Air duct with silencer
Patent Information
- Application Number
- JP2024006770
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2024-01-19
- Publication Date
- 2025-08-01
Smart Images
Figure 2025112511000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to an air duct with a muffler configured by arranging a muffler at an intermediate position in the air duct.
Background Art
[0002] The air duct is used, for example, as a duct for air conditioning. The cross-sectional area (size of the cross-section) of the air duct may vary depending on the position in the air flow direction due to circumstances such as the arrangement space in the air flow direction. As an example of an air duct whose cross-sectional area varies depending on the position in the air flow direction, the air duct described in Patent Document 1 can be cited. This air duct is configured by connecting a plurality of different-diameter ducts in series.
Prior Art Documents
Patent Documents
[0003]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0004] In an air duct with a changing cross-sectional area, a sound of a specific frequency resonates inside the air duct, and this sound travels through the air duct to the outlet of the air duct, which may cause problems such as noise or abnormal noise.
[0005] The problem of the present invention is to solve the above problems of the prior art and provide an air duct with a muffler that can effectively silence the sound of a specific frequency that resonates in an air duct with a changing cross-sectional area.
Means for Solving the Problems
[0006] To solve this problem, the present invention has the following configuration. [1] An air duct with a silencer, comprising an air duct whose cross-sectional area in a cross-section intersecting the air flow direction varies depending on the position in the air flow direction, and a silencer that silences the sound in the air duct. The silencer has a vibrating body that silences the sound in the air duct by vibrating due to the sound in the air duct. The silencer is provided in a target section sandwiched between two locations that are at different positions in the air flow direction and have a changing cross-sectional area in the air duct. The portion of the vibrating body where the displacement during vibration is the largest is arranged at a position closer to the antinode than to the node in the sound pressure distribution of the sound resonating in the target section. An air duct with a silencer. [2] The portion of the vibrating body where the displacement during vibration is the largest is arranged at a position closer to the antinode than to the node in the sound pressure distribution of at least one resonance mode among the first to third resonance modes of the resonance sound in the target section. The air duct with a silencer according to [1]. [3] The silencer further has a fixed end portion that serves as a fixed end when the vibrating body vibrates. The air duct with a silencer according to [1] or [2]. [4] The fixed end portion is formed of the same material as the vibrating body. The air duct with a silencer according to any one of [1] to [3]. [5] The vibrating body is arranged at a position surrounding the air duct, and the fixed end portion protrudes at least to one of the inner and outer sides of the air duct more than the vibrating body. The air duct with a silencer according to any one of [1] to [4]. [6] The silencer includes a housing. Inside the housing, the target section of the air duct extends, and a part of the wall of the housing constitutes the vibrating body. The air duct with a silencer according to any one of [1] to [5]. [7] In the air duct, the cross-sectional area of the section continuous with the target section at at least one of the two locations is smaller than the cross-sectional area of the target section. The air duct with a silencer according to any one of [1] to [6]. [8] The vibrating body is provided in an end region located on at least one side of the end regions on both sides within the target section. The air duct with a silencer according to any one of [1] to [7]. [9] In the air passage, the cross-sectional area of the section continuous with the target section at one of the two locations is smaller than the cross-sectional area of the target section, and the cross-sectional area of the section continuous with the target section at the other of the two locations is smaller than the cross-sectional area of the target section, and the vibrating body is provided in both end regions on both sides within the target section, the air passage with a silencer according to any one of [1] to [8].
[10] In the air passage, the cross-sectional area of the section continuous with the target section at one of the two locations is smaller than the cross-sectional area of the target section, and the cross-sectional area of the section continuous with the target section at the other of the two locations is larger than the cross-sectional area of the target section. The vibrating body is provided in the end region on one side among the end regions on both sides within the target section, the air passage with a silencer according to any one of [1] to [9].
Effect of the Invention
[0007] According to the present invention, it is possible to provide an air passage with a silencer provided with a silencer capable of effectively silencing the sound of a specific frequency that resonates in the air passage whose cross-sectional area changes.
Brief Description of the Drawings
[0008]
Figure 1
Figure 2
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Figure 9
Mode for Carrying Out the Invention
[0009] The air duct with a muffler of the present invention will be described in detail below with reference to the preferred embodiments shown in the accompanying drawings. Note that the following embodiments are merely examples given for ease of understanding of the present invention and do not limit the present invention. That is, the configuration of the present invention can be changed or improved from the following embodiments without departing from the gist thereof. In addition, the materials, shapes, etc. of each member used for carrying out the present invention can be arbitrarily set according to the use of the present invention and the technical level at the time of carrying out the present invention, etc., unless otherwise specified. The present invention also includes equivalents thereof.
[0010] In addition, in this specification, the numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In addition, in this specification, "orthogonal" and "parallel" shall include the range of errors acceptable in the technical field to which the present invention belongs. For example, "orthogonal" and "parallel" in this specification mean that they are within a range of less than ±10° with respect to strict orthogonality or parallelism. Note that the error from strict orthogonality or parallelism is preferably 5° or less, and more preferably 3° or less.
[0011] In addition, in this specification, the meanings of "the same" and "identical" may include the range of errors generally acceptable in the technical field to which the present invention belongs. In addition, in this specification, the meanings of "all", "entire area", and "all" include not only the case of 100%, but also the range of errors generally acceptable in the technical field to which the present invention belongs. For example, cases of 99% or more, 95% or more, or 90% or more may be included.
[0012] In addition, "noise reduction" in the present invention means eliminating sound, and is a concept that includes both the meanings of sound insulation and sound absorption. Sound insulation means shielding sound, in other words, not allowing sound to pass through. Also, sound shielding includes the reflection of sound (acoustics) and the cancellation of sound (acoustics). Sound absorption means reducing reflected sound, that is, absorbing sound (acoustics).
[0013] <<Air duct with silencer according to this embodiment>> An air duct with a silencer (hereinafter referred to as the air duct with a silencer 10) according to an embodiment of the present invention (hereinafter referred to as this embodiment) will be described with reference to FIG. 1. As shown in FIG. 1, the air duct with a silencer 10 is configured by arranging a silencer 30 at an intermediate position in the air duct 20, and its use is not particularly limited. For example, it may be used for air conditioning in a building, air cooling in electrical equipment, or air conditioning in vehicles such as automobiles and airplanes.
[0014] <Air duct> The air duct 20 is a ventilation path for flowing air, and corresponds to, for example, a duct for air conditioning. "Air" is not particularly limited, and means, for example, an artificial air and a flow of gas (airflow). The composition of the air or gas constituting the air and the ratio of each component are not particularly limited, but hereinafter, the case of blowing normal air will be assumed for explanation.
[0015] In the following description, "upstream side" means the upstream side in the direction in which air flows (hereinafter referred to as the "air blowing direction"), that is, the inlet side of the air duct 20. "Downstream side" means the downstream side in the air blowing direction, that is, the outlet side of the air duct 20. In the following description, it is assumed that the air duct 10 with a silencer is arranged such that the air blowing direction is horizontal. Therefore, when two directions orthogonal to the air blowing direction are defined as the "first direction" and the "second direction", in the present embodiment, for convenience of explanation, as shown in FIG. 1, the first direction is the "vertical direction" and the second direction is the "depth direction". Also, the upper side in the vertical direction is the "upper side", the lower side in the vertical direction is the "lower side", the front side in the depth direction is the "front side", and the rear side in the depth direction is the "rear side". However, the "vertical direction" and the "depth direction" mentioned here are defined based on the arrangement form of the air duct 10 with a silencer in the present embodiment, and the definitions of the first direction and the second direction are different according to the arrangement form of the air duct 10 with a silencer.
