JP2007218379A - Shaft member for hydrodynamic bearing device and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive shaft member for a hydrodynamic bearing device exerting a high hydrodynamic effect. <P>SOLUTION: A pair of rolling dies 12, 13 which have protruded portions 12b shaped corresponding to a recessed portion 7 to be transferred and formed into a shaft raw material 11 are used for rolling and forming the recessed portion 7 on the outer peripheral face 11a of the shaft raw material 11 for generating hydrodynamic pressure. Next, an original thickness portion of the recessed portion 7 is pushed out to the periphery to form a bulged portion 15 near the recessed portion 7 in the peripheral region 8. Then, rolling dies 16, 17 which have plane portions 16b on the opposite face 16a of one rolling die 16 are used for plane-rolling the shaft raw material 11 in which the recessed portion 7 is formed. Thus, the bulged portion 15 formed at the peripheral region 8 of the recessed portion 7 is flattened by the plane portion 16b to equalize a surface 8a in the peripheral region 8 into a flat state. A second hardened layer 18 is formed on the lower layer of the crushed bulged portion 15 by plane rolling. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a shaft member for a hydrodynamic bearing device and a manufacturing method thereof.

  The hydrodynamic bearing device supports the shaft member in a relatively rotatable manner by the hydrodynamic action of the fluid generated in the bearing gap. Recently, the hydrodynamic bearing device utilizes its excellent rotational accuracy, high-speed rotational performance, quietness, etc. More specifically, for example, a magnetic disk device such as an HDD, a CD-ROM, a CD-R / RW, a DVD-ROM / RAM, etc. As a spindle motor bearing device mounted on an optical disk device, a magneto-optical disk device such as MD, MO, etc., a motor bearing such as a polygon scanner motor of a laser beam printer (LBP), a color wheel motor of a projector, or a fan motor. Used as a device.

  For example, in a hydrodynamic bearing device incorporated in a spindle motor for HDD, a configuration in which both a radial bearing portion that supports a shaft member in a radial direction or a thrust bearing portion that supports a shaft direction in a thrust direction is constituted by a hydrodynamic bearing is known. . In this case, a dynamic pressure groove as a dynamic pressure generating portion is formed on either the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member facing the bearing sleeve, and the radial bearing is disposed in the radial bearing gap between both surfaces. The part is often formed. In addition, a dynamic pressure groove is formed on one end surface of the flange portion provided on the shaft member and an end surface of the bearing sleeve facing the flange portion, and a thrust bearing portion is formed in the thrust bearing gap between both surfaces. (See, for example, Patent Document 1).

  The dynamic pressure grooves are formed, for example, in a state of being arranged in a herringbone shape, a spiral shape, or the like on the outer peripheral surface of the shaft member. As a method for forming this type of dynamic pressure groove, for example, cutting (see, for example, Patent Document 2), etching (see, for example, Patent Document 3), and the like are known.

Further, for example, rolling is known as a processing means capable of forming dynamic pressure grooves at a lower cost than the above-described cutting and etching. In this case, grinding is often performed after the rolling process to finish the surface of the material (for example, see Patent Document 4).
JP 2003-239951 A Japanese Patent Laid-Open No. 08-196056 Japanese Patent Laid-Open No. 06-158357 Japanese Patent Laid-Open No. 07-114766

  This type of grinding is often centerless due to the size of the workpiece (shaft member), but with this method, the grinding center (grinding center) and dynamic pressure groove rolling The processing center (rolling processing center) does not always match, and a considerable amount may deviate depending on the processing conditions. In this case, the roundness of the ground surface is maintained, but the grinding allowance of the outer peripheral surface varies greatly depending on the location. For this reason, the depth of the dynamic pressure grooves formed by rolling on the outer peripheral surface varies greatly, and there is a possibility that sufficient dynamic pressure action cannot be exhibited.

  Further, in machining such as grinding, generation of chips is inevitable. For this reason, it is necessary to carefully perform a cleaning process for removing chips remaining in the dynamic pressure grooves, resulting in an increase in cost.

  An object of the present invention is to provide a low-cost shaft member for a hydrodynamic bearing device that can exhibit a high dynamic pressure action.

  In order to solve the above-mentioned problems, the present invention provides a method in which a concave portion for generating a fluid dynamic pressure action in a bearing gap is formed by rolling, and a raised portion generated in a peripheral region of the concave portion by rolling is flat rolled. A shaft member for a hydrodynamic bearing device, characterized in that the shaft member is flattened. Further, the present invention provides a first rolling process in which a concave portion for generating a fluid dynamic pressure action in a bearing gap is formed by rolling, and a raised portion generated in a peripheral region of the concave portion by the first rolling process is planar rolled. The manufacturing method of the shaft member for fluid dynamic bearing devices including the 2nd rolling process of flattening with a. The concave portion here may be any shape as long as it is for generating a fluid dynamic pressure action in the bearing gap, and the shape thereof is not limited. For example, the concave portion includes an axial groove shape, a circumferential groove shape, an inclined groove shape, a cross groove shape, an intermittent groove shape in the axial direction or the circumferential direction, a dimple shape, and the like.

