JP2012189089A - Fluid dynamic pressure bearing device and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To highly precisely form recessed parts, while reducing time and effort in forming the recessed parts for generating dynamic pressure by form rolling on the external peripheral surface of a shaft member.SOLUTION: A fluid dynamic pressure bearing device 1 has a plurality of recessed parts (dynamic pressure grooves Aa) for generating dynamic pressure action to lubricating oil interposed in a radial bearing gap, on the external peripheral surface 21a of a shaft part 21 which forms the radial bearing gap between the inner peripheral surface 8a of a bearing sleeve 8 and the external peripheral surface. The shaft part 21 has a surface cured layer formed by applying heat treatment to a shaft material and the dynamic pressure grooves Aa are formed by applying form rolling to the surface cured layer.

Description

  The present invention relates to a fluid dynamic bearing device and a manufacturing method thereof.

  A fluid dynamic pressure bearing device is a bearing that non-contact-supports a bearing member and a shaft member inserted in the inner periphery of the bearing member in a non-contact manner by a dynamic pressure action of a lubricating fluid (for example, lubricating oil) generated in a bearing gap. Device. This fluid dynamic pressure bearing device has characteristics such as high-speed rotation, high rotation accuracy, and low noise. Recently, a disk drive device (for example, a magnetic disk drive device such as an HDD or the like, a CD) In addition, it is suitably used as a motor bearing device such as a spindle motor of an optical disc driving apparatus such as a DVD or a Blu-ray disc, a polygon scanner motor of a laser beam printer (LBP), or a fan motor of an electric device.

  For example, a fluid dynamic bearing device incorporated in a spindle motor of a disk drive device supports a radial bearing portion that supports relative rotation of the bearing member and the shaft member in the radial direction, and supports relative rotation of the bearing member and the shaft member in the thrust direction. In general, the radial bearing portion is a so-called hydrodynamic bearing among the two bearing portions. When the radial bearing portion is constituted by a dynamic pressure bearing, a concave portion (for example, a dynamic pressure) for generating fluid dynamic pressure in the radial bearing gap is formed on the inner circumferential surface of the bearing member or the outer circumferential surface of the shaft member facing each other through the radial bearing gap. A plurality of pressure grooves are provided. The dynamic pressure groove is generally formed in a minute groove having a groove depth and a groove width of about several μm to several tens of μm. As a method for accurately forming such a minute groove, for example, the following What is described in Patent Document 1 is known.

  Specifically, a compression force is applied to the sintered metal material in a state where a core rod having a groove type portion corresponding to the dynamic pressure groove shape is inserted on the outer peripheral surface of the cylindrical sintered metal material processed into the bearing member. In addition, the sintered metal material generated by the release of the compression force after the inner peripheral surface of the sintered metal material bites into the outer peripheral surface of the core rod to transfer the shape of the groove mold part to the inner peripheral surface of the sintered metal material. The core rod is extracted from the inner periphery of the sintered metal material without breaking the shape of the dynamic pressure groove using the spring back.

  However, when molding dynamic pressure grooves on the inner peripheral surface of a sintered metal material as described above, it is necessary to apply a considerably large pressing force to the sintered metal material. The force applied to the die (die) arranged on the outer periphery of the sintered metal material in order to constrain the outer peripheral surface of the metal material also becomes considerably large. Therefore, the core rod and the die are likely to be worn out, and it is necessary to frequently replace the mold, which contributes to an increase in the cost of forming the dynamic pressure groove and hence the manufacturing cost of the fluid dynamic bearing device. . Therefore, as a means for reducing the formation cost of the dynamic pressure groove, attention has been paid again to forming the dynamic pressure groove on the outer peripheral surface of the shaft member.

  The shaft member is generally formed of a high-strength and high-rigidity metal material such as hardened stainless steel. As a method for forming a plurality of dynamic pressure grooves on the outer peripheral surface of such a metal shaft member, cutting, etching, rolling, etc. can be adopted, but among these, high precision dynamic pressure grooves are compared. There is a tendency that rolling that can be formed easily and at low cost is used heavily. For example, Patent Document 2 below describes a specific procedure that is generally employed when a dynamic pressure groove is formed by rolling on the outer peripheral surface of a shaft member. More specifically, first, a rolling die is pressed against a shaft material finished to a predetermined shaft diameter, a dynamic pressure groove is formed on the outer peripheral surface of the shaft material, and then the shaft material is subjected to heat treatment to obtain a quenched shaft. Then, the outer peripheral surface including the dynamic pressure groove and the hill portion defining the dynamic pressure groove is formed with a predetermined accuracy by performing final finishing such as grinding on the outer peripheral surface of the quenching shaft having the dynamic pressure groove formed on the outer peripheral surface. A shaft member as a finished product is obtained.

JP 11-294458 A Japanese Patent Laid-Open No. 7-114766

  As described in the above-mentioned Patent Document 2, if a rolling process is performed on an unheat-treated shaft material, since the material meat tends to plastically flow, there is an advantage that a dynamic pressure groove can be easily formed. is there. However, on the other hand, the thickness of the material greatly rises on both sides of the convex portion 100 as the rolling die is pressed, so that the groove depth is likely to vary greatly between the dynamic pressure grooves 101 (see FIG. 10). Because heat treatment is performed with the internal stress accumulated in the material, deformation due to strain is likely to occur, and final finishing such as grinding is essential to ensure the desired rotational accuracy. Moreover, there is a problem that the allowance for meat in the final finishing is large (a lot of material loss).

  Further, when the shaft material is subjected to heat treatment, an oxide film called “black skin” is formed on the surface of the quenched shaft (surface layer portion of the surface hardened layer). If the black skin remains, the black skin peels off as the fluid pressure in the radial bearing gap increases during the operation of the bearing, which may cause contamination and reduce bearing performance. Therefore, in the manufacturing process of the shaft member, a removal process for removing the black skin is generally performed separately from the final finishing such as grinding. If the shaft material is heat-treated after forming the dynamic pressure grooves as in the above procedure, black skin will remain in each dynamic pressure groove, but the groove depth and width are micron. It is not easy to completely remove the black skin remaining in the dynamic pressure grooves formed in the order minute grooves. Of course, if removal processing such as barrel processing is performed, the black skin in the dynamic pressure grooves can be removed, but batch processing is required, resulting in an increase in processing costs.

