MULTIBLADE CENTRIFUGAL FAN

Abstract

 At least one of a negative pressure side connection surface 5d and a positive pressure side connection surface 5e is configured such that an angle formed by a line connecting a first negative pressure side connection part with a second negative pressure side connection part and a substantially center line in a cross-sectional view in which the blade 5 is cut in a center axis direction of an impeller 1 at an arbitrary position, or an angle formed by a line connecting a first positive pressure side connection part with a second positive pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position becomes smaller than 90°.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The present invention relates to a sirocco fan which is a multiblade centrifugal fan used in an air conditioner or the like for example.

Description of the Related Art

[0002] Conventionally, a multiblade centrifugal fan of this kind includes a scroll casing 101 and an impeller 102, as illustrated in FIG. 10, FIG. 11 and FIG. 12 (for example, see Japanese Patent No. 4736748).

[0003] The multiblade centrifugal fan includes a scroll casing 101 including an air outlet 103 and a bellmouth 104 serving as an air inlet; and a multiblade centrifugal impeller 102 disposed inside the scroll casing 101, including many blades 107 annularly arranged from a main plate 106 integrated with a bearing 105, and blowing off air sucked from an inlet 108 formed at an end in a rotation axis direction facing the bellmouth 104 into a centrifugal direction from between the blades 107 (W in the figure). A holding ring 109 for holding the blades 107 is provided on an axial end part on an outer periphery of the impeller 102, and on an axial outer end of the holding ring 109, a cylindrical body 110 is integrally extended so as to reach substantially the same position as an exit side end edge 104a of the bellmouth 104 or a position to mutually overlap with the exit side end edge 104a, and an outer peripheral surface of the cylindrical body 110 is extended in a circular arc shape so that a diameter of the outer peripheral surface is gradually enlarged from the outer peripheral surface at the axial outer end of the holding ring 109. Thus, a circulating flow W' in which part of an air flow blown off in the centrifugal direction from the impeller 102 passes through a gap between the bellmouth 104 and the cylindrical body 110 and is sucked again from the inlet 108 is suppressed, and noise due to the circulating flow W' can be reduced.

[0004] However, in the conventional configuration, an axial end part 107a of the blade 107 is a roughly flat shape as illustrated in FIG. 12, and there is a problem that, when the circulating flow W' flows in from the axial end part of the blade 107 and returns between the blades 107, the air flow separates at a corner of the axial end part of the blade 107 and noise increases.

SUMMARY OF THE INVENTION

[0005] In order to solve the conventional problem, a multiblade centrifugal fan of the present invention is configured such that, in the multiblade centrifugal fan including: an impeller including a main plate, a plurality of blades disposed on an outer periphery of the main plate radially with respect to a center axis of the main plate, and a holding ring to fix an outer periphery of the plurality of blades on a side opposite to a part where the blades and the main plate are joined; and a scroll casing disposed to surround the impeller, the scroll casing including an air outlet, and a bellmouth serving as an air inlet, each of the blades is stretched in a direction from the main plate to the holding ring and includes a suction surface having a negative pressure when the impeller is rotated, a pressure surface having a positive pressure when the impeller is rotated, a blade side part being an axial end part of the impeller, at least one negative pressure side connection surface configured between the suction surface and the blade side part, and at least one positive pressure side connection surface configured between the pressure surface and the blade side part, and an angle formed by either one of a line connecting a first negative pressure side connection part with a second negative pressure side connection part and a line connecting a first positive pressure side connection part with a second positive pressure side connection part, and a substantially center line in a cross-sectional view in which the blade is cut in a center axis direction of the impeller at an arbitrary position is smaller than 90°, the first negative pressure side connection part being a connection part of the blade side part and the negative pressure side connection surface, the second negative pressure side connection part being a connection part of the suction surface and the negative pressure side connection surface, the first positive pressure side connection part being a connection part of the blade side part and the positive pressure side connection surface, the second positive pressure side connection part being a connection part of the pressure surface and the positive pressure side connection surface.

[0006] Thus, since the angle formed by either one of the line connecting the first negative pressure side connection part with the second negative pressure side connection part and the line connecting the first positive pressure side connection part with the second positive pressure side connection part, and the substantially center line in the cross-sectional view in which the blade is cut in the center axis direction of the impeller at an arbitrary position is smaller than 90°, the connection part is formed at an obtuse angle compared to a roughly right-angled square shape, and separation of an air flow colliding with the blade side part is reduced. Thus, the air flow which collides with the blade side part and separates sticks again to the connection surface and flows into the suction surface and the pressure surface along the negative pressure side connection surface or the positive pressure side connection surface.

