US20120003109A1

US20120003109A1 - Blower fan

Info

Publication number: US20120003109A1
Application number: US13/171,650
Authority: US
Inventors: Jumpei KITAMURA
Original assignee: Nidec Corp
Current assignee: Nidec Corp
Priority date: 2010-07-01
Filing date: 2011-06-29
Publication date: 2012-01-05
Also published as: CN102312846A; JP2012013022A

Abstract

A blower fan includes an impeller cup; a shaft including an end arranged to project axially upward from the impeller cup; a rotor magnet fixed to the shaft; a first bearing and a second bearing arranged axially above and below, respectively, the impeller cup; a first bearing support portion and a second bearing support portion arranged to support the first and second bearings, respectively; and a first housing and a second housing arranged on axially upper and lower sides, respectively. The first and second housings are joined to each other at an axial level higher than an axial position of a joint between the second housing and a second joining portion arranged to join the second housing and the second bearing support portion to each other.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a blower fan capable of being used, for example, to cool an electronic device.
2. Description of the Related Art
Outer-rotor motors, in which a rotor is arranged outside of a stator, have been predominantly used as motors for driving blower fans because of an easier assembling procedure, a reduced number of parts, and so on. In addition, in terms of performance, the outer-rotor motors have a greater moment of inertia and are able to achieve increased driving torque, and are therefore able to maintain a constant speed more easily.
Meanwhile, as electronic devices have become increasingly dense in recent years, the amount of heat generated from the electronic devices has increased. There has accordingly been a demand for blower fans used to cool such electronic devices to rotate at a greater speed to provide a greater cooling effect. However, in outer-rotor motors, an increased rotational speed of the blower fan leads to an increased vibration because of the great moment of inertia of the outer-rotor motors which thus may cause a problem in terms of strength.
Use of inner-rotor motors, in which the rotor is arranged inside of the stator, allows a greater rotational speed, because the inner-rotor motors have a smaller moment of inertia than the outer-rotor motors.
U.S. 2009/0180901, for example, describes a conventional blower fan using an inner-rotor motor. This blower fan includes a motor support portion in which a support portion arranged to support a bearing and a support portion arranged to support a stator are defined by a single continuous member.
The blower fan using the inner-rotor motor as described in U.S. 2009/0180901 (hereinafter referred to simply as an “inner-rotor blower fan”), however, has a disadvantage as compared to a blower fan using an outer-rotor motor (hereinafter referred to simply as an “outer-rotor blower fan”) because of its structure.
Specifically, in the inner-rotor blower fan, a bearing support portion, a rotor holder (a rotor magnet), a stator, a stator support portion, an impeller cup, and blades are sequentially arranged in this order from a rotation axis to a radial outside. In addition, specified radial gaps are arranged between the bearing support portion and the rotor holder, between the rotor holder and the stator, and between the stator support portion and the impeller cup.
In contrast, in the outer-rotor blower fan, a bearing support portion, a stator, a rotor holder (a rotor magnet), an impeller cup, and blades are arranged, and the bearing support portion additionally functions as a stator support portion. Since the impeller cup is press fitted to an outer circumference of the rotor holder, a specified radial gap is arranged only between the stator and the impeller cup.
As described above, the inner-rotor blower fan has a greater number of components arranged in a radial direction than the outer-rotor blower fan, and accordingly has a disadvantage of an increased radial dimensions. Moreover, the inner-rotor blower fan includes a greater number of gaps between the components, and therefore also has a disadvantage of an inability to secure a large radial clearance.
Furthermore, as mentioned above, the inner-rotor blower fan is capable of producing only a relatively small driving torque as compared to the outer-rotor blower fan. Therefore, the inner-rotor blower fan needs to have an increased axial dimension of the rotor magnet in order to increase the driving torque. As such, the inner-rotor blower fan also has a disadvantage of the increased axial dimension.

