PATENT ABSTRACT
A spindle motor for a hard disc drive. The spindle motor includes an oil outflow prevention part mounted at an inner side of an oil inlet, preventing oil from flowing out through the oil inlet, but allowing an outflow of air bubbles that are generated due to gasification of the oil. Accordingly, the contamination of the spindle motor due to oil that has flowed out is decreased.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Patent Application No. 2002-71965, filed Nov. 19, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a spindle motor for a hard disc drive, and particularly, to a spindle motor for a hard disc drive having an oil outflow prevention apparatus preventing outflow of oil from a fluid dynamic bearing used in the spindle motor.  
           [0004]    2. Description of the Related Art  
           [0005]    In general, a spindle motor, used in a hard disc drive, having a large capacity and a high rotational speed, utilizes a fluid dynamic bearing having less driving friction than a ball bearing for reducing noise and non-repeatable run-out (NRRO) in the hard disc drive. The fluid dynamic bearing forms an oil film between a rotating member and a fixed member, and is able to support the rotating member with pressure generated during rotation. Accordingly, the rotating member and the fixed member can be kept from direct contact, and frictional resistances can be reduced. In order to effectively generate a required pressure to form the oil film, a groove, used in generating dynamic pressure, is formed, e.g., in a spiral pattern, on the rotating member and at least one side of the fixed member.  
           [0006]    Accordingly, a radial bearing having a groove used in generating dynamic pressure is formed on a circumferential surface so that oil in bearing clearances, with respect to a sleeve, can support a load in the radial direction of the shaft with the dynamic pressure generated by the groove. Further, a thrust bearing, having grooves used in generating dynamic pressure, is formed on upper and lower surfaces of a thrust plate so that oil in bearing clearances, with respect to a shaft and a sleeve, can support a load in the axial direction of the shaft. The dynamic pressure generated by the grooves facilitates stable operations.  
           [0007]    [0007]FIG. 1 is a side, cross-sectional view of a conventional spindle motor having a radial bearing, as well as a thrust bearing, to support loads in the radial and axial directions of a shaft thereof.  
           [0008]    Referring to FIG. 1, bearing clearances are provided between a shaft  150  and a sleeve  130  of a spindle motor  100 . Grooves  131 , used in generating dynamic pressure, are formed at upper and lower sections of the inner circumferential surface of the sleeve  130 .  
           [0009]    A base  110  is positioned at a lower section of the shaft  150 , and a thrust plate  151  and a thrust flange  153  are mounted on the base  110 . Although not shown in FIG. 1, grooves (not shown) used in generating dynamic pressure between the thrust plate  151 , the thrust flange  153 , and the sleeve  130  are also provided.  
           [0010]    The bearing clearances are provided to form a path between the sleeve  130 , the outer circumferential surface of the shaft  150 , the thrust plate  151 , and the thrust flange  153 .  
           [0011]    An oil inlet  160  is provided at one side of the sleeve  130  through the outer circumferential surface to the inner circumferential surface thereof. The oil inlet  160  is also provided at the base  110  adjacent to the side of the flange  153 . Oil, provided through the oil inlet  160 , is filled into the bearing clearances to support the shaft  150 , with the pressure generated by the grooves, when the shaft  150  is rotated.  
           [0012]    In the conventional hard disc drive spindle motor, having a structure as described above, as the shaft is rotated, the oil is subject to heat generated by friction. As temperature increases, due to frictional heat generated in the bearing clearances, the air bubbles in the oil, provided into the bearing clearances, are thermally expanded. Consequently, a problem occurs in that non-repeatable run-out (NRRO) critical to driving characteristics, driving resistances, and consumption power increases. Therefore, a separate vent is formed, or the oil inlet as shown in FIG. 1, is used to eliminate the air bubbles from the bearing clearances.  
           [0013]    [0013]FIG. 2 shows a state in which the oil flows out from the conventional spindle motor shown in FIG. 1. Referring to FIG. 2, as the air bubbles flow out through the oil inlet  160 , the oil also flows out from the bearing clearances. The oil, that has flowed out, contaminates the inside of the spindle motor. Further, as the oil has flowed out, a deficiency of oil in the bearing clearances occurs. Accordingly, abrasion of frictional members is accelerated and their life cycles are reduced, or in a severe case, the spindle motor cannot be driven.  
