Low power spindle motor with a fluid dynamic thrust bearing having a reduced outer diameter

#The following invention relates to electronic spindle motors of the type used in disk drives and in particular relates to improvements in fluid thrust 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 known to wear parts, and in time increased 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, noise and vibration, all of which are undesirable in a disk drive motor.

#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 side cut-away view of an electronic spindle motor having a shaft with an integrated thrust-washer and a first thrust bearings provided between the thrust-washer and the bearing sleeve and a second thrust bearing provided between the thrust-washer and a counter-plate.

#FIG. 2 is a perspective view of the shaft inserted into a bearing sleeve and having a plurality of herringbone grooves.

#As shown in FIG. 1, a compact electronic spindle motor 10 preferably includes a central shaft 12 supporting for rotation a rotor 14 having a hub 16. When the motor 10 is used in a disc drive, the hub 16 will support and carry a magnetic disc (not shown) during rotation. The rotor 14 comprises an annular vertical rotor support wall 24, which supports rotor magnets 26. A stator 18 preferably includes an annular vertical stator support wall 20, which supports a plurality of stator windings 22 such that the stator windings are located in opposing relationship with rotor magnets 26.

#The stator support wall 20 defines an inner cylindrical hole 28. A bearing sleeve 30 is inserted into the inner cylindrical hole 28 and is fixedly mounted therein. The bearing sleeve 30 may be glued to the inner wall of the hole 28. In the preferred embodiment, the bearing sleeve 30 has an inner bore 32 with substantially cylindrical walls and an opening on each side of the bore. A bottom opening of the bore is preferably closed with a counter-plate 34. The central shaft 12 is preferably inserted into the bore 32 through its top opening such that a gap 40 is formed between an outer surface of the shaft 12 and an inner surface of the bore 32.

#The central shaft 12 preferably includes a vertical cylinder portion 38 and a thrust-washer portion 36 formed integrally with the vertical cylinder portion 38 and extending outwardly therefrom. The bore 32 of the bearing sleeve preferably includes a vertical portion 44 and an outwardly extended portion 42, which has an inner diameter greater than the inner diameter of the vertical portion 44. When the shaft 12 is inserted into the bore 32, the vertical cylinder portion 38 of the shaft 12 is preferably located substantially within the vertical portion 44 of the bore 32. Similarly, the thrust-washer portion 36 of the shaft 12 is preferably located substantially within the outwardly extended portion 42 of the bore 32.