Foil bearing

Abstract

To provide a foil bearing capable of inhibiting deterioration of reliability for each of first support portions and second support portions.SOLUTION: In a foil bearing 10, when a load input from the rotating body increases, a bump foil 40 is deformed to increase one of the number of the first support portions 50 that contact an outer circumferential surface 30a of a top foil 30 and the number of second support portions 60 that contact an inner circumferential surface 20a of a housing 20 before increasing the other one of the numbers.SELECTED DRAWING: Figure 4

Description

Technical Field

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[0003] , , <0​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​A foil bearing for solving the above problems comprises a housing having a through hole through which a rotating body is inserted, a thin plate-shaped top foil having a bearing surface facing the rotating body, and a thin plate-shaped bump foil having a first support portion that contacts the outer circumferential surface of the top foil, a second support portion that contacts the inner circumferential surface of the housing, and a connecting portion that connects the first support portion and the second support portion so that they are alternately arranged along the rotational direction of the rotating body, and the first support portion and the second support portion extend in the rotational direction to elastically support the top foil, wherein the bump foil deforms such that when the load from the rotating body increases, the number of the first support portions that contact the outer circumferential surface of the top foil and the number of the second support portions that contact the inner circumferential surface of the housing increase, and the gist of the bump foil is that when the load from the rotating body increases, the number of the first support portions that contact the outer circumferential surface of the top foil and the second support portions that contact the inner circumferential surface of the housing increase first, and then the number of the other increases.

[0007] According to this, as the load from the rotating body increases, the foil bearing increases the number of either the first support portion that contacts the outer circumferential surface of the top foil or the second support portion that contacts the inner circumferential surface of the housing, followed by an increase in the number of the other support portion. Therefore, the number of support portions that bear the load can be increased for each of the first and second support portions. As a result, a decrease in reliability can be suppressed for each of the first and second support portions.

[0008] In the foil bearing, the bump foil is arranged in an arc shape between the housing and the top foil so as to reduce its diameter, and when the load from the rotating body increases, one end of the connecting portion on the first support portion side becomes the second support portion, the other end of the connecting portion on the second support portion side becomes the first support portion, and after the other end of the connecting portion contacts the outer circumferential surface of the top foil, one end of the connecting portion may contact the inner circumferential surface of the housing.

[0009] According to this, compressive stress is generated on the top foil side of the bump foil, while tensile stress is generated on the housing side. Furthermore, when a load is applied to the bump foil, tensile stress is generated on the top foil side of the second support, while compressive stress is generated on the housing side of the second support. Simultaneously, when a load is applied to the bump foil, compressive stress is generated on the top foil side of the first support, while tensile stress is generated on the housing side of the first support. In other words, on the top foil side of the first support, compressive stress is generated due to the elastic deformation of the bump foil, as well as compressive stress due to the input load. Simultaneously, on the housing side of the first support, tensile stress is generated due to the elastic deformation of the bump foil, as well as tensile stress due to the input load.

[0010] In such a bump foil, as the load from the rotating body increases, the other end of the connecting section becomes the first support section, so the load is supported not only by the first support section but also by the other end of the connecting section. Subsequently, one end of the connecting section becomes the second support section. Therefore, the load can be supported using both ends of the connecting section.

[0011] Therefore, compared to the case where the load is continuously supported only by the first support until the load is supported by the other end of the connecting section, the stress generated in the first support can be reduced. As a result, even if the stress generated with the curvature of the bump foil and the stress generated with the input of the load coincide in the compression or tension direction of the first support, damage to the first support can be more easily suppressed.

[0012] With respect to the foil bearing, the bump foil may be arranged such that the radial height of the rotating body from one end of the connecting portion to the first support portion is lower than the radial height of the rotating body from the other end of the connecting portion to the second support portion.

[0013] According to this, when the load input from the top foil increases and both ends of the connecting section bend, the other end of the connecting section that bends toward the lower-height first support section contacts the outer surface of the top foil before the one end of the connecting section that bends toward the second support section. Therefore, the other end of the connecting section can be made to contact the top foil as the first support section. Then, after the other end of the connecting section has contacted the top foil as the first support section, if the load increases further, the one end of the connecting section can be made to contact the housing as the second support section.

[0014] Regarding the foil bearing, one end of the connecting portion may be bent in an arc shape toward the first support portion, and the other end of the connecting portion may be bent in an arc shape toward the second support portion, and the bump foil may be arranged such that the arc radius of one end of the connecting portion is larger than the arc radius of the other end of the connecting portion.

[0015] According to this, one end of the connecting part is more easily bent than the other end, so the other end of the connecting part contacts the outer surface of the top foil before the one end of the connecting part. Therefore, the other end of the connecting part can be made to contact the top foil as a first support part. After the other end of the connecting part has contacted the top foil as a first support part, if the load increases further, the one end of the connecting part can be made to contact the housing as a second support part.

[0016] In the foil bearing, the bump foil is arranged in an arc shape between the housing and the top foil so as to expand in diameter, and when the load from the rotating body increases, one end of the connecting portion on the first support portion side becomes the second support portion, and the other end of the connecting portion on the second support portion side becomes the first support portion, and after one end of the connecting portion contacts the inner circumferential surface of the housing, the other end of the connecting portion may contact the outer circumferential surface of the top foil.

[0017] According to this, tensile stress is generated on the top foil side of the bump foil, while compressive stress is generated on the housing side. Furthermore, when a load is applied to the bump foil, compressive stress is generated on the top foil side of the first support and tensile stress is generated on the housing side of the first support. Simultaneously, when a load is applied to the bump foil, tensile stress is generated on the top foil side of the second support and compressive stress is generated on the housing side of the second support. In other words, on the top foil side of the second support, tensile stress is generated not only due to the elastic deformation of the bump foil but also due to the input of the load. Simultaneously, on the housing side of the second support, compressive stress is generated not only due to the elastic deformation of the bump foil but also due to the input of the load.

[0018] In such a bump foil, as the load from the rotating body increases, one end of the connecting section becomes a second support section, so the load is supported not only by the second support section but also by the end of the connecting section. Subsequently, the other end of the connecting section becomes a first support section. Therefore, the load can be supported using both ends of the connecting section.

[0019] Therefore, compared to the case where the load is continuously supported only by the second support until the load is supported by one end of the connecting section, the stress generated in the second support can be reduced. As a result, even if the stress generated with the curvature of the bump foil and the stress generated with the input of the load coincide in the compression or tension direction of the second support, damage to the second support can be more easily suppressed.

[0020] With respect to the foil bearing, the bump foil may be arranged such that the radial height of the rotating body from the other end of the connecting portion to the second support portion is lower than the radial height of the rotating body from one end of the connecting portion to the first support portion.

[0021] According to this, when the load input from the top foil increases and both ends of the connecting portion bend, one end of the connecting portion that has bent toward the lower-height second support portion contacts the inner peripheral surface of the housing earlier than the other end of the connecting portion that has bent toward the first support portion. Therefore, one end of the connecting portion can be brought into contact with the housing as the second support portion. Then, after one end of the connecting portion contacts the housing as the second support portion, when the load further increases, the other end of the connecting portion can be brought into contact with the top foil as the first support portion.

