Hard disk drive and pivot assembly bearing device

A hard disk drive according to an embodiment of the present invention includes a pivot assembly bearing device with a shaft, rolling bearings and a sleeve, a cylindrical convex portion formed in a cover member at the upper side, protruding inward, and fixed to an upper end surface of the shaft, a convex portion formed on a base member at the lower side, protruding inward, and fixed to a lower end surface of the shaft, and a labyrinth gap formed by opposing an outer peripheral surface of the convex portion to an inner peripheral surface of a sleeve in a radial direction and/or by opposing an outer peripheral surface of the convex portion to the inner peripheral surface of the sleeve in a radial direction.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2015-184133 filed in Japan on Sep. 17, 2015.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hard disk drive including a pivot assembly bearing device, and a pivot assembly bearing device.

2. Description of the Related Art

Hard disk drives are conventionally known, which have a pivot assembly bearing device configured to support a swing arm having a magnetic head for recording and reproducing signals.FIG. 12is a cross-sectional view of a configuration of a conventional pivot assembly bearing device. As illustrated inFIG. 12, the conventional pivot assembly bearing device100has a configuration in which a cylindrical sleeve101relatively rotatably supports a cylindrical shaft103through a pair of axially-spaced rolling bearings102each including an inner race102a, an outer race102b, and rolling bodies102c. The pivot assembly bearing device100having such a configuration fixes the shaft103to a base member of a hard disk drive, fits the sleeve101into a mounting hole104formed in a swing arm and swingably supports the swing arm.

With recent increase in processing speed, and capacity and density of information recorded in hard disk drives, the distance between a magnetic head and a magnetic disk has been reduced, and even fine foreign matter which has not been so significant causes failure of the hard disk drives. Thus, it is increasingly important to maintain cleanliness in the hard disk drives. The rolling bearing uses lubricant, but out-particles are generated by gasification or microparticulation of the lubricant, and a technique for keeping the out-particles from reducing cleanliness in a hard disk drive is demanded. In consideration of such a background, a pivot assembly bearing device is proposed, which keeps out-particles from reducing cleanliness in a hard disk drive (e.g., see Japanese Patent Application Laid-open No. 2013-48005). In particular, a technique is proposed in which sealing plates105and106are disposed at an upper end portion of the sleeve101to form a labyrinth gap, and the out-particles are kept from scattering outside the pivot assembly bearing device100, as illustrated inFIG. 12.

However, as a result of an extensive study, the inventors of the present invention have found that even if sealing performance of a single pivot assembly bearing device is improved, scattering of the out-particles outside the pivot assembly bearing device cannot be effectively suppressed.FIG. 13is a schematic diagram illustrating airflow around the conventional pivot assembly bearing device. In the hard disk drives, airflow is generally generated around the magnetic disk with the rotation of the magnetic disk. As indicated by an arrow A1inFIG. 13, airflow passing through the pivot assembly bearing device partially flows into the pivot assembly bearing device100, from a gap between a cover member107of the hard disk drive and an axial end surface of the sleeve101. Airflow flowing into the pivot assembly bearing device100is discharged from the pivot assembly bearing device100to the outside, as indicated by an arrow A2inFIG. 13. Therefore, the out-particles retained in the pivot assembly bearing device100are scattered outside the pivot assembly bearing device100by this airflow, and the scattered particles reduce the cleanliness in the hard disk drive.

SUMMARY OF THE INVENTION

A hard disk drive according to one aspect of the present invention may include a pivot assembly bearing device, the pivot assembly bearing device having a rolling bearing, a shaft and a sleeve and supporting a swing arm, the rolling bearing having an outer race and an inner race, the shaft having an outer peripheral surface on which the inner race is fixed, the sleeve having an inner peripheral surface on which the outer race is fixed. The hard disk drive comprises: a first convex portion that is cylindrical and/or a second convex portion that is cylindrical, the first convex portion being formed on a cover member positioned on an upper side of the hard disk drive, protruding toward an inside of the hard disk drive, and being fixed to an upper end surface of the shaft, the second convex portion being formed on a base member being positioned on a lower side of the hard disk drive, protruding toward an inside of the hard disk drive, and being fixed to a lower end surface of the shaft, an outer peripheral surface of the first convex portion and/or an outer peripheral surface of the second convex portion being opposed to an inner peripheral surface of the sleeve in a radial direction to form a labyrinth gap.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A configuration and operation of a hard disk drive according to an embodiment of the present invention is described below with reference to the drawings. In the following description, the terms such as “upper” and “lower” are only used to indicate directions in the drawings, and the terms are not intended to limit the position of the hard disk drive in the present invention.