[0016] When blowing artificial air, as a blowing source, for example, a device equipped with an electric motor such as a motor and operating to blow air by starting the electric motor may be used. Specifically, it is a blowing fan constituting an air conditioner or a blowing fan for ventilation. As the fan, known fans such as an axial flow fan (propeller fan), a sirocco fan, a turbo fan, a centrifugal fan, and a line flow fan (registered trademark) can be used. For example, the aforementioned blowing source is located on the upstream side of the air duct 20, and the air sent from the blowing source flows through the air duct 20.
[0017] The cross-sectional area of the air duct 20 varies depending on the position in the air blowing direction. Note that the "cross-sectional area" means the cross-sectional area of a cross-section orthogonal (intersecting) to the air blowing direction. More specifically, it means the cross-sectional area in the cross-section of the ventilation space surrounded by the wall (the wall of the ventilation pipe) surrounding the air duct 20. In the following description, unless otherwise specified, the "cross-section" means a "cross-section orthogonal to the air blowing direction", and the "cross-sectional area" means the "cross-sectional area of a cross-section orthogonal to the air blowing direction".
[0018] Note that the cross-sectional area of the air duct 20 means the cross-sectional area of the ventilation space surrounded by the air duct 20 regardless of whether a sound-absorbing material (not shown) is arranged in the ventilation space. Examples of the sound-absorbing material include porous materials such as foams, foam materials, and non-woven fabric-based sound-absorbing materials.
[0019] As shown in FIG. 1, the air passage 20 has a target section 23 sandwiched between two locations where the cross-sectional area changes. The two locations where the cross-sectional area changes are provided at different positions from each other in the air blowing direction. In the following description, among the two locations where the cross-sectional area changes, the location on the upstream side is referred to as the "upstream location 21", and the location on the downstream side is referred to as the "downstream location 22".
[0020] As shown in FIG. 1, the air passage 20 has a front section 24 as a section continuous with the target section 23 at the upstream location 21. Further, the air passage 20 has a rear section 25 as a section continuous with the target section 23 at the downstream location 22. More specifically, the air passage 20 is composed of three ventilation pipes corresponding to the three sections 23, 24, and 25, and each of the upstream location 21 and the downstream location 22 corresponds to a connection portion between two adjacent ventilation pipes among the three ventilation pipes. Note that the target section 23 in the air passage 20 corresponds to a muffler 30 described later, and the ventilation pipe corresponding to the target section 23 corresponds to a housing 31 described later that constitutes the muffler 30.
[0021] Here, the "cross-sectional area" in each of the three ventilation pipes means the cross-sectional area inside the pipe. More specifically, it means the cross-sectional area at a position adjacent to the upstream location 21 or the downstream location 22. In other words, it means the cross-sectional area of the end portion of the ventilation pipe. Therefore, when the cross-sectional area of the ventilation pipe changes along the axial direction of the ventilation pipe and the cross-sectional area is different between the central portion and the end portion in the axial direction of the ventilation pipe, the cross-sectional area of the ventilation pipe means the cross-sectional area of the end portion of the ventilation pipe.
[0022] In the following description, it is assumed that the ventilation pipes corresponding to the respective sections 23, 24, and 25 extend linearly along the air blowing direction and have a constant cross-sectional area in the air blowing direction. However, the present invention is not limited to this. For example, the ventilation pipes may be curved and have a cross-sectional area that changes in the air blowing direction.
[0023] The cross-sectional shapes of the ventilation pipes in each section 23, 24, 25 are not particularly limited, and may be, for example, circular, rectangular (square), quadrilateral other than rectangular, polygon other than quadrilateral, or irregular. The cross-sectional shapes of the ventilation pipes in each section 23, 24, 25 may be the same or different. In the following description, it is assumed that the cross-sectional shape of the ventilation pipe (housing 31) in the target section 23 is rectangular, and the cross-sectional shapes of the ventilation pipes in the front section 24 and the rear section 25 are circular.
[0024] The material of the ventilation pipes corresponding to each section 23, 24, 25 is not particularly limited, and metal materials, resin materials, paper materials, reinforced plastic materials, carbon fiber, etc. can be used. However, from the viewpoint of ensuring moldability and design freedom, resin materials are preferred. Examples of resin materials include acrylic resin, polymethyl methacrylate, polycarbonate, polyamideimide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, ABS resin (acrylonitrile, flame-retardant ABS resin, butadiene, styrene copolymer synthetic resin), polypropylene, triacetyl cellulose (TAC), polypropylene (PP), polyethylene (PE), polystyrene (PS), ASA (acrylate styrene acrylonitrile) resin, polyvinyl chloride (PVC) resin, and PLA (polylactic acid) resin, etc. Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP).
[0025] The air passage 20 is formed by joining adjacent ventilation pipes among the three ventilation pipes corresponding to the three sections 23, 24, and 25, for example, by fastening using welding, adhesion, screws, or the like. Alternatively, the air passage 20 may be formed by integrally (i.e., seamlessly) forming the three ventilation pipes corresponding to the three sections 23, 24, and 25, for example, by injection molding (especially blow molding).
[0026] In the example shown in FIG. 1, the central axes of the ventilation pipes corresponding to the respective sections 23, 24, and 25 are located on the same imaginary line extending in the air supply direction. However, it is not limited thereto, and the central axes of the ventilation pipes corresponding to the respective sections 23, 24, and 25 may be offset from each other in the vertical direction and the depth direction.
[0027] Here, in the example shown in FIG. 1, the ventilation pipe (housing 31) corresponding to the target section 23 constitutes an expansion portion in the air passage 10 with a silencer. Therefore, the cross-sectional area of the section (front section 24) continuous with the target section 23 at the upstream location 21 (one of the two locations) is smaller than the cross-sectional area of the target section 23. Also, the cross-sectional area of the section (rear section 25) continuous with the target section 23 at the downstream location 22 (the other of the two locations) is smaller than the cross-sectional area of the target section 23. In other words, in the example shown in FIG. 1, the cross-sectional area of the ventilation pipe corresponding to the front section 24 is smaller than the cross-sectional area of the ventilation pipe (housing 31) corresponding to the target section 23, and the cross-sectional area of the ventilation pipe corresponding to the rear section 25 is smaller than the cross-sectional area of the ventilation pipe (housing 31) corresponding to the target section 23.
[0028] Thus, in the target section 23, the cross-sectional area of the ventilation pipe is larger than the sections 24 and 25 located before and after in the air supply direction. That is, the ventilation pipe (housing 31) corresponding to the target section 23 forms an expansion portion in the air passage 10 with a silencer and functions as a so-called expansion silencer. Thereby, the silencing effect due to resonance in the expansion silencer can be exerted. Note that the cross-sectional areas of the ventilation pipes corresponding to the front section 24 and the rear section 25 may be the same as each other or different from each other.
[0029] The equivalent circle diameter of the ventilation pipes corresponding to each of the sections 23, 24, and 25, and the ratio of the cross-sectional areas of the ventilation pipes differ depending on the field of use where the air passage 10 with a silencer is utilized, and are appropriately set according to the size of the equipment in which the air passage 10 with a silencer is used, the required ventilation performance, and the like. Note that the "equivalent circle diameter" means a virtual circle diameter calculated backward when assuming that the cross-sectional area of a ventilation pipe with a non-circular cross-section is the cross-sectional area of a circle.
