Sound-dampening structure and automotive muffler equipped therewith

Abstract

To provide a silencing structure which can improve silencing performance per unit volume.SOLUTION: A silencing structure 10 includes: a housing 20 having an outer cylinder wall 21 with a closed cross-sectional shape formed along a waveguide direction C; and an inner cylinder 30 having an inner cylinder wall 31 in a closed cross-sectional shape, which is arranged in the outer cylinder wall 21 of the housing 20, penetrates inside along the waveguide direction C and has a waveform space through which air can pass. The inner cylinder 30 includes a mesh structure 40 in which an opening ratio of openings 32 and 33 of the inner cylinder 30 to a projected area of the housing 20 in the waveguide direction C is 32.6% or more, and mesh opening for covering a periphery of the waveguide space B along an outer peripheral shape of the openings 32 and 33 so as to form the inner cylinder wall 31 of the inner cylinder 30 is 5 μm to 132 μm and opening ratio is 1% to 42%, and is configured so that air can pass into the outer cylinder wall 21 of the housing 20 from the inside of the inner cylinder 30 through the mesh structure 40.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a tubular soundproof structure.

Background Art

[0002] As a technology related to a soundproof structure, for example, Patent Document 1 discloses an expansion chamber. In the technology described in this document, a plurality of holes are formed in the peripheral wall surface of a pipe in the expansion chamber region of a muffler, and the flow resistance of air is defined by changes in the design values of the holes.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, due to its nature, the expansion chamber has a cross-sectional area in the expansion chamber region that is significantly larger than the cross-sectional area of the inlet. Therefore, there is a problem that the volume occupied by the expansion chamber with respect to the ventilation portion is large, and inevitably the entire device becomes large and lacks compactness. In addition, when applying a similar structure to noise control of ventilation components in an engine room, sufficient space is required in the engine room, and there is a problem that the practicality of the application is lacking. Therefore, the present invention has been made by paying attention to such problems, and an object thereof is to provide a soundproof structure that can improve the soundproof performance per unit volume.

Means for Solving the Problems

[0005] To solve the above problems, a sound-absorbing structure according to one aspect of the present invention comprises: an outer cylinder having an outer cylinder wall with a closed cross-sectional shape along the wave-guiding direction; an inner cylinder having an opening that opens at both ends in the wave-guiding direction and an inner cylinder wall that has a closed cross-sectional shape along the outer circumference of the opening and is formed to penetrate along the wave-guiding direction, defining a wave-guiding space through which air can pass; and a mesh structure that is wound so as to cover the periphery of the wave-guiding space formed by the inner cylinder wall or wound along the outer circumference of the opening so as to form the inner cylinder wall itself, and is provided so as to allow air to pass from the inner cylinder wall of the inner cylinder toward the cavity between the outer cylinder wall of the outer cylinder, wherein the inner cylinder has an opening ratio of 32.6% or more of the projected area of ​​the outer cylinder in the wave-guiding direction, and the mesh structure is composed of mesh members with a mesh opening of 5 μm to 132 μm and a mesh opening ratio of 1% to 42%. [Effects of the Invention]

[0006] According to the present invention, it is possible to improve the sound insulation performance per unit volume. [Brief explanation of the drawing]

