Abstract:
A pair of bosses are formed in the vicinity of a cut out portion of a lower casing from which a lead circuit section, which is integrally formed with a switch circuit section a flexible printed circuitry is led out. Three engagement holes are arranged in a longitudinal direction of the lead circuit section with predetermined intervals at both end portions of a widthwise direction thereof. The lead circuit section is folded such that all the respective three engagement holes are fitted with the respective bosses while providing surplus length portion in the form of S-shape, and then led out from the cut out portion. The upper casing having a pair of hold-down members are combined with the lower casing such that the hold-down members are engaged with the respective bosses to constitute a casing which serves as a switch unit.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a lead out structure for a lead circuit section connected to a flexible printed circuitry housed in a casing of a switch unit. 
     Door trims for vehicles such as automobiles are normally provided with electrical equipment such as a switch unit including power window switches for use in opening and closing window glasses, door mirror driving switches and so on; and courtesy lamps that are switched off when doors are shut and switched on when opened. In order to connect these kinds of electrical equipment, the door trim is rigged with a number of electric wires and connectors. Such wiring operation is very troublesome because it is carried out blindly through the working window of a door panel. Moreover, many parts for use in electrical mechanism-to mechanism connection are required, which will also result in arduous work of incorporating and connecting them. 
     In consequence, there has recently been employed a flat circuitry for wiring to complete the connection of electrical equipment (e.g., Japanese Patent Publication No. 9-309390A). A switch holder  1  in a related flat circuitry has been so configured as shown in FIG.  4 . 
     In FIG. 4, the upper-side terminal section  3  of a flexible printed circuitry  2  is bent at a right angle and inserted into and fixed to a switch holder  1 . The flexible printed circuitry  2  includes a plastic insulating film  4  and a plurality of parallel printed circuits  5  arranged in the insulating film  4 . Further, an engagement hole  6  is bored in four corners of the insulating film  4  and a plurality of contacts  7  following the respective printed circuits  5  are provided in the upper-side terminal section  3  of the flexible printed circuitry  2 . 
     The plastic switch holder  1  comprises a rectangular base plate  8  and a frame-like cover  9  that is pivotal with respect to the base plate  8 . The cover  9  is coupled to the base plate  8  by, for example, thin-walled hinges that are integral therewith. A frame wall  10  is uprightly provided to both sides of the base plate  8 . Further, an elastic retaining arm  12  and a curved elastic flap  13  with respect to a door trim  11  are projected from the outer wall face of each frame wall  10 . In other words, the elastic retaining arm  12  is provided on the rear end portion of each frame wall  10 , whereas the elastic flap  13  is provided on the front end portion thereof. Each elastic retaining arm  12  has a retaining projection  14  and a releasing member  15 . Moreover, engagement holes  17  with respect to the locking projections  16  provided to the cover  9  are formed in the frame wall  10 . 
     Positioning pins  19  each having conical tilted guide faces  18  relative to the respective retaining holes  6  of the flexible printed circuitry  2  are projected from the base plate  8 . Further, an opening  20  is provided in the cover  9 , so that the contacts  7  of the flexible printed circuitry  2  and the positioning pins  19  can be located within the opening  20 . Incidentally, the tilted guide face  18  may be continuous from the upper to lower ends of the positioning pin  19 . 
     The terminal section  3  of the flexible printed circuitry  2  is positionally mounted on the base plate  8  by mating the engagement holes  6  with the respective positioning pins  19 . Then the locking projections  16  are fitted in the respective engagement holes  17  by closing the cover  9 , which is locked in such a condition that it clamps the terminal section  3 . The positioning pins  19  are so positioned as to project within the opening  20 . Due to the positioning pins  19 , the contacts  7  are precisely positioned. 
     FIG. 5 shows a state wherein a flat circuitry  21  has been incorporated in the door trim  11 . More specifically, an opening  22  is formed in the door trim  11 , and a pair of insertion guides  23  with respect to the switch holder  1  of the flat circuitry  21 . are provided in the direction of thickness of the door trim  11 . The insertion guides  23  are L-shaped and projected from the upper wall  24  within the opening  22 . Moreover, an engagement hole (not shown) is formed in each insertion guide  23  with respect to the retaining projection  14  of the elastic retaining arm  12  of the switch holder  1 . The switch holder  1  is supported by the elastic retaining arms  12  and the elastic flaps  13  between the pair of insertion guides  22  so as to be movable in the widthwise direction thereof. 
