JP2008039104A - Fluid bearing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid bearing device capable of accurately and freely controlling the porosity of a sintered bearing sleeve to thereby exhibit high bearing performance, and being reducible size. <P>SOLUTION: A bearing member 8 formed of a sintered metal is formed by integrating a first area 81 and a second area 82 which are composed of powder having different particle sizes. The porosity of the first area 81 is higher than that of the second area 82, and a radial bearing surface forming a radial bearing clearance described below with a shaft 31 is formed on the inside surface 83 of the first area 81. The integration of the first area 81 and the second area 82 is performed by molding a first compact 11 corresponding to the first area 81 and a second compact 12 corresponding to the second area 82 by powder compacting, respectively, and sintering them in a combined state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a hydrodynamic bearing device.

  The hydrodynamic bearing device supports a shaft member so as to be relatively rotatable with a fluid film of a fluid generated in a bearing gap. This type of bearing device has features such as high-speed rotation, high rotation accuracy, and low noise, and more specifically as a bearing device for motors installed in various electrical equipment including information equipment. As a bearing device for a spindle motor of a disk drive in an optical disk device such as a magnetic disk device such as CD-ROM, CD-R / RW, DVD-ROM / RAM, or a magneto-optical disk device such as MD or MO, or a laser It is preferably used as a bearing device for a motor such as a polygon scanner motor of a beam printer (LBP), a color wheel motor of a projector, or a fan motor.

  For example, in a hydrodynamic bearing device incorporated in an HDD spindle motor, one or both of a radial bearing portion that supports a shaft member in the radial direction and a thrust bearing portion that supports the shaft member in a thrust direction are configured by a dynamic pressure bearing. There is a case. In this case, a dynamic pressure groove that forms a dynamic pressure generating portion is formed on either the inner peripheral surface of the bearing sleeve or the outer peripheral surface of the shaft member facing the bearing sleeve, and the radial bearing gap between the two surfaces is radial. A bearing part is often formed. (For example, see Patent Document 1).

  The bearing sleeve constituting the bearing is often formed of sintered metal in order to circulate and supply, for example, lubricating oil to the bearing gap and obtain stable bearing performance. Usually, this type of bearing sleeve is formed by compressing and molding metal powder into a predetermined shape (mostly cylindrical) and then sintering, and is used in a state where the internal holes are impregnated with lubricating oil. (For example, see Patent Document 2).

  Further, in this type of hydrodynamic bearing device, a seal member is usually provided at the opening of the housing in order to prevent the lubricating oil filling the bearing gap and the like from leaking to the outside. A seal space is formed between the outer peripheral surface. This type of seal space also has a so-called oil buffer, and the volume of the seal space is larger than the amount of change in volume of the lubricating oil filled in the internal space of the housing due to thermal expansion or contraction within the operating temperature range. Is set to be large. Therefore, even when there is a change in the volume of the lubricating oil accompanying a temperature change, the oil level of the lubricating oil is always maintained in the seal space, and at least the lubricating oil does not leak to the outside due to a change in the ambient temperature (for example, (See Patent Document 3).

  Thus, since the bearing sleeve forms a radial bearing gap with the outer peripheral surface of the shaft member, high surface accuracy is required for the surface forming the radial bearing gap. As described above, when the bearing sleeve is formed of sintered metal, for example, a method of increasing secondary workability (such as dimension sizing) after sintering by reducing (decreasing) the density of the sintered body. Can be considered.

  However, since the porosity of the bearing sleeve is increased by reducing the sintered body density, the amount of lubricating oil retained in the bearing internal space is increased accordingly. An increase in the oil retention amount inevitably leads to an increase in the buffer volume, which inevitably requires a large seal space volume, for example, an axial dimension, which consequently hinders downsizing of the hydrodynamic bearing device. Will be a factor.

  As means for solving this problem, for example, means described in Japanese Patent Laid-Open No. 2002-327203 (Patent Document 4) can be considered. The sintered sleeve disclosed in this document has a higher porosity (porosity) in the inner peripheral side portion than the outer peripheral side portion, and the bearing sleeve can be used as a bearing sleeve with lubricating oil held in the inner peripheral side portion. used. In addition, regarding the manufacturing method, when sintering the integrally molded powder, the sintering temperature of the inner peripheral side portion is set to be lower than the sintering temperature of the outer peripheral side portion. It can be formed.

  In the case of the sintered sleeve formed by the above means, the porosity is higher in the inner peripheral side portion having the radial bearing surface, so that the secondary workability in such a region can be improved, and thereby the inner surface having the radial bearing surface can be improved. The peripheral surface can be finished with high accuracy. Moreover, since the porosity is lower in the outer peripheral portion, the amount of fluid (lubricating oil, etc.) impregnated in the sintered sleeve is smaller than that in the sintered sleeve formed so as to have the same porosity as the inner peripheral portion throughout. Can be reduced.

