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 a thrust foil bearing.

Background Art

[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 to face a thrust collar provided on a rotating shaft. The bearing surface of the thrust foil bearing is constituted by 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 generate an unintended movement due to vibration and impact. Due to the unintended movement of the rotating shaft, for example, the thrust collar may move in the axial direction. Also, due to the unintended movement of the rotating shaft, the thrust collar may tilt. 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

Patent Document 2

Patent Document 3

Patent Document 4

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0005] The load capacity of a thrust foil bearing is affected by the form of a fluid lubricating film. Therefore, in order to exhibit a desired load capacity, it is necessary to generate a desired fluid lubricating film. The form of the desired fluid lubricating film is affected by the shape of a gap between a top foil piece and a thrust collar. The wedge-shaped gap is formed by an inclined surface provided on a 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 the intended configuration due to machining errors or the like. When the inclined surface does not have the intended configuration, the wedge-shaped gap also does not have the intended configuration. As a result, the load capacity of the thrust foil bearing may not reach the desired capacity.

[0007] This disclosure describes a thrust foil bearing capable of exhibiting a desired load capacity.

MEANS FOR SOLVING THE PROBLEMS

[0008] The thrust foil bearing of this disclosure includes a base plate having an insertion hole through which a rotating shaft is inserted and a support surface, a plurality of top foil pieces supported by the support surface, a stepped member that is placed on the support surface, formed separately from the base plate, and includes a plurality of stepped support portions configured by a plurality of stepped surfaces, and a plurality of bump foil pieces that are disposed between the top foil pieces and the base plate and are disposed on each of the plurality of stepped support portions and include contact portions that contact the stepped surfaces.

ADVANTAGES OF THE INVENTION

[0009] The thrust foil bearing of this disclosure can exhibit a desired load capacity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010]

Figure 1

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Figure 15

Embodiments for Carrying Out the Invention

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

[0012] The thrust foil bearing has a step member that is separate from the base plate. According to this step member, it is easy to reduce the deviation of the step dimension from the design value. As a result, a decrease in load capacity due to the deviation of the step dimension is suppressed. Therefore, the thrust foil bearing can exhibit a desired load capacity.

[0013] The plurality of step support portions of the thrust foil bearing described above may be provided so as to surround the insertion hole. According to such a configuration, the plurality of step support portions can be provided around the insertion hole.

[0014] The first plate member of the thrust foil bearing described above may include a first clamped portion including an arcuate outer peripheral edge, and a first support region provided between the first clamped portion and the insertion hole when viewed in the direction of the axis of the insertion hole. The second plate member may include a second clamped portion including an arcuate outer peripheral edge, and a second support region provided between the second clamped portion and the insertion hole when viewed in the direction of the axis of the insertion hole. The step support portion may be formed by laminating the first support region and the second support region. Even with such a configuration, a desired load capacity can be exhibited.

[0015] The shape of the second support region of the thrust foil bearing described above may be different from the shape of the first support region when viewed in the direction of the axis of the insertion hole. According to such a configuration, a virtual inclined surface for supporting the bump foil piece can be formed.

[0016] The first support region of the thrust foil bearing described above may include an inner peripheral edge that extends so as to surround the insertion hole. The inner peripheral edge may include a first inner peripheral edge portion and a second inner peripheral edge portion. The distance from the axis of the insertion hole to the first inner peripheral edge portion may be different from the distance from the axis of the insertion hole to the second inner peripheral edge portion. Even with such a configuration, a desired load capacity can be exhibited.

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

[0018] The number of through holes of the thrust foil bearing described above may be different from the number of stepped support portions. Even with such a configuration, the stepped member can be fixed to the base plate.

[0019] Hereinafter, embodiments for implementing the thrust foil bearing of the present disclosure will be described in detail with reference to the accompanying drawings. The same reference numerals are assigned to the same elements shown in the drawings. Redundant descriptions regarding the same elements will be omitted.

