Radial foil bearing and foil assembly

Abstract

This radial foil bearing (5) comprises a top foil (20) and a bump foil (30) that are mounted on an insertion hole (11) while being overlapped with each other. The inner circumferential surface of the insertion hole (11) is provided with a groove portion (12). The top foil (20) includes a foil body (21) and bent portions (22) that are bent toward the groove portion (12). The bump foil (30) includes a foil body (31) and bent portions (32) that are bent toward the groove portion (12). Each among opening portions (38) of the foil body (31) is positioned at a position corresponding to the bent portion (22) on the side on which said opening portion (38) is provided, and when viewed from the thickness direction of the top foil (20) when the same is flattened, the opening portions (38) have larger outer shapes than the bent portions (22).

Description

Radial foil bearing and foil assembly

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

[0002] A radial foil bearing is a type of journal bearing that rotatably supports a rotating shaft, and includes a foil serving as a bearing surface surrounding the outer periphery of the rotating shaft. The foil is elastically displaceable in the radial direction. When the rotating shaft rotates at a low speed, the foil elastically supports the load of the rotating shaft while in contact with the rotating shaft. On the other hand, when the rotating shaft rotates at a high speed, the rotating shaft is supported by the foil in a non-contact manner due to the wedge effect of a fluid film formed between the rotating shaft and the foil. Accordingly, radial foil bearings are generally known to have higher durability than rolling bearings, and produce less noise caused by vibration and friction (see Patent Document 1).

[0003] Japanese Unexamined Patent Publication No. 2013-217425

[0004] A radial foil bearing includes a bearing housing having an insertion hole for a rotating shaft, a top foil that functions as a bearing surface, and a bump foil that is arranged radially outward of the top foil and elastically supports the top foil. In conventional bearing structures, the bump foil is attached by welding to the inner peripheral surface of the insertion hole, or by being fitted into a groove on the inner peripheral surface using a fixing member, which has been a factor increasing the number of man-hours in the assembly of radial foil bearings.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a radial foil bearing and a foil assembly that can improve assembling performance.

[0006] A radial foil bearing according to a first aspect of the present disclosure comprises a bearing housing provided with a through hole for a rotating shaft, and a top foil and a bump foil placed in the through hole in a stacked state, wherein a groove is provided on the inner circumferential surface of the through hole, the top foil includes a first foil body and first bent portions provided on both sides of the first foil body in the circumferential direction of the through hole and bent toward the groove, the bump foil includes a second foil body and second bent portions provided on both sides of the second foil body in the circumferential direction and bent toward the groove, the first bent portion and the second bent portion on at least one of the sides in the circumferential direction are offset from each other in the axial direction, the second foil body includes an opening provided on at least one of the sides of the second foil body in the circumferential direction, the opening is located at a position corresponding to the first bent portion on the side on which the opening is provided, and has an outer shape larger than the first bent portion when viewed from the thickness direction of the top foil when unfolded in plan.

[0007] A foil assembly fitted into an insertion hole of a radial foil bearing according to a second aspect of the present disclosure includes a top foil comprising a first foil body having a predetermined width in a first direction and extending in a second direction, and a first bent portion provided on both sides of the first foil body in the second direction and bent in the second direction, and a van that overlaps the top foil, comprising a second foil body having a predetermined width in a first direction and extending in a second direction, and a second bent portion provided on both sides of the second foil body in the second direction and bent in the second direction. The top foil comprises a top foil and a bump foil, wherein the first and second bends on at least one of the two sides in the second direction are offset from each other in the first direction, the second foil body includes an opening provided on at least one of the two sides of the second foil body in the second direction, and with the top foil superimposed on the bump foil, the opening is located at a position corresponding to the first bend on the side on which the opening is provided, and the opening has an outer shape larger than the first bend when viewed from the thickness direction of the top foil.

[0008] According to this disclosure, it is possible to provide radial foil bearings and foil assemblies that can improve ease of assembly.

