Foil bearing device

Abstract

This foil bearing device for rotatably supporting a rotating shaft is provided with: an annular member having an insertion hole through which the rotating shaft is inserted; a top foil having an arc-shaped cross-section and disposed between the inner peripheral surface of the annular member and the outer peripheral surface of the rotating shaft so as to surround the entire outer periphery of the rotating shaft; and a bump foil that supports the top foil from the outer peripheral side of the top foil and that is supported on the inner peripheral surface of the annular member, and that, in a cross-section orthogonal to the center line of the top foil, causes the angle position of an imaginary line extending upward in the direction of gravity from the center line of the top foil to be 0 degree. The angle position of the imaginary line, which increases as the imaginary line rotates in the rotation direction of the rotation shaft with the center line of the top foil as the rotation center, is defined as 360 degrees when the imaginary line rotates one circle. The top foil includes a first region in which at least one through hole penetrating through the top foil is formed at an angular position of 240 degrees or more and less than 360 degrees, and a second region in which no through hole penetrating through the top foil is formed at an angular position of 0 degrees or more and less than 240 degrees.

Description

Technical Field

[0001] The present invention relates to a foil bearing device for rotatably supporting a rotating shaft. Background Art

[0002] Foil bearings consist of a top foil that forms a bearing surface for the rotating shaft of a turbo blower or turbo compressor, and a corrugated foil that elastically supports the top foil. As the shaft rotates, a fluid film (air film) forms between the top foil's bearing surface and the shaft, rotatably supporting the shaft via this air film. This type of foil bearing automatically forms an appropriate air film based on the shaft's rotational speed, making it particularly effective for high-speed rotating shafts.

[0003] To stably support the rotating shaft using an air film, it is necessary to maintain the pressure of the air film appropriately. For example, Patent Document 1 discloses a foil bearing device that includes a communicating hole formed in a top foil and a valve that opens and closes the communicating hole according to the pressure (dynamic pressure) of the air film.

[0004] Previous technical literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-046913 Summary of the Invention

[0007] Technical issues to be solved by the invention

[0008] The air film includes a region (referred to as a reduced pressure region) that expands as it moves downstream in the rotational direction of the rotating shaft. In the reduced pressure region, the air film pressure becomes negative, which acts as an excitation force for the rotating shaft to vibrate, potentially reducing the vibration stability of the rotating shaft. However, Patent Document 1 discloses a technique in which a valve is opened to release the dynamic pressure to the outer circumference of the top foil when the dynamic pressure of the air film increases in regions other than the reduced pressure region. However, this technique does not address the issue of negative pressure generated in the reduced pressure region.

[0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a foil bearing device capable of improving the vibration stability of a rotating shaft.

[0010] Means for solving technical problems

[0011] In order to achieve the above-mentioned object, the foil bearing device involved in the present invention is a foil bearing device for rotatably supporting a rotating shaft, which comprises: an annular member having an insertion hole for inserting the rotating shaft; a top foil with an arc-shaped cross section, arranged to surround the entire outer circumference of the rotating shaft between the inner circumferential surface of the annular member and the outer circumferential surface of the rotating shaft; and a corrugated foil, which supports the top foil from the outer circumferential side of the top foil and is supported on the inner circumferential surface of the annular member, and on a cross section perpendicular to the center line of the top foil, if a direction is taken from the center line of the top foil to the direction of gravity, the top foil is The angular position of an imaginary line extending upward from the top foil is set to 0 degrees, and the angular position when the imaginary line rotates one circle, which increases as the imaginary line rotates around the center line of the top foil in the rotation direction of the rotation axis, is defined as 360 degrees. The top foil includes a first region in which the angular position of at least one through hole penetrating the top foil is greater than or equal to 240 degrees and less than 360 degrees, and a second region in which the angular position of no through hole penetrating the top foil is greater than or equal to 0 degrees and less than 240 degrees.

[0012] Effects of the Invention

[0013] According to the foil bearing device of the present invention, the vibration stability of the rotating shaft can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 The diagram schematically shows the structure of an electric compressor including foil bearing devices according to several embodiments.

[0015] Figure 2 This is a cross-sectional view schematically showing the structure of a foil bearing device according to one embodiment.

[0016] Figure 3 This is a development view showing the inner peripheral surface of the top foil according to one embodiment.