     The flexible printed circuitry  2  is made immovable by fitting the positioning pins  19  in the engagement holes  6  respectively provided in the four corners of the insulating film  4  and holding down the flexible printed circuitry.  2  with the cover  9 . 
     The flexible printed circuitry  2  is prepared by printing switching circuits on the film to form an extremely thin contact switch. Although the flexible printed circuitry  2  is immovably fixed by fitting the positioning pins  19  in the respective engagement holes  6  and made immovable by holding it down with the cover  9 , the film-like lead circuit section is drawn from the switching circuit section. Consequently, the film-like lead circuit section is strong enough to withstand the tensile force applied in its longitudinal direction. When force is applied in a direction perpendicular to the longitudinal direction of the film-like lead circuit section (in its widthwise direction), however, excessive force as tensile stress is to be applied to one side portion of the circuit section. 
     When the tensile stress is applied from the outside to the flexible printed circuitry  2  like this, the operating switches may not easily be turned on as the switch contacts become displaced. When further excessive tensile stress is applied from the outside to the flexible printed circuitry  2 , the problem is that the disconnection of switching circuits occurs. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention is provide a structure wherein a switching circuitry is formed integrally with a lead circuitry whereby to prevent stress from being applied to the switching circuitry even when tensile stress is applied to the lead circuitry while the lead circuitry is being wired and conveyed, to prevent the switching circuitry from being displaced even when excessive stress acts on the lead circuitry; and to prevent the lead circuitry from being broken even when excessive stress acts on the lead circuitry. 
     In order to accomplish the object above, according to the present invention, there is provided a structure comprising: 
     a flexible printed circuitry including a lead circuit section integrally provided with a switch circuit section, and at least one engagement hole is formed on a part of the lead circuit section; 
     a lower casing having a side wall provided with a cut out portion from which the lead circuit section is led out, and at least one boss formed in the form of S-shape, to which the engagement hole is fitted to mount the flexible printed circuitry thereon; and 
     an upper casing combined with the lower casing to constitute a casing which serves as a switch circuit unit, the upper casing having at least one hold-down member engaged with the boss to hold down the lead circuit section onto the lower casing. 
     Since the switching circuitry is formed integrally with the lead circuitry whereby it is possible to prevent stress from being applied to the switching circuitry even when tensile stress is applied to the lead circuitry while the lead circuitry is being wired and conveyed; to prevent the switching circuitry from being displaced even when excessive stress acts on the lead circuitry; and to prevent the lead circuitry from being broken even when further excessive stress acts on the lead circuitry. 
     Preferably, at least three engagement holes are formed on the lead circuit section so as to be arranged in a longitudinal direction thereof with predetermined intervals. The lead circuit section is folded such that all the engagement holes are fitted with the boss to be mounted on the lower casing while providing surplus length portions in the vicinity of the boss, and then led out from the cut out portion. 
     Preferably, a pair of the at least three engagement holes are formed on the lead circuit section at both end portions in a widthwise direction thereof. A pair of bosses are formed on the lower casing so as to fit with the respective at least three engagement holes. A pair of hold-down members are formed on the upper casing so as to engage with the respective bosses. 
     Accordingly, even when tensile stress is applied to the lead circuit section while the lead circuit section is being wired or conveyed, such stress can be absorbed by the engagement holes and further stress can be absorbed by the surplus length portion. Therefore, the stress is prevented from being applied to the switching circuit section and even when the excessive stress acts on the lead circuit section, the displacement and breakage of the switching circuit section can be prevented. 
     Preferably, the hold-down member is a tubular member into which the boss is fitted. 
     Since the front end of the hold-down member holds down the lead circuit section fitted with the engagement hole, tensile stress applied to the lead circuit section while the lead circuit section is being wired or conveyed can be further surely absorbed. Therefore, the stress is prevented from being applied to the switching circuit section and even when the excessive stress acts on the lead circuit section, the displacement and breakage of the switching circuit section can be prevented. 
     Preferably, reinforcing dummy patterns are formed on the flexible printed circuitry at both end portions in a widthwise direction thereof. 
     Since the lead circuit section is formed with reinforcing dummy patterns capable of withstanding tensile stress, the breakage of the lead circuit section, and the displacement of the switching circuit section can be surely prevented. 
     Preferably, a protective film or a copper foil is formed on the lead circuit section so as to surround the engagement hole. 
     Since force is applied most strongly to the engagement hole formed in the lead circuit section when the lead circuit section is being wired or conveyed, the provision of the protective films or copper foils on the peripheries of the engagement hole can prevent the breakage of the engagement hole and the displacement of the switching circuit section. 