[0007]  The multiblade centrifugal fan of the present invention suppresses a disturbance of a circulating flow in which part of the air flow blown off in the centrifugal direction from the impeller passes through a gap between the bellmouth and the holding ring and is sucked again from the blade side part to between the blades, and noise due to the circulating flow can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] 

FIG. 1 is a perspective view of a multiblade centrifugal fan in a first embodiment of the present invention;

FIG. 2 is an A-A' sectional view of the multiblade centrifugal fan in the first embodiment of the present invention;

FIG. 3 is a B-B' sectional view of the multiblade centrifugal fan in the first embodiment of the present invention;

FIG. 4 is a perspective view of an impeller of the multiblade centrifugal fan in the first embodiment of the present invention;

FIG. 5 is a perspective view of a blade of the multiblade centrifugal fan in the first embodiment of the present invention;

FIG. 6 is a C-C' sectional view of the blade in the first embodiment of the present invention;

FIG. 7(A) is a C-C' sectional view of the blade in the first embodiment of the present invention;

FIG. 7(B) is a D-D' sectional view of the blade in the first embodiment of the present invention;

FIG. 8 is a diagram of a polygonal shape of a cross section of the blade in the first embodiment of the present invention;

FIG. 9 is a perspective view of a connection part of the blade and a holding ring in the first embodiment of the present invention;

FIG. 10 is a horizontal sectional view at an axial center of a conventional multiblade centrifugal fan;

FIG. 11 is a perspective view of the blade of the conventional multiblade centrifugal fan; and

FIG. 12 is an X-X' sectional view of the blade of the conventional multiblade centrifugal fan.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0009] A first invention is configured such that, in the multiblade centrifugal fan including: an impeller including a main plate, a plurality of blades disposed on an outer periphery of the main plate radially with respect to a center axis of the main plate, and a holding ring to fix an outer periphery of the plurality of blades on a side opposite to a part where the blades and the main plate are joined; and a scroll casing disposed to surround the impeller, the scroll casing including an air outlet, and a bellmouth serving as an air inlet, each of the blades is stretched in a direction from the main plate to the holding ring and includes a suction surface having a negative pressure when the impeller is rotated, a pressure surface having a positive pressure when the impeller is rotated, a blade side part being an axial end part of the impeller, at least one negative pressure side connection surface configured between the suction surface and the blade side part, and at least one positive pressure side connection surface configured between the pressure surface and the blade side part, and an angle formed by either one of a line connecting a first negative pressure side connection part with a second negative pressure side connection part and a line connecting a first positive pressure side connection part with a second positive pressure side connection part, and a substantially center line in a cross-sectional view in which the blade is cut in a center axis direction of the impeller at an arbitrary position is smaller than 90°, the first negative pressure side connection part being a connection part of the blade side part and the negative pressure side connection surface, the second negative pressure side connection part being a connection part of the suction surface and the negative pressure side connection surface, the first positive pressure side connection part being a connection part of the blade side part and the positive pressure side connection surface, the second positive pressure side connection part being a connection part of the pressure surface and the positive pressure side connection surface.

[0010] Thus, since the angle formed by either one of the line connecting the first negative pressure side connection part with the second negative pressure side connection part and the line connecting the first positive pressure side connection part with the second positive pressure side connection part, and the substantially center line in the cross-sectional view in which the blade is cut in the center axis direction of the impeller at an arbitrary position is smaller than 90°, the connection part is formed at an obtuse angle compared to a roughly right-angled square shape, and separation of an air flow colliding with the blade side part is reduced. Thus, the air flow which collides with the blade side part and separates sticks again to the connection surface and flows into the suction surface and the pressure surface along the negative pressure side connection surface or the positive pressure side connection surface.

[0011] Therefore, a disturbance of a circulating flow in which part of the air flow blown off in the centrifugal direction from the impeller passes through a gap between the bellmouth and the holding ring and is sucked again from the blade side part to between the blades is suppressed, and noise due to the circulating flow can be reduced.

[0012]  A second invention is that at least one of the negative pressure side connection surface and the positive pressure side connection surface is in an arc shape in the cross-sectional view in which the blade is cut in the center axis direction of the impeller at the arbitrary position.

[0013] Thus, by making at least one of the negative pressure side connection surface and the positive pressure side connection surface be in the arc shape in the cross-sectional view in which the blade is cut in the center axis direction of the impeller at the arbitrary position, the separation of the air flow colliding with the blade side part is reduced, compared to a polygon with sides. In addition, generally, when a speed of the air flow is low, the separation of the air flow increases.