[0017] Figure 4 Yes Figure 2 FIG. 1 is a diagram showing an example of a state in which the rotating shaft is rotating.

[0018] Figure 5 Is to express Figure 4 A graph showing the relationship between the corresponding angular position and the pressure of the air film.

[0019] Figure 6 This is a developed view showing the inner peripheral surface of a top foil according to another embodiment.

[0020] Figure 7 This is a development view showing the inner peripheral surface of a top foil according to still another embodiment in a developed state.

[0021] Figure 8This is a diagram schematically showing the structure of a top foil according to still another embodiment. DETAILED DESCRIPTION

[0022] Hereinafter, a foil bearing device according to an embodiment of the present invention will be described with reference to the accompanying drawings. The above embodiment shows one aspect of the present invention and does not limit the present invention, and any changes can be made within the scope of the technical concept of the present invention.

[0023] Figure 1 1 is a diagram schematically showing the structure of an electric compressor 100 including a foil bearing device 1 according to several embodiments. Figure 1 As shown, the electric compressor 100 includes a rotating shaft 102 , an electric motor 104 that rotates the rotating shaft 102 , an impeller 106 that compresses a fluid by rotating integrally with the rotating shaft 102 , a housing 108 that accommodates the electric motor 104 and the impeller 106 , and the foil bearing device 1 .

[0024] The foil bearing device 1 rotatably supports a rotating shaft 102. The foil bearing device 1 supports the rotating shaft 102 in contact with the rotating shaft 102 until the rotational speed of the rotating shaft 102 reaches a floating speed at which the rotating shaft 102 floats. Once the rotational speed of the rotating shaft 102 reaches the floating speed, the foil bearing device 1 supports the rotating shaft 102 in a non-contact state via a fluid film (hereinafter referred to as an air film A) formed between the inner circumferential surface 5 (bearing surface) of the top foil 4 and the outer circumferential surface 110 of the rotating shaft 102.

[0025] While the present invention illustrates an example where the foil bearing device 1 is applied to an electric compressor 100, the device to which the foil bearing device 1 is applied is not limited to the electric compressor 100. The foil bearing device 1 according to the present invention is applicable to a rotating device including a rotating shaft 102, and is particularly applicable to a rotating device including a rotating shaft 102 capable of high-speed rotation. For example, the rotating device includes a turbocharger or a turbo blower.

[0026] <Foil bearing device>

[0027] (structure)

[0028] The structure of a foil bearing device 1 according to one embodiment will be described. Figure 2 This is a cross-sectional view schematically showing the structure of a foil bearing device 1 according to one embodiment, and the foil bearing device 1 is observed after being cut along a direction perpendicular to the axial direction of the rotating shaft 102 (hereinafter referred to as the axial direction D1). Figure 2 As shown in the example, the foil bearing device 1 includes an annular member 2 , a top foil 4 , and a bump foil 6 .

[0029] The annular member 2 has an insertion hole 3 through which the rotating shaft 102 is inserted. In one embodiment, the annular member 2 has a cylindrical shape, and the inner diameter of the annular member 2 is larger than the outer diameter of the rotating shaft 102. In some embodiments, the housing 108 of the electric compressor 100 includes the annular member 2. In this case, the annular member 2 is a part of the housing 108.

[0030] The top foil 4 has an arc shape and is arranged between the inner peripheral surface 7 of the annular member 2 and the outer peripheral surface 110 of the rotating shaft 102 so as to surround the entire outer periphery of the rotating shaft 102. The top foil 4 is formed by bending a flexible metal plate made of stainless steel into a cylindrical shape, for example. Figure 2 In the illustrated embodiment, one end portion 10 of the top foil 4 in the circumferential direction D2 (hereinafter referred to as "circumferential direction D2") is bent outward in the radial direction D3 (hereinafter referred to as "radial direction D3") of the top foil 4. The top foil 4 is arranged inside the annular member 2 in a state where the one end portion 10 in the circumferential direction D2 is held by the annular member 2. The other end portion 12 of the top foil 4 in the circumferential direction D2 is slightly separated from the one end portion 10 in the circumferential direction D2. Figure 2 In the illustrated embodiment, the top foil 4 is formed from a single metal sheet. This eliminates the outflow of the air film A to the outside of the top foil 4 from any portion other than the through-holes 8 described below, thereby facilitating the achievement of the functions and effects described below. However, the present invention is not limited to this embodiment. Although not illustrated, in some embodiments, the foil bearing device 1 includes a plurality of separate top foils 4 arranged continuously along the circumferential direction D2.