However, the above-described manufacturing method attempts to make a difference in porosity after sintering by making the heating temperature (sintering temperature) during sintering different between the inner peripheral portion and the outer peripheral portion. Therefore, the control is not easy, and it is difficult to obtain the required porosity with high accuracy. In particular, when the porosity is varied depending on the temperature difference during sintering, the size of the porosity depends on the degree of growth of neck bonds between particles, so there is a limit to the difference in porosity that can be given between the inner and outer circumferences. Yes, it is difficult to create a large porosity difference. In addition, by suppressing the degree of sintering (growth of neck bonding) in an attempt to increase the porosity at the inner peripheral portion, the sintering action of the portion may be insufficient, and sufficient strength may not be obtained. There is. In this case, the bearing performance may be deteriorated due to the wear of the bearing surface caused by the continuous use.
JP 2003-239951 A Japanese Patent Laid-Open No. 11-182551 JP 2003-65324 A JP 2002-327203 A

  In view of the above circumstances, the present invention provides a hydrodynamic bearing device that can freely control the porosity of a sintered bearing sleeve with high accuracy and thereby exhibits high bearing performance and can be downsized. Technical issue.

  In order to solve the above problems, the present invention includes a bearing gap, a sintered metal bearing member having a bearing surface facing the bearing gap, and a shaft member inserted into the inner periphery of the bearing member. In which the shaft member is supported by the fluid film of the fluid so as to be relatively rotatable, the bearing member is formed by integrating two regions made of powders having different particle sizes from each other. A hydrodynamic bearing device is provided in which a bearing surface is provided in a region having a high porosity. Here, the porosity refers to the ratio of the sum of the volume of each internal hole per unit volume of the bearing member. Moreover, the particle size here includes the meaning of particle size distribution.

  Thus, the present invention is characterized by forming a sintered metal bearing member composed of two regions having different porosity from each other by integrating two regions composed of powders having different particle sizes. Is. According to this, since the porosity can be controlled only by adjusting the particle size of the powder, compared with the case of controlling by the temperature at the time of sintering and the pressure (compression amount) at the time of compacting, The porosity can be set with high accuracy. In addition, since regions having different porosity (to be formed bodies) can be separately compacted, the porosity can be freely set in each region without any restriction between the regions, and the pores between both regions can be set. It is possible to make a large difference in rate. In addition, during sintering, there is no need to vary the sintering temperature between the two regions, so as in the conventional case, the strength and wear resistance are reduced due to differences in the degree of sintering (neck bond growth). Thus, high bearing performance can be ensured.

  Also, by providing the bearing surface in a relatively high porosity region of both regions constituting the bearing member, the bearing surface is provided in a region on the side where the secondary workability after sintering is relatively high. As a result, the bearing surface can be finished with high accuracy and ease. On the other hand, since the region having no bearing surface does not require secondary workability as the region having the bearing surface, it can be a region having a relatively low porosity, thereby impregnating the bearing member. The amount of fluid produced can be greatly reduced compared to that of conventional bearing members. Therefore, the amount of fluid held in the bearing device can be reduced, and thereby the axial dimension of the seal space serving as the buffer space can be reduced. Therefore, it is possible to reduce the size of the hydrodynamic bearing device while exhibiting high bearing performance.

  Thus, the present invention is characterized in that a sintered metal bearing member is formed by integrating two regions made of powders having different particle sizes from each other. As a specific means, for example, a means of compressing and molding powders having different particle sizes and then integrating a plurality of molded regions by sintering can be considered. Also, after individually compacting, means for integrating further sintered materials by means such as press fitting, means for integrating one sintered body by press-fitting into the other sintered body, or separate A means for integrating the powder compacted and sintered by ultrasonic welding, a means for integrating (adhering and fixing) with an adhesive, and the like are conceivable. Since these exemplary means are all integrated after compacting, the type (including composition) and size of the raw material powder to be used for each region having different porosity, the shape of each region, etc. It can be easily set according to the required characteristics for the area.

  Among these, the means for integrating by sintering in particular does not require so high dimensional accuracy or positioning accuracy between the surfaces fixed to each other as compared with the case of integration by press fitting or the like. Also, in this kind of sintered body, a sizing process for correcting dimensional changes after sintering is essential, but if integrated by sintering, a sizing process for dimensional correction is integrated into a member. However, the sizing process can be simplified as compared with the case where sizing is individually performed on a plurality of members before integration. Further, since the integration is performed simultaneously with the sintering, it is not necessary to separately provide a process for integrating a plurality of members as in the case of integrating by bonding. Therefore, it is possible to reduce the manufacturing cost and the work time as a whole.

  The bearing surface of the bearing member can be provided with a dynamic pressure generating part for generating a fluid dynamic pressure action in the bearing gap. In this case, the formation of the dynamic pressure generating portion is preferably performed after the integration of the two regions made of powders having different particle sizes, particularly after the integration by sintering. According to this, it is possible to avoid a situation in which the shape accuracy of the dynamic pressure generating part (groove, etc.) is reduced due to sintering, as in the case of providing the dynamic pressure generating part at the stage of compacting, for example. A dynamic pressure generator having accuracy can be obtained.

