Foil bearing

Abstract

To provide a foil bearing (thrust foil bearing) that eliminates localized strong contact between the bearing surface and the surface opposite the bearing surface, generates stable dynamic pressure, and ensures load capacity. [Solution] The foil bearing comprises a foil holder and a plurality of leaves attached to the foil holder, each having a bearing surface facing a rotating member, and arranged in a line in the circumferential direction of the foil holder, wherein the pitch of the leaves is longer on the outer diameter side than on the inner diameter side. The leaves have a top foil portion provided on one side in the circumferential direction and having a bearing surface, and a back foil portion provided on the other side in the circumferential direction of the top foil portion and facing the surface opposite to the bearing surface of the top foil portion of the adjacent leaf. The back foil portion has a convex portion on the outer diameter side of the arc line passing through the center of the leaf in the inner and outer diameter directions.

Description

Technical Field

[0001] The present invention relates to foil bearings, and particularly to thrust foil bearings in which a bearing surface is formed by arranging a plurality of leaves in the circumferential direction.

Background Art

[0002] Bearings that support the main shafts of turbo machines such as gas turbines and turbochargers are required to withstand harsh environments such as high temperatures and high-speed rotation. As bearings suitable for use under such harsh conditions, foil bearings (thrust foil bearings) as described in Patent Document 1 and Patent Document 2 have attracted attention. A foil bearing is one in which a bearing surface is constituted by a thin film (leaf) having flexibility with low rigidity against bending, and a fluid film (for example, an air film) is formed in a bearing gap formed between the shaft and the bearing surface of the leaf during rotation of the shaft to support the shaft in a non-contact manner. According to this foil bearing, by forming the bearing surface with leaves, the deflection of the bearing surface is allowed, and the bearing surface follows and deforms due to displacement and thermal expansion of the shaft, etc., so that it has the advantage of being able to stably support the shaft even under harsh conditions.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in a thrust foil bearing, the pitches are different between the inner diameter side and the outer diameter side of the leaf. For this reason, on the inner diameter side where the pitch is short, when adjacent leaves in the circumferential direction are overlapped and assembled, the leaves are difficult to bend, and the foil is likely to float.

[0005] Furthermore, the raised inner diameter side may experience strong contact with the shaft end face (the surface opposite the bearing surface) during operation, potentially resulting in uneven contact and preventing the acquisition of the required load capacity.

[0006] Therefore, in view of these circumstances, the present invention aims to provide a foil bearing (thrust foil bearing) that eliminates localized strong contact between the bearing surface and the surface facing the bearing surface, generates stable dynamic pressure, and ensures load capacity. [Means for solving the problem]

[0007] The foil bearing of the present invention comprises a foil holder and a plurality of leaves attached to the foil holder, each having a bearing surface facing a rotating member, and arranged in a line in the circumferential direction of the foil holder, wherein the leaf has a pitch on the outer diameter side that is longer than the pitch on the inner diameter side, and the leaf has a top foil portion provided on one side in the circumferential direction and having the bearing surface, and a back foil portion provided on the other side in the circumferential direction of the top foil portion and facing the side of the adjacent leaf opposite to the bearing surface of the top foil portion, and the back foil portion has a convex portion on the outer diameter side of the arc line passing through the center of the leaf in the inner and outer diameter directions.

[0008] According to the foil bearing of the present invention, the back foil portion has a convex portion on the outer diameter side of the arc line passing through the center of the leaf in the inner and outer diameter direction. Therefore, the side of the relative rotating member that rotates relative to the foil holder facing the bearing surface can be made higher, thereby weakening the contact on the inner diameter side and effectively preventing strong contact. Furthermore, the side of the relative rotating member that rotates relative to the foil holder facing the bearing surface can be made the highest point of the leaf, which makes it easier for the inner diameter side to move downward.

[0009] By providing a protrusion, the side of the leaf that rotates relative to the foil holder facing the bearing surface can be made higher on the outer diameter side of the leaf. In other words, since raising the height only requires providing a protrusion, productivity is excellent.

[0010] In this range of protrusions, the position is offset from the bearing surface, which effectively prevents localized contact with the dynamic pressure surface and ensures stable load capacity. Conversely, if protrusions are provided on the bearing surface, localized contact with the dynamic pressure surface occurs, making it impossible to ensure stable load capacity. Furthermore, the area connecting the bearing part and the fixed part has a narrow surface width, making it susceptible to deformation due to stress concentration.

