Silencers and air supply systems

Abstract

The present invention provides a silencer and air supply system capable of broadbandly silencing low-frequency noise generated by a sound source within a housing of an air supply system. To silence the noise generated by the sound source within the housing, the silencer and air supply system of the present invention include a resonant silencer at a location within the air supply system that is connected to the space where the sound source resides. When the resonant silencer's individual resonant wavelength is λ, the distance from the resonant silencer to the sound source is less than λ / 2. The fundamental resonant frequency of the resonant silencer is below the upper limit of the sound frequency determined by the dimensions of the housing.

Description

Technical Field

[0001] The present invention relates to a silencer, and more particularly to a silencer used in an air supply system having a housing and configured to silence noise generated from a sound source within the housing. Furthermore, the present invention relates to an air supply system equipped with the silencer. Background Art

[0002] In air supply systems such as air blowers for air conditioners, silencers are sometimes placed in the air flow path (ventilation path) to reduce mechanical noise and other noise. One example of this is the technology described in Patent Document 1. This technology uses a resonant silencer to silence the sound generated by the electric blower.

[0003] Specifically, the electric blower disclosed in Patent Document 1 comprises: an impeller having multiple blades; an air guide having multiple fixed blades arranged around the impeller; a motor that drives a rotating shaft to which the impeller is fixed; and a generally cylindrical fan housing having an air intake inlet at the center for airflow into the impeller and an exhaust outlet on the side, secured to the motor so as to enclose the impeller and the air guide. Furthermore, the electric blower comprises: a soundproof cylinder having an exhaust outlet and airtightly secured to the fan housing so as to enclose the entire motor; a generally cylindrical silencer having a recessed portion of a predetermined width and depth on its circumference, disposed at a predetermined location on the surface of the motor; and a thin film portion having flexibility on the open end surface of the recessed portion of the silencer. This structure allows the electric blower to achieve sound attenuation by causing resonance of a specific frequency determined by the depth of the recess.

[0004] Previous technical literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2008-036065 Summary of the Invention

[0007] Technical issues to be solved by the invention

[0008] The air supply system generates noise over a wide bandwidth. Low-frequency sounds below 1kHz, in particular, are difficult to muffle using conventional sound-absorbing materials such as porous materials. Furthermore, conventional resonance mufflers, including the one described in Patent Document 1, muffle only a single frequency that coincides with the resonant frequency, resulting in narrow-band noise reduction. This means that conventional resonance mufflers cannot adequately muffle noise in the air supply system, necessitating a technology that can muffle low-frequency sounds over a wide bandwidth.

[0009] An object of the present invention is to solve the above-mentioned problems of the conventional technology and to provide a noise reduction device capable of silencing low-frequency sounds in a wide band of noise generated from a sound source in a housing included in an air supply system.

[0010] Furthermore, an object of the present invention is to provide an air supply system including the above-mentioned silencer.

[0011] Organizations for solving technical problems

[0012] The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by the following configuration.

[0013] [1] A silencer for use in an air supply system having a housing and for silencing noise generated by a sound source within the housing, the silencer being characterized in that a resonant silencer is provided at a position in the air supply system connected to a space where the sound source is located, wherein, when the resonant wavelength of the resonant silencer alone is set to λ, the distance between the resonant silencer and the sound source is less than λ / 2, and the basic resonant frequency of the resonant silencer is less than an upper limit frequency of the sound determined by the size of the housing.

[0014] [2] The silencer according to [1], wherein:

[0015] The noise is silenced by the first silencer, which is the basic resonance of the resonance silencer.

[0016] [3] The silencer according to [2], wherein:

[0017] The portion of the resonance silencer that acts on the noise has an end portion of the resonance silencer that is closest to the sound source, and the noise is silenced by the first and second silencers. The second silencer is generated by interference between the reflected sound generated by the noise reflected by the resonance silencer and the noise in the area between the sound source and the end portion of the resonance silencer. The frequency of the second silencer is higher than that of the first silencer.

[0018] [4] The silencer according to any one of [1] to [3], wherein:

[0019] The interior of the resonance muffler is communicated with the space where the sound source is located.

[0020] [5] The silencer according to any one of [1] to [4], comprising:

[0021] The vent is used to allow air supplied in the air supply system to pass through.

[0022] [6] The silencer according to any one of [1] to [5], wherein:

[0023] An insert made of at least one of a foam material, a nonwoven fabric, and a porous material is arranged inside the resonance muffler.

[0024] [7] The silencer according to any one of [1] to [6], further comprising a silencer body different from the resonance silencer

[0025] [8] The silencer according to [7], wherein:

[0026] The portion of the resonance silencer that acts on noise has an end portion of the resonance silencer that is the portion closest to the sound source, and the silencer is arranged in a region between the sound source and the end portion of the resonance silencer.

[0027] [9] The silencer according to [7] or [8], wherein:

[0028] The silencer is made of any one of a foam material, a non-woven fabric, and a porous material.

[0029]

[10] The silencer according to any one of [7] to [9], wherein:

[0030] A silencer is arranged outside the ventilation portion for allowing air supplied in the air supply system to pass therethrough.

[0031]

[11] An air supply system comprising:

[0032] An air supply system body having a sound source inside the housing; and

[0033] The silencer device according to any one of [1] to

[10] .

[0034]

[12] The air supply system according to

[11] , wherein:

[0035] The air supply system body supplies air through the rotation of the rotating body.

[0036]

[13] The air supply system according to

[12] , wherein:

[0037] The noise generated from the sound source in the housing includes the noise generated by the rotation of the rotating body.

[0038]

[14] The air supply system according to any one of

[11] to

[13] , wherein:

[0039] The air supply system body inhales air from the first end side of the air supply system body and exhausts air from the second end side of the air supply system body. The silencer is arranged at least on the second end side of the first end and the second end of the air supply system body.

[0040]

[15] The air supply system according to

[14] , wherein:

[0041] The silencers are respectively arranged on the first end side and the second end side of the air supply system body.

[0042]

[16] The air supply system according to any one of

[11] to

[15] , wherein:

[0043] The air supply system main body has rotating wings of an axial flow fan, and a ventilation portion is provided in the silencer for allowing air supplied by the axial flow fan to pass through. The area of ​​the cross section of the ventilation portion perpendicular to the rotation axis of the axial flow fan is smaller than the area of ​​the circle surrounded by the track through which the front end of the wing farthest from the rotation axis passes when the axial flow fan rotates.

[0044]

[17] The air supply system according to any one of

[11] to

[16] , wherein:

[0045] The part of the resonance silencer that acts on noise has an end portion of the resonance silencer that is closest to the sound source, the air supply system main body has a rotating blade of an axial flow fan, and the silencer device has a silencer body that is different from the resonance silencer, and the silencer body is closer to the rotating blade than the end portion of the resonance silencer.

[0046]

[18] The air supply system according to any one of

[11] to

[17] , wherein:

[0047] The main body of the air supply system is the blower.

[0048]

[19] The air supply system according to

[18] , wherein:

[0049] A heat exchanger is provided in the air supply system body.

[0050]

[20] The air supply system according to any one of

[11] to

[19] , wherein:

[0051] The air supply system main body has the rotating wings of an axial flow fan, the resonance silencer is an air column resonance type resonator with an opening portion, and the silencer device has a first end wall and a second end wall arranged on opposite sides of the rotating shaft of the axial flow fan, and an air vent is provided in the central portion of each of the first end wall and the second end wall, and the peripheral portion of the air vent in the second end wall is recessed toward the first end wall side, and a silencer composed of at least one of a foam material, a non-woven fabric and a porous material is arranged in the recessed portion provided by the peripheral portion of the air vent in the second end wall, and the silencer is closer to the rotating wings than the opening portion.