  The bearing surface provided in the relatively high porosity region of the bearing member having the above-described configuration may include a radial bearing surface that faces the radial bearing gap, or a thrust surface that faces the thrust bearing gap. It may include a bearing surface. Alternatively, the bearing surface may further include a thrust bearing surface in addition to the radial bearing surface.

  As described above, according to the present invention, it is possible to freely control the porosity of a sintered bearing sleeve with high accuracy, thereby providing a hydrodynamic bearing device that exhibits high bearing performance and can be downsized. It becomes possible to do.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. The “up and down” direction in the following description merely indicates the up and down direction in each drawing for the sake of convenience, and does not specify the installation direction, usage mode, or the like of the hydrodynamic bearing device.

  FIG. 1 conceptually shows a configuration example of a spindle motor including a hydrodynamic bearing device 1 according to an embodiment of the present invention. The spindle motor is used for information equipment such as an HDD equipped with a magnetic disk, for example, and includes a hydrodynamic bearing device 1 that rotatably supports a shaft member 3 having a hub 2 attached to one end in a radial direction, and a radius, for example. A drive unit 4 including a stator coil 41 and a rotor magnet 42 opposed to each other with a gap in the direction, and a bracket 5 are provided. The stator coil 41 is fixed to the bracket 5, and the rotor magnet 42 is fixed to the hub 2. The housing 6 of the hydrodynamic bearing device 1 is fixed to the inner periphery of the bracket 5. Further, as shown in the figure, the hub 2 holds the disks 7 (two in FIG. 1). In the spindle motor configured as described above, when the stator coil 41 is energized, the rotor magnet 42 is rotated by the exciting force generated between the stator coil 41 and the rotor magnet 42, and accordingly, is fixed to the hub 2. The disc 7 rotates together with the shaft member 3.

  FIG. 2 shows the hydrodynamic bearing device 1. The hydrodynamic bearing device 1 includes a housing 6, a sintered metal bearing member 8 fixed to the inner periphery of the housing 6, a lid portion 9 that closes one end of the housing 6, and the housing 6 and the bearing member 8. And a shaft member 3 that relatively rotates, and a seal portion 10.

  The shaft member 3 is formed of a metal material such as SUS steel, for example, and includes a shaft portion 31 and a flange portion 32 provided integrally or separately at the lower end of the shaft portion 31. The shaft portion 31 is formed with large-diameter surfaces 33 and 34 that form radial bearing gaps of radial bearing portions R1 and R2 described later between the shaft member 31 and the large-diameter surfaces 33 and 34. A tapered surface 35 is formed which is connected on the side opposite to the flange portion 32 and gradually decreases in diameter in a direction away from the flange portion 32.

  The housing 6 is formed in a cylindrical shape with a metal material such as brass or a resin material, for example, and has a shape in which both axial ends thereof are opened. A first inner peripheral surface 61 for fixing a lid 9 described later is formed on the inner periphery of the lower end of the housing 6. Further, the inner diameter is different from that of the first inner peripheral surface 61, and the outer peripheral surface 86 of the bearing member 8 is bonded to the second inner peripheral surface 62 of the housing 6 positioned above the inner peripheral surface 61. It is fixed by appropriate means such as adhesion and press-fitting), press-fitting, and welding (including ultrasonic welding and laser welding).

  The bearing member 8 has a sleeve shape as a whole, and is formed of, for example, sintered metal made of powder containing copper, iron, or both as main components.

  More specifically, the bearing member 8 is made of powders having different particle sizes and is formed by integrating two regions having different porosity, here, the first region 81 and the second region 82. The porosity of the first region 81 is higher than the porosity of the second region 82, and a radial bearing surface that forms a radial bearing gap, which will be described later, is provided between the inner peripheral surface 83 of the first region 81 and the shaft portion 31. It has been. Moreover, in this embodiment, the 1st area | region 81 is mainly cylindrical, and also makes the shape which protruded in the hook shape toward the outer-diameter side from the end. A thrust bearing surface that forms a thrust bearing gap of a thrust bearing portion T <b> 1 to be described later is provided between the lower end surface 85 of the flange portion 84 and the flange portion 32 of the shaft member 3.

Here, the porosity refers to the ratio of the total volume of the internal holes per unit volume of the bearing member 8, and is specifically calculated by the following equation.
Porosity [%] = 100−Density ratio [%] = {1− (ρ1 / ρ0)} × 100
ρ1: density of the bearing member 8 (refer to the column of JIS Z 2501 dry density for the measurement method)
ρ0: True density of the material having the same composition as the bearing member 8 It has been found that the porosity decreases almost linearly as the density ratio increases, and therefore the porosity can be obtained by obtaining the density ratio. . As in the present invention, when the bearing member 8 is composed of regions having different porosities (first region 81, second region 82), in the above formula, The area 81 ”or the“ second area 82 ”may be replaced.

