JP7731746B2 - Foil bearings - Google Patents

Description

The present invention relates to a foil bearing.

Foil bearings have a bearing surface made of a flexible thin film (foil) with low bending rigidity, and support a load while allowing the bearing surface to flex (see, for example, Patent Document 1 below). When the shaft rotates, a fluid film (e.g., an air film) is formed between the shaft and the foil, and this fluid film supports the shaft without contact. As the foil flexes, an appropriate bearing gap is automatically formed according to operating conditions such as the shaft rotation speed, load, and ambient temperature, resulting in excellent stability and enabling support of a high-speed rotating shaft.

JP 2017-96324 A

As mentioned above, in foil bearings, the foil normally flexes freely in response to the load applied to the bearing surface, automatically adjusting the size of the bearing gap and supporting the load. However, if a load greater than the foil bearing's load capacity is applied to the bearing surface due to temporary shaft vibration, the shaft and foil, or the foil and foil holder, may come into contact, and in the worst case scenario, the foil may be damaged. To prevent foil damage, it is necessary to increase the viscosity of the lubricant to increase the load capacity, but this increases torque, and there is a limit to the load capacity that can be achieved, especially in foil bearings that use air as a lubricant.

Therefore, the present invention aims to prevent foil damage when excessive load is applied to the bearing surface.

In order to solve the above problems, the present invention provides a foil bearing comprising a foil having a bearing surface and a cylindrical foil holder having the foil attached to an inner peripheral surface thereof, the foil bearing supporting the rotating member in a radially non-contact manner by a fluid film generated in a bearing gap between the bearing surface of the foil and the rotating member, wherein:
an elastic member having a lower rigidity than the foil holder is provided on an outer peripheral surface of the foil holder;
The foil holder is attached to another member only via the elastic member.

In order to solve the above-mentioned problems, the present invention provides a foil bearing comprising a foil having a bearing surface and a disc-shaped foil holder to which the foil is attached at one axial end face, the foil supporting the rotating member in a non-contact manner in a thrust direction by a fluid film generated in a bearing gap between the bearing surface of the foil and the rotating member, wherein:
an elastic member having a lower rigidity than the foil holder is provided on an end surface on the other axial side of the foil holder;
The foil holder is attached to another member only via the elastic member.

In this way, the foil bearing of the present invention is characterized by the fact that the foil holder is attached to another component (e.g., a casing) via only an elastic member. When the load applied to the bearing surface of this foil bearing is within the load capacity, the flexibility of the foil automatically adjusts the bearing gap, and the rotating component is supported without contact by a fluid film in the bearing gap. On the other hand, when a load exceeding the load capacity is applied to the bearing surface, the elastic member temporarily bends, preventing contact between the rotating component and the foil.

For example, if an elastic member is provided over the entire area between the foil holder and another component, it is extremely difficult to make the elasticity of the elastic member uniform throughout the entire area, resulting in variations in the elasticity of the elastic member depending on the location and unstable bearing performance. Therefore, it is preferable to provide the elastic member in a partial area of the mounting surface of the foil holder to the other component. That is, in the case of a radial foil bearing, it is preferable to provide the elastic member in a partial circumferential area or a partial axial area of the outer peripheral surface of the foil holder. Furthermore, in the case of a thrust foil bearing, it is preferable to provide the elastic member in a partial circumferential area or a partial radial area of the end face on the other axial side of the foil holder. This makes it easier to adjust the elasticity of the elastic member for each location, thereby stabilizing bearing performance. For example, it is preferable to provide the elastic member in an area that overlaps the area where the bearing gap is smallest, in a direction perpendicular to the bearing surface.

In the above-mentioned foil bearing, it is preferable that the rigidity (elastic modulus) of the elastic member when pressed against the bearing surface while the rotating member is stationary is greater than the rigidity of the foil at that time.

As described above, the foil bearing of the present invention can prevent damage to the foil when excessive load is applied to the bearing surface.

