JP2008073793A - Impact tool - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an impact tool which lowers noise and prevents falling of dampers without lowering tightening capacity. <P>SOLUTION: The impact tool applies rotating impact force on a head end tool by installing a rotating impact mechanism on a spindle rotated and driven by a motor and by intermittently transmitting the rotating impact force generated by the rotating impact mechanism to the head end tool through an anvil 3 from hammers engaged with each other. The anvil 3 is divided into two in the axial direction, a recessed part 3a is formed on one end surface in the axial direction of one 3A of divided pieces, a large diametrical part (one end part in the axial direction) 3f of the other divided piece 3B is inserted into the recessed part 3a, the rubber damper (first damper) 11 is interposed in a clearance in the axial direction between the large diametrical part 3f of the divided piece 3B and the recessed part 3a of the divided piece 3A, and the rubber damper (second damper) 12 is interposed in a clearance in the circumferential direction formed between the recessed part 3a of the divided piece 3A and the large diametrical part 3f of the divided piece 3B. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an impact tool for generating a rotating impact force and performing a required operation such as screw tightening.

  An impact tool as one form of an electric power tool is a tool that generates a rotating striking force using a motor as a driving source to rotate a tip tool, and intermittently imparts striking force to the tool to perform operations such as screw tightening. However, since it has features such as small recoil and high tightening ability, it is widely used at present. However, since the rotary impact mechanism that generates the rotational impact force is provided, noise during operation is large, and this noise is a problem.

  FIG. 9 shows a longitudinal section of a general impact tool conventionally used.

  The conventional impact tool shown in FIG. 9 uses the battery pack 1 as a power source, the motor 2 as a drive source, drives the rotary impact mechanism, and rotates and strikes the anvil 3 to intermittently apply the rotary impact force to the tip tool. To the screw and perform operations such as screw tightening.

  In the rotary impact mechanism portion built in the hammer case 4 of the impact tool, the rotation of the output shaft (motor shaft) 2a of the motor 2 is decelerated via the planetary gear mechanism 5 and transmitted to the spindle 6, and the spindle 6 Is driven to rotate at a predetermined speed. Here, the spindle 6 and the hammer 7 are connected by a cam mechanism. The cam mechanism is formed on the V-shaped spindle cam groove 6 a formed on the outer peripheral surface of the spindle 6 and the inner peripheral surface of the hammer 7. Further, it is composed of a V-shaped hammer cam groove 7a and a ball 8 which engages with these cam grooves 6a, 7a.

  Further, the hammer 7 is always urged by the spring 9 in the tip direction (rightward in FIG. 9), and when stationary, the ball 8 and the cam grooves 6a and 7a are engaged with each other so that a gap is formed between the hammer 7 and the end face of the anvil 3. In the position. And the convex part is each symmetrically formed in two places on the rotation plane where the hammer 7 and the anvil 3 oppose each other. The rotation direction of the screw, the tip tool, and the anvil 3 is constrained to each other. In FIG. 9, reference numeral 10 denotes a bearing metal that rotatably supports the anvil 3.

  Thus, when the spindle 6 is rotationally driven as described above, the rotation is transmitted to the hammer 7 via the cam mechanism, and the convex portion of the hammer 7 is transferred to the anvil 3 before the hammer 7 is rotated halfway. The anvil 3 is rotated by engaging with the convex portion of the cam. When the relative reaction occurs between the hammer 7 and the spindle 6 due to the reaction force of the engagement, the hammer 7 is inserted into the spindle cam groove 6a of the cam mechanism. Along with this, the spring 9 is compressed and starts to move backward toward the motor 2 side.

  When the protrusion of the hammer 7 moves over the protrusion of the anvil 3 by the backward movement of the hammer 7 and the engagement between the two is released, the hammer 7 accumulates in the spring 9 in addition to the rotational force of the spindle 7. While being accelerated rapidly in the rotational direction and forward by the action of the elastic energy and the cam mechanism, the spring 9 is moved forward by the biasing force of the spring 9, and the convex portion is reengaged with the convex portion of the anvil 3 to rotate integrally. Begin to. At this time, since a strong rotational impact force is applied to the anvil 3, the rotational impact force is transmitted to the screw via the tip tool attached to the anvil 3.

