Abstract:
A bearing retainer unit is formed by an insert-molding technique to cast a molded component of the bearing retainer unit utilizing a bearing bushing. A first mold die, having a circumferential surface shaped to correspond to at least a portion of the inner circumferential surface of a bearing-positioning portion of the molded component, and a second mold die, having an abutment that abuts against an axial end face of the first die, are readied. A molten material is then injected into the mold to form the molded part, thereby forming the die-parting line on the inner circumferential surface of the component&#39;s bearing positioning portion, positioned at the radially outer side of the abutment.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to bearing retainer units provided with a bearing bushing that anchors a bearing mechanism made up of upper- and lower-end bearings, and to electric motors furnished with such bearing retainer units.  
         [0003]     2. Description of the Related Art  
         [0004]     Motors furnished with a metal bearing bushing for anchoring upper-/lower-end bearing-equipped bearing mechanisms are known. For example, impeller-encompassing fan housings are formed, from synthetic resin, integrally with a motor support part for supporting the motor, and a cylindrical metal bearing liner is insert-molded into the motor support part. An upper-end bearing and a lower-end bearing, for rotatably supporting the rotor component of the motor, are fixed to the inner circumferential surface of the bearing liner, while the stator component of the motor is fixed to the outer circumferential surface of the bearing liner.  
         [0005]     Along the inner periphery of the bearing liner, a projecting part that supports the upper- and lower-end bearings is by a pressing operation formed extending radially from the bearing-liner inner periphery. A consequence of this method is that precision-forming the projecting part is difficult. Furthermore, the excessive stress that acts on the bearing liner in press-forming the projecting part can compromise the roundness of the cylindrical bearing liner, leading to the bearings or stator being installed tilted.  
         [0006]     Lack of precision in the bearing liner components leads to canted rotation of the rotor, such that noise issues from the bearings, and gives rise to the problem of excess load being placed on the bearings, decreasing their lifespan.  
         [0007]     Thus, due to the bearing liner and the projecting part being produced by press-forming in a pressing operation, improving the precision of the bearing liner components, and the precision of the motor rotation, has been elusive.  
       BRIEF SUMMARY OF THE INVENTION  
       [0008]     In one example of the bearing retainer unit of the present invention, the bearing retainer unit is formed by an insert molding method using at least a pair of mold dies that includes a first die and a second die, and the bearing retainer unit is used in an electric motor provided with a rotor that rotates centered on its rotational axis.  
         [0009]     The bearing retainer unit includes a metal bearing bushing and a molded part. The bearing bushing is formed cylindrically, and its cylindrical surface has a communicating hole whereby the inside and outside of the cylinder communicate. The molded part includes a molded cylinder portion, a cylindrical bearing positioning portion that along the inner side of the bushing covers its inner surface, and a linking portion that links the molded cylinder portion and the bearing positioning portion.  
         [0010]     The bearing bushing is positioned in the internal space formed by the pair of mold dies, and the first die, which has a circumferential surface shaped to correspond to at least part of the inner circumferential surface of the bearing positioning portion, and the second die, which has an abutment lent a form to correspond to an axial end face of the first die, are closed, readying the mold.  
         [0011]     Then, a molten material is injected into the internal space to form the molded part, thereby forming the parting line on the inner circumferential surface of the bearing positioning portion, positioned at the radially outer side of the abutment.  
         [0012]     Another bearing retainer unit of the present invention is provided with a metal bearing bushing and a molded part. The bearing bushing is formed cylindrically, and in its cylindrical surface has a communicating hole whereby the inside and outside of the cylinder communicate. The molded part is provided with a molded cylinder portion, a cylindrical bearing positioning portion that along the inner side of the bushing covers its inner surface, and a linking portion that links the molded cylinder portion and the bearing positioning portion.  
         [0013]     The bearing bushing is positioned in the internal space formed by the pair of mold dies, and the first die, which has a constricted circumferential surface, and the second die, which has an abutment lent a form to correspond to an axial end face of the first die, with the constricted circumferential surface of the first die therein being tapered heading toward the abutment along the inner surface of the bearing bushing are closed, readying the mold.  
         [0014]     Then, a molten material is injected into the internal space to form the molded part, thereby forming a tapered bore in the bearing positioning portion.  
         [0015]     Still another bearing retainer unit of the present invention is provided with a metal bearing bushing and a molded part. The bearing bushing is formed cylindrically, and in its cylindrical surface has a communicating hole whereby the inside and outside of the cylinder communicate. The molded part is provided with a molded cylinder portion, a cylindrical bearing positioning portion that along the inner side of the bushing covers its inner surface, and a linking portion that links the molded cylinder portion and the bearing positioning portion.  
         [0016]     The bearing bushing is positioned in the internal space formed by the pair of mold dies, and the first die, which has a circumferential surface shaped to correspond to at least part of the inner circumferential surface of the bearing positioning portion, and the second die, which has an abutment lent a form to correspond to an axial end face of the first die, are closed, readying the mold.  
         [0017]     A molten material is then injected into the internal space to form the molded part, thereby forming a bearing-positioning-part upper-edge portion, and an upper recess is that is located in the outer circumferential margin of, and indents downward from, the upper edge portion.  
