JP7534271B2 - Sound suppressor - Google Patents

Description

This disclosure relates to a sound absorbing device.

Patent document 1 discloses a double-tube silencer that includes an outer tube and an inner tube, and uses the space between the outer tube and the inner tube to provide a Helmholtz resonator and a side-branch silencer.

Patent No. 6676662

In the above-mentioned double-tube structure silencer, it is possible to improve the low-frequency sound silencing effect by, for example, increasing the length of the double tube or increasing the cross-sectional area of the double tube, but this can cause problems with the installation requirements on the vehicle and the workability of the pipes.

One aspect of the present disclosure aims to provide a technology that can improve the low-frequency sound deadening effect by using a double-tube structure.

One aspect of the present disclosure is a silencing device comprising an exhaust pipe of a double pipe structure and a space forming member. The exhaust pipe comprises an inner pipe through which exhaust gas passes, and an outer pipe arranged to surround the outer periphery of the inner pipe. The space forming member is connected to the upstream or downstream of the exhaust pipe and has a first silencing space which is a space for silencing. The inner pipe has a first inner pipe and a second inner pipe aligned in the flow direction of the exhaust gas, and is arranged so that either one of the end of the first inner pipe on the second inner pipe side and the end of the second inner pipe on the first inner pipe side is inserted into the other. The first inner pipe is arranged between the space forming member and the second inner pipe. A holding member is arranged in the gap formed between the first inner pipe and the second inner pipe. The second silencing space which is a space for silencing formed between the second inner pipe and the outer pipe is connected to the first silencing space via a third silencing space formed between the first inner pipe and the outer pipe. The cross-sectional area of the first silencing space in a cross section perpendicular to the flow direction of the exhaust gas is larger than the cross-sectional area of the second silencing space in a cross section perpendicular to the flow direction of the exhaust gas.

In this configuration, the space forming member and the exhaust pipe are connected so that the first silencing space and the second silencing space are in communication. That is, at the connection portion between the space forming member and the exhaust pipe, the first silencing space and the second silencing space are not separated, and a space is formed in which the first silencing space and the second silencing space are continuous. Therefore, a larger space can be used as a resonance chamber by the first silencing space, the second silencing space, and the third silencing space which is a space connecting the first silencing space and the second silencing space. This allows the double pipe structure to be used to improve the silencing effect of low frequencies.

In one aspect of the present disclosure, the space forming member may be a double-pipe structure including a connecting pipe connected to the first inner pipe and an outer casing member arranged to surround the outer periphery of the connecting pipe. The first silencing space may be a space formed between the outer casing member and the connecting pipe. With this configuration, for example, a muffler with a double-pipe structure can be used as the space forming member. In this way, since both the space forming member and the exhaust pipe have a double-pipe structure, radiant heat can be reduced over a wide range. As a result, even if a device such as a battery, in which a temperature rise is undesirable, is arranged near the space forming member and the exhaust pipe, the heat damage to the device can be reduced, and the range in which the device can be installed is expanded. As a result, in a hybrid vehicle, for example, in which a battery is installed, it is possible to expand the battery arranged near the space forming member and the exhaust pipe.

In one aspect of the present disclosure, the space-forming member may be formed integrally with a catalytic device having a catalyst that purifies exhaust gas. With this configuration, a catalyst-integrated muffler in which the space-forming member and catalytic device are integrally formed can be used, thereby saving space in the exhaust system under the floor of the vehicle.

1 is a schematic cross-sectional view showing a noise suppressor having a configuration in which a muffler is connected to the upstream side of a resonating double pipe. 2 is an enlarged cross-sectional view of a connection portion between a muffler and a resonating double pipe in the silencer of FIG. 1 . 13 is an enlarged cross-sectional view of a connecting portion of a comparative example in which a muffler and a resonance double pipe are connected in a state in which the first silencing space and the second silencing space are separated from each other. FIG. 11 is a graph showing the relationship between frequency and noise reduction volume in an example and a comparative example which are configurations of the present embodiment. 4 is a schematic cross-sectional view showing a configuration in which a muffler provided in a silencer does not have a catalytic device. FIG. 1 is a schematic cross-sectional view showing a configuration in which a plurality of connecting holes are provided in a connecting pipe of a muffler included in a noise suppression device. FIG. 1 is a schematic cross-sectional view showing a noise suppressor in which an outer tube of a resonating double tube is inserted inside an outer member of a muffler. 8 is an enlarged cross-sectional view of a connection portion between a muffler and a resonating double pipe in the silencer of FIG. 7 . 1 is a schematic top view showing a noise suppressor having a configuration in which a muffler is connected to the downstream side of a resonating double pipe. FIG.

Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings.
[1. Configuration]
The silencer 100 shown in Fig. 1 is a device for reducing exhaust noise used in an exhaust system that constitutes an exhaust gas flow path of an internal combustion engine. The silencer 100 is provided, for example, in a hybrid vehicle or the like equipped with a battery 200. The silencer 100 may also be provided in a vehicle that does not have a battery 200. The silencer 100 includes a muffler 1, a resonance double pipe 2, and a holding member 3. In the example shown in Fig. 1, the resonance double pipe 2 has a bent shape that matches the shape of the battery 200 that is arranged near the silencer 100. In this embodiment, the muffler 1 is arranged upstream of the resonance double pipe 2.

The muffler 1 includes an outer casing member 11, a first inner pipe 12, a connecting pipe 13, a catalytic device 14, an upstream cone 15, and a separator 19. In this embodiment, the muffler 1 is a catalyst-integrated muffler formed integrally with a catalytic device 14 having a catalyst 141 that purifies exhaust gas G. The muffler 1 has a double-pipe structure including the first inner pipe 12, a connecting pipe 13 connected to the first inner pipe 12, and an outer casing member 11 arranged to surround the outer circumferential surfaces of the first inner pipe 12 and the connecting pipe 13. The muffler 1 has a first silencing space 16, which is a space for silencing formed between the outer casing member 11 and the connecting pipe 13. The muffler 1 exerts a silencing effect by the first silencing space 16.

1 and 2, the outer casing member 11 is a cylindrical metal pipe formed so that the downstream end of the outer casing member 11 is tapered toward the central axis of the muffler 1. Specifically, the outer casing member 11 has, in order from the upstream side, a first straight pipe section 111, a first truncated cone section 112, and a second straight pipe section 113. The first straight pipe section 111 and the second straight pipe section 113 each have a straight pipe-shaped portion whose diameter does not change. The diameter of the first straight pipe section 111 is larger than the diameter of the second straight pipe section 113. The first truncated cone section 112 is a truncated cone-shaped portion whose cross-sectional area gradually decreases from the downstream end of the first straight pipe section 111 toward the upstream end of the second straight pipe section 113. The catalytic device 14 is disposed inside the first straight pipe section 111. An upstream cone 15 is provided at the opening at the upstream end of the first straight pipe section 111, which connects to the exhaust pipe located upstream of the muffler 1. Exhaust gas G flowing through the exhaust pipe located upstream of the muffler 1 is introduced into the outer casing member 11 through the upstream cone 15.

The first inner pipe 12 and the connecting pipe 13 are metal pipes through which the exhaust gas G passes. The first inner pipe 12 and the connecting pipe 13 are arranged in the outer casing member 11 so as to be aligned in the flow direction of the exhaust gas G. The first inner pipe 12 is arranged downstream of the connecting pipe 13.

The first inner pipe 12 is a straight pipe whose diameter does not change, and is disposed inside the second straight pipe section 113 of the outer casing member 11. A first gap 17 that communicates with the first silencing space 16 is formed between the second straight pipe section 113 and the first inner pipe 12. The downstream end 121 of the first inner pipe 12 protrudes downstream from the downstream end 113A of the second straight pipe section 113 of the outer casing member 11. In other words, the downstream end 121 of the first inner pipe 12 is disposed so as not to be surrounded by the second straight pipe section 113.

The connecting pipe 13 has a third straight pipe section 131 and a second truncated cone section 132. The third straight pipe section 131 is a section whose diameter does not change, that is, a straight pipe section. The second truncated cone section 132 is a truncated cone section whose cross-sectional area gradually decreases from the downstream end of the third straight pipe section 131 toward the upstream end of the first inner pipe 12. The connecting pipe 13 is disposed inside the first straight pipe section 111 of the outer casing member 11 and the first truncated cone section 112 of the outer casing member 11. The upstream end of the connecting pipe 13 is connected to the separator 19. The separator 19 has a wall section 191 that is provided so as to intersect, more preferably perpendicular to, the flow direction of the exhaust gas G, and an opening section 192 formed in the center of the wall section 191. The opening section 192 protrudes with a reduced diameter as it approaches the downstream side. The downstream end of the opening section 192 is connected to the upstream end of the connecting pipe 13 described above. In addition, the catalytic converter 14 is provided upstream of the separator 19 with a space in the flow direction of the exhaust gas G. As a result, the exhaust gas G that has passed through the catalytic converter 14 passes through the separator 19, the connecting pipe 13, and the first inner pipe 12, is discharged from the muffler 1, and is introduced into the inside of the resonance double pipe 2.

