Thrust foil bearing

Abstract

The thrust foil bearing (5) comprises: a base plate (10) orthogonal to the rotation center axis (8); a back foil (30) mounted on the base plate (10) and including a plurality of back foil sheets (31) arranged circumferentially along the rotation center axis (8) of the base plate; and a top foil (20) including a plurality of top foil sheets (21) arranged circumferentially and covering the plurality of back foil sheets (31). Each back foil sheet (31) includes: a belt portion (32) extending from the inner circumferential side of the back foil (30) toward the outer circumferential side; and a wave portion (33) extending from a base end portion (33a) connected to the belt portion (32) as a fixed end portion to a front end portion (33b) as a free end portion, and including a bend portion (35) protruding toward the top foil (20) between the base end portion (33a) and the front end portion (33b).

Description

Technical Field

[0001] This disclosure relates to thrust foil bearings. Background Technology

[0002] A thrust foil bearing is a type of fluid bearing that supports a rotating body in a non-contact manner by forming a fluid film between the thrust foil bearing and the rotating body. The rotating body is movably positioned along its axial direction and moves slightly due to vibration, impact, etc.

[0003] Regardless of the minute movements of such a rotating body, the thrust foil bearing needs to maintain the formation of a fluid film. Therefore, the thrust foil bearing comprises a thin metal plate inclined relative to the rotating body. The thin metal plate is configured to flex axially, forming a fluid film together with the rotating body and creating a wedge-shaped flow path for increasing internal pressure. Patent Document 1 discloses a thrust foil bearing comprising: a plurality of top foils serving as the aforementioned thin metal plate, and a plurality of corrugated foils elastically supporting the plurality of top foils.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2020-037975

[0005] Patent Document 1 describes a corrugated sheet composed of a series of continuous corrugated plates with mountain and valley sections. The corrugated plates are formed using a molding process employing a die. However, the fluid film formed by the thrust foil bearing is only a few μm thick, making it extremely thin. Therefore, high dimensional accuracy is required for the corrugated plates during the molding process. Consequently, when forming the corrugated plates, the mountain and valley sections are formed individually using a die to suppress deformation of the corrugated plate shape. This process is time-consuming, significantly increasing manufacturing costs. Summary of the Invention

[0006] This disclosure is made in view of the above circumstances, with the aim of providing a thrust foil bearing having a back foil capable of reducing the number of manufacturing steps and suppressing shape deformation.

[0007] One aspect of the thrust foil bearing disclosed herein comprises: a base plate orthogonal to a rotational central axis; a back foil disposed on the base plate and comprising a plurality of back foil sheets arranged circumferentially along the rotational central axis; and a top foil comprising a plurality of top foil sheets arranged circumferentially and covering the plurality of back foil sheets, each of the back foil sheets comprising: a band portion extending from an inner circumferential side of the back foil toward an outer circumferential side; and a wave portion extending from a base end portion connected to the band portion as a fixed end portion to a front end portion as a free end portion, and including a curved portion between the base end portion and the front end portion portion that is elastically deformably projecting toward the top foil.

[0008] Alternatively, the wave section may be connected to only one of the edges on one side and the other side of the strip section in the width direction. Alternatively, the wave section may be divided into multiple waveplates arranged along the extension direction of the strip section. Alternatively, the back foil may include an annular first connecting portion located radially outward of the multiple back foils and connected to the strip section of each back foil. Alternatively, the back foil may include an annular second connecting portion located radially inward of the multiple back foils and connected to the strip section of each back foil.

[0009] According to this disclosure, a thrust foil bearing with a back foil that can reduce the number of manufacturing steps and suppress deformation of the shape can be provided. Attached Figure Description

[0010] Figure 1 This is a side view of an example of a turbomachinery using a thrust foil bearing according to an embodiment of the present disclosure.

[0011] Figure 2 This is a side view of the thrust foil bearing according to the embodiment.

[0012] Figure 3 This is a front view of the thrust foil bearing of the embodiment.

[0013] Figure 4A This is the front view of the top foil in the implementation method.

[0014] Figure 4B This is a front view of the back foil of the implementation method.

[0015] Figure 4C This is a front view of the back foil of the embodiment.

[0016] Figure 4D This is a side view showing the top foil and back foil mounted on the base plate.

