JP2010255694A - Ball joint - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball joint without causing a lubrication failure between a ball stud and a seat or the abrasion of the seat even if a rotary range of the ball stud and a socket is only a certain limited range. <P>SOLUTION: Sliding resistance to an inner peripheral part of the seat 40 of a ball 36 is set larger than the relative rotational resistance of the inner peripheral part of the sheet 40 and the socket 34. Thus, when the ball stud and the socket relatively rotate, a strong position of a mutually pushing force of the ball and the inner peripheral surface of the seat is rotatably moved to the seat by rotating the seat to the socket together with the ball by relative rotation around the axis of the ball stud of the ball and the socket. Thus, the lubrication failure and seat abrasion can be prevented without losing grease only in a specific position of the seat. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ball joint.

  Generally, the ball joint has a ball stud having a ball portion that forms a sphere, and a stud portion that is integrally connected thereto, and a socket that holds the ball portion via a seat. Since the ball stud and the socket can be relatively rotated around the center of the ball portion, the ball stud rotates the member fixed to the stud portion of the ball stud and the member fixed to the socket to each other. It is possible to connect in a movable manner. Further, in the relative rotation of the ball stud and the socket, the ball portion and the seat slide with each other, so that grease is interposed between the members so that the members slide smoothly. ing. Ball joints are used in suspension arm connecting portions and the like in vehicle suspensions, and in the following patent documents, ball joints are used in vehicle suspensions.

JP 2006-77845 A

  In the ball joint, at a position where the force with which the ball portion and the inner peripheral portion of the seat press against each other (hereinafter sometimes referred to as “high load position”), the grease is pushed out. When the member fixed to the ball stud and the member fixed to the socket rotate relative to each other, even if grease is pushed out from the high load position, the relative load moves the high load position on the seat. Therefore, the grease is not lost only from a specific part of the sheet. However, if the change in the relative position between the ball stud and the socket is small during relative rotation, the movement of the high load position in the seat is also reduced, and the high load position continues to stay at a certain part of the seat. For this reason, grease may be lost at a portion of the seat at a high load position, resulting in poor lubrication. Furthermore, if the grease is lost and the portion of the seat comes into contact with the ball portion, the inner peripheral portion of the seat may be worn. In view of such circumstances, the present invention provides a ball joint that does not cause poor lubrication between the ball stud and the seat or wear of the seat even when the relative position change between the ball stud and the socket is small. This is the issue.

  In order to solve the above problems, a ball joint according to the present invention is a ball joint for connecting two members, (A) a socket fixed to the other of the two members, and (B) an inner peripheral portion. A ball stud of the ball stud, and a seat held by the socket on the outer periphery, and the ball stud and the socket with respect to relative rotation around the axis of the ball stud, the sliding resistance of the ball portion with respect to the seat, The relative rotation resistance of at least a part of the inner circumference of the seat and the socket is increased, and relative rotation in one direction between the socket and at least a part of the inner circumference of the seat is allowed and relative rotation in the opposite direction is prohibited. It is characterized by having a mechanism to perform.

  The relative rotational resistance between at least a part of the inner peripheral portion of the sheet and the socket is, for example, when the sheet is formed of a single member, the inner peripheral portion of the sheet rotates with respect to the socket. The resistance due to sliding between the outer periphery of the sheet and the socket. The relative rotational resistance in the case where the sheet is composed of a plurality of members is the resistance when the member located in the inner periphery of the sheet rotates with respect to the socket. These are resistance due to sliding between each other, and resistance due to sliding between a member located on the outer peripheral portion and the socket.

  In addition, the relative rotation in one direction between the socket and at least a part of the inner peripheral portion of the sheet is similar to the above description when the sheet is composed of a single member, the sheet is relative to the socket. Means rotating in one direction. Moreover, when the sheet | seat is comprised from several members, it means that the member located in the inner peripheral part rotates in one direction with respect to a socket.

  According to the ball joint of the present invention, when the ball portion and the socket rotate relative to each other around the axis of the ball stud, in one rotation (forward rotation), at least a part of the inner peripheral portion of the seat It can rotate with respect to the socket together with the part. In the other rotation (reverse rotation), the sheet cannot rotate with respect to the socket. That is, the sheet can be rotated only in one direction, and the high load position on the sheet can be rotated only in one direction. Therefore, the grease is not lost only from a specific part of the sheet. That is, it is possible to prevent poor lubrication between the ball portion and the seat and wear of the seat.

