Foil bearing and rotating machine

Abstract

Provided is a foil bearing provided with a top foil, a bump foil, and a housing, the foil bearing being provided with a cylindrical part that surrounds the bump foil and supports the bump foil from the outer peripheral side of the bump foil, and in a cross-section orthogonal to the central axis of the housing, if the position of the upper end of the inner peripheral surface of the housing is defined as a position of 0 DEG in the circumferential direction, the position of the upper end of the inner peripheral surface of the housing is greater than the position of 0 DEG in the circumferential direction. When the shaft is rotated and floated from the bearing surface, the rotation direction of the shaft is defined as the forward direction of the circumferential position, and in a cross section orthogonal to the central axis of the housing, the rotation direction of the shaft is defined as the forward direction of the circumferential position. The average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion in the range of 160-200 DEG in the circumferential direction is smaller than the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion in the range of 0-360 DEG in the circumferential direction.

Description

Technical Field

[0001] The invention relates to a foil bearing and a rotating machine. Background Art

[0002] Patent Document 1 discloses a foil bearing comprising a top foil, a bump foil, and a cylindrical housing surrounding them. This foil bearing discloses that the bump foil is composed of a supporting portion that contacts the inner surface of the housing and does not move circumferentially, and a corrugated elastic portion that is supported by the supported portion and elastically deflects radially due to surface pressure from the back foil. By adjusting the height and angle of the corrugations, vibration of the supported shaft is suppressed.

[0003] Previous technical literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Publication No. 2009-299748 Summary of the Invention

[0006] Technical issues to be solved by the invention

[0007] In the foil bearing described in Patent Document 1, fine-tuning the height and angle of the complex pleated elastic portion is difficult in manufacturing. If the height and angle of the pleats vary due to manufacturing errors or changes over time, the effect of suppressing shaft vibration is likely to be limited.

[0008] In view of the above circumstances, an object of at least one embodiment of the present invention is to provide a foil bearing capable of suppressing shaft vibration with a simple structure, and a rotating machine including the foil bearing.

[0009] Means for solving technical problems

[0010] To achieve the above-mentioned object, a foil bearing according to at least one embodiment of the present invention includes:

[0011] a top foil including a bearing surface opposite the shaft;

[0012] a corrugated foil supporting the top foil from an outer peripheral side of the top foil; and

[0013] a cylindrical housing accommodating the top foil and the bump foil,

[0014] The foil bearing has:

[0015] a cylindrical portion surrounding the bump foil and supporting the bump foil from an outer peripheral side of the bump foil,

[0016] On a cross section perpendicular to the central axis of the housing, if the position of the upper end of the inner circumferential surface of the housing is defined as the 0° position in the circumferential direction of the housing, and the rotation direction of the shaft is defined as the positive direction of the circumferential position,

[0017] Then, when the shaft rotates and floats from the bearing surface, on a cross section perpendicular to the central axis of the housing, the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion within the range of 160° to 200° in the circumferential direction is smaller than the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion within the range of 0° to 360° in the circumferential direction.

[0018] To achieve the above-mentioned object, a rotary machine according to at least one embodiment of the present invention includes the above-mentioned foil bearing and the shaft.

[0019] Effects of the Invention

[0020] According to at least one embodiment of the present invention, a foil bearing capable of suppressing shaft vibration with a simple structure and a rotary machine including the foil bearing are provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a diagram schematically showing an example of a cross section perpendicular to the axial direction in the foil bearing 2 according to one embodiment, and shows the foil bearing 2 in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0022] Figure 2 This is a diagram schematically showing an example of a cross section perpendicular to the axial direction in a foil bearing 02 according to a comparative embodiment, and shows the foil bearing 02 in a state where the shaft 04 rotates and floats from the bearing surface.

[0023] Figure 3 about Figure 1 The cross section of the foil bearing 2 shown shows the pressure distribution of the air film formed between the shaft 4 and the top foil 6 when the shaft 4 rotates and floats from the bearing surface 14, that is, the air film pressure distribution C1.

[0024] Figure 4 This is a diagram schematically showing an example of a cross section perpendicular to the axial direction in the foil bearing 2 according to one embodiment, and schematically showing the cross section of the foil bearing 2 in a state where the rotation of the shaft 4 is stopped.

[0025] Figure 5 Yes Figure 1 The schematic cross-sectional view of an example of a more specific structure of the foil bearing 2 shown in FIG. 1 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0026] Figure 6 Is used to illustrate Figure 5 The diagram showing the influence of thermal expansion of the first base foil portion 10 a in the foil bearing 2 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0027] Figure 7 Yes Figure 1 The schematic cross-sectional view of an example of a more specific structure of the foil bearing 2 shown in FIG. 1 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0028] Figure 8 It is used to illustrate the effect on Figure 7 The diagram showing the influence of the tensile load on the first base foil portion 10 c in the foil bearing 2 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0029] Figure 9 Yes Figure 1 The schematic cross-sectional view of an example of a more specific structure of the foil bearing 2 shown in FIG. 1 and FIG. 2 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 .

[0030] Figure 10 This is a schematic cross-sectional view showing an example of the structure of a foil bearing 2 according to another embodiment, and shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 .

[0031] Figure 11A It's about Figure 10 The schematic cross-sectional view of a portion of the foil bearing 2 shows a state in which the rotation of the shaft 4 is stopped, and shows an example of a portion of the cross section of the foil bearing 2 perpendicular to the axial direction.

[0032] Figure 11B It's about Figure 10 The foil bearing 2 shown is a schematic cross-sectional view of a portion of the foil bearing 2 showing a state in which the shaft 4 rotates and floats from the bearing surface 14 , and shows a portion of the cross section perpendicular to the axial direction in the foil bearing 2 .

[0033] Figure 12 This is a schematic cross-sectional view showing an example of the structure of a foil bearing 2 according to another embodiment, and shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 .

[0034] Figure 13 1 is a schematic diagram showing an example of a rotary machine 50 including a foil bearing 2 . DETAILED DESCRIPTION

[0035] Hereinafter, several embodiments of the present invention will be described with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in the embodiments or shown in the drawings are not intended to limit the scope of the invention but are merely illustrative examples.

[0036] For example, expressions such as "in a certain direction", "along a certain direction", "parallel", "orthogonal", "center", "concentric" or "coaxial" indicate relative or absolute configurations, and not only strictly indicate such configurations, but also indicate a state of relative displacement at an angle or distance with a tolerance or to obtain the same degree of functionality.

