Foil bearing and method for manufacturing foil bearing

Abstract

This foil bearing is for supporting a rotary shaft and comprises a top foil, a back foil, and a bearing housing. Let an initial shape be defined as the shape of the top foil in a state where the top foil is not accommodated in the bearing housing and the top foil is not being subjected to an external force, in which case the radius of curvature of at least a portion of the inner surface of the top foil in the initial shape is greater than the radius of curvature of the inner surface of the bearing housing in a cross section orthogonal to an axial direction of the top foil.

Description

Foil bearing and method for manufacturing foil bearing

[0001] The present disclosure relates to foil bearings and methods of manufacturing foil bearings.

[0002] A foil bearing includes a top foil arranged along the outer circumferential surface of a rotating shaft, a back foil arranged on the outer circumferential side of the top foil, and a bearing housing that accommodates the top foil and back foil. If distortion such as undulation occurs in the top foil during assembly of the foil bearing, desired bearing performance cannot be achieved. Patent Document 1 describes that the foil bearing has thin-walled portions at both ends of the top foil, which make the ends more susceptible to elastic deformation, resulting in the top foil taking a shape that follows the rotating shaft.

[0003] Patent No. 5929626

[0004] Since the thickness of a typical top foil is less than 1 mm (for example, 0.1 mm to 0.2 mm), high manufacturing precision is required to achieve a distribution in the thickness of the top foil as described in Patent Document 1, which is likely to result in increased manufacturing costs.

[0005] In view of the above circumstances, at least one embodiment of the present disclosure aims to provide a foil bearing and a manufacturing method thereof that can suppress the occurrence of undulations in the top foil while suppressing increases in manufacturing costs.

[0006] In order to achieve the above object, a foil bearing according to at least one embodiment of the present disclosure is a foil bearing for supporting a rotating shaft, comprising: a top foil arranged along an outer peripheral surface of the rotating shaft; a back foil arranged on the outer peripheral side of the top foil; and a bearing housing that accommodates the top foil and the back foil, wherein, if the shape of the top foil when it is not accommodated in the bearing housing and is not subjected to an external force is defined as an initial shape, in a cross section perpendicular to the axial direction of the top foil, the radius of curvature of at least a portion of the inner surface of the top foil in the initial shape is larger than the radius of curvature of the inner peripheral surface of the bearing housing.

[0007] According to at least one embodiment of the present disclosure, a foil bearing and a manufacturing method thereof are provided that can suppress the occurrence of undulations in the top foil while suppressing an increase in manufacturing costs.

[0008] 6 is a schematic cross-sectional view perpendicular to the axial direction of a foil bearing 2 according to one embodiment. FIG. 7 is a schematic cross-sectional view for explaining a load F in the opposite direction to the load acting on the top foil 6 from each ridge portion 8d of the back foil 8. FIG. 8 is a diagram showing a change in the shape of the top foil 6 when the magnitude of the load F is changed. FIG. 9 is a diagram showing an example of a cross-section perpendicular to the axial direction in the initial shape of the top foil 6. FIG. 10 is a diagram showing another example of a cross-section perpendicular to the axial direction in the initial shape of the top foil 6. FIG. 11 is a flowchart showing an example of a method for manufacturing the foil bearing 2 described above. FIG. 12 is a schematic diagram for explaining an example of details of the manufacturing method shown in FIG. 13 is a schematic diagram for explaining another example of details of the manufacturing method shown in FIG.

[0009] Several embodiments of the present disclosure will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of components described as embodiments or shown in the drawings are merely illustrative examples and are not intended to limit the scope of the invention. For example, expressions expressing relative or absolute arrangements, such as "in a certain direction," "along a certain direction," "parallel," "orthogonal," "center," "concentric," or "coaxial," not only strictly express such arrangements, but also express relative displacements with a tolerance or angle or distance to the extent that the same function is achieved. For example, expressions expressing the equality of things, such as "same," "equal," and "homogeneous," not only express strict equality, but also express tolerance or differences to the extent that the same function is achieved. For example, expressions expressing shapes such as a square or cylindrical shape not only express shapes such as a square or cylindrical shape in the strict geometric sense, but also express shapes including concave and convex portions, chamfered portions, etc., to the extent that the same effect is achieved. On the other hand, the expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions that exclude the presence of other elements.