[0031] In the present invention, the circumferential direction D2 is the circumferential direction centered on the center line O1 of the top foil 4. Figure 2 On the paper, the direction from the other end 12 of the top foil 4 toward the one end 10 (in the counterclockwise direction) is defined as one side in the circumferential direction D2, and the direction from the one end 10 of the top foil 4 toward the other end 12 (in the clockwise direction) is defined as the other side in the circumferential direction D2. The radial direction D3 is a direction perpendicular to the centerline O1. The direction closer to the centerline O1 is defined as the inner side in the radial direction D3, and the direction farther from the centerline O1 is defined as the outer side in the radial direction D3.

[0032] The bump foil 6 has an arc shape and is arranged to surround the entire outer circumference of the top foil 4. The bump foil 6 is supported by the inner circumferential surface 7 of the annular member 2. The bump foil 6 is formed by bending a flexible metal plate made of stainless steel into a cylindrical shape. Figure 2 In the illustrated embodiment, the bump foil 6 extends throughout the entire circumferential direction D2 and contacts the inner circumferential surface 7 of the annular member 2. The bump foil 6 is configured to pass through one end 10 of the top foil 4. Although not shown, in some embodiments, the foil bearing device 1 includes a plurality of separate bump foils 6 arranged continuously along the circumferential direction D2.

[0033] The bump foil 6 includes multiple undulations 14 that protrude toward the top foil 4 and at least partially abut against the top foil 4. Each of the undulations 14 protrudes in a direction away from the inner circumferential surface 7 of the annular member 2 (i.e., inward in radial direction D3) and is curved in an arc shape. The tops of the undulations 14 abut against the top foil 4. The undulations 14 are spaced apart along the circumferential direction D2, giving the bump foil 6 a wavy shape. This bump foil 6 elastically supports the top foil 4.

[0034] like Figure 2 As shown, when observing a cross section of the foil bearing device 1 cut along a direction perpendicular to the axial direction D1 of the rotating shaft 102, the angular position θ of an imaginary line L extending upward in the gravity direction D4 from the center line O1 of the top foil 4 is defined as 0 degrees. This angular position θ increases as the imaginary line L rotates toward the other side (counterclockwise) in the circumferential direction D2, which is the rotation direction of the rotating shaft 102, with the center line O1 of the top foil 4 as the rotation center. The angular position θ when the imaginary line L rotates once is defined as 360 degrees. Figure 2 In the illustrated embodiment, the other end portion 12 of the top foil 4 is located at an angular position θ that is greater than or equal to 350 degrees and less than 360 degrees.

[0035] Figure 3 FIG. 1 is a development view showing the inner peripheral surface 5 of the top foil 4 according to one embodiment. Figure 3 As shown, the top foil 4 includes a first region R1 where the angular position θ is greater than or equal to 240 degrees and less than 360 degrees, and a second region R2 where the angular position θ is greater than or equal to 0 degrees and less than 240 degrees. Furthermore, the top foil 4 has a plurality of through-holes 8 formed therein that penetrate the top foil 4 in the first region R1. On the other hand, the top foil 4 has no through-holes 8 formed therein in the second region R2.

[0036] exist Figure 3 In the illustrated embodiment, the plurality of through holes 8 include a first through hole 8A (8) and a second through hole 8B (8) having an angular position θ different from that of the first through hole 8A in the first region R1. In other words, the first through hole 8A and the second through hole 8B are respectively arranged along the circumferential direction D2. The first through hole 8A and the second through hole 8B overlap each other at least partially in the axial direction D1. The plurality of through holes 8 also include a third through hole 8C (8) arranged on the side opposite to the first through hole 8A across the second through hole 8B in the circumferential direction D2. The first through hole 8A, the second through hole 8B, and the third through hole 8C each have a circular shape with the same diameter.

[0037] exist Figure 3In the illustrated embodiment, the plurality of through holes 8 include a first through hole 8A and a first axial through hole 8D (8) arranged along the axial direction D1 in the first region R1. The first through hole 8A and the first axial through hole 8D overlap each other at least partially in the circumferential direction D2. The plurality of through holes 8 also include a second axial through hole 8E (8) arranged on the opposite side of the first through hole 8A across the first axial through hole 8D in the axial direction D1. The first through hole 8A, the first axial through hole 8D, and the second axial through hole 8E each have a circular shape with the same diameter.

