Low-noise pipe, silencer, and vacuum cleaner

Abstract

The present invention reduces noise carried through the interior of a pipe. A low-noise pipe according to an aspect of the present disclosure comprises: a pipe body having a first inlet and a first outlet for gas and a circumferential wall including an inner circumferential surface that defines a distribution channel that connects the first inlet with the first outlet to circulate gas from the first inlet toward the first outlet; and a plurality of protrusions protruding from the circumferential wall, wherein the tips of the protrusions are located farther inside the pipe body than the inner circumferential surface located more on the first-inlet side than the tips of the protrusions.

Description

Sound-reducing pipes, silencers, vacuum cleaners

[0001] This disclosure relates to a noise reduction pipe, a silencer, for reducing noise. This application claims priority to Japanese Patent Application No. 2023-186728, filed on October 31, 2023, the contents of which are incorporated herein by reference.

[0002] In recent years, attention has been focused on biomimetics, a technology that mimics and utilizes the diverse functions of living organisms. Nature Technology (registered trademark) is known as an example of a manufacturing method that employs biomimetic technology in electrical products and the like.

[0003] BACKGROUND ART Conventionally, as a silencer for reducing noise contained in an air flow, a technique for reducing noise by passing the air flow containing noise through a pipe is known (for example, Patent Document 1).

[0004] Japanese Patent Application Laid-Open No. 2005-220871

[0005] However, in the above-described conventional technology, air flows forcefully inside the pipe, which causes vortices in the flowing air (wind), which creates a new problem of noise.

[0006] One aspect of the present disclosure aims to reduce noise flowing inside a pipe.

[0007] In order to solve the above problems, a sound-reducing pipe according to one embodiment of the present disclosure comprises a pipe body having a first inlet and a first outlet for gas, and a peripheral wall including an inner surface that connects the first inlet and the first outlet and forms a flow passage for circulating gas from the first inlet to the first outlet, and a plurality of protrusions protruding from the peripheral wall, the tips of the protrusions being located inside the pipe body relative to the inner surface which is located closer to the first inlet than the tips of the protrusions.

[0008] According to one aspect of the present disclosure, noise flowing inside a pipe can be reduced.

[0009] 7 is a cross-sectional view showing an example of the configuration of a silencer according to embodiment 1. FIG. 8 is a perspective view of a sound-reducing pipe mounted on the silencer shown in FIG. 1. FIG. 9 is a side view of the sound-reducing pipe shown in FIG. 2. FIG. 10 is an enlarged view of region E in FIG. 1. FIG. 11 is a plan view of an arbitrary one of a plurality of protrusions formed on the pipe body of the sound-reducing pipe shown in FIG. 2, viewed from the inside of the pipe body in the radial direction of the pipe body. FIG. 12 is a front view of the sound-reducing pipe shown in FIG. 2, viewed from the introduction portion side. FIG. 13 is a perspective view showing an enlarged view of a protrusion in a sound-reducing pipe according to embodiment 2. FIG. 14 is a plan view, a cross-sectional view taken along arrows A-A, and a cross-sectional view taken along arrows B-B, showing an enlarged view of the protrusion shown in FIG. 7. FIG. 15 is a cross-sectional view showing an example of the configuration of a silencer according to embodiment 3. FIG. 16 is a cross-sectional view showing an enlarged view of a portion of the sound-reducing pipe of two modified examples. FIG. 17 is a schematic view showing components of a vacuum cleaner according to embodiment 4.

[0010] First Embodiment Hereinafter, one embodiment of the present disclosure will be described in detail.

[0011] (Outline of silencer) Fig. 1 is a cross-sectional view showing an example of the configuration of a silencer 1 according to embodiment 1. Note that Fig. 1 not only shows the cross section, but also the structure visible on the far side of the cross section. As shown in Fig. 1, the silencer 1 includes a noise reduction pipe 10 and a housing 2. A noise source 3 is located at one end of the noise reduction pipe 10. The noise source 3 is a device that generates noise. The noise source 3 may be, for example, a fan that generates an airflow.

[0012] The sound-reducing pipe 10 includes a pipe body 11, a plurality of protrusions 112, and an introduction portion 13. The sound-reducing pipe 10 reduces noise transmitted inside. The pipe body 11 has a first inlet 11A through which gas flows in, a first outlet 11B through which gas flows out, and a peripheral wall 11D. The peripheral wall 11D includes an inner circumferential surface 11C that connects the first inlet 11A and the first outlet 11B and forms a flow passage through which gas flows from the first inlet 11A to the first outlet 11B.

