Hydrodynamic bearing device

Abstract

To realize reduction in thickness and high-rotation accuracy of a fluid dynamic pressure bearing device, by suppressing deformation on an inner peripheral surface as much as possible to fix a bearing to a housing, even in the bearing with a small axial dimension.SOLUTION: An axial dimension L of a sintered oil-containing bearing 8 is equal to or less than 4.8 mm, a thickness dimension t is equal to or more than 0.5 mm and equal to or less than 2.0 mm, and a ratio L / D1 of the axial dimension L to the outer diameter dimension D1 is set to be equal to or more than 0.35 and equal to or less than 0.8.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] A sintered oil-impregnated bearing is a bearing in which lubricating oil is impregnated into internal pores of a porous body formed of sintered metal. As the shaft portion inserted into the inner circumference rotates relative to the shaft portion, the lubricating oil impregnated into the internal pores oozes out to the sliding portion with the shaft portion to form an oil film, and the shaft portion is rotationally supported via this oil film. Such a bearing, due to its excellent rotational accuracy and quietness, is used as a bearing device for motors mounted in various electric devices including information devices. More specifically, it is suitable for use as a bearing device for a spindle motor in a disk drive device for HDD, CD, DVD, and Blu-ray disk, a fan motor incorporated in these disk drive devices and PCs, or a polygon scanner motor incorporated in a laser beam printer (LBP).

[0003] Further, on at least one of the inner circumferential surface and the axial end surface of the sintered oil-impregnated bearing, a hydrodynamic generation portion such as a hydrodynamic groove may be formed in order to further improve quietness and increase the service life. Here, as a method of forming a hydrodynamic groove, so-called hydrodynamic groove sizing is known. In this sizing, for example, the sintered body to be the bearing is axially compressed between an upper punch and a lower punch, and the sintered body is press-fitted into the inner circumference of the die, causing the sintered body to bite into the molding die on the outer circumference of the sizing pin previously inserted into the inner circumference of the sintered body. Thereby, the shape of the molding die, that is, the shape corresponding to the hydrodynamic groove, is transferred to the inner circumferential surface of the sintered body, and a hydrodynamic groove as a radial hydrodynamic generation portion is formed (see, for example, Patent Document 1).

[0004] In recent years, with the miniaturization and thinning of information devices, there has been a demand for miniaturization of various motors mounted on information devices. For example, the cooling fan motors used in notebook computers and the like are thin, and there is also a demand for thinning of the bearing devices used in these motors. On the other hand, a cooling performance equal to or higher than the conventional level is required. Since the thinning of the bearing device leads to a reduction in the bearing area, there is an increased risk of a decrease in bearing rigidity by the amount of the reduced bearing area, not only when the size of the impeller (fan) is increased, but also when the size of the impeller is maintained.

[0005] Here, Patent Document 2 describes a sintered oil-impregnated bearing having a dynamic pressure groove array region provided on the inner peripheral surface, the axial dimension of which is 6 mm or less, and the density ratio of the entire bearing is 80% or more and 95% or less. Further, according to the bearing having the above configuration, since the density ratio of the entire bearing is made more uniform than in the conventional case, sufficient bearing rigidity can be expected even when the axial dimension is reduced by omitting the lubricating fluid reservoirs (recesses) between the conventional dynamic pressure groove array regions.

[0006] The bearing having the above configuration is usually fixed to the inner periphery of the housing by a predetermined means. Here, as a fixing means for the housing, a method of fixing the outer peripheral surface of the bearing to the inner peripheral surface of the housing by adhesion (see, for example, Patent Document 3), or a method of press-fitting the bearing into the inner periphery of the housing (see, for example, Patent Document 4) is known. Further, as another fixing means, after introducing the bearing into the inner periphery of a housing having a shape in which one axial end side is open and the other end side is closed, a seal member is introduced into the inner periphery of the housing, and the bearing is axially sandwiched between this seal member and the bottom of the housing, and the seal member in the sandwiched state is fixed to the inner peripheral surface of the housing, thereby fixing the bearing at a predetermined axial position on the inner periphery of the housing (see, for example, Patent Document 5) is known.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

[0008] By the way, recently, for cooling fan motors used in notebook computers and the like, further thinning has been progressing, and further reduction in the axial dimension of the bearings used in such motors has been demanded. On the other hand, when the axial dimension of the bearing becomes smaller, the area where the radial dynamic pressure generating portion can be formed decreases accordingly, and the dynamic pressure that can be generated in the radial bearing clearance also becomes smaller. Therefore, it becomes difficult to support the shaft portion (rotating body such as an impeller) with high precision, and there is a risk of causing a decrease in rotational accuracy (NRRO). For example, as described in Patent Document 2, it is possible to improve the bearing rigidity and thus the rotational accuracy by providing thrust dynamic pressure grooves on both end faces of the bearing. However, in that case, it is necessary to provide a thrust bearing clearance for generating dynamic pressure between the opposing surfaces in the axial direction. In that case, as described in Patent Document 5, the means of sandwiching the bearing between the seal member and the housing cannot be adopted as the fixing means for the housing. Further, considering the situation where the adhesive blocks the thrust dynamic pressure grooves provided on the axial end faces or the axial grooves provided on the outer peripheral surface of the bearing for smooth circulation of the lubricating oil, as described in Patent Document 3, it is also difficult to adopt adhesion as the fixing means for the bearing housing.

[0009] For example, as described in Patent Document 4, if the bearing is fixed to the inner circumference of the housing by press-fitting, there is no worry that the thrust bearing clearance will be crushed or that the thrust dynamic pressure groove or the axial groove will be blocked. On the other hand, if an attempt is made to firmly fix the bearing to the housing by press-fitting, it is necessary to take a large interference during press-fitting, so the possibility that the inner circumferential surface of the bearing will be deformed to a non-negligible extent during press-fitting increases. Since the deformation of the inner circumferential surface leads to the deformation of the radial dynamic pressure generating portion, this type of deformation should be avoided as much as possible. In particular, as the axial dimension of the bearing becomes smaller, it is necessary to take a larger interference during press-fitting, so this type of problem tends to become apparent.

[0010] In view of the above circumstances, the technical problem to be solved by the present invention is to make it possible to suppress the deformation of the inner circumferential surface as much as possible and fix the bearing to the housing even for a bearing having a small axial dimension, thereby achieving both thinning and high rotational accuracy of the fluid dynamic pressure bearing device.

Means for Solving the Problem

[0011] The solution to the above problem is achieved by a sintered oil-impregnated bearing according to the present invention. That is, this bearing is a sintered metal bearing obtained by compression-molding metal powder into a cylindrical shape to form a green compact and sintering the formed green compact, in which a lubricating fluid is impregnated in internal pores and a radial dynamic pressure generating portion is formed on the inner circumferential surface. The sintered oil-impregnated bearing is characterized in that the axial dimension L is 4.8 mm or less, the thickness dimension t is 0.5 mm or more and 2.0 mm or less, and the ratio L / D1 of the axial dimension L to the outer diameter dimension D1 is 0.35 or more and 0.8 or less.