The resonance double pipe 2 is an exhaust pipe with a double pipe structure including a second inner pipe 21 and an outer pipe 22. The resonance double pipe 2 has a second silencing space 23, which is a space for silencing sound formed between the second inner pipe 21 and the outer pipe 22. The resonance double pipe 2 exerts a silencing effect due to the second silencing space 23. In addition, the resonance double pipe 2 can reduce the radiant heat of the exhaust gas G due to its double pipe structure.

The second inner pipe 21 is a metal pipe through which the exhaust gas G passes. Specifically, the exhaust gas G discharged from the muffler 1 is introduced into the second inner pipe 21 from the opening of the upstream end 211 of the second inner pipe 21, and is discharged from the opening of the downstream end 212 of the second inner pipe 21. The second inner pipe 21 has a shape in which the upstream end 211 and the downstream end 212 each have an enlarged diameter.

The outer pipe 22 is a metal pipe arranged to surround the outer peripheral surface of the second inner pipe 21. The downstream end 222 of the outer pipe 22 has a shape in which the diameter is reduced so that the inner peripheral surface of the outer pipe 22 can abut against the outer peripheral surface of the second inner pipe 21. A second gap 24 communicating with the second silencing space 23 is formed between the upstream end 211 of the second inner pipe 21 and the outer pipe 22. The second gap 24 may be formed over the entire circumference in the circumferential direction, or may be formed in a partial range in the circumferential direction. In addition, when the second gap 24 is formed in a partial range in the circumferential direction, the second inner pipe 21 and the outer pipe 22 may be in direct contact with each other in the remaining range in the circumferential direction, or an interposition may be interposed between the second inner pipe 21 and the outer pipe 22. The interposition may be the same as the holding member 3 described later. The outer pipe 22 has a length longer than the second inner pipe 21 in the flow direction of the exhaust gas G. The upstream end 221 of the outer pipe 22 protrudes outward from the upstream end 211 of the second inner pipe 21. In other words, the second inner pipe 21 is covered by the outer pipe 22 while being positioned inside the upstream end 221 of the outer pipe 22.

As shown in FIG. 2, the downstream end of the muffler 1 is inserted into the inside of the resonance double tube 2, thereby connecting the muffler 1 and the resonance double tube 2. Specifically, the outer casing 11 and the outer tube 22 are arranged so that the downstream end 113A of the second straight tube section 113 of the outer casing member 11 of the muffler 1 is inserted into the inside of the upstream end 221 of the outer tube 22 of the resonance double tube 2. The outer peripheral surface of the downstream end 113A of the second straight tube section 113 abuts against the inner peripheral surface of the upstream end 221 of the outer tube 22. The second straight tube section 113 of the outer casing member 11 and the outer tube 22 are fixed by welding or the like, thereby connecting the muffler 1 and the resonance double tube 2.

The first inner tube 12 and the second inner tube 21 are arranged so that the downstream end 121 of the first inner tube 12 of the muffler 1 is inserted inside the upstream end 211 of the second inner tube 21 of the resonant double tube 2. A third gap 25 is formed between the outer circumferential surface of the downstream end 121 of the first inner tube 12 and the inner circumferential surface of the upstream end 211 of the second inner tube 21, and a holding member 3 is arranged in the third gap 25. The first inner tube 12 and the second inner tube 21 are slidably held by the holding member 3.