[0009] 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 3 is a side view of the top foil according to this embodiment. Figure 4A is a perspective view of an example of a top foil. Figure 4B is a perspective view of an example of a top foil. Figure 4C is a perspective view of an example of a top foil. Figure 5A is a side view of a bump foil according to this embodiment. Figure 5B is a side view of a partially enlarged view of the foil body of the bump foil. Figure 6A is a perspective view of an example of a bump foil. Figure 6B is a perspective view of an example of a bump foil. Figure 6C is a perspective view of an example of a bump foil. Figure 7 is a side view showing an example of a state in which the top foil is superimposed on the bump foil. Figure 8 is a diagram for explaining an example of the process of rolling the top foil and bump foil into a cylindrical shape. Figure 9A is a side view of a foil assembly according to a first modified example. Figure 9B is a side view of a foil assembly according to a second modified example. Figure 9C is a side view of the foil assembly according to the third modified example. Figure 10 is a diagram illustrating the non-intersecting region.

[0010] 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, "axial direction," "circumferential direction," "radial direction," "first direction," and "second direction" will be defined as follows.

[0011] 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.

[0012] 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 extending from an arbitrary point on the reference axis 7 on a plane perpendicular to the reference axis 7. The first and second directions are the directions referenced when the top foil 20 and bump foil 30 are unfolded in a plane. The first direction is parallel to the axial direction AD, and the second direction is intersecting the first direction, for example, the direction perpendicular to the first direction when the circumferential direction CD is unfolded in a straight line.

[0013] First, a turbomachine 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 turbomachine 1. The turbomachine 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. Hereafter, for convenience of explanation, the radial foil bearing 5 will be simply referred to as bearing 5.

[0014] 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.

[0015] Figure 2 is a front view of the bearing 5. As shown in Figure 2, the bearing 5 comprises a bearing housing 10, one top foil 20, and one bump foil 30. The bearing housing 10 accommodates at least the top foil 20 and the bump foil 30 in the through hole 11. That is, the top foil 20 and the bump foil 30 are placed in the through hole 11 overlapping each other in the radial direction RD and rolled up in the circumferential direction CD. The top foil 20 is located radially inward of the bump foil 30. The bump foil 30 is located radially outward of the top foil 20. That is, the bump foil 30 is located between the inner circumferential surface 11a of the through hole 11 and the top foil 20. The top foil 20 and the bump foil 30 constitute a foil assembly 8.

[0016] 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.

[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 into the through hole 11 with the top foil 20 and bump foil 30 housed in the through hole 11. That is, the bump foil 30, the top foil 20, and the outer surface 2a of the rotating shaft 2 are positioned in that order from the inner circumferential surface 11a of the through hole 11 toward the radial direction RD inward. 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] A groove 12 is formed on the inner circumferential surface 11a of the insertion hole 11. The groove 12 opens to 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 groove 12 accommodates the bent portions 22, 22 of the top foil 20 and the bent portions 32, 32 of the bump foil 30. The width of the groove 12 along the circumferential direction CD is set to a value that allows the bent portions 22 to be spaced apart along the circumferential direction CD, and the bent portions 32 to be spaced apart along the circumferential direction CD. The bent portions 22 and 32 in the groove 12 are positioned such that at least a portion of each overlaps with each other when viewed from the axial direction AD, but does not overlap with each other when viewed from the radial direction RD, on at least one of the two sides of the circumferential direction CD.

[0019] The top foil 20 is a single metal foil that surrounds almost the entire circumference of the rotating shaft 2. The top foil 20 is placed inside the insertion hole 11 in a cylindrical shape that surrounds the outer circumference of the rotating shaft 2. The top foil 20 includes a foil body (first foil body) 21 that faces the rotating shaft 2. The foil body 21 extends in the circumferential direction CD along the cylindrical shape of the inner circumferential surface 11a of the insertion hole 11 and functions as a bearing surface facing the rotating shaft 2.

[0020] The bump foil 30 is a single metal foil that surrounds almost the entire circumference of the rotating shaft 2. Similar to the top foil 20, the bump foil 30 is also placed in the insertion hole 11 in a cylindrical shape that surrounds the outer circumference of the rotating shaft 2. The bump foil 30 includes a foil body (second 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 cylindrical shape of the inner circumferential surface 11a of the insertion hole 11. The foil body 31 is formed in a wave-like shape that extends in the circumferential direction CD while meandering in the radial direction RD of the foil body 31, and elastically supports the top foil 20.

