Sintered oil-impregnated bearing and fluid dynamic bearing device equipped with this bearing

Abstract

To enable mass production of a sintered oil-containing bearing capable of ensuring an ability to draw lubricant into the center side of a bearing from a dynamic pressure groove while avoiding increase in the size of a bearing device, to prevent the lubricant from leaking to the outside of the bearing.SOLUTION: A radial dynamic pressure generation part 11 is formed on an inner peripheral surface 8a of a sintered oil-containing bearing 8. The radial dynamic pressure generation part 11 has a plurality of inclined dynamic pressure grooves 11a inclined with respect to a circumferential direction of the inner peripheral surface 8a, and a plurality of hill parts 11b provided between the inclined dynamic pressure grooves 11a. The hill part 11b is provided with a reduced diameter part 13 in which an inner diameter of the hill part 11b decreases from an axial center side to an axial end side of the inner peripheral surface 8a.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a sintered oil-impregnated bearing and a hydrodynamic bearing device provided with this bearing, and particularly relates to a sintered oil-impregnated bearing having a radial hydrodynamic generating portion and a hydrodynamic bearing device provided with this bearing.

Background Art

[0002] A sintered oil-impregnated bearing is a bearing formed of sintered metal and is used in a state where lubricating oil is impregnated into internal pores of a porous body. Specifically, as the shaft portion inserted into the inner circumference of the sintered oil-impregnated bearing rotates relative to the shaft portion, the lubricating oil impregnated into the internal pores seeps out to the sliding portion with the shaft portion to form an oil film, and the shaft portion is rotationally supported through this oil film. Such a bearing is suitable as a bearing device for a motor mounted in various electric devices including information devices, more specifically, for a spindle motor in a disk drive device for HDD, CD, DVD, Blu-ray disk, for a fan motor incorporated in these disk drive devices and PCs, or for a polygon scanner motor incorporated in a laser beam printer (LBP).

[0003] Furthermore, to further improve quietness and extend the lifespan of sintered oil-impregnated bearings, dynamic pressure generating sections (radial dynamic pressure generating sections), such as dynamic pressure grooves, may be formed on the inner circumferential surface. As radial dynamic pressure generating sections, for example, a so-called herringbone shape is known, which consists of a plurality of dynamic pressure grooves arranged in different directions relative to the circumferential direction of the inner circumferential surface of the bearing (see, for example, Patent Document 1). In addition, when the radial dynamic pressure generating section takes the above-described configuration, for example, by making the longitudinal dimension of one inclined dynamic pressure groove larger than the longitudinal dimension of the other inclined dynamic pressure groove, a differential pressure of the lubricating oil pulling force by each inclined dynamic pressure groove is generated, and by arranging the inclined dynamic pressure groove with the relatively larger longitudinal dimension on the external communication side (axial opening side of the housing) of the fluid dynamic pressure bearing device, the differential pressure of the pulling force generates a flow of lubricating oil from the axial opening side to the closed side of the housing as a whole, aiming to prevent leakage of lubricating oil. A fluid dynamic pressure bearing device has been proposed (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-306036 [Patent Document 2] Japanese Patent Publication No. 2007-147082 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the fluid dynamic bearing device described in Patent Document 1, leakage of lubricating oil is prevented by the differential pressure generated by varying the longitudinal dimensions of the inclined dynamic grooves. On the other hand, in this type of bearing device, the magnitude of the differential pressure is affected not only by the longitudinal dimensions of the inclined dynamic grooves, but also by variations in dimensions and shapes that are difficult to avoid in mass production, such as variations in the groove depth of the inclined dynamic grooves, the shape accuracy (straightness, etc.) of the inner surface of the bearing, the shape accuracy (straightness, etc.) of the outer surface of the shaft, or the dimensional accuracy of the bearing gap between the inner surface of the bearing and the outer surface of the shaft (variation in the axial direction, etc.).

[0006] Furthermore, the greater the difference between the longitudinal dimension of the inclined dynamic pressure groove located on the axial opening side of the housing and the longitudinal dimension of the inclined dynamic pressure groove located on the axial closing side of the housing, the greater the lubricating oil draw-in force. However, increasing the longitudinal dimension of the inclined dynamic pressure groove increases the axial dimension of the sintered oil-impregnated bearing and, consequently, the fluid dynamic pressure bearing device. In addition, in spindle motors equipped with this type of bearing device, the center of gravity of the rotating body is often located relatively high, making the upper part of the sintered oil-impregnated bearing prone to wear. As the sintered oil-impregnated bearing wears down, the bearing clearance increases, and as a result of the decrease in the differential pressure, it becomes difficult to obtain a satisfactory draw-in force for lubricating oil toward the axial center of the housing, increasing the risk of lubricating oil leakage.

[0007] In view of the above circumstances, the technical problem to be solved by the present invention is to enable mass production of sintered oil-impregnated bearings that can prevent lubricating oil from leaking out of the bearing by ensuring the pulling force of the lubricating oil toward the center of the bearing by the dynamic pressure groove, while avoiding an increase in the size of the bearing device. [Means for solving the problem]

[0008] The aforementioned problems are solved by the sintered oil-impregnated bearing according to the present invention. Specifically, this bearing is a sintered metal bearing obtained by compressing metal powder into a cylindrical shape to form a compact, and then sintering the formed compact, wherein lubricating oil is impregnated into the internal voids and a radial dynamic pressure generating portion is formed on the inner circumferential surface, and the radial dynamic pressure generating portion is characterized by having a plurality of inclined dynamic pressure grooves inclined with respect to the circumferential direction of the inner circumferential surface and a plurality of mounds provided between the inclined dynamic pressure grooves, and the mounds are provided with a reduced diameter portion in which the inner diameter of the mound decreases from the axial center side to the axial end side of the inner circumferential surface.

[0009] The inventors focused on the shape of the ridges between inclined dynamic pressure grooves, which have conventionally been assumed to have a constant inner diameter in the axial direction. They discovered that when the inner diameter of the ridges decreases from the axial center to the axial end of the bearing's inner surface, the lubricating oil pull-in force by the inclined dynamic pressure grooves between the ridges improves. The present invention is based on this finding, and by providing the aforementioned reduced-diameter portion in the ridges between the inclined dynamic pressure grooves, the lubricating oil pull-in force by the inclined dynamic pressure grooves between the ridges can be increased. Therefore, even when the lubricating oil pull-in force toward the bearing center is insufficient for the precision reasons mentioned above, or when the pull-in force decreases due to bearing wear, providing the reduced-diameter portion in the ridges between the inclined dynamic pressure grooves, which are responsible for the lubricating oil pull-in force toward the bearing center, makes it possible to compensate for the deficiency or decrease in the pull-in force and obtain the required amount of pull-in force. Consequently, when mass-producing and using sintered oil-impregnated bearings like the present invention, it is possible to prevent lubricating oil from leaking out of the bearing over a long period of time.

[0010] Furthermore, in the sintered oil-impregnated bearing according to the present invention, the value obtained by subtracting the inner diameter dimension at the second end on the axial end side from the inner diameter dimension at the first end on the axial center side of the reduced diameter portion may be greater than 0 μm and less than or equal to 1.5 μm.

