JP7577005B2 - Foil Bearings - Google Patents

Description

The present invention relates to a foil bearing.

The main shaft of a gas turbine or turbocharger rotates at extremely high speeds, and the turbine blades are exposed to high temperature environments. The main shaft is often supported by oil-lubricated rolling bearings or oil dynamic bearings, but when lubrication with liquids such as lubricating oil is difficult, when it is difficult to install separate accessories for a lubricating oil circulation system from the standpoint of energy efficiency, or when resistance due to shearing of the liquid becomes a problem, foil bearings, a type of air dynamic bearing, may be used.

Foil bearings have a bearing surface made of a flexible thin film (foil) with low bending stiffness, and support the load by allowing the foil to flex. When the shaft rotates, a fluid film (air film) is formed between the shaft and the bearing surface of the foil, and the shaft is supported without contact via this fluid film. In foil bearings, the flexibility of the foil automatically creates an appropriate bearing gap according to the operating conditions, such as the shaft rotation speed, load, and ambient temperature. Therefore, foil bearings provide excellent shaft support stability and can be used for shafts that rotate at high speeds.

In order for a foil bearing to stably support a shaft, the foil on which the bearing surface is formed must be able to deform in response to shaft displacement and thermal expansion. For this reason, managing the rigidity of the foil is important for foil bearings.

For example, the following Patent Document 1 shows a so-called leaf-type foil bearing in which multiple foils are arranged so that some of them overlap, and the overlapping parts give the bearing surface springiness. In this foil bearing, a circumferential gap is formed between the upstream end of the most downstream foil of three adjacent foils and the downstream end of the most upstream foil. This reduces the rigidity of the downstream end of each foil, making it easier for the downstream end of each foil to displace in a direction that widens the bearing gap in response to shaft displacement, etc., and preventing contact between the downstream end of the foil and the rotating member.

In addition, in the leaf-type thrust foil bearing shown in the following Patent Document 2, a recessed portion is provided at the end of the inner diameter side of each foil, where the circumferential middle portion is recessed (concave) toward the outer diameter side. In a leaf-type thrust foil bearing, the circumferential pitch between adjacent foils becomes smaller toward the inner diameter side, so the rigidity of the inner diameter side of each foil is higher than the rigidity of the outer diameter side. Therefore, by providing a recessed portion at the end of the inner diameter side with high rigidity and removing the portion that is likely to come into contact with the rotating member, it is possible to avoid contact between the end of the inner diameter side of the foil and the rotating member.

JP 2017-82913 A JP 2020-34085 A

However, if a circumferential gap is provided between the foils as in Patent Document 1 above, or if a recess is provided at the end of the foil on the inner diameter side as in Patent Document 2 above, the area of the bearing surface formed on the foil is reduced, resulting in a decrease in the load capacity.

The present invention aims to provide a foil bearing that can stably support a larger load by adjusting the rigidity of the foil without reducing the load capacity.

To solve the above problem, the present invention provides a foil bearing having a foil on which a bearing surface is formed, in which a thin-walled portion is provided at the end of the foil, the thickness of which is thinner than the adjacent area on the opposite side to the edge of the end.

In this way, in the present invention, the rigidity of the end of the foil is reduced by providing a thin portion at this portion. As a result, when the rotating member to be supported rotates, the end of the foil is more likely to be displaced away from the rotating member due to the fluid pressure generated in the bearing gap between the rotating member and the bearing surface of the foil. This ensures that the end of the foil can follow the displacement and thermal expansion of the rotating member, and prevents contact between the end of the foil and the rotating member. In this case, the rigidity of the end of the foil can be adjusted by simply adjusting the thickness of the thin portion, without reducing the area of the bearing surface of each foil.

It is preferable that the thickness of the thin-walled portion is not uniform, but is gradually thinner as it approaches the edge of the end. This makes it possible to ensure a certain degree of rigidity in the thin-walled portion by making the thickness of the area away from the edge relatively thick, thereby preventing this portion from bending due to the fluid pressure in the bearing gap.

