JP5981902B2 - Centrifugal fan - Google Patents

Description

  The present invention relates to a centrifugal fan that sends wind to a combustion device or the like.

  A centrifugal fan is known as a blower used for a combustion device or the like (for example, Patent Document 1). The centrifugal fan includes a cylindrical impeller in which a plurality of blade pieces are arranged radially with respect to the rotation shaft, and a scroll casing that houses the impeller. This scroll casing is formed in a cylindrical shape whose radius with respect to the rotation axis of the impeller increases in the rotation direction of the impeller, and a cover plate covering one end side in the axial direction of the rotation shaft has a bell mouth-shaped opening. Is provided. Moreover, the air flow path is extended in the tangential direction from the surrounding surface by the side with the larger radius of a scroll casing. When the impeller is rotated, air blows out from the inner side to the outer side of the impeller, so that the air sucked from the opening can be sent to a combustion device connected to the blower passage.

  When such a centrifugal fan is used, generation of a large noise may be a problem. This noise includes noise generated by the centrifugal fan itself (single noise) and noise caused by resonance in the entire apparatus including the centrifugal fan (resonant sound). Of these, it has been found from experience that resonance can be suppressed by reducing the diameter (opening area) of the opening of the centrifugal fan.

JP 2005-180179 A

  However, when the diameter of the opening of the centrifugal fan is reduced, the single noise of the centrifugal fan tends to increase, and there is a problem that it is difficult to suppress the single noise while suppressing the resonance sound.

  The present invention has been made in response to the above-described problems of conventional techniques, and an object of the present invention is to provide a centrifugal fan that can achieve both suppression of resonance noise and suppression of unit noise.

In order to solve the above-described problems, the centrifugal fan of the present invention employs the following configuration. That is,
An impeller in which a plurality of blade pieces erected from the outer edge portion of the rotating disk are arranged radially with respect to the rotating shaft, the impeller is accommodated therein, and the radius with respect to the rotating shaft is the rotation of the impeller A scroll casing formed in a cylindrical shape that increases in the direction, a cover plate that covers one end side in the axial direction of the rotary shaft of the scroll casing, and is provided with a bellmouth-shaped first opening; An air passage extending in a tangential direction from a peripheral surface having a larger radius with respect to the rotating shaft, and rotating the impeller to send air to a casing of a combustion apparatus connected to the air passage In centrifugal fans,
On the side of the lid plate opposite to the scroll casing, a guide plate having a bell mouth-shaped second opening that is located inside the first opening and guides air to the inside of the impeller, the lid The plate is provided with a gap for bringing the pressure between the second opening and the blade piece close to the pressure outside the scroll casing ,
The area of the gap is set in a range of 3% to 15% with respect to the opening area of the second opening.

As described above, it is known that in the centrifugal fan, if the diameter of the opening is reduced, the resonance noise can be suppressed, but the single noise increases. Here, the reason why single noise is generated is considered as follows. First, the basic flow of air due to the rotation of the impeller is such that the air that has entered the inside of the impeller through the opening travels in the axial direction of the rotation axis of the impeller and passes between the blade pieces. And blow out outward. However, in the vicinity of the tongue (the connection portion between the peripheral surface of the scroll casing having a smaller radius and the air passage), the air flow is blocked and the pressure increases, so that the air flows backward from the outside to the inside of the impeller. Is likely to occur. Also, on the tip side of the bell mouth shaped opening (inside the impeller), the opening area is reduced and the flow velocity of the air passing therethrough increases, so the portion where the pressure decreases (negative pressure generating portion) This occurs between the tip and the impeller blades, which increases the backflow of air. Then, this reverse flow disturbs the basic flow, and unit noise is generated. Therefore, in the centrifugal fan of the present invention, a predetermined gap is provided between the lid plate provided with the first opening and the guide plate provided with the second opening. Since this gap serves as a passage for communicating the negative pressure generating portion ( between the second opening and the blade piece ) with the outside of the centrifugal fan (scroll casing) , the negative pressure generating portion can be relieved. it can. As a result, the backflow of air in the vicinity of the tongue is weakened, so that the single unit noise of the centrifugal fan can be suppressed even if the opening area of the second opening is reduced so that no resonance noise is generated. .

