Radial foil bearing

Abstract

To provide a radial foil bearing which can prevent abrasion of a coating which may easily occur before an air film is stabilized to reduce abrasion powder.SOLUTION: A radial foil bearing 20 includes: a top foil 22 including a coating 25 which contacts with a rotary shaft 15; a back foil 23 disposed at the outer periphery side of the top foil 22; and a bearing housing 45 which is disposed so as to enclose the back foil 23. The top foil 22 includes: support receiving parts 27 elastically supported by the back foil 23; and support avoidance parts 28 which are apart from the back foil 23. A thickness Tb of the support receiving part 27 is smaller than that of the support avoidance part 28.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Radial foil bearings are known (see Patent Documents 1 to 5). Radial foil bearings have a thin top foil that surrounds a rotating shaft, and the top foil is elastically supported by a thin back foil and a housing. Radial foil bearings support the rotating shaft by forming an air film between the top foil and the rotating shaft. Loads and impacts from the rotating shaft are applied to the top foil. Therefore, a heat-resistant and wear-resistant coating is uniformly applied to the contact surface of the top foil with the rotating shaft. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-82909 [Patent Document 2] Japanese Patent Application Publication No. 2018-150971 [Patent Document 3] Japanese Patent Application Publication No. 2019-82195 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-190761 [Patent Document 5] International Publication No. 2014 / 098005 Summary of the Invention [Problem to be solved by the invention]

[0004] In the initial stage of rotation when the rotating shaft starts to drive, the coating interferes with the rotating shaft and is prone to wear until the air film formation stabilizes. The wear particles generated by this wear may become mixed into the cooling air, so it is desirable to minimize the generation of this wear particles.

[0005] The present disclosure describes a radial foil bearing that can prevent coating wear, which tends to occur before the air film stabilizes, and reduce the generation of wear debris. [Means for solving the problem]

[0006] A radial foil bearing according to one embodiment of the present disclosure comprises a top foil having a coating that contacts a rotating shaft, a back foil arranged on the outer periphery of the top foil, and a bearing housing arranged to surround the back foil, wherein the top foil comprises a support receiving portion elastically supported by the back foil and a support avoidance portion spaced apart from the back foil, and the thickness of the support receiving portion is thinner than that of the support avoidance portion.

[0007] In the early stages of rotation when an air film begins to form, the support avoidance portion is easily deflected because it is separated from the back foil, and this deflection allows it to avoid interference with the rotating shaft. On the other hand, the support receiving portion supported by the back foil is less likely to deflect and is more susceptible to interference with the rotating shaft. However, the thickness of the top foil is not uniform and has a thickness distribution, and the support receiving portion, which is more likely to interfere with the rotating shaft, is thinner than the support avoidance portion. Therefore, interference between the coating and the rotating shaft can be suppressed in the early stages of rotation until the air film stabilizes. As a result, wear of the coating is prevented and the generation of wear powder can be reduced.

[0008] In some embodiments, the support receiving portions and the support avoiding portions may be arranged alternately in the circumferential direction of the rotating shaft. By arranging the support avoiding portions and the support receiving portions of different thicknesses alternately in the circumferential direction of the rotating shaft, a thickness distribution occurs in the top foil in the circumferential direction, and the air film thickness changes in the circumferential direction, making it easier to form a pressure distribution. As a result, a wedge effect is more easily obtained, and the load capacity that can support the rotating shaft can be increased.

[0009] In some aspects, the back foil may include a plurality of elastic portions that are curved and elastically deformable and are arranged in the circumferential direction to elastically support the support receiving portion, and a plurality of bottom portions that are formed between adjacent elastic portions and spaced apart from the support avoidance portion. The top foil forms an air film between itself and the rotation shaft while being elastically supported by the plurality of elastic portions. The bottom portions form a gap that allows the support avoidance portion to deflect.

[0010] In some embodiments, the elastic portion may be disposed facing the support receiving portion and abut against the support receiving portion to elastically support the support receiving portion. The elastic portion can elastically support the support receiving portion by directly contacting the support receiving portion.

[0011] In some embodiments, an intermediate foil may be provided between the top foil and the back foil, and the elastic portion may elastically support the support receiving portion via the intermediate foil. By interposing the intermediate foil between the top foil and the back foil, friction occurs between the top foil and the intermediate foil, and further friction occurs between the intermediate foil and the back foil, thereby improving damping performance.

[0012] In some embodiments, the top foil includes a base material having an inner circumferential surface facing the rotation shaft, the coating is provided on the inner circumferential surface of the base material, and the thickness of the coating on the support receiving portion may be thinner than the thickness of the coating on the support avoiding portion. The thickness distribution of the top foil can be formed by the thickness distribution of the coating.

