Duct

Abstract

To provide a duct capable of silencing noises of different frequency bands by a single side branch and contributing to improvement of comfortability.SOLUTION: The duct 10 has a duct body 21 into which air is sucked, and a rib 22 which is erected from a bottom part 26 of the duct body 21 in non-contact with the lid part and has a different height in the middle so as to face a wall surface of the duct body 21. One end of the rib 22 is joined to the wall surface, and the other end of the rib 22 is separated from the wall surface.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a duct. Here, the term "duct" is a general term for a tube, duct, pipe, etc. that transports gas (mainly air). [Background technology]

[0002] In recent years, efforts to provide access to sustainable transportation systems that take into consideration vulnerable users such as the elderly, people with disabilities, and children have been gaining momentum. To achieve this, we are focusing on research and development to further improve transportation safety, convenience, and comfort through development of vehicle livability.

[0003] For example, a known duct has an air inlet in the duct body, and an internal passage of the duct body that contains a box-type resonator and two tubular resonators separated by ribs. In this duct, air and water are guided from the air inlet into the internal passage of the duct body. The water guided into the internal passage adheres to the inner wall of the duct body, separating it from the air and being discharged to the outside of the duct body.

[0004] Here, a portion of the air introduced into the internal passage is introduced into the box-type resonator and two tubular resonators (hereinafter sometimes referred to as side branches), where it is reflected inside each resonator and returned to the internal passage. Therefore, the air is subjected to a resonance effect by the box-type resonator and the two side branches. This makes it possible, for example, to reduce noise in different frequency bands (hereinafter sometimes referred to as noise reduction) (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-161158 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with conventional ducts, in order to muffle noises in different frequency bands, it is necessary to provide a box-type resonator and two side branches (that is, multiple resonators) in the internal passage of the duct body.

[0007] An object of the present invention is to provide a duct that can muffle noises in different frequency bands with a single side branch, thereby contributing to improved comfort. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention proposes the following means. (1) The duct according to the present invention has a duct body (e.g., duct body 21 in the embodiment) into which gas is drawn, and ribs (e.g., ribs 22, 102 in the embodiment) that rise from one side of the bottom (e.g., bottom 26 in the embodiment) and the cover (e.g., cover 27 in the embodiment) of the duct body to the other side without contact, and that have different heights along the way so as to face the wall surface of the duct body, with one end of the rib joined to the wall surface and the other end of the rib spaced apart from the wall surface.

[0009] With this configuration, a side branch can be provided inside the duct body using the wall surface and ribs of the duct body. The side branch reflects sound waves (hereinafter sometimes referred to as "sound") guided from the duct body, and through a resonance effect in which the reflected sound interferes with the sound transmitted through the duct body, generating the so-called side branch effect and reducing the sound in the duct.

[0010] Here, the rib is raised without contacting the other of the bottom and lid of the duct body. This allows the inside of the side branch to communicate with the inside of the duct body. In other words, the side branch is formed with an open cross section rather than a closed one. This allows the sound reduction characteristics of the side branch to be smoothed, reducing sound over a wide frequency range. It also prevents deterioration due to anti-resonance.

[0011] Furthermore, the height of the ribs is varied along the way, allowing for different branch lengths within a single side branch. By ensuring different branch lengths, it is possible to reflect different frequency bands of sound from the side branch. This allows the reflected sounds of different frequency bands to interfere with the sound transmitted to the duct body, reducing the sounds of different frequency bands. In this way, the rib is raised without contacting either the bottom or the cover of the duct body, and the height of the rib varies along the way. This makes it possible to muffle noise in different frequency bands with a single side branch, thereby contributing to improved comfort. Hereinafter, the different frequencies reflected from the side branches may be referred to as "silence frequencies."

[0012] Furthermore, by providing a rib on the other of the bottom and lid of the duct body, the rib can also be used as a rigidity member, thereby increasing the rigidity of the duct body. Furthermore, by providing ribs along the duct body, it is possible to provide a rectifying effect on the gas sucked into the duct body.