It is the schematic of the suspension apparatus comprised including the ball joint of 1st Example of this invention. It is sectional drawing of the ball joint of 1st Example. It is a schematic diagram which shows the position where the force with which a ball | bowl part and a sheet | seat press is strong. It is sectional drawing of the ball joint of 2nd Example.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as modes for carrying out the present invention. In addition, this invention is not limited to the following Example, This invention can be implemented with the various form to which the various change and improvement were performed based on the knowledge of those skilled in the art.

  FIG. 1 is an external view of a vehicle suspension apparatus 10 provided for a rear wheel that is a driven wheel. The suspension device 10 is an independent suspension type and is a multi-link type. The suspension device 10 includes an axle carrier 12, a suspension spring 14, a shock absorber 16, a suspension arm, and the like. The axle carrier 12 holds wheels (not shown) in a rotatable state. The axle carrier 12 is rotatably connected to one end of each suspension arm of the first upper arm 18, the second upper arm 20, the first lower arm 22, the second lower arm 24, and the toe control arm 26. The other end of each suspension arm is rotatably supported by the vehicle body. Therefore, the wheel and the axle carrier 12 can swing with respect to the vehicle body by these suspension arms. Further, one end of the shock absorber 16 is attached to the second lower arm 24. Therefore, depending on the swing of the second lower arm 24 due to the vertical movement of the vehicle body, the shock absorber 16 generates a damping force against vibration accompanying the approach and separation between the wheel and the vehicle body, and the suspension spring 14 that operates together with the shock absorber 16. It elastically supports the wheel and the vehicle body.

  In the suspension device 10 configured as described above, the ball joint 30 which is the ball joint of the first embodiment is used for the connection between the axle carrier 12 and the toe control arm 26. FIG. 2A is a cross-sectional view of the ball joint 30. The ball joint 30 is roughly composed of a ball stud 32 and a socket 34, and the ball stud 32 is further composed of a ball portion 36 having a spherical shape and a stud portion 38 having an axis. The ball stud 32 and the socket 34 are made of steel, and the ball portion 36 is accommodated in the socket 34.

  A resin sheet 40 is disposed between the ball portion 36 and the socket 34. That is, the seat 40 holds the ball portion 36 at the inner peripheral portion, and the seat 40 is held by the socket 34 at the outer peripheral portion. As will be described later, the ball portion 36 and the seat 40 can slide with respect to each other, and the socket 34 and the seat 40 rotate around the axis of the ball stud 32 (hereinafter sometimes referred to as “stud axis”). Can slide on each other. Grease not shown is interposed between the ball portion 36 and the seat 40 and between the socket 34 and the seat 40 so that the respective members slide smoothly. As described above, the ball portion 36 is covered with the backup sheet 42 in the state where the ball portion 36 is accommodated in the socket 34. The backup sheet 42 is held by a cap 44 fitted in the socket 34.

  In the vehicle suspension apparatus 10, the ball stud 32 is fixed to the axle carrier 12 at the stud portion 38. More specifically, the stud portion 38 has a screw portion 46 formed on the tip end side, and a tapered portion 48 formed between the screw portion 46 and the ball portion 36. The tapered portion 48 is inserted into a tapered hole 50 provided in the axle carrier 12, and a nut (not shown) is screwed into the screw portion 46, whereby the ball joint 30 is fixed to the axle carrier 12. On the other hand, the socket 34 is fixed to one end of the toe control arm 26.

  Further, in order to prevent dust and water from entering the inside of the socket 34 from the lower part of the socket 34 in a state where the ball joint 30 is fixed to the axle carrier 12, the dust boot 52 is connected to the lower part of the socket 34 and the axle carrier. 12. Since the dust boot 52 is made of flexible rubber, it can be deformed according to the operation of the socket 34 and the axle carrier 12.

  The mounting direction in fixing the ball joint 30 to the axle carrier 12 will be further described. The connecting part on the vehicle body side of the toe control arm 26 is configured such that the toe control arm 26 swings about one axis. That is, according to the vertical movement of the vehicle body, the toe control arm 26 swings on a plane substantially perpendicular to the rotation axis of the connecting portion on the vehicle body side. If this surface is called a rocking surface, the ball stud 32 is fixed to the axle carrier 12 so that the stud axis is inclined with respect to the rocking surface.