[0010] 1 is a schematic cross-sectional view perpendicular to the axial direction of a foil bearing 2 according to one embodiment. As shown in FIG. 1, the foil bearing 2 is configured to rotatably support a rotating shaft 4, and includes a top foil 6, a back foil 8, and a bearing housing 10.

[0011] The top foil 6 is substantially cylindrical and is disposed along the outer peripheral surface 4a of the rotating shaft 4 so as to surround the rotating shaft 4, facing the outer peripheral surface 4a. The top foil 6 is formed by bending a flexible, strip-shaped metal plate material into a cylindrical shape with the long side direction being the circumferential direction and the short side direction being the axial direction. A fixed end 6a, which is one circumferential end of the top foil 6, is bent radially outward of the top foil 6 and inserted into a retaining groove 12 of the bearing housing 10. A free end 6b, which is the other circumferential end of the top foil 6, faces the fixed end 6a at a circumferential distance. The top foil 6 is disposed inside the bearing housing 10 with the fixed end 6a held in the retaining groove 12. The thickness of the top foil 6 is constant regardless of the axial position of the top foil 6 and is also constant regardless of the circumferential position of the top foil 6.

[0012] The back foil 8 is substantially cylindrical and is disposed on the outer periphery of the top foil 6 so as to surround the top foil 6. The back foil 8 is formed by bending a flexible, band-shaped corrugated metal material into a cylindrical shape with the long side direction being the circumferential direction and the short side direction being the axial direction. A fixed end 8a, which is one circumferential end of the back foil 8, is bent radially outward from the back foil 8 and inserted into a retaining groove 12 of the bearing housing 10. A free end 8b, which is the other circumferential end of the back foil 8, faces the fixed end 8a with a circumferential gap therebetween. In the illustrated example, the retaining groove 12 of the bearing housing 10 is formed at the uppermost portion 11t of the inner circumferential surface 11 of the bearing housing 10, and the fixed end 6a of the top foil 6 and the fixed end 8a of the back foil 8 are fixed to the uppermost portion 11t of the inner circumferential surface 11 of the bearing housing 10.

[0013] The back foil 8 is disposed inside the bearing housing 10 with its fixed end 8a held in the holding groove 12. The back foil 8 is disposed radially outward of the top foil 6 and is located between the inner circumferential surface 11 of the bearing housing 10 and the top foil 6. The back foil 8 elastically supports the top foil 6.

[0014] The back foil 8 includes a plurality of valleys 8c in contact with the inner circumferential surface 11 of the bearing housing 10 and a plurality of peaks 8d in contact with the outer surface 16 of the top foil 6. The valleys 8c and peaks 8d are alternately arranged in the circumferential direction of the bearing housing 10 from the fixed end 8a to the free end 8b, forming a plurality of wave shapes. Each peak 8d is curved in an arc shape so as to protrude toward the outer surface 16 of the top foil 6. Each valley 8c is curved so as to be concave in a direction away from the outer surface 16 of the top foil 6 (so as to protrude toward the inner circumferential surface 11 of the bearing housing 10). The circumferential direction of the back foil 8 coincides with the circumferential direction of the top foil 6 and the circumferential direction of the bearing housing 10.

[0015] When the rotating shaft 4 is not rotating, each valley portion 8c of the back foil 8 is in contact with the inner circumferential surface 11 of the bearing housing 10, and each peak portion 8d of the back foil 8 is in contact with the outer surface 16 of the top foil 6. When the rotating shaft 4 rotates, the top foil 6 elastically deforms radially outward, causing air to enter between the rotating shaft 4 and the top foil 6, forming an air film, and the top foil 6 rotatably supports the rotating shaft 4 in a non-contact state via the air film. When the top foil 6 elastically deforms radially outward, each peak portion 8d of the back foil 8 is pushed by the top foil 6 and elastically deforms radially outward, so that the top foil 6 is elastically supported by the back foil 8.

