Acoustic impedance change structure and ventilation type silencer

Abstract

Provided is: a ventilation-type silencer with a high absorption rate, that suppresses the occurrence of wind noise, and having a high muffling effect in a low-frequency band; and an acoustic impedance structure. In an acoustic impedance change structure in which sound propagates, there are at least a first impedance matching region in which the acoustic impedance connected to an inlet portion gradually decreases, an acoustic impedance constant region, and an outlet portion in the stated order, where the acoustic impedance in the inlet portion is Zin, acoustic impedance in the acoustic impedance constant region is Zcham, and the acoustic impedance in the outlet portion is Zout, Zcham<Zin and Zcham<Zout are satisfied, and there is a first termination structure that is acoustically connected to the acoustic impedance constant region.

Description

[Technical Field]

[0001] The present invention relates to an acoustic impedance changing structure and a ventilation type silencer. [Background technology]

[0002] In a vent pipe that transports gas, a cavity-type silencer is known as a silencer that silences noise from a gas supply source or the like midway through the vent pipe. The cavity-type silencer is installed midway through the vent pipe and has an expansion chamber with a cross-sectional area larger than that of the vent pipe.

[0003] For example, Patent Document 1 describes an expansion type silencer in which gas flow pipes are attached to both the front and rear ends of a cylindrical container and sound-absorbing material is attached to the inner surface of the side wall of the container, in which the radial thickness of the sound-absorbing material is varied gradually in the axial direction and the inner surface of the sound-absorbing material is tapered. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-229415 Summary of the Invention [Problem to be solved by the invention]

[0005] Ventilation silencers are used to reduce noise from blowers, fans, etc. Generally, expansion silencers reflect sound to silence it, but there is a demand for ventilation silencers that absorb sound rather than reflect it.

[0006] When a reflective silencer is used, the sound reflected by the silencer interferes with the incident sound, causing the sound pressure distribution in front of the silencer's entrance to have a dense / sparse distribution, with the sound pressure amplitude increasing at dense locations. This widely distributed sound excites vibrations in the housing in front of the silencer (such as vibrations of hoses and ducts), which causes noise to easily radiate outside, creating a problem. In addition, the reflected sound can sometimes be re-reflected and return, further increasing the sound pressure. For this reason, there was a demand for a ventilation-type silencer that silences sound by absorbing it rather than reflecting it.

[0007] Furthermore, in the expansion type silencer, there is a problem in that wind noise is generated when wind flows into the expansion chamber.

[0008] Furthermore, in expansion-type silencers, strong reflections at the entrance to the expansion chamber cause strong longitudinal resonance within the expansion chamber, resulting in frequencies that are transmitted resonantly (frequencies that have no sound-silencing effect). Countermeasures for the transmitted resonance that occurs on the low-frequency side have been particularly difficult.

[0009] The object of the present invention is to solve the problems of the above-mentioned conventional technology, and to provide a ventilation type silencer and an acoustic impedance structure that are high in absorption rate, suppress the generation of wind noise, and have a high silencing effect in the low frequency band. [Means for solving the problem]

[0010] In order to solve this problem, the present invention has the following configuration. [1] An acoustic impedance changing structure through which sound propagates, a first impedance matching region connected to the inlet portion and having a gradually decreasing acoustic impedance; A constant acoustic impedance region; an outlet portion, at least in this order; Let Z be the acoustic impedance at the entrance. in and the acoustic impedance in the constant acoustic impedance region is Z cham and the acoustic impedance at the outlet is Z outThen, Z cham <Z in , and Z cham <Z out Fulfilling A varying acoustic impedance structure having a first termination structure acoustically connected to the constant acoustic impedance region. [2] The acoustic impedance variable structure according to [1], wherein the first termination structure is acoustically connected to the constant acoustic impedance region and the first impedance matching region. [3] A second impedance matching region is disposed between the constant acoustic impedance region and the outlet, is connected to the outlet, and has a gradually increasing acoustic impedance; The acoustic impedance variable structure according to [1] or [2], having a second termination structure connected to the constant acoustic impedance region. [4] An inlet-side ventilation pipe, an expansion section communicating with the inlet-side ventilation pipe and having a larger cross-sectional area than the inlet-side ventilation pipe, and an outlet-side ventilation pipe communicating with the expansion section and having a smaller cross-sectional area than the expansion section; a first opening structure that gradually reduces acoustic impedance from the connection between the expansion section and the inlet-side ventilation pipe toward the outlet-side ventilation pipe; A ventilation type silencer having a first rear space surrounded by a first opening structure, a side surface of the extension portion on the inlet side ventilation pipe side, and a peripheral surface of the extension portion, and open to the outlet side ventilation pipe side of the extension portion. [5] The ventilation type silencer according to [4], wherein the first opening structure has a cutoff frequency fc determined by the shape of the first opening structure of 2000 Hz or less. [6] A ventilation silencer according to [4] or [5], wherein, in the flow direction of the sound waves within the ventilation silencer, when the length of the extension portion is L and the length of the first opening structure is a, 0.2≦a / L≦0.8. [7] A second opening structure having a cross-sectional area that gradually decreases from within the expansion section toward the connection between the expansion section and the outlet ventilation pipe; A ventilation type silencer according to any one of [4] to [6], having a second back space that is surrounded by the second opening structure, the side surface of the extension portion on the outlet side vent pipe side, and the peripheral surface of the extension portion, and is open to the inlet side vent pipe side of the extension portion. [8] The ventilation type silencer according to [7], wherein the second opening structure has a cutoff frequency fc determined by the shape of the second opening structure of 2000 Hz or less. [9] A ventilation silencer according to [7] or [8], wherein, in the flow direction of the sound waves within the ventilation silencer, the length of the extension portion is L and the total length of the first opening structure and the second opening structure is a2, and 0.2≦a2 / L≦0.8.

[10] The ventilation type silencer according to any one of [4] to [9], wherein the ratio of the acoustic impedance at the entrance of the back space to the minimum acoustic impedance of the back space is 1.1 or more.

[11] The ventilation type silencer according to any one of [4] to

[10] , which has a sound absorbing structure in at least a part of the extension part.

[12] The ventilation type silencer according to

[11] , wherein the sound absorbing structure is a porous sound absorbing material.

[13] A ventilation type silencer according to

[11] or

[12] , wherein at least a part of the sound absorbing structure is arranged along the housing of the extension part.

[14] The ventilation type silencer according to any one of

[11] to

[13] , wherein the sound absorbing structure is in contact with the maximum diameter portion of at least one of the first opening structure and the second opening structure.

[15] A sound-absorbing structure is disposed between the first opening structure and the second opening structure; The ventilation type silencer according to any one of

[11] to

[13] , which is not disposed in at least one of the first rear space and the second rear space.

[16] A ventilation type silencer according to any one of [4] to

[15] , wherein the change in acoustic impedance in at least one of the first opening structure and the second opening structure is continuous to the outside of the extension portion.

[17] The ventilation type silencer according to any one of [4] to

[16] , wherein the average roughness Ra of the inner surface of at least one of the first opening structure and the second opening structure is 1 mm or less.

[18] The ventilation type silencer according to any one of [4] to

[17] , wherein the cross-sectional shape of the extension part is circular or rectangular.

[19] The ventilation type silencer according to any one of [4] to

[17] , wherein the first opening structure is not closed in cross section at the end on the outlet side ventilation pipe side.

[20] The ventilation type silencer according to any one of [7] to

[19] , wherein the second opening structure is not closed in cross section at the end on the inlet side ventilation pipe side.

[21] The ventilation type silencer according to any one of [4] to

[20] , wherein the first opening structure has a region where the thickness becomes thinner toward the outlet-side ventilation pipe side.

[22] The ventilation type silencer according to any one of [7] to

[21] , wherein the second opening structure has a region where the thickness becomes thinner toward the inlet side ventilation pipe.

[23] A ventilation type silencer according to any one of [7] to

[22] , wherein the connection position with the first opening structure on the side of the extension portion and the connection position with the second opening structure are located in the center of the side.

[24] The ventilation type silencer according to any one of [7] to

[23] , wherein the shapes of the first opening structure and the second opening structure have two-fold or more symmetry.