         [0018]     The present invention enables anchoring the bearings into the bearing positioning portion easily and with high precision. Accordingly, it is possible to realize high-precision and superiorly reliable bearing retainer units, and motors provided with such bearing retainer units.  
         [0019]     It should be understood that in the explanation of the present invention, when positional relationships among and orientations of the different components are described as being up/down or left/right, ultimately positional relationships and orientations that are in the drawings are indicated; positional relationships among and orientations of the components once having been assembled into an actual device are not indicated.  
         [0020]     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 THE SEVERAL VIEWS OF THE DRAWINGS  
       [0021]      FIG. 1  is an overall sectional view depicting a motor according to a first embodiment of the present invention;  
         [0022]      FIG. 2  is a partly-in-section, oblique view illustrating key portions of the motor in  FIG. 1 ;  
         [0023]      FIG. 3  is a partly-in-section, oblique view illustrating a bearing bushing from the motor in  FIG. 1 ;  
         [0024]      FIG. 4  is a vertical sectional view illustrating a bearing retainer unit from  FIG. 1 ;  
         [0025]      FIG. 5  is an enlarged sectional view illustrating a bearing positioning portion from  FIG. 1 ;  
         [0026]      FIGS. 6 and 7  are sectional views each illustrating part of a bearing-retainer-unit molding process;  
         [0027]      FIG. 8  illustrates a method for machining the bearing bushing in  FIG. 1 , wherein  FIG. 8A  is a vertical sectional view and  FIG. 8B  is a horizontal sectional view;  
         [0028]      FIG. 9  is a key-portion sectional view that illustrates a motor bearing-retainer unit according to a second embodiment of the present invention;  
         [0029]      FIG. 10  is a key-portion sectional view that illustrates a motor bearing-retainer unit according to a third embodiment of the present invention;  
         [0030]      FIG. 11  depicts key portions of a motor bearing bushing according to a fourth embodiment of the present invention, wherein  FIG. 11A  is a vertical sectional view and  FIG. 11B  is a horizontal sectional view;  
         [0031]      FIG. 12  is a key-portion, enlarged sectional view of a motor bearing-retainer unit according to a fifth embodiment of the present invention;  
         [0032]      FIG. 13  is a sectional view of a motor bearing-retainer unit according to a sixth embodiment of the present invention;  
         [0033]      FIG. 14  is a sectional view of a motor bearing-retainer unit according to a seventh embodiment of the present invention; and  
         [0034]      FIG. 15  is a sectional view of a motor according to an eighth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]     Below, embodiments of a motor having the bearing retainer unit of the present invention are described in detail. The basic configuration in the second through eighth embodiments is the same as in the first embodiment, and therefore the explanation focuses on the portions that differ.  
       First Embodiment  
       [0036]     As shown in  FIG. 1 , fan motor A is provided with a motor  4  equipped with an impeller inside of a fan housing  21 . The fan is an axial flow fan in which airflow induced by rotation of an impeller  41  passes through the inside of the fan housing  21 , and flows in from one side in the direction of the axis and is discharged from the other side. An axial flow fan is shown in the first embodiment, but the present invention can also be applied in a centrifugal fan. In  FIG. 1 , straight line L 1  indicates the rotational axis of the motor, wherein “axial” orientation means the path along which the rotational axis L 1  extends.  
         [0037]     The motor  4  is provided with a rotor, a stationary section, and a bearing mechanism that supports the rotor. The rotor is provided with the impeller  41 , a cup-shaped yoke  42  formed from magnetic material fixed to the inside of the impeller  41 , a magnet  43  fixed to the inside of the yoke  42 , and a shaft  44  fixed in the center of the yoke  42 .  
         [0038]     The stationary section is furnished with: a stator  45  that radially opposes the magnet  43 ; a bearing bushing  48  on the outer periphery of which the stator  45  is supported, and on the inner periphery of which an upper bearing  46  and a lower bearing  47  are respectively supported; and a circuit board  49 .  
         [0039]     The bearing mechanism includes the upper bearing  46  and the lower bearing  47 , and rotatably supports the rotor. The upper bearing  46  and the lower bearing  47  are ball bearings, and a preload is applied to them by a spring provided in the bottom end portion of the shaft  44 . It will be appreciated that sliding bearings can also be employed for the upper bearing  46  and the lower bearing  47 .  
         [0040]     A configuration in which a yoke provided with a driving magnet is fixed inside an impeller-mounting cup-like member, wherein the cup-like member is formed integrally with the impeller and a shaft is provided in the center thereof, can also be employed. Also, in the stator  45 , insulators  45   b , formed of synthetic resin, are mounted along the top/bottom of a stator core  45   a  having a through-hole penetrating its midportion and being formed by laminating silicon steel plates; and the coils are wound via this structure.  
         [0041]     As shown in  FIG. 2 , the fan housing  21  is formed in a rectangular shape having an inner circumferential surface that surrounds the impeller  41 . In the inside center of the fan housing  21 , a circular disk-shaped motor support portion  22  that supports the bearing bushing  48  of the impeller-attached motor  4 , and a plurality of linking portions  23  that extend in an approximately radial shape and support the motor support portion  22 , are provided. The fan housing  21 , the motor support portion  22 , and the linking portions  23  are formed as a single body with injection molding using synthetic resin. A gap between the fan housing  21  and the motor support portion  22  is an exhaust port for the fan motor A.  
