Air spring

Abstract

To provide an air spring which is further improved by eliminating the displaceable movement and exfoliation of a slide sheet which is attached to a stopper by further devising the structure.SOLUTION: In an air spring having a vehicle-body side upper support part 11, a bogie-side lower support part 12 arranged below the upper support part, and a diaphragm 13 composed of a material having flexibility, and arranged over the upper support part 11 and the lower support part 12, a stopper S is constituted in which an upper abutment part 11c of the upper support part 11 and a lower abutment part 12b of the lower support part 12 abut on each other in association with the relative proximal movement of the upper support part 11 and the lower support part 12 by a prescribed amount in the vertical direction, one 12b of the upper abutment part 11c and the lower abutment part 12b is provided with a slide sheet 1 which can abut on the other 11c of either of the upper abutment part 11c and the lower abutment part 12b, and a movement regulation mechanism K is arranged for regulating the relative movement of one 12b and the slide sheet 1 to the inner diameter side and the outer diameter side with respect to an axis P of the diaphragm 13.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an air spring used mainly in railway vehicles and the like, and more specifically, to an air spring having an upper support portion on the car body side, a lower support portion on the bogie side arranged below the upper support portion, and a diaphragm made of a flexible material and deployed across the upper support portion and the lower support portion. [Background technology]

[0002] In air springs, a stopper that maintains a certain degree of elasticity and prevents the vehicle body from descending too far is often provided as a measure in case the diaphragm is deflated due to a puncture, etc. Air springs having a stopper that functions during deflation are known, such as those disclosed in Patent Document 1 and Patent Document 2.

[0003] The stopper and the sliding member that comes into contact with the stopper during deflation are provided with a sliding sheet that reduces frictional resistance caused by rubbing between the stopper and the sliding member. In Patent Document 1, the sliding sheet is a third sliding plate (60) made of fluororesin and arranged on the upper end of the elastic stopper material (50) (see FIG. 1 in Patent Document 1), and in Patent Document 2, the sliding sheet is arranged on the lower surface of the upper plate (2) (see FIG. 1 in Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2003-294073 A [Patent Document 2] JP 2016-125541 A Summary of the Invention [Problem to be solved by the invention]

[0005] During deflation when the stopper in the air spring acts, the sliding member and the sliding sheet rub against each other under load, but with age and during durability testing, the sliding sheet can shift or peel off.

[0006] An object of the present invention is to provide an improved air spring by further improving the structure to prevent the sliding sheet provided on the stopper from shifting or peeling off. [Means for solving the problem]

[0007] The present invention relates to an air spring having an upper support portion 11 on the vehicle body side, a lower support portion 12 on the bogie side arranged below the upper support portion 11, and a diaphragm 13 made of a flexible material and arranged across the upper support portion 11 and the lower support portion 12. And , As the upper support portion 11 and the lower support portion 12 are moved vertically toward each other by a predetermined distance, a stopper S is formed in which the upper contact portion 11c of the upper support portion 11 and the lower contact portion 12b of the lower support portion 12 come into contact with each other. A sliding sheet 1 is provided on either the upper contact portion 11c or the lower contact portion 12b, the sliding sheet 1 being capable of contacting the other one 11c of the upper contact portion 11c or the lower contact portion 12b. A movement restriction mechanism K is provided to restrict the relative movement of either one of the two 12b and the sliding sheet 1 in the radially inward and radially outward directions with respect to the axis P of the diaphragm 13. And, The sliding sheet 1 is a sheet material made of fluororesin, The sliding sheet 1 is adhered to either one of the two 12b. The movement restriction mechanism K is configured by providing a side wall on either one of the sliding sheets 12b, the side wall having a height less than the thickness of the sliding sheet 1 and abutting against the side edge of the sliding sheet 1. It is characterized by:

[0008] The second present invention is characterized in that, in the present invention, the movement restricting mechanism K is configured by providing, on either one 12b, an inner wall 2 abutting the radially inner end relative to the axial center P of the sliding sheet 1 and an outer wall 3 abutting the radially outer end, each having a height less than the thickness of the sliding sheet 1.

[0009] The third invention is characterized in that in the second invention, the inner wall 2 and / or the outer wall 3 are formed into a wall having an arc shape with respect to the axis P.

