Blower with silencer and moving body with propeller

Abstract

A blower with a silencer is provided that suppresses amplification of wind noise and can appropriately mute fan sound. The blower with a silencer comprises a fan and a silencer for muffler fan sound. The silencer has a resonant characteristic and is positioned at a location spatially connected to the sound field of the fan sound. The sum of the absorptivity and reflectivity of the silencer at the resonant frequency is 10% to 43%, and the normalized half-value width is greater than 0.05 and less than 0.25.

Description

Technical Field

[0001] The present invention relates to a blower with a muffler and a moving body with a propeller Background Art

[0002] In information equipment such as personal computers (PCs), server computers, projectors, and copiers, axial-flow fans are used to cool the interior of the equipment and exhaust heated air. Furthermore, in devices such as dryers and fans, fans (primarily axial-flow fans) are used for ventilation.

[0003] Furthermore, in aircraft such as helicopters, autonomously flying UAVs (Unmanned Aerial Vehicles) such as so-called unmanned aerial vehicles (UAVs), and flying cars, propellers (propeller fans) rotate to generate lift and generate air, enabling flight (aerial movement). Hereinafter, such devices are referred to as "propeller-equipped moving objects."

[0004] Noise can be generated by axial-flow fans, propellers, and propeller-equipped moving objects (hereinafter collectively referred to as "blowers") used for cooling or air supply, as described above. The noise generated by blowers, whose frequency is determined by the number of blades and rotational speed, has high sound pressure at specific frequencies and very strong pure tone (tonal) components, causing irritation.

[0005] In the following description, "fan" and "axial flow fan" include propellers (propeller fans).

[0006] Even if a porous sound absorbing material commonly used for sound absorption is used to reduce noise as described above, the volume is reduced uniformly over a wide frequency band. Therefore, if the sound pressure is high only at a specific frequency as described above, it is relatively difficult to reduce the sound pressure at that specific frequency.

[0007] Furthermore, when using porous sound-absorbing materials, the volume needs to be increased to achieve a sufficient sound-absorbing effect. However, since the air volume generated by the fan must be ensured, there are limitations on the size of the porous sound-absorbing materials, making it difficult to achieve both high ventilation and sound insulation performance.

[0008] In order to silence the fan noise generated at such a specific frequency, it has been proposed to use a resonance-type silencer.

[0009] For example, Patent Document 1 describes a fan device comprising: a rotatable blade member; a gas flow path for allowing gas to flow into the interior and outwardly through the rotation of the blade member; an inclined surface for expanding the flow path toward the exterior; and a housing having a recessed portion provided on the inclined surface. Patent Document 1 describes that this fan device absorbs sound by causing sound to resonate with air within the recessed portion.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2005-248734 Summary of the Invention

[0013] Technical issues to be solved by the invention

[0014] According to the research conducted by the present inventors, when a resonator is placed within the flow path of the airflow (wind) generated by an axial fan, wind noise caused by the fan's wind is generated in the resonator's structural components, such as recesses, resulting in the resonator amplifying the wind noise. Furthermore, if wind continues to strike the surface of the resonator's resonant structure, the resonance is suppressed. Therefore, particularly in resonators placed at high airflow rates, there is a problem of reduced noise cancellation due to resonance and amplified wind noise.

[0015] The present invention aims to solve the above-mentioned problems of the prior art and to provide a blower with a silencer that suppresses amplification of wind noise and can appropriately muffle the sound generated by the fan. Furthermore, the present invention aims to provide a mobile object with a propeller that includes the blower with a silencer.

[0016] Means for solving technical problems

[0017] The present invention solves the problem by the following configuration.

[0018] [1] A blower with a silencer, comprising a fan and a silencer for silencing the sound generated by the fan.

[0019] The muffler has resonance characteristics.

[0020] The silencer is placed in a position connected to the sound field space of the sound generated by the fan.

[0021] The total of the absorptivity and reflectivity of the muffler at a resonance frequency measured using an acoustic tube is 10% to 43%, and the normalized half-value width is greater than 0.05 and not more than 0.25.

[0022] [2] The air blower with a silencer according to [1], wherein the silencer is connected to the inner space of the fan.

[0023] [3] The air blower with a silencer according to [2], wherein the silencer has a flow path communicating with the internal space of the fan.

[0024] [4] The blower with a silencer according to any one of [1] to [3], wherein the resonant frequency measured by the sound pipe of the silencer deviates by 1% to 10% from the frequency of the discrete frequency sound caused by the fan.

[0025] [5] The blower with a silencer according to [4], wherein the silencer is connected to a position where the sound pressure distribution of the discrete frequency sound caused by the fan is high.

[0026] The resonant frequency of the silencer is lower than the frequency of the discrete frequency sound.

[0027] [6] The blower with a silencer according to [4], wherein the silencer is connected to a position where the sound pressure distribution at the frequency of the discrete frequency sound caused by the fan is low,

[0028] The resonant frequency of the silencer is higher than the frequency of the discrete frequency sound.

[0029] [7] The blower with a silencer according to any one of [1] to [6], wherein the silencer is an air column resonator,

[0030] The resonant tube of the air column resonator has a bent structure.

[0031] [8] The blower with a silencer according to any one of [1] to [7], wherein the silencer is composed of a combination of a resonator and a porous sound-absorbing material.

[0032] [9] The blower with a silencer according to any one of [1] to [8], wherein the fan is an axial flow fan,

[0033] When viewed from the axial direction of the axial flow fan, the muffler is arranged at a position that does not overlap with an area formed by the rotation of the rotor blades.

[0034]

[10] The blower with a silencer according to any one of [1] to [9], wherein the fan is an axial flow fan with fixed wings,

[0035] The muffler is connected to at least one of the fixed wing openings between the fixed wing.

[0036]

[11] The air blower with a silencer according to

[10] , wherein silencers are connected to all the fixed wing openings.

[0037]

[12] A mobile object with a propeller, comprising the blower with a silencer according to any one of [1] to

[11] ,

[0038] The fan of the blower with a muffler is a propeller, and the air moves by the rotation of the propeller.

[0039]

[13] The mobile object with a propeller according to

[12] , wherein the silencer of the blower with a silencer is arranged around the propeller to form a propeller shroud.

[0040]

[14] A mobile body with a propeller according to

[12] or

[13] , wherein when the silencer of the blower with a silencer is viewed from the direction of the rotation axis of the propeller, the outer shape of the silencer is a circle or an arc.

[0041]

[15] The propeller-equipped vehicle according to

[14] , wherein the muffler is an air column resonator having a bent resonance tube,

[0042] When the muffler is viewed from the direction of the rotation axis, a portion of the resonance tube is curved in an arc shape.

[0043] Effects of the Invention

[0044] According to the present invention, a blower with a silencer can be provided that suppresses amplification of wind noise and can appropriately silence the sound generated by the fan. In addition, according to the present invention, a mobile object with a propeller can be provided that includes a blower with a silencer. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a perspective view schematically showing an example of the blower with a silencer according to the present invention.

[0046] Figure 2 Observed from direction A Figure 1 Front view of the blower with silencer.

[0047] Figure 3 yes Figure 2 BB line cross-sectional view.

[0048] Figure 4 It is a cross-sectional view schematically showing another example of the blower with a silencer according to the present invention.

[0049] Figure 5 It is a cross-sectional view schematically showing another example of the blower with a silencer according to the present invention.

[0050] Figure 6 It is a cross-sectional view schematically showing an example of a muffler.

[0051] Figure 7 It is a cross-sectional view schematically showing another example of a muffler.

[0052] Figure 8 It is a cross-sectional view schematically showing another example of a muffler.

[0053] Figure 9 It is a cross-sectional view schematically showing another example of a muffler.

[0054] Figure 10 It is a cross-sectional view schematically showing another example of a muffler.

[0055] Figure 11 It is a cross-sectional view schematically showing another example of the blower with a silencer according to the present invention.

[0056] Figure 12 This is a perspective view schematically showing another example of the blower with a silencer according to the present invention.

[0057] Figure 13 This is a partial enlarged view of the shell.

[0058] Figure 14 This is a diagram conceptually showing an example of a method for measuring sound pressure distribution.

[0059] Figure 15 This is a graph showing an example of the measurement results of the sound pressure distribution.

[0060] Figure 16 This is a graph showing the relationship between frequency and absorptivity + reflectivity.

[0061] Figure 17 It is a diagram for explaining the method of measuring the noise amount in the example.

[0062] Figure 18 It is a graph showing the relationship between frequency and sound pressure.

[0063] Figure 19 It is a graph showing the relationship between frequency and sound pressure.

[0064] Figure 20 It is a graph showing the relationship between frequency and sound pressure.

[0065] Figure 21 This is a graph showing the relationship between frequency and reflectivity + absorptivity.

[0066] Figure 22 This is a graph showing the relationship between frequency and reflectivity + absorptivity.

[0067] Figure 23 It is a graph showing the relationship between frequency and sound pressure level.

[0068] Figure 24 It is a graph showing the relationship between frequency and sound pressure level.

[0069] Figure 25 It is a graph showing the relationship between frequency and sound pressure level.

[0070] Figure 26 It is a graph showing the relationship between frequency and sound pressure level.

[0071] Figure 27 This is a graph showing the measurement results of noise generated during the flight of a mobile object with a propeller.

[0072] Figure 28 This is a cross-sectional view of a muffler mounted on a mobile object with a propeller.

[0073] Figure 29 This is a graph showing the results of acoustic tube measurements performed on a muffler mounted on a mobile object with a propeller.

[0074] Figure 30 This is a plan view of a mobile object with a propeller used for sound pressure measurement.

[0075] Figure 31 This is a graph showing the results of sound pressure measurement using a moving object with a propeller.

[0076] Figure 32 FIG. 1 is a diagram showing an air column resonator used in the examples.

[0077] Figure 33 This is a graph showing the results of acoustic tube measurements of the noise cancellation effect of an air column resonance structure with a sound absorbing body.

[0078] Figure 34 This is a graph showing the results of sound pressure measurement of an air column resonance structure with a sound absorbing body. DETAILED DESCRIPTION

[0079] Hereinafter, the present invention will be described in detail.

[0080] The following description of the constituent elements is based on representative embodiments of the present invention, but the present invention is not limited to these embodiments.

[0081] In addition, in this specification, the numerical range expressed using "to" means a range including the numerical values described before and after "to" as the lower limit and the upper limit.

[0082] [Blower with silencer]

[0083] The blower with silencer of the present invention,

[0084] It has a fan and a muffler for muffle the sound produced by the fan.

[0085] The muffler has resonance characteristics.

