Pivot assembly bearing and disk drive device

A pivot assembly bearing includes: a sleeve, a shaft inserted into the sleeve, a pair of rolling bearings disposed between the sleeve and the shaft such that the rolling bearings are separated apart from each other in an axial direction. The rolling bearings include an inner ring fixed to the shaft, an outer ring fixed to the sleeve, and a rolling element provided between the inner ring and the outer ring. In at least one of the rolling bearings, a first sealing member contacts an end face of the outer ring facing an outer side in the axial direction. Thus, a first labyrinth gap between the first sealing member and an end face of the inner ring facing the outer side in the axial direction, and a second labyrinth gap between the first sealing member and the shaft are formed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by reference the entire contents of Japanese Patent Application No. 2014-228573 filed in Japan on Nov. 11, 2014 and Japanese Patent Application No. 2015-141288 filed in Japan on Jul. 15, 2015.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pivot assembly bearing used for a magnetic disk drive device, for example, and in particular to a sealing structure having a sealing gap.

2. Description of the Related Art

A typical pivot assembly bearing has a structure in which a sleeve is rotatably supported around the outer circumference of the shaft through rolling bearings. A pair of rolling bearings is provided so that the rolling bearings are separated apart from each other in the axial direction. In such a pivot assembly bearing, improvements have been strongly demanded in terms of preventing emission of particles caused by leakage or evaporation of oil contained in a lubricant filled in the pivot assembly bearing. Emitted particles adhered to disk or a magnetic head causes reading and writing errors. Reducing such emission of particles thus results in a favorable influence on the lifetime and the failure rate of the magnetic disk drive device. Reducing the emission of particles from the pivot assembly bearing is demanded at a higher level in particular for the pivot assembly bearings applied to a hard disk drive device used in a server.

As measures for reducing the emission of particles, technologies have been known and disclosed in Japanese Laid-open Patent Publication No. 2006-077924 and Japanese Laid-open Patent Publication No. 2008-069920, for example. In the technologies, an annular sealing member is disposed between the shaft and the sleeve on both end portions in the axial direction, a flange integrated with the shaft is provided, and a labyrinth gap is provided between the sealing member or the flange and the rolling bearing or the shaft. Another technology has been developed in which a magnetic fluid seal is provided between the sleeve and the shaft (Japanese Laid-open Patent Publication No. 2002-027701). These measures for reducing the emission of particles also function as measures for reducing contamination of pivot assembly bearing caused by foreign materials coming from outside of bearings.

Considering the above-described measures for reducing the emission of particles, the former technology still includes a minute gap even though it is a labyrinth gap. Accordingly, the emission of particles caused by an airflow passing through the gap cannot be completely prevented. Usage of the magnetic fluid seal in the latter technology eliminates the gap where air flows because the gap is filled with a magnetic fluid. However, the magnetic fluid seal raises the cost and may require a special process in assembly.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve, at least partially, the problems in the conventional technology.

A pivot assembly bearing may include: a sleeve; a shaft inserted into the sleeve; a pair of rolling bearings disposed between the sleeve and the shaft such that the rolling bearings are separated apart from each other in an axial direction, the rolling bearings including: an inner ring fixed to the shaft; an outer ring fixed to the sleeve; and a rolling element provided between the inner ring and the outer ring; and, at least in one of the rolling bearings, a first sealing member contacting an end face of the outer ring facing an outer side of the pivot assembly bearing in the axial direction, forming a first labyrinth gap between the first sealing member and an end face of the inner ring facing the outer side in the axial direction, and forming a second labyrinth gap between the first sealing member and the shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to accompanying drawings.

FIG. 1Aillustrates a hard disk drive device1to which a pivot assembly bearing10A according to an embodiment is applied. The hard disk drive device1is a storage device of a computer. In the hard disk drive device1, a magnetic head4provided on the tip of a magnetic head arm3swingably supported by the pivot assembly bearing10A illustrated inFIG. 1Bmoves above a magnetic disk5. This operation allows the hard disk drive device1to record information on the magnetic disk5and read the recorded information from the magnetic disk5.