If the range of the thin-walled portion is too wide, the rigidity of the thin-walled portion will be too low, and this portion may not function as a bearing surface, resulting in a reduced load capacity. Therefore, it is preferable that the dimension of the thin-walled portion in the direction perpendicular to the extension direction of the edge of the end portion be 1 mm or less.

The present invention can be applied, for example, to leaf-type foil bearings. That is, the present invention can also be characterized as a foil bearing having a plurality of foils arranged in the rotational direction of the rotating member to be supported, with the region including the downstream end of each foil overlapping the foil adjacent to the downstream side, and with a bearing surface formed in this region, in which the downstream end of each foil is provided with a thin-walled portion that is thinner than the region adjacent to the upstream side.

In the leaf-type foil bearing described above, by forming a gap in the rotational direction between the upstream end of the most downstream foil and the downstream end of the most upstream foil among the three adjacent foils, the rigidity of the downstream end of each foil can be reduced. If this gap is made too large, there is a risk of the load capacity decreasing, but in the present invention, a thin-walled portion is provided at the downstream end of each foil to reduce rigidity, so the above gap does not need to be very large and can be, for example, 0.5 mm or less.

In foil bearings, the foil slides against the rotating member when starting and stopping, so a lubricating coating may be applied to the surface (bearing surface) of the foil. In this case, there is a concern that the lubricating coating may peel off from the substrate due to sliding with the rotating member. Therefore, it is preferable that the foil has a substrate and a lubricating coating formed on the substrate surface and provided with the bearing surface, and that the surface roughness of the substrate surface in the thin-walled portion is greater than the surface roughness of the substrate surface in an adjacent region. In this way, by increasing the surface roughness of the substrate surface in the thin-walled portion, micro-recesses are formed on the substrate surface, and the lubricating coating penetrates into these micro-recesses, thereby improving the adhesion between the lubricating coating and the substrate.

In the lubricating coating, a resin-based or inorganic binder is used to fix the lubricating components (such as fluorine or molybdenum disulfide) to the substrate. Resin-based binders have high adhesion to the foil, but are difficult to deform, so there is a concern that they may reduce the tracking ability of the foil. On the other hand, inorganic binders are less likely to change the properties (rigidity) of the foil, but have lower adhesion to the foil than resin-based binders. Therefore, by increasing the surface roughness of the substrate surface in the thin-walled portion as described above and providing a lubricating coating containing an inorganic binder on this surface, it is possible to improve the sliding properties of the bearing surface while avoiding a decrease in adhesion between the substrate and the lubricating coating and a decrease in the tracking ability of the foil.

As described above, by providing a thin-walled portion at the end of the foil, the rigidity of the end of the foil can be adjusted without reducing the area of the bearing surface, i.e., without reducing the load capacity. This makes it possible to stably support a large load while preventing contact between the foil and the rotating member.

FIG. 1 is a diagram conceptually showing a configuration of a gas turbine. FIG. 2 is a cross-sectional view showing a support structure of a rotor in the gas turbine. FIG. 2 is a cross-sectional view of a radial foil bearing. FIG. 2 is a plan view of the thrust foil bearing as viewed from the bearing surface side. FIG. 2 is a plan view showing a foil holder and one foil of a thrust foil bearing. 5 is a cross-sectional view taken along line XX in FIG. 4. 13A and 13B are plan views of a foil member formed by connecting a plurality of foils. FIG. 11 is a plan view showing a state in which two foil members are temporarily assembled. 13 is a plan view showing a state in which two temporarily assembled foil members are placed on a foil holder. FIG. 12 is a plan view showing a state in which a fixing member is attached to the foil holder of FIG. 11 . 6A to 6F are cross-sectional views of the downstream end of the foil (Y portion in FIG. 6). 13A and 13B are cross-sectional views of the downstream end of a foil according to another embodiment.

The following describes an embodiment of the present invention with reference to the drawings.

Figure 1 conceptually shows the configuration of a gas turbine, a type of turbomachinery. This gas turbine mainly comprises a turbine 1 and a compressor 2, each of which has a blade row, a generator 3, a combustor 4, and a regenerator 5. The turbine 1, compressor 2, and generator 3 are provided with a common shaft 6 that extends horizontally, and this shaft 6, the turbine 1, and the compressor 2 form a rotor that can rotate together.