  Thereafter, the same operation is repeated, and the rotational impact force is intermittently repeatedly transmitted from the tip tool to the screw, and the screw is screwed into a member to be fastened such as wood to be fastened.

  By the way, during the work using such an impact tool, the hammer 7 also performs a back-and-forth motion at the same time as the rotational motion. Therefore, these motions serve as a vibration source, and the fastened member is pivoted through the anvil 3, the tip tool, and the screw. Excited in the direction generates a loud noise.

Here, it is known that the noise energy from the fastening object accounts for a large proportion of the noise during work using the impact tool, and it is necessary to keep the excitation force transmitted to the fastening object small to reduce the noise. There are various countermeasures for this purpose (for example, see Patent Documents 1 and 2).
JP 7-237152 A JP 2002-254335 A

  In Patent Document 1, an anvil is divided into two members, a torque transmission portion is formed between the two members, and a cushioning material is interposed in an axial gap so that an axial tool acting on a tip tool or a screw is applied. Proposals have been made to reduce noise by reducing force. Here, a square recess is formed on one of the two members, and a square protrusion is formed on the other, and the torque transmitting portion is configured with a square uneven shape, a spline shape, or the like for connecting the two members in a non-rotatable manner. ing.

  However, when a torque is applied to the torque transmission part, a large frictional force is generated between both members, and this frictional force hinders relative movement in the axial direction of both members. The direction force could not be made too small, and the noise reduction effect was insufficient.

  Further, in Patent Document 2, the torque transmission part is made by rolling parts such as balls and rollers as key elements, and by engaging the key elements with grooves provided in both the two parts of the anvil. Proposals have been made to reduce the frictional force in the axial direction between the two members by configuring the torque transmission portion.

  However, in such a configuration, there is a problem that the surface pressure at the contact portion between the key element and the groove is very high, so that the parts are quickly worn and the structure is complicated and the manufacturing cost is high.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an impact tool capable of reducing noise and preventing a damper from dropping without causing a decrease in tightening capability.

  In order to achieve the above object, according to the first aspect of the present invention, a rotary hammering mechanism is mounted on a spindle that is rotationally driven by a motor, and a rotary hammering force generated by the rotary hammering mechanism is engaged with each other through a hammer and an anvil. In an impact tool that imparts a rotational impact force to the tip tool by intermittently transmitting to the tip tool, the anvil is divided into two in the axial direction, and a concave portion is formed on one axial end surface of one split piece A, One end of the other split piece B in the axial direction is inserted into the recess, and a first damper is interposed in the axial gap between the one end of the split piece B in the axial direction and the recess of the split piece A, and the split piece A second damper is interposed in a circumferential gap formed between the concave portion of A and one axial end portion of the split piece B.

  According to a second aspect of the present invention, in the first aspect of the invention, the concave portion of the divided piece A is a rectangular hole, and a space formed between the four corners of the rectangular hole and one axial end of the divided piece B is provided. The second damper is provided for each.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, an engagement claw a is formed in the recess of the divided piece A, and an engagement claw b is formed on the outer periphery of one end of the divided piece B. The second damper is interposed between the engaging claws a and b, and a circumferential clearance is formed between the engaging claws a and b when there is no load.

  According to a fourth aspect of the present invention, in the third aspect of the present invention, a convex portion intermittently engaged with the convex portion of the hammer is formed on the other axial end surface of the divided piece A, and the convex portion is formed. The engagement claw a is formed at a position where the movement is performed.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, a protrusion is integrally provided on the axial end surface of the second damper.

  According to the first aspect of the present invention, the one axial end of the other divided piece B is inserted into the recess formed in the one axial end surface of the one divided piece A of the anvil divided into two in the axial direction, Since the first damper is interposed in the axial gap between the axial end of the split piece B and the concave portion of the split piece A, direct contact between the split pieces A and B is prevented, and a rotary impact mechanism that is a vibration source Is absorbed by the first damper. Further, since the second damper is interposed in the circumferential gap formed between the concave portion of the split piece A and one axial end of the split piece B, the circumferential vibration from the rotary impact mechanism that is the vibration source is the first. Absorbed by 2 dampers.

