JP2012225385A - Hub-integrated shaft, fluid dynamic pressure bearing device including same, and spindle motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve yield and productivity of a material of a rotor hub assembled in a fluid dynamic pressure bearing device.SOLUTION: The hub part 3 of a hub-integrated shaft 9 is made of sintered metal. As a result, large quantity of chips is not generated unlike the case of forming the hub part 3 by machining, Thus, yield and productivity of a material of the hub part 3 are improved. The formation of the hub part 3 by the sintered metal achieves finishing with higher size accuracy than forging. Thus, the amount of working by post-working is reduced to improve productivity.

Description

  The present invention relates to a hub integrated shaft, a fluid dynamic pressure bearing device including the same, and a spindle motor.

  The fluid dynamic pressure bearing device supports a shaft portion so as to be relatively rotatable by a dynamic pressure action of lubricating oil generated in a radial bearing gap between an inner peripheral surface of a bearing member and an outer peripheral surface of the shaft portion. Since the fluid dynamic bearing device has excellent rotational accuracy and quietness, for example, for spindle motors of various disk drive devices (such as HDD magnetic disk drive devices and CD-ROM optical disk drive devices), laser beams, etc. It is suitably used for a polygon scanner motor of a printer (LBP) or a color wheel motor of a projector.

  For example, in a fluid dynamic pressure bearing device incorporated in a spindle motor for HDD or a spindle motor for optical disk, a rotating body (magnetic disk or optical disk) is mounted on a rotor hub fixed to a shaft member. Such a rotor hub has been manufactured by cutting out from a bar (see, for example, Patent Document 1) or forging (see, for example, Patent Document 2).

JP 2006-226523 A JP 2009-264571 A

  However, when the rotor hub is cut out, a large amount of chips are generated, resulting in a low material yield and a long processing time. In addition, since the amount of machining is large, the frequency of tool change is increased, the equipment stop time is lengthened, the productivity is lowered, and the tool cost is increased.

  On the other hand, if the rotor hub is manufactured by forging, chips are not generated, so that the yield of the material is increased. However, since the rotor hub has a complex shape that protrudes from the shaft portion to the outer diameter and has a rotating body mounting surface on which a rotating body such as a disk is mounted, it is very difficult to form with high precision by forging. Have difficulty. For this reason, it is necessary to perform forging in many times, and processing time becomes long. Moreover, since the rotating body mounting surface of the rotor hub affects the rotation accuracy of the rotating body, high dimensional accuracy is required, but the forming accuracy by forging is not so high, and the amount of processing by post-processing increases.

  The problem to be solved by the present invention is to increase the yield and productivity of the material of the rotor hub incorporated in the fluid dynamic bearing device.

  The present invention made in order to solve the above-mentioned problems comprises a shaft portion, and a hub portion provided to protrude from the shaft portion to the outer diameter and having a rotating body mounting surface orthogonal to the axial direction, and the outer peripheral surface of the shaft portion Is a hub-integrated shaft for a fluid dynamic pressure bearing device facing a radial bearing gap, and is characterized in that at least the hub portion is formed of sintered metal.

  In this way, by forming the hub part from sintered metal, there is no generation of chips compared to the case of manufacturing by cutting, so that the yield of materials is improved and the processing time is shortened to produce. Improves. In addition, since the sintered metal hub is obtained by sintering a green compact obtained by compression molding (molding) metal powder, it has better formability than forging process in which metal material is plastically flowed. High and excellent dimensional accuracy can be obtained. This eliminates the need for post-processing or reduces the amount of processing by post-processing, so that the productivity of the hub-integrated shaft is improved compared to the case of forming by forging.

  Recently, information devices such as notebook personal computers represented by netbooks have been made thinner, and 2.5 inch HDD spindle motors used for these devices are also required to be made thinner. Along with this, miniaturization (reduction in axial dimension) of the fluid dynamic bearing device incorporated in the spindle motor is required, and the hub portion tends to be thinned as a countermeasure. When the hub portion is thinned, the fastening area with the shaft member is reduced, so that the lack of fastening strength between the two becomes a problem.

  In order to eliminate the above problems, for example, the shaft portion and the hub portion may be fixed by sintered diffusion bonding. Specifically, the metal powder is compression-molded to form a green compact having the same shape as the hub portion, and the shaft portion is press-fitted into the green compact and sintered in an integrated state, whereby the hub portion and The shaft portion is fixed by diffusion bonding. Diffusion bonding can provide higher fastening strength than press-fitting or bonding, so even if the hub part is thinned and the fastening area with the shaft part is reduced, the shaft part and hub part have sufficient strength. It can be fixed with.

