Radial foil bearing and rotary machine

Abstract

To inhibit deterioration of performance caused by collapse of a shape of a top foil.SOLUTION: A radial foil bearing includes: a housing having a shaft hole for inserting a shaft; a top foil which is disposed in the shaft hole and formed by one thin plate disposed so as to enclose the shaft in a circumferential direction of the shaft hole; and a back foil which is disposed so as to enclose the top foil in the circumferential direction between an inner peripheral surface of the shaft hole and the top foil and has elastic support parts for elastically supporting the top foil in a radial direction of the shaft hole. The top foil has engagement pieces protruding to the outer side in the radial direction. The inner peripheral surface has engagement grooves capable of engaging with the engagement pieces. Both ends as seen in the circumferential direction of the top foil respectively have supported parts elastically supported by the elastic support parts.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to radial foil bearings and rotary machines. [Background technology]

[0002] For example, the radial foil bearings described in Patent Documents 1 and 2 include a thin top foil surrounding a shaft, a thin back foil surrounding the top foil, and a cylindrical housing that accommodates the top foil and the back foil. In such radial foil bearings, both ends of the top foil are locked in locking grooves formed on the inner circumferential surface of the housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-020463 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-119095 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the above-described radial foil bearing, since space must be secured for both ends of the top foil to engage with the locking grooves in the bearing housing, both ends of the top foil tend to be widely spaced outward in the radial direction, making the shape of the top foil when viewed from the axial direction prone to significant deformation from a perfect circle. When the shape of the top foil is deformed in this way, the bearing clearance between the shaft and the top foil becomes uneven in the circumferential direction, increasing the likelihood of the top foil coming into strong partial contact with the shaft. Such contact can lead to a deterioration in the performance of the radial foil bearing, such as a shortened lifespan of the radial foil bearing due to accelerated wear at the contact points of the top foil.

[0005] The present disclosure describes a radial foil bearing and a rotary machine that can suppress performance degradation caused by deformation of the top foil. [Means for solving the problem]

[0006] A radial foil bearing according to one embodiment of the present disclosure comprises a housing having an axial hole for inserting a shaft, a top foil arranged in the axial hole and composed of a single thin plate arranged to surround the shaft circumferentially of the axial hole, and a back foil arranged between the inner surface of the axial hole and the top foil to surround the top foil circumferentially and having an elastic support portion that elastically supports the top foil in the radial direction of the axial hole, wherein the top foil has a locking piece that protrudes radially outward, the inner surface has a locking groove that can be engaged with the locking piece, and both circumferential ends of the top foil each have a supported portion that is elastically supported by the elastic support portion.

[0007] The above-described radial foil bearing has a structure in which the locking pieces of the top foil are locked into the locking grooves of the housing. Therefore, the top foil can be mechanically fixed to the housing without welding. This prevents distortion of the top foil due to heat generated during welding. Furthermore, both ends of the top foil each have a supported portion that is elastically supported in the radial direction by the elastic support portion of the back foil. When both ends of the top foil are elastically supported in the radial direction by the elastic support portion of the back foil, the support rigidity of the back foil supporting the top foil is prevented from being lower at both ends of the top foil than at other portions. This prevents both ends of the top foil from widening outward in the radial direction. As a result, the top foil can be maintained in a nearly perfectly circular shape when viewed axially of the shaft hole. This prevents the top foil from partially coming into strong contact with the shaft. This prevents degradation of the performance of the radial foil bearing, such as a shortened lifespan of the radial foil bearing due to accelerated wear at the contact points of the top foil.

[0008] In some embodiments, both ends of the top foil face each other in the circumferential direction, and when viewed from the axial direction of the axial hole, the top foil may have a gap formed between both ends of the top foil in the circumferential direction. In this case, it is possible to maintain the top foil in a shape closer to a perfect circle than when both ends of the top foil are arranged to overlap each other.

[0009] In some embodiments, the back foil may be formed of a single thin plate arranged to surround the top foil in the circumferential direction, with both circumferential ends of the back foil facing each other in the circumferential direction, and the back foil may have a slit formed between both ends of the back foil in the circumferential direction when viewed in the axial direction of the axial hole. In this case, the support rigidity of the back foil supporting the top foil can be maintained more uniformly in the circumferential direction compared to when both ends of the back foil are arranged to overlap each other. As a result, it is possible to maintain the top foil in a shape closer to a perfect circle.

[0010] In some embodiments, at least one of the slits in the top foil and the slits in the back foil may be located at a different position in the circumferential direction from the locking groove. Because it is necessary to secure space for the locking pieces of the top foil to engage with the locking grooves in the bearing housing, the support rigidity of the back foil supporting the top foil is likely to be lower than at other positions in the bearing housing. In contrast, the above-described configuration can prevent a situation in which the forces tending to open both ends of the top foil radially outward and the forces tending to open both ends of the back foil radially outward act together at the positions of the engagement grooves, where the support rigidity is relatively low. As a result, it is possible to maintain the top foil in a shape closer to a perfect circle.

[0011] In some embodiments, the slits in the top foil and the back foil may be located at positions different from the locking grooves in the circumferential direction. In this case, the forces tending to open the ends of the top foil and the back foil can be prevented from acting at the positions of the engagement grooves, where the support rigidity is relatively low. As a result, it is possible to maintain the top foil in a shape closer to a perfect circle.

[0012] In some embodiments, the slits in the top foil may be located at different positions in the circumferential direction from the slits in the back foil. In this case, it is possible to prevent the forces tending to open both ends of the top foil and the forces tending to open both ends of the back foil from acting at the same position. As a result, it is possible to maintain the top foil in a shape closer to a perfect circle.

[0013] In some embodiments, the locking piece may be provided in an intermediate portion of the top foil located between both ends. By providing the locking piece that engages with the locking groove of the bearing housing in an intermediate portion of the top foil other than both ends, the positions of both ends of the top foil can be shifted relative to the positions of the locking groove. This prevents a situation in which a force that tends to open the both ends of the top foil acts at the position of the engagement groove, where the support rigidity is relatively low. As a result, it becomes possible to maintain the top foil in a shape closer to a perfect circle.

[0014] In some embodiments, the locking piece may be a bent piece formed by bending a portion of the top foil outward in the radial direction. When the locking piece is formed from a portion of the top foil in this manner, the number of parts can be reduced compared to when the locking piece is formed from a separate part from the top foil. As a result, the assembly work of the radial foil bearing is easier.

[0015] In some embodiments, the locking piece may be formed on a side edge of the top foil in the axial direction of the axial hole. In this case, the locking piece can be easily formed on the top foil by simply making a slit in the side edge of the top foil and bending the slit portion.

[0016] In some embodiments, the locking piece may extend radially as viewed from the axial direction of the shaft hole and face the side surface of the locking groove with a gap in the circumferential direction. When a gap is provided between the locking piece and the side surface of the locking groove, the top foil is permitted to slide relative to the bearing housing. In this case, when the shaft rotates and whirls, the frictional force between the bearing housing and the top foil can act as a damping force that suppresses axial vibration of the shaft. As a result, the rotational stability of the shaft can be improved.

[0017] In some embodiments, the back foil may have a slit through which the locking piece passes in the radial direction. In this case, it is possible to easily realize a configuration in which the locking piece of the top foil is locked into the locking groove of the bearing housing.

[0018] In some embodiments, the slit may extend in the axial direction from a side edge of the back foil in the axial direction of the axial hole. In this case, the slit for passing the locking piece can be easily formed in the back foil by simply cutting out the side edge of the back foil.

[0019] In some embodiments, the back foil may have a plurality of peaks that protrude radially inward as viewed from the axial direction of the axial hole and are aligned in the circumferential direction, and a plurality of valleys that are respectively disposed between the peaks in the circumferential direction, the elastic support portion being formed by the plurality of peaks, and the slit being formed in at least one of the valleys. In this case, a situation in which the support rigidity of the back foil is reduced due to the formation of the slit can be avoided, and the support rigidity of the back foil can be maintained more uniformly in the circumferential direction. As a result, it is possible to maintain the top foil in a shape that is closer to a perfect circle.

