Radial foil bearing

Abstract

A radial foil bearing (5) comprises a housing (10) that has an insertion hole (11) for a shaft (2), and a top foil (20) that is provided inside the insertion hole (11). On the inner surface (11a) of the insertion hole (11), a groove section (12) that extends in the axial direction of the insertion hole (11) is provided. The top foil (20) is provided with a body section (21) that functions as a bearing surface for the shaft (2), and a first end section (22) and a second end section (23) that are positioned respectively on the forward side and the backward side of the body section (21) in the rotation direction of the shaft (2). The second end section (23) has a hook shape, and a portion thereof is accommodated in the groove section (12).

Description

Radial Foil Bearings

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

[0002] A radial foil bearing is a type of journal bearing that rotatably supports a rotating shaft and has a foil as a bearing surface that surrounds the outer periphery of the rotating shaft. The foil is elastically displaceable in the radial direction RD, and when the rotating shaft rotates at a low speed, it contacts the rotating shaft and elastically supports its load. On the other hand, when the rotating shaft rotates at a high speed, the wedge effect of the fluid film formed between the rotating shaft and the foil supports the rotating shaft without contacting the foil. Therefore, radial foil bearings are generally known to have higher durability and lower noise due to vibration and friction than rolling bearings.

[0003] As a related art, Patent Document 1 discloses a radial foil bearing that includes a top foil having a bearing surface and a bump foil that elastically supports the top foil.

[0004] JP 2023-051044 A

[0005] The foils mentioned above are very thin and easily bendable. Furthermore, the diameter of the shaft insertion hole is relatively small, measuring only a few tens of millimeters. For these reasons, the foils are manually attached to the insertion holes. This means that radial foil bearings are difficult to assemble, making efficient mass production difficult.

[0006] The present disclosure has been made in consideration of the above-mentioned circumstances, and aims to provide a radial foil bearing that can be easily assembled.

[0007] A radial foil bearing according to an aspect of the present disclosure comprises a housing having a shaft insertion hole and a top foil provided within the insertion hole, the inner surface of which is provided with a groove extending in the axial direction of the insertion hole, the top foil including a main body portion which functions as a bearing surface for the shaft, and a first end portion and a second end portion located respectively on the front and rear sides of the main body portion in the rotational direction of the shaft, the second end portion having a hook shape and a portion of which is accommodated in the groove portion.

[0008] In a cross section perpendicular to the axial direction, a path length from a bent portion between the main body and the first end to a portion of the first end that is located farthest from the main body may be set to a value equal to or less than a length of a region of an inner surface of the groove that is located forward of the first end in the rotation direction and that is contactable with the first end.

[0009] The second end may include an area capable of surface contact with the inner surface of the groove or the first end in a circumferential direction of the insertion hole, and the area may be located at a position on the surface of the second end closest to the bend between the main body and the second end.

[0010] The radial foil bearing may include a fixing member provided on each side of the groove in the axial direction and configured to restrict movement of the top foil along the axial direction. The fixing member may have a part on a rear side in the rotation direction as viewed from the axial direction that is cut out as a notch, and the second end may include an opposing part that faces the notch in the circumferential direction of the insertion hole.

[0011] According to the present disclosure, it is possible to provide a radial foil bearing that can improve assembly efficiency.

[0012] FIG. 1 is a side view of an example of a turbo machine 1. FIG. 2 is a front view of a radial foil bearing according to the present embodiment. FIG. 3 is a side view of a top foil according to the present embodiment. FIG. 4A is a plan view of an example of a top foil. FIG. 4B is a plan view of another example of a top foil. FIG. 5 is a cross-sectional view of an end of the top foil and its surroundings. FIG. 6A is a cross-sectional view for explaining displacement of the end when the top foil is subjected to torque. FIG. 6B is a cross-sectional view for explaining displacement of the end when the top foil is subjected to torque. FIG. 7A is a side view of an example of a back foil. FIG. 7B is a partially enlarged side view of a main body of the back foil. FIG. 8A is a view for explaining an example of a process for rolling the top foil and the back foil into a cylindrical shape. FIG. 8B is a view for explaining an example of a process for rolling the top foil and the back foil into a cylindrical shape. FIG. 9 is a view of a fixing member according to the present embodiment as viewed from the axial direction. FIG. 10 is a perspective view showing a modified example of the top foil when the fixing member is applied.

