Radial foil bearing

Abstract

To provide a radial foil bearing that can suppress the excessive progression of wear on the top foil. [Solution] The bearing 5 comprises a bearing housing 10 having a through hole 11 for a rotating shaft 2, a top foil 20 provided in the through hole 11, and a bump foil 30 provided between the inner circumferential surface 12 of the through hole 11 and the top foil 20, and including a plurality of peaks 33 aligned in the circumferential direction CD of the through hole 11. The plurality of peaks 33 include a plurality of first peaks 33A and at least one second peak 33B that is closer to the end of the bump foil 30 in the circumferential direction CD than the plurality of first peaks 33A. The inner circumferential surface 12 includes a first region 12a on which the first peaks 33A are placed and a second region 12b on which the second peaks 33B are placed. The height of the second peaks 33B along the radial direction of the through hole 11 is smaller than the radial distance between the position of the top foil 20 in the first region 12a and the position of the inner circumferential surface 12 in the second region 12b.

Description

【Technical Field】 【0001】 The present disclosure relates to a radial foil bearing. 【Background Art】 【0002】 A radial foil bearing is a type of journal bearing that rotatably supports a rotating shaft, and includes a top foil as a bearing surface surrounding the outer circumference of the rotating shaft, and a bump foil that supports the top foil while elastically deforming. When the rotating shaft rotates at high speed, the pressure between the rotating shaft and the top foil increases, and a fluid film having a wedge-shaped cross section is formed. Due to the formation of this fluid film, the radial foil bearing supports the rotating shaft in a non-contact manner. Therefore, generally, it is known that a radial foil bearing has higher durability and less noise due to vibration and friction than a rolling bearing (see Patent Document 1). 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 International Publication No. 2020 / 202793 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 The bump foil has a plurality of peaks. The peaks are arranged in the circumferential direction and elastically support the top foil. The bump foil is composed of one or more foils that curve in the circumferential direction. Therefore, it is not possible to provide a peak at a location where the ends of the foils abut against each other, and the pitch of the peaks in the circumferential direction may become locally long. In this case, the contact pressure between the top foil and the bump foil at that location increases, and wear of the top foil tends to progress. 【0005】 This disclosure is made in view of the circumstances described above and aims to provide a radial foil bearing capable of suppressing excessive wear of the top foil. [Means for solving the problem] 【0006】 A radial foil bearing according to one aspect of the present disclosure comprises a bearing housing having a through hole for a rotating shaft, a top foil provided in the through hole, and a bump foil provided between the inner circumferential surface of the through hole and the top foil, and including a plurality of ridges arranged in the circumferential direction of the through hole, wherein the plurality of ridges include a plurality of first ridges and at least one second ridge that is closer to the end of the bump foil in the circumferential direction than the plurality of first ridges, and the inner circumferential surface includes a first region on which the first ridges are placed and a second region on which the second ridges are placed, and the height of the second ridges along the radial direction of the through hole is smaller than the radial distance between the position of the top foil in the first region and the position of the inner circumferential surface in the second region. [Effects of the Invention] 【0007】 According to this disclosure, it is possible to provide a radial foil bearing that can suppress the excessive progression of wear on the top foil. [Brief explanation of the drawing] 【0008】 [Figure 1] This is a side view of an example of a turbomachine to which a radial foil bearing according to this embodiment is applied. [Figure 2] This is a front view of an example of a radial foil bearing according to this embodiment. [Figure 3A] This is a side view of the bump foil according to this embodiment when it is unfolded in a planar manner. [Figure 3B] This is a partially enlarged side view of the foil body of a bump foil. [Figure 4A] This is a side view of the end of the bump foil and its