JP7221713B2 - Silencer - Google Patents

Description

The present disclosure relates to silencers.

In an exhaust system of an internal combustion engine, a muffler is known in which sound absorbing materials with different densities are arranged outside an exhaust pipe provided with a plurality of holes for the purpose of reducing noise in different frequency ranges (see Patent Document 1). .

JP-A-2000-110544

In the muffler described above, the muffling effect can be enhanced by increasing the number of holes or by increasing the area of the holes. However, when the number or area of the holes increases, the sound pressure decreases at the holes in the exhaust pipe, and nodes of the standing wave tend to form in the exhaust pipe. As a result, there is a possibility that the target sound pressure level reduction cannot be achieved.

An object of one aspect of the present disclosure is to provide a muffler capable of suppressing the occurrence of nodes of standing waves while obtaining a muffling effect in different frequency ranges.

One aspect of the present disclosure is an exhaust pipe having a plurality of communication holes through which exhaust gas passes; a shell disposed outside the exhaust pipe; disposed between the exhaust pipe and the shell; A muffler including a first sound absorbing material and a second sound absorbing material arranged to cover a plurality of communication holes. The second sound absorbing material has lower air permeability than the first sound absorbing material, and is at least positioned at a position where a node of the standing wave is formed in the exhaust pipe when the plurality of communication holes are covered only with the first sound absorbing material. placed.

According to such a configuration, the second sound absorbing material with low air permeability is arranged at the position where the node of the standing wave occurs when the communicating hole is covered only with the first sound absorbing material. Compared to the case where the communication hole is covered with a chisel, the sound pressure is less likely to decrease in the portion overlapping the communication hole in the exhaust pipe, and the generation of nodes of the standing wave is suppressed. As a result, while suppressing the generation of standing waves of new frequencies, it is possible to obtain a silencing effect in different frequency regions by combining the first sound absorbing material and the second sound absorbing material.

In one aspect of the present disclosure, the first sound absorbing material may be arranged outside the second sound absorbing material in the radial direction of the exhaust pipe. According to such a configuration, since the exhaust gas that has passed through the second sound absorbing material reaches the first sound absorbing material, it is possible to muffle the noise by the first sound absorbing material. As a result, the silencing effect in the high-frequency range is enhanced by the highly breathable first sound absorbing material.

One aspect of the present disclosure may further include a cover that contacts the second sound absorbing material from the outside in the radial direction of the exhaust pipe. According to such a configuration, the radial movement of the second sound absorbing material is restricted by the cover. That is, it is possible to suppress the displacement of the second sound absorbing material in the radial direction of the exhaust pipe. Therefore, it is possible to promote the effect of suppressing the generation of nodes of standing waves and the effect of silencing noise.

In one aspect of the present disclosure, the cover may be fixed to the exhaust pipe at both ends in the axial direction of the exhaust pipe. According to such a configuration, it is possible to suppress positional displacement of the second sound absorbing material in the axial direction of the exhaust pipe. Therefore, it is possible to further promote the effect of suppressing the generation of nodes of standing waves and the effect of silencing.

In one aspect of the present disclosure, at least one end of the cover in the axial direction of the exhaust pipe may be an open end spaced apart from the exhaust pipe. According to such a configuration, since the cover does not contact the exhaust pipe at the opening end portion of the cover of the exhaust pipe, the communication hole can be formed also at the opening end portion of the cover of the exhaust pipe. As a result, the area in which the communication hole can be formed in the exhaust pipe is increased. As a result, the silencing effect of the first sound absorbing material and the second sound absorbing material can be promoted.

In one aspect of the present disclosure, the cover may have a plurality of auxiliary communication holes provided in a portion facing the outer peripheral surface of the exhaust pipe. According to such a configuration, it is possible to ensure the flow of exhaust gas between the first sound absorbing material and the second sound absorbing material while suppressing the displacement of the second sound absorbing material. As a result, the silencing effect of the first sound absorbing material and the second sound absorbing material can be promoted.

FIG. 1 is a schematic diagram showing an exhaust system according to an embodiment. FIG. 2 is a schematic cross-sectional view of the muffler of the embodiment. 3 is a schematic cross-sectional view of a silencer of an embodiment different from that of FIG. 2. FIG. FIG. 4 is a schematic cross-sectional view of a silencer of an embodiment different from FIGS. 2 and 3. FIG. FIG. 5 is a schematic cross-sectional view of a silencer of an embodiment different from that of FIGS. 2 to 4. FIG.