[0011] The number of the aforementioned protrusions may be set to be less than or equal to the number of leaves, or one protrusion may be provided for each leaf.

[0012] It is preferable that the height of the protrusion be greater than 0 mm and less than or equal to 0.2 mm. If it is less than 0 mm, it will not be considered high enough, and if it is greater than 0.2 mm, it will be too high, and there is a risk that the contact will be too strong due to this protrusion. [Effects of the Invention]

[0013] According to the present invention, the foil does not experience localized strong contact with the surface facing the bearing surface, thereby generating stable dynamic pressure and ensuring load capacity. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of a gas turbine. [Figure 2] This is a cross-sectional view showing the support structure for the main shaft of a gas turbine. [Figure 3] This is a cross-sectional view of a thrust foil bearing incorporated into the support structure of the main shaft of a gas turbine. [Figure 4] This is a front view of a thrust foil bearing. [Figure 5] This is an enlarged front view of the leaf of a foil bearing. [Figure 6] Figure 4 is an enlarged cross-sectional view along line XX. [Figure 7]Shows a state where a plurality of leaves are arranged along the circumferential direction, (a) is a plan view of the main part, (b) is a plan view of two adjacent leaves in the circumferential direction, and (c) is a perspective view of two adjacent leaves in the circumferential direction. [Figure 8] It is a simplified cross-sectional view showing the relationship between the fixed part and the convex part. [Figure 9] It is a simplified perspective view of one leaf. [Figure 10] It is a chart at diameter A in FIG. 4. [Figure 11] It is a chart between diameter A and diameter B in FIG. 4. [Figure 12] It is a chart at diameter B in FIG. 4. [Figure 13] It is a diagram showing the height of the surface of the foil when the convex part is not present on all the leaves. [Figure 14] It is a simplified cross-sectional view of the main part without the convex part. [Figure 15] Shows the case with a convex part, (a) is a simplified plan view of the surface shape, (b) is a perspective view of the surface shape, and (c) is a graph showing the result of the fitting test. [Figure 16] Shows the case without a convex part, (a) is a simplified plan view of the surface shape, (b) is a perspective view of the surface shape, and (c) is a graph showing the result of the fitting test.

Mode for Carrying Out the Invention

[0015] FIG. 1 conceptually shows the configuration of a gas turbine, which is a type of turbomachine. This gas turbine mainly includes a turbine 1 and a compressor 2 that form a blade row, a generator 3, a combustor 4, and a regenerator 5. The turbine 1, the compressor 2, and the generator 3 are provided with a common main shaft 6 extending in the horizontal direction, and a rotor that can rotate integrally with the main shaft 6, the turbine 1, and the compressor 2 is formed.

[0016] Air drawn in through the intake port 7 is compressed by the compressor 2, heated in the regenerator 5, and then sent to the combustor 4. Fuel is mixed with this compressed air and burned, and the high-temperature, high-pressure gas rotates the turbine 1. The rotational force of the turbine 1 is transmitted to the generator 3 via the main shaft 6, and the generator 3 rotates to generate electricity, which is output via the inverter 8. Since the gas after rotating the turbine 1 is relatively hot, this gas is sent to the regenerator 5 to exchange heat with the compressed air before combustion, thereby reusing the heat from the gas after combustion. After heat exchange in the regenerator 5, the gas passes through the exhaust heat recovery device 9 before being discharged as exhaust gas.

[0017] Figure 2 shows an example of a rotor support structure in the gas turbine described above. In this support structure, radial bearings 10 are arranged at two locations in the axial direction, and thrust bearings 20, 20 are arranged on both sides in the axial direction of the thrust collar 6a provided on the main shaft 6. The main shaft 6 is supported so as to be rotatable in the radial direction and in both thrust directions by these radial bearings 10 and thrust bearings 20.

[0018] In this support structure, the region between the turbine 1 and the compressor 2 is a high-temperature environment because it is adjacent to the turbine 1, which is rotated by high-temperature, high-pressure gas. In this high-temperature environment, lubricants such as oil and grease deteriorate and evaporate, making it difficult to use conventional bearings (such as rolling bearings) that use these lubricants. Therefore, pneumatic bearings, particularly the foil bearing (thrust foil bearing 20) according to the present invention, are suitable as bearings 10 and 20 used in this type of support structure.