  As described above, since the first and second dampers provided in the anvil absorb the vibration in the axial direction and the circumferential direction, the propagation of the vibration to the fastening target is suppressed, and the noise of the impact tool is reduced. .

  Further, since the first and second dampers are housed in the recesses of the anvil split piece A, the dampers are reliably prevented from falling off the anvil, and the impact tool can be stably operated. .

  According to invention of Claim 2, the recessed part of the division | segmentation piece A is made into a rectangular hole, and the 2nd damper is each in each of the space formed between the axial direction one ends of the division | segmentation piece B at the four corners of this rectangular hole, respectively. Since it is provided, the four second dampers are evenly arranged in the circumferential direction, and circumferential vibration is absorbed substantially equally by each damper.

  According to the third aspect of the present invention, the second damper is interposed between the engaging claw a formed in the recess of the divided piece A and the engaging claw b formed on the outer periphery of one end of the divided piece B. In addition, since a circumferential clearance is formed between the engaging claws a and b when there is no load, the circumferential direction is caused by elastic deformation of the second damper until the engaging claws a and b come into contact with each other. When vibration is absorbed and excessive torque is applied to the anvil, both the engaging claws a and b come into contact with each other, and torque is directly transmitted from the divided piece A to the divided piece B without passing through the second damper. Tightening ability of the impact tool is enhanced.

  According to the fourth aspect of the present invention, the convex portion that intermittently engages the convex portion of the hammer is formed on the other axial end surface of the split piece A, and the engaging claw a is formed at the position where the convex portion is formed. Therefore, the strength of the engaging claw a is reinforced by the convex portion, and the durability of the divided piece and thus the entire impact tool is enhanced.

  According to the invention of claim 5, since the protrusion is integrally provided on the axial end surface of the second damper, the end surface of the second damper is positioned on the axially inner side of the end surfaces of the split pieces A and B. Direct contact between the main body excluding the protrusion of the second damper and the end faces of the split pieces A and B is avoided, and no excessive shearing stress is generated in the second damper, and the second damper is damaged by cracking. The durability can be improved by preventing. Further, when the second damper is elastically deformed, the deformation is released by the protrusions. Therefore, the vibration absorption capacity can be increased by setting the spring constant in the circumferential direction of the second damper small.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

  1 is a longitudinal sectional view of a rotary impact mechanism portion of an impact tool according to the present invention, FIG. 2 is an enlarged detail view of a portion A in FIG. 1, and FIG. 3 is a side sectional view of an anvil of the impact tool (BB in FIG. 6). 4 is an enlarged detail view of a portion C in FIG. 3, FIG. 5 is a side sectional view of the anvil of the impact tool (a sectional view taken along the line DD in FIG. 6), and FIG. 6 is an arrow E in FIG. FIG. 7 is a view similar to FIG. 6 with the rubber damper removed, and FIG. 8 is a perspective view of the rubber damper. In these drawings, the same elements as those shown in FIG. It is attached.

  The impact tool according to the present embodiment is a cordless hand-held tool using the battery pack 1 as a power source and the motor 2 as a drive source, and the configuration of the impact tool is the same as that of the conventional impact tool shown in FIG. It is the same as that. Therefore, in the following description, the description of the same configuration as that shown in FIG. 9 is omitted, and only the characteristic configuration of the present invention will be described.

  In the impact tool according to the present embodiment, the anvil 3 is divided into two pieces in the axial direction to form divided pieces 3A and 3B, and the axial cushioning is provided in the recess 3a formed on one axial end surface of the one divided piece 3A. One rubber damper 11 fulfilling a function and four rubber dampers 12 fulfilling a circumferential buffer function are housed.

  The one divided piece 3A is formed in a substantially cylindrical shape, and a circular hole 3b is formed at the center of the shaft. A linear convex portion 3c passing through the center is integrally formed on the end surface of the divided piece 3A on the hammer 7 side, and one end surface of the hammer 7 (an end surface facing the divided piece 3A) is 2 Two fan-shaped convex portions 7b are integrally formed at symmetrical positions separated by an angle of 180 ° in the circumferential direction, and these convex portions 7b and the convex portions 3c formed on the divided piece 3A are counter-rotated as described later. Disengage intermittently every time.