[0013] The introduction section 13 is connected to the first inlet 11A of the pipe body 11. The introduction section 13 has a second inlet 13A through which gas flows in and a second outlet 13B through which gas flows out. The second outlet 13B is connected to the first inlet 11A of the pipe body 11. The introduction section 13 is funnel-shaped, with the second outlet 13B side narrower than the second inlet 13A side. The introduction section 13 has, for example, a truncated cone shape when viewed from the side, and introduces the airflow into the pipe body 11.

[0014] By providing the introduction section 13, it becomes easier to introduce airflow into the pipe body 11, and also it promotes the reflection of sound on the inner surface of the introduction section 13, thereby suppressing the reflection of sound introduced into the pipe body 11.

[0015] A plurality of protrusions 112 protrude from the peripheral wall 11D of the pipe body 11. Details of the sound-reducing pipe 10, including the protrusions 112, will be described later. A plurality of through holes 111 are formed in the peripheral wall 11D of the pipe body 11. The plurality of through holes 111 are aligned in the axial direction of the pipe body 11. The plurality of through holes 111 are also aligned in the circumferential direction of the pipe body 11.

[0016] The housing 2 is arranged to surround at least a portion of the pipe body 11 of the sound-reducing pipe 10. The housing 2 is, for example, a cylindrical housing. The housing 2 may have a sound-absorbing material 21 arranged on its inner surface. The sound-absorbing material 21 absorbs sound. The housing 2 forms a silencing space S that communicates with the interior of the pipe body 11 via a plurality of through-holes 111. The silencing space S is located between the pipe body 11 and the housing 2 and is a closed space that is connected only to the space inside the pipe body 11 (the space through which gas flows) via the plurality of through-holes 111. However, the silencing space S is not limited to a closed space, and the housing 2 may have a structure in which, for example, the wall surface on the first inlet 11A side or the wall surface on the first outlet 11B side is open.

[0017] (Sound-absorbing mechanism) In Fig. 1, arrow Y indicates the direction of airflow. As shown by arrow Y, gas flows inside the pipe main body 11 from the first inlet 11A toward the first outlet 11B. At this time, part of the noise is diffracted and passes through the through-holes 111 into the sound-absorbing space S, where it disappears. By providing sound-absorbing material 21 on the inner surface of the housing 2, where sound is reflected, sound is absorbed by the sound-absorbing material 21, and the noise flowing inside the pipe main body 11 can be more effectively reduced.

[0018] (Sound-reducing pipe suitable for silencer) Fig. 2 is a perspective view of the sound-reducing pipe 10 mounted on the silencer 1 shown in Fig. 1. Fig. 3 is a side view of the sound-reducing pipe 10 shown in Fig. 2. As shown in Figs. 2 and 3, the pipe body 11 is narrower on the first outlet 11B side than on the first inlet 11A side. More specifically, the inner diameter of the pipe body 11 gradually decreases from the upstream side to the downstream side along the airflow direction (arrow Y). The pipe body 11 has a tapered shape. The cross section of the pipe body 11 is not limited to a circular shape and may be an elliptical shape, for example.

[0019] By forming the pipe body 11 in such a tapered shape, the air flowing inside can be made to collide with the protrusion 112 without the protrusion 112 being inclined greatly.

[0020] The sound-reducing pipe 10 has a plurality of protrusions 112 protruding from the peripheral wall 11D of the pipe body 11. The tips 112A of the protrusions 112 are located further inside the pipe body 11 than the inner peripheral surface 11C, which is located closer to the first inlet 11A than the tips 112A of the protrusions 112. The interior of the pipe body 11 may also be referred to as the side of the central axis X of the pipe body 11 or the inside of the pipe body 11. The protrusions 112 may protrude toward the upstream side of the airflow. In this embodiment, the protrusions 112 are provided so as to protrude from the periphery of the through hole 111 toward the interior of the through hole 111 when viewed from the opening direction of the through hole 111.

[0021] Fig. 4 is an enlarged view of region E in Fig. 1. In Fig. 4, line F1 indicates the inner circumferential surface 11C of the pipe body 11 in cross section. In Fig. 4, line F2 indicates a line that passes through the tip 112A of one of the multiple protrusions 112 and is parallel to the axis of the pipe body 11.