[0019] Next, the configuration of a foil bearing (thrust foil bearing) suitable for the thrust bearing of the gas turbine will be described.

[0020] As shown in Figure 3, the thrust foil bearing 20 has a disc-shaped foil holder 21 and a plurality of leaves (foils) 22 attached to the end face (leaf-compatible surface) 21a of the foil holder 21. In this embodiment, thrust foil bearings 20, 20 are provided on both axial sides of the thrust collar 6a. These thrust foil bearings 20, 20 have a structure that is symmetrical in the axial direction with respect to the thrust collar 6a. In the following, the side downstream in the direction of fluid flow relative to the leaves 22 when the main shaft 6 is rotating will be referred to as the "downstream side," and the opposite side will be referred to as the "upstream side."

[0021] The foil holder 21 is generally made of metal, resin, or the like. In this embodiment, however, as will be described later, a portion of the leaf 22 (outer diameter edge) is welded and fixed to the foil holder 21, so it is preferable to make the foil holder 21 out of metal. The foil holder 21 is a hollow disc shape having a central hole (inner hole) 31 into which the main shaft 6 is inserted. Multiple leaves 22 are attached to one end face 21a of the foil holder 21. The other end face 21c of the foil holder 21 is fixed to the housing of the equipment (a gas turbine in this embodiment) into which the thrust foil bearing 20 is incorporated.

[0022] The leaf 22 is made of a metal that is highly springy and easy to process, such as steel or a copper alloy. The leaf 22 is made of a thin metal sheet (foil) with a thickness of about 20 μm to 200 μm. In an air hydrodynamic bearing that uses air as a fluid film as in this embodiment, since there is no oil in the atmosphere, it is preferable to form the leaf 22 from stainless steel or bronze.

[0023] As shown in Figure 4, the leaves 22 are arranged in a circumferential direction with a phase shift. Each leaf 22 has a bearing surface S (see Figure 6) facing the rotating shaft member, and multiple leaves are arranged in a circumferential direction of the foil holder. As shown in Figure 5, each leaf 22 has a top foil portion 22a provided on one side in the circumferential direction and having the bearing surface S, and a back foil portion 22b provided on the other side in the circumferential direction of the top foil portion and facing the surface opposite to the bearing surface S of the top foil portion 22a of the adjacent leaf 22, and the top foil portion 22a and the back foil portion 22b constitute the main body portion 22c. In this case, as shown in Figure 7(c), etc., one leaf 22 (leaf 22) is overlapped by at least half a pitch of its circumferential length on another leaf 22 (leaf 22) that is adjacent to it in the circumferential direction.

[0024] Multiple leaves 22 have a convex shape 221 at the downstream end (tip) in the direction of rotation, which protrudes downstream, and a concave shape 222 at the upstream end (rear end) in the direction of rotation, which is recessed downstream. The top of the convex shape is rounded, i.e., a rounded shape 22a1, and the bottom 222a of the concave shape 222 is also rounded. In other words, the convex shape 221 at the front end and the concave shape 222 at the rear end form a so-called herringbone shape. By forming them in this herringbone shape, it is possible to draw fluid (e.g., air) into the radial central region of the thrust bearing gap during the rotation of the main shaft 6, thereby increasing the load capacity of the thrust foil bearing.

[0025] Furthermore, an arc portion 22d is provided at the outer diameter end of the main body portion 22c of the leaf 22 (composed of the top foil portion 22a and the back foil portion 22b), and an arc portion 22e is provided at the inner diameter end of the main body portion 22c. Both the arc portions 22d and 22e are centered on the rotation center O of the main shaft 6.

[0026] Figure 6 shows an enlarged cross-sectional view along line XX in Figure 4. As shown, with the leaves 22 attached to the foil holder 21, the bearing surface S provided on the top foil portion 22a of each leaf 22 directly faces the thrust collar 6a in the axial direction, and the back foil portion 22b of the downstream adjacent leaf 22 is positioned behind the top foil portion 22a of each leaf 22 (opposite the bearing surface S). In other words, the back foil portion 22b of each leaf 22 is positioned between the top foil portion 22a of the upstream adjacent leaf 22 and the foil holder 21. Note that the arrow Z in Figure 6 indicates the direction of rotation.