[0021] The top foil 20 will be described in detail. Figure 3 is a side view of the top foil 20 according to this embodiment. Figures 4A to 4C are perspective views of examples of the top foil 20. Figures 3 to 4C show the top foil 20 in a state where the foil body 21 is unfolded in a planar manner.

[0022] As described above, the top foil 20 includes a foil body 21. The foil body 21 has a substantially rectangular outer shape with its edges extending in the circumferential direction CD and the axial direction AD. That is, when the foil body 21 is unfolded in a planar manner, it has a predetermined width in the first direction and a substantially rectangular shape that extends in the second direction. The foil body 21 also has a circumferential length L1 in the circumferential direction CD that allows it to be rolled into a cylindrical shape. On the other hand, the length along the axial direction AD is arbitrary as long as the top foil 20 functions as a bearing surface, and is, for example, approximately equal to the axial direction AD of the bearing housing 10. When the top foil 20 is fitted into the insertion hole 11, the foil body 21 functions as a bearing surface for the rotating shaft 2.

[0023] The top foil 20 includes bent portions (first bent portions) 22 provided on each side in the circumferential direction CD. As shown in Figures 4A to 4C, the bent portions 22 are provided on a part of the edge portion (first edge portion) 27 that extends in the axial direction AD (first direction) on each side. In other words, the bent portion 22 has a part of the axial direction AD cut out.

[0024] For example, as shown in Figure 4A, the bent portion 22 is cut out in the center of the axial direction AD. Alternatively, as shown in Figure 4B, the bent portion 22 is cut out while leaving the center of the axial direction AD intact. Alternatively, as shown in Figure 4C, one side of the bent portion 22 in the circumferential direction CD is cut out in the center of the axial direction AD, while the other side of the bent portion 22 in the circumferential direction CD is cut out while leaving the center of the axial direction AD intact.

[0025] When the top foil 20 is fitted into the insertion hole 11, the bent portion 32 of the bump foil 30 is located in this cutout. In other words, the bent portion (first bent portion) 22 and the bent portion (second bent portion) 32 on the same side are offset from each other in the axial direction. However, the offset of both bent portions 22 and 32 in the axial direction is not necessarily limited to both sides of the circumferential direction CD, as long as the foil body 21 and the foil body 31 of the bump foil 30 can be superimposed on each other (i.e., in contact with each other) when unfolded in a planar state. In other words, it is sufficient that the bent portion (first bent portion) 22 and the bent portion (second bent portion) 32 on at least one of the two sides are offset from each other in the axial direction.

[0026] The widths of each bent portion 22 along the axial direction AD may be the same or different from each other. Therefore, when viewed from the second direction (circumferential direction CD), the bent portions 22 on both sides may overlap in at least a part, or they may not overlap.

[0027] The bent portion 22 is bent radially outward from the foil body 21 (see Figure 2). In other words, when the foil body 21 is unfolded in a planar manner, the bent portion 22 is bent in a second direction relative to the circumferential direction CD when it is unfolded linearly. The bent portion 22 is formed, for example, by bending a part of the foil that makes up the top foil 20 in the opposite direction to the direction in which the foil body 21 is rolled up. As a result, the bent portion 22 in the insertion hole bends from the foil body 21 toward the groove 12.

[0028] As shown in Figure 3, the bent portion 22 may have a return portion 25. The return portion 25 is provided as the tip of at least one of the bent portions 22 on both sides in the circumferential direction CD. The return portion 25 extends from one side to the other in the circumferential direction CD. For example, the bent portion 22 is formed in a substantially L-shape when viewed from the axial direction AD. This prevents the pin 50 (51) (see Figure 8) that is hooked onto the bent portion 22 from coming off the bent portion 22 when the top foil 20 is rolled up. When the bent portions 22 are provided on both sides in the circumferential direction CD, the top foil 20 can have a shape that is symmetrical with respect to a center line extending from the center in the circumferential direction CD in the axial direction AD (see Figures 4A and 4B). In this case, the restrictions on the orientation (position) when overlapping with the bump foil 30 are relaxed, and assembly is improved.

