Patent Publication Number: US-8542459-B2

Title: Spindle motor and storage disk drive

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a spindle motor and more specifically to a spindle motor for use in a storage disk drive. 
     2. Description of the Related Art 
     Motors including a bearing mechanism using fluid dynamic pressure have often been used in storage disk drives. A spindle motor disclosed in JP-A 2009-136143 includes a fixed shaft, an annular bearing component, a rotor component, and an annular cover. The bearing component is arranged on an upper end portion of the fixed shaft. The bearing component is integrally provided with the fixed shaft. The rotor component is arranged radially outward of the fixed shaft. The annular cover is arranged above the bearing component. A radially outer end portion of the annular cover is adhered to an upper end portion of the rotor component. An outer circumferential surface of the bearing component is arranged opposite an inner circumferential surface of the upper end portion of the rotor component. A seal gap is defined between the outer circumferential surface of the bearing component and the inner circumferential surface of the upper end portion of the rotor component. The seal gap is covered by the annular cover. Paragraph [0043] of JP-A 2009-136143 states: “The annular cover  330  defines a labyrinth seal  348  arranged to additionally seal the seal gap  332  together with an upper end surface of the bearing component  318 .” 
     Another conventional dynamic pressure fluid bearing apparatus included in a spindle motor is disclosed in JP-A 2007-162759. This conventional dynamic pressure fluid bearing apparatus includes a shaft body and a tubular sleeve body inside which the shaft body is inserted. The shaft body is fixed to a base plate of the motor. The sleeve body is fixed to a rotor of the motor. The shaft body is provided with a first thrust flange and a second thrust flange. The first thrust flange and the second thrust flange are both annular and are arranged on an upper side and a lower side of the sleeve body, respectively. In the dynamic pressure fluid bearing apparatus, a radial bearing portion is defined between the shaft body and the sleeve body, and a thrust bearing portion is defined between each of the two thrust flanges and the sleeve body. In addition, the sleeve body includes communicating holes defined therein to provide communication between two thrust gaps. Tapered seal portions are defined in the vicinity of upper and lower end openings of the communicating holes. 
     Another example of a known fluid dynamic bearing motor is disclosed in U.S. Pat. No. 6,991,376. This fluid dynamic bearing motor includes a shaft, a top plate, a bottom plate, and a hub. The top plate is fixed to an upper end of the shaft and the bottom plate is fixed to a lower end of the shaft. The hub is arranged between the top plate and the bottom plate, and is supported so as to be rotatable with respect to the shaft. The hub includes a recirculation channel extending therethrough defined therein. An upper portion of the hub includes a projecting portion arranged radially outward of an outer edge portion of the top plate. A capillary seal is defined between the projecting portion and the outer edge portion of the top plate. A lower portion of the hub includes another projecting portion arranged radially outward of an outer edge portion of the bottom plate. A capillary seal is also defined between the other projecting portion and the outer edge portion of the bottom plate. The influence of a pressure gradient of a lubricating oil in each of the capillary seals is minimized by the recirculation channel being arranged radially inward of the capillary seals. 
     In some motors, a cap member is arranged in a rotating portion to cover a seal gap. The motor described in JP-A 2009-136143 is an example of one of these motors. In such a motor, there is a gap between the cap member and a component of a stationary portion which defines the seal gap, and this gap may permit an evaporated lubricating oil to pass therethrough to an outside of the motor. Moreover, an attempt to ensure sufficient rigidity of the cap member by increasing the thickness of the cap member leads to a failure to reduce the overall thickness of the motor. Moreover, a reduction in the thickness of the cap member may result in a reduction in the precision with which the cap member is shaped, and may lead to a contact of the cap member with the stationary portion during rotation of the motor. 
     In the motor disclosed in JP-A 2007-162759, a difference in pressure between the upper tapered seal portion and the lower tapered seal portion is large because of the large axial distance between a surface of a lubricating oil in the upper tapered seal portion and a surface of the lubricating oil in the lower tapered seal portion. Therefore, when the motor is oriented in a variety of directions, the surface of the lubricating oil in each tapered seal portion will fluctuate greatly. Because of this, it is necessary to provide a complicated design to prevent a leakage of the lubricating oil. 
     Similarly, with respect to the motor disclosed in U.S. Pat. No. 6,991,376, a difference in pressure between the upper capillary seal and the lower capillary seal is large because of the large axial distance between a surface of the lubricating oil in the upper capillary seal and a surface of the lubricating oil in the lower capillary seal. 
     SUMMARY OF THE INVENTION 
     A motor according to a preferred embodiment of the present invention includes a stationary portion and a rotating portion. The stationary portion includes a stator. The rotating portion includes a rotor magnet. The rotating portion is rotatably supported by the stationary portion through a lubricating oil. The stationary portion includes a shaft portion and an upper thrust portion. The shaft portion is centered on a central axis extending in a vertical direction. The upper thrust portion is arranged to extend radially outward from an upper portion of the shaft portion. The rotating portion includes a sleeve portion, a tubular portion, and a seal cap. The sleeve portion is arranged opposite to an outer circumferential surface of the shaft portion and a lower surface of the upper thrust portion. The tubular portion is arranged to extend upward from an outer edge portion of the sleeve portion, and is arranged opposite to an outer circumferential surface of the upper thrust portion. The seal cap is annular and arranged above the tubular portion. The lower surface of the upper thrust portion and an upper surface of the sleeve portion are arranged to together define an upper thrust gap therebetween. The lubricating oil is located in the upper thrust gap. The outer circumferential surface of the upper thrust portion and an inner circumferential surface of the tubular portion are arranged to together define an upper seal portion therebetween. The upper thrust gap is arranged to be in communication with the upper seal portion. The upper seal portion includes a surface of the lubricating oil located therein. The seal cap includes a first seal cap lower surface and a second seal cap lower surface. The first seal cap lower surface is an annular surface facing axially downward. The second seal cap lower surface is an annular surface facing axially downward, and is arranged radially outward of the first seal cap lower surface. The tubular portion includes a first tubular portion upper surface and a second tubular portion upper surface. The first tubular portion upper surface is an annular surface arranged axially opposite to the first seal cap lower surface. The second tubular portion upper surface is an annular surface arranged radially outward of the first tubular portion upper surface, and is arranged to be in contact with the second seal cap lower surface. The first tubular portion upper surface includes an oil-repellent film region covered with an oil-repellent film. The first tubular portion upper surface and the first seal cap lower surface are arranged to together define a substantially annular radially extending gap therebetween. According to various preferred embodiments of the present invention, prevention of leakage of the lubricating oil out of the motor is achieved. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a storage disk drive according to a first preferred embodiment of the present invention. 
         FIG. 2  is a cross-sectional view of a motor according to the first preferred embodiment. 
         FIG. 3  is a cross-sectional view of a bearing mechanism according to the first preferred embodiment. 
         FIG. 4  is a cross-sectional view of the bearing mechanism according to the first preferred embodiment. 
         FIG. 5  is a cross-sectional view of a sleeve portion according to the first preferred embodiment. 
         FIG. 6  is a bottom view of a shaft portion and an upper thrust portion according to the first preferred embodiment. 
         FIG. 7  is a plan view of a lower thrust portion according to the first preferred embodiment. 
         FIG. 8  is a cross-sectional view of the bearing mechanism according to the first preferred embodiment. 
         FIG. 9  is a bottom view of an inner tubular portion of a bearing mechanism according to another preferred embodiment of the present invention. 
         FIG. 10  is a cross-sectional view of a bearing mechanism in a motor according to a second preferred embodiment of the present invention. 
         FIG. 11  is a cross-sectional view of a motor according to a third preferred embodiment of the present invention. 
         FIG. 12  is a cross-sectional view of a bearing mechanism according to the third preferred embodiment. 
         FIG. 13  is a cross-sectional view of a seal cap according to the third preferred embodiment. 
         FIG. 14  is a bottom view of the seal cap according to the third preferred embodiment. 
         FIG. 15  is a diagram illustrating a seal cap according to another preferred embodiment of the present invention. 
         FIG. 16  is a diagram illustrating an upper hub tubular portion according to another preferred embodiment of the present invention. 
         FIG. 17  is a diagram illustrating an upper hub tubular portion according to yet another preferred embodiment of the present invention. 
         FIG. 18  is a cross-sectional view of a storage disk drive according to a fourth preferred embodiment of the present invention. 
         FIG. 19  is a diagram illustrating a seal cap according to yet another preferred embodiment of the present invention. 
         FIG. 20  is a diagram illustrating a seal cap according to yet another preferred embodiment of the present invention. 
         FIG. 21  is a diagram illustrating a seal cap according to yet another preferred embodiment of the present invention. 
         FIG. 22  is a diagram illustrating a seal cap according to yet another preferred embodiment of the present invention. 
         FIG. 23  is a diagram illustrating a shaft portion and an upper thrust portion according to another preferred embodiment of the present invention. 
         FIG. 24  is a diagram illustrating a shaft portion and an upper thrust portion according to yet another preferred embodiment of the present invention. 
         FIG. 25  is a bottom view of a shaft portion and an upper thrust portion according to yet another preferred embodiment of the present invention. 
         FIG. 26  is a plan view of a lower thrust portion according to another preferred embodiment of the present invention. 
         FIG. 27  is a cross-sectional view of a motor according to another preferred embodiment of the present invention. 
         FIG. 28  is a cross-sectional view illustrating a seal cap, a tubular portion, and their vicinities according to a preferred embodiment of the present invention. 
         FIG. 29  is a cross-sectional view illustrating a seal cap and a tubular portion according to a preferred embodiment of the present invention. 
         FIG. 30  is a cross-sectional view illustrating a seal cap and a tubular portion according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     It is assumed herein that an upper side and a lower side in a direction parallel or substantially parallel to a central axis of a motor are referred to as an “upper side” and a “lower side”, respectively. Note that the terms “vertical direction”, “upper side”, “lower side”, and the like as used herein are not meant to indicate relative positions or directions of different members or portions when actually installed in a device. Also note that directions parallel to or substantially parallel to the central axis are referred to by the term “axial direction”, “axial”, or “axially”, that directions radiating from the central axis are simply referred to by the term “radial direction”, “radial”, or “radially”, and that a circumferential direction about the central axis is simply referred to by the term “circumferential direction”, “circumferential”, or “circumferentially”. 
     First Preferred Embodiment 
       FIG. 1  is a cross-sectional view of a storage disk drive  1  including a spindle motor (hereinafter referred to simply as a “motor”)  12  according to a first preferred embodiment of the present invention. The storage disk drive  1  is preferably a so-called hard disk drive. The storage disk drive  1  preferably includes three disks  11 , the motor  12 , an access portion  13 , and a housing  14 , for example. The motor  12  is arranged to rotate the disks  11 , on which information is stored. The access portion  13  is arranged to read and/or write information from or to the disks  11 . In other words, the access portion  13  may be arranged to perform at least one of reading and writing of information from or to the disks  11 . 
     The housing  14  preferably includes a lower housing member  141  and an upper plate member  142 . The lower housing member  141  is in the shape of a box without a lid. The upper plate member  142  preferably has a flat shape, such as that of a plate. The disks  11 , the motor  12 , and the access portion  13  are arranged inside the lower housing member  141 . The upper plate member  142  is fitted to the lower housing member  141  to define the housing  14 . An interior space of the storage disk drive  1  is preferably a clean space with no dirt or dust, or only an extremely small amount of dirt or dust. In the present preferred embodiment, the interior space of the storage disk drive  1  is filled with air. Note that the interior space of the storage disk drive  1  may alternatively be filled with helium gas, hydrogen gas, a mixture of either or both of these gases and air, or any other desirable gas. 