[0020] In some embodiments, the back foil may have a plurality of peaks that protrude radially inward as viewed from the axial direction of the axial hole and are aligned in the circumferential direction, and a plurality of valleys that are respectively disposed between the plurality of peaks in the circumferential direction, the elastic support portion may be formed by the plurality of peaks, and the supported portion may be a portion that contacts at least one of the plurality of peaks. In this case, a configuration in which both ends of the top foil are elastically supported by the back foil can be easily realized.

[0021] A rotary machine according to one embodiment of the present disclosure includes any one of the radial foil bearings described above, a shaft inserted into a shaft hole of a housing and supported by the radial foil bearing, a turbine disposed at one end of the shaft, and a compressor disposed at the other end of the shaft. Because the rotary machine includes any one of the radial foil bearings described above, it is possible to maintain the top foil in a shape close to a perfect circle. In other words, it is possible to maintain a uniform gap between the top foil and the shaft in the circumferential direction. This prevents the top foil from coming into partial strong contact with the shaft. As a result, it is possible to prevent performance degradation of the radial foil bearing, such as a shortened lifespan of the radial foil bearing due to accelerated wear at the contact points of the top foil. [Effects of the Invention]

[0022] According to some aspects of the present disclosure, there are provided a radial foil bearing and a rotary machine that can suppress performance degradation caused by deformation of the top foil. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a cross-sectional view showing a rotary machine according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a radial foil bearing included in the rotary machine of FIG. [Figure 3] FIG. 3 is a cross-sectional view taken along line III-III in FIG. [Figure 4]FIG. 4 is a perspective view showing the top foil of the radial foil bearing of FIG. 2 in an expanded state. [Figure 5] Fig. 5(a) is a plan view showing the top foil of Fig. 4. Fig. 5(b) is a side view showing the top foil of Fig. 4. [Figure 6] Fig. 6(a) is a plan view showing the back foil of the radial foil bearing of Fig. 2 in a developed state, and Fig. 6(b) is a side view showing the back foil of Fig. 6(a). [Figure 7] FIG. 7 is a cross-sectional view showing a radial foil bearing according to a modified example. [Figure 8] FIG. 8 is a perspective view showing the top foil of the radial foil bearing of FIG. 7 in an expanded state. [Figure 9] Fig. 9(a) is a plan view showing the top foil of Fig. 8. Fig. 9(b) is a side view showing the top foil of Fig. 8. [Figure 10] Fig. 10(a) is a plan view showing the back foil of the radial foil bearing of Fig. 7 in an expanded state, and Fig. 10(b) is a side view showing the back foil of Fig. 10(a). [Figure 11] FIG. 11 is a cross-sectional view showing a radial foil bearing according to another modified example. [Figure 12] FIG. 12 is a perspective view showing the top foil of the radial foil bearing of FIG. 11 in an expanded state. [Figure 13] Fig. 13(a) is a plan view showing the top foil of Fig. 12. Fig. 13(b) is a side view showing the top foil of Fig. 12. [Figure 14] FIG. 14 is a cross-sectional view showing a radial foil bearing according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0024] 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 description will be omitted.

[0025] <Rotating machinery> First, a rotary machine 1 according to this embodiment will be described with reference to Fig. 1. 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 shaft 15. The turbine 2 includes a turbine impeller 4 provided at one 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 the other end of the shaft 15, and a compressor housing 7 that houses the compressor impeller 5.

[0026] A rotor 11 of the electric motor 10 is disposed, for example, at the center of a shaft 15. The rotor 11 is fixed to the shaft 15 and is rotatable together with the shaft 15. A stator 12 of the electric motor 10 is disposed 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.

[0027] 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 through 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 as it passes 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.

[0028] The shaft 15 is rotatably supported around the rotation axis H via a plurality of bearings. At least one of the plurality of bearings is 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 20a, 20b are provided at both ends of the shaft 15. The radial foil bearings 20a, 20b are air bearings that support the shaft 15 in the radial direction (i.e., the direction perpendicular to the rotation axis H).

[0029] 1, a thrust collar 17 and a pair of thrust air bearings 18a, 18b are provided between the compressor impeller 5 and one of the radial foil bearings 20b closer to the compressor impeller 5. The thrust collar 17 is a disk-shaped member formed to protrude like a flange around the periphery of the shaft 15. The pair of thrust air bearings 18a, 18b are provided at positions sandwiching the thrust collar 17. A spacer 19 is provided between the pair of thrust air bearings 18a, 18b, surrounding the thrust collar 17. The thrust collar 17 and the pair of thrust air bearings 18a, 18b support the shaft 15 in the thrust direction (i.e., the direction parallel to the rotation axis H).

[0030] <Radial foil bearing> Next, the configuration of the radial foil bearings 20a, 20b will be described in detail with reference to Figures 2 to 5. The radial foil bearings 20a, 20b have the same configuration. Therefore, in the following description, the pair of radial foil bearings 20a, 20b will be collectively referred to as "radial foil bearing 20."

[0031] As shown in FIG. 2 , the radial foil bearing 20 includes a top foil 25, a back foil 35 surrounding the top foil 25, and a bearing housing 45 (housing) that accommodates the top foil 25 and the back foil 35. The bearing housing 45 has a shaft hole 46 through which the shaft 15 is inserted. The shaft hole 46 is a circular hole with the rotation axis H as its central axis, and penetrates the bearing housing 45 in the direction of extension of the rotation axis H. In the following description, the direction in which the shaft hole 46 extends, i.e., the direction in which the rotation axis H extends, will be referred to as the “axial direction D1.” The radial direction of the shaft hole 46, i.e., the direction perpendicular to the rotation axis H, will be referred to as the “radial direction D2.” The circumferential direction along the inner circumferential surface 46 a of the shaft hole 46, i.e., the direction along a ring centered on the rotation axis H, will be referred to as the “circumferential direction D3.” In this embodiment, the shaft hole 46 will be described as including the inner circumferential surface 46a and the internal space surrounded by the inner circumferential surface 46a.

[0032] The bearing housing 45 is, for example, a cylindrical member having sufficient strength to support the shaft 15 when it is stopped from rotating. The shaft 15 is disposed so as to pass through the center of an axial hole 46 in the bearing housing 45. An inner circumferential surface 46a of the axial hole 46 surrounds the shaft 15 in the circumferential direction D3 and faces the outer circumferential surface 15a of the shaft 15 with a gap therebetween. As shown in FIG. 3 , the inner circumferential surface 46a has a pair of locking grooves 471, 472 at both ends in the axial direction D1. The pair of locking grooves 471, 472 are disposed symmetrically with respect to the center of the inner circumferential surface 46a in the axial direction D1. Therefore, when viewed from the axial direction D1, the pair of locking grooves 471, 472 are disposed in positions overlapping each other. The pair of locking grooves 471, 472 have the same configuration. Hereinafter, when the pair of locking grooves 471, 472 is described without distinguishing between them, the pair of locking grooves 471, 472 will be collectively referred to as the "locking groove 47."

[0033] The locking groove 47 is a rectangular groove recessed outward in the radial direction D2 at the end of the inner circumferential surface 46a in the axial direction D1. The locking groove 47 reaches the end face of the bearing housing 45 in the axial direction D1. The locking groove 47 includes a bottom surface 47a recessed outward in the radial direction D2 relative to the inner circumferential surface 46a, and a side surface 47b connecting the bottom surface 47a and the inner circumferential surface 46a in the radial direction D2. The bottom surface 47a is, for example, a surface parallel to the inner circumferential surface 46a. The side surface 47b is, for example, a surface perpendicular to the inner circumferential surface 46a and the bottom surface 47a. Furthermore, as shown in FIG. 2, the locking groove 47 includes a pair of side surfaces 47c and 47d facing each other with a gap in the circumferential direction D3. The pair of side surfaces 47c, 47d connect the bottom surface 47a and the inner peripheral surface 46a in the radial direction D2, and are formed perpendicular to the bottom surface 47a and the inner peripheral surface 46a.