[0038] (Function and Effect)

[0039] The operation and effects of the foil bearing device 1 according to one embodiment will be described. Figure 4 Yes Figure 2 The diagram shows an example of a state in which the rotating shaft 102 is rotating. The rotating shaft 102 rotates at a rotation speed that is higher than the floating rotation speed.

[0040] like Figure 4 As shown, the foil bearing device 1 supports the rotating shaft 102 in a non-contact state via the air film A. The rotating shaft 102 is about to fall due to its own weight. The rotating shaft 102 rotates and approaches the portion of the inner circumference 5 of the top foil 4 where the angular position θ is greater than 180 degrees. That is, Figure 4 On the paper, the rotation axis 102 moves to the right by the rotation. Figure 4 In the illustrated case, the air film A is thinnest at the angular position θ of 210 degrees. Furthermore, the air film A becomes thinner as the angular position θ moves from 0 degrees to 210 degrees, and becomes thicker as the angular position θ moves from 210 degrees to 360 degrees (the thickness of the air film A increases).

[0041] Figure 5 Is to express Figure 4 The graph of the relationship between the corresponding angular position θ and the pressure of the air film A. Figure 5 In FIG. 1 , the horizontal axis represents the angular position θ, and the vertical axis represents the pressure of the air film A. Figure 5 The pressure of the air film A in the air film is expressed as a gauge pressure. When the pressure of the air film A is the same as the pressure (atmospheric pressure) around the air film A, it becomes 0 Pa. Furthermore, a pressure less than 0 Pa is considered a negative pressure, and a pressure greater than 0 Pa is considered a positive pressure. Figure 5 In FIG. 1 , the pressure of the air film A when supporting the rotating shaft 102 in the foil bearing device 1 according to one embodiment is represented by a solid line as P1. Furthermore, the pressure of the air film A when the plurality of through-holes 8 are not formed in the first region R1 of the top foil 4 (comparative example) is represented by a dotted line as P2.

[0042] like Figure 4As shown, when the rotating shaft 102 is rotating, in the first region R1 where the angular position θ is greater than or equal to 240 degrees and less than 360 degrees, the air film A becomes thinner as the angular position θ increases, and the pressure of the air film A decreases. Figure 5 As shown, in the first region R1 , the pressure of the air film A may become negative. This negative pressure becomes an excitation force that vibrates the rotating shaft 102 , thereby reducing the vibration stability of the rotating shaft 102 .

[0043] According to one embodiment, the top foil 4 is formed with a plurality of through holes 8 in the first region R1. Therefore, even if the pressure of the air film A becomes negative, the air on the outer peripheral side of the top foil 4 can flow into the air film A through the plurality of through holes 8, thereby preventing the pressure of the air film A from becoming negative. Figure 5 As shown, the pressure of the air film A is prevented from becoming less than 0 Pa. Therefore, the excitation force is suppressed from increasing, and the vibration stability of the rotating shaft 102 can be improved.

[0044] If the through-holes 8 are formed throughout the entire circumference of the top foil 4, the pressure of the air film A supporting the rotating shaft 102 decreases, and the air film A becomes thinner, which may cause the rotating shaft 102 to contact the top foil 4. According to one embodiment, the top foil 4 does not have the through-holes 8 formed in the second region R2, thereby suppressing the reduction in the pressure of the air film A and suppressing the contact between the rotating shaft 102 and the top foil 4. In particular, if Figure 5 As shown, unlike the air film A in the first region R1, the air film A in the second region R2 often reaches a positive pressure of 0 Pa or higher. Therefore, there is no need for air to flow into the air film A in the second region R2 through the through-holes 8. In contrast, the top foil 4 does not have through-holes 8 formed in the second region R2, thereby preventing the air film A in the second region R2 from flowing out to the outer circumference of the top foil 4 through the through-holes 8. Consequently, the pressure of the air film A can be maintained at a high positive pressure sufficient to smoothly support the rotating shaft 102. More specifically, the pressure of the air film A at the angular position θ of 210 degrees is maintained at a high positive pressure, thereby stably supporting the rotating shaft 102.

