Abstract:
A vehicle switch is capable of properly switching on/off electrical connection between fixed contacts. The fixed contacts of the switch are oppositely disposed on a substrate so as to be parallel to a moving direction of a moveable piece. A barrier constituted by a dent or a projection is disposed between the fixed contacts to increase the creeping distance between the fixed contacts. With such a simple structure, the vehicle switch can suppress degradation of insulation characteristics between the fixed contacts, whereby the electrical connections between the fixed contacts are properly established or cut-off.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a switch mainly fixed to a vehicle to detect the opening/closing of a vehicle door. 
   BACKGROUND ART 
   In recent years, a car often includes a switch fixed at a car body side of a door section so as to detect the opening/closing of a door. A signal detected by the switch is used for turning ON or OFF the room light, locking or unlocking doors, or the like. Such a detecting switch is also used for controlling highly advanced security systems, for example, known as the keyless entry system. Here will be described a conventional switch for a vehicle with reference to  FIGS. 7 and 8 . 
     FIG. 7  is a sectional view of a conventional switch for a vehicle (hereinafter, referred to as a vehicle switch), and  FIG. 8  is an exploded perspective view of the vehicle switch. Insulating resin case  21  has a box-like structure in which the top surface is open. Operation component  22  includes generally cylindrical-shaped operation head  22 A in the upper section. Operation component  22  is housed in case  21  so as to be movable in the vertical direction. Substrate  23  is made of insulating resin and formed into a flat plate. On both surfaces of substrate  23 , a plurality of wiring patterns (not shown) are formed and then a resistance element and other electronic components are mounted thereon. In addition, on the right surface of substrate  23  as seen in  FIG. 7 , fixed contacts  24 A and  24 B made of metal are oppositely disposed so as to be substantially parallel to the moving direction of operation component  22 . 
   Fixed contacts  24 A and  24 B are connected via the wiring patterns to a plurality of terminals  25 , and terminals  25  are fixed in the lower section of substrate  23 . Substrate  23  is accommodated in case  21 , with the bottom end being held by holder  26 . Movable piece  27  is made of a metallic thin plate and is substantially U-shaped. The bottom and one arm of the “U” are held by the bottom section of operation component  22 . The other arm of the “U” has contact hooks  27 A and  27 B at the lower end. Contact hooks  27 A and  27 B make contact with fixed contacts  24 A and  24 B, respectively. 
   Coil spring  28  is assembled between the inner bottom of case  21  and the bottom of operation component  22  under a slight initial compression to urge component  22  upwardly. Mounting plate  29  is made of a steel plate. Case  21  is fixed to the left side of mounting plate  29 , and on the right side of plate  29 , mounting hole  29 A is disposed. Waterproof cover  30 , which is made of rubber, thermoplastic elastomer, or the like, covers the upper surfaces of operation head  22 A and mounting plate  29 . 
   In the actual use of the vehicle switch structured as described above, terminals  25  protruding from the bottom of case  21  are connected to an electronic circuit (not shown) of a car. The switch is attached to a part of the chassis (not shown) facing an end of a door (not shown) by a screw (not shown) through mounting hole  29 A. 
   Now will be described the workings of the vehicle switch. Contact hooks  27 A and  27 B, as shown in  FIG. 7 , make contact with fixed contacts  24 A and  24 B, respectively. While the electrical connection is maintained (i.e., during the ON-state), fixed contacts  24 A and  24 B carry, for example, a current of 1-10 mA at 12 volts d. c. via movable piece  27 . When the door confronting the switch is closed, the edge of the closed door pushes operation head  22 A covered with waterproof cover  30 . Operation component  22  moves downwardly and compresses coil spring  28 . By the downward movement, contact hooks  27 A and  27 B also downwardly slide on fixed contacts  24 A and  24 B, respectively, and contact hook  27 B leaves from fixed contact  24 B. At this moment, the electrical connections between fixed contacts  24 A and  24 B are broken (i.e., the fixed contacts are in the OFF-state). The signal indicating the OFF-state between contacts  24 A and  24 B is sent to the electronic circuit of the car, so that each component carries out an operation that should be done in the OFF-state, namely turning OFF the room light, enabling the automatic door lock system, a burglar alarm system, etc. 
   When the door gets opened, the edge of the door leaves operation head  22 A, and accordingly, operation component  22  urged by coil spring  28  moves upwardly. The upward movement brings movable piece  27  up, so that the contact hooks of movable piece  27  make contact with corresponding fixed contacts, i.e., the contacts are in the ON-state, as shown in FIG.  7 . The signal thus indicating the ON-state is sent to the electronic circuit of the car, so that the room light is turned ON, and other related components carry out each predetermined operation. Such a vehicle switch having the structure and behavior as described above is disclosed, for example, in Japanese Patent Application Non-Examined Publication No. 2003-132761. 