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

[0021] The radial foil bearing 7 supports the rotating shaft 1 in a direction orthogonal to the axis A (radial direction). The thrust foil bearings 3A and 3B support the rotating shaft 1 in a direction along the axis A (thrust direction). The disk-shaped thrust collar 4 is attached to the rotating shaft 1. The thrust foil bearings 3A and 3B sandwich the thrust collar 4.

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

[0023] The 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 peripheral portion 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 abuts against the housing 5 by tightening with the fastening bolt 41.

[0024] Hereinafter, with reference to Figs. 3 to 10, the thrust foil bearing 3A will be described in detail. The configuration of the thrust foil bearing 3B is the same as that of the thrust foil bearing 3A. Therefore, 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 with reference to 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 rotation shaft 1 is inserted. Also, the "axial direction" is the direction in which the rotation shaft 1 extends. The "radial direction" is the direction along the diameter of the insertion hole 30a. The "radial direction" is the direction that intersects 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 rotation 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 far 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 that of a disk. 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 a precise cylindrical shape. The rotation 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 rotation shaft 1.

[0028] The support surface 30b is a flat surface. The support surface 30b extends in a direction orthogonal to the axial direction of the insertion hole 30a. The support surface 30b faces the thrust collar 4. Around the insertion hole 30a formed in the support surface 30b, a plurality of top foil pieces 11, a plurality of bump foil pieces 21, and a step member 50 are arranged. The step member 50 is attached to the support surface 30b. A part 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. Even if there are inclusions, the top foil piece 11 itself may function as a member that receives a load. 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 the top foil pieces 11 is seven. The plurality of top foil pieces 11 may be collectively referred to as a top foil. The number of the bump foil pieces 21 is also seven. The plurality of bump foil pieces 21 may be collectively referred to as a bump foil. The top foil pieces 11 and the bump foil pieces 21 are arranged at equal intervals along the circumferential direction. The number of the top foil pieces 11 is not limited to seven. The number of the top foil pieces 11 may be less than seven. The number of the top foil pieces 11 may be more than seven. The number of the bump foil pieces 21 is not limited to seven. The number of the bump foil pieces 21 may be less than seven. The number of the bump foil pieces 21 may be more than seven.

[0030] The top foil piece 11 has an inclined portion 12 and a mounting portion 13. The inclined portion 12 is inclined upward from the upstream side to the downstream side in the rotation direction R of the rotary shaft 1 along the circumferential direction. The inclined portion 12 of the top foil piece 11 faces the thrust collar 4. Being inclined upward means being in a form that gradually separates from the base plate 30 from the upstream side to the downstream side in the rotation direction R. Being inclined upward means being in a form that approaches the thrust collar 4 from the upstream side to the downstream side in the rotation direction R. The mounting portion 13 is connected to the inclined portion 12 via a bent portion 14. The mounting 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 vertex of the fan-shaped inclined portion 12 is notched. 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, with reference to the rotation direction R of the rotary shaft 1, 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. Assume that the rotation direction R of the rotary shaft 1 is counterclockwise. The definitions of the inclined portion front end 12a and the inclined portion rear end 12b are illustrative. Therefore, the inclined portion front end 12a and the inclined portion rear end 12b may be determined according to definitions different from the above. The rotation direction R of the rotary shaft 1 may also be clockwise.

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

[0033] As shown in FIG. 5, the inclined portion front end 12a is connected to the mounting portion 13 via the bent portion 14. The bent portion 14 includes a first bend 14a and a second bend 14b. The first bend 14a is the portion where the mounting portion 13 is connected to the bent portion 14. The second bend 14b is the portion where the bent portion 14 is connected to the inclined portion 12. Both the first bend 14a and the second bend 14b are 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 the 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 rotation axis 1. The initial inclination angle is the angle formed by the inclined portion 12 of the top foil piece 11 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 bending 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 bending portion 14. The mounting portion 13 is fixed to the base plate 30 by the fixing element 11f. For example, spot welding may be employed for fixing the mounting portion 13 to the base plate 30. A screw fastening structure may be employed for fixing 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 respectively disposed on each of a plurality of step support portions 51 described later. The shape of the bump foil piece 21 is fan-shaped in plan view. The size of the bump foil piece 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 piece 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 fan-shaped in plan view. The vertex of the fan-shaped bump foil piece 21 is notched. 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 reference to the rotation direction R of the rotating shaft 1, the upstream side may be defined as the bump foil front end 21a. Further, 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 peripheral 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 peaks 22r1, 22r2, 22r3 and four valleys 22s1, 22s2, 22s3, 22s4 (contact portions). In the following description, when it is not necessary to distinguish the peaks 22r1, 22r2, 22r3 from each other, they are simply referred to as the peak 22r. When it is not necessary to distinguish the valleys 22s1, 22s2, 22s3, 22s4 from each other, they are simply referred to as the valley 22s.