Embodiments to which the present disclosure is applied will be described below with reference to the drawings.
[1. First Embodiment]
[1-1. composition]
An exhaust system 10 shown in FIG. 1 constitutes an exhaust gas flow path of an internal combustion engine 11 . The exhaust system 10 includes a catalytic converter 12, a main muffler 13, and a muffler 1 as a sub-muffler.

Examples of the internal combustion engine 11 to which the exhaust system 10 is applied include, but are not limited to, those used for driving or generating power in transportation equipment such as automobiles, railroads, ships, construction machinery, and power generation facilities.

The muffler 1 is arranged downstream of the main muffler 13 . However, the muffler 1 may be arranged upstream of the main muffler 13 (that is, between the catalytic converter 12 and the main muffler 13).

The muffler 1 includes an exhaust pipe 2, a shell 3, a first sound absorbing material 4, and a second sound absorbing material 5, as shown in FIG.

<Exhaust pipe>
The exhaust pipe 2 is a metal pipe through which the exhaust gas G passes. In this embodiment, the exhaust pipe 2 extends to the inside of the main muffler 13 as shown in FIG.

The exhaust pipe 2, as shown in FIG. and an enlarged diameter portion 23 that is enlarged along.

The communication hole 21 is arranged in the portion of the straight portion 22 of the exhaust pipe 2 located inside the shell 3 along the entire circumferential direction. However, the communication holes 21 do not necessarily have to be arranged in the entire circumferential direction of the exhaust pipe 2 .

The size and interval of the communication holes 21 can be designed appropriately. However, the total opening area of the communication holes 21 is such that at least one node of the standing wave can be formed in the exhaust pipe 2 inside the shell 3 . Note that the node of the standing wave formed in the exhaust pipe 2 inside the shell 3 is formed when the pressure of the exhaust gas G in the exhaust pipe 2 is reduced by the communication hole 21 and the exhaust pipe 2 is opened. It is formed by being in a state to be considered.

The shape of the communication hole 21 is not limited to a perfect circle, and may be an ellipse, a polygon, or the like. Further, the communication hole 21 may have a shape having a louver formed by cutting and raising a portion of the pipe wall of the exhaust pipe 2 to the outside.

<Shell>
The shell 3 is a metal pipe arranged outside the exhaust pipe 2 so as to surround the outer peripheral surface of the exhaust pipe 2 . The inner diameter of the shell 3 is larger than the outer diameter of the exhaust pipe 2 .

The first opening 31 and the second opening 32 of the shell 3 each decrease in diameter outward in the axial direction of the exhaust pipe 2 . The first opening 31 and the second opening 32 are fixed to the outer peripheral surface of the exhaust pipe 2 by welding, for example.

The shell 3 surrounds the outer peripheral surface of the exhaust pipe 2 , thereby forming a space between the shell 3 and the exhaust pipe 2 in which a first sound absorbing material 4 and a second sound absorbing material 5 can be arranged.

<Sound absorbing material>
The first sound absorbing material 4 is arranged between the exhaust pipe 2 and the shell 3 and arranged so as to partially cover the plurality of communication holes 21 .

Specifically, the first sound absorbing material 4 is arranged to circumferentially surround a portion of the straight portion 22 of the exhaust pipe 2 near the first opening 31 of the shell 3 (that is, an upstream portion). The first sound absorbing material 4 is in contact with a plurality of communication holes 21 on the upstream side among the communication holes 21 of the exhaust pipe 2 .

The first sound absorbing material 4 fills the space between the exhaust pipe 2 and the shell 3 together with the second sound absorbing material 5 described later. Therefore, no gap exists between the exhaust pipe 2 and the shell 3 . The first sound absorbing material 4 is arranged so as to reach from the outer peripheral surface of the exhaust pipe 2 to the inner peripheral surface of the shell 3 in the radial direction of the exhaust pipe 2 .

As the material of the first sound absorbing material 4, for example, inorganic fibers such as glass fiber can be used. As the first sound absorbing material 4, in addition to an aggregate of inorganic fibers (for example, glass wool), a woven, knitted or nonwoven fabric of inorganic fibers, a structure in which inorganic fibers are partially bound with a binder, or the like can be used.