   In the conventional vehicle switch described above, the ON/OFF-states of the electrical connections of fixed contacts  24 A and  24 B are established by the sliding movement of movable piece  27 . As contact hooks  27 A,  27 B are repeatedly rubbed against fixed contacts  24 A,  24 B over and over again, metallic abrasion powders of contact hooks  27 A,  27 B and fixed contacts  24 A,  24 B tend to accumulate between fixed contacts  24 A and  24 B. Besides, the distance between fixed contacts  24 A and  24 B is short and the surface is flat. If substrate  24  becomes wet as water accidentally comes into case  21 , the structure cannot maintain satisfactory insulation characteristics between fixed contacts  24 A and  24 B. 
   SUMMARY OF THE INVENTION 
   The vehicle switch of the present invention contains a substrate having a plurality of fixed contacts, and a movable piece having contact sections that correspondingly make contact with the fixed contacts. The fixed contacts are oppositely disposed on the substrate so as to be substantially parallel to the moving direction of the movable piece. A barrier constituted by, a dent or a projection is disposed between the fixed contacts. Forming a dent or a projection increases the creeping distance between the fixed contacts. By virtue of the structure, degradation of insulation characteristics between the fixed contacts can be minimized, even in the case that metal abrasion powders accumulate between the fixed contacts, or in the case that the substrate becomes wet because of accidental intrusion of water. That is, a switch with reliable electrical connections can be obtained. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of a vehicle switch of an exemplary embodiment of the present invention. 
       FIG. 2  is an exploded perspective view of the switch shown in FIG.  1 . 
       FIG. 3  is a sectional view of the switch shown in  FIG. 1  in operation. 
     FIG.  4 A and  FIG. 4B  are perspective views of the essential part of the vehicle switch shown in FIG.  1 . 
       FIG. 5  is a perspective view of a switch having another structure according to the embodiment of the present invention. 
       FIG. 6  is a general view of a car on which the vehicle switch of the embodiment of the present invention is mounted. 
       FIG. 7  is a sectional view of a conventional vehicle switch. 
       FIG. 8  is an exploded perspective view of the conventional switch shown in FIG.  7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Exemplary Embodiment 
     FIG. 1  is a sectional view of a vehicle switch of an exemplary embodiment of the present invention, and  FIG. 2  is an exploded perspective view of the switch. Insulating resin case  1  has a box-like structure in which the top surface is open. Operation component  2  includes generally cylindrical-shaped operation head  2 A in the upper section. Operation component  2  is housed in case  1  so as to be movable in the vertical direction. Substrate  11  is made of insulating resin and formed into a flat plate. On both surfaces of substrate  11 , a plurality of wiring patterns (not shown) are formed and then a resistance element and other electronic components are mounted thereon. In addition, on the right surface of substrate  11  as seen in  FIG. 1 , fixed contacts  12 A and  12 B are oppositely disposed so as to be substantially parallel to the moving direction of operation component  2 . 
   Fixed contacts  12 A and  12 B are connected via the wiring patterns to a plurality of terminals  13 , and terminals  13  are fixed in the lower section of substrate  11 . Substrate  11  is accommodated in case  1 , with the bottom end being held by holder  6 . Movable piece  7  is made of a metallic thin plate and is substantially U-shaped. The bottom and one arm of the “U” are held by the bottom section of operation component  2 . The other arm of the “U” has contact hooks (contact sections)  7 A and  7 B at the lower end. Contact hooks  7 A and  7 B make contact with fixed contacts  12 A and  12 B, respectively. Fixed contact  12 A has a length larger than fixed contact  12 B in the moving direction of operation component  2 . Slit  14  is disposed at about the midpoint position between fixed contacts  12 A and  12 B. Slit  14  is so formed that both ends of the slit exceed outwardly the upper and the lower ends of fixed contact  12 B. 
   Coil spring  8  is assembled between the inner bottom of case  1  and the bottom of operation component  2 , under a slight initial compression, to urge component  2  upwardly, i.e., in the direction away from substrate  11 . Mounting plate  9  is made of steel plate. Case  1  is fixed to the left side of mounting plate  9 , and mounting hole  9 A is disposed on the right side of plate  9 . Waterproof cover  10 , which is made of flexible resin such as rubber or thermoplastic elastomer, covers the upper surfaces of operation head  2 A and mounting plate  9 . In the actual use of vehicle switch (hereinafter, switch)  20  structured as described above, terminals  13  protruding from the bottom of case  1  are connected to an electronic circuit (not shown) of a car. Fixed contact  12 B is to be connected on the side of the electric power supply of the electronic circuit of the car; on the other hand, fixed contact  12 A is to be connected on the ground side of the electronic circuit. 
     FIG. 6  shows