Vehicle seats

Abstract

To provide a vehicular seat comprising a vibration suppression function on a coupling structure at low cost.SOLUTION: There is provided a vehicular seat comprising a cushion frame. The cushion frame comprises: a first member; a second member; and a coupling structure for coupling the first and second members. The coupling structure comprises: a cylindrical first collar fixed to the first member; a cylindrical second collar inserted into an inside of the first collar; a bolt inserted into the second collar; a first elastic body provided between the first collar and the second member, in an axial direction of the bolt; and a second elastic body held by the first and second collars in a bolt radial direction. An inner diameter of the first collar is varied along the axial direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to vehicle seats. [Background technology]

[0002] In a cushion frame for a vehicle seat, a connecting structure using bolts and nuts is used to connect two members (see Patent Document 1). In this connecting structure, an elastic body such as rubber is inserted between two coaxially arranged cylindrical bodies (i.e., collars) to suppress the transmission of vibration. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-26507 Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-described connecting structure, flange-like locking portions are provided on both ends of the elastic body to prevent it from slipping out of the collar. This makes it difficult to insert the elastic body. Furthermore, the molding process is complicated, requiring multiple die-cutting operations during molding of the elastic body. As a result, the manufacturing cost of the vehicle seat increases.

[0005] An object of one aspect of the present disclosure is to provide a vehicle seat that can provide a vibration suppression function to a connecting structure at low cost. [Means for solving the problem]

[0006] One aspect of the present disclosure is a vehicle seat (1) including a seat cushion (2) and a cushion frame (4) that supports the seat cushion (2). The cushion frame (4) has a first member (41), a second member (42), and a connecting structure (46) that connects the first member (41) and the second member (42).

[0007] The connecting structure 46 includes a cylindrical first collar 412 fixed to the first member 41, a cylindrical second collar 422 inserted inside the first collar 412, a bolt 461 inserted through the second collar 422, a nut 462 threaded onto the bolt 461, a first elastic body 464 disposed between the first collar 412 and the second member 42 in the axial direction of the bolt 461, and a second elastic body 465 sandwiched between the first collar 412 and the second collar 422 in the radial direction of the bolt 461. The inner diameter of the first collar 412 varies along the axial direction.

[0008] With this configuration, because the inner diameter of the first collar (412) varies in the axial direction, the second elastic body (465) is held by frictional force at the portion of the first collar (412) where the inner diameter is smallest. Therefore, detachment of the second elastic body (465) can be prevented without providing a flange-shaped locking portion on the second elastic body (465). As a result, the second elastic body (465) can be easily inserted between the first collar (412) and the second collar (422), and the molding cost of the second elastic body (465) can be reduced.

[0009] In one aspect of the present disclosure, the first collar (412) may have a contact portion (412A) that contacts the second elastic body (465) in the radial direction of the bolt (461) and a facing portion (412B) that is spaced apart from the second elastic body (465) and faces the second elastic body (465) in the radial direction of the bolt (461). The length of the contact portion (412A) along the axial direction of the first collar (412) may be smaller than the length of the facing portion (412B) along the axial direction of the first collar (412). With this configuration, the contact area between the first collar (412) and the second elastic body (465) is reduced, thereby suppressing the influence of the vibration characteristics of the second elastic body (465) on the vibration characteristics of the first elastic body (464). As a result, the vibration suppression performance of each of the first elastic body (464) and the second elastic body (465) can be improved.

[0010] In one embodiment of the present disclosure, the first collar (412) may have a tapered portion (412B) whose inner diameter changes continuously along the axial direction of the first collar (412). Such a configuration facilitates the insertion of the second elastic body (465).

[0011] In one embodiment of the present disclosure, the first collar (412) may have a step portion (412D) whose inner diameter changes discontinuously along the axial direction of the first collar (412). This configuration can improve the retention effect of the second elastic body (465).