[0012] The inventors have found that even when the axial dimension L of the sintered metal bearing is made smaller than before (4.8 mm or less), by setting the thickness dimension t of the bearing and the ratio L / D1 of the axial dimension L to the outer diameter dimension D1 within respective predetermined numerical ranges, it is possible to suppress as much as possible the deformation occurring on the inner peripheral surface of the cylindrical sintered body due to press-fitting into the housing or the like. The present invention has been made in view of the above findings. When the axial dimension L of the sintered oil-impregnated bearing is reduced (to 4.8 mm or less) compared to the prior art, the thickness dimension t is set in the range of 0.5 to 2.0 mm, and the ratio L / D1 of the axial dimension L to the outer diameter dimension D1 of the bearing is made a value significantly smaller than 1 (0.35 to 0.8). By making the bearing of such a shape and size, for example, when press-fitting into the inner periphery of the housing described above, regardless of the magnitude of the axial dimension L, it is possible to suppress as much as possible the deformation occurring on the inner peripheral surface of the sintered body that becomes the bearing due to press-fitting. As a result, even when the interference during press-fitting is set larger due to the reduction of the axial dimension L, the shape of the radial dynamic pressure generating portion (a groove shape is typical) can be maintained with high precision. Therefore, it becomes possible to stably exhibit the required radial bearing performance while firmly fixing the bearing to the inner periphery of the housing. Further, when forming a radial dynamic pressure generating portion such as a dynamic pressure groove on the inner peripheral surface of the bearing by dynamic pressure groove sizing or the like, by setting the thickness dimension t to 2.0 mm or less, the radial compressive force generated by press-fitting into the die can be sufficiently transmitted to the surface layer portion of the inner peripheral surface of the sintered body that becomes the bearing. Therefore, the radial dynamic pressure generating portion can be accurately and stably formed. Accordingly, this also makes it possible to stably exhibit the required radial bearing performance. Further, by setting the thickness dimension t to 0.5 mm or more, it is possible to secure the necessary thrust bearing area on one end face in the axial direction of the bearing. As a result, even when a thrust bearing portion is provided only on one side in the axial direction of the bearing, excellent rotational accuracy can be exhibited. For example, the other end face in the axial direction of the bearing can be brought into contact with the housing for axial positioning, and it becomes possible to easily manage the thrust bearing clearance. Therefore, it becomes possible to stably exhibit the required thrust bearing performance.

[0013] In addition, in the sintered oil-impregnated bearing according to the present invention, the density ratio may be 86% or more and 92% or less. Here, the "density ratio" means a value (percentage) obtained by dividing the density of the porous body forming the sintered oil-impregnated bearing by the density assuming that there are no pores in the porous body.

[0014] In this way, by setting the density ratio of the sintered oil-impregnated bearing to 86% or more, particularly during dynamic pressure groove sizing, the press-fitting force into the die is sufficiently transmitted to the surface layer portion of the inner peripheral surface of the bearing as a radial compressive force, and it becomes possible to transfer and form a dynamic pressure groove with a sufficient depth on the inner peripheral surface of the bearing. Further, by suppressing the density ratio to 92% or less, an excessive load on the sizing die can be suppressed, so that good dynamic pressure groove sizing can be stably and continuously carried out. In particular, by setting the bearing to the above-described axial dimension L and flat shape and setting the density ratio within the above range, while obtaining good bite property of the sizing pin with respect to the inner peripheral surface and thus good formability of the dynamic pressure groove and the like, it becomes possible to reliably suppress deformation of the inner peripheral surface due to press-fitting into the housing.

[0015] In addition, in the sintered oil-impregnated bearing according to the present invention, the ratio D1 / D2 of the outer diameter dimension D1 to the inner diameter dimension D2 may be 2.0 or more and 3.0 or less.

[0016] In this way, by setting the ratio D1 / D2 of the outer diameter dimension D1 to the inner diameter dimension D2 to be 2.0 or more and 3.0 or less, the bite property of the sizing pin with respect to the inner peripheral surface and thus the formability of the dynamic pressure groove and the like can be ensured. Further, by determining the ratio D1 / D2 of the outer diameter dimension D1 to the inner diameter dimension D2 in combination with the preferable numerical range of the above-described thickness dimension t, it becomes possible to more effectively apply the radial compressive force generated by press-fitting into the die to the surface layer portion of the inner peripheral surface of the sintered body.

[0017] In addition, in the sintered oil-impregnated bearing according to the present invention, the inner diameter dimension D2 may be 1.5 mm or more and 2.0 mm or less.

[0018] Thus, by setting the inner diameter dimension D2 to 1.5 mm or more, it is possible to ensure the biting property of the sizing pin with respect to the inner peripheral surface, and thus the formability of the hydrodynamic groove or the like. Further, by determining the suitable range of the inner diameter dimension D2 in combination with the suitable numerical range of the thickness dimension t described above, a sufficient amount of springback can be generated in the sintered body (porous body). As a result, for example, even a hydrodynamic groove with an appropriate depth (about 1 to 4 mm) can be reliably formed on the inner peripheral surface. Further, by suppressing the inner diameter dimension D2 to 2.0 mm or less, it is possible to avoid a situation where the outer diameter dimension D1 and thus the thickness dimension t increase more than necessary, and it is possible to reliably transmit the radial compressive force due to the press-fitting of the die to the surface layer portion of the inner peripheral surface.

[0019] Further, in the sintered oil-impregnated bearing according to the present invention, a thrust hydrodynamic generation portion may be formed on one end surface in the axial direction, and the other end surface in the axial direction may have a flat shape.

[0020] As described above, according to the sintered oil-impregnated bearing of the present invention, even when a thrust bearing portion is provided only on one side in the axial direction of the bearing, excellent rotational accuracy can be exhibited. Therefore, the flat other end surface in the axial direction of the bearing can be brought into contact with the housing for axial positioning, and it is possible to easily manage the thrust bearing clearance. Therefore, the thrust rigidity can be improved by the hydrodynamic pressure generated by the thrust hydrodynamic generation portion provided on one end surface in the axial direction, and it is possible to stably exhibit excellent thrust bearing performance.

[0021] Further, the sintered oil-impregnated bearing according to the above description preferably includes, for example, the sintered oil-impregnated bearing, a housing to which the sintered oil-impregnated bearing is fixed on the inner periphery, a rotating body having a shaft portion inserted into the inner periphery of the sintered oil-impregnated bearing, and a radial bearing portion that non-contact supports the shaft portion in the radial direction by a lubricating fluid film formed in the radial bearing clearance between the inner peripheral surface of the sintered oil-impregnated bearing and the outer peripheral surface of the shaft portion by the hydrodynamic action of the radial hydrodynamic generation portion. It can be preferably provided as a fluid dynamic pressure bearing device.