[0086] The silencer is placed in a position connected to the sound field space of the sound generated by the fan.

[0087] The total of the absorptivity and reflectivity of the muffler at a resonance frequency measured using an acoustic tube is 10% to 43%, and the normalized half-value width is greater than 0.05 and not more than 0.25.

[0088] The structure of the blower with a silencer according to the present invention will be described with reference to the drawings.

[0089] Figure 1 It is a perspective view schematically showing an example of a preferred embodiment of the blower with a silencer according to the present invention. Figure 2 Observed from direction A Figure 1 main view. Figure 3 yes Figure 2 BB line cross-sectional view.

[0090] Figures 1 to 3 The blower 10 with a silencer shown includes an axial flow fan 12 having a housing 16 , a motor 14 , and rotor blades 18 , and a silencer 30 .

[0091] The axial flow fan 12 is basically a well-known axial flow fan that rotates a rotor having a plurality of blades to impart kinetic energy to gas, thereby blowing the gas in the axial direction.

[0092] Specifically, the axial flow fan 12 includes a housing 16 , a motor 14 mounted on the housing 16 , and a rotor 18 including a shaft 20 mounted on the motor 14 for rotation and blades 22 projecting radially outward from the shaft 20 .

[0093] In the following description, the rotation axis of the shaft 20 (rotating blade 18) is simply referred to as the "rotating axis," and the direction of the rotation axis of the shaft 20 (rotating blade 18) is simply referred to as the "axial direction." Furthermore, the radial direction of the shaft 20 (rotating blade 18) is simply referred to as the "radial direction." Furthermore, the rotation direction of the rotor blade 18 is also referred to as the "circumferential direction."

[0094] The motor 14 is a typical electric motor that rotates the rotor 18 .

[0095] The shaft portion 20 of the rotor blade 18 is substantially cylindrical, and one bottom surface thereof is attached to the rotating shaft of the motor 14 , and is rotated by the motor 14 .

[0096] The blades 22 are formed on the peripheral surface of the shaft portion 20 so as to protrude radially outward from the peripheral surface. The rotor 18 has a plurality of blades 22, and the plurality of blades 22 are arranged in the circumferential direction of the peripheral surface of the shaft portion 20. Figures 1 to 3In the illustrated example, the rotor 18 is configured to include four blades 22 , but the present invention is not limited thereto, and any configuration may be sufficient as long as the rotor 18 includes a plurality of blades 22 .

[0097] Furthermore, the shape of the blades 22 can be a shape used in a conventionally known axial flow fan.

[0098] The thickness of the blade 22 in the rotation axis direction is approximately 5 mm to 200 mm. Furthermore, the thickness of the shaft portion 20 is approximately 5 mm to 200 mm.

[0099] Furthermore, it is preferable that the maximum value of the thickness of the blade 22 in the rotation axis direction is substantially the same as the thickness of the shaft portion 20 .

[0100] The diameter of the shaft portion 20 is approximately 10 mm to 1500 mm. The outer diameter of the rotor blade 18, that is, the outer diameter passing through the radially distal end of the blade 22, is approximately 20 mm to 2000 mm.

[0101] The rotor 18 having blades 22 is rotated by the motor 14, thereby generating airflow (wind) along the direction of the rotation axis. The direction of the airflow is not limited and can flow from the motor 14 side to the opposite direction of the motor 14 along the rotation axis, or from the same side as the motor 14 to the motor 14 side.

[0102] The housing 16 is fixed with the motor 14 and surrounds the radial circumference of the rotatable rotor blades 18 (blades 22 ).

[0103] The thickness of the housing 16 in the direction of the rotation axis is thicker than the thickness of the blades 22 and the shaft 20 so as to protect the rotor blade 18 from the outside.

[0104] The housing 16 comprises a support portion 16a that supports the motor 14 on one side in the direction of the rotation axis; an outer frame portion 16b that surrounds the rotor blades 18 from the radially outer side; a cover portion 16c that covers the region of the shaft portion 20 on the other side in the direction of the rotation axis; and fixed blades 16d that protrude radially outward from the support portion 16a and / or the cover portion 16c and connect the support portion 16a and / or the cover portion 16c to the outer frame portion 16b. The fixed blades 16d have a known blade shape and function to straighten the airflow generated by the rotation of the rotor blades 18.

[0105] The outer frame 16b has a cubic shape and includes an opening 17 extending in one direction. The support portion 16a is disposed on one side of the opening 17 of the outer frame 16b, and the cover portion 16c is disposed on the other side of the opening. The opening 17 of the outer frame 16b corresponds to the internal space of the axial-flow fan of the present invention. In the following description, the opening 17 of the outer frame 16b is also referred to as the internal space 17.

[0106] The diameter of the support portion 16a may be large enough to support the motor 14 without obstructing the flow of airflow generated by the rotation of the rotor blades 18. As an example, the diameter of the support portion 16a is substantially the same as the diameter of the shaft portion 20.

[0107] Likewise, the diameter of the cover 16c may be such that it can protect the shaft 20 from the outside and does not obstruct the flow of airflow generated by the rotation of the rotor blades 18. As an example, the diameter of the cover 16c is substantially the same as the diameter of the shaft 20.

[0108] The width and number of the fixed blades 16d may be such that they can reliably fix the support portion 16a and the outer frame portion 16b, and the cover portion 16c and the outer frame portion 16b, respectively, and do not obstruct the flow of airflow generated by the rotation of the rotor blades 18.

[0109] The thickness of the housing 16 in the direction of the rotation axis only needs to be able to protect the rotor blades 18 from the outside and suppress the radial air flow in the air flow generated by the rotation of the rotor blades 18 to increase the air volume in the direction of the rotation axis. The thickness can be approximately 1.01 to 3.00 times the thickness of the blades 22 and / or the shaft 20.

[0110] In the illustrated example, the housing 16 includes a support portion 16a that supports the motor 14 and a cover portion 16c that covers the shaft 20 . However, the housing 16 may include only the support portion 16a that supports the motor 14 without the cover portion 16c that covers the shaft 20 .

[0111] Furthermore, in the housing 16, at least one of the components connecting the support portion 16a and the outer frame 16b, and the components connecting the cover portion 16c and the outer frame 16b, need only be the fixed wing 16d; the other component may simply be a connecting portion connecting the components. Furthermore, if the airflow generated by the rotation of the rotor blade 18 flows toward the support portion 16a, the component connecting the support portion 16a and the outer frame 16b may be the fixed wing 16d. If the airflow generated by the rotation of the rotor blade 18 flows toward the cover portion 16c, the component connecting the cover portion 16c and the outer frame 16b may be the fixed wing 16d. Alternatively, the housing 16 may not have the fixed wing 16d. In other words, the component connecting the support portion 16a and the outer frame 16b, and the component connecting the cover portion 16c and the outer frame 16b, need not have a blade shape and may not function to straighten the airflow generated by the rotation of the rotor blade 18.

[0112] The axial flow fan 12 may have various structures that are known in the art.

[0113] For example, in Figures 1 to 3In the illustrated example, the axial flow fan 12 has holes 16 e into which fastening members such as screws are inserted when the axial flow fan 12 is fixed to various devices.

[0114] The silencer 30 is positioned adjacent to the sound field space of the sound generated by the axial flow fan 12. The sound field space comprises the interior of the axial flow fan 12 and the near-field region of sound that leaks out from the opening 17 of the axial flow fan 12. The near-field region of sound that leaks out from the opening end is defined as a region with a sound pressure level that is 20 dB lower than the sound pressure level at the center of the opening 17 of the axial flow fan 12. The near-field region of sound can be determined through simulation of the axial flow fan or by actually measuring the spatial distribution of sound pressure using, for example, a microphone with a probe.

[0115] The muffler 30 is preferably positioned so as to connect to the internal space 17 of the axial fan 12. Here, the connection between the muffler 30 and the internal space 17 means that the portion of the muffler 30 that allows sound waves to enter the muffler 30 in order to achieve the muffler function is in communication with the internal space 17. For example, in a Helmholtz resonator or an air column resonator, the opening corresponds to the portion for sound waves to enter. Furthermore, in a membrane resonator, the membrane surface corresponds to the portion for sound waves to enter.

[0116] exist Figure 3 In the illustrated example, the silencers 30 are Helmholtz resonators 30 a , and four of them are arranged on the outer peripheral surface of the outer frame portion 16 b of the housing 16 .

[0117] As is well known, the Helmholtz resonator 30a comprises a housing 32 having an interior space 36 and an opening 34 that connects the interior space 36 with the exterior. The Helmholtz resonator 30a has a structure in which the air in the interior space 36 acts as a spring, while the air in the opening 34 acts as a mass, causing mass-spring resonance. Furthermore, sound absorption occurs through thermoviscous friction near the wall of the opening 34.

[0118] In the following description, when there is no need to distinguish between types of silencers such as the Helmholtz resonator 30 a , the air column resonator 30 b and the film resonator 30 c described later, they are collectively referred to as the silencer 30 .

[0119] like Figure 3 As shown, the Helmholtz resonator 30a is arranged with its opening 34 facing the interior space 17 of the housing 16. A through-hole 15 is formed in the outer frame 16b of the housing 16 at a position corresponding to the opening 34 of the Helmholtz resonator 30a, extending from the outer circumference to the inner circumference of the outer frame 16b. Thus, the opening 34 of the Helmholtz resonator 30a communicates with the interior space 17 of the housing 16 via the through-hole 15. Thus, the Helmholtz resonator 30a is connected to the interior space 17.

[0120] Here, in the blower 10 with a silencer of the present invention, it has the following structure: the silencer has a resonance characteristic, and the sum of the absorption rate and the reflectivity of the silencer at the resonance frequency measured using a sound tube is 10% to 43%, and the normalized half-value width is greater than 0.05 and less than 0.25. That is, the silencer has a resonance characteristic with a low resonance peak and a wide (broadband). In addition, the normalized half-value width is set to a value obtained by dividing the half-value width (Hz) by the resonance frequency (Hz). In addition, the absorption rate and reflectivity of the silencer at the resonance frequency can be measured by a four-microphone method using a sound tube. The method for measuring the absorption rate and reflectivity is based on ASTM E2611, and the same measurement can be performed using WinZac MTX manufactured by Nihon Onkyo Engineering Co., Ltd.

[0121] In the following description, the resonance characteristic with a low resonance peak and a wide (broadband) is also referred to as "weak resonance". As an example, as described later Figure 11 As shown in Example 1, the resonant characteristics of the muffler with weak resonant characteristics show that the sum of the absorptivity and reflectivity at the resonant frequency (the maximum value of the sum of the absorptivity and reflectivity near resonance) is as low as approximately 26%, and the half-value width is as wide as approximately 212 Hz. The normalized half-value width is 0.12.