  Therefore, the present invention reduces the time and effort required to form a recess for rolling the dynamic fluid pressure action in the lubricating fluid interposed in the radial bearing gap on the outer peripheral surface of the shaft member, while generating dynamic pressure. An object of the present invention is to reduce the cost of a fluid dynamic bearing device capable of forming a concave portion for use with high accuracy, and thereby exhibiting desired bearing performance.

  The inventors of the present application based on the knowledge that the depth dimension required for the concave portion (the concave portion for generating dynamic pressure) for generating the dynamic pressure in the lubricating fluid interposed in the radial bearing gap is on the order of microns. As a result, they have found specific means to achieve the above-mentioned purpose.

  That is, the present invention created to achieve the above object includes a bearing member, a shaft member inserted into the inner periphery of the bearing member, and an inner peripheral surface of the bearing member and an outer peripheral surface of the shaft member. In the fluid dynamic pressure bearing device, the shaft member is provided with a plurality of recesses for generating a dynamic pressure action on the lubricating fluid interposed in the radial bearing gap on the outer peripheral surface of the shaft member. It has a surface hardened layer formed by subjecting the shaft material to heat treatment, and the concave portion is formed by rolling the surface hardened layer. The shape of the “recess” here is not particularly limited, and includes dimples (dents) in addition to so-called dynamic pressure grooves such as axial grooves extending in the axial direction and inclined grooves inclined with respect to the axial direction. .

  As described above, the dynamic pressure generating recess provided on the outer peripheral surface of the shaft member has a required depth dimension on the micron order, and therefore is transferred to a hardened surface layer (quenched shaft) formed by heat treatment. Even when the fabrication process is performed, a recess having a predetermined depth dimension can be formed. If the concave portions are formed by rolling the hardened surface layer, the meat on both sides of the convex portions generated by rolling is compared with the case of rolling the unheated shaft material. It is possible to reduce the amount of swell and to prevent variations in the depth dimension between the recesses. In addition, it is not necessary to heat-treat the shaft material after the recess is formed by rolling, that is, in a state where internal stress is accumulated in the shaft material, so that deformation due to strain hardly occurs. Therefore, the final finishing can be omitted depending on the case, and the processing amount can be reduced even when the final finishing is performed. Furthermore, the removal process of the black skin formed in the surface layer part (outer surface of the quenching shaft) of the surface hardened layer can be executed prior to the rolling process due to the configuration of the present invention. Since the outer peripheral surface of the quenching shaft before the rolling process has a substantially smooth cylindrical surface shape without minute irregularities such as concave portions for generating dynamic pressure, the black skin can be easily removed. As a result, the black skin peels off from the shaft member and becomes contaminated, and it is difficult for a problem that the bearing performance deteriorates to occur.

  In order to effectively enjoy the various effects described above, a surface hardened layer having a hardness of HV450 or higher is formed, and the surface hardened layer may be subjected to a rolling process.

  The radial bearing gap can be formed at two locations separated in the axial direction. In this way, moment rigidity can be increased while suppressing an increase in rotational torque. In this case, it is desirable to provide a cylindrical middle relief portion having a smaller diameter than the bottom portion of the concave portion in a region located between the two radial bearing gaps on the outer peripheral surface of the shaft member. In this way, the inner peripheral surface of the bearing member is formed into a perfect circular cylindrical surface having a constant diameter, and the manufacturing cost is reduced, while the shaft member and the inner peripheral surface of the bearing member are spaced from each other. A lubricating fluid reservoir can be provided. If a lubricating fluid pool is provided between two radial bearing gaps adjacent to each other in the axial direction, the radial bearing gap can be always filled with abundant lubricating fluid, and the rotational accuracy in the radial direction can be stabilized.

  If the bearing member is made of sintered metal, the lubricating fluid held in the internal pores can be oozed out into the radial bearing gap, so there is a further situation where the lubricating fluid to be interposed in the radial bearing gap is insufficient. Effectively prevented. Further, since the concave portion for generating fluid dynamic pressure in the radial bearing gap is provided on the outer peripheral surface of the shaft member, there is no need to provide a concave portion for generating dynamic pressure on the inner peripheral surface of the bearing member. The inner peripheral surface of the member can be formed into a smooth cylindrical surface. For this reason, even if the bearing member is formed of sintered metal, the manufacturing cost is increased as much as possible when the concave portion for generating dynamic pressure is molded on the inner peripheral surface of the sintered metal bearing member. Is prevented.

  The shaft member may include a shaft portion having a concave portion for generating dynamic pressure, and a flange portion provided at one end of the shaft portion and forming a thrust bearing gap between the end surface of the bearing member. The shaft portion and the flange portion can be provided integrally. However, in the configuration of the present invention in which the concave portion for generating dynamic pressure is formed by rolling, the concave portion is provided when the flange portion is provided integrally with the shaft portion. There is a possibility that the workability of the steel will deteriorate. Therefore, it is desirable that the flange portion is attached and fixed to one end of the shaft portion by an appropriate means. The method of fixing the flange part to the shaft part is not particularly limited, and press-fitting, bonding, press-fitting adhesion (combination of press-fitting and bonding), welding, welding, caulking, etc., are adopted depending on the shape of the flange part and the forming material. Can do.

  In this case, a plurality of recesses for generating fluid dynamic pressure in the thrust bearing gap can be provided on the end face of the flange portion that forms the thrust bearing gap with the end face of the bearing member. In this way, it is not necessary to form a recess for generating fluid dynamic pressure in the thrust bearing gap on the end face of the bearing member facing through the thrust bearing gap, thereby reducing the manufacturing cost of the bearing member. be able to.