[0014] Thus, even in a case where a difference from a pressure of a space between the bellmouth and the holding ring is relatively small and the speed of the circulating flow is low, the air flow which collides with the blade side part and separates sticks again to the connection surface in the arc shape and flows into the suction surface and the pressure surface along the negative pressure side connection surface or the positive pressure side connection surface.

[0015] Therefore, even during a low-load operation in which a speed of the impeller is low and the circulating flow becomes relatively slow, the disturbance is suppressed, and the noise due to the circulating flow can be reduced.

[0016] A third invention is that, for the arc shape of the negative pressure side connection surface or the positive pressure side connection surface, a curvature is reduced from an inner periphery of the impeller to the outer periphery.

[0017]  Generally, when the curvature of the arc shape is large, the separation when the air flow collides becomes small. Thus, even in the case where a difference between the pressure of the air between the bellmouth and the holding ring and the pressure of the air between the blades on an inner peripheral side of the impeller is relatively small and the speed of the circulating flow becomes low, the separation of the air flow which collides with the blade side part on the inner periphery of the impeller is reduced, and the air flow sticks again to the connection surface in the arc shape, and flows into the suction surface and the pressure surface along the connection surface.

[0018] Therefore, even during a silent operation in which the rotation of the impeller becomes minimum and the circulating flow becomes slow, the separation of the air flow on the connection surface on the impeller inner peripheral side is suppressed, and the noise due to the circulating flow can be reduced.

[0019] Hereinafter, the embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited by the embodiment.

(Embodiment 1)

[0020] FIG. 1 illustrates a perspective view of the multiblade centrifugal fan in a first embodiment of the present invention. In addition, FIG. 2 illustrates an A-A' cross section of the multiblade centrifugal fan in the first embodiment of the present invention. FIG. 3 illustrates a B-B' cross section of the multiblade centrifugal fan in the first embodiment of the present invention. FIG. 4 illustrates a perspective view of the impeller of the multiblade centrifugal fan in the first embodiment of the present invention. In FIG. 1 to FIG. 4, the multiblade centrifugal fan includes an impeller 1 and a scroll casing 2.

[0021] The impeller 1 includes a main plate 3, a bearing 4 disposed at a substantially center of the main plate 3 and integrated with the main plate 3, a plurality of blades 5 disposed on the outer periphery of the main plate 3 radially with respect to the center axis of the main plate 3 so as to be tilted forward to a rotation direction M, and a holding ring 6 which fixes the outer periphery of the plurality of blades 5 on a side opposite to a part where the blades 5 and the main plate 3 are joined. To the bearing 4, a rotating shaft of a fan motor (not illustrated) is pivoted.

[0022] The scroll casing 2 includes an air outlet 7, a bellmouth 8 serving as an air inlet, and a tongue part 9 in a circular arc shape disposed at a position at which a gap between the outer periphery of the impeller 1 and the inner periphery of the scroll casing 2 is minimum.

[0023] FIG. 5 illustrates a perspective view of the blade of the multiblade centrifugal fan in the first embodiment of the present invention. In addition, FIG. 6 illustrates a C-C' cross section of the blade in the first embodiment of the present invention.

[0024] In FIG. 5, the blade 5 is stretched in an axial direction between the main plate 3 and the holding ring 6, and includes: a suction surface 5a where the pressure of the air becomes low in the case where the impeller 1 is rotated in a rotating direction M; a pressure surface 5b where the pressure of the air becomes high in the case that the impeller 1 is rotated in the rotating direction M; a blade side part 5c to be an axial end part of the impeller 1; a negative pressure side connection surface 5d including the suction surface 5a and the blade side part 5c; a positive pressure side connection surface 5e including the pressure surface 5b and the blade side part 5c; a first negative pressure side connection part 5f to be a connection part of the blade side part 5c and the negative pressure side connection surface 5d: a second negative pressure side connection part 5g to be a connection part of the suction surface 5a and the negative pressure side connection surface 5d; a first positive pressure side connection part 5h to be a connection part of the blade side part 5c and the positive pressure side connection surface 5e; and a second positive pressure side connection part 5i to be a connection part of the pressure surface 5b and the positive pressure side connection surface 5e.

