WO2008053867A1

WO2008053867A1 - Centrifugal fan

Info

Publication number: WO2008053867A1
Application number: PCT/JP2007/071075
Authority: WO
Inventors: Seiji Shirahama; Kazuo Ogino; Yasuji Tsubakishita; Akira Sadamoto
Original assignee: Panasonic Corporation
Priority date: 2006-11-02
Filing date: 2007-10-30
Publication date: 2008-05-08

Abstract

A centrifugal fan used for ventilation fan devices etc., in which noise in a wider frequency range can be reduced and the frequency of reducible noise is adjustable. The centrifugal fan has, received in an outer shell, an electric motor to which an impeller is connected, a casing for surrounding the impeller and having a bell mouth-shaped suction opening on one side of the casing, and a bell mouth-shaped orifice having an opening concentric with the suction opening and having a diameter less than or equal to the diameter of the suction opening. A member for closing a gap between an end of the orifice and the casing is formed from a material for noise absorption structure, and a resonance-type sound absorption structure is formed by using a space, formed by the orifice, as a rear air layer.

Description

Specification

Centrifugal blower

Technical field

TECHNICAL FIELD [0001] The present invention relates to a centrifugal fan used for ventilation and ventilation equipment and the like.

Background art

[0002] Conventionally, this type of centrifugal fan is known to be used for a centrifugal fan etc., and has an orifice in the opening on one surface of the shell, which is different from the suction casing having a bellmouth-like suction port. There is. An example of such a conventional centrifugal fan is described in, for example, Patent Document 1.

Hereinafter, the conventional centrifugal fan will be described with reference to FIG.

As shown in FIG. 31, the conventional centrifugal fan includes an outer shell 101 having an opening on one side, an electric motor 104 having an impeller 103 fixed to a top surface 102 in the outer shell 101, and an impeller 103. It has an encasing casing 105 and a suction casing 107 having a suction port 106. Then, the suction casing 107 is separated by a predetermined gap h, and the orifice 109 having a suction hole 108 equal or smaller than the suction port 106 is separated by a gap size i between the lower end 110 of the suction casing 107 and the end 111 of the orifice 109 The resonance space 112 is configured to be provided. In addition, on one surface of the orifice 109, a Dari nole 113 and a discharge port 114 provided on one side surface of the outer shell 101 are provided.

In the above configuration, when the impeller 103 rotates, the suctioned air passes from the grille 113 through the suction hole 108 of the orifice 109, enters the impeller 103 from the suction port 106 of the suction casing 107, and is boosted by the impeller 103. The ink passes through the inside of the casing 105 and is discharged from the discharge port 114. At this time, the rotational noise generated when the pressure is raised by the impeller 103, the turbulent noise generated by the vortices generated when passing through the casing 105, and the noise of the noise generated within the casing 105 are radiated from the suction port 106. A portion of which enters the resonant space 112 from an inlet 115 with gap size i. Among the sound waves of the incident noise, sound waves of a frequency specified by the volume and shape of the resonance space 112 cause air column resonance in the resonance space 112, or the entrance 115 and the resonance space 112 are Helmholtz. Resonant muffling by acting as a resonator Be done.

The frequency of noise to be resonantly silenced in the resonance space 112 is specified by the volume and shape of the resonance space 112. In such a conventional centrifugal fan, since the range in which the volume and shape of the resonance space 112 can be adjusted is narrow, there is a problem that the frequency range of noise that can be resonantly muffled is narrow. It is required to expand the frequency range of noise that can be

Further, in order to mute low frequency noise, it is necessary to increase the volume of the resonance space 112, and there is a problem that the size of the shell 101 is increased. Therefore, the size of the shell 101 is changed. There is a need to be able to silence lower frequency noises without having to do so.

[0008] In addition, since the volume of the resonance space 112 can not be easily changed, the resonance muffling is performed when the main frequency of the noise changes depending on the state of installation of the centrifugal fan, or when there are noises of multiple projecting frequencies. There is a problem that the effect of noise reduction is diminished, and it is required to be able to adjust the frequency that can be silenced.

Patent Document 1: Patent No. 3279834

Disclosure of the invention

The present invention solves such conventional problems, and can widen the frequency range of noise that can be silenced, and can silence low frequency noise without changing the size of the shell. Provided is a centrifugal fan capable of adjusting the frequency of noise that can be silenced.

[0010] Therefore, the centrifugal fan according to the present invention is provided with an electric motor in which an impeller is rotatably coupled around an axis of rotation in an outer shell provided with an opening, and a casing having an inlet and surrounding the periphery of the impeller. And a bellmouth-like orifice having an opening in communication with the opening of the shell. And, it is a centrifugal fan that resonates and muffles the noise emitted from the suction port by the resonance space formed by the orifice, and the sound wave of the noise entering the resonance space from the inlet between the end of the orifice and the casing The part of the path to the reflection was made longer.

[0011] Thereby, since the low frequency noise can be muted without increasing the volume of the resonance space, a centrifugal fan can be obtained which can reduce the noise of a desired frequency without enlarging the outer shell. Be In the centrifugal fan according to the present invention, an electric motor in which an impeller is connected rotatably around a rotation shaft in an outer shell provided with an opening, and a casing having a suction port surrounding the periphery of the impeller, And a bellmouth-like orifice having an opening communicating with the opening of the shell. Then, a member for closing the gap between the end of the orifice and the casing is used as a sound absorbing structure material, and a space formed by the orifice is used as a back air layer to form a resonance type sound absorbing structure. It was a blower.

Thus, the resonance type sound absorbing structure can be formed by the member closing the gap and the space formed by the orifice, so that the frequency range of noise that can be muffled can be expanded, and noise that can be muffled can be obtained. You can adjust the frequency.

Brief description of the drawings

FIG. 1A is a side sectional view showing a centrifugal fan according to a first embodiment of the present invention.

FIG. 1B is a partial cross-sectional view showing a centrifugal fan according to Embodiment 1 of the present invention.

[FIG. 2] FIG. 2 is a diagram showing the principle of a Helmholtz resonator.

[FIG. 3A] FIG. 3A is a side cross-sectional view showing the experimental object of the experiment for confirming the muffling effect of the centrifugal fan according to the first embodiment of the present invention.

[FIG. 3B] FIG. 3B is a bottom view showing the experimental object of the experiment for confirming the muffling effect of the centrifugal fan according to Embodiment 1 of the present invention.

[FIG. 4] FIG. 4 is a view showing the muffling effect of the centrifugal fan according to the first embodiment of the present invention.

[FIG. 5] FIG. 5 is a side sectional view showing a centrifugal fan according to a second embodiment of the present invention.

[FIG. 6] FIG. 6 is a side sectional view showing a centrifugal fan according to a third embodiment of the present invention.

[FIG. 7] FIG. 7 is a side sectional view showing a centrifugal fan according to a fourth embodiment of the present invention.

[FIG. 8] FIG. 8 is a side sectional view showing a centrifugal fan according to a fifth embodiment of the present invention.

[FIG. 9] FIG. 9 is a side sectional view showing a centrifugal fan according to a sixth embodiment of the present invention.

[FIG. 10] FIG. 10 is a side sectional view showing a centrifugal fan according to a seventh embodiment of the present invention.

[FIG. 11] FIG. 11 is a side sectional view showing a centrifugal fan according to an eighth embodiment of the present invention.

[FIG. 12] FIG. 12 is a side sectional view showing a centrifugal fan according to a ninth embodiment of the present invention.

[FIG. 13A] FIG. 13A is a side sectional view showing a centrifugal fan according to a tenth embodiment of the present invention.

[FIG. 13B] FIG. 13B is a partial bottom view of the centrifugal fan according to the tenth embodiment of the present invention. is there.

[FIG. 14] FIG. 14 is a side sectional view showing a centrifugal fan according to an eleventh embodiment of the present invention.

[FIG. 15] FIG. 15 is a side sectional view showing a centrifugal fan according to a twelfth embodiment of the present invention.

[FIG. 16] FIG. 16 is a side sectional view showing a centrifugal fan according to a thirteenth embodiment of the present invention.

[FIG. 17A] FIG. 17A is a side sectional view showing a centrifugal fan according to a fourteenth embodiment of the present invention.

[FIG. 17B] FIG. 17B is a partial bottom view of the centrifugal fan according to a fourteenth embodiment of the present invention.

[FIG. 18] FIG. 18 is a side sectional view showing a centrifugal fan according to a fifteenth embodiment of the present invention.

[FIG. 19] FIG. 19 is a side sectional view showing a centrifugal fan according to a sixteenth embodiment of the present invention.

[FIG. 20A] FIG. 20A is a side sectional view showing a centrifugal fan according to a seventeenth embodiment of the present invention.

[FIG. 20B] FIG. 20B is a partial bottom sectional view showing a centrifugal fan according to a seventeenth embodiment of the present invention.

FIG. 21 is a side sectional view showing a centrifugal fan according to an eighteenth embodiment of the present invention.

FIG. 22 is a side sectional view showing a centrifugal fan according to a nineteenth embodiment of the present invention.

[FIG. 23] FIG. 23 is a side sectional view showing a centrifugal fan according to a twentieth embodiment of the present invention.