[0122] Generally, a resonator is used to mute a peak sound with high sound pressure at a specific frequency. In order to further improve the mute effect of the resonance in the mute system, it is possible to use a resonator with a high and steep resonance peak. For example, as described below Figure 11 As shown in Comparative Example 1, a resonator is used in which the sum of the absorptivity and the reflectivity at the resonant frequency is as high as 56% or more and the half-value width is as narrow as 84 Hz or less (normalized half-value width is 0.3). However, as described above, when such a resonator with a steep resonance peak is used in the silencing of a fan that generates an airflow, wind noise caused by the wind from the fan is generated in the structural parts such as the recessed parts of the resonator, thereby causing the problem of the wind noise being amplified by the resonator near the resonant frequency of the resonator. For example, since there is an opening in the case of a Helmholtz resonator and an air column resonator, wind noise is generated by the contact of the wind with the opening, resulting in the generated wind noise being amplified by the resonator. In addition, if the wind continues to blow on the surface of the resonant structure of the resonator, there is an effect of suppressing the silencing based on the resonance. For example, in the case of a Helmholtz resonator and an air column resonator, if the wind continues to blow on the surface part of the opening, it is difficult for the sound wave to propagate from the opening to the inside of the resonator, thereby suppressing the resonance peak. Furthermore, in the case of membrane resonators, if wind continues to blow against the membrane surface, the membrane's vibration is suppressed, leading to reduced resonance. Therefore, especially in resonators deployed under high wind flow, there is a problem of reduced noise cancellation due to resonance and amplified wind noise.

[0123] In contrast, the blower with a silencer of the present invention uses a silencer with weak resonance characteristics in the silencing of the fan. The resonator has a resonance characteristic with a low resonance peak value of 10% to 43% with a sum of an absorptivity and a reflectivity, so that the wind noise generated by the structural part of the resonator can be suppressed from being amplified by the resonator. In addition, since the resonator has a wide (broadband) resonance characteristic with a normalized half-value width greater than 0.05 and less than 0.25, it can be seen that the phase change at a slightly deviated frequency near the resonance frequency and the mutual cancellation caused by interference can be used for silencing. Even if the resonance peak (the height of the resonance peak) is suppressed by the wind, the resonance width (the width to the peak valley) and the corresponding phase change are not suppressed, so the silencing effect can be exerted. Therefore, when the wind continues to blow on the surface of the resonant structure of the resonator and suppresses the resonance, it is possible to effectively silence the sound.

[0124] In this way, regarding the trade-off between the existing conditions of the resonator that works well on peak sound and the amplification of wind noise caused by the resonator, the air blower with a silencer of the present invention weakens the resonance of the silencer and makes the silencing mechanism depend on the mutual cancellation caused by interference, thereby suppressing the amplification of wind noise and being able to appropriately silence the sound generated by the fan.

[0125] To suppress amplification of wind noise and appropriately muffle fan sound, the sum of the absorptivity and reflectivity of the muffler at the resonant frequency should be 10% to 43%, preferably 14% to 35%, and more preferably 18% to 30%. Furthermore, the normalized half-value width should be greater than 0.05 and less than 0.25, preferably 0.08 to 0.20, more preferably 0.10 to 0.15, and most preferably 0.11 to 0.14.

[0126] And, in Figures 2 and 3 In the example shown, the Helmholtz resonator 30 a is used as a silencer, but the present invention is not limited to this.

[0127] For example, Figure 4 As shown in the example, the air column resonator 30b may be used as a silencer. As is well known, the air column resonator generates standing waves in a resonance tube having an opening to cause resonance. Figure 4 In the illustrated muffler blower 10, air column resonators 30b are disposed on four outer peripheral surfaces of the outer frame 16b of the housing 16 of the axial fan 12. The openings of the four air column resonators 30b are connected to the fixed blade opening (internal space 17) (not shown).

[0128] In addition, Figure 4In the example shown, the air column resonator 30b is configured as a resonance tube extending radially outward from the axial fan 12, but the present invention is not limited thereto. If the air column resonator 30b opens to the internal space 17, the resonance tube may extend axially or circumferentially.

[0129] And, as Figure 5 As shown in the example, a film type resonator 30c can also be used as a silencer. It has a frame 40 and a film 42, and the film 42 supported on the frame 40 in a vibratory manner vibrates to resonate. Figure 5 In the illustrated blower 10 with a silencer, a film-type resonator 30c is disposed on the outer peripheral surface of the outer frame portion 16b of the housing 16 of the axial fan 12. The film-type resonator 30c is disposed with the membrane 42 facing the housing 16 and connected to the fixed blade opening (internal space 17) via a through portion formed in the housing 16.

[0130] The frame 40 is in the shape of a rectangular parallelepiped with an opening having a bottom formed on one side. In other words, the frame 40 is in the shape of a bottomed box with one side open.

[0131] The film 42 is a film-like member that covers the opening surface of the frame 40 where the opening is formed, fixes the peripheral edge portion to the frame 40 , and supports the frame 40 in a vibration-capable manner.

[0132] Furthermore, a back space 44 surrounded by the frame 40 and the film 42 is formed on the back side of the film 42 (the frame 40 side). Figure 5 In the example shown, the back space is an enclosed closed space.

[0133] The following examples illustrate methods for achieving weak resonance in a muffler. However, these methods are not limited to the following. The following structures all act as a resistance to resonant vibration. Consequently, the peak noise reduction at the resonant frequency decreases, and the full width at half maximum (FWHM) increases accordingly.

[0134] As a method of making the resonance characteristics of the silencer weak, there is a method of configuring the silencer by combining a resonator and a porous sound absorbing material.

[0135] As an example, Figure 6 As shown in FIG. 1 , the muffler having weak resonance characteristics has a structure in which a porous sound absorbing material 46 is arranged in the internal space 36 of the Helmholtz resonator 30a. Alternatively, as shown in FIG. Figure 7 As shown in FIG. 1 , a porous sound absorbing material 46 is arranged so as to cover the opening 34 of the Helmholtz resonator 30a. Figure 6 and Figure 7While the example uses a Helmholtz resonator as the resonator, similarly to the air column resonator, a porous sound-absorbing material can be placed inside (inside the resonant tube), or a porous sound-absorbing material, cloth, non-woven fabric, or porous through-plate can be placed at the opening of the air column resonator. The entire interior does not need to be filled with porous sound-absorbing material; a structure in which porous sound-absorbing material is attached only to the wall is also possible.

[0136] The type, size, flow resistance, density, porosity, etc. of the porous sound absorbing material can be appropriately set so that the sum of the absorption rate and reflectivity of the muffler at the resonant frequency is 10% to 43% and the normalized half-value width is greater than 0.05 and less than 0.25.

[0137] As the type of porous sound-absorbing material, known porous sound-absorbing materials can be appropriately utilized. For example, various known porous sound-absorbing materials can be utilized, including foam materials and materials containing fine air pockets, such as expanded urethane, soft urethane foam, wood, sintered ceramic particles, and phenol foam; fiber and non-woven materials such as glass wool, rock wool, microfiber (such as Thinsulate manufactured by 3M Company); floor mats, carpets, meltblown non-woven fabrics, metal non-woven fabrics, polyester non-woven fabrics, metal wool, felt, insulation boards, and glass non-woven fabrics; nanofiber materials such as wood wool cement boards, silica nanofibers, and gypsum boards.

[0138] Furthermore, the flow resistance of the porous sound absorbing material is not particularly limited, but is preferably 1000 to 100000 (Pa·s / m 2 ), more preferably 3000 to 80000 (Pa·s / m 2 ), more preferably 5000 to 50000 (Pa·s / m 2 ).

[0139] The flow resistance of a porous sound-absorbing material can be evaluated by measuring the sound absorption coefficient of a porous sound-absorbing material with a thickness of 1 cm at normal incidence and fitting it with the Miki model (J. Acoust. Soc. Jpn., 11(1)). pp. 19-24 (1990). Alternatively, it can be evaluated according to "ISO 9053".

[0140] Furthermore, multiple porous sound-absorbing materials with different flow resistances can be stacked.

[0141] As a method of setting the resonance characteristics of the muffler to weak resonance characteristics, Figure 8 As shown in FIG. 1 , there is a method of forming a structure in which the interior of the resonance tube 37 of the air column resonator 30 b is bent.

[0142] The position, angle, number of bends, internal rounding, etc. can be appropriately set so that the sum of the absorptivity and reflectivity of the muffler at the resonant frequency is 10% to 43% and the normalized half-value width is greater than 0.05 and less than 0.25.

[0143] From the perspective of ease of manufacturing, the number of bends is preferably one. Furthermore, if the resonance becomes too weak, the angle can be reduced or the corner of the inner bend can be rounded to facilitate sound propagation.

[0144] Furthermore, as a method of making the resonance characteristics of the muffler weak, there is a method of providing a through hole or a gap communicating with the internal space of the muffler. For example, Figure 9 The air column resonator 30b shown has a structure in which a second opening 39 communicating with the interior of the resonance tube 37 is provided on the closed surface side of the resonance tube 37. Alternatively, Figure 10 The film type resonator 30c shown has a second opening portion on the back side of the frame 40 that connects the back space 44 and the outside. In this case, when the resonator has the second opening portion, the resonator is arranged at a position where the second opening portion is not connected to the internal space of the axial flow fan. Figure 9 and Figure 10 While the examples above use air column resonators or membrane resonators, similar to the Helmholtz resonator, a second opening communicating with the internal space can also be provided. Furthermore, any location that allows sound exchange with the outside can be created without through-holes, such as by creating a gap when attaching the back panel or by using a porous through-plate as the back panel.

[0145] The size, position, number, and overall opening ratio of the second openings may be appropriately set so that the sum of the absorptivity and reflectivity of the muffler at the resonant frequency is 10% to 43% and the normalized half-value width is greater than 0.05 and less than 0.25.

[0146] Furthermore, one method for reducing the resonance characteristics of a muffler to a weaker resonance is to narrow the flow path within the muffler. For example, in the case of an air column resonator, the inner diameter of the resonance tube can be reduced. Similarly, in the case of a slit-side air column resonator, the slit width can be reduced. Furthermore, in the case of a Helmholtz resonator, the diameter of the opening can be reduced.

[0147] The flow path does not have to be uniformly narrow, and may be a gradually narrowing structure, an expanding structure, etc. A tapered structure often has advantages in the manufacture of a use model.

