Radial foil bearing, rotary machine, and method for assembling radial foil bearing

Abstract

A radial foil bearing according to the present invention comprises: a bearing housing which includes a housing end surface and a shaft hole that opens in the housing end surface; and a foil unit which includes at least one foil that is inserted in the shaft hole. The foil includes a foil body part which is disposed inside the shaft hole and a protrusion piece which is disposed outside the shaft hole, which protrudes radially outward of the shaft hole with respect to the foil body part, and which faces the housing end surface in the axial direction of the shaft hole. The bearing housing includes a protrusion which protrudes in the axial direction from the housing end surface and which faces the protrusion piece in the rotational direction of a shaft inserted in the shaft hole.

Description

Radial foil bearing, rotating machine, and method of assembling radial foil bearing

[0001] The present disclosure relates to a radial foil bearing, a rotating machine, and a method of assembling a radial foil bearing.

[0002] For example, Patent Documents 1 and 2 disclose technologies related to radial foil bearings. Patent Document 1 discloses a foil bearing including a cylindrical foil holder and a foil inserted into the foil holder. In this foil bearing, the inner circumferential surface of the foil bent into a cylindrical shape functions as a bearing surface for the shaft. In this foil bearing, a recess is formed at the end of the inner circumferential surface of the foil, in an area different from the area that serves as the bearing surface. The foil is formed with an engaging portion that fits into the recess. When the engaging portion is fitted into the recess, the engaging portion is pressed against both circumferential side surfaces of the recess.

[0003] The above-mentioned foil bearing is provided with an engagement structure including such an engagement portion and recess, thereby preventing the foil from rotating together with the shaft due to sliding between the shaft and the foil. When the engagement structure is formed in an area different from the bearing surface, as in the above-mentioned foil bearing, the degree of design freedom for the shape of the bearing surface is increased compared to when the engagement structure is formed in an area that becomes the bearing surface, making it possible to improve bearing performance.

[0004] JP 2019-019914 A International Publication No. 2017 / 169676

[0005] However, when the above-described locking structure is adopted, when assembling the foil to the foil holder, the foil must be precisely positioned in the rotational direction relative to the foil holder so that the engagement portions can be pressed against both circumferential sides of the recess. In this case, assembling the foil to the foil holder is difficult, and it is expected that the assembly will take a long time. Therefore, foil bearings equipped with the above-described locking structure have room for improvement in terms of ease of assembly.

[0006] The present disclosure describes a radial foil bearing, a rotating machine, and a method for assembling a radial foil bearing that can improve assembly efficiency.

[0007] A radial foil bearing according to one aspect of the present disclosure includes a bearing housing including a housing end face and a shaft hole opening into the housing end face, and a foil unit including at least one foil inserted into the shaft hole. The foil includes a foil main body portion disposed inside the shaft hole and a protruding piece disposed outside the shaft hole, protruding radially outward from the foil main body portion and facing the housing end face in the axial direction of the shaft hole. The bearing housing includes a protrusion protruding axially from the housing end face and facing the protruding piece in the rotational direction of a shaft inserted into the shaft hole.

[0008] According to some aspects of the present disclosure, there are provided a radial foil bearing, a rotating machine, and a method for assembling a radial foil bearing that can improve assembly efficiency.

[0009] FIG. 1 is a cross-sectional view showing an example of a rotary machine. FIG. 2 is a perspective view showing an example of a radial foil bearing. FIG. 3 is a front view showing an example of a radial foil bearing. FIG. 4 is a plan view showing an example of a top foil in an expanded state. FIG. 5 is a plan view showing an example of a back foil piece in an expanded state. FIG. 6(a) is a perspective view showing an example of a manufacturing process for a radial foil bearing. FIG. 6(b) is a perspective view showing a manufacturing process subsequent to the manufacturing process of FIG. 6(a). FIG. 6(c) is a perspective view showing a manufacturing process subsequent to the manufacturing process of FIG. 6(b).

[0010] A radial foil bearing according to one aspect of the present disclosure includes a bearing housing including a housing end face and a shaft hole opening into the housing end face, and a foil unit including at least one foil inserted into the shaft hole. The foil includes a foil main body portion disposed inside the shaft hole and a protruding piece disposed outside the shaft hole, protruding radially outward from the foil main body portion and facing the housing end face in the axial direction of the shaft hole. The bearing housing includes a protrusion protruding axially from the housing end face and facing the protruding piece in the rotational direction of a shaft inserted into the shaft hole.

[0011] When assembling the above-mentioned radial foil bearing, after inserting the foil into the axial bore of the bearing housing, the foil is rotated in the rotational direction relative to the bearing housing until the protruding piece of the foil abuts against the protrusion protruding from the end face of the housing. When the radial foil bearing is in use, the protruding piece of the foil abuts against the protrusion on the end face of the housing in the rotational direction, thereby stopping the rotation of the foil relative to the bearing housing. Unlike conventional structures that stop the rotation of the foil by fitting an engagement portion of the foil into a recess formed in the bearing housing, this structure, which stops the rotation of the foil by abutting the protruding piece against the protrusion, does not require precise alignment of the rotational position of the foil relative to the bearing housing. Therefore, the foil can be easily assembled to the bearing housing by simply inserting the foil into the axial bore and abutting the protruding piece against the protrusion. Therefore, the above-mentioned radial foil bearing reduces the difficulty of assembling the foil to the bearing housing and shortens the time required for assembly. In other words, the assembly of the radial foil bearing is improved.

[0012] In some embodiments, the protrusion may be a columnar protruding pin formed separately from the bearing housing and attached to the end face of the housing. In this way, if the protrusion is formed separately from the bearing housing, unlike when the protrusion is formed integrally with the bearing housing, the work of machining the end face of the housing to form the protrusion is not required, and the bearing housing can be easily formed.

[0013] In some embodiments, the foil may include a first protruding piece formed on a first edge portion in the rotation direction and a second protruding piece formed on a second edge portion in the opposite direction to the rotation direction. The protrusion may be arranged to abut only the first protruding piece of the first and second protruding pieces. In this case, a structure that stops the rotation of the foil by the abutment of the protruding piece against the protrusion can be suitably formed.

[0014] In some embodiments, the foil unit may include multiple foils arranged along the rotational direction. The bearing housing may include multiple protrusions arranged along the rotational direction. Each of the multiple protrusions may be disposed between adjacent protrusions of a first foil and a second foil. In this case, the rotation of each foil relative to the bearing housing can be stopped by abutting the protrusions of each foil against the corresponding protrusions in the rotational direction. Furthermore, when a single protrusion is disposed between the protrusions of the first foil and the protrusions of the second foil, as in the above configuration, the spacing between the protrusions in the rotational direction can be maintained wider than when two or more protrusions are disposed between the protrusions of the first foil and the protrusions of the second foil. This reduces the risk of the protrusions of the foil interfering with the protrusions when inserting the foil into the shaft hole. Therefore, with the above configuration, even when multiple protrusions are provided to stop the rotation of the multiple foils, the foils can be easily assembled to the bearing housing.

[0015] In some embodiments, the protrusion disposed between the protruding piece of the first foil and the protruding piece of the second foil may abut against the protruding piece of the first foil in the rotational direction. The protruding piece of the second foil may be spaced apart from the protrusion. In this case, the risk of the protruding piece of the second foil interfering with the protrusion when inserting the foil into the axial hole can be reduced, making it easier to assemble the foil into the bearing housing.

