Centrifugal blowers and ventilation fans

Abstract

A centrifugal blower comprises: a drive motor; an impeller (4) having a main plate (26) that is fixed to a rotating shaft of the drive motor and that rotates, and a plurality of vanes (27) erected in an annular form at intervals on the outer peripheral portion of the main plate (26); and a fan casing that has an intake port facing the main plate (26), and that houses the impeller (4). The main plate (26) is overall inclined so that the distance from the intake port increases from the inner diameter side to the outer diameter side, and the main plate has a horizontal surface portion (114) that is a flat surface perpendicular to the rotation axis at the center in the radial direction. The outer peripheral portion on which the plurality of vanes (27) are erected is inclined such that the distance from the intake port increases from the inner diameter side to the outer diameter side.

Description

[Technical Field]

[0001] The present disclosure relates to a centrifugal blower and a ventilation fan having an impeller. [Background technology]

[0002] Axial-flow impellers and centrifugal impellers are widely used as impellers for ventilation fans. In particular, to ventilate airtight rooms, a high static pressure is required from the blower, so centrifugal blowers using centrifugal impellers are commonly used. Centrifugal blowers are designed to blow out the sucked air in the centrifugal direction of the rotating shaft, so inertial forces act on the suction flow. Therefore, the flow through the impeller forms a velocity distribution biased toward the main plate of the impeller, and the radius of curvature of the flow is small near the blade tip of the impeller, making it difficult for air to flow. Because centrifugal blowers form the velocity distribution described above, inclined and curved surfaces are provided on the main plate of the impeller to facilitate the flow in the radial direction of the impeller.

[0003] Patent Document 1 discloses an impeller having a boss portion, a plurality of blades, and a boss plate as a main plate connecting the boss portion and the plurality of blades. The boss plate is configured with a smoothly curved, almost uniformly inclined surface. Furthermore, the outer periphery of the boss plate, where the plurality of blades are arranged, has a gentler slope than the inclined surface on the inner diameter side. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 3458426 Summary of the Invention [Problem to be solved by the invention]

[0005] In Patent Document 1, the boss plate has a substantially uniformly inclined surface, which increases the airflow velocity inside the impeller, resulting in increased pressure loss, increased noise, and reduced airflow. Furthermore, the boss plate has a substantially uniformly inclined surface, which makes molding difficult. Furthermore, the inclination of the outer periphery of the boss plate is gentler than the inclined surface on the inner diameter side, which makes it difficult for the airflow inside the impeller to flow toward the blade roots, preventing the roots of the impeller blades from functioning properly and reducing airflow.

[0006] The present disclosure has been made in view of the above, and has an object to provide a centrifugal fan that can increase air volume, reduce noise, and is easy to mold. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the centrifugal blower of the present disclosure includes a drive motor, a main plate that rotates while being fixed to the rotary shaft of the drive motor, an impeller having a plurality of blades that are arranged in an annular shape at intervals on the outer periphery of the main plate, and a fan casing that has an intake port facing the main plate and houses the impeller. The main plate is inclined overall so that the distance from the intake port increases from the inner diameter side to the outer diameter side. , complex The outer peripheral portion on which the blades are erected is inclined so that the distance from the suction port increases from the inner diameter side to the outer diameter side. The main plate has a first inclined portion, a second inclined portion, and a third inclined portion from the inner diameter side to the outer diameter side. , a horizontal plane portion that is a plane perpendicular to the rotation axis, and a fourth inclined portion as an outer peripheral portion. and The inclination of the second inclined portion is approximately the same as the inclination of the fourth inclined portion, The inclination of the first inclined portion is greater than the inclination of the third inclined portion. Moreover, the inclination of the third inclined portion is greater than the inclination of the second inclined portion and the inclination of the fourth inclined portion. [Effects of the Invention]

[0008] The centrifugal fan according to the present disclosure has the advantages of being able to increase the air volume, reduce noise, and facilitate molding. [Brief explanation of the drawings]

