JPH0816175A - 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 opposite to the side face of the flow pipe 49 within a secondary sound source chamber 47 formed adjacently to the silencing chamber 45. The active silencer described above has an upstream side microphone 65 and downstream side microphone 67 which are arranged in the positions on the upstream side and downstream side of the secondary sound source 55 in the silencing chamber 45 and in positions approximately symmetrical with the center of the secondary sound source 55, a subtracting means 73 which subtracts the electric signal of the downstream side microphone 67 from the electric signal of the upstream side microphone 65 and an inverting means 79 which inverts the electric signal subtracted by this subtracting means 73 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. 2 and 3 show an active silencer of this type. In FIG. 2, reference numeral 11 indicates 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]

According to another aspect of the present invention, there is provided an active muffler in which a gas flow pipe is inserted into a muffler chamber formed in a muffler body, and the gas flow passage pipe is located in the muffler chamber. A through-hole is formed in the part to be formed, in the secondary sound source chamber formed adjacent to the silencing chamber, an active silencer in which a secondary sound source is arranged facing the side surface of the flow pipe,
An upstream microphone and a downstream microphone arranged at positions upstream and downstream of the secondary sound source in the silencing chamber and at positions substantially symmetrical with respect to the center of the secondary sound source; It has a subtracting means for subtracting the electric signal of the downstream microphone from the electric signal of the side microphone, and an inverting means for inverting the electric signal subtracted by the subtracting means and outputting it to the secondary sound source.

According to a second aspect of the present invention, in the active silencer according to the first aspect, a filter for suppressing frequency components other than gas noise in the electric signal from the subtracting means is arranged after the subtracting means. Is.

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

[0013]

In the active silencer according to the first aspect, the gas noise and the radiated sound from the secondary sound source are mainly detected by the upstream microphone arranged upstream of the secondary sound source, while the gas noise is the secondary sound source. Since the sound is muted while passing the front of the secondary sound source, the sound emitted from the secondary sound source is mainly detected by the downstream microphone arranged downstream of the secondary sound source.

Further, since the upstream microphone and the downstream microphone are arranged at positions substantially symmetrical with respect to the center of the secondary sound source, the secondary sound source detects the secondary microphone from the upstream microphone and the downstream microphone. The radiated sound has the same sound pressure level.

Therefore, when the subtracting means subtracts the electrical signal of the downstream microphone from the electrical signal of the upstream microphone, the subtracted electrical signal becomes a signal of only gas noise, and only this electrical signal is inversion means. Since it is inverted by and is output to the secondary sound source, the radiated sound from the secondary sound source hardly forms a closed circuit.

In the active silencer of the second aspect, the filter suppresses frequency components other than gas noise in the electric signal from the subtraction means, so that the gas noise is effectively silenced. 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.

[0018]

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 parts by a pair of partition walls 43 arranged at predetermined intervals, 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, for example, a round speaker, is provided in the opening 53.
Is arranged. 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. Thus, in this embodiment, the upstream microphone 65 and the downstream microphone 67 are arranged on the upstream side and the downstream side of the diaphragm 63 of the speaker 55 in the muffling chamber 45.

The upstream microphone 65 and the downstream microphone 67 are acoustically equivalent to the speaker 55, that is, in this embodiment, the speaker 55.
Are arranged at positions substantially symmetrical with respect to the center of the.

The upstream microphone 65 and the downstream microphone 67 are connected to the subtraction circuit 73. The subtraction circuit 73 subtracts the electric signal of the downstream microphone 67 from the electric signal of the upstream microphone 65.

The subtraction circuit 73 is connected to the inverting circuit 79 via the filter 75 and the power amplifier 77.
The filter 75 suppresses frequency components other than exhaust noise in the electric signal from the subtraction circuit 73.

The power amplifier 77 amplifies the electric signal from the filter 75. The inverting circuit 79 is the power amplifier 7
The electric signal from 7 is inverted and output to the speaker 55.

In the active silencer described above, the speaker 55
The exhaust noise and the radiated sound from the diaphragm 63 are mainly detected by the upstream microphone 65 arranged on the upstream side of the diaphragm 63.