Like the first sound absorbing material 4 , the second sound absorbing material 5 is arranged between the exhaust pipe 2 and the shell 3 and is arranged so as to partially cover the communication holes 21 . Specifically, the second sound absorbing material 5 is arranged to circumferentially surround a portion of the straight portion 22 of the exhaust pipe 2 near the second opening 32 of the shell 3 (that is, a downstream portion). The second sound absorbing material 5 is in contact with a plurality of communication holes 21 on the downstream side among the communication holes 21 of the exhaust pipe 2 . All the communication holes 21 of the exhaust pipe 2 are covered with either the first sound absorbing material 4 or the second sound absorbing material 5 .

In this embodiment, as shown in FIG. 2, the second sound absorbing material 5 is arranged downstream of the first sound absorbing material 4 in the flow direction of the exhaust gas G. As shown in FIG. The second sound absorbing material 5 is arranged so as to reach from the outer peripheral surface of the exhaust pipe 2 to the inner peripheral surface of the shell 3 in the radial direction of the exhaust pipe 2 .

The same material as the first sound absorbing material 4 can be used for the second sound absorbing material 5 . However, the second sound absorbing material 5 has lower air permeability than the first sound absorbing material 4 . Therefore, for example, the second sound absorbing material 5 having a high density has a low natural frequency, and therefore reduces the sound pressure in the low frequency range more than the first sound absorbing material 4 does.

Here, "poor air permeability" means, for example, large pressure loss when gas is passed through. The air permeability of the sound absorbing material can be adjusted, for example, by changing the density of the sound absorbing material, the material of the sound absorbing material, the structure of the sound absorbing material (for example, the arrangement of the constituent fibers), and the like.

Therefore, for example, by making the density of the second sound absorbing material 5 higher than that of the first sound absorbing material 4 , the air permeability of the second sound absorbing material 5 can be made lower than that of the first sound absorbing material 4 . Further, by changing the material of the first sound absorbing material 4 and the second sound absorbing material 5 while maintaining the same density, the air permeability of the second sound absorbing material 5 can be made lower than that of the first sound absorbing material 4 . Furthermore, the air permeability of the second sound absorbing material 5 may be made lower than that of the first sound absorbing material 4 by changing both the density and material.

[1-2. action]
When the exhaust pipe 2 of the muffler 1 does not have the communication hole 21, a standing wave W1 of the exhaust gas G is generated in the exhaust pipe 2 in the exhaust system 10 as shown in FIG.

The standing wave W1 is a primary mode waveform in which both ends of the exhaust pipe 2 are nodes. Standing wave nodes are formed in areas where the pressure is greatly reduced. For example, a joint is formed at a portion where the radial end portion of the exhaust pipe 2 is enlarged, a portion where the exhaust pipe 2 is open, or the like. Further, in a place where the total area of the communication holes 21 of the exhaust pipe 2 is somewhat larger than the flow passage cross-sectional area of the exhaust pipe 2, the sound pressure in the exhaust pipe 2 decreases, and the standing wave nodes are formed. It is formed.

On the other hand, when the plurality of communication holes 21 of the exhaust pipe 2 in which the standing wave W1 is formed are covered only with the first sound absorbing material 4, the exhaust gas is discharged from the plurality of communication holes 21, so the sound in the exhaust pipe 2 is The pressure drops and two standing waves W2 and W3 are formed in the exhaust pipe 2 instead of the standing wave W1. A node S in FIG. 1 is a matching point between the node of the standing wave W2 and the node of the standing wave W3. When the communication hole 21 located on the outer peripheral side of the node S in the side surface of the exhaust pipe 2 is covered with the second sound absorbing material 5, a standing wave W4 is formed instead of the standing waves W2 and W3. This is for the following reasons. That is, by covering the communication hole 21 at the position where the node S is formed with the second sound absorbing material 5 having lower air permeability than the first sound absorbing material 4, the total area of the openings of the communication hole 21 is substantially reduced. As a result, the amount of the exhaust gas G discharged to the outside of the exhaust pipe 2 decreases, making it difficult for the sound pressure to decrease, so that the node S is not formed. Since the sound pressure in the exhaust pipe 2 is lowered, the sound pressure of the standing wave W4 is lower than the sound pressure of the standing waves W1, W2 and W3.

As described above, the first sound absorbing material 4 is made of an air permeable material such that standing waves W2 and W3 are formed when the communication hole 21 of the exhaust pipe 2 is covered. The second sound absorbing material 5 is made of an air permeable material that does not form standing waves W2 and W3 when the communication hole 21 of the exhaust pipe 2 is covered.

