Centrifugal Blower

Abstract

To provide a centrifugal blower capable of reducing noise.SOLUTION: A centrifugal blower 1 is equipped with a main plate 10, a shroud 20, and a plurality of blades 30. A front edge 31 of the blade 30 is provided on the inner side in a diametrical direction of an inner peripheral wall 211 of an opening portion 21 of the shroud 20. On a surface facing the opposite side to the main plate 10 of the front edge 31, a lower height position 71 and a higher height position 72 are provided. The lower height position 71 is a part that is located closer to the main plate 10 side than a connection part 73 on the diametrically inner side of the connection part 73 of the inner peripheral wall 211 of the opening portion 21 of the shroud 20 and the blade 30, and is provided along a surface perpendicular to an axis CL. The higher height position 72 is a part that is located on the opposite side to the main plate 10 with respect to the lower height portion 71 on the diametrically inner side of the lower height portion 71. The lower height portion 71 and the higher height portion 72 form a recessed shape 70 on a surface facing the opposite side to the main plate 10 of the front edge 31.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a centrifugal blower that takes in air from one side in the axial direction of the rotation of an impeller and blows it out in a direction away from the axial center. [Background technology]

[0002] Conventionally, there is known a centrifugal blower in which an impeller having a main plate, a shroud, and a plurality of blades is rotatably provided inside a case (see Patent Document 1). In the impeller of the centrifugal blower described in Patent Document 1, the leading edge of the blade is provided on a side closer to the axis of rotation than the inner peripheral wall of the opening provided in the center of the shroud. Furthermore, the surface of the leading edge facing away from the main plate extends perpendicular to the axis. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-203481 A Summary of the Invention [Problem to be solved by the invention]

[0004] According to the inventors' study, a centrifugal blower has a characteristic that air flowing from an air intake port provided in a case into a flow passage formed between a plurality of blades (hereinafter referred to as an "inter-blade flow passage") flows toward the main plate and is less likely to flow along the surface of the shroud on the inter-blade flow passage side (hereinafter referred to as an "underside of the shroud"). Therefore, when the air flowing from the air intake port into the inter-blade flow passage separates from the underside of the shroud and a vortex generated by the separation (hereinafter referred to as a "separation vortex") becomes large, a problem occurs in that noise increases. To address such a problem, the centrifugal blower described in the above-mentioned Patent Document 1 has room for improvement in terms of the blade shape.

[0005] In view of the above, an object of the present invention is to reduce noise in a centrifugal blower. [Means for solving the problem]

[0006] In order to achieve the above object, according to the invention of claim 1, in a centrifugal blower, A rotatably mounted main plate (10); an annular shroud (20) provided opposite the main plate and having an opening (21) at the center through which air flows; a plurality of blades (30) arranged at predetermined intervals around an axis (CL) that is a center of rotation between the shroud and the main plate and connected to the shroud and the main plate; An upper case (53) having an upper case body (56) covering the surface of the shroud opposite to the main plate, an air suction port (51) provided in the upper case body at a position corresponding to the opening, and a bell mouth (57) extending cylindrically from the inner peripheral edge of the air suction port toward the main plate. Equipped with When a virtual circle is defined with its center at the center on a virtual plane perpendicular to the axis, and the radial side of the virtual circle closer to the axis is called the radial inner side, and the opposite side is called the radial outer side, The leading edge (31) of the blade is provided radially inward of the inner circumferential wall (211) of the opening of the shroud, A low-level portion (71) is provided on a surface of the leading edge facing away from the main plate, the low-level portion (71) being located radially inward of a connection point (73) between the inner circumferential wall of the opening of the shroud and the blade and closer to the main plate than the connection point and provided along a plane perpendicular to the axis, and a high-level portion (72) is provided radially inward of the low-level portion and located on the opposite side to the main plate from the low-level portion, The low and high parts form a recess (70) on the front edge of the surface facing away from the main plate. And, An end of the bellmouth on the main plate side is located on the opposite side to the main plate with respect to a connection point between the inner circumferential wall of the opening of the shroud and the blade.

[0007] According to this, the direction of the air flowing from the opening of the shroud into the inter-blade passage becomes close to the shape of the underside of the shroud due to the Coanda effect, in which the air flows along the concave shape formed on the leading edge of the blade. Therefore, the air flowing from the opening of the shroud into the inter-blade passage is prevented from separating from the underside of the shroud, reducing separation vortices and reducing noise.

[0008] Furthermore, the efficiency of the blower is improved by suppressing the separation of air from the rear surface of the shroud, so that the rotation speed of the blower can be reduced under the same air volume conditions, and the vibration caused by the rotation is reduced, resulting in reduced noise.