[0148] The diameter and angle of the internal flow path may be appropriately set so that the sum of the absorptivity and reflectivity of the muffler at the resonance frequency is 10% to 43% and the normalized half-value width is greater than 0.05 and less than 0.25.

[0149] Here, in Figure 1 In the illustrated example, the muffler 30 is arranged outside the housing 16 and connected to the internal space 17 of the axial flow fan 12 via the through hole 15 formed in the outer frame portion 16 b of the housing 16 , but the present invention is not limited thereto.

[0150] For example, Figure 11 As shown, the silencer 30 (a Helmholtz resonator 30 a in the illustrated example) may be disposed within the interior space 17 of the axial flow fan 12 .

[0151] Furthermore, the silencer 30 only needs to be placed in a position connected to the sound field space of the sound generated by the fan. Figure 12 As shown, the muffler 30 may be configured to be arranged outside the housing 16 and at a position not connected to the internal space 17 of the axial flow fan 12. Figure 12 In the example shown, the Helmholtz resonator 30a is positioned downstream of the axial flow fan 12 in the airflow direction. Furthermore, the Helmholtz resonator 30a is positioned so as not to block the airflow from the axial flow fan 12. Specifically, it is positioned around a region that serves as a passage for the air blown by the axial flow fan 12. Furthermore, the opening 34 of the Helmholtz resonator 30a is positioned in the axial direction of the axial flow fan 12.

[0152] From the viewpoint of air permeability, the muffler 30 is preferably arranged at a position that does not overlap with a region formed by the rotation of the rotor blades 18 when viewed in the axial direction of the axial flow fan 12 .

[0153] Furthermore, the blower with a silencer of the present invention can achieve a silencing effect even when strong winds are blowing, so the silencer 30 can be preferably arranged to be connected to the internal space of the axial flow fan 12. This can reduce the overall size (volume).

[0154] And, as Figure 1 As shown, the blower with a silencer of the present invention may have a plurality of silencers.

[0155] Furthermore, the blower with a silencer of the present invention may be equipped with different types of silencers.

[0156] Here, axial-flow fan 12 rotates its multiple-bladed rotors, imparting kinetic energy to the air and blowing it axially. Consequently, axial-flow fan 12 generates sound at a specific frequency determined by factors such as the rotational speed and number of blades, where the sound pressure reaches a maximum. In the following description, sound at a specific frequency determined by factors such as the rotational speed and number of blades of axial-flow fan 12, where the sound pressure reaches a maximum, is referred to as discrete-frequency sound.

[0157] Specifically, discrete frequency sound is a sound having a TNR (tone-to-noise ratio) or a PR (prominence ratio) of 3 dB or more as defined in the European standard ECMA-74 Prominent discrete tone.

[0158] Thus, the axial fan 12 generates a sound having a maximum sound pressure at a specific frequency. In the present invention, the resonant frequency measured by the acoustic tube of the muffler is preferably deviated by 1% to 10% from the frequency of the discrete frequency sound.

[0159] Generally, a resonator sets a resonant frequency substantially the same as the frequency of a sound to be silenced (discrete frequency sound), and silences the sound of that frequency (discrete frequency sound) by utilizing a resonance phenomenon.

[0160] In contrast, the present invention achieves a noise cancellation effect by utilizing phase changes at slightly offset frequencies near the resonant frequency, by designing the muffler's resonant frequency to deviate by 1% to 10% from the frequency of the discrete-frequency sound. This utilizes mutual cancellation caused by interference, further enhancing the muffler's effectiveness. This allows for effective noise cancellation even when wind continuously strikes the resonant structure, suppressing resonance.

[0161] The resonant frequency of the silencer is preferably offset by 2% to 8% relative to the frequency of the discrete-frequency sound, more preferably by 3% to 5%, and even more preferably by 3% to 4%. The frequency offset is represented by "|frequency of the discrete-frequency sound - resonant frequency of the silencer| / frequency of the discrete-frequency sound."

[0162] The resonant frequency of the Helmholtz resonator 30a is determined by the volume of the internal space 36 enclosed by the housing 32 and the area and length of the opening 34. Therefore, by adjusting the volume of the internal space of the housing 32 and the area and length of the opening 34 of the Helmholtz resonator 30a, the frequency of the resonant sound can be appropriately set.

[0163] Furthermore, the resonant frequency of the air column resonator 30b is determined by the length of the resonance tube, etc. Therefore, by adjusting the depth of the resonance tube, the size of the opening, etc., the frequency of the resonant sound can be appropriately set.

[0164] The resonant frequency of the membrane resonator 30c is determined by the size (size of the vibration surface, i.e., the size of the opening of the frame 40), thickness, hardness, etc. of the membrane 42. Therefore, by adjusting the size, thickness, hardness, etc. of the membrane 42, the frequency of the resonant sound can be appropriately set.

[0165] Furthermore, when a resonator is constructed with an internal space and a through-hole (opening) connecting the internal space with the outside, whether the structure produces air column resonance or Helmholtz resonance is determined by the size and position of the through-hole, the size of the internal space, and other factors. Therefore, by appropriately adjusting these factors, it is possible to select either air column resonance or Helmholtz resonance.

[0166] On the other hand, in the case of Helmholtz resonance, since thermoviscous friction must be generated within the through-hole, it is preferably somewhat narrow. Specifically, if the through-hole is rectangular, the short side length is preferably 0.5 mm to 20 mm, more preferably 1 mm to 15 mm, and even more preferably 2 mm to 10 mm. If the through-hole is circular, the diameter is preferably within the above range.

[0167] Furthermore, if the axial fan 12 generates multiple discrete frequency sounds, the muffler 30 only needs to have a resonant frequency that deviates by 1% to 10% from at least one of the discrete frequency sounds. It is more preferable to have a muffler that satisfies the aforementioned resonant frequency conditions for each of the multiple discrete frequency sounds.

[0168] In addition, as a resonator, it is preferable to use a resonator having a flow path connected to the internal space 17 of the axial flow fan 12. That is, as a resonator, it is preferable to use a Helmholtz resonator 30a or an air column resonator 30b. As described above, the resonant frequency of the membrane type resonator 30c depends on the size of the membrane 42 (vibration surface). Specifically, in order to adjust the resonant frequency of the membrane type resonator 30c to a low frequency, it is necessary to increase the size of the membrane 42 (vibration surface). However, it is difficult to adjust the resonant frequency within the range that can be configured (connected) to the axial flow fan 12. On the other hand, in the case of the Helmholtz resonator 30a and the air column resonator 30b, it is sufficient to have a flow path (opening portion) connected to the internal space 17. Since the resonant frequency can be adjusted without increasing the opening portion itself, it is possible to easily connect to the internal space 17 of the axial flow fan 12, for example, when the resonant frequency is adjusted to a low frequency.

[0169] Here, when the muffler 30 is connected to a location where the sound pressure distribution at the frequencies of the discrete-frequency sounds generated by the axial-flow fan 12 is high, the resonant frequency of the muffler is preferably deviated by 1% to 10% lower than the frequency of the discrete-frequency sounds. Furthermore, when the muffler 30 is connected to a location where the sound pressure distribution at the frequencies of the discrete-frequency sounds generated by the axial-flow fan 12 is low, the resonant frequency of the muffler is preferably deviated by 1% to 10% higher than the frequency of the discrete-frequency sounds.

[0170] The resonance of the silencer 30 shifts its phase (the phase of the reflected sound) by 180 degrees from low to high frequencies, centered around the resonant frequency. Because the present invention uses a resonator with a wide resonance width, this phase shift also occurs gradually over a wide frequency range. By designing the reflected sound phase appropriately for discrete frequency sounds, and selecting an interference relationship that cancels out the sound emitted from the sound source (the fan blades), a noise cancellation effect is achieved.

[0171] It is inferred that when the muffler 30 is connected to a location where the sound pressure distribution at the frequency of the discrete-frequency sound generated by the axial-flow fan 12 is high, if the resonant frequency of the muffler is deviated from the frequency of the discrete-frequency sound, the reflected sound from the resonator is emitted at a phase delayed relative to the resonant frequency at the frequency of the discrete-frequency sound, resulting in a mutually canceling phase relationship between the sound passing through the fixed airframe other than the location where the muffler is installed. On the other hand, when the muffler 30 is connected to a location where the sound pressure distribution at the frequency of the discrete-frequency sound generated by the axial-flow fan 12 is low, the resonant frequency of the muffler is deviated from the frequency of the discrete-frequency sound, and the phase of the reflected sound is emitted ahead of the resonant frequency. Since it can be inferred that the phase is different at locations with high and low sound pressure, it is believed that reversing the phase design of the muffler to achieve mutual cancellation is appropriate.

[0172] It is generally known that when an axial flow fan is placed in a duct, a pattern is formed in the axial direction, that is, a sound pressure distribution is generated. Furthermore, according to research conducted by the present inventors, a sound pressure distribution is generated circumferentially within the interior space of the axial flow fan. The reason for the circumferential sound pressure distribution within the interior space of the axial flow fan is presumed to be that, in the axial flow fan 12, the casing 16 has a support portion 16a for positioning the rotating blades 18 and the motor 14 at the radial center, and a fixed blade 16d (or a connecting portion that does not function as a blade) for connecting the support portion 16a to the outer frame portion 16b. Each blade 22 serves as an aerodynamic sound source, emitting sound through pressure fluctuations on its surface. The emitted sound is confined by the nearby fixed blade 16d (at a distance much smaller than the wavelength of the sound). In other words, it is believed that the presence of multiple sound sources that move with rotation and the presence of the nearby fixed blade 16d result in complex acoustic interference, resulting in deviations in the propagation of sound waves in the circumferential direction and a sound pressure distribution in the circumferential direction. In particular, in order to prevent the sound emitted from the blades from increasing, the number of fixed blades and the number of rotating blades are basically different. Therefore, the number of sound sources and the number of fixed parts are different, which causes complex interference.

[0173] Therefore, in the present invention, the connection position of the muffler can be set not only in the axial direction but also in the circumferential direction according to the sound pressure distribution at the frequency of the discrete-frequency sound generated by the axial-flow fan 12 .

[0174] In particular, when the axial fan 12 has the fixed blades 16d, the circumferential sound pressure distribution has a greater deviation. Similarly, when the fixed blades 16d are arranged downstream of the airflow generated by the rotation of the rotor blades 18, the circumferential sound pressure distribution has a greater deviation.

[0175] Furthermore, when the axial flow fan 12 includes the stationary blades 16 d and the number of blades of the rotary blades 18 is greater than the number of blades of the stationary blades 16 d , the deviation of the sound pressure distribution in the circumferential direction becomes larger.