[0022] As shown by the straight line F1 in Fig. 4, in this embodiment, the inner circumferential surface 11C of the pipe body 11 approaches the central axis X of the pipe body 11 as it moves from the upstream side to the downstream side of the airflow. As shown by the straight line F2 in Fig. 4, by utilizing this shape, the tip 112A of the protrusion 112 is positioned more inward on the pipe body 11 than the inner circumferential surface 11C, which is positioned closer to the first inlet 11A than the tip 112A of the protrusion 112.

[0023] In this embodiment, by providing the protrusions 112 on the pipe body 11, the airflow flowing from the first inlet 11A to the first outlet 11B collides with the protrusions 112, and the vortices in the airflow can be broken down by the protrusions 112. This can reduce noise.

[0024] Furthermore, since the protrusion 112 has a portion that protrudes toward the first inlet 11A, the airflow flowing from the first inlet 11A toward the first outlet 11B is likely to collide with the protrusion 112.

[0025] Furthermore, when viewed from the opening direction of the through-hole 111, the protrusions are provided so as to protrude from the periphery of the through-hole 111 toward the inside of the through-hole 111. This allows the vortex to be subdivided, and the air (sound) introduced into the through-hole 111 to be separated from the air flowing through the pipe body 11, thereby improving the sound reduction effect in the sound-absorbing space S.

[0026] Figure 5 is a plan view of any one of the protrusions 112 formed on the pipe body 11 of the sound-reducing pipe 10 shown in Figure 2, viewed from the inside (axial side) of the pipe body 11 in the radial direction of the pipe body 11. The radial direction of the pipe body 11 is a direction perpendicular to the axial direction of the pipe body 11. In Figure 5, the arrows indicate the direction of the airflow bent by the protrusion 112.

[0027] As shown in FIG. 5, the protrusion 112 protrudes from the periphery of the through-hole 111 on the first outlet 11B side toward the first inlet 11A side.

[0028] With this configuration, the airflow flowing from the first inlet 11A to the first outlet 11B is more likely to collide with the protrusions 112, and vortices contained in the airflow can be broken down by the protrusions 112. This makes it less likely that sound contained in the airflow will be hindered from penetrating, by diffraction, from the through holes 111 into the silencing space S located on the outer periphery of the pipe body 11. At the same time, it is possible to promote the sound contained in the airflow from penetrating, by reflection, into the silencing space S from the through holes 111.

[0029] Furthermore, the outer shape 112B of the protrusion 112 on one side in the circumferential direction of the pipe body 11 and the outer shape 112C of the protrusion 112 on the other side in the circumferential direction may have shapes asymmetric with each other with respect to the axial direction of the pipe body 11.

[0030] By making the protrusions 112 asymmetrical, the asymmetric ridge (edge) shape of the protrusions 112 can change the direction in which the airflow bends when it collides with the ridge. This allows the airflow to be dispersed in various directions, generating vortices in different directions. This allows the vortices contained in the airflow to be further subdivided. Furthermore, by making the protrusions 112 provided on the through-holes 111 asymmetrical, the diffraction direction of the sound entering the silencing space S through the through-holes 111 can be dispersed, thereby more effectively reducing noise.

[0031] As an example, as shown in Figure 5, the outer shape 112B on one side of the protrusion 112 in the circumferential direction may be convex on one side, and the outer shape 112C on the other side of the protrusion 112 in the circumferential direction may be concave on the other side.

[0032] This configuration creates a twisted shape that combines convex and concave curves, which causes the airflow to swirl in different directions at each ridge, while at the same time dispersing the diffraction direction of the sound that enters the sound-absorbing space S, thereby more effectively achieving the effect of promoting the cancellation of sounds.

[0033] Fig. 6 is a front view of the sound reduction pipe 10 shown in Fig. 2, with the introduction section 13 side facing forward. As shown in Fig. 6, a plurality of ribs 131 extending from the second inlet 13A side to the second outlet 13B side may be formed on the inner surface of the introduction section 13.

[0034] When viewed from the second inlet 13A side, the multiple ribs 131 may be arranged radially around the second outlet 13B, and may have portions 131A that are inclined in the same direction relative to the radial direction of a circle centered on the center of the second outlet 13B. The center of the second outlet 13B is coincident with the central axis X of the pipe body 11.