[0034] The top foil 25 is housed in the axial hole 46 of the bearing housing 45. The top foil 25 is made of a single thin metal plate and is arranged in a cylindrical shape so as to surround the shaft 15 in the circumferential direction D3. The inner circumferential surface of the top foil 25 is configured as a bearing surface 25a that faces the outer circumferential surface 15a of the shaft 15. The bearing surface 25a has a circular shape when viewed from the axial direction D1. When the shaft 15 rotates, the bearing surface 25a is maintained in a state where a gap is formed between the bearing surface 25a and the outer circumferential surface 15a of the shaft 15. The outer circumferential surface 25b of the top foil 25 faces the inner circumferential surface 46a of the axial hole 46 via the back foil 35.

[0035] 4, the top foil 25 has, for example, a rectangular shape with the circumferential direction D3 as the longitudinal direction and the axial direction D1 as the transverse direction. The top foil 25 includes a pair of side edges 26, 27 located at both ends in the axial direction D1 and extending in the circumferential direction D3, and a pair of end edges 28, 29 located at both ends in the circumferential direction D3 and extending in the axial direction D1. In this embodiment, the pair of side edges 26, 27 each constitute a long side of the top foil 25. The pair of end edges 28, 29 each constitute a short side of the top foil 25.

[0036] The top foil 25 has a pair of end portions P11, P12 located at both ends in the circumferential direction D3, and an intermediate portion P13 located between the pair of end portions P11, P12 in the circumferential direction D3. The pair of end portions P11, P12 are portions that abut against the peak portions 41 (see FIGS. 6(a) and 6(b)) of the back foil 35, which will be described later. Hereinafter, the pair of end portions P11, P12 may be referred to as the “end portions P11, P12” of the top foil 25.

[0037] One end portion P11 includes the edge 29 and a portion extending from the edge 29 to a position shifted inward in the circumferential direction D3. When viewed from the radial direction D2, the end portion P11 has a size sufficient to encompass, for example, one peak portion 41 (see FIGS. 6(a) and 6(b)) of the back foil 35, which will be described later. For example, the width of the end portion P11 in the circumferential direction D3 may be the same as the width of one peak portion 41 in the circumferential direction D3. The other end portion P12 includes the edge 28 and a portion extending from the edge 28 to a position shifted inward in the circumferential direction D3. For example, the width of the end portion P12 in the circumferential direction D3 may be the same as the width of one peak portion 41 in the circumferential direction D3, similar to the end portion P11. The middle portion P13 is a portion sandwiched between both end portions P11 and P12 of the top foil 25. Therefore, the intermediate portion P13 refers to the entire portion located between the end portion P11 and the end portion P12 in the circumferential direction D3.

[0038] Furthermore, as shown in FIG. 4, the top foil 25 includes a plurality of (four in this embodiment) locking pieces 30a, 30b, 30c, and 30d that protrude outward in the radial direction D2. Each of the locking pieces 30a, 30b, 30c, and 30d is, for example, a bent piece formed by bending a portion of the top foil 25 outward in the radial direction D2. That is, each of the locking pieces 30a, 30b, 30c, and 30d is formed by a single piece of the top foil 25. Each of the locking pieces 30a, 30b, 30c, and 30d is formed, for example, in the circumferential direction D3 of the intermediate portion P13. The locking pieces 30a and 30b are formed on the side edge 26 of the intermediate portion P13, and the locking pieces 30c and 30d are formed on the side edge 27 of the intermediate portion P13.

[0039] The locking pieces 30a, 30b are formed by slits in the side edge 26 of the intermediate portion P13. As shown in FIG. 5(a), these slits are formed along T-shaped slit lines C11. Specifically, slits are made along slit lines C2 extending from the side edge 26 in the axial direction D1, and then slits are made along slit lines C1 extending from the end of slit line C2 to both sides in the circumferential direction D3. The portions on both sides of the slit line C2 are then pushed open outward in the radial direction D2, thereby rising from their state along the circumferential direction D3 to the outside in the radial direction D2. This forms the locking pieces 30a, 30b that stand outward in the radial direction D2 relative to the intermediate portion P13. The locking pieces 30c, 30d are similarly formed by T-shaped slit lines C11 in the side edge 27 of the intermediate portion P13.

[0040] The locking pieces 30a and 30b formed in this manner are arranged side by side at a distance in the axial direction D1 on the side edge 26 of the intermediate portion P13. The locking pieces 30c and 30d are arranged side by side at a distance in the axial direction D1 on the side edge 27 of the intermediate portion P13. The locking pieces 30c and 30d are arranged in positions symmetrical to the locking pieces 30a and 30b with respect to the center of the intermediate portion P13 in the axial direction D1. Therefore, when viewed from the axial direction D1, the locking pieces 30c and 30d are arranged in positions overlapping the locking pieces 30a and 30b, respectively. The locking pieces 30a, 30b, 30c, and 30d have, for example, the same shape as one another. Hereinafter, when the locking pieces 30a, 30b, 30c, and 30d are described without distinction, they will be collectively referred to as "locking pieces 30."

[0041] As shown in FIG. 4, the locking piece 30 has, for example, a rectangular plate shape having a certain width in the axial direction D1 and extending outward in the radial direction D2. When viewed in the axial direction D1, as shown in FIG. 5(b), the locking piece 30 extends linearly outward in the radial direction D2. For example, the locking piece 30 is formed perpendicular to the intermediate portion P13. The locking piece 30 may be inclined from a direction perpendicular to the intermediate portion P13. The length of the locking piece 30 in the radial direction D2 is set to be shorter than the depth of the locking groove 47 (see FIG. 3). The depth of the locking groove 47 is the distance in the radial direction D2 from the bottom surface 47a of the locking groove 47 to the inner circumferential surface 46a. The width of the locking piece 30 in the axial direction D1 is set to be smaller than the width of the locking groove 47 in the axial direction D1. The width of the locking groove 47 in the axial direction D1 is the distance in the axial direction D1 from the side surface 47b of the locking groove 47 to the end face of the bearing housing 45 on which the locking groove 47 is formed. In this embodiment, the distance in the circumferential direction D3 between the pair of end edges 28, 29 is narrower than the distance in the circumferential direction D3 between the pair of locking pieces 30a, 30b. The distance in the circumferential direction D3 refers to the narrower of the distances along one side and the other side in the circumferential direction D3.

[0042] As shown in FIG. 2 , the back foil 35 is accommodated in the axial hole 46 of the bearing housing 45 together with the top foil 25. The back foil 35 is made of a single thin metal plate and is arranged cylindrically to surround the top foil 25. Therefore, the back foil 35 is arranged between the inner circumferential surface 46a of the axial hole 46 and the outer circumferential surface 25b of the top foil 25. The back foil 35 is supported in the radial direction D2 by the inner circumferential surface 46a of the axial hole 46. The back foil 35 also elastically supports the top foil 25 in the radial direction D2. For example, a bump foil formed from a corrugated thin plate is used as the back foil 35. The back foil 35 is not limited to a bump foil having such a shape, and foils having other shapes may be used as long as they can elastically support the top foil 25. For example, the back foil 35 may be a foil formed by cutting multiple blades out of a single thin plate.

[0043] 6(a), the back foil 35 as a whole has, for example, a rectangular shape when viewed from the radial direction D2, with the circumferential direction D3 as the longitudinal direction and the axial direction D1 as the transverse direction. The back foil 35 includes a pair of side edges 36, 37 located at both ends in the axial direction D1 and extending in the circumferential direction D3, and a pair of end edges 38, 39 located at both ends in the circumferential direction D3 and extending in the axial direction D1. The pair of side edges 36, 37 each constitute a long side of the back foil 35. The pair of end edges 38, 39 each constitute a short side of the back foil 35.