  The fluid dynamic pressure bearing device according to the present invention described above can be suitably used by being incorporated in a motor having a stator coil and a rotor magnet, for example, a spindle motor for a disk drive device.

  Moreover, in order to achieve said objective, in this invention, it forms between the bearing member, the shaft member inserted in the inner periphery of a bearing member, the inner peripheral surface of a bearing member, and the outer peripheral surface of a shaft member. In a method of manufacturing a fluid dynamic bearing device, comprising a radial bearing gap, and a plurality of recesses for generating a dynamic pressure effect on a lubricating fluid interposed in the radial bearing gap on an outer peripheral surface of the shaft member. A heat treatment step for forming a hardened shaft having a surface hardened layer by applying a heat treatment; and a rolling step for forming a concave portion by subjecting the surface hardened layer of the hardened shaft to a rolling process. A method for manufacturing a fluid dynamic bearing device is provided.

  In this case, in the rolling process, it is desirable to use a rolling mold in which at least the concave portion forming portion for forming the concave portion is formed to have a hardness of HV100 or more higher than the surface hardened layer of the quenching shaft. Thereby, the concave part for dynamic pressure generation of a predetermined shape and a predetermined depth can be formed in the surface hardened layer.

  A removal step for removing the surface layer portion (black skin) of the surface hardened layer can be further provided between the heat treatment step and the rolling step. As described above, because of the configuration of the present invention, the outer peripheral surface of the quenching shaft before the rolling process is formed in a generally smooth cylindrical surface without minute irregularities, so that the black skin can be easily removed. Can do. As a result, it is possible to easily prevent the black skin from being peeled off from the shaft member to be contaminated and causing a problem that the bearing performance is deteriorated.

  After the rolling process, a finishing process for finishing the outer peripheral surface of the quenching shaft with a predetermined accuracy can be further provided. As described above, if the configuration of the present invention is adopted, the amount of bulging of the meat generated by the rolling process can be reduced, and the degree of deformation caused by quenching can be reduced. It can be omitted. Therefore, it is sufficient to provide this finishing step as necessary. Note that the finishing method is not particularly limited, and grinding, polishing, plastic working, and the like can be employed.

  As described above, according to the present invention, it is possible to reduce the time required for forming the concave portion for generating fluid dynamic pressure in the radial bearing gap by rolling on the outer peripheral surface of the shaft member, while increasing the concave portion. It becomes possible to form with accuracy. As a result, the cost of the fluid dynamic bearing device capable of exhibiting the desired bearing performance can be reduced.

It is sectional drawing which shows notionally an example of the spindle motor for information equipment with which the fluid dynamic pressure bearing apparatus was integrated. 1 is a cross-sectional view including a shaft of a fluid dynamic bearing device according to a first embodiment of the present invention. (A) A figure is a figure which shows the upper end surface of a flange part, (b) A figure is a figure which shows the lower end surface of a flange part. It is a block diagram which shows the manufacturing process of the axial part which comprises a shaft member. It is a front view which shows a rolling process typically, (a) A figure is a figure which shows the state immediately after a rolling start, (b) A figure is a figure which shows the state after completion | finish of rolling. It is a figure which shows notionally the principal part of the axial part after a finishing process. It is a shaft-containing sectional view of a fluid dynamic bearing device according to a second embodiment of the present invention. It is a shaft-containing sectional view of a fluid dynamic bearing device according to a third embodiment of the present invention. It is a shaft-containing sectional view of a fluid dynamic bearing device according to a fourth embodiment of the present invention. It is a figure which shows the problem of the conventional method typically.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 conceptually shows a configuration example of a spindle motor for information equipment in which a fluid dynamic pressure bearing device is incorporated. The spindle motor is used in a disk drive device such as an HDD, and includes a fluid dynamic bearing device 1 that rotatably supports a shaft member 2, a disk hub 3 fixed to the shaft member 2, and a radial direction, for example. The stator coil 4 and the rotor magnet 5 that are opposed to each other through the gap, and the motor base 6 are provided. The stator coil 4 is attached to the outer periphery of the motor base 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The bearing member 9 of the fluid dynamic bearing device 1 is fixed to the inner periphery of the motor base 6. The disk hub 3 holds one or a plurality of disks D (two in the illustrated example), and the disk D is clamped and fixed in the axial direction by a clamper (not shown) screwed to the shaft member 2 and the disk hub 3. Is done. In the above configuration, when the stator coil 4 is energized, the rotor magnet 5 is rotated by the electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the disk hub 3 and the disk D held by the disk hub 3 are rotated. It rotates integrally with the shaft member 2.

  FIG. 2 shows a fluid dynamic bearing device 1 according to the first embodiment of the present invention. The fluid dynamic pressure bearing device 1 includes a bearing member 9 having both ends opened in the axial direction, a shaft member 2 inserted into the inner periphery of the bearing member 9, and a lid member 10 that closes one end opening of the bearing member 9. The internal space is filled with lubricating oil (shown by dense dotted hatching) as a lubricating fluid. In the present embodiment, the bearing member 9 is configured by the bearing sleeve 8 in which the shaft member 2 is inserted into the inner periphery and the housing 7 in which the bearing sleeve 8 is held (fixed) in the inner periphery. In the following, for the sake of convenience, the description will be given with the side on which the lid member 10 is provided as the lower side and the opposite side in the axial direction as the upper side.

  The bearing sleeve 8 is formed in a cylindrical shape with a porous body made of sintered metal, for example, a sintered metal porous body mainly composed of copper or iron. The bearing sleeve 8 can be made of a porous material other than sintered metal, such as a porous resin or ceramics, or a solid (non-porous) metal material such as brass or stainless steel. You can also. The inner peripheral surface 8a of the bearing sleeve 8 is formed as a smooth cylindrical surface without irregularities, and the outer peripheral surface 8d of the bearing sleeve 8 is provided with axial grooves 8d1 at one or a plurality of locations in the circumferential direction. Is formed on a smooth cylindrical surface without irregularities. The lower end surface 8b of the bearing sleeve 8 is formed as a flat surface without irregularities, and the upper end surface 8c is formed with an annular groove 8c1 and a radial groove 8c2 whose outer diameter end is connected to the annular groove 8c1. Yes.