  2B is a cross-sectional view of the ball joint 30 taken along the line AA in FIG. 2A, and the seat 40 will be described in detail below with reference to FIGS. 2A and 2B. To do. The seat 40 has a cylindrical shape in which the lower portion is slightly tapered, and is disposed so as to surround the ball portion 36. The inner peripheral portion of the seat 40 is formed along the spherical surface of the ball portion 36. The seat 40 can only rotate about the center axis of the socket 34.

  In the uppermost part of the sheet 40, a part of the sheet 40 is cut, and a plurality of strip-shaped pieces are formed. The small piece is integrated with the sheet 40 because its long side extends in the circumferential direction of the sheet 40 and one of its short sides is not cut. Further, the small piece is bent up toward the outer side in the radial direction of the sheet 40. If this small piece is called a claw 64, a plurality of claw 64 is provided at equal intervals on the circumference of the uppermost portion of the sheet 40.

  A plurality of teeth 66 slightly wider than the width of the claw 64 are formed on the inner wall of the socket 34 at equal intervals on the circumference of the portion facing the claw 64. When the sheet 40 and the socket 34 rotate with respect to each other, the sheet 40 cannot rotate with respect to the socket 34 because the top of the claw 64 is hooked on the teeth 66 in a certain direction. Also, with respect to the opposite direction, the claw 64 can bend and get over the top of the tooth 66, so that the sheet 40 can rotate with respect to the socket 34. That is, the pawl 64 and the teeth 66 constitute a ratchet mechanism that functions like a so-called one-way clutch. Referring to the rotation of the seat 40 in FIG. 2B, the seat 40 is allowed to rotate clockwise with respect to the socket 34, but is not allowed to rotate counterclockwise. In the following description, the relative rotation of the sheet 40 and the socket 34 in the direction in which the claw 64 is not latched by the teeth 66 is referred to as normal rotation, and the relative rotation in the direction in which the claw 64 is latched by the teeth 66. This is called reverse rotation.

  Incidentally, in the ball joint 30 of the present embodiment, the claws 64 are provided at seven places at equal intervals, and the teeth 66 are provided at 48 places at equal intervals. That is, when one of the plurality of claws 64 is hooked on a certain tooth 66, the other claws 64 are configured not to be hooked on any tooth 66. In other words, two or more of the plurality of claws 64 are not hooked on the teeth 66 at the same time. Further, while the sheet 40 rotates forward and the top of the hooked claw 64 moves to a position where it is hooked on the adjacent tooth 66, the other six claws 64 are sequentially moved to other teeth. 66 is moved to a position where it can be hooked. Therefore, the seven claws 64 can be latched with the 48 teeth 66 and 48 × 7 = 336 times while the sheet 40 makes one rotation with respect to the socket 34.

  In the ball joint 30 configured as described above, the ball stud 32 and the socket 34 can rotate relative to each other. Therefore, the ball joint 30 connects the axle carrier 12 fixed to the ball stud 32 and the toe control arm 26 fixed to the socket 34 so as to be relatively rotatable. When the ball stud 32 and the socket 34 are rotated relative to each other around the stud axis in the relative rotation between the ball stud 32 and the socket 34, the ball portion 36 and the seat 40 can rotate relative to each other around the stud axis. 40 can also rotate relative to each other about the stud axis.

  In the ball joint 30 of the present embodiment, the tightening allowance between the socket 34 and the seat 40 is determined so that the seat 40 and the ball portion 36 rotate with respect to the socket 34. That is, by adjusting the tightening allowance, the friction between the socket 34 and the seat 40 is adjusted, and the resistance in the relative rotation between the ball portion 36 and the seat 40, that is, the sliding resistance is the relative force between the seat 40 and the socket 34. The fastening margin between the socket 34 and the seat 40 is determined so as to be larger than the resistance in rotation, that is, the relative rotational resistance.