[0022] Regarding the foil bearing, one end of the connecting portion may be bent in an arc shape over the first support portion, the other end of the connecting portion may be bent in an arc shape over the second support portion, and the bump foil may be arranged such that the arc radius of the other end of the connecting portion is larger than the arc radius of one end of the connecting portion.

[0023] According to this, since the other end of the connecting portion is more likely to bend than one end of the connecting portion, one end of the connecting portion contacts the inner peripheral surface of the housing earlier than the other end of the connecting portion. Therefore, one end of the connecting portion can be brought into contact with the housing as the second support portion. Then, after one end of the connecting portion contacts the housing as the second support portion, when the load further increases, the other end of the connecting portion can be brought into contact with the top foil as the first support portion.

Advantages of the Invention

[0024] According to the present invention, it is possible to suppress a decrease in reliability for each of the first support portion and the second support portion.

Brief Description of the Drawings

[0025] [Figure 1] FIG. 1 is a schematic configuration diagram showing a centrifugal compressor equipped with a foil bearing. [Figure 2] FIG. 2 is a diagram showing a bump foil before elastic deformation. [Figure 3] FIG. 3 is a cross-sectional view of the foil bearing. [Figure 4] FIG. 4 is a partial cross-sectional view of the bump foil before reaching a first predetermined value. [Figure 5] Figure 5 is a partial cross-sectional view of the bump foil after it has reached the first predetermined value. [Figure 6] Figure 6 is a partial cross-sectional view of the bump foil after it has reached the second predetermined value. [Figure 7] Figure 7 is a partial cross-sectional view of the bump foil of the second embodiment. [Figure 8] Figure 8 is a cross-sectional view of the bump foil before elastic deformation. [Figure 9] Figure 9 is a partial cross-sectional view of the bump foil of the third embodiment. [Figure 10] Figure 10 is a partial cross-sectional view showing the bump foil when it reaches a first predetermined value. [Figure 11] Figure 11 is a partial cross-sectional view showing the bump foil when it reaches a second predetermined value. [Figure 12] Figure 12 is a partial cross-sectional view showing a bump foil of the fourth embodiment. [Modes for carrying out the invention]

[0026] (First embodiment) The first embodiment of the foil bearing will be described below with reference to Figures 1 to 6. Note that the foil bearing in this embodiment is mounted on a centrifugal compressor.

[0027] <Centrifugal compressor> As shown in Figure 1, the centrifugal compressor 100 comprises two foil bearings 10, a housing 101, an electric motor 102, a rotating body 103, and an impeller 104. The housing 101 has a motor chamber 101a and an impeller chamber 101b. The electric motor 102 is housed in the motor chamber 101a. The rotating body 103 is a rotating shaft that rotates under the drive of the electric motor 102. The rotating body 103 extends into the motor chamber 101a and the impeller chamber 101b. The impeller 104 is attached to the rotating body 103.

[0028] The impeller 104 is housed in the impeller chamber 101b. The electric motor 102, the rotating body 103, and the impeller 104 are housed in the housing 101. When the rotating body 103 rotates due to the drive of the electric motor 102, the impeller 104 rotates. As the impeller 104 rotates, fluid is drawn into the impeller chamber 101b from outside the housing 101. The fluid drawn into the impeller chamber 101b is compressed as the impeller 104 rotates. The compressed fluid is discharged to the outside of the housing 101.

[0029] The two foil bearings 10 support the rotating body 103 in the radial direction Rd. The radial direction Rd is the radial direction of the rotating body 103. The two foil bearings 10 are positioned on either side of the electric motor 102 in the axial direction of the rotating body 103. The two foil bearings 10 are fixed to the housing 101.

[0030] <Foil bearing> As shown in Figure 3, the foil bearing 10 comprises a cylindrical housing 20, a thin plate-shaped top foil 30, and three thin plate-shaped bump foils 40. Note that Figure 3 shows the foil bearing 10 in a state when the rotating body 103 is not rotating.

[0031] <Bearing Housing> The housing 20 has a through hole 20c through which the rotating body 103 is inserted. The rotating body 103 is inserted through the through hole 20c of the housing 20. In the following description, the axial direction of the housing 20 will be simply referred to as "axial direction A," and the circumferential direction of the housing 20 will be simply referred to as "rotational direction B," which is the rotational direction of the rotating body 103. The radial direction of the housing 20 will be simply referred to as "radial direction C."

[0032] The housing 20 has an inner circumferential surface 20a. Retaining grooves 20b are formed on the inner circumferential surface 20a of the housing 20. Three retaining grooves 20b are formed on the inner circumferential surface 20a. The three retaining grooves 20b are arranged at equal intervals in the rotational direction B. The retaining grooves 20b extend in the axial direction A. The material forming the housing 20 is, for example, aluminum.

[0033] <Top Foil> The top foil 30 is positioned inside the housing 20. The top foil 30 has a bearing surface 30b facing the rotating body 103, and an outer peripheral surface 30a on the opposite side of the bearing surface 30b in the thickness direction of the top foil 30. A gap K is defined between the inner peripheral surface 20a of the housing 20 and the outer peripheral surface 30a of the top foil 30. The top foil 30 is a thin plate positioned between the rotating body 103 and the housing 20. The top foil 30 is formed by curving a long, flexible metal plate. The top foil 30 is substantially cylindrical. The axial direction of the top foil 30 coincides with axial direction A. The axial direction of the top foil 30 is referred to as "axial direction A". The circumferential direction of the top foil 30 coincides with the rotation direction B. The circumferential direction of the top foil 30 is referred to as "rotation direction B". The radial direction of the top foil 30 coincides with radial direction C. The radial direction of the top foil 30 is denoted as "radial direction C". The top foil 30 is formed by curving a long metal sheet into a cylindrical shape, extending the long edge in the rotational direction B and the short edge in the axial direction A. The metal sheet forming the top foil 30 is made of, for example, stainless steel or an Inconel® type nickel alloy. In other words, the top foil 30 is made of a material with higher hardness than the material forming the housing 20.

[0034] The top foil 30 comprises a fixed end 31 and a free end 32. The fixed end 31 is located at one end of the long side of the metal plate material forming the top foil 30, and the free end 32 is located at the other end. The fixed end 31 is located at one end of the top foil 30 in the rotation direction B, and the free end 32 is located at the other end of the top foil 30 in the rotation direction B. The fixed end 31 is formed by bending the metal plate material forming the top foil 30. The fixed end 31 is inserted into one of the three retaining grooves 20b. The fixed end 31 is fixed to the retaining groove 20b by an axial retaining member such as a circlip. The free end 32 is opposite the base end of the fixed end 31 at a distance in the rotation direction B. Therefore, the top foil 30 is non-annular with a portion cut out.