  When the concave portion for generating dynamic pressure is formed on the surface of the shaft member by rolling, the meat pushed around the concave portion due to rolling remains as a raised portion between the concave portion and the surrounding area. Since this type of raised portion is formed on the surface of the surrounding region that should originally become the bearing surface, the surface of the raised portion functions as if it is a bearing surface, resulting in a decrease in the support area (increase in contact surface pressure). . In this case, the load concentrates on the raised portion and the portion is damaged, so that the shape of the bearing surface is impaired, and as a result, the bearing performance may be deteriorated or the shaft member may be deteriorated in durability.

  On the other hand, in the present invention, the raised portion generated in the peripheral area of the recessed portion formed by rolling is flattened by plane rolling. Planar rolling is a method of rolling a workpiece while maintaining a pair of rolling molds having a plane at a predetermined facing distance, and it is relatively easy to manage the facing distance with high accuracy. Therefore, the processing center does not deviate much from the rolling processing center of the recess compared with the grinding processing. Therefore, while reliably removing the raised portion, the shaft member capable of exhibiting high bearing performance while maintaining the surface of the surrounding region and the shape of the concave portion with high accuracy, particularly keeping the depth of the dynamic pressure generating concave portion uniform. Can be obtained. In addition, by pressing the outer peripheral surface of the shaft member sequentially and partially with the facing interval kept constant, it is possible to ensure that only the raised portion is pressed without excessively pressing the surface of the surrounding area that becomes the bearing surface. It can be flattened by crushing. In addition, since almost no chips are generated, it is not necessary to carefully perform a cleaning process for removing chips as in machining such as grinding. Therefore, the cleaning process can be simplified and the processing cost can be reduced.

  As described above, in the shaft member in which the raised portion is flattened, the ratio h / d of the height h of the raised portion to the depth d of the recessed portion is preferably 0.1 or less. In general, the depth of the dynamic pressure generating recess is preferably determined in accordance with the size of the bearing gap, and as the required bearing gap becomes smaller, the bearing surface that forms the bearing gap becomes higher. Accuracy (for example, roundness or cylindricity) is required. The ratio h / d is set from such a viewpoint. By removing the ridges by plane rolling so that the ratio of the height h of the ridges to the depth d of the recesses is within the above range, a high dynamic rate is obtained. A recess and a bearing surface that can exert a pressure action can be obtained.

  The ratio h / d is naturally desirably 0 because it is desirable that the ridges are completely removed. However, in practice, h / d = 0 is too high due to a problem in processing accuracy. If the close accuracy is aimed too much, the surface of the surrounding area is deformed and the bearing surface accuracy is lowered. For this reason, the lower limit of the ratio h / d is preferably set to 0.01, or this value is preferably processed. Of course, it is preferable to set h / d within the above range in consideration of the function, accuracy, cost, etc. required for the hydrodynamic bearing.

  The shaft member for a fluid dynamic bearing device having the above-described configuration can be suitably provided as, for example, a fluid dynamic bearing device including the shaft member.

  As described above, according to the present invention, a shaft member for a hydrodynamic bearing device capable of exhibiting a high dynamic pressure action can be provided at a low cost.

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

  FIG. 1 is a sectional view of a fluid dynamic bearing device 1 according to an embodiment of the present invention. In the figure, a hydrodynamic bearing device 1 includes a shaft member 2 and a bearing member 3 capable of inserting the shaft member 2 into the inner periphery.

  In this embodiment, the bearing member 3 is a bottomed cylindrical body composed of an electroformed part 4 and a molded part 5, and is integrally injection-molded with resin using the electroformed part 4 that is integral with the master or a separate part as an insert part. . The inner peripheral surface 4a of the electroformed portion 4 facing the outer peripheral surface 2a of the shaft member 2 has a perfect circle shape.

  The shaft member 2 has a shaft shape with a constant diameter, and is made of, for example, various carbon steel, chrome steel, stainless steel and various alloy steels, which are relatively highly workable metal materials (in terms of hardness, about 200 Hv to 400 Hv). Produced. Of course, it is also possible to use a material whose hardness is increased to the above numerical range by quenching or the like.

  On the entire or partial region of the outer peripheral surface 2 a of the shaft member 2, a plurality of lubricating oil dynamic pressure effects are generated in the radial bearing gap 6 between the outer peripheral surface 2 a and the inner peripheral surface 4 a of the electroformed part 4. A recess 7 is formed. In this embodiment, the concave portion 7 is composed of an inclined groove 9a and an inclined groove 9b that are continuous at one end in the circumferential direction and are inclined in a direction away from each other toward the other end in the circumferential direction. The plurality of recesses 7 having such a shape are arranged at predetermined intervals in the circumferential direction so as to form a so-called herringbone shape. In this case, each concave portion 7 (inclined grooves 9a, 9b) and their surrounding region 8 constitute a dynamic pressure generating portion 10 that generates a dynamic pressure action of the lubricating oil in the radial bearing gap 6. Further, in this embodiment, the dynamic pressure generating section 10 having the above-described configuration is provided at two locations separated vertically in the axial direction.

