Patent Publication Number: US-2022228618-A1

Title: Clip attachment structure

Description:
RELATED APPLICATIONS 
     This application claims the priority of Japanese Patent Application No. 2021-007707 filed on Jan. 21, 2021. The disclosure of the prior application is hereby incorporated herein in the entirety by reference. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     This invention relates to a clip attachment structure. 
     Description of Related Art 
     Japanese Laid-Open Patent Publication No. 2009-270615 describes such a clip attachment structure that a shaft portion of a clip body is inserted into a pedestal of a target member and the clip body is rotated around the axis by operation pieces, whereby fastening blades dig into a peripheral surface of the pedestal and thus the clip body and the target member are joined to each other. 
     However, in the case of the above clip, it is necessary to perform two operations of insertion and then rotation, and therefore workability is low. In addition, the axial hole of the pedestal into which the shaft portion of the clip body is inserted has a special shape, i.e., an elongated-hole shape, and therefore versatility is low. Accordingly, a structure having a simpler shape is desired. 
     An object of this invention is to provide a clip attachment structure that facilitates attachment work to an attachment-target member and has a simpler shape in an attachment portion of the attachment-target member. 
     SUMMARY OF THE INVENTION 
     A clip attachment structure for solving the aforementioned problem is a clip attachment structure in which a clip having a head portion and a leg portion protruding downward therefrom is attached such that the leg portion is inserted into a cylindrical insertion hole of an attachment-target member. The clip has a plurality of plate-shaped engagement protrusions arranged in an insertion direction into the insertion hole, the plate-shaped engagement protrusions extending outward from an outer circumferential surface of the leg portion in a non-elastically-deformed state. The engagement protrusions have sharpened corners at outermost edge portions corresponding to most distant positions from an axis of the leg portion on upper surfaces or lower surfaces thereof, the sharpened corners being sharpened to have a corner radius less than 0.2 mm. The sharpened corners include engagement corners configured to, at a time of insertion into the insertion hole, slide on an inner circumferential wall surface of the insertion hole while the engagement protrusions are elastically deformed, and after the insertion, form an engaged state of digging into the inner circumferential wall surface by elastic restoration of the engagement protrusions, thus preventing the clip from coming off from the insertion hole. 
     With the aforementioned configuration according to this invention, the clip is inserted into a simple cylindrical insertion hole. In each engagement protrusion pressed to the inner circumferential wall surface of the insertion hole, a corner at the outermost edge thereof is formed to be a sharpened corner that is substantially not rounded, instead of being rounded to be smoothly curved as in the conventional one. Thus, the sharpened corner (engagement corner) of the engagement protrusion more readily and more firmly digs into the inner circumferential wall surface of the insertion hole, and therefore coming-off from the insertion hole can be assuredly prevented simply by inserting the leg portion. Such a labor as to rotate the clip after insertion into an elongated hole in order to cause digging as in the conventional case is not needed. 
     Each engagement protrusion may be formed so as to satisfy L 1 ×⅓≤L 2  at least for an 80% region on the leg portion side in a length direction thereof, where L 1  is a length of the engagement protrusion and L 2  is a plate thickness thereof. With this configuration, each engagement protrusion is formed to have a certain thickness or more over a range up to a position close to the distal end. Thus, stiffness of each engagement protrusion is enhanced, so that the engagement corners can more firmly dig into the inner circumferential wall surface of the insertion hole. In addition, even if a force in a come-off direction is applied after the digging, each engagement protrusion is hardly bent owing to the stiffness, and therefore can sufficiently withstand the force, thereby preventing the clip from coming off. The corresponding part in the conventional clip is designed on the premise that this part is bent so as to reduce insertion resistance at the time of insertion, and therefore cannot have such a thickness as prescribed in this invention. 
     Here, regarding at least one of the engagement corners of each engagement protrusion, in a cross-section including the engagement corner and the axis of the leg portion, the length of a straight line PQ from a vertex P of the engagement corner to a connection point Q between the engagement protrusion and the leg portion is defined as the length L 1  of the engagement protrusion. Further, in a direction perpendicular to, of the upper and lower surfaces of the engagement protrusion, the surface having the engagement corners, a length from the surface to the other surface is defined as the plate thickness L 2  of the engagement protrusion. The length direction of the engagement protrusion is defined as the extending direction of the straight line PQ. In a case where each engagement protrusion has a plurality of engagement corners, L 2  and L 1  only have to satisfy the above relationship in the above cross-section including any of the engagement corners. 
     The engagement corners may be arranged so as to be distributed on a predetermined helix coaxial with the axis of the leg portion, thus serving as thread crests, so that the clip in the engaged state is allowed to be pulled out from the insertion hole by being rotated in a predetermined direction around the axis. With this configuration, for example, if the head portion at the upper end of the leg portion is provided with an engagement portion (jig engagement portion, e.g., cross-shaped groove) for rotating the clip toward the ascending-direction side of the helix by a predetermined jig, the clip can be detached from the insertion hole by the jig, and the clip can be reused. 
     The clip attachment structure may include insertion completion notification means configured to cause one or more of sound, a tactile sense, and shape change when the leg portion is inserted to a predetermined depth in the insertion hole. With this configuration, when a worker inserts the clip into the insertion hole, the worker can be notified of completion of the attachment. Thus, the clip can be assuredly inserted to a predetermined depth in the insertion hole. Depending on a place where the attachment work is performed, sound might be hardly heard. Therefore, if notification of attachment completion can be given by tactile sense or shape change, the worker can more easily recognize the attachment completion. 