[0016] In some aspects, the foil unit may include, as foils, a top foil bent into a cylindrical shape along the inner circumferential surface of the axial hole, and a plurality of back foil pieces aligned in the rotational direction between the inner circumferential surface and the top foil. The bearing housing may include a plurality of protrusions aligned in the rotational direction. Each of the plurality of protrusions may be disposed between a protruding piece of a first back foil piece and a protruding piece of a second back foil piece that are adjacent to each other among the plurality of back foil pieces. The protruding piece of the top foil may overlap the protruding piece of the first back foil piece, or may abut in the rotational direction against a protrusion disposed between the protruding piece of the first back foil piece and the protruding piece of the second back foil piece. In this configuration, a single protrusion abuts in the rotational direction against the protruding piece of the top foil overlapping the protruding piece of the first back foil piece. Therefore, a single protrusion can be used to both detent the rotation of the first back foil piece and the rotation of the top foil. This allows for a reduced number of protrusions and a wider spacing between the protrusions in the rotational direction compared to when separate protrusions for detent rotation of the first back foil piece and the top foil are provided. This further effectively reduces the risk of the protruding piece of the foil interfering with the protrusion when inserting the foil into the axial hole. As a result, assembly of the foil into the bearing housing is made easier. Furthermore, overlapping the protruding piece of the top foil with the protruding piece of the first back foil piece increases the mechanical strength of these protruding pieces. This avoids the risk of the protruding piece deforming when abutting against the protrusion, thereby releasing the rotation stop of the top foil and the first back foil piece.

[0017] In some embodiments, the top foil may include, as protruding pieces, a first protruding piece formed on a first edge portion in the rotational direction and a second protruding piece formed on a second edge portion in the opposite direction to the rotational direction and facing the first protruding piece at a distance from the first protruding piece in the rotational direction. The first protruding piece may overlap the protruding piece of the first back foil piece. The second protruding piece may overlap the protruding piece of the second back foil piece and may be spaced apart from a protrusion disposed between the protruding piece of the first back foil piece and the protruding piece of the second back foil piece. In this case, the risk of the protruding piece of the first back foil piece and the protruding piece of the second back foil piece interfering with the protrusion when the first back foil piece and the second back foil piece are inserted into the axial hole can be reduced, making it easier to assemble the foils to the bearing housing.

[0018] A rotary machine according to one aspect of the present disclosure includes any one of the radial foil bearings described above, a shaft inserted into a shaft hole of a bearing housing and rotatably supported by the radial foil bearing, and an impeller attached to an end of the shaft. Because this rotary machine includes any one of the radial foil bearings described above, the assembly of the radial foil bearing can be improved as described above.

[0019] A method for assembling a radial foil bearing according to one embodiment of the present disclosure is a method for assembling any of the radial foil bearings described above. This assembly method includes the steps of inserting a foil into an axial hole of a bearing housing and rotating the foil unit in the rotational direction relative to the bearing housing until the protruding piece abuts against the protrusion in the rotational direction. As described above, the above assembly method allows for easy assembly of the foil into the bearing housing by simply inserting the foil into the axial hole of the bearing housing and then abutting the protruding piece against the protrusion. Therefore, the above assembly method can improve the ease of assembly of the radial foil bearing.

[0020] In some aspects, the method for assembling a radial foil bearing may further include, before the step of inserting the foil into the axial bore, a step of attaching a protrusion formed separately from the bearing housing to the housing end face by hammering the protrusion into the housing end face. In this way, when the protrusion is formed separately from the bearing housing, unlike when the protrusion is formed integrally with the bearing housing, the work of machining the housing end face to form the protrusion is not required, and the bearing housing can be easily formed.

[0021] In some embodiments, the step of inserting foils into the axial hole of the bearing housing may include the steps of: inserting a top foil bent into a cylindrical shape along the inner circumferential surface of the axial hole into the axial hole; and, after the step of inserting the top foil into the axial hole, inserting multiple back foil pieces aligned along the rotational direction between the inner circumferential surface and the top foil. If the multiple back foil pieces are inserted into the axial hole before the top foil is inserted into the axial hole, a restoring force is generated inside the axial hole, causing the multiple back foil pieces to return to their original flat shape. Therefore, in order to subsequently insert the top foil into the axial hole, a mechanism is required to maintain the multiple back foil pieces in a shape that follows the inner circumferential surface of the axial hole. In contrast, if the multiple back foil pieces are inserted into the axial hole after the top foil is inserted into the axial hole, the restoring force of the top foil previously inserted into the axial hole can be used to maintain the multiple back foil pieces in a shape that follows the inner circumferential surface of the axial hole. As a result, a mechanism for adjusting the shape of the multiple back foil pieces is not required, making it easier to assemble the foils into the bearing housing.

[0022] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicated descriptions will be omitted as appropriate.

[0023] <Rotating Machine> First, a rotating machine 1 according to this embodiment will be described with reference to Fig. 1 . The rotating machine 1 is, for example, an electrically assisted turbocharger. The rotating machine 1 includes a turbine 2, a compressor 3, an electric motor 10, and a shaft 15. The turbine 2 includes a turbine impeller 4 provided at a first end of the shaft 15 and a turbine housing 6 that houses the turbine impeller 4. The compressor 3 includes a compressor impeller 5 provided at a second end of the shaft 15 and a compressor housing 7 that houses the compressor impeller 5.

[0024] The rotor 11 of the electric motor 10 is disposed, for example, at the center of the shaft 15. The rotor 11 is fixed to the shaft 15 and is rotatable together with the shaft 15. The stator 12 of the electric motor 10 is disposed so as to surround the rotor 11. The stator 12 is fixed to a motor housing 13 provided between the turbine housing 6 and the compressor housing 7. The stator 12 is able to rotate the rotor 11 by generating a magnetic field around the shaft 15. Cooperation between the rotor 11 and the stator 12 assists in the rotation of the shaft 15.

[0025] In the rotary machine 1, exhaust gas discharged from the internal combustion engine flows into the turbine housing 6 through the scroll passage 6a and rotates the turbine impeller 4 about the rotation axis H. The exhaust gas that rotates the turbine impeller 4 is discharged from the discharge port 6b of the turbine housing 6. When the turbine impeller 4 rotates as described above, the compressor impeller 5 rotates via the shaft 15. At this time, torque is applied to the shaft 15 by the electric motor 10, thereby assisting the rotation of the shaft 15 and the compressor impeller 5. The rotating compressor impeller 5 draws in external air through the suction port 7b of the compressor housing 7. This air is compressed while passing through the compressor impeller 5 and the scroll passage 7a. The compressed air is discharged from the discharge port of the compressor housing 7 and supplied to the internal combustion engine.

[0026] The shaft 15 is rotatably supported around the rotation axis H by a plurality of bearings. The shaft 15 is designed to rotate in only one direction around the rotation axis H and is not designed to rotate in the opposite direction. At least one of the plurality of bearings is an example of a radial foil bearing according to an embodiment of the present disclosure. In the example shown in FIG. 1 , a pair of radial foil bearings 20 are provided at both ends of the shaft 15. The radial foil bearings 20 are air bearings that support the shaft 15 in the radial direction. The radial direction is a direction perpendicular to the rotation axis H.

[0027] In the rotary machine 1, a thrust collar 17 and a pair of thrust air bearings 18 are provided between the compressor impeller 5 and one of the pair of radial foil bearings 20 that is closer to the compressor impeller 5. The thrust collar 17 and the pair of thrust air bearings 18 support the shaft 15 in the thrust direction. The thrust direction is a direction parallel to the rotation axis H.