[FIG. 24] FIG. 24 is a side sectional view showing a centrifugal fan according to a twenty-first embodiment of the present invention.

[FIG. 25] FIG. 25 is a side sectional view showing a centrifugal fan according to a twenty-second embodiment of the present invention.

[FIG. 26A] FIG. 26A is a side sectional view showing a centrifugal fan according to a twenty-third embodiment of the present invention.

[FIG. 26B] FIG. 26B is a partial bottom sectional view showing a centrifugal fan according to a twenty-third embodiment of the present invention.

[FIG. 27] FIG. 27 is a side sectional view showing a centrifugal fan according to a twenty-fourth embodiment of the present invention.

[FIG. 28] FIG. 28 is a side sectional view showing a centrifugal fan according to a twenty-fifth embodiment of the present invention.

[FIG. 29] FIG. 29 is a side sectional view showing a centrifugal fan according to a twenty-sixth embodiment of the present invention.

[FIG. 30] FIG. 30 is a side sectional view showing a centrifugal fan according to Embodiment 27 of the present invention.

[FIG. 31] FIG. 31 is a side sectional view showing a conventional centrifugal fan.

Explanation of sign

1 Centrifugal fan

2 opening Outer shell Rotary shaft Impeller Motor Suction port Side wall Discharge port Casing Discharge port Electrical part Ceiling material No-duct material Opening part Resonant space End part Resonant space End part Wall body Inlet area Inlet area area Throat area Cavity Part Test object Circular pipe Sound receiving side Circular pipe 32 Transmission loss per frequency without walls

33 Transmission loss per frequency with walls

34 End face of wall

35 Screw holder

36 screw

37 screws

38 inner wall

39 Outer wall

40 double pipes

41 bulkhead

42 Outer space

43 Motor side outer wall

44 Space behind

c sound speed

D Inner diameter of wall

Inner diameter of Di inlet

F frequency

h gap

i gap size

L throat length

La axial depth length

Lr radial depth length

S throat area

TL transmission loss

V cavity volume

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to an electric motor in which an impeller is connected rotatably around a rotation axis in an outer shell provided with an opening, a casing having a suction port surrounding the periphery of the impeller, and communication with the outer opening. And a bellmouth shaped orifice having an opening. The centrifugal fan resonates and muffles the noise emitted from the suction port by the resonance space formed by the orifice, and the sound waves of the noise entering the resonance space from the inlet between the end of the orifice and the casing are reflected It is a centrifugal fan that is designed to lengthen part of the route to the end. As the low frequency noise can be muted without increasing the volume of the resonance space, the noise of the desired frequency can be reduced without increasing the outer diameter. It is a centrifugal fan whose mouth is bellmouth-like. The flow of air into the casing can be smoothed, and the blowing efficiency can be improved and noise can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan having a scroll-shaped casing. The dynamic pressure of the air flowing out of the impeller is efficiently converted to static pressure and the discharge port force can be discharged S, so that the blowing efficiency can be improved and the noise can be reduced without enlarging the outer shell.

Furthermore, the present invention is a centrifugal fan in which the opening of the orifice is concentric with the suction port of the casing. The noise from the suction port of the casing can be smoothly guided to the entire resonance space, and the suction air can be smoothly guided to the casing, so noise of a desired frequency can be reduced without enlarging the outer shell. .

Further, the present invention is a centrifugal fan according to the present invention, wherein the opening of the orifice has a diameter equal to or less than the diameter of the suction port. Since noise from the suction port of the casing can be efficiently introduced to the resonance space, noise of a desired frequency can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan in which the path until some of the sound waves of noise incident from the entrance of the resonance space is reflected at the deepest part of the resonance space is lengthened. As the lower frequency noise can be muted without increasing the volume of the resonance space, noise of a desired frequency can be reduced without increasing the outer diameter.

Further, the present invention is a centrifugal fan in which a wall is provided in a resonance space, and a part of a path until a sound wave of noise is reflected is lengthened. The sound wave of noise can propagate around the wall and the path until part of the sound wave of noise is reflected can be lengthened, and the low frequency noise can be silenced without increasing the volume of the resonance space. be able to. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

Further, according to the present invention, the wall provided in the resonance space is concentric with the inlet and one end of the wall is concentric with the suction port. It is a centrifugal fan which is a cylindrical tube in contact with the The sound wave of the noise emitted from the suction port travels around the wall only once in U-curve, and the sound wave of noise can be smoothly transmitted to the deepest part of the path where the sound wave of noise is reflected. Lower frequency noise can be silenced without increasing the volume. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

In addition, according to the present invention, the inner diameter D of the cylindrical tubular wall concentric with the suction port provided in the resonance space D

The centrifugal blower has a relationship of D> Di + 2i between the inner diameter Di of the suction port and the gap size i of the inlet. The distance between the inlet and the wall can be sufficiently separated, and part of the sound waves of noise coming into the resonance space is reflected by the wall near the inlet and the amount of sound waves of noise entering the inside of the resonance space is reduced. Can be suppressed. Therefore, lower frequency noise can be silenced without reducing the amount of sound waves to be resonantly silenced.

The present invention also relates to the inner diameter D of a cylindrical tubular wall concentric with the suction port provided in the resonance space.

The centrifugal fan has a relationship of D <Di + 2i between the inner diameter Di of the suction port and the gap size i of the inlet. The area of the inlet region surrounded by the cylindrical tubular wall and the orifice corresponding to the throat area of the Helmholtz resonator can be reduced, and the cylindrical tubular wall of the cavity space corresponding to the cavity volume. The back volume can be increased. Therefore, the low frequency noise can be silenced by the function of the Helmholtz resonator.

Further, according to the present invention, the cylindrical tubular wall concentric with the suction port provided in the resonance space, the end force S of the orifice, and the thickness of the end of the orifice and the wall so as to overlap in the radial direction Centrifugal blower. The radial depth of the inlet region, which is surrounded by the upper end of the cylindrical tubular wall and the end of the orifice, which corresponds to the throat length of the Helmholtz resonator, can be increased. Therefore, the low frequency noise can be silenced by the work of the Helmholtz resonator.

The present invention is also a centrifugal fan in which the inner diameter D of the cylindrical tubular wall is not uniform in the circumferential direction. There is a part where the length of the path until the sound wave of the noise emitted from the suction port is reflected is different. Therefore, sound waves of noises of a plurality of frequencies can be resonantly muffled in the resonance space, and a plurality of low frequency noises can be muffled without increasing the volume of the resonance space, and a desired frequency can be obtained without enlarging the outline. Noise can be reduced. [0027] The present invention is also a centrifugal fan in which the height of the cylindrical tubular wall is not uniform in the circumferential direction. At the upper end of the cylindrical tubular wall and at the end of the orifice corresponding to the throat length of the Helmholtz resonator, the length of the path until the sound wave of the noise emitted from the inlet reflects is different. There is a part where the axial depth of the enclosed entrance area is different. As a result, sound waves of noises of plural frequencies can be resonantly muffled in the resonance space, and plural low frequency noises can be muffled without increasing the volume of the resonance space, and a desired outer diameter can be obtained. Frequency noise can be reduced.

Furthermore, the present invention is a centrifugal fan having a gap size i of the inlet to the resonance space not uniform in the circumferential direction. The axial depth length of the inlet region surrounded by the upper end of the cylindrical tubular wall and the end of the orifice, which corresponds to the throat length of the Helmholtz resonator, is circumferentially different. For this reason, sound waves of noise of a plurality of frequencies are resonated and silenced by the function of the Helmholtz resonator in the resonance space.

Further, the present invention is a centrifugal fan capable of adjusting the inner diameter D of a cylindrical tubular wall concentric with the suction port provided in the resonance space. Even if the frequency of the suction noise is changed due to the installation condition of the centrifugal fan, etc., the noise reduction frequency can be adjusted by changing the inner diameter D of the cylindrical tubular wall, and the resonance space can be adjusted. Lower frequency noise can be silenced without increasing the volume. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan capable of adjusting the height of a cylindrical tubular wall concentric with an inlet provided in a resonance space. Even if the frequency of the noise radiated from the suction port changes due to the operating condition of the centrifugal fan, etc., the frequency of noise can be adjusted by changing the height of the cylindrical tubular wall, and the volume of the resonance space can be reduced. Low frequency noise can be silenced without increasing the size. Therefore, it is possible to reduce the noise of the desired frequency S without enlarging the shell.