The retaining member 3 extends along the entire circumferential direction in the third gap 25 between the first inner pipe 12 and the second inner pipe 21. Specifically, the retaining member 3 is ring-shaped so as to reduce the ring-shaped third gap 25 formed between the first inner pipe 12 and the second inner pipe 21 in the circumferential direction. In other words, the retaining member 3 is arranged so as to close the third gap 25 between the first inner pipe 12 and the second inner pipe 21. Note that the shape of the retaining member is not limited to a ring shape, and for example, the retaining member may have an area in the circumferential direction where the retaining member is not present. The retaining member 3 is fixed by welding or the like to the outer peripheral surface of the downstream end 121 of the first inner pipe 12 or the inner peripheral surface of the upstream end 211 of the second inner pipe 21 to prevent it from falling off. The retaining member 3 may be prevented from falling off by other methods, such as providing a protrusion on the outer circumferential surface of the downstream end 121 of the first inner pipe 12 or the inner circumferential surface of the upstream end 211 of the second inner pipe 21. The retaining member 3 is formed to be capable of restricting the passage of exhaust gas G. In this embodiment, the retaining member 3 is a ring member, such as a wire mesh, formed from a high-density material, such as stainless steel fiber. The use of stainless steel fiber as the retaining member 3 improves sealing properties and makes it easier to restrict the passage of exhaust gas G.

As described above, by connecting the muffler 1 and the resonance double pipe 2, the first silencing space 16 of the muffler 1 and the second silencing space 23 of the resonance double pipe 2 are connected via the first gap 17 and the second gap 24. The cross-sectional area of the first silencing space 16 in the flow direction of the exhaust gas G, i.e., in a cross section perpendicular to the central axis of the muffler 1, is larger than the cross-sectional area of the second silencing space 23 in a cross section perpendicular to the central axis of the resonance double pipe 2.

[2. Comparison with Comparative Example]
Next, a comparison between Example 1 and Comparative Example 1 conducted to confirm the effects of the present disclosure will be described.

Example 1 is the silencer 100 of the present embodiment shown in Figures 1 and 2. Comparative Example 1 is a silencer 100b in which the muffler 1b and the resonance double tube 2b are connected in a state in which the first silencing space 16b of the muffler 1b and the second silencing space 23b of the resonance double tube 2b are not connected, i.e., are separated, as shown in Figure 3. As shown in Figure 3, the first silencing space 16b of the muffler 1b is blocked by the first holding member 3b arranged in the gap formed between the outer casing member 11b and the first inner tube 12b. The second silencing space 23b of the resonance double tube 2b is blocked by the second holding member 3b arranged in the gap formed between the second inner tube 21b and the outer tube 22b. The connecting pipe 13b may have a plurality of communication holes 133 that communicate between the inside and outside of the connecting pipe 13b. The rest of the configuration of the noise suppressor 100b is not significantly different from the configuration of the noise suppressor 100 of this embodiment, so a detailed description of the configuration will be omitted.

The relationship between frequency (horizontal axis) and silencing volume (vertical axis) in Comparative Example 1 and Example 1 is shown in Figure 4. In Comparative Example 1, the first silencing space 16b of the muffler 1b and the second silencing space 23b of the resonance double tube 2b each function as a resonance chamber. Therefore, in Comparative Example 1, a silencing effect is obtained due to the different silencing characteristics of the muffler 1b and the resonance double tube 2b. On the other hand, in Example 1, the space in which the first silencing space 16 of the muffler 1 and the second silencing space 23 of the resonance double tube 2 are continuous through the first gap 17 and the second gap 24 can function as one large resonance chamber. As a result, in Example 1, a larger space can be used as a resonance chamber compared to Comparative Example 1, so that a lower frequency silencing effect can be obtained. In other words, in Example 1, the first gap 17 and the second gap 24 connecting the first silencing space 16 and the second silencing space 23 also function as resonance chambers, so the area functioning as a resonance chamber is increased compared to Comparative Example 1, and a stronger low-frequency silencing effect can be obtained.

3. Effects
According to the embodiment described above in detail, the following effects can be obtained.
(3a) In this embodiment, the muffler 1 and the resonance double tube 2 are connected so that the first silencing space 16 of the muffler 1 and the second silencing space 23 of the resonance double tube 2 communicate with each other through the first gap 17 and the second gap 24. That is, at the connection portion between the muffler 1 and the resonance double tube 2, the first silencing space 16 and the second silencing space 23 are not separated, and a space in which the first silencing space 16 and the second silencing space 23 are continuous is formed. Therefore, a larger space can be used as a resonance chamber by the first silencing space 16, the second silencing space 23, the first gap 17, and the second gap 24. As a result, the low-frequency silencing effect can be improved by using a double tube structure that can reduce the radiant heat of the exhaust gas G.

