Radial foil bearing and method for manufacturing radial foil bearing

Abstract

A radial foil bearing is provided with: a top foil having a facing surface facing a rotating shaft; a bump foil disposed on an outer side opposite to the facing surface of the top foil; and a bearing housing configured to surround the bump foil. The bump foil is provided with: a cylindrical portion surrounding the top foil in a cylindrical shape; and an elastic piece portion that is adjacent to the cylindrical portion in the axial direction of the rotating shaft, is deformable independently of the cylindrical portion, and is deployable in the circumferential direction. The elastic sheet portion is supported by the bearing housing.

Description

Technical Field

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

[0002] For example, the radial foil bearing described in Patent Document 1 includes a thin plate-shaped top foil surrounding a rotating shaft, a thin plate-shaped bump foil surrounding the top foil, and a cylindrical housing accommodating the top foil and the bump foil. In addition, the radial foil bearings described in Patent Documents 2 to 5 do not include a bump foil, but include a top foil directly elastically supported by the housing.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2004-190761

[0004] Patent Document 2: International Publication No. 2014 / 098005

[0005] Patent Document 3: Japanese Patent Application Publication No. 2017-82909

[0006] Patent Document 4: Japanese Patent Application Publication No. 2018-150971

[0007] Patent Document 5: Japanese Patent Application Publication No. 2019-82195

[0008] In the above-mentioned radial foil bearing, there is still a problem in stably supporting the rotating shaft during high-speed rotation. Summary of the invention

[0009] The present disclosure describes a radial foil bearing that can stably support a rotating shaft during high-speed rotation and a method for manufacturing the radial foil bearing.

[0010] A radial foil bearing of an example of the present disclosure is a radial foil bearing, comprising: a top foil having an opposing surface opposed to a rotating shaft; a bump foil arranged on the side opposite to the opposing surface of the top foil, i.e., on the outside; and a bearing housing arranged to surround the bump foil. The bump foil comprises: a cylindrical portion that surrounds the top foil into a cylindrical shape; and an elastic sheet portion that is adjacent to the cylindrical portion in the axial direction of the rotating shaft and can be deformed independently of the cylindrical portion and can be expanded in the circumferential direction. The elastic sheet portion is supported by the bearing housing.

[0011] The bump foil has a cylindrical portion and an elastic sheet portion, and the elastic sheet portion can be deformed independently of the cylindrical portion. The elastic sheet portion is directly or indirectly supported by the bearing housing, and supports the top foil via the cylindrical portion adjacent in the axial direction. In addition, the elastic sheet portion can be supported by the bearing housing while being expanded in the circumferential direction, so that it can stably support the rotating shaft against vibrations of the rotating shaft rotating at high speed.

[0012] In some examples, the elastic sheet and the cylindrical portion may be formed integrally, and the bump foil may have a slit structure for separating the elastic sheet from the cylindrical portion in a manner that allows the elastic sheet to deform independently of the cylindrical portion. The elastic sheet and the cylindrical portion are provided integrally, so that when the cylindrical portion is provided, the appropriate provision of the elastic sheet is also provided. As a result, the assembly performance when the bump foil is provided can be improved.

[0013] In some examples, the corrugated foil may include a connecting portion that connects the cylindrical portion and the elastic sheet portion, and the elastic sheet portion may include a peak edge portion formed on the opposite side of the connecting portion in the circumferential direction, and a side edge portion extending from the peak edge portion to the connecting portion. The peak edge portion may also be formed by a slit structure in a manner that becomes a free end. The peak edge portion that becomes a free end can move with the connecting portion connected to the cylindrical portion as a fulcrum.

[0014] In some examples, the bump foil may include a first end edge as an end portion on one side in the axial direction and a second end edge on the side opposite to the first end edge in the axial direction, the slit structure may include a slit forming a peak edge portion and a side slit connected to the slit and forming a side edge portion, and the slit and the side slit may be provided so as to be separated from the first end edge and the second end edge and closed in the bump foil. It becomes easy to form an elastic piece having a desired elastic force at a position separated from the first end edge or the second end edge of the bump foil, for example, at a position close to the center in the axial direction.

[0015] In some examples, the corrugated foil may include a first end edge as an end on one side in the axial direction, and a second end edge on the side opposite to the first end edge in the axial direction. The slit structure may also include a slit forming a peak edge portion. The slit is open at the first end edge or the second end edge, and at least a part of the side edge portion may also be formed at the first end edge or the second end edge where the slit is opened. The slit forming the peak edge portion that becomes the free end is open at the first end edge or the second end edge of the corrugated foil. Therefore, the peak edge portion can be easily formed by cutting a notch from the first end edge or the second end edge.

[0016] In some examples, the slit structure may include a slit forming a peak edge. The elastic sheet may include a plurality of mountain portions arranged adjacent to each other in the circumferential direction and capable of being expanded in the circumferential direction by elastic deformation. The slit may also be between the mountain portions arranged adjacent to each other, avoiding the mountain portions and extending along the mountain portions. It is difficult to damage the elastic function of the plurality of mountain portions that can be expanded in the circumferential direction by elastic deformation.

[0017] In some examples, the slit structure may include a slit forming a peak edge, a plurality of elastic sheets are arranged in a circumferential direction, and the peak edge of one adjacent elastic sheet and the peak edge of another adjacent elastic sheet may be formed by a common slit. By making the slits forming the peak edge of one adjacent elastic sheet and the peak edge of another adjacent elastic sheet common, the interval between adjacent elastic sheets can be reduced, and the shape, size, and number of elastic sheets formed in the circumferential direction can be easily optimized.

[0018] In some examples, the slit structure may also include a side slit for forming a side edge portion, and the width of the slit in the circumferential direction may be greater than the width of the side slit in the axial direction. For example, if a common slit is used to form a peak edge portion of an elastic sheet portion on one side and a peak edge portion of an elastic sheet portion on the other side that are adjacent in the circumferential direction, when the elastic sheet portion is unfolded, the peak edge portion of the elastic sheet portion on one side and the peak edge portion of the elastic sheet portion on the other side move in a direction of approaching each other. Here, the width of the slit is larger than the width of the side slit, so it becomes easier to prevent the peak edges from interfering with each other compared to the case where the width of the slit is the same as the width of the side slit.

[0019] In some examples, a fixed foil may be provided, which is configured to surround the bump foil and support the elastic sheet. The fixed foil can inhibit the elastic sheet from extending outward from the cylindrical portion and prevent the elastic function from being reduced. In addition, by providing the fixed foil, friction is generated between the bump foil and the fixed foil, and the attenuation is improved.

