JP2023144590A - Sintered oil-containing bearing, and fluid dynamic bearing device comprising the same - Google Patents

Abstract

[Problem] A sintered oil-impregnated bearing that can prevent lubricating oil from leaking to the outside of the bearing by ensuring the drawing force of lubricating oil toward the center of the bearing through dynamic pressure grooves, while avoiding increasing the size of the bearing device. enables mass production. A radial dynamic pressure generating part 11 is formed on an inner peripheral surface 8a of a sintered oil-impregnated bearing 8. The radial dynamic pressure generating section 11 includes a plurality of inclined dynamic pressure grooves 11a that are inclined with respect to the circumferential direction of the inner circumferential surface 8a, and a plurality of hill portions 11b provided between the inclined dynamic pressure grooves 11a. The hill portion 11b is provided with a reduced diameter portion 13 in which the inner diameter of the hill portion 11b decreases from the axial center side to the axial end side of the inner circumferential surface 8a. [Selection diagram] Figure 4

Description

The present invention relates to a sintered oil-impregnated bearing and a fluid dynamic bearing device equipped with this bearing, and more particularly to a sintered oil-impregnated bearing having a radial dynamic pressure generating section and a fluid dynamic pressure bearing device equipped with this bearing.

A sintered oil-impregnated bearing is a bearing formed of sintered metal, and is used in a state in which the internal pores of a porous body are impregnated with lubricating oil. Specifically, in this bearing, as the shaft inserted into the inner periphery of the sintered oil-impregnated bearing rotates relative to each other, lubricating oil impregnated into the internal hole oozes out onto the sliding part with the shaft, forming an oil film. The shaft is rotatably supported via this oil film. Due to its excellent rotational precision and quietness, such bearings are used as bearing devices for motors installed in various electrical devices including information equipment, and more specifically, in HDDs, CDs, DVDs, and Blu-ray discs. It is suitably used as a bearing device for a spindle motor in a disk drive device, a fan motor built into these disk drive devices, a PC, etc., or a polygon scanner motor built into a laser beam printer (LBP).

Furthermore, a dynamic pressure generating section (radial dynamic pressure generating section) such as a dynamic pressure groove may be formed on the inner circumferential surface of the sintered oil-impregnated bearing with the aim of further improving quietness and extending the service life. As a radial dynamic pressure generating section, for example, a so-called herringbone shape is known, which is formed by arranging a plurality of dynamic pressure grooves that are inclined in different directions with respect to the circumferential direction of the inner circumferential surface of the bearing. (For example, see Patent Document 1). In addition, when the radial dynamic pressure generating section has 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, each inclined dynamic pressure In addition to generating a differential pressure in the lubricating oil drawing force between the grooves, one inclined dynamic pressure groove with a relatively large longitudinal dimension is arranged on the external communication side of the fluid dynamic pressure bearing device (the axial opening side of the housing). As a result, the fluid dynamic pressure bearing device aims to generate a flow of lubricating oil from the axially open side of the housing toward the closed side by the differential pressure of the above-mentioned pulling force, and to prevent lubricating oil from leaking. It has been proposed (for example, see Patent Document 2).

Japanese Patent Application Publication No. 2000-306036 Japanese Patent Application Publication No. 2007-147082

In the fluid dynamic pressure bearing device described in Patent Document 1, leakage of lubricating oil is prevented by differential pressure generated by varying the longitudinal dimensions of the inclined dynamic pressure grooves. On the other hand, in this type of bearing device, the magnitude of the differential pressure is determined not only by the longitudinal dimension of the inclined dynamic pressure grooves, but also by variations in the groove depth of the inclined dynamic pressure grooves, and by the shape accuracy of the inner peripheral surface of the bearing. For mass-produced products, there are important issues such as the shape accuracy (straightness, etc.) of the outer circumferential surface of the shaft, or the dimensional accuracy of the bearing gap between the inner circumferential surface of the bearing and the outer circumferential surface of the shaft (variation in the axial direction, etc.). It also depends on variations in size and shape that are difficult to avoid.

Furthermore, the larger the difference between the longitudinal dimension of the inclined dynamic pressure groove located on the axially open side of the housing and the longitudinal dimension of the inclined dynamic pressure groove located on the axially closed side of the housing, the greater the lubricating oil drawing force. However, as the longitudinal dimension of the inclined dynamic pressure groove is increased, the axial dimension of the sintered oil-impregnated bearing and thus of the fluid dynamic pressure bearing device increases. Furthermore, in a spindle motor equipped with this type of bearing device, the center of gravity of the rotating body is often located relatively upward, so that the upper portion of the sintered oil-impregnated bearing is likely to wear out. As the sintered oil-impregnated bearing wears, the bearing gap increases and the above differential pressure decreases, making it difficult to obtain a satisfactory lubricating oil drawing force toward the axial center of the housing, which prevents lubricating oil from leaking. There is an increased risk of inviting

In view of the above circumstances, the technical problem to be solved by the present invention is to avoid increasing the size of the bearing device while ensuring the drawing force of the lubricating oil to the center of the bearing by the dynamic pressure groove, so that the lubricating oil does not flow to the outside of the bearing. The purpose of the present invention is to enable mass production of sintered oil-impregnated bearings that can prevent oil leakage.

The above problems are achieved by the sintered oil-impregnated bearing according to the present invention. In other words, this bearing is a sintered metal bearing obtained by compression-molding metal powder into a cylindrical shape to form a compact, and then sintering the formed compact, and the internal cavity is lubricated. In a sintered oil-impregnated bearing that is impregnated with oil and has a radial dynamic pressure generating section formed on its inner circumferential surface, the radial dynamic pressure generating section has a plurality of inclined dynamic pressure grooves that are inclined with respect to the circumferential direction of the inner circumferential surface. , a plurality of ridges provided between the inclined dynamic pressure grooves, and the ridges have a contraction whose inner diameter decreases from the axial center of the inner circumferential surface toward the axial end. It is characterized by the fact that it has a diameter section.

The present inventor focused on the shape of the hill between the inclined dynamic pressure grooves, which was conventionally assumed to have a constant inner diameter in the axial direction, and discovered that the inner diameter of the hill is at the axial center of the inner peripheral surface of the bearing. It has been found that the drawing force of lubricating oil by the inclined dynamic pressure grooves between the hill portions is improved when the pressure decreases from the side toward the end in the axial direction. The present invention has been made based on the above findings, and by providing the above-mentioned reduced diameter portion in the hill portion between the inclined dynamic pressure grooves, it is possible to increase the drawing force of lubricating oil by the inclined dynamic pressure groove between the hill portions. can. Therefore, even if the force to draw the lubricating oil toward the center of the bearing is insufficient due to the accuracy reasons mentioned above, or if the force to draw the lubricant decreases due to wear and tear on the bearing, the lubricant will still be drawn toward the center of the bearing. By providing a diameter-reduced portion in the hill portion between the inclined dynamic pressure grooves that play a role, it is possible to compensate for the shortage or decrease in the pulling force and obtain the necessary amount of pulling force. Therefore, when the sintered oil-impregnated bearing of the present invention is mass-produced and used, it is possible to prevent lubricating oil from leaking out of the bearing for a long period of time.