[0039] The support portion 22 may employ, for example, the spring foil described in Japanese Patent Application Laid-Open No. 2006-57652 and Japanese Patent Application Laid-Open No. 2004-270904. The support portion 22 may also employ a bump foil or the like described in Japanese Patent Application Laid-Open No. 2009-299748. The spring foil described in Japanese Patent Application Laid-Open No. 2006-57652 and Japanese Patent Application Laid-Open No. 2004-270904 is used for a radial bearing. Similarly, the bump foil described in Japanese Patent Application Laid-Open No. 2009-299748 is also used for a radial bearing. By developing the foil used for the radial bearing in a planar shape, an annular plate-shaped foil is obtained. This foil can be used as the support portion 22 of the thrust foil bearing 3A.

[0040] The base end 21e of the bump foil extends from the inner circumference toward the outer circumference. When the front end 21a of the bump foil is virtually extended, it intersects the axis A. Unlike the front end 21a of the bump foil, even if the base end 21e of the bump foil is virtually extended, it does not intersect the axis A. The direction in which the base end 21e of the bump foil extends is parallel to the direction in which the peak portion 22r and the valley portion 22s extend. The peak portion 22r and the valley portion 22s are alternately arranged along the direction orthogonal to the direction in which the base end 21e of the bump foil extends.

[0041] As shown in FIG. 5, the valley portion 22s includes a flat surface. The plurality of valley portions 22s1, 22s2, 22s3, 22s4 are arranged at equal intervals. All the valley portions 22s do not contact the top foil piece 11. The valley portion 22s1 contacts the base plate 30. The valley portion 22s1 includes the base end 21e of the bump foil. The valley portion 22s1 (the first portion) is not fixed to the base plate 30. The base end 21e of the bump foil is a free end. The base end 21e of the bump foil is not fixed. The front end 21a of the bump foil is also a free end. The front end 21a of the bump foil is not fixed. When a load acts on the bump foil piece 21, the base end 21e and the front end 21a of the bump foil can move.

[0042] The valleys 22s2, 22s3, 22s4 (second part) are in contact with the step member 50. For example, the valley 22s4 is fixed to the step member 50 by the fixing element 21f. The valley 22s4 includes the bump foil rear end 21b. For the fixing of the bump foil rear end 21b to the step member 50, spot welding may be employed, for example. A screw fastening structure may be employed for the fixing of 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, with reference to the rotational direction R, the mounting position of the bump foil piece 21 is the downstream end. On the other hand, with reference to the rotational 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 with reference to the rotational direction R.

[0043] The peak 22r is an arch-shaped part. The height of the peak 22r is constant. The plurality of peaks 22r1, 22r2, 22r3 are arranged at equal intervals. The peak 22r is in contact with the inclined part 12 of the top foil piece 11. The peak 22r is not in contact with the base plate 30. The peak 22r is not in contact with the step support part 51 either. The peak 22r1 connects the valleys 22s1, 22s2. The peak 22r2 connects the valleys 22s2, 22s3. The peak 22r3 connects the valleys 22s3, 22s4.

