JP2004197889A - Dynamic-pressure bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent negative pressure of a lubrication fluid from occurring inside a housing, and at the same time, to maintain a thrust bearing clearance at a thrust bearing part to a proper value. <P>SOLUTION: A bearing sleeve 8, which is formed of a porous body made of a sintered metal, is provided with inner fine pores (structure fine pores of the porous body) and surface openings which are formed by opening the inner fine pores on the surface. The transmission factor k of the bearing sleeve 8 defined by the following formula is set within the range of 1×10<SP>-15</SP>-1×10<SP>-14</SP>m<SP>2</SP>. ν<SB>x</SB>=-(k/μ)(Δp/Δx), here, it is set as follows; v<SB>x</SB>: flow velocity in an X direction of a fluid inside the porous body, k : transmission factor, μ : viscosity of the fluid, and Δp/Δx : pressure gradient in the X direction of the fluid inside the porous body. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dynamic bearing device that rotatably supports a shaft member in a non-contact manner by a dynamic pressure action of lubricating oil generated in a bearing gap. This bearing device is an information device, for example, a magnetic disk drive such as an HDD or FDD, an optical disk drive such as a CD-ROM, a CD-R / RW, or a DVD-ROM / RAM, or a magneto-optical disk drive such as an MD or MO. It is suitable for a spindle motor such as a laser scanner, a polygon scanner motor of a laser beam printer (LBP), or a small motor such as an electric device such as an axial fan.
[0002]
[Prior art]
For a spindle motor for information equipment represented by a disk drive, use a dynamic pressure bearing that excels in these required characteristics in place of a rolling bearing for reasons such as high rotational accuracy, high damping, and low noise. Cases are increasing.
[0003]
For example, in a hydrodynamic bearing device incorporated in a spindle motor of a disk drive device such as an HDD, a radial bearing portion that rotatably supports a shaft member in a radial direction in a non-contact manner, and a non-contact support rotatably supports a shaft member in a thrust direction. A dynamic pressure bearing having a groove (dynamic pressure groove) for generating dynamic pressure on the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member is used as the radial bearing portion (for example, Patent Document 1, Non-Patent Document 1). The radial bearing portion is often provided at two locations separated in the axial direction in order to enhance the function of supporting the shaft in the radial direction. As the thrust bearing portion, for example, a dynamic pressure groove provided on both end surfaces of a flange portion of a shaft member or a surface opposed thereto (an end surface of a bearing sleeve, an end surface of a thrust member fixed to a housing, or the like). A pressure bearing is used. Further, in order to prevent the lubricating fluid inside the housing from leaking to the outside, a seal portion is often provided at the opening of the housing.
[0004]
The bearing sleeve is generally formed of a solid metal material such as stainless steel or a copper alloy. However, the present applicant has attempted to reduce the manufacturing cost and suppress the deterioration of the lubricating fluid to improve the durability. For this reason, a configuration in which a bearing sleeve is formed of a porous body of a sintered metal has been proposed (for example, see Patent Document 1 and Non-Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-61641 [Non-Patent Document 1]
"Nikkei Mechanical" published by Nikkei BP, October 1, 2000,
No. 553, p. 49-55
[0006]
[Problems to be solved by the invention]
In the hydrodynamic bearing device having the above configuration, when the shaft member rotates, the lubricating fluid around the radial bearing portion and the thrust bearing portion is drawn into the center of the bearing gap of each bearing portion by the pumping action (drawing action) of the dynamic pressure groove. While the fluid pressure (fluid dynamic pressure) at the center of the bearing gap increases, the gap between the radial bearings, the gap near the boundary between the shaft and the flange, the gap on the outer peripheral side of the flange, etc. The lubricating fluid held at the pressure may decrease in pressure and become negative pressure. As described above, when a local negative pressure is generated in the lubricating fluid inside the housing, air dissolved in the lubricating fluid appears as bubbles, which adversely affects the bearing function and durability, and also causes leakage of the lubricating fluid. It may cause.
