Method of manufacturing noise eliminator

Abstract

To improve the assemblability of a pipe.SOLUTION: A first end of a first pipe is arranged in a housing so as to manufacture a noise eliminator. A second pipe is inserted into the first pipe from outside the housing, and the second pipe is therefore arranged in the housing. The second pipe is inserted from a second end of the first pipe located on the opposite side from the first end of the first pipe. The noise eliminator is thus manufactured which retains the first pipe connected to the second pipe inside an end of the housing. A first end of the second pipe is moved by the insertion to a position beyond at least the first end of the first pipe. A second end of the second pipe located on the opposite side from the first end of the second pipe is arranged inside the first pipe.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a muffler.

Background Art

[0002] In an exhaust system of an internal combustion engine, a muffler is used that includes two pipes: an inlet pipe for introducing exhaust gas into the housing and an outlet pipe for discharging exhaust gas from the housing.

[0003] For example, in Patent Document 1, when the first pipe is inserted inside the first end of the housing, after reducing the diameter of the second end of the housing, which is opposite to the first end, by spinning, the second pipe is inserted into the housing from the reduced-diameter second end, thereby suppressing the displacement of the pipes of the muffler. A technique is disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the prior art as disclosed in Patent Document 1, in order to ensure the insertability when inserting the second pipe through the reduced-diameter portion of the housing into the first pipe, the tip of the first pipe was subjected to flaring. If this flaring is not performed, the assemblability of the two pipes may decrease.

[0006] One aspect of the present disclosure is to improve the assemblability of pipes.

Means for Solving the Problems

[0007] One aspect of the present disclosure is a method for manufacturing a muffler, comprising preparing a housing and disposing a second pipe. Preparing the housing means preparing a housing having a central portion, and first and second cylindrical end portions that are located on both sides of the central portion and have a smaller diameter than the central portion, wherein the first pipe is inserted into the first cylindrical end portion and the first end of the first pipe is disposed inside the housing.

[0008] Disposing the second pipe includes inserting the second pipe into the first pipe disposed in the housing from the outside of the housing so as to dispose the second pipe inside the housing. Disposing the second pipe includes inserting the second pipe from the second end of the first pipe, which is located on the side opposite to the first end of the first pipe, and moving the first end of the second pipe to a position that at least passes through the first end of the first pipe and where the second end of the second pipe, which is located on the side opposite to the first end of the second pipe, is disposed inside the first pipe.

[0009] The muffler is configured to hold the first pipe to which the second pipe is connected inside the first cylindrical end portion. According to such a manufacturing method, even if no flaring process or the like is performed on the first end of the first pipe, the second pipe can be easily inserted into the first pipe. Therefore, the assemblability between the first pipe and the second pipe is improved.

[0010] In one aspect of the present disclosure, disposing the second pipe may include moving the first end of the second pipe inserted from the second end of the first pipe at least inside the second cylindrical end portion so that the second pipe is held inside the second cylindrical end portion in a state where the second pipe is connected to the first pipe.

[0011] According to such a manufacturing method, the assemblability between the housing and the second pipe is improved. In one aspect of the present disclosure, the housing may be formed by reducing the diameters of the first end of the cylindrical body and the second end of the cylindrical body, which is located on the side opposite to the first end of the cylindrical body.

[0012] Preparing the housing may include providing a first cylindrical end portion, disposing a first end of the first pipe inside the housing, and providing a second cylindrical end portion. Providing the first cylindrical end portion may include reducing the diameter of a first end of the cylindrical body. Disposing the first end of the first pipe inside the housing may include inserting the first pipe into the first cylindrical end portion. Providing the second cylindrical end portion may include reducing the diameter of a second end of the cylindrical body with the first pipe inserted into the first cylindrical end portion.

[0013] Disposing the second pipe may include moving at least an inner end of the second pipe inserted from a second end of the first pipe to inside the second cylindrical end portion such that the second pipe is held inside the second cylindrical end portion with the second pipe connected to the first pipe.

[0014] According to such a manufacturing method, even if no flaring process or the like is performed on the first end of the first pipe, the second pipe can be easily inserted into the first pipe. Therefore, the assemblability of the first pipe, the second pipe, and the housing is improved.

[0015] One aspect of the present disclosure is a method for manufacturing a muffler, comprising connecting, providing a first cylindrical end portion, providing a second cylindrical end portion, and disposing. Connecting includes connecting the first pipe and the second pipe such that, by inserting the second pipe inside the first pipe, a first end of the second pipe is disposed outside the first pipe and a second end of the second pipe located on a side opposite to the first end of the second pipe is disposed inside the first pipe.

[0016] Providing the first cylindrical end portion includes providing, at a first end of the cylindrical body, a first cylindrical end portion having a smaller diameter than the cylindrical body. Providing the second cylindrical end portion includes providing, at a second end of the cylindrical body located on a side opposite to the first end of the cylindrical body, a second cylindrical end portion having a smaller diameter than the cylindrical body.

[0017] Configuring includes at least partially disposing a connected first pipe and second pipe within a cylindrical body. Configuring includes disposing at least a part of the first pipe inside the first cylindrical end portion by inserting a second pipe connected to the first pipe from a first end of the second pipe into the first cylindrical end portion, and disposing at least a part of the second pipe inside the second cylindrical end portion, and disposing a first end of the first pipe inside the cylindrical body.

[0018] The muffler is configured to hold the first pipe inside the first cylindrical end portion and hold the second pipe connected to the first pipe inside the second cylindrical end portion. According to such a manufacturing method, even if the first end of the first pipe is not subjected to flaring or the like, the second pipe can be easily inserted into the first pipe. Therefore, the assemblability between the first pipe and the second pipe is improved.

[0019] In one aspect of the present disclosure, providing the second cylindrical end portion may include providing the second cylindrical end portion substantially coaxially with the first cylindrical end portion. In this way, when the second pipe is inserted into the second cylindrical end portion, the position where the second pipe is inserted into the second cylindrical end portion is less likely to shift. Therefore, the assemblability between the housing and the second pipe is improved. In one aspect of the present disclosure, providing the second cylindrical end portion may include providing the second cylindrical end portion such that an inner diameter of a portion of the cylindrical body adjacent to the second cylindrical end portion becomes smaller as it approaches the second cylindrical end portion.