     According to the present invention, there is also provided a method comprising the steps of: 
     preparing a flexible printed circuitry including a lead circuit section integrally provided with a switch circuit section, and at three engagement holes are arranged on a lead circuit section in a longitudinal direction thereof with predetermined intervals; 
     preparing a lower casing having a side wall provided with a cut out portion from which the lead circuit section is led out, and a boss formed in the vicinity of the cut out portion; 
     folding the lead circuit section such that all the engagement holes are fitted with the boss while providing surplus length portions in the form of S-shape in order to mount the flexible printed circuitry onto the lower casing; 
     leading out the lead circuit section from the cut out portion; and 
     combining an upper casing having a hold-down member with the lower casing such that the hold-down member engages with the boss to hold down the lead circuit section onto the lower casing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is an overall perspective view of an application of a lead out structure for a lead wire harness section connected to a flexible printed circuitry housed in a casing of a switch unit, according to one embodiment of the present invention; 
     FIG. 2 is an exploded perspective view showing how to assemble the portion A shown in FIG. 1; 
     FIG. 3 is a diagram illustrating a procedure for mounting the lead wire harness section of the flexible printed circuitry shown in FIG. 1; 
     FIG. 4 is an exploded perspective view of a state where a related flexible printed circuitry is assembled in a switch holder; and 
     FIG. 5 is an exploded perspective view of a state where flexible printed circuitry shown in FIG.  4 . is assembled into a door trim. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description will now be given of one embodiment of the present invention with reference of the preferred embodiment. 
     FIG. 1 is a perspective view showing a lead out structure for a lead wire harness section connected to a flexible printed circuitry housed in a casing of a switch unit. FIG. 2 is an exploded perspective view showing how to assemble the portion A shown in FIG.  1 . 
     As shown in FIG. 1, an arm rest portion  31  is formed on a door trim  30  in such a manner as to project from the back face  32  of the door trim  30 . A plastic upper casing  33  is fitted to the arm rest portion  31 , and a lower casing  32  is fitted in the upper casing  33 , the upper casing  33  and the lower casing  34  constituting a housing case  35 . A switching circuit section  36  is housed in the housing case  35 , and a lead wire harness section  37  is connected to the switching circuit section  36 . The switching circuit section  36  and the lead wire harness section  37  constitute a flexible printed circuitry  38 . The flexible printed circuitry  38  (may be called FPC) is prepared through the steps of printing switching circuits on a flexible film-like plastic material and connecting lead wires to the respective switching circuits by printed wiring in order to form an integrated component. The lead wire harness section  37  of the flexible printed circuitry  38  is led from the housing case  35  outside, a connector  39  being connected to the front end of the lead wire harness section  37 . The connector  39  is used to connect the flexible printed circuitry  38  to an external circuitry (ECU). 
     The portion A of FIG. 1 is configured as shown in FIG.  2 . More specifically, a cutout portion  41  for use in taking out the lead wire harness section  37  is formed in the sidewall  40  of the lower casing  34  forming the housing case  35 . Bosses  43  and  44  stands upright on the base  42  of the lower casing  34  where the cutout portion  41  is formed. 
     On the base  45  of the upper casing  33 , hold-down members  46  and  47  are provided in opposite positions to the respective bosses  43  and  44  of the lower casing  34 . The hold-down members  46  and  47  are cylindrical and the bosses  43  and  44  are fitted in and used to cover the hold-down members  46  and  47  when the upper casing  33  is stacked on the lower casing  34 . 
     On the other hand, pairs of through-holes  48 ,  49 ,  50 ,  41 ,  52  and  53  are provided in three places of both end portions of the lead wire harness section  37  of the flexible printed circuitry  38  at predetermined intervals in the longitudinal direction. 
     The through-holes  48  and  49 ,  50  and  51 , and  52  and  53  in pairs are provided in such a manner that the through-holes  48 ,  50  and  52  are formed at predetermined intervals. Moreover, the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  are formed in places that do not interfere with the printed wiring of the lead wire harness section  37 , that is, both side end portions in the widthwise direction of the lead wire harness section  37 . Plastic protective films  54 ,  55 ,  56 ,  57 ,  58  and  59  are affixed to the peripheries of the respective through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  in order to prevent the peripheral edges of the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  from being easily damaged when stress is applied to the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  as the lead wire harness section  37  is pulled. The protective films  54 ,  55 ,  56 ,  57 ,  58  and  59  may be replaced with copper foil. 