FIG. 1 is a diagram conceptually illustrating a configuration of a gas turbine. FIG. 2 is a cross-sectional view showing a rotor support structure in the gas turbine. FIG. 2 is a front view of a radial foil bearing according to an embodiment of the present invention, as seen from the axial direction, which is incorporated into the support structure. FIG. 2 is a plan view of a foil incorporated in the radial foil bearing. FIG. 2 is an axial cross-sectional view of the radial foil bearing. FIG. 2 is a cross-sectional view of a thrust foil bearing incorporated in the support structure. FIG. 2 is a front view of the thrust foil bearing as viewed from the axial direction. 8 is a cross-sectional view taken along line XX in FIG. 7. FIG. 3 is a diagram showing an elastic hysteresis curve of the radial foil bearing. FIG. 3 is a cross-sectional view of an apparatus for measuring the elastic hysteresis curve. FIG. 10 is a front view of a radial foil bearing according to another embodiment, as viewed from the axial direction. FIG. 12 is an axial cross-sectional view of the radial foil bearing of FIG. 11 . 1 is a cross-sectional view of a thrust foil bearing according to one embodiment of the present invention.

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

Figure 1 conceptually illustrates the configuration of a gas turbine, a type of turbomachinery. This gas turbine primarily comprises a turbine 1 and compressor 2, each with a blade row, a generator 3, a combustor 4, and a regenerator 5. The turbine 1, compressor 2, and generator 3 share a common horizontal shaft 6, which together with the turbine 1 and compressor 2 form a rotor that can rotate integrally. Air drawn in through an intake port 7 is compressed by the compressor 2, heated by the regenerator 5, and then sent to the combustor 4. This compressed air is mixed with fuel and combusted, generating high-temperature, high-pressure gas to rotate the turbine 1. The rotational force of the turbine 1 is transmitted to the generator 3 via the shaft 6, which then rotates to generate electricity, which is then output via an inverter 8. Because the gas after rotating the turbine 1 is relatively hot, this gas is sent to the regenerator 5 and heat-exchanged with the compressed air before combustion, thereby reusing the heat of the combustion gas. 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 an example of a rotor support structure for the gas turbine. In this support structure, a foil bearing 10 (hereinafter referred to as a "radial foil bearing 10") that supports the shaft 6 in the radial direction is arranged at one axial location. In addition, foil bearings 20 (hereinafter referred to as "thrust foil bearings 20") that support the thrust collar 6a in the thrust direction are arranged on both axial sides of the thrust collar 6a provided on the shaft 6.

The basic configuration of the radial foil bearing 10 will be explained below. Note that in the following explanation, the upstream and downstream sides of the fluid flow direction associated with the rotation of the shaft 6 will be referred to as the "upstream side" and "downstream side," respectively.

As shown in Figure 3, the radial foil bearing 10 supports the shaft 6 in the radial direction using a fluid film formed between the bearing and the shaft 6, which serves as a rotating member inserted into the inner circumference. The radial foil bearing 10 of this embodiment is an air dynamic bearing that uses air as the pressure-generating fluid. The radial foil bearing 10 has a cylindrical foil holder 11 and multiple foils 12 (five in the illustrated example) attached to the inner surface 11a of the foil holder 11.

The foil holder 11 is made of metal or resin. Examples of metals that form the foil holder 11 include sintered metal and ingot material (e.g., steel). The foil holder 11 has a cylindrical inner circumferential surface 11a and an outer circumferential surface 11b. Axial grooves 11c are formed on the inner circumferential surface 11a of the foil holder 11 at multiple locations (five locations in the illustrated example) spaced apart in the circumferential direction. Both axial ends of each axial groove 11c open to the end face of the foil holder 11.

The foil 12 is made of a metal that is highly springy and easy to work, such as steel or a copper alloy. The foil 12 is formed by pressing or electric discharge machining a metal foil with a thickness of approximately 20 μm to 200 μm. It is preferable to use foil 12 made of stainless steel or bronze.