[0052] Effects of the Invention

[0053] According to the present invention, it is possible to provide a silencer capable of silencing low-frequency sounds in a wide band of noise generated from a housing sound source included in an air supply system, and an air supply system including the silencer. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a perspective view schematically showing an air supply system according to one embodiment of the present invention.

[0055] Figure 2 yes Figure 1 The front view of the air supply system is shown.

[0056] Figure 3 Yes Figure 2 Figure 2 of section II.

[0057] Figure 4 It means in Figure 2 The cutting surface when cutting the silencer in the JJ section.

[0058] Figure 5 It is a cross-sectional view of the air supply system according to the first modification.

[0059] Figure 6 It is a cross-sectional view of an air supply system according to a second modification.

[0060] Figure 7 It is a cross-sectional view of an air supply system according to a third modified example.

[0061] Figure 8 This is an illustration of the structural model.

[0062] Figure 9 It is a graph showing the simulation results and actual measurement results of the silencer volume when the structural model is used (Example 1).

[0063] Figure 10 Graphs showing simulation results of the acoustic tube model and the actual machine model for the respective amounts of silencer.

[0064] Figure 11 It is a diagram showing simulation results regarding the spatial distribution of the sound pressure level at 230 Hz.

[0065] Figure 12 It is a diagram showing simulation results regarding the spatial distribution of the sound pressure level at 403 Hz.

[0066] Figure 13 This is a diagram showing the distribution of local velocity corresponding to the spatial distribution of the sound pressure level at 403 Hz.

[0067] Figure 14 This is a graph showing the sound elimination frequencies calculated by changing the distance between the position of the internal sound source and the end of the resonance silencer for each of the first and second sound elimination methods of the silencer according to the present invention.

[0068] Figure 15This is a graph showing the amount of silencer calculations performed by changing the distance between the position of the internal sound source and the end of the resonance silencer for each of the first and second silencers of the silencer according to the present invention.

[0069] Figure 16 This is a diagram showing a model of the air supply device used in Reference Example 1.

[0070] Figure 17 This is a diagram showing a model of an air supply device used in Comparative Example 1.

[0071] Figure 18 This is a diagram showing a model of an air supply device used in Comparative Example 2.

[0072] Figure 19 Graphs showing the measurement results of the sound pressures of Reference Example 1 and Comparative Example 1.

[0073] Figure 20 1 and 2 are graphs showing the measurement results of the sound pressures of Comparative Examples 1 and 2, respectively.

[0074] Figure 21 It is a graph showing the measurement results of the sound pressure of each of Example 1 and Comparative Example 1.

[0075] Figure 22 This is a graph showing the results of reference calculation and actual measurement results regarding sound pressure in Reference Example 1.

[0076] Figure 23 This is a graph showing the results of reference calculation and actual measurement results regarding sound pressure in Example 1.

[0077] Figure 24 1 and 2 are graphs showing the simulation results of the sound pressure of each of Example 1 and Example 2.

[0078] Figure 25 3 is a graph showing the simulation results of the sound pressure of each of Example 1 and Example 3. DETAILED DESCRIPTION

[0079] Hereinafter, the present invention will be described in detail. In addition, the description of the components described below is based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.

[0080] In addition, the numerical range expressed using "to" in this specification means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0081] Furthermore, in this specification, the terms "orthogonal," "parallel," and "perpendicular" encompass the tolerances generally permitted in the technical field to which this invention pertains. For example, "orthogonal" also encompasses deviations from strictly orthogonal within a range of less than ±10°, and the tolerance for strictly orthogonal is preferably 3° or less.

[0082] Furthermore, for the angles involved in the following description, deviations within a range of less than ±10° may be permitted for the strict angles.

[0083] Furthermore, in this specification, “same”, “identical” and “identical” include an error range generally allowed in the technical field to which the present invention belongs.

[0084] [About the noise reduction device of the present invention]

[0085] The silencer of the present invention is a silencer for an air supply system having a shell and for silencing noise generated from a sound source in the shell. Furthermore, the silencer of the present invention is provided with a resonance silencer at a position connected to the space where the sound source is located in the air supply system. Here, the connection of the resonance silencer to the space where the sound source is located means that the resonance silencer exists in the space (sound field space) that transmits the noise generated from the sound source. For example, when the resonance silencer is a resonator of an air column resonance type or a Helmholtz resonance type, it means that its opening is connected to the interior of the shell. Alternatively, when the resonance silencer is a membrane type resonator, it means that the space facing the membrane surface is connected to the interior of the shell.

[0086] In addition, in the embodiment where the resonance silencer is connected to the space where the sound source is located, a porous sound absorbing material or a structure made of a breathable material such as cloth or non-woven fabric may be inserted in the middle.

[0087] Furthermore, in systems equipped with an air supply fan, the sound source is located at the tip of the fan's rotor blades (hereinafter referred to as the blade tip). Specifically, the location of the sound source can be determined by imaging the sound field space with a sound camera. Furthermore, by placing a conventional microphone near the location of the hypothesized sound source (e.g., the fan's rotor blades), measuring the sound pressure while varying the microphone's position, the sound source can be located at the location where the sound pressure level reaches a peak.

[0088] Furthermore, in the muffler of the present invention, when the resonance wavelength of the resonance muffler alone is λ, the distance between the resonance muffler and the sound source, that is, the distance between the resonance muffler and the sound source, is less than λ / 2.

[0089] The resonant wavelength λ of a resonant muffler can be defined as λ = C0 / fr, taking the peak frequency of transmission loss when a plane wave is incident on the resonant muffler as fr (Hz). Here, C0 is the speed of sound (m / s). The acoustic tube method is an experimental method for measuring muffler characteristics using acoustic plane waves, and transmission loss can be measured using the four-microphone transfer function method (specified in ASTM 2611E). The fundamental resonant frequency (i.e., the lowest resonant frequency) can be determined from the peak frequency of the measured transmission loss, and the resonant frequency λ can be calculated using the above equation.

[0090] As referenced later Figure 4 As shown, when a resonance muffler has an opening and extends from the side wall, a sound tube of the same size as the opening can be connected to the opening, and the resonance muffler can be measured with the structure located on the side wall. Similarly, for a resonance muffler formed by separating a ventilation portion, the sound tube can be arranged in the same manner as described above.

[0091] Furthermore, the distance between the resonant muffler and the sound source is the distance between the end of the resonant muffler and the sound source. The end of the resonant muffler is the portion of the resonant muffler that is closest to the sound source among the parts that act on the noise. If the resonant muffler is an air column resonance type or Helmholtz resonance type resonator, the portion of the opening of the resonator closest to the sound source corresponds to the end. If the resonant muffler is a membrane resonator, the portion of the membrane surface closest to the sound source corresponds to the end.

[0092] Furthermore, in the silencer of the present invention, the fundamental resonance frequency (resonance frequency in the primary mode) of the resonance silencer is equal to or lower than an upper limit frequency of sound determined by the size of the housing.

[0093] The upper limit frequency of sound is defined in JIS A 1405-2:2007, "Determination of sound absorption and impedance of acoustic tubes - Part 2: Transfer function method." For a circular tube, with its inner diameter d (m) and the speed of sound c0 (m / s), and the upper limit frequency of sound fu (Hz), the equation fu < 0.58 × c0 / d holds true. Furthermore, for a square tube, with its maximum cross-sectional dimension d (m), the equation fu < 0.50 × c0 / d holds true.