[0030] When the air passage 10 with a silencer is used in an air conditioner, as the equivalent circle diameter of the ventilation pipe corresponding to the front section 24 (rear section 25), for example, 150 mm or less is preferable, 100 mm or less is more preferable, and 75 mm or less is even more preferable. Further, when a plurality of ventilation pipes corresponding to the front section 24 (rear section 25) are passed through a duct with an equivalent circle diameter of 75 mm or less, the equivalent circle diameter of the ventilation pipe is preferably 30 mm or less.
[0031] Also, when the cross-sectional area of the ventilation pipe in the target section 23 is P and the cross-sectional area of the ventilation pipe in the front section 24 is Q, as the ratio of the cross-sectional areas P / Q, 1.5 or more is preferable, 2.0 or more is more preferable, and 3.0 or more is even more preferable. The ratio of the cross-sectional areas P / Q is determined, for example, based on the constraints of the arrangement space and the general cross-sectional area ratio. The "general cross-sectional area ratio" is determined based on the constraint conditions in each phase such as design, manufacture, and transportation. Examples of the constraint conditions include the selectable sizes of ventilation pipes based on the specifications of the ventilation pipes, and the manufacturing difficulty level according to the ratio of the cross-sectional areas when joining ventilation pipes with different cross-sectional areas to each other.
[0032] In the example shown in FIG. 1, the upstream portion 21 is configured such that the cross-sectional area decreases from the target section 23 toward the front section 24. More specifically, when the cross-sectional area of the ventilation pipe corresponding to the target section 23 is defined as P and the cross-sectional area of the ventilation pipe corresponding to the front section 24 is defined as Q, the configuration is such that the cross-sectional area switches in one step from the cross-sectional area P to the cross-sectional area Q (<P). However, it is not limited to this. For example, the upstream portion 21 may be configured such that the cross-sectional area changes stepwise in multiple steps or changes continuously and smoothly from the cross-sectional area P to the cross-sectional area Q.
[0033] Similarly, in the example shown in FIG. 1, the downstream portion 22 is configured such that the cross-sectional area decreases from the target section 23 toward the rear section 25. More specifically, when the cross-sectional area of the ventilation pipe corresponding to the rear section 25 is defined as R, the configuration is such that the cross-sectional area switches in one step from the cross-sectional area P to the cross-sectional area R (<P). However, it is not limited to this. For example, the downstream portion 22 may be configured such that the cross-sectional area changes stepwise in multiple steps or changes continuously and smoothly from the cross-sectional area P to the cross-sectional area R.
[0034] <Muffler> As shown in FIG. 1, the muffler 30 is provided in the target section 23 of the air passage 20 and is specifically composed of a housing 31. As described above, the muffler 30 corresponds to the target section 23 in the air passage 20, and the housing 31 corresponds to the ventilation pipe corresponding to the target section 23. The muffler 30 has a function of muffling the sound in the air passage 20 (the sound that has entered the air passage 20).
[0035] [Housing] Inside the housing 31, the target section 23 of the air passage 20 extends. The cross-sectional area of the housing 31 corresponds to the cross-sectional area of the ventilation pipe of the target section 23, and specifically means the cross-sectional area in the cross-section of the ventilation space surrounded by the wall of the housing 31.
[0036] The cross-sectional shape of the housing 31 is not particularly limited as described in the description of the ventilation pipe corresponding to the target section 23. However, in this embodiment, it will be described as having a rectangular shape. The housing 31 defines the outer edge of the muffler 30 and forms a rectangular parallelepiped (hexahedron) box that extends in the air blowing direction. Among the plurality (six) of walls constituting the housing 31, through holes are respectively provided in the upstream wall and the downstream wall arranged at intervals in the air blowing direction. The end of the ventilation pipe corresponding to the front section 24 is connected to the through hole on the upstream side, and the end of the ventilation pipe corresponding to the rear section 25 is connected to the through hole in the wall on the downstream side.
[0037] The housing 31 may be configured by joining adjacent walls among the six walls to each other by welding, adhesion, or fastening using screws or the like, or may be configured by forming two housing pieces constituting the housing 31 by injection molding or the like and joining the housing pieces to each other, or may be configured by integrally (seamlessly) forming the housing 31 by injection molding (especially blow molding) or the like.
[0038] The housing 31 may be composed of one type of material or may be composed of a combination of multiple types of materials. Specifically, at least one of the six walls constituting the housing 31 may be composed of a different type of material from the other walls, or one wall may be composed of multiple types of materials.
[0039] As shown in FIG. 1, the housing 31 has two side walls 32 arranged at intervals in the vertical direction among the six walls constituting the housing 31. Each of the upper and lower two side walls 32 is a wall that extends in the air blowing direction. Specifically, as shown in FIG. 1, it is composed of two vibrating bodies 33, two fixed ends 34, and a peripheral portion 35. The fixed end 34 fixes the end of the vibrating body 33, and the peripheral portion 35 constitutes the portion of the side wall 32 excluding the vibrating body 33 and the fixed end 34.
[0040] [Vibrating body] The vibrating body 33 vibrates due to the sound in the air passage 20, more specifically, the sound of a specific frequency that resonates in the air passage 20, thereby eliminating the sound of the specific frequency that resonates in the air passage 20. That is, when the vibrating body 33 vibrates, the sound energy in the air passage 20 is converted into vibration energy and consumed as vibration energy. As a result, the sound (resonant sound) of a specific frequency in the air passage 20 can be eliminated. In other words, the vibrating body 33 utilizes vibration to perform a sound elimination function and selectively eliminates sounds of a specific frequency (frequency band). The vibrating body 33 forms a part of the side wall 32 and is disposed at a position surrounding the air passage 20 (specifically, the target section 23). In this way, by having the vibrating body 33 form a part of the side wall 32, the housing 31 (the muffler 30) can have a simple configuration.
[0041] The vibrating body 33 is in a plate shape (membrane shape) and is configured to vibrate at its natural frequency. To make it easier for the vibrating body 33 to vibrate, it is preferable to make the natural frequency of the vibrating body 33 approach the frequency of the sound that resonates in the target section 23 (the frequency f1 described later). The natural frequency of the vibrating body 33 is determined according to the material of the vibrating body 33 (Young's modulus, Poisson's ratio, density, etc.), shape, and planar size, thickness, and the fixing structure of the fixing end 34 described later. The vibrating body 33 vibrates in a vibration mode of fundamental vibration (primary vibration) or higher-order vibration according to its natural frequency.
[0042] The material of the vibrating body 33 is selected in consideration of physical property values such as Young's modulus, Poisson's ratio, and density so that the natural frequency corresponds to the frequency of the sound that resonates in the target section 23. The material of the vibrating body 33 may be the same as the material of other parts of the housing 31 (including the fixing end 34 and the peripheral part 35), or may be a different material. Specific examples of the material of the housing 31 are described in the explanation of the material of the ventilation pipe corresponding to the target section 23, so the explanation is omitted here. Also, the material of the vibrating body 33 is assumed to be selected from the candidates for the material of the housing 31.
[0043] The vibrating body 33 may be configured to be thinner than the thickness of the side wall 32 (especially the peripheral portion 35). In particular, when the vibrating body 33 and the peripheral portion 35 are made of the same material, it is preferably configured to be thinner than the thickness of the peripheral portion 35. Specifically, when the vibrating body 33 and the peripheral portion 35 are made of the same material, when the thickness of the peripheral portion 35 is t, it is preferable to set the thickness of the vibrating body 33 to 0.01×t to 0.46×t. Thereby, while the vibrating body 33 can be vibrated appropriately, it is possible to suppress an excessive weakening of the structural strength of the housing 31.
