JP6622054B2 - Foil bearing - Google Patents

Description

  The present invention relates to a foil bearing.

  A main shaft of a turbo machine (for example, a gas turbine or a turbocharger) rotates at a high speed in a high temperature environment. In addition, in turbomachinery, it may be difficult to separately provide an auxiliary machine for oil circulation from the viewpoint of energy efficiency, and the shear resistance of lubricating oil may be an obstacle to high-speed rotation of the spindle. Therefore, as the bearing for supporting the main shaft of the turbomachine, an air dynamic pressure bearing using air as a pressure generating fluid is often used instead of a rolling bearing or a dynamic pressure bearing using a lubricating oil.

  As an air dynamic pressure bearing, one in which both a rotating bearing surface and a stationary bearing surface are made of a rigid body is generally used. However, in this type of air dynamic pressure bearing, if the gap width management of the bearing gap formed between both bearing surfaces is insufficient, the self-excited shaft called a whirl when the stability limit is exceeded. Swing is likely to occur. Therefore, in a general air dynamic pressure bearing, in order to exhibit the bearing performance stably, it is necessary to manage the gap width of the bearing gap with high accuracy. However, in an environment where the temperature change is large, such as a turbo machine, the bearing gap width is likely to fluctuate due to the effect of thermal expansion, making it difficult to stably exhibit the bearing performance.

  A foil bearing is known as a bearing that can easily manage the gap width of a bearing gap even in an environment in which a whirl is not easily generated and a temperature change is large. A foil bearing consists of a thin metal plate (foil) that has low rigidity against bending and supports the load by allowing the bearing surface to bend. It is characterized by being automatically adjusted to an appropriate width according to conditions and the like. For example, Patent Document 1 below discloses an example of a radial foil bearing that supports a radial load.

  By the way, in the foil bearing, especially when the shaft rotates at a low speed, the rigidity (pressure) of the air film formed in the bearing gap is not sufficiently increased. In order to suppress the wear of the bearing surface and the increase in rotational torque due to such sliding contact, Patent Document 1 discloses that a DLC film and titanium aluminite are formed on the surface of each foil that forms a bearing gap with the shaft. It is disclosed to form a film such as a ride film or a molybdenum disulfide film.

JP 2012-92967 A

  While the shaft is stopped, as shown in FIG. 19, the coating 21 formed on the outer peripheral surface of the shaft 6 and the surface of the foil 12 is in contact with a wide range. Even if rotation of the shaft 6 is started in this state, air is not drawn smoothly between the outer peripheral surface of the shaft 6 in the close contact state and the coating 21, so that sufficient pressure is not generated in the wedge space. The problem is that the ascent of the aircraft is delayed. The shaft levitation delay causes various problems such as energy loss.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a foil bearing that can quickly float a shaft at the time of startup and can maintain the effect over a long period of time.

  In order to solve the above-described problems, the present invention provides a top foil portion having a bearing surface that forms a bearing gap between the shaft to be supported and a back surface of the top foil portion, and the top foil portion is elastic. A foil bearing that supports the relative rotation of the shaft in a non-contact state with fluid pressure generated in the bearing gap, and particles are supplied to the bearing gap, and the top foil section A fluid control unit is provided that generates a fluid flow from both end portions in a direction along the surface and perpendicular to the relative rotation direction to a region between the both end portions.

  By supplying the particles into the bearing gap in this way, the particles interposed between the two surfaces facing each other via the bearing gap function as a spacer while the rotation side member (for example, the shaft) is stopped. A minute gap is formed between the two surfaces. In this case, since air is easily drawn into the minute gap immediately after the shaft starts rotating, it is possible to promptly generate fluid dynamic pressure in the wedge space and to float the shaft early.

  Further, since the fluid control unit generates a fluid flow from the both end portions of the top foil portion toward the region between the both ends of the top foil portion, it is possible to prevent particles from leaking outside the bearing clearance. Therefore, even if the foil bearing is used for a long period of time, the particles in the bearing gap are not depleted, and the above-described effect produced by the particles can be obtained for a long period of time.

  The fluid control unit can be formed by a step in the width direction of the bearing gap. This step can be formed by elastically deforming the top foil portion following the shape of the support portion. In this case, the flow direction of the fluid can be controlled by arbitrarily changing the shape of the fluid control part (step) by adjusting the support reaction force at each part of the support part.