[0176] When the number of rotor blades 18 exceeds the number of fixed blades 16d, multiple rotor blades 18 may exist in the space (fixed blade opening) between adjacent fixed blades 16d when viewed axially. Because each rotor blade 18 can be considered a sound source, two sound sources exist within a single fixed blade opening. In this case, the sound waves generated by each sound source interact within the fixed blade opening due to interference, etc., resulting in greater deviation in the circumferential sound pressure distribution within the single fixed blade opening.

[0177] Regarding the sound pressure distribution in the inner space of the axial flow fan (hereinafter also referred to as the sound pressure distribution of the axial flow fan), for example, Figure 13 As shown, in the space between the adjacent fixed blades 16d (fixed blade opening), when the axial flow fan is in operation, as shown in FIG. Figure 14 As shown, the probe microphone PB for measuring the sound pressure can be placed in the fixed wing opening along the circumferential direction ( Figure 14 Left and right direction) and axial direction ( Figure 14 Scan and measure in the up and down directions).

[0178] An example of the sound pressure distribution of the axial flow fan measured in this way is shown in FIG. Figure 15 In. Figure 15 As shown in the figure, a sound pressure distribution having positions with high sound pressure and positions with low sound pressure is generated in the circumferential direction of the axial flow fan.

[0179] The probe microphone PB has a probe attached to the front end of the microphone. For example, the probe has a 1.5mm hole diameter, a 2.5mm outer diameter, and a 50mm sleeve length. This probe microphone PB is inserted into the interior of an axial-flow fan to measure sound pressure. The thin probe minimizes wind influence and enables measurement of localized sound pressure.

[0180] Here, "having a sound pressure distribution in the circumferential direction of the axial fan" means that the difference between the maximum and minimum sound pressure values in the circumferential sound pressure distribution is 6 dB or greater. The difference between the maximum and minimum sound pressure values is calculated from the average value by performing five or more measurements at each point.

[0181] Furthermore, the position with high sound pressure in the circumferential direction of the axial flow fan is set to P. max And set the minimum value to P min , then P max -0.4×(P max -P min ) or higher. And, the position with low sound pressure is set to have P min +0.4×(P max -P min ) below the sound pressure.

[0182] Here, in the case of a plurality of silencers, each silencer 30 can be configured to be connected to a location of the axial flow fan 12 where the sound pressure is high, and the resonant frequency of the silencer can be deviated to a lower side relative to the frequency of the discrete frequency sound. Alternatively, each silencer 30 can be configured to be connected to a location of the axial flow fan 12 where the sound pressure is low, and the resonant frequency of the silencer can be deviated to a higher side relative to the frequency of the discrete frequency sound. Alternatively, each silencer 30 can be configured to be connected to a location of the axial flow fan 12 where the sound pressure is high or low, and the resonant frequency of the silencer can be deviated to a lower side or a higher side relative to the frequency of the discrete frequency sound.

[0183] Furthermore, when the axial flow fan 12 has a plurality of fixed blades 16d, silencers are preferably connected to at least two of the fixed blade openings between adjacent fixed blades 16d, and more preferably to all of the fixed blade openings.

[0184] Hereinafter, the constituent elements of the silencer will be described.

[0185] As materials for the frames, shells and resonance tubes of membrane resonators, Helmholtz resonators and air column resonators (hereinafter collectively referred to as "frame materials"), metal materials, resin materials, reinforced plastic materials and carbon fibers can be cited. As metal materials, for example, metal materials such as aluminum, titanium, magnesium, tungsten, iron, steel, chromium, chromium-molybdenum, nickel-chromium-molybdenum, copper and alloys thereof can be cited. Furthermore, as resin materials, for example, resin materials such as acrylic resin, polymethyl methacrylate, polycarbonate, polyamide-imide, polyarylate, polyetherimide, polyacetal, polyetheretherketone, polyphenylene sulfide, polysulfone, polyethylene terephthalate, polybutylene terephthalate, polyimide, ABS resin (acrylonitrile, butadiene and styrene copolymerized resin), polypropylene and triacetyl cellulose can be cited. Examples of reinforced plastic materials include carbon fiber reinforced plastics (CFRP) and glass fiber reinforced plastics (GFRP). Examples include natural rubber, chloroprene rubber, butyl rubber, EPDM (ethylene / propylene / diene rubber), silicone rubber, and rubbers including cross-linked structures thereof.

[0186] Furthermore, various honeycomb core materials can be used as frame materials. Honeycomb core materials are lightweight and highly rigid, making them readily available. Honeycomb core materials made from various materials, such as aluminum honeycomb cores, FRP honeycomb cores, paper honeycomb cores (manufactured by Shin Nippon Feather Core Co., Ltd. and Showa Aircraft Industry Co., Ltd.), and thermoplastic resin (PP, PET, PE, PC, etc.) honeycomb cores (manufactured by GIFU INDUSTRY CO., LTD., such as TECCELL), can be used as the frame.

[0187] Furthermore, as a frame material, a structure containing air, i.e., a foam material, a hollow material, a porous material, etc. can also be used. When a large number of resonators are used, in order to prevent air from passing between the individual units, a frame can be formed using, for example, a foam material with independent bubbles. For example, 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 independent bubble bodies, compared to continuous bubble bodies, since they do not allow sound, water, gas, etc. to pass through and have high structural strength, they are suitable for use as frame materials. Furthermore, if the above-mentioned porous sound-absorbing body has sufficient support, the frame can be formed only from the porous sound-absorbing body, or the materials cited as materials for the porous sound-absorbing body and the frame can be combined and used, for example, by mixing or kneading. By using a material system that contains air in the interior, the device can be made lightweight. Furthermore, thermal insulation properties can be imparted.

[0188] Here, from the viewpoint of being able to be arranged in a position where high temperature may be generated, the frame material is preferably made of a material having a higher heat resistance than that of a flame retardant material. Heat resistance can be defined, for example, by the time required to satisfy Article 108, Paragraph 2 of the Regulations for the Enforcement of the Building Standards Act. A flame retardant material is defined when the time required to satisfy Article 108, Paragraph 2 of the Regulations for the Enforcement of the Building Standards Act is 5 minutes or more and less than 10 minutes, a quasi-non-combustible material is defined when the time required to satisfy Article 108, Paragraph 2 of the Regulations for the Enforcement of the Building Standards Act is 10 minutes or more and less than 20 minutes, and a non-combustible material is defined when the time required to satisfy Article 108, Paragraph 2 of the Regulations for the Enforcement of the Building Standards Act is 20 minutes or more. However, heat resistance is generally defined for each field. Therefore, depending on the field in which the blower with a silencer is used, the frame material can be made of a material having a heat resistance equal to or greater than the flame retardancy defined in that field.

[0189] The wall thickness (frame thickness) of the frame and the housing is not particularly limited and can be set, for example, based on the size of the opening cross section of the frame.

[0190] As the material of the film 42, various metals such as aluminum, titanium, nickel, permalloy, 42 alloy, kovar, nickel-chromium, copper, beryllium, phosphor bronze, brass, nickel silver, tin, zinc, iron, tantalum, niobium, molybdenum, zirconium, gold, silver, platinum, palladium, steel, tungsten, lead and iridium can be used; PET (polyethylene terephthalate), TAC (triacetyl cellulose), PVDC (polyvinylidene chloride), PE (polyethylene), PVC (polyvinyl chloride), PMP (polymethylpentene), COP (cycloolefin polymer), Z Resin materials such as EONOR, polycarbonate, PEN (polyethylene naphthalate), PP (polypropylene), PS (polystyrene), PAR (polyarylate), aramid, PPS (polyphenylene sulfide), PES (polyethersulfone), nylon, polyester, COC (cyclic olefin copolymer), cellulose acetate butyrate, nitrocellulose, cellulose derivatives, polyamide, polyamide-imide, POM (polyoxymethylene), PEI (polyetherimide), polyrotaxane (sliding ring materials, etc.), and polyimide can also be used. In addition, glass materials such as thin film glass and fiber-reinforced plastic materials such as CFRP (carbon fiber reinforced plastic) and GFRP (glass fiber reinforced plastic) can also be used. In addition, natural rubber, chloroprene rubber, butyl rubber, EPDM, silicone rubber, etc., as well as rubbers containing cross-linked structures thereof can be used. Alternatively, a material composed of a combination of these can be used.

[0191] Furthermore, when a metal material is used, the surface may be plated with metal from the viewpoint of suppressing rust or the like.

[0192] From the viewpoint of excellent durability against heat, ultraviolet rays, external vibration, and the like, a metal material is preferably used as the material of the film 42 in applications requiring durability.

[0193] Furthermore, the film is not particularly limited to the method for fixing the frame, and can appropriately utilize a method using a double-sided tape or adhesive, mechanical fixing methods such as screwing, compression bonding, etc. As for the fixing method, similar to the frame material and the film, it is also possible to select from the viewpoints of heat resistance, durability, and water resistance. For example, as an adhesive, it is possible to select the heat-resistant epoxy adhesive "Duralco series" manufactured by CEMEDINE Co., Ltd. "Super X" series, ThreeBond Co., Ltd. "3700 series (heat-resistant)", TAIYO WIRE CLOTH CO., LTD., etc. Furthermore, as a double-sided tape, it is possible to select the high heat-resistant double-sided tape 9077 manufactured by 3M Company, etc. In this way, various fixing methods can be selected for the required characteristics.

[0194] The thickness of film 42 is preferably less than 100 μm, more preferably 70 μm or less, and even more preferably 50 μm or less. Furthermore, if the thickness of film 42 varies, the average thickness may be within the above range. On the other hand, thinner films can be difficult to handle. The film thickness is preferably 1 μm or greater, more preferably 5 μm or greater.

[0195] The Young's modulus of the film 42 is preferably 1000 Pa to 1000 GPa, more preferably 10000 Pa to 500 GPa, and most preferably 1 MPa to 300 GPa.

[0196] The density of the membrane 42 is preferably 10 kg / m 3 ~30000kg / m 3 , more preferably 100 kg / m 3 ~20000kg / m 3 , most preferably 500kg / m 3 ~10000kg / m 3 .

[0197] In the film resonator, the thickness of the back space 44 is preferably 10 mm or less, more preferably 5 mm or less, and even more preferably 3 mm or less. Even if the thickness of the back space varies, the average value may be within the above range.

[0198] The method of attaching the muffler (resonator) to the casing of the axial flow fan is not particularly limited, and known fixing methods such as methods using adhesives, adhesives, double-sided tapes, and mechanical methods such as screw fastening can be appropriately used.