[0020] In this way, when the second pipe is inserted into the second cylindrical end portion, the second pipe is easily guided by the second cylindrical end portion. Therefore, the assemblability between the housing and the second pipe is improved.

[0021]

[0022] ​In one aspect of the present disclosure, the second pipe may include a holding member on the outer peripheral surface of the second end. The outer diameter including the holding member at the second end of the second pipe may be greater than or equal to the inner diameter of the first pipe before the second pipe is inserted into the first pipe.

[0023] According to such a configuration, when the second pipe is inserted into the first pipe, the second pipe can be held by the first pipe while suppressing damage to the inner surface of the first pipe by the second pipe.

[0024] In one aspect of the present disclosure, the first pipe may include a main body portion and a reduced-diameter portion. The main body portion is located between the second end of the first pipe and the first end of the first pipe, which is opposite to the first end of the first pipe. The reduced-diameter portion is located between the main body portion and the second end of the first pipe. The inner diameter of the second end of the first pipe may be larger than the inner diameter of the main body portion. The inner diameter of the reduced-diameter portion may be formed to decrease as it approaches the main body portion.

[0025] According to such a configuration, it is easy to insert the second pipe into the first pipe. Therefore, the assemblability between the first pipe and the second pipe is improved.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Mode for Carrying Out the Invention

[0027] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the drawings. [1. First Embodiment] [1-1. Configuration of Muffler] The muffler 1 shown in FIG. 1 is a component mounted on a vehicle such as an automobile and constitutes at least a part of the exhaust gas flow path generated by the internal combustion engine of the vehicle.

[0028] The muffler 1 includes a housing 10, a first pipe 20, and a second pipe 30. The housing 10 is a metal member that is cylindrical as a whole. The housing 10 functions as an outer pipe that covers the first pipe 20 and the second pipe 30.

[0029] The housing 10 has a first cylindrical end portion 11, a second cylindrical end portion 12, a central portion 13, a first inclined portion 14, and a second inclined portion 15. The inner surface of the housing 10 defines the internal space 16 of the housing 10.

[0030] The first cylindrical end portion 11 and the second cylindrical end portion 12 are located on both sides of the housing 10 with respect to the central portion 13 located at the center of the housing 10, and are cylindrical portions having a diameter smaller than that of the central portion 13. The exhaust gas flows into the interior of the housing 10 through the second cylindrical end portion 12 and flows out of the housing 10 through the first cylindrical end portion 11. Hereinafter, the flow path of the exhaust gas flowing inside the housing 10 is referred to as flow path A. "The interior of the housing 10" includes the space between the first pipe 20 and the housing 10, the space between the second pipe 30 and the housing 10, the interior of the first pipe 20, and the interior of the second pipe 30. "The upstream side" means the upstream side of the flow path A. "The downstream side" means the downstream side of the flow path A. The first cylindrical end portion 11 is located on the downstream side of the central portion 13. The second cylindrical end portion 12 is located on the upstream side of the central portion 13.

[0031] The first inclined portion 14 is adjacent to the first cylindrical end portion 11 in the housing 10 and is located between the first cylindrical end portion 11 and the central portion 13. The inner diameter of the first inclined portion 14 decreases as it approaches the first cylindrical end portion 11 from the central portion 13.

[0032] The second inclined portion 15 is adjacent to the second cylindrical end portion 12 in the housing 10 and is located between the second cylindrical end portion 12 and the central portion 13. The inner diameter of the second inclined portion 15 decreases as it approaches the second cylindrical end portion 12 from the central portion 13.

[0033] In the present embodiment, both the first inclined portion 14 and the second inclined portion 15 are in a tapered shape. The first inclined portion 14 and the second inclined portion 15 are not limited to the tapered shape, and may be curved, for example.

[0034] The first pipe 20 is a metal pipe extending substantially linearly. The first pipe 20 is disposed on the downstream side inside the housing 10. The first pipe 20 functions as an outlet pipe for discharging the exhaust gas from the housing 10. The first pipe 20 is held inside the first cylindrical end portion 11. A part of the first pipe 20 may be disposed outside the first cylindrical end portion 11.

[0035] The first pipe 20 includes a first main body portion 21, a first large-diameter portion 22, a first through hole 23, and a first reduced-diameter portion 24. The first main body portion 21 has a first connecting portion 21a. The first large-diameter portion 22 has a first abutting portion 22a.

[0036] The first main body portion 21 is a portion located between the upstream end and the downstream end of the first pipe 20. The first connecting portion 21a is a portion that connects to the second pipe 30 at the upstream end of the first main body portion 21. The first connecting portion 21a is located inside the housing 10.

[0037] The first large-diameter portion 22 is located at the downstream end of the first pipe 20. The inner diameter of the first large-diameter portion 22 is larger than the inner diameter of the first main body portion 21. The first abutting portion 22a is a portion located on the outer peripheral surface of the first large-diameter portion 22 and is fixed by abutting against the first cylindrical end portion 11. In the present embodiment, the first abutting portion 22a is press-fitted into the first cylindrical end portion 11. According to another example, a part of the first main body portion 21 of the first pipe 20 may be arranged so as to be located outside the housing 10 through the first cylindrical end portion 11. In this case, the first abutting portion 22a of the first pipe 20 that abuts against the first cylindrical end portion 11 may be located upstream of the first large-diameter portion 22.

[0038] The first through hole 23 is a hole that penetrates from the inside to the outside of the first pipe 20. The first through hole 23 is provided on the side surface of the first pipe 20. In particular, the first through hole 23 is provided in a region located inside the housing 10 on the side surface of the first main body portion 21. One first through hole 23 may be provided, or a plurality of first through holes 23 may be provided.

[0039] The first reduced-diameter portion 24 is located between the first main body portion 21 and the first large-diameter portion 22 and connects the first main body portion 21 and the first large-diameter portion 22. The inner diameter of the first reduced-diameter portion 24 is formed to become smaller as it approaches the first main body portion 21. The first reduced-diameter portion 24 may be formed in a tapered shape or in a stepped shape.

[0040] The second pipe 30 is a metal pipe that extends in a substantially straight line. The second pipe 30 is disposed on the upstream side inside the housing 10. The second pipe 30 functions as an inlet pipe for introducing exhaust gas into the inside of the housing 10. The second pipe 30 is held inside the second cylindrical end portion 12. A part of the second pipe 30 may be disposed outside the second cylindrical end portion 12.