[0044] The back foil 35 has a pair of end portions P21, P22 located at both ends in the circumferential direction D3, and an intermediate portion P23 located between the pair of end portions P21, P22 in the circumferential direction D3. Hereinafter, the pair of end portions P21, P22 may be referred to as "end portions P21, P22" of the back foil 35. One end portion P21 includes an edge 39 and a portion extending from the edge 39 to a position shifted inward in the circumferential direction D3. The end portion P21 may include, for example, a peak 41 located at the edge 39 and a valley 42 adjacent to the peak 41. The other end portion P22 includes an edge 38 and a portion extending from the edge 38 to a position shifted inward in the circumferential direction D3. The end portion P22 may include, for example, a peak 41 located at the edge 38 and a valley 42 adjacent to the peak 41. The intermediate portion P23 is a portion sandwiched between both end portions P21, P22 of the back foil 35. In other words, the intermediate portion P23 refers to the entire portion located between the end portion P21 and the end portion P22 in the circumferential direction D3.

[0045] As shown in FIGS. 6( a) and 6(b), the back foil 35 is composed of a plurality of peaks 41 and a plurality of valleys 42. The peaks 41 and valleys 42 are alternately arranged along the circumferential direction D3. As shown in FIG. 6(b), each peak 41 is curved so as to protrude inward in the radial direction D2 when viewed from the axial direction D1, generating an elastic force in the radial direction D2. Each peak 41 is configured as an elastic support portion for elastically supporting the top foil 25 in the radial direction D2. Each peak 41 extends continuously in the axial direction D1 from the side edge 36 to the side edge 37 of the back foil 35. Each valley 42 is disposed between the peaks 41 in the circumferential direction D3. Each valley 42 is a flat portion connecting the peaks 41 and forming a recess relative to each peak 41. Like each of the peaks 41, each of the valleys 42 extends continuously in the axial direction D1 from the side edge 36 to the side edge 37 of the back foil 35.

[0046] Furthermore, the back foil 35 has a plurality of (four in this embodiment) slits 40a, 40b, 40c, and 40d. Each of the slits 40a, 40b, 40c, and 40d is, for example, a notch formed in the back foil 35 so as to extend in the axial direction D1. Each of the slits 40a, 40b, 40c, and 40d is formed at a position corresponding to each of the locking pieces 30a, 30b, 30c, and 30d, i.e., at a position overlapping each of the locking pieces 30a, 30b, 30c, and 30d in the radial direction D2. Each of the slits 40a, 40b, 40c, and 40d is formed, for example, in a middle portion P23 of the back foil 35.

[0047] The slits 40a, 40b extend from a side edge 36 of the intermediate portion P23 in the axial direction D1 at positions spaced apart in the circumferential direction D3. The slit 40a is formed, for example, in the side edge 36 of a valley portion 42 between two peak portions 41. The slit 40b is formed, for example, in the side edge 36 of another valley portion 42 adjacent to the valley portion 42 in which the slit 40a is formed, across one peak portion 41. The slits 40c, 40d extend from a side edge 37 of the intermediate portion P23 in the axial direction D1 at positions spaced apart in the circumferential direction D3. The slit 40c is formed, for example, in the side edge 37 of the valley portion 42 in which the slit 40a is formed. The slit 40b is formed, for example, in the side edge 37 of the valley portion 42 in which the slit 40b is formed.

[0048] The slits 40c and 40d are disposed symmetrically to the slits 40a and 40b with respect to the center of the intermediate portion P23 in the axial direction D1. Therefore, when viewed from the axial direction D1, the slits 40a and 40b are disposed in positions overlapping with the slits 40a and 40b, respectively. The slits 40a, 40b, 40c, and 40d have, for example, the same shape as one another. Hereinafter, when the slits 40a, 40b, 40c, and 40d are described without distinction, they will be collectively referred to as "slits 40."

[0049] The width of the slit 40 in the circumferential direction D3 is set to be larger than the thickness of the locking piece 30 in the circumferential direction D3 (i.e., the plate thickness of the top foil 25) (see FIG. 2). The width of the slit 40 in the circumferential direction D3 may be the same as or smaller than the width of the valley portion 42 in the circumferential direction D3. The length of the slit 40 in the axial direction D1 is set to be longer than the width of the locking piece 30 in the axial direction D1 (see FIG. 3). Therefore, the slit 40 has a size that allows the locking piece 30 to pass through in the radial direction D2.

[0050] As shown in FIG. 2 , when the top foil 25 and the back foil 35 are housed in the axial hole 46, the peaks 41 of the back foil 35 are arranged at equal intervals around the entire circumference in the circumferential direction D3. Each peak 41 abuts against the outer peripheral surface 25b of the top foil 25 and elastically supports the outer peripheral surface 25b in the radial direction D2. The peaks 41 are arranged not only between the middle portion P13 of the top foil 25 and the inner peripheral surface 46a of the axial hole 46, but also between both end portions P11, P12 of the top foil 25 and the inner peripheral surface 46a. Therefore, both end portions P11, P12 of the top foil 25 are elastically supported by the peaks 41 of the back foil 35, similar to the middle portion P13. Each valley 42 of the back foil 35 abuts against the inner peripheral surface 46a of the axial hole 46 and is supported in the radial direction D2 by the inner peripheral surface 46a.

[0051] Each of the end portions P11, P12 of the top foil 25 is elastically supported by one of the plurality of peak portions 41. Therefore, each of the end portions P11, P12 has a supported portion PA, PB (see FIG. 5(a)) elastically supported by the peak portion 41. The supported portion PA is a contact portion of the end portion P11 with the peak portion 41. The supported portion PB is a contact portion of the end portion P12 with the peak portion 41. In the example shown in FIG. 5(a), the supported portion PA extends continuously from the side edge 26 to the side edge 27 at the center of the end portion P11 in the circumferential direction D3. Similarly, the supported portion PB extends continuously in the axial direction D1 from the side edge 26 to the side edge 27 at the center of the end portion P12 in the circumferential direction D3. The supported portions PA, PB do not need to extend in the axial direction D1 from the side edge 26 to the side edge 27, but may be provided on at least a part of each of the end portions P11, P12.

[0052] In the state shown in FIG. 2, both end portions P11, P12 of the top foil 25 are arranged to face each other in the circumferential direction D3. The phrase "both end portions P11, P12 facing each other in the circumferential direction D3" does not mean that both end portions P11, P12 are arranged to overlap each other, but rather that both end portions P11, P12 are arranged to face each other in the circumferential direction D3. The state in which both end portions P11, P12 are arranged to face each other in the circumferential direction D3 includes a state in which, when viewed from the axial direction D1, a tangent to the top foil 25 contacting the end portion P11 and a tangent to the top foil 25 contacting the end portion P12 are arranged to overlap each other, as well as a state in which these tangents intersect each other. The both end portions P11, P12 are arranged, for example, close to each other in the circumferential direction D3 with a gap therebetween. The both end portions P11, P12 may also be arranged to contact each other. When viewed from the axial direction D1, a gap (boundary) S1 is formed in the top foil 25 between both end portions P11, P12. The gap S1 is formed at one location in the circumferential direction D3 of the top foil 25. When both end portions P11, P12 are disposed so as to contact each other, the gap S1 may be the boundary between both end portions P11, P12.

[0053] Similarly, both end portions P21, P22 of the back foil 35 are arranged to face each other in the circumferential direction D3. "The end portions P21, P22 facing each other in the circumferential direction D3" means that the end portions P21, P22 are arranged to face each other in the circumferential direction D3, rather than to overlap each other. "The end portions P21, P22 are arranged to face each other in the circumferential direction D3" includes a state in which, when viewed from the axial direction D1, a tangent to the back foil 35 contacting the end portion P21 and a tangent to the back foil 35 contacting the end portion P22 are arranged to overlap each other, as well as a state in which these tangents intersect each other. The end portions P21, P22 are arranged, for example, close to each other in the circumferential direction D3 with a gap therebetween. The end portions P21, P22 may also be arranged to face each other. When viewed from the axial direction D1, a gap (boundary) S2 is formed in the back foil 35 by the gap between both end portions P21, P22. The gap S2 is formed at one location in the circumferential direction D3 of the back foil 35. When both end portions P21, P22 are disposed so as to contact each other, the gap S2 may be the boundary between both end portions P21, P22.