[0013] (2) In the above aspect, the height of the ribs may be varied in a stepped manner.

[0014] With this configuration, by varying the height of the ribs in a stepped manner, different branch lengths can be achieved in stages in a single side branch, thereby generating different silencing frequencies in stages.

[0015] (3) In the above aspect, the height of the rib may be varied in a sloped manner.

[0016] With this configuration, the height of the ribs is made to vary in a sloped manner, so that different silencing frequencies can be generated at the locations where the height of the ribs changes gradually.

[0017] (4) In the above aspect, a reflective portion (e.g., reflective portion 23 in the embodiment) may be provided at one end where the rib is joined, in a direction intersecting the rib and protruding in the same height direction as the rib.

[0018] With this configuration, the distance to the depth of the side branch can be adjusted to be shorter by providing a local reflecting portion at one end where the rib is joined. This shortens the depth of the side branch, thereby increasing the silencing frequency. Therefore, sounds in different frequency bands can be more effectively reduced. Furthermore, the silencing frequency can be adjusted as desired by adjusting the position of the reflecting portion in the longitudinal direction of the side branch.

[0019] (5) In the above aspect, the stepped rib may have two or more steps.

[0020] With this configuration, by providing two or more stepped ribs, the height of the ribs can be made different for each step. This allows multiple noise silencing frequencies to be generated in stages in a single side branch. For example, if there are multiple frequencies to be silenced, noise can be silenced in multiple frequency bands by increasing the number of rib steps accordingly. The number of rib steps can be set as desired.

[0021] (6) In the above aspect, both ends of the reflecting portion may be spaced apart from the wall surface and the rib.

[0022] With this configuration, by separating both ends of the reflecting section from the wall surface and the rib, a first passage can be provided between the reflecting section and the wall surface. Furthermore, a second passage can be provided between the reflecting section and the rib. Therefore, sound guided to the side branch can be guided to the depth of the side branch through the first and second passages. The guided sound can be reflected in the depth. In this way, the sound guided to the side branch can be reflected by both the deep section and the reflection section, which allows the distance of the side branch to be varied in the reflection section, thereby generating different silencing frequencies. [Effects of the Invention]

[0023] According to the present invention, noises in different frequency bands can be silenced with a single side branch, which can contribute to improving comfort. [Brief explanation of the drawings]

[0024] [Figure 1] FIG. 2 is a perspective view showing a state in which a fan is connected to a duct in the first embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a perspective view showing the inside of the duct in the first embodiment with a lid removed. [Figure 4] FIG. 4 is an enlarged perspective view of a portion IV in FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] 4 is a graph showing the amount of noise attenuation by the duct of the first embodiment and the duct of Comparative Example 1. [Figure 8] FIG. 10 is a cross-sectional view showing a duct in Comparative Example 2. [Figure 9] 10 is a graph showing the amount of noise attenuation by the duct of the first embodiment and the duct of Comparative Example 2. [Figure 10] FIG. 10 is a perspective view showing the inside of a duct in a second embodiment of the present invention with a lid removed. [Figure 11] 10 is a graph showing the amount of noise attenuation by the duct of the second embodiment and the duct of Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, a duct according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, air is used as an example of a gas to be applied to the duct, but it is also possible to apply a gas other than air to the duct. Although an intake duct installed upstream of the fan is used as an example of a duct, a similar effect can be achieved by installing an exhaust duct downstream, which can also reduce noise. In the case of an exhaust duct, the flow of air and sound waves is reversed compared to an intake duct. [First embodiment] FIG. 1 is a perspective view showing a state in which a fan is connected to a duct. <Duct> 1, the duct 10 is connected to a fan 14 via a first communication passage 12. The fan 14 is connected to a cooled part 18 via, for example, a second communication passage 16. In the following, the cooled part 18 will be described using a battery 18 as an example, but the cooled part 18 is not limited to a battery 18.