[0009] [Figure 1]1 is a cross-sectional view showing the configuration of a ventilation fan equipped with a centrifugal blower according to an embodiment; [Figure 2] FIG. 1 is a plan view showing a configuration of a ventilation fan equipped with a centrifugal blower according to an embodiment; [Figure 3] FIG. 1 is a plan view showing a configuration of a ventilation fan equipped with a centrifugal blower according to an embodiment; [Figure 4] FIG. 1 is a perspective view showing a configuration of an impeller of a centrifugal blower according to an embodiment; [Figure 5] 1 is a top view showing the configuration of an impeller of a centrifugal blower according to an embodiment; [Figure 6] 1 is a cross-sectional view showing the configuration of an impeller of a centrifugal blower according to an embodiment; [Figure 7] 1 is an enlarged cross-sectional view showing the configuration of a main plate of an impeller of a centrifugal blower according to an embodiment; [Figure 8] 1 is a cross-sectional view showing the configuration of a main plate and blades of an impeller of a centrifugal blower according to an embodiment; [Figure 9] 10 is a cross-sectional view showing a modified example of the main plate of the impeller of the centrifugal fan according to the embodiment; [Figure 10] 10 is a partial cross-sectional view of a modified example of the main plate of the impeller of the centrifugal blower according to the embodiment; [Figure 11] FIG. 10 is a diagram showing a comparison of performance between the centrifugal blower according to the embodiment and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a centrifugal blower and a ventilation fan according to an embodiment will be described in detail with reference to the drawings.

[0011] Embodiment FIG. 1 is a cross-sectional view showing the configuration of a ventilation fan equipped with a centrifugal fan according to an embodiment. FIG. 2 is a plan view showing the configuration of a ventilation fan equipped with a centrifugal fan according to an embodiment. FIG. 3 is a plan view showing the configuration of a ventilation fan equipped with a centrifugal fan according to an embodiment. A decorative grill of the ventilation fan is omitted in FIG. 2. In FIG. 3, the decorative grill of the ventilation fan is omitted and a terminal cover is open. FIG. 4 is a perspective view showing the configuration of an impeller of a centrifugal fan according to an embodiment. FIG. 5 is a top view showing the configuration of an impeller of a centrifugal fan according to an embodiment. FIG. 6 is a cross-sectional view taken along line VI-VI of FIG. 5. FIG. 7 is an enlarged cross-sectional view showing the configuration of a main plate of an impeller of a centrifugal fan according to an embodiment. FIG. 7 is a cross-sectional view taken along line VII-VII of FIG. 5. FIG. 8 is a cross-sectional view showing the configuration of a main plate and blades of an impeller of a centrifugal fan according to an embodiment.

[0012] As shown in Figures 1 to 3, ventilation fan 100 is a duct ventilation fan. Ventilation fan 100 is placed above the ceiling through opening 23 formed in ceiling 22 and is connected to duct 14 leading to the outdoors to ventilate indoor air. Ventilation fan 100 includes ventilation fan main body 2, duct connection port 8, and centrifugal blower 1. Hereinafter, centrifugal blower 1 will be simply referred to as blower 1. Duct connection port 8 is provided on the side of ventilation fan main body 2 and extends perpendicularly from the side surface of ventilation fan main body 2. Duct connection port 8 extends exhaust port 10, which serves as an outlet for airflow W, to a position where it communicates with duct 14. Ventilation fan 100 and duct 14 are connected by inserting duct connection port 8 into duct 14. Blower 1 is a ventilation driver that circulates the air to be ventilated. Ventilation fan main body 2 houses and secures blower 1.

[0013] The ventilation fan 100 is placed in an opening 23 in the ceiling 22, and is fixed to the ceiling 22 by inserting screws through screw holes 24 provided in the flange 2a of the ventilation fan body 2. The ventilation fan 100 is equipped with a decorative grill 12, which is a design component, to prevent the internal components, including the fan casing 6, from being visible and spoiling the appearance. The decorative grill 12 has two springs 13, and is fixed to the ventilation fan body 2 by hooking the springs 13 onto spring fixing components 7 attached to the fan casing 6. The front of the ventilation fan 100 is covered by the decorative grill 12. The springs 13 are attached to the decorative grill 12 by spring fixing components 21.

[0014] The ventilation fan body 2 is box-shaped with an open bottom and an exhaust port 10 on the side. The opening on the bottom of the ventilation fan body 2 serves as an air intake port. A duct connection port 8 is connected to the exhaust port 10. A drive motor 3 for the blower 1 is attached to the top plate 25 of the ventilation fan body 2.

[0015] Blower 1 has drive motor 3, impeller 4 coupled to rotary shaft 3a of drive motor 3, and fan casing 6 that houses impeller 4. Fan casing 6 has suction port 5. Impeller 4 forms airflow W that flows from suction port 5 into fan casing 6 and flows out from exhaust port 10 of ventilation fan body 2. Drive motor 3 drives impeller 4. As described above, drive motor 3 is fixed to top plate 25.

