Abstract:
An apparatus to render the shield of a bail bearing unnecessary and to improve the lubricity inside a fan motor is presented. A bearing housing is integrally formed with a base of the fan motor, and a shield part is formed at one end of the bearing housing. A ball bearing, spacer and sleeve bearing are set inside from the other end of the bearing housing, and these are fixed in place by pressing in a retainer cap. The interior of the bearing housing is then shielded at each end by the shield part and the retainer cap, making the need for a shielded ball bearing unnecessary. A rotational shaft, to which a rotor and impeller are attached, is supported by the ball bearing and the sleeve bearing. Inside the bearing housing, lubricating oil passes back and forth between the ball bearing and sleeve bearing, thereby enabling the elimination of insufficiencies in lubricating oil, and improving lubricity.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority from Japanese Patent Application No. 2002-195748 filed on Jul. 4, 2002.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an apparatus for a fan motor used in the cooling of equipment and the like containing electronic parts.  
           [0004]    2.Description of the Related Art  
           [0005]    Generally, in electronic equipment such as, for instance, personal computers, servers and copiers containing electronic parts, compact fan motors are installed for the purposes of cooling the interior of the assembly or the individual electronic parts.  
           [0006]    One example of this type of conventional axial flow fan motor that is installed in such equipment and the like is explained with reference to FIG. 11. As shown in FIG. 11, with regard to fan motor  1 , a ball bearing  5  and a sleeve bearing  6  are set inside a cylindrical bearing housing  4  that is integrally formed with base  3  of casing  2  made of synthetic resin, and the shaft  7  is supported by these bearings  5  and  6  so as to be capable of rotating. For the purposes of dust proofing and preventing splashing of lubricating oil, ball bearing  5  is provided with a shield, while the sleeve bearing  6  consists of porous material of sintered metal or the like that is impregnated with lubricating oil.  
           [0007]    The rotor  8  of the motor is attached to the tip of shaft  7 , and stator  9  of the motor is fixed to the periphery of bearing housing  4  opposite rotor  8 . An impeller  11  made of synthetic resin and furnished with multiple fins  10  fits into the outer side of rotor  8 . A PC board (print substrate)  12  incorporating a drive circuit that serves to drive the motor is attached to the periphery of the base of bearing housing  4 . In the figure, reference numeral  13  is the stop ring that prevents shaft  7  from coming off, and  14  is the lead wire that serves to energize the PC board  12 .  
           [0008]    As a result of this configuration, when the drive circuit of PC board  12  is energized via lead wire  14 , stator  9  generates a magnetic field and causes rotor  8  to rotate, with the result that impeller  11  rotates and air flow occurs in a uniform direction inside casing  2 . Consequently, by installing fan motor  1  in the appropriate part of the electronic equipment, it is possible to cool the individual electronic parts or the interior of the assembly of the electronic equipment.  
           [0009]    In the aforementioned conventional fan motor  1 , however, there are the following problems. Using a ball bearing provided with a shield adds to the manufacturing costs. Further, as the structure is such that ball bearing  5  and sleeve bearing  6  are fit in from both ends of bearing housing  4 , and their positions in the axial direction are determined by contact with the central stage part, the fitting part of ball bearing  5  and the fitting part of sleeve bearing  6  of bearing housing  4  are molded by separate metal dies (i.e., an upper die and a lower die). Consequently, it becomes difficult to assure the concentricity of ball bearing  5  and sleeve bearing  6 . Moreover, due to the reduced lubricity of sleeve bearing  6  bearing life is limited.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, the present invention is directed to the construction and operation of a fan motor that not only makes the ball bearing shield unnecessary, but also achieves a longer life for the ball bearing. The construction of the fan motor is such that it is provided with a cylindrical bearing housing fixed to a base, a pair of bearings set inside the bearing housing, a rotational shaft supported by the pair of bearings, a stator fixed to the outer periphery of the bearing housing, a rotor that faces the stator and that is fixed to the side of the rotational shaft, and an impeller that is fixed to the side of the rotational shaft.  
