JP6651397B2 - Foil bearing - Google Patents

Description

  The invention relates to a foil bearing.

  A foil bearing has a bearing surface made of a thin metal sheet (foil) having flexibility. When the foil bends, a bearing gap is formed according to operating conditions such as a shaft rotation speed, a load, and an ambient temperature. It has the feature that it is automatically adjusted to an appropriate width.

  For example, Patent Document 1 below discloses a foil bearing called a bump type as an example of a foil bearing. This foil bearing includes a top foil having a bearing surface, and a corrugated back foil (bump foil) for elastically supporting the top foil from behind. On the back foil, ridges in contact with the top foil and flat valleys are alternately formed in the rotation direction of the shaft.

JP 2013-87789 A

  In the foil bearing disclosed in Patent Document 1, when the pressure in the bearing gap increases with the rotation of the shaft, the back foil is compressed in the width direction of the bearing gap via the top foil. At this time, the corrugated back foil is deformed so as to crush each peak, but the deformation resistance at that time is large, and the back foil has high rigidity as a whole, so the flexibility of the top foil is reduced. Tends to run out. If the flexibility of the top foil is insufficient, the function of automatically adjusting the clearance between the bearings is impaired, and problems such as easy contact between the shaft and the top foil are caused.

  Therefore, the present inventors have proposed a foil bearing having a back foil 120 as shown in FIG. 22 in an earlier application (Japanese Patent Application No. 2015-234626). The back foil 120 includes a flat portion 121 (intermediate portion), a plurality of upper protruding portions 122 (first protruding portions) protruding from the flat portion 121 toward the top foil, and a side opposite to the top foil 110 from the flat portion 121. And a plurality of protruding lower convex portions 123 (second protruding portions).

  As shown in FIG. 23, the back foil 120 is disposed between the top foil 110 and the foil holder 102 (in FIG. 23, the back foil 120 is schematically shown by a spring). When the shaft rotates, a wedge-shaped bearing gap C is formed between the bearing surface of the top foil 110 and the end face 103a of the thrust collar 103 provided on the shaft, and the fluid in the large gap portion C1 of the bearing gap C passes through the small gap. The fluid pressure is increased by being pushed into the portion C2. Due to this fluid pressure, the back foil 120 is elastically compressed in the width direction of the bearing gap C (vertical direction in FIG. 23), whereby the width of the bearing gap C is automatically adjusted. At this time, since the flat portion 121 (see FIG. 22) of the back foil 120 is a portion having a relatively low rigidity with respect to the compressive force, when the compressive force is applied to the back foil 120, first, the flat portion 121 (see FIG. 22). Deforms to absorb the compressive force. Therefore, the rigidity of the entire back foil can be reduced and the flexibility of the bearing surface can be increased, as compared with the back foil having a waveform as disclosed in Patent Document 1.

  As shown in FIG. 24, the top foil 110 has a plurality of upper convex portions 122 provided on the back foil 120, from behind at a plurality of positions separated in a direction orthogonal to the rotation direction of the shaft (the left-right direction in FIG. 24). Contact supported. In this case, of the top foil 110, the contact portion A with the upper convex portion 122 of the back foil 120 has high rigidity, and the periphery of the contact portion A has low rigidity. Therefore, when the top foil 110 is pressed against the back foil 120 by the fluid pressure generated in the bearing gap C, as shown in FIG. 25, the area around the contact portion A is closer to the thrust collar 103 than the contact portion A. (Lower side in the figure), whereby a concave portion B is formed in a region between the contact portions A. In this case, as indicated by an arrow in FIG. 26, the fluid pushed into the small clearance portion C2 of the bearing clearance C is likely to flow to the downstream side via the concave portion B, and as shown by a solid line in the lower part of FIG. The fluid pressure P gradually increased from the large gap C1 to the small gap C2 drops early in the small gap C2, and the supporting force is reduced.

  Under the circumstances described above, according to the present invention, the top foil is supported in contact with the back foil at a plurality of locations separated in a direction orthogonal to the relative rotation direction of the shaft (hereinafter, this direction is referred to as a “rotation orthogonal direction”). It is an object of the present invention to increase a supporting force by suppressing a decrease in fluid pressure in a bearing gap in a foil bearing.