Further, in the sintered oil-impregnated bearing according to the present invention, the value obtained by subtracting the inner diameter dimension at the second end portion on the axial end side from the inner diameter dimension at the first end portion on the axial center side of the reduced diameter portion is 0 μm. It may be more than 1.5 μm or less.

In this way, by setting the inner diameter dimension difference between both axial ends of the reduced diameter section provided on the hill to a maximum of 1.5 μm or less, the diameter difference formed between the outer circumferential surface of the shaft and the inner circumferential surface of the bearing is reduced. , it is possible to keep fluctuations in the axial direction of the bearing clearance (radial bearing clearance), which is normally controlled to a width of several μm, within an allowable range. This makes it possible to increase the above-mentioned pulling force while minimizing the negative effect that the provision of the reduced diameter part has on the bearing clearance, making it possible to stably exert a sufficient pulling force. becomes.

Further, in the sintered oil-impregnated bearing according to the present invention, the inner diameter dimension of the reduced diameter portion may be tapered from the axial center side toward the axial end side.

In this way, by tapering the shape of the reduced diameter portion, it is possible to suppress the adverse effect that the provision of the reduced diameter portion has on the radial bearing clearance. Therefore, this configuration also makes it possible to stably exert a sufficient pulling force.

Further, 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.

In this way, by changing the groove depth of the inclined dynamic pressure groove, even if the hill portion wears out due to continued use of the bearing, the initial groove depth is large enough. , the required groove depth can be maintained even after wear. Therefore, it becomes possible to exhibit the required dynamic pressure action and thus the bearing performance over a long period of time.

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

Even if the inner diameter of the inclined dynamic pressure groove is constant in the axial direction, by reducing the inner diameter of the hill portion toward the end in the axial direction (by providing a reduced diameter portion), the diameter of the inclined dynamic pressure groove can be reduced. The groove depth can be increased from the axial center side toward the axial end sides. Furthermore, by making the inner diameter of the inclined dynamic pressure groove constant in the axial direction as described above, the formability of the inclined dynamic pressure groove is stabilized. If the formability of the inclined dynamic pressure groove is stable, the formability of the hill part will also be stable, especially when the forming mold bites into the inner circumferential surface of the bearing and the hill part bulges and deforms inward. , it becomes possible to stably form a highly accurate radial dynamic pressure generating section with little variation in dimensions.

Further, in the sintered oil-impregnated bearing according to the present invention, the radial dynamic pressure generating section includes a plurality of first inclined dynamic pressure grooves which are inclined in different directions with respect to the circumferential direction and which are adjacent in the axial direction. It may have a groove and a second inclined dynamic pressure groove, and a hill portion may be provided between the first inclined dynamic pressure groove and between the second inclined dynamic pressure groove. Additionally, in this case, a diameter-reduced portion is provided in the hill between the first inclined dynamic pressure grooves, the first inclined dynamic pressure grooves are located on the axial end side, and the second inclined dynamic pressure grooves are 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.

In this way, by relatively increasing the longitudinal dimension of the inclined dynamic pressure groove (the first inclined dynamic pressure groove) located on the axial end side, lubrication from the axial end side to the axial center side can be increased. The drawing force of oil becomes dominant, and the differential pressure of the drawing force in this direction can be increased. In addition, in this configuration, since the reduced diameter portion is provided in the hill portion between the first inclined dynamic pressure grooves having a relatively large longitudinal dimension, it is possible to further increase the pulling force in the above-mentioned direction. Therefore, even if the pulling force in each direction varies due to various factors such as variations in dimensional accuracy and shape accuracy, the lubricating oil can be drawn (flow) from the axial end toward the center. It is possible to generate this stably and more reliably prevent leakage to the outside of the bearing.

Further, the sintered oil-impregnated bearing according to the above description includes, for example, the sintered oil-impregnated bearing, a housing having a configuration in which one axial end is open and the other end is closed, and the sintered oil-impregnated bearing is fixed to the inner periphery. A radial bearing is formed between the inner circumferential surface of the sintered oil-impregnated bearing and the outer circumferential surface of the shaft by the dynamic pressure action of the rotating body, which has a shaft inserted into the inner circumference of the sintered oil-impregnated bearing, and the radial dynamic pressure generating section. The present invention can suitably be provided as a fluid dynamic pressure bearing device including a radial bearing portion that supports the shaft portion in a radial direction in a non-contact manner with a film of lubricating oil formed in the gap.

Further, in the fluid dynamic pressure bearing device according to the present invention, the radial dynamic pressure generating portions are provided at two locations separated in the axial direction on the inner circumferential surface of the sintered oil-impregnated bearing, and each radial dynamic pressure generating portion is a plurality of first inclined dynamic pressure grooves and second inclined dynamic pressure grooves which are inclined in different directions with respect to the direction and which are adjacent in the axial direction, and between the first inclined dynamic pressure grooves; A plurality of hill portions may be provided between the second inclined dynamic pressure groove and the second inclined dynamic pressure groove. Further, in this case, in one of the two radial dynamic pressure bearing parts, which is located on the axial opening side of the housing, the first inclined dynamic pressure groove is located on the axial end side, and the second radial dynamic pressure groove is located on the axial end side. The inclined dynamic pressure grooves may be located on the central side in the axial direction, and a reduced diameter portion may be provided at the hill portion between the first inclined dynamic pressure grooves.

In this way, the radial dynamic pressure generating parts each having a set of inclined dynamic pressure grooves and a hill part are provided at two locations separated in the axial direction, and the inclined dynamic pressure generating part is arranged at the position closest to the opening side of the housing. By providing a diameter-reduced portion in the hill portion between the pressure grooves, the dynamic pressure of the lubricating oil can be increased at two locations separated in the axial direction, and the drawing force of the lubricating oil can be increased. Therefore, for example, even if the first inclined dynamic pressure groove and the second inclined dynamic pressure groove have the same longitudinal dimension, it is possible to create a flow of lubricating oil from the housing opening side to the closed side. Therefore, in this case, it is possible to reduce the axial dimension of the sintered oil-impregnated bearing, which in turn makes it possible to downsize the fluid dynamic bearing device.

As mentioned above, the fluid dynamic pressure bearing device according to the above explanation secures the lubricating oil drawing force by the dynamic pressure groove while avoiding the increase in the size of the bearing device, and prevents the lubricating oil from leaking to the outside of the bearing. Since this can be prevented, it can be suitably provided, for example, as a motor equipped with this fluid dynamic pressure bearing device.