[0016] The electric wire connection device 20 and the drive motor 3 are electrically connected by an electric wire. The electric wire connection device 20 is isolated from the air passage by a terminal cover 11 to prevent the intrusion of dust and moisture. Power supplied through an external power supply cable flows to the drive motor 3 via the electric wire connection device 20, and the electrical energy is converted into rotational motion of the rotary shaft 3a of the drive motor 3. The drive motor 3 transmits the rotational motion to the impeller 4, causing the impeller 4 to rotate, and an airflow W is formed in the air passage formed by the fan casing 6 and the air inlet 5.

[0017] The duct connection port 8 has a stepped outer shape with different diameters. Because the duct connection port 8 has a stepped outer shape with different diameters, it can be connected to ducts 14 with different diameters, improving the ease of taping and other operations. A shutter 9 that opens and closes with wind pressure is provided inside the duct connection port 8. The shutter 9 opens with wind pressure when the ventilation fan 100 is operating, and closes the duct connection port 8 under its own weight when the ventilation fan 100 is stopped. By providing the shutter 9 inside the duct connection port 8, it is possible to prevent outside wind from entering the room when the ventilation fan 100 is stopped.

[0018] The duct 14 extends to the outdoors and is connected to a hood or the like provided on the exterior wall of the building, forming a ventilation air passage for ventilating the air inside the house.

[0019] The bottom of the fan casing 6 is open, forming an intake port 5. Air drawn into the fan casing 6 from the intake port 5 is sent by the blower 1 along the inner wall of the fan casing 6 to the exhaust port 10, as indicated by airflow W, and is then exhausted to the outdoors via the duct connection port 8 and the duct 14. The fan casing 6 is fixed to the top plate 25 of the ventilation fan body 2 with screws. A spring fixing part 7 for attaching the decorative grille 12 is formed on the open side of the fan casing 6.

[0020] The rotation shaft 16 of the terminal cover 11 is inserted into a rotation hole 15 provided in the fan casing 6. The terminal cover 11 is opened and closed by rotating around the rotation shaft 16. Because the terminal cover 11 can be opened and closed, access to the electric wire connection device 20 is possible, and external power supply electric wires can be easily inserted from the indoor side. The terminal cover 11 is equipped with a finger hook 17 to make it easier to open. When the terminal cover 11 is closed, a protective wall 18 provided on the fan casing 6 improves the level of sealing. In addition, the protective wall 18 is provided with a locking protrusion 19 that allows the terminal cover 11 to be locked, making it possible to maintain the closed state.

[0021] As shown in Figures 4 to 8, the impeller 4 includes a main plate 26, a plurality of blades 27, and a reinforcing ring 28. In Figures 4, 6, 7, and 8, the impeller 4 is shown upside down compared to the arrangement in Figure 1. The main plate 26 is fixed to a rotating shaft 3a of a drive motor 3 attached to a top plate 25 of the ventilation fan body 2, and rotates around the rotating shaft 3a. The intake port 5 of the fan casing 6 faces the main plate 26. The plurality of blades 27 are provided on the outer periphery of the main plate 26 and are erected in an annular shape at predetermined intervals. The blades 27 have a shape that extends in a direction along the rotating shaft 3a. The annular reinforcing ring 28 is attached to the outer periphery of the blades 27 and secures the ends of the plurality of blades 27.

[0022] In this embodiment, main plate 26 is generally inclined overall so that the distance from suction port 5 increases from the inner diameter side toward the outer diameter side. Main plate 26 has a horizontal surface portion 114 extending in a direction perpendicular to rotation shaft 3a at approximately the radial center portion, and has inclined surface portions radially inward and radially outward of horizontal surface portion 114 that are inclined so as to move away from suction port 5 of fan casing 6 as they progress from the inner diameter side to the outer diameter side. The radial center portion of main plate 26 where horizontal surface portion 114 is provided refers to the radial center portion of the range excluding a flat portion formed in a portion of main plate 26 to which rotation shaft 3a of drive motor 3 is fixed (a portion on the inner diameter side of first inclined portion 111 in main plate 26 shown in FIG. 8 ).

