JP2020125711A - Muffler - Google Patents

Abstract

To provide a muffler which can attain sound deadening effect at different frequency domains while inhibiting occurrence of nodes of a standing wave.SOLUTION: One embodiment of the disclosure is a muffler including: an exhaust pipe in which exhaust gas passes and which has communication holes; a shell disposed at the outer side of the exhaust pipe; and a first sound absorption material and a second sound absorption material which are disposed between the exhaust pipe and the shell and arranged so as to cover the communication holes. The second sound absorption material has air permeability lower than the first sound absorption material and is disposed in at least a position in the exhaust pipe where nodes of a standing wave are formed in a case that the communication holes are covered only by the first sound absorption material.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to silencers.

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

JP 2000-110544 A

In the silencer described above, the silencing effect is enhanced by increasing the number of holes or 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 the node of the standing wave is easily formed in the exhaust pipe. As a result, there is a possibility that the aimed reduction of the sound pressure level cannot be achieved.

An aspect of the present disclosure is to provide a silencer that suppresses the occurrence of a node of a standing wave and obtains a silencing effect in different frequency regions.

One aspect of the present disclosure, while the exhaust gas passes through the inside, an exhaust pipe having a plurality of communication holes, a shell arranged outside the exhaust pipe, and arranged between the exhaust pipe and the shell, It is a silencer provided with a first sound absorbing material and a second sound absorbing material arranged so as to cover a plurality of communication holes. The second sound absorbing material has a lower air permeability than the first sound absorbing material, and when the plurality of communication holes are covered with only the first sound absorbing material, the second sound absorbing material is at least at a position where a node of a standing wave is formed in the exhaust pipe. Will be placed.

With such a configuration, the second sound absorbing material having low air permeability is arranged at the position where the node of the standing wave is generated when the communication hole is covered with only the first sound absorbing material, and thus the first sound absorbing material is provided. Compared with the case where the communication hole is covered with only the sound hole, the sound pressure is less likely to drop in the portion of the exhaust pipe that overlaps with the communication hole, and the occurrence of nodes of standing waves is suppressed. As a result, it is possible to obtain the sound deadening effect in different frequency regions depending on the combination of the first sound absorbing material and the second sound absorbing material while suppressing the generation of the standing wave of the new frequency.

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. With such a configuration, the exhaust gas that has passed through the second sound absorbing material reaches the first sound absorbing material, so that the sound can be silenced by the first sound absorbing material. As a result, the sound deadening effect in the high frequency region by the first sound absorbing material having high air permeability is enhanced.

One aspect of the present disclosure may further include a cover that comes into contact with the second sound absorbing material from the outside in the radial direction of the exhaust pipe. According to such a configuration, the movement of the second sound absorbing material in the radial direction is limited by the cover. That is, it is possible to suppress the positional deviation of the second sound absorbing material in the radial direction of the exhaust pipe. Therefore, the effect of suppressing the occurrence of knots of the standing wave and the sound deadening effect can be promoted.

In one aspect of the present disclosure, both ends of the cover in the axial direction of the exhaust pipe may be fixed to the exhaust pipe. With such a configuration, it is possible to suppress the positional deviation of the second sound absorbing material in the axial direction of the exhaust pipe. Therefore, the effect of suppressing the occurrence of nodes of the standing wave and the sound deadening effect can be further promoted.

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 that is separated from the exhaust pipe. With such a configuration, the cover does not contact the exhaust pipe at the opening end portion of the cover in the exhaust pipe, so that the communication hole can be formed also in the opening end portion of the cover in the exhaust pipe. As a result, the area where the communication hole can be formed in the exhaust pipe increases. As a result, the sound deadening 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. With such a configuration, it is possible to secure the flow of the exhaust gas between the first sound absorbing material and the second sound absorbing material while suppressing the positional deviation of the second sound absorbing material. As a result, the sound deadening 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 of the embodiment. FIG. 2 is a schematic cross-sectional view of the silencer of the embodiment. FIG. 3 is a schematic sectional view of a silencer according to an embodiment different from that of FIG. FIG. 4 is a schematic cross-sectional view of a silencer according to an embodiment different from FIGS. 2 and 3. FIG. 5 is a schematic sectional view of a silencer according to an embodiment different from those of FIGS. 2 to 4.

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

The internal combustion engine 11 to which the exhaust system 10 is applied is not particularly limited, and examples thereof include those used for driving or generating electricity in transportation equipment such as automobiles, railroads, ships, construction machines, 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).