[25] The ventilation type silencer according to any one of [7] to

[24] , wherein the length of the first opening structure in the flow path direction is longer than the length of the second opening structure. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a ventilation type silencer and an acoustic impedance structure that have a high absorption rate, suppress the generation of wind noise, and have a high noise absorbing effect in the low frequency band. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a block diagram of an example of an acoustic impedance changing structure of the present invention. [Figure 2] FIG. 2 is a block diagram of another example of an acoustic impedance changing structure of the present invention. [Figure 3] 1 is a cross-sectional view conceptually showing an example of a ventilation type silencer of the present invention. [Figure 4] 1 is a conceptual diagram for explaining the correspondence between the ventilation type silencer of the present invention and an acoustic impedance changing structure. FIG. [Figure 5] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. [Figure 6] 10 is a conceptual diagram for explaining the relationship between the length of the extension portion and the length of the opening structure. FIG. [Figure 7] FIG. 10 is a cross-sectional view conceptually showing an example of an opening structure. [Figure 8] FIG. 10 is a cross-sectional view conceptually showing another example of an opening structure. [Figure 9] FIG. 10 is a cross-sectional view conceptually showing another example of an opening structure. [Figure 10] FIG. 10 is a perspective view conceptually showing another example of an opening structure. [Figure 11] FIG. 10 is a perspective view conceptually showing another example of an opening structure. [Figure 12] FIG. 10 is a perspective view conceptually showing another example of an opening structure. [Figure 13] FIG. 10 is a conceptual diagram for explaining the shape of another example of a ventilation type silencer. [Figure 14] 1 is a graph showing the relationship between frequency and absorptance. [Figure 15] 10 is a graph showing the relationship between the length of the opening structure and the average value of the absorptance. [Figure 16] 10 is a graph showing the relationship between the length of the opening structure and the average value of the absorptance. [Figure 17] 10 is a graph showing the relationship between the length of the opening structure and the average value of the absorptance. [Figure 18] 10 is a graph showing the relationship between the length of the opening structure and the average value of the absorptance. [Figure 19] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 20] 10 is a graph showing the relationship between the maximum diameter of the aperture structure and the frequency at which the transmission loss is maximized. [Figure 21] 10 is a graph showing the relationship between impedance ratio and frequency ratio. [Figure 22] 10 is a graph showing the relationship between the length of the opening structure and the maximum sound insulation frequency. [Figure 23] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 24] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 25] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 26] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 27] 1 is a graph showing the relationship between frequency and absorptance. [Figure 28] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 29] 1 is a graph showing the relationship between frequency and absorptance. [Figure 30] 1 is a graph showing the relationship between frequency and absorptance. [Figure 31] 1 is a graph showing the relationship between frequency and transmission loss. [Figure 32] 1 is a graph showing the relationship between frequency and absorptance. [Figure 33] 10 is a graph showing the relationship between the length of the aperture structure and the calculated vorticity value. [Figure 34] 10 is a graph showing the relationship between the length of the aperture structure and the calculated vorticity value. [Figure 35] 10A and 10B are diagrams for explaining the shape of an opening structure of a comparative example. [Figure 36] 10 is a graph showing the relationship between position and hole area ratio. [Figure 37] 10 is a graph showing the relationship between position and estimated impedance value. [Figure 38] 1 is a graph showing the relationship between frequency and absorptance. [Figure 39] 1 is a graph showing the relationship between frequency and absorptance. [Figure 40] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. [Figure 41] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. [Figure 42] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. [Figure 43] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. [Figure 44] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. [Figure 45] FIG. 3 is a cross-sectional view conceptually showing another example of a ventilation type silencer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below. The following description of the components will be given based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, the terms "perpendicular" and "parallel" include the range of error acceptable in the technical field to which the present invention pertains. For example, "perpendicular" and "parallel" mean an error within a range of less than ±10° from strict perpendicular or parallel, and the error from strict perpendicular or parallel is preferably 5° or less, and more preferably 3° or less. In this specification, the terms "same" and "identical" include a margin of error generally accepted in the technical field.

[0014] [Acoustic impedance change structure] The acoustic impedance changing structure of the present invention comprises: An acoustic impedance changing structure through which sound propagates, a first impedance matching region connected to the inlet portion and having a gradually decreasing acoustic impedance; A constant acoustic impedance region; an outlet portion, at least in this order; Let Z be the acoustic impedance at the entrance. in and the acoustic impedance in the constant acoustic impedance region is Z cham and the acoustic impedance at the outlet is Z out Then, Z cham <Z in , and Z cham <Zout Fulfilling A variable acoustic impedance structure has a first termination structure acoustically connected to the constant acoustic impedance region.

[0015] FIG. 1 is a block diagram schematically showing an example of an acoustic impedance changing structure according to the present invention. The acoustic impedance varying structure 1a shown in FIG. 1 is for propagating sound and has an inlet section 2, a first impedance matching region 3, a constant acoustic impedance region 4, a first termination structure 5, and an outlet section 6. The inlet section 2, first impedance matching region 3, constant acoustic impedance region 4, and outlet section 6 are connected in this order, and the first termination structure 5 is connected to the first impedance matching region 3 in parallel with the constant acoustic impedance region 4. The constant acoustic impedance region 4 and the first termination structure 5 are acoustically connected. In other words, the first termination structure 5 is acoustically connected to the constant acoustic impedance region 4 and the first impedance matching region 3.

[0016] The constant acoustic impedance region 4 is a region where the acoustic impedance is approximately constant. in and the acoustic impedance in the constant acoustic impedance region 4 is Z cham and the acoustic impedance at the outlet 6 is Z out Then, Z cham <Z in , and Z cham <Z out That is, the acoustic impedance of the inlet portion 2 and the outlet portion 6 is greater than the acoustic impedance of the constant acoustic impedance region 4.

[0017] Here, acoustic impedances include characteristic impedance Zs and acoustic impedance ZA. Characteristic impedance Zs is a quantity specific to a material (fluid) and is determined by the product of density and the speed of sound. Acoustic impedance ZA is the ratio of pressure to flow rate at each location. In the case of a duct where sound propagation can be considered as a plane wave (approximately, sound wavelength / 2 ≥ duct diameter), if the duct cross-sectional area at that location is S, then flow rate is determined as cross-sectional area S × particle velocity, and so the relationship with characteristic impedance holds as acoustic impedance ZA = 1 / S × Zs. In other words, if the fluid medium is the same (characteristic impedance is constant), acoustic impedance ZA is inversely proportional to the cross-sectional area. Even if there is a duct extension larger than sound wavelength / 2, the above relationship holds true as long as the incident light is a plane wave (when the diameter of the vent pipe on the incident side is approximately λ / 2 or less). The acoustic impedance in the present invention is the above-mentioned ZA, that is, a quantity that is inversely proportional to the cross-sectional area of ​​the plane perpendicular to the flow path direction at each position.

[0018] The first impedance matching region 3 has a structure in which the acoustic impedance gradually decreases.

[0019] That is, the acoustic impedance changing structure 1a has a constant acoustic impedance region 4 between the entrance section 2 and the exit section 6, which has a smaller acoustic impedance than the entrance section 2 and the exit section 6, and the entrance section 2 and the constant acoustic impedance region 4 are connected by a first impedance matching region 3 in which the acoustic impedance gradually decreases.

[0020] In such an acoustic impedance changing structure 1a, sound enters through the entrance 2, passes through the first impedance matching region 3, enters the constant acoustic impedance region 4, and some of it enters the first termination structure 5, is reflected back, passes through the constant acoustic impedance region 4 and reaches the exit 6.

[0021] Here, the acoustic impedance varying structure preferably includes a second impedance matching region 7, which is disposed between the constant acoustic impedance region 4 and the outlet 6 and is connected to the outlet 6, and in which the acoustic impedance gradually increases, and a second termination structure 8, which is connected in parallel to the constant acoustic impedance region 4. The constant acoustic impedance region 4 and the second termination structure 8 are acoustically connected.

[0022] FIG. 2 is a block diagram schematically showing another example of the acoustic impedance changing structure of the present invention. 2 includes an entrance section 2, a first impedance matching region 3, a constant acoustic impedance region 4, a first termination structure 5, a second impedance matching region 7, a second termination structure 8, and an exit section 6. The entrance section 2, first impedance matching region 3, constant acoustic impedance region 4, second impedance matching region 7, and exit section 6 are connected in this order, with the first termination structure 5 connected to the first impedance matching region 3 in parallel with the constant acoustic impedance region 4, and the second termination structure 8 connected to the second impedance matching region 7 in parallel with the reduced acoustic impedance region.

[0023] The second impedance matching region 7 has a structure in which the acoustic impedance gradually increases.

[0024] That is, the acoustic impedance varying structure 1a has a constant acoustic impedance region 4 between the entrance section 2 and the exit section 6, which has a smaller acoustic impedance than the entrance section 2 and the exit section 6, and the entrance section 2 and the constant acoustic impedance region 4 are connected by a first impedance matching region 3 in which the acoustic impedance gradually decreases, and the constant acoustic impedance region 4 and the exit section 6 are connected by a second impedance matching region 7 in which the acoustic impedance gradually increases.

[0025] In such an acoustic impedance changing structure 1b, sound enters through the entrance 2, passes through the first impedance matching region 3, enters the constant acoustic impedance region 4, and some of it enters the first termination structure 5 and is reflected back, and some of it enters the second termination structure 8 and is reflected back, and from the constant acoustic impedance region 4 it passes through the second impedance matching region 7 and reaches the exit 6.

[0026] The function of such an acoustic impedance changing structure will be explained below using the function of a ventilation type silencer.

[0027] [Ventilated silencer] The ventilation type silencer of the present invention comprises: The ventilation system has an inlet-side ventilation pipe, an expansion section communicating with the inlet-side ventilation pipe and having a larger cross-sectional area than the inlet-side ventilation pipe, and an outlet-side ventilation pipe communicating with the expansion section and having a smaller cross-sectional area than the expansion section, a first opening structure that gradually reduces acoustic impedance from the connection between the expansion section and the inlet-side ventilation pipe toward the outlet-side ventilation pipe; This is a ventilation type silencer that has a first back space that is surrounded by the first opening structure, the side surface of the extension portion on the inlet side ventilation pipe side, and the peripheral surface of the extension portion, and is open to the outlet side ventilation pipe side of the extension portion.

[0028] The configuration of the ventilation type silencer of the present invention will be described with reference to the drawings. FIG. 3 is a schematic cross-sectional view showing one example of an embodiment of the ventilation type silencer of the present invention.

[0029] As shown in FIG. 3, the ventilation silencer 10 has a cylindrical inlet-side ventilation pipe 12, an extension 14 connected to one open end face of the inlet-side ventilation pipe 12, a cylindrical outlet-side ventilation pipe 16 connected to the end face of the extension 14 opposite to the inlet-side ventilation pipe 12, a first opening structure 20, a second opening structure 24, and a porous sound-absorbing material 30.