[0035] <Bump Foil> The three bump foils 40 are positioned in the gap K between the housing 20 and the top foil 30. Each of the three bump foils 40 is positioned radially C outward from the top foil 30 and radially C inward from the housing 20. Each of the three bump foils 40 elastically supports the top foil 30 between the housing 20 and the top foil 30. The three bump foils 40 are positioned at a predetermined interval in the rotational direction B. The thickness of each of the three bump foils 40 is thinner than the thickness of the top foil 30. In other words, each of the three bump foils 40 is thin.

[0036] Each of the three bump foils 40 is formed by elastically deforming a flexible, elongated metal plate 49 into a substantially arc shape while forming a first support portion 50, a second support portion 60, and a connecting portion 70 on it. In other words, each of the three bump foils 40 includes a first support portion 50 that contacts the outer circumferential surface 30a of the top foil 30, a second support portion 60 that contacts the inner circumferential surface 20a of the housing 20, and a connecting portion 70 that connects the first support portion 50 and the second support portion 60 so that they are alternately arranged along the rotation direction B of the rotating body 103.

[0037] Each of the three bump foils 40 is elastically deformed to curve in the rotation direction B of the rotating body 103. The metal plate 49 has a first surface 49a on one of its two surfaces in the thickness direction and a second surface 49b on the other surface. The first surface 49a is the surface on the housing 20 side of the two surfaces in the thickness direction. The second surface 49b is the surface on the top foil 30 side of the two surfaces in the thickness direction.

[0038] The circumferential direction of the bump foil 40 coincides with the rotational direction B. The circumferential direction of the bump foil 40 is referred to as "rotational direction B". The radial direction of the bump foil 40 coincides with the radial direction C. The radial direction of the bump foil 40 is referred to as "radial direction C". The short side direction of the metal plate material 49 coincides with the axial direction A. The long side direction of the metal plate material 49 coincides with the rotational direction B. The metal plate material 49 is formed from, for example, stainless steel or an Inconel-type nickel alloy. The metal plate material 49 is formed from a material with higher hardness than the material forming the housing 20.

[0039] Each of the three bump foils 40 has a fixed end 41 and a free end 42. The fixed end 41 is located at one end of the long side of the metal plate material 49, and the free end 42 is located at the other end. The fixed end 41 of each bump foil 40 is inserted into each retaining groove 20b. One fixed end 41 is inserted into one retaining groove 20b together with the fixed end 31 of the top foil 30. The fixed end 41 inserted into the retaining groove 20b together with the fixed end 31 of the top foil 30 is fixed to the retaining groove 20b together with the fixed end 31 of the top foil 30 by an axial retaining member such as a circlip. The remaining two fixed ends 41 are fixed to each of the remaining two retaining grooves 20b by an axial retaining member such as a circlip. In adjacent bump foils 40 in the rotation direction B, the free end 42 of one bump foil 40 is positioned at a predetermined distance from the fixed end 41 of the other bump foil 40. The means for fixing the fixed ends 31 and 41 to the retaining grooves 20b may be changed as appropriate.

[0040] Since all three bump foils 40 have the same shape, we will use one bump foil 40 as an example to provide a detailed explanation, and omit detailed explanations of the remaining two bump foils 40.

[0041] The following description will explain the bump foil 40 when the rotating body 103 is not rotating. The bump foil 40 comprises a plurality of first support portions 50, a plurality of second support portions 60, a plurality of connecting portions 70, a plurality of first bent portions 71, a plurality of second bent portions 72, a first end plate portion 81, and a second end plate portion 82.

[0042] Each of the plurality of first support portions 50 is in contact with the outer circumferential surface 30a of the top foil 30. Each of the plurality of second support portions 60 is in contact with the inner circumferential surface 20a of the housing 20. Each of the plurality of connecting portions 70 connects the first support portions 50 and the second support portions 60 such that the first support portions 50 and the second support portions 60 are arranged alternately along the rotational direction B of the rotating body 103. The bump foil 40 elastically supports the top foil 30 by the first support portions 50 and the second support portions 60 extending in the rotational direction B of the rotating body 103.

[0043] The connecting portion 70 has a rectangular shape when viewed in the radial direction C. When the connecting portion 70 is viewed in the radial direction C, the longer side of the rectangle extends in the axial direction A, and the shorter side of the rectangle extends in the rotational direction B. When viewed in the axial direction A, the connecting portion 70 extends approximately in the rotational direction B.

[0044] As shown in Figure 4, in the gap K, the connecting portion 70 is located closer to the outer circumferential surface 30a of the top foil 30 than the intermediate position in the radial direction C. In the gap K, the connecting portion 70 is located closer to the outer circumferential surface 30a of the top foil 30 than the inner circumferential surface 20a of the housing 20 in the radial direction C. The distance between the first surface 49a of the connecting portion 70 and the inner circumferential surface 20a of the housing 20 is distance K1. The distance between the second surface 49b of the connecting portion 70 and the outer circumferential surface 30a of the top foil 30 is distance K2. When no load from the rotating body 103 is applied to the top foil 30, at any position in the rotation direction B of the connecting portion 70, distance K1 is longer than distance K2.

[0045] Each of the multiple first support portions 50 protrudes from the second surface 49b at the connecting portion 70 toward the outer peripheral surface 30a of the top foil 30. Each of the multiple first support portions 50 is sandwiched between a pair of connecting portions 70. Each of the multiple first support portions 50 is formed by bending a metal plate material 49 that forms the bump foil 40. Each of the multiple first support portions 50 has a first arc portion 50a at the tip in the direction of protrusion from the connecting portion 70. When viewing the first support portion 50 in the axial direction A, the inner and outer surfaces of the first arc portion 50a are bent in an arc shape. The first arc portion 50a is in contact with the outer peripheral surface 30a of the top foil 30 at the second surface 49b of the first arc portion 50a.

[0046] Each of the multiple second support portions 60 protrudes from the first surface 49a at the connecting portion 70 toward the inner circumferential surface 20a of the housing 20. Each of the multiple second support portions 60 is sandwiched between a pair of connecting portions 70. Each of the multiple second support portions 60 is formed by bending a metal plate material 49 that forms the bump foil 40. Each of the multiple second support portions 60 has a second arc portion 60a at the tip in the direction of protrusion from the connecting portion 70. When viewing the second support portion 60 in the axial direction A, the inner and outer surfaces of the second arc portion 60a are curved in an arc shape. The second arc portion 60a is in contact with the inner circumferential surface 20a of the housing 20 at the first surface 49a of the second arc portion 60a.

[0047] Each of the multiple connecting portions 70 is formed between the first support portion 50 and the second support portion 60 when the first support portion 50 and the second support portion 60 are formed on the metal plate material 49 that forms the bump foil 40.