[0029] The bent portion 22 is located radially outward from the foil body 21. Therefore, when the rolled top foil 20 is fitted into the insertion hole 11, the bent portion 22 is housed in the groove 12. This limits excessive displacement (rotation) of the top foil 20 (foil body 21) along the circumferential direction CD.

[0030] For the sake of explanation, the bent portion 22 located on one side of the foil body 21 in the circumferential direction CD will be referred to as bent portion 22a, and the bent portion 22 located on the other side of the foil body 21 in the circumferential direction CD will be referred to as bent portion 22b. As described later, a pin 50 for rolling up the foil body 21 is attached to the bent portion 22a together with the foil body 31 (described later) (see Figure 8). Similarly, a pin 51 for rolling up the foil body 21 is attached to the bent portion 22b (see Figure 8).

[0031] The bump foil 30 will be described in detail. Figure 5A is a side view of the bump foil 30. Figure 5B is a partially enlarged side view of the foil body 31 of the bump foil 30. Figures 6A to 6C are perspective views of an example of the bump foil 30. Figures 5A to 6C show the bump foil 30 in a planar unfolded state.

[0032] As shown in Figure 5A, the bump foil 30 includes a foil body 31. Similar to the foil body 21 of the top foil 20, the foil body 31 also has a rectangular outer shape with its edges extending in the circumferential direction CD and the axial direction AD. That is, when the foil body 31 is unfolded in a planar manner, it has a predetermined width in the first direction and a substantially rectangular shape that extends in the second direction. The foil body 31 also has a circumferential length L2 that allows it to be rolled into a cylindrical shape. This length L2 is greater than or equal to the length L1 of the foil body 21 and is a value that allows the rolled-up bump foil 30 to be fitted into the insertion hole 11.

[0033] By setting the length L2 to a value longer than the length L1, for example, the area on which the bump portion 33 can be formed can be increased. Also, in the insertion hole 11, the distance between the edges 37, 37 on both sides of the foil body 31 in the circumferential direction CD is reduced, so for example, the width of the groove portion 12 along the circumferential direction CD can be narrowed. Furthermore, the length along the axial direction AD is arbitrary as long as the bump foil 30 functions as an elastic support surface for the top foil 20 as a bearing surface, and is approximately equal to the length of the axial direction AD of the bearing housing 10.

[0034] When the bump foil 30 is fitted into the insertion hole 11, the foil body 31 is positioned between the foil body 21 of the top foil 20 and the inner circumferential surface 11a of the insertion hole 11. In other words, the foil body 31 is positioned radially outward from the foil body 21.

[0035] 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. As an example of how this wave shape is formed, the foil body 31 includes bump portions (peaks) 33 and connecting portions (troughs) 34 that are alternately arranged in the circumferential direction CD.

[0036] The bump portion 33 has an arch-shaped cross-section that protrudes to one side (radially inward) in the radial direction RD, 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 two adjacent bump portions 33, 33a of 33. The base portion 33a is the part of the bump portion 33 that is located most radially outward when the bump foil 30 is rolled up. When the bump foil 30 is subjected to a radially outward load, the connecting portion 34 contacts the inner circumferential surface 11a of the through hole 11 or an auxiliary foil (not shown), supporting the bump portion 33 that is subjected to the load.

[0037] The bump foil 30 includes bent portions (second bent portions) 32 provided on each side in the circumferential direction CD. As shown in Figures 6A to 6C, the bent portions 32 are provided on a part of the edge portion (second edge portion) 37 that extends in the axial direction AD (first direction) on each side. In other words, the bent portion 32 has a part of the axial direction AD cut out.

[0038] For example, as shown in Figure 6A, the bent portion 32 is cut out, leaving the central part in the axial direction AD. Alternatively, as shown in Figure 6B, the bent portion 32 is cut out in the central part in the axial direction AD. Alternatively, as shown in Figure 6C, one side of the bent portion 32 in the circumferential direction CD is cut out in the central part in the axial direction AD, and the other side of the bent portion 32 in the circumferential direction CD is cut out, leaving the central part in the axial direction AD. In any case, when the bump foil 30 is fitted into the insertion hole 11, the bent portion 22 of the top foil 20 is located in this cut-out portion.