[0016] In a conventional foil bearing, when the foil bearing is assembled, the top foil may be deformed by the load from the peaks of the back foil, resulting in an unintended shape. Therefore, the present inventors came up with a method of calculating a shape (see FIG. 3 ) resulting from the outward expansion of the top foil 6 by applying a load F (see FIG. 2 ) opposite to the load that the top foil 6 receives from the peaks 8 d of the back foil 8 to the inner surface 14 of the top foil 6 having a desired shape (e.g., a perfect circle) using FEM analysis (analysis using the finite element method) at each circumferential position where the peaks 8 d of the back foil 8 contact the top foil 6, and then determining the calculated shape or a shape approximating the calculated shape as the initial shape of the top foil 6. In this specification, the initial shape of the top foil 6 refers to the shape of the top foil 6 when the top foil 6 is not housed in the bearing housing 10 and is not subjected to an external force, and corresponds to the shape of the top foil 6 when, for example, the top foil 6 is placed on a horizontal surface so that the axial direction of the top foil 6 coincides with the vertical direction when not housed in the bearing housing 10. Note that Figure 3 shows the change in shape of the top foil 6 when the magnitude of the load F is changed (the shape of the top foil 6 for each load F).

[0017] Below, several examples of the initial shape of the top foil 6 determined using the above method will be described. Fig. 4 is a diagram showing an example of a cross section perpendicular to the axial direction of the top foil 6 in the initial shape of the top foil 6. Fig. 5 is a diagram showing another example of a cross section perpendicular to the axial direction of the top foil 6 in the initial shape of the top foil 6.

[0018] In some embodiments, as shown in Figures 4 and 5, for example, in a cross section perpendicular to the axial direction of the top foil 6, the inner surface 14 of the top foil 6 in its initial shape includes a first portion 21, a second portion 22 that is located closer to the fixed end 6a of the top foil 6 (one end side of the top foil 6) than the first portion 21 in the circumferential direction of the top foil 6 and has a smaller radius of curvature than the first portion 21, and a third portion 23 that is located closer to the free end 6b of the top foil 6 (the other end side of the top foil 6) than the first portion 21 in the circumferential direction of the top foil 6 and has a smaller radius of curvature than the first portion 21.

[0019] 4 and 5, the first portion 21, the second portion 22, and the third portion 23 are each a circular arc. In this case, if the radius of curvature of the first portion 21 is defined as R1, the radius of curvature of the second portion 22 is defined as R2, the radius of curvature of the third portion 23 is defined as R3, and the radius of curvature of the inner circumferential surface 11 of the bearing housing 10 is defined as R0, then R1 is larger than each of R2, R3, and R0. Furthermore, each of R2 and R3 is equal to or larger than R0, and may even be larger than R0. Note that the radius of curvature of the inner circumferential surface 11 of the bearing housing 10 is the radius of curvature of a circle that defines the inner circumferential surface 11.

[0020] 4 , in a cross section perpendicular to the axial direction of the top foil 6, the inner surface 14 of the top foil 6 in its initial shape is configured by three circular arcs, and one end and the other end of the first portion 21 in the circumferential direction are connected to the second portion 22 and the third portion 23, respectively. Furthermore, one end of the second portion 22 in the circumferential direction is connected to the fixed end portion 6a, and the third portion 23 forms the free end portion 6b. Furthermore, in the initial shape of the top foil 6, the radius of curvature R1 of the first portion 21 is the largest among the radii of curvature R1, R2, and R3 of the three circular arcs that form the inner surface 14.

[0021] 5 , in a cross section perpendicular to the axial direction of the top foil 6, the inner surface 14 of the top foil 6 in its initial shape is configured by seven circular arcs, and includes a fourth portion 24, a fifth portion 25, a sixth portion 26, and a seventh portion 27 in addition to the first portion 21 to the third portion 23. In the circumferential direction of the top foil 6, the fourth portion 24 is provided between the first portion 21 and the second portion 22 and adjacent to the second portion 22. In the circumferential direction of the top foil 6, the fifth portion 25 is provided between the first portion 21 and the third portion 23 and adjacent to the third portion 23. In the circumferential direction of the top foil 6, the sixth portion 26 is provided between the first portion 21 and the fourth portion 24 and adjacent to the first portion 21 and the fourth portion 24. In the circumferential direction of the top foil 6, the seventh portion 27 is provided between the first portion 21 and the fifth portion 25 and adjacent to the first portion 21 and the fifth portion 25. In addition, one end of the second portion 22 in the circumferential direction is connected to the fixed end portion 6a, and the third portion 23 forms the free end portion 6b. In addition, in the initial shape of the top foil 6, the radius of curvature R1 of the first portion 21 is the largest among the radii of curvature R1 to R7 of the seven circular arcs that form the inner surface 14.

