Thrust foil bearing

Abstract

To exert a desired load capacity.SOLUTION: A thrust foil bearing comprises: a base plate having an insertion hole inserted with a rotating shaft, and a support face; a plurality of top foil pieces supported by the support face; a step member placed on the support face, formed separately from the base plate, and constituted of a plurality of step faces; and a plurality of bump foil pieces including trough parts arranged between the top foil pieces and the base plate, arranged at the plurality of step support parts, and contacting with the step faces, respectively.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] Patent Document 1 discloses a thrust foil bearing used as a bearing for a high-speed rotating body. The thrust foil bearing disclosed in Patent Document 1 is disposed facing a thrust collar provided on a rotating shaft. The bearing surface of the thrust foil bearing is composed of a flexible foil, which is a thin metal plate. The thrust foil bearing has a foil structure for flexibly supporting the bearing surface. The rotating shaft may undergo unintended movement due to vibration and impact. For example, the thrust collar may move in the axial direction due to the unintended movement of the rotating shaft. Furthermore, the thrust collar may tilt due to the unintended movement of the rotating shaft. The thrust foil bearing can absorb the movement of the thrust collar caused by the movement of the rotating shaft.

[0003] The thrust foil bearing includes a plurality of top foil pieces and a plurality of bump foil pieces. The top foil pieces are supported by the bump foil pieces. When the thrust collar rotates, a lubricating fluid is introduced between the top foil pieces and the thrust collar. The lubricating fluid forms a wedge-shaped fluid lubricating film between the top foil pieces and the thrust collar. As a result of the formation of the fluid lubricating film, the load capacity of the thrust foil bearing is exerted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent No. 6065917 [Patent Document 2] JP 2006-57652 A [Patent Document 3] JP 2004-270904 A [Patent Document 4] JP 2009-299748 A Summary of the Invention [Problem to be solved by the invention]

[0005] The load capacity of a thrust foil bearing is affected by the shape of the fluid lubrication film. Therefore, in order to achieve a desired load capacity, it is necessary to generate a desired fluid lubrication film. The desired shape of the fluid lubrication film is affected by the shape of the gap between the top foil piece and the thrust collar. The wedge-shaped gap is formed by an inclined surface provided on the base plate.

[0006] For example, the inclined surface may be formed by cutting or the like. The inclined surface formed by cutting may not have an intended configuration due to processing errors or the like. If the inclined surface does not have an intended configuration, the wedge-shaped gap may not have an intended configuration either. As a result, the load capacity of the thrust foil bearing may not be as desired.

[0007] The present disclosure describes a thrust foil bearing capable of providing desired load capabilities. [Means for solving the problem]

[0008] The thrust foil bearing of the present disclosure comprises a base plate having a support surface and an insertion hole through which a rotating shaft is inserted, a plurality of top foil pieces supported on the support surface, a step member placed on the support surface and formed separately from the base plate and including a plurality of step support portions constituted by a plurality of step surfaces, and a plurality of bump foil pieces arranged between the top foil piece and the base plate, arranged on each of the plurality of step support portions, and including a contact portion in contact with the step surface. Effect of the Invention

[0009] The thrust foil bearings of the present disclosure are capable of providing desired load capabilities. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a side view showing an example of a turbomachine to which a thrust foil bearing according to the present disclosure is applied. [Diagram 2] FIG. 2 is a cross-sectional view showing a thrust foil bearing of the present disclosure. [Diagram 3] FIG. 3 is a perspective view showing a part of the thrust foil bearing of the present disclosure in an exploded state. [Figure 4] Figure 4(a) is a plan view of a top foil piece, and Figure 4(b) is a plan view of a bump foil piece. [Diagram 5] FIG. 5 is an enlarged cross-sectional view showing a main portion of the thrust foil bearing of the present disclosure. [Figure 6] FIG. 6 is a perspective view of a step member provided in the thrust foil bearing of the present disclosure. [Figure 7] FIG. 7 is an enlarged perspective view of a stepped support portion. [Figure 8] FIG. 8 is a perspective view of a first shim that constitutes the step member. [Figure 9] FIG. 9 is a perspective view of a second shim that constitutes the step member. [Figure 10] FIG. 10 is a perspective view of a third shim that constitutes the step member. [Figure 11] FIG. 11 is an enlarged cross-sectional view showing a main part of the thrust foil bearing of the first modification. [Figure 12] FIG. 12 is a diagram for explaining the function and effect of the thrust foil bearing of the first modification. [Figure 13] FIG. 13 is an enlarged cross-sectional view showing a main part of a thrust foil bearing according to the second modification. [Figure 14] FIG. 14 is a perspective view showing a main part of a thrust foil bearing according to the third modification. [Figure 15] FIG. 15 is an enlarged cross-sectional view showing a main part of a thrust foil bearing according to the fourth modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The thrust foil bearing of the present disclosure comprises a base plate having a support surface and an insertion hole through which a rotating shaft is inserted, a plurality of top foil pieces supported on the support surface, a step member placed on the support surface and formed separately from the base plate and including a plurality of step support portions constituted by a plurality of step surfaces, and a plurality of bump foil pieces arranged between the top foil piece and the base plate, arranged on each of the plurality of step support portions, and including a contact portion in contact with the step surface.

[0012] The thrust foil bearing has a step member that is separate from the base plate. This step member makes it easier to reduce deviations in step dimensions from the design values. As a result, the reduction in load capacity caused by deviations in step dimensions is suppressed. Therefore, the thrust foil bearing can exhibit the desired load capacity.

[0013] The plurality of stepped support portions of the thrust foil bearing may be provided so as to surround the insertion hole. According to this configuration, the plurality of stepped support portions can be provided around the insertion hole.

[0014] The first plate member of the thrust foil bearing may include a first clamped portion including an arc-shaped outer peripheral edge, and a first support region provided between the first clamped portion and the insertion hole when viewed from the axial direction of the insertion hole. The second plate member may include a second clamped portion including an arc-shaped outer peripheral edge, and a second support region provided between the second clamped portion and the insertion hole when viewed from the axial direction of the insertion hole. The stepped support portion may be formed by stacking the first support region and the second support region. This configuration also allows the desired load capacity to be exhibited.

[0015] The shape of the second support region of the thrust foil bearing may be different from the shape of the first support region when viewed from the axial direction of the insertion hole. With this configuration, a virtual inclined surface that supports the bump foil piece can be formed.

[0016] The first support region of the thrust foil bearing may include an inner circumferential edge extending to surround the insertion hole. The inner circumferential edge may include a first inner circumferential edge portion and a second inner circumferential edge portion. The distance from the axis of the insertion hole to the first inner circumferential edge portion may be different from the distance from the axis of the insertion hole to the second inner circumferential edge portion. With this configuration as well, the desired load capacity can be exhibited.