[0013] Hereinafter, several embodiments of the present disclosure will be described. Note that common parts in each drawing are denoted by the same reference numerals, and duplicated explanations will be omitted. For convenience of explanation, the axial direction Z, circumferential direction CD, radial direction RD, and rotational direction TD are defined as follows:

[0014] The axial direction Z is the extension direction of a reference axis 7 (see FIG. 1 ). The reference axis 7 corresponds to the central axes of the shaft 2, the thrust bearing 4, and the radial foil bearing 5. The reference axis 7 also corresponds to the central axis of an insertion hole 11 provided in the radial foil bearing 5.

[0015] The circumferential direction CD is the direction of extension of a circle on an imaginary plane 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 an arbitrary point on the reference axis 7. The rotational direction TD is the direction of rotation TD of the shaft 2, and is the direction from one side of the circumferential direction CD to the other side.

[0016] The foil according to this embodiment also defines a longitudinal direction LD and a transverse direction SD. The longitudinal direction LD and the transverse direction SD correspond to the circumferential direction CD and the axial direction Z, respectively, when the foil according to this embodiment (such as the top foil 20) is rolled around the reference axis 7. The normal direction ND is a direction perpendicular to an imaginary plane including the longitudinal direction LD and the transverse direction SD.

[0017] First, a turbomachine 1 to which a radial foil bearing 5 according to this embodiment is applied will be described. Fig. 1 is a side view of an example of the turbomachine 1. The turbomachine 1 includes a shaft 2, an impeller 3, a thrust bearing 4, a pair of radial foil bearings 5, 5, and a housing 6 that accommodates these. Note that Fig. 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 a bearing 5.

[0018] The bearing 5 rotatably supports the shaft 2. The impeller 3 is attached to the end of the shaft 2. The impeller 3 is housed in the housing 6 with a tip clearance formed between it and the housing 6. The thrust bearing 4 includes a thrust collar 4a and a pair of bearing pads 4b. The thrust collar 4a is a circular plate having a predetermined thickness in the axial direction Z and is fixed to the shaft 2. The thrust bearing 4 is sandwiched between the pair of bearing pads 4b. This limits the range of movement of the thrust bearing 4 along the axial direction Z.

[0019] Figure 2 is a front view of the bearing 5. As shown in Figure 2, the bearing 5 includes a housing 10, a top foil 20, and a back foil 30. The top foil 20 is rolled into a cylindrical shape and is located inside the insertion hole 11 of the housing 10. Similarly, the back foil 30 is also rolled into a cylindrical shape and is located inside the insertion hole 11. The back foil 30 is located between the top foil 20 and the inner surface 11a of the insertion hole 11. The back foil 30 is also called a bump foil.

[0020] The housing 10 has an insertion hole 11 for the shaft 2. The insertion hole 11 extends in the axial direction Z and passes through the housing 10. A top foil 20 and a back foil 30 are provided in the insertion hole 11. The shaft 2 is inserted into the insertion hole 11 with the top foil 20 and the back foil 30 attached to the insertion hole 11. The housing 10 shown in FIG. 2 has a cylindrical outer shape. However, the outer shape of the housing 10 is arbitrary as long as the insertion hole 11 is formed.

[0021] A groove 12 is formed on the inner surface 11a of the insertion hole 11. The groove 12 opens to the inner surface 11a and extends from one end face to the other end face of the housing 10 in the axial direction Z. Parts of the ends 22, 23 of the top foil 20 and parts of the ends 32, 32 of the back foil 30 are accommodated in the groove 12.

[0022] The width of the groove 12 along the circumferential direction CD is set to a value that allows the ends 22, 23 to be aligned in the circumferential direction CD at intervals, and the ends 32, 32 to be aligned in the circumferential direction CD at intervals. The depth of the groove 12 along the radial direction RD is set to a value within a range that does not interfere with the formation of a fluid film by the main body 21 when the ends 23 abut against the bottom surface 12 c of the groove 12.