SUMMARY OF THE INVENTION

According to preferred embodiments of the present invention, in a blower fan including an inner-rotor motor, one end of a shaft is arranged to project axially upward from an impeller cup. In addition, a pair of bearings are arranged such that one of the bearings is arranged near the end of the shaft axially above the impeller cup, and the other bearing is arranged near the other end of the shaft axially below the impeller cup. Moreover, bearing support portions each of which is arranged to support a separate one of the bearings are joined to separate housings that are divided from each other in the axial direction.
Specifically, a blower fan according to a preferred embodiment of the present invention preferably includes an impeller including a substantially cylindrical impeller cup including a cover portion, and a plurality of blades arranged on an outer circumferential surface of the impeller cup; a shaft fixed directly or indirectly to the impeller cup that includes an end arranged to project axially upward from the cover portion of the impeller cup; a rotor magnet fixed either directly or indirectly to the shaft; a first bearing arranged axially above the cover portion of the impeller cup, and arranged to support the shaft such that the shaft is rotatable with respect to the stator; a first bearing support portion arranged to support the first bearing; a first housing arranged radially outward of the impeller on an axially upper side; a first joining portion arranged to join the first housing and the first bearing support portion to each other; a second bearing arranged axially below the cover portion of the impeller cup, and arranged to support the shaft such that the shaft is rotatable; a second bearing support portion arranged to support the second bearing; a second housing arranged radially outward of the impeller on an axially lower side; a second joining portion arranged to join the second housing and the second bearing support portion to each other; a stator arranged radially outward of the rotor magnet and opposite the rotor magnet; and a stator support portion arranged to support the stator. The first and second housings are arranged to be joined to each other at a level higher than that of a position of joint between the second joining portion and the second housing.
In the above-described preferred embodiments, two separate bearings are preferably arranged one axially above and the other axially below the rotor magnet and the stator, which define portions of a motor, while at the same time two separate bearing support portions are arranged one axially above and the other axially below the rotor magnet and the stator. This makes it possible to reduce the radial dimensions of the motor, and to thereby realize an inner-rotor blower fan that possesses reduced radial dimensions. Moreover, the assemblage of the blower fan is more easily accomplished because the two bearing support portions arranged at upper and lower levels, respectively, are joined to separate housings that are divided from each other in the axial direction.
The impeller cup may also preferably include a recessed portion defined in a central portion of the cover portion, and at least a lower end of the first bearing support portion may be arranged inside the recessed portion. In this case, an inner-rotor blower fan with a reduced increase in axial dimensions thereof is realized.
A preferred embodiment of the present invention is able to realize an inner-rotor blower fan with a reduced radial dimension and a reduced increase in axial dimensions thereof.
The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating the structure of a blower fan according to a preferred embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating the structure of a blower fan according to an example modification of a preferred embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view illustrating the structure of a blower fan according to another preferred embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view illustrating the structure of a blower fan according to yet another preferred embodiment of the present invention.