[0017] The clamped portion of the thrust foil bearing may have a through hole through which a fastening member for fastening the stepped member to the base plate is inserted. With this configuration, the stepped member can be fastened to the base plate.

[0018] The number of through holes in the thrust foil bearing may be different from the number of the stepped support parts. With this configuration, the stepped member can be fixed to the base plate.

[0019] Hereinafter, a detailed description will be given of an embodiment of a thrust foil bearing according to the present disclosure with reference to the accompanying drawings. Note that the same elements shown in the drawings are given the same reference numerals. Duplicate descriptions of the same elements will be omitted.

[0020] 1 is a side view showing an example of a turbomachine to which the thrust foil bearing of the present disclosure is applied. An impeller 2 is attached to an end of a rotating shaft 1. A tip clearance 6 exists between the impeller 2 and a housing 5. The rotating shaft 1 is supported by thrust foil bearings 3A and 3B and a radial foil bearing 7.

[0021] Radial foil bearing 7 supports rotating shaft 1 in a direction (radial direction) perpendicular to axis A. Thrust foil bearings 3A, 3B support rotating shaft 1 in a direction (thrust direction) along axis A. A circular thrust collar 4 is attached to rotating shaft 1. Thrust foil bearings 3A, 3B sandwich thrust collar 4 between them.

[0022] As shown in Fig. 2, thrust foil bearing 3A is disposed between thrust collar 4 and impeller 2. Thrust foil bearing 3B is disposed between thrust collar 4 and radial foil bearing 7. The configuration of thrust foil bearing 3A is the same as the configuration of thrust foil bearing 3B. Each of thrust foil bearings 3A and 3B has a plurality of top foil pieces 11, a plurality of bump foil pieces 21, a base plate 30, and a step member 50.

[0023] A cylindrical bearing spacer 40 is disposed between the base plate 30 of the thrust foil bearing 3A and the base plate 30 of the thrust foil bearing 3B. The base plate 30 of the thrust foil bearing 3A is connected to the thrust foil bearing 3B by a fastening bolt 41. A through hole 42 for inserting the fastening bolt 41 is formed in the outer periphery of the base plate 30. The tip of the fastening bolt 41 is screwed into the screw hole 31 of the housing 5. The base plate 30 of the thrust foil bearing 3A is in contact with the housing 5 by being fastened by the fastening bolt 41.

[0024] Hereinafter, the thrust foil bearing 3A will be described in detail with reference to Figures 3 to 10. The configuration of the thrust foil bearing 3B is the same as the configuration of the thrust foil bearing 3A, so a detailed description of the thrust foil bearing 3B will be omitted.

[0025] In the following description, the positional relationship of each member will be described based on the insertion hole 30a provided in the base plate 30. For example, the "axial direction" is the direction in which the axis A of the insertion hole 30a extends. The "axial direction" is the direction in which the rotating shaft 1 is inserted. The "axial direction" is the direction in which the rotating shaft 1 extends. The "radial direction" is the direction along the diameter of the insertion hole 30a. The "radial direction" is the direction intersecting with the axis A when viewed in the direction of the axis A of the insertion hole 30a. The "circumferential direction" is the direction along the inner circumferential surface of the insertion hole 30a. The "circumferential direction" is the direction around the axis A of the insertion hole 30a. In the above description, the "axial direction", "radial direction", and "circumferential direction" are defined based on the axis A of the insertion hole 30a. The "axial direction", "radial direction", and "circumferential direction" may be defined based on the axis of the rotating shaft 1 instead of the axis A of the insertion hole 30a.

[0026] As shown in FIG. 3, the base plate 30 constitutes the outermost part of the thrust foil bearing 3A in the axial direction. The outermost part of the thrust foil bearing 3A means the side farther from the thrust collar 4. The base plate 30 is an annular plate member. The base plate 30 is a metal plate. As an example, the thickness of the base plate 30 is about several mm. The outer shape of the base plate 30 may be different from a circular plate. The outer shape of the base plate 30 may be rectangular. The base plate 30 has an insertion hole 30a, a support surface 30b, and a back surface 30c.

[0027] The insertion hole 30a is a through hole. The insertion hole 30a extends from the support surface 30b to the back surface 30c. The insertion hole 30a does not necessarily have to be strictly cylindrical. The rotating shaft 1 (see FIG. 2) is disposed in the insertion hole 30a. The inner diameter of the insertion hole 30a is larger than the outer diameter of the rotating shaft 1.

[0028] The support surface 30b is a flat surface. The support surface 30b extends in a direction perpendicular to the axial direction of the insertion hole 30a. The support surface 30b faces the thrust collar 4. A plurality of top foil pieces 11, a plurality of bump foil pieces 21, and a step member 50 are arranged around the insertion hole 30a formed in the support surface 30b. The step member 50 is attached to the support surface 30b. A portion of the top foil piece 11 is attached to the support surface 30b. The top foil piece 11 is supported by the bump foil piece 21. The top foil piece 11 itself may function as a member that receives a load even if an intervening object is present. The bump foil piece 21 is supported by the base plate 30 and the step member 50. The top foil piece 11 is supported by the base plate 30 and the step member 50 via the bump foil piece 21.

[0029] The number of top foil pieces 11 is seven. A plurality of top foil pieces 11 may be collectively referred to as top foils. The number of bump foil pieces 21 is also seven. A plurality of bump foil pieces 21 may be collectively referred to as bump foils. The top foil pieces 11 and the bump foil pieces 21 are arranged at equal intervals along the circumferential direction. The number of top foil pieces 11 is not limited to seven. The number of top foil pieces 11 may be less than seven. The number of top foil pieces 11 may be more than seven. The number of bump foil pieces 21 is not limited to seven. The number of bump foil pieces 21 may be less than seven. The number of bump foil pieces 21 may be more than seven.

[0030] The top foil piece 11 has an inclined portion 12 and an attachment portion 13. The inclined portion 12 inclines upward from the upstream side to the downstream side in the rotation direction R of the rotating shaft 1 along the circumferential direction. The inclined portion 12 of the top foil piece 11 faces the thrust collar 4. Inclined upward means that the inclined portion 12 gradually moves away from the base plate 30 from the upstream side to the downstream side in the rotation direction R. Inclined upward means that the inclined portion 12 approaches the thrust collar 4 from the upstream side to the downstream side in the rotation direction R. The attachment portion 13 is connected to the inclined portion 12 via a bent portion 14. The attachment portion 13 is fixed to the base plate 30.

