker 55 to control the pair of speakers 55 separately. good.

Further, in the above-mentioned embodiment, an example in which the present invention is used to reduce the noise of the exhaust system of the engine has been described, but the present invention is also similar to the reduction of the noise of the intake system of the engine. Can be applied.

In the case of this intake system, in the above-described embodiment, the exhaust gas is replaced with the intake gas, and the exhaust pipe is replaced with the intake pipe. Further, in the case of the exhaust system, the exhaust flow and the conduction direction of the noise were the same, but in the case of the intake system, the intake flow and the conduction direction of the noise are opposite, so the concept of upstream and downstream is
Read it based on noise.

[0038]

As described above, in the active silencer according to the first aspect of the present invention, the sound emitted from the front surface and the sound emitted from the rear surface of the diaphragm of the secondary sound source have opposite phases. As for the signal, the electrical signals that are canceled by each other and output from the microphone become almost only gas noise signals,
Since only this electric signal is inverted by the inverting means and output to the secondary sound source, the radiated sound from the secondary sound source almost does not form a closed circuit, and howling can be reliably prevented. .

In the active silencer according to the second aspect, since the pressure receiving surface of the microphone is covered with the sound wave transmitting member, unnecessary high frequency sound waves are attenuated by the sound wave transmitting member, and heat is cut off. It is possible to prevent foreign matter from adhering to the surface.

In the active silencer of the third aspect, noise in the exhaust gas can be surely silenced. The active silencer according to claim 4 has an advantage that noise in intake gas can be surely silenced.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an active silencer of the present invention.

FIG. 2 is a cross-sectional view showing details of the communication hole of FIG. 1 and its vicinity.

FIG. 3 is a sectional view showing an example of a conventional active silencer.

FIG. 4 is a cross-sectional view of FIG.

[Explanation of symbols]

 41 silencer body 45 silencer chamber 47 speaker chamber 49 exhaust pipe 51 small hole 55 speaker 65 microphone 71 filter 75 inverting circuit

Claims (4)

[Claims] 1. A silencer chamber (45) formed in a silencer body (41) is inserted with a flow pipe (49) through which a gas flows, and the silencer chamber (45) of this flow pipe (49).
A through hole (51) is formed in a portion located inside, and the sound deadening chamber (45) is provided in a secondary sound source room (47) formed adjacent to the sound deadening chamber (45) through a partition wall (43). ), A secondary sound source (55) for radiating a sound wave is arranged toward the upstream side of the secondary sound source (55) of the partition wall (43) or to the secondary sound source (55). A communication hole (6) provided in close proximity to connect the silencing chamber (45) and the secondary sound source chamber (47)
4), the microphone (65) arranged at or near the communication hole (64), and an inverting means (75) for inverting an electric signal from the microphone (65) and outputting the inverted signal to the secondary sound source (55). An active silencer characterized by having. 2. The active silencer according to claim 1, wherein the pressure receiving surface (65a) of the microphone (65) is covered with a sound wave transmitting member (69). 3. The active silencer according to claim 1 or 2, wherein the gas is exhaust gas from an engine. 4. The active silencer according to claim 1, wherein the gas is an intake gas from an engine.