[0022] Further, in the hydrodynamic bearing device according to the present invention, when the inner diameter dimension of the sintered oil-impregnated bearing is D2 and the interference during press-fitting of the sintered oil-impregnated bearing into the housing is M, a relationship shown in Formula 1 may hold between the interference M and the inner diameter dimension D2 of the sintered oil-impregnated bearing.

Number

[0023] By determining the values of the interference M and the inner diameter dimension D2 such that the relationship shown in Formula 1 holds between the interference M (i.e., the difference between the outer diameter dimension D1 of the sintered oil-impregnated bearing and the inner diameter dimension D0 of the housing) and the inner diameter dimension D2 of the sintered oil-impregnated bearing, while firmly fixing the sintered oil-impregnated bearing to the housing, it is possible to very effectively suppress the deformation occurring on the inner peripheral surface of the cylindrical sintered body due to press-fitting into the housing (to 1 μm or less in terms of cylindricity). Therefore, it becomes possible to mass-produce a hydrodynamic bearing device with high rotational accuracy with good yield.

[0024] Further, the hydrodynamic bearing device according to the present invention may further include a first thrust bearing portion that non-contactly supports the shaft portion in the thrust direction by a film of lubricating fluid formed in a thrust bearing gap between the end surface on the other axial side of the rotating body facing in the thrust direction and the end surface on one axial side of the sintered oil-impregnated bearing.

[0025] Also, in this case, the hydrodynamic bearing device according to the present invention may be provided with a thrust dynamic pressure generating portion on the end surface on one axial side of the sintered oil-impregnated bearing facing the disk portion of the hub portion as the rotating body in the thrust direction.

[0026] Further, the hydrodynamic bearing device according to the present invention may further include a second thrust bearing portion that contact-supports the end portion on the other axial side of the shaft portion in the thrust direction by the end surface on one axial side of the housing.

[0027] Thus, by providing the first thrust bearing portion between the rotating body and the sintered oil-impregnated bearing facing each other in the thrust direction, and also providing the second thrust bearing portion for contact-supporting the shaft portion between the shaft portion and the housing facing each other in the thrust direction, it becomes possible to exhibit sufficient bearing rigidity in the thrust direction while making the sintered oil-impregnated bearing as simple in shape as possible. Further, at this time, by providing the thrust dynamic pressure generating portion on the end surface on one axial side of the sintered oil-impregnated bearing facing the disk portion of the hub portion as the rotating body in the thrust direction, the thrust dynamic pressure generating portion can be formed with high precision. Therefore, it becomes possible to exhibit extremely excellent thrust bearing performance.

[0028] As described above, the hydrodynamic bearing device according to the above description can achieve both thinning and high rotational accuracy of the hydrodynamic bearing device. Therefore, for example, it can be suitably provided as a motor equipped with this hydrodynamic bearing device.

Advantages of the Invention

[0029] From the above, according to the present invention, even for a bearing with a small axial dimension, deformation of the inner peripheral surface can be suppressed as much as possible, and the bearing can be fixed to the housing. Therefore, it becomes possible to achieve high rotational accuracy while reducing the thickness of the hydrodynamic bearing device.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0032] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following description, when viewed from the sintered oil-impregnated bearing, the side of the disk portion of the hub portion is treated as the "upper side", and the side of the bottom portion of the housing is treated as the "lower side". Of course, this up-down direction does not limit the actual installation mode and use mode of the product.

[0033] FIG. 1 conceptually shows a configuration example of a fan motor 1 according to this embodiment. This fan motor 1 includes a hydrodynamic bearing device 2, a plurality of fans 4 provided on a rotating body 3 of the hydrodynamic bearing device 2, and a drive unit 5 for rotating these fans 4 integrally with the rotating body 3. The drive unit 5 is composed of, for example, a coil 5a and a magnet 5b opposed to each other via a radial gap. In this embodiment, the coil 5a is fixed to a base portion 6 on the fixed side of the fan motor 1, and the magnet 5b is fixed to the rotating body 3 on the rotating side of the fan motor 1, respectively.

[0034] In the fan motor 1 having the above configuration, when an electric current is applied to the coil 5a, the magnet 5b rotates by the exciting force between the coil 5a and the magnet 5b, and by this rotation, a plurality of fans 4 erected on the outer peripheral edge of the rotating body 3 rotate integrally with the rotating body 3. By this rotation, each fan 4 generates an air flow in a direction corresponding to its shape (here, for example, an air flow radially outward), and an air flow from the upper side to the lower side in the axial direction of the fan motor 1 is secondarily generated in a form drawn into this air flow. By generating an air flow around the fan motor 1 in this way, it is possible to cool an information device (not shown) to which the fan motor 1 is attached.

[0035] Further, when an air flow is generated in the axial direction of the fan motor 1 as described above, a force (reaction force) in the direction opposite to this air flow is generated on the rotating body 3 of the fluid dynamic pressure bearing device 2. A magnetic force (repulsive force) in the direction to cancel out the reaction force acts between the coil 5a and the magnet 5b, and a thrust load generated by the difference in magnitude between the reaction force and the magnetic force acts on the thrust bearing portions T1, T2 (see FIG. 2 described later) of the fluid dynamic pressure bearing device 2. The magnetic force in the direction to cancel out the reaction force can be generated, for example, by arranging the coil 5a and the magnet 5b with an axial shift (detailed illustration is omitted). Further, when the rotating body 3 rotates, a radial load acts on the shaft portion 10 of the fluid dynamic pressure bearing device 2 described later. This radial load acts on the radial bearing portions R1, R2 of the fluid dynamic pressure bearing device 2.

[0036] FIG. 2 shows a cross-sectional view of the fluid dynamic pressure bearing device 2 incorporated in the fan motor 1. This fluid dynamic pressure bearing device 2 includes a housing 7, a sintered oil-impregnated bearing 8 fixed to the inner periphery of the housing 7, and a rotating body 3 that rotates relative to the sintered oil-impregnated bearing 8.

[0037] The rotating body 3 has a hub portion 9 disposed on the upper end opening side of the housing 7 and a shaft portion 10 inserted into the inner periphery of the sintered oil-impregnated bearing 8.

[0038] As shown in FIGS. 1 and 2, the hub portion 9 includes a disk portion 9a that covers the upper end opening side of the housing 7, a first cylindrical portion 9b that extends axially downward from the disk portion 9a, a second cylindrical portion 9c that is located radially outside the first cylindrical portion 9b and extends axially downward from the disk portion 9a, and a flange portion 9d that extends further radially outward from the axial lower end of the second cylindrical portion 9c. The disk portion 9a faces one end face (upper end face 8b) of the sintered oil-impregnated bearing 8 fixed to the inner periphery of the housing 7. Further, a plurality of fans 4 are provided integrally with the hub portion 9 in a standing manner from the outer peripheral edge of the flange portion 9d.