Air drawn in from the intake port 7 is compressed by the compressor 2, heated by the regenerator 5, and 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 shaft 6, which generates electricity as the generator 3 rotates, and this electricity is output via the inverter 8. As the gas after rotating the turbine 1 is relatively hot, this gas is sent to the regenerator 5 and heat is exchanged between this gas and the compressed air before combustion, reusing the heat of 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.

Figure 2 shows the rotor support structure, in particular the support structure for the shaft 6 between the turbine 1 and the compressor 2 in the axial direction. This region is adjacent to the turbine 1, which is rotated by high-temperature, high-pressure gas, so an air dynamic bearing, in particular a foil bearing, is preferably used here. Specifically, the shaft 6 is supported in the radial direction by a radial foil bearing 10, and a thrust collar 6a provided on the shaft 6 is supported in both thrust directions by a pair of thrust foil bearings 20.

The radial foil bearing 10 is, for example, a leaf-type foil bearing. In this embodiment, as shown in FIG. 3, it is composed of a cylindrical outer member 11, into whose inner circumference the shaft 6 is inserted and which is fixed to the housing 50, and a number of foils 12, which are fixed to the inner circumferential surface 11a of the outer member 11 and are arranged at equal intervals in the circumferential direction.

The foil 12 is made of a foil material with a thickness of about 20 μm to 200 μm, which is made of a metal that is highly springy and easy to process, such as a steel material or a copper alloy. In an air dynamic bearing that uses air as a fluid film, as in this embodiment, there is no lubricating oil in the atmosphere, so the rust prevention effect of oil cannot be expected. In this case, it is preferable to use a foil made of stainless steel or bronze.

The end 12a of each foil 12 downstream in the direction of rotation of the shaft 6 (see the arrow in Figure 3) is a free end, and the end 12b upstream in the direction of rotation is fixed to the outer member 11. The upstream end 12b of the foil 12 is fitted and fixed in an axial groove 11b formed in the inner peripheral surface 11a of the outer member 11. The region including the downstream end 12a of the foil 12 is placed on top (inner diameter side) of the foil 12 adjacent to the downstream side, and the inner diameter side surface of this region becomes the radial bearing surface 12c. Between the radial bearing surface 12c formed on each foil 12 and the outer peripheral surface 6b of the shaft 6, a wedge-shaped radial bearing gap Gr is formed with a narrower radial width toward the downstream side.

The thrust foil bearings 20 support the shaft 6 in the thrust direction, and in the illustrated example, a thrust foil bearing 20 is disposed on each side of the axial direction of a thrust collar 6a provided on the shaft 6 (see FIG. 2).

As shown in FIG. 4, the thrust foil bearing 20 comprises a foil holder 21, a number of foils 22 attached to the end face of the foil holder 21 in a circumferential arrangement, and a fixing member 23 that fixes the foils 22 to the foil holder 21.

The foil holder 21 is disk-shaped and has a through hole at its center through which the shaft 6 is inserted (see FIG. 5). A number of foils 22 are attached to the end face of the foil holder 21 that faces the thrust collar 6a.

As shown in FIG. 4, the foils 22 are arranged at equal pitches in the circumferential direction of the foil holder 21 (i.e., the rotational direction of the shaft 6). FIG. 5 shows only one of the multiple foils 22 arranged in the circumferential direction, with the other foils omitted. As shown in the figure, each foil 22 is integrally provided with a main body portion 22a constituting a top foil portion Tf and a back foil portion Bf, which will be described later, and an extension portion 22b extending from the main body portion 22a toward the outer diameter side.

The main body 22a of the foil 22 has an edge (downstream edge) 22c at the downstream end in the rotation direction (arrow direction in Figures 4 and 5), an edge (upstream edge) 22d at the upstream end in the rotation direction, an inner diameter edge 22e connecting the inner diameter ends of the downstream edge 22c and the upstream edge 22d, and an outer diameter edge 22f connecting the outer diameter ends of the downstream edge 22c and the upstream edge 22d. In the illustrated example, both the inner diameter edge 22e and the outer diameter edge 22f of each foil 22 are formed as arcs centered on the axis. The downstream edge 22c has a convex shape with a radial middle part protruding downstream, and the upstream edge 22d has a concave shape with a radial middle part recessed downstream. In the illustrated example, the downstream edge 22c and the upstream edge 22d have the same curved shape, so that multiple foils 22 can be efficiently cut out from one foil.