[0020] An example of the present disclosure is a method for manufacturing a radial foil bearing, the radial foil bearing comprising: a top foil having an opposing surface opposed to a rotating shaft; a bump foil arranged on the outside of the top foil; and a bearing housing arranged to surround the bump foil. The manufacturing method comprises the following steps: a step of rolling up a stack formed by overlapping a top foil in an unfolded state and a bump foil in an unfolded state to form a cylindrical foil assembly; and a step of inserting the foil assembly into a cylindrical bearing housing so as to surround the rotating shaft. The bump foil comprises: a cylindrical portion that surrounds the top foil into a cylindrical shape; and an elastic sheet portion that is adjacent to the cylindrical portion in the axial direction of the rotating shaft and can be deformed independently of the cylindrical portion and can be expanded in the circumferential direction. By inserting the foil assembly into the bearing housing, the elastic sheet portion is supported by the bearing housing. By this manufacturing method, a radial foil bearing that can stably support a rotating shaft during high-speed rotation while improving assemblability can be manufactured.

[0021] In some examples, in the step of forming the foil assembly, the fixed foil in the unfolded state is arranged to overlap the bump foil on the side opposite to the top foil to form a stack, and the stack is rolled up to form the foil assembly. This can prevent the reduction of elastic function and manufacture a radial foil bearing with improved damping performance.

[0022] According to some examples of the present disclosure, it is possible to stably support a rotating shaft during high-speed rotation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a cross-sectional view showing an example of a rotating machine.

[0024] Figure 2 This is a perspective view showing an example of a radial foil bearing.

[0025] Figure 3 This is a cross-sectional view of a radial foil bearing cut along a section perpendicular to the rotation axis.

[0026] Figure 4 is a perspective view of the foil assembly.

[0027] Figure 5 The bump foil in the unfolded state is shown. (a) is a top view of the bump foil, and (b) is a perspective view of the bump foil.

[0028] Figure 6 This is a schematic cross-sectional view for explaining the functionality of a radial foil bearing.

[0029] Figure 7 The figures are stereoscopic views showing the process of manufacturing radial foil bearings, (a) is a stereoscopic view showing the state where the top foil, wave foil and fixed foil are arranged up and down, (b) is a stereoscopic view showing the foil assembly (laminate) before rolling up, and (c) is a stereoscopic view showing the state where the foil assembly is inserted into the bearing housing.

[0030] Figure 8 This is a schematic cross-sectional view for functionally illustrating a radial foil bearing according to a modified example.

[0031] Fig. 9 The first modification example of the bump foil is shown, and is a plan view of the bump foil in an extended state as seen from the back, with a portion thereof being enlarged.

[0032] Fig.10 FIG. 2 shows a second modification of the bump foil and is a plan view of the bump foil in an extended state as seen from the back side. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. In the description of the accompanying drawings, the same elements are denoted by the same reference numerals, and repeated descriptions are omitted.

[0034] Figure 1A rotary machine 1 is shown. The rotary machine 1 is, for example, an electrically assisted turbocharger. The rotary machine 1 includes a turbine 2, a compressor 3, an electric motor 10, and a rotating shaft 15. The turbine 2 includes a turbine impeller 4 provided at one end of the rotating shaft 15, and a turbine housing 6 for accommodating the turbine impeller 4. The compressor 3 includes a compressor impeller 5 provided at the other end of the rotating shaft 15, and a compressor housing 7 for accommodating the compressor impeller 5.

[0035] The rotor 11 of the electric motor 10 is arranged, for example, at the center of the rotating shaft 15. The rotor 11 is fixed to the rotating shaft 15 and can rotate together with the rotating shaft 15. The stator 12 of the electric motor 10 is arranged so as to surround the rotor 11. The stator 12 is fixed to the motor housing 13 provided between the turbine housing 6 and the compressor housing 7. The stator 12 can rotate the rotor 11 by generating a magnetic field around the rotating shaft 15. The rotation of the rotating shaft 15 is assisted by the cooperation of the rotor 11 and the stator 12.

[0036] In the rotary machine 1, the exhaust gas discharged from the internal combustion engine flows into the turbine housing 6 through the vortex flow path 6a, causing the turbine impeller 4 to rotate around the rotation axis H. The exhaust gas that rotates the turbine impeller 4 is discharged through the exhaust port 6b of the turbine housing 6. As described above, if the turbine impeller 4 rotates, the compressor impeller 5 rotates via the rotating shaft 15. At this time, torque is applied to the rotating shaft 15 by the electric motor 10, thereby assisting the rotation of the rotating shaft 15 and the compressor impeller 5. The rotating compressor impeller 5 inhales external air through the intake port 7b of the compressor housing 7. The air is compressed while passing through the compressor impeller 5 and the vortex flow path 7a. The compressed air is discharged from the exhaust port of the compressor housing 7 and supplied to the above-mentioned internal combustion engine.

[0037] The rotating shaft 15 is supported via a plurality of bearings so as to be rotatable about the rotating axis H. At least one of the plurality of bearings is a radial foil bearing 20 of the present disclosure. Figure 1 In the example shown, a pair of radial foil bearings 20 are provided at both ends of the rotating shaft 15. The radial foil bearings 20 are air bearings that support the rotating shaft 15 in the radial direction (that is, in a direction perpendicular to the rotating axis H).

[0038] In the rotary machine 1 of the present disclosure, a thrust ring 17 and a pair of thrust air bearings 18 are provided between the radial foil bearing 20 on the side closer to the compressor impeller 5 in a pair of radial foil bearings 20 and the compressor impeller 5. The thrust ring 17 is a disc-shaped component formed in a flange-like manner extending around the rotating shaft 15. The pair of thrust air bearings 18 are provided at positions sandwiching the thrust ring 17. A spacer 19 surrounding the thrust ring 17 is provided between the pair of thrust air bearings 18. The thrust ring 17 and the pair of thrust air bearings 18 support the rotating shaft 15 in the thrust direction (i.e., the direction parallel to the rotation axis H).

[0039] <Radial foil bearing>

[0040] Next, refer to Figure 2 , Figure 3 An example of the radial foil bearing 20 will be described in detail. The rotary machine 1 of the present disclosure includes a pair of radial foil bearings 20, but the pair of radial foil bearings 20 have substantially the same structure. Therefore, one radial foil bearing 20 will be described below as a representative.

[0041] The radial foil bearing 20U includes a foil assembly 21 and a bearing housing 45 that accommodates the foil assembly 21. The foil assembly 21 includes a top foil 22, a bump foil 23 surrounding the top foil 22, and a fixed foil 24 surrounding the bump foil 23. When the rotating shaft 15 rotates, an air film is formed between the rotating shaft 15 and the top foil 22. By forming this air film, the radial foil bearing 20 rotatably supports the rotating shaft 15.

[0042] <Bearing housing>

[0043] The bearing housing 45 is a substantially cylindrical housing having an axial hole 46 through which the rotating shaft 15 is inserted. The foil assembly 21 is accommodated inside the axial hole 46 in a manner surrounding the rotating shaft 15. That is, the bearing housing 45 is configured to surround the bump foil 23 with the fixed foil 24 interposed therebetween. For example, the bearing housing 45 includes a cylindrical inner peripheral surface on the inner side. The inner peripheral surface can be considered as the outer peripheral surface of the axial hole 46. The inner peripheral surface is opposite to the foil assembly 21 and substantially supports the foil assembly 21.