[0010] The fourth present invention is characterized in that, in the present invention, the movement restricting mechanism K is configured by providing an engagement recess 4 in one of the sides 12b, the engagement recess 4 having a depth less than the thickness of the sliding sheet 1 and into which the sliding sheet 1 is fitted.

[0011] The fifth aspect of the present invention is characterized in that in the fourth aspect of the present invention, a plurality of the fitting recesses 4 are disposed in a distributed manner in the circumferential direction with respect to the axis P. Effect of the Invention

[0014] When the diaphragm is deflated, the stopper acts to cause the sliding sheet and either the upper or lower contact portion to move relatively while rubbing strongly inward and outward mainly in the radial direction of the axis. However, the movement restriction mechanism restricts the relative movement of the sliding sheet and the portion where it is provided (either the upper or lower contact portion) inward and outward radial directions with respect to the axis of the diaphragm, so that the sliding sheet does not shift or peel off during deflation.

[0015] As a result, by further improving the structure, it is possible to provide an improved air spring by eliminating the misalignment and peeling of the sliding sheet provided on the stopper. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a partially cutaway front view showing an air spring according to a first embodiment; [Diagram 2] The lower contact portion of the air spring in FIG. 1 is shown in (a) plan view and (b) cross-sectional view. [Diagram 3] FIG. 11 is a partially cutaway front view showing an air spring according to a second embodiment; [Figure 4] FIG. 4 shows the lower contact portion of the air spring in FIG. 3, where (a) is a plan view and (b) is a cross-sectional view. [Diagram 5] FIG. 11 is a cross-sectional front view of an air spring according to a third embodiment. [Figure 6] The lower contact part of the air spring in Figure 5 is shown. (a) is a plan view of a half cut along the axis, and (b) is a cross-sectional view. [Figure 7] The structure of the movement restriction mechanism is shown in a vertically enlarged deformed view. (A) is a cross-sectional view taken along line XX in FIG. 2(A), (B) is a cross-sectional view taken along line YY in FIG. 4, and (C) is a cross-sectional view taken along line ZZ in FIG. 6. [Figure 8] Chart showing durability test data for sliding sheets DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the air spring according to the present invention will be described with reference to the drawings, in which an air spring for a railway vehicle is described. In addition, in order to make the structure of the movement restriction mechanism K easier to understand, Fig. 7(A) to (C) are shown as principle diagrams (deformed diagrams) enlarged in the vertical direction.

[0018] [Embodiment 1] As shown in Figure 1, the air spring A for railway vehicles consists of an air spring section c and a laminated rubber section d placed underneath it, and is configured as an upper and lower two-stage suspension mechanism with a vertical (up-down) axis P. The air spring section c is composed of an upper support section 11 which faces the railway vehicle (an example of a car body, not shown), a lower support section (the lower support section on the bogie side) 12 which is arranged below it, and a diaphragm 13 which is made of a flexible material such as rubber and is arranged across the upper support section 11 and the lower support section 12. The laminated rubber portion d includes an elastic portion 15 having a laminated rubber structure formed between the upper and lower portions of a base portion 14 supported by a dolly (not shown) and the lower support portion 12 described above.

[0019] The upper support portion 11 is composed of an upper steel plate 11a and a lower steel plate 11b which are stacked and integrated to present a circular shape when viewed from the direction of the axis P, a bottomed cylindrical upper abutment portion 11c made of sheet metal which is fixed to the underside of the upper abutment portion 11c, and a support shaft 11d. A ring-shaped receiving portion 16 made of rubber (elastic material) is integrally provided on the radially outer side of the upper abutment portion 11c and on the radially outer side and underside of the lower steel plate 11b. The support shaft 11d having the axis P is attached in a state where it protrudes upward from the upper abutment portion 11c penetrating the upper and lower steel plates 11a, 11b, and is supported by the body (not shown) of a passenger car or the like.

[0020] The receiving portion 16 covers the radially outer portion of the lower steel plate 11b in a manner that prevents rusting, and is configured to be able to elastically receive the upper portion 13a of the diaphragm 13 over a wide area. An upper sliding plate 8 made of a material with excellent sliding properties, such as a stainless steel plate, is attached to the lower surface (notation omitted) of the upper contact portion 11c (an example of "the other of the upper contact portion and the lower contact portion").