Further, according to the present invention, at least one cylindrical tubular wall concentric with the suction port of the casing and having one end contacting the casing and at least one cylindrical tubular body concentric with the suction port of the casing and one end contacting the orifice The walls are alternately arranged in the radial direction. The sound waves of noise can form a labyrinth structure that propagates alternately around the wall and propagates. The path to reflection of part of the sound wave can be made longer, and the power of the low frequency noise can be suppressed without increasing the volume of the resonance space. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

Further, the present invention is a centrifugal fan in which a cylindrical tubular wall concentric with a suction port provided in a resonance space is integrally molded with a casing. The suction port, the cylindrical tubular wall concentric with the wall, and the casing can be made as one part. Therefore, the number of parts can be reduced, the manufacturing cost can be reduced, and noise of a desired frequency can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan provided with a partition that divides a resonance space into a plurality of parts. Since the sound waves of the noise emitted from the suction port are resonantly muffled in the resonant volume of multiple volumes, multiple low frequency noises can be silenced without increasing the volume of the resonant space. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

The present invention is also a centrifugal fan in which wall bodies of different shapes are provided in each of a plurality of resonance spaces, and a part of the path until sound waves of noise are reflected in each of the resonance spaces is elongated. It is possible to lengthen part of the propagation path of the sound wave of the noise in the resonance space of multiple volumes, and to reduce the noise of a plurality of lower frequencies without increasing the volume of the resonance space. Therefore, it is possible to reduce the noise of the desired frequency without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan having different clearance sizes i at the inlets of the plurality of resonance spaces. It is possible to set the length of the inlet region surrounded by the cylindrical tubular wall and the end of the orifice corresponding to the throat length of the Helmholtz resonator in a plurality of resonance spaces, thereby increasing the volume of the resonance space. Instead, multiple lower frequency noises can be silenced by the action of Helmholtz resonators. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan in which an outer peripheral space surrounded by a side wall and an outer shell of a casing is used as a resonance space. The volume of the resonance space can be increased, the path from the inlet to the deepest part can be lengthened, and lower frequency noise can be silenced. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

The present invention also provides a resonance space in the back space between the motor side outer wall of the casing and the outer shell. It is a centrifugal fan designed to be used as The volume of the resonance space can be increased, the path from the inlet to the deepest part can be lengthened, and lower frequency noise can be silenced. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

Further, according to the present invention, there is provided an electric motor in which an impeller is connected in a rotatable manner about an axis of rotation in an outer shell provided with an opening, a casing having a suction port surrounding the periphery of the impeller, and an outer shell A member having a bellmouth-like orifice having an opening communicating with the opening, the member closing the gap between the end of the orifice and the casing serving as a sound absorbing structural material, and the space formed by the orifice behind the air It is a centrifugal fan characterized by forming a resonance type sound absorbing structure as a layer. It is possible to form a resonance type sound absorbing structure S by a member closing the gap and a space formed by the orifice. Therefore, the range of noise frequencies that can be silenced can be expanded.

Yes

Furthermore, the present invention is a centrifugal fan in which the suction port of the casing has a bell mouth shape.

The flow of air into the casing can be smoothed, and the blowing efficiency can be improved and noise can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan in which the casing has a scroll shape. The dynamic pressure of the air flowing out of the impeller is efficiently converted to static pressure, and the discharge port force can be discharged. Therefore, the blowing efficiency can be improved and the noise can be reduced without enlarging the outer shell.

Furthermore, the present invention is a centrifugal fan in which the opening of the orifice is concentric with the suction port of the casing. Noise from the suction port of the casing can be smoothly led to the entire resonance space, and suction air can be smoothly led to the casing. Therefore, noise of a desired frequency can be reduced without enlarging the shell.

Furthermore, the present invention is a centrifugal fan having an orifice opening diameter equal to or less than the diameter of the suction port. Noise from the suction port of the casing can be efficiently led to the resonance space. Therefore, noise of a desired frequency can be reduced without increasing the size of the shell.

Furthermore, the present invention is a centrifugal fan using a film-like material as a member closing a gap. A membrane-like sound absorbing structure of a resonance type sound absorbing structure can be formed by forming a vibrating system in which the membrane-like material forms a mass and the space as the back air layer becomes a panel. Therefore, the range of noise frequencies that can be silenced can be expanded. Further, the present invention is a centrifugal fan, wherein a member closing the gap is a perforated plate. A type of perforated plate sound absorption structure of a resonance type sound absorbing structure in which sound is absorbed by the same principle as a Helmholtz resonator by forming a vibration system in which the air in the hole part of the holed plate becomes a mass and the back air layer becomes a panel. Can be formed. Therefore, the force S can be expanded by expanding the range of noise frequencies that can be silenced.

Further, the present invention is a centrifugal fan using a porous material as a member closing the gap. A relatively high frequency noise can be absorbed by the porous material itself, and the porous material forms a vibration system in which the mass and the back air layer form a panel, forming a kind of porous sound absorbing structure of a resonance type sound absorbing structure. can do. Therefore, relatively low frequency noise can be silenced, and the range of noise frequencies that can be silenced can be expanded.

Further, the present invention is a centrifugal fan characterized in that a wall is provided in a space, and the thickness of the back air layer is increased. The length of the path along which sound waves of noise travel around the wall in the space can be regarded as the thickness of the back air layer in the resonant sound absorbing structure. As a result, the thickness of the back air layer can be increased, and low-frequency noise can be silenced without changing the size of the shell.

Furthermore, the present invention is the centrifugal fan, wherein the wall provided in the space is a cylindrical tube that is concentric with the suction port and one end is in contact with the casing. The sound wave of noise travels around the wall in the space. The path is U-curve only once, and the sound wave of noise can be propagated smoothly. Therefore, the thickness of the back air layer can be more stably increased, and low frequency noise can be silenced without changing the size of the outer shell by the wall of a simple structure.

The present invention is also a centrifugal fan in which the inner diameter D of the cylindrical tubular wall concentric with the suction port provided in the space is not uniform in the circumferential direction. By partially differing the inner diameter D of the cylindrical tubular wall, there may be portions where the thickness of the back air layer differs. As a result, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded.

Furthermore, the present invention is a centrifugal fan in which the height of the cylindrical tubular wall concentric with the suction port provided in the space is not uniform in the circumferential direction. The partially different heights of the cylindrical tubular wall result in portions with different thicknesses of the back air layer. Therefore, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded. Further, the present invention is a centrifugal fan capable of adjusting the inner diameter of a cylindrical tubular wall concentric with a suction port provided in a space. The thickness of the back air layer can be adjusted by adjusting the inner diameter of the cylindrical tubular wall. Therefore, the frequency of noise that can be muffled can be adjusted.

Furthermore, the present invention is a centrifugal fan in which the height of the cylindrical tubular wall concentric with the suction port provided in the space can be adjusted. The thickness of the back air layer can be adjusted by adjusting the height of the cylindrical tubular wall. Therefore, the frequency of noise that can be muffled can be adjusted.

Further, according to the present invention, at least one cylindrical tubular wall concentric with the suction port of the casing and having one end in contact with the casing and at least one cylindrical tubular body concentric with the suction port with the casing and one end being in contact with the orifice The walls are alternately arranged in the radial direction. The sound wave of noise in the space can be made into a labyrinth structure in which sound waves of the noise circulate around the wall and propagate alternately, so that the thickness of the back air layer can be made thicker, and without changing the size of the outer shell Noise can be silenced.

Furthermore, the present invention is a centrifugal fan provided with a partition that divides a space formed by an orifice into a plurality of parts. It is possible to form a plurality of resonant sound absorbing structures having different shapes and volumes of space. Therefore, noises of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be broadened.

Further, the present invention is a centrifugal fan including a member for closing the gap in each of a plurality of spaces divided by the partition wall, and at least two types of members being applied. Several types of resonant sound absorbing structures can be formed. Therefore, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded.

Further, the present invention is a centrifugal fan in which wall bodies of different shapes are provided in each of a plurality of spaces divided by partition walls, and the thickness of the back air layer is increased in each space. Each of the divided spaces can form a resonant sound absorbing structure with a different thickness of the back air layer. Therefore, it is possible to muffle noises of multiple frequencies and to expand the range of noise frequencies that can be muffled by the force S.

Further, the present invention is a centrifugal fan in which an outer peripheral space surrounded by a side wall and an outer shell of a casing is used as a back air layer. The space S can be used as an air layer behind the resonant sound absorbing structure. Therefore, the thickness of the back air layer can be made thicker, Low frequency noise can be silenced without changing the size of the shell.

Further, the present invention is a centrifugal fan in which the rear side space between the motor side outer wall and the outer shell of the casing is used as a rear air layer. The back side space can be used as the back air layer of the resonance type sound absorbing structure. Therefore, the thickness of the back air layer can be increased, and low frequency noise can be silenced without changing the size of the outer shell.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1

As shown in Fig. 1A and IB, a centrifugal fan 1 used as a ceiling-embedded ventilation fan has an inner size of 265 mm square and a height of 195 mm and an outer shell 3 with an opening 2 on the lower surface, centering on a rotation shaft 4 A motor 6 connected with a multi-blade impeller 5 with a diameter of 180 mm so as to be pivotable, and the periphery of the impeller 5 and a bell mouth on the lower surface, an inlet 7 with an inner diameter Di of 150 mm, and a side wall 8 And a casing 10 having a discharge port 9. The side wall 8 of the casing 10 has a scroll shape in which the air path gradually expands toward the discharge port 9, and the discharge port 9 of the casing 10 is a discharge adapter 12 through a discharge opening 11 provided on one side surface of the outer shell 3. It is in communication with In a part between the casing 10 and the outer shell 3, an electric part 13 for housing electric parts such as a connection connector and a terminal for electrically connecting the motor 6 and an external power supply is disposed. There is a flange portion 14 on the outer periphery of the lower surface of the outer shell 3 and the outer shell 3 is fixed to the ceiling material 15 with screws etc through the holes 16 provided in the flange portion 14. It is joined to the discharge port 9 via the discharge adapter 12.

The inner diameter of the casing 10 is equal to or less than that of the suction port 7 concentric with the suction port 7.