     The three disks  11  are fixed to a rotor hub of the motor  12  through a clamper  151  and spacers  152  such that the disks  11  are arranged at regular intervals in a direction parallel or substantially parallel to a central axis J 1  of the motor  12 . The access portion  13  includes six heads  131 , six arms  132 , and a head actuator mechanism  133 . Each of the heads  131  is arranged in close proximity to one of the disks  11  to read and write information from or to the disk  11 . Note that the head  131  may be arranged to perform at least one of the reading and writing of information from or to the disk  11 . Each of the arms  132  is arranged to support an associated one of the heads  131 . The head actuator mechanism  133  is arranged to move each of the arms  132  to move an associated one of the heads  131  relative to an associated one of the disks  11 . The above mechanism enables the head  131  to make access to a desired location on the disk  11  with the head  131  being arranged in close proximity to the rotating disk  11 . Note that the number of disks  11  is not limited to three, but may instead be one, two, or any other desirable number greater than three. 
       FIG. 2  is a cross-sectional view of the motor  12 . The motor  12  is an outer-rotor motor. The motor  12  includes a stationary portion  2 , which is a stationary assembly, and a rotating portion  3 , which is a rotating assembly. In  FIG. 2 , a fluid dynamic bearing mechanism (hereinafter referred to as a “bearing mechanism”) defined by a portion of the stationary portion  2  and a portion of the rotating portion  3  is indicated by reference numeral “ 4 ”. The rotating portion  3  is supported through a lubricating oil  45  such that the rotating portion  3  is rotatable about the central axis J 1  of the motor  12  with respect to the stationary portion  2 . 
     The stationary portion  2  preferably includes a base plate  21 , i.e., a base portion, a stator  22 , a shaft portion  41 , an upper thrust portion  42 , and a lower thrust portion  43 . The base plate  21  and the lower housing member  141  illustrated in  FIG. 1  are preferably integrally defined by a single monolithic member and define a portion of the housing  14 . The stator  22  is fixed to a circumference of a cylindrical holder  211  defined in the base plate  21 . A hole portion is defined inside the holder  211 . Note that the base plate  21  and the lower housing member  141  may be defined by separate members. The shaft portion  41  and the upper thrust portion  42  are defined by a single monolithic member. The shaft portion  41  includes a screw hole defined in an upper portion thereof. Referring to  FIG. 1 , a central portion  143  of the upper plate member  142  is recessed axially downward. Hereinafter, the central portion  143  will be referred to as a “plate central portion  143 ”. A screw  161 , for example, is preferably inserted into a through hole defined in the plate central portion  143  and the screw hole of the shaft portion  41 , so that the plate central portion  143  and the shaft portion  41  are fixed to each other. A lower surface of the plate central portion  143  is arranged in direct contact with an upper surface of the upper thrust portion  42 , whereby the upper plate member  142  is securely fixed to the motor  12 . Moreover, because the shaft portion  41  and the upper thrust portion  42  are defined by a single monolithic member, an improvement in strength is achieved with which the upper plate member  142  is joined to the motor  12 . 
     Referring to  FIG. 2 , the rotating portion  3  includes a rotor hub  31  and a rotor magnet  32 . The rotor hub  31  preferably includes a substantially cylindrical sleeve portion  5 , a cover portion  311 , and a cylindrical portion  312 . The cover portion  311  is arranged to extend radially outward from an upper portion of the sleeve portion  5 . The cylindrical portion  312  is arranged to extend axially downward from an outer edge portion of the cover portion  311 . The rotor magnet  32  is fixed to an inside of the cylindrical portion  312 . The rotor magnet  32  is arranged radially opposite the stator  22 . The rotating portion  3  is arranged to be rotated in response to a torque that is generated between the stator  22  and the rotor magnet  32 . Note that, if so desired, the sleeve portion  5  may be defined by a member separate from the cover portion  311  and the cylindrical portion  312 . In this case, the sleeve portion  5  is fixed to the cover portion  311 . 
       FIG. 3  is an enlarged view of the bearing mechanism  4 . The bearing mechanism  4  preferably includes the shaft portion  41 , the upper thrust portion  42 , the lower thrust portion  43 , the sleeve portion  5 , an annular seal cap  44 , i.e., a cap member, and the lubricating oil  45 . As mentioned above, each of the shaft portion  41 , the upper thrust portion  42 , and the lower thrust portion  43  preferably defines a portion of the stationary portion  2 , while each of the sleeve portion  5  and the seal cap defines a portion of the rotating portion  3 . The shaft portion  41  is, for example, press fitted so as to be fixed to a hole portion defined inside the lower thrust portion  43 . The shaft portion  41  is arranged to orient in the vertical direction along the central axis J 1 . The upper thrust portion  42  includes an upper plate portion which is preferably flat, such that it possesses the shape of a plate, and arranged to extend radially outward from the upper portion of the shaft portion  41 . The shaft portion  41  and the upper thrust portion  42  are preferably made of stainless steel or the like, for example. An outer circumferential surface  422  of the upper thrust portion  42  includes an inclined surface that is angled in a radially inward direction with increasing height. The upper thrust portion  42  preferably includes a downward recessed shoulder portion  423  defined in an outer edge portion of the upper surface thereof. 
     The lower thrust portion  43  preferably includes a lower plate portion  431  and an outer tubular portion  432 . The lower thrust portion  43  preferably is made of copper, high-strength brass, or the like, for example. The lower plate portion  431  is arranged to extend radially outward from a lower portion of the shaft portion  41 . The outer tubular portion  432  is arranged to extend upward from an outer edge portion of the lower plate portion  431 . An upper portion of an outer circumferential surface of the outer tubular portion  432  includes an inclined surface  433  that is angled in the radially inward direction with decreasing height. 
     In assembling the motor  12 , a lower portion of the outer circumferential surface of the outer tubular portion  432  is fixed to an inner circumferential surface of the holder  211  of the base plate  21  through, for example, an adhesive. In comparison to press fitting, the above method enables the vertical positioning of the outer tubular portion  432  relative to the base plate  21  to be achieved with greater precision, whereby improved precision in the height of the motor  12  is achieved. 
     The sleeve portion  5  includes an inner tubular portion  51  and a flange portion  52 . The sleeve portion  5  is preferably made of stainless steel, aluminum, copper, or the like, for example. The inner tubular portion  51  is arranged in a substantially cylindrical space defined between the outer tubular portion  432  and the shaft portion  41 . The flange portion  52  is arranged to project radially outward from an upper portion of the inner tubular portion  51 . The axial thickness of the flange portion  52  is preferably a half or less than a half of the axial dimension of an inner circumferential surface  511  of the inner tubular portion  51 , for example. Both an upper surface  521  and a lower surface  522  of the flange portion  52  are preferably arranged to be substantially perpendicular to the central axis J 1 . The flange portion  52  includes a communicating hole  61  arranged to extend through the flange portion  52  in the vertical direction. The number of communicating holes  61  preferably is one, for example, in the present preferred embodiment. However, if so desired, two or more communicating holes  61  could also be defined in the flange portion. 
     The cover portion  311  of the rotor hub  31  includes an upper hub tubular portion  53  and a lower hub tubular portion  54 . The upper hub tubular portion  53  is arranged substantially in the shape of a cylinder, and is arranged to extend axially upward from an outer edge portion of the sleeve portion  5 , i.e., an outer edge portion of the flange portion  52 . The upper hub tubular portion  53  is arranged radially outward of the upper thrust portion  42 . An inner circumferential surface  531  of the upper hub tubular portion  53  includes a portion that is angled in the radially inward direction with increasing height. Hereinafter, the upper hub tubular portion  53  and the seal cap  44 , which are arranged above the outer edge portion of the flange portion  52  and each of which defines a portion of the rotating portion  3 , will be collectively referred to as an “upper hub annular portion  591 ”. 
     The lower hub tubular portion  54  is arranged substantially in the shape of a cylinder, and is arranged to extend downward from the outer edge portion of the flange portion  52 . The lower hub tubular portion  54  is arranged radially outward of the outer tubular portion  432  of the lower thrust portion  43 . An inner circumferential surface  541  of the lower hub tubular portion  54  includes a portion that is angled in the radially inward direction with decreasing height. Note that the upper and lower hub tubular portions  53  and  54  may be defined by members separate from the flange portion  52  or the cover portion  311 . 
     The seal cap  44  preferably includes a cap cylindrical portion  441  and a cap cover portion  442 . The cap cylindrical portion  441  is centered on the central axis J 1 . The cap cover portion  442  is substantially annular, and is arranged to extend radially inward from the cap cylindrical portion  441 . The cap cylindrical portion  441 , which is an outer edge portion of the seal cap  44 , is fitted to the upper hub tubular portion  53 , whereby the seal cap  44  is attached to the sleeve portion  5 . When the seal cap  44  is attached to the upper hub tubular portion  53 , the cap cylindrical portion  441  is arranged in direct radial contact with an outer circumferential surface of the upper hub tubular portion  53 , and the cap cover portion  442  is arranged in axial contact with an upper surface of the upper hub tubular portion  53 . The cap cylindrical portion  441  and the upper hub tubular portion  53  together define a tubular portion of the upper hub annular portion  591  which is arranged to extend upward from the outer edge portion of the flange portion  52 . In addition, the cap cover portion  442  defines an annular cover portion of the upper hub annular portion  591  which is arranged to extend radially inward from the tubular portion. A radially inner portion of the cap cover portion  442  is arranged above a bottom portion of the shoulder portion  423 . 
     Referring to  FIG. 2 , the rotating portion  3 , which includes the sleeve portion  5 , is arranged to rotate through the lubricating oil  45  with respect to the shaft portion  41 , the upper thrust portion  42 , and the lower thrust portion  43  while the motor  12  is driven. 
       FIG. 4  is an enlarged view of an upper portion of the bearing mechanism  4 . An outer circumferential surface  411  of the shaft portion  41  is arranged radially opposite the inner circumferential surface  511  of the inner tubular portion  51  of the sleeve portion  5 . A radial gap  62  is defined between the shaft portion  41  and the inner tubular portion  51 . The radial width of the radial gap  62  is preferably in the range of about 2 μm to about 4 μm, for example. Referring to  FIG. 3 , an axial gap  63  is defined between a lower end of the inner tubular portion  51  and the lower plate portion  431 . Hereinafter, the gap  63  will be referred to as a “lower end gap  63 ”. Note that, in the present preferred embodiment, the radial gap  62  corresponds to a first gap. 
     Referring to  FIG. 4 , a gap  64  in the shape of a cylinder is defined between an outer circumferential surface  512  of the inner tubular portion  51  and an inner circumferential surface  434  of the outer tubular portion  432 . Hereinafter, the gap  64  will be referred to as a “cylindrical gap  64 ”. Referring to  FIG. 3 , the cylindrical gap  64  is arranged in communication with the radial gap  62  through the lower end gap  63 . The radial width of the cylindrical gap  64  is preferably greater than the radial width of the radial gap  62  and smaller than the diameter of the communicating hole  61 . Note that, in the present preferred embodiment, the cylindrical gap  64  corresponds to a second gap. 