[0039] The widths of each bent portion 32 along the axial direction AD may be the same or different from each other. Therefore, when viewed from the second direction (circumferential direction CD), the bent portions 32 on both sides may overlap in at least a part, or they may not overlap.

[0040] When viewed from the axial direction AD, the position and shape of the bent portion 32 are similar to those of the bent portion 22 of the top foil 20. That is, for example, the bent portions 32 are provided at both ends of the foil body 31 in the circumferential direction CD and extend in the axial direction AD. The bent portions 32 are formed by folding (rolling) a part of the foil constituting the bump foil 30 in the opposite direction to the direction in which the foil body 31 is rolled.

[0041] The bent portion 32 within the insertion hole is bent from the foil body 31 toward the groove portion 12. In other words, when the bump foil 30 is laid flat, the bent portion 32 is bent toward the second direction described above. However, the direction in which the bent portion 32 bends toward the second direction does not have to coincide with the direction in which the bent portion 22 bends toward the second direction.

[0042] Similar to the bent portion 22, the bent portion 32 may also have a return portion 35 provided at its tip. The return portion 35 is provided on at least one of the bent portions 32 on either side in the circumferential direction CD. The return portion 35 extends from one side to the other in the circumferential direction CD. When bent portions 32 are provided on both sides in the circumferential direction CD, the bump foil 30 can have a shape that is symmetrical with respect to a center line extending from the center in the circumferential direction CD in the axial direction AD. In this case, the restrictions on the orientation (position) when the top foils 20 are stacked are relaxed, and assembly is improved.

[0043] For convenience of description, the bent portion 32 located on one side of the foil body 31 in the circumferential direction CD is referred to as a bent portion 32a, and the bent portion 32 located on the other side of the foil body 31 in the circumferential direction CD is referred to as a bent portion 32b. As will be described later, a pin 50 for rolling the foil body 31 together with the foil body 21 is engaged with the bent portion 32a (see FIG. 8). Similarly, a pin 51 for rolling the foil body 31 is engaged with the bent portion 32b (see FIG. 8).

[0044] As shown in FIGS. 6A to 6C, an opening (notched portion) 38 is formed in the bump foil 30 (foil body 31). The opening 38 is provided on at least one of both sides in the circumferential direction CD. In other words, the opening 38 is formed in at least one of the edge portions 37, 37 on both sides of the foil body 31 in the circumferential direction CD. The opening 38 is located at a position corresponding to the bent portion 22 of the top foil 20 on the side where the opening 38 is provided.

[0045] The opening 38 has an outer shape larger than the bent portion 22 when viewed from the thickness direction of the top foil 20 in a flatly developed state. "Having an outer shape larger than the bent portion 22 when viewed from the thickness direction of the top foil 20 in a flatly developed state" means a state in which the outer edge of the bent portion 22 projected in the planar direction does not intersect the outer edge of the bump foil 30 projected in the planar direction. For example, assume a case where the pin 50 (51) is engaged with the bent portions 22, 32 on one side in a state where the flatly developed foil body 21 and foil body 31 are flatly developed. At this time, the outer edge forming the opening 38, which is projected onto a projection plane orthogonal to the thickness direction of both foils, does not intersect the outer edge of the bent portion 22, and is located on the outer periphery (on the outer side) of the bent portion 22.

[0046] The boundary of the opening 38 may be formed by the outer edge of the bump foil 30 projected in the planar direction and the outer edge of the bent portion 22 projected in the planar direction, when the top foil 20 and the bump foil 30 that are each developed into a flat plane are stacked. That is, a line segment connecting a point on the outer edge of the bent portion 22 projected in the planar direction and the closest point on the outer edge of the bump foil 30 projected in the planar direction is drawn, and from the shape formed by tracing this line segment over the outer edge of the bent portion 22 projected in the planar direction, the region overlapping with the outer edge of the bump foil 30 projected in the planar direction may be excluded to define the boundary of the opening 38.