[0007]
In order to prevent or suppress the above phenomenon, the dynamic pressure groove of the radial bearing portion on the seal portion side is formed in an asymmetric shape in the axial direction, and the pumping force of the lubricating fluid is larger on the seal portion side than on the thrust member side. Although it is conceivable to maintain the lubricating fluid inside the housing at a positive pressure, a negative pressure is actually generated due to a machining error in the dimensions and shape of the radial bearing gap. However, as a result, the floating amount of the shaft member with respect to the thrust member becomes excessive, and as a result, the thrust bearing gap of the thrust bearing portion on the bearing sleeve side becomes too small, so that a sufficient oil film thickness may not be secured.
[0008]
It is an object of the present invention to prevent the generation of a negative pressure of a lubricating fluid inside a housing and to maintain a thrust bearing gap of a thrust bearing at an appropriate value.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a housing, a bearing sleeve fixed to the housing, a shaft member having a shaft portion and a flange portion, a thrust portion provided on one end side of the housing, and a bearing sleeve. A radial bearing portion provided between the peripheral surface and the outer peripheral surface of the shaft portion for supporting the shaft portion in a radially non-contact manner by a dynamic pressure action of lubricating oil generated in the radial bearing gap, and both end surfaces of the flange portion and the bearing sleeve. A thrust bearing portion provided between the thrust bearing portion and the thrust portion, the thrust bearing portion having a herringbone-shaped dynamic pressure groove, and supporting the flange portion in the thrust direction in a non-contact manner by dynamic pressure action of lubricating oil generated in the thrust bearing gap; In a hydrodynamic bearing device provided with a seal portion provided on an end side, a bearing sleeve is formed of sintered metal, and an internal space of the bearing sleeve is formed in an internal space of the housing. Umate, lubricating fluid is filled, the following equation _{ν x = - (k / μ} ) (Δp / Δx)
ν _x : Flow velocity in the X direction of the fluid inside the porous body k: Permeability μ: Viscosity of the fluid Δp / Δx: Permeability k of the bearing sleeve defined by the pressure gradient in the X direction of the fluid inside the porous body is An arrangement is provided that is between 1 × 10 ^{−15 and} 1 × 10 ⁻¹⁴ m ² . The value of the transmittance k here is the value of the transmittance of the base material (inside) of the bearing sleeve, and the value of the transmittance on the surface may be the same as or smaller than that of the base material (inside).
[0010]
As the sintered metal forming the bearing sleeve, for example, one or more metal powders selected from copper, iron, and aluminum are used as a main material, and tin, zinc, lead, graphite, Powders obtained by mixing powders of molybdenum sulfide or the like or alloy powders thereof, molding and sintering can be used. A bearing sleeve made of such a sintered metal has a large number of internal pores as a porous body structure, and surface apertures formed by opening the internal pores on the outer surface. By impregnating the internal pores with a lubricating fluid (lubricating oil, etc.), it is possible to increase the amount of oil retained in the entire device, to seep out the lubricating fluid from the internal pores into the bearing gap, Since the lubricating fluid returns to the internal pores, deterioration of the lubricating fluid hardly occurs, and the life of the bearing is improved. When a dynamic pressure groove is formed on the inner peripheral surface of the bearing sleeve, the dynamic pressure groove can be easily formed by press working (for example, a core rod having a groove shape corresponding to the shape of the dynamic pressure groove is used). Pressure is applied to the inner peripheral surface of the bearing sleeve to transfer the shape of the dynamic pressure groove to the inner peripheral surface.)
[0011]
Here, the above relational expression is called Darcy's law, and the transmittance k of the bearing sleeve as a porous body can be obtained from the above relational expression. The Darcy's law is described, for example, in Item 106 of “Tribology Handbook” (Yokendo, edited by Japan Society of Tribology).
[0012]
In the above configuration, the thrust portion may be integrally provided at one end of the housing, or may be configured by fixing a thrust member to one end of the housing. Further, the seal portion may be provided integrally with the other end of the housing, or may be configured by fixing a seal member to the other end of the housing.