[0044] <Step member> 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 machining such as being cut out from a single metal block. The step member 50 is prepared by a process different from that of the base plate 30. The base plate 30 is also prepared by a process different from that of the step member 50. The individually prepared base plate 30 and step member 50 form the thrust foil bearings 1A and 1B through an assembly process that integrates them. For example, when the base plate 30 and the 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. There is a boundary line between the base plate 30 and the step member 50 where the base plate 30 and the step member 50 are in contact with each other and distinguish the base plate 30 and the step member 50 from each other.

[0045] The step member 50 has a plurality of step support portions 51 and a sandwiched portion 53. The step support portions 51 support the bump foil pieces 21. The number of step support portions 51 included in the step member 50 is seven. The number of step support portions 51 may be more than seven. The number of step support portions 51 may be less than seven. The step support portions 51 are arranged at approximately equal intervals in the circumferential direction. The shape of the sandwiched portion 53 is an annulus in plan view. The outer peripheral edge of the sandwiched portion 53 is arc-shaped. The shape of the step member 50 shown in Fig. 6 is an annulus in plan view. The sandwiched portion 53 has an outer peripheral edge 53e that is a continuous arc. As used in this specification, "arc" includes a closed arc as shown in Fig. 6. A closed arc includes, for example, an arc with a central angle of 360 degrees. "Arc" also includes a part of an annulus as shown in Modification Example 3 described later. A part of an annulus includes, for example, an arc with a central angle less than 360 degrees. For an arc with a central angle less than 360 degrees that includes the outer peripheral edge in the sandwiched portion, it is illustrated as Modification Example 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 inside the sandwiched portion 53. The plurality of step support portions 51 are integral with the sandwiched 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, in the state where the stepped 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. Or, 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] Further, a second through-hole 56 is formed in the clamped portion 53. 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 the second reference circle that is the reference for the arrangement of the second through-holes 56 may be smaller than the diameter of the first reference circle that is the reference for the arrangement of the first through-holes 55. The second through-hole 56 may be formed inside the first through-hole 55. As shown in FIG. 5, the fastening bolt 43 fixes the stepped 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 includes 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 plate members made of metal. The thicknesses of the first shim 60, the second shim, and the third shim 80 are each constant. The shapes of the first shim 60, the second shim, and the third shim 80 are plate-like. The first shim 60, the second shim 70, and the third shim 80 are laminated in their thickness directions.

[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 Shim> As shown in FIGS. 7 and 8, the first shim 60 (first plate member) includes a plurality of first step support regions 61 (first support regions) and a first sandwiched portion 63.

[0051] The first step support region 61, together with the second step support region 71 and the third step support region 81 described later, constitutes a step support portion 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 the 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 plurality of first step support regions 61 are the same. The plurality of first step support regions 61 are arranged in the circumferential direction along the first clamped portion 63. The planar shape of the first clamped portion 63 is an annular ring. The plurality of first step support regions 61 are arranged inside the first clamped portion 63. A groove 67 extending from the outer diameter side to the inner diameter side is formed between two circumferentially adjacent first step support regions 61. The groove 67 has a reduced portion 67a and an enlarged 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, as approaching the axis A, the interval between the circumferentially adjacent first step support regions 61 becomes narrower. The circumferential width of the enlarged portion 67b increases from the outer diameter side to the inner diameter side. In the enlarged portion 67b, as approaching the axis A, the interval between the circumferentially adjacent first step support regions 61 becomes wider.

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

[0055] As shown in FIG. 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 that is arc-shaped and a second inner peripheral edge portion 61d2 that is arc-shaped. 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 based on the rotation direction R, the first inner peripheral edge portion 61d1 is on the upstream side of the second inner peripheral edge portion 61d2.

[0056] The distance from the axis A to the first inner peripheral edge portion 61d1 is defined as the first radius. The distance from the axis A to the second inner peripheral edge portion 61d2 is defined as the second radius. The first radius of the first inner peripheral edge portion 61d1 is larger than the second radius of the second inner peripheral edge portion 61d2. The first inner peripheral edge portion 61d1 is farther from the axis A than the second inner peripheral 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 notch 61p is a portion surrounded by the connecting edge portion 61d3 and the first inner peripheral edge portion 61d1.