Overall Configuration of Hard Disk Drive

First, an overall configuration of the hard disk drive according to an embodiment of the present invention is described with reference toFIG. 1.

FIG. 1is a perspective view of the overall configuration of the bard disk drive according to an embodiment of the present invention. As illustrated inFIG. 1, a hard disk drive1according to an embodiment of the present invention includes a swing arm3swingably supported by a pivot assembly bearing device2fitted into a mounting hole. The pivot assembly bearing device2is described later. In this hard disk drive1, a magnetic head4disposed at an end of the swing arm3moves on a magnetic disk5being rotated, records information on the magnetic disk5, and reads the information recorded in the magnetic disk5.

Configuration of Pivot Assembly Bearing Device

First Embodiment

Next, a configuration of the pivot assembly bearing device according to a first embodiment of the present invention is described with reference toFIGS. 2 to 4.FIG. 2is a cross-sectional view of the configuration of the pivot assembly bearing device according to the first embodiment of the present invention.FIG. 3is a partially enlarged cross-sectional view of a configuration around a rolling bearing in the pivot assembly bearing device illustrated inFIG. 2.FIG. 4is a schematic diagram illustrating airflow around the pivot assembly bearing device according to the first embodiment of the present invention.

As illustrated inFIG. 2, the pivot assembly bearing device2according to the first embodiment of the present invention includes a pair of upper and lower rolling bearings23disposed between a cylindrical shaft21and a cylindrical sleeve22. Each of the rolling bearings23includes an inner race23afixedly bonded on en outer peripheral surface21aof the shaft21, an outer race23bfixedly bonded on an inner peripheral surface22bof the sleeve22, a plurality of rolling bodies23cprovided between the inner race23aand the outer race23b, and an annular holder23dconfigured to hold the rolling bodies23c. The sleeve22is longer than the shaft21, and has an upper end surface22fdisposed to be positioned above an upper end surface21fof the shaft21, and a lower and surface22ddisposed to be positioned below a lower surface of an outer flange21bof the shaft21which is described later. Such a configuration allows the pivot assembly bearing device2incorporated into the hard disk drive to form a labyrinth gap as described later.

The shaft21is a cylindrical member having an outer flange21bradially protruding, at a lower end portion. The outer flange21bhas an upper surface21b1on the inner peripheral side, and a lower end surface23a1of the inner race23aof the upper rolling bearing23disposed on the axially lower side abuts on the upper surface21b1. By this way, the inner race23aof the rolling bearing23at the axially lower side is positioned with respect to the shaft21in the vertical direction (axial direction). The outer flange21bhas an outer peripheral surface21b2disposed opposite to the inner peripheral surface22bof the sleeve22through a gap. The outer flange21bhas an upper surface on the outer peripheral side, and an annular stepped portion21cis formed on the upper surface to avoid making contact with the outer race23bof the rolling bearing23disposed on the axially lower side.

The outer flange21bhas a lower surface21b3fixed on an upper surface (protruding surface) of a cylindrical convex portion11a(second convex portion). The cylindrical convex portion11ais formed on a base member11positioned on the lower side of the hard disk drive1, and protruding toward the inside of a casing of the hard disk drive1. An annular bonding area21dextending in a circumferential direction is formed at a position on the outer peripheral surface21aof the shaft21, corresponding to each of the rolling bearings23disposed vertically. A boss21eand a through-hole disposed coaxially with the shaft21are provided in a lower end surface of the shaft21. The boss21eis fitted to an inner peripheral surface of the convex portion11a. Screw threads are formed in an upper end portion and a lower end portion of the through-hole, and screws not illustrated are tightened into the screw threads. Therefore, the pivot assembly bearing device2is fixed to the base member11on the lower side of the hard disk drive1through the convex portion11a, and is fixed to a cover member12on the upper side of the hard disk drive device through a convex portion12a.