[0011] In this way, by limiting the difference in inner diameter between the axial ends of the reduced-diameter section provided on the hill to a maximum of 1.5 μm or less, the axial fluctuation of the bearing clearance (radial bearing clearance), which is formed between the outer circumferential surface of the shaft and the inner circumferential surface of the bearing and is normally controlled to a width of several μm, can be kept within an acceptable range. As a result, the negative impact of the reduced-diameter section on the bearing clearance can be minimized while increasing the above-mentioned pulling force, making it possible to stably exert a sufficiently large pulling force.

[0012] Furthermore, in the sintered oil-impregnated bearing according to the present invention, the inner diameter of the reduced diameter portion may decrease in a tapered manner from the axial center side toward the axial end side.

[0013] Thus, by making the shape of the reduced-diameter section tapered, the adverse effects of the reduced-diameter section on the radial bearing clearance can be suppressed. Therefore, this configuration also makes it possible to stably exert a sufficiently large pulling force.

[0014] Furthermore, in the sintered oil-impregnated bearing according to the present invention, the groove depth of the inclined dynamic pressure groove may increase from the axial center side toward the axial end side.

[0015] In this way, by changing the groove depth of the inclined dynamic pressure groove, even if the raised portion wears down due to continuous use of the bearing, the initial groove depth is sufficiently large, so the required groove depth can be maintained even after wear. Therefore, it is possible to exert the required dynamic pressure action and, consequently, the bearing performance over a long period of time.

[0016] Furthermore, in the sintered oil-impregnated bearing according to the present invention, the inner diameter of the inclined dynamic pressure groove may be constant in the axial direction.

[0017] Even if the inner diameter of the inclined dynamic pressure groove is kept constant in the axial direction, the groove depth of the inclined dynamic pressure groove can be increased from the axial center towards the axial end by reducing the inner diameter of the ridge portion toward the axial end (by providing a reduced diameter portion). Furthermore, as described above, keeping the inner diameter of the inclined dynamic pressure groove constant in the axial direction stabilizes the formability of the inclined dynamic pressure groove. If the formability of the inclined dynamic pressure groove is stable, especially when a molding method is used in which the molding die is pressed into the inner circumferential surface of the bearing and the ridge portion is deformed to bulge toward the inner diameter, the formability of the ridge portion will also be stable, making it possible to stably form a highly accurate radial dynamic pressure generating section with little dimensional variation.

[0018] Furthermore, in the sintered oil-impregnated bearing according to the present invention, the radial dynamic pressure generating section has a plurality of first and second inclined dynamic pressure grooves, which are inclined dynamic pressure grooves that are inclined in different directions with respect to the circumferential direction and adjacent in the axial direction, and a mound may be provided between the first and second inclined dynamic pressure grooves and between the second inclined dynamic pressure grooves. In this case, a reduced diameter section may be provided in the mound between the first inclined dynamic pressure grooves, the first inclined dynamic pressure groove may be located on the axial end side, the second inclined dynamic pressure groove may be located on the axial center side, and the longitudinal dimension of the first inclined dynamic pressure groove may be larger than the longitudinal dimension of the second inclined dynamic pressure groove.

[0019] In this way, by relatively increasing the longitudinal dimension of the inclined dynamic pressure groove (first inclined dynamic pressure groove) located on the axial end side, the pull-in force of lubricating oil from the axial end side to the axial center side becomes dominant, and the differential pressure of the pull-in force in that direction can be increased. In addition, in this configuration, a reduced diameter section is provided in the ridge between the first inclined dynamic pressure grooves, which have a relatively large longitudinal dimension, so the pull-in force in the above-mentioned direction can be further increased. Therefore, even if fluctuations occur in the pull-in force in each direction due to various factors such as variations in dimensional accuracy and shape accuracy, it is possible to stably generate the pull-in (flow) of lubricating oil from the axial end side to the center side, and to more reliably prevent leakage to the outside of the bearing.

[0020] Furthermore, the sintered oil-impregnated bearing described above can be suitably provided as a fluid dynamic pressure bearing device comprising, for example, the sintered oil-impregnated bearing, a housing having an open end in the axial direction and a closed end, to which the sintered oil-impregnated bearing is fixed on the inner circumference, a rotating body having a shaft portion inserted into the inner circumference of the sintered oil-impregnated bearing, and a radial bearing portion that, by the dynamic pressure action of the radial dynamic pressure generating portion, provides non-contact radial support to the shaft portion with a film of lubricating oil formed in the radial bearing gap between the inner surface of the sintered oil-impregnated bearing and the outer surface of the shaft portion.

[0021] Further, in the hydrodynamic bearing device according to the present invention, radial hydrodynamic generating portions are provided at two axially separated positions on the inner peripheral surface of the sintered oil-impregnated bearing. Each radial hydrodynamic generating portion has a plurality of first inclined hydrodynamic grooves and second inclined hydrodynamic grooves that are inclined in different directions with respect to the circumferential direction and are adjacent to each other in the axial direction. A plurality of mound portions may be provided between the first inclined hydrodynamic grooves and between the second inclined hydrodynamic grooves, respectively. Also, in this case, in one of the two radial hydrodynamic bearing portions located on the axially open side of the housing, the first inclined hydrodynamic groove is located on the axially end side, the second inclined hydrodynamic groove is located on the axially central side, and a reduced diameter portion may be provided on the mound portion between the first inclined hydrodynamic grooves.

[0022] Thus, by providing radial hydrodynamic generating portions each having a set of inclined hydrodynamic grooves and mound portions at two axially separated positions, and providing a reduced diameter portion on the mound portion between the inclined hydrodynamic grooves arranged at the position closest to the open side of the housing, it is possible to increase the hydrodynamic pressure of the lubricating oil at two axially separated positions while increasing the suction force of the lubricating oil. Therefore, for example, even when the longitudinal dimension is made the same by the first inclined hydrodynamic groove and the second inclined hydrodynamic groove, it is possible to create a flow of lubricating oil from the open side of the housing toward the closed side. Thus, in this case, the axial dimension of the sintered oil-impregnated bearing can be reduced, and as a result, the miniaturization of the hydrodynamic bearing device can be achieved.

[0023] As described above, the hydrodynamic bearing device according to the above description can prevent the leakage of lubricating oil to the outside of the bearing while ensuring the suction force of the lubricating oil by the hydrodynamic grooves while avoiding the enlargement of the bearing device. Therefore, for example, it can be suitably provided as a motor provided with this hydrodynamic bearing device.

Advantages of the Invention

[0024] From the above, according to the present invention, it is possible to mass-produce a sintered oil-impregnated bearing that can prevent the leakage of lubricating oil to the outside of the bearing while ensuring the suction force of the lubricating oil to the central side of the bearing by the hydrodynamic grooves while avoiding the enlargement of the bearing device.