     Referring to  FIG. 4 , a gap  651  is defined between a region of the upper surface  521  of the flange portion  52  which is radially inward of the communicating hole  61  and a lower surface  421  of the upper thrust portion  42 , which is arranged axially opposite the upper surface  521 . Hereinafter the gap  651  will be referred to as an “upper thrust gap  651 ”. In addition, a gap  652  is defined between a region of the lower surface  522  of the flange portion  52  which is radially inward of the communicating hole  61  and an upper surface  435  of the outer tubular portion  432 . Hereinafter, the gap  652  will be referred to as a “lower thrust gap  652 ”. The upper and lower thrust gaps  651  and  652  are arranged in communication with each other through the communicating hole  61 . In the bearing mechanism  4 , the radial gap  62 , the lower end gap  63 , the cylindrical gap  64 , the upper and lower thrust gaps  651  and  652 , and the communicating hole  61  are arranged from a radial inside to a radial outside in this order. Note that, in the present preferred embodiment, the lower thrust gap  652  corresponds to a third gap. 
     The inner circumferential surface  531  of the upper hub tubular portion  53  is arranged radially opposite the outer circumferential surface  422  of the upper thrust portion  42 . A gap  661  is defined between the upper hub tubular portion  53  and the upper thrust portion  42 . The upper thrust gap  651  is arranged in communication with the gap  661 . The gap  661  is preferably arranged radially outward of the radial gap  62 , the upper thrust gap  651 , and the communicating hole  61 . The gap  661  is arranged to gradually increase in width with increasing height, that is, with decreasing distance from an upper end opening of the gap  661 . Hereinafter, the gap  661  will be referred to as an “upper seal gap  661 ”. In addition, the upper seal gap  661  is arranged to be angled toward the central axis J 1  with increasing height. In other words, the upper seal gap  661  is arranged to be angled to the left in  FIG. 4  with increasing height. A surface of the lubricating oil  45  is located in the upper seal gap  661 . The lubricating oil  45  is retained in the upper seal gap  661  through capillary action. An upper seal portion  661   a  arranged to retain the lubricating oil  45  is thus defined in the upper seal gap  661 . The inner circumferential surface  531  and the outer circumferential surface  422  are preferably coated with oil-repellent films  86  above the surface of the lubricating oil  45  in the upper seal gap  661 . The upper end opening of the upper seal gap  661  is covered with the cap cover portion  442  of the seal cap  44 . 
     The inner circumferential surface  541  of the lower hub tubular portion  54  is arranged radially opposite the inclined surface  433  of the outer tubular portion  432 . A gap  662  extending downward is defined between the lower hub tubular portion  54  and the outer tubular portion  432 . The gap  662  is arranged radially outward of the radial gap  62 , the lower end gap  63 , the cylindrical gap  64 , the lower thrust gap  652 , and the communicating hole  61 . The gap  662  is arranged to gradually increase in width with decreasing height, that is, with decreasing distance from a lower end opening of the gap  662 . Hereinafter, the gap  662  will be referred to as a “lower seal gap  662 ”. In addition, the lower seal gap  662  is arranged to be angled toward the central axis J 1  with decreasing height. That is, the lower seal gap  662  is arranged to be inclined to the left in  FIG. 4  with decreasing height. A surface of the lubricating oil  45  is located in the lower seal gap  662 . The lubricating oil  45  is retained in the lower seal gap  662  through capillary action. A lower seal portion  662   a  arranged to retain the lubricating oil  45  is defined in the lower seal gap  662 . The inner circumferential surface  541  and the inclined surface  433  are coated with oil-repellent films  86  below the surface of the lubricating oil  45  in the lower seal gap  662 . The same holds true for other preferred embodiments described below. In the bearing mechanism  4 , the upper and lower seal gaps  661  and  662  are arranged in communication with each other through the communicating hole  61 . 
     The axial distance between the surface of the lubricating oil  45  in the upper seal portion  661   a  and the surface of the lubricating oil  45  in the lower seal portion  662   a  is shorter than the axial length of the radial gap  62 . Moreover, the length of the communicating hole  61  is shorter than the axial distance between the surface of the lubricating oil  45  in the upper seal portion  661   a  and the surface of the lubricating oil  45  in the lower seal portion  662   a . It is assumed here that the distance between the surface of the lubricating oil  45  in the upper seal portion  661   a  and the surface of the lubricating oil  45  in the lower seal portion  662   a  refers to the distance between an upper end of the surface of the lubricating oil  45  in the upper seal portion  661   a  and a lower end of the surface of the lubricating oil  45  in the lower seal portion  662   a.    
     Referring to  FIG. 3 , the radially outside diameter of the upper seal gap  661  is preferably substantially equal to the radially outside diameter of the lower seal gap  662 . This makes it possible to arrange the communicating hole  61  to extend in parallel or substantially in parallel with the central axis J 1 . It is assumed here that the outside diameter of the upper seal gap  661  refers to the outside diameter of an innermost portion of the upper seal gap  661 , and that the outside diameter of the lower seal gap  662  refers to the outside diameter of an innermost portion of the lower seal gap  662 . 
     In the bearing mechanism  4 , the communicating hole  61  and a space  6  extending from the upper seal gap  661  to the lower seal gap  662  through the upper thrust gap  651 , the radial gap  62 , the lower end gap  63 , the cylindrical gap  64 , and the lower thrust gap  652  are continuously filled with the lubricating oil  45 . When the bearing mechanism  4  is constructed, the lubricating oil  45  is fed into the bearing mechanism  4  through the lower seal gap  662  with the lower seal gap  662  arranged to face axially upward in the direction of gravity. It is possible to control the amount of the lubricating oil  45  by visually identifying the height of the surface of the lubricating oil  45  in the lower seal gap  662 . 
     Note that the visual identification may be conducted either with eyes alone or with a magnified view of the lower seal gap  662  with the aid of a device such as, for example, a microscope. Also note that the visual identification may be conducted with a magnified image of the lower seal gap  662  shown on a screen with the aid of a device. 
       FIG. 5  is a cross-sectional view of the sleeve portion  5 . In  FIG. 5 , the shape of the sleeve portion  5  beyond a cross section thereof is also depicted. The inner tubular portion  51  includes an upper radial dynamic pressure groove array  711  and a lower radial dynamic pressure groove array  712 . The upper radial dynamic pressure groove array  711  is defined in a portion of the inner circumferential surface  511  which is on an upper side of a substantial axial middle thereof. The lower radial dynamic pressure groove array  712  is defined in a portion of the inner circumferential surface  511  which is on a lower side of the substantial axial middle thereof. In  FIG. 5 , dynamic pressure grooves are indicated by cross-hatching. Also in other figures referenced below, dynamic pressure grooves are indicated by cross-hatching. The upper radial dynamic pressure groove array  711  is includes a collection of grooves arranged in, for example, a herringbone pattern, that is, a collection of a plurality of grooves each of which is arranged substantially in the shape of the letter “V” in horizontal orientation along a circumferential direction of the inner circumferential surface  511 . The axial dimension of an upper portion of the upper radial dynamic pressure groove array  711  is preferably arranged to be greater than that of a lower portion of the upper radial dynamic pressure groove array  711 . Hereinafter, the upper portion and the lower portion of the upper radial dynamic pressure groove array  711  will be referred to as a “groove upper portion  711   a ” and a “groove lower portion  711   b ”, respectively. The lower radial dynamic pressure groove array  712  is also defined by grooves arranged in the herringbone pattern. The axial dimension of a groove upper portion  712   a  of the lower radial dynamic pressure groove array  712  is arranged to be smaller than that of a groove lower portion  712   b  of the lower radial dynamic pressure groove array  712 . 
     The lower thrust gap  652  illustrated in  FIG. 4  is arranged at a level higher than that of an upper end of the groove upper portion  712   a  of the lower radial dynamic pressure groove array  712 . In the radial gap  62 , a radial dynamic pressure bearing  81  arranged to generate a radial fluid dynamic pressure acting on the lubricating oil  45  is defined through the upper and lower radial dynamic pressure groove arrays  711  and  712 . Hereinafter, an upper dynamic pressure bearing portion corresponding to the upper radial dynamic pressure groove array  711  will be referred to as an “upper radial dynamic pressure bearing portion  811 ”, while a lower dynamic pressure bearing portion corresponding to the lower radial dynamic pressure groove array  712  will be referred to as a “lower radial dynamic pressure bearing portion  812 ”. The lower radial dynamic pressure bearing portion  812  is arranged to overlap in a radial direction with a fixing region  436  where the lower portion of the outer circumferential surface of the outer tubular portion  432  and the holder  211  of the base plate  21  illustrated in  FIG. 3  are fixed to each other. 
     Note that it is enough that the level of the lower thrust gap  652  should be arranged to be higher than that of the upper end of at least one of the dynamic pressure grooves constituting the lower radial dynamic pressure groove array  712 . Also note that the level of the lower thrust gap  652  may be arranged to be higher than that of the upper end of each of all the dynamic pressure grooves constituting the lower radial dynamic pressure groove array  712 . These arrangements fall within the scope of preferred embodiments of the present invention. 
       FIG. 6  is a bottom view of the shaft portion  41  and the upper thrust portion  42 . In  FIG. 6 , a position corresponding to the communicating hole  61  is indicated by a chain double-dashed line. The same holds true for  FIG. 7 . The lower surface  421  of the upper thrust portion  42  includes an upper thrust dynamic pressure groove array  721  arranged in a spiral pattern defined therein. The upper thrust dynamic pressure groove array  721  is arranged radially inward of a circle  731  which is centered on the central axis J 1  and which touches an upper end opening of the communicating hole  61  at a radially outer point. Note that, in the case where the upper end opening is provided with a chamfer, the upper thrust dynamic pressure groove array  721  is arranged radially inward of a circle which is centered on the central axis J 1  and which touches the chamfer at a radially outer point. In addition, an outer circumferential portion of the upper thrust dynamic pressure groove array  721  is arranged to overlap with the upper end opening of the communicating hole  61 . In the upper thrust gap  651  illustrated in  FIG. 4 , a dynamic pressure bearing portion  821 , which is a dynamic pressure generation portion arranged to generate a fluid dynamic pressure acting on the lubricating oil  45  in a thrust direction, is defined through the upper thrust dynamic pressure groove array  721 . Hereinafter, the dynamic pressure bearing portion  821  will be referred to as an “upper thrust dynamic pressure bearing portion  821 ”. 
     Note that it is enough that at least one of the dynamic pressure grooves defining the upper thrust dynamic pressure groove array  721  should be arranged radially inward of the circle  731 . Also note that all of the dynamic pressure grooves defining the upper thrust dynamic pressure groove array  721  may be arranged radially inward of the circle  731 . These arrangements fall within the scope of preferred embodiments of the present invention. 
       FIG. 7  is a plan view of the lower thrust portion  43 . The upper surface  435  of the outer tubular portion  432  includes a lower thrust dynamic pressure groove array  722  arranged in the spiral pattern defined therein. The lower thrust dynamic pressure groove array  722  is arranged radially inward of a circle  732  which is centered on the central axis J 1  and which touches a lower end opening of the communicating hole  61  at a radially outer point. Note that, in the case where the lower end opening is provided with a chamfer, the lower thrust dynamic pressure groove array  722  is arranged radially inward of a circle which is centered on the central axis J 1  and which touches the chamfer at a radially outer point. In addition, an outer circumferential portion of the lower thrust dynamic pressure groove array  722  is arranged to overlap with the lower end opening of the communicating hole  61 . In the lower thrust gap  652  illustrated in  FIG. 4 , a dynamic pressure bearing portion  822 , which is a dynamic pressure generation portion arranged to generate a fluid dynamic pressure acting on the lubricating oil  45  in the thrust direction, is defined through the lower thrust dynamic pressure groove array  722 . Hereinafter, the dynamic pressure bearing portion  822  will be referred to as a “lower thrust dynamic pressure bearing portion  822 ”. 