[0028] <Radial foil bearing> The radial foil bearing 20 will be described in detail with reference to Figures 2 and 3. The rotary machine 1 is provided with a pair of radial foil bearings 20. The pair of radial foil bearings 20 have the same structure. One of the radial foil bearings 20 will be described below as a representative example.

[0029] 2 and 3 , the radial foil bearing 20 includes a foil unit 30 and a bearing housing 40 that accommodates the foil unit 30. The foil unit 30 includes a top foil 31 and a back foil 33 that surrounds the top foil 31. When the shaft 15 rotates, an air film is formed between the shaft 15 and the top foil 31. By forming this air film, the radial foil bearing 20 supports the shaft 15 so that it can rotate freely.

[0030] <Bearing Housing> As shown in FIG. 2 , the bearing housing 40 is a cylindrical casing having a shaft hole 41. The shaft hole 41 penetrates the bearing housing 40 along the direction in which the rotation axis H extends. In the following description, the "axial direction D1" is the direction along the rotation axis H that passes through the center of the shaft hole 41. The "axial direction D1" coincides with the axial direction of the shaft 15 when the shaft 15 is inserted through the shaft hole 41. The "circumferential direction D2" is the circumferential direction of the shaft hole 41 based on the rotation axis H. The "circumferential direction D2" coincides with the circumferential direction of the shaft 15 when the shaft 15 is inserted through the shaft hole 41. The "rotational direction D21" is the direction of the "circumferential direction D2" in which the shaft 15 supported by the radial foil bearing 20 rotates when the radial foil bearing 20 is in use. The "radial direction D3" is the direction perpendicular to the rotation axis H or the direction along the diameter of the shaft hole 41 (see FIG. 1 ). The "radial direction D3" coincides with the radial direction of the shaft 15 when the shaft 15 is inserted through the shaft hole 41.

[0031] The bearing housing 40 is disposed so as to surround the foil unit 30 with the foil unit 30 accommodated inside the axial hole 41. The bearing housing 40 includes an inner circumferential surface 40a that surrounds the axial hole 41, an outer circumferential surface 40b facing the opposite side from the inner circumferential surface 40a, and two housing end faces 40c that connect the inner circumferential surface 40a and the outer circumferential surface 40b. Each of the inner circumferential surface 40a and the outer circumferential surface 40b is a circumferential surface centered on the rotation axis H. The pair of housing end faces 40c are end faces located at both ends of the bearing housing 40 along the axial direction D1. The pair of housing end faces 40c are, for example, perpendicular to the rotation axis H.

[0032] The axial hole 41 is a circular hole extending along the axial direction D1 between the pair of housing end faces 40c. The axial hole 41 is open to each of the pair of housing end faces 40c. The axial hole 41 can be defined as a space surrounded by the inner circumferential surface 40a of the bearing housing 40. The inner circumferential surface 40a surrounds the shaft 15 inserted into the axial hole 41. When the shaft 15 is inserted into the axial hole 41, the rotation axis H of the shaft 15 coincides with the central axis of the axial hole 41. The foil unit 30 is arranged between the inner circumferential surface 40a and the shaft 15.

[0033] Three (a plurality of) protruding pins 43 are provided on each housing end face 40c. Each protruding pin 43 is, for example, a columnar protrusion protruding from the housing end face 40c in the axial direction D1. Each protruding pin 43 is, for example, cylindrical with the axial direction D1 as the central axis direction. Each protruding pin 43 is formed separately from the bearing housing 40. Each protruding pin 43 is inserted into and fixed in a respective hole formed in the housing end face 40c. Each protruding pin 43 may be formed integrally with the bearing housing 40 or may be a part of the bearing housing 40. The material of each protruding pin 43 may be, for example, a metal material or another material.

[0034] The protruding pins 43 are arranged, for example, at equal intervals along the circumferential direction D2. The intervals between the protruding pins 43 along the circumferential direction D2 may also be unequal. For example, the protruding pins 43 are arranged at positions on the housing end face 40c that are farther from the inner circumferential surface 40a and the outer circumferential surface 40b. For example, the protruding pins 43 are arranged closer to the inner circumferential surface 40a than to the outer circumferential surface 40b in the radial direction D3. Each protruding pin 43 may be in contact with at least one of the inner circumferential surface 40a and the outer circumferential surface 40b. Hereinafter, when the three protruding pins 43 are to be individually described, the three protruding pins 43 will be referred to as the "first protruding pin 43A," the "second protruding pin 43B," and the "third protruding pin 43C," respectively. The first protruding pin 43A, the second protruding pin 43B, and the third protruding pin 43C are arranged in order along the rotational direction D21.

[0035] <Foil Unit> The foil unit 30 includes a top foil 31 and a back foil 33. The top foil 31 and the back foil 33 are each formed of metal foil and are flexible. The top foil 31 and the back foil 33 are each inserted into the axial hole 41 in a bent cylindrical shape. The top foil 31 is arranged in the axial hole 41 so as to surround the shaft 15. The back foil 33 is arranged between the top foil 31 and the inner circumferential surface 40a. The back foil 33 is arranged in the axial hole 41 so as to surround the top foil 31.

[0036] 2 and 3, the top foil 31 is formed from a single foil (thin plate). The top foil 31 is curved into a cylindrical shape along the inner circumferential surface 40a when inserted into the axial hole 41. The top foil 31 may include multiple top foil pieces aligned along the circumferential direction D2.

[0037] As shown in Figure 4, the top foil 31 in an unfolded state is a rectangular metal foil including a pair of long sides 311 extending in the longitudinal direction D2A and a pair of short sides 312 extending in the lateral direction D1A. The longitudinal direction D2A corresponds to the circumferential direction D2 when the top foil 31 is wound into a cylindrical shape. The lateral direction D1A corresponds to the axial direction D1 when the top foil 31 is wound into a cylindrical shape. Each long side 311 is a side edge of the top foil 31 extending along the longitudinal direction D2A. Each short side 312 is an end edge of the top foil 31 extending along the lateral direction D1A.

[0038] A pair of slits 313a are formed in a first edge portion 31a of the top foil 31, which includes one short side 312. A pair of slits 313b are formed in a second edge portion 31b of the top foil 31, which includes the other short side 312. The first edge portion 31a is an end portion of the top foil 31 in the longitudinal direction D2A. The first edge portion 31a is an end portion of the top foil 31 in the rotation direction D21 (see FIG. 2) when the top foil 31 is bent into a cylindrical shape. The second edge portion 31b is an end portion of the top foil 31 opposite to the first edge portion 31a. The second edge portion 31b is an end portion of the top foil 31 in the opposite direction to the rotation direction D21 (see FIG. 2) when the top foil 31 is bent into a cylindrical shape.

[0039] The pair of slits 313a are cut into one of the short sides 312 and extend linearly from the short side 312 along the longitudinal direction D2A. The pair of slits 313a are formed, for example, at positions symmetrical with respect to the center of the top foil 31 in the short direction D1A. The pair of slits 313b are cut into the other short side 312 and extend linearly from the short side 312 along the longitudinal direction D2A. The pair of slits 313b are formed, for example, on extensions of the pair of slits 313a.

[0040] The top foil 31 includes a top foil main body portion 314 (foil main body portion) and a pair of top foil side edge portions 315. Each top foil side edge portion 315 is a side edge portion of the top foil 31 that includes the long side 311. The top foil main body portion 314 is an intermediate portion located between the pair of top foil side edge portions 315 in the short direction D1A. Each top foil side edge portion 315 includes a first protruding piece P1a, a second protruding piece P1b, and a connecting portion P2.