[0026] When the fan 14 is driven, the duct 10 blows out air from the fan 14. When the air is blown out from the fan 14, the air is sucked into the fan 14. Thus, the air is sucked into the inside of the duct 10. Moisture is removed from the sucked air inside the duct 10, and the air is guided to the fan 14 via the first communication passage 12. The air guided to the fan 14 is blown out from the fan 14 and guided to the battery 18 via the second communication passage 16. The battery 18 is cooled by the guided air.

[0027] <Duct body> Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1. Fig. 3 is a perspective view showing the inside of the duct with the cover removed. As shown in FIGS. 2 and 3, the duct 10 has a duct body 21, a rib 22, and a reflecting portion . The duct body 21 is formed into a generally rectangular shape in a plan view. The duct body 21 has a peripheral wall 25, a bottom 26, and a lid 27. The peripheral wall 25 has a first long wall 31, a second long wall 32, a first short wall 33, and a second short wall 34. The first long wall 31 and the second long wall 32 are arranged opposite each other. The first short wall 33 and the second short wall 34 are arranged opposite each other. The peripheral wall 25 is formed into a generally rectangular frame by the first long wall 31, the second long wall 32, the first short wall 33, and the second short wall 34. The bottom 26 is provided at the lower end of the peripheral wall 25. The lid 27 is provided at the upper end of the peripheral wall 25.

[0028] FIG. 4 is an enlarged perspective view of part IV in FIG. As shown in FIGS. 3 and 4 , the first long wall 31 has an inlet 36. The inlet 36 draws air from the outside of the duct body 21 into the inside of the duct body 21. The first short wall 33 has, for example, a first wall 41, a second wall 42, a third wall 43, and a fourth wall 44. The first wall 41 is provided along the inlet 36. The second wall 42 is disposed at an angle from the first wall 41 toward the outside of the duct body 21. The third wall 43 is disposed from the second wall 42 along the second short wall 34. The fourth wall 44 is disposed at an angle from the third wall 43 to the second long wall 32. The first short wall 33 has a bulge 45 formed by the second wall 42, the third wall 43, and a portion 44a of the fourth wall 44. The bulge 45 bulges outward from the duct body 21 in a generally trapezoidal shape.

[0029] <Rib> 2 and 4, the rib 22 extends from the bottom (one side) 26 of the duct body 21 to the lid (the other side) 27 without contacting the rib 22. Therefore, a space S is formed between the rib 22 and the lid 27. The rib 22 is provided on the first short wall 33 at a distance from and facing each wall surface of the second wall 42, the third wall 43, and part 44a of the fourth wall 44 (i.e., the wall surface of the bulging portion 45).

[0030] By providing ribs 22 on bottom 26 of duct main body 21, side branch 48 is formed with a U-shaped cross section by ribs 22, bulging portion 45, and portion 26a of bottom 26. The interior of side branch 48 is in communication with the interior of duct main body 21 via space S. Hereinafter, portion 26a of the bottom may be referred to as "branch bottom 26a." In the first embodiment, an example will be described in which the ribs 22 rise from the bottom portion 26 without contacting the lid portion 27, but this is not limiting. As another example, the ribs 22 may rise from the lid portion 27 without contacting the bottom portion 26.

[0031] The rib 22 has a first rib 51 and a second rib 52. A base end 51a of the first rib 51 (one end of the rib 22) is joined to the wall surface of the first wall 41 at the first short wall 33. Therefore, the base end of the side branch 48 is closed by the wall surface of the second wall 42. Hereinafter, the wall surface of the second wall 42 may be referred to as the "depth portion 42" of the side branch 48. The first rib 51 extends linearly along the third wall 43 toward the portion 44a of the fourth wall 44. The first rib 51 is provided on the first short wall 33 so as to face the respective wall surfaces of the second wall 42 and the third wall 43. The second wall 42 and the third wall 43 are portions that form a part of the bulge portion 45. The first rib 51 is provided at a distance from the respective wall surfaces of the second wall 42 and the third wall 43. A second rib 52 is provided integrally with the tip of the first rib 51.

