JP2013044395A - Fluid dynamic-pressure bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a shaft-fixed type fluid dynamic-pressure bearing device having a bearing sleeve made of a sintered metal, preventing pressure decrease of an oil film inside a radial bearing gap, and decreasing volume of a sealing space by decreasing the amount of oil.SOLUTION: In a bearing sleeve 8, the porosity in the radial bearing surface regions in the axial direction (a first region H1 and a second region H2) is decreased (to 11% or less), and the porosity in the non-radial bearing surface region (a third region H3) therebetween in the axial direction is increased to be greater than the reduced porosity.

Description

  The present invention relates to a fluid dynamic bearing device.

  Due to its high rotational accuracy and quietness, the fluid dynamic pressure bearing device is a magnetic disk drive device for information equipment (for example, HDD), an optical disk drive device such as CD, DVD, Blu-ray disc, or a magneto-optical disk such as MD, MO, etc. It is suitably used for spindle motors such as drive devices.

  For example, HDD disk drive devices tend to increase the number of installed disks as the capacity of the HDD increases. As the number of mounted discs increases, the weight increases, so that the shake when the disc is rotated increases, and the read accuracy of the disc may decrease. For this reason, the fluid dynamic pressure bearing device incorporated in the HDD is required to have a higher load capacity.

  As a fluid dynamic pressure bearing device, a shaft rotation type that rotates a shaft member inserted in the inner periphery of a bearing sleeve is generally used. However, in the case of a shaft rotation type fluid dynamic pressure bearing device, a disk hub carrying a disk is fixed to the end of the shaft member, and the intermediate part of the shaft member is cantilevered by a radial bearing portion (oil film in the radial bearing gap) It becomes a state to support. For this reason, when the number of disks mounted on the disk hub increases and the weight increases, there is a risk that the deflection of the disk will increase.

  On the other hand, for example, Patent Document 1 discloses a fixed shaft type fluid dynamic bearing device in which a shaft member is a fixed side and a bearing sleeve is a rotating side. In this case, since the fixed part between the rotating member (bearing sleeve and housing) and the disk hub can be provided in the axial direction region of the radial bearing part, the disk hub can be stabilized even when the number of mounted disks increases. Can be supported, and disc swing is suppressed.

  Further, in the fluid dynamic pressure bearing device described in Patent Document 1, the bearing sleeve is formed of sintered metal. Thereby, the lubricating oil impregnated in the internal pores of the sintered metal oozes out from the surface opening of the bearing sleeve into the radial bearing gap and the thrust bearing gap, and the lubricity in each bearing gap is improved.

JP 2011-74951 A

  However, the following problems arise when the bearing sleeve on the rotating side is made of sintered metal.

  (1) The oil in the radial bearing gap is released from the surface opening of the sintered metal bearing sleeve to the inside, so that the pressure of the oil film in the radial bearing gap decreases, so-called “dynamic pressure release” occurs. In particular, in the case of the fixed shaft type, the lubricating oil impregnated inside the sintered metal moves to the outer diameter side due to centrifugal force when the sintered metal bearing sleeve rotates, so that the oil in the radial bearing gap is removed. It becomes easy to come out inside the bearing sleeve. In order to prevent this, if the surface of the bearing sleeve is subjected to a sealing process such as rotation sizing or coating, the cost is increased due to an increase in the number of steps.

  (2) The amount of oil increases by impregnating the internal pores of the sintered metal with oil, and the volume change of the oil accompanying a temperature change increases. For this reason, it is necessary to increase the seal space that absorbs the volume change of the oil, leading to an increase in the size of the fluid dynamic bearing device. In particular, when both ends in the axial direction of the housing are opened and seal spaces are formed at both ends, the oil level held in the seal space varies under the influence of gravity. For this reason, it is necessary to improve the sealing performance by increasing the capillary force by narrowing the width of the seal space. However, since the volume of the seal space is reduced by narrowing the width of the seal space, it is necessary to further increase the axial dimension of the seal space, leading to further increase in size of the fluid dynamic bearing device. In order to avoid this, if the bearing span of the radial bearing portion is shortened by an amount corresponding to the increase in the seal space, the bearing rigidity of the radial bearing portion is reduced.

  The present invention has been made in view of the above circumstances, and in a shaft-fixed fluid dynamic pressure bearing device having a sintered metal bearing sleeve, while suppressing the pressure drop of the oil film in the radial bearing gap. It is an object to be solved to reduce the volume of the seal space by reducing the amount of oil.