  In the hub integrated shaft as described above, required characteristics are different between the shaft portion and the hub portion. That is, since the outer peripheral surface of the shaft portion faces the radial bearing gap, high dimensional accuracy and wear resistance are required. For this reason, the shaft portion is preferably formed of a material having high hardness. On the other hand, the hub part is often made of a material whose hardness is slightly lower than that of the shaft part because bending stress is often applied by a clamper or the like that fixes the rotating body, and cracks may occur if the hardness is too high. Is preferred. Therefore, by forming the shaft portion and the hub portion separately, the shaft portion and the hub portion can be formed of materials satisfying the characteristics required for each. Specifically, while the hub portion is formed of sintered metal, the shaft portion can be a machined product, or the shaft portion can be a sintered metal product separate from the hub portion.

  Moreover, in order to eliminate said malfunction, you may integrally mold a shaft part and a hub part with a sintered metal. Specifically, the metal powder is compression-molded to form a green compact having the same shape as the hub integrated shaft, and the green compact is sintered to form a sintered metal hub integrated shaft. In this case, since there is no boundary between the hub portion and the shaft portion, sufficient fastening strength can be obtained between the hub portion and the shaft portion even when the hub portion is thinned.

  When the end surface of the hub made of sintered metal faces the thrust bearing gap, the lubricating fluid held in the minute recesses on the surface of the sintered metal is supplied to the thrust bearing gap, so that it faces through the thrust bearing gap. The lubricity between the hub portion and the mating material is improved, and the wear resistance and seizure resistance are improved.

  Since the surface accuracy of the outer peripheral surface of the shaft portion is directly linked to the accuracy of the radial bearing gap, it is necessary to finish it as highly accurately as possible. For this reason, it is preferable to grind the outer peripheral surface of the shaft portion. In particular, if the outer peripheral surface of the shaft portion is ground with respect to the rotating body mounting surface of the hub portion, the relative positional accuracy of the rotating body mounting surface with respect to the outer peripheral surface of the shaft portion is increased, so the rotational accuracy of the rotating body is increased. Improvement can be expected.

  A radial dynamic pressure generating portion that generates a dynamic pressure action on the lubricating fluid in the radial bearing gap can be formed on the outer peripheral surface of the shaft portion. In particular, when the shaft portion is formed of sintered metal, if the radial dynamic pressure generating portion is formed on the outer peripheral surface of the shaft portion by rolling, the plastic flow of the material at the time of rolling processing is determined by the internal pores of the sintered metal. Therefore, the surface of the shaft portion can be prevented from rising due to the rolling process, and the radial dynamic pressure generating portion can be formed with high accuracy.

  The hub integrated shaft as described above is lubricated in a hub integrated shaft, a bearing member into which the shaft portion of the hub integrated shaft is inserted, and a radial bearing gap between the outer peripheral surface of the shaft portion and the inner peripheral surface of the bearing member. It can be incorporated in a fluid dynamic pressure bearing device including a radial bearing portion that supports the shaft portion so as to be relatively rotatable by the fluid dynamic pressure action. Further, such a fluid dynamic pressure bearing device can be incorporated into a HDD spindle motor or an optical disk spindle motor.

  As described above, according to the present invention, the yield of the material of the hub integrated shaft and the productivity can be improved by forming the hub portion with sintered metal.

It is sectional drawing of the spindle motor for HDD. It is sectional drawing of the fluid dynamic pressure bearing apparatus integrated in the said spindle motor. (A)-(d) is sectional drawing which shows the manufacturing process of the hub integrated shaft which concerns on one Embodiment of this invention integrated in the said fluid dynamic pressure bearing apparatus. It is sectional drawing of the bearing sleeve of the said fluid dynamic pressure bearing apparatus. It is a top view of the said bearing sleeve. It is a bottom view of the said bearing sleeve. (A)-(d) is sectional drawing which shows the manufacturing process of the hub integrated shaft which concerns on other embodiment. (A)-(c) is sectional drawing which shows the manufacturing process of the hub integrated shaft which concerns on other embodiment.