[0030] As shown in FIG. 4, the inlet-side ventilation pipe 12 is provided at the inlet portion 2 (Z in) in the extension portion 14, and the region between the first opening structure 20 and the second opening structure 24 corresponds to the constant acoustic impedance region 4 (indicated by Z cham The outlet side ventilation pipe 16 corresponds to the outlet portion 6 (indicated by Z in FIG. 4 ). out 4), and the first opening structure 20 corresponds to the first impedance matching region 3 (indicated by Z mach1 4), and the second opening structure 24 corresponds to the second impedance matching region 7 (indicated by Z mach2 In addition, in FIG. 4, the porous sound absorbing material is not shown.

[0031] The inlet vent pipe 12 is a cylindrical member that transports gas flowing in from one open end face to the expansion section 14 connected to the other open end face.

[0032] The outlet-side ventilation pipe 16 is a cylindrical member that transports gas that flows in from one open end surface connected to the expansion portion 14 to the other open end surface.

[0033] The cross-sectional shape of the inlet vent pipe 12 and the outlet vent pipe 16 (hereinafter collectively referred to as the vent pipes) may be various shapes such as circular, rectangular, triangular, etc. Furthermore, the cross-sectional shape of the vent pipe does not have to be constant in the axial direction of the central axis of the vent pipe. For example, the diameter of the vent pipe may vary in the axial direction.

[0034] The inlet-side vent pipe 12 and the outlet-side vent pipe 16 may have the same cross-sectional shape and cross-sectional area, or may have different shapes and / or cross-sectional areas. In the example shown in Fig. 3, the inlet-side vent pipe 12 and the outlet-side vent pipe 16 are arranged so that their central axes coincide, but this is not limitative, and the central axes of the inlet-side vent pipe 12 and the outlet-side vent pipe 16 may be misaligned.

[0035] In the following description, the direction in which the inlet vent pipe 12, the expansion portion 14, and the outlet vent pipe 16 are arranged is also referred to as the flow path direction.

[0036] The expansion section 14 is disposed between the inlet ventilation pipe 12 and the outlet ventilation pipe 16 and transports the gas flowing in from the inlet ventilation pipe 12 to the outlet ventilation pipe 16 .

[0037] The cross-sectional area of ​​the expansion section 14 perpendicular to the flow path direction is larger than that of the inlet vent pipe 12 and also larger than that of the outlet vent pipe 16. That is, for example, if the cross-sectional shapes of the inlet vent pipe 12, the outlet vent pipe 16, and the expansion section 14 are circular, the diameter of the cross section of the expansion section 14 is larger than the diameters of the inlet vent pipe 12 and the outlet vent pipe 16.

[0038] The cross-sectional shape of the expansion section 14 may be various shapes such as circular, rectangular, triangular, etc. Furthermore, the cross-sectional shape of the expansion section 14 does not have to be constant in the axial direction of the central axis of the expansion section 14. For example, the diameter of the expansion section 14 may vary in the axial direction.

[0039] A first opening structure 20 is arranged at the position where the expansion section 14 connects to the inlet side ventilation pipe 12, and a second opening structure 24 is arranged at the position where the expansion section 14 connects to the outlet side ventilation pipe 16. In addition, a porous sound-absorbing material 30 is arranged along the inner peripheral surface of the expansion section 14.

[0040] The porous sound-absorbing material 30 is a type of sound-absorbing structure in the present invention, and is disposed within the expansion section 14 to absorb and muffle sound. In the illustrated example, the porous sound-absorbing material 30 is disposed along the inner peripheral surface of the expansion section 14. In addition, in the illustrated example, the length of the porous sound-absorbing material 30 in the flow path direction substantially coincides with the length of the expansion section 14 in the flow path direction. Furthermore, it is preferable that the thickness of the porous sound-absorbing material 30 in a direction perpendicular to the flow path direction is such that it does not overlap with the air vent pipe when viewed from the flow path direction. In the illustrated example, the porous sound-absorbing material 30 is thick enough to contact the maximum diameter portion of the first opening structure 20 and the maximum diameter portion of the second opening structure 24.

[0041] For example, if the expansion section 14 is cylindrical, the porous sound-absorbing material 30 may have a cylindrical shape that fits along the circumferential surface of the expansion section 14. Also, if the expansion section 14 is square-tube shaped, the porous sound-absorbing material 30 may have a square-tube shape that fits along the circumferential surface of the expansion section 14.

[0042] The first opening structure 20 is disposed adjacent to the connecting portion with the inlet-side vent pipe 12 within the expansion section 14, and has a structure that gradually reduces acoustic impedance from the inlet-side vent pipe 12 side toward the outlet-side vent pipe 16 side. In the example shown in Fig. 3, the first opening structure 20 has a cylindrical shape with an opening area that gradually increases from the end of the inlet-side vent pipe 12 toward the end on the outlet-side vent pipe 16 side, thereby gradually reducing acoustic impedance.

[0043] In the illustrated example, the shape and area of ​​the opening of the first opening structure 20 on the inlet side vent pipe 12 side are approximately the same as the cross-sectional shape and cross-sectional area of ​​the inlet side vent pipe 12. In addition, the end face of the first opening structure 20 on the outlet side vent pipe 16 side is not in contact with the circumferential surface of the extension section 14. In the illustrated example, the end face of the first opening structure 20 on the outlet side vent pipe 16 side is in contact with the porous sound-absorbing material 30 arranged along the inside of the circumferential surface of the extension section 14.

[0044] The first opening structure 20 does not contact the peripheral surface of the extension section 14, and therefore forms a first rear space 22 between the first opening structure 20 and the extension section 14. Specifically, the first rear space 22 is a space surrounded by the first opening structure 20, the side surface of the extension section 14 on the inlet side ventilation pipe 12 side, and the peripheral surface of the extension section 14, as shown by the area indicated by the dashed line in FIG. 3. This first rear space 22 is open on the outlet side ventilation pipe 16 side. As shown in FIG. 4, this first rear space 22 is formed by the first termination structure 5 (Z in FIG. 4). end1 (denoted by ).

[0045] The second opening structure 24 is disposed adjacent to the connecting portion with the outlet-side vent pipe 16 within the expansion section 14, and has a structure that gradually increases the acoustic impedance from the side of the inlet-side vent pipe 12 toward the side of the outlet-side vent pipe 16. In the example shown in Fig. 3, the second opening structure 24 has a cylindrical shape with an opening area that gradually decreases from the end of the inlet-side vent pipe 12 toward the end of the outlet-side vent pipe 16, thereby gradually increasing the acoustic impedance.

[0046] In the illustrated example, the shape and area of ​​the opening of the second opening structure 24 on the side of the outlet-side vent pipe 16 are approximately the same as the cross-sectional shape and cross-sectional area of ​​the outlet-side vent pipe 16. Furthermore, the end face of the second opening structure 24 on the side of the inlet-side vent pipe 12 does not contact the circumferential surface of the extension section 14. In the illustrated example, the end face of the second opening structure 24 on the side of the inlet-side vent pipe 12 contacts the porous sound-absorbing material 30 arranged along the inside of the circumferential surface of the extension section 14.

[0047] The second opening structure 24 does not contact the peripheral surface of the extension section 14, and therefore forms a second rear space 26 between the second opening structure 24 and the extension section 14. Specifically, the second rear space 26 is a space surrounded by the second opening structure 24, the side surface of the extension section 14 on the outlet-side ventilation pipe 16 side, and the peripheral surface of the extension section 14, as shown by the broken line in FIG. 3. This second rear space 26 is open on the inlet-side ventilation pipe 12 side. As shown in FIG. 4, this second rear space 26 is formed by the second termination structure 8 (Z in FIG. 4). end2 (denoted by ).

[0048] As mentioned above, silencers with expansion chambers muffle sound by reflecting it. When a reflection-type silencer is used, the sound reflected by the silencer interferes with the incident sound, resulting in a large amplitude and dense distribution of sound pressure in front of the silencer's entrance. This large, distributed sound excites vibrations in the housing in front of the silencer (such as hose and duct vibrations), which can easily radiate noise to the outside, creating a problem. In addition, the reflected sound can sometimes be reflected back, further increasing the sound pressure. For this reason, there was a demand for a ventilation-type silencer that muffles sound by absorbing it rather than reflecting it.

[0049] Furthermore, in the expansion type silencer, there is a problem in that wind noise is generated when wind flows into the expansion chamber.

[0050] Furthermore, in expansion-type silencers, strong reflections at the entrance to the expansion chamber cause strong longitudinal resonance within the expansion chamber, resulting in frequencies that are transmitted resonantly (frequencies that have no sound-silencing effect). Countermeasures for the transmitted resonance that occurs on the low-frequency side have been particularly difficult.

[0051] In contrast, the ventilation type silencer of the present invention has a first opening structure 20 that gradually reduces the acoustic impedance from the connection between the extension section 14 and the inlet side ventilation pipe 12 toward the outlet side ventilation pipe 16 side, and therefore can suppress reflection of sound when it propagates from the inlet side ventilation pipe 12 to the extension section 14, and can increase the sound that propagates into the extension section 14. Therefore, the amount of sound absorbed by the sound absorbing structure (porous sound absorbing material) arranged in the extension section 14 can be increased, and sound silencing by sound absorption can be performed favorably.