  For example, foils are arranged at a plurality of locations in the relative rotation direction, and each foil is provided with the top foil portion and an under foil portion that supports an adjacent top foil portion from behind, and the under foil portion constitutes the support portion. can do.

  If the notch part recessed in the relative rotation direction is provided at the rear end of the underfoil part, the top foil part is elastically deformed following the shape of the notch part, so only the shape of the notch part is changed. It becomes possible to control the shape of the fluid control part (step part).

  By making the particle size of the particles smaller than the minimum width of the bearing gap, it becomes difficult for the particles to bite into the minimum width portion of the bearing gap during rotation of the shaft. Therefore, the unstable behavior of the shaft can be suppressed.

  Top foil portions are arranged at a plurality of locations in the relative rotation direction, and a wide portion in which the width of the bearing gap is made larger than the minimum width is provided at a boundary portion between adjacent top foil portions, which is opposite to the wide portion. If the top foil part on the rotation direction side is provided with a circulation hole that penetrates the front and back of the top foil part and opens to the wide part, the top foil part is deposited on the top foil part by the flow of fluid ejected from the circulation hole. Particles can be blown away. For this reason, the particles can flow in the bearing gap.

  As described above, according to the present invention, fluid dynamic pressure can be quickly generated in the wedge space, and the shaft can be quickly levitated. Therefore, it becomes possible to quickly shift the rotation-side member to the steady rotation state. Further, since the particles can be prevented from leaking out of the bearing gap, the above effect can be stably obtained over a long period of time.

It is a figure which shows schematic structure of a micro gas turbine. It is a figure which shows schematic structure of the rotor support structure of a micro gas turbine. It is sectional drawing of the foil bearing concerning this invention. It is a top view of foil. It is the top view which looked at two foils connected from the back side. It is a perspective view showing the state where three foils were temporarily assembled. It is a perspective view which shows a mode that the temporary assembly of foil is attached to a foil holder. It is sectional drawing which expands and shows a foil duplication part. It is sectional drawing which expands and shows a top foil part (steady-state rotation state of a shaft). It is sectional drawing which expands and shows a top foil part (just after a shaft rotation start). It is the top view which looked at two foils connected from the surface side. It is a figure which expands and represents the XX sectional view in FIG. It is the YY sectional view taken on the line in FIG. It is the top view which looked at two foils connected from the surface side. It is the top view which looked at two foils connected from the surface side. It is the top view which looked at two foils connected from the surface side. It is sectional drawing which expanded and represented the radial foil bearing. It is sectional drawing which shows other embodiment of a radial foil bearing. It is sectional drawing which expands and shows the top foil part of the conventional foil bearing.

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

  FIG. 1 conceptually shows a configuration of a gas turbine device called a micro gas turbine as an example of a turbo machine. The gas turbine apparatus includes a turbine 1 having a blade row, a compressor 2, a generator 3, a combustor 4, and a regenerator 5 as main components. The turbine 1 and the compressor 2 are attached to a shaft 6 extending in the horizontal direction and constitute a rotor on the rotating side together with the shaft 6. One axial end of the shaft 6 is connected to the generator 3. When this micro gas turbine is operated, air is sucked from the air inlet 7, and the sucked air is compressed by the compressor 2 and heated by the regenerator 5 and then sent to the combustor 4. The combustor 4 mixes fuel with compressed and heated air and burns the fuel to generate high-temperature and high-pressure gas, and the turbine 1 is rotated by the gas. When the turbine 1 rotates, the rotational force is transmitted to the generator 3 via the shaft 6, and the generator 3 is rotationally driven. The electric power generated by rotating the generator 3 is output via the inverter 8. Since the gas after rotating the turbine 1 is at a relatively high temperature, the heat of the gas after combustion is regenerated by sending this gas to the regenerator 5 and exchanging heat with the compressed air before combustion. Use. The gas that has been subjected to heat exchange in the regenerator 5 is discharged as exhaust gas after passing through the exhaust heat recovery device 9.