[1-3. effect]
According to the embodiment detailed above, the following effects are obtained.
(1a) As described above, when the communication hole 21 is covered only with the first sound absorbing material 4, the second sound absorbing material 5 with low air permeability is arranged at the position where the node of the standing wave is generated. Compared to the case where the communication hole 21 is covered only with the sound absorbing material 4, the sound pressure is less likely to decrease in the portion overlapping the communication hole 21 in the exhaust pipe 2, and the generation of the node S of the standing wave is suppressed. As a result, it is possible to suppress the generation of standing waves of new frequencies, and to obtain a silencing effect in different frequency ranges by combining the first sound absorbing material 4 and the second sound absorbing material 5 .

[2. Second Embodiment]
[2-1. composition]
A muffler 1A shown in FIG. The exhaust pipe 2, the shell 3, the first sound absorbing material 4 and the second sound absorbing material 5 are the same as those of the silencer 1 of FIG.

<Cover>
The cover 6 is a cylindrical member that contacts the second sound absorbing material 5 from the outside in the radial direction of the exhaust pipe 2 . A cover 6 is arranged between the exhaust pipe 2 and the shell 3 .

The cover 6 has at least one auxiliary communication hole 61 provided in a portion facing the outer peripheral surface of the exhaust pipe 2 . A first end portion 62 and a second end portion 63 of the cover 6 in the axial direction of the exhaust pipe 2 are both tapered toward the tip, and the tip is welded to the outer peripheral surface of the exhaust pipe 2, for example. is fixed to The communicating hole 21 is not formed in the portion of the outer peripheral surface of the exhaust pipe 2 to which the first end portion 62 and the second end portion 63 are fixed.

A space between the cover 6 and the exhaust pipe 2 is filled with the second sound absorbing material 5 . The first sound absorbing material 4 fills the gap between the cover 6 and the shell 3 . Therefore, in this embodiment, the first sound absorbing material 4 is arranged outside the second sound absorbing material 5 in the radial direction of the exhaust pipe 2 .

Only the first sound absorbing material 4 is arranged in the radial direction of the exhaust pipe 2 in the upstream region of the silencer 1A. In the area where the cover 6 of the muffler 1A is arranged, a two-layer structure of the second sound absorbing material 5 and the first sound absorbing material 4 is formed in the radial direction of the exhaust pipe 2 .

[2-2. effect]
According to the embodiment detailed above, the following effects are obtained.
(2a) By arranging the first sound absorbing material 4 outside the second sound absorbing material 5 in the radial direction of the exhaust pipe 2, the exhaust gas G passing through the second sound absorbing material 5 reaches the first sound absorbing material 4. Therefore, the first sound absorbing material 4 can muffle the noise. As a result, the silencing effect in the high frequency region by the first sound absorbing material 4 with high air permeability is enhanced. Further, the exhaust gas G that has passed through the first sound absorbing material 4 can be muffled by the second sound absorbing material 5 . As a result, the silencing effect in the low frequency range is also enhanced.

(2b) The arrangement of the cover 6 restricts the movement of the second sound absorbing material 5 in the radial direction. That is, positional deviation of the second sound absorbing material 5 in the radial direction of the exhaust pipe 2 can be suppressed. Therefore, it is possible to promote the effect of suppressing the generation of nodes of standing waves and the effect of silencing noise.

(2c) Since both ends of the cover 6 are fixed to the exhaust pipe 2, positional displacement of the second sound absorbing material 5 in the axial direction of the exhaust pipe 2 can be suppressed. Therefore, it is possible to further promote the effect of suppressing the generation of nodes of standing waves and the effect of silencing.

(2d) The cover 6 has the auxiliary communication hole 61, thereby suppressing the displacement of the second sound absorbing material 5 and ensuring the flow of the exhaust gas G between the first sound absorbing material 4 and the second sound absorbing material 5. can do. As a result, the silencing effect of the first sound absorbing material 4 and the second sound absorbing material 5 can be promoted.

[3. Third Embodiment]
[3-1. composition]
A muffler 1B shown in FIG. 4 includes an exhaust pipe 2, a shell 3, a first sound absorbing material 4, a second sound absorbing material 5, and a cover 6B. The silencer 1B is the same as the silencer 1A of FIG. 3 except for the first end 62B of the cover 6B.

A first end 62B of the cover 6B is an open end spaced apart from the exhaust pipe 2 . That is, the cover 6B is not closed at the upstream first end 62B. Therefore, the first sound absorbing material 4 and the second sound absorbing material 5 are in contact with each other along the axial direction of the exhaust pipe 2 at the first end portion 62B. A downstream second end portion 63B of the cover 6B is fixed to the exhaust pipe 2 . That is, the communication hole 21 of the exhaust pipe 2 is also formed in a portion of the outer peripheral surface of the exhaust pipe 2 that overlaps the first end portion 62B in the radial direction.