[0013] In some embodiments, the top foil includes a base material having an inner circumferential surface facing the rotation shaft, the coating is provided on the inner circumferential surface of the base material, and the thickness of the base material in the support receiving portion may be thinner than the thickness of the base material in the support avoiding portion. The thickness distribution of the top foil can be formed by the thickness distribution of the base material, and for example, the thickness of the coating can be made uniform. By making the coating thickness uniform, it is possible to reduce unevenness in the load capacity of the top foil and substantially improve the load capacity.

[0014] In some aspects, the support receiving portion may have a concave curved surface facing the rotation shaft and recessed with respect to the rotation shaft, and the support avoiding portion may have a convex curved surface facing the rotation shaft and protruding with respect to the rotation shaft. By providing the concave curved surface and the convex curved surface, resistance when an air film is generated between the top foil and the rotation shaft is reduced, and the air film can be formed smoothly. [Effects of the Invention]

[0015] According to some aspects of the present disclosure, it is possible to prevent the coating from wearing away before the air film stabilizes, thereby reducing the generation of wear debris. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a cross-sectional view showing a rotary machine. [Figure 2] FIG. 2 is a cross-sectional view showing an example of a radial foil bearing according to an embodiment. [Figure 3] FIG. 3 shows an enlarged portion of a radial foil bearing, where (a) is a cross-sectional view showing the initial stage of rotation of the rotating shaft, and (b) is an explanatory diagram showing the state in which the air film is stable. [Figure 4] Figure 4 shows radial foil bearings with modified top foils, where (a) is a cross-sectional view of a radial foil bearing with a top foil according to a first modified example, and (b) is a cross-sectional view of a radial foil bearing with a top foil according to a second modified example. [Figure 5] FIG. 5 is an enlarged cross-sectional view showing a part of a radial foil bearing according to a modified example. [Figure 6] FIG. 6 shows the rotation of the rotating shaft and the formation of an air film, where (a) is an explanatory diagram showing the initial stage of rotation of the rotating shaft, and (b) is an explanatory diagram showing the state in which the air film is stable. [Figure 7] FIG. 7 shows an enlarged view of a portion of a radial foil bearing according to a comparative example, where (a) is a cross-sectional view showing the state in which the rotating shaft is stopped, and (b) is a cross-sectional view showing the state in which an air film is formed by the rotating shaft. [Figure 8]FIG. 8 shows the relationship between the progress of wear and the load capacity, where (a) is an explanatory diagram showing the initial stage of rotation, and (b) is an explanatory diagram showing the state after wear has occurred. [Figure 9] Figure 9 shows the relationship between wear progression and load capacity, where (a) is an explanatory diagram showing the state in which the air film has been reformed, and (b) is an explanatory diagram showing the state in which the rotating shaft and the base material are in metallic contact. [Figure 10] Figure 10 shows a schematic diagram of the pressure distribution of the air film, where (a) is an explanatory diagram when a radial foil bearing according to an example of the embodiment is used, and (b) is an explanatory diagram when a radial foil bearing according to a comparative example is used. DETAILED DESCRIPTION OF THE INVENTION

[0017] 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.

[0018] 1 shows a rotary machine 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 rotary shaft 15. The turbine 2 has a turbine impeller 4 provided at one end of the rotary shaft 15, and a turbine housing 6 that houses the turbine impeller 4. The compressor 3 has a compressor impeller 5 provided at the other end of the rotary shaft 15, and a compressor housing 7 that houses the compressor impeller 5.

[0019] A rotor 11 of the electric motor 10 is disposed, for example, at the center of a rotating shaft 15. The rotor 11 is fixed to the rotating shaft 15 and is rotatable together with the rotating 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 rotating shaft 15. The cooperation of the rotor 11 and the stator 12 assists in the rotation of the rotating shaft 15.

[0020] 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 rotary shaft 15. At this time, torque is applied to the rotary shaft 15 by the electric motor 10, thereby assisting the rotation of the rotary 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.

[0021] The rotating shaft 15 is supported rotatably around the rotation axis H via a plurality of bearings. At least one of the plurality of bearings is the radial foil bearing 20 of the present disclosure. In the example shown in FIG. 1 , a pair of radial foil bearings 20 are provided at both ends of the rotating shaft 15. The radial foil bearings 20 are air bearings that support the rotating shaft 15 in the radial direction (i.e., the direction perpendicular to the rotation axis H).