[0094] The upper limit frequency of sound indicates the upper limit of frequencies at which sound modes other than plane waves do not exist, that is, the upper limit of frequencies at which only plane waves can propagate. Furthermore, the natural sound modes of general propagation tubes, including those of the shell of the present invention, are determined by the tube's dimensions and shape. For circular and square tubes, the above equations are used to determine the natural sound modes. For other shapes, for example, the lowest-order natural sound mode can be determined by modeling the tube using the finite element method of sound and performing eigenvalue analysis. This frequency can then be used as the upper limit frequency of sound.

[0095] As described above, the silencer of the present invention can reduce low-frequency sounds below 1kHz from the noise generated by the sound source within the housing to a wideband. This is because the silencer of the present invention reduces noise through a combination of noise reduction dominated by the resonance of the resonant silencer (hereinafter referred to as "first noise reduction") and noise reduction dominated by near-field interference in the area between the sound source and the end of the resonant silencer (hereinafter referred to as "second noise reduction"). The first noise reduction is the fundamental resonance of the resonant silencer, that is, the lowest-order resonance.

[0096] The near-field region is an area extremely close to the sound source, and is an area near the sound source to the extent that the high-frequency components that do not propagate far away and attenuate are also not attenuated. Here, if the corresponding wave number k0 (= 2π×f0 / c0) is defined when the speed of sound is set to c0 and its frequency is set to f0, then within the range of high frequencies where the wave number k>k0, it attenuates spatially and exponentially as derived from the wave equation. This high-frequency component is called near-field sound. The near-field region is an area where near-field sound also contributes to interference. Near-field sound attenuates to the extent of wavelength λ. In addition, since interference requires sound to go back and forth, the distance when determining the near-field region is not set to λ but to λ / 2. Therefore, in this embodiment, the region where the distance from the sound source along the flow path of the air in the air supply system is less than λ / 2 is equivalent to the near-field region.

[0097] Near-field interference, as used in this disclosure, refers to interference generated in the near-field region, encompassing the near-field sound between the sound source and the resonant muffler. Specifically, it involves interference between the sound reflected from the resonant muffler and the sound radiated from the sound source. The inclusion of near-field interference increases the interference effect on the far-field region, and this interference affects the sound source, thereby suppressing the sound radiated from the sound source compared to far-field interference.

[0098] Furthermore, the frequency of the first muffler and the frequency of the second muffler are different from each other, but both are located in a frequency band with relatively high sound pressure on the low-frequency side below 1kHz in the sound pressure distribution (spectrum) within the shell determined by the shape and size of the shell. Specifically, the frequency of the first muffler is the basic resonant frequency of the resonant muffler, and the frequency of the second muffler is a frequency higher than the frequency of the first muffler (refer to Figure 10 ).

[0099] The noise reduction mechanism of the noise reduction device of the present invention will be described again in the following section.

[0100] [Structure of the air supply system of the present invention]

[0101] Regarding the structure of the air supply system of the present invention, Figures 1 to 4 The preferred specific examples will be described below. Figure 1 It is a schematic perspective view showing an air supply system (hereinafter referred to as an air supply system 10 ) according to one embodiment of the present invention. Figure 2 yes Figure 1 A front view of the air supply system 10 is shown. Figure 3 Yes Figure 2 Figure 2 of section II. Figure 4 It means in Figure 2 The cutting surface when cutting the silencer 30 in the JJ section. Figure 4 In the figure, the silencer 40 described later is omitted.

[0102] The air supply system 10 is used to supply air to a predetermined air supply destination, and Figure 1 As shown, there is an air supply system main body 12 and a silencer 30.

[0103] Hereinafter, the air supply system main body 12 and the silencer device 30 will be described separately.

[0104] (Air supply system main body)

[0105] like Figure 1 and Figure 3 As shown, the air supply system body 12 includes a housing 14 surrounding a sound source and supplies air by rotating a rotating body provided in the housing 14. For example, the air supply system body 12 is a blower, particularly a blower for air conditioning, and includes an axial flow fan 16 as a rotating body.

[0106] The axial flow fan 16 is a well-known axial flow fan, and has a rotor blade 16a including a plurality of blades. The rotor blade 16a has a plurality of blades. Figure 1 and Figure 3 The rotor blade 16a shown has, for example, four blades. However, the number of blades is not particularly limited. The shape of the blades of the rotor blade 16a can be the same as that used in a known axial flow fan.

[0107] In addition, hereinafter, the axial direction of the rotating shaft 16b is simply referred to as the "axial direction", and the radial direction of the rotating shaft 16b is simply referred to as the "radial direction".

[0108] The casing 14 is a box-shaped or cylindrical casing, sized to fully enclose the entire axial fan 16. An intake port 14a is provided at one axial end of the casing 14, the first end (strictly speaking, the upstream end in the air supply direction), and an exhaust port 14b, consisting of a circular hole, is provided at the other axial end, the second end (strictly speaking, the downstream end in the air supply direction). If the centerline of the rotating shaft 16b of the axial fan 16 is extended, the center of the exhaust port 14b is located on this extended centerline.

[0109] In addition, the air intake port 14a and the air exhaust port 14b may have the same size as each other or different sizes from each other.

[0110] Furthermore, inside the housing 14 (ie, inside the air supply system main body 12), on the upstream side of the axial flow fan 16, a Figure 1 and Figure 3 The heat exchanger 18 is shown. The heat exchanger 18 is composed of, for example, a fin coil, a fin hose, or a heat exchange plate. It exchanges heat with the air entering the housing 14 through the air intake 14a, thereby heating or cooling the air. As described above, the heat exchanger 18 allows air and air to ventilate, and therefore allows sound to pass through without blocking it.

[0111] In the air supply system main body 12 constructed as described above, the axial flow fan 16 is rotated by a motor (not shown), imparting kinetic energy to the air, thereby supplying air in the axial direction of the rotating shaft 16b. At this point, the air supply system main body 12 draws air in through the air intake 14a located at the first end, heats or cools the absorbed air through the heat exchanger 18, and exhausts it through the exhaust 14b located at the second end. As a result, the temperature-controlled air is supplied to the designated air supply destination.

[0112] Furthermore, as an accessory of the air supply system main body 12 , a cylindrical adapter (not shown) extending to the air supply destination may be attached to the exhaust port 14 b , and air may be supplied through the adapter.

[0113] Then, in the air supply system main body 12, when the axial flow fan 16 rotates within the casing 14, noise (referred to as fluid mechanical noise or air noise) is generated from the tips of the rotor blades 16a due to the air being blocked by the rotating blades. In other words, the noise generated from the sound source within the casing 14 includes the noise generated by the rotation of the axial flow fan 16 as a rotating body.

[0114] The blade tip of the rotor blade 16 a is a portion of the rotor blade 16 a that is farthest from the rotation axis 16 b .

[0115] The noise is released from the housing 14 through the exhaust port 14b along with the sent air. The noise generated by the axial flow fan 16 rotating in the housing 14 has a high sound pressure over a wide band at low frequencies (a wide sound pressure distribution).

[0116] On the other hand, Figure 1 and Figure 3 As shown, a silencer 30 is installed on the downstream wall of the shell 14 (i.e., the second end side of the air supply system body 12), and the above-mentioned noise passing through the exhaust port 14b is silenced by the silencer 30, mainly reducing the sound pressure on the low-frequency side.