           [0011]    An embodiment of the present invention is characterized by shielding the interior of the bearing housing by forming a shield part at one end of the bearing housing that extends in the radial direction to the vicinity of the rotational shaft, setting the pair of bearings inside the bearing housing from the other end of the bearing housing, and affixing a cap member to the other end of the bearing housing.  
           [0012]    As a result of this configuration, the interior of the bearing housing is shielded by the shield part and the cap member. This allows for effective dust-proofing of the interior of the housing and the bearings, prevention of splashing of lubricating oil, and allows for use of a bearing without a shield. Furthermore, as a result of this configuration, the pair of bearings is respectively fixed in place by contacting the shield part and the cap member. One can also easily assure the concentricity of the pair of bearings by means of a structure that has the pair of bearings fit into the interior of the housing from one direction. Moreover, inside the shielded bearing housing, lubricating oil passes back and forth between the pair of bearings.  
           [0013]    In yet another embodiment of the present invention, the fan motor is characterized by the fact that the pair of bearings can be either an unshielded ball bearing and a sleeve bearing, or a shielded ball bearing and a sleeve bearing.  
           [0014]    As a result of either of these configurations, lubricating oil can pass back and forth between the unshielded/shielded ball bearing and the sleeve bearing.  
           [0015]    The present invention, including its features and advantages, will become more apparent from the following detailed description with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a longitudinal section view of the fan motor according to a first embodiment of the present invention.  
         [0017]    [0017]FIG. 2 is a longitudinal section view of the fan motor according to a second embodiment of the present invention.  
         [0018]    [0018]FIG. 3 is a longitudinal section view of the fan motor according to a third embodiment of the present invention.  
         [0019]    [0019]FIG. 4 is a longitudinal section view of the fan motor according to a fourth embodiment of the present invention.  
         [0020]    [0020]FIG. 5 is a frontal view of the spacer of the fan motor shown in FIG. 1.  
         [0021]    [0021]FIG. 6 is a cross-sectional view along line A-A of the spacer shown in FIG. 5.  
         [0022]    [0022]FIG. 7 is an enlarged longitudinal section view of the sleeve bearing of the fan motor shown in FIG. 1.  
         [0023]    [0023]FIG. 8 is an enlarged longitudinal section view of a modified example of the sleeve bearing of the fan motor shown in FIG. 1.  
         [0024]    [0024]FIG. 9 is an enlarged longitudinal section view of the retainer cap of the fan motor shown in FIG. 2.  
         [0025]    [0025]FIG. 10 is a frontal view of the retainer cap shown in FIG. 9.  
         [0026]    [0026]FIG. 11 is a longitudinal section view of a conventional fan motor according to the prior art.  
     
    
     DETAILED DESCRIPTION  
       [0027]    Below, different embodiments of the present invention are explained with reference to the drawings.  
         [0028]    Referring now to FIG. 1, a first embodiment of the present invention is described. As shown in the figure, fan motor  20  is provided with a synthetic resin casing  25  having a cylindrical venturi part  21  that has a tapered inner surface, a base  23  that is fixed in place by multiple ribs  22  radially extending at the center of one end of venturi part  21 , and a cylindrically-shaped bearing housing  24  that is integrally molded with the bottomed base  23 . The bearing housing  24  extends from base  23  into the interior of casing  25  in a manner concentric with venturi part  21 .  
         [0029]    Formed at one end of bearing housing  24  is a bottom shield part  26  having formed therein an aperture  26 A at the center. The shield part  26  extends radially to the vicinity of rotational shaft  31 . Into aperture  26 A is inserted a cylindrical part  45 , formed at a base of hub  33 , that is attached to the tip of rotational shaft  31 . A sufficiently, small clearance gap of 30-50 μm is formed between cylindrical part  45  and aperture  26 A.  