[0045] like Figure 5 As shown, the pressure of the air film A varies depending on the angular position θ. According to one embodiment, the first through-hole 8A, the second through-hole 8B, and the third through-hole 8C are arranged in a manner corresponding to the angular position θ, thereby further improving the vibration stability of the rotating shaft 102. Furthermore, the diameters of the first through-hole 8A, the second through-hole 8B, and the third through-hole 8C may differ from each other and may have shapes other than circular, such as a rectangle.

[0046] The pressure of the air film A may vary depending on the axial direction D1. According to one embodiment, the first through-hole 8A, the first axial through-hole 8D, and the second axial through-hole 8E are arranged in a manner corresponding to the pressure of the air film A in the axial direction D1, thereby further improving the vibration stability of the rotating shaft 102. Furthermore, the first through-hole 8A, the first axial through-hole 8D, and the second axial through-hole 8E may have different diameters and may have shapes other than circular, such as rectangles.

[0047] In some embodiments, the foil bearing device 1 determines the shape or position of each of the plurality of through-holes 8 based on the weight of the rotating shaft 102 and the rated speed of the rotating shaft 102 (i.e., the magnitude of the negative pressure). In some embodiments, the foil bearing device 1 determines the density or number of the plurality of through-holes 8 based on the weight of the rotating shaft 102 and the rated speed of the rotating shaft 102.

[0048] In some embodiments, a plurality of through-holes 8 are formed in the portion of the top foil 4 where the angular position θ is greater than or equal to 240 degrees and less than or equal to 300 degrees in the first region R1. In this case, no through-holes 8 may be formed in the portion of the top foil 4 where the angular position θ is greater than or equal to 300 degrees and less than or equal to 360 degrees. With this configuration, when the top foil 4 is configured to close the gap between the one end portion 10 and the other end portion 12, the strength of each of the one end portion 10 and the other end portion 12 can be maintained.

[0049] In some embodiments, the plurality of through-holes 8 include large-diameter holes arranged along the axial direction D1 and small-diameter holes having a smaller diameter than the large-diameter holes. Furthermore, when the inner circumferential surface 5 of the top foil 4 is expanded and viewed, the distance from an imaginary straight line passing through the center of the top foil 4 in the axial direction D1 is shorter than that of the small-diameter holes. In the first region R1, the absolute value of the negative pressure of the air film A may increase toward the center in the axial direction D1. This configuration effectively suppresses or eliminates the negative pressure at the center of the air film A.

[0050] In one embodiment, a plurality of circular through-holes 8 are formed in the top foil 4 , but the present invention is not limited to this embodiment. Figure 6 This is a development view showing the inner peripheral surface 5 of the top foil 4 according to another embodiment in a developed state. Figure 7 This is a development view showing the inner peripheral surface 5 of the top foil 4 according to still another embodiment in a developed state. Figure 8 This is a diagram schematically showing the structure of a top foil 4 according to still another embodiment.

[0051] In another embodiment, Figure 6As shown in the example, one through-hole 8 is formed in the top foil 4. The through-hole 8 includes a slit 20 (8) having an axial cutout portion 22 and a pair of rotational cutout portions 24A and 24B.

[0052] The axial cutout portion 22 is cut into a straight line along the axial direction D1. The pair of rotational cutout portions 24A and 24B are cut into a straight line from the axial cutout portion 22 toward the upstream side in the rotational direction, that is, one side in the circumferential direction D2. Moreover, the pair of rotational cutout portions 24A and 24B are arranged one above the other along the axial direction D1. The pair of rotational cutout portions 24A and 24B overlap each other at least partially in the axial direction D1. The pair of rotational cutout portions 24A and 24B are opposed to each other. The slit 20 has a U-shape that protrudes toward the other side in the circumferential direction D2.

[0053] exist Figure 6 In the illustrated embodiment, one end 4a of the top foil 4 on one side in the axial direction D1 is defined as the 0% position relative to the length of the top foil 4 in the axial direction D1. Furthermore, the other end 4b is defined as the 100% position relative to the length of the top foil 4 in the axial direction D1, as the position increases from the one end 4a toward the other end 4b. One end 22a of the axial cutout 22 is located within a range greater than 0% and less than 10%, while the other end 22b is located within a range greater than 90% and less than 100%. One cutout 24A of the pair of rotational cutouts is cut from one end 22a of the axial cutout 22 toward one side in the circumferential direction D2. The other cutout 24B of the pair of rotational cutouts is cut from the other end 22b of the axial cutout 22 toward one side in the circumferential direction D2.