     Note that it is enough that at least one of the dynamic pressure grooves defining the lower thrust dynamic pressure groove array  722  should be arranged radially inward of the circle  732 . Also note that all of the dynamic pressure grooves defining the lower thrust dynamic pressure groove array  722  may be arranged radially inward of the circle  732 . These arrangements fall within the scope of preferred embodiments of the present invention. 
     Even when the upper thrust dynamic pressure groove array  721  is arranged to overlap with the upper end opening of the communicating hole  61 , and the lower thrust dynamic pressure groove array  722  is arranged to overlap with the lower end opening of the communicating hole  61 , a difference in pressure between an interior and an exterior of the communicating hole  61  is eliminated through the inclusion of a region where neither the upper thrust dynamic pressure groove array  721  nor the lower thrust dynamic pressure groove array  722  is provided. As a result, a reduction in the difference in pressure between the upper and lower seal portions  661   a  and  662   a  is achieved. 
     While the motor  12  is driven, the inner tubular portion  51  of the sleeve portion  5  is supported by the radial dynamic pressure bearing  81  in the radial direction with respect to the shaft portion  41 , while the flange portion  52  is supported by a thrust dynamic pressure bearing defined by the upper and lower thrust dynamic pressure bearing portions  821  and  822  in the thrust direction with respect to the upper thrust portion  42  and the outer tubular portion  432 . 
     At this time, each of the upper and lower radial dynamic pressure groove arrays  711  and  712  illustrated in  FIG. 5  generates a dynamic pressure by pumping the lubricating oil  45  to a middle portion thereof. As described above, the groove lower portion  711   b  of the upper radial dynamic pressure groove array  711  is arranged to be shorter than the groove upper portion  711   a  thereof, while the groove upper portion  712   a  of the lower radial dynamic pressure groove array  712  is arranged to be shorter than the groove lower portion  712   b  thereof. The radial dynamic pressure bearing  81  as a whole is arranged to generate little pressure acting on the lubricating oil  45  in the vertical direction. 
     Meanwhile, in the upper thrust gap  651  illustrated in  FIG. 4 , a pressure acting on the lubricating oil  45  in the direction of the shaft portion  41  is generated by the upper thrust dynamic pressure bearing portion  821 . The pressure on the lubricating oil  45  is thereby increased in an axially upper portion of the radial gap  62  and a radially inner portion of the upper thrust gap  651 , whereby generation of an air bubble is prevented therein. 
     In the lower thrust dynamic pressure bearing portion  822 , a pressure acting on the lubricating oil  45  in the direction of the cylindrical gap  64  is generated. The pressure on the lubricating oil  45  is increased in an axially lower portion of the radial gap  62 , the lower end gap  63 , the cylindrical gap  64 , and a radially inner portion of the lower thrust gap  652 , whereby generation of an air bubble is prevented in the cylindrical gap  64  and the lower end gap  63 . As described above, in the motor  12 , a pressure is applied to the lubricating oil  45  throughout an entire circulation channel of the lubricating oil  45  except for the communicating hole  61 , so that a sufficient bearing performance of the bearing mechanism  4  is ensured. 
     Next, the structure of the upper seal gap  661  and its vicinity within the motor  12  will now be described below. Referring to  FIG. 8 , the shoulder portion  423  of the upper thrust portion  42  preferably includes an inner cylindrical surface  741 , an outer annular surface  742 , and an annular groove portion  743 . The inner cylindrical surface  741  is substantially cylindrical, and is arranged radially inward of the outer circumferential surface  422  to extend in the axial direction. The inner cylindrical surface  741  is arranged radially outward of the radial dynamic pressure bearing  81  illustrated in  FIG. 4 . An upper end of the inner cylindrical surface  741  is arranged at a level higher than that of an upper end of the outer circumferential surface  422 . The outer annular surface  742  is arranged radially outward of the inner cylindrical surface  741 , and radially inward of the outer circumferential surface  422 . The outer annular surface  742  is an annular surface perpendicular or substantially perpendicular to the central axis J 1 . The outer annular surface  742  is arranged at an axial level lower than that of the upper end of the inner cylindrical surface  741 . The groove portion  743  is arranged between the inner cylindrical surface  741  and the outer annular surface  742 . The groove portion  743  is recessed axially downward relative to the outer annular surface  742 . Note that the shoulder portion  423  does not cause a significant decrease in rigidity of the upper thrust portion  42  because the upper thrust portion  42  is arranged to have a sufficient thickness between the lower surface  421  and a combination of the outer annular surface  742  and a bottom surface of the groove portion  743 . 
     A radially extending gap  663   a , which is annular and arranged to extend radially, is defined between a lower surface of the cap cover portion  442  of the seal cap  44  and the outer annular surface  742 . An axially extending gap  663   b , which is annular, is defined between a radially inner edge  443  of the cap cover portion  442  and the inner cylindrical surface  741 . An upper portion of the upper seal gap  661  is continuous with the radially extending gap  663   a . The radially extending gap  663   a  is continuous with the axially extending gap  663   b  through a gap  663   c  defined between the cap cover portion  442  and the groove portion  743 . Hereinafter, the gap  663   c  will be referred to as a “groove portion gap  663   c ”. The axially extending gap  663   b  is arranged to open into a space above the upper thrust portion  42 . The upper seal gap  661  is thus arranged in communication with the space above the upper thrust portion  42  through the radially extending gap  663   a , the groove portion gap  663   c , and the axially extending gap  663   b . Hereinafter, the radially extending gap  663   a , the groove portion gap  663   c , and the axially extending gap  663   b  will be collectively referred to as a “communicating gap  663 ”. The radially extending gap  663   a  is a region where the communicating gap  663  has a locally decreased axial width. The axially extending gap  663   b  is a region where the communicating gap  663  has a locally decreased radial width. 
     The axial width of the radially extending gap  663   a  is arranged to be smaller than the maximum radial width of the upper seal gap  661 . In other words, the axial width of the radially extending gap  663   a  is arranged to be smaller than the radial distance between an edge  422   a  where the outer annular surface  742  and the outer circumferential surface  422  meet and an upper edge of a chamfer  531   a  defined in an inner top portion of the upper hub tubular portion  53 . Note that, in the case where a chamfer is defined between the outer annular surface  742  and the outer circumferential surface  422 , the maximum radial width of the upper seal gap  661  refers to the radial distance between an upper edge of this chamfer and the upper edge of the chamfer  531   a  of the upper hub tubular portion  53 . 
     An excessively large axial width of the radially extending gap  663   a  and an excessively large radial width of the axially extending gap  663   b  will lead to a significant reduction in an effect of reducing axial and radial flows of air therein. On the other hand, an excessively small axial width of the radially extending gap  663   a  and an excessively small radial width of the axially extending gap  663   b  will lead to an increased probability of contacting between the seal cap  44  and the upper thrust portion  42 . Therefore, the axial width of the radially extending gap  663   a  is preferably set at an appropriate value to reduce the axial flow of air therein, and the radial width of the axially extending gap  663   b  is preferably set at an appropriate value to reduce the radial flow of air therein, and also to prevent a contact of the seal cap  44  with the upper thrust portion  42 . 
     For example, the axial width of the radially extending gap  663   a  is preferably arranged in the range of about 0.05 mm to about 0.2 mm. Specifically, the axial width of the radially extending gap  663   a  is more preferably arranged in the range of about 0.05 mm to about 0.1 mm, for example. The radial width of the axially extending gap  663   b  is preferably arranged in the range of about 0.05 mm to about 0.2 mm, for example. As with the axial width of the radially extending gap  663   a , the radial width of the axially extending gap  663   b  is arranged to be smaller than the maximum radial width of the upper seal gap  661 . Moreover, the axial width of the radially extending gap  663   a  is preferably arranged to be smaller than the radial width of the axially extending gap  663   b.    
     In the motor  12 , the communicating gap  663  is arranged to have a labyrinth structure, including a radially extending gap and an axially extending gap, and therefore, an air containing an evaporated lubricating oil in the upper seal gap  661  is prevented from traveling to an outside of the motor  12  therethrough. In particular, because the communicating gap  663  is arranged radially inward of the upper seal gap  661 , a centrifugal force acting on an air in the communicating gap  663  in the direction of the upper seal gap  661  is generated while the motor  12  is driven. This contributes to an additional prevention of the travel of the air containing the evaporated lubricating oil to the outside of the motor  12 . Note that the motor  12  has an increased resistance against a flow of air in the communicating gap compared with a motor in which a communicating gap in communication with the outside of the motor is arranged radially outward of the seal gap. Furthermore, a circumferential air current is generated in the axially extending gap  663   b , and this contributes to preventing air from traveling between the space above the upper thrust portion  42  and the groove portion gap  663   c . It is easy to secure a sufficient radial dimension of the radially extending gap  663   a  in the communicating gap  663 . The radially extending gap  663   a  having a small width and a large radial dimension makes it possible to secure a sufficient resistance against the flow of air therein. 
     The motor  12  according to the first preferred embodiment has been described above. The provision of the radially extending gap  663   a  and the axially extending gap  663   b  in the motor  12  contributes to reducing evaporation of the lubricating oil  45 , and achieving an improvement in a life of the motor  12 . Because the upper seal portion  661   a  is arranged in a radially outer portion of the bearing mechanism  4 , it is possible to secure a sufficient space to arrange the communicating gap  663  in a radially inner portion of the bearing mechanism  4 . 
     The provision of the groove portion  743  in the shoulder portion  423  of the upper thrust portion  42  makes it possible to arrange the inner edge  443  of the seal cap  44  in closer proximity to the inner cylindrical surface  741 , and makes it easier to define the axially extending gap  663   b , than in the case where a curved surface smoothly joining the inner cylindrical surface  741  and the outer annular surface  742  to each other is defined instead of the groove portion  743 . 
     In the bearing mechanism  4 , the axial distance between the surface of the lubricating oil  45  in the upper seal portion  661   a  and the surface of the lubricating oil  45  in the lower seal portion  662   a  is shorter than the axial length of the radial dynamic pressure bearing  81 . The axial length of the radial dynamic pressure bearing  81  refers to the distance between an upper end and a lower end of the radial dynamic pressure bearing  81 . More specifically, the axial length of the radial dynamic pressure bearing  81  refers to the distance between an upper end of the groove upper portion  711   a  of the upper radial dynamic pressure groove array  711  and a lower end of the groove lower portion  712   b  of the lower radial dynamic pressure groove array  712 . Note that a portion that does not contribute to the function of the dynamic pressure bearing may exist between the upper and lower ends. The same holds true for other preferred embodiments of the present invention described below. A reduction in a difference in pressure between the upper seal portion  661   a  and the lower seal portion  662   a  is achieved by arranging the upper seal portion  661   a  and the lower seal portion  662   a  to be closer to each other in the axial direction as described above. This prevents a leakage of the lubricating oil  45 . 
     Moreover, the axial length of the communicating hole is shorter than the axial distance between the upper seal portion  661   a  and the lower seal portion  662   a . This contributes to reducing the amount of the lubricating oil  45  arranged in the communicating hole  61 , and at the same time to reducing channel resistance. A reduction in a difference in pressure between the upper and lower seal gaps  661  and  662  owing to influence of channel resistance and gravity acting on the lubricating oil  45  in the communicating hole  61  is achieved. This contributes to reducing movement of the lubricating oil  45  between the upper and lower seal gaps  661  and  662 , and further prevents leakage of the lubricating oil  45 . 