[0021] The lower support portion 12 is composed of a ring-shaped base plate 12a and a disk-shaped metallic lower abutment portion 12b that is bolted to the upper surface of the base plate 12a, and is configured so that the lower bead portion 13b, which is the lower part of the diaphragm 13, is placed on and supported by a lower receiving seat 19 that is fixed to the outer periphery of the base plate 12a. A fluororesin sliding sheet 1 is attached to the upper side of the lower abutment portion 12b (an example of "either the upper abutment portion or the lower abutment portion"). The lower receiving seat 19 is composed of a steel plate reinforcing portion 21 and a rubber receiving member 22 that is laminated on it.

[0022] The base 14 is formed of a cylindrical shaft 23 having the same axis P as the support shaft 11d, and a flange plate 24 that is integrally fitted to the upper part of the cylindrical shaft 23, and the cylindrical shaft 23 is supported by a bogie frame (not shown). The laminated rubber part d is a hollow structure of a known structure in which multiple cylindrical elastic layers 25 made of rubber and hard plates 26 made of metal are alternately stacked and integrated between the upper and lower parts of the flange plate 24 of the base 14 and the base plate 12a of the lower support part 12. The cylindrical shaft 23 is placed and supported on the bogie frame (not shown) by being fitted into a shaft hole (not shown) formed in the bogie frame (not shown).

[0023] 1 and 2, a stopper S is configured in which the upper contact portion 11c and the lower contact portion 12b come into contact with each other as the upper support portion 11 and the lower support portion 12 move relatively close to each other in the vertical direction by a predetermined amount. The lower contact portion 12b is provided with a sliding sheet 1 that can come into contact with the upper contact portion 11c. The stopper S is configured in such a way that the upper contact portion 11c and the lower contact portion 12b come into contact with each other via the upper sliding plate 8 and the sliding sheet 1. Note that the stopper S may be configured in such a way that the upper contact portion 11c comes into contact with the sliding sheet 1.

[0024] 2(A) and (B), a movement restriction mechanism K is provided that restricts the relative movement of the lower contact portion 12b and the sliding sheet 1 in the radially inward and radially outward directions with respect to the axis P. The lower contact portion 12b is formed with a circumferential mounting recess 6 having a bottom surface 6a that is one step lower than the top surface 5, a central hole 7, and six mounting holes 9 that open into the mounting recess 6. The mounting holes 9, which are arranged at equal angles around the axis P, are holes for bolting the base plate 12a and the lower contact portion 12b.

[0025] In the mounting recess 6, three arc-shaped sliding sheets 1 are provided at equal angles around the axis P, with three mounting holes 9 at every other location. A notch 1a is formed in the circumferential center of each arc-shaped sliding sheet 1, which opens to the outer periphery and avoids the mounting holes 9. Each sliding sheet 1 is bonded in a fitted state to the mounting recess 6 so that it cannot move in the radial direction. In other words, the radially inner end 1b of the sliding sheet 1 faces the inner wall 2 of the mounting recess 6, and the radially outer end 1c of the sliding sheet 1 faces the outer wall 3 of the mounting recess 6 (see Figure 7(A)).

[0026] The movement restricting mechanism K is configured by providing the lower contact portion 12b with an inner wall 2 that contacts the inner diameter end 1b of the sliding sheet 1 with respect to the axis P and an outer wall 3 that contacts the outer diameter end 1c, respectively, in a state having a height h less than the thickness t of the sliding sheet 1. The height h of the inner wall 2 and the outer wall 3 (the depth of the mounting recess 6) and the thickness t of the sliding sheet 1 are set to 0.3t ≦ h < t. The inner wall 2 and the outer wall 3 are arc-shaped walls with respect to the axis P.

[0027] When the air spring A deflates due to a puncture or the like of the diaphragm 13, the upper support portion 11 descends and the stopper S where the upper sliding plate 8 and the sliding sheet 1 come into contact functions, and the upper support portion 11 does not descend any further and is configured to be in a suspended state supported by the elastic portion 15. When the air spring A deflates, during driving to the garage or during driving until the business closing time on that day, the air spring portion c is displaced, and the stopper S, that is, the upper sliding plate 8 and the sliding sheet 1 rub horizontally while receiving a load.