  Further, as shown in FIGS. 6 and 7, the concave portion 3a having a rectangular hole shape is formed on the other end surface of the divided piece 3A (the end surface facing the other divided piece 3B). Two quadrant-shaped engaging claws 3d are integrally formed at two positions on the side corner portion at symmetrical positions separated by an angle of 180 ° in the circumferential direction. Here, as shown in FIGS. 6 and 7, the two engaging claws 3d are formed at circumferential positions where the convex portions 3c formed on the end face of the split piece 3A are formed.

  As shown in FIGS. 3 and 5, the other divided piece 3B is formed by integrally forming a large-diameter portion 3f at one end of a hollow shaft portion 3e. As shown in FIGS. 6 and 7, four arc-shaped curved concave portions 3g are formed at an equal angle (90 °) pitch in the circumferential direction, and a total of four convex engaging claws 3h are formed between these concave portions 3g. They are formed at an equiangular (90 °) pitch. A hexagonal hole-shaped tip tool mounting portion 3i is formed at the shaft center portion of the shaft portion 3e of the divided piece 3B, and the shaft center portion of the large diameter portion 3f is formed at the shaft center portion of the divided piece 3A. A circular hole 3j having the same diameter as that of the formed circular hole 3b is formed concentrically.

  Thus, in the anvil 3, as shown in FIGS. 3 to 5, the large-diameter portion 3f of the other divided piece 3B is inserted into the recess 3a of the one divided piece 3A. As shown in FIG. 4, spaces S as radial gaps are formed between the four recesses 3g formed on the outer periphery of the large-diameter portion 3f of the split piece 3B at the four corners in the recess 1a of the split piece 3A. A cylindrical rubber damper 12 as shown in FIG. 8 is interposed in the space S so that the axial direction thereof coincides with the axial direction of the anvil 3.

  Here, each rubber damper 12 has a cylindrical protrusion 12a integrally formed perpendicularly to the surface at the center of both end faces in the axial direction. As shown in FIG. 5, it is prevented by a ring plate-shaped retaining washer 13 attached to the outer periphery of the split piece 3B.

  As shown in FIGS. 3 to 5, the plate-like rubber damper is disposed in the axial gap formed between the back end surface of the recess 3 a of the split piece 3 </ b> A and the end face of the large diameter portion 3 f of the split piece 3 </ b> B. As shown in FIG. 5, a part of the rubber damper 11 (the position of the two rubber dampers 12 interposed in the space S where the engaging claw 3 d of the divided piece 3 </ b> A does not exist) is provided. A convex portion 11 a is formed, and this convex portion 11 a abuts against one protrusion 12 a of the rubber damper 12 to position the rubber damper 12 in the axial direction with the retaining washer 13. As shown in FIG. 3, one protrusion 12a of two rubber dampers 12 interposed in the space S where the engaging claws 3d face is in contact with the end surfaces of the engaging claws 3d, and these rubber dampers 12 are The engagement claw 3d and the retaining washer 13 are positioned in the axial direction.

  By the way, in a no-load state where torque is not transmitted to the anvil 3, as shown in detail in FIG. 4, an axial gap δ1 is formed between the end faces of the split piece 3A and the split piece 3B, and As shown in FIG. 6, a circumferential clearance δ2 is formed between the engaging claws 3d and 3h. Therefore, when no load is applied, the split pieces 3A and 3B of the anvil 3 are not in direct contact with either the circumferential direction or the axial direction.

  Thus, as shown in FIG. 1, the anvil 3 is housed in the hammer case 4 with the shaft portion 3 e of the divided piece 3 </ b> B being rotatably supported by the bearing metal 10. The tip 6 of the spindle 6 inserted through a circular hole 3b formed at the center is supported so as to be capable of relative rotation and axial movement with respect to the divided piece 3B (see FIG. 2). As shown in FIG. 2, the tip of the spindle 6 passes through the circular hole 3b of the divided piece 3A of the anvil 3 and is fitted into the circular hole 3j of the other divided piece 3B.

  Further, as shown in FIG. 1, a tip tool 14 is detachably mounted on a hexagonal hole-shaped tip tool mounting portion 3i formed at the shaft center portion of the shaft portion 3e of the split piece 3B of the anvil 3. The hammer 7 including the convex portion 7b engaged with and disengaged from the convex portion 3c formed on the outer end surface of the split piece 3A is always urged toward the anvil 3 side (front end direction) by the spring 9.