[0031] As shown in FIG. 4(a), the inclined portion 12 is fan-shaped in plan view. The apex of the fan-shaped inclined portion 12 is cut out. The inner periphery of the inclined portion 12 is an arc. The outer periphery of the inclined portion 12 is also an arc. The inclined portion 12 is substantially trapezoidal in plan view. The inclined portion 12 has an inclined portion front end 12a, an inclined portion rear end 12b, an inclined portion inner peripheral end 12c, and an inclined portion outer peripheral end 12d. The inclined portion front end 12a and the inclined portion rear end 12b extend in the radial direction. For example, the downstream side may be defined as the inclined portion rear end 12b and the upstream side may be defined as the inclined portion front end 12a, based on the rotation direction R of the rotating shaft 1. The rotation direction R of the rotating shaft 1 is assumed to be counterclockwise. The definitions of the inclined portion front end 12a and the inclined portion rear end 12b are merely examples. Therefore, the inclined portion front end 12a and the inclined portion rear end 12b may be defined according to a different definition from that described above. The rotation direction R of the rotating shaft 1 may also be clockwise.

[0032] The inclined portion rear end 12b is a free end and is not fixed.

[0033] As shown in Fig. 5, the inclined portion front end 12a is connected to the mounting portion 13 via a bent portion 14. The bent portion 14 includes a first bend 14a and a second bend 14b. The first bend 14a is a portion where the mounting portion 13 is connected to the bent portion 14. The second bend 14b is a portion where the bent portion 14 is connected to the inclined portion 12. Both the first bend 14a and the second bend 14b have obtuse angles.

[0034] The inclined portion 12 is supported by the bump foil piece 21. The inclined portion 12 is inclined with respect to the support surface 30b. For example, the inclination of the inclined portion 12 is based on an initial inclination angle determined by the first bend 14a and the second bend 14b. As a result, the inclined portion 12 gradually moves away from the base plate 30 along the rotation direction R of the rotating shaft 1. The initial inclination angle is the angle that the inclined portion 12 of the top foil piece 11 makes with respect to the support surface 30b of the base plate 30 when the load is zero.

[0035] The radial length of the mounting portion 13 is the same as the length of the bent portion 14. The shape of the mounting portion 13 is a strip extending in the radial direction. The length of the mounting portion 13 may be different from the length of the bent portion 14. The mounting portion 13 is fixed to the base plate 30 by a fixing element 11f. For example, spot welding may be used to fix the mounting portion 13 to the base plate 30. A screw fastening structure may be used to fix the mounting portion 13 to the base plate 30.

[0036] The bump foil pieces 21 are arranged in the circumferential direction. The bump foil pieces 21 are disposed between the top foil piece 11 and the base plate 30. The bump foil pieces 21 are disposed on each of a plurality of step support portions 51 described below. The shape of the bump foil pieces 21 is fan-shaped in a plan view. The size of the bump foil pieces 21 is smaller than the size of the inclined portion 12 of the top foil piece 11. Therefore, the bump foil pieces 21 are covered by the top foil piece 11. The shape of the bump foil pieces 21 is the same as the shape of the top foil piece 11.

[0037] As shown in FIG. 4(b), the shape of the bump foil piece 21 is a sector in plan view. The apex of the sector-shaped bump foil piece 21 is cut out. The inner periphery of the bump foil piece 21 is an arc. The outer periphery of the bump foil piece 21 is also an arc. The bump foil piece 21 has a bump foil front end 21a, a bump foil rear end 21b, a bump foil inner peripheral end 21c, a bump foil outer peripheral end 21d, and a bump foil base end 21e. The bump foil front end 21a and the bump foil rear end 21b extend in the radial direction. For example, with respect to the rotation direction R of the rotating shaft 1, the upstream side may be defined as the bump foil front end 21a. Furthermore, the downstream side may be defined as the bump foil rear end 21b. The bump foil base end 21e is formed between the bump foil front end 21a and the bump foil outer circumferential end 21d.

[0038] The bump foil piece 21 has a support portion 22. The support portion 22 elastically supports the inclined portion 12 of the top foil piece 11. The support portion 22 is a corrugated foil. The support portion 22 has three peak portions 22r1, 22r2, and 22r3, and four valley portions 22s1, 22s2, 22s3, and 22s4 (contact portions). In the following description, when it is not necessary to distinguish between the peak portions 22r1, 22r2, and 22r3, they will be simply referred to as peak portion 22r. When it is not necessary to distinguish between the valley portions 22s1, 22s2, 22s3, and 22s4, they will be simply referred to as valley portion 22s.

[0039] The support portion 22 may employ, for example, a spring foil as described in JP 2006-57652 A and JP 2004-270904 A. The support portion 22 may employ a bump foil as described in JP 2009-299748 A. The spring foils as described in JP 2006-57652 A and JP 2004-270904 A are used for radial bearings. Similarly, the bump foil as described in JP 2009-299748 A is also used for radial bearings. A foil as a circular plate is obtained by developing a foil used for a radial bearing into a planar shape. This foil can be used as the support portion 22 of the thrust foil bearing 3A.

[0040] The bump foil base end 21e extends from the inner circumference toward the outer circumference. If the bump foil front end 21a is virtually extended, it will intersect with the axis A. Unlike the bump foil front end 21a, the bump foil base end 21e does not intersect with the axis A even if it is virtually extended. The direction in which the bump foil base end 21e extends is parallel to the direction in which the peaks 22r and valleys 22s extend. The peaks 22r and valleys 22s are alternately arranged along a direction perpendicular to the direction in which the bump foil base end 21e extends.

[0041] As shown in FIG. 5, the valley portion 22s includes a flat surface. The multiple valley portions 22s1, 22s2, 22s3, and 22s4 are arranged at equal intervals. None of the valley portions 22s contacts the top foil piece 11. The valley portion 22s1 contacts the base plate 30. The valley portion 22s1 includes the bump foil base end 21e. The valley portion 22s1 (first portion) is not fixed to the base plate 30. The bump foil base end 21e is a free end. The bump foil base end 21e is not fixed. The bump foil front end 21a is also a free end. The bump foil front end 21a is also not fixed. When a load acts on the bump foil piece 21, the bump foil base end 21e and the bump foil front end 21a can move.

[0042] The valleys 22s2, 22s3, and 22s4 (second portion) contact the step member 50. For example, the valley 22s4 is fixed to the step member 50 by a fixing element 21f. The valley 22s4 includes the bump foil rear end 21b. For example, spot welding may be used to fix the bump foil rear end 21b to the step member 50. A screw fastening structure may be used to fix the bump foil rear end 21b to the step member 50. The welding position is the mounting position of the bump foil piece 21 in the circumferential direction. Therefore, based on the rotation direction R, the mounting position of the bump foil piece 21 is the downstream end. On the other hand, based on the rotation direction R, the mounting position of the top foil piece 11 is the upstream end. The mounting position of the bump foil piece 21 is opposite to the position of the top foil piece 11 based on the rotation direction R.