         [0042]     The motor support portion  22  is fastened to the metal bearing bushing  48  by insert molding. On the inner circumferential surface of the bearing bushing  48  a synthetic resin bearing positioning portion  6  is provided. The upper bearing  46  makes contact with and is fixed to an upper edge portion  61  of the bearing positioning portion  6 , and the lower bearing  47  makes contact with and is fixed to a lower edge portion  62  of the bearing positioning portion  6 . The bearing positioning portion  6  is formed when insert molding the bearing bushing  48  to the motor support portion  22 . That is, as shown in  FIG. 2 , with this motor  4 , a bearing retainer unit  2  is configured such that the bearing bushing  48 , the fan housing  21 , the motor support portion  22 , the linking portions  23 , and the bearing positioning portion  6  are made a single body.  
         [0043]     Following is a detailed description of the bearing retainer unit  2 .  
         [0044]     The bearing bushing  48  is formed by press processing such as deep draw processing of a metal member. As shown in  FIG. 3 , the bearing bushing  48  is provided with a cylinder portion  48   a  and a flange portion  48   b . The upper bearing  46  and the lower bearing  47  are held by the inner circumferential portion of the cylinder portion  48   a , and the stator  45  is held by the outer circumferential portion. In the cylinder portion  48   a , a plurality of communicating holes  48   c  are formed that are in communication with the bushing inner surface and the bushing outer surface of the cylinder portion  48   a.    
         [0045]     A stepped portion  48   d  projecting in the radial direction from the bushing outer surface of the cylinder portion  48   a  is provided on the bottom side of the cylinder portion  48   a . The inner surface of the cylinder portion  48   a  is formed with a flush shape in the direction of the axis. The dimension of the outer diameter of the stepped portion  48   d  is more than the dimension of the outer diameter of the outer circumferential portion of the top side of the cylinder portion  48   a . That is, the average value of the outer dimension of a first outer surface  48   a   1  below the stepped portion  48   d  is more than the average value of the outer dimension of a second outer surface  48   a   2  above the stepped portion  48   d . The plurality of communicating holes  48   c  are provided in a region below the stepped portion  48   d  and disposed uniformly at four locations on the cylinder (only two locations are shown in  FIG. 3 ). The bearing bushing  48  may also be formed by cutting processing.  
         [0046]     As shown in  FIG. 4 , the bearing retainer unit  2  is provided with a molded cylinder portion  24  that faces toward a flange portion  48   b  from the outer circumferential surface somewhat above the stepped portion  48   d  of the cylinder portion  48   a , the linking portions  23  that close off and seal the communicating holes  48   c , and the aforementioned bearing positioning portion  6  that covers the inner circumferential surface of the bearing bushing  48 . The motor support portion  22  is formed such that it covers all of the top face and outer circumferential surface of the flange portion  48   b  and part of the bottom face of the flange portion  48   b . A cylinder-portion upper edge portion  24   a  of the molded cylinder portion  24  that covers the bottom side outer circumferential surface of the cylinder portion  48   a  is formed in a ring-like shape as a horizontal face perpendicular to the direction of the axis. Each communicating hole  48   c  is obstructed by the bearing positioning portion  6 , the linking portions  23 , and the molded cylinder portion  24 , so the communicating holes  48   c  are not exposed to the outside air. Also, an external-air exposed portion  48   e  exposed to the outside air is formed on the radially inner side of the flange portion  48   b.    
         [0047]     The stator  45  is fit to the outer circumferential surface of the bearing bushing  48  and fixed by bonding, mounted to the cylinder-portion upper edge portion  24   a  of the molded cylinder portion  24 , and thus positioned. The top inner circumferential wall of the insulator  45   b  is lightly pressed into the outer peripheral face of the cylinder portion  48   a . Thus, when fixing the stator  45  to the bearing bushing  48  by bonding, even if the adhesive is not hardened, the stator  45  is temporarily attached to the bearing bushing  48 . With process steps such as temporarily holding the stator  45  using a jig or the like, or temporarily storing the stator  45  until the adhesive hardens, being therefore unnecessary, the stator  45  installation operation is made efficient.  
         [0048]     Further, as shown in  FIG. 4 , a protrusion  22   b  that protrudes in the direction of the axis is provided as a single body with the cylinder-portion upper edge portion  24   a  of the molded cylinder portion  24 . The protrusion  22   b  is housed by a notched groove (not shown) provided in the inner circumferential surface of the stator core  45   a , and functions as a positioner and rotation stopper that positions the stator  45  at a predetermined position in the direction of rotation.  
         [0049]     Heat produced at the stator  45  is released via the bearing bushing  48 , and the release of heat is enhanced because the external-air exposed portion  48   e  is present on the bottom face of the flange portion  48   b . It is desirable to secure as wide a space as possible for the external-air exposed portion  48   e , in a range that the joint strength of the bearing bushing  48  and the motor support portion  22  is not hindered. The external-air exposed portion  48   e  is suitable for releasing heat because it is at a location in the fan motor A that is easily exposed to the outside air.  