As illustrated inFIGS. 1B and 2, the pivot assembly bearing10A is a bearing device that enables a cylindrical sleeve20and a shaft40rotating relatively by inserting the shaft40into a rolling bearing30disposed inside the sleeve20.

In the pivot assembly bearing10A, the shaft40is fixed to the bottom part of a case6illustrated inFIG. 1A, and the sleeve20is fitted into a mounting hole2aof a base portion2of the magnetic head arm3. This structure enables the sleeve20to rotate and then the magnetic head arm3swings accompanied with the rotation of the sleeve20.

The following describes the pivot assembly bearing10A according to the embodiment with reference toFIGS. 2 to 5B.

As illustrated inFIG. 2, the pivot assembly bearing10A has the following structure. A pair of rolling bearings30is disposed inside the cylindrical sleeve20and separated apart from each other in the axial direction (in the transverse direction inFIG. 2). The sleeve20is rotatably supported in relation to the shaft40through the pair of rolling bearings30.

The rolling bearing30is a ball bearing including an inner ring31, an outer ring32, and a plurality of spherical rolling elements33held between the inner ring31and the outer ring32. The rolling elements33are rotatably retained in a row in the circumferential direction by a not-illustrated retainer disposed between the inner ring31and the outer ring32. The inner ring31is fixed to an outer circumferential surface42of the shaft40, and the outer ring32is fasten to an inner circumferential surface23of the sleeve20. The rolling bearings30are fixed to the shaft40and the sleeve20by adhesive, for example. In the rolling bearings30, a lubricant such as grease is filled between the inner ring31and the outer ring32.

The shaft40is a cylindrical member having a through-hole40ain its center and a flange41at the right end portion inFIG. 2. The flange41includes a disk part41bextending in the radial direction and a cylindrical part41cprojecting from the outer circumference of the disk part41bin the axial direction. The shaft40has an annular projection44at its end on the side where the flange41is provided. The annular projection44surrounds an opening of the through-hole40a. The outer circumferential surface of the cylindrical part41cof the flange41faces an annular recess20aformed at the end portion of the inner circumferential surface23of the sleeve20. The inner circumferential surface of the cylindrical part41cof the flange41faces the outer circumferential surface of the outer ring32of the rolling bearing30on the right side. The flange41has an annular groove41aon its inner surface side, which faces the end face of the outer ring32in the rolling bearing30on the right side. InFIG. 2, when the inner ring31of the rolling bearing30on the left side is pushed in the right direction, the outer ring32of the rolling bearing30on the left side contacts a spacer21. As a result, the outer ring32of the rolling bearing30on the right side is pushed via the spacer21. Subsequently, the inner ring31of the rolling bearing30on the right side contacts the inner surface of the flange41, whereby a preload is applied to both of the rolling bearings30.

As illustrated inFIG. 3, a labyrinth gap63is provided between the outer circumferential surface of the flange41and the inner circumferential surface of the annular recess20aof the sleeve20. A labyrinth gap63ais provided between an end face of the outer ring32of the rolling bearing30on the right side and the disk part41bof the flange41. A labyrinth gap63bis provided between the outer circumferential surface of the outer ring32and the inner circumferential surface of the cylindrical part41cof the flange41. This structure provides a labyrinth gap having a longer distance in comparison with the conventional art.

As illustrated inFIG. 2, the sleeve20has the spacer21in the central part of the inner circumferential surface23in the axial direction. The spacer21has a smaller inner diameter than that in the ends of the sleeve20. As illustrated inFIG. 4, the spacer21has a positioning part21aand an inclined clearance part21b. The positioning part21ais formed on a step surface on the spacer21and is orthogonal to the inner circumferential surface23of the sleeve20. The inclined clearance part21bis provided to an inner position in the axial direction extending from the positioning part21a. The outer ring32contacts the positioning part21a, whereby the two rolling bearings30are positioned in the axial direction. A preload is applied to the two rolling bearings30positioned in such a manner. Then, the inner ring31is fixed to the outer circumferential surface of the shaft40and the outer ring32is fixed to the inner circumferential surface23of the sleeve20by adhesive.