[0043] The peak portion 22r is an arch-shaped portion. The height of the peak portion 22r is constant. The multiple peak portions 22r1, 22r2, and 22r3 are arranged at equal intervals. The peak portion 22r contacts the inclined portion 12 of the top foil piece 11. The peak portion 22r does not contact the base plate 30. The peak portion 22r does not contact the step support portion 51 either. The peak portion 22r1 connects the valley portions 22s1 and 22s2. The peak portion 22r2 connects the valley portions 22s2 and 22s3. The peak portion 22r3 connects the valley portions 22s3 and 22s4.

[0044] <Step material> As shown in FIG. 6, the step member 50 is separate from the base plate 30. The step member 50 is placed on the support surface 30b. "Separate" means that the step member 50 and the base plate 30 are not formed by processing such as cutting out from one metal block. The step member 50 is prepared by processing separate from the base plate 30. The base plate 30 is also prepared by processing separate from the step member 50. The individually prepared base plate 30 and step member 50 undergo an assembly process to integrate them to form the thrust foil bearings 1A and 1B. For example, when the base plate 30 and step member 50 are integrated by a fastening member such as a bolt, the step member 50 can be removed from the base plate 30 by releasing the fastening. Between the base plate 30 and the step member 50, there is a boundary line where the base plate 30 and the step member 50 are in contact with each other and which separates the base plate 30 and the step member 50.

[0045] The step member 50 has a plurality of step support parts 51 and a clamped part 53. The step support parts 51 support the bump foil piece 21. The number of step support parts 51 that the step member 50 has is seven. The number of step support parts 51 may be more than seven. The number of step support parts 51 may be less than seven. The step support parts 51 are arranged at approximately equal intervals in the circumferential direction. The shape of the clamped part 53 is a ring in a plan view. The outer periphery of the clamped part 53 is arc-shaped. The shape of the step member 50 shown in FIG. 6 is a ring in a plan view. The clamped part 53 has an outer periphery 53e that is a continuous arc. In this specification, the term "arc" includes a closed arc as shown in FIG. 6. The closed arc includes, for example, an arc with a central angle of 360 degrees. The term "arc" includes a portion of a ring, as will be described in Modification 3 below. A portion of a ring includes, for example, an arc with a central angle of less than 360 degrees. A clamped portion that includes an outer periphery and has a central angle of less than 360 degrees is exemplified as Modification 3. The arc does not necessarily have to be a perfect circle or a part of a perfect circle. A plurality of step support portions 51 are provided on the inside of clamped portion 53. The plurality of step support portions 51 are integral with clamped portion 53.

[0046] The first through hole 55 is formed in the clamped portion 53. The first through hole 55 is for the bearing spacer 40. The number of the first through holes 55 is, for example, four. The arrangement of the first through holes 55 along the circumferential direction may have a central angle of approximately 90 degrees. As shown in FIG. 2, when the step member 50 is arranged on the base plate 30, the support surface 30b of the base plate 30 is exposed from the first through hole 55. The first through hole 55 overlaps with the through hole 42 of the base plate 30. The bearing spacer 40 is inserted into the first through hole 55. The inner diameter of the first through hole 55 is the same as the outer diameter of the bearing spacer 40. Alternatively, the inner diameter of the first through hole 55 is slightly larger than the outer diameter of the bearing spacer 40. The first end surface 40a of the bearing spacer 40 arranged in the first through hole 55 abuts against the base plate 30 of the thrust foil bearing 3A. The second end surface 40b of the bearing spacer 40 abuts against the base plate 30 of the thrust foil bearing 3B.

[0047] The clamped portion 53 further has a second through hole 56 formed therein. The second through hole 56 is for the fastening bolt 43. The number of the second through holes 56 is, for example, two. The arrangement of the second through holes 56 along the circumferential direction may have a central angle of approximately 180 degrees. The diameter of a second reference circle that is the reference for the arrangement of the second through holes 56 may be smaller than the diameter of a first reference circle that is the reference for the arrangement of the first through holes 55. The second through hole 56 may be formed on the inside of the first through hole 55. As shown in FIG. 5, the fastening bolt 43 fixes the step member 50 to the base plate 30. The tip portion of the fastening bolt 43 is screwed into the screw hole 32 of the base plate 30. Therefore, the second through hole 56 overlaps with the screw hole 32 of the base plate 30. The inner diameter of the second through hole 56 may be smaller than the inner diameter of the first through hole 55.

[0048] As shown in Fig. 3, the step member 50 has a first shim 60 (plate member), a second shim 70 (plate member), and a third shim 80 (plate member). The first shim 60, the second shim 70, and the third shim 80 are metal plate members. The first shim 60, the second shim, and the third shim 80 each have a constant thickness. The first shim 60, the second shim, and the third shim 80 are each plate-shaped. The first shim 60, the second shim 70, and the third shim 80 are stacked in their thickness direction.

[0049] The number of shims constituting the step member 50 is the same as the number of peak portions 22r of the bump foil piece 21. In the configuration shown in FIG. 5, the number of peak portions 22r is three. Therefore, the number of shims is also three. The number of shims constituting the step member 50 is one less than the number of valley portions 22s. In the configuration shown in FIG. 5, the number of valley portions 22s is four. Therefore, the number of shims is three, which is one less than four.

[0050] <First Sim> As shown in FIGS. 7 and 8, the first shim 60 (first plate member) includes a plurality of first stepped support regions 61 (first support regions) and a first clamped portion 63.

[0051] The first step support region 61, together with a second step support region 71 and a third step support region 81 described below, constitute the step support part 51. The first step support region 61 has a first step support front end face 61a, a first step support rear end face 61b, and a first step inner peripheral region 61c.

[0052] The first shim 60 has a first shim back surface 60b and a first shim main surface 60f. The first shim back surface 60b contacts the base plate 30. The first shim main surface 60f contacts the second shim 70. The entire surface of the first shim back surface 60b contacts the support surface 30b of the base plate 30. The first shim main surface 60f has a portion that contacts the second shim 70 and a portion that does not contact the second shim 70. The portion that does not contact the second shim 70 is included in the first step support region 61. The portion of the first step support region 61 that does not contact the second shim 70 is a first step surface 61s. The first step surface 61s is connected to the first step support front end surface 61a. The first step surface 61s supports the valley portion 22s2 of the bump foil piece 21 (see FIG. 5).