[0022] In the rotary machine 1 of the present disclosure, a thrust collar 17 and a pair of thrust air bearings 18 are provided between the compressor impeller 5 and one of the pair of radial foil bearings 20 that is closer to the compressor impeller 5. The thrust collar 17 is a disk-shaped member formed to protrude like a flange around the periphery of the rotating shaft 15. The pair of thrust air bearings 18 are provided at positions sandwiching the thrust collar 17. A spacer 19 is provided between the pair of thrust air bearings 18 to surround the thrust collar 17. The thrust collar 17 and the pair of thrust air bearings 18 support the rotating shaft 15 in the thrust direction (i.e., the direction parallel to the rotation axis H).

[0023] <Radial foil bearing> Next, an example of the radial foil bearing 20 will be described in detail with reference to Figures 2 and 3. The rotary machine 1 of the present disclosure includes a pair of radial foil bearings 20, and the pair of radial foil bearings 20 have substantially the same structure. Therefore, one of the radial foil bearings 20 will be described below as a representative example.

[0024] The radial foil bearing 20 includes a foil assembly 21 and a bearing housing 45 that accommodates the foil assembly 21. The foil assembly 21 includes a top foil 22 and a back foil 23. The back foil 23 is disposed on the outer circumferential side of the top foil 22 so as to surround the top foil 22. The outer circumferential side of the top foil 22 means the side opposite to the inner circumferential side that faces the rotating shaft 15. When the rotating shaft 15 rotates, an air film AL is formed between the rotating shaft 15 and the top foil 22. By forming this air film AL, the radial foil bearing 20 rotatably supports the rotating shaft 15.

[0025] The bearing housing 45 is a substantially cylindrical casing having a shaft hole 46 through which the rotating shaft 15 is inserted. The foil assembly 21 is housed inside the shaft hole 46 so as to surround the rotating shaft 15. The shaft hole 46 passes through the bearing housing 45 in the direction in which the rotation axis H extends. In the following description, the direction in which the shaft hole 46 extends, i.e., the direction in which the rotation axis H extends, will be referred to as the "rotation axis 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 of the rotating shaft 15, i.e., the direction along a ring centered on the rotation axis H, will be referred to as the "circumferential direction D3."

[0026] The bearing housing 45 is, for example, a member having sufficient strength to support the rotating shaft 15 when the rotation is stopped. The rotating shaft 15 is arranged to pass through the center of a shaft hole 46 of the bearing housing 45. A foil assembly 21 rolled into a cylindrical shape is arranged between the rotating shaft 15 and an inner circumferential surface 46a of the shaft hole 46.

[0027] The foil assembly 21 includes a top foil 22 and a back foil 23 that is arranged to surround the top foil 22. The top foil 22 and the back foil 23 are each formed from a thin metal plate and are flexible.

[0028] The back foil 23 is cylindrical and includes an inner circumferential surface 23a facing the top foil 22 and an outer circumferential surface 23b opposite the inner circumferential surface 23a. The back foil 23 also includes a plurality of elastic portions 32 arranged side by side in the circumferential direction D3 and a plurality of bottom portions 33. The plurality of bottom portions 33 are respectively provided between adjacent elastic portions 32. The elastic portions 32 are curved in an arc shape in a cross-sectional view and have flexibility that allows them to expand in the circumferential direction D3. The cross-section in this cross-sectional view is a cross-section obtained by cutting the back foil 23 along a plane along the circumferential direction D3 and is also a cross-section perpendicular to the rotation axis H.

[0029] The elastic portions 32 are elastically deformable and abut against the top foil 22 to elastically support it. The top foil 22 is elastically supported by the multiple elastic portions 32 and forms an air film AL between it and the rotating shaft 15. The bottom portion 33 is provided to connect the bases of adjacent elastic portions 32 and is spaced apart from the top foil 22. The bottom portion 33 is a portion that abuts against and is held by the inner circumferential surface 46a of the shaft hole 46 of the bearing housing 45, and is not expected to have any substantial elastic function. The bottom portion 33 forms a gap Sp that allows for deflection of the support avoidance portion 28, which will be described later.

[0030] The top foil 22 is cylindrical and formed by rolling a rectangular thin plate, and both longitudinal ends are open and not joined together. The ends of the top foil 22 are provided with locking portions 22x that are locked to the back foil 23. The cylindrical top foil 22 has an inner peripheral contact surface 22a that faces the rotation shaft 15 and an outer peripheral surface 22b that is opposite the contact surface 22a. The top foil 22 is positioned so that both ends are in upper positions opposite the vertical direction (downward).