[0052] Furthermore, wind noise is a phenomenon that occurs when vortices are generated at positions where the acoustic impedance changes suddenly. In contrast, the ventilation silencer of the present invention has the first opening structure 20 that gradually reduces the acoustic impedance, so it is possible to suppress the generation of vortices when sound propagates from the inlet ventilation pipe 12 to the extension part 14, thereby preventing the generation of wind noise.

[0053] Furthermore, the ventilation type silencer of the present invention forms a first back space 22 between the first opening structure 20 and the extension portion 14. This first back space 22 acts as a resonator with a lower resonance frequency than a normal air column resonator (the action of a Helmholtz resonator is mixed in) because the size of the opening communicating with the extension portion 14 is reduced by the first opening structure, and it is possible to silence sounds in the low frequency band.

[0054] 3 has, as a preferred embodiment, a second opening structure 24 that gradually increases the acoustic impedance from within the extension portion 14 toward the connection between the extension portion 14 and the outlet-side ventilation pipe 16. By having the second opening structure 24, it is possible to suppress excitation of vibrations of the housing, and also to suppress reflected sound from returning by re-reflection, thereby further increasing the sound pressure.

[0055] In addition, the ventilation type silencer 10a has a second opening structure 24, which suppresses reflection of sound as it propagates from the extension section 14 to the outlet side ventilation pipe 16, suppresses the generation of vortices, and prevents the generation of wind noise.

[0056] Furthermore, since the ventilation type silencer 10a forms the second back space 26 between the second opening structure 24 and the extension portion 14, the second back space 26 has a smaller opening size that communicates with the extension portion 14, and therefore acts as a resonator with a lower resonance frequency than a normal air column resonator (the effect of a Helmholtz resonator is mixed in), and can silence sounds in the low frequency band.

[0057] The first opening structure 20 and the second opening structure 24 have basically the same configuration except for their different placement positions and orientations, and therefore in the following description, when there is no need to distinguish between the first opening structure 20 and the second opening structure 24, they will be collectively referred to as the "opening structures."

[0058] In the example shown in FIG. 3, the ventilation type silencer 10a is configured to have the second opening structure 24, but is not limited to this and may have at least the first opening structure 20.

[0059] 3, the porous sound-absorbing material 30 is arranged over the entire area of ​​the extension section 14 in the flow path direction, that is, the porous sound-absorbing material 30 is arranged also in the first rear space 22 and the second rear space 26, but this is not limiting. For example, as in the ventilation type silencer 10b shown in FIG. 5, the porous sound-absorbing material 30 may be arranged between the first opening structure 20 and the second opening structure 24, and not in at least one of the first rear space 22 and the second rear space 26.

[0060] A configuration in which the porous sound-absorbing material 30 is disposed in the first back space 22 and the second back space 26 can increase the amount of sound absorption. On the other hand, a configuration in which the porous sound-absorbing material 30 is not disposed in at least one of the first back space 22 and the second back space 26 can effectively muffle low-frequency band sounds by utilizing the effect of the back space as a Helmholtz resonator.

[0061] Furthermore, it is not necessary to arrange porous sound-absorbing material on the entire surface of the extension portion 14. For example, a rectangular extension portion can have porous sound-absorbing material arranged on two opposing surfaces, with no porous sound-absorbing material arranged on the remaining two surfaces. This eliminates the need for porous sound-absorbing material on two surfaces, thereby making it possible to achieve a thinner ventilation type silencer. Furthermore, the thickness of the porous sound-absorbing material may be varied depending on the location, and for example, the porous sound-absorbing material arranged on the two opposing surfaces may be thin porous sound-absorbing material.

[0062] 40 , for example, in an extension section 14 having a rectangular cross section, the porous sound-absorbing material 30 may be arranged so as to be in contact with the first opening structure 22 and the second opening structure 24, and a space 14a may be formed on the back side of the porous sound-absorbing material 30 (the side opposite to the first opening structure 22 and the second opening structure 24). In this configuration, the wind flowing through the ventilation type silencer does not easily pass through the porous sound-absorbing material 30, so the wind flow path smoothly connects from the first opening structure 22 to the porous sound-absorbing material 30 and the second opening structure 24, resulting in a structure that is less likely to generate wind noise. This configuration makes it possible to reduce the amount of porous sound-absorbing material 30 used compared to when porous sound-absorbing material 30 is arranged in the entire extension section 14.

[0063] Furthermore, if the length of the first opening structure 20 in the flow path direction is a, the length of the second opening structure 24 in the flow path direction is b, and the length of the extension section 14 in the flow path direction is L (see Figure 6), in the case where the ventilation type silencer has the first opening structure 20 and the second opening structure 24, when the sum of the length a of the first opening structure 20 in the flow path direction and the length b of the second opening structure 24 in the flow path direction is a2, it is preferable that 0.2≦a2 / L≦0.8, more preferably 0.3≦a2 / L≦0.7, and even more preferably 0.4≦a2 / L≦0.6.

[0064] Furthermore, when the ventilation type silencer has a configuration having a first opening structure 20 but not a second opening structure 24, the length a of the first opening structure 20 in the flow path direction and the length L of the extension portion 14 in the flow path direction are preferably 0.2≦a / L≦0.8, more preferably 0.25≦a / L≦0.65, and even more preferably 0.3≦a / L≦0.5.

[0065] When the ratio of the total length of the opening structures (or the length of the first opening structures) to the length of the extension section 14 is large, it is possible to more effectively suppress the reflection of sound propagating from the inlet side ventilation pipe 12 to the extension section 14, or the reflection of sound propagating from the extension section 14 to the outlet side ventilation pipe 16. On the other hand, when the ratio of the total length of the opening structures (or the length of the first opening structures) to the length of the extension section 14 is small, the area with which sound comes into contact with the porous sound-absorbing material 30 increases, and the sound absorption effect can be further improved.

[0066] Furthermore, it is preferable that the length a of the first opening structure 20 is longer than the length b of the second opening structure 24. By increasing the length of the first opening structure 20, it is possible to preferably prevent the sound propagating from the inlet-side ventilation pipe 12 to the extension section 14 from being reflected, while increasing the area over which the sound comes into contact with the porous sound-absorbing material 30, thereby further enhancing the sound absorption effect.

[0067] Here, the shape of the opening structure is not particularly limited as long as it is configured so that the acoustic impedance changes gradually. Examples of the opening structure will be described with reference to Figs.

[0068] The opening structure 20a shown in FIG. 7 has a truncated cone shape and has an opening that penetrates from the upper base to the lower base. The opening structure 20b shown in FIG. 8 has a shape obtained by rotating a curved line convex toward the central axis around the central axis. FIG. 8 can also be said to have a shape in which the peripheral surface of the truncated cone cylindrical shape shown in FIG. 7 is curved convexly toward the central axis. The curved shape of the peripheral surface of the opening structure 20b can be various shapes as long as the cross-sectional area gradually increases along the central axis. For example, the opening structure 20b can have a peripheral shape expressed by an exponential function in a cross section parallel to the central axis. Alternatively, the opening structure 20b can have a peripheral shape expressed by 1 / 4 of an elliptical arc in a cross section parallel to the central axis. 9 has a shape that has, along the central axis, a portion where the diameter monotonically increases, a portion where the diameter is constant, and a portion where the diameter monotonically increases. That is, in the aperture structure 20c, the acoustic impedance changes stepwise.

[0069] The opening structure 20d shown in Fig. 10 has two curved plate-like members, and the width between the two plate-like members gradually increases from one end to the other end. Furthermore, the opening structure 20d is open in the vertical direction in the figure. The opening structure may be only one of the structures shown in Fig. 10. As shown in Fig. 41, a gradually enlarging opening structure can be realized by using a structure in which one side is a wall and the other side is a curved plate-like member.

[0070] In this way, the opening structures may be configured so that they are not closed in cross section at the end on the other vent pipe side, i.e., the first opening structure may be configured so that they are not closed in cross section at the end on the outlet vent pipe side, and the second opening structure may be configured so that they are not closed in cross section at the end on the inlet vent pipe side.

[0071] 11 has a rectangular cross-sectional shape, and has a shape in which the cross-sectional area expands along the central axis while maintaining a similar shape. That is, the opening structure 20e has a truncated quadrangular pyramid shape and has an opening that penetrates from the upper base to the lower base. The opening structure 20f shown in FIG. 12 has a shape in which each of the four side surfaces of the opening structure 20e shown in FIG. 11 is convex toward the central axis when viewed in a cross section perpendicular to the central axis, and has a shape in which the cross-sectional area expands along the central axis while maintaining a similar shape.

[0072] Furthermore, the opening structure is not limited to a shape in which the cross section expands as in the above-mentioned examples, and may have a configuration in which the thickness of the opening structure (20g, 24g) at the end gradually decreases, as in the example shown in FIG. 42. That is, the first opening structure 20g has the same cross section as the inlet-side vent pipe 12, and the thickness of the end on the outlet-side vent pipe 16 side gradually decreases toward the outlet-side vent pipe 16 side. The second opening structure 24g has the same cross section as the outlet-side vent pipe 16, and the thickness of the end on the inlet-side vent pipe 12 side gradually decreases toward the inlet-side vent pipe 12 side. The first opening structure 20g and the inlet-side vent pipe 12 may be formed integrally. The second opening structure 24g and the outlet-side vent pipe 16 may be formed integrally.