[0013]
When the dynamic pressure groove of the thrust bearing portion is formed in a spiral shape, the transmittance k of the bearing sleeve defined by the above equation is set to 5 × 10 ⁻¹⁵ to 1 × 10 ⁻¹⁴ m ² .
[0014]
Further, in the above configuration, in order to effectively prevent a negative pressure from being generated in the lubricating fluid inside the housing, radial bearings are provided at a plurality of locations separated in the axial direction, and dynamic pressure grooves are formed in the radial bearings. It is preferable that the radial bearing portion provided at the location closest to the seal portion is configured such that the pumping force of the lubricating fluid by the dynamic pressure groove is greater on the seal portion side than on the thrust portion side. More specifically, the dynamic pressure grooves of the radial bearing portion can be formed asymmetrically in the axial direction. For example, when the dynamic pressure groove is a herringbone shape, the axial dimension of the groove portion on the seal portion side is made larger than the axial dimension of the groove portion on the thrust portion side, or the number of grooves on the seal portion side, the groove angle. , Groove depth, etc. are different from the thrust part side. Alternatively, while the dynamic pressure groove of the radial bearing portion is formed symmetrically in the axial direction, a relief portion that forms a clearance larger than the bearing clearance on the surface of a mating member facing the thrust portion side end region of the dynamic pressure groove is provided. By providing the groove, the axial dimension of the groove on the thrust portion side may be artificially made smaller than the axial dimension of the groove portion on the seal portion side.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0016]
FIG. 1 shows an example of a configuration of a spindle motor for information equipment incorporating a hydrodynamic bearing device 1 according to this embodiment. The spindle motor is used in a disk drive device such as an HDD, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 2 in a non-contact manner, a rotor (disk hub) 3 mounted on the shaft member 2, For example, a stator 4 and a rotor magnet 5 are provided facing each other via a radial gap. The stator 4 is attached to the outer periphery of the bracket 6, and the rotor magnet 5 is attached to the inner periphery of the disk hub 3. The housing 7 of the hydrodynamic bearing device 1 is mounted on the inner periphery of the bracket 6. The disk hub 3 holds one or more disks D such as magnetic disks. When the stator 4 is energized, the rotor magnet 5 generates a rotating magnetic field in cooperation with the stator 4, whereby the disk hub 3 and the shaft member 2 rotate integrally.
[0017]
FIG. 2 shows the dynamic pressure bearing device 1. The dynamic pressure bearing device 1 is configured by constituting components of a housing 7, a shaft member 2, a bearing sleeve 8, and a seal member 10.
[0018]
A first radial bearing portion R1 and a second radial bearing portion R2 are provided between the inner peripheral surface 8a of the bearing sleeve 8 and the outer peripheral surface 2a1 of the shaft portion 2a of the shaft member 2 so as to be separated in the axial direction. Further, a first thrust bearing portion T1 is provided between a lower end surface 8c of the bearing sleeve 8 and an upper end surface 2b1 of the flange portion 2b of the shaft member 2, and an inner bottom surface 7c1 of a bottom portion 7c of the housing 7 and a flange portion 2b. The second thrust bearing portion T2 is provided between the lower end surface 2b2 and the lower end surface 2b2. For the sake of convenience, the description will proceed with the bottom 7c side of the housing 7 being the lower side and the opposite side being the upper side.
[0019]
The housing 7 is, for example, formed of a soft metal material such as brass or a resin material such as a thermoplastic resin into a bottomed cylindrical shape having an open upper end, and is formed integrally with the cylindrical side portion 7b and the side portion 7b. And a bottom 7c. A herringbone-shaped or spiral-shaped dynamic pressure groove is formed in a region serving as a thrust bearing surface of the inner bottom surface 7c1 of the bottom portion 7c (a surface forming a thrust bearing gap of the second thrust bearing portion T2) (not shown). ).