[0117] In the above example, the air supply system main body 12 is a blower, but the present invention is not limited thereto and may also be a compressor, exhaust fan, or vacuum pump. Furthermore, the air supply system main body 12 can be used for various purposes, including indoor and outdoor units of air conditioners for cooling and heating, car air conditioners, air purifiers, ventilation fans, fans, circulators, dehumidifiers, humidifiers, jet engines, cooling fans for computers and server computers, other cooling fans, and windmills.

[0118] Furthermore, in the above example, the rotating body of the air supply system main body 12 is an axial flow fan 16, but the fan as a rotating body may be, for example, a centrifugal fan, a backward fan (turbo fan), an airfoil fan, a radial fan, a blade fan (paddle fan), a multi-blade fan (multi-blade fan), a tube centrifugal fan, a diagonal flow fan, an axial flow fan, a blade axial flow fan, a tube axial flow fan, a propeller fan, a reverse axial flow fan, a cross flow fan (cross flow fan) or a vortex fan, etc.

[0119] Furthermore, the rotating body is not limited to a fan, and may be a blower or compressor used in a turbo compressor or a turbo blower, etc. Furthermore, it is also possible to use an air supply system body using a rotating body other than the above-mentioned types.

[0120] (Silencer)

[0121] The silencer 30 silences noise generated by a sound source within the casing 14 of the air supply system main body 12 , specifically, noise (fluid mechanical noise or aerodynamic noise) caused by the rotor blades 16 a of the axial flow fan 16 cutting through the air during rotation.

[0122] Regarding the muffler 30, in the front view Figure 2 It is shown as a roughly rectangular shape, as shown in the top view. Figure 4The silencer 30 is at least arranged on the second end side of the air supply system body 12 and is mounted on the end face of the exhaust side of the housing 14. Figure 1 Although the illustrated embodiment is different from the embodiment, the silencer 30 may be disposed on each of the first end side and the second end side of the air supply system main body 12 .

[0123] The silencer 30 has a cavity for ventilation (i.e., a vent 32 described below). This cavity is attached to and fixed to the housing 14 while communicating with the interior of the housing 14. The mechanism for securing the silencer 30 to the housing 14 is not particularly limited. For example, the silencer 30 may be bonded to the end surface of the housing 14 using an adhesive or adhesive tape, or it may be secured to the housing 14 using fasteners such as screws or bolts. Alternatively, a convex portion such as a boss may be provided on one side of the silencer 30 and the housing 14, and a concave portion such as an insertion hole may be provided on the other side. The convex portion may be inserted into the concave portion, engaging the two, thereby securing the silencer 30 to the housing 14. Furthermore, when a cylindrical adapter is attached to the exhaust port 14b of the housing 14, the cylindrical adapter can be inserted into the cavity of the silencer 30 to secure the silencer 30 to the housing 14.

[0124] like Figure 3 As shown, the silencer 30 has a vent 32 formed by a cavity portion penetrating the silencer 30 in the axial direction, and a resonance silencer 34 disposed around the vent 32. The resonance silencer 34 is, for example, an air column resonance type resonator. Figure 3 In the illustrated embodiment, the pipe forming the internal space is bent into an L-shape, extends radially outward, then bends substantially vertically and extends in the axial direction.

[0125] The silencer 30 of this embodiment includes a first end wall 36, a second end wall 37, and a side wall 38, which form an air column resonance resonator. Specifically, the first end wall 36 is a rectangular plate located at the end of the silencer 30 on the exhaust side (the side opposite the housing 14 in the axial direction). The second end wall 37 is located at the end opposite the first end wall 36 (the side on the housing 14 side) and is a rectangular plate with an outer edge the same size as the first end wall 36. The side wall 38 is a square cylindrical portion that connects the first end wall 36 and the second end wall 37 in the axial direction.

[0126] like Figure 2 and Figure 3As shown, circular or rectangular ventilation holes 36a and 37a are provided in the center of each of the first end wall 36 and the second end wall 37. The ventilation portion 32 is formed by a generally cylindrical cavity extending between the axial ends of the muffler 30. Furthermore, the centers of the ventilation holes 36a and 37a are aligned on the same straight line. For example, if the center line of the rotating shaft 16b of the axial flow fan 16 is extended, the centers of the ventilation holes 36a and 37a can be aligned on the extension line. Furthermore, the two ventilation holes 36a and 37a preferably have the same diameter, but can also have different diameters.

[0127] like Figure 4 As shown, the periphery of the vent hole 37a in the second end wall 37 is recessed toward the first end wall 36, forming a recessed portion. The first end wall 36, second end wall 37, and side wall 38 constructed as described above form an air column resonance resonator with an L-shaped pipe cross section. Specifically, the first end wall 36 and second end wall 37 form the two ends of the air column resonance resonator in the axial direction.

[0128] The portion of the second end wall 37 located axially closest to the axial flow fan 16 may be formed by utilizing the outer wall of the casing 14 of the air supply system body 12 (specifically, the outer wall on the exhaust side).

[0129] And, as Figure 3 and 4 As shown, the gap between the edge portion of the vent hole 36a of the first end wall 36 and the edge portion of the vent hole 37a of the second end wall 37 forms the opening portion 35 of the air column resonance type resonator. The opening portion 35 corresponds to the portion that acts on the noise in the air column resonance type resonator. Moreover, the end of the opening portion 35 closest to the sound source side corresponds to the end of the resonance silencer 34. Furthermore, the distance (axial spacing) between the front end of the rotating wing 16a of the axial flow fan 16, that is, the sound source and the end of the resonance silencer 34 is less than λ / 2 as described above, more preferably less than λ / 4, and particularly preferably less than λ / 6.

[0130] The interior of the resonance muffler 34 is surrounded by a first end wall 36, a second end wall 37, and side walls 38. It communicates with the interior of the housing 14, where the sound source resides, through an opening 35. Noise generated on the air supply system main body 12 side then enters the resonance muffler 34 through the opening 35.

[0131] The vent 32 is a cavity portion provided for allowing the air supplied in the air supply system 10, specifically the air flow generated by the rotation of the axial flow fan 16, to pass through. Figure 3 and 4 As shown, the vent portion 32 extends straightly in the axial direction and communicates with the housing 14 of the air supply system body 12. Figure 3As shown, it is connected to the exhaust port 14 b (opening on the exhaust side) of the housing 14 .

[0132] The diameter of the vent 32 is the same as or smaller than the diameter of the exhaust port 14b. Figure 3 As shown, the diameter of the vent 32 can be substantially the same as the outer diameter of the rotor blades 16a of the axial flow fan 16. Here, the outer diameter of the rotor blades refers to the diameter of the circle enclosed by the orbital path (hereinafter referred to as the orbital circle for convenience) along which the blade tips of the rotor blades 16a of the axial flow fan 16 rotate during rotation. In other words, the cross-sectional area of ​​the vent 32 (strictly speaking, the area of ​​the cross-section perpendicular to the rotation axis 16b of the axial flow fan 16) can be the same as the area of ​​the orbital circle.

[0133] In addition, if Figure 5 As shown, the cross-sectional area of ​​the vent 32 can be smaller than the area of ​​the orbital circle. In this case, the noise level decreases as the cross-sectional area decreases. By shaping the middle portion, it is possible to ensure sufficient air flow while minimizing the obstruction of the airflow generated by the axial fan 16. For example, the shape of the muffler 40 or the wall is preferably connected continuously from the axial fan 16 to the vent 32 in an inclined structure (e.g., a tapered shape).