Orifice 19 having a bellmouth-like opening 18 of 148 mm is disposed so as to close the opening 2 of the shell 3 with a predetermined gap h (60 mm) from the suction port 7 of the casing 10. A resonance space 20 is formed between it and the orifice 19. The end 21 of the orifice 19 is at a position separated from the lower surface of the casing 10 by a gap size i (20 mm). Further, a cylindrical tubular wall 22 concentric with the suction port 7 of the casing 10 is integrally provided on the lower surface of the casing 10, and the cylindrical tubular wall 22 is 2 mm thick and 28 mm high. The inner diameter D of the wall is 216 mm, and between the inner diameter Di (150 mm) of the inlet of the casing 10 and the gap dimension i (20 mm) between the end 21 of the orifice 19 and the casing, D> Di + It is a 2i relationship.

In the above configuration, when the impeller 5 is rotated by the motor 6, the suctioned air passes from the opening 2 through the opening 18 of the orifice 19, and is smoothly slipped from the bellmouth inlet 7 of the casing 10 to the impeller 5. Entered and boosted by impeller 5. Then, the dynamic pressure is efficiently converted into static pressure through the interior of the scroll-shaped casing 10, and is discharged from the discharge adapter 12 to the duct 17 and discharged to the outside. The diameter of the opening 18 of the orifice 19 is equal to or smaller than the inner diameter D of the suction port of the casing 10, and has a sufficiently wide area, and has a bell mouth shape for smoothly introducing suction air. Therefore, the aerodynamic performance of the centrifugal fan 1 is not reduced due to the pressure loss.

Also, at the same time, rotational noise generated when the pressure is raised by the impeller 5, turbulent noise due to vortices generated when passing through the inside of the casing 10, and noise amplified by resonance in the casing 10 Sound is emitted downward from the suction port 7. The part of the sound wave of the noise emitted from the suction port 7 of the casing 10 is transmitted from the inlet 23 formed between the end 21 of the orifice 19 and the casing 10 to the resonance space 20 while It will be incident. The suction port 7 of the casing 10 and the resonance space 20 communicate with each other through an inlet 23. At this time, the opening 18 of the orifice 19 is concentric with the inlet 7 of the casing 10, and the diameter of the opening 18 of the orifice 19 is equal to or less than the inner diameter Di of the inlet of the casing 10. Therefore, a part of the sound wave of the noise emitted from the suction port 7 of the casing 10 has a configuration that is easy to enter the resonance space 20 from the inlet 23 formed between the end 21 of the orifice 19 and the casing 10 It has become.

Among the sound waves of the noise that entered the resonance space 20 from the inlet 23, a part of the sound waves of the frequency specified by the volume and shape of the resonance space 20 has air column resonance in the resonance space 20. The entrance region 24 surrounded by the cylindrical tubular wall 22 and the orifice 19 and the volume 25 in the resonance space 20 behind the cylindrical tubular wall 22 function as a Helmholtz resonator, etc. , Resonance silenced.

The frequency of noise to be muffled by air column resonance depends on the length of the path to the structure (in this case, the casing 10 and the outer shell 3) to which the sound wave incident from the inlet 23 is reflected. The length of the path is longer, the lower the frequency. Further, the frequency F to be muffled by the function of the Helmholtz resonator is expressed by FIG. 2 and the following equation (1). In equation (1), c is the velocity of sound, S is the throat area, L is the throat length, and V is the cavity volume.

[0066] [Number 1]

In the case of the centrifugal blower 1 having the configuration of the first embodiment, the inlet region 24 surrounded by the cylindrical tubular wall 22 and the orifice 19 in FIG. 1A and IB corresponds to the throat 26 in FIG. Similarly, the volume 25 of the resonance space 20 behind the cylindrical tubular wall 22 corresponds to the cavity 27.

At this time, the presence of the cylindrical tubular wall 22 in the resonance space 20 causes sound waves of noise to propagate around the wall 22 and propagate, until the sound waves of noise entering the resonance space 20 are reflected. It is possible to lengthen part of the route. Therefore, the frequency of the noise to be resonantly silenced can be lowered. Further, in the structure (in this case, the casing 10 and the outer shell 3) to which the sound wave incident from the inlet 23 is reflected, the path to the deepest part where the sound wave path from the inlet 23 is longest is made longer. Because of this, lower frequency noise can be resonantly silenced.

[0069] Lengthening a part of the path to reflection of the sound wave of noise incident on the resonance space 20 means that part of the sound wave goes around the wall 22 by providing the wall 22 as in this example. Therefore, part of the path until the sound wave is reflected may be made longer as compared with the case where the wall 22 is not provided. For example, as an example of a case in which a part of the sound wave is turned around, a structure as a means for turning a part of the sound wave may be provided in the resonance space 20.

Further, the wall 22 is a cylindrical tube concentric with the suction port 7 of the casing 10 and has a shape in which one end is in contact with the lower surface of the casing 10, the sound wave force S of the noise radiated from the suction port 7 After entering the resonance space 20 from the inlet 23, the path around the wall 22 is only one U-curve S. Therefore, it is possible to transmit the sound wave of noise smoothly to the deepest part of the path where the sound wave of noise is reflected. As a result, it came from the entrance 23 of the resonance space 20 By lengthening the path until some of the noise sound waves are reflected at the deepest part of the resonance space 20, lower frequency noise can be silenced without increasing the volume of the resonance space. Therefore, a centrifugal fan can be obtained which can reduce noise of a desired frequency without increasing the size of the shell. Here, the innermost part means the innermost part of the resonance space 20, that is, the farthest position, as viewed from the entrance 23 of the resonance space 20.

In addition, since the relationship between the inner diameter Di of the inlet and the gap size i of the inlet 23 is D〉 Di + 2i, the distance between the inlet 23 and the wall 22 should be sufficiently large. it can. As a result, a part of the sound waves of noise intended to enter the resonance space 20 is reflected by the wall 22 in the vicinity of the inlet 23 and the amount of sound waves of noise entering the resonance space 20 is suppressed from decreasing. It is possible to suppress a decrease in the amount of sound waves to be muffled.

As described above, since low frequency noise can be muted without increasing the volume of the resonance space 20, noise of a desired frequency can be reduced without increasing the size of the outer shell 3.

Yes

Further, since the wall body 22 and the casing 10 can be made into one part, the number of parts can be reduced and the manufacturing cost can be reduced.

FIGS. 3A, 3 B and FIG. 4 show an outline and a graph of the experimental object 28 when the muffling in the resonance space 20 is experimentally confirmed. In this experiment, for the purpose of efficiency, the size of the test object 28 corresponding to the centrifugal fan 1 is 1⁄4 of that of the centrifugal fan 1 and the casing 10 is cylindrically tubular for simplification. The distance h between the casing 10 and the orifice 19 corresponds to 60 mm in the centrifugal fan 1, the gap size i of the inlet 23 corresponds to 20 mm, the inside diameter D of the cylindrical tubular wall 22 corresponds to 216 mm, Is equivalent to 28 mm.

The sound wave emitted from the circular pipe 30 corresponding to the suction port 7 of the casing 10 is the receiving side circular pipe

The amount transmitted to 31 was measured, and the amount of resonant noise cancellation in the resonance space 20, that is, the transmission loss TL was measured.

The horizontal axis of the graph in FIG. 4 is the frequency F of the sound wave, and the vertical axis is the transmission loss TL, which is a noise reduction effect. The dotted line in the graph of FIG. 4 indicates the transmission loss 32 for each frequency when there is no wall, and the solid line indicates the transmission loss 33 for each frequency when there is a wall. It is confirmed that the frequency F at which the power transmission loss TL is maximum is decreasing. The

The cylindrical tubular wall 22 can lengthen part of the sound wave path of noise incident on the resonance space 20 and bends the path in a U shape on the cross section passing through the rotation axis 4. The shape should be good. Therefore, the same effect can be obtained even if the shape is a polygonal tube or an elliptical tube, or even if the center of the tube 10 and the inlet 7 of the casing 10 are offset.

In this configuration, the resonance space 20 formed by the orifice 19 is a product on which the force orifice 19 formed by being surrounded by the orifice 19, the casing 10 and the shell 3 and the centrifugal blower 1 are mounted. The resonance space 20 may be surrounded by other structures such as a filter, a heater, an electrical component or a case of the electrical component, or the like. The air column resonance occurs in the resonance space 20, the inlet region 24 surrounded by the cylindrical tubular wall 22 and the orifice 19, and the volume 25 in the resonance space 20 behind the cylindrical tubular wall 22 is Helmholtz. The same effect can be obtained as long as the structure is resonantly silenced by acting as a resonator.

Furthermore, the centrifugal blower 1 achieves the same effect even when mounted on a wall instead of a ceiling.

Second Embodiment

Next, a second embodiment of the present invention will be described. The description of the same parts as those of the first embodiment of the present invention will be omitted, and only the parts unique to the second embodiment will be described.

In the second embodiment, as shown in FIG. 5, the inner diameter D of the cylindrical tubular wall concentric with the suction port 7 provided in the resonance space 20 is 160 mm, and the inner diameter Di (150 mm) of the suction port 7 and the inlet There is a relationship of D · Di + 2i with the gap dimension i (20 mm) of the part 23.

