JP2018059554A - Foil bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a foil from being damaged due to local contact between a shaft and the foil.SOLUTION: A foil bearing 1 includes a foil unit 20 having a bearing surface X facing a shaft 2 to be supported, and relatively rotatably supports the shaft 2 by a fluid pressure generating in a bearing clearance C between the bearing surface X and the shaft 2. The foil unit 20 has a metal foil 21, and a soft layer (soft sheet 22) composed of a material lower in the coefficient of elasticity than that of the foil 21.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a foil bearing.

  A foil bearing has a flexible thin plate (foil) that forms the bearing surface. When the foil is bent, the bearing clearance is appropriate depending on the operating conditions such as the rotational speed, load, and ambient temperature of the shaft. It is characterized by being automatically adjusted to a wide width.

  As the foil bearing, for example, (1) a bump type foil bearing having a top foil having a bearing surface and a back foil (bump foil) that elastically supports this from the back (for example, see Patent Document 1), (2 ) A leaf type foil bearing that does not have a back foil and is provided so that a plurality of top foils (leaf foils) partially overlap each other, and gives spring properties to the top foil at the overlapping portions (see, for example, Patent Document 2) (3) A multi-arc foil bearing (for example, see Patent Document 3) in which a plurality of foils are arranged side by side in the circumferential direction and both ends of each foil in the circumferential direction are held by a foil holder is known.

Japanese Utility Model Publication No. 61-36725 JP-A-4-54309 JP 2014-1119094 A

  In the foil bearing as described above, when the shaft rotates at a low speed such as when the shaft is started or stopped, the fluid pressure in the bearing gap is low, so that the foil and the shaft repeatedly contact and slide. In general, since the foil and the shaft are both made of metal, adhesion occurs on the sliding surface between the foil and the shaft, which may increase frictional torque and eventually cause seizure or damage to the bearing surface. In order to prevent such a problem, a low friction coating such as a DLC film, a titanium aluminum nitride film, or a molybdenum disulfide film may be formed on the surface of the foil or the shaft (see Patent Document 3). .

  However, even when the low friction coating as described above is applied, the low friction coating is quickly worn out due to local contact with the shaft, and wear, seizure, and damage may occur from this portion.

  Specifically, for example, in a leaf-type foil bearing, as shown in FIG. 26, the downstream region of each foil 21 ′ is arranged on the upstream region of the foil 21 ′ adjacent thereto, Thereby, overlapping portions W ′ of the foil 21 ′ are formed at a plurality of locations in the circumferential direction. In this foil bearing, when the fluid pressure in the bearing gap increases, each foil 21 'is pressed against the foil holder 10'. At this time, in each foil 21 ′, the overlapping portion W ′ supported by the other foil 21 ′ is less likely to be displaced toward the foil holder 10 ′ than the other circumferential regions (that is, the rigidity is high). . For this reason, when the shaft is started / stopped, as shown in FIG. 27, the bearing surface X 'preferentially contacts the shaft in the overlapping portion W, so that this portion is likely to be worn. In particular, as shown in the drawing, when the overlapping portion W ′ of the metal foil 21 ′ is sandwiched between the metal shaft 2 ′ and the metal foil holder 21 ′, the contact between the bearing surface X ′ and the shaft 2 ′ is brought about. The surface pressure of the part increases and wear or the like is likely to occur.

  In addition, when vibration or conical motion occurs in the shaft inserted in the inner periphery of the foil bearing and the shaft is inclined with respect to the central axis of the foil bearing, the shaft is moved to the axial end (edge portion) of the bearing surface of the foil bearing. Contact with high surface pressure locally. For this reason, in the bearing surface of the foil, the region near the end portion in the axial direction is likely to be worn.

  In view of the above circumstances, an object of the present invention is to prevent foil damage in a foil bearing due to local contact between a shaft and the foil.

  The present invention, which has been made to solve the above-mentioned problems, includes a foil unit having a bearing surface facing a shaft to be supported, and the shaft is relatively moved by a fluid pressure generated in a bearing gap between the bearing surface and the shaft. In the foil bearing that is rotatably supported, the foil unit includes a metal foil and a soft layer made of a material having a lower elastic modulus than the foil.

  Thus, in the foil bearing of the present invention, the foil unit having the bearing surface includes a soft layer that is softer (lower elastic modulus) than the metal foil. When the shaft comes into contact with the bearing surface of the foil unit, the soft layer is deformed, so that the bearing surface is deformed following the shaft (see FIG. 10). As a result, the contact area between the bearing surface and the shaft is increased, the contact surface pressure is reduced, and damage to the bearing surface can be prevented.