  And, in the centrifugal fan of the present invention, if the area of the gap is too small (less than 3% with respect to the opening area of the second opening), the negative pressure in the negative pressure generating portion is not sufficiently relaxed, Since the single unit noise of the centrifugal fan tends to increase suddenly, it is effective to set the gap area to 3% or more with respect to the opening area of the second opening. Further, when the area of the gap is increased, it is the same as that of the second opening and the resonance sound generated by the entire apparatus including the centrifugal fan is deteriorated. The area of the gap is preferably set to 15% or less. As described above, it is not only necessary to provide a gap between the cover plate and the guide plate, and the area of the gap should be limited to a range of 3% to 15% with respect to the opening area of the second opening. For the first time, it is possible to achieve both the suppression of the single unit noise of the centrifugal fan and the suppression of the resonance sound of the entire apparatus including the centrifugal fan.

  The “area of the gap” in the present invention refers to the minimum area of the cross-sectional area as a passage where the gap communicates between the negative pressure generating portion in the centrifugal fan and the outside of the centrifugal fan.

In the centrifugal fan of the present invention described above, the gap may be provided only in a predetermined region on the tongue side instead of the entire circumference of the second opening .

  As described above, since air tends to flow backward in the vicinity of the tongue portion, by providing a gap at least on the tongue portion side around the second opening portion to relieve the negative pressure in the negative pressure generating portion, It becomes possible to weaken the backflow and suppress the noise of the centrifugal fan. Further, in order to suppress the resonance sound of the entire apparatus including the centrifugal fan, it is advantageous to reduce the area of the gap. Therefore, by limiting the area where the gap is provided, the noise of the centrifugal fan is suppressed. Therefore, it is possible to prevent the deterioration of the resonance sound while ensuring a gap for the purpose.

It is the perspective view which showed the state which decomposed | disassembled the centrifugal fan 10 of a present Example. It is explanatory drawing which showed a mode that the centrifugal fan 10 rotated the impeller 20 and sent out a wind. It is explanatory drawing which showed the backflow of the air produced in the vicinity of the tongue part 50c. 4 is a graph showing the relationship between the ratio of the area of the gap G to the opening area of the suction port 72 and the noise value measured for the combustion device provided with the centrifugal fan 10. 4 is a graph showing the relationship between the ratio of the area of the gap G to the opening area of the suction port 72 and the ease with which resonance noise is generated in the combustion apparatus provided with the centrifugal fan 10. It is explanatory drawing which showed the centrifugal fan 10 of the modification.

  FIG. 1 is a perspective view showing a state in which the centrifugal fan 10 of this embodiment is disassembled. The centrifugal fan 10 is connected to a combustion device (not shown) incorporating a burner, for example, and is used to send combustion air to the burner. As illustrated, the centrifugal fan 10 includes an impeller 20 that generates wind by rotating, a drive motor 30 that rotates the impeller 20, a fan case 50 that houses the impeller 20, and the like.

  The impeller 20 of the present embodiment is a so-called sirocco fan, and a plurality of blade pieces 24 that are elongated in the axial direction of the rotary shaft 32 of the drive motor 30 are arranged radially at predetermined intervals with respect to the rotary shaft 32. It has a cylindrical shape. One end (the lower end in the figure) of these wing pieces 24 is attached to the outer edge portion of the substantially circular rotating disk 22, and the other end (the upper end in the figure) of the wing piece 24 is attached to the annular support plate 26. It is attached. The rotary disc 22 is fixed to the rotary shaft 32 of the drive motor 30 at the center, and the impeller 20 rotates around the rotary shaft 32 by the drive of the drive motor 30.