         [0030]    Inside bearing housing  24 , ball bearing  27 , that contacts shield part  26 , and cylindrical spacer  28 , that contacts both ball bearing  27  and sleeve bearing  29 , are inserted via an aperture in the side of base  23  and set in place. The bottomed, cylindrically-shaped retainer cap  30  is then pressed into the aperture in the side of base  23  of bearing housing  24 , and contacts sleeve bearing  29 , fixing in place ball bearing  27 , spacer  28 , and sleeve bearing  29 . Thus, the interior of bearing housing  24  is shielded from the exterior at each respective end by shield part  26  and retainer cap  30 .  
         [0031]    As ball bearing  27 , one may use an unshielded ball bearing that is not provided with a shield.  
         [0032]    On spacer  28 , as shown in FIGS. 5 and 6, multiple oil grooves  46  are provided in the axial direction on the outer periphery (four are illustrated in the figures), and multiple oil grooves  47  are respectively formed in the radial direction on both end faces (four are illustrated in the figures). It is to be understood, of course, that more or less oil grooves may be used depending on specifications.  
         [0033]    The sleeve bearing  29  consists of porous material made of sintered metal or the like, and is impregnated with lubricating oil. Preferably, the end of sleeve bearing  29  on the retainer cap  30  side is sealed, or the density of the sintering may be raised so that the lubricating oil that impregnates sleeve bearing  29  does not flow out to retainer cap  30  side. As shown in FIGS. 7 and 8, a chamfer  48  or a stage  49  can be formed on an edge of sleeve bearing  29  aperture on the ball bearing  27  side that allows for easy insertion of rotational shaft  31 . Moreover, as it is possible to collect lubricating oil in chamfer  48  or stage  49 , it is possible to supply sufficient lubricating oil to the sliding surfaces of sleeve bearing  29  and rotational shaft  31 . The compatibility of the lubricating oils used in ball bearing  27  and sleeve bearing  29  has been taken into account so that they can be mixed and used.  
         [0034]    The rotational shaft  31  is inserted through ball bearing  27  and sleeve bearing  29 , and is supported thereby so that it is capable of rotating. A stop ring  32  is attached to rotational shaft  31 , and rotational shaft  31  is locked in place by the contact of stop ring  32  with ball bearing  27 . A hub  33 , made of zinc die cast, is attached to the tip of rotational shaft  31 , and additionally a rotor  34  is attached to hub  33 .  
         [0035]    The rotor  34  covers bearing housing  24  and consists of a bottomed, cylindrically-shaped yoke  35 , whose bottom part is attached to hub  33 , and an annular permanent magnet  36  fixed to the inner periphery of yoke  35 . An impeller  38  possessing multiple fins  37  is press-fitted into the outer periphery of yoke  35 . Instead of providing a separate hub  33 , it is also acceptable to directly insert rotational shaft  31  into an impeller  38  made of synthetic resin that is integrated with the hub.  
         [0036]    A stator  39  that faces the inner periphery of rotor  34  is attached to the outer periphery of bearing housing  24 . The stator  39  consists of a core  40  that radially extends facing the inner periphery of permanent magnet  36  of the rotor  34  side, a bobbin  41  mounted on core  40 , a coil  42  that is wound around bobbin  41 , and a PC board  43  that is fixed to bobbin  41  and that is arranged at the periphery of the base of bearing housing  24 . The central part in the axial direction of permanent magnet  36  is offset to the side of base  23  relative to the central part in the axial direction of core  40 .  
         [0037]    The brushless DC motor consists of rotor  34  and stator  39 , and a drive circuit is provided in PC board  43  for purposes of driving the pertinent brushless DC motor. A lead wire  44  is connected to PC board  43  in order to energize the drive circuit. The lead wire  44  is arranged so as to pass along one of the ribs  22 , and extends to the exterior of casing  25 .  
         [0038]    Next, the operation, of the fan motor with the above configuration is explained.  
         [0039]    By energizing lead wire  44 , the drive circuit mounted in PC board  43  controls the current that flows to coil  42 , sequentially magnetizes core  40 , and rotates rotor  34  in a uniform direction. As a result of this, impeller  38  is rotated in a uniform direction, and it is possible to blow air in a uniform direction corresponding to its rotation. At this time, as the central part in the axial direction of permanent magnet  36  of rotor  34  is offset to the side of base  23  relative to the central part in the axial direction of core  40  of the stator  39 , rotor  34  is attracted in the direction away from base  23  by the magnetic field generated by stator  39 , and as a result of the force in the axial direction induced by this it is possible to preload ball bearing  27 .  