[0012] Note that the symbols in the parentheses above are examples showing the correspondence with the specific configurations, etc. described in the embodiments described below, and the present disclosure is not limited to the specific configurations, etc. shown by the symbols in the parentheses above. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic perspective view showing a vehicle seat according to an embodiment. [Figure 2] FIG. 2 is a schematic perspective view of a cushion frame in the vehicle seat of FIG. [Figure 3] FIG. 3 is a schematic side view showing a part of the cushion frame of FIG. [Figure 4] 4 is a schematic exploded perspective view of the first connecting structure and the second connecting structure of the cushion frame of FIG. 2. FIG. [Figure 5] FIG. 5 is a schematic cross-sectional end view taken along line VV in FIG. [Figure 6] 6A is a schematic perspective view of an elastic member in the first connecting structure of FIG. 4, and FIG. 6B is a schematic perspective view of a third elastic body in the first connecting structure of FIG. [Figure 7] FIG. 7 is a schematic cross-sectional end view showing an enlarged view of the first collar and its vicinity in FIG. [Figure 8] 8A and 8B are enlarged schematic cross-sectional end views of the first collar and its vicinity in an embodiment different from that shown in FIG. [Figure 9]FIG. 9 is a schematic cross-sectional end view showing an enlarged view of the vicinity of the first collar in an embodiment different from that shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings. [1. First embodiment] [1-1.Configuration] The vehicle seat 1 shown in FIG. 1 includes a seat cushion 2, a seat back 3, a cushion frame 4, a back frame 5, a seat belt 6, a belt anchor 7, and a retractor 8.

[0015] The vehicle seat 1 is used as a seat for a passenger vehicle. Note that the directions in the following description and in each drawing refer to directions when the vehicle seat 1 is assembled to the vehicle (i.e., the passenger vehicle). In this embodiment, the width direction of the seat coincides with the left-right direction of the vehicle, and the front of the seat coincides with the front of the vehicle.

[0016] The seat cushion 2 is a portion for supporting the buttocks of a seated person. The seat back 3 is a portion for supporting the back of a seated person. The cushion frame 4 supports the seat cushion 2. The back frame 5 supports the seat back 3.

[0017] The seat belt 6 is worn by the seat occupant by being stretched from one shoulder of the seat back 3 (the right shoulder in this embodiment) across the seat back 3 in the seat width direction to the seat width direction end of the seat cushion 2 (the left end in this embodiment).

[0018] The belt anchor 7 is a guide that pulls the seat belt 6 out from the inside of the seat back 3 and pulls the seat belt 6 back into the inside of the seat back 3. The belt anchor 7 is attached to the back frame 5.

[0019] The retractor 8 is a device that retracts the seat belt 6. The retractor 8 is held by the back frame 5 inside the seat back 3. The seat belt 6 is stretched between the retractor 8 and a belt anchor 7 inside the seat back 3.

[0020] <Cushion frame> As shown in FIG. 2, the cushion frame 4 includes a first side frame 41, a leg 42, a second side frame 43, and a plurality of connecting rods 44A, 44B, and 44C.

[0021] The first side frame 41 and the second side frame 43 each extend in the front-rear direction and are spaced apart from each other in the seat width direction. The leg 42 is connected to a lower end of the first side frame 41. A plurality of connecting rods 44A, 44B, and 44C each connect the first side frame 41 and the second side frame 43 in the seat width direction.

[0022] As shown in FIG. 3, the first side frame 41 and the leg 42 are connected in the vertical direction by a first connecting structure 46 and a second connecting structure 47.

[0023] 4, the first side frame 41 has a side panel 411. The leg 42 has a leg panel 421. The leg panel 421 has a first opening 421A and a second opening 421B through which the bolt 461 is inserted.

[0024] <First connection structure> The first connecting structure 46 has a first collar 412, a second collar 422, a bolt 461, a nut 462, an auxiliary member 463, a first elastic body 464, a second elastic body 465, and a third elastic body 466. The first elastic body 464 and the second elastic body 465 constitute an elastic member 467.

[0025] The first collar 412 is a cylindrical member fixed, for example, by welding, to a bottom wall 411A of the side panel 411 that extends in the seat front-rear direction (that is, has a plate surface that intersects with the up-down direction).

[0026] The first collar 412 penetrates the bottom wall 411A in the thickness direction. The second collar 422 and the bolt 461 are inserted through the first collar 412. The detailed shape of the first collar 412 will be described later.

