Abstract:
The present invention provides a bearing comprised of a hydrodynamic bearing and a pivot bearing, which can be used with a spindle motor. It also provides a spindle motor utilizing a hydrodynamic bearing and a pivot bearing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a divisional of application Ser. No. 10/387,047, filed Mar. 12, 2003 now U.S. Pat. No. 7,008,110 application Ser. No. 10/387,047 claims priority from U.S. Provisional Patent Application No. 60/363,784, filed Mar. 12, 2002. Application Ser. No. 10/387,047 also claims priority from Fed. Rep. Of Germany Patent Application Nos. DE10232933.8, filed Jul. 19, 2002, DE10237848.7, filed Aug. 19, 2002, and DE10240634, filed Sep. 2, 2002. 
   BACKGROUND OF THE INVENTION 
   The following invention relates to electronic spindle motors of the type used in disk drives and in particular relates to improvements in fluid bearings for such motors. 
   Disc drive systems have been used in computers and other electronic devices for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle, the information being accessed by means of transducers located on a pivoting arm which moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information; thus the discs must be rotationally stable. 
   Electric spindle motors of the type used in disk drives conventionally rely on ball bearings to support a rotary member, such as a rotating hub, on a stationary member, such as a shaft. Ball bearings are wear parts and in time friction will cause failure of the motor. In addition, ball bearings create debris in the form of dust or fine particles that can find their way into “clean” chambers housing the rotary magnetic disks which are driven by the motor. The mechanical friction inherent in ball bearings also generates heat and noise, both of which are undesirable in a disk drive motor. 
   Fluid dynamic bearings represent a considerable improvement over conventional ball bearings in spindle drive motors. In these types of systems, lubricating fluid—either gas or liquid—functions as the actual bearing surface between a stationary base or housing in the rotating spindle or rotating hub of the motor. For example, liquid lubricants comprising oil, more complex ferro-magnetic fluids or even air have been utilized in hydrodynamic bearing systems. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a spindle motor with a fluid dynamic pivot bearing which saves run-current and, therefore, reduces power consumption of the spindle motor. The present inventions combines the benefit of increased stability provided by hydrodynamic bearings with the benefit of low power consumption provided by pivot bearings. 
   The above and other objects, aspects, features and advantages of the invention will be more readily apparent from the description of the preferred embodiments thereof taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is illustrated by way of example and not limitation and the figures of the accompanying drawings in which like references denote like or corresponding parts, and in which: 
       FIG. 1  is a is a side cut-away view of an electronic spindle motor having a rotational shaft, a magnetic shield, and a journal bearing according to the first embodiment of the present invention. 
       FIG. 2  is a side cut-away view of an electronic spindle motor having a fixed shaft, a journal bearing, a counterplate, and a thrust bearing according to the second embodiment of the present invention. 
       FIG. 3  is a side cut-away view of an electronic spindle motor having a rotational shaft, a journal bearing, a counterplate, and a thrust bearing according to the second embodiment of the present invention. 
       FIG. 4  is a side cut-away view of an electronic spindle motor having a rotational shaft, a thrust-washer, a journal bearing, a counterplate, and a thrust bearing according to the third embodiment of the present invention. 
       FIG. 5  is a side cut-away view of an electronic spindle motor having a fixed shaft, a thrust-washer, a journal bearing, a counterplate, and a thrust bearing according to the third embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The first embodiment of the present invention is shown in  FIG. 1 . A spindle motor includes a stator  10  and a rotor  6  that is arranged for rotation relative to stator  10 . 
   The rotor  6  comprises a rotor hub  18  and a tubular shaft  20  fixed coaxially to the rotor hub  18 . A rotor magnet  12  is bonded to the inner side of a circumferential wall of the rotor hub  18 . The outer side of the circumferential wall of the rotor hub  18  is shaped to hold a magnetic disk (not shown). 
   Stator  10  comprises bracket  4  which is to be mounted on a disk drive device (not shown); sleeve  8 ; core  52 , which is fixedly mounted to bracket  4 , and coils  54  wound on the core  52 . Coils  54  are radially spaced by a small gap from and arranged opposite to the rotor magnet  12 . 
   Sleeve  8  is a tubular member into which is formed a cylindrical hole  85 . With the exception of its upper most portion, cylindrical hole  85  has a constant radius A. The uppermost portion of cylindrical hole  85  has a slightly increased radius to provide for a capillary seal  11 . Cap  9  is affixed to the upper surface of sleeve  8 . Cap  9  has an inner radius B that is less than the radius of cylindrical hole  85 . The cap  9  prevents the shaft  20  from being dislodged from cylindrical hole  85  when the motor receives a physical shock. 