  The present invention, which has been made to solve the above-mentioned problems, includes a shaft member on the fixed side, a bearing member made of sintered metal on the inner periphery, the shaft member inserted on the inner periphery, and a bearing sleeve on the inner periphery. A cylindrical housing having an outer peripheral surface fixed and opening at both ends in the axial direction, and a first seal portion and a second seal provided to protrude from the outer peripheral surface of the shaft member to the outer diameter and disposed on both axial sides of the bearing sleeve The bearing sleeve is moved in the radial direction by the dynamic pressure action of the oil film generated in the radial bearing gap between the radial bearing surface provided on the outer peripheral surface of the shaft portion and the radial bearing surface provided on the inner peripheral surface of the bearing sleeve. And a dynamic bearing action of an oil film generated in a thrust bearing gap between a radial bearing portion supported on the shaft, a thrust bearing surface provided on one end surface of the bearing sleeve, and a thrust bearing surface provided on the end surface of the first seal portion. , Bearing sleeve Oil film generated in a thrust bearing gap between a first thrust bearing portion supported in one thrust direction, a thrust bearing surface provided on the other end surface of the bearing sleeve, and a thrust bearing surface provided on an end surface of the second seal portion A second thrust bearing portion that supports the bearing sleeve in the other thrust direction, a first seal space formed between the outer peripheral surface of the first seal portion and the inner peripheral surface of the housing; A second seal space formed between the outer peripheral surface of the seal portion and the inner peripheral surface of the housing, and the lubricating oil is filled between the first seal space and the second seal space, A shaft-fixed type fluid dynamic pressure bearing device in which an oil surface is held in a second seal space, wherein the porosity in the axial region of the radial bearing surface of the bearing sleeve is determined in the axial region other than the radial bearing surface. Porosity Wherein the remote made smaller.

  By reducing the porosity in the axial direction region of the radial bearing surface among the bearing sleeves made of sintered metal, the surface open area ratio of the radial bearing surface is reduced and the fluidity of the oil inside the bearing sleeve is reduced. Can be suppressed. For this reason, it is difficult for oil in the radial bearing gap to escape into the bearing sleeve, and a decrease in the pressure of the oil film in the radial bearing gap can be suppressed. In this case, since the sealing process of the radial bearing surface can be reduced or omitted, the machining cost can be reduced. Further, by reducing the porosity of the bearing sleeve, the amount of oil impregnated in the bearing sleeve can be reduced. As a result, the volume change of the oil is reduced, so that the volume of the seal space and thus the axial dimension of the seal portion can be reduced, and the fluid dynamic pressure bearing device can be downsized or the bearing span can be increased. it can.

  At this time, if the porosity of the entire bearing sleeve is reduced, the fluidity of the oil decreases in the entire area inside the bearing sleeve, so that the circulation of the oil flowing back and forth between the inside and the outside of the bearing sleeve is hindered. There is a risk of causing deterioration. Therefore, if a region having a high porosity is provided in the bearing sleeve, the fluidity of the oil in this region can be improved, and early deterioration of the oil can be prevented. In particular, when centrifugal force is applied to the bearing sleeve as described above, the oil impregnated in the region with a large porosity moves to the outer diameter side, so that the inner peripheral surface of this region moves into the bearing sleeve. Since the oil is easily drawn, circulation of the oil is promoted.

  Therefore, if the porosity in the axial region of the radial bearing surface of the bearing sleeve is reduced and the porosity in the axial region other than the radial bearing surface is relatively increased, the above effects can be obtained. it can. That is, the porosity in the axial region of the radial bearing surface may be made smaller than the porosity in the axial region other than the radial bearing surface.

As a result of intensive studies by the present inventors, if the porosity in the axial direction region of the radial bearing surface is at most 11% among the sintered sleeves made of sintered metal, it is about the same as a bearing sleeve made of solid metal. It became clear that the oil film pressure was obtained. “Porosity” is expressed by the following formula. Here, the sintered density is the weight per unit amount of the apparent volume including the internal pores of the sintered body. In addition, the true density is the density when there is no pore in the composition of the sintered body, that is, the weight per unit amount of the actual volume not including the internal pores of the sintered body. Calculated from element density.
Porosity = [(true density−sintered density) / true density] × 100
(Sintering density = weight / apparent volume, true density = weight / actual volume)

For example, when the bearing sleeve is made of a sintered metal containing 60% or more of copper, if the density in the axial region of the radial bearing surface is 7.4 g / cm ³ or more, the porosity of this region is 11% or less. can do. Further, when the bearing sleeve is made of a sintered metal containing 60% or more of iron, if the density in the axial region of the radial bearing surface is 7.1 g / cm ³ or more, the porosity of this region is 11% or less. can do.

  In the fluid dynamic pressure bearing device described above, a thrust dynamic pressure generating portion that generates a dynamic pressure action on the oil film of the thrust bearing gap on one of the thrust bearing surfaces facing each other through the thrust bearing gap of the first and second thrust bearing portions. Can be formed. Further, in the fluid dynamic pressure bearing device described above, a radial dynamic pressure generating portion that generates a dynamic pressure action on the oil film of the radial bearing gap can be formed on one of the radial bearing surfaces facing each other through the radial bearing gap.