[0041] The second pipe 30 has a second connecting portion 31, a second abutting portion 32, and a second through hole 33. The second connecting portion 31 is a portion where the second pipe 30 connects to the first pipe 20 at the downstream end of the second pipe 30. The second connecting portion 31 is located inside the housing 10. The second connecting portion 31 is provided with a holding member 4 on the outer peripheral surface. In FIG. 1, the members located inside the first pipe 20 are represented by broken lines. Specifically, the second connecting portion 31 and the holding member 4 are represented by transparency. The same applies to FIGS. 4B, 7C, and 7D.

[0042] The holding member 4 is a belt-shaped member having a thickness and elastically deforms. In this embodiment, as an example, the holding member 4 is a wire mesh. The wire mesh is formed by weaving or intertwining filamentous metals. The holding member 4 is configured to apply a radial force to the first pipe 20 and the second pipe 30 between the first pipe 20 and the second pipe 30 by elastic deformation to hold the first pipe 20 and the second pipe 30.

[0043] The outer diameter of the second pipe 30 is smaller than either the inner diameter of the second cylindrical end portion 12 or the inner diameter of the first pipe 20. The outer diameter of the second connecting portion 31 including the holding member 4 is substantially the same as the inner diameter of the first pipe 20 or slightly larger than the inner diameter of the first pipe 20 in a state before the second connecting portion 31 is inserted into the first pipe 20.

[0044] The second connecting portion 31 of the second pipe 30 is held inside the first connecting portion 21a of the first pipe 20. The holding member 4 is compressed between the outer peripheral surface of the second connecting portion 31 and the inner peripheral surface of the first connecting portion 21a. That is, the second pipe 30 is press-fitted into the first connecting portion 21a by the holding member 4 at the second connecting portion 31. Thereby, the first pipe 20 and the second pipe 30 are connected. The second connecting portion 31 is not fixed to the first connecting portion 21a, and the second pipe 30 is slidable within the first pipe 20 together with the holding member 4.

[0045] The first connecting portion 21a of the first pipe 20 and the second connecting portion 31 of the second pipe 30, which are the portions where the first pipe 20 and the second pipe 30 are connected, are both located inside the housing 10. 。 The second abutting portion 32 is a portion located on the upstream side of the second pipe 30 and is fixed in contact with the second cylindrical end portion 12. The second abutting portion 32 shown in FIG. 1 is located at the upstream end of the second pipe 30. However, the second abutting portion 32 may be located downstream of the upstream end of the second pipe 30. In other words, the upstream end of the second pipe 30 may be located upstream of the second cylindrical end portion 12.

[0046] The second through hole 33 is a hole that penetrates from the inside to the outside of the second pipe 30. The second through hole 33 is provided on the side surface of the second pipe 30. In particular, the second through hole 33 is provided in a region between the second connecting portion 31 and the second abutting portion 32 on the side surface of the second pipe 30. One second through hole 33 may be provided, or a plurality of second through holes 33 may be provided.

[0047] The exhaust gas flows into the inside of the muffler 1 from the upstream opening of the second pipe 30. That is, the exhaust gas passes through the inside of the second abutting portion 32 and flows through the portion of the second pipe 30 located inside the housing 10. The exhaust gas flows from the second pipe 30 into the first pipe 20 through the second connecting portion 31 and the first connecting portion 21a, passes through the inside of the first abutting portion 22a, and is discharged from the downstream opening of the first pipe 20 to the outside of the muffler 1.

[0048] At this time, the exhaust gas passes through the first through-hole 23 and the second through-hole 33 and flows out from the inside of the first pipe 20 and the second pipe 30 into the internal space 16 of the housing 10. Since the muffler 1 is affected by the expansion and interference of the exhaust gas due to this internal space 16, it exhibits a sound absorption effect. The internal space 16 may be filled with a sound-absorbing material in order to improve the sound absorption effect. An outer periphery of at least one of the first pipe 20 and the second pipe 30 may be provided with a sound-absorbing material or a pipe that covers the outer periphery of the first pipe 20 or the second pipe 30.

[0049] [1-2. Manufacturing method of muffler] As shown in FIG. 2, the manufacturing method of the muffler 1 includes a first cylindrical end forming step S110, a first pipe arranging step S120, a second cylindrical end forming step S130, and a second pipe arranging step S140. The manufacturing method of the muffler 1 is executed in the order of the first cylindrical end forming step S110, the first pipe arranging step S120, the second cylindrical end forming step S130, and the second pipe arranging step S140. The second cylindrical end forming step S130 may be executed before the first pipe arranging step S120. Each step will be described with reference to FIGS. 3 and 4.

[0050] [1-2-1. First cylindrical end forming step] The housing 10 is formed by reducing the diameters of the first end and the second end opposite to the first end of the cylindrical member, the cylindrical body 10a.

[0051] As shown in FIG. 3A, the first cylindrical end forming step S110 is a step of forming the first cylindrical end 11 on the cylindrical body 10a. The first cylindrical end 11 is formed by reducing the diameter of the downstream end of the cylindrical body 10a. The diameter reduction process means reducing a cylindrical member in the radial direction to form a cylindrical shape with a smaller diameter than its circumference. Hereinafter, the diameter reduction process will also be simply referred to as diameter reduction. The diameter reduction can be realized by, for example, spinning, but may also be realized by other processing methods such as pressing.

[0052] Due to the diameter reduction for forming the first cylindrical end portion 11, a first inclined portion 14 is formed in a portion of the cylindrical body 10a adjacent to the upstream side of the first cylindrical end portion 11. [1-2-2. First Pipe Arrangement Step] As shown in FIGS. 3B and 3C, the first pipe arrangement step S120 is a step of disposing the first connection portion 21a of the first pipe 20 inside the cylindrical body 10a by inserting the first pipe 20 into the first cylindrical end portion 11 of the cylindrical body 10a.

[0053] The first pipe 20 enters the inside of the cylindrical body 10a from the upstream opening of the cylindrical body 10a and is inserted into the first cylindrical end portion 11. The first abutting portion 22a in the first pipe 20 abuts against the first cylindrical end portion 11. The first connection portion 21a is disposed inside the cylindrical body 10a.