     The clip may be attached to the attachment-target member such that the leg portion is inserted into the insertion hole at a stage after penetrating through a through hole of an intervening member separate from the attachment-target member. With this configuration, the intervening member as a third member is interposed between the attachment-target member and the clip firmly attached to each other, thus coming into a held state. Thus, a structure in which these three members are more firmly attached to each other can be achieved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a clip attachment structure according to a first embodiment; 
         FIG. 2  is a front view of a clip in  FIG. 1 ; 
         FIG. 3  is a side view of the clip in  FIG. 1 ; 
         FIG. 4  is a sectional view along line IV-IV in  FIG. 3 ; 
         FIG. 5  is an enlarged view of part V in  FIG. 4 ; 
         FIG. 6  is an enlarged view of part VI in  FIG. 2 ; 
         FIG. 7  is an enlarged view of part VII in  FIG. 3 ; 
         FIG. 8  is an enlarged perspective view of a part of the clip in  FIG. 1 , as seen from an obliquely lower side; 
         FIG. 9  is an enlarged view of part IX in  FIG. 8 ; 
         FIG. 10  is a sectional view along line X-X in  FIG. 3 , illustrating a procedure for attaching the clip in  FIG. 1  to an attachment-target member; 
         FIG. 11  is a sectional view following  FIG. 10 ; 
         FIG. 12  is a sectional view following  FIG. 11 ; 
         FIG. 13  is a sectional view along line A-A in  FIG. 4 , schematically showing a first engagement protrusion when the clip is being inserted into an insertion hole; 
         FIG. 14  is a sectional view following  FIG. 13 ; 
         FIG. 15  is a sectional view following  FIG. 14 ; 
         FIG. 16  is a sectional view along line B-B in  FIG. 4 , schematically showing a second engagement protrusion when the clip is being inserted into the insertion hole; 
         FIG. 17  is a sectional view following  FIG. 16 ; 
         FIG. 18  is a sectional view following  FIG. 17 ; 
         FIG. 19  is an exploded perspective view of a clip attachment structure according to a first modification; 
         FIG. 20  is a sectional view illustrating a procedure for attaching a clip in  FIG. 19  to an attachment-target member; 
         FIG. 21  is a sectional view following  FIG. 20 ; 
         FIG. 22  is a sectional view following  FIG. 21 ; 
         FIG. 23  is an exploded perspective view of a clip attachment structure according to a second modification; 
         FIG. 24  is a sectional view illustrating a procedure for attaching a clip in  FIG. 23  to an attachment-target member; 
         FIG. 25  is a sectional view following  FIG. 24 ; 
         FIG. 26  is a sectional view following  FIG. 25 ; 
         FIG. 27  is a perspective view of a clip used in a third modification; 
         FIG. 28  is an exploded perspective view of a clip attachment structure in  FIG. 27 ; 
         FIG. 29  is a front view of a clip in  FIG. 27 ; 
         FIG. 30  is a side view of the clip in  FIG. 27 ; 
         FIG. 31  is a sectional view along line XXXI-XXXI in  FIG. 30 ; 
         FIG. 32  is an enlarged view of part XXXII in  FIG. 29 ; 
         FIG. 33  is an enlarged view of part XXXIII in  FIG. 30 ; 
         FIG. 34  is a sectional view along line E-E in  FIG. 31 , schematically showing the first engagement protrusion when the clip is being inserted into the insertion hole; 
         FIG. 35  is a view following  FIG. 34 ; 
         FIG. 36  is a view following  FIG. 35 ; 
         FIG. 37  is a sectional view of a clip attachment structure according to a fourth modification; 
         FIG. 38  is a sectional view schematically showing an engagement protrusion when a clip in a fifth modification is being inserted into an insertion hole; 
         FIG. 39  is a view following  FIG. 38 ; 
         FIG. 40  is a view following  FIG. 39 ; and 
         FIG. 41  is a sectional view along line A-A in FIG.  4 , schematically showing another method for prescribing the plate thickness of the engagement protrusion. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of this invention will be described with reference to the drawings. 
     A clip attachment structure according to this embodiment is a structure  100  (see  FIG. 12 ) in which a clip  1  shown in  FIGS. 1 to 3  is attached such that a leg portion  2  is inserted into a cylindrical insertion hole  11  of an attachment-target member  10  shown in  FIG. 1 . Here, the attachment-target member  10  is a vehicular member and has the straight-cylindrical insertion hole  11  having an axis in a direction substantially vertical to a main surface of the attachment-target member  10 . 
     The cylindrical insertion hole in this invention may be any hole having an inner circumferential wall surface forming an annular shape along the same curved surface as the outer circumferential surface of a predetermined cylindrical shape forming a substantially cylindrical shape. The shapes of a bottom surface and an opening of the insertion hole are not particularly limited, and the insertion hole may be a through hole or a bottomed hole. The substantially cylindrical shape includes a case where the shape has error of ±5% for the hole width (diameter) in the radial direction perpendicular to the axis of the insertion hole, and a case where the shape has a draft taper angle of 1 degree or less. Such error is tolerated also for the aforementioned substantially vertical direction. 
     As shown in  FIGS. 2 and 3 , the clip  1  has, integrally, a head portion  4 , the leg portion  2  protruding downward from the head portion  4 , and plate-shaped engagement protrusions  3  extending in an obliquely upward-and-outward direction from the outer circumferential surface of the leg portion  2 . Here, the clip  1  and the attachment-target member  10  are formed as injection-molded products of resin. 
     The leg portion  2  is a columnar part to be inserted from a lower end (distal end) of the head portion  4  into the insertion hole  11  of the attachment-target member  10 . The direction (axial direction) of an axis  2   z  of the leg portion  2  coincides with an insertion direction I into the insertion hole  11 . 
     The head portion  4  has a shape spreading outward (outer circumferential side) from the axis  2   z  side at the upper end (base end) of the leg portion  2 . Here, the head portion  4  spreads substantially in a disk shape centered on the axis  2   z . When the leg portion  2  is inserted into the insertion hole  11 , a lower surface  4 D of the head portion  4  opposes and faces an opening peripheral surface  12  of the insertion hole  11 , and therefore the head portion  4  is not inserted into the insertion hole  11  (see  FIGS. 10 to 12 ). 
     As shown in  FIGS. 2 and 3 , a plurality of engagement protrusions  3  are formed so as to be arranged at equal intervals in the insertion direction I on the leg portion  2 . Each engagement protrusion  3  is formed in a plate shape extending in an obliquely upward-and-outward direction from the outer circumferential surface of the leg portion  2  in a natural state (a non-elastically-deformed state in which elastic deformation is not caused). In each engagement protrusion  3 , the distal-end side thereof opposite to the leg portion  2  side can be elastically deformed in the up-down direction, with the leg portion  2  side as a fulcrum. 
