Pneumatic bearing

Abstract

To make a radial displaceable amount of a rotor as small as possible without using a bump foil curve-molded in a wave-shape, in a pneumatic bearing of a radial foil bearing type.SOLUTION: A bearing 1 supporting a rotor in a non-contact manner includes: a housing 2 defining a cylindrical inner surface 2a; a top foil 5 uniformly curved and fixed to surround a rotor 4 rotating inside the cylindrical inner surface; and plural interposition foils 6_1 to 6_3 uniformly curved and laminated in a peripheral direction of the cylindrical inner surface between the cylindrical inner surface of the housing and the outer peripheral surface of the top foil, and fixed to the cylindrical inner surface. Each of the interposition foils has a portion d cut-out at a pattern, the patterns of the portions being different from each other. In each region in a face direction of the interposition foil, a cut-out portion exists on at least one layer in the lamination direction of the interposition foil.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an air bearing in the form of a radial bearing, and more particularly to a foil bearing in which a foil surrounds a rotating shaft.

Background Art

[0002] An air bearing in the form of a radial bearing, in which a foil surrounds a rotating shaft, is used as a bearing for rotatably supporting a shaft-shaped rotating body of various rotating machines such as a turbocharger, a gas turbine, and an air compressor. In the structure of such an air bearing (radial foil bearing), typically, on the cylindrical inner surface of a housing through which a rotating body passes, bump foils formed in a wavy shape along the circumferential direction are mounted over the entire circumference, and a top foil formed by curving a flat foil so as to surround the entire circumference of the rotating body is disposed between the top foil and the inner rotating body. In operation, when the rotating body rotates, the pressure between the surface of the rotating body and the top foil increases (a gas film is formed), the rotating body floats up, and is rotatably supported in the radial direction in a non-contact manner with the top foil. On the other hand, the top foil expands in diameter in the radial direction and is elastically supported by contacting the bump foil at its outer circumference, and the gap (bearing gap) between the outer surface of the rotating body and the inner surface of the top foil is adjusted. As an example of an air bearing using such bump foils, for example, in Patent Document 1, while a second top foil is interposed between the top foil and the bump foil, the top foil is formed to be more flexible so that the top foil can easily expand in diameter even when the rotation of the rotating body is low, and the rotating body can easily float up. At high speeds of rotation, the top foil contacts the second top foil, and the rigidity of the top foil increases, thereby suppressing excessive expansion of the top foil. In Patent Document 2, a configuration in which two sets of bearings are arranged in the axial direction of the bearing and a key groove for holding a foil is formed on the inner side of the cylinder of the housing (journal sleeve) is proposed.

Prior Art Documents

Patent Document

[0003]

Patent Document 1

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an air bearing using a bump foil as described above, the bump foil is formed by evenly and alternately bending a thin metal plate into a wave shape. However, such bending processing is quite difficult, and in the completed bump foil, it is difficult to significantly suppress variations in radial elastic characteristics along the circumferential and axial directions. Further, during the operation of the bearing, the expanded top foil comes into contact with the bump foil and is elastically supported. The wave-shaped bump foil can be elastically expanded by a distance equal to twice the amplitude of the wave (the distance between the peak and the valley). Therefore, the amount of displaceable radial displacement of the rotating body is relatively large. When a structure such as a blade is attached outside the bearing of the rotating body, in order to prevent the radial tip of the structure from contacting the inner wall of the housing existing radially outward, the clearance (chip clearance) between the radial tip of the structure and the inner wall of the housing also needs to be set relatively large corresponding to the expandable amount of the bump foil. However, in that case, a decrease in the operating efficiency of the rotating machine may be caused. Therefore, from the viewpoint of the operating efficiency of the rotating machine, it is preferable to suppress the displaceable amount of the rotating body in the radial direction as small as possible in order to reduce the chip clearance.

[0005] In view of the above circumstances, the main problem of the present invention is to suppress the amount of displaceable radial displacement of the rotating body as small as possible without using a bump foil formed into a wave shape in an air bearing of the radial foil bearing type.

[0006] Regarding this point, the inventor of the present invention has found that a function similar to that of the bump foil formed into a wave shape can be achieved by a plurality of foils in which a thin flat plate is curved and laminated along the circumferential direction of the cylindrical inner surface of the housing, each foil being cut out in a different pattern from each other, and in each region of the foil, there is a cut-out portion in at least one layer in the lamination direction of the foil, and the amount of displacement in the radial direction of the rotating body can be made smaller than that of the bump foil formed into a wave shape. In the present invention, this finding is utilized.