[0023] As long as these set conditions are satisfied, the cross-sectional shape of the groove 12 perpendicular to the axial direction Z may be any shape, for example, a rectangle as shown in Fig. 2. In this case, the inner surface of the groove 12 has a pair of side surfaces 12a and 12b facing each other in the circumferential direction CD and a bottom surface 12c connecting the side surfaces 12a and 12b. The side surface 12a is located on one side in the circumferential direction CD (the front side in the rotational direction TD), and the side surface 12b is located on the other side in the circumferential direction CD (the rear side in the rotational direction TD).

[0024] The top foil 20 is a sheet of metal foil (thin metal plate) that extends in the circumferential direction CD and surrounds almost the entire circumference of the shaft 2, and has a thickness that allows elastic deformation (flexibility).

[0025] The top foil 20 includes a main body portion 21 that faces the shaft 2. The main body portion 21 is a flat foil without any irregularities, and is rolled into a cylindrical shape when the top foil 20 is attached to the insertion hole 11. The rolled main body portion 21 faces the shaft 2 and functions as a bearing surface for the shaft 2.

[0026] Like the top foil 20, the back foil 30 is a single metal foil (thin metal plate) that extends in the circumferential direction CD and surrounds almost the entire circumference of the shaft 2, and has a thickness that allows it to be elastically deformed (flexible).

[0027] The back foil 30 includes a main body portion 31 that surrounds the outer periphery of the rolled main body portion 21. The main body portion 31 is a foil formed in a corrugated shape, and is rolled into a cylindrical shape when the top foil 20 is fitted into the insertion hole 11. As described above, the main body portion 31 has a corrugated cross-sectional shape that extends in the longitudinal direction LD (circumferential direction CD) while meandering in the normal direction ND (radial direction RD) of the main body portion 31. This corrugated cross-sectional shape elastically supports the top foil 20.

[0028] An intermediate foil (not shown) may be provided between the back foil 30 and the top foil 20. Also, an auxiliary foil (see FIG. 8A) 40 may be provided between the inner surface 11a of the insertion hole 11 and the back foil 30. Like the top foil 20, both the intermediate foil and the auxiliary foil are metal foils (thin plates) without irregularities, and have a thickness that allows elastic deformation (flexibility).

[0029] The top foil 20 will be described in detail. Fig. 3 is a side view of the top foil 20 according to this embodiment. Fig. 4A is a plan view of an example of the top foil 20. Fig. 4B is a plan view of another example of the top foil 20.

[0030] As described above, the top foil 20 includes a main body portion 21 that functions as a bearing surface for the shaft 2. Before installation, the main body portion 21 is flat in both the longitudinal direction LD and the lateral direction SD. The main body portion 21 has a substantially rectangular outer shape and a length in the longitudinal direction LD (circumferential direction CD) that allows it to be rolled into a cylindrical shape. Furthermore, the length along the lateral direction SD (axial direction Z) is substantially equal to the depth of the insertion hole 11.

[0031] As shown in Fig. 3, the top foil 20 has a pair of end portions 22, 23 located on both sides in the longitudinal direction LD. The end portion 22, which serves as a first end portion, is located on one side in the longitudinal direction LD. The end portion 23, which serves as a second end portion, is located on the other side in the longitudinal direction LD. As shown in Fig. 2, when the top foil 20 is rolled up and attached to the insertion hole 11, the end portion (first end portion) 22 is located on the front side of the main body portion 21 in the rotation direction TD of the shaft 2. On the other hand, the end portion (second end portion) 23 is located on the rear side of the main body portion 21 in the rotation direction TD of the shaft 2.

[0032] As shown in Figures 4A and 4B, the end portion 22 and the end portion 23 each have a portion cut out in the short-side direction SD (axial direction Z). For example, as shown in Figure 4A, the end portion 22 (23) has a central portion cut out in the short-side direction SD (axial direction Z). Alternatively, as shown in Figure 4B, the end portion 22 (23) is cut out leaving only the central portion in the short-side direction SD (axial direction Z). When the top foil 20 is attached to the insertion hole 11, the end portion 32 of the back foil 30 is positioned in this cut-out portion.

[0033] When the main body portion 21 is rolled into a cylindrical shape, the end portions 22 and 23 are located radially outward from the main body portion 21. Therefore, when the top foil 20 is attached to the insertion hole 11, the end portions 22 and 23 are housed in the groove portions 12. This restricts excessive positional deviation (rotation) of the top foil 20 (main body portion 21) along the circumferential direction CD.