[0009] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a plan view of a centrifugal blower according to a first embodiment. [Diagram 2] 2 is a cross-sectional view taken along line II-II of FIG. 1. [Diagram 3] 3 is a cross-sectional view of a part of the impeller and a part of the upper case taken along line III-III in FIG. 1. [Figure 4] FIG. 4 is an enlarged view of the leading edge of the wing and its vicinity shown in FIG. 3. [Diagram 5] FIG. 5 is an enlarged view of part V in FIG. [Figure 6] 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 5 is an explanatory diagram for explaining the flow of air from the air inlet to the inter-blade flow passage at the same location as FIG. 4. [Figure 8] 5 is an experimental result showing the relationship between the depth of the recessed shape and noise in the centrifugal blower according to the first embodiment. [Figure 9] 5 is an enlarged view of a portion of a centrifugal blower according to a second embodiment, the portion corresponding to FIG. 4. [Figure 10] 5 is an enlarged view of a portion of a centrifugal blower according to a third embodiment, the portion corresponding to FIG. 4. [Figure 11] 5 is an enlarged view of a portion of the centrifugal blower of the comparative example corresponding to FIG. 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, the same or equivalent parts are denoted by the same reference numerals, and the description thereof will be omitted.

[0012] (First embodiment) A centrifugal blower according to a first embodiment will be described. Hereinafter, the centrifugal blower will be simply referred to as a "blower." As shown in Figs. 1 to 3, the blower 1 according to the first embodiment includes an impeller 2 including a main plate 10, a shroud 20, and a plurality of blades 30, a motor 40 for rotating the impeller 2, and a case 50 for housing the impeller 2 and the motor 40. The blower 1 is used for various purposes, such as a vehicle seat air conditioner, an air conditioner, or a ventilation system.

[0013] In the following description, a virtual circle is defined on a virtual plane perpendicular to the axis CL of rotation of the impeller 2, with the axis CL at its center, and the radial side of the virtual circle on the axis CL side is referred to as the "radial inner side," and the radial side of the virtual circle opposite the axis CL is referred to as the "radial outer side." Additionally, the direction in which the axis CL extends is referred to as the "axial direction."

[0014] The configuration of the impeller 2 will be described. The main plate 10 of the impeller 2 is provided so as to be rotatable by the torque output by the motor 40. The main plate 10 has a central portion 11 fixed to the rotating shaft 41 of the motor 40, a fixed portion 12 fixed to the outer wall of the central portion 11 in the radial direction, and an annular portion 13 provided radially outward from the fixed portion 12 and joined to the plurality of blades 30. The central portion 11 of the main plate 10 is formed in a mountain shape that gradually moves away from the air intake port 51 of the upper case 53 from the rotating shaft 41 side toward the radially outward direction. Therefore, the central portion 11 of the main plate 10 functions as a guide surface that guides the air sucked from the air intake port 51 of the upper case 53 to a flow path (hereinafter referred to as an "inter-blade flow path") formed between the plurality of blades 30. The central portion 11 of the main plate 10 constitutes a part of the motor rotor 42 described later. Furthermore, the fixing portion 12 of the main plate 10 is used to fix the plurality of blades 30 and the shroud 20 which are integrally formed with the fixing portion 12 to the motor rotor 42 .

[0015] The shroud 20 is provided so as to face the main plate 10 in the axial direction. The shroud 20 has an opening 21 in the center through which air flows in. Therefore, the shroud 20 is formed in an annular shape. The shroud 20 has a shroud cylindrical portion 22 that extends in a cylindrical shape from the inner peripheral edge on the opening 21 side toward the opposite side to the main plate 10. The shroud 20 also has a plurality of shroud side projections 23 that extend in a cylindrical shape toward the opposite side to the main plate 10 at a position radially outward of the shroud cylindrical portion 22. In this embodiment, three shroud side projections 23 are provided.

[0016] The blades 30 are provided between the shroud 20 and the main plate 10, and are arranged at a predetermined interval around the axis CL which is the rotation center of the impeller 2. The blades 30 extend backward in the rotation direction from a leading edge 31 to a trailing edge 32. That is, the impeller 2 of this embodiment is a turbofan. An end 33 of the blade 30 on the shroud 20 side in the axial direction is connected to the shroud 20. An end 34 of the blade 30 on the main plate 10 side in the axial direction is connected to the fixed portion 12 and the annular portion 13 of the main plate 10. Therefore, the impeller 2 of this embodiment is a closed fan.

[0017] In this embodiment, the leading edge 31 of the blade 30 is provided radially inward of the inner circumferential wall 211 of the opening 21 of the shroud 20. In the following description, the leading edge 31 of the blade 30 may be referred to as the "blade leading edge 31." The shape of the blade leading edge 31 will be described in detail later.