[0044] The outer shape of the vibrating body 33 is not particularly limited. For example, it may be circular, rectangular (square), a quadrilateral other than a rectangle, a polygon other than a quadrilateral, or an irregular shape. Further, the vibrating body 33 may be a flat plate, or may be a non-flat plate (such as a plate bent in an arcuate or wavy shape). That is, the vibrating surface of the vibrating body 33 may be any of a flat surface, a curved surface (a curved surface), and an uneven surface.
[0045] Although not shown in FIG. 1, the vibrating body 33 extends in the depth direction, and may extend from one end to the other end of the housing 31 (side wall 32) in the depth direction, or may extend only to the central portion in the depth direction. Regarding the length (dimension) of the vibrating body 33 in the air blowing direction, when the distance between the inner surfaces of the upstream wall and the downstream wall of the housing 31 is defined as L (see FIG. 1), it is preferably L / 2 or less, and more preferably L / 4 or less. Thereby, in the sound pressure distribution (see FIG. 1) due to the primary resonance mode described later in the housing 31, it is possible to avoid the vibrating body 33 being located at both the antinode and the node of the sound pressure distribution. Note that the arrangement position of the vibrating body 33 in the air blowing direction with respect to the side wall 32 (housing 31) will be described later.
[0046] In the following description, it is assumed that the vibrating body 33 is a flat plate (that is, the vibrating surface is a flat surface) having the same thickness throughout its entire area, its outer shape is rectangular, and it extends from one end to the other end of the housing 31 in the depth direction. The planar size (area) of the vibrating body 33 is preferably such that it fits within the end region of the target section 23 described later. The larger the planar size, the lower the natural frequency of the vibrating body 33 will be.
[0047] The vibration surface of the vibrating body 33 is preferably parallel to the air blowing direction, but may be inclined with respect to the air blowing direction. The inclination angle of the vibration surface with respect to the air blowing direction is preferably 30° or less, more preferably 15° or less, and even more preferably 3° or less. In particular, in order to suppress the generation of wind noise and the increase in pressure loss, etc., for the vibrating body 33 adjacent to the upstream side location 21 (the location where the cross-sectional area expands in the example shown in FIG. 1) and the downstream side, the vibration surface thereof is preferably 15° or less. Also, in order to suppress the generation of wind noise and the increase in pressure loss, etc., for the vibrating body 33 adjacent to the upstream side and the downstream side location 22 (the location where the cross-sectional area shrinks in the example shown in FIG. 1), the vibration surface thereof is preferably 30° or less. Further, when the housing 31 including the vibrating body 33 is formed by injection molding, considering the draft angle when removing the housing 31 from the mold of the injection molding machine, it is preferable that the vibration surface of the vibrating body 33 is 3° or less. In the following description, it is assumed that the vibration surface of the vibrating body 33 is parallel to the air blowing direction, and the vibration direction of the vibration surface corresponds to the vertical direction shown in FIG. 1.
[0048] The natural frequency of the vibrating body 33 can be specified by known natural frequency analysis or natural frequency calculation. The measured value of the natural frequency can be obtained as a frequency response by exciting using an impulse hammer such as "GK-3100" manufactured by Ono Sokki Co., Ltd., measuring the vibration with an acceleration detector, and converting it to a frequency by an FFT (Fast Fourier Transform) analyzer. At this time, by performing measurements at multiple points, the vibration mode can also be analyzed by actual measurement. Also, a testing machine provided as a set such as "Natural Frequency Measurement System CAT-SA02 NF" manufactured by Lion Co., Ltd. may be used. Regarding the actual measurement procedure of the natural frequency, it can be obtained, for example, in accordance with JISG0602, JISB0908, JISC60068-2-81, etc. regarding the test methods of vibration and shock. The calculation of the natural frequency can be performed by general structural mechanics simulations. Specifically, for various commercial software or self-developed software such as COMSOL, ANSYS, and Abaqus, the natural frequency can be calculated by inputting the size of the material, physical property values of the material (Young's modulus, density, Poisson's ratio, etc.), and surrounding restraint conditions.
[0049] [Fixed end] The fixed end portion 34 serves as a fixed end when the vibrating body 33 vibrates, and its reflection condition is determined by the structure and material of the vibrating body 33 (vibrating surface) and the structure and material of the fixed end portion 34. The fixed end portion 34 forms a part of the side wall 32 and fixes the ends of the vibrating body 33, more specifically, the four sides of the rectangular vibrating body 33. In the present embodiment, the fixed end portion 34 is located at each corner portion (bent portion) on the upstream side, the front side, and the back side in the housing 31. Since these corner portions are more rigid than other parts of the housing 31, the fixed end portion 34 can effectively exhibit the function as a fixed end. In this way, since the muffler 30 has the fixed end portion 34, the vibrating body 33 can vibrate appropriately at the set natural frequency.
[0050] The material of the fixed end portion 34 may be the same as or different from the materials of the other portions of the side wall 32 (including the vibrating body 33 and the peripheral portion 35). The material of the fixed end portion 34 shall be selected from among the candidate materials of the housing 31. Note that the material of the peripheral portion 35 shall also be selected from among the candidate materials of the housing 31. In this way, by forming the fixed end portion 34 of the same material as at least one of the vibrating body 33 and the peripheral portion 35, the muffler 30 can have a simple structure.
[0051] As a method of fixing the vibrating body 33 to the fixed end portion 34, welding, adhesion, fastening using screws, etc. may be used, or the vibrating body 33 and the fixed end portion 34 may be integrally (i.e., seamlessly) formed by injection molding or the like. Further, the fixed end portion 34 may continuously fix the vibrating body 33 along the periphery (four sides) of the vibrating body 33, or may intermittently fix the vibrating body 33 along the periphery (four sides) of the vibrating body 33 by spot welding or the like. Also, the fixed end portion 34 does not have to fix all four sides of the vibrating body 33. For example, at least two sides arranged in the air supply direction may be fixed.
[0052] Note that the fixed end portion 34 is fixed to the peripheral portion 35 on the side opposite to the vibrating body 33, but the fixing method is not particularly limited. For example, welding, adhesion, fastening using screws, etc. may be used, or the fixed end portion 34 and the peripheral portion 35 may be integrally (i.e., seamlessly) formed by injection molding or the like. When the fixed end portion 34 and the peripheral portion 35 are integrally formed by injection molding or the like, the vibrating body 33 may also be integrally formed together with the fixed end portion 34 and the peripheral portion 35.
[0053] Here, the fixed end portion 34 may protrude at least on one of the inner and outer sides of the air passage 20 with respect to the vibrating body 33. "The inner side of the air passage 20" means the side of the ventilation space with respect to the side wall 32, and "the outer side of the air passage 20" means the side opposite to the ventilation space with respect to the side wall 32, i.e., the external space side. Note that the fixed end portion 34 may have the same thickness as the vibrating body 33 without protruding on either the inner or outer side of the air passage 20 with respect to the vibrating body 33.
[0054] In the example shown in FIG. 1, the fixed end portion 34 protrudes both inside and outside (upper side and lower side) of the air passage 20 with respect to the vibrating body 33, and has a solid rib (column) shape. Note that the rib may be either a solid rib or a hollow rib.