The sleeve22has an outer peripheral surface22afixedly fitted into an inner peripheral surface31aof a mounting hole31formed in the swing arm3(seeFIG. 1). A fixing method includes bonding, press-fitting, or a tolerance ring, but any of them may be used. A pair of upper and lower outer race fitting portions22cto which the outer races23bof the rolling bearings23are fitted is formed in the inner peripheral surface22bof the sleeve22, and the outer races23bof the pair of upper and lower rolling bearings23are correspondingly fitted to outer race fitting portions22c. Therefore, the pair of the rolling bearings23is positioned with respect to the sleeve22in the axial direction (vertical direction), and an axial distance (vertical interval) between the upper and lower rolling bearings23is held at a predetermined distance. Note that the outer flange21bof the shaft21has an outer diameter set smaller than a diameter of the outer race fitting portion22cof the sleeve22, and larger than an inner diameter of the outer race23bof the rolling bearing23.

The lower end surface22dof the sleeve22is opposed to an inner surface11bof the base member11through a gap. Furthermore, the sleeve22has a lower inner peripheral surface22eopposed to an outer peripheral surface11a1of the convex portion11athrough a gap. Thus, the labyrinth gap having a plurality of bent portions is formed between the outer peripheral surface21b2of the outer flange21band the outer peripheral surface11a1of the convex portion11a, and the lower inner peripheral surface22eof the sleeve22, and between the lower end surface22dof the sleeve22and the inner surface11bof the base member11.

As illustrated inFIG. 3, in a space between the outer peripheral surface21aof the shaft21and the inner peripheral surface22bof the sleeve22, an annular sealing member24is disposed at an upper portion of the upper rolling bearing23. An inclined surface is formed at a corner between an upper surface24aand an outer peripheral surface of the sealing member24to provide a cut-out portion24a1. The sealing member24has an upper surface24awhich is disposed opposite to a lower surface12a2(protruding surface) of the convex portion12a(example of first convex portion), through a gap. The convex portion12a(example of first convex portion) is formed on the cover member12positioned on the upper side of the hard disk drive1, and protrudes toward the inside of the hard disk drive1. Furthermore, the outer peripheral surface of the sealing member24is fixedly bonded to the inner peripheral surface22bof the sleeve22, and further an inner peripheral surface24bof the sealing member24is disposed opposite to the outer peripheral surface21aof the shaft21, through a gap. The sealing member24has a lower surface abutting on the outer race23bof the rolling bearing23. Since a preload is applied to the rolling bearing23, an end surface of the inner race23ais positioned slightly lower than an end surface of the outer race23b. Therefore, a minute gap communicating with the labyrinth gap is formed between the lower surface of the sealing member24and the end surface of the inner race.

The inner peripheral surface22bof the sleeve22is opposed to an outer peripheral surface12a1of the convex portion12aof the cover member12through a gap. The upper end surface22fof the sleeve22is opposed to an inner surface12bof the cover member12through a gap. Thus, the labyrinth gap having a plurality of bent portions is formed between the outer peripheral surface21aof the shaft21and the inner peripheral surface24bof the sealing member24, between the lower surface12a2of the convex portion12aand the upper surface24aof the sealing member24, between the inner peripheral surface22bof the sleeve22and the outer peripheral surface12a1of the convex portion12a, and between the upper end surface22fof the sleeve22and the inner surface12bof the cover member12.

As indicated by the arrow A3inFIG. 4, according to the hard disk drive1having such a configuration, the labyrinth gap having the plurality of bent portions formed by opposing the inner peripheral surface22bof the sleeve22to the convex portion12aof the cover member12avoids airflow generated around the magnetic disk5due to the rotation of the magnetic disk5entering the pivot assembly bearing device2. Further, even if the airflow enters the pivot assembly bearing device2, as the labyrinth gap has the plurality of bent portions with a narrow gap width, the flow rate of the airflow is reduced. Still further, as indicated by the arrow A4inFIG. 4, the labyrinth gap formed by the shaft21, the sleeve22, the sealing member24, and the cover member12can minimize discharge of the airflow, and the rate of airflow discharged from the pivot assembly bearing device2to the outside can be further reduced. Still another further, the cut-out portion24a1formed at an upper portion of the sealing member24forms an enlarged gap portion at an intermediate portion of the labyrinth gap. The flow rate of the airflow is reduced in the enlarged gap portion, and the flow rate of the airflow is further reduced in the proximity of the outlet, and thus, the flow rate of the airflow discharged from the pivot assembly bearing device2to the outside can be further reduced. In the present embodiment, the cut-out portion24a1is provided in the corner between the upper surface24aand the outer peripheral surface of the sealing member24, but the cut-out portion24a1may be provided between the upper surface24aand the inner peripheral surface of the sealing member24.