[0007] [Figure 1] This is an explanatory diagram of one embodiment of a sound-absorbing structure according to one aspect of the present invention. Figure (a) shows a schematic cross-sectional view along the waveguide direction, and Figure (b) shows an enlarged view of the main part of (a) (the part enclosed by a dashed line and indicated by an arrow), along with an image of a standing wave. [Figure 2] This is an explanatory diagram of a confirmation test apparatus for verifying the effect of a sound-absorbing structure according to one aspect of the present invention (the first and second embodiments shown in Table 1 (including an example in which the inner cylinder wall wraps around the frame)). [Figure 3] This is a schematic diagram illustrating the mesh structure of a sound-absorbing structure according to one aspect of the present invention. [Figure 4] This graph shows the results of the verification test in the second embodiment (relationship between frequency and sound pressure level). [Figure 5]This graph shows excerpts of the results of the verification tests (relationship between frequency and sound pressure level) in embodiment 5 of the first and second embodiments. [Figure 6] This graph shows the results of the verification test in the first embodiment (relationship between frequency and sound pressure level). [Figure 7] This graph shows the results of the verification test in the second embodiment (relationship between frequency and sound pressure level). [Figure 8] This is an explanatory diagram of a confirmation test apparatus for verifying the effect of a sound-absorbing structure according to one aspect of the present invention (the third and fourth embodiments shown in Table 2). [Figure 9] This is a schematic diagram illustrating a sound-absorbing structure according to one aspect of the present invention (the third and fourth embodiments shown in Table 2 (including an example of a pipe structure in which the inner wall is made of perforated metal)). [Figure 10] This graph shows an excerpt of the results of the verification test in the third embodiment (relationship between frequency and sound pressure level). [Figure 11] This graph shows an excerpt of the results of the verification test in the fourth embodiment (relationship between frequency and sound pressure level). [Modes for carrying out the invention]

[0008] The following describes one embodiment of the present invention, with reference to the drawings as appropriate. Note that the drawings are schematic. Therefore, it should be noted that the relationship and ratios between thickness and planar dimensions may differ from those of reality, and there may be differences in dimensional relationships and ratios between drawings. Furthermore, the embodiments described below illustrate devices and methods for realizing the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the material, shape, structure, arrangement, etc., of the components.

[0009] [Configuration of the sound-dampening structure] As shown in Figure 1, the sound-absorbing structure 10 of this embodiment comprises an outer cylinder housing 20 and an inner cylinder 30 provided inside the housing 20. The housing 20 has an outer cylinder wall 21 with a closed cross-sectional shape along the waveguide direction C. The closed cross-sectional shape (transverse shape) of the outer cylinder wall 21 can be, for example, rectangular or circular. A front wall 22 is provided at the front end of the outer cylinder wall 21 of the housing 20 so as to cover the end, and a rear wall 23 is provided at the rear end so as to cover the end, thereby defining a cavity A within the housing.

[0010] The inner cylinder 30 is positioned within the outer cylinder wall 21 of the housing 20 along the waveguide direction C, connecting the central portion of the front wall 22 and the central portion of the rear wall 23 to each other. Openings 30f and 30r are formed at the front and rear of the inner cylinder 30 in the axial direction, opening into the central portions of the front wall 22 and the rear wall 23, respectively. The opening ratio of the openings 30f and 30r is set to 32.6% or more of the projected area of ​​the housing 20 in the waveguide direction C (i.e., the projected area of ​​the front and rear walls 32 and 33). In this configuration, the inner cylinder 30 is fixed with an inner cylinder wall 31 having a closed cross-sectional shape formed along the waveguide direction C, through which a waveguide space B capable of passing air (gas) is formed. The closed cross-sectional shape (cross-sectional shape) of the inner cylinder wall 31 can be, for example, rectangular or circular.

[0011] In this embodiment, the inner cylinder 30 has a mesh structure 40 that covers the periphery of the waveguide space B along the outer circumferential surfaces of the openings 30f and 30r before and after the waveguide direction C, so as to form an inner cylinder wall 31 along the waveguide direction C. The mesh structure 40 of this embodiment is constructed by winding a mesh member around a frame-shaped frame along the outer circumference of the front and rear openings 30f and 30r so as to form the inner cylinder wall 31 itself. As a result, the sound-absorbing structure 10 of this embodiment allows air (gas) to pass from inside the inner cylinder wall 31 to the cavity A in the outer cylinder wall 21 of the housing 20 through the mesh structure 40.