[0048] The first bent portion 71 is provided at the boundary between the first support portion 50 and the connecting portion 70, and the second bent portion 72 is provided at the boundary between the second support portion 60 and the connecting portion 70. The first bent portion 71 is formed by bending the metal plate 49 to form the first support portion 50. The first bent portion 71 is formed at one end of the connecting portion 70, and the second bent portion 72 is formed at the other end of the connecting portion 70. The first bent portion 71, that is, one end of the connecting portion 70, is bent in an arc shape toward the first support portion 50. The second bent portion 72, that is, the other end of the connecting portion 70, is bent in an arc shape toward the second support portion 60. The first bent portion 71 and the second bent portion 72 are a two-stage spring structure that generates elastic force by bending under load from the top foil 30. When the rotating body 103 is not rotating, the first bent portion 71 is not in contact with the housing 20 and the top foil 30, and the second bent portion 72 is also not in contact with the housing 20 and the top foil 30.

[0049] The connecting portion 70 is inclined such that the first bent portion 71 side is closer to the housing 20 than the second bent portion 72 side. In other words, the connecting portion 70 extends in the rotational direction B such that it gradually approaches the top foil 30 as it moves from the first bent portion 71 to the second bent portion 72.

[0050] The bump foil 40 has a first boundary T1 and a second boundary T2. The first boundary T1 is the boundary between the connecting portion 70 and the first support portion 50 on the second surface 49b of the metal plate material 49. The first boundary T1 is the portion of the metal plate material 49 that is bent to form the first support portion 50. The second boundary T2 is the boundary between the connecting portion 70 and the second support portion 60 on the first surface 49a of the metal plate material 49. The second boundary T2 is the portion of the metal plate material 49 that is bent to form the second support portion 60.

[0051] Let the imaginary line connecting the first boundary T1 of the bump foil 40 along the rotation direction B be a virtual circle F. The bump foil 40 is placed in the void K in an elastically deformed state. As shown in Figure 2, the bump foil 40 before being placed in the gap K, that is, before elastic deformation, is almost flat when viewed in the axial direction A. The radius of the virtual circle F of the bump foil 40 before being placed in the gap K is larger than the radius of the bump foil 40 after elastic deformation for placement in the gap K. Therefore, the radius of the arc of the bump foil 40 after elastic deformation for placement in the gap K is smaller than the radius of the arc of the bump foil 40 before being placed in the gap K. Consequently, the bump foil 40 placed in the gap K is positioned in an arc shape between the housing 20 and the top foil 30 so as to reduce its diameter.

[0052] As shown in Figure 3, the bump foil 40 positioned in the gap K is biased outward in the radial direction C by the restorative force from its elastically deformed state back to its original shape. The biasing direction N of the bump foil 40 is from the top foil 30 toward the housing 20.

[0053] As shown in Figure 4, the bump foil 40 is reduced in diameter to accommodate its placement in the void K. As a result, tensile stress is generated on the first surface 49a of the bump foil 40, as indicated by arrow Y1, and compressive stress is generated on the second surface 49b of the bump foil 40, as indicated by arrow Y2.

[0054] The dimension in the radial direction C from the first boundary T1 to the outer circumferential surface 30a of the top foil 30 is the height H1 of the first support portion 50 from the connecting portion 70. Height H1 is the height in the radial direction C of the rotating body 103 from one end of the connecting portion 70 to the first support portion 50. Height H1 of the first support portion 50 is the length from the first bend portion 71 to the tip of the first support portion 50 in the radial direction C. The dimension in the radial direction C from the second boundary T2 to the inner circumferential surface 20a of the housing 20 is the height H2 of the second support portion 60 from the connecting portion 70. Height H2 is the height in the radial direction C of the rotating body 103 from the other end of the connecting portion 70 to the second support portion 60. Height H2 of the second support portion 60 is the length from the second bend portion 72 to the tip of the second support portion 60 in the radial direction C.

[0055] The height H1 of the first support portion 50 is lower than the height H2 of the second support portion 60. In other words, the height H2 of the second support portion 60 is higher than the height H1 of the first support portion 50. Due to the relationship between heights H1 and H2, the connecting portion 70 is located closer to the top foil 30 than the midpoint of the radial direction C in the gap K.

[0056] Let ΔH be the difference between the height H1 of the first support section 50 and the height H2 of the second support section 60. The safety factor is the resistance to damage when a load is applied to the first support section 50 and the second support section 60. The safety factor of the first support section 50 and the safety factor of the second support section 60 are lower as the heights H1 and H2 are higher and higher as the heights H1 and H2 are lower. Also, the greater the stress generated when the bump foil 40 is bent, the lower the safety factor of the first support section 50 and the second support section 60.

[0057] The upper limit of the dimension of the gap K in which the bump foil 40 is positioned is when no load is applied to the top foil 30. In other words, the upper limit of the gap K is predetermined. Therefore, heights H1 and H2 are determined by the degree of curvature of the bump foil 40 and the upper limit of the gap K. If one of heights H1 or H2 increases, the other decreases. Therefore, as ΔH increases, the safety factor of the support at a higher height decreases, while the safety factor of the support at a lower height increases.

[0058] Specifically, the height H1 of the first support part 50 is lower than the height H2 of the second support part 60. The lower the height H1 of the first support part 50, the higher the safety factor of the first support part 50. If the height H1 of the first support part 50 is lower, the height H2 of the second support part 60 will be higher, and therefore the safety factor of the second support part 60 will be lower. The heights H1 and H2 are set so that the safety factor of the first support part 50 and the safety factor of the second support part 60 are the same. However, within the range of the desired safety factor, the safety factors of the first support part 50 and the safety factor of the second support part 60 may be different, as long as neither the first support part 50 nor the second support part 60 is unlikely to be damaged.

[0059] As shown in Figure 3, the first end plate portion 81 is provided between the base end of the fixed end portion 41 of the bump foil 40 and the second support portion 60. The second end plate portion 82 is provided between the free end portion 42 of the bump foil 40 and the second support portion 60.

[0060] <Deformation of top foil and bump foil> When the centrifugal compressor 100 starts to operate, the rotating body 103 rotates. When the rotational speed of the rotating body 103 reaches a predetermined speed, a fluid film is formed between the rotating body 103 and the top foil 30. The dynamic pressure of this fluid film causes the rotating body 103 to float relative to the top foil 30. This fluid film supports the rotating body 103 in the radial direction Rd while keeping it in non-contact with the top foil 30.

[0061] As the rotating body 103 rotates and a fluid film is formed, the top foil 30 elastically deforms due to the fluid film, expanding outward in the radial direction C of the housing 20. The radial direction C outward refers to the direction from the axis of the housing 20 toward the inner circumferential surface 20a within the radial direction C. As a result, a load is applied from the top foil 30 to the first support part 50 due to the displacement of the top foil 30 toward the radial direction C of the housing 20. Along with the load applied to the first support part 50, a load is also applied to the second support part 60.

[0062] As the rotational speed of the rotating body 103 increases from a predetermined number of rotations, the load also increases. As the load increases, the top foil 30 presses the first support portion 50 of the bump foil 40 toward the housing 20.