  FIG. 2 conceptually shows an example of a rotor support structure in the micro gas turbine shown in FIG. In this support structure, the radial bearing 10 is disposed around the shaft 6, and the thrust bearings 30 are disposed on both sides in the axial direction of the flange portion 6 b provided on the shaft 6. The shaft 6 is supported by the radial bearing 10 and the thrust bearing 30 so as to be rotatable in both the radial direction and the thrust direction. In this support structure, the region between the turbine 1 and the compressor 2 becomes a high temperature atmosphere because it is adjacent to the turbine 1 rotated by high temperature and high pressure gas. In addition, the shaft 6 rotates at a rotational speed of tens of thousands rpm or more. Therefore, as the bearings 10 and 30 used in this support structure, an air dynamic pressure bearing, particularly a foil bearing is suitable.

  Hereinafter, a foil bearing which is an embodiment of the present invention and is suitable for the above-described radial bearing 10 for a micro gas turbine will be described with reference to the drawings.

  As shown in FIG. 3, the radial foil bearing 10 is disposed at a plurality of locations in the rotational direction of the shaft 6 on the foil holder 11 having a cylindrical inner peripheral surface 11 a and the inner peripheral surface 11 a of the foil holder 11. Foil 12. The foil bearing 10 in the illustrated example is a so-called multi-arc type foil bearing in which three foils 12 are arranged in the circumferential direction on an inner peripheral surface 11a. A shaft 6 is inserted on the inner diameter side of the foil 12.

  The foil holder 11 can be formed of metal (for example, steel material) such as sintered metal or melted material. On the inner peripheral surface 11 a of the foil holder 11, axial grooves 11 b serving as attachment portions of the foils 12 are formed at a plurality of locations (the same number as the number of foils) separated in the rotation direction R.

  The foil 12 is formed by processing a belt-like foil having a thickness of about 20 μm to 200 μm made of a metal having a high spring property and good workability, such as a steel material or a copper alloy, into a predetermined shape by pressing or the like. Typical examples of steel materials and copper alloys include carbon steel and brass. However, in general carbon steel, there is no lubricating oil in the atmosphere and the antirust effect by oil cannot be expected. It tends to occur. Further, brass may cause cracks due to processing strain (this tendency becomes stronger as the Zn content in brass increases). Therefore, it is preferable to use a stainless steel or bronze foil as the belt-like foil.

  As shown in FIG. 4, the foil 12 has a first region 12 a on the rotation direction R side of the shaft 6 and a second region 12 b on the counter rotation direction side.

  The first region 12a includes a top foil portion 12a1 that forms the bearing surface X, and both ends of a direction N (hereinafter simply referred to as “orthogonal direction N”) that is along the surface of the top foil portion 12a1 and orthogonal to the rotational direction R. And a convex portion 12a2 provided in the center and projecting in the rotation direction R. A minute notch 12a3 extending in the counter-rotating direction from the foil edge is provided at the base end of the convex portion 12a2.

  At the rear end 12d (end on the counter-rotation direction side) of the second region 12b, two notches 12b2 that are spaced apart in the orthogonal direction N and are recessed toward the rotation direction R are formed. The width dimension in the orthogonal direction N of each notch 12b2 is gradually reduced toward the rotation direction R. In the present embodiment, the case where the entire cutout portion 12b2 is formed in an arc shape is illustrated, but each cutout portion 12b2 can also be formed in a substantially V shape with the top portion being pointed. Protruding portions 12b1 that protrude in the counter-rotating direction are formed on both sides of each cutout portion 12b2 in the orthogonal direction.

  At the boundary between the first region 12a and the second region 12b and at both ends and the center in the orthogonal direction N, insertion ports 12c1, 12c2, and 12c1 into which the convex portions 12a2 of the adjacent foils 12 are inserted are provided. Among these, the insertion ports 12 c 1 at both ends extend linearly in the orthogonal direction N and open at both ends of the foil 12. The central insertion port 12c2 includes a linear notch portion extending along the orthogonal direction N, and a wide notch portion extending from the notch portion in the counter-rotating direction and having a circular arc at the tip. Become. The first region 12a and the second region 12b are connected by the region 12c3 between the insertion ports 12c1, 12c2, and 12c1.

  As shown in FIG. 5, the two foils 12 are connected by inserting the convex portions 12a2, 12a2, 12a2 of one foil 12 into the insertion ports 12c1, 12c2, 12c1 of the adjacent foils 12, respectively. Can do. In the figure, one of the two foils 12 after the combination is given a gray color.