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

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

As shown in FIG. 2, the exhaust pipe 2 has a plurality of communication holes 21 that communicate the inside of the exhaust pipe 2 and the outside of the exhaust pipe 2, a straight portion 22 having a constant diameter, and a flow direction of the exhaust gas G. It has the diameter expansion part 23 which expanded the diameter 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 over 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 appropriately designed. However, the total opening area of the communication holes 21 is large enough to form at least one standing wave node inside the exhaust pipe 2 inside the shell 3. In the inside of the shell 3, the node of the standing wave formed in the exhaust pipe 2 is that 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 open. It is formed by entering the state 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 in which a part of the wall of the exhaust pipe 2 is cut and raised 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 portion 31 and the second opening portion 32 of the shell 3 are each reduced in diameter toward the outside 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.

By surrounding the outer peripheral surface of the exhaust pipe 2, the shell 3 forms a space between the exhaust pipe 2 and a first sound absorbing member 4 and a second sound absorbing member 5 which will be described later.

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

Specifically, the first sound absorbing material 4 is arranged so as 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 upstream communication holes 21 of 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, there is no space between the exhaust pipe 2 and the shell 3. The first sound absorbing material 4 is arranged so as to reach 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 fiber 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 fabric, a knitted fabric or a non-woven fabric of inorganic fibers, a structure in which inorganic fibers are partially hardened with a binder, or the like can be used.

Similar to 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 cover a part of the plurality of communication holes 21. Specifically, the second sound absorbing material 5 is arranged so as 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 downstream communication holes 21 of 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 the present embodiment, as shown in FIG. 2, the second sound absorbing material 5 is arranged on the downstream side of the first sound absorbing material 4 in the flow direction of the exhaust gas G. 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 a 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, so that the sound pressure in the low frequency region is lower than that of the first sound absorbing material 4.

Here, "low air permeability" means that the pressure loss is large when a gas is passed, for example. 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 constituent fibers), or 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, the air permeability of the second sound absorbing material 5 can be made lower than that of the first sound absorbing material 4 by changing the material while keeping the first sound absorbing material 4 and the second sound absorbing material 5 at the same density. Furthermore, the air permeability of the second sound absorbing material 5 may be lower than that of the first sound absorbing material 4 by changing both the density and the material.

[1-2. Action]
When the exhaust pipe 2 of the muffler 1 does not have the communication hole 21, the 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 waveform of a primary mode in which both ends of the exhaust pipe 2 have nodes. The nodes of the standing wave are formed in a portion where the pressure is greatly reduced. For example, a node is formed in a portion where the radial end of the exhaust pipe 2 is expanded, a portion where the exhaust pipe 2 is open, and the like. Further, when the total area of the communication holes 21 of the exhaust pipe 2 is, for example, larger than the flow passage cross-sectional area of the exhaust pipe 2 to some extent, the sound pressure in the exhaust pipe 2 is reduced, and a node of a standing wave is generated. It is formed.

On the other hand, when the plurality of communication holes 21 of the exhaust pipe 2 where the standing wave W1 is formed is covered with only the first sound absorbing material 4, the exhaust gas is discharged from the plurality of communication holes 21, so that the sound inside the exhaust pipe 2 is reduced. The pressure decreases, and two standing waves W2 and W3 are formed in the exhaust pipe 2 instead of the standing wave W1. The node S in FIG. 1 is the coincidence 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 on 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 reason. 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 a 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 exhaust gas G discharged to the outside of the exhaust pipe 2 decreases, and the sound pressure is less likely to decrease, so that the node S is not formed. Since the sound pressure in the exhaust pipe 2 is reduced, the sound pressure of the standing wave W4 is lower than that of the standing waves W1, W2, W3.

As described above, the first sound absorbing member 4 is made of a breathable material such that the 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 a breathable material so that the standing waves W2 and W3 are not formed when the communication hole 21 of the exhaust pipe 2 is covered.

[1-3. effect]
According to the embodiment described in detail above, the following effects can be obtained.
(1a) As described above, by disposing the second sound absorbing material 5 having low air permeability at the position where the node of the standing wave is generated when the communication hole 21 is covered with only the first sound absorbing material 4, As compared with the case where the communication hole 21 is covered with only one sound absorbing member 4, the sound pressure is less likely to drop in the portion of the exhaust pipe 2 that overlaps with the communication hole 21, and the occurrence of the node S of the standing wave is suppressed. As a result, it is possible to obtain a sound deadening effect in different frequency regions depending on the combination of the first sound absorbing material 4 and the second sound absorbing material 5 while suppressing the generation of a standing wave of a new frequency.

[2. Second Embodiment]
[2-1. Constitution]
A muffler 1A shown in FIG. 3 includes an exhaust pipe 2, a shell 3, a first sound absorbing material 4, a second sound absorbing material 5, and a cover 6. 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. The 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. Further, both the first end portion 62 and the second end portion 63 of the cover 6 in the axial direction of the exhaust pipe 2 are reduced in diameter toward the tip, and the tip is, for example, welded to the outer peripheral surface of the exhaust pipe 2. It is fixed to. The communication hole 21 is not formed in the portion of the outer peripheral surface of the exhaust pipe 2 where the first end 62 and the second end 63 are fixed.