[0034] First, the end portion 23 will be described in detail. Figure 5 is a cross-sectional view of the end portion 23 and its surroundings according to this embodiment. These cross-sectional views are perpendicular to the axial direction Z. However, for ease of explanation, the inner surface 11a of the insertion hole 11 and the main body portion 21 of the top foil 20 are shown as flattened views. The cross-sectional shape of the groove portion 12 is rectangular.

[0035] The end portion 23 is bent relative to the main body portion 21 in the direction opposite to the direction in which the main body portion 21 is rolled (see FIG. 2), thereby forming a hook shape. The hook shape forms an inner space 25 (see FIG. 3), into which a pin 50 (see FIG. 8A) used when rolling the main body portion 21 can be inserted.

[0036] For example, as shown in Figure 5, the end portion 23 is folded twice in the direction opposite to the direction in which the main body portion 21 is rolled. In this case, the end portion 23 has a first portion 23a and a second portion 23b. The first portion 23a extends substantially radially outward from a bent portion 23d between the main body portion 21 and the end portion 23. The second portion 23b extends rearward in the rotational direction TD from the first portion 23a.

[0037] The curvature of the bent portion 23e between the first portion 23a and the second portion 23b is arbitrary. The curvature of the bent portion 23e may be large, as shown by the solid line, or small, as shown by the dotted line. The end portion 23 may be bent three or more times to form the hook shape. For example, if the end portion 23 is bent three times, the end portion 23 will have a third portion 23c extending from the second portion 23b, as shown by the dotted line in FIG. 5 .

[0038] The length of the first portion 23a along the radial direction RD may be set to a value that enables the second portion 23b to slide on the bottom surface 12c of the groove portion 12. In this case, contact of the second portion 23b with the bottom surface 12c prevents the main body portion 21 in the vicinity of the bent portion 23d from bending excessively outward in the radial direction, thereby preventing a deterioration in the bearing performance of the main body portion 21.

[0039] The end 23 includes a region 23f that can come into surface contact with the end 22 in the circumferential direction CD. In this embodiment, the region 23f is a flat surface that is located closest to the bent portion 23d on the surface of the end 23. The region 23f is set in the first portion 23a at a position closest to the bent portion 23d. In the example shown in FIG. 5, the region 23f is set in the first portion 23a.

[0040] The top foil 20 receives torque in the rotational direction TD due to the fluid flow caused by the rotation of the shaft 2. At this time, the end portion 23 may shift forward in the rotational direction and be supported by the end portion 22. If the torque increases further in this state, the end portion 23 may deform excessively, increasing the likelihood that the main body portion 21 near the end portion 23 may bend in the radial direction. In other words, the bearing performance of the main body portion 21 is likely to deteriorate. Therefore, in this embodiment, the end portion 23 is in surface contact with the end portion 22 in the region 23f. This distributes the torque transmitted to the end portion 22 and suppresses stress concentration that deforms the end portion 23. Therefore, local excessive bending of the main body portion 21 near the bend portion 23d can be suppressed, and deterioration of the bearing performance of the main body portion 21 can be suppressed.

[0041] Furthermore, because torque is applied to the end 23 from the main body, a new moment is generated around the contact point between the end 23 and the end 22. This moment also contributes to the deformation of the end 23. However, the region 23f is the closest to the bent portion 23d in the first portion 23a. Therefore, the moment generated by the torque can be suppressed, and excessive deformation of the end 23 can be suppressed. From this perspective, excessive local bending of the main body 21 near the bent portion 23d can be suppressed, and a decrease in the bearing performance of the main body 21 can be suppressed.

[0042] Next, the end portion 22 will be described in detail. Figures 6A and 6B are cross-sectional views illustrating the displacement of the end portion 22 when the top foil 20 is subjected to torque. These cross-sectional views are perpendicular to the axial direction Z. The left view of Figure 6A shows the state before the end portion 22 is displaced, and the right view of Figure 6A shows the state after the end portion 22 is displaced. This is also true for Figure 6B. However, for ease of explanation, the inner surface 11a of the insertion hole 11 and the main body portion 21 of the top foil 20 are developed in a plane. The cross-sectional shape of the groove portion 12 is rectangular.

