JP2020016152A - Centrifugal fan - Google Patents

Abstract

To provide a centrifugal fan capable of reducing noise resulting from the inflow of air by devising the shape of an inside wall face of an air suction part of a casing.SOLUTION: A centrifugal fan 100 includes: an impeller 120 including a plurality of vanes 121 arranged in an inside space on the axial center side and in an annular area around the inside space, and adapted to be rotated for exhausting air from the inside space through the plurality of vanes 121 in the centrifugal direction; a spiral casing housing the impeller 120 in a rotatable state; and a suction port 114 provided as an opening at a position facing the inside space of the impeller 120 for guiding air to the inside space of the impeller 120. Inside the suction port 114, there are provided an upstream side region 118a as a first region whose inner diameter is gradually smaller toward the impeller 120, and a downstream side region 118b as a second region which is on the side nearer the impeller 120 than the upstream side region 118a and whose inner diameter is gradually larger toward the impeller 120.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a centrifugal blower with reduced noise.

  BACKGROUND ART Centrifugal blowers are widely used for air blowing, ventilation, cooling, and the like in home appliances, OA equipment, and air conditioners for industrial use and vehicles. There is a demand for a centrifugal blower used in these devices and apparatuses to reduce noise generated from the centrifugal blower.

  In the centrifugal blower described in Patent Literature 1, a momentum adding mechanism 43 that adds momentum so that an airflow flows along a top 413 of the air suction unit 411 is provided in an air suction unit 411 formed in a casing. ing. The momentum adding mechanism 43 is provided on at least a part of the outer wall surface 415 outside the top 413 protruding toward the upstream side of the air flow in the air suction unit 411. As a result, noise is reduced and air blowing efficiency is improved.

  In the centrifugal blower of Patent Literature 1, the diameter of the inner wall surface portion 414 of the air suction portion 411 of the casing 4 gradually decreases from the upstream side of the air flow to the downstream end portion 412, and the downstream side of the air suction portion 411. The side end portion 412 constitutes a portion having the minimum diameter in the inner wall surface portion 414. The outer wall 415 extends from the top 413 of the air suction section 411 protruding upstream of the air flow to the end 415 a of the outer wall 415 outside the top 413 of the air suction section 411. A momentum adding mechanism 43 that adds momentum so that the airflow flows along the top 413 is provided.

  In this structure, the airflow flowing in from the side of the air suction portion 411 is disturbed when going over the protrusion 431 provided in front of the top portion 413, and the airflow having passed over the protrusion 431 causes the airflow after the protrusion 431. A turbulent boundary layer is formed on the surface of the portion 411. In the turbulent boundary layer, the momentum of the airflow away from the surface of the air suction unit 411 is added to the airflow near the surface of the air suction unit 411. For this reason, the speed difference between the airflow near the surface of the air suction unit 411 and the airflow away from the surface of the air suction unit 411 is reduced. Thereby, separation of the airflow near the top 413 of the air suction unit 411 is suppressed, and noise caused by separation of the airflow at the air suction unit 411 can be reduced.

JP-A-2017-125405

  The centrifugal blower described in Patent Literature 1 has a momentum in an outer peripheral range reaching an end 415a of the outer wall portion 415 outside the top 413 so that an airflow from the outer wall portion 415 flows along the top 413. Is provided with a momentum adding mechanism 43 for adding a momentum.

  However, in the centrifugal blower described in Patent Literature 1, the diameter of the inner wall surface 414 of the air suction portion 411 of the casing 4 gradually decreases from the upstream side of the air flow toward the downstream end 412, and The downstream end 412 of the suction portion 411 forms a portion having a minimum diameter on the inner wall surface 414. For this reason, the reduction of noise caused by the inflow of air into the air suction section is not always sufficient.

  An object of the present invention is to provide a centrifugal blower that can reduce noise caused by inflow of air by devising the shape of an inner wall surface of an air suction portion of a casing in view of the above viewpoint.

