Patent Publication Number: US-2012043842-A1

Title: Hydrodynamic bearing assembly and motor including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2010-0079475 filed on Aug.17, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a hydrodynamic bearing assembly and a motor including the same, and more particularly, to a hydrodynamic bearing assembly allowing for increased stability by improving an unmating force and a motor including the same. 
     2. Description of the Related Art 
     An information storage device, a hard disk drive (HDD) uses a read/write head to write data to, or read data from a disk. 
     The hard disk drive requires a disk driving device capable of driving a disk, and, as the disk driving device, a small-sized spindle motor is used. 
     The small-sized spindle motor uses a hydrodynamic bearing assembly and a lubricating fluid is interposed between a shaft and a sleeve of the hydrodynamic bearing assembly to support the shaft by fluid pressure generated from the lubricating fluid. 
     Further, a bottom end of the sleeve is coupled with a base cover in such a manner as to have a gap therebetween, in order to receive the lubricating fluid. As a method of fixing the base cover to the sleeve, various methods such as welding, caulking, bonding, or the like, may be used, which may be optionally applied according to a structure and a process of a product. 
     However, a welding method is advantageous in shortening working time and improving sealability, but may change a dimension of the sleeve due to tension of the sleeve and the base cover after welding, in view of the process characteristics of the welding, thereby causing characteristic defects. 
     Further, a bonding method has an unmating force smaller than the welding method, such that a bond layer may be broken when a mechanical impact or thermal impact is applied, and, as a result, may cause a fatal flaw in performance. 
     In addition, a caulking method requires a separate structure for caulking, such that the process thereof is complicated. 
     Therefore, research into a hydrodynamic bearing assembly capable of withstanding external impacts by improving an unmating force while having a simplified process and a motor including the hydrodynamic bearing assembly is urgently needed. 
     SUMMARY OF THE INVENTION 
     An object of the present invention provides a hydrodynamic bearing assembly allowing for an increased unmating force in a hydrodynamic bearing and sufficiently withstanding a high-speed rotation of a motor and external impacts by changing a structure of a base cover, and a motor including the same. 
     According to an exemplary embodiment of the present invention, there is provided a hydrodynamic bearing assembly including a sleeve supporting a shaft to allow a top portion of the shaft to be protruded upwardly in an axial direction and including a coupling part of which a bottom end is protrusively formed; a base cover coupled with a bottom of the sleeve in the axial direction while maintaining a gap therebetween; and a support part formed at an outer end portion of the base cover and formed to be protruded in the axial direction such that an outer peripheral surface thereof is in contact with and coupled to an inner peripheral surface of the coupling part of the sleeve. 
     The support part may be formed to be protruded upwardly or downwardly in the axial direction along the inner peripheral surface of the coupling part. 
     The support part may be protruded upwardly and downwardly in the axial direction along the inner peripheral surface of the coupling part. 
     The coupling part may be provided with an insertion groove concavely formed along the inner peripheral surface to allow the support part to be inserted thereinto. 
     The insertion groove of the coupling part may be concavely formed to have a shape corresponding to the support part. 
     According to another exemplary embodiment of the present invention, there is provided a motor including: a hydrodynamic bearing assembly including a sleeve supporting a shaft to allow a top portion of the shaft to be protruded upwardly in an axial direction and including a coupling part of which a bottom end is protrusively formed, a base cover coupled with a bottom of the sleeve in the axial direction while maintaining a gap therebetween, and a support part formed at an outer end portion of the base cover and formed to be protruded in the axial direction such that an outer peripheral surface thereof is in contact with and coupled to an inner peripheral surface of the coupling part of the sleeve; a stator including a core coupled with an outer peripheral surface of the sleeve and having a coil wound therearound for generating a rotational driving force; and a rotor having a magnet mounted on a surface thereof, the magnet facing the wound coil in order to be rotated with respect to the stator. 
     The support part maybe formed to be protruded upwardly and downwardly, or upwardly or downwardly in the axial direction along the inner peripheral surface of the coupling part. 
     The coupling part may be provided with an insertion groove that is concavely formed along the inner peripheral surface to allow the support part to be inserted thereinto. 