     As shown in  FIGS. 4 and 5 , each engagement protrusion  3  has an outermost edge portion corresponding to the most distant position from the axis  2   z  of the leg portion  2 , in an outer edge portion of one of an upper surface  3 C and a lower surface  3 D (here, only the lower surface  3 D). Here, as shown in  FIGS. 8 and 9 , in all the engagement protrusions  3 , outermost edge portions  3   d   1 ,  3   d   3  can be specified among outer edge portions  3   d   0  to  3   d   4  of the lower surface  3 D. At least the outermost edge portions  3   d   1 ,  3   d   3  are formed as sharpened corners sharpened so as to have a corner radius less than 0.2 mm, or more desirably, a corner radius not greater than 0.1 mm. At the time of inserting the clip  1  into the insertion hole  11  and after the insertion (after completion of the insertion) as shown in  FIGS. 10 to 12 , the sharpened corners  3   d   1 ,  3   d   3  serve as engagement corners ( 3   d   1 ,  3   d   3 ) to interfere and engage with an inner circumferential wall surface  11   r  (see  FIGS. 13 to 15 and 16 to 18 ). 
     In this embodiment, all the outer edge portions  3   d   0  to  3   d   4  of the lower surface  3 D of each engagement protrusion  3  are the above-described sharpened corners and have a corner radius of 0 mm. The lower surface  3 D is a flat surface. Meanwhile, in each engagement protrusion  3 , all the other corners (e.g., corner surfaces a, b, c, e, f, g, h (see  FIG. 5 )) except for the outer edge portions  3   d   0  to  3   d   4  of the lower surface  3 D are formed as mild curved (rounded) surfaces. The upper surface  3 C is a flat surface. 
     At the time of insertion into the insertion hole  11 , the engagement corners  3   d   1 ,  3   d   3  slide on the inner circumferential wall surface  11   r  (see  FIGS. 14 and 17 ) and the engagement protrusion  3  is elastically deformed such that the distal-end side (engagement corner  3   d   1 ,  3   d   3  side) thereof is bent upward. Meanwhile, after insertion into the insertion hole  11  (after completion of the insertion), the engagement corners  3   d   1 ,  3   d   3  form an engaged state of digging into the inner circumferential wall surface  11   r  by elastic restoration of the engagement protrusion  3  (see  FIGS. 15 and 18 ). By this engagement, the clip  1  is prevented from coming off from the insertion hole  11 , and the clip  1  is attached to the attachment-target member  10 , thus forming the attachment structure  100 . 
     Here, the engagement corners  3   d   1 ,  3   d   3  are lower edges of the corner surfaces e, g, on both end sides in the circumferential direction about the axis  2   z , of a distal-end surface  3 T at the most distant position from the axis  2   z  of the leg portion  2  in each engagement protrusion  3  (see inside broken-line circles in  FIGS. 5 to 7 and 9 ). The distal-end surface  3 T forms the engagement corners  3   d   1 ,  3   d   3 , together with the lower surface  3 D, and is an elevation surface extending in the up-down direction from the engagement corners  3   d   1 ,  3   d   3  which are connection portions with the lower surface  3 D. Further, the distal-end surface  3 T is one of all side surfaces  3 A,  3 B,  3 T of the engagement protrusion  3 , and is formed by surfaces t, c, e, f, g, h including a flat center portion and curved corners therearound. The side surface  3 A is formed by surfaces s, a (see  FIG. 6 ), and the side surface  3 B is formed by surfaces u, b (see  FIG. 7 ). 
     In this invention, the engagement protrusion is formed to be thicker than the conventional one. More specifically, the engagement protrusion  3  is formed to be thicker not only at the base-end side but over a range up to the distal-end side, and has higher stiffness over the entirety from the base-end side to the distal-end side than the conventional one. Thus, after the leg portion  2  is inserted into the insertion hole  11  (after completion of the insertion), the engagement protrusion  3  more readily digs into the inner circumferential wall surface  11   r.    
     The plate thickness of the engagement protrusion  3  is set to satisfy the following prescription. That is, the engagement protrusion  3  forming a plate shape is formed to satisfy such a condition that, as shown in  FIG. 13 , where the length thereof is denoted by L 1  and the plate thickness thereof is denoted by L 2 , the plate thickness L 2  is not less than ⅓ of the length L 1  (L 1 ×⅓≤L 2 ), in at least an 80% region (OQ) on the leg portion  2  side in the length direction. 
     In this case, regarding at least one (here,  3   d   1 ) of the engagement corners  3   d   1 ,  3   d   3  of each engagement protrusion  3 , in a cross-section including the engagement corner ( 3   d   1 ) and the axis  2   z  of the leg portion  2  (see  FIG. 13 ), the length of a straight line PQ from a vertex P of the engagement corner  3   d   1  to a connection point Q between the engagement protrusion  3  and the leg portion  2  is defined as the length L 1  of the engagement protrusion  3 . Further, in a direction perpendicular to, of the upper and lower surfaces of the engagement protrusion  3 , the surface having the engagement corners  3   d   1 ,  3   d   3  (here, lower surface  3 D), a length from the surface (lower surface  3 D) to the other surface (upper surface  3 C) is defined as the plate thickness L 2  of the engagement protrusion  3 . The length direction of the engagement protrusion  3  is defined as the extending direction of the straight line PQ. In the case where the engagement protrusion  3  has a plurality of engagement corners  3   d   1 ,  3   d   3  as in this embodiment, the above relationship between L 1  and L 2  need not be satisfied for all the plurality of engagement corners  3   d   1 ,  3   d   3 , and only has to be satisfied for one or more of them (here,  3   d   1 ). 
     Further, in a 20% region (PO) on the distal-end side opposite to the leg portion  2  in the length direction of the engagement protrusion  3 , the plate thickness L 2  of the engagement protrusion  3  here is prescribed as follows. That is, the engagement protrusion  3  is prescribed such that, in the 20% region (PO) on the distal-end side of the engagement protrusion  3  in the above cross-section (see  FIG. 13 ), an outer edge line M formed by end points, on the side opposite to the straight line PQ, of a cut line C cutting the engagement protrusion  3  along the direction perpendicular to the straight line PQ passes a position coinciding with a straight line RP extending from an end R on the leg portion  2  side of the outer edge line M to the vertex P of the engagement corner  3   d   1 , or a position outward thereof (on the side away from the straight line PQ). 