     Furthermore, the cylindrical gap  64 , which corresponds to the second gap, is arranged to be in communication with a lower portion of the radial gap  62 , which corresponds to the first gap, while at the same time the lower thrust gap  652 , which corresponds to the third gap, is arranged axially above the lower radial dynamic pressure bearing portion  812 . This arrangement makes it possible to arrange the lower thrust gap  652  to be closer to the upper thrust gap  651 , making it easier to reduce the length of the communicating hole  61 , which is arranged to make the upper and lower thrust gaps  651  and  652  in communication with each other. As a result, the upper seal portion  661   a  and the lower seal portion  662   a  are arranged to be closer to each other. 
     The communicating hole  61  is arranged to extend in parallel or substantially in parallel with the central axis J 1  to reduce a difference between the distance from the upper end opening of the communicating hole  61  to the upper seal gap  661  and the distance from the lower end opening of the communicating hole  61  to the lower seal gap  662 . This arrangement contributes to further reducing the difference in pressure between the upper and lower seal gaps  661  and  662 . 
     Furthermore, the end opening of each of the upper and lower seal gaps  661  and  662  is arranged to be angled to face the central axis J 1 . Therefore, during rotation of the motor  12 , the lubricating oil  45  is pressed inward in each of the upper and lower seal gaps  661  and  662  through a centrifugal force. This prevents a leakage of the lubricating oil  45 . As a result, designing of the motor  12  is made easier. 
     The upper thrust dynamic pressure groove array  721  is arranged to extend radially outward to such an extent that the outer circumferential portion thereof overlaps with the communicating hole  61  in plan view. As a result, a thrust dynamic pressure is efficiently obtained, and a portion of the flange portion  52  which is close to the outer edge portion thereof is supported by the upper thrust dynamic pressure bearing portion  821 . This contributes to more stable support of the sleeve portion  5 . The same holds true for the lower thrust dynamic pressure groove array  722 . 
     In the motor  12 , the lower thrust gap  652  is arranged in the upper portion of the bearing mechanism  4 . Accordingly, a space is secured below the lower thrust gap  652 , and the fixing region  436  where the outer tubular portion  432  and the base plate  21  are fixed to each other can be arranged in this space. This enables the fixing region  436  to have a sufficient axial dimension. In the motor  12 , a greater axial length of the radial gap  62  is preferred because an increase in the axial length of the radial dynamic pressure bearing  81  can thereby be achieved, and an improvement in rigidity of the bearing mechanism  4  against an external force acting in such a direction as to tilt the rotating portion  3  can also be achieved. The fixing region  436  is arranged to overlap with at least a portion of the lower radial dynamic pressure bearing portion  812  in the radial direction. As a result, both an increase in the axial length of the radial gap  62  and an increase in the axial dimension of the fixing region  436  are achieved. Moreover, an area surrounding a lower portion of the radial dynamic pressure bearing  81  is surrounded by the base plate  21 . This results in increased rigidity of the surroundings of the lower portion of the radial dynamic pressure bearing  81 . Moreover, a reduction in the thickness of the motor  12  as a whole in a direction parallel or substantially parallel to the central axis J 1  is achieved. 
     Because the shaft portion  41  and the upper thrust portion  42  are preferably defined by a single continuous monolithic member, and because the lower plate portion  431  and the outer tubular portion  432  are preferably defined by a single continuous monolithic member, a reduction in the number of components of the motor  12  and a reduction in the number of steps required to assemble the motor  12  are achieved. It is easy to define the communicating hole  61  in the sleeve portion  5  because the communicating hole  61  is arranged to have a small axial length and to extend in parallel or substantially in parallel with the central axis J 1 . A reduction in the total amount of the lubricating oil  45  is also achieved. Note that the diameter of the communicating hole  61  may be reduced to as small as the width of the cylindrical gap  64  to achieve an additional reduction in the amount of the lubricating oil  45 . 
       FIG. 9  is a bottom view of the inner tubular portion  51 . Referring to  FIG. 9 , in the motor  12 , a lower surface of the inner tubular portion  51  may include a thrust dynamic pressure groove array  723  defined therein. A thrust dynamic pressure bearing portion arranged to support the inner tubular portion  51  in the thrust direction is thereby defined in the lower end gap illustrated in  FIG. 3 . In this case, a dynamic pressure generation portion that functions as a thrust dynamic pressure bearing portion may not necessarily be arranged in the lower thrust gap  652 . Note, however, that it is preferable that a dynamic pressure groove array which defines a dynamic pressure generation portion arranged to induce a radially inward pressure acting on the lubricating oil  45  should be arranged in the lower thrust gap. In the case of the structure illustrated in  FIG. 9 , the axial width of the lower thrust gap is preferably arranged to be greater than that of the lower end gap. The same holds true for a second preferred embodiment of the present invention described below. 
     Second Preferred Embodiment 
       FIG. 10  is a diagram illustrating a portion of a bearing mechanism  4   a  in a motor according to the second preferred embodiment of the present invention. A sleeve portion  5   a  of the bearing mechanism  4   a  includes an upper inner tubular portion  55 . The upper inner tubular portion  55  is annular and arranged to extend axially upward from a radially inner portion of the flange portion  52 . Hereinafter, the inner tubular portion  51 , which is arranged below the flange portion  52 , will be referred to as a “lower inner tubular portion  51 ” when the inner tubular portion  51  is distinguished from the upper inner tubular portion  55 . An upper thrust portion  42   a  includes an upper plate portion  424  and an upper outer tubular portion  425 . The upper plate portion  424  is arranged to extend radially outward from the upper portion of the shaft portion  41 . The upper outer tubular portion  425  is arranged to extend downward from an outer edge portion of the upper plate portion  424 . Hereinafter, the plate portion  431  of the lower thrust portion  43  will be referred to as a “lower plate portion  431 ” when the plate portion  431  is distinguished from the upper plate portion  424 . The outer tubular portion  432  will be referred to as a “lower outer tubular portion  432 ” when the outer tubular portion  432  is distinguished from the upper outer tubular portion  425 . The bearing mechanism  4   a  is otherwise similar in structure to the bearing mechanism  4  in the motor  12  according to the first preferred embodiment of the present invention. Note that like members or portions are designated by like reference numerals in the following description. 
     The upper thrust portion  42   a  includes the shoulder portion  423  recessed axially downward and defined between an upper surface of the upper plate portion  424  and an outer circumferential surface  429  of the upper outer tubular portion  425 . While some of the reference symbols shown in  FIG. 8  are omitted in  FIG. 10 , the radially extending gap  663   a  is defined between the outer annular surface  742  of the shoulder portion  423  and the lower surface of the cap cover portion  442  as in  FIG. 8 . In addition, the axially extending gap  663   b  is defined between the inner cylindrical surface  741  and the inner edge  443  of the cap cover portion  442 . Thus, as in the first preferred embodiment, a reduction in the evaporation of the lubricating oil  45  through the upper seal portion  661   a , and an improvement in the life of the motor are achieved. 
     Referring to  FIG. 10 , a gap  671  is defined between an upper surface  551  of the upper inner tubular portion  55  and a lower surface  426  of the upper plate portion  424  in the axial direction, i.e., in the vertical direction in  FIG. 10 . Hereinafter, the gap  671  will be referred to as an “upper end gap  671 ”. In addition, a cylindrical gap  672  is defined between an outer circumferential surface  552  of the upper inner tubular portion  55  and an inner circumferential surface  427  of the upper outer tubular portion  425  in the radial direction. Hereinafter, the gap  672  will be referred to as an “upper cylindrical gap  672 ”. Hereinafter, the cylindrical gap  64 , which is defined between the outer circumferential surface  512  of the lower inner tubular portion  51  and the inner circumferential surface  434  of the lower outer tubular portion  432 , will be referred to as a “lower cylindrical gap  64 ” when the cylindrical gap  64  is distinguished from the upper cylindrical gap  672 . 
     An upper thrust dynamic pressure groove array  721  similar to that illustrated in  FIG. 6  is defined in a lower surface  428  of the upper outer tubular portion  425  of the upper thrust portion  42   a . As a result, the upper thrust dynamic pressure bearing portion  821  is defined in the upper thrust gap  651  between the lower surface  428  of the upper outer tubular portion  425  and the upper surface  521  of the flange portion  52 . In the bearing mechanism  4   a , the upper thrust dynamic pressure bearing portion  821  and the radial dynamic pressure bearing  81  are arranged in communication with each other through the upper cylindrical gap  672  and the upper end gap  671 . 
     The upper seal portion  661   a  is defined between the outer circumferential surface  429  of the upper outer tubular portion  425  and the inner circumferential surface  531  of the upper hub tubular portion  53 . The lower seal portion  662   a  is defined between the inclined surface  433  of the lower outer tubular portion  432  and the inner circumferential surface  541  of the lower hub tubular portion  54 . The upper seal portion  661   a  and the lower seal portion  662   a  are arranged in communication with each other through the communicating hole  61 . The axial distance between the upper end of the surface of the lubricating oil  45  in the upper seal portion  661   a  and the lower end of the surface of the lubricating oil  45  in the lower seal portion  662   a  is preferably longer than the length of the communicating hole and shorter than the length of the radial dynamic pressure bearing  81 . 
     Also in the second preferred embodiment of the present invention, the axial distance between the surface of the lubricating oil  45  in the upper seal portion  661   a  and the surface of the lubricating oil  45  in the lower seal portion  662   a  is shorter than the length of the radial dynamic pressure bearing  81 . This arrangement contributes to reducing the difference in pressure between the upper and lower seal portions  661   a  and  662   a . This contributes to preventing a leakage of the lubricating oil  45 . Furthermore, the length of the communicating hole  61  being shorter than the distance between the upper seal portion  661   a  and the lower seal portion  662   a  makes it easier to prevent any leakage of the lubricating oil  45 . 
     Providing the upper cylindrical gap  672  and the lower cylindrical gap  64  contributes to reducing the length of the communicating hole  61 . The reduced length of the communicating hole  61  contributes to arranging the upper seal portion  661   a  and the lower seal portion  662   a  to be closer to each other, whereby a leakage of the lubricating oil  45  is more easily prevented. Moreover, the upper end gap  671  and the upper cylindrical gap  672  are arranged between the upper thrust dynamic pressure bearing portion  821  and the radial dynamic pressure bearing  81 . This arrangement contributes to increased pressure on the lubricating oil  45  in the upper end gap  671  and the upper cylindrical gap  672 , whereby generation of an air bubble is prevented therein. 
     In the bearing mechanism  4   a , the upper surface  551  of the upper inner tubular portion  55  may include a thrust dynamic pressure groove array similar to the thrust dynamic pressure groove array  723  illustrated in  FIG. 9  defined therein. This results in a thrust dynamic pressure bearing portion being defined in the upper end gap  671  to support the upper inner tubular portion  55  in the thrust direction. In this case, a dynamic pressure generation portion that functions as an upper thrust dynamic pressure bearing portion may not necessarily be arranged in the upper thrust gap  651 . Note, however, that it is preferable that a dynamic pressure groove array which defines a dynamic pressure generation portion arranged to produce a radially inward pressure acting on the lubricating oil  45  should be arranged in the upper thrust gap  651 . The axial width of the upper end gap  671  is preferably greater than that of the upper thrust gap  651 . 
     Third Preferred Embodiment 
       FIG. 11  is a diagram illustrates a motor  12   a  according to a third preferred embodiment of the present invention. In the motor  12   a , the sleeve portion  5 , an upper hub tubular portion  53   a , and the lower hub tubular portion  54  are preferably defined by a single continuous monolithic member. In addition, the cover portion  311  and the cylindrical portion  312  are preferably defined by a single continuous monolithic member. The upper hub tubular portion  53   a  includes an annular projecting portion  532  arranged to project upward. A seal cap  44   a  is arranged to be annular and centered on the central axis J 1 . In the motor  12   a , the upper hub tubular portion  53   a  defines the tubular portion of the upper hub annular portion  591 . In addition, the seal cap  44   a  defines the annular cover portion of the upper hub annular portion  591 . The motor  12   a  is otherwise substantially similar in structure to the motor  12  according to the first preferred embodiment of the present invention. 