[0028] As shown in FIGS. 2 and 7(A), since the inner diameter end 1b and the outer diameter end 1c, which are most of the periphery of the arc-shaped sliding sheet 1, are physically constrained by the inner wall 2 and the outer wall 3, even if it is strongly rubbed against the upper sliding plate 8 in a state of receiving a load, the sliding sheet 1 does not peel off from the lower contact portion 12b (from the mounting recess 6) and a state with excellent durability in which it functions is obtained. In this case, if the ratio of the height h of the inner wall 2 and the outer wall 3 to the thickness t of the sliding sheet 1 is less than 30%, there is a risk that the sliding sheet 1 will move or peel off early. The risk increases as the ratio decreases.

[0029] For example, the thickness t of the sliding sheet 1 and the height h of the wall are effective as the movement restricting mechanism K even when h = 0.95t, but it is predicted that the durability will be affected because the sliding sheet 1 will stop functioning when its thickness decreases by 5%. Furthermore, if the thickness t of the sliding sheet 1 is small relative to the wall height h, there is a risk that the contact portion (for example, the portion (metal portion) radially outer than the sliding sheet 1 on the upper surface 5) will come into contact when tilted, so a certain thickness or more is considered necessary to ensure contact with the sliding sheet 1. Therefore, taking into account the durability and inclination of the sliding sheet 1, the realistic relationship between the thickness t of the sliding sheet 1 and the wall height h is thought to be approximately 0.3t≦h<0.7t, and preferably 0.3t≦h<0.6t or 0.35t≦h<0.55t.

[0030] [Embodiment 2] An air spring A according to embodiment 2 is shown in Fig. 3. This air spring A is basically the same as the air spring A according to embodiment 1 shown in Fig. 1, and corresponding parts are given the same reference numerals and their explanations are omitted, and only different parts will be explained.

[0031] The upper support part 11 is composed of a support part main body 11e having a circular shape when viewed from the direction of the axis P, a ring-shaped bead retainer 11f bolted to the outer circumferential underside of the support part main body 11e, and a support shaft 11d, etc. An upper sliding plate 8 made of a material having excellent sliding properties is provided on an upper contact part 11c which is the underside of the support part main body 11e.

[0032] 3 and 4, the lower support part 12 is composed of an open-ring-shaped base plate 12a and a lower abutment part 12b that is housed on the upper surface inside the base plate 12a and is bolted at one point passing through the axis P. A lower bead part 13b, which is the lower part of the diaphragm 13, is placed on a lower support seat 19 formed on the outer periphery of the base plate 12a and is received and supported. The base plate 12a is bolted to the uppermost hard plate 28 of the elastic part 15 of the laminated rubber structure.

[0033] 3 and 4(A) and (B), the lower contact portion 12b has a laminated rubber structure made up of upper and lower hard plates 10, 10 and an elastic layer 17 between the upper and lower hard plates 10, 10. A cylindrical boss 18 having an axis P is provided on the upper hard plate 10 made of a circular steel plate or the like, and an axial bolt 10a having an axis P is provided in a downwardly protruding state on the lower hard plate 10 made of a circular steel plate or the like. A female thread portion 18a is formed penetrating the inside of the boss 18.

[0034] A peripheral outer wall 3 is formed at the outer circumferential end of the upper hard plate 10, the radial length of which is small relative to the axis P and which protrudes slightly upward, and the boss 18 is fixed to the upper hard plate 10 with its upper end protruding slightly upward beyond the upper surface 10b of the upper hard plate 10. The height of the outer wall 3 and the boss 18 relative to the upper surface 10b are both h.

[0035] Each of the sliding sheets 1, 1 having a substantially semicircular shape (semicircular arc shape) is provided on the upper hard plate 10 with its radially inner end 1b abutting against the inner wall 2, which is the outer peripheral surface of the boss 18, and its radially outer end 1c abutting against (the inner peripheral surface of) the outer wall 3. The thickness t of the sliding sheet 1 is greater than the height h of the inner wall 2 and the outer wall 3 (t>h).