[0039] In this embodiment, the shaft portion 10 is formed separately from the hub portion 9, and its upper end is fixed to the mounting hole 9e provided in the hub portion 9. Here, the shaft portion 10 has an outer peripheral surface 10a with a constant outer diameter dimension, and, for example, a lower end portion 10b having a partial spherical shape that is continuous with the lower end of the outer peripheral surface 10a. That is, the shaft portion 10 has a shape that can be inserted into the inner circumference of the sintered oil-impregnated bearing 8 from one axial side. The shaft portion 10 having the above configuration may be integrally formed with, for example, the hub portion 9 from the same material. Alternatively, one of the shaft portion 10 and the hub portion 9 formed of different materials may be used as an insert part, and the other may be formed by injection molding of metal or resin.

[0040] The housing 7 has a shape with an open upper end and a closed lower end. Further, a sintered oil-impregnated bearing 8 is fixed to the inner peripheral surface 7a of the housing 7, and the outer peripheral surface 7b of the housing 7 is fixed to the base portion 6 (see FIG. 1). The axial opposing interval between the upper end surface 7c of the housing 7 and the lower end surface 9a1 of the disk portion 9a of the hub portion 9 is larger than the opposing interval between the upper end surface 8b of the sintered oil-impregnated bearing 8 and the lower end surface 9a1 of the disk portion 9a, and here, it is set to a size such that it can be regarded as having substantially no influence on the increase in lost torque during rotational driving.

[0041] On the upper side of the outer circumference of the housing 7, a tapered seal surface 7d with an increasing outer diameter dimension toward the upper side is formed. This tapered seal surface 7d forms an annular seal space S in which the radial opposing interval gradually decreases from the closed side (lower side) to the open side (upper side) of the housing 7 between the inner peripheral surface 9b1 of the first cylindrical portion 9b. This seal space S communicates with the outer diameter side of the thrust bearing clearance of the first thrust bearing portion T1, which will be described later, during the rotation of the shaft portion 10 and the hub portion 9, and enables the circulation of lubricating oil between the bearing internal space including each bearing clearance. Further, in a state where the lubricating oil is filled in the internal holes of the sintered oil-impregnated bearing 8 and the bearing internal space, the filling amount of the lubricating oil is adjusted so that the oil level (gas-liquid interface) of the lubricating oil is always maintained within the seal space S (see FIG. 2).

[0042] Also, when the housing 7 has the seal structure as described above, the coil 5a is positioned radially outside the first cylindrical portion 9b of the hub portion 9, and the first cylindrical portion 9b and the coil 5a are arranged so as to partially overlap in the axial direction. Thereby, the housing 7, and thus the fluid dynamic bearing device 2, is made thinner (the axial dimension is reduced).

[0043] Also, in the present embodiment, a thrust receiving portion 11 for receiving the lower end portion 10b of the spherical shaft portion 10 is provided at the bottom portion 7e of the housing 7. That is, this thrust receiving portion 11 always contacts the lower end portion 10b of the shaft portion 10 in the completed state of the fluid dynamic bearing device 2, enabling the shaft portion 10 to be rotationally supported. Note that the contact position between the shaft portion 10 and the thrust receiving portion 11 is preferably set such that the vertical position of the thrust receiving portion 11 with respect to the bearing contact surface 7f of the housing 7 is within the vertical region of the chamfered portion 8e on the inner surface of, for example, the sintered oil-impregnated bearing 8.

[0044] The material and composition of the housing 7 are arbitrarily selected in principle, and for example, known materials such as resin and metal can be appropriately adopted according to the fixing means of the sintered oil-impregnated bearing 8 to the housing 7 described later.

[0045] The sintered oil-impregnated bearing 8 is a porous body of sintered metal formed by compression-molding a predetermined raw material powder and has a cylindrical shape. In the present embodiment, as shown in FIG. 4 and the like, it has a cylindrical shape. In the entire or a part of the inner peripheral surface 8a of the sintered oil-impregnated bearing 8, a region in which a plurality of dynamic pressure grooves 8a1 are arranged as a radial dynamic pressure generating portion is formed. In the present embodiment, as shown in FIG. 3, this dynamic pressure groove 8a1 arrangement region includes a plurality of dynamic pressure grooves 8a1 inclined at a predetermined angle with respect to the circumferential direction, an inclined ridge portion 8a2 that partitions these dynamic pressure grooves 8a1 in the circumferential direction, and a band portion 8a3 that extends in the circumferential direction and partitions each dynamic pressure groove 8a1 in the axial direction (both the inclined ridge portion 8a2 and the band portion 8a3 are hatched portions in FIG. 3), and they are arranged in a herringbone shape and are formed at two locations continuously in the axial direction. In this case, both the upper dynamic pressure groove 8a1 arrangement region A1 and the lower dynamic pressure groove 8a1 arrangement region A2 are formed axially symmetrically with respect to the axial center line (a virtual line connecting the axial center of the band portion 8a3 in the circumferential direction), and their axial dimensions are equal to each other.

[0046] In the entire or a part of the upper end surface 8b of the sintered oil-impregnated bearing 8, a region in which a plurality of dynamic pressure grooves 8b1 are arranged as a thrust dynamic pressure generating portion is formed. In the present embodiment, for example, as shown in FIG. 4, a region in which a plurality of dynamic pressure grooves 8b1 extending spirally are arranged side by side in the circumferential direction is formed. At this time, the spiral direction of the dynamic pressure groove 8b1 is set in a direction corresponding to the rotation direction of the rotating body 3. The dynamic pressure groove 8b1 arrangement region having the above configuration forms a thrust bearing clearance of a first thrust bearing portion T1, which will be described later, between it and the lower end surface 9a1 of the disk portion 9a of the opposing hub portion 9 when the fluid dynamic pressure bearing device 2 shown in FIG. 2 is rotationally driven.

[0047] A thrust dynamic pressure generating portion is not formed on the lower end surface 8c of the sintered oil-impregnated bearing 8. That is, in the present embodiment, as shown in FIG. 5, the lower end surface 8c has a flat shape. The lower end surface 8c abuts on the housing 7 radially outside the housing 7 and the thrust receiving portion 11. In this case, the vertical position of the bearing contact surface 7f of the housing 7 is appropriately set within a range in which the vertical clearance between the upper end surface 8b of the sintered oil-impregnated bearing 8 and the lower end surface 9a1 of the hub portion 9 can function as a thrust bearing clearance.

[0048] On the outer peripheral surface 8d of the sintered oil-impregnated bearing 8, one or a plurality of (five in this embodiment) axial grooves 8d1 are formed (see FIG. 4 for example). In a state where the sintered oil-impregnated bearing 8 is fixed to the housing 7, these axial grooves 8d1 form a flow path for lubricating oil between the inner peripheral surface 7a of the housing 7 (see FIG. 2).