[0199] Furthermore, the back space 44 of the membrane-type resonator 30c only needs to be roughly divided to block air flow. Besides being a completely closed space, it may also have partial openings in the membrane 42 or the frame 40. This partial opening is preferable because the gas in the back space expands or contracts due to temperature changes, exerting tension on the membrane 42, thereby changing the hardness of the membrane 42 and preventing changes in the sound absorption characteristics.

[0200] Forming through-holes in membrane 42 allows for propagation of airborne sound. This changes the acoustic impedance of membrane 42. Furthermore, the through-holes reduce the mass of membrane 42. This allows for control of the resonant frequency of membrane resonator 30c. The locations where through-holes are formed are not particularly limited.

[0201] Here, in Figure 1In the examples shown, the air supply mechanism with a silencer is configured to have an axial flow fan 12 as a fan and suppress the noise of the axial flow fan (propeller fan), but is not limited to this and can also be applied to previously known fans such as multi-blade fans, turbo fans, centrifugal fans, and linear flow fans (registered trademarks).

[0202] A multi-blade fan draws air in from the direction of the rotation axis of its bladed rotor and delivers air perpendicular to the axis, with air outlets located on its side. Therefore, for example, if the fan is a multi-blade fan, the muffler can be positioned so as to contact the air outlet. In this case, the muffler is preferably positioned so as not to obstruct the multi-blade fan's air outlet.

[0203] In the case of other fans such as multi-blade fans, when silencing the sound generated by the fan, in order to effectively silence the sound, it is preferably arranged in the air supply path of the fan. However, since the silencer is affected by the wind, the silencer effect based on resonance is reduced, and the wind noise is amplified. In contrast, by arranging a weaker silencer, the amplification of the wind noise is suppressed and the sound generated by the fan can be properly silenced.

[0204] Furthermore, a blower with a silencer having the same structure as the above-mentioned structure can also be applied to mobile objects with propellers, such as helicopters and UAVs, that have propeller fans serving as axial-flow fans. That is, a mobile object with a propeller that is equipped with the blower with a silencer can be realized. With this mobile object with a propeller, the noise generated by the rotation of the propeller during flight can be appropriately silenced. In particular, during flight, there are mainly people below the mobile object with a propeller (on the propeller exhaust side), so it is important to silence the noise in the downward direction, and the silencer can appropriately silence this noise.

[0205] In a mobile object with a propeller, it is desirable that the muffler of the muffler-equipped blower be arranged at a position where it can appropriately muffle the noise, for example, around the propeller that is the main sound source.

[0206] Examples Figure 30 In the following description, a multi-rotor propeller-equipped vehicle 50 is shown. A muffler 30 can be disposed adjacent to each of a plurality of (e.g., four) propellers 52. In this case, by disposing the muffler 30 radially outward of each propeller 52 (on the side farther from the vehicle's main body 54), the muffler 30 can be configured as part of a propeller guard 56. The propeller guard 56 is a frame disposed radially outward of each propeller 52 to prevent contact with the propeller 52.

[0207] Furthermore, the outer shape of the silencer 30 used in the mobile body 50 with a propeller (specifically, the housing 33 of the silencer 30) may be a circle or an arc when viewed from the rotation axis direction of the propeller 52. Figure 30 As shown, the muffler 30 arranged around each propeller 52 in the propeller shroud 56 may be bent along the circumferential direction of each propeller 52. In this case, the muffler 30 functions well as the propeller shroud 56 and allows the wind generated by the propeller to flow unimpeded.

[0208] The type of the muffler 30 used in the mobile body 50 with a propeller is not particularly limited, and may be, for example, Figure 28 The air column resonator 30b is shown. Figure 28 1 and 2 are diagrams showing a cross section of the air column resonator 30 b , and strictly speaking, are diagrams showing a cross section perpendicular to the rotation axis of the propeller 52 .

[0209] As described above, the air column resonator 30b may be curved into an arc shape along the circumferential direction of the propeller 52 in order to function as the propeller shroud 56. Specifically, when the air column resonator 30b is viewed from the direction of the rotation axis of the propeller 52, at least a portion of the resonance tube 37 formed within the casing 33 of the muffler 30 may be curved into an arc shape along the circumferential direction of the propeller 52.

[0210] In addition, if Figure 28 As shown, the resonance tube 37 can be bent into an L-shape. Specifically, the arc-shaped casing 33 is provided with an opening 35 at a position facing the nearest propeller 52. Specifically, the casing 33 includes an arc-shaped portion and a portion extending from one end of the arc toward the opening 35. These portions intersect in an L-shape to form the resonance tube 37.

[0211] Example

[0212] The present invention will be described in more detail below with reference to the following examples. The materials, amounts used, ratios, treatment contents, and treatment sequences shown in the following examples may be modified as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the following examples.

[0213] [Axial-flow fan]

[0214] A San Ace 60 axial-flow fan (Model: 9GA0624P1G03, manufactured by Sanyo Denki Co., Ltd.) was prepared. The fan's housing measures 60 mm x 60 mm and is 38 mm thick. The fan has five fixed blades and seven rotating blades. When the rated current is applied to the fan, the fan's peak sound (discrete frequency sound) exhibits a basic pattern around 1800 Hz.

[0215] [Sound pressure distribution of axial flow fans]

[0216] The sound pressure distribution in the internal space of the axial flow fan was measured as follows.

[0217] A custom-made probe (aperture 1.5 mm, outer diameter 2.5 mm, sleeve length 50 mm) was installed at the front end of a microphone (4152N, manufactured by ACO Co., Ltd.) to produce a probe microphone PB. Figure 14 The instrument is inserted into the fixed blade opening of an axial fan and scanned circumferentially and axially to measure the sound pressure. Initially, the instrument is positioned near the fixed blade in the circumferential direction and 1mm away from the rotating blade in the axial direction. The instrument is then moved circumferentially at 1mm intervals, scanning circumferentially. After completing the circumferential scan, the instrument is moved 1mm toward the near-front side (opposite the rotating blade) and scanned circumferentially again, measuring the sound pressure at each measurement point. This circumferential and axial movement is repeated to measure the sound pressure within the fixed blade opening.

[0218] The sound pressure of the fundamental discrete frequency sound at each measurement point is extracted and plotted at each measurement position, thereby showing the spatial distribution of the sound pressure at the discrete frequency (1.8 kHz) ( Figure 15 ) In addition, regarding the sound pressure of the discrete frequency sound, the surrounding sound pressure is considered to be the sound pressure caused by the background wind noise and removed to obtain the sound pressure of the discrete frequency sound.

[0219] Figure 15 The area inside the fan is the fixed wing opening, and the fixed wing blades are located at both ends of the circumference. Figure 15 It can be seen that around the circumference of the axial-flow fan, there is a sparse and dense distribution of sound pressure within a 30dB range. The sound pressure increases near the fixed blades and decreases near the center of the fixed blade opening. Thus, the circumferential sound pressure distribution within the internal space of the axial-flow fan was determined through actual measurements.

[0220] [Example 1]

[0221] The silencer used a PVC air column resonator (outer diameter 10 mm, inner diameter 6 mm, inner length (resonance tube length) 48 mm) with a gap between the closed surface and the PVC tube. The PVC tube was cut roughly. The resonant frequency of the acoustic tube of this air column resonator was measured to be 1736 Hz.

[0222] The reflection and absorption performance of the muffler was measured using a 4-microphone method using an acoustic tube. The transmittance and reflectance were measured in accordance with ASTM E2611 and can be measured using a WinZac MTX manufactured by Nihon Onkyo Engineering Co., Ltd. The results are shown in Figure 16 The air column resonator was placed inside a 60mm square acoustic tube with the same internal dimensions as the fan and the measurement was performed. The opening of the resonance tube was placed roughly toward the sound source. Figure 16 As shown, the sum of the absorption rate and the reflectivity of the silencer at the resonant frequency is about 26%, the half-value width is about 212 Hz, and the normalized half-value width is 0.12.

[0223] According to the above sound pressure distribution measurement results, the air column resonator is connected to the position of the axial fan where the sound pressure is high (near the fixed blade (circumferential, axial) = (3mm, 13mm)). In addition, this position is the maximum sound pressure P in the circumferential sound pressure distribution. max and the minimum value P min Become a P max -0.4×(P max -P min ) or above. In an axial flow fan, the number of fixed blades is five, so there are also five fixed blade openings. Thus, an air column resonator is connected to each of the five fixed blade openings.

[0224] An opening (through hole) with a diameter of 10 mm is provided on the housing at the location where the air column resonator is inserted.

[0225] A fan with a silencer, equipped with five air column resonators, was fabricated by inserting an air column resonator into each through-hole in the housing. The ends of the air column resonators were adjusted so as not to protrude into the interior of the axial flow fan. If they protrude into the fan, wind would hit the corners of the air column resonators, easily generating wind noise. Therefore, it was desirable to avoid obstructing the air duct.

[0226] [Comparative Example 1]

[0227] As a silencer, a PVC air column resonator with a single-side closed tube (outer diameter 10 mm, inner diameter 6 mm, inner length (resonance tube length) 48 mm) was used. The silencer was identical to that used in Example 1, except for the gap in the closed portion of the PVC tube. In other words, the silencer was identical to the air column resonator used in Example 1, except for the gap in the closed portion. The resonant frequency of this air column resonator was 1680 Hz.

[0228] The reflection and absorption properties of the muffler were measured in the same manner as in Example 1. The results are shown in Figure 16 In. Figure 16 As shown, the sum of the absorption rate and the reflectivity of the silencer at the resonant frequency is about 0.56%, the half-value width is about 84 Hz, and the normalized half-value width is 0.3.

[0229] [evaluate]

[0230] The noise level (sound pressure) of the manufactured muffler-equipped blowers of the Examples and Comparative Examples was measured. Furthermore, as Reference Example 1, the noise level of a single axial-flow fan was measured (peak frequency 1800 Hz). Furthermore, the noise level was measured when the peak frequency was changed to 1900 Hz by varying the power supply (Reference Example 2).

[0231] like Figure 17 As shown, a 1m square box with empty front and back sides is made of an acrylic plate with a thickness of 10mm, and a sound-absorbing urethane with a thickness of 10cm (not shown) is pasted on the entire inner side surface to make a measuring box 100. In the center of the measuring box 100, a blower 10 with a silencer is arranged using a base 102. The direction of the airflow generated by the axial flow fan is arranged corresponding to the open surface of the measuring box 100. A microphone MP1 (4152N, manufactured by ACO Co., Ltd.) is arranged at a position 1m away from the axial flow fan toward the axial exhaust side and 0.5m away from it in the vertical direction, and a microphone MP2 (4152N, manufactured by ACO Co., Ltd.) is arranged at a position 1m away from the axial flow fan toward the exhaust side and 0.5m away from it in the horizontal direction.