  One end surface 2b of the shaft member 2 has a substantially spherical shape, and abuts against the upper end surface 4b1 of the bottom 4b of the opposing electroformed portion 4 when the shaft member 2 is inserted into the inner periphery of the bearing member 3.

  Lubricating oil is injected from the air release side of the radial bearing gap 6 between the bearing member 3 and the shaft member 2. Thereby, the hydrodynamic bearing device 1 in which the bearing internal space including the radial bearing gap 6 is filled with the lubricating oil is completed.

  In the hydrodynamic bearing device 1 having the above-described configuration, when the shaft member 2 is relatively rotated, the dynamic pressure generating portions 10 and 10 provided on the outer peripheral surface 2a of the shaft member 2 and the inner peripheral surface of the electroformed portion 4 facing them The dynamic pressure action of the lubricating oil is generated in the radial bearing gap 6 between 4a and 4a. Thereby, the first radial bearing portion R1 and the second radial bearing portion R2 that support the shaft member 2 so as to be relatively rotatable in the radial direction are formed.

  Further, at the time of relative rotation of the shaft member 2, one end surface 2b of the shaft member 2 is contact-supported (pivot supported) to the upper end surface 4b1 of the bottom portion 4b. Thereby, the thrust bearing portion T1 that supports the shaft member 2 so as to be relatively rotatable in the thrust direction is formed.

  Hereinafter, an example of the manufacturing process of the shaft member 2 will be described with reference to FIGS.

  FIG. 2 conceptually shows a step of forming the concave portion 7 having the shape shown in FIG. 1 on the outer peripheral surface 11a of the shaft material 11 made of the above material by rolling (recess rolling step). Of the pair of rolling dies 12 and 13 (in this example, a flat die), on the opposing surface 12a of one rolling die 12, a convex portion 12b having a shape corresponding to the concave portion 7 to be transferred to the shaft material 11 is formed. Is provided. As shown to Fig.3 (a), in the state before rolling, the outer peripheral surface 11a of the shaft raw material 11 is smooth.

  The shaft material 11 is introduced between the rolling dies 12, 13, and the other rolling die 13 is slid relative to the one rolling die 12, so that the shaft material 11 is a convex portion of the rolling die 12. Press and roll over the 12b formation region. Thereby, the concave part 7 (dynamic pressure generating part 10) having the shape shown in FIG.

  At this time, as shown in FIG. 3B, a first work-hardened layer 14 a is formed by rolling on the surface layer portion 14 of the recess 7 formed on the outer peripheral surface 11 a of the shaft material 11. Moreover, the meat which was originally in the recessed part 7 is extruded to circumference | surroundings with rolling. As a result, as shown in FIG. 3 (b), a bulge (protrusion 15) occurs in the vicinity of the recess 7 in the surrounding region 8.

  After forming the recess 7 in the shaft material 11 by rolling, the shaft material 11 is subjected to planar rolling (planar rolling process). The rolling dies 16, 17 used here have the same shape as the rolling dies 12, 13, as shown in FIG. 4, for example, and the opposing surface 16a of one of the rolling dies 16 corresponds to the recess 7. Instead of the convex portion 12b having a shape, a flat portion 16b is provided.

  As shown in FIG. 4, the shaft material 11 is introduced between the rolling dies 16, 17, and the other rolling die 17 is slid relative to the one rolling die 16. One rolling die 16 is pressed and rolled on the flat portion 16b forming region. Thereby, the raised portion 15 generated in the peripheral region 8 of the recess 7 is crushed by the flat portion 16b provided on the opposing surface 16a, and the surface 8a of the peripheral region 8 is smoothed as shown in FIG. 3C, for example. Smoothed (flattened). In this case, a second work-hardened layer 18 by plane rolling is formed on the lower layer portion of the crushed raised portion 15.

  In this way, the outer peripheral surface 11a of the shaft material 11 is sequentially and partially pressed by rolling and forming the shaft material 11 in which the concave portion 7 is formed by rolling with the flat surface portion 16b. Therefore, it is possible to reliably crush and flatten only a necessary portion, that is, the raised portion 15 without excessively pressing the surface 8a of the surrounding region 8 serving as a bearing surface. Further, since the facing distance between the rolling dies 16 and 17 can be managed with high accuracy, the processing center at the time of flat surface rolling is the processing at the time of rolling the recess 7 compared to conventional processing means (grinding, etc.). It is possible to prevent the deviation from the center as much as possible. Therefore, it is possible to remove the raised portion 15 while keeping the shape accuracy of the bearing surface (surface 8a) and the concave portion 7 high, and particularly keeping the depth of the concave portion 7 uniform, and the radial bearing gaps 6 and 6 are sufficient. The dynamic pressure action of the large-sized lubricating oil can be stably exhibited. In particular, as in this embodiment, by using the shaft material 11 manufactured from a metal material having relatively excellent workability (200 Hv to 400 Hv in terms of hardness), the raised portion 15 generated when the recess 7 is rolled. Can be easily removed by plane rolling. In addition, since the deformation resistance of the shaft material 11 is smaller than that of a full surface press or the like, the burden on the rolling mold (dies 16 and 17) can be reduced, and the life of the mold can be extended.