  FIG. 3 is a schematic diagram showing the force acting on the ball portion 36 from the toe control arm 26. This force acts in the direction in which the arm axis extends to the center of the ball portion 36. Therefore, at a position where the ball portion 36 and the inner peripheral portion of the seat 40 intersect with the arm axis, the force acting from the toe control arm 26 acts on the ball portion 36 from the inner peripheral portion of the seat 40 and the reaction thereof. A force acts on the inner peripheral portion of the seat 40 from the ball portion 36. Therefore, this position in the ball portion 36 and the inner peripheral portion of the seat 40 is a high load position where the ball portion 36 and the inner peripheral portion of the seat 40 are pressed against each other with a strong force. While the vehicle is running, the relative position between the ball portion 36 and the socket 34 changes in accordance with the swinging of the toe control arm 26, and the high load position moves accordingly. A region where the high load position is moved by the swinging of the toe control arm 26 in the inner peripheral portion of the seat 40 is referred to as a high load region.

  In FIG. 2A, the direction in which the center of the ball portion 36 moves in accordance with the swing of the toe control arm 26 is indicated by an arrow. When the toe control arm 26 swings, the ball stud 32 and the socket 34 rotate relative to each other, and the relative position between the ball portion 36 and the socket 34 changes accordingly. In this change in the relative position, the stud axis is inclined with respect to the swing surface, so that the ball portion 36 and the socket 34 are relatively rotated around the stud axis. When the relative rotation direction is the positive rotation direction, as described above, the sliding resistance between the ball portion 36 and the seat 40 is larger than the relative rotational resistance between the seat 40 and the socket 34. Together with the ball portion 36, it rotates with respect to the socket 34. That is, the sheet 40 slides with respect to the socket 34. On the other hand, when the relative rotation direction is the reverse rotation direction, the seat 40 cannot be rotated by the ratchet mechanism even when the sliding resistance is larger than the relative rotation resistance. Therefore, the seat 40 slides with respect to the ball portion 36.

  In the ball joint 30 configured as described above, the seat 40 and the socket 34 relatively rotate in one direction. Therefore, according to the ball joint 30 in the present embodiment, the seat 40 rotates in one direction with respect to the socket 34, and accordingly, the high load region in the seat 40 is rotated in one direction. As a result, even if the grease is pushed out from the high load region, the grease is not lost only from a specific part of the sheet 40. That is, in the ball joint 30, poor lubrication and wear of the seat 40 are prevented.

  Further, in the sheet 40 and the socket 34 of the present embodiment, the claw 64 is moved to a position where the claw 64 is hooked on the teeth 66 at a fine pitch. The sheet 40 is hooked on the teeth 66, and the reverse rotation of the sheet 40 is prohibited. For this reason, even when the swinging stroke of the toe control arm 26 is small and the relative rotation of the ball portion 36 and the socket 34 around the stud axis is small, the seat 40 and the socket 34 can continue to rotate normally.

  In the present embodiment, in the vehicle suspension apparatus 10, the configuration other than the ball joint 80 is the same, and therefore the description other than the ball joint 80 is omitted. Further, the ball joint 80 is roughly configured in the same manner by the same members as the ball joint 30 in the first embodiment, and therefore, the description of the same members and configurations as the ball joint 30 is omitted. .

  4A is a cross-sectional view of the side surface of the ball joint 80, and FIG. 4B is a cross-sectional view of the ball joint 80 taken along the line BB in FIG. 4A. The ball portion 36 is accommodated in a steel socket 82, and a resin sheet 84 is disposed between the ball portion 36 and the socket 82. That is, the seat 84 holds the ball portion 36 at the inner peripheral portion, and the seat 84 is held by the socket 82 at the outer peripheral portion. The sheet 84 includes a first fixed sheet 86, a second fixed sheet 88, and a rotating sheet 90. The first fixed sheet 86 and the second fixed sheet 88 are outer peripheral portions of the sheet 84, and are fixed to the inner peripheral portion of the socket 82 with a gap provided therebetween. A part of the inner peripheral part of the first fixed sheet 86 and the second fixed sheet 88 is a part of the inner peripheral part of the sheet 84 and is in contact with the ball part 36. The inner peripheral portion of the rotating sheet 90 is also a part of the inner peripheral portion of the seat 84 and is in contact with the ball portion 36. The rotating sheet 90 is sandwiched between the ball portion 36 and the first fixed sheet 86 and the second fixed sheet 88. The rotating sheet 90 can slide with respect to the ball portion 36, the first fixed sheet 86, and the second fixed sheet 88. Therefore, grease (not shown) is interposed between the ball portion 36 and the rotating sheet 90 and between the first fixed sheet 86 and the second fixed sheet 88 and the rotating sheet 90. Thus, in a state where the ball portion 36 is accommodated in the socket 82, the ball portion 36 is covered by the upper portion of the second fixed sheet 88, and the second fixed sheet 88 is a cap 92 fitted in the socket 82. Is held by.