[0063] As shown in Figure 5, the first support portion 50 elastically deforms so as to stretch in the rotational direction B, and the first bent portion 71 and the second bent portion 72 bend, with the first bent portion 71 gradually approaching the inner circumferential surface 20a of the housing 20. At the same time, the second bent portion 72 bends, and the second bent portion 72 gradually approaches the outer circumferential surface 30a of the top foil 30. In other words, the load input from the top foil 30 increases, causing both ends of the connecting portion 70 to bend.

[0064] As a result of this elastic deformation, a compressive stress, as shown by arrow Y3, is generated on the second surface 49b of the first support portion 50, which is the surface facing the top foil 30, and a tensile stress, as shown by arrow Y4, is generated on the first surface 49a of the first support portion 50, which is the surface facing the housing 20. At the same time, a tensile stress, as shown by arrow Y4, is generated on the second surface 49b of the second support portion 60, which is the surface facing the top foil 30, and a compressive stress, as shown by arrow Y3, is generated on the first surface 49a of the second support portion 60, which is the surface facing the housing 20. In other words, as shown by arrows Y2 and Y3, the second surface 49b of the first support portion 50 experiences compressive stress due to the elastic deformation of the bump foil 40, as well as compressive stress due to the input of a load. At the same time, as shown by arrows Y1 and Y4, the first surface 49a of the first support portion 50 experiences tensile stress due to the elastic deformation of the bump foil 40, as well as tensile stress due to the input of a load. In other words, in the first support section 50, the stress generated due to the curvature of the bump foil 40 and the stress generated due to the input of a load coincide in the compression direction or the tension direction.

[0065] Then, as shown in Figure 5, when the load reaches a first predetermined value, the second bent portion 72, which is the other end of the connecting portion 70, comes into contact with the outer circumferential surface 30a of the top foil 30. In other words, the second bent portion 72, which is the other end of the connecting portion 70, comes into contact with the outer circumferential surface 30a of the top foil 30 as the first support portion 50. Until the load reaches the first predetermined value, the only contact point with the outer circumferential surface 30a of the top foil 30 was the first support portion 50, but when the load reaches the first predetermined value, the contact points with the outer circumferential surface 30a of the top foil 30 become the first support portion 50 and the second bent portion 72. In other words, as the load from the rotating body 103 increases, the number of first support portions 50 that come into contact with the outer circumferential surface 30a of the top foil 30 increases.

[0066] Furthermore, when the load reaches a first predetermined value, the load is supported not only by the first support portion 50 and the second support portion 60, but also by the second bent portion 72. At this time, since the first bent portion 71 is not in contact with the housing 20, no stress concentration occurs in the first bent portion 71.

[0067] As shown in Figure 6, when the load further exceeds the first predetermined value and the load from the rotating body 103 increases, the first support portion 50 and the second support portion 60 elastically deform to extend in the rotational direction B, and the bending of the first bent portion 71 and the second bent portion 72 progresses. When the load reaches the second predetermined value, the first bent portion 71 comes into contact with the inner circumferential surface 20a of the housing 20. In other words, the first bent portion 71, which is one end of the connecting portion 70, comes into contact with the inner circumferential surface 20a of the housing 20 as the second support portion 60. As a result, when the load from the rotating body 103 increases, the number of second support portions 60 that come into contact with the inner circumferential surface 20a of the housing 20 increases. Thus, when the load from the rotating body 103 increases, the bump foil 40 deforms such that the number of first support portions 50 that come into contact with the outer circumferential surface 30a of the top foil 30 increases, and then the number of second support portions 60 that come into contact with the inner circumferential surface 20a of the housing 20 increases. As a result, the load is supported by the first support portion 50, the second support portion 60, the first bent portion 71, and the second bent portion 72.

[0068] According to the first embodiment described above, the following effects can be obtained. (1-1) When the load from the rotating body 103 increases, the number of first support parts 50 that contact the outer circumferential surface 30a of the top foil 30 increases compared to before the load increased. Furthermore, when the load from the rotating body 103 increases even further, the number of second support parts 60 that contact the inner circumferential surface 20a of the housing 20 increases. As a result, the number of loads that can be supported by each of the first support parts 50 and the second support parts 60 increases, thus suppressing a decrease in reliability.

[0069] (1-2) As the load from the rotating body 103 increases, the second bent portion 72 becomes the first support portion 50, so the load is supported not only by the first support portion 50 but also by the second bent portion 72. Subsequently, the first bent portion 71 becomes the second support portion 60. Therefore, the load can be supported using both ends of the connecting portion 70. For this reason, the stress generated in the first support portion 50 can be reduced compared to the case where the load is continuously supported only by the first support portion 50 until the load is supported using the second bent portion 72. As a result, even if the stress generated with the curvature of the bump foil 40 and the stress generated with the input of the load coincide in the compression direction or the tension direction of the first support portion 50, damage to the first support portion 50 can be easily suppressed.

[0070] (1-3) Since the height H1 of the first support portion 50 is lower than the height H2 of the second support portion 60, when the load input from the top foil 30 increases and both ends of the connecting portion 70 bend, the second bent portion 72, which bends toward the lower first support portion 50, contacts the outer surface 30a of the top foil 30 before the first bent portion 71, which bends toward the second support portion 60. For this reason, the second bent portion 72 can be made to contact the top foil 30 as the first support portion 50.

[0071] (1-4) The foil bearing 10 is equipped with three bump foils 40 and has a reduced diameter. For example, compared to the case where there is only one bump foil 40, self-excited vibration in the bump foil 40 can be suppressed.

[0072] (1-5) Even if the stress generated due to the reduction in diameter of the bump foil 40 and the stress generated due to the input of a load coincide in the compression direction or the tension direction of the first support portion 50, the timing of contact with the outer surface 30a of the top foil 30 can be staggered. This makes it easier to suppress damage to the top foil 30.

[0073] (Second embodiment) Next, a second embodiment of the foil bearing 10 will be described with reference to Figure 7. In the second embodiment, detailed explanations of parts similar to those in the first embodiment will be omitted.

[0074] The biasing direction N of the bump foil 40 is, as in the first embodiment, in the direction from the top foil 30 toward the housing 20. As shown in Figure 7, in the gap K between the inner circumferential surface 20a of the housing 20 and the outer circumferential surface 30a of the top foil 30, the connecting portion 70 is located at an intermediate position in the radial direction C. The distance between the first surface 49a of the connecting portion 70 and the inner circumferential surface 20a of the housing 20 is distance K1. The distance between the second surface 49b of the connecting portion 70 and the outer circumferential surface 30a of the top foil 30 is distance K2. Distances K1 and K2 are the same.

[0075] The first arc portion 50a of the first support portion 50 is an arc with an arc radius r1. The second arc portion 60a of the second support portion 60 is an arc with an arc radius r2. The arc radius r2 of the second arc portion 60a is smaller than the arc radius r1 of the first arc portion 50a. Therefore, when a load is applied, the second support portion 60 is less likely to spread in the rotational direction B than the first support portion 50.