[0044] The shaft hole 46 penetrates the bearing housing 45 in the direction in which the rotation axis H extends. In the following description, the direction in which the shaft hole 46 extends, that is, the direction in which the rotation axis H (rotation axis 15) extends is referred to as the "axial direction D1" (refer to Figure 4 ). In addition, the radial direction of the shaft hole 46, that is, the direction perpendicular to the rotation axis H (rotation axis 15), is referred to as the "radial direction D2". In addition, the circumferential direction of the rotation axis 15, that is, the direction along the ring centered on the rotation axis H, is referred to as the "circumferential direction D3".

[0045] The bearing housing 45 is, for example, a member having sufficient strength to support the rotating shaft 15 that has stopped rotating. The rotating shaft 15 is arranged in a manner that passes through the center of the shaft hole 46 of the bearing housing 45. A foil assembly 21 rolled into a tube is arranged between the inner circumferential surface 46a of the shaft hole 46 and the rotating shaft 15. A locking structure 31 protruding in the radial direction D2 is provided on the foil assembly 21, and a locking groove 46b for accommodating the locking structure 31 is provided on the inner circumferential surface 46a of the shaft hole 46. The locking structure 31 is provided in a manner extending in the axial direction D1, and the locking groove 46b is a longitudinal groove extending in the axial direction D1 in a manner to accommodate the locking structure 31. The width of the locking groove 46b in the circumferential direction D3 corresponds to the width of the locking structure 31 in the circumferential direction D3, and the locking groove 46b can abut against the locking structure 31 in the circumferential direction D3. If the foil assembly 21 is to move in the circumferential direction D3 of the rotating shaft 15, the locking structure 31 will interfere with the locking groove 46b. As a result, the rotation of the foil assembly 21 is suppressed.

[0046] <Foil Components>

[0047] like Figure 2 , Figure 3 and Figure 4 As shown, the foil assembly 21 includes a top foil 22, a bump foil 23, and a fixed foil 24. The top foil 22, the bump foil 23, and the fixed foil 24 are each formed of a thin metal plate and have flexibility. The top foil 22, the bump foil 23, and the fixed foil 24 are stacked in sequence, and present a cylindrical shape with the top foil 22 on the inner circumference side.

[0048] <Top foil>

[0049] The cylindrical top foil 22 includes an inner peripheral surface facing the rotation shaft 15 and an outer peripheral surface 22b on the opposite side to the inner peripheral surface. The inner peripheral surface is an opposing surface 22a facing the rotation shaft 15. The top foil 22 in the unfolded state is a substantially rectangular thin plate without slits or the like, and both ends in the longitudinal direction are first hooks 31a bent into an L-shape.

[0050] <Wave Foil>

[0051] The cylindrical bump foil 23 includes an inner peripheral surface 23a facing the top foil 22 and an outer peripheral surface 23b opposite to the inner peripheral surface 23a. Figure 5 ) is a thin plate that is substantially rectangular in a plan view, and both ends of the length direction D4 are second hooks 31b bent into an L-shape. In addition, the length direction D4 means the circumferential direction D3 in the state of rolling up the bump foil 23. Therefore, in the following description, except for the case where the length direction D4 and the circumferential direction D3 need to be distinguished and described, they are uniformly described as the circumferential direction D3.

[0052] The corrugated foil 23 is different from the top foil 22, and has a plurality of peaks 32 arranged in a manner arranged along the circumferential direction D3. The peaks 32 refer to a shape portion that protrudes inwardly bulging with the inner circumferential surface 23a as a reference, and a valley 33 is formed between the plurality of peaks 32 at the inner circumferential surface 23a. In addition, if the outer circumferential surface 23b is used as a reference, the peaks 32 become recessed portions, and the valleys 33 become bulging portions. In addition, the peaks 32 disclosed in the present invention are formed in a corrugated plate shape with concave and convex shapes that are bent in the circumferential direction D3 alternately, but may be discontinuous but interrupted in the middle, and partially formed with peaks. In addition, it may be not a corrugated plate shape, but a convex curved surface shape that forms a dome shape or a part of a sphere.

[0053] The mountain portion 32 is curved into an arc shape in the cross-sectional view, and can be expanded along the circumferential direction D3 by elastic deformation, for example, it has flexibility. This cross-sectional view is assumed to be a cross-sectional view when the bump foil 23 is cut with a surface along the circumferential direction D3. The mountain portion 32 is set to bulge toward the inner side facing the top foil 22. When the foil assembly 21 is formed, the top 32a of the arc-shaped mountain portion 32 can abut against the outer peripheral surface 22b of the top foil 22. In the bump foil 23 of the present embodiment, a plurality of mountain portions 32 are arranged along the circumferential direction D3, and the top 32a of each mountain portion 32 extends along the axial direction D1. Therefore, if a load in the radial direction D2 is applied to the bump foil 23, the bump foil 23 is deformed in a manner of extending (expanding) along the circumferential direction D3 from the vicinity of the portion to which the load is applied.

[0054] The bump foil 23 includes a cylindrical portion 25, an elastic portion 26, and a connecting portion 27 that connects the cylindrical portion 25 and the elastic portion 26. The cylindrical portion 25 is a portion that surrounds the top foil 22 in a cylindrical shape. The cylindrical portion 25 is, for example, a portion that is continuous and uninterrupted from one end of the bump foil 23 to the other end in the circumferential direction D3. In addition, the cylindrical portion 25 means a portion that is continuous and uninterrupted in the circumferential direction D3, for example, a portion that is not divided by a slit extending in the axial direction D1 in the middle of the circumferential direction D3. In addition, the cylindrical portion 25 does not need to be completely cut in the axial direction D1, so the situation of deviation in the axial direction D1 is not excluded. For example, the cylindrical portion 25 can be bent in the axial direction D1 between the end of one end of the bump foil 23 and the end of the other end, that is, in the middle of the circumferential direction D3, or it can be a structure that forms a continuous curved shape in the circumferential direction D3.

[0055] The elastic portion 26 is provided integrally with the cylindrical portion 25. The elastic portion 26 includes a first elastic piece 28A and a second elastic piece 28B extending from the coupling portion 27 in the circumferential direction D3. The first elastic piece 28A and the second elastic piece 28B are arranged adjacent to the cylindrical portion 25 in the axial direction D1, and can be deformed independently of the cylindrical portion 25. Therefore, for example, when a load is applied only to the first elastic piece 28A and the second elastic piece 28B, the first elastic piece 28A and the second elastic piece 28B are greatly deformed in the circumferential direction D3, while the cylindrical portion 25 is hardly deformed. As a result, the expansion of the first elastic piece 28A and the second elastic piece 28B in the circumferential direction D3 becomes larger than that of the cylindrical portion 25.