As shown in FIG. 4, each foil 12 has a top foil portion 12a, an insertion portion 12b provided downstream of the top foil portion 12a (left side of FIG. 4), and a back foil portion 12c provided upstream of the top foil portion 12a (right side of FIG. 4). The inner diameter surface of the top foil portion 12a functions as a bearing surface that faces the outer peripheral surface of the shaft 6 in the radial direction (see FIG. 3). The insertion portion 12b extends downstream (left side of FIG. 4) from both axial ends of the top foil portion 12a. A recess 12d is provided on the outer axial edge of the insertion portion 12b. A substantially U-shaped cutout portion 12e is provided on the upstream edge of the back foil portion 12c. An insertion port 12f is provided at the boundary between the top foil portion 12a and the back foil portion 12c. The insertion portion 12b of each foil 12 is inserted into the insertion port 12f of the adjacent foil 12 downstream (see Figure 5), and is further inserted into the axial groove 11c of the foil holder 11 (see Figure 3).

A retaining member 13 is attached to the foil holder 11 to prevent the foil 12 from coming out of the foil holder 11. In this embodiment, recesses 11d are formed on both axial ends of the inner peripheral surface 11a of the foil holder 11 (see Figure 5), and annular retaining members 13 are disposed in these recesses 11d. The inner peripheral surface of the retaining member 13 is provided contiguous with the inner peripheral surface 11a of the foil holder 11 on the same cylindrical surface. The retaining member 13 fits into the recess 12d of the insertion portion 12b of the foil 12 inserted into the axial groove 11c. The retaining member 13 engages with the foil 12 in the axial direction, thereby preventing the foil 12 from coming out of the axial direction. The retaining member 13 engages with the foil 12 in the circumferential direction, thereby preventing the foil 12 from coming out of the circumferential direction.

The back foil portion 12c of each foil 12 is arranged between the top foil portion 12a of the adjacent foil 12 on the upstream side and the inner peripheral surface 11a of the foil holder 11 (see Figure 3). As a result, the top foil portion 12a of each foil 12 is supported from the outer diameter side by the back foil portion 12c of the adjacent foil 12.

Next, the configuration of the thrust foil bearing 20 will be explained.

As shown in Figure 6, the thrust foil bearings 20, 20 arranged on both axial sides of the thrust collar 6a have an axially symmetrical structure with the thrust collar 6a at the center. The thrust foil bearing 20 of this embodiment has a hollow, disk-shaped foil holder 21 and multiple foils 22 attached to one end face 21a of the foil holder 21 (the end face facing the thrust collar 6a). The other end face 21b of the foil holder 21 is fixed to the casing 15 of the gas turbine.

As shown in FIG. 7, the foils 22 are arranged in a circumferentially offset manner. As shown in FIG. 8, each foil 22 has a top foil portion 22a with a bearing surface and a back foil portion 22b that is continuous with the top foil portion 22a upstream. The upstream end of each foil 22 is fixed to the foil holder 21 by appropriate means such as welding. When the foils 22 are attached to the foil holder 21, as shown in FIG. 8, the bearing surface of the top foil portion 22a of each foil 22 directly faces the thrust collar 6a in the axial direction, and the back foil portion 22b of the adjacent foil 22 downstream is located behind the top foil portion 22a of each foil 22 (on the opposite side from the bearing surface). In other words, the back foil portion 22b of each foil 22 is located between the top foil portion 22a of the adjacent foil 22 upstream and the foil holder 21.

3 and 8, a radial bearing gap is formed between the inner diameter surface (bearing surface) of the top foil portion 12a of each foil 12 of the radial foil bearing 10 and the outer circumferential surface of the shaft 6. At the same time, a thrust bearing gap is formed between the bearing surface of the top foil portion 22a of each foil 22 of the thrust foil bearing 20 and the end face of the thrust collar 6a. At this time, the top foil portions 12a, 22a ride up and curve onto the back foil portions 12c, 22b of the adjacent foils 12, 22, forming a wedge-like shape that narrows toward the downstream side. Air is forced into the narrow side of these wedge-shaped bearing gaps, increasing the pressure of the air film in each bearing gap. This pressure provides non-contact support for the shaft 6 in the radial and thrust directions. At this time, due to the flexibility of the foils 12 and 22, the bearing surfaces of each foil 12 and 22 deform arbitrarily in response to operating conditions such as the load, rotational speed of the shaft 6, and ambient temperature, so the radial bearing gap and thrust bearing gap are automatically adjusted to an appropriate width depending on the operating conditions.

