Patent Application
20100232967
1. Field of the Invention
The present invention relates to a centrifugal fan used for the purpose of air blowing or the like.
2. Description of the Related Art
In conventional centrifugal fans, a plurality of blades are arranged in a circumferential direction with respect to a rotation axis, and a motor is driven to rotate the blades to take in air along an axial direction and discharge the air in a radial direction. The motor includes a stator portion and a rotor portion, and the rotor portion is supported so that it is able to rotate with respect to the stator portion. The blades are secured to a cylindrical rotor holder, and the blades are thereby arranged to rotate together with the rotor holder.
In such conventional centrifugal fans, when the air which has been drawn in along the axial direction is discharged in the radial direction, the flow of air is disturbed near an outer circumferential surface of the rotor holder, and especially at a lower end portion thereof. This disturbance generates noise.
In connection with this type of problem, JP-A 2005-160264 describes a technique to reduce the noise. According to this technique, the outer circumferential surface of the cylindrical rotor holder is arranged to slope to smooth the air flow, thereby reducing the noise.
JP-A 2004-229468 describes another conventional centrifugal fan with a structure that is designed to smooth the air flow.
In addition, JP-A 2007-23877 discloses a technique of providing an annular support plate to support a plurality of blades, and securing the support plate to an opening portion or a side surface of the rotor holder by insert molding.
In order to smooth the air flow, it is desirable that the outer circumferential surface of the rotor holder be arranged to slope in a curved fashion. In this case, however, since the stator portion is arranged inside the rotor holder, an outer circumferential surface of an armature (a winding portion) defining a portion of the stator portion will need to be arranged to slope in accordance with a slope angle of the outer circumferential surface of the rotor holder. As such, the shape of the outer circumferential surface of the armature places a constraint on the shape of the outer circumferential surface of the rotor holder. This makes it practically difficult to provide an arbitrary sloping shape (e.g., a curved shape) to the outer circumferential surface of the rotor holder.
According to a preferred embodiment of the present invention, a centrifugal fan includes a stator portion; a substantially cylindrical rotor holder; an annular support plate secured to an outer circumferential surface and/or a lower end portion of the rotor holder, and arranged to spread radially outward from the rotor holder; and a plurality of blades secured to the support plate. The plurality of blades are arranged to be spaced from the outer circumferential surface of the rotor holder and arranged in a circumferential direction with respect to the rotor holder. The support plate is preferably defined by an integral unit including a substantially annular blade support portion arranged radially farthest from the rotor holder to support the plurality of blades; a cylindrical portion arranged radially closest to the rotor holder to encircle the outer circumferential surface of the rotor holder; and a sloping portion arranged between the blade support portion and the cylindrical portion to slope from an upper end portion of the cylindrical portion to the blade support portion.
According to this centrifugal fan, the inclusion of the sloping portion which is arranged to slope, preferably in a curved fashion, radially outward away from the rotor holder in the support plate, to which the blades are secured, contributes to a smooth radial discharge of air which has been taken in along an axial direction without the need to modify the shape of the outer circumferential surface of the rotor holder. Moreover, since the blade support portion, the cylindrical portion, and the sloping portion can be provided integrally (by, for example, molding) to define the support plate, the sloping portion can be defined by any arbitrary shape. Thus, the support plate, which is arranged to produce the aforementioned beneficial effects and contributes to a reduction in noise, can be formed easily, making it possible to manufacture the centrifugal fan with a stable strength at a low cost.
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.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the preferred embodiments described below, and that variations and modifications can be made appropriately as long as desired effects and arrangements of the present invention are not impaired. Also note that the preferred embodiments described below may be combined with other embodiments. For the sake of convenience, it is assumed herein that an upward/downward direction is defined by a direction moving along a central axis J, and that a side on which a base portion 41 described below is arranged is referred to as a lower side, while the opposite side along the central axis J is referred to as an upper side. Note that the central axis J may not necessarily be in parallel with the direction of gravity and can be arranged in any direction.
As illustrated in
The rotor portion 3 preferably includes a rotor holder 31 and a field magnet 32. The rotor holder 31 is substantially defined by the shape of a covered cylinder. The field magnet 32 is secured to an inside of a side wall portion of the rotor holder 31. The stator portion 4 includes the base portion 41, an armature 42, and a bearing support portion 43. The bearing support portion 43 is arranged to protrude upward from the base portion 41. The armature 42 is secured to an outer surface of the bearing support portion 43. Ball bearings 52 are arranged at upper and lower positions along the central axis J inside the bearing support portion 43.