[0012] In particular, the mesh structure 40 of this embodiment is composed of mesh members having a mesh opening F of 5 μm to 132 μm and an inner wall opening ratio of 1 to 42%. Here, it is preferable that the mesh structure 40 constituting the inner cylinder wall 31 of the inner cylinder 30 is a mesh laminate in which a plurality of the above mesh members are stacked around the waveguide space B. Further, in the sound absorption structure 10 of the present embodiment, the portion of the cavity A behind the mesh structure 40 can be an air layer, or can be a porous layer in which a porous body (50) through which air can pass is filled in the cavity A.

[0013] [Function and effect of sound absorption structure] Next, the function and effect of the sound absorption structure 10 of the present embodiment will be described. As described above, in the sound absorption structure 10 of the present embodiment, the opening ratios of the openings 30f and 30r of the inner cylinder 30 with respect to the projected area in the wave guiding direction C of the housing 20 are 32.6% or more, and a mesh structure 40 that covers the periphery of the wave guiding space B is adopted for a portion of the inner cylinder wall 31. In particular, the mesh structure 40 of the present embodiment covers the outer surfaces of the openings 30f and 30r of the inner cylinder 30 with a mesh member having a mesh opening of 5 μm to 132 μm and an opening ratio of 1% to 42%. Since an air layer or a porous layer is provided in the cavity A behind the mesh structure 40, sound waves incident on the wave guiding space B along the wave guiding direction C can be passed through air (gas) via the mesh structure 40 surrounding the periphery of the wave guiding space B.

[0014] As a result, according to the sound absorption structure 10 of the present embodiment, in the cavity A, as shown in the image in Fig. 1(b), a standing wave W of a specific frequency (1 / 4 wavelength (L = λ / 4)) corresponding to the length L of the cavity A is created, and the standing wave W repeats vibrations in the cavity A (1 / 4 resonance effect). By cooperating with the energy attenuation effect of the mesh structure 40, the 1 / 4 resonance effect is promoted (sound absorption promotion effect). Therefore, according to the sound absorption structure 10 of the present embodiment, compared with the prior art, due to this 1 / 4 resonance effect and its sound absorption promotion effect, a sound absorption phenomenon is efficiently generated, and while the entire acoustic device is configured compactly, due to the friction between air particles that exhibits a synergistic effect, efficient sound absorption performance per unit volume can be achieved.

[0015] [Examples] The following describes the verification tests regarding the mesh opening value at which the sound-dampening effect of the present invention is observed, based on examples and comparative examples. Components corresponding to the above embodiments are indicated by reference numerals in parentheses. First, the first and second embodiments will be described. The first and second embodiments are examples in which the inner cylinder wall (31) is a mesh structure (40) wound around a frame. Figure 2 shows a schematic diagram of the test apparatus.

[0016] As shown in the figure, this test apparatus 100 has an acoustic tube 110 with a diameter of Φ100 mm arranged along the waveguide direction C so as to face the sound source S. Various sound-absorbing structures (10) prepared in advance for verification tests are arranged coaxially at the end of the acoustic tube 110 opposite to the sound source S. Subsequently, white noise between 100Hz and 4096Hz was output from the sound source S and sequentially passed through the sound-dampening structures (10) of various embodiments and comparative examples to dampen the sound. The sound pressure after passing through the sound-dampening structures (10) of various embodiments and comparative examples was measured as an output using a microphone E installed at the end of the sound-dampening structure (10).

[0017] The sound-absorbing structures (10) prepared for verification tests as various examples and comparative examples were constructed by wrapping mesh members of various specifications around the rectangular frame of the inner cylinder (30) five times in the circumferential direction to form the inner cylinder wall (31). Afterward, the mesh members were fixed together with double-sided tape to form a mesh laminate (41) consisting of multiple layers. Finally, the housing (20) having an outer cylindrical wall (21) was attached so as to cover the outside of the inner cylinder (30).