[0022] In some embodiments, as shown in Figures 1, 4 and 5, for example, the center P1 (see Figures 4 and 5) of the first portion 21 in the circumferential direction of the top foil 6 is located on the fixed end 6a side of the top foil 6 in the circumferential direction relative to the lowest position Pb (see Figure 1) on the inner surface 14 of the top foil 6 when the top foil 6 is assembled into the foil bearing 2 (see Figure 1).

[0023] Here, a description will be given of the effects achieved by the foil bearing 2 according to some embodiments described using Figures 1 to 5. For example, in the foil bearing 2 according to some embodiments shown in Figures 4 and 5, in a cross section perpendicular to the axial direction of the top foil 6, the radius of curvature of at least a portion of the inner surface 14 of the top foil 6 in its initial shape (e.g., the radius of curvature R1 of the first portion 21) is larger than the radius of curvature R0 of the inner circumferential surface 11 of the bearing housing 10. Therefore, by accommodating the top foil 6 within the bearing housing 10, the top foil 6 elastically deforms so as to adhere to the back foil 8, thereby making it possible to suppress undulation of the top foil 6.

[0024] In addition, generally, near both ends of the top foil 6 in the circumferential direction, it is difficult for the top foil 6 to conform to the inner circumferential surface 11 of the bearing housing 10 or the outer circumferential surface 4 a of the rotating shaft 4. However, in the foil bearing 2, the radius of curvature R2 of the second portion 22 located on one end side of the top foil 6 relative to the first portion 21 in the circumferential direction of the top foil 6 and the radius of curvature R3 of the third portion 23 located on the other end side of the top foil 6 relative to the first portion 21 in the circumferential direction of the top foil 6 are smaller than the radius of curvature R1 of the first portion 21. This makes it possible to form the top foil 6 in a shape that conforms to the inner circumferential surface 11 of the bearing housing 10 or the outer circumferential surface 4 a of the rotating shaft 4 while suppressing the occurrence of undulations in the top foil 6, thereby stably obtaining desired bearing characteristics. Furthermore, compared to the foil bearing described in Patent Document 1, there is no need to provide a distribution in the thickness of the top foil 6, which suppresses an increase in the manufacturing cost of the foil bearing 2.

[0025] FIG. 6 is a flowchart illustrating an example of a manufacturing method for the foil bearing 2 described above. FIG. 7 is a schematic diagram illustrating details of the manufacturing method shown in FIG. 6 . As shown in FIGS. 6 and 7 , in S101, the top foil 6 is wound around a rod-shaped member 30 having a cross-sectional shape defined by the inner surface 14 of the top foil 6 in the initial shape of the top foil 6 described above (for example, the initial shape shown in FIG. 4 or 5 ) (winding step). Here, the rod-shaped member 30 may be made of, for example, metal or ceramic. Next, in S102, the top foil 6 wound around the rod-shaped member 30 is heated in a heating furnace 32 such as an electric furnace (heat treatment step). Note that in another embodiment, as shown in FIG. 8 , a rod-shaped heater 30A may be used as the rod-shaped member 30. In this case, in S102, the top foil 6 wound around the rod-shaped heater 30A may be heated by the rod-shaped heater 30A instead of the heating furnace 32. Next, in S103, the foil bearing 2 is manufactured by attaching the top foil 6 and the back foil 8 to the inside of the bearing housing 10 (attaching step).

[0026] According to the manufacturing method of the foil bearing 2 described using Figures 6 to 8, by including the above-mentioned heat treatment step, springback (the phenomenon in which the top foil 6 tries to return to its pre-processing shape) of the top foil 6 can be suppressed, and the above-mentioned initial shape of the top foil 6 can be accurately formed into the desired shape.