FIG. 5 is a schematic cross-sectional view illustrating the structure of a blower fan according to yet another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the preferred embodiments, a direction parallel or substantially parallel to a rotation axis and a radial direction centered on the rotation axis will be referred to simply as an “axial direction” and a “radial direction”, respectively. Note that the present invention is not limited to the preferred embodiments described below. Also note that the preferred embodiments described below may be combined with other preferred embodiments of the present invention.
FIG. 1 is a schematic cross-sectional view illustrating the structure of a blower fan 100 according to a preferred embodiment of the present invention. The blower fan 100 according to the present preferred embodiment preferably is an axial fan using an inner-rotor motor.
Referring to FIG. 1, the blower fan 100 includes a rotor 20 arranged to rotate about a rotation axis J together with a shaft 30, a stator 60 arranged radially outward of the rotor 20 and opposite the rotor 20, and an impeller 10 arranged to rotate together with the shaft 30. The rotor 20 preferably includes a substantially cylindrical rotor holder 21 fixed to the shaft 30, and a rotor magnet 22 fixed to an outer circumferential surface of the rotor holder 21. In addition, the stator 60 is preferably supported by a stator support portion 61. The impeller 10 preferably includes a substantially cylindrical impeller cup 11 including a cover portion arranged to be fixed to the shaft 30, and a plurality of blades 12. The blades 12 are arranged on an outer circumferential surface of the impeller cup 11, and arranged radially outward of the stator 60. The blower fan 100 is arranged to draw in air from one axial side and discharge the air to the other axial side through the rotation of the blades 12. In the following description, an inlet side and an outlet side along the axial direction will be referred to as an “upper side” and a “lower side”, respectively, for the sake of convenience.
Note that the impeller cup 11 may not necessarily be directly fixed to the shaft 30. For example, the impeller cup 11 may be indirectly fixed to the shaft 30 by being fixed to the rotor holder 21 fixed to the shaft 30. In that case, the rotor holder 21 may be joined to the impeller cup 11 through, for example, insert molding. Also note that, although the rotor magnet 22 is fixed to the rotor holder 21 that is fixed to the shaft 30 in the present preferred embodiment, the rotor magnet 22 could instead be directly fixed to the shaft 30 if so desired, as mentioned below.
In the present preferred embodiment, one end of the shaft 30 is arranged to project axially upward from the cover portion of the impeller cup 11. A bearing arranged to support the shaft 30 such that the shaft 30 is rotatable is divided into a first bearing 40 a arranged axially above the cover portion of the impeller cup 11, and a second bearing 40 b arranged axially below the cover portion of the impeller cup 11. Moreover, a first bearing support portion 50 a arranged to support the first bearing 40 a and a second bearing support portion 50 b arranged to support the second bearing 40 b are separately arranged, one above and the other below, in the axial direction. Furthermore, a recessed portion 11 a is defined in a central portion of the cover portion of the impeller cup 11, and at least a lower end of the first bearing support portion 50 a is arranged inside the recessed portion 11 a. Here, each of the first and second bearings 40 a and 40 b may be defined by bearing structure, such as, for example, a ball bearing.
A housing arranged to cover an outer circumference of the impeller 10 is divided into a first housing 51 a and a second housing 51 b arranged radially outward of the impeller 10. The first housing 51 a is arranged axially above the second housing 51 b. The first housing 51 a is joined to the first bearing support portion 50 a through a first joining portion 52 a. The second housing 51 b is joined to the second bearing support portion 50 b through a second joining portion 52 b. The first and second housings 51 a and 51 b are joined to each other at a level higher than that of a joint between the second joining portion 52 b and the second housing 51 b.
Here, each of the first and second joining portions 52 a and 52 b is arranged to permit air currents to pass therethrough in the axial direction. For example, each of the first and second joining portions 52 a and 52 b may be defined by ribs. The ribs may be arranged to extend radially from outside surfaces of the first and second bearing support portions 50 a and 50 b to inside surfaces of the first and second housings 51 a and 51 b, respectively, so as to cross the air currents passing therethrough in the axial direction.
The radial dimension of the first joining portion 52 a and that of the second joining portion 52 b are preferably different from each other. An increase in the radial dimension of the first joining portion 52 a contributes to reducing an obstruction of the passage of incoming air currents from above in the axial direction. In addition, the wind velocity of the air currents is increased when the radial dimension of the second joining portion 52 b is arranged to be smaller than that of the first joining portion 52 a.
That is, according to a preferred embodiment of the present invention, in the blower fan 100 including the inner-rotor motor, one end of the shaft 30 is arranged to project axially upward from the impeller cup 11. In addition, the bearing 40 a is arranged near the end of the shaft 30 axially above the impeller cup 11, while the bearing 40 b is arranged near the other end of the shaft 30 axially below the impeller cup 11. Moreover, the bearing support portions 50 a and 50 b arranged to support the bearings 40 a and 40 b, respectively, are joined to the housings 51 a and 51 b, respectively, which are divided from each other in the axial direction.
According to the present preferred embodiment, each of the bearing and the bearing support portion preferably includes two members separated from each other in the axial direction and arranged one above the rotor magnet 22 and the stator 60, and the other below the rotor magnet 22 and the stator 60. That is, the bearing and the bearing support portion are prevented from being provided in a same radial plane as the arrangement of components including the rotor magnet 22 and the stator 60. Moreover, because a need to arrange a gap between the bearing support portion and the rotor magnet 22 is eliminated, it is possible to secure a large radial clearance between different components. All of this makes it possible to reduce the radial dimension of the motor.