An annular support plate 2 is secured to an outer circumferential surface and/or a lower end portion of the rotor holder 31. The support plate 2 is arranged to spread radially outward from the rotor holder 31 and support the blades 10. The blades 10 are arranged in a circumferential direction with respect to the rotor holder 31, and secured to the support plate 2. The blades 10 are spaced from the outer circumferential surface of the rotor holder 31. The support plate 2 and the blades 10 together define an impeller portion.
A bushing 51 is secured to a center of a cover portion of the rotor holder 31, and a shaft 50 is preferably press fitted, for example, into the bushing 51. The shaft 50 is inserted inside the bearing support portion 43, and rotatably supported by the ball bearings 52. Here, the shaft 50 and the ball bearings 52 together define a bearing mechanism to support the rotor portion 3 and the blades 10 such that the rotor portion 3 and the blades 10 are rotatable with respect to the stator portion 4.
In the centrifugal fan having the above-described structure, a drive current is supplied to the armature 42 to produce a torque centered on the central axis J between the armature 42 and the field magnet 32, so that the blades 10, which are fixed in relation to the rotor holder 31, rotate about the central axis J together with the shaft 50 secured to the rotor holder 31.
In the present preferred embodiment, the support plate 2, which is secured to the outer circumferential surface and/or the lower end portion of the rotor holder 31, preferably includes three portions. Specifically, the support plate 2 preferably has an integral structure including a substantially annular blade support portion 21, a cylindrical portion 22, and a sloping portion 23. The blade support portion 21 is arranged radially farthest from the rotor holder 31 to support the blades 10. The cylindrical portion 22 is arranged in contact with the outer circumferential surface of the rotor holder 31. The sloping portion 23 is arranged between the cylindrical portion 22 and the blade support portion 21 to slope in a curved fashion from an upper end portion of the cylindrical portion 22 to the blade support portion 21. The support plate 2 is arranged to assume a smooth curve in cross section from the cylindrical portion 22 to a radially outermost portion of the support plate 2.
The inclusion of the sloping portion 23, which is arranged to slope in a curved fashion while extending radially outward away from the outer circumferential surface of the rotor holder 31, in the support plate 2 arranged to support the blades contributes to a smooth radial discharge of air which has been taken in along an axial direction. In addition, the inclusion of the cylindrical portion 22, which is arranged in contact with the outer circumferential surface of the rotor holder 31, in the support plate 2 contributes to firm and reliable securing of the support plate 2 to the rotor holder 31. Moreover, since the blade support portion 21, the cylindrical portion 22, and the sloping portion 23, which together define the support plate 2, are preferably defined integrally, (by, for example molding) with one another, the sloping portion 23 can be constructed in an arbitrary shape. Thus, the support plate 2 can be easily formed and still is capable of producing the aforementioned beneficial effects. It is thus possible to manufacture the centrifugal fan at a low cost while maintaining stable strength thereof and achieving a noise reduction.
In the present preferred embodiment, it is preferable that the securing of the support plate 2 to the rotor holder 31 be accomplished by, for example, insert molding. The insert molding according to the present preferred embodiment will now be described in detail below, but any other desirable manufacturing method could be used.
The rotor holder 31 preferably has, at the lower end portion thereof, a protruding portion (a flange portion) 33 arranged to protrude radially outward from the rotor holder 31. The protruding portion 33 is preferably insert-molded with a lower end portion of the cylindrical portion 22 of the support plate 2, so that the support plate 2 is secured to the rotor holder 31. However, the protruding portion 33 could be provided through any desirable method.
The support plate 2 can be easily integrally defined by the blade support portion 21, the cylindrical portion 22, and the sloping portion 23 by injection molding or the like, using two molds which are separated from each other along the central axis J for mold release. As illustrated in
The protruding extent of the protruding portion 33 needs to be constant around the circumference of the rotor holder 31, in order for the support plate 2 to be secured to the rotor holder 31 with a constant strength around the circumference of the rotor holder 31. This may lead to the cylindrical portion 22 having a thickness greater than that of the blade support portion 21 and the sloping portion 23. In this case, at the time of the injection molding, the greater-thickness cylindrical portion 22 may undergo a deformation (or the occurrence of a sink mark) as a result of mold shrinkage. When the cylindrical portion 22 experiences such a deformation, the strength with which the support plate 2 is secured to the rotor holder 31 may be reduced, and in some cases, the cylindrical portion 22 may even experience a breakage.