[0027] The present disclosure is not limited to the above-described embodiments, but also includes modifications to the above-described embodiments and appropriate combinations of these modifications.

[0028] For example, the inner surface 14 of the top foil 6 when the foil bearing 2 is assembled does not have to be a perfect circle in a cross section along the axial direction, but may be, for example, an ellipse, or a shape consisting of multiple arcs.

[0029] Furthermore, in some of the above-described embodiments, examples have been given in which the inner surface 14 of the top foil 6 in the initial shape of the top foil 6 consists of three arcs (see Figure 4) and seven arcs (see Figure 5) in a cross section perpendicular to the axial direction of the top foil 6, but the number of arcs constituting the inner surface 14 of the top foil 6 in the initial shape of the top foil 6 is not particularly limited, and may be, for example, three or more, or may be, for example, five to seven, etc.

[0030] 4 , at least one of the first portion 21, the second portion 22, and the third portion may be a curve other than a circular arc. That is, at least one of the radius of curvature of the first portion 21, the radius of curvature of the second portion 22, and the radius of curvature of the third portion may vary depending on the circumferential position of the top foil 6. For example, in a cross section perpendicular to the axial direction of the top foil 6, if the radius of curvature of the inner surface 14 of the top foil 6 in its initial shape is maximum at position P1, the radius of curvature of the inner surface 14 may continuously decrease from position P1 toward one end of the inner surface 14 in the circumferential direction of the top foil 6, and the radius of curvature of the inner surface 14 may continuously decrease from position P1 toward the other end of the inner surface 14 in the circumferential direction of the top foil 6.

[0031] The contents described in each of the above embodiments can be understood, for example, as follows.

[0032] [1] A foil bearing according to at least one embodiment of the present disclosure (e.g., the above-mentioned foil bearing 2) is a foil bearing for supporting a rotating shaft (e.g., the above-mentioned rotating shaft 4), and comprises: a top foil (e.g., the above-mentioned top foil 6) arranged along the outer circumferential surface of the rotating shaft; a back foil (e.g., the above-mentioned back foil 8) arranged on the outer circumferential side of the top foil; and a bearing housing (e.g., the above-mentioned bearing housing 10) that accommodates the top foil and the back foil, wherein, if the shape of the top foil when it is not accommodated in the bearing housing and is not subjected to an external force is defined as an initial shape, in a cross section perpendicular to the axial direction of the top foil, the radius of curvature of at least a part of the inner surface of the top foil (e.g., the above-mentioned inner surface 14) in the initial shape is larger than the radius of curvature of the inner circumferential surface of the bearing housing (e.g., the above-mentioned radius of curvature R0).

[0033] According to the foil bearing described in [1] above, the radius of curvature of the inner surface of the top foil in its initial shape is larger than the radius of curvature of the inner circumferential surface of the bearing housing. Therefore, when the top foil is housed in the bearing housing, it elastically deforms so as to adhere to the back foil. This allows the top foil to be shaped to fit the inner surface of the bearing housing and the outer surface of the rotating shaft while suppressing the occurrence of undulations in the top foil, thereby enabling the desired bearing characteristics to be stably obtained. Furthermore, because there is no need to provide a thickness distribution in the top foil as described in Patent Document 1, increases in manufacturing costs can be suppressed.

[0034] [2] In some embodiments, in the foil bearing described in [1] above, in a cross section perpendicular to the axial direction of the top foil, the inner surface of the top foil in the initial shape (e.g., the above-mentioned inner surface 14) includes: a first portion (e.g., the above-mentioned first portion 21); a second portion (e.g., the above-mentioned second portion 22) located on one end side of the top foil relative to the first portion in the circumferential direction of the top foil and having a smaller radius of curvature than the first portion; and a third portion (e.g., the above-mentioned third portion 23) located on the other end side of the top foil relative to the first portion in the circumferential direction of the top foil and having a smaller radius of curvature than the first portion, and the radius of curvature of the first portion in the initial shape (e.g., the above-mentioned radius of curvature R1) is larger than the radius of curvature of the inner surface of the bearing housing (e.g., the above-mentioned radius of curvature R0).