  In order to solve the above problems, the present invention includes a top foil portion having a bearing surface, and a back foil portion that elastically supports the top foil portion from behind, and with the relative rotation of a shaft, In a foil bearing that supports the shaft in a non-contact manner with a fluid pressure generated in a bearing gap between the shaft and the bearing surface, the back foil portion moves the top foil portion in a direction orthogonal to a relative rotation direction of the shaft. A first support portion that is in contact with and supported at a plurality of locations spaced apart from each other, and a second support portion that is provided downstream of the first support portion and that continuously supports the top foil portion in a direction orthogonal to the relative rotation direction. And a support portion.

  When the fluid pressure in the bearing gap increases with the relative rotation of the shaft, the top foil portion is contact-supported by the first support portion of the back foil portion at a plurality of locations separated in the rotation orthogonal direction. Is deformed on the side away from the shaft (side on which the bearing gap is widened), and a recess is formed on the bearing surface (see FIG. 25). In the present invention, the region of the top foil portion on the downstream side of the concave portion is continuously supported in the rotation orthogonal direction by the second support portion of the back foil portion, so that the rigidity of this region is increased. As a result, even when the fluid pressure in the bearing gap is increased, the region of the top foil portion supported by the second support portion of the back foil portion is less likely to be deformed to the side away from the shaft. Then, a weir that is one step higher than the concave portion (disposed on the shaft side) is formed. In this case, the fluid that has flowed to the downstream side through the concave portion of the top foil portion is blocked by the weir formed on the downstream side, so that the outflow of the fluid from the bearing gap is suppressed. Therefore, as shown by the dotted line in the lower part of FIG. 21, a decrease in the fluid pressure in the small clearance portion C2 of the bearing clearance C is suppressed, and the supporting force is increased.

  It is preferable that the second support portion of the back foil portion is in continuous contact with the top foil portion over the entire region in the rotation orthogonal direction. Thereby, a weir is formed on the downstream side of the concave portion of the top foil portion over the entire length in the rotation orthogonal direction, so that a decrease in fluid pressure can be more effectively suppressed.

  The second support portion may be formed of, for example, a curved portion that protrudes toward the top foil portion.

  In the above-described foil bearing, for example, a flat portion, a plurality of upper protrusions projecting from the flat portion to the top foil portion side, and a plurality of projecting portions projecting from the flat portion to the opposite side to the top foil portion are provided on the back foil portion. And a plurality of upper protrusions can constitute a first support portion. Alternatively, a corrugated portion having a plurality of peaks and valleys extending in a direction intersecting with the rotation direction of the shaft in the back foil portion alternately in the relative rotation direction is provided, and the peak portion of the corrugated portion is firstly provided. A support can be configured.

  As described above, according to the present invention, since a decrease in the fluid pressure in the bearing gap is suppressed, the supporting force of the foil bearing can be increased.

It is a sectional view of a foil bearing concerning a first embodiment of the present invention. It is a top view of a foil bearing. It is a perspective view of the top foil and the back foil provided in the foil bearing. It is a top view of a back foil. It is a perspective view of a back foil. It is sectional drawing of the downstream end part of a back foil. It is sectional drawing of the downstream end part of the back foil which concerns on another example. FIG. 5 is a sectional view taken along line VV of FIG. 2. It is a top view of a top foil. FIG. 10 is a sectional view taken along line U-U in FIG. 9. FIG. 10 is a sectional view taken along line TT of FIG. 9. It is sectional drawing of a foil bearing. It is a top view of a back foil concerning a second embodiment. It is sectional drawing of the foil bearing which concerns on 3rd embodiment. The upper part is a plan view of the back foil according to the fourth embodiment, and the lower part is a sectional view taken along line YY of the plan view. It is sectional drawing of the back foil which concerns on 5th Embodiment. It is sectional drawing of the foil bearing which concerns on 6th Embodiment. FIG. 18 is a plan view of a foil of the foil bearing of FIG. 17. It is a top view of the foil concerning a 7th embodiment. FIG. 20 is a perspective view of a foil bearing having the foil of FIG. 19. It is sectional drawing of the foil bearing which concerns on 8th Embodiment. It is a perspective view of the back foil proposed in the prior application. FIG. 23 is a sectional view of a foil bearing having the back foil of FIG. 22. FIG. 24 is a cross-sectional view taken along line WW of FIG. 23, showing a state in which fluid pressure in the bearing gap is low. FIG. 24 is a cross-sectional view taken along line WW of FIG. 23, showing a state in which the fluid pressure in the bearing gap is high. FIG. 24 is a plan view of a top foil of the foil bearing of FIG. 23.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the foil bearing 10 according to the first embodiment of the present invention is an air film formed between the shaft 2 and a disk-shaped thrust collar 3. This is a supporting thrust foil bearing. The foil bearing 10 has a disk-shaped foil holder 11, and a top foil 12 and a back foil 13 attached to an end face 11 a of the foil holder 11. In the present embodiment, as shown in FIG. 2, a plurality of (six in the illustrated example) fan-shaped top foils 12 and back foils 13 are arranged side by side in the rotation direction of the shaft 2 (the circumferential direction of the foil holder 11). You. In the following, the leading side in the rotation direction of the shaft 2 (the direction of the arrow R in FIG. 2), that is, the downstream side in the flow direction of the fluid with respect to the top foil 12 during the rotation of the shaft 2, is referred to as “downstream side”, and vice versa. The side is called "upstream".