The pivot assembly bearing10A has an annular seal plate (a first sealing member)50disposed at the end portion on the left side as illustrated inFIG. 2. The seal plate50is disposed for sealing the gap between the sleeve20and the shaft40and its outer circumferential surface52is fixed to the inner circumferential surface23of the sleeve20by adhesive for example.

As illustrated inFIG. 5A, in the end portion on the left side of the pivot assembly bearing10A inFIG. 2, an end face31aof the inner ring31of the rolling bearing30on the left side is positioned on the axially inner side (to the right side inFIG. 5A) in relation to an end face32aof the outer ring32. The seal plate50contacts with the end face32aof the outer ring32. A first labyrinth gap61is formed between the seal plate50and the end face31aof the inner ring31. A second labyrinth gap (a sealing gap)62is formed between the annular inner circumferential surface (an annular surface)53of the seal plate50and the shaft40.

To obtain the above-described structure, the inner ring31is fixed to the shaft40as described above while a preload is applied to the inner ring31toward the inner side in the axial direction. Accordingly, as illustrated inFIG. 5A, the end face32aof the outer ring32is positioned axially outside (to the left side inFIG. 5A) in relation to the end face31aof the inner ring31by an amount equivalent to an axial play in the rolling bearing30. By contacting the seal plate50to the end face32aof the outer ring32and fixing the outer ring32and the seal plate50to the inner circumferential surface23of the sleeve20, the first labyrinth gap61is formed between the seal plate50and the end face31aof the inner ring31. The first labyrinth gap61is readily formed using a flat disk having no step as the seal plate50by contacting the seal plate50to the end face32aof the outer ring32positioned on the axially outside direction relative to the end face31aof the inner ring31. The seal plate50can thus be manufactured at lower cost by press working, for example. An annular second labyrinth gap62is provided between the seal plate50and the shaft40. The second labyrinth gap62can be formed by making the inner diameter of the seal plate50slightly larger than the outer diameter of the shaft40. The second labyrinth gap62is adjusted to have a gap size capable of retaining a lubricating fluid by capillarity. Setting the labyrinth gaps in that manner provides the first labyrinth gap61and the second labyrinth gap62with narrower sizes compared to the conventional art. This structure can effectively prevent leakage and scattering of lubricating oil, or contamination by foreign materials coming from outside pivot assembly bearing even when the labyrinth sealing structure includes only the first labyrinth gap61and the second labyrinth gap62.

As illustrated inFIG. 5B, retaining the lubricating fluid through the entire circumference of the annular second labyrinth gap62provides fluid seal70that can further improve the sealing function. In this case, the lubricating fluid is favorably retained in the second labyrinth gap62by the capillary force if the seal plate50has the cylindrical inner circumferential surface53facing the outer circumferential surface42of the shaft40and providing the second labyrinth gap62, and each of the corner portions between the inner circumferential surface53and both end faces54includes a tapered surface55that gradually separates from the shaft40as the distance from the inner circumferential surface53increases in the axial direction, thereby gradually widening the second labyrinth gap62toward both ends.

The fluid seal70herein refers to a sealing structure in which the lubricating fluid is retained through the entire circumference of the annular second labyrinth gap62formed by the seal plate50for sealing the second labyrinth gap62. As for the fluid seal70, filling the second labyrinth gap62with liquid oil as the lubricating fluid provides an oil film having an appropriate thickness due to the capillarity. Therefore, the oil film can seal the second labyrinth gap62. Any kind of oil can be used to provide the fluid seal70as far as the oil have the viscosity sufficient to retain the oil in the second labyrinth gap62by capillarity. The same kind of oil as the base oil of the grease enclosed between the inner ring31and the outer ring32is preferably used because it has no adverse effect on the grease. Examples of such a base oil include an ester oil, a mineral oil, and a synthetic oil.