[0025] In addition, in FIG. 6, the negative pressure side connection surface 5d and the positive pressure side connection surface 5e are formed in the arc shape on a C-C' cross section such that an angle formed by a line connecting the first negative pressure side connection part with the second negative pressure side connection part and the substantially center line in the C-C' cross-sectional view, and an angle formed by a line connecting the first positive pressure side connection part with the second positive pressure side connection part and the substantially center line in the C-C' cross-sectional view become smaller than 90°.

[0026] For the multiblade centrifugal fan configured as described above, the operation and the function will be described hereinafter. First, as illustrated in FIG. 2, by rotation of the impeller 1 in the rotating direction M, air W between the plurality of blades 5 is jetted to the outer periphery of the impeller 1 by the blades 5, collides with the inner periphery of the scroll casing 2, then flows along the inner periphery of the scroll casing 2 in the same direction as the rotating direction M, and is blown off from the air outlet 7. Then, the pressure of the air at the inner periphery of the impeller 1 declines, and the air is made to flow from the bellmouth 8 into the impeller 1 by a pressure difference from an atmospheric pressure.

[0027]  The air is blown by the series of flow, and in the multiblade centrifugal fan like the one of the present embodiment in particular, the air jetted to the outer periphery of the impeller 1 at a high speed is converted to the pressure when the speed is lowered as the gap between the impeller 1 and the scroll casing 2 is enlarged from the tongue part 9, and compatibility of a high air volume and a static pressure is realized.

[0028] After the air flow W to be a main flow collides with the inner periphery of the scroll casing 2, a part is attracted to the part where the pressure of the air is low between the blades 5 and a circulating flow W' flowing in from the blade side part 5c is generated. Since the negative pressure side connection surface 5d and the positive pressure side connection surface 5e are configured in the arc shape on the C-C' cross section such that the angle formed by the line connecting the first negative pressure side connection part with the second negative pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position, and the angle formed by the line connecting the first positive pressure side connection part with the second positive pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position become smaller than 90°, the respective connection parts 5f, 5g, 5h and 5i are formed at an obtuse angle compared to a roughly right-angled square shape, and the separation of the air flow colliding with the blade side part 5c is reduced.

[0029] Thus, the air flow which collides with the blade side part 5c and separates sticks again to the negative pressure side connection surface 5d and the positive pressure side connection surface 5e, and flows into the suction surface 5a and the pressure surface 5b along a wall surface as it is.

[0030] As described above, in the present embodiment, since the negative pressure side connection surface 5d and the positive pressure side connection surface 5e are configured in the arc shape such that the angle formed by the line connecting the first negative pressure side connection part with the second negative pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position, and the angle formed by the line connecting the first positive pressure side connection part with the second positive pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position become smaller than 90°, the separation of the air flow colliding with the blade side part 5c is reduced, and the air flow which collides with the blade side part 5c and separates sticks again to the negative pressure side connection surface 5d and the positive pressure side connection surface 5e, and flows into the suction surface 5a and the pressure surface 5b along a wall surface as it is. Therefore, the disturbance of the circulating flow W' in which part of the air flow blown off in the centrifugal direction from the impeller 1 passes through the gap between the bellmouth 8 and the holding ring 6 and is sucked again from the blade side part 5c to between the blades 5 is suppressed, and the noise due to the circulating flow W' can be reduced.

[0031] In addition, FIG. 7 illustrates a comparison diagram of the curvature on the cross section of the blade in the first embodiment of the present invention.

[0032] By making the curvature of the arc shape of the negative pressure side connection surface 5d and the positive pressure side connection surface 5e in the present embodiment smaller on a D-D' cross section corresponding to the outer peripheral side of the blade 5 than on the C-C' cross section corresponding to the inner peripheral side of the blade 5 as illustrated in FIG. 7, even in the case where the difference between the pressure of the air between the bellmouth 8 and the holding ring 6 and the pressure of the air between the blades 5 on the inner peripheral side of the impeller 1 is relatively small and the speed of the circulating flow W' becomes low, the separation of the air flow colliding with the blade side part 5c on the inner peripheral side of the impeller 1 is reduced, and the air flow sticks again to the negative pressure side connection surface 5d and the positive pressure side connection surface 5e in the arc shape, and flows into the suction surface 5a and the pressure surface 5b along the wall surface as it is.

[0033] Therefore, even during the silent operation in which the rotation of the impeller 1 becomes minimum and the circulating flow W' becomes slow, the separation of the air flow on the negative pressure side connection surface 5d and the positive pressure side connection surface 5e on the inner peripheral side of the impeller 1 is suppressed, and the noise due to the circulating flow W' can be reduced.