(3b) In this embodiment, the first inner tube 12 and the second inner tube 21 are slidably held by the holding member 3 disposed between the first inner tube 12 and the second inner tube 21. This reduces the effects of differences in thermal expansion and thermal contraction between the first inner tube 12 and the second inner tube 21.

(3c) In this embodiment, the first inner tube 12 is inserted into the second inner tube 21 and arranged so as to overlap, so that they can support each other, and thus fluctuations in the positions of the first inner tube 12 and the second inner tube 21 inside the outer casing member 11 and the outer tube 22 are suppressed. That is, even if there is no spacer or the like in the first gap 17 between the outer casing member 11 and the first inner tube 12 and the second gap 24 between the outer tube 22 and the upstream end 211 of the second inner tube 21, it is possible to easily maintain the positions of the first inner tube 12 and the second inner tube 21 relative to the outer casing member 11 and the outer tube 22. That is, compared to Comparative Example 1 having two holding members 3b shown in FIG. 3, the number of holding members can be reduced. As a result, it is possible to make it difficult for abnormal noise to occur when the positions of the first inner tube 12 and the second inner tube 21 change and hit the outer casing member 11 and the outer tube 22.

(3d) In this embodiment, since both the muffler 1 and the resonance double tube 2 have a double tube structure, radiant heat can be reduced over a wide range. In addition, the first inner tube 12 is inserted into the inside of the second inner tube 21 and arranged so as to overlap, and the holding member 3 is arranged in the third gap 25 formed between the first inner tube 12 and the second inner tube 21. Therefore, exhaust gas is less likely to flow into the gap between the second inner tube 21 and the outer tube 22 in the double tube structure, specifically the second gap 24 and the second silencing space 23, and the radiant heat of the resonance double tube 2 can be reduced. This reduces heat damage to the battery 200, which is arranged near the muffler 1 and the resonance double tube 2 and is undesirable for a rise in temperature, and expands the range in which the battery 200 can be installed. As a result, in, for example, a hybrid vehicle in which the battery 200 is installed, it is possible to expand the battery 200 arranged near the muffler 1 and the resonance double tube 2.

(3e) In this embodiment, the muffler 1 is a catalyst-integrated muffler formed integrally with the catalytic converter 14, so that the space required for the exhaust system under the floor of the vehicle can be reduced.
(3f) In this embodiment, the holding member 3 is formed to be capable of restricting the passage of exhaust gas, and therefore the sealing performance of the holding member 3 is improved, and exhaust gas flowing from the first inner pipe 12 to the second inner pipe 21 is less likely to flow into the second silencing space 23. This improves the function of the resonance double pipe 2 as a Helmholtz resonator. Also, in the resonance double pipe 2, the radiant heat due to exhaust gas can be further reduced.

The outer member 11 and the connecting pipe 13 of the muffler 1 correspond to an example of a space forming member, the first inner pipe 12, the second inner pipe 21 and the outer pipe 22 correspond to an example of an exhaust pipe, and the first gap 17 and the second gap 24 correspond to the third silencing space.

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-described embodiments and can take various forms.

(4a) In the above embodiment, a catalyst-integrated muffler 1 formed integrally with the catalytic device 14 was exemplified, but the configuration of the muffler is not limited to this. For example, the muffler may be formed separately from the catalytic device 14. As in the silencer 100c shown in FIG. 5, the catalytic device does not have to be disposed inside the outer casing 11 of the muffler 1c.

(4b) As in the silencer 100d shown in FIG. 6, the connecting pipe 13d of the muffler 1d may have one or more holes, preferably multiple communication holes 133, that connect the inside and outside of the connecting pipe 13d. Below, the case where there are multiple communication holes 133 will be described, but the effect can also be obtained with one hole. The multiple communication holes 133 provided in the connecting pipe 13d allow the exhaust gas passing through the inside of the connecting pipe 13d to expand into the space between the outer casing member 11 and the connecting pipe 13d through the multiple communication holes 133, thereby obtaining a sound-deadening effect due to expansion. In addition, the multiple communication holes 133 can suppress noise caused by pulsation of the vehicle engine.