As described above, according to the present invention, it is possible to prevent the leakage of lubricating oil to the outside of the bearing by ensuring the drawing force of the lubricating oil to the center side of the bearing by the dynamic pressure groove while avoiding an increase in the size of the bearing device. It becomes possible to mass produce sintered oil-impregnated bearings.

FIG. 1 is a sectional view of a motor according to an embodiment of the present invention. 2 is a sectional view of the fluid dynamic bearing device shown in FIG. 1. FIG. 3 is a cross-sectional view of the sintered oil-impregnated bearing shown in FIG. 2. FIG. 3. They are (a) an XX sectional view and (b) a YY sectional view of the sintered oil-impregnated bearing shown in FIG. 3. FIG. 4 is an axial end view of the sintered oil-impregnated bearing shown in FIG. 3 when viewed from the direction of arrow Z. 4 is a diagram for explaining the process of molding the radial dynamic pressure groove shown in FIG. 3, in which (a) shows the sintering before inserting the signing pin, and (b) shows the sintering at the beginning of press-fitting the sintered body into the die. It is a sectional view of the body. These are diagrams for explaining the process of molding the radial dynamic pressure groove shown in Figure 3, in which (a) is when the press-fitting operation into the sintered body has been completed, and (b) is when the sintered body has been demolded from the die. It is a sectional view at the time. FIG. 3 is a sectional view of a fluid dynamic bearing device according to another embodiment of the present invention.

Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 shows an example of the configuration of a spindle motor according to this embodiment. This spindle motor M is used, for example, in a disk drive device of an HDD, and is connected to a fluid dynamic pressure bearing device 1, a disk hub 3 fixed to a shaft member 2 of the fluid dynamic pressure bearing device 1, and a gap in the radial direction, for example. The drive unit 4 includes a bracket 5 and a drive unit 4 consisting of a stator coil 4a and a rotor magnet 4b facing each other via a stator coil 4a and a rotor magnet 4b. 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 periphery of the bracket 5. The disk hub 3 holds a predetermined number of disks 6 (two in FIG. 1). When the stator coil 4a is energized, the rotor magnet 4b rotates, and accordingly, the disk 6 held by the disk hub 3 rotates together with the shaft member 2.

FIG. 2 shows a cross-sectional view of a fluid dynamic bearing device 1 according to an embodiment of the present invention. This fluid dynamic bearing device 1 includes a housing 7, a sintered oil-impregnated bearing 8 disposed on the inner periphery of the housing 7, a shaft member 2 inserted into the inner periphery of the sintered oil-impregnated bearing 8, and a sintered oil-impregnated bearing 8 arranged on the inner periphery of the housing 7. It includes a seal member 9 that seals one end in the axial direction, and a lid member 10 that closes the other end in the axial direction of the housing 7. The internal space of the housing 7 is filled with lubricating oil. In the following description, for convenience, the side on which the seal member 9 is provided is assumed to be the upper side, and the opposite side in the axial direction is assumed to be the lower side. Of course, this vertical direction does not limit the actual manufacturing manner and usage manner of the fluid dynamic bearing device 1 in any way.

The housing 7 has an overall cylindrical shape and is open at least at one end in the axial direction. In this embodiment, the housing 7 has a configuration in which both ends in the axial direction are open, and a seal member 9 is disposed on the upper end side in the axial direction of the housing 7, and a lid member 10 is disposed on the lower end side in the axial direction. There is.

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 disposed at the center of the housing 7 in the axial direction. The inner diameter dimension 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 the first inner circumferential surface 7a by appropriate means.

A second inner circumferential surface 7b for forming a second seal space S2, which will be described later, between the housing 7 and the seal member 9 is provided on the inner circumferential upper end side. The inner diameter dimension of the second inner circumferential surface 7b is larger than the inner diameter dimension of the first inner circumferential surface 7a. Furthermore, in this embodiment, the second inner circumferential surface 7b has a tapered shape in which the inner diameter increases from the lower end in the axial direction toward the upper end in the axial direction.

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

In this embodiment, the seal member 9 integrally includes a cylindrical portion 9a and an inner flange portion 9b extending radially inward from an axially upper end of the cylindrical portion 9a. In this case, for example, with the lower end surface of the inner flange portion 9b in contact with the upper end surface 8c of the sintered oil-impregnated bearing 8, and the inner peripheral surface of the cylindrical portion 9a in contact with the outer peripheral surface 8d of the sintered oil-impregnated bearing 8, A seal member 9 is fixed to the sintered oil-impregnated bearing 8. Note that the means for fixing the seal member 9 and the sintered oil-impregnated bearing 8 is arbitrary, and the seal member 9 is fixed to the sintered oil-impregnated bearing 8 by, for example, adhesion.

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 lower end toward the upper end in the axial direction, and is in contact with the outer circumferential surface 2a1 of the opposing shaft portion 2a. In between, a first seal space S1 is formed in which the radial clearance decreases from the upper end side to the lower end side in the axial direction (see FIG. 2). The first seal space S1 acts to draw in the lubricating oil from the upper end side to the lower end side in the axial direction, so that the oil level of the lubricating oil can always be maintained within the axial range of the first seal space S1.

Further, the outer circumferential surface 9d of the seal member 9 (the outer circumferential surface of the cylindrical portion 9a) is formed so that the outer diameter dimension is constant in the axial direction, and is spaced between the second inner circumferential surface 7b of the opposing housing 7. , forming a second seal space S2 in which the size of the radial gap decreases from the upper end side to the lower end side in the axial direction (see FIG. 2). Since the second seal space S2 has a larger axial dimension than the first seal space S1, it has a buffer function to absorb the volume change due to the temperature change of the lubricating oil filled in the internal space of the housing 7. The lubricating oil level can always be maintained within the axial range of the second seal space S2 within the expected temperature change range.

The shaft member 2 includes a shaft portion 2a and a flange portion 2b provided integrally or separately at the lower end of the shaft portion 2a. The portion of the outer circumferential surface 2a1 of the shaft portion 2a that faces the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 is free of unevenness, except that a hollow portion 2c in the form of a cylindrical surface with a relatively small diameter is provided. It is formed with no smooth cylindrical surface. Further, the upper end surface 2b1 and the lower end surface 2b2 of the flange portion 2b are formed into smooth flat surfaces.

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 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 a dynamic pressure effect on the lubricating oil within the thrust bearing gap of the thrust bearing portion T2. Although not shown in the drawings, this thrust dynamic pressure generating section, like the thrust dynamic pressure generating section 14 of the sintered oil-impregnated bearing 8 described later, includes, for example, a spiral-shaped dynamic pressure groove and a convex part that partitions this dynamic pressure groove. It is constructed by alternately arranging shaped hill portions in the circumferential direction (see FIG. 5).

