Abstract:
Herein disclosed a bearing unit including: a dynamic pressure fluid bearing adapted to receive a rotary shaft inserted thereinto; a unit main body surrounding the outside of the fluid bearing; a lid member covering an upper opening of the unit main body with the rotary shaft inserted into the dynamic fluid bearing; lubricating oil poured into the unit main body; and an oil thrower ring rotating together with the rotary shaft in a space defined between an upper end of the fluid bearing and the lid member; wherein a gap defined between the lid member and the oil thrower ring is tapered in cross-section so as to be progressively reduced in the distance therebetween as the gap is spaced apart from the center of the rotary shaft.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present invention contains subject matter related Japanese Patent Application JP 2006-216337 filed in the Japan Patent Office on Aug. 9, 2006, the entire contents of which being incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a bearing unit in which a dynamic fluid bearing adapted to receive a rotary shaft inserted thereinto is covered by a unit main body and to a motor using the bearing unit. 
         [0004]    2. Description of the Related Art 
         [0005]      FIG. 8  is a schematic cross-sectional view for assistance in explaining a bearing unit provided with a non-contact rotational seal (hereinafter, simply referred to as “the seal”) in related art. A bearing unit  30  is configured as below. A shaft  34  is rotatably supported by a slide bearing  31  and a thrust bearing  39  (a pivot bearing in this case). A non-contact rotational seal  30   a  is composed of a gap portion  37  defined between the shaft  34  and a gap-forming member  38  and tapered in cross-section axially-inwardly from the slide bearing  31  for preventing leakage of lubricating oil. A stator member  36  holds the slide bearing  31 , the thrust bearing  39  and the gap-forming member  38 . 
         [0006]    Then, a description is made of how the gap portion  37  tapered axially-inwardly from the slide bearing  31  provides a non-contact rotational seal for retaining lubricating oil inside the bearing unit. 
         [0007]    Fluid tends to move in a narrower width due to the capillary phenomenon. If it is intended to retain lubricating oil inside the bearing unit, then the bearing unit is preferably provided with a gap that is tapered in cross-section toward the inside thereof. The lubricating oil in the gap thus tapered will move toward the inside of the bearing unit for retainment. 
         [0008]    In this case, the drawing pressure P generated by the capillary phenomenon is represented by the equation, P=2γ cos θ/r, where γ is surface tension occurring between lubricating oil and a lubricating oil-contact object (if this object is the shaft  34 , it is made of stainless steel or duralumin; if the object is the gap-forming member  38 , it is made of metal or resin), θ is a contact angle between the lubricating oil and the lubricating oil-contact object and r is a width of the gap portion  37 . 
         [0009]    That is to say, P∝1/r; therefore, the lubricating oil is drawn toward the inside of the bearing unit having a smaller gap width r for retainment. 
         [0010]    In this way, the non-contact rotational seal  30   a  in the related art can seal the lubricating oil of the rotational portion in a non-contact manner by devising the shape of the seal portion and using the surface tension of the lubricating oil. Because of the non-contact seal, the non-contact rotational seal  30   a  is of an excellent lubricating oil sealing system that has no torque loss and maintains excellent rotational-mechanical accuracy such as no axial vibration. 
         [0011]      FIG. 9  is a cross-sectional view of a seal portion extracted from the bearing unit  40  illustrated in Japanese Patent Laid-open No. 2005-127514 (hereinafter referred as Patent Document 1). The seal portion of the bearing unit  40  intends to solve the difficulty of thinning which is a defect of the bearing unit  30  shown in  FIG. 8 . That is to say, a gap portion  47  defined by the end face of a slide bearing  41  and a gap-forming member  48  is tapered in cross-section toward the shaft  44 . 
         [0012]      FIG. 10  is a cross-sectional view of a seal portion extracted from the bearing unit  50  illustrated in Japanese Patent Laid-open No. 2004-36892 (hereinafter referred as Patent Document 2). The seal portion of the bearing unit  50  is provided on the end face portion of a slide bearing  51  with a gap portion  57  which is defined by a plate-like member  58   b  and a gap-forming member  58   a  so as to be tapered in cross-section toward the outside. 