  In the above fluid dynamic bearing device, when the bearing sleeve is rotated, the oil in the thrust bearing gaps of the first and second thrust bearing portions flows to the outer diameter side. For this reason, the oil in the radial bearing gap communicating with the inner diameter end of the thrust bearing gap may flow into the thrust bearing gap, and the oil film pressure in the radial bearing gap may further decrease. Therefore, if the thrust dynamic pressure generating part is a pump-in type in which the lubricating oil in the thrust bearing gap flows to the inner diameter side, the oil in the thrust bearing gap of the first and second thrust bearing parts flows to the inner diameter side. Since oil flows into the radial bearing gap, the pressure of the oil film in the radial bearing gap can be maintained.

  By the way, in order to prevent the generation of negative pressure in the space between the outer peripheral surface of the shaft member and the bearing sleeve (the space including the radial bearing gap), one of the inclined grooves is extended as the radial dynamic pressure generating portion in the axial direction. An asymmetric herringbone-shaped dynamic pressure groove may be provided. In this case, the bearing span may be reduced as much as one of the inclined grooves is extended. Therefore, if the thrust dynamic pressure generating portion is a pump-in type as described above, oil is sent from the thrust bearing gap into the space between the outer peripheral surface of the shaft member and the bearing sleeve. Occurrence can be prevented. Thereby, since the herringbone-shaped dynamic pressure groove as the radial dynamic pressure generating portion can be formed in an axially symmetric shape, the reduction of the bearing span can be avoided.

  The thrust dynamic pressure generating portion can be formed, for example, by pressing on both end faces of the bearing sleeve. Alternatively, the thrust dynamic pressure generating portion can be formed on the end surfaces of the first seal portion and the second seal portion by pressing.

  The radial dynamic pressure generating portion can be formed, for example, by pressing on the inner peripheral surface of the bearing sleeve. Alternatively, the radial dynamic pressure generating portion can be formed on the outer peripheral surface of the shaft member by rolling.

  As described above, according to the shaft-fixed fluid dynamic bearing device according to the present invention, the radial bearing is reduced by reducing the porosity in the axial region of the radial bearing surface in the sintered sleeve made of sintered metal. The pressure drop in the oil film in the gap can be suppressed to prevent the radial bearing force from decreasing, and the volume of the seal space can be reduced by reducing the amount of oil, reducing the size of the hydrodynamic bearing device or expanding the bearing span. Can be achieved.

It is sectional drawing of the spindle motor of the disk drive device of HDD incorporating the fluid dynamic pressure bearing apparatus which concerns on embodiment of this invention. It is sectional drawing of the said fluid dynamic pressure bearing apparatus. It is a bottom view of the 1st seal part of the above-mentioned fluid dynamic pressure bearing device. It is a top view of the 2nd seal part of the above-mentioned fluid dynamic pressure bearing device. It is a front view of the shaft member of the fluid dynamic pressure bearing device concerning other embodiments.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a sectional view of a spindle motor for information equipment incorporating a fluid dynamic bearing device 1 according to the present invention. This spindle motor is used, for example, in an HDD disk drive device, and includes a stator coil 4 provided on the fixed side (base 6a) and a rotor magnet 5 provided on the rotation side (disk hub 3). The fluid dynamic pressure bearing device 1 is a so-called fixed shaft type in which the shaft member 2 is on the fixed side and the housing 7 and the bearing sleeve 8 are on the rotation side. In the present embodiment, both axial ends of the shaft member 2 are fixed. In the illustrated example, the lower end portion of the shaft member 2 is fixed to the base 6a and the upper end portion is fixed to the cover 6b. The disk hub 3 is fixed to the outer peripheral surface of the housing 7. A predetermined number (two in the illustrated example) of disks D are mounted on the disk hub 3. The fixed portion between the disk hub 3 and the housing 7 is provided on the outer diameter side of the radial bearing portions R1 and R2. Specifically, the axial region of the fixed portion between the disc hub 3 and the housing 7 overlaps at least a part of the axial region of the radial bearing portions R1 and R2 in the radial direction, and in the illustrated example, the radial bearing portions R1 and R2 are overlapped. It overlaps with the whole area of the axial direction in the radial direction. In the spindle motor configured as described above, when the stator coil 4 is energized, the rotor magnet 5 rotates, and accordingly, the disk hub 3, the disk D, the housing 7, and the bearing sleeve 8 rotate together.

  As shown in FIG. 2, the fluid dynamic bearing device 1 includes a shaft member 2 on the fixed side, a shaft sleeve 2 on the inner periphery, a bearing sleeve 8 on the rotation side, and a bearing sleeve on the inner peripheral surface 7a. 8 is fixed and has a cylindrical housing 7 that is open at both ends in the axial direction, and a first seal portion 10 that protrudes from the outer peripheral surface 2a of the shaft member 2 to the outer diameter side and is disposed on both axial sides of the bearing sleeve. And the second seal portion 11. In the following, for convenience of explanation, in the axial direction, the side where the shaft member 2 protrudes greatly from the housing 7 is defined as the lower side, and the opposite side is defined as the upper side.