[0020]
The shaft member 2 is formed of, for example, a metal material such as stainless steel, and includes a shaft portion 2a and a flange portion 2b provided integrally or separately at a lower end of the shaft portion 2a. An outer peripheral surface 2a1 of the shaft portion 2a is provided with a slightly smaller diameter sunk portion 2a2. In the same figure, the extent of the small diameter of the squeezed portion 2a2 is shown in a state exaggerated considerably from the actual size.
[0021]
The bearing sleeve 8 is formed of, for example, a porous body made of a sintered metal, particularly a porous body of a sintered metal containing copper as a main component, and is fixed at a predetermined position on the inner peripheral surface of the housing 7. The bearing sleeve 8 made of a sintered metal porous body has internal pores (texture pores of the porous body) and surface apertures formed by opening the internal pores on the surface.
[0022]
On the inner peripheral surface 8a of the bearing sleeve 8, two upper and lower regions serving as radial bearing surfaces (surfaces forming a radial bearing gap between the first radial bearing portion R1 and the second radial bearing portion R2) are separated in the axial direction. Is provided. As shown in FIG. 3, the region serving as the radial bearing surface of the first radial bearing portion R1 is provided with a herringbone-shaped dynamic pressure groove. For example, a plurality of dynamic pressure grooves 8a1 inclined in one axial direction are provided in the circumferential direction. A first region R1a arranged, a second region R1b in which a plurality of dynamic pressure grooves 8a2 inclined in the other axial direction are arranged in a circumferential direction, and an annular region between the first region R1a and the second region R1b. And a region R1c. The axial length of the first region R1a is greater than the second region R1b, and the dynamic pressure groove 8a1 of the first region R1a and the dynamic pressure groove 8a2 of the second region R1b are axially centered (axial direction) of the annular region R1c. (The center of the groove). Further, the first region R1a having a long axial length is located on the upper end surface 8b side, and the second region R1b having a short axial length is located on the lower end surface 8c side. Similarly, the region serving as the radial bearing surface of the second radial bearing portion R2 also includes a herringbone-shaped dynamic pressure groove, and a plurality of dynamic pressure grooves 8a3 inclined in one axial direction are arranged in the circumferential direction. One region R2a, a second region R2b in which a plurality of dynamic pressure grooves 8a4 inclined in the other axial direction are arranged in the circumferential direction, and R2c between the first region R2a and the second region R2b. . However, unlike the first radial bearing portion R1, the axial length of the first region R2a and the axial length of the second region R2b are equal, and the dynamic pressure grooves 8a3 of the first region R2a and the dynamic pressure grooves of the second region R2b are provided. 8a4 has an axially symmetric shape with respect to the axial center (axial groove center) of the annular region R2c. Further, chamfers 8d, 8e, 8f and 8g are formed at the inner and outer corners of the upper end face 8b and the lower end face 8c, respectively.
[0023]
A herringbone-shaped or spiral-shaped dynamic pressure groove is formed in a region of the lower end surface 8c of the bearing sleeve 8 serving as a thrust bearing surface (a surface forming a thrust bearing gap of the first thrust bearing portion T1) ( Not shown).
[0024]
When each of the dynamic pressure grooves of the first thrust bearing portion T1 (the lower end face 8c of the bearing sleeve 8) and the second thrust bearing portion T2 (the inner bottom surface 7c1 of the housing 7) has a herringbone shape, the following formula of the bearing sleeve 8 is used. The transmittance k defined by
Set within the range of 1 × 10 ^-15 to 1 × 10 ^-14 m ² .
ν _x = − (k / μ) (Δp / Δx)
ν _x : flow velocity in the X direction of the fluid inside the porous body k: permeability μ: viscosity of the fluid Δp / Δx: pressure gradient in the X direction of the fluid inside the porous body
When the dynamic pressure grooves of the first thrust bearing portion T1 (the lower end surface 8c of the bearing sleeve 8) and the second thrust bearing portion T2 (the inner bottom surface 7c1 of the housing 7) are formed in spiral shapes, respectively, The transmittance k defined by the equation is
Set within the range of 5 × 10 ^-15 to 1 × 10 ^-14 m ² .