[0053] The shapes of the first step support regions 61 are the same. The first step support regions 61 are arranged in the circumferential direction along the first held portion 63. The planar shape of the first held portion 63 is a ring. The first step support regions 61 are arranged inside the first held portion 63. A groove 67 extending from the outer diameter side to the inner diameter side is formed between two first step support regions 61 adjacent in the circumferential direction. The groove 67 has a reduced portion 67a and an expanded portion 67b. The circumferential width of the reduced portion 67a decreases from the outer diameter side to the inner diameter side. In the reduced portion 67a, the interval between the adjacent first step support regions 61 becomes narrower as the axis A is approached. The circumferential width of the expanded portion 67b increases from the outer diameter side to the inner diameter side. In the expanded portion 67b, the interval between the adjacent first step support regions 61 increases as the axis A is approached.

[0054] The first step support region 61 includes a first cutout 61p. The first cutout 61p is formed by cutting out a part of the first step inner circumferential region 61c. The first cutout 61p is formed on the upstream side of the first step inner circumferential region 61c along the rotation direction R. The first cutout 61p is formed on the first step support front end face 61a side.

[0055] 7, the first step support region 61 has a step inner peripheral edge 61d. The step inner peripheral edge 61d includes a first inner peripheral edge portion 61d1 having an arc shape and a second inner peripheral edge portion 61d2 having an arc shape. The first inner peripheral edge portion 61d1 is connected to the first step support front end face 61a. The second inner peripheral edge portion 61d2 is connected to the first step support rear end face 61b. When the rotation direction R is used as a reference, the first inner peripheral edge portion 61d1 is located upstream of the second inner peripheral edge portion 61d2.

[0056] The distance from the axis A to the first inner circumferential edge portion 61d1 is defined as a first radius. The distance from the axis A to the second inner circumferential edge portion 61d2 is defined as a second radius. The first radius of the first inner circumferential edge portion 61d1 is greater than the second radius of the second inner circumferential edge portion 61d2. The first inner circumferential edge portion 61d1 is farther from the axis A than the second inner circumferential edge portion 61d2.

[0057] The first inner peripheral edge portion 61d1 is connected to the second inner peripheral edge portion 61d2 by a connecting edge portion 61d3. The connecting edge portion 61d3 may extend along the radial direction. The connecting edge portion 61d3 may be inclined with respect to the radial direction. The connecting edge portion 61d3 is inclined with respect to the radial direction. The first cutout 61p is a portion surrounded by the connecting edge portion 61d3 and the first inner peripheral edge portion 61d1.

[0058] The second inner peripheral edge portion 61d2 is located inside the first inner peripheral edge portion 61d1. The first stepped inner peripheral region 61c is a region surrounded by an imaginary line extending the first inner peripheral edge portion 61d1 in the radial direction, the second inner peripheral edge portion 61d2, the connecting edge portion 61d3, and the first stepped support rear end surface 61b. The first stepped inner peripheral region 61c includes an inner peripheral surface overlapping region 61c1 and an inner peripheral surface exposed region 61c2 (see FIG. 8). The inner peripheral surface overlapping region 61c1 overlaps with the second shim 70 and the third shim 80 described later. At the boundary between the inner peripheral surface overlapping region 61c1 and the inner peripheral surface exposed region 61c2, a step equivalent to two shims is generated, which is formed by the end faces of the second shim 70 and the third shim 80.

[0059] The inner circumferential surface exposed region 61c2 does not overlap with the second shim 70. The inner circumferential surface exposed region 61c2 is exposed. The inner circumferential surface exposed region 61c2 includes the connecting edge portion 61d3. The inner circumferential surface overlapping region 61c1 includes the first step support rear end surface 61b. The position of the inner circumferential surface exposed region 61c2 is upstream of the inner circumferential surface overlapping region 61c1. The area of ​​the inner circumferential surface exposed region 61c2 is larger than the area of ​​the inner circumferential surface overlapping region 61c1.

[0060] As shown in FIG. 8, the first clamped portion 63 constitutes the clamped portion 53 together with the second clamped portion 73 and the third clamped portion 83 described later. The first clamped portion 63 has a first clamped outer peripheral surface 63a and a first clamped inner peripheral surface 63b. The first clamped outer peripheral surface 63a is a part that constitutes the outer peripheral edge 53e. The planar shape of the first clamped outer peripheral surface 63a is a closed arc (ring). The first clamped portion 63 has a first hole portion 63s that constitutes the first through hole 55 and a second hole portion 63t that constitutes the second through hole 56.

[0061] <Second Sim> As shown in FIGS. 7 and 9, the second shim 70 (second plate member) includes a plurality of second stepped support regions 71 (second support regions) and a second clamped portion 73.

[0062] The second step support region 71 has a second step support front end face 71a, a second step support rear end face 71b, and a second step inner peripheral region 71c.

[0063] The second shim 70 has a second shim back surface 70b in contact with the first shim main surface 60f and a second shim main surface 70f in contact with the third shim 80. The second shim back surface 70b is in contact with the first shim main surface 60f. The second shim main surface 70f is in contact with the third shim 80. The entire surface of the second shim back surface 70b is in contact with the first shim main surface 60f. The second shim main surface 70f has a portion in contact with the third shim 80 and a portion not in contact with the third shim 80. The portion not in contact with the third shim 80 is included in the second step support region 71. The portion of the second step support region 71 that is not in contact with the third shim 80 is the second step surface 71s. The second step surface 71s supports the valley portion 22s3 of the bump foil piece 21 (see FIG. 5).

[0064] The second step surface 71s includes a second step support front end surface 71a. The circumferential length from the second step support front end surface 71a to the second step support rear end surface 71b is shorter than the circumferential length from the first step support front end surface 61a to the first step support rear end surface 61b. The first step surface 61s is formed by this difference in circumferential length. Due to the difference in circumferential length, the second step support front end surface 71a is shifted by an offset amount P (see FIG. 7) from the first step support front end surface 61a. The difference in circumferential length corresponds to the offset amount P. The offset amount P may be the same as the pitch of the valley portions 22s of the bump foil piece 21.

[0065] The second step support region 71 includes a second cutout 71p. The second cutout 71p is formed by cutting out a portion of the second step inner circumferential region 71c. The second cutout 71p is formed on the upstream side of the second step inner circumferential region 71c along the rotation direction R. The second cutout 71p is formed on the second step support front end face 71a side.

[0066] The second stepped support region 71 has a stepped inner peripheral edge 71d, similar to the first stepped support region 61. The stepped inner peripheral edge 71d includes a first inner peripheral edge portion 71d1, a second inner peripheral edge portion 71d2, and a connecting edge portion 71d3. The shape of the first inner peripheral edge portion 71d1 is a circular arc. The shape of the second inner peripheral edge portion 71d2 is also a circular arc. The connecting edge portion 71d3 connects the first inner peripheral edge portion 71d1 and the second inner peripheral edge portion 71d2. The radius of the first inner peripheral edge portion 71d1 of the second stepped support region 71 is the same as the radius of the first inner peripheral edge portion 61d1 of the first stepped support region 61. The radius of the second inner peripheral edge portion 71d2 of the second stepped support region 71 is also the same as the radius of the second inner peripheral edge portion 61d2 of the first stepped support region 61. The circumferential length of the second inner circumferential edge 71d2 of the second stepped support region 71 is shorter than the circumferential length of the second inner circumferential edge 61d2 of the first stepped support region 61. As a result, an inner circumferential surface exposed region 61c2 is formed.