[0027] The second collar 422 is a cylindrical member arranged on the upper surface of the leg panel 421 so that its hollow portion communicates with the first opening 421A. The second collar 422 has a disk-shaped flange 422A that contacts the leg panel 421, and a cylindrical main body 422B that extends upward (i.e., toward the first side frame 41) from the flange 422A.

[0028] The main body 422B of the second collar 422 is inserted inside the first collar 412 and penetrates the first side frame 41. The axial upper end of the main body 422B is positioned higher than the axial upper end of the first collar 412. A bolt 461 is inserted through the second collar 422. In addition, the second collar 422 is not directly fixed to the leg panel 421.

[0029] The bolt 461 is inserted through the first side frame 41 and the leg 42. In detail, the bolt 461 is inserted through the leg panel 421, the second collar 422, the elastic member 467, the first collar 412, the third elastic body 466, the auxiliary member 463, and the nut 462.

[0030] The head of the bolt 461 is located on the opposite side of the leg 42 from the first side frame 41 (i.e., below the leg 42). The bolt 461 is inserted from the leg 42 side when assembling the cushion frame 4. In this embodiment, the head of the bolt 461 contacts the leg panel 421 from below.

[0031] The nut 462 is threadedly engaged with the bolt 461. The nut 462 is disposed at a position where the nut 462 and the leg 42 sandwich the first side frame 41 in the axial direction of the bolt 461 (i.e., above the first side frame 41). In this embodiment, the nut 462 contacts the auxiliary member 463 from above.

[0032] Auxiliary member 463 is a disk-shaped member having an opening at the center through which bolt 461 is inserted. The inner diameter of auxiliary member 463 is smaller than the inner diameter of main body 422B of second collar 422. The outer diameter of auxiliary member 463 is larger than the outer diameter of third elastic body 466.

[0033] 5, the auxiliary member 463 is disposed so as to sandwich the second collar 422 together with the leg 42 in the axial direction of the bolt 461. In addition, an elastic member 467, a side panel 411, a first collar 412, and a third elastic body 466 are disposed between the auxiliary member 463 and the leg 42. The upper end of the main body 422B of the second collar 422 in the axial direction contacts the lower surface of the auxiliary member 463.

[0034] The first elastic body 464 is a cylindrical member through which the bolt 461 is inserted. The first elastic body 464 is made of, for example, rubber. The first elastic body 464 is disposed between the first collar 412 and the leg 42 in the axial direction of the bolt 461.

[0035] Specifically, the first elastic body 464 is disposed between the lower end of the first collar 412 and the flange 422A of the second collar 422 in the axial direction of the bolt 461, and is in contact with the lower end of the first collar 412 and the flange 422A.

[0036] By fastening the bolt 461 and the nut 462, the first elastic body 464 is compressed in the axial direction of the bolt 461 by the flange portion 422A of the second collar 422 and the lower end portion of the first collar 412 in the axial direction. The first elastic body 464 is provided over the entire circumferential direction of the bolt 461.

[0037] The second elastic body 465 is a cylindrical member through which the bolt 461 is inserted. The second elastic body 465 is formed integrally with the first elastic body 464. In other words, the first connecting structure 46 has an elastic member 467 in which the first elastic body 464 and the second elastic body 465 are integrated.

[0038] The lower end portion of the second elastic body 465 in the axial direction is connected to the first elastic body 464 in the radial direction of the bolt 461. The elastic member 467 is fixed to the second collar 422 by, for example, adhesive.

[0039] The second elastic body 465 is sandwiched between the first collar 412 and the second collar 422 in the radial direction of the bolt 461. Specifically, the inner peripheral surface of the second elastic body 465 is in contact with the outer peripheral surface of the main body 422B of the second collar 422, and the outer peripheral surface of the second elastic body 465 is in contact with the inner peripheral surface of the first collar 412. The second elastic body 465 is inserted into the internal space of the first collar 412 in a state where it is attached to the second collar 422.

[0040] The upper end portion of the second elastic body 465 in the axial direction is located higher than the upper end portion of the first elastic body 464. In other words, the axial length of the second elastic body 465 is greater than the axial length of the first elastic body 464. In addition, the upper end portion of the second elastic body 465 in the axial direction is separated from the auxiliary member 463.