  When vibration or conical motion occurs on the shaft, end portions in the direction perpendicular to the rotational direction of the shaft (both ends in the axial direction for radial foil bearings and outer diameter ends for thrust foil bearings) in the foil unit are likely to come into contact with the shaft. Therefore, it is preferable to provide a soft layer in a region including the end portion in the foil unit.

  The foil unit includes a top foil portion having the bearing surface and a back foil portion disposed behind the top foil portion, and the top foil portion and the back foil portion are stacked in a thickness direction. When the overlapping portions are provided at a plurality of locations separated in the circumferential direction, the rigidity of the bearing surface is particularly high in the overlapping portion. Therefore, it is particularly effective to reduce the contact surface pressure between the bearing surface and the shaft by providing a soft layer in the overlapping portion.

  A soft layer can be comprised with the soft sheet | seat which consists of a material whose elastic modulus is lower than the said foil, for example.

  Alternatively, the soft layer may be integrated with the foil to form a composite foil. In this case, the positional deviation between the foil and the soft layer is avoided, and the soft layer can be selectively disposed at the intended portion.

  For example, if a composite foil is formed by adhering a soft layer to a partial region of a foil having a uniform thickness, the composite foil becomes thick only in the region where the soft layer is provided. It may be difficult to manage the thickness. Therefore, if the thickness of the composite foil is made uniform by providing a thin portion on the foil and providing a soft layer on the thin portion, the above-mentioned problems can be avoided.

  The soft layer can be formed of a material mainly composed of resin, rubber, or graphite, for example.

  As described above, by providing the soft layer in the foil unit, the contact surface pressure between the shaft and the bearing surface is relieved, so that damage to the foil can be prevented.

It is sectional drawing of the foil bearing which concerns on one Embodiment of this invention. It is a top view of foil. It is the top view which looked at two foils connected from the back side. It is a perspective view which shows the state which connected the foil of 3 sheets in the cylinder shape. It is a perspective view which shows the state which has arrange | positioned the soft sheet | seat behind foil. It is a perspective view which shows the state which rounded the temporary assembly of the foil and the soft sheet | seat to the cylindrical shape. It is a perspective view which shows a mode that the temporary assembly of a foil and a soft sheet | seat is attached to a foil holder. It is sectional drawing which expands and shows the foil bearing of FIG. FIG. 2 is a cross-sectional view of the foil bearing of FIG. 1 with the circumferential direction converted into a straight line. It is sectional drawing which expands and shows the contact part of a shaft and a bearing surface. (A)-(c) is sectional drawing which shows the example of the laminated structure of the foil unit in which the bearing surface was formed in foil. (A)-(c) is sectional drawing which shows the example of the laminated structure of the foil unit in which the bearing surface was formed in the soft sheet | seat. It is a side view of a composite foil. It is a side view which shows the curved state at the time of the high temperature of the composite foil of FIG. It is a perspective view which shows the other example of a composite foil. FIG. 16 is a cross-sectional view of a foil bearing having the composite foil of FIG. 15 with the circumferential direction converted into a straight line. It is a perspective view which shows the other example of a composite foil. It is sectional drawing of the foil bearing which has the composite foil of FIG. 17, and the circumferential direction is converted into a straight line and shown. It is a perspective view which shows the other example of a composite foil. It is sectional drawing in the YY line of the composite foil of FIG. (A)-(d) is sectional drawing which shows the example of the laminated structure of the foil unit containing a composite foil. It is sectional drawing which shows a leaf type foil bearing. It is sectional drawing which shows a bump type foil bearing. It is a perspective view which shows a leaf type thrust foil bearing. It is sectional drawing in the DD line | wire in FIG. It is sectional drawing of the conventional leaf type foil bearing. It is sectional drawing which expands and shows the contact part of the superposition | polymerization part and axis | shaft of foil.

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

  FIG. 1 shows a foil bearing 1 according to an embodiment of the present invention. The foil bearing 1 supports the shaft 2 inserted in the inner periphery in the radial direction. The foil bearing 1 includes a tubular foil holder 10 and a foil unit 20 attached to an inner peripheral surface 10a of the foil holder 10. The foil unit 20 is provided with a bearing surface X that faces the outer peripheral surface 2a of the shaft 2 in the radial direction. In the following, the rotation direction leading side of the shaft 2 (see the arrow R in FIG. 1), that is, the downstream side in the fluid flow direction with respect to the foil unit 20 when the shaft 2 rotates is referred to as “downstream side” and vice versa. The side is called the “upstream side”.

