JP2015055312A - Fluid dynamic pressure bearing device, and inner member manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain deterioration of bearing rigidity in a sintered metallic inner member on the outer periphery of which a radial dynamic pressure generation part is formed by roll-processing.SOLUTION: A fluid dynamic pressure bearing device comprises: an outer member 20; an inner member 10 made of sintered metal; a radial bearing gap R formed between an outer periphery 11 of the inner member 10 and an inner periphery 20a of the outer member; a thrust bearing gap T formed between both axial ends 12 of the inner member 10 and an inner face 20b of the outer member 20; lubrication oil filling the radial bearing gap R and the thrust bearing gap T; and a radial dynamic pressure generation part (a dynamic pressure groove 11a) formed on the outer periphery 11 of the inner member 10 by roll-processing. Porosity of the inner member 10 ia made to 20% or more.

Description

  The present invention relates to a fluid dynamic pressure bearing device that supports an inner member so as to be relatively rotatable by a dynamic pressure action of lubricating oil generated in a bearing gap between the inner member and the outer member, and an inner member incorporated therein. It relates to the manufacturing method.

  A motor mounted on an electric device such as a ventilation fan incorporates a bearing, and the rotating shaft is supported by the bearing so as to be relatively rotatable. As this type of bearing, a so-called rolling bearing comprising an outer ring, an inner ring, a plurality of rolling elements interposed therebetween, and a cage for holding the plurality of rolling elements is generally used ( For example, Patent Document 1).

  For example, a small ventilation fan installed in a house, especially a small ventilation fan provided in a 24-hour ventilation system, is required to be low in cost, but the rolling bearing is composed of many parts as described above. Therefore, there is a limit to cost reduction. Moreover, since the ventilation fan of the said system is fundamentally operated continuously, it is calculated | required that it is especially low noise. However, rolling bearings avoid the generation of so-called cage noise caused by collision between the cage pocket and rolling elements during operation, and friction noise caused by rolling of the rolling elements on the raceway surface of the inner and outer rings. Since it is not possible, it is difficult to meet the demand for further improvement in quietness.

  In view of the above circumstances, a fluid dynamic pressure bearing may be used as a bearing incorporated in a motor such as a ventilation fan. For example, a fluid dynamic pressure bearing device disclosed in Patent Document 2 includes an inner member and outer members that surround the outer peripheral surface and both end surfaces of the inner member. When the inner member rotates, the inner member A radial bearing gap is formed between the outer peripheral surface of the outer member and the inner peripheral surface of the outer member, and a thrust bearing gap is formed between each axial end surface of the inner member and the inner side surface of the outer member. The inner member is rotatably supported by the dynamic pressure generated in the lubricating oil in the radial bearing gap and the thrust bearing gap. Thus, by replacing the rolling bearing with a fluid dynamic pressure bearing, the cost is reduced by reducing the number of parts and the quietness is improved.

  In the above fluid dynamic pressure bearing device, the inner member is formed of sintered metal, and the dynamic pressure groove is formed on the outer peripheral surface thereof by rolling. As a result, the plastic flow of the inner member due to the compression of the rolling process can be absorbed by the internal pores of the sintered metal, so that the rise of the surface of the inner member due to the plastic flow is suppressed, and the dynamic pressure is applied to the outer peripheral surface of the inner member. The groove can be formed with high accuracy.

  In the above fluid dynamic pressure bearing device, the outer member is constituted by a first outer member that forms one thrust bearing gap and a second thrust bearing gap that forms the other thrust bearing gap. In this fluid dynamic bearing device, the thrust bearing gap is set as follows. First, the inner side surfaces of the first and second outer members are brought into contact with both axial end surfaces of the inner member so that the thrust bearing gap is zero. Thereafter, the first outer member and the second outer member are relatively moved in the axial direction, and the inner side surface of the outer member is separated from the end surface of the inner member by the set value of the thrust bearing gap, The thrust bearing gap is set by fixing the first outer member and the second outer member in the state. Thus, the thrust bearing gap can be set with high accuracy and easily by setting the thrust bearing gap by the amount of movement of the outer member relative to the inner member.

JP 2000-249142 A JP 2011-231874 A

  However, when the dynamic pressure grooves are formed on the outer peripheral surface of the inner member made of sintered metal by rolling, usually both end surfaces in the axial direction of the inner member are not restrained. In some cases, not only the outer peripheral surface (radial bearing surface) of the inner member but also both axial end surfaces (thrust bearing surfaces) of the inner member. Specifically, as shown in an exaggerated manner in FIG. 11, the material of the inner member 101 plastically flows on both sides in the axial direction due to the compression of the rolling process on the outer peripheral surface 101a of the inner member 101. The outer peripheral portion of the end surface 101b of the inner member 101 may rise. Due to the swelled portion 101c, the thrust bearing gap T may become non-uniform and the bearing rigidity in the thrust direction may be reduced. In particular, when the thrust bearing gap T is set by the amount of movement of the outer member 102 relative to the inner member 101 as in Patent Document 2, the raised portion 101 c of the end surface 101 b of the inner member 101 and the inner surface of the outer member 102 are set. 102a abuts (see the dotted line in FIG. 11), the height (axial dimension) α of the raised portion 101c is already between the end surface 101b of the inner member 101 and the inner side surface 102a of the outer member 102. An axial gap is formed. Thereafter, when the inner surface 102a of the outer member 102 is separated from the end surface 101b of the inner member 101 by the set value Δ of the thrust bearing gap T, the end surface 101b of the inner member 101 and the inner surface of the outer member 102 are separated. The size of the thrust bearing gap T ′ with respect to 102a is the total amount of the height α of the raised portion 101c and the set value Δ of the thrust bearing gap (T ′ = Δ + α). As described above, when the thrust bearing gap T ′ larger than the set value Δ is formed, the lubricating oil pressure in the thrust bearing gap T ′ may not be sufficiently increased, and the bearing rigidity in the thrust direction may be insufficient.