[0041] 6A, second elastic body 465 has holding portion 465A and a plurality of protrusions 465B. Holding portion 465A is a cylindrical portion. The outer circumferential surface of holding portion 465A does not contact first collar 412.

[0042] The multiple protrusions 465B are arranged at regular intervals in the circumferential direction of the holding portion 465A. The protrusions 465B are portions that protrude radially outward from the outer circumferential surface of the holding portion 465A. The protrusions 465B are compressed in the radial direction of the holding portion 465A by the second collar 422 and the first collar 412.

[0043] The multiple protrusions 465B extend in the axial direction of the second elastic body 465 from the lower end to the upper end of the second elastic body 465. The thickness of the protrusions 465B is constant along the axial direction. It is also preferable that the number of protrusions 465B is an odd number. Having an odd number of protrusions 465B makes it easier for the second elastic body 465 to be centered. As a result, the vibration suppression effect is improved.

[0044] The third elastic body 466 shown in Fig. 6B is a ring-shaped member through which the bolt 461 is inserted. The material of the third elastic body 466 is, for example, rubber. As shown in Fig. 5, the third elastic body 466 is disposed between the first collar 412 and the auxiliary member 463 in the axial direction of the bolt 461, and is in contact with the first collar 412 and the auxiliary member 463. The third elastic body 466 is fixed to the lower surface of the auxiliary member 463 by, for example, adhesive.

[0045] The third elastic body 466 has a base portion 466A and a guide portion 466B. The base portion 466A is compressed in the axial direction of the bolt 461 by the upper end portion of the first collar 412 in the axial direction and the lower surface of the auxiliary member 463 due to the fastening of the bolt 461 and the nut 462.

[0046] Guide portion 466B protrudes from base portion 466A in the axial direction of first collar 412 and surrounds the radially outer side of first collar 412. Specifically, guide portion 466B is a cylindrical portion protruding downward from the lower surface of base portion 466A.

[0047] The outer peripheral surface of the first collar 412 is in contact with the inner peripheral surface of the guide portion 466B. In other words, the first collar 412 is inserted into the guide portion 466B. The base portion 466A and the guide portion 466B are each provided over the entire circumferential direction of the bolt 461.

[0048] First collar 412 is sandwiched between first elastic body 464 and third elastic body 466 in the axial direction of bolt 461. Therefore, there is no gap between auxiliary member 463 and flange 422A of second collar 422 that communicates with the interior of first collar 412. In other words, the internal space of first collar 412 is sealed by auxiliary member 463, third elastic body 466, first elastic body 464, and second collar 422.

[0049] The spring constant of the third elastic body 466 is greater than the spring constant of the first elastic body 464 (i.e., the elastic member 467). In other words, the third elastic body 466 is harder and less likely to deform than the first elastic body 464. Therefore, the third elastic body 466 has a greater ability to restrict the input of load than the first elastic body 464. In addition, the third elastic body 466 also exerts the effect of suppressing abnormal noise caused by vibrations in the first connecting structure 46.

[0050] <First color shape> 7, the inner diameter of first collar 412 varies along the axial direction. Specifically, first collar 412 has a contact portion 412A and an opposing portion 412B.

[0051] Contact portion 412A is a portion that contacts convex portion 465B of second elastic body 465 in the radial direction of bolt 461, and compresses second elastic body 465 together with second collar 422. The inner diameter of contact portion 412A is constant along the axial direction of first collar 412. Contact portion 412A is the portion of first collar 412 where the inner diameter is smallest.

[0052] The facing portion 412B is a portion that is separated from the second elastic body 465 in the radial direction of the bolt 461 and faces the second elastic body 465. The facing portion 412B is provided below the contact portion 412A. In other words, the facing portion 412B is provided continuously at a position closer to the first elastic body 464 than the contact portion 412A in the axial direction of the bolt 461.

[0053] The facing portion 412B is a tapered portion whose inner diameter changes continuously along the axial direction of the first collar 412. Specifically, the inner diameter of the facing portion 412B increases downward so that the distance from the second elastic body 465 increases.

[0054] The internal space of the facing portion 412B expands in diameter toward the end (i.e., the lower end) into which the second elastic body 465 is inserted. Such a tapered portion of the facing portion 412B facilitates the insertion of the second elastic body 465.