     The engagement protrusion  3  having the plate thickness L 2  prescribed as described above is formed to be thicker than the conventional one, and has such a shape that the distal-end surface  3 T proximally opposes the inner circumferential wall surface  11   r  of the insertion hole  11  at the time of inserting the leg portion  2  into the insertion hole  11  and after the insertion. In this embodiment, the distal-end surface  3 T of the engagement protrusion  3  approaches the inner circumferential wall surface  11   r  such that parts (engagement corners  3   d   1 ,  3   d   3 ) of the lower edge dig into the inner circumferential wall surface  11   r  and also the upper-edge side comes close to the inner circumferential wall surface  11   r , so that the entire distal-end surface  3 T forms a surface inclined from the inner circumferential wall surface  11   r . Here, when the engagement protrusion  3  is in the natural state (non-elastically-deformed state) (see  FIGS. 13 and 16 ), at both the engagement corner  3   d   1  and the engagement corner  3   d   3 , an angle θn in the radial direction between the distal-end surface  3 T and the direction of the axis  2   z  is not less than 0 degrees and not greater than 30 degrees, or the distal-end surface  3 T and the direction of the axis  2   z  are parallel to each other. 
     Here, θn is shown as an angle between the distal-end surface  3 T and the inner circumferential wall surface  11   r  substantially parallel to the axis  2   z  when the engagement protrusion  3  is in the natural state (non-elastically-deformed state). In  FIGS. 14, 15, 17 , and  18 , θs and θb denote angles between the distal-end surface  3 T and the direction of the axis  2   z  (inner circumferential wall surface  11   r ) when the engagement protrusion  3  slides on the inner circumferential wall surface  11   r  or the engagement protrusion  3  is in an engaged state. 
     As shown in  FIGS. 2 and 3 , the clip  1  has reinforcement plate portions  6 . The reinforcement plate portions  6  have plate shapes extending in the insertion direction I and protruding outward from a plurality of positions in the circumferential direction on the outer circumferential surface of the leg portion  2  (here, from four sides of the outer circumferential surface; see  FIG. 4 ). Here, each engagement protrusion  3  is formed over an area between the reinforcement plate portions  6  adjacent to each other in the circumferential direction. Thus, the strength and stiffness of the engagement protrusion  3  are enhanced, so that the engagement protrusion  3  assuredly digs into the inner circumferential wall surface  11   r  (see  FIG. 7 ). 
     As shown in  FIGS. 4 and 5 , each engagement protrusion  3  is cut out on the outer sides of neighboring connection areas with both reinforcement plate portions  6  connected on both sides in the circumferential direction, so that cutouts  3 V,  3 U are formed. Thus, elasticity of the engagement protrusion  3  is slightly enhanced on the distal-end side (distal-end surface  3 T side), thereby facilitating insertion into the insertion hole  11  to a certain extent. 
     The cutout  3 V does not appear in a cross-section including the engagement corner  3   d   1  and the axis  2   z  of the leg portion  2  (A-A cross-section in  FIG. 4 ; see  FIGS. 13 to 15 ), but appears in a cross-section including the engagement corner  3   d   3  and the axis  2   z  of the leg portion  2  (B-B cross-section in  FIG. 4 ; see  FIGS. 16 to 18 ). That is, in the engagement protrusion  3 , on the engagement corner  3   d   3  side, the cutout  3 V is present at an intermediate part, so that the distal-end side (engagement corner  3   d   1  side) which is the outer side from the cutout  3 V is a little more bendable. Therefore, the engagement protrusion  3  in this embodiment has the first engagement corner  3   d   1  where high stiffness is imparted over a range up to the distal-end side, thus having an effect of deeply and assuredly digging into the inner circumferential wall surface  11   r  of the insertion hole  11 , and the second engagement corner  3   d   3  where the distal-end side is more bendable than on the first engagement corner  3   d   1  side owing to the cutout  3 V, thus having an effect of facilitating insertion by elastic deformation. In the case where there are a plurality of engagement corners in the engagement protrusion  3 , the plate thickness L 2  of the engagement protrusion  3  only has to be prescribed using at least one of the engagement corners as a reference. In this embodiment, the first engagement corner  3   d   1  is used as a reference, and L 1  and L 2  defined using the first engagement corner  3   d   1  as a reference satisfy the above prescription of the plate thickness L 2  (see  FIG. 13 ). 
     The engagement protrusion  3  in this embodiment will be described more specifically. 
     As shown in  FIG. 2 , the engagement protrusions  3  are formed symmetrically with respect to the axis  2   z  between a first side (right side in  FIG. 2 ) and a second side (left side in  FIG. 2 ) opposite thereto in a first perpendicular direction  2   x  of perpendicular directions (radial directions) perpendicular to the axis  2   z  of the leg portion  2 . In addition, as shown in  FIG. 3 , the engagement protrusions  3  are formed symmetrically with respect to the axis  2   z  also between a first side (right side in  FIG. 3 ) and a second side (left side in  FIG. 3 ) opposite thereto in a second perpendicular direction  2   y  perpendicular to both the axis  2   z  and the first perpendicular direction  2   x . As shown in  FIG. 4 , the engagement protrusions  3  in this embodiment are formed such that four engagement protrusions  3  are present so as to surround the leg portion  2  along the circumferential direction of the leg portion  2 , and a plurality of sets of the four engagement protrusions  3  are arranged at predetermined intervals in the direction of the axis  2   z  (axial direction). 
     In  FIG. 4 , two pairs of engagement protrusions  3  respectively present adjacently across the reinforcement plate portions  6  on the first side (upper side in  FIG. 4 ) and the second side (lower side in  FIG. 4 ) in the first perpendicular direction  2   x , correspond to, in  FIG. 2 , the engagement protrusions  3  shown on the front sides of the left and right reinforcement plate portions  6 , and the engagement protrusion  3  present on the back sides of the left and right reinforcement plate portions  6  and therefore not shown. The pair of engagement protrusions  3  present on the front and back sides of the reinforcement plate portion  6  at the left in  FIG. 2  form flat-plate shapes extending in an obliquely upward-and-outward direction (obliquely upward-and-leftward direction in  FIG. 2 ) at the same angle with respect to the axis  2   z  of the leg portion  2  in the first perpendicular direction  2   x , and as shown in  FIG. 6 , both upper surfaces  3 C on the shallow side and both lower surfaces  3 D on the deep side in the insertion direction I extend on the same planes S 1  and S 2 , respectively. Here, the planes S 1  and S 2  are parallel to each other. Meanwhile, the pair of engagement protrusions  3  present on the front and back sides of the reinforcement plate portion  6  at the right in  FIG. 2  form flat-plate shapes extending in an obliquely upward-and-outward direction (obliquely upward-and-rightward direction in  FIG. 2 ) at the same angle with respect to the axis  2   z  of the leg portion  2  in the first perpendicular direction  2   x , and as in the relationships between the upper surface  3 C and S 1  and between the lower surface  3 D and S 2  in  FIG. 6 , both upper surfaces  3 C on the shallow side and both lower surfaces  3 D on the deep side in the insertion direction I extend on the same planes S 3  and S 4 , respectively. Here, the planes S 3  and S 4  are also parallel to each other. 