  Next, the operation of the impact tool having the above configuration will be described.

  In the rotary impact mechanism, the rotation of the output shaft (motor shaft) 2a of the motor 2 is decelerated through the planetary gear mechanism 5 and transmitted to the spindle 6, and the spindle 6 is driven to rotate at a predetermined speed. In this way, when the spindle 6 is driven to rotate, the rotation is transmitted to the hammer 7 via the cam mechanism, and the hammer 7 has its convex portion 7b projected to the convex portion of the split piece 3A of the anvil 3 before half rotation. The divided piece 3A is rotated by engaging with 3c.

  When relative rotation occurs between the hammer 7 and the spindle 6 due to the reaction force (engagement reaction force) associated with the engagement between the projection 7b of the hammer 7 and the projection 3c of the split piece 3A of the anvil 3, 7 starts to retract toward the motor 2 side while compressing the spring 9 along the spindle cam groove 6a of the cam mechanism.

  When the convex portion 7b of the hammer 7 gets over the convex portion 3c of the split piece 3A of the anvil 3 by the backward movement of the hammer 7 and the engagement between the two is released, the hammer 7 adds to the rotational force of the swivel 6; The elastic energy accumulated in the spring 9 and the cam mechanism rapidly accelerate in the rotational direction and forward, and move forward by the urging force of the spring 9, and the convex portion 7 b becomes the convex portion 3 c of the anvil 3 again. Engage and begin to rotate the anvil 3. At this time, a strong rotational striking force is applied to the anvil 3, but it is formed between the recessed portion 3a of one divided piece 3A divided into two in the axial direction of the anvil 3 and the large diameter portion 3f of the other divided piece 3B. Since the rubber damper 11 is interposed in the axial gap, the direct contact between the divided pieces A and B is prevented, and the axial vibration from the rotary striking mechanism as a vibration source is absorbed by the rubber damper 11.

  Further, since the rubber dampers 12 are interposed in the spaces S formed at the four corners of the recess 3a of the divided piece 3A, the circumferential vibration from the rotary impact mechanism that is a vibration source is absorbed by the elastic deformation of the four rubber dampers 12.

  As described above, since the vibrations in the axial direction and the circumferential direction are absorbed by the one rubber damper 11 and the four rubber dampers 12 provided in the anvil 3, the propagation of the vibration to the fastening target is suppressed and the noise of the impact tool is reduced. Realized. In particular, in the present embodiment, the concave portion 3a of the divided piece 3A is formed into a rectangular hole, and the space S formed between the four corners of the rectangular hole 3a and the concave portion 3g formed in the large diameter portion 3f of the divided piece 3B. Since each of the rubber dampers 12 is provided, the four rubber dampers 12 are equally arranged in the circumferential direction, and the circumferential vibration is absorbed almost equally by each rubber damper 12.

  Since the rubber dampers 11 and 12 are housed in the recesses 3a of the split piece 3A of the anvil 3, the rubber dampers 11 and 12 are reliably prevented from falling off the anvil 3, and the impact tool can be stably operated. It becomes possible.

  In the present embodiment, the rubber damper 12 is interposed between the engaging claw 3d formed in the recess 3a of the divided piece 3A and the engaging claw 3h formed on the outer periphery of the large diameter portion 3f of the divided piece 3B. In addition, since the circumferential clearance δ2 is formed between the engaging claws 3d and 3h when there is no load, the circumferential vibration is caused by the elastic deformation of the rubber damper 12 until the engaging claws 3d and 3h come into contact with each other. When excessive torque is applied to the anvil 3, both engaging claws 3d and 3h come into direct contact as shown in FIG. 7, and torque is not applied to the divided piece 3B from the divided piece 3A without the rubber damper 12. Is transmitted directly, so that the tightening ability of the impact tool is enhanced.

  Furthermore, in the present embodiment, a convex portion 3c that intermittently engages with the convex portion 7b of the hammer 7 is formed on the other end surface in the axial direction of the divided piece 3A, and is engaged at a position where the convex portion 3c is formed. Since the claw 3d is formed, the strength of the engaging claw 3d is reinforced by the convex portion 3c, and the durability of the divided piece 3A and the impact tool as a whole is enhanced.

