Abstract:
A fastener for connecting plate members includes a male member, and a female member to be inserted into mounting holes of the plate members. The female member includes a cylinder body for receiving the main body therein, a projecting portion formed on an outer periphery of the cylinder body at one end thereof, and protruding portions formed at the other end thereof. A first engaging portion is formed on an outer surface of a main body of the male member or an inner surface of the cylinder body, and a second engaging portion engaging the first engaging portion is formed on the inner surface or the outer surface. The second engaging portion has two engaging sections and a smooth surface portion interposed therebetween. When the male member is inserted into the female member, the male member can be easily engaged with the female member.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
   The present invention relates to a fastener for fixing laminated plate members. 
   A conventional fastener for fixing laminated plate members is shown in FIG.  12  and  FIG. 13 , which is disclosed in Japanese Utility Model Publication (KOKOKU) No. S58-60016. 
   A fastener  100  comprises a grommet  102  and a pin  104 , which are formed of a flexible resin. The grommet  102  is inserted into mounting holes  110  and  112  of plate members  106  and  108 , which are positioned and laminated, and the pin  104  is inserted into the grommet  102 , so that the plate members  106  and  108  are fixed so as not to be separated from each other. 
   The grommet  102  includes a cylinder member  122  provided with a flange  120 , and when the cylinder member  122  is inserted into the mounting holes  110  and  112 , the flange  120  abuts against the upper plate member  106  to regulate the position of the grommet  102  in an inserting direction. On an inner peripheral surface of the cylinder member  122 , four engagement claws  124  (three engagement claws  124  are shown in the figure) are formed near a mouth of the cylinder member  122  in a peripheral direction at equal intervals therebetween. Below each engagement claw  124  (a distal end side of the inserting direction), there is formed a slit  126  which is cut up to a distal end portion of the cylinder member  122 , and accordingly, the distal end side of the cylinder body  122  is divided into four to form four elastic pieces  128  in a cantilever shape. Also, an inner peripheral surface side of each elastic piece  128  constitutes a protruding portion  130  that protrudes inwardly. 
   The pin  104  includes a pin main body  134  having a flange  132  at a head portion thereof. A male screw  136  is formed in a substantially entire area of a straight portion of an outer peripheral surface of the pin main body  134 , and a distal end portion  138  has a tapered shape. 
   When the pin  104  is inserted into the grommet  102 , the male screw  136  engages the claws  124 , and receives an insertion load. When the pin  104  is further inserted as it is, the distal end portion  138  of the pin  104  pushes the protruding portions  130 , and the elastic pieces  128  are expanded. Thereafter, the pin  104  is inserted until the flange  132  of the pin  104  abuts against a concave portion  140  formed on an upper surface of the flange  120  of the grommet  102 , so that the elastic pieces  128  are expanded to the maximum and engaged with the mounting hole  112 . This engagement condition is maintained by engagement between the male screw  136  and the engagement claws  124 , and accordingly, the plate members  106  and  108  are clamped and fixed by the flange  120  and the elastic pieces  128 . 
   In the conventional fastener  100  described above, however, since the male screw  136  is inserted while being always caught by the engagement claws  124  as the pin  104  is inserted into the grommet  102 , a heavy insertion load is generated and maintained through the whole insertion process. This continuous insertion load causes poor workability and an additional burden to an operator. 
   The present invention has been made in view of the foregoing, and an object of the invention is to provide a fastener in which an insertion load is reduced and workability is improved. 
   Further objects and advantages of the invention will be apparent from the following description of the invention. 