[0027] When the spindle 6 rotates in one direction circumferentially (in the direction of arrow Z1 in Figure 4), a bearing gap C is formed between the bearing surface S of each leaf 22 of the thrust foil bearing 20 and the end face of the thrust collar 6a. At this time, each leaf 22 rides up onto the adjacent leaf 22 and bends, so the bearing gap C forms a wedge shape that narrows towards the downstream side (in Figure 6, each leaf 22 is simplified to a flat plate shape). The air in the large gap C1 of this wedge-shaped bearing gap C is pushed into the small gap C2, increasing the pressure of the air film in the bearing gap C, and this pressure provides non-contact support to the spindle 6 in the thrust direction. At this time, the leaves 22 elastically deform according to operating conditions such as load, spindle 6 rotation speed, and ambient temperature, so the bearing gap C is automatically adjusted to an appropriate width according to the operating conditions. Therefore, even under harsh conditions such as high temperature and high rotation speed, the bearing gap C can be managed to an optimal width, making it possible to stably support the spindle 6.

[0028] Incidentally, an extended portion (fixed portion) 50 is provided at the outer diameter side edge of each leaf 22, and this extended portion (fixed portion) 50 is fixed, for example, by YAG laser welding. Incidentally, a YAG laser is a solid-state laser, and in addition to solid-state lasers, gaseous lasers can also be used for laser welding, and CO2 laser welding using a gaseous laser such as a CO2 laser may also be used.

[0029] Furthermore, on the outer diameter side of the leaf 22, the side facing the bearing surface S (the side of the relative rotating member that rotates relative to the foil holder, in this case the thrust collar 6a) is made higher to weaken contact on the inner diameter side. That is, a convex portion 51 is provided in the area H shown by the hatching in Figure 7(a), with the thrust collar 6a side being convex. In this case, two leaves 22 adjacent to one leaf 22 in the circumferential direction are overlapped by at least half a pitch of their circumferential length, and a convex portion is provided on the leaf 22 located below the overlapping portion, convex toward the other leaf 22 and pushing up the back foil portion side of the other leaf 22. It is preferable that the convex portion 51 is arranged in the area H shown by the cross patching in Figure 7(a). This range H is located on the back foil portion 22b side of one leaf 22, on the outer diameter side of the arc line L that passes through the inner and outer diameter center of each top foil portion 22, and on the inner diameter side of the fixing portion 50 (see Figures (a), (b), and (c)). In other words, it is provided on one leaf 22 near the fixing portion 50 in the overlapping portion of adjacent leaves 22 in the circumferential direction. By arranging it in this way, the function of the protrusion 51, which will be described later, can be effectively performed. Here, the function of the protrusion 51 is to "raise the relative rotating member side that rotates relative to the foil holder 21 facing the bearing surface S on the outer diameter side of the leaf 22." Note that the illustration of the protrusion 51 is omitted in Figures 7(a) and 7(c).

[0030] As shown in Figure 9, the protrusion 51 measures the shape of the leaf 22 in the normal direction (Z) relative to the bearing surface S of the leaf 22 on the side of the relative rotating member that rotates relative to the foil holder 21, with respect to the XY plane, and corrects the inclination and deformation of the leaf 22 so that when the bearing surface S of the leaf 22 on the side of the relative rotating member that rotates relative to the foil holder 21 is viewed from above, the outer diameter side of the leaf 22 is the highest point of the leaf 22, and is provided on each leaf 22.

[0031] In this case, the range may span the entire range H, or it may be smaller than this range.

[0032] By the way, Figure 10 is a chart of line A1 at diameter A in Figure 4, Figure 11 is a chart of line D1 between line A1 at diameter A and line B1 at diameter B in Figure 4, and Figure 12 is a chart of line B1 at diameter B in Figure 4.

[0033] Diameter A is the diameter of circle A1 formed at the outer edge 22a11 of the tip radius portion 22a1 of the leaf 22, as shown in Figure 7, and Figure 10 shows the height in a cross-section along this circle A1. Diameter B is the diameter of circle B1 formed at the inner diameter end of the extended portion (fixed portion) 50, as shown in Figure 7, and Figure 11 shows the height in a cross-section along circle D1, which is midway between circles A1 and B1, and Figure 12 shows the height in a cross-section along circle B1.