The extension portion 22b extends from the main body portion 22a toward the outer diameter side. A plurality of foils 22 are arranged in a circumferential direction on the end face of the foil holder 21, and the outer diameter portion of the extension portion 22b of each foil 22 (the area shown by cross-hatching in FIG. 5) is sandwiched between the foil holder 21 and the fixing member 23, which are then fastened and fixed with bolts or the like, thereby fixing each foil 22 to the foil holder 21 (see FIG. 4).

The foil 22 is made of the same material as the foil 12 of the radial foil bearing 10. Specific examples of the material of the foil 22 are the same as those of the foil 12, so a description is omitted.

Figures 4 and 5 show the thrust foil bearing 20 arranged on one axial side of the thrust collar 6a. The thrust foil bearing 20 arranged on the other axial side of the thrust collar 6a has a similar configuration to the thrust foil bearing 20 described above, except that the plan view from the bearing surface side is a mirror image of Figures 4 and 5, and the direction of rotation of the shaft 6 (arrow) in the figures is opposite.

As shown in FIG. 6, the foils 22 of the thrust foil bearing 20 are arranged in a circumferential direction on the end face 21a of the foil holder 21, with the phases shifted by approximately half a pitch. The region including the downstream end edge 22c of each foil 22 rides up on the foil 22 adjacent to the downstream side (the thrust collar 6a side), and this region constitutes the top foil portion Tf. The region including the upstream end edge 22d of each foil 22 is arranged below the top foil portion Tf of the foil 22 adjacent to the upstream side (the foil holder 21 side), and this region constitutes the back foil portion Bf that elastically supports the top foil portion Tf from behind. A thrust bearing surface S that faces one end face 6a1 of the thrust collar 6a is formed on the surface of the top foil portion Tf of each foil 22.

6, any three adjacent foils 22 are represented as foils 22(1), 22(2), and 22(3). Between the downstream edge 22c(1) of the most upstream foil 22(1) and the upstream edge 22d(3) of the most downstream foil 22(3), a gap C is provided in the rotational direction (circumferential direction). In this embodiment, the gap C is provided uniformly over the entire radial direction. By providing the above-mentioned gap C, the springiness of the downstream end of each foil 22 (downstream edge 22c and its vicinity) is increased, and the rigidity of this portion can be reduced. If the above-mentioned gap C is made too large, the springiness of the downstream end of the foil 22 may be excessively reduced, resulting in a shortage of load capacity. Therefore, it is preferable that the above-mentioned gap C is in the range of 0<C≦2 mm.

The thrust foil bearing 20 can be manufactured by the following procedure. First, two foil members 60 of the same shape as shown in Figures 7(A) and (B) are manufactured (one of the foil members 60 is shown with dots in Figures 7 to 10 for ease of understanding). Each foil member 60 is integrally formed with a plurality of foils 22 and an annular connecting portion 61 that connects the outer diameter ends of the foils 22. Half of the foils 22 to be assembled in the thrust foil bearing 20 are provided in each foil member 60 at equal intervals along the circumferential direction. The main body portions 22a of adjacent foils 22 are divided by cuts 62, and a space 63 is provided between the extension portions 22b of adjacent foils 22 in the circumferential direction. The extension portions 22b of each foil 22 are integrated with the connecting portion 61 via joints 61a.

Next, as shown in FIG. 8, one foil member 60 is stacked on the other foil member 60. At this time, the two foil members 60 are shifted by half the pitch of the foil 22, and the downstream portion of each foil 22 (main body portion 22a) of one foil member 60 is placed on the upstream portion of the foil 22 (main body portion 22a) of the other foil member 60 via the cut 62.

