Abstract:
There is provided a spindle motor including: a sleeve forming a dynamic pressure generation space with a shaft; a hub including a main wall portion surrounding a circumference of the sleeve; and a cover disposed between the sleeve and the hub, wherein the sleeve and the cover have a storage unit formed therebetween, the storage unit storing a lubricating fluid.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of Korean Patent Application No. 10-2011-0140128 filed on Dec. 22, 2011, 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 and, more particularly, to a spindle motor able to minimize shortage of a lubricating fluid. 
         [0004]    2. Description of the Related Art 
         [0005]    A hard disk drive (HDD) includes a disk driving device, e.g., a small spindle motor, for driving a disk. 
         [0006]    A small spindle motor has a hydrodynamic bearing structure so as to be reduced in size. In a hydrodynamic bearing structure, a fluid (i.e., a lubricating fluid) provided between a shaft, a rotating member, and a sleeve, a fixed member, serves as a bearing in a mechanical structure. 
         [0007]    However, since the spindle motor rotates at high speed, the lubricating fluid provided between the shaft and the sleeve may be evaporated by a large amount of heat or may be leaked between the sleeve and a thrust plate. 
         [0008]    Thus, development of a spindle motor in which evaporation of a lubricating fluid due to high speed rotation of the spindle motor and leakage of the lubricating fluid are minimized is required. 
         [0009]    Meanwhile, Patent Documents 1 and 2 disclose a structure for storing a lubricating fluid. However, Patent Documents 1 and 2 have a structure in which a storage space of a lubricating fluid is open to the outside, lacking the capability to effectively prevent evaporation of a lubricating fluid. 
       RELATED ART DOCUMENT 
       [0010]    (Patent Document 1) KR2007-103903 A 
         [0011]    (Patent Document 2) JP2006-161988 A 
       SUMMARY OF THE INVENTION 
       [0012]    An aspect of the present invention provides a spindle motor able to minimize evaporation and leakage of a lubricating fluid. 
         [0013]    According to an aspect of the present invention, there is provided a spindle motor including: a sleeve forming a dynamic pressure generation space with a shaft; a hub including a main wall portion surrounding the circumference of the sleeve; and a cover disposed between the sleeve and the hub, wherein the sleeve and the cover have a storage unit formed therebetween, the storage unit storing a lubricating fluid. 
         [0014]    The sleeve may include a flow channel allowing the lubricating fluid to circulate therethrough. 
         [0015]    The cover may have a recess connecting the flow channel and the dynamic pressure generation space. 
         [0016]    The storage unit may be formed in the cover. 
         [0017]    The storage unit may be formed in the sleeve. 
         [0018]    The cover and the hub may have a flow space formed therebetween to allow the lubricating fluid to move therein. 
         [0019]    The cover may have a dynamic pressure groove formed in a surface thereof facing the hub. 
         [0020]    The cover may be formed of a porous material. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0022]      FIG. 1  is a cross-sectional view of a spindle motor according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is a cross-sectional view of a spindle motor according to a second embodiment of the present invention; 
           [0024]      FIG. 3  is a cross-sectional view of a spindle motor according to a third embodiment of the present invention; and 
           [0025]      FIG. 4  is a bottom perspective view of a cover illustrated in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0026]    As a storage capacity of hard disk drives (HDD) has increased, a spindle motor able to rotate at high speeds has come to be required. 
         [0027]    Namely, an existing spindle motor has a rotational speed of about 5400 rpm, requiring a relatively long time to write data to a large capacity HDD or read data stored on a large capacity HDD. 
         [0028]    Thus, a spindle motor having a rotational speed of 7200 rpm or greater has been developed. However, in the case of the spindle motor having a high rotational speed, a lubricating fluid may be easily evaporated by heat generated during the high speed rotation, whereby durability of the spindle motor may be degraded. 
         [0029]    In order to solve such a problem, the present invention may provide a spindle motor having a lubricating fluid storage space to minimize evaporation of the lubricating fluid due to high speed rotation. 
         [0030]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. 
         [0031]    In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements. 
         [0032]      FIG. 1  is a cross-sectional view of a spindle motor according to a first embodiment of the present invention.  FIG. 2  is a cross-sectional view of a spindle motor according to a second embodiment of the present invention.  FIG. 3  is a cross-sectional view of a spindle motor according to a third embodiment of the present invention.  FIG. 4  is a bottom perspective view of a cover illustrated in  FIG. 3 . 