[0037] For example, “same,” “equal,” and “homogeneous” are expressions indicating that objects are in an equal state, and they not only strictly refer to an equal state, but also a state in which there is a tolerance or a difference in the degree to which the same function can be achieved.

[0038] For example, expressions indicating shapes such as a quadrilateral and a cylinder not only indicate shapes such as a quadrilateral and a cylinder in a strict geometric sense, but also indicate shapes including concave and convex portions, chamfered portions, etc., within a range that can achieve the same effect.

[0039] On the other hand, the expression “having”, “having”, “complete”, “including” or “having” a constituent element is not an exclusive expression that excludes the existence of other constituent elements.

[0040] Figure 1 This is a diagram schematically showing an example of a cross section perpendicular to the axial direction in a foil bearing 2 according to one embodiment.

[0041] Figure 1 The foil bearing 2 shown is a radial bearing that rotatably supports a shaft 4 (rotating shaft) of a rotary machine, and includes a top foil 6 , a bump foil 8 , a base foil 10 , and a housing 12 . Figure 1 The diagram shows a state in which the shaft 4 rotates and floats from the bearing surface 14 of the top foil 6 (a state in which the shaft 4 is separated from the bearing surface 14 of the top foil 6 ).

[0042] The housing 12 has a cylindrical shape. Hereinafter, unless otherwise specified, "circumferential direction" refers to the circumferential direction of the housing 12, "axial direction" refers to the axial direction of the housing 12, and "radial direction" refers to the radial direction of the housing 12. Furthermore, the position of the upper end 20t of the inner circumferential surface 20 of the housing 12 is defined as the 0° position in the circumferential direction, and the rotational direction s of the shaft 4 is defined as the positive direction of the circumferential position. Specifically, the circumferential position increases from the position of the upper end 20t of the inner circumferential surface 20 of the housing 12 (the 0° position) toward the downstream side in the rotational direction s of the shaft 4. Hereinafter, "upstream side" refers to the upstream side in the rotational direction s of the shaft 4, and "downstream side" refers to the downstream side in the rotational direction s of the shaft 4.

[0043] like Figure 1 As shown, the housing 12 accommodates a portion of the shaft 4, the top foil 6, the bump foil 8, and the base foil 10. That is, the housing 12 is provided so as to surround a portion of the shaft 4, the top foil 6, the bump foil 8, and the base foil 10. Inside the housing 12, the shaft 4, the top foil 6, the bump foil 8, and the base foil 10 are arranged in this order from the inner side in the radial direction.

[0044] The top foil 6 is roughly cylindrical in shape, formed, for example, by bending a flexible metal strip into a roughly cylindrical shape. The top foil 6 extends circumferentially and includes a bearing surface 14 (inner circumferential surface) that opposes the outer circumferential surface 5 of the shaft 4. One circumferential end of the top foil 6 is fixed to the housing 12 as a fixed end 6a, while the other circumferential end of the top foil 6 is a free end 6b. The fixed end 6a is formed by bending one circumferential end of the top foil 6 radially outward. The free end 6b is circumferentially separated and faces the fixed end 6a. Therefore, the top foil 6 is formed as a non-annular shape with a portion of the circumference cut away, so that the inner and outer circumferential spaces of the top foil 6 are connected between the fixed end 6a and the free end 6b.

[0045] The bump foil 8 is roughly cylindrical and is bent into a wave shape as it moves from one side of the circumference toward the other side, alternating between the radially inner and outer sides. The bump foil 8 is bent into a wave shape as it moves from one side of the circumference toward the other side, alternating between the top foil 6 and the base foil 10. The bump foil 8 is formed, for example, by bending a flexible metal strip into a roughly cylindrical shape. The bump foil 8 extends circumferentially between the top foil 6 and the base foil 10, with one end of the bump foil 8 in the circumferential direction being fixed to the housing 12 as a fixed end 8a, and the other end of the bump foil 8 in the circumferential direction being a free end 8b. The free end 8b of the bump foil 8 is opposed to the fixed end 8a in a state separated in the circumferential direction of the bump foil 8. Therefore, the bump foil 8 is formed into a non-annular shape with a portion of the circumference cut off, so that the space on the inner circumference side of the bump foil 8 and the space on the outer circumference side are connected between the fixed end 8a and the free end 8b.

[0046] The bump foil 8 has a plurality of valleys 8c and a plurality of peaks 8d. Each valley 8c is curved in an arc shape, concave in the radial direction toward the side opposite the top foil 6, and contacts the inner circumferential surface of the base foil 10. Each peak 8d is curved in an arc shape, protruding in the radial direction toward the top foil 6, and contacts the outer circumferential surface of the top foil 6. The valleys 8c and peaks 8d are arranged alternately in the circumferential direction from the fixed end 8a toward the free end 8b.

[0047] The base foil 10 is arranged along the inner circumferential surface 20 of the shell 12. The base foil 10 is arranged opposite to the outer circumferential surface 13 of the bump foil 8 and extends in the circumferential direction so as to surround the bump foil 8. The base foil 10 is cylindrical, and the outer circumferential surface of the base foil 10 is fixed to the inner circumferential surface 20 of the shell 12 by, for example, welding. The fixed end 8a of the bump foil 8 and the fixed end 6a of the top foil 6 can be fixed to the shell 12 via the base foil 10 by welding to the base foil 10 while overlapping each other in the radial direction, for example, or can be fixed to the shell 12 by direct welding or the like via a notch portion (not shown) provided in the base foil 10. In Figure 1 In the exemplary embodiment shown, the fixed end 8a of the bump foil 8 and the fixed end 6a of the top foil 6 are fixed to the housing 12 at a 0° position in the circumferential direction. Figure 1 In the illustrated exemplary embodiment, the base foil 10 corresponds to the cylindrical portion 15 that supports the bump foil 8 from the outer peripheral side of the bump foil 8 .

[0048] In the foil bearing 2 described above, when the shaft 4 rotates, the top foil 6 elastically deforms radially outward, and gas (e.g., air) intrudes between the shaft 4 and the bearing surface 14 of the top foil 6 to form a gas film (hereinafter referred to as a "gas film"). The shaft 4 is lifted from the bearing surface 14 of the top foil 6 by the dynamic pressure of the gas film.

[0049] The air film between the shaft 4 and the bearing surface 14 of the top foil 6 causes the top foil 6 to elastically deform radially outward. Consequently, the top foil 6 presses the peaks 8d of the bump foil 8, which are in contact with the outer circumference of the top foil 6, radially outward. As a result, the bump foil 8 and the top foil 6 elastically deform radially outward together. Consequently, the bump foil 8 elastically supports the top foil 6 from its outer circumference (radially outward).

