Abstract:
A hydrodynamic bearing unit and a manufacturing method therefor that reduce manufacturing costs and prevent leakage of lubricating oil are provided. The bearing unit includes a shaft, a sleeve which is rotatably mounted to the shaft and which forms a radial bearing in cooperation with the shaft, and a pair of seal members which are fixed to the shaft, which form respective thrust bearing parts in cooperation with the sleeve, and which seal lubricating oil circulating in the bearing unit. The shaft has a large-diameter part functioning as one of the seal members. The other seal member is fixed to the shaft by press-fitting.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to a hydrodynamic bearing unit used in a magnetic disc drive or the like and a method of manufacturing the unit.  
         BACKGROUND ART  
         [0002]    A conventional hydrodynamic bearing unit includes a sealing member separate from a shaft. Lubricating oil is injected by dipping the bearing unit entirely into the lubricating oil in a vacuum and then restoring the bearing unit to atmospheric pressure. Alternatively, the lubricating oil is dropped into a bearing in assembling the bearing unit. The conventional hydrodynamic bearing unit and a method of manufacturing the unit will be explained.  
           [0003]    [0003]FIG. 12 is a sectional view of an essential part of the conventional dynamic bearing unit. The bearing unit includes shaft  101  implanted in a base (not shown) and a cylindrical sleeve  103  rotatably mounted to shaft  101 . Both ends of sleeve  103  have respective inside diameters larger than that of a center part of sleeve  103 . Opposed faces of shaft  101  and sleeve  103  cooperatively form a radial bearing. The bearing unit further includes a first seal member  102  and a second seal member  104  disposed at respective lower and upper parts of the bearing unit. Faces of first seal member  102  and sleeve  103  facing each other in a longitudinal direction of shaft  101  cooperatively form a thrust bearing. And faces of second seal member  104  and sleeve  103  facing each other in the longitudinal direction of shaft  101  cooperatively form another thrust bearing. Faces of first seal member  102  and sleeve  103  facing each other in a radial direction of shaft  101  cooperatively form V-shaped capillary seal  106  for sealing the lubricating oil. And faces of second seal member  104  and sleeve  103  facing each other in the radial direction of shaft  101  cooperatively form another V-shaped capillary seal  106  for sealing the lubricating oil.  
           [0004]    First seal member  102  is fixed to shaft  101  by press fitting with a jig (not shown) at a desired mounting height. Then, sleeve  103  is introduced to shaft  101 , and subsequently, second seal member  104  is fixed to shaft  101  by press fitting with a jig to provide the bearing unit.  
           [0005]    The bearing unit is dipped entirely into the lubricating oil under vacuum and then restored to the atmospheric pressure, and thereby the lubricating oil is injected by a difference in pressure. Alternatively, the bearing unit has the lubricating oil dropped therein when being assembled.  
           [0006]    The above-described bearing unit, since including the seal members separate from the shaft, is subject to assembly errors in the many assembly steps, thus precluding cost reduction.  
         DISCLOSURE OF THE INVENTION  
         [0007]    A hydrodynamic bearing unit includes a shaft including a large-diameter part, a sleeve mounted rotatably to the shaft, and a seal member forming a thrust bearing in cooperation with the sleeve. The large-diameter part and the sleeve cooperatively form another thrust bearing. The bearing unit is assembled without error in but a few assembly steps.  
           [0008]    A jig including an annular elastic member seals an oil seal defined by the sleeve and the seal member or the large-diameter part, and lubricating oil is injected into the bearing unit by vacuum suction. The jig is fixed to the shaft by a magnet, a screw or engagement between an engaging projection and a recess. Thus, only one end of the bearing unit is required to be cleaned after the injection of the lubricating oil. Further, an opening of one capillary seal can be sealed easily, and the jig can be detached easily after the injection of the lubricating oil. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    [0009]FIG. 1 is a sectional view of an essential part of a hydrodynamic bearing unit in accordance with a first exemplary embodiment of the present invention.  
         [0010]    [0010]FIG. 2 is a sectional of an essential part of a hydrodynamic bearing unit in accordance with the first embodiment.  
         [0011]    [0011]FIG. 3 is a sectional view of an essential part of a hydrodynamic bearing unit in accordance with the first embodiment.  
         [0012]    [0012]FIG. 4 is a sectional view of an essential part of a hydrodynamic bearing unit having a jig mounted thereon in accordance with a second exemplary embodiment of the present invention.  
         [0013]    [0013]FIG. 5 is a sectional view of an essential part of a hydrodynamic bearing unit having a jig mounted thereon in accordance with the second embodiment.  
         [0014]    [0014]FIG. 6 is a sectional view of an essential part of a hydrodynamic bearing unit having a jig mounted thereon in accordance with the second embodiment.  
         [0015]    [0015]FIG. 7 is a sectional view of an essential part of a hydrodynamic bearing unit in accordance with a third exemplary embodiment of the present invention.  