     As shown in  FIG. 2 , the clip  1  has elastic latch pieces  5  as insertion completion notification means of this invention. 
     When the leg portion  2  is inserted to a predetermined depth in the insertion hole  11  and thus the insertion is completed, the insertion completion notification means causes at least one of sound, a tactile sense, and shape change, thereby notifying an attachment worker that the attachment is completed. 
     In this embodiment, each elastic latch piece forming the insertion completion notification means has an elastic piece portion  5 M extending from the lower surface  4 D of the head portion  4  (or from the upper-end side of the leg portion  2 ) obliquely outward so as to be separated from the leg portion  2  toward the insertion direction I in the natural state (non-elastically-deformed state), and a distal-end latch portion  5 L provided at the distal end of the elastic piece portion  5 M and being capable of forming a latched state in which the elastic piece portion  5 M is elastically deformed toward the shallow side in the insertion direction I so that the distal-end latch portion  5 L moves around to the upper side of the outer edge of the head portion  4  so as to be latched, thereby preventing restoration to the natural state position. 
     The elastic latch piece  5  is formed such that, in the elastic piece portion  5 M, the base-end side connected to the head portion  4  (or leg portion  2 ) is more readily elastically deformable than the other region in the length direction of the elastic piece portion  5 M. Thus, as shown in  FIGS. 10 to 12 , the distal-end side of the elastic latch piece  5  can be swung (pivoted) up/down with the base-end side as a fulcrum. Through this swing, the elastic latch piece  5  can bring the distal-end latch portion  5 L close to an outer edge latch portion  4 L provided at the outer edge of the head portion  4 , and further, by riding over the outer edge latch portion  4 L, can form a latched state with the outer edge latch portion  4 L (a downward-detachment prevented state; see  FIG. 12 ). 
     Then, the attachment worker can perceive sound and a tactile sense caused when the distal-end latch portion  5 L rides over the outer edge latch portion  4 L, and further can visually recognize shape change thereof. Thus, the attachment worker can recognize that the leg portion  2  of the clip  1  is inserted to a predetermined depth in the insertion hole  11  and attachment is completed. In this latched state, the elastic piece portion  5 M is pressed to the lower surface  4 D side of the head portion  4  by the opening peripheral surface  12  of the insertion hole  11  and thus is kept in a state of extending outward along the lower surface  4 D. 
     Here, the elastic latch pieces  5  are formed on both sides across the axis  2   z  in the direction perpendicular to the axis  2   z  (here, the first perpendicular direction  2   x ). In addition, in the head portion  4 , the outer edge latch portions  4 L to be latched with the distal-end latch portions  5 L of the elastic latch pieces  5  are formed as thin portions which are thinner than the center area around the axis  2   z  so that the distal-end latch portions  5 L can easily ride over them. 
     The attachment procedure for attaching the clip  1  to the attachment-target member  10  will be described with reference to  FIGS. 10 to 18 . 
     First, as shown in  FIG. 10 , the leg portion of the clip  1  is inserted into the cylindrical insertion hole  11  of the attachment-target member  10  from the distal end  2 T positioned opposite to the head portion  4  such that both axes  2   z  and  11   z  coincide with each other. The distal end  2 T of the leg portion  2  is tapered so as to facilitate insertion into the insertion hole  11 . 
     As the leg portion  2  is inserted into the insertion hole  11 , the four engagement protrusions  3  at the lowermost stage among the engagement protrusions  3  come into contact with the opening peripheral surface  12  of the insertion hole  11  (see  FIGS. 13 and 16 ). Then, by further pushing the leg portion  2  into the insertion hole  11 , each engagement protrusion  3  is pushed into the insertion hole  11  while the distal-end side thereof is elastically deformed toward the shallow side (upper side) in the insertion direction I, and thus the leg portion  2  is further inserted while the engagement corners  3   d   1 ,  3   d   3  slide on the inner circumferential wall surface  11   r  (see  FIGS. 14 and 17 ). After the engagement protrusions  3  at the lowermost stage are pushed into the insertion hole  11 , the engagement protrusions  3  at the next stage come into contact with the opening peripheral surface  12  of the insertion hole  11 , and then, after they are pushed into the insertion hole  11 , the engagement protrusions  3  at the further next stage come into contact with the opening peripheral surface  12 . That is, for every time of the contact, the leg portion  2  is further pushed into the insertion hole  11 , whereby the leg portion  2  is inserted into the insertion hole  11 . In all the engagement protrusions  3  pushed into the insertion hole  11 , the distal-end sides thereof are elastically deformed to bend upward, and the engagement corners  3   d   1 ,  3   d   3  thereof slide on the inner circumferential wall surface  11   r  (see  FIGS. 14 and 17 ). 
     However, actually, rather than pushing the engagement protrusions  3  into the insertion hole  11  stage by stage sequentially, the attachment worker pushes them into the insertion hole  11  entirely by one pushing operation through the stages up to the final stage (uppermost stage) of the engagement protrusions  3  or near the final stage. 
     As the engagement protrusions  3  are moved into the insertion hole  11 , the elastic latch pieces  5  come into contact with the opening peripheral surface  12  of the insertion hole  11  as shown in  FIG. 11 . With further movement, the elastic latch pieces  5  are pushed up by the opening peripheral surface  12  so as to approach the head portion  4 , and are swung (pivoted) with the base-end sides as fulcrums. Thus, the distal-end latch portions  5 L approach the outer edges of the head portion  4  from the lower side. Then, when the engagement protrusions  3  at the final stage (uppermost stage) are moved into the insertion hole  11  and thus the leg portion  2  is inserted to a predetermined depth in the insertion hole  11 , the elastic latch pieces  5  are further swung (pivoted), and as shown in  FIG. 12 , the distal-end latch portions  5 L ride over the outer edges of the head portion  4 , so as to be latched with the outer edges (outer edge latch portions  4 L) at positions after the riding, thus coming into a latched state. Thus, the insertion of the clip  1  into the insertion hole  11  is completed and the attachment structure  100  is formed. 