[0047] The opening 38 has a shape that allows the bent portion 22 to pass through the opening 38 when the top foil 20 is stacked on the bump foil 30. For example, the length L3 of the opening 38 along the axial direction AD is set to a value equal to or greater than the length of the bent portion 22 inserted through the opening 38 along the axial direction AD. In addition, the length L4 of the opening 38 along the circumferential direction CD is equal to or greater than the length of the bent portion 22 inserted through the opening 38 along the axial direction AD, and is set to a value that prevents the foil body 31 of the bump foil 30 from being deflected (not placed in an energy storage state) when the top foil 20 is stacked on the bump foil 30.

[0048] When the top foil 20 developed into a flat plane is stacked on the bump foil 30 developed into a flat plane along the thickness direction thereof, the bent portion 22 on at least one of both sides in the circumferential direction CD approaches the bent portion 32 via the opening 38. For example, when the openings 38 are formed on both sides in the circumferential direction CD, the bent portion 22 of the top foil 20 is positioned in the region where the openings 38 are formed in the foil body 31.

[0049] The position of the opening 38 is set according to the position of the bent portion 22 of the top foil 20 that is stacked on the bump foil 30. In the example shown in FIG. 6A, the openings 38 are formed at the edge portions 37, 37 on both sides of the foil body 31. Further, at each edge portion 37, the openings 38 are formed on both sides of the bent portion 32 in the axial direction AD. In this case, the top foil 20 shown in FIG. 4A is stacked on the bump foil 30.

[0050] Alternatively, as shown in Figure 6B, the opening 38 may be formed in the center of the edges 37, 37 on both sides of the foil body 31. In this case, the top foil 20 shown in Figure 4B is superimposed on the bump foil 30.

[0051] As shown in Figure 6C, the opening 38 may be formed at the center of the axial direction AD on one edge 37, and on both sides of the axial direction AD on the other edge 37. In this case, the top foil 20 shown in Figure 4C is superimposed on the bump foil 30. In all three examples above, the bent portion 22 and the bent portion 32 are offset from each other in the axial direction AD on both sides in the circumferential direction CD.

[0052] The opening 38 may be formed on only one side of the foil body 31 in the circumferential direction CD. In this case, when the top foil 20 is placed on top of the bump foil 30, a step is required to temporarily tilt the top foil 20 relative to the bump foil 30 so that the bent portion 22 on one side of the foil body 21 is hooked onto the edge portion 37 or opening 38 on one side of the foil body 31. However, the total area of ​​the opening 38 formed in the foil body 31 is reduced, and the area on which the bump portion 33 can be formed is increased.

[0053] Figure 7 is a side view showing an example of a state in which the top foil 20 is superimposed on the bump foil 30 (i.e., foil assembly 8). This figure shows the relative positions of the top foil 20 shown in Figure 4A and the bump foil 30 shown in Figure 6A, or the relative positions of the top foil 20 shown in Figure 4B and the bump foil 30 shown in Figure 6B.

[0054] Figure 8 illustrates an example of the process of rolling the top foil 20 and bump foil 30 into a cylindrical shape in order to install them into the insertion hole 11. First, the top foil 20 is placed on the flattened bump foil 30, and the two are overlapped. At this time, the bent portion 22 passes through the opening 38. Then, a pin 50 is placed on the bent portion 22a and a pin 51 is placed on the bent portion 22b to maintain the planar shape of the top foil 20 and bump foil 30.

[0055] Next, the foil body 21 and foil body 31 are clamped with a predetermined force using the pin 50 and the dummy shaft 102. The dummy shaft 102 is a cylindrical member having the same or slightly smaller diameter as the rotation axis 2. While maintaining the state in which the bent portion 22b is hooked onto the pin 51, the pin 51 is gradually moved in the direction indicated by the arrow, and the foil body 21 and foil body 31 are wrapped around the dummy shaft 102.

[0056] As described above, the top foil 20 is located radially inward of the bump foil 30. Therefore, the length of the top foil 20 (foil body 21) along the circumferential direction CD is slightly shorter than the length of the bump foil 30 (foil body 31) along the same direction. Consequently, as shown in Figure 7, when the top foil 20 is placed on top of the bump foil 30 in a planar unfolded state, the distance between the bent portion 22a and the bent portion 22b is shorter than the distance between the bent portion 32a and the bent portion 32b. Therefore, the bent portions 22a and 22b are located between the bent portions 32a and 32b. Thus, when both foils are planar unfolded, the pin 50 is hooked onto the bent portion 22a and the pin 51 is hooked onto the bent portion 22b.