  The present invention includes an impeller that includes an inner space on the shaft center side and a plurality of blades disposed around the inner space, and that rotates to exhaust air from the inner space in a centrifugal direction through the space between the plurality of blades. A spiral-shaped casing in which the impeller is rotatably housed inside, and a suction port provided in the casing, wherein the suction port is provided at a position facing the inner space of the impeller. An opening, inside the suction port, a first region surface forming a space in which the inner diameter gradually decreases toward the impeller, and a side closer to the impeller than the first region surface. And a centrifugal blower having a second region surface forming a space in which the inner diameter gradually increases toward the impeller.

  In the present invention, when the length of the suction port in the axial direction is L1, and the length of the second region surface in the axial direction is L2, a structure satisfying L2> (1/2) L1 is preferable. In the present invention, when the inside diameter of the space inside the second region surface that is not on the impeller side is R1, and the inside diameter of the space inside the second region surface on the impeller side is R2. , R2 / R1 <1.03 are preferred.

  In the present invention, a structure in which a portion of the second region surface closest to the impeller is located inside the impeller is preferable. In the present invention, a structure in which an annular protrusion extending toward the outside in the axial direction of the casing is provided on the most upstream side of the suction port is preferable. Further, in this structure, a structure in which a step is provided between the first region surface and the annular projection is preferable.

  ADVANTAGE OF THE INVENTION According to this invention, the centrifugal blower which can reduce the noise resulting from inflow of air is obtained by devising the shape of the inner side wall surface of the air suction part of a casing.

FIG. 2 is a perspective view of the centrifugal blower according to the first embodiment. It is sectional drawing of the centrifugal blower of Example 1 shown in FIG. It is the elements on larger scale of FIG. It is sectional drawing of the centrifugal blower of Example 2. It is sectional drawing of the centrifugal blower of the modification of Example 2. It is sectional drawing of the centrifugal blower of a comparative example. FIG. 7 is a diagram illustrating a relationship between a sound pressure level of noise and a frequency in an air volume region A. FIG. 6 is a diagram illustrating a relationship between a sound pressure level of noise and a frequency in an air volume area B; It is a figure which shows the conventional centrifugal fan (patent document 1).

1. Example 1
FIG. 1 is a perspective view of the centrifugal blower 100 according to the first embodiment. FIG. 2 is a sectional view of the centrifugal blower 100 shown in FIG. FIG. 3 is a partially enlarged view of FIG.

(Overview)
The centrifugal blower 100 includes an inner space on the shaft center side and a plurality of blades 121 arranged in an annular portion around the inner space. An impeller 120 that exhausts in the direction, a spiral casing 110 that accommodates the impeller 120 in a rotatable state inside, and an opening provided at a position facing the inner space of the impeller 120. A suction port 114 for introducing air; an upstream area surface 118a (see FIG. 2) surrounding the first area whose inner diameter gradually decreases toward the impeller 120; A downstream region surface 118b is provided on the side closer to the impeller 120 than the region surface 118a and surrounds a second region whose inner diameter gradually increases toward the impeller 120.

(Structure of centrifugal blower)
FIG. 1 shows a blower 100 according to the embodiment. The blower 100 includes a casing 110. The casing 110 includes an upper casing 111 formed of a resin and a lower casing 112 formed of a resin. An impeller 120 having a plurality of blades 121 is rotatably (rotatably) housed inside the casing 110.

  Inside the casing 110, a spiral flow path 113 (see FIG. 2) is formed. The flow channel 113 has a structure in which a portion where a gap between the impeller 120 and the casing 110 is minimum is a starting end, and a cross-sectional area is gradually increased from the portion in the circumferential direction. A discharge port 115 is formed at the end of the channel 113. That is, the spiral flow path 113 has a structure in which the cross-sectional area gradually increases toward the discharge port 115.