[0134] The resonance muffler 34 is positioned so as to surround the vent 32 and not to obstruct the flow of air within the vent 32. Furthermore, the opening 35 of the resonance muffler 34 is positioned radially opposite the vent 32 and is provided continuously in an annular shape along the edges of the vent holes 36a and 37a. However, this is not limiting; the opening 35 may also be formed discontinuously at predetermined intervals in the circumferential direction of the vent 32 (along the edges of the vent holes 36a and 37a).

[0135] Furthermore, the resonant muffler 34 is not limited to an air column resonance type resonator and can also be a Helmholtz resonance type resonator. Whether the resonant muffler 34 is an air column resonance type or a Helmholtz resonance type resonator is determined by the size and position of the opening 35 and the size of the internal space of the resonator. Therefore, by appropriately adjusting these, it is possible to select which resonant structure is the air column resonance or the Helmholtz resonance.

[0136] Furthermore, if the resonant muffler 34 is of the air column resonance type, a narrow opening 35 will reflect sound waves from the opening 35, making it difficult for sound waves to enter the internal space. Therefore, it is preferable that the opening 35 be somewhat wide. Specifically, the width (axial length) of the opening 35 is preferably 1 mm or greater, more preferably 3 mm or greater, and even more preferably 5 mm or greater. If the opening 35 is circular, the diameter is preferably within the above range.

[0137] Furthermore, the resonant silencer 34 may be a membrane-type resonant resonator. In this case, the resonant silencer 34 comprises a frame and a membrane supported by the frame in a vibrating state, with a rear space enclosed by the frame and the membrane. The membrane resonates when it vibrates. The membrane-type resonant resonator is positioned so as not to obstruct the flow of air in the vent 32, with the membrane being approximately parallel to the axial direction and facing radially inward.

[0138] The resonance muffler 34 may be any one of an air column resonance type resonator, a Helmholtz resonance type resonator, and a membrane type resonator, or may be a combination of two or three of them.

[0139] Here, the materials of the various parts of the resonance muffler 34 (for example, the first end wall 36, the second end wall 37, and the side wall 38) when the resonance muffler 34 is a membrane resonator or a Helmholtz resonator, and the material of the frame when the resonance muffler 34 is a membrane resonator are collectively referred to as "frame materials." Examples of the frame material include metal materials, resin materials, reinforced plastic materials, and carbon fibers.

[0140] Examples of the metal material include aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium-molybdenum, nichrome-molybdenum, copper, stainless steel, and alloys thereof. Furthermore, the frame material can be formed by processing a so-called metal plate.

[0141] Examples of the resin material include acrylic resin, polymethyl methacrylate, polycarbonate, polyamide-imide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, ABS resin (acrylonitrile, butadiene, styrene copolymer resin), polypropylene, and triacetyl cellulose.

[0142] Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP: Carbon Fiber Reinforced Plastics) and glass fiber reinforced plastics (GFRP: Glass Fiber Reinforced Plastics).

[0143] As the frame material, natural rubber, chloroprene rubber, butyl rubber, EPDM (ethylene-propylene-diene rubber), silicone rubber, and rubbers including cross-linked structures thereof can be used.

[0144] Furthermore, honeycomb core materials can also be used as frame materials. Honeycomb core materials are lightweight and highly rigid, making them readily available. Specifically, honeycomb materials made of various raw materials can be used as frame materials, including aluminum honeycomb, FRP honeycomb, paper honeycomb (manufactured by ShinNippon Feather Core Co., Ltd., Showa Aircraft Industry Co., Ltd., etc.), and thermoplastic resin honeycomb (manufactured by Gifu Plastic Industry Co., Ltd., TECCELL, etc.).

[0145] Furthermore, as a frame material, a structure including air, specifically a foam material, a hollow material or a porous material can be used. When a plurality of resonators are formed, in order to prevent ventilation between the resonators, for example, a foam material with independent bubbles can be used. Specifically, various materials such as independent bubble polyurethane, independent bubble polystyrene, independent bubble polypropylene, independent bubble polyethylene and independent bubble rubber sponge can be selected. By using an independent bubble body, compared with a continuous bubble body, sound, water and gas are not allowed to pass through, and the structural strength is large, so it is suitable for use as a frame material. In addition, when the porous sound-absorbing body has sufficient support, only the porous sound-absorbing body can be used as the frame material. As described above, by using a structure containing air inside as a frame material, the silencer 30 can be made lighter and the silencer 30 can be given heat insulation.

[0146] Furthermore, when the resonance silencer 34 is a membrane-type resonator, metal materials, resin materials, reinforced plastic materials, carbon fibers, and rubbers can be used as the material of the membrane.

[0147] And, as Figure 6 As shown, a sound absorbing insert 39 may be disposed inside the resonance silencer 34. This allows for wide-band sound at frequencies other than the aforementioned first and second silencers.

[0148] Insert 39 may be any one of a foam material, a nonwoven fabric, and a porous material, or a combination of two or more. Known materials can be used to form insert 39. For example, foam materials such as urethane foam, soft urethane foam, wood, sintered ceramic particles, phenol foam, and materials containing minute air pockets; glass wool, rock wool, microfibers such as Thinsulate manufactured by 3M; carpets, rugs, meltblown nonwoven fabrics, metal nonwoven fabrics, polyester nonwoven fabrics, metal wool, felt, insulation boards, fiber and nonwoven fabric materials such as glass nonwoven fabrics; wood wool cement board; nanofiber materials such as silica nanofibers; and gypsum board.

[0149] And, as Figure 3 As shown, the silencer 30 further includes a silencer body 40, which is different from the resonance silencer 34. The silencer body 40 is a component that absorbs sound to reduce noise. Specifically, similar to the insert 39 described above, the silencer body 40 can be made of any one of a foam material, a nonwoven fabric, and a porous material, or a combination of two or more. The specific material of the silencer body 40 can be the same as the material of the insert 39 mentioned above.

[0150] like Figure 3 As shown, the silencer 40 is arranged radially outward from the vent 32, and is positioned so as not to obstruct the flow of air in the vent 32. Specifically, the silencer 40 is arranged in the region axially between the rotor blades 16a (i.e., the sound source) of the axial flow fan 16 and the end of the resonance muffler 34, so as to surround the vent 32. The silencer 40 arranged in this region is located closer to the rotor blades 16a than to the opening 35 including the end of the resonance muffler 34.

[0151] Furthermore, to prevent the size of the silencer 30 from increasing due to the provision of the silencer 40, the silencer 40 may be disposed within a recessed portion formed by recessing the periphery of the vent hole 37a in the second end wall 37 constituting the resonance silencer 34. This allows the silencer 40 to be provided in a compact manner.

[0152] Furthermore, by using the silencer 40 formed in an annular shape, the silencer 40 can be arranged continuously in the circumferential direction of the ventilation portion 32. In this case, as shown in FIG. Figure 3 As shown, the through hole 40a in the center of the muffler 40 may be a straight hole, or Figure 7 As shown, the hole may also be a cone-shaped hole.

[0153] Alternatively, the silencer 40 may be provided discontinuously at predetermined intervals in the circumferential direction of the ventilation portion 32 .

[0154] [Regarding the Noise Elimination Mechanism of the Noise Elimination Device of the Present Invention]

[0155] In order to clarify the noise reduction mechanism of the noise reduction device 30 of the present invention, a structural model described below was created and the noise reduction amount of the resonance noise reduction device 34 was calculated by simulation. The structural model corresponds to the actual device of Example 1 described below.