  The shaft member 2 is made of, for example, stainless steel and has a substantially cylindrical shape. For example, when applied to a spindle motor of a 2.5 inch HDD disk drive device, the diameter of the shaft member 2 is in the range of 2 to 4 mm. The lower end portion of the shaft member 2 is integrally provided with a press-fit portion 2b that protrudes downward from the lower opening of the housing 7 and has a slightly smaller diameter than other regions. The press-fit portion 2b is formed in the fixing hole 6a1 of the base 6a. It is press-fitted and fixed. An axial screw hole 2c is formed at the upper end of the shaft member 2, and a bolt or the like (not shown) is fixed to the screw hole 2c through a fixing hole 6b1 provided in the cover 6b. 2 is fixed to the cover 6b.

  A radial bearing surface is formed on the outer peripheral surface 2a of the shaft member 2, and in the illustrated example, radial bearing surfaces 2a1, 2a2 are formed at two locations separated in the axial direction. Radial dynamic pressure generating portions are respectively formed on the radial bearing surfaces 2a1 and 2a2. In the present embodiment, herringbone-shaped dynamic pressure grooves G1 and G2 are formed as radial dynamic pressure generating portions. In the illustrated example, the dynamic pressure grooves G1 and G2 each have an axially symmetric shape. The groove depths of the dynamic pressure grooves G1 and G2 are set, for example, in the range of 2.5 to 5 μm. The dynamic pressure grooves G1 and G2 are formed by rolling, for example. Specifically, by pressing the mold, a part of the outer peripheral surface 2a of the shaft member 2 is recessed to form the dynamic pressure grooves G1 and G2, and the regions between the circumferential directions of the dynamic pressure grooves G1 and G2 are formed. It becomes hill part G1'G2 '.

  Of the outer peripheral surface 2a of the shaft member 2, cylindrical surfaces 2a3 and 2a4 are formed on the shaft end sides of the radial bearing surfaces 2a1 and 2a2. The cylindrical surfaces 2a3 and 2a4 are continuously provided on the same cylindrical surface as the hill portions G1 'and G2'. The cylindrical surfaces 2a3 and 2a4 function as fixed surfaces to which the first seal portion 10 and the second seal portion 11 are fixed. Between the axial directions of the radial bearing surfaces 2a1 and 2a2 of the outer peripheral surface 2a of the shaft member 2, an escape portion 2a5 formed with a slightly smaller diameter than the radial bearing surfaces 2a1 and 2a2 (dynamic pressure grooves G1 and G2) is formed. . The upper and lower ends of the escape portion 2a5 are continuous with the radial bearing surfaces 2a1 and 2a2 through the inclined surface.

  The bearing sleeve 8 is formed of a sintered metal in a substantially cylindrical shape. For example, a copper-based sintered metal mainly composed of copper, a copper-iron-based sintered metal mainly composed of iron, or copper and iron. In this embodiment, it is formed with a copper iron-based sintered metal. A radial bearing surface facing the radial bearing surfaces 2a1 and 2a2 of the shaft member 2 via a radial bearing gap is provided on the inner peripheral surface 8a of the bearing sleeve 8. In the illustrated example, the inner peripheral surface 8a of the bearing sleeve 8 is a smooth cylindrical surface without irregularities, and this cylindrical inner peripheral surface 8a functions as a radial bearing surface. Thrust bearing surfaces facing the thrust bearing surfaces of the first seal portion 10 and the second seal portion 11 with a thrust bearing gap are provided on the upper end surface 8b and the lower end surface 8c of the bearing sleeve. In the illustrated example, the upper end surface 8b and the lower end surface 8c of the bearing sleeve are flat surfaces without irregularities, and the upper end surface 8b and the lower end surface 8c function as thrust bearing surfaces.

Of the bearing sleeve 8, the porosity in the axial region of the radial bearing surface is set to 11% or less. Specifically, in the bearing sleeve 8, an axial region (first region H1) above the lower end of the upper radial bearing surface, and an axial region below the upper end of the lower radial bearing surface ( The porosity in the second region H2) is set to 11% or less, respectively. For example, when the bearing sleeve 8 is made of a copper iron-based sintered metal containing 60% or more of copper, the density in the first region H1 and the second region H2 is set to 7.4 g / cm ³ or more. When the bearing sleeve is made of a copper-iron sintered metal containing 60% or more of iron, the density in the first region H1 and the second region H2 is set to 7.1 g / cm ³ or more. The porosity in the first region H1 and the second region H2 is preferably as small as possible, but the lower limit is about 9% in consideration of the strength of the molding die for molding the sintered metal.

