Radial foil bearing

Abstract

This radial foil bearing (5) comprises: a bearing housing (10) having an insertion hole (11) for a rotary shaft (2); one top foil (20) provided in the insertion hole (11); and one bump foil (30) provided between an inner peripheral surface (11a) of the insertion hole (11) and the top foil (20) and including a plurality of crests (33) arranged in the circumferential direction of the insertion hole (11). The inner peripheral surface (11a) is provided with accommodation grooves (14) extending along the axial direction of the insertion hole (11). The bump foil (30) includes protrusions (35) protruding toward the inner side of the accommodation grooves (14) and placed in an elastically deformable state.

Description

Radial foil bearing

[0001] The present disclosure relates to a radial foil bearing.

[0002] A radial foil bearing is a type of journal bearing that rotatably supports a rotating shaft. The radial foil bearing includes a top foil as a bearing surface surrounding the outer circumference of the rotating shaft, and bump foils that support the top foil while elastically deforming. When the rotating shaft is rotating at high speed, a fluid film is formed between the rotating shaft and the top foil. The radial foil bearing supports the rotating shaft in a non-contact manner by the wedge effect of this fluid film. Therefore, generally, it is known that the radial foil bearing has higher durability and less noise due to vibration and friction than a rolling bearing (see Patent Document 1).

[0003] International Publication No. 2020 / 202793

[0004] The bump foils have a plurality of protrusions arranged in the circumferential direction of the rotating shaft. The protrusions protrude toward the top foil. When the top foil receives a load from the rotating shaft, the load is transmitted to the protrusions, and the protrusions support the top foil while elastically deforming. At this time, the unstable vibration of the rotating shaft is attenuated by the friction generated between the bump foils and peripheral members such as the top foil and the housing of the rotating shaft.

[0005] On the other hand, each protrusion receiving a load tends to elastically deform so as to open its curved surface (i.e., to collapse). However, since two adjacent protrusions in the circumferential direction are connected to each other, they press the forces trying to open against each other. In this case, the elastic deformation of each protrusion is likely to be suppressed, and the above-mentioned friction is less likely to occur.

[0006] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a radial foil bearing capable of promoting the attenuation of unstable vibration of a rotating shaft.

[0007] A radial foil bearing according to one aspect of the present disclosure comprises a bearing housing having a through hole for a rotating shaft, a top foil provided in the through hole, and a bump foil provided between the inner circumferential surface of the through hole and the top foil, and including a plurality of ridges arranged in the circumferential direction of the through hole, wherein the inner circumferential surface is provided with a groove extending along the axial direction of the through hole, and the bump foil includes a projection that protrudes toward the inside of the groove and is in a state that is elastically deformable.

[0008] The protrusion may be separated from at least one of the sides forming the inner surface of the groove. The protrusion may have dimensions that separate it from the inner surface of the groove. The protrusion may be separated from each other in the circumferential direction of the insertion hole and may include a pair of side portions that flare outwards from the foil body where the peaks of the bump foil are lined up toward the inside of the groove. The top of the protrusion and the groove may be separated from each other. The protrusion is connected to the peak closest to the protrusion among the plurality of peaks via a connecting portion, and the length of the connecting portion along the circumferential direction may be greater than or equal to the difference between the width of the groove and the width of the protrusion along the circumferential direction. When the bump foil is installed on the inner circumferential surface, the peak closest to the protrusion among the plurality of peaks is separated from the groove by a predetermined distance along the circumferential direction, and the predetermined distance may be at least one and no more than three times the value obtained by subtracting the width of the peak along the circumferential direction from the length of the peak along the curvature direction.

[0009] According to this disclosure, it is possible to provide a radial foil bearing that can promote the damping of unstable vibrations of the rotating shaft.

