Abstract:
The bearing of the present invention comprises a hub  110  for driving recording media; a sleeve  120  for rotatably support the hub  110  to define a hydrodynamic pressure generating space  110   a  between the hub  110  and the sleeve  120 , the sleeve  120  being formed with a fluid outlet  125   b  through which the fluid passes at the predetermined position; a plurality of recesses  125   a  for generating hydrodynamic pressure, the recesses  125  being formed on at least one of the hub  110  and the sleeve  120  to be opened toward the hydrodynamic pressure generating space  110   a ; and a fluid circulating member  130  for circulating the fluid out-flowing from the fluid outlet  125   b  to the hydrodynamic pressure generating space  110   a , the member  130  being fixedly combined with the hub  110  to slidably support the sleeve  120.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a hydrodynamic pressure bearing, and more particularly, to a hydrodynamic pressure bearing enabling to repeatedly circulate fluid for generating hydrodynamic pressure therein.  
         [0003]     2. Description of the Related Art  
         [0004]     A hydrodynamic pressure bearing serves to generate the driving force of a spindle motor being installed in a hard disk driver and the like. One of examples, Japanese Patent Registration No. 2,937,833 discloses  ┌ Bearing seal system ┘ , which is illustrated with reference to  FIGS. 3 and 4 .  
         [0005]     As shown, the bearing seal system is composed of a shaft  31  and a radial bearing section  24 .  
         [0006]     The radial bearing section  24  is arranged on the shaft-orientations outside, and provided with a clearance change section  50  for preventing leakage of the oil  15  present between the bearing section  24  and the shaft  21 . Also, an oil surface section  15   a  of the oil  15  filled up the cylinder-like bag part  40  is set up to be located in the clearance change section  50 .  
         [0007]     The clearance change section  50  has a clearance change circles edge  50   a  set as the shaft-orientations most inner edge by the side of the radial bearing  24  and a clearance change section outer edge  50   b  set as the outermost edge of the clearance change section  50 . The clearance change circles edge  50   a  is smallest and the clearance change section outer edge  50   b  is largest, and also a clearance tilt angle α is made therebetween.  
         [0008]     Although the inner capacity of the bag part  40  is not constant during manufacturing or injection of the oil  15 , the inner capacity of the bag part  40  is changed by the rise of the shaft  31  or heat due to the rotation of the shaft  31 , or the change of the amount of the oil  15  due to the inner mixed air is raised, the constant amount of oil  15  will always be kept in the bearing section  24  without leakage since the inner capacity of the clearance change section  50  is relatively greater than the inner capacity of the bag part  40  or radial bearing section  24 .  
         [0009]     However, the sealing system described above has a drawback that may not keep the oil in the bag part  40  and then raise oil leakage if variation of conditions such as viscosity of oil or heat generated by the rotation of the shaft and the like exceeds the design criteria thereof.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, the present invention is directed to a Fluid circulation type hydrodynamic pressure bearing that substantially obviates one or more problems due to limitations and disadvantages of the related art.  
         [0011]     One object of the present invention is to provide a hydrodynamic pressure bearing enabling to prevent an outward leakage of the fluid regardless of the change of the surrounding condition by repeatedly circulating the fluid in the bearing through a fluid circulating member.  
         [0012]     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a vibration motor comprises: a driving member for driving writing medium; a supporting member for rotatably supporting the driving member to have a hydrodynamic pressure generating space formed between the supporting member and the driving member, the supporting member being formed with a fluid outlet through which the fluid passes; a plurality of recesses for generating hydrodynamic pressure, the recesses being formed on at least one of the driving member and the supporting member to be open toward the hydrodynamic pressure generating space; a fluid circulating member for circulating the fluid passed through the fluid outlet, the fluid circulating member being fixedly combined with the driving member to slidably support the supporting member.  
         [0013]     The supporting member may have a shaft combining portion with which the driving member is axially combined and a hydrodynamic pressure generating portion for generating hydrodynamic pressure, also the fluid outlet may be formed to be open from the hydrodynamic pressure generating portion toward the fluid circulating member. Further, the fluid circulating member may have a fluid keeping space for keeping the fluid passed through the fluid outlet during a predetermined time and a fluid sending hole for sending the fluid kept in the fluid keeping space to the hydrodynamic pressure generating space. Wherein, the fluid keeping space may be formed to have a wedge shape section in which a portion open toward the fluid outlet is smaller than a portion open toward the fluid sending hole. At this time, the fluid kept in the fluid keeping space is sent to the fluid sending hole by the capillary action, and the fluid keeping space may be formed to have 0°˜90° of upper surface thereof.  