         [0050]     As shown in  FIG. 4 , the bearing positioning portion  6  is formed in a cylindrical shape, and along with being connected to the linking portion  23  that seals each communicating hole  48   c , is formed extended upward such that it covers the bushing inner surface. The positioning portion upper edge portion  61  and the positioning portion lower edge portion  62  of the bearing positioning portion  6  are formed in a ring-like shape as flat faces perpendicular to the direction of the axis.  
         [0051]     The bottom end face of the upper bearing  46  makes contact with the upper edge portion  61 , and thus the upper bearing  46  is positioned at a predetermined position in the direction of the axis. The upper end face of the lower bearing  47  makes contact with the lower edge portion  62 , and thus the lower bearing  47  is positioned at a predetermined position in the direction of the axis. The upper edge portion  61  and the lower edge portion  62  are formed at a position in the axial direction that neither the bearing  46  or the bearing  47  protrudes from the bearing bushing  48  when the upper bearing portion  46  and the lower bearing portion  47  have been positioned. The positioning of both the bearing  46  and the bearing  47  can also be performed via, for example, a spring or a spacer in the upper edge portion  61  and the lower edge portion  62 .  
         [0052]     As shown in  FIG. 4 , an annular upper recess  63  that indents downward from the upper edge portion  61  is formed in the outer circumferential margin of the upper edge portion  61  of the bearing positioning portion  6 . Likewise, an annular lower recess  64  that indents upward from the lower edge portion  62  is formed in the outer circumferential margin of the lower edge portion  62  of the bearing positioning portion  6 . Because the upper recess  63  and the lower recess  64  are formed in the outer circumferential margins of the upper edge portion  61  and the lower edge portion  62 , even if a burr B is formed between the inner surface of the bushing and the outer circumferential surface of the bearing positioning portion  6 , the burr B is formed within the upper recess  63  and the lower recess  64 . The length of the burr B in the axial direction is shorter than the length from the bottom face of the upper recess  63  to the upper edge portion  61  in the axial direction. That is, the burr B does not protrude upward from the upper end face  61 . This is also true for a burr within the lower recess  64 .  
         [0053]     As a result, because the burr B does not protrude from the upper edge portion  61  and the lower edge portion  62 , it does not interfere when the upper bearing  46  and the lower bearing  47  make contact with the upper edge portion  61  and the lower edge portion  62 . It is possible to perform positioning of the upper bearing  46  and the lower bearing  47  in the direction of the axis with high precision. In this case, with respect to the volume of the upper recess  63  and the lower recess  64 , it is preferable that depth d and width r are set as large as possible, while insuring a surface area sufficient for positioning to be possible by the bearings  46  and  47  making contact with the upper edge portion  61  and the lower edge portion  62 . Here, the shape of the upper recess  63  and the lower recess  64  is rectangular in cross-section, but various other shapes may also be adopted, such as an approximately triangular shape.  
         [0054]     If the bearing bushing  48  and the injection molding die are formed as designed, burrs will not occur. However, it becomes more difficult to prevent the occurrence of burrs due to errors in the constituent components or die abrasion, or molding conditions, as the number of pieces produced increases. It is possible to decrease the occurrence of burrs by strictly controlling the component precision of the bearing bushing  48  and shortening the period for changing dies, but this leads to an increase in cost.  
         [0055]     On the other hand, with the present embodiment, by providing the upper recess  63  and the lower recess  64  as stated above, even if burrs occur there is no effect on positioning of the bearings. That is, with the present embodiment, by adopting a configuration in which the occurrence of burrs is permitted to some extent, it is possible to relax the precision of each component and also to extend the period for changing dies, so that it is possible to produce a bearing retainer unit without increased cost.  
         [0056]     Next is a description of a method for producing the bearing retainer unit  2 , with reference to  FIG. 6  and  FIG. 7 . For the sake of convenience, the description is made with a movable die  150  used for the first die, and a stationary die  100  used for the second die. Also, a stationary die  100  may be used for the first die, and a movable die  150  used for the second die.  
         [0057]     The movable die  150  is combined from above with the stationary die  100  in which the bearing bushing  48  is disposed, configuring an internal space  130  (see  FIG. 7 ) between the dies  100  and  150 . In  FIGS. 6 and 7 , die portions that correspond to the fan housing  21  and the linking portions  23  are not shown, for the sake of clarity of the figures.  
         [0058]     Gates  101  are formed at a plurality of locations in the stationary die  100 , and molten thermoplastic resin is injected through the gates  101 . The gates  101  are located at positions where the motor support portion  22  is molded. The thermoplastic resin, which is a molten material injected from the gates  101 , flows toward the fan housing  21 , and toward the bearing positioning portion  6  via the communicating holes  48   c  of the bearing bushing  48 . After the thermoplastic resin has hardened following injection, when the stationary die  100  and the movable die  150  are separated from each other, the bearing retainer unit  2  is held by the movable die  150  and attempts to separate from the stationary die along with the movable die  150 . At this time, because an injector pin for separating the molded component is provided on the movable die  150 , the bearing retainer unit  2  is separated from the movable die  150  by the injector pin. The bearing retainer unit  2  is held by the movable die  150  because the molded surface area of the movable die  150  is larger than the stationary die  100 . The fan housing  21 , the motor support portion  22 , the molded cylinder portion  24 , and the bearing positioning portion  6  are formed by insert-molding.  