     Referring to  FIG. 12 , in the motor  12   a , a radially outer edge  444  of the seal cap  44   a  is tightly fitted to an inner circumferential surface of the projecting portion  532 . Note that the outer edge  444  may be fixed to the upper hub tubular portion  53   a  preferably through, for example, an adhesive. Also note that the outer edge  444  may be fixed to the upper hub tubular portion  53   a  through, for example, a combination of the tight fit and use of the adhesive, if so desired. 
       FIG. 13  is a cross-sectional view of the seal cap  44   a .  FIG. 14  is a bottom view of the seal cap  44   a . The inner edge  443  of the seal cap  44   a  preferably includes an inner annular projecting portion  461  arranged to project downward. A lower surface of the seal cap  44   a  includes a recessed portion  462  recessed upward. The depth of the recessed portion  462  is preferably arranged in the range of about 10 μm to about 50 μm, for example. Referring to  FIG. 12 , the upper thrust portion  42  includes a groove portion  744  having a great depth and defined between the inner cylindrical surface  741 , which is arranged radially inward of the outer circumferential surface  422 , and the outer annular surface  742 , which is arranged radially outward of the inner cylindrical surface  741 . The upper end of the inner cylindrical surface  741  is arranged at an axial level higher than that of the upper end of the outer circumferential surface  422  and that of the outer annular surface  742 . 
     A lower end of the inner annular projecting portion  461  of the seal cap  44   a  is arranged inside the groove portion  744 . The radially extending gap  663   a , which is annular and arranged to extend perpendicularly or substantially perpendicularly to the central axis J 1 , is defined between a bottom surface  445  of the recessed portion  462 , which is perpendicular or substantially perpendicular to the central axis J 1 , and the outer annular surface  742  of the upper thrust portion  42 . 
     The axial width of the radially extending gap  663   a  is arranged to be smaller than the maximum radial width of the upper seal gap  661 . In other words, the axial width of the radially extending gap  663   a  is arranged to be smaller than the radial distance between an upper edge of a chamfer  661   b  defined between the outer annular surface  742  and the outer circumferential surface  422  and an upper edge of a chamfer  661   c  defined at an inner top portion of the upper hub tubular portion  53   a . Note that, in the case where the upper thrust portion  42  and the upper hub tubular portion  53   a  are not provided with the chamfers  661   b  and  661   c , respectively, in the upper portion of the upper seal gap  661 , the maximum radial width of the upper seal gap  661  refers to the radial distance between an upper edge of the outer circumferential surface  422  and an upper edge of the inner circumferential surface  531  of the upper hub tubular portion  53   a.    
     The axial width of the radially extending gap  663   a  is preferably arranged in the range of about 0.05 mm to about 0.2 mm, for example. The radially extending gap  663   a  is continuous with the upper portion of the upper seal gap  661 . Each of the outer annular surface  742  and the bottom surface  445  of the recessed portion  462  is coated with an oil-repellent agent about its entire circumference. Hereinafter, an annular region that surrounds the central axis J 1  and which is coated with an oil-repellent film  86  on the bottom surface  445  of the recessed portion  462  of the seal cap  44   a  will be referred to as a “first oil-repellent film region  851 ”. An annular region that surrounds the central axis J 1  and which is coated with an oil-repellent film  86  on the outer annular surface  742  will be referred to as a “second oil-repellent film region  852 ”. 
     A strong physical shock to the motor  12   a  may cause droplets of the lubricating oil  45  in the upper seal gap  661  to be scattered, so that some of the droplets may be adhered to the lower surface of the seal cap  44   a  or the outer annular surface  742 . Provision of the first and second oil-repellent film regions  851  and  852  in the motor  12   a  contributes to prevention of the droplets of the lubricating oil  45  from traveling radially inward on the lower surface of the seal cap  44   a  or the outer annular surface  742 . The lubricating oil  45  is thus prevented from traveling through the radially extending gap  663   a  to be leaked out of the motor  12   a . In other words, the lubricating oil  45  is prevented from traveling radially inward beyond the first and second oil-repellent film regions  851  and  852 . Moreover, the provision of the first oil-repellent film region  851  and the second oil-repellent film region  852  contributes to more effective prevention of a leakage of the lubricating oil  45  out of the upper seal gap  661 . Furthermore, because the radially extending gap  663   a  is a minute gap, the provision of at least one of the first oil-repellent film region  851  and the second oil-repellent film region  852  reduces the leakage of the lubricating oil  45  out of the upper seal gap  661 . 
     Referring to  FIGS. 13 and 14 , the lower surface of the seal cap  44   a  includes shoulder portions  462   a  and  462   b . The shoulder portion  462   a  is annular and arranged to extend radially inward from the bottom surface  445  while extending downward. The shoulder portion  462   b  is annular and arranged to extend radially outward from the bottom surface  445  while extending downward. As illustrated in  FIG. 12 , the shoulder portion  462   a , which is arranged radially inward of the bottom surface  445 , is arranged radially inward of the radially extending gap  663   a . It is possible to use the shoulder portions  462   a  and  462   b  illustrated in  FIGS. 13 and 14  as marks to properly apply the oil-repellent agent onto the bottom surface  445  of the seal cap  44   a . Note that, if so desired, the oil-repellent agent may be applied to the shoulder portions  462   a  and  462   b  as well. 
     As illustrated in  FIG. 12 , the axially extending gap  663   b , which is arranged to open into the space above the upper thrust portion  42 , is defined between the inner annular projecting portion  461  and the inner cylindrical surface  741 . The radial width of the axially extending gap  663   b  is preferably arranged in the range of about 0.05 mm to about 0.2 mm, for example. The radially extending gap  663   a  is arranged in communication with the axially extending gap  663   b  through the groove portion gap  663   c , which is defined between the groove portion  744  and the seal cap  44   a . In the motor  12   a , the communicating gap  663 , which is arranged to communicate the upper seal gap  661  with the space above the upper thrust portion  42 , is defined by the radially extending gap  663   a , the groove portion gap  663   c , and the axially extending gap  663   b.    
     Also in the third preferred embodiment of the present invention, the inclusion of the radially extending gap  663   a  and the axially extending gap  663   b  in the communicating gap  663  contributes to preventing an air containing an evaporated lubricating oil in the upper seal gap  661  from traveling to the outside of the motor  12   a . This contributes to reducing the evaporation of the lubricating oil  45 , and thereby achieving an improvement in a usable life of the motor  12   a . Moreover, because the lower end of the inner annular projecting portion  461  is arranged inside the groove portion  744 , a further reduction in the evaporation of the lubricating oil  45  is achieved. The same holds true for similar structures in other preferred embodiments described below. 
     The provision of the groove portion  744  in the upper thrust portion  42  makes it possible to arrange the inner annular projecting portion  461  in close proximity to the inner cylindrical surface  741 . Thus, the axially extending gap  663   b  can be easily defined. The provision of the inner annular projecting portion  461  in the seal cap  44   a  contributes to an increased axial dimension of the axially extending gap  663   b , and also to an increased rigidity of the seal cap  44   a . In particular, because flexural strength of the seal cap  44   a  is thereby improved, the seal cap  44   a  is prevented from undergoing a deformation when the seal cap  44   a  is, for example, press fitted to be thereby fixed to the projecting portion  532 . The motor  12   a  is able to achieve a reduction in the axial thickness of the seal cap  44   a , and a reduction in the total size of the motor  12   a . Regarding a storage disk drive including the motor  12   a , when the upper plate member  142  of the housing  14  as illustrated in FIG.  1  is fixed to the motor  12   a , a strong force may be applied to the upper thrust portion  42 . Even if that happens, the force is absorbed by bending of the inner cylindrical surface  741  and the groove portion  744 , and the lower surface  421  of the upper thrust portion  42  is prevented from undergoing a substantial deformation. As a result, a reduction in performance of the upper thrust dynamic pressure bearing portion  821  is substantially prevented. 
       FIG. 15  is a diagram illustrating a portion of a motor  12   a  according to another preferred embodiment of the present invention. The radially outer edge  444  of the seal cap  44   a  of the motor  12   a  includes an outer annular projecting portion  463  arranged to project upward. An outer circumferential surface of the outer annular projecting portion  463  is tightly fitted and thereby fixed to the projecting portion  532 . The inclusion of the outer annular projecting portion  463  in the seal cap  44   a  contributes to an increase in an area where the seal cap  44   a  is in direct contact with the projecting portion  532 . The increase in the contact area contributes to an improvement in strength with which the seal cap  44   a  is, for example, press fitted to the projecting portion  532 . Note that, in the case where the outer annular projecting portion  463  and the projecting portion  532  are fixed to each other through, for example, an adhesive, an improvement in adhesive strength therebetween is achieved. 
       FIG. 16  is a diagram illustrating a motor  12   a  according to yet another preferred embodiment of the present invention. The projecting portion  532  of the upper hub tubular portion  53   a  includes a raised portion  533  that is raised radially inward. In the motor  12   a , an upper edge of the outer edge  444  of seal cap  44   a  and the raised portion  533  are arranged in contact with each other in the axial direction. This contributes to more effectively preventing the seal cap  44   a  from coming off the upper hub tubular portion  53   a . When the seal cap  44   a  is fixed to the upper hub tubular portion  53   a , the outer edge  444  of the seal cap  44   a  is moved downward while undergoing an upward elastic deformation when being in contact with the raised portion  533 , and once the outer edge  444  is moved downward beyond the raised portion  533 , the outer edge  444  regains its original shape thanks to resilience. 
       FIG. 17  is a diagram illustrating the upper seal gap  661  and its vicinity of a motor according to yet another preferred embodiment of the present invention. An upper portion  530  of the upper hub tubular portion  53   a  includes a shoulder portion  534 . The shoulder portion  534  is arranged in a region that is radially inward of the projecting portion  532  and which is axially opposed to the seal cap  44   a , and is arranged to extend radially outward while extending upward. In the upper portion  530  of the upper hub tubular portion  53   a , the shoulder portion  534 , an inner annular surface  535 , which is annular and centered on the central axis J 1  and which is arranged radially inward of the shoulder portion  534 , and the chamfer  661   c  are coated with an oil-repellent film  86  throughout their entire circumference. Hereinafter, the shoulder portion  534 , the inner annular surface  535 , and the chamfer  661   c  will be collectively referred to as a “third oil-repellent film region  853 ”. In addition, as in the case of  FIG. 12 , the lower surface of the seal cap  44   a  and the outer annular surface  742  of the upper thrust portion  42  are provided with the first and second oil-repellent film regions  851  and  852 , respectively. 
     Providing the third oil-repellent film region  853 , which is annular and arranged to surround the central axis J 1 , in the upper portion  530  of the upper hub tubular portion  53   a  contributes to preventing a leakage of the lubricating oil  45  due to a centrifugal force when the rotation of the motor  12  is examined before the attachment of the seal cap  44   a . It is possible to use the shoulder portion  534  as a mark to properly apply the oil-repellent agent onto the inner annular surface  535  and the chamfer  661   c  of the upper hub tubular portion  53   a.    