  The foil holder 10 is formed in a cylindrical shape with a metal such as a sintered metal or a molten material (for example, steel). The axial direction groove | channel 10b used as the attachment part of the foil unit 20 is formed in the several places spaced apart in the circumferential direction among the internal peripheral surfaces 10a of the foil holder 10. FIG. If there is no problem in heat resistance and strength, the foil holder 10 may be formed of resin.

  The foil unit 20 includes a metal foil 21 and a soft sheet 22 as a soft layer. In the present embodiment, a plurality of foils 21 and the same number of soft sheets 22 as the foils 21 are arranged in the circumferential direction on the inner peripheral surface 10 a of the foil holder 10. The soft sheet 22 is arranged behind each foil 21 (outside diameter side). In the illustrated example, the foil 21 and the soft sheet 22 are arranged at three locations on the inner peripheral surface 10 a of the foil holder 10.

  The foil 21 is formed of a metal having a high spring property and good workability, such as a steel material or a copper alloy. The foil 21 is formed by processing a metal belt-like foil having a thickness of about 20 μm to 200 μm into a predetermined shape by pressing or the like. Typical examples of steel materials and copper alloys include carbon steel and brass. However, in general carbon steel, since there is no lubricating oil in the atmosphere and the antirust effect by the oil cannot be expected, corrosion due to rust is likely to occur. Further, brass may cause cracks due to processing strain (this tendency becomes stronger as the Zn content in brass increases). Therefore, it is preferable to use a stainless steel or bronze foil as the belt-like foil.

  As shown in FIG. 2, the foil 21 includes a top foil portion Tf having a bearing surface X, a convex portion 21a extending downstream from the top foil portion Tf (left side in FIG. 2), and an upstream side from the top foil portion Tf. And a backfoil portion Bf extending on the right side in FIG.

  The convex portion 21a extends along the surface of the top foil portion Tf and in a direction orthogonal to the rotation direction R of the shaft 2 (in the present embodiment, the axial direction, the vertical direction in FIG. 2, hereinafter referred to as the rotation orthogonal direction N). Provided at a plurality of spaced apart locations. In this embodiment, the case where the convex part 21a is formed in three places separated in the rotation orthogonal direction N is illustrated. Of the downstream end portion of the top foil portion Tf, a minute notch 21b extending from the foil edge portion to the upstream side is provided in the vicinity of each convex portion 21a.

  At the upstream end of the backfoil portion Bf, two notches 21c that are spaced apart in the rotation orthogonal direction N and recessed toward the downstream are formed. The width dimension in the rotation orthogonal direction N of each notch 21c is gradually reduced toward the downstream side. In this embodiment, the case where the whole notch part 21c is formed in circular arc shape is illustrated, However, Each notch part 21c can also be formed in the substantially V shape which made the top part the pointed shape. Protruding portions 21d that protrude upstream are formed on both sides of the cutout portion 21c in the rotation orthogonal direction N.

  A slit-like difference in which the convex portions 21a of the adjacent foils 21 are inserted into a plurality of locations (the same number as the convex portions 21a) at the boundary between the top foil portion Tf and the back foil portion Bf and separated in the rotation orthogonal direction N. A slot 21e is provided. Among these, the insertion ports 21 e at both ends extend linearly along the rotation orthogonal direction N, and are opened at both ends of the foil 21, respectively. The central insertion port 21e includes a linear notch portion extending along the rotation orthogonal direction N and a wide notch portion extending upstream from the notch portion and having a circular arc at the tip.

  The soft sheet 22 is a flexible thin plate provided separately from the foil 21 and is a material having a lower elastic modulus (particularly, an elastic modulus with respect to compressive force in the thickness direction) than the metal foil 21. It is formed. Examples of the material of the flexible sheet 22 include resin materials such as fluororesin, polycarbonate (PC), polyacetal (POM), and polyether ether ketone (PEEK), rubber materials such as silicon rubber, and carbon such as graphite and carbon fiber. The material which made the main component etc. are mentioned. Examples of the material mainly composed of carbon include, for example, those composed only of graphite, those composed only of carbon fiber, those obtained by combining carbon fiber and graphite, carbon fiber and / or graphite and binder (for example, organic or inorganic material) A composite material composed of) can be used. Since these materials have softness and flexibility, they do not hinder the elasticity of the top foil portion Tf.