[0055] The length L1 of the contact portion 412A along the axial direction of the first collar 412 is smaller than the length L2 of the opposing portion 412B along the axial direction of the first collar 412. The length L1 of the contact portion 412A along the axial direction of the first collar 412 is preferably between 1 / 3 and 1 / 2 of the total length of the first collar 412 along the axial direction.

[0056] 8A, first collar 412 may further have an upper tapered portion 412C whose inner diameter continuously increases upward. A portion of upper tapered portion 412C faces second elastic body 465 in the radial direction of bolt 461. In the example of FIG. 8A, contact portion 412A of first collar 412 is sandwiched between facing portion 412B (i.e., lower tapered portion) and upper tapered portion 412C in the axial direction of first collar 412.

[0057] 8B, instead of the tapered portion, first collar 412 may have first step portion 412D and second step portion 412E whose inner diameter changes discontinuously along the axial direction of first collar 412. First step portion 412D and second step portion 412E are provided at the respective continuous portions between contact portion 412A and two opposing portions 412B.

[0058] 8B, the two facing portions 412B are provided above and below the contact portion 412A, respectively. The contact portion 412A is provided at a position closer to the first elastic body 464 in the axial direction of the bolt 461 than the upper facing portion 412B. In addition, the inner diameters of the two facing portions 412B are constant along the axial direction. By providing such first step portion 412D and second step portion 412E, the holding effect of the second elastic body 465 can be improved.

[0059] 9, the lower facing portion 412B in Fig. 8B may be configured as a tapered portion. The inner diameter of the lower facing portion 412B increases downward so that the distance to the second elastic body 465 increases.

[0060] <Second connection structure> The second connecting structure 47 shown in FIG. 4 has a first collar 412, a second collar 422, a bolt 461, a nut 462, an auxiliary member 463, an elastic member 467 (i.e., a first elastic body 464 and a second elastic body 465), and a third elastic body 466, which are similar to the first connecting structure 46.

[0061] The second connecting structure 47 connects the first side frame 41 and the leg 42 in the up-down direction, further forward of the seat than the first connecting structure 46. The axial direction of the bolt 461 in the second connecting structure 47 is the same as that of the first connecting structure 46. Furthermore, other configurations are also the same as those of the first connecting structure 46, and therefore description thereof will be omitted.

[0062] [1-2.Effects] According to the embodiment described above in detail, the following effects can be obtained. (1a) Because the inner diameter of the first collar 412 changes in the axial direction, the second elastic body 465 is held by frictional force at the portion of the first collar 412 where the inner diameter is smallest. Therefore, detachment of the second elastic body 465 can be suppressed without providing a flange-shaped locking portion on the second elastic body 465. As a result, the second elastic body 465 can be easily inserted between the first collar 412 and the second collar 422, and the molding cost of the second elastic body 465 can be reduced.

[0063] (1b) The length L1 of the contact portion 412A is smaller than the length L2 of the facing portion 412B, thereby reducing the contact area between the first collar 412 and the second elastic body 465. This reduces the influence of the vibration characteristics of the second elastic body 465 on the vibration characteristics of the first elastic body 464. As a result, the vibration suppression performance of each of the first elastic body 464 and the second elastic body 465 can be improved.

[0064] 2. Other Embodiments Although the embodiments of the present disclosure have been described above, it goes without saying that the present disclosure is not limited to the above-described embodiments and can take on various forms.

[0065] (2a) In the vehicle seat of the above embodiment, the position at which the connecting structure is provided is not limited to the position described above. For example, the connecting structure may be provided on the second side frame. Furthermore, the components connected by the connecting structure are not limited to the side frame and the leg. For example, the connecting structure may connect the side frame and the slide rail. Furthermore, the connecting direction in the connecting structure is not limited to the vertical direction, but may be a direction intersecting the vertical direction (for example, the horizontal direction).

[0066] (2b) In the vehicle seat of the above embodiment, the first elastic body and the third elastic body do not necessarily have to be cylindrical or annular. For example, the first elastic body and the third elastic body may have a notch in a portion in the circumferential direction. Furthermore, the connecting structure does not necessarily have to include the auxiliary member and the third elastic body.