[0076] The dimension of the first support portion 50 in the rotation direction B is width W1. The width W1 of the first support portion 50 is the distance between the first bent portions 71 at both ends of the first support portion 50 in the rotation direction B. The dimension of the second support portion 60 in the rotation direction B is width W2. The width W2 of the second support portion 60 is the distance between the second bent portions 72 at both ends of the second support portion 60 in the rotation direction B. Since the arc radius r2 of the second support portion 60 is smaller than the arc radius r1 of the first support portion 50, the width W2 is smaller than the width W1. The first bent portion 71 is an arc with an arc radius r3. The second bent portion 72 is an arc with an arc radius r4.

[0077] The arc radius r3 of the first bend 71 is greater than the arc radius r4 of the second bend 72. In other words, the arc radius r4 of the second bend 72 is smaller than the arc radius r3 of the first bend 71. Therefore, when a load is applied, the first bend 71 is more easily bent than the second bend 72.

[0078] <Deformation of top foil and bump foil> When the load is less than the first predetermined value, the first bent portion 71 is not in contact with the outer circumferential surface 30a of the top foil 30, and the second bent portion 72 is not in contact with the inner circumferential surface 20a of the housing 20.

[0079] The arc radius 1 of the first arc portion 50a of the first support portion 50 is greater than the arc radius 2 of the second arc portion 60a of the second support portion 60, and the arc radius 3 of the first bent portion 71 is greater than the arc radius 4 of the second bent portion 72. Therefore, the first support portion 50 is more elastically deformable than the second support portion 60, and the first bent portion 71 is more easily bent than the second bent portion 72. Therefore, when the load reaches a first predetermined value, the first support portion 50 deforms to extend in the rotational direction B more than the second support portion 60, and the first bent portion 71 bends more than the second bent portion 72.

[0080] As a result, as shown in Figure 5, when the load reaches a first predetermined value, the second bent portion 72 comes into contact with the outer circumferential surface 30a of the top foil 30. In other words, the second bent portion 72, which is the other end of the connecting portion 70, comes into contact with the outer circumferential surface 30a of the top foil 30 as the first support portion 50. Until the load reaches the first predetermined value, the only contact point with the outer circumferential surface 30a of the top foil 30 was the first support portion 50, but once the load reaches the first predetermined value, the contact points with the outer circumferential surface 30a of the top foil 30 become the first support portion 50 and the second bent portion 72. In other words, as the load from the rotating body 103 increases, the number of first support portions 50 that come into contact with the outer circumferential surface 30a of the top foil 30 increases.

[0081] Furthermore, when the load reaches a first predetermined value, the load is supported not only by the first support portion 50 and the second support portion 60, but also by the second bent portion 72. At this time, since the first bent portion 71 is not in contact with the housing 20, no stress concentration occurs in the first bent portion 71.

[0082] As the load further exceeds the first predetermined value and the load from the rotating body 103 increases, the first support portion 50 and the second support portion 60 elastically deform to further extend in the rotation direction B, and the bending of the first bent portion 71 and the second bent portion 72 progresses. Then, when the load reaches the second predetermined value, as shown in Figure 6, the first bent portion 71 comes into contact with the inner circumferential surface 20a of the housing 20. In other words, the first bent portion 71, which is one end of the connecting portion 70, comes into contact with the inner circumferential surface 20a of the housing 20 as the second support portion 60. As a result, as the load from the rotating body 103 increases, the number of second support portions 60 that come into contact with the inner circumferential surface 20a of the housing 20 increases. Thus, as the load from the rotating body 103 increases, the bump foil 40 deforms such that the number of first support portions 50 that come into contact with the outer circumferential surface 30a of the top foil 30 increases, and then the number of second support portions 60 that come into contact with the inner circumferential surface 20a of the housing 20 increases.

[0083] According to the second embodiment described above, in addition to the effects described in (1-1), (1-2), (1-4), and (1-5) of the first embodiment, the following effects can be obtained. (2-1) The arc radius r3 of the first bent portion 71 is greater than the arc radius r4 of the second bent portion 72. Therefore, the first bent portion 71 is easier to bend than the second bent portion 72, and the second bent portion 72 contacts the outer surface 30a of the top foil 30 before the first bent portion 71. Therefore, the second bent portion 72 can be made to contact the top foil 30 as the first support portion 50. After the second bent portion 72 has contacted the top foil 30 as the first support portion 50, if the load increases further, the first bent portion 71 can be made to contact the housing 20 as the second support portion 60.

[0084] (Third embodiment) Next, a third embodiment of the foil bearing 10 will be described with reference to Figures 8 to 11. In the third embodiment, detailed explanations of parts similar to those in the first embodiment will be omitted.

[0085] As shown in Figure 8, the bump foil 40 before being placed in the gap K, that is, before elastic deformation, is arc-shaped when viewed in the axial direction A. The radius of the virtual circle F of the bump foil 40 before being placed in the gap K is smaller than the radius of the bump foil 40 after elastic deformation for placement in the gap K. Therefore, the radius of the arc of the bump foil 40 after elastic deformation for placement in the gap K is larger than the radius of the arc of the bump foil 40 before being placed in the gap K. Consequently, the bump foil 40 placed in the gap K is positioned in an arc shape between the housing 20 and the top foil 30 so as to expand in diameter.

[0086] As shown in Figure 9, the bump foil 40 is placed in the gap K in a curved state such that the radius of the arc is larger than before it was placed in the gap K. The bump foil 40 placed in the gap K is biased inward in the radial direction C by the restoring force from the elastically deformed state back to its original shape. The biasing direction N of the bump foil 40 is in the direction from the housing 20 toward the top foil 30.

[0087] The bump foil 40 is enlarged in diameter to accommodate its placement in the void K. As a result, tensile stress is generated on the second surface 49b of the bump foil 40, as shown by arrow Y1, and compressive stress is generated on the first surface 49a of the bump foil 40, as shown by arrow Y2.

[0088] The radial dimension C from the first boundary T1 to the outer circumferential surface 30a of the top foil 30 is the height H1 of the first support portion 50 from the connecting portion 70. Height H1 is the radial dimension C of the rotating body 103 from one end of the connecting portion 70 to the first support portion 50. The radial dimension C from the second boundary T2 to the inner circumferential surface 20a of the housing 20 is the height H2 of the second support portion 60 from the connecting portion 70. Height H2 is the radial dimension C of the rotating body 103 from the other end of the connecting portion 70 to the second support portion 60.

[0089] The height H1 of the first support portion 50 is higher than the height H2 of the second support portion 60. In other words, the height H2 of the second support portion 60 is lower than the height H1 of the first support portion 50. Due to the relationship between heights H1 and H2, the connecting portion 70 is located closer to the housing 20 than the midpoint of the radial direction C.

[0090] <Deformation of top foil and bump foil> As the rotational speed of the rotating body 103 increases from a predetermined number of rotations, the load also increases. As the load increases, the top foil 30 presses the first support portion 50 of the bump foil 40 toward the housing 20.