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

  FIG. 1 shows a spindle motor used in, for example, a 2.5-inch HDD disk drive device. This spindle motor includes a fluid dynamic pressure bearing device 1 that rotatably supports a hub integrated shaft 9 according to an embodiment of the present invention, a bracket 6 to which the fluid dynamic pressure bearing device 1 is attached, and a radial gap. And a stator magnet 4 and a rotor magnet 5 which are opposed to each other. The stator coil 4 is attached to the bracket 6, and the rotor magnet 5 is attached to the hub integrated shaft 9 via the yoke 10. The hub integrated shaft 9 holds a predetermined number of disks D (one in the illustrated example) as a rotating body. When the stator coil 4 is energized, the rotor magnet 5 is rotated by electromagnetic force between the stator coil 4 and the rotor magnet 5, whereby the hub integrated shaft 9 and the disk D are rotated together.

  As shown in FIG. 2, the fluid dynamic bearing device 1 includes a hub integrated shaft 9 having a shaft portion 2 and a hub portion 3, and a bearing member that rotatably supports the hub integrated shaft 9. In the present embodiment, the shaft portion 2 and the hub portion 3 of the hub integrated shaft 9 are formed separately. In the present embodiment, the bearing member includes a bearing sleeve 8 in which the shaft portion 2 of the hub integrated shaft 9 is inserted on the inner periphery, and a bottomed cylindrical housing 7 that holds the bearing sleeve 8 on the inner periphery. The A retaining member 11 is provided at the lower end of the shaft portion 2 of the hub integrated shaft 9. In the following, for convenience of explanation, the opening side of the housing 7 in the axial direction is the upper side and the closing side is the lower side.

  The shaft portion 2 is formed in a substantially cylindrical shape having an outer diameter of about 2 to 4 mm. In the present embodiment, the shaft portion 2 is formed by machining (for example, turning) of metal (melting material, for example, iron-based metal, particularly stainless steel). The shaft portion 2 is orthogonal to the axial direction formed between the large-diameter outer peripheral surface 2a having a straight cylindrical surface without irregularities, the small-diameter outer peripheral surface 2b provided above the large-diameter outer peripheral surface 2a. And a shoulder surface 2c. The large-diameter outer peripheral surface 2a of the shaft portion 2 functions as a radial bearing surface that faces the radial bearing gap. An axial through hole 2d is provided in the shaft center of the shaft portion 2, and a thread groove is formed on the inner peripheral surface of the through hole 2d.

  The hub portion 3 includes a rotating body mounting surface extending from the upper end portion of the shaft portion 2 to the outer diameter and orthogonal to the axial direction. The hub portion 3 of the present embodiment includes a disc portion 3a that covers the opening of the housing 7, a cylindrical portion 3b that extends downward in the axial direction from the outer diameter end of the disc portion 3a, and an outer diameter further from the lower end portion of the cylindrical portion 3b. It is comprised with the collar part 3c extended in. The lower end surface 3a1 of the disk portion 3a functions as a thrust bearing surface that faces the thrust bearing gap. A disk mounting surface 3d as a rotating body mounting surface is formed on the upper end surface of the flange portion 3c, and a disk fitting surface 3e is formed on the outer peripheral surface of the cylindrical portion 3b. The disk D is fitted onto the disk fitting surface 3e and placed on the disk mounting surface 3d. In this state, the upper surface of the disk D is pressed by a clamper (not shown) and pressed onto the disk mounting surface 3d. Is held by the hub portion 3. The upper part of the through hole 2d of the shaft part 2 functions as a screw hole for fixing the clamper.

  The hub portion 3 is formed of a sintered metal (for example, a sintered metal containing iron as a main component). Specifically, first, as shown in FIG. 3 (a), a hub pressure having a disk portion 3a ′, a cylindrical portion 3b ′, and a flange portion 3c ′ having the same shape as the hub portion 3 by compression molding metal powder. Powder 3 'is formed. Then, as shown in FIG. 3B, the small-diameter outer peripheral surface 2b of the shaft portion 2 is lightly press-fitted into the inner peripheral surface 3a3 ′ of the hub green compact 3 ′, and the disk portion 3a ′ of the hub green compact 3 ′. The lower end surface 3a1 ′ is brought into contact with the shoulder surface 2c of the shaft portion 2, and the shaft portion 2 and the hub green compact 3 ′ are integrated. By putting this integrated product into a sintering furnace and heating it at a predetermined sintering temperature (see FIG. 3C), the hub compact 3 'is sintered to form the hub portion 3, The inner peripheral surface 3a3 of the hub portion 3 and the small-diameter outer peripheral surface 2b of the shaft portion 2 are diffusion bonded. Thereby, the hub integrated shaft 9 in which the shaft portion 2 and the hub portion 3 are fixed by sintering diffusion bonding is obtained (see FIG. 3D). Thus, sufficient fastening strength is obtained even when the hub portion 3 is thinned (for example, when the thickness is 1 mm or less) by fixing the shaft portion 2 and the hub portion 3 by sintering diffusion bonding. be able to.