[0043] The end portion 22 is bent relative to the main body portion 21 in a direction opposite to the direction in which the main body portion 21 is rolled (see FIG. 2). For example, as shown in FIG. 6A, the end portion 22 is bent only once. That is, the end portion 22 has a first portion 22a that extends linearly radially outward from the bent portion 22d.

[0044] Alternatively, the end portion 22 may be bent multiple times. For example, as shown in FIG. 6B , the end portion 22 is bent three times. The end portion 22 shown in FIG. 6B has a first portion 22a, a second portion 22b, and a third portion 22c. The second portion 22b extends forward in the rotational direction TD from the first portion 22a. The third portion 22c extends radially inward from the second portion 22b. In either case, the angle formed between the first portion 22a and the main body portion 21 may be 90 degrees. That is, this angle is not limited to 90 degrees.

[0045] Here, the path length Lc is defined. The path length Lc is the length of the path of the end portion 22 from the bent portion 22d to the portion 22g in a cross section perpendicular to the axial direction Z. The portion 22g is located at the position of the end portion 22 farthest from the main body portion 21. When there are multiple portions 22g, the maximum path length among these portions 22g is used.

[0046] In this embodiment, the path length Lc is set to a value equal to or less than the length Ls of a region 12d on the inner surface of the groove portion 12 in a cross section perpendicular to the axial direction Z. The region 12d is a part of the inner surface of the groove portion 12 that is located forward of the end portion 22 in the rotational direction and that can come into contact with the end portion 22. In the example shown in Figures 6A and 6B, at least a part of the side surface 12a of the groove portion 12 corresponds to the region 12d.

[0047] In the example shown in FIG. 6A , the outermost edge 22e of the end 22 (first portion 22a) corresponds to the aforementioned portion 22g. The path length Lc is the length of the path from the bent portion 22d to the outermost edge 22e. In the example shown in FIG. 6B , the bent portion 22f between the second portion 22b and the third portion 22c corresponds to the aforementioned portion 22g. In this case, the path length Lc is the length of the path from the bent portion 22d to the bent portion 22f, via the second portion 22b and the third portion 22c. In both examples, the path length Lc is set to a value equal to or less than the length Ls of the region 12d.

[0048] As described above, when the shaft 2 rotates, a torque in the rotation direction TD due to the rotation of the shaft 2 is generated in the top foil 20. When this torque causes the end 23 to come into contact with the end 22 and reach a state where it is supported by the end 22, the end 22 is subjected to pressure from the end 23 due to the torque.

[0049] In the example shown in FIG. 6A , the end portion 22 (first portion 22 a) receives this pressure and moves forward in the rotational direction, coming into surface contact with region 12 d on the side surface 12 a of the groove portion 12. The length of the first portion 22 a along the radial direction RD satisfies the above-described condition. Therefore, the first portion 22 a remains in surface contact with region 12 d. In other words, deformation of the end portion 22 that excessively bends at least the main body portion 21 near the bent portion 22 d in the radial direction RD can be avoided. Therefore, local excessive bending of the main body portion 21 near the bent portion 22 d can be suppressed, and a deterioration in the bearing performance of the main body portion 21 can be suppressed.

[0050] This effect can also be achieved in the example shown in FIG. 6B . That is, the end portion 22 receives pressure from the radial forward direction and moves forward in the direction of rotation, with the third portion 22c coming into surface contact with the region 12d. If the pressure further increases and the end portion 22 deforms, as shown in the left diagram of FIG. 6B , the first portion 22a and the second portion 22b move forward in the direction of rotation while the third portion 22c is in contact with the region 12d. At this time, the second portion 22b bends to widen the angle it forms with the first portion 22a. As a result, the bent portion 22f moves radially outward. However, even with this deformation, the bent portion 22f does not strike the corner 12e between the side surface 12a and the bottom surface 12c while the first portion 22a and the second portion 22b move forward in the direction of rotation. In other words, it is possible to avoid deformation of the end portion 22 that would excessively bend the main body portion 21 near the bend portion 22d in the radial direction RD, and to suppress the resulting deterioration in the bearing performance of the main body portion 21.