[0050] exist Figure 1 In the foil bearing 2 shown, when the shaft 4 is rotating and floating from the bearing surface 14 (for example, when the shaft 4 is rotating at the rated speed of the rotating machine including the shaft 4), the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 160° to 200° is smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360°. Furthermore, the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 160° to 200° is smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range other than 160° to 200°. The range other than 160° to 200° in the circumferential direction represents a combination of the 0° to 160° range and the 200° to 360° range in the circumferential direction, corresponding to the -160° to 160° range in the circumferential direction. Furthermore, the distance r between the central axis O of the shell 12 and the inner circumferential surface 16 of the base foil 10 within the 0° to 360° range in the circumferential direction is minimized at a position within the 160° to 200° range in the circumferential direction (in the example shown, at or near 180°).

[0051] Here, the effect of the foil bearing 2 is as follows: Figure 2 The comparison method shown is used for comparison.

[0052] Figure 2 The foil bearing 02 according to the comparative embodiment shown does not include a base foil, and the inner peripheral surface 020 of the housing 012 faces the outer peripheral surface 013 of the bump foil 08. The housing 012 corresponds to the cylindrical portion 015 that supports the bump foil 08 from the outer peripheral side of the bump foil 08. Figure 2In the comparative embodiment shown, the distance r between the central axis O of the housing 012 and the cylindrical portion 015 is constant throughout the range of 0° to 360° in the circumferential direction.

[0053] exist Figure 2 In the figure, the air film pressure distribution C0 represents the pressure distribution of the air film formed between the shaft 04 and the top foil 06 when the shaft 04 rotates and floats from the bearing surface 014. The curve representing the air film pressure distribution C0 increases in pressure as it moves upward relative to the surface of the top foil 06. In other words, the radial distance from the surface of the top foil 06 to the air film pressure distribution C0 at a specific angular position in the circumferential direction represents the pressure of the air film at that specific angular position. The greater the radial distance from the surface of the top foil 06 to the air film pressure distribution C0, the greater the air film pressure.

[0054] like Figure 2 As shown in the air film pressure distribution C0, in a comparative manner, an asymmetric air film pressure distribution is generated relative to the straight line connecting 0° and 180° in the circumferential direction, with the peak of the air film pressure being at a position further downstream than the 180° position in the circumferential direction, thereby causing an increase in the vibration of each of the shaft 04 and the foil bearing 02.

[0055] In a cross section perpendicular to the central axis O of the housing 012, when the shaft 04 rotates and floats from the bearing surface 014, the pressure distribution of the air film formed between the shaft 04 and the top foil 06 has a peak pressure at a position downstream of the 180° position in the circumferential direction, and is asymmetric with respect to the line connecting 0° and 180° in the circumferential direction. Consequently, this asymmetric pressure distribution increases the vibration of the shaft 04 and the foil bearing 02. This air film pressure distribution can be made closer to a symmetric shape with respect to the line connecting 0° and 180° in the circumferential direction by reducing the gap (bearing clearance) between the top foil 06 and the shaft 04. However, reducing the bearing clearance in the initial state (when the shaft 04 is stopped) increases the contact load on the shaft 04 and the top foil 06, potentially increasing the starting torque of the shaft 04 or degrading the coating of the top foil 06.

[0056] In contrast, in Figure 1 In the foil bearing 2 shown, when the shaft 4 rotates and floats from the bearing surface 14, the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 160° to 200° (the range near 180° in the circumferential direction) is smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360°. Thus, by locally reducing the gap between the shaft 4 and the top foil 6 within the range near 180° in the circumferential direction, as shown in FIG. Figure 3As shown in the film pressure distribution C1 (the pressure distribution of the film formed between the shaft 4 and the top foil 6), the peak of the film pressure can be shifted to near 180°, and the film pressure distribution C1 can be made nearly symmetrical about a line connecting 0° and 180° in the circumferential direction. Consequently, vibrations of the shaft 4 and the foil bearing 2 can be suppressed. Furthermore, since complex corrugations are not required on the bump foil 8 as in Patent Document 1, vibrations of the shaft 4 and the foil bearing 2 can be suppressed with a simple and low-cost structure. Furthermore, compared to a case where the bearing clearance in the initial state (when the shaft 4 is stopped) is reduced, an increase in the starting torque of the shaft 4 and degradation of the coating of the top foil 6 can be suppressed.

[0057] Figure 4 This is a diagram schematically showing an example of a cross section perpendicular to the axial direction in the foil bearing 2 according to one embodiment, and schematically showing the cross section of the foil bearing 2 in a state where the shaft 4 is removed from the foil bearing 2 .

[0058] In several embodiments, for example, Figure 4 As shown, when the shaft 4 is removed from the foil bearing 2, the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 varies with circumferential position within at least a portion of the 180° to 270° range in the circumferential direction. Furthermore, when the shaft 4 is removed from the foil bearing 2, the average value of the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 within the 180° to 270° range in the circumferential direction is smaller than the average value of the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 within the 90° to 180° range in the circumferential direction. Furthermore, when the shaft 4 is removed from the foil bearing 2, the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 within the 0° to 360° range in the circumferential direction is at its minimum within the 180° to 270° range in the circumferential direction. That is, when the shaft 4 is removed from the foil bearing 2, the minimum value of the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 within the range of 180° to 270° in the circumferential direction is smaller than the minimum value of the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 within the range other than 180° to 270° in the circumferential direction.

[0059] exist Figure 4In the exemplary embodiment shown, when the shaft 4 is stopped, the top foil 6 includes, within a circumferential range of 180° to 270°, a portion 6c where the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 decreases as it moves downstream, and a portion 6d where the distance d increases as it moves downstream. This portion 6d is circumferentially adjacent to the downstream side of portion 6c. Furthermore, the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 is minimized at the boundary between these portions 6c and 6d. Furthermore, the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 is constant throughout the circumferential range outside of the 180° to 270° range, except for the aforementioned bent portion constituting the fixed end 6a of the top foil 6. Furthermore, a region where the distance d between the central axis O of the housing 12 and the bearing surface 14 of the top foil 6 is constant may be provided between the portion 6 d and the portion 6 c .

[0060] according to Figure 4 In the foil bearing 2 shown, when the shaft 4 rotates and floats from the bearing surface 14, the top foil 6 undergoes thermal deformation due to heat. This causes the bearing surface 14 of the top foil 6 to assume a nearly perfect circular shape in a cross section perpendicular to the axial direction. Therefore, when the shaft 4 rotates and floats from the bearing surface 14, the air film pressure distribution C1 can be made more uniform, thereby suppressing vibrations of both the shaft 4 and the foil bearing 2 with a simple and low-cost structure.

