WO2017073603A1

WO2017073603A1 - Foil bearing

Info

Publication number: WO2017073603A1
Application number: PCT/JP2016/081706
Authority: WO
Inventors: 真人吉野
Original assignee: Ntn株式会社
Priority date: 2015-10-28
Filing date: 2016-10-26
Publication date: 2017-05-04
Also published as: JP6629042B2; JP2017082912A

Abstract

In this foil bearing, each of foils 12 is provided with: a top foil section 12A1 provided with a bearing surface X; and an under foil section 12B that is elastically deformable and that is arranged behind the top foil section. One end of the under foil section 12B in the circumferential direction is configured as a free end capable of movement in the circumferential direction. The under foil section 12B is formed by causing a plurality of foil materials 121, 122 having different shapes to overlap.

Description

Foil bearing

The present invention relates to a foil bearing.

¡The main shaft of a turbomachine (for example, a gas turbine or turbocharger) rotates at 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, a structure 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 unlikely to occur 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.

Japanese Patent Laying-Open No. 2015-52345

The foil bearing described in Patent Document 1 has a plurality of foils arranged in the rotational direction, and each foil is provided with a top foil part having a bearing surface and an elastically deformable underfoil part. The underfoil portion is disposed behind the top foil portion of another foil, and one end in the circumferential direction is configured as a free end that can move in the circumferential direction.

ばね One of the factors that influence the bearing performance of this type of foil bearing is the spring stiffness of the underfoil. This spring rigidity should be designed to the optimum size for each part of the underfoil part. Conventionally, since the underfoil part is made of a single foil material, the spring rigidity is set for each part of the underfoil part. This is difficult to optimize, and this is an obstacle to improving the bearing performance of the foil bearing.

Therefore, an object of the present invention is to increase the degree of freedom in designing the spring rigidity of the underfoil portion.

In order to solve the above-described problems, the present invention has a foil disposed at a plurality of locations in a relative rotational direction between the shaft to be supported, and a top foil portion having a bearing surface on each foil, and a top An under-foil portion that is elastically deformable disposed behind the foil portion, and a foil bearing in which one end in the circumferential direction of the under-foil portion is configured as a free end that is movable in the circumferential direction. A plurality of foil materials are formed to overlap each other.

In this way, if the underfoil part has a multilayer structure (multiple underfoil part) in which multiple foil materials are stacked, the spring rigidity can be adjusted by the individual foil material, so the spring rigidity of the entire underfoil part is optimal. It becomes easy to make it. Specifically, the spring rigidity of the underfoil portion is optimized by making the plurality of foil materials constituting the multi-layer underfoil portion different shapes or by making the materials or thicknesses of the plurality of foil materials different. be able to.

In addition, with such a configuration, it is possible to allow micro-sliding between a plurality of foil materials constituting the underfoil portion. Therefore, it is possible to enhance the effect of absorbing vibration generated in the rotation side member.

If the plurality of foil materials constituting the underfoil portion have different lengths in the circumferential direction, it becomes easy to provide a difference in spring rigidity in the circumferential direction of the underfoil portion. Therefore, it becomes possible to increase the wedge angle in the wedge space, thereby increasing the pressure of the fluid film to stabilize the rotation side member, to make an early transition to the steady rotation of the rotation side member, and the like.

If the plurality of foil materials constituting the underfoil portion have different width dimensions in the direction along the bearing surface and in the direction perpendicular to the circumferential direction, one end of the thickness direction of the foil is formed at both ends of the underfoil portion in the direction. It is possible to reduce the rigidity of the springs at both ends by removing the partial area. As a result, the top foil portion facing both ends can be easily deformed. For example, even when the rotation side member swings conically, it is possible to prevent the shaft and foil from hitting the edge.

By engaging the other end in the circumferential direction of the underfoil portion with the other foil in the circumferential direction, the underfoil portion can be held by the other foil and can be prevented from falling off. This engagement can be performed by crossing another foil at the boundary between the top foil portion and the under foil portion of each foil. The crossing of the foils can be performed, for example, by inserting the other foil into a slit provided in one foil.

