JP2008169953A - Connection structure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a connection structure sufficiently reducing friction by more effectively feeding a lubricant to a sliding portion by pivoting or turning. <P>SOLUTION: The connection structure is a connection structure provided with: an arm part 2; a spherical part 3 bonded to an end of the arm part 2; a support part 4 for supporting the spherical part 3 such that the arm part 2 is pivoted and turned; and storage parts 8, 9 for storing the lubricant between the support part 4 and the spherical part 3. When the arm part 2 is positioned at a predetermined pivoting or turning position, the spherical part 3 is provided with a recession part 10 opened to the storage part 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a connection structure suitable for being applied mainly to suspension devices and steering devices of vehicles such as passenger cars, trucks, buses and the like.

Conventionally, there is a ball joint as described in Patent Document 1 as a connection structure used in a suspension device that supports a knuckle that rotatably supports a vehicle wheel in a swingable manner with respect to a vehicle body. This ball joint is used to swingably connect the arm and knuckle of the suspension device, and includes a stud, a ball, a support seat, and a grease compartment, and a dimple is provided in a portion that contacts the support seat of the ball. . This dimple is provided for the purpose of reducing the friction between the ball and the support sheet as much as possible by supplying lubricant inside the grease compartment, that is, grease, to the sliding portion between the ball and the support sheet. . Such a ball joint can be similarly applied to the connection between the tie rod end of the steering device and the knuckle or the connection of the stabilizer to the knuckle.
JP 2005-188645 A

  However, in such a ball joint, since the dimples are arranged regardless of the swing or rotation position from the neutral position with respect to the support sheet of the stud, the swing or rotation of the stud with respect to the support sheet is The grease inside the grease compartment is effectively replenished to all the dimples, and the grease supplied from the grease compartment to the dimples is effectively applied to the sliding portion of the support seat and the ball based on the swing or rotation of the stud. There is a problem that it is difficult to say that the friction between the ball and the support sheet is sufficiently reduced.

  In view of the above problems, an object of the present invention is to provide a connection structure that can effectively reduce friction by supplying a lubricant to a sliding portion by swinging or rotating more effectively.

In order to solve the above problem, the connecting structure according to the present invention is:
Arms,
A spherical portion coupled to an end of the arm,
A support part for supporting the spherical part so that the arm part can swing and rotate;
A connection structure comprising a storage portion for storing a lubricant between the support portion and the spherical portion,
When the arm portion is located at a predetermined swinging or rotating position, the spherical portion includes a recess that opens to the storage portion.

  The swing means that the central axis of the arm portion is inclined from the angle formed at the neutral position with respect to the central axis of the support portion, and the rotation means that the arm portion is centered on the central axis. To rotate. The swing and the rotation are combined movements in a connection structure applied to an actual vehicle.

  Moreover, the said storage part is suitably arrange | positioned considering the friction between the said support part and the said spherical part, One may be provided and multiple places may be provided. That is, the concave portion is appropriately provided so as to open at the predetermined swing or rotation position corresponding to each of the storage portions. By providing such a recess, the following operational effects can be obtained.

  Further, the connecting structure is specifically a ball joint, and the arm portion typically indicates a stud, the spherical portion indicates a ball, and the support portion indicates a support seat. The lubricant is typically grease, and the storage portion specifically refers to a grease compartment.

Here, in the connection structure,
It is preferable that the concave portion extends including the equator of the spherical portion. The equator is a large circle having the maximum diameter extending along the outer peripheral surface of the spherical portion with the intersection of the spherical portion and the central axis of the arm portion as both poles and the line connecting the two poles as the center. .

  According to this, due to the fact that the concave portion is disposed on the equator where the relative circumferential speed and the relative circumferential displacement of the spherical portion with respect to the support portion are the largest, the arm portion swings and rotates. The relative circumferential speed and the relative circumferential displacement of the concave portion with respect to the support portion can be increased.