[0035] According to the foil bearing described in [2] above, the radius of curvature of the first portion in its initial shape is larger than the radius of curvature of the inner circumferential surface of the bearing housing, and therefore, by housing the top foil in the bearing housing, the top foil elastically deforms so as to adhere to the back foil, thereby suppressing undulation of the top foil. Generally, the top foil has difficulty conforming to the inner surface of the bearing housing or the outer surface of the rotating shaft near both ends of the top foil in the circumferential direction of the top foil. However, in the foil bearing described in [2] above, the radius of curvature of the second portion located on one end side of the top foil relative to the first portion in the circumferential direction of the top foil and the radius of curvature of the third portion located on the other end side of the top foil relative to the first portion in the circumferential direction of the top foil are smaller than the radius of curvature of the first portion. This makes it possible to form the top foil into a shape that conforms to the inner surface of the bearing housing or the outer surface of the rotating shaft while suppressing undulation of the top foil, thereby stably achieving desired bearing characteristics. Furthermore, since there is no need to provide a distribution in the thickness of the top foil as described in Patent Document 1, increases in manufacturing costs can be suppressed.

[0036] [3] In some embodiments, in the foil bearing described in [2] above, in the initial shape, the radius of curvature of the second portion (e.g., the above-mentioned radius of curvature R2) is larger than the radius of curvature of the inner surface of the bearing housing, and the radius of curvature of the third portion (e.g., the above-mentioned radius of curvature R3) is larger than the radius of curvature of the inner surface of the bearing housing.

[0037] According to the foil bearing described in [3] above, by accommodating the top foil in the bearing housing, the top foil elastically deforms so as to adhere to the back foil, thereby suppressing the occurrence of undulations in the top foil.

[0038] [4] In some embodiments, in the foil bearing according to either of [2] or [3] above, in the initial shape, each of the first portion, the second portion, and the third portion is an arc.

[0039] According to the foil bearing described in [4] above, the foil bearing described in [2] or [3] above can be easily manufactured.

[0040] [5] In some embodiments, in the foil bearing described in any of [2] to [4] above, the top foil includes a fixed end portion (e.g., the above-mentioned fixed end portion 6a) fixed to the bearing housing on the one end side of the top foil in the circumferential direction of the top foil, in a cross section perpendicular to the axial direction of the top foil, the inner surface of the top foil in the initial shape is composed of a plurality of arcs, the radius of curvature of the first portion is the largest among the radii of curvature of the plurality of arcs, and the center of the first portion in the circumferential direction of the top foil (e.g., the above-mentioned center P1) is located on the fixed end side in the circumferential direction of the top foil with respect to the lowest position on the inner surface of the top foil (e.g., the above-mentioned position Pb) when the top foil is incorporated into the foil bearing.

[0041] In a typical foil bearing, the fixed end of the top foil is fixed to the uppermost part of the inner circumferential surface of the bearing housing, and the free end of the top foil faces the fixed end of the top foil across a gap, so that the top foil has an asymmetric shape with respect to a vertical plane including the central axis of the bearing housing, and the back foil also has an asymmetric shape with respect to a vertical plane including the central axis of the bearing housing. In this case, as described in [5] above, when the top foil is incorporated into the foil bearing, by positioning a point corresponding to the center of the first portion in the circumferential direction of the top foil on the fixed end side in the circumferential direction of the top foil with respect to the lowest position on the inner surface of the top foil, it may be possible to enhance the above-mentioned effect of forming the top foil in a shape that follows the inner surface of the bearing housing and the outer surface of the rotating shaft while suppressing the generation of undulations in the top foil.

[0042] [6] In some embodiments, in the foil bearing described in any of [2] to [5] above, at least one of the radius of curvature of the first portion, the radius of curvature of the second portion, and the radius of curvature of the first portion varies depending on the circumferential position of the top foil.

[0043] As described in [6] above, in the initial shape, each of the first portion, the second portion, and the third portion may not be an arc, and the radius of curvature of each of the first portion, the second portion, and the third portion may vary continuously depending on the circumferential position of the top foil. In this case, the minimum value of the radius of curvature of the first portion may be equal to or greater than each of the maximum values ​​of the radius of curvature of the second portion and the third portion, or may be greater than each of the maximum values ​​of the radius of curvature of the second portion and the third portion.