[0054] according to Figure 6 In the illustrated embodiment, by forming the U-shaped slits 20, when the pressure of the air film A becomes negative, the suction portion 4c of the top foil 4 surrounded by the slits 20 can be drawn toward the rotating shaft 102, thereby making the thickness of the air film A substantially uniform (a parallel gap can be formed). This suppresses the decrease in the pressure of the air film A caused by the air film A becoming thicker as the angular position θ increases, thereby preventing the pressure of the air film A from becoming negative.

[0055] according to Figure 6 In the illustrated embodiment, one end 22a of the slit 20 is located within a range greater than 0% and less than 10%, while the other end 22b is located within a range greater than 90% and less than 100%. Therefore, the suction portion 4c of the top foil 4 is ensured to be long along the axial direction D1, thereby preventing the pressure of the air film A from becoming negative over the entire or a large portion of the axial direction D1.

[0056] In addition, Figure 6In the illustrated embodiment, the slit 20 has a U-shape, but the present invention is not limited to this embodiment. The slit 20 may have any structure as long as it forms the suction portion 4c. For example, one of the pair of rotational cutouts, 24A, is cut from between one end 22a and the other end 22b of the axial cutout 22 toward one side in the circumferential direction D2.

[0057] Additionally, in another embodiment, Figure 7 As shown in the example, the through hole 8 includes a rectangular long hole 30 (8) extending long along the axial direction D1. The long hole 30 has one end 30a located within a range greater than 0% and less than 10% of the length of the top foil 4 in the axial direction D1, and the other end 30b located within a range greater than 90% and less than 100%. Figure 8 In the illustrated embodiment, the elongated hole 30 and the apex 15 of the undulation 14 overlap in the circumferential direction D2 (the rotational direction of the rotation shaft 102). The apex 15 of the undulation 14 overlaps with the center 31 of the elongated hole 30 in the circumferential direction D2. The length of the elongated hole 30 in the circumferential direction D2 is shorter than the length of the undulation 14.

[0058] according to Figure 7 and Figure 8 In the illustrated embodiments, even if the pressure of the air film A becomes negative, air can flow into the negatively pressured air film A through the elongated holes 30, thereby preventing the pressure of the air film A from becoming negative. Furthermore, when the pressure of the air film A becomes greater than the positive pressure, the elongated holes 30 are closed by the corrugated portion 14 to prevent the outflow of the air film A. Thus, the pressure of the air film A can be maintained at a pressure greater than the positive pressure.

[0059] according to Figure 7 In the illustrated embodiment, one end 30a of the slot 30 is within a range greater than 0% and less than 10%, while the other end 30b is within a range greater than 90% and less than 100%. This prevents the pressure of the air film A from becoming negative over the entire or most of the axial direction D1.

[0060] In the above-described embodiments, only the plurality of circular through-holes 8A to 8E ( Figure 3 The illustrated embodiment), the U-shaped slit 20 ( Figure 6 In some embodiments, at least two of the circular through-hole 8A, the slit 20, and the long hole 30 are formed in the top foil 4.

[0061] The contents described in each of the above embodiments can be understood, for example, as follows.

[0062] [1] A foil bearing device 1 according to the present invention is a foil bearing device that rotatably supports a rotating shaft 102 and includes:

[0063] The annular member 2 has an insertion hole 3 for the rotating shaft to be inserted through;

[0064] The top foil 4 having an arc-shaped cross section is arranged between the inner peripheral surface 7 of the annular member and the outer peripheral surface 110 of the rotating shaft so as to surround the entire outer periphery of the rotating shaft;

[0065] and

[0066] The bump foil 6 supports the top foil from the outer peripheral side of the top foil and is supported on the inner peripheral surface of the annular member.

[0067] When observing a cross section cut in a direction perpendicular to the axial direction D1 of the rotation shaft, if the angular position θ of an imaginary line L extending upward in the gravity direction D4 from the center line O1 of the top foil is set to 0 degrees, the angular position when the imaginary line rotates one circle about the center line of the top foil in the rotation direction of the rotation shaft is defined as 360 degrees.