Brief Description of the Drawings

[0025] [Figure 1] It is a cross-sectional view of a motor according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view of the hydrodynamic bearing device shown in FIG. 1. [Figure 3] It is a cross-sectional view of the sintered oil-impregnated bearing shown in FIG. 2. [Figure 4] It is (a) the X-X cross-sectional view and (b) the Y-Y cross-sectional view of the sintered oil-impregnated bearing shown in FIG. 3. [Figure 5] It is an axial end face view of the sintered oil-impregnated bearing shown in FIG. 3 as viewed from the direction of arrow Z. [Figure 6] It is a diagram for explaining the process of molding the radial hydrodynamic groove shown in FIG. 3. (a) is before inserting the singeing pin, and (b) is a cross-sectional view of the sintered body at the start of press-fitting the sintered body into the die. [Figure 7] It is a diagram for explaining the process of molding the radial hydrodynamic groove shown in FIG. 3. (a) is the time when the press-fitting operation into the sintered body is completed, and (b) is a cross-sectional view at the time when the sintered body is removed from the die. [Figure 8] It is a cross-sectional view of a hydrodynamic bearing device according to another embodiment of the present invention.

Mode for Carrying Out the Invention

[0026] Hereinafter, an embodiment of the present invention will be described based on the drawings. <​Figure 1 shows an example configuration of a spindle motor according to this embodiment. This spindle motor M is used, for example, in the disk drive of an HDD, and comprises a fluid dynamic bearing device 1, a disk hub 3 fixed to the shaft member 2 of the fluid dynamic bearing device 1, a drive unit 4 consisting of a stator coil 4a and a rotor magnet 4b facing each other across a radial gap, and a bracket 5. The stator coil 4a is fixed to the bracket 5, and the rotor magnet 4b is fixed to the disk hub 3. The fluid dynamic bearing device 1 is fixed to the inner circumference of the bracket 5. A predetermined number of disks 6 (2 in Figure 1) are held in the disk hub 3. When current is supplied to the stator coil 4a, the rotor magnet 4b rotates, and consequently, the disks 6 held in the disk hub 3 rotate together with the shaft member 2.

[0028] Figure 2 shows a cross-sectional view of a fluid dynamic bearing device 1 according to one embodiment of the present invention. This fluid dynamic bearing device 1 comprises a housing 7, a sintered oil-impregnated bearing 8 disposed on the inner circumference of the housing 7, a shaft member 2 inserted into the inner circumference of the sintered oil-impregnated bearing 8, a seal member 9 that seals one axial end of the housing 7, and a lid member 10 that closes the other axial end of the housing 7. The internal space of the housing 7 is filled with lubricating oil. For convenience, in the following description, the side on which the seal member 9 is provided will be referred to as the upper side, and the opposite side in the axial direction will be referred to as the lower side. Of course, this upper and lower direction does not limit the actual manufacturing and usage of the fluid dynamic bearing device 1 in any way.

[0029] The housing 7 is cylindrical in shape overall, with at least one end in the axial direction being open. In this embodiment, the housing 7 is open at both ends in the axial direction, with a sealing member 9 disposed at the upper end in the axial direction and a cover member 10 disposed at the lower end in the axial direction.

[0030] A first inner circumferential surface 7a having a predetermined inner diameter is provided on the inner circumference of the housing 7. In this embodiment, the first inner circumferential surface 7a is located on the axial center side of the housing 7. The inner diameter of the first inner circumferential surface 7a is constant in the axial direction. The outer circumferential surface 8d of the sintered oil-impregnated bearing 8 is fixed to this first inner circumferential surface 7a by appropriate means.

[0031] A second inner circumferential surface 7b is provided on the upper inner end side of the housing 7 to form a second seal space S2, which will be described later, between it and the seal member 9. The inner diameter of the second inner circumferential surface 7b is larger than the inner diameter of the first inner circumferential surface 7a. In this embodiment, the second inner circumferential surface 7b has a tapered shape in which the inner diameter increases from the lower axial end to the upper axial end.

[0032] A third inner circumferential surface 7c is provided on the lower inner end side of the housing 7 for fixing the lid member 10. In this embodiment, the inner diameter of the third inner circumferential surface 7c is larger than the inner diameter of the first inner circumferential surface 7a.

[0033] In this embodiment, the seal member 9 integrally comprises a cylindrical portion 9a and an inner flange portion 9b extending radially inward from the axial upper end of the cylindrical portion 9a. In this case, for example, the lower end surface of the inner flange portion 9b abuts against the upper end surface 8c of the sintered oil-impregnated bearing 8, and the inner circumferential surface of the cylindrical portion 9a abuts against the outer circumferential surface 8d of the sintered oil-impregnated bearing 8, with the seal member 9 fixed to the sintered oil-impregnated bearing 8. The means of fixing the seal member 9 to the sintered oil-impregnated bearing 8 is arbitrary; for example, the seal member 9 can be fixed to the sintered oil-impregnated bearing 8 by adhesive.

[0034] The inner circumferential surface 9c of the sealing member 9 (the inner circumferential surface of the inner flange portion 9b) has a tapered shape in which the inner diameter increases from the axial lower end to the upper end, forming a first sealing space S1 between it and the outer circumferential surface 2a1 of the opposing shaft portion 2a, where the radial gap decreases from the axial upper end to the lower end (see Figure 2). The first sealing space S1 draws in lubricating oil from the axial upper end to the lower end, thereby keeping the oil level of the lubricating oil always within the axial range of the first sealing space S1.

[0035] Furthermore, the outer circumferential surface 9d of the sealing member 9 (the outer circumferential surface of the cylindrical portion 9a) is formed such that its outer diameter is constant in the axial direction, forming a second sealing space S2 between it and the second inner circumferential surface 7b of the opposing housing 7, where the radial gap size decreases from the upper end to the lower end in the axial direction (see Figure 2). Since the second sealing space S2 has a larger axial dimension than the first sealing space S1, it has a buffer function that absorbs the volume change due to temperature changes of the lubricating oil filled in the internal space of the housing 7, and can always maintain the oil level of the lubricating oil within the axial range of the second sealing space S2 within the range of expected temperature changes.

[0036] The shaft member 2 comprises a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. Of the outer circumferential surface 2a1 of the shaft portion 2a, the portion facing the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 is formed as a smooth cylindrical surface without irregularities, except for the presence of a relatively small diameter cylindrical relief portion 2c. In addition, the upper end surface 2b1 and lower end surface 2b2 of the flange portion 2b are formed as smooth, flat surfaces.

[0037] The lid member 10 is fixed to the third inner circumferential surface 7c of the housing 7 by appropriate means. The upper end surface 10a of the lid member 10 is provided with an annular thrust bearing surface that forms a thrust bearing gap of the thrust bearing portion T2 between it and the lower end surface 2b2 of the flange portion 2b of the opposing shaft member 2. This thrust bearing surface is provided with a dynamic pressure generating section (thrust dynamic pressure generating section) for generating dynamic pressure in the lubricating oil in the thrust bearing gap of the thrust bearing portion T2. ​​Although not shown in the figures, this thrust dynamic pressure generating section is configured, for example, by alternately arranging spiral-shaped dynamic pressure grooves and convex mounds that divide these dynamic pressure grooves in the circumferential direction, similar to the thrust dynamic pressure generating section 14 of the sintered oil-impregnated bearing 8 described later (see Figure 5).