[0054] As shown in FIG. 2 , the slit S1 of the top foil 25 and the slit S2 of the back foil 35 are located at different positions from the locking groove 47 in the circumferential direction D3. That is, neither of the slits S1, S2 overlaps with the locking groove 47 in the radial direction D2, but is shifted in the circumferential direction D3 from that position. This state can also be described as a state in which the phase of the slits S1, S2 is shifted with respect to the phase of the locking groove 47, with reference to the rotation direction of the shaft 15. For example, the slits S1, S2 are located on the opposite side of the locking groove 47 with respect to the rotation axis H in the radial direction D2. For example, the slits S1, S2 are located at the same position as each other. That is, the slits S1, S2 overlap with each other in the radial direction D2. In this embodiment, the end P11 and the end P12 of the top foil 25 are supported by two peaks 41, 41 of the back foil 35 that are adjacent to each other in the circumferential direction D3. A gap S2 is interposed between the two peaks 41, 41 adjacent to each other in the circumferential direction D3.

[0055] On the other hand, the locking pieces 30 of the top foil 25 and the slits 40 of the back foil 35 are located at the same position as the locking groove 47 in the circumferential direction. That is, the locking pieces 30 and the slits 40 are located so as to overlap with the locking groove 47 in the radial direction D2. In this state, the locking pieces 30 pass through the slits 40 and are disposed in the locking groove 47. The locking pieces 30 are disposed in the locking groove 47 with gaps between them and the side surfaces 47c and 47d. Specifically, the locking pieces 30a and 30b are aligned in the circumferential direction D3 in the locking groove 471 and are disposed with gaps between them and the side surfaces 47c and 47d. As a result, the distance W1 between the locking pieces 30a and 30b in the circumferential direction D3 is smaller than the distance W2 between the locking grooves 471 in the circumferential direction D3. Distance W1 refers to the distance in the circumferential direction D3 from the surface of locking piece 30a facing side surface 47c to the surface of locking piece 30b facing side surface 47d. Distance W2 refers to the distance in the circumferential direction D3 between side surface 47c and side surface 47d. Locking pieces 30c and 30d are also arranged with respect to locking groove 472, similar to locking pieces 30a and 30b.

[0056] The locking pieces 30 arranged in this manner pass through the slits 40 and come into contact with the side surfaces 47c, 47d of the locking groove 47 in the circumferential direction D3, thereby restricting movement of the top foil 25 and the back foil 35 in the circumferential direction D3 relative to the bearing housing 45. Furthermore, as shown in Fig. 3, the locking pieces 30 are arranged to face the side surfaces 47b of the locking groove 47 with a gap in the axial direction D1. The locking pieces 30 that have passed through the slits 40 are locked onto the side surfaces 47b in the axial direction D1, thereby restricting movement of the top foil 25 and the back foil 35 in the axial direction D1 relative to the bearing housing 45. Therefore, the state in which the locking pieces 30 are locked in the locking grooves 47 refers to both a state in which the locking pieces 30 abut against the side surfaces 47c, 47d of the locking grooves 47, thereby restricting movement of the top foil 25 in the circumferential direction D3 relative to the bearing housing 45, and a state in which the locking pieces 30 abut against the side surface 47b of the locking grooves 47, thereby restricting movement of the top foil 25 in the axial direction D1 relative to the bearing housing 45. In this embodiment, the locking pieces 30 that are locked in the locking grooves 47 are formed not at both end portions P11, P12 of the top foil 25 but at an intermediate portion P13 that is different from both end portions P11, P12. Therefore, both end portions P11, P12 are free ends that are not locked to the bearing housing 45. A pair of locking pieces 30 (e.g., locking pieces 30a, 30b) aligned in the circumferential direction D3 are positioned offset in the circumferential direction D3 from both end portions P11, P12, which are free ends.

[0057] When assembling the radial foil bearing 20 having the above configuration, first, the top foil 25 having the locking pieces 30, the back foil 35 having the slits 40, and the bearing housing 45 having the locking grooves 47 are prepared. To form the locking pieces 30, slits are made along the T-shaped slit lines C11 shown in FIG. 5(a) by, for example, blanking. Then, the slits in the top foil 25 are pushed open outward in the radial direction D2 by, for example, pressing. This forms the locking pieces 30 in the top foil 25. The slits 40 are formed in the back foil 35 by, for example, wire cutting. The locking grooves 47 are formed in the inner circumferential surface 46a using, for example, an end mill.

[0058] The top foil 25 and the back foil 35 are then assembled into the bearing housing 45. Specifically, first, the locking pieces 30 are passed through the slits 40, and the top foil 25 and the back foil 35 are then overlapped with each other. The top foil 25 and the back foil 35 are then rolled into a cylindrical shape so that the radius of curvature of the overlapping top foil 25 and back foil 35 is smaller than the inner diameter of the axial hole 46. The top foil 25 and the back foil 35 are then inserted into the axial hole 46 with the positions of the locking pieces 30 and the slits 40 aligned with the positions of the locking grooves 47 in the circumferential direction D3. The top foil 25 and the back foil 35 are then released from the axial hole 46. As a result, the locking pieces 30 that have passed through the slits 40 are positioned in the locking grooves 47, and the radial foil bearing 20 shown in FIG. 2 is obtained. Then, the shaft 15 is inserted into the bearing surface 25 a of the top foil 25 , whereby the shaft 15 is assembled to the bearing housing 45 .

[0059] When the shaft 15 rotates, an air film is formed between the shaft 15 and the top foil 25 in response to the rotation of the shaft 15. When the pressure of this air film increases, the top foil 25 is pushed outward in the radial direction D2, and the back foil 35 is compressed in the radial direction D2 while elastically deforming. The shaft 15 is then supported by the pressure of the air film formed in the bearing gap between the shaft 15 and the top foil 25. In other words, the shaft 15 is rotatably supported without contacting the top foil 25.

[0060] <Action and effect> Next, the effects achieved by the radial foil bearing 20 and the rotary machine 1 according to this embodiment will be described together with the problems of the related art.

[0061] In conventional radial foil bearings, the top foil and back foil are sometimes fixed to the bearing housing by spot welding to prevent them from falling off. However, when the top foil is fixed to the bearing housing by welding in this manner, there is a risk that the heat generated during welding will cause distortion in the top foil. Distortion of the top foil can adversely affect the accuracy of the bearing gap between the top foil and the shaft, potentially resulting in reduced performance of the radial foil bearing.

[0062] On the other hand, a radial foil bearing 120 shown in FIG. 14 is known as a structure in which a top foil is mechanically fixed to a bearing housing without welding. In this radial foil bearing 120, a locking groove 147 is formed in an inner circumferential surface 146a of a shaft hole 146 of a bearing housing 145, and both end portions P111, P112 of the top foil 125 are locked in the locking groove 147 while being bent outward in the radial direction D2. Both end portions P121, P122 of the back foil 135, together with both end portions P111, P112 of the top foil 125, are also bent outward in the radial direction D2 and locked in the locking groove 147. In this structure in which the top foil 125 is mechanically fixed to the bearing housing 145, it is possible to avoid distortion of the top foil 125 that would occur by using welding.

[0063] 14, however, it is necessary to secure a space (i.e., an inner portion of the locking groove 147) at the positions of both ends P111, P112 of the top foil 125 to lock both ends P111, P112 to the bearing housing 145. In this space, the top foil 125 is not elastically supported by the back foil 135, and therefore the support rigidity of the back foil 135 supporting both ends P111, P112 of the top foil 125 is lower than the support rigidity of the back foil 135 supporting other portions of the top foil 125. As a result, as shown in FIG. 14, both ends P111, P112 are widely open outward in the radial direction D2, and the shape of the top foil 125 as viewed from the axial direction D1 is significantly deformed from a perfect circle.