[0010] Figure 1 is a side view of an example of a turbomachinery to which the radial foil bearing according to this embodiment is applied. Figure 2 is a front view of the radial foil bearing according to this embodiment. Figure 3A is a side view of the bump foil according to this embodiment when it is unfolded in plan. Figure 3B is a partially enlarged side view of the foil body of the bump foil. Figure 3C is a partially enlarged side view of the foil body of the bump foil. Figure 4 is a diagram for explaining the elastic deformation of the ridges and protrusions according to this embodiment. Figure 5A is a diagram showing one modified example of the protrusion according to this embodiment. Figure 5B is a diagram showing one modified example of the protrusion according to this embodiment. Figure 5C is a diagram showing one modified example of the protrusion according to this embodiment. Figure 6 is a diagram showing an example of the relative positional relationship between the ridges and grooves according to this embodiment. Figure 7 is a diagram showing an example of the relative positional relationship between the ridges and grooves according to this embodiment.

[0011] Several embodiments of this disclosure will be described below. Common parts in each figure will be denoted by the same reference numerals, and redundant explanations will be omitted. For the sake of clarity, the axial, circumferential, and radial directions will be defined as follows.

[0012] The axial direction AD is the extension direction of the reference shaft 7 (see Figure 1). The reference shaft 7 corresponds to the central axis of the rotating shaft 2, the thrust bearing 4, and the radial foil bearing 5. The reference shaft 7 also corresponds to the central axis of the through hole 11 provided in the radial foil bearing 5.

[0013] The circumferential direction CD is the extension direction of a circle on a virtual plane that is centered on a point on the reference axis 7 and perpendicular to the reference axis 7. The radial direction RD is the direction of extension on a plane perpendicular to the reference axis 7, starting from any point on the reference axis 7.

[0014] A turbomachinery 1 to which the radial foil bearing 5 according to this embodiment is applied will be described. Figure 1 is a side view of an example of the turbomachinery 1. The turbomachinery 1 comprises a rotating shaft 2, an impeller 3, a thrust bearing 4, a pair of radial foil bearings 5, 5, and a housing 6 that accommodates them. Figure 1 shows one of the pair of radial foil bearings 5, 5. Hereinafter, for convenience of explanation, the radial foil bearing 5 will be simply referred to as bearing 5.

[0015] The bearing 5 rotatably supports the rotating shaft 2. An impeller 3 is attached to the end of the rotating shaft 2. The impeller 3 is housed in the housing 6 with a tip clearance between it and the housing 6. The thrust bearing 4 comprises a thrust collar 4a and a pair of bearing pads 4b, 4b. The thrust collar 4a is a disc having a predetermined thickness in the axial direction AD and is fixed to the rotating shaft 2. The thrust collar 4a is sandwiched between the pair of bearing pads 4b, 4b. This limits the range of movement of the thrust collar 4a along the axial direction AD.

[0016] Figure 2 is a front view of the bearing 5. As shown in Figure 2, the bearing 5 comprises a bearing housing 10, a top foil 20, and a bump foil 30. The bearing housing 10 accommodates at least the top foil 20 and the bump foil 30.

[0017] The bearing housing 10 is provided with a through hole 11. The through hole 11 extends in the axial direction AD and penetrates the bearing housing 10. The rotating shaft 2 is inserted through the through hole 11 with the top foil 20 and bump foil 30 housed in the through hole 11. As shown in Figure 2, the bearing housing 10 has a cylindrical outer shape. However, the outer shape of the bearing housing 10 is arbitrary as long as the through hole 11 is formed.

[0018] An intermediate foil (not shown) may be provided between the top foil 20 and the bump foil 30. An auxiliary foil (not shown) may also be provided between the inner circumferential surface 11a of the insertion hole 11 and the bump foil 30. Both the intermediate foil and the auxiliary foil are smooth, metal foils (thin sheets), similar to the top foil 20. The intermediate foil is used, for example, to adjust the distance between the top foil 20 and the outer circumferential surface 2a of the rotating shaft 2. The auxiliary foil, on the other hand, is used, for example, to roll the top foil 20 and the bump foil 30 into a cylindrical shape.