[0073] 42, when the inlet-side ventilation pipe 12 and the outlet-side ventilation pipe 16 have an inner diameter of 30 mm and a thickness of 2 mm, the ratio of the area of ​​the inner diameter (34 mm diameter) of the tip end (the other ventilation pipe side) to the area of ​​the inner diameter of the base end (the ventilation pipe side to be connected) of the first opening structure 20 g and the second opening structure 24 g is 1.28, and when the thickness is 3 mm, the ratio of the area of ​​the inner diameter of the tip end to the area of ​​the inner diameter of the base end is 1.44, and the first opening structure 20 g and the second opening structure 24 g each have a structure in which the acoustic impedance changes sufficiently. As in the example shown in FIG. 42, by configuring the first opening structure 20 g and the second opening structure 24 g to have regions where the thickness gradually decreases, the change in acoustic impedance can be made gentler and wind noise can be reduced. It is also desirable to have the outer shape of the opening structure kept constant and gradually widen the inside, but it may also be possible to have a structure in which the tip is made thin and pointed.

[0074] Furthermore, as in the example shown in Figure 42, the first opening structure 20g and the second opening structure 24g may have a region with a constant thickness over a certain length and a region where the thickness gradually becomes thinner toward the tip, or may be composed only of a region where the thickness gradually becomes thinner. Furthermore, the opening structure may have an expanding cross-sectional shape (external shape) as shown in the examples of FIGS. 3 to 12, and the thickness of the end portion may be gradually reduced.

[0075] In this way, the opening structure can have a variety of shapes as long as it is configured so that the acoustic impedance changes gradually. When the cross-sectional shape of the expansion portion 14 is circular, it is preferable that the opening structure has a circular cross-sectional shape as in the examples shown in Figures 7 to 9, and when the cross-sectional shape of the expansion portion 14 is rectangular, it is preferable that the opening structure has a substantially rectangular cross-sectional shape as in the examples shown in Figures 10 to 12.

[0076] The cross-sectional shape of the opening structure perpendicular to the central axis preferably has two-fold or more symmetry, and more preferably has four-fold or more symmetry.

[0077] Furthermore, the change in acoustic impedance due to the opening structure may be a monotonic change, may have a changing rate, or may change stepwise.

[0078] In order to suppress reflection of sound as it propagates from the inlet ventilation pipe 12 to the expansion section 14, the ratio of the minimum acoustic impedance to the maximum acoustic impedance in the opening structure is preferably 0.6 or less, more preferably 0.5 or less, and even more preferably 0.35 or less.

[0079] Furthermore, it is preferable that the cutoff frequency fc determined by the shape of the opening structure is 2000 Hz or less.

[0080] The cutoff frequency fc is determined by the shape and length of the wide opening structure, and represents the high-pass filter characteristics in which sounds with frequencies above fc pass through without loss, but sounds with frequencies below fc are reflected exponentially in the longitudinal direction and no longer propagate. In the case of an aperture structure that expands exponentially as shown in Figure 8, when the radius r = r0 × exp(m × x) (m is the shape constant of the aperture structure, x is the position in the flow path direction, and r0 is the radius of the inlet), it is determined by fc = m × c0 / 2pi (c0 is the speed of sound, and pi is the circular constant). If the length of the opening structure in the flow path direction is a and the radius of the end of the opening structure is R, then R = r0 × exp(m × L), so m = 1 / L × ln(R / r0), and therefore fc is determined as c0 × ln(R / r0) / (2pi × L).

[0081] Since sound above fc easily passes through the silencer and is more easily absorbed, reducing fc can improve absorption. fc can be reduced by increasing the length L or by reducing the maximum diameter R of the opening structure. The above describes an aperture structure that expands exponentially, but for other shapes, the cutoff frequency fc can be similarly determined by solving the wave equation to find the solution conditions for wave propagation.

[0082] According to sound energy using A-weighting, the energy in the audible range is approximately 50% below 2kHz and approximately 50% above 2kHz, so if fc is below 2kHz, 50% of the energy can be transmitted without loss. Therefore, fc should be below 2000Hz, more preferably below 1250Hz (70% energy), even more preferably below 1000Hz (80%), and most preferably below 630Hz (90%).

[0083] Also, as shown in Figure 3, the connection positions on the side of the expansion section 14 with the inlet side ventilation pipe 12 and the first opening structure 20, as well as the connection positions with the outlet side ventilation pipe 16 and the second opening structure 24 are not particularly limited, but are preferably located in the center of the side of the expansion section 14.

[0084] 3, the inlet-side ventilation pipe 12 and the outlet-side ventilation pipe 16 are configured so that their central axes are aligned in the same straight line, but this is not limiting. For example, as in the examples shown in FIGS. 43 and 44, the inlet-side ventilation pipe 12 and the outlet-side ventilation pipe 16 may be configured so that their central axes are not aligned in the same straight line. Even in such a configuration, the first opening structure and the second opening structure can be disposed.

[0085] 43, the first opening structure 20h has a configuration in which two plate-like members are arranged facing each other, and the two plate-like members are curved so as to bend the flow path in the direction connecting the inlet side vent pipe 12 and the outlet side vent pipe 16, and the tip side of one of the plate-like members (the outlet side vent pipe 16 side) has a wide structure (curved structure) in which the acoustic impedance changes. Also, the second opening structure 24h has a configuration in which two plate-like members are arranged facing each other, and the two plate-like members are curved so as to bend the flow path from the direction connecting the inlet side vent pipe 12 and the outlet side vent pipe 16 to the flow direction of the outlet side vent pipe 16, and the tip side of one of the plate-like members (the inlet side vent pipe 12 side) has a wide structure (curved structure) in which the acoustic impedance changes. In the example shown in Figure 43, the first opening structure 20h and the second opening structure 24h are configured so that one of the plate-like members has a wide structure in which the acoustic impedance changes, but both plate-like members may also be configured so that they have a wide structure (curved structure) in which the acoustic impedance changes. The flow velocity of the air flowing from the inlet side ventilation pipe 12 to the outlet side ventilation pipe 16 becomes larger on the outside side of the flow path bent at the inlet side, so by providing a wide structure (curved structure) that changes the acoustic impedance on the outside side of the flow path bent at the inlet part, as shown in Figure 43, the flow velocity on the outside side can be particularly reduced, which is a desirable configuration for reducing wind noise.

[0086] In addition, the first opening structure of Figure 44 has two plate-like members with different radii of curvature, and by increasing the radius of curvature of the plate-like member on the outside of the curved flow path or by increasing its length, the acoustic impedance can be configured to change gradually.

[0087] Furthermore, even if the central axes of the inlet side ventilation pipe 12 and the outlet side ventilation pipe 16 are not collinear, the opening structure may have a region where the thickness gradually decreases, thereby allowing the acoustic impedance to change gradually. In the example shown in Fig. 45, the first opening structure 20j is made of two plate-like members, and the two plate-like members are curved so as to bend the flow path in the direction connecting the inlet side ventilation pipe 12 and the outlet side ventilation pipe 16. In addition, the tip side (the outlet side ventilation pipe 16 side) of the plate-like members constituting the first opening structure 20j has a region where the wall thickness gradually becomes thinner. In addition, the second opening structure 24j is made of two plate-like members, and the two plate-like members are curved so as to bend the flow path from the direction connecting the inlet side ventilation pipe 12 and the outlet side ventilation pipe 16 to the flow direction of the outlet side ventilation pipe 16. In addition, the tip side (the inlet side ventilation pipe 12 side) of the plate-like members has a region where the wall thickness gradually becomes thinner.

[0088] Furthermore, as shown in Figure 45, even in a configuration in which the central axes of the inlet side ventilation pipe 12 and the outlet side ventilation pipe 16 are not collinear, a space 14a may be formed on the back side of the porous sound-absorbing material 30 (the side opposite to the first opening structure 22j and the second opening structure 24j).

[0089] Furthermore, the average roughness Ra of the inner surface of the aperture structure (the surface on the central axis side) is preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.1 mm or less. By reducing the average roughness Ra of the inner surface of the aperture structure, it is possible to suppress wind noise caused by vortices being generated by the wind flowing over the surface of the aperture structure being separated.

[0090] Furthermore, the change in acoustic impedance of the opening structure may be continuous to the outside of the extension section 14. For example, as shown in FIG. 13 , the first opening structure 20 may be disposed from the inlet-side vent pipe 12 to the inside of the extension section 14, and may have a shape in which the cross-sectional area increases from the end on the inlet-side vent pipe 12 side toward the end on the extension section 14 side so that the acoustic impedance gradually decreases therebetween. Similarly, as shown in FIG. 13 , the second opening structure 24 may be disposed from the extension section 14 to the inside of the outlet-side vent pipe 16, and may have a shape in which the cross-sectional area decreases from the end on the extension section 14 side toward the end on the outlet-side vent pipe 16 side so that the acoustic impedance gradually increases therebetween. This configuration can make the change in impedance smoother.

[0091] Furthermore, when it is assumed that the ventilation type silencer of the present invention will be used in connection with a hose, it is desirable that the inlet and outlet of the ventilation type silencer have an uneven shape and / or a bellows shape on the outer circumferential surface. When connected to a hose, this will be tightly fastened, thereby preventing wind leakage, sound leakage, sound reflection, etc.

[0092] In the first back space 22 and the second back space, the ratio of the acoustic impedance at the entrance of the back space to the minimum acoustic impedance of the back space is preferably 1.1 or more, and more preferably 1.4 or more. When the acoustic impedance ratio is 1.1, the frequency at which the transmission loss is maximum shifts to the lower frequency side by about 5%, and when the acoustic impedance ratio is 1.4, the frequency at which the transmission loss is maximum shifts to the lower frequency side by about 10%, allowing for more efficient sound attenuation at low frequencies. This will be explained in the examples below.