[0156] <About the structural model>

[0157] The structural model is Figure 8The model of the air supply system 10 shown. The air supply system main body 12 of the air supply system 10 is a "MULTICUBE" air conditioner manufactured by Daikin Industries, Ltd. This is a personal air conditioner with an internal heat exchanger and uses an axial flow fan 16 with a rotor blade diameter of 310 mm for air supply.

[0158] The housing dimensions are 550 mm wide x 360 mm high x 400 mm deep, with an opening (i.e., exhaust port 14b) of 350 mm in diameter provided on the exhaust side. An optional product can be used to convert the opening diameter to 250 mm.

[0159] Furthermore, in the structural model, a silencer 30 having a resonance silencer 34 forming an L-shaped air column resonance structure is installed on the exhaust side of the housing of the air conditioner. Figure 8 As shown, a 70mm long cylindrical inner tube is attached to the opening of the housing 14. A 350mm outer diameter annular plate with an opening of 250mm diameter is attached to the end of the inner tube. The annular plate is made of acrylic and has a thickness of 5mm. The inner space of the inner tube forms a ventilation portion 32, through which air flows out of the air conditioner. The air supply intensity of the air conditioner is set to High mode.

[0160] Moreover, if Figure 8 As shown, a square outer cylinder is attached to the outer edge of the housing 14, and a rectangular plate measuring 550 mm wide by 360 mm long and having an opening with a diameter of 250 mm is attached to the end of the outer cylinder (the end opposite the housing 14). This forms a resonance muffler 34 with an L-shaped air column resonance structure, which is arranged at the exhaust-side front end of the housing 14 so that the exhaust port 14b and the vent 32 are aligned.

[0161] In addition, the dimensions of each part of the resonance silencer 34 (specifically, Figure 4 , the values ​​represented by the symbols d1, d2, h, t1, t2 and w) are as follows.

[0162] d1=250mm, d2=350mm, h=360mm

[0163] t1=60mm, t2=70mm, w=550mm

[0164] And, as Figure 8 As shown, a ring-shaped sound-absorbing urethane with an outer diameter of 350 mm and a 250 mm opening in the center is arranged inside the inner cylinder. The sound-absorbing urethane forms a silencer 40, and has a thickness of 70 mm and a flow resistance of 10^4 Rayls. Figure 8As shown, the sound-absorbing urethane is arranged so as to be accommodated in the corner portion bent into an L-shape in the air column resonance type resonance muffler 34 .

[0165] Simulation results

[0166] The simulation results using the above structural model are shown in Figure 9 .like Figure 9 As shown, the simulated noise cancellation amount corresponds well to the measured value (specifically, the measured result of Example 1 described later). Furthermore, the simulation results clearly show that a wideband noise cancellation effect with multiple peaks in the low-frequency region can be obtained.

[0167] Here, for the purpose of dividing the sound source in the housing 14 (hereinafter also referred to as the internal sound source), The amount of sound attenuation in a system in which the above-mentioned resonance silencer 34 is installed on a sound pipe was calculated by constructing a simulation model (hereinafter referred to as the sound pipe model). That is, the incident wave was treated as a plane wave from a distance and the transmittance and reflectance of the sound were calculated, and the absorption and transmission losses were calculated. In addition, the sound attenuation effect when the resonance silencer 34 was installed in an actual machine model with an internal sound source (a model in which the silencer 40 was removed from the above-mentioned structural model) was also calculated. The calculation results of each amount of sound attenuation are shown in FIG. Figure 10 .

[0168] The acoustic tube model exhibits a single peak frequency for noise cancellation. This is a common tendency in conventional resonators. On the other hand, the actual machine model exhibits noise cancellation peaks at multiple, distinct frequencies, specifically around 230 Hz and 400 Hz.

[0169] The above results demonstrate that installing the resonant silencer 34 in the internal sound source system achieves broadband noise cancellation in the low-frequency range, a characteristic of the present invention. To investigate this mechanism, the spatial distribution of acoustic characteristics (sound pressure and local velocity) at the two noise cancellation peaks was calculated.

[0170] First, the spatial distribution of the sound pressure level at 230 Hz is shown in FIG. Figure 11 .exist Figure 11 In the diagram, the upper side is the exhaust side and the lower side is the intake side. Figure 11 It can be seen that the sound pressure is high inside the L-shaped resonant muffler 34, while the sound pressure is low near the opening on the exhaust side of the muffler 30. It is speculated that the radiated sound from the resonant muffler 34 cancels out the sound components that resonate within the resonant muffler 34 and are radiated to the outside of the air supply system 10. Therefore, it can be seen that the resonance characteristics of the resonant muffler 34 dominate the sound reduction peak at 230 Hz, which is on the lower frequency side.

[0171] Next, the spatial distribution of the sound pressure level at 403 Hz is shown in FIG. Figure 12 , and the corresponding local velocity distribution is shown in Figure 13 .from Figure 12 It can be seen that inside the L-shaped resonance muffler 34, there is no relatively high sound pressure, and it is not a simple resonance phenomenon. Figure 13 It can be seen that in the vertical direction (i.e., axial direction), the phase of the local velocity from the internal sound source and the phase of the local velocity of the reflected sound radiated from the resonance silencer 34 are opposite, so a canceling interference occurs. At this time, it is speculated that the sound stays and is confined in the area between the position of the internal sound source and the position of the end of the resonance silencer 34 (hereinafter referred to as the "middle layer" for convenience), making it difficult for the sound to be radiated to the outside. This is consistent with Figure 12 The situation that the sound pressure in the middle layer increases is consistent.

[0172] As described above, it can be seen that the broadbandization is based on the following: the noise reduction characteristics of the present invention in the low-frequency region are the first noise reduction near 230 Hz dominated by the resonance phenomenon of the resonance silencer 34 and the second noise reduction near 403 Hz dominated by the near-field interference (sound limitation) in the intermediate layer.

[0173] In the second silencing, the distance between the internal sound source and the end of the resonance silencer 34, namely, the thickness of the intermediate layer, becomes important. Therefore, the frequency and amount of noise reduction were calculated for each of the first and second silencing, using the thickness of the intermediate layer as a parameter. Furthermore, similar to the above-mentioned structural model, the L-shaped resonance silencer 34 was positioned on the exhaust port 14b side of the housing 14, and the thickness of the intermediate layer was varied.

[0174] Regarding the above calculation results, Figure 14 The mute frequency is shown in Figure 15 The amount of silenced sound is shown in . In addition, λ in each figure represents the resonance wavelength of the resonance silencer 34 alone measured by the acoustic tube.

[0175] As the thickness of the intermediate layer increases, the amount of muffling in the first muffler gradually decreases. That is, regarding resonance on the low-frequency side, the end of the resonant muffler 34 is positioned closer to the internal sound source, and its muffling becomes greater. Furthermore, if the thickness of the intermediate layer is greater than approximately λ / 4, the amount of muffling in the second muffler also gradually decreases. Then, if the thickness of the intermediate layer becomes approximately λ / 2, the amount of muffling in the first muffler is less than 1dB, making it virtually impossible to achieve the broadband muffling effect that is the effect of the present invention. Furthermore, the thicker the intermediate layer, the larger the muffler device.

[0176] In summary, it is believed that a thickness of the intermediate layer less than λ / 2 is necessary to achieve the broadband noise reduction effect of the present invention. Furthermore, considering the magnitude of the noise reduction in the second noise reduction, the thickness of the intermediate layer is preferably less than λ / 4.