[0019] A fixing groove 12 is formed on the inner circumferential surface 11a of the insertion hole 11. The fixing groove 12 opens onto the inner circumferential surface 11a and extends from one end face to the other end face of the bearing housing 10 in the axial direction AD. The flanges 22, 22 of the top foil 20 and the flanges 32, 32 of the bump foil 30 are accommodated in the fixing groove 12.

[0020] Furthermore, a accommodating groove (groove portion) 14 is formed on the inner circumferential surface 11a of the insertion hole 11. The accommodating groove 14 is provided in the circumferential direction CD at a position facing the projection 35 described later, and accommodates the projection 35. The accommodating groove 14 opens onto the inner circumferential surface 11a and extends from one end face to the other end face of the bearing housing 10 in the axial direction AD.

[0021] The inner surface 14a of the receiving groove 14 includes a pair of side surfaces 14b, 14b and a bottom surface 14c connecting the pair of side surfaces 14b, 14b. The pair of side surfaces 14b, 14b are planes parallel to each other and extend in the radial direction RD and the axial direction AD. The bottom surface 14c connects the ends of the pair of side surfaces 14b, 14b outside the radial direction RD. The bottom surface 14c is a plane perpendicular to the radial direction. The pair of side surfaces 14b, 14b and the bottom surface 14c form a rectangular cross-section perpendicular to the axial direction AD. However, the cross-section of the receiving groove 14 is not limited to a rectangle.

[0022] The accommodating groove 14 accommodates the protruding portion 35 in a flexible state. For this reason, the width W1 of the accommodating groove 14 along the circumferential direction CD is greater than or equal to the width W2 of the protruding portion 35 along the same direction (see Figure 3C). Also, the depth D of the accommodating groove 14 along the radial direction RD is greater than the height (length) H of the protruding portion 35 along the same direction (see Figure 3C). For this reason, the protruding portion 35 accommodated in the accommodating groove 14 is separated from at least one of the pair of side surfaces 14b, 14b and also separated from the bottom surface 14c when unloaded. For example, the protruding portion 35 is accommodated while separated from all of the pair of side surfaces 14b, 14b and the bottom surface 14c. Note that "unloaded" refers to the state in which the bump foil 30 is not receiving any load from the rotating shaft 2.

[0023] Furthermore, the receiving groove 14 does not necessarily have a bottom surface 14c. In this case, the pair of side surfaces 14b, 14b extend from the inner circumferential surface 11a of the bearing housing 10 to the outer circumferential surface of the bearing housing 10, forming a slit that penetrates the bearing housing. Also, the side surfaces 14b, 14b in this embodiment are flat and extend to the bottom surface 14c at a constant interval from each other. However, the shape of the side surfaces 14b is not limited to this, and the portion connecting to the bottom surface 14c may be curved. In other words, the receiving groove 14 can have various cross-sectional shapes, not just a rectangular cross-sectional shape.

[0024] The top foil 20 is a single metal foil that surrounds almost the entire circumference of the rotating shaft 2. The top foil 20 includes a foil body 21 that faces the rotating shaft 2. The foil body 21 extends in the circumferential direction CD along the inner circumferential surface 11a of the insertion hole 11 and functions as a bearing surface facing the rotating shaft 2. Therefore, unlike the foil body 31 of the bump foil 30 described later, the foil body 21 does not have alternating repeating bumps and grooves.

[0025] The bump foil 30 is a single metal foil that surrounds almost the entire circumference of the rotating shaft 2. The bump foil 30 is provided between the inner circumferential surface 11a of the insertion hole 11 and the top foil 20. The bump foil 30 includes a foil body 31 that surrounds the outer circumference of the rotating shaft 2. The foil body 31 extends in the circumferential direction CD along the inner circumferential surface 11a of the insertion hole 11.