  For example, after forming a dynamic pressure groove on the outer peripheral surface of the inner member by rolling, sizing the inner member to eliminate the rise of the end surface of the inner member can be considered. However, when sizing the inner member, the outer peripheral surface is compressed, so that the dynamic pressure groove formed on the outer peripheral surface is crushed and the groove depth becomes shallow, and the bearing rigidity in the radial direction may be reduced.

  In view of the above circumstances, the present invention is a technical problem to be solved for suppressing a decrease in bearing rigidity in an inner member made of sintered metal in which a radial dynamic pressure generating portion is formed on the outer peripheral surface by rolling. And

  The present invention made in order to solve the above problems includes an outer member, an inner member made of sintered metal disposed on the inner periphery of the outer member, an outer peripheral surface of the inner member, and an inner member of the outer member. The radial bearing gap formed between the circumferential surface, the axial end of the inner member and the inner surface of the outer member facing the axial end, and the other axial end of the inner member A thrust bearing gap formed between the end face of the outer member and the inner side surface of the outer member facing in the axial direction, the lubricating oil filled in the radial bearing gap and the thrust bearing gap, and the outer peripheral surface of the inner member In addition, the fluid dynamic pressure bearing device includes a radial dynamic pressure generating portion formed by rolling, and the porosity of the inner member is 20% or more.

  Further, the present invention made to solve the above-mentioned problems includes a radial bearing surface provided on the outer peripheral surface, a thrust bearing surface provided on both end surfaces in the axial direction, and generation of radial dynamic pressure formed on the radial bearing surface. A compression molding step of forming a green compact by compressing a mixed metal powder, and a green compact. Sintering the body at a predetermined sintering temperature to form a sintered body, a sizing process for shaping the sintered body into a predetermined size, and after the sizing process, the sintered body is not restrained from both sides in the axial direction. And forming a radial dynamic pressure generating portion on the outer peripheral surface of the sintered body by rolling, and setting the conditions of each step so that the porosity is 20% or more. .

  As described above, by setting the porosity of the sintered metal inner member to 20% or more, the radial dynamic pressure generating portion is molded on the outer peripheral surface without restricting both end surfaces of the inner member. Even if it exists, the rise | swell of the axial direction both end surfaces of an inner member can be suppressed to the height (for example, 5 micrometers or less) which does not affect a thrust bearing clearance gap. Thereby, since the surface accuracy of the axial direction both end surfaces of the inner member can be maintained with high accuracy, the thrust bearing gap can be set with high accuracy, and excellent bearing rigidity in the thrust direction can be obtained. In this case, since it is not necessary to perform sizing after the radial dynamic pressure generating portion is formed, it is possible to avoid a decrease in bearing rigidity in the radial direction due to a decrease in accuracy of the radial dynamic pressure generating portion. The porosity is the ratio of the pore volume to the volume of the sintered metal, and can be roughly estimated by, for example, the aperture ratio at the cut surface of the sintered metal.

  Moreover, this invention made | formed in order to solve the said subject is the outer member, the inner member which consists of a sintered metal distribute | arranged to the inner periphery of an outer member, the outer peripheral surface of an inner member, and an outer member A radial bearing gap formed between the inner peripheral surface of the inner member and the inner member between one end surface in the axial direction of the inner member and the inner surface of the outer member facing in the axial direction, and the shaft of the inner member. A thrust bearing gap formed between the other end face in the direction and the inner surface of the outer member facing the axial direction, a lubricating oil filled in the radial bearing gap and the thrust bearing gap, and an inner member A hydrodynamic bearing device including a radial dynamic pressure generating portion formed by rolling on an outer peripheral surface, wherein an outer peripheral region of both end surfaces in the axial direction of an inner member is axially inward of the inner peripheral region in advance. The outer peripheral area is moved outward in the axial direction by plastic flow by the above rolling process. A.

  Further, the present invention made to solve the above-mentioned problems includes a radial bearing surface provided on the outer peripheral surface, a thrust bearing surface provided on both end surfaces in the axial direction, and generation of radial dynamic pressure formed on the radial bearing surface. A compression molding step of forming a green compact by compressing a mixed metal powder, and a green compact. A sintering process for forming a sintered body by firing the body at a predetermined sintering temperature, and a sizing process for forming a radial bearing surface and a thrust bearing surface on the sintered body by shaping the sintered body to a predetermined size. And a rolling step for forming a radial dynamic pressure generating portion on the outer peripheral surface of the sintered body by a rolling process without restraining the sintered body from both sides in the axial direction after the sizing step. The outer peripheral area of both ends of the bonded body in the axial direction is more axially inner than the inner peripheral area. It is not formed retracted, and moves the outer peripheral region of the axial end surfaces of the sintered body axially outwardly by plastic flow due to the rolling.

  As described above, the axial direction of the inner member after the rolling process is preliminarily retracted to the inner side in the axial direction in consideration of the bulge caused by the rolling process. Both end surfaces can be formed with excellent surface accuracy. Thereby, since the thrust bearing gap can be set with high accuracy, excellent bearing rigidity in the thrust direction can be obtained. In this case, since it is not necessary to perform sizing after the radial dynamic pressure generating portion is formed, it is possible to avoid a decrease in bearing rigidity in the radial direction due to a decrease in accuracy of the radial dynamic pressure generating portion.

