JP3394165B2 - Suction port structure of centrifugal blower - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a suction port structure of a centrifugal blower, and more particularly, to reducing noise generated in the suction port and external emission of wind noise of blades. The present invention relates to a sound absorbing structure of a blower that can be used. 2. Description of the Related Art There are various types of noise generated by a blower, but it is necessary to reduce noise on the side of the suction port where the emitted sound is greatest. That is, when a duct hose or the like is not connected to the suction port, a vortex sound generated on the inner wall of the suction port and a wind noise of the blades come out from the opening of the suction port. Therefore, the noise measurement of the blower is measured at a position, for example, 1 meter away from the suction port where the noise is highest. By the way, the structure near the suction port often has the structure shown in FIG. In centrifugal blowers,
Although the impeller 6 is covered with the impeller casing 8, the impeller rotates between the side plate 7 a located on the upstream side of the impeller shaft 6 b of the centrifugal blade 7 and the casing 8 surrounding the impeller 6. A gap 8a is provided for convenience. This causes the following adverse effects. The air pressurized by the blades remains in the impeller casing 8, while the air 25 flowing into the impeller 6 has a slightly negative pressure. Therefore, the impeller inlet 6a passes through the gap 8a from the high pressure casing space.
A secondary flow 31 is generated. This secondary flow not only changes its direction largely at the end of the side plate 7a at the impeller inlet 6a and flows into the impeller as indicated by an arrow 31a, but also merges with the intake air 25. That is inevitable. [0005] When the suction hose 34 for connecting the duct hose 33 is provided and the duct hose is not connected, the flow of the secondary flow which flows backward to the intake air 25 as indicated by the arrow 31b. Occurs and the suction cylinder 3
A vortex 35 is also generated near the inner wall of No. 4. Furthermore, when a pool is formed even on the substantially conical surface of the impeller boss 21, the generation of the vortex 36 there may be promoted. [0006] In addition to the noise caused by the generation of the vortex, it is well known that wind noise is generated on the inflow side of the blade when the intake air flows into the blade. These noises are emitted to the outside from the air inlet opening to the atmosphere as described above. Therefore, at present, measures have been taken to reduce the noise emitted from the suction port. One of them is an example in which a sound-absorbing cover is attached to a suction port, and the cover usually forms a kind of maze. This is based on the idea that noise emitted from the suction port can be absorbed or reduced in a maze when passing through the sound absorbing cover. FIG. 10 shows an example of a sound absorbing structure provided with a sound absorbing cover. This means that a short duct 41 is connected to the suction port 2 and a disk 42 fixed to the outer periphery near the tip thereof orthogonally to the impeller shaft 6b, and toward the suction port 2 so as to cover this disk. It comprises a shallow cylindrical sound absorbing pan 43 attached. A ring-shaped suction flow inlet 44 is provided between the peripheral edge of the disk 42 and the edge of the sound absorbing pan 43. A sound absorbing material 4 is provided on the side of the disk opposite to the impeller.
The sound absorbing material 46 is also attached to a portion corresponding to the bottom of the sound absorbing pan 43. In addition, duct 4
The sound absorbing material 47 which is formed so as not to disturb the flow on the inner surface of 1.