  In addition, when the removal of the raised portion 15 is performed by machining such as grinding, the generation of chips is inevitable. However, the removal of the raised portion 15 is performed by plane rolling as in the present invention. The generation of powder can be reduced as much as possible. As a result, the subsequent cleaning process can be simplified, and cost reduction can be achieved.

  In the shaft material 11 (shaft member 2) after the above-described plane rolling, for example, as shown in FIG. 3D, the ratio h / d of the height h of the raised portion 15 to the depth d of the recess 7 is It is preferable that it is 0.1 or less. In this illustrated example, the depth d of the recess 7 is represented by a radial distance from the surface 8a serving as the bearing surface to the bottom surface 7a of the recess 7, and the height h of the raised portion 15 is flattened from the surface 8a. It is represented by the radial distance to the top 15a of the raised ridge 15. By flattening the raised portion 15 by plane rolling so that the ratio h / d is within the above range, only the top portion 15a of the raised portion 15 becomes the bearing surface, and the bearing area is prevented from being substantially reduced. Thus, the recess 7 and the bearing surface (surface 8a) that can exhibit a high dynamic pressure action can be obtained. On the other hand, if the value of h / d is too close to 0, that is, if the bulging portion 15 is completely removed, the surface 8a of the surrounding region 8 as well as the bulging portion 15 will not be affected due to processing accuracy. There is a risk of deformation, which may cause a decrease in bearing surface accuracy. Therefore, in practice, the lower limit of the ratio h / d is set to 0.01, and it is preferable to perform processing with this value as a target.

  Of course, if the purpose is to correct the bearing surface and there is no particular problem in processing, the ratio h / d is set to 0, that is, not only the raised portion 15 but also the peripheral region 8 serving as the bearing surface. It is also possible to perform rolling by adjusting the facing distance between the rolling dies 16 and 17 so as to positively press the surface 8a.

  In addition, it is also possible to perform post-processing, such as heat processing, after the said plane rolling, as needed. This is because the surface 8a of the peripheral region 8 of the concave portion 7 may be in sliding contact with the inner peripheral surface 4a of the opposing electroformed portion 4 when the shaft member 2 rotates, particularly when starting and stopping. By performing the heat treatment as described above, the hardness of the surface layer portion including the bearing surface (surface 8a) can be increased. Thereby, it is possible to suppress the abrasion of the concave portion 7 and the surface 8a serving as the bearing surface, and to stably exhibit a high dynamic pressure action over a long period of time. Although various means can be used as the heat treatment, it is preferable to use a heat treatment that can be performed at as low a temperature as possible, for example, a nitriding treatment, in order to avoid deformation during the heat treatment as much as possible.

  Moreover, in this embodiment, the rolling dies 12 and 13 provided with the convex part 12b for rolling the concave part 7 on one opposing surface 12a, and the ridge generated by the rolling of the concave part 7 on the one opposing surface 16a. Although the case where the rolling dies 16 and 17 provided with the flat portion 16b for flattening the portion 15 is used has been described, a series of rolling dies may be performed using these integrated dies. it can. FIG. 5 shows an example. For example, on one surface of the rolling die 19 facing the other rolling die 20, the convex portion 12b for rolling the concave portion 7 and the raised portion 15 are flattened. And a plane portion 16b for the purpose. In this case, the convex portion 12b and the flat surface portion 16b are arranged so that the convex portion 12b presses the outer peripheral surface 11a of the shaft raw material 11 before the flat surface portion 16b in accordance with the pressing rolling of the workpiece (the shaft raw material 11). It is installed.

  By rolling the shaft blank 11 using such rolling dies (rolling dies 19 and 20), the concave portion 7 is first formed by rolling on the outer peripheral surface 11a of the shaft blank 11, and then provided forward in the rolling direction. The raised portion 15 generated around the concave portion 7 in the surrounding region 8 is crushed and flattened by the flat portion 16b. Therefore, the rolling formation of the recess 7 and the removal of the raised portion 15 (smoothing of the surrounding region surface 8a serving as the bearing surface) can be performed in one step, and the process can be simplified. In addition, by performing the rolling formation of the recess 7 and the removal of the raised portion 15 with a common rolling die, both processes can be performed without changing the facing distance between the rolling dies 19 and 20 to be used. Therefore, a series of rolling can be performed without shifting the processing center at the time of rolling the recess 7 and the processing center at the time of flat surface rolling. Accordingly, it is possible to manufacture the shaft member 2 capable of exhibiting a high dynamic pressure action while keeping the depth of the concave portion 7 after removing the raised portion 15 constant without variation.