[0036] 7(B), the height h of the outer wall 3 of the upper hard plate 10 from the top surface 10b and the protruding height h of the boss 18 from the top surface 10b are set to 30% or more and 70% or less (0.3t≦h<0.7t) of the thickness t of the sliding sheet 1. In the air spring A of the second embodiment as well, the movement restricting mechanism K is configured by providing the inner wall 2 abutting against the radially inner end 1b with respect to the axis P of the sliding sheet 1 and the outer wall 3 abutting against the radially outer end 1c at the lower abutment portion 12b, respectively, with a height h less than the thickness t of the sliding sheet 1.

[0037] [Embodiment 3] The air spring A according to Embodiment 3 is shown in FIG. 5. This air spring A is basically the same as the air spring A according to Embodiments 1 and 2 shown in FIGS. 1 and 3, and the corresponding parts are denoted by the same reference numerals and the description thereof is omitted, and the different parts will be described.

[0038] As shown in FIGS. 5 and 6, the lower support portion 12 is composed of only a lower contact portion 12b that covers the uppermost rigid plate 28 from above and is bolted to the uppermost rigid plate 28. The lower bead portion 13b, which is the lower part of the diaphragm 13, is placed on and received and supported by the lower seat 19 formed on the outer peripheral portion of the lower contact portion 12b.

[0039] Two mounting holes 9, 9 and a center hole 20 are formed in the lower support portion 12, and four fitting recesses 4 and two long grooves 27 are formed on the upper surface side. The fitting recesses 4 and the long grooves 27 are portions recessed (dropped) downward from the upper surface 12c of the lower support portion 12. Each fitting recess 4 is a portion recessed by a depth h in a rectangular shape (rounded square) with sides facing the axis P, and the sliding sheet 1 having the same shape and the same dimensions in plan view is provided in the fitting recess 4 in a state of being adhered to the bottom surface 4a.

[0040] That is, as shown in FIGS. 6 and 7(C), the movement restricting mechanism K of the air spring A according to Embodiment 3 is configured by providing the lower contact portion 12b with fitting recesses 4 having a depth h less than the thickness t of the sliding sheet 1 and into which the sliding sheet 1 is fitted. The four fitting recesses 4 are dispersedly arranged at equal angles in the circumferential direction with respect to the axis P.

[0041] The inner peripheral wall 4b of the fitting recess 4 and the lower part of the outer peripheral wall 1d of the sliding sheet 1 are in contact (close contact, or opposed without a gap or opposed with a small gap), and the depth h of the fitting recess 4 is set to 30% or more of the thickness t of the sliding sheet 1. Specifically, the depth h is 30% or more and less than 100% of the thickness t (0.3t ≦ h < t), and actually, it is set to 30% or more and 70% or less (0.3t ≦ h ≦ 0.7t).

[0042] 〔Regarding the effects〕 As described above, in the air spring A according to the present invention, a sliding sheet 1 capable of contacting the other of the upper abutment portion 11c and the lower abutment portion 12b is provided on either the upper abutment portion 11c or the lower abutment portion 12b, and a movement restriction mechanism K is provided to restrict relative movement of the either one 12b and the sliding sheet 1 radially inward and outward with respect to the axis P of the diaphragm 13.

[0043] A stopper S is provided to suppress the amount of descent of the upper support part 11 so that even if the diaphragm 13 deflates, the cushioning effect of the laminated rubber part d will enable the car to run to the garage or continue commercial running for that day. The sliding sheet 1, which is a component of the stopper S, was previously attached to the upper contact part in a state in which it was prevented from moving radially outward, but with this structure, depending on the conditions, the sliding sheet 1 could shift radially inward, which could cause it to peel off or become damaged.

[0044] The movement restriction mechanism K according to embodiments 1 to 3 prevents at least the sliding sheet 1 from slipping in both the radially inward and outward directions. Therefore, even if the air spring A is used in a deflated state in which the upper sliding plate 8 (or the upper abutment portion 11c) and the sliding sheet 1 rub against each other strongly, the movement restriction mechanism K prevents slippage in both directions of movement when the sheet 1 rubs against each other, thereby preventing problems such as slippage or peeling off of the sliding sheet 1.

[0045] [Another embodiment] For example, in the air spring A shown in Fig. 3 or 4, two sliding sheets 1, 1 may be connected to provide one doughnut-shaped sliding sheet 1. In this case, the movement restricting mechanism K restricts the relative movement of the sliding sheet 1 in the radially inward and radially outward directions, but at the same time, the sliding sheet 1 is fitted into the lower contact portion 12b.