  The upper casing 111 has a suction port 114 that opens in the axial direction. Here, the axis is a rotation axis of the impeller 120, and the axial direction is an extending direction thereof. The lower casing 112 is provided with fixing legs (not shown) for attaching and fixing the lower casing 112 to another device or a housing, and a motor 130 (see FIG. 2) for rotating the impeller 120 is attached.

  As shown in FIG. 2, the impeller 120 is fixed to a rotating shaft (shaft 131) of the motor 130, and when the motor 130 rotates, the impeller 120 rotates. When the impeller 120 rotates, air is sucked in from the suction port 114 and guided to the inside of the impeller 120 (the inner space on the shaft center side). This air is blown out of the impeller 120 in the centrifugal direction by the action of the blade 121. The air blown out from the impeller 120 flows through the spiral flow path 113 toward the discharge port 115 in FIG.

(Structure of impeller)
The impeller 120 has a cup-shaped hub 122 forming a bottom surface, a plurality of blades 121 arranged in an axially upright state on an outer annular portion on the hub 122, and a hub 122 opposite to the plurality of blades 121. And an annular connection ring 123 for connecting the ends on the side. The blades 121 are all of the same shape, have forward blade shapes that are concave with respect to the rotation direction of the impeller 120, and are evenly arranged in the circumferential direction. An inner space is provided inside the plurality of blades 121 (on the shaft center side), and when the impeller 120 rotates, air is blown from the inner space through the blades 121 in a centrifugal direction.

  The hub 122 has a boss 124 protruding in the center at the center, and a through hole is formed in the boss 124. The shaft 131 of the motor 130 is press-fitted into the through hole, and the impeller 120 is connected to the shaft 131. The shaft 131 is a rotating shaft of the motor 130, and also serves as a rotating shaft of the impeller 120 by being coupled to the impeller 120. The hub 122, the plurality of blades 121, and the connection ring 123 are integrally formed of resin.

(Casing structure)
As shown in FIG. 1, the casing 110 includes an upper casing 111 and a lower casing 112, and the spiral casing 110 is formed by connecting the upper casing 111 and the lower casing 112. An opening serving as a suction port 114 is formed at the center of the upper casing 111.

  The suction port 114 is an opening provided at a position facing the inside space of the impeller 120 of the casing 110 (the space inside the annularly arranged blades). When the impeller 120 rotates, air is discharged in the centrifugal direction from the inside (the inner space) of the blade 121 through a gap formed between the adjacent blades 121. At this time, air flows into the inside of the blade 121 (inside space) from the suction port 114.

  The suction port 114 is configured using a circular opening portion of the cylindrical portion 116 having a cylindrical structure and a portion inside the cylindrical portion 116. The cylindrical portion 116 has an outer wall 117 and an inner wall 118, and a substantially columnar space surrounded by the inner wall 118, in other words, a space inside the inner wall 118 serves as the suction port 114. The inner wall portion 118 guides the air flowing into the suction port 114 to the inside of the impeller 120.

  The inner wall portion 118 has a shape that is convex toward the inner peripheral side from the upper end to the lower end of the inner wall portion 118. More specifically, on the upper portion (upstream side) of the inner wall portion 118, an upstream region surface 118a in which the inner diameter of the cylindrical portion 116 gradually decreases toward the downstream side is provided. Further, a lower region surface 118b in which the inner diameter of the cylindrical portion 116 gradually increases toward the downstream side is provided at a lower portion (downstream side) of the inner wall portion 118. A boundary portion 119 is provided at a boundary between the upstream region surface 118a and the downstream region surface 118b. At the boundary 119, the inside diameter of the suction port 114 is minimum. That is, the space inside the annular upstream region surface 118a is a first space whose inner diameter gradually decreases as approaching the impeller 120, and the space inside the annular downstream region surface 118b approaches the impeller 120. Becomes a second space in which the inner diameter gradually increases. Then, a boundary portion between the two spaces is a portion surrounded by an annular boundary portion 119.