Thus, according to the present invention, the degree of freedom in designing the spring rigidity of the underfoil portion can be increased. Therefore, it becomes easy to design a foil bearing suitable for various applications.

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 the foil overlap part of a foil bearing. It is sectional drawing which expands and shows the foil overlap part of a foil bearing. It is a top view of the foil material on the front side. It is a top view of the foil material of a back side. It is an expanded sectional view showing a foil duplication part typically (just after the start of rotation of a shaft). It is an expanded sectional view showing a foil overlap part typically (at the time of steady rotation of an axis). It is a top view of the foil material on the front side. It is a top view of the foil material of a back side. It is sectional drawing in the direction N orthogonal to the rotation direction of a foil overlap part. It is an expanded sectional view of the principal part of a foil holder.

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.

In the present invention, a so-called multi-arc type is used as the foil bearing suitable for the radial bearing 10 for the micro gas turbine. The basic configuration of the multi-arc foil bearing will be described below with reference to FIGS. As will be described later, the present invention is characterized in that each foil 12 of the foil bearing is formed of a plurality of foil materials stacked on each other. In FIG. 8), in order to facilitate understanding, the description will be made assuming that each foil 12 is formed of a single foil material.

[Basic configuration of multi-arc foil bearing]
As shown in FIG. 3, the multi-arc radial foil bearing 10 includes a foil holder 11 having a cylindrical inner peripheral surface 11 a, and a plurality of rotational directions of the shaft 6 on the inner peripheral surface 11 a of the foil holder 11. And a foil 12 disposed at a location. The foil bearing 10 of the example of illustration has illustrated the case where the foil 12 is arrange | positioned in three places of the internal peripheral surface 11a. A shaft 6 is inserted on the inner diameter side of each foil 12.

The foil holder 11 can be formed of, for example, a metal (for example, a steel material) such as a sintered metal or a 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 material constituting each foil 12 is processed into a predetermined shape by pressing or the like a belt-like foil having a thickness of about 20 μm to 200 μm made of a metal having high spring properties and good workability, such as a steel material or a copper alloy. Is formed. 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 12a on the rotation direction R side of the shaft 6 and a second region 12b on the counter-rotation direction side.

The first region 12a includes a top foil portion 12a1 that forms the bearing surface X, and a plurality of directions N along the surface of the top foil portion 12a1 and orthogonal to the rotational direction R (hereinafter simply referred to as “orthogonal direction N”). And a convex portion 12a2 extending in a direction protruding to the rotation direction R side. In this embodiment, the case where the convex part 12a2 is formed in the three places of the said orthogonal direction is illustrated. A minute notch 12a3 extending in the counter-rotating direction from the foil edge is provided at the base end of each convex portion 12a2.

At the rear end 12d (end portion on the counter-rotation direction side) of the second region 12b, two cutout portions 12b2 that are spaced apart in the orthogonal direction N and 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 N.

A slit-like insertion port into which the convex portions 12a2 of the adjacent foils 12 are inserted at a boundary portion between the first region 12a and the second region 12b and at a plurality of locations in the orthogonal direction N (the same number as the convex portions 12a2). 12c1 is 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 12c1 includes a linear cutout portion extending along the orthogonal direction N, and a wide cutout portion extending from the cutout 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.

As shown in FIG. 5, the two foils 12 can be connected by inserting each convex portion 12 a 2 of one foil 12 into the insertion port 12 c 1 of the adjacent foil 12. 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 periphery shape by 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.

As shown in FIG. 8, in the state where each foil 12 is attached to the foil holder 11, two adjacent foils 12 cross each other. On the rotation direction R side with respect to the intersecting portion, the convex portion 12a2 of one foil 12 wraps behind the other foil 12 through the insertion port 12c1 of the other foil 12, and the axial groove 11b of the foil holder 11 Has been inserted. Further, the top foil portion 12 a 1 of the other foil 12 constitutes the bearing surface X. On the counter-rotation direction side of the intersecting portion, the top foil portion 12a1 of one foil 12 constitutes the bearing surface X, and the second region 12b of the other foil wraps behind the one foil 12 and covers the underfoil portion. Constitute. The end of the underfoil portion 12b on the counter-rotation direction side is a free end, and the position of the end varies in the circumferential direction (rotation direction and counter-rotation direction) according to the elastic deformation of the underfoil portion 12b. The end portion of the underfoil portion 12b on the rotation direction R side is in a state of being engaged with another foil 12 (the one foil) in the circumferential direction at the intersecting portion.