  By the way, when the shaft portion 2 is press-fitted into the hub green compact 3 ′ as described above, if the pressure on the fitting surface of both is increased, that is, the small-diameter outer peripheral surface 2b of the shaft portion 2 and the hub green compact 3 ′. If the press-fitting allowance with the inner peripheral surface 3a3 ′ is increased, the fastening strength by diffusion bonding between the shaft portion 2 and the hub portion 3 can be increased. However, since the hub green compact 3 'is in a state of low strength before sintering, if the press-fitting allowance with the shaft portion 2 is too large, the hub green compact 3' may be deformed or damaged. In particular, when the hub portion 3 is thinned, there is a high possibility that the hub compact 3 'is deformed or damaged by press fitting. Therefore, the press-fitting allowance between the shaft portion 2 and the hub green compact 3 ′ is sufficiently fastened by diffusion bonding between the shaft portion 2 and the hub portion 3 without causing deformation or damage to the hub green compact 3 ′. In this embodiment, the press-fitting allowance is set within a range of 5 to 15 μm (for example, about 10 μm).

  Moreover, since the hub part 3 contacts the lubricating fluid (in this embodiment, lubricating oil) filled in the fluid dynamic bearing device 1, the lubricating oil leaks to the outside through the internal pores of the sintered metal. It is necessary to prevent this. For example, the density of the sintered metal is increased so that all the internal pores become independent pores, or the surface of the hub portion 3 (for example, the surface in contact with the lubricating oil, particularly the thrust bearing surface) is sealed with polishing or coating. Oil leakage can be prevented.

  In addition, after the hub integrated shaft 9 is formed, a grinding finish may be applied to a surface that requires particularly high accuracy. In the present embodiment, the large-diameter outer peripheral surface 2a (radial bearing surface) of the shaft portion 2 is ground. In addition, the lower end surface 3a1 (thrust bearing surface) of the disk portion 3a and the lower end surface 2e of the shaft portion 2 that affects the accuracy of the thrust bearing gap may be ground. Furthermore, the disc mounting surface 3d and the disc fitting surface 3e of the hub portion 3 may be ground. In the present embodiment, first, the disk mounting surface 3d and the disk fitting surface 3e of the hub portion 3 are ground and then the ground surface is used as a reference (for example, a jig is applied to the ground surface). The large diameter outer peripheral surface 2a and the lower end surface 2e of the shaft portion 2 and the lower end surface 3a1 of the disc portion 3a are ground. Thereby, since the positional accuracy of the disk mounting surface 3d and the disk fitting surface 3e with respect to the radial bearing surface and the thrust bearing surface is set with high accuracy, the rotational accuracy of the disk D is increased.

  As described above, even when the hub portion 3 of the hub integrated shaft 9 is ground, the sintered metal hub portion 3 is formed with high dimensional accuracy. The shortening and the tool cost can be reduced.

  The retaining member 11 is made of metal or resin, and has a disk-shaped flange portion 11a and a fixing portion 11b extending upward from the axis of the flange portion 11a. A screw groove is formed on the outer periphery of the fixing portion 11b, and is screwed to the lower end of the screw hole formed on the inner peripheral surface of the through hole 2d of the shaft portion 2. The flange portion 11 a protrudes to an outer diameter from the large-diameter outer peripheral surface 2 a of the shaft portion 2, and the upper end surface 11 a 1 is in contact with the lower end surface 2 e of the shaft portion 2. The flange portion 11 a is disposed between the lower end surface 8 c of the bearing sleeve 8 and the upper end surface 7 b 1 of the bottom portion 7 b of the housing 7 in the axial direction. The flange portion 11 a fixed to the lower end of the shaft portion 2 and the bearing sleeve 8 are engaged in the axial direction, whereby the shaft portion 2 is prevented from coming off from the bearing sleeve 8.