  The lid member 10 is formed in a plate shape with a metal material. Although details will be described later, the upper end surface 10a of the lid member 10 has an annular region that forms a thrust bearing gap of the second thrust bearing portion T2 between the upper end surface 10a and the lower end surface 22b of the flange portion 22 of the shaft member 2. The annular region is formed on a smooth flat surface, and is not provided with a concave portion for generating a dynamic pressure action in the lubricating oil interposed in the thrust bearing gap, such as a dynamic pressure groove.

  The housing 7 is formed of a molten material (for example, a solid metal material such as brass or stainless steel) in a substantially cylindrical shape with both axial ends open, and holds the bearing sleeve 8 and the lid member 10 on the inner periphery. The main body portion 7a and the seal portion 7b extending from the upper end of the main body portion 7a to the inner diameter side are integrally provided. A relatively small-diameter small-diameter internal peripheral surface 7a1 and a relatively large-diameter large-diameter internal peripheral surface 7a2 are provided on the internal peripheral surface of the main body 7a, and the small-diameter internal peripheral surface 7a1 and the large-diameter internal peripheral surface are provided. A bearing sleeve 8 and a lid member 10 are fixed to 7a2. The fixing means for the bearing sleeve 8 and the lid member 10 with respect to the housing 7 is not particularly limited, and can be fixed by appropriate means such as press-fitting, adhesion, press-fitting adhesion, and welding. In the present embodiment, the bearing sleeve 8 is fixed to the inner periphery of the housing 7 by so-called gap bonding in which the bearing sleeve 8 is fitted into the small diameter inner circumferential surface 7a1 of the main body 7a and an adhesive is interposed in the gap. . An annular groove 7a3 functioning as an adhesive reservoir is formed at a predetermined position in the axial direction of the small-diameter inner peripheral surface 7a1, and the annular sleeve 7a3 is filled with an adhesive and solidified, whereby a bearing sleeve for the housing 7 is formed. 8 is improved in adhesive strength.

  The inner peripheral surface 7b1 of the seal portion 7b is formed in a tapered surface shape that is gradually reduced in diameter toward the lower side, and has a radial dimension toward the lower side between the outer peripheral surface 21a of the opposing shaft member 2 (shaft portion 21). Is formed in a wedge-shaped seal space S. The upper end surface 8c of the bearing sleeve 8 is in contact with the lower end surface 7b2 (the inner diameter side region thereof) of the seal portion 7b, whereby relative positioning in the axial direction of the bearing sleeve 8 with respect to the housing 7 is achieved. Yes. The outer diameter side region of the lower end surface 7b2 of the seal portion 7b gradually recedes upward toward the outer diameter side to form an annular gap with the upper end surface 8c of the bearing sleeve 8. An inner diameter end portion of the annular gap is connected to an annular groove 8 c 1 on the upper end surface 8 c of the bearing sleeve 8.

  The housing 7 having the above configuration may be a resin injection molded product. In this case, the housing 7 may be injection molded with resin using the bearing sleeve 8 as an insert part. The housing 7 can be an injection molded product of a low melting point metal represented by a magnesium alloy or an aluminum alloy, or can be a so-called MIM molded product.

  The shaft member 2 includes a shaft portion 21 that is formed of a hardened stainless steel (for example, SUS420J2) in a solid shaft shape, and a flange portion 22 that projects from the lower end of the shaft portion 21 to the outer diameter side. For example, the flange portion 2b is formed in an annular shape with the same kind of stainless steel as the shaft portion 21 or a porous body of sintered metal, and is appropriately fitted to the outer periphery of the lower end of the shaft portion 21 such as press-fitting, bonding, press-fitting adhesion, welding, or the like. It is fixed by means. An annular groove 21b is formed in the fixing region of the flange portion 22 in the outer peripheral surface 21a of the shaft portion 21. For example, when the flange portion 22 is fixed to the shaft portion 21 using an adhesive, the annular groove 21b is formed. Since it functions as an adhesive reservoir, the fixing strength of the flange portion 22 with respect to the shaft portion 21 can be improved. Further, by fitting a convex portion formed on the inner peripheral surface of the flange portion 22 into the annular groove 21b, it is possible to increase the pull-out strength of the flange portion 22.

  On the outer peripheral surface 21 a of the shaft portion 21, cylindrical regions serving as radial bearing surfaces A <b> 1 and A <b> 2 that form a radial bearing gap between the inner peripheral surface 8 a of the opposing bearing sleeve 8 are formed at two positions in the axial direction. Has been. The radial bearing surfaces A1 and A2 are each provided with a plurality of dynamic pressure grooves Aa (indicated by cross-hatching in FIG. 2) as recesses that generate dynamic pressure action on the lubricating oil interposed in the radial bearing gap. Here, a plurality of dynamic pressure grooves Aa are arranged in a herringbone shape. In this embodiment, each dynamic pressure groove Aa provided on the upper radial bearing surface A1 is formed axially asymmetric with respect to the axial center m (the axial center of the region between the upper and lower inclined grooves). The axial dimension X1 of the upper region from the axial center m is larger than the axial dimension X2 of the lower region. On the other hand, each dynamic pressure groove Aa provided on the lower radial bearing surface A2 is formed symmetrically in the axial direction. The groove depth of each dynamic pressure groove Aa is about several μm.