  The porosity of the first region 81 and the porosity of the second region 82 can be set in any range as long as the above-described magnitude relationship is satisfied. In this case, with respect to the porosity of the first region 81, the necessary minimum oil content is ensured, and the secondary workability (deformability after sintering) of the inner peripheral surface 83 serving as the radial bearing surface, particularly described later. It is sufficient that the formability of the dynamic pressure generating part A to be secured is ensured to some extent. Further, the porosity of the lubricating oil may be such that the lubricating oil does not escape from the surface of the dynamic pressure generating portion A into the region 81 and can sufficiently exhibit the dynamic pressure action by the dynamic pressure generating portion A. The clearance can also be improved by adjusting (lowering) the surface opening ratio of the dynamic pressure generating portion A formation region by, for example, rotational sizing before groove sizing.

  One or a plurality of (three in the illustrated example) axial grooves G1 are formed on the outer peripheral surface 86 of the bearing member 8. The axial groove G <b> 1 forms a fluid flow path for lubricating oil between the bearing member 8 and the second inner peripheral surface 62 of the opposing housing 6 in a state where the bearing member 8 is fixed at a predetermined position on the inner periphery of the housing 6.

  The upper end surface 87 of the bearing member 8 is formed with an annular groove G2 and a radial groove G3 that is connected to the outer diameter side of the annular groove G2 and opens to the inner peripheral surface 83 side. Among these, the annular groove G2 is connected to the axial groove G1 (fluid flow path) through the axial clearance between the bearing member 8 and the seal portion 10 in a state where the seal portion 10 is fixed to the inner periphery of the housing 6. ing. Further, the radial groove G3 connected to the annular groove G2 on the outer diameter side thereof opens to the inner peripheral surface 83 side, and is connected to a radial bearing gap formed between the inner peripheral surface 83 and the large diameter surface 33. .

  Two dynamic pressure generating portions A and B are formed on the inner peripheral surface 83 (radial bearing surface) of the bearing member 8 so as to be separated from each other in the axial direction. Among these, as shown in FIG. 3, the axially upper dynamic pressure generating portion A has a so-called herringbone shape in which a plurality of dynamic pressure grooves A1 and dynamic pressure grooves A2 having different inclination directions are arranged in the circumferential direction. It is arranged in. Similarly, the dynamic pressure generating portion B on the lower side in the axial direction is formed by arranging a plurality of dynamic pressure grooves B1 and dynamic pressure grooves B2 having different inclination directions in the circumferential direction, so as to form a so-called herringbone shape. These dynamic pressure generating portions A and B face the large-diameter surfaces 33 and 34 of the shaft portion 31 in a state where the shaft portion 31 is inserted into the inner periphery of the bearing member 8, respectively, and the shaft portion 31 (the shaft member 3). During rotation, radial bearing gaps of first radial bearing portion R1 and second radial bearing portion R2, which will be described later, are formed between large-diameter surfaces 33 and 34 facing each other (see FIG. 2).

  In this embodiment, the dynamic pressure generating part A located on the one end opening side (upper side) of the housing 6 has an axial center m (the axial center of the region between the upper and lower dynamic pressure grooves A1 and A2). The axial dimension X1 of the dynamic pressure groove A1 formation region above the axial center m is larger than the axial dimension X2 of the lower dynamic pressure groove A2 formation region. Further, as shown in FIG. 3, the dynamic pressure grooves A1 and A2 are on the same plane as the region excluding the dynamic pressure generating portion A on the inner peripheral surface 83, and are located on the lower side in the axial direction of the inner peripheral surface. Regarding the pressure generating part B, both of the dynamic pressure grooves B1 and B2 are on the same plane as the region of the inner peripheral surface 83 excluding the dynamic pressure generating part B.

  On the entire or partial region of the lower end surface 85 (thrust bearing surface) of the bearing member 8, as shown in FIG. 4, for example, a region where a plurality of dynamic pressure grooves C1 are arranged in a spiral shape is formed as the dynamic pressure generating portion C. It is formed. This dynamic pressure groove C1 formation region (dynamic pressure generating portion C) faces the upper end surface 36 of the flange portion 32, and when the shaft member 3 rotates, between the upper end surface 36 and the first thrust bearing portion T1 described later. A thrust bearing gap is formed (see FIG. 2).

  An annular first chamfered portion 88 is formed between the inner peripheral surface 83 and the lower end surface 85 of the bearing member 8. An annular second chamfered portion 89 is also formed between the inner peripheral surface 83 and the upper end surface 87.

  Hereinafter, the manufacturing method of the bearing member 8 having the above-described configuration will be described by taking as an example a case where integration is performed by sintering after molding.