[0031] The top foil 22 includes a support receiving portion 27 elastically supported by the back foil 23, and a support avoidance portion 28 spaced apart from the back foil 23. The support receiving portion 27 is a portion that abuts at least the elastic portion 32, and the support avoidance portion 28 is a portion that faces at least the bottom portion 33 and forms a gap Sp between it and the bottom portion 33. An air film AL is formed between the rotation shaft 15 and the top foil 22 due to the rotation of the rotation shaft 15. As the air film AL is formed, the top foil 22 is pressed toward the back foil 23. As a result, the top foil 22 abuts against and is elastically supported by the elastic portion 32, and further bends to follow the curvature of the elastic portion 32 and curves so as to bulge toward the bottom portion 33. In addition, the support receiving portion 27 in one example of the present disclosure also includes a portion where the top foil 22 may bend due to the formation of the air film AL, resulting in the possibility of it coming into contact with the elastic portion 32, and the support avoidance portion 28 is an area other than the support receiving portion 27.

[0032] The top foil 22 has support avoidance portions 28 and support receiving portions 27 arranged alternately in the circumferential direction D3, and the thickness Tb of the support receiving portions 27 is thinner than the thickness Ta of the support avoidance portions 28. Furthermore, the top foil 22 has a thickness distribution, with thicker and thinner portions arranged alternately in the circumferential direction D3. The inner circumferential surface 28a of the support avoidance portion 28 is a curved surface that curves along the circumferential direction D3. The inner circumferential surface 27a of the support receiving portion 27 is a curved surface that curves along the circumferential direction D3. The support receiving portions 27 are thinner than the thickness Tb of the support avoidance portions 28. Furthermore, the inner circumferential surface 27a of the support receiving portion 27 and the inner circumferential surface 28a of the support avoidance portion 28 are curved in the same direction. Therefore, a step is created between the support receiving portion 27 and the support avoidance portion 28.

[0033] The top foil 22 includes a cylindrical base material 26 made of, for example, a metal plate. The base material 26 has an inner circumferential surface 26a facing the rotating shaft 15, and a coating 25 is provided on the inner circumferential surface 26a. The coating 25 is made of, for example, resin. The coating 25 is provided to improve heat resistance and wear resistance when a load or impact is applied from the rotating shaft 15. The coating 25 prevents metallic contact between the rotating shaft 15 and the base material 26, protecting the base material 26 and preventing seizure. The thickness of the base material 26 is substantially uniform in the circumferential direction D3. The thickness of the coating 25 is thinner at the support receiving portion 27 than at the support avoidance portion 28. The inner circumferential surfaces of the support avoidance portion 28 and the support receiving portion 27 are formed by the coating 25. The thickness distribution of the top foil 22 is formed by the thickness distribution of the coating 25.

[0034] A difference can be provided between the thickness of the coating 25 of the support avoidance portion 28 and the thickness of the coating 25 of the support receiving portion 27. This difference in thickness can be, for example, 1 μm or more and 0.1 mm or less. The thicknesses of the base material 26 of the support avoidance portion 28 and the support receiving portion 27 are substantially the same, and can be calculated from the thickness of the top foil 22 described above.

[0035] Next, modified examples of the top foil 22 will be described with reference to Fig. 4. Fig. 4(a) is a cross-sectional view showing a first modified example. In the top foil 22 according to the first modified example, support avoidance portions 28A and support receiving portions 27A are alternately arranged in the circumferential direction D3. The thickness Tb of the support receiving portions 27A is thinner than the thickness Ta of the support avoidance portions 28A. Furthermore, the top foil 22 has a thickness distribution, with thick portions and thin portions alternately arranged in the circumferential direction D3.

[0036] The support receiving portion 27A faces the rotating shaft 15 and has a concave curved surface 27b recessed relative to the rotating shaft 15. The support avoidance portion 28 faces the rotating shaft 15 and has a convex curved surface 28b protruding relative to the rotating shaft 15. The support receiving portion 27A is thinner than the thickness Ta of the support avoidance portion 28A. That is, of the support avoidance portion 28A and the support receiving portion 27A, the support avoidance portion 28A with the thicker thickness Ta has the convex curved surface 28b, while the support receiving portion 27A with the thinner thickness Tb has the concave curved surface 27b. This reduces the step between the support receiving portion 27A and the support avoidance portion 28A. As a result, resistance when forming an air film AL between the top foil 22 and the rotating shaft 15 is reduced, allowing the air film AL to be formed smoothly. The top foil 22 has a coating 25A provided on the inner circumferential surface 26a of the base material 26. The concave curved surface 27b of the support receiving portion 27A and the convex curved surface 28b of the support avoiding portion 28A are formed by the coating 25.

[0037] 4(b) is a cross-sectional view showing a second modified example. In the top foil 22 according to the second modified example, support avoidance portions 28B and support receiving portions 27B are alternately arranged in the circumferential direction D3, and the thickness Tb of the support receiving portions 27B is thinner than the thickness Ta of the support avoidance portions 28B. The top foil 22 has a thickness distribution, and thick portions and thin portions are alternately arranged in the circumferential direction D3. The portions with a thicker thickness Ta are support avoidance portions 28B, and the portions with a thinner thickness Tb are support receiving portions 27B.