[0018] The case 50 has an upper case 53 and a lower case 54. The upper case 53 is a member that covers the shroud 20 side of the impeller 2. The lower case 54 is a member that covers the main board 10 side of the impeller 2 and houses the motor 40 and the circuit board 60. The upper case 53 and the lower case 54 are fixed at a predetermined distance by pillars, screws, etc. (not shown). In FIG. 1, the positions where pillars, etc. are provided between the upper case 53 and the lower case 54 are indicated by circles with reference numeral 55.

[0019] The upper case 53 has an upper case main body 56 that covers the surface of the shroud 20 opposite to the main plate 10, an air suction port 51 provided in the upper case main body 56 at a position corresponding to the opening 21 of the shroud 20, and a bell mouth 57 that extends cylindrically from the inner peripheral edge of the air suction port 51 toward the main plate 10. The bell mouth 57 is a portion that introduces air from the outside to the impeller 2. For that reason, the corner portion of the bell mouth 57 opposite to the main plate 10 is curved, and the end portion of the bell mouth 57 on the main plate 10 side is also curved.

[0020] The upper case 53 also has a plurality of case side projections 52 extending cylindrically toward the shroud 20 at a position radially outward from the bellmouth 57. In this embodiment, two case side projections 52 are provided. The two case side projections 52 are provided between the three shroud side projections 23 provided on the shroud 20. Therefore, in the gap flow passage 25 between the upper case 53 and the shroud 20, a labyrinth portion 26 is formed by the case side projections 52 and the shroud side projections 23.

[0021] The lower case 54 has a lower case main body 58 that covers the main plate 10 side of the impeller 2, and a central cylinder 59 provided in the center of the lower case main body 58. The rotating shaft 41 and motor stator 43 of the motor 40 are attached to the central cylinder 59. In this embodiment, for example, an outer rotor type brushless DC motor is used as the motor 40.

[0022] The rotating shaft 41 of the motor 40 is rotatably provided inside the central cylinder portion 59 via a bearing 44. The central portion 11 of the motor rotor 42 is fixed to the axial end of the rotating shaft 41 of the motor 40. The motor rotor 42 has the central portion 11 of the main plate 10 described above, the magnet holding portion 14 extending from the outer edge of the central portion 11 of the main plate 10 to the opposite side of the shroud 20 in the axial direction, and the magnet 45 provided on the radially inner side of the magnet holding portion 14. The fixing portion 12 of the main plate 10 is fixed to the radially outer outer wall of the magnet holding portion 14 by press-fitting or the like. This joins the motor rotor 42 and the impeller 2. The magnet 45 provided on the radially inner side of the magnet holding portion 14 has different types of magnetic poles alternately arranged in the circumferential direction of the magnet holding portion 14.

[0023] The motor stator 43 is provided radially inward of the magnet 45. The motor stator 43 is fixed to a radially outer surface of the central cylinder portion 59. The motor stator 43 has a three-phase coil 46 configured, for example, by Y connection or Δ connection, and a stator core 461. A three-phase AC current is supplied to the three-phase coil 46 from a circuit board 60.

[0024] In the above-described configuration, when power and a drive signal are supplied from the connector 47 to the circuit board 60, a three-phase AC current is supplied from the circuit board 60 to the three-phase coil 46 of the motor stator 43, causing the impeller 2 to rotate together with the rotating shaft 41 and the motor rotor 42. When the impeller 2 rotates, as shown by the arrow AF1 in Fig. 2, air flowing in from the air intake port 51 of the upper case 53 passes through the inter-blade flow passage and is blown out radially outward from between the upper case 53 and the lower case 54.

[0025] Next, the shape of the blade leading edge 31 will be described in detail.

[0026] 4, the blade leading edge 31 is a portion of the blade 30 that is provided radially inward from the inner circumferential wall 211 of the opening 21 of the shroud 20. A recessed shape 70 is formed on a surface of the blade leading edge 31 that faces away from the main plate 10. The recessed shape 70 is formed by a low portion 71 and a high portion 72.

[0027] The low portion 71 is a portion located radially inward of a connection point 73 between the inner circumferential wall 211 of the opening 21 of the shroud 20 and the blade 30, and closer to the main plate 10 than the connection point 73. The low portion 71 is provided along a plane perpendicular to the axis CL. In this specification, "the low portion 71 is provided along a plane perpendicular to the axis CL" includes a state in which, when the low portion 71 is viewed from the rotation direction of the blade 30, the low portion 71 is parallel to an imaginary plane perpendicular to the axis CL, and also includes a state in which the low portion 71 is slightly curved or inclined with respect to the imaginary plane.

[0028] The high-level portion 72 is a portion located radially inward of the low-level portion 71 and on the opposite side of the main plate 10 from the low-level portion 71. The high-level portion 72 is at approximately the same height in the axial direction as a connection point 73 between the inner circumferential wall 211 of the opening 21 of the shroud 20 and the blade 30. Note that the high-level portion 72 may be located closer to the main plate 10 than the connection point 73 in the axial direction, or may be located on the opposite side of the main plate 10 than the connection point 73.