  The soft sheet 22 has a rectangular shape and is curved in a substantially cylindrical shape along the inner peripheral surface 10 a of the foil holder 10. The axial dimension of the soft sheet 22 is substantially the same as the axial dimension of the top foil portion Tf of the foil 21 (that is, the axial dimension of the bearing surface X). For example, the axial dimension of the soft sheet 22 may be the same as the axial dimension of the top foil part Tf, or may be slightly smaller or slightly larger than the axial dimension of the top foil part Tf. . The circumferential dimension of the soft sheet 22 is smaller than the circumferential dimension of the top foil portion Tf (that is, the circumferential dimension of the bearing surface X).

  As shown in FIG. 3, the two foils 21 can be connected by inserting each convex portion 21 a of one foil 21 into the insertion port 21 e of the adjacent foil 21. In the figure, one of the two foils 21 after the combination is given a gray color.

  Then, as shown in FIG. 4, after three foils 21 are connected in a cylindrical shape by the same coupling method as in FIG. 3, as shown in FIG. The sheet 22 is arranged. Thereafter, as shown in FIG. 6, the temporary assembly of the three foils 21 and the soft sheet 22 is rounded into a substantially cylindrical shape, and between the top foil portion Tf of each foil 21 and the back foil portion Bf of the other foil 21. The soft sheet 22 is sandwiched between the two. In this state, as shown in FIG. 7, the temporary assembly is inserted into the inner periphery of the foil holder 10 from one axial side (see arrow). Specifically, while inserting the temporary assembly into the inner periphery of the foil holder 10, the convex portion 21 a of each foil 21 is inserted into the axial groove 10 b opened on one end face of the foil holder 10 from one axial direction. Plug in. As described above, the foil unit 20 including the three foils 21 and the soft sheet 22 is attached to the inner peripheral surface 10a of the foil holder 10 in a state of being arranged in the circumferential direction.

  As shown in FIG. 8, when the foil unit 20 is attached to the foil holder 10, the two adjacent foils 21 intersect with each other. On the upstream side of the intersecting portion, the top foil portion Tf of one foil 21 forms a bearing surface X, and the back foil portion Bf of the other foil 21 is disposed behind the top foil portion Tf. On the other hand, on the downstream side of the intersecting portion, the top foil portion Tf of the other foil 21 constitutes the bearing surface X, and the convex portion 21a of the one foil 21 is formed through the insertion port 21e of the other foil 21. , Wraps around behind the other foil 21 and is inserted into the axial groove 10 b of the foil holder 10. The upstream end portion of the back foil portion Bf is a free end, and the position of the end portion varies in the circumferential direction according to the elastic deformation of the back foil portion Bf. The downstream end portion of the back foil portion Bf is in a state of being engaged with the other foil 21 (the one foil 21) in the circumferential direction at the intersecting portion.

  The foil bearing 1 is provided at a plurality of locations (three locations in the present embodiment) where overlapping portions W (see FIG. 9) in which the top foil portion Tf and the back foil portion Bf are stacked in the thickness direction are separated in the circumferential direction. Then, the flexible sheet 22 is disposed in the overlapping portion W. The soft sheet 22 is disposed so as to overlap the bearing surface X and the width direction of the bearing gap C (radial direction in the present embodiment). In the illustrated example, the soft sheet 22 is disposed between the top foil portion Tf and the back foil portion Bf of the overlapping portion W. The downstream end of the soft sheet 22 is disposed on the back foil portion Bf (inner diameter side). The upstream end portion of the soft sheet 22 is disposed on the upstream side of the back foil portion Bf and is in contact with the inner peripheral surface 10 a of the foil holder 10.

  In the foil bearing 1, the adjacent foils 21 are engaged with each other in the circumferential direction so as to stick to each other. Thereby, the top foil part Tf of each foil 21 protrudes to the outer diameter side, and is curved into a shape along the inner peripheral surface 10 a of the foil holder 10. The movement of each foil 21 to the downstream side is restricted because the convex portion 21a of each foil 21 abuts against the axial groove 10b, but the movement of each foil 21 to the upstream side is not restricted. For this reason, each foil 21 can be minutely slid (reciprocated) in the circumferential direction with respect to the inner peripheral surface 10 a of the foil holder 10.

  As shown exaggeratedly in FIG. 9, the convex portion 21a of the foil 21 inserted into the axial groove 10b of the foil holder 10 is slightly inclined by an angle θ with respect to the tangential direction of the inner peripheral surface 10a of the foil holder 10. Therefore, in the vicinity of the convex portion 21a, the top foil portion Tf tends to be curved so as to be convex toward the inner diameter side. Further, the top foil portion Tf rides on the back foil portion Bf together with the soft sheet 22 so as to be separated from the inner peripheral surface 10a of the foil holder 10 toward the downstream side (side approaching the outer peripheral surface 2a of the shaft 2). It will be in a state inclined to. As described above, a wedge space that narrows toward the downstream side is formed between the bearing surface X of the top foil portion Tf and the outer peripheral surface 2a of the shaft 2.