[0023] In addition, in this embodiment, the outer peripheral portion of the main plate 26, on which the plurality of blades 27 are erected, is inclined so that the distance from the suction port 5 increases from the inner diameter side to the outer diameter side. That is, the shape of the outer peripheral portion of the main plate 26 is created so that the axial position on the main plate 26 corresponding to the outer peripheral position of the blades 27 is farther from the suction port 5 of the fan casing 6 than the axial position on the main plate 26 corresponding to the inner peripheral position of the blades 27. The axial position is a position along the axial direction of the rotation shaft 3a. In FIG. 6 , imaginary line B corresponds to the position of the suction port 5 of the fan casing 6. The length from the suction port 5 to the axial position on the main plate 26 corresponding to the inner peripheral position of the blades 27 is defined as h1. The length from the suction port 5 to the axial position on the main plate 26 corresponding to the outer peripheral position of the blades 27 is defined as h2. In this embodiment, the shape and inclination of the outer peripheral portion of the main plate 26 are designed so that h2 > h1.

[0024] 5, a plurality of openings 29 are provided on the inner diameter side of horizontal surface portion 114 in main plate 26. The plurality of openings 29 are formed at intervals along the circumferential direction of main plate 26. In the embodiment, an annular protrusion 30 for preventing resonance is provided on the back surface of main plate 26 opposite the surface facing suction port 5.

[0025] The shape of the impeller 4 will be described in more detail with reference to Figure 8. The main plate 26 has, from the center side of the rotary shaft 3a toward the outer diameter side, a first inclined portion 111, a second inclined portion 112, a third inclined portion 113, a horizontal surface portion 114, and a fourth inclined portion 115 corresponding to the outer periphery.

[0026] If the degree of inclination of each part is expressed as the length in the direction of the rotation axis 3a / the length in the radial direction, the relationship is as follows: inclination of the first inclined part 111 > inclination of the third inclined part 113 > inclination of the fourth inclined part 115 ≒ inclination of the second inclined part 112 > inclination of the horizontal surface part 114.

[0027] The first inclined portion 111 is a portion of the motor's rotating shaft 3a ranging from the central axis O to a radius R1. The radius of the main plate 26, i.e., the length from the central axis O to the outer periphery of the blade 27, is defined as R5. The radius R1 of the first inclined portion 111 is approximately 1 / 3 of the radius R5. That is, R1 ≈ (1 / 3) × R5. The first inclined portion 111 has a cross-sectional shape that is a linear plane and has a shape that is rotationally symmetrical with respect to the central axis O. The first inclined portion 111 has a structure for fixing the main plate 26 to the rotating shaft 3a of the drive motor 3. Meanwhile, in terms of airflow, the pressure near the radial center is not high, and the impact on air volume and noise is small, so there are no significant limitations on the shape of the first inclined portion 111.

[0028] The second inclined portion 112 is a portion ranging from the position of radius R1 to the position of radius R2. R2 > R1. Radius R2 is approximately 2 / 3 of radius R5. That is, R2 ≈ (2 / 3) × R5. A plurality of openings 29 are provided at circumferential intervals from the second inclined portion 112 to the third inclined portion 113. In FIG. 5, six openings 29 are provided. The cross-sectional shape of the second inclined portion 112 is a linear plane, and the shape of the second inclined portion 112, except for the openings 29, is rotationally symmetrical with respect to the central axis O. The second inclined portion 112 forms a conical surface that is substantially identical to that of the fourth inclined portion 115. That is, the inclination of the second inclined portion 112 is approximately the same as that of the fourth inclined portion 115. "The same degree of inclination" includes the same inclination, as well as a difference in inclination angle of 2 degrees or less.

[0029] The third inclined portion 113 is a portion ranging from the position of radius R2 to the position of radius R3. R3 > R2. The radial width of the third inclined portion 113 is approximately 1 / 2 of the blade width LW. The blade width LW is the radial width of the blade 27. In other words, (R3 - R2) ≒ (1 / 2) × LW. As described above, a plurality of openings 29 are provided at intervals in the circumferential direction from the second inclined portion 112 to the third inclined portion 113. The cross-sectional shape of the third inclined portion 113 is a linear plane, and the shape of the third inclined portion 113, except for the openings 29, is rotationally symmetrical with respect to the central axis O. The inclination of the third inclined portion 113 is greater than the inclination of the second inclined portion 112.

[0030] The horizontal surface portion 114 is the portion ranging from the position of radius R3 to the position of radius R4. R4>R3. The width of the horizontal surface portion 114 is approximately the same as the wingspan LW. In other words, (R4-R3)≒LW. The horizontal surface portion 114 has a linear cross-sectional shape and has a shape that is rotationally symmetrical with respect to the central axis O. The horizontal surface portion 114 is a plane that is perpendicular to the rotation axis 3a.