         [0016]    [0016]FIG. 8 is an enlarged sectional view of the essential part of the hydrodynamic bearing unit in accordance with the third embodiment.  
         [0017]    [0017]FIG. 9 is a sectional view of an essential part of the hydrodynamic bearing unit in accordance with the third embodiment.  
         [0018]    [0018]FIG. 10 is an enlarged sectional view of the essential part of the hydrodynamic bearing unit in accordance with the third embodiment.  
         [0019]    [0019]FIG. 11 is a sectional view of an essential part of a magnetic disc drive in accordance with a fourth exemplary embodiment of the present invention.  
         [0020]    [0020]FIG. 12 is a sectional view of an essential part of a conventional hydrodynamic bearing unit. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    (Exemplary Embodiment 1)  
         [0022]    Referring to FIGS.  1 - 3 , a first exemplary embodiment of the present invention will be described. FIGS.  1 - 3  are sectional views illustrating an essential part of a hydrodynamic bearing unit in accordance with the first embodiment of this invention.  
         [0023]    As shown in FIG. 1, the bearing unit includes a shaft  1  having a large-diameter part  2  at a lower part thereof, cylindrical sleeve  3  rotatably mounted to shaft  1 , and seal member  4  disposed at an upper part of the bearing unit. Sleeve  3  has both ends thereof having respective inside diameters larger than a diameter of a center part thereof. Respective opposing faces of shaft  1  and sleeve  3  cooperatively form a radial bearing. The bearing unit of the embodiment has a simple structure since it utilizes the seal member and the shaft corresponding to first seal member  102  and shaft  101  unitarily formed in the conventional bearing unit. Shaft  1  and sleeve  3  cooperatively form a radial bearing. Large-diameter part  2  of shaft  1 , seal member  4  and sleeve  3  cooperatively form a thrust bearing. In other words, the thrust bearing includes a first thrust bearing part cooperatively formed by seal member  4  and sleeve  3  and a second thrust bearing part cooperatively formed by large-diameter part  2  and sleeve  3 . Seal member  4  is fixed to shaft  1  by, for example, press fitting or shrinkage fitting.  
         [0024]    If an axial length L1 of seal member  4  is longer than an axial length L2 of large-diameter part  2  in a direction parallel with an axial direction of rotation, a surface of a disk is prevented from being contaminated due to leaking or splashing lubricating oil, even in cases where the lubricating oil undergoes thermal expansion or has air penetrated thereinto.  
         [0025]    In machining or grinding of an outer peripheral surface of shaft  1 , a small-diameter part of shaft  1  and top and bottom faces of large-diameter part  2  undergo the grinding simultaneously. This arrangement allows a lower end part  1   b  of shaft  1  to be large in diameter as shown in FIG. 2. In other words, since it is not necessary for a first seal member to be fixed to the shaft by press-fitting as was the case with the conventional bearing unit. Therefore, regardless of the inside diameter of sleeve  3 , shaft  1  can include the lower end part  1   b  having the larger diameter than other of the part  1   b  of shaft  1 . This allows shaft  1  to be strong mechanically.  
         [0026]    As shown in FIG. 3, a length L3 from a bottom end of sleeve  3  to the face of sleeve  3  that faces the top face of large-diameter part  2  is longer than axial length L2 of large-diameter part  2 . Second seal member  4  is press-fitted until seal member  4  contacts with sleeve  3  while the bottom end of sleeve  3  is aligned flush with the bottom of large-diameter part  2 . This provides the thrust bearing with a desired axial clearance (L3-L2).  
         [0027]    According to the present embodiment described above, shaft  1  and the unitarily formed first seal member allow the bearing unit to have a simple structure and to be assembled accurately and easily. This reduces the number of components as well as cost.  
         [0028]    (Exemplary Embodiment 2)  
         [0029]    A method of manufacturing a hydrodynamic bearing unit in accordance with a second exemplary embodiment of the present invention will be described with reference to FIGS.  4 - 6 . The hydrodynamic bearing unit of the present embodiment has a similar basic structure to that of the foregoing first exemplary embodiment. Thus, similar elements are denoted by the same reference numerals, and are not described in detail.  
         [0030]    [0030]FIG. 4 is a sectional view of an essential part of the bearing unit having a jig mounted thereon for injection of lubricating oil. Seal member  4  is made of a magnetic material. Attractive force between seal member  4  and an annular magnet  5  provided on disc-like jig  8  presses annular elastic member  7 , which is preferably made of rubber, onto jig  8  against an opening portion of capillary seal  6  for sealing the lubricating oil, thereby sealing a top part of the bearing unit.  
         [0031]    The bearing unit has an upper part sealed and a lower part dipped in a vessel containing the lubricating oil. The unit is held in a vacuum and then is restored to atmospheric pressure. This injects the lubricating oil into the bearing unit by a change in air pressure as if the oil is drawn into the bearing unit.  