[0017] Figure 5A This is a diagram used to illustrate the forming process of the back foil in the comparative example.

[0018] Figure 5B This is a diagram illustrating the forming process of the back foil in the embodiment.

[0019] Figure 6A This is a three-dimensional view of the wave portion of a modified embodiment.

[0020] Figure 6B This is a three-dimensional view of the wave portion of a modified embodiment.

[0021] Figure 6C This is a three-dimensional view of the wave portion of a modified embodiment.

[0022] Figure 6DThis is a three-dimensional view of the wave portion of a modified embodiment.

[0023] Figure 6E This is a three-dimensional view of the wave portion of a modified embodiment.

[0024] Figure 6F This is a front view of the wave section of a modified embodiment.

[0025] Figure 6G This is a front view of the wave section of a modified embodiment.

[0026] Figure 7 This is a front view of the back foil of a modified embodiment. Detailed Implementation

[0027] Hereinafter, several embodiments of this disclosure will be described. Furthermore, common parts will be labeled with the same reference numerals in all figures, and repeated descriptions will be omitted. For ease of explanation, the axial direction Z, circumferential direction CD, rotational direction TD, and radial direction RD will be defined.

[0028] The Z-axis is the rotation center axis 8 (refer to...) Figure 1 The extension direction of the thrust foil bearing 5 is as follows: The rotation center axis 8, for example, is the central axis of the shaft 2 (which is a rotating body) or the thrust ring 4, and is a reference axis used to determine the position of each component in the thrust foil bearing 5 of this embodiment. The circumferential direction CD is the circumferential direction centered on the rotation center axis 8. The rotation direction TD is the rotation direction of the shaft 2, which coincides with one direction of the circumferential direction CD. Furthermore, the radial direction RD extends from the rotation center axis 8 in a plane orthogonal to it.

[0029] First, an overview of the thrust foil bearing 5 in this embodiment will be given.

[0030] Figure 1 This is a side view of an example of a turbomachinery 1 using the thrust foil bearing 5 of this embodiment. Figure 1 As shown, the turbomachinery 1 includes a shaft 2, an impeller 3, a thrust ring 4, a pair of thrust foil bearings 5, a radial foil bearing 6, and a housing 7 that houses them.

[0031] Shaft 2 is rotatably supported by radial foil bearings 6. Impeller 3 is mounted at the end of shaft 2. Impeller 3 is housed within housing 7 with a head clearance between it and housing 7. Thrust ring 4 is a circular plate of a specified thickness along the Z-axis and is fixed to shaft 2. Thrust ring 4 is held in place by a pair of thrust foil bearings 5. This limits the range of movement of thrust ring 4 along the Z-axis.

[0032] When the thrust ring 4 stops, it is positioned in a state where it can contact the top foil 21. When the thrust ring 4 begins to rotate, it rotates while intermittently or continuously rubbing against the top foil 21. At this time, through the rotation of the thrust ring 4, fluid flows into the wedge-shaped flow path formed between the two, and the pressure in the flow path increases. Then, as the rotational speed of the thrust ring 4 increases and the pressure increases further, the top foil 20 flexes towards the back foil 30, and the thrust ring 4 moves away from the top foil 20. As a result, a fluid film is formed between the thrust ring 4 and the top foil 21, and the thrust ring 4 begins to rotate relative to the top foil 21 in a non-contact manner.

[0033] The back foil 31 is disposed between the top foil 21 and the base plate 10, constituting an elastic member supporting the top foil 21. If the pressure within the flow path changes due to the thrust of the thrust ring 4, the deflection of the top foil 21 changes according to the changed pressure. The back foil 31 supports the top foil 21 to prevent excessive deflection. Thus, by maintaining an appropriate gap between the top foil 21 and the thrust ring 4, the thrust ring 4 can be supported in a non-contact manner.

[0034] Next, the structure of the thrust foil bearing 5 will be described.

[0035] Figure 2 This is a side view of the thrust foil bearing 5 of this embodiment. Figure 3 This is a front view of the thrust foil bearing 5 in this embodiment. Figure 3 A portion of the top foil 20 is omitted from the diagram. As shown in the figure above, the thrust foil bearing 5 includes a base plate 10, a top foil 20, and a back foil 30.