[0061] Figure 5 Yes Figure 1 The schematic cross-sectional view of an example of a more specific structure of the foil bearing 2 shown in FIG. 1 and FIG. 2 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 . Figure 5 The foil bearing 2 is shown in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0062] In several embodiments, for example, Figure 5 As shown, the base foil 10 includes a first base foil portion 10a, which is circumferentially arranged over at least a portion of a circumferential range of 160° to 200°; and a second base foil portion 10b, which is circumferentially connected to both ends 10a1 and 10a2 of the first base foil portion 10a. The linear expansion coefficient of the first base foil portion 10a is smaller than that of the second base foil portion 10b. For example, the first base foil portion 10a can be formed from a material containing iron, and the second base foil portion 10b can be formed from a material containing copper.

[0063] exist Figure 5In the exemplary embodiment shown, the first base foil portion 10a is circumferentially disposed within a range of 150° to 210° in the circumferential direction. More specifically, the first base foil portion 10a is disposed within a range from a position between 150° and 180° (e.g., the 160° position) to a position between 180° and 210° (e.g., the 200° position), including the 180° position. Furthermore, the second base foil portion 10b is circumferentially disposed throughout a range of 0° to 360° in the circumferential direction, excluding the range within which the first base foil portion 10a is disposed. More specifically, the second base foil portion 10b is circumferentially disposed within a range from the 0° position in the circumferential direction to the upstream end 10a1 of the first base foil portion 10a and within a range from the downstream end 10a2 of the first base foil portion 10a to 360°. That is, the second base foil portion 10b is provided along the circumferential direction from the downstream end 10a2 of the first base foil portion 10a in the circumferential direction, through a 360° position in the circumferential direction, to the upstream end 10a1 of the first base foil portion 10a. The first base foil portion 10a and the second base foil portion 10b are each fixed to the inner circumferential surface 20 of the housing 12 by, for example, welding.

[0064] exist Figure 5 In the foil bearing 2 shown, if the temperature of the base foil 10 rises due to shaft rotation, the thermal expansion in the circumferential direction of the first base foil portion 10a having a relatively large linear expansion coefficient ( Figure 6 The thermal expansion shown by the arrow e1 is constrained by the second base foil portion 10b with a relatively small linear expansion coefficient and cannot be extended in the circumferential direction, as shown in FIG. Figure 6 As indicated by arrow e2, the first base foil portion 10a rises radially inward. Therefore, when the shaft 4 rotates and rises from the bearing surface 14, the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 160° to 200° is smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360°. Furthermore, the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360° is minimized at a position within the circumferential range of 160° to 200° (in the illustrated example, at or near 180°).

[0065] Therefore, the bump foil 8 is radially inwardly pushed up by the first base foil portion 10a, narrowing the gap between the shaft 4 and the top foil 6 within the circumferential area where the first base foil portion 10a is provided. Consequently, by shifting the peak of the film pressure to near 180°, the film pressure distribution C1 can be made nearly symmetrical about a line connecting 0° and 180° in the circumferential direction. This allows for the suppression of vibrations in the shaft 4 and the foil bearing 2 with a simple and low-cost structure. Furthermore, as described above, by using materials with different linear expansion coefficients for the first and second base foil portions 10a, the thickness of the base foil 10 can be adjusted at low cost without requiring complex processing.

[0066] Figure 7 Yes Figure 1 The schematic cross-sectional view of an example of a more specific structure of the foil bearing 2 shown in FIG. 1 and FIG. 2 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 . Figure 7 The foil bearing 2 is shown in a state where the shaft 4 rotates and floats from the bearing surface 14 .

[0067] In several embodiments, for example, Figure 7 As shown, the base foil 10 includes a first base foil portion 10c circumferentially disposed over at least a portion of a circumferential range of 160° to 200°, and a second base foil portion 10d circumferentially connected to both ends 10c1 and 10c2 of the first base foil portion 10c. The first base foil portion 10c is formed from a material having a negative Poisson's ratio, and is configured such that the thickness (radial thickness) of the first base foil portion 10c increases with respect to a tensile load in the circumferential direction.

[0068] exist Figure 7 In the exemplary embodiment shown, the first base foil portion 10c is circumferentially disposed within a range of 150° to 210° in the circumferential direction. More specifically, the first base foil portion 10c is disposed within a range from a position between 150° and 180° (e.g., the 160° position) to a position between 180° and 200° (e.g., the 200° position), including the 180° position. Furthermore, the second base foil portion 10d is circumferentially disposed throughout a range of 0° to 360° in the circumferential direction, excluding the range within which the first base foil portion 10c is disposed. More specifically, the second base foil portion 10d is circumferentially disposed within a range from the 0° position in the circumferential direction to the upstream end 10c1 of the first base foil portion 10c and within a range from the downstream end 10c2 of the first base foil portion 10c to 360°. That is, the second base foil portion 10d is provided along the circumferential direction from the downstream end 10c2 of the first base foil portion 10c in the circumferential direction, through a 360° position in the circumferential direction, to the upstream end 10c1 of the first base foil portion 10c. The first base foil portion 10c and the second base foil portion 10d are each fixed to the inner circumferential surface 20 of the housing 12 by, for example, welding.

[0069] exist Figure 7 In the foil bearing 2 shown, when the shaft 4 rotates, an air film is formed between the shaft 4 and the top foil 6, generating an air film pressure distribution. Therefore, the base foil 10 receives a load on the inner peripheral surface 20, as shown in FIG. Figure 8 As shown by the arrow e3, it bears the tensile load in the circumferential direction. Figure 8 As shown by arrow e4, the thickness (radial thickness) of the first base foil portion 10c increases near 180° in the circumferential direction. Therefore, when the shaft 4 rotates and floats from the bearing surface 14, the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 160° to 200° is smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360°. Furthermore, the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360° is minimized at a position within the circumferential range of 160° to 200° (in the illustrated example, at or near 180°).

[0070] Therefore, the bump foil 8 is radially inwardly pushed up by the first base foil portion 10c, narrowing the gap between the shaft 4 and the top foil 6 within the circumferential area where the first base foil portion 10c is provided. Consequently, by shifting the peak of the film pressure to near 180°, the film pressure distribution C1 can be made nearly symmetrical about a line connecting 0° and 180° in the circumferential direction, thereby suppressing vibrations of the shaft 4 and the foil bearing 2 with a simple and low-cost structure.