[0056] In addition, as described later, the first elastic sheet 28A and the second elastic sheet 28B are formed by the slit structure 40, and the first elastic sheet 28A and the second elastic sheet 28B can be deformed independently of the cylindrical portion 25 by means of the slit structure 40. That is, due to the width of the slit structure 40, the first elastic sheet 28A and the second elastic sheet 28B can be deformed in the circumferential direction D3 without affecting each other. In addition, the thickness of the metal plate constituting the corrugated foil 23 is uniform in the present disclosure. Therefore, the first elastic sheet 28A and the second elastic sheet 28B become structures that are easier to deform than the cylindrical portion 25.

[0057] The first elastic piece 28A and the second elastic piece 28B are supported by the cylindrical inner peripheral surface of the bearing housing 45. In addition, "supported by the bearing housing 45" includes both a case where they are directly supported by contacting the bearing housing 45 and a case where they are indirectly supported by an intervening object between the bearing housing 45. In the present disclosure, the fixing foil 24 is provided as the intervening object, and the first elastic piece 28A and the second elastic piece 28B are indirectly supported by the bearing housing 45.

[0058] The first elastic piece 28A and the second elastic piece 28B are bent in a flexible manner and can be unfolded in the circumferential direction D3 in an elastically deformable manner. The first elastic piece 28A includes: a peak edge 28a, which is formed on the opposite side of the circumferential direction D3 with respect to the connecting portion 27; and a side edge 28b, which extends from the peak edge 28a to the connecting portion 27. In addition, the second elastic piece 28B includes: a peak edge 28a, which is formed on the opposite side of the circumferential direction D3 with respect to the connecting portion 27; and a side edge 28b, which extends from the peak edge 28a to the connecting portion 27. Here, "formed on the opposite side of the circumferential direction D3 with respect to the connecting portion 27" means the position of the end portion on the opposite side of the connecting portion 27 with respect to the circumferential direction D3 as a reference.

[0059] The first elastic piece 28A can also be described as extending from the coupling portion 27 in a direction with the circumferential direction D3 as a reference. The second elastic piece 28B can also be described as extending from the coupling portion 27 in a direction opposite to the direction with the circumferential direction D3 as a reference. In addition, it can be described as: a peak edge portion 28a is formed at each front end of the first elastic piece 28A and the second elastic piece 28B, and the peak edge portion 28a is a free end that can move with the coupling portion 27 as a fulcrum.

[0060] If the expanded bump foil 23 (see Figure 4 ) is rolled into a cylindrical shape, the first elastic sheet 28A and the second elastic sheet 28B are, for example, arranged to extend in a state bent in the tangential direction toward the cylindrical portion 25. The wave foil 23 is surrounded by the fixed foil 24, which is, for example, formed by rolling up a substantially rectangular thin plate without forming slits, etc. In a state surrounded by the fixed foil 24, the first elastic sheet 28A and the second elastic sheet 28B abut against the fixed foil 24 and are pressed. As a result, the state in which the first elastic sheet 28A and the second elastic sheet 28B extend in a manner of springing up from the cylindrical portion 25 is eliminated. The first elastic sheet 28A and the second elastic sheet 28B abut against the fixed foil 24, thereby being bent into an arc shape respectively. In addition, the first elastic sheet 28A and the second elastic sheet 28B abut against the fixed foil 24 in a state bent into an arc shape, thereby elastically supporting the cylindrical portion 25, and further elastically supporting the top foil 22 via the cylindrical portion 25.

[0061] As described above, the elastic portion 26 includes a first elastic sheet portion 28A and a second elastic sheet portion 28B, and the first elastic sheet portion 28A and the second elastic sheet portion 28B are bent into an arc shape. In the present disclosure, a plurality of peaks 32 are provided on the first elastic sheet portion 28A and the second elastic sheet portion 28B. The peaks 32 are already bent into an arc shape in a state before the bump foil 23 is rolled up. On the other hand, the "arc shape" of the first elastic sheet portion 28A and the second elastic sheet portion 28B is not formed in a state before the bump foil 23 is rolled up, but is a shape that is separately grasped from the arc shape of the peaks 32 and is formed by rolling up the bump foil 23. For example, in the case of understanding the first elastic sheet portion 28A and the second elastic sheet portion 28B functionally, for convenience, the plurality of peaks 32 are omitted, and it can be understood as an arc shape without projections and depressions (refer to Figure 6 ). Functionally, the cylindrical portion 25 also omits the plurality of peaks 32, and can be understood as a cylindrical shape without projections and depressions. Figure 6 In the figure, the mountain portion 32 is simply expressed as an elastic body in terms of function, for example, as a spring in a simplified shape. Figure 8 In, Yamabe 32 and Figure 6 Likewise, the spring is shown in a simplified shape.

[0062] As a functional concept, the first elastic sheet 28A with the hill 32 omitted can be assumed to be a curved plate-like portion extending from the joint 27 along the circumferential direction D3. That is, the curved plate-like portion can be understood as a simple shape that is bent into an arc shape without fluctuation. The second elastic sheet 28B is also similar. As a result of functionally omitting the hill 32, it can be understood as a simple shape that is bent into an arc shape without fluctuation. In addition, the center of curvature of the arc shape of the first elastic sheet 28A and the second elastic sheet 28B becomes the position on the inner side of the bump foil 23. In addition, the position on the inner side of the bump foil 23 refers to a position on the inner side closer to the rotating shaft 15 than the bump foil 23. In addition, the radius of curvature of the first elastic sheet 28A is larger than the radius of curvature of the cylindrical portion 25, and the radius of curvature of the second elastic sheet 28B is larger than the radius of curvature of the cylindrical portion 25. In addition, the mountain portion 32 formed on the first elastic piece 28A and the second elastic piece 28B is an arc shape with the center of curvature located outside the bump foil 23, and its technical significance is different from the arc shape of the first elastic piece 28A and the second elastic piece 28B. Here, the position outside the bump foil 23 refers to a position outside the rotating shaft 15 that is farther away from the bump foil 23.

[0063] Next, the slit structure 40 provided in the bump foil 23 will be described. First, the bump foil 23 includes: a first end edge 23c as an end on one side in the axial direction D1, and a second end edge 23d on the side opposite to the first end edge 23c in the axial direction D1. The slit structure 40 may form the first elastic piece 28A or the second elastic piece 28B independently of the first end edge 23c and the second end edge 23d, or may form the first elastic piece 28A or the second elastic piece 28B in cooperation with the first end edge 23c or the second end edge 23d.

[0064] The slit structure 40 has a function as a boundary separating the first elastic sheet portion 28A and the second elastic sheet portion 28B from the tubular portion 25, and forms a portion where the first elastic sheet portion 28A and the second elastic sheet portion 28B are connected to the coupling portion 27. The slit structure 40 includes a first slit continuous portion 41 forming the first elastic sheet portion 28A, and a second slit continuous portion 42 forming the second elastic sheet portion 28B.