[0036] The base plate 10 is a flat metal plate orthogonal to the rotation center axis 8, and has a specified thickness (e.g., a few mm). The base plate 10 is, for example, fixed to the housing 7. The shape of the base plate 10 is not limited to... Figure 3 The circle shown can also be rectangular, for example. The base plate 10 has a flat surface 11 facing the thrust ring 4. A through hole 12 is formed on the flat surface 11. The through hole 12 is formed around the rotation center axis 8 and extends through the base plate 10. A shaft 2 is inserted into the through hole 12.

[0037] Furthermore, depending on the method of applying the thrust foil bearing 5, it is also possible to consider a case where the shaft does not pass through the thrust foil bearing 5. In this case, the thrust ring is fixed to the end of the shaft, and on the other hand, the through hole 12 is not formed. In addition, the position of the rotation center axis of the shaft is defined on the base plate 10, and the relative positions of the top foil 20 and the back foil 30 with respect to the base plate 10 are defined based on the position of this rotation center axis.

[0038] Figure 4AThis is a front view of the top foil 20. The top foil 20 is formed from a flexible metal sheet. The top foil 20 includes a plurality of top foil sheets 21 and an annular connecting portion 22, which is placed on a back foil 30, which is placed on a flat surface 11 of the base plate 10.

[0039] In this embodiment, multiple top foils 21 are arranged at equal angular intervals along the circumferential direction CD. For example, as... Figure 4A As shown, multiple top foils 21 are arranged at 60-degree intervals around the rotation center axis 8. Each top foil 21 has a generally fan-shaped shape with its vertex side cut out in an arc, and covers the back foil 31 of the back foil 30 (at least the wave portion 33 described later) (see reference). Figure 3 ).

[0040] The top foil 21 of this embodiment has an edge portion 21a located on the rear side of the rotation direction TD and extending radially, and an edge portion 21b located on the front side of the rotation direction TD and extending radially. The edge portion 21a is configured as the fixed end of the top foil 21, while the edge portion 21b is configured as the free end of the top foil 21. In addition, the top foil 21 is inclined at a predetermined angle as it moves away from the base plate 10 from the edge portion 21a toward the edge portion 21b.

[0041] The top foil 20 includes a connecting portion 22 disposed radially outside the plurality of top foil sheets 21 and supporting the plurality of top foil sheets 21. The connecting portion 22 is formed in an annular shape and is connected to the edge portion 21a of each top foil sheet 21. By fixing the connecting portion 22 to the base plate 10, the edge portion 21a is stably located on the flat surface 11.

[0042] Each top foil 21, together with the thrust ring 4, forms a wedge-shaped flow path 9 (see reference). Figure 2 As the rotating thrust ring 4 approaches the top foil 20, the pressure within the flow path 9 increases. Due to this increased pressure, the pressing force of the top foil 21 against the wave portion 33 of the back foil 31 increases. The wave portion 33 elastically deforms from its initial state due to this increased pressing force, resulting in a reduction in the tilt angle of the top foil 21, thus maintaining the gap between the thrust ring 4 and the top foil 20.

[0043] Figure 4B This is the front view of the back foil 30. Figure 4C This is the front view of the back foil 31. Figure 4D This is a side view showing the top foil 21 and the back foil 31 mounted on the base plate 10. Like the top foil 20, the back foil 30 is also formed from a flexible metal sheet. The back foil 30 includes a plurality of back foils 31 arranged at intervals on a circumferentially spaced CD.

[0044] Multiple back foils 31 are arranged at equal angular intervals along the circumferential CD. For example, as... Figure 4B As shown, multiple back foils 31 are arranged at 60-degree intervals around the rotation center axis 8. Each back foil 31 has a generally fan-shaped profile with an arc cut at its apex. Figure 4C As shown, the back foil 31 includes a plurality of strips 32, at least one wave section 33 connected to each strip 32, and a connecting section 34.

[0045] The connecting portion 34 is located radially outward from the plurality of strip portions 32 and the plurality of wave portions 33, and connects the plurality of strip portions 32. For example, as Figure 4C As shown, the connecting portion 34 is formed as an arc with a predetermined width in the radial direction and is connected to the end of each belt portion 32.