Then, the two foil members 60 provisionally assembled as described above are placed on the end surface 21a of the foil holder 21 (see FIG. 9). At this time, the outer diameter end of the extension portion 22b of each foil 22 is arranged along the outer diameter end of the end surface 21a of the foil holder 21. In addition, the connecting portion 61 of the foil member 60 is arranged on the outer diameter side of the foil holder 21. In this state, as shown in FIG. 10, the extension portion 22b of each foil 22 is sandwiched between the foil holder 21 and the fixing member 23, and the foil holder 21 and the fixing member 23 are fixed with bolts or the like (not shown). As a result, each foil 22 is fixed to the foil holder 21, and the foil bearing intermediate product 80 is completed.

Then, the joints 61a that protrude beyond the foil holder 21 and the fixing member 23 on the outer diameter side are cut, and the connecting portions 61 are separated from each foil 22. This completes the thrust foil bearing 20 shown in FIG. 4.

When the shaft 6 supported by the radial foil bearing 10 and thrust foil bearing 20 as described above rotates, an air film is formed in the radial bearing gap Gr between the radial bearing surface 12c of the foil 12 of the radial foil bearing 10 and the outer peripheral surface 6b of the shaft 6, and the shaft 6 is supported in a non-contact manner in the radial direction via this air film (see FIG. 3). At the same time, an air film is formed in the thrust bearing gap Gt between the thrust bearing surface S of the foil 22 of each thrust foil bearing 20 and the end face of the thrust collar 6a facing it, and the thrust collar 6a is supported in a non-contact manner in both thrust directions via this air film (see FIG. 6).

At this time, due to the flexibility of the foils 12 of the radial foil bearing 10 and the foils 22 of the thrust foil bearing 20, the bearing surfaces of the foils 12, 22 deform arbitrarily according to the operating conditions, such as the load, the rotational speed of the shaft 6, and the ambient temperature, so that the radial bearing gap Gr and the thrust bearing gap Gt are automatically adjusted to an appropriate width according to the operating conditions. Therefore, even under harsh conditions such as high temperature and high speed rotation, the radial bearing gap Gr and the thrust bearing gap Gt can be managed to an optimal width, and the shaft 6 can be stably supported. Note that the actual widths of the radial bearing gap Gr and the thrust bearing gap Gt are very small, on the order of several tens of μm, but are exaggerated in Figures 3 and 6.

In addition, in this embodiment, the upstream edge 22d of the foil 22 of the thrust foil bearing 20 has a concave shape (herringbone shape) with the radial middle part recessed downstream, so that a step is formed in the top foil part Tf of the foil 22 layered on top of it, following the concave upstream edge 22d. The air in the thrust bearing gap Gt that flows downstream as the shaft 6 rotates is drawn into the radial central region along the step, which makes it easier to increase the air pressure in the thrust bearing gap Gt, and the load capacity of the thrust foil bearing 20 can be increased.

The following describes the configuration of the end of the foil 22 of the thrust foil bearing 20, which is a characteristic feature of the present invention.

A thin-walled portion 22g is provided at the downstream end (downstream edge 22c and its vicinity) of each foil 22 of the thrust foil bearing 20, which is thinner than the adjacent area on the opposite side (upstream side in this embodiment) of the downstream edge 22c (the boundary between the thin-walled portion 22g and the adjacent area on the upstream side is shown by a dotted line in FIG. 5). In this embodiment, the thin-walled portion 22g is provided over the entire downstream edge 22c of each foil 22. The thickness of the area of each foil 22 except for the thin-walled portion 22g is constant. A bearing surface S is formed over the entire top foil portion Tf including the thin-walled portion 22g.

Specific examples of the shape of the thin-walled portion 22g are shown in Figures 11(A) to (F). In these examples, the thickness of the thin-walled portion 22g gradually becomes thinner as it approaches the downstream edge 22c. In the examples shown in Figures 11(A) to (C), the thin-walled portion 22g has an asymmetric shape in the thickness direction. Specifically, an inclined surface is provided on the surface of the thin-walled portion 22g on the bearing surface S side (upper surface in Figure 11) that is displaced toward the side away from the thrust collar 6a (lower side in Figure 11) as it approaches the downstream edge 22c. For example, such an inclined surface may be a concave curved surface that is convex downwards (see Figure 11(A)), a convex curved surface that is convex upwards (see Figure 11(B)), or a flat inclined surface (see Figure 11(C)). The surface of the thin-walled portion 22g on the opposite side to the bearing surface S (lower surface in Figure 11) is composed of a flat surface that is continuous with the adjacent area on the upstream side.