The sintered oil-impregnated bearing 8 is made of a porous body of sintered metal and is formed into a cylindrical shape. The metal structure constituting this porous body is basically arbitrary, and for example, the metal structure of pure copper (including industrial pure copper) or copper alloy, and the metal structure of pure iron (including industrial pure iron) or stainless steel. A metal structure mainly containing at least one of the metal structures of iron alloys can be adopted. Further, the internal pores of the sintered oil-impregnated bearing 8 are impregnated with lubricating oil.

The inner circumferential surface 8a of the sintered oil-impregnated bearing 8 has a cylindrical radial bearing surface that forms radial bearing gaps of the radial bearing sections R1 and R2 between the outer circumferential surface 2a1 of the opposing shaft section 2a. They are placed at separate locations. As shown in FIG. 3, radial dynamic pressure generating portions 11 and 12 are formed on the two radial bearing surfaces, respectively, for generating a dynamic pressure effect on the lubricating oil within the radial bearing gap.

Here, the first radial dynamic pressure generating section 11 located above the inner circumferential surface 8a in the axial direction includes a plurality of first inclined dynamic pressure grooves 11a arranged along the circumferential direction of the inner circumferential surface 8a, It has a plurality of first hill portions 11b formed between one inclined dynamic pressure groove 11a. The first inclined dynamic pressure groove 11a is inclined at a predetermined angle with respect to the circumferential direction of the inner peripheral surface 8a, and provides lubrication between the shaft member 2 and the sintered oil-impregnated bearing 8 when the shaft member 2 rotates, which will be described later. It has the effect of drawing oil toward the center of the bearing to increase dynamic pressure (the effect of generating a drawing force in the direction indicated by arrow F1 in FIG. 2).

Further, in the present embodiment, the first radial dynamic pressure generating section 11 includes a plurality of second inclined dynamic pressure grooves 11c and a plurality of second inclined dynamic pressure grooves 11c, in addition to the first inclined dynamic pressure grooves 11a and the first hill portions 11b. It has a hill portion 11d. 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 groove 11c is inclined in the opposite direction and at the same angle as the first inclined dynamic pressure groove 11a with respect to the circumferential direction of the inner circumferential surface 8a, and the second inclined dynamic pressure groove 11c is inclined in the opposite direction and at the same angle as the first inclined dynamic pressure groove 11a. At this time, the lubricating oil between the shaft member 2 and the sintered oil-impregnated bearing 8 is drawn toward the end of the bearing to increase the dynamic pressure (an action that generates a pulling force in the direction indicated by arrow F2 in FIG. 2). play.

In this embodiment, the longitudinal dimension of the first inclined dynamic pressure groove 11a is larger than the longitudinal dimension of the second inclined dynamic pressure groove 11c. Here, since the magnitude of the inclination angle of the first inclined dynamic pressure groove 11a and the second inclined dynamic pressure groove 11c is equal, the longitudinal dimension of the first inclined dynamic pressure groove 11a is equal to the longitudinal direction of the second inclined dynamic pressure groove 11c. In this case, the axial dimension L1 of the first inclined dynamic pressure groove 11a becomes larger than the axial dimension L2 of the second inclined dynamic pressure groove 11c (see FIG. 3). Furthermore, the first inclined dynamic pressure groove 11a located at the uppermost side of the inner circumferential surface 8a is formed up to the upper end of the inner circumferential surface 8a (the chamfered portion between the inner circumferential surface 8a and the upper end surface 8c). The upper end of the first inclined dynamic pressure groove 11a is open). On the other hand, among the inclined dynamic pressure grooves 12a and 12c constituting the second radial dynamic pressure generation section 12, the lower end of the first inclined dynamic pressure groove 12a located on the axial end side (lowest end side) of the inner circumferential surface 8a is located closer to the center in the axial direction than the lower end of the inner circumferential surface 8a (see FIG. 3).

A perfectly circular band portion 11e extending along the circumferential direction of the inner circumferential surface 8a is provided between the first inclined dynamic pressure groove 11a and the second inclined dynamic pressure groove 11c. This band portion 11e defines a first inclined dynamic pressure groove 11a and a second inclined dynamic pressure groove 11c. Further, the lower end of the first hill portion 11b in the axial direction and the band portion 11e are continuous, and the upper end of the second hill portion 11d in the axial direction and the band portion 11e are continuous. Here, the inner diameter dimension at the lower end in the axial direction of the first hill portion 11b is equal to the inner diameter dimension of the band portion 11e. Further, the inner diameter dimension at the upper end in the axial direction of the second hill portion 11d is equal to the inner diameter dimension of the band portion 11e.

Here, in the first hill portion 11b located on the axial end side of the sintered oil-impregnated bearing 8, as shown in FIG. 4(a), the inner diameter dimension of the first hill portion 11b is axially A reduced diameter portion 13 is provided that decreases in diameter from the center in the direction toward the end in the axial direction. This reduced diameter portion 13 is provided in at least a portion of the first hill portion 11b in the longitudinal direction. In this embodiment, the reduced diameter portion 13 is provided over the entire first hill portion 11b. Further, the reduced diameter portion 13 has a tapered shape in which the inner diameter is reduced. The inner diameter dimension D1 at the first end portion 11b1 on the axial center side of the first hill portion 11b is larger than the inner diameter dimension D2 at the second end portion 11b2 on the axial end side of the first hill portion 11b, and the difference D1 -D2 is set to, for example, 1.5 μm or less. On the other hand, the inner diameter dimension of the second hill portion 11d is constant over the entire area (see FIGS. 3 and 4(a)).

The groove depth of the first inclined dynamic pressure groove 11a increases from the axial center side toward the axial end side. In this embodiment, since the inner diameter of the first inclined dynamic pressure groove 11a is constant (see FIG. 4(a)), the amount of increase in the groove depth is the amount of increase in the inner diameter of the first hill portion 11b (hereinafter referred to as is equal to the inner diameter difference 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. Further, the groove depth d2 at the second end portion 11a2 on the axial end side of the first inclined dynamic pressure groove 11a is more than 2.5 μm and less than 6.5 μm. On the other hand, the groove depth of the second inclined dynamic pressure groove 11c is constant over the entire area (see FIGS. 3 and 4(a)).