[0041] The connection portion P2 is a portion that connects the first protruding piece P1a and the second protruding piece P1b to the top foil main body portion 314. The connection portion P2 is continuous with the top foil main body portion 314 in the short-side direction D1A. The first protruding piece P1a is a portion that extends from the connection portion P2 in the longitudinal direction D2A. The first protruding piece P1a is adjacent to the top foil main body portion 314 in the short-side direction D1A with the slit 313a in between. The first protruding piece P1a is separated from the top foil main body portion 314 in the short-side direction D1A by the slit 313a. The first protruding piece P1a can deform independently from the top foil main body portion 314. The second protruding piece P1b is a portion that extends from the connection portion P2 to the opposite side of the first protruding piece P1a along the longitudinal direction D2A. The second protruding piece P1b is adjacent to the top foil main body 314 in the short-side direction D1A with the slit 313b in between. The second protruding piece P1b is separated from the top foil main body 314 in the short-side direction D1A by the slit 313b. The second protruding piece P1b can be deformed independently from the top foil main body 314. The first protruding piece P1a and the second protruding piece P1b have, for example, the same shape and dimensions as each other.

[0042] 2 and 3 , the top foil 31 is inserted into the axial hole 41 in a rolled-up cylindrical state. As a result, the first end edge 31a of the top foil 31 faces the second end edge 31b of the top foil 31 with a gap in the circumferential direction D2. When the top foil 31 is inserted into the axial hole 41, the top foil main body 314 is disposed inside the axial hole 41, and the top foil side edge 315 is disposed outside the axial hole 41. In other words, the top foil main body 314 is accommodated in the axial hole 41, and the top foil side edge 315 is not accommodated in the axial hole 41 but protrudes outside the axial hole 41. The top foil side edge 315 protrudes in the axial direction D1 from the housing end surface 40c.

[0043] The top foil main body 314 accommodated in the axial hole 41 is maintained in a state bent into a cylindrical shape along the inner circumferential surface 40a. The connection portion P2 of the top foil side edge portion 315 protruding outward from the axial hole 41 is also maintained in a state bent into a cylindrical shape following the top foil main body 314. The first projecting piece P1a and the second projecting piece P1b separated from the top foil main body 314 extend from the connection portion P2 along a tangential direction of the cylindrically bent connection portion P2 without following the top foil main body 314. The first projecting piece P1a and the second projecting piece P1b project outward in the radial direction D3 relative to the top foil main body 314. The first projecting piece P1a and the second projecting piece P1b face the housing end face 40c in the axial direction D1.

[0044] The first protruding piece P1a and the second protruding piece P1b protruding outward in the radial direction D3 relative to the top foil main body 314 means that the first protruding piece P1a and the second protruding piece P1b are disposed at positions protruding outward in the radial direction D3. The direction in which the first protruding piece P1a and the second protruding piece P1b extend does not necessarily have to be along the radial direction D3. The first protruding piece P1a and the second protruding piece P1b of each top foil side edge 315 face the housing end face 40c in the axial direction D1, thereby preventing movement of the top foil 31 in the axial direction D1 relative to the bearing housing 40. The first protruding piece P1a and the second protruding piece P1b may abut against the housing end face 40c or may be spaced apart from the housing end face 40c.

[0045] The first protruding piece P1a and the second protruding piece P1b face each other at a distance from each other along the circumferential direction D2 and extend in directions that intersect with each other. Of the three protruding pins 43, the first protruding pin 43A is disposed between the first protruding piece P1a and the second protruding piece P1b in the circumferential direction D2. The first protruding piece P1a abuts against the first protruding pin 43A in the rotational direction D21. The second protruding piece P1b is spaced apart from the first protruding pin 43A in the rotational direction D21. The first protruding pin 43A is disposed so as to abut only against the first protruding piece P1a of the first protruding piece P1a and the second protruding piece P1b. The first protruding piece P1a abuts against the first protruding pin 43A in the rotational direction D21, thereby preventing rotation of the top foil 31 relative to the bearing housing 40 in the rotational direction D21. The diameter of the first protruding pin 43A is, for example, smaller than the distance in the circumferential direction D2 between the tip of the first protruding piece P1a and the tip of the second protruding piece P1b. In this specification, the abutment of the first element against the second element includes both a case in which the first element directly contacts the second element and a case in which the first element indirectly contacts the second element via another element. The first element refers to any element (e.g., the first protruding pin 43A) that forms the radial foil bearing 20. The second element refers to an element (e.g., the first protruding piece P1a) that forms the radial foil bearing 20 and is different from the first element.

[0046] <Back Foil> As shown in FIGS. 2 and 3 , the back foil 33 includes three (plural) back foil pieces P33. Each back foil piece P33 is, for example, a corrugated foil (thin plate). When inserted into the axial hole 41, the back foil pieces P33 are lined up in the circumferential direction D2 along the inner circumferential surface 40a and are curved so as to form a cylindrical shape as a whole when viewed along the axial direction D1. The back foil pieces P33 have, for example, the same shape and dimensions as each other. The back foil pieces P33 are, for example, lined up at equal intervals along the circumferential direction D2. Hereinafter, when the three back foils 33 are described separately, the three back foils 33 will be referred to as a "first back foil piece P33A," a "second back foil piece P33B," and a "third back foil piece P33C." The first back foil piece P33A, the second back foil piece P33B, and the third back foil piece P33C are arranged in order along the rotation direction D21.

[0047] The back foil piece P33 includes peaks 33A that curve along the inner circumferential surface 40a and protrude outward in the radial direction D3, and valleys 33B that are recessed inward in the radial direction D3 relative to the peaks 33A. The peaks 33A and valleys 33B are alternately arranged along the circumferential direction D2. The valleys 33B are arranged between adjacent peaks 33A in the circumferential direction D2. The valleys 33B directly or indirectly abut against the inner circumferential surface 40a of the bearing housing 40. The peaks 33A directly or indirectly abut against the top foil 31. Each back foil piece P33 elastically supports the top foil 31 by changing the curvature (flexure) of the peaks 33A.

[0048] As shown in FIG. 5 , the unfolded back foil piece P33 is a rectangular metal foil including a pair of long sides 331 extending in the longitudinal direction D1B and a pair of short sides 332 extending in the lateral direction D2B. The longitudinal direction D1B corresponds to the axial direction D1 when the back foil piece P33 is wound into a cylindrical shape. The lateral direction D2B corresponds to the circumferential direction D2 when the back foil piece P33 is wound into a cylindrical shape. Each short side 332 is a side edge of the back foil piece P33 extending along the lateral direction D2B. Each long side 331 is an edge of the back foil piece P33 extending along the longitudinal direction D1B.

[0049] A pair of slits 333a are formed in a first edge portion 33a of the back foil piece P33, which includes one long side 331. A pair of slits 333b are formed in a second edge portion 33b of the back foil piece P33, which includes the other long side 331. The first edge portion 33a is an end portion of the back foil piece P33 in the short direction D2B. The first edge portion 33a is an end portion of the back foil piece P33 in the rotation direction D21 (see FIG. 2) in a curved state. The second edge portion 33b is an end portion of the back foil piece P33 opposite to the first edge portion 33a. The second edge portion 33b is an end portion of the back foil piece P33 in the opposite direction to the rotation direction D21 (see FIG. 2) in a curved state.