[0026] The foil body 31 is formed in a wave-like shape that meanders in the radial direction RD and extends in the circumferential direction CD. The bump foil 30 is placed in the insertion hole 11 in a cylindrical shape that surrounds the outer circumference of the rotation shaft 2, and elastically supports the top foil 20.

[0027] Figure 3A is a side view of the bump foil 30 when it is unfolded in a planar manner. Figures 3B and 3C are partially enlarged side views of the foil body 31 of the bump foil 30. As shown in Figure 3A, the foil body 31 is formed in a wave shape that meanders in the radial direction RD and extends in the circumferential direction CD. As an example of how this wave shape is formed, the foil body 31 includes alternating peaks 33 and connecting portions 34 in the circumferential direction CD. In other words, the foil body 31 has a plurality of peaks 33 arranged in the circumferential direction CD. The peaks 33 extend in the axial direction AD from one edge to the other edge of the foil body 31 in the axial direction AD.

[0028] The peak portion 33 has an arch-shaped cross-section that protrudes radially inward and deforms elastically in response to the load on the rotation axis 2 via the top foil 20. On the other hand, the connecting portion 34 extends in the circumferential direction CD and connects the base portions 33a, 33a of two adjacent peak portions 33, 33. The base portion 33a is the part of the peak portion 33 that is located furthest outward in the radial direction RD when the bump foil 30 is rolled up. When the bump foil 30 is subjected to a load outward in the radial direction RD, the connecting portion 34 contacts the inner circumferential surface 11a of the insertion hole 11 and supports the peak portion 33.

[0029] As shown in Figure 3C, the bump foil 30 includes a projection 35. The projection 35 protrudes toward the inside of the receiving groove 14. In this embodiment, the projection 35 is formed by deforming a part of the thin plate constituting the bump foil 30. In other words, the projection 35 protrudes radially outward from the surface on which the peaks 33 are provided. The projection 35 may extend in the axial direction AD from one edge to the other edge of the foil body 31 in the axial direction AD, or it may be formed partially (for example, intermittently) along the axial direction AD. The projection 35 is connected to the peaks 33 via a connecting portion 36 provided on the bump foil 30. That is, the connecting portion 36 is located between the peak closest to the projection 35 among the multiple peaks 33 and the projection 35 (for example, the side portion 35a), and connects them.

[0030] The projection 35 includes a pair of side portions 35a, 35a. The pair of side portions 35a, 35a are spaced apart from each other in the circumferential direction CD. The pair of side portions 35a, 35a also extend from the foil body 31 toward the inside of the receiving groove 14. For example, as shown in Figure 3C, the pair of side portions 35a, 35a are parallel to each other.

[0031] The projection 35 includes a bottom portion 35b. The bottom portion 35b connects the ends of a pair of side portions 35a, 35a located on the outside of the radial direction RD. The bottom portion 35b (top portion) is formed, for example, in a planar shape perpendicular to the radial direction RD.

[0032] The protrusion 35 is positioned in a state where it can be elastically deformed within the housing groove 14. Specifically, the protrusion 35 is positioned so that it can bend due to the force from the circumferential direction CD caused by the peak 33. Therefore, when the protrusion 35 is inserted into the housing groove 14, the protrusion 35 does not undergo deformation that presses against the inner surface 14a of the housing groove 14. For example, the protrusion 35 has dimensions that allow it to be separated from the inner surface 14a of the housing groove 14. Therefore, when the protrusion 35 is housed in the housing groove 14, it is separated from at least one of the pair of side surfaces 14b, 14b in an unloaded state. In other words, in this case, the side surfaces of the protrusion 35 can be further prevented from elastically biasing the inner surface 14a by the protrusion 35. In this embodiment, it is also separated from the bottom surface 14c. That is, the top of the protrusion 35 is separated from the inner surface of the housing groove 14. Therefore, the structure is less likely to hinder elastic deformation.