         [0014]     Further, the fluid sending hole may be formed to pass through the upper and lower surfaces of the fluid circulating member.  
         [0015]     In the present invention, when the driving member is driven, the fluid kept in the fluid keeping space is applied with centrifugal force and it is sent to the fluid sending hole by centrifugal force.  
         [0016]     It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]     The accompanying drawings, which are included to provide a further understanding of the invention are incorporated and constitute as a part of this application, illustrate embodiment(s) of the invention and together with the descriptions serve to explain the principle of the invention. In the drawings:  
         [0018]      FIG. 1  is a cross sectional view schematically illustrating a hydrodynamic pressure bearing according to the preferred embodiment of the present invention;  
         [0019]      FIG. 2  is a partial enlarged view illustrating a stopper and sealing cap of  FIG. 1 ;  
         [0020]      FIG. 3  is a cross sectional view schematically illustrating a conventional bearing seal system; and  
         [0021]      FIG. 4  is a partial enlarged view of  FIG. 3 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.  
         [0023]     As shown in  FIG. 1 , a hydrodynamic pressure bearing  100  according to a preferred embodiment of the present invention comprises a hub  110 , a sleeve  120  and a fluid circulating member  130 .  
         [0024]     The hub  110  serves to mount recording media (not shown) such as a hard-disk thereon and rotate it, and it has an annular hydrodynamic pressure generating space  110   a  being formed in central portion thereof. Also, the hub  110  has an shaft portion  111  and a rim portion  115  formed on the inside and outside respectively with respect to the hydrodynamic pressure generating space  110   a.    
         [0025]     The shaft portion  111  is integrally extended from an inner central portion of the hub  110 , and an end portion thereof is tapered to be easily rotated.  
         [0026]     The rim portion  115  is integrally extended from a shaft portion  111  of the hub  110 , and an end portion thereof is extended to be longer than the end portion of the shaft portion  111 .  
         [0027]     The sleeve  120  serves to rotatably support the hub  110 , and it has a shaft combining portion  121  and a hydrodynamic pressure generating portion  125  formed on the central portion and both rim thereof, respectively.  
         [0028]     The shaft combining portion  121  has an upper portion formed with a shaft combining recess  121   a  thereon, into which the shaft portion  111  is inserted, and a lower portion being downwardly extended and fixedly combined with the base  140  of the spindle motor (not shown).  
         [0029]     The hydrodynamic pressure generating portion  125  is integrally formed with the shaft combining portion  121 , and it is inserted into the hydrodynamic pressure generating space  110   a  formed in the hub  110 . Wherein, the hydrodynamic pressure generating portion  125  has an annular shape corresponding to the space  110   a  so as to be inserted into the space  110   a  in closely contact.  
         [0030]     Also, the hydrodynamic pressure generating portion  125  has a plurality of hydrodynamic pressure generating recesses  125   a  with a predetermined shape formed on an upper surface, an outer periphery surface and a lower surface, respectively, and the fluid outlet  125   b  slantingly formed on a portion connected with the shaft combining portion  121 .  
         [0031]     In this embodiment, the fluid outlet  125   b  is formed slantingly, but alternately, it may be formed in certain structures, which the fluid well flows out, and the fluid outlet  125   b  may be disposed not in the fluid circulating member  130  but on the lower hydrodynamic pressure surface of the sleeve  120 , between the lower hydrodynamic pressure surface and the side surface of the sleeve  120 , or to connect with the side surface of the sleeve  120 .  
         [0032]     Also, in this embodiment, the hydrodynamic pressure generating recesses  125   a  is formed in the sleeve  120 , alternately, the recesses  125   a  may be formed on an inner periphery surface of the hub  110  face to the corresponding portion of the sleeve  120  or, alternately they may be formed on both the sleeve  120  and the inner periphery surface of the hub  110  in turn.  
         [0033]     The fluid circulating member  130  serves to repeatedly re-circulate the fluid flowing out through the fluid outlet  125   b  formed in the sleeve  120  toward the hydrodynamic pressure generating space  110   a . Also, the member  130  has a stopper  131  not only supporting the sleeve  120 , particularly the hydrodynamic pressure generating portion  125  but also providing the hydrodynamic pressure generating space  110   a , and a sealing cap  135  sealing a lower surface of the stopper  135  so as to prevent outward leakage of the fluid.  
         [0034]     The stopper  131  has an annular shape, and a first hub combining portion  132  and a sleeve supporting portion  133  integrally formed with each other.  
         [0035]     The first hub combining portion  132  is fixedly combined with an inner periphery surface of the rim portion  115  of the hub  110 , thereby the stopper  131  being rotated together with the hub  110 .  