  Of the bearing sleeve 8, the porosity in the axial region (third region H3) between the first region H1 and the second region H2 is set to be larger than the porosity in the first region H1 and the second region H2. For example, it is set larger than 11%. Note that the porosity in the third region H3 is preferably as large as possible, but the upper limit is about 15% in consideration of the formability of the sintered metal and the like.

  A communication passage 12 is provided between the outer peripheral surface 8d of the bearing sleeve 8 and the inner peripheral surface 7a of the housing 7 to communicate a first seal space S1 and a second seal space S2, which will be described later. In the present embodiment, a predetermined number of axial grooves 8d1 extending in the axial direction are formed on the outer peripheral surface 8d of the bearing sleeve 8, and for example, three axial grooves 8d1 are formed at equally spaced positions in the circumferential direction. In the assembled state of the fluid dynamic bearing device 1, as shown in FIG. 2, a communication path 12 is formed by the axial groove 8 d 1 of the bearing sleeve 8 and the inner peripheral surface 7 a of the housing 7. Both seal spaces S1 and S2 formed in the opening portions at both ends of the housing 7 are communicated. In this embodiment, the radial dynamic pressure generating portion is formed in an axially symmetric shape, but the dynamic pressure grooves G1 and G2 cannot be formed in a completely axially symmetric shape and are slightly unsatisfactory due to processing errors. Formed in balance. For this reason, the oil in the radial bearing gap is pushed in one axial direction (upper or lower), and the oil may leak out from one seal space on the side where the oil is pushed. Therefore, by providing the communication passage 12 that communicates both the seal spaces S1 and S2 as described above, it is possible to avoid a situation in which oil is unevenly distributed in one seal space and to prevent oil leakage.

  The bearing sleeve 8 is manufactured through a forming process, a sintering process, and a sizing process. First, in the forming step, a mixed metal powder containing copper-based metal powder and iron-based metal powder is compression-molded to form a substantially cylindrical green compact. Specifically, the green compact is formed by pressing the mixed metal powder filled in the cavity of the forming die (not shown) from the upper and lower sides with the upper punch and the lower punch. Next, in the sintering step, the green compact is sintered at a predetermined sintering temperature, whereby the metal powders are bonded to form a sintered body. In the sizing process, the sintered body is further compression-molded to increase the dimensional accuracy. Specifically, the green compact is shaped to a predetermined size by pressing a sintered body placed inside a sizing die (not shown) from above and below with an upper punch and a lower punch. Thus, the bearing sleeve 8 is completed. In the present embodiment, sealing processing such as rotational sizing is not performed after the sizing process. That is, the surface of the bearing sleeve 8 remains in a state where it is molded in the sizing process.

  In the above forming process, the upper and lower end surfaces of the green compact are directly pressed by the upper and lower punches, so that the density in the vicinity thereof is higher than in other regions. In the above sizing process, the upper and lower end surfaces of the sintered body are directly pressed by the upper and lower punches, so that the density in the vicinity thereof is higher than in other regions. Accordingly, the density in the vicinity of the upper and lower end surfaces of the bearing sleeve 8 is relatively higher than the density of other regions, and the porosity of the first region H1 and the second region H2 is smaller than the porosity of the third region H3. Further, in order to reduce the porosity in the first region H1 and the second region H2 of the bearing sleeve 8, specifically, in order to set the porosity to 11% or less, in one or both of the forming process and the sizing process. It is necessary to set the compression rate higher than usual. In this case, the biting between the forming mold and the green compact, or the sizing mold and the sintered body is strong, and there is a risk that the mold release becomes difficult. However, the inner peripheral surface 8a of the bearing sleeve 8 is uneven as described above. By using a cylindrical surface shape without any shape, the molded product can be easily taken out from the mold.

  The housing 7 is formed in a cylindrical shape with a metal material or a resin material. In this embodiment, the housing 7 is formed in a cylindrical shape having both axial ends opened by brass (see FIG. 2). The outer peripheral surface 8d of the bearing sleeve 8 is fixed to the inner peripheral surface 7a of the housing 7 by, for example, gap adhesion. The method of fixing the housing 7 and the bearing sleeve 8 is not limited to this, and for example, means such as press-fitting, press-fitting with an adhesive interposed, or welding (including ultrasonic welding and laser welding) can be employed.

  The first seal portion 10 and the second seal portion 11 are formed in a ring shape with a metal material or a resin material, and are formed by, for example, pressing a metal plate. The first seal portion 10 and the second seal portion 11 are fixed to the cylindrical surfaces 2a3 and 2a4 of the outer peripheral surface 2a of the shaft member 2 by any means such as press fitting, adhesion, welding, welding, and caulking. The outer peripheral surface 10a of the first seal portion 10 and the outer peripheral surface 11a of the second seal portion 11 have a tapered surface shape that gradually increases in diameter toward the axial center. Between the outer peripheral surface 10a of the first seal portion 10 and the outer peripheral surface 11a of the second seal portion 11 and the cylindrical inner peripheral surface 7a of the housing 7, the radial width gradually increases toward the axial center. A reduced wedge-shaped first seal space S1 and second seal space S2 are formed.