  Further, the present invention made to solve the above problems includes an outer member, an inner member made of a sintered metal disposed on an inner periphery of the outer member, an outer peripheral surface of the inner member, and the outer member. A radial bearing gap formed between the inner peripheral surface of the member, an axial end surface of the inner member and the inner surface of the outer member facing the axial direction of the inner member, and the inner member A thrust bearing gap formed between the other end face in the axial direction and the inner side surface of the outer member facing the axial direction, the lubricating oil filled in the radial bearing gap and the thrust bearing gap, and the inner member The hydrodynamic bearing device is provided with a radial dynamic pressure generating portion formed by rolling on the outer peripheral surface of the outer member, and the inner side surface of the outer member is provided on the flat portion and the outer diameter side of the flat portion. And an escape portion that recedes axially outward from the flat portion.

  In this way, by providing a relief portion that is retracted axially outward from the flat portion on the outer diameter side of the flat portion of the inner side surface of the outer member, this relief portion is axially formed by rolling the inner member. It can be made to oppose in the axial direction to the rising part formed in the outer peripheral area | region of both end surfaces. Thus, by making the raised portion face the escape portion, the accuracy of the thrust bearing gap is prevented from being lowered by the raised portion, and excellent bearing rigidity in the thrust direction can be maintained. In this case, since it is not necessary to perform sizing after the radial dynamic pressure generating portion is formed, it is possible to avoid a decrease in bearing rigidity in the radial direction due to a decrease in accuracy of the radial dynamic pressure generating portion.

  In the fluid dynamic pressure bearing device as described above, the surface area ratio of at least the radial bearing clearance and the thrust bearing clearance (radial bearing surface and thrust bearing surface) of the inner member is 20% or less. Is preferred. When the surface opening ratio of the radial bearing surface and the thrust bearing surface is larger than 20%, the lubricating oil filled in each bearing gap easily enters the inside from the surface opening of the inner member. This is because the pressure is not sufficiently increased, and there is a risk of insufficient bearing rigidity.

  Further, in the fluid dynamic pressure bearing device as described above, the outer member has a first outer member having an inner surface facing one end surface in the axial direction of the inner member, and the other end surface in the axial direction of the inner member. And a second outer member having an inner surface facing each other, and is particularly effective when the thrust bearing gap is set by relatively moving the first outer member and the second outer member in the axial direction. .

  As described above, according to the present invention, in the inner member made of sintered metal in which the radial dynamic pressure generating portion is formed on the outer peripheral surface by rolling, the reduction in the bearing rigidity in the radial direction and the thrust direction is suppressed. Can do.

It is a longitudinal cross-sectional view of the bearing unit for ventilation fan motors. 1 is a longitudinal sectional view of a fluid dynamic bearing device according to an embodiment of the present invention. (A) is the side view which looked at the inward member from A direction of FIG. 2, (b) is the side view seen from the B direction, (c) is the side view seen from the C direction. It is sectional drawing which shows the compression molding process of an inner member. It is sectional drawing which shows the sizing process of an inner member. It is sectional drawing which shows the rolling process of an inner member. It is sectional drawing which shows the assembly process of a fluid dynamic pressure bearing apparatus. It is an expanded sectional view of the inward member of the fluid dynamic pressure bearing device concerning other embodiments. It is an expanded sectional view of the fluid dynamic bearing device concerning other embodiments. It is an expanded sectional view of the fluid dynamic bearing device concerning other embodiments. It is an expanded sectional view of the conventional fluid dynamic bearing device.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is an axial sectional view of a bearing unit 1 incorporating a fluid dynamic bearing device 4 according to an embodiment of the present invention. The bearing unit 1 is used, for example, by being incorporated in a small ventilation fan motor (more strictly speaking, an inner rotor type motor for a ventilation fan) of a 24-hour ventilation system installed in a living room of a house. The bearing unit 1 is a motor rotor for rotatably supporting a rotating body including a rotating shaft 2, a motor rotor 3 fixed to the outer peripheral surface of the rotating shaft 2, and a fan 6 provided at an end of the rotating shaft 2. 3, and a pair of fluid dynamic bearing devices 4, 4 disposed between the rotating shaft 2 and the housing 5. A spring 7 is disposed in a compressed state between the fluid dynamic bearing device 4 and the housing 5 on one axial side (the right side in the figure). The stator is not shown.

  As shown in FIG. 2, the fluid dynamic bearing device 4 includes an inner member 10, and an outer member 20 in which the inner member 10 is arranged on the inner periphery and rotatably supports the inner member 10. The inner peripheral surface 13 of the inner member 10 is fixed to the outer peripheral surface of the rotating shaft 2 by press-fitting or bonding (see FIG. 1). The outer peripheral surface 22a2 of the outer member 20 is fitted to the inner peripheral surface of the housing 5 and attached so as to be slidable in the axial direction (see FIG. 1). Lubricating oil is interposed between the surfaces of the inner member 10 and the outer member 20 (radial bearing gap R and thrust bearing gap T) facing each other in the axial direction and the radial direction (see FIG. 2). Note that the fluid dynamic bearing devices 4 and 4 in FIG. 1 have the same structure.