[0026]
As shown in FIG. 2, the seal member 10 is annular, and is fixed to the inner periphery of the upper end of the side portion 7 b of the housing 7 by appropriate means such as press-fitting or bonding. The inner peripheral surface 10a of the seal member 10 forms a seal space S with the outer peripheral surface 2a1 of the shaft portion 2a, and the lower end surface of the seal member 10 contacts the upper end surface 8b of the bearing sleeve 8.
[0027]
The shaft portion 2a of the shaft member 2 is inserted into the inner peripheral surface 8a of the bearing sleeve 8, and the flange portion 2b is accommodated in a space between the lower end surface 8c of the bearing sleeve 8 and the inner bottom surface 7c1 of the housing 7. The regions (two upper and lower regions) of the inner peripheral surface 8a of the inner peripheral surface 8a of the bearing sleeve 8 oppose the outer peripheral surface 2a1 of the shaft portion 2a via the radial bearing gap. The region of the lower end surface 8c of the bearing sleeve 8 serving as the thrust bearing surface faces the upper surface 2b1 of the flange portion 2b via the thrust bearing gap, and the region of the inner bottom surface 7c1 of the housing 7 serving as the thrust bearing surface is a flange. The lower surface 2b2 of the portion 2b is opposed to the lower surface 2b2 via a thrust bearing gap. A gap portion larger than the radial bearing gap is formed between the slack portion 2a2 of the shaft portion 2a and the inner peripheral surface 8a of the bearing sleeve 8 (the region between the radial bearing portions R1 and R2) (X portion). A gap (Y portion) is formed near the boundary between the shaft portion 2a and the flange portion 2b, and a gap larger than the radial bearing gap is formed between the outer peripheral surface of the flange portion 2b and the inner peripheral surface of the housing 7. A portion (Z portion) is formed.
[0028]
The internal space of the housing 7 sealed with the seal member 10 is filled with a lubricating fluid, for example, lubricating oil, including the internal pores of the bearing sleeve 8, and the oil level of the lubricating oil is maintained in the seal space S. .
[0029]
When the shaft member 2 rotates, a dynamic pressure of the lubricating oil is generated in the radial bearing gap, and the shaft portion 2a of the shaft member 2 is rotatably non-rotatable in the radial direction by an oil film of the lubricating oil formed in the radial bearing gap. Contact supported. Thus, a first radial bearing portion R1 and a second radial bearing portion R2 that rotatably support the shaft member 2 in the radial direction in a non-contact manner are configured. At the same time, a dynamic pressure of lubricating oil is generated in the thrust bearing gap, and the flange portion 2b of the shaft member 2 is rotatably and non-contactly supported in both thrust directions by a lubricating oil film formed in the thrust bearing gap. . Thus, a first thrust bearing portion T1 and a second thrust bearing portion T2 that rotatably support the shaft member 2 in the thrust direction in a non-contact manner are configured.
[0030]
As described above, the dynamic pressure grooves 8a1 and 8a2 of the first radial bearing portion R1 are formed asymmetrically in the axial direction, and the dynamic pressure groove 8a1 whose axial dimension is lower than the axial center is smaller than the dynamic pressure groove 8a1. 8a2 is larger than the axial dimension (FIG. 3). Therefore, when the shaft member 2 rotates, the pumping force (pulling force) of the lubricating oil by the dynamic pressure groove 8a1 becomes relatively larger than the pumping force of the lubricating oil by the dynamic pressure groove 8a2. The lubricating oil filled in the internal space of the housing 7 is pressurized toward the bottom 7c. The pressurizing action of the lubricating oil and the transmittance k of the bearing sleeve 8 are in the range of 1 × 10 ⁻¹⁵ to 1 × 10 ⁻¹⁴ m ² (or 5 × 10 ⁻¹⁵ to 1 × 10 ⁻¹⁴ m ² ). The pressure of the lubricating oil filled in the internal space of the housing 7 is maintained at a positive pressure including the gaps (X, Y, Z). At the same time, the thrust bearing gap of the first thrust bearing portion T1 and the thrust bearing gap of the second thrust bearing portion T2 are also maintained at appropriate values.