  The seat 84 will be described in more detail. The lower portion of the inner periphery of the first fixed sheet 86 is formed along the spherical surface of the ball portion 36, and the upper portion sandwiches the rotating sheet 90. Recessed for. Further, in the inner peripheral portion of the second fixed sheet 88, the upper portion thereof is formed along the spherical surface of the ball portion 36, and the lower portion thereof is recessed to sandwich the rotating sheet 90. The rotating sheet 90 is formed in a cylindrical shape, and a lower portion thereof is sandwiched between the ball portion 36 and the first fixed sheet 86, and an upper portion thereof is sandwiched between the ball portion 36 and the second fixed sheet 88. . Further, the inner peripheral portion of the rotating sheet 90 is formed along the spherical surface of the ball portion 36, and the outer peripheral portion is formed so as to be in close contact with the respective recesses of the first fixed sheet 86 and the second fixed sheet 88. Has been.

  At the intermediate portion in the height direction of the rotating sheet 90, that is, at the portion located in the gap between the first fixed sheet 86 and the second fixed sheet 88, a part of the rotating sheet 90 is cut and strip-shaped small pieces are formed. Is formed. Since the long side of the small piece extends in the circumferential direction of the rotating sheet 90 and one of the short sides is not cut, the small piece is integrated with the rotating sheet 90. Further, the small piece is bent and raised toward the outer side in the radial direction of the rotating sheet 90. If this small piece is called a claw 94, a plurality of claws 94 are provided at equal intervals on the circumference of the intermediate portion of the rotating sheet 90. Further, the gap between the first fixed sheet 86 and the second fixed sheet 88 is provided so as to be slightly wider than the width of the claw 94, and the claw 94 can be positioned within the gap.

  A plurality of teeth 96 slightly wider than the width of the claw 94 are formed at equal intervals on the circumference of the inner wall of the socket 82 facing the claws 94. When the rotating sheet 90 and the socket 82 rotate with respect to each other, the rotating sheet 90 cannot rotate with respect to the socket 82 because the top of the claw 94 is hooked on the teeth 96 in a certain direction. . Further, in the opposite direction, the claw 94 can bend and get over the top of the tooth 96, so that the rotating sheet 90 can rotate with respect to the socket 82. That is, the claw 94 and the tooth 96 constitute a ratchet mechanism that functions like a so-called one-way clutch. Regarding the rotation of the rotating sheet 90 in FIG. 4B, the rotating sheet 90 is allowed to rotate clockwise with respect to the socket 82, but is not allowed to rotate counterclockwise. In the following description, the rotation of the rotating sheet 90 and the socket 82 relative to the direction in which the claw 94 is hooked by the teeth 96 is referred to as normal rotation. Rotating is called reverse rotation.

  Incidentally, in the ball joint 80 of the present embodiment, the claws 94 are provided at four locations, and the teeth 96 are provided at 31 locations. Similarly to the first embodiment, when the rotating sheet 90 and the socket 82 are engaged with one tooth 96 of one of the plurality of claws 94, the other claw 94 is attached to which tooth 96. Is configured so as not to be hooked.

  In the ball joint 80 configured as described above, the ball stud 32 and the socket 82 can be relatively rotated. Therefore, the ball joint 80 connects the axle carrier 12 fixed to the ball stud 32 and the toe control arm 26 fixed to the socket 82 so as to be relatively rotatable. In the relative rotation of the ball stud 32 and the socket 82, when the relative rotation about the stud axis is made, the ball portion 36 and the rotating seat 90 can rotate relative to each other about the stud axis, The rotating sheets 90 can also rotate relative to each other around the stud axis.

  In the ball joint 80 of the present embodiment, the rotating seat 90 is configured to rotate with respect to the socket 82 together with the ball portion 36 for the reason described later. That is, the resistance in the relative rotation between the ball portion 36 and the rotating sheet 90, that is, the sliding resistance is set larger than the resistance in the relative rotation between the rotating sheet 90 and the socket 82, that is, the relative rotational resistance.