     The insertion groove of the coupling part may be concavely formed to have a shape corresponding to the support part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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: 
         FIG. 1  is a schematic cross-sectional view of a motor according to an exemplary embodiment of the present invention; 
         FIG. 2  is a schematic cross-sectional view of a motor according to another exemplary embodiment of the present invention; 
         FIG. 3  is a schematic cross-sectional view of a hydrodynamic bearing assembly provided in the motor according to the exemplary embodiment of the present invention; 
         FIGS. 4 through 7  are schematic cross-sectional views of other examples of section A shown in  FIG. 3 ; and 
         FIG. 8  is a schematic cross-sectional view of a recording disk driving device having the motor mounted thereon according to the exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. While those skilled in the art could readily devise many other varied embodiments that incorporate the teachings of the present invention through the addition, modification or deletion of elements, such embodiments may fall within the scope of the present invention. 
     The same or equivalent elements are referred to by the same reference numerals throughout the specification. 
       FIG. 1  is a schematic cross-sectional view of a motor according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , a motor  400  according to an exemplary embodiment of the present invention may include a hydrodynamic bearing assembly  100 , a stator  200 , and a rotor  300 . 
     The hydrodynamic bearing assembly  100  may include a shaft  110 , a sleeve  120 , a thrust plate  130 , a cap member  140 , and a base cover  150 . 
     First, in defining terms regarding directions, when viewed in  FIGS. 1 and 2 , an axial direction refers to a vertical direction based on the shaft  110 . An outer-diameter direction refers to an outer edge direction of the rotor  300  based on the shaft  110  and an inner diameter direction refers to a central direction of the shaft  110  based on an outer edge of the rotor  300 . 
     The sleeve  120  may support the shaft  110  such that a top portion of the shaft  110  is protruded upwardly in an axial direction and may include a coupling part  125  of which a bottom end is protrusively formed. 
     The coupling part  125  has a configuration in which it is coupled to and in contact with a support part  155  of the base cover  150  to be described below, which will be described in detail with reference to  FIGS. 3 through 7 . 
     The sleeve  120  may be formed by forging Cu or Al or sintering a Cu—Fe-based alloy powder or a SUS-based powder. 
     In this case, the shaft  110  is inserted into a shaft hole  122  of the sleeve  120  to have a micro gap therebetween, the micro gap being filled with a lubricating fluid, and the rotation of the rotor  300  may be more smoothly supported by a radial dynamic groove provided on at least one of an outer diameter of the shaft  110  and an inner diameter of the sleeve  120 . 
     The radial dynamic groove is formed in an inner side the sleeve  120 , that is, an inner portion of the shaft hole  122  of the sleeve  120  and forms a pressure deflected to one side at the time of the rotating of the shaft  110 . 
     However, as described above, it is to be noted that the radial dynamic groove is not necessarily provided at the inner side of the sleeve  120  and may be provided in an outer-diameter portion of the shaft  110  and the number of radial dynamic grooves is not limited. 
     The sleeve  120  is provided with a bypass channel  124  formed to allow the top and the bottom of the sleeve  120  to be in communication with each other, thereby dispersing and balancing the pressure of the lubricating fluid in the hydrodynamic bearing assembly  100  and moving the lubricating fluid in order to discharge bubbles, or the like, present in the hydrodynamic bearing assembly  100  through circulation. 
     In this case, the bottom of the sleeve  120  in the axial direction may be provided with the base cover  150  that is coupled with the sleeve  120  while maintaining a gap therebetween, the gap receiving the lubricating fluid. 
     The base cover  150  may serve as a bearing supporting the bottom surface of the shaft  110 , as the base cover  150  receives the lubricating fluid in the gap between the base cover  150  and the sleeve  120 . 
     In addition, the base cover  150  may include the support part  155  that is formed at an outer end portion thereof, may be formed to be protruded in an axial direction, and may have an outer peripheral surface coupled with an inner peripheral surface of the coupling part  125  of the sleeve  120 . The coupling structure of the support part  155  and the coupling part  125  will be described in detail with reference to  FIGS. 3 through 7 . 
     The thrust plate  130  includes a hole that is disposed upwardly of the sleeve  120  in an axial direction and corresponds to a cross section of the shaft  110  at the center thereof, such that the shaft  110  may be inserted into the hole. 
     In this case, the thrust plate  130  is separately manufactured and may be coupled with the shaft  110 ; it may be integrally formed with the shaft  110  at the time of the manufacturing thereof and is rotated along the shaft  110  at the time of the rotation movement of the shaft  110 . 
     In addition, the top surface of the thrust plate  130  may be provided with a thrust dynamic groove that provides a thrust dynamic pressure to the shaft  110 . 
     As described above, the thrust dynamic groove is not necessarily formed on the top surface of the thrust plate  130  and may also be formed on the inner peripheral surface of the cap member  140  corresponding to the top surface of the thrust plate  130 , which will be described below, or the top surface of the sleeve  120  corresponding to the bottom surface of the thrust plate  130 . 