[0071] Figure 9 Yes Figure 1 The schematic cross-sectional view of an example of a more specific structure of the foil bearing 2 shown in FIG. 1 and FIG. 2 shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 .

[0072] In several embodiments, for example, Figure 9 As shown, at least one slit 30 is formed on the base foil 10 in at least a portion of the range of 0° to 360° in the circumferential direction except for the range of 160° to 200°. Figure 9In the exemplary embodiment shown, multiple slits 30 are formed at intervals along the circumferential direction within the range of 0° to 160°, and multiple slits 30 are formed at intervals along the circumferential direction within the range of 200° to 360°. In other words, multiple slits 30 are formed at intervals along the circumferential direction within the range of -160° to 160°. Each slit 30 extends circumferentially. Furthermore, no slits 30 are formed within the range of 160° to 200°. Therefore, the rigidity of the portion 10e of the base foil 10 belonging to the range of 160° to 200° in the circumferential direction is higher than the rigidity of the portion 10f belonging to the range other than 160° to 200° in the circumferential direction. The portion 10f of the base foil 10 in which the slit 30 is formed in the circumferential direction is easily deformed radially outward due to the force received from the bump foil 8. In contrast, the portion 10e of the base foil 10 in which the slit 30 is not formed is not easily deformed radially outward even if it receives force from the bump foil 8.

[0073] exist Figure 9 In the foil bearing 2 shown, when the shaft 4 is stopped (the initial state of the foil bearing 2), the inner diameter of the base foil 10 remains constant regardless of its circumferential position. However, when the shaft 4 rotates and floats from the bearing surface 14, the top foil 6 and bump foil 8 are displaced radially outward by the pressure of the air film formed between the shaft 4 and the top foil 6, exerting a radially outward force on the inner circumferential surface of the base foil 10. Therefore, when the shaft 4 rotates and floats from the bearing surface 14, the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 160° to 200° (a range where the rigidity of the base foil 10 is relatively high) is smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface 16 of the base foil 10 within the circumferential range of 0° to 360°, excluding the range of 160° to 200° (a range where the rigidity of the base foil 10 is relatively low). The distance r between the central axis O of the shell 12 and the inner peripheral surface 16 of the base foil 10 in the circumferential range of 0° to 360° is minimum at a position in the circumferential range of 160° to 200° (180° or near 180° in the example shown).

[0074] Therefore, by locally reducing the gap between the shaft 4 and the top foil 6 in the range of approximately 180° in the circumferential direction, the peak of the air film pressure can be shifted to approximately 180°, and the air film pressure distribution C1 can be made close to a symmetrical shape with respect to the straight line connecting 0° and 180° in the circumferential direction. Therefore, the vibration of each of the shaft 4 and the foil bearing 2 can be suppressed with a simple and low-cost structure. In addition, for example, Figure 5 Compared to the structure shown, since the base foil 10 can be formed of a single material, the vibration of each of the shaft 4 and the foil bearing 2 can be suppressed with a lower-cost structure.

[0075] Figure 10This is a schematic cross-sectional view showing an example of the structure of a foil bearing 2 according to another embodiment, and shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 .

[0076] exist Figure 10 In the embodiment shown, the base foil 10 is provided within a range including at least a portion of 160° to 200° in the circumferential direction. More specifically, the base foil 10 is provided within a range including the 180° position from position P1 between 150° and 180° in the circumferential direction (for example, the 160° position) to position P2 between 180° and 210° (for example, the 200° position), and is not provided within a range from position P2 in the circumferential direction through 360° to position P1. Therefore, the inner circumferential surface 20 of the housing 12 includes portions that are opposed to the outer circumferential surface 13 of the bump foil 8 on both sides of the range in which the base foil 10 is provided in the circumferential direction. Therefore, in Figure 10 In the embodiment shown, within the range where the base foil 10 is provided in the circumferential direction, the base foil 10 is opposed to the bump foil 8 and supports the bump foil 8. Within the range where the base foil 10 is not provided in the circumferential direction, the housing 12 is opposed to the bump foil 8 and supports the bump foil 8. Furthermore, the rigidity of the top foil 6 is higher than that of the bump foil 8, and the rigidity of the base foil 10 is higher than that of the top foil 6. Figure 10 In the illustrated embodiment, the base foil 10 and the housing 12 constitute a cylindrical portion 15 that supports the bump foil 8 from the outer peripheral side of the bump foil 8 .

[0077] Even in Figure 10 In the illustrated structure, when the shaft 4 is rotating and floating from the bearing surface 14, the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface of the cylindrical portion 15 within the circumferential range of 160° to 200° is also smaller than the average value of the distance r between the central axis O of the housing 12 and the inner circumferential surface of the cylindrical portion 15 within the circumferential range of 0° to 360°. Furthermore, the distance r between the central axis O of the housing 12 and the inner circumferential surface of the cylindrical portion 15 is the distance between the central axis O and the inner circumferential surface 16 of the base foil 10 within the circumferential range where the base foil 10 is provided, and is the distance between the central axis O and the inner circumferential surface 20 of the housing 12 within the circumferential range where the base foil 10 is not provided.

[0078] Furthermore, when the shaft rotates and floats from the bearing surface, the distance r between the central axis O of the housing 12 and the inner peripheral surface of the cylindrical portion 15 within the range of 0° to 360° in the circumferential direction takes a minimum value at a position within the range of 160° to 200° in the circumferential direction (in the example shown, at a position of 180° or near 180°).

[0079] exist Figure 10 In the foil bearing 2 shown, when the rotation of the shaft 4 is stopped, Figure 11AAs shown, the effect of the steps 40 formed at both ends of the base foil 10 in the circumferential direction due to the thickness t of the base foil 10 is absorbed by the deformation of the bump foil 8, so the effect of the steps 40 does not appear in the shape of the top foil 6. In contrast, when the shaft 4 rotates and floats from the bearing surface 14, as shown in FIG. Figure 11B As shown, due to the pressure of the air film between the shaft 4 and the top foil 6, the top foil 6 and the bump foil 8 are pressed radially outward and deformed accordingly with the step 40. Therefore, the distance d between the center axis of the housing 12 and the bearing surface 14 of the top foil 6 within the range where the base foil 10 is set in the circumferential direction is smaller than the distance d between the center axis of the housing 12 and the bearing surface 14 of the top foil 6 within the range where the base foil 10 is not set in the circumferential direction.