[0054] At this time, the first abutting portion 22a may be fixed to the first cylindrical end portion 11. The fixing may be realized, for example, by performing at least one of press-fitting, welding, and diameter expansion. In the present embodiment, in this step, the first abutting portion 22a is press-fitted into the first cylindrical end portion 11. Further, by spot-welding the periphery of the first cylindrical end portion 11, the first abutting portion 22a is temporarily fixed to the first cylindrical end portion 11. The first abutting portion 22a may be fixed to the first cylindrical end portion 11 in a step subsequent to this step.

[0055] [1-2-3. Second Cylindrical End Portion Forming Step] As shown in FIG. 3C, the second cylindrical end portion forming step S130 is a step of forming the second cylindrical end portion 12 on the cylindrical body 10a with the first pipe 20 inserted into the first cylindrical end portion 11. The second cylindrical end portion 12 is formed by reducing the diameter of the upstream end portion of the cylindrical body 10a. The second cylindrical end portion 12 is formed substantially coaxially with the first cylindrical end portion 11.

[0056] Due to the diameter reduction for forming the second cylindrical end portion 12, a second inclined portion 15 is formed in a portion of the cylindrical body 10a adjacent to the downstream side of the second cylindrical end portion 12. The housing 10 is obtained by forming the first cylindrical end portion 11 and the second cylindrical end portion 12 on the cylindrical body 10a in this way.

[0057] [1-2-4. Second Pipe Arrangement Step] As shown in FIG. 4A, in the second pipe arrangement step S140, the second pipe 30 is arranged inside the housing 10 by inserting the second pipe 30 from the outside of the housing 10 into the first pipe 20 in which the first connecting portion 21a is arranged inside the housing 10.

[0058] The second pipe 30 is inserted into the inside of the first pipe 20 from the downstream end portion (that is, the first large diameter portion 22) of the first pipe 20 with the upstream end portion (that is, the end portion on the side where the holding member 4 is not provided) as the leading end. After the leading end of the second pipe 30 is inserted into the first large diameter portion 22 of the first pipe 20, it is guided to the first main body portion 21 by the first reduced diameter portion 24. In the present embodiment, the leading end of the second pipe 30 corresponds to the second abutting portion 32.

[0059] When the insertion of the second pipe 30 into the first pipe 20 proceeds, the second connecting portion 31 and the holding member 4 at the downstream end portion of the second pipe 30 are inserted into the inside of the first pipe 20. Since the outer diameter of the second connecting portion 31 including the holding member 4 is substantially the same as the inner diameter of the first pipe 20 or slightly larger than the inner diameter of the first pipe 20, the second pipe 30 and the holding member 4 are press-fitted into the first pipe 20. In the present embodiment, the press-fitting of the second pipe 30 and the holding member 4 into the first pipe 20 is advanced using a rod-shaped press-fitting jig 5 having a diameter smaller than the inner diameter of the first pipe 20. The press-fitting jig 5 may be solid or hollow. In the press-fitting jig 5, at least a part of the portion that abuts against the second pipe 30 when the second pipe 30 is press-fitted presses at least a part of the wall thickness portion of the second pipe 30.

[0060] As shown in FIG. 4B, when the insertion of the second pipe 30 into the first pipe 20 further proceeds, the leading end of the second pipe 30 comes out of the outside of the first pipe 20, advances upstream into the internal space 16 of the housing 10, and is inserted into the second cylindrical end portion 12.

[0061] The second pipe 30 passes through the second cylindrical end portion 12 and advances upstream until it abuts against a receiving jig 6 that is outside the housing 10 and located upstream of the second cylindrical end portion 12. The receiving jig 6 may be in contact with the second cylindrical end portion 12 or may be separated from the second cylindrical end portion 12. When the tip of the second pipe 30 abuts against the receiving jig 6, the second pipe placement step S140 ends.

[0062] When the second pipe placement step S140 ends, both the second connecting portion 31 and the holding member 4 are press-fitted inside the first pipe 20. The second pipe 30 is connected to the first pipe 20 through the holding member 4 at the second connecting portion 31. In the present embodiment, the holding member 4 is press-fitted into the first connecting portion 21a. Therefore, the second pipe 30 is connected at the first connecting portion 21a of the first pipe 20. The first connecting portion 21a and the second connecting portion 31 are not fixed, and the second pipe 30 is slidable with respect to the first pipe 20 via the holding member 4.

[0063] The second abutting portion 32 is in contact with the second cylindrical end portion 12. The second abutting portion 32 may be fixed to the second cylindrical end portion 12. The fixing may be realized, for example, by performing at least one of press-fitting, welding, and diameter expansion. The second abutting portion 32 may be fixed to the second cylindrical end portion 12 in a process after this step.

[0064] As described above, the housing 10 is formed from the cylindrical body 10a, and the first pipe 20 and the second pipe 30 are arranged inside the housing 10, whereby the muffler 1 is obtained. [1-3. Function, Effect] According to the embodiment described above, the following functions and effects are obtained.

[0065] (1a) In the second pipe placement step S140, the second pipe 30 is inserted into the first pipe 20 from the downstream end of the first pipe 20. According to such an insertion, even if the upstream end of the first pipe 20 is not subjected to a flaring process or the like, the second pipe 30 can be easily inserted into the first pipe 20. Therefore, the assemblability between the first pipe 20 and the second pipe 30 is improved.

[0066] (1b) In the second cylindrical end portion forming step S130, the second cylindrical end portion 12 is formed coaxially with the first cylindrical end portion 11. By reducing the diameter to form the second cylindrical end portion 12, a second inclined portion 15 is formed in a portion of the cylindrical body 10a adjacent to the second cylindrical end portion 12. The inner diameter of the second inclined portion 15 becomes smaller as it approaches the second cylindrical end portion 12 from the central portion 13.

[0067] According to such a configuration of the housing 10 or the cylindrical body 10a, in the second pipe arranging step S140, the second pipe 30 is guided by the second inclined portion 15, making it easier to insert into the second cylindrical end portion 12. Therefore, the assemblability between the second pipe 30 and the second cylindrical end portion 12 is improved.

[0068] (1c) The second pipe 30 is inserted into the first pipe 20 from the first large diameter portion 22 of the first pipe 20. The inner diameter of the first large diameter portion 22 is larger than the inner diameter of the first main body portion 21. The first reduced diameter portion 24 connects the first main body portion 21 and the first large diameter portion 22. The inner diameter of the first reduced diameter portion 24 is formed to become smaller as it approaches the first main body portion 21.