[0035] The portion 131A imparts a swirling component to the airflow introduced into the pipe body 11. By imparting a swirling component to the airflow, reflection or diffraction in the silencing space S can be promoted, thereby promoting sound attenuation in the silencing space S. Here, the multiple ribs 131 have a curved shape, but they may also have a linear shape extending in a direction inclined relative to the radial direction.

[0036] [Embodiment 2] Another embodiment of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0037] Figure 7 is an enlarged perspective view of the protrusion 113 in the sound-reducing pipe according to embodiment 2. Figure 8 is an enlarged plan view, an A-A cross-sectional view, and a B-B cross-sectional view of the protrusion 113 shown in Figure 7. Reference numeral 801 denotes the plan view, reference numeral 802 denotes the A-A cross-sectional view, and reference numeral 803 denotes the B-B cross-sectional view. This embodiment differs from embodiment 1 only in the shape of the protrusion 113.

[0038] As indicated by reference numeral 801, the protrusion 113 protrudes from the peripheral wall 11D of the pipe body 11, and protrudes from the periphery of the through-hole 111 provided in the peripheral wall 11D on the first outlet 11B side toward the first inlet 11A. Furthermore, as indicated by reference numerals 802 and 803, the tip 113A of the protrusion 113 protrudes from the inner peripheral surface 11C further inward from the pipe body 11 than the inner peripheral surface 11C of the pipe body.

[0039] With this structure, the airflow flowing through the flow passage of the pipe body 11 is more likely to collide with the protrusions 113. As a result, vortices contained in the airflow are broken down into smaller pieces, thereby reducing noise.

[0040] [Embodiment 3] Yet another embodiment of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0041] Fig. 9 is a cross-sectional view showing an example of the configuration of a silencer 1A according to embodiment 3. Note that Fig. 9 shows not only the cross section but also the structure visible on the far side of the cross section. The silencer 1A includes a noise reduction pipe 10A and a housing 2.

[0042] The sound-reducing pipe 10A includes a first group 121 and a second group 122. The first group 121 and the second group 122 are alternately arranged along the axial direction of the sound-reducing pipe 10A. The first group 121 includes a plurality of through holes 111 and a plurality of protrusions 112 aligned in the circumferential direction. The second group 122 includes a plurality of through holes 111 and a plurality of protrusions 112 aligned in the circumferential direction. However, the plurality of through holes 111 and the plurality of protrusions 112 of the first group 121 and the plurality of through holes 111 and the plurality of protrusions 112 of the second group 122 are offset from each other in the circumferential direction. The first group 121 and the second group 122, which are offset from each other in the circumferential direction in this manner, may be provided over the entire pipe body 11, or may be provided in a partial region.

[0043] With the above-described configuration, the sound reduction pipe 10A allows the airflow flowing through the sound reduction pipe 10A to efficiently collide with the protrusions 112. Furthermore, the sound reduction pipe 10A can efficiently distribute the positions at which vortices are subdivided.

[0044] (Modifications) Figure 10 is an enlarged cross-sectional view of a portion of a sound-attenuation pipe according to two modifications. In Figure 10, the arrows indicate the direction of the airflow bent by the protrusions. Reference numeral 1001 denotes the sound-attenuation pipe 10B, and reference numeral 1002 denotes the sound-attenuation pipe 10C. The peripheral walls 11D of the sound-attenuation pipes 10B and 10C do not necessarily have to have through-holes. Furthermore, the pipe body 11 of the sound-attenuation pipes 10B and 10C does not have to have a tapered shape as described above, and may instead be cylindrical.

[0045] As shown by reference numeral 1001, the sound-reducing pipe 10B has a plurality of protrusions 114 protruding inward from the inner circumferential surface 11C as a plurality of protruding parts protruding from the peripheral wall 11D. The protrusions 114 protrude obliquely from the inner circumferential surface 11C toward the upstream side of the airflow (the first inlet side) and toward the inside of the pipe body 11. A space is formed between a wall surface 114A on the upstream side of the airflow of the protrusions 114 and the inner circumferential surface 11C. The angle between the wall surface 114A and the inner circumferential surface 11C is an acute angle. The angle between a wall surface 114B on the downstream side of the airflow of the protrusions 114 and the inner circumferential surface 11C is an obtuse angle.