Like the first radial dynamic pressure generating section 11, the second radial dynamic pressure generating section 12 located on the lower side of the inner circumferential surface 8a in the axial direction includes a plurality of first inclined dynamic pressure grooves 12a and a plurality of first hill sections. 12b, a plurality of second inclined dynamic pressure grooves 12c, a plurality of second hill portions 12d, and a band portion 12e. Here, the longitudinal dimension of the first inclined dynamic pressure groove 12a and the longitudinal dimension of the second inclined dynamic pressure groove 12c are equal. In this embodiment, since the first inclined dynamic pressure groove 12a and the second inclined dynamic pressure groove 12c have the same inclination angle, the longitudinal dimension of the first inclined dynamic pressure groove 12a is the same as that of the second inclined dynamic pressure groove 12c. When equal to the longitudinal dimension, the axial dimension L3 of the first inclined dynamic pressure groove 12a becomes equal to the axial dimension L4 of the second inclined dynamic pressure groove 12c (see FIG. 3). The groove depth of each inclined dynamic pressure groove 12a, 12c is constant over the entire area. The inner diameter dimensions of the first hill portion 12b and the second hill portion 12d are both constant over the entire area (see FIG. 4(b)). That is, the reduced diameter portion 13 is not provided in the hill portions 12b and 12d of the second radial dynamic pressure generating portion 12. Of course, the above-described dimensional relationship between the inclined dynamic pressure grooves 12a, 12c and the hill portions 12b, 12d is merely an example. 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 (eg, decrease toward the lower end). The groove depth of the first inclined dynamic pressure groove 12a may similarly vary in the axial direction (decreasing toward the lower end side).

In this case, as shown in FIG. It is constant up to the first end 11b1 of the first hill 11b, and decreases from the axial center to the axial upper end (the second end 11b2 of the first hill 11b). On the other hand, the radial bearing gap G2 in the second radial dynamic pressure generating section 12 is constant over the entire axial direction, as shown in FIG. 4(b). The radial bearing gap G1 in the reduced diameter portion 13 is desirably equal to or larger than the above-mentioned inner diameter difference D1-D2 (maximum 1.5 μm).

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 section T1 between the upper end surface 2b1 of the opposing flange section 2b. As shown in FIG. 5, a dynamic pressure generating section (thrust dynamic pressure generating section) 14 is formed on this thrust bearing surface to generate a dynamic pressure effect on the lubricating oil in the thrust bearing gap of the thrust bearing section T1. ing. The illustrated thrust dynamic pressure generation section 14 is configured by alternately arranging spiral-shaped thrust dynamic pressure grooves 14a and convex hill portions 14b that partition the thrust dynamic pressure grooves 14a in the circumferential direction. . The height dimension of the hill portion 14b is constant over the entire area. Further, the upper end surface 2b1 and the groove bottom surface of the thrust dynamic pressure groove 14a are on the same plane.

As shown in FIG. 3, an annular groove 8c1 having a wedge-shaped cross section is formed at a radially intermediate position on the upper end surface 8c of the sintered oil-impregnated bearing 8. Further, radial grooves 8c2 connecting the annular groove 8c1 and the inner circumferential surface 8a are formed at a plurality of locations in the circumferential direction on the radially inner side of the annular groove 8c1 of the upper end surface 8c.

A plurality of (for example, three) axial grooves 8d1 extending in the axial direction are formed on the outer peripheral surface 8d of the sintered oil-impregnated bearing 8. In this embodiment, the plurality of axial grooves 8d1 are formed at equal intervals apart from each other in the circumferential direction. These axial grooves 8d1, together with the annular groove 8c1 and the radial groove 8c2, form a circulation path for lubricating oil in the bearing internal space, thereby making it possible to ensure a smooth lubricating oil supply state (details will be described later). ).

An example of a method for manufacturing the sintered oil-impregnated bearing 8 having the above structure will be described below.

The sintered oil-impregnated bearing 8 according to the present invention includes a powder compacting step (s1) in which raw powder is compression-molded to obtain a compact, and a sintering step (s1) in which the compact is sintered to obtain a sintered compact 8S. s2) and sizing the sintered body 8S to form inclined dynamic pressure grooves 11a, 11c, 12a, 12c forming the radial dynamic pressure generating parts 11, 12 on at least the inner circumferential surface 8Sa of the sintered body 8S. It mainly includes a pressure groove sizing step (s3). If necessary, after the sintering process (s2) and before the dynamic pressure groove sizing process (s3), a dimensional sizing process is performed in which the sintered body 8S is sized, and the inner peripheral surface 8Sa of the sintered body 8S is A rotational sizing process for performing rotational sizing may also be provided.

(s1) Powder compacting process First, a raw material powder that will become the material of the sintered oil-impregnated bearing 8 that will become the final product is prepared, and this is compression-molded into a predetermined shape by die press molding. Specifically, although not shown, a die, a core pin inserted into a hole of the die, a lower punch disposed between the die and the core pin and configured to be movable up and down with respect to the die; Then, compression molding of the raw material powder is performed using a molding die composed of a die and an upper punch configured to be movable relative to both the lower punch (elevating and lowering). In this case, the space defined by the inner peripheral surface of the die, the outer peripheral surface of the core pin, and the upper end surface of the lower punch is filled with raw material powder, and then the upper punch is lowered with the lower punch fixed. and pressurizes the packed raw material powder in the axial direction. Then, the upper punch is lowered to a predetermined position while applying pressure, and the raw powder is compressed to a predetermined axial dimension, thereby forming a green compact.

Here, the raw material powder used includes one or more kinds of arbitrary metal powders. In this embodiment, a raw material powder mainly containing pure copper powder and stainless steel powder as an iron alloy powder is used. Of course, pure iron powder may be used instead of stainless steel powder, or iron alloy powder 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. In short, the composition of the raw material powder may be set so that the sintered oil-impregnated bearing 8 obtained by sintering has the above-mentioned metal structure. Of course, substances other than the above-mentioned metal powders can also be blended into the raw material powder, such as graphite or amide wax-based solid lubricant powder.

(s2) Sintering process After obtaining the green compact as described above, the green compact is sintered at a temperature that corresponds to the composition of the raw powder, especially the metal powder contained in the raw powder. A solid 8S is obtained (see Figure 6). For example, when the raw material powder contains pure copper powder as described above, the temperature during sintering is set to 750° C. or higher and lower than the melting point of copper.

(s3) Dynamic pressure groove sizing process By performing predetermined mold forming (dynamic pressure groove sizing) on the sintered body 8S obtained through the above steps s1 and s2, the inner circumferential surface 8Sa of the sintered body 8S is Inclined dynamic pressure grooves 11a, 11c, 12a, and 12c forming radial dynamic pressure generating portions 11 and 12 are formed. As shown in FIG. 6(a), the forming device 20 used here includes a die 21 having a press-fit hole 21a of the sintered body 8S, and a sizing pin 22 arranged so as 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 be movable up and down relative to the die 21; It has an upper punch 24 configured. In this case, the inner diameter of the press-fit hole 21a of the die 21 is appropriately set according to the press-fit allowance of the sintered body 8S to be sized. Further, a first mold 22a having a shape corresponding to the dynamic pressure grooves 11a, 11c, 12a, 12c to be molded is provided on the outer peripheral surface of the sizing pin 22 (see FIG. 6(a)), and an upper punch A second molding die having a shape corresponding to the thrust dynamic pressure groove 14a of the lower end surface 8b to be molded is provided on the upper end surface 24a of 24 (not shown).

