Centrifugal fan

Abstract

The centrifugal fan includes an impeller for producing the flow of air by rotation, and a motor for rotating the impeller. The impeller includes a plurality of main blades and a plurality of auxiliary blades. In the centrifugal fan, the turbulent flow of air flowing near the outer surface of the cup part is suppressed and the noise of the centrifugal fan is reduced by connecting the auxiliary blades to the outer surface of the cup part. An opening passing through with respect to the center axis direction is formed between two adjacent auxiliary wings, and the opening end on the lower side of the opening is inclined towards a stator side, whereby some air that flowed to the outer surface efficiently flows into the cup part, thereby supplying air to the stator and suppressing temperature rise of the stator.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a electrically operated centrifugal fan used in air blasting.

2. Description of the Related Art

Conventionally, an impeller with a plurality of blades arranged in the circumferential direction with the rotating axis as the center is arranged in the centrifugal fan for taking air in the axis direction and exhausting air in the radial direction, and various modifications are made on the impeller to achieve a quieter sound, to improve air volume property, and to suppress lowering in performance involved in the temperature rise of the motor.

For example, a multi-blade fan in which an inducer section is coupled to the inner side of the blade is disclosed. Furthermore, an impeller is disclosed in which the fan efficiency is enhanced compared to the sirocco fan of general shape of the same size by having the shape of the blade as a combination of a turbo fan and a sirocco fan.

The technique is disclosed in which the impeller configuration includes an air current guiding means of a plate shape perpendicular to the rotating shaft on the inner side of the blade, and which air current guiding means is arranged on the movement path of the air current to change the pattern of the air current thereby reducing the noise, and a technique is disclosed of forming an opening communicating to the air hole between the blades at the lower part of the impeller thereby reducing the noise or the current value of when the impeller rotates.

In the centrifugal fan where the impeller including a cup part for accommodating a motor at the central part is used, turbulent flow of air tends to produce near the outer surface of the cup part, and the noise of the centrifugal fan increases when such turbulent flow moves away from the cup part towards the outer side and flows into the blades arranged in the circumferential direction. Furthermore, since air is less likely to be supplied to the inside of the cup part, the heat generated at the stator accommodated in the cup part tends to remain therein, and thus becomes essential to suppress the temperature rise of the stator.

BRIEF SUMMARY OF THE INVENTION

In the present invention, the production of the turbulent flow caused by the air flowing near the outer surface of the cup part is efficiently suppressed, and the noise of the centrifugal fan is reduced by arranging the auxiliary blades. Air is also supplied to the stator by the auxiliary blades, and thus the temperature rise of the stator is also suppressed.

The present invention relates to a centrifugal fan comprising: a cup part of substantially bottomed cylindrical shape with a cylindrical yoke portion having a predetermined center axis as center; a field magnet fixed on an inner surface of the cup part; an impeller, including a blade assembly connected to the cup part and arranged radially in an annular region on the outer side of the cup part, taking in air from the bottom side of the cup part and exhausting air in a direction away from the center axis when rotating with the cup part, the blade assembly including: a plurality of main blades arranged along the periphery of the impeller; and a plurality of auxiliary blades connected to the outer surface of the cup part and directly or indirectly connected with the plurality of main blades at an opening side of the cup part between the outer surface of the cup part and the plurality of main blades; a housing including a side wall part for covering the periphery of the impeller, a base part for covering the opening side of the cup part, and a cover part formed with an air intake port facing the bottom of the cup part, a width of a flow path between the side wall part and the impeller gradually widening towards an air exhaust port; a bearing mechanism for rotatably supporting the cup part with respect to the base part with the center axis as the center; and a stator, fixed to the base part and having at least one part positioned in the cup part, for generating a torque having the center axis as the center between the field magnet.