[0032] The second rib 52 extends from the tip of the first rib 51 along the wall surface of the portion 44a of the fourth wall 44. The second rib 52 is provided at an angle relative to the first rib 51. That is, the rib 22 is formed in a state in which the first rib 51 and the second rib 52 are bent. The tip of the second rib 52 (the other end of the rib 22) is spaced apart from the wall surface of the portion 44a of the fourth wall 44. Therefore, an opening 48a is provided at the tip of the side branch 48. As a result, the interior of the side branch 48 is in communication with the interior of the duct main body 21 via the opening 48a. The second rib 52 is one step lower in height from the bottom 26 than the first rib 51. That is, the rib 22 is formed so that the height differs in two steps at a position midway between the first rib 51 and the second rib 52.

[0033] In the first embodiment, an example of a stepped rib having two different heights will be described, but this is not limiting. As another example, the stepped rib 22 may have two or more different heights. In the first embodiment, an example is described in which the height of the second rib 52 is set one step lower than the height of the first rib 51, but this is not limiting. As another example, for example, the height of the first rib 51 may be set one step lower than the height of the second rib 52. Furthermore, in the first embodiment, an example is described in which the rib 22 is formed in a bent state by the first rib 51 and the second rib 52. However, this is not limitative. As another example, the rib 22 may be formed in a straight line.

[0034] FIG. 5 is a cross-sectional view taken along line VV in FIG. 4 and 5, the branch bottom portion 26a has a raised portion 55. The raised portion 55 has a step surface 56 and a raised surface 57. The step surface 56 rises from the branch bottom portion 26a into the inside of the side branch 48 between the first rib 51 and the third wall 43. The raised surface 57 extends from the step surface 56 to the second wall 42.

[0035] <Reflector> FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4 to 6, the reflecting portion 23 is provided on the raised surface 57 at a location on the base end side of the first rib 51 (i.e., on the depth portion 42 side, on one end side of the rib 22). The reflecting portion 23 is provided, for example, along the wall surface of the second wall 42 in a direction intersecting (crossing) the first rib 51. The reflecting portion 23 protrudes from the raised surface 57 in the same height direction as the first rib 51. Both ends of the reflecting portion 23 are spaced apart from the wall surface of the third wall 43 and the first rib 51. In the first embodiment, an example in which the reflecting portion 23 protrudes from the raised surface 57 will be described, but the present invention is not limited to this. As another example, for example, when the rib 22 is raised from the lid portion 27 (see FIG. 2) without contacting the bottom portion 26, the reflecting portion 23 may protrude from the lid portion 27.

[0036] As described above, according to the duct 10 of the first embodiment, as shown in FIG. 4, the side branch 48 can be provided inside the duct main body 21 by the wall surface of the bulging portion 45 and the rib 22. The side branch 48 reflects sound waves (hereinafter sometimes referred to as "sound") guided from the duct main body 21 through the opening 48a at the wall surface of the depth portion 42 with a phase shift. The reflected sound is transmitted to the duct main body from the opening 48a of the side branch 48. The sound reflected by the side branch 48 interferes with the sound transmitted inside the duct main body 21 due to resonance, generating the so-called side branch effect, thereby canceling out each other's sounds. This reduces the sound in the duct 10. Here, for example, the length of the side branch 48 is preferably approximately ¼ wavelength.