vicinity in a radial foil bearing according to this embodiment. [Figure 4B]This is a side view of the end of the bump foil and its vicinity in a radial foil bearing according to a first modified example of this embodiment. [Figure 4C] This is a side view of the end of the bump foil and its vicinity in a radial foil bearing according to a second modified example of this embodiment. [Figure 4D] This is a side view of the end of the bump foil and its vicinity in a radial foil bearing according to a third modified example of this embodiment. [Modes for carrying out the invention] 【0009】 Several embodiments of this disclosure will be described below. Common parts in each figure will be denoted by the same reference numerals, and redundant explanations will be omitted. For the sake of clarity, the axial, circumferential, and radial directions will be defined as follows. 【0010】 The axial direction AD is the direction of extension of the reference shaft 7 (see Figure 1). The reference shaft 7 corresponds to the central axis of the rotating shaft 2, the thrust bearing 4, and the radial foil bearing 5. The reference shaft 7 also corresponds to the central axis of the through hole 11 provided in the radial foil bearing 5. 【0011】 The circumferential direction CD is the extension direction of a circle on a virtual plane that is centered on a point on the reference axis 7 and perpendicular to the reference axis 7. The radial direction RD is the direction of extension on a plane perpendicular to the reference axis 7, starting from any point on the reference axis 7. 【0012】 First, a turbomachine 1 to which the radial foil bearing 5 according to this embodiment is applied will be described. Figure 1 is a side view of an example of the turbomachine 1. The turbomachine 1 comprises a rotating shaft 2, an impeller 3, a thrust bearing 4, a pair of radial foil bearings 5, 5, and a housing 6 that accommodates them. Note that Figure 1 shows one of the pair of radial foil bearings 5, 5. Hereafter, for convenience of explanation, the radial foil bearing 5 will be simply referred to as bearing 5. 【0013】 The bearing 5 rotatably supports the rotating shaft 2. An impeller 3 is attached to the end of the rotating shaft 2. The impeller 3 is housed in the housing 6 with a tip clearance between it and the housing 6. The thrust bearing 4 comprises a thrust collar 4a and a pair of bearing pads 4b, 4b. The thrust collar 4a is a disc having a predetermined thickness in the axial direction AD and is fixed to the rotating shaft 2. The thrust collar 4a is sandwiched between the pair of bearing pads 4b, 4b. This limits the range of movement of the thrust collar 4a along the axial direction AD. 【0014】 Figure 2 is a front view of an example of a bearing 5. As shown in Figure 2, the bearing 5 comprises a bearing housing 10, a top foil 20, and a bump foil 30. The bearing housing 10 accommodates at least the top foil 20 and the bump foil 30. 【0015】 The bearing housing 10 is provided with a through hole 11. The through hole 11 extends in the axial direction AD and penetrates the bearing housing 10. The rotating shaft 2 is inserted through the through hole 11 with the top foil 20 and bump foil 30 housed in the through hole 11. As shown in Figure 2, the bearing housing 10 has a cylindrical outer shape. However, the outer shape of the bearing housing 10 is arbitrary as long as the through hole 11 is formed. 【0016】 A groove 13 opening to the inner circumferential surface 12 may be formed on the inner circumferential surface 12 of the insertion hole 11. In this case, for example, a retaining member 14 for holding the end of the top foil 20 is housed in the groove 13. The groove 13 and the retaining member 14 are provided in a second region 12b of the inner circumferential surface 12. However, the method of holding the top foil 20 and the bump foil 30 is not limited to the method used for the retaining member 14. 【0017】 The top foil 20 is a single metal foil that surrounds substantially the entire circumference of the rotary shaft 2. The top foil 20 is placed in the insertion hole 11 in a state of being rolled into a cylindrical shape so as to surround the outer circumference of the rotary shaft 2. The top foil 20 includes a foil body 21 facing the rotary shaft 2. The foil body 21 extends in the circumferential direction CD along the inner circumferential surface 12 of the insertion hole 11 and functions as a bearing surface facing the rotary shaft 2. Therefore, unlike the foil body 31 of the bump foil 30, the foil body 21 does not have a cross-section of alternately repeating concavities and convexities. 