[0177] Example

[0178] The present invention will be described in detail below based on Examples 1 to 3. The materials, amounts used, ratios, treatment contents, and treatment sequences shown in the following examples may be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[0179] [Example 1]

[0180] Example 1 uses Figure 8 The same structure as the above-mentioned structural model was used as an actual machine. In Experiment 1, the distance between the position of the internal sound source and the position of the end of the resonance silencer 34, that is, the thickness of the intermediate layer was set to 120 mm.

[0181] [Reference Example 1]

[0182] In Reference Example 1, we used Figure 16 The air supply device 52 shown is constructed from the air conditioner (MULTICUBE, manufactured by Daikin Industries, Ltd.), which constitutes the air supply system main body 12 in Example 1. The air supply device 52 has a structure in which a 70 mm long cylinder 54 is attached only to the exhaust port 14b (350 mm diameter) of the housing 14. In other words, Reference Example 1 does not include the silencer of Example 1. Other than this, the conditions are the same as those of Example 1.

[0183] In addition, for Figure 16 The parts of the air supply device 52 shown in the figure that are the same as those in the first embodiment are marked with Figure 8 The same symbols as those in .

[0184] [Comparative Example 1]

[0185] In Comparative Example 1, Figure 17 As shown, a circular plate 56 with an outer diameter of 350 mm and an opening of 250 mm in diameter is attached to the end of the cylinder 54 in Reference Example 1. That is, the opening on the exhaust side is reduced to 250 mm, and other conditions are the same as those in Reference Example 1.

[0186] In addition, for Figure 17 The parts of the device shown in the figure that are the same as those in Reference Example 1 are marked with Figure 16 The same symbols as those in .

[0187] [Comparative Example 2]

[0188] In Comparative Example 2, Figure 18 As shown, the cylinder 54 in the device of Comparative Example 1 is provided with a 350 mm outer diameter and a central portion having That is, the sound absorbing urethane 58 is filled in the area outside the exhaust opening of the cylinder 54 of Comparative Example 1. The thickness of the sound absorbing urethane 58 is 70 mm, and the flow resistance is 10^4 Rayls.

[0189] (Measurement of sound)

[0190] In each of Example 1, Reference Example 1, and Comparative Examples 1 and 2, sound measurements were performed while the air conditioner was running and the axial flow fan 16 was rotating. For the sound measurements, microphones were placed at positions offset by 1 meter in both the depth and height directions from the center of the exhaust opening, and sound pressure was measured at a position not directly exposed to the wind.

[0191] The measurement results of Reference Example 1 and Comparative Example 1 are shown in FIG. Figure 19 By reducing the diameter of the exhaust opening, high-frequency noise is reduced, but low-frequency noise, including narrow-band noise around 450 Hz (noise with high sound pressure), still remains.

[0192] The measurement results of Comparative Examples 1 and 2 are shown in FIG. Figure 20 In Comparative Example 2, although the noise of high-frequency sounds above 1 kHz is reduced due to the effect of the sound-absorbing urethane 58 compared to Comparative Example 1, the noise of low-frequency sounds does not decrease compared to Comparative Example 1 and tends to increase with frequency.

[0193] The measurement results of Example 1 and Comparative Example 1 are shown in Figure 21 In Example 1, compared with Comparative Example 1 in which the opening diameter on the exhaust side is the same, the noise in the region above 600 Hz is reduced, and the noise in the frequency band around 450 Hz, which could not be reduced in the other examples (Reference Example 1, Comparative Example 1, and Comparative Example 2), can also be silenced.

[0194] Furthermore, for each of Example 1, Reference Example 1, and Comparative Examples 1 and 2, the noise level across all frequency bands was evaluated using the A-characteristic sound pressure level. The difference in noise level with respect to Reference Example 1 was calculated and shown in Table 1. The A-characteristic sound pressure level is the noise level (unit: dBA) obtained by integrating the volume after performing A-characteristic correction, which takes into account the sensitivity of the human ear, across the entire audible frequency band.

[0195] [Table 1]

[0196] Reference Example 1 Comparative Example 1 Comparative Example 2 Example 1 Noise level in all frequency bands (dBA) 60.1 58.7 57.8 54.4 Difference from Reference Example 1 (dBA) - 1.4 2.3 5.7

[0197] As shown in Table 1, the installation of the resonance muffler 34 reduces noise by 5.7 dBA compared to the original state (Reference Example 1), and by 4.3 dBA compared to Comparative Example 1, which has the same exhaust opening diameter. Generally speaking, a difference of 3 dBA is sufficiently perceptible to the average person's hearing. Therefore, Example 1 exhibits a high noise reduction effect while maintaining the same exhaust opening diameter. Furthermore, even when using only conventional sound-absorbing material (specifically, sound-absorbing urethane 58) as in Comparative Example 2, the difference from Comparative Example 1 is only 0.9 dBA. In contrast, Example 1 achieves a greater noise reduction effect due to the effect of the resonance muffler 34.

[0198] Furthermore, when measuring the sound pressure, the sound was recorded at the position where the measurement microphone was arranged, and the results of the comparison were listened to. The difference between Example 1 and Comparative Examples 1 and 2 was clearly recognized.

[0199] (See comparison of calculation and experimental results)

[0200] Reference calculations corresponding to the above-mentioned sound pressure measurement experiments were performed. Specifically, for each of Reference Example 1, Comparative Examples 1-2, and Example 1, the housing housing the axial flow fan was modeled using the finite element method calculation software "COSMOL Multiphysics." The axial flow fan was then treated as an internal sound source, and a dipole sound source was placed at the tip of the axial flow fan's rotor blades to calculate the sound pressure distribution. Furthermore, to verify the calculated results, a sound pressure distribution measurement experiment was conducted using semi-silent room sound.

[0201] Regarding the original state, the opening diameter corresponding to the exhaust side is The results of reference calculation and experiment are shown in Figure 22 From the comparison of the two results, it can be seen that the reference calculation results reproduce the experimental results well.

[0202] Similarly, regarding the state where the resonance muffler is configured, that is, the state corresponding to Example 1, it can be seen from the comparison of the reference calculation and the experimental results that Figure 23 As shown, the results of the reference calculations reproduce the experimental results well.

[0203] In summary, the reference calculations were compared with experiments using a semi-silent room. The results showed that the reference calculations could reproduce the experiments (actual measurements) with sufficient accuracy.

[0204] Furthermore, the results of modeling and calculations for each of the device configurations of Reference Example 1, Comparative Examples 1-2, and Example 1 showed that the spectral profiles and the amount of attenuation obtained from conventional laboratory experiments were well reproduced. The calculated results of the amount of attenuation are shown in Table 2.

[0205] [Table 2]

[0206]

[0207] In the first embodiment, a feature is that a plurality of noise cancellation peaks are present in the low frequency region to achieve broadband noise cancellation. Figure 9 In the figure, the measured value and simulation result of the muffler volume of Example 1 are shown when a resonance muffler is installed. Figure 9 In the noise level of the resonance silencer, the noise level of the resonance silencer is calculated by blocking the inlet of the resonance silencer with a wall and subtracting the value of the evaluation from the noise level. Figure 9 As shown in FIG. 1 , when the resonance silencer is set, silencer peaks appear near 200 Hz and 350-500 Hz.