[0046] Multiple strips 32 are spaced apart on the circumferential CD and extend parallel to the flat surface 11 of the base plate 10. Each strip 32 extends from the inner circumferential side of the back foil 30 toward the outer circumferential side. For example, as Figure 4C As shown, it can also be a direction parallel to a radial RD (i.e., a specific azimuth angle). Alternatively, the extension direction of the strip 32 can also be multiple radial RDs with different azimuth angles.

[0047] Each belt portion 32 includes: an end portion 32a connected to the connecting portion 34, and an end portion 32b located radially inward from the end portion 32a. The belt portion 32 also includes: an edge portion 32c on one side in the width direction, and an edge portion 32d on the other side in the width direction. The width direction referred to here is a direction substantially orthogonal to the extending direction (long side direction) of the belt portion 32, for example, a circumferential direction CD.

[0048] The wave portion 33 has a width shorter than the total length of the belt portion 32 along the radial direction RD. The wave portion 33 extends from the base end portion 33a, which is a fixed end connected to the belt portion 32, to the front end portion 33b, which is a free end. Furthermore, the wave portion 33 includes an elastically deformable bend portion 35 between the base end portion 33a and the front end portion 33b. That is, the wave portion 33 extends from the base end portion 33a along a predetermined direction (e.g., circumferential direction CD) to the front end portion 33b while being cantilevered by the belt portion 32.

[0049] As described above, the wave section 33 is cantilevered and supported by the belt section 32. Therefore, when only one wave section 33 is provided for one belt section 32, the base end portion 33a of the wave section 33 is connected to either the edge portion 32c or the edge portion 32d of the belt section 32. When two wave sections 33 are provided for one belt section 32, the base end portion 33a of one of the two wave sections 33 is connected to the edge portion 32c of the belt section 32, and the base end portion 33a of the other of the two wave sections 33 is connected to the edge portion 32d of the belt section 32.

[0050] The curved portion 35 extends from the base end 33a to the front end 33b in a manner that protrudes toward the top foil 21. That is, the curved portion 35 is bent into an arch shape that protrudes toward the top foil 21. By forming it into an arch shape, the curved portion 35 can be elastically deformed, the wave portion 33 elastically supports the top foil 21, and can be elastically deformed relative to the pressure applied via the top foil 21.

[0051] The height of the bend 35 along the axial direction Z is set according to the tilt angle set for the top foil 21. Specifically, as Figure 4D as well as Figure 6B As shown, for the multiple bends 35 adjacent to the circumferential CD, their positions are set to be higher the further forward they are in the rotational direction TD. Furthermore, the heights of the multiple bends 35 adjacent to each other on the circumferential CD can also be the same (see reference). Figure 6B In this case, for example, such as Figure 4D As shown by the dashed line, a recess 13 is formed in the flat surface 11. The bottom surface 13a of the recess 13 is inclined at the same angle as the tilt angle of the top foil 21 after installation, and a wave portion 33 is provided on the bottom surface 13a.

[0052] The front end portion 33b of the wave portion 33 is not connected to other components of the back foil 30, including the strip portion 32, but is located in a position that can contact the base plate 10. When the wave portion 33 is pressed towards the base plate 10, the front end portion 33b slides on the base plate 10 in a direction away from the strip portion 32. That is, the front end portion 33b functions as a foot of the wave portion 33 that can prevent excessive bending only in the vicinity of the base end portion 33a and promote elastic deformation of the bending portion 35.

[0053] As described above, the back foil 30 is formed by forming a thin metal sheet using a mold 50. The wave portion 33 and the strip portion 32 are formed into a single piece in one forming process.

[0054] Figure 5A This is a diagram used to illustrate the forming process of the back foil 131 in the comparative example. Figure 5B This is a diagram illustrating the forming process of the back foil 31 in this embodiment. Figure 5A As shown, in the comparative example, it is assumed that mold 150 is used to form three wave portions 133 from metal sheet 140. For ease of explanation, the portion of metal sheet 140 in which the central wave portion 133 is formed will be denoted as 140a, and the portions of wave portions 133 on both sides thereon will be denoted as 140b.