InFIG. 5B, the sealing gap (the second labyrinth gap62) is provided between the seal plate50and the outer circumferential surface42of the shaft40. However, the present invention also includes a fluid seal structure in which a sealing gap is provided to the side of the inner circumferential surface23of the sleeve20instead of the side of the shaft40. In this structure, the seal plate50is configured to contact the end face31aof the inner ring31instead of the end face32aof the outer ring32.

In the pivot assembly bearing10A, the emission of particles caused by leakage or evaporation of lubricating oil (base oil) contained in the grease filled inside the pivot assembly bearing10A, and contamination by foreign materials from outside is reduced by the seal plate50at the end portion on the left side where the seal plate50is provided. In addition, the emission of particles and contamination by foreign materials are reduced by the flange41at the end portion on the right side where the flange41is provided. In addition, the minute labyrinth gaps61,62,63,63a, and63beach hardly allow particles and foreign materials to pass therethrough, thereby effectively reducing the emission of particles and the contamination by foreign materials.

In particular, as the fluid seal70having the second labyrinth gap62filled with the oil is provided at the end portion on the left side where the seal plate50is disposed, the emission of particles and foreign materials passing through the second labyrinth gap62are completely prevented. The fluid seal70retains the lubricating fluid only by capillary force, which eliminates the necessity of an expensive magnetic fluid and a permanent magnet as in a magnetic fluid seal. The fluid seal70according to the embodiment can be therefore realized at lower cost and with a reduced number of parts in comparison with a magnetic fluid seal. Accordingly, the fluid seal70has advantages in terms of cost reduction and easiness in assembly.

The tapered surface55is provided on both ends in the axial direction (the width direction) of the inner circumferential surface53of the seal plate50. The second labyrinth gap62has a tapered portion at both ends where the gap gradually widen. If the oil of the fluid seal70reaches one of the tapered portions at both ends of the second labyrinth gap62, the oil is led to the central portion of the second labyrinth gap62in the axial direction due to the capillarity. As a result, the oil of the fluid seal70is prevented from flowing out, whereby the oil always remains in the central portion of the second labyrinth gap62. That is, the fluid seal70shows more stable sealing function.

In the present embodiment, the end portion on the left side where the seal plate50is disposed is provided with the first labyrinth gap61formed by applying a preload to the end face31aof the inner ring31of the rolling bearing30. This means that the size of the first labyrinth gap61is equivalent to the axial play in the rolling bearing30. Therefore, the first labyrinth gap61narrower than the conventional art can be obtained easily. This structure can prevent leakage and scattering of lubricating oil, and contamination by foreign materials from outside more effectively.

The following describes a pivot assembly bearing10B according to another embodiment including a structure similar to the above-described embodiment with reference toFIGS. 6 to 7B. In the reference drawings and descriptions below, common numerals are assigned to similar components to the above-described embodiment, and overlapping explanation thereof will be omitted.

As illustrated inFIG. 6, the pivot assembly bearing10B according to the other embodiment does not have the above-described flange41in the shaft40. On both end portions of the shaft40, the seal plate50fixed to the inner circumferential surface23of the sleeve20and the annular outer seal plate (the second sealing member)51positioned outside the seal plate50are disposed. Each of the outer seal plates51is press-fitted or bonded to a step43provided on both end portions of the shaft40, thereby being fixed to the shaft40. Each of the outer seal plates51faces the inner circumferential surface of the sleeve20. As illustrated inFIG. 7A, a gap64is provided between the outer seal plate51and the inner circumferential surface of the sleeve20, while a gap65is provided between the outer seal plate51and the seal plate50. In such a manner, the pivot assembly bearing10B according to the other embodiment has the same labyrinth structure on both end portions.