     The three through-holes  48 ,  50  and  52  formed in one end portion of the lead wire harness section  37  of the flexible printed circuitry  38 , and the three through-holes  49 ,  51  and  53  formed in the other end portion thereof ensure that the lead wire harness section  37  can withstand the stress applied from the outside by means of the three through-holes on one side and the six through-holes on both sides in total by folding the lead wire harness section  37  into an S-shape and fitting the bosses  43  and  44  in the respective layer-to-layer through-holes. 
     As the switching circuit section  36  is formed integrally with the lead wire harness section  37 , force is applied most strongly to the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  formed in the lead wire harness section  37  when the tensile stress is applied to the lead wire harness section  37  while the lead wire harness section  37  is being wired or conveyed. In other words, the provision of the protective films (or copper foils)  54 ,  55 ,  56 ,  57 ,  58  and  59  on the peripheries of the respective through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  can prevent the breakage of the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  because of the damage caused to the peripheries of the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  and also the displacement of the switching circuit section  36 , which results in preventing the lead wire harness section  37  from being broken. 
     In this case, the hold-down members  46  and  47  may be long enough to hold down the lead wire harness section  37  so as to prevent the lead wire harness section  37  from slipping off the bosses  43  and  44  fitted in the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53 , and may also be long enough to keep holding down the lead wire harness section  37  when the bosses  43  and  44  are fitted therein. 
     Further, reinforcing dummy patterns  60  and  61  are formed over the whole length of the lead wire harness section  37  of the flexible printed circuitry  38  on both the respective sides of the lead wire harness section  37  of the flexible printed circuitry  38 . The reinforcing dummy patterns  60  and  61  are formed simultaneously with patterns for use in forming the lead wires of the lead wire harness section  37 . The reinforcing dummy patterns  60  and  61  are used to prevent the lead wire harness section  37  from being broken when the lead wire harness section  37  is pulled for some reason and other and undergoes tensile stress. 
     Consequently, as the switching circuit section  36  is formed integrally with the lead wire harness section  37 , the reinforcing dummy patterns  60  and  61  formed on both the respective sides and in the longitudinal direction of the lead wire harness section  37  prevent the breakage of the lead wire harness section  37  and also the displacement of the switching circuit section  36  even when the tensile stress is applied to the lead wire harness section  37  while the lead wire harness section  37  is being wired or conveyed, which results in preventing the lead wire harness section  37  from being broken. 
     As shown in FIG. 3, the lead wire harness section  37  of the flexible printed circuitry  38  is subjected to the following process through the steps of inserting the bosses  43  and  44  of the lower casing  34  into the respective through-holes  48  and  49  of the lead wire harness section  37 , folding the lead wire harness section  37  inside out, inserting the bosses  43  and  44  into the respective through-holes  50  and  51  on top of the through-holes  48  and  49 , folding the lead wire harness section  37  inside out again, inserting the bosses  43  and  44  into the respective through-holes  52  and  53  on top of the through-holes  50  and  51 , and drawing the lead wire harness section  37  outside through the cutout portion  41  of the lower casing  34 . Thus, the lead wire harness section  37  provides a surplus length portion formed around the bosses  43  and  44 . 
     When the upper casing  33  is put on the lower casing  34  as shown by an arrow A, the through-holes  48 ,  49 ,  50 ,  51 ,  52  and  53  with the bosses  42  and  43  fitted therein allow the lead wire harness section  37  of the flexible printed circuitry  38  to provide the surplus length portion within the housing case  35 . As the switching circuit section  36  is formed integrally with the lead wire harness section  37 , the lead wire harness section  37  contained in the lower casing  34  as the surplus length portion absorbs tensile stress even when the tensile stress is applied to the lead wire harness section  37  while the lead wire harness section  37  is being wired or conveyed, which results in preventing the displacement of the switching circuit section  36  and also the breakage of the lead wire harness section  37 . 
     A lead out structure for the lead wire harness section of the flexible printed circuitry according to the invention is applicable to not solely switching units of automobile doors as described in the above embodiment of the invention but also any structure for leading out a lead wire harness section of a flexible printed circuitry extending from a circuit section (a terminal circuit section etc.) housed in a casing mounted in each portion of an automobile as any electrical equipment. 
     Although the present invention has been shown and described with reference to specific preferred embodiments, various changes and modifications will be apparent to those skilled in the art from the teachings herein. Such changes and modifications as are obvious are deemed to come within the spirit, scope and contemplation of the invention as defined in the appended claims.