     The cap member  140  is a member that is press-fitted in the top portion of the thrust plate  130  to seal the lubricating fluid between the cap member  140  and the thrust plate  130 , and a circumferential groove is formed in an outer-diameter direction such that the cap member  140  is press-fitted in the thrust plate  130  and the sleeve  120 . 
     The bottom surface of the cap member  140  may have a protrusion in order to seal the lubricating fluid. This is because that a capillary phenomenon and the surface tension of the lubricating fluid are used in order to prevent the lubricating fluid from being leaked to the outside at the time of the driving of the motor. 
     The stator  200  may include a coil  210 , a core  220 , and a base  230 . 
     In other words, the stator  200  may be a fixing structure that includes the coil  210  generating an electromagnetic force having a predetermined size at the time of the applying of power and a plurality of cores  220  around which the coil  210  is wound. 
     The core  220  is fixedly disposed on the top of the base  230  on which a printed circuit substrate (not shown) printed with a circuit pattern is provided, and the top surface of the base  230  corresponding to the winding coil  210  may be provided with a plurality of coil holes having a predetermined size penetrating through the top surface thereof in order to expose the winding coil  210  downwardly and the winding coil  210  may be electrically connected with the printed circuit board (not shown) in order to supply external power. 
     The outer peripheral surface of the sleeve  120  may be press-fittedly inserted into the base  230  and fixed thereto, and the core  220  on which the coil  210  is wound may also be inserted into the base  230 . The base  230  and the sleeve  120  may be assembled by applying an adhesive to the inner surface of the base  230  or the outer surface of the sleeve  120 . 
     The rotor  300  is a rotating structure that is rotatably provided with respect to the stator  200  and may include a rotor case  310  having an annular ring magnet  320  corresponding to the core  220  while having a predetermined interval therefrom provided at an inner peripheral surface thereof. 
     The magnet  320  is a permanent magnet of which an N pole and an S pole are alternately magnetized in a circumferential direction to generate a magnetic force having a predetermined strength. 
     In this case, the rotor case  310  may be configured of a hub base  312  that is press-fitted and fixed to the top portion of the shaft  110  and a magnet support part  314  that extends in an outer-diameter direction from the hub base  312  and is bent downwardly in an axial direction to support the magnet  320  of the rotor  300 . 
       FIG. 2  is a schematic cross-sectional view of a motor according to another exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , a motor  500  according to another exemplary embodiment of the present invention has the same configuration and effect as that of the exemplary embodiment above described, other than the thrust plate  130  and a part  316  of the rotor case  310 , and thus, the following description thereof will be omitted. 
     The thrust plate  130  is disposed at the bottom of the sleeve  120  in an axial direction and coupled with the shaft  110 . 
     That is, the thrust plate  130  may be coupled with the shaft  110  by screwing, bonding, welding, or the like, and the thrust dynamic groove that provides the thrust dynamic pressure to the shaft  110  may be formed on at least one of the top surface and the bottom surface of the thrust plate  130 . 
     In this case, as compared with the exemplary embodiment above described, the disposition position of the thrust plate  130  based on the shaft  110  is different, but the function and effect of the thrust plate  130  are the same. 
     Further, the rotor case  310  of the motor  500  according to another exemplary embodiment of the present invention may be configured of the hub base  312  that is press-fitted and fixed to the top portion of the shaft  110  and the magnet support part  314  that extends in an outer-diameter direction from the hub base  312  and is bent downwardly in an axial direction to support the magnet  320  of the rotor  300 . 
     In addition, the rotor case  310  may provided with the wall part  316  formed to extend downwardly in an axial direction in order to seal the lubricating fluid between the wall part  316  and the sleeve  120 . 
     The interval between the wall part  316  and the sleeve  120  maybe gradually widened downwardly in an axial direction in order to prevent the lubricating fluid from being leaked to the outside at the time of the driving of the motor. To this end, the outer peripheral surface of the sleeve  120  corresponding to the wall part  316  maybe formed to be tapered in an inner-diameter direction. 
       FIG. 3  is a schematic cross-sectional view of a hydrodynamic bearing assembly provided in the motor according to the exemplary embodiment of the present invention and  FIGS. 4 through 7  are schematic cross-sectional views of other examples of section A shown in  FIG. 3 . 
     Referring to  FIGS. 3 through 7 , the hydrodynamic bearing assembly  100 , provided in the motor  400  according to the exemplary embodiment of the present invention, may include a configuration of the coupling structure of the base cover  150  and the sleeve  120 . 
     The base cover  150  may include the support part  155  at the outer end portion thereof such that the outer peripheral surface thereof is coupled to and in contact with the inner peripheral surface of the coupling part  125  of the sleeve  120 . 
     As shown in  FIG. 3 , the support part  155  is formed at the outer end portion of the base cover  150  and is protrudedly formed downwardly in an axial direction to be coupled with the coupling part  125  of the sleeve  120 . 
     That is, the support part  155  may mean that the outer end portion of the base cover  150  is formed to be bent downwardly in an axial direction, which may expand an area coupled with the sleeve  120 . 
     As a result, the area to which the adhesive is applied is expanded, thereby increasing the unmating force allowing for sufficiently withstanding external impacts, or the like, in the axial direction. 
     Generally, the unmating force indicates a degree to which the coupling of the base cover  150  and the sleeve  120  is maintained by the impact upwardly or downwardly in an axial direction and may depend on the coupling area in the axial direction between the base cover  150  and the sleeve  120 . 
     Therefore, the hydrodynamic bearing assembly  100  according to the exemplary embodiment of the present invention may increase the coupling area in which the base cover  150  is coupled with the coupling part  125  of the sleeve  120  through the support part  155  formed at the outer end portion of the base cover  150 , thereby improving the unmating force. 
     In addition, as shown in  FIGS. 4 and 5 , the support part  155  of the base cover  150  may be formed to be protruded upwardly in the axial direction and the inner peripheral surface of the coupling part  125  of the sleeve  120  may be provided with an insertion groove  127  into which the support part  155  is inserted. 
     The insertion groove  127  may be concavely formed along the inner peripheral surface of the coupling part  125  and may be a groove having a shape corresponding to the shape of the support part  155 . 
     When the insertion groove  127  is larger than the shape of the support part  155 , an empty space within the insertion groove  127  may be filled with an adhesive and when the insertion groove  127  corresponds to the shape of the support part  155 , the outer peripheral surface of the support part  155  may be in contact with and coupled to the inner surface of the insertion groove. 
     In addition, as shown in  FIGS. 6 and 7 , the support part  155  of the base cover  150  may be formed to be protruded upwardly and downwardly in an axial direction and the inner peripheral surface of the coupling part  125  of the sleeve  120  may be provided with the insertion groove  127  into which the portion of the support part  155 , protruded upwardly is inserted. 
     In this case, the insertion groove  127  has the same configuration and effect as that shown in  FIGS. 4 and 5  and has the same configuration and effect as in the above-mentioned exemplary embodiment, with the exception that the support part  155  is protruded in both directions, that is, upwardly and downwardly. 
       FIG. 8  is a schematic cross-sectional view of a recording disk driving device having the motor mounted thereon according to the exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , a recording disk driving device  600  on which the motor  400  is mounted according to the exemplary embodiment of the present invention is a hard disk driving device and may include the motor  400 , a head transfer part  610 , and a housing  620 . 
     The motor  400  has all of the characteristics of the motor according to the exemplary embodiment of the present invention described above and may have a recording disk  630  mounted thereon. 
     The head transfer part  610  may transfer a head  615  detecting information on the recording disk  630  mounted on the motor  400  to a surface of the recording disk to be detected. 
     In this case, the head  615  may be disposed on a support member  617  of the head transfer part  610 . 
     The housing  620  may include a motor mounting plate  627  and a top cover  625  shielding the top of the motor mounting plate  627  in order to form an inner space accommodating the motor  400  and the head transfer part  610 . 
     As set forth above, the hydrodynamic bearing assembly and the motor including the same according to the exemplary embodiments of the present invention may allow for the improvement of the unmating force so as to sufficiently withstand the external impact. 
     Further, the exemplary embodiments of the present invention may improve the unmating force to thereby improve the performance and the operation stability of the hydrodynamic bearing assembly. 
     As set forth above, the hydrodynamic bearing assembly  100  and the motors  400  and  500  including the same according to the exemplary embodiments of the present invention may expand the coupling area in which the support part  155  of the base cover  150  and the coupling part  125  of the sleeve  120  are coupled in the axial direction, thereby improving the unmating force. 
     Therefore, the unmating force is improved to increase the resistance force withstanding the external impact, thereby improving the stability of the motors  400  and  500 . 
     While the present invention has been shown and described in connection with the exemplary 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.