  The upstream region surface 118a which is on the upstream side from the boundary portion 119 is formed as a curved surface in which the inner diameter of the cylindrical portion 116 gradually decreases from the inlet of the suction port 114 toward the boundary portion 119. The downstream region surface 118b downstream from the boundary portion 119 is formed as an inclined surface (taper surface) in which the inner diameter of the cylindrical portion 116 gradually increases toward the downstream (as approaching the impeller 120). That is, the inside diameter of the suction port 114 gradually decreases from the inlet toward the downstream side, reaches the boundary portion 119 that is the minimum inside diameter part, and gradually increases from the inside toward the downstream side.

  As shown in FIG. 3, an annular convex portion 125 extends from the lower portion of the cylindrical portion 116 in the direction of the impeller 120. The inside of the annular convex portion 125 forms a part of the downstream region surface 118b. The tip of the annular convex portion 125 slightly protrudes inside the impeller 120. For this reason, the lower end of the downstream area surface 118 b slightly enters the inside of the impeller 120. The lower end of the inner wall portion 118 (the tip of the annular convex portion 125) is chamfered.

  The length in the axial direction from the lower end portion (the most downstream portion) of the inner wall portion 118 to the boundary portion 119 with respect to the entire length L1 (length in the axial direction of the inner wall portion 118) of the suction port 114 in the axial direction. It is preferable that the upper end of the portion L2 is located upstream of the midpoint of the total length L1 of the suction port 114. That is, a relationship of L2> (1/2) L1 is preferable. Note that the maximum value of L2 is about L2 = (3/4) L1.

  In addition, the boundary 119 shown in FIG. 3, that is, the lower end (the end on the impeller 120 side) of the downstream region surface 118b with respect to the inner diameter of the suction port 114 (the minimum inner diameter of the suction port 114) R1 at the upper end of the downstream region surface 118b. The ratio of the inner diameter R2 of the suction port 114 is preferably within 103%. That is, it is preferable to satisfy the relationship of R2 / R1 <1.03 (provided that R1 <R2). Note that the minimum value of (R2 / R1) is about 1.015. Here, since R2 is an opening that flows into the impeller 120, when R2 is constant and R1 is varied, if R2 / R1 becomes 1.03 or more, R1 which is the minimum inner diameter of the suction port 114 becomes small. As a result, the flow velocity of the air flowing into the suction port 114 is increased, which results in increased noise, which is not preferable.

  The distal end of the annular convex portion 125 that constitutes the lowermost end of the lower end of the inner wall portion 118 with the rounded surface is located inside the connection ring 123 of the impeller 120, and is connected to the upper surface of the blade 121. They face each other with a slight gap. The small gap forms a labyrinth seal 126, which prevents a part of the flow of air blown to the outer peripheral side of the impeller 120 from flowing back inside the suction port 114.

Devices and devices that use centrifugal blowers have a resistance that impedes the flow of air. This resistance is called system impedance (or also called ventilation resistance). When a centrifugal blower is used in a device having a predetermined system impedance, it can be divided into two air volume regions (in this embodiment, two air volume regions A and B) at a certain point. FIG. 7 is a diagram showing the relationship between the sound pressure level of noise and the frequency in the air volume region A of the first embodiment shown in FIG. Here, the air volume region A is a region where the air volume is 70 to 100 m ³ / h. In FIG. 7, the dashed line shows the characteristics when the air suction unit of the comparative example shown in FIG. 6 is adopted.

  FIG. 6 shows a centrifugal blower 150 having a tapered wall surface 152 whose diameter gradually decreases as the inner diameter of the intake port 151 constituting the air suction part goes downstream (approaches the impeller). From FIG. 7, it is understood that the noise level of Example 1 is reduced in the entire frequency band as compared with the structure of the comparative example shown in FIG. 6.

  Hereinafter, the reason why the noise level is suppressed will be considered. First, the difference in flow velocity in the radial direction inside the suction port 114 is corrected by the presence of the upstream-side area surface 118a. Therefore, separation of the airflow from the inner wall surface 118 is suppressed, and generation of noise is suppressed.