   Shaft  20  extends through hub  18  and cap  9  down into cylindrical hole  85 . The portion of shaft  20  that is inserted into cylindrical hole  85  comprises an upper shaft section  205  and a lower shaft section  206 . Upper shaft section  205  has a constant radius C that is greater than the inner radius B of the cap  9  and that is slightly less than the radius of cylindrical hole  85 . Lower shaft section  206  is a contiguous with upper shaft section  205  and the radius of lower shaft section  206  decreases from the radius C of upper shaft section  205  to a radius of zero at the bottom of cylindrical hole  85 . Hence lower shaft section  206  is in contact with sleeve  8  at a pivot point  13 . 
   The gap comprised of the spaces between sleeve  8  and shaft  20  is filled with an appropriate lubricating fluid. Pressure generating grooves  14  are formed either onto the outer surface of upper shaft section  205  or onto the inner surface of sleeve  8  opposite to upper shaft section  205  so as to create a journal bearing. If necessary, a second set of grooves can be added to form a second journal bearing. Additionally, pressure generating grooves can be placed on the bottom of lower shaft section  206  or on the opposing surface of sleeve  8  to minimize material contact between the shaft  20  and the sleeve  8 . 
   A magnetic shield  15  is attached to bracket  4 . Magnetic shield  15  interacts with rotor magnet  12  to apply a downward force on rotor  6 . 
   The second embodiment of the present invention is shown in  FIG. 2  and in  FIG. 3 . The rotating shaft version of this spindle motor is shown in  FIG. 3 . A spindle motor includes a stator  10  and a rotor  6  that is arranged for rotation relative to stator  10 . 
   The rotor  6  comprises a rotor hub  18  and a tubular shaft  20  fixed coaxially to the rotor hub  18 . A rotor magnet  12  is bonded to the inner side of a circumferential wall of the rotor hub  18 . The outer side of the circumferential wall of the rotor hub  18  is shaped to hold a magnetic disk (not shown). 
   Stator  10  comprises bracket  4  which is to be mounted on a disk drive device (not shown); sleeve  8 ; core  52 , which is fixedly mounted to bracket  4 , and coils  54  wound on the core  52 . Coils  54  are radially spaced by a small gap from and arranged opposite to rotor magnet  12 . 
   Sleeve  8  is a tubular member into which is formed a cylindrical hole  85 . Cylindrical hole  85  has a constant radius A. Directly above cylindrical hole  85  and coaxial with cylindrical hole  85  is counterplate opening  88 . Counterplate opening  88  extends from the top of cylindrical hole  85  to the upper surface of sleeve  8 . Counterplate opening  88  has a constant radius B that is greater than the radius A of the cylindrical hole  85 . Counterplate  19  is securely fit inside of counterplate opening  88 . Counterplate  19  has an inner radius C that is less than the radius of cylindrical hole  85 . The inner radius of counterplate  19  increases near the top of counterplate  19  to provide for capillary seal  11 . 
   Shaft  20  extends through hub  18  and counterplate  19  down into cylindrical hole  85 . The portion of shaft  20  that is inserted into cylindrical hole  85  comprises an upper shaft section  205  and a lower shaft section  206 . Upper shaft section  205  has a constant radius C that is greater than the inner radius B of the counterplate  19  and that is slightly less than the radius A of cylindrical hole  85 . Lower shaft section  206  is a contiguous with upper shaft section  205  and the radius of lower shaft section  206  decreases from the radius C of upper shaft section  205  to a radius of zero at the bottom of cylindrical hole  85 . Hence lower shaft section  206  is in contact with sleeve  8  at a pivot point  13 . 
   The gap comprised of the spaces between sleeve  8 , counterplate  19  and shaft  20  is filled with an appropriate lubricating fluid. Pressure generating grooves  14  are formed either onto the outer surface of upper shaft section  205  or onto the inner surface of sleeve  8  opposite to upper shaft section  205  so as to create a journal bearing. If necessary, a second set of grooves can be added to form a second journal bearing. Pressure generating grooves  16  are formed either on the upper surface of upper shaft section  205  or on the opposing surface of counterplate  19  so as to create a thrust bearing. Additionally, pressure generating grooves may be placed on the bottom of lower shaft section  206  or on the opposing surface of sleeve  8  to minimize material contact between the shaft  20  and the sleeve  8 . 
   The fixed shaft version the second embodiment is shown in  FIG. 2 . It includes a stator  10  and a rotor  6  that is arranged for rotation relative to stator  10 . 
   The rotor  6  comprises a rotor hub  18  and sleeve  8  fixed coaxially to rotor hub  18 . A rotor magnet  12  is bonded to the inner side of a circumferential wall of the rotor hub  18 . The outer side of the circumferential wall of the rotor hub  18  is shaped to hold a magnetic disk (not shown). 