  Of the outer peripheral surface 21a of the shaft portion 21, between the two radial bearing surfaces A1 and A2, there is a cylindrical intermediate escape portion 23 that is retracted (formed to a smaller diameter) to the inner diameter side than the bottom portion of the dynamic pressure groove Aa. Is provided. By providing such an intermediate relief portion 23 on the outer peripheral surface 21a of the shaft portion 21, a cylindrical lubricating oil reservoir is formed between the inner peripheral surface 8a of the bearing sleeve 8 formed on a cylindrical surface having a constant diameter. Is done. As a result, during bearing operation, the lubricating oil reservoir and the two radial bearing gaps adjacent to each other in the axial direction can always be filled with abundant lubricating oil, so that the rotational accuracy in the radial direction can be stabilized.

  As shown in FIG. 3A, the thrust bearing surface that forms the thrust bearing gap of the first thrust bearing portion T <b> 1 between the upper end surface 22 a of the flange portion 22 and the lower end surface 8 b of the opposing bearing sleeve 8. B is provided. The thrust bearing surface B is provided with a plurality of dynamic pressure grooves Ba as recesses for generating a dynamic pressure action in the lubricating oil interposed in the thrust bearing gap of the first thrust bearing portion T1, and here, The dynamic pressure grooves Ba are arranged in a spiral shape. Further, as shown in FIG. 3B, a thrust bearing gap of the second thrust bearing portion T2 is formed between the lower end surface 22b of the flange portion 22 and the upper end surface 10a of the facing lid member 10. A thrust bearing surface C is provided. The thrust bearing surface C is provided with a plurality of dynamic pressure grooves Ca as concave portions for generating a dynamic pressure action in the lubricating oil interposed in the thrust bearing gap of the second thrust bearing portion T2, in the circumferential direction, The dynamic pressure grooves Ca are arranged in a spiral shape. Either one or both of the dynamic pressure grooves Ba and Ca can be arranged in a herringbone shape.

  As shown in FIG. 4, the shaft member 2 having the above-described configuration is a lower end of the shaft portion 21 manufactured through the shaft material manufacturing process P1, the heat treatment process P2, the removal process P3, the rolling process P4, and the finishing process P5 in this order. In addition, it is completed by fixing the flange portion 22 manufactured in a separate process. Hereafter, each process for manufacturing the axial part 21 is explained in full detail.

(1) Shaft material production process P1
In this shaft material manufacturing process P1, by performing predetermined processing on a short bar material cut out to a predetermined length from a long bar material, a portion excluding the dynamic pressure groove Aa becomes a shaft part 21 as a finished product. Obtain a shaft material finished in an approximate shape. Specifically, for example, by turning a short bar material, the intermediate escape portion 23 and the annular groove 21b are formed on the outer peripheral surface, and by tapping one end of the bar material, A shaft blank having an open screw hole (for screwing the clamper, not shown) is obtained. The rough shape of the shaft material can be obtained by plastic working such as forging in addition to machining such as turning.

(2) Heat treatment process P2
In this heat treatment step P2, the shaft material obtained in the shaft material production step P1 is subjected to heat treatment on at least the outer peripheral surface, whereby a hardened shaft 21 ′ having a surface hardened layer having a hardness of HV450 or more, more preferably HV500 or more. [See FIG. 5A]. The heat treatment method is not particularly limited, and induction hardening, vacuum quenching, carburizing quenching, carbonitriding quenching, and other quenching, and tempering after quenching can be appropriately combined. The heat treatment may be performed so that a hardened surface layer having a thickness larger than the depth of the dynamic pressure groove Aa to be formed is formed, and not necessarily so that the entire shaft material is hardened (quenched). Also good.

(3) Removal step P3
In this rough finishing process P3, an oxide film also called a black skin formed on the surface of the quenched shaft 21 'as the quenched shaft 21' (surface hardened layer) is formed by subjecting the shaft material to heat treatment. Is removed. The black skin (oxide film) is removed, for example, by subjecting the quenching shaft 21 'to centerless polishing.

(4) Rolling process P4
In this rolling process P4, the hydrodynamic groove Aa is formed on the outer peripheral surface of the quenching shaft 21 'by rolling the surface hardened layer of the quenching shaft 21' (from which the black skin has been removed). In this embodiment, as shown in FIGS. 5 (a) and 5 (b), a dynamic pressure groove Aa as a recess is formed on the outer peripheral surface of the quenching shaft 21 'by using a pair of rolling dies 31, 32 provided so as to be relatively slidable. Formed by rolling. A dynamic pressure groove forming portion 34 as a concave portion forming portion is provided on the surface of each rolling die 31, 32 facing the other side. The dynamic pressure groove forming portion 34 is configured by arranging convex portions 33 corresponding to individual dynamic pressure groove Aa shapes in a herringbone shape. The height dimension of the convex portion 33 is determined by grinding a predetermined amount of the outer peripheral surface of the quenching shaft 21 ′ including the convex hill portion defining the dynamic pressure groove Aa in the finishing step P5 described later. The predetermined depth is set larger than the required groove depth of the dynamic pressure groove Aa. In addition, the hardness of at least the dynamic pressure groove forming portion 34 (the plurality of convex portions 33) of the rolling dies 31 and 32 is set to be HV100 or more higher than the surface hardened layer of the quenching shaft 21 ′.

  Then, as shown in FIG. 5 (a), after introducing the quenching shaft 21 ′ between the rolling dies 31, 32, the rolling dies 31, 32 are relatively moved, and the dynamic pressure groove forming portion 34 of the rolling dies 31, 32. Is pressed against the outer peripheral surface of the quenching shaft 21 '. As a result, as shown in FIG. 5 (b), of the outer peripheral surface of the quenching shaft 21 ', the meat in the portion where the convex portion 33 of the dynamic pressure groove forming portion 34 is pressed is plastically flowed and pushed out. As a result, a hill portion defining the dynamic pressure groove Aa is formed, and at the same time, the dynamic pressure groove Aa is formed. In the present embodiment, as described above, the height dimension of each convex portion 33 constituting the dynamic pressure groove forming portion 34 is set to be larger than the required groove depth of the dynamic pressure groove Aa. The groove depth of the dynamic pressure groove Aa at this stage is deeper than the depth of the dynamic pressure groove Aa provided on the outer peripheral surface of the shaft portion 21 (shaft member 2) as a finished product.