[0051] As described above, as long as the condition for the path length Lc is satisfied, the number of times that the end portion 22 is bent is not limited to 1. However, naturally, the fewer the number of times that the end portion 22 is bent, the fewer the manufacturing steps, and the simpler the configuration of the top foil 20 becomes.

[0052] Also, the number of times that the end portion 22 is bent may be zero. In other words, in the top foil 20 rolled into a cylindrical shape, the end portion 23 of the top foil 20 located forward in the direction of rotation may also serve as the end portion of the main body portion 21. Therefore, in this case, the end portion 23 is not located inside the groove portion 12. When the end portion 23 moves forward in the direction of rotation due to the torque described above, the end portion 23 comes into contact with the side surface 12 a of the groove portion 12.

[0053] The back foil 30 will now be described in detail. Fig. 7A is a side view of an example of the back foil 30. Fig. 7B is a side view in which the main body portion 31 of the back foil 30 is partially enlarged.

[0054] 7A , the back foil 30 includes a main body portion 31. Like the main body portion 21 of the top foil 20, the main body portion 31 also has a rectangular outer shape and has a length in the longitudinal direction LD (circumferential direction CD) that allows it to be rolled into a cylindrical shape. In addition, the length in the short direction SD (axial direction Z) is approximately equal to the length in the axial direction Z of the insertion hole 11. When the back foil 30 is attached to the insertion hole 11, the main body portion 31 is located between the main body portion 21 of the top foil 20 and the inner surface 11 a of the insertion hole 11.

[0055] The main body portion 31 is formed in a wave shape that extends in the longitudinal direction LD (circumferential direction CD) while meandering in the normal direction ND (radial direction RD) of the main body portion 31. As an example of the wave shape, the main body portion 31 includes bump portions 33 and connecting portions 34 that are alternately arranged in the longitudinal direction LD (circumferential direction CD).

[0056] The bump portion 33 has an arch-shaped cross section that protrudes to one side in the normal direction ND (radially inward), and elastically deforms in response to the load of the shaft 2 applied 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 bump portions 33, 33. The base portions 33a are the portions of the bump portions 33 that are located most radially outward when the back foil 30 is rolled. When the back foil 30 is subjected to a radially outward load, the connecting portion 34 comes into contact with the inner surface 11a of the insertion hole 11 or the auxiliary foil 40 (see FIG. 8A ) and supports the bump portion 33 that receives the load.

[0057] The back foil 30 includes a pair of end portions 32, 32. The position and shape of the end portions 32 are similar to those of the end portion 23 of the top foil 20. That is, the end portions 32 are provided at both ends of the main body portion 31 in the longitudinal direction LD (circumferential direction CD) and extend in the axial direction Z. The end portions 32 are bent in the direction opposite to the direction in which the main body portion 31 is rolled, forming a hook shape. As with the end portions 23, a pin 50 (see FIG. 8A ) used when rolling the main body portion 31 can also be inserted into an inner space 35 formed by the hook shape of the end portions 32. In this embodiment, the hook shapes at both ends of the main body portion 31 are each bent two or more times in the direction opposite to the direction in which the main body portion 31 is rolled.

[0058] 8A and 8B are diagrams illustrating an example of a process for rolling the top foil 20 and the back foil 30 into a cylindrical shape. In this example, an auxiliary foil 40 is also rolled up together with the top foil 20 and the back foil 30. The auxiliary foil 40 is a metal foil including a main body portion 41 having a shape similar to that of the main body portion 21 and an end portion 42 having a shape similar to that of the end portion 32. The pin 50 shown in FIG. 8B is operated by, for example, an assembly robot (not shown) such as a picking robot.

[0059] 8A , three foils, namely, the auxiliary foil 40, the back foil 30, and the top foil 20, are stacked in this order and placed on, for example, a flat stage 52. Next, the pseudo shaft 102 is placed near the center of the top foil 20. The pseudo shaft 102 is a cylindrical member having a diameter equal to or slightly smaller than that of the shaft 2.