       SUMMARY OF THE INVENTION 
       [0013]    Like the bearing unit  30  shown in  FIG. 8 , the non-contact seal  30   a  which needs to form the gap portion  37  extending toward the shaft requires some degree of thickness because of taper formation and of preparation for a rise in the level of the lubricating oil resulting from thermal expansion. Thus, the non-contact seal  30   a  has a defect in which it is difficult to reduce the thickness of the bearing unit  30 . 
         [0014]    The gap portion  47  of the bearing unit  40  shown in  FIG. 9  is not located on the route, indicated with arrow A, through which the lubricating oil leaks from between the shaft  44  and the inner circumferential surface of the slide bearing  41  or the radial bearing device to the outside of the bearing unit  40 . Thus, although the bearing unit  40  plays a role of positively feeding the lubricating oil to the sliding surface between the shaft  44  and the slide bearing  41 , it has a problem in which it is impossible to produce an excellent effect of preventing the lubricating oil from leaking to the outside and from splashing. 
         [0015]    Similarly, the bearing unit  50  shown in  FIG. 10  is not located on the route, indicated with arrow A, through which the lubricating oil leaks. Thus, the bearing unit  50  has a defect in which it cannot produce an excellent effect of preventing the lubricating oil from leaking and splashing resulting from the rotation of the shaft  54 . 
         [0016]    In other words, the bearing unit  50  is not distinctive in playing the role of positively drawing the lubricating oil into the inside but prevents the mist of the lubricating oil splashing resulting from the rotation of the shaft  54  from diffusing outward for reuse. 
         [0017]    As described above, the non-contact seals in the related art cannot overcome the defects in which since it is necessary to provide a tapered gap in the axial direction, thinning is difficult, and while it is intended to provide thinning, since the seal is not located on the outflow path of the lubricating oil, it is difficult to prevent the leakage of the lubricating oil. 
         [0018]    According to an embodiment of the present invention, there is provided a bearing unit including: a dynamic pressure fluid bearing adapted to receive a rotary shaft inserted thereinto; a unit main body surrounding the outside of the fluid bearing; a lid member covering an upper opening of the unit main body with the rotary shaft inserted into the fluid bearing; lubricating oil poured into the unit main body; and an oil thrower ring rotating together with the rotary shaft in a space defined between an upper end of the fluid bearing and the lid member; wherein a gap defined between the lid member and the oil thrower ring is tapered in cross-section so as to be progressively reduced in the distance therebetween as the gap is spaced apart from the center of the rotary shaft. 
         [0019]    According to another embodiment of the present invention, there is provided a motor using the bearing unit described above. 
         [0020]    In the embodiment of the present invention described above, the oil thrower ring rotating together with the rotary shaft is provided between the upper portion of the dynamic pressure fluid bearing and the lid member and the gap defined between the oil thrower ring and the lid member is tapered in cross-section so as to be reduced in the distance therebetween as it is spaced apart from the center of the rotary shaft. Thus, the path of the lubricating oil is partitioned by the oil thrower ring to extend along a direction perpendicular to the rotary shaft in a reciprocative manner. In addition, the lubricating oil can be led toward the inside of the bearing unit by the gap tapered between the oil thrower ring and the lid member. 
         [0021]    In particular, according to the invention, since the oil thrower ring is rotated together with the rotary shaft, the lubricating oil can forcibly be led toward the inside of the bearing unit by the centrifugal force resulting from the rotation of the oil thrower ring. 
         [0022]    Accordingly, the present invention can produce the following effects. The gap which is tapered in cross-section so as to be progressively reduced in the distance thereof as it is spaced apart from the center of the shaft can extend the path of the lubricating oil in the direction perpendicular to the shaft. Thus, the entire bearing unit can be reduced in thickness. In addition, the direction of the surface tension of the tapered portion conforms to the direction of the centrifugal force resulting from the rotation of the oil thrower ring. The path of the lubricating oil is elongate and has a labyrinth structure. Thus, excellent lubricating oil retaining performance can be exhibited. 