[0018] In the verification test regarding the mesh opening value at which the sound-dampening effect is achieved, various specifications and their mesh information are shown in Table 1 below. As shown in the table, three comparative examples (Aspects 1-3 of the first comparative example) were prepared as sound-absorbing structures (10) for verification testing, and nine examples (Aspects 1-9 of the first embodiment) were prepared in which only mesh material was wound around the inner cylinder wall (31) to form a mesh structure (40) and an air layer was made inside the cavity (A). Furthermore, nine examples (Aspects 1 to 9 of the second embodiment) were prepared in which a mesh member was wound around the inner cylinder wall (31) to form a mesh structure (40) and a porous material (50) was filled into the cavity (A). In other words, this verification test corresponds to an example in which the mesh structure (40) is wound along the outer circumference shape of the opening (30f, 30r) so as to form the inner cylinder wall (31) itself (Invention 1).

[0019] [Table 1]

[0020] In the same table, in the three first comparative examples, embodiment 1 (No Sample) is one in which the portion corresponding to the inner cylinder wall (31) is composed only of a frame-shaped frame oriented in the direction of the waveguide, and no mesh member is wound around it (thus the aperture ratio is 100%). Furthermore, Embodiment 2 (Pipe) is an example in which the portion corresponding to the inner cylindrical wall (31) is replaced with an acrylic plate instead of a mesh member (thus with an opening ratio of 0%), and Embodiment 3 (Kyuon) is an example in which the portion corresponding to the inner cylindrical wall (31) is not wrapped with a mesh member and only a porous body (50) is placed inside the cavity (A).

[0021] The first embodiment corresponds to an example in which the cavity (A) is an air layer. It also corresponds to an example in which the cross-sectional shape of the inner cylinder wall (31) of the inner cylinder (30) is rectangular (Invention 3). Furthermore, it corresponds to an example in which the mesh structure (40) is a mesh laminate formed by stacking multiple mesh members (Invention 5). Furthermore, the second embodiment corresponds to an example in which a porous body (50) is placed inside the cavity (A). In the case of the second embodiment, the porous body (50) is placed in close contact with the outside of the mesh structure (40) which is the inner cylinder wall (31) of the inner cylinder (30) (Invention 2). White Cuon (sound-absorbing material for walls manufactured by Tokyo Soundproofing Co., Ltd.) was used as the porous body (50).

[0022] The mesh material used in this verification test was nylon mesh manufactured by AS ONE Corporation. As shown in Figure 3, the mesh material used in this verification test is constructed in a mesh-like manner with numerous rectangular openings formed by intersecting fibers in the warp and weft directions. Examples of both plain weave and twill weave were prepared. The specifications of the mesh are shown in Table 1, Figure 3, and the following formula. In the following formula, F (mm) is the mesh opening, d (mm) is the fiber diameter, and ε (%) is the opening ratio. ε = (F / (F + d)) 2 ×100

[0023] In this verification test, we first confirmed the sound-dampening effect depending on the presence or absence of the mesh structure (40) and the degree of mesh opening F of the mesh M. Figure 4 shows graphs of the measurement results for the sound-dampening structures (10) used for verification tests in aspects 1 to 9 of the second embodiment, along with aspect 1 of the first comparative example. In the graph shown in the figure, the lower the graph is located in the figure, the better the sound-dampening performance compared to the graph for the first comparative example, embodiment 1 (where the inner cylinder wall is only a frame-shaped structure). However, if the mesh opening F of the mesh M is smaller than that of embodiment 1 of the second embodiment (mesh opening of 5 μm), the sound-dampening effect between 2,000 Hz and 3,600 Hz is reduced, so embodiment 1 of the second embodiment is excluded from the present invention.

[0024] In other words, as can be seen in the figure, compared to the conventional technology which does not incorporate a mesh structure (40) as shown in Embodiment 1 of the first comparative example, it can be seen that, except for Embodiment 1 of the second embodiment (mesh opening of 5 μm), by adopting a mesh structure (40) in which a mesh member with a mesh opening F of mesh M of 5 μm to 132 μm is wound along the waveguide direction C, the sound absorption performance per unit volume can be improved (Invention 1).