  As a result, the lubricant supplied from the storage part to the concave part at the predetermined position causes the spherical part to be displaced by a large relative circumferential displacement of the concave part with respect to the support part as the arm part swings or rotates. And the sliding portion between the support portion and the friction portion at the sliding portion between the spherical portion and the support portion can be effectively reduced.

here,
When the movement of the arm portion of the connection structure is dominated by swinging rather than turning,
It is preferable that the concave portion extends in the meridian direction of the spherical portion. Note that the meridian is a great circle connecting intersections of the spherical portion with the central axis of the arm portion as both poles and connecting the two poles on the outer peripheral surface of the spherical portion.

  According to this, when the movement of the arm portion is more dominant than the rotation, the recess is extended in a meridian direction parallel to the swing direction so that the arm portion has a predetermined shape. When the lubricant is supplied from the storage portion into the concave portion when positioned at the swing position, the lubricant is supplied to the spherical portion while the arm portion swings from the predetermined swing position to the neutral position again. And can be effectively transported to the sliding portion between the support portion and the support portion. Thereby, the friction in the sliding part of the said spherical part and the said support part can be reduced effectively.

Also,
When the movement of the arm portion of the connection structure is more pivotal than swinging,
It is preferable that the concave portion extends in the direction of the latitude of the spherical portion. The latitude line is a small circle extending in parallel with the equator on the outer peripheral surface of the spherical portion with the intersection point of the spherical portion with the central axis of the arm portion as both poles and the line connecting the two poles as the center.

  According to this, when the movement of the arm part is more dominant than the swinging movement, the arm part is made to extend in a predetermined direction by extending the concave part in a parallel direction parallel to the turning direction. When the lubricant is supplied from the storage portion into the concave portion when positioned in the rotation position, the lubricant is supplied to the spherical portion in the process in which the arm portion rotates from the predetermined rotation position to the neutral position again. And can be effectively transported to the sliding portion between the support portion and the support portion. Thereby, the friction in the sliding part of the said spherical part and the said support part can be reduced effectively.

Furthermore, in the connection structure,
It is preferable that a linear groove is provided at a location other than the concave portion of the spherical portion.

  According to this, as the arm portion swings or rotates, the lubricant supplied to the sliding portion between the spherical portion and the support portion by the concave portion is further spread over the entire sliding portion. Thus, friction at the sliding portion between the spherical portion and the support portion can be further effectively reduced.

Furthermore, in the connection structure,
When the movement of the arm portion of the connection structure is dominated by swinging rather than turning,
It is preferable that the linear groove extends in the direction of the latitude of the spherical portion.

  According to this, when the movement of the arm portion is more dominant than the rotation, the linear groove extends in the direction of the parallel to the swing direction so that the recess causes the The lubricant conveyed to the sliding portion between the spherical portion and the support portion can be more effectively spread over the entire sliding portion between the spherical portion and the support portion. Thereby, the friction in the sliding part of the said spherical part and the said support part can be reduced further effectively.

Alternatively, in the connection structure,
In the case where the movement of the arm portion of the connection structure is more dominant than the swing, the linear groove is preferably extended in the meridian direction of the spherical portion.

  According to this, when the movement of the arm part is more dominant than the swinging, the linear groove extends in the meridian direction perpendicular to the turning direction, so that the concave part causes the The lubricant conveyed to the sliding portion between the spherical portion and the support portion can be more effectively spread over the entire sliding portion between the spherical portion and the support portion. Thereby, the friction in the sliding part of the said spherical part and the said support part can be reduced further effectively.

  ADVANTAGE OF THE INVENTION According to this invention, the connection structure which can supply a lubricant | lubricant to a sliding part by rock | fluctuation or rotation more effectively and can fully reduce friction can be provided.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 is a schematic view showing an embodiment of a ball joint according to the present invention with a part thereof broken. FIG. 2 is a schematic view showing a part of one embodiment of the ball joint according to the present invention.

  As shown in FIG. 1, the ball joint 1 includes a stud 2, a ball 3, a support sheet 4, a housing 5, a stopper 6, a dust cover 7, a grease compartment 8, a grease compartment 9, and a concave groove. 10, a linear trace 11, and a linear trace 12. Here, the upper side in FIG. 1 indicates the upper side, and the lower side in FIG. 1 indicates the lower side.

  The stud 2 is connected to a knuckle of a suspension device (not shown) and is formed of a metal such as cast iron to constitute an arm portion. The lower end portion of the stud 2 is formed in a tapered shape and is rigidly coupled to the upper side of the ball 3. Has been.