Is provided, and the intake air flows into the impeller 6 through the space between the sound absorbing materials. Although the intake air follows the curved flow path and enters the impeller, the speed is still low at the time of passing through the impeller, and there is no particular problem as long as the intake air can secure a predetermined air volume. On the other hand, noise generated in the suction port 2 and the impeller 6 is partially absorbed by the sound absorbing members 47, 46, and 45 while following the maze. Noise tends to be reduced. However, since the intake air enters through the ring-shaped suction flow inlet, the flow toward the opening 41a of the duct 41 is in all directions. Such a flow tends to generate a vortex 48 in the vicinity of the inner wall of the duct immediately after the opening edge or the like, and this vortex has a drawback that noise reduction is hindered. [0010] In the blower having the above-mentioned sound-absorbing pan, if it is installed outdoors, rainwater may enter when air is taken in, and it is needless to say that it is not preferable. In addition, when the sound absorbing material deteriorates, it enters the impeller with the intake air and eventually disappears, which has a drawback that it cannot withstand long-term use. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide a sound absorbing device provided at a suction port, which can prevent a backflow of a secondary flow from a high pressure side in the inside thereof, For smooth inflow of intake air,
Suppressing the generation of eddy currents caused by air flow as much as possible to improve the sound reduction effect, and furthermore, absorbing the unavoidable wind noise of the blades as much as possible and releasing it to the outside An object of the present invention is to provide an inlet structure of a centrifugal blower which can achieve a reduction. SUMMARY OF THE INVENTION The present invention is a centrifugal blower whose suction port is open to the atmosphere, and reduces vortex noise generated near the suction port and wind noise generated from rotating blades. For a suction port structure having a sound absorbing structure for the purpose. As shown in FIG. 1, the suction port 2 has a perforated inner panel 9A and an air layer 10 defining a suction flow introduction space 4 connected to an impeller inlet 6a. A suction box 5 having a non-porous outer panel 9B surrounding the panel 9A is attached. The suction flow introduction space 4 has a substantially semi-cylindrical space 4A extending in the direction of the impeller shaft 6b, a substantially trapezoidal shape connected to the substantially semi-cylindrical space 4A, extending in a direction orthogonal to the impeller shaft 6b, and having an end open to the atmosphere. The space 4B has a substantially bell-shaped cross section (see FIG. 2). The arc-shaped portion 9b of the inner panel 9A that defines the substantially semi-cylindrical space 4A is formed in the substantially semi-cylindrical space 4A.
The opening 3p of the guide portion 3a allows the intake air flowing into the impeller inlet 6a to flow from the substantially trapezoidal space side of the substantially semicylindrical space 4A without passing through the entire periphery of the substantially semicylindrical space 4A. And have the same diameter. And the back surface of the inner panel 9A is the sound absorbing material 11A, 11B, 11C.
While the inner surface of the outer panel 9B is also covered with the sound absorbing material 11D. According to the present invention, a suction box connected to the impeller inlet is provided, and a suction flow introduction space formed in the suction box is
A substantially semi-cylindrical space extending in the axial direction of the impeller is provided, which forms a sound pool for wind noise generated by the blades, and facilitates sound absorption by the sound absorbing material through the sound absorbing holes of the inner panel. The arc-shaped portion of the inner panel that defines the substantially semi-cylindrical space mainly allows the intake air flowing into the impeller inlet from the substantially semi-cylindrical space to pass through substantially the entire periphery of the substantially semi-cylindrical space. The flow into the impeller is stable because it has the same diameter as the opening of the impeller inlet so that it flows from the substantially trapezoidal space side of the semi-cylindrical space, and the generation of vortices at the impeller inlet is also suppressed. You. Furthermore, since the substantially semi-cylindrical space is continuous with a substantially trapezoidal space extending in a direction orthogonal to the impeller axis,
The sound reduction effect while passing through a curved road is increased. Therefore, the noise level emitted from the suction port to the outside decreases,
The noise generated by the blower is reduced. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a suction port structure of a centrifugal blower according to the present invention will be described in detail with reference to the drawings showing an embodiment of an apparatus for implementing the same. FIG. 1 is a cross-sectional view of a main part of a centrifugal blower 1 having a sound-absorbing structure for reducing noise generated in a suction port that is open to the atmosphere without a duct hose connected thereto and near the suction port. It shows the structure of the suction port. The sound absorbing structure attached to the suction port 2 is a suction box 5 defining a suction flow introduction space 4 connected to the impeller inlet 6a. In the example shown in the figure, a suction guide 3 having a guide part 3a that spreads like a trumpet is interposed between the suction box 5 and the impeller inlet 6a. The suction guide 3 is arranged coaxially with the impeller inlet 6a, and the inner surface of the guide portion 3a facing the impeller inlet is widened toward the impeller. Therefore, the above-mentioned suction flow introduction space 4 is in a state of being connected to the impeller inlet 6 a via the suction guide 3. The suction guide 3 is for guiding the intake air smoothly to the impeller inlet 6a, and may be an aluminum die-cast product or a molded product such as rubber or plastic. The suction guide 3 has double cylindrical lips 3A and 3B on the impeller entrance side. The outer peripheral lip 3A is inserted into a gap 8a between the side plate 7a located on the upstream side in the direction of the impeller shaft 6b of the centrifugal impeller 7 and the impeller casing 8 surrounding the impeller 6, thereby closing the gap. Thus, the end of the side plate 7a of the centrifugal blade 7 is covered by the double lips 3A, 3B. The lips 3A and 3B prevent the pressurized air in the impeller casing 8 from returning to the impeller inlet 6a. In order to prevent the double cylindrical lips 3A, 3B from contacting the impeller 6 and hindering the rotation of the centrifugal blade 7, the distance between the side plate 7a of the centrifugal blade 7 and each lip 3A, 3B is, for example, 1 mm. Or 1.5m
A gap of about m (the gap is not shown in the figure) is secured. The suction box 5 is provided with a guide portion 3a of the suction guide 3.