In this embodiment, the pressure-increasing effect is enhanced by providing a cutout 12e on the upstream edge of the back foil portion 12c of the foil 12 of the radial foil bearing 10 (see Figure 5). That is, when the pressure of the air film in the radial bearing gap increases with rotation of the shaft 6, this pressure causes the foil 12 to deflect, causing a depression in the area P of the top foil portion 12a of each foil 12 that is not supported by the back foil portion 12c. As a result, the area supported by the back foil portion 12c becomes higher than the area P, forming a step along the cutout 12e in the top foil portion 12a. This causes the fluid flowing along the top foil portion 12a to flow along the step and be concentrated toward the axial center, making it easier for the pressure to increase (see the arrow in Figure 5).

Furthermore, each foil 12 of the radial foil bearing 10 is not completely fixed to the foil holder 11, but is movable relative to the foil holder 11. Therefore, while the shaft 6 is rotating, minute sliding occurs between each foil 12 and the foil holder 11, and between adjacent foils 12. The frictional energy caused by this minute sliding can damp vibrations of the shaft 6.

The following provides a detailed explanation of the mounting structure of the foil holder 11 of the radial foil bearing 10 to another component (the casing 15), which is a characteristic feature of the present invention.

An elastic member 14 is provided on the outer peripheral surface 11b of the foil holder 11 (see Figures 3 and 5). The elastic member 14 is formed from a material with lower rigidity (a material with a low elastic modulus) than the foil holder 11, such as rubber or resin. The foil holder 11 is fixed to the casing 15 of the gas turbine only via the elastic member 14. In other words, the outer peripheral surface 11b of the foil holder 11 and the inner peripheral surface of the casing 15 are not in contact with each other, with the elastic member 14 interposed between them. Therefore, elastic deformation of the elastic member 14 allows the entire radial foil bearing 10, including the foil holder 11, to move slightly in the radial direction relative to the casing 15.

In this embodiment, the elastic member 14 is provided in a partial axial region, for example, at two locations spaced apart in the axial direction (see Figure 5). The elastic member 14 is formed, for example, by an annular O-ring and is disposed in an annular groove 11e formed in the outer peripheral surface 11b of the foil holder 11. The radial depth of the annular groove 11e is smaller than the diameter of the elastic member 14. Therefore, the elastic member 14 protrudes from the outer peripheral surface 11b of the foil holder 11. When the radial foil bearing 10 is attached to the inner periphery of the casing 15, the elastic member 14 is compressed radially between the inner periphery of the casing 15 and the outer peripheral surface 11b of the foil holder 11 (the bottom surface of the annular groove 11e).

As already mentioned, the radial foil bearing 10 supports the radial load applied to the bearing surface of the foil 12 via the fluid film in the radial bearing gap using the elastic force of the foil 12. When the radial load applied to the bearing surface is small, the elastic force of the foil 12 alone can support the shaft 6 without contact. On the other hand, when an excessive radial load is applied to the bearing surface, the elastic member 14 attached to the outer periphery of the foil holder 11 elastically deforms, causing the entire foil bearing 10, including the foil holder 11, to move radially relative to the casing 15 and absorb the radial load. This avoids contact between the shaft 6 and the foil 12, maintains the fluid film in the radial bearing gap, and supports the shaft 6 without contact.