  The upper end surface 11a1 of the flange portion 11a functions as a thrust bearing surface that faces the thrust bearing gap. Since the lower end surface 2e of the shaft portion 2 is a high-precision flat surface by grinding finish, the upper end surface 11a1 of the flange portion 11a is in good contact with the entire lower end surface 2e of the shaft portion 2, and thereby the shaft portion 2, the flange portion 11a can be positioned with high accuracy. In addition, since the upper end surface 11a1 of the flange portion 11a and the lower end surface 2e of the shaft portion 2 are brought into close contact with each other around the circumference, the penetration of the lubricating oil into the through hole 2d of the shaft portion 2 can be suppressed. The risk that the lubricating oil filled inside leaks out through the through hole 2d can be reduced.

  The bearing sleeve 8 is formed in a cylindrical shape from metal or resin, and in this embodiment, is formed from a sintered metal containing copper as a main component, for example. The inner peripheral surface 8a of the bearing sleeve 8 functions as a radial bearing surface that faces the radial bearing gap. As shown in FIG. 4, herringbone-shaped dynamic pressure grooves 8a1 and 8a2 are formed on the surface as radial dynamic pressure generating portions, for example, in two regions separated in the axial direction (cross hatching is a hill portion). ). In the illustrated example, the upper dynamic pressure groove 8a1 is formed asymmetrically in the axial direction. Specifically, the axial dimension X1 of the region above the axial center part m is the axial dimension X2 of the lower region. (X1> X2). The lower dynamic pressure groove 8a2 is formed symmetrically in the axial direction. An axial groove 8d1 is formed over the entire length in the axial direction on the outer peripheral surface 8d of the bearing sleeve 8. For example, three axial grooves 8d1 are equally arranged in the circumferential direction.

  The upper end surface 8b and the lower end surface 8c of the bearing sleeve 8 each function as a thrust bearing surface that faces the thrust bearing gap. As shown in FIGS. 5 and 6, for example, pump-in type spiral dynamic pressure grooves 8b1 and 8c1 are formed on these surfaces as thrust dynamic pressure generating portions (cross hatching is a hill portion). An axial groove 8 d 1 is formed on the outer peripheral surface 8 d of the bearing sleeve 8. The number of the axial grooves 8d1 is arbitrary. For example, three axial grooves 8d1 are arranged at equal intervals in the circumferential direction.

  The housing 7 is formed of metal or resin, and in this embodiment, is formed by, for example, resin injection molding. As shown in FIG. 2, the housing 7 is formed in a bottomed cylindrical shape integrally having a side portion 7a and a bottom portion 7b. The inner peripheral surface 7a1 of the side portion 7a is formed in a straight cylindrical surface shape. At the upper end of the outer peripheral surface of the side portion 7a, as shown in FIG. 2, a tapered seal surface 7a3 that gradually increases in diameter upward is formed. The seal surface 7a3 forms an annular seal space S whose radial dimension is gradually reduced upward, between the seal surface 7a3 and the inner peripheral surface 3b1 of the cylindrical portion 3b of the hub portion 3. When the hub integrated shaft 9 is rotated, the seal space S is provided through a gap between the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 7a2 of the housing 7, so that the thrust of the first thrust bearing portion T1. It communicates with the outer diameter side of the bearing gap and the upper end of the axial groove 8d1. The capillary force of the seal space S prevents the lubricating oil filled in the housing 7 from leaking out.

  The fluid dynamic bearing device 1 composed of the above-described members can be assembled as follows. First, the shaft portion 2 of the hub integrated shaft 9 is inserted into the inner periphery of the bearing sleeve 8, and in this state, the fixing portion 11 b of the retaining member 11 is fixed to the lower end of the through hole 2 d of the shaft portion 2 with a temporary assembly product. Configure. At this time, positioning of the flange portion 11a with respect to the shaft portion 2 is performed by bringing the upper end surface 11a1 of the flange portion 11a into contact with the lower end surface 2e of the shaft portion 2. Since the axial dimension L2 (see FIG. 2) between the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 11a1 of the flange portion 11a is determined in the state of this temporary assembly, this axial direction The total amount of the thrust bearing gaps of the first and second thrust bearing portions T1, T2 is set by the difference (L2-L1) between the dimension L2 and the axial dimension L1 between the both end faces 8b, 8c of the bearing sleeve 8. The