[0065] The first slit continuous portion 41 (see Figure 5) comprises: a slit 43 forming a peak edge portion 28a; and two (plural) side slits 44 connected in a manner communicating with the slit 43 to form a side edge portion 28b. The slit 43 extends, for example, in the axial direction D1. The slit 43 separates the front end of the first elastic sheet portion 28A from the cylindrical portion 25 so as to form the peak edge portion 28a. The side slit 44 extends in a direction intersecting with the slit 43. The direction intersecting with the slit 43 includes not only a case of being orthogonal to the longitudinal direction of the slit 43, but also a direction inclined relative to the direction orthogonal to the slit 43. The side slit 44 is provided to be connected to both ends of the slit 43. The side slit 44 extends in the circumferential direction D3 so as to separate the side edge portion 28b of the first elastic sheet portion 28A from the cylindrical portion 25.

[0066] The slit 43 and the side slit 44 of the present disclosure are separated from the first end edge 23c and the second end edge 23d as the two side edges of the bump foil 23, and do not reach the first end edge 23c or the second end edge 23d. That is, the slit 43 and the side slit 44 are not opened at the first end edge 23c or the second end edge 23d but are closed in the bump foil 23.

[0067] In addition, the slit 43 is provided between the adjacently arranged mountain portions 32 avoiding the mountain portions 32. In addition, the slit 43 is provided at the position of the valley portion 33 in a manner extending along the mountain portions 32. That is, the peak edge portion 28a, which is the free end of the first elastic piece portion 28A and the second elastic piece portion 28B, is provided in a manner along the valley portion 33. By providing the peak edge portion 28a avoiding the mountain portions 32, it is possible to prevent the situation where the elastic function of the mountain portions 32 is hindered.

[0068] The second slit continuous portion 42 has substantially the same structure as the first slit continuous portion 41, and includes a slit 43 and two (plural) side slits 44. The second slit continuous portion 42 is provided symmetrically with the first slit continuous portion 41 in the circumferential direction D3 of the rotation shaft 15.

[0069] The connecting portion 27 is disposed between the first slit continuous portion 41 and the second slit continuous portion 42. The connecting portion 27 is a portion that connects and integrates the first elastic sheet portion 28A and the second elastic sheet portion 28B with the tubular portion 25. The distance from the connecting portion 27 to the slit 43 of the first slit continuous portion 41 is the same as the distance from the connecting portion 27 to the slit 43 of the second slit continuous portion 42. In addition, the distance from the connecting portion 27 to the slit 43 of the first slit continuous portion 41 may be different from the distance from the connecting portion 27 to the slit 43 of the second slit continuous portion 42.

[0070] In the present disclosure, a plurality of first slit continuous portions 41 and second slit continuous portions 42 are formed in the bump foil 23. As a result, a plurality of first elastic pieces 28A and second elastic pieces 28B are formed. Also, a plurality of elastic portions 26 are formed by forming a plurality of first elastic pieces 28A and second elastic pieces 28B.

[0071] like Figure 5 As shown, for example, in the expanded state, the first slit continuous portion 41 and the second slit continuous portion 42 are alternately formed along the circumferential direction D3 in the wave foil 23. As a result, in the expanded state, the first elastic sheet portion 28A and the second elastic sheet portion 28B are formed in a manner alternately arranged along the circumferential direction D3. A single elastic portion 26 is formed by a combination (elastic sheet unit) of the first elastic sheet portion 28A and the second elastic sheet portion 28B adjacent to each other in the circumferential direction D3. The wave foil 23 of the present disclosure, for example, comprises along the circumferential direction D3: a first elastic sheet unit 29A, a second elastic sheet unit 29B and a third elastic sheet unit 29C. When the wave foil 23 is rolled up, three (plural) elastic portions 26 (see FIG. 2 ) arranged in the circumferential direction D3 are formed by the first elastic sheet unit 29A, the second elastic sheet unit 29B and the third elastic sheet unit 29C. Figure 6 ).

[0072] The peak edge 28a of the first elastic sheet unit 29A and the peak edge 28a of the second elastic sheet unit 29B are formed by a common slit 43. Specifically, the slit 43 of the second elastic sheet unit 28B forming the first elastic sheet unit 29A is common to the slit 43 of the first elastic sheet unit 28A forming the second elastic sheet unit 29B. In addition, the slit 43 of the second elastic sheet unit 28B forming the second elastic sheet unit 29B is common to the slit 43 of the first elastic sheet unit 28A forming the third elastic sheet unit 29C. That is, in the present disclosure, the peak edge 28a of one adjacent elastic portion 26 and the peak edge 28a of another elastic portion 26 are formed by a common slit 43. By making the peak edge 28a of one adjacent elastic portion 26 and the peak edge 28a of another adjacent elastic portion 26 common through a single slit 43, the interval between the adjacent elastic portions 26 can be reduced. As a result, it becomes easy to optimize the shape, size, number of the elastic portions 26 formed in the circumferential direction D3, and the like.

[0073] <Fixed foil>

[0074] like Figure 3 and Figure 4 As shown, the cylindrical fixed foil 24 is arranged in a manner of surrounding the bump foil 23, and supports the elastic part 26, that is, the first elastic piece 28A and the second elastic piece 28B. When the fixed foil 24 is supported on the elastic part 26, it can be supported in a state where the elasticity of the first elastic piece 28A and the second elastic piece 28B is given, or it can be supported in a state where the elasticity is not generated. The fixed foil 24 has: an inner peripheral surface 24a facing the bump foil 23, and an outer peripheral surface 24b as a side opposite to the inner peripheral surface 24a. The fixed foil 24 in the unfolded state is a roughly rectangular thin plate, and the two ends in the circumferential direction D3 are third hooks 31c bent into an L shape.

[0075] like Figure 2 and Figure 3 As shown, the top foil 22, the bump foil 23, and the fixed foil 24 are stacked in order from the inner circumferential side opposite to the rotating shaft 15. The first hooks 31a formed at both ends of the top foil 22, the second hooks 31b formed at both ends of the bump foil 23, and the third hooks 31c formed at both ends of the fixed foil 24 are arranged in an overlapping manner to form a locking structure 31. The locking structure 31 is accommodated in the locking groove 46b of the bearing housing 45.

[0076] <Variation examples of radial foil bearing>

[0077] Figure 8 2 is a schematic cross-sectional view for functionally explaining a radial foil bearing of a modified example. In addition, a radial foil bearing 20A of the modified example has substantially the same structure and components as the radial foil bearing 20 described above. Therefore, the same reference numerals are given to the same structure and components and detailed descriptions are omitted. The radial foil bearing 20A has: a foil assembly 21A, and a bearing housing 45 that accommodates the foil assembly 21A. The foil assembly 21A does not have a fixed foil 24, and is formed by a top foil 22 and a bump foil 23. The elastic portion 26 of the bump foil 23 is in direct contact with the bearing housing 45 to elastically support the cylindrical portion 25, and elastically supports the top foil 22 via the cylindrical portion 25. In addition, the elastic portion 26 is bent while being in direct sliding contact with the bearing housing 45.