[0069] According to such a configuration of the first pipe 20, in the second pipe arranging step S140, it is easy to insert the second pipe 30 into the first pipe 20 from the first large diameter portion 22, and it is easy to insert the second pipe 30 from the first large diameter portion 22 through the first reduced diameter portion 24 into the first main body portion 21. Therefore, the assemblability between the first pipe 20 and the second pipe 30 can be improved.

[0070] (1d) In the first pipe arranging step S120, the first pipe 20 is inserted into the housing 10 with the first cylindrical end portion 11 formed on the housing 10. According to such a process, compared with the case where the first cylindrical end portion 11 is formed after the first pipe 20 is disposed inside the housing 10, the position of the first pipe 20 is less likely to shift. Therefore, the shift of the position of the first pipe 20 can be suppressed.

[0071] Furthermore, a member for supporting the first pipe 20 inside the housing 10 becomes unnecessary until the first cylindrical end portion 11 is formed. Therefore, the types of members required for manufacturing the muffler 1 can be reduced.

[0072] (1e) In the second pipe arrangement step S140, the second pipe 30 is inserted into the housing 10 in a state where the second cylindrical end portion 12 is formed in the housing 10. According to such a process, compared with the case where the second cylindrical end portion 12 is formed after the second pipe 30 is disposed inside the housing 10, the position of the second pipe 30 is less likely to shift. Therefore, the shift of the position of the second pipe 30 can be suppressed.

[0073] Furthermore, a member for supporting the second pipe 30 inside the housing 10 becomes unnecessary until the second cylindrical end portion 12 is formed. Therefore, the types of members required for manufacturing the muffler 1 can be reduced.

[0074] (1f) The first connecting portion 21a and the second connecting portion 31 of the first pipe 20, which is the portion where the first pipe 20 and the second pipe 30 are connected, are both located inside the housing 10. The first connecting portion 21a and the second connecting portion 31 are not fixed and are slidable via the holding member 4.

[0075] According to such a configuration, when expansion or contraction due to the heat of the exhaust gas occurs in the first pipe 20 and the second pipe 30, both can expand and contract in the axial direction. Therefore, an excessive load is not applied to the first pipe 20 and the second pipe 30, and the occurrence of buckling can be suppressed.

[0076] (1g) Since the second connecting portion 31 in the second pipe 30 is provided with the holding member 4 on the outer peripheral surface, it is possible to prevent the second pipe 30 from damaging the inner surface of the first pipe 20 in the process of inserting the second pipe 30 into the first pipe 20.

[0077] (1h) After the second pipe arrangement step S140, the first pipe 20 can be fixed to the first cylindrical end portion 11, and the second pipe 30 can be fixed to the second cylindrical end portion 12 by welding, diameter expansion, or the like. Therefore, the first pipe 20 and the second pipe 30 can be fixed to the housing 10 more firmly.

[0078] [1-4. Corresponding relationships between terms] In the above embodiment, the upstream end portion and the first connecting portion 21a of the first pipe 20 correspond to an example of the first end of the first pipe, and the downstream end portion and the first large-diameter portion 22 of the first pipe 20 correspond to an example of the second end of the first pipe.

[0079] The upstream end portion and the second abutting portion 32 of the second pipe 30 correspond to an example of the first end of the second pipe, and the downstream end portion and the second connecting portion 31 of the second pipe 30 correspond to an example of the second end of the second pipe.

[0080] The downstream end portion of the cylindrical body 10a corresponds to an example of the first end of the cylindrical body, and the upstream end portion of the cylindrical body 10a corresponds to an example of the second end of the cylindrical body. The first cylindrical end portion forming step S110 corresponds to an example of providing the first cylindrical end portion, and the first pipe arrangement step S120 corresponds to an example of arranging the first end of the first pipe inside the housing. . The second cylindrical end portion forming step S130 corresponds to an example of providing the second cylindrical end portion, and the second pipe arrangement step S140 corresponds to an example of arranging the second pipe. The first cylindrical end portion forming step S110, the first pipe arrangement step S120, and the second cylindrical end portion forming step S130 correspond to an example of preparing the housing.

[0081] [2. Second Embodiment] [2-1. Configuration of the muffler] The manufacturing method of the muffler 1 in the second embodiment manufactures the same muffler 1 as in the first embodiment. The differences between the second embodiment and the first embodiment will be described below. Note that the same reference numerals as those in the first embodiment denote the same components, and reference is made to the preceding description.

[0082] [2-2. Manufacturing method of muffler] As shown in FIG. 5, the manufacturing method of the muffler 1 in the second embodiment includes a pipe connection step S210, a first cylindrical end formation step S220, a second cylindrical end formation step S230, and a connecting pipe arrangement step S240. The manufacturing method of the muffler 1 in the second embodiment is executed in the order of the pipe connection step S210, the first cylindrical end formation step S220, the second cylindrical end formation step S230, and the connecting pipe arrangement step S240. However, the order of executing the pipe connection step S210, the first cylindrical end formation step S220, and the second cylindrical end formation step S230 is not particularly limited, and they may be executed in any order. At least two of the pipe connection step S210, the first cylindrical end formation step S220, and the second cylindrical end formation step S230 may be executed in parallel. Each step will be described with reference to FIGS. 6 and 7.

[0083] [2-2-1. Pipe connection step] As shown in FIG. 6, the pipe connection step S210 is a step of connecting the first pipe 20 and the second pipe 30 by inserting the second pipe 30 inside the first pipe 20.

[0084] The second pipe 30 is inserted inside the first pipe 20 from the first large-diameter portion 22 of the first pipe 20 with the end on the side not provided with the holding member 4 as the leading end. After the leading end of the second pipe 30 is inserted into the first large-diameter portion 22 of the first pipe 20, it is guided to the first main body portion 21 by the first reduced-diameter portion 24. In this embodiment, the leading end of the second pipe 30 corresponds to the second abutting portion 32.

[0085] When the insertion of the second pipe 30 into the first pipe 20 proceeds, the second connecting portion 31 and the holding member 4 of the second pipe 30 are inserted inside the first pipe 20. Since the outer diameter of the second connecting portion 31 including the holding member 4 is substantially the same as the inner diameter of the first pipe 20 or slightly larger than the inner diameter of the first pipe 20, the second pipe 30 and the holding member 4 are press-fitted into the first pipe 20. In the present embodiment, the press-fitting of the second pipe 30 and the holding member 4 into the first pipe 20 is advanced by using a rod-shaped press-fitting jig 5 having a diameter smaller than the inner diameter of the first pipe 20.