Means for Solving the Problem

[0007] According to the present invention, the above problem is solved by a radial foil bearing that supports a rotating body in a non-contact manner, a housing that defines a cylindrical inner surface, a top foil disposed between the housing and the rotating body that rotates inside the cylindrical inner surface thereof, uniformly curved along the circumferential direction of the cylindrical inner surface of the housing so as to surround the rotating body, and one end in the circumferential direction thereof being fixed to the cylindrical inner surface of the housing, a plurality of intervening foils disposed between the cylindrical inner surface of the housing and the outer peripheral surface of the top foil, uniformly curved and laminated along the circumferential direction of the cylindrical inner surface of the housing, one end in the circumferential direction thereof being fixed to the cylindrical inner surface of the housing, each of the intervening foils having a cut-out portion in a different pattern from each other, and in each region in the plane direction of the intervening foil, there being a cut-out portion in at least one layer in the lamination direction of the intervening foil, and including when the rotating body rotates, the outer surface of the top foil expands in diameter and contacts the inner surface of the intervening foil, and the rotating body is supported in a non-contact manner in the radial direction inside the top foil by the bearing.

[0008] In the above configuration, the "rotating body" may be, as already mentioned, the shaft-like rotating body of various rotating machines such as turbochargers, gas turbines, and air compressors, and a structure such as blades extending radially outside the bearing may be formed. The "radial foil bearing" is a type of radial bearing. A top foil formed by uniformly curving a flat thin plate is arranged between the outer surface of the rotating body and the cylindrical inner surface of the housing on the outer periphery of the bearing, with an appropriate gap left between the rotating body. When the rotating body rotates, pressure is generated between the outer surface of the rotating body and the inner surface of the top foil due to the wedge effect. As the top foil expands in diameter, the rotating body floats inside the top foil and is supported in a non-contact manner by an air bearing. The "housing" is a part that serves as a base for rotatably supporting the rotating body in a rotating machine and defines a cylindrical inner surface that serves as a bearing surface for receiving the rotating body rotatably as described above. The "top foil" may be a foil formed by uniformly curving a flat thin plate that is usually used in a radial foil bearing. The plurality of laminated "interposed foils" are provided outside the top foil on the cylindrical inner surface of the housing as described above and are provided in place of the conventional bump foils. Each of the interposed foils is, like the top foil, a foil formed by uniformly curving a flat thin plate, but as described above, has portions cut out in different patterns from each other. In the state where the interposed foils are laminated, in each region in the plane direction of the interposed foils, a portion cut out in at least one layer in the lamination direction of the interposed foils is configured to exist.

[0009] According to the above configuration, when the rotating body rotates inside the top foil, an air film with increased pressure due to the wedge effect is formed between the outer surface of the rotating body and the inner surface of the top foil, similar to the case of a conventional air bearing. As the top foil expands in diameter, the rotating body floats. When the top foil contacts the intervening foil, the intervening foil is laminated such that there is a cut-out portion in at least one of the laminated foils in all regions thereof. Thus, in the cut-out portion, the top foil or the laminated intervening foil elastically displaces in the radial direction, performing the same function as the (conventional) bump foil that elastically supports the top foil. In the case of the laminated intervening foil in the present invention, it is only necessary to perform partial cutting on each intervening foil, and unlike the conventional bump foil, corrugated bending processing is not required. Therefore, the processing of each intervening foil is significantly easier than that of the conventional bump foil. Also, in the intervening foil according to the present invention, the amount of displaceability in the radial direction during rotation of the rotating body is equal to the thickness of the intervening foil with the cut-out portion formed, and is considerably smaller than twice the amplitude of the wave of the conventional bump foil. Thus, it is also advantageous in that the amount of displaceability of the rotating body in the radial direction can be suppressed to be as small as possible.

[0010] In the configuration of the bearing of the present invention described above, the number of laminated intervening foils is preferably 3 or more in order to ensure sufficient strength of the intervening foil (however, the number of layers may be selected so as not to be excessive so as not to increase the weight of the bearing).