[0064] Such deformation of the top foil 125 causes non-uniformity in the bearing gap between the shaft 15 and the top foil 125. Non-uniformity in the bearing gap increases the likelihood that the top foil 125 will make strong contact with the shaft 15 in certain areas. Such contact of the top foil 125 with the shaft 15 may result in a decrease in performance of the radial foil bearing 120. For example, when assembling the shaft 15 to the radial foil bearing 120, the shaft 15 is inserted into the top foil 125 by expanding the top foil 125. At this time, the top foil 125 is likely to make strong contact with the shaft 15 in areas where the bearing gap is narrow, i.e., in areas of the top foil 125 that extend inward in the radial direction D2. Such strong contact of the top foil 125 with the shaft 15 accelerates wear at the contact points of the top foil 125 with the shaft 15, potentially shortening the life of the radial foil bearing 120.

[0065] Furthermore, when the shaft 15 is rotated while assembled to the radial foil bearing 120, the shaft 15 rotates while rubbing against the bearing surface of the top foil 125, and air is drawn in between the shaft 15 and the top foil 125 as the shaft 15 rotates. As a result, an air film is formed between the shaft 15 and the top foil 125, and the shaft 15 is lifted and supported by the pressure of the air film. Here, when the shaft 15 starts to rotate from a stopped state, if there is a portion where the top foil 125 makes strong contact with the shaft 15, wear will be accelerated at that contact portion. Furthermore, the contact pressure of the top foil 125 against the shaft 15 will become excessively large at that contact portion. In this case, it will be difficult for an air film to form between the shaft 15 and the top foil 125 during rotation of the shaft 15, and the rotation speed of the shaft 15 required to form the air film (i.e., the lift rotation speed required to lift the shaft 15) may become excessively high.

[0066] In this embodiment, the locking pieces 30 of the top foil 25 are configured to lock into the locking grooves 47 of the bearing housing 45. Therefore, similar to the radial foil bearing 120 shown in FIG. 14 , the top foil 25 can be mechanically fixed to the bearing housing 45 without welding. Therefore, distortion of the top foil 25 due to heat generated during welding can be avoided. Furthermore, in this embodiment, each of the end portions P11 and P12 of the top foil 25 includes a supported portion PA and a supported portion PB that are elastically supported in the radial direction D2 by the peak portions 41 of the back foil 35. When the end portions P11 and P12 are elastically supported in the radial direction D2 by the peak portions 41, the support rigidity of the back foil 35 that supports the top foil 25 can be prevented from being lower at the end portions P11 and P12 than at other portions. This prevents the end portions P11 and P12 from being significantly open outward in the radial direction D2. As a result, the top foil 25 can be maintained in a shape close to a perfect circle when viewed from the axial direction D1. In other words, the bearing clearance between the top foil 25 and the shaft 15 can be maintained uniform in the circumferential direction D3. This prevents the top foil 25 from coming into partial strong contact with the shaft 15. As a result, a reduction in the lifespan of the radial foil bearing 20 due to accelerated wear at the contact points of the top foil 25 can be suppressed. Therefore, according to this embodiment, a reduction in performance of the radial foil bearing 20 caused by deformation of the top foil 25 can be suppressed. Furthermore, by maintaining a uniform bearing clearance, an increase in the contact pressure of the top foil 25 with the shaft 15 can be suppressed, making it easier for an air film to form between the shaft 15 and the top foil 25 during rotation of the shaft 15. As a result, an increase in the levitation rotation speed required for levitating the shaft 15 can be suppressed.

[0067] In this embodiment, both end portions P11, P12 of the top foil 25 face each other in the circumferential direction D3, and when viewed from the axial direction D1, the top foil 25 forms a gap S1 between both end portions P11, P12 in the circumferential direction D3. In this case, the top foil 25 can be maintained in a shape closer to a perfect circle than when both end portions P11, P12 are arranged to overlap each other.

[0068] In this embodiment, the back foil 35 is formed of a single thin plate arranged to surround the top foil 25 in the circumferential direction D3, and both end portions P21, P22 of the back foil 35 in the circumferential direction D3 face each other in the circumferential direction D3. When viewed from the axial direction D1 of the axial hole 46, the back foil 35 forms a gap S2 between both end portions P21, P22 in the circumferential direction D3. In this case, the support rigidity of the back foil 35 that supports the top foil 25 can be maintained more uniformly in the circumferential direction D3 compared to when both end portions P21, P22 are arranged to overlap each other. As a result, the top foil 25 can be maintained in a shape that is closer to a perfect circle.

[0069] In this embodiment, the slit S1 in the top foil 25 and the slit S1 in the back foil 35 are both located at positions different from the locking groove 47 in the circumferential direction D3. At the position of the locking groove 47 in the bearing housing 45, the support rigidity of the back foil 35 supporting the top foil 25 is likely to be lower than at other positions on the bearing housing 45 due to the need to secure space for locking with the locking piece 30. In contrast, with the above-described configuration, it is possible to prevent the forces tending to open the both ends P11, P12 of the top foil 25 and the both ends P11, P12 of the back foil 35 from acting at the positions of the engagement grooves where the support rigidity is relatively low. As a result, the top foil 25 can be maintained in a shape closer to a perfect circle.

[0070] In this embodiment, the locking pieces 30 are provided in the middle portion P13 of the top foil 25. In this way, by providing the locking pieces 30 that engage with the locking grooves 47 in the middle portion P13 other than the end portions P11, P12 of the top foil 25, the positions of the end portions P11, P12 of the top foil 25 can be shifted relative to the position of the locking groove 47. This makes it possible to avoid a situation in which a force that tries to open the end portions P11, P12 is applied at the position of the engagement groove where the support rigidity is relatively low. As a result, the top foil 25 can be maintained in a shape that is closer to a perfect circle.

[0071] In this embodiment, the locking piece 30 is a bent piece formed by bending a part of the top foil 25 outward in the radial direction D2. When the locking piece 30 is formed from a part of the top foil 25 in this way, an increase in the number of parts can be suppressed compared to when the locking piece 30 is formed from a part separate from the top foil 25. As a result, the assembly work of the radial foil bearing 20 is facilitated.

[0072] In this embodiment, the locking pieces 30 are formed on the side edges 26, 27 of the top foil 25. In this case, the locking pieces 30 can be easily formed on the top foil 25 by the simple process of making slits in the side edges 26, 27 of the top foil 25 and bending the slit portions.

[0073] In this embodiment, the locking pieces 30 extend in the radial direction D2 when viewed from the axial direction D1 of the shaft hole 46, and face the side surfaces 47c, 47d of the locking groove 47 with a gap in the circumferential direction D3. When a gap is provided between the locking pieces 30 and the side surfaces 47c, 47d, the top foil 25 is allowed to slide relative to the bearing housing 45. In this case, when the shaft 15 rotates and whirls, the frictional force between the bearing housing 45 and the top foil 25 can act as a damping force that suppresses axial vibration of the shaft 15. As a result, the rotational stability of the shaft 15 can be improved.

[0074] In this embodiment, the back foil 35 has slits 40 that allow the locking pieces 30 to pass through in the radial direction D2. In this case, a configuration in which the locking pieces 30 of the top foil 25 are locked in the locking grooves 47 of the bearing housing 45 can be easily realized.

[0075] In this embodiment, the slits 40 extend in the axial direction D1 from the side edges 36, 37 of the back foil 35. In this case, the slits 40 for passing the locking pieces 30 can be easily formed in the back foil 35 by the simple task of cutting out the side edges 36, 37 of the back foil 35.

[0076] In this embodiment, the slits 40 are formed in the valley portions 42 of the back foil 35. In this way, by forming the slits 40 in locations other than the peak portions 41 of the back foil 35, it is possible to prevent a situation in which the support rigidity of the back foil 35 decreases at the positions of the slits 40. As a result, it is possible to maintain the support rigidity of the back foil 35 uniform in the circumferential direction D3, and therefore it is possible to maintain the top foil 25 in a shape that is closer to a perfect circle.