  The inner member 10 has an annular shape and a substantially cylindrical bearing portion 10 a having a substantially rectangular cross section, and a substantially cylindrical fixing that is provided on the inner periphery of the bearing portion 10 a and is fixed to the outer peripheral surface of the rotary shaft 2. Part 10b. In the present embodiment, the bearing portion 10a and the fixed portion 10b are integrally formed. In FIG. 2, a conceptual boundary between the bearing portion 10a and the fixed portion 10b is indicated by a dotted line.

  The inner member 10 is formed of a sintered metal, for example, a copper-based, iron-based, or copper-iron-based sintered metal. In this embodiment, it is formed of a copper iron-based sintered metal having a copper blending ratio of 20 to 80%. If the copper content is less than 20%, there will be a problem with the formability and lubricity of the dynamic pressure groove. On the other hand, if the copper content exceeds 80%, the iron content will be too low and wear resistance may be insufficient. Because there is. The porosity of the inner member 10 is 20% or more, preferably 25% or more. This is to prevent the end surface 12 from rising due to the rolling process of the dynamic pressure groove 11a of the outer peripheral surface 11 to be described later. On the other hand, if the porosity of the inner member 10 is too large, the strength may be insufficient. Moreover, the outer peripheral surface 11 which forms a radial bearing surface at least among the inward members 10 makes the surface opening rate of a sintered member 2-20%. This is because if the surface opening ratio is less than 2%, the circulation of the lubricating oil is not sufficient, and if the surface opening ratio exceeds 20%, the pressure of the lubricating oil decreases.

  The outer peripheral surface 11 of the bearing portion 10a of the inner member 10 forms a cylindrical surface, and this surface functions as a radial bearing surface. A dynamic pressure groove 11a is formed on the outer peripheral surface 11 of the bearing portion 10a as a radial dynamic pressure generating portion. In the present embodiment, for example, a herringbone-shaped dynamic pressure groove 11 a as shown in FIG. 3B is formed on the entire outer peripheral surface 11. End surfaces 12 on both axial sides of the bearing portion 10a of the inner member 10 extend in a direction orthogonal to the axial direction, and these surfaces function as thrust bearing surfaces. Dynamic pressure grooves 12a are formed as thrust dynamic pressure generating portions on the end faces 12 on both axial sides of the bearing portion 10a. In this embodiment, for example, as shown in FIGS. 3A and 3C, a herringbone-shaped dynamic pressure groove 12 a is formed on the entire end surface 12. In addition, in FIG. 3, the hill part formed between the dynamic pressure grooves 11a and between the dynamic pressure grooves 12a is each shown by cross hatching.

  The fixed portion 10b protrudes outward in the axial direction from the end surfaces 12 on both axial sides of the bearing portion 10a, and the outer peripheral surface 14 of the protruding portion faces the inner diameter end of the outer member 20 in the radial direction. The inner peripheral surface 13 of the fixed portion 10 b is fixed to the outer peripheral surface of the rotating shaft 2.

  As shown in FIG. 2, the outer member 20 faces the outer peripheral surface 11 of the inner member 10 in the radial direction and the inner peripheral surface 20 a that faces the outer peripheral surface 11 in the radial direction, and both axial end surfaces 12 of the inner member 10. And a pair of inner side surfaces 20b. The outer member 20 of the present embodiment includes an annular first outer member 21 and second outer member 22 having an L-shaped cross section. The first outer member 21 integrally includes a cylindrical portion 21a and a flat plate portion 21b extending from the one axial end of the cylindrical portion 21a (the right end in FIG. 2) to the inner diameter side. The second outer member 22 integrally includes a cylindrical portion 22a and a flat plate portion 22b extending from the other axial end of the cylindrical portion 22a (the left end in FIG. 2) to the inner diameter side. In the present embodiment, for example, the first outer member 21 and the second outer member 22 are formed by pressing a metal plate. A stainless steel plate, a cold-rolled steel plate, etc. can be used for a metal plate, The plate | board thickness is about 0.1-1 mm. The outer peripheral surface 21a2 of the cylindrical portion 21a of the first outer member 21 and the inner peripheral surface 22a1 of the cylindrical portion 22a of the second outer member 22 are fixed by adhesion, press fitting, or the like, and in the present embodiment, both are press-fitted. It is fitted and fixed without any gaps.

  As shown in FIG. 2, the inner peripheral surface 20a of the outer member 20 (that is, the inner peripheral surface 21a1 of the cylindrical portion 21a of the first outer member 21) is formed as a smooth cylindrical surface and functions as a radial bearing surface. . The inner side surface 20b on the axial direction side of the outer member 20 (that is, the inner side surface 21b1 of the flat plate portion 21b of the first outer member 21 and the inner side surface 22b1 of the flat plate portion 22b of the second outer member 22) is smooth. Each of them functions as a thrust bearing surface. A radial bearing gap R is formed between the inner peripheral surface 20 a (radial bearing surface) of the outer member 20 and the outer peripheral surface 11 (radial bearing surface) of the bearing portion 10 a of the inner member 10. Thrust bearing gaps T are formed between the inner side surfaces 20b (thrust bearing surfaces) on both axial sides and the axial end surfaces 12 (thrust bearing surfaces) of the bearing portion 10a of the inner member 10, respectively.