[0049] Next, referring to FIG. 3, various dimensions of the sintered oil-impregnated bearing 8 will be described. The axial dimension L (axial distance between both end faces 8b and 8c) of the sintered oil-impregnated bearing 8 is set to 4.8 mm or less, preferably 3.0 mm or less, and more preferably 1.8 mm or less, from the viewpoint of thinning the hydrodynamic bearing device 2 and thus the fan motor 1. On the other hand, from the viewpoint of ensuring the required radial bearing rigidity, the axial dimension L is set to 0.8 mm or more, preferably 1.1 mm or more.

[0050] The inner diameter dimension D2 of the sintered oil-impregnated bearing 8 (precisely, the inner diameter dimension of the band portion 8a3 that becomes the minimum diameter portion together with the inclined hill portion 8a2 on the inner peripheral surface 8a) is arbitrary as long as the thickness dimension t of the sintered oil-impregnated bearing 8 is set within the range described later. However, from the viewpoint of ensuring the biting property of the sizing pin against the inner peripheral surface 8a during dynamic pressure groove sizing, it is desirable that it is 1.2 mm or more, and more desirably 1.5 mm or more. On the other hand, from the viewpoint of avoiding a situation where it becomes difficult to reliably transmit the press-fitting force during dynamic pressure groove sizing to the surface layer portion of the inner peripheral surface 8a due to the resulting excessive increase in the thickness dimension t, it is desirable that the inner diameter dimension D2 is 2.5 mm or less, and more desirably 2.0 mm or less.

[0051] The outer diameter dimension D1 of the sintered oil-impregnated bearing 8 is arbitrary as long as the ratio of the thickness dimension t and the axial dimension L to the outer diameter dimension D1 of the sintered oil-impregnated bearing 8 is set within the range described later. However, in consideration of the necessary inner diameter dimension D2 and thickness dimension t, it is desirable that it is 2.5 mm or more, and more desirably 3.0 mm or more. From the same viewpoint, it is desirable that the outer diameter dimension D1 is 6.0 mm or less.

[0052] The ratio D1 / D2 of the outer diameter dimension D1 to the inner diameter dimension D2 is preferably set to be 2.0 or more and 3.0 or less from the viewpoint of ensuring the biting property of the sizing pin with respect to the inner peripheral surface 8a and, consequently, the formability of the dynamic pressure groove 8a1.

[0053] The thickness dimension t {=(D1 - D2) / 2} of the sintered oil-impregnated bearing 8 is preferably set to be 0.75 mm or more from the viewpoint of ensuring, for example, the necessary thrust bearing area on the upper end surface 8b. On the other hand, from the viewpoint of enabling sufficient compressive force from the die to be transmitted to the surface layer portion of the inner peripheral surface of the sintered body during sizing of the dynamic pressure groove, the thickness dimension t is preferably set to be 2.0 mm or less.

[0054] Also, the ratio of the axial dimension L to the outer diameter dimension D1 is set to be 0.35 or more and 0.8 or less from the viewpoint of suppressing deformation of the inner peripheral surface of the sintered body (and thus the inner peripheral surface 8a of the sintered oil-impregnated bearing 8) during press-fitting into the housing 7 described later.

[0055] Next, the composition of the sintered oil-impregnated bearing 8 will be described. This sintered oil-impregnated bearing 8 is obtained by compression molding and sintering raw material powder that contains the largest amount of either copper-based powder or iron-based powder and the second largest amount of the other. In other words, the porous body of the sintered oil-impregnated bearing 8 substantially has a composition with one of copper and iron as the main component and the other as the second component (the second most abundant component). Here, the copper-based powder includes not only pure copper powder but also copper alloy powder. Also, pure copper includes not only copper with a purity of 100% but also copper with a purity of 99.99% or more, which is recognized as industrially pure copper. Similarly, the iron-based powder here includes not only pure iron powder but also iron alloy powder such as stainless steel. Also, the pure iron here includes not only iron with a purity of 100% but also iron with a purity of 99.99% or more, which is recognized as industrially pure iron. As long as the above composition (powder mixing ratio) is established, the types and mixing ratios of the powders that become the third and subsequent components are arbitrary.

[0056] As the composition of the raw material powder (powder mixing ratio), for example, [copper-based powder: 50 to 70% by weight, iron-based powder: 30 to 48% by weight, tin powder: 0 to 5%] is applicable. As a specific example, [pure iron powder of 140 mesh or less: 38 to 42% by weight, tin powder of 330 mesh or less: 1 to 3%, pure copper powder of 200 mesh or less: the balance] can be cited.

[0057] Next, the density ratio of the sintered oil-impregnated bearing 8 will be described. The density ratio of the entire bearing of this sintered oil-impregnated bearing 8 is set to 80% or more and 95% or less, preferably 86% or more and 92% or less. The setting of the density ratio can be achieved, for example, by adjusting the material, particle size (distribution), mixing ratio, etc. of the metal powder used as the raw material. In addition, the variation of the density ratio at this time can be evaluated using the porosity with a certain phase relationship with the density ratio. Here, the porosity is represented by the volume ratio (percentage) of pores per unit volume of the bearing. According to the empirical rule, it shows an almost negative phase relationship (-1 correlation coefficient) with the density ratio.

[0058] Also, the surface opening ratio of the inner peripheral surface 8a, particularly the inner peripheral surface of the inclined hill portion 8a2 and the belt portion 8a3 that become the radial bearing surface, is adjusted to, for example, 2% or more and 15% or less. The adjustment of the surface opening ratio can be achieved, for example, by the rotary sizing described later.

[0059] The sintered oil-impregnated bearing 8 having the above configuration is manufactured, for example, through a powder compacting process S1, a sintering process S2, a hydrodynamic groove sizing process S3, and an oil impregnation process S4. Hereinafter, taking the case where a dimensional sizing process S21 and a rotary sizing process S22 are provided after the sintering process S2 and before the hydrodynamic groove sizing process S3 as an example, the details of each process will be described.

[0060] (S1) Powder Compacting Process First, prepare the raw material powder that will be the material for the final sintered oil-impregnated bearing 8, and compress and mold this powder into a predetermined shape by die pressing. Specifically, although not shown in the drawings, a molding die is used which is composed of a die, a core pin inserted and arranged in the hole of the die, a lower punch arranged between the die and the core pin and configured to be able to move up and down with respect to the die, and an upper punch configured to be able to relatively displace (move up and down) with respect to both the die and the lower punch. In this case, the raw material powder is filled into 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. 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 green compact. At this time, the axial dimension of the green compact can be set within an appropriate range by controlling the distance between the lower end surface of the upper punch and the upper end surface of the lower punch, more specifically, the bottom dead center of the upper punch, according to the target axial dimension (more precisely, set in consideration of the dimensional changes due to subsequent sintering treatment and various sizing).