Perforated inner panel 9A defining a suction flow introduction space 4 connected to the outer panel 9B, and an outer panel 9B disposed outside the perforated inner panel 9B.
Is formed. For example, a punching metal is used for the inner panel 9A, and a punching hole of about 3 mm to 8 mm is used as the sound absorbing hole 9a. The outer panel 9B surrounds the inner panel 9A with the air layer 10 interposed therebetween, and is non-porous and blocks sound in the air layer so as not to be directly emitted to the outside. The suction flow introducing space 4 defined by the inner panel 9A includes a substantially semi-cylindrical space 4A and a substantially trapezoidal space 4B. The substantially semi-cylindrical space 4A is
The suction guide 3 is formed so as to extend in the direction of the impeller shaft 6b from the end of the guide portion 3a on the side opposite to the impeller. The depth L in the direction of the impeller shaft 6b is selected to be a length approximating the diameter D of the opening on the side opposite to the impeller of the guide portion 3a. It is enough. The substantially trapezoidal space 4B is continuous with the substantially semi-cylindrical space 4A, extends in a direction perpendicular to the impeller shaft 6b, and has an end open to the atmosphere. Accordingly, the cross section of the suction flow introduction space 4 is substantially bell-shaped as shown in FIG. 2 when the substantially semi-cylindrical space 4A and the substantially trapezoidal space 4B are combined. The depth of the substantially trapezoidal space 4B may be the same as that of the substantially semi-cylindrical space 4A (see FIG. 1). As a result, the vertical cross section of the flow path in the suction flow introduction space 4 forms an elbow. Therefore, the noise generated by the impeller or the like travels straight and turns, thereby exhibiting a noise reduction effect. As shown in FIG. 1, the inner panel 9A and the outer panel 9B have a sound absorbing material 11A,
11B, 11C and 11D are attached. As the sound absorbing material, a known material such as urethane foam is used,
It is in the form of a sponge. The sound absorbing material 11A covering in a bell shape covers the inner panel 9A without being in close contact with the back surface of the inner panel 9A, and the same applies to the sound absorbing materials 11B and 11C arranged perpendicular to the impeller shaft 6b.
Further, the outer panel 9B is also covered with the sound absorbing material 11D so as to be in close contact with the inner surface thereof or not to adhere thereto. The reason why most of the sound absorbing material is not brought into close contact with the panel is to enhance the sound absorbing effect. In particular, in the inner panel 9A, the sound absorbing material 11 is inserted through the sound absorbing holes 9a.
Propagation of the sound to the air layer 10 via A, 11B, and 11C is promoted, and the sound reduction effect is improved. For this purpose, the sound absorbing material 11A is connected to the air opening 5a of the suction box 5 as shown in FIG.
, But is not adhered to other parts. The sound absorbing material 11D on the inner surface of the outer panel 9B only needs to be tightly fixed near the air opening of the suction box 5 only. As shown in the figure, the sound absorbing material 11B, 1
When the air layer is not secured at the location 1C, the sound absorbing material may be simply stored between the inner panel 9A and the outer panel 9B. In the example shown in the figure, the inner panel 9
The opening 5a of the suction box 5 formed by A opens downward and faces the ground side. This is because rainwater can be prevented from entering the suction port 2 when the blower is installed outdoors. However, in the case of indoor installation, the opening 5a may be directed rightward, leftward or upward. The opening 5a
Is selected to be equal to or larger than the opening area of the impeller inlet 6a. The suction box 5 will be described in more detail.