  And as shown in FIG. 6, each foil 12 can be made into the state of a temporary assembly by connecting the three foils 12 in the circumferential shape with the joint method similar to FIG. The foil bearing 10 is assembled by making this temporary assembly into a cylindrical shape and inserting it into the inner periphery of the foil holder 11 in the direction of arrow B2, as shown in FIG. Specifically, while inserting the temporary assembly of the three foils 12 into the inner periphery of the foil holder 11, the convex portion 12 a 2 of each foil 12 is opened in the axial groove 11 b (opened on one end face of the foil holder 11. 7)) from one side in the axial direction. As described above, the three foils 12 are attached to the inner peripheral surface 11a of the foil holder 11 in a state of being arranged in the rotation direction R.

  In this state, as shown in FIG. 8, the convex portion 12 a 2 formed at the end portion in the rotation direction R of each foil 12 is held by the foil holder 11 behind the adjacent foil 12. Specifically, the convex portion 12a2 of each foil 12 is fitted in the axial groove 11b of the foil holder 11 through the insertion port 12c1 (12c2) of the adjacent foil 12. On the other hand, the second region 12b located on the counter-rotating direction side of each foil 12 is arranged between the top foil portion 12a1 of the adjacent foil 12 and the inner peripheral surface 11a of the foil holder 11 to constitute an underfoil portion. . The underfoil portion 12b functions as a support portion that elastically supports the top foil portion 12a1 of the adjacent foil 12 from behind. A portion where the top foil portion 12a1 and the underfoil portion 12b overlap constitutes a foil overlap portion W. The foil overlapping portions W are formed at a plurality of locations (three locations in the present embodiment) in the rotation direction R.

  In this foil bearing 10, as shown in FIG. 3, one end (convex portion 12 a 2) on the rotation direction R side of each foil 12 is attached to the foil holder 11, and the region on the counter-rotation direction side is engaged with other foils 12. In a combined state. As a result, the adjacent foils 12 are in a state of sticking to each other in the rotation direction R, so that the top foil part 12a1 of each foil 12 projects to the foil holder 11 side, and the shape along the inner peripheral surface 11a of the foil holder 11 To curve. The movement of each foil 12 in the rotation direction R side is restricted because the convex portion 12a2 of each foil 12 hits the axial groove 11b, but the movement of each foil 12 in the counter rotation direction side is not restricted, Each foil 12 is movable in the counter-rotating direction.

  As shown in FIG. 8, since the axial groove 11 b is provided to be inclined by an angle θ1 with respect to the tangential direction of the inner peripheral surface of the foil holder 11, in the vicinity of the convex portion 12 a 2 inserted into the axial groove 11, The top foil portion 12a1 tends to bend in the direction opposite to the bending direction of the entire foil 12 (the bending direction of the inner peripheral surface 11a of the foil holder 11). Moreover, the top foil part 12a1 rises in a state inclined in a direction away from the inner peripheral surface 11a of the foil holder 11 by riding on the underfoil part 12b. By these actions, the top foil portion 12a1 is elastically supported by the foil holder 11, and therefore the top foil portion 12a1 can be deformed following the displacement of the shaft 6, thermal expansion, or the like.

  As shown in FIG. 3, during one-way rotation of the shaft 6, a wedge space is formed between the bearing surface X of the top foil portion 12 a 1 and the outer peripheral surface of the shaft 6. Since the shaft 6 receives the levitation force due to the pressure of the air film generated in the wedge space, an annular radial bearing gap C is formed between the bearing surface X of each foil 12 and the shaft 6, and the shaft 6 is formed in the foil 12. On the other hand, it is supported rotatably in a non-contact state. Due to the elastic deformation of the top foil portion 12a1, the clearance width of the radial bearing clearance C is automatically adjusted to an appropriate width according to operating conditions and the like, so that the rotation of the shaft 6 is stably supported. In FIG. 3, the clearance width of the radial bearing clearance C is exaggerated for easy understanding (the same applies to FIGS. 9, 10, 12, and 17 to 19).