   Sleeve  8  is a tubular member into which is formed a cylindrical hole  85 . Cylindrical hole  85  has a constant radius A. Directly below cylindrical hole  85  and coaxial with cylindrical hole  85  is counterplate opening  88 . Counterplate opening  88  extends from the bottom of cylindrical hole  85  to the lower surface of sleeve  8 . Counterplate opening  88  has a constant radius B that is greater than the radius A of the cylindrical hole  85 . Counterplate  19  is securely fit inside of counterplate opening  88 . Counterplate  19  has an inner radius C that is less than the radius of cylindrical hole  85 . The radius of shaft  20  decreases near the bottom of counterplate  19  to provide for capillary seal  11 . 
   Stator  10  comprises bracket  4 , shaft  20 , core  52  fixedly fitted to bracket  4 ; and coils  54  wound on the core  52 . Stator  10  is radially spaced by a small gap from and arranged opposite to the rotor magnet  12 . 
   Shaft  20  extends through hub  18  and counterplate  19  up into cylindrical hole  85 . The portion of shaft  20  that is inserted into cylindrical hole  85  comprises an upper shaft section  205  and a lower shaft section  206 . However, in this fixed shaft version of the second embodiment, upper shaft section  205  is physically below lower shaft section  206 . Upper shaft section  205  has a constant radius C that is greater than the inner radius B of the counterplate  19  and that is slightly less than the radius A of cylindrical hole  85 . Lower shaft section  206  is a contiguous with upper shaft section  205  and the radius of lower shaft section  206  decreases from the radius C of upper shaft section  205  to a radius of zero at the top of cylindrical hole  85 . Hence lower shaft section  206  is in contact with sleeve  8  at a pivot point  13 . 
   The gap comprised of the spaces between sleeve  8 , counterplate  19  and shaft  20  is filled with an appropriate lubricating fluid. Pressure generating grooves  14  are formed either onto the outer surface of upper shaft section  205  or onto the inner surface of sleeve  8  opposite to upper shaft section  205  so as to create a journal bearing. If necessary, a second set of grooves can be added to form a second journal bearing. Pressure generating grooves  16  are formed either on the upper surface of upper shaft section  205  or on the opposing surface of counterplate  19  so as to create a thrust bearing. Additionally, pressure generating grooves may be placed on the top of lower shaft section  206  or on the opposing surface of sleeve  8  to minimize material contact between the shaft  20  and the sleeve  8 . 
   The third embodiment of the present invention is shown in  FIG. 4  and in  FIG. 5 . The rotating shaft version of this spindle motor is shown in  FIG. 4 . It includes a stator  10  and a rotor  6  that is arranged for rotation relative to stator  10 . 
   Rotor  6  comprises a rotor hub  18  and a tubular shaft  20  fixed coaxially to the rotor hub  18 . A rotor magnet  12  is bonded to the inner side of a circumferential wall of the rotor hub  18 . The outer side of the circumferential wall of the rotor hub  18  is shaped to hold a magnetic disk (not shown). 
   Stator  10  comprises bracket  4 , which is to be mounted on a disk drive device (not shown); sleeve  8 ; core  52 , which is fixedly mounted to bracket  4 ; and coils  54  wound on the core  52 . Coils  54  are radially spaced by a small gap from and arranged opposite to the rotor magnet  12 . 
   Sleeve  8  is a tubular member into which is formed a cylindrical hole  85 . Cylindrical hole  85  has a constant radius A. Directly above cylindrical hole  85  and coaxial with cylindrical hole  85  is thrust-washer opening  89 . Thrust-washer opening  89  has a constant radius D that is greater than the radius A of the cylindrical hole  85  Directly above thrust-washer opening  89  and coaxial with thrust-washer opening  89  is counterplate opening  88 . Counterplate opening  88  extends from the top of thrust-washer opening  89  to the upper surface of sleeve  8 . Counterplate opening  88  has a constant radius B that is greater than the radius D of thrust-washer opening  89 . Counterplate  19  is securely fit inside of counterplate opening  88 . Counterplate  19  has at its lowest point an inner radius C that is the same as the radius A of cylindrical hole  85 . However, the inner radius of counterplate  19  increases near the top of counterplate  19  to provide for capillary seal  11 . 
   Shaft  20  extends into sleeve  8  through hub  18 , counterplate  19 , thrust-washer opening  89 , and cylindrical hole  85 . The portion of shaft  20  that is inserted into sleeve  8  comprises an upper shaft section  205  and a lower shaft section  206 . Upper shaft section  205  has a constant radius C that is less than the radius A of cylindrical hole  85 . Lower shaft section  206  is a contiguous with upper shaft section  205  and the radius of lower shaft section  206  decreases from the radius C of upper shaft section  205  to a radius of zero at the bottom of cylindrical hole  85 . Hence lower shaft section  206  is in contact with sleeve  8  at a pivot point  13 . Thrust-washer  207  is fixedly attached to shaft  20 . Thrust-washer  207  has an outer radius E that is slightly less than the radius of thrust-washer opening  89 . Thrust-washer  207  contains a channel  208  that provides for the circulation of lubricating fluid. The distance between thrustwasher  207  and counterplate  19  is preferably between 4 and 7 microns. The distance between thrustwasher  207  and sleeve  8  is preferably 0.1 mm. Providing this relatively large diameter between the thrust-washer  207  and sleeve  8  reduces power consumption. 