[0029] The low-level portion 71 and the high-level portion 72 are connected by a smooth curved surface. Specifically, as shown in Fig. 5, which is an enlarged view of part V in Fig. 4, the portion where the low-level portion 71 and the high-level portion 72 are connected has a first curved surface 74 and a second curved surface 75. The first curved surface 74 is a curved surface that is convex toward the air suction port 51 side (i.e., the side opposite the main plate 10) on the low-level portion 71 side of the high-level portion 72. The second curved surface 75 is a curved surface that is convex toward the main plate 10 side on the radially outer side of the first curved surface 74 (i.e., on the low-level portion 71 side of the first curved surface 74).

[0030] In FIG. 5, the tangency between the arc of the first curved surface 74 and the arc of the first curved surface 74 at a portion radially inward from the first curved surface 74 is indicated by reference symbol P1, the tangency between the arc of the first curved surface 74 and the arc of the second curved surface 75 is indicated by reference symbol P2, and the tangency between the arc of the second curved surface 75 and the arc of the first curved surface 74 at a portion radially outward from the second curved surface 75 is indicated by reference symbol P3. Here, when the blade leading edge 31 is viewed from the rotation direction of the blade 30, the radius of curvature of the first curved surface 74 is R1, and the radius of curvature of the second curved surface 75 is R2. In this case, the radius of curvature R1 of the first curved surface 74 and the radius of curvature R2 of the second curved surface 75 have a relationship of R1>R2. Although not shown, a flat surface may be provided between the first curved surface 74 and the second curved surface 75, or the first curved surface 74 and the second curved surface 75 may have a flat surface in a part thereof.

[0031] 6 is a cross-sectional view taken along line VI-VI in FIG. 4. That is, FIG. 6 is a cross-sectional view of the low-level portion 71 of the blade leading edge 31 cut along a plane perpendicular to the direction in which the blade 30 extends from the leading edge 31 to the trailing edge 32. In the cross-section shown in FIG. 6, the radius of curvature of the corner portion 36 on the suction surface 35 side of the low-level portion 71 is R3, and the radius of curvature of the corner portion 38 on the pressure surface 37 side of the low-level portion 71 is R4. In this case, the radius of curvature R1 of the first curved surface 74, the radius of curvature R2 of the second curved surface 75, the radius of curvature R3 of the corner portion 36 on the suction surface 35 side of the low-level portion 71, and the radius of curvature R4 of the corner portion 38 on the pressure surface 37 side of the low-level portion 71 have the relationships R1>R3>R4 and R2>R3>R4.

[0032] 4, the blade 30 has a standing wall portion 39 between a connection portion 73 between the blade 30 and the inner circumferential wall 211 of the opening 21 of the shroud 20 and the low-position portion 71. The standing wall portion 39 is provided parallel to the inner circumferential wall 211 of the opening 21 of the shroud 20. A portion 391 where the standing wall portion 39 and the low-position portion 71 are connected is a curved surface. That is, the radially outer portion 391 of the low-position portion 71 and a radially inner portion of the low-position portion 71 (i.e., the second curved surface 75) are both curved surfaces.

[0033] As shown in Fig. 4, in the present embodiment, the distance Da between the point or surface closest to the main board 10 among the lower portions 71 and the point or surface farthest from the main board 10 among the upper portions 72 is defined as the "depth Da of the recessed shape 70". Further, as shown in Fig. 3, the distance Db between the main board 10 and the shroud 20 on the trailing edge 32 side of the blade 30 is defined as the "blade exit height Db". The depth Da of the recessed shape 70 and the blade exit height Db have a relationship of 0 < Da ≤ Db × 0.09. That is, the depth Da of the recessed shape 70 is greater than 0 and is set to 9% or less of the blade exit height Db. This is based on the results of experiments conducted by the inventors of the present invention, and the results of those experiments will be described later.

[0034] Furthermore, as shown in Fig. 3, in the present embodiment, the outer diameter of the main board side end of the bellmouth 57 is Dc, and the outer diameter of the circle connecting the points or surfaces closest to the main board 10 among the lower portions 71 provided on the plurality of blades 30 in the rotational direction is Dw. At this time, the outer diameter Dc of the main board side end of the bellmouth 57 and the outer diameter Dw of the points or surfaces closest to the main board 10 among the lower portions 71 have a relationship of Dc < Dw. Thereby, when the impeller 2 rotates, the air flowing into the inter-blade flow path along the inner peripheral wall 571 of the bellmouth 57 hits the recessed shape 70 formed at the leading edge 31 of the blade, so that the air is likely to be affected by the Coanda effect in which the air flows along the recessed shape 70.