Furthermore, as described above, providing the elastic member 14 in a partial region of the outer peripheral surface 11b of the foil holder 11 makes it easier to adjust the elasticity of the elastic member 14 for each location, thereby providing the necessary elasticity where needed. In this embodiment, of the overlapping regions of the top foil portion 12a and back foil portion 12c of adjacent foils 12, region Q near the axially outer end (the region supported near the upstream end of the back foil portion 12c) is the region closest to the outer peripheral surface of the shaft 6. In other words, the radial bearing gap is smallest in this region Q. The elastic member 14 is provided on the outer periphery of this region Q, i.e., in the region overlapping with region Q in the radial direction (the direction perpendicular to the bearing surface). In this way, providing the elastic member 14 only on the outer periphery of region Q closest to the shaft 6 provides the desired elasticity to this portion, thereby avoiding contact between region Q and the shaft 6.

Figure 9 shows the difference in rigidity between a radial foil bearing with an elastic member 14 and a radial foil bearing without an elastic member 14. The dotted line in Figure 9 is the elastic hysteresis curve of the above-mentioned radial foil bearing 10 with an elastic member 14, and the solid line is the elastic hysteresis curve of a conventional radial foil bearing 10' without an elastic member. These elastic hysteresis curves were measured using the device shown in Figure 10. First, the radial foil bearings 10, 10' are attached to the inner circumference of a cylindrical jig. The foil holder 11 of the radial foil bearing 10 is attached to the inner circumference of the jig 31 via only the elastic member 14 (see Figure 10), and the outer surface of the foil holder of the radial foil bearing 10' is fixed directly to the inner surface of the jig (not shown). Then, a fixed shaft 32 is inserted into the inner circumference of the radial foil bearings 10, 10'. A drive means 33 is attached to the outer circumference of the jig 31. A load is applied to the jig 31 in the diameter direction by the driving means 33, and the load at this time is measured by the load sensor 34, while the displacement of the jig 31 in the diameter direction is measured by the displacement sensor 35. From these loads and displacements, the elastic hysteresis curve shown in Figure 9 is obtained.

As can be seen from Figure 9, in the central region A of the curve, i.e., in the range of relatively light loads, the static stiffness (slope Ka) of radial foil bearings 10 and 10' is approximately the same. In other words, in this load range, it is believed that the elasticity (springiness) of the foil supports the shaft. On the other hand, in the end region B of the curve, i.e., in the range of relatively heavy loads, the static stiffness (slope Kb') of the foil bearing with an elastic member, shown by the dotted line, is smaller than the static stiffness (slope Kb) of the foil bearing without an elastic member, shown by the solid line. In other words, in this load range, it is believed that the foil bearing 10' without an elastic member supports the shaft by the rigidity of the foil holder, while the foil bearing 10 with an elastic member supports the shaft by the elasticity of the elastic member.

In this way, in the above-mentioned radial foil bearing 10 having the elastic member 14, when the load applied to the bearing surface is small, the load is supported by the elasticity of the foil 12, but when the load applied to the bearing surface increases, the load is supported by the elasticity of the elastic member 14 in addition to the elasticity of the foil 12. In this way, by using the elasticity of the elastic member 14 to support loads that cannot be supported by the elasticity of the foil 12, the bearing surface can be elastically supported even when an excessive load is applied to the bearing surface, so the foil 12 and shaft 6 can be maintained in a non-contact state and damage to the foil 12 can be prevented.

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

The embodiment shown in Figures 11 and 12 differs from the above embodiment in that elastic members 14 are provided in a circumferential region of the outer peripheral surface 11b of the foil holder 11 of the radial foil bearing 10. The elastic members 14 are provided at multiple circumferentially spaced locations (five locations in the illustrated example). For example, axial grooves 11f are provided at multiple circumferential locations on the outer peripheral surface 11b of the foil holder 11, and elastic members 14 extending in the axial direction are fixed to each axial groove 11f (see Figure 12). The elastic members 14 are provided in the circumferential region where the top foil portion 12a and back foil portion 12c of adjacent foils 12 overlap. Of the bearing surface provided on the top foil portion 12a, the circumferential region supported by the back foil portion 12c is closest to the shaft 6. Therefore, by providing the elastic members 14 only in this circumferential region, the desired elasticity can be imparted to this portion, preventing contact between the foil 12 and the shaft 6.