  Further, as in this embodiment, burrs may be generated at the peripheral edge of the recess 7 by forming the groove-like recess 7 (inclined grooves 9a, 9b) by rolling, but the rolling having the flat portion 16b. By performing rolling by molding, such burrs can be removed, or the peripheral edge of the recess 7 can be appropriately chamfered. Thereby, at the time of relative rotation of the shaft member 2, it is possible to avoid wear of the inner peripheral surface 4a of the electroformed portion 4 serving as a sliding mating surface as much as possible, or to avoid damage such as galling, thereby improving the durability of the bearing. it can.

  Moreover, in this embodiment, the inner peripheral surface of the bearing member 3 that forms the radial bearing gap 6 between the shaft member 2 and the recess 7 (the inclined grooves 9a and 9b) formed by rolling is formed on the electroformed portion 4. Since the inner peripheral surface 4a is formed, the inner peripheral surface 4a can be formed with high accuracy, whereby the radial bearing gap 6 can be set to be narrower. Rather, depending on the required bearing performance, if the width of the radial bearing gap 6 is small and can be managed with high accuracy, it is necessary to arrange a plurality of recesses 7 in a complicated shape (herringbone shape, etc.). There is no. For example, even in a dynamic pressure generating portion constituted by a recess 7 having a simple shape (a shape that can be more easily processed) such as an axial groove 22 to be described later and a dimple 32, a high dynamic pressure action is applied to the radial bearing gap. It becomes possible to bring

  As mentioned above, although one embodiment of the present invention was described, the present invention is not limited to this embodiment and can adopt other configurations. Hereinafter, the other structure of this invention is demonstrated based on FIGS.

  In the above embodiment, the concave portion 7 is constituted by the inclined groove 9a and the inclined groove 9b, and the case where the concave portions 7 having such a shape are arranged in a herringbone shape is exemplified. For example, as shown in FIG. The axial groove 22 as the recess 7 can also be formed on the outer peripheral surface 21 a of the shaft member 21. In this case, the plurality of axial grooves 22 are formed at predetermined intervals in the circumferential direction as shown in FIG. These axial grooves 22 and the surrounding area 23 constitute a dynamic pressure generating portion 24. Therefore, although not shown, the shaft member 21 is inserted into the inner periphery of the bearing member 3 shown in FIG. 1 and the shaft member 21 is rotated relative to the bearing member 3 so that it is filled with lubricating oil. The dynamic pressure of the lubricating oil is generated by the dynamic pressure generating portion 24 in the radial bearing gap, thereby forming a radial bearing portion that supports the shaft member 21 in a non-contact manner in the radial direction with respect to the bearing member 3.

  The shaft member 21 having the axial groove 22 is formed through a recess rolling process and a planar rolling process, as in the above embodiment. As a result, for example, as shown in FIG. 7A, a first work hardened layer 25 a is formed in the surface layer portion 25 of the axial groove 22 by the recess rolling process. Further, a raised portion 26 (broken line portion in the figure) generated around the axial groove 22 on the surface 23a of the peripheral region 23 is flattened by plane rolling, and a second portion by plane rolling is formed on the lower layer portion of the raised portion 15. The work hardening layer 27 is formed. In this case, for example, in addition to the rolling dies 12, 13, 16, and 17 shown in FIGS. 2 and 4, the rolling dies 19 and 20 shown in FIG. 5 can be used.

  Also in this embodiment, the raised surface 26 generated in the peripheral region 23 by rolling of the recess 7 (axial groove 22) is flattened by plane rolling, so that the bearing surface (surface 23a) and the recess 7 (axial groove) While the shape accuracy of 22) is kept high, the raised portion 26 can be removed while keeping the groove depth d of the axial groove 22 uniform, and a high dynamic pressure action can be exhibited.

  As the axial groove 22 that can be formed, as shown in FIG. 7A, in addition to the curved surface 22a having an arcuate cross section that protrudes toward the center in the axial direction, for example, as shown in FIG. 7B. In addition, an axial groove 22 configured by a plane 22b whose cross-sectional shape is a chord with respect to the arc of the outer peripheral surface 21a is conceivable. Alternatively, as shown in FIG. 7C, the axial groove 22 having a configuration in which rising portions 22c are provided at both ends in the circumferential direction of the plane 22b so that a step is formed between the plane 22b and the outer peripheral surface 21a. Alternatively, as shown in FIG. 7 (d), there is an axial groove 22 constituted by a curved surface 22d having a cross-sectional shape in which the groove depth is constant in the axial direction and the circumferential direction and is convex toward the outer diameter side. It can be formed.