     While the leg portion  2  is moving into the insertion hole  11 , as shown in  FIGS. 14 and 17 , the distal-end side of each engagement protrusion  3  slides on the inner circumferential wall surface  11   r  while bending toward the direction (upward) opposite to the insertion direction I by the force of inserting the clip  1  into the insertion hole  11 . Then, when the insertion of the clip  1  into the insertion hole  11  is completed and the insertion force is eliminated, the engagement protrusion  3  is elastically restored so that the engagement corners  3   d   1 ,  3   d   3  start to dig into the inner circumferential wall surface  11   r . Thus, as shown in  FIGS. 15 and 18 , owing to the digging, the leg portion  2  of the clip  1  is fixed to the insertion hole  11  in a come-off prevented state. In this way, the clip  1  is fixed while forming an engaged state of digging into the insertion hole  11 , thus forming the attachment structure  100  to the attachment-target member  10 . 
     In this embodiment, when the above digging is further advanced, not only the engagement corners  3   d   1 ,  3   d   3  but also the sharpened corner  3   d   2  connecting these digs into the inner circumferential wall surface  11   r . However, while the clip  1  is being inserted into the insertion hole  11 , the sharpened corner  3   d   2  has no contact with the inner circumferential wall surface  11   r  and does not slide on the inner circumferential wall surface  11   r . Therefore, even though the sharpened corner  3   d   2  does not have sliding resistance during insertion of the clip  1 , the sharpened corner  3   d   2  serves as a sub engagement corner (which may be referred to as auxiliary engagement corner) that can dig into the inner circumferential wall surface  11   r  after the insertion. The sub engagement corner may be absent as long as the engagement corners are present. 
     At the time of inserting the clip  1  into the insertion hole  11 , the attachment worker for the clip  1  can hear contact sound caused at each time as the engagement protrusions  3  sequentially hit and contact with the opening peripheral surface  12  of the insertion hole  11 . In addition, the attachment worker can also perceive a tactile sense due to the contact, as well as the contact sound. However, since the engagement protrusions  3  are formed in the same shape, the attachment worker cannot determine, with only the contact sound and the tactile sense, whether or not the clip  1  is inserted to a predetermined depth in the insertion hole  11 , i.e., whether or not the insertion is completed. 
     Regarding this, in this embodiment, when the insertion of the clip  1  into the insertion hole  11  is completed, the distal-end latch portions  5 L of the elastic latch pieces  5  ride over the outer edges of the head portion  4  and thus come into a latched state of being latched with the outer edges at positions after the riding. With this latching, sound and a tactile sense are caused, whereby completion of the insertion of the clip  1  into the insertion hole  11  can be determined. The engagement protrusions  3  and the elastic latch pieces  5  are completely different from each other in stiffness and shape, and therefore cause completely different sounds and tactile senses. Thus, the sound and the tactile sense of the latching can be recognized so as to be clearly distinguished from those caused by the engagement protrusions  3 . Further, since the latched state of the elastic latch pieces  5  is visually apparent, completion of the insertion can be determined also by visual recognition. 
     Although one embodiment of this invention has been described above, this embodiment is merely illustrative, this invention is not limited thereto, and various modifications such as additions and omissions may be made on the basis of the knowledge of a person skilled in the art without departing from the scope of the claims. 
     Hereinafter, embodiments other than the above embodiment, and modifications thereof will be described. It is noted that parts having the same functions as those in the above embodiment are denoted by the same reference characters, and the detailed description thereof is omitted. The above embodiment, and the following modifications and other embodiments, may be combined to be implemented as appropriate as long as no technical contradiction arises. 
     The attachment-target member  10  in the above embodiment may be any member that at least has a cylindrical insertion hole, and is not limited to the above-described one. 
     The insertion completion notification means (elastic latch pieces  5 ) in the above embodiment enables the attachment worker to recognize completion of insertion of the clip  1  into the insertion hole  11  by sound, a tactile sense, and shape change. However, the insertion completion notification means only has to cause at least one of sound, a tactile sense, and shape change when the insertion is completed. Among these, if one or both of a tactile sense and shape change can be caused, the attachment worker can recognize completion of the insertion even when the working space is in a harsh condition due to noise or the like. In this invention, the insertion completion notification means (elastic latch pieces  5  in the above embodiment) may be omitted. 
     A first modification of the above embodiment will be described with reference to  FIGS. 19 to 22 . 
     In the first modification, as shown in  FIG. 19 , the clip  1  having the same shape as in the above embodiment, the attachment-target member  10  (here, plate-shaped member) having a boss  13  protruding in a tubular shape, and an intervening member  20  (counterpart member) to be held between the head portion  4  of the clip  1  and the attachment-target member  10 , are provided to form the attachment structure  100  (see  FIG. 22 ). A through hole  21  is formed in the intervening member  20 , and the attachment-target member  10  has the cylindrical insertion hole  11  formed in the boss  13  protruding from a main surface thereof. The clip  1  is attached to the attachment-target member  10  such that the leg portion  2  is inserted into the insertion hole  11  at a stage after penetrating through the through hole  21  of the plate-shaped intervening member  20 . Thus, the attachment structure  100  (see  FIG. 22 ) of the clip  1  is formed with the intervening member  20  held between the attachment-target member  10  and the clip  1 . That is, the attachment structure  100  is such a structure that the intervening member  20  is assembled with the attachment-target member  10  using the clip  1 . 