[0050] The pair of slits 333a are cut into one of the long sides 331 and extend linearly from the long side 331 along the short side direction D2B. The pair of slits 333a are formed, for example, at positions symmetrical with respect to the center of the back foil piece P33 in the longitudinal direction D1B. The pair of slits 333b are cut into the other long side 331 and extend linearly from the long side 331 along the short side direction D2B. The pair of slits 333b are formed, for example, on extensions of the pair of slits 333a.

[0051] The back foil piece P33 includes a back foil main body portion 334 (foil main body portion) and a pair of back foil side edge portions 335. Each back foil side edge portion 335 is a side edge portion of the back foil piece P33 that includes the short side 332. The back foil main body portion 334 is an intermediate portion located between the pair of back foil side edge portions 335 in the longitudinal direction D1B. Each back foil side edge portion 335 includes a first protruding piece P3a, a second protruding piece P3b, and a connecting portion P4.

[0052] The connection portion P4 connects the first protruding piece P3a and the second protruding piece P3b to the back foil main body portion 334. The connection portion P4 is continuous with the back foil main body portion 334 in the longitudinal direction D1B. The first protruding piece P3a extends from the connection portion P4 in the short direction D2B. The first protruding piece P3a is adjacent to the back foil main body portion 334 in the longitudinal direction D1B, with the slit 333a in between. The first protruding piece P3a is separated from the back foil main body portion 334 in the longitudinal direction D1B by the slit 333a. The first protruding piece P3a can deform independently from the back foil main body portion 334. The second protruding piece P3b extends from the connection portion P4 to the opposite side from the first protruding piece P3a along the short direction D2B. The second protruding piece P3b is adjacent to the back foil main body portion 334 in the longitudinal direction D1B, with the slit 333b in between. The second protruding piece P3b is separated from the back foil main body portion 334 in the longitudinal direction D1B by the slit 333b. The second protruding piece P3b can be deformed independently of the back foil main body portion 334. The first protruding piece P3a and the second protruding piece P3b have, for example, the same shape and dimensions as each other.

[0053] 2 and 3, the back foil piece P33 is disposed between the inner circumferential surface 40a and the top foil 31. When the back foil piece P33 is inserted into the axial hole 41, the back foil main body portion 334 is disposed inside the axial hole 41, and the back foil side edge portion 335 is disposed outside the axial hole 41. In other words, the back foil main body portion 334 is housed in the axial hole 41, and the back foil side edge portion 335 is not housed in the axial hole 41 but protrudes outside the axial hole 41. The back foil side edge portion 335 protrudes in the axial direction D1 with respect to the housing end face 40c.

[0054] The back foil main body portion 334 accommodated in the axial hole 41 is maintained in a curved state along the inner circumferential surface 40a. The connection portion P4 of the back foil side edge portion 335 protruding outward from the axial hole 41 is also maintained in a curved state following the back foil main body portion 334. The first protruding piece P3a and the second protruding piece P3b separated from the back foil main body portion 334 extend in opposite directions from the connection portion P4 along the tangential direction of the curved connection portion P4 without following the back foil main body portion 334. The first protruding piece P3a and the second protruding piece P3b protrude outward in the radial direction D3 relative to the back foil main body portion 334. The first protruding piece P3a and the second protruding piece P3b face the housing end face 40c in the axial direction D1. The first protruding piece P3a and the second protruding piece P3b of each back foil side edge portion 335 face the housing end face 40c in the axial direction D1, thereby preventing movement of the back foil piece P33 in the axial direction D1 relative to the bearing housing 40. The first protruding piece P3a and the second protruding piece P3b may be in contact with the housing end face 40c in the axial direction D1, or may be spaced apart from the housing end face 40c.

[0055] As shown in FIGS. 2 and 3 , a first back foil piece P33A (first foil), a second back foil piece P33B (second foil), and a third back foil piece P33C are arranged at equal intervals along the circumferential direction D2 between the inner circumferential surface 40a of the bearing housing 40 and the top foil 31. The first protruding piece P3a of the first back foil piece P33A is disposed at the same position as the first protruding piece P1a of the top foil 31 in the circumferential direction D2. The first protruding piece P3a of the first back foil piece P33A overlaps the first protruding piece P1a of the top foil 31. The first protruding piece P3a of the first back foil piece P33A abuts against the first protruding pin 43A in the rotational direction D21 while overlapping the first protruding piece P1a of the top foil 31. This prevents the first back foil piece P33A from rotating relative to the bearing housing 40.

[0056] The second protruding piece P3b of the first back foil piece P33A extends in the opposite direction to the first protruding piece P3a of the first back foil piece P33A and faces, at a distance, the first protruding piece P3a of the third back foil piece P33C adjacent to the first back foil piece P33A in the circumferential direction D2. Therefore, the first protruding pin 43A is disposed so as to abut only the first protruding piece P3a of the first and second protruding pieces P3b of the first back foil piece P33A in the rotational direction D21. The third protruding pin 43C is disposed between the second protruding piece P3b of the first back foil piece P33A and the first protruding piece P3a of the third back foil piece P33C in the circumferential direction D2. The second protruding piece P3b of the first back foil piece P33A and the first protruding piece P3a of the third back foil piece P33C face the third protruding pin 43C in the circumferential direction D2.

[0057] The first protruding piece P3a of the third back foil piece P33C abuts against the third protruding pin 43C in the rotational direction D21. The second protruding piece P3b of the first back foil piece P33A is spaced apart from the third protruding pin 43C. The first protruding piece P3a of the third back foil piece P33C abuts against the third protruding pin 43C in the rotational direction D21, thereby preventing rotation of the third back foil piece P33C in the rotational direction D21 relative to the bearing housing 40. The diameter of the third protruding pin 43C is, for example, smaller than the distance in the circumferential direction D2 between the tip of the second protruding piece P3b of the first back foil piece P33A and the tip of the first protruding piece P3a of the third back foil piece P33C.

[0058] The second protruding piece P3b of the third back foil piece P33C extends in the opposite direction to the first protruding piece P3a of the third back foil piece P33C. The second protruding piece P3b of the third back foil piece P33C faces, at an interval in the circumferential direction D2, the first protruding piece P3a of the second back foil piece P33B adjacent to the third back foil piece P33C in the circumferential direction D2. Therefore, the third protruding pin 43C is disposed so as to abut only the first protruding piece P3a of the first protruding piece P3a and the second protruding piece P3b of the third back foil piece P33C in the rotational direction D21. The second protruding pin 43B is disposed between the second protruding piece P3b of the third back foil piece P33C and the first protruding piece P3a of the second back foil piece P33B in the circumferential direction D2. The second protruding piece P3b of the third back foil piece P33C and the first protruding piece P3a of the second back foil piece P33B face the second protruding pin 43B in the circumferential direction D2.

[0059] The first protruding piece P3a of the second back foil piece P33B abuts against the second protruding pin 43B in the rotational direction D21. The second protruding piece P3b of the third back foil piece P33C is spaced apart from the second protruding pin 43B. The first protruding piece P3a of the second back foil piece P33B abuts against the second protruding pin 43B in the rotational direction D21, thereby preventing rotation of the second back foil piece P33B in the rotational direction D21 relative to the bearing housing 40. The diameter of the second protruding pin 43B is, for example, smaller than the distance in the circumferential direction D2 between the tip of the second protruding piece P3b of the third back foil piece P33C and the tip of the first protruding piece P3a of the second back foil piece P33B.