  The ball 3 is rigidly connected to or integrally formed with the end portion of the stud 2 and is also formed of a metal such as cast iron to constitute a spherical portion.

  The support sheet 4 is made of synthetic resin, and its inner peripheral surface forms a partial spherical shape including the equator on the side opposite to the stud 2 of the ball 3, and its outer peripheral surface forms a substantially cylindrical shape. The bearing 2 is configured to support the ball 3 so that the stud 2 can swing and rotate with respect to the support sheet 4.

  The housing 5 is also formed of a metal such as cast iron so that the inner peripheral surface of the housing 5 surrounds and supports the outer peripheral surface of the support sheet 4, and the upper end of the housing 5 is on the stud 2 side of the equator of the ball 3 of the support sheet 4. This is also formed so as to overhang so as to support the portion that supports and overhangs.

  In addition, the upper end portion of the housing 5 is opened with a gap with respect to the stud 2 so that the tapered portion of the stud 2 can swing to a position indicated by a two-dot chain line in FIG. The housing 5 is connected to an arm of a suspension device (not shown) or formed integrally with the arm.

  The stopper 6 is also a disc formed of a metal such as cast iron. The stopper 6 is fitted to the lower end portion of the housing 5 and fixed by crimping the lower end portion of the housing 5. Is to be fixed against.

  The dust cover 7 is formed of rubber rubber for preventing dust from entering the sliding portion between the ball 3 and the support sheet 4, and the lower end portion thereof is fixed to the groove portion 5 a of the housing 5 by the wire 7 a. It is.

  The grease compartment 8 is configured such that grease as a lubricant is sealed in a space defined between the dust cover 7 and the stud 2, the ball 3, and the upper end portion of the housing 5. Part.

  The grease compartment 9 is configured by enclosing grease, which is a lubricant, in a space formed in a columnar shape at the lower end of the support sheet 4 and constitutes a second storage section.

  The concave groove 10 is provided on the outer peripheral surface of the ball 3 and extends in the meridian direction of the outer peripheral surface of the ball 3. It is formed in the shape of a plane parallel to it, and constitutes a recess.

  The concave groove 10 is provided on the outer peripheral surface of the ball 3 at four positions every 90 degrees as viewed from above, and the stud 2 indicated by a two-dot chain line in FIG. 1 is relative to the support seat 4 or the central axis C2 of the housing 5. When it is located at the swinging position that makes the maximum inclination angle α, the upper end portion 10a of the concave groove 10 has a length L on the meridian across the equator of the ball 3 so as to open into the grease compartment 8. Has been extended.

  In the cross section perpendicular to the extending direction, the linear mark 11 extends in the meridian direction to the portion excluding the concave groove 10 on the outer peripheral surface of the ball 3, for example, as shown in FIG. It is provided so as to have a triangular cross section as shown, and constitutes a linear groove.

  In the cross section perpendicular to the extending direction, for example, as shown in FIG. It is provided to have a triangular cross section as shown, and this also constitutes a linear groove.

  The ball joint 1 configured as described above connects a knuckle and an arm of a suspension device (not shown) so as to be swingable and rotatable. Here, the swinging means that the center axis C1 of the stud 2 is inclined from the angle formed at the neutral position with respect to the center axis C2 of the support seat 4 or the housing 5. Further, the rotation means that the stud 2 rotates around its central axis C1.

  According to the ball joint 1 like the present Example 1, the following effects can be obtained. That is, in the swing position where the stud 2 indicated by a two-dot chain line in FIG. 1 forms the maximum inclination angle α with respect to the center axis C2 of the support seat 4 or the housing 5, the grease compartment is inserted into the concave groove 10 via the upper end portion 10a. Grease is supplied from 8.

  Thereafter, as the stud 2 swings with respect to the support sheet 4 and the housing 5 and moves to the neutral position and the swing position inclined to the opposite side, the concave groove 10 has a large relative circumferential direction with respect to the support sheet 4. The grease supplied into the concave groove 10 can be transported to the sliding portion between the ball 3 and the support sheet 4 with displacement. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet 4 can be reduced effectively.