     In this case, the attachment procedure for attaching the clip  1  to the attachment-target member  10  is as follows. First, the leg portion  2  is inserted into the through hole  21  of the plate-shaped intervening member  20 , and at the subsequent stage, the leg portion is inserted also into the insertion hole  11  of the attachment-target member  10  (see  FIG. 20 ). Thereafter, the leg portion  2  is inserted into the through hole  21  and the insertion hole  11  in the same manner as in the above embodiment (see  FIG. 21  and then  FIG. 22 ). The insertion of the leg portion  2  into the insertion hole  11  is also the same as in the above embodiment, and thus is performed such that the engagement protrusions  3  slide on the inner circumferential wall surface  11   r  while being elastically deformed (see  FIG. 14 ). When the engagement protrusions  3  at the final stage (uppermost stage) move into the insertion hole  11  and the leg portion  2  is inserted to a predetermined depth in the insertion hole  11 , as shown in  FIG. 22 , the intervening member  20  abuts on (closely contacts with) the opening peripheral surface  12  of the attachment-target member  10 , and on the opposite side, an opening peripheral surface  22  around the through hole  21  of the intervening member  20  comes into contact with the elastic latch pieces  5  (insertion completion notification means), and then the opening peripheral surface  22  pushes up the elastic latch pieces  5  so as to approach the head portion  4 . With this pushing, the distal-end latch portions  5 L of the elastic latch pieces  5  ride over the outer edges of the head portion  4 , to come into a latched state. Thus, the insertion of the clip  1  into the insertion hole  11  is completed. This completion can be recognized by the attachment worker through sound and a tactile sense due to the latching, visual recognition of the latched state (visual recognition of shape change), and the like, as in the above embodiment. In addition, at the time of the completion, the engagement protrusions  3  dig into the inner circumferential wall surface  11   r  of the insertion hole  11 , as in the above embodiment (see  FIG. 15 ). 
     A second modification of the above embodiment will be described with reference to  FIGS. 23 to 26 . 
     In the second modification, as shown in  FIG. 23 , the clip  1  having the same shape as in the above embodiment except for the head portion  4 , and the attachment-target member  10  having the cylindrical insertion hole  11 , are provided to form the attachment structure  100  (see  FIG. 26 ). The head portion  4  has an umbrella shape spreading outward from the base end of the leg portion  2  toward the distal-end side of the leg portion  2 , and an outer circumferential portion  4 R thereof serves as the insertion completion notification means of this invention. 
     In this case, the attachment procedure for attaching the clip  1  to the attachment-target member  10  is basically the same as in the above embodiment (see  FIG. 24  and then  FIG. 25 ). However, when the leg portion  2  is inserted into the insertion hole  11  and reaches to a predetermined depth, as shown in  FIG. 26 , the umbrella-shaped outer circumferential portion  4 R of the head portion  4  comes into contact with the opening peripheral surface  12  of the attachment-target member  10 , so that the opening peripheral surface  12  pushes up the outer circumferential portion  4 R to the upper side. With this pushing, the outer circumferential portion  4 R changes from the umbrella shape spreading outward toward the distal-end side of the leg portion  2  (see  FIG. 25 ), to a reverse umbrella shape in which the outer circumferential side is bent by being pushed up (see  FIG. 26 ). Thus, the insertion of the clip  1  into the insertion hole  11  is completed, whereby the attachment structure  100  for the clip  1  is formed. This completion can be easily recognized by the attachment worker through sound and a tactile sense due to bending of the outer circumferential portion  4 R, visual recognition of the reverse umbrella shape (visual recognition of shape change), and the like. 
     A third modification of the above embodiment will be described with reference to  FIGS. 27 to 33 . 
     The clip  1  of the third modification has almost the same shape as in the above embodiment except that some of the engagement protrusions  3  are replaced with engagement protrusions  9  as shown in  FIGS. 27 and 28 . As with the engagement protrusions  3 , a plurality of engagement protrusions  9  are formed so as to be arranged in the insertion direction I on the leg portion  2 . Engagement corners  3   d   1 ,  3   d   3 ,  9   d   1 ,  9   d   3  of the respective engagement protrusions  3 ,  9  are formed so as to be distributed on a helix coaxial with the axis  2   z  of the leg portion  2 . With the distributed arrangement on the helix, the clip  1  cannot be directly pulled out upward from the insertion hole  11  in a state in which the attachment structure  100  is formed, but can be pulled out like a screw by being rotated in a predetermined direction around the axis  2   z.    
     The engagement corners  3   d   1 ,  3   d   3 ,  9   d   1 ,  9   d   3  of the respective engagement protrusions  3 ,  9  are formed so as to be distributed on one helix coaxial with the axis  2   z  or a plurality of helices arranged in parallel in the direction of the axis  2   z  (axial direction) coaxially therewith (here, two helices H 1 , H 2  that do not overlap each other) (see  FIG. 27 ). Therefore, for example, if the head portion  4  is provided with an engagement portion  8  (jig engagement portion; here, cross-shaped groove) for rotating the clip  1  toward the ascending-direction side of the helices by a predetermined jig (e.g., screwdriver), the clip can be easily detached from the insertion hole  11  by the jig. In addition, the clip  1  can be reused. 
     As shown in  FIGS. 29 and 30 , regarding the engagement protrusions  3 ,  9  of the third modification, the engagement protrusions  3  on one of the sides adjacent to each other across the reinforcement plate portion  6  are formed in a plate shape extending in an obliquely upward-and-outward direction from the outer circumferential surface of the leg portion  2  in the natural state (non-elastically-deformed state), and thus are formed in the same shape as in the above embodiment. Meanwhile, the engagement protrusions  9  on the other side are formed in a plate shape extending in an obliquely downward-and-outward direction from the outer circumferential surface of the leg portion  2  in the natural state. As in the above embodiment, the distal-end side of each engagement protrusion  3 ,  9  can be elastically deformed in the up-down direction with the leg portion  2  side as a fulcrum. The description of the engagement protrusions  3  is omitted because they have the same shape as in the above embodiment. 
     The engagement protrusions  9  will be specifically described. In each engagement protrusion  9  extending in an obliquely downward-and-outward direction, outermost edge portions  9   d   1 ,  9   d   3  at the most distant positions from the axis  2   z  among outer edge portions  9   d   0  to  9   d   4  of a lower surface  9 D are formed as sharpened corners (see  FIGS. 31 to 33 ). Here, all the outer edge portions  9   d   0  to  9   d   4  are formed as sharpened corners. The sharpened corners  9   d   1 ,  9   d   3  forming the outermost edge portions serve as engagement corners to interfere and engage with the inner circumferential wall surface  11   r  at the time of inserting the clip  1  into the insertion hole  11  and after the insertion (see  FIG. 34 ). At the time of insertion into the insertion hole  11 , the engagement corners  9   d   1 ,  9   d   3  slide on the inner circumferential wall surface  11   r  (see  FIG. 35 ) and each engagement protrusion  9  is elastically deformed such that the distal-end side (sharpened corner  9   d   1 ,  9   d   3  side) thereof is bent upward. Meanwhile, after the insertion, the engagement corners  9   d   1 ,  9   d   3  form an engaged state of digging into the inner circumferential wall surface  11   r  by elastic restoration of the engagement protrusion  9  (see  FIG. 36 ). 