         [0032]    Instead of magnet  5 , screw  9  and a screw hole  1   a  of shaft  1  may fix jig  8  to the bearing unit, as shown in FIG. 5.  
         [0033]    Alternatively, as shown in FIG. 6, jig  8 , which is preferably made of resin, may be provided with a leg and a projection  8   a  at a tip of the leg. Projection  8   a  may be engaged in a recess  3   b  provided at an upper part of an outer peripheral surface of sleeve  3  by an elastic deformation of jig  8 . Elastic member  7  is thus pressed toward the opening of capillary seal  6 , thereby sealing seal  6 .  
         [0034]    According to this embodiment, one of the top opening and a bottom opening of the bearing unit is sealed by the jig, and only the other opening of the bearing unit is dipped into the lubricating oil. Thereby, all that is required to be cleaned is the opening into which the lubricating oil is injected. This improves cleaning operability, and reduces cost.  
         [0035]    (Exemplary Embodiment 3)  
         [0036]    Referring to FIGS.  7 - 10 , a third exemplary embodiment will be described. FIG. 7 and FIG. 9 are sectional views illustrating an essential part of a hydrodynamic bearing unit in accordance with the present embodiment. FIG. 8 and FIG. 10 are enlarged sectional views illustrating the essential parts of FIGS. 7 and 9, respectively. Elements similar to those described in the foregoing embodiments are denoted by the same reference numerals.  
         [0037]    As shown in FIG. 7 and FIG. 8, sleeve  3  of the present embodiment includes plural through-holes  3   a  arranged concentrically with respective capillary seals  6  provided at top and bottom openings of the bearing unit. Large-diameter part  2  and seal member  4  have respective corners facing through-holes  3   a,  and these corners are chamfered more than two of the other corners.  
         [0038]    As shown in FIG. 9 and FIG. 10, sleeve  3  has a corner facing capillary seal  6  for sealing lubricating oil, and this corner of sleeve  3  may be chamfered so that an opening of through-hole  3   a  of sleeve  3  may be positioned below a thrust bearing part.  
         [0039]    This enables an atmospheric pressure to be easily applied to the lubricating oil. As a result, even if the lubricating oil moves unevenly between the top and bottom openings of the bearing unit due to external shock or vibration, the oil is directed back promptly in the bearing unit. This prevents the lubricating oil from leaking.  
         [0040]    (Exemplary Embodiment 4)  
         [0041]    A fourth exemplary embodiment will be described with reference to FIG. 11. FIG. 11 is a sectional view of an essential part of a magnetic disc drive in accordance with the fourth embodiment of the present invention. Elements similar to those described in the foregoing embodiments are denoted by the same reference numerals. Shaft  1  is implanted in a base  11 , and sleeve  3  has, at its outer periphery, a substantially-cylindrical motor hub  10  fixed by engagement on the sleeve  3 . Motor hub  10  has a central hole  10   a,  and a flange  10   b  extending radially inwardly above central hole  10   a.  Flange  10   b  covers sleeve  3  and an end of second seal member  4 , and is provided with plural through-holes  10   c  reaching an end of sleeve  3 . Thus, when components are to be replaced, motor hub  10  can be detached from the bearing unit by inserting a pin into through-hole  10   c  of flange  10   b  to press the end of sleeve  3 . This facilitates the replacement of the components. In addition, flange  10   b  can seal the bearing unit.  
       INDUSTRIAL APPLICABILITY  
       [0042]    The present invention relates to a hydrodynamic bearing unit for, for example, a magnetic disc drive, and to a method of manufacturing the unit.  
         [0043]    The bearing unit can be assembled without error in a few process steps.  
         [0044]    According to the manufacturing method, only one of the end portions of the bearing unit is required to be cleaned after having the lubricating oil injected thereinto. Further, an opening of one of capillary seals can be sealed easily, and a jig can be detached easily after the injection of the lubricating oil.  
         [0045]    [0045] 1  Shaft  
         [0046]    [0046] 1   a  Screw Hole  
         [0047]    [0047] 2  First Seal Member  
         [0048]    [0048] 3  Sleeve  
         [0049]    [0049] 3   a  Through-Hole  
         [0050]    [0050] 3   b  Recess  
         [0051]    [0051] 4  Second Seal Member  
         [0052]    [0052] 5  Magnet  
         [0053]    [0053] 6  Capillary Seal  
         [0054]    [0054] 7  Elastic Body  
         [0055]    [0055] 8  Jig  
         [0056]    [0056] 8   a  Projection  
         [0057]    [0057] 9  Screw  
         [0058]    [0058] 10  Motor Hub  
         [0059]    [0059] 10   a  Center Hole  
         [0060]    [0060] 10   b  Flange  
         [0061]    [0061] 10   c  Through-Hole