Other features, elements, steps, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view showing a configuration of a centrifugal fan of one embodiment of the present invention;

FIG. 2 is a plan view showing the centrifugal fan;

FIG. 3 is a perspective view showing an impeller;

FIG. 4 is a plan view showing another example of the impeller;

FIG. 5 is a plan view showing another example of the impeller;

FIG. 6 is a cross sectional view showing another example of the impeller;

FIG. 7 is a cross sectional view showing another example of the impeller;

FIG. 8 is a plan view showing another example of the impeller;

FIG. 9 is a plan view showing another example of the impeller;

FIG. 10 is a cross sectional view showing another example of an auxiliary blade;

FIG. 11 is a cross sectional view showing another example of an auxiliary blade;

FIG. 12 is a cross sectional view showing another example of an auxiliary blade;

FIG. 13 is a cross sectional view showing another example of an auxiliary blade;

FIG. 14 is a cross sectional view showing another example of an auxiliary blade;

FIG. 15 is a cross sectional view showing another example of an auxiliary blade;

FIG. 16 is a cross sectional view showing another example of an auxiliary blade; and

FIG. 17 is a cross sectional view showing another example of an auxiliary blade.

DETAILED DESCRIPTION OF INVENTION

The centrifugal fan according to the present invention will now be described for each embodiment with reference to the drawings. The present invention is not limited to the examples described below.

FIG. 1 is a view showing a configuration of a centrifugal fan 1 according to one embodiment of the present invention, and shows a longitudinal cross section cut along a plane including a center axis J1. FIG. 2 is a plan view showing the centrifugal fan 1. The illustration of the end portions of a housing 10 on both left and right sides are omitted in FIG. 1, and a state in which a cover part (denoted with reference character 111 in FIG. 1) of the upper surface of the housing 10 is removed is shown in FIG. 2. As shown in FIGS. 1 and 2, the centrifugal fan 1 includes an impeller 2 for generating the flow of air by rotating, and a motor 3, connected to the impeller 2, for rotating the impeller 2 about a predetermined center axis J1, where the impeller 2 and the motor 3 are housed in the housing 10. The centrifugal fan 1 is used as a power operated fan for air cooling the electrical products and electronic equipments.

As shown in FIG. 1, the housing 10 includes a cover part 111 formed with an air intake port 12, and a base part 112 attached with a stator section 31 to be hereinafter described, and further includes a side wall part 113 that covers the outer periphery of the impeller 2, as shown in FIG. 2. The housing 10 is assembled by attaching the cover part 111 to a housing main body 11 including the base part 112 and the side wall part 113 shown in FIG. 2, and a flow path of the air is formed (i.e., flow of air generated by rotation of impeller 2 is adjusted and fed by housing 10) as the housing 10 surrounds the impeller 2. The width of the flow path between the side wall part 113 and the impeller 2 has a shape that gradually widens towards an air exhaust port 13 (see FIG. 2), and the space between the base part 112 and the side wall part 113 in the housing 10 is blocked.

The motor 3 is an outer rotor type motor, as shown in FIG. 1, and includes a stator section 31 which is a fixed assembly, and a rotor section 32 which is a rotating assembly, where the rotor section 32 is rotatably supported with respect to the stator section 31 with the center axis J1 as the center by a bearing mechanism to be hereinafter described. The following description is made with the rotor section 32 side as the upper side and the stator section 31 side as the lower side along the center axis J1 for the sake of convenience, but the center axis J1 does not necessarily need to coincide with the direction of gravitational force.

The stator section 31 is fixed to a base part 112 which is the lower surface of the housing 10, and a bearing holding part 311 of a substantially cylindrical shape having the center axis J1 as the center and projecting upward (i.e., rotor section 32 side) from the base part 112 is attached at a cylindrical region formed at the center part of the base part 112. On the inner side of the bearing holding section 311, ball bearings 312, 313 serving as bearing mechanism are arranged on the upper and lower sections in the center axis J1 direction and a pre-load spring 314 is arranged on the lower side of the ball bearing 313.

The stator section 31 further includes a stator 315 fixed on the periphery of the bearing holding part 311 (i.e., fixed to the base part 112 at the periphery of the bearing holding part 311), and a circuit substrate 316 electrically connected to the stator 315 between the stator 315 and the base part 112 and mounted with electronic components for current control to the stator 315.

The rotor section 32 includes a cup part 321 of a substantially bottomed cylindrical shape having the center axis J1 as the center and having an opening 3211 facing downward (i.e., opening 3211 facing the base part 112), a substantially cylindrical field magnet 322 fixed to the inner surface of the cup part 321 and facing the stator 315, and a shaft 323 projecting downward from the bottom of the cup part 321 (i.e., region of substantially circular disc shape at the upper end of the cup part 321).