  The fan case 50 includes a substrate 52 that is fixed to the main body of the drive motor 30, a peripheral wall plate 54 that is curved so as to surround the outer periphery of the impeller 20, and a cover plate that faces the substrate 52 via the peripheral wall plate 54. 56 is joined. The lid plate 56 is provided with a bell mouth shaped opening 58 with the inside facing the inside of the fan case 50. The center of the opening 58 is collinear with the rotating shaft 32, and the inner diameter of the opening 58 is smaller than the inner diameter of the impeller 20. The opening 58 in this embodiment corresponds to the “first opening” in the present invention.

  Further, a guide plate 70 provided with a bell mouth-shaped suction port 72 that guides air to the inside of the impeller 20 is attached to the outside (upper surface side in the drawing) of the cover plate 56 of the fan case 50. Since the center of the suction port 72 is collinear with the rotation shaft 32 and the inner diameter of the suction port 72 is smaller than the inner diameter of the opening 58, the suction port 72 is located inside the opening 58. The guide plate 70 of the present embodiment is provided with three convex portions 74 projecting toward the lid plate 56 side (downward in the figure), avoiding the same straight line. When the guide plate 70 is overlaid on the cover plate 56, the tips of the convex portions 74 abut against the cover plate 56, so that a predetermined gap G is provided between the cover plate 56 and the guide plate 70. It is fixed using a set screw 76. The role of the gap G will be described in detail later. Moreover, the suction inlet 72 of a present Example is corresponded to the "2nd opening part" of this invention.

  FIG. 2 is an explanatory view showing a state in which the centrifugal fan 10 rotates the impeller 20 to send out wind. FIG. 2 shows a cross-sectional view of the centrifugal fan 10 cut along a plane perpendicular to the rotation shaft 32 of the drive motor 30. First, as shown in the figure, the fan case 50 (peripheral wall plate 54) includes a scroll casing 50a surrounding the impeller 20 and a blower passage 50b connected to a combustion device or the like through which the centrifugal fan 10 sends air. . The scroll casing 50 a is formed in a cylindrical shape whose radius increases with respect to the rotation shaft 32 of the drive motor 30 in the rotation direction of the impeller 20 (counterclockwise in the illustrated example). An air passage 50b having a rectangular cross section extends from the peripheral surface of the scroll casing 50a on the larger radius side in a tangential direction, and a discharge port 60 is provided at the end of the air passage 50b.

  The plurality of blade pieces 24 of the impeller 20 are provided with the outer peripheral side curved in the rotation direction of the impeller 20. When the impeller 20 is rotated by driving the drive motor 30, a flow of air from the inside to the outside of the impeller 20 is generated by centrifugal force, and air taken in from the suction port 72 blows out between the plurality of blade pieces 24. In FIG. 2, the air flow in the centrifugal fan 10 is indicated by a one-dot chain line arrow. The blown air advances while rotating along the inner surface of the scroll casing 50a of the fan case 50 (peripheral wall plate 54), and is discharged from the discharge port 60 through the air passage 50b.

  However, in the vicinity of the connection portion (tongue portion) 50c between the peripheral surface of the scroll casing 50a on the side having the smaller radius and the air passage 50b, a backflow of air from the outside to the inside of the impeller 20 occurs.

  FIG. 3 is an explanatory view showing the backflow of air generated in the vicinity of the tongue 50c. FIG. 3 shows a cross-sectional view of the centrifugal fan 10 taken along a plane that includes the rotating shaft 32 of the drive motor 30 and faces the tongue 50c. The arrow of the dashed-dotted line in the figure has shown the flow of the air in the centrifugal fan 10. FIG. First, in the vicinity of the tongue 50c, the air flow generated by the rotation of the impeller 20 collides with the tongue 50c without being discharged from the discharge port 60, thereby increasing the pressure.