【0018】 The bump foil 30 is, for example, a single metal foil that surrounds substantially the entire circumference of the rotary shaft 2. The bump foil 30 is provided between the inner circumferential surface 12 of the insertion hole 11 and the top foil 20 and elastically supports the top foil 20 from the radially outer side. The bump foil 30 includes a foil body 31 that surrounds the outer circumference of the rotary shaft 2. The foil body 31 extends in the circumferential direction CD along the inner circumferential surface 12 of the insertion hole 11. 【0019】 The bump foil 30 may be composed of a plurality of foils (not shown) arranged in the circumferential direction CD. In this case, each foil constituting the bump foil 30 is held or fixed in the insertion hole 11 by a corresponding groove portion (not shown) or by welding to the inner circumferential surface 12 or other methods. 【0020】 FIG. 3A is a side view of the bump foil 30 in a planar development. FIG. 3B is a side view of the foil body 31 of the bump foil 30 partially enlarged. As shown in FIG. 3A, the foil body 31 has a wavy cross-section that extends in the circumferential direction CD while meandering in the radial direction RD of the foil body 31. 【0021】 As an example of constituting this wavy cross-section, the foil body 31 has ridges 33 and connecting portions 34 that are alternately arranged in the circumferential direction CD. Each ridge 33 extends in the axial direction AD and is arranged in the circumferential direction CD via the connecting portion 34. On the other hand, the connecting portion 34 connects two adjacent ridges 33 in the circumferential direction CD. 【0022】 The peak portion 33 has an arch-shaped cross-section that protrudes radially inward and deforms elastically in response to the load from the rotation axis 2 via the top foil 20. On the other hand, the connecting portion 34 extends in the circumferential direction CD and connects the base portions 33a, 33a of two adjacent peak portions 33, 33. The base portion 33a is the part of the peak portion 33 that is located furthest outward in the radial direction RD when the bump foil 30 is rolled up. When the bump foil 30 is subjected to a load outward in the radial direction RD, the connecting portion 34 contacts the inner circumferential surface 12 of the insertion hole 11 and supports the peak portion 33. 【0023】 Figure 4A is a side view of the end portion 30a of the bump foil 30 and its vicinity in the bearing 5. For the sake of explanation, the end portion 30a is assumed to be located near the groove 13, and the retaining member 14 installed in the groove 13 is not shown. Also, the dashed line in Figure 4A shows, as a comparative example, the case in which a peak of the same height as the first peak 33A is provided in the second region 12b. 【0024】 As shown in Figure 4A, the inner circumferential surface 12 includes a first region 12a and a second region 12b. These regions are arranged in the circumferential direction CD. In contrast, the multiple peaks 33 include multiple first peaks 33A placed on the first region 12a and at least one second peak 33B placed on the second region 12b. 【0025】 The second peak 33B is closer to the end 30a of the bump foil 30 than the multiple first peaks 33A. Therefore, the second peak 33B includes at least one of the multiple peaks 33 that is closest to the end 30a. When multiple second peaks 33B are provided, they are arranged adjacent to each other and toward the first peaks 33A, while including the peak 33 that is closest to the end 30a. 【0026】 The height H2 of the second peak 33B along the radial RD is smaller than the distance D along the radial RD between the position of the top foil 20 in the first region 12a and the position of the inner circumferential surface 12 in the second region 12b. For example, as shown in Figure 4A, multiple first peaks 33A have the same height H1 along the radial RD. On the other hand, the height H2 of the second peak 33B in the radial RD is smaller than the height H1 of the first peak 33A. 【0027】 The height H2 and spacing D mentioned above can be confirmed, for example, when the top foil 20 and bump foil 30 are mounted in the insertion hole 11 and are in an unloaded state. An unloaded state means that the top foil 20 and bump foil 30 are not subjected to deformation due to the load from the rotating shaft 2. Similar dimensional confirmation is also possible in the modified examples described later. 