[0031]
【Example】
[Example 1]
In the hydrodynamic bearing device 1 having the configuration shown in FIG. 2, the hydrodynamic grooves of the first thrust bearing portion T1 (the lower end surface 8c of the bearing sleeve 8) and the second thrust bearing portion T2 (the inner bottom surface 7c1 of the housing 7) are respectively formed. The relationship between the transmittance k of the bearing sleeve 8 and the pressure of the lubricating oil in the Z portion when the shaft member 2 is rotated at 7200 rpm and a thrust load of 0.5 N in a herringbone shape, and the transmittance of the bearing sleeve 8. The relationship between k and the thrust bearing gap of the second thrust bearing portion T2 was determined by calculation. The results are shown in FIGS. 4 to 7, solid circles and ▲, dotted lines and 、 and ▲ indicate calculation results under the following conditions, respectively.
[0032]
[Solid line ●]
The radial bearing gaps of the first radial bearing portion R1 and the second radial bearing portion R2 are each tapered from the upper side to the lower side in FIG. The radial bearing gap at the center of R1c is 1 μm larger in diameter than the radial bearing gap at the center of the annular region R2c of the second radial bearing R2. The transmittance of the inner peripheral surface 8a and the lower end surface 8c of the bearing sleeve 8 is the same as the transmittance k of the base material (inside).
[Solid line ▲]
The radial bearing gaps of the first radial bearing portion R1 and the second radial bearing portion R2 are each tapered from the upper side to the lower side in FIG. 2, and the annular region R1c of the first radial bearing portion R1 is formed. Is smaller by 1 μm in diameter than the radial bearing gap at the center of the annular region R2c of the second radial bearing portion R2. The transmittance of the inner peripheral surface 8a and the lower end surface 8c of the bearing sleeve 8 is the same as the transmittance k of the base material (inside).
[Dotted line ●]
The radial bearing gaps of the first radial bearing portion R1 and the second radial bearing portion R2 are each tapered from the upper side to the lower side in FIG. The radial bearing gap at the center of R1c is 1 μm larger in diameter than the radial bearing gap at the center of the annular region R2c of the second radial bearing R2. The transmittance of the inner peripheral surface 8a and the lower end surface 8c of the bearing sleeve 8 is 1/10 of the transmittance k of the base material (inside).
[Dotted line ▲]
The radial bearing gaps of the first radial bearing portion R1 and the second radial bearing portion R2 are each tapered from the upper side to the lower side in FIG. 2, and the annular region R1c of the first radial bearing portion R1 is formed. Is smaller by 1 μm in diameter than the radial bearing gap at the center of the annular region R2c of the second radial bearing portion R2. The transmittance of the inner peripheral surface 8a and the lower end surface 8c of the bearing sleeve 8 is 1/10 of the transmittance k of the base material (inside).
[0033]
The reason why the radial bearing gap is tapered under the above conditions is to take into account machining errors of the shaft portion 2a and the bearing sleeve 8. The calculation data indicated by the dotted line takes into consideration that a part of the surface opening on the inner peripheral surface may be sealed by sizing or bearing surface forming processing when the bearing sleeve 8 is manufactured.
[0034]
The calculation data shown in FIGS. 4 and 5 are obtained when a thrust load is applied vertically downward in FIG. 2, and the calculation data shown in FIGS. 6 and 7 show that this type of hydrodynamic bearing device is used in an inverted posture. Considering that the thrust load may be applied, the thrust load is applied vertically upward in FIG.
[0035]
The total amount of the thrust bearing gap of the first thrust bearing portion T1 and the thrust bearing gap of the second thrust bearing portion T2 is 18 μm, and this total amount is constant. 5 and 7 show only the value of the thrust bearing gap of the thrust bearing portion T2.
[0036]
In addition, the dimension difference (R1a-R1b) of the axial dimension of the dynamic pressure grooves 8a1 and 8a2 in the first radial bearing portion R1 is 150 μm, which is common to all calculation data.