  At this time, since the lower end surface 2e of the shaft portion 2 of the hub integrated shaft 9 and the lower end surface 3a1 of the disk portion 3a of the hub portion 3 are both ground and finished with reference to the disk mounting surface 3d, these The axial dimension between them is set with high accuracy. Accordingly, by bringing the upper end surface 11a1 of the flange portion 11a into contact with the lower end surface 2e of the shaft portion 2, the axial dimension L2 between the upper end surface 11a1 of the flange portion 11a and the lower end surface 3a1 of the disk portion 3a of the hub portion 3 is determined. Is set with high accuracy. On the other hand, since the bearing sleeve 8 is formed of a sintered metal having excellent formability, the axial dimension L1 between the both end faces 8b and 8c is set with high accuracy. Therefore, the total amount of the thrust bearing gaps of the first and second thrust bearing portions T1 and T2 set by the difference between these axial dimensions (L2−L1) is set with high accuracy.

  Thus, the temporary assembly bearing sleeve 8 in which the thrust bearing clearance is set is inserted into the inner periphery of the housing 7, and the outer peripheral surface 8 d of the bearing sleeve 8 is bonded to the inner peripheral surface 7 a 1 of the housing 7 with clearance, press-fit, and adhesive interposed. Fix by press fitting below. Then, the fluid dynamic bearing device 1 shown in FIG. 2 is completed by filling the space inside the housing 7 including the internal pores of the bearing sleeve 8 with the lubricating oil. At this time, the oil level is held inside the seal space S.

  When the hub integrated shaft 9 rotates, a radial bearing gap is formed between the inner peripheral surface 8a of the bearing sleeve 8 and the large-diameter outer peripheral surface 2a of the shaft portion 2, and a radial dynamic pressure generating portion (dynamic pressure groove 8a1, 8a2) increases the pressure of the lubricating oil filled in the radial bearing gap, and this pressure (dynamic pressure action) constitutes radial bearing portions R1 and R2 that support the hub integrated shaft 9 in a non-contact manner so as to be rotatable in the radial direction. Is done.

  At the same time, between the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 8b of the bearing sleeve 8, and between the upper end surface 11a1 of the flange portion 11a and the lower end surface 8c of the bearing sleeve 8. Each thrust bearing gap is formed, and the thrust dynamic pressure generating portion (dynamic pressure grooves 8b1, 8c1) increases the pressure of the lubricating oil filled in each thrust bearing gap, and this pressure (dynamic pressure action) integrates the hub. A first thrust bearing portion T1 that supports the shaft 9 in a non-contact manner so as to be rotatable in one of the thrust directions (lifting direction), and a second thrust member that supports the hub-integrated shaft 9 in a non-contact manner so as to be freely rotatable in the other thrust direction (the pushing-down direction). And a thrust bearing portion T2.

  At this time, since the bearing sleeve 8 is formed of sintered metal, the lubricating oil impregnated in the internal pores of the bearing sleeve 8 is supplied from the inner peripheral surface 8a and the upper and lower end surfaces 8b and 8c to the radial bearing gap and the thrust bearing gap. Thus, the lubricity in the radial bearing portions R1, R2 and the thrust bearing portions T1, T2 is improved. Further, since the hub portion 3 is formed of sintered metal, the lubricating oil impregnated in the internal pores of the hub portion 3 is supplied to the thrust bearing gap. Even if the surface of the hub part 3 is subjected to sealing treatment, the surface of the hub part 3 is usually not completely smoothed, and innumerable minute recesses are formed on the surface. Lubricating oil held in the minute recesses is supplied to the thrust bearing gap. Thereby, the lubricity in the first thrust bearing portion T1 is further enhanced, and the wear resistance and seizure resistance of the hub portion 3 and the bearing member (the bearing sleeve 8 in the present embodiment) are further improved. In particular, when a downward load applied to the hub portion 3 is large (for example, when a plurality of discs D are mounted), the hub portion 3 that faces the thrust bearing gap of the first thrust bearing portion T1 as described above. It is effective to increase the lubricity by making the bearing sleeve 8 both made of sintered metal.