[0208] Then, a model corresponding to Example 1 was made (ie, Figure 8 The structural model shown in the figure was used to simulate the attenuation of the resonance muffler. The results showed that the simulated attenuation was in good agreement with the experimental value (refer to Figure 10 ). Then, it was confirmed from the simulation that in the structural model corresponding to Example 1, a broadband noise cancellation effect with multiple peaks in the low-frequency region can be obtained.

[0209] [Example 2]

[0210] In Example 1, Figure 24 As shown in FIG. 4 , a relatively noisy region remains near 400 Hz. In Example 2, a further noise reduction measure is implemented by installing a second resonance silencer whose resonance frequency matches its frequency band.

[0211] Specifically, a second resonance silencer was added to the exhaust side of Example 1 to simulate the noise reduction effect. The second resonance silencer is a straight-extending linear air column resonator, different from the L-shaped air column resonator. Specifically, it is a hollow structure surrounded by a 550mm×360mm×60mm plate, with a hole in the center of the two plates. through-hole.

[0212] The simulation results of the sound pressure level in Example 2 are shown in FIG. Figure 24 By adding a second resonance silencer, it is possible to achieve noise cancellation around 400 Hz. By providing multiple resonance silencers, a wider range of noise cancellation effects can be achieved.

[0213] [Example 3]

[0214] In Example 3, a 60mm long, 250mm inner diameter cylindrical body was attached to the exhaust opening of Example 1. In the original configuration (Comparative Example 1), only a 5mm thick plate was installed at the exhaust opening. This dispersed sound within the housing, and high-angle sound was also radiated to the outside (outside the housing). In contrast, by attaching the cylindrical body to the exhaust opening, it is expected that high-angle sound will be eliminated.

[0215] exist Figure 25 Spectra measured for the sound pressure level in Example 1 and the sound pressure level in Example 3 with the cylinder installed are shown in FIG. Figure 25 It can be seen that by installing the cylinder, the expected effect can be achieved, and the overall sound pressure level can be reduced centered on the peak value.

[0216] In summary, Examples 1 to 3 are within the scope of the present invention, and in all examples, the noise from the internal sound source is reduced from the low-frequency side to the broadband, so the effect of the present invention is significant.

[0217] Explanation of symbols

[0218] 10-air supply system, 12-air supply system body, 14-frame, 14a-air intake port, 14b-exhaust port, 16-axial flow fan, 16a-rotating blade, 16b-rotating shaft, 18-heat exchanger, 30-silencer, 32-ventilation portion, 34-resonance silencer, 35-opening portion, 36-first wall, 36a-ventilation hole, 37-second wall, 37a-ventilation hole, 38-side wall, 39-insert, 40-silencer, 40a-through hole, 52-air supply device, 54-cylinder, 56-annular plate, 58-sound-absorbing urethane.

Claims

1. A silencer for use in an air supply system having a housing and for silencing noise generated from a sound source within the housing, wherein: A resonance muffler is provided at a position connected to the space where the sound source is located in the air supply system. The air supply system includes a rotary blade of an axial flow fan. The resonance muffler is an air column resonance type resonator having an opening. The muffler device includes a first end wall and a second end wall arranged on opposite sides of the rotating shaft of the axial flow fan. A vent hole is provided at the central portion of each of the first end wall and the second end wall. The portion of the second end wall located around the vent hole is recessed toward the first end wall, whereby the resonance muffler is formed by the first end wall, the second end wall, and the side wall connecting the first end wall and the second end wall in the axial direction. The gap between the edge of the vent hole of the first end wall and the edge of the vent hole of the second end wall forms the opening of the resonance muffler. The internal space of the resonance muffler is a space surrounded by the first end wall, the second end wall and the side wall, and is connected to the space where the sound source is located through the opening. A sound-absorbing body made of at least one of a foam material, a non-woven fabric, and a porous material is disposed in a recessed portion of the second end wall that is located around the vent hole. The muffler is closer to the rotor blade than the opening. When the resonance wavelength of the resonance muffler is set to λ, the distance between the resonance muffler and the sound source is less than λ / 2. The fundamental resonance frequency of the resonance muffler is equal to or lower than an upper limit frequency of sound determined by the size of the housing.

2. The silencing device according to claim 1, wherein: The noise is silenced by first silencer due to the resonance of the resonance silencer, which is the basic resonance of the resonance silencer.

3. The silencing device according to claim 2, wherein: The portion of the resonance silencer that acts on the noise has an end portion of the resonance silencer that is the portion closest to the sound source. The noise is silenced by the first and second silencing methods, wherein the second silencing method is generated by interference between the reflected sound generated by the noise reflected by the resonant silencer and the noise in the area between the sound source and the end of the resonant silencer. The frequency of the second noise cancellation is higher than the frequency of the first noise cancellation.

4. The silencing device according to any one of claims 1 to 3, wherein: The interior of the resonance muffler is communicated with the space where the sound source is located.

5. The silencing device according to any one of claims 1 to 3, wherein: The silencer is provided with a vent portion for allowing the air supplied in the air supply system to pass therethrough.

6. The silencing device according to any one of claims 1 to 3, wherein: An insert made of at least one of a foam material, a non-woven fabric, and a porous material is arranged inside the resonance muffler.

7. The silencing device according to any one of claims 1 to 3, wherein: This silencer further includes a silencer body different from the resonance silencer.

8. The silencing device according to claim 7, wherein: The portion of the resonance silencer that acts on the noise has an end portion of the resonance silencer that is the portion closest to the sound source. The muffler is disposed in a region between the sound source and an end portion of the resonance muffler.

9. The silencing device according to claim 7, wherein: The muffler is made of at least one of a foam material, a non-woven fabric, and a porous material.

10. The silencing device according to claim 7, wherein: The silencer is arranged outside a vent portion for allowing air supplied by the air supply system to pass therethrough.

11. An air supply system comprising: An air supply system body having a sound source inside the housing; and The noise reduction device according to any one of claims 1 to 10.

12. The air supply system according to claim 11, wherein: The air supply system main body supplies air through the rotation of the rotating body.

13. The air supply system according to claim 12, wherein: The noise generated from the sound source in the housing includes noise generated by the rotation of the rotating body.

14. The air supply system according to any one of claims 11 to 13, wherein: The air supply system body inhales air from a first end side of the air supply system body and exhausts air at a second end side of the air supply system body. The silencer is disposed at least on the second end side of the air supply system body, of the first end and the second end.

15. The air supply system according to claim 14, wherein: The silencer devices are respectively arranged on the first end side and the second end side of the air supply system body.

16. The air supply system according to any one of claims 11 to 13, wherein: The air supply system body is provided with a rotary blade of an axial flow fan. The muffler device is provided with a ventilator for allowing the air supplied by the axial flow fan to pass through. The area of ​​a cross section of the ventilation portion perpendicular to the rotation axis of the axial flow fan is smaller than the area of ​​a circle surrounded by a track along which the blade tip farthest from the rotation axis of the rotor blade passes when the axial flow fan rotates.

17. The air supply system according to any one of claims 11 to 13, wherein: The portion of the resonance silencer that acts on the noise has an end portion of the resonance silencer that is the portion closest to the sound source. The air supply system body is provided with a rotary blade of an axial flow fan. The silencer device includes a silencer body different from the resonance silencer. The silencer body is closer to the rotor blade than an end portion of the resonance silencer.

18. The air supply system according to any one of claims 11 to 13, wherein: The main body of the air supply system is a blower.

19. The air delivery system according to claim 18, wherein: A heat exchanger is provided in the air supply system body.

20. The air supply system according to any one of claims 11 to 13, wherein: The rotary blades of the axial flow fan are provided on the air supply system body.

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