[0031] The fourth inclined portion 115 is a portion ranging from the position of radius R4 to the position of radius R5. R5>R4. The width of the fourth inclined portion 115 is approximately 1.5 times the blade width LW. In other words, (R5-R4)≒(3 / 2)×LW. On the suction port 5 side of the fourth inclined portion 115, a plurality of blades 27 are provided, spaced apart and arranged in a ring shape. The blade width LW and the radius R5 satisfy the following relationship: (1 / 10)×R5≦LW≦(2 / 10)×R5

[0032] The fourth inclined portion 115 has a shape that is rotationally symmetrical with respect to the central axis O. As described above, the fourth inclined portion 115 is formed such that the length h2 from the suction port 5 to the position of the fourth inclined portion 115 corresponding to the position on the outer periphery of the blade 27 is longer than the length h1 from the suction port 5 to the position of the fourth inclined portion 115 corresponding to the position on the inner periphery of the blade 27. The cross-sectional shape of the fourth inclined portion 115 is a linear plane, and is formed by a conical surface that is substantially the same as that of the second inclined portion 112.

[0033] An annular protrusion 30 is provided on the rear surface of the fourth inclined portion 115. That is, the position of radius R30 where the annular protrusion 30 is provided is preferably in the range from the position of radius R4 to the position of radius R5.

[0034] According to this embodiment, the main plate 26 is generally inclined overall so that the distance from the suction port 5 increases from the inner diameter side toward the outer diameter side, and is provided with a horizontal surface 114 extending in a direction perpendicular to the rotation axis 3a at approximately the center in the radial direction. In other words, the main plate 26 of the impeller 4 is configured by combining a steeply inclined surface and a horizontal surface 114, thereby providing space within the impeller 4. This makes it possible to reduce the wind speed of the airflow before it enters the blades 27 of the impeller 4, preventing an increase in pressure loss. In addition, the airflow within the impeller 4 is more likely to flow in the outer diameter direction.

[0035] By providing the horizontal surface portion 114 on the main plate 26, the air inside the impeller 4 tends to flow in the outer diameter direction, but it becomes more difficult for the air inside the impeller 4 to flow toward the root side of the blades 27, making it difficult for the blades 27 of the impeller 4 to function sufficiently in the axial direction as a whole. For this reason, in this embodiment, the shape of the outer periphery of the main plate 26 is formed so that h2 > h1. This creates an airflow E that draws air toward the root side of the blades 27 of the impeller 4, as shown in Figure 7, and is expected to enable the blades 27 of the impeller 4 to function sufficiently in the axial direction as a whole.

[0036] Furthermore, providing the horizontal surface portion 114 on the main plate 26 improves the flow of air blown out from other than the base of the blades 27. Furthermore, making h2 > h1 improves the flow of air blown out from the base side of the blades 27. Therefore, the distribution of the air blown out from the blades 27 of the impeller 4 is made uniform in the axial direction, which is expected to reduce noise and increase the air volume.

[0037] If the main plate 26 does not have a horizontal surface, the alignment position of the mold will be inclined, which requires high precision during molding and also causes severe wear to the mold. In this embodiment, the main plate 26 has a horizontal surface portion 114, so the alignment position of the mold can be made to a horizontal surface. This makes it easier to mold the main plate 26 and also reduces wear to the mold.

[0038] In addition, in the embodiment, since a plurality of openings 29 are provided in the main board 26, the weight of the impeller 4 can be reduced, and the amount of resin can be reduced. Further, the opening 29 can obtain an air-cooling effect on the drive motor 3.

[0039] FIG. 9 is a cross-sectional view showing a modified example of the main board of the impeller of the centrifugal blower according to the embodiment. FIG. 10 is a partial cross-sectional view of a modified example of the main board of the impeller of the centrifugal blower according to the embodiment. In the modified example shown in FIGS. 9 and 10, the fourth inclined portion 115a is a convex curved surface toward the suction port 5.

[0040] At this time, the inclination of the fourth inclined portion 115a gradually increases from the position of the inner diameter side radius R4 to the position of the outer diameter side radius R5. The inclination at the position of the radius R4 is approximately the same as the inclination of the second inclined portion 112. That is, the inclination of the second inclined portion 112 ≒ the inclination of the fourth inclined portion 115a at the position of the radius R4 < the inclination of the fourth inclined portion 115a at the position of the radius R5.