  The convex portion 33 (dynamic pressure groove forming portion 34) for forming the dynamic pressure groove Aa on the outer peripheral surface of the quenching shaft 21 'can be provided only on one of the rolling dies 31, 32.

(5) Finishing process P5
In this finishing process P5, the outer peripheral surface of the quenching shaft 21 ′, in which the dynamic pressure grooves Aa are formed by rolling on the outer peripheral surface in the rolling process P4, is finished with a predetermined accuracy. Specifically, in the outer peripheral surface of the quenching shaft 21 ′, cylindrical regions in which the dynamic pressure grooves Aa are formed by rolling are formed (the radial bearing surfaces A 1 and A 2 in the shaft portion 21 are formed. By subjecting the cylindrical region) to grinding, polishing, or plastic working, the convex hill Ab defining the dynamic pressure groove Aa is finished to a predetermined height, and a dynamic pressure groove Aa having a predetermined depth is obtained. It is done. Further, the axial region other than the axial region serving as the radial bearing surfaces A1 and A2, for example, the middle escape portion 23 is also finished with a predetermined accuracy (see FIG. 6 above). Thereby, the shaft part 21 as a finished product is obtained.

  In the fluid dynamic pressure bearing device 1 having the above-described configuration, when the shaft member 2 rotates, each of the radial portions between the radial bearing surfaces A1 and A2 of the shaft portion 21 and the inner peripheral surface 8a of the bearing sleeve 8 facing the shaft member 2 is radial. A bearing gap is formed. As the shaft member 2 rotates, the pressure of the oil film formed in both radial bearing gaps is increased by the dynamic pressure action of the dynamic pressure grooves Aa, Aa, and as a result, the radial that supports the shaft member 2 in a non-contact manner in the radial direction. The bearing portions R1 and R2 are spaced apart from each other in two axial directions. At the same time, a thrust bearing provided between the thrust bearing surface B provided on the upper end surface 22a of the flange portion 22 and the lower end surface 8b of the bearing sleeve 8 facing the thrust bearing surface B, and on the lower end surface 22b of the flange portion 22. The first and second thrust bearing gaps are formed between the surface C and the upper end surface 10a of the lid member 10 facing the surface C, respectively. As the shaft member 2 rotates, the pressure of the oil film formed in both thrust bearing gaps is increased by the dynamic pressure action of the dynamic pressure grooves Ba and Ca. As a result, the shaft member 2 is not contacted in both thrust directions. Supporting first and second thrust bearing portions T1, T2 are formed.

  Further, since the seal space S has a wedge shape in which the radial dimension is gradually reduced toward the inner side of the housing 7, the lubricating oil in the seal space S is pulled into the inner side of the housing 7 by a pulling action due to capillary force. It is drawn toward. Further, the seal space S has a buffer function for absorbing the volume change amount accompanying the temperature change of the lubricating oil filled in the internal space of the housing 7, and the oil surface of the lubricating oil is kept within the range of the assumed temperature change. It is always held in the seal space S. Therefore, lubricating oil leakage from the inside of the housing 7 is effectively prevented.

  In addition, as described above, the upper dynamic pressure groove Aa has the axial dimension X1 in the upper region from the axial center m larger than the axial dimension X2 in the lower region. The pulling force of the lubricating oil by the dynamic pressure groove Aa is relatively larger in the upper region than in the lower region. Due to such differential pressure of the pulling force, the lubricating oil filled in the gap between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 21a1 of the shaft portion 21 flows downward, and the first thrust bearing portion T1 Thrust bearing clearance → Axial fluid passage 11 formed by the axial groove 8d1 of the bearing sleeve 8 → Annular space formed by the upper peripheral chamfer or the like of the bearing sleeve 8 → The annular groove 8c1 and the radial groove 8c2 of the bearing sleeve 8 It is circulated through a path called a fluid passage formed by the above and is again drawn into the radial bearing gap of the first radial bearing portion R1.

  By adopting such a configuration, the pressure balance of the lubricating oil is maintained, and at the same time, the generation of bubbles accompanying the generation of local negative pressure, the occurrence of lubricant leakage and vibration due to the generation of bubbles, etc. The problem can be solved. Since the sealing space S communicates with the above circulation path, even if bubbles are mixed in the lubricating oil for some reason, when the bubbles circulate with the lubricating oil, the lubricating oil in the sealing space S It is discharged from the oil surface (gas-liquid interface) to the outside air. Therefore, adverse effects due to bubbles can be prevented more effectively.

  As described above, the dynamic pressure groove Aa provided on the outer peripheral surface 21a of the shaft member 2 (shaft portion 21) has a required groove depth on the order of microns, so that the quenched shaft 21 ′ (surface hardened layer). The inventors of the present application have found that the dynamic pressure groove Aa having a predetermined groove depth can be formed as long as the necessary minimum conditions are satisfied even when the rolling process is performed. And if the dynamic pressure groove Aa as the concave portion for generating dynamic pressure is formed by rolling the hardened surface of the quenching shaft 21 ', the rolling process is performed on the unheat-treated shaft material. Thus, the amount of rising of the meat on both sides of the convex Ab (see FIG. 6) generated by rolling is reduced, and the groove depth is less likely to vary between the dynamic pressure grooves Aa immediately after rolling. In addition, it is not necessary to heat-treat the shaft material after the dynamic pressure groove Aa is formed by rolling, that is, in a state where internal stress is accumulated in the shaft material. Therefore, even when the finishing step P5 is provided as in the present embodiment and a predetermined final finish is applied to the quenching shaft 21 'in the finishing step P5, the amount of processing can be reduced.