         [0023]    As described above, the bearing unit according to the embodiments of the invention is thin and can provide excellent lubricating oil retaining performance; therefore, the motor mounted with the bearing unit of the invention can suitably applied to electronic equipment such as personal computers and video equipment such as televisions which require thinness and a long life. In addition, the bearing unit of the invention is such that the oil thrower ring also serves as a locking member of the rotary shaft; therefore, the number of component parts can be reduced compared with that of the related art. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1  is a schematic cross-sectional view for assistance in explaining a bearing unit according to a first embodiment; 
           [0025]      FIG. 2  is an enlarged cross-sectional view for assistance in explaining a major portion of the bearing unit according to the first embodiment; 
           [0026]      FIG. 3  is an enlarged cross-sectional view for assistance in explaining a major portion of a bearing unit according to a second embodiment; 
           [0027]      FIG. 4  is an enlarged cross-sectional view for assistance in explaining a major portion of a bearing unit according to a third embodiment; 
           [0028]      FIG. 5  is an enlarged cross-sectional view for assistance in explaining a major portion of a bearing unit according to a fourth embodiment; 
           [0029]      FIG. 6  is a schematic view of a fan motor provided with one of the bearing units of the embodiments; 
           [0030]      FIG. 7  is a schematic cross-sectional view for assistance in explaining a unit-forming method; 
           [0031]      FIG. 8  is a schematic cross-sectional view for assistance in explaining a bearing unit equipped with a non-contact rotational seal in related art; 
           [0032]      FIG. 9  is an enlarged schematic cross-sectional view of a seal portion extracted from the bearing unit described in Patent Document 1; and 
           [0033]      FIG. 10  is an enlarged schematic cross-sectional view of a seal portion extracted from the bearing unit described in Patent Document 2. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0034]    Preferred embodiments of the present invention will hereinafter be described with reference to the drawings.  FIG. 1  is a schematic cross-sectional view for assistance in explaining a bearing unit of a first embodiment. A bearing unit  10  according to the first embodiment is configured as below. A shaft  14  is rotatably supported by a slide bearing  11  and a thrust bearing  19  (a pivot bearing in this case). An oil thrower ring  15  is integrally attached to the shaft  14  so as to be rotatable therewith. A gap portion  17  is defined between the oil thrower ring  15  and a gap-forming member  18  which is a lid member so as to be tapered in cross-section radially toward the outside from the shaft  14 . Thus, a non-contact rotational seal  10   a  is configured to prevent leakage of lubricating oil. A stator member  16  holds the slide bearing  11 , the thrust bearing  19  and the gap-forming member  18 . 
         [0035]    The non-contact seal  10   a  of the bearing unit  10  according to the embodiment has a feature that the oil thrower ring  15  and the gap-forming member  18  form the gap portion tapered in cross-section in a direction of drawing lubricating oil into the inside of the bearing unit and the oil thrower ring  15  is rotated integrally with the shaft  14 . 
         [0036]    That is to say, the direction of drawing the lubricating oil into the tapered gap portion  17  conforms to the direction of a centrifugal force generated by the rotation of the oil thrower ring  15 . Therefore, performance can be provided for more firmly retaining lubricating oil. 
         [0037]    The slide bearing  11  is a dynamic pressure fluid bearing in which lubricating oil is interposed between the shaft  14  and the slide bearing  11  to radially support the bearing  11  for rotation with low friction. The lubricating oil is filled inside the stator member  11  and is prevented from leaking upward by the gap-forming member  18  covering the upper opening of the stator member  16 . 
         [0038]      FIG. 2  is an enlarged schematic cross-sectional view for assistance in explaining the major portion of the bearing unit according to the first embodiment. The oil thrower ring  15  attached to the shaft  14  is a ring member made of metal or resin and fixedly fitted to the groove of the shaft  14 . Alternatively, the oil thrower ring  15  may firmly be secured to the shaft  14  with an adhesive or by welding or the like as necessary. 
         [0039]    The oil thrower ring  15  is perpendicularly attached to the shaft  14  to partition the gap between the upper surface of the slide bearing  11  and the gap-forming member  18 . This forms the gap portion  17  on the upper side of the oil thrower ring  15  and a gap portion  13  on the lower side thereof. 
         [0040]    There is provided a small gap between the end of the oil thrower ring  15  and the gap-forming member  18 . Specifically, a lubricating oil flow passage A is formed which extends between the upper portion of the slide bearing  11  and the gap between the gap-forming member  18  and the shaft  14  as indicated with a dashed line in  FIG. 2 . The lubricating oil can reciprocate perpendicularly to the shaft  14 . In short, the lubricating oil flow passage A can be extended perpendicularly to the shaft  14 , whereby the bearing unit  10  can be reduced in thickness while ensuring a sufficient length of the flow passage. 