In the present invention, the suction flow introducing space 4 is composed of a substantially semi-cylindrical space 4A and a substantially trapezoidal space 4B. Specifically, as shown in FIG. . And the round opening 3p of the edge of the guide part 3a opened in the shape of a trumpet of the suction guide 3 is arranged as close as possible in the substantially semi-cylindrical space 4A. That is, the arc-shaped portion 9b of the inner panel 9A that defines the substantially semi-cylindrical space 4A allows the suction air flowing into the suction guide 3 from the substantially semi-cylindrical space 4A to flow through the entire semi-cylindrical space 4A. It has substantially the same diameter as the opening 3p of the guide portion 3a so as to flow mainly from the substantially trapezoidal space 4B side of the substantially semi-cylindrical space 4A without passing through the periphery. As can be seen with reference to FIG. 3A, when the entire periphery of the circular opening 3p of the guide portion 3a is separated from the inner panel 9A forming the suction flow introduction space 4, the suction is performed. The air flows in from all directions as indicated by the arrow 12. As a result, the flows entering the suction guide 3 become unstable due to, for example, interfering with each other, and small eddies are easily generated everywhere on the inner wall of the opening. However, if the space around the upper half of the opening 3p is as small as possible as shown in FIG. 3B, the intake air from the substantially trapezoidal space 4B directly enters the opening 3p as shown by an arrow 13, Unnecessary turbulence of the flow in the suction guide 3 is suppressed. Returning to FIG. 1, at the opening 5a of the suction box 5, the tip of the inner panel 9A is bent round to the tip of the outer panel 9B so as to facilitate smooth entry of the intake air. Preferably. The rounded inner panel 9A and the outer panel 9B are not so large that the sound absorbing materials 11B and 11C must be interposed. Therefore, although not shown, the inner panel is not bent and a trumpet-shaped guide cap is provided. Or the like may be fitted into the opening. The sound absorbing wall on the impeller side of the substantially trapezoidal space 4B is bent obliquely or in an arc shape at a portion connected to the suction guide 3, and expands in a trumpet shape with the guide portion 3a and the wall surface of the substantially trapezoidal space 4B. Is considered to be continuous. Of course, although not shown, the trumpet-shaped portion of the guide portion may be extended to the inner panel so as to be smoothly connected to the vertical surface of the inner panel. Incidentally, if the cone-shaped surface of the blade boss 21 in FIG. 1 is deeply curved, stagnation may occur there and a vortex may be generated. In such a case, it is necessary to shape the shape of the blade boss so that the flow from the suction guide 3 flows smoothly with little disturbance. The noise reduction effect of 0.5 dB (A) may be obtained only by this improvement. According to the above configuration, the suction guide 3
The suction box 5 is attached to the suction port 2 in the following manner. The suction guide 3 faces the impeller inlet 6a, and its double cylindrical lips 3A and 3B are covered so as to cover the end of the side plate 7a located on the upstream side of the centrifugal blade 7 in the direction of the impeller shaft 6b. The gap 8a between the side plate 7a and the impeller casing 8 is closed by the outer peripheral lip 3A. Next, the outer peripheral portion 4 of the suction guide 3 on the impeller side.
The bolts 22 (see FIG. 1) are inserted into the fool holes 3b of the overhanging portion 3m as shown in FIG. 4 (a), and the ends thereof are screwed into the screw holes provided in the impeller casing 8. I do. By rotating the impeller 6 with the bolt slightly applied, the suction guide 3 is centered so that the double lips 3A, 3B of the suction guide 3 do not touch the side plate 7a of the centrifugal blade 7. After fixing the suction guide 3 with the bolts 22, the suction box 5 is brought close to the suction guide 3, and the long screw rod 23 is inserted through the suction box 5 from the side opposite to the impeller. If the tip of the threaded rod is screwed into each of the screw holes 3c of the overhanging portion 3n as shown in FIG. 4B provided at four places on the outer periphery of the suction guide 3 on the side opposite to the impeller, the suction box 5 is sucked. It is fixed to the impeller casing 8 via the guide 3. Note that the upper 3
The book passes through the air layer 10 as shown in FIG. 2, but the lower one penetrates the substantially trapezoidal space 4B. Needless to say, the intake air is not disturbed by such a screw rod. As can be seen from such a mounting procedure, since the screw rod 23 is not disposed in the substantially semi-cylindrical space 4A, the inner panel 9A defining the substantially semi-cylindrical space is formed.