[0034] It can be seen that the height of the protrusion 51 in the cross-section along circle D1 is higher than the height of other parts. The height of the protrusion 51 is set to approximately 0.05 mm to 0.1 mm. Note that the heights in Figures 11 to 13 include the wall thickness of the leaf 11 (for example, 0.04 mm).

[0035] Figure 14 shows the foil height in a shaded diagram, where darker colors indicate greater height. Within range 70, there are darker areas, which represent the convex portions 51. Within range 71, there are no dark areas representing the convex portions 51. This indicates that no convex portions 51 are provided within this range 71. In other words, the convex portions 51 may be provided on all leaves 22 or on any leaves 22; Figure 14 shows the case where they are not provided on all leaves 22.

[0036] In this way, by providing the protrusion 51, the contact between the foil holder facing the bearing surface S and the relative rotating inner diameter side can be weakened, and as shown in Figure 8, the outer diameter side of the other leaf 22 that is superimposed on one leaf 22 is pushed up. As a result, the contact with the inner diameter side of the foil 22a that corresponds to the bearing surface S is weakened. In contrast, if such a protrusion 51 is not present, as shown in Figure 15, the outer diameter side is not pushed up, so the contact with the inner diameter side that corresponds to the bearing surface 3 becomes stronger.

[0037] In this invention, the back foil portion 22b is provided with a convex portion 51 on the outer diameter side of the arc line L that passes through the center of the leaf 22 in the inner and outer diameter directions. Therefore, the side of the relative rotating member that rotates relative to the foil holder 21 facing the bearing surface S can be made higher, thereby weakening the contact on the inner diameter side and effectively preventing strong contact. As a result, stable dynamic pressure can be generated and load capacity can be secured. Furthermore, the side of the relative rotating member that rotates relative to the foil holder facing the bearing surface can be made the highest among the leaves, which makes it easier for the inner diameter side to move downward.

[0038] By providing the leaf 22 with a convex portion 51 on the side facing the bearing surface S and rotating relative to the foil holder 21, the side facing the bearing surface S and rotating relative to the foil holder 21 can be made higher on the outer diameter side of the leaf 22. In other words, since raising the height only requires providing the convex portion 51, productivity is excellent.

[0039] By providing the protrusion 51 in this range, it is positioned away from the bearing surface S, which effectively prevents localized contact with the dynamic pressure surface S and ensures stable load capacity. In contrast, if the protrusion 51 is provided on the bearing surface S, localized contact with the dynamic pressure surface S will occur, making it impossible to ensure stable load capacity. Furthermore, the area connecting the bearing part S and the extended part (fixed part) 50 has a narrow surface width, making it easy to induce deformation by utilizing stress concentration.

[0040] The protrusion 51 only needs to be within range H, and may span the entire range H.

[0041] The number of protrusions 51 can be set to be less than or equal to the number of leaves, or one protrusion may be provided for each leaf.

[0042] It is preferable that the height of the protrusion be greater than 0 mm and less than or equal to 0.2 mm. If it is less than 0 mm, it will not be considered high enough, and if it exceeds 0.2 mm, it will be too high, and there is a risk that the contact will be too strong due to this protrusion.

[0043] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above and is capable of various modifications. The thrust foil bearing described above is not limited to the gas turbines described above, but can also be used, for example, as a bearing to support the rotor of a supercharger. Furthermore, the thrust foil bearing described above is not limited to turbomachinery such as gas turbines and superchargers, but can be widely used as a bearing for vehicles such as automobiles, which are used under limitations such as difficulty in lubrication with liquids such as lubricating oil, difficulty in separately providing auxiliary equipment for a lubricating oil circulation system from the viewpoint of energy efficiency, or problems with resistance due to liquid shear, and also as a bearing for industrial equipment.

[0044] Furthermore, while the thrust foil bearing described above is a pneumatic bearing that uses air as the pressure-generating fluid, it is not limited to this; other gases can be used as the pressure-generating fluid, or liquids such as water or oil can be used. In addition, although the case of rotating the shaft member has been described, the thrust foil bearing described above can also be used when the leaf side is rotated in the opposite direction.