[0011] When the bearing of the present invention rotates the rotating body, when the outer surface of the top foil expands in diameter and contacts the inner surface of the intervening foil, in the top foil, the portion corresponding to the region where the cut-out portion of the innermost foil of the intervening foil exists protrudes locally radially outward more than the other portions, that is, a recess is formed radially outward in the top foil. (That is, the top foil is formed to have flexibility such that such a recess is formed.) When a partial recess is formed in the top foil facing the rotating body, it is advantageous in that the rotating body easily floats from the top foil.

Advantages of the Invention

[0012] Thus, according to the present invention described above, instead of the conventional corrugated bump foil, as described above, by using an intervening foil which is a plurality of laminated foils and has a cut-out portion in at least one layer in the lamination direction over its entire area, elastic support of the top foil similar to that of the bump foil can be achieved without the need for the troublesome process of curving a flat thin plate into a corrugated shape. Further, since the displaceable amount of the intervening foil is an amount corresponding to the thickness of the cut-out foil, it can be suppressed to be significantly smaller than that of the conventional corrugated bump foil. Thereby, when a structure such as a blade is attached outside the bearing of the rotating body, it becomes possible to make the chip clearance smaller, and an improvement in the operating efficiency of the rotating machine is expected. The configuration of the present invention may be applied to a radial foil bearing used for supporting a rotating body such as a rotating shaft of various rotating machines such as a motor - generator, a gas turbine, a turbocharger, and an air compressor.

[0013] Other objects and advantages of the present invention will become apparent from the following description of the preferred embodiments of the present invention.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Description of Reference Numerals

[0015] 1... bearing, 2... housing, 2a... inner surface of housing, 2b... foil fixing portion, 3... inner space of housing, 4... rotating body, 5... top foil, 6_1, 6_2, 6_3... interposed foils, d... cut-out portion

Best Mode for Carrying Out the Invention

[0016] Structure of the bearing The air bearing according to this embodiment is used as a foil bearing in the form of a radial bearing for supporting a rotating body such as a rotating shaft of various rotating machines such as a turbocharger, an air compressor, and a gas turbine engine. As schematically depicted in FIG. 1, in the air bearing 1, a housing 2 fixed to a non-rotating portion of the rotating machine, similar to a conventional radial foil bearing, has a cylindrical inner surface 2a defining an inner space 3 through which the rotating body 4 is inserted, and a foil fixing portion 2b for fixing one end of a plurality of foils 5 to 6_3 curved along the inner side thereof. Immediately outside the rotating body 4, a top foil 5 formed by uniformly curving a flat thin plate into a cylindrical shape is disposed. And in the case of the air bearing 1 of this embodiment, instead of the bump foil formed in a wave shape in a conventional similar air bearing, between the top foil 5 and the housing inner surface 2a, as shown decomposed in FIGS. 2(A) and (B), there are a plurality of laminated foils formed by uniformly curving a flat thin plate into a cylindrical shape, and foils (interposed foils) 6_1 to 6_3 having regions cut out in different patterns are disposed.

[0017] More specifically, in the bearing 1 of the present embodiment, in the intermediate foils 6_1, 6_2, 6_3 wound around the outside of the top foil 5, as can be understood from FIG. 3(A), regions (cut-out portions) d_6_1, d_6_2, d_6_3 each cut out in a different pattern are formed. When the intermediate foils 6_1, 6_2, 6_3 are laminated, the cut-out portions are formed such that in all regions of the intermediate foils, there is at least one layer with a foil and at least one layer with a cut-out portion (d_6_1, d_6_2, d_6_3). For example, FIG. 3(B) shows the regions where the cut-out portions d_6_1, d_6_2, d_6_3 of each layer exist in a state where the intermediate foils 6_1, 6_2, 6_3 of FIG. 3(A) are laminated. It will be understood that anywhere in the entire area of the intermediate foils, one of the cut-out portions d_6_1, d_6_2, d_6_3 exists. Also, referring to FIG. 3(C), it is understood that in the entire circumference of the laminated intermediate foils, there is at least one layer with a foil and at least one layer with a cut-out portion d. Note that it is preferable that the pattern of the cut-out portions is formed such that the number of layers of the cut-out portions d matches so that the rigidity in the lamination direction is substantially uniform over the entire area of the laminated intermediate foils (in that case, the number of layers with a foil also matches over the entire area of the intermediate foils).