According to this configuration, the area of the inlet region 24 surrounded by the cylindrical tubular wall 22 and the orifice 19 corresponding to the throat area S of the Helmholtz resonator can be reduced. Further, in the resonance space 20 corresponding to the cavity volume V, a force S can be made to increase the volume behind the cylindrical tubular wall 22. Therefore, by the function of the Helmholtz resonator, it is possible to cancel the lower frequency noise with the force S.

Third Embodiment

Next, a third embodiment of the present invention will be described. The description of the same parts as those in the first embodiment of the present invention will be omitted, and only the parts unique to the third embodiment will be described. In the third embodiment, as shown in FIG. 6, a cylindrical tubular wall 22 concentric with the suction port 7 provided in the resonance space 20 has a thickness of 20 mm and a face with an end face 34 of the wall and a 5 mm clearance. The end 21 of the orifice 19 is disposed so that the area between the end face 34 of the wall and the end 21 of the orifice 19 constitutes an inlet area 24 !.

According to this configuration, the radial depth Lr of the inlet portion area 24 surrounded by the end face 34 of the cylindrical tubular wall and the end 21 of the orifice 19 corresponding to the throat length L of the Helmholtz resonator. Can be made longer. Therefore, the low frequency noise can be silenced by the work of the Helmholtz resonator.

If the end 21 of the orifice 19 and the end face 34 of the wall are longer in the radial direction, the same effect can be obtained even if only the end face is thicker.

Embodiment 4

A fourth embodiment of the present invention will next be described. Descriptions of parts similar to those in Embodiment 1 of the present invention will be omitted, and only parts unique to Embodiment 4 will be described.

In the fourth embodiment, as shown in FIG. 7, the inner diameter D of the cylindrical tubular body is configured to be 216 mm in part and 160 mm in part, which is not uniform in the circumferential direction.

[0089] According to this configuration, by partially differing the inner diameter D of the cylindrical tubular wall, there are portions where the suction port 7 force, and the length of the path until the sound wave of the emitted noise is reflected, differ. Therefore, sound waves of noises of multiple frequencies can be resonantly silenced in the resonance space 20.

Fifth Embodiment

A fifth embodiment of the present invention will next be described. The description of the same parts as those of the first embodiment of the present invention will be omitted, and only the parts unique to the fifth embodiment will be described.

In the fifth embodiment, as shown in FIG. 8, the height of the cylindrical tubular wall 22 is 28 mm in part, 40 mm in part, and is uniform in the circumferential direction! / I see.

According to this configuration, the partially different heights of the cylindrical tubular wall 22 result in portions having different lengths of paths until sound waves of noise emitted from the suction port 7 are reflected. In addition, there are portions where the axial depth length La of the inlet portion area 24 surrounded by the cylindrical tubular wall 22 and the orifice 19 corresponds to the throat length L of the Helmholtz resonator. Therefore, sound waves of noise of a plurality of frequencies can be resonantly silenced in the resonance space 20. Embodiment 6

A sixth embodiment of the present invention will now be described. The description of the same parts as those in the first embodiment of the present invention will be omitted, and only the parts unique to the sixth embodiment will be described.

In the sixth embodiment, as shown in FIG. 9, the gap dimension i of the inlet 23 to the resonance space 20 is a centrifugal fan which is 20 mm in part, 14 mm in part, and is not uniform in the circumferential direction. .

According to this configuration, the axial depth length La of the inlet portion region 24 surrounded by the cylindrical tubular wall 22 and the orifice 19 corresponding to the throat length L of the Helmholtz resonator is different in the circumferential direction. Therefore, the sound waves of noises of a plurality of frequencies in the resonance space 20 can be resonated and muffled by the action of the Helmholtz speaker.

Embodiment 7

A seventh embodiment of the present invention will now be described. The description of the same parts as those of the first embodiment of the present invention will be omitted, and only the parts unique to the seventh embodiment will be described.

In Embodiment 7, as shown in FIG. 10, screw receptacle 35 is provided on the lower surface of casing 10.

A cylindrical tubular wall 22 provided with screw holes 36 is fixed by means of a screw 37 and is adapted to be removable, and is configured to be able to be fitted with a cylindrical tubular wall 22 of different inner diameter D.

With this configuration, even if the frequency of the noise radiated from the suction port 7 changes due to the installation state of the centrifugal fan 1, etc., the muffling frequency is adjusted by changing the inner diameter D of the cylindrical tubular wall 22. can do.

Embodiment 8

An eighth embodiment of the present invention will now be described. The description of the same parts as those in the first embodiment of the present invention will be omitted, and only the parts unique to the eighth embodiment will be described.

[0100] In the eighth embodiment, as shown in FIG. 11, a cylindrical tubular wall body 22 concentric with the suction port 7 provided in the resonance space 20 is a double pipe constituted of an inner wall 38 and an outer wall 39. The height of the wall 22 is adjustable by sliding the outer wall 39

[0101] With this configuration, even if the frequency of the noise radiated from the suction port 7 changes due to the operating condition of the centrifugal fan 1, etc., noise can be muted by changing the height of the cylindrical tubular wall 22. Frequency can be adjusted.

Embodiment 9

A ninth embodiment of the present invention will now be described. The description of the same parts as those of the first embodiment of the present invention will be omitted, and only the parts unique to the ninth embodiment will be described.

In the ninth embodiment, as shown in FIG. 12, a cylindrical tubular wall 22 concentric with the suction port 7 of the casing 10 and in contact with the casing 10 at one end has an inner diameter D of 180 mm and 240 mm. And a cylindrical tubular wall 22 concentric with the suction port 7 of the casing 10 and having an inner diameter D of 216 mm, one end of which is in contact with the orifice 19, arranged in the resonance space 20 It has become.

According to this configuration, a labyrinth structure in which sound waves of noise wrap around wall 22 alternately and propagate inside resonance space 20 can be obtained, and a path until part of the sound waves of noise is reflected can be obtained. You can do it longer. Therefore, low frequency noise can be silenced without increasing the volume of the resonance space 20.

Tenth Embodiment

A tenth embodiment of the present invention will now be described. The description of the same parts as those in the first embodiment of the present invention will be omitted, and only the parts unique to the tenth embodiment will be described.

In the tenth embodiment, as shown in FIGS. 13A and 13B, partition walls 41 for dividing the resonance space 20 into two with different volumes are provided on a plane passing through the rotation axis 4 and each resonance space 2 One end force S of a different height to 0, a cylindrical tubular wall 22 concentric with the suction port 7 in contact with the casing 10 is provided!

According to this configuration, the sound waves of the noise emitted from the suction port 7 are resonantly muffled in the resonance space 20 of different volumes, and one of the paths through which the sound waves of the noise propagate in the divided resonance space 20. You can lengthen the department. Therefore, a plurality of lower frequency noises can be silenced without increasing the volume of the resonance space 20.

Embodiment 11

An eleventh embodiment of the present invention will now be described. Descriptions of parts similar to those in Embodiment 1 of the present invention will be omitted, and only parts unique to Embodiment 11 will be described.

In the eleventh embodiment, as shown in FIG. 14, a resonance space divided into two by a partition wall 41 is provided. 20 Each of the inlets 23 has a gap size i of 20 mm on one side and 14 mm on the other side.

The gap size i of 3 is configured differently.

According to this configuration, the throat length of the Helmholtz resonator in each of the two resonance spaces 20 is obtained.

The length of the inlet region 24 surrounded by the cylindrical tubular wall 22 and the orifice 19 corresponding to L can be set. Therefore, a plurality of lower frequency noises that do not increase the volume of the resonance space 20 can be muffled by the work of the Helmholtz resonator.

Embodiment 12

A twelfth embodiment of the present invention will now be described. The description of the same parts as those in the first embodiment of the present invention will be omitted, and only the parts unique to the twelfth embodiment will be described.

In the twelfth embodiment, as shown in FIG. 15, an outer peripheral space 42 surrounded by the side wall 8 and the outer shell 3 of the casing 10 is a resonant space constituted by the orifice 19, the casing 10 and the outer shell 3. Becomes in communication with 20!

According to this configuration, the outer peripheral space 42 can be used as the resonance space 20. As a result, the volume of the resonance space 20 can be increased, and the path from the inlet 23 to the deepest part can be lengthened, and noises of lower frequencies can be silenced.

Embodiment 13

A thirteenth embodiment of the present invention will now be described. The description of the same parts as the first embodiment of the present invention will be omitted, and only the parts unique to the thirteenth embodiment will be described.

According to the thirteenth embodiment, as shown in FIG.

In the centrifugal fan 1 having a configuration projecting from 0, the rear space 44 between the motor side outer wall 43 of the casing 10 and the outer shell 3 communicates with the outer peripheral space 42 surrounded by the side wall 8 and outer shell 3 of the casing 10 The outer peripheral space 42 is in communication with the resonant space 20 which is constituted by the orifice 19, the casing 10 and the outer shell 3! /.

With this configuration, the back space 44 and the outer space 42 can be used as the resonance space 20. As a result, the volume of the resonance space 20 can be increased, and the path from the inlet 23 to the deepest part can be lengthened, so that low frequency noise can be silenced.