  Further, in the present embodiment, since the protrusions 12a are integrally provided on both axial end surfaces of each rubber damper 12, the end surface of the rubber damper 12 is positioned on the inner side in the axial direction of the end surfaces of the divided pieces 3A and 3B. 12 is prevented from directly contacting the end face of the divided pieces 3A and 3B, and no excessive shearing stress is generated in the rubber damper 12, and the rubber damper 12 is prevented from being damaged by cracks and thus durable. Improvement is achieved. In addition, when the rubber damper 12 is elastically deformed, the deformation is released by the protrusions 12a. Therefore, the vibration absorbing ability can be increased by setting the spring constant in the circumferential direction of the rubber damper 12 small.

  INDUSTRIAL APPLICABILITY The present invention is particularly useful for reducing noise by applying it to an impact tool such as a hammer drill for generating a rotating impact force to perform a required work.

It is a longitudinal cross-sectional view of the rotary impact mechanism part of the impact tool which concerns on this invention. It is the A section enlarged detail drawing of FIG. It is a sectional side view of the anvil of the impact tool according to the present invention (a sectional view taken along line BB in FIG. 6). FIG. 4 is an enlarged detail view of a C part in FIG. 3. It is a sectional side view (DD sectional view taken on the line of FIG. 6) of the anvil of the impact tool according to the present invention. It is a figure of the arrow E direction of FIG. FIG. 7 is a view similar to FIG. 6 with the rubber damper removed. It is a perspective view of a rubber damper. It is a longitudinal cross-sectional view of the conventional impact tool.

Explanation of symbols

1 Battery pack 2 Motor 2a Motor output shaft (motor shaft)
3 Anvil 3A Anvil segment (Division A)
3B Anvil split piece (split piece B)
3a Concave portion of divided piece A 3b Circular hole of divided piece A 3c Convex portion of divided piece A 3d Engaging claw (engaging claw a) of divided piece A
3e Shaft portion of divided piece B 3f Large diameter portion of divided piece B 3g Recessed portion of divided piece B 3h Engaging claw (engaging claw b) of divided piece B
3i Tip tool mounting portion of split piece B 3j Round hole of split piece B 4 Hammer case 5 Planetary gear mechanism 6 Spindle 6a Spindle cam groove 7 Hammer 7a Hammer cam groove 7b Protruding portion 7c Circular hole 8 Ball 9 Spring 10 Bearing metal 11 Rubber damper ( First damper)
11a Convex part of rubber damper 12 Rubber damper (second damper)
12a Rubber damper projection 13 Retaining washer 14 Tip tool S Space δ1 Axial clearance δ2 Radial clearance

Claims (5)

A rotary hammering mechanism is mounted on a spindle that is driven to rotate by a motor, and the rotary hammering force generated by the rotary hammering mechanism is intermittently transmitted from the mutually engaged hammers to the tip tool via the anvil, and then rotated to the tip tool. In impact tools that give impact force,
The anvil is divided into two in the axial direction, a concave portion is formed on one axial end surface of one divided piece A, one axial end portion of the other divided piece B is inserted into the concave portion, and the axial direction of the divided piece B A circumferential gap formed between the concave portion of the split piece A and one axial end portion of the split piece B, with a first damper interposed in the axial gap between the one end portion and the concave portion of the split piece A An impact tool characterized in that a second damper is interposed.   The concave portion of the divided piece A is a rectangular hole, and the second damper is provided in each of the spaces formed between the four corners of the rectangular hole and one axial end of the divided piece B. The impact tool according to claim 1.   An engaging claw a is formed in the recess of the split piece A, an engaging claw b is formed on the outer periphery of one end of the split piece B, and the second damper is interposed between the engaging claws a and b. The impact tool according to claim 1, wherein a circumferential clearance is formed between the engaging claws a and b when no load is applied.   A projecting portion that intermittently engages with the projecting portion of the hammer is formed on the other end surface in the axial direction of the divided piece A, and the engaging claw a is formed at a position where the projecting portion is formed. The impact tool according to claim 3. The impact tool according to any one of claims 1 to 4, wherein a protrusion is integrally provided on the axial end surface of the second damper.

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