[0058] The position of the second inner peripheral edge portion 61d2 is inside the first inner peripheral edge portion 61d1. The first step inner peripheral region 61c is a region surrounded by a virtual line obtained by 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 step support rear end face 61b. The first step 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 for two shims formed by the end faces of the second shim 70 and the third shim 80 occurs.

[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 stepped 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, which will be described later. The first clamped portion 63 has a first clamped outer circumferential surface 63a and a first clamped inner circumferential surface 63b. The first clamped outer circumferential surface 63a is a part that constitutes the outer peripheral edge 53e. The planar shape of the first clamped outer circumferential surface 63a is a closed arc (annular 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] <The second shim> 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 stepped support region 71 has a second stepped support front end surface 71a, a second stepped support rear end surface 71b, and a second stepped inner circumferential region 71c.

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

[0064] The second-step difference 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 difference 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 displaced by a displacement amount P (see Fig. 7) with respect to the first-step support front end surface 61a. The difference in circumferential length corresponds to the displacement amount P. The displacement amount P may be the same as the pitch of the valley portion 22s of the bump foil piece 21.

[0065] The second-step support region 71 includes a second notch 71p. The second notch 71p is formed by cutting off a part of the second-step inner circumferential region 71c. The second notch 71p is formed on the upstream side of the second-step inner circumferential region 71c along the rotation direction R. The second notch 71p is formed on the second-step support front end surface 71a side.

[0066] Similar to the first-step support region 61, the second-step support region 71 also has a step inner peripheral edge 71d. The step 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 an arc. The shape of the second inner peripheral edge portion 71d2 is also an 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-step support region 71 is the same as the radius of the first inner peripheral edge portion 61d1 of the first-step support region 61. The radius of the second inner peripheral edge portion 71d2 of the second-step support region 71 is also the same as the radius of the second inner peripheral edge portion 61d2 of the first-step support region 61. The circumferential length of the second inner peripheral edge portion 71d2 of the second-step support region 71 is shorter than the circumferential length of the second inner peripheral edge portion 61d2 of the first-step support region 61. As a result, an inner peripheral surface exposed region 61c2 is formed.

[0067] In the second step support area 71, a corner 71e is formed at the portion where the first inner peripheral edge 71d1 and the second step support front end surface 71a are connected. The corner 71e coincides with the corner 61e where the connecting edge 61d3 of the first step support area 61 and the first inner peripheral edge 61d1 are connected.

[0068] The second step inner peripheral area 71c is different from the first step inner peripheral area 61c. The entire surface of the second step inner peripheral area 71c is an overlapping area. The third shim 80 overlaps the entire surface of the second step inner peripheral area 71c. For example, the circumferential length of the second inner peripheral edge 61d2 of the second step support area 71 is shorter than the circumferential length of the second inner peripheral edge 61d2 of the first step support area 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 73s and a hole 73t. The hole 73s constitutes the first through hole 55. The hole 73t constitutes the second through hole 56.

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

[0071] The third step support area 81 has a third step support front end surface 81a, a third step support rear end surface 81b, and a third step inner peripheral 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 is in contact with the second shim main surface 70f. The third shim main surface 80f is where the trough portion 22s4 is fixed. The entire surface of the third shim back surface 80b is in contact with the second shim main surface 70f. The third step support region 81 has a third step surface 81s. The trough 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 trough 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 surface 81a to the third step support rear end surface 81b is shorter than the circumferential length from the second step support front end surface 71a to the second step support rear end surface 71b. The second step surface 71s is formed by the difference in this circumferential length. The second step support front end surface 71a is displaced by a displacement amount P with respect to the third step support front end surface 81a.