  The foil holder 11 is formed of metal, resin, or the like. The foil holder 11 has a hollow disk shape having an inner hole 11b into which the shaft 2 is inserted. A plurality of top foils 12 and back foils 13 are attached to one end surface 11a of the foil holder 11. The other end face 11c of the foil holder 11 is fixed to a housing of a facility (for example, a turbo machine such as a gas turbine) in which the foil bearing 10 is incorporated.

  The top foil 12 and the back foil 13 are formed of a metal having high spring properties and good workability, for example, steel or a copper alloy. The top foil 12 and the back foil 13 are formed of a thin metal plate (foil) having a thickness of about 20 μm to 200 μm. In an air dynamic pressure bearing using air as the fluid film as in the present embodiment, since the lubricating oil does not exist in the atmosphere, it is preferable to form the top foil 12 and the back foil 13 with stainless steel or bronze.

  The top foil 12 functions as a top foil portion Tf having a bearing surface X. The top foil 12 has a smooth bearing surface X with no irregularities, as shown in FIGS. The upstream end 12a of the top foil 12 is fixed to the end face 11a of the foil holder 11 by welding or the like. The downstream end 12b of the top foil 12 is a free end. The top foil 12 is formed by performing a punching process or an electric discharge process on a flat foil.

  The back foil 13 functions as a back foil portion Bf that supports the top foil 12 from behind. The back foil 13 has a fan shape having substantially the same shape as the top foil 12 in a plan view, and is arranged directly below the top foil 12 (see FIG. 3). The upstream end 13a of the back foil 13 is fixed to the end face 11a of the foil holder 11 by welding or the like.

  As shown in FIG. 4, the back foil 13 has a first area Q1 occupying most of the area except for both ends in the circumferential direction, and a second area Q2 provided at the downstream end. In the first region Q <b> 1 of the back foil 13, first support portions that are in contact with the top foil 12 at a plurality of locations separated in the radial direction are provided. In the present embodiment, as shown in FIG. 5, in the first region Q1, a flat portion 13b, a plurality of upper protrusions 13c protruding from the flat portion 13b toward the top foil 12, and a top foil 12 from the flat portion 13b. A plurality of lower convex portions 13d protruding to the opposite side are provided, and the upper convex portion 13c constitutes a first support portion. Note that the upper convex portion 13c and the lower convex portion 13d are named "upper" and "lower" so that their relative positional relationships can be easily understood, but this limits the usage of the foil bearing 10. It is not the purpose.

  The flat portion 13b, the upper protruding portion 13c, the lower protruding portion 13d, and the below-described curved portion 13e of the back foil 13 have a uniform thickness. Each of the upper convex portion 13c and the lower convex portion 13d is formed in a substantially hemispherical shape. Since the insides of the upper convex portion 13c and the lower convex portion 13d are hollow, when the back foil 13 is viewed from one side of the front and back sides, for example, as shown in FIG. The region where 13d exists is a concave portion. In FIG. 4, the lower convex portion 13d serving as a concave portion is hatched for easy understanding. A flat portion 13b is provided all around the upper convex portion 13c and the lower convex portion 13d. The upper protruding portion 13c and the lower protruding portion 13d are respectively distributed over the entire first region Q1. The upper projection 13c contacts the back surface of the top foil 12 (the surface opposite to the bearing surface X), and the lower projection 13d contacts the end surface 11a of the foil holder 11.