[0038] The sintered oil-impregnated bearing 8 is formed in a cylindrical shape from a porous body of sintered metal. The metal structure constituting this porous body is, in principle, arbitrary, and for example, a metal structure mainly consisting of at least one of the following can be used: a metal structure of pure copper (including industrial pure copper) or a copper alloy, and a metal structure of pure iron (including industrial pure iron) or an iron alloy such as stainless steel. Furthermore, the internal pores of the sintered oil-impregnated bearing 8 are impregnated with lubricating oil.

[0039] On the inner circumferential surface 8a of the sintered oil-impregnated bearing 8, cylindrical radial bearing surfaces are provided at two axially spaced locations, forming radial bearing gaps of radial bearing portions R1 and R2 between them and the outer circumferential surface 2a1 of the opposing shaft portion 2a. As shown in Figure 3, radial dynamic pressure generating portions 11 and 12 are formed on the two radial bearing surfaces, respectively, to generate dynamic pressure in the lubricating oil within the radial bearing gaps.

[0040] Here, the first radial dynamic pressure generating section 11, located on the axially upper side of the inner circumferential surface 8a, has a plurality of first inclined dynamic pressure grooves 11a arranged along the circumferential direction of the inner circumferential surface 8a, and a plurality of first mounds 11b formed between the first inclined dynamic pressure grooves 11a. The first inclined dynamic pressure grooves 11a are inclined at a predetermined angle with respect to the circumferential direction of the inner circumferential surface 8a, and when the shaft member 2, which will be described later, rotates, they draw the lubricating oil between the shaft member 2 and the sintered oil-impregnated bearing 8 toward the center of the bearing, thereby increasing the dynamic pressure (generating a pulling force in the direction indicated by arrow F1 in Figure 2).

[0041] Furthermore, in this embodiment, the first radial dynamic pressure generating section 11 has a plurality of second inclined dynamic pressure grooves 11c and a plurality of second ridges 11d, in addition to the first inclined dynamic pressure groove 11a and the first ridge 11b. In this case, the plurality of first inclined dynamic pressure grooves 11a and the plurality of second inclined dynamic pressure grooves 11c are arranged in a herringbone shape. That is, the second inclined dynamic pressure grooves 11c are inclined in the opposite direction to the first inclined dynamic pressure grooves 11a with respect to the circumferential direction of the inner circumferential surface 8a and by the same angle, and when the shaft member 2 rotates, as will be described later, they draw the lubricating oil between the shaft member 2 and the sintered oil-impregnated bearing 8 toward the bearing end side, thereby increasing the dynamic pressure (generating a pulling force in the direction indicated by arrow F2 in Figure 2).

[0042] In this embodiment, the longitudinal dimension of the first inclined hydrodynamic groove 11a is greater than the longitudinal dimension of the second inclined hydrodynamic groove 11c. Here, since the inclination angles of the first inclined hydrodynamic groove 11a and the second inclined hydrodynamic groove 11c are equal, when the longitudinal dimension of the first inclined hydrodynamic groove 11a is greater than the longitudinal dimension of the second inclined hydrodynamic groove 11c, the axial dimension L1 of the first inclined hydrodynamic groove 11a is greater than the axial dimension L2 of the second inclined hydrodynamic groove 11c (see Figure 3). Furthermore, the first inclined hydrodynamic groove 11a, located at the uppermost end of the inner circumferential surface 8a, is formed up to the upper end of the inner circumferential surface 8a (the upper end of the first inclined hydrodynamic groove 11a opens into the chamfered portion between the inner circumferential surface 8a and the upper end surface 8c). On the other hand, of the inclined dynamic pressure grooves 12a and 12c that constitute the second radial dynamic pressure generating section 12, the lower end of the first inclined dynamic pressure groove 12a, which is located on the axial end side (lowest end side) of the inner circumferential surface 8a, is located axially closer to the center than the lower end of the inner circumferential surface 8a (see Figure 3).

[0043] A circular band 11e is provided between the first inclined dynamic pressure groove 11a and the second inclined dynamic pressure groove 11c, extending along the circumferential direction of the inner circumferential surface 8a. This band 11e separates the first inclined dynamic pressure groove 11a from the second inclined dynamic pressure groove 11c. Furthermore, the axial lower end of the first mound 11b is continuous with the band 11e, and the axial upper end of the second mound 11d is continuous with the band 11e. Here, the inner diameter dimension at the axial lower end of the first mound 11b is equal to the inner diameter dimension of the band 11e. Also, the inner diameter dimension at the axial upper end of the second mound 11d is equal to the inner diameter dimension of the band 11e.

[0044] Here, the first mound 11b located on the axial end side of the sintered oil-impregnated bearing 8 is provided with a reduced diameter section 13, as shown in Figure 4(a), in which the inner diameter of the first mound 11b decreases as it moves from the axial center side to the axial end side of the inner circumferential surface 8a. This reduced diameter section 13 is provided in at least a part of the longitudinal direction of the first mound 11b. In this embodiment, the reduced diameter section 13 is provided over the entire area of ​​the first mound 11b. Furthermore, this reduced diameter section 13 has a tapered shape in which the inner diameter decreases. The inner diameter D1 at the first end 11b1 on the axial center side of the first mound 11b is larger than the inner diameter D2 at the second end 11b2 on the axial end side of the first mound 11b, and the difference D1-D2 is set to, for example, 1.5 μm or less. On the other hand, the inner diameter of the second mound 11d is constant over its entire area (see Figures 3 and 4(a)).

[0045] The groove depth of the first inclined dynamic pressure groove 11a increases from the axial center side towards the axial end side. In this embodiment, since the inner diameter dimension of the first inclined dynamic pressure groove 11a is constant (see Figure 4(a)), the increase in groove depth is equal to the increase in the inner diameter dimension of the first ridge portion 11b (here, the difference in inner diameter dimensions D1-D2). As an example, the groove depth d1 at the first end portion 11a1 on the axial center side of the first inclined dynamic pressure groove 11a is 2.5 μm or more and 5.0 μm or less. Also, the groove depth d2 at the second end portion 11a2 on the axial end side of the first inclined dynamic pressure groove 11a is greater than 2.5 μm and 6.5 μm or less. On the other hand, the groove depth of the second inclined dynamic pressure groove 11c is constant throughout its entire length (see Figures 3 and 4(a)).