[0232] The fan was operated and the noise level was evaluated using the average value of the sound pressure measured by two microphones. The results are shown in Figure 18 and Figure 19 .

[0233] from Figure 19 Comparing Comparative Example 1 with Reference Example 1 reveals that significant noise cancellation is not achieved for the target discrete frequency sound of approximately 1800 Hz. Furthermore, at frequencies near this discrete frequency sound, the sound pressure is higher than in the reference example. This is due to wind noise.

[0234] In contrast, from Figure 18 Comparison of Example 1 with Reference Example 1 shows that a significant silencing effect can be achieved for discrete frequency sounds of approximately 1800 Hz near the resonant frequency. Furthermore, it can be seen that the sound pressure does not increase near the discrete frequency, and the generation of wind noise can be suppressed. Furthermore, it can be seen that a silencing effect can also be achieved for higher-order second-order discrete frequency sounds. In other words, it can be seen that a silencing effect can be achieved not only at frequencies near the resonant frequency of the resonator, but also at higher-order frequencies, demonstrating a special effect that is beneficial for silencing the axial flow fan.

[0235] Furthermore, it was confirmed that the wind speed and air volume of the blower with a muffler of Example 1 did not change compared to the conventional axial flow fan (Reference Example 1).

[0236] [Example 2]

[0237] Instead of the air column resonator used in Example 1, an L-shaped air column resonator (made of ABS resin, one-side closed tube structure, flow path length (resonance tube length) 48 mm) with its opening located at a position bent 90° relative to the resonance tube was used. The resonant frequency of this air column resonator was 1826 Hz. The reflection and absorption performance of this silencer was measured in the same manner as in Example 1. The results are shown in FIG. Figure 21 In. Figure 21 As shown in Figure 1, the sum of the absorption and reflectance of the silencer at the resonant frequency is approximately 21%, the half-value width is approximately 234 Hz, and the normalized half-value width is 10.6.

[0238] The air column resonator is mounted to the through hole of the casing of the axial flow fan in such a manner that the extension direction of the resonance tube becomes axial. Since the casing is the same as that of Example 1, the air column resonator is connected to a position where the circumferential sound pressure of the axial flow fan is high (near the fixed wing (circumferential, axial) = (3mm, 13mm)). By making the air column resonator an L-shaped air column resonator and mounting it on the axial flow fan in such a manner that the extension direction of the resonance tube becomes axial, the overall area of the blower with a silencer viewed from the axial direction can be made smaller and more compact than that of Example 1.

[0239] [evaluate]

[0240] The noise level was measured in the same manner as above except that the power supply was changed and the peak frequency was changed to 1900 Hz. Figure 20 middle.

[0241] from Figure 20 Comparison of Example 2 and Reference Example 2 demonstrates a significant noise reduction effect for discrete frequency sounds near the resonant frequency of approximately 1900 Hz. Furthermore, higher-order second- and third-order discrete frequency sounds can also be reduced. This demonstrates that even a compact L-shaped air column resonator exhibits noise reduction effectiveness.

[0242] Furthermore, it was confirmed that the wind speed and air volume of the blower with a muffler of Example 2 did not change compared to the conventional axial flow fan (Reference Example 2).

[0243] [Example 3]

[0244] Two through holes (Φ1 mm) were opened on the back of the air column resonator (outer diameter 10 mm, inner diameter 6 mm, inner length (resonance tube length) 44 mm) made of a PVC single-side closed tube (through holes were opened on an acrylic plate using a laser cutter).

[0245] The resonant frequency of the air column resonator is 1840 Hz. The reflection and absorption performance of the muffler were measured in the same manner as in Example 1. The results are shown in Figure 22 In. Figure 22 As shown in Figure 1, the sum of the absorption and reflectance of the silencer at the resonant frequency is approximately 43%, the half-value width is approximately 104 Hz, and the normalized half-value width is 14.5.

[0246] The fan was mounted in the same arrangement as in Example 1 and the measurement was performed. Figure 23 The noise spectrum is shown in Figure 2. Peak noise reduction is approximately 14 dB, demonstrating a significant noise reduction effect. However, there is a significant sound amplification region slightly below the peak. This corresponds to wind noise caused by the resonant tube. Since the reflectivity + absorption rate of the resonance is greater than in Examples 1 and 2, this generates significant wind noise.

[0247] [Simulation 1]

[0248] The relationship between the connection position of the muffler and the resonant frequency of the muffler was investigated using simulations using the finite element method software COMSOL MultiPhysics (ver. 5.3, COMSOL Inc.).

[0249] Create an internal space model of the axial flow fan and set the sound source to reproduce the phase of the fan. Corresponding to the axial flow fan used in the above embodiment, there are five fixed blades and seven rotating blades.

[0250] Using this model, simulations were performed to calculate the sound pressure distribution within the interior of the axial fan. The simulations confirmed a sound pressure distribution with high sound pressure around the fixed blades and low sound pressure near the center of the fixed blade openings.

[0251] Furthermore, the spatial distribution of sound pressure was investigated by calculation while changing the frequency within the range of 1600-2000 Hz, but it was confirmed that there was almost no difference in the distribution.

[0252] Based on the simulation results, a muffler was connected at a location with high sound pressure within the sound pressure distribution of the fan's discrete frequency sound (1800 Hz). To achieve a resonant frequency of 1730 Hz, the muffler was modeled as an air column resonator with two 1 mm diameter second openings in a closed surface with an outer diameter of 10 mm, an inner diameter of 6 mm, and an inner length (resonance tube length) of 48 mm.

[0253] Using this simulation model, the sound pressure at a position 1 m away from the fan in the axial direction and 0.5 m away in the vertical direction, and at a position 1 m away from the fan in the axial direction and 0.5 m away in the horizontal direction, was calculated for each frequency, and the average value was calculated as the sound pressure level. Figure 24 middle.

[0254] In this simulation, the phase distribution of the sound pressure emission from the sound source is calculated at each frequency to obtain the peak sound. In other words, the volume or the amount of sound deadening when the frequency is the peak sound (NZ sound of the fan) is shown for each frequency.

[0255] Similarly, a muffler is connected at a low sound pressure position in the sound pressure distribution of the discrete frequency sound (1800 Hz) of the fan, and the sound pressure is calculated for each frequency, and the average value is obtained as the sound pressure level. Figure 25 middle.

[0256] from Figure 24 It can be seen that when the muffler is connected to a location with high sound pressure in the sound pressure distribution inside the fan, the sound pressure level of the noise can be further reduced at frequencies higher than the resonant frequency of the muffler (1730 Hz in the figure, where the noise shows a maximum value in the simulation). Therefore, it can be seen that when the muffler is connected to a location with high sound pressure in the sound pressure distribution inside the fan, by setting the resonant frequency of the muffler to a frequency lower than the frequency of the discrete frequency sound of the fan, the discrete frequency sound of the fan can be more appropriately silenced.

[0257] On the other hand, from Figure 25 It can be seen that when the muffler is connected to a location with low sound pressure in the sound pressure distribution inside the fan, the sound pressure level of the noise can be further reduced at frequencies lower than the resonant frequency of the muffler. Therefore, it can be seen that when the muffler is connected to a location with low sound pressure in the sound pressure distribution inside the fan, the resonant frequency of the muffler is set to a frequency higher than the frequency of the discrete frequency sound of the fan, thereby more appropriately muffling the discrete frequency sound of the fan.

[0258] [Example 4]

[0259] Next, the relationship between the connection position of the silencer and the resonance frequency of the silencer was studied using an actual device.

[0260] By using the blower with a silencer of Example 1, the fan speed is varied by changing the power, and the discrete frequency sound can be changed. For each speed, the noise level (sound pressure) of the blower with a silencer is measured in the same way as in Example 1. The relationship between frequency and noise level (sound pressure level) is shown in Figure 26 The discrete frequency sound was measured by changing the rotation speed from around 1600Hz to around 1900Hz. Figure 26 , the relationship between frequency and sound pressure level is shown by changing the line type for each rotation speed.

[0261] The gentle peak centered around 1670 Hz indicates amplification of wind noise caused by the resonance of the silencer (air column resonator). Even if the discrete frequency sound is changed, there is almost no change.

[0262] On the other hand, each measurement shows a peak of approximately 20 dB, representing the discrete frequency sound at each rotational speed. At the rotational speed indicated by the solid line in the graph, the peak height of this discrete frequency sound is smaller than at other rotational speeds. This indicates that the discrete frequency sound is being muted. In this case, the muting occurs around 1800 Hz.

[0263] In addition, the resonant frequency (1730 Hz) measured using the acoustic tube is also indicated by a line in the figure.

[0264] From this, it can be seen that the relationship is: the amplification frequency of wind noise (1670 Hz) < the resonance frequency of the sound tube (1730 Hz) < the cancellation frequency of discrete frequency sound (1800 Hz).

[0265] In agreement with the predictions made in the above simulations, it was confirmed with an actual device that the noise cancellation frequency of the discrete frequencies appears on the higher frequency side than the resonance frequency of the silencer.

[0266] [Example 5]

[0267] L-shaped air column resonators are used to reduce the noise generated by propellers during unmanned aerial vehicle flight. Specifically, the study used the DJI Mavic Air 2 unmanned aerial vehicle to investigate the reduction of peak noise during flight. Specifically, the study examined the noise reduction effect when the unmanned aerial vehicle was suspended and stationary at an altitude of 1.2 meters above the ground.

[0268] To investigate noise reduction, we first measured the sound pressure while the UAV was in flight, with a dedicated propeller guard installed. The sound pressure measurements were conducted on a floor covered with sound-absorbing material. Specifically, a windshielded microphone was installed 1.1 meters below the UAV and 0.2 meters laterally offset from it. In other words, the microphone was positioned 10 cm above the sound-absorbing material. Sound pressure measurements were performed in the 1 / 24 octave band.

[0269] The sound pressure measurement results are shown in Figure 27 The vertical axis in the figure represents the sound pressure level (dBA). Figure 27 It can be seen that the rotation of the propeller generates a large number of peak sounds. Specifically, the first peak sound is a sound at 227 Hz, the second peak sound is a sound at 453 Hz, and high-order peak sounds corresponding to integer multiples of these frequencies are also generated.