  While the shaft 2 is rotating, the air film generated in the wedge space has a high pressure, so that the shaft 2 receives a levitation force. Therefore, as shown in FIG. 1, an annular bearing gap C (radial bearing gap) is formed between the bearing surface X of each foil 21 and the shaft 2, and the shaft 2 rotates without contacting the foil 21. It is supported freely. At this time, in the top foil portion Tf, the elastic force of the curved portion convex toward the inner diameter side provided near the downstream end portion, the elastic force of the portion riding on the back foil portion Bf, and the inside of the foil holder 10 The spring force in the radial direction is imparted to the bearing surface X by the elastic restoring force of the foil 21 that attempts to return from the curved shape along the peripheral surface 10a to the original shape. In the present embodiment, not only the top foil portion Tf but also the soft sheet 22 curves on the back foil portion Bf, so that the soft sheet 22 is elastic together with the top foil portion Tf by the pressure of the air film in the bearing gap C. Deform. Due to the elastic force of the top foil portion Tf and the soft sheet 22, a spring property in the radial direction of the bearing surface X is imparted. Due to the spring property of the bearing surface X, the width of the bearing gap C is automatically adjusted to an appropriate width according to operating conditions and the like, so that the rotation of the shaft 2 is stably supported. In the drawings, the width of the bearing gap C is exaggerated for easy understanding.

  During rotation of the shaft 2, the top foil portion Tf is pressed against the back foil portion Bf by the pressure of the air film in the bearing gap C, so that a portion of the top foil portion Tf that rides on the back foil portion Bf has a bearing gap. A step in the width direction of C (radial direction in the present embodiment) is formed. As shown in FIG. 3, when the notch portion 21c is provided at the upstream end portion of the back foil portion Bf of each foil 21, this step becomes a herringbone shape corresponding to the shape of the notch portion 21c. . Since the fluid flowing along the top foil portion Tf flows along the herringbone-shaped step (see the arrow in FIG. 3), the high pressure of the fluid at two locations in the rotation orthogonal direction N of the bearing gap C Part is formed. Thereby, it becomes possible to support the moment load while enhancing the floating effect of the shaft 2. In the present embodiment, as shown in FIG. 2, since the notch 21b is formed in the top foil portion Tf to locally reduce the rigidity of the top foil portion Tf, the top foil portion Tf is notched portion 21c. The deformation is performed smoothly even when it is deformed along the line.

  During low-speed rotation such as immediately after the shaft 2 is started or immediately before it is stopped, the pressure of the air film in the bearing gap C is insufficient, so that the bearing surface X of the foil 21 and the outer peripheral surface 2a of the shaft 2 slide in contact with each other. Therefore, a low friction coating such as a DLC film, a titanium aluminum nitride film, a tungsten disulfide film, or a molybdenum disulfide film is applied to either or both of the bearing surface X of the foil 21 and the outer peripheral surface 2a of the shaft 2. It may be formed.

  In the foil bearing 1, the foil unit 20 includes the soft sheet 22. In the present embodiment, the soft sheet 22 is disposed in a region of the bearing surface X where the rigidity in the width direction of the bearing gap C is high, specifically, the overlapping portion W of the top foil portion Tf and the back foil portion Bf. ing. As shown in FIG. 10, when the bearing surface X of the foil 21 and the outer peripheral surface 2 a of the shaft 2 come into contact with each other, the soft sheet 22 is deformed so that the bearing surface X follows the outer peripheral surface 2 a of the shaft 2. Deform. As a result, the contact area between the bearing surface X and the outer peripheral surface 2a of the shaft 2 is increased, so that the contact surface pressure between the two is reduced, and damage to the foil 21 and early peeling of the low friction coating can be prevented. .

  Further, when vibration or conical motion occurs on the shaft 2, the shaft 2 comes into contact with the axial end of the bearing surface X. In this embodiment, since the soft sheet 22 is provided in a region including at least the axial end of the bearing surface X (in the illustrated example, the entire axial direction), the shaft 2 contacts the axial end of the bearing surface X. Even if it does, damage to the foil 21 can be prevented because the flexible sheet | seat 22 deform | transforms as mentioned above.