[0046] The second radial dynamic pressure generating section 12, located on the axial lower side of the inner circumferential surface 8a, has, like the first radial dynamic pressure generating section 11, a plurality of first inclined dynamic pressure grooves 12a, a plurality of first mounds 12b, a plurality of second inclined dynamic pressure grooves 12c, a plurality of second mounds 12d, and a band 12e. Here, the longitudinal dimension of the first inclined dynamic pressure groove 12a is equal to the longitudinal dimension of the second inclined dynamic pressure groove 12c. In this embodiment, since the magnitude of the inclination angles of the first inclined dynamic pressure groove 12a and the second inclined dynamic pressure groove 12c are equal, when the longitudinal dimension of the first inclined dynamic pressure groove 12a is equal to the longitudinal dimension of the second inclined dynamic pressure groove 12c, the axial dimension L3 of the first inclined dynamic pressure groove 12a is equal to the axial dimension L4 of the second inclined dynamic pressure groove 12c (see Figure 3). The groove depth of each inclined dynamic pressure groove 12a, 12c is constant throughout the entire area. The inner diameter dimensions of both the first mound 12b and the second mound 12d are constant throughout their entire length (see Figure 4(b)). In other words, the mounds 12b and 12d of the second radial dynamic pressure generating section 12 do not have a reduced diameter section 13. Of course, the dimensional relationships of each inclined dynamic pressure groove 12a, 12c and each mound 12b, 12d described above are merely examples. For example, the inner diameter dimension of the first inclined dynamic pressure groove 12a, located at the lowest end of the inner circumferential surface 8a, may vary in the axial direction (for example, decreasing towards the lower end). Similarly, the groove depth of the first inclined dynamic pressure groove 12a may also vary in the axial direction (decreasing towards the lower end).

[0047] In this case, the radial bearing gap G1 between the shaft portion 2a and the sintered oil-impregnated bearing 8 in the first radial dynamic pressure generating portion 11 is constant from the axial lower end to the axial center (more precisely, the first end portion 11b1 of the first ridge portion 11b), as shown in Figure 4(a), and decreases from the axial center to the axial upper end (the second end portion 11b2 of the first ridge portion 11b). On the other hand, the radial bearing gap G2 in the second radial dynamic pressure generating portion 12 is constant throughout its entire axial range, as shown in Figure 4(b). It is desirable that the radial bearing gap G1 in the reduced diameter portion 13 be greater than or equal to the inner diameter difference D1-D2 (maximum of 1.5 μm) mentioned above.

[0048] The lower end surface 8b of the sintered oil-impregnated bearing 8 is provided with an annular thrust bearing surface that forms a thrust bearing gap of the thrust bearing portion T1 between it and the upper end surface 2b1 of the opposing flange portion 2b. As shown in Figure 5, a dynamic pressure generating portion (thrust dynamic pressure generating portion) 14 is formed on this thrust bearing surface to generate dynamic pressure in the lubricating oil within the thrust bearing gap of the thrust bearing portion T1. The thrust dynamic pressure generating portion 14 in the illustrated example is composed of spiral-shaped thrust dynamic pressure grooves 14a and convex mounds 14b that demarcate the thrust dynamic pressure grooves 14a, arranged alternately in the circumferential direction. The height dimension of the mounds 14b is constant throughout the entire area. In addition, the upper end surface 2b1 and the groove bottom surface of the thrust dynamic pressure grooves 14a are on the same plane.

[0049] As shown in Figure 3, an annular groove 8c1 with a wedge-shaped cross-section is formed at the radial midpoint of the upper end surface 8c of the sintered oil-impregnated bearing 8. Furthermore, radial grooves 8c2 connecting the annular groove 8c1 and the inner circumferential surface 8a are formed at multiple locations in the circumferential direction radially inward from the annular groove 8c1 on the upper end surface 8c.

[0050] Multiple axial grooves 8d1 (for example, three) extending in the axial direction are formed on the outer circumferential surface 8d of the sintered oil-impregnated bearing 8. In this embodiment, the multiple axial grooves 8d1 are formed at positions that are equally spaced apart from each other in the circumferential direction. These axial grooves 8d1, together with the annular groove 8c1 and radial groove 8c2 described above, form a circulation path for lubricating oil in the internal space of the bearing, thereby ensuring a smooth supply of lubricating oil (details will be described later).

[0051] The following describes an example of a manufacturing method for the sintered oil-impregnated bearing 8 with the above configuration.

[0052] The sintered oil-impregnated bearing 8 according to the present invention mainly comprises a powder compaction step (s1) to obtain a compacted powder by compressing raw material powder, a sintering step (s2) to obtain a sintered body 8S by sintering the compacted powder, and a dynamic pressure groove sizing step (s3) to apply sizing to the sintered body 8S and form inclined dynamic pressure grooves 11a, 11c, 12a, 12c that form radial dynamic pressure generating parts 11, 12 on at least the inner circumferential surface 8Sa of the sintered body 8S. If necessary, a dimensional sizing step to apply dimensional sizing to the sintered body 8S after the sintering step (s2) and before the dynamic pressure groove sizing step (s3) and a rotational sizing step to apply rotational sizing to the inner circumferential surface 8Sa of the sintered body 8S may be provided.

[0053] (s1) Powder compaction process First, the raw material powder that will be the material for the final product, the sintered oil-impregnated bearing 8, is prepared and compressed into a predetermined shape by die press molding. Specifically, although not shown in the diagram, the raw material powder is compressed using a molding die consisting of a die, a core pin inserted into the hole of the die, a lower punch disposed between the die and the core pin and configured to move up and down relative to the die, and an upper punch configured to be displaced (moved up and down) relative to both the die and the lower punch. In this case, the raw material powder is filled into the space formed by the inner circumferential surface of the die, the outer circumferential surface of the core pin, and the upper end surface of the lower punch. Then, with the lower punch fixed, the upper punch is lowered, and the filled raw material powder is pressurized in the axial direction. Then, while pressurizing, the upper punch is lowered to a predetermined position, and the raw material powder is compressed to a predetermined axial dimension, thereby forming a compacted powder body.

[0054] Here, the raw material powder used contains one or more types of arbitrary metal powders. In this embodiment, the raw material powder mainly contains pure copper powder and stainless steel powder as an iron alloy powder. Of course, pure iron powder may be used instead of stainless steel powder, or iron alloy powders other than stainless steel may be used. Alternatively, a mixed powder of iron alloy powder such as stainless steel powder and pure iron powder may be added to pure copper powder and used as the raw material powder. The point is to set the composition of the raw material powder so that the sintered oil-impregnated bearing 8 obtained by sintering has the above-described metallic structure. Of course, substances other than the above-described metal powders may also be blended into the raw material powder, for example, graphite or amide wax-based solid lubricant powder may be blended.

[0055] (s2) Sintering process As described above, after obtaining a compacted powder, this compacted powder is sintered at a temperature corresponding to the composition of the raw material powder, particularly the metal powder contained in the raw material powder, to obtain a sintered body 8S (see Figure 6). For example, if the raw material powder contains pure copper powder as described above, the sintering temperature is set to 750°C or higher and below the melting point of copper.

[0056] (s3) Dynamic pressure groove sizing process By performing a predetermined mold molding (dynamic groove sizing) on ​​the sintered body 8S obtained through the above steps s1 and s2, inclined dynamic pressure grooves 11a, 11c, 12a, and 12c that form radial dynamic pressure generating parts 11 and 12 are formed on the inner circumferential surface 8Sa of the sintered body 8S. The molding apparatus 20 used here, as shown in Figure 6(a), includes a die 21 having a press-fit hole 21a for the sintered body 8S, a sizing pin 22 positioned to be insertable into the press-fit hole 21a of the die 21, a lower punch 23 disposed between the die 21 and the sizing pin 22 and configured to move up and down relative to the die 21, and an upper punch 24 configured to move up and down relative to either the die 21 or the lower punch 23. In this case, the inner diameter of the press-fit hole 21a of the die 21 is appropriately set according to the press-fit amount of the sintered body 8S to be sized. Furthermore, the outer circumferential surface of the sizing pin 22 is provided with a first mold 22a having a shape corresponding to the dynamic pressure grooves 11a, 11c, 12a, and 12c to be formed (see Figure 6(a)), and the upper end surface 24a of the upper punch 24 is provided with a second mold having a shape corresponding to the thrust dynamic pressure groove 14a of the lower end surface 8b to be formed (not shown).