[0035] Although the minimum value of the outer diameter Dc of the bellmouth 57 is not particularly defined, by making the outer diameter Dc of the bellmouth 57 larger than the inner diameter of the upper portion 72, the air flowing into the inter-blade flow path along the inner peripheral wall 571 of the bellmouth 57 hits the recessed shape 70, so that it is likely to be affected by the Coanda effect.

[0036] Note that on the surface of the leading edge 31 of the blade 30 facing the radially inner side, a stepped portion 82 in which recesses 80 and protrusions 81 are alternately arranged in the axial direction is provided. The stepped portion 82 is also called a serration portion. The stepped portion 82 is provided at a position a predetermined distance away from the main board 10 among the leading edge 31 of the blade.

[0037] Here, for comparison with the blower 1 of the above-described first embodiment, a blower 100 of a comparative example will be described.

[0038] 11, in the blower 100 of the comparative example, the blade leading edge 31 is also provided radially inward from the inner circumferential wall 211 of the opening 21 of the shroud 20. However, in the blower 100 of the comparative example, a concave shape is not formed in the surface 101 of the blade leading edge 31 facing away from the main plate 10. That is, in the blower 100 of the comparative example, when the blade leading edge 31 is viewed from the rotation direction of the blade 30, the surface 101 of the blade leading edge 31 facing away from the main plate 10 is a surface perpendicular to the axis CL from the connection point 73 between the inner circumferential wall 211 of the opening 21 of the shroud 20 and the blade 30 toward the radially inward direction.

[0039] In the blower 100 of the comparative example, when the impeller 2 rotates, the air flowing into the inter-blade passage from the air inlet 51 of the upper case 53 flows toward the main plate 10 side and does not easily flow along the surface of the shroud 20 on the inter-blade passage side (hereinafter referred to as "shroud back surface 201"), as shown by the arrow AF2 in Fig. 11. Therefore, when the air flowing into the inter-blade passage from the opening 21 of the shroud 20 separates from the shroud back surface 201 and the separation vortex SV generated by the separation becomes large, a problem occurs in that noise increases.

[0040] In contrast, the blower 1 of the first embodiment has the following effect as shown in Fig. 7. That is, in the blower 1 of the first embodiment, when the impeller 2 rotates, as shown by the arrow AF3 in Fig. 7, the direction of the airflow of the air flowing from the air inlet 51 of the upper case 53 into the inter-blade flow passage becomes close to the shape of the shroud back surface 201 due to the Coanda effect in which the air flows along the recessed shape 70 formed in the blade leading edge 31. The recessed shape 70 is a shape that is effective for generating the Coanda effect on the air flowing from the air inlet 51 into the inter-blade flow passage. Therefore, the air that flows along the recessed shape 70 and then flows into the inter-blade flow passage is suppressed from separating from the shroud back surface 201. Therefore, the blower 1 of the first embodiment can reduce noise because the separation vortex SV near the shroud back surface 201 is reduced.

[0041] 3, in the blower 1 of the first embodiment, the concave shape 70 is formed on the surface of the blade leading edge 31 facing away from the main plate 10, so that the distance Dh between the end 221 of the shroud tubular portion 22 on the opposite side to the main plate 10 and the low portion 71 of the concave shape 70 is greater than that of the blower 100 of the comparative example. Therefore, the flow velocity of air (hereinafter referred to as "backflow air") flowing back from the air outlet 24 on the radial outer side of the impeller 2 through the gap flow passage 25 between the upper case 53 and the shroud 20 to the opening 21 side of the shroud 20 can be slowed down when it collides with the low portion 71 of the concave shape 70. Generally, the magnitude of noise is proportional to the sixth power of the flow velocity, so that noise can be reduced by slowing down the flow velocity.

[0042] Next, the results of an experiment conducted on the relationship between the depth of the recessed shape 70 and noise in the fan 1 according to the first embodiment are shown in FIG.

[0043] The horizontal axis of the graph in Fig. 8 indicates the depth Da of the recessed shape 70 as a ratio to the blade outlet height Db. Note that a depth Da of the recessed shape 70 of 0% is the same as the configuration of the blower 100 of the comparative example described above. Meanwhile, the vertical axis of the graph in Fig. 8 indicates the noise level (i.e., A-weighted sound pressure level). Note that in this experiment, a blower with a blade outlet height Db of 4 mm was used, and the noise level was measured when electricity was applied to the motor 40 to rotate the impeller 2 at a constant rotation speed.