  Further, when the soft sheet 22 is formed of a material containing graphite as a main component, graphite has a higher thermal conductivity than stainless steel generally used as the foil 21, so that the shaft 2 and the bearing surface X Since the heat generated at the contact portion is easily diffused through the soft sheet 22 in close contact with the top foil portion Tf, seizure can be prevented.

  Further, during the rotation of the shaft 2, a minute slide occurs between the foil 21 and the inner peripheral surface 10a of the foil holder 10 or the axial groove 10b. The vibration of the shaft 2 can be attenuated by the frictional energy generated by the minute sliding. In order to adjust the frictional force due to such micro-sliding, a low friction coating as described above may be formed on one or both of the surfaces that slide with each other.

  When the soft sheet 22 is formed of a material containing graphite as a main component, graphite is excellent in self-lubricating performance, so that the frictional force between the foils 21 or between the foil 21 and the foil holder 10 is reduced. There is a concern about the reduction of the vibration damping effect. In this case, by forming minute irregularities on one or both of the soft sheet 22 and the sliding surface with plastic working (for example, press working) or by increasing the surface roughness by machining or the like. The frictional force of the sliding part may be adjusted.

  Hereinafter, although other embodiment of this invention is described, description is abbreviate | omitted about the point similar to said embodiment.

  For example, in the above embodiment, the foil unit 20 has a three-layer structure in which the foils 21 and the soft sheets 22 are alternately stacked {see FIG. 11B}. Not limited to this, two layers or four or more layers may be used. For example, the foil unit 20 shown in FIG. 11 (a) has a two-layer structure in which foils 21 and soft sheets 22 are alternately stacked, and the foil unit 20 shown in FIG. 11 (c) includes the foil 21 and the soft sheets. A four-layer structure in which 22 and 22 are alternately stacked is formed. In any of the foil units 20 shown in FIG. 11, the most axial layer is the foil 21, and the bearing surface X is formed on the foil 21.

  Moreover, although the case where the bearing surface X was formed in the foil 21 was shown in said embodiment, you may form not only this but the bearing surface X in the soft sheet | seat 22. FIG. In particular, if the soft sheet 22 is formed of a material containing graphite as a main component, the graphite sheet is excellent in self-lubricating property, so that the sliding between the shaft 2 and the bearing surface X is performed without performing a separate low friction coating treatment. Resistance is reduced, and torque during low-speed rotation of the shaft is reduced. For example, in the foil unit 20 shown in FIGS. 12A to 12C, two to four layers of foils 21 and soft sheets 22 are alternately laminated, and the softest sheet 22 is formed on the most axial side layer. A bearing surface X is formed on 22.

  In the above embodiment, the soft layer (soft sheet 22) and the foil 21 are provided separately. However, as shown in FIG. 13, the soft layer and the foil 21 are arranged in the thickness direction of the foil 21. The composite foil 23 may be formed by being integrated in the stacked state. For example, in the foil bearing 1 shown in FIG. 1, the composite foil 23 may be configured by attaching a soft sheet 22 to the back surface of the foil 21 (the surface opposite to the bearing surface X) by bonding or the like.

  At this time, since the materials of the foil 21 and the flexible sheet 22 are different, the linear expansion coefficients are different. Due to the difference in the linear expansion coefficient, the composite foil 23 in which the foil 21 and the soft sheet 22 are bonded is curved at a high temperature. Specifically, for example, the metal foil 21 has a larger coefficient of linear expansion than the soft sheet 22 mainly composed of graphite. Therefore, at high temperatures, the foil 21 is curved so that the foil 21 is convex as shown in FIG. . Utilizing this property, for example, if the bearing surface X is formed on the foil 21 of the composite foil 23, the bearing surface X becomes convex at a high temperature, so that a wedge space is easily formed and the bearing rigidity is increased. On the other hand, if the bearing surface X is formed on the soft sheet 22 of the composite foil 23, the bearing surface X becomes concave at a high temperature, so that it becomes difficult to form a wedge space and the bearing rigidity is lowered. Thus, by using the composite foil 23, it becomes possible to control the bearing rigidity at high temperatures.

  Moreover, when forming the composite foil 23, the deformation | transformation of the bearing surface X is controllable by devising the shape and position of a soft layer. For example, in the embodiment shown in FIG. 15, a soft sheet 22 having a notch 22 a is attached to the back surface (surface opposite to the bearing surface X) of the top foil portion Tf of the foil 21. The notch 22a has the same shape as the notch 21c provided in the back foil Bf in FIG. On the other hand, the back foil portion Bf of the foil 21 has a rectangular shape having no notch.