[0037]
From the calculation data shown in FIG. 4, when the radial bearing gap of the first radial bearing portion R1 is larger than the radial bearing gap of the second radial bearing portion R2 (●), the transmittance k of the bearing sleeve 8 is 1 × 10 ^−15. It can be seen that when the value is smaller than m ² , the Z portion becomes a negative pressure. On the other hand, from the calculation data shown in FIG. 5, when the radial bearing gap of the first radial bearing portion R1 is smaller than the radial bearing gap of the second radial bearing portion R2 (▲), the transmittance k of the bearing sleeve 8 is 1 × 10 ^If it is smaller than ⁻¹⁵ m ^2, the thrust bearing gap of the second thrust bearing portion T2 becomes excessively large, and the thrust bearing gap of the first thrust bearing portion T1 becomes less than 1 μm, so that a sufficient oil film thickness cannot be secured. Further, from the calculation data shown in FIG. 4, it is predicted that when the transmittance k of the bearing sleeve 8 becomes larger than 1 × 10 ⁻¹⁴ m ² , the pressure in the Z portion approaches 0 atm, and in some cases, the pressure becomes negative. .
[0038]
From the calculation data shown in FIGS. 4 and 5, regardless of the magnitude relationship between the radial bearing gap of the first radial bearing portion R1 and the radial bearing gap of the second radial bearing portion R2, no negative pressure is generated in the Z portion, and In order to ensure that both the thrust bearing gap of the first thrust bearing portion T1 and the thrust bearing gap of the second thrust bearing portion T2 are 1 μm or more, the transmittance k of the bearing sleeve 8 must be 1 × 10 ⁻¹⁵ to 1 × 10 ^−. It can be seen that ¹⁴ m ² should be used. Similar results were obtained from the calculation data shown in FIGS. 6 and 7 assuming use in an inverted posture.
[0039]
[Example 2]
8 and 9 show the dynamic pressure grooves of the first thrust bearing portion T1 (lower end surface 8c of the bearing sleeve 8) and the second thrust bearing portion T2 (the inner bottom surface 7c1 of the housing 7) in the first embodiment. It is a calculation result when changing from a herringbone shape to a spiral shape, and corresponds to FIGS. 4 and 5, respectively. FIGS. 10 and 11 show calculation results assuming use in an inverted posture under similar changing conditions, and correspond to FIGS. 6 and 7, respectively.
[0040]
From the calculation data shown in FIGS. 8 to 11, no negative pressure is generated in the Z portion, and the thrust bearing gap of the first thrust bearing portion T1 and the thrust bearing gap of the second thrust bearing portion T2 are both 1 μm or more. For this purpose, it can be seen that the transmittance k of the bearing sleeve 8 may be set to 5 × 10 ⁻¹⁵ to 1 × 10 ⁻¹⁴ m ² .
【The invention's effect】
According to the present invention, it is possible to prevent the generation of a negative pressure of the lubricating fluid inside the housing, and at the same time, it is possible to maintain the thrust bearing gap of the thrust bearing at an appropriate value.
[Brief description of the drawings]
FIG. 1 is a sectional view of a spindle motor for information equipment using a hydrodynamic bearing device according to the present invention.
FIG. 2 is a cross-sectional view showing one embodiment of a hydrodynamic bearing device according to the present invention.
FIG. 3 is a sectional view of a bearing sleeve.
FIG. 4 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the pressure of lubricating oil in a clearance inside the housing when the dynamic pressure groove of the thrust bearing is formed in a herringbone shape.
FIG. 5 is a view showing the relationship between the transmittance k of the bearing sleeve and the thrust bearing gap of the thrust bearing portion when the dynamic pressure groove of the thrust bearing portion has a herringbone shape.
FIG. 6 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the pressure of the lubricating oil in the gap inside the housing when the dynamic pressure groove of the thrust bearing is formed in a herringbone shape.
FIG. 7 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the thrust bearing gap of the thrust bearing portion when the dynamic pressure groove of the thrust bearing portion has a herringbone shape.