In the example shown in Figures 11(D) to (F), the thin-walled portion 22g has a symmetrical shape in the thickness direction. Specifically, on both sides of the thin-walled portion 22g in the thickness direction, an inclined surface is provided that is displaced toward the center of the foil 22 in the thickness direction as it approaches the downstream edge 22c. For example, such an inclined surface may be a concave curved surface that is convex toward the center of the thickness direction (see Figure 11(D)}, a convex curved surface that is convex toward the outside in the thickness direction (see Figure 11(E)}, or a flat inclined surface (see Figure 11(F)}. In this way, if the thin-walled portion 22g has a symmetrical shape in the thickness direction, the foil 22 can be used for thrust foil bearings with opposite rotation directions by flipping the foil 22 over. In other words, a common foil 22 can be used for a pair of thrust foil bearings 20 (see Figure 2) provided on both sides of the thrust collar 6a.

If the width A of the thin-walled portion 22g (the dimension in the direction perpendicular to the extension direction of the downstream edge 22c) is too large, the rigidity of the downstream end of the thrust bearing surface S may become too small, resulting in insufficient load capacity. For this reason, it is preferable that the width A of the thin-walled portion 22g be 1 mm or less.

The thin-walled portion 22g may be provided over the entire downstream end of each foil 22 as shown in FIG. 5, or may be provided over a portion of the downstream end of each foil 22, such as a portion including the apex of the downstream edge 22c (the portion located most downstream). The width A and thickness of the thin-walled portion 22g may vary depending on the location.

When the shaft 6 rotates, as shown in FIG. 6, the downstream end of each foil 22 is closest to the thrust collar 6a. In this embodiment, the downstream end of each foil 22 is provided with a thin portion 22g, which reduces the rigidity of this region (resistance to displacement away from the thrust collar 6a (to the lower side in FIG. 6)). As a result, the downstream end (thin portion 22g) of each foil 22 is easily displaced away from the thrust collar 6a by the pressure of the air film in the thrust bearing gap Gt, preventing contact between the downstream end of each foil 22 and the thrust collar 6a. In this case, the rigidity of the downstream end of each foil 22 can be adjusted simply by adjusting the thickness of the thin portion 22g of each foil 22, so that the area of the bearing surface S of each foil 22 does not change and the load capacity is maintained.

In the illustrated example, the thickness of the thin-walled portion 22g becomes thinner toward the downstream edge 22c (left side of FIG. 11). This makes it possible to ensure a certain degree of rigidity in the upstream portion of the thin-walled portion 22g (area away from the downstream edge 22c) by making the thickness thicker. This makes it possible to prevent the upstream portion of the thin-walled portion 22g from bending due to the fluid pressure in the thrust bearing gap Gt.

As shown in FIG. 6, in this embodiment, among the three adjacent foils 22(1), 22(2), and 22(3), a circumferential gap C is provided between the downstream edge 22c(1) of the most upstream foil 22(1) and the upstream edge 22d(3) of the most downstream foil 22(3), thereby reducing the rigidity of the downstream end of each foil 22. However, if this gap C is too large, it is not preferable because the load capacity decreases. In this embodiment, since the springiness is reduced by the thickness of the thin portion 22g of the foil 22 as described above, the above gap C can be made small, for example, C≦0.5 mm. Note that the above gap C may be omitted if not particularly necessary.

Next, we will explain the manufacturing method of the foil 22 having the thin-walled portion 22g as described above, and in particular the processing method of the foil member 60 (see Figure 7).