The shaft 323 is attached to the cup part 321 by being press fit and fixed to the bush 324 fixed at the bottom of the cup part 321, and inserted to the bearing holding part 311 and rotatably supported by the ball bearings 312, 313. An engagement member 3231 for engaging the spring 314 is attached to the vicinity of the lower end of the shaft 323, where the shaft 323 and the ball bearings 312, 313 are held at the appropriate positions when preload is applied to the ball bearing 313 by the spring 314.

In the centrifugal fan 1, the ball bearings 312, 313 serve as the bearing mechanism for rotatably supporting the cup part 321 with respect to the base part 112 with the center axis J1 as the center. When the drive current supplied to the stator 315 via the circuit substrate 316 is controlled and a torque (i.e. rotational force) having the center axis J1 as the center is generated between the stator 315 and the field magnet 322, the shaft 323 as well as the impeller 2 including the blade assembly 22 connected to the cup part 321 rotate with the cup part 321 with the center axis J1 as the center. The shaft 323 may be directly attached to the cup part 321 without the bush 324 in between.

In the centrifugal fan 1, the opening 3211 side of the cup part 321 is covered by the base part 112, and the inner side of the cup part 321 is arranged with a yoke member 3212 of a substantially bottomed cylindrical shape including a cylindrical yoke portion 321a having the center axis J1 as the center. The yoke member 3212 is made of metal having magnetism, the field magnet 322 is attached to the inner surface of the yoke part 321a, and the bush 324 is attached to the center of the bottom thereof. The outer side of the cup part 321 is arranged with an outer side cup part 3213 of substantially bottomed cylindrical shape made of resin, which is integrally molded with the entire impeller 2, and is press fit and fixed with the yoke member 3212. The configuration of the cup part 321 is not limited to the configuration of FIG. 1, and for example, the yoke member 3212 may be a cylindrical shape, the outer side cup part 3213 may be connected to the shaft 323 or the bush 324, or the outer side cup part 3213 may be omitted and the impeller 2 may be directly connected to the opening of the yoke member 3212.

FIG. 3 is a perspective view showing the impeller 2 and the outer side cup part 3213 integrally molded with the impeller 2. The impeller 2 includes the blade assembly 22 arranged radially in the annular region (having center axis J1 as center) on the outer side of the cup part 321, as shown in FIGS. 1 to 3. In the centrifugal fan 1, the air is taken in from the air intake port 12 facing the upper side (i.e., bottom side of the cup part 321) of the impeller 2 and the air is exhausted in a direction away from the center axis J1, when the impeller 2 rotates with the cup part 321, whereby the air is introduced to the air exhaust port 13 along the side wall part 113 as described above.

The blade assembly 22 includes a plurality of main blades 221 arranged along the periphery of the impeller 2 at a distance from the outer surface 321b of the cup part 321 (outer cup part 3213), and a plurality of auxiliary blades 222 arranged between the cup part 321 and the plurality of main blades 221 along the outer surface 321b of the cup part 321. In FIG. 2, the distal end of the main blade 221 is hidden except for one section, but each of the plurality of main blades 221 are formed as forward blades inclined in the rotating direction 51 of the impeller 2 while being directed to the outer side. The plurality of main blades 221 have the lower ends on the base part 112 side perpendicular to the center axis J1 and coupled by an annular plate 23 having the center axis J1 as the center, and the upper ends coupled by an annular coupling part 24, which are integrally molded. In FIG. 2, one section of the coupling part 24 is omitted to show the shape of the main blade 221 (same as in FIGS. 4 to 7).

Each of the plurality of auxiliary blades 222 is a backward blade inclined to the side opposite the rotating direction 51 of the impeller 2 while being directed to the outer side as shown in FIG. 2, and is connected to the outer surface 321b of the outer side cup part 3213 of the cup part 321, and also has the outermost region of the auxiliary blades 222 connected to the region on the inner side of the annular plate 23. The auxiliary blade 222 is directly connected to one main blade 221 for every two main blades 221 on the base part 112 side, and each of the plurality of auxiliary blades 222 is continued to one of the plurality of main blades 221, as shown in FIGS. 1 and 2. Thus, the region between the main blade 221 and the auxiliary blade 222 functions as a rib, and the auxiliary blades 222 itself also function as the rib, whereby the rigidity of the impeller 2 is enhanced.