   SUMMARY OF THE INVENTION 
   To achieve the aforementioned object, the first aspect of the present invention provides a fastener inserted into mounting holes formed in plate members for fixing the plate members in a laminated state. The fastener is formed of a female member, and a male member. The female member has a cylinder body to be inserted into the mounting holes, a projecting portion, an engaging portion, and a protruding portion. In the female member, the projecting portion is provided on an outer peripheral surface of the cylinder body at one end, and has a larger diameter than the mounting holes. The engaging portion is provided on an inner peripheral surface of the cylinder body, and at the other end of the cylinder body, the protruding portion is provided along the inner peripheral surface at a position closer to a distal end side in an inserting direction than the engaging portion. The other end of the cylinder body with the protruding portion can be expanded and engaged with the mounting holes. The male member has a male member main body with two ends, a projecting portion having a diameter larger than that of the male member main body and provided at one end thereof, a first male screw formed on an outer peripheral surface of the male member main body, and a second male screw formed on the outer peripheral surface of the male member main body at a predetermined interval spaced from the first male screw. The second male screw is located at a position closer to the other end of the male member main body than the first male screw. The male member main body presses the protruding portion outwardly when the male member main body is inserted into the cylinder body of the female member more than a predetermined depth. 
   In the fastener according to the first aspect of the invention, when the main body of the male member is inserted into the cylinder body of the female member, the second male screw formed on the outer peripheral surface of the main engages the engaging portion formed on the inner peripheral surface of the cylinder body. Accordingly, the male member is held by the female member to be temporarily assembled. Also, in this temporarily assembled condition, since the main body of the male member does not press the protruding portion formed on the inner peripheral surface of the female member, the expanding portion of the female member is not expanded. 
   When the female member in this temporarily assembled condition is inserted into the mounting holes of the plate members, the projecting portion formed on the outer peripheral surface of the cylinder body abuts against one of the plate members. Thus, the position of the female member in the inserting direction is set. When the male member is further inserted into the female member, an insertion load is created due to an engagement of the second male screw with the engaging portion. This load is maintained until the second male screw is disengaged from the engaging portion. When the second male screw is disengaged from the engaging portion, the insertion load is released. From this point, the male member again can be easily inserted into the female member until the first male screw reaches the engaging portion. When the first male screw reaches the engaging portion, the insertion load is created again. 
   Once the male member reaches the predetermined depth at the end of or during the insertion with a low load, the main body of the male member starts to press the protruding portion outwardly to expand the end of the female member. Also, this engaging condition is maintained by the engagement between the first male screw and the engaging portion. Therefore, the laminated plate members are clamped and fixed by the projecting portion of the female member. 
   Accordingly, when the male member is inserted into the female member in the operation of fixing the plate members, since there is a period when an insertion load is released, the workability is improved, and burden to an operator is reduced. 
   According to the second aspect of the invention, a fastener may be formed of a male member having a male member main body; and a female member having a cylinder body, a projecting portion, a first female screw, a second female screw, and a protruding portion. In the male member, the male member main body is provided with an engaging portion on an outer peripheral surface thereof. In the female member, the cylinder body is designed to be inserted into the mounting holes and to receive the male member main body therein. The projecting portion is provided on an outer peripheral surface of one end of the cylinder body and has a diameter larger than those of the mounting holes. The first female screw is formed on an inner peripheral surface of the cylinder body, and capable of engaging the engaging portion of the male member main body inserted therein. The second female screw is formed on the inner peripheral surface of the cylinder body at a predetermined interval spaced from the first female screw, and is located at a position closer to a distal end side in an inserting direction of the male member main body than the first female screw. The second female screw engages the engaging portion when the male member main body is inserted into the female member more than a predetermined depth. The protruding portion is formed on the inner peripheral surface of the cylinder body at a position closer to the distal end side in the inserting direction of the male member main body than the second female screw, and the protruding portion is pressed outwardly by the male member main body when the male member main body is inserted more than the predetermined depth. The distal end of the female member is expanded and engaged with the mounting holes when the protruding portion is pressed outwardly. 
   In the fastener according to the second aspect of the invention, when the main body of the male member is inserted into the cylinder body of the female member, the engaging portion formed on the outer peripheral surface of the main body of the male member engages the first female screw formed on the inner peripheral surface of the cylinder body. Accordingly, the male member is held by the female member to be temporarily assembled. Also, in this temporarily assembled condition, since the main body of the male member does not press the protruding portion formed on the inner peripheral surface of the female member, the distal end of the female member is not expanded. 