  The inner diameter end of the flat plate portion 21 b of the first outer member 21 and the inner diameter end of the flat plate portion 22 b of the second outer member 22 have an appropriate radial clearance from the outer peripheral surface 14 of the fixed portion 10 b of the inner member 10. Opposite. In the illustrated example, tapered surfaces 21b2 and 22b2 having diameters increased outward in the axial direction are formed at the inner diameter ends of the flat plate portions 21b and 22b, and between the tapered surfaces 21b2 and 22b2 and the outer peripheral surface 14 of the fixing portion 10b. A wedge-shaped seal space S is formed. The seal space S prevents leakage of the lubricating oil. Furthermore, if an oil repellent is applied to the end surface 15 of the fixed portion 10b of the inner member 10 and the outer end surface of the outer member 20 (the outer end surfaces of the flat plate portions 21b and 22b), oil leakage from the seal space S can be ensured. Can be prevented.

  The internal space of the fluid dynamic bearing device 4 having the above configuration is filled with lubricating oil including the internal pores of the sintered metal inner member 10. As shown in FIG. 2, the lubricating oil is filled in the gap between the inner member 10 and the outer member 20, and the outer diameter side (radial bearing gap R side) is generated by the capillary force of the thrust bearing gap T and the seal space S. ). The oil surface of the lubricating oil is held in the thrust bearing gap T or the seal space S.

  When the rotating shaft 2 rotates, the pressure of the oil film in the radial bearing gap R of each fluid dynamic bearing device 4 is increased by the dynamic pressure groove 11a, and the rotating shaft 2 and the inner member 10 are moved outward by the dynamic pressure action of the oil film. The member 20 is supported in a non-contact manner in the radial direction. At the same time, the pressure of the oil film in the thrust bearing gap T of each fluid dynamic pressure bearing device 4 is increased by the dynamic pressure groove 12a, so that the rotary shaft 2 and the inner member 10 are in both thrust directions with respect to the outer member 20. Non-contact support (see FIG. 2).

  When a dynamic pressure action is generated in the lubricating oil in the thrust bearing gap T, the outer member 20 of the fluid dynamic pressure bearing device 4 on the left side in the figure slides to the left side in the figure to compress the spring 7, thereby both fluid dynamic pressures. The thrust bearing gap T of the bearing devices 4 and 4 is ensured. Thus, the thrust bearing gap T can be set with high accuracy by fitting the outer member 20 to the housing 5 so as to be movable in the axial direction. Thereby, the inner member 10 is reliably non-contact supported with respect to the outer member 20, and generation | occurrence | production of the noise by contact sliding can be prevented more reliably.

  Next, a method for manufacturing the inner member 10 will be described.

  The inner member 10 includes a compression molding step (see FIG. 4) for forming a green compact M ′ by compression molding a mixed metal powder M containing copper and iron, and the green compact M ′ at a predetermined sintering temperature. A sintering process for forming the sintered body M ″ by firing, a sizing process for shaping the sintered body M ″ into a predetermined dimension (see FIG. 5), and a radial dynamic pressure generating portion (dynamic pressure) on the sintered body M ″. The groove 11a) is manufactured through a rolling process (see FIG. 6) for forming by rolling. In this embodiment, in the sizing process, the sintered body M "is shaped simultaneously with the shaping of the sintered body M". A thrust dynamic pressure generating portion (dynamic pressure groove 12a) is formed on the end face of the.

  In the compression molding process, the mixed metal powder M is filled in the cavity formed by the die 41, the core pin 42, and the lower punch 43 (see FIG. 4A), and the mixed metal powder M is compressed from above by the upper punch 44. Thus, a green compact M ′ having substantially the same shape as the inner member 10 is formed (see FIG. 4B). At this time, the porosity of the green compact M ′ is adjusted so that the porosity of the sintered body M ″ described later is 20% or more. Specifically, the filling amount of the mixed metal powder M is adjusted. Thus, the porosity of the green compact M ′ is adjusted. The green compact M ′ thus formed is fired in the sintering step to obtain a sintered body M ″.

  In the sizing process, the sintered body M ″ is shaped to a predetermined size by a sizing die. Specifically, the core pin 51 is inserted into the inner periphery of the sintered body M ″ and the sintered body is moved by the upper and lower punches 52 and 53. M ″ is restrained from both upper and lower sides (see FIG. 5A). In this state, the sintered body M ″, the core pin 51, and the upper and lower punches 52 and 53 are lowered together, and the sintered body M ″ is moved to the die 54. (Refer to FIG. 5B.) As a result, the outer peripheral surface 11 of the sintered body M ″ (the outer peripheral surface of the die 54, the outer peripheral surface of the core pin 51, and the end surfaces of the upper and lower punches 52, 53). Radial bearing surface), inner peripheral surface 13, and axial end surfaces 12 (thrust bearing surfaces). At this time, forming portions (not shown) corresponding to the dynamic pressure grooves 12a are provided on the end surfaces of the upper and lower punches 52 and 53, and the forming portions are pressed against the both end surfaces 12 in the axial direction of the sintered body M ″. The groove 12a is formed.As described above, since the surface area ratio of the axial end faces 12 of the inner member 10 is preferably 20% or less, the sintered body M ″ after the sizing step When the surface area ratio of the axial end faces 12 exceeds 20%, it is preferable to perform a sealing process such as burnishing.