[0037] 2 and 4, the rib 22 is raised from the bottom 26 relative to the lid 27 of the duct main body 21 without contacting it. Therefore, the inside of the side branch 48 is connected to the inside of the duct main body 21 via the space S. That is, the side branch 48 is formed with an open cross section at the space S, rather than a closed cross section. Therefore, the characteristics of the sound reduced by the side branch 48 are smoothed, making it possible to reduce sound over a wide frequency range. Furthermore, by connecting the inside of the side branch 48 to the inside of the duct main body 21 via the space S, deterioration due to anti-resonance can also be suppressed.

[0038] Furthermore, the height of the ribs 22 is made different midway between the first rib 51 and the second rib 52. This allows different branch lengths to be ensured in the single side branch 48. By ensuring different branch lengths, sounds of different frequency bands can be reflected from the side branch 48. This allows the reflected sounds of different frequency bands to interfere with the sound transmitted to the duct main body 21, thereby reducing the sounds of different frequency bands. In this way, the ribs 22 are raised without contacting the lid portion 27 of the duct body 21, and the height of the ribs 22 varies along the way. This allows, for example, a single side branch 48 to muffle noise in different frequency bands, which in turn contributes to improved comfort. Hereinafter, the different frequencies reflected from the side branch 48 may be referred to as "silence frequencies."

[0039] Furthermore, by providing the ribs 22 on the bottom 26 of the duct body 21, the ribs 22 can also be used as rigid members, thereby increasing the rigidity of the duct body 21 (particularly the bottom 26). Furthermore, by providing ribs 22 along the bulging portion 45 of the duct body 21, the duct body 21 can have a rectifying effect on the air sucked into it from the suction port 36.

[0040] Furthermore, the height of the rib 22 is varied in a stepped manner, thereby ensuring different branch lengths in stages in a single side branch 48. This allows different silencing frequencies to be generated in stages.

[0041] Furthermore, as shown in Figures 4 to 6, the reflecting portion 23 is provided at a location on the side of the depth portion 42. This allows the distance of the side branch 48 to the depth portion 42 to be adjusted to be shorter. This allows the silencing frequency to be increased by shortening the depth of the side branch 48. This allows for even better reduction of sounds in different frequency bands. Note that the silencing frequency can be adjusted as desired by adjusting the position of the reflecting portion 23 in the longitudinal direction of the side branch 48.

[0042] In addition, the stepped ribs 22 shown in FIG. 4 may have two or more steps. This allows the height of the ribs 22 to differ for each step. This allows multiple noise silencing frequencies to be generated in stages in a single side branch 48. For example, if there are multiple frequencies to be silenced, noise can be silenced in multiple frequency bands by increasing the number of steps of the ribs 22 accordingly. The number of steps of the ribs 22 can be set as desired.

[0043] 4 to 6, both ends of the reflecting portion 23 are spaced apart from the wall surface of the third wall 43 and the first rib 51. Therefore, a first passage 61 can be provided between the reflecting portion 23 and the wall surface of the third wall 43. Furthermore, a second passage 62 can be provided between the reflecting portion 23 and the first rib 51. This allows sound guided to the side branch 48 to be guided to the depth portion 42 of the side branch 48 through the first passage 61 and the second passage 62. The guided sound can be reflected by the depth portion 42. Furthermore, the sound guided to the side branch 48 can also be reflected by the reflecting portion 23.

[0044] In this way, the sound guided to the side branch 48 can be reflected by both the depth section 42 and the reflection section 23. This allows the distance of the side branch to be varied in the reflection section 23, thereby generating different silencing frequencies.

[0045] Here, a step surface 56 of the raised portion 55 is provided on the branch bottom portion 26a. The step surface 56 is raised from the branch bottom portion 26a into the inside of the side branch 48. Therefore, the sound guided to the side branch 48 can also be reflected by the step surface 56. This allows the distance of the side branch to vary at the step surface 56, making it possible to generate different silencing frequencies more appropriately.