  In the ball joint 30 of the first embodiment, the sliding resistance between the ball portion 36 and the inner peripheral portion of the seat 40 is adjusted between the socket 34 and the seat 40 by adjusting the tightening allowance between the socket 34 and the seat 40. The friction between the members was adjusted so as to be larger than the relative rotational resistance. In the friction between the members, the friction can be adjusted depending on the material of the members. That is, since the friction coefficient between these members differs depending on the material of each member, the friction can be adjusted. In the first embodiment, since the socket 34 and the ball portion 36 are made of steel and the seat 40 is made of resin, the friction coefficient between the ball portion 36 and the seat 40 and the friction between the socket 34 and the seat 40 are obtained. The coefficients will be the same. Therefore, in order to make the sliding resistance larger than the relative rotational resistance due to the difference in frictional force, it is necessary to reduce the tightening allowance between the socket 34 and the seat 40.

  In the ball joint 80 of the present embodiment, in order to make the friction coefficient between the ball portion 36 and the rotating sheet 90 larger than the friction coefficient between the rotating sheet 90, the first fixed sheet 86 and the second fixed sheet 88, The combination of is different. More specifically, in the ball joint 80 of the present embodiment, the socket 82 and the ball portion 36 are made of steel, and the first fixed sheet 86, the second fixed sheet 88, and the rotating sheet 90 are made of resin. The friction coefficient in the contact between the steel and the resin is larger than the friction coefficient in the resin-to-resin contact. The friction coefficient with the second fixed sheet 88 becomes larger. Therefore, in the ball joint 80, the friction between the ball portion 36 and the rotating sheet 90 can be made larger than the friction between the rotating sheet 90 and the first fixed sheet 86 and the second fixed sheet 88. The sliding resistance between the rotating sheet 90 and the rotating sheet 90 can be made larger than the relative rotating resistance between the rotating sheet 90 and the socket 82.

  In FIG. 4A, the direction in which the center of the ball portion 36 moves in accordance with the swing of the toe control arm 26 is indicated by an arrow. When the toe control arm 26 swings, the ball stud 32 and the socket 82 rotate relative to each other, and the relative position between the ball portion 36 and the socket 82 changes accordingly. In this change in the relative position, the stud axis is inclined with respect to the swing surface, so that the ball portion 36 and the socket 82 are relatively rotated around the stud axis. If the relative rotation direction is the positive rotation direction, as described above, the sliding resistance between the ball portion 36 and the rotating sheet 90 is larger than the relative rotating resistance between the rotating sheet 90 and the socket 82. 90 rotates together with the ball portion 36 with respect to the socket 82. That is, the rotating sheet 90 slides with respect to the first fixed sheet 86 and the second fixed sheet 88. On the other hand, when the relative rotation direction is the reverse rotation direction, the rotating sheet 90 cannot be rotated by the ratchet mechanism even when the sliding resistance is larger than the relative rotation resistance. Therefore, the rotating sheet 90 slides with respect to the ball portion 36.

  In the ball joint 80 configured as described above, the rotating seat 90 and the socket 82 relatively rotate in one direction. Therefore, according to the ball joint 30 in the present embodiment, the rotating sheet 90 rotates in one direction with respect to the socket 82, and accordingly, the high load region in the rotating sheet 90 is rotated in one direction. As a result, even if the grease is pushed out from the high load region, the grease is not lost only from a specific part of the rotating sheet 90. That is, in the ball joint 80, poor lubrication and wear of the rotating seat 90 are prevented.

  30: Ball joint 32: Ball stud 34: Socket 36: Ball part 40: Seat

Claims (1)

A ball joint for connecting two members,
A socket fixed to the other of the two members;
Holding a ball portion of the ball stud at an inner peripheral portion, and a sheet held by the socket at an outer peripheral portion;
Regarding the relative rotation of the ball stud and the socket around the axis of the ball stud, the sliding resistance of the ball portion with respect to the seat is compared with the relative rotational resistance of at least a part of the inner peripheral portion of the seat and the socket. And a mechanism for allowing relative rotation in one direction and prohibiting relative rotation in the opposite direction between the socket and at least a part of the inner periphery of the seat.

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