Therefore, the out-particles retained in the pivot assembly bearing device2can be kept from being scattered by airflow to the outside of the pivot assembly bearing device2, and thus the cleanliness in the hard disk drive1can be kept from being deteriorated by the scattered out-particles. InFIG. 4, only airflow in an upper portion of the hard disk drive1is illustrated, but also in a lower portion of the hard disk drive1, the labyrinth gap is formed by the sleeve22, and the convex portion11aof the base member11. Therefore, also in the lower portion of the hard disk drive1, the flow rate of the airflow discharged from the pivot assembly bearing device2to the outside is reduced, and the out-particles can be kept from being scattered by the airflow to the outside of the pivot assembly bearing device2. Furthermore, in the present embodiment, the labyrinth gaps are formed at both of the upper and lower portions of the hard disk drive1, but the labyrinth gap may be formed at any of the upper and lower portions of the hard disk drive1.

First Modification

FIG. 5is a cross-sectional view of a configuration of a modification of the pivot assembly bearing device illustrated inFIG. 2. In the above embodiment, the annular sealing member24is disposed at the upper portion of the upper rolling bearing23, but, as illustrated inFIG. 5, the sealing member24may be omitted so that an upper end surface of the upper rolling bearing23may be disposed opposite to the lower surface12a2(protruding surface) of the convex portion12aof the cover member12. In such a configuration, since the labyrinth gap is formed between the sleeve22and the cover member12, the out-particles retained in the pivot assembly bearing device2can be kept from being scattered by airflow to the outside of the pivot assembly bearing device2. Furthermore, according to such a configuration, a distance between the upper rolling bearing23and the lower rolling bearing23can be increased by the thickness of the omitted sealing member24, and axial rigidity of the pivot assembly bearing device2can be increased. Alternatively, the whole length of the sleeve22can be reduced by the thickness of the omitted sealing member24, and thus, the hard disk drive advantageously can have a reduced thickness.

Second Modification

FIGS. 6 to 8are cross-sectional views of configurations of modifications of the cut-out portion illustrated inFIG. 3. In the first embodiment, the inclined surface is formed at a corner of the upper surface24aof the sealing member24to provide the cut-out portion24a1. However, as illustrated inFIG. 6 or 7, a curved surface instead of the inclined surface may be formed at a corner of the upper surface24aof the sealing member24to provide a cut-out portion24a2or24a3. Further, as illustrated inFIG. 8, a step may be formed at a corner of the upper surface24aof the sealing member24to form a cut-out portion24a4. The cut-out portion may be formed also in the inner peripheral surface of the sealing member24. As described above, the cut-out portion may be formed into any shape and at any position, as long as the cut-out portion is formed in the upper surface24aor the inner peripheral surface of the sealing member24, the enlarged gap portion is formed in the intermediate portion of the labyrinth gap, and the enlarged gap portion reduces the flow rate of the airflow.

Second Embodiment

Next, a configuration of a pivot assembly bearing device according to a second embodiment of the present invention is described with reference toFIG. 9.FIG. 9is a cross-sectional view of a configuration of the pivot assembly bearing device according to the second embodiment of the present invention. The pivot assembly bearing device according to the second embodiment of the present invention is different from the pivot assembly bearing device according to the first embodiment only in configurations of the sleeve22and the mounting hole31of the swing arm. Thus, only the configurations of the sleeve22and the mounting hole31of the swing arm are described below.

As illustrated inFIG. 9, in the present embodiment, the lower end surface22dof the sleeve22is disposed, through a gap, opposite to an upper surface11a2(protruding surface) of convex portion11aformed at the base member11on the lower side, and the upper end surface22fof the sleeve22is disposed, through a gap, opposite to the lower surface12a2(protruding surface) of the convey portion12aformed on the cover member12on the upper side. Further, an upper end portion31aand a lower end portion31baround the mounting hole31are disposed, through gaps, opposite to the inner surface12bof the cover member12and the inner surface11bof the base member11, respectively. Still further, an upper inner peripheral surface31cand a lower inner peripheral surface31dof the mounting hole31are disposed, through gaps, opposite to the outer peripheral surface12a1of the convex portion12aand the outer peripheral surface11a1of the convex portion11a.

As described above, in the present embodiment, a labyrinth gap is formed on the upper side of the pivot assembly bearing device2, between the upper end portion31aaround the mounting hole31and the inner surface12bof the cover member12, the upper inner peripheral surface31cof the mounting hole31and the outer peripheral surface12a1of the convex portion12a, and the upper end surface22fof the sleeve22and the lower surface12a2(protruding surface) of the convex portion12a. Furthermore, a labyrinth gap is formed on the lower side of the pivot assembly bearing device2, between the lower end portion31baround the mounting hole31and the inner surface11bof the base member11, the lower inner peripheral surface31dof the mounting hole31and the outer peripheral surface11a1of the convex portion11a, and the lower end surface22dof the sleeve22and the upper surface11a2of the convex portion11a.