フォ A foil overlapping portion W in which the foils overlap each other at the portion where the top foil portion 12a1 and the underfoil portion 12b overlap each other. The foil overlapped portion W is formed at a plurality of locations in the rotation direction R (the same number as the foil 12 and three locations in the present embodiment).

In this foil bearing 10, 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 another foil 12 in the circumferential direction. is there. As a result, the adjacent foils 12 are in a state of sticking to each other in the circumferential direction, so that the top foil portion 12a1 of each foil 12 projects to the foil holder 11 side, and has a shape along the inner peripheral surface 11a of the foil holder 11. Bend. 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 including the free end of the underfoil portion 12b.

As shown in FIG. 8, since the axial groove 11b is provided with a slight inclination by an angle θ1 with respect to the tangential direction of the inner peripheral surface of the foil holder 11, the vicinity of the convex portion 12a2 inserted into the axial groove 11 Then, 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. Accordingly, a wedge space is formed between the bearing surface X of the top foil portion 12a1 and the outer peripheral surface of the shaft 6. The top foil portion 12a1 is supported by the elastically deformable underfoil portion 12b, so that the top foil portion 12a1 can be deformed following the displacement or thermal expansion of the shaft 6.

During the one-way rotation of the shaft 6, the air film generated in the wedge space becomes a high pressure, so that the shaft 6 receives a levitation force. Therefore, 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 rotatably supported in a non-contact state with respect to the foil 12. 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 radial width of the radial bearing gap C is exaggerated for easy understanding (the same applies to FIG. 9).

In this embodiment, as shown in FIG. 5, a notch 12b2 is provided at the rear end 12d of the second region 12b of each foil 12. While the shaft 6 is rotating, the top foil portion 12a1 of the foil overlapped portion W is pressed against the underfoil portion 12b and elastically deformed due to fluid pressure, so that the top foil 12a1 riding on the underfoil portion 12b has a bearing gap. A step in the width direction of C is formed. This level | step difference becomes a shape corresponding to the herringbone shape of the notch 12b2. Since the fluid flowing along the top foil portion 12a1 flows along the step (see the arrow), fluid pressure generating portions are formed at two locations in the orthogonal direction N in the bearing gap C. This makes it possible to support the moment load while enhancing the floating effect of the shaft 6. In the present embodiment, as shown in FIG. 4, since the notch 12a3 is formed in the top foil part 12a1 to reduce the rigidity of the top foil part 12a1, the top foil part 12a1 extends along the notch part 12b2. Even when deforming, the deformation is performed smoothly.

[Characteristic configuration of the present invention]
In the multi-arc type foil bearing described above, as shown in FIG. 9, a plurality of (two in this embodiment)

foil materials

121 and 122 are stacked to form each foil 12 in a multilayer structure. The point has a characteristic configuration.

FIG. 10 shows a plan view of the foil material 121 on the front side (side facing the bearing gap C) of the two

foil materials

121 and 122, and the plane of the foil material 122 on the back side (side away from the bearing gap C). The figure is shown in FIG. As shown in FIGS. 10 and 11, each

foil material

121, 122 has a first region 12 a having a top foil portion 12 a 1 and a convex portion 12 a 2 and an underfoil portion as in the foil 12 shown in FIG. 4. A second region 12b and an insertion port 12c1 located at the boundary between the first region 12a and the second region 12b are formed.

In the two

foil members

121 and 122 shown in FIGS. 10 and 11, the insertion port 12c1 and the region on the rotation direction R side of the insertion port 12c1 are formed in the same shape. Therefore, when the two

foil members

121 and 122 are overlapped with the position of the insertion opening 12c1, the first regions 12a of both the

foil members

121 and 122 are completely overlapped without one protruding from the other. It becomes a state.