   The gap comprised of the spaces between sleeve  8 , counterplate  19 , thrust-washer  207 , and shaft  20  is filled with an appropriate lubricating fluid. Pressure generating grooves  14  are formed either onto the outer surface of upper shaft section  205  or onto the inner surface of sleeve  8  opposite to upper shaft section  205  so as to create a journal bearing. If necessary, a second set of grooves can be added to form a second journal bearing. Pressure generating grooves  16  are formed either on the upper surface of thrust-washer  207  or on the opposing surface of counterplate  19  so as to create a thrust bearing. Additionally, pressure generating grooves may be placed on the bottom of lower shaft section  206  or on the opposing surface of sleeve  8  to minimize material contact between the shaft  20  and the sleeve  8 . 
   The fixed shaft version the third embodiment is shown in  FIG. 5 . It includes a stator  10  and a rotor  6  that is arranged for rotation relative to stator  10 . 
   Rotor  6  comprises a rotor hub  18  and sleeve  8  fixed coaxially to the rotor hub  18 . A rotor magnet  12  is bonded to the inner side of a circumferential wall of the rotor hub  18 . The outer side of the circumferential wall of the rotor hub  18  is shaped to hold a magnetic disk (not shown). 
   Sleeve  8  is a tubular member into which is formed a cylindrical hole  85 . Cylindrical hole  85  has a constant radius A. Directly below cylindrical hole  85  and coaxial with cylindrical hole  85  is thrust-washer opening  89 . Thrust-washer opening  89  has a constant radius D that is greater than the radius A of the cylindrical hole  85  Directly below thrust-washer opening  89  and coaxial with thrust-washer opening  89  is counterplate opening  88 . Counterplate opening  88  extends from the bottom of thrust-washer opening  89  to the lower surface of sleeve  8 . Counterplate opening  88  has a constant radius B that is greater than the radius D of thrust-washer opening  89 . Counterplate  19  is securely fixed inside of counterplate opening  88 . Counterplate  19  has at its highest point an inner radius C that is the same as the radius A of cylindrical hole  85 . However, the radius of shaft  20  decreases near the bottom of counterplate  19  to provide for capillary seal  11 . 
   Stator  10  comprises bracket  4 ; shaft  20 ; core  52 , which is fixedly mounted to bracket  4 ; and coils  54  wound on the core  52 . Coils  54  are radially spaced by a small gap from and arranged opposite to the rotor magnet  12 . 
   Shaft  20  extends into sleeve  8  through hub  18 , counterplate  19 , thrust-washer opening  89 , and cylindrical hole  85 . The portion of shaft  20  that is inserted into sleeve  8  comprises an upper shaft section  205  and a lower shaft section  206 . However, in this fixed shaft version of the third embodiment, upper shaft section  205  is physically below lower shaft section  206 . Upper shaft section  205  has a constant radius C that is less than the radius A of cylindrical hole  85 . Lower shaft section  206  is a contiguous with upper shaft section  205  and the radius of lower shaft section  206  decreases from the radius C of upper shaft section  205  to a radius of zero at the top of cylindrical hole  85 . Hence lower shaft section  206  is in contact with sleeve  8  at a pivot point  13 . Thrust-washer  207  is fixedly attached to shaft  20 . Thrust-washer  207  has an outer radius E that is slightly less than the radius of thrust-washer opening  89 . Thrust-washer  207  contains a channel  208  that provides for the circulation of lubricating fluid. The distance between thrustwasher  207  and counterplate  19  is preferably between 4 and 7 microns. The distance between thrustwasher  207  and sleeve  8  is preferably 0.1 mm. Providing this relatively large diameter between the thrust-washer  207  and sleeve  8  reduces power consumption. 
   The gap comprised of the spaces between sleeve  8 , counterplate  19 , thrust-washer  207 , and shaft  20  is filled with an appropriate lubricating fluid. Pressure generating grooves  14  are formed either onto the outer surface of upper shaft section  205  or onto the inner surface of sleeve  8  opposite to upper shaft section  205  so as to create a journal bearing. If necessary, a second set of grooves can be added to form a second journal bearing. Pressure generating grooves  16  are formed either on the lower surface of thrust-washer  207  or on the opposing surface of counterplate  19  so as to create a thrust bearing. Additionally, pressure generating grooves may be placed on the top of lower shaft section  206  or on the opposing surface of sleeve  8  to minimize material contact between the shaft  20  and the sleeve  8 .