[0057] From this state, as the top foil 20 and bump foil 30 are gradually wrapped around the simulated shaft 102, the difference in their radii of curvature causes the bent portion 32a to gradually approach the bent portion 22a, and the bent portion 32b to approach the bent portion 22b. When the top foil 20 and bump foil 30 are completely wrapped around the simulated shaft 102, the bent portions 22a and 32a are aligned in approximately a straight line. Similarly, the bent portions 22b and 32b are also aligned in approximately a straight line.

[0058] Next, the phase of the dummy shaft 102 and the bearing housing 10 (through hole 11) is aligned so that all the bent portions are inserted into the groove 12. Then, the dummy shaft 102, with the top foil 20 and bump foil 30 wrapped around it, is inserted into the through hole 11.

[0059] Next, pins 50 and 51 are removed to release the top foil 20 and bump foil 30 from wrapping around the dummy shaft 102. Furthermore, the dummy shaft 102 is removed from the insertion hole 11. As a result, the top foil 20 and bump foil 30 expand toward the inner circumferential surface 11a of the insertion hole 11 by their own elastic force and are fitted into the insertion hole 11.

[0060] As shown in this example, since the bump foil 30 has an opening 38 that allows the insertion of the bent portion 22, the top foil 20 and the bump foil 30 can be placed on a flat surface and overlapped regardless of the difference in length between them along the circumferential direction CD. That is, the top foil 20 can be overlapped onto the bump foil 30 without causing the bump foil 30 to bend. Furthermore, one top foil 20 can be overlapped onto one bump foil 30 and installed into the insertion hole 11 all at once. In other words, the ease of assembly of the radial foil bearing can be improved.

[0061] Figures 9A to 9C are side views of a modified foil assembly 8 according to this embodiment. As shown in these figures, the opening 38 may be formed on only one of the two sides of the foil body 31 in the circumferential direction. Also, the ends of the bent portions 22 and 32 do not need to be bent, as long as a jig such as a corresponding pin can be attached when rolling up the top foil 20 and the bump foil 30. Furthermore, the bent portions 22 and 32 may be composed of curved surfaces centered on an axis parallel to the axial direction AD.

[0062] As shown in Figure 10, when the top foil 20 and the bump foil 30 are attached to the bearing housing 10, a gap is formed between the bent portion 22a and the foil body 31 in the circumferential direction CD. More specifically, if we consider the trajectory when the bent portion 22a is moved in the circumferential direction CD along the foil body 21 toward the bent portion 22b, with the position of the bent portion 22a as the starting point and maintaining the same orientation relative to the center of the insertion hole 11, then the first non-intersecting region 41 is included in the three-dimensional region formed by this trajectory (shown by the dotted line in Figure 10). The first non-intersecting region 41 is a region that has the bent portion 22a as its end face and extends in the circumferential direction CD without intersecting the bump foil 30.

[0063] Here, H is the height difference between the bump portion (peak portion) 33 and the connecting portion (valley portion) 34 of the bump foil 30 (see Figure 5B), and R is the radius of the support surface (in this embodiment, the inner circumferential surface 11a of the insertion hole 11) that supports the connecting portion 34. Also, the connection portion between the bent portion 22a and the foil body 21 is indicated by 22c, and the connection portion between the bent portion 22b and the foil body 21 is indicated by 22d, and the angle from the connection portion 22c to the connection portion 22d via the foil body 21 in the circumferential direction CD is defined as θ. In this case, the first non-intersecting region 41 may extend over an angular range wider than (H / R)θ.

[0064] In particular, the bent portion 22a has a portion that extends along the foil body 21 toward the bent portion 22b from the position where it bends from the foil body 21 (i.e., the position of the connecting portion 22c), and when the top foil 20 is unfolded in a plane, the width of this portion is W, then the first non-intersecting region 41 may exist in an angular range wider than (H / R)θ + W / R.