[0060] The second protruding piece P3b of the second back foil piece P33B extends in the opposite direction to the first protruding piece P3a of the second back foil piece P33B. The second protruding piece P3b of the second back foil piece P33B faces the first protruding piece P3a of the first back foil piece P33A adjacent to the second back foil piece P33B in the circumferential direction D2 at a distance. Therefore, the second protruding pin 43B is positioned so as to abut only the first protruding piece P3a of the first protruding piece P3a and the second protruding piece P3b of the second back foil piece P33B in the rotational direction D21. The second protruding piece P3b of the second back foil piece P33B is positioned at the same position as the second protruding piece P1b of the top foil 31 in the circumferential direction D2. The second protruding piece P3b of the second back foil piece P33B overlaps the second protruding piece P1b of the top foil 31. The first protruding piece P3a of the second back foil piece P33B overlaps the second protruding piece P1b of the top foil 31 and faces the first protruding pin 43A with a gap therebetween in the circumferential direction D2.

[0061] In this way, the three protruding pins 43 are disposed one by one between two of the three back foil pieces P33 that are adjacent to each other in the circumferential direction D2. Therefore, only one protruding pin 43 is disposed between two adjacent back foil pieces P33, and no more than two protruding pins are disposed between each pair of adjacent back foil pieces P33. In this case, the number of protruding pins 43 provided on the housing end surface 40c is the same as the number of back foil pieces P33. Each protruding pin 43 faces the first protruding piece P3a of each back foil piece P33 in the circumferential direction D2 and directly or indirectly abuts against the first protruding piece P3a.

[0062] This prevents rotation of each back foil piece P33 relative to the bearing housing 40. In this manner, each protruding pin 43 functions to prevent rotation of the corresponding back foil piece P33. Furthermore, one protruding pin 43 (e.g., the first protruding pin 43A) abuts against the first protruding piece P1a of the top foil 31 and the first protruding piece P3a of the first back foil piece P33A, which are stacked on top of each other, and therefore functions to prevent rotation of both the top foil 31 and the back foil piece P33. The number of protruding pins 43 may be greater than the number of back foil pieces P33. For example, a protruding pin having the function of preventing rotation of the top foil 31 and a protruding pin having the function of preventing rotation of the back foil piece P33 may be provided separately, and these protruding pins may be positioned at different positions in the circumferential direction D2. In this case, the number of protruding pins is the total number of the top foils 31 and the back foil pieces P33.

[0063] <Method of Assembling Radial Foil Bearing> A method of assembling the radial foil bearing 20 will be described with reference to FIGS. 6(a) to 6(c).

[0064] 6(a), the first protruding pins 43A, the second protruding pins 43B, and the third protruding pins 43C are attached to the housing end faces 40c of the bearing housing 40 by driving the first protruding pins 43A, the second protruding pins 43B, and the third protruding pins 43C into the housing end faces 40c of the bearing housing 40. The first protruding pins 43A, the second protruding pins 43B, and the third protruding pins 43C are arranged, for example, at equal intervals along the circumferential direction D2.

[0065] Next, as shown in Figures 6(b) and 6(c), the foil unit 30 including the top foil 31, the first back foil piece P33A, the second back foil piece P33B, and the third back foil piece P33C is installed in the bearing housing 40.

[0066] Specifically, as shown in FIG. 6( b), the top foil 31 rolled into a cylindrical shape is first inserted into the axial hole 41 of the bearing housing 40. At this time, the first protruding piece P1a and the second protruding piece P1b of the top foil 31, which are located outside the axial hole 41, are deformed so as to open outward in the radial direction D3 due to a restoring force that attempts to return them to their original shape, and they face the housing end face 40c in the axial direction D1. A first protruding pin 43A driven into the housing end face 40c is disposed between the first protruding piece P1a and the second protruding piece P1b. Thereafter, the top foil 31 is rotated relative to the bearing housing 40 in the rotational direction D21 until the first protruding piece P1a of the top foil 31 abuts against the first protruding pin 43A.

[0067] Next, as shown in FIG. 6( c), the first back foil piece P33A, the second back foil piece P33B, and the third back foil piece P33C are inserted between the inner circumferential surface 40a of the bearing housing 40 and the top foil 31. At this time, the first protruding piece P3a and the second protruding piece P3b of each of these back foil pieces P33A, P33B, and P33C are deformed by a restoring force that attempts to return them to their original shapes, and they face the housing end surface 40c in the axial direction D1. A first protruding pin 43A is disposed between the first protruding piece P3a of the first back foil piece P33A and the second protruding piece P3b of the second back foil piece P33B. A second protruding pin 43B is disposed between the first protruding piece P3a of the second back foil piece P33B and the second protruding piece P3b of the third back foil piece P33C. A third protruding pin 43C is disposed between the first protruding piece P3a of the third back foil piece P33C and the second protruding piece P3b of the first back foil piece P33A.

[0068] Thereafter, the first back foil piece P33A, the second back foil piece P33B, and the third back foil piece P33C are rotated in the rotation direction D21 relative to the bearing housing 40 until the first protruding piece P3a of the first back foil piece P33A, the first protruding piece P3a of the second back foil piece P33B, and the first protruding piece P3a of the third back foil piece P33C abut against the first protruding pin 43A, the second protruding pin 43B, and the third protruding pin 43C, respectively. As a result, the first protruding piece P3a of the first back foil piece P33A is overlapped with the first protruding piece P1a of the top foil 31, and the second protruding piece P3b of the second back foil piece P33B is overlapped with the second protruding piece P1b of the top foil 31.

[0069] Through the above steps, assembly of the foil unit 30 to the bearing housing 40 is completed. The timing for rotating the top foil 31 may be after the back foil piece P33 is inserted into the axial hole 41. In this case, the top foil 31 and the back foil piece P33 inserted into the axial hole 41 may be rotated together. The back foil piece P33 may be inserted into the axial hole 41 before the top foil 31 is inserted into the axial hole 41.

[0070] The effects obtained by the radial foil bearing 20, the rotary machine 1, and the method for assembling the radial foil bearing 20 according to this embodiment will be described.

[0071] As described above, when assembling the radial foil bearing 20 according to this embodiment, after inserting the top foil 31 into the axial hole 41 of the bearing housing 40, the top foil 31 is rotated in the rotational direction D21 relative to the bearing housing 40 until the first protruding piece P1a of the top foil 31 abuts against the protruding pin 43. Similarly, after inserting the back foil piece P33 into the axial hole 41, the back foil piece P33 is rotated in the rotational direction D21 relative to the bearing housing 40 until the first protruding piece P3a of the back foil piece P33 abuts against the protruding pin 43. This completes the assembly of the foil unit 30 to the bearing housing 40.

[0072] In this structure, the rotation of the top foil 31 and the back foil piece P33 is stopped by the first protruding pieces P1a, P3a abutting against the protruding pin 43. This structure, unlike a conventional structure in which the rotation of the foils is stopped by fitting the engagement portions of the foils into recesses formed in the bearing housing, does not require precise alignment of the positions of the top foil 31 and the back foil piece P33 in the rotational direction D21 relative to the bearing housing 40. Therefore, after inserting the top foil 31 and the back foil piece P33 into the axial hole 41, the foil unit 30 can be easily assembled to the bearing housing 40 by simply butting the first protruding pieces P1a, P3a against the protruding pin 43. Therefore, according to this embodiment, the difficulty of assembling the foil unit 30 to the bearing housing 40 can be reduced, and the time required for assembly can be shortened. In other words, the assembly of the radial foil bearing 20 according to this embodiment can be improved.