  The number of the axial grooves 22 formed on the outer periphery of the shaft member 21 is preferably 3 or more in consideration of the dynamic pressure action of the lubricating oil. For the same reason, the circumferential angle α indicating the circumferential width of the axial groove 22 is preferably 10 ° to 60 °, and the groove depth d of the axial groove 22 is preferably 2 μm to 20 μm. Further, when viewed from both sides of low torque and high rigidity, the ratio of the total area of the axial groove 22 to the total area of the surface 23a of the peripheral region 23 (if the axial length of the axial groove 22 is uniform) The area ratio is {α / (360 ° −α)}.) Is preferably 15% to 70%.

  FIG. 6 illustrates a configuration in which a plurality of axial grooves 22 extending in the axial direction over the entire region where the radial bearing portion is to be formed (dynamic pressure generating portion 24) are arranged in parallel in the circumferential direction. In addition to this, for example, as shown in FIG. 8, a configuration in which the axial grooves 22 are intermittently provided in the axial direction may be employed. The other configuration is the same as that in the case where the axial groove 22 extending over the entire axial length of the dynamic pressure generating portion 24 is provided, and the description thereof is omitted.

  In the above-described embodiment, the inclined grooves 9a and 9b and the axial groove 22 are exemplified as the concave portion 7, but it is of course possible to form the concave portion 7 having a shape other than the groove. FIG. 9A shows an example thereof, and a plurality of dimples 32 as the recesses 7 are dispersed and arranged in a partial region of the outer peripheral surface 31 a of the shaft member 31. In this case, the dynamic pressure generating portion 34 is configured by the plurality of dimples 32 and their surrounding regions 33. Therefore, although not shown, the shaft member 31 is inserted into the inner periphery of the bearing member 3 shown in FIG. 1 and the shaft member 31 is rotated relative to the bearing member 3 to be filled with lubricating oil. Thus, a dynamic pressure action of the lubricating oil by the dynamic pressure generating portion 34 occurs in the radial bearing gap, thereby forming a radial bearing portion that supports the shaft member 31 in a non-contact manner in the radial direction with respect to the bearing member 3.

  The shaft member 31 having the dimples 32 is formed through a recess rolling process and a planar rolling process, as in the above embodiment. As a result, for example, as shown in FIG. 9B, a first work hardened layer 35 a is formed on the surface layer portion 35 of the dimple 32 by the recess rolling process. Further, a raised portion 36 (broken line portion in the figure) generated around the dimple 32 on the surface 33a of the surrounding region 33 is flattened by plane rolling, and a second process by plane rolling is applied to a lower layer portion of the raised portion 36. A hardened layer 37 is formed. In this case, for example, in addition to the rolling dies 12, 13, 16, and 17 shown in FIG. 2 and FIG. 4, the rolling dies 19 and 20 shown in FIG. .

  Also in this embodiment, the shape of the bearing surface (surface 33a) and the recess 7 (dimple 32) is obtained by flattening the raised portion 36 generated in the surrounding region 33 by rolling the recess 7 (dimple 32) by plane rolling. While maintaining high accuracy, in particular, the raised portion 36 can be removed while keeping the depth d of the dimple 32 uniform, and a high dynamic pressure action can be exhibited.

  As the size of the dimple 32, for example, as shown in FIGS. 9A and 9B, the ratio a / A of the width a in the major axis direction of the dimple 32 to the shaft diameter A is 0.1 or more and 0. It is preferable to set it to 0.4 or less. Moreover, it is preferable that the depth d of the dimple 32 is, for example, about 1 to 10 times the width of the radial bearing gap that the outer peripheral surface 31a of the shaft member 31 faces. With dimples 32 of this size, unlike the conventional dimples provided on the shaft member, it is possible to form a dynamic pressure generating portion 34 that generates a high dynamic pressure action, and even when the radial bearing gap width is small. It works effectively as an oil sump. Further, from the viewpoint of lowering the torque and increasing the rigidity, the ratio of the total area of the dimple 32 forming region to the total area of the surface 33a of the peripheral region 33 is preferably 10% to 70%. Further, as the shape of the dimple 32, for example, as shown in FIG. 9C, the ratio a / b of the major axis width a to the minor axis width b is in the range of 1.0 (perfect circle shape) to 2.0. However, even the dimple 32 having a shape outside the above range can be formed without any problem.

  In the above embodiment, the inclined grooves 9a and 9b, the axial grooves 22, the dimples 32, and the like are exemplified as the recesses 7. However, the present invention produces a dynamic pressure action of lubricating oil in the bearing gap such as the radial bearing gap 6. Therefore, the present invention can be applied to the concave portion 7 having a shape other than the above as long as it is a concave portion.

  The shaft member for a hydrodynamic bearing device and the hydrodynamic bearing device including the shaft member described above can be used by being incorporated in a spindle motor for information equipment, for example. A configuration example in which the dynamic pressure bearing device shaft member 31 is applied to the motor spindle will be described below with reference to FIG. In addition, about the site | part and member which make the structure and effect | action same as embodiment shown in FIGS. 1-9, the same reference number is attached | subjected and duplication description is abbreviate | omitted.