[0057] Here, the first mold 22a is composed of a convex molding section 22a1 that molds the first inclined dynamic pressure grooves 11a, 12a and the second inclined dynamic pressure grooves 11c, 12c, and a concave molding section 22a2 that molds the first mounds 11b, 12b and the second mounds 11d, 12d, and the bands 11e, 12e.

[0058] In this case, with the exception of the portion of the concave molding section 22a2 corresponding to the first ridge 11b of the first radial dynamic pressure generating section 11 (the diameter reduction molding section 22a3), the outer diameter dimension of the convex molding section 22a1 and the outer diameter dimension of the area of ​​the outer circumferential surface of the sizing pin 22 other than the first molding die 22a are set to be the same. Furthermore, the axial dimension H1 of the diameter reduction molding section 22a3 is set to be larger than the axial dimension H2 of the diameter reduction section 13 (first ridge 11b) to be molded (see Figures 7(a) and (b) described later).

[0059] Furthermore, the outer diameters of the convex molded portion 22a1 and the concave molded portion 22a2 are set such that half the difference in outer diameter dimensions between the convex molded portion 22a1 and the concave molded portion 22a2 is greater than, for example, the target value of the groove depth of the inclined dynamic pressure grooves 11a, 11c, 12a, and 12c to be formed.

[0060] Next, one aspect of dynamic pressure groove sizing using the molding apparatus 20 with the above configuration will be described. First, as shown in Figure 6(a), with the sintered body 8S placed on the upper end surface 21b of the die 21, the upper punch 24 and sizing pin 22 are lowered from above. This inserts the sizing pin 22 into the inner circumference of the sintered body 8S, and the first molding die 22a, which is provided on the outer circumference of the sizing pin 22, is brought into radial opposition with the inner circumferential surface 8Sa. At this point, the first molding die 22a is positioned such that the upper end of the reduced diameter molding portion 22a3 of the first molding die 22a and the upper end of the reduced diameter portion 13 (first mound portion 11b) to be molded are in the same axial position (see Figure 6(b)).

[0061] Then, from the state shown in Figure 6(b), the upper punch 24 is further lowered to press against the upper end surface 8Sc of the sintered body 8S. This pushes the sintered body 8S into the press-fit hole 21a of the die 21, compressing the outer circumferential surface 8Sd of the sintered body 8S, and causing the inner circumferential surface 8Sa to bite into the first molding die 22a of the sizing pin 22 that was previously inserted into the inner circumference. Furthermore, from this state, the upper punch 24 is lowered further to clamp the sintered body 8S between the upper punch 24 and the lower punch 23, and the sintered body 8S, whose deformation in the outer diameter direction is constrained by the die 21, is compressed in the axial direction, causing the inner circumferential surface 8Sa to bite into the first molding die 22a even further (see Figure 7(a)). The sizing pin 22 moves downward as the sintered body 8S descends as the inner circumferential surface 8Sa of the sintered body 8S bites into the first molding die 22a. In this way, the shape of the first mold 22a, specifically the shapes of the convex molding section 22a1, the concave molding section 22a2, and the reduced diameter molding section 22a3, are transferred to the inner circumferential surface 8Sa, thereby forming the first inclined dynamic pressure grooves 11a, 12a and the second inclined dynamic pressure grooves 11c, 12c, the first mounds 11b, 12b and the second mounds 11d, 12d, the band sections 11e, 12e, and the reduced diameter section 13 (see Figure 7(b)). At the same time, the second mold provided on the lower end surface 24a of the upper punch 24 bites into the lower end surface 8Sb of the sintered body 8S, transferring the shape of the second mold to the lower end surface 8Sb, and forming the corresponding thrust dynamic pressure groove 14a and mound 14b.

[0062] After forming predetermined radial dynamic pressure generating sections 11, 12 and thrust dynamic pressure generating sections on the inner circumferential surface 8Sa and lower end surface 8Sb of the sintered body 8S in this manner, the die 21 is lowered relative to the lower punch 23 to release the constraint on the sintered body 8S by the die 21 (see Figure 7(b)). As a result, the sintered body 8S experiences springback in the outward direction, increasing the outer diameter of the outer circumferential surface 8Sd and the inner diameter of the inner circumferential surface 8Sa. Furthermore, by raising the upper punch 24 to release the axial constraint on the sintered body 8S by the upper punch 24 and the lower punch 23 (see Figure 7(b)), the sintered body 8S experiences springback in the axial direction, increasing the axial dimensions of the outer circumferential surface 8Sd and the inner circumferential surface 8Sa. In this way, after the die 21 descends, the sintered body 8S undergoes springback in the outward direction, causing the inner circumferential surface 8Sa to expand in diameter. This allows the sizing pin 22 to be removed from the sintered body 8S while minimizing interference between the protruding hill portions 11b, 11d, 12b, 12d and the convex molded portion 22a1. Furthermore, by adjusting the amount of springback, interference between the reduced diameter portion 13 provided on the first hill portion 11b and the convex molded portion 22a1 can also be minimized, allowing the sizing pin 22 to be removed from the sintered body 8S. This results in a sintered body 8S with radial dynamic pressure generating portions 11, 12 and a reduced diameter portion 13 formed on the inner circumferential surface 8a, i.e., a sintered oil-impregnated bearing 8 in the form shown in Figures 3 to 5. The inner diameter of the sintered oil-impregnated bearing 8 manufactured through the above sizing process is, for example, 1 to 5 mm, the outer diameter is 3 to 8 mm, and the axial dimension is 2 to 15 mm.

[0063] Subsequently, the sintered oil-impregnated bearing 8 is completed by impregnating the internal pores with lubricating oil. Alternatively, the sintered oil-impregnated bearing 8 may be impregnated with lubricating oil after being assembled to the housing 7. In short, as long as the internal space of the bearing, including the internal pores of the sintered oil-impregnated bearing 8, is filled with lubricating oil when the fluid dynamic pressure bearing device 1 shown in Figure 2 is completed, the impregnation method and timing are arbitrary. Furthermore, various oils can be used as lubricants, but when provided for disk drive devices such as HDDs, ester-based lubricants with excellent low evaporation rates and low viscosity, such as dioctyl sebacate (DOS) and dioctyl azelate (DOZ), are preferably used, taking into account temperature changes during use or transportation.