FIG. 8 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the pressure of the lubricating oil in the clearance inside the housing when the dynamic pressure groove of the thrust bearing is formed in a spiral shape.
FIG. 9 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the gap of the thrust bearing of the thrust bearing when the dynamic pressure groove of the thrust bearing has a spiral shape.
FIG. 10 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the pressure of the lubricating oil in the clearance inside the housing when the dynamic pressure groove of the thrust bearing has a spiral shape.
FIG. 11 is a diagram showing the relationship between the transmittance k of the bearing sleeve and the thrust bearing gap of the thrust bearing when the dynamic pressure groove of the thrust bearing has a spiral shape.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Dynamic pressure bearing device 2 Shaft member 2a Shaft portion 2b Flange portion 7 Housing 7c1 Inner bottom surface 8 Bearing sleeve 8a Inner peripheral surface 10 Seal member R1 Radial bearing portion R2 Radial bearing portion T1 Thrust bearing portion T2 Thrust bearing portion

Claims (3)

A housing, a bearing sleeve fixed to the housing, a shaft member having a shaft portion and a flange portion, a thrust portion provided on one end side of the housing, an inner peripheral surface of the bearing sleeve, and an outer periphery of the shaft portion A radial bearing portion that is provided between the bearing portion and the radial bearing portion and that supports the shaft portion in a non-contact manner in the radial direction by a dynamic pressure action of lubricating oil generated in a radial bearing gap; both end surfaces of the flange portion, the bearing sleeve and the thrust portion; A thrust bearing portion provided between the first and second bearings, the herringbone-shaped dynamic pressure groove, the thrust bearing portion non-contactly supporting the flange portion in the thrust direction by the dynamic pressure action of lubricating oil generated in the thrust bearing gap, and the other end of the housing. And a seal portion provided on the side,
The bearing sleeve is formed of a sintered metal,
The internal space of the housing is filled with a lubricating fluid, including the internal pores of the bearing sleeve,
The following equation ν _x = − (k / μ) (Δp / Δx)
ν _x : Flow velocity in the X direction of the fluid inside the porous body k: Permeability μ: Viscosity Δp / Δx: Permeability k of the bearing sleeve defined by the pressure gradient in the X direction of the fluid inside the porous body Is 1 × 10 ⁻¹⁵ to 1 × 10 ⁻¹⁴ m ² . A housing, a bearing sleeve fixed to the housing, a shaft member having a shaft portion and a flange portion, a thrust portion provided on one end side of the housing, an inner peripheral surface of the bearing sleeve, and an outer periphery of the shaft portion A radial bearing portion that is provided between the bearing portion and the radial bearing portion and that supports the shaft portion in a non-contact manner in the radial direction by a dynamic pressure action of lubricating oil generated in a radial bearing gap; both end surfaces of the flange portion, the bearing sleeve and the thrust portion; A thrust bearing portion provided between the thrust bearing portion, the thrust bearing portion being provided in a thrust direction in a non-contact manner by a dynamic pressure action of lubricating oil generated in a thrust bearing gap, and the other end of the housing. A hydrodynamic bearing device comprising a seal portion provided in
The bearing sleeve is formed of a sintered metal,
The internal space of the housing is filled with a lubricating fluid, including the internal pores of the bearing sleeve,
The following equation ν _x = − (k / μ) (Δp / Δx)
ν _x : Flow velocity in the X direction of the fluid inside the porous body k: Permeability μ: Viscosity Δp / Δx: Permeability k of the bearing sleeve defined by the pressure gradient in the X direction of the fluid inside the porous body Is 5 × 10 ⁻¹⁵ to 1 × 10 ⁻¹⁴ m ² . The radial bearing portion is provided at a plurality of locations spaced apart in the axial direction, the radial bearing portion has a dynamic pressure groove, and the radial bearing portion provided at a location closest to the seal portion has the dynamic bearing portion. 3. The hydrodynamic bearing device according to claim 1, wherein a pumping force of the lubricating fluid by the pressure groove is configured to be larger on the seal portion side than on the thrust portion side. 4.

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