[0068] The top foil includes a first region R1 where the angular position is greater than or equal to 240 degrees and less than 360 degrees and where at least one through hole 8 is formed therethrough, and a second region R2 where the angular position is greater than or equal to 0 degrees and less than 240 degrees and where no through hole is formed therethrough.

[0069] When the rotating shaft is rotating, in the first region where the angular position is greater than 240 degrees and less than 360 degrees, the gap between the top foil and the rotating shaft becomes larger as the angular position increases. Therefore, the pressure of the fluid film (air film) formed between the top foil and the rotating shaft decreases, and there is a possibility of negative pressure. Moreover, this negative pressure becomes an excitation force that causes the rotating shaft to vibrate, thereby reducing the vibration stability of the rotating shaft. According to the structure described in [1] above, the top foil is formed with a through hole in the first region. Therefore, even if the pressure of the fluid film becomes negative pressure, the fluid (air) located on the outer peripheral side of the top foil can flow into the fluid film through the through hole, thereby suppressing the pressure of the fluid film from becoming negative pressure. Therefore, the excitation force is suppressed from becoming larger, thereby improving the vibration stability of the rotating shaft.

[0070] Therefore, if through holes are formed throughout the entire circumference of the top foil, the pressure of the fluid film supporting the rotating shaft will decrease, making the fluid film thinner, which may cause the rotating shaft to contact the top foil. According to the structure described in [1] above, the top foil does not form through holes in the second region, thereby suppressing the pressure drop of the fluid film, thereby suppressing the contact between the rotating shaft and the top foil. In particular, the fluid film in the second region is different from the fluid film in the first region and is mostly positive pressure. Therefore, there is no need to allow the fluid to flow into the fluid film in the second region through the through holes. In contrast, no through holes are formed in the second region of the top foil, thereby preventing the fluid film in the second region from flowing out to the outer peripheral side of the top foil through the through holes. Therefore, it is possible to ensure the pressure of the fluid film that can smoothly support the rotating shaft.

[0071] [2] In some embodiments, in the structure described in [1] above,

[0072] The at least one through hole includes a plurality of through holes 8A, 8D, and 8E arranged along the axial direction of the rotation shaft in the first region.

[0073] The pressure of the fluid film sometimes varies depending on the axial direction. According to the structure described in [2] above, the plurality of through holes are arranged in a manner corresponding to the magnitude of the pressure of the fluid film in the axial direction, thereby further improving the vibration stability of the rotating shaft.

[0074] [3] In some embodiments, in the structure described in [1] or [2] above,

[0075] The at least one through-hole includes a first through-hole 8A and a second through-hole 8B having an angular position different from that of the first through-hole in the first region.

[0076] The pressure of the fluid film becomes different in magnitude depending on the angular position. According to the structure described in [3] above, the first through hole and the second through hole are arranged in a manner corresponding to the angular position, thereby further improving the vibration stability of the rotating shaft.

[0077] [4] In some embodiments, in the structure described in any one of [1] to [3] above,

[0078] The at least one through hole includes a slit 20 having an axial cutout portion 22 cut out along the axial direction of the rotating shaft and a pair of rotational cutout portions 24A and 24B cut from the axial cutout portion toward the upstream side in the rotational direction and arranged along the axial direction.

[0079] According to the structure described in [4] above, when the pressure of the fluid film becomes negative, the portion of the top foil surrounded by the slit is sucked toward the rotating shaft, thereby making the size of the gap between the portion of the top foil and the rotating shaft uniform or approximately uniform. Therefore, the decrease in the pressure of the fluid film caused by the increase in the gap as the angular position increases is suppressed, and the pressure of the fluid film can be prevented from becoming negative.

[0080] [5] In some embodiments, in the structure described in [4] above,

[0081] If one end 4a of the top foil in the axial direction is defined as a position at 0% of the length of the top foil in the axial direction, and the other end is defined as a position at 100% of the length of the top foil in the axial direction as the position increases from the one end toward the other end 4b of the top foil,

[0082] Then one end 22a of the axial cutout portion is located in a range greater than 0% and less than 10%, and the other end 22b is located in a range greater than 90% and less than 100%.

[0083] One of the pair of rotation direction cutouts 24A is cut from the one end of the axial direction cutout toward the upstream side in the rotation direction.

[0084] The other cutout portion 24B of the pair of rotational direction cutout portions is cut out from the other end of the axial direction cutout portion toward the upstream side in the rotational direction.