  The second region Q2 of the back foil 13 is provided with a second support portion that is in continuous contact with the top foil 12 in the radial direction. In the present embodiment, a curved portion 13e protruding toward the top foil 12 is provided in the second region Q2, and the curved portion 13e constitutes a second support portion. The curved portion 13e continuously extends in the radial direction, and extends, for example, in the direction along the edge of the downstream end portion 12b (free end) of the top foil 12, in the illustrated example, in the radial direction. The curved portion 13e is provided in the entire radial direction of the second region Q2, and continuously contacts the radially entire region of the top foil 12. As shown in FIG. 6, a substantially cylindrical curved surface provided at the top of the curved portion 13 e is in contact with the top foil 12. The upstream end of the curved portion 13e is continuous with the flat portion 13b of the first region Q1. The downstream end of the curved portion 13e is curved along the end surface 11a of the foil holder 11. Thereby, when the bending portion 13e is compressed, the downstream end of the bending portion 13e can be smoothly deformed while sliding on the end surface 11a of the foil holder 11.

  Note that, as shown in FIG. 7, the downstream end of the curved portion 13e may be separated from the end surface 11a of the foil holder 11. In this case, the bending portion 13e is easily displaced in the axial direction, and the rigidity when the back foil 13 is compressed can be suppressed.

  The back foil 13 is formed by pressing a foil. In the present embodiment, after a flat foil material having a predetermined shape is formed by punching or electrical discharge machining, the foil material is subjected to press working to form a flat portion 13b, an upper convex portion 13c, a lower convex portion 13d, and a curved portion. The back foil 13 is formed by simultaneously molding the portion 13e. In addition, the punching of the foil material and the forming of the flat portion 13b, the upper convex portion 13c, the lower convex portion 13d, and the curved portion 13e can be simultaneously performed by press working. The thickness dimension (axial dimension) of the entire back foil 13 including the upper projection 13c and the lower projection 13d is about 0.5 to 2 mm. The protrusion amounts of the upper convex portion 13c and the curved portion 13e with respect to the flat portion 13b are substantially the same. In addition, the arrangement pattern of the upper convex part 13c and the lower convex part 13d shown in FIG. 4 is only an example, and an arbitrary arrangement pattern different from that of FIG. 4 can be adopted as needed.

  As shown in FIG. 8, when the shaft 2 and the thrust collar 3 rotate in one circumferential direction (the direction of the arrow R), a bearing is provided between the bearing surface X of each top foil 12 of the foil bearing 10 and the end surface 3 a of the thrust collar 3. A gap C is formed. At this time, since the top foil 12 is curved, the bearing gap C has a wedge shape that becomes narrower toward the downstream side. The pressure of the air film in the bearing clearance C is increased by the air in the large clearance C1 of the wedge-shaped bearing clearance C being pushed into the small clearance C2. Contact supported. At this time, the bearing surface X of the top foil 12 is elastically deformed according to the operating conditions such as the load, the rotation speed of the shaft 2 and the ambient temperature, so that the bearing gap C is automatically adjusted to an appropriate width according to the operating conditions. You. Therefore, even under severe conditions such as high temperature and high speed rotation, the bearing gap C can be controlled to the optimum width, and the shaft 2 can be stably supported.

  As described above, when the air pressure in the bearing gap C (particularly, the small gap C2) is increased, the top foil 12 is pressed against the back foil 13. More specifically, most of the top foil 12 except for the upstream end 12 a and the downstream end 12 b is supported in contact with the upper protrusion 13 c of the back foil 13 and the downstream end 12 b of the top foil 12. A nearby area is supported in contact with the curved portion 13e of the back foil 13. At this time, of the top foil 12, the contact portion A in contact with the upper convex portion 13c (first support portion) of the back foil 13 has high rigidity, and the periphery of the contact portion A has low rigidity. Therefore, as shown in FIGS. 9 to 11, a region of the top foil 12 between the contact portions A in the radial direction is deformed toward the foil holder 11 side (below the FIGS. 10 and 11) from the contact portions A, A concave portion B is formed in this area. On the other hand, a region of the top foil 12 where the curved portion 13e (second support portion) of the back foil 13 is in contact has high rigidity and is hardly deformed toward the foil holder 11 by air pressure. A weir D, which is one step higher, is formed. The weir D continuously extends in the radial direction, and in this embodiment, extends over the entire length of the top foil 12 in the radial direction (see FIG. 9).