Furthermore, the bearing support portions arranged at an axially upper position and an axially lower position, respectively, are joined to the separate housings divided from each other, one above and the other below, in the axial direction. Therefore, it is possible to prepare an assembly made up of the first housing 51 a combined with the first joining portion 52 a and the first bearing support portion 50 a, and an assembly made up of the second housing 51 b combined with the second joining portion 52 b and the second bearing support portion 50 b (and the stator support portion 61), before starting assemblage of the blower fan 100. This thereby makes it easier to assemble the blower fan 100 of the present preferred embodiment.
In FIG. 1, the second joining portion 52 b is preferably shaped so as to have a uniform axial dimension. Referring to FIG. 2, however, the second joining portion 52 b may be shaped so as to include a cutout portion defined in a radially outer end portion thereof, the cutout portion extending axially downward from, for example, an upper end portion thereof. Also in this case, the first and second housings 51 a and 51 b are joined to each other at a level higher than that of a position of the joint between the second joining portion 52 b and the second housing 51 b.
Furthermore, because the first bearing 40 a is arranged axially above the impeller cup 11, the first bearing 40 a is directly exposed to air currents that are introduced into the blower fan 100 from the inlet side. As a result, an improvement in a heat radiation effect of the first bearing 40 a is achieved.
Furthermore, as a result of one end of the shaft 30 being arranged to project axially upward from the impeller cup 11, it is possible to increase a bearing span (the term “bearing span” refers to an axial distance between the first and second bearings 40 a and 40 b) to close to the maximum axial dimension of the blower fan 100. This leads to an improved axial balance of the blower fan 100 to thereby allow the blower fan 100 to be stable with limited vibration. Here, it may be supposed that when one end of the shaft 30 is arranged to project axially upward from the impeller cup 11, the axial dimension of the blower fan 100 is increased. Note, however, that it is possible to reduce the increase in the axial dimension of the blower fan 100 by defining the recessed portion 11 a in the central portion of the cover portion of the impeller cup 11, and arranging at least the lower end of the first bearing support portion 50 a inside the recessed portion 11 a.
In the present preferred embodiment, the first housing 51 a, the first bearing support portion 50 a, and the first joining portion 52 a are preferably molded in one piece of a resin or the like preferably through injection molding, for example. The second housing 51 b, the second bearing support portion 50 b, and the second joining portion 52 b are also preferably molded in one piece of a resin or the like preferably through injection molding, for example. Note that, in this case, it is not necessary that boundaries between the first and second bearing support portions 50 a and 50 b and the first and second joining portions 52 a and 52 b, respectively, and boundaries between the first and second housings 51 a and 51 b and the first and second joining portions 52 a and 52 b, respectively, should be defined definitely.
Here, as illustrated in FIG. 1, each of the first and second bearing support portions 50 a and 50 b may be defined by a metallic member. In this case, the metallic members may be coupled to the first and second housings 51 a and 51 b, respectively, preferably through, for example, insert molding. Moreover, the stator support portion 61 may also be defined by a metallic member. In this case, as illustrated in FIG. 1, the second bearing support portion 50 b and the stator support portion 61 may be coupled to a base portion 53. Thus, a sufficient vibration-resistant strength of each of the bearing support portions 50 a and 50 b is secured even when the blower fan 100 is caused to rotate at a great speed, and heat that is generated from the stator 60 is sufficiently radiated even when the blower fan 100 is caused to operate for a long time.
Furthermore, the second joining portion 52 b may be arranged to define stationary vanes. In this case, the stationary vanes serve to regulate the flow of air currents that are to be discharged in the axial direction, and to achieve a wind acceleration effect by converting centrifugal components of the air currents into axial components thereof.
Furthermore, it is possible to widen a space between the stator support portion 61 and the shaft 30 because the axial dimension of the second bearing support portion 50 b arranged to support the second bearing 40 b can be reduced. Therefore, as illustrated in FIG. 1, it is possible to arrange a circuit board 70 having a large area in that space. A Hall element arranged to detect a change in magnetic flux which involves the rotation of the rotor magnet 22, a motor driving-use IC arranged to control supply of currents to coils of the stator 60, and so on, for example, may preferably be mounted on the circuit board 70. Note that another circuit board 71 may be arranged in a space below the second bearing support portion 50 b.
Here, in the case of the blower fan 100 in which the inner-rotor motor is used, the rotor magnet 22 is fixed to the outer circumferential surface of the rotor holder 21 as illustrated in FIG. 1, and it is therefore impossible to press fit the impeller cup 11 to the outer circumferential surface of the rotor holder 21. Therefore, it is not possible to use the rotor holder 21 to maintain the strength of the impeller cup 11. As illustrated in FIG. 1, it is therefore preferable to arrange an annular metallic member 80 in an opening end portion of the impeller cup 11 in order to increase the strength of the impeller cup 11. In this case, the annular metallic member 80 may be coupled to the impeller cup 11 preferably through, for example, insert molding. Moreover, the rotor holder 21, in addition to the annular metallic member 80, may be coupled to the impeller cup 11 through insert molding.
Next, with reference to FIG. 1, a method of assembling the blower fan 100 according to the present preferred embodiment will now be described below. Note that the method of assembling the blower fan 100 is not limited to the method described below, and that the order of steps in assembling the blower fan 100, methods by which components of the blower fan 100 are assembled, and so on may be modified appropriately.
First, the second housing 51 b provided with the second bearing support portion 50 b, the second joining portion 52 b, and the stator support portion 61 are prepared. An axially upper end portion of the second housing 51 b is at least arranged at a level higher than that of an upper end of the second joining portion 52 b. Note here that the second bearing support portion 50 b, the second joining portion 52 b, and the stator support portion 61 may be molded of, for example, a resin or the like preferably through injection molding to be formed integrally together with the second housing 51 b. Also note that each of the second bearing support portion 50 b and the stator support portion 61 may preferably be defined by, for example, a metallic member. In this case, each of the metallic members may be coupled to the second housing 51 b through insert molding.