[0044] As shown in the graph of Fig. 8, as a result of this experiment, when the depth Da of the recessed shape 70 is greater than 0 and within the range of 9% or less, the noise level can be reduced. That is, it was found from the experiment that the depth Da of the recessed shape 70 and the blade outlet height Db have a noise reduction effect in the relationship of 0 < Da ≤ Db × 0.09. Also, it was found that a greater noise reduction effect can be obtained by setting the depth Da of the recessed shape 70 to 1 to 8%, more preferably 2 to 7% of the blade outlet height Db. Specifically, in the blower used in the experiment, when the depth Da of the recessed shape 70 was set to 5% of the blade outlet height Db, the noise level could be reduced by 0.4 dBA compared to the blower 100 of the comparative example.

[0045] The blower 1 of the first embodiment described above has the following operational effects.

[0046] (1) In the blower 1 of the first embodiment, a recessed shape 70 is formed by a lower portion 71 and a higher portion 72 on the surface of the leading edge 31 of the blade facing the side opposite to the main board 10. According to this, the air flowing into the inter-blade flow path from the air suction port 51 of the upper case 53 through the opening 21 of the shroud 20 follows the recessed shape 70 formed on the leading edge 31 of the blade due to the Coanda effect of the air flow, and the direction of the air flow becomes closer to the shape of the back surface 201 of the shroud. Therefore, it is possible to suppress the air flowing into the inter-blade flow path from the opening 21 of the shroud 20 from peeling off from the back surface 201 of the shroud, and reduce the peeling vortex SV, so that the noise can be reduced.

[0047] Also, by forming the recessed shape 70 on the surface of the blade 30 facing the side opposite to the main board 10, the distance Dh between the end portion 221 of the shroud cylinder portion 22 on the side opposite to the main board 10 and the lower portion 71 of the recessed shape 70 becomes longer. Therefore, it is possible to slow down the flow velocity when the reverse flow air flowing back from the air outlet 24 on the outer side in the radial direction of the impeller 2 through the gap flow path 25 to the opening 21 side of the shroud 20 collides with the lower portion 71 of the recessed shape 70. Generally, since the magnitude of the noise is proportional to the sixth power of the flow velocity, the noise can be reduced by slowing down the flow velocity.

[0048] Furthermore, by suppressing the separation of air from the back surface 201 of the shroud, the efficiency of the blower 1 is improved. Therefore, under the condition of the same air volume, the rotational speed of the blower 1 can be reduced, and the vibration caused by rotation is reduced, so that the noise can be reduced.

[0049] (2) In the first embodiment, the outer diameter Dc of the bellmouth 57 of the upper case 53 and the outer diameter Dw of the point or surface closest to the main board 10 in the lower portion 71 have a relationship of Dc < Dw. According to this, by slowing down the flow velocity when the reverse flow air collides with the lower portion 71 of the concave shape 70, the noise can be reduced.

[0050] (3) In the first embodiment, the connection portion between the lower portion 71 and the upper portion 72 (that is, the second curved surface 75 and the first curved surface 74) is a curved surface. According to this, the turbulence of the air flow at the connection portion between the lower portion 71 and the upper portion 72 can be suppressed, and the noise can be reduced.

[0051] (4) In the first embodiment, both the radially inner portion (that is, the second curved surface 75) and the radially outer portion 391 of the lower portion 71 are curved surfaces. According to this, the turbulence of the air flow at the radially inner portion (that is, the second curved surface 75) and the radially outer portion 391 of the lower portion 71 can be suppressed, and the noise can be reduced.

[0052] (5) In the first embodiment, the radius of curvature R1 of the first curved surface 74 connecting the lower portion 71 and the upper portion 72 and the radius of curvature R2 of the second curved surface 75 have a relationship of R1 > R2. According to this, by increasing the radius of curvature R1 of the first curved surface 74 that promotes the air flowing in from the air suction port 51 of the upper case 53 to flow radially outward, the radial flow component due to the Coandă effect increases, so that the separation of air from the back surface 201 in the inter-blade flow path can be suppressed.

[0053] (6) In the first embodiment, the radius of curvature R1 of the first curved surface 74, the radius of curvature R2 of the second curved surface 75, the radius of curvature R3 of the corner portion 36 on the negative pressure surface 35 side of the lower portion 71, and the radius of curvature R4 of the corner portion 38 on the positive pressure surface 37 side of the lower portion 71 have the relationships of R1 > R3 > R4 and R2 > R3 > R4. According to this, the airflow corresponding to the recessed shape 70 formed at the blade leading edge 31 is likely to flow in the order of the larger radius of curvature. Therefore, the radial flow component can be increased by the radius of curvature R1 of the first curved surface 74 and the radius of curvature R2 of the second curved surface 75, and peeling from the shroud back surface 201 can be suppressed. Furthermore, by making the radius of curvature R3 of the corner portion 36 on the negative pressure surface 35 side of the lower portion 71 larger than the radius of curvature R4 of the corner portion 38 on the positive pressure surface 37 side of the lower portion 71, it is also possible to suppress the airflow flowing into the negative pressure surface 35 side of the blade 30 from peeling off from the negative pressure surface 35. Therefore, by reducing the speed variation in the rotation direction of the blade 30, noise can be reduced.