[0038] The top foil 22 includes a coating 25B provided on the inner circumferential surface 26a of the base material 26B. The thickness of the base material 26B is thinner at the support receiving portion 27 than at the support avoidance portion 28. The coating 25B has a step due to the change in thickness of the base material 26B, but the thickness of the coating 25B at the support avoidance portion 28 is the same as the thickness of the coating 25B at the support receiving portion 27. The thickness distribution of the top foil 22 is formed by the thickness distribution of the base material 26B. In this modification, the thickness of the coating 25B is substantially uniform. By making the thickness of the coating 25B uniform, it is possible to reduce unevenness in the load capacity of the top foil 22 and substantially improve the load capacity. The load capacity of the top foil 22 refers to its substantial durability, and refers to the period required for the rotating shaft 15 to wear down the coating 25B and reach the base material 26B.

[0039] The thickness of the coating 25B of the support-avoiding portion 28B and the support-receiving portion 27B is substantially the same. Regarding the thickness of the base material 26B, the thickness of the support-receiving portion 27B is thinner than the thickness of the support-avoiding portion 28B. A difference can be made between the thickness of the base material 26B of the support-avoiding portion 28B and the thickness of the base material 26B of the support-receiving portion 27B. This difference in thickness can be, for example, 1 μm or more and 0.1 mm or less.

[0040] Next, a radial foil bearing 20A according to a modified example will be described with reference to Fig. 5. The radial foil bearing 20A has the same structure and members as the above-described radial foil bearing 20. Therefore, the same reference numerals are used to designate the same structure and members as the above-described radial foil bearing 20, and detailed description thereof will be omitted.

[0041] The radial foil bearing 20A includes a foil assembly 21A and a bearing housing 45 that accommodates the foil assembly 21A. The foil assembly 21A includes a top foil 22 and a back foil 23 that is arranged on the outer circumferential side of the top foil 22. The foil assembly 21A also includes a cylindrical intermediate foil 29 between the top foil 22 and the back foil 23. The back foil 23 includes a plurality of elastic portions 32 that are arranged side by side in the circumferential direction D3, and a plurality of bottom portions 33 that are provided between adjacent elastic portions 32.

[0042] The top foil 22 includes a support receiving portion 27 that is elastically supported by the back foil 23, and a support avoidance portion 28 that is spaced apart from the back foil 23. The elastic portion 32 elastically supports the support receiving portion 27 via the intermediate foil 29, rather than directly. In the top foil 22, the support avoidance portions 28 and the support receiving portions 27 are alternately arranged in the circumferential direction D3, and the thickness of the support receiving portion 27 is thinner than the thickness of the support avoidance portion 28. In addition, the top foil 22 has a thickness distribution, with thick portions and thin portions alternately arranged in the circumferential direction D3.

[0043] In the radial foil bearing 20A, the support receiving portion 27 of the top foil 22 is a portion that overlaps at least the contact portion between the intermediate foil 29 and the elastic portion 32. In addition, the support avoidance portion 28 is a portion that faces at least the bottom portion 33 and forms a gap Sp between itself and the bottom portion 33, assuming a structure in which the intermediate foil 29 is omitted.

[0044] Next, the functions and effects of the radial foil bearings 20 and 20A will be explained in comparison with the radial foil bearing 100. The radial foil bearings 20 and 20A basically have the same functions and effects. Therefore, the radial foil bearing 20 will be explained as a representative, and the functions and effects of the radial foil bearing 20A will be described later, focusing on the differences.

[0045] First, a radial foil bearing 100 according to a comparative example will be described with reference to Fig. 7. Fig. 7 shows an enlarged view of a portion of the radial foil bearing 100. Fig. 7(a) is a cross-sectional view showing a state in which the rotating shaft 115 is stationary, and Fig. 7(b) is a cross-sectional view showing a state in which the rotating shaft 115 is rotating and forming an air film AL.

[0046] 7, the radial foil bearing 100 includes a top foil 122 arranged to surround the rotating shaft 115, and a back foil 123 arranged to surround the top foil 122. The top foil 122 and the back foil 123 are housed in a bearing housing 145. The top foil 122 includes a base material 126 and a coating 125. The thickness of the top foil 122 is uniform and does not have any thickness distribution.