[0064] In the fluid dynamic pressure bearing device 1 having the above configuration, before the relative rotation between the shaft member 2 and the sintered oil-impregnated bearing 8 begins, radial bearing gaps G1 and G2 are formed between the two radial bearing surfaces provided on the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 and the outer circumferential surface 2a1 of the shaft portion 2a facing them (see Figures 4(a) and (b)). As the relative rotation between the shaft member 2 and the sintered oil-impregnated bearing 8 begins, the pressure of the oil film formed in the two radial bearing gaps G1 and G2 is increased by the dynamic pressure action of the radial dynamic pressure generating parts 11 and 12 (inclined dynamic pressure grooves 11a, 11c, 12a, 12c). As a result, radial bearing portions R1 and R2 that non-contactly support the shaft member 2 so as to be able to rotate relative to it in the radial direction are formed at two locations spaced apart in the axial direction (see Figure 2). In this configuration, by providing a central relief portion 2c on the outer circumferential surface 2a1 of the shaft portion 2a, a cylindrical lubricating oil reservoir is formed between the two radial bearing gaps G1 and G2. Therefore, oil film breakdown in each radial bearing gap G1 and G2, i.e., a decrease in the bearing performance of the radial bearing portions R1 and R2, can be prevented as much as possible.

[0065] Furthermore, during relative rotation between the shaft member 2 and the sintered oil-impregnated bearing 8, the dynamic pressure action of the thrust dynamic pressure generating unit 14 provided on the lower end surface 8b causes a lubricating oil film to form between the lower end surface 8b of the sintered oil-impregnated bearing 8 and the upper end surface 2b1 of the flange portion 2b facing the thrust bearing surface, and the pressure of this oil film is increased. Additionally, the dynamic pressure action of the thrust dynamic pressure generating unit provided on the upper end surface 10a of the cover member 10 causes a lubricating oil film to form between the upper end surface 10a of the cover member 10 and the lower end surface 2b2 of the flange portion 2b facing the upper end surface 10a (forming a thrust bearing gap), and the pressure of this oil film is increased. As a result, thrust bearing portions T1 and T2 are formed that non-contactly support the shaft member 2 so that it can rotate relative to it in one thrust direction and in the other.

[0066] Furthermore, the longitudinal dimension L1 of the first inclined dynamic pressure groove 11a, which forms the first radial dynamic pressure generating section 11 provided on the inner circumferential surface 8a of the sintered oil-impregnated bearing 8, is larger than the longitudinal dimension L2 of the second inclined dynamic pressure groove 11c (see Figure 3). Therefore, when the shaft member 2 rotates, the pulling force F1 of the lubricating oil toward the bearing center by the first inclined dynamic pressure groove 11a exceeds the pulling force F2 of the lubricating oil toward the bearing end by the second inclined dynamic pressure groove 11c. Due to this difference in pulling force, the lubricating oil filling the radial bearing gap G1 as a whole creates a flow toward the axial downward side of the sintered oil-impregnated bearing 8, and is drawn back into the radial bearing gap of the first radial bearing section R1 by following a path 15 consisting of the axial groove 8d1, the gap between the lower end surface of the inner flange 9b of the seal member 9 and the upper end surface 8c of the sintered oil-impregnated bearing 8, the annular groove 8c1, and the radial groove 8c2. In other words, a circulation path 15 for lubricating oil, including radial bearing gaps G1 and G2, is formed within the internal space of the bearing. This prevents the phenomenon of localized negative pressure in the lubricating oil within the internal space of the bearing, thereby avoiding problems such as bubble generation due to negative pressure, lubricating oil leakage and deterioration of bearing performance caused by bubble generation, and vibration. Furthermore, if bubbles are mixed into the lubricating oil for any reason, they are discharged into the outside air from the oil surface (gas-liquid interface) of the lubricating oil in each seal space S1 and S2 as they circulate with the lubricating oil, thus effectively preventing adverse effects from the bubbles.

[0067] On the other hand, due to the dimensional or shape accuracy problems mentioned above, or due to wear at the upper end of the first ridge portion 11b of the first radial dynamic pressure generating portion 11 during continuous use, the radial bearing gap G1 may widen on the bearing end side. When the radial bearing gap G1 widens, the dynamic pressure action of the lubricating oil by the first inclined dynamic pressure groove 11a decreases, so the pulling force F2 by the second inclined dynamic pressure groove 11c becomes dominant over the pulling force F1 by the first inclined dynamic pressure groove 11a, and in some cases, there is a concern that the lubricating oil may flow back from the axial center side to the axial upper end side of the inner circumferential surface 8a.

[0068] In the sintered oil-impregnated bearing 8 according to this embodiment, a reduced diameter portion 13 is provided on the first ridge portion 11b between the first inclined dynamic pressure grooves 11a, where the inner diameter dimension decreases as the inner diameter dimension decreases from the axial center side to the axial upper end side of the inner circumferential surface 8a (see Figure 4(a)). This makes it possible to increase the pulling force F1 of the lubricating oil towards the axial center side generated in the radial bearing gap G1 by the first inclined dynamic pressure grooves 11a between the first ridge portions 11b. Therefore, even if the pulling force F1 of the lubricating oil towards the bearing axial center side is insufficient due to the dimensional accuracy reasons mentioned above, or if the pulling force F1 decreases due to wear of the sintered oil-impregnated bearing 8, it is possible to compensate for the deficiency or decrease in the pulling force F1 and obtain the required pulling force F1. Accordingly, even when the sintered oil-impregnated bearing 8 described in this embodiment is mass-produced and used, it is possible to prevent leakage of lubricating oil to the outside of the bearing, and in this embodiment, leakage to the outside of the fluid dynamic pressure bearing device 1 through the respective seal spaces S1 and S2, over a long period of time.

[0069] Furthermore, as in this embodiment, if the pulling force F1 of the lubricating oil toward the axial center can be increased to prevent leakage of the lubricating oil outside the fluid dynamic bearing device 1, the axial dimension of the first seal space S1, which is directly connected to the radial bearing gap G1, can be reduced. In this case, by providing a second seal space S2 radially outward from the first seal space S1, it is possible to maintain the required sealing performance while ensuring the buffer function of the lubricating oil. In addition, with the seal member 9 in the form shown in Figure 2, the increase in the axial dimension of the fluid dynamic bearing device 1 due to the provision of the seal member 9 can be substantially limited to the axial dimension of the inner flange portion 9b, thus contributing to the thinning (miniaturization) of the fluid dynamic bearing device 1.

[0070] Although one embodiment of the present invention has been described above, the sintered oil-impregnated bearing and the fluid dynamic bearing apparatus equipped with this bearing according to the present invention are not limited to the above-described embodiments and can take any form within the scope of the present invention.

[0071] Figure 8 shows a cross-sectional view of a fluid dynamic bearing device 31 according to another embodiment of the present invention. As shown in Figure 8, the fluid dynamic bearing device 31 in this embodiment differs from the fluid dynamic bearing device 1 shown in Figure 2 in that it has only a first seal space S1. More specifically, in the fluid dynamic bearing device 31 according to this embodiment, the seal member 32 is integrated with the upper end of the housing 7, and the first seal space S1 is formed between the inner circumferential surface 32a of the seal member 32 and the outer circumferential surface 2a1 of the shaft portion 2a facing this inner circumferential surface 32a.