  First, the raw material powder containing the metal powder as a main component is compression-molded to form the first molded body 11 corresponding to the first region 81. Further, a raw material powder having a particle size different from that of the first molded body 11 is compression-molded, and the second molded body 12 corresponding to the second region 82 is molded. In this embodiment, the 1st molded object 11 is comprised by the cylinder part 111 and the collar part 112 which protruded to the outer-diameter side from the end of the cylinder part 111, as shown in FIG. The inner peripheral surface 113 of the cylindrical portion 111 is a region that becomes a radial bearing surface in the state of becoming the bearing member 8 after being integrated with the second molded body 12, and in the stage before integration, the dynamic pressure generating portion A , B is a perfect circle. Similarly, the lower end surface 114 (end surface opposite to the cylindrical portion 111) of the flange portion 112 is a region that becomes a thrust bearing surface, and has a planar shape that does not have the dynamic pressure generating portion C at the stage before integration. . The 2nd molded object 12 makes a substantially cylindrical shape, as shown in FIG. In addition, the raw material powder of both the molded objects 11 and 12 should just be a thing from which a particle size differs, and it does not ask | require whether the said powder is the same material or a different material.

  Next, as shown in FIG. 7, the first molded body 11 and the second molded body 12 are combined by fitting the second molded body 12 to the cylindrical portion 111 of the first molded body 11 and heated at a predetermined temperature. As a result, each molded body 11, 12 is sintered, and the outer peripheral surface 115 of the first molded body 11 (cylindrical part 111) serving as the fitting surface, the inner peripheral surface 121 of the second molded body 12, and the first molding. The upper end surface 116 of the body 11 (the flange portion 112) and the lower end surface 122 of the second molded body 12 are sinter bonded. Thereby, the 1st molded object 11 and the 2nd molded object 12 are integrated. At this time, the outer diameter d1 of the first molded body 11 (cylinder part 111) is preferably slightly smaller than the inner diameter d2 of the second molded body 12. This is because the compacts 11 and 12 before sintering are very fragile, and there is a possibility that defects may occur even when they are slightly caught during the combination.

  After passing through the above-mentioned sintering step, dimension sizing is performed on the integrated product (sintered product) of the molded bodies 11 and 12, and the integrated product is corrected to an appropriate size or shape. Thereafter, groove sizing is performed on the inner peripheral surface 113 of the cylindrical portion 111 forming the inner peripheral surface of the integrated product. Specifically, a molding die (pin) having a shape following the dynamic pressure generating portions A and B shown in FIG. 3 is pressed against the inner peripheral surface 113 of the integrated product, and the inner peripheral surface 113 is deformed following the molding die. As a result, the dynamic pressure generating portions A and B are formed. Similarly, the dynamic pressure generating portion C is molded by pressing a molding die having a shape following the dynamic pressure generating portion C shown in FIG. 4 against the lower end surface 114 of the integrated product and deforming the lower end surface 114 following the forming die. Is done. Thereby, the bearing member 8 shown in FIG. 3 is completed.

  In this way, by individually sintering and integrating the powder compacts that have been compacted, there is no need to provide a separate process for integration. Further, a sufficient fixing force can be obtained between the molded bodies 11 and 12 by sintering. At this time, by forming the first molded body 11 and the second molded body 12 with the same or the same material (the main components are the same), the binding force at the time of sintering can be further increased. Further, in this embodiment, during the sintering, the dimensions of both the molded bodies 11 and 12 are such that the outer circumferential surface 115 and the inner circumferential surface 121 that are sinter-bonded with each other are brought into contact with each other due to expansion of the molded bodies 11 and 12. (Thickness), raw material composition, etc. are defined. Therefore, as described above, even if the outer diameter d1 of the first molded body 11 is slightly smaller than the inner diameter d2 of the second molded body 12, it is possible to sinter bond between the both surfaces 115 and 121. Become.

  The lid portion 9 that closes the lower end side of the housing 6 is formed of, for example, a metal material or a resin material, and is fixed to a first inner peripheral surface 61 provided at the inner peripheral lower end of the housing 6.

  For example, a dynamic pressure generating portion D having an arrangement mode similar to that in FIG. 4 (the spiral direction is reversed) is formed on the entire upper surface 91 or a partial annular region of the lid portion 9. The dynamic pressure generating portion D faces the lower end surface 37 of the flange portion 32, and forms a thrust bearing gap of a second thrust bearing portion T2 to be described later with the lower end surface 37 when the shaft portion 31 rotates (FIG. 2). See).

  The seal portion 10 as a sealing means is formed of a metal material or a resin material separately from the housing 6 and is fixed to the inner periphery of the upper end of the housing 6 by means such as press fitting, adhesion, welding, welding or the like. In this embodiment, the sealing portion 10 is fixed in a state where the lower end surface 101 of the sealing portion 10 is in contact with the upper end surface 87 of the bearing member 8 (see FIG. 2).