  As already described, in the foil bearing 10, the top foil portion 12 a 1 and the outer peripheral surface of the shaft 6 are in contact immediately after the rotation of the shaft 6 is started and immediately before the shaft 6 is stopped. In order to improve the wear resistance and lubricity at the contact portion, as shown in FIG. 9, the outer peripheral surface of the shaft 6 and the surface of the top foil portion 12a1 (surface facing the shaft) facing each other through the bearing gap C. Of these, the coating film 21 is formed on one or both of them (FIG. 9 illustrates the case where the coating film 21 is formed on the surface of the top foil portion 12a1). As this coating 21, for example, a DLC film, a titanium aluminum nitride film, a tungsten disulfide film, a molybdenum disulfide film, or a resin film can be used. The film 21 is formed at least on the surface of the top foil portion 12a1, but the film 21 may be formed on the other surface of the foil 12 (for example, the entire surface including the back surface of the foil 12). Further, the coating 21 may be formed on the inner peripheral surface 11 a of the foil holder 11.

  In the foil bearing 10 of the present invention, a large number of particles 23 are supplied into the radial bearing gap C when the assembly is completed. As shown in FIG. 9, during the rotation of the shaft 6, the particles 23 float and flow in the radial bearing gap C.

  As shown in FIG. 10, when the shaft 6 is stopped, the particles 23 are interposed between two surfaces (in this embodiment, the outer peripheral surface of the shaft 6 and the surface of the coating 21) facing each other through the radial bearing gap C. In order to function as a spacer, a minute gap Cs is formed between these two surfaces. Unlike the conventional structure shown in FIG. 19, the two surfaces do not adhere to each other. Therefore, air is likely to be drawn into the minute gap Cs immediately after the rotation of the shaft 6 is started (air flow is indicated by a black arrow in the figure), and sufficient air pressure (dynamic pressure) is quickly applied to the wedge space. It can be generated and the shaft 6 can be lifted. Therefore, the shaft 6 can be quickly shifted to steady rotation.

  Even when the particles 23 are caught between the two surfaces forming the bearing gap C during the rotation of the shaft 6, the particles 23 roll with the rotation of the shaft 6. It is possible to reduce the frictional force generated in. Therefore, even when the wear of the coating 21 progresses, the surface of the top foil portion 12a1 and the outer peripheral surface of the shaft 6 are not abruptly worn. Since both surfaces are worn mildly in this way, the top foil portion 12a1 and the shaft 6 are not immediately subjected to fatal damage (adhesion, seizure, etc.). The wear powder generated by the mild wear and the wear powder of the coating 21 have the same function as the above-described particles 23 and form a minute gap Cs when the shaft 6 is stopped. Therefore, the particles 23 in the bearing gap C for some reason. Even when the number decreases, the shaft 6 can be quickly shifted to steady rotation. In addition, when both the shaft 6 and the foil 12 are formed of a steel material, the wear powder generated by the wear of these members is immediately oxidized to iron oxide.

When the hardness of the particles 23 is higher than the hardness of the surface of the top foil portion 12a1 or the outer peripheral surface of the shaft 6, the particles 23 function as abrasive grains and are formed by oxidizing the wear powder of the base material (this wear powder is oxidized). Production of the oxide powder). As described above, since the wear powder contributes to the formation of the gap Cs at the start-up, there is no particular problem in promoting the generation of the wear powder itself. On the other hand, when the hardness of the particles 23 is about the same as or less than the surface of the top foil portion 12a1 or the surface of the shaft 6, the particles 23 are difficult to bite between the surface of the top foil portion 12a1 and the surface of the shaft 6. Therefore, the unstable behavior of the shaft 6 (rotational torque fluctuation or the like) can be suppressed. Accordingly, the material of the particles 23 is not particularly limited. For example, powders of metal oxides such as iron oxide (Fe ₂ O ₃ ) and alumina (Al ₂ O ₃ ), molybdenum disulfide (MoS ₂ ), and two Sulfide powder such as tungsten sulfide (WS ₂ ), soft metal powder such as copper (Cu), silver (Ag), tin (Sn), zinc (Zn), carbon-based powder represented by graphite powder, etc. It can be widely used as the particles 23. The powder illustrated above may use only 1 type, and may mix and use multiple types.

  In particular, when a steel material is used as the material of the foil 12 and the shaft 6, the main element (Fe) of the particle is the same as the main element contained in the material of the foil 12 and the shaft 6 by using iron oxide as the particle 23. Will do. In this case, since the wear powder (oxidized wear powder) generated from the foil 12 and the shaft member 6 has the same composition as the particles 23 and has the same function as the particles 23, the management of the minute gap Cs is easier. Thus, the shaft 6 can be stably shifted to the steady rotation state. Further, when particles having excellent lubricity, such as copper powder, are used as the particles 23, the frictional force at the sliding contact portion between the shaft 6 and the top foil portion 12a1 is reduced, so that the shaft is unstable. Can be suppressed.