[0060] Next, as shown in FIG. 8B , the end portions 22 (23), 32, and 42 on both sides of each foil are aligned in a substantially straight line. While maintaining this state, the pin 50 is inserted into the end portions 22 (23), 32, and 42 of each foil from the axial direction Z. Then, the pin 50 inserted into the end portions 22 (23), 32, and 42 is moved to a position P corresponding to the groove portion 12. This operation lifts up the end portions 22, 32, and 42, and the main portions 21, 31, and 41 are wrapped around the outer peripheral surface 102a of the pseudo shaft 102. Furthermore, while maintaining this state, the pseudo shaft 102 is inserted into the insertion hole 11 of the housing 10. Thereafter, the pin 50 is removed from the end portions 22, 32, 42 while preventing all of the foils 20, 30, 40 from slipping out of the insertion holes 11, and the attachment of the foils 20, 30, 40 to the insertion holes 11 is completed.

[0061] In this embodiment, the shape of the end 42 of the auxiliary foil 40 is the same as the shape of the end 32, but the shape of the end 42 may be different from the shape of the end 32. Furthermore, the shape of the end 42 in this embodiment is a shape that is bent three times in the direction opposite to the direction in which the main body 41 is rolled, but it may also be a shape that is bent twice, or a shape that is bent any other number of times.

[0062] Next, the operation of the bearing 5 will be described. When the shaft 2 is stationary, the shaft 2 is in contact with the top foil 20 (main body portion 21) and is elastically supported by the back foil 30 via the top foil 20. When the shaft 2 is rotating at a relatively low speed, such as during startup, the shaft 2 rotates while remaining in contact with part of the top foil 20. However, except for the part of the top foil 20 that is in contact with the shaft 2, the fluid between the shaft 2 and the top foil 20 begins to flow in the same direction as the rotation direction TD of the shaft 2, forming a fluid film (hereinafter referred to as a fluid film).

[0063] Until the rotation speed of the shaft 2 reaches a certain value, the shaft 2 comes into contact with the top foil 20 and blocks the flow of fluid along the circumferential direction CD. On the other hand, while the shaft 2 is rotating, the flow of fluid toward the contact point between the shaft 2 and the top foil 20 continues. The film pressure of the fluid film increases as the rotation speed of the shaft 2 increases. When the film pressure exceeds a certain value due to the increase in rotation speed, the shaft 2 separates from the top foil 20 (floats). In other words, the shaft 2 is supported by the bearing 5 without contact via the fluid film.

[0064] The film pressure of this fluid film acts on the top foil 20 and presses the individual bump portions 33 of the back foil 30 that are in contact with the top foil 20. At this time, the bump portions 33 are pushed outward in both directions in the circumferential direction CD. That is, the back foil 30 elastically supports the top foil 20 due to the elastic deformation of the bump portions 33, and allows the top foil 20 to deform and displace.

[0065] The top foil 20 according to this embodiment is rolled into a cylindrical shape immediately before being attached to the insertion hole 11. In other words, by alternately stacking predetermined spacers (not shown) and the main body 21, multiple top foils 20 can be placed flat. Furthermore, the top foil 20 can be rolled into a cylindrical shape and then attached to the insertion hole of the housing simply by using a simple jig such as a pin and a pseudo shaft. This process is highly reproducible, and therefore, a series of automatic operations, such as bending the top foil 20 and attaching it to the insertion hole 11, can be smoothly performed by an assembly robot. In other words, the assembly of the bearing 5 can be improved.

[0066] Fig. 9 is a view of the fixing member 60 according to this embodiment as viewed from the axial direction Z. Fig. 10 is a perspective view showing a modified example of the top foil 20 when the fixing member 60 is applied. As shown in Fig. 9, the fixing member 60 may be attached to the housing 10. The fixing member 60 restricts the top foil 20 from moving in the axial direction Z within the insertion hole 11.

[0067] 9 , the fixing member 60 is a small, approximately rectangular piece that covers a portion of the groove 12 from the axial direction Z. The fixing members 60 are provided on both sides of the groove 12 in the axial direction Z. Accordingly, a mounting groove 13 for the fixing member is formed in the housing 10. The width of the fixing member 60 in the circumferential direction CD is set to a value less than the width of the mounting groove 13 in the same direction.