  The air pushed into the small gap C2 with the rotation of the shaft 2 passes through the concave portion B of the top foil 12 and flows downstream (see the arrow S in FIGS. 9 and 11). However, since the weir D continuously extending in the radial direction is provided on the downstream side of the concave portion B, the flow of air to the downstream side is regulated. This makes it difficult for air to escape from the small gap C2 to the downstream side, and suppresses a decrease in air pressure in the small gap C2 (see the dotted line in the lower part of FIG. 23), so that the supporting force of the foil bearing 10 can be increased. .

  During rotation of the shaft 2, as shown in FIG. 12, the top foil 12 receives the pressure P due to the air pressure generated in the bearing gap C, so that the back foil 13 is compressed in the pressure P direction via the top foil 12. Force acts. Since the flat portion 13b has a thin plate shape extending in a direction perpendicular to the direction of the pressure P, the flat portion 13b is a portion of the back foil 13 having a low rigidity against the compressive force. Therefore, when a compressive force is applied to the back foil 13, the flat portion 13b first deforms and absorbs the compressive force as shown by the two-dot chain line in FIG. Therefore, the rigidity of the back foil 13 can be locally reduced as compared with the back foil portion of the existing bump type foil bearing that does not have such a flat portion. As a result, the flexibility of the bearing surface X increases, so that the bearing surface X easily deforms following the displacement of the shaft 2 and the like. The bearing gap C is automatically adjusted to an optimum width, and the thrust collar 3 and the top foil 12 are adjusted. Can be reliably prevented.

  In addition, at the time of low-speed rotation immediately before the stop of the shaft 2 or immediately after the start, the bearing surface X of each top foil 12 and the end surface 3a of the thrust collar 3 make sliding contact with each other. A low friction coating such as a titanium aluminum nitride film, a tungsten disulfide film, or a molybdenum disulfide film may be formed.

  During the rotation of the shaft 2, a minute sliding occurs between the top foil 12 and the back foil 13 or between the back foil 13 and the end face 11 a of the foil holder 11. The vibration of the shaft 2 can be attenuated by the frictional energy due to the minute sliding. In order to adjust the frictional force due to such minute sliding, a low friction coating as described above may be formed on one or both of the sliding surfaces.

  The present invention is not limited to the above embodiment. Hereinafter, other embodiments of the present invention will be described, but the description of the same points as the above embodiments will be omitted.

  In the above-described foil bearing 10, the rigidity of the bearing surface X can be partially controlled by changing the distribution density of the upper convex portion 13c and the lower convex portion 13d provided in the first region Q1 of the back foil 13 depending on the location. it can. For example, in the second embodiment shown in FIG. 13, the densities of the upper convex portions 13c and the lower convex portions 13d increase toward the downstream side. In this case, the rigidity of the back foil 13 in the compression direction (axial direction) increases toward the downstream side. This makes it difficult for the bearing surface X of the top foil 12 to be deformed in a direction away from the thrust collar 3 (a direction in which the bearing gap C is widened) toward the downstream side, so that a wedge-shaped bearing gap C is easily formed. . In FIG. 13, the back foil 13 is simplified and shown as a rectangle.

  Further, in the above-described foil bearing 10, a bearing surface having a predetermined shape can be obtained by changing the height of the upper convex portion 13c and the lower convex portion 13d provided in the first region Q1 of the back foil 13 depending on the location. For example, in the third embodiment shown in FIG. 14, the height (axial dimension) of the back foil 13 including the upper convex portion 13c and the lower convex portion 13d increases toward the downstream side. As a result, the bearing surface X of the top foil 12 tends to be displaced toward the thrust collar 3 toward the downstream side, and a wedge-shaped bearing gap C is easily formed.