[0085] According to the structure described in [5] above, it is possible to suppress the pressure of the fluid film from becoming negative pressure over the entire or most part of the axial direction.

[0086] [6] In some embodiments, in the structure described in any one of [1] to [5] above,

[0087] The corrugated foil comprises a corrugated portion 14 protruding toward the top foil.

[0088] The at least one through hole and the apex 15 of the wave portion overlap with each other in the rotation direction of the rotation axis.

[0089] According to the structure described in [6] above, even if the pressure of the fluid film becomes negative, the fluid (air) can flow into the negative pressure fluid film through the through hole, thereby preventing the pressure of the fluid film from becoming negative. Moreover, when the pressure of the fluid film becomes greater than the positive pressure, the through hole is closed by the wave portion, thereby ensuring that the pressure of the fluid film is greater than the positive pressure.

[0090] Explanation of symbols

[0091] 1- foil bearing device, 2- annular member, 3- insertion hole, 4- top foil, 4a- one end of the top foil, 4b- the other end of the top foil, 5- inner circumferential surface of the top foil, 6- corrugated foil, 7- inner circumferential surface of the annular member, 8- through hole, 8A- first through hole, 8B- second through hole, 14- corrugated portion, 15- apex, 20- slit, 22- axial cutout portion, 22a- one end of the axial cutout portion, 22b- the other end of the axial cutout portion, 24A- One of the notch portions in the pair of rotating direction notch portions, 24B-the other notch portion in a pair of rotating direction notch portions, 30-long hole, 100-electric compressor, 102-rotating shaft, 104-electric motor, 106-impeller, 108-housing, 110-outer peripheral surface of the rotating shaft, A-air film, D1-axial direction, D2-circumferential direction, D3-radial direction, D4-gravity direction, L-imaginary line, O1-center line, R1-first region, R2-second region.

Claims

1. A foil bearing device that rotatably supports a rotating shaft, the foil bearing device comprising: an annular member having an insertion hole for the rotating shaft to be inserted through; a top foil having an arcuate cross section, arranged between the inner peripheral surface of the annular member and the outer peripheral surface of the rotating shaft so as to surround the entire outer periphery of the rotating shaft; and a corrugated foil supporting the top foil from an outer peripheral side of the top foil and supported on the inner peripheral surface of the annular member; On a cross section perpendicular to the axis of the rotation shaft, if the angular position of an imaginary line extending upward in the direction of gravity from the center line of the top foil is set to 0 degrees, the angular position when the imaginary line rotates one circle with the center line of the top foil as the rotation center is defined as 360 degrees. The top foil includes a first region having at least one through hole formed therethrough and having an angular position of 240 degrees or more and less than 360 degrees, and a second region having no through hole formed therethrough and having an angular position of 0 degrees or more and less than 240 degrees.

2. The foil bearing device according to claim 1, wherein The at least one through-hole includes a plurality of through-holes arranged along the axial direction of the rotation shaft in the first region.

3. The foil bearing device according to claim 1 or 2, wherein: The at least one through-hole includes a first through-hole and a second through-hole having an angular position different from that of the first through-hole in the first region.

4. The foil bearing device according to claim 1 or 2, wherein: The at least one through hole includes a slit having an axial cutout portion cut out along the axial direction of the rotating shaft and a pair of rotational cutout portions cut from the axial cutout portion toward the upstream side in the rotational direction and arranged along the axial direction.

5. The foil bearing device according to claim 4, wherein: If one end of the top foil in the axial direction is defined as a position at 0% of the length of the top foil in the axial direction, and the other end is defined as a position at 100% of the length of the top foil in the axial direction as the position increases from the one end toward the other end of the top foil, Then one end of the axial cutout portion is within a range greater than 0% and less than 10%, and the other end is within a range greater than 90% and less than 100%. One of the pair of rotation direction cutouts is cut from the one end of the axial direction cutout toward the upstream side in the rotation direction. The other of the pair of rotational direction notch portions is cut from the other end of the axial direction notch portion toward the upstream side in the rotational direction.

6. The foil bearing device according to claim 1 or 2, wherein: The corrugated foil includes a corrugated portion protruding toward the top foil, The at least one through hole and the apex of the wave portion overlap with each other in the rotation direction of the rotation axis.

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