   When the temporarily assembled female member is inserted into the mounting holes of the plate members, the projecting portion formed on the outer peripheral surface of the cylinder body abuts against the plate member. Thus, the position of the female member in the inserting direction is set. When the male member is inserted into the female member, an insertion load is caused by the engagement between the first female screw and the engaging portion. The insertion load is maintained until the first female screw is disengaged from the engaging portion. When the first female screw is disengaged from the engaging portion, the insertion load is released until the engaging portion reaches the second female screw. After the engaging portion reaches the second female member, the insertion load occurs again. 
   Once the male member reaches a predetermined depth at the end of or during the insertion with a low load, the main body of the male member presses the protruding portion outwardly to expand the expanding portion of the female member. Accordingly, in the female member, the expanded distal end engages the mounting holes, and the engagement condition is maintained by the engagement between the engaging portion and the second female screw. As a result, the laminated plate members are clamped and fixed by the projecting portion of the female member. 
   As described above, even in the structure in which the engaging portion is formed on the outer peripheral surface of the main body of the male member and the two female screws disposed at a predetermined interval are formed on the cylinder of the female member, the insertion load can be released when inserting the male member into the female member, resulting in an improvement in workability. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an exploded perspective view of a fastener according to an embodiment of the invention in a condition that a grommet and pin are separated; 
       FIG. 2  is a perspective view of a grommet according to an embodiment of the invention; 
     FIGS.  3 (A) and  3 (B) are views showing the grommet in  FIG. 2 , wherein FIG.  3 (A) is a top plan view thereof, and FIG.  3 (B) is a front view thereof; 
     FIGS.  4 (A) and  4 (B) are views showing the grommet in  FIG. 2 , wherein FIG.  4 (A) is a rear view thereof, and FIG.  4 (B) is a bottom plan view thereof; 
     FIGS.  5 (A) and  5 (B) are views showing the grommet in  FIG. 2 , wherein FIG.  5 (A) is a cross sectional view taken along line  5 A— 5 A in FIG.  3 (A), and FIG.  5 (B) is a cross sectional view taken along line  5 B— 5 B in FIG.  3 (A); 
       FIG. 6  is a perspective view of a pin according to an embodiment of the invention; 
     FIGS.  7 (A) to  7 (E) are views showing the pin in  FIG. 6 , wherein FIG.  7 (A) is a top plan view thereof; FIG.  7 (B) is a left side view thereof; FIG.  7 (C) is a front view thereof; FIG.  7 (D) is a right side view thereof; and FIG.  7 (E) is a bottom plan view thereof; 
     FIGS.  8 (A) and  8 (B) are views showing the pin in  FIG. 6 , wherein FIG.  8 (A) is a rear view thereof, and FIG.  8 (B) is a cross sectional view taken along line  8 B— 8 B in FIG.  7 (A); 
       FIG. 9  is a partly sectional view for explaining steps of fixing a louver to a panel by a fastener according to an embodiment of the invention, in which a temporarily assembled fastener is inserted into mounting holes; 
       FIG. 10  is a partly sectional view for explaining steps of fixing a louver to a panel by the fastener according to the embodiment of the invention, in which the pin is partly inserted into the grommet; 
       FIG. 11  is a partly sectional view for explaining steps of fixing the louver to the panel by the fastener according to the embodiment of the invention, in which the pin is completely inserted into the grommet to fix the louver to the panel; 
       FIG. 12  is a partly sectional view for explaining steps of fixing plate members by a conventional fastener, in which a grommet is inserted into mounting holes; and 
       FIG. 13  is a partly sectional view for explaining steps of fixing plate members by a conventional fastener, in which the pin is completely inserted into the grommet to fix the plate members. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereunder, embodiments of the invention will be explained with reference to the accompanied drawings. 
     FIG. 1  shows an exploded perspective view of a fastener (fastening device) according to an embodiment of the invention, and a fastener  10  is formed of a grommet  12  and a pin  14 , which are formed by a flexible resin.  FIG. 2  to FIG.  5 (B) shows the grommet  12 , and  FIG. 6  to FIG.  8 (B) shows the pin  14 . 