  The inner peripheral surface 102 of the seal portion 10 faces the tapered surface 35 of the shaft portion 31 in a state where the shaft member 3 is assembled in the hydrodynamic bearing device 1, and the radial dimension is upward between the tapered surface 35. A seal space S that gradually expands toward is formed.

  After assembling the respective components formed as described above, lubricating oil is injected into the bearing internal space from the opening side of the seal space S by predetermined means, for example, vacuum impregnation means. As a result, the hydrodynamic bearing device 1 in which the bearing internal space including each radial bearing gap, the thrust bearing gap, and the internal holes of the bearing member 8, particularly the internal holes of the first region 81 having a relatively high porosity, is filled with the lubricating oil. Is completed. At this time, it is preferable to set the volume and the oil level so that the volume of the seal space S is larger than at least the volume change amount associated with the temperature change of the lubricating oil filled in the internal space of the hydrodynamic bearing device 1. Thereby, the oil level of the lubricating oil is maintained in the seal space S, and at least the lubricating oil does not leak to the outside due to a change in ambient temperature.

  Various types of lubricating oil can be used as the lubricating oil injected into the hydrodynamic bearing device 1, but the lubricating oil provided to the hydrodynamic bearing device (dynamic pressure bearing device) for a disk drive device such as an HDD includes An ester-based lubricating oil excellent in low evaporation rate and low viscosity, such as dioctyl sebacate (DOS), dioctyl azelate (DOZ) and the like can be suitably used.

  In the hydrodynamic bearing device 1 configured as described above, when the shaft member 3 rotates, the dynamic pressure generating portion A (dynamic pressure groove A1 and A2 forming region) provided on the inner peripheral surface 83 of the bearing member 8 is the outer periphery of the shaft portion 31. It faces the surface (large diameter surface 33) via a radial bearing gap. As the shaft member 3 rotates, the lubricating oil filled in the bearing internal space is pushed toward the axial center of the dynamic pressure grooves A1 and A2, and the pressure rises. Due to the dynamic pressure action of the dynamic pressure grooves A1 and A2, the first radial bearing portion R1 that supports the shaft member 3 in a non-contact manner in the radial direction is formed (upper region in FIG. 2). Further, in the radial bearing gap formed between the dynamic pressure generating part B and the outer peripheral surface (large diameter surface 34) opposed to the dynamic pressure generating part B, the lubricating oil is pushed into the axial direction center side of the dynamic pressure grooves B1 and B2, The pressure rises. Due to the dynamic pressure action of the dynamic pressure grooves B1 and B2, the second radial bearing portion R2 that supports the shaft member 3 in a non-contact manner in the radial direction is formed (lower region in FIG. 2).

  At the same time, a thrust bearing gap between the dynamic pressure generating portion C (dynamic pressure groove C1 formation region) provided on the lower end surface 85 of the bearing member 8 and the upper end surface 36 of the flange portion 32 opposed thereto, and a lid In the thrust bearing gap between the dynamic pressure generating portion D provided on the upper end surface 91 of the portion 9 and the lower end surface 37 of the flange portion 32 opposite to the dynamic pressure generating portion D, an oil film of lubricating oil is generated by the dynamic pressure action of the dynamic pressure groove C1 and the like. Are formed respectively. The first thrust bearing portion T1 and the second thrust bearing portion T2 that support the shaft member 3 in a non-contact manner in the thrust direction are configured by the pressure of these oil films.

  Here, by forming the inner peripheral surface 83 of the bearing member 8 forming the radial bearing gap in the first region 81 having a relatively high porosity, the surface accuracy of the inner peripheral surface 83 serving as the radial bearing surface is increased. It can be finished with high accuracy and low cost. Further, the entire area of the bearing member 8 is impregnated by lowering (densifying) the porosity of the second region 82 that does not have a region to be a bearing surface such as the inner peripheral surface 83 compared to the first region 81. The amount of oil can be greatly reduced compared to conventional sintered bearing members. Accordingly, the amount of lubricating oil retained in the internal space of the hydrodynamic bearing device 1 can be reduced, thereby reducing the axial dimension of the seal space S serving as a buffer space, thereby reducing the size of the hydrodynamic bearing device 1. In particular, it is possible to reduce the thickness.

  In addition, since the bearing member 8 is formed by integrating the first region 81 and the second region 82 made of powder having different particle sizes, the porosity can be controlled with high accuracy only by adjusting the particle size of the powder. It can be easily performed. Further, since the regions 81 and 82 having different porosities can be separately compacted, the porosities can be set freely. Further, since it is not necessary to make the sintering temperature different between the two regions 81 and 82 during the sintering, the strength and abrasion resistance due to the lack of sintering action in the first region 81 having a relatively high porosity. A decrease in wearability can be avoided, and thereby high bearing performance can be exhibited.