[0046] With such a shape of the protrusion 114, the airflow is divided so as to wrap around the protrusion 114, and the vortex is subdivided.

[0047] As shown by reference numeral 1002, the sound-reducing pipe 10C includes a plurality of protrusions 115 protruding inward from the inner circumferential surface 11C as protruding parts protruding from the peripheral wall 11D. The protrusions 115 protrude from the inner circumferential surface 11C toward the inside of the pipe body. A wall surface 115A on the upstream side of the airflow of the protrusions 115 (the side of the first inlet) may be perpendicular to the inner circumferential surface 11C, for example. No space is formed between the wall surface 115A and the inner circumferential surface 11C. An obtuse angle is formed between a wall surface 115B on the downstream side of the airflow of the protrusions 115 and the inner circumferential surface 11C.

[0048] In the case of the shape of the protrusion 115 that protrudes inward from the inner circumferential surface 11C, the airflow is divided so as to spiral around the protrusion 115, and the vortex can be more suitably subdivided.

[0049] In this way, the sound-reducing pipe may be configured to have a plurality of protrusions 114 , 115 that protrude from the inner circumferential surface 11C of the pipe body 11 toward the inside of the pipe body 11 .

[0050] By providing the protrusions 114, 115 on the pipe body 11, the airflow flowing from the upstream side to the downstream side (from the first inlet to the first outlet) collides with the protrusions 114, 115, and the vortices contained in the airflow can be broken down by the protrusions 114, 115. Because the vortices contained in the airflow become smaller, noise can be reduced.

[0051] [Embodiment 4] Yet another embodiment of the present disclosure will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0052] Fig. 11 is a schematic diagram showing the components of a vacuum cleaner 100 according to a fourth embodiment. The vacuum cleaner 100 includes a silencer 1, a suction unit 4, a removal unit 5, a blower 6, and a blower unit 7. The suction unit 4 is a unit that sucks in dust using an airflow. The removal unit 5 removes the dust sucked in through the suction unit 4 from the gas. The removal unit 5 may include a filter. The blower 6 has a fan or the like that generates an airflow and blows the gas. The blower 6 can be a noise source. The blower unit 7 is a unit that blows the gas sent out from the blower 6 to the outside.

[0053] The silencer 1 is disposed in the flow path from the blower 6 to the blower 7. The airflow flows, for example, through the suction section 4, the removal section 5, the blower 6, the silencer 1, and the blower 7 in that order. The silencer 1 can muffle noise generated by the suction section 4, the removal section 5, or the blower 6. Note that the vacuum cleaner 100 may also be provided with a silencer that includes the other sound-reducing pipes described above.

[0054] [Summary] The sound-reducing pipe according to aspect 1 of the present disclosure comprises a pipe body having a first inlet and a first outlet for gas, and a peripheral wall including an inner circumferential surface that connects the first inlet and the first outlet and forms a flow passage for circulating gas from the first inlet to the first outlet, and a plurality of protrusions protruding from the peripheral wall, the tips of the protrusions being located inside the pipe body relative to the inner circumferential surface that is located closer to the first inlet than the tips of the protrusions.

[0055] In a sound-reducing pipe according to a second aspect of the present disclosure, in the first aspect, the protrusion may protrude toward the first inlet.

[0056] In a sound-reducing pipe according to aspect 3 of the present disclosure, in the above-mentioned aspects 1 or 2, the outer shape of one side of the protrusion in the circumferential direction and the outer shape of the other side of the protrusion in the circumferential direction may be asymmetrical with respect to each other in the axial direction of the pipe body.

[0057] In a sound-reducing pipe according to aspect 4 of the present disclosure, in aspect 3 above, the outer shape of one side of the protrusion in the circumferential direction may be convex toward the one side, and the outer shape of the other side of the protrusion in the circumferential direction may be concave toward the other side.

[0058] In a sound-reducing pipe according to aspect 5 of the present disclosure, in any of aspects 1 to 4 above, the protrusion may protrude from the inner circumferential surface toward the inside of the pipe body.

[0059] In a sound-reducing pipe according to aspect 6 of the present disclosure, in any of aspects 1 to 5 above, a plurality of through holes may be formed in the peripheral wall, and when viewed from the opening direction of the through holes, the protrusions may protrude from the periphery of the through holes toward the inside of the through holes.