The present invention is not limited to radial foil bearings, but can also be applied to thrust foil bearings. For example, as shown in Figure 13, an elastic member may be provided on the other end surface 21b of the foil holder 21 of the thrust foil bearing 20, and the elastic member may be interposed between the foil holder 21 and the casing 15. In this case, the foil holder 21 does not come into contact with the casing 15, and is attached only via the elastic member. The elastic member may, for example, be multiple radially extending strip-shaped members arranged radially, or multiple O-rings of different diameters arranged coaxially.

In the above embodiment, a foil bearing in which spring properties are imparted to the bearing surface by overlapping multiple foils is shown, but the foil bearings to which the present invention can be applied are not limited to this. For example, the present invention can be applied to a bump-type foil bearing having a top foil with a bearing surface and a corrugated bump foil that supports the top foil from the side opposite the bearing surface, and an elastic member can be provided on the mounting surface of the foil holder to the casing.

A radial foil bearing 10 with an elastic member 14 attached to a foil holder 11 and a shaft 6 inserted into its inner periphery may be integrated into a radial foil bearing unit. Also, a pair of thrust foil bearings 20 with an elastic member attached to a foil holder 21 and a thrust collar 6a disposed between them may be integrated into a thrust foil bearing unit. Alternatively, a radial foil bearing 10, a pair of thrust foil bearings 20, and a shaft 6 with a thrust collar 6a may be integrated into a foil bearing unit.

Foil bearings such as those described above can be used not only in gas turbines, but also in other turbomachinery such as superchargers, and for supporting other rotating components.

6 Shaft 6a Thrust collar 10 Radial foil bearing (foil bearing)
11 foil holder 12 foil 13 retaining member 14 elastic member 15 casing (other member)
20 Thrust foil bearing (foil bearing)
21 foil holder 22 foil

Claims (7)

A foil bearing includes a foil having a bearing surface and a cylindrical foil holder to which the foil is attached on its inner circumferential surface, wherein the rotating member is supported in a non-contact manner in the radial direction by a fluid film generated in a bearing gap between the bearing surface of the foil and the rotating member , and the width of the bearing gap is automatically adjusted due to the flexibility of the foil,
an elastic member having a lower rigidity than the foil holder is provided on an outer peripheral surface of the foil holder;
The foil holder is attached to another member only via the elastic member ,
A foil bearing in which the rigidity of the elastic member when pressed against a bearing surface while the rotating member is stationary is greater than the rigidity of the foil at that time . A foil bearing includes a foil having a bearing surface and a disk-shaped foil holder to which the foil is attached at one axial end face, wherein the rotating member is supported in a non-contact manner in the thrust direction by a fluid film generated in a bearing gap between the bearing surface of the foil and the rotating member , and the width of the bearing gap is automatically adjusted due to the flexibility of the foil,
an elastic member having a lower rigidity than the foil holder is provided on an end surface on the other axial side of the foil holder;
The foil holder is attached to another member only via the elastic member ,
A foil bearing in which the rigidity of the elastic member when pressed against a bearing surface while the rotating member is stationary is greater than the rigidity of the foil at that time . A foil bearing as described in claim 1, wherein the elastic member is provided on a circumferential region or an axial region of the outer peripheral surface of the foil holder. A foil bearing as described in claim 2, wherein the elastic member is provided on a partial circumferential region or a partial radial region of the end face on the other axial side of the foil holder. A foil bearing as described in claim 3 or 4, wherein the elastic member is provided in an area that overlaps the area where the bearing gap is smallest in a direction perpendicular to the bearing surface. A foil bearing unit comprising the foil bearing according to any one of claims 1 to 5 and the rotating member. A turbomachine comprising the foil bearing according to any one of claims 1 to 5 and the rotating member.