[0025] Next, we examined the difference in sound-dampening effect depending on whether or not the porous material (50) was filled into the cavity (A). Figure 5 shows excerpts of two graphs, one for embodiment 5 of the first embodiment and the other for embodiment 5 of the second embodiment. As can be seen in the figure, when comparing embodiments having the same mesh structure (40) in the inner cylinder wall (31), it can be seen that embodiment 5 of the second embodiment, which has a porous body (50) in the cavity (A), exhibits a higher sound-dampening effect than embodiment 5 of the first embodiment, which does not have a porous body (50) in the cavity (A) (Invention 2).

[0026] Next, we examined the difference in sound-dampening effect between the first comparative example (Aspect 2) and the first example (Aspect 1 to Aspect 9). Figure 6 shows graphs of the measurement results for the first comparative example (Aspect 2) and the first example (Aspects 1 to 9). As shown in the figure, it can be seen that the sound-dampening structures (10) according to each embodiment of the first embodiment, in which a mesh structure (40) is provided on the inner circumferential wall (31) of the inner cylinder (30), exhibit a higher sound-dampening effect than embodiment 2 of the first comparative example. Next, we compared the difference in sound-dampening effect between the first comparative example (porous body single structure) and the second embodiment which incorporated a mesh structure (40). The graph of the measurement results is shown in Figure 7. As shown in the figure, compared to the porous body-only structure of the first comparative example embodiment 3, the second embodiment (particularly embodiments 5 to 7) which incorporates a mesh structure (40) has a mesh opening that provides a higher sound-dampening effect.

[0027] The most effective mesh opening is the mesh structure (40) of embodiment 5 of the second embodiment (mesh opening 42 μm + porous material). Comparing embodiment 3 of the first comparative example (porous material single structure) with embodiment 5 of the second embodiment in the same figure, it can be seen that embodiment 5 of the second embodiment has a particularly high sound-dampening effect at 2500 Hz and above. Thus, it can be seen that the sound-absorbing structure (10) of the second embodiment, which has both a mesh structure (40) and a porous layer (50), exhibits higher sound-absorbing performance than the sound-absorbing structure (10) of the third embodiment of the first comparative example, which has only a porous layer (50) and no mesh structure (40).

[0028] However, based on the results of each verification test, it is thought that if the mesh opening F of the mesh members constituting the mesh structure (40) is smaller than 5 μm, the sound pressure energy from the waveguide space B will have difficulty reaching the back of the cavity A, thus reducing the sound-dampening effect. Furthermore, if the mesh opening F of the mesh members constituting the mesh structure (40) becomes larger than 132 μm, the sound wave energy attenuation effect decreases, which is thought to reduce the sound-dampening effect. Therefore, the mesh structure (40) of the embodiment according to the present invention is preferably composed of mesh members with an opening of 5 μm to 132 μm and a mesh opening ratio of 1% to 42%.

[0029] Next, the third and fourth embodiments will be described. The sound-absorbing structure (10) of the third and fourth embodiments is an example in which a mesh structure (40) is wound around the waveguide space B defined by the inner cylinder wall (31). A schematic diagram of the test apparatus is shown in Figure 8. As shown in the figure, in the third and fourth embodiments, a cylindrical pipe made of perforated metal (hereinafter also referred to as "perforated pipe") was used as the inner cylinder (30), and a mesh member was wound around the outer circumference of the inner cylinder wall (31) of the inner cylinder (30) to provide a mesh structure (40). A confirmation test was then conducted to verify the sound-dampening effect in this case.