[0060] In a sound-reducing pipe according to aspect 7 of the present disclosure, in the above-mentioned aspect 6, the protrusion may protrude from the peripheral edge of the through hole on the first outlet side toward the first inlet side.

[0061] In a sound-reducing pipe according to aspect 8 of the present disclosure, in any of aspects 1 to 7 above, the pipe body may be narrower on the first outlet side than on the first inlet side.

[0062] In a sound-reducing pipe according to aspect 9 of the present disclosure, in any of aspects 1 to 8 above, the pipe may have a second inlet and a second outlet for gas, the second outlet having an introduction section connected to the first inlet of the pipe body, and the introduction section may be narrower on the second outlet side than on the second inlet side.

[0063] In a sound-reducing pipe according to aspect 10 of the present disclosure, in the above-mentioned aspect 9, a plurality of ribs extending from the second inlet side to the second outlet side may be formed on the inner surface of the introduction portion.

[0064] In a sound-reducing pipe according to aspect 11 of the present disclosure, in the above-described aspect 10, when viewed from the second inlet side, the multiple ribs may be arranged radially around the second outlet and may have portions inclined in the same direction relative to the radial direction of a circle centered on the center of the second outlet.

[0065] A silencer according to aspect 12 of the present disclosure comprises a sound-reducing pipe according to any one of aspects 6 to 8 above, and a housing that surrounds at least a portion of the pipe body and forms a sound-reducing space that communicates with the interior of the pipe body via the plurality of through holes.

[0066] A vacuum cleaner according to aspect 13 of the present disclosure includes the silencer according to aspect 12 above and a blower that blows the gas.

[0067] This disclosure includes a technical idea that focuses on the serrations on an owl's wings, and thus relates to biomimetics.

[0068] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure.

Claims

1. A sound-reducing pipe comprising: a pipe body having a first inlet and a first outlet for gas, and a peripheral wall including an inner circumferential surface that connects the first inlet and the first outlet and forms a flow passage for circulating gas from the first inlet to the first outlet, and a plurality of protrusions protruding from the peripheral wall, the tips of the protrusions being located inside the pipe body relative to the inner circumferential surface that is located on the first inlet side relative to the tips of the protrusions.

2. A sound-reducing pipe as claimed in claim 1, wherein said protrusion protrudes towards said first inlet side.

3. A sound-reducing pipe as set forth in claim 1, wherein the outer shape of one side of the protrusion in the circumferential direction and the outer shape of the other side of the protrusion in the circumferential direction are asymmetrical with respect to the axial direction of the pipe body.

4. A sound-reducing pipe as set forth in claim 3, wherein the outer shape of one side of said protrusion in the circumferential direction is convex toward said one side, and the outer shape of the other side of said protrusion in the circumferential direction is concave toward said other side.

5. A sound-reducing pipe as claimed in claim 1, wherein said protrusion protrudes from said inner peripheral surface towards the inside of said pipe body.

6. A sound-reducing pipe as described in claim 1, wherein a plurality of through holes are formed in the peripheral wall, and when viewed from the opening direction of the through holes, the protrusions protrude from the periphery of the through holes toward the inside of the through holes.

7. A sound-reduction pipe as set forth in claim 6, wherein said protrusion protrudes from the peripheral edge of said through hole on the first outlet side toward said first inlet side.

8. A sound-reducing pipe as set forth in claim 6, wherein said pipe body is narrower on the first outlet side than on the first inlet side.

9. A sound-reducing pipe as described in claim 1, comprising an introduction section having a second inlet and a second outlet for gas, the second outlet being connected to the first inlet of the pipe body, the introduction section being narrower on the second outlet side than on the second inlet side.

10. A sound-reducing pipe as set forth in claim 9, wherein a plurality of ribs extending from the second inlet side to the second outlet side are formed on the inner surface of said introduction portion.

11. A sound-reducing pipe as described in claim 10, wherein, when viewed from the second inlet side, the multiple ribs are arranged radially around the second outlet and have portions that are inclined in the same direction relative to the radial direction of a circle centered on the center of the second outlet.

12. A silencer comprising: a sound-reducing pipe as claimed in any one of claims 6 to 8; and a housing that surrounds at least a portion of the pipe body and forms a sound-reducing space that communicates with the inside of the pipe body via the multiple through holes.

13. A vacuum cleaner comprising: a silencer according to claim 12; and a blower for blowing the gas.

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