[0073] As in this embodiment, the protruding pin 43 may be formed separately from the bearing housing 40 and attached to the housing end surface 40c. In this way, when the protruding pin 43 is formed separately from the bearing housing 40, unlike when the protruding pin 43 is formed integrally with the bearing housing 40, the work of machining the housing end surface 40c to form the protruding pin 43 is not required, and the bearing housing 40 can be easily formed. Furthermore, when the foil unit 30 is installed in the bearing housing 40 after the protruding pin 43 is attached to the housing end surface 40c, the foil unit 30 does not interfere with the driving of the protruding pin 43, unlike when the foil unit 30 is installed in the bearing housing 40 and then the protruding pin 43 is attached to the housing end surface 40c. As a result, the assembly of the foil unit 30 to the bearing housing 40 can be made even easier.

[0074] As in the present embodiment, the protruding pin 43 may contact only the first protruding piece P3a of the first protruding piece P3a and the second protruding piece P3b of the back foil piece P33. In this case, a structure can be preferably formed in which the rotation of the back foil piece P33 is stopped by the abutment of the first protruding piece P3a against the protruding pin 43.

[0075] As in the present embodiment, the first protruding pin 43A may be disposed between the first protruding piece P3a of the first back foil piece P33A and the second protruding piece P3b of the second back foil piece P33B, which are adjacent to each other. The first protruding piece P1a of the top foil 31 may overlap the first protruding piece P3a of the first back foil piece P33A and may abut against the first protruding pin 43A in the rotational direction D21. In this case, one protruding pin 43 can be used to stop the rotation of both the first back foil piece P33A and the top foil 31. Therefore, compared to a case in which a protruding pin for stopping the rotation of the first back foil piece P33A and a protruding pin for stopping the rotation of the top foil 31 are separately provided, the number of protruding pins 43 can be reduced and the intervals between the protruding pins 43 in the circumferential direction D2 can be maintained wide. This effectively reduces the risk that the top foil 31 and the back foil piece P33 will interfere with the protruding pin 43 when inserting the top foil 31 and the back foil piece P33 into the axial hole 41. As a result, assembly of the foil unit 30 to the bearing housing 40 becomes even easier.

[0076] Furthermore, by overlapping the first protruding piece P1a of the top foil 31 with the first protruding piece P3a of the first back foil piece P33A, the mechanical strength of the first protruding pieces P1a, P3a is increased. This prevents the first protruding pieces P1a, P3a from deforming and releasing the rotation prevention mechanism for the top foil 31 and the first back foil piece P33A when the first protruding pieces P1a, P3a contact the protruding pin 43. Furthermore, when the top foil 31 and the back foil piece P33 are formed separately, a highly wear-resistant material can be selected for the top foil 31, which can slide on the shaft 15, and a highly damping material can be selected for the back foil piece P33, which elastically supports the top foil 31. In other words, materials suitable for the respective functions of the top foil 31 and the back foil piece P33 can be selected.

[0077] As in the present embodiment, the top foil 31 may include a first protruding piece P1a formed on the first edge portion 31a and a second protruding piece P1b formed on the second edge portion 31b. The first protruding piece P1a may overlap the first protruding piece P3a of the first back foil piece P33A. The second protruding piece P1b may overlap the second protruding piece P3b of the second back foil piece P33B and may be spaced apart from the protruding pin 43. In this case, the risk of the back foil piece P33 interfering with the protruding pin 43 when inserting the back foil piece P33 into the shaft hole 41 can be reduced, making it easier to assemble the foil unit 30 to the bearing housing 40.

[0078] As in the present embodiment, after the top foil 31 is inserted into the axial hole 41, multiple back foil pieces P33 may be inserted between the inner circumferential surface 40a and the top foil 31. If multiple back foil pieces are inserted into the axial hole 41 and then the top foil 31 is inserted into the axial hole 41, a restoring force is generated inside the axial hole 41 that causes the multiple back foil pieces P33 to return to their original flat shape. Therefore, in order to subsequently insert the top foil 31 into the axial hole 41, a mechanism is required to maintain the multiple back foil pieces P33 in a shape that conforms to the inner circumferential surface 40a. In contrast, if multiple back foil pieces P33 are inserted into the axial hole 41 after the top foil 31 is inserted into the axial hole 41, the restoring force of the top foil 31 that was previously inserted into the axial hole 41 can be used to maintain the multiple back foil pieces P33 in a shape that conforms to the inner circumferential surface 40a. As a result, a mechanism for adjusting the shapes of the multiple back foil pieces P33 is not required, so that assembly of the foil unit 30 to the bearing housing 40 can be performed even more easily.

[0079] The radial foil bearing, rotary machine, and radial foil bearing assembly method of the present disclosure are not limited to the above-described embodiments and can be modified in various ways. For example, the "protrusion" of the present disclosure does not necessarily have to be a cylindrical protruding pin. For example, the "protrusion" of the present disclosure may be a protruding pin of another shape, such as a rectangular column, or may be another element, such as a rib rising from the end face of the housing. The number of "protrusions" of the present disclosure does not have to be three, but may be one, two, four, or more. The shape, arrangement, and number of the "protruding pieces" of the present disclosure are not limited to the above-described embodiments and can be modified as appropriate as long as they can abut against the "protrusion" of the present disclosure in the rotational direction. For example, the "protruding pieces" of the present disclosure may be bent pieces in which a portion of the foil is bent radially outward.

[0080] The "foil" of the present disclosure may include both a top foil portion that functions as a top foil and a back foil portion that functions as a back foil. In this case, multiple foils, each including a top foil portion and a back foil portion, may be arranged side by side in the circumferential direction. The "foil" of the present disclosure may be a top foil, a back foil piece or a back foil including the back foil piece, or an integrated foil having a top foil portion and a back foil portion. The "back foil" of the present disclosure is not limited to a bump foil formed in a corrugated shape, and may be a foil having another shape as long as it can elastically support the top foil.

[0081] <Additional Notes> The present disclosure is [1] "a radial foil bearing comprising: a bearing housing including a housing end face and a shaft hole opening into the housing end face; and a foil unit including at least one foil inserted into the shaft hole, wherein the foil includes a foil main body portion arranged inside the shaft hole; and a protruding piece arranged outside the shaft hole, protruding radially outward from the foil main body portion of the shaft hole and facing the housing end face in the axial direction of the shaft hole, and the bearing housing includes a protrusion protruding from the housing end face in the axial direction and facing the protruding piece in the rotational direction of a shaft inserted into the shaft hole."

[0082] The present disclosure is [2] "The radial foil bearing described in [1], wherein the protrusion is a columnar protruding pin formed separately from the bearing housing and attached to the end face of the housing."

[0083] The present disclosure is [3] "A radial foil bearing according to [1] or [2], wherein the foil includes, as the protruding pieces, a first protruding piece formed on a first end edge portion in the rotational direction and a second protruding piece formed on a second end edge portion in the opposite direction to the rotational direction, and the protrusion is arranged so as to abut only the first protruding piece of the first protruding piece and the second protruding piece."

[0084] The present disclosure is [4] "A radial foil bearing according to any one of [1] to [3], wherein the foil unit includes a plurality of foils aligned along the rotation direction, the bearing housing includes a plurality of protrusions aligned along the rotation direction, and each of the plurality of protrusions is disposed between the protruding piece of a first foil and the protruding piece of a second foil that are adjacent to each other among the plurality of foils."