  Furthermore, due to the configuration of the present invention, it is possible to perform the removal process of the black skin formed on the outer surface of the quenching shaft 21 ′ before performing the rolling process. The outer peripheral surface of the quenching shaft 21 ′ before the rolling process has a substantially smooth cylindrical surface shape that does not have minute irregularities (repetition of irregularities) such as the dynamic pressure groove Aa and the hill Ab that defines the dynamic pressure groove Aa. The black skin can be removed easily. Therefore, there is no black skin at the bottom of the dynamic pressure groove Aa formed on the outer peripheral surface 21a of the shaft portion 21, and the hardened surface layer is exposed. As a result, it is possible to effectively prevent the problem that the black skin peels off from the shaft portion 21 of the shaft member 2 during the operation of the fluid dynamic pressure bearing device 1 to cause contamination and the bearing performance deteriorates. .

  Of the two surfaces forming the radial bearing gap, the bearing sleeve 8 has a relationship in which the dynamic pressure groove Aa is provided on the outer peripheral surface 21 a of the shaft portion 21 and the intermediate relief portion 23 is provided on the outer peripheral surface 21 a of the shaft portion 21. The inner peripheral surface 8a (the inner peripheral surface of the bearing member) is formed into a smooth cylindrical surface without any irregularities. Therefore, when manufacturing the bearing sleeve 8 made of sintered metal, the inner peripheral surface and the outer peripheral surface are straightened with respect to the sintered body obtained by sintering the green compact of the raw material powder ( By performing (sizing), the manufacturing process is completed, and there is no need to provide a step of pressure-forming a recess for generating dynamic pressure on the inner peripheral surface. Therefore, the die cost can be reduced through simplification of the shape, and the manufacturing cost of the bearing sleeve 8 and the fluid dynamic pressure bearing device 1 as a whole can be reduced.

  From the above, according to the present invention, it is possible to reduce the labor when forming the dynamic pressure groove Aa as a recess for generating fluid dynamic pressure in the radial bearing gap on the outer peripheral surface of the shaft member 2 by rolling. However, the dynamic pressure groove Aa can be formed with high accuracy. Thereby, cost reduction of the fluid dynamic pressure bearing apparatus 1 which can exhibit desired bearing performance can be achieved.

  In the above description, in the manufacturing process for obtaining the shaft portion 21 in which the dynamic pressure groove Aa is formed on the outer peripheral surface 21a, the finishing step P5 for finishing the outer peripheral surface of the quenched shaft 21 ′ with a predetermined accuracy is provided. Since the dynamic pressure groove Aa can be formed with higher accuracy than the conventional method due to the configuration of the present invention, the finishing step P5 is not necessarily provided. If the finishing process P5 is omitted, it is possible to contribute to further cost reduction of the shaft member 2, and thus the fluid dynamic bearing device 1.

  In the above, the shaft portion 21 and the flange portion 22 constituting the shaft member 2 are separated, and the flange portion 22 manufactured in a separate process is formed at the lower end of the shaft portion 21 in which the dynamic pressure groove Aa is formed on the outer peripheral surface 21a. Although the shaft member 2 is obtained by fixing the shaft member 21, the shaft portion 21 and the flange portion 22 are integrally formed by using a shaft material that is integrally provided with a disk-shaped portion that becomes the flange portion 22. It is also possible to do.

  The present invention is not limited to the above embodiment. Hereinafter, a fluid dynamic bearing device 1 according to another embodiment to which the present invention is applicable will be described with reference to the drawings. In other embodiments described below, from the viewpoint of simplifying the description, the same reference numerals are assigned to substantially the same members / parts as those of the above-described embodiment, and the duplicate description is omitted.

  FIG. 7 is an axial cross-sectional view of the fluid dynamic bearing device 1 according to the second embodiment of the present invention. The main difference of the fluid dynamic bearing device 1 shown in FIG. 2 from that shown in FIG. 2 is that the housing 7 is integrally provided with a disc-shaped bottom 7c that closes the lower end of the cylindrical body 7a. The seal space S is formed by the ring-shaped seal member 12 fixed to the inner periphery of the upper end of the main body portion 7a. That is, the second thrust bearing gap of the second thrust bearing portion T2 is formed between the lower end surface 22b of the flange portion 22 and the upper end surface 7c1 of the housing bottom portion 7c, and the seal space S is formed in the seal member 12. It is formed between the inner peripheral surface 12 a and the outer peripheral surface 21 a of the shaft portion 21. A step portion 7d is provided at the boundary between the main body portion 7a and the bottom portion 7c of the housing 7, and the lower end surface 8b of the bearing sleeve 8 is brought into contact with the step portion 7d, whereby a bearing sleeve for the housing 7 is provided. A relative axial position of 8 is determined.

  FIG. 8 is an axial cross-sectional view of the fluid dynamic bearing device 1 according to the third embodiment of the present invention. The main differences of the fluid dynamic pressure bearing device 1 shown in FIG. 2 from that shown in FIG. 2 are that an annular portion 3a and a substantially cylindrical tubular portion 3b extending in the axial direction from the outer diameter end of the annular portion 3a. Is provided at the upper end portion of the shaft member 2 (shaft portion 21), the lower end surface 3a1 of the annular portion 3a of the disc hub 3 and the upper side of the housing 7 (main body portion 7a) facing this. A seal is provided between the end surface 7a4 and the second thrust bearing gap of the second thrust bearing portion T2 and between the upper outer peripheral surface 7a5 of the housing 7 and the inner peripheral surface 3b1 of the cylindrical portion 3b of the disk hub 3. The space S is provided. In this embodiment, the shaft portion 21 is formed in a thick cylindrical shape, and the flange portion 22 is fixed to the lower end of the shaft portion 21 with screws.

  FIG. 9 is an axial cross-sectional view of the fluid dynamic bearing device 1 according to the fourth embodiment of the present invention. The main difference of the fluid dynamic pressure bearing device 1 shown in FIG. 2 from that shown in FIG. 2 is that the flange portion 24 arranged on the upper side of the bearing sleeve 8 is fixed to the outer peripheral surface 21a of the shaft portion 21, and the shaft member 2 is fixed. The seal space S that holds the oil level of the lubricating oil is formed between the outer peripheral surfaces 22c, 24c of both flange portions 22, 24 and the inner peripheral surface 7a1 of the housing 7 (main body portion 7a), and the flange. The second thrust bearing gap of the second thrust bearing portion T2 is formed between the lower end surface 24a of the portion 24 and the upper end surface 8c of the bearing sleeve 8.