(4c) The connecting pipe 13 and the first inner pipe 12 may be integral or separate.
(4d) In the above embodiment, in the connecting portion between the muffler 1 and the resonance double tube 2, the downstream end 113A of the second straight pipe section 113 of the outer casing member 11 of the muffler 1 is inserted into the upstream end 221 of the outer tube 22 of the resonance double tube 2. However, the method of connecting the muffler 1 and the resonance double tube 2 is not limited to this. For example, as in the silencer 100e shown in Figs. 7 and 8, the upstream end 221 of the outer tube 22 of the resonance double tube 2 may be inserted into the downstream end 113E of the second straight pipe section 113e of the outer casing member 11e of the muffler 1e. In this way, since the method of connecting the muffler and the resonance double tube is not limited, when the outer casing member and the outer tube are fixed by welding or the like, the connecting method can be changed to correspond to welding depending on the equipment held, such as a welding pattern from the muffler side or a welding pattern from the resonance double tube side.

(4e) In the above embodiment, the silencer 100 is configured such that the muffler 1 is disposed upstream of the resonance double tube 2, but the arrangement of the resonance double tube and the muffler is not limited to this. For example, as in the silencer 100f shown in FIG. 9, the muffler 1f may be disposed downstream of the resonance double tube 2f. The resonance double tube 2f and the muffler 1f are connected so that the first silencing space formed inside the muffler 1f and the second silencing space formed inside the resonance double tube 2f communicate with each other, as in the case of the resonance double tube 2 and the muffler 1 of this embodiment.

(4f) In the above embodiment, a muffler 1 with a double-pipe structure is exemplified, but the muffler may have a structure other than a double-pipe structure having a first silencing space 16. For example, the muffler may have a housing and an exhaust pipe that are shaped other than tubular, and may have a first silencing space within the housing.

(4g) The function of one component in the above embodiments may be distributed among multiple components, or the functions of multiple components may be integrated into one component. In addition, part of the configuration of the above embodiments may be omitted. In addition, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. All aspects included in the technical idea identified from the wording of the claims are embodiments of the present disclosure.

1, 1b to 1f... muffler, 2, 2b, 2f... resonating double tube, 3, 3b... retaining member, 11, 11b, 11e... outer casing member, 12, 12b... first inner tube, 13, 13b, 13d... connecting pipe, 14... catalytic device, 15... upstream cone, 16, 16b... first silencing space, 17... first gap, 19... separator, 24... second gap, 25... third gap, 21, 21b... second inner tube, 22, 22b ...Outer pipe, 23, 23b...Second silencing space, 100, 100b to 100f...Sound muffling device, 111...First straight pipe section, 112...First truncated cone section, 113, 113e...Second straight pipe section, 113A, 113E, 121, 211, 212, 221, 222...End part, 131...Third straight pipe section, 132...Second cone Base, 133...Communication hole, 141...Catalyst, 191...Wall, 192...Opening, 200...Battery.

Claims (3)

A silencing device comprising: an exhaust pipe having a double pipe structure, the exhaust pipe including an inner pipe through which exhaust gas passes and an outer pipe arranged to surround the outer periphery of the inner pipe; and a space forming member connected to the upstream or downstream of the exhaust pipe, the space forming member having a first silencing space which is a space for silencing noise,
the inner pipe includes a first inner pipe and a second inner pipe aligned in a flow direction of exhaust gas, and is arranged such that one of an end portion of the first inner pipe on the second inner pipe side and an end portion of the second inner pipe on the first inner pipe side is inserted into the other,
the first inner tube is disposed between the space forming member and the second inner tube,
a holding member is disposed in a gap formed between the first inner tube and the second inner tube,
a second silencing space for silencing sound formed between the second inner pipe and the outer pipe communicates with the first silencing space via a third silencing space formed between the first inner pipe and the outer pipe;
A cross-sectional area of the first silencing space in a cross section perpendicular to the flow direction is larger than a cross-sectional area of the second silencing space in a cross section perpendicular to the flow direction,
the space forming member has a double pipe structure including a connecting pipe connected to the first inner pipe and an outer shell member arranged to surround an outer periphery of the connecting pipe,
The first silencing space is a space formed between the outer shell member and the connecting pipe,
A noise absorbing device , wherein the first silencing space has no intervening object disposed between the connecting pipe and the outer casing member . 2. The noise suppressor according to claim 1,
A sound absorbing device, wherein there is no intervening object disposed between the inner pipe and the outer pipe in the second silencing space and the third silencing space. The silencer according to claim 1 or 2,
The space forming member is integrally formed with a catalytic converter having a catalyst for purifying exhaust gas.

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