  When this composite foil 23 is attached to the foil holder 10, as shown in FIG. 16, the soft sheet 22 of each composite foil 23 is placed on the rectangular back foil portion Bf of the other composite foil 23. . When the pressure of the air film in the bearing gap C is increased with the rotation of the shaft, the top foil portion Tf is pressed against the back foil portion Bf via the soft sheet 22 having the notch portion 22a. Thereby, since the herringbone-shaped level | step difference is formed in two places spaced apart to the axial direction among the top foil parts Tf, the effect similar to said embodiment can be acquired.

  In the composite foil 23 shown in FIG. 17, a soft sheet 22 having a notch 22 a is attached to the front side surface (the surface on the bearing surface X side) of the back foil portion Bf of the foil 21. When the pressure of the air film in the bearing gap C is increased with the rotation of the shaft, the top foil portion Tf is pressed against the soft sheet 22 as shown in FIG. Thereby, the herringbone-shaped level | step difference is formed in two places spaced apart to the axial direction among the top foil parts Tf, and the effect similar to said embodiment can be acquired.

  In the embodiment shown in FIG. 19, the soft layer S is provided only at the axial end portion (in the illustrated example, both axial ends) of the foil 21. Thereby, it is possible to prevent damage to the axial end portion of the foil 21 when vibration or conical motion occurs on the shaft with the minimum necessary soft layer S. In particular, in the top foil portion Tf of the foil 21, the region P adjacent to the upstream side of the convex portion 21 a inserted into the axial groove 10 b of the foil holder 10 is curved so as to be convex toward the inner diameter side and is axially Because it comes out, it is easy to come into contact with the shaft (see FIG. 9). Accordingly, among the axial end portions of the foil 21, the region P adjacent to the upstream side of the convex portion 21 a and including the apex of the convex curved portion on the inner diameter side, or the region Q overlapped with this region P in the thickness direction It is preferable to provide the soft layer S. In the illustrated example, the soft layer S is provided in both the regions P and Q of the foil 21, and in particular, the soft layer S is provided over the entire circumferential length at both axial ends of the foil 21. In addition, the soft layer S may be provided only on one of the top foil portion Tf or the back foil portion Bf.

  As described above, when the soft layer S is provided in a partial region of the foil 21, as shown in FIG. 20, the thin portion 21f is provided in a part of the foil 21, and the soft layer S is provided in the thin portion 21f. It is preferable to make the thickness of the entire composite foil 23 uniform. Thereby, even when the soft layer S is provided, the thickness of the foil unit 20 made of only the foil 21 is not changed, and the thickness can be easily managed.

  When the soft layer S is provided at the axial direction end portion of the foil 21 as described above, the overlapping portion of the foil unit 20 can be configured as shown in, for example, FIGS. In FIG. 21A, the soft layer S is provided only at the axial end of the front side surface (the bearing surface X side surface) of the back foil portion Bf. In FIG. 21B, the soft layer S is provided only at the axial end of the back surface (surface opposite to the bearing surface X) of the top foil portion Tf.

  In FIG.21 (c), the soft layer S is provided in the axial direction edge part of the surface of the front side of the back foil part Bf, and the axial direction edge part of the back surface of the top foil part Tf. In this case, since the thickness of the soft layer S is doubled as compared with FIGS. 21A and 21B, the deformation amount of the soft layer S is increased and the effect of reducing the contact surface pressure is enhanced.

  In FIG.21 (d), the soft layer S is provided only in the axial direction edge part of the surface (bearing surface X) of the front side of the top foil part Tf. In this case, the sliding resistance when the shaft 2 contacts can be reduced by forming the soft layer S with a material having high slidability (for example, a material mainly composed of graphite).

  In the above embodiment, a so-called multi-arc radial foil bearing has been exemplified as the foil bearing 1, but the form of the foil bearing to which the present invention is applicable is not limited thereto. For example, the present invention can be applied to a so-called leaf type foil bearing 1 shown in FIG. In the foil bearing 1, the foil unit 20 includes a plurality of foils 21 (leafs) having a downstream end as a free end and an upstream end as a fixed end. Of each foil 21, the downstream region functions as the top foil portion Tf, and the upstream region functions as the back foil portion Bf. In the leaf type foil bearing 1, the foil unit 20 has a soft layer, so that the same effect as described above can be obtained. In the illustrated example, a composite sheet 23 is configured by attaching a soft sheet 22 to the back (outer diameter side) of the top foil portion Tf of the foil 21. The foil 21 and the soft sheet 22 may be provided separately.