  Further, in this embodiment, the lower end surface 85 of the bearing member 8 that forms a thrust bearing gap with the flange portion 32 is formed in the first region 81 having a relatively high porosity, like the inner peripheral surface 83. Therefore, the secondary workability (sizing property) after sintering of the lower end surface 85 serving as the thrust bearing surface can be improved, and the lower end surface 85 having high surface accuracy can be easily obtained.

  In this embodiment, the first chamfered portion 88 and the second chamfered portion 89 are provided between the inner peripheral surface 83 and the lower end surface 85 of the bearing member 8 and between the inner peripheral surface 83 and the upper end surface 87, respectively. Provided. These chamfered portions 88 and 89 are usually formed for the purpose of taking in as much lubricating oil as possible to escape out of the radial bearing gap into the bearing member 8 and supplying as much lubricating oil as possible to the radial bearing gap. Therefore, it is preferable that the surface opening ratio of the chamfered portions 88 and 89 is larger than the surface opening ratio of the inner peripheral surface 83. By adopting such a configuration, as much lubricating oil as possible can be returned to the radial bearing gap, thereby making it possible to obtain the best lubricity and the effect of preventing the deterioration of the lubricating oil by making maximum use of the lubricating oil. In particular, as in the present invention, a region including the bearing surface such as the inner peripheral surface 83 (first region 81) is partially made high in porosity, and the remaining region (second region 82) is compared with the first region 81. Therefore, it is an effective means in the case of a configuration in which the oil retention amount is kept to a minimum as the low porosity.

  Furthermore, in this embodiment, the groove length (axial dimension X1) of the axially upper dynamic pressure groove A1 in the dynamic pressure generating part A is set to the axially lower dynamic pressure groove, for example, as shown in FIG. The axial length G1 is provided on the outer peripheral surface 86 of the bearing member 8, and the annular groove G2 and the radial groove G3 are provided on the upper end surface 87, respectively, while being larger than the groove length A2 (axial dimension X2). With this configuration, the lubricating oil flowing into the radial bearing gap is separated from the flow along the dynamic pressure grooves A1 and A2 by the axially asymmetrical dynamic pressure grooves A1 and A2 from the upper end surface 87 to the lower end surface 85 side. Then, the thrust bearing gap of the first thrust bearing portion T1 → the axial groove G1 → the outer radial side axial gap between the bearing member 8 and the seal portion 10 → the annular groove G2 → the radial groove G3. Then, it returns to the upper radial bearing gap again. In this way, by forming a lubricating oil circulation passage in the bearing internal space, the lubricating oil circulation in the bearing internal space can be further enhanced, or the occurrence of a local negative pressure state can be avoided as much as possible. This makes it possible to exhibit high bearing performance over a long period of time. In particular, even when the bearing member 8 with a reduced impregnation amount is used as in the present invention, a stable lubricating performance can be obtained without incurring a lack of lubricating oil or causing deterioration. In FIG. 2, as an example, the axial groove G1, the annular groove G2, and the radial groove G3 are formed on the bearing member 8 side. However, a part or all of these are opposed to the second inner periphery of the housing 6 facing each other. It can also be provided on the surface 62 or the lower end surface 101 side of the seal portion 10.

  As mentioned above, although one Embodiment of this invention was described, this invention is not limited to the said form. As long as the bearing member 8 having the above-described configuration is provided, the present invention can be applied to a hydrodynamic bearing device having another form.

  Moreover, although the case where the bearing member 8 was comprised with the 1st area | region 81 and the 2nd area | region 82 was demonstrated in the said embodiment, of course, it can also comprise in 3 or more area | regions. In any case, each region is formed by dividing it into two or more green compacts (for example, in the case of the first compact 11 shown in FIG. 5, the cylindrical part 111 and the flange part 112 are separately molded. It is also possible. Further, the bearing member 8 is not limited to a sleeve shape, and may have another shape as a finished product. Of course, in this case, the two regions made of powders having different particle sizes are not limited to the shape shown in FIG. 3 but can take various shapes according to the shape of the bearing member 8 as a finished product.

  Moreover, in the said embodiment, as an example of the manufacturing method of the bearing member 8, the 1st molded object 11 and the 2nd molded object 12 used as the 1st area | region 81 and the 2nd area | region 82 of the bearing member 8 were separately compacted. Although the case where it integrated by sintering was demonstrated later, it can manufacture also by means other than this.

  Specifically, the first molded body 11 and the second molded body 12 having the shapes shown in FIGS. 5 and 6 are respectively compacted and sintered separately, and then the first molded body 11 as a sintered body. Similarly, it is also possible to integrate the second molded body 12 as a sintered body by press-fitting and sizing the sintered body. In this case, both of the moldings are performed so that the outer diameter dimension d1 (see FIG. 5) of the first molded body 11 press-fitted into each other is larger than the inner diameter dimension d2 (see FIG. 6) of the second molded body 12. The bodies 11 and 12 are preferably molded. When the amount of change in the radial dimension after sintering has a size that affects the press-fitting allowance (absolute value of d1-d2), each of the molded bodies 11 is also taken into account the amount of change in dimension after sintering. , And 12 molding dimensions may be determined.