[0030] The verification test method, as shown in Figure 8, is the same as in the first and second embodiments described above, in which white noise of 100Hz-4096Hz is output from a sound source S placed at the end of an acoustic tube 110 with a diameter of Φ100. In the third and fourth embodiments, white noise was silenced by passing it through a sound-dampening structure (10) using a perforated pipe as the inner cylinder wall (31), and the sound pressure after passing through the sound-dampening structure (10) was measured as the output using a microphone E, similar to the first and second embodiments. Each sound-absorbing structure (10) for the verification test according to the third embodiment is composed of an outer cylinder housing (20), an inner cylinder (30) made of perforated pipe, and a mesh member that forms a mesh structure (40). In the fourth embodiment, a porous body (50) is further included in the cavity (A). As shown in Figure 9, the perforated pipe in this verification test has a 60° staggered perforation arrangement, with perforation diameter D, perforation pitch P, and opening ratio of the inner circumferential wall surface N (%), where N = (90.6 × D²) / P².

[0031] In other words, this verification test corresponds to an example in which a mesh structure (40) is wound around the inner cylinder wall (31) of the inner cylinder (30) to cover the waveguide space B (Invention 1). Furthermore, the inner cylinder wall (31) of the inner cylinder (30), which is made of a perforated pipe, corresponds to an example in which its cross-sectional structure is circular (Invention 4). The details of each sound-absorbing structure (10) for the verification test are shown in Table 2 below. In each sound-absorbing structure (10) for the verification test, the perforated pipe that serves as the inner cylinder (30) is one in which the opening ratio of the opening to the projected area of ​​the housing that serves as the outer cylinder (20) in the waveguide direction C is 32.6% or more.

[0032] [Table 2]

[0033] In Table 2, in the second comparative example, embodiment 1 (Pipe), the inner cylinder wall (31) is made by covering the perimeter of the pipe with vinyl film and masking tape instead of a mesh structure (40) as the member surrounding the inner cylinder (30) made of perforated pipe. Furthermore, Embodiment 2 of the Second Comparative Example (No Sample) represents a frame + housing (20) without a mesh structure (40), while Embodiment 3 of the Second Comparative Example (Kyuon) represents a structure with a porous material (50) in the cavity (A) but without a mesh structure (40). Also, D3 represents a diameter of Φ3cm (open area 32.6%), and D5 represents a diameter of Φ5cm (open area 35.4%).

[0034] First, we examined the difference in sound-dampening effect between a perforated pipe with an inner wall (31) having an opening ratio of 32.6% (Aspect 4 of the Second Comparative Example) and a perforated pipe with a mesh structure (40) around it (Aspects 1 and 3 of the Third Embodiment). Figure 10 shows an excerpt of the examination results. As can be seen in the graphs of aspects 1 and 3 of the third embodiment shown in Figure 10, when a mesh structure (40) is attached around the inner cylinder wall (31) of the inner cylinder (30) made of perforated pipe, a higher sound-dampening effect was confirmed in the entire frequency range compared to aspect 4 of the second comparative example, in which the inner cylinder wall (31) was made of perforated pipe alone. Furthermore, as can be seen by comparing the first embodiment of the third embodiment and the third embodiment of the third embodiment shown in the same figure, even when the type of mesh member is changed, attaching the mesh structure (40) around the inner cylinder wall (31) of the inner cylinder (30) made of perforated pipe resulted in a higher sound-dampening effect across the entire frequency range than when the inner cylinder wall (31) was made of perforated pipe alone (Invention 1).

[0035] Next, the sound absorption effect when a mesh structure (40) and a porous material (50) are attached to the perforated pipe was compared and confirmed between embodiment 6 of the second comparative example and embodiments 1 and 3 of the fourth embodiment. A portion of the results of the confirmation test is shown in Figure 11. As shown in aspects 1 and 3 of the fourth embodiment in the same figure, it was confirmed that the sound-dampening effect is improved in almost the entire frequency range when a mesh structure (40) is attached around the perforated pipe while the porous body (50) is present (Invention 2).