[0091] As shown in Figure 10, the first support portion 50 and the second support portion 60 elastically deform so as to stretch in the rotational direction B, and the first bent portion 71 and the second bent portion 72 bend, with the first bent portion 71 gradually approaching the inner circumferential surface 20a of the housing 20. At the same time, the second bent portion 72 bends, and the second bent portion 72 gradually approaches the outer circumferential surface 30a of the top foil 30.

[0092] As a result of this elastic deformation, a compressive stress, indicated by arrow Y3, is generated on the second surface 49b side of the first support portion 50, and a tensile stress, indicated by arrow Y4, is generated on the first surface 49a side of the first support portion 50. Simultaneously, a tensile stress, indicated by arrow Y4, is generated on the second surface 49b side of the second support portion 60, and a compressive stress, indicated by arrow Y3, is generated on the first surface 49a side of the second support portion 60. In other words, as shown by arrows Y1 and Y4, on the second surface 49b side of the second support portion 60, a tensile stress is generated not only due to the elastic deformation of the bump foil 40, but also due to the input of the load. Simultaneously, on the first surface 49a side of the second support portion 60, as shown by arrows Y2 and Y3, a compressive stress is generated not only due to the elastic deformation of the bump foil 40, but also due to the input of the load. In other words, in the second support portion 60, the stress generated due to the curvature of the bump foil 40 and the stress generated due to the input of the load coincide in the compression direction or the tension direction.

[0093] Then, as shown in Figure 10, when the load reaches a first predetermined value, the first bent portion 71 comes into contact with the inner circumferential surface 20a of the housing 20. In other words, the first bent portion 71, which is one end of the connecting portion 70, comes into contact with the inner circumferential surface 20a of the housing 20 as the second support portion 60. Until the load reaches the first predetermined value, the only point of contact with the inner circumferential surface 20a of the housing 20 was the second support portion 60, but once the load reaches the first predetermined value, the points of contact with the inner circumferential surface 20a of the housing 20 become the second support portion 60 and the first bent portion 71. In other words, as the load from the rotating body 103 increases, the number of second support portions 60 that come into contact with the inner circumferential surface 20a of the housing 20 increases.

[0094] Furthermore, when the load reaches a first predetermined value, the load is supported not only by the first support portion 50 and the second support portion 60, but also by the first bent portion 71. At this time, since the second bent portion 72 is not in contact with the top foil 30, no stress concentration occurs in the second bent portion 72.

[0095] As shown in Figure 11, when the load further exceeds the first predetermined value and the load from the rotating body 103 increases, the first support portion 50 and the second support portion 60 elastically deform to extend in the rotational direction B, and the bending of the first bent portion 71 and the second bent portion 72 progresses. When the load reaches the second predetermined value, the second bent portion 72 comes into contact with the outer circumferential surface 30a of the top foil 30. In other words, the second bent portion 72, which is the other end of the connecting portion 70, comes into contact with the outer circumferential surface 30a of the top foil 30 as the first support portion 50. As a result, when the load from the rotating body 103 increases, the number of first support portions 50 that come into contact with the outer circumferential surface 30a of the top foil 30 increases. Thus, when the load from the rotating body 103 increases, the bump foil 40 deforms such that the number of second support portions 60 that come into contact with the inner circumferential surface 20a of the housing 20 increases, and then the number of first support portions 50 that come into contact with the outer circumferential surface 30a of the top foil 30 increases. As a result, the load is supported by the first support portion 50, the second support portion 60, the first bent portion 71, and the second bent portion 72.

[0096] According to the third embodiment described above, in addition to the effects described in (1-1) and (1-4) of the first embodiment, the following effects can be obtained. (3-1) As the load from the rotating body 103 increases, the first bent portion 71 becomes the second support portion 60, so the load is supported not only by the second support portion 60 but also by the first bent portion 71. Subsequently, the second bent portion 72 becomes the first support portion 50. Therefore, the load can be supported using both ends of the connecting portion 70. For this reason, the stress generated in the second support portion 60 can be reduced compared to the case where the load is continuously supported only by the second support portion 60 until the load is supported using the first bent portion 71. As a result, even if the stress generated with the curvature of the bump foil 40 and the stress generated with the input of the load coincide in the compression direction or the tension direction of the second support portion 60, it becomes easier to suppress damage to the second support portion 60.

[0097] (3-2) The height H2 of the second support portion 60 is lower than the height H1 of the first support portion 50. When the load input from the top foil 30 increases and both ends of the connecting portion 70 bend, the first bent portion 71, which bends toward the lower second support portion 60, contacts the inner surface 20a of the housing 20 before the second bent portion 72, which bends toward the first support portion 50. Therefore, the first bent portion 71 can be made to contact the housing 20 as the second support portion 60. After the first bent portion 71 has contacted the housing 20 as the second support portion 60, if the load increases further, the second bent portion 72 can be made to contact the top foil 30 as the first support portion 50.

[0098] (Fourth embodiment) Next, a fourth embodiment of the foil bearing 10 will be described with reference to Figure 12. In the fourth embodiment, detailed explanations of parts similar to those in the third embodiment will be omitted.

[0099] The biasing direction N of the bump foil 40 is, as in the third embodiment, in the direction from the housing 20 toward the top foil 30. In the gap K between the inner circumferential surface 20a of the housing 20 and the outer circumferential surface 30a of the top foil 30, the connecting portion 70 is located at an intermediate position in the radial direction C. The distance between the first surface 49a of the connecting portion 70 and the inner circumferential surface 20a of the housing 20 is distance K1. The distance between the second surface 49b of the connecting portion 70 and the outer circumferential surface 30a of the top foil 30 is distance K2. Distances K1 and K2 are the same.

[0100] The first arc portion 50a of the first support portion 50 is an arc with an arc radius r1. The second arc portion 60a of the second support portion 60 is an arc with an arc radius r2. The arc radius r2 of the second arc portion 60a is greater than the arc radius r1 of the first arc portion 50a. In other words, the arc radius r1 of the first arc portion 50a is smaller than the arc radius r2 of the second arc portion 60a. Therefore, when a load is applied, the second support portion 60 is more likely to spread in the rotational direction B than the first support portion 50. Also, the width W2 of the second support portion 60 is greater than the width W1 of the first support portion 50.

[0101] The first bend 71 is an arc with a radius r3. The second bend 72 is an arc with a radius r4. The radius r3 of the first bend 71 is smaller than the radius r4 of the second bend 72. Therefore, when a load is applied, the second bend 72 bends more easily than the first bend 71.

[0102] <Deformation of top foil and bump foil> When the load is less than the first predetermined value, the first bent portion 71 is not in contact with the outer circumferential surface 30a of the top foil 30, and the second bent portion 72 is not in contact with the inner circumferential surface 20a of the housing 20.

[0103] The arc radius r1 of the first arc portion 50a of the first support portion 50 is smaller than the arc radius r2 of the second arc portion 60a of the second support portion 60, and the arc radius r4 of the second bent portion 72 is larger than the arc radius r3 of the first bent portion 71. Therefore, the second support portion 60 is more elastically deformable than the first support portion 50, and the second bent portion 72 is more easily bent than the first bent portion 71. Therefore, when the load reaches a first predetermined value, the second support portion 60 deforms to extend in the rotational direction B more than the first support portion 50, and the second bent portion 72 bends more than the first bent portion 71.