[0044] [7] A method for manufacturing a foil bearing according to at least one embodiment of the present disclosure is a method for manufacturing a foil bearing according to any one of [1] to [6] above, comprising: a winding step (e.g., the above-mentioned step S101) of winding the top foil around a rod-shaped member (e.g., the above-mentioned rod-shaped member 30) having a cross-sectional shape defined by the inner surface of the top foil in the initial shape; a heat treatment step (e.g., the above-mentioned step S102) of heating the top foil wound around the rod-shaped member; and an attachment step (e.g., the above-mentioned step S103) of attaching the top foil to the inside of the bearing housing.

[0045] According to the method for manufacturing a foil bearing described in [7] above, by including the heat treatment step, springback of the top foil (the phenomenon in which the foil tends to return to its pre-processing shape) can be suppressed, and the top foil of the foil bearing described in any of [1] to [6] above can be precisely shaped to the desired shape.

[0046] 2 Foil bearing 4 Rotating shaft 4a Outer peripheral surface 6 Top foil 6a Fixed end 6b Free end 8 Back foil 8a Fixed end 8b Free end 8c Root portion 8d Peak portion 10 Bearing housing 11 Inner peripheral surface 11t Top portion 12 Retaining groove 14 Inner surface 16 Outer surface 21 First portion 22 Second portion 23 Third portion 24 Fourth portion 25 Fifth portion 26 Sixth portion 27 Seventh portion 30 Metal rod 30A Rod-shaped heater 32 Heating furnace

Claims

1. A foil bearing for supporting a rotating shaft, comprising: a top foil arranged along the outer peripheral surface of the rotating shaft; a back foil arranged on the outer peripheral side of the top foil; and a bearing housing that accommodates the top foil and the back foil, wherein, if the shape of the top foil when it is not accommodated in the bearing housing and is not subjected to an external force is defined as an initial shape, in a cross section perpendicular to the axial direction of the top foil, the radius of curvature of at least a portion of the inner surface of the top foil in the initial shape is larger than the radius of curvature of the inner peripheral surface of the bearing housing.

2. A foil bearing according to claim 1, wherein, in a cross section perpendicular to the axial direction of the top foil, the inner surface of the top foil in the initial shape includes: a first portion; a second portion located closer to one end of the top foil than the first portion in the circumferential direction of the top foil and having a smaller radius of curvature than the first portion; and a third portion located closer to the other end of the top foil than the first portion in the circumferential direction of the top foil and having a smaller radius of curvature than the first portion, and wherein the radius of curvature of the first portion in the initial shape is larger than the radius of curvature of the inner surface of the bearing housing.

3. The foil bearing according to claim 2, wherein, in the initial shape, the radius of curvature of the second portion is larger than the radius of curvature of the inner peripheral surface of the bearing housing, and the radius of curvature of the third portion is larger than the radius of curvature of the inner peripheral surface of the bearing housing.

4. The foil bearing according to claim 2, wherein in the initial shape, each of the first portion, the second portion, and the third portion is an arc.

5. A foil bearing according to claim 2, wherein the top foil includes a fixed end portion fixed to the bearing housing on the one end side of the top foil in the circumferential direction of the top foil, wherein in a cross section perpendicular to the axial direction of the top foil, the inner surface of the top foil in the initial shape is constituted by a plurality of arcs, wherein the radius of curvature of the first portion is the largest among the radii of curvature of the plurality of arcs, and wherein the center of the first portion in the circumferential direction of the top foil is located on the fixed end side in the circumferential direction of the top foil with respect to the lowest position on the inner surface of the top foil when the top foil is incorporated into the foil bearing.

6. The foil bearing according to claim 2, wherein at least one of the radius of curvature of the first portion, the radius of curvature of the second portion, and the radius of curvature of the third portion varies depending on the circumferential position of the top foil.

7. A foil bearing manufacturing method for manufacturing a foil bearing according to any one of claims 1 to 6, comprising: a winding step of winding the top foil around a rod-shaped member having a cross-sectional shape defined by the inner surface of the top foil in its initial shape; a heat treatment step of heating the top foil wound around the rod-shaped member; and an attachment step of attaching the top foil to the inside of the bearing housing.

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