The foil member 60 is formed from a single piece of foil material. Methods for processing the foil material include, for example, wire cutting and laser processing, but both methods result in burrs on the processed surface. If the burrs formed on the foil 22 fall off and get into the thrust bearing gap Gt, in the worst case scenario, this could lead to damage to the foil 22. In addition, because there are restrictions on the wire diameter and laser diameter, the width of the cut 62 between the foils 22 (i.e., the rotational gap C between the foils 22 of the thrust foil bearing 20 shown in Figure 6) cannot be made very small.

Therefore, it is preferable to form the foil member 60 by etching the foil material. Etching is a processing method that dissolves unnecessary parts of the foil material, and does not produce burrs on the processed surface. Furthermore, with etching, the foil member 60 can be obtained in the desired shape simply by masking the surfaces of the foil material that are not to be removed, so the width of the cut 62 between the foils 22 (i.e., the size of the gap C in Figure 6) can be freely set.

In this embodiment, the foil material is masked and etched to form the foil member 60 having the shape shown in FIG. 7. The foil member 60 at this time has a uniform thickness over the entire area. Then, the foil member 60 is masked over all areas except the areas where the thin-walled portions 22g of each foil 22 are formed (see FIG. 5), and etched to form the thin-walled portions 22g at the downstream end of each foil 22. The surface of the thin-walled portion 22g processed by etching usually has a concave curved surface as shown in FIG. 11(A) or (D). By etching only one side of the foil, a concave curved surface as shown in FIG. 11(A) is formed, and by etching both sides of the foil, a concave curved surface as shown in FIG. 11(D) is formed.

The thin-walled portion 22g can be formed not only by etching, but also by molding (press molding) or machining. The thin-walled portion 22g having the cross-sectional shape shown in Figures 11(B), (C), (E), and (F) can be formed by molding or machining, or by adjusting the etching processing conditions.

The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but duplicate explanations of points similar to the above-described embodiment will be omitted.

In the thrust foil bearing 20, the bearing surface S of the foil 22 slides against the thrust collar 6a when starting and stopping. Therefore, by providing a lubricating film on the bearing surface S of each foil 22, the sliding properties of the bearing surface S are improved. For example, in the example shown in Figure 12 (A) and Figure 12 (B), each foil 22 has a substrate 24 and a lubricating film 25 formed on the surface of the substrate 24, and the bearing surface S is provided on the lubricating film 25. The lubricating film 25 is provided on at least the downstream end of the main body portion 22a of the foil 22, for example, on the entire area of the top foil portion Tf (bearing surface S).

The lubricating coating 25 may be one using a resin-based binder or one using an inorganic binder. The functions required of the lubricating coating 25 include sliding properties (low friction) against the thrust collar 6a and adhesion to the base material 24 of the foil 22. The lubricating coating 25 using a resin-based binder has excellent adhesion to the base material 24 and wear resistance, but the thickness of the coating may change the original characteristics (flexibility) of the base material 24 of the foil 22, which may reduce the tracking ability of the foil 22. On the other hand, the lubricating coating 25 using an inorganic binder is less likely to change the characteristics of the base material 24 of the foil 22, but has the problem of low adhesion to the base material 24 and being easily peeled off from the base material 24.

Therefore, in this embodiment, the surface roughness of the substrate 24 in the thin portion 22g of each foil 22 is made larger than the surface roughness of the substrate 24 in the adjacent region on the upstream side. Specifically, for example, by etching the thin portion 22g, the surface roughness of the thin portion 22g becomes larger than the surface roughness of the unetched surface. Therefore, after forming the substrate (foil member 60) having the shape shown in FIG. 7, etching is performed only on the downstream end of each foil 22, thereby forming the thin portion 22g in this region and at the same time roughening the surface of the substrate 24 in this region to form countless minute recesses 24a. Part of the lubricating coating 25 enters the minute recesses 24a formed in this way, improving the adhesion between the substrate 24 and the lubricating coating 25.

After the thrust foil bearing 20 is installed in the gas turbine, a break-in operation is performed, causing the bearing surface S of each foil 22 to slide against the thrust collar 6a, and a load is applied to the area including the downstream end of the foil 22. This load removes excess lubricating coating 25, reducing the variation in thickness of the lubricating coating 25, and also presses the lubricating coating 25 into the minute recesses 24a formed on the surface of the substrate 24 of the thin portion 22g of the foil 22, improving the adhesion between the substrate 24 and the lubricating coating 25. Note that a lubricating coating 25 using a resin-based binder can also be used, but the coating is hard and requires a long break-in operation, so a lubricating coating 25 using an inorganic binder is advantageous in terms of productivity.