In particular, when the impeller 2 is molded by resin, the molding (resin injection, take out from die etc.) of the impeller 2 is facilitated by connecting the main blade 221 and the auxiliary blade 222 using the annular plate 23 on the base part 112 side. If problems do not arise in terms of rigidity and molding of the impeller 2, the main blade 221 and the auxiliary blade 222 may obviously be separated, and the plurality of auxiliary blades 222 may be indirectly connected to the plurality of main blades 221 by way of the annular plate 23. The auxiliary blade 222 may be connected to the outer surface of the yoke member 3212 (see FIG. 1) through insert molding and the like.

In the blade assembly 22, the main blade 221 and the auxiliary blade 222 are preferably continued in terms of smoothly flowing the air in from the auxiliary blade 222 to the main blade 221. On the other hand, the flow-in efficiency of the air to the main blade 221 enhances if an obstacle is not arranged between the cup part 321 and the main blade 221. The main blade 221 and the auxiliary blade 222 are designed so as to be continued in the centrifugal fan 1 and the width in the center axis J1 direction of the impeller 2 between the main blade 221 and the auxiliary blade 222 (i.e., boundary) is made small, and thus the turbulent flow suppressing effect by the auxiliary blade 222 is obtained, and the influence of the auxiliary blade 222 on the property (e.g., static pressure-air volume property) of the centrifugal fan 1 caused by the air flow generated at the main blade 221 is reduced. A specific preferable designing condition includes having the width (denoted with reference character W in FIG. 1) in the center axis J1 direction of the impeller 2 between the plurality of main blades 221 and the plurality of auxiliary blades 222 to be less than or equal to ⅓ of the length (denoted with reference character L) in the center axis J1 direction of the plurality of main blades 221. Since the turbulent flow region becomes wider at the vicinity of the lower part of the outer surface by the air flowing along the outer surface of the cup part 321, the edge 2222 on the side away from the base part 112 of the auxiliary blade 222 is inclined towards the base part 112 while extending towards the outer side from the outer surface 321b of the cup part 321, and the width of the auxiliary blade 222 with respect to the center axis J1 direction is gradually increased from the peripheral side of the impeller 2 towards the cup part 321 in the centrifugal fan 1, as shown in FIG. 1. As a result, the production of turbulent flow is efficiently suppressed without lowering the fan property. The width in the center axis J1 direction of the impeller 2 between the main blade 221 and the auxiliary blade 222 is a minimum width in the up and down direction between one main blade 221 and one auxiliary blade 222 when the main blade 221 and the auxiliary blade 222 are directly connected (i.e., width in the up and down direction of a rib shaped region the annular region when focusing only on a substantially concave region of annular shape having the center axis J1 as the center between the plurality of main blades 221 and the plurality of auxiliary blades 222), and is the thickness of the annular plate 23 when the main blade 221 and the auxiliary blade 222 are indirectly connected by way of the annular plate 23.

A plurality of openings 25 passing through with respect to the center axis J1 direction between the plurality of auxiliary blades 222 are further arranged in the impeller 2, as shown in FIGS. 1 to 3. As shown in FIG. 1, the opening ends of the base part 112 side of the plurality of openings 25 include an edge 2221 on the base part 112 side of the plurality of auxiliary blades 222, and the region 251 (i.e., region on the inner side of the annular plate 23) on the plurality of main blades 221 side of the opening end is brought closer to the base part 112 than the region 252 (i.e., region on the opening 3211 side of the cup part 321) on the center axis J1 side.

Therefore, the opening end inclines towards a gap between the stator 315 and the circuit substrate 316. In order to incline the opening end, the edge 2221 on the base part 112 side of the auxiliary blade 222 is inclined towards the base part 112 while extending towards the outer side from the opening 3211 of the cup part 321.

The configuration of the centrifugal fan 1 has been described, where a plurality of auxiliary blades connected to the outer surface 321b and directly connected to the main blade 221 on the base part 112 side (may be indirectly connected by way of the annular plate 23) are arranged between the outer surface 321b of the cup part 321 and the main blade 221 in the centrifugal fan 1, whereby the air flowing near the outer surface 321b of the cup part 321 is taken in by the auxiliary blade 222 and thus the air is smoothly introduced into the main blade 221 without stagnating. As a result, the production of the turbulent flow at the vicinity of the outer surface 321b of the cup part 321 is suppressed, the air is smoothly flowed to the main blade 221, and noise of the centrifugal fan 1 is reduced.