         [0040]    As it is possible to prevent the invasion of foreign matter, dust and the like, and prevent the splashing of the lubricating oil of ball bearing  27  by shielding the interior of bearing housing  24  from the exterior by shield part  26  and retainer cap  30 , it is unnecessary to have an, expensive shielded ball bearing, and one can reduce the manufacturing cost. By forming a stage (not shown) on cylindrical part  45  of hub  33  that is attached to shield part  26  and rotational shaft  31 , and by forming their clearance gap in a labyrinthine shape, it is possible to heighten the dust-proofing effect and the leakage prevention effect for the lubricating oil. Moreover, in expectation of a still more heightened shielding effect, one can also use a shielded ball bearing as ball bearing  27 .  
         [0041]    As lubricating oil reciprocally passes between ball bearing  27  and sleeve bearing  29  via oil grooves  46 ,  47  of spacer  28  inside shielded bearing housing  26 , any insufficiency of lubricating oil can be eliminated, and thus a longer life for ball bearing  27  and sleeve bearing  29  can be brought about. By sealing the end part of sleeve bearing  29  on the retainer cap  30  side, or by raising the sintering density of the sleeve bearing  29 , outflow of the lubricating oil that impregnates the sleeve bearing  29  towards the retainer cap  30  can be prevented and thus the amount of lubricating oil consumed can be reduced.  
         [0042]    As bearing housing  24  is configured so that ball bearing  27  and sleeve bearing  29  are inserted and set from the aperture in the side of base  23 , their fitting parts can be molded/cast from one metal die (i.e., without the need for an upper die and a lower die) without occurrence of undercutting. Consequently, it is possible to easily assure the concentricity of ball bearing  27  and sleeve bearing  29 .  
         [0043]    Referring now to FIG. 2, a second embodiment of the present invention is described. As the second embodiment has largely the same configuration as the above-described first embodiment, except that it is provided with a spring-action preloading mechanism for the ball bearing, the parts that are identical to those in the first embodiment are hereinafter given the same reference numerals and a detailed explanation is given only for the parts that are different.  
         [0044]    As shown in FIG. 2, in the fan motor  50  pertaining to the second embodiment, rotational shaft  31 , towards the base  23 , is formed as a spherically-shaped surface part  51  and a slide member  52  is installed so as to be able to slide inside retainer cap  30  and to contact this spherical part  51 . By means of the spring force of coil spring  53  that is interposed between slide member  52  and retainer cap  30 , rotational shaft  31  is pressed in the direction away from base  23 , and ball bearing  27  is preloaded. At the point of contact of slide member  52  with rotational shaft  31 , a slipper  54  made of synthetic resin is provided in order to alleviate friction. Moreover, as retainer cap  30  also serves the additional function of receiving the spring action of coil spring  53 , as shown in FIG. 9 and FIG. 10, engagement claws  55  are formed at both ends of retainer cap  30  in the radial direction. The engagement claws  55  engage by snapping onto base  23 , and in addition to securing ball bearing  27 , spacer  28  and sleeve bearing  29 , they support the spring force of coil spring  53 .  
         [0045]    As a result of this configuration, in addition to the operations and effects of the above-described first embodiment, it is possible to regularly preload rotational shaft  31  in the axial direction by means of coil spring  53 , with the result that one can minimize the movement of the rotating parts in the axial direction, and lengthen bearing life.  
         [0046]    Referring now to FIG. 3, a third embodiment of the present invention is described. As the third embodiment has largely the same configuration as the above-described first and second, embodiments, except that the ball bearing and sleeve bearing are arranged in the opposite manner with omission of the spacer, the parts that are identical to those of the above-described embodiments are hereinafter given the same reference numerals and a detailed explanation is given only for the parts that are different.  