  In addition, by extending the concave groove 10 in the meridian direction of the ball 3, when the movement of the stud 2 is more dominant than the rotation, the stud 2 is the maximum indicated by the two-dot chain line in FIG. When it is positioned at the swing position that forms the inclination angle α, the grease is easily supplied from the grease compartment 8 to the concave groove 10, and the stud 2 swings from the swing position that forms the maximum inclination angle α to the neutral position again. In the process, the grease can be effectively conveyed to the sliding portion between the ball 3 and the support sheet 4. Also by this, the friction in the sliding part of the ball | bowl 3 and the support sheet 4 can be reduced effectively.

  Further, by providing the linear marks 11 extending in the direction of the latitude of the ball 3, when the movement of the stud 2 is more dominant than the rotation, the line 2 extends in the direction of the latitude perpendicular to the swing direction. By extending the trace 11, the grease conveyed to the sliding portion between the ball 3 and the support sheet 4 by the concave groove 10 by the edge action of the linear trace 11 is transferred between the ball 3 and the support sheet 4. The entire sliding portion can be distributed more effectively. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced further effectively.

  In addition, by extending the linear mark 12 also in the meridian direction of the ball 3, when the rotation of the stud 2 is dominant rather than the swing, the line mark 12 extends in the meridian direction perpendicular to the rotation direction. By extending the trace 12, the grease conveyed to the sliding portion between the ball 3 and the support sheet 4 by the concave groove 10 by the edge action of the linear trace 12 is transferred between the ball 3 and the support sheet 4. The entire sliding portion can be distributed more effectively. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced further effectively.

  Note that the linear scar 11 and the linear scar 12 have, for example, a square cross-sectional shape as shown in FIG. 2B in addition to the triangular cross-sectional shape shown in FIG. It is good also as a thing, and it is good also as a thing of U-shaped cross-sectional shape as shown in FIG.2 (c).

  Further, in the first embodiment, the shape of the groove bottom of the concave groove 10 is a plane parallel to the central axis of the stud 2, but a spherical shape parallel to the outer peripheral surface of the ball 3. It can also be.

  Further, by providing the concave groove 10 across the equator plane of the ball 3 as in the first embodiment, a larger load acts when the load direction is the central axis C2 direction of the housing 5, that is, the vertical direction. Since the contact area of the lower surface of the ball 3 with respect to the support sheet 4 can be increased, a more advantageous configuration can be obtained from the viewpoint of load support.

  In the first embodiment described above, the concave groove 10 is extended in the meridian direction across the equator of the ball 3, but the grease in the grease compartment 9 is conveyed to the sliding portion between the ball 3 and the support sheet 4. It is also possible to provide the ball 3 at another position for the purpose. A second embodiment related thereto will be described below.

  FIG. 3 is a schematic view showing an embodiment of a ball joint according to the present invention. The ball joint shown in FIG. 3 is composed of the same constituent elements as the ball joint shown in FIG. 1 except for the concave groove, so that the same constituent elements are denoted by the same reference numerals, and overlapping description is omitted. It shall be omitted.

  As shown in FIG. 3, the ball joint 21 includes a stud 2, a ball 3, a support sheet 4, a housing 5, a stopper 6, a dust cover 7, a grease compartment 8, a grease compartment 9, and a concave groove. 30, linear traces 11, and linear traces 12.

  The concave groove 30 is provided on the outer peripheral surface of the ball 3 and extends in the meridian direction of the outer peripheral surface of the ball 3, and the groove bottom is formed in a planar shape parallel to the center C 3 of the ball 3. And constitutes a recess.

  The concave groove 30 is provided on the outer peripheral surface of the ball 3 at four positions every 90 degrees as viewed from above, and the stud 2 indicated by a two-dot chain line in FIG. 1 is relative to the support seat 4 or the central axis C2 of the housing 5. When positioned at the swinging position having the maximum inclination angle α, the lower end 30a of the concave groove 30 has a length L on the meridian below the equator of the ball 3 so that it opens into the grease compartment 9. So that it is extended.