         [0059]     The stationary die  100  and the movable die  150  are provided with an upper conical frustum portion  151  and a lower conical frustum portion  102  that form the inner circumferential surface of the bearing positioning portion  6 . By combining the stationary die  100  and the movable die  150 , the upper conical frustum portion  151  and the lower conical frustum portion  102  make contact, forming an abutment  131 . The upper conical frustum portion  151  and the lower conical frustum portion  102  each have a circumferential surface whose diameter is reduced closer to the abutment  131 .  
         [0060]     When the molten thermoplastic resin hardens, a parting line L 2  (see  FIG. 4 ) is formed on the smallest inner diameter portion of the inner circumferential surface of the bearing positioning portion  6 , that is, on the bearing positing portion inner circumferential surface positioned outside in the radial direction of the abutment  131 .  
         [0061]     The stationary die  100  and the movable die  150  are shown as a single member, but they may also be configured separated into a plurality of members. For example, a configuration may be adopted in which the upper conical frustum portion  151  and the lower conical frustum portion  102  are divided for the stationary die  100  and the movable die  150 . When it is desired to mold a bearing retainer unit in which the arrangement of the upper bearing and the lower bearing is modified, because it is possible to produce the bearing retainer unit by only exchanging the dies of the upper conical frustum portion and the lower conical frustum portion, the bearing retainer unit can be produced inexpensively. A molten material is not limited to thermoplastic resin; it may also be metal such as aluminum or zinc.  
         [0062]     The bearing positioning portion  6  is formed as a cylinder that is comparatively long in the axial direction. Thus, the inner circumferential surface of the bearing positioning portion  6  is formed by the circumferential surface of the upper conical frustum portion  151  and the lower conical frustum portion  102 . Thus, compared to a case in which the inner circumferential surface of a length in the direction of the axis that is the same as that of the bearing positioning portion is formed with one die, it is possible to shorten the respective lengths of the upper conical frustum portion  151  and the lower conical frustum portion  102  in the direction of the axis.  
         [0063]     Accordingly, when separating the bearing retainer unit  2  from the dies, the relative moving distance of the upper conical frustum portion  151  and the lower conical frustum portion  102  relative to the dies  100  and  150  is shortened. Thus, even in the case of a bearing positioning portion with a comparatively small thickness in the radial direction, when separating the dies  100  and  150 , it is possible to prevent molding defects wherein due to pulling on the dies  100  and  150  the bearing positioning portion is peeled off or broken.  
         [0064]     The relative moving distance of the upper conical frustum portion  151  and the lower conical frustum portion  102  when separating the dies  100  and  150  can be made short in a case in which the smallest inner diameter portion on the inner circumferential surface of the bearing positioning portion is formed in the center of the inner circumferential surface of the bearing positioning portion in the direction of the axis, but according to the molding circumstances it is not necessary for the smallest inner diameter portion on the inner circumferential surface of the bearing positioning portion to be formed in the center.  
         [0065]     An upper reduced diameter inner circumferential surface  65  and a lower reduced diameter inner circumferential surface  66  of the bearing positioning portion  6  have a diameter that is reduced closer to the abutment  131  between the upper conical frustum portion  151  and the lower conical frustum portion  102 , and thus in comparison to the case of molding inner circumferential surfaces with the same inner diameter, there is little frictional force between the molded faces (the upper reduced diameter inner circumferential surface  65  and the lower reduced diameter inner circumferential surface  66 ) and the die faces (the circumferential surface of the lower conical frustum portion  102  and the circumferential surface of the upper conical frustum portion  151 ) that acts when separating the dies. Thus, because the load that acts on the bearing positioning portion  6  when separating the dies is small, it is possible to prevent molding defects wherein the bearing positioning portion  6  is peeled off or broken.  
         [0066]     The bearing bushing  48  is provided with the flange portion  48   b  and thus has high rigidity. Moreover, rigidity is high because the dimensions of the lower portion of the bearing bushing  48  in the axial direction are comparatively thick. Thus, even if the injection pressure when performing injection molding is high, the bearing bushing  48  is not easily deformed. If a high injection pressure can be used, fluidity of the injected thermoplastic resin becomes good, and it is possible to improve the quality of the molded components.  
         [0067]     The external-air exposed portion  48   e  of the bearing bushing  48  is used as a face for axial positioning when the bearing bushing  48  is disposed in the stationary die  100 . The bottom face of the flange portion  48   b  that forms the external-air exposed portion  48   e  is used as a reference surface during press-forming of the bearing bushing  48 . Thus, because the planarity of the external-air exposed portion  48   e  is favorable, by using the external-air exposed portion  48   e  as the positioning face, it is possible to dispose the bearing bushing  48  in the stationary die  100  with good precision. As a result, in the bearing retainer unit  2  there is good squareness of the bearing bushing  48  in the horizontal direction. Even in the case that the bottom face of the flange portion is not used as the reference face when performing press processing for the bearing bushing, because the flange portion is present, the bearing bushing is stable when disposed in the stationary die, and squareness is better than when the flange portion is not present.  