[0055] Thus, by the fixed end portion 34 protruding at least to one of the inside and outside of the air passage 20 with respect to the vibrating body 33, the fixed end portion 34 becomes longer in the vertical direction than the vibrating body 33. Thereby, the rigidity of the fixed end portion 34 can be increased, and as a result, the fixed end portion 34 can function more appropriately as the fixed end of the vibrating body 33.
[0056] Note that the fixed end portion 34 is not limited to the rib shape. For example, the fixed end portion 34 may have a shape in which a portion corresponding to the fixed end portion 34 of the side wall 32 bulges inside or outside the air passage 20 more than the other portions of the side wall 32. Such a bulged portion can be formed, for example, by performing bead processing or the like on a portion corresponding to the fixed end portion 34 of the side wall 32. Further, a portion corresponding to the vibrating body 33 of the side wall 32 may be formed in a recessed shape that is recessed inside or outside the air passage 20 more than the other portions of the side wall 32. Such a recessed shape can be formed, for example, by performing drawing processing or the like on a portion corresponding to the vibrating body 33 of the side wall 32. In this case, as the fixed end portion 34, a portion that is bent from the vibrating body 33, extends in the vertical direction, and is connected to the peripheral portion 35 corresponds.
[0057] Thus, the fixed end portion 34 is not limited to the rib shape, and may be any portion that has a length in the vertical direction as compared with the vibrating body 33. Thereby, the rigidity of the fixed end portion 34 when the vibrating body 33 vibrates in the vertical direction can be increased, and as a result, the fixed end portion 34 can function more appropriately as the fixed end of the vibrating body 33.
[0058] In addition, when the fixed end portion 34 protrudes inside or outside the air passage 20 from the vibrating body 33, a case may occur where one of the vibrating body 33 and the fixed end portion 34 protrudes more inward (ventilation space side) in the air passage 20 than the other. Such a protruding portion may be a factor in the generation of aerodynamic noise in the air passage 20. Therefore, the length by which one of the vibrating body 33 and the fixed end portion 34 protrudes more inward than the other in the air passage 20 is preferably 15 mm or less, more preferably 7 mm or less, and even more preferably 1 mm or less. This is because the thickness (plate thickness) of the resin housing 31 is preferably in the range of 1 mm to 5 mm, and the above-mentioned protruding length is preferably 3 times or less the thickness (plate thickness) of the housing. Thereby, while ensuring the function of the fixed end portion 34 as a fixed end, the generation of aerodynamic noise in the air passage 20 can be suppressed.
[0059] In the above description, the relationship between the vibrating body 33 and the fixed end portion 34 has been described, but the same applies to the relationship between the fixed end portion 34 and the peripheral portion 35. That is, the fixed end portion 34 may protrude at least one of the inside and outside of the air passage 20 more than the peripheral portion 35, or may have the same thickness as the peripheral portion 35 without protruding either inside or outside the air passage 20 with respect to the peripheral portion 35.
[0060] [Arrangement position of the vibrating body] Next, the arrangement position of the vibrating body 33 in the target section 23 will be described. The vibrating body 33 has a portion where the displacement is the largest during vibration (hereinafter, also referred to as the "maximum displacement portion"). More specifically, the maximum displacement portion of the vibrating body 33 corresponds to the belly portion of the waveform during vibration in the vibrating body 33.
[0061] In the following description, it is assumed that the vibration mode of the vibrating body 33 is the fundamental vibration (primary vibration). In this case, the maximum displacement portion of the vibrating body 33 corresponds to the center of gravity position of the vibrating body 33. This is because the vibrating body 33 vibrates about the center of gravity of the vibrating body 33. In the present embodiment, since the vibrating body 33 is a rectangular plate having the same thickness throughout its entire area, the center of gravity position of the vibrating body 33 is assumed to correspond to the center position of the vibrating body 33 in the air blowing direction and the depth direction.
[0062] More specifically, in the target section 23 of the air passage 20, as shown in FIG. 1, a sound of a specific frequency f1 (= V / (2×L)×n) resonates inside the housing 31. L represents the length of the section with a cross-sectional area of P, and in the example shown in FIG. 1, it is the distance from the upstream wall to the downstream wall of the housing 31 in the air blowing direction. n is a value of 1 to 3 corresponding to the order of the 1st to 3rd resonance modes.
[0063] The example shown in FIG. 1 is an example where the lowest-order 1st resonance mode at the frequency f1 occurs in the target section 23, and the sound pressure distribution due to that resonance mode is shown by a broken line in the figure. In the nodal part of the sound pressure distribution, the sound pressure does not change, while in the antinodal part of the sound pressure distribution, the sound pressure periodically varies between the positive maximum value and the negative maximum value. That is, in the sound pressure distribution, the closer to the antinode, the greater the sound pressure variation, and the closer to the node, the smaller the sound pressure variation. In the example shown in FIG. 1, the nodal part of the sound pressure distribution is located at the center of the target section 23 in the air blowing direction, and the antinodal part of the sound pressure distribution is located at both ends within the target section 23.
[0064] Here, the maximum displacement part of the vibrating body 33 is located closer to the antinode than the node in the sound pressure distribution of the sound in the air passage 20 that resonates in the target section 23. More specifically, when the distance from the antinode to the node in the sound pressure distribution within the target section 23 is defined as D, the maximum displacement part of the vibrating body 33 is preferably located within D / 2 on each of the upstream side and the downstream side in the air blowing direction with respect to the position of the antinode of the sound pressure distribution, and more preferably within D / 4. In the case shown in FIG. 1, the position of the antinode of the sound pressure distribution is located at the end in the air blowing direction of the housing 31, and the portion with the maximum displacement of the vibrating body 33 is located at the center of the vibrating body 33 in the air blowing direction. Therefore, a deviation of half the length of the vibrating body 33 in the air blowing direction may occur between the portion with the maximum displacement of the vibrating body 33 and the position of the antinode of the sound pressure distribution. In the muffler 30 of the present embodiment, it is conceivable to eliminate sound in the frequency range of 300 to 1 kHz. In that case, the length of the vibrating body 33 in the air blowing direction is about 40 to 300 mm, so half of that length is 20 to 150 mm. Here, since the distance D in the frequency band to be silenced (300 to 1 kHz) is about 75 mm to 300 mm, half of the length of the vibrating body 33 in the air blowing direction corresponds to D / 2 to D / 4. Therefore, it can be said that the portion with the maximum displacement of the vibrating body 33 is preferably located within D / 2 on the upstream side and the downstream side in the air blowing direction with respect to the position of the antinode of the sound pressure distribution, and more preferably within D / 4.
[0065] The vibrating body 33 is provided at both end regions on both sides in the target section 23 (housing 31) corresponding to the position of the antinode of the sound pressure distribution within the target section 23. Thereby, in any of the vibrating bodies 33, the portion with the maximum displacement can be appropriately arranged at a position closer to the antinode than the node in the sound pressure distribution. The length of the "end region" in the air blowing direction is preferably within the range of L / 2 toward the downstream side (upstream side) with reference to the inner surface of the upstream wall (downstream wall) of the housing 31, more preferably within the range of L / 4, and even more preferably within the range of L / 6. In particular, the length of the end region in the air blowing direction is preferably smaller than the distance D from the antinode to the node of the sound pressure distribution, preferably within the range of L / 2 in the case of the first resonance mode, within the range of L / 4 in the case of the second resonance mode, and within the range of L / 6 in the case of the third resonance mode.