  According to the ball joint 21 as in the second embodiment, the following operational effects can be obtained. That is, in the swing position where the stud 2 indicated by a two-dot chain line in FIG. 1 makes the maximum inclination angle α with respect to the center axis C2 of the support seat 4 or the housing 5, the grease compartment is inserted into the concave groove 30 via the lower end 30a. Grease is supplied from 9.

  Further, as the stud 2 subsequently swings with respect to the support sheet 4 and the housing 5 and moves to the neutral position and the swing position inclined to the opposite side, the concave groove 30 has a large relative relationship with the support sheet 4. With the circumferential displacement, the grease supplied into the concave groove 30 can be conveyed to the sliding portion between the ball 3 and the support sheet 4. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced effectively.

  Further, by extending the concave groove 30 in the meridian direction of the ball 3, when the movement of the stud 2 is more dominant than the rotation, the stud 2 is the maximum indicated by the two-dot chain line in FIG. When it is positioned at the swinging position that forms the inclination angle α, the grease is easily supplied from the grease compartment 9 to the concave groove 30, and the stud 2 again moves from the swinging position that forms the maximum inclination angle α to the neutral position and the opposite side. In the process of swinging, the grease can be effectively conveyed to the sliding portion between the ball 3 and the support sheet 4. Also by this, the friction in the sliding part of the ball | bowl 3 and the support sheet 4 can be reduced effectively.

  Further, by providing the linear marks 11 extending in the direction of the latitude of the ball 3, when the movement of the stud 2 is more dominant than the rotation, the line 2 extends in the direction of the latitude perpendicular to the swing direction. By extending the trace 11, the grease conveyed to the sliding portion between the ball 3 and the support sheet 4 by the concave groove 30 by the edge action of the linear trace 11 is transferred between the ball 3 and the support sheet 4. The entire sliding portion can be distributed more effectively. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced further effectively.

  In addition, by extending the linear mark 12 also in the meridian direction of the ball 3, when the rotation of the stud 2 is dominant rather than the swing, the line mark 12 extends in the meridian direction perpendicular to the rotation direction. By extending the trace 12, the grease conveyed to the sliding portion between the ball 3 and the support sheet 4 by the concave groove 30 by the edge action of the linear trace 12 is transferred between the ball 3 and the support sheet 4. The entire sliding portion can be distributed more effectively. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced further effectively.

  Further, by providing the concave groove 30 in the formation direction below the equator plane of the ball 3 as in the second embodiment, the load direction is larger when the load direction is a direction perpendicular to the central axis C2 direction of the housing 5. Since the contact area with respect to the support sheet 4 of the surface near the equator of the ball 3 on which the load acts can be increased, a more advantageous configuration can be obtained from the viewpoint of load support.

  In the second embodiment, the shape of the groove bottom of the concave groove 30 is a plane parallel to the central axis of the stud 2, but the outer surface of the ball 3 is the same as in the first embodiment. It can also be parallel and spherical.

  In the first and second embodiments described above, the concave groove 10 or the concave groove 30 is extended in the meridian direction of the ball 3, but the movement of the ball joint is more dominant than the swinging movement. In this case, it is effective to move the grease compartment 9 provided below the ball 3 to the side so that the extending direction of the concave groove is also the latitude direction. A third embodiment related thereto will be described below.

  FIG. 4 is a schematic view showing an embodiment of a ball joint according to the present invention. In addition, since the ball joint shown in FIG. 4 is comprised by the component similar to the ball joint shown in FIG. 1 except a concave groove and a grease compartment, it attaches | subjects the same code | symbol about a common component, and overlaps. The explanation will be omitted.

  As shown in FIG. 4, the ball joint 31 includes a stud 2, a ball 3, a support sheet 4, a housing 5, a stopper 6, a dust cover 7, a grease compartment 8, a grease compartment 39, and a concave groove. 40, linear traces 11, and linear traces 12.

  The grease compartment 39 is configured by enclosing grease, which is a lubricant, in spaces formed in an arc column shape at four positions every 90 degrees in the circumferential direction on the side of the support sheet 4 and on the side of the housing 5. It constitutes the second storage part.