  FIG. 10 shows a cross-sectional view of the motor 40 in which the hydrodynamic bearing device 41 is incorporated. The motor 40 is used as a spindle motor for a disk drive device such as an HDD, and is mounted on the shaft member 31 and a dynamic pressure bearing device 41 that rotatably supports the shaft member 31 in a non-contact manner. A rotor (disk hub) 42, a stator coil 43 and a rotor magnet 44 that are opposed to each other with a gap in the radial direction, for example, and a bracket 45 are provided. The stator coil 43 is attached to the outer periphery of the bracket 45, and the rotor magnet 44 is attached to the inner periphery of the disk hub 42. The disk hub 42 holds one or a plurality of disks D such as a magnetic disk (two in FIG. 10). When the stator coil 43 is energized, the rotor magnet 44 is rotated by electromagnetic force between the stator coil 43 and the rotor magnet 44, whereby the disc D held by the disc hub 42 and the disc hub 42 is integrated with the shaft member 31. Rotate to.

  In this embodiment, the hydrodynamic bearing device 41 includes a bearing member 46 and a shaft member 31 inserted into the inner periphery of the bearing member 46. The bearing member 46 includes a bottomed cylindrical electroformed portion 47 having one end opened, and a molded portion 48 formed integrally with the electroformed portion 47. The bearing member 46 is injection-molded integrally with the molding part 48 with resin using, for example, an electroformed part 47 that is integral with or separate from the master as an insert part.

  As shown in FIG. 10, a plurality of dimples 32 as the recesses 7 are formed on the outer peripheral surface 31 a of the shaft member 31. Further, the one end surface 31 b of the shaft member 31 has a spherical shape, and abuts on the upper end surface 47 b 1 of the bottom 47 b of the opposing electroformed portion 47 when the shaft member 31 is inserted into the inner periphery of the bearing member 46. An annular groove 31c is formed in an end region of the outer peripheral surface 31a of the shaft member 31 which is a fixed region of the disk hub 42. The shaft member 31 having the annular groove 31c is formed integrally with the disc hub 42 by, for example, molding using the shaft member 31 as an insert part. In this case, the annular groove 31 c acts as a retaining for the shaft member 31 of the disk hub 42. In addition to the annular groove 31c, the outer peripheral surface of the shaft member needs to be processed, and those having a shape that can be rolled in the rolling process described above can be simultaneously processed. Since the other configuration conforms to the description in the above embodiment, the description is omitted.

  The shaft member 31 configured as described above is inserted into the inner periphery of the bearing member 46, and lubricating oil is injected into the internal space of the bearing member 46. Thereby, the dimple 32 formed in the gap space between the inner peripheral surface 47a of the electroformed portion 47 and the upper end surface 47b1 of the bottom portion 47b and the outer peripheral surface 31a of the shaft member 31 opposed thereto is formed. The hydrodynamic bearing device 41 in which the bearing internal space is filled with lubricating oil is completed.

  In the dynamic pressure bearing device 41 configured as described above, when the shaft member 31 rotates, the dynamic pressure generating portion 34 formed on the outer peripheral surface 31 a of the shaft member 31 is connected to the inner peripheral surface (the electroformed portion 47 of the electroformed portion 47). A radial bearing gap 49 is formed between the inner circumference 47a). As the shaft member 31 rotates, the lubricating oil in the radial bearing gap 49 produces a dynamic pressure action by the dynamic pressure generating portion 34, and the pressure rises. Thus, a radial bearing portion R11 that supports the shaft member 31 so as to be rotatable in the radial direction is formed. At the same time, a thrust bearing portion T11 that supports the shaft member 31 rotatably in the thrust direction is formed between the one end surface 31b of the shaft member 31 and the upper end surface 47b1 of the electroformed portion 47 opposed thereto.

  Thus, by using the shaft member 31 with the raised portion 36 flattened and having the bearing surface (surface 33a) having high surface accuracy as the shaft member of the hydrodynamic bearing device 41, the shaft member 31 and the bearing are provided. Sliding wear with the member 46 can be reduced, and the width of the radial bearing gap 49 can be managed with high accuracy. Therefore, it is possible to avoid the situation where the dynamic pressure action generated in the radial bearing gap 49 is reduced due to wear of the dimple 32 provided on the shaft member 31 or the surrounding area 33 as much as possible, and to exhibit stable bearing performance over a long period of time. Is possible.

  In addition, by providing the dynamic pressure generating portion 34 (the concave portion 7 for generating the dynamic pressure action) on the shaft member 31 side, machining (particularly, compared to the case where the dynamic pressure generating portion 34 is provided on the bearing member 46 side) Rolling process) is easy. For this reason, it is possible to easily meet the demand for downsizing the motor.