[0033] Next, the operation of the bearing 5 will be explained. Figure 4 is a diagram illustrating the elastic deformation of the peak portion 33 and the protruding portion 35.

[0034] When the rotating shaft 2 is stationary, it is in contact with the top foil 20 (foil body 21) and is elastically supported by the bump foil 30 via the top foil 20. When the rotating shaft 2 is rotating at a relatively low speed, such as during startup, the rotating shaft 2 rotates while remaining in contact with a portion of the top foil 20. However, except for the portion of the top foil 20 that is in contact with the rotating shaft 2, the fluid between the rotating shaft 2 and the top foil 20 begins to flow in the same direction as the rotation of the rotating shaft 2, forming a fluid film (hereinafter referred to as a fluid film).

[0035] Until the rotational speed of the rotating shaft 2 reaches a certain value, the rotating shaft 2 is in contact with the top foil 20, obstructing the fluid flow along the circumferential direction CD. On the other hand, while the rotating shaft 2 is rotating, the fluid flow toward the contact point between the rotating shaft 2 and the top foil 20 continues. The internal pressure of the fluid film increases as the rotational speed of the rotating shaft 2 increases. When the internal pressure exceeds a certain value due to the increase in rotational speed, the rotating shaft 2 separates from the top foil 20 (levitates). In other words, the rotating shaft 2 is supported non-contact via the fluid film by the bearing 5.

[0036] The internal pressure of this fluid film acts on the top foil 20, pressing against the individual peaks 33 of the bump foil 30 that are in contact with the top foil 20. At this time, as shown in Figure 4, the peaks 33 are spread out on both sides in the circumferential direction CD. That is, the bump foil 30 elastically supports the top foil 20 through the elastic deformation of the peaks 33, and allows deformation and displacement of the top foil 20. In other words, the foil bodies 21 and 31 support the rotation shaft 2 between the rotation shaft 2 and the inner circumferential surface 11a of the insertion hole 11.

[0037] As described above, the protrusion 35 is in a state where it can be elastically deformed within the housing groove 14. Therefore, when the peak 33 is elastically deformed, the protrusion 35 also undergoes elastic deformation. Specifically, as shown in Figure 4, when the peak 33 is crushed radially outward and pushed outward on both sides of the circumferential direction CD, the connecting portions 36, 36 located on both sides of the housing groove 14 slide on the inner circumferential surface 11a so as to move closer to each other. The other connecting portions 34 also slide on the inner circumferential surface 11a toward one side or the other side in the circumferential direction.

[0038] As the connecting portions 36, 36 move closer to each other, the pair of side portions 35a, 35a also swing (tilt) so as to move closer to each other around the connection point with the bottom portion 35b. In accordance with this, the bottom portion 35b also curves. In other words, since the elastic deformation of the protrusions 35 in the housing groove 14 is permitted, the interference between the spreading forces of each peak 33 is suppressed, and the interference of these forces on the elastic deformation of the peaks 33 is mitigated. Furthermore, the interference of these forces on the sliding of the connecting portions 34, 36 on the inner circumferential surface 11a is also mitigated. Therefore, the bump foil 30 can deform relatively freely compared to the case where the protrusions 35 are not provided. As a result, friction between the bump foil 30 and the top foil 20, and friction between the bump foil 30 and the inner circumferential surface 11a are more likely to occur, which can promote the damping of unstable vibrations of the rotating shaft 2 that occur during rotation. Thus, the stability of the rotational movement of the rotating shaft can be improved.

[0039] Furthermore, in the bump foil 30, the portion where the protrusion 35 is provided has reduced rigidity against bending. Therefore, a multi-arc shape in which the top foil and bump foil are divided into multiple parts in the circumferential direction can be simulated. As a result, the spring component that destabilizes the axial support is reduced, and improved stability can be expected.

[0040] In this embodiment, unlike the conventional foil bearing described above, the bump foil is not divided, and a single bump foil 30 is located over substantially the entire inner circumferential surface 11a of the insertion hole 11. In other words, the above-mentioned effects can be obtained with a single bump foil 30, and the ease of assembly and manufacturing of the bearing is maintained.