[0054] (7) In the first embodiment, the depth Da of the recessed shape 70 and the blade outlet height Db have the relationship of 0 < Da ≤ Db × 0.09. According to this, as a result of the experiments conducted by the inventors, it was found that a noise reduction effect can be obtained by setting the depth Da of the recessed shape 70 to 9% or less of the blade outlet height Db.

[0055] (8) In the first embodiment, the shroud 20 has a shroud cylinder portion 22 that extends in a cylindrical shape from the inner peripheral edge on the opening 21 side toward the side opposite to the main board 10. Also, the blade 30 has a standing wall portion 39 that extends toward the main board 10 side in parallel with the inner peripheral wall 211 of the opening 21 of the shroud 20 from the connection portion 73 between the inner peripheral wall 211 of the opening 21 of the shroud 20 and the blade 30. According to this, the airflow flowing along the recessed shape 70 formed at the blade leading edge 31 is likely to flow to the shroud back surface 201. Therefore, peeling of air from the shroud back surface 201 can be suppressed.

[0056] (Second Embodiment) The second embodiment will be described. The second embodiment is similar to the first embodiment except that the recessed shape 70 is partially changed. Therefore, only the differences from the first embodiment will be described.

[0057] As shown in FIG. 9, in the blower 1 of the second embodiment, a concave shape 70 is formed on the surface of the blade leading edge 31 facing away from the main plate 10. The concave shape 70 is formed by a low-level portion 71 and a high-level portion 72. In the second embodiment, the first curved surface 74 described in the first embodiment is not provided at the portion where the low-level portion 71 and the high-level portion 72 are connected. The radially outer portion of the high-level portion 72 is substantially at a right angle. However, in the second embodiment, the radially inner portion 751 and the radially outer portion 391 of the low-level portion 71 are both curved surfaces. As a result, in the second embodiment, the turbulence of the airflow at the radially inner portion 751 and the radially outer portion 391 of the low-level portion 71 can be suppressed, and noise can be reduced.

[0058] The blower 1 of the second embodiment also has the same configuration as the first embodiment except for the configuration described above, and can achieve the same effects as the first embodiment.

[0059] Third embodiment A third embodiment will be described. The third embodiment is similar to the first embodiment, except that a part of the recessed shape 70 is changed, and only the parts different from the first embodiment will be described.

[0060] As shown in FIG. 10, in the blower 1 of the third embodiment, a recessed shape 70 is formed on the surface of the blade leading edge 31 facing away from the main plate 10. The recessed shape 70 is formed by a low-level portion 71 and a high-level portion 72. In the third embodiment, as in the first embodiment, the portion where the low-level portion 71 and the high-level portion 72 are connected has a first curved surface 74 and a second curved surface 75. The radius of curvature R1 of the first curved surface 74 and the radius of curvature R2 of the second curved surface 75 have a relationship of R1>R2. In the third embodiment, the portion 391 where the low-level portion 71 and the vertical wall portion 39 are connected forms an approximately right angle.

[0061] Also in the blower 1 of the third embodiment, by increasing the radius of curvature R1 of the first curved surface 74, which encourages the air flowing in from the opening 21 of the shroud 20 to flow radially outward, the radial flow component due to the Coanda effect increases, thereby suppressing separation of the air from the underside 201 of the shroud.

[0062] The blower 1 of the third embodiment also has the same configuration as the first embodiment, and can achieve the same effects as the first embodiment.

[0063] (Other embodiments) (1) In each of the above embodiments, the impeller 2 of the blower 1 is described as a turbofan. However, the present invention is not limited to this and may be, for example, a sirocco fan, a radial fan, or a cross-flow fan.

[0064] (2) In each of the above embodiments, the motor 40 is described as an outer rotor type brushless DC motor. However, the present invention is not limited to this. For example, the motor 40 may be an inner rotor type brushless DC motor, an AC motor, or the like.

[0065] (3) In each of the above embodiments, the shroud 20 has been described as having the shroud tubular portion 22, the shroud side projections 23, and the like, but is not limited thereto, and the shroud 20 does not necessarily have to have these configurations.

[0066] (4) In each of the above embodiments, the main plate 10 has been described as having the central portion 11, the fixed portion 12, the annular portion 13, etc. However, this is not limited thereto. For example, the main plate 10 may be one in which the central portion 11, the fixed portion 12, the annular portion 13, etc. are integrally formed.

[0067] (5) In each of the above embodiments, the blower 1 has been described as including the case 50. However, this is not limiting, and the blower 1 does not necessarily have to include the case 50.