Embodiment 14

A fourteenth embodiment of the present invention will now be described. In the same parts as the first embodiment of the present invention The description will be omitted, and only the parts unique to the fourteenth embodiment will be described.

In Embodiment 14, as shown in FIGS. 17A and 17B, a centrifugal fan 1 used as a ceiling-embedded ventilation fan has an inner size of 265 mm square, a height of 195 mm, and an outer shell provided with an opening 2 on the lower surface. An electric motor 6 in which a multi-bladed impeller 5 of 180 mm in diameter is connected rotatably in a rotation shaft 4 in 3 and an impeller 5 is surrounded, and a bellmouth is formed on the lower surface and the inner diameter of the suction port Di There is a casing 10 with a 15 O mm inlet 7 and an outlet 9 on the side wall 8! /. The side wall 8 of the casing 10 has a scroll shape in which the air path gradually expands toward the discharge port 9, and the discharge port 9 of the casing 10 has a discharge adapter 11 through a discharge opening 11 provided on one side surface of the outer shell 3. It communicates with 12. In a part between the casing 10 and the outer shell 3, an electric part 13 for housing electric parts such as a connection connector and a terminal for electrically connecting the motor 6 and the external power supply is disposed. There is a flange portion 14 on the outer periphery of the lower surface of the outer shell 3 and the outer shell 3 is fixed to the ceiling material 15 with a screw or the like through a hole 16 provided in the flange portion 14. It is joined to the discharge port 9 via the discharge adapter 12.

Further, the inner diameter of the suction port 7 of the casing 10 is equal to or less than that of the suction port 7 in a concentric manner.

Orifice 19 with a 148 mm bell-mouth shaped opening 18 separated from the suction port 7 of the casing 10 by 60 mm so as to close the opening 2 of the shell 3 and surrounded by the casing 10, the orifice 19 and the shell 3 Space 70 is formed. Further, the end 21 of the orifice 19 is located 20 mm away from the lower surface of the casing 10 to form a gap 72, and the bluish sheet 73 is a film-like material 73 as a member for closing the gap 72 so as to close the gap 72. Is provided. A vinyl sheet, which is a film-like material 73 as a sound-absorbing structure material that is a member for closing the gap 72, is a mass, and a space 70 is an air layer 74 behind the film-like material 73 to form a vibration system that is a panel. Thereby, a kind of film-like sound absorbing structure of the resonance type sound absorbing structure is formed.

A space 72 is provided between the suction port 7 of the casing 10 and the space 70, and the force at which the suction port 7 of the casing 10 and the space 70 are in communication is a gap in the communicating space 72. A boule sheet, which is a film-like material 73, is provided to block the part 72, the suction port 7 and the space 70 are cut off, and the space 70 becomes an air layer 74 behind the film-like material 73.

In the above-described configuration, when the impeller 5 is rotated by the motor 6, the suction air is an opening of the main body.

A bellmouth-like inlet 7 of casing 10 is passed from 2 through orifice 19 of orifice 19. It enters the smoother impeller 5, is pressurized by the impeller 5, passes through the interior of the scroll-shaped casing 10, the dynamic pressure is efficiently converted to static pressure, discharged from the discharge adapter 12 into the duct 17, and discharged outdoors. . Although the diameter of the opening 18 of the orifice 19 is equal to or less than the inner diameter Di of the suction port of the casing 10, it has a sufficiently large area and has a bell mouth shape for smoothly introducing suction air. Because of this, it is impossible to reduce the aerodynamic performance of the centrifugal fan 1 which causes pressure loss.

At the same time, rotational noise generated when the pressure is raised by the impeller 5, turbulent noise due to vortices generated when passing through the inside of the casing 10, and noise amplified by resonance in the casing 10. Sound waves are emitted downward from the suction port 7. A portion of the sound wave of the noise emitted from the suction port 7 of the casing 10, while being forced, is a membrane-like material installed in the gap portion 72 formed between the end 21 of the orifice 19 and the casing 10. Material It strikes the boule sheet which is 73. At this time, the opening 18 of the orifice 19 is concentric with the suction port 7 of the casing 10, and the diameter of the opening 18 of the orifice 19 is equal to or less than the inner diameter D of the suction port of the casing 10. Therefore, a part of the sound wave of the noise radiated from the suction port 7 of the casing 10 is sent to the film-like material 73 installed in the gap 72 formed between the end 21 of the orifice 19 and the casing 10 It is configured to be easy to enter. At this time, the resonance type is achieved by a space 70 surrounded by the orifice 19, the casing 10 and the outer shell 3, and a bul sheet which is a film-like material 73 for closing the gap 72 between the end 21 of the orifice 19 and the lower surface of the casing 10. A kind of membrane-like sound absorbing structure of sound absorbing structure is formed. Therefore, when the frequency of the sound wave of the noise incident on the boule sheet which is the film-like material 73 matches the resonance frequency of the vibration system of the film-like sound absorbing structure, the boule sheet which is the film-like material 73 vibrates and the inside The friction absorbs the sound waves and can mute some of the noise. Further, the frequency which can be muffled by the function of the film-like sound absorbing structure can be changed by the thickness, surface density and mass of the film-like material 73, the tension for installing the film-like material 73, the thickness of the air layer 74, etc. To expand the range of noise frequencies that can be done by force S.

The same effect as the film-like material 73 can be obtained by using cellophane, an aluminum film, a polyethylene film or the like in addition to the boule sheet.

The space 70 to be the back air layer 74 is a structure to the extent that a resonance type sound absorbing structure is formed. Even if there is a gap or the like that communicates well to the outside if it is surrounded by a circle, the same effect can be obtained as the degree of the effect is inferior.

In this configuration, the space 70 formed by the orifice 19 is formed by the orifice 19, the casing 10 and the shell 3, and the force orifice 19 formed by being enclosed by the shell 3 and the centrifugal fan 1 are other products. It may be a space 70 surrounded by a structure, such as a filter, a heater, an electrical component or a case of an electrical component. When the space 70 becomes an air layer 74 behind the film-like material 73 to form a vibration system to be a panel, a kind of film-like sound absorbing structure of a resonance type sound absorbing structure is formed, and similar, You can get the effect.

The centrifugal blower 1 achieves the same effect even when mounted on the wall sideways instead of the ceiling.

Embodiment 15

A fifteenth embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the fifteenth embodiment will be described.

In the fifteenth embodiment, as shown in FIG. 18, a hard fiber board with an aperture ratio of 10%, in which a large number of small holes 75 with a diameter of 5 mm are opened, is installed as a perforated plate 76 to close the gap 72. The configuration is

With this configuration, the air in the small holes 75 of the perforated plate 76 acts as a mass, and a space 70 surrounded by the orifice 19, the casing 10 and the outer shell 3 forms a spring system as a back air layer 74. A type of resonant sound absorbing structure is formed with a perforated plate sound absorbing structure that absorbs sound on the same principle as the Helmholtz resonator. When a part of the sound wave of the noise emitted from the suction port 7 of the casing 10 enters the perforated plate 76, the frequency of the sound wave of the incident noise matches the resonance frequency of the vibration system of the perforated plate sound absorption structure. The energy of the sound wave of the frequency to be absorbed is absorbed by the friction loss due to the air of the portion of the small hole 75 vibrating violently. Therefore, part of the noise can be silenced. At this time, the frequency that can be muffled by the function of the perforated plate sound absorption structure can be changed by the thickness and aperture ratio of the perforated plate 76, the diameter and pitch of the small holes 75, the thickness of the rear air layer 74, etc. The frequency range of can be expanded.

In addition to the hard fiber board, the perforated board 76 may be a plaster board or an aluminum board. The same effect can be obtained even if it is used.

The same effect can be obtained even with a plate in which a large number of slit-like elongated holes are formed, in which a large number of circular small holes 75 are open.

Embodiment 16

A sixteenth embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the sixteenth embodiment will be described.

In the sixteenth embodiment, as shown in FIG. 19, a flexible urethane foam is used as the porous material 77, and the configuration is such that the space 72 is closed.

According to this configuration, when a part of the sound wave of the noise emitted from the suction port 7 of the casing 10 is incident on the porous material 77, the noise of the frequency depending on the sound absorption characteristics of the porous material 77 itself is It can absorb sound waves. In addition, sound waves of noise transmitted through the porous material 77 and reflected by the orifices 19 and the casing 10 and the shell 3 enter the porous material 77 again, whereby sound waves of noise can be absorbed. Further, a porous material 77 forms a mass, and a space 70 surrounded by the orifice 19 and the casing 10 and the outer shell 3 as a back air layer 74 forms a vibration system which becomes a panel, and a kind of porous sound absorbing structure Form a Among the sound waves of the incident noise, the energy of the sound wave of the frequency whose frequency coincides with the resonance frequency of the vibration system of the porous sound absorbing structure is that the air inside the porous material 77 itself or the porous material 77 vibrates. Is absorbed by friction loss. Therefore, part of the noise can be silenced. At this time, frequencies that can be muffled by the function of the porous sound absorbing structure include the material of the porous material 77, thickness, sound absorbing characteristics, thickness of the back air layer 74, overlapping of porous materials 77 having different sound absorbing characteristics, etc. The range of noise frequencies that can be muffled can be expanded.