   Firstly, the grommet  12  will be explained. The grommet  12  includes a cylinder body  22  that is provided with a circular flange  20  at an upper end portion of an outer peripheral surface thereof. The flange  20  has a substantially tapered shape, in which an end portion side of an upper surface is gently sloped downwardly, and a circular concave portion  24  having a diameter larger than that of the cylinder body  22  is formed at a center of the upper surface of the flange  20 . 
   The cylinder body  22  has a tapered shape in which a diameter of an outer peripheral surface of a distal end portion  23  is reduced toward the distal end side, so as to be easily inserted into mounting holes of plate members. Also, the cylinder body  22  is provided with an insertion hole  26  into which the pin  14  is inserted, and a tapered portion  28  that constitutes an inclined surface having a diameter reduced toward an insertion direction is formed at a mouth of the insertion hole  26 . The tapered portion  28  can easily guide the pin  14  into the insertion hole  26 . 
   A female screw  30  is formed on an inner peripheral surface of the insertion hole  26  at a position slightly deeper than the mouth. The female screw  30  has round screw threads, in which apexes of sections of respective screw threads are substantially circular arc forms, and is provided with two threads (two leads). An insertion direction distal end side of the female screw  30  is provided with four slits  32 , which are formed by cutting the cylinder wall of the cylinder body  22  up to the distal end portion and disposed in a circumferential direction at intervals of 90 degrees. The slits  32  divide the distal end side of the cylinder body  22  into four cantilever-like elastic pieces  34 . 
   An inner peripheral surface of each elastic piece  34  is provided with a protruding portion  36 , which has an upper portion constituting a tapered surface  36 A having a diameter decreased toward the distal end side and is protruded inwardly, and an outer peripheral surface of each elastic piece  34  is provided with a concave or groove  38 . The concave  38  makes a wall thickness of the elastic piece  34  substantially constant, and prevents sink upon molding. The elastic piece  34  bends elastically to be expanded when the protruding portion  36  is pressed outwardly. 
   The pin  14  includes a pin main body  42  provided with a circular flange  40  formed at a head thereof. The flange  40  has a diameter slightly smaller than that of the circular concave portion  24  of the grommet  12 , and has an upper surface gently curved to constitute a substantially spherical surface. A cross recess or Phillips screw slot  44  is formed at a central portion of the upper surface of the flange  40 . 
   In the pin main body  42 , a male screw  46  is formed below the flange  40  on an outer peripheral surface thereof, and a male screw  48  is formed at a side closer to the distal end side than the male screw  46  by having a predetermined interval between the male screw  46  and the male screw  48 . The male screw  46  and the male screw  48  have round screw threads, in which apexes of sections of the respective screw threads are substantially circular arc forms. An outside diameter and a root diameter of the screws are made uniformly, and the pitch and the lead angle are made in accordance with those of the female screw  30  of the grommet  12 . 
   Further, a portion between the male screw  46  and the male screw  48  constitutes a cylindrical smooth portion  50  having a diameter smaller than a diameter at roots of these screws, and a distal end portion  52  of the pin main body  42  has a tapered form. 
   Next, operations of the embodiment of the invention will be explained.  FIG. 9  to  FIG. 11  shows steps of fixing a louver to a panel by the fastener  10 . 
   Firstly, before the fastener  10  is assembled with the louver and the panel, the pin  14  is inserted into the grommet  12  to assemble the fastener  10  temporarily. In this case, as shown in  FIG. 9 , the pin  14  is inserted into the grommet  12  in such a degree that the male screw  48  formed at the distal end side of the pin main body  42  is inserted inside the insertion hole  26  of the cylinder body  22 . Accordingly, the male screw  48  of the pin main body  42  engages the female screw  30 , and the pin  14  is held by the grommet  12  temporarily. 