  In the above embodiment, the case where the bearing members 3 and 46 are constituted by the electroformed parts 4 and 47 and the resin molded parts 5 and 48 is exemplified, but it is not particularly limited to this structure. For example, instead of the electroformed parts 4 and 47, a sleeve member made of sintered metal can be used to constitute the bearing member. Further, it is possible to integrally form the bearing members 3 and 47 with a metal material, or to integrally form the bearing members 3 and 47 with a resin composition having improved slidability and wear resistance. Alternatively, the bracket 45, which is a member on the motor 40 side, can be integrally formed of the same material (metal or resin) as the bearing member 46. Further, the forming method is not particularly limited, and various forming means such as machining, plastic working, or injection molding can be employed.

  1 and 10 exemplify the case where the thrust bearing portions T1 and T11 are so-called pivot bearings, the present invention is configured so that the pivot bearing includes a concave portion such as a dynamic pressure groove and its surrounding region. The present invention can also be applied to a dynamic pressure bearing configured to support the shaft member 2 in a non-contact manner in the thrust direction with a dynamic pressure generating portion constituted by: In this case, although not shown in the drawing, the shaft member 2 is provided with a flange portion that projects to the outer diameter side of the shaft member 2, for example, and a dynamic pressure generating recess such as an inclined groove or dimple is rolled on the end surface of the flange portion. Then, the end surface is rolled by, for example, a round die having a smooth cylindrical surface, etc., thereby flattening the raised portion caused by the rolling of the recess, and the surface that becomes the thrust bearing surface (around the recess) The surface accuracy of the surface of the region can be increased.

  In the above embodiment, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing devices 1 and 41 and generates the hydrodynamic action in the radial bearing gap or the like. A fluid capable of generating a pressure action, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or a lubricating grease may be used.

1 is a cross-sectional view of a fluid dynamic bearing device according to an embodiment of the present invention. It is a figure which shows notionally the process of rolling a recessed part in the shaft member for dynamic-pressure bearing apparatuses. (A) is a cross-sectional view near the outer peripheral surface layer portion of the shaft member before rolling, (b) is a cross-sectional view near the surface layer portion of the concave portion and its peripheral region after rolling the concave portion, and (c) is after flat surface rolling. Sectional drawing of the surface layer part vicinity of the recessed part of this, and its peripheral region, (d) is an expanded sectional view of the protruding part periphery after plane rolling. It is a figure which shows notionally the process of rolling and shaping | molding the outer peripheral surface of the shaft member for dynamic pressure bearing apparatuses on a plane. It is a figure which shows notionally the plane rolling process which concerns on another form. (A) is a side view of the shaft member which concerns on other embodiment of this invention, (b) is an axis orthogonal sectional view of a shaft member. (A) is an expanded sectional view which shows one shape of the axial direction groove | channel formed in the shaft member, (b)-(d) is an expanded sectional view in which all show the other shape of an axial direction groove | channel. It is a side view of the shaft member concerning other embodiments of the present invention. (A) is a side view of the shaft member which concerns on other embodiment, (b) is an enlarged view which shows the cross-sectional shape of the dimple formed in the shaft member, (c) is an enlarged view which shows the planar shape of a dimple. It is sectional drawing which shows notionally the example of 1 structure of the motor for information devices incorporating the hydrodynamic bearing apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 41 Dynamic pressure bearing apparatus 2 Shaft member 3 for dynamic pressure bearing apparatuses 3 Bearing member 4 Electroformed part 6 Radial bearing gap 7 Recess 8 Peripheral area 9a, 9b Inclined groove 10 Dynamic pressure generating part 11 Shaft material 12, 13 Rolling die 12b Convex part 14a First work hardening layer 15 Raised parts 16, 17 Rolling die 16b Plane part 18 Second work hardening layer 21 Axial member 22 Axial groove 23 Surrounding area 26 Raised part 31 Shaft member 32 Dimple 33 Surrounding area 36 Raised portion 40 Motor d, d, d Depth of recess h Height of raised portion R1, R2, R11 Radial bearing portion T1, T11 Thrust bearing portion

Claims (5)

In the shaft member for the hydrodynamic bearing device in which the concave portion for generating the hydrodynamic action of the fluid in the bearing gap is formed by rolling,
A shaft member for a hydrodynamic bearing device, wherein a raised portion generated in a peripheral region of the recess by the rolling is flattened by planar rolling.   The shaft member for a hydrodynamic bearing device according to claim 1, wherein a ratio h / d of a height h of the raised portion to a depth d of the concave portion is 0.1 or less.   The shaft member for a hydrodynamic bearing device according to claim 1 or 2, wherein a ratio h / d of a height h of the raised portion to a depth d of the concave portion is 0.01 or more.   A fluid dynamic bearing device comprising the shaft member for a fluid dynamic bearing device according to claim 1.   A first rolling step for forming a recess for rolling fluid pressure in the bearing gap by rolling, and a first rolling step for flattening the raised portion around the recess by the first rolling step by plane rolling. A method for manufacturing a shaft member for a hydrodynamic bearing device including two rolling steps.

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