[0046] The number of sliding sheets 1 may be three or five or more for the air spring. In addition, the material of the sliding sheet 1 may be any material with a low friction coefficient, such as a synthetic resin material other than fluororesin.

[0047] [Reference information] For reference, data from the slippage durability test is shown in Fig. 8. The chart in Fig. 8 shows data indicating the maximum number of times the test specimen (sliding sheet) peels off in relation to the thickness t of the sliding sheet 1 and the height (groove depth) h of the inner wall 2 and the outer wall 3 in the air spring having the structure (embodiment 2) shown in Figs. 3 and 4. That is, although not shown in the figure, a slippage durability test was conducted in which a jig simulating the upper sliding plate 8 was brought into contact with the upper surface of the sliding sheet 1 from above with a predetermined load, and the lower support part 12 was repeatedly moved back and forth from side to side (laterally).

[0048] In the graph of Figure 8, the number of cycles refers to the number of times the above-mentioned back and forth movement was repeated, and the range of cycles at which peeling (delamination) occurred from the upper surface 10b of the hard plate 10 of the sliding sheet 1 is marked as ×, and any range below that is marked as ◯. The thickness t of the sliding sheet 1 is constant at 2.4 mm, and data is taken for three heights h of the inner wall 2 and the outer wall 3: 0.5 mm, 1.0 mm, and 1.2 mm. The number of cycles indicates the maximum number of cycles in that range, for example, "200" indicates a range of 101 to 200 cycles.

[0049] According to Figure 8, when the height h of the inner and outer walls 2, 3 was 0.5 mm, peeling of the sliding sheet 1 occurred between 101 and 200 cycles, and when the height h of the inner and outer walls 2, 3 was 1.0 mm, peeling of the sliding sheet 1 occurred between 601 and 700 cycles. When the height h of the inner and outer walls 2, 3 was 1.2 mm, the sliding sheet 1 did not peel off up to 1000 cycles (0.5 / 2.4=approximately 20.8%, 1.0 / 2.4=approximately 41.7%, 1.2 / 2.4=50%). [Explanation of symbols]

[0050] 1 Slippery sheet 2. Inner wall 3 Outer wall 4. Fitting recess 11 Upper support part 11c Upper contact part 12 Lower support part 12b Lower contact part 13 Diaphragm K Movement control mechanism P axis center S stopper

Claims

1. An air spring having an upper support portion on a car body side, a lower support portion on a bogie side arranged below the upper support portion, and a diaphragm made of a flexible material and disposed across the upper support portion and the lower support portion, a stopper is formed in which an upper contact portion of the upper support portion and a lower contact portion of the lower support portion come into contact with each other as the upper support portion and the lower support portion move relatively closer to each other in the up-down direction by a predetermined amount, a sliding sheet capable of contacting the other of the upper contact portion and the lower contact portion is provided on one of the upper contact portion and the lower contact portion; a movement restriction mechanism is provided to restrict relative movement between the one of the two and the sliding sheet in the radially inward and radially outward directions with respect to the axis of the diaphragm, The sliding sheet is a sheet material made of a fluororesin, The sliding sheet is adhered to either one of the above, The movement restriction mechanism is an air spring configured by providing a side wall on either one of the two sides, the side wall having a height less than the thickness of the sliding sheet and abutting against a side edge of the sliding sheet.

2. The air spring according to claim 1, wherein the movement restricting mechanism is configured by providing, on either one of the sliding sheets, an inner wall abutting the radially inner end relative to the axis of the sliding sheet and an outer wall abutting the radially outer end thereof, each having a height less than the thickness of the sliding sheet.

3. The air spring according to claim 2 , wherein the inner wall and / or the outer wall is formed into an arc-shaped wall with respect to the axis.

4. 2. The air spring according to claim 1, wherein the movement restriction mechanism is configured by providing a fitting recess in either one of the springs, the fitting recess having a depth less than a thickness of the sliding sheet and into which the sliding sheet is fitted.

5. The air spring according to claim 4 , wherein a plurality of the fitting recesses are disposed in a distributed manner in a circumferential direction about the axis.

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