[0067] (2c) In the vehicle seat of the above embodiment, the second elastic body does not necessarily have to be integrated with the first elastic body, and may be a member independent of the first elastic body.

[0068] (2d) In the vehicle seat of the above embodiment, the bolt may be inserted from the auxiliary member side (i.e., from above) during assembly of the cushion frame. The auxiliary member may be integrated with the nut or bolt. For example, an auxiliary member that contacts the second elastic body may be provided on the washer portion of the nut or the head of the bolt.

[0069] (2e) The vehicle seat of the above embodiment can also be applied to seats used in automobiles other than passenger cars, and seats used in vehicles other than automobiles, such as railway cars, ships, and aircraft.

[0070] (2f) The function of one component in the above embodiments may be distributed among multiple components, or the functions of multiple components may be integrated into one component. Also, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments. All aspects included in the technical idea identified by the wording of the claims are embodiments of the present disclosure. [Explanation of symbols]

[0071] 1...vehicle seat, 2...seat cushion, 3...seat back, 4...Cushion frame, 5...Back frame, 6...Seat belt, 7...belt anchor, 8...retractor, 41...first side frame, 42...leg, 46...first connecting structure, 47...second connecting structure, 411...side panel, 411A...bottom wall, 412...first collar, 412A...contact portion, 412B...opposing portion, 412C...upper tapered portion, 412D, 412E...step portion, 421...leg panel, 421A...first opening, 421B...second opening, 422...second collar, 422A...flange portion, 422B...Main body, 461...Bolt, 462...Nut, 463...Auxiliary member, 464...first elastic body, 465...second elastic body, 465A...holding portion, 465B...protrusion, 466...third elastic body, 466A...base portion, 466B...guide portion, 467...elastic member.

Claims

1. Seat cushion and a cushion frame supporting the seat cushion; Equipped with The cushion frame is A first member; A second member; a connecting structure that connects the first member and the second member; and The connecting structure is a cylindrical first collar fixed to the first member; a cylindrical second collar inserted inside the first collar; a bolt inserted through the second collar; a nut threaded onto the bolt; a first elastic body disposed between the first collar and the second member in the axial direction of the bolt; a second elastic body sandwiched between the first collar and the second collar in the radial direction of the bolt; and The first collar has an inner diameter that varies along the axial direction, The second elastic body has a plurality of protrusions that protrude radially outward.

2. Seat cushion and a cushion frame supporting the seat cushion; Equipped with The cushion frame is A first member; A second member; a connecting structure that connects the first member and the second member; and The connecting structure is a cylindrical first collar fixed to the first member; a second collar having a cylindrical main body inserted inside the first collar and a disk-shaped flange protruding outward from the main body; a bolt inserted through the second collar; a nut threaded onto the bolt; a first elastic body disposed between the first collar and the second member in the axial direction of the bolt; a second elastic body sandwiched between the first collar and the flange portion of the second collar in the radial direction of the bolt; and The vehicle seat, wherein the first collar has an inner diameter that changes along the axial direction.

3. Seat cushion and a cushion frame supporting the seat cushion; Equipped with The cushion frame is A first member; A second member; a connecting structure that connects the first member and the second member; and The connecting structure is a cylindrical first collar fixed to the first member; a cylindrical second collar inserted inside the first collar; a bolt inserted through the second collar; a nut threaded onto the bolt; a first elastic body disposed between the first collar and the second member in the axial direction of the bolt; a second elastic body sandwiched between the first collar and the second collar in the radial direction of the bolt; and The first color is a contact portion that contacts the second elastic body in the radial direction of the bolt; an opposing portion that is spaced apart from the second elastic body in the radial direction of the bolt and faces the second elastic body; and The first collar has an inner diameter that varies along the axial direction, A vehicle seat, wherein a length of the contact portion along the axial direction of the first collar is smaller than a length of the opposing portion along the axial direction of the first collar.

4. The vehicle seat according to any one of claims 1 to 3, The first collar has a tapered portion whose inner diameter changes continuously along the axial direction of the first collar.

5. The vehicle seat according to any one of claims 1 to 4, The first collar has a step portion in which an inner diameter discontinuously changes along an axial direction of the first collar.

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