           [0014]    In addition, fine metal particles, produced during the assembly of the frictional members, can be mixed with the oil in the bearing clearances. The metal particles can cause damage to the frictional surface of the shaft, or obstruct the driving of the motor as they flow out with the oil.  
         SUMMARY OF THE INVENTION  
         [0015]    The present invention provides a spindle motor for a hard disc drive including an oil outflow prevention apparatus preventing an outflow of oil, but allowing an outflow of air bubbles, from bearing clearances, when a shaft is rotated.  
           [0016]    A hard disc drive, spindle motor, according to an aspect of the present invention includes a base, a thrust plate mounted on the base forming bearing clearances with respect to a shaft, and supporting the shaft in the thrust direction, a sleeve accommodating the shaft forming bearing clearances between the inner circumferential surface of the sleeve and the outer circumferential surface of the shaft, and supporting the shaft in the radial direction when the shaft is rotated. The motor also includes a starter core mounted at the outer side of the sleeve, and a hub to which the shaft is fixed, having an assembly of a yoke and a magnet provided at a position corresponding the starter core to produce electromagnetic forces through interactions with the starter core. An oil inlet is at one side of the sleeve through the outer circumferential surface to the inner circumferential surface of the sleeve, and through which oil is provided into the bearing clearances. An oil outflow prevention apparatus is mounted at an inner side of the oil inlet preventing the oil from flowing out through the oil inlet, but allowing outflow of air bubbles, generated due to gasification of the oil, while the shaft is rotated.  
           [0017]    Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    These and/or other aspects and advantages of the invention will become apparent, and more readily appreciated, from the following description of the embodiments taken in conjunction with the accompanying drawings in which:  
         [0019]    [0019]FIG. 1 is a side cross-sectional view of a conventional hard disc drive spindle motor;  
         [0020]    [0020]FIG. 2 shows a state in which oil has flowed out from the conventional spindle motor shown in FIG. 1;  
         [0021]    [0021]FIG. 3 is a side, cross-sectional view of a hard disc drive, spindle motor having an oil outflow prevention apparatus according to an aspect of the present invention;  
         [0022]    [0022]FIG. 4 is an exploded perspective view of an oil outflow prevention apparatus according to an aspect of the present invention;  
         [0023]    [0023]FIG. 5 is a cross-sectional view of the oil outflow prevention apparatus taken along line V-V′ in FIG. 4; and  
         [0024]    [0024]FIG. 6 is an exploded perspective view of an oil outflow prevention apparatus according to another preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below to explain the present invention by referring to the figures.  
         [0026]    Referring to FIG. 3, a hard disc drive, spindle motor  200 , according to an aspect of the present invention, includes a base  210 , a hub  270 , and a shaft  250 . The shaft  250  is rigidly fixed to the hub  270 , and rotated in accordance with the rotation of the hub  270 . A thrust plate  251  is mounted on the base  210 , and a thrust flange  253  is mounted on the thrust plate  251 . The thrust flange  253  is rigidly fixed into the lower side of the shaft  250 .  
         [0027]    A sleeve  230  is mounted above the thrust plate  251  and the thrust flange  253 , and the shaft  250  is inserted into, and can be rotated in, the inner circumferential section of the sleeve  230 . Bearing clearances are provided at the sections where the sleeve  230 , the shaft  250 , the thrust plate  251 , and the thrust flange  253  contact each other.  
         [0028]    Although not shown in FIG. 3, grooves are provided for generating dynamic pressure, e.g., in a spiral pattern, at a surface where the thrust plate  251  and the thrust flange  253  contact each other, and at a surface where the thrust flange  253  and the sleeve  230  contact each other. The grooves generate dynamic pressure, while the shaft is rotated, so that oil fills into the bearing clearances to support the shaft  250  in the axial direction.  
         [0029]    Grooves  231  are also provided, for generating a dynamic pressure, at the upper and the lower sides of the inner circumferential section of the sleeve  230 . While the shaft  250  is rotated, the grooves  231  generate dynamic pressure so that oil fills into the bearing clearances to support the shaft  250  in the radial direction.  
         [0030]    The thrust plate  251 , the thrust flange  253  and the sleeve  230 , and the shaft  250  and the sleeve  230 , form fluid dynamic bearings, and the grooves  231  generate dynamic pressure when the shaft  250  is rotated so that oil fills into the bearing clearances to support the shaft  250  in the radial direction.  