[0041] Figures 5A to 5C show several modified examples of the protruding portion 35. As shown in Figure 5A, the pair of side portions 35a, 35a may be arranged in a flared shape from the foil body 31 toward the inside of the housing groove 14. That is, the pair of side portions 35a, 35a may be inclined with respect to the radial direction RD such that the distance between them along the circumferential direction CD increases as they move radially outward. In other words, the angle between each side portion 35a and the connecting portion 36 is set to less than 90 degrees.

[0042] In the modification shown in Fig. 5A, each side portion 35a is already inclined in a direction inclined by the movement of the connecting portion 36 along the circumferential direction CD. That is, each side portion 35a is placed in a state where it is likely to be inclined in that direction, and the entire protruding portion 35 is easily elastically deformed. Therefore, the elastic deformation of the above-described ridge portion 33 and the interference of the force against the sliding of the connecting portions 34 and 36 on the inner peripheral surface 11a can be further alleviated.

[0043] As long as the desired performance regarding the above-described interference mitigation is obtained, as shown in Fig. 5B, the pair of side portions 35a, 35a may be arranged in a tapered shape from the foil main body 31 toward the inside of the accommodation groove 14. That is, the pair of side portions 35a, 35a may be inclined with respect to the radial direction RD such that the distance between them along the circumferential direction CD becomes narrower as they go toward the outer side in the radial direction. In this case as well, elastic deformation of the protruding portion 35 is possible.

[0044] The bottom portion 35b is not limited to a planar shape. For example, as shown in Fig. 5C, the bottom portion 35b may be a curved surface. In this case, the portion located most outside in the radial direction of the bottom portion 35b is the top, and the portion closest to the bottom surface 14c of the bottom portion 35b. The curvature of each position of the curved surface in the cross section orthogonal to the axial direction AD may be constant or may change.

[0045] Figs. 6 and 7 are diagrams showing an example of the relative positional relationship between the ridge portion 33 and the accommodation groove 14. Figs. 6 and 7 show the states before and after the bump foil 30 is displaced to one side in the circumferential direction CD while the protruding portion 35 is elastically deformed in a state where the bump foil 30 is installed on the inner peripheral surface 11a. As shown in Fig. 6, the length L of the connecting portion 36 along the circumferential direction CD may have a value greater than or equal to the difference between the width W1 of the accommodation groove 14 and the width W2 of the protruding portion 35. That is, the length L, the width W1, and the width W2 may satisfy the relationship shown by the following formula (1). (W1 - W2) ≤ L ··· (1)

[0046] Hereinafter, for convenience of explanation, among the plurality of ridge portions 33, the leftmost ridge portion 33 closest to the protruding portion 35 is denoted as the ridge portion 33A. Due to the vibration of the rotating shaft 2, a load is applied to the bump foil 30 via the top foil 20. This load expands some of the plurality of ridge portions 33 in the circumferential direction CD (crushes them radially outward). Therefore, the ridge portion 33A may move entirely in the circumferential direction CD due to the elastic deformation of other neighboring ridge portions 33. The lower diagram in FIG. 6 assumes a state where the leftmost ridge portion 33A has moved to the rightmost position. As a result, the protruding portion 35 flexes, and further, a part of it contacts the inner surface (side surface 14b) of the accommodation groove 14.

[0047] On the other hand, the length L, widths W1, and W2 satisfy the relationship shown in the above formula (1). Therefore, even when the protruding portion 35 contacts the side surface 14b, the base portion 33a of the ridge portion 33A remains on the inner peripheral surface 11a. Therefore, the function of the ridge portion 33A as a spring can be maintained.