[0041] Further, as shown in FIG. 10, when R4 < Ra1 < Ra2 < R5, the inclination at the position of the radius Ra2 is larger than the inclination at the position of the radius Ra1.

[0042] According to the modified example, since the fourth inclined portion 115a is a convex curved surface toward the suction port 5, a Coandă effect is added to the flow on the root side of the blade 27, and an increase in the air volume of the blower can be expected.

[0043] FIG. 11 is a diagram showing a performance comparison between the centrifugal blower according to the embodiment and a comparative example. As the comparative example, an impeller having a main board with a uniform inclined surface except for the outer peripheral portion and a gentler inclination than the inclined surface on the inner diameter side at the outer peripheral portion was used as in Patent Document 1. As the impeller of the embodiment, the impeller 4 shown in FIGS. 6 and 7 was used. The plurality of blades of the impeller of the comparative example and the plurality of blades of the impeller of the embodiment were the same. The outer diameter of both impellers was set to 140 mm. When the static pressure is 0 Pa, the rotational speed of the impeller of the comparative example is 1659 min -1 " and the rotational speed of the impeller of the embodiment is 1656 min -1When the static pressure was 50 Pa, the rotation speed of the impeller of the comparative example was 1659 min -1 The rotation speed of the impeller in this embodiment is 1657 min -1 When the static pressure was 100 Pa, the rotation speed of the impeller of the comparative example was 1660 min -1 The rotation speed of the impeller in this embodiment is 1657 min -1 As can be seen from Figure 11, at the same static pressure, the air volume was approximately 6 m 3 / h increase, and the noise level was reduced by approximately 0.1 to 0.6 dB.

[0044] The configurations shown in the above embodiments are examples of the content of the present invention, and may be combined with other known technologies, and some of the configurations may be omitted or modified within the scope of the gist of the present invention. [Explanation of symbols]

[0045] 1 centrifugal blower (blower), 2 ventilation fan body, 2a flange, 3 drive motor, 3a, 16 rotating shaft, 4 impeller, 5 intake port, 6 fan casing, 7, 21 spring fixing part, 8 duct connection port, 9 shutter, 10 exhaust port, 11 terminal cover, 12 decorative grill, 13 spring, 14 duct, 15 rotation hole, 17 finger hook portion, 18 protective wall, 19 locking protrusion, 20 electric wire connection device, 22 ceiling, 23 opening, 24 screw hole, 25 top plate, 26 main plate, 27 blade, 28 reinforcing ring, 29 opening, 30 protrusion, 100 ventilation fan, 111 first inclined portion, 112 second inclined portion, 113 third inclined portion, 114 horizontal surface portion, 115, 115a fourth inclined portion.

Claims

1. A drive motor; an impeller having a main plate that is fixed to a rotary shaft of a drive motor and rotates, and a plurality of blades that are annularly arranged at intervals on the outer periphery of the main plate; a fan casing having an inlet facing the main plate and accommodating the impeller; Equipped with The main plate is The inclination is such that the distance from the suction port increases from the inner diameter side to the outer diameter side as a whole, The outer circumferential portion on which the plurality of blades are erected is inclined so that the distance from the suction port increases from the inner diameter side to the outer diameter side, The main plate has, from the inner diameter side to the outer diameter side, a first inclined portion, a second inclined portion, a third inclined portion, a horizontal surface portion that is a plane perpendicular to the rotation axis, and a fourth inclined portion as the outer circumferential portion, the inclination of the second inclined portion is approximately the same as the inclination of the fourth inclined portion, the inclination of the first inclined portion is greater than the inclination of the third inclined portion, and the inclination of the third inclined portion is greater than the inclination of the second inclined portion and the inclination of the fourth inclined portion. A centrifugal blower characterized by:

2. The outer periphery of the main plate is a curved surface that is convex toward the suction port.

2. The centrifugal blower according to claim 1, wherein the centrifugal blower is a centrifugal blower.

3. The main plate has a plurality of openings arranged along the circumferential direction on the inner diameter side of the horizontal surface portion.

2. The centrifugal blower according to claim 1, wherein the centrifugal blower is a centrifugal blower.

4. A centrifugal blower according to any one of claims 1 to 3; a ventilation fan body in which the centrifugal blower is housed; A ventilation fan comprising:

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