Here, the first mold 22a has a convex molding part 22a1 for molding the first inclined dynamic pressure grooves 11a, 12a and the second inclined dynamic pressure grooves 11c, 12c, the first hill parts 11b, 12b, and the second inclined dynamic pressure grooves 11b, 12b. It is composed of hill portions 11d and 12d, and a concave molding portion 22a2 for molding the band portions 11e and 12e.

In this case, the outer diameter dimension and sizing of the convex molded part 22a1 are excluded from the concave molded part 22a2, except for the part corresponding to the first hill part 11b of the first radial dynamic pressure generating part 11 (the reduced diameter part molded part 22a3). The outer diameter of the outer peripheral surface of the pin 22 in a region other than the first mold 22a is set to be the same. Further, the axial dimension H1 of the reduced diameter portion forming portion 22a3 is set larger than the axial dimension H2 of the reduced diameter portion 13 (first hill portion 11b) to be formed (see FIG. 7(a) and (see (b)).

Also, half of the difference in outer diameter between the convex molded part 22a1 and the concave molded part 22a2 is set to be larger than the target value of the groove depth of the inclined dynamic pressure grooves 11a, 11c, 12a, 12c to be molded, for example. The outer diameter of the convex molded portion 22a1 and the outer diameter of the concave molded portion 22a2 are set respectively.

Next, one aspect of dynamic pressure groove sizing using the molding apparatus 20 having the above configuration will be described. First, as shown in FIG. 6A, with the sintered body 8S placed on the upper end surface 21b of the die 21, the upper punch 24 and the sizing pin 22 are lowered from above. Thereby, the sizing pin 22 is inserted into the inner circumference of the sintered body 8S, and the first mold 22a provided on the outer circumference of the sizing pin 22 is made to face the inner circumferential surface 8Sa in the radial direction. At this point, the upper end of the reduced diameter part forming part 22a3 of the first mold 22a and the upper end of the reduced diameter part 13 (first hill part 11b) to be formed are at the same axial position. The first mold 22a is arranged (see FIG. 6(b)).

Then, from the state shown in FIG. 6(b), only the upper punch 24 is continuously lowered to press the upper end surface 8Sc of the sintered body 8S. As a result, the sintered body 8S is pushed into the press-fit hole 21a of the die 21, the outer peripheral surface 8Sd of the sintered body 8S is pressed, and the inner periphery is inserted into the first mold 22a of the sizing pin 22 inserted into the inner periphery in advance. Surface 8Sa bites. Further, from this state, the upper punch 24 is further lowered to sandwich the sintered body 8S between the upper punch 24 and the lower punch 23, and the sintered body is restrained from deforming in the outer radial direction by the die 21. By pressing 8S in the axial direction, the inner circumferential surface 8Sa further bites into the first mold 22a (see FIG. 7(a)). Note that the sizing pin 22 descends as the sintered body 8S descends as the inner circumferential surface 8Sa of the sintered body 8S bites into the first mold 22a. In this way, the shape of the first mold 22a, specifically the shape of the convex molded part 22a1, the concave molded part 22a2, and the reduced diameter part molded part 22a3, are each transferred to the inner peripheral surface 8Sa, The first inclined dynamic pressure grooves 11a, 12a, the second inclined dynamic pressure grooves 11c, 12c, the first hill portions 11b, 12b, the second hill portions 11d, 12d, the band portions 11e, 12e, and the reduced diameter portion 13 are formed. (See Figure 7(b)). At this 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, so that the shape of the second mold is transferred to the lower end surface 8Sb, and the corresponding thrust Dynamic pressure grooves 14a and hill portions 14b are formed.

After forming the predetermined radial dynamic pressure generating parts 11, 12 and thrust dynamic pressure generating part on the inner peripheral surface 8Sa and lower end surface 8Sb of the sintered body 8S in this way, the die 21 is moved relative to the lower punch 23. to release the restraint of the sintered body 8S by the die 21 (see FIG. 7(b)). As a result, the sintered body 8S springs back in the outer diameter direction, and the outer diameter dimension of the outer circumferential surface 8Sd and the inner diameter dimension of the inner circumferential surface 8Sa increase. Further, by raising the upper punch 24 and releasing the axial restraint of the sintered body 8S by the upper punch 24 and the lower punch 23 (see FIG. 7(b)), the sintered body 8S is axially Springback occurs in the direction, and the axial dimensions of the outer circumferential surface 8Sd and the inner circumferential surface 8Sa increase. In this way, after the die 21 is lowered, the sintered body 8S springs back in the outer diameter direction, and the inner circumferential surface 8Sa expands in diameter, so that the hill portions 11b and 11d formed to protrude inwardly. , 12b, 12d and the convex molded portion 22a1 as much as possible, and the sizing pin 22 can be extracted from the sintered body 8S. In addition, at this time, 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 is avoided as much as possible, and the sizing pin 22 is It can be extracted from the sintered body 8S. As a result, the sintered body 8S in which the radial dynamic pressure generating parts 11, 12 and the reduced diameter part 13 are formed on the inner peripheral surface 8a, that is, the sintered oil-impregnated bearing 8 in the form shown in FIGS. 3 to 5 is obtained. Can be done. The sintered oil-impregnated bearing 8 manufactured through the above sizing process has, for example, an inner diameter of 1 to 5 mm, an outer diameter of 3 to 8 mm, and an axial dimension of 2 to 15 mm.

Thereafter, the internal pores are impregnated with lubricating oil, thereby completing the sintered oil-impregnated bearing 8. Note that after the sintered oil-impregnated bearing 8 is assembled into the housing 7, the sintered oil-impregnated bearing 8 may be impregnated with lubricating oil. In short, if the internal space of the sintered oil-impregnated bearing 8 including the internal cavity is filled with lubricating oil when the fluid dynamic bearing device 1 shown in FIG. is optional. In addition, various types of lubricating oil can be used, but when provided for disk drive devices such as HDDs, oils with low evaporation rate and low viscosity are required, taking into account temperature changes during use or transportation. Ester-based lubricating oils with excellent properties, such as dioctyl sebacate (DOS) and dioctyl azelate (DOZ), can be suitably used.