[0061] (S2) Sintering process After obtaining the green compact as described above, the green compact is sintered at a temperature corresponding to the type of the raw material powder (the melting point of the main component metal) to obtain a sintered body.

[0062] (S21) Dimension sizing process, and (S22) Rotary sizing process Then, dimension sizing is performed on the sintered body to correct the outer diameter dimension, inner diameter dimension, and axial dimension of the sintered body to dimensions according to the final product, and at the same time, the surface opening ratio of the inner peripheral surface 8a is adjusted to a ratio suitable for a hydrodynamic bearing (for example, the numerical range described above: 2 - 15%). At this stage, the predetermined hydrodynamic groove 8a1 arrangement regions A1, A2 are not yet formed on the inner peripheral surface of the sintered body. Similarly, although not shown in the drawings, the predetermined hydrodynamic groove 8b1 arrangement region is not yet formed on the upper end surface of the sintered body.

[0063] (S3) Hydrodynamic groove sizing process By performing predetermined hydrodynamic groove sizing on the sintered body obtained through the above series of steps, hydrodynamic groove array regions A1 and A2 are formed on the inner peripheral surface of the sintered body that becomes the inner peripheral surface 8a of the sintered oil-impregnated bearing 8. The forming device used here is not shown in the drawings, but it includes a die having a press-fitting hole for the sintered body, a sizing pin disposed so as to be insertable into the press-fitting hole of the die, a lower punch disposed between the die and the sizing pin and configured to be relatively movable up and down with respect to the die, and an upper punch configured to be movable up and down with respect to both the die and the lower punch. In this case, the inner diameter dimension of the press-fitting hole of the die is appropriately set according to the press-fitting allowance of the sintered body to be sized. Further, a forming die having a shape corresponding to the hydrodynamic groove array regions A1 and A2 (see FIG. 3) to be formed is provided on the outer peripheral surface of the sizing pin, and a forming die having a shape corresponding to the hydrodynamic groove 8b1 array region (see FIG. 4) to be formed is provided on the lower end surface of the upper punch.

[0064] Next, an example of hydrodynamic groove sizing using the above forming device will be described. First, with the sintered body placed on the upper end surface of the die, the upper punch and the sizing pin are lowered from above. As a result, the sizing pin is inserted into the inner periphery of the sintered body, and the forming die provided on the outer periphery of the sizing pin is opposed to the inner peripheral surface of the sintered body in the radial direction. Then, after this forming die reaches a predetermined axial position on the inner peripheral surface, only the upper punch is continuously lowered to press the upper end surface of the sintered body. As a result, the sintered body is pushed into the press-fitting hole of the die, the outer peripheral surface of the sintered body is compressed, and the inner peripheral surface of the sintered body bites into the forming die of the sizing pin previously inserted into the inner periphery. Further, from this state, the upper punch is further lowered to sandwich the sintered body between the upper punch and the lower punch, and by axially compressing the sintered body in a state where the deformation in the outer diameter direction is restricted by the die, the inner peripheral surface bites further into the forming die. In this way, the shape of the forming die is transferred to the inner peripheral surface of the sintered body, and the hydrodynamic groove array regions A1 and A2 are formed on this inner peripheral surface. Also, at this time, the forming die provided on the lower end surface of the upper punch bites into the upper end surface of the sintered body, so that the shape of the forming die of the upper punch is transferred to the upper end surface, and the corresponding hydrodynamic groove 8b1 array region is formed.

[0065] After forming the predetermined dynamic pressure groove 8a1, 8b1 arrangement regions on the inner peripheral surface and the upper end surface of the sintered body in this manner, the die is relatively lowered with respect to the lower punch to release the restraint state of the sintered body by the die. As a result, the sintered body undergoes springback in the outer diameter direction, and it becomes possible to remove the sintered body from the sizing pin. At this time, the required amount of springback is such that the mold provided on the sizing pin does not catch in the axial direction with the inner peripheral surface of the sintered body after sizing (particularly the dynamic pressure groove 8a1 arrangement regions A1, A2). Therefore, considering the groove depth (several μm) of the dynamic pressure groove 8a1 to be formed, the thickness dimension of the sintered body, that is, the thickness dimension t of the sintered oil-impregnated bearing 8 (see FIG. 3) is set. In the present embodiment, by setting the thickness dimension t to 0.5 mm or more and 2.0 mm or less as described above, it is possible to form the dynamic pressure groove 8a1 with the required depth and pull out the sizing pin used for forming from the sintered body after sizing without catching.

[0066] (S4) Oil-impregnation process By impregnating the internal pores of the sintered body obtained as described above with lubricating oil as a lubricating fluid, the sintered oil-impregnated bearing 8 is completed.

[0067] Here, various lubricating oils can be used. For example, ester-based lubricating oils with a low evaporation rate and little viscosity decrease at low temperatures, or fluorine-based lubricating oils with better resistance than ester-based lubricating oils are preferably used. Also, from the perspective of kinematic viscosity, for example, lubricating oils showing a kinematic viscosity of 20 cSt or more and 170 cSt or less at 40°C and a kinematic viscosity of 2 cSt or more and 50 cSt or less at 100°C are preferably used.

[0068] The above sintered oil-impregnated bearing 8 is fixed to the inner circumference of the housing 7 by known means such as press-fitting (including press-fitting with adhesion), adhesion, welding, etc. In the present embodiment, the sintered oil-impregnated bearing 8 is press-fitted into the inner circumference of the housing 7 to position and fix the sintered oil-impregnated bearing 8 with respect to the housing 7. FIG. 6 is a diagram for explaining the outline of the press-fitting process. As shown in FIG. 6, the sintered oil-impregnated bearing 8 is introduced from the opening side of the housing 7 and press-fitted to fix the sintered oil-impregnated bearing 8 to the inner circumference of the housing 7. Here, the size of the interference M during press-fitting is the value obtained by subtracting the inner diameter dimension D0 of the housing 7 from the outer diameter dimension D1 of the sintered oil-impregnated bearing 8, and the interference M is set so that the interference M and the outer diameter dimension D2 of the sintered oil-impregnated bearing satisfy the relationship shown in the above-mentioned mathematical formula 1.

[0069] During the above press-fitting, the sintered oil-impregnated bearing 8 is pushed in until the lower end surface 8c of the sintered oil-impregnated bearing 8 abuts against the bearing contact surface 7f of the housing 7, so that the sintered oil-impregnated bearing 8 is fixed to the housing 7 in a state where the vertical positioning of the sintered oil-impregnated bearing 8 with respect to the housing 7 is performed. Then, by inserting the shaft portion 10 of the rotating body 3 into the inner circumference of the sintered oil-impregnated bearing 8, the fluid dynamic pressure bearing device 2 is completed. In this case, the interface of the lubricating oil is held in the seal space S (see FIG. 2).