         [0041]    Further, the configuration of the present embodiment has the tapered gap portion  17  provided on the mid-course of the lubricating oil flow passage A and a long course from the sliding portion relative to the shaft  14  to the external portion of the bearing and provide a labyrinth structure, which can exhibit an effect of sufficiently retaining lubricating oil. 
         [0042]    Needless to say, this configuration intends to prevent the lubricating oil from flowing out from the gap portion  13  between the slide bearing  11  and the oil thrower ring  15  via the tapered gap portion  17 . Therefore, the other portions such as the fastening portion of the stator member  16  to the gap-forming member  18  and the fastening portion of the shaft  14  to the oil thrower ring  15  may be sealed by an adhesive, laser welding or a sealing member such as rubber. 
         [0043]    The bearing unit  10  configured as described above can reliably prevent leakage of the lubricating oil by the tapered gap portion  17  drawing the lubricating oil from the center of the shaft  14  to the outside thereof and by the action of the centrifugal force resulting from the shaft  14  and the oil thrower ring  15 . 
         [0044]      FIG. 3  is an enlarged schematic cross-sectional view for assistance in explaining a major portion of a bearing unit according to a second embodiment. A non-contact seal  10   a  of this embodiment further enhances lubricating oil-retaining performance resulting from surface tension compared with the non-contact seal provided for the bearing unit  10  shown in  FIGS. 1 and 2 . 
         [0045]    The non-contact seal  10   a  is distinctive in providing a continuously tapered gap formed as below. A gap portion  13  between the upper portion of a slide bearing  11  and an oil thrower ring  15  is tapered in cross-section toward a sliding surface, i.e., the center of the shaft  14 . In addition, a gap portion  17  between the oil thrower ring  15  and a gap-forming member  18  is progressively reduced in the distance therebetween with increasing distance from the sliding surface, i.e., the center of the shaft  14 . 
         [0046]    In the embodiment shown in  FIG. 3 , to form the continuously tapered gap described above, the oil thrower ring  15  is formed to extend obliquely upward with respect to the shaft  14 . The tapered gap  17  allows the lubricating oil to be drawn in a direction opposite to the shaft  14 . In addition, the gap portion  13  is tapered in cross-section to allow the lubricating oil to be drawn toward the shaft  14 . In other words, since also the gap portion  13  is tapered additionally to the tapered gap portion  17 , a force of drawing the lubricating oil by use of the capillary phenomenon is increased to make it possible to positively prevent the leakage of the lubricating oil. 
         [0047]      FIG. 4  is an enlarged schematic cross-sectional view for assistance in explaining the major portion of a bearing unit according to a third embodiment. As with the second embodiment shown in  FIG. 3 , a non-contact seal  10   a  is continuously tapered in cross-section with an oil thrower ring  15  located between gap portions. However, the oil thrower ring  15  is formed to extend perpendicularly to the shaft  14  and the upper end of a slide bearing  11  is slantly formed to provide a lower gap portion with a lower tapered shape. 
         [0048]    Similarly to the above embodiments, the bearing unit  10  of the third embodiment forms the continuously tapered gaps. Thus, the tapered shape is increased in length to enhance performance for drawing the lubricating oil. 
         [0049]      FIG. 5  is an enlarged schematic cross-sectional view for assistance in explaining the major portion of a bearing unit according to a fourth embodiment. A non-contact seal  10   a  of a bearing unit  10  is such that an oil thrower ring  15  is formed integrally with a shaft  14 . While in the embodiments described earlier the oil thrower ring  15  is separately attached to the shaft  14 , in the present embodiment the oil thrower ring  15  is formed integrally with the shaft  14  when the shaft  14  is formed by cutting or the like. 
         [0050]    The configuration of the present embodiment provides the same performance of drawing the lubricating oil as that of the embodiment shown in  FIG. 2 . The direction of drawing the lubricating oil into the tapered gap portion  17  conforms to the direction of a centrifugal force generated by the rotation of the oil thrower ring  15 . Therefore, performance can be provided for more firmly retaining lubricating oil. 