[0080] Therefore, by locally reducing the gap between the shaft 4 and the top foil 6 within the circumferential area where the base foil 10 is located, the peak of the film pressure can be shifted to approximately 180°, and the film pressure distribution C1 can be made nearly symmetrical about a line connecting 0° and 180° in the circumferential direction. This allows for the suppression of vibrations in both the shaft 4 and the foil bearing 2 using a simple and low-cost structure.

[0081] Figure 12 This is a schematic cross-sectional view showing an example of the structure of a foil bearing 2 according to another embodiment, and shows an example of a cross section perpendicular to the axial direction in the foil bearing 2 .

[0082] exist Figure 12 In the illustrated embodiment, the foil bearing 2 does not include a base foil, and the housing 12 constitutes a cylindrical portion 15 that supports the bump foil 8 from the outer peripheral side of the bump foil 8 .

[0083] exist Figure 12 In the foil bearing 2 shown, the average inner diameter r of the housing 12 within the range of 160° to 200° in the circumferential direction is smaller than the average inner diameter r of the housing 12 within the range of 0° to 360° in the circumferential direction. In other words, the average inner diameter r of the housing 12 within the range of 160° to 200° in the circumferential direction is smaller than the average inner diameter r of the housing 12 within the range other than 160° to 200° in the circumferential direction (the range of -160° to 160° in the circumferential direction). Figure 12 In the structure shown, more specifically, the inner diameter r of the housing 12 within a range of 180° from a position P1 between 150° and 180° in the circumferential direction (for example, a position of 160°) to a position P2 between 180° and 210° (for example, a position of 200°) is smaller than the inner diameter r of the housing 12 within a range from the position P1 in the circumferential direction through positions of 360° to the position P2.

[0084] Even in Figure 12In the structure shown, when the shaft 4 rotates and floats from the bearing surface 14, the average value of the distance r between the center axis O of the housing 12 and the inner peripheral surface of the cylindrical portion 15 (the inner peripheral surface 20 of the housing 12) in the range of 160° to 200° in the circumferential direction is also smaller than the average value of the distance r between the center axis O of the housing 12 and the inner peripheral surface of the cylindrical portion 15 (the inner peripheral surface 20 of the housing 12) in the range of 0° to 360° in the circumferential direction. Furthermore, the distance r between the center axis O of the housing 12 and the inner peripheral surface of the cylindrical portion 15 (the inner peripheral surface 20 of the housing 12) in the range of 0° to 360° in the circumferential direction takes the minimum value at a position in the range of 160° to 200° in the circumferential direction (a position at or near 180° in the example shown). Therefore, due to the Figure 10 11 , the peak of the film pressure can be shifted to near 180° so that the film pressure distribution C1 is close to a shape symmetrical with respect to a straight line connecting 0° and 180° in the circumferential direction, thereby suppressing the vibrations of the shaft 4 and the foil bearing 2 with a simple and low-cost structure.

[0085] Figure 13 Schematic diagram showing an example of a rotary machine 50 including the foil bearing 2 according to each of the above-mentioned embodiments. Figure 13 In the exemplary embodiment shown, the rotary machine 50 is a turbocharger, which includes a turbine 52, a compressor 54 connected to the turbine 52 via a shaft 4, and a pair of foil bearings 2 that rotatably support the shaft 4. The pair of foil bearings 2 are provided on the shaft 4 at positions separated from each other in the axial direction.

[0086] The present invention is not limited to the above-described embodiment, and includes a form in which modifications are added to the above-described embodiment, or a form in which these forms are appropriately combined.

[0087] For example, a turbocharger is shown as an example of a rotating machine to which the foil bearing is applied. However, the rotating machine to which the foil bearing is applied is not limited to the turbocharger, and may be, for example, a turbine or a compressor.

[0088] The contents described in each of the above-mentioned embodiments can be understood, for example, as follows.

[0089] (1) A foil bearing according to at least one embodiment of the present invention (for example, the foil bearing 2 described above) includes:

[0090] A top foil (e.g., the top foil 6 ) includes a bearing surface (e.g., the bearing surface 14 ) facing the shaft (e.g., the shaft 4 );

[0091] a bump foil (for example, the bump foil 8 described above) supporting the top foil from an outer peripheral side of the top foil; and

[0092] A cylindrical housing (for example, the housing 12 ) accommodates the top foil and the bump foil,

[0093] The foil bearing includes a cylindrical portion (for example, the cylindrical portion 15 ) that surrounds the bump foil and supports the bump foil from the outer peripheral side of the bump foil.

[0094] On a cross section perpendicular to the central axis of the housing, if the position of the upper end of the inner circumferential surface of the housing (for example, the upper end 20t) is defined as the 0° position in the circumferential direction of the housing, and the rotation direction of the shaft is defined as the positive direction of the circumferential position,

[0095] Then, when the shaft rotates and floats from the bearing surface, on a cross section perpendicular to the central axis of the housing, the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion within the range of 160° to 200° in the circumferential direction is smaller than the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion within the range of 0° to 360° in the circumferential direction.

[0096] In conventional foil bearings, in a cross section perpendicular to the central axis of the housing, when the shaft rotates and floats from the bearing surface, the pressure distribution of the air film formed between the shaft and the top foil has a peak in the air film pressure at a position downstream of the 180° position in the circumferential direction, and is asymmetric with respect to a straight line connecting 0° and 180° in the circumferential direction. Therefore, due to this asymmetric pressure distribution of the air film, the vibration of each of the shaft and the foil bearing increases. In contrast, according to the foil bearing described in (1) above, when the shaft rotates and floats from the bearing surface, the average value of the distance between the central axis of the housing and the inner peripheral surface of the cylindrical portion in the range of 160° to 200° in the circumferential direction (the range near 180° in the circumferential direction) is smaller than the average value of the distance between the central axis of the housing and the inner peripheral surface of the cylindrical portion in the range of 0° to 360° in the circumferential direction. Therefore, compared to a case where the distance between the housing's central axis and the inner circumferential surface of the cylindrical portion is constant within a circumferential range of 0° to 360° when the shaft rotates and floats from the bearing surface, the bearing clearance (the clearance between the shaft and the top foil) can be locally reduced near 180° in the circumferential direction when the shaft rotates and floats from the bearing surface. This shifts the peak of the air film pressure on a cross section perpendicular to the housing's central axis to near 180°, allowing the air film pressure distribution to become symmetrical about the line connecting 0° and 180° in the circumferential direction. Consequently, vibrations of both the shaft and the foil bearing can be suppressed. Furthermore, since complex corrugations are not required on the bump foil, as in Patent Document 1, vibrations of both the shaft and the foil bearing can be suppressed with a simple and low-cost structure. Furthermore, compared to a case where the bearing clearance is reduced in the initial state (when the shaft is stopped), increases in the shaft's starting torque and degradation of the top foil coating can be suppressed.