[0078] <Modification example of corrugated foil>

[0079] Fig. 9 1 is a plan view illustrating a bump foil 23A according to a first modification example, and showing a part of an outer peripheral surface 23 b of the bump foil 23A in an expanded state in an enlarged manner. Fig.10 1 is a plan view illustrating a bump foil 23B according to the second modification and showing an outer peripheral surface 23b of the bump foil 23B in an expanded state. The bump foil 23A according to the first modification and the bump foil 23B according to the second modification can be used for the radial foil bearings 20 and 20A described above, respectively.

[0080] The bump foil 23A has a slit structure 40A that separates the first elastic sheet 28C and the second elastic sheet 28D in a deformable manner independently of the cylindrical portion 25. In the first elastic sheet 28C and the second elastic sheet 28D adjacent to each other in the circumferential direction D3, the peak edge 28a of the first elastic sheet 28C and the peak edge 28a of the second elastic sheet 28D are formed by a common slit 43A. The width Wa of the slit 43A is greater than the width Wb of the side slit 44A. The width Wa of the slit 43A means the width of the bump foil 23 in the circumferential direction D3, and means the width in the circumferential direction D3 when the bump foil 23 is rolled up. In addition, the width Wb of the side slit 44A means the width in the axial direction D1.

[0081] When the first elastic piece 28C and the second elastic piece 28D are bent and expanded, the peak edge 28a of the first elastic piece 28C and the peak edge 28a of the second elastic piece 28D move in a direction close to each other. Here, the width Wa of the slit 43A forming the peak edge 28a is greater than the width Wb of the side slit 44A, so it is easier to prevent the peak edges 28a from interfering with each other compared to the case where the width of the slit 43 and the width of the side slit 44 are the same.

[0082] like Fig.10 As shown, the corrugated foil 23B of the second modified example includes: an end portion on one side of the axial direction D1, namely a first end edge 23c, and a second end edge 23d on the side opposite to the first end edge 23c in the axial direction D1. The cylindrical portion 25B of the corrugated foil 23B is arranged at a position separated from the first end edge 23c and the second end edge 23d. For example, the cylindrical portion 25B includes a central area between the first end edge 23c and the second end edge 23d, and is arranged in a manner extending along the circumferential direction D3 (circumferential direction D3). The corrugated foil 23B includes a first elastic piece 28E and a second elastic piece 28F adjacent to the cylindrical portion 25B in the axial direction D1. That is, the first elastic piece 28E and the second elastic piece 28F are arranged between the first end edge 23c or the second end edge 23d and the cylindrical portion 25B.

[0083] The corrugated foil 23B has a slit structure 40B, and the slit structure 40A makes the first elastic piece 28E and the second elastic piece 28F independent of the cylindrical portion 25B and deformably separated. The slit structure 40B includes: a slit 43B forming the peak edge 28a, and a side slit 44B connected to the slit 43B and forming the side edge 28b. The slit 43B is open at the first end edge 23c or the second end edge 23d.

[0084] At least a portion of the side edge portion 28b of the first elastic sheet 28E and the second elastic sheet 28F is formed at the first end edge 23c or the second end edge 23d. Specifically, among a pair (plurality) of side edge portions 28b forming the first elastic sheet 28E, a portion of the side edge portion 28b is formed at the first end edge 23c or the second end edge 23d, and the other side edge portion 28b is formed by the side slit 44B. In addition, among a pair (plurality) of side edge portions 28b forming the second elastic sheet 28F, a portion of the side edge portion 28b is formed at the first end edge 23c or the second end edge 23d, and the other side edge portion 28b is formed by the side slit 44B. That is, in the case of the corrugated foil 23B of the second modified example, the slit structure 40B cooperates with the first end edge 23c or the second end edge 23d to form the first elastic sheet 28E or the second elastic sheet 28F.

[0085] <Method for manufacturing radial foil bearing>

[0086] Next, refer to Figure 7The following describes a method for manufacturing the radial foil bearing 20. The manufacturing method of the present disclosure includes a foil forming step, a foil assembly forming step, and a foil assembly setting step.

[0087] The foil forming step includes: a top foil forming step, a bump foil forming step, and a fixed foil forming step. In the top foil forming step, a first plate-shaped member made of metal is processed into a predetermined shape (e.g., a rectangle) to form a top foil 22 in an unfolded state. In addition, both ends of the top foil 22 in the circumferential direction D3 are bent to form a first hook 31a. In addition, in the manufacturing method of the radial foil bearing 20A of the above-mentioned modified example, the fixed foil forming step can be omitted. In addition, when using the top foil 22, the bump foil 23, 23A, 23B, and the fixed foil 24 processed into a desired shape, the foil forming step can also be omitted.

[0088] In the bump foil forming process, the second plate-like member made of metal is processed into a predetermined shape (for example, a rectangle) to form the bump foil 23 in the unfolded state. The two ends of the bump foil 23 in the circumferential direction D3 are bent to form the second hook 31b. In addition, a slit structure 40 for forming the cylindrical portion 25 and the elastic portion 26 is formed on the bump foil 23. The elastic portion 26 includes a first elastic sheet 28A, 28C, 28E and a second elastic sheet 28B, 28D, 28F. In addition, the bump foil 23 is processed to form a plurality of arc-shaped mountain portions 32. In the present disclosure, by forming the slit structure 40, the cylindrical portion 25 and the elastic portion 26 can be formed integrally when the bump foil 23 is rolled up. That is, there is no need to combine a plurality of components to form the elastic portion 26. In addition, the slit structure 40 can be formed before the mountain portion 32 is formed, or it can be formed after the mountain portion 32 is formed.

[0089] In the fixing foil forming step, the third plate-shaped member made of metal is processed into a predetermined shape (for example, a rectangle) to form the expanded fixing foil 24. Both ends of the fixing foil 24 in the circumferential direction D3 are bent to form third hooks 31c.

[0090] like Figure 7 As shown in (b) and (c) of FIG. 1 , in the foil assembly forming step, the stack formed by overlapping the top foil 22 in the unfolded state, the bump foil 23 in the unfolded state, and the top foil 22 in the unfolded state is rolled up to form a cylindrical foil assembly 21. When forming the foil assembly 21, the first hook 31a, the second hook 31b, and the third hook 31c are overlapped to form the locking structure 31. When the bump foil 23 is rolled up to form the foil assembly 21, the elastic portion 26 is formed by the slit structure 40.