         [0033]    A spindle motor according to a first embodiment of the present invention will be described with reference to  FIG. 1 . 
         [0034]    A spindle motor  100  according to the first embodiment of the present invention may include a base member  110 , an electromagnet  120 , a sleeve  130 , a shaft  140 , a hub  150 , a permanent magnet  160 , and a cover  170 . A storage unit  240  storing a lubricating fluid  200  may be formed between the sleeve  130  and the cover  170 . 
         [0035]    The base member  110  may be a member firmly fixed to a body of a hard disk drive device so as not to be moved. Thus, the base member  110  may be a body or a portion of the hard disk drive device. The base member  110  may be formed of a metal (e.g., an aluminum alloy, or the like). The base member  110  may have an installation hole allowing the sleeve  130  to be installed therein. 
         [0036]    The installation hole may have the same diameter as that of an outer diameter of the sleeve  130  or may have a diameter having a difference within a certain tolerance range. An first main wall portion  114  may be upwardly protruded from the edge of the installation hole in order to stably support the circumference of the sleeve  130 . A plurality of electromagnets  120  may be installed on the first main wall portion  114 . 
         [0037]    The electromagnet  120  may be disposed in a circular manner based on the installation hole, and may generate electromagnetic force upon receiving a current from the outside. To this end, the electromagnet  120  may include a core and a coil. 
         [0038]    The sleeve  130  may be installed in the base member  110 . The sleeve  130  may be firmly fixed to the base member  110  in a press-fitting manner, and may be fixedly bonded thereto using an adhesive, or the like, as necessary. The sleeve  130  may have a through hole accommodating the shaft  140 . Here, the diameter of the through hole may be greater than an outer diameter of the shaft  140 . 
         [0039]    A dynamic pressure generation space  210 , provided with the lubricating fluid  200 , may be formed between an inner surface of the sleeve  130  and an outer surface of the shaft  140 . In detail, although not shown, fluid dynamic pressure grooves in the form of the teeth of a comb may be formed in the sleeve  130  or the shaft  140  to generate dynamic pressure when the shaft  140  is rotated. 
         [0040]    The fluid dynamic pressure grooves may have any shape among a herringbone shape, a spiral shape, and a helical shape, and may have any shape as long as they generate dynamic pressure. 
         [0041]    The shaft  140  may be rotatably installed in the sleeve  130 . The shaft  140  may be installed to penetrate the sleeve  130  and have an extended portion extending outwardly (i.e., upwardly based on  FIG. 1 ) of the sleeve  130 . The extended portion may have the same area as that of the shaft  140 , or may have a different area thereto, as in the present embodiment. 
         [0042]    The hub  150  may be coupled to the shaft  140 . In detail, the hub  150  may be coupled to the extended portion  142  of the shaft  140  and may be rotated together with the shaft  140 . For reference, a shaft coupling hole  152  into which the shaft  140  is inserted may be formed in the hub  150 . 
         [0043]    The hub  150  may have a second main wall portion  154  and a third main wall portion  156 . 
         [0044]    The second main wall portion  154  may be formed to extend downwardly in the vicinity of the sleeve  130  of the hub  150 . The downwardly extending second main wall portion  154  may surround the circumference of the sleeve  130 . The second main wall portion  154  may restrain a fluid from being leaked to the outside of the sleeve  130 . 
         [0045]    A flow space  230  through which the lubricating fluid  200  passes may be formed between the second main wall portion  154  and the sleeve  130 . In detail, a space between the second main wall portion  154  and the sleeve  130  may be connected to the dynamic pressure generation space  210  between the sleeve  130  and the shaft  140  and provided with the lubricating fluid  200 . The lubricating fluid provided in the space may be provided to the dynamic pressure generation space  210  so that a shortage of the lubricating fluid may not exist in the dynamic pressure generation space  210 . 
         [0046]    The third main wall portion  156  may extend downwardly from the edge of the hub  150 . The downwardly extending third main wall portion  156  may surround the outside of the electromagnet  120 . 
         [0047]    The permanent magnet  160  may be installed on the third main wall portion  156 . In detail, the permanent magnet  160  may be disposed on the third main wall portion  156  such that it faces the electromagnet  120  disposed on the first main wall portion  114 . The permanent magnet  160  generates electromagnetic force equivalent to that of the electromagnet  140 . Thus, the electromagnet  120  and the permanent magnet  160  may form a magnetic field having a certain magnitude to allow the shaft  140  and the hub  150  to be rotated. 