[0066] In the example shown in FIG. 1, two vibrating bodies 33 are provided on each side wall 32. However, between the two side walls 32, the two vibrating bodies 33 located on the upstream side face each other in the vertical direction with the ventilation space of the air passage 20 interposed therebetween. Similarly, the two vibrating bodies 33 located on the downstream side face each other in the vertical direction with the ventilation space of the air passage 20 interposed therebetween.
[0067] As described above, in the air passage 10 with a muffler, the sound of a specific frequency f1 that resonates within the target section 23 causes the vibrating body 33 to vibrate, thereby silencing the sound of frequency f1. At this time, by bringing the natural frequency of the vibrating body 33 closer to the frequency f1, the vibrating body 33 can be effectively vibrated. Also, in order to vibrate the vibrating body 33 more effectively, in the air blowing direction, it is preferable to bring the position of the maximum displacement portion of the vibrating body 33 closer to the position of the antinode of the sound pressure distribution, and it is even better to make them coincide. In this regard, in the present embodiment, the maximum displacement portion of the vibrating body 33 is arranged at a position closer to the antinode than the node in the sound pressure distribution. Thereby, the vibrating body 33 can be vibrated more effectively, and as a result, the sound of a specific frequency f1 that resonates in the air passage 20 with a changing cross-sectional area can be effectively silenced.
[0068] Also, in the example shown in FIG. 1, the explanation was made on the premise of an example where the lowest-order primary resonance mode at the frequency f1 occurs in the target section 23, but it is not limited to this. For example, in the case of higher-order (second to third order) resonance modes at the frequency f1, this configuration may also be applied. More specifically, even in the case of a higher-order resonance mode, the antinode of the sound pressure distribution in the target section 23 will be at least located in the end regions on both sides within the target section 23 (see FIG. 2). For this reason, the maximum displacement portion of the vibrating body 33 provided in the end region of the target section 23 will be arranged near the antinode located at the outermost end among the antinodes of the sound pressure distribution, and the vibrating body 33 can be effectively vibrated. As a result, the sound of a specific frequency f1 that resonates in the air passage 20 with a changing cross-sectional area can be effectively silenced.
[0069] Thus, the resonance mode applied in the air passage 10 with a muffler is not limited to the first-order resonance mode, and can be applied to at least one of the first- to third-order resonance modes of the resonance sound in the target section 23. And in any of the applied resonance modes, since the maximum displacement portion of the vibrating body 33 can be arranged at a position closer to the antinode (specifically, the antinode located at the outermost end) than the node in the sound pressure distribution, the sound of a specific frequency f1 resonating in the air passage 20 can be effectively silenced.
[0070] Note that in the case of higher-order resonance modes, since the number of antinodes in the sound pressure distribution increases compared to the first-order resonance mode, a configuration in which the vibrating body 33 is provided according to the number of antinodes, for example, the air passage 10A with a muffler shown in FIG. 2, can more effectively silence the sound of a specific frequency f1 resonating in the air passage 20. The air passage 10A with a muffler shown in FIG. 2 will be described in the paragraph of "Other Embodiments" below.
[0071] <<Other Embodiments>> In the above embodiment, as shown in FIG. 1, the muffler 30 is assumed to have a plurality (four) of vibrating bodies 33. However, it is not limited thereto. For example, the muffler 30 may have at least one vibrating body 33. Specifically, the muffler 30 may have one vibrating body 33, and the one vibrating body 33 may be provided at one of the end regions on both sides within the target section 23 on one of the two side walls 32.
[0072] Also, in the above embodiment, the configuration in which the muffler 30 has four vibrating bodies 33 has been described. However, it is not limited thereto. For example, the number of vibrating bodies 33 may be increased according to the vibration mode.
[0073] More specifically, since the number of antinodes in the sound pressure distribution within the target section 23 increases according to the order of the resonance mode, by increasing the number of vibrating bodies 33 according to the number of antinodes, the sound of frequency f1 can be more effectively silenced. For example, as in the example shown in FIG. 2, compared with the example shown in FIG. 1, corresponding to the position of the antinode of the sound pressure distribution, two new vibrating bodies 33 may be additionally provided in the intermediate region sandwiched between the end regions on both sides within the target section 23. In this way, by increasing the number of vibrating bodies 33 according to the vibration mode, the sound of a specific frequency f1 resonating in the air passage 20 can be more effectively silenced.
[0074] Also, in the above-described embodiment, the housing 31 is configured to form an extended portion. However, it is not limited thereto, and for example, like the air passage 10B with a silencer shown in FIG. 3, the cross-sectional area of the air passage 20 may be configured to expand or contract stepwise along the air blowing direction. More specifically, in the air passage 20, the cross-sectional area of the section continuous with the target section 23 at one of the upstream section 21 and the downstream section 22 may be smaller than the cross-sectional area of the target section 23. Also, the cross-sectional area of the section continuous with the target section 23 at the other of the upstream section 21 and the downstream section 22 may be larger than the cross-sectional area of the target section 23.
[0075] In the example shown in FIG. 3, the cross-sectional area of the ventilation pipe corresponding to the front section 24 is smaller than the cross-sectional area of the housing 31, and the cross-sectional area of the ventilation pipe corresponding to the rear section 25 is larger than the cross-sectional area of the housing 31. That is, the cross-sectional area of the air passage 20 expands stepwise toward the downstream side in the air blowing direction. Alternatively, although not shown, the cross-sectional area of the ventilation pipe corresponding to the front section 24 may be larger than the cross-sectional area of the housing 31, and the cross-sectional area of the ventilation pipe corresponding to the rear section 25 may be smaller than the cross-sectional area of the housing 31. That is, the cross-sectional area of the air passage 20 may contract stepwise toward the downstream side in the air blowing direction.
[0076] In the example shown in FIG. 3, in the target section 23 of the air passage 20, a sound of a specific frequency f2 (= V / (4×L)×n) resonates inside the housing 31, and the lowest-order first resonance mode at the frequency f2 occurs. The antinode portion of the sound pressure distribution is located in the upstream end region within the target section 23, and the node portion of the sound pressure distribution is located in the downstream end region within the target section 23. Therefore, the vibrating body 33 is provided in the upstream end region within the target section 23 corresponding to the position of the antinode of the sound pressure distribution within the target section 23. As a result, the portion with the maximum displacement of the vibrating body 33 is appropriately arranged at a position closer to the antinode than the node in the sound pressure distribution, and the sound of the specific frequency f2 resonating in the air passage 20 can be effectively silenced.
[0077] Note that even if the cross-sectional area of the air passage 20 gradually decreases toward the downstream side in the air supply direction, only the direction of the air supply direction is reversed, and in the target section 23, a sound pressure distribution of the same frequency f2 as the configuration in FIG. 3 occurs, and the sound of the specific frequency f2 resonating in the air passage 20 can be effectively silenced.
[0078] Also, in the example shown in FIG. 3, the configuration having one vibrating body 33 has been described, but it is not limited thereto. For example, the number of vibrating bodies 33 may be increased according to the vibration mode. For example, as in the air passage 10C with a silencer shown in FIG. 4, compared with the example shown in FIG. 3, two new vibrating bodies 33 may be added in the intermediate region sandwiched between the end regions on both sides within the target section 23 corresponding to the position of the antinode of the sound pressure distribution. In this way, by increasing the number of vibrating bodies 33 according to the vibration mode, the sound of the specific frequency f2 resonating in the air passage 20 can be effectively silenced.