[0091] In the foil assembly installation step, the foil assembly 21 is inserted into the bearing housing 45 so as to surround the rotating shaft 15, thereby forming the radial foil bearing 20. Specifically, the foil assembly 21 is inserted into the shaft hole 46 of the bearing housing 45. The axial direction D1 (refer to Figure 1 ) is provided at the end portion thereof to restrict the displacement of the foil assembly 21 in the axial direction D1.

[0092] Next, the effects exerted by the radial foil bearings 20 and 20A of the present disclosure will be described.

[0093] The bump foils 23, 23A, 23B of the radial foil bearings 20, 20A include a cylindrical portion 25 and elastic pieces 28A to 28F. The elastic pieces 28A to 28F can be deformed independently of the cylindrical portion 25. The elastic pieces 28A to 28F are directly or indirectly supported by the bearing housing 45, and support the top foil 22 via the cylindrical portion 25 adjacent to the axial direction D1. In addition, the elastic pieces 28A to 28F can be expanded in the circumferential direction D3 while being directly or indirectly supported by the bearing housing 45.

[0094] The elastic pieces 28A to 28F of the radial foil bearing 20 are bent while indirectly sliding in contact with the bearing housing 45, and the elastic pieces 28A to 28F of the radial foil bearing 20A are bent while directly sliding in contact with the bearing housing 45. When the elastic pieces 28A to 28F are elastically deformed and expanded while being indirectly or directly supported by the bearing housing 45, the cylindrical portion 25 is elastically supported, and the top foil 22 is elastically supported via the cylindrical portion 25. As a result, the radial foil bearings 20 and 20A can resist vibrations of the rotating shaft 15 rotating at a high speed, and can stably support the rotating shaft 15.

[0095] In the present disclosure, the elastic pieces 28A to 28F are integrally formed with the tubular portion 25, so that when the tubular portion 25 is installed, the elastic pieces 28A to 28F are properly installed. As a result, the assembly performance when installing the bump foils 23, 23A, and 23B can be improved.

[0096] In addition, the bump foils 23, 23A, and 23B include a connecting portion 27 that connects the elastic pieces 28A to 28F to the cylindrical portion 25. The elastic pieces 28A to 28F each include a peak edge 28a formed on the opposite side of the connecting portion 27 in the circumferential direction D3, and a side edge 28b extending from the peak edge 28a to the connecting portion 27. The peak edge 28a is formed by the slit structure 40, 40A, and 40B so as to become a free end, and can therefore move with the connecting portion 27 as a fulcrum.

[0097] The elastic pieces 28A to 28F elastically support the rotating shaft 15 via the top foil 22 by themselves being unfolded. In addition, the elastic pieces 28A to 28F include a plurality of peaks 32 arranged adjacent to each other in the circumferential direction D3. The plurality of peaks 32 can be elastically deformed and unfolded in the circumferential direction D3. The radial foil bearings 20 and 20A include a plurality of peaks 32, so that in addition to the unfolding of the elastic pieces 28A to 28F, the top foil 22 can also be elastically supported by the unfolding of each of the plurality of peaks 32. In addition, the slits 43, 43A, and 43B forming the peak edge 28a of the elastic pieces 28A to 28F are arranged between the adjacently arranged peaks 32 to avoid the peaks 32. As a result, it is difficult to damage the elastic function of the plurality of peaks 32 that can be unfolded in the circumferential direction D3 by elastic deformation.

[0098] In addition, the radial foil bearing 20, 20A of the present disclosure includes a fixed foil 24 that supports the first elastic pieces 28A, 28C, 28E and the second elastic pieces 28B, 28D, 28F. The fixed foil 24 can suppress the first elastic pieces 28A, 28C, 28E and the second elastic pieces 28B, 28D, 28F from protruding outward from the cylindrical portion 25, thereby preventing the reduction of the elastic function. In addition, by providing the fixed foil 24, friction is generated between the bump foil 23 and the fixed foil 24, thereby improving the damping property.

[0099] In addition, in the first elastic pieces 28A, 28C, 28E and the second elastic pieces 28B, 28D, 28F adjacent to each other in the circumferential direction D3, the peak edge portions 28a of the first elastic pieces 28A, 28C, 28E and the peak edge portions 28a of the second elastic pieces 28B, 28D, 28F are formed by the common slits 43, 43A, 43B. By making the slits 43A and 43B common, the interval between the adjacent first elastic pieces 28A, 28C, 28E and the second elastic pieces 28B, 28D, 28F can be reduced, and it becomes easy to optimize the shapes, sizes, and numbers of the first elastic pieces 28A, 28C, 28E and the second elastic pieces 28B, 28D, 28F formed in the circumferential direction D3.

[0100] In addition, in the corrugated foil 23A of the modification example 1, the width Wa of the slit 43A in the circumferential direction D3 is larger than the width Wb of the side slit 44A in the axial direction D1. For example, if the peak edge 28a of the first elastic sheet 28C and the peak edge 28a of the second elastic sheet 28D are formed by the common slit 43A, when the first elastic sheet 28C or the second elastic sheet 28D is unfolded, the peak edges 28a move in a direction close to each other. Here, the width Wa of the slit 43A is larger than the width Wb of the side slit 44A, so it becomes easier to prevent the peak edges 28a from interfering with each other compared to the case where the width of the slit and the width of the side slit are the same.

[0101] In the bump foil 23, 23A, the slits 43, 43B and the side slits 44, 44B of the slit structures 40, 40A are provided to be separated from the first end edge 23c and the second end edge 23d of the bump foil 23, 23A. In addition, the slits 43, 43B and the side slits 44, 44B are provided to be closed in the bump foil 23, 23A. As a result, it becomes easy to form the first elastic piece 28A, 28C and the second elastic piece 28B, 28D having a desired elastic force at a position separated from the first end edge 23c or the second end edge 23d, for example, at a position close to the center in the axial direction D1.

[0102] In addition, the slit structure 40B of the bump foil 23B of the second modification example includes a slit 43B for forming the peak edge portion 28a, and the slit 43B is open at the first end edge 23c or the second end edge 23d. As a result, the peak edge portion 28a can be easily formed by cutting a notch from the first end edge 23c or the second end edge 23d.

[0103] In addition, the plurality of peaks 32 are provided in addition to the elastic pieces 28A to 28F and also in the connection part 27. The connection part 27 is less likely to bend than the elastic pieces 28A to 28F. In contrast, the elastic pieces 28A to 28F are more likely to bend as they move away from the connection part 27 and approach the peak edge 28a in the circumferential direction D3. The elastic supporting force of the peaks 32 with respect to the top foil 22 becomes smaller as it moves closer to the peak edge 28a of the elastic pieces 28A to 28F. Therefore, the elastic supporting force is the largest at the connection part 27, and becomes smaller as it approaches the peak edge 28a of the elastic pieces 28A to 28F. That is, the elastic supporting force of the top foil 22 supported by the plurality of peaks 32 is not uniform in the circumferential direction D3 but varies. By arranging the plurality of peaks 32 in such a manner that the elastic supporting force varies, the stability of the top foil 22 that vibrates due to interference with the rotating shaft 15 can be improved, and the stability when supporting the rotating shaft 15 that rotates at a high speed can be improved.