[0086] When the insertion of the second pipe 30 into the first pipe 20 further proceeds, the tip of the second pipe 30 comes out of the outside of the first pipe 20. At this time, the second connecting portion 31 of the second pipe 30 is disposed inside the first pipe 20. In the present embodiment, the second connecting portion 31 is disposed inside the first connecting portion 21a located at the end of the first pipe 20 opposite to the first large-diameter portion 22.

[0087] In this way, in the pipe connection step S210, the second contact portion 32 in the second pipe 30 is disposed outside the first pipe 20. The second connecting portion 31 in the second pipe 30 is disposed inside the first pipe 20. The first pipe 20 and the second pipe 30 are connected.

[0088] [2-2-2. First cylindrical end forming step] As shown in FIG. 7A, the first cylindrical end forming step S220 is a step of providing a first cylindrical end 11 to a cylindrical body 10a which is a cylindrical member.

[0089] The first cylindrical end forming step S220 is the same step as the first cylindrical end forming step S110. That is, the first cylindrical end 11 is provided by reducing the diameter of the downstream end portion of the cylindrical body 10a.

[0090] Due to the diameter reduction for providing the first cylindrical end 11, a first inclined portion 14 is provided in a portion adjacent to the upstream side of the first cylindrical end 11 in the cylindrical body 10a. [2-2-3. Second cylindrical end forming step] As shown in FIG. 7B, the second cylindrical end portion forming step S230 is a step of providing the second cylindrical end portion 12 to the cylindrical body 10a.

[0091] The second cylindrical end portion forming step S230 is the same step as the second cylindrical end portion forming step S130. That is, the second cylindrical end portion 12 is provided by reducing the diameter of the upstream end portion of the cylindrical body 10a. The second cylindrical end portion 12 is provided substantially coaxially with the first cylindrical end portion 11.

[0092] Due to the diameter reduction for providing the second cylindrical end portion 12, a second inclined portion 15 is provided in a portion adjacent to the downstream side of the second cylindrical end portion 12 in the cylindrical body 10a. The housing 10 is obtained by providing the first cylindrical end portion 11 and the second cylindrical end portion 12 to the cylindrical body 10a in this way.

[0093] [2-2-4. Connecting Pipe Arrangement Step] As shown in FIG. 7C, the connecting pipe arrangement step S240 is a step of arranging the connected first pipe 20 and second pipe 30 at least partially inside the cylindrical body 10a. In this step, the first pipe 20 and the second pipe 30 are maintained in a connected state without being separated from each other.

[0094] The second pipe 30 connected to the first pipe 20 is inserted into the inside of the cylindrical body 10a from the first cylindrical end portion 11 with the end portion on the side where the holding member 4 is not provided as the leading end. The leading end of the second pipe 30 is the upstream end portion of the second pipe 30. In the present embodiment, the leading end of the second pipe 30 corresponds to the second abutting portion 32.

[0095] When the insertion of the connected first pipe 20 and second pipe 30 into the cylindrical body 10a proceeds, the upstream end portion of the first pipe 20 (in the present embodiment, the first connecting portion 21a) enters the inside of the cylindrical body 10a from the first cylindrical end portion 11.

[0096] As shown in FIG. 7D, when the insertion of the second pipe 30 into the cylindrical body 10a of the first pipe 20 further proceeds, the tip of the second pipe 30 is inserted into the second cylindrical end portion 12, and the second contact portion 32 is disposed inside the second cylindrical end portion 12. Further, the first contact portion 22a of the first pipe 20 is disposed inside the first cylindrical end portion 11. The upstream end of the first pipe 20 is disposed inside the cylindrical body 10a.

[0097] At this time, the upstream end of the second pipe 30 is located inside the second cylindrical end portion 12. The downstream end of the second pipe 30 is located inside the cylindrical body 10a. That is, the second connection portion 31 and the holding member 4 are located inside the upstream end (i.e., the first connection portion 21a) of the first pipe 20 located inside the cylindrical body 10a. The downstream end of the first pipe 20 is located inside the first cylindrical end portion 11. However, the upstream end of the second pipe 30 may be located outside the cylindrical body 10a. The downstream end of the second pipe 30 only needs to be inside the first pipe 20 and may be located outside the cylindrical body 10a. The downstream end of the first pipe 20 may be located outside the cylindrical body 10a. In this step or a step subsequent to this step, the first contact portion 22a may be fixed to the first cylindrical end portion 11. The second contact portion 32 may be fixed to the second cylindrical end portion 12. The fixing method may be realized by performing at least one of, for example, press-fitting, welding, and diameter expansion. In this embodiment, the first contact portion 22a is fixed by being press-fitted into the first cylindrical end portion 11. The second contact portion 32 is fixed to the second cylindrical end portion 12 in a step subsequent to this step.

[0098] As described above, the housing 10 is formed from the cylindrical body 10a, and the connected first pipe 20 and second pipe 30 are disposed inside the housing 10, whereby the muffler 1 is obtained.

[0099] [2-3. Operation and Effect] [2-3. Operation, Effect] According to the second embodiment described above, the same effects as those of the first embodiment can be obtained. In addition, according to the second embodiment, providing the first cylindrical end portion 11 and the second cylindrical end portion 12 on the cylindrical body 10a and connecting the first pipe 20 and the second pipe 30 can be executed independently of each other. For this reason, the number of manufacturing steps can be reduced.

[0100] [2-4. Corresponding relationships between terms] In the above embodiment, the upstream end portion of the first pipe 20 and the first connecting portion 21a correspond to an example of the first end of the first pipe.

[0101] The upstream end portion of the second pipe 30 and the second abutting portion 32 correspond to an example of the first end of the second pipe, and the downstream end portion of the second pipe 30 and the second connecting portion 31 correspond to an example of the second end of the second pipe.