         [0068]     The bearing positioning portion  6  and the motor support portion  22  are connected by the thermoplastic resin filled inside the plurality of communicating holes  48   c . Thus, even when the bearing bushing  48  is pressured by the molding material when injection molding is performed and attempts to move, the thermoplastic resin in the communicating holes  48   c  resists, so that such movement can be prevented. Also, even assuming that a load from the upper bearing  46  and the lower bearing  47  in the direction of the axis, which acts on the bearing positioning portion  6  after assembly of the fan motor A, exceeds the fixing force of the bearing bushing  48  and the bearing positioning portion  6 , the bearing positioning portion  6  is held by the thermoplastic resin filled into the communicating holes  48   c , so it is possible to prevent the bearing positioning portion  6  from falling out from the bearing bushing  48 .  
         [0069]     As shown in  FIG. 3 , the communicating holes  48   c  have a hole shape that is a flat oval in the direction of the axis. With such an oval shape, it is possible to reduce the hole height of the communicating holes  48   c  in comparison to a true circle or an oval that is flat in the rotational direction with the same opening area. Accordingly, it is possible to dispose the cylinder-portion upper edge portion  24   a  of the motor support portion  22  lower.  
         [0070]     As shown in  FIG. 8A , a method for processing four communicating holes  48   c  includes, with a columnar portion  201  of a die  200  inserted into and closely fit to the bearing bushing  48 , pressing punches  210  from the outer circumferential side of the bearing bushing  48  toward the inside in the radial direction, thus forming the communicating holes  48   c . As shown in  FIG. 8B , this hole processing step is performed twice for each group of two communicating holes  48   c  that face each other among the four communicating holes. As shown in  FIG. 8A , in the columnar portion  201 , in the outer circumferential surface, vertical grooves  202  for peeling away removed fragments formed when processing the communicating holes  48   c  are provided at four places in locations that correspond to the communicating holes  48   c.    
         [0071]     As shown in  FIG. 8B , with respect to the processing procedure, first one group of communicating holes  48   c  facing left and right in  FIG. 8B  are processed, and afterward a group of communicating holes  48   c  facing up and down in  FIG. 8B  are processed. That is, communicating holes  48   c  in four locations are processed with the processing divided into two instances. There are two reasons for following this sort of procedure.  
         [0072]     The first reason is to prevent a removed fragment S that has been removed by the punches  210  from interfering with a removed fragment S of other communicating holes  48   c , and thus causing defects during processing. That is, when a plurality of the communicating holes  48   c  are processed at the same time, the smaller the interval between each adjacent communicating hole  48   c , the greater the risk that those removed fragments S will lie in between the bearing bushing  48  and the columnar portion  201 , causing a defect to occur in which the bearing bushing  48  cannot be removed from the die  200 . Thus, by making the interval between the plurality of communicating holes  48   c  processed at the same time as large as possible, it is possible to prevent the aforementioned defects. In the present embodiment, one group of communicating holes  48   c  that are processed at the same time, are arranged opposing each other centered around the rotational axis L 1  (180 degree interval in the direction of rotation), so they have the most separated positional relationship possible.  
         [0073]     The second reason is in order to suppress a reduction in circularity of the bearing bushing  48  accompanying hole processing. Because stresses act on the bearing bushing  48  from opposing radial directions centered around the rotational axis L 1 , those stresses are cancelled. Moreover, because the directions of the stress that acts during the first instance and second instance of processing are offset from each other by 90 degrees in the rotational direction, stress that acts during the second instance of processing corrects deformities that occurred during the first instance of processing, and as a result the amount of deformation of the bearing bushing  48  is reduced.  
         [0074]     For the above reasons, with the present embodiment, the mechanism that positions the pair of bearings  46  and  47  in the bearing bushing  48  is provided at the same time as injection molding of the bearing retainer unit  2 , so not only is it possible to realize cost reductions due to reduced man-hours, it is also possible to realize dramatic cost reductions due to forming the bearing bushing  48  with press processing.  
         [0075]     At this time, with a configuration that provides a mechanism that positions a pair of bearings in for example a bearing bushing by plastic deformation in press processing, there are the disadvantages that it is difficult to elicit precision of the positioning face where the bearings are positioned, and that the circularity of the bearing bushing decreases. Thus, it is not possible to assemble a motor with high precision. In order to address these conventional problems, in the present embodiment, a mechanism that positions the pair of bearings  46  and  47  at predetermined positions is formed by the injection molded bearing positioning portion  6  as described above. Moreover, the bearing positioning portion  6  is provided with the upper reduced-diameter inner circumferential surface  65  and the lower reduced-diameter inner circumferential surface  66 , and the upper recess  63  and the lower recess  64 , and formed such that the parting line L 2  is positioned in approximately the center of the bearing positioning portion  6 , and thus molding defects are prevented.  