[0093] Materials for forming the vent pipe, extension portion, and opening structure include metal materials, resin materials, reinforced plastic materials, carbon fiber, etc. Metal materials include, for example, aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium molybdenum, nichrome molybdenum, and alloys thereof. Examples of resin materials include acrylic resin (PMMA), polymethyl methacrylate, polycarbonate, polyamide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate (PET), polyimide, triacetyl cellulose (TAC), polypropylene (PP), polyethylene (PE), polystyrene (PS), ABS resin (acrylonitrile, butadiene, styrene copolymer synthetic resin), flame-retardant ABS resin, ASA resin (acrylonitrile, styrene, acrylate copolymer synthetic resin), PVC (polyvinyl chloride) resin, and PLA (polylactic acid) resin. Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP).

[0094] From the viewpoint of weight reduction and ease of molding, it is preferable to use a resin material as the material for the ventilation type silencer. Also, as mentioned above, it is preferable to use a material with high rigidity from the viewpoint of sound insulation in the low frequency range. From the viewpoint of weight reduction and sound insulation, the density of the members constituting the ventilation type silencer is 0.5 g / cm 3 ~2.5g / cm 3 It is preferable that:

[0095] As described above, the ventilation type silencer of the present invention may have a sound absorbing structure within the expansion portion.

[0096] Examples of sound-absorbing structures include porous sound-absorbing materials, plates or membranes with fine through-holes (micro-perforated plates (MPPs)), and resonant sound-absorbing structures such as air column resonators and Helmholtz resonators.

[0097] The porous sound-absorbing material is not particularly limited, and conventionally known sound-absorbing materials can be appropriately used. For example, foams, foam materials (urethane foam (e.g., "Calmflex F Series" by Inoac Corporation, urethane foam by Hikarisha, "MIF" by Tokai Rubber Industries, etc.), soft urethane foam, ceramic particle sintered material, phenol foam, melamine foam ("Basotect" by BASF (Japanese name: "Basotect")), polyamide foam, etc.), nonwoven fabric sound-absorbing materials (microfiber nonwoven fabric (e.g., "Thinsulate" by 3M, "Milife MF" by ENEOS Techno Materials, "Micromat" by Taihei Felt Industries, etc.), polyamide foam, etc.), etc. Various known sound-absorbing materials can be used, including polyester nonwoven fabrics (for example, "White Qon" by Tokyo Bouon Co., Ltd., "QonPET" by Bridgestone KBG Corporation, and "Synthfiber" by Toray Industries, Inc.), plastic nonwoven fabrics such as acrylic fiber nonwoven fabrics, natural fiber nonwoven fabrics such as wool and felt, metal nonwoven fabrics, glass nonwoven fabrics, cellulose nonwoven fabrics, and other materials containing minute air bubbles (glass wool, rock wool, nanofiber sound-absorbing materials (silica nanofiber, acrylic nanofiber (for example, "XAI" by Mitsubishi Chemical Corporation)). Alternatively, a sound-absorbing material having a two-layer structure consisting of a thin, high-density surface nonwoven fabric and a low-density backing nonwoven fabric may be used. For sound-absorbing materials that are provided with multiple layers of different densities, such as a two-layer structure consisting of a thin, high-density, low-porosity surface nonwoven fabric and a low-density, high-porosity backing nonwoven fabric layer, or a polyurethane-based material with a surface coating, it is desirable to position the high-density layer (low-porosity layer) as the flow path surface in order to improve the fluid characteristics (wind flow).

[0098] Micro-perforated plates include aluminum micro-perforated plates (Suohno manufactured by Daiken Corporation) and polyvinyl chloride resin micro-perforated plates (Di-Noc manufactured by 3M), and can also absorb sound using plates or membranes with countless through-holes about 100 μm in diameter and a back space.

[0099] It is desirable that these materials have non-combustible, flame-retardant and self-extinguishing properties. It is also desirable that the entire ventilation type silencer has non-combustible, flame-retardant and self-extinguishing properties. [Example]

[0100] The present invention will be described in more detail below with reference to examples. The materials, amounts used, ratios, treatment contents, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the examples shown below.

[0101] [Comparative Example 1] An extension section was created by preparing a cylinder with an inner diameter of 80 mm and a length of 200 mm, and two disks with the same diameter as both end faces of the cylinder and a 28 mm diameter hole in the center. The disks were attached to both end faces of the cylinder and acoustically sealed with tape. Cylindrical inlet and outlet vent pipes with an inner diameter of 28 mm and a length of 50 mm were prepared, and connected by aligning the center of the hole on the end face of the extension section with the center of the cylinder. The extension section and vent pipe were made of ABS resin using a 3D printer (manufactured by XYZ Printing Co., Ltd.). The ABS resin was 3 mm thick. A 15mm thick porous sound-absorbing material (QonPET, manufactured by Bridgestone KBG Corporation) was placed along the inner wall of the cylinder within the expansion section, creating a ventilation silencer with air in a 50mm diameter area within the expansion section and 15mm of porous sound-absorbing material around the outer periphery.

[0102] According to the transfer matrix measurement method using an acoustic tube (ASTM E2611), the transmittance and reflectance of sound incident on a ventilation silencer were measured using a four-terminal microphone method using an acoustic tube. The absorption rate, which is the amount lost within the ventilation silencer, was calculated by defining the absorption rate as (1 - transmittance - reflectance).

[0103] Comparative Example 2 Two straight hollow cylinders made of ABS (outer diameter 31 mm, inner diameter 28 mm, length 50 mm) were prepared and attached with the centers of their openings aligned with the connection positions of the inlet side ventilation pipe and the outlet side ventilation pipe in the expansion section of Comparative Example 1. In this way, a ventilation type silencer with two 50 mm straight tubes inside was produced. In other words, the opening structure of Comparative Example 2 does not change the acoustic impedance. The absorption rate of the produced ventilation type silencer was determined in the same manner as in Comparative Example 1.

[0104] [Example 1] Two horn-shaped tubes (narrow inner diameter 28 mm, wide inner diameter 50 mm, length in the flow path direction 50 mm, thickness 1.5 mm, made of ABS) with openings on both sides were fabricated using a 3D printer. The horn diameter expanded exponentially. A ventilation silencer was produced in the same manner as in Comparative Example 1, except that this horn-shaped tube was used as the opening structure, and the narrow side (28 mm diameter side) opening was aligned and attached to the connection part between the expansion part and the inlet side ventilation pipe and the connection part between the expansion part and the outlet side ventilation pipe. The absorption rate of the produced ventilation type silencer was determined in the same manner as in Comparative Example 1. The results are shown in the graph of FIG.

[0105] In Comparative Example 1, which had no opening structure, and Comparative Example 2, which had a straight tubular opening structure, the absorption rate was approximately 50% at most. On the other hand, in the case of Example 1 of the present invention, the absorption increased as the frequency increased, and the absorption rate was 85% or more at 2000 Hz or higher. In this way, it can be seen that the absorption rate inside the extension portion can be increased by providing an opening structure in which the acoustic impedance changes gradually.

[0106] [Examples 2 to 7] The length of the expansion portion was kept at 200 mm, the porous sound-absorbing material was not changed, and the diameter at both ends of the opening structure was not changed, but the length of the opening structure was changed, and opening structures were produced in the same manner as in Example 1. The length of the opening structure was 20 mm in Example 2, 30 mm in Example 3, 40 mm in Example 4, 60 mm in Example 5, 70 mm in Example 6, and 80 mm in Example 7. The absorbency was evaluated for each example in the same manner.

[0107] [Comparative Examples 3 to 8] Except for changing the length of the aperture structure, aperture structures were fabricated in the same manner as in Comparative Example 2. The length of the aperture structure was 20 mm in Comparative Example 3, 30 mm in Comparative Example 4, 40 mm in Comparative Example 5, 60 mm in Comparative Example 6, 70 mm in Comparative Example 7, and 80 mm in Comparative Example 8. The absorbency was evaluated for each comparative example in the same manner.

[0108] In order to compare the amount of absorption across all frequencies for the measured absorption rates of each Example and Comparative Example, two indices were calculated: the average value of the absorption rate from 100 to 4000 Hz (logarithmically integrated on the frequency axis) and the average value of the absorption rate from 1000 Hz to 4000 Hz. The results are shown in the graphs of FIGS.

[0109] 15 and 16 show that providing an aperture structure in which the acoustic impedance changes gradually increases the absorption rate compared to when there is no aperture structure. On the other hand, it was also found that providing a straight tubular aperture structure reduces the absorption rate. In the case of the straight pipe opening structure, it is presumed that the absorption rate was uniformly reduced because the area in contact with the porous sound-absorbing material was reduced by adding the structure. In the case of an opening structure with a gradual change in acoustic impedance, the absorption rate was highest when the length was 50 mm. As the length of the opening structure increased, the effect of suppressing sound reflection at the connection between the expansion section and the ventilation pipe improved, which increased the absorption rate, but the area in contact with the porous sound-absorbing material decreased, which decreased the absorption rate.

[0110] Comparative Example 9 A ventilation type silencer was produced in the same manner as in Comparative Example 1, except that the length of the extension portion was set to 300 mm.

[0111] [Examples 8 to 14] Ventilation type silencers were produced in the same manner as in Examples 1 to 7, except that the length of each extension portion was set to 300 mm.