[0104] In the manufacturing method of the radial foil bearing 20 described above, in the foil assembly forming step, the top foil 22, the bump foils 23, 23A, 23B, and the fixed foil 24 are rolled up to form the foil assembly 21, and in the foil assembly setting step, the foil assembly 21 is inserted into the bearing housing 45 and set so as to surround the rotating shaft 15. This manufacturing method can improve the assemblability when manufacturing the radial foil bearing 20. In addition, according to the radial foil bearing 20 manufactured by this manufacturing method, the rotating shaft 15 can be stably supported when rotating at a high speed.

[0105] In the above-mentioned manufacturing method, the foil assembly 21 is formed by rolling up the fixed foil 24 in the unfolded state in addition to the top foil 22 in the unfolded state and the bump foil 23 in the unfolded state. However, it is also possible to manufacture the radial foil bearing 20A in which the fixed foil 24 is omitted. When manufacturing the radial foil bearing 20A, the foil assembly 21A is formed by overlapping and rolling up the top foil 22 in the unfolded state and the bump foil 23 in the unfolded state. In the foil assembly setting step, the foil assembly 21A is inserted into the bearing housing 45 so as to surround the rotating shaft 15.

[0106] The radial foil bearing disclosed in the present invention is not limited to the above-mentioned examples, but can be subjected to various other deformations. For example, the above-mentioned examples can also be combined with each other according to the required purpose and effect. In addition, the elastic sheet can also be made into a structure in which a plurality of hills are omitted. For example, the first elastic sheet can also be made into a plate-like portion in the shape of an arc without a plurality of hills in the shape of an arc. In addition, the second elastic sheet can also be made into a plate-like portion in the shape of an arc without a plurality of hills in the shape of an arc.

[0107] Description of Reference Numerals

[0108] 15…rotating shaft; 20, 20A…radial foil bearing; 21, 21A…foil assembly; 45…bearing housing; 22…top foil; 23, 23A, 23B…wave foil; 23c…first end edge; 23d…second end edge; 24…fixed foil; D1…axial direction; D3…circumferential direction; 22a…opposing surface; 32…mountain portion; 25…cylindrical portion; 27…joining portion; 28A, 28C, 28E…first elastic sheet portion; 28B, 28D, 28F…second elastic sheet portion; 28a…peak edge portion; 28b…side edge portion; 40, 40A, 40B…slit structure; 43, 43A, 43B…slit; 44, 44A, 44B…side slit; Wa…width of slit; Wb…width of side slit.

Claims

1. A radial foil bearing, characterized in that: have: a top foil having an opposing surface opposed to the rotation axis; a bump foil disposed on the side opposite to the facing surface of the top foil, that is, on the outer side; and a bearing housing configured to surround the bump foil, The bump foil includes: a cylindrical portion that surrounds the top foil in a cylindrical shape; and an elastic sheet portion that is adjacent to the cylindrical portion in the axial direction of the rotating shaft and can be deformed independently of the cylindrical portion and can be expanded in the circumferential direction. The elastic piece portion is supported by the bearing housing.

2. The radial foil bearing according to claim 1, characterized in that The elastic sheet portion is formed integrally with the cylindrical portion. The bump foil includes a slit structure that separates the elastic piece portion from the cylindrical portion so that the elastic piece portion can be deformed independently of the cylindrical portion.

3. The radial foil bearing according to claim 2, characterized in that The bump foil includes a connecting portion connecting the cylindrical portion and the elastic sheet portion. The elastic piece portion includes: a peak edge portion formed on the opposite side of the connecting portion in the circumferential direction, and a side edge portion extending from the peak edge portion to the connecting portion. The peak edge portion is formed by the slit structure so as to become a free end.

4. The radial foil bearing according to claim 3, characterized in that The bump foil includes a first end edge as an end portion on one side in the axial direction, and a second end edge on a side opposite to the first end edge in the axial direction. The slit structure includes: a slit forming the peak edge portion, and a side slit connected to the slit and forming the side edge portion. The slit and the side slit are provided to be separated from the first end edge and the second end edge and to be closed inside the bump foil.

5. The radial foil bearing according to claim 3, characterized in that The bump foil includes a first end edge as an end portion on one side in the axial direction and a second end edge on a side opposite to the first end edge in the axial direction. The slit structure includes a slit forming the peak edge portion, The slit is open at the first end edge or the second end edge, At least a portion of the side edge portion is formed at the first end edge or the second end edge where the slit is opened.

6. The radial foil bearing according to claim 3, characterized in that The slit structure includes a slit forming the peak edge portion, The elastic sheet portion includes: a plurality of peaks arranged adjacent to each other in the circumferential direction and capable of being expanded in the circumferential direction by elastic deformation; The slit is between the adjacently arranged mountain portions, avoiding the mountain portions and extending along the mountain portions.

7. The radial foil bearing according to claim 3, characterized in that The slit structure includes a slit forming the peak edge portion, The elastic sheet parts are arranged in a plurality along the circumferential direction. The peak edge portion of one of the adjacent elastic pieces and the peak edge portion of the other adjacent elastic piece are formed by the common slit.

8. The radial foil bearing according to claim 7, characterized in that The slit structure further comprises: a side slit forming the side edge portion, The width of the slit in the circumferential direction is greater than the width of the side slit in the axial direction.

9. The radial foil bearing according to claim 1, characterized in that A fixed foil is further provided which is arranged to surround the bump foil and supports the elastic piece portion in a state where elasticity is imparted to the elastic piece portion.

10. A method for manufacturing a radial foil bearing, characterized in that: The radial foil bearing includes: a top foil including an opposing surface facing a rotating shaft; a bump foil arranged outside the top foil; and a bearing housing arranged to surround the bump foil. The method for manufacturing the radial foil bearing comprises the following steps: The step of rolling up a stack of the top foil in an expanded state and the corrugated foil in an expanded state to form a cylindrical foil assembly; and a step of inserting the foil assembly into a cylindrical bearing housing so as to surround the rotating shaft; The bump foil includes: a cylindrical portion that surrounds the top foil in a cylindrical shape; and an elastic sheet portion that is adjacent to the cylindrical portion in the axial direction of the rotating shaft and can be deformed independently of the cylindrical portion and can be expanded in the circumferential direction. The elastic piece portion is supported by the bearing housing by inserting the foil assembly into the bearing housing.

11. The method for manufacturing a radial foil bearing according to claim 10, characterized in that: In the step of forming the foil assembly, the fixed foil in an unfolded state is arranged to overlap the bump foil on the side opposite to the top foil to form the stack, and the stack is rolled up to form the foil assembly.

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