[0085] The present disclosure is [5] "A radial foil bearing according to [4], wherein the protrusion arranged between the protruding piece of the first foil and the protruding piece of the second foil abuts against the protruding piece of the first foil in the rotational direction, and the protruding piece of the second foil is spaced apart from the protrusion."

[0086] The present disclosure is [6] "A radial foil bearing according to any of [1] to [3], wherein the foil unit includes, as the foils, a top foil bent into a cylindrical shape along an inner circumferential surface of the axial hole, and a plurality of back foil pieces aligned along the rotation direction between the inner circumferential surface and the top foil, the bearing housing includes a plurality of protrusions aligned along the rotation direction, each of the plurality of protrusions being arranged between the protruding piece of a first back foil piece and the protruding piece of a second back foil piece that are adjacent to each other among the plurality of back foil pieces, the protruding piece of the top foil overlapping the protruding piece of the first back foil piece and abutting in the rotation direction against the protrusion arranged between the protruding piece of the first back foil piece and the protruding piece of the second back foil piece."

[0087] The present disclosure is [7] "The radial foil bearing described in [6], wherein the top foil includes, as the protruding pieces, a first protruding piece formed on a first end edge portion in the rotational direction, and a second protruding piece formed on a second end edge portion in the opposite direction to the rotational direction and facing the rotational direction with a gap between the first protruding piece, the first protruding piece overlapping the protruding piece of the first back foil piece, and the second protruding piece overlapping the protruding piece of the second back foil piece and being spaced apart from the protrusion arranged between the protruding piece of the first back foil piece and the protruding piece of the second back foil piece."

[0088] The present disclosure is [8] "a rotary machine comprising: a radial foil bearing according to any one of [1] to [7]; a shaft inserted into the axial hole of the bearing housing and rotatably supported by the radial foil bearing; and an impeller attached to an end of the shaft."

[0089] The present disclosure is [9] "A method for assembling a radial foil bearing according to any one of [1] to [7], comprising the steps of: inserting the foil into the axial hole of the bearing housing; and rotating the foil unit in the rotational direction relative to the bearing housing until the protruding piece abuts against the protrusion in the rotational direction."

[0090] The present disclosure is

[10] "A method for assembling a radial foil bearing according to [9], further comprising the step of attaching the protrusion, which is formed separately from the bearing housing, to the housing end face by driving the protrusion into the housing end face before the step of inserting the foil into the axial hole."

[0091] The present disclosure is

[11] "A method for assembling a radial foil bearing according to [9] or

[10] , wherein the step of inserting the foil into the axial hole of the bearing housing includes: a step of inserting a top foil bent into a cylindrical shape along the inner circumferential surface of the axial hole into the axial hole; and a step of inserting a plurality of back foil pieces aligned along the rotation direction between the inner circumferential surface and the top foil after the step of inserting the top foil into the axial hole."

[0092] REFERENCE SIGNS LIST 1 Rotating machine 15 Shaft 20 Radial foil bearing 30 Foil unit 31 Top foil (foil) 31a, 33a First edge portion 31b, 33b Second edge portion 33 Back foil 40 Bearing housing 40a Inner peripheral surface 40c Housing end surface 41 Shaft hole 43 Protruding pin (protrusion) 314 Top foil main body portion (foil main body portion) 334 Back foil main body portion (foil main body portion) D1 Axial direction D2 Circumferential direction D21 Rotational direction P1a First protruding piece P1b Second protruding piece P33, P33A, P33B, P33C Back foil piece (foil) P33A First back foil piece (first foil) P33B Second back foil piece (second foil)

Claims

1. A radial foil bearing comprising: a bearing housing including a housing end face and a shaft hole opening into the housing end face; and a foil unit including at least one foil inserted into the shaft hole, wherein the foil includes a foil main body portion arranged inside the shaft hole; and a protruding piece arranged outside the shaft hole, protruding radially outward from the foil main body portion of the shaft hole and facing the housing end face in the axial direction of the shaft hole, and wherein the bearing housing includes a protrusion protruding in the axial direction from the housing end face and facing the protruding piece in the direction of rotation of a shaft inserted into the shaft hole.

2. A radial foil bearing according to claim 1, wherein the protrusion is a columnar protruding pin formed separately from the bearing housing and attached to the end face of the housing.

3. A radial foil bearing as set forth in claim 1, wherein the foil includes, as its projecting pieces, a first projecting piece formed on a first end edge portion in the direction of rotation and a second projecting piece formed on a second end edge portion in the opposite direction to the direction of rotation, and the protrusion is arranged so as to abut only the first projecting piece of the first and second projecting pieces.

4. A radial foil bearing according to claim 1, wherein the foil unit includes a plurality of the foils aligned along the rotational direction, the bearing housing includes a plurality of the protrusions aligned along the rotational direction, and each of the plurality of protrusions is disposed between the protruding piece of a first foil and the protruding piece of a second foil that are adjacent to each other among the plurality of foils.

5. A radial foil bearing according to claim 4, wherein the protrusion disposed between the protruding piece of the first foil and the protruding piece of the second foil abuts against the protruding piece of the first foil in the rotational direction, and the protruding piece of the second foil is spaced apart from the protrusion.

6. A radial foil bearing according to claim 1, wherein the foil unit includes, as the foils, a top foil bent into a cylindrical shape along the inner circumferential surface of the axial hole, and a plurality of back foil pieces aligned in the rotational direction between the inner circumferential surface and the top foil, and the bearing housing includes a plurality of protrusions aligned in the rotational direction, each of the plurality of protrusions being arranged between the protruding piece of a first back foil piece and the protruding piece of a second back foil piece that are adjacent to each other among the plurality of back foil pieces, and the protruding piece of the top foil is overlapped with the protruding piece of the first back foil piece and abuts in the rotational direction against the protrusion arranged between the protruding piece of the first back foil piece and the protruding piece of the second back foil piece.

7. A radial foil bearing according to claim 6, wherein the top foil includes, as its protruding pieces, a first protruding piece formed on a first end edge portion in the rotational direction, and a second protruding piece formed on a second end edge portion in the opposite direction to the rotational direction and facing the rotational direction with a gap between it and the first protruding piece, wherein the first protruding piece is overlapped with the protruding piece of the first back foil piece, and the second protruding piece is overlapped with the protruding piece of the second back foil piece and is spaced apart from the protrusion disposed between the protruding piece of the first back foil piece and the protruding piece of the second back foil piece.

8. A rotary machine comprising: a radial foil bearing according to any one of claims 1 to 7; a shaft inserted into the axial hole of the bearing housing and rotatably supported by the radial foil bearing; and an impeller attached to an end of the shaft.

9. A method for assembling a radial foil bearing according to any one of claims 1 to 7, comprising the steps of: inserting the foil into the axial hole of the bearing housing; and rotating the foil unit in the rotational direction relative to the bearing housing until the protruding piece abuts against the projection in the rotational direction.

10. A method for assembling a radial foil bearing according to claim 9, further comprising the step of attaching the protrusion, which is formed separately from the bearing housing, to the housing end face by driving the protrusion into the housing end face before the step of inserting the foil into the axial hole.

11. A method for assembling a radial foil bearing as set forth in claim 9, wherein the step of inserting the foil into the axial hole of the bearing housing includes the steps of: inserting a top foil bent into a cylindrical shape along the inner circumferential surface of the axial hole into the axial hole; and, after the step of inserting the top foil into the axial hole, inserting a plurality of back foil pieces aligned along the rotational direction between the inner circumferential surface and the top foil.

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