The arc-shaped portion 9b has substantially the same diameter as the opening 3p of the guide portion 3a. As a result, the intake air flowing into the suction guide 3 from the substantially semi-cylindrical space 4A does not pass through the entire periphery of the substantially semi-cylindrical space described in FIG. It flows from the substantially trapezoidal space side of the cylindrical space 4A. The above-mentioned threaded rod does not necessarily have to penetrate the air layer. Although not shown, the threaded rod may be penetrated by the sound absorbing material or the diameter of the arc-shaped portion of the inner panel may be slightly larger than the edge opening of the guide portion. You may make it large and let it pass near the inner surface of an arc-shaped part. In the latter case, the screw rod penetrates into the substantially semi-cylindrical space, but there is no problem if the screw rod is thin. A part of the arc-shaped portion of the inner panel in the state as shown in FIG. 2 may be locally expanded outwardly, and a space for disposing the threaded rod may be provided at that portion. According to the suction port structure assembled to the blower in this way, the air 25 sucked from the substantially trapezoidal space 4B goes to the substantially semi-cylindrical space 4A, from there through the suction guide 3 and to the impeller inlet. Enter 6a. During this time, the flow of the intake air 25 moves smoothly without generating a vortex that causes noise. It is needless to say that the flow from the substantially semi-cylindrical space 4A to the suction guide 3 from the substantially trapezoidal space 4B side and the mutual interference of the inflow air near the opening of the guide portion 3a is reduced as much as possible. As can be seen from FIG. 1, the air in the impeller casing 8 pressurized by the rotating blades 7 does not flow back to the impeller inlet 6a by the double lips 3A, 3B of the suction guide 3. The generation of swirling noise there is also avoided. Of course, generation of a little noise together with the wind noise caused by the blades is inevitable. However, these sounds reach the substantially semi-cylindrical space 4A via the suction guide 3. Most of the noise propagates directly from the suction guide 3 in the direction of the impeller shaft 6b. Approximately semi-cylindrical space 4A
, The intake air is flowing from the substantially trapezoidal space 4B,
Propagation noise tends to stagnate in a sound accumulation space centered on the impeller shaft 6b, and is absorbed by the sound absorbing materials 11A and 11B via the sound absorbing holes 9a of the inner panel 9A. The sound that has passed through the sound absorbing material is attenuated by the air layer 10, and is further absorbed by the sound absorbing material 11D and is then shielded by the outer panel 9B. The remaining noise is absorbed through the inner panel 9A while passing through the substantially trapezoidal space 4B so as to be opposite to the flow of the intake air 25. In this way, the sound is reduced to the outside due to the sound reduction by following the elbow-shaped passage in the suction box 5, the sound absorbing effect by the sound absorbing materials 11B and 11C, and the backflow preventing effect by the intake air. The noise in the blower is measured on the extension of the suction port 2 and at a distance of, for example, 1 meter from the suction port as described above. As shown in FIG. The noise level when equipped with (see ○) is lower than when not equipped (see △).