  The lower end surface 10b of the first seal portion 10 and the upper end surface 11b of the second seal portion 11 each function as a thrust bearing surface. A thrust dynamic pressure generating portion is formed on each thrust bearing surface. In the present embodiment, a pump-in type thrust dynamic pressure generating portion that causes oil in the thrust bearing gap to flow to the inner diameter side is formed, and in the illustrated example, pump-in type spiral dynamic pressure grooves G3 and G4 are formed ( 3 and 4). Spiral hill portions G3 'and G4' are formed between the circumferential directions of the dynamic pressure grooves G3 and G4. In the illustrated example, the inner diameter ends of the hill portions G3 'and G4' are connected by an annular flat portion. The thrust dynamic pressure generating portion is formed by, for example, pressing, and in this embodiment, the thrust dynamic pressure generating portion is formed simultaneously with the pressing of the first seal portion 10 and the second seal portion 11.

  The fluid dynamic bearing device 1 including the above components is assembled as follows. First, the shaft member 2 is inserted into the inner periphery of the bearing sleeve 8 and the first seal portion 10 and the second seal portion 11 are fitted from both axial ends of the shaft member 2. A thrust bearing gap between the end surface 10b of the first seal portion 10 and the upper end surface 8b of the bearing sleeve 8 and a thrust between the end surface 11b of the second seal portion 11 and the lower end surface 8c of the bearing sleeve 8 are provided. The first seal portion 10 and the second seal portion 11 are fixed to the shaft member 2 with the bearing gap set to a predetermined amount. At this time, since the outer circumferences of the bearing sleeve 8 and the seal portions 10 and 11 are not covered with the housing 7, the size of the thrust bearing gap can be confirmed from the outer circumference, and the thrust bearing gap can be set easily and accurately. be able to. Then, a sub-assembly including the shaft member 2, the bearing sleeve 8, the first seal portion 10, and the second seal portion 11 is inserted into the inner periphery of the housing 7, and the inner peripheral surface 7 a of the housing 7 and the outer peripheral surface of the bearing sleeve 8. 8d is fixed.

  Then, by injecting lubricating oil into the space between the fixed side members (the shaft member 2, the first seal portion 10, and the second seal portion 11) and the rotation side members (the bearing sleeve 8 and the housing 7). Thus, the fluid dynamic bearing device 1 is completed. Specifically, the space between the first seal space S1 and the second seal space S2 is filled with lubricating oil including the internal pores of the bearing sleeve 8 without interruption, and the oil level is always the first seal space S1 and It is held inside the second seal space S2.

  At this time, the amount of oil impregnated in the internal pores of the bearing sleeve 8 may be reduced by reducing the porosity in a part of the bearing sleeve 8 (in the present embodiment, the first region H1 and the second region H2). it can. Thereby, since the volume change of the oil injected into the fluid dynamic pressure bearing device 1 is suppressed, the volumes of the first seal space S1 and the second seal space S2 can be reduced. Accordingly, the size (particularly the axial dimension) of the first seal portion 10 and the second seal portion 11 can be reduced, so that the fluid dynamic bearing device 1 can be downsized, or the bearing sleeve 8 can be reduced. Can be extended in the axial direction to expand the bearing span and improve the bearing rigidity.

  In the fluid dynamic pressure bearing device 1 configured as described above, when the disk hub 3, the housing 7, and the bearing sleeve 8 rotate together, the inner peripheral surface 8 a (radial bearing surface) of the bearing sleeve 8 and the outer peripheral surface of the shaft member 2. A radial bearing gap is formed between the radial bearing surfaces 2a1 and 2a2 of 2a. Then, the pressure of the oil film in the radial bearing gap is increased by the dynamic pressure grooves G1 and G2, and the radial bearing portions R1 and R2 that support the rotation-side member including the bearing sleeve 8 in the radial direction without contact by this dynamic pressure action are shafts. It is formed in two places separated in the direction.

  At the same time, between the upper end surface 8b (thrust bearing surface) of the bearing sleeve 8 and the lower end surface 10b (thrust bearing surface) of the first seal portion 10, and the lower end surface 8c (thrust bearing surface) of the bearing sleeve 8. ) And the upper end surface 11b (thrust bearing surface) of the second seal portion 11, respectively, a thrust bearing gap is formed. Then, the pressure of the oil film in both thrust bearing gaps is increased by the dynamic pressure grooves G3, G4, and the thrust bearing portions T1, T2 for supporting the rotating side member including the bearing sleeve 8 in the non-contact manner in both thrust directions by this dynamic pressure action. Is formed.