[0072] When the fluid dynamic bearing device 31 has the above configuration, the axial dimension of the first seal space S1 adjacent to the radial bearing gap G1 can be made larger compared to the fluid dynamic bearing device 1 shown in Figure 2. Therefore, by providing the sintered oil-impregnated bearing 33 of the fluid dynamic bearing device 31 with a reduced diameter portion 13 similar to that in Figure 4(a), the force pulling the lubricating oil towards the center of the bearing can be increased, creating a flow of lubricating oil from the radial bearing gap G1 on the axial upper side to the radial bearing gap G2 on the axial lower side. With this configuration, the fluid dynamic bearing device 31 can be given a sufficient effect to prevent lubricating oil leakage, so that, for example, similar to the sintered oil-impregnated bearing 8 shown in Figure 3, the longitudinal dimension of the first inclined dynamic pressure groove in the first radial dynamic pressure generating portion 34 on the axial upper side of the sintered oil-impregnated bearing 33 can be made the same size as the longitudinal dimension of the second inclined dynamic pressure groove. Thus, the axial dimension of the sintered oil-impregnated bearing 33 can be made smaller than that of the sintered oil-impregnated bearing 8 shown in Figure 2.

[0073] Furthermore, although the above description has focused on the application of the present invention to a fluid dynamic bearing device 1,31 equipped with a shaft member 2 (rotating body) to which a disk hub 3 is fixed, the present invention can also be suitably applied to a fluid dynamic bearing device equipped with a shaft member 2 (rotating body) to which a fan or polygon mirror is fixed. In other words, the present invention can be suitably applied not only to a spindle motor M for disk driving as shown in Figure 1, but also to fluid dynamic bearing devices incorporated into other electrical equipment such as fan motors and polygon scanner motors for laser beam printers (LBPs). [Explanation of Symbols]

[0074] 1. Fluid dynamic pressure bearing device 2 Shaft member 2a Shaft 2a1 Outer surface 2b Flange section 2c Middle Escape Club 3. Disk Hub 4. Drive Unit 4a Stator coil 4b Rotor Magnet 5 brackets 6 discs 7 Housing 7a First inner surface 7b Second inner peripheral surface 7c Third inner peripheral surface 8 Sintered oil-impregnated bearing 8S sintered body 8a,8Sa Inner surface 8b,8Sb Bottom end surface 8c,8Sc top surface 8c1 Ring groove 8c2 radial groove 8d,8Sd Outer surface 8d1 Axial groove 9. Sealing member 9a Cylindrical part 9b Inner flange 9c Inner surface 9d Outer surface 10 Lid member 10a Upper end surface 11. First radial dynamic pressure generation unit 11a First inclined dynamic pressure groove 11b First hill 11c Second inclined dynamic pressure groove 11d Second hill 11e Obi 12 Second radial dynamic pressure generation unit 12a,12c Inclined dynamic pressure groove 12b,12d Hill part 12e Obi 13 Reduced diameter part 14. Thrust dynamic pressure generation section 14a Thrust Dynamic Groove 14b Hill 15 Circulation path 20 Molding equipment 21 Dies 22 sizing pins 22a First mold 22a1 Convex molded part 22a2 Concave molding part 22a3 Reduced diameter part molding part 23. Lower punch 24 Upper punch 31 Fluid Dynamic Pressure Bearing Device 32 sealing member 32a Inner surface 33 Sintered oil-impregnated bearing 34 First radial dynamic pressure generation unit D1, D2 Inner diameter dimensions F1 Pulling force (bearing center side) F2 Pulling force (bearing end side) G1, G2 radial bearing clearance H1 Axial dimension (reduced diameter molded section) H2 Axial dimension (reduced diameter section) L1, L2, L3, L4 Axial dimensions (inclined dynamic groove) M Spindle Motor R1, R2 radial bearing section S1 First Seal Space S2 Second Seal Space T1, T2 thrust bearing section

Claims

1. A sintered metal bearing obtained by compressing metal powder into a cylindrical shape to form a compact, and then sintering the formed compact, wherein the internal void is impregnated with lubricating oil and a radial dynamic pressure generating portion is formed on the inner circumferential surface, The radial dynamic pressure generating section has a plurality of first inclined dynamic pressure grooves and a plurality of second inclined dynamic pressure grooves, which are inclined in different directions from each other with respect to the circumferential direction of the inner surface and are adjacent in the axial direction of the inner surface, It has a plurality of mounds provided between the first inclined dynamic pressure grooves and between the second inclined dynamic pressure grooves, The hill portion between the second inclined dynamic pressure grooves is provided with a reduced diameter portion in which the inner diameter of the hill portion decreases as it moves from the axial center side to the axial end side of the inner circumferential surface. The first inclined dynamic pressure groove is located on the axial center side, and the second inclined dynamic pressure groove is located on the axial end side, A sintered oil-impregnated bearing characterized in that the longitudinal dimension of the second inclined dynamic pressure groove is larger than the longitudinal dimension of the first inclined dynamic pressure groove.

2. The sintered oil-impregnated bearing according to claim 1, wherein the value obtained by subtracting the inner diameter dimension at the second end on the axial end side from the inner diameter dimension at the first end on the axial center side of the reduced diameter portion is greater than 0 μm and less than or equal to 1.5 μm.

3. The sintered oil-impregnated bearing according to claim 1 or 2, wherein the inner diameter of the reduced diameter portion tapers as it moves from the axial center side toward the axial end side.

4. The sintered oil-impregnated bearing according to claims 1 to 3, wherein the groove depth of the second inclined dynamic pressure groove increases from the axial center side toward the axial end side.

5. The sintered oil-impregnated bearing according to claim 4, wherein the inner diameter of the second inclined dynamic pressure groove is constant in the axial direction.

6. A fluid dynamic bearing device comprising: a sintered oil-impregnated bearing as described in claim 1; a housing having an open end in the axial direction and a closed end, to which the sintered oil-impregnated bearing is fixed on the inner circumference; a rotating body having a shaft portion inserted into the inner circumference of the sintered oil-impregnated bearing; and a radial bearing portion that, by the dynamic pressure action of the radial dynamic pressure generating portion, provides non-contact radial support to the shaft portion with a film of lubricating oil formed in the radial bearing gap between the inner surface of the sintered oil-impregnated bearing and the outer surface of the shaft portion.

7. The radial dynamic pressure generating portions are provided at two locations on the inner circumferential surface of the sintered oil-impregnated bearing that are separated in the axial direction, and each radial dynamic pressure generating portion has a plurality of first inclined dynamic pressure grooves and a plurality of second inclined dynamic pressure grooves that are inclined in different directions with respect to the circumferential direction and adjacent in the axial direction of the inner circumferential surface, and a plurality of the aforementioned mounds are provided between the first inclined dynamic pressure grooves and between the second inclined dynamic pressure grooves, respectively. The fluid dynamic pressure bearing device according to claim 6, wherein in one of the two radial dynamic pressure bearing portions, the radial dynamic pressure generating portion located on the axial opening side of the housing, the first inclined dynamic pressure groove is located on the axial center side, the second inclined dynamic pressure groove is located on the axial end side, and the reduced diameter portion is provided in the hill portion between the second inclined dynamic pressure grooves.

8. A motor equipped with a fluid dynamic pressure bearing device according to claim 6 or 7.

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