[0102] The downstream end portion of the cylindrical body 10a corresponds to an example of the first end of the cylindrical body, and the upstream end portion of the cylindrical body 10a corresponds to an example of the second end of the cylindrical body. The pipe connection step S210 corresponds to an example of connecting the first pipe and the second pipe, the first cylindrical end portion forming step S220 corresponds to an example of providing the first cylindrical end portion, the second cylindrical end portion forming step S230 corresponds to an example of providing the second cylindrical end portion, and the connected pipe arrangement step S240 corresponds to an example of arranging.

[0103] [3. 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.

[0104] (3a) In the above embodiment, the inner peripheral surface of the first connecting portion 21a in the first pipe 20 may be reduced in diameter. The outer peripheral surface of the second connecting portion 31 in the second pipe 30 may be increased in diameter. According to such a configuration, the holding member 4 disposed between the inner peripheral surface of the first connecting portion 21a and the outer peripheral surface of the second connecting portion 31 is in a more compressed state. For this reason, the resistance to vibration received from a vehicle or the like is improved at the connecting portion between the first pipe 20 and the second pipe 30.

[0105] (3b) In the above embodiment, the upstream end portion of the second pipe 30 may be reduced in diameter. According to such a configuration, it is easy to insert the second pipe 30 into the second cylindrical end portion 12 in the second pipe arrangement step S140 or the connecting pipe arrangement step S240.

[0106] (3c) In the above embodiment, the second abutting portion 32 in the second pipe 30 may be increased in diameter. According to such a configuration, it is easy to fix the second abutting portion 32 to the second cylindrical end portion 12. This is easy.

[0107] (3d) In the above embodiment, the first pipe 20 is disposed at the first cylindrical end portion 11 on the downstream side of the housing 10, and the second pipe 30 is disposed at the second cylindrical end portion 12 on the upstream side of the housing 10. However, the arrangement of the first pipe 20 and the second pipe 30 is not limited to this. For example, the first pipe 20 may be disposed at the second cylindrical end portion 12 on the upstream side of the housing 10, and the second pipe 30 may be disposed at the first cylindrical end portion 11 on the downstream side of the housing 10.

[0108] (3e) The first cylindrical end portion 11 and the second cylindrical end portion 12 are both formed by reducing the diameter of the upstream or downstream end portion of the cylindrical body 10a. However, instead of reducing the diameter of the cylindrical body 10a, the first cylindrical end portion 11 and the second cylindrical end portion 12 may be provided with another reduced-diameter member at the upstream or downstream end portion of the cylindrical body 10a by welding or the like. The other member may function as the first cylindrical end portion 11 or the second cylindrical end portion 12.

[0109] (3f) The first through-hole 23 is provided in one or more of the first pipes 20. The second through-hole 33 is provided in one or more of the second pipes 30. However, in the silencer 1, it is sufficient that at least one of the first through-hole 23 and the second through-hole 33 is provided in one or more of the first pipe 20 and the second pipe 30. For example, when the first through-hole 23 is provided in the first pipe 20, the second through-hole 33 may not be provided in the second pipe 30. Alternatively, when the second through-hole 33 is provided in the second pipe 30, the first through-hole 23 may not be provided in the first pipe 20.

[0110] (3g) A plurality of functions of one component in the above embodiment may be realized by a plurality of components, or one function of one component may be realized by a plurality of components. Further, a plurality of functions of a plurality of components may be realized by one component, or one function realized by a plurality of components may be realized by one component. Further, a part of the configuration of the above embodiment may be omitted. Further, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of another of the above embodiments.

[0111] [Technical idea disclosed in this specification] [Item 1] A method for manufacturing a silencer, comprising: preparing a housing including a central portion and first and second cylindrical end portions that are cylindrical end portions having a diameter smaller than that of the central portion and are located on both sides of the central portion, wherein the first pipe is inserted into the first cylindrical end portion and the first end of the first pipe is disposed inside the housing; disposing the second pipe inside the housing by inserting the second pipe into the first pipe disposed in the housing from the outside of the housing; and Placing the second pipe includes inserting the second pipe from the second end of the first pipe, which is located on the side opposite to the first end of the first pipe, and moving the first end of the second pipe to a position that passes at least through the first end of the first pipe and where the second end of the second pipe, which is located on the side opposite to the first end of the second pipe, is disposed inside the first pipe. The muffler is configured to hold the first pipe to which the second pipe is connected inside the first cylindrical end portion. Method for manufacturing a muffler.

[0112] [Item 2] A method for manufacturing a muffler according to Item 1, wherein placing the second pipe includes moving the first end of the second pipe, which is inserted from the second end of the first pipe with the second pipe connected to the first pipe, at least to the inside of the second cylindrical end portion so that the second pipe is held inside the second cylindrical end portion. Method for manufacturing a muffler.

[0113] [Item 3] A method for manufacturing a muffler according to Item 1, wherein the housing is formed by reducing the diameters of the first end of the cylindrical body and the second end of the cylindrical body, which is located on the side opposite to the first end of the cylindrical body. Preparing the housing includes providing the first cylindrical end portion on the cylindrical body by reducing the diameter of the first end of the cylindrical body, placing the first end of the first pipe inside the housing by inserting the first pipe into the first cylindrical end portion, providing the second cylindrical end portion on the cylindrical body by reducing the diameter of the second end of the cylindrical body with the first pipe inserted into the first cylindrical end portion, and includes Arranging the second pipe includes moving the first end of the second pipe inserted from the second end of the first pipe at least inside the second cylindrical end portion so that the second pipe is held inside the second cylindrical end portion while the second pipe is connected to the first pipe. Method for manufacturing a muffler.

[0114] [Item 4] A method for manufacturing a muffler, connecting the first pipe and the second pipe such that by inserting the second pipe inside the first pipe, the first end of the second pipe is disposed outside the first pipe and the second end of the second pipe located on the side opposite to the first end of the second pipe is disposed inside the first pipe; providing a first cylindrical end portion having a diameter smaller than that of the cylindrical body at the first end of the cylindrical body; providing a second cylindrical end portion having a diameter smaller than that of the cylindrical body at the second end of the cylindrical body located on the side opposite to the first end of the cylindrical body; arranging the connected first pipe and second pipe at least partially inside the cylindrical body; including The arranging includes disposing at least a part of the first pipe inside the first cylindrical end portion, disposing at least a part of the second pipe inside the second cylindrical end portion, and disposing the first end of the first pipe inside the cylindrical body by inserting the second pipe connected to the first pipe from the first end of the second pipe into the first cylindrical end portion. The muffler is configured to hold the first pipe inside the first cylindrical end portion and hold the second pipe connected to the first pipe inside the second cylindrical end portion. Method for manufacturing a muffler.