Therefore, also in the present embodiment, the out-particles retained in the pivot assembly bearing device2can be kept from being scattered by airflow to the outside of the pivot assembly bearing device2, and thus the cleanliness in the hard disk drive1can be kept from being deteriorated by the out-particles. Furthermore, in the present embodiment, the labyrinth gaps are formed at both of the upper and lower portions of the hard disk drive1, but the labyrinth gap may be formed at any of the upper and lower portions of the hard disk drive1.

Third Modification

FIG. 10is a cross-sectional view of a configuration of a modification of the pivot assembly bearing device illustrated inFIG. 9. In the second embodiment, the sleeve22is disposed between the shaft21and the mounting hole31. However, the sleeve22may be omitted and a spacer member26configured to position the rolling bearings23may be provided between the upper and lower rolling bearings23, as illustrated inFIG. 10. According to such a configuration, the outer diameter of the shaft21can be increased by a thickness of the omitted sleeve22in order to increase the axial rigidity of the pivot assembly bearing device, or the pivot assembly bearing device2can have a size reduced by the thickness of the omitted sleeve22, without changing the outer diameter of the shaft21.

For the pivot assembly bearing device according to the first embodiment ofFIG. 2(Implemented Example), maximum flow rates of outward airflow in the proximity of the outlet of the labyrinth gap at the upper portion and outward airflow in the proximity of the outlet of the labyrinth gap at the lower portion were evaluated by fluid analysis, changing the gap width “a” of the axial gap and the gap width “b” of the radial gap near each of the upper and lower outlets of the labyrinth gaps.FIG. 4shows the gap width “a” of the axial gap, the gap width “b” of the radial gap, and outward airflow A4in the labyrinth gap at the upper portion. The gap width “a” of the axial gap, the gap width “b” of the radial gap, and outward airflow in the labyrinth gap at the lower portion is similar toFIG. 4. In addition, with respect to a conventional pivot assembly bearing device illustrated inFIG. 12, maximum flow rates of outward airflow (airflow A2illustrated inFIG. 13) around an outlet of a labyrinth gap at an upper portion and outward airflow around an outlet of a labyrinth gap at a lower portion were also determined by fluid analysis. Evaluation results of comparison between a maximum flow rats in a conventional example and maximum flow rate in the Implemented Example are illustrated inFIG. 11. In this evaluation, the gap width “a” is equal to the gap width “b” at both the lower portion and the upper portion. Note that, numerical values in the Implemented Example inFIG. 11represent the ratio of the maximum flow rate of airflow in the Implemented Example compared to the maximum flow rate of airflow in the conventional example. That is, the maximum flow rate of the conventional example corresponds to 100% inFIG. 11. InFIG. 11, the upper outlet represents the area of the radial gap which is located near the upper end surface of the sleeve in the labyrinth gap formed at the upper portion of the pivot assembly hearing device illustrated inFIG. 2, and the lower outlet represents the area of the radial gap area which is located near the lower end surface of the sleeve in the labyrinth gap formed at the lower portion of the pivot assembly bearing device illustrated inFIG. 2.

As illustrated inFIG. 11, in the Implemented Example, the maximum flow rates of the outward airflow are reduced at the upper outlet and the lower outlet as the widths “a” and “b” are reduced, compared with the conventional example. Therefore, according to the pivot assembly bearing device of the Implemented Example, it was confirmed that formation of the labyrinth gap suppresses discharge of airflow from the outlet side of the pivot assembly bearing device, and the out-particles generated in the pivot assembly bearing device can be kept from scattering outside. In addition, it is predicted fromFIG. 11that when the gap width is not less than 0.37 mm, the maximum flow rate at the lower outlet in the Implemented Example is equal to that of the conventional example. Accordingly, in order to reduce scattering of the out-particles to the outside, the gap width is preferably less than 0.37 mm in the proximity of the outlets of the labyrinth gaps at the upper and lower portions.

The hard disk drive and the pivot assembly bearing device according to the embodiment of the present invention can minimize the deterioration of the cleanliness in the hard disk drive caused by the out-particles originated from the pivot assembly device.