  In this way, the particles 23 are formed of the same kind of material (a material having a common main element) as the material of either one or both of the foil 12 and the shaft 6 in consideration of the effect that is regarded as important, or the foil 12. And different materials (materials having different main elements) different from any of the materials of the shaft 6.

  The particle size of the particles 23 is preferably smaller than the minimum width Cmin of the bearing gap C. Specifically, the particles 23 are selected so that the average particle size of the particles 23 when measured using a laser diffraction / scattering method is smaller than the minimum width Cmin of the bearing gap C. Thereby, during the steady rotation of the shaft 6, the particles 23 smoothly pass through the minimum width portion of the bearing gap C, so that the unstable behavior of the shaft 6 can be reduced. Further, it is preferable to select the particles 23 so that the average particle size of the particles 23 is equal to or greater than the surface roughness of the shaft 6 and the top foil portion 12a1 (arithmetic average roughness defined in JIS B 0601).

  By the way, when the particles 23 flow and float in the bearing gap C in this way, it is necessary to prevent the particles 23 from leaking from the bearing gap C by some means. If a contact-type seal used in a seal device such as a rolling bearing is used as a leakage prevention structure, the torque loss increases, and the seal member deteriorates early in a high-temperature environment such as the vicinity of the turbine. Function may be impaired. On the other hand, in a non-contact seal using a labyrinth gap or the like, it becomes difficult to manage the gap width because of thermal expansion when used in a high temperature environment, and it becomes difficult to obtain a stable sealing function.

  In view of such circumstances, in the present invention, the flow of air in the bearing gap C is positively controlled to prevent leakage of the particles 23 from the bearing gap C.

  FIG. 11 shows a specific example of this idea, and is a plan view showing a state in which the joined body of two foils 12 shown in FIG. 5 is viewed from the surface side opposite to FIG. As shown in FIG. 11, in the present invention, the top foil portion 12 a 1 is provided with a fluid control portion 24 that generates an air flow from both end portions 121 and 122 in the orthogonal direction toward a region between the both end portions.

  FIG. 12 is an enlarged view of a cross section taken along line XX in FIG. As shown in FIG. 12, the fluid control unit 24 can be formed by, for example, a tapered step portion provided on the surface of the top foil portion 12a1. The step portion 24 has a step S in the width direction of the bearing gap C. As already described, since the top foil portion 12a1 rides on the underfoil portion 12b in the foil overlap portion W, the region of the top foil portion 12a1 that overlaps the rear end 12d of the underfoil portion 12b. A step S is formed in the vicinity. While the shaft 6 is rotating, the top foil portion 12a1 is pressed against the underfoil portion 12b by the fluid pressure. Therefore, the top foil portion 12a1 is notched 12b2 provided at the rear end 12d of the underfoil portion 12b (FIG. 2). It is elastically deformed so as to follow the shape of reference. A notch 12a3 is formed in the top foil part 12a1, and the rigidity of the top foil part 12a1 is lowered by the notch 12a3, so that the top foil part 12a1 can be elastically deformed smoothly.

  At this time, since the cutout portion 12b2 has a shape recessed toward the rotation direction R, when viewed in a cross section in the orthogonal direction N (YY cross section in FIG. 12), as shown in FIG. 13, the top foil portion 12a1 Is deformed into a concave shape with the center line passing through the top of the notch 12b2 as the bottom. A one-dot chain line in FIG. 11 represents an example of a contour line of the step portion 24 having the above configuration.

  By forming the stepped portion 24 having such a form in the top foil portion 12a1, during rotation of the shaft 6, as shown in FIG. 11, both ends of the top foil portion 12a1 are placed in the bearing gap C facing the stepped portion 24. From 121 and 122, an air flow (indicated by an arrow) in a direction inclined with respect to the orthogonal direction N is generated toward the region therebetween. Since the particles 23 in the bearing gap C ride in the air flow and flow in the bearing gap C, it is possible to prevent the particles 23 from leaking out of the bearing gap C. While the shaft 6 is stopped, the particles 23 adhere to the outer peripheral surface of the shaft 6 and the surface of the top foil portion 12a1 due to van der Waals force or the like, so that the leakage of the particles 23 from the bearing gap C is suppressed. As a result, even if the foil bearing 10 is used for a long period of time, the particles 22 in the bearing gap C are not depleted, and the above-described effects produced by the particles 23 can be obtained over a long period of time.