         [0047]    As shown in FIG. 3, in the fan motor  56  pertaining to the third embodiment, sleeve, bearing  29  is press-fitted into bearing housing  24  and contacts shield part  26 . The ball bearing  27  fits into the somewhat larger diameter aperture side of the bearing housing and is fixed in place as one end contacts stage  57  while the other end contacts retainer cap  30 . In rotational shaft  31 , a stop-ring  32  is attached to the base of spherical part  51 , and contacts ball bearing  27 . Moreover, there is no cylindrical part  45  formed in hub  33 , and shield part  26  of bearing housing  24 , and rotational shaft  31  directly face each other with a specified clearance of 30-50 μm.  
         [0048]    As a result of this configuration, it is possible to omit spacer  28 . In this case, similar to the above-described first and second embodiments, the discharge to the outside of the lubricating oil that impregnates the sleeve bearing  29  can be impeded by sealing the end face of sleeve bearing  29  that is on the side opposite ball bearing  27 , that is, the shield part  26  side, or by increasing the density of the sintering, and thus the amount of lubricating oil consumed can be reduced.  
         [0049]    Referring now to FIG. 4, a fourth embodiment of the present invention is described. As the fourth embodiment has largely the same configuration as the above-described first embodiment, except that the direction of the preloading due to the magnetic field of the stator is reversed and the attachment positions of the permanent magnet of the rotor and stop-ring of the shaft are different, the parts that are identical to those of the above-described first embodiment are hereinafter given the same reference numerals and a detailed explanation is given only for the parts that are different.  
         [0050]    As shown in FIG. 4, in the fan motor  58  pertaining to the fourth embodiment, the permanent magnet  36  of rotor  34  extends in the axial direction to the vicinity of the bottom part of yoke  35 , and its central part in the axial direction is offset to the opposite side of base  23  relative to the central part in the axial direction of the stator  39 .  
         [0051]    As a result of this configuration, rotor  34  is attracted towards base  23  by the magnetic field generated by stator  39 , and it is possible to preload ball bearing  27  by this force in the axial direction.  
         [0052]    In the above-described embodiments, the description concerns a configuration that uses a ball bearing and a sleeve bearing as a pair of bearings, however, it is to be understood that this invention is not limited thereto, and that it is possible to have both be ball bearings or sleeve bearings, and/or to use other suitable types of bearings. Moreover, the present invention is described in the context of a fan motor, however, it is also to be understood that the present invention is not limited thereto, and can be similarly applied to blowers with larger pressure ratios than fan motors. Lastly, it is to be understood that in addition to its essential meaning, the term “fan motor” employed in this specification shall also be taken to include those blowers with larger pressure ratios.  
         [0053]    With the fan motor as described above, as the interior of the bearing housing is shielded by the shield part and the cap member, dust-proofing of the housing interior and bearings can be effectively achieved and splashing of lubricating oil can be prevented without using a bearing provided with a shield. As a result, it is unnecessary to have an expensive shielded ball bearing and the manufacturing costs can be reduced.  
         [0054]    Furthermore as the configuration of the fan motor is such that the pair of bearings can be set inside the bearing house from one side, it is possible to mold the bearing fitting parts of the bearing housing from one metal die, and thus the concentricity of the pair of bearings can be easily assured.  
         [0055]    Moreover, as lubricating oil passes back and forth between the pair of bearings inside the bearing housing that has been shielded, insufficiencies in lubricating oil can be eliminated and a longer life for the bearings can be achieved.  
         [0056]    And yet further with the fan motor described above, by furnishing the bearing housing with a shield part and a retainer cap, the pair of bearings can be retained in place in the bearing housing by contact with the shield part and the retainer cap.  
         [0057]    In the foregoing description, the apparatus and method of the present invention have been described with reference to specific examples. It is to be understood and expected that variations in the principles of the apparatus and method herein disclosed may be made by one skilled in the art and it is intended that such modifications, changes, and substitutions are to be included within the scope of the present invention as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense.