Patent Publication Number: US-2013234551-A1

Title: Hydrodynamic bearing assembly and spindle motor including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2012-0023798 filed on Mar. 8, 2012, 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 spindle motor including the same. 
     2. Description of the Related Art 
     A small-sized spindle motor used in a hard disk drive (HDD) is generally provided with a hydrodynamic bearing assembly, and a bearing clearance formed between a shaft and a sleeve of the hydrodynamic bearing assembly is filled with a lubricating fluid such as oil. Fluid dynamic pressure is generated in the lubricating fluid filling the bearing clearance when the lubricating fluid is compressed, thereby rotatably supporting the shaft. 
     That is, dynamic pressure is generally generated in the hydrodynamic bearing assembly through spiral-shaped grooves formed in an axial direction and herringbone-shaped grooves formed in a circumferential direction, thereby promoting stability in rotational driving characteristics of the spindle motor. 
     Meanwhile, in accordance with the recent increase in storage capacities of hard disk drives, a technical problem in which vibrations generated during the driving of the spindle motor should be reduced has been encountered. That is, in order for the hard disk drive to be driven without errors due to vibrations generated during the driving of the spindle motor, improvements in the performance of the hydrodynamic bearing assembly included in the spindle motor have been demanded. 
     In addition, in order to improve the performance of the hydrodynamic bearing assembly, there is a need to increase an interval (that is, a bearing span length) between the herringbone shaped grooves to move the center of rotation upwardly, thereby promoting stability in the driving of the spindle motor. 
     In addition, the spindle motor has been used in portable electronic devices, such that demand for decreased power consumption has increased. 
     The development of a structure capable of decreasing power consumption while promoting stability in the driving of the motor as described above has been urgently demanded. 
     RELATED ART DOCUMENT  
     
         
         (Patent Document 1) Japanese Patent Laid-Open Publication No. 2006-022031 
       
    
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides a hydrodynamic bearing assembly capable of stably rotating a rotor by securing a bearing span length while preventing the generation of negative pressure, and capable of easily discharging air bubbles, as well as a spindle motor including the same. 
     According to an aspect of the present invention, there is provided a hydrodynamic bearing assembly including: a sleeve supporting a shaft so that an upper end portion of the shaft is protruded therefrom in an upward axial direction and forming a bearing clearance between the sleeve and the shaft, the bearing clearance being filled with a lubricating fluid; a housing partially enclosing an outer peripheral surface of the sleeve; a rotor hub coupled to the upper end portion of the shaft and including an extension wall part partially facing an outer surface of an upper end portion of the sleeve and partially extended to be disposed outwardly of the housing; a stopper provided on a lower end portion of the shaft to be protruded outwardly in a radial direction to be caught by a lower end portion of the sleeve; a cover member provided on a lower end portion of the housing; and a circulation hole provided between the sleeve and the housing to allow a lower portion of the sleeve to be in communication with an upper end portion of the housing. 
     The housing and the cover member may be provided integrally with each other. 
     The housing and the cover member provided integrally with each other may be formed by press molding. 
     The shaft and the rotor hub may be provided integrally with each other. 
     Upper and lower radial dynamic pressure grooves for generating fluid dynamic pressure at the time of rotational driving of the shaft may be formed in an outer surface of the shaft or an inner surface of the sleeve. 
     The sleeve may be provided with a communication hole allowing an area between the upper and lower radial dynamic pressure grooves in the bearing clearance between the shaft and the sleeve to be in communication with the circulation hole. 
     The upper end portion of the sleeve may be provided with a chamfer along an edge thereof, and a portion of the rotor hub facing the chamfer may have a shape corresponding to that of the chamfer. 
     A liquid-vapor interface may be formed between an inner surface of the extension wall part and an outer surface of the housing. 
     A first thrust dynamic pressure groove for generating thrust fluid dynamic pressure may be formed in at least one of an upper surface of the shaft or the stopper and a lower surface of the sleeve. 
     A second thrust dynamic pressure groove for generating thrust fluid dynamic pressure may be formed in at least one of a lower surface of the rotor hub and an upper surface of the sleeve. 
     The circulation hole may be formed by a circulation groove provided in an outer surface of the sleeve in an axial direction and an inner surface of the housing. 
     The circulation hole may be formed by a cut part obtained by cutting an outer surface of the sleeve in an axial direction and an inner surface of the housing. 
     The upper end portion of the sleeve may be provided with a flange protruded outwardly to be positioned on the upper end portion of the housing. 
     According to another aspect of the present invention, there is provided a spindle motor including: the hydrodynamic bearing assembly as described above; and a stator coupled to an outer side of the housing and including a core having a coil wound therearound, the coil generating rotational driving force. 
    
    
     
       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 showing a spindle motor according to an embodiment of the present invention; 
         FIGS. 2A and 2B  are perspective views showing a sleeve according to an embodiment of the present invention; 
         FIG. 3  is a schematic cross-sectional view showing a spindle motor according to another embodiment of the present invention; 
         FIGS. 4A and 4B  are perspective views showing a sleeve according to another embodiment of the present invention; 
         FIG. 5  is a cross-sectional view schematically showing a spindle motor according to another embodiment of the present invention; and 
         FIGS. 6A and 6B  are perspective views showing a sleeve according to another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. However, it should be noted that the spirit of the present invention is not limited to the embodiments set forth herein and that those skilled in the art and understanding the present invention could easily accomplish retrogressive inventions or other embodiments included in the spirit of the present invention by the addition, modification, and removal of components, but those are to be construed as being included in the spirit of the present invention. 
     Moreover, detailed descriptions related to well-known functions or configurations will be ruled out in order not to unnecessarily obscure subject matters of the present invention. 
       FIG. 1  is a schematic cross-sectional view showing a spindle motor according to an embodiment of the present invention; and  FIGS. 2A and 2B  are perspective views showing a sleeve according to the embodiment of the present invention. 
     Referring to  FIGS. 1 through 2B , a spindle motor  100  according to the embodiment of the present invention may include a base member  110 , a shaft  120 , a sleeve  130 , a housing  140 , a rotor hub  150 , a stopper  160 , and a cover member  170 . 
     The spindle motor  100  may be a motor used in a hard disk drive for driving a recoding disk. 
     Here, terms with respect to directions will be defined. As viewed in  FIG. 1 , an axial direction refers to a vertical direction, that is, a direction from a lower portion of the shaft  120  toward an upper portion thereof or a direction from the upper portion of the shaft  120  toward the lower portion thereof, while a radial direction refers to a horizontal direction, that is, a direction from an outer peripheral surface of the rotor hub  150  toward the shaft  120  or from the shaft  120  toward the outer peripheral surface of the rotor hub  150 . 
     In addition, a circumferential direction refers to a circumference of a circle having a predetermined radius based on the shaft. For example, the circumferential direction refers to a rotation direction along the outer peripheral surface of the rotor hub  150  or the shaft  120 . 
     Further, the hydrodynamic bearing assembly according to the embodiment of the present invention, which includes members related to a principle of a bearing utilizing fluid dynamic pressure, may include members other than the base member  110 . That is, the hydrodynamic bearing assembly may include the shaft  120 , the sleeve  130 , the housing  140 , the rotor hub  150 , the stopper  160 , and the cover member  170 . 
     The base member  110 , a fixed member, may configure a stator  20 . Here, the stator  20 , which refers to all fixed members (all members except for rotating members), may include the base member  110 , the sleeve  130 , the housing  140 , and the like. 
     In addition, the base member  110  may include an installation part  112  having the housing  140  insertedly installed therein. The installation part  112  maybe protruded in an upward axial direction and include an installation hole  112   a  formed therein so that the housing  140  may be insertedly installed therein. 
     In addition, the installation part  112  may include a seat surface  112   b  formed on an outer peripheral surface thereof so that a stator core  104  having a coil  102  wound therearound may be seated thereon. That is, the stator core  104  may be fixedly installed on the outer peripheral surface of the installation part  112  by an adhesive in a state in which it is seated on the seat surface  112   b.    
     However, the stator core  104  may also be installed on the outer peripheral surface of the installation part  112  in a press-fitting scheme without using the adhesive. That is, a scheme of installing the stator core  104  is not limited to the use of the adhesive. 
     The shaft  120 , a rotating member, may configure a rotor  40 . Here, the rotor  40  refers to a member rotatably supported by the stator  20  to thereby rotate. 
     Meanwhile, the shaft  120  may be rotatably supported by the sleeve  130 . In addition, as shown in  FIG. 1 , the stopper  160  may include a first thrust dynamic pressure groove  122  formed in an upper surface thereof in order to generate thrust fluid dynamic pressure at the time of the rotation of the shaft  120 . 
     Meanwhile, the first thrust dynamic pressure groove  122  is not limited to being formed in the upper surface of the stopper  160 , but may also be formed on a lower surface of the sleeve  130  disposed to face the upper surface of the stopper  160 . 
     As described above, the first thrust dynamic pressure groove  122  is formed in the upper surface of the stopper  160  or the lower surface of the sleeve  130  disposed to face the upper surface of the stopper  160 , whereby the shaft  120  may smoothly rotate due to the first thrust dynamic pressure groove  122 . 
     Meanwhile, the first thrust dynamic pressure groove  122  may have a herringbone shape or a spiral shape. However, the first thrust dynamic pressure groove  122  is not limited to having the above-mentioned shape, but may have any shape as long as the fluid dynamic pressure may be generated at the time of the rotation of the shaft  120 . 
     Meanwhile, the shaft  120  may include upper and lower radial dynamic pressure grooves  123  and  124  formed in the outer peripheral surface thereof in order to generate fluid dynamic pressure at the time of rotational driving thereof. In addition, the upper and lower radial dynamic pressure grooves  123  and  124  may be disposed to be spaced apart from each other by a predetermined interval and have a herringbone shape. 
     Meanwhile, a lower end portion of the shaft  120  may be provided with the stopper  160  caught by a lower end of the sleeve  130  to limit excessive floating of the shaft  120 . That is, the stopper  160  may be provided to be protruded outwardly from the lower end of the shaft  120  in the radial direction and disposed under the sleeve  130  to limit excessive floating of the rotating member including the shaft  120  at the time of an operation of the spindle motor. Therefore, the first thrust dynamic pressure groove  122  may be provided in a lower surface of the stopper  160  or in an upper surface of the cover member  170  corresponding to the lower surface of the stopper  160 . 
     The sleeve  130 , a fixed member configuring the stator  20  together with the housing  140  and the base member  110 , may rotatably support the shaft  120  and form a bearing clearance C filled with a lubricating fluid. The sleeve  130  may be formed by sintering a Cu—Fe-based alloy powder or a SUS-based powder. However, the sleeve  130  is not limited to being formed by the sintering scheme, but may also be formed by other schemes. 
     Meanwhile, the sleeve  130  may be inserted into the installation part  112  of the base member  110  in a state in which it is fixed to the inside of the housing  140 , such that it may be indirectly fixedly installed in the base member  110 . That is, an outer peripheral surface of the housing  140  may be adhered to an inner peripheral surface of the installation part  112  by using an adhesive or by other schemes. 
     Here, only a portion of the sleeve  130  may be included in the housing  140 . That is, as shown in  FIG. 1 , an upper end portion of the sleeve  130  is not enclosed by the housing  140 , but may be exposed, to directly face an extension wall part  152  protruded from the rotor hub  150  to be described below in a downward axial direction. 
     Further, the sleeve  130  may include a shaft hole  132  formed therein, wherein the shaft hole  132  has the shaft  120  inserted thereinto. Further, in the case in which the shaft  120  is insertedly disposed in the shaft hole  132  of the sleeve  130 , an inner peripheral surface of the sleeve  130  and the outer peripheral surface of the shaft  120  may be spaced apart from each other by a predetermined interval to form the bearing clearance C therebetween. 
     Here, the bearing clearance C will be described in more detail. As described above, the sleeve  130  forms the bearing clearance C filled with the lubricating fluid. This bearing clearance C indicates a clearance formed by the shaft  120  and the sleeve  130 , a clearance formed by the upper end portion of the sleeve  130  and the rotor hub  150 , a clearance formed by the housing  140  and the stopper  160 , a clearance formed by the sleeve  130  and the extension wall part  152 , and a clearance formed by the cover member  170  and a lower surface of the shaft  120 . 
     In addition, the spindle motor  100  according to the present embodiment may have a structure in which the lubricating fluid fills the entire bearing clearance C. This structure may be called a full-fill structure. 
     Meanwhile, the sleeve  130  may include upper and lower radial dynamic pressure grooves formed in the inner peripheral surface thereof in order to generate fluid dynamic pressure at the time of the rotational driving of the shaft  120 . In addition, the upper and lower radial dynamic pressure grooves may be disposed to be spaced apart from each other by a predetermined interval and have a herringbone or spiral shape. 
     Further, the sleeve  130  and the housing  140  may include a circulation hole  136  formed therebetween in order to connect upper and lower portions of the sleeve  130  to each other. The circulation hole  136  may be provided as a circulation groove  136   a  or a cut part  136   b  formed in at least one of an outer peripheral surface of the sleeve  130  and an inner peripheral surface of the housing  140 . 
     In the case in which the circulation hole  136  is provided as the circulation groove  136   a  formed along the outer peripheral surface of the sleeve  130  to allow the upper and lower portions of the sleeve  130  to be in communication with each other, the circulation groove  136   a  may be formed by forming a groove in a side of the sleeve  130  in the vertical direction (the axial direction based on  FIG. 1 ). Since the housing  140  does not enclose the entire outer surface of the sleeve  130 , the circulation groove  136   a  may be formed up to a portion at which an upper end of the housing  140  is positioned. 
     Further, in the case in which the circulation hole  136  is provided as the cut part  136   b  along the outer peripheral surface of the sleeve  130  to allow the upper and lower portions of the sleeve  130  to be in communication with each other, the cut part  136   b  may be formed by cutting the side of the sleeve  130  in the vertical direction (the axial direction based on  FIG. 1 ). Since the outer peripheral surface of the sleeve  130  and the inner peripheral surface of the housing  140  have a circular shape, when the outer peripheral surface of the sleeve  130  is cut in the vertical direction (in the axial direction based on  FIG. 1 ), a space between the sleeve  130  and the housing  140  is naturally formed, such that the first circulation hole  136  may be provided. In this case, since the housing  140  does not enclose the entire outer surface of the sleeve  130 , the cut part  136   b  may be formed up to the portion at which the upper end of the housing  140  is positioned. 
     Further, in the case in which the circulation hole is formed along the inner peripheral surface of the housing  140 , the circulation hole may be formed by using the same scheme as the scheme of forming the circulation hole in the outer peripheral surface of the sleeve  130 . 
     Meanwhile, the sleeve  130  may be provided with a communication hole  137  allowing the bearing clearance C between the shaft  120  and the sleeve  140  to be in communication with the circulation hole  136 . Here, the communication hole  137  may allow a portion between the upper and lower radial dynamic pressure grooves  123  and  124  to be in communication with the circulation hole  136 . 
     According to the present embodiment, the communication hole  137  is provided to prevent negative pressure from being generated between the upper and lower radial dynamic pressure grooves  123  and  124 , whereby a bearing span length may be increased. That is, even though the upper radial bearing has an unbalanced herringbone shape which pumps the lubricating fluid toward a second thrust bearing formed by a second thrust dynamic pressure groove  159  and the lower radial bearing has an unbalanced herringbone shape which pumps the lubricating fluid toward a first thrust bearing formed by the first thrust dynamic pressure groove  122 , since the generation of negative pressure may be prevented by the communication hole  137  provided between the upper and lower radial dynamic pressure grooves  123  and  124 , the bearing span length may be increased to improve rotational characteristics of the spindle motor while reducing power consumption. 
     Here, the bearing span length indicates a distance between a region in which maximum dynamic pressure is generated while the lubricating fluid is pumped by the upper radial dynamic pressure groove  123  and a region in which maximum dynamic pressure is generated while the lubricating fluid is pumped by the lower radial dynamic pressure groove  124 . 
     That is, the communication hole  137  is installed in the sleeve  130 , such that a spaced distance between the upper and lower radial dynamic pressure grooves  123  and  124  is increased, whereby the bearing span length may be increased. Therefore, the rotational characteristics may be improved and the power consumption may be reduced. 
     The housing  140  may enclose the sleeve  130  such that it may be coupled to the outer peripheral surface of the sleeve  130 . More specifically, the sleeve  130  may be inserted into the inner peripheral surface of the housing  140  and be coupled thereto by press-fitting or bonding. Since the upper end portion of the sleeve  130  is provided to be exposed, the housing  140  may be coupled to the sleeve  130  except for an outer surface of the upper end portion of the sleeve  130 . 
     Therefore, since the housing  140  may have a short length in the axial direction, in the case in which the housing is manufactured in a pressing scheme, the housing may be easily manufactured. 
     The housing  140  may be coupled to the outer peripheral surface of the sleeve  130  containing oil to prevent the oil from being leaked. 
     In addition, an outer surface of the upper end portion of the housing  140  and the extension wall part  152  protruded from the rotor hub  150  in the downward axial direction may have an oil interface formed therebetween. That is, the bearing clearance C is filled with the oil, sealed by a capillary phenomenon. According to the present embodiment, a sealing part of the fluid may be formed between the outer surface of the housing  140  and the inner surface of the extension wall part  152 . A position of the oil interface may be changed according to whether or not the spindle motor is operated. 
     Therefore, the outer surface of the upper end portion of the housing  140  or the inner surface of the extension wall part  152  may be tapered so that the oil is easily sealed. That is, the outer surface of the upper end portion of the housing  140  or the inner surface of the extension wall part  152  may be inclined so that an interface between the lubricating fluid and air is easily formed. 
     Meanwhile, the housing  140  may include the cover member  170  installed on a lower end portion thereof. 
     The cover member  170 , a fixed member configuring the stator  20  together with the base member  110 , the sleeve  130 , and the housing  140  described above, may be installed on the lower end portion of the housing  140  to serve to prevent the lubricating fluid filling the bearing clearance C from being leaked to the lower end portion of the housing  140 . 
     Here, the cover member  170  may be bonded to the lower end portion of the housing  140  by an adhesive and/or welding. 
     In addition, the cover member  170  may be provided integrally with the housing  140 . In the case in which the housing  140  and the cover member  170  are provided integrally with each other, the housing  140  and the cover member  170  may be manufactured integrally with each other by press molding. 
     The rotor hub  150 , a rotating member configuring the rotor  40  together with the shaft  120 , may be coupled to the upper end portion of the shaft  120  and include the extension wall part  152  extended to be disposed outwardly of the sleeve  130 . 
     Meanwhile, the rotor hub  150  may include a rotor hub body  154  provided with an mounting hole  154   a  into which the upper end portion of the shaft  120  is inserted, a magnet mounting part  156  extended from an edge of the rotor hub body  154  in the downward axial direction, and a disk seat part  158  extended outwardly from a distal end of the magnet mounting part  156  in the radial direction. 
     In addition, the magnet mounting part  156  may have a driving magnet  156   a  installed on an inner surface thereof, and the driving magnet  156   a  is disposed to face a front end of the stator core  104  having the coil  102  wound therearound. 
     Meanwhile, the driving magnet  156   a  may have an annular ring shape and be a permanent magnet generating magnetic force having a predetermined strength by alternately magnetizing an N pole and an S pole in the circumferential direction. 
     Here, the rotational driving of the rotor hub  150  will be briefly described. When power is supplied to the coil  102  wound around the stator core  104 , driving force capable of rotating the rotor hub  150  may be generated by electromagnetic interaction between the driving magnet  156   a  and the stator core  104  having the coil  102  wound therearound. 
     Therefore, the rotor hub  150  may rotate. In addition, the shaft  120  on which the rotor hub  150  is fixedly installed may rotate together with the rotor hub  150  by the rotation thereof. 
     Further, the above-mentioned extension wall part  152  may be extended from a lower surface of the rotor hub body  154  in the downward axial direction. 
     The extension wall part  152  may partially face the outer surface of the upper end portion of the sleeve  130  and be partially disposed outwardly of the housing  140 . That is, since the upper end portion of the sleeve  130  is not enclosed by the housing  140 , the upper end portion of the sleeve  130  may directly face the extension wall part  152 , and the bearing clearance C formed by the upper end portion of the sleeve  130  and the extension wall part  152  may be filled with the lubricating fluid. 
     Meanwhile, the rotor hub  150  may be provided integrally with the shaft  120 . 
     In addition, the second thrust dynamic pressure groove  159  for generating thrust fluid dynamic pressure may be formed in at least one of the upper surface of the sleeve  130  and the lower surface of the rotor hub body  154  facing the upper surface of the sleeve  130 . 
     Therefore, at the time of the rotation of the shaft  120 , the thrust fluid dynamic pressure is generated, whereby the rotation of the rotor hub  150  may be more stably supported. 
     Hereinafter, a spindle motor according to another embodiment of the present invention will be described with reference to the accompanying drawings. However, a detailed description of the same components as the above-mentioned components will be omitted. 
       FIG. 3  is a schematic cross-sectional view showing a spindle motor according to another embodiment of the present invention; and  FIGS. 4A and 4B  are perspective views showing a sleeve according to another embodiment of the present invention. 
     Referring to  FIGS. 3 through 4B , a spindle motor  200  according to another embodiment of the present invention may include abase member  110 , a shaft  120 , a sleeve  130 ′, a housing  140 , a rotor hub  150 ′, a stopper  160 , and a cover member  170 . That is, the spindle motor  200  according to this embodiment of the present invention has the same components as those of the spindle motor according to the embodiment of the present invention shown in  FIGS. 1 through 2B  except for the sleeve  130 ′ and the rotor hub  150 ′. Therefore, a detailed description of the same components will be omitted. 
     According to this embodiment of the present invention, an upper end portion of the sleeve  130 ′ may be provided with a chamfer  139  in the circumferential direction, and a portion of the rotor hub  150 ′, that is, a rotor hub body  154 ′ facing the chamfer  139  may have a shape corresponding to that of the chamfer  139 . 
     When the portion of the rotor hub  150 ′ facing the chamfer  139  has this shape, since a contact area between a rotating member (that is, the rotor hub  150 ′) and a fixed member (that is, the sleeve  130 ′) is decreased, friction is decreased, such that the spindle motor may be operated at low current. 
       FIG. 5  is a schematic cross-sectional view showing a spindle motor according to another embodiment of the present invention; and  FIGS. 6A and 6B  are perspective views showing a sleeve according to another embodiment of the present invention. 
     Referring to  FIGS. 5 through 6B , a spindle motor  300  according to another embodiment of the present invention may include abase member  110 , a shaft  120 , a sleeve  130 ″, a housing  140 , a rotor hub  150 , a stopper  160 , and a cover member  170 . That is, the spindle motor  300  according to another embodiment of the present invention has the same components as those of the spindle motor according to the embodiment of the present invention shown in  FIGS. 1 through 23  except for the sleeve  130 ″. Therefore, a detailed description of the same components will be omitted. 
     According to this embodiment of the present invention, an upper end portion of the sleeve  130 ″ may be provided with a flange  138  in the circumferential direction. The flange  138  may be positioned on the upper end portion of the housing  140  into which the sleeve is inserted. 
     As set forth above, according to embodiments of the present invention, a bearing span length is secured while the generation of negative pressure is prevented, whereby a motor may be stably operated. 
     In addition, a hydrodynamic bearing assembly capable of being stably operated by easily discharging air bubbles and capable of decreasing power consumption due to low friction current, and a spindle motor including the same may be provided. 
     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.