In the above embodiment, the thin-walled portion 22g is provided at the downstream end of each foil 22 of the thrust foil bearing 20, but the location where the thin-walled portion 22g is provided is not limited to this. For example, the thin-walled portion 22g may be provided at the inner diameter end (inner diameter edge 22e and its vicinity) of each foil 22. Alternatively, the thin-walled portion 22g may be provided at both the downstream end and the inner diameter end of each foil 22.

The above-mentioned thrust foil bearing is just one example, and the configuration of the foils and foil holder may be different from that described above. For example, in the above embodiment, the multiple foils 12 of the radial foil bearing 10 are formed separately one by one, but some or all of the multiple foils 12 may be integrally formed from a single foil while being connected by a connecting portion. Also, after all of the foils 22 of the thrust foil bearing 20 are formed separately, each foil 22 may be attached to the foil holder 21.

The present invention is not limited to leaf-type foil bearings, and can be applied to other foil bearings. For example, the present invention can be applied to so-called bump-type foil bearings, in which a corrugated bump foil supports the foil from behind (the side opposite the bearing surface) to impart springiness to the foil. In this case, by providing a thin-walled portion in an area of the foil that includes an end portion (e.g., the downstream end portion) that is likely to slide against the rotating member, the springiness of this end portion can be reduced, and sliding with the rotating member can be prevented.

The present invention is not limited to thrust foil bearings, but can also be applied to radial foil bearings. For example, the downstream end of each foil 12 of the radial foil bearing 10 shown in FIG. 3 can be provided with a thin-walled portion that is thinner than the adjacent upstream region.

Reference Signs List 6: shaft 6a; thrust collar 10: radial foil bearing 11: outer member 12: foil 20: thrust foil bearing 21: foil holder 22: foil 22a: main body portion 22b: extension portion 22g: thin-walled portion 23: fixing member 24: substrate 24a: minute recess 25: lubricating coating 60: foil member Bf: back foil portion Tf: top foil portion Gr: radial bearing gap Gt: thrust bearing gap S: thrust bearing surface

Claims (7)

A foil bearing includes a plurality of foils arranged in a rotational direction of a rotating member to be supported, and a foil holder to which the plurality of foils are attached, and a region including a downstream end of each foil is arranged to overlap an adjacent foil on the downstream side, and a bearing surface is formed in this region,
a downstream end of each foil is a free end that is not attached to the foil holder;
The downstream end of each foil has a convex shape in which an intermediate portion in a direction perpendicular to the rotation direction and the thickness direction of each foil protrudes downstream,
A foil bearing in which a thin-walled portion is provided in an area including the apex of the convex downstream end of each foil, the thickness of which is thinner than that of the adjacent upstream area. A foil bearing as described in claim 1, in which the thickness of the thin-walled portion gradually decreases as it approaches the edge of the end portion. A foil bearing according to claim 1 or 2, in which the dimension of the thin-walled portion in a direction perpendicular to the direction in which the edge of the end extends is 1 mm or less. A foil bearing according to any one of claims 1 to 3, in which a gap is formed in the rotational direction between the upstream end of the most downstream foil and the downstream end of the most upstream foil among the three adjacent foils. The foil bearing according to claim 4, in which the gap in the rotational direction is 0.5 mm or less. In a foil bearing having a foil on which a bearing surface is formed,
a thin-walled portion is provided at an end of the foil, the thin-walled portion being thinner than an adjacent region on the opposite side of the edge of the end;
the foil has a substrate and a lubricating coating formed on a surface of the substrate and provided with the bearing surface;
A foil bearing in which the surface roughness of the substrate in the thin-walled portion is greater than the surface roughness of the substrate in an adjacent region. The foil bearing according to claim 6, wherein the lubricating coating contains an inorganic binder.

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