     In this third modification, the sharpened corner  9   d   1  is a first engagement corner, and the sharpened corner  9   d   3  is a second engagement corner. An upper surface  9 C and the lower surface  9 D are flat surfaces parallel to each other. Of side surfaces  9 A,  9 B,  9 T, the side surface  9 T is a distal-end surface of the engagement protrusion  9 . 
     For the thicknesses of the engagement protrusions  3 ,  9 , the same prescription as in the above embodiment is applied (see  FIGS. 13 and 34 ). The engagement protrusion  9  is also formed with the thickness based on the same prescription (see  FIG. 34 ) as in the engagement protrusion  3 , and has such a shape that the distal-end surface  9 T proximally opposes the inner circumferential wall surface  11   r  of the insertion hole  11  at the time of inserting the leg portion  2  into the insertion hole  11  (see  FIG. 35 ) and after the insertion (see  FIG. 36 ). Here, in the natural state (non-elastically-deformed state) (see  FIG. 34 ), the distal-end surface  9 T is inclined such that an angle θn in the radial direction between the distal-end surface  9 T and the direction of the axis  2   z  (inner circumferential wall surface  11   r ) is not less than 0 degrees and not greater than 30 degrees. 
     A fourth modification of the above embodiment will be described with reference to  FIG. 37 . 
     In the fourth modification, the head portion  4  of the clip  1  is provided with an assembly portion  7  to be assembled with another member  30  different from the attachment-target member  10 . Then, the attachment structure  100  for the clip  1  is formed in a state in which the other member  30  is assembled with the assembly portion  7 . 
     A fifth modification of the above embodiment will be described with reference to  FIGS. 38 to 40 . 
     In the fifth modification, an outermost edge portion  9   c   1  is present at the most distant position from the axis  2   z  of the leg portion  2 , in an outer edge portion of the upper surface  9 C of the engagement protrusion  9  extending obliquely downward from the leg portion  2 . The outermost edge portion  9   c   1  is formed as a sharpened corner, and serves as an engagement corner. Thus, at the time of insertion into the insertion hole  11 , the engagement corner  9   c   1  slides on the inner circumferential wall surface  11   r  (see  FIG. 39 ) and the engagement protrusion  9  is elastically deformed such that the distal-end side (sharpened corners  9   d   1 ,  9   d   3  side) thereof is bent upward. Meanwhile, after the insertion, the engagement corner  9   c   1  forms an engaged state of digging into the inner circumferential wall surface  11   r  by elastic restoration of the engagement protrusion  9  (see  FIG. 40 ). The cross-sections shown in  FIGS. 38 to 40  are similar to the cross-section in  FIG. 13 , and are cross-sections cut so as to include the axis  2   z  of the leg portion  2  and the engagement corner  9   c   1  in the engagement protrusion  9 . The engagement protrusions  9  in the fifth modification may be replaced with the engagement protrusions  3  extending obliquely upward from the leg portion  2 . 
     The plate thickness L 2  of the engagement protrusions  3  applicable in this invention may be prescribed by another method. 
     For example, P and Q used in the prescription in the above embodiment may be set by a method different from the above method. The cross-section of the engagement protrusion  3  in  FIG. 41  is a cross-section obtained by cutting the engagement protrusion  3  in the same manner as in  FIG. 13 . In this cross-section, the engagement corner  3   d   1  is set as a vertex P, an approximate straight line is set so as to pass the engagement corner  3   d   1  along a ridge line extending from the vertex P to the base-end side (leg portion  2  side) of the engagement protrusion  3 , and then the intersection of the approximate straight line and a cut plane D obtained by cutting the engagement protrusion  3  from the leg portion  2  can be set as a connection point Q between the engagement protrusion  3  and the leg portion  2 . Such prescription is effective for a case where the lower surface  3 D or the upper surface  3 C of the engagement protrusion  3  is not flat, a case of having a large thickened portion  3 E provided at an upper/lower part on the base-end side of the engagement protrusion  3  so as to smoothly connect the engagement protrusion  3  and the leg portion  2 , or the like. 
     Alternatively, the plate thickness L 2  of the engagement protrusion  3  may be prescribed as follows. That is, in the natural state (non-elastically-deformed state), regarding at least one (here,  3   d   1 ) of the engagement corners  3   d   1 ,  3   d   3 , the plate thickness L 2  of the engagement protrusion  3  may be prescribed such that, in the cross-section in  FIG. 13  or  FIG. 41  including the engagement corner  3   d   1  and the axis  2   z  of the leg portion  2 , the length L 2  of the cut line C in the 80% region (OQ) on the leg portion  2  side excluding the 20% region (PO) on the distal-end side in the region of the straight line PQ satisfies L 1 ×⅓≤L 2  irrespective of the cut position, and in the 20% region (PO) on the distal-end side, the outer edge line M formed by end points of the cut line C on the side opposite to the straight line PQ passes a position coinciding with the straight line RP extending from the end R on the leg portion  2  side of the outer edge line M to the vertex P of the engagement corner  3   d   1 , or a position outward thereof. 
     The plate thickness of the engagement protrusions in this invention may satisfy at least one of all the prescriptions described above. 
     DESCRIPTION OF THE REFERENCE CHARACTERS 
     
         
         
           
               100  clip attachment structure 
               1  clip 
               2  leg portion 
               3 ,  9  engagement protrusion 
               3   d   0  to  3   d   4 ,  9   d   0  to  9   d   4 ,  9   c   1  outer edge portion (sharpened corner) 
               3   d   1 ,  3   d   3 ,  9   d   1 ,  9   d   3 ,  9   c   1  engagement corner 
               4  head portion 
               4 R outer circumferential portion (insertion completion notification means) 
               5  elastic latch piece (insertion completion notification means) 
               10  attachment-target member 
               11  insertion hole 
               20  intervening member 
               21  through hole 
             L 1  length of engagement protrusion 
             L 2  plate thickness of engagement protrusion 
             I insertion direction