[0065] As shown in Figure 10, a gap is also formed between the bent portion 22b of the top foil 20 and the foil body 31 in the circumferential direction CD. More specifically, if we consider the trajectory when the bent portion 22b is moved in the circumferential direction CD along the foil body 21 toward the bent portion 22a, with the position of the bent portion 22b as the starting point and maintaining the same orientation relative to the center of the insertion hole 11, the second non-intersecting region 42 is included in the three-dimensional region formed by this trajectory (shown by the dotted line in Figure 10). The second non-intersecting region 42 is a region that has the bent portion 22b as its end face and extends in the circumferential direction CD without intersecting the bump foil 30.

[0066] The combined region of the first non-intersecting region 41 and the second non-intersecting region 42 may extend over an angular range wider than (H / R)θ.

[0067] In particular, the bent portion 22b has a portion that extends along the foil body 21 toward the bent portion 22a from the position where it bends from the foil body 21 (i.e., the position of the connecting portion 22d), and when the top foil 20 is unfolded in a plane, the width of this portion is W', and the region formed by combining the first non-intersecting region 41 and the second non-intersecting region 42 may exist in an angular range wider than (H / R)θ + (W + W') / R.

[0068] 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.

[0069] 5 Radial foil bearing 8 Foil assembly 10 Bearing housing 11 Through hole 11a Inner circumferential surface 12 Groove 20 Top foil 21 Foil body 22, 22a, 22b Bent section (first bend) 25 Return section 30 Bump foil 31 Foil body 32, 32a, 32b Bent section (second bend) 33 Bump section 33a Base 34 Connecting section 35 Return section 38 Opening

Claims

1. A radial foil bearing comprising a bearing housing provided with a through hole for a rotating shaft, and a top foil and a bump foil placed in the through hole in a stacked state, wherein a groove is provided on the inner circumferential surface of the through hole, the top foil includes a first foil body and first bent portions provided on both sides of the first foil body in the circumferential direction of the through hole and bent toward the groove, the bump foil includes a second foil body and second bent portions provided on both sides of the second foil body in the circumferential direction and bent toward the groove, the first bent portion and the second bent portion on at least one of the sides in the circumferential direction are offset from each other in the axial direction, the second foil body includes an opening provided on at least one of the sides of the second foil body in the circumferential direction, the opening is located at a position corresponding to the first bent portion on the side on which the opening is provided, and has an outer shape larger than the first bent portion when viewed from the thickness direction of the top foil when unfolded in plan.

2. The radial foil bearing according to claim 1, wherein each of the first and second bends on one of the sides in the circumferential direction includes a return portion extending toward the other first and second bends on the other side in the circumferential direction.

3. The radial foil bearing according to claim 2, wherein the return portion is provided on each of the first and second bent portions on both sides in the circumferential direction.

4. The radial foil bearing according to claim 1, wherein the openings are provided on each of the two sides of the second foil body in the circumferential direction.

5. The radial foil bearing according to any one of claims 1 to 4, wherein the second foil body has a longer circumferential length than the first foil body.

6. A foil assembly to be fitted into the insertion hole of a radial foil bearing, comprising: a top foil having a predetermined width in a first direction and extending in a second direction, and a first bent portion provided on both sides of the first foil body in the second direction and bent in the second direction; a bump foil having a predetermined width in a first direction and extending in a second direction, and a second bent portion provided on both sides of the second foil body in the second direction and bent in the second direction, which is superimposed on the top foil, wherein the first bent portion and the second bent portion on at least one of the sides in the second direction are offset from each other in the first direction; the second foil body includes an opening provided on at least one of the sides of the second foil body in the second direction; and with the top foil superimposed on the bump foil, the opening is located at a position corresponding to the first bent portion on the side on which the opening is provided. A foil assembly in which the opening has an outer shape larger than the first bent portion when viewed from the thickness direction of the top foil.

7. The foil assembly according to claim 6, wherein each of the first and second bends on one of the sides in the second direction has a return portion extending toward the other first and second bends on the other side in the second direction.

8. The foil assembly according to claim 7, wherein the return portion is provided on each of the first and second bent portions on both sides in the second direction.

9. The foil assembly according to claim 6, wherein the openings are provided on each of the two sides of the second foil body in the second direction.

10. The foil assembly according to any one of claims 6 to 9, wherein the second foil body has a length in the second direction that is longer than the first foil body.

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