[0074] The third step support region 81 does not include a notch. Among the plurality of shims constituting the step member 50, the uppermost shim may not include a notch. The distance from the axis A to the third step inner peripheral edge 81d is the same as the distance from the axis A to the second inner peripheral edge portion 61d2 of the first step support region 61. The distance from the axis A to the step inner peripheral edge 81d of the third step support region 81 is the same as the distance from the axis A to the second inner peripheral edge portion 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] <Function 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 plane. The thrust foil bearings 3A and 3B exert a supporting force by means of 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 portions 22s. The inclination of the bump foil piece 21 is determined by the shape of the step member 50 in contact with the valley portions 22s. For example, the inclination of the bump foil piece 21 can be regarded as a virtual inclined plane 200. The virtual inclined plane 200 is a virtual plane that virtually connects the portions of the step member 50 with which the valley portions 22s are respectively in contact. For example, between the valley portions 22s2 and 22s3, it is not necessary to be a continuously increasing slope in height. The inventors have conceived that between the valley portions 22s2 and 22s3 may include steps with a discontinuous increase in height. The inventors have further conceived that in order to realize a virtual inclined plane by means of steps, shims with precisely controlled thickness may be laminated.

[0078] The thrust foil bearings 3A and 3B include 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 disposed between the top foil pieces 11 and the base plate 30 and disposed 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. According to the step member 50, it is easy to reduce the deviation of the step dimension from the design value. As a result, a decrease in the load capacity due to the deviation of the step dimension is suppressed. Therefore, the thrust foil bearings 3A and 3B can exhibit a desired load capacity.

[0080] The plurality of step support portions 51 of the thrust foil bearings 3A and 3B are provided so as to surround the insertion hole 30a. According to such a configuration, the plurality of step 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 sandwiched portion 63 including an arcuate outer peripheral edge and a first step support region 61 provided between the first sandwiched portion 63 and the insertion hole 30a when viewed in the direction of the axis A of the insertion hole 30a. The second shim 70 includes a second sandwiched portion 73 including an arcuate outer peripheral edge and a second step support region provided between the second sandwiched portion 73 and the insertion hole 30a when viewed in the direction of the axis A of the insertion hole 30a. The step support portion 51 is formed by laminating the first step support region 61 and the second step support region 71. Also with such a configuration, a desired load capacity can be exhibited.

[0082] The shape of the second step support region 71 of the thrust foil bearings 3A and 3B is different from the shape of the first step support region 61 when viewed in the direction of the axis A of the insertion hole 30a. According to such a configuration, a virtual inclined surface 200 that supports the bump foil piece 21 can be formed.

[0083] The first step support region 61 of the thrust foil bearings 3A and 3B includes a step inner peripheral edge 61d that extends so as to surround the insertion hole 30a. The step 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. Even with such a configuration, a desired load capacity can be exhibited.

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

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

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

[0087] <Modification Example 1> FIG. 11 is a cross-sectional view showing a main part of the thrust foil bearing 3S of Modification 1. The thrust foil bearing 3S of Modification 1 has a stepped member 50S. The stepped 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 valleys 22s. The valley 22s1 contacts the support surface 30b. The valley 22s2 contacts the first shim 60S. The valley 22s3 contacts the second shim 70S. The valley 22s4 contacts the third shim 80S. The valley 22s5 contacts the fourth shim 90S. The valley 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 were the same as each other. In Modification 1, 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 the thickness (t1). The thickness of the second shim 70S is the thickness (t2). The thickness (t2) is larger than the thickness (t1). The thickness of the third shim 80S is the thickness (t3). The thickness of the fourth shim 90S is the thickness (t4). The thickness of the fifth shim 100S is the 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 stepped 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 also be said that the inclined portion 12S is convex toward the thrust collar 4.

[0089] Figure 12 shows the load capacity of the thrust foil bearing 3A and the load capacity of the thrust foil bearing 3S of Modification 1. The horizontal axis x indicates the circumferential position. The vertical axis P(x) indicates the pressure of the fluid lubricating film. The vertical axis P(x) indicates the load capacity of the thrust foil bearings 3A and 3S. Graph G11a shows the load capacity of the thrust foil bearing 3A of the embodiment. Graph G11b shows the load capacity of the thrust foil bearing 3S of Modification 1. Referring to graphs G11a and G11b, it can be seen that the pressure of the fluid lubricating film of the thrust foil bearing 3S is higher by the amount of the region G11c indicated by the mesh. This increase is due to the fact that the inclined portion 12S of the top foil piece 11S is curved.