[0067] A corner 71e is formed at a portion where the first inner circumferential edge 71d1 and the second step support front end face 71a are connected in the second step support region 71. The corner 71e coincides with the corner 61e where the connecting edge 61d3 and the first inner circumferential edge 61d1 of the first step support region 61 are connected.

[0068] The second step inner circumferential region 71c is different from the first step inner circumferential region 61c. The entire surface of the second step inner circumferential region 71c is an overlapping region. The third shim 80 overlaps the entire surface of the second step inner circumferential region 71c. For example, the circumferential length of the second inner circumferential edge portion 61d2 of the second step support region 71 is shorter than the circumferential length of the second inner circumferential edge portion 61d2 of the first step support region 61.

[0069] The second clamped portion 73 has a second clamped outer peripheral surface 73a and a second clamped inner peripheral surface 73b. The second clamped outer peripheral surface 73a is a part that constitutes the outer peripheral edge 53e together with the first clamped outer peripheral surface 63a. The planar shape of the second clamped outer peripheral surface 73a is a closed arc (ring). The second clamped portion 73 has a hole portion 73s and a hole portion 73t. The hole portion 73s constitutes the first through hole 55. The hole portion 73t constitutes the second through hole 56.

[0070] <Third Sim> As shown in FIGS. 7 and 10, the third shim 80 includes a plurality of third step support regions 81 and a third clamped portion 83.

[0071] The third step support region 81 has a third step support front end face 81a, a third step support rear end face 81b, and a third step inner circumferential edge 81d.

[0072] The third shim 80 has a third shim back surface 80b and a third shim main surface 80f. The third shim back surface 80b contacts the second shim main surface 70f. The third shim main surface 80f has the valley portion 22s4 fixed thereto. The entire surface of the third shim back surface 80b contacts the second shim main surface 70f. The third step support region 81 has a third step surface 81s. The valley portion 22s4 of the bump foil piece 21 is fixed to the third step surface 81s (see FIG. 5). The fixing element 21f for fixing the valley portion 22s4 may be fixed only to the third shim 80. The fixing element 21f may be fixed not only to the third shim 80 but also to other elements.

[0073] The circumferential length from the third step support front end face 81a to the third step support rear end face 81b is shorter than the circumferential length from the second step support front end face 71a to the second step support rear end face 71b. The second step surface 71s is formed by this difference in circumferential length. The second step support front end face 71a is shifted from the third step support front end face 81a by a shift amount P.

[0074] The third step support region 81 does not include a notch. Of the multiple shims constituting the step member 50, the shim located at the top does not need to include a notch. The distance from the axis A to the third step inner circumferential edge 81d is the same as the distance from the axis A to the second inner circumferential edge 61d2 of the first step support region 61. The distance from the axis A to the step inner circumferential edge 81d of the third step support region 81 is the same as the distance from the axis A to the second inner circumferential edge 61d2 of the second step support region 71.

[0075] The third clamped portion 83 has a third clamped outer peripheral surface 83a and a third clamped inner peripheral surface 83b. The third clamped outer peripheral surface 83a is a part that constitutes the outer peripheral edge 53e together with the first clamped outer peripheral surface 63a and the second clamped outer peripheral surface 73a. The planar shape of the third clamped outer peripheral surface 83a is a closed arc (ring). The third clamped portion 83 has a hole portion 83s that constitutes the first through hole 55 and a hole portion 83t that constitutes the second through hole 56.

[0076] <Action and effect> The laminated structure of the first shim 60, the second shim 70 and the third shim 80 described above constitutes a virtual inclined surface. The thrust foil bearings 3A, 3B exert a supporting force by a lubricating fluid film formed between the top foil piece 11 and the thrust collar 4. The lubricating fluid film is affected by the shape of the gap formed between the top foil piece 11 and the thrust collar 4. The shape of the gap is set by the inclination of the top foil piece 11. The top foil piece 11 is supported by the bump foil piece 21. The bump foil piece 21 is supported by the step member 50. The shape of the gap is determined by the shape of the step member 50.

[0077] As shown in FIG. 5, the bump foil piece 21 is in contact with the step member 50. However, the entire surface of the bump foil piece 21 is not in contact with the step member 50. The bump foil piece 21 is in contact with the step member 50 at the valley portion 22s. The inclination of the bump foil piece 21 is determined by the shape of the step member 50 in contact with the valley portion 22s. For example, the inclination of the bump foil piece 21 can be regarded as a virtual slope 200. The virtual slope 200 is a virtual surface that virtually connects the parts of the step member 50 that the valley portions 22s contact. For example, the slope between the valley portions 22s2 and 22s3 does not need to be a slope whose height increases continuously. The inventors have conceived that the slope between the valley portions 22s2 and 22s3 may include a step whose height increases discontinuously. The inventors further came up with the idea that in order to realize a virtual slope by using a step, shims with precisely controlled thicknesses can be stacked.

[0078] The thrust foil bearings 3A, 3B comprise a base plate 30 having an insertion hole 30a through which the rotating shaft 1 is inserted and a support surface 30b, a plurality of top foil pieces 11 supported by the support surface 30b, a step member 50 placed on the support surface and formed separately from the base plate 30, and including a plurality of step support portions 51 constituted by a plurality of step surfaces 61s, 71s, 81s, and a plurality of bump foil pieces arranged between the top foil piece 11 and the base plate 30, arranged on each of the plurality of step support portions 51, and including valley portions 22s in contact with the step surfaces 61s, 71s, 81s.

[0079] The thrust foil bearings 3A and 3B have a step member 50 that is separate from the base plate 30. The step member 50 makes it easier to reduce the deviation of the step dimension from the design value. As a result, the decrease in load capacity caused by the deviation of the step dimension is suppressed. Therefore, the thrust foil bearings 3A and 3B can exhibit the desired load capacity.

[0080] The plurality of stepped support portions 51 of the thrust foil bearings 3A, 3B are provided so as to surround the insertion hole 30a. According to this configuration, the plurality of stepped support portions 51 can be provided around the insertion hole 30a.