[0046] Next, the amount of noise attenuation by the duct 10 of the first embodiment will be described with reference to FIGS. 4 and 7 to 9. FIG. First, an example in which the amount of noise attenuation by the duct 10 of the first embodiment is compared with that of Comparative Example 1 will be described with reference to FIGS. FIG. 7 is a graph showing the amount of noise attenuation by the duct of the first embodiment and the duct of Comparative Example 1. In Figure 7, the vertical axis represents attenuation and the horizontal axis represents frequency. The attenuation of the duct 10 according to the first embodiment is shown by a solid line graph G1. The attenuation of the duct according to Comparative Example 1 is shown by a dashed line graph G2. The duct of the Comparative Example is the duct 10 of the first embodiment without the rib 22. In other words, the duct of Comparative Example 1 does not have the side branch 48 of the first embodiment.

[0047] 7, it can be seen that the duct 10 of the first embodiment has a larger amount of noise attenuation at seven frequencies from F1 to F7 than the duct of Comparative Example 1 shown in graph G2. In other words, it was confirmed that the duct 10 of the first embodiment, which is provided with a single side branch 48, can appropriately attenuate noise in seven different frequency bands from F1 to F7.

[0048] Next, an example of comparing the amount of noise attenuation by the duct 10 of the first embodiment with Comparative Example 2 will be described with reference to FIGS. 4, 8, and 9. FIG. Fig. 8 is a cross-sectional view showing a duct in Comparative Example 2. Fig. 9 is a graph showing the amount of noise attenuation by the duct of the first embodiment and the duct of Comparative Example 2. 9, the vertical axis represents attenuation, and the horizontal axis represents frequency. The attenuation of the duct 10 according to the first embodiment is shown by a solid line in graph G1. The attenuation of the duct according to comparative example 1 is shown by an imaginary line in graph G2. The attenuation of the duct 200 according to comparative example 2 is shown by an imaginary line in graph G3.

[0049] As shown in Fig. 8, the duct 200 of Comparative Example 2 is obtained by replacing the side branch 48 provided in the duct 10 of the first embodiment with a side branch 201. The side branch 201 is raised until the rib 202 contacts the lid portion 27. In other words, the side branch 201 is sealed with a rectangular cross section.

[0050] 9, the duct 200 of Comparative Example 2 exhibits a greater amount of noise attenuation at four frequencies from F8 to F11 than the duct of Comparative Example 1 shown in graph G2. In contrast, the duct 10 of the first embodiment exhibits a greater amount of noise attenuation at seven frequencies from graphs G1 to F7 than the duct 200 of Comparative Example 2 shown in graph G3. In other words, it was confirmed that the duct 10 of the first embodiment, provided with a single side branch 48, can appropriately muffle noise in seven different frequency bands from F1 to F7.

[0051] Next, a duct according to a second embodiment will be described with reference to Figures 10 and 11. In the second embodiment, the same or similar members as those in the duct 10 of the first embodiment will be denoted by the same reference numerals, and detailed description thereof will be omitted.

[0052] [Second embodiment] FIG. 10 is a perspective view showing the inside of the duct in the second embodiment with the cover removed. As shown in Fig. 10, the duct 100 has a rib 102 instead of the rib 22 of the first embodiment. The other configuration of the duct 100 is the same as that of the duct 10 of the first embodiment. Like the rib 22 of the first embodiment, the rib 102 rises from the bottom (one side) 26 of the duct main body 21 without contacting the lid (other side) 27 (see Fig. 2). By providing the rib 102 on the bottom 26 of the duct main body 21, the rib 102, the bulge 45, and a part 26a of the bottom 26 (see Fig. 2) form a side branch 108 having a U-shaped cross section.

[0053] The rib 102 includes a first rib 51 and a second rib 104. The second rib 104 extends from the tip of the first rib 51 along the wall surface of the portion 44a of the fourth wall 44. The second rib 104 is provided at an angle relative to the first rib 51. That is, the rib 102 is formed such that the first rib 51 and the second rib 104 are bent. The tip of the second rib 104 (the other end of the rib 102) is spaced apart from the wall surface of the portion 44a of the fourth wall 44. Therefore, an opening 108a is provided at the tip of the side branch 108. As a result, the interior of the side branch 108 is in communication with the interior of the duct main body 21 via the opening 108a.