  The axial groove 8d1 formed in the outer peripheral surface 8d of the bearing sleeve 8 forms a communication path through which lubricating oil can flow. This communication path can prevent a local negative pressure from being generated in the lubricating oil filled in the housing 7. In particular, in the present embodiment, as shown in FIG. 3, the upper dynamic pressure groove 8a1 formed in the inner peripheral surface 8a of the bearing sleeve 8 is formed in an axially asymmetric shape, so that the rotation of the hub integrated shaft 9 is performed. Along with this, the lubricating oil in the radial bearing gap is pushed downward, and the lubricating oil circulates through the communication path, thereby reliably preventing the generation of local negative pressure.

  The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the same code | symbol is attached | subjected to the location which has the same function as said embodiment, and duplication description is abbreviate | omitted.

  In the above embodiment, the case where the shaft portion 2 is formed by machining of the molten material is shown. However, the present invention is not limited thereto, and the shaft portion 2 is separated from the hub portion 3 as shown in FIG. It may be a sintered metal product. In this case, first, a hub compact 3 ′ having the same shape as the hub portion 3 is formed (see FIG. 7A), and the same as the shaft portion 2 is formed on the inner peripheral surface 3a3 ′ of the hub compact 3 ′. The small-diameter outer peripheral surface 2b ′ of the shaped axial compact 2 ′ is press-fitted, and the lower end surface 3a1 ′ of the disk portion 3a ′ of the hub compact 3 ′ is brought into contact with the shoulder surface 2c ′ of the axial compact 2 ′. They are brought into contact with each other (see FIG. 7B). By sintering this integrated product (see FIG. 7C), the shaft compact 2 'and the hub compact 3' are sintered to form the shaft 2 and the hub 3 simultaneously. The small-diameter outer peripheral surface 2b of the shaft portion 2 and the inner peripheral surface 3a3 of the hub portion 3 are fixed by diffusion bonding (see FIG. 7 (d)). The shaft portion 2 and the hub portion 3 can be formed of a sintered material that satisfies the characteristics required for each. For example, the shaft portion 2 can be formed of a sintered metal whose main component is copper, and the hub portion 3 can be formed of a sintered metal whose main component is iron. Not limited to this, the shaft portion 2 and the hub portion 3 may be formed of the same material.

  In the above embodiment, the shaft portion 2 is press-fitted into the unsintered hub green compact 3 ′ (see FIG. 3), or the shaft is not sintered into the non-sintered green compact 3 ′. The green compact 2 ′ is press-fitted (see FIG. 7), but is not limited thereto. For example, the hub green compact 3 ′ and the shaft green compact 2 ′ may be pre-sintered to increase the strength and then press-fitted and integrated, and the integrated product may be further sintered (not shown).

  In the above-described embodiment, the shaft portion 2 and the hub portion 3 of the hub integrated shaft 9 are formed separately. However, the present invention is not limited to this. For example, as shown in FIG. 3 may be integrally formed of sintered metal. In this case, a green compact 9 ′ having a shaft portion 2 ′ and a hub portion 3 ′ having the same shape as the shaft portion 2 and the hub portion 3 of the hub integrated shaft 9 is formed (see FIG. 8A). By sintering the body 9 '(see FIG. 8 (b)), the sintered metal hub integrated shaft 9 having the shaft portion 2 and the hub portion 3 is integrally formed (see FIG. 7 (d)). . In this case, since the shaft portion 2 and the hub portion 3 are formed of the same material, the hub integrated shaft 9 may be subjected to surface hardening treatment or coating treatment as necessary. For example, surface hardening treatment or the like may be applied to the large-diameter outer peripheral surface 2a (radial bearing surface) of the shaft portion 2 or the lower end surface 3a1 (thrust bearing surface) of the disk portion 3a of the hub portion 3.

  In the above-described embodiment, the case where the radial dynamic pressure generating portions (dynamic pressure grooves 8a1 and 8a2) are formed on the inner peripheral surface 8a of the bearing sleeve 8 is shown. A radial dynamic pressure generator may be formed on the large-diameter outer peripheral surface 2a (not shown). In particular, when the shaft portion 2 is formed of a sintered metal as shown in FIGS. 7 and 8, if the radial dynamic pressure generating portion is formed by rolling, the plasticity of the material of the shaft portion 2 when rolled. Since the flow can be absorbed by the internal pores of the sintered metal, the large-diameter outer peripheral surface 2a of the shaft portion 2 does not rise, and the radial dynamic pressure generating portion can be accurately formed.