Next, the stator 60 provided with a stator core having coils wound thereabout and the circuit board 70 to which end portions of wires of the coils are connected (i.e., a stator assembly) is prepared. Then, the stator assembly is inserted from axially above into the stator support portion 61 and fixed thereto. The stator assembly may be, for example, press fitted to the stator support portion 61 with application of a slight force, adhered to the stator support portion 61, or connected to the stator support portion 61 using any other desirable method.
Next, the second bearing 40 b (which is, for example, a ball bearing) is inserted from axially below into the second bearing support portion 50 b.
Next, an assembly (i.e., a rotor assembly) preferably including the shaft 30, the rotor 20 (i.e., the rotor holder 21 and the rotor magnet 22), and the impeller 10 (i.e., the impeller cup 11 and the blades 12), the latter two being fixed to the shaft 30, is prepared. Then, the rotor assembly is inserted from axially above into the second bearing 40 b.
Next, the first housing 51 a provided with the first bearing support portion 50 a and the first joining portion 52 a is prepared, and the first housing 51 a is fixed to the second housing 51 b. Here, the first housing 51 a may be fixed to the second housing 51 b through, for example, snap fitting, welding, or any other desirable fixing method. Note here that the first bearing support portion 50 a and the first joining portion 52 a may preferably be molded from a resin or the like through, for example, injection molding integrally with the first housing 51 a. Also note that the first bearing support portion 50 a may be defined by a metallic member. In this case, the metallic member may be coupled to the first housing 51 a through, for example, insert molding.
Finally, the first bearing 40 a (which is, for example, a ball bearing) is inserted from axially above into the first bearing support portion 50 a, and fixed through a ring 90, defined by, for example, a snap ring, washer, etc. Meanwhile, the second bearing 40 b is fixed through a coil spring 91 and a washer, to thereby exert an axial force on the shaft 30.
As described above, because the bearing support portions 50 a and 50 b, which are arranged respectively at upper and lower levels, are coupled respectively to the housings 51 a and 51 b, which are divided from each other in the axial direction, it is possible to separately prepare the assembly made up of the first housing 51 a combined with the first joining portion 52 a and the first bearing support portion 50 a, and the assembly including the second housing 51 b combined with the second joining portion 52 b and the second bearing support portion 50 b (and, in addition, the stator support portion 61), before starting the assemblage of the blower fan 100. This facilitates the assemblage of the blower fan 100.
Next, structures of blower fans according to other preferred embodiments of the present invention will now be described below with reference to FIGS. 3, 4, and 5. FIGS. 3 to 5 are each a schematic cross-sectional view illustrating the structure of a blower fan according to a preferred embodiment of the present invention.
A blower fan 110 illustrated in FIG. 3 is different from the blower fan 100 illustrated in FIG. 1 in that a lower end portion 61 a of the stator support portion 61, which is preferably defined by a metallic member, is arranged to extend further downward in the axial direction, and that a lower end portion of the second joining portion 52 b is arranged substantially at the same level as that of the lower end portion 61 a of the stator support portion 61. This structure of the blower fan 110 contributes to maintaining the strength of the second joining portion 52 b through the stator support portion 61, which is defined by a metallic member.
A blower fan 120 illustrated in FIG. 4 is different from the blower fan 100 illustrated in FIG. 1 in that each of the first bearing support portion 50 a, the second bearing support portion 50 b, and the stator support portion 61 is preferably made of a single monolithic resin member. This structure of the blower fan 120 makes it possible to easily mold, of a resin or the like, the first housing 51 a integrally with the first bearing support portion 50 a and the first joining portion 52 a through injection molding, and also makes it possible to easily mold, of the resin or the like, the second housing 51 b integrally with the second bearing support portion 50 b, the second joining portion 52 b, and the stator support portion 61 preferably through, for example, injection molding.
A blower fan 130 illustrated in FIG. 5 is different from the blower fan 100 illustrated in FIG. 1 in that the rotor magnet 22 is directly fixed to the shaft 30.
As described above, according to preferred embodiments of the present invention, the bearings 40 a and 40 b, and the bearing support portions 50 a and 50 b, are arranged separately, one above and the other below, in the axial direction so that no bearing support portion is arranged radially inside the stator 60. In a conventional inner-rotor blower fan, a rotor magnet needs to be fixed to an outer circumferential surface of a rotor holder arranged radially outside a bearing support portion. However, a need for this is eliminated in preferred embodiments of the present invention, because no bearing support portion is arranged radially inside the stator 60. This makes it possible to fix the rotor magnet 22 directly to the shaft 30 as illustrated in FIG. 5. This in turn makes it possible to reduce the size of the outside diameter of the stator 60. Note that this makes it possible to widen the gap between the stator support portion 61 and the impeller cup 11, which in turn makes it possible to arrange the stator support portion 61 and the impeller cup 11 to overlap with each other in the radial direction as illustrated in FIG. 5. This makes it possible to extend the lower end portion of the impeller cup 11 further downward in the axial direction, thereby increasing the area of each of the blades 12. A blower fan that enables a greater air volume is thereby realized.
In addition to the structure of the blower fan 130 illustrated in FIG. 5, there are a variety of possible structures of blower fans in which the rotor magnet 22 is directly fixed to the shaft 30. For instance, it is possible to reduce the inside diameter of the impeller cup 11 in accordance with a reduction in the outside diameter of the stator 60. This makes it possible to realize a blower fan with a reduced radial dimension. Also, a reduction in the inside diameter of the stator 60 while maintaining the outside diameter of the stator 60 makes it possible to reduce the axial dimension of the stator 60. This makes it possible to realize a blower fan with reduced axial dimensions.
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.