In the fluid dynamic bearing device 1 having the above configuration, before the relative rotation between the shaft member 2 and the sintered oil-impregnated bearing 8 starts, two radial bearing surfaces provided on the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 and Radial bearing gaps G1 and G2 are respectively formed between the outer circumferential surface 2a1 of the shaft portion 2a facing the shaft portion 2a (see FIGS. 4(a) and 4(b)). Then, as the relative rotation between the shaft member 2 and the sintered oil-impregnated bearing 8 starts, the pressure of the oil film formed in the gaps G1 and G2 of both radial bearings increases , 11c, 12a, 12c), and as a result, radial bearing portions R1 and R2 that support the shaft member 2 relatively rotatably in the radial direction in a non-contact manner are formed at two locations spaced apart in the axial direction. (See Figure 2). At this time, a cylindrical lubricating oil reservoir is formed between the two radial bearing gaps G1 and G2 by providing the hollow part 2c on the outer circumferential surface 2a1 of the shaft part 2a. Therefore, it is possible to prevent the oil film from running out in each of the radial bearing gaps G1 and G2, that is, from deteriorating the bearing performance of the radial bearing portions R1 and R2 as much as possible.

In addition, when the shaft member 2 and the sintered oil-impregnated bearing 8 rotate relative to each other, the lower end surface 8b of the sintered oil-impregnated bearing 8 faces the thrust bearing surface due to the dynamic pressure action of the thrust dynamic pressure generating section 14 provided on the lower end surface 8b. A lubricating oil film is formed between the upper end surface 2b1 of the flange portion 2b and the pressure of the oil film is increased. Further, due to the dynamic pressure action of the thrust dynamic pressure generation section provided on the upper end surface 10a of the lid member 10, a gap is created between the upper end surface 10a of the lid member 10 and the lower end surface 2b2 of the flange portion 2b facing the upper end surface 10a. A lubricating oil film is formed (a thrust bearing gap is formed), and the pressure of the oil film is increased. As a result, thrust bearing portions T1 and T2 are formed that support the shaft member 2 in a non-contact manner so as to be relatively rotatable in one thrust direction and the other thrust direction.

Further, the longitudinal dimension L1 of the first inclined dynamic pressure groove 11a forming the first radial dynamic pressure generating section 11 provided on the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 is the longitudinal direction dimension L1 of the second inclined dynamic pressure groove 11c. larger than dimension L2 (see Figure 3). Therefore, when the shaft member 2 rotates, the drawing force F1 of the lubricating oil toward the bearing center side by the first inclined dynamic pressure groove 11a is increased by the drawing force F2 of lubricating oil toward the bearing end side by the second inclined dynamic pressure groove 11c. exceed. Due to this difference in pulling force, the lubricating oil filling the radial bearing gap G1 causes a flow toward the axially downward side of the sintered oil-impregnated bearing 8 as a whole, and from the thrust bearing gap of the first thrust bearing portion T1, Following the 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, the first radial bearing section It is drawn into the radial bearing gap of R1 again. That is, a lubricating oil circulation path 15 including radial bearing gaps G1 and G2 is formed in the bearing internal space. This prevents the lubricating oil pressure in the bearing internal space from becoming locally negative, causing the generation of air bubbles due to the generation of negative pressure, and the leakage of lubricating oil and deterioration of bearing performance due to the generation of air bubbles. , problems such as generation of vibrations are avoided. In addition, if air bubbles are mixed into the lubricating oil for some reason, they will be discharged to the outside air from the oil surface (air-liquid interface) of the lubricating oil in each seal space S1, S2 as the air bubbles circulate with the lubricating oil. Therefore, the adverse effects of air bubbles are effectively prevented.

On the other hand, due to the above-mentioned problems with dimensional accuracy or shape accuracy, or due to wear and tear of the first hill portion 11b of the first radial dynamic pressure generating portion 11 at the upper end due to continued use, the radial bearing clearance G1 is reduced at the bearing end. There is a risk of it spreading on the 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 by the second inclined dynamic pressure groove 11c is greater than the pulling force F1 by the first inclined dynamic pressure groove 11a. The force F2 becomes dominant, and there is a concern that in some cases, the lubricating oil may flow backward from the axial center side of the inner circumferential surface 8a to the axially upper end side.

In the sintered oil-impregnated bearing 8 according to the present embodiment, the reduced diameter portion 13 is formed in the first inclined dynamic pressure groove 11a, and the diameter decreases from the axial center side to the axially upper end side of the inner circumferential surface 8a. It was provided in the first hill portion 11b in between (see FIG. 4(a)). Thereby, it is possible to increase the drawing force F1 of the lubricating oil toward the center in the axial direction, which is generated in the radial bearing gap G1 by the first inclined dynamic pressure groove 11a between the first hill portions 11b. Therefore, even if the drawing force F1 of lubricating oil toward the center in the bearing axial direction is insufficient due to the above-mentioned dimensional accuracy reason, or if the drawing force F1 decreases due to wear and tear of the sintered oil-impregnated bearing 8, the above-mentioned It becomes possible to obtain the necessary magnitude of the pulling force F1 by compensating for the shortage or decrease in the pulling force F1. Therefore, even when the sintered oil-impregnated bearing 8 described in this embodiment is mass-produced and used, the lubricating oil may leak to the outside of the bearing, and in this embodiment, the fluid dynamic bearing device It becomes possible to prevent leakage to the outside for a long period of time.

Furthermore, as in the present embodiment, if it is possible to prevent the lubricating oil from leaking out of the fluid dynamic bearing device 1 by increasing the force F1 that draws the lubricating oil toward the center in the axial direction, the radial bearing gap G1 The axial dimension of the first seal space S1 directly connected to can be reduced. In this case, by providing the second seal space S2 outside the first seal space S1 in the radial direction, it is possible to maintain the required sealing performance while ensuring the buffer function of the lubricating oil. Furthermore, with the seal member 9 having the form shown in FIG. 2, the increase in the axial dimension of the fluid dynamic bearing device 1 due to the provision of the seal member 9 is suppressed to substantially the axial dimension of the inner flange portion 9b. Therefore, it can also contribute to making the fluid dynamic bearing device 1 thinner (smaller).

Although one embodiment of the present invention has been described above, the sintered oil-impregnated bearing according to the present invention and the fluid dynamic pressure bearing device equipped with this bearing are not limited to the above-mentioned exemplary embodiments, and can be used within the scope of the present invention. It can take any form.

FIG. 8 shows a cross-sectional view of a fluid dynamic bearing device 31 according to another embodiment of the present invention. As shown in FIG. 8, the fluid dynamic bearing device 31 in this embodiment differs from the fluid dynamic bearing device 1 shown in FIG. 2 in that it has only the first seal space S1. Specifically, in the fluid dynamic bearing device 31 according to the present embodiment, the seal member 32 is integrated with the upper end portion of the housing 7, and the inner circumferential surface 32a of the seal member 32 and the inner circumferential surface 32a are connected to each other. A first seal space S1 is formed between the outer peripheral surfaces two a1 of the opposing shaft portions 2a.