  The structure of the comparative example shown in FIG. 6 has a tapered wall surface 152 whose diameter gradually decreases as the inner diameter of the intake port 151 constituting the air intake section goes downstream (approaching the impeller). The flow velocity of the air flowing into the nozzle 151 is increased, which causes a high noise level when the air is sucked between the blades. On the other hand, in the present embodiment, the diameter gradually increases after passing through the boundary 119 and the cross-sectional area of the flow path increases. The flow velocity of the generated air decreases. For this reason, the level of noise generated when being sucked between the blades is suppressed.

2. Example 2
FIG. 4 shows a sectional view of the second embodiment. In this example, in the structure of the first embodiment shown in FIG. 2, an annular projection 140 that projects in the axial direction is provided at the upper end of the inner wall portion 118 of the suction port 114. By providing the annular projection 140, it is possible to improve the resonance sound generated by the air flowing into the suction port 114.

  Further, as shown in FIG. 5, on the inner peripheral side of the annular protrusion 140 provided at the upper end of the inner wall 118 of the suction port 114, a joint between the annular protrusion 140 and the inner wall 118 is provided. Alternatively, a planar step portion 141 may be formed. Also in this case, it is possible to improve the resonance sound generated by the air flowing into the suction port 114.

FIG. 8 is a diagram showing the relationship between the sound pressure level and the frequency of the noise of the first and second embodiments in the air volume region B. Here, the air volume region B is a case where the air volume is 100 to 140 m ³ / h.

  Referring to FIG. 8, the first embodiment of FIG. 2 shows a large sound pressure level near about 500 Hz. This sound is assumed to be a resonance sound generated by the air flowing into the suction port. On the other hand, in Example 2, the large sound pressure level observed at about 500 Hz disappears, and the noise level is reduced in all frequency bands. Also, it has been confirmed that the same result as that of FIG. 4 can be obtained in the modified example (FIG. 5) of the second embodiment.

100 blower, 110 casing, 111 upper casing, 112 lower casing, 113 flow path, 114 suction port, 115 discharge port, 116 cylindrical part, 117 outer wall part, 118 inner wall part, Reference numeral 118a: upstream region surface, 118b: downstream region surface, 119: boundary portion, 120: impeller, 121: blade, 122: hub, 123: connecting ring, 124: boss portion, 125: annular convex portion, 126 ... Labyrinth seal, 130: motor, 131: shaft, 140: annular projection, 141: stepped portion, 150: centrifugal blower, 151: intake port, 152: wall surface.

Claims (6)

An impeller that includes an inner space on the shaft center side and a plurality of blades disposed around the inner space, and performs exhaust in a centrifugal direction from the inner space by rotating between the plurality of blades,
A spiral casing in which the impeller is rotatably housed inside,
And a suction port provided in the casing,
The suction port is an opening provided at a position facing the inner space of the impeller,
A first region surface inside the suction port, the space defining an inner diameter gradually decreasing toward the impeller;
A centrifugal blower which is closer to the impeller than the first area surface and has a second area surface forming a space whose inner diameter gradually increases toward the impeller. The length of the suction port in the axial direction is L1,
When the length of the second region surface in the axial direction is L2,
The centrifugal blower according to claim 1, wherein L2> (1/2) L1. The inside diameter of the end of the space inside the second area surface that is not on the impeller side is R1,
When the inner diameter of the end portion on the impeller side of the space inside the second region surface is R2,
3. The centrifugal blower according to claim 1, wherein R2 / R1 <1.03.   The centrifugal blower according to any one of claims 1 to 3, wherein a portion of the second area surface closest to the impeller is located inside the impeller.   The centrifugal blower according to any one of claims 1 to 4, wherein an annular protrusion extending toward the outside in the axial direction of the casing is provided on the most upstream side of the suction port. The centrifugal blower according to claim 5, wherein a step is provided between the first area surface and the annular projection.

Images