In the centrifugal fan 1, heat generated in the stator 315 tends to remain when the motor 3 rotates since at least one part of the stator 315 is positioned in the cup part 321, but since the opening 25 passing through with respect to the center axis J1 direction is arranged between two adjacent auxiliary blades 222, some air flowing along the outer surface 321b of the cup part 321 flows into the inside of the cup part 321 (region where air flows out from the cup part 321 is also formed on the air exhaust port 13 side), and furthermore, the air is efficiently sent to the cup part 321 as the air current is produced in the vicinity of the opening 25 by the auxiliary blade 222, whereby the temperature rise of the stator 315 is suppressed by supplying air to the stator 315. Although it depends on the designing condition, if the temperature of the stator 315 is about 115° C. in the impeller in which the opening 25 is not formed, the temperature lowers to about 47° C. by arranging the opening 25.

The supply efficiency of the air flowing towards the stator 315 can be enhanced, and cooling of the circuit substrate 316 can be performed by inclining the opening ends on the base part 112 side of the plurality of openings 25 toward the stator 315 or the circuit substrate 316 (in particular, toward the gap between the stator 315 and the circuit substrate 316).

Various other shapes for the main blade 221 and the auxiliary blade 222 of the impeller 2 will now be described. FIGS. 4 to 9 are views showing other examples of the impeller. Each auxiliary blade 222 is a backward blade in the impeller 2 shown in FIG. 2, but the shape of the auxiliary blade is not limited to the backward blade, and each auxiliary blade 222a may be a forward blade as in the impeller 2a shown in FIG. 4, or each auxiliary blade 222b may be a radial blade extending linearly in the radial direction from the cup part 321 as in the impeller 2b shown in FIG. 5. The main blade 221 of the impeller 2a and the impeller 2b is a forward blade, similar to in the impeller 2.

A comparison experiment in the noise value of the impellers 2, 2a, 2b and the impeller (not shown) arranged only with the main blade 221 was performed, which result was 54.1 dB(A), 55.2 dB(A), 54.8 dB(A), and 55.8 dB(A). Therefore, the noise value is apparently reduced the most by having the auxiliary blade 222 as the backward blade when the main blade 221 is formed as the forward blade to enhance the static pressure of the fan. The noise is still reduced by arranging the auxiliary blade even if the auxiliary blade is not the backward blade.

The main blade is not limited to the forward blade as in the impeller 2 of FIG. 2, and for example, may be the main blade 221a, which is the radial blade, as in the impeller 2c shown in FIG. 6 or the main blade 221b, which is the backward blade, as in the impeller 2d shown in FIG. 7.

In the blade assembly 22 of the impeller 2, one main blade 221 and one auxiliary blade 222 may be connected for every three or more main blades 221, or the auxiliary blade 222 may be continuously formed to all the main blades 221 as in the impeller 2e shown in FIG. 8. The shape of the auxiliary blade is not limited to a flat plate shape, and each auxiliary blade 222c may be curved while extending to the peripheral side of the impeller 2f from the cup part 321 when looking at the impeller 2f from the upper side, as shown in FIG. 9.

Furthermore, the connecting range of the auxiliary blade 222 and the cup part 321 is not only the range from the middle to the lower end of the outer surface 321b of the cup part 321 with respect to the center axis J1 direction, as shown in FIG. 1, and may be the range from the upper end to the lower end of the cup part 321 as shown in FIG. 10, the range from the middle to the middle of the outer surface 321b with respect to the center axis J1 direction, as shown in FIG. 11, or may be the range from the upper end to lower than the lower end of the cup part 321, as shown in FIG. 12. Furthermore, the edges 2221, 2222 of the lower side and the upper side of the auxiliary blade 222 may be curved, as shown in FIG. 13, or the edge 2222 of the upper side and the edge 2223 parallel to the center axis J1 may be continued, as shown in FIGS. 14 and 15.

Therefore, the shape, number, and size of the blade may be changed in variety of ways, and the shape etc. of the main blade 221 and the auxiliary blade 222 are determined based on the equipment on which the centrifugal fan 1 is mounted, the air volume property that is required etc. The production of turbulent flow at the vicinity of the outer surface 321b of the cup part 321 is suppressed and the noise is reduced for any type of main blade 221 and auxiliary blade 222.