[0034] In addition, in the present invention, both of the negative pressure side connection surface 5d and the positive pressure side connection surface 5e are formed in the arc shape on the axial cross section of the blade 5 such that the angle formed by the line connecting the first negative pressure side connection part with the second negative pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position, and the angle formed by the line connecting the first positive pressure side connection part with the second positive pressure side connection part and the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position become smaller than 90°; however, a similar effect can be obtained with either one.

[0035] In addition, FIG. 8 illustrates a diagram of a polygonal shape of the cross section of the blade in the first embodiment of the present invention.

[0036] In the present embodiment, shapes of the negative pressure side connection surface 5d and the positive pressure side connection surface 5e are in the arc shape in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position; however, the similar effect can be obtained even in the case of the polygonal shape such as a two-side shape as illustrated in FIG. 8. In the case where the speed of the circulating flow W' is low and the separation of the air flow tends to increase in particular, by making the shape be in the arc shape, the separation of the circulating flow W' on the negative pressure side connection surface 5d and the positive pressure side connection surface 5e can be suppressed to be small and the noise due to the circulating flow W' can be suppressed.

[0037] In addition, FIG. 9 illustrates a perspective view of the connection part of the blade and the holding ring in the first embodiment of the present invention.

[0038] For the connection part of the blade 5 and the holding ring 6 in the present embodiment, by configuring a groove part 10 such that the angle formed with the substantially center line in the cross-sectional view in which the blade 5 is cut in the center axis direction of the impeller 1 at the arbitrary position becomes smaller than 90° for at least either one of the side of the suction surface 5a and the side of the pressure surface 5b, the separation of the circulating flow W' at the connection part of the holding ring 6 and the blade 5 is suppressed, and the noise of the multiblade centrifugal fan can be reduced further.

[0039]  As described above, the multiblade centrifugal fan according to the present invention suppresses the separation at the blade side part of the circulating flow in which part of the air flow jetted from the impeller outer periphery flows in from between the blades, and is applicable for purposes of an air conditioner, an air cleaner, a drier and a car air conditioner or the like.

1

impeller

2

scroll casing

3

main plate

5

blade

5a

suction surface

5b

pressure surface

5c

blade side part

5d

negative pressure side connection surface

5e

positive pressure side connection surface

5f

first negative pressure side connection part

5g

second negative pressure side connection part

5h

first positive pressure side connection part

5i

second positive pressure side connection part

6

holding ring

7

air outlet

8

bellmouth

Claims

1. A multiblade centrifugal fan comprising: an impeller (1) including a main plate (3), a plurality of blades (5) disposed on an outer periphery of the main plate radially with respect to a center axis of the main plate, and a holding ring (6) to fix an outer periphery of the plurality of blades on a side opposite to a part where the blades and the main plate are joined; and a scroll casing disposed to surround the impeller, the scroll casing (2) including an air outlet (7), and a bellmouth (8) serving as an air inlet,
characterized in that each of the blades is stretched in a direction from the main plate to the holding ring and includes a suction surface (5a) having a negative pressure when the impeller is rotated, a pressure surface (5b) having a positive pressure when the impeller is rotated, a blade side part (5c) being an axial end part of the impeller, at least one negative pressure side connection surface (5d) configured between the suction surface and the blade side part, and at least one positive pressure side connection surface (5e) configured between the pressure surface and the blade side part, and
an angle formed by either one of a line connecting a first negative pressure side connection part (5f) with a second negative pressure side connection part (5g) and a line connecting a first positive pressure side connection part (5h) with a second positive pressure side connection part (5i), and a substantially center line in a cross-sectional view in which the blade is cut in a center axis direction of the impeller at an arbitrary position is smaller than 90°, the first negative pressure side connection part being a connection part of the blade side part and the negative pressure side connection surface, the second negative pressure side connection part being a connection part of the suction surface and the negative pressure side connection surface, the first positive pressure side connection part being a connection part of the blade side part and the positive pressure side connection surface, the second positive pressure side connection part being a connection part of the pressure surface and the positive pressure side connection surface.

2. The multiblade centrifugal fan according to claim 1, wherein at least one of the negative pressure side connection surface and the positive pressure side connection surface is in an arc shape in the cross-sectional view in which the blade is cut in the center axis direction of the impeller at the arbitrary position.

3. The multiblade centrifugal fan according to claim 1 or 2, wherein, an arc shape of the negative pressure side connection surface or the positive pressure side connection surface has a curvature reduced from an inner periphery to an outer periphery of the impeller.

Drawing