         [0051]    Since the oil thrower ring  15  formed integrally with the shaft  14  is provided, a process of separately attaching an oil thrower ring  15  to the shaft  14  can be omitted. In addition, the number of component parts can be reduced and reliability resulting from the integral formation can be increased. 
         [0052]    In general, if at least a radial bearing device is a dynamic pressure bearing formed with herring bone-shaped or axially shaped dynamic pressure generating grooves, it is significantly important to retain lubricating oil indispensable to form an oil film. The non-contact seals  10   a  of the embodiments can provide an effect sufficient to cope with this. Needless to say, also the thrust bearing device may be a dynamic pressure bearing. 
         [0053]      FIG. 6  is a schematic diagram of a fan motor on which any one of the bearing units according to the embodiments is mounted. This fan motor includes a rotor  60 , a base plate  61 , a housing  62 , a rotation drive circuit  63 , a core  64 , a winding  65 , an impeller  66 , a magnetic case  67 , a magnet  68 , a case  69 , and a bearing unit  10 . 
         [0054]    The housing  62  is provided outside the bearing unit  10 . The bearing unit  10  is secured to the base plate  61  via the housing  62 . Coils composed of the cores  64  and windings  65  are attached to the housing  62 . The coils are opposed to the magnets  68  of the rotor  60  rotatable with a shaft of the bearing unit  10 . The rotor  60  is provided with a plurality of the impellers  66 . The impellers  66  rotate together with the rotor  60  to generate air flow. 
         [0055]    Any one of the bearing units according to the embodiments described above is used as the bearing unit  10  of such a fan motor to reduce the thickness of the entire fan motor. In addition, it is possible to effectively prevent lubricating oil from leaking from the bearing unit  10 , thereby enhancing reliability of the fan motor. 
         [0056]    A description is next made of a method of manufacturing the bearing unit according to the present embodiment. For the bearing units  10  according to the first, second, third and fourth embodiments shown in  FIGS. 1 ,  3 ,  4  and  5 , respectively, the stator member  16  is preliminarily molded with resin and the thrust bearing  19  and slide bearing  11  are assembled into the stator member  16 . Thereafter, the oil thrower ring  15  is attached to the shaft  14 . In the fourth embodiment shown in  FIG. 5 , the oil thrower ring  15  is formed integrally with the shaft  14 ; therefore, it is not necessary to attach the oil thrower  15  to the shaft  14 . Next, the shaft  14  attached with the oil thrower ring  15  is inserted into the central hole of the slide bearing  11 . 
         [0057]    Thereafter, the gap-forming member  18  is pressably put on the upper portion of the slide bearing  11  assembled into the stator member  16 . The lubricating oil is injected into the inside defined by the stator member  16  and the gap-forming member  18 . Incidentally, the lubricating oil may be injected before the shaft is inserted after the slide bearing  11  has been assembled into stator portion  16 . 
         [0058]    Unit molding may be conceivable in which the slide bearing  11 , the shaft  14  and the oil thrower ring  15  are assembled along with molding of the stator member  16  in addition to the manufacturing method described above.  FIGS. 7A and 7B  are schematic cross-sectional views for assistance in explaining the unit molding method. Referring to  FIG. 7A , the slide bearing  11  is first inserted into a lower support member  18   a  made of metal and the shaft  14  provided with the oil thrower ring  15  is inserted into the central hole of the slide bearing  11 . The gap-forming member  18  made of the same metal as the lower support member  18   a  is joined to the lower support member  18   a  by welding or the like to constitute an inner structure. 
         [0059]    Then, the inner structure configured as described above is disposed in a cavity  101  of left and right molds  100  and gripped by the molds  100 . Specifically, the gap-forming member  18  and the lower support member  18   a  are disposed in the cavity  101  of the molds  100  while the shaft  14  extending from the gap-forming member  18  is gripped and held by the molds  100 . In this state, melting resin is poured into the cavity  101  of the molds  100  and cured. Then, the left and right molds  100  are opened and the bearing unit  10  is taken out therefrom. In this way, the bearing unit  10  in which the internal structure is assembled into the stator member  16  can be unit-molded as shown in  FIG. 7B . 
         [0060]    Incidentally, while the bearing units  10  according to the embodiments are each applied to the fan motor as described above, the present invention is not limited to this. The present invention can be applied to motor equipment (e.g., various types of memory media drives) other than the fan motor. 
         [0061]    It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.