[0055] When the metal sheet 140 is clamped by the upper die 151 and the lower die 152, the upper die 151 and the lower die 152 contact the metal sheet 140 at multiple locations. If the friction at these contact points is too strong, the movement and stretching of the metal sheet 140 are restricted, internal stress remains, and the shape is easily deformed. For example, as... Figure 5A As shown, when three wave sections 133 are formed at once, two sections 140b, 140b move in directions that are separated from each other. As a result, the section 140a of the metal sheet 140 between them is overstretched, and internal stress such as deformation is easily retained.

[0056] On the other hand, in this embodiment, the wave section 33 is formed only on one side of a strip section 32, or is formed on both sides respectively. That is, the number of wave sections 33 provided on a strip section 32 is at most two.

[0057] Therefore, in a cross-sectional view taken at a cross section including a strip 32 and a wave portion 33 formed on one side thereof, and orthogonal to the support surface which is the surface on which the back foil 131 is disposed, only a single hill is formed as the wave portion 33 on one side of the strip 32. Here, a hill refers to a structure including a bottom closest to the support surface and a peak provided between the bottom and the strip 32. Here, the peak is not limited to that in this embodiment and may also have width. At the hill, the bottom may be able to abut against the support surface, but the portion between the bottom and the strip 32 is not formed to be able to abut against the support surface.

[0058] Although the bottom is a region with width when viewed in section in this embodiment, it may also be a point when viewed in section. Furthermore, although the belt portion 32 is also formed in this embodiment to be able to abut against the support surface, it may also be formed to have a gap between the belt portion 32 and the support surface.

[0059] In addition, in this embodiment, the front end portion 33b is included in the bottom. However, the term "forming only a single hill" also includes the remaining portion of the front end portion 33b that extends from the bottom toward the opposite side of the belt portion 32 without forming a hill (i.e., it also includes the case where the front end portion 33b is away from the support surface).

[0060] like Figure 5B As shown, when the metal sheet 40, which serves as the base material for the wave section 33 and the strip section 32, is sandwiched between the upper mold 51 and the lower mold 52, the upper mold 51 and the lower mold 52 contact the metal sheet 40 at multiple locations. Similar to the comparative example, at these contact points, the friction locally intensifies.

[0061] However, in this embodiment, for a single strip 32, the number of wave portions 33 formed using the mold 50 is at most two, and in any wave portion 33, the front end 33b is formed as a free end. Therefore, when the metal sheet 40 is clamped by the upper mold 51 and the lower mold 52, sliding and stretching of the portion 40a that forms the wave portion 33 in the metal sheet 40 is allowed in the left or right direction as shown in FIG. 5. In other words, the wall surface of this portion 40a is constrained by excessive friction. As a result, the wave portion 33 and the strip portion 32 can be formed into the desired shape without deformation. In addition, since residual stress is reduced, deformation of the formed wave portion 33 and strip portion 32 can also be suppressed.

[0062] In this embodiment, a plurality of strip portions 32 are provided on a back foil 31. That is, a plurality of wave portions 33 are provided on a back foil 31. However, as Figure 5B As shown, one end of each wave section 33 is formed as a free end, which can suppress the generation of deformation. That is, multiple wave sections 33 can be formed in one forming process, which can reduce the number of manufacturing steps compared to the case of forming a group of continuous wave plates with mountain and valley sections by repeatedly positioning and forming the metal sheet 40.

[0063] Next, variations of this embodiment will be described.

[0064] Figures 6A-6G This is a diagram illustrating the wave section 33 of a modified example of this embodiment. Figures 6A-6E This is a three-dimensional view of wavelet 33 in the modified example. Figure 6F as well as Figure 6G This is the front view of wavelet 33 in the modified example. (Example:) Figure 6A as well as Figure 6B As shown, the heights of the multiple wavelets 33 can be the same or different. This is as described above.

[0065] Alternatively, the wave portion 33 may be connected to either one of the edge portions 32c on one side and the edge portion 32d on the other side in the width direction of the strip portion 32. For example, as Figure 6C As shown, the multiple wave portions 33 may also extend only from the edge portion 32c of the strip portion 32 corresponding to each wave portion 33 along a predetermined direction (e.g., circumferential CD). Alternatively, it may be as follows: Figure 6D As shown, multiple wave sections 33 may also extend only from the edge portion 32d of the strip portion 32 corresponding to each wave section 33 along a predetermined direction (e.g., circumferential CD). By unifying the relative positions of the wave sections 33 with respect to each strip portion 32, the distribution of the positions of the wave sections 33 can be made uniform, and the positional offset of the contact point with the top foil 21 can be reduced.