[0045] Incidentally, in this embodiment, the protrusion 51 provided on the back foil portion 22b was projected toward the leaf located above, but conversely, the protrusion may be provided so that it projects from the leaf located above toward the leaf located below. Even in this case, the foil 22 does not experience localized strong contact with the surface facing the bearing surface S, thereby generating stable dynamic pressure and ensuring load capacity. [Examples]

[0046] As shown in Figure 15, a thrust foil bearing with a protrusion on the foil and as shown in Figure 16, a thrust foil bearing without a protrusion on the foil were formed, and a break-in test was performed on them. Here, the break-in test is a preliminary operation to break in the slight contact area of ​​the dynamic pressure surface S while applying a specified load (e.g., 350N) in the thrust direction, in order to generate a stable dynamic pressure effect. The presence or absence of contact on the dynamic pressure surface S is determined by the current value of the drive motor used for the test. In addition, if an overcurrent occurs, in order to prevent damage to the bearing, the load is temporarily removed and the test is interrupted, and then the test is performed again by applying pressure. This is repeated thereafter. Figure 16(a) shows a simplified plan view of the surface shape of the thrust foil bearing according to the present invention, Figure 16(b) shows a perspective view of the surface shape of the thrust foil bearing according to the present invention, and Figure 16(c) shows a graph showing the break-in test results of the thrust foil bearing according to the present invention. As can be seen from Figure 16(b), the presence of a convex portion on the outer diameter side of the foil makes the outer diameter side of the foil higher. Figure 16(a) shows a simplified plan view of the surface shape of a conventional thrust foil bearing, Figure 16(b) shows a perspective view of the surface shape of a conventional thrust foil bearing, and Figure 16(c) shows a graph of the settling test results of a conventional thrust foil bearing.

[0047] The samples with protrusions were welded and fixed using YAG laser welding, while the samples without protrusions were welded and fixed using laser marker welding. The mechanism by which protrusions form on the foil is presumed to be related to the laser output setting used for welding. When the leaf portion is held down with a jig and the extended portion (fixed portion) is left free during welding, deformation is likely to occur in the narrow section connecting the foil bearing portion and the extended portion (fixed portion) due to factors such as thermal contraction of the extended portion (fixed portion), resulting in the formation of protrusions on the foil after welding. For this reason, it was found that protrusions are more likely to form with YAG laser welding, which has a higher output than laser marker welding.

[0048] As can be seen from the test results shown in Figure 16(c), the shape without the protrusion frequently failed to reach the specified load capacity (e.g., 350N), and there was a tendency for the test to be interrupted more often due to eddy current generation. In contrast, as can be seen from the test results shown in Figure 15(c), these problems were less likely to occur. That is, the presence of the protrusion on the outer diameter side of the foil makes the outer diameter side of the foil higher, and the inner diameter side of the foil is more likely to move in a direction that lowers at the apex of the protrusion. As a result, the contact between the foil and the inner diameter side of the shaft is weaker than in the shape without the protrusion, and strong localized contact can be avoided. [Explanation of Symbols]

[0049] 11 Leaf 22 Leaf 22a Top foil section 22a1 Tip rounded section 22a11 Outer edge 50 Extension part (fixed part) 51 Convex part

Claims

1. A foil bearing comprising a foil holder and a plurality of leaves attached to the foil holder, each having a bearing surface facing a rotating member, and arranged in a line in the circumferential direction of the foil holder, wherein the pitch of the leaves on the outer diameter side is longer than the pitch on the inner diameter side, The leaf has a top foil portion provided on one side in the circumferential direction and having the bearing surface, and a back foil portion provided on the other side in the circumferential direction of the top foil portion and facing the side of the adjacent leaf's top foil portion opposite to the bearing surface. The foil bearing is characterized in that the back foil portion has a convex portion on the outer diameter side of the arc line passing through the central part of the leaf in the inner and outer diameter direction.

2. The foil bearing according to claim 1, characterized in that the number of protrusions is set to be less than or equal to the number of leaves.

3. The foil bearing according to claim 1, characterized in that the aforementioned protrusions are provided for each leaf.

4. The foil bearing according to claim 1, characterized in that the height of the protrusion is greater than 0 mm and less than or equal to 0.2 mm.

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