[0090] The thrust foil bearing 3S of Modification 1 can improve the load capacity of the thrust foil bearing 3S by varying the thicknesses of the first shim 60S, the second shim 70S, the third shim 80S, the fourth shim 90S, and the fifth shim 100S.

[0091] <Modification 2> Figure 13 is a cross-sectional view showing the main part of the thrust foil bearing 3R of Modification 2. In the above embodiment, the displacement amount P was constant. As shown in Figure 13, the stepped members 50R of Modification 2 have the first shim 60, the second shim 70, the third shim 80, the fourth shim 90, and the fifth shim 100 arranged according to different displacement amounts P1, P2, P3, P4, and P5. The thicknesses of the first shim 60, the second shim 70, the third shim 80, the fourth shim 90, and the fifth shim 100 are the same as each other, but it is not necessarily required that the thicknesses of all the shims be the same.

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

[0093] In the stepped member 50R of Modification 2, the upper shims have larger displacement amounts P. For example, the area of the second stepped surface 71s is larger than the area of the first stepped surface 61s. The areas of the third stepped surface 81s, the fourth stepped surface 91s, and the fifth stepped surface 101s also correspond to the respective displacement amounts P2, P3, and P4.

[0094] The bump foil piece 21R is supported by the stepped member 50R. The inclined portion 12R of the top foil piece 11R supported by the bump foil piece 21R curves so as to be convex upstream along the rotation direction R. As a result, similar to Modification 2, the load capacity of the thrust foil bearing 3R can be improved.

[0095] In Modification 2, the second shim 70 does not directly support the trough portion 22s2 of the bump foil piece 21R. In other words, the bump foil piece 21 does not contact the second shim 70. Further, the trough portions 22s4 and 22s45 are in contact with the fourth shim 90. According to such a configuration, the shape of the inclined portion 12R of the top foil piece 11R can also be formed as a cubic curved surface instead of a simple quadratic function curved surface. In the example shown in FIG. 13, the top foil piece 11R curves such that the downstream side in the rotation direction R of the inclined portion 12R gradually warps upward. Thereby, the load capacity on the downstream side in the rotation direction R of the top foil piece 11R can be improved.

[0096] The top foil piece 11R of Modification 2 has opposite convex directions on the upstream side and the downstream side of the inclined portion 12R. As a result, the cross-section of the inclined portion 12R of the top foil piece 11R is reverse S-shaped.

[0097] <Modification 3> In the above description, the step member 50 is exemplified as a single member that is annular in plan view. The step member 50 is not limited to a single annular member. For example, the step member may be composed of a plurality of step member pieces. The number of step member pieces constituting the step member may be two. The number of step member pieces constituting the step member may be an integer of two or more. FIG. 14 shows an example of a step member 50C 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 sandwiched portion 53T included in the step member piece 50T is also an arc.

[0098] <Modification 4> In the above description, the bump foil base end 21e of the bump foil piece 21 was 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. According to 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 Modification> For example, the step member 50 may include a plurality of shims having different thicknesses and be configured according to different amounts of displacement P from each other.

Explanation of Reference Numerals

[0100] 1 Rotation axis 3A, 3B, 3R, 3S Thrust foil bearing 11 Top foil piece 21 Bump foil piece 22s1, 22s2, 22s3, 22s4 Valley portion 30 Base plate 30a Insertion hole 30b Support surface 55 First through-hole 56 Second through-hole 50, 50R, 50S Step members 51 Step support part 53 Clamped part 60 First shim (first plate member) 61 First step support region (first support region) 61d Step inner periphery (inner periphery) 61d1 First inner peripheral part 61d2 Second inner peripheral part 61s First step surface 63 First clamped part 70 Second shim (second plate member) 71 Second step support region (second support region) 71s Second step surface 73 Second clamped part 80 Third shim 81 Third step support region 81s Third step surface 83 Third clamped part Axis A