  Next, the basic flow of air in the fan case 50 will be described. The tip of the bell mouth-shaped suction port 72 provided on the guide plate 70 is closer to the back side (rotary disc 22 side) of the impeller 20 than the tip of the bell mouth-shaped opening 58 provided on the lid plate 56. The air that has entered and is guided to the inside of the impeller 20 by the suction port 72 flows toward the back side in the axial direction of the rotating shaft 32. Therefore, the air is blown out of the impeller 20 through the plurality of blade pieces 24 mainly from the portion on the rotating disk 22 side (lower side in the drawing) from the center of the blade pieces 24. . On the other hand, the backflow in the tongue portion 50c mainly occurs on the cover plate 56 side (upper side in the drawing) from the center of the blade piece 24. In particular, between the cover plate 56 and the support plate 26 of the impeller 20, air is not easily pushed back by the blade piece 24 of the rotating impeller 20, so that air easily flows from the outside to the inside of the impeller 20.

  Further, at the tip side of the bell mouth-shaped suction port 72 (inside the fan case 50), the opening area is reduced, so that the flow velocity of the air passing therethrough increases, and the portion where the pressure decreases due to the venturi effect (negative pressure) (Generated portion) occurs between the tip of the suction port 72 and the blade piece 24 of the impeller 20. By reducing the pressure at the negative pressure generating portion, the backflow of air at the tongue 50c is strengthened. Such a backflow of air disturbs the basic flow of air generated by the rotation of the impeller 20, thereby generating noise.

  Therefore, in the centrifugal fan 10 of this embodiment, the predetermined gap G is provided between the cover plate 56 and the guide plate 70 of the fan case 50 as described above. The gap G serves as a passage for communicating a negative pressure generating portion generated between the tip of the bell mouth-shaped suction port 72 and the blade piece 24 of the impeller 20 to the outside of the fan case 50. The negative pressure can be relieved to approach the pressure outside the fan case 50. Thereby, since the backflow of the air generated in the vicinity of the tongue portion 50c is weakened, it is possible to suppress the noise (unit noise) generated by the centrifugal fan 10.

  In addition, the guide plate 70 of the present embodiment is provided with the convex portions 74 at three locations avoiding the same straight line, and the tips of the convex portions 74 abut against the lid plate 56, thereby A predetermined gap G can be secured between the guide plate 70 and the guide plate 70. Since the plane passing through the three points that are not on the same straight line is fixed to one, the guide plate 70 can be stabilized with respect to the cover plate 56. As a result, the vibration sound due to the rattling of the guide plate 70 can be reduced. Occurrence can be prevented.

  Further, by forming a resonator with a casing such as a combustion device to which the centrifugal fan 10 is connected, a resonance sound may be emitted from the entire device including the centrifugal fan 10 to generate noise. Such resonance noise is likely to occur when the opening area of the suction port 72 through which air flows into the inside of the impeller 20 of the centrifugal fan 10 is increased. In the centrifugal fan 10 according to the present embodiment, even if the opening area of the suction port 72 is reduced so as not to generate a resonance sound, the predetermined gap G is provided between the lid plate 56 and the guide plate 70, whereby the centrifugal fan 10 is centrifuged. It is possible to suppress noise generated by the fan 10. The gap G in the present embodiment is not intended to increase the opening area through which air flows, but is intended to alleviate the negative pressure at the negative pressure generating portion. Therefore, it is only necessary to relieve the negative pressure, and it is not necessary to increase the area of the gap G to the extent that the resonance noise is deteriorated. Note that the area of the gap G refers to the area of the outer periphery of the opening 58 where the height of the gap G is minimized when the gap G is provided around the entire circumference of the bell mouth shaped opening 58 as in this embodiment. The minimum area obtained by multiplying the length by the height of the gap G shall be said. Further, when the gap G is provided in a part of the outer periphery of the bell mouth shaped opening 58, the arc length of the portion of the outer periphery of the opening 58 provided with the gap G is multiplied by the height of the gap G. It shall be the minimum area.