[0077] In this embodiment, the supported portions PA, PB of the top foil 25 are contact portions with the peak portions 41 of the back foil 35. In this case, a configuration in which both end portions P11, P12 of the top foil 25 are elastically supported by the back foil 35 can be easily realized.

[0078] The radial foil bearing 20 and the rotating machine 1 of the present disclosure are not limited to the above-described embodiment. The specific aspects of the radial foil bearing 20 and the rotating machine 1 of the present disclosure may be appropriately modified without departing from the spirit of the claims.

[0079] <Variation 1> The radial foil bearing 20A shown in FIG. 7 includes a top foil 25A, a back foil 35A, and a bearing housing 45A. As shown in FIGS. 7 and 8, the arrangement of the locking pieces 30A in the top foil 25A differs from that of the top foil 25 according to the above-described embodiment. For example, the distance W11 between the locking pieces 301a and 301b in the circumferential direction D3 corresponds to the width in the circumferential direction D3 of two peaks 41 of the back foil 35A. The width W12 in the circumferential direction D3 of the locking groove 47A in the bearing housing 45A is set to be slightly larger than the distance W11 between the locking pieces 301a and 301b. The end P11 and end P12 of the top foil 25A are supported by two peaks 41, 41 adjacent to each other in the circumferential direction D3.

[0080] As shown in FIG. 9(a), each of the locking pieces 301a, 301b, 301c, and 301d is formed by a slit along an L-shaped slit line C12. When forming the locking piece 301a, a slit is made along a slit line C4 extending from the side edge 26 in the axial direction D1 and a slit line C3 extending from the end of the slit line C3 in the circumferential direction D3. Then, the inner portion of the L-shaped slit line C12 is pushed open outward in the radial direction D2, thereby forming the locking piece 301a that rises outward in the radial direction D2, as shown in FIG. 9(b). Similarly, the locking pieces 301b, 301c, and 301d are formed by the L-shaped slit line C12.

[0081] As shown in FIG. 10 , the arrangement of the slits 40A in the back foil 35A differs from that of the back foil 35 according to the above-described embodiment. The slits 40A are formed in both end portions P21 and P22 of the back foil 35A. Specifically, the slits 401a and 401c are formed in the valley portions 42 of the end portion P22 of the back foil 35A. The slit 401a is formed in the side edge 36 of the valley portions 42 of the end portion P22, and the slit 401c is formed in the side edge 37 of the valley portions 42 of the end portion P22. The slits 401b and 401d are formed in the valley portions 42 of the end portion P21 of the back foil 35A. The slit 401b is formed in the side edge 36 of the valley portions 42 of the end portion P21, and the slit 401d is formed in the side edge 37 of the valley portions 42 of the end portion P21.

[0082] 7, when the top foil 25A and the back foil 35A are accommodated in the bearing housing 45A, the gap S1 between the two end portions P11, P12 of the top foil 25A is located at a different position from the locking groove 47A in the circumferential direction D3, as in the above-described embodiment. Specifically, the gap S1 is located on the opposite side of the locking groove 47A from the locking groove 47A in the radial direction D2 with respect to the rotation axis H. On the other hand, the gap S2 between the two end portions P21, P22 of the back foil 35A is located at the same position as the locking groove 47A in the circumferential direction D3. Therefore, the gap S2 is located at a different position from the gap S1 in the circumferential direction D3. In other words, when the rotation direction of the shaft 15 is used as a reference, it can be said that the phase of the gap S2 is the same as the phase of the locking groove 47 but different from the phase of the gap S1. Conversely, the gap S1 may be located at the same position as the locking groove 47A in the circumferential direction D3, and the gap S2 may be located at a different position from the locking groove 47A and the gap S1 in the circumferential direction D3. In other words, the phase of the gap S1 may be the same as the phase of the locking groove 47A and may be different from the phase of the gap S2.

[0083] Even with this configuration, the supported portions PA and PB of both end portions P11 and P12 of the top foil 25A are elastically supported in the radial direction D2 by the two peaks 41 and 41 of the back foil 35A, respectively, so that the top foil 25A can be maintained in a shape close to a perfect circle, as in the above-described embodiment. Furthermore, since the slit S1 of the top foil 25A is located at a different position in the circumferential direction D3 from the slit S1 of the back foil 35A, it is possible to prevent a situation in which the forces tending to open the both end portions P11 and P12 of the top foil 25A and the forces tending to open the both end portions P21 and P22 of the back foil 35A overlap and act at the same position. As a result, it is possible to maintain the top foil 25A in a shape closer to a perfect circle.

[0084] <Variation 2> The radial foil bearing 20B shown in Fig. 11 has a configuration in which the top foil 25A of the above-described radial foil bearing 20A is replaced with a top foil 25B. Unlike the top foil 25A, the top foil 25B has locking pieces 30B formed on both end portions P11 and P12. Specifically, as shown in Fig. 12, locking pieces 302a and 302c are formed on the edge 28 of the end portion P12, and locking pieces 302b and 302d are formed on the edge 29 of the end portion P11.

[0085] As shown in Figure 13(a), each of the locking pieces 302a, 302b, 302c, and 302d is formed by a slit along a linear slit line C13. When forming the locking piece 302a, a slit is made along the slit line C13 extending from the end edge 28 in the circumferential direction D3 at a position offset in the axial direction D1 from the side edge 26. Then, by bending the portion between the slit line C13 and the side edge 26 outward in the radial direction D2, the locking piece 302a rising outward in the radial direction D2 is formed as shown in Figure 13(b). The locking pieces 302b, 302c, and 302d are formed in a similar manner.

[0086] 11, when the top foil 25B and the back foil 35A are accommodated in the bearing housing 45A, the gap S1 between the end portions P11, P12 of the top foil 25B and the gap S2 between the end portions P21, P22 of the back foil 35A are both located at the same position as the locking groove 47 in the circumferential direction D3. In other words, when the rotation direction of the shaft 15 is used as a reference, the phase of the gaps S1, S2 is the same as the phase of the locking groove 47. Even in this configuration, the supported portions PA, PB of the end portions P11, P12 of the top foil 25B are elastically supported in the radial direction D2 by the two ridge portions 41, 41 of the back foil 35A, respectively. Therefore, as in the above-described embodiment, it is possible to maintain the top foil 25B in a shape close to a perfect circle. The supported portions PA and PB of the end portions P11 and P12 of the top foil 25B are supported by two adjacent peaks 41 of the back foil 35A in the circumferential direction D3, respectively. A gap S2 is interposed between the two adjacent peaks 41 in the circumferential direction D3.

[0087] <Other variations> The radial foil bearing and rotary machine according to the present disclosure are not limited to the above-described embodiment and modifications, and various other modifications are possible. For example, the above-described embodiment and modifications may be combined with each other depending on the required purpose and effect. Furthermore, the radial foil bearing does not need to be cylindrical as long as it has a circular shaft hole, and may have other shapes, such as a rectangular tube. The back foil does not need to be formed from a single thin plate, but may be divided along the circumferential direction. In other words, the back foil may be formed from multiple back foil pieces divided along the circumferential direction. The locking pieces of the top foil do not need to be folded pieces formed from part of the top foil, and may be formed, for example, from a separate member from the top foil. The shape, arrangement, and number of the locking pieces of the top foil are not limited to the above-described embodiment and modifications, and can be changed as appropriate, as long as they can be engaged with the locking grooves of the bearing housing. Accordingly, the shape, arrangement, and number of the slits in the back foil can also be changed as appropriate.

[0088] <Additional Notes> The present disclosure provides: [1] "a housing having an axial hole for inserting a shaft; a top foil that is disposed in the axial hole and is configured by a single thin plate that is disposed so as to surround the shaft in a circumferential direction of the axial hole; a back foil disposed between an inner peripheral surface of the axial hole and the top foil so as to surround the top foil in the circumferential direction, the back foil having an elastic support portion that elastically supports the top foil in the radial direction of the axial hole, The top foil has a locking piece that protrudes outward in the radial direction, The inner circumferential surface has a locking groove that can be locked with the locking piece, The top foil has two circumferential end portions, each of which has a supported portion that is elastically supported by the elastic support portion, forming a radial foil bearing.