         [0031]    A starter core  211  is mounted on the base  210 , and at the outer side of the sleeve  230 , and an assembly of a yoke  271  and a magnet  272  is provided at a position corresponding to the starter core  211  to produce electromagnetic forces through interaction with the starter core  211 .  
         [0032]    The starter core  211  and the assembly of the yoke  271  and the magnet  272  interact with each other, and produce electromagnetic forces. As the electromagnetic forces rotate the hub  270 , the shaft  250 , fixed to the hub  270 , is also rotated.  
         [0033]    An oil inlet  260  is at one side of the sleeve  230  through the outer circumferential surface to the inner circumferential surface of the sleeve  230 . Another oil inlet  260  is also provided at the other side of the sleeve  230  facing the side surface of the thrust flange  253 . Therefore, the bearing clearances are able to be filled with oil, provided from outside, through the oil inlets  260 .  
         [0034]    An oil outflow prevention apparatus  290  is installed in the oil inlets  260 . Referring to FIGS. 4 and 5, the oil outflow prevention apparatus  290  includes a locking member  291 , a filtering member  294 , and a fixing member  297 .  
         [0035]    The locking member  291  has a cylindrical shape, and a circular opening  293  is formed at the center of the locking member  291 . A flange  293   a  is provided between the outer circumference of the opening  293  and the outer circumference of the locking member  291 . A plurality of locking holes  292  are located in the flange  293   a  at predetermined intervals along the circumferential direction thereof. The locking holes  292  are cone-shaped, having tapers in the direction where the filtering member  294  and the fixing member  297  are engageable.  
         [0036]    The filtering member  294  has a cylindrical shape, and a circular opening  296  is at the center of the filtering member  294 . A flange  296   a  is provided between the outer circumference of the opening  296  and the outer circumference of the filtering member  294 . A plurality of perforations  295  are located in the flange  296   a  at predetermined intervals along the circumferential direction thereof. According to an aspect of the invention, a membrane is mounted at the opening  296 . The membrane passes air bubbles, but not oil. Therefore, during the rotation of the shaft  250 , the outflow of the oil, filled in the bearings of the spindle motor, through the membrane can be prevented, while the air bubbles can flow out through the membrane.  
         [0037]    The fixing member  297  has a cylindrical shape, and a circular opening  299  at the center of the fixing member  297 . A flange  299   a  is provided between the outer circumference of the opening  299  and the outer circumference of the fixing member  297 . A plurality of protrusions  298  are located on the flange  299   a  at predetermined intervals along the circumferential direction thereof. The protrusions  298  are cone-shaped having tapers, and insertable into the locking holes  292 .  
         [0038]    When the locking member  291 , the filtering member  294 , and the fixing member  297  are assembled, the protrusions  298  are inserted into the locking holes  292  through the perforations  295 . The oil outflow prevention apparatus  290  assembly as described above is engageable with a projected hooking member  261  formed at the inner side of the oil inlet  260 . While a pair of hooking members  261 , symmetrically formed and placed are shown in FIG. 4, a varied number of hooking members  261  can be formed along the inner circumferential direction.  
         [0039]    Referring to FIG. 6, an oil outflow prevention apparatus according to an aspect of the present invention is shown including a membrane  391 , attached at the entrance of the oil inlet  260  using adhesives. For attaching the membrane  391  at the entrance of the oil inlet  260 , adhesives can be applied either to the edge of the membrane  391  or to the border of the entrance, or a double-sided adhesive tape can be used.  
         [0040]    It is noted that the oil can be provided, through the oil inlet  260  into the bearing clearances, by making the bearing clearances vacuous with a predetermined device, or tool, and using a pressure difference. Thereafter, the oil outflow prevention apparatus  290  is installed in the oil inlet  260  to prevent outflow of the oil, through the oil inlet  260 , when the shaft  250  is rotated.  
         [0041]    As described above, in a hard disc drive, spindle motor according to an aspect of the present invention, the membrane installed in the entrance of the oil inlet can prevent outflow of oil from bearing clearances while allowing the outflow of air bubbles generated when a shaft is rotated, and therefore, the contamination of the spindle motor due to an outflow of oil can be effectively prevented.  
         [0042]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.