【0028】 As described above, the second peak 33B is provided near the end 30a of the bump foil 30. When the bump foil 30 is formed by one foil, the end 30a faces the other end of that foil, and when the bump foil 30 is formed by multiple foils, it faces the end of the adjacent foil, in the circumferential direction CD. That is, when the bump foil 30 is fitted into the insertion hole 11, a joint is formed where the ends of the bump foil 30 face each other. On the other hand, the second peak 33B is located in the second region 12b of the inner circumferential surface 12. In other words, as shown in Figure 2, the joint of the bump foil 30 is located in the second region 12b. 【0029】 As can be understood from the positions of the grooves 13 and retaining members 14 shown in Figure 2, the peaks 33 are not formed at the aforementioned joints. Therefore, the pitch of the peaks 33 along the circumferential direction CD widens in the second region 12b, and the contact pressure between the top foil 20 and the peaks 33 tends to be higher in the second region 12b compared to that in the first region 12a. 【0030】 Therefore, in this embodiment, the height H2 of the second peak 33B along the radial direction RD is set to a value smaller than the distance D along the radial direction RD between the position of the top foil 20 in the first region 12a and the position of the inner circumferential surface 12 in the second region 12b. As a result, when a load is applied to the top foil 20, the top foil 20 contacts the second peak 33B at a position radially outward from the contact position with the first peak 33A. Consequently, compared to the case where all peaks 33 have the same height, the contact pressure between the top foil 20 and the second peak 33B is reduced, and excessive wear of the top foil 20 in the second region 12b can be suppressed. In other words, the durability of the bearing 5 can be improved. 【0031】 Figure 4B is a side view of the end portion 30a of the bump foil 30 and its vicinity in the bearing 5 according to the first modified example. Figure 4C is a side view of the end portion 30a of the bump foil 30 and its vicinity in the bearing 5 according to the second modified example. As shown in Figures 4B and 4C, the bearing 5 may further include a shim foil 40 provided in the first region 12a. 【0032】 As shown in Figure 4B, the sim foil 40 is located between the top foil 20 and the bump foil 30 in the first region 12a. In this case, the end 40a of the sim foil 40 is located between the respective peaks of the adjacent first peak 33A and second peak 33B. 【0033】 Alternatively, as shown in Figure 4C, the shim foil 40 is located between the bump foil 30 and the inner circumferential surface 12 in the first region 12a. In this case, the end portion 40a of the shim foil 40 is located between the second peak 33B and the inner circumferential surface 12. 【0034】 In both the first and second modified examples, the height H2 of the second peak 33B is less than or equal to the height H1 of the first peak 33A. Therefore, as in the configuration shown in Figure 4A, the height H2 of the second peak 33B is less than the gap D by at least the thickness of the shim foil 40. As a result, when a load is applied to the top foil 20 of the first modified example, the top foil 20 contacts the second peak 33B at a position radially outward from the contact point with the first peak 33A. 【0035】 On the other hand, when a load is applied to the top foil 20 of the second modified example, the top foil 20 contacts the second peak 33B at approximately the same position as the contact position with the first peak 33A in the radial direction RD. However, since the second peak 33B is separated from the inner circumferential surface 12, the top foil 20 is allowed to undergo further radial outward displacement in the second region 12b. 【0036】 Therefore, in all of the modified examples, the contact pressure between the top foil 20 and the second ridge 33B is reduced compared to the case where all the ridges 33 have the same height, and excessive wear of the top foil 20 in the second region 12b can be suppressed. 【0037】 Furthermore, in the first and second modified examples, the height H1 of the first peak 33A and the height H2 of the second peak 33B can be set to the same value. In this case, all peaks 33 can be formed, for example, using the same mold, thereby suppressing an increase in manufacturing costs. 【0038】 Figure 4D is a side view of the end portion 30a of the bump foil 30 and its vicinity in a bearing 5 according to a third modified example. As shown in Figure 4D, the second region 12b may be located radially outward relative to the first region 12a. In this case, the boundary 12c between the first region 12a and the second region 12b is located between the second peak 33B and the inner circumferential surface 12, forming a step between the two regions. Also, the height H2 of the second peak 33B is less than or equal to the height H1 of the first peak 33A. The end portion 30a of the bump foil 30 may be provided so as to be spaced apart from the second region 12b by a distance equal to this value. 