The embodiments of the present invention have been described, but the present invention is not limited to the above embodiments, and various modifications are possible.

For example, the shape of the edge 2222 on the upper side of the auxiliary blade 222 may be a shape in which a step is formed in the middle, as shown in FIG. 16. Alternatively, the edges 2221 of the plurality of auxiliary blades 222d may be extended horizontally from the opening 3211 of the cup part 321 to the outer side so that the shape of the plurality of auxiliary blades 222d is substantially triangular, and the outermost region of the plurality of auxiliary blades 222d may be connected only to the region on the inner side of the annular plate 23, as shown in FIG. 17. In this case as well, the production of the turbulent flow at the outer surface 321b of the cup part 321 is suppressed and the noise is reduced, and moreover, the temperature rise of the stator 315 is suppressed since the opening 25 is arranged between two adjacent auxiliary blades 222d and the air is supplied to the inside of the cup part 321 by the action of the auxiliary blade 222d and the opening 25.

The entire stator 315 is substantially accommodated in the cup part 321 in the above embodiment, but only one part of the stator 315 may be positioned in the cup part 321 when the stator 315 is arranged in the concave part formed around the center axis J1 of the base part 112. Furthermore, a sleeve bearing and the like may be used for the bearing mechanism other than the ball bearing.

The annular plate 23 does not need to be a plate perpendicular to the center axis J1, and the cross section at the plane including the center axis J1 may be inclined from the direction perpendicular to the center axis J1 as in the inclined surface of a frustum of circular cone. Moreover, air is supplied from the opening 25 to the stator 315 in the embodiment, but the opening 25 does not need to be arranged if the opening 25 does not need to be arranged due to reasons that the temperature rise of the stator 315 is within the tolerable range.

While the present invention has been described with respect to preferred embodiments, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the present invention which fall within the true spirit and scope of the invention.

Claims

1. A centrifugal fan comprising:

a cup part of substantially bottomed cylindrical shape with a cylindrical yoke portion having a predetermined center axis as center;

a field magnet fixed on an inner surface of the cup part;

an impeller, including a blade assembly connected to the cup part and arranged radially in an annular region on the outer side of the cup part, taking in air from the bottom side of the cup part and exhausting air in a direction away from the center axis when rotating with the cup part, the blade assembly including: a plurality of main blades arranged along the periphery of the impeller; and a plurality of auxiliary blades connected to the outer surface of the cup part and directly or indirectly connected with the plurality of main blades at an opening side of the cup part between the outer surface of the cup part and the plurality of main blades;

a housing including a side wall part for covering the periphery of the impeller, a base part for covering the opening side of the cup part, and a cover part formed with an air intake port facing the bottom of the cup part, a width of a flow path between the side wall part and the impeller gradually widening towards an air exhaust port;

a bearing mechanism for rotatably supporting the cup part with respect to the base part with the center axis as the center; and

a stator, fixed to the base part and having at least one part positioned in the cup part, for generating a torque having the center axis as the center between the field magnet.

2. The centrifugal fan according to claim 1, wherein the width in the center axis direction of the impeller between the plurality of main blades and the plurality of auxiliary blades is less than or equal to ⅓ the length in the center axis direction of the plurality of main blades.

3. The centrifugal fan according to claim 1, wherein the impeller includes a plurality of openings passing through with respect to the center axis direction between the plurality of auxiliary blades.

4. The centrifugal fan according to claim 3, wherein edges on the base part side of the plurality of auxiliary blades are inclined towards the base part while extending from the opening of the cup part to the outer side; the opening ends on the base part side of the plurality of openings include the edges, and a region on the plurality of main blades side of the opening end is closer to the base part than a region on the center axis side.

5. The centrifugal fan according to claim 4, wherein edges on the side away from the base part of the plurality of auxiliary blades are inclined towards the base part while extending to the outer side.

6. The centrifugal fan according to claim 1, wherein the ends on the base part side of the plurality of main blades are coupled by an annular plate having the center axis as the center, and outermost regions of the plurality of auxiliary blades are connected to the regions on the inner side of the annular plate.

7. The centrifugal fan according to claim 1, wherein each of the plurality of auxiliary blades is connected to one of the plurality of main blades.