Claims

1. A blower fan comprising:

an impeller including a substantially cylindrical impeller cup including a cover portion, and a plurality of blades arranged on an outer circumferential surface of the impeller cup;

a shaft fixed directly or indirectly to the impeller cup, and including an end arranged to project axially upward from the cover portion of the impeller cup;

a rotor magnet fixed directly or indirectly to the shaft;

a first bearing arranged axially above the cover portion of the impeller cup, and arranged to support the shaft such that the shaft is rotatable with respect to the stator;

a first bearing support portion arranged to support the first bearing;

a first housing arranged radially outward of the impeller on an axially upper side;

a first joining portion arranged to join the first housing and the first bearing support portion to each other;

a second bearing arranged axially below the cover portion of the impeller cup, and arranged to support the shaft such that the shaft is rotatable with respect to the stator;

a second bearing support portion arranged to support the second bearing;

a second housing arranged radially outward of the impeller on an axially lower side;

a second joining portion arranged to join the second housing and the second bearing support portion to each other;

a stator arranged radially outward of the rotor magnet and opposite the rotor magnet; and

a stator support portion arranged to support the stator; wherein

the first and second housings are joined to each other at an axial level higher than an axial position of a joint between the second joining portion and the second housing.

2. The blower fan according to claim 1, wherein

the impeller cup includes a recessed portion defined in a central portion of the cover portion; and

at least a lower end of the first bearing support portion is arranged inside the recessed portion.

3. The blower fan according to claim 1, wherein

the first housing, the first bearing support portion, and the first joining portion are integral with one another; and

the second housing, the second bearing support portion, and the second joining portion are integral with one another.

4. The blower fan according to claim 3, wherein the first bearing support portion and the second bearing support portion are defined by metallic members coupled to the first housing and the second housing, respectively, by being at least partially embedded within the first housing and the second housing.

5. The blower fan according to claim 1, wherein the second joining portion defines a stationary vane.

6. The blower fan according to claim 1, further comprising a substantially cylindrical rotor holder fixed to the shaft, wherein the rotor magnet is fixed to an outside wall of the rotor holder.

7. The blower fan according to claim 6, wherein the rotor holder is coupled to the impeller cup by being at least partially embedded within the impeller cup.

8. The blower fan according to claim 3, wherein the second housing, the second bearing support portion, the second joining portion, and the stator support portion are integral with one another.