On the other hand, the underfoil portions 12b of the two

foil members

121 and 122 have different shapes by varying the lengths in the rotation direction R. 9 to 11 illustrate, as an example, a case where the length of the underfoil portion 12b of the front foil material 121 is made shorter than that of the underfoil portion 12b of the back foil material 122.

Note that in FIGS. 10 and 11, the shape of the foil 12 shown in FIG. 4 is simplified. Specifically, the convex portion 12a2 and the insertion port 12c1 of the first region 12a are arranged at two places in the orthogonal direction N. Further, the notch 12b2 at the rear end 12d of the second region 12b is omitted. Of course, each

foil material

121, 122 may be provided with the same number (three) of protrusions 12a2 and insertion ports 12c1 as the foil 12 shown in FIG. Moreover, you may form notch part 12b2 similar to the foil 12 shown in FIG. 4 in the rear end 12d of the 2nd area | region 12b of each foil material 121,122.

The foil bearing 10 is assembled in the same procedure as described with reference to FIGS. At this time, the two

foil members

121 and 122 stacked on each other are handled as one foil 12 shown in FIGS. That is, as shown in FIG. 5, when the foils 12 are connected to each other, another foil 12 made of the two

foil members

121 and 122 is inserted into the insertion port 12 c 1 where the two

foil members

121 and 122 overlap each other. The overlapping convex portions 12a2 are inserted. Further, when the three foils 12 connected in a circumferential shape are attached to the foil holder 11, the overlapping convex portions 12a2 of the

foil materials

121 and 122 are inserted into the axial grooves 11b of the foil holder 11 (FIG. 9).

Through the above assembly process, as shown in FIG. 9, the foil bearing 10 includes a multilayer top foil portion 12 </ b> A <b> 1 in which the top foil portions 12 a 1 of the

foil materials

121 and 122 are stacked, and a foil material of the separate foil 12. A multi-layer underfoil portion 12B is formed by overlapping the underfoil portions 12b of 121 and 122. The bearing surface X is formed on the surface of the top foil portion 12a1 on the front side of the multilayer top foil portion 12A1. The multilayer underfoil portion 12B is behind (back side) the multilayer top foil portion 12A1 and elastically supports the multilayer top foil portion 12A1. The end portions on the counter-rotation direction side of the multilayer underfoil portion 12 </ b> B constitute free ends, and the end portions on the rotation direction side are engaged with other foils 12 in the circumferential direction. Moreover, the foil overlap part W is formed by the multilayer top foil part 12A1 and the multilayer underfoil part 12B overlapping.

The multilayer underfoil portion 12B is formed with a multilayer portion E1 in which two underfoil portions 12b overlap each other and a single layer portion E2 composed of only one underfoil portion 12b out of the two underfoil portions 12b. The The multilayer part E1 is located on the rotation direction R side with respect to the single layer part E2.

FIG. 12 and FIG. 13 schematically show a cross-sectional structure of the foil overlap portion W when each of the foils 12 described above is attached to the foil holder 11. Of both figures, FIG. 12 shows a state immediately after the start of rotation of the shaft 6, and FIG. 13 shows a state during steady rotation of the shaft 6.

As shown in FIG. 12, when the shaft 6 starts to rotate, the multi-layer top foil portion 12A1 receives the air pressure P in the direction of the arrow generated in the bearing gap C and the width dimension of the bearing gap C increases (lower in the figure). ), And the multilayer top foil portion 12A1 is pressed against the multilayer underfoil portion 12B as shown in FIG. Further, in a region other than the foil overlapping portion W, the multilayer top foil portion 12A1 is pressed against the inner peripheral surface 11a of the foil holder 11.

In the multilayer underfoil portion 12B, the spring stiffness of the multilayer portion E1 formed by the two

foil materials

121 and 122 is larger than the spring stiffness of the single layer portion E2 formed by the single foil material 122. . Due to the difference in spring rigidity, during the rotation of the shaft 6, as shown in FIG. 13, the multilayer top foil portion 12A1 bends slightly in the area facing the multilayer portion E1 (small deformation amount), and the single layer portion E2 It bends greatly in the area opposite to (large deformation amount). Therefore, when forming each foil 12 with one foil material, the wedge angle α of the wedge space formed between the bearing surface X of the multilayer top foil portion 12A1 and the outer peripheral surface of the shaft 6 (FIG. 8 and the like). Compared to the reference). As the wedge angle α of the wedge space increases, the air pressure generated in each wedge space increases, so that the shaft 3 can be shifted to steady rotation at an early stage, and the stability of the shaft 6 during steady rotation is enhanced. It becomes possible.