  In the fourth embodiment shown in FIG. 15, a corrugated portion 13f is provided in the first region Q1 of the back foil 13. The corrugated portion 13f has a plurality of peaks 13f1 and valleys 13f2 extending along a direction intersecting with the rotation direction of the shaft 2 alternately in the rotation direction of the shaft 2. The peak portion 13f1 of the corrugated portion 13f forms a first support portion that supports the top foil 12 from behind. The ridges 13f1 and the valleys 13f2 extend in a direction intersecting the edge of the downstream end of the backfoil 13, and in the illustrated example, extend in a direction parallel to the edge of the upstream end 13a of the backfoil 13. In this case, at the downstream end of the first region Q <b> 1, ridges 13 f 1 are provided at a plurality of locations separated in the radial direction, and these ridges 13 f 1 contact the top foil 12. The curved portion 13e is provided in the second region Q2 as in the above-described embodiment.

  The back foil 13 having the corrugated portion 13f as shown in FIG. 15 can be formed by, for example, press working. In this case, since the flat foil material is bent into a corrugated shape, the dimension in a plan view (the dimension in the direction orthogonal to the extending direction of the crest 13f1) is reduced accordingly. Therefore, the design of the flat foil material before the press working is extremely complicated because it is necessary to set the shape and the size in consideration of the size reduction by the press working.

  On the other hand, as shown in FIG. 5, a back foil 13 having a dimple-shaped upper convex portion 13c and a lower convex portion 13d is formed by pressing a flat foil material to locally elongate the material to thereby form an upper convex portion. 13c and the lower convex portion 13d can be formed. In this case, since the entire dimensions in plan view hardly change by the press working, the upper convex portion 13c and the lower convex portion 13d can be freely designed, and the design of the back foil 13 is facilitated.

  In the fifth embodiment shown in FIG. 16, the second support part of the back foil part Bf is configured by the rod-shaped member 15. The rod-shaped member 15 is formed of metal or resin. The rod-shaped member 15 continuously extends in the radial direction, and extends, for example, in the direction along the edge of the downstream end portion 12b of the top foil 12, specifically, in the radial direction. The rod-shaped member 15 is fixed to the surface of the second region Q2 of the back foil 13 (the surface on the top foil 12 side) by welding or the like. When the pressure in the bearing gap C increases, the rod-shaped member 15 continuously contacts the top foil portion Tf in the radial direction. The cross-sectional shape of the rod-shaped member 15 is not limited to FIG. 16 and may be, for example, an upwardly convex semicircular shape.

  In the sixth embodiment shown in FIG. 17, a foil member 14 integrally including a top foil portion Tf and a back foil portion Bf is provided (the back foil portion Bf is shown by a dotted pattern). The upstream end of each foil member 14 is attached to the foil holder 11. When the plurality of foil members 14 are attached to the foil holder 11, the back foil portion Bf of the adjacent foil member 14 is disposed between the top foil portion Tf of each foil member 14 and the foil holder 11. As shown in FIG. 18, the first region Q1 of the back foil portion Bf of each foil member 14 is provided with first support portions that contact and support the top foil portion Tf at a plurality of radially separated locations. In the illustrated example, a flat portion 13b, an upper convex portion 13c (open circle) as a first support portion, and a lower convex portion 13d (hatched circle) are provided in the first region Q1. In the second region Q2 of the back foil portion Bf of each foil member 14, a second support portion that continuously supports the top foil portion Tf in the radial direction is provided. In the illustrated example, a curved portion is used as the second support portion. 13e is provided.

  In the seventh embodiment shown in FIG. 19, similarly to the embodiment shown in FIG. 17, each foil member 14 has a top foil portion Tf and a back foil portion Bf. Is different from the embodiment shown in FIG. The foil member 14 shown in FIG. 19 has a main body 14 a having a top foil portion Tf and a back foil portion Bf, and a fixing portion 14 b extending outward from the main body 14 a to be fixed to the foil holder 11. The edge 14a1 at the downstream end and the edge 14a2 at the upstream end of the main body 14a both have a shape in which the radial center is bulged downstream. The back foil portion Bf is provided with a flat portion 13b, an upper convex portion 13c (open circle) as a first support portion, a lower convex portion 13d (hatched circle), and a curved portion 13e as a second support portion. The curved portion 13e extends in a direction substantially parallel to the edge 14a1 of the downstream end of the main body 14a. As described above, the curved portion 13e does not necessarily have to be parallel to the radial direction, and may have any shape as long as it can continuously contact the top foil portion Tf in the radial direction. When the foil member 14 shown in FIG. 19 is attached to the foil holder 11, as shown in FIG. 20, the back foil portion Bf of each foil member 14 is hidden behind the top foil portion Tf of the adjacent foil member 14, and the top foil portion Only Tf is exposed on the front side (thrust collar side).