  At this time, since the porosity of the first region H1 and the second region H2 of the bearing sleeve 8 is small as described above, in the radial bearing surface and the thrust bearing surface formed in the first region H1 and the second region H2. Since the surface open area ratio is small, the infiltration of oil from these bearing surfaces into the bearing sleeve 8 can be suppressed. Further, when the bearing sleeve 8 rotates, centrifugal force is applied to the oil impregnated inside the bearing sleeve 8, but these regions are impregnated due to the low porosity of the first region H1 and the second region H2. The flow of oil to the outer diameter side can be suppressed. As a result, the oil in the radial bearing gap and the thrust bearing gap is less likely to escape into the bearing sleeve 8, and the oil film pressure drop that occurs in each bearing gap can be prevented.

  Further, since the thrust dynamic pressure generating portion is a pump-in type, the oil in the thrust bearing gap is pushed into the inner diameter side, and the space between the outer peripheral surface 2a of the shaft member 2 and the inner peripheral surface 8a of the bearing sleeve 8 ( Oil flows into the space including the radial bearing clearance from both sides in the axial direction. As a result, oil is supplied to a region between the axial directions of the first radial bearing portion R1 and the second radial bearing portion R2 (space facing the escape portion 2a5), and generation of negative pressure in this region can be prevented. Therefore, the radial dynamic pressure generating portion does not need to have an axially asymmetric shape, but can have an axially symmetric shape as shown in FIG. 2, and a reduction in bearing span can be avoided.

  The present invention is not limited to the above embodiment. Hereinafter, although other embodiment of this invention is described, the same code | symbol is attached | subjected to the location which has the same structure and function as the said embodiment, and duplication description is abbreviate | omitted.

  For example, in the above embodiment, herringbone-shaped dynamic pressure grooves G1 and G2 as shown in FIG. 2 are shown as the radial dynamic pressure generating portion, but the present invention is not limited to this. For example, as shown in FIG. 5, an annular smooth portion G5 may be provided in the center portion in the axial direction of the dynamic pressure grooves G1 and G2. The smooth portion G5 is continuous on the same cylindrical surface as the hill portions G1 'and G2'.

  Further, the radial dynamic pressure generating portion is not limited to the herringbone-shaped dynamic pressure groove, but can be configured by a spiral-shaped dynamic pressure groove or an axial groove having a step shape or a wave shape in the circumferential direction. Alternatively, the radial dynamic pressure generating unit can be configured by a multi-arc surface obtained by combining a plurality of arcs.

  Further, in the above embodiment, the radial dynamic pressure generating portion is formed on the radial bearing surfaces 2 a 1 and 2 a 2 of the shaft member 2, but the radial dynamic pressure generating portion is not limited to this and the inner peripheral surface 8 a of the bearing sleeve 8. You may form in the radial bearing surface provided in this. In this case, the radial dynamic pressure generating portion can be formed by, for example, pressing, and in particular, can be press-molded simultaneously with the sizing process of the bearing sleeve 8. Or you may comprise what is called a perfect-circular bearing by which both the radial bearing surface of the inner peripheral surface 8a of the bearing sleeve 8 and the radial bearing surface 2a1, 2a2 of the outer peripheral surface 2a of the shaft member 2 are cylindrical surfaces. . In this case, a dynamic pressure generating portion that actively generates the dynamic pressure action is not formed, but the dynamic pressure action is generated by a slight swing of the bearing sleeve 8.

  In the above embodiment, the thrust dynamic pressure generating portion is formed on the end surface 10b of the first seal portion 10 and the end surface 11b of the second seal portion 11. However, the present invention is not limited to this, and the thrust dynamic pressure generating portion is a bearing. You may form in the thrust bearing surface provided in the upper-and-lower-end surfaces 8b and 8c of the sleeve 8. FIG. In this case, the thrust dynamic pressure generating portion can be formed by, for example, pressing, and in particular, can be press-molded simultaneously with the sizing process of the bearing sleeve 8.

  In the above embodiment, pump-in type spiral-shaped dynamic pressure grooves G3 and G4 as shown in FIGS. 3 and 4 are shown as the thrust dynamic pressure generating portion. However, the present invention is not limited to this. For example, although not shown in the drawing, the thrust dynamic pressure generating portion can be configured by a herringbone-shaped dynamic pressure groove or a radial groove having a step shape or a wave shape in the circumferential direction.

  In the above-described embodiment, the first seal portion 10 and the second seal portion 11 are both formed separately from the shaft member 2. However, the present invention is not limited to this. For example, one seal portion is connected to the shaft member. 2 may be integrally formed.

  In the above embodiment, the case where the bearing sleeve 8 is not subjected to the sealing treatment has been described. However, the present invention is not limited thereto, and the sealing treatment such as rotational sizing may be performed after the sizing step. Even in this case, since the surface opening ratio is reduced by reducing the porosity of the bearing sleeve 8, it is possible to reduce the processing cost by reducing the burden of the sealing process.