     Moreover, when the lubricating oil  45  is injected into the bearing mechanism  4  through the lower seal gap  662  illustrated in  FIG. 4  with the bearing mechanism  4  turned upside down, the provision of the second and third oil-repellent film regions  852  and  853  contributes to preventing a portion of the lubricating oil  45  which has flowed into the upper seal gap  661  from traveling beyond the outer annular surface  742  of the upper thrust portion  42  or the upper portion  530  of the upper hub tubular portion  53   a.    
     Note that, in the bearing mechanism  4 , the position of the third oil-repellent film region  853  may be modified appropriately as long as at least a portion of the third oil-repellent film region  853  is arranged radially inward of the shoulder portion  534 . For example, an upper portion of the inner circumferential surface  531  may define a portion of the third oil-repellent film region. Also note that the oil-repellent film  86  may not necessarily be arranged to extend over the shoulder portion  534 , but the third oil-repellent film region may be arranged to extend over only the inner annular surface  535 , the chamfer  661   c , and the upper portion of the inner circumferential surface  531 . Also note that the third oil-repellent film region may be arranged to extend over only the inner annular surface  535 , and that the third oil-repellent film region may be arranged to extend over only the chamfer  661   c.    
     Fourth Preferred Embodiment 
       FIG. 18  is a diagram illustrating a portion of a storage disk drive  1  including a motor according to a fourth preferred embodiment of the present invention. The structure of this motor is similar to that of the motor  12   a  illustrated in  FIG. 11 . An upper surface  440  of the seal cap  44   a  according to the present preferred embodiment includes a surface  440   a  that is arranged at an axial level higher than that of a surrounding area and which is arranged axially opposite an outer edge portion of a lower surface  143   a  of the plate central portion  143  of the housing. Note that the upper surface  440  refers to a surface whose normal is pointed axially upward. In the storage disk drive  1 , an annular, radially extending gap  663   d  is defined between the surface  440   a  and the lower surface  143   a  of the plate central portion  143 . Hereinafter, the radially extending gap  663   a , which is defined between the seal cap  44   a  and the upper thrust portion  42  will be referred to as a “first radially extending gap  663   a ”, while the gap  663   d  will be referred to as a “second radially extending gap  663   d ”. The axial width of the second radially extending gap  663   d  is preferably arranged in the range of about 0.05 mm to about 0.2 mm, for example. The second radially extending gap  663   d  is arranged in communication with the axially extending gap  663   b  through a gap  663   e  defined between the lower surface  143   a  of the plate central portion  143  and a radially inner portion of the upper surface  440  of the seal cap  44   a . Note that the axial width of the gap  663   e  is also preferably arranged in the range of about 0.05 mm to about 0.2 mm, for example. 
     In the storage disk drive  1 , a communicating gap  664  arranged to bring the upper seal gap  661  into communication with the space outside the motor includes the first radially extending gap  663   a , the groove portion gap  663   c , the axially extending gap  663   b , the gap  663   e , and the second radially extending gap  663   d . As is the case with the first radially extending gap  663   a  and the axially extending gap  663   b , the second radially extending gap  663   d  is a region that has a locally decreased width within the communicating gap  664  and which has a width smaller than the maximum radial width of the upper seal gap  661 . 
     Also in the fourth preferred embodiment, a reduction in the evaporation of the lubricating oil  45  is achieved because the communicating gap  664  is arranged to have a labyrinth structure, including radially extending gaps and an axially extending gap. The provision of the second radially extending gap  663   d , which has a decreased axial width, contributes to an additional reduction in the evaporation of the lubricating oil  45 . 
     While preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described preferred embodiments, but a variety of modifications are possible. For example, referring to  FIG. 19 , in a modification of the third preferred embodiment, the lower surface of the seal cap  44   a  may include an annular raised portion  464  arranged to project downward. In this case, an oil-repellent agent is applied onto a surface  464   a  of the raised portion  464  which is perpendicular to the central axis J 1 . The seal cap  44   a  includes an annular shoulder portion  464   b  arranged to extend radially inward from the surface  464   a  while extending upward, and an annular shoulder portion  464   c  arranged to extend radially outward from the surface  464   a  while extending upward. It is possible to use the shoulder portions  464   b  and  464   c  as marks for proper application of the oil-repellent agent. 
     The region where the oil-repellent agent is to be applied is made easily identifiable by arranging a portion of the lower surface of the seal cap  44   a  which is radially inward of the radially extending gap  663   a  at a level higher or lower than that of a portion of the lower surface of the seal cap  44   a  which defines the radially extending gap  663   a . Furthermore, referring to  FIG. 20 , the lower surface of the seal cap  44   a  may include a minute recessed portion  465  defined by an annular cut. The minute recessed portion  465  is arranged radially inward of the radially extending gap  663   a  illustrated in  FIG. 12 . The oil-repellent agent is applied onto a portion of the lower surface of the seal cap  44   a  which is radially outward of the minute recessed portion  465 . Alternatively, the lower surface of the seal cap  44   a  may include an annular, minute raised portion. 
     As described above, the provision of an annular shoulder portion extending upward or downward while extending radially inward in at least a portion of the lower surface of the seal cap  44   a  which is radially inward of the radially extending gap  663   a  makes it easier to properly apply the oil-repellent agent onto a portion of the lower surface of the seal cap  44   a  which is radially outward of the shoulder portion. The same holds true for the first radially extending gap  663   a  illustrated in  FIG. 18 . Regarding the upper hub tubular portion  53   a  illustrated in  FIG. 12 , the third oil-repellent film region  853  may be arranged in the chamfer  661   c , which is arranged in the vicinity of an upper end opening of the upper seal gap  661 , and an area surrounding the chamfer  661   c , unless the oil-repellent film  86  applied thereto affects the attachment of the seal cap  44   a . In each of the first, second, and fourth preferred embodiments, as well as in the third preferred embodiment, the first and second oil-repellent film regions may be arranged in the lower surface of the seal cap  44  or  44   a  and the outer annular surface  742  of the upper thrust portion  42  or  42   a , respectively. The third oil-repellent film region may be arranged in the upper portion of the upper hub tubular portion  53  or  53   a.    
     Referring to  FIG. 21 , in a modification of the third preferred embodiment, an inner annular projecting portion  466  projecting upward may be arranged at the inner edge  443  of the seal cap  44   a  such that the axially extending gap  663   b  is defined between the inner annular projecting portion  466  and the inner cylindrical surface  741 . The inner edge  443  including an annular projecting portion arranged to project in the axial direction makes it easier to secure a sufficient length of the axially extending gap  663   b  while securing a sufficient rigidity of the seal cap  44   a.    
     Referring to  FIG. 22 , the inner edge  443  of the seal cap  44   a  may be arranged to extend perpendicularly or substantially perpendicularly to the central axis J 1 . Even in this case, it is possible to define a radially extending gap having a large radial dimension below the seal cap  44   a , and thereby reduce the evaporation of the lubricating oil  45 . Referring to  FIG. 23 , in a modification of the first preferred embodiment, the upper thrust portion  42  and the shaft portion  41  may be defined by separate members. In this case, the shaft portion  41  is inserted into the upper thrust portion  42  from below, and a portion  471  of the upper thrust portion  42  which is defined in the upper portion thereof and which is arranged to project radially inward is arranged in axial contact with an upper end of the shaft portion  41 . Axial positioning of the upper thrust portion  42  relative to the shaft portion  41  is thereby achieved. The provision of the portion  471  contributes to securely preventing a downward movement of the upper thrust portion  42 . Also, referring to  FIG. 24 , the outer circumferential surface  411  of the shaft portion  41  may include a shoulder portion  472 . In this case, a radially inner end portion of a bottom portion of the upper thrust portion  42  can be arranged in axial contact with the shoulder portion  472  to achieve the axial positioning of the upper thrust portion  42  relative to the shaft portion  41 . The same holds true for other preferred embodiments. 
     The seal cap  44  or  44   a  may be welded to the upper hub tubular portion  53  or  53   a , for example. The lower thrust portion  43  and the base plate  21  may be defined by a single continuous member, for example. In this case, a reduction in the number of components of the motor is achieved. Also, in each of the first and second preferred embodiments, the shaft portion  41  and the upper thrust portion  42  may be defined by separate members. Also, the lower plate portion  431  and the outer tubular portion  432  may be defined by separate members. Also, the lower thrust portion  43  and the shaft portion  41  may be defined by a single continuous member. 
     In the groove upper portion of the upper radial dynamic pressure groove array  711  illustrated in  FIG. 5 , a plurality of oblique grooves may be arranged to extend obliquely along the grooves constituting the upper radial dynamic pressure groove array  711 . Also, in the groove upper portion, each of the grooves constituting the upper radial dynamic pressure groove array  711  may be arranged to have a greater depth than in the groove lower portion. This leads to an increased axially downward pressure acting on the lubricating oil  45 . The same holds true for the groove lower portion of the lower radial dynamic pressure groove array  712 . Also, the upper portion and the lower portion of each of the grooves that define the upper radial dynamic pressure groove array  711  may be arranged to have substantially the same length. Also, the upper portion and the lower portion of each of the grooves that constitute the lower radial dynamic pressure groove array  712  may be arranged to have substantially the same length. A variety of modifications can be made to the length, depth, width, and so on of each of the dynamic pressure grooves without departing from the scope and spirit of the present invention. 
     Each of the upper thrust dynamic pressure groove array  721  and the lower thrust dynamic pressure groove array  722  may be arranged in the herringbone pattern. In this case, a radially outer portion of each of upper thrust dynamic pressure grooves that define the upper thrust dynamic pressure groove array  721  is arranged to have a length greater than that of a radially inner portion thereof, and a radially outer portion of each of lower thrust dynamic pressure grooves that define the lower thrust dynamic pressure groove array  722  is arranged to have a length greater than that of a radially inner portion thereof, in order to generate a radially inward pressure acting on the lubricating oil  45 . Note that a plurality of oblique grooves may be arranged between the radially outer portions of the thrust dynamic pressure grooves. The radially outer portion of each thrust dynamic pressure groove may be arranged to have a depth greater than that of the radially inner portion thereof. Although a direction in which the lubricating oil  45  circulates has not been specified in the description of any of the above-described preferred embodiments, the direction in which the lubricating oil  45  circulates may be determined to be either a counterclockwise direction or a clockwise direction in  FIG. 4 . 
     In  FIG. 4 , in the case where the lower surface  421  of the upper thrust portion  42  is arranged to have a sufficient area, the upper thrust dynamic pressure groove array  721  may be arranged radially inward of the upper end opening of the communicating hole  61  as illustrated in  FIG. 25 . Furthermore, the upper thrust dynamic pressure groove array  721  may be arranged farther radially inward of the communicating hole  61  than in the case of  FIG. 25 . Similarly, in the case where the upper surface  435  of the outer tubular portion  432  is arranged to have a sufficient area, the lower thrust dynamic pressure groove array  722  may be arranged radially inward of the lower end opening of the communicating hole  61  as illustrated in  FIG. 26 . Furthermore, the lower thrust dynamic pressure groove array  722  may be arranged farther radially inward of the communicating hole  61  than in the case of  FIG. 26 . In the upper and lower thrust gaps  651  and  652 , an upper thrust dynamic pressure groove array and a lower thrust dynamic pressure groove array may be arranged in the upper surface  521  and the lower surface  522 , respectively, of the flange portion  52 . Also, a radial dynamic pressure groove array may be arranged in the outer circumferential surface  411  of the shaft portion  41 . 