[0104] As a result, as shown in Figure 10, when the load reaches a first predetermined value, the first bent portion 71 comes into contact with the inner circumferential surface 20a of the housing 20. In other words, the first bent portion 71, which is one end of the connecting portion 70, comes into contact with the inner circumferential surface 20a of the housing 20 as the second support portion 60. Until the load reaches the first predetermined value, the only point of contact with the inner circumferential surface 20a of the housing 20 was the second support portion 60, but when the load reaches the first predetermined value, the points of contact with the inner circumferential surface 20a of the housing 20 become the second support portion 60 and the first bent portion 71. Therefore, when the load reaches the first predetermined value, the load is supported not only by the first support portion 50 and the second support portion 60, but also by the first bent portion 71. At this time, since the second bent portion 72 is not in contact with the top foil 30, no stress concentration occurs in the second bent portion 72.

[0105] When the load further exceeds the first predetermined value, the first support portion 50 and the second support portion 60 elastically deform to extend in the rotational direction B, and the bending of the first bent portion 71 and the second bent portion 72 progresses. Then, as shown in Figure 11, the second bent portion 72 comes into contact with the outer circumferential surface 30a of the top foil 30. As a result, the load is supported by the first support portion 50, the second support portion 60, the first bent portion 71, and the second bent portion 72.

[0106] According to the fourth embodiment described above, in addition to the effects described in (1-1), (1-4) of the first embodiment and (3-1) of the third embodiment, the following effects can be obtained. (4-1) The arc radius r4 of the second bend 72 is greater than the arc radius r3 of the first bend 71. Since the second bend 72 is easier to bend than the first bend 71, the first bend 71 contacts the inner circumferential surface 20a of the housing 20 before the second bend 72. For this reason, the first bend 71 can be made to contact the housing 20 as the second support 60. After the first bend 71 has contacted the housing 20 as the second support 60, if the load increases further, the second bend 72 can be made to contact the top foil 30 as the first support 50.

[0107] Furthermore, each of the above embodiments can be implemented with the following modifications. The above embodiments and the following modifications can be combined with each other to the extent that they do not contradict each other technically. ○The connecting portion 70 does not have to be inclined such that the first bent portion 71 side is closer to the top foil 30 than the second bent portion 72 side. In other words, the connecting portion 70 may extend in the rotational direction B without being inclined.

[0108] ○ In the first embodiment, the bump foil 40 may have an arc radius r2 at the second arc portion 60a of the second support portion 60 that is smaller than the arc radius r1 at the first arc portion 50a of the first support portion 50, while also having an arc radius r4 at the second bend portion 72 that is smaller than the arc radius r3 at the first bend portion 71.

[0109] ○ In the third embodiment, the bump foil 40 may have an arc radius r1 at the first arc portion 50a of the first support portion 50 that is smaller than the arc radius r2 at the second arc portion 60a of the second support portion 60, while also having an arc radius r3 at the first bend portion 71 that is smaller than the arc radius r4 at the second bend portion 72.

[0110] ○ In each bump foil 40, the number of first support parts 50 and the number of second support parts 60 may be changed as appropriate. ○ Although three bump foils 40 were used, one substantially cylindrical bump foil 40 may also be used. In this case, only one retaining groove 20b of the housing 20 is required. The number of first support parts 50 and the number of second support parts 60 should be changed to a number that allows the bump foils 40 to adequately and elastically support the top foil 30.

[0111] ○ The first end plate portion 81 and the second end plate portion 82 of the bump foil 40 may be omitted. ○ The foil bearing 10 is not limited to supporting the rotating body 103 of the centrifugal compressor 100 in the radial direction Rd. The application of the foil bearing 10 may be changed as appropriate. [Explanation of Symbols]

[0112] C...radial direction, H1, H2...height, Rd...radial direction, r1~r4...arc radius, 10...foil bearing, 20...housing, 20a...inner circumferential surface, 30...top foil, 30a...outer circumferential surface, 30b...bearing surface, 40...bump foil, 50...first support part, 60...second support part, 70...connecting part, 103...rotating body.

Claims

1. A housing having a through hole formed through which a rotating body is inserted, A thin plate-shaped top foil having a bearing surface facing the rotating body, A thin plate-shaped bump foil comprises a first support portion that contacts the outer circumferential surface of the top foil, a second support portion that contacts the inner circumferential surface of the housing, and a connecting portion that connects the first support portion and the second support portion so that they are alternately arranged along the rotational direction of the rotating body, wherein the first support portion and the second support portion extend in the rotational direction to elastically support the top foil, The bump foil is a foil bearing that deforms such that when the load from the rotating body increases, the number of first support portions that contact the outer circumferential surface of the top foil and the number of second support portions that contact the inner circumferential surface of the housing increase. The bump foil is characterized in that, when the load from the rotating body increases, it deforms such that the number of either the first support portion that contacts the outer circumferential surface of the top foil or the second support portion that contacts the inner circumferential surface of the housing increases, followed by the number of the other.

2. The bump foil is arranged in an arc shape between the housing and the top foil so as to reduce its diameter, and when the load from the rotating body increases, one end of the connecting portion on the first support portion side becomes the second support portion, and the other end of the connecting portion on the second support portion side becomes the first support portion. The foil bearing according to claim 1, wherein the other end of the connecting portion contacts the outer circumferential surface of the top foil, and then one end of the connecting portion contacts the inner circumferential surface of the housing.

3. The foil bearing according to claim 2, wherein the bump foil is arranged such that the radial height of the rotating body from one end of the connecting portion to the first support portion is lower than the radial height of the rotating body from the other end of the connecting portion to the second support portion.

4. One end of the connecting portion is bent in an arc shape toward the first support portion, The other end of the connecting portion is bent in an arc shape towards the second support portion, The foil bearing according to claim 2, wherein the bump foil is arranged such that the arc radius at one end of the connecting portion is greater than the arc radius at the other end of the connecting portion.

5. The bump foil is arranged in an arc shape between the housing and the top foil so as to expand in diameter, and when the load from the rotating body increases, one end of the connecting portion on the first support portion side becomes the second support portion, and the other end of the connecting portion on the second support portion side becomes the first support portion. The foil bearing according to claim 1, wherein one end of the connecting portion contacts the inner circumferential surface of the housing, and then the other end of the connecting portion contacts the outer circumferential surface of the top foil.

6. The foil bearing according to claim 5, wherein the bump foil is arranged such that the radial height of the rotating body from the other end of the connecting portion to the second support portion is lower than the radial height of the rotating body from one end of the connecting portion to the first support portion.

7. One end of the connecting portion is bent in an arc shape toward the first support portion, The other end of the connecting portion is bent in an arc shape towards the second support portion, The foil bearing according to claim 5, wherein the bump foil is arranged such that the arc radius at the other end of the connecting portion is greater than the arc radius at one end of the connecting portion.

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