[0270] Next, an L-shaped air column resonator was made to eliminate the sound at the second peak sound frequency of 453 Hz. Figure 28 As shown, the air column resonator is set as an arc-shaped resonator corresponding to the propeller shape of the unmanned aerial vehicle (marked with the symbol 30b in the figure). In addition, the diameter of the propeller is 183 mm. In order to surround the propeller, the diameter of the inner side (the side close to the propeller) of the air column resonator 30b is set to 190 mm, the diameter of the outer side (the side away from the propeller) is set to 230 mm, and the height is set to 11 mm. The inner edge and the outer edge of the air column resonator 30b are respectively set to arcs, and the angle (center angle) of each arc is set to 100°. In addition, by ensuring a sufficient length for the air column resonance and making the angle between the frame of the dedicated propeller shroud structure and the air column resonator 30 consistent, it is easy to install the air column resonator 30b. In addition, the above-mentioned angle is determined in a way that does not generate unnecessary vibration.

[0271] In addition, an arc-shaped opening portion 35 with an angle of 4° is provided at one end of the shell 33 of the air column resonator 30b. The width of the arc-shaped opening portion 35 (the length in the circumferential direction of the propeller) is 6.6 mm. By providing the opening portion 35, a resonance tube 37 bent into an L shape is provided in the shell 33. The thickness of the side wall of the shell 33 is 2.5 mm, and the thickness of the upper wall and the lower wall are 1 mm respectively. That is, in the resonance tube 37 inside the shell 33, its inner diameter is 192.5 mm, and its outer diameter is 227.5 mm, in other words, the width is 17.5 mm. In addition, the height of the resonance tube 37 is 9 mm.

[0272] Acrylic material was used in the production of the air column resonator 30b. Specifically, 1mm thick acrylic plates were used for the upper and lower walls, and 3mm thick acrylic plates were used for the other parts. Each part was cut with a laser cutter and then joined together using an acrylic adhesive from Acrysunday Co., Ltd. to form the above-mentioned shape. Figure 28 The air column resonator 30b is shown.

[0273] The weight of each air column resonator 30b is 15g, and the weight of four air column resonators is 60g. On the other hand, the weight of the dedicated propeller shroud is 90g, so a relatively lightweight air column resonator structure can be achieved.

[0274] The noise reduction effect of the air column resonator 30 b was measured using an acoustic tube having a diameter of 8 cm. Figure 29 The measurement results are shown in FIG. The vertical axis in the figure represents the reflectivity + absorptivity of the incident sound. Figure 29 It can be seen that the first resonance of the air column resonator 30b occurs at a frequency of 468 Hz, and the reflectivity + absorptivity at this frequency is 29.3%. Furthermore, the half-value width is 32 Hz, and the normalized half-value width is 0.068. These values meet the numerical conditions specified in the present invention. It is inferred that these values are achieved by using the air column resonator structure 30b having the resonance tube 37 bent into an L-shape midway.

[0275] Next, the same number of the air column resonators 30b as the number of propellers of the unmanned aerial vehicle (specifically, four) is produced, as shown in FIG. Figure 30 As shown, each air column resonator 30b was fixed to the upper portion of the propeller shroud 56 of an unmanned aerial vehicle (a mobile object 50 with a propeller in the figure). The unmanned aerial vehicle was then flown, and in-flight sound pressure measurements were performed. The position of the air column resonator 30b was offset approximately 1 cm toward the air supply side (upward) relative to the propeller 52 of the unmanned aerial vehicle.

[0276] The sound pressure measurement results are shown in Figure 31 The dotted line in the figure is a curve when the air column resonator 30b is not used, and the solid line is a curve when the air column resonator 30b is fixed to the propeller shroud 56. Figure 31 It can be seen that the desired noise cancellation effect is achieved at a frequency of 453Hz. Specifically, the sound pressure can be reduced from 53.1dBA to 45.7dBA, achieving a noise cancellation effect of 7.4dB based on the evaluation value in the 1 / 24 octave band. Furthermore, as mentioned above, since the measurement position (microphone position) is below the UAV, it has been confirmed that noise cancellation in the downward direction, which is a problem, can be achieved on mobile objects with propellers such as UAVs.

[0277] In addition to its sound-absorbing function, each manufactured air column resonator 30b also functions as a part of the propeller shroud 56. Specifically, by surrounding the propeller with the air column resonator 36b, wind is rectified to facilitate flow and people and objects are prevented from coming into contact with the rotating propeller 52.

[0278] [Example 6]

[0279] Instead of flying the unmanned aerial vehicle, the unmanned aerial vehicle was fixed and the sound pressure was measured under the same conditions as in Example 5. When the propeller 52 was rotated while the unmanned aerial vehicle was fixed, a peak sound was generated at around 1400 Hz. Accordingly, an air column resonator 30b was produced to silence the sound at 1400 Hz. The inner diameter, outer diameter, and height of the air column resonator 30b were set to the same dimensions as in Example 5. On the other hand, the width of the opening 35 formed on the shell 33 was set to 5 mm, and the arc angle (center angle) formed by the outer edge of the air column resonator 30b was set to 32°.

[0280] The air column resonator 30 b is regarded as one unit (one), and five air column resonators 30 b are arranged in an arc shape, thereby manufacturing a propeller shroud composed of the air column resonators 30 b. Figure 32 A portion of the propeller shroud of the fabricated air column resonator is shown in FIG. Furthermore, a 5 mm thick sound absorber made of "QonPET," a nonwoven sound absorbing material manufactured by Bridgestone KBG Co., Ltd., was placed at the opening 35 (the inlet of the resonance tube 37) of each air column resonator 30b, covering the opening 35. In other words, in Example 6, an air column resonator structure with a sound absorber was fabricated.

[0281] The results of the measurements using the acoustic tube are shown in the table below regarding the noise cancellation effect under the above conditions. Figure 33 In. From Figure 33 It can be seen that at a frequency of 1342 Hz, the reflectivity + absorptivity is 28.7%, the half-value width is 162 Hz, and the normalized half-value width is 0.12.

[0282] Furthermore, the aforementioned air column resonance structure with sound absorbers was installed on the exhaust side of the propeller shroud 56 for an unmanned aerial vehicle, and sound pressure measurements were performed. The air column resonance structure with sound absorbers was positioned 3 cm below the propeller 52 toward the exhaust side. Sound pressure measurements were performed using a windshield microphone installed on the exhaust side.

[0283] Figure 34The results of the measurement when the air column resonance structure with the sound absorbing body is installed (solid line graph) and the results of the measurement when it is not installed (dashed line graph) are shown. Figure 34 It is understood that by installing the air column resonator structure with the sound absorber, it is possible to mute the peak sound at a frequency slightly higher than the resonant frequency of 1342 Hz of the air column resonator 30 b alone, specifically, at 1390 Hz.

[0284] According to the above results, the effects of the present invention are remarkable.

[0285] Explanation of symbols

[0286] 10-Blower with silencer, 12-Axial fan, 14-Motor, 15-Through hole, 16-Casing, 16a-Support, 16b-Outer frame, 16c-Hood, 16d-Fixed blade, 16e-Hole, 17-Inner space, 18-Rotating blade, 20-Shaft, 22-Blade, 30-Silencer, 30a-Helmholtz resonator, 30b-Air column resonator, 30c-Membrane resonator, 32, 33-Casing, 34, 35-Openings, 36-Inner space, 37-Resonance tube, 40-Frame, 42-Membrane, 44-Back space, 50-Moving object with propeller, 52-Propeller, 54-Main body, 56-Propeller guard, 100-Measurement box, 102-Base, PB-Probe, MP1-Microphone, MP2-Microphone

Claims

1. A blower with a muffler, comprising a fan and a muffler for muffle the sound generated by the fan. The muffler has a resonance characteristic, The muffler is arranged at a position connected to the sound field space of the sound generated by the fan. The sum of the absorptivity and reflectivity of the muffler at the resonant frequency measured using a sound tube is 10% to 43%, and the normalized half-value width is greater than 0.05 and less than 0.

25. Here, the absorptivity and reflectivity of the muffler at the resonant frequency are measured by a four-microphone method using a sound tube in accordance with ASTM E2611. The normalized half-value width is a value obtained by dividing the half-value width of the resonance peak of the muffler by the resonance frequency.

2. The blower with a silencer according to claim 1, wherein: The muffler is connected to the inner space of the fan.

3. The blower with a silencer according to claim 2, wherein: The muffler includes a flow path communicating with the internal space of the fan.

4. The blower with a silencer according to any one of claims 1 to 3, wherein: The resonant frequency of the muffler measured by the sound pipe deviates by 1% to 10% from the frequency of the discrete frequency sound caused by the fan.

5. The blower with a silencer according to claim 4, wherein: The muffler is connected at a position where the sound pressure distribution at the frequency of the discrete frequency sound caused by the fan is high. The resonant frequency of the muffler is lower than the frequency of the discrete frequency sound.

6. The blower with a silencer according to claim 4, wherein: The muffler is connected at a position where the sound pressure distribution at the frequency of the discrete frequency sound caused by the fan is low. The resonant frequency of the silencer is higher than the frequency of the discrete frequency sound.

7. The blower with a silencer according to any one of claims 1 to 3, wherein: The muffler is an air column resonator, The resonant tube of the air column resonator has a bent structure.

8. The blower with a silencer according to any one of claims 1 to 3, wherein: The silencer is composed of a resonator and porous sound-absorbing materials.

9. The blower with a silencer according to any one of claims 1 to 3, wherein: The fan is an axial flow fan, The muffler is arranged at a position that does not overlap with a region formed by the rotation of the rotor blades when viewed from the axial direction of the axial flow fan.

10. The blower with a silencer according to any one of claims 1 to 3, wherein: The fan is an axial flow fan with fixed wings, The muffler is connected to at least one of the fixed-wing openings between the fixed wings.

11. The blower with a silencer according to claim 10, wherein: The muffler is connected to all the fixed wing openings.

12. A mobile object with a propeller, comprising the blower with a silencer according to any one of claims 1 to 11, The fan of the air blower with a muffler is a propeller, and the air blower flies by the rotation of the propeller.

13. The propeller-equipped moving object according to claim 12, wherein: The muffler of the muffler-equipped blower is arranged around the propeller to form a propeller shroud.

14. The propeller-equipped moving object according to claim 12 or 13, wherein: When the silencer of the blower with silencer is viewed from the direction of the rotation axis of the propeller, the outer shape of the silencer is a circle or an arc.

15. The propeller-equipped moving object according to claim 14, wherein: The muffler is an air column resonator with a bent resonance tube. When the muffler is viewed from the rotation axis direction, a portion of the resonance tube is curved in an arc shape.

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