[0097] (2) In some embodiments, in the foil bearing described in (1) above,

[0098] When the shaft rotates and floats from the bearing surface, the distance between the central axis of the housing and the inner peripheral surface of the cylindrical portion takes a minimum value at a position within a range of 160° to 200° in the circumferential direction.

[0099] According to the foil bearing described in (2) above, the peak value of the air film pressure on a cross section perpendicular to the central axis of the housing can be shifted to approximately 180°, making the air film pressure distribution close to a shape that is symmetrical about a line connecting 0° and 180° in the circumferential direction. Therefore, vibrations of the shaft and the foil bearing can be suppressed. Furthermore, since complex corrugated shapes, such as those described in Patent Document 1, are not required on the corrugated foil, vibrations of the shaft and the foil bearing can be suppressed with a simple and low-cost structure.

[0100] (3) In some embodiments, in the foil bearing described in (1) or (2) above,

[0101] When the shaft is removed from the foil bearing, an average value of the distance between the central axis of the housing and the inner peripheral surface of the top foil within a range of 180° to 270° in the circumferential direction is smaller than an average value of the distance between the central axis of the housing and the inner peripheral surface of the top foil within a range of 90° to 180° in the circumferential direction.

[0102] According to the foil bearing described in (3) above, when the shaft rotates and floats from the bearing surface, the top foil is thermally deformed by heat, thereby allowing the bearing surface of the top foil to approach a true circular shape in a cross section perpendicular to the axial direction. Therefore, the air film pressure distribution can be made more uniform when the shaft rotates and floats from the bearing surface, thereby effectively suppressing vibrations of the shaft and the foil bearing with a simple structure.

[0103] (4) In some embodiments, in the foil bearing described in any one of (1) to (3) above,

[0104] When the shaft is removed from the foil bearing, the distance between the central axis of the housing and the inner peripheral surface of the top foil takes a minimum value at a position within a range of 180° to 270° in the circumferential direction.

[0105] According to the foil bearing described in (4) above, when the shaft rotates and floats from the bearing surface, the top foil is thermally deformed due to heat, thereby making the cross-section of the top foil's bearing surface (a cross-section perpendicular to the axial direction) close to a true circle. Therefore, the air film pressure distribution can be made more uniform when the shaft rotates and floats from the bearing surface, thereby effectively suppressing the vibration of each of the shaft and the foil bearing with a simple and low-cost structure.

[0106] (5) In some embodiments, in the foil bearing described in any one of (1) to (4),

[0107] The cylindrical portion includes a base foil (for example, the above-described base foil 10 ) disposed along the inner peripheral surface of the housing.

[0108] According to the foil bearing described in (5) above, vibrations of the shaft and the foil bearing can be suppressed with a simple structure and at low cost.

[0109] (6) In some embodiments, in the foil bearing described in (5) above,

[0110] The base foil comprises:

[0111] a first base foil portion (for example, the first base foil portion 10 a ) provided along the circumferential direction within a range including at least a portion of 160° to 200° in the circumferential direction; and

[0112] At least one second base foil portion (for example, the second base foil portion 10 b ) is connected to both ends of the first base foil portion in the circumferential direction.

[0113] The linear expansion coefficient of the first base foil portion is smaller than the linear expansion coefficient of the second base foil portion.

[0114] According to the foil bearing described in (6), if the temperature of the base foil rises due to the rotation of the shaft, the circumferential thermal expansion of the first base foil portion having a relatively large linear expansion coefficient is restrained by the second base foil portion having a relatively small linear expansion coefficient, and the first base foil portion floats radially inward. Therefore, when the shaft rotates and floats from the bearing surface, the average value of the distance between the central axis of the housing and the inner peripheral surface of the base foil in the range of 160° to 200° in the circumferential direction is smaller than the average value of the distance between the central axis of the housing and the inner peripheral surface of the base foil in the range of 0° to 360° in the circumferential direction. Therefore, the corrugated foil is pushed radially inward by the first base foil portion, and the gap between the shaft and the top foil in the range where the first base foil portion is provided in the circumferential direction becomes narrower. Therefore, by shifting the peak of the film pressure to near 180°, the film pressure distribution can be made close to a shape symmetrical with respect to the straight line connecting 0° and 180° in the circumferential direction, and the vibration of each of the shaft and the foil bearing can be suppressed with a simple and low-cost structure. Furthermore, as described above, by using materials having different linear expansion coefficients for the first base foil portion and the second base foil portion, the thickness of the base foil can be adjusted at low cost without requiring complicated processing.

[0115] (7) In some embodiments, in the foil bearing described in any one of (5) or (6),

[0116] The rigidity of a portion of the base foil within the range of 160° to 200° in the circumferential direction is higher than the rigidity of a portion of the base foil within the range other than 160° to 200° in the circumferential direction.

[0117] According to the foil bearing described in (7), when the base foil is subjected to a radially outward force caused by the pressure of the air film formed between the shaft and the top foil when the shaft rotates, the base foil is more easily compressed and deformed in the radial direction within the range of 160° to 200° in the circumferential direction than within the range other than 160° to 200° in the circumferential direction. Therefore, when the shaft rotates and floats from the bearing surface, the average value of the distance between the central axis of the housing and the inner peripheral surface of the base foil within the range of 160° to 200° in the circumferential direction (the range where the rigidity of the base foil is relatively high) is smaller than the average value of the distance between the central axis of the housing and the inner peripheral surface of the base foil within the range of 0° to 360° in the circumferential direction. Therefore, as described above, the vibration of the shaft and the foil bearing can be suppressed with a simple and low-cost structure.

[0118] (8) In some embodiments, in the foil bearing described in any one of (5) or (7),

[0119] At least one slit (for example, the plurality of slits 30 ) is formed in the base foil in at least a portion of the range excluding 160° to 200° in the circumferential direction.

[0120] According to the foil bearing described in (8), the rigidity of the portion of the base foil that is not within the circumferential range of 160° to 200° can be reduced with a simple structure. Thus, the structure and effect of (7) can be achieved with a simple structure. Furthermore, compared to the structure shown in (5), for example, since the base foil can be formed from a single material, vibrations of the shaft and the foil bearing can be suppressed with a more cost-effective structure.

[0121] (9) In some embodiments, in the foil bearing described in (5) above,

[0122] The base foil is provided in a range including at least a portion of 160° to 200° in the circumferential direction.