  As other means, for example, means for integrating powder compacted and sintered separately by ultrasonic welding, means for integrally fixing with an adhesive, or the like can be used. Alternatively, the compacting and integration of the compacts 11 and 12 can be performed in the compacting process by devising a method of filling the compacting mold.

  The hydrodynamic bearing device 1 having the above-described configuration is not limited to the above-described spindle motor for HDD, but also includes optical disk devices such as CD-ROM, CD-R / RW, and DVD-ROM / RAM, and magneto-optical disk devices such as MD and MO. The present invention can be suitably applied as a bearing device for electrical equipment including information equipment such as a spindle motor mounted on such information equipment. In addition, as in the present invention, if the hydrodynamic bearing device is configured so that the maximum lubrication efficiency can be obtained with a minimum amount of oil, the bearing performance can be further reduced in the size of the bearing device or information equipment on which the bearing device is mounted. It can cope with low cost without dropping. Therefore, it can be suitably provided as a bearing device having high reliability even for devices that require stable rotation performance (bearing performance) for a long period of time, such as a server HDD. Also for disk drives equipped with a plurality of disks 7 corresponding to the increase in capacity of information equipment, or for motors that require high rotational performance (bearing performance) under high-speed rotation. Furthermore, it is possible to provide a hydrodynamic bearing device that can exhibit stable bearing performance over a long period even for a relatively small motor such as a fan motor.

  In the above embodiment, the radial bearing portions R1 and R2 and the thrust bearing portions T1 and T2 are configured to generate the dynamic pressure action of the lubricating fluid by the herringbone shape or spiral shape dynamic pressure grooves. However, the present invention is not limited to this. That is, the bearing member 8 according to the present invention only needs to be formed by integrating a plurality of regions having different porosity formed by compression molding powders having different particle sizes, and the presence or absence of a dynamic pressure generating portion is a problem. Must not. Therefore, in the hydrodynamic bearing device according to the present invention, the dynamic pressure generating portion may be provided not on the bearing member 8 side but on a member facing the bearing member 8 side, or a so-called dynamic pressure generating portion having no dynamic pressure generating portion. It may constitute a fluid perfect circle bearing. Moreover, as a dynamic pressure generation part, the dynamic pressure generation part (for example, a step bearing, a multi-arc bearing etc.) which makes not only the above-mentioned arrangement | positioning shape but the arbitrary forms can be comprised.

  Further, in the above description, the lubricating oil is exemplified as the fluid that fills the inside of the hydrodynamic bearing device 1 and can form a fluid film of the fluid in the radial bearing gap or the thrust bearing gap. In addition, a fluid capable of generating a fluid film, for example, a gas such as air, a fluid lubricant such as a magnetic fluid, or a lubricating grease may be used.

It is sectional drawing of the spindle motor which comprised the hydrodynamic bearing apparatus which concerns on 1st embodiment of this invention. It is sectional drawing of a hydrodynamic bearing apparatus. It is sectional drawing of the bearing member made from a sintered metal. It is the top view which looked at the bearing member shown in FIG. 3 from the direction of arrow a. It is sectional drawing of the 1st molded object used as the 1st area | region of a bearing member. It is sectional drawing of the 2nd molded object used as the 2nd area | region of a bearing member. It is a figure which shows notionally the integration process of a 1st molded object and a 2nd molded object.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluid dynamic bearing device 3 Shaft member 6 Housing 8 Bearing member 9 Lid part 10 Seal part 11 1st molded object 12 2nd molded object 81 1st area | region 82 2nd area | region 83 Inner peripheral surface 85 Lower end surface 111 Cylindrical part 112 ridge part A , B, C, D Dynamic pressure generating portions A1, A2, B1, B2, C1 Dynamic pressure grooves R1, R2 Radial bearing portion T1, T2 Thrust bearing portion S Seal space

Claims (5)

A bearing member made of a sintered metal having a bearing gap, a bearing surface facing the bearing gap, and a shaft member inserted into the inner periphery of the bearing member, and a shaft member formed of a fluid film formed in the bearing gap In the hydrodynamic bearing device that supports the relative rotation,
A fluid bearing comprising a bearing member in which two regions made of powders having different particle sizes are integrated, and a bearing surface is provided in a region having a relatively high porosity among the two regions. apparatus.   The hydrodynamic bearing device according to claim 1, wherein both regions are integrated by sintering.   The hydrodynamic bearing device according to claim 1, wherein a dynamic pressure generating portion for generating a dynamic pressure action of fluid in the bearing gap is provided on the bearing surface.   The hydrodynamic bearing device according to claim 1, wherein the bearing surface includes a radial bearing surface facing a radial bearing gap.   The hydrodynamic bearing device according to claim 4, wherein the bearing surface further includes a thrust bearing surface facing the thrust bearing gap.

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