[0048] As shown in FIG. 7, the ridge portion 33A is separated from the accommodation groove 14 by a predetermined distance P along the circumferential direction CD. And this distance P may have a value Sn that is not less than 1 times and not more than n times the value S obtained by subtracting the width Lw of the ridge portion 33 along the circumferential direction CD from the length Lc of the ridge portion 33 along the bending direction. The value of n is, for example, 3.

[0049] Due to the vibration of the rotating shaft 2, a load is applied to the bump foil 30 via the top foil 20. This load expands some of the plurality of ridge portions 33 in the circumferential direction CD (crushes them radially outward). Therefore, the ridge portion 33A may move entirely in the circumferential direction due to the elastic deformation of other neighboring ridge portions 33. The lower diagram in FIG. 7 assumes a state where the leftmost ridge portion 33A has moved to the rightmost position. As a result, the protruding portion 35 flexes, and further, a part of it contacts the inner surface (side surface 14b) of the accommodation groove 14.

[0050] When one peak 33 is completely crushed radially outward, the increase in the width of the peak 33 along the circumferential direction is equal to S, which is the length Lc of the peak 33 along the curvature direction minus the width Lw of the peak 33 along the circumferential direction CD. Furthermore, the number of peaks 33 that are crushed radially outward is not limited to one. However, the amount of displacement of each peak 33 radially outward decreases as it moves away from the peak 33 that is under the greatest load. Therefore, the maximum distance traveled by the peak 33A along the circumferential direction CD is less than the value obtained by multiplying the number of crushed peaks 33 by the value S.

[0051] Considering this trend, for example, we assumed that the number of peaks 33 that are substantially completely crushed is 3, and that the minimum movement distance of the peaks 33A along the circumferential direction CD is 1 times the value S, and the maximum movement distance is 3 times the value S. By separating the peaks 33A from the housing groove 14 by this distance, even if multiple peaks 33 are deformed by the load, the base 33a of the peaks 33A remains on the inner circumferential surface 11a, and the function of the peaks 33A as a spring is maintained.

[0052] This disclosure is not limited to the embodiments described above, but includes all modifications within the meaning and scope of the claims as indicated by the claims. For example, the dimensions assumed in the numerical analysis described above are illustrative and can be modified as appropriate, as long as the effects described above are achieved.

Claims

1. A radial foil bearing comprising: a bearing housing having a through hole for a rotating shaft; a top foil provided in the through hole; and a bump foil provided between the inner circumferential surface of the through hole and the top foil, including a plurality of ridges arranged in the circumferential direction of the through hole, wherein the inner circumferential surface is provided with a groove extending along the axial direction of the through hole, and the bump foil includes a projection that protrudes toward the inside of the groove and is in a state that is elastically deformable.

2. The radial foil bearing according to claim 1, wherein the protrusion is separated from at least one of the side surfaces forming the inner surface of the groove.

3. The radial foil bearing according to claim 1, wherein the protrusion has dimensions that allow it to be separated from the inner surface of the groove.

4. The radial foil bearing according to any one of claims 1 to 3, wherein the protrusions are spaced apart from each other in the circumferential direction of the insertion hole and include a pair of side portions that flare outwards from the foil body where the peaks of the bump foil are arranged toward the inside of the groove.

5. The top of the protrusion and the groove are spaced apart from each other, the radial foil bearing according to any one of claims 1 to 3.

6. The radial foil bearing according to any one of claims 1 to 3, wherein the protruding portion is connected to the peak of the plurality of peaks closest to the protruding portion via a connecting portion, and the length of the connecting portion along the circumferential direction is greater than or equal to the difference between the width of the groove along the circumferential direction and the width of the protruding portion.

7. The radial foil bearing according to any one of claims 1 to 3, wherein, when the bump foil is installed on the inner circumferential surface, the peak among the plurality of peaks closest to the protruding portion is located a predetermined distance from the groove along the circumferential direction, and the predetermined distance is at least one and no more than three times the value obtained by subtracting the width of the peak along the circumferential direction from the length of the peak along the curvature direction.

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