[0066] Alternatively, the wave section 33 can also be divided by at least one slit 36 ​​into a plurality of waveplates 37 arranged along the extending direction of the strip section 32. That is, as Figure 6E As shown, slit 36 ​​extends within wave section 33 in a predetermined direction (e.g., circumferential CD). Therefore, waveplates 37 are arranged along the extension direction of strip section 32. Slit 36 ​​can also be applied in any of the above-described arrangements. As an example, Figure 6F Indicates in Figure 4C The example shown is of a back foil 31 with a slit 36. Additionally, Figure 6G Indicates will Figure 4C The back foil 31 shown is changed to Figure 6C The shape shown further forms an example of slit 36. With the pressure distribution occurring in the wedge-shaped flow path due to the segmentation of the wave section 33, each wave section 33 can move independently, thereby ensuring followability.

[0067] The dimensions of the multiple wave sections 33 (waveplates 37) can also be different from each other. The dimensions referred to here include, for example, the height, width, length from the base end 33a to the front end 33b, radius of curvature of the curved portion 35, and the dimensions of the shape as viewed from the Z-axis. By individually changing the dimensions of the wave sections 33 (waveplates 37), the positional distribution of the spring constant in the back foil 31 can be manipulated.

[0068] Figure 7 This is a front view of the back foil 30 in a modified embodiment of this invention. Figure 7 As shown, the back foil 30 may also include a connecting portion (first connecting portion) 38. The connecting portion 38 is located radially outside the plurality of back foil sheets 31 and is formed in a ring shape to surround the plurality of back foil sheets 31. In addition, the connecting portion 38 is connected to and supports the strap portion 32 of each back foil sheet 31. The relative position of the back foil sheets 31 is determined by the connection with the connecting portion 38. Therefore, positioning of the back foil sheets 31 relative to the base plate 10 becomes easy. Alternatively, through holes 38a may be provided at multiple locations of the connecting portion 38. In this case, the same through holes (not shown) may also be provided in the top foil 20, and the back foil 30 and the top foil 20 may be fixed to the base plate 10 by using screws or the like through these through holes 38a. Thus, the plurality of back foil sheets 31 can be fixed together.

[0069] The back foil 30 may also include Figure 7The connecting portion (second connecting portion) 39 is shown by the dashed line in the figure. The connecting portion 39 is located radially inside the plurality of back foils 31. When the bottom plate 10 has through holes 12, the connecting portion 39 is located radially inside the plurality of back foils 31 and radially outside the through holes 12. The connecting portion 39 is connected to at least one strip portion 32 of each back foil 31. Through the connecting portion 39, undesirable deformation of the inner peripheral portion of the top foil 20 (e.g., warping of the thrust ring) can be suppressed.

[0070] Furthermore, this disclosure is not limited to the above-described embodiments, but rather includes all modifications within the meaning and scope equivalent to the claims as stated in the claims.

Claims

1. A thrust foil bearing, characterized in that, have: The base plate is orthogonal to the axis of rotation. A back foil, which is placed on the base plate and includes a plurality of back foil sheets arranged circumferentially along the central axis of rotation; as well as A top foil comprising a plurality of top foils arranged along the circumference and covering the plurality of back foils. Each of the aforementioned back foils includes: The strip extends from the inner circumferential side of the back foil toward the outer circumferential side; and The wave portion extends from a base end connected to the strip portion as a fixed end to a front end end as a free end, and includes a curved portion that can elastically deformably protrude toward the top foil between the base end end and the front end end.

2. The thrust foil bearing according to claim 1, characterized in that, The wave section is connected only to one of the edge portions on one side and the other side in the width direction of the band section.

3. The thrust foil bearing according to claim 1 or 2, characterized in that, The wave section is divided into multiple waveplates arranged along the extension direction of the band section.

4. The thrust foil bearing according to claim 1, characterized in that, The back foil includes an annular first connecting portion located radially outside the plurality of back foil sheets and connected to the strip portion of each of the back foil sheets.

5. The thrust foil bearing according to claim 4, characterized in that, The back foil includes an annular second connecting portion located radially inside the plurality of back foil sheets and connected to the strip portion of each of the back foil sheets.

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