Claims

1. A base plate having an insertion hole through which a rotating shaft is inserted and a support surface, A plurality of top foil pieces supported on the support surface, A stepped member placed on the support surface and including a plurality of stepped support portions formed by a plurality of stepped surfaces, A plurality of bump foil pieces disposed between the top foil pieces and the base plate and disposed on each of the plurality of stepped support portions, The stepped member has a first plate member disposed on the support surface and a second plate member laminated on the first plate member, The first plate member includes a first inner peripheral edge portion and a second inner peripheral 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 peripheral region located between a virtual line extending in a direction surrounding the insertion hole from the first inner peripheral edge portion and the second inner peripheral edge portion, The first stepped inner peripheral region includes an inner peripheral surface overlapping region overlapping the second plate member and an inner peripheral surface exposed region not overlapping the second plate member, a thrust foil bearing.

2. A base plate having an insertion hole through which a rotating shaft is inserted and a support surface, A plurality of top foil pieces supported on the support surface, A stepped member placed on the support surface and including a plurality of stepped support portions formed by a plurality of stepped surfaces, A plurality of bump foil pieces disposed between the top foil pieces and the base plate and disposed on each of the plurality of stepped support portions, The stepped member has a first plate member disposed on the support surface and a second plate member laminated on the first plate member, The second plate member includes a first inner peripheral edge portion and a second inner peripheral edge portion located closer to the axis of the insertion hole than the first inner peripheral edge portion, The first plate member includes a first stepped inner peripheral region located closer to the axis of the insertion hole than the first inner peripheral edge portion when viewed in the direction of the axis of the insertion hole, The first stepped inner peripheral region includes an inner peripheral surface overlapping region overlapping the second plate member and an inner peripheral surface exposed region not overlapping the second plate member, a thrust foil bearing.

3. A base plate having an insertion hole through which a rotating shaft is inserted and a support surface, A plurality of top foil pieces supported on the support surface, A stepped member placed on the support surface and including a plurality of stepped support portions formed by a plurality of stepped 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 step support portions. The step member has a first plate member disposed on the support surface and a second plate member laminated 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 extending from the outer diameter side to the inner diameter side is formed between the two support regions. The groove includes an enlarged portion. A thrust foil bearing in which a width of the enlarged portion in a direction surrounding the insertion hole expands from the outer diameter side toward the inner diameter side. **Claim 4** A base plate having an insertion hole through which a rotating shaft is inserted and a support surface, A plurality of top foil pieces supported by the support surface, A step member placed on the support surface and including 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 step support portions. The step member has a first plate member disposed on the support surface and a second plate member laminated on the first plate member. When viewed from the direction of the axis of the insertion hole, the first plate member includes an inner peripheral surface exposed region located closer to the axis of the insertion hole than the inner peripheral edge portion of the second plate member and not overlapping the second plate member, and an inner peripheral surface overlapping region located side by side with the inner peripheral surface exposed region in a direction surrounding the insertion hole and overlapping the second plate member. A thrust foil bearing. **Claim 5** The plurality of step support portions are provided so as to surround the insertion hole. The thrust foil bearing according to any one of claims 1 to 4. **Claim 6** The first plate member, A first clamped portion including an arcuate outer peripheral edge, A first support region provided between the first clamped portion and the insertion hole when viewed from the direction of the axis of the insertion hole. The second plate member, A second clamped portion including an arcuate outer peripheral edge, A second support region provided between the second clamped portion and the insertion hole when viewed from the direction of the axis of the insertion hole. The step support portion is formed by laminating the first support region and the second support region. The thrust foil bearing according to any one of claims 1 to 4. **Claim 7** The shape of the second support region is different from the shape of the first support region when viewed from the direction of the axis of the insertion hole. The thrust foil bearing according to claim 6. **Claim 8** The thrust foil bearing according to claim 6, wherein the first held portion and the second held portion have through holes through which fastening members for fastening the stepped 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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