In addition, in the foil overlap portion W, the multi-layer top foil portion 12A1 rides on the plurality of under-foil portions 12B having the foil thickness of two sheets, so that a step formed on the multi-layer top foil portion 12A1 ( The step in the width direction of the bearing gap C) increases. Also from this point, the wedge angle α of the wedge space can be increased, and the above effect can be made more remarkable.

Note that in FIG. 12 and FIG. 13, for ease of understanding, the deformation modes of the

respective foil materials

121 and 122 and the gaps formed between the

respective foil materials

121 and 122 are illustrated as simplified as possible. Therefore, in the actual foil bearing 10, the

foil materials

121 and 122 are not necessarily deformed in the mode shown in FIGS. 12 and 13, and in the mode shown in FIGS. 12 and 13 between the

foil materials

121 and 122. A gap is not always formed.

In the above description, the length of the underfoil portion 12b of the foil material 121 on the front side out of the two

foil materials

121 and 122 constituting the multilayer underfoil portion 12B is longer than that of the underfoil portion 12b of the foil material 122 on the back side. Although the case of shortening was illustrated, conversely, even if the length of the front side underfoil portion 12b is longer than the length of the backside underfoil portion 12b, the multilayer underfoil portion 12B is surrounded by the same manner as described above. A difference in spring rigidity can be formed in the direction, and an effect equivalent to the above can be obtained.

FIG. 14 and FIG. 15 show that the underfoil portion 12b is formed in different shapes by making the width dimension in the orthogonal direction N of the underfoil portions 12b of the two

foil members

121 and 122 different. In the present embodiment, the width dimension L2 of the underfoil portion 12b of the foil material 122 on the back side is made smaller than the width dimension L1 of the underfoil portion 12b of the foil material 121 on the front side (L2 <L1).

If it is such a structure, as shown in FIG. 16, in the foil overlapping part W, the both ends of the orthogonal | vertical direction N of the multilayer underfoil part 12B will be the form which was thinned by the thickness direction partial area | region. In this case, since the spring stiffness at both ends of the multilayer underfoil portion 12B is reduced, both ends in the orthogonal direction N of the multilayer top foil portion 12A1 are deformed following the displacement of the shaft 6 as compared with the central portion. It becomes easy to do. Therefore, such edge contact can be prevented even when there is a concern about edge contact between the shaft 6 and the bearing surface X, such as when the shaft 6 is used in a conical manner. When the shaft 6 and the bearing surface X come into contact with the edge, the contact surface pressure increases, and thus the foil 12 and the shaft 6 are likely to be worn. However, the configuration shown in FIG. Can do.

FIG. 16 illustrates the case where the width dimension of the underfoil portion 12b of the back foil material 122 in the multilayer underfoil portion 12B is reduced, but the underside of the front foil material 121 is opposite to FIG. The same effect can be obtained even if the width dimension of the foil part 12b is made smaller than that of the underfoil part 12b on the back side. In addition to removing the partial thickness region at both ends of the multilayer underfoil portion 12B in this way, the same effect can be obtained by removing the partial thickness region at both ends of the multilayer top foil portion 12A1. Can be obtained. For example, in the multi-layer top foil part 12A1, the top foil part 12a1 of the foil material 122 on the back side is similar to the above even if the width dimension is smaller than the width dimension of the top foil part 12a1 of the foil material 121 on the front side. An effect can be obtained.

14 and 15, as in the embodiment shown in FIG. 9, the circumferential length of the underfoil portion 12 b of the rear foil material 122 is the circumferential length of the underfoil portion 12 b of the front foil material 121. However, it is also possible to reverse the long / short relationship between them, or to make them both the same length.