  In the rolling process, the dynamic pressure grooves 11a are formed by rolling on the outer peripheral surface 11 of the sintered body M ″. Specifically, as shown in FIGS. 6 (a) and 6 (b), the sintered body is formed. By rolling the outer peripheral surface 11 of the sintered body M ″ forward (on the right side in the figure) while pressing the outer peripheral surface 11 of the sintered body M ″ in a state where M ″ is not restrained from both sides in the axial direction, the shape of the molding body 61 is changed to the shape of the sintered body M ″. The dynamic pressure groove 11a is formed by transferring to the outer peripheral surface 11. At this time, the plastic flow of the sintered body M ″ due to the compression of the rolling process can be absorbed by the internal pores of the sintered metal. As a result, the swell of the outer peripheral surface 11 of the sintered body M ″ due to the plastic flow is suppressed, and the dynamic flow is suppressed. The pressure groove 11a can be formed with high accuracy. Further, when the outer peripheral surface 11 is rolled without restraining the axial end surfaces 12 of the sintered body M ″ as described above, not only the outer peripheral surface 11 but also the axial end surfaces 12 are raised by plastic flow. However, when the porosity of the sintered body M ″ is 20% or more, the swell of the axial end faces 12 due to plastic flow can be suppressed. As described above, the surface area ratio of the outer peripheral surface 11 of the inner member 10 is preferably 20% or less. Usually, the surface opening ratio of the outer peripheral surface 11 of the sintered body M ″ is reduced to 20% or less by crushing the outer peripheral surface 11 of the sintered body M ″ by rolling, but the outer peripheral surface 11 of the sintered body M ″ after the rolling process. In the case where the surface opening ratio of the surface exceeds 20%, sealing treatment may be performed. Thus, the inner member 10 is completed.

  Next, a method for assembling the fluid dynamic bearing device 4 will be described.

  First, as shown in FIG. 7A, the lower end surface 12 of the bearing portion 10 a of the inner member 10 is brought into contact with the inner side surface 22 b 1 of the flat plate portion 22 b of the second outer member 22. Next, as shown in FIG. 7B, the first outer member 21 is assembled to the second outer member 22. Specifically, the outer peripheral surface 21a2 of the cylindrical portion 21a of the first outer member 21 is fitted through the radial gap without being press-fitted into the inner peripheral surface 22a1 of the cylindrical portion 22a of the second outer member 22. The lower end surface 21 b 1 of the flat plate portion 21 b is brought into contact with the upper end surface 12 of the bearing portion 10 a of the inner member 10.

  Thereafter, as shown in FIG. 7C, the inner member 10 and the first outer member 21 are raised with respect to the second outer member 22, and the lower end surface 12 of the bearing portion 10 a of the inner member 10. And the inner surface 22b1 of the flat plate portion 22b of the second outer member 22 are separated from each other, and an axial gap Δ corresponding to the total amount of both thrust bearing gaps T is formed therebetween. In this state, an instantaneous adhesive is injected into the radial gap between the cylindrical portion 21a of the first outer member 21 and the cylindrical portion 22a of the second outer member 22, and this is cured so that the first outer member The direction member 21 and the second outer member 22 are temporarily fixed, and the setting of the thrust bearing gap T is completed.

  Then, a thermosetting adhesive (for example, epoxy-based adhesive) is formed in a radial gap between the outer peripheral surface 21a2 of the cylindrical portion 21a of the first outer member 21 and the inner peripheral surface 22a1 of the cylindrical portion 22a of the second outer member 22. By injecting the agent, the radial gap is completely sealed. At this time, by providing the tapered surface 22a3 at the end of the cylindrical portion 22a of the second outer member 22, injection of the thermosetting adhesive is facilitated. Thereafter, the subassembly made of the inner member 10 and the outer member 20 is fired to solidify the thermosetting adhesive.

  Lubricating oil is injected between the inner member 10 and the outer member 20 assembled as described above, including the internal pores of the inner member 10 made of sintered metal. After that, the fluid dynamic pressure bearing device 4 is heated to a set temperature exceeding the maximum temperature (upper limit) assumed in the usage environment, and the lubricating oil overflowing from the seal space S due to thermal expansion at this time is wiped off. Thereafter, the lubricating oil contracts by cooling to room temperature, and the oil surface is retracted to the bearing inner side (outer diameter side) and held in the vicinity of the inner diameter side end of the thrust bearing gap T or in the seal space S. Thereby, if it is in the assumed temperature range, lubricating oil will not leak by thermal expansion. Thus, the fluid dynamic bearing device 4 is completed.

  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 function similar to said embodiment, and duplication description is abbreviate | omitted.

  In the above embodiment, the porosity of the inner member 10 is set to 20% or more to prevent the axial end faces 12 from rising due to the rolling process to the outer peripheral surface 11 of the inner member 10, It is not limited to this. For example, in the embodiment shown in FIG. 8, the outer peripheral area 12b of the axially opposite end faces 12 of the sintered body M ″ after the sizing process is retracted axially inward from the inner peripheral area 12c (dotted line in FIG. 8). At this time, the axial retreat amount β of the outer peripheral region 12b with respect to the inner peripheral region 12c (the retreat amount of the most retracted portion) is set to about 5 to 10 μm. The entire circumference of the region 12b is continuously retracted, and the area of the outer peripheral region 12b that has been retracted is about 1/3 to 1/2 of the entire end surface 12. Rolled to the outer peripheral surface 11 of the sintered body M ″. When the dynamic pressure groove 11a is formed by processing, the outer peripheral area 12b of the axial end faces 12 moves outward in the axial direction by plastic flow. Thereby, the outer peripheral area | region 12b of the axial direction both end surface 12 of the inner member 10 is distribute | arranged to the substantially the same axial direction position as the inner peripheral area | region 12c (refer the continuous line of FIG. 8). For example, when the outer peripheral region 12b is set to ± 5 μm or less, preferably ± 3 μm or less with respect to the inner peripheral region 12c, the entire end surface 12 (the outer peripheral region 12b and the inner peripheral region 12c) can function as a thrust bearing surface.