[0079] The air passages 10, 10A, 10B, 10C with silencers shown in FIGS. 1 to 4 described above are common in the following points. That is, in the air passage 20, the cross-sectional area of the section continuous with the target section 23 is smaller than the cross-sectional area of the target section 23 at at least one of the upstream section 21 and the downstream section 22. And the vibrating body 33 is provided in the end region located on the side of at least one location (the location where the cross-sectional area becomes smaller with respect to the target section 23) among the end regions on both sides within the target section 23. As a result, in at least one vibrating body 33, the maximum displacement portion thereof is arranged at a position closer to the antinode (specifically, the antinode located at the outermost end) than the node in the sound pressure distribution. Consequently, it is possible to effectively eliminate the sound of a specific frequency that resonates within the air passage 20.
[0080] Also, in the above-described embodiment, the housing 31 is configured to form an expansion portion, but it is not limited thereto. It may be configured such that the housing 31 forms a contraction portion, like the air passage 10D with a silencer shown in FIG. 5. More specifically, the cross-sectional area of the ventilation pipe corresponding to the front section 24 may be larger than the cross-sectional area of the housing 31. Also, the cross-sectional area of the ventilation pipe corresponding to the rear section 25 may be larger than the cross-sectional area of the housing 31.
[0081] In the example shown in FIG. 5, in the target section 23 of the air passage 20, the sound of a specific frequency f3 (=V / (2×L)×n) resonates within the housing 31, and the lowest-order first resonance mode at the frequency f3 occurs. The antinode portion of the sound pressure distribution is located in the intermediate region sandwiched between the end regions on both sides within the target section 23. Therefore, the vibrating body 33 is provided in the intermediate region within the target section 23 corresponding to the position of the antinode of the sound pressure distribution within the target section 23. As a result, the maximum displacement portion of the vibrating body 33 is appropriately arranged at a position closer to the antinode than the node in the sound pressure distribution, and it is possible to effectively eliminate the sound of the specific frequency f3 that resonates within the air passage 20.
[0082] Also, in the example shown in FIG. 5, the configuration having two vibrating bodies 33 has been described, but it is not limited thereto. For example, the number of vibrating bodies 33 may be increased according to the vibration mode. For example, like the air duct 10E with a silencer shown in FIG. 6, compared with the example shown in FIG. 5, corresponding to the positions of the antinodes of the sound pressure distribution, in the intermediate region sandwiched between the end regions on both sides within the target section 23, two new vibrating bodies 33 may be added. In this way, by increasing the number of vibrating bodies 33 according to the vibration mode, the sound of a specific frequency f3 resonating within the air duct 20 can be effectively silenced.
Example
[0083] Hereinafter, the present invention will be described more specifically with reference to examples. The materials, usage amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed 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.
[0084] Simulations 1 to 3 were conducted on the effects of the air duct with a silencer according to the present invention. The simulations were performed using the acoustic module of the finite element method calculation software COMSOL Multiphysics (COMSOL, Inc.).
[0085] <Simulation 1> Simulation 1 was performed by setting three conditions (Reference Example 1, Comparative Example 1, and Example 1) for the air duct with a silencer corresponding to FIGS. 1 and 2, specifically, in a configuration where the housing forms an expansion section.
[0086] [Reference Example 1] In Reference Example 1, a calculation model of the air duct with a silencer corresponding to FIGS. 1 and 2 was generated. Specifically, the housing was a box with a rectangular cross-section, and the ventilation pipes corresponding to the front section and the rear section were ventilation pipes with a circular cross-section, respectively. Regarding the inner dimensions of the housing, the length in the air supply direction was set to 260 mm, the length in the depth direction was set to 80 mm, and the length in the vertical direction was set to 50 mm. As the physical property values of the housing, the density was 952 kg / m 3 3, the Young's modulus was set to 1.2 GPa, the Poisson's ratio was set to 0.35, and the loss coefficient was set to 0.0312. For the dimensions (inner diameter) of the cross-sections of the ventilation pipes corresponding to the front section and the rear section, both were set to 30 mm. In Reference Example 1, without providing a vibrating body, the thickness of the side wall of the housing was made the same throughout the entire area.
[0087] [Comparative Example 1] Comparative Example 1 is different from Reference Example 1 in that it has a configuration with a vibrating body, but is the same as Reference Example 1 under other conditions. In the configuration shown in FIG. 1, it had a configuration with four vibrating bodies, but in Comparative Example 1, it had a configuration with one vibrating body. Specifically, one vibrating body was arranged at the center of the side wall in the air blowing direction (the middle region of the target section) on one side wall. The outer shape of the vibrating body was made rectangular, its planar size was set to 65 mm × 65 mm, and its thickness was set to 1.5 mm.
[0088] [Example 1] Example 1 is different from Comparative Example 1 in the arrangement position of the vibrating body on the side wall, but is the same as Comparative Example 1 under other conditions. Specifically, in Example 1, one vibrating body was arranged at one end of the side wall in the air blowing direction (one end region of the target section) on one side wall.
[0089] [Results of Simulation 1] A simulation was conducted on the relationship between the frequency of the sound passing through the above-described calculation model of the air passage with a muffler and the sound transmission loss by the muffler. The results are shown in FIG. 7. In FIG. 7, the horizontal axis represents the frequency and the vertical axis represents the transmission loss. In Reference Example 1 without a vibrating body, the transmission loss significantly decreased around 690 Hz. In contrast, in Comparative Example 1 and Example 1 with a vibrating body, the natural frequencies of the vibrating bodies were both around 670 Hz, and a silencing peak appeared around that frequency. On the other hand, the size of the silencing peak was larger in Example 1 than in Comparative Example 1. Specifically, the transmission loss in Comparative Example 1 was about 5.5 dB, while the transmission loss in Example 1 was about 16 dB. From this, it was found that Example 1 can obtain a better silencing effect than Comparative Example 1.
[0090] <Simulation 2> In Simulation 2, three conditions (Reference Example 1, Comparative Example 1, and Example 1) were set and performed on a duct with a muffler corresponding to FIGS. 3 and 4. Specifically, the cross-sectional area of the duct expands or contracts stepwise along the air supply direction.
[0091] [Reference Example 2] In Reference Example 2, a calculation model of a duct with a muffler corresponding to FIGS. 3 and 4 was generated. Specifically, the housing was a box with a rectangular cross-section, the ventilation pipe corresponding to the front section was a ventilation pipe with a rectangular cross-section, and the ventilation pipe corresponding to the rear section was a ventilation pipe with a circular cross-section. Regarding the inner dimensions of the housing, the length in the air supply direction was set to 150 mm, the length in the depth direction was set to 80 mm, and the length in the vertical direction was set to 50 mm. As the physical property values of the housing, the density was 952 kg / m 3 , the Young's modulus was set to 1.2 GPa, the Poisson's ratio was set to 0.35, and the loss coefficient was set to 0.0312. The inner dimension (diameter inside the pipe) of the ventilation pipe corresponding to the front section was set to 30 mm. The dimensions of the cross-section of the ventilation pipe corresponding to the rear section were set to 130 mm × 130 mm. In Reference Example 2, without providing a vibrating body, the thickness of the side wall of the housing was made the same throughout the entire area.
[0092] [Comparative Example 2] Comparative Example 2 is different from Reference Example 2 in that it has a configuration with a vibrating body, but other conditions are the same as those in Reference Example 2. In the configuration shown in FIG. 3, it had a configuration with two vibrating bodies, but in Comparative Example 2, it was configured to have one vibrating body. Specifically, one vibrating body was arranged on one side wall at the downstream end of the side wall (the end region on the rear section side within the target section). The outer shape of the vibrating body was rectangular, its planar size was set to 65 mm × 65 mm, and its thickness was set to 1.0 mm.