In general, the frequency of noise that can be absorbed by porous material 77 is relatively high, and the frequency of noise that can be muffled by the porous sound absorbing structure is relatively low, so the range of noise frequencies that can be muted simultaneously can be expanded. be able to.

Further, as the porous material 77, the same effect can be obtained by using glass wool, rock wool or the like in addition to the soft urethane foam.

Also, in order to prevent the scattering of the porous material 77, the porous material 77 is used as a cloth or other sound wave. The same effect can be obtained even with a configuration covered with a permeable material.

Furthermore, even if a material having sound absorbing properties other than the porous material 77, for example, a porous molded plate material such as a rock wool plate, or a soft material such as a sponge, the same effect can be obtained. Force S.

Embodiment 17

A seventeenth embodiment of the present invention will now be described. The description of the same parts as the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the seventeenth embodiment will be described.

In the seventeenth embodiment, as shown in FIGS. 20A and 20B, a bullet sheet which is a film-like material 73 is provided so as to close the gap 72, and the boule sheet which is a film-like material 73 becomes a mass. 70 forms an air layer 74 behind the film-like material 73 to form a vibration system to be a panel. As a result, the centrifugal fan 1 in which a kind of membrane-like sound absorbing structure of the ring-type sound absorbing structure is formed is integrally provided on the lower surface of the casing 10 with a cylindrical tubular wall 78 concentric with the suction port 7 of the casing 10. The cylindrical tubular wall 78 has a thickness of 2 mm and a height of 28 mm, and the inner diameter D of the wall is 21 mm! // o.

It is generally known that the frequency that can be muffled by the membrane sound absorbing structure is inversely proportional to the square root of the thickness of the back air layer 74. With this configuration, sound waves of noise travel around the wall 78 in the space 70. The length of the convoluted path can be regarded as the thickness of the back air layer 74. Therefore, the thickness of the back air layer 74 can be increased, and the frequency of noise that can be muffled can be reduced, so that the noise of lower frequencies can be silenced without changing the size of the shell 3. That power S.

Further, since the cylindrical tubular wall body 78 is a cylindrical tubular body coaxial with the suction port 7 integrated with the casing 10 at one end, a path for sound waves of noise to wrap around the wall body 78 in the space 70. There is only one U-bend. Therefore, sound waves of noise can be smoothly transmitted, and the thickness of the back air layer 74 can be more stably increased, and the size of the outer shell 3 is not changed by the wall 78 having a simple structure. The lower frequency noise can be silenced.

In this configuration, even when the gap portion 72 is closed by the film-like material 73 and the force gap portion 72 is closed by the perforated plate 76, noise generated by the perforated plate sound absorption structure is eliminated. Since the frequency is inversely proportional to the square root of the thickness of the back air layer 74, the frequency that can be muted similarly is reduced It is possible to do S. Further, when the gap portion 72 is closed by the porous material 77, the frequency of noise muffled by the porous sound absorbing structure is inversely proportional to the thickness of the back air layer 74, so the frequency which can be muffled similarly is reduced. be able to.

Furthermore, the cylindrical tubular wall body 78 can be any shape that can elongate the path of the sound wave in the space 70 and can bend the path in a U-shape on the cross section passing through the rotation axis 4 . Therefore, the same effect can be obtained even if the shape is a polygonal tube or an elliptical tube, or if the center of the tube 10 and the inlet 7 of the casing 10 are shifted.

Embodiment 18

An eighteenth embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the eighteenth embodiment will be described.

In the eighteenth embodiment, as shown in FIG. 21, the boule sheet which is the film-like material 73 is provided so as to close the gap 72, the boule sheet which is the film-like material 73 becomes a mass, and the space 70 is the film. The air layer 74 behind the material 73 forms a vibration system to be a panel. A centrifugal fan 1 in which a kind of membrane sound absorbing structure of a resonance type sound absorbing structure is formed by this, a cylindrical tubular wall body 78 concentric with the suction port 7 of the casing 10 is integrally provided on the lower surface of the casing 10, The cylindrical tubular wall 78 is 2 mm thick and 28 mm high, and the inner diameter D of the wall is 216 mm in part, 160 mm in part, and is not uniform in the circumferential direction.

According to this configuration, due to the partial difference in the inner diameter D of the cylindrical tubular wall, there is a portion where the thickness of the back air layer ₇₄ is different. Therefore, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded.

Embodiment 19

A nineteenth embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the nineteenth embodiment will be described.

In the nineteenth embodiment, as shown in FIG. 22, the bale sheet which is a film-like material 73 is provided so as to close the gap 72, the boule sheet which is a film-like material 73 becomes a mass, and the space 70 is a film. The air layer 74 behind the material 73 forms a vibration system to be a panel. A centrifugal fan 1 in which a kind of membrane sound absorbing structure of a resonance type sound absorbing structure is formed by this, a cylindrical tubular wall body 78 concentric with the suction port 7 of the casing 10 is integrally provided on the lower surface of the casing 10, The cylindrical tubular wall 78 is 2 mm thick, the inner diameter D of the wall is 216 mm, the height is 28 mm in part, 40 mm in part, and it is not circumferentially uniform.

[0150] According to this configuration, the partially different heights of the cylindrical tubular wall members 78 result in portions where the thickness of the back air layer ₇₄ is different. Therefore, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded.

Embodiment 20

A twentieth embodiment of the present invention will now be described. The description of the same parts as the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twentieth embodiment will be described.

In the twentieth embodiment, as shown in FIG. 23, the boule sheet which is a film-like material 73 is provided so as to close the gap 72, the boule sheet which is a film-like material 73 is a mass, and the space 70 is a film. The air layer 74 behind the material 73 forms a vibration system to be a panel. The centrifugal fan 1 in which a kind of membrane sound absorption structure of resonance type sound absorption structure is formed by this is provided with a screw receiver 79 on the lower surface of the casing 10 and a cylindrical tubular wall body 78 provided with a screw 80 fixed by the screw 81. It is designed to be removable and attach a cylindrical tubular wall 78 of different internal diameter D with force S.

With this configuration, even if the frequency of the noise radiated from the suction port 7 changes due to the installation state of the centrifugal fan 1, etc., the thickness of the back air layer 74 can be increased by changing the inner diameter D of the cylindrical tubular wall. Because it can be adjusted, the frequency of noise that can be muffled can be adjusted.

Embodiment 21

A twenty-first embodiment of the present invention will now be described. The description of the same parts as the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-first embodiment will be described.

In the twenty-first embodiment, as shown in FIG. 24, the bale sheet which is a film-like material 73 is provided so as to close the gap 72, the boule sheet which is a film-like material 73 is a mass, and the space 70 is a film. The air layer 74 behind the material 73 forms a vibration system to be a panel. A cylindrical tubular wall body 78 concentric with the suction port 7 provided in the space 70 of the centrifugal blower 1 in which a kind of membrane sound absorbing structure of a resonance type sound absorbing structure is thus formed is constituted by an inner side wall 82 and an outer side wall 83 The height of the wall 78 can be adjusted by sliding the outer wall 83. According to this configuration, since the thickness of the back air layer 74 can be adjusted by adjusting the height of the cylindrical tubular wall body 78, the frequency of noise that can be muffled can be adjusted.

(Embodiment 22)

A twenty-second embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-second embodiment will be described.

In the twenty-second embodiment, as shown in FIG. 25, the boule sheet which is a film-like material 73 is provided so as to close the gap 72, the boule sheet which is a film-like material 73 is a mass, and the space 70 is a film. The air layer 74 behind the material 73 forms a vibration system to be a panel. A cylindrical tubular wall body 78 whose one end is in contact with the casing 10 concentrically with the suction port 7 of the casing 10 in the space 70 of the centrifugal fan 1 in which a kind of membrane sound absorption structure of resonance type sound absorption structure is formed. Two wall bodies 78 with an inner diameter D of 180 mm and 240 mm, and a cylindrical tubular wall body 78 with an inner diameter D of 216 mm, which is concentric with the suction port 7 of the casing 10 and one end contacts the orifice 19 There is.

With this configuration, a labyrinth structure in which sound waves of noise travel around the wall 78 alternately and propagate in the space 70 can be made, and the thickness of the back air layer 74 can be made thicker. Low frequency noise can be silenced without changing the size of 3.

(Embodiment 23)

A twenty-third embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-third embodiment will be described.

In the twenty-third embodiment, as shown in FIGS. 26A and 26B, the boule sheet as the film-like material 73 is provided so as to close the gap 72, and the bule sheet as the film-like material 73 becomes a mass. 70 forms an air layer 74 behind the film-like material 73 to form a vibration system to be a panel. A centrifugal fan 1 in which a kind of membrane sound absorbing structure of a resonance type sound absorbing structure is formed by this is provided with a partition wall 85 which divides the space 70 into two with different volumes on a plane passing through the rotation shaft 4.

With this configuration, it is possible to form a plurality of resonance type sound absorbing structures having different shapes and volumes of the space 70 to be the back air layer 74. Therefore, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded.

Embodiment 24 A twenty-fourth embodiment of the present invention will now be described. The description of the same parts as the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-fourth embodiment will be described.