[0112] [Examples 15 to 19] Ventilation type silencers were produced in the same manner as in Example 8, except that the lengths of the opening structures were set to 90 mm, 100 mm, 110 mm, 120 mm, and 130 mm, respectively.

[0113] The absorbance was measured in the same manner as above for Comparative Example 9 and Examples 8 to 19, and two indices were calculated for the measured absorbance of each Example and Comparative Example: the average absorbance from 100 to 4000 Hz and the average absorbance from 1000 Hz to 4000 Hz. The results are shown in the graphs of FIGS.

[0114] 17 and 18 show that by providing an opening structure in which the acoustic impedance gradually changes, the absorption rate is higher than in Comparative Example 9, which does not have an opening structure. Furthermore, the absorption rate is particularly high when the length of the opening structure is approximately 50 mm to 110 mm, and the absorption rate at 1 kHz or higher is greatest when the length is 70 to 80 mm.

[0115] [simulation] To obtain the ideal resonance characteristics of the ventilation silencer, a simulation was performed using the finite element method (COMSOL MultiPhysics ver. 5.5, COMSOL Inc.). The transmission losses were determined for Calculation Example 1, which was performed under the same conditions as Comparative Example 1, Calculation Example 2, which was performed under the same conditions as Comparative Example 2, Calculation Example 3, which was performed under the same conditions as Example 1, and Calculation Example 4, which was the same as Calculation Example 3 except that the maximum diameter of the opening structure was set to 70 mm. No sound-absorbing material was used in any of the calculations. The results are shown in Figure 19.

[0116] Calculation Example 1, which does not have an opening structure, shows a spectrum with transmission resonance (wavelength λ / 2 resonance). By installing an opening structure, the back space formed between the opening structure and the peripheral surface of the expansion section resonates, significantly insulating sound at specific frequencies. In Calculation Example 2, which has a straight-tube opening structure, the resonance corresponds to the resonance of a one-sided closed tube, where a is approximately λ / 4, assuming the length of the opening structure is a. Calculation Examples 3 and 4 show that installing an opening structure can also insulate sound at lower frequencies. If we assume that only the change in the open-end correction at the entrance to the back space contributes to the resonance frequency, then when the diameter of the opening structure is small (when the entrance area of ​​the back space is large), the open-end correction becomes larger, resulting in lower frequencies. In fact, lower frequencies are observed when the diameter of the opening structure is large, indicating that the principle of resonance has changed. The acoustic impedance is highest at the entrance to the back space due to its small area, and the acoustic impedance is lower inside the back space. Although the structure is different from Helmholtz resonance (a structure with a narrow opening and a closed space at the back), it is thought that the low frequency was achieved using a similar principle.

[0117] Calculation Example 4, where the maximum diameter of the aperture structure was 70 mm, had a larger shift to the low frequency side than Calculation Example 3, where the maximum diameter of the aperture structure was 50 mm. Models were created in which the maximum diameter was changed in 5 mm increments from 30 mm to 75 mm, and the frequency at which the transmission loss was maximum was determined for each model. The results are shown in Figure 20.

[0118] Using Calculation Example 2, which has a straight-tube opening structure, as a reference, a graph is shown in Figure 21, with the ratio of the resonant frequency to the resonant frequency of Calculation Example 2 on the vertical axis and the ratio of the acoustic impedance at the entrance to the outlet of the back space on the horizontal axis.

[0119] It was found that the frequency ratio changes as the -0.205 power of the impedance ratio. The frequency shift was 0.95 or less when the impedance ratio was 1.1 or more, and 0.90 or less when the impedance ratio was 1.4 or more.

[0120] Next, the length of the opening structure in Calculation Examples 2 to 4 was changed in 10 mm increments within the range of 20 mm to 80 mm, and the above-mentioned resonance frequency was calculated. The results are shown in Figure 22.

[0121] It can be seen that, regardless of the length, an opening structure with a gradually changing acoustic impedance is better able to insulate low-frequency sounds than a straight-tube opening structure. It can also be seen that an opening structure with a larger maximum diameter, i.e., a narrower entrance to the back space (higher acoustic impedance), is better able to insulate low-frequency sounds. From the above, it can be seen that by having an opening structure in which the acoustic impedance changes gradually, it is possible to not only increase the absorption rate but also improve sound insulation on the low frequency side. Since the wavelength is longer at lower frequencies, it is difficult to insulate sound with a silencer of the same size, but the ventilation type silencer of the present invention can insulate sound on the low frequency side with the same size.

[0122] [Comparative Examples 10 to 13] 3M Thinsulate was used as a porous sound-absorbing material, and the flow resistivity was adjusted by tearing it to reduce its density or compressing it to set the flow resistivity to 1000, 5000, 10000, and 20000 (Pa·s / m 2 ) were used to prepare ventilation type silencers of Comparative Examples 10 to 13. The flow resistivity was measured using a homemade device based on ISO 9053. It can also be determined in the same way using a flow resistance measurement system such as AirReSys manufactured by Nihon Onkyo Engineering Co., Ltd.

[0123] [Examples 20 to 23] The ventilation silencers of Examples 20 to 23 were produced in the same manner as Comparative Examples 10 to 13, except that the opening structure used in Example 1 was attached to the connection part of the expansion part with the inlet side ventilation pipe and the connection part of the expansion part with the outlet side ventilation pipe.

[0124] The transmission loss spectrum for each was calculated using the same transfer matrix method as in Comparative Example 1. Figures 23 to 26 show the transmission loss with and without an opening structure when the same porous sound-absorbing material was used. Figure 23 shows the transmission loss for a flow resistivity of 1000 (Pa s / m 2 ), and Figure 24 shows the flow resistivity of 5000 (Pa·s / m 2 ), and Figure 25 shows the flow resistivity of 10,000 (Pa·s / m 2 ), and Figure 26 shows the flow resistivity of 20,000 (Pa·s / m 2 ) is the case.

[0125] 23 to 26 show that the transmission loss on the low frequency side can be increased regardless of the flow resistivity. The larger the flow resistivity, the more the transmission loss peak shifted to the lower frequency side. This is presumably because the speed of sound in porous sound-absorbing material is slower than the speed of sound in air, which shifts the resonant frequency to the lower frequency side.

[0126] [Examples 24 to 26] Example 22 (flow resistivity 10000 (Pa·s / m 2 )) By cutting off a portion of both ends of the porous sound-absorbing material, the length of the porous sound-absorbing material was shortened so that the porous sound-absorbing material was not at the end of the expansion section. The cut-off length was 20 mm in Example 24 (length of porous sound-absorbing material: 160 mm), 40 mm in Example 25 (length of porous sound-absorbing material: 120 mm), and 60 mm in Example 26 (length of porous sound-absorbing material: 80 mm). Since the length of the opening structure was 50 mm, in Example 26 the porous sound-absorbing material was not in the back space.

[0127] The transmission loss and absorptance of Examples 24 to 26 were measured in the same manner as above, and the results are shown in Figures 27 and 28. From Figure 27, it can be seen that a high absorption rate can be obtained even if only a portion of the sound absorbing material is porous. Furthermore, from FIG. 28, it can be seen that the resonance effect of the back space on the transmission loss is seen in all examples and can be controlled by the amount of porous sound-absorbing material in the back space.

[0128] [Examples 27 and 28 and Comparative Example 14] As Example 27, a ventilation type silencer was produced in the same manner as Example 1, except that it did not have the second opening structure. As Example 28, a ventilation type silencer was produced in the same manner as in Example 27, except that the length of the first opening structure was set to 100 mm. As Comparative Example 14, a ventilation type silencer was produced in the same manner as in Example 1, except that it did not have the first opening structure. The absorbency of the prepared Examples 27 and 28 and Comparative Example 14 was measured in the same manner as above.

[0129] FIG. 29 shows a graph of the absorbance of Examples 1, 27 and 28. 29 shows that Examples 27 and 28, which have only the first opening structure arranged on the inlet side, have a higher absorption coefficient than Example 1, which has opening structures on both the inlet and outlet sides. Furthermore, the average sound absorption coefficient from 100 to 4000 Hz was 0.37 for Example 1, while Example 27 was 0.38 and Example 28 was 0.42.

[0130] FIG. 30 is a graph showing the absorbance of Example 27 and Comparative Example 14. Figure 30 shows that even with the same aperture structure, high absorption is observed when it is attached to the entrance side, but the absorption rate is approximately 50% when it is attached to the exit side. It is thought that even when an aperture structure is attached only to the exit side, a steep change in acoustic impedance occurs on the entrance side of the expansion section, causing reflection and reducing the absorption rate.

[0131] [Examples 29 and 30] A comparison was made between ventilation type silencers in which the total length of the opening structure was kept constant and the lengths of the first opening structure and the second opening structure were changed. In Example 29, a ventilation type silencer was produced in the same manner as in Example 1 except that the length of the first opening structure was 70 mm and the length of the second opening structure was 30 mm. In Example 30, a ventilation type silencer was produced in the same manner as in Example 1 except that the length of the first opening structure was 30 mm and the length of the second opening structure was 70 mm. The absorptance and transmission loss of the prepared Examples 29 and 30 were measured in the same manner as above.

[0132] FIG. 31 is a graph of the transmission loss of Examples 1, 29 and 30. From Figure 31, it can be seen that changing the length of the first opening structure and the second opening structure changes the volume of the back space, which changes the resonance frequency and therefore the transmission loss peak. Furthermore, in Examples 29 and 30, the first opening structure and the second opening structure have different lengths and back spaces of different volumes, so two transmission loss peaks appear. Both have the effect of increasing the transmission loss on the low frequency side. Furthermore, in Examples 29 and 30, the back spaces are simply swapped between the inlet and outlet sides, so the transmission losses are almost the same.