  In the embodiment described above, the bearing member 9 is configured by the housing 7 and the bearing sleeve 8 fixed to the inner periphery of the housing 7, but the bearing member 9 is provided in a portion corresponding to the housing 7 and the bearing sleeve 8. A corresponding portion may be integrally provided.

  Further, in the above, the radial bearing portions R1 and R2 made of a dynamic pressure bearing are configured by arranging the dynamic pressure grooves Aa as the concave portions for generating dynamic pressure in the herringbone shape on the outer peripheral surface 21a of the shaft portion 21. However, the dynamic pressure grooves Aa can be arranged in a spiral shape or a step shape (a plurality of axial grooves extending in the axial direction are arranged in the circumferential direction). Further, the concave portion for generating dynamic pressure can be constituted by a dimple having a hollow shape instead of the groove shape as described above.

  Moreover, in the above embodiment, the dynamic pressure grooves Ba and Ca as the concave portions for generating the dynamic pressure are arranged in a spiral shape (or herringbone shape) on the end surface of the flange portion 22 to thereby form a thrust bearing made of a dynamic pressure bearing. Although the case where the portions T1 and T2 are configured has been described, either one or both of the dynamic pressure grooves Ba and Ca can be formed radially (step bearings). Further, the concave portion for generating the dynamic pressure is a member end surface facing the end surfaces 22a, 22b of the flange portion 22 through the thrust bearing gap (the lower end surface 8b of the bearing sleeve 8 or the lid member in the embodiment shown in FIG. 2). 10 on the upper end face 10a). Furthermore, although illustration is omitted, it is also possible to constitute a thrust bearing portion with a so-called pivot bearing that does not provide the flange portion 22 on the shaft member 2 and contacts and supports one end (lower end) of the shaft portion 21.

  In the above embodiment, the lubricating oil is used as the lubricating fluid that fills the internal space of the fluid dynamic bearing device 1, but the fluid dynamics using a lubricating grease, a magnetic fluid, or a gas such as air as the lubricating fluid. The present invention can also be preferably applied to the pressure bearing device 1.

  In the above description, the case where the present invention is applied to the fluid dynamic bearing device 1 in which the shaft member 2 is the rotation side and the bearing sleeve 8 and the like is the stationary side has been described. The present invention can also be preferably applied to the fluid dynamic bearing device 1 in which the bearing is the stationary side and the bearing sleeve 8 is the rotating side.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 7 Housing 8 Bearing sleeve 9 Bearing member 10 Lid member 21 Shaft part 21 'Hardening shaft 22 Flange part 23 Middle relief | exclusion part 31, 32 Rolling die 33 Convex part 34 Dynamic pressure groove formation part Aa Dynamic Pressure groove (concave)
Ba Dynamic pressure groove (concave)
Ca dynamic pressure groove (concave)
R1, R2 Radial bearing portion T1 First thrust bearing portion T2 Second thrust bearing portion

Claims (10)

A bearing member; a shaft member inserted in the inner periphery of the bearing member; and a radial bearing gap formed between the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft member. In the fluid dynamic pressure bearing device provided with a plurality of recesses for generating a dynamic pressure action in the lubricating fluid interposed in the radial bearing gap,
The fluid dynamic bearing device, wherein the shaft member has a surface hardened layer formed by subjecting the shaft material to heat treatment, and the concave portion is formed by rolling the surface hardened layer.   The fluid dynamic bearing device according to claim 1, wherein the hardness of the surface hardened layer is HV450 or more. Radial bearing gaps are formed at two locations separated in the axial direction,
2. The fluid dynamics according to claim 1, wherein a cylindrical middle escape portion having a smaller diameter than a bottom portion of the concave portion is provided in a region located between two radial bearing gaps on an outer peripheral surface of the shaft member. Pressure bearing device.   The fluid dynamic bearing device according to claim 1, wherein the bearing member is formed of a sintered metal.   The fluid dynamic pressure bearing according to claim 1, wherein the shaft member includes a shaft portion having the concave portion and a flange portion that is attached and fixed to one end of the shaft portion and forms a thrust bearing gap between the end surface of the bearing member. apparatus.   6. The fluid dynamic pressure bearing device according to claim 5, wherein a plurality of recesses for generating a dynamic pressure action on the lubricating fluid interposed in the thrust bearing gap are provided on an end face of the flange portion forming the thrust bearing gap. A bearing member; a shaft member inserted in the inner periphery of the bearing member; and a radial bearing gap formed between the inner peripheral surface of the bearing member and the outer peripheral surface of the shaft member. In the manufacturing method of the fluid dynamic pressure bearing device provided with a plurality of recesses for generating a dynamic pressure action in the lubricating fluid interposed in the radial bearing gap,
A heat treatment step for forming a hardened shaft having a surface hardened layer by subjecting the shaft material to a heat treatment; and a rolling step for forming the concave portion by subjecting the surface hardened layer of the hardened shaft to a rolling process. A method for manufacturing a fluid dynamic pressure bearing device.   The method for manufacturing a fluid dynamic bearing device according to claim 7, wherein in the rolling step, at least a concave portion forming portion for forming the concave portion uses a rolling die having a hardness of HV100 or higher than the hardened surface layer.   The method for manufacturing a fluid dynamic bearing device according to claim 7, further comprising a removing step for removing a surface layer portion of the surface hardened layer between the heat treatment step and the rolling step.   8. The method of manufacturing a fluid dynamic bearing device according to claim 7, further comprising a finishing step for finishing the outer peripheral surface of the quenching shaft with a predetermined accuracy after the rolling step.

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