[0036] Furthermore, as can be seen by comparing the first aspect of the fourth embodiment and the third aspect of the third embodiment shown in the same figure, it was confirmed that even when the type of mesh structure (40) is changed while the porous body (50) is present, the sound-dampening effect can be improved in almost the entire frequency range if the mesh structure (40) is attached around the perforated pipe. The above verification test confirmed that, overall, the sound-dampening structure (10) with a mesh structure (40) attached around the perforated pipe was able to improve the sound-dampening effect compared to the second comparative example. Furthermore, it was found that the sound-absorbing structure (10) in which a mesh structure (40) is attached around the inner wall (31) of a perforated pipe inner cylinder (30) and a porous material (50) is placed inside the cavity (A) has the highest sound-absorbing effect.

[0037] As described above, the sound-absorbing structure (10) of the above embodiment and example can improve the sound-absorbing performance per unit volume. In particular, the sound-absorbing structure (10) of the above embodiment and example is suitable as an automobile silencer because, in the case of a tubular sound-absorbing structure, it is possible to improve the sound-absorbing performance per unit volume while making the entire device smaller and more compact compared to the sound-absorbing technology exemplified in Patent Document 1 (Invention 6).

[0038] It should be noted that the sound-absorbing structure according to the present invention is not limited to the above embodiments or examples, and various modifications are possible without departing from the spirit of the present invention. For example, the mesh members constituting the mesh structure 40 are not limited to a mesh structure made of fibers; if they are plastic meshes, the mesh structure can be formed by extrusion, orientation, or expansion. Furthermore, the constituent materials can be, for example, polypropylene, polyethylene, nylon, PVC, or PTFE. In the case of metal mesh, the mesh structure may be formed by weaving, braiding, welding, expanding, sintering, or photochemical etching from steel or other metals. [Explanation of Symbols]

[0039] 10 Sound deadening structure 20 Housing (outer cylinder) 21 Outer cylinder wall 22 Front wall 23 Back wall 30 Inner cylinder 31 Inner cylinder wall 32 openings 33 Opening 40 mesh structure 41 Mesh Laminate 50 Porous material 100 Test equipment 110 Sound tube A Cavity B Waveguide space C Waveguide direction D Drilling diameter d Fiber diameter E Microphone F Eye opening S sound source T Opposite direction M Mesh W standing wave ε mesh aperture ratio

Claims

1. An outer cylinder having an outer cylinder wall with a closed cross-sectional shape along the wave-guiding direction, An inner cylinder having an opening disposed within the outer wall of the outer cylinder and opening at both ends in the wave guiding direction, and an inner cylinder wall having a closed cross-sectional shape along the outer circumference of the opening and being formed to penetrate along the wave guiding direction, thereby defining a wave guiding space inside through which air can pass; A mesh structure is wound around the periphery of the waveguide space by the inner cylinder wall or wound along the outer circumference shape of the opening to form the inner cylinder wall itself, and is provided to allow air to pass through toward the cavity between the inner cylinder wall of the inner cylinder and the outer cylinder wall of the outer cylinder, Equipped with, The inner cylinder has an opening ratio of 32.6% or more relative to the projected area of ​​the outer cylinder in the waveguide direction. The aforementioned mesh structure is characterized by being composed of mesh members with an opening of 11 μm to 132 μm and a mesh opening ratio of 1% to 42%.

2. The sound-absorbing structure according to claim 1, wherein the cavity between the inner wall of the inner cylinder and the outer wall of the outer cylinder is filled with a porous material through which air can pass.

3. The sound-absorbing structure according to claim 1, wherein the inner wall of the inner cylinder has a rectangular cross-sectional shape.

4. The sound-absorbing structure according to claim 1, wherein the inner wall of the inner cylinder has a circular cross-sectional shape.

5. The sound-absorbing structure according to claim 1, wherein the mesh structure is a mesh laminate formed by stacking a plurality of the mesh members.

6. A muffler for an automobile, characterized by having a sound-dampening structure according to any one of claims 1 to 5.

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