[0133] FIG. 32 is a graph of the absorbance of Examples 1, 29 and 30. As can be seen from Figure 32, the maximum absorption rate is approximately 90% in both cases. Example 29, in which the length of the first opening structure is longer, shows a higher absorption rate from the low frequency side. The importance of preventing reflection by the first opening structure on the entrance side is clear from Example 27 and Comparative Example 14, so when the lengths of the two opening structures are different, it is desirable to make the length of the first opening structure on the entrance side longer. Furthermore, in the prediction of wind noise below, a longer length of the first opening structure on the entrance side can reduce wind noise, so it is preferable to increase the length of the first opening structure.

[0134] Next, to calculate the amount of wind noise generated, a fluid calculation (CFD) was performed using the COMSOL CFD module. The wind speed incident from the inlet ventilation pipe was set to 20 m / s, and the pressure at the outlet was set to 0, and the RANS k-ω model was used for turbulent flow calculations. The calculations were performed using a sufficiently small mesh with particularly fine mesh near the wall.

[0135] Wind noise (turbulent noise) occurs when vortices are generated by turbulence caused by wind, which then generate smaller vortices, and the vibration of these tiny vortices produces sound. Therefore, we compared the amount of vortices generated inside ventilation silencers (volume integral value of vorticity) as the amount of wind noise generated from similar structures.

[0136] Fluid calculations were performed on the ventilation type silencers of Comparative Example 1 and Examples 1 to 7. The results are shown in FIG. The vorticity was greatest in Comparative Example 1, and decreased as the length of the opening structure increased. It can be seen that wind noise tends to decrease by increasing the length of the opening structure and gradual changes in acoustic impedance. This is presumably a reasonable result, as vortices and turbulence generally tend to occur where there are steep steps or slopes.

[0137] The total length of the first and second opening structures was set to 100 mm, and the length of the first opening structure was set to 30 mm, 40 mm, 50 mm, 60 mm, and 70 mm, and the vorticity was calculated in the same manner as above. The results are shown in Figure 34.

[0138] As can be seen from Figure 34, even when the total length of the opening structures is the same, the vorticity was smaller when the length of the first opening structure on the inlet side was longer. In other words, by lengthening the first opening structure and shortening the second opening structure, it is possible to reduce wind noise while maintaining the surface area that comes into contact with the porous sound-absorbing material in the expansion section.

[0139] [Comparative Examples 15 and 16] A ventilation type silencer was produced in the same manner as in Example 1, except that an opening structure having the same shape as the opening structure of Example 1 made of punched metal as shown in FIG. 35 was used. The opening ratio of the punched metal was 60%. In Comparative Example 15, the hole diameter was 5.8 mm and the pitch was 10 mm. In Comparative Example 16, the hole diameter was 1.15 mm and the pitch was 2 mm.

[0140] The area ratio of the holes in such a perforated metal in the flow path direction repeatedly increases and decreases, as shown in Figure 36. Therefore, the opening structure made of a perforated metal has a large increase and decrease in acoustic impedance in the flow path direction, as shown in Figure 37.

[0141] The absorbances of Comparative Examples 15 and 16 were measured in the same manner as above. The absorbance of Comparative Example 15 is shown in Figure 38, and the absorbance of Comparative Example 16 is shown in Figure 39. Compared with the absorption rate of Example 1, the absorption rates of both Comparative Examples 15 and 16 were smaller, and were almost the same as that of Comparative Example 1, which had no opening structure. Because the acoustic impedance of the opening structure made of perforated metal fluctuated greatly in the flow path direction, the reflection reduction effect of impedance matching was almost eliminated. The above results clearly demonstrate the effectiveness of the present invention. [Explanation of symbols]

[0142] 1a, 1b Acoustic impedance change structure 2 Entrance 3. First Impedance Matching Area 4. Constant acoustic impedance region 5 First termination structure 6 Exit section 7 Second impedance matching area 8 Second termination structure 10a, 10b Ventilation type silencer 12 Inlet ventilation pipe 14 Extension 16 Outlet side ventilation pipe 20 First opening structure 20a~20j opening structure 22 1st back space 24, 24g~24j 2nd opening structure 26 2nd rear space 30 Porous sound-absorbing material

Claims

1. An acoustic impedance changing structure through which sound propagates, a first impedance matching region connected to the inlet portion and having a gradually decreasing acoustic impedance; A constant acoustic impedance region; an outlet portion, at least in this order; The acoustic impedance at the inlet is Z in and the acoustic impedance in the constant acoustic impedance region is Z cham and the acoustic impedance at the outlet is Z out Then, Z cham <Z in , and Z cham <Z out Fulfilling a varying acoustic impedance structure having a first termination structure acoustically connected to the constant acoustic impedance region and the first impedance matching region;

2. a second impedance matching region disposed between the constant acoustic impedance region and the outlet, connected to the outlet, and having a gradually increasing acoustic impedance; The acoustic impedance varying structure according to claim 1 , further comprising: a second termination structure connected to the constant acoustic impedance region.

3. an inlet-side ventilation pipe; an expanded section communicating with the inlet-side ventilation pipe and having a larger cross-sectional area than the inlet-side ventilation pipe; and an outlet-side ventilation pipe communicating with the expanded section and having a smaller cross-sectional area than the expanded section, a first opening structure that gradually reduces acoustic impedance from a connection between the expansion portion and the inlet-side ventilation pipe toward the outlet-side ventilation pipe; a first rear space that is surrounded by the first opening structure, a side surface of the extension portion on the inlet side vent pipe side, and a peripheral surface of the extension portion, and that is open to the outlet side vent pipe side of the extension portion, A ventilation type silencer, wherein the first rear space is in communication with the space within the first opening structure.

4. 4. The ventilation type silencer according to claim 3, wherein the first opening structure has a cutoff frequency fc determined by its shape of 2000 Hz or less.

5. 5. The ventilation silencer according to claim 3, wherein, in the flow direction of the sound wave in the ventilation silencer, the length of the extension portion is L and the length of the first opening structure is a, and 0.2≦a / L≦0.

8.

6. a second opening structure whose cross-sectional area gradually decreases from within the expansion section toward a connection section between the expansion section and the outlet-side ventilation pipe; The second opening structure, the side surface of the extension portion on the outlet side vent pipe side, and the peripheral surface of the extension portion, and has a second back space that is open to the inlet side vent pipe side of the extension portion, any one of claims 3 to 5. A ventilation type silencer according to any one of claims 3 to 5.

7. 7. The ventilation type silencer according to claim 6, wherein the second opening structure has a cutoff frequency fc determined by its shape of 2000 Hz or less.

8. In the flow direction of the sound wave in the ventilation silencer, the length of the extension portion is L, and the total length of the first opening structure and the second opening structure is a 2 When this is the case, 0.2≦a 2 8. The ventilation type silencer according to claim 6 or 7, wherein / L≦0.

8.

9. The ventilation type silencer according to any one of claims 3 to 8, wherein the ratio of the acoustic impedance at the entrance of the back space to the minimum acoustic impedance of the back space is 1.1 or more.

10. The ventilation type silencer according to any one of claims 3 to 9, wherein at least a part of the extension portion has a sound absorbing structure.

11. 11. The ventilation type silencer according to claim 10, wherein the sound absorbing structure is a porous sound absorbing material.

12. 12. The ventilation type silencer according to claim 10 or 11, wherein at least a part of the sound absorbing structure is arranged along the housing of the extension part.

13. The ventilation type silencer according to any one of claims 10 to 12, wherein the sound absorbing structure is in contact with a maximum diameter portion of at least one of the first opening structure and the second opening structure.

14. the sound absorbing structure is disposed between the first opening structure and the second opening structure; The ventilation type silencer according to any one of claims 10 to 12, wherein the silencer is not disposed in at least one of the first rear space and the second rear space.

15. A ventilation type silencer according to any one of claims 3 to 14, wherein the change in acoustic impedance in at least one of the first opening structure and the second opening structure is continuous to the outside of the extension portion.

16. The ventilation type silencer according to any one of claims 3 to 15, wherein the average roughness Ra of the inner surface of at least one of the first opening structure and the second opening structure is 1 mm or less.

17. The ventilation type silencer according to any one of claims 3 to 16, wherein the cross-sectional shape of the extension portion is circular or rectangular.

18. The ventilation type silencer according to any one of claims 3 to 16, wherein the first opening structure is not closed in cross section at the end portion on the outlet side ventilation pipe side.

19. The ventilation type silencer according to any one of claims 6 to 18, wherein the second opening structure is not closed in a cross section at the end portion on the inlet side ventilation pipe side.

20. The ventilation type silencer according to any one of claims 3 to 19, wherein the first opening structure has a region where the thickness becomes thinner toward the outlet side ventilation pipe.

21. The ventilation type silencer according to any one of claims 6 to 20, wherein the second opening structure has a region where the thickness becomes thinner toward the inlet side ventilation pipe.

22. The connection position with the first opening structure on the side surface of the extension portion and the connection position with the second opening structure are located in the center of the side surface. A ventilation type silencer according to any one of claims 6 to 21.

23. The ventilation type silencer according to any one of claims 6 to 22, wherein the shapes of the first opening structure and the second opening structure are two-fold symmetric or more.

24. The ventilation type silencer according to any one of claims 6 to 23, wherein a length of the first opening structure in the flow path direction is longer than a length of the second opening structure.

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