[0123] The cylindrical portion is composed of the base foil and the outer shell,

[0124] The inner peripheral surface of the housing includes portions facing the bump foil on both sides of the range in the circumferential direction where the base foil is provided.

[0125] According to the foil bearing described in (9), when the shaft rotates, the pressure of the air film between the shaft and the top foil pushes the top foil and the corrugated foil radially outward. Therefore, the deformation of the top foil and the base foil in the range on both sides of the range where the base foil is provided in the circumferential direction (the range where the base foil is not provided) becomes larger than that in the range where the base foil is provided in the circumferential direction. Therefore, when the shaft rotates and floats from the bearing surface, the bearing clearance (the clearance between the shaft and the top foil) in the range where the base foil is provided in the circumferential direction can be made smaller than the bearing clearance in the range on both sides of the base foil in the circumferential direction. As a result, the peak of the air film pressure on the cross section perpendicular to the central axis of the housing can be shifted to near 180°, and the air film pressure distribution can be made close to a shape symmetrical with respect to the straight line connecting 0° and 180° in the circumferential direction. Therefore, the vibration of the shaft and the foil bearing can be suppressed with a simple and low-cost structure.

[0126] (10) In some embodiments, in the foil bearing according to any one of (1) to (4) above,

[0127] An average inner diameter of the housing within a range of 160° to 200° in the circumferential direction is smaller than an average inner diameter of the housing within a range of 0° to 360° in the circumferential direction.

[0128] According to the foil bearing described in (10), when the shaft rotates, the pressure of the air film between the shaft and the top foil pushes the top foil and the corrugated foil radially outward. Therefore, the deformation of the top foil and the base foil in the range of the inner diameter of the shell in the circumferential direction is larger than that in the range of the inner diameter of the shell in the circumferential direction. Therefore, when the shaft rotates and floats from the bearing surface, the bearing clearance (the clearance between the shaft and the top foil) in the circumferential direction of about 180° can be made smaller than the bearing clearance in the other ranges in the circumferential direction. As a result, the peak of the air film pressure on the cross section perpendicular to the central axis of the shell can be moved to near 180°, and the pressure distribution of the air film can be made close to a shape symmetrical with respect to the straight line connecting 0° and 180° in the circumferential direction. Therefore, the vibration of the shaft and the foil bearing can be suppressed with a simple and low-cost structure.

[0129] (11) A rotary machine according to at least one embodiment of the present invention (for example, the rotary machine 50 ) includes the foil bearing according to any one of (1) to (10) above and the shaft.

[0130] According to the rotating machine described in (11), since the foil bearing according to any one of (1) to (10) is provided, vibrations of the shaft and the foil bearing can be suppressed with a simple and low-cost structure.

[0131] Explanation of symbols

[0132] 2- foil bearing, 4- shaft, 5- outer peripheral surface, 6- top foil, 6a, 8a- fixed end, 6b, 8b- free end, 6c, 6d, 10e, 10f- part, 8- wave foil, 8c- valley part, 8d- peak part, 10- base foil, 10a, 10c- first base foil part, 10a1, 10c1- upstream end, 10a2, 10c2- downstream end, 10b, 10d- second base foil part, 12- housing, 13- outer peripheral surface, 14- bearing surface, 15- cylindrical part, 16, 20- inner peripheral surface, 20t- upper end, 30- slit, 40- step, 50- rotating machinery, 52- turbine, 54- compressor.

Claims

1. A foil bearing comprising: a top foil including a bearing surface opposite the shaft; a corrugated foil supporting the top foil from an outer peripheral side of the top foil; and a cylindrical housing accommodating the top foil and the bump foil, The foil bearing has: a cylindrical portion surrounding the bump foil and supporting the bump foil from an outer peripheral side of the bump foil, On a cross section perpendicular to the central axis of the housing, if the position of the upper end of the inner circumferential surface of the housing is defined as the 0° position in the circumferential direction of the housing, and the rotation direction of the shaft is defined as the positive direction of the circumferential position, Then, when the shaft rotates and floats from the bearing surface, on a cross section perpendicular to the central axis of the housing, the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion within the range of 160° to 200° in the circumferential direction is smaller than the average value of the distance between the central axis of the housing and the inner circumferential surface of the cylindrical portion within the range of 0° to 360° in the circumferential direction.

2. The foil bearing according to claim 1, wherein When the shaft rotates and floats from the bearing surface, the distance between the central axis of the housing and the inner peripheral surface of the cylindrical portion takes a minimum value at a position within a range of 160° to 200° in the circumferential direction.

3. The foil bearing according to claim 1, wherein When the shaft is removed from the foil bearing, an average value of the distance between the central axis of the housing and the inner peripheral surface of the top foil within a range of 180° to 270° in the circumferential direction is smaller than an average value of the distance between the central axis of the housing and the inner peripheral surface of the top foil within a range of 90° to 180° in the circumferential direction.

4. The foil bearing according to claim 1, wherein When the shaft is removed from the foil bearing, the distance between the central axis of the housing and the inner peripheral surface of the top foil takes a minimum value at a position within a range of 180° to 270° in the circumferential direction.

5. The foil bearing according to claim 1, wherein The cylindrical portion includes a base foil arranged along the inner peripheral surface of the housing.

6. The foil bearing according to claim 5, wherein The base foil comprises: a first base foil portion provided along the circumferential direction within a range including at least a portion of 160° to 200° in the circumferential direction; and at least one second base foil portion connected to both ends of the first base foil portion in the circumferential direction; The linear expansion coefficient of the first base foil portion is smaller than the linear expansion coefficient of the second base foil portion.

7. The foil bearing according to claim 5, wherein: The rigidity of a portion of the base foil within the range of 160° to 200° in the circumferential direction is higher than the rigidity of a portion of the base foil within the range other than 160° to 200° in the circumferential direction.

8. The foil bearing according to claim 5, wherein At least one slit is formed in the base foil in at least a portion of a range other than 160° to 200° in the circumferential direction.

9. The foil bearing according to claim 5, wherein: The base foil is provided in a range including at least a portion of 160° to 200° in the circumferential direction. The cylindrical portion is composed of the base foil and the outer shell, The inner peripheral surface of the housing includes portions facing the bump foil on both sides of the range in the circumferential direction where the base foil is provided.

10. The foil bearing according to claim 1, wherein An average inner diameter of the housing within a range of 160° to 200° in the circumferential direction is smaller than an average inner diameter of the housing within a range of 0° to 360° in the circumferential direction. 11 . A rotating machine comprising the foil bearing according to claim 1 and the shaft.

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