  The present invention can also be applied to the so-called bump type foil bearing 1 shown in FIG. In the foil bearing 1, the foil unit 20 has a corrugated foil 21 (back foil portion Bf) and a cylindrical foil 21 (top foil portion Tf) as separate bodies, and the top foil portion Tf and the foil holder 10. The back foil portion Bf is disposed between the two. In the bump type foil bearing 1, the foil unit 20 has a soft layer, so that the same effect as described above can be obtained. In the illustrated example, a soft sheet 22 having substantially the same shape as the top foil portion Tf is disposed between the top foil portion Tf and the back foil portion Bf. The top foil portion Tf and the soft sheet 22 may be provided separately, or may be bonded to each other to constitute the composite foil 23 (see FIG. 13). Further, instead of or in addition to the soft sheet 22 described above, the soft sheet 22 having substantially the same shape as that of the soft foil 22 may be placed on the back foil portion Bf.

  Furthermore, the present invention can be applied to a thrust foil bearing. FIG. 24 shows a leaf type thrust foil bearing as an example of the thrust foil bearing 3. As shown in FIG. 25, among the foils 21 constituting the foil unit 20, the downstream region functions as the top foil portion Tf, and the upstream region functions as the back foil portion Bf. When the shaft rotates in the R direction, a bearing gap C (thrust bearing gap) is formed between the thrust collar 2b provided on the shaft and the bearing surface X of the top foil portion Tf, and the pressure of the air film in the bearing gap C Thus, the shaft is supported in a non-contact manner in the thrust direction. In the thrust foil bearing 3, the foil unit 20 has a soft layer, so that the same effect as described above can be obtained. In the illustrated example, the soft sheet 22 is disposed between the top foil portion Tf and the back foil portion Bf. The top foil portion Tf and the soft sheet 22 may be provided separately, or may be bonded to each other to constitute the composite foil 23 (see FIG. 13).

  In the above description, the case where the shaft 2 is the rotation side member and the foil holder 10 is the fixed side member is illustrated, but conversely, the shaft 2 is the fixed side member and the foil holder 10 is the rotation side member. The present invention can also be applied to cases. However, in this case, since the foil unit 20 serves as a rotation side member, it is necessary to design the foil unit 20 in consideration of deformation of the entire foil unit 20 due to centrifugal force.

  Moreover, the foil bearing concerning this invention can be used as a foil bearing which supports the rotor of turbomachines including a gas turbine and a supercharger, for example. In addition, the foil bearing according to the present invention can be widely used as a bearing for vehicles such as automobiles, and further as a bearing for industrial equipment. Further, each foil bearing of the present embodiment is an air dynamic pressure bearing using air as a pressure generating fluid, but is not limited thereto, and other gases can be used as the pressure generating fluid, or water or oil It is also possible to use a liquid such as

1, 3 Foil bearing 2 Shaft 10 Foil holder 20 Foil unit 21 Foil 22 Soft sheet (soft layer)
23 Composite foil Tf Top foil part Bf Back foil part X Bearing surface W Superposition part C Bearing clearance

Claims (8)

In a foil bearing comprising a foil unit having a bearing surface facing a shaft to be supported, and supporting the shaft so as to be relatively rotatable by a fluid pressure generated in a bearing gap between the bearing surface and the shaft,
A foil bearing in which the foil unit includes a metal foil and a soft layer made of a material having a lower elastic modulus than the foil.   2. The foil bearing according to claim 1, wherein the soft layer is provided in a region including an end portion of the foil unit in a direction orthogonal to a rotation direction of the shaft. The foil unit includes a top foil portion having the bearing surface, and a back foil portion disposed behind the top foil portion,
The overlapping portions where the top foil portion and the back foil portion are overlapped in the thickness direction are provided at a plurality of locations separated in the circumferential direction,
The foil bearing of Claim 1 or 2 which provided the said soft layer in the said superposition | polymerization part.   The foil bearing according to any one of claims 1 to 3, wherein the soft layer is formed of a soft sheet made of a material having a lower elastic modulus than the foil.   The foil bearing according to any one of claims 1 to 3, wherein the foil unit includes a composite foil that integrally includes the soft layer and the foil.   The foil bearing according to claim 5, wherein a thickness of the composite foil is made uniform by providing a thin portion on the foil and providing the soft layer on the thin portion.   The foil bearing according to any one of claims 1 to 6, wherein the soft layer contains resin, rubber, or graphite as a main component. A composite foil used for foil bearings,
A composite foil integrally having a metal foil and a soft layer made of a material having a lower elastic modulus than the foil.

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