  In the above embodiment, an example in which the fluid dynamic pressure bearing device according to the present invention is incorporated in a spindle motor of an HDD disk drive device is shown. It can also be applied to a polygon scanner motor of a laser beam printer (LBP) or a color wheel motor of a projector.

DESCRIPTION OF SYMBOLS 1 Fluid dynamic pressure bearing apparatus 2 Shaft member 7 Housing 8 Bearing sleeve 10 1st seal part 11 2nd seal part 12 Communication path D Disk G1, G2 Dynamic pressure groove (radial dynamic pressure generating part)
G3, G4 Dynamic pressure groove (Thrust dynamic pressure generator)
H1 1st region (Axial direction region of radial bearing surface)
H2 2nd area (Axial direction area of radial bearing surface)
H3 3rd region (Axial region other than radial bearing surface)
R1 1st radial bearing part R2 2nd radial bearing part T1 1st thrust bearing part T2 2nd thrust bearing part S1 1st seal space S2 2nd seal space

Claims (12)

The shaft member on the fixed side, the shaft member is inserted on the inner periphery, the sintered metal bearing sleeve on the rotation side, the outer peripheral surface of the bearing sleeve is fixed on the inner peripheral surface, and both ends in the axial direction are open A cylindrical housing, a first seal portion and a second seal portion which are provided to protrude from the outer peripheral surface of the shaft member to the outer diameter, and are arranged on both axial sides of the bearing sleeve, and the outer peripheral surface of the shaft member A radial bearing portion that supports the bearing sleeve in a radial direction by a dynamic pressure action of an oil film generated in a radial bearing gap between a radial bearing surface provided on the inner surface of the bearing sleeve and a radial bearing surface provided on the inner peripheral surface of the bearing sleeve; The bearing sleeve is thrust by the dynamic pressure action of the oil film generated in the thrust bearing gap between the thrust bearing surface provided on one end surface of the bearing sleeve and the thrust bearing surface provided on the end surface of the first seal portion. A thrust bearing gap between a first thrust bearing portion that is supported in one direction and a thrust bearing surface provided on the other end surface of the bearing sleeve and a thrust bearing surface provided on an end surface of the second seal portion. A first seal space formed between a second thrust bearing portion that supports the bearing sleeve in the other thrust direction by the dynamic pressure action of the generated oil film, and an outer peripheral surface of the first seal portion and an inner peripheral surface of the housing. And a second seal space formed between the outer peripheral surface of the second seal portion and the inner peripheral surface of the housing, and lubricates the space between the first seal space and the second seal space. A shaft-fixed type fluid dynamic bearing device that is filled with oil and has an oil level held in the first seal space and the second seal space,
The fluid dynamic bearing device according to claim 1, wherein a porosity in an axial region of the radial bearing surface of the bearing sleeve is smaller than a porosity in an axial region other than the radial bearing surface.   The fluid dynamic bearing device according to claim 1, wherein a porosity in an axial region of the radial bearing surface of the bearing sleeve is 11% or less. The fluid dynamic bearing device according to claim 2, wherein the bearing sleeve is made of a sintered metal containing 60% or more of copper, and a density in an axial region of the radial bearing surface is 7.4 g / cm ³ or more. ^3. The fluid dynamic bearing device according to claim 2, wherein the bearing sleeve is made of a sintered metal containing 60% or more of iron, and a density in an axial region of the radial bearing surface is 7.1 g / cm ³ or more.   The thrust dynamic pressure generating part that generates a dynamic pressure action on the oil film of the thrust bearing gap is formed on one of the thrust bearing surfaces facing each other through the thrust bearing gap of the first and second thrust bearing parts. 5. The fluid dynamic bearing device according to any one of 4 above.   The fluid dynamic pressure bearing device according to claim 5, wherein a radial dynamic pressure generating portion that generates a dynamic pressure action on an oil film of the radial bearing gap is formed on one of the radial bearing surfaces facing each other through the radial bearing gap.   The fluid dynamic pressure bearing device according to claim 6, wherein the thrust dynamic pressure generating portion is a pump-in type that allows the lubricating oil in the thrust bearing gap to flow toward the inner diameter side.   The fluid dynamic pressure bearing device according to claim 7, wherein the radial dynamic pressure generating portion is an axially symmetrical herringbone-shaped dynamic pressure groove.   The fluid dynamic pressure bearing device according to claim 5, wherein the thrust dynamic pressure generating portion is formed by pressing on both end faces of the bearing sleeve.   The fluid dynamic pressure bearing device according to claim 5, wherein the thrust dynamic pressure generating portion is formed by pressing on end surfaces of the first seal portion and the second seal portion.   The fluid dynamic pressure bearing device according to claim 6, wherein the radial dynamic pressure generating portion is formed on the inner peripheral surface of the bearing sleeve by pressing.   The fluid dynamic bearing device according to claim 6, wherein the radial dynamic pressure generating portion is formed on a peripheral surface of the shaft member by rolling.

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