When the fluid dynamic pressure 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 pressure bearing device 1 shown in FIG. 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 shown in FIG. It is possible to create a flow of lubricating oil from the radial bearing gap G1 on the upper side in the direction to the radial bearing gap G2 on the lower side in the axial direction. With this configuration, it is possible to provide the fluid dynamic pressure bearing device 31 with a sufficient effect of preventing leakage of lubricating oil. The longitudinal dimension of the first inclined dynamic pressure groove in the first radial dynamic pressure generating section 34 on the axially upper side of the oil-impregnated bearing 33 can be made the same as the longitudinal dimension of the second inclined dynamic pressure groove. Therefore, 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 FIG.

Furthermore, in the above description, the present invention is applied to the fluid dynamic bearing device 1, 31 that includes the shaft member 2 (rotating body) to which the disk hub 3 is fixed. The present invention can also be preferably applied to a fluid dynamic bearing device equipped with a shaft member 2 (rotating body) to which a fan or a polygon mirror is fixed. That is, the present invention applies not only to a spindle motor M for driving a disk as shown in FIG. It can also be preferably applied to bearing devices.

1 Fluid dynamic pressure bearing device 2 Shaft member 2a Shaft portion 2a1 Outer peripheral surface 2b Flange portion 2c Center relief portion 3 Disc hub 4 Drive portion 4a Stator coil 4b Rotor magnet 5 Bracket 6 Disk 7 Housing 7a First inner peripheral surface 7b Second inner surface Circumferential surface 7c Third inner circumferential surface 8 Sintered oil-impregnated bearing 8S Sintered body 8a, 8Sa Inner circumferential surface 8b, 8Sb Lower end surface 8c, 8Sc Upper end surface 8c1 Annular groove 8c2 Radial groove 8d, 8Sd Outer circumferential surface 8d1 Axial groove 9 Seal member 9a Cylindrical portion 9b Inner flange portion 9c Inner circumferential surface 9d Outer circumferential surface 10 Lid member 10a Upper end surface 11 First radial dynamic pressure generating portion 11a First inclined dynamic pressure groove 11b First hill portion 11c Second inclined dynamic pressure groove 11d Second hill portion 11e Band portion 12 Second radial dynamic pressure generating portions 12a, 12c Inclined dynamic pressure grooves 12b, 12d Hill portion 12e Band portion 13 Reduced diameter portion 14 Thrust dynamic pressure generating portion 14a Thrust dynamic pressure groove 14b Hill portion 15 Circulation path 20 Molding device 21 Die 22 Sizing pin 22a First mold 22a1 Convex molded portion 22a2 Concave molded portion 22a3 Reduced diameter portion molded portion 23 Lower punch 24 Upper punch 31 Fluid dynamic pressure bearing device 32 Seal member 32a Inner peripheral surface 33 Sintered oil-impregnated bearing 34 First radial dynamic pressure generating portion D1, D2 Inner diameter dimension F1 Pulling force (bearing center side)
F2 Retraction force (bearing end side)
G1, G2 Radial bearing clearance H1 Axial dimension (reduced diameter part molded part)
H2 Axial dimension (reduced diameter part)
L1, L2, L3, L4 Axial dimension (inclined dynamic pressure groove)
M Spindle motor R1, R2 Radial bearing part S1 First seal space S2 Second seal space T1, T2 Thrust bearing part

Claims (9)

A sintered metal bearing obtained by compression-molding metal powder into a cylindrical shape to form a compact, and sintering the formed compact, the internal cavity being impregnated with lubricating oil, In sintered oil-impregnated bearings in which a radial dynamic pressure generating section is formed on the inner peripheral surface,
The radial dynamic pressure generating section has a plurality of inclined dynamic pressure grooves inclined with respect to the circumferential direction of the inner peripheral surface, and a plurality of hill portions provided between the inclined dynamic pressure grooves,
A sintered oil-impregnated bearing characterized in that the hill portion is provided with a reduced diameter portion in which the inner diameter dimension of the hill portion decreases from the axial center side of the inner circumferential surface toward the axial end side. . The value obtained by subtracting the inner diameter dimension at the second end portion on the axial end side from the inner diameter dimension at the first end portion on the axial center side of the reduced diameter portion is greater than 0 μm and 1.5 μm or less. The sintered oil-impregnated bearing according to claim 1. The sintered oil-impregnated bearing according to claim 1 or 2, wherein the inner diameter dimension of the reduced diameter portion decreases in a tapered shape from the axial center side toward the axial end side. The sintered oil-impregnated bearing according to claim 1, wherein the groove depth of the inclined dynamic pressure groove increases from the axial center side toward the axial end side. The sintered oil-impregnated bearing according to claim 4, wherein the inner diameter dimension of the inclined dynamic pressure groove is constant in the axial direction. The radial dynamic pressure generating section includes a plurality of first inclined dynamic pressure grooves and second inclined dynamic pressure grooves, which are inclined in different directions with respect to the circumferential direction and are adjacent to each other in the axial direction. and has
The hill portions are provided between the first inclined dynamic pressure grooves and the second inclined dynamic pressure grooves, and the reduced diameter portion is provided in the hill portion between the second inclined dynamic pressure grooves,
The first inclined dynamic pressure groove is located on the central side in the axial direction, the second inclined dynamic pressure groove is located on the end side in the axial direction, and the longitudinal dimension of the second inclined dynamic pressure groove is The sintered oil-impregnated bearing according to claim 1, which is larger than the longitudinal dimension of the first inclined dynamic pressure groove. A sintered oil-impregnated bearing according to claim 1, a housing having a configuration in which one axial end side is open and the other end side is closed, and the sintered oil-impregnated bearing is fixed to the inner periphery; A radial bearing gap is formed between the inner peripheral surface of the sintered oil-impregnated bearing and the outer peripheral surface of the shaft by the dynamic pressure action of a rotating body having a shaft inserted into the circumference and the radial dynamic pressure generating section. a radial bearing section that supports the shaft section in a radial direction in a non-contact manner with a film of lubricating oil. The radial dynamic pressure generating portions are provided at two locations separated in the axial direction on the inner peripheral surface of the sintered oil-impregnated bearing, and each of the radial dynamic pressure generating portions is inclined in different directions with respect to the circumferential direction. and a plurality of first inclined dynamic pressure grooves and second inclined dynamic pressure grooves adjacent to each other in the axial direction, and between the first inclined dynamic pressure grooves and the second inclined dynamic pressure groove. Each of the plurality of hill portions is provided between the grooves,
In one of the two radial dynamic pressure bearing sections located on the axial opening side of the housing, 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 center side. 8. The fluid dynamic bearing device according to claim 7, wherein the dynamic pressure groove is located on the axial end side, and the reduced diameter portion is provided on a hill between the second inclined dynamic pressure grooves. A motor comprising the fluid dynamic bearing device according to any one of claims 1 to 8.

Images