As illustrated inFIG. 7A, in both end portions of the pivot assembly bearing10B, the seal plate50contacts the end face32aof the outer ring32. The first labyrinth gap61is provided between the seal plate50and the end face31aof the inner ring31. The annular second labyrinth gap62is provided between the seal plate50and the shaft40. Also, in the pivot assembly bearing10B according to the other embodiment, setting the labyrinth gaps in that manner provides the first labyrinth gap61and the second labyrinth gap62in narrower sizes in comparison with the conventional art. This effectively prevents leakage and scattering of lubricating oil, or contamination by foreign materials from outside even when only by the labyrinth sealing structure including the first labyrinth gap61and the second labyrinth gap62.

Also, in the pivot assembly bearing10B according to the other embodiment as illustrated inFIG. 7B, similarly to the above-described embodiment, the second labyrinth gap62may be filled with oil and thus the fluid seal70may be provided, thereby further improving the sealing capability.

In the pivot assembly bearing10B, the fluid seal70is provided on both end portions. This structure can prevent the emission of particles and the contamination by foreign materials, sufficiently and stably. The tapered surface55of the seal plate50constitutes a capillary seal, thereby preventing the oil of the fluid seal70from flowing out.

The outer seal plate51is disposed outside the seal plate50, thereby achieving effect of preventing the emission of particles and the contamination by the foreign materials more effectively. The outer seal plate51can also prevent the oil of the fluid seal70from flowing out due to airflow.

Also in the other embodiment, the first labyrinth gap61is obtained by applying a preload to the end face31aof the inner ring31of the rolling bearing30, in the same manner as the above-described embodiment. As a result, the first labyrinth gaps61are readily formed and made as narrow as possible. The pivot assembly bearing10B can therefore prevent leakage and scattering of lubricating oil, and contamination by foreign materials from outside more effectively.

The hard disk drive device1illustrated inFIG. 1, in which the magnetic head arm3is swingably supported by the pivot assembly bearing10A according to the above-described embodiment, can maintain internal cleanliness, and thus increases the reliability of the device. Similar advantages can be achieved when the pivot assembly bearing10B is adopted instead of the pivot assembly bearing10A.

Different variations in the shape of the annular surface facing the sealing gap in the first sealing member are possible as described below.

In the above-described embodiments, the seal plate50constitutes the first sealing member. The first sealing member includes the annular surface (the inner circumferential surface53) facing the annular sealing gap (the above-described second labyrinth gap62) provided in such a shape that at least the annular sealing gap does not widen toward the axially central portion of the annular surface, so that the capillary force acts toward the central portion of the annular sealing gap. This structure thus effectively prevents the oil filled in the sealing gap from flowing out.

FIGS. 8A to 8Dillustrate different variations in which the inner circumferential surface53of the seal plate50facing the second labyrinth gap62is provided in such a manner that at least the second labyrinth gap62does not widen toward the central portion of the inner circumferential surface53in the axial direction. However, the present invention is not limited to these variations.

FIG. 8Aillustrates a variation in which each of the tapered surfaces55is provided on both sides of the cylindrical inner circumferential surface53, that is, on the corner portions between the cylindrical inner circumferential surface53and the end face54on both sides.FIG. 8Billustrates a variation in which the tapered surface55has a larger area in comparison withFIG. 8Aand the cylindrical surface is positioned in the central portion in the axial direction.FIG. 8Cillustrates a variation in which the inner circumferential surface53is a convex surface provided without the cylindrical surface in the central portion. The inner circumferential surface53is constituted by two tapered surfaces that meet at the central portion. Thus, the central portion of the inner circumferential surface53projects toward the direction perpendicular to the axial direction looking like a triangle vertice in a sectional view.FIG. 8Dillustrates a variation in which the inner circumferential surface53is defined by a convex circular arc projecting toward the second labyrinth gap62in a sectional view. In any of these variations, filling the second labyrinth gap62with oil forms the fluid seal70because the oil is retained in the central portion of the second labyrinth gap62by the capillary force.

As described above, the present invention can be applied to a pivot assembly bearing that swingably supports a magnetic head arm in a magnetic disk drive device, for example. More particularly, the present invention can be suitably applied to a hard disk drive device used for a server.