[0047] Next, with reference to FIGS. 8 and 9, the relationship between the progression of wear and the load capacity when the radial foil bearing 100 is used will be described. FIG. 8(a) is an explanatory diagram showing the initial stage of rotation of the rotating shaft 115, and FIG. 8(b) is an explanatory diagram showing a state in which the air film AL breaks and wear occurs in the initial stage of rotation. When the rotating shaft 115 starts to rotate, air is trapped between the rotating shaft 115 and the top foil 122, forming the air film AL (see FIG. 8(a)). Here, the rotating shaft 115 applies a static load Fb (load capacity) in the vertical direction to the air film AL and the radial foil bearing 100 due to its own weight. The air film AL is unstable in the initial stage of rotation and may break. When the air film AL breaks, the rotating shaft 115 comes into contact with the radial foil bearing 100, causing wear on the coating 125 of the top foil 122 (see FIG. 8(b)). Wear of the coating 125 is likely to occur at a position vertical to (below) the rotation shaft 115 .

[0048] As shown in FIG. 7B, as the air film AL forms, the top foil 122 curves to conform to the elastic portion 132 of the back foil 123. The top foil 122 includes a first portion 127 that contacts the elastic portion 132 and a second portion 128 that does not contact the elastic portion 132. The second portion 128 curves away from the rotational shaft 115, and the first portion 127 is positioned closer to the rotational shaft 115 than the second portion 128. Because the thickness of the first portion 127 and the second portion 128 is the same, the first portion 127, which is positioned closer to the rotational shaft 115, is prone to wear due to interference with the rotational shaft 115. Wear of the coating 125 on the top foil 122 generates wear debris. The wear debris may enter, for example, the cooling air that cools the rotating machine, potentially causing contamination.

[0049] FIG. 9(a) is an explanatory diagram showing a state in which the air film AL has been reformed, and FIG. 9(b) is an explanatory diagram showing a state in which the rotating shaft 115 has reached the base material 126. The coating 125 is worn away by contact with the rotating shaft 115, causing a change in the shape of the bearing surface. This change in the bearing surface ultimately causes the ruptured air film AL to be reformed (see FIG. 9(b)). The rotating shaft 115 stops when the rotating machine is stopped. The rotating shaft 115 starts rotating again when the rotating machine is started again. Repeated rotation and stopping of the rotating shaft 115 causes wear of the coating 125, and eventually the rotating shaft 115 reaches the base material 126 of the top foil 122. As a result, metallic contact occurs between the rotating shaft 115 and the base material 126, eventually leading to seizure (see FIG. 9(b)).

[0050] As described above, in the radial foil bearing 100, the coating 25 is likely to wear out before the air film AL stabilizes. In contrast, the radial foil bearing 20 according to one example of the present disclosure can prevent the coating 25 from wearing out, which tends to occur before the air film AL stabilizes, and reduce the generation of wear debris. As a result, contamination caused by wear debris can be reduced. This will be described in detail below with reference to FIGS. 3, 6, and 10.

[0051] FIG. 3 is an enlarged cross-sectional view of a portion of the radial foil bearing 20. FIG. 6 shows the formation of an air film AL when the radial foil bearing 20 is used. FIG. 6(a) is an explanatory diagram showing the state of the rotating shaft 15 at an early stage of rotation, and FIG. 6(b) is an explanatory diagram showing the state when the air film AL is stable. FIG. 10 schematically shows the pressure distribution of the air film AL. FIG. 10(a) is an explanatory diagram when the radial foil bearing 20 is used, and FIG. 10(b) is an explanatory diagram when the radial foil bearing 100 is used.

[0052] The rotating shaft 15 applies a static load Fa (load capacity) to the radial foil bearing 20. As shown in FIG. 6A, an air film AL is formed between the rotating shaft 15 and the top foil 22 during the initial rotation of the rotating shaft 15 (see FIG. 3B). During the initial rotation, the support avoidance portion 28 is easily deflected because it is spaced from the back foil 23. This deflection allows the support avoidance portion 28 to avoid interference with the rotating shaft 15. Meanwhile, the support receiving portion 27 is less likely to deflect because it is supported by the elastic portion 32 of the back foil 23, making it more susceptible to interference from the rotating shaft 15. However, the thickness of the top foil 22 is not uniform; it has a thickness distribution. The support receiving portion 27, which is more likely to interfere with the rotating shaft 15, is thinner than the support avoidance portion 28. Therefore, during the initial rotation until the air film AL stabilizes, interference between the top foil 22 and the rotating shaft 15 can be suppressed. As a result, wear of the coating 25 is prevented, and the generation of wear debris can be reduced.

[0053] Furthermore, even when the radial foil bearing 20 is used, the coating 25 will wear due to the static load Fa applied by the rotating shaft 15 to the radial foil bearing 20, although this wear is less than that of the radial foil bearing 100. This wear ultimately optimizes the air film thickness between the rotating shaft 15 and the top foil 22 (see FIG. 6(b)). As a result, the static load Fa (load capacity) with which the radial foil bearing 20 can support the rotating shaft 15 increases. Note that the air film thickness may also be optimized by wear in the radial foil bearing 100. However, in the case of the radial foil bearing 100, the amount of wear debris generated before the air film thickness is optimized is greater than in the case of the radial foil bearing 20. In other words, the radial foil bearing 20 makes it easier to optimize the air film thickness while reducing the generation of wear debris.