         [0076]     Also, the bearing bushing  48  is provided with the flange portion  48   b , and so there is good squareness relative to the horizontal face of the bearing retainer unit  2 , so that the molding precision is improved. Thus, the pair of bearings  46  and  47  can be installed in the bearing positioning portion  6  with good precision, with the result that it is possible to improve rotational precision of the motor. Also, the flange portion  48   b  is strongly supported by the motor support portion  22 , and thus it is possible to prevent defects during rotation such as tilting or breaking of the bearing bushing  48 .  
         [0077]     For the above reasons, with the present embodiment, it is possible to realize a fan motor A that has low cost and rotates with high precision.  
       Second Embodiment  
       [0078]     As shown in  FIG. 9 , formed in the cylinder portion  48   a  that faces the bearing positioning portion  6  in the radial direction is a ridge  481  that protrudes inside in the radial direction from the inner surface of the cylinder portion  48   a . The ridge  481 , in a manner similar to the function of the aforementioned communicating holes  48   c , prevents movement of the bearing bushing  48  when molding the bearing retainer unit  2 , and can improve the fixing force of the cylinder portion  48   a  and the bearing positioning portion  6 . Because the operating effects of the aforementioned communicating holes  48   c  and the operating effects of the ridge  481  are both obtained in this configuration, it is suitable for, for example, a fan motor in which a great load acts on the bearings than in the first embodiment.  
         [0079]     The ridge  481  can be formed by pressing that presses from the outer circumferential surface of the cylinder portion  48   a  toward the inside in the radial direction, and is preferably provided at a plurality of locations in the inner circumferential surface of the cylinder portion  48   a.    
         [0080]     In the case of this configuration, although there is concern that the circularity of the bearing bushing  48  will be degraded, because the ridge  481  is formed at a position separated from the pair of bearings  46  and  47 , even if the circularity is off, there is almost no effect on the precision of installation of the pair of bearings  46  and  47  with respect to the bearing positioning portion. Also, the ridge  481  does not require the same precision as the positioning face for performing positioning of the pair of bearings  46  and  47 , and so it is not accompanied by cost increases due to high precision processing.  
         [0081]     A furrow (not shown) that is hollow from the inner surface of the cylinder portion  48   a  to the outside in the radial direction may also be formed. Also, it is possible to obtain the same effects by roughly forming the inner surface of the cylinder portion  48   a  using blast processing.  
         [0082]     Also, because the fixing force of the bearing bushing  48  and the resin is improved and movement by the molding material during injection molding is prevented, penetrating holes or notches may be provided, or surface treatment that increases the face roughness may be performed, such that resistance of the surface of the flange portion  48   b  of the bearing bushing  48  to a molten material increases.  
       Third Embodiment  
       [0083]     As shown in  FIG. 10 , an upper outer wall portion  611  extended upward from the upper edge portion  61  and having a cylindrical shape that covers the inner surface of the bearing bushing  48  is formed in the outer edge portion of the upper edge portion  61  of the bearing positioning portion  6 . Also, a lower outer wall portion  621  extended downward from the lower edge portion  62  and having a cylindrical shape that covers the inner surface of the bearing bushing  48  is formed in the lower end portion of the bearing positioning portion  6 .  
         [0084]     The upper edge portion  61  of the bearing positioning portion  6  makes contact with the lower end portion of the upper bearing  46 , and the inner circumferential surface of the upper outer wall portion  611  makes contact with the outer circumferential portion of the upper bearing  46 . The lower edge portion  62  of the bearing positioning portion  6  makes contact with the upper end portion of the lower bearing  47 , and the inner circumferential portion of the lower outer wall portion  621  makes contact with the upper end portion of the lower bearing  47 .  
         [0085]     With this configuration, the upper edge portion  61  and the upper outer wall portion  611  are formed as a single body from the same material, so no border appears in the outer edge portion of the upper edge portion  61  between the bearing positioning portion  6  and the bearing bushing  48 . This is also true for the outer edge portion of the lower edge portion  62 .  
         [0086]     Accordingly, because burrs do not occur in the outer edge portion of either the upper edge portion  61  and the lower edge portion  62 , it is possible to perform positioning of the upper bearing  46  and the lower bearing  47  without providing the upper recess  63  and the lower recess  64  described in the first embodiment. Because a change in dimensions relative to the first embodiment occurs to the extent of the dimensions in the radial direction of the upper outer wall portion  611  and the lower outer wall portion  621 , it is necessary, for example, to increase the diameter of the bearing bushing  48  or to decrease the diameter of the pair of bearings  46  and  47 .  
       Fourth Embodiment  
       [0087]     As shown in  FIG. 11 , the communicating holes  48   c  of the bearing bushing  48  are not limited to an oval shape as described in the first embodiment; they may be circular or rectangular, and they are not limited to four in number. Also, a configuration may be adopted in which the communicating holes  48   c  are not made to penetrate by removing part of the bearing bushing  48 , but as shown in  FIG. 11A , part of the bearing bushing  48  is cut open and modified so as to extend inside in the radial direction, or as shown in  FIG. 11B , part of the bearing bushing  48  is cut open and modified inside in the radial direction and in the direction of rotation. In either case, it is possible to modify the flow direction in which a molten material flows from the communicating holes  48   c . In addition, because the circumferential edge of the communicating hole  48   c  protrudes in the radial direction, it is possible to improve the fixing force of the bearing positioning portion  6 .  