It was confirmed that the power consumption was reduced by 15 dB (A) to 20 dB (A). By the way, when the suction box 5 was not turned downward, that is, when the suction box 5 was turned upward or sideways, the degree of reduction of the noise level was hardly changed, and the effect of the present apparatus was remarkable. Since the inner panel 9A made of punched metal is employed, the sound absorbing materials 11A, 11B and the like deteriorate with time and erode at the sound absorbing hole 9a as compared with the case where the sound absorbing material is exposed. Even if the sound absorbing material is lost, most of the sound absorbing material remains in the air layer 10, so that a sharp decrease in the sound absorbing effect is prevented. FIG. 6 is an external view of the centrifugal blower 1 provided with the present suction port structure. The air volume of the blower is adjusted on the discharge port side. For this reason, the damper 27 is interposed in the discharge port 26. In this example, the tip of the damper gate is formed in a sawtooth shape so as to suppress the generation of vortices or the growth thereof. For example, the air volume may be reduced to about 20%, but the noise generated there is generally rarely transmitted to the suction port side via the impeller casing 8. However, it goes without saying that even with such propagation, the sound is reduced by the suction box 5 and the like. FIG. 7 shows an example in which the upper half portion of the suction guide 3 is formed in a cylindrical shape, and the opening 3p of that portion has the same diameter as the arc-shaped portion 9b of the inner panel 9A. Therefore, the rounded guide portion 3a is only the lower half as shown in FIG. With such a suction guide, noise reduction is achieved in the same manner as in the above example. As can be inferred from this, when the lower half portion of the guide portion is also a cylinder, the suction guide is no longer necessary, and the suction box may be directly connected to the impeller inlet. Which form is adopted may be determined according to the capacity and size of the blower, and it goes without saying that the depth of the substantially semi-cylindrical space is appropriately changed.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a main part of a centrifugal blower provided with a suction port structure according to the present invention. FIG. 2 is a sectional view taken along line II-II in FIG. FIG. 3A is a diagram illustrating the flow of air when the intake air flowing into the suction guide is caused to flow from the entire periphery of the substantially semi-cylindrical space, and FIG. 3B is a diagram illustrating the intake air flowing into the suction guide. FIG. 4 is an explanatory diagram of the flow of air when the air is allowed to flow from the substantially trapezoidal space side of the substantially semi-cylindrical space. 4A is an end view of the suction guide taken along line IV-IV in FIG. 1, and FIG. 4B is an end view of the suction guide taken along line VV in FIG. FIG. 5 is a graph showing measured data of noise generation levels of a centrifugal fan having an inlet structure and a fan not having the same. FIG. 6 is a schematic external perspective view of a centrifugal blower having a suction port structure. FIG. 7 is a sectional view of an essential part of a suction port structure of a centrifugal blower equipped with a suction guide having a cylindrical upper half. 8 is a sectional view taken along line VIII-VIII in FIG. 7; FIG. 9 is an explanatory diagram of a vortex causing noise generated at or near the suction port and a flow flowing backward from the impeller casing to the impeller inlet. FIG. 10 is a cross-sectional view of a main part of a centrifugal blower as a conventional technique to which a sound absorbing device having a cover-type structure is attached. [Explanation of Signs] 1 ... Centrifugal blower, 2 ... Suction port, 4 ... Suction flow introduction space,
4A: substantially semi-cylindrical space, 4B: substantially trapezoidal space, 5: suction box, 6: impeller, 6a: impeller entrance, 6b: impeller shaft,
7: centrifugal blade (rotating blade), 9A: inner panel, 9
B ... Outer panel, 9a ... Sound absorption hole, 10 ... Air layer, 1
1A, 11B, 11C, 11D: sound absorbing material; 25: intake air.

Claims (1)

(57) [Claim 1] A centrifugal blower whose suction port is open to the atmosphere, for reducing noise generated near the suction port and wind noise generated from rotating blades. In the suction port structure having a sound absorbing structure, the suction port includes a perforated inner panel that defines a suction flow introduction space connected to an impeller inlet, and a non-porous outer panel that surrounds the inner panel through an air layer. A suction box having an outer panel is attached, the suction flow introduction space includes a substantially semi-cylindrical space extending in the axial direction of the impeller, and an end extending in a direction perpendicular to the axis of the impeller and connected to the substantially semi-cylindrical space. An arc-shaped portion of an inner panel defining an approximately semi-cylindrical space is formed by an open substantially trapezoidal space, and has a substantially bell-shaped cross section. Inlet air flowing into The impeller inlet has substantially the same diameter as the impeller inlet so as to flow mainly from the substantially trapezoidal space side of the substantially semicylindrical space without passing through the entire periphery of the substantially semicylindrical space. While being coated with material
A suction port structure for a centrifugal blower, wherein an inner surface of the outer panel is also covered with a sound absorbing material.