[0070] Note that the above-described oil-impregnation step S4 may be performed, for example, after fixing the sintered body that becomes the sintered oil-impregnated bearing 8 to the inner circumference of the housing 7.

[0071] In the fluid dynamic pressure bearing device 2 having the above-described configuration, when the shaft portion 10 (rotating body 3) rotates, the regions (the dynamic pressure groove 8a1 arrangement regions A1 and A2 at the upper and lower two places) on the inner peripheral surface 8a of the sintered oil-impregnated bearing 8 that serve as the radial bearing surfaces face the outer peripheral surface 10a of the shaft portion 10 with a radial bearing clearance therebetween. Then, as the shaft portion 10 rotates, the lubricating oil in the radial bearing clearance is pushed toward the axial center side of each dynamic pressure groove 8a1 arrangement region A1 and A2, and the pressure of the lubricating oil rises in the region on the axial center side (here, the belt portion 8a3). Due to the dynamic pressure action of such dynamic pressure grooves 8a1, the first radial bearing portion R1 and the second radial bearing portion R2 that rotatably and non-contactly support the shaft portion 10 in the radial direction are respectively configured to be separated in the axial direction.

[0072] Also, an oil film of lubricating oil is formed in the thrust bearing gap between the upper end surface 8b (the region where the dynamic pressure grooves 8b1 are arranged) of the sintered oil-impregnated bearing 8 and the lower end surface 9a1 of the hub portion 9 facing the upper end surface 8b by the dynamic pressure action of the dynamic pressure grooves 8b1. Then, a first thrust bearing portion T1 that non-contactly supports the rotating body 3 in the thrust direction is configured by the pressure of this oil film. Further, the lower end portion 10b of the shaft portion 10 is rotatably and contact-supported by a thrust receiving portion 11 provided at the bottom portion 7e of the housing 7, whereby a second thrust bearing portion T2 that contact-supports the rotating body 3 in the thrust direction is configured.

[0073] As described above, in the sintered oil-impregnated bearing 8 according to the present embodiment, when the axial dimension L thereof is reduced (to 4.8 mm or less) compared to the prior art, the thickness dimension t is set to 0.5 mm or more and 2.0 mm or less, and the ratio of the axial dimension L to the outer diameter dimension D1 is set to a value significantly smaller than 1 (0.35 or more and 0.8 or less). By making the sintered oil-impregnated bearing 8 have such a shape and size, when press-fitting into the inner circumference of the housing 7 described above, regardless of the size of the axial dimension L, the deformation generated on the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 due to press-fitting can be suppressed as much as possible. As a result, even when the interference M during press-fitting is set larger due to the reduction of the axial dimension L, the shape of the dynamic pressure groove 8a1 arrangement regions A1 and A2 as the radial dynamic pressure generation part can be maintained with high precision. Therefore, while firmly fixing the sintered oil-impregnated bearing 8 to the inner circumference of the housing 7, it is possible to stably exhibit the required radial bearing performance. Further, when forming the dynamic pressure groove 8a1 arrangement regions A1 and A2 (see FIG. 3) on the inner circumferential surface 8a of the sintered oil-impregnated bearing 8 by dynamic pressure groove sizing or the like, by setting the thickness dimension t to 2.0 mm or less, the radial compressive force generated by press-fitting into the die can be sufficiently transmitted to the inner circumferential surface surface layer part of the sintered body that becomes the sintered oil-impregnated bearing 8. Therefore, the dynamic pressure groove 8a1 arrangement regions A1 and A2 can be accurately and stably formed. Thus, also by this, it is possible to stably exhibit the required radial bearing performance. Further, by setting the thickness dimension t to 0.5 mm or more, it is possible to secure the necessary thrust bearing area on one end face in the axial direction of the sintered oil-impregnated bearing 8 (here, the upper end face 8b). As a result, even when a thrust bearing part (here, the first thrust bearing part T1) is provided only on one side in the axial direction of the sintered oil-impregnated bearing 8, excellent rotational accuracy can be exhibited, so that the lower end face 8c of the sintered oil-impregnated bearing 8 can be brought into contact with the housing 7 for axial positioning, and it becomes possible to easily manage the thrust bearing clearance. Therefore, it is possible to stably exhibit the required thrust bearing performance.

[0074] Also, when assembling the hydrodynamic bearing device 2 by press-fitting the sintered oil-impregnated bearing 8 into the housing 7 as in this embodiment, if the inner diameter dimension of the sintered oil-impregnated bearing 8 is D2 and the interference during press-fitting of the sintered oil-impregnated bearing 8 into the housing 7 is M, by determining the values of the interference M and the inner diameter dimension D2 so that the interference M and the inner diameter dimension D2 satisfy the relationship shown in the above-mentioned mathematical formula 1, while firmly fixing the sintered oil-impregnated bearing 8 to the housing 7, it is possible to very effectively suppress the deformation occurring on the inner peripheral surface of the cylindrical sintered body due to press-fitting into the housing 7 (to 1 μm or less in terms of cylindricity). Therefore, it becomes possible to mass-produce the high-rotation-accuracy hydrodynamic bearing device 2 with good yield.

[0075] As described above, one embodiment of the present invention has been explained. However, the sintered oil-impregnated bearing according to the present invention and the hydrodynamic bearing device provided with this bearing are not limited to the above-exemplified forms, and can take any form within the scope of the present invention.

[0076] FIG. 7 shows a cross-sectional view of a hydrodynamic bearing device 12 according to another embodiment of the present invention. As shown in FIG. 7, the hydrodynamic bearing device 12 in this embodiment is different from the hydrodynamic bearing device 2 shown in FIG. 2 in that it has only the first thrust bearing portion T1. Specifically, in the hydrodynamic bearing device 2 according to this embodiment, a predetermined thrust-direction gap always exists between the lower end surface 10c of the shaft portion 10 and the upper end surface 7e1 of the bottom portion 7e of the housing 7. Here, the magnitude of the facing interval (thrust-direction gap) between the upper end surface 7e1 of the bottom portion 7e and the lower end surface 10c of the shaft portion 10 is larger than the facing interval between the upper end surface 8b of the sintered oil-impregnated bearing 8 and the lower end surface 9a1 of the disk portion 9a, and here, it is set to a magnitude that can be regarded as not substantially affecting the increase in lost torque during rotational drive. Since the other configurations are the same as those of the hydrodynamic bearing device 2 shown in FIG. 2 and the like, detailed description is omitted.