[0018] In the above configuration, the top foil and the intermediate foils may be formed from flat thin plates (with a thickness of 0.1 mm or less) of materials (such as metals, alloys, etc.) commonly used in foil bearings. In this regard, in the present embodiment, each of the intermediate foils only needs to be cut out from a flat thin plate in the above-described pattern and uniformly curved into a cylindrical shape, which is advantageous in that the forming process is significantly simpler than the case of curving a flat thin plate into small waves like a conventional bump foil.

[0019] In the above configuration, as long as the pattern of the cut-out portion is such that the foil exists in at least one layer and the cut-out portion exists in at least one layer in all regions of the interposed foil, it may be a pattern different from FIGS. 2 and 3. For example, as illustrated in FIG. 4, it may be an interposed foil in which a cut-out portion is formed. Also, the number of foils laminated in the interposed foil may be any number as long as it is plural. (However, if the number of layers is small, the strength decreases, and if the number of layers increases, the weight also increases. Therefore, an appropriate number of layers may be selected in consideration of strength and weight. Typically, it may be three layers.)

[0020] Operation of the bearing In the bearing of the above-described embodiment, basically, the interposed foil functions to contact the top foil during the rotation of the rotating body and elastically support it, similar to the bump foil in an air bearing using a conventional bump foil. More specifically, due to the wedge effect caused by the rotation of the rotating body, when the top foil expands in diameter and presses against the interposed foil, the adjacent interposed foil in each region of the interposed foil where the cut-out portion is formed elastically displaces. As a result, similar to the bump foil, it serves as a cushion for the top foil, and the bearing clearance between the inner surface of the top foil and the outer surface of the rotating body is appropriately adjusted. In this regard, as described in the "Summary of the Invention" section, while the displaceable amount of the conventional bump foil is twice the amplitude of its wave, the displaceable amount of the interposed foil in this embodiment is equal to the number of layers of the foil in which the cut-out portion exists. Therefore, the displaceable amount of the top foil and the displaceable amount in the radial direction of the rotating body can be suppressed to be smaller than when using the conventional bump foil.

[0021] According to computational experiments, when the thickness of the top foil is set to an appropriate practical value in the bearing, when the top foil expands in diameter due to the wedge effect and contacts the intermediate foil, in the top foil, a region where the portion contacting the cutout portion of the innermost layer of the intermediate foil protrudes radially outward more than other portions (a dent when viewed from the inside of the top foil) is formed. Due to the formation of such a "dent" in the top foil, the rotating body can float more quickly and advantageously from the top foil during rotation.

[0022] In the case of the bearing of the present embodiment as described above, since the displaceable amount in the radial direction of the rotating body during rotation can be suppressed to be smaller, the tip clearance of the tip of a structure such as a blade formed outside the bearing of the rotating body can also be made smaller, and thus it is also advantageous in that the operating efficiency of the rotating machine can be improved.

[0023] The above description has been made in relation to the embodiments of the present invention, but many modifications and changes are easily possible for those skilled in the art, and the present invention is not limited to only the embodiments illustrated above, and it will be apparent that the present invention can be applied to various devices without departing from the concept of the present invention.

Claims

1. A radial foil bearing for non - contact support of a rotating body, comprising: a housing having a cylindrical inner surface; a top foil disposed between the housing and the rotating body that rotates inside the cylindrical inner surface of the housing, uniformly curved along the circumferential direction of the cylindrical inner surface of the housing so as to surround the rotating body, and one end in the circumferential direction thereof being fixed to the cylindrical inner surface of the housing; a plurality of intermediate foils disposed between the cylindrical inner surface of the housing and the outer peripheral surface of the top foil, uniformly curved and laminated along the circumferential direction of the cylindrical inner surface of the housing, and one end in their circumferential direction being fixed to the cylindrical inner surface of the housing, each of the intermediate foils having portions cut out in different patterns, and in each region in the plane direction of the intermediate foils, there being portions cut out in at least one layer in the lamination direction of the intermediate foils; and when the rotating body rotates, the outer surface of the top foil expands in diameter and contacts the inner surface of the intermediate foils, and the rotating body is supported radially in a non - contact manner inside the top foil.

2. The bearing according to Claim 1, wherein in the plurality of intermediate foils, three or more layers of the intermediate foils are laminated.

3. The bearing according to Claim 1, wherein when the rotating body rotates and the outer surface of the top foil expands in diameter and contacts the inner surface of the intermediate foils, in the top foil, the portion facing the region where the cut - out portion of the innermost foil among the intermediate foils exists protrudes locally radially outward more than the other portions.

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