  On the other hand, as shown in FIG. 14, when the underfoil portion 12 b is not provided with the notch portion 12 b 2 and the rear end 12 d of the underfoil portion 12 b is a straight line parallel to the orthogonal direction N, as shown in FIG. 11. Since the inclined air flow does not occur, the above effect cannot be obtained.

  In the foil bearing of this embodiment, as shown in FIG. 12, the bearing gap C becomes the minimum width Cmin in the vicinity of the end portion on the rotation direction R side of the stepped portion 24 in the foil overlapped portion W. Of the portion having the minimum width Cmin, a region intersecting with the extended line at the top of each notch 12b2 is the maximum pressure generating portion of the bearing gap C. In the present embodiment, since the maximum pressure generating portions are formed at two locations in the orthogonal direction N, the moment load can be supported by one foil bearing 10.

  In the embodiment shown in FIG. 11, the rear end 12d adjacent to both end portions 121 and 122 of the underfoil portion 12b is formed in a straight line parallel to the orthogonal direction N, but as shown in FIG. In addition, the rear end 12d may be integrated with the notch 12b2 in an inclined shape that smoothly connects to the concave notch 12b2. As a result, the inclination angle of the air flow in the vicinity of the foil end portions 121 and 122 is further increased as compared with the embodiment shown in FIG. 11, so that the leakage of the particles 23 outside the bearing gap can be more reliably prevented. It becomes.

  Further, in the embodiment shown in FIG. 11, the case where the two notches 12b2 are formed in the orthogonal direction N is exemplified, but the number of the notches 12b2 is arbitrary. As an example, FIG. 16 illustrates a case where the number of the notches 12b2 is one. In this case, in the orthogonal direction N, the maximum pressure generating portion in the radial bearing gap C is formed only at one place.

  In the above description, the case where the shape of the stepped portion 24 formed in the top foil portion 12a1 is controlled by changing the shape of the cutout portion 12b1 is exemplified. It is possible to control by any method other than. For example, a method of controlling the shape of the stepped portion 24 by forming a number of protruding portions protruding in the width direction of the bearing gap C in the underfoil portion 12b and changing the arrangement pattern of the protruding portions, A method of controlling the shape of the stepped portion 24 by implanting a large number of fiber bodies standing on the inner peripheral surface 11a on the peripheral surface 11a and changing the density pattern of the fiber bodies can be considered. In any method, the projecting portion and the fiber body constitute a support portion that elastically supports the top foil portion 12a1.

  By the way, like the foil bearing 10 of this invention, when the particle | grains 23 are made to flow into the bearing clearance C, the particle | grains 23 become easy to deposit on the specific location of the surface of the top foil part 12a1. For example, in the multi-arc radial foil bearing 10, as shown in FIG. 17, a wide portion C 1 wider than the minimum width Cmin is formed in the bearing gap C near the boundary portion 25 between two adjacent foils 12. However, since the wide portion C1 is a region where the air flow is stagnant, the particles 23 are likely to be deposited on the surface of the top foil portion 12a1 on the rotation direction side of the wide portion C1, particularly on the rotation direction side. When the particles 23 accumulate in a specific place in this way, the number of particles 23 flowing through the bearing gap C is reduced by that amount, so that the above-described effect produced by the particles 23 is reduced. Note that FIG. 17 illustrates a state in which each member is developed in a planar shape for easy understanding.

  In order to solve the above problem, as shown in FIG. 17, in the wide portion C1, the top foil 12a1 on the side opposite to the rotation direction with respect to the boundary portion 25 passes through the front and back and opens to the wide portion C1. 26 is preferably formed. By forming the flow hole 26 in this way, when the shaft 6 starts to rotate, air is drawn into the flow hole 26 from the space behind the top foil portion 12a1 in the form of being drawn into the air flow in the bearing gap C. Thus, an air flow is ejected toward the wide portion C1. Since the accumulated particles 23 are blown off by this air flow, the particles 23 can flow again in the bearing gap C. Accordingly, the particles 23 can be effectively used.