         [0048]    A plurality of disks may be installed on the third main wall portion  156 . Here, the disks may be members for writing and magnetic information to the HDD and reading information therefrom. 
         [0049]    The cover  170  may be disposed between the sleeve  130  and the hub  150 . 
         [0050]    The cover  170  may be formed of a porous material or may be fabricated through a sintering method such that the cover  170  may have a plurality of pores formed therein. The cover  170  may absorb a lubricating fluid therein, so that the cover  170  itself may be used as a lubricating fluid storage space. 
         [0051]    The cover  170  may have a step  174 . The step  174  may be formed in a lower surface of the cover  170  (i.e., a surface facing the sleeve  130 ), and may be formed to extend in a circumferential direction of the cover  170 . 
         [0052]    The step  174  may form the storage unit  240  storing the lubricating fluid between the lower surface of the cover  170  and the upper surface of the sleeve  130 . 
         [0053]    The cover  170  may have a dynamic pressure groove. In detail, a fluid dynamic pressure groove may be formed in a surface of the cover  170  facing the hub  150 . With this structure, physical contact between the hub  150  and the cover  170  is minimized, whereby abrasion of the cover  170  may be prevented. 
         [0054]    The spindle motor  100  configured as described above may further include the lubricating fluid storage unit formed between the sleeve  130 , the cover  170 , and the second main wall portion  154 , and thus, the shortage of the lubricating fluid due to high speed rotation of the spindle motor may be minimized. 
         [0055]    Other embodiments of the present invention will be described with reference to  FIGS. 2 through 4 . 
         [0056]    The spindle motor  100  according to the second embodiment of the present invention may be differentiated from that of the first embodiment, in that a step  132  is formed in the sleeve  130 . 
         [0057]    In the present embodiment, the lubricating fluid storage unit  240  may be formed in the sleeve  130 . In detail, the lubricating fluid storage unit  240  may be formed in the step  132  of the sleeve  130  and the lower surface of the cover  170 . 
         [0058]    In the spindle motor  100  configured as described above, since the lubricating fluid storage unit  240  is formed by processing the relatively thick sleeve  130 , the lubricating fluid storage unit  240  can be easily formed and can easily extend. 
         [0059]    The spindle motor  100  according to the third embodiment of the present invention may be differentiated from the foregoing embodiments, in that a flow channel  220  is formed in the sleeve  130 . 
         [0060]    Also, the spindle motor  100  according to the third embodiment of the present invention may be differentiated from the foregoing embodiments, in that a recess  172  is formed in the cover  170 . 
         [0061]    The sleeve  130  may have the flow channel  220  connected to the dynamic pressure generation space  210 . The flow channel  220  may be formed to penetrate the sleeve  130  in a vertical direction and may be connected to the dynamic pressure generation space  210  and the recess  172  of the cover  170 . 
         [0062]    The flow channel  220  may allow the lubricating fluid  200  to circulate such that the dynamic pressure generation space  210  is filled with a predetermined amount of lubricating fluid  200 . 
         [0063]    The cover  170  may have the recess  172  and the step  174 . In detail, as shown in  FIG. 4 , the recess  172  and the step  174  may be formed in the lower surface of the cover  170 . 
         [0064]    The recess  172  may be connected to the flow channel  220 , and may be connected to the flow space  230  between the hub  150  and the cover  170  as necessary. 
         [0065]    The recess  172  may allow the lubricating fluid  200  provided in the dynamic pressure generation space  210  and the flow channel  220  to circulate smoothly, and the step  174  may form the lubricating fluid storage unit  240  between the cover  170  and the sleeve  130 . 
         [0066]    The spindle motor  100  configured as described above has a structure in which the lubricating fluid  200  circulates through the dynamic pressure generation space  210 , the flow channel  200  and the flow space  230 , and thus, heat generated when the spindle motor  100  is rotated may be naturally dissipated to the outside in the circulation process of the lubricating fluid  200 . 
         [0067]    In addition, since the present embodiment has the structure preventing a shortage of the lubricating fluid due to the lubricating fluid of the storage unit  240 , insufficiency of the lubricating fluid due to high speed rotation of the spindle motor  100  can be minimized. 
         [0068]    As set forth above, according to embodiments of the invention, since a relatively large lubricating fluid storage space is provided, a degradation in the performance of the spindle motor due to evaporation of a lubricating fluid can be minimized. 
         [0069]    While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.