[0081] The first shim 60 of the thrust foil bearings 3A and 3B includes a first clamped portion 63 including an arc-shaped outer circumferential edge, and a first stepped support region 61 provided between the first clamped portion 63 and the insertion hole 30a as viewed from the direction of the axis A of the insertion hole 30a. The second shim 70 includes a second clamped portion 73 including an arc-shaped outer circumferential edge, and a second stepped support region provided between the second clamped portion 73 and the insertion hole 30a as viewed from the direction of the axis A of the insertion hole 30a. The stepped support portion 51 is formed by stacking the first stepped support region 61 and the second stepped support region 71. With this configuration, the desired load capacity can also be exhibited.

[0082] The shape of the second stepped support region 71 of the thrust foil bearings 3A, 3B differs from the shape of the first stepped support region 61 when viewed from the direction of the axis A of the insertion hole 30a. With this configuration, it is possible to form an imaginary inclined surface 200 that supports the bump foil piece 21.

[0083] The first stepped support region 61 of the thrust foil bearings 3A, 3B includes a stepped inner peripheral edge 61d that extends to surround the insertion hole 30a. The stepped inner peripheral edge 61d includes a first inner peripheral edge portion 61d1 and a second inner peripheral edge portion 61d2. The distance from the axis A of the insertion hole 30a to the first inner peripheral edge portion 61d1 is different from the distance from the axis A of the insertion hole 30a to the second inner peripheral edge portion 61d2. With this configuration as well, the desired load capacity can be exhibited.

[0084] The clamped portion 53 of the above-mentioned thrust foil bearings 3A, 3B has a second through hole 56 through which a fastening bolt 43 is inserted for fixing the first shim 60, the second shim 70, and the third shim 80 to the base plate 30. With this configuration, the step member 50 can be attached to the base plate 30.

[0085] The number of second through holes 56 of the above-described thrust foil bearings 3A, 3B is different from the number of stepped support portions 51. The stepped member 50 can be attached to the base plate 30 with such a configuration as well.

[0086] The thrust foil bearing of the present disclosure is not limited to the above embodiments.

[0087] <Variation 1> FIG. 11 is a cross-sectional view showing a main part of a thrust foil bearing 3S of the first modification. The thrust foil bearing 3S of the first modification has a step member 50S. The step member 50S has a first shim 60S, a second shim 70S, a third shim 80S, a fourth shim 90S, and a fifth shim 100S. The bump foil piece 21S has six valley portions 22s. The valley portion 22s1 contacts the support surface 30b. The valley portion 22s2 contacts the first shim 60S. The valley portion 22s3 contacts the second shim 70S. The valley portion 22s4 contacts the third shim 80S. The valley portion 22s5 contacts the fourth shim 90S. The valley portion 22s6 contacts the fifth shim 100S. In the above embodiment, the thicknesses of the first shim 60, the second shim 70, and the third shim 80 are the same. In the first modification, the thicknesses of the first shim 60S, the second shim 70S, the third shim 80S, the fourth shim 90S, and the fifth shim 100S are different from each other.

[0088] The thickness of the first shim 60S is thickness (t1). The thickness of the second shim 70S is thickness (t2). The thickness (t2) is greater than the thickness (t1). The thickness of the third shim 80S is thickness (t3). The thickness of the fourth shim 90S is thickness (t4). The thickness of the fifth shim 100S is thickness (t5). The first shim 60S is the thickest. The fifth shim 100S is the thinnest. The inclined portion 12S of the top foil piece 11S realized by the step member 50S is curved. The inclined portion 12S is curved so that the inclination with respect to the support surface 30b gradually decreases. For example, it can be said that the inclined portion 12S is convex toward the thrust collar 4.

[0089] FIG. 12 shows the load capacity of the thrust foil bearing 3A and the load capacity of the thrust foil bearing 3S of the modified example 1. The horizontal axis x indicates the circumferential position. The vertical axis P(x) indicates the pressure of the fluid lubrication film. The vertical axis P(x) indicates the load capacity of the thrust foil bearings 3A and 3S. The graph G11a shows the load capacity of the thrust foil bearing 3A of the embodiment. The graph G11b shows the load capacity of the thrust foil bearing 3S of the modified example 1. Referring to the graphs G11a and G11b, it can be seen that the pressure of the fluid lubrication film of the thrust foil bearing 3S is higher by the area G11c shown by the mesh. This increase is due to the curved inclined portion 12S of the top foil piece 11S.

[0090] In the thrust foil bearing 3S of the first modification, the first shim 60S, the second shim 70S, the third shim 80S, the fourth shim 90S, and the fifth shim 100S have different thicknesses, thereby improving the load capacity of the thrust foil bearing 3S.

[0091] <Variation 2> Fig. 13 is a cross-sectional view showing a main part of a thrust foil bearing 3R of modified example 2. In the above embodiment, the offset amount P was constant. As shown in Fig. 13, in the step member 50R of modified example 2, a first shim 60, a second shim 70, a third shim 80, a fourth shim 90, and a fifth shim 100 are arranged according to different offset amounts P1, P2, P3, P4, and P5. The first shim 60, the second shim 70, the third shim 80, the fourth shim 90, and the fifth shim 100 have the same thickness, but it is not necessary that all the shims have the same thickness.

[0092] The second step support front end face 71a of the second shim 70 is shifted by a shift amount P1 with respect to the first step support front end face 61a of the first shim 60. The third step support front end face 81a of the third shim 80 is shifted by a shift amount P2 with respect to the second step support front end face 71a of the second shim 70. The difference between the shift amounts P1 and P2 is the difference between the area of ​​the first step surface 61s and the area of ​​the second step surface 71s. Similarly, the fourth step support front end face 91a of the fourth shim 90 is shifted by a shift amount P3 with respect to the third step support front end face 81a of the third shim 80. The fifth step support front end face 100a of the fifth shim 100S is shifted by a shift amount P5 with respect to the fourth step support front end face 91a of the fourth shim 90.

[0093] In the step member 50R of the second modification, the upper shim has a larger displacement amount P. For example, the area of ​​the second step surface 71s is larger than the area of ​​the first step surface 61s. The areas of the third step surface 81s, the fourth step 91s, and the fifth step surface 101s also correspond to the respective displacement amounts P2, P3, and P4.

[0094] The bump foil piece 21R is supported by a step member 50R. The inclined portion 12R of the top foil piece 11R supported by the bump foil piece 21R is curved so as to be convex toward the upstream side along the rotation direction R. As a result, similar to the second modification, the load capacity of the thrust foil bearing 3R can be improved.

[0095] In the second modification, the second shim 70 does not directly support the valley portion 22s2 of the bump foil piece 21R. In other words, the bump foil piece 21 does not contact the second shim 70. Furthermore, the valley portion 22s4 and the valley portion 22s45 contact the fourth shim 90. With this configuration, the shape of the inclined portion 12R of the top foil piece 11R can be formed into a cubic curved surface instead of a simple quadratic curved surface. In the example shown in FIG. 13, the top foil piece 11R is curved so that the downstream side of the inclined portion 12R in the rotation direction R gradually warps up. This can improve the load capacity of the top foil piece 11R on the downstream side in the rotation direction R.