  In the above embodiment, the herringbone-shaped dynamic pressure grooves 8a1 and 8a2 are formed as the radial dynamic pressure generating portion. However, the present invention is not limited to this, and other dynamic pressure grooves such as a spiral shape, a multi-arc bearing, The radial dynamic pressure generating unit may be configured by a step bearing or the like. Alternatively, the radial dynamic pressure generating portion is not provided, and the large-diameter outer peripheral surface 2a of the shaft portion 2 and the inner peripheral surface 8a of the bearing sleeve 8 may both be smooth cylindrical surfaces.

  Further, in the above embodiment, the thrust dynamic pressure generating portions (dynamic pressure grooves 8b1 and 8c1) are formed on the upper end surface 8b and the lower end surface 8c of the bearing sleeve 8. A thrust dynamic pressure generating portion may be formed on the lower end surface 3a1 of the disk portion 3a of the hub portion 3 and the upper end surface 11a1 of the flange portion 11a of the retaining member 11 that are opposed to each other via a gap.

  In the above-described embodiment, the spiral dynamic pressure grooves 8b1 and 8c1 are formed as the thrust dynamic pressure generating portion. However, the present invention is not limited to this, and the thrust dynamic pressure is generated by a herringbone-shaped dynamic pressure groove or a step bearing. You may comprise a generating part.

  In the above embodiment, the lubricating fluid is a lubricating oil. However, the present invention is not limited to this. For example, a fluid such as a magnetic fluid or air can be used.

  In the above embodiment, the hub integrated shaft 9 according to the present invention is incorporated in the fluid dynamic bearing device of the HDD spindle motor. However, the present invention is not limited to this. For example, the hub integrated shaft of the present invention is applied to a fluid dynamic pressure bearing device of a spindle motor for optical disks such as CD and DVD, a fluid dynamic pressure bearing device of a polygon scanner motor, or a fluid dynamic pressure bearing device of a color wheel motor. You can also.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft part 2 'Shaft compact 3 Hub part 3' Hub compact 4 Stator coil 5 Rotor magnet 6 Bracket 7 Housing 8 Bearing sleeve 9 Hub integrated shaft 9 'Compact 10 Yoke 11 Removal Stopping member D Disc R1, R2 Radial bearing portion T1, T2 Thrust bearing portion S Seal space

Claims (13)

A fluid dynamic pressure bearing comprising: a shaft portion; and a hub portion provided to protrude from the shaft portion to an outer diameter and having a rotating body mounting surface orthogonal to the axial direction, wherein an outer peripheral surface of the shaft portion faces a radial bearing gap A hub integrated shaft for the device,
A hub-integrated shaft, wherein at least the hub portion is formed of sintered metal.   The hub integrated shaft according to claim 1, wherein the shaft portion and the hub portion are fixed by sintered diffusion bonding.   The hub integrated shaft according to claim 2, wherein the shaft portion is a machined product.   The hub integrated shaft according to claim 2, wherein the shaft portion is a sintered metal product separate from the hub portion.   The hub integrated shaft according to claim 1, wherein the shaft portion and the hub portion are integrally formed of sintered metal.   The hub integrated shaft according to any one of claims 1 to 5, wherein an end surface of the hub portion faces a thrust bearing gap.   The hub integrated shaft according to claim 1, wherein at least an outer peripheral surface of the shaft portion is ground.   The hub integrated shaft according to claim 7, wherein the outer peripheral surface of the shaft portion is ground with respect to the rotating body mounting surface of the hub portion.   The hub integrated shaft according to any one of claims 1 to 8, wherein a radial dynamic pressure generating portion for generating a dynamic pressure action in a lubricating fluid in a radial bearing gap is formed on an outer peripheral surface of the shaft portion.   The hub integrated shaft according to claim 4 or 5, wherein a radial dynamic pressure generating portion for generating a dynamic pressure action in the lubricating fluid in the radial bearing gap is formed on the outer peripheral surface of the shaft portion by rolling.   A hub integrated shaft according to any one of claims 1 to 10, a bearing member into which a shaft portion of the hub integrated shaft is inserted, and a radial bearing gap between an outer peripheral surface of the shaft portion and an inner peripheral surface of the bearing member. A fluid dynamic pressure bearing device comprising a radial bearing portion that supports the shaft portion so as to be relatively rotatable by the dynamic pressure action of the generated lubricating fluid.   A spindle motor for HDD comprising the fluid dynamic bearing device according to claim 11.   An optical disk spindle motor comprising the fluid dynamic bearing device according to claim 11.

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