[0068] The present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope of the claims. Moreover, the above-described embodiments are not unrelated to each other, and can be appropriately combined, except when the combination is clearly impossible. Moreover, in each of the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential, except when they are specifically stated to be essential or when they are clearly considered to be essential in principle. Moreover, in each of the above-described embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiments are mentioned, they are not limited to the specific numbers, except when they are specifically stated to be essential or when they are clearly limited to a specific number in principle. Moreover, in each of the above-described embodiments, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., except when they are specifically stated to be essential or when they are clearly limited to a specific shape, positional relationship, etc. in principle. [Explanation of symbols]

[0069] 1 Centrifugal blower 10 Main plate 20 Shroud 21 Opening 30 wings 70 Concave shape 71 Lower part 72 High part 73 Connection points 211 Inner wall

Claims

1. In centrifugal blowers, A rotatably mounted main plate (10); An annular shroud (20) provided opposite the main plate and having an opening (21) at the center through which air flows in; A plurality of blades (30) are arranged at predetermined intervals around an axis (CL) serving as a rotation center between the shroud and the main plate and are connected to the shroud and the main plate; an upper case (53) having an upper case body (56) covering a surface of the shroud opposite to the main plate, an air suction port (51) provided in the upper case body at a position corresponding to the opening, and a bell mouth (57) extending cylindrically from an inner peripheral edge of the air suction port toward the main plate, When a virtual circle is defined with the axis as its center on a virtual plane perpendicular to the axis, and the radial side of the virtual circle closer to the axis is referred to as the radial inner side, and the opposite side is referred to as the radial outer side, The leading edge (31) of the blade is provided radially inward of the inner circumferential wall (211) of the opening of the shroud, a low-level portion (71) is provided on a surface of the leading edge facing away from the main plate, the low-level portion (71) being located radially inward from a connection point (73) between the inner circumferential wall of the opening and the blade and closer to the main plate than the connection point and along a plane perpendicular to the axis; and a high-level portion (72) is provided radially inward from the low-level portion and on the opposite side to the main plate from the low-level portion, A recessed shape (70) is formed on a surface of the leading edge facing away from the main plate by the low-level portion and the high-level portion, a main plate side end of the bell mouth is located on an opposite side to the main plate with respect to the connection point.

2. A centrifugal blower as described in claim 1, wherein the outer diameter of the bellmouth is Dc and the outer diameter of a circle connecting in the direction of rotation the points or faces of the low-position portions provided on the plurality of blades that are closest to the main plate is Dw, such that Dc < Dw.

3. The centrifugal blower according to claim 1 or 2, wherein a radially inner portion (75, 751) of the lower portion is curved.

4. 4. The centrifugal blower according to claim 1, wherein a radially inner portion and a radially outer portion of said lower portion are both curved.

5. A portion where the low-level portion and the high-level portion are connected has a first curved surface (74) that is a convex curved surface on the low-level portion side of the high-level portion and opposite to the main plate, and a second curved surface (75) that is a convex curved surface on the radially outer side of the first curved surface and toward the main plate, 5. The centrifugal blower according to claim 1, wherein, when the leading edge is viewed from the direction of rotation of the blade, a radius of curvature of the first curved surface is R1 and a radius of curvature of the second curved surface is R2, and a relationship of R1 > R2 is satisfied.

6. A portion where the low-level portion and the high-level portion are connected has a first curved surface (74) that is a curved surface that is convex on the low-level portion side of the high-level portion and is opposite to the main plate, and a second curved surface (75) that is a curved surface that is convex on the main plate side radially outward of the first curved surface, and when the leading edge is viewed from the rotation direction of the blade, the radius of curvature of the first curved surface is R1 and the radius of curvature of the second curved surface is R2, 6. The centrifugal blower according to claim 1, further comprising: a corner portion (36) of the low-position portion on a negative pressure surface (35) side has a radius of curvature R3, and a corner portion (38) of the low-position portion on a positive pressure surface (37) side has a radius of curvature R4, when the low-position portion is viewed in a cross section perpendicular to a direction in which the blade extends from the leading edge to the trailing edge, the radius of curvature R1 > R3 > R4 and the radius of curvature R2 > R3 > R4 are satisfied.

7. 7. The centrifugal blower according to claim 1, wherein a distance between a point or surface of said low portion closest to said main plate and a point or surface of said high portion farthest from said main plate is Da, and a distance between said main plate and said shroud on a trailing edge side of said blade is Db, where Da satisfies the relationship: 0<Da≦Db×0.

09.

8. The shroud has a shroud cylindrical portion (22) extending cylindrically from an inner peripheral edge on the opening side toward an opposite side to the main plate, 8. The centrifugal blower according to claim 1, wherein the blade has a vertical wall portion (39) extending from a connection point between the inner circumferential wall of the opening and the blade toward the main plate in parallel with the inner circumferential wall (211) of the opening of the shroud.

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