  FIG. 4 is a graph showing the relationship between the ratio of the area of the gap G to the opening area of the suction port 72 and the noise value measured for the combustion device provided with the centrifugal fan 10. As shown in the figure, when the area of the gap G provided between the cover plate 56 and the guide plate 70 is increased with respect to the opening area of the suction port 72, the noise value decreases. This is because the negative pressure generating portion in the fan case 50 (the portion between the tip of the suction port 72 and the blade piece 24 of the impeller 20) communicates with the outside of the fan case 50 to increase the negative area G. It is considered that the generation of noise of the centrifugal fan 10 is suppressed because the negative pressure in the pressure generation portion is reduced and the backflow of air near the tongue portion 50c is weakened.

  However, if the area of the gap G is too small (less than 3% with respect to the opening area of the suction port 72), it is sufficient as a passage for communicating the negative pressure generating portion in the fan case 50 and the outside of the fan case 50. It does not function and the noise level tends to increase rapidly. Therefore, in order to suppress the noise of the centrifugal fan 10, it is effective to set the ratio of the area of the gap G to 3% or more with respect to the opening area of the suction port 72.

  FIG. 5 is a graph showing the relationship between the ratio of the area of the gap G to the opening area of the suction port 72 and the ease with which the resonance sound is generated in the combustion apparatus including the centrifugal fan 10. In a combustion apparatus that burns a mixed gas of fuel gas and combustion air with a burner, it is necessary to mix the fuel gas and the combustion air at an appropriate ratio (air-fuel ratio) in order to properly burn the mixed gas. . When the supply amount of fuel gas (gas supply amount) becomes larger than the gas supply amount (reference value) at an appropriate air-fuel ratio (the supply amount of combustion air is small relative to the appropriate air-fuel ratio), Resonance noise tends to occur. FIG. 5 shows the result of obtaining the rate of change at the point of time when the resonance is generated (generation limit) by increasing the gas supply amount from the reference value (rate of change 0%), with the area of the gap G being different. Has been. The curve in FIG. 5 represents the generation limit of the resonance sound. The resonance sound is not generated in the lower left part of the curve, and the resonance sound is generated in the upper right part of the curve.

  As shown in FIG. 5, when the ratio of the area of the gap G to the opening area of the suction port 72 is small (less than 3%), resonance occurs until the gas supply amount increases by 10% with respect to the reference value. There is no sound. However, when the ratio of the area of the gap G is increased, resonance sound is easily generated in the same manner as the opening area of the suction port 72 is increased, and the change rate of the gas supply amount until the resonance sound generation limit is reduced ( The allowable range of the gas supply amount that does not generate resonance noise is narrowed). When the area of the gap G exceeds 20% with respect to the opening area of the suction port 72, a resonance noise is generated even if the gas supply amount is the reference value (even if the air / fuel ratio is appropriate). For this reason, the area of the gap G is preferably small in order to suppress the resonance noise.

  In particular, before the combustion device is shipped, the gas supply amount is adjusted so as to obtain an appropriate air-fuel ratio (reference value), but an error of about 5% may occur. Therefore, it is necessary to secure a margin of 5% as a change rate of the gas supply amount up to the resonance sound generation limit with respect to the reference value so that no resonance sound is generated even if there is such an error. Therefore, as shown in FIG. 5, if the ratio of the area of the gap G to the opening area of the suction port 72 is set to 15% or less, the change rate of the gas supply amount up to the resonance sound generation limit is 5%. %, Which is effective for suppressing the resonance noise of the combustion apparatus including the centrifugal fan 10.

  As is clear from the above description, the gap G is not simply provided between the lid plate 56 and the guide plate 70, and the area of the gap G is reduced from 3% to the opening area of the suction port 72. For the first time, it is possible to achieve both suppression of noise generated by the centrifugal fan 10 and suppression of resonance noise generated by the entire apparatus such as a combustion apparatus including the centrifugal fan 10 by limiting to the range of 15%.