On the other hand, since the exhaust noise is silenced while passing in front of the speaker 55, the diaphragm 63 of the speaker 55 is eliminated.
Radiated sound from the diaphragm 63 is mainly detected by the downstream microphone 67 disposed on the downstream side of the.

Further, since the upstream microphone 65 and the downstream microphone 67 are arranged at positions substantially symmetrical with respect to the center of the speaker 55, the upstream microphone 6
5 and the speaker 55 detected by the downstream microphone 67
The radiated sound from is at the same sound pressure level.

Therefore, when the subtraction circuit 73 subtracts the electric signal of the downstream microphone 67 from the electric signal of the upstream microphone 65, the subtracted electric signal becomes a signal of only exhaust noise, and only this electric signal is generated. , The phase is inverted by the inverting circuit 79 and output to the speaker 55,
By emitting a erasing sound having a phase opposite to that of the exhaust gas noise from the speaker 55, so-called active muffling is performed.

Then, the subtraction circuit 7 is operated by the filter 75.
Frequency components other than exhaust noise in the electric signal from 3 are suppressed. Then, in the above-described active silencer, when the electric signal of the downstream microphone 67 is subtracted from the electric signal of the upstream microphone 65 by the subtraction circuit 73, the subtracted electric signal becomes a signal of exhaust noise only, Since only this electric signal is inverted by the inverting circuit 79 and output to the speaker 55, the sound emitted from the speaker 55 does not form a closed circuit, and howling can be reliably prevented.

In the active silencer described above, the filter 75 suppresses frequency components other than exhaust noise in the electric signal from the subtraction circuit 73, so that only exhaust noise can be effectively silenced.

In the embodiment described above, microphones 65 and 67 are arranged upstream and downstream of one speaker 55 of the pair of speakers 55, and the pair of speakers 55 are controlled by signals from these microphones. However, the present invention is not limited to such examples,
For example, the other speaker 55 may be provided with a similar control system to separately control the pair of speakers 55.

Further, in the above-mentioned embodiment, the 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, the exhaust gas is replaced with the intake gas and the exhaust pipe is replaced with the intake pipe in the above-described embodiment. 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.

[0037]

As described above, in the active silencer of the first aspect, when the subtracting means subtracts the electric signal of the downstream microphone from the electric signal of the upstream microphone,
The subtracted electric signal becomes a signal of only gas noise,
Since only this electric signal is inverted by the inverting means and output to the secondary sound source, the emitted sound from the secondary sound source does not form a closed circuit, and howling can be reliably prevented.

In the active silencer of the second aspect, since the frequency components other than the gas noise in the electric signal from the subtracting means are suppressed by the filter, only the gas noise can be effectively silenced.

In the active silencer of the third aspect, noise in the exhaust gas can be effectively silenced. The active silencer according to claim 4 has an advantage that noise in the intake gas can be effectively 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 sectional view showing an example of a conventional active silencer.

3 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 upstream microphone 67 downstream microphone 73 subtraction circuit 75 filter 79 inversion 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 the secondary sound source chamber (47) formed adjacent to the silencing chamber (45) so as to face the side surface of the flow pipe (49). Secondary sound source (5
5) in the active silencer, wherein the secondary sound source (5) is located at a position upstream and downstream of the secondary sound source (55) in the silencing chamber (45).
5) The upstream microphone (65) and the downstream microphone (6) arranged at positions substantially symmetrical with respect to the center of
7), subtraction means (73) for subtracting the electric signal of the downstream microphone (67) from the electric signal of the upstream microphone (65), and inverting the electric signal subtracted by the subtraction means (73) An active silencer having an inverting means (79) for outputting to a secondary sound source (55). 2. The active silencer according to claim 1, wherein the subtracting means (73) is provided after the subtracting means (73).
An active silencer characterized in that a filter (75) for suppressing frequency components other than gas noise in the electric signal from is disposed. 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 or 2, wherein the gas is an intake gas to the engine.