   Secondly, the grommet  12  of the temporarily assembled fastener  10  is inserted into the mounting holes  64  and  66  of the louver  60  and the panel  62 , which are positioned and laminated. Here, a position of the fastener  10  in the inserting direction is regulated by the flange  20  of the grommet  12  that abuts against the upper surface of the louver  60 . 
   When the pin  14  is inserted into the grommet  12 , an insertion load is created. When the male screw  48  is disengaged from the female screw  30 , the cylindrical portion  50  is positioned at the female screw  30  to release the insertion load, so that the pin  14  can be inserted further with less insertion load. 
   While passing through the cylindrical portion  50 , the distal end portion  52  of the pin main body  42  and the female screw  48  reach the protruding portions  36  of the cylinder body  22 . When the pin  14  is further inserted from this position, the elastic pieces  34 , in which the protruding portions  36  are pressed by the distal end portion  52  and the male screw  48 , are gradually expanded as shown in FIG.  10 . Incidentally, in the condition that the elastic pieces  34  have just started expanding, since the force necessary for bending the elastic pieces  34  is small, the insertion load of the pin  14  does not increase greatly. 
   As the pin  14  is further inserted, the male screw  46  reaches the female screw  30  to engage therewith, so that the insertion load appears again. Then, the pin  14  is inserted until the flange  40  of the pin  14  abuts against the circular concave portion  24  of the grommet  12 , the flange  40  is accommodated in the circular concave portion  24 , and the elastic pieces  34  are expanded at the maximum to engage the mounting hole  66 . This engaging condition is maintained by the engagement between the male screw  46  and the female screw  30 . Therefore, the louver  60  and the panel  62 , which are laminated, are clamped and fixed by the flange  20  of the grommet  12 . 
   Also, in the case of removing the fastener  10 , a Phillips type screw driver is inserted into the cross recess  44  of the pin  14  to turn the pin  14  in a predetermined direction, so that the pin  14  is removed from the grommet  12 . Accordingly, the elastic pieces  34  of the grommet  12  return to the original state, and the grommet  12  in which the engagement condition is released can be pulled out from the mounting holes  64  and  66 . 
   Incidentally, although the fastener  10  is inserted into the mounting holes  64  and  66  after the fastener  10  is temporarily assembled in the steps described above, the grommet  12  is inserted into the mounting holes  64  and  66  in advance, and then the pin  14  can be inserted into the grommet  12 . 
   As described above, in the fastener  10  according to the embodiment of the invention, when the pin  14  is inserted into the grommet  12  to fix the louver  60  to the panel  62 , there is a period that the insertion load is released. Therefore, the workability is improved as compared with the conventional fastener, and burden to an operator is reduced. 
   Incidentally, although the one female screw  30  is formed in the grommet  12  side and the two male screws  46  and  48  disposed at the predetermined interval are formed in the pin  14  side in the aforementioned embodiment, the number of the female screw and the number of the male screws can be switched. Namely, the same object can be achieved in a structure that one male screw is provided in the pin side and two female screws disposed at the predetermined interval are formed in the grommet side. 
   Also, the female screw  30  formed in the grommet  12  side can be any form as long as it can engage the male screws  46  and  48  and can be detached by turning the pin  14  at the time of disassembling. The female screw  30  can be, for example, claws or projections. Also, the same thing can be applied in the case that the number of the female screw and the number of the male screws are switched, and in this case, a male screw in the pin side can be replaced by claws or the like. 
   Also, the shape of the flange  20  formed in the grommet  12  side is not limited to the one in the embodiment, and it can be a rectangular shape or the like as long as the flange  20  can regulate the position of the grommet  12  inserted into the mounting holes  64  and  66 . Further, the flange  20  can be a projected portion other than the flange. 
   Also, the numbers and the shapes of the elastic pieces  34  and the protruding portions  36  formed in the grommet side  12  are not limited to those in the embodiment, and can be adequately modified in accordance with shapes and depths of the mounting holes. 
   Since the fastener of the invention has the structure as described above, the insertion load is lowered, and assembling workability is improved. 
   While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.