[0093] [Example 2] Example 2 is different from Comparative Example 2 in the arrangement position of the vibrating body on the side wall, but is the same as Comparative Example 2 under other conditions. Specifically, in Example 2, one vibrating body was arranged at the end on the front section side of the side wall (the end region on the front section side in the target section) on one side wall.
[0094] [Results of Simulation 2] A simulation was carried out on the relationship between the frequency of the sound passing through the calculation model of the air duct with a muffler described above and the sound transmission loss by the muffler. The results are shown in FIG. 8. In FIG. 8, the horizontal axis represents the frequency and the vertical axis represents the transmission loss. In Reference Example 2 without a vibrating body, the transmission loss significantly decreased around 525 Hz. In contrast, in Comparative Example 2 and Example 2 with a vibrating body, the natural frequencies of the vibrating bodies both existed around 487 Hz, and a sound absorption peak appeared around that frequency. On the other hand, the magnitude of the sound absorption peak was larger in Example 2 than in Comparative Example 2. Specifically, the transmission loss of Comparative Example 2 was about 13.5 dB, while the transmission loss of Example 2 was about 23 dB. Thus, it was found that Example 2 can obtain a better sound absorption effect than Comparative Example 2.
[0095] <Simulation 3> Simulation 3 was carried out by setting three conditions (Reference Example 3, Comparative Example 3, and Example 3) for the air duct with a muffler corresponding to FIGS. 5 and 6, specifically, in a configuration where the housing forms a reduced portion.
[0096] [Reference Example 3] In Reference Example 3, a calculation model of the air duct with a muffler corresponding to FIGS. 5 and 6 was generated. Specifically, the housing was a box with a rectangular cross-section, and the ventilation pipes corresponding to the front section and the rear section were both ventilation pipes with a rectangular cross-section. Regarding the inner dimensions of the housing, the length in the air supply direction was set to 240 mm, the length in the depth direction was set to 80 mm, and the length in the vertical direction was set to 50 mm. As the physical property values of the housing, the density was 952 kg / m 3 , the Young's modulus was set to 1.2 GPa, the Poisson's ratio was set to 0.35, and the loss coefficient was set to 0.0312. The cross-sectional dimensions of the ventilation pipes corresponding to the front section and the rear section were both set to 130 mm × 130 mm. In Reference Example 3, without providing a vibrating body, the thickness of the side wall of the housing was made the same throughout the entire area.
[0097] [Comparative Example 3] Comparative Example 3 is different from Reference Example 3 in that it has a configuration with a vibrating body, but other conditions are the same as those in Reference Example 3. In the configuration shown in FIG. 5, it had a configuration with four vibrating bodies, but in Comparative Example 3, it was configured to have one vibrating body. Specifically, one vibrating body was arranged on one side wall at one end of the side wall in the air supply direction (one end region of the target section). The outer shape of the vibrating body was made rectangular, its planar size was set to 65 mm × 65 mm, and its thickness was set to 1.5 mm.
[0098] [Example 3] Example 3 is different from Comparative Example 3 in the arrangement position of the vibrating body on the side wall, but other conditions are the same as those in Comparative Example 3. Specifically, in Example 3, one vibrating body was arranged on one side wall at the center of the side wall in the air supply direction (the middle region of the target section).
[0099] [Results of Simulation 3] A simulation was carried out on the relationship between the frequency of the sound passing through the calculation model of the air duct with a muffler described above and the sound transmission loss by the muffler. The results are shown in FIG. 9. In FIG. 9, the horizontal axis represents the frequency and the vertical axis represents the transmission loss. In Reference Example 3 without a vibrating body, the transmission loss significantly decreased around 630 Hz. In contrast, in Comparative Example 3 and Example 3 with a vibrating body, the natural frequencies of the vibrating bodies both existed around 670 Hz, and a sound attenuation peak appeared around that frequency. On the other hand, the magnitude of the sound attenuation peak was larger in Example 3 than in Comparative Example 3. Specifically, the transmission loss in Comparative Example 3 was about 14 dB, while the transmission loss in Example 3 was about 25 dB. From this, it was found that Example 3 can obtain a better sound attenuation effect than Comparative Example 3.
[0100] From the results of the simulation described above, the effects of the present invention are apparent.
Explanation of Signs
[0101] 10, 10A, 10B, 10C, 10D, 10E Air duct with silencer 20 Air duct 21 Upstream location 22 Downstream location 23 Target section 24 Front section (section continuous with the target section) 25 Rear section (section continuous with the target section) 30 Silencer 31 Housing 32 Side wall 33 Vibrating body 34 Fixed end 35 Peripheral part D, L Distance f1, f2, f3 Frequency P, Q, R Cross-sectional area
Claims
1. An air passage with a muffler, comprising: an air passage whose cross-sectional area in a cross-section intersecting the air blowing direction varies depending on the position in the air blowing direction; and a muffler that muffles the sound in the air passage, wherein the muffler has a vibrating body that muffles the sound in the air passage by vibrating due to the sound in the air passage, and is provided in a target section sandwiched between two positions that are different from each other in the air blowing direction and where the cross-sectional area changes in the air passage, and a portion of the vibrating body where the displacement during vibration is the largest is arranged at a position closer to the antinode than to the node in the sound pressure distribution of the sound in the air passage that resonates in the target section. An air passage with a muffler.
2. The portion of the vibrating body where the displacement during vibration is the largest is arranged at a position closer to the antinode than to the node in the sound pressure distribution of at least one resonance mode among the first to third resonance modes of the resonance sound in the target section. The air passage with a muffler according to claim 1.
3. The muffler further has a fixed end portion that serves as a fixed end when the vibrating body vibrates. The air passage with a muffler according to claim 1.
4. The fixed end portion is formed of the same material as the vibrating body. The air passage with a muffler according to claim 3.
5. The vibrating body is arranged at a position surrounding the air passage, and the fixed end portion protrudes at least to one of the inner side and the outer side of the air passage with respect to the vibrating body. The air passage with a muffler according to claim 3.
6. The muffler includes a housing, inside the housing, the target section of the air passage extends, and a part of the wall of the housing constitutes the vibrating body. The air passage with a muffler according to claim 1.
7. In the air passage, the cross-sectional area of a section continuous with the target section at at least one of the two locations is smaller than the cross-sectional area of the target section. The air passage with a muffler according to claim 1.
8. The vibrating body is provided in an end region located on the side of at least one of the two locations among the end regions on both sides in the target section. The air passage with a muffler according to claim 7.
9. In the air passage, the cross-sectional area of a section continuous with the target section at one of the two locations is smaller than the cross-sectional area of the target section, and the cross-sectional area of a section continuous with the target section at the other of the two locations is smaller than the cross-sectional area of the target section. The vibration body is provided in any of the end regions on both sides within the target section, and the air passage with a silencer according to claim 1.
10. In the air passage, the cross-sectional area of the section continuous with the target section at one of the two locations is smaller than the cross-sectional area of the target section, and the cross-sectional area of the section continuous with the target section at the other of the two locations is larger than the cross-sectional area of the target section. The vibration body is provided in the end region on the side of the one location among the end regions on both sides within the target section, and the air passage with a silencer according to claim 1.
Citation Information
Patent Citations
JP1987052736U
Cited By
Flexible composite ventilation and noise elimination channel structure, prefabricated cabin and cabinet
CN121545482A