[3-2. effect]
According to the embodiment detailed above, the following effects are obtained.
(3a) By making the first end 62B the open end, the cover 6 does not contact the exhaust pipe 2 at the open end of the cover 6 of the exhaust pipe 2. A communication hole 21 can be formed. This increases the area in which the communication hole 21 can be formed in the exhaust pipe 2 . As a result, the silencing effect of the first sound absorbing material 4 and the second sound absorbing material 5 can be promoted.

[4. Other embodiments]
Although the embodiments of the present disclosure have been described above, it is needless to say that the present disclosure is not limited to the above embodiments and can take various forms.

(4a) In the muffler of the above embodiment, a gap may be formed between the exhaust pipe 2 and the shell 3 that is not filled with the first sound absorbing material 4 and the second sound absorbing material 5 . Further, a third sound absorbing material having air permeability different from that of the first sound absorbing material 4 and the second sound absorbing material 5 may be further arranged between the exhaust pipe 2 and the shell 3 . The third sound absorbing material is arranged so as to partially cover the communication hole 21 of the exhaust pipe 2 .

(4b) In the mufflers 1A and 1B of the above embodiments, the covers 6 and 6B do not necessarily have the auxiliary communication holes 61 . Moreover, the silencers 1A and 1B do not necessarily have to have the covers 6 and 6B. For example, the second sound absorbing material 5 may be held outside the exhaust pipe 2 by a fixing means such as a binder.

(4c) In the silencer 1B of the above embodiment, the cover 6B may be open at the second end 63B instead of the first end 62B. Also, both ends of the cover 6B may be open ends. For example, a muffler 1C shown in FIG. 5 includes a cover 6C with both a first end 62C and a second end 63C spaced apart from the exhaust pipe 2 .

(4d) In the silencer of the above embodiment, the upstream side and the downstream side may be interchanged. That is, the upstream end and downstream end of the muffler may be reversed.

(4e) The function of one component in the above embodiments may be distributed as multiple components, or the functions of multiple components may be integrated into one component. Also, part of the configuration of the above embodiment may be omitted. Also, at least a part of the configuration of the above embodiment may be added, replaced, etc. with respect to the configuration of the other above embodiment. It should be noted that all aspects included in the technical idea specified by the wording in the claims are embodiments of the present disclosure.

1, 1A, 1B, 1C... Silencer, 2... Exhaust pipe, 3... Shell, 4... First sound absorbing material,
5 Second sound absorbing material 6, 6B, 6C Cover 10 Exhaust system 11 Internal combustion engine
DESCRIPTION OF SYMBOLS 12... Catalytic converter, 13... Main muffler, 21... Communication hole, 22... Straight part,
23... Expanded diameter portion, 31... First opening, 32... Second opening, 61... Auxiliary communication hole,
62, 62B, 62C... first end, 63, 63B, 63C... second end.

Claims (6)

an exhaust pipe having a plurality of communication holes through which exhaust gas passes;
a shell disposed outside the exhaust pipe;
a first sound absorbing material and a second sound absorbing material arranged between the exhaust pipe and the shell and arranged to cover the plurality of communication holes;
with
The second sound absorbing material has lower air permeability than the first sound absorbing material, and when the plurality of communication holes are covered only with the first sound absorbing material, a node of the standing wave is generated at least in the exhaust pipe. covering the formed position from the radially outer side of the exhaust pipe;
A muffler, wherein each of the first sound absorbing material and the second sound absorbing material is in contact with at least one of the plurality of communication holes. A muffler according to claim 1,
A muffler, wherein the first sound absorbing material is arranged outside the second sound absorbing material in the radial direction of the exhaust pipe. A muffler according to claim 2,
The muffler further comprising a cover that abuts on the second sound absorbing material from the outside in the radial direction of the exhaust pipe. A muffler according to claim 3,
The cover is a muffler, wherein both axial ends of the exhaust pipe are fixed to the exhaust pipe. A muffler according to claim 3,
A muffler, wherein at least one end of the cover in the axial direction of the exhaust pipe is an open end spaced apart from the exhaust pipe. A muffler according to any one of claims 3 to 5,
The muffler, wherein the cover has a plurality of auxiliary communication holes provided in a portion facing the outer peripheral surface of the exhaust pipe.

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