  The concave groove 40 is provided on the outer peripheral surface of the ball 3, extends in the latitude direction and the equator direction of the outer peripheral surface of the ball 3, and the groove bottom has a planar shape parallel to the center C <b> 3 of the ball 3. And constitutes a recess.

  The concave groove 40 is provided on the outer peripheral surface of the ball 3 at four positions every 90 degrees as viewed from above, and is concave when the stud 2 is positioned at a rotational position with respect to the support seat 4 or the housing 5 shown in FIG. A groove 40 extends to open into the grease compartment 39.

  According to the ball joint 31 of the third embodiment, when the rotation of the stud 2 is more dominant than the swing, the concave portion 40 is extended in the parallel direction parallel to the rotation direction. When the stud 2 is located at the rotational position shown in FIG. 4, grease is supplied from the grease compartment 39 into the concave groove 40, and the stud 2 is regrown from the rotational position shown in FIG. 4 to the neutral position again. Can be effectively transported to the sliding portion between the ball 3 and the support sheet 4. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet 4 can be reduced effectively.

  Furthermore, by providing the linear trace 11 extending in the latitude direction of the ball 3, the linear trace 11 is extended in the latitude direction perpendicular to the swing direction based on the swing of the stud 2, Due to the edge action of the linear mark 11, the grease conveyed to the sliding portion between the ball 3 and the support sheet 4 by the concave groove 40 is more effectively applied to the entire sliding portion between the ball 3 and the support sheet 4. Can be spread. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced further effectively.

  In addition, by extending the linear trace 12 also in the meridian direction of the ball 3, by extending the linear trace 12 in the meridian direction perpendicular to the rotation direction based on the rotation of the stud 2, Due to the edge action of the linear mark 12, the grease conveyed to the sliding portion between the ball 3 and the support sheet 4 by the concave groove 40 is more effectively applied to the entire sliding portion between the ball 3 and the support sheet 4. Can be spread. Thereby, the friction in the sliding part of the ball | bowl 3 and the support sheet | seat 4 can be reduced further effectively.

  In the third embodiment, the shape of the groove bottom of the concave groove 40 is a plane parallel to the central axis of the stud 2, but the outer periphery of the ball 3 is the same as in the first and second embodiments. It can also be a spherical surface parallel to the surface.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and substitutions are made to the above-described embodiments without departing from the scope of the present invention. be able to.

  The present invention relates to a ball joint of a vehicle, and can provide a connecting structure that can sufficiently reduce friction by supplying a lubricant to a sliding portion by swinging or rotating more effectively. Therefore, it is useful when applied to various vehicles such as ordinary passenger cars, trucks and buses.

It is a mimetic diagram showing one embodiment of a ball joint concerning the present invention. It is a mimetic diagram showing one embodiment of a ball joint concerning the present invention. It is a mimetic diagram showing one embodiment of a ball joint concerning the present invention. It is a mimetic diagram showing one embodiment of a ball joint concerning the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ball joint 2 Stud 3 Ball 4 Bearing sheet 5 Housing 6 Stopper 7 Dust cover 8 Grease compartment 9 Grease compartment 10 Concave groove 11 Linear trace 12 Linear trace 21 Ball joint 30 Concave groove 31 Ball joint 39 Grease compartment 40 Concave groove

Claims (7)

Arms,
A spherical portion coupled to an end of the arm,
A support part for supporting the spherical part so that the arm part can swing and rotate;
A connection structure comprising a storage portion for storing a lubricant between the support portion and the spherical portion,
The connection structure, wherein the spherical portion includes a concave portion that opens to the storage portion when the arm portion is located at a predetermined swing or rotation position.   The connection structure according to claim 1, wherein the concave portion extends including the equator of the spherical portion.   The connecting structure according to claim 1, wherein the concave portion extends in a meridian direction of the spherical portion.   The connection structure according to claim 1, wherein the concave portion extends in a direction of a latitude line of the spherical portion.   The connecting structure according to any one of claims 1 to 4, wherein a linear groove is provided in a portion other than the concave portion of the spherical portion.   The connecting structure according to claim 5, wherein the linear groove extends in a direction of a latitude line of the spherical portion.   The connecting structure according to claim 5, wherein the linear groove extends in a meridian direction of the spherical portion.

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