[0089] The present disclosure states, [2] "the two end portions of the top foil face each other in the circumferential direction, The radial foil bearing according to [1], wherein, when viewed from the axial direction of the shaft hole, the top foil forms a gap between the both end portions of the top foil in the circumferential direction.

[0090] The present disclosure states, [3] "The back foil is composed of a single thin plate arranged to surround the top foil in the circumferential direction, Both end portions of the back foil in the circumferential direction face each other in the circumferential direction, The radial foil bearing according to [2], wherein, when viewed from the axial direction of the shaft hole, the back foil forms a gap between the both end portions of the back foil in the circumferential direction.

[0091] The present disclosure is [4] "A radial foil bearing according to [3], wherein at least one of the slits in the top foil and the slits in the back foil is located at a position different from the locking groove in the circumferential direction."

[0092] The present disclosure is [5] "A radial foil bearing according to [4], wherein the slit in the top foil and the slit in the back foil are both located at positions different from the locking groove in the circumferential direction."

[0093] The present disclosure is [6] "A radial foil bearing according to [4] or [5], wherein the slit in the top foil is located at a different position in the circumferential direction from the slit in the back foil."

[0094] The present disclosure is [7] "A radial foil bearing according to any one of [1] to [6], wherein the locking piece is provided in an intermediate portion of the top foil located between the two end portions."

[0095] The present disclosure is [8] "A radial foil bearing according to any one of [1] to [7], wherein the locking piece is a bent piece formed by bending a part of the top foil outward in the radial direction."

[0096] The present disclosure is [9] "A radial foil bearing according to [8], wherein the locking piece is formed on a side edge of the top foil in the axial direction of the shaft hole."

[0097] The present disclosure is

[10] "A radial foil bearing described in any one of [1] to [9], wherein the locking piece extends in the radial direction when viewed from the axial direction of the shaft hole, and faces the side surface of the locking groove with a gap in the circumferential direction."

[0098] The present disclosure is

[11] "A radial foil bearing according to any one of [1] to

[10] , wherein the back foil has a slit that allows the locking piece to pass through in the radial direction."

[0099] The present disclosure is

[12] "A radial foil bearing according to

[11] , wherein the slit extends in the axial direction from a side edge of the back foil in the axial direction of the shaft hole."

[0100] The present disclosure states,

[13] "The back foil has a plurality of peaks that protrude radially inward as viewed from the axial direction of the shaft hole and are aligned in the circumferential direction, and a plurality of valleys that are respectively disposed between the peaks in the circumferential direction, the elastic support portion is constituted by the plurality of peaks, The radial foil bearing according to

[12] , wherein the slit is formed in at least one of the plurality of valley portions.

[0101] The present disclosure states,

[14] "The back foil has a plurality of peaks that protrude radially inward as viewed from the axial direction of the shaft hole and are aligned in the circumferential direction, and a plurality of valleys that are respectively disposed between the peaks in the circumferential direction, the elastic support portion is constituted by the plurality of peaks, The radial foil bearing according to any one of [1] to

[13] , wherein the supported portion is a contact portion with at least one of the plurality of peaks.

[0102] The present disclosure relates to

[15] a radial foil bearing according to any one of [1] to

[14] , the shaft inserted into the axial hole of the housing and supported by the radial foil bearing; a turbine disposed at one end of the shaft; and a compressor disposed at the other end of the shaft. [Explanation of symbols]

[0103] 1 Rotating Machinery 2 turbines 3 Compressor 15 shaft 20, 20a, 20b, 20A, 20B Radial foil bearings 25, 25A, 25B Top Foil 26,27,36,37 side edge 30,30a,30b,30c,30d,30A,30B,301a,301b,301c,301d,302a,302b,302c,302d Locking piece 35,35A Back Foil 40, 40a, 40b, 40c, 40d, 40A, 401a, 401b, 401c, 401d Slit 42 Valley 41 Mountain part (elastic support part) 45 Bearing housing (housing) 46 Shaft hole 46a Inner surface 47,47A,471,472 Locking groove 47b, 47c, 47d Side D1 Axial direction D2 radial direction D3 Circumferential direction P11, P12, P21, P22 both ends P13,P23 middle part PA,PB Supported part S1, S2 gap

Claims

1. a housing having an axial hole for inserting a shaft; a top foil that is disposed in the axial hole and is configured by a single thin plate that is disposed so as to surround the shaft in a circumferential direction of the axial hole; a back foil disposed between an inner peripheral surface of the axial hole and the top foil so as to surround the top foil in the circumferential direction, the back foil having an elastic support portion that elastically supports the top foil in the radial direction of the axial hole, The top foil has a locking piece that protrudes outward in the radial direction, The inner circumferential surface has a locking groove that can be locked with the locking piece, A radial foil bearing, wherein both circumferential ends of the top foil each have a supported portion that is elastically supported by the elastic support portion.

2. the two end portions of the top foil face each other in the circumferential direction, The radial foil bearing according to claim 1 , wherein the top foil forms a gap between the two end portions of the top foil in the circumferential direction when viewed in the axial direction of the shaft hole.

3. the back foil is formed of a single thin plate arranged to surround the top foil in the circumferential direction, Both end portions of the back foil in the circumferential direction face each other in the circumferential direction, The radial foil bearing according to claim 2 , wherein the back foil forms a gap between the both end portions of the back foil in the circumferential direction when viewed in the axial direction of the shaft hole.

4. The radial foil bearing according to claim 3 , wherein at least one of the slits in the top foil and the slits in the back foil is located at a position different from the locking groove in the circumferential direction.

5. The radial foil bearing according to claim 4 , wherein the slit in the top foil and the slit in the back foil are both located at positions different from the locking groove in the circumferential direction.

6. The radial foil bearing according to claim 4 , wherein the gap in the top foil is located at a position different from the gap in the back foil in the circumferential direction.

7. The radial foil bearing according to claim 1 , wherein the locking piece is provided in an intermediate portion of the top foil located between the two end portions.

8. The radial foil bearing according to claim 1 , wherein the locking piece is a bent piece formed by bending a part of the top foil outward in the radial direction.

9. The radial foil bearing according to claim 8 , wherein the locking piece is formed on a side edge of the top foil in the axial direction of the shaft hole.

10. 2. The radial foil bearing according to claim 1, wherein the locking piece extends in the radial direction when viewed from the axial direction of the shaft hole, and faces a side surface of the locking groove with a gap in the circumferential direction.

11. The radial foil bearing according to claim 1 , wherein the back foil has a slit through which the locking piece passes in the radial direction.

12. The radial foil bearing according to claim 11 , wherein the slit extends in the axial direction from a side edge of the back foil in the axial direction of the shaft hole.

13. the back foil has a plurality of peaks that protrude radially inward as viewed from the axial direction of the shaft hole and are aligned in the circumferential direction, and a plurality of valleys that are respectively disposed between the peaks in the circumferential direction, the elastic support portion is constituted by the plurality of peaks, The radial foil bearing according to claim 12 , wherein the slit is formed in at least one of the plurality of valley portions.

14. the back foil has a plurality of peaks that protrude radially inward as viewed from the axial direction of the shaft hole and are aligned in the circumferential direction, and a plurality of valleys that are respectively disposed between the peaks in the circumferential direction, the elastic support portion is constituted by the plurality of peaks, The radial foil bearing according to claim 1 , wherein the supported portion is a contact portion with at least one of the plurality of ridges.

15. A radial foil bearing according to any one of claims 1 to 14; the shaft inserted into the axial hole of the housing and supported by the radial foil bearing; a turbine disposed at one end of the shaft; a compressor disposed at the other end of the shaft.

Images