【0039】 The effects of the third modification are the same as those of the second modification. That is, when a load is applied to the top foil 20 of the third modification, the top foil 20 contacts the second peak 33B at approximately the same position as the contact position with the first peak 33A in the radial direction RD. However, since the second peak 33B is separated from the inner circumferential surface 12, the top foil 20 is allowed to undergo further radial outward displacement in the second region 12b. 【0040】 Therefore, compared to the case where all the ridges 33 have the same height, the contact pressure between the top foil 20 and the second ridge 33B is reduced, and excessive wear of the top foil 20 in the second region 12b can be suppressed. Also, as with the second modified example, all the ridges 33 can be formed, for example, using the same mold, thereby suppressing an increase in manufacturing costs. 【0041】 In any embodiment, the width W2 of the second peak 33B along the circumferential direction CD of the insertion hole 11 (see Figure 4A) may be equal to the width W1 of the first peak 33A along the circumferential direction CD (see Figure 4A), or it may be smaller than the width W1. As described above, by setting the height H2 of the second peak 33B to a value smaller than the spacing D, the contact pressure between the top foil 20 and the second peak 33B can be reduced. However, the amplitude of the radial RD of the top foil 20 generated by external excitation tends to increase in the second region 12b. 【0042】 By narrowing the width W2 of the second peak 33B compared to the width W1 of the first peak 33A, the rigidity of the second peak 33B is increased. The increased rigidity of the second peak 33B and the contact between it and the top foil 20 reduces the amplitude of the top foil 20 near the joint of the top foil 20 (i.e., in the second region 12b). Furthermore, by narrowing the width W2 of the second peak 33B, the top of the second peak 33B moves closer to the joint of the top foil 20. This reduces the proportion of the top foil 20 located in the second region 12b, thereby reducing the amplitude of the top foil 20 near the joint. 【0043】 This disclosure is not limited to the embodiments described above, but includes all modifications within the meaning and scope of the claims as indicated by the claims. [Explanation of symbols] 【0044】 5...Bearing (radial foil bearing), 10...Bearing housing, 11...Through hole, 12...Inner circumferential surface, 12a...First region, 12b...Second region, 12c...Boundary, 13...Groove, 14...Retaining member, 20...Top foil, 21...Foil body, 30...Bump foil, 30a...End, 31...Foil body, 33...Climb, 33a...Base, 33A...First crest, 33B...Second crest, 34...Connecting part, 40...Shim foil, 40a...End

Claims

[Claim 1] A bearing housing having a hole for inserting a rotating shaft, A top foil provided within the aforementioned insertion hole, A bump foil is provided between the inner circumferential surface of the insertion hole and the top foil, and includes a plurality of ridges arranged in the circumferential direction of the insertion hole, Equipped with, The plurality of peaks include a plurality of first peaks and at least one second peak that is closer to the end of the bump foil in the circumferential direction than the plurality of first peaks. The inner circumferential surface includes a first region on which the first peak is placed and a second region on which the second peak is placed. The height of the second peak along the radial direction of the insertion hole is smaller than the radial distance between the position of the top foil in the first region and the position of the inner circumferential surface in the second region. Radial foil bearing. [Claim 2] In the radial direction, the height of the second peak is smaller than the height of the first peak. The radial foil bearing according to claim 1. [Claim 3] The first region further comprises a shim foil located between the top foil and the bump foil, or between the bump foil and the inner circumferential surface. The radial foil bearing according to claim 1. [Claim 4] The second region is located radially outward from the first region. The radial foil bearing according to claim 1. [Claim 5] The width of the second peak along the circumferential direction is smaller than the width of the first peak along the circumferential direction. A radial foil bearing according to any one of claims 1 to 4.

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