  In the above embodiment, the bulging of the axial end faces 12 of the inner member 10 due to the rolling process is suppressed as much as possible. On the other hand, the embodiment shown in FIGS. 9 and 10 suppresses a decrease in the supporting force in the thrust direction even when the axial end surfaces 12 of the inner member 10 are raised. In the embodiment shown in FIG. 9, only the inner side surface 20 b of the outer member 20 that faces the both axial end surfaces 12 of the inner member 10 in the axial direction (in FIG. 9, only the inner side surface 20 b of the first outer member 21 is shown. ) Is provided in the inner peripheral region, and a relief portion 20b2 is provided in the outer peripheral region, which is recessed outward in the axial direction from the flat portion 20b1. In the illustrated example, the relief portion 20b2 is a flat surface perpendicular to the axial direction, and is formed on the entire circumference of the outer peripheral region of the inner side surface 20b. A raised portion 12d is formed in the outer peripheral region of both axial end surfaces 12 of the inner member 10 (only one end surface 12 in the axial direction is shown in FIG. 9), and a flat surface is formed in the inner peripheral region 12c. In the end surface 12, a dynamic pressure groove 12a is formed across the inner peripheral region 12c and the raised portion 12d. Note that the size of the raised portion 12d is exaggerated.

  A thrust bearing gap T is formed between the inner peripheral region 12 c of the end surface 12 of the inner member 10 and the flat portion 20 b 1 of the inner surface 20 b of the outer member 20. The raised portion 12d of the end surface 12 of the inner member 10 and the relief portion 20b2 of the inner side surface 20b of the outer member 20 face each other in the axial direction. The retreating amount δ1 of the escape portion 20b2 of the outer member 20 with respect to the flat portion 20b1 is set to be larger than the swell amount δ2 of the rising portion 12d of the inner member 10 with respect to the inner peripheral region 12c. Accordingly, when the thrust bearing gap T is set by the method shown in FIG. 7, the raised portion 12d of the end surface 12 of the inner member 10 and the inner side surface 20b of the outer member 20 do not contact each other, and the inner peripheral region 12c. And the flat portion 20b1 can be brought into contact with each other, so that the thrust bearing gap T can be set with high accuracy.

  The embodiment shown in FIG. 10 is an embodiment shown in FIG. 9 in that the relief portion 20b2 formed on the inner side surface 20b of the outer member 20 is a tapered surface inclined outward in the axial direction toward the outer diameter side. And different. Also in this case, when the inner peripheral region 12c and the flat portion 20b1 are brought into contact with each other in setting the thrust bearing gap T, the raised portion 12d of the inner member 10 and the escape portion 20b2 of the outer member 20 are not in contact. As described above, the retraction amount of the escape portion 20b2 from the flat portion 20b1 is set.

  In the above embodiment, the bearing portion 10a and the fixed portion 10b of the inner member 10 are integrally formed. However, the present invention is not limited to this, and the bearing portion 10a and the fixed portion 10b are formed separately. Also good. The inner peripheral surface of the bearing portion 10a and the outer peripheral surface of the fixed portion 10b are fixed by an appropriate method such as press-fitting, gap adhesion, press-fitting adhesion (press-fitting with an adhesive interposed). At this time, the bearing portion 10a and the fixed portion 10b may be formed of different materials. For example, since the bearing portion 10a can slide with the outer member 20, it is formed of copper iron-based sintered metal with an emphasis on wear resistance, while the fixed portion 10b does not slide with the outer member 20. The steel can be formed of iron-based sintered metal or melted material with emphasis on strength. Note that the bearing portion 10a and the fixed portion 10b do not necessarily have to be formed of different materials, and may be formed of the same material separately.

  In addition, when the dynamic pressure grooves 11a and 12a are for one-way rotation as shown in FIG. 3, the first outer member 21 and the second outer member 22 have different hue surfaces in order to identify the rotation direction. By doing so, it is possible to prevent erroneous assembly. In order to form surfaces having different hues, for example, materials having different hues may be used or surface treatment may be performed.

  In the above-described embodiment, the case where the dynamic pressure grooves 12a are formed on the both axial end surfaces 12 of the inner member 10 is shown. However, the present invention is not limited thereto, and the dynamic pressure grooves are formed on the inner side surface 20b of the outer member 20. It may be formed. In this case, the dynamic pressure grooves can be formed simultaneously with the pressing of the first outer member 21 and the second outer member 22.

  In the above-described embodiment, the case where both the dynamic pressure grooves 11a and 12a have a herringbone shape is shown. However, the present invention is not limited to this, and other shapes such as a spiral shape and a step shape may be used. In particular, the dynamic pressure groove 12a formed on the thrust bearing surface is preferably a pump-out type that pushes lubricating oil to the outer diameter side (not shown). Thereby, since lubricating oil is positively supplied to the radial bearing gap R, generation of negative pressure can be prevented.

  In the above embodiment, the case where the inner member 10 is the rotation side and the outer member 20 is the fixed side is shown. On the contrary, the inner member 10 is the fixed side, the outer member. 20 may be the rotation side.

  Further, the configuration of the embodiment described above can be appropriately combined. For example, the configuration in which the porosity of the inner member 10 is set to 20% or less, the outer peripheral region 12b of the both end surfaces 12 in the axial direction of the sintered body M ″. Are configured to be retracted inward in the axial direction from the inner peripheral region 12c (see FIG. 8), and a configuration in which the escape portion 20b2 is provided in the outer peripheral region of the inner side surface 20b of the outer member 20 (see FIG. 9). Any two or all of them may be provided.