As described above, in the present invention, the underfoil portion of the foil bearing 10 is constituted by the multilayer underfoil portion 12B in which a plurality of

foil materials

121 and 122 are stacked. In this case, the spring rigidity of each part can be optimized in the multilayer underfoil part 12B as a whole by making the spring rigidity of each

foil material

121, 122 different. For this reason, the degree of freedom in designing the underfoil portion is increased, and the foil bearing that is suitable for use conditions can be easily designed. Specifically, as shown in FIGS. 10, 11, 14, and 15, the under-foil portions 12 b of the

foil members

121 and 122 have different shapes, so that the springs in the rotational direction R and the orthogonal direction N can be obtained. A difference in stiffness can be provided. In addition, the same effect can be obtained even if the multilayer underfoil portion 12B is configured by foil materials 121 and 122 (whether the shape is the same or different) having different materials and thicknesses.

In addition, in this embodiment, the under foil portion of the foil bearing 10 and the top foil portion have a multilayer structure in which a plurality of

foil materials

121 and 122 are stacked. Therefore, the micro sliding between the

foil materials

121 and 122 which comprise the multilayer top foil part 12A1 and the multilayer underfoil part 12B can be permitted. As a result, the effect of absorbing the vibration of the shaft 6 is enhanced, so that the unstable behavior of the shaft 6 can be prevented and its rotation can be stably supported.

Incidentally, the axial groove 11b formed in the foil holder 11 is formed in a direction substantially tangential to the inner peripheral surface 11a as shown in FIG. The axial groove 11b can be formed by wire cutting or the like. However, when the wire is simply reciprocated, as shown in FIG. This becomes the edge 11c ′. When the edge 11c ′ is formed at the outlet of the axial groove 11b as described above, the vicinity of the edge 11c ′ is deformed when the shaft 6 collides with this portion, and this influence affects the bearing surface X, thereby improving the bearing performance. May decrease. In order to prevent such a problem, it is preferable to provide a chamfer 11c at the end of the outlet portion of the axial groove 11b on the rotation direction R side as shown in FIG. The chamfer 11c can be formed, for example, by bending the wire traveling direction 90 ° toward the inner peripheral surface 11a at the final stage of the return stroke of the wire during wire cutting. Of course, the chamfered portion 11c can be formed by dropping the edge 11c 'in post-processing (cutting or the like) after the formation of the axial groove 11b.

In the above description, a so-called multi-arc radial foil bearing has been exemplified as the foil bearing 10. However, the form of the foil bearing is not limited to this, and an underfoil portion that can be elastically deformed behind the top foil portion. The present invention can be applied to an arbitrary form of foil bearing in which the circumferential end of the underfoil portion is configured with a free end that is movable in the circumferential direction. Moreover, if it is a foil bearing which has this structure, this invention is applicable not only to the radial foil bearing which supports a radial load but to the thrust foil bearing which supports a thrust load.

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 12a1 top foil portion 12A1 multilayer top foil portion 12b under foil portion 12B multilayer under foil portion 12d rear end 121 foil material 122 foil material C bearing gap R rotational direction N direction orthogonal to rotational direction X bearing surface

Claims

There are foils arranged at a plurality of positions in the relative rotational direction between the shafts to be supported, and each foil has a top foil part having a bearing surface and an elastically deformable material arranged behind the top foil part. In the foil bearing which is provided with an underfoil portion, and configured with one end in the circumferential direction of the underfoil portion as a free end movable in the circumferential direction,
A foil bearing, wherein the underfoil portion is formed by stacking a plurality of foil materials.
The foil bearing according to claim 1, wherein the plurality of foil members constituting the underfoil portion have different shapes.
The foil bearing according to claim 2, wherein the plurality of foil members constituting the underfoil portion have different lengths in the circumferential direction.
The foil bearing according to claim 2, wherein the plurality of foil members constituting the underfoil portion have different width dimensions in a direction orthogonal to the circumferential direction.
The foil bearing according to claim 1 or 2, wherein the plurality of foil members constituting the underfoil portion are made of different materials or thicknesses.
The foil bearing according to any one of claims 1 to 5, wherein the other circumferential end of the underfoil portion is engaged with another foil in the circumferential direction.