  In the above embodiments, the case where the present invention is applied to a thrust foil bearing is shown. However, the present invention can also be applied to a radial foil bearing that supports a shaft in a radial direction. For example, in the eighth embodiment shown in FIG. 21, the present invention is applied to a so-called leaf-type radial foil bearing 20. The radial foil bearing 20 has a cylindrical foil holder 21 and a plurality of foil members 22 which are attached to the inner peripheral surface 21a of the foil holder 21 in a circumferential direction. In each foil member 22, a downstream region functions as a top foil portion Tf, and an upstream region functions as a back foil portion Bf. The back foil portion Bf (shown by a dotted pattern) of each foil member 22 has first support portions (for example, upper convex portions) at a plurality of locations separated in the rotation orthogonal direction (axial direction), similarly to the above embodiment. Is provided, and a second support portion (for example, a curved portion) that is in continuous contact with the top foil portion Tf in the axial direction is provided on the downstream side. When the shaft 2 rotates, a bearing gap C is formed between the bearing surface of the top foil portion Tf and the outer peripheral surface of the shaft 2.

  In the above embodiment, the case where the second support portion (curved portion) is in contact with the entire region in the rotation orthogonal direction of the top foil portion Tf has been described. However, the present invention is not limited thereto. May be slightly smaller than the top foil portion Tf, and the second support portion may contact and support an area of the top foil portion Tf other than the end in the direction orthogonal to the rotation.

  In the above embodiment, the case where the foil bearing is fixed and the shaft 2 is rotated has been described. However, the present invention is not limited to this, and the shaft 2 may be fixed and the foil bearing may be rotated. However, if the foil bearing is rotated, the foil may be damaged by centrifugal force. Therefore, it is preferable to fix the foil bearing as in the above embodiment.

  Further, the above-described foil bearing can be used as a bearing for a main shaft of a turbo machine such as a gas turbine or a turbocharger, a bearing for a vehicle such as an automobile, or a bearing for an industrial device. It is.

  Further, the above-described foil bearing can be used not only as an air dynamic pressure bearing using air as a pressure generating fluid, but also as an oil dynamic pressure bearing using lubricating oil as a pressure generating fluid.

2 Shaft 3 Thrust collar 10 Foil bearing 11 Foil holder 12 Top foil 13 Back foil 13b Flat part 13c Upper convex part (first support part)
13d Lower convex portion 13e Curved portion (second support portion)
Tf Top foil Bf Back foil C Bearing gap C1 Large gap C2 Small gap X Bearing surface

Claims (5)

A top foil portion having a bearing surface and a back foil portion for elastically supporting the top foil portion from behind are provided, and the relative rotation of the shaft causes a bearing gap between the shaft and the bearing surface. In a foil bearing for supporting the shaft in a non-contact manner with a fluid pressure,
The back foil portion, the top foil portion, a first support portion that contacts and supports at a plurality of locations separated in a direction orthogonal to the relative rotation direction of the shaft, provided at the downstream end of the back foil portion , A foil bearing, comprising: a second support section that continuously supports the top foil section in a direction orthogonal to the relative rotation direction.   2. The foil bearing according to claim 1, wherein the second support portion of the back foil portion continuously contacts the top foil portion in an entire region in a direction orthogonal to the relative rotation direction. 3.   The foil bearing according to claim 1, wherein the second support portion of the back foil portion is configured by a curved portion that is convex toward the top foil portion.   The back foil portion includes a flat portion, a plurality of upper protrusions protruding from the flat portion toward the top foil portion, and a plurality of lower protrusions protruding from the flat portion to the opposite side to the top foil portion. 4. The foil bearing according to claim 1, wherein the plurality of upper convex portions constitute the first support portion. 5.   The back foil portion includes a corrugated portion having a plurality of peaks and valleys extending in a direction intersecting with the relative rotation direction alternately in the relative rotation direction, wherein the plurality of peaks are the first support. The foil bearing according to any one of claims 1 to 3, which constitutes a part.

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