The second sound absorbing material 5 is filled in the space between the cover 6 and the exhaust pipe 2. The first sound absorbing material 4 is filled in the space between the cover 6 and the shell 3. Therefore, in the present 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.

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

[2-2. effect]
According to the embodiment described in detail above, the following effects can be obtained.
(2a) The first sound absorbing member 4 is arranged outside the second sound absorbing member 5 in the radial direction of the exhaust pipe 2 so that the exhaust gas G passing through the second sound absorbing member 5 reaches the first sound absorbing member 4. Therefore, it is possible to muffle the sound by the first sound absorbing material 4. As a result, the sound deadening effect in the high frequency region by the first sound absorbing material 4 having high air permeability is enhanced. Further, the exhaust gas G that has passed through the first sound absorbing material 4 can be silenced by the second sound absorbing material 5. As a result, the silencing effect in the low frequency region is also enhanced.

(2b) By disposing the cover 6, the radial movement of the second sound absorbing material 5 is restricted. That is, it is possible to suppress the positional deviation of the second sound absorbing material 5 in the radial direction of the exhaust pipe 2. Therefore, the effect of suppressing the occurrence of knots of the standing wave and the sound deadening effect can be promoted.

(2c) Since both ends of the cover 6 are fixed to the exhaust pipe 2, the positional deviation of the second sound absorbing member 5 in the axial direction of the exhaust pipe 2 can be suppressed. Therefore, the effect of suppressing the occurrence of nodes of the standing wave and the sound deadening effect can be further promoted.

(2d) Since the cover 6 has the auxiliary communication hole 61, the displacement of the second sound absorbing material 5 is suppressed, and the flow of the exhaust gas G is secured between the first sound absorbing material 4 and the second sound absorbing material 5. can do. As a result, the sound deadening effect of the first sound absorbing material 4 and the second sound absorbing material 5 can be promoted.

[3. Third Embodiment]
[3-1. Constitution]
The 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 portion 62B of the cover 6B.

The first end portion 62B of the cover 6B is an open end that is separated from the exhaust pipe 2. That is, in the cover 6B, the first end 62B on the upstream side is not closed. 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. The downstream second end 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 radially overlaps the first end portion 62B.

[3-2. effect]
According to the embodiment described in detail above, the following effects can be obtained.
(3a) By making the first end portion 62B the open end, the cover 6 does not contact the exhaust pipe 2 at the open end portion of the cover 6 in the exhaust pipe 2, so that the open end portion of the cover 6 in the exhaust pipe 2 is also made. The communication hole 21 can be formed. As a result, the area where the communication hole 21 can be formed in the exhaust pipe 2 increases. As a result, the sound deadening 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 goes without saying that the present disclosure is not limited to the above embodiments and can take various forms.

(4a) In the silencer of the above embodiment, a space not filled with the first sound absorbing material 4 and the second sound absorbing material 5 may be formed between the exhaust pipe 2 and the shell 3. Further, between the exhaust pipe 2 and the shell 3, a third sound absorbing material different in breathability from the first sound absorbing material 4 and the second sound absorbing material 5 may be further arranged. The third sound absorbing material is arranged so as to cover a part of the communication hole 21 of the exhaust pipe 2.

(4b) In the silencers 1A and 1B of the above embodiment, the covers 6 and 6B do not necessarily have to have the auxiliary communication hole 61. Further, the mufflers 1A and 1B do not necessarily have to include 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 have the second end 63B as an open end instead of the first end 62B. Further, both ends of the cover 6B may be open ends. For example, the silencer 1C shown in FIG. 5 includes a cover 6C in which both the first end portion 62C and the second end portion 63C are separated 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 the downstream end of the silencer may be reversed.

(4e) The functions of one constituent element in the above-described embodiment may be distributed as a plurality of constituent elements, or the functions of a plurality of constituent elements may be integrated into one constituent element. Moreover, you may omit a part of structure of the said embodiment. Further, at least a part of the configuration of the above-described embodiment may be added to or replaced with the configuration of the other above-described embodiment. It should be noted that all aspects included in the technical idea specified by the wording recited 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... 2nd sound absorbing material, 6, 6B, 6C... Cover, 10... Exhaust system, 11... Internal combustion engine,
12... Catalytic converter, 13... Main muffler, 21... Communication hole, 22... Straight part,
23... expanded diameter part, 31... 1st opening part, 32... 2nd opening part, 61... auxiliary communication hole,
62, 62B, 62C... 1st end part, 63, 63B, 63C... 2nd end part.

Claims (6)

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

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