       Fifth Embodiment  
       [0088]     In the present embodiment, as illustrated in  FIG. 12 , a cylinder portion recess  22   c  that indents downward from a cylinder-portion upper edge portion  24   a  is formed in the inner circumferential margin of the cylinder-portion upper edge portion  24   a  of the molded cylinder portion  24 .  
         [0089]     In the inner circumferential portion of the bottom face of the cylinder portion recess  22   c , a burr B is formed extended upward from the bottom face and with a length that does not protrude from the cylinder-portion upper edge portion  24   a . With this configuration, it is possible to prevent positioning errors of the stator  45  due to the burr B making contact with the stator  45 . That is, it is possible to position the stator  45  in the cylinder-portion upper edge portion  24   a  with high precision.  
         [0090]     The cylinder portion recess  22   c  can be used as a collection groove for adhesive when fixing the stator  45 .  
       Sixth Embodiment  
       [0091]     As shown in  FIG. 13 , a smallest inner diameter portion r 1  of the bearing positioning portion  6  is formed in the lower end portion of the inner circumferential surface of the bearing positioning portion  6 . That is, the inner circumferential surface of the bearing positioning portion  6  is a reduced diameter inner circumferential surface  67  whose diameter is reduced from the upper end portion toward the lower end portion.  
         [0092]     The movable die of this embodiment is provided with a circumferential surface whose diameter is reduced toward the abutment of the movable die and the stationary die. The reduced diameter inner circumferential surface  67  is formed by the circumferential surface of a single die. Also, a parting line L 2  is formed in the lower end portion of the reduced diameter inner circumferential surface  67  positioned outside in the radial direction of the abutment.  
         [0093]     In this embodiment as well, the reduced diameter inner circumferential surface  67  is formed such that its inner diameter is enlarged in the direction that the movable die separates from the stationary die (upward in  FIG. 13 ), so the load that acts on the bearing positioning portion when separating the movable die is small, and thus it is possible to prevent molding defects such as the bearing positioning portion peeling or breaking.  
         [0094]     Although omitted from the figures, the smallest inner diameter portion can also be formed in the upper end portion of the inner circumferential surface of the bearing positioning portion. In this case, the inner circumferential surface of the bearing positioning portion has a shape whose diameter decreases from the lower end portion toward the upper end portion.  
       Seventh Embodiment  
       [0095]     As shown in  FIG. 14 , the bearing positioning portion  6  has a uniform inner diameter in the direction of the axis, and the parting line L 2  is formed at a position sufficiently separated from the upper end portion and the lower end portion of the bearing positioning portion  6  in the direction of the axis.  
         [0096]     When forming the parting line L 2  in any of the upper end portion and the lower end portion of the bearing positioning portion, the movement distance that the movable die separates relative to the stationary die after injection molding is increased, so molding defects are more likely to occur in the bearing positioning portion.  
         [0097]     On the other hand, in the present embodiment, because the inner circumferential surface of the bearing positioning portion is formed by two dies, it is possible to shorten the movement distance of the respective dies, so it is possible to prevent molding defects even in the case of a bearing positioning portion having a uniform inner diameter.  
       Eighth Embodiment  
       [0098]     In each of the embodiments described above a fan motor was given by way of example, but the motor of the present invention is also applicable to motors with other applications. For example, it is applicable to main motors for driving a driving portion in a piece of office equipment or the like, and to spindle motors or the like that drive a recording disk.  
         [0099]     In the present embodiment, a main motor A 1  in  FIG. 15  is given as an example. The magnetic circuit portions of the main motor A 1  are substantially the same as in the fan motor A of the first embodiment. The lower end portion of the shaft  44  is linked to the driving portion of a piece of office equipment, and transmits torque produced by the motor to that driving portion. The stator  45  is fixed in contact with the stepped portion  48   d  of the bearing bushing  48 . The motor support portion  22  is formed as a single body with the bearing bushing  48 , and is linked to the bearing positioning portion  6  via the plurality of communicating holes  48   c . The motor support portion  22  of the main motor A 1  is installed in a predetermined portion of the piece of office equipment using a fixing means such as a screw. The circuit board  49  is screwed to the motor support portion  22 .  
         [0100]     The bearing retainer unit  2  in the present embodiment is provided with the motor support portion  22 , the bearing bushing  48 , and the bearing positioning portion  6 . Because it is necessary in the main motor A 1  to configure the stationary section strongly, aluminum is used as a molten material when performing insert molding.  
         [0101]     It is possible with this embodiment to obtain the same effects as each of the embodiments described above. Also, it is possible to apply each of the embodiments described above in the present embodiment.  
         [0102]     Only selected embodiments have been chosen to illustrate the present invention. To those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made herein without departing from the scope of the invention as defined in the appended claims. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and not for limiting the invention as defined by the appended claims and their equivalents.