  The centrifugal fan 10 of the present embodiment described above includes the following modifications. In the following, modifications will be described focusing on differences from the above-described embodiment.

  FIG. 6 is an explanatory diagram showing a modified centrifugal fan 10. First, FIG. 6A shows a plan view of the modified centrifugal fan 10 as viewed from the inlet 72 side. In the above-described embodiment, the predetermined gap G between the cover plate 56 and the guide plate 70 is provided so as to surround the suction port 72. On the other hand, in the centrifugal fan 10 of the modified example, as shown by hatching in FIG. 6A, the region where the gap G is provided around the suction port 72 is the one on the tongue 50c side. It is limited to the part area.

  FIG. 6B shows a perspective view of the modified guide plate 70 separated from the cover plate 56. The guide plate 70 of the modified example is not provided with the convex portion 74 of the above-described embodiment, and instead, the raised portion 78 raised on the side opposite to the lid plate 56 is at a position corresponding to the tongue portion 50c. Is provided. When the guide plate 70 is overlapped with the lid plate 56, portions other than the raised portions 78 of the guide plate 70 are in close contact with the lid plate 56, and a gap G is provided between the raised portion 78 and the lid plate 56.

  As described above, in the vicinity of the tongue portion 50c, the pressure on the outside of the impeller 20 is high and the pressure on the inside is low, and air backflow tends to occur. Therefore, by providing a gap G at least on the tongue 50c side around the suction port 72 to relieve the negative pressure, the backflow of air near the tongue 50c can be weakened. As a result, the centrifugal fan 10 is Noise generated can be suppressed. Further, in order to suppress the resonance noise generated by the entire apparatus such as the combustion apparatus including the centrifugal fan 10, it is advantageous to reduce the area of the gap G. Therefore, by limiting the region in which the gap G is provided, it is possible to prevent the deterioration of the resonance sound while securing the gap G for suppressing the noise of the centrifugal fan 10.

  The centrifugal fan 10 of this embodiment and the modification has been described above, but the present invention is not limited to the above-described embodiment and modification, and can be implemented in various modes without departing from the scope of the invention. Is possible.

10 ... Centrifugal fan, 20 ... Impeller, 22 ... Rotating disc,
24 ... Wings, 26 ... Support plate, 30 ... Drive motor,
32 ... Rotating shaft, 50 ... Fan case, 50a ... Scroll casing,
50b ... Air blow path, 50c ... Tongue part, 52 ... Substrate,
54 ... peripheral wall plate, 56 ... lid plate, 58 ... opening,
60 ... discharge port, 70 ... guide plate, 72 ... suction port,
74 ... convex part, 76 ... set screw.

Claims (2)

An impeller in which a plurality of blade pieces erected from the outer edge portion of the rotating disk are arranged radially with respect to the rotating shaft, the impeller is accommodated therein, and the radius with respect to the rotating shaft is the rotation of the impeller A scroll casing formed in a cylindrical shape that increases in the direction, a cover plate that covers one end side in the axial direction of the rotary shaft of the scroll casing, and is provided with a bellmouth-shaped first opening; An air passage extending in a tangential direction from a peripheral surface having a larger radius with respect to the rotating shaft, and rotating the impeller to send air to a casing of a combustion apparatus connected to the air passage In centrifugal fans,
On the side of the lid plate opposite to the scroll casing, a guide plate having a bell mouth-shaped second opening that is located inside the first opening and guides air to the inside of the impeller, the lid The plate is provided with a gap for bringing the pressure between the second opening and the blade piece close to the pressure outside the scroll casing ,
An area of the gap is set in a range of 3% to 15% with respect to an opening area of the second opening. The centrifugal fan according to claim 1, wherein
The scroll casing has a tongue portion that is a portion connecting a peripheral surface on a side having a small radius with respect to the rotation shaft and the air passage,
The gap is the not the entire periphery of the second opening, a centrifugal fan, characterized in that provided in limited to a predetermined area of the tongue side.

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