[0054] Furthermore, in the case of the radial foil bearing 100 according to the comparative example, the thickness of the top foil 122 is constant in the circumferential direction of the rotating shaft 115 (see FIG. 10(b)). Therefore, the width of the air film AL formed between the rotating shaft 115 and the top foil 122, i.e., the air film thickness, changes little in the circumferential direction Da, and the pressure distribution of the air film AL is small, making it difficult to obtain a wedge effect. As a result, it is difficult to increase the static load (load capacity) that can support the rotating shaft 115.

[0055] In contrast, the top foil 22 of the radial foil bearing 20 has support avoidance portions 28 and support receiving portions 27 with different thicknesses Ta and Tb, and the support avoidance portions 28 and support receiving portions 27 are arranged alternately in the circumferential direction D3 (see FIG. 10(a)). Therefore, a thickness distribution occurs in the top foil 22 in the circumferential direction D3, and the air film thickness changes in the circumferential direction D3, making it easier to form a pressure distribution. As a result, a wedge effect is more easily achieved, and the static load (load capacity) that the radial foil bearing 20 can support for the rotating shaft 15 increases.

[0056] The elastic portion 32 of the radial foil bearing 20 is disposed facing the support receiving portion 27, and abuts against the support receiving portion 27 to elastically support the support receiving portion 27. In other words, the elastic portion 32 can elastically support the support receiving portion 27 by directly contacting the support receiving portion 27.

[0057] Next, the operation and effect of the radial foil bearing 20A according to the modified example will be described. The radial foil bearing 20A includes an intermediate foil 29 between the top foil 22 and the back foil 23. The elastic portion 32 of the back foil 23 elastically supports the support receiving portion 27 via the intermediate foil 29.

[0058] The top foil 22 includes a support avoidance portion 28 and a support receiving portion 27 that is thinner than the support avoidance portion 28. An intermediate foil 29 is present between the support avoidance portion 28 and the back foil 23. The support avoidance portion 28 and a portion of the intermediate foil 29 that overlaps the support avoidance portion 28 are spaced apart from the back foil 23 and therefore easily deflect. This deflection prevents interference between the coating 25 of the support avoidance portion 28 and the rotating shaft 15. Meanwhile, the support receiving portion 27 is supported by the elastic portion 32 of the back foil 23 via the intermediate foil 29. Therefore, the support avoidance portion 28 is less likely to deflect and is more susceptible to interference from the rotating shaft 15. However, the thickness of the top foil 22 is not uniform but has a thickness distribution. The support receiving portion 27, which is more likely to interfere with the rotating shaft 15, is thinner than the support avoidance portion 28. Therefore, interference between the top foil 22 and the rotating shaft 15 can be suppressed during the initial stage of rotation until the air film AL stabilizes. As a result, wear of the coating 25 is prevented, and the generation of wear particles can be reduced.

[0059] Furthermore, since the radial foil bearing 20A includes the intermediate foil 29, friction occurs between the top foil 22 and the intermediate foil 29, and friction also occurs between the intermediate foil 29 and the back foil 23. As a result, damping performance can be improved.

[0060] The radial foil bearing according to the present disclosure is not limited to the above-described examples, and various other modifications are possible. For example, the above-described examples may be combined with each other depending on the required purpose and effect. Furthermore, the support avoidance portion and the support receiving portion having different thicknesses do not need to be provided around the entire circumference of the top foil in the circumferential direction of the rotating shaft, but may be provided only in the lower portion that is more susceptible to the static load of the rotating shaft. For example, in a cylindrical top foil having both ends, the support avoidance portion and the support receiving portion may be provided at least in a lower position opposite to the both ends located above the rotating shaft. Furthermore, the thickness of the base material of the support receiving portion may be thinner than the thickness of the base material of the support avoidance portion, and the thickness of the coating of the support receiving portion may be thinner than the thickness of the coating of the support avoidance portion.