An effective measure against this problem will now be described below with reference to
As illustrated in
Referring to
Notice here that the provision of the thickness reducing portion 24a in the cylindrical portion 22 results in a corresponding reduction in the thickness of the cylindrical portion 22. This may lead to a decrease in the strength with which the support plate 2 is secured to the rotor holder 31.
As a measure against this problem, it is preferable that, as illustrated in
In the present preferred embodiment, the cylindrical portion 22 of the support plate 2 is preferably arranged in contact with the outer circumferential surface of the rotor holder 31. As illustrated in
Furthermore, as illustrated in
In the present preferred embodiment, the support plate is preferably arranged to assume a smooth curve in cross section from the cylindrical portion 22 to the radially outermost portion of the support plate 2. Note, however, that the support plate 2 may also be arranged to assume a straight line in cross section from a radially outermost portion of the sloping portion 23 to the radially outermost portion of the support plate 2 if so desired.
As illustrated in
Furthermore, as illustrated in
Furthermore, in the present preferred embodiment, the protruding portion 33 is preferably insert-molded with the lower end portion of the cylindrical portion 22 of the support plate 2, so that the support plate 2 is secured to the rotor holder 31. Note, however, that the support plate 2 may be secured to the rotor holder 31 by other methods than the insert molding. Examples of such other methods include press fit, adhesion, heat welding, and ultrasonic welding, for example.
Furthermore, in the present preferred embodiment, the blades 10 may be integrally molded with the support plate 2. In this case, the blades 10 may be integrally molded with the support plate 2 while at the same time the protruding portion 33 is insert-molded with the lower end portion of the cylindrical portion 22 of the support plate 2, so that the blades 10 are fixed in relation to the rotor holder 31 at the same time.
Furthermore, as illustrated in
In the first preferred embodiment, the thickness reducing portion 24a is preferably defined in a portion of the cylindrical portion 22 of the support plate 2 to make the thickness of the cylindrical portion 22 substantially equal to the thickness of the sloping portion 23. Notice here that, as illustrated in
In a second preferred embodiment of the present invention, a thickness reducing portion is preferably defined so as to extend upward from the axially lower side. A method for defining such a thickness reducing portion will now be described below with reference to
As illustrated in
Since the protruding portions 33, which are provided at the lower end portion of the rotor holder 31, are spaced from one another in the circumferential direction, an insert mold designed to define a thickness reducing portion can be inserted from the lower side of the rotor holder 31 at any circumferential position where no protruding portion 33 is provided. Therefore, as illustrated in
In the present preferred embodiment, as illustrated in
In the present preferred embodiment, no particular limitations are placed on the shape or number of the protruding portions 33 which are spaced from one another in the circumferential direction. For example, as illustrated in FIGS. 8A and 8B, each of the protruding portions 33 may be arranged to have a smooth curved line.
As illustrated in
In a case where both axial and radial dimensions of the blades 10 are large, the outer reinforcing ring 60 alone may not be sufficient to prevent a deformation of the blades 10. As illustrated in
When the inner reinforcing ring 61 exists within the flow path of air which has been taken in along the axial direction, the flow of air may be disturbed thereby. Accordingly, as illustrated in
Since the outer reinforcing ring 60 is attached to the radially outer ends of the blades 10, the outside diameter of the centrifugal fan increases correspondingly. When the inner reinforcing ring 61 is attached to the radially inner ends of the blades 10, sufficient reinforcement can be obtained even if the radial dimension of the outer reinforcing ring 60 is reduced correspondingly. Therefore, the attachment of the inner reinforcing ring 61 enables a decrease in the radial dimension of the outer reinforcing ring 60, and increases design flexibility in the radial dimension of the centrifugal fan. Note that only the inner reinforcing ring 61 may be attached to the blades 10, without the attachment of the outer reinforcing ring 60.
Also note that a thickness reducing portion may be defined to extend downward from the axially upper end of the cylindrical portion, with the use of the rotor holder according to the second preferred embodiment.
While preferred embodiments of the present invention have been described above, it is to be understood that the foregoing description is in all aspects illustrative and not restrictive, and that a variety of modifications are possible. For example, in the above-described preferred embodiments, a bearing mechanism of a ball bearing type is preferably used as a bearing mechanism for a motor, for example. Note, however, that an oilless bearing using a sleeve may be used in other preferred embodiments, for example.
While preferred embodiments of the present invention have been described above, these are illustrated only by way of example, and it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-061313 | Mar 2009 | JP | national |