[0115] [Item 5] A method for manufacturing a muffler according to item 3 or item 4, Providing the second cylindrical end portion includes providing the second cylindrical end portion substantially coaxially with the first cylindrical end portion. Method for manufacturing a muffler.

[0116] [Item 6] A method for manufacturing a muffler according to any one of Items 3 to 5, wherein providing the second cylindrical end portion includes providing the second cylindrical end portion such that an inner diameter of a portion of the cylindrical body adjacent to the second cylindrical end portion becomes smaller as it approaches the second cylindrical end portion. Method for manufacturing a muffler.

[0117] [Item 7] A method for manufacturing a muffler according to any one of Items 1 to 6, wherein the second pipe is provided with a holding member on an outer peripheral surface of the second end of the second pipe, an outer diameter including the holding member at the second end of the second pipe is equal to or greater than an inner diameter of the first pipe in a state before the second pipe is inserted into the first pipe. Method for manufacturing a muffler.

[0118] [Item 8] A method for manufacturing a muffler according to any one of Items 1 to 7, wherein the first pipe has a main body portion located between a second end of the first pipe located on a side opposite to the first end of the first pipe and the first end of the first pipe, and a reduced-diameter portion located between the main body portion and the second end of the first pipe, an inner diameter of the second end of the first pipe is larger than an inner diameter of the main body portion, an inner diameter of the reduced-diameter portion is formed to become smaller as it approaches the main body portion. Method for manufacturing a muffler.

Explanation of reference numerals

[0119] 1... Silencer, 10... Housing, 10a... Cylindrical body, 11... First cylindrical end, 12... Second cylindrical end, 13... Central part, 20... First pipe, 21... First main body part, 21a... First connecting part, 22... First large-diameter part, 22a... First contact part, 30... Second pipe, 31... Second connecting part, 32... Second contact part.

Claims

1. A method for manufacturing a muffler, comprising: preparing a housing having a central portion and first and second cylindrical end portions located on both sides of the central portion and having a smaller diameter than the central portion, wherein a first pipe is inserted into the first cylindrical end portion and a first end of the first pipe is disposed inside the housing; disposing a second pipe inside the housing by inserting the second pipe into the first pipe from outside the housing; including: disposing the second pipe includes inserting the second pipe from a second end of the first pipe located on a side opposite to the first end of the first pipe, and moving a first end of the second pipe to a position passing at least through the first end of the first pipe and where a second end of the second pipe located on a side opposite to the first end of the second pipe is disposed inside the first pipe; the muffler is configured to hold the first pipe connected to the second pipe inside the first cylindrical end portion; A method for manufacturing a muffler.

2. The method for manufacturing a muffler according to claim 1, wherein disposing the second pipe includes moving the first end of the second pipe inserted from the second end of the first pipe to at least inside the second cylindrical end portion such that the second pipe is held inside the second cylindrical end portion with the second pipe connected to the first pipe; A method for manufacturing a muffler.

3. The method for manufacturing a muffler according to claim 1, wherein the housing is formed by reducing the diameters of a first end of a cylindrical body and a second end of the cylindrical body located on a side opposite to the first end of the cylindrical body, and preparing the housing includes: providing the first cylindrical end portion on the cylindrical body by reducing the diameter of the first end of the cylindrical body; disposing the first end of the first pipe inside the housing by inserting the first pipe into the first cylindrical end portion; and providing the second cylindrical end portion on the cylindrical body by reducing the diameter of the second end of the cylindrical body with the first pipe inserted into the first cylindrical end portion; including: Arranging the second pipe includes moving the first end of the second pipe inserted from the second end of the first pipe to at least inside the second cylindrical end portion so that the second pipe is held inside the second cylindrical end portion while the second pipe is connected to the first pipe. Method for manufacturing a muffler.

4. A method for manufacturing a muffler, comprising: Connecting the first pipe and the second pipe so that the first end of the second pipe is disposed outside the first pipe and the second end of the second pipe located on the side opposite to the first end of the second pipe is disposed inside the first pipe by inserting the second pipe inside the first pipe; Providing a first cylindrical end portion having a smaller diameter than the cylindrical body at the first end of the cylindrical body; At the second end of the cylindrical body located on the side opposite to the first end of the cylindrical body, Providing a second cylindrical end portion having a smaller diameter than the cylindrical body; Disposing the connected first pipe and second pipe at least partially inside the cylindrical body; including The arranging includes disposing at least a part of the first pipe inside the first cylindrical end portion, disposing at least a part of the second pipe inside the second cylindrical end portion, and disposing the first end of the first pipe inside the cylindrical body by inserting the second pipe connected to the first pipe from the first end of the second pipe into the first cylindrical end portion. The muffler is configured to hold the first pipe inside the first cylindrical end portion and hold the second pipe connected to the first pipe inside the second cylindrical end portion. Method for manufacturing a muffler.

5. A method for manufacturing a muffler according to claim 3 or claim 4, wherein providing the second cylindrical end portion includes providing the second cylindrical end portion substantially coaxially with the first cylindrical end portion. Method for manufacturing a muffler.

6. A method for manufacturing a muffler according to claim 3 or claim 4, wherein providing the second cylindrical end portion includes providing the second cylindrical end portion such that an inner diameter of a portion of the cylindrical body adjacent to the second cylindrical end portion decreases as it approaches the second cylindrical end portion. Method for manufacturing a muffler.

7. A method for manufacturing a muffler according to any one of claims 1 to 4, wherein the second pipe is provided with a holding member on an outer peripheral surface of the second end of the second pipe. The outer diameter including the holding member at the second end of the second pipe is greater than or equal to the inner diameter of the first pipe in a state before inserting the second pipe into the first pipe. Method for manufacturing a muffler.

8. A method for manufacturing a muffler according to any one of Claims 1 to 4, The first pipe has a main body portion located between the second end of the first pipe located on the side opposite to the first end of the first pipe and the first end of the first pipe, and a reduced diameter portion located between the main body portion and the second end of the first pipe. The inner diameter of the second end of the first pipe is larger than the inner diameter of the main body portion. The inner diameter of the reduced diameter portion is formed to become smaller as it approaches the main body portion. Method for manufacturing a muffler.

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