[0096] In the top foil piece 11R of the second modification, the inclined portion 12R is convex in opposite directions on the upstream side and the downstream side, so that the cross section of the inclined portion 12R of the top foil piece 11R has an inverted S-shape.

[0097] <Modification 3> In the above description, the step member 50 is exemplified as a single member that is a ring in plan view. The step member 50 is not limited to a single ring-shaped member. For example, the step member may be composed of multiple step member pieces. The number of step member pieces that constitute the step member may be two. The number of step member pieces that constitute the step member may be an integer of two or more. FIG. 14 illustrates an example of a step member 50C that is composed of two step member pieces 50T. As shown in FIG. 14, the outer peripheral edge 50C1 of the step member piece 50T is arc-shaped. The outer peripheral edge 53T1 of the clamped portion 53T included in the step member piece 50T is also arc-shaped.

[0098] <Modification 4> In the above description, the bump foil base end 21e of the bump foil piece 21 is in contact with the base plate 30. For example, as shown in FIG. 15, the bump foil base end 21e of the bump foil piece 21D may be disposed on the first step surface 61s. With this configuration, the bump foil piece 21 is in contact with the step member 50. However, the bump foil piece 21 is not in contact with the base plate 30.

[0099] <Further variations> For example, the step member 50 may be provided with a plurality of shims having different thicknesses and configured according to different offset amounts P. [Explanation of symbols]

[0100] 1 Rotation axis 3A, 3B, 3R, 3S Thrust foil bearings 11 Top foil piece 21 Bump foil piece 22s1,22s2,22s3,22s4 Tanibe 30 Base Plate 30a Insertion hole 30b Support surface 55 First through hole 56 Second Through Hole 50, 50R, 50S Step material 51 Step support part 53 Clamped part 60 First shim (first plate member) 61 First step support area (first support area) 61d Step inner edge (inner edge) 61d1 First inner edge 61d2 Second inner edge 61s 1st step surface 63 First clamped part 70 Second shim (second plate member) 71 Second step support area (second support area) 71s 2nd step surface 73 Second clamped part 80 3rd Sim 81 Third step support area 81s 3rd step surface 83 Third clamped part A axis

Claims

1. a base plate having a support surface and an insertion hole through which the rotating shaft is inserted; A plurality of top foil pieces supported on the support surface; A step member is placed on the support surface and includes a plurality of step support portions formed by a plurality of step surfaces; a plurality of bump foil pieces disposed between the top foil piece and the base plate and disposed on each of the plurality of stepped support portions; the step member has a first plate member disposed on the support surface and a second plate member stacked on the first plate member, The first plate member includes a first inner circumferential edge portion and a second inner circumferential edge portion. the first inner peripheral edge portion is located farther from the axis of the insertion hole than the second inner peripheral edge portion; the first plate member includes a first stepped inner circumferential region located between the second inner circumferential edge portion and an imaginary line extending in a direction surrounding the insertion hole from the first inner circumferential edge portion, A thrust foil bearing, wherein the first step inner circumferential region includes an inner circumferential surface overlap region that overlaps with the second plate member and an inner circumferential surface exposed region that does not overlap with the second plate member.

2. a base plate having a support surface and an insertion hole through which the rotating shaft is inserted; A plurality of top foil pieces supported on the support surface; A step member is placed on the support surface and includes a plurality of step support portions formed by a plurality of step surfaces; a plurality of bump foil pieces disposed between the top foil piece and the base plate and disposed on each of the plurality of stepped support portions; the step member has a first plate member disposed on the support surface and a second plate member stacked on the first plate member, the second plate member includes a first inner circumferential edge portion and a second inner circumferential edge portion located closer to an axis of the insertion hole than the first inner circumferential edge portion, the first plate member includes a first stepped inner circumferential region located closer to the axis of the insertion hole than the first inner circumferential edge portion when viewed from a direction of the axis of the insertion hole, A thrust foil bearing, wherein the first step inner circumferential region includes an inner circumferential surface overlap region that overlaps with the second plate member and an inner circumferential surface exposed region that does not overlap with the second plate member.

3. a base plate having a support surface and an insertion hole through which the rotating shaft is inserted; A plurality of top foil pieces supported on the support surface; A step member is placed on the support surface and includes a plurality of step support portions formed by a plurality of step surfaces; a plurality of bump foil pieces disposed between the top foil piece and the base plate and disposed on each of the plurality of stepped support portions; the step member has a first plate member disposed on the support surface and a second plate member stacked on the first plate member, The first plate member includes two support regions adjacent to each other in a direction surrounding the insertion hole, A groove is formed between the two support regions, the groove extending from the outer diameter side to the inner diameter side, the groove includes an enlarged portion; A thrust foil bearing, wherein a width of the expanded portion in a direction surrounding the insertion hole expands from the outer diameter side toward the inner diameter side.

4. a base plate having a support surface and an insertion hole through which the rotating shaft is inserted; A plurality of top foil pieces supported on the support surface; A step member is placed on the support surface and includes a plurality of step support portions formed by a plurality of step surfaces; a plurality of bump foil pieces disposed between the top foil piece and the base plate and disposed on each of the plurality of stepped support portions; the step member has a first plate member disposed on the support surface and a second plate member stacked on the first plate member, The first plate member includes an inner circumferential region. the inner circumferential region includes an inner circumferential surface overlap region that overlaps with the second plate member and an inner circumferential surface exposed region that does not overlap with the second plate member, A thrust foil bearing, wherein the inner circumferential surface overlap region and the inner circumferential surface exposed region are arranged in a direction surrounding the insertion hole.

5. The thrust foil bearing according to any one of claims 1 to 4, wherein the plurality of stepped support portions are provided so as to surround the insertion hole.

6. The first plate member is A first clamped portion including an arc-shaped outer circumferential edge; a first support region provided between the first clamped portion and the insertion hole as viewed from the axial direction of the insertion hole, The second plate member is A second clamped portion including an arc-shaped outer circumferential edge; a second support region provided between the second clamped portion and the insertion hole as viewed from the axial direction of the insertion hole, The thrust foil bearing according to any one of claims 1 to 4, wherein the stepped support portion is formed by stacking the first support region and the second support region.

7. The thrust foil bearing according to claim 6 , wherein a shape of the second support region is different from a shape of the first support region when viewed in the axial direction of the insertion hole.

8. The thrust foil bearing according to claim 6 , wherein the first clamped portion and the second clamped portion have through holes through which fastening members for fastening the step member to the base plate are inserted.

9. The thrust foil bearing according to claim 8 , wherein the number of the through holes is different from the number of the stepped support portions.

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