In the twenty-fourth embodiment, as shown in FIG. 27, in the space 70 divided into two by the partition wall 85, one of the gaps 72 is closed by a bul sheet which is a film-like material 73. . In addition, the gap portion 72 of the other space 70 is closed with a hard fiber board having a hole area ratio of 10% in which a large number of small holes 75 having a diameter of 5 mm which is a perforated plate 76 are opened.

According to this configuration, since two types of resonance type sound absorbing structures can be formed, noises of a plurality of frequencies can be silenced, and the frequency range of noises that can be silenced can be expanded.

Note that one of the gaps 72 in the divided space 70 may not be closed, and resonance silencing may be performed by air column resonance in the space 70.

(Embodiment 25)

A twenty-fifth embodiment of the present invention will now be described. The description of the same parts as the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-fifth embodiment will be described.

[0168] In the twenty-fifth embodiment, as shown in FIG. 28, in each of the spaces 70 divided into two by the partition wall 85, cylindrical tubular tubes concentric with the suction port 7 with one end of different heights contacting the casing 10 Walls 78 are provided, and the thickness of the back air layer 74 is increased in each space 70.

According to this configuration, the space 70 divided into two by the partition wall 85 is provided with wall bodies 78 of different shapes, and the divided spaces 70 each have different thicknesses of the back air layer 74. Can be formed. Therefore, noise of multiple frequencies can be silenced, and the range of noise frequencies that can be silenced can be expanded.

[0170] A cylindrical tubular wall body 78 concentric with the suction port 7 and having one end installed in each of the spaces 70 divided into two by the partition wall 85 and in contact with the casing 10 has an inner diameter and Also, even if their combination is different, the same effect can be obtained with force S.

Embodiment 26

A twenty-sixth embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-sixth embodiment will be described. In the twenty-sixth embodiment, as shown in FIG. 29, the boule sheet which is a film-like material 73 is provided so as to close the gap 72, the boule sheet which is a film-like material 73 becomes a mass, and the space 70 is a film. The air layer 74 behind the material 73 forms a vibration system to be a panel. An outer peripheral space 86 surrounded by the side wall 8 and the outer shell 3 of the casing 10 is surrounded by the orifice 19, the casing 10, and the outer shell 3 in the centrifugal fan 1 in which a kind of membrane sound absorbing structure of resonance type sound absorbing structure is formed. It communicates with the space 70.

According to this configuration, the outer peripheral space 86 can be used as the air layer 74 behind the resonance type sound absorbing structure. Therefore, the thickness of the back air layer 74 can be made thicker, and the lower frequency noise can be silenced without changing the size of the outer shell 3.

(Embodiment 27)

Twenty-Seventh Embodiment A twenty-seventh embodiment of the present invention will now be described. The description of the same parts as those in the fourteenth embodiment of the present invention will be omitted, and only the parts unique to the twenty-seventh embodiment will be described.

In the twenty-seventh embodiment, as shown in FIG. 30, the bale sheet which is a film-like material 73 is provided so as to close the gap 72, the boule sheet which is a film-like material 73 is a mass, and the space 70 is a film. The air layer 74 behind the material 73 forms a vibration system to be a panel. As a result, in the centrifugal fan 1 in which a kind of membrane sound absorbing structure of the resonance type sound absorbing structure is formed, a part of the motor 6 protrudes from the casing 10 in the outer shell 3, and the motor side outer wall 87 of the casing 10 and the outer shell 3 The back side space 88 between them communicates with the outer peripheral space 86 surrounded by the side wall 8 and the outer shell 3 of the casing 10, and the outer peripheral space 86 communicates with the space 70 constituted by the orifice 19 and the casing 10 and the outer shell 3. doing.

[0176] With this configuration, it is possible to use the back space 88 together with the outer space 86 as a back air layer 74 of the resonant sound absorbing structure S. Therefore, the thickness of the back air layer 74 can be made thicker, and the lower frequency noise can be silenced without changing the size of the outer shell.

Industrial applicability

The present invention can expand the frequency range of noise that can be muffled, and can reduce lower frequency noise without changing the size of the shell, and can adjust the frequency of noise that can be muffled. It provides a blower and its industrial applicability is extremely high.

Claims

The scope of the claims

[1] An electric motor in which an impeller is coupled rotatably around a rotation axis in an outer shell provided with an opening, a casing having a suction port that surrounds the periphery of the impeller, and the opening and the opening of the outer shell A centrifugal fan, comprising: a bellmouth-like orifice having an opening for passing therethrough; and a resonant space formed by the orifice for resonating and silencing noise emitted from the suction port;

A centrifugal fan according to claim 1, wherein a part of a path from the inlet between the end of the orifice and the casing to the sound wave of noise entering the resonance space is elongated.

[2] The centrifugal fan according to claim 1, wherein the opening of the orifice is concentric with the suction port of the casing.

[3] The centrifugal fan according to claim 1, wherein the opening of the orifice has a diameter equal to or less than that of the suction port.

[4] The centrifugal fan according to claim 1, wherein a path of a part of the sound wave of noise incident from the inlet of the resonance space is reflected in the deepest part of the resonance space.

[5] The centrifugal fan according to claim 1, wherein a wall is provided in the resonance space, and a part of a path until a sound wave of noise incident on the resonance space is reflected is lengthened.

[6] The centrifugal fan according to claim 5, wherein the wall provided in the resonance space is a cylindrical tube concentric with the suction port and in contact with the casing at one end.

[7] The inner diameter D of the cylindrical tubular wall concentric with the suction port provided in the resonance space is a relationship of D> Di + 2i between the inner diameter Di of the suction port and the gap size i of the inlet portion. Become

The centrifugal fan according to claim 6.

[8] The inner diameter D of the cylindrical tubular wall concentric with the suction port provided in the resonance space is a relationship of D <Di + 2i between the inner diameter Di of the suction port and the gap size i of the inlet portion. Become

The centrifugal fan according to claim 6.

[9] The centrifugal fan according to any one of claims 6 to 8, wherein the inner diameter of the cylindrical tubular wall concentric with the suction port provided in the resonance space is not uniform in the circumferential direction.

[10] The centrifugal fan according to any one of claims 6 to 8, wherein the height of the cylindrical tubular wall concentric with the suction port provided in the resonance space is not uniform in the circumferential direction.

[11] The centrifugal fan according to any one of [1] to [8], wherein a dimension of a gap of the inlet to the resonance space is not uniform in a circumferential direction.

[12] The centrifugal fan according to any one of claims 6 to 8, wherein the height of the cylindrical tubular wall concentric with the suction port provided in the resonance space is adjustable.

[13] At least one cylindrical tubular wall concentric with the suction port of the casing, one end contacting the casing, and at least one cylindrical tubular wall concentric with the suction port of the casing, one end contacting the orifice The centrifugal fan according to any one of claims 4 to 5, wherein the bodies are arranged alternately in the radial direction.

[14] The centrifugal fan according to claim 6, wherein the cylindrical tubular wall concentric with the suction port provided in the resonance space is integrally molded with the casing.

[15] The centrifugal fan according to Claim 1, wherein an outer peripheral space surrounded by the side wall of the casing and the outer shell is used as the resonance space.

[16] The centrifugal fan according to claim 15, wherein a space behind the motor-side outer wall of the casing and the outer shell is used as the resonance space.

[17] A motor in which an impeller is coupled rotatably around a rotation axis in an outer shell provided with an opening, a casing having a suction port that surrounds the periphery of the impeller, and the opening and the opening of the outer shell A bellmouth-like orifice having an opening through which

A member for closing a gap between the end of the orifice and the casing is used as a material for a sound absorbing structure, and a space formed by the orifice is formed as a back air layer to form a resonant sound absorbing structure. Do,

Centrifugal blower.

[18] The centrifugal fan according to claim 17, wherein the opening of the orifice is concentric with the suction port of the casing.

[19] The centrifugal fan according to claim 17, wherein the opening of the orifice has a diameter equal to or less than that of the suction port.

[20] The centrifugal fan according to claim 17, wherein the member closing the gap is a film-like material.

[21] The centrifugal fan according to claim 17, wherein the member closing the gap is a perforated plate.

[22] The centrifugal fan according to claim 17, wherein the member closing the gap is a porous material.

[23] A wall is provided in the space, and the thickness of the back air layer is increased, characterized in that

The centrifugal fan according to 7.

24. The centrifugal fan according to claim 23, wherein the wall provided in the space is a cylindrical tube concentric with the suction port and in contact with the casing at one end.

[25] The centrifugal fan according to claim 24, wherein the inner diameter of the cylindrical tubular wall concentric with the suction port provided in the space is not uniform in the circumferential direction.

[26] The centrifugal fan according to any one of claims 24 or 25, wherein the height of the cylindrical tubular wall concentric with the suction port provided in the space is not uniform in the circumferential direction.

[27] At least one cylindrical tubular wall concentric with the suction port of the casing and having one end in contact with the casing, and at least one cylinder concentric with the suction port in the casing and one end being in contact with the orifice The centrifugal fan according to claim 17, wherein the tubular walls are arranged alternately in the radial direction.

[28] The centrifugal fan according to claim 17, wherein an outer peripheral space surrounded by a side wall and an outer shell of the casing is used as a back air layer.

[29] The centrifugal fan according to Claim 17, wherein a rear space between the motor side outer wall of the casing and the outer shell is used as a rear air layer.