         [0036]     The sleeve supporting-portion  133  is extended from the first hub combining portion  131  and has a portion of the lower surface slantingly formed from a free end thereof. The slope formed on the sleeve supporting portion  133  may range from 0° to 90°.  
         [0037]     Also, the sleeve supporting portion  133  has the free end disposed adjacent to a slant portion of the shaft combining portion  121  of the sleeve  120 , and a fluid sending hole  131  formed on a portion adjacent to the first hub combining part  131  to pass through the stopper  131  up and down.  
         [0038]     The sealing cap  135  has an annular shape, and a second hub combining portion  136  and a fluid keeping portion  137 .  
         [0039]     The second hub combining portion  136  is fixedly combined with an inner periphery surface of the rim portion  115  of the hub  110 , thereby the sealing cap  135  being rotated together with the hub  110 . Wherein, the second hub combining portion  136  is also fixedly combined with a lower surface of the first hub combing portion  132  of the stopper  131 .  
         [0040]     The fluid keeping portion  137  is located below the sleeve supporting portion  133  of the stopper  131 , and it has a free end disposed adjacent to the slanting portion of the shaft combining part  121  of the sleeve  120 . Wherein, between the supporting portion  133  and the keeping portion  137 , is made with a fluid keeping space  130   a  illustrated in wedge shape in the drawings. Further, wherein, the fluid keeping space  130   a  has an angle of the upper surface thereof ranging from 0° to 90° since the sleeve supporting portion  133  of the stopper  131  has the slanting surface ranging from 0° to 90°.  
         [0041]     Next, with reference to  FIG. 2 , the process of circulating the fluid in the hydrodynamic pressure bearing  100  of  FIG. 1  will be explained in detail.  
         [0042]     The fluid  150  is injected into the hydrodynamic pressure generating space  110   a  provided between the hub  110  and the sleeve  120  at the time of manufacturing of the hydrodynamic pressure bearing  100  or of injecting of additional fluid. At this time, the fluid  150  is injected through a portion indicated by “A” or “B” portion, and air or bubble in the space  110   a  flows out through the “B” or “A” portion during the injection of the fluid  150 .  
         [0043]     First, once the hub  110  begins to rotate under a condition of the hydrodynamic pressure generating space  110   a  filled with the fluid  150 , the fluid  150  flows into the sleeve  120 , particularly the central portion (changeable depending on the design criteria) of the hydrodynamic pressure generating portion  125  along the hydrodynamic pressure generating recess  125   a.    
         [0044]     Thereafter, while the flow of the fluid is accelerated, the hydrodynamic pressure is generated between the hub  110  and the sleeve  120 , that is, in the hydrodynamic pressure generating space  110   a  where the hub  110  and the sleeve  120  set opposite each other, and thereby the hub  110  being raised from the sleeve  120  and rotated under that state.  
         [0045]     Next, while the certain time lapses away, the fluid  150  is gradually heated by the frictional heat caused by the rotation of the hub  110  and then expanded, a portion of the expanded fluid  150  flows out through the fluid outlet  125   b  formed in the sleeve  120 .  
         [0046]     The out fluid  150  on this wise is kept by the fluid circulating member  130 , particularly the stopper  131  until it reaches a designed amount, and if it exceeds the designed amount, it flows to the fluid keeping space  130   a  provided between the stopper  131  and the sealing cap  135 .  
         [0047]     Next, when centrifugal force is generated in the stopper  131  and sealing cap  135  rotating together with the hub  110  by the rotating force of the hub  110 , it is applied to the fluid  150  kept in the fluid keeping space  130   a  having wedge shape.  
         [0048]     At this time, the fluid applied with centrifugal force gradually flows into the fluid keeping space  130   a , that is into a portion where an area becomes narrower in wedge shape, and the pressure P 1  at that portion becomes greater than the pressure P 2  between the hydrodynamic pressure generating space  110   a  and the stopper  131 , and thereby the fluid  150  flowing from down to up along the fluid sending hole  131   a  and finally flowing into the hydrodynamic pressure generating space  110   a . At this time, the fluid  150  is also applied with capillary force due to the wedge shape of the fluid keeping space  130   a , and this force helps the fluid  150  to flow into the hydrodynamic pressure generating space  110   a . Like this way, the fluid  150  can be circulated in arrow direction by centrifugal force and capillary force.  
         [0049]     According to the hydrodynamic pressure bearing of the present invention, even though exterior conditions such as viscosity of fluid or heat caused by the rotation of the shaft etc. exceed the design range thereof, fluid may be kept in the bearing without outflow since the fluid present in the hydrodynamic pressure generating space provided in the bearing is repeatedly circulated.  
         [0050]     It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.