1 Bearing unit 2 Rotating shaft 3 Motor rotor 4 Fluid dynamic pressure bearing device 5 Housing 6 Fan 7 Spring 10 Inner member 11 Outer peripheral surface 11a Dynamic pressure groove 12 End surface 12a Dynamic pressure groove 12b Outer peripheral region 12c Inner peripheral region 12d Swelling portion 20 Member 20a Inner peripheral surface 20b Inner side surface 20b1 Flat portion 20b2 Escape portion R Radial bearing gap T Thrust bearing gap S Seal space M Mixed metal powder M 'Green compact M "Sintered body

Claims (7)

A radial formed between an outer member, an inner member made of sintered metal disposed on the inner periphery of the outer member, and an outer peripheral surface of the inner member and an inner peripheral surface of the outer member Between the bearing gap, one end surface in the axial direction of the inner member and the inner surface of the outer member facing in the axial direction, and the other end surface in the axial direction of the inner member and the axial direction thereof Rolled on the outer peripheral surface of the inner member, the thrust bearing gap formed between the inner side surfaces of the outer member facing each other, the lubricating oil filled in the radial bearing gap and the thrust bearing gap. A fluid dynamic pressure bearing device comprising a radial dynamic pressure generating portion formed by machining,
A fluid dynamic bearing device in which the porosity of the inner member is 20% or more. A radial formed between an outer member, an inner member made of sintered metal disposed on the inner periphery of the outer member, and an outer peripheral surface of the inner member and an inner peripheral surface of the outer member Between the bearing gap, one end surface in the axial direction of the inner member and the inner surface of the outer member facing in the axial direction, and the other end surface in the axial direction of the inner member and the axial direction thereof Rolled on the outer peripheral surface of the inner member, the thrust bearing gap formed between the inner side surfaces of the outer member facing each other, the lubricating oil filled in the radial bearing gap and the thrust bearing gap. A fluid dynamic pressure bearing device comprising a radial dynamic pressure generating portion formed by machining,
Fluid dynamic pressure bearing in which outer peripheral regions of both end surfaces in the axial direction of the inner member are previously retracted axially inward from the inner peripheral region, and the outer peripheral region is moved outward in the axial direction by plastic flow by the rolling process. apparatus. A radial formed between an outer member, an inner member made of sintered metal disposed on the inner periphery of the outer member, and an outer peripheral surface of the inner member and an inner peripheral surface of the outer member Between the bearing gap, one end surface in the axial direction of the inner member and the inner surface of the outer member facing in the axial direction, and the other end surface in the axial direction of the inner member and the axial direction thereof Rolled on the outer peripheral surface of the inner member, the thrust bearing gap formed between the inner side surfaces of the outer member facing each other, the lubricating oil filled in the radial bearing gap and the thrust bearing gap. A fluid dynamic pressure bearing device comprising a radial dynamic pressure generating portion formed by machining,
A fluid dynamic bearing device, wherein an inner side surface of the outer member includes a flat portion and a relief portion provided on an outer diameter side of the flat portion and retracted axially outward from the flat portion.   The fluid dynamic pressure bearing device according to any one of claims 1 to 3, wherein a surface opening ratio of at least the radial bearing gap and the thrust bearing gap in the inner member is 20% or less.   The outer member has a first outer member having an inner surface facing one end surface in the axial direction of the inner member, and a second outer member having an inner surface facing the other end surface in the axial direction of the inner member. 4. The fluid according to claim 1, wherein the thrust bearing gap is set by relatively moving the first outer member and the second outer member in the axial direction. Hydrodynamic bearing device. A fluid formed of sintered metal, having a radial bearing surface provided on the outer peripheral surface, a thrust bearing surface provided on both axial end surfaces, and a radial dynamic pressure generating portion formed on the radial bearing surface A method of manufacturing an inner member of a hydrodynamic bearing device,
A compression molding process in which a mixed metal powder is compression molded to form a green compact, a sintering process in which the green compact is fired at a predetermined sintering temperature to form a sintered body, and the sintered body has a predetermined size. By shaping the radial bearing surface and the thrust bearing surface into the sintered body, and after the sizing process, the sintered body is not restrained from both sides in the axial direction. A rolling step of forming the radial dynamic pressure generating portion on the outer peripheral surface of the material by rolling,
A method for manufacturing an inner member of a fluid dynamic bearing device, wherein the conditions of each step are set so that the porosity is 20% or more. A fluid formed of sintered metal, having a radial bearing surface provided on the outer peripheral surface, a thrust bearing surface provided on both axial end surfaces, and a radial dynamic pressure generating portion formed on the radial bearing surface A method of manufacturing an inner member of a hydrodynamic bearing device,
A compression molding process in which a mixed metal powder is compression molded to form a green compact, a sintering process in which the green compact is fired at a predetermined sintering temperature to form a sintered body, and the sintered body has a predetermined size. By shaping the radial bearing surface and the thrust bearing surface into the sintered body, and after the sizing process, the sintered body is not restrained from both sides in the axial direction. A rolling step of forming the radial dynamic pressure generating portion on the outer peripheral surface of the material by rolling,
An outer peripheral region of both end surfaces in the axial direction of the sintered body is formed in advance by forming an outer peripheral region of both end surfaces in the axial direction of the sintered body by retreating inward in the axial direction from the inner peripheral region. A method for manufacturing an inner member of a fluid dynamic pressure bearing device that moves the shaft outward in the axial direction.

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