     In each of the above-described preferred embodiments, the upper seal gap  661  may be arranged to have a substantially uniform width. In that case, a dynamic pressure groove array is arranged in at least one of the outer circumferential surface  422  of the upper thrust portion  42  and the inner circumferential surface  531  of the upper hub tubular portion  53  to define a so-called pumping seal. A dynamic pressure acting on the lubricating oil  45  in the direction of an interior of the upper seal gap  661  is thereby generated to retain the lubricating oil  45 . The same holds true for the lower seal gap  662 . Each of the upper seal portion  661   a  and the lower seal portion  662   a  may not necessarily be arranged to extend in parallel or substantially in parallel with the central axis J 1 , but may be arranged to be angled significantly with respect to the central axis J 1 . 
     Referring to  FIG. 27 , the cap cylindrical portion  441  of the seal cap  44  may be fixed to an inside of the upper hub tubular portion  53 . In this case, an inner circumferential surface of the tubular portion of the upper hub annular portion  591  is defined by an inner circumferential surface of the cap cylindrical portion  441 , and the upper seal gap  661  is defined between the inner circumferential surface of the cap cylindrical portion  441  and the outer circumferential surface  422  of the upper thrust portion  42 . The cap cylindrical portion  441  may be regarded as a portion of the upper hub tubular portion  53 . It is, however, more preferable that at least the inner circumferential surface of the tubular portion of the upper hub annular portion  591  is defined by the inner circumferential surface of the upper hub tubular portion  53  or  53   a  so that the volume of the lubricating oil  45  in the upper seal gap  661  can be checked and verified before the attachment of the seal cap  44 . In the upper hub annular portion  591 , the upper hub tubular portion and the seal cap may be defined by a single continuous member, for example. Also, in the case where the likelihood of a leakage of the lubricating oil  45  is low, the seal cap  44  or  44   a  may be eliminated with the upper hub annular portion being defined by only the upper hub tubular portion  53  or  53   a.    
       FIG. 28  is a cross-sectional view illustrating a seal cap  44   a , a tubular portion  54 , and their vicinities according to a preferred embodiment of the present invention. The structure of a motor  12   a  according to the present preferred embodiment is preferably identical or substantially identical to that of the motor  12   a  illustrated in  FIG. 11 . 
     The seal cap  44   a  preferably includes a first plate portion  467 , a second plate portion  469 , and a joining portion  468 . Each of the first and second plate portions  467  and  469  is substantially annular in shape, and is arranged to extend radially. The joining portion  468  is annular in shape, and is arranged to extend radially outward and axially downward from an outer edge of the first plate portion  467 . The first plate portion  467  is joined to the second plate portion  469  through the joining portion  468 . The second plate portion  469  is arranged radially outward of and axially below the first plate portion  467 . 
     The first plate portion  467  includes a “first seal cap lower surface”  467   a , which is an annular surface facing axially downward. The second plate portion  469  includes a “second seal cap lower surface”  469   a , which is an annular surface facing axially downward. The joining portion  468  includes a “joining portion lower surface”  468   a , which is an annular surface extending radially outward and axially downward. The first seal cap lower surface  467   a  is joined to the second seal cap lower surface  469   a  through the joining portion lower surface  468   a . The second seal cap lower surface  469   a  is arranged radially outward of and axially below the first seal cap lower surface  467   a.    
     The tubular portion  54  preferably includes a “first tubular portion upper surface”  541 , a “second tubular portion upper surface”  543 , and a “connection portion upper surface”  542 . Each of the first and second tubular portion upper surfaces  541  and  543  is an annular surface extending radially outward. The connection portion upper surface  542  is an annular surface extending radially outward and axially downward. The first tubular portion upper surface  541  is joined to the second tubular portion upper surface  543  through the connection portion upper surface  542 . The second tubular portion upper surface  543  is arranged radially outward of and axially below the first tubular portion upper surface  541 . The first tubular portion upper surface  541  is arranged axially opposite to the first seal cap lower surface  467   a . The first tubular portion upper surface  541  preferably includes a chamfer  541   a  in a radially inner portion thereof. Although the first tubular portion upper surface  541  is preferably annular in shape in the present preferred embodiment, a first tubular portion upper surface according to another preferred embodiment of the present invention may alternatively be a surface in the shape of the letter “C”, i.e., an annular surface including a cutout portion. 
     The first seal cap lower surface  467   a  and the first tubular portion upper surface  541  are arranged opposite to each other with a third radially extending gap  663   e  intervening therebetween. The third radially extending gap  663   e  is arranged to extend radially in substantially annular shape. The third radially extending gap  663   e  is preferably arranged to have a minimum axial width greater than a minimum axial width of an annular first radially extending gap  663   a  defined between the first seal cap lower surface  467   a  and an outer annular surface  742 , which is an upper surface of an upper thrust portion. 
     A strong shock to the motor  12   a  may cause droplets of a lubricating oil  45  in an upper seal gap  661  to be scattered, so that some of the droplets may be adhered to the first seal cap lower surface  467   a  or the first tubular portion upper surface  541 . Since the minimum axial width of the third radially extending gap  663   e  is preferably greater than the minimum axial width of the first radially extending gap  663   a , the droplets of the lubricating oil  45  are prevented or substantially prevented from moving radially outward in the third radially extending gap  663   e . Thus, the lubricating oil  45  is prevented or substantially prevented from leaking out of the motor  12   a  by passing through the third radially extending gap  663   e . That is, the structure of the present preferred embodiment prevents or substantially prevents the lubricating oil  45  from moving radially outward beyond an oil-repellent film region  854 . 
     An adhesive  90  is preferably arranged between the seal cap  44   a  and the tubular portion  54 , and includes an upper surface  901  and a lower surface  902 . The upper surface  901  is arranged above the seal cap  44   a , while the lower surface  902  is arranged below the seal cap  44   a.    
     The second tubular portion upper surface  543  is arranged to be in contact with the second seal cap lower surface  469   a . The lower surface  902  of the adhesive  90  is arranged between the joining portion lower surface  468   a  and the connection portion upper surface  542 . Note that the lower surface  902  of the adhesive  90  is preferably arranged radially outward of the first tubular portion upper surface and radially inward of the second tubular portion upper surface according to a preferred embodiment of the present invention. 
     Since the lower surface  902  of the adhesive  90  is arranged between the joining portion lower surface  468   a  and the connection portion upper surface  542 , the lubricating oil  45  is prevented or substantially prevented from leaking out of the motor  12   a  through the third radially extending gap  663   e.    
     The adhesive  90  is arranged between a projecting portion  532  and an upper surface of the seal cap  44   a  according to the present preferred embodiment. That is, a gap between the projecting portion  532  and the upper surface of the seal cap  44   a  is sealed with the adhesive  90 . The adhesive  90  is arranged with the upper surface  901  at an axial top thereof. 
     The seal cap  44   a  preferably includes a projecting surface  490  including a normal that is positioned above surrounding portions of the upper surface of the seal cap  44   a  is arranged to point axially upward. Thus, even when the amount of the adhesive  90  applied is large, the upper surface  901  of the adhesive  90  is prevented from extending radially inward beyond the projecting surface  490 . 
     Moreover, the upper surface  901  of the adhesive  90  prevents or substantially prevents the lubricating oil  45  from leaking out of the motor  12   a  through a gap between a lower surface of the seal cap  44   a  and an upper surface of the tubular portion  54 . Furthermore, since the gap between the projecting portion  532  and the upper surface of the seal cap  44   a  is sealed with the adhesive  90 , entry and exit of a gas through the gap is prevented, leading to an improvement in airtightness of a storage disk drive. Note that another sealant may be used in place of the adhesive  90 , if so desired. For example, a resin material other than the adhesive may alternatively be used as the sealant. 
     The first tubular portion upper surface  541  preferably includes the oil-repellent film region  854 , on which an annular oil-repellent film  86  surrounding the central axis is arranged. Note that the oil-repellent film region  854  is arranged in at least a portion of the first tubular portion upper surface  541 . Specifically, the entire oil-repellent film region  854  may be arranged in one of the chamfer  541   a  and a remaining portion of the first tubular portion upper surface  541 . Also, the oil-repellent film region  854  may be arranged in both the chamfer  541   a  and the remaining portion of the first tubular portion upper surface  541 . 
     A strong shock to the motor  12   a  may cause droplets of the lubricating oil  45  in the upper seal gap  661  to be scattered, so that some of the droplets may be adhered to the first seal cap lower surface  467   a  or the first tubular portion upper surface  541 . At this time, the oil-repellent film region  854  prevents or substantially prevents the droplets of the lubricating oil  45  from moving radially outward in the third radially extending gap  663   e . As a result, the lubricating oil  45  is prevented or substantially prevented from leaking out of the motor  12   a  by passing through the third radially extending gap  663   e . That is, the lubricating oil  45  is prevented or substantially prevented from moving radially outward beyond the oil-repellent film region  854 . 
       FIG. 29  is a cross-sectional view illustrating a seal cap  44   a  and a tubular portion  54  according to a preferred embodiment of the present invention. 
     In the above-described preferred embodiment, the first tubular portion upper surface  541  preferably is arranged axially above the second tubular portion upper surface  543 , and the connection portion upper surface  542  is an inclined surface extending radially outward and axially downward. In the present preferred embodiment illustrated in  FIG. 29 , a first tubular portion upper surface  544 , a connection portion upper surface  545 , and the second tubular portion upper surface  543  are preferably arranged at substantially the same axial position. Thus, the axial width of the third radially extending gap  663   e  between the first seal cap lower surface  467   a  and the first tubular portion upper surface  544  is increased, leading to more effective prevention of a leakage of the lubricating oil  45  out of the motor  12   a  through the third radially extending gap  663   e . That is, the lubricating oil  45  is prevented or substantially prevented from moving radially outward beyond the oil-repellent film region  854 . 
       FIG. 30  is a cross-sectional view illustrating a seal cap  44   a  and a tubular portion  54  according to a preferred embodiment of the present invention. 
     The seal cap  44   a  includes a first plate portion  467  and a cylindrical “second outer annular projecting portion”  470  arranged to extend axially downward from a radially outer edge of the first plate portion  467 . 
     As illustrated in  FIG. 30 , an outer edge of the seal cap  44   a  may include the second outer annular projecting portion  470  arranged to project downward. The second outer annular projecting portion  470  preferably includes a “third seal cap lower surface”  470   a , which is an annular surface facing axially downward. The third seal cap lower surface  470   a  is arranged to be in contact with the second tubular portion upper surface  543 . Thus, an increase in the axial dimension of an area at which an outer circumferential surface of the second outer annular projecting portion  470  and the projecting portion  532  are fixed to each other is achieved. As a result, an improvement in rigidity of the seal cap  44   a  is achieved. 
     Note that, although the second outer annular projecting portion  470  is preferably arranged to extend axially downward in the present preferred embodiment, the present invention is not limited to the present preferred embodiment. For example, the second outer annular projecting portion  470  may alternatively be arranged to project axially upward in another preferred embodiment of the present invention. 
     All of the first plate portion  467 , the second plate portion  469 , and the joining portion  468  are preferably defined by cutting processes. Note, however, that only one or two of the first plate portion  467 , the second plate portion  469 , and the joining portion  468  may be defined by the cutting processes. For example, only the first plate portion  467  may be defined by the cutting process while both the second plate portion  469  and the joining portion  468  are defined by press working. 
     The seal cap  44   a  may be fitted to the projecting portion  532  through press fit, through a combination of press fit and adhesion, through welding, through crimping, etc. 
     Features of the above-described preferred embodiments and modifications thereof may be combined as appropriate as long as no conflict arises. 
     Preferred embodiments of the present invention is specifically applicable to motors used to drive a disk, however, the present invention is also usable in other types of motors. 
     Only selected preferred 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 present invention as defined in the appended claims. Furthermore, the foregoing description of the preferred 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.