[0068] The mounting groove 13 extends from a predetermined position radially outward from the groove portion 12 (for example, the outer peripheral surface of the housing) to the groove portion 12. The width of the mounting groove 13 along the same direction is equal to or greater than the width of the groove portion 12 along the same direction. The depth of the mounting groove 13 along the axial direction Z is equal to or greater than the thickness of the fixing member 60. A screw hole (not shown) for a screw (not shown) that penetrates the fixing member 60 is formed in the bottom surface 13c of the mounting groove 13.

[0069] The fixing member 60 has a base 61 placed on the bottom surface 13c, and a protrusion 62 protruding radially inward from the base 61 and covering a part of the groove 12. The base 61 has a through hole 63 formed therein, through which the above-mentioned screw is inserted. The through hole 63 may be a countersunk hole as shown in FIG. 9 .

[0070] When the fixing member 60 is attached to the attachment groove 13, the protrusion 62 is located at a position where it can come into contact with at least the end 23 of the end 22 and the end 23. Therefore, when the top foil 20 having the shape shown in FIG. 4A moves in the axial direction Z, at least the end 23 of the end 22 and the end 23 comes into contact with the protrusion 62. This restricts movement of the top foil 20 in the axial direction Z, and prevents the top foil 20 from being exposed from the insertion hole 11.

[0071] 10 , the protrusion 62 of the fixing member 60 may have a portion on the rear side in the rotational direction TD cut out as a notch 64 when viewed from the axial direction Z. In this case, the end portion 23 includes a facing portion 23g that faces the notch 64 in the circumferential direction CD. The facing portion 23g serves as a part (expansion portion) of the first portion 23a of the end portion 23, and extends radially outward from the bent portion 23d in the space radially below the notch 64 and also extends along the axial direction Z.

[0072] When the above-mentioned torque is generated in the top foil 20, the opposing portion 23g comes into contact with the surface 64a of the cutout portion 64, restricting further forward movement of the end portion 23 in the rotation direction and preventing the end portion 23 from accidentally coming into contact with the end portion 22. Furthermore, by restricting the movement of the end portion 23, deformation of the main body portion 21 near the end portion 22 is suppressed, and deterioration of bearing performance is suppressed.

[0073] 9, the notch 64 may be formed in a portion of the protrusion 62 on the forward side in the rotational direction. In this case, the end 22 is also provided with a facing portion (not shown) similar to the facing portion 23g, which restricts further movement of the end 22 backward in the rotational direction.

[0074] 4B , the above-described opposing portion may be provided at the end portion 23 of the back foil 30. In this case, the fixing member 60 limits the swing range of the back foil 30 along the rotation direction.

[0075] The present disclosure is not limited to the above-described embodiments, but is defined by the claims and includes all modifications within the meaning and scope of the claims. For example, the dimensions assumed in the above numerical analysis are merely illustrative and may be modified as appropriate as long as the effects described above are obtained.

Claims

1. A radial foil bearing comprising: a housing having a through hole for a shaft; and a top foil provided within the through hole, wherein a groove extending in the axial direction of the through hole is provided on the inner surface of the through hole, the top foil includes a main body that functions as a bearing surface for the shaft, and a first end and a second end located respectively on the front and rear sides of the main body in the rotational direction of the shaft, and the second end has a hook shape, and a portion of it is received in the groove.

2. A radial foil bearing as described in claim 1, wherein the first end is bent so that a portion of it is accommodated in the groove, and in a cross section perpendicular to the axial direction, the path length from the bent portion between the main body and the first end to the part of the first end that is located farthest from the main body is set to a value less than the length of an area of ​​the inner surface of the groove that is located forward of the first end in the direction of rotation and that can come into contact with the first end.

3. A radial foil bearing as set forth in claim 1 or 2, wherein the second end includes an area capable of surface contact with the inner surface of the groove or the first end in the circumferential direction of the insertion hole, and the area is located at a position on the surface of the second end closest to the bend between the main body and the second end.

4. The radial foil bearing according to claim 1, further comprising fixing members provided on both sides of the groove in the axial direction, for restricting movement of the top foil along the axial direction.

5. A radial foil bearing according to claim 4, wherein a portion of the fixed member on the rear side in the rotational direction when viewed from the axial direction is cut out as a notch, and the second end includes an opposing portion that faces the notch in the circumferential direction of the insertion hole.

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