[0054] The second rib 104 is formed in a sloped (inclined) shape so that the height from the bottom 26 gradually decreases from the first rib 51 toward the tip. That is, the rib 102 is formed so that the height changes in a sloped shape at a midpoint that is the boundary between the first rib 51 and the second rib 104.

[0055] In the second embodiment, an example will be described in which the height of the second rib 104 is reduced in a slope relative to the height of the first rib 51, but this is not limiting. As another example, for example, the height of the first rib 51 may be reduced in a slope relative to the height of the second rib 104. In the second embodiment, the rib 102 is formed in a bent state by the first rib 51 and the second rib 104. However, the present invention is not limited to this. As another example, the rib 102 may be formed in a straight line.

[0056] According to the duct 100 of the second embodiment described above, the height of the ribs 102 is varied in a sloping manner. This allows different silencing frequencies to be generated at locations where the height of the ribs 102 changes gradually. Furthermore, the ribs 102 are raised without contacting the lid portion 27 (see FIG. 2) of the duct main body 21. This allows noise in different frequency bands to be silencing with a single side branch 108, for example, which ultimately contributes to improved comfort.

[0057] Furthermore, according to the duct 100 of the second embodiment, it is possible to obtain the same functions and effects as the duct 10 of the first embodiment.

[0058] Next, an example of comparing the amount of noise attenuation by the duct 10 of the second embodiment with that of Comparative Example 1 will be described with reference to FIG. FIG. 11 is a graph showing the amount of noise attenuation by the duct 100 of the second embodiment and the duct of Comparative Example 1. In FIG. 11, the vertical axis represents attenuation, and the horizontal axis represents frequency. The attenuation of the duct 100 according to the second embodiment is shown by solid line graph G4. The attenuation of the duct according to Comparative Example 1 is shown by dashed line graph G2. The duct of the comparative example is the duct 100 according to the second embodiment without the rib 102. The duct of Comparative Example 1 does not include the side branch 108 according to the second embodiment. In other words, the duct of Comparative Example 1 has the same configuration as the duct of Comparative Example 1 shown in FIG. 7.

[0059] 11, the duct 100 of the second embodiment attenuates noise more significantly at four frequencies from F12 to F15 than the duct of Comparative Example 1 shown in graph G2. That is, it was confirmed that the duct 100 of the second embodiment, which is provided with a single side branch 108, can adequately attenuate noise in four different frequency bands from F12 to F15.

[0060] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0061] In addition, within the scope of the spirit of the present invention, the components in the above-described embodiments may be replaced with well-known components as appropriate, and the above-described modifications may be combined as appropriate. [Explanation of symbols]

[0062] 10...Duct 21...Duct body 22,102…ribs 23…Reflector 26…bottom 27…Gaibu

Claims

1. a duct body into which gas is drawn; a rib having a height that varies midway and that faces a wall surface of the duct body, the rib being raised from one of the bottom and the cover of the duct body without contacting the other; A duct, characterized in that one end of the rib is joined to the wall surface and the other end of the rib is spaced from the wall surface.

2. 2. The duct according to claim 1, wherein the height of the ribs varies in a stepped manner.

3. 2. The duct according to claim 1, wherein the height of the ribs varies in a sloping manner.

4. 2. The duct according to claim 1, further comprising a reflecting portion at one end where the rib is joined, the reflecting portion being provided in a direction intersecting the rib and projecting in the same height direction as the rib.

5. The duct according to claim 2, wherein the stepped rib has two or more steps.

6. The reflecting portion is 5. The duct of claim 4, wherein both ends are spaced apart from said wall surface and said rib.

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