[0061] The configurations of various aspects of the present disclosure will be described below. [1] A radial foil bearing, a top foil with a coating in contact with the rotating shaft; a back foil disposed on the outer circumferential side of the top foil; a bearing housing arranged to surround the back foil, The top foil includes a support receiving portion elastically supported by the back foil and a support avoiding portion spaced apart from the back foil, A radial foil bearing, wherein the support receiving portion is thinner than the support avoiding portion. [2] The radial foil bearing according to [1], wherein the support receiving portions and the support avoidance portions are alternately arranged in the circumferential direction of the rotating shaft. [3] The radial foil bearing described in [2], wherein the back foil is curved and elastically deformable, and comprises a plurality of elastic portions arranged in the circumferential direction to elastically support the support receiving portion, and a plurality of bottom portions formed between adjacent elastic portions and spaced apart from the support avoidance portion. [4] The radial foil bearing according to [3], wherein the elastic portion is arranged facing the support receiving portion and abuts against the support receiving portion to elastically support the support receiving portion. [5] an intermediate foil between the top foil and the back foil; The radial foil bearing according to [3], wherein the elastic portion elastically supports the support receiving portion via the intermediate foil. [6] the top foil includes a base material having an inner circumferential surface facing the rotation shaft, the coating is provided on the inner circumferential surface of the base material, The radial foil bearing according to [1] or [2], wherein the thickness of the coating on the support receiving portion is thinner than the thickness of the coating on the support avoiding portion. [7] the top foil includes a base material having an inner circumferential surface facing the rotation shaft, the coating is provided on the inner circumferential surface of the base material, The radial foil bearing according to [1] or [2], wherein the thickness of the base material of the support receiving portion is thinner than the thickness of the base material of the support avoidance portion. [8] the support receiving portion faces the rotation shaft and has a concave curved surface that is recessed with respect to the rotation shaft, The radial foil bearing according to any one of [1] to [7], wherein the support avoidance portion faces the rotating shaft and has a convex curved surface that protrudes toward the rotating shaft. [9] A radial foil bearing, a top foil with a coating in contact with the rotating shaft; a back foil disposed on the outer circumferential side of the top foil; a bearing housing arranged to surround the back foil, A radial foil bearing, wherein the top foil has a thickness distribution, with thick portions and thin portions alternately arranged in the circumferential direction of the rotating shaft. [Explanation of symbols]

[0062] 20,20A Radial Foil Bearing 45 bearing housing 22 Top Foil 23 Back Foil AL Air Membrane D3 Circumferential direction of the rotating shaft 23a Inner surface of base material 32 Elastic part 33 Bottom 25, 25A, 25B coating 26,26B Base material 27, 27A, 27B Support receiving part 28,28A,28B Support avoidance part Tb Thickness of support Ta Thickness of the support avoidance part 28b Convex curved surface 27b Concave curved surface 29 Intermediate Foil

Claims

1. A radial foil bearing, a top foil with a coating in contact with the rotating shaft; a back foil disposed on the outer circumferential side of the top foil; a bearing housing arranged to surround the back foil, The top foil includes a support receiving portion elastically supported by the back foil and a support avoiding portion spaced apart from the back foil, A radial foil bearing, wherein the support receiving portion is thinner than the support avoiding portion.

2. The radial foil bearing according to claim 1 , wherein the support receiving portions and the support avoiding portions are alternately arranged in the circumferential direction of the rotating shaft.

3. 3. The radial foil bearing according to claim 2, wherein the back foil is provided with a plurality of elastic portions that are curved and elastically deformable, and that are arranged in the circumferential direction and elastically support the support receiving portion, and a plurality of bottom portions that are formed between adjacent elastic portions and are spaced apart from the support avoidance portion.

4. 4. The radial foil bearing according to claim 3, wherein the elastic portion is disposed facing the support receiving portion and abuts against the support receiving portion to elastically support the support receiving portion.

5. an intermediate foil between the top foil and the back foil; The radial foil bearing according to claim 3 , wherein the elastic portion elastically supports the support receiving portion via the intermediate foil.

6. the top foil includes a base material having an inner circumferential surface facing the rotation shaft, the coating is provided on the inner circumferential surface of the base material, The radial foil bearing according to claim 1 , wherein the thickness of the coating on the support receiving portion is thinner than the thickness of the coating on the support avoiding portion.

7. the top foil includes a base material having an inner circumferential surface facing the rotation shaft, the coating is provided on the inner circumferential surface of the base material, The radial foil bearing according to claim 1 , wherein the thickness of the base material of the support receiving portion is thinner than the thickness of the base material of the support avoiding portion.

8. the support receiving portion faces the rotation shaft and has a concave curved surface that is recessed with respect to the rotation shaft, The radial foil bearing according to claim 1 , wherein the support avoidance portion has a convex curved surface that faces the rotation shaft and protrudes toward the rotation shaft.

9. A radial foil bearing, a top foil with a coating in contact with the rotating shaft; a back foil disposed on the outer circumferential side of the top foil; a bearing housing arranged to surround the back foil, A radial foil bearing, wherein the top foil has a thickness distribution, with thick portions and thin portions alternately arranged in the circumferential direction of the rotating shaft.

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