  In the above description, a so-called multi-arc radial foil bearing is exemplified as the foil bearing, but the form of the foil bearing is not limited to this, and the present invention can be applied to a foil bearing of any form. . For example, as shown in FIG. 18, the present invention is also applied to a so-called leaf-type foil bearing in which each end (front end) on the rotation direction R side is a free end among the foils 12 arranged in the rotation direction R. be able to. In the leaf-type foil bearing, among the leaves 12 attached to the foil holder 11, the region on the rotation direction R side forms the top foil portion 12a1, and the region on the counter-rotating side is the top foil portion behind the top foil portion 12a1. The underfoil part 12b (support part) which supports 12a1 is comprised. When the top foil part 12a1 rides on the underfoil part 12b, elasticity is given to the top foil part 12a1. The shape of the stepped portion 24 can be controlled by changing the shape of the rear end 12d by providing a notch at the rear end 12d of the underfoil portion 12b. Although not shown, the present invention can be similarly applied to a thrust foil bearing (see reference numeral 30 in FIG. 2) in which a thrust bearing gap is formed between the shaft 6 and the top foil portion.

  Further, in the above description, the case where the shaft 6 is the rotation side member and the foil holder 11 is the fixed side member is illustrated, but conversely, the shaft 6 is the fixed side member and the foil holder 11 is the rotation side member. In this case, the present invention can be applied. However, in this case, since the foil 12 serves as a rotation side member, it is necessary to design the foil 12 in consideration of deformation of the entire foil 12 due to centrifugal force.

  Furthermore, the foil bearing according to the present invention is not limited to the gas turbine described above, and can be used as, for example, a foil bearing that supports a rotor of a supercharger. The foil bearing according to the present invention is not limited to the above examples, and can be widely used as a bearing for a vehicle such as an automobile and further as a bearing for industrial equipment. Further, each foil bearing of the present embodiment is an air dynamic pressure bearing using air as a pressure generating fluid, but is not limited thereto, and other gases can be used as the pressure generating fluid, or water or oil It is also possible to use a liquid such as

6 shaft 10 foil bearing 11 foil holder 11a inner peripheral surface 11b axial groove (mounting portion)
12 foil 12a 1st area | region 12a1 top foil part 12b 2nd area | region (underfoil part)
12b1 Protruding part 12b2 Notch part 12d Rear end 21 Coating 23 Particle 25 Boundary part 26 Flowing hole 121, 122 Both ends C Bearing gap C1 Wide part R Rotating direction N Along the surface of the top foil part and perpendicular to the rotating direction

Claims (7)

A top foil portion having a bearing surface that forms a bearing gap with a shaft to be supported, and a support portion that is disposed behind the top foil portion and elastically supports the top foil portion, In the foil bearing that supports the relative rotation of the shaft in a non-contact state by the fluid pressure generated in the bearing gap,
The bearing gap has intentionally supplied plurality of particles, said particles is interposed as a spacer between the shaft and the bearing surface during rotation stop, and the top foil section, along the surface The foil bearing is provided with a fluid control unit that generates a fluid flow from both ends in a direction perpendicular to the relative rotation direction to a region between the both ends.   The foil bearing according to claim 1, wherein the fluid control unit is formed by a step in the width direction of the bearing gap.   The foil bearing according to claim 2, wherein the step is formed by elastically deforming a top foil portion following the shape of the support portion.   Foil is disposed at a plurality of locations in the relative rotation direction, each top foil portion is provided with the top foil portion and an under foil portion that supports an adjacent top foil portion from behind, and the under foil portion constitutes the support portion. The foil bearing of any one of claim | item 1-3.   The foil bearing of Claim 4 which provided the notch part recessed in the said relative rotation direction in the rear end of the underfoil part.   The foil bearing according to any one of claims 1 to 5, wherein a particle diameter of the particles is smaller than a minimum width of the bearing gap.   Top foil portions are arranged at a plurality of locations in the relative rotation direction, and a wide portion in which the width of the bearing gap is made larger than the minimum width is provided at a boundary portion between adjacent top foil portions, which is opposite to the wide portion. The foil bearing of any one of Claims 1-6 which provided the through-hole which penetrates the front and back of the said top foil part, and opens to the said wide part in the top foil part of the rotation direction side.

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