[0077] Also in the hydrodynamic bearing device 12 according to the present embodiment, when the axial dimension L is set to 4.8 mm or less, the thickness dimension t is set to 0.5 mm or more and 2.0 mm or less, and the ratio of the axial dimension L to the outer diameter dimension D1 is made a value significantly smaller than 1 (0.35 or more and 0.8 or less). Therefore, the dynamic pressure groove 8a1 array regions A1 and A2 as the radial dynamic pressure generation portions can be accurately and stably formed, and the required radial bearing performance can be stably exhibited. Further, since a necessary thrust bearing area can be secured on the upper end surface 8b of the sintered oil-impregnated bearing 8, excellent rotational accuracy can be exhibited even when a thrust bearing portion (first thrust bearing portion T1) is provided only on the upper end surface 8b side of the sintered oil-impregnated bearing 8. Thus, as shown in FIG. 7, sufficient thrust bearing performance can be exhibited without supporting the lower end surface 10c of the shaft portion 10 in the thrust direction, and cost reduction can be achieved by omitting the thrust receiving portion 11 and simplifying the lower end shape of the shaft portion 10 by that much.

[0078] Of course, for either one or both of the radial dynamic pressure generation portions (the dynamic pressure groove 8a1 array regions A1 and A2 in FIG. 3) formed between the radial bearing portions R1 and R2 and the outer peripheral surface 10a of the shaft portion 10, a known radial dynamic pressure generation portion having a shape other than the dynamic pressure groove, such as a so-called multi-arc shape, a step shape, or a wave shape, can be adopted.

[0079] Further, in the above description, the housing 7 of the hydrodynamic bearing device 2 is fixed to the inner periphery of the base portion 6 of the fan motor 1. However, for example, the housing 7 may be directly attached to the base portion (not shown) of the information device to which the fan motor 1 is attached. Alternatively, a portion corresponding to these base portions may be provided integrally with the housing 7.

[0080] Also, in the above description, by arranging the magnet 5b and the coil 5a with an axial shift, an external force for pressing the shaft portion 10 (rotating body 3) against the bottom 7e side of the housing 7 was applied. However, the means for applying such an external force to the shaft portion 10 is not limited to the above. Although not shown, for example, by arranging a magnetic member capable of attracting the magnet 5b axially opposite to the magnet 5b, the above magnetic force can also be applied to the rotating body 3. Further, when the thrust as the reaction force of the blowing action is sufficiently large and the shaft portion 10 can be pressed downward only by this thrust, the magnetic force (magnetic attraction force) as the external force for pressing the shaft portion 10 downward may be omitted.

[0081] Also, in the above description, the case where the present invention is applied to the hydrodynamic bearing device 2 in which the rotating body 3 having the fan 4 is fixed to the shaft portion 10 has been described. However, the present invention can also be preferably applied to the hydrodynamic bearing device 2 in which a disk hub having a disk mounting surface or a polygon mirror is fixed to the shaft portion 10 as the rotating body 3. That is, the present invention can be preferably applied not only to the fan motor 1 as shown in FIG. 1 but also to the hydrodynamic bearing device 2 incorporated in other electric devices such as a spindle motor for a disk device and a polygon scanner motor for a laser beam printer (LBP).

Explanation of Reference Numerals

[0082] 1 Fan motor 2, 12 Hydrodynamic bearing device 3 Rotating body 4 Fan 5 Driving part 5a Coil 5b Magnet 6 Base part 7 Housing 7c Upper end face 7d Seal surface 8 Sintered oil-impregnated bearing 8a Inner peripheral surface 8a1 Hydrodynamic groove 8a2 Inclined mound 8a3 Band part Upper end surface of 8b Dynamic pressure groove of 8b1 Lower end surface of 8c Outer peripheral surface of 8d Axial groove of 8d1 Hub portion 9 Disk portion 9a Lower end surface of 9a1 Cylindrical portions 9b, 9c Flange portion 9d Mounting hole 9e Shaft portion 10 Outer peripheral surface of 10a Lower end portion of 10b Lower end surface of 10c Thrust receiving portion 11 Dynamic pressure groove array regions A1, A2 Inner diameter dimension D0 of the housing Outer diameter dimension D1 of the sintered oil-impregnated bearing Inner diameter dimension D2 of the sintered oil-impregnated bearing Axial dimension L Radial bearing portions R1, R2 Seal space S Thickness dimension t Thrust bearing portions T1, T2

Claims

1. A sintered metal bearing obtained by compression molding metal powder into a cylindrical shape to form a green compact and sintering the formed green compact, wherein in a sintered oil-impregnated bearing in which a lubricating fluid penetrates into internal pores and a radial dynamic pressure generating portion is formed on the inner peripheral surface, the axial dimension L is 4.8 mm or less, the thickness dimension t is 0.5 mm or more and 2.0 mm or less, and the ratio L / D1 of the axial dimension to the outer diameter dimension D1 is 0.35 or more and 0.8 or less, a sintered oil-impregnated bearing characterized by; a housing in which the sintered oil-impregnated bearing is press-fitted and fixed to the inner periphery; a rotating body having a shaft portion inserted into the inner periphery of the sintered oil-impregnated bearing; a radial bearing portion that non-contactly supports the shaft portion in the radial direction by a film of the lubricating fluid formed in a radial bearing clearance between the inner peripheral surface of the sintered oil-impregnated bearing and the outer peripheral surface of the shaft portion by the dynamic pressure action of the radial dynamic pressure generating portion; a first thrust bearing portion that non-contactly supports the shaft portion in the thrust direction by a film of the lubricating fluid formed in a thrust bearing clearance between the end surface on the other axial side of the rotating body facing in the thrust direction and the end surface on one axial side of the sintered oil-impregnated bearing; A hydrodynamic bearing device comprising.

2. The hydrodynamic bearing device according to claim 1, wherein the density ratio is 86% or more and 92% or less.

3. The hydrodynamic bearing device according to claim 1 or 2, wherein the ratio D1 / D2 of the outer diameter dimension D1 to the inner diameter dimension D2 is 2.0 or more and 3.0 or less.

4. The hydrodynamic bearing device according to any one of claims 1 to 3, wherein the inner diameter dimension D2 is 1.5 mm or more and 2.0 mm or less.

5. The hydrodynamic bearing device according to any one of claims 1 to 4, wherein a thrust dynamic pressure generating portion is formed on the end surface on one axial side, and the end surface on the other axial side has a flat shape.

6. The hydrodynamic bearing device according to claim 1, wherein when the inner diameter dimension of the sintered oil-impregnated bearing is D2 and the interference during press-fitting of the sintered oil-impregnated bearing to the housing is M, the relationship shown in Formula 1 holds between the inner diameter dimension D2 of the sintered oil-impregnated bearing. 【Number 1】

7. The hydrodynamic bearing device according to claim 1, wherein a thrust dynamic pressure generating portion is provided on the end surface on one axial side of the sintered oil-impregnated bearing facing the disk portion of the hub portion as the rotating body in the thrust direction.

8. The end on the other axial side of the shaft portion is in contact with the end surface on one axial side of the housing in the thrust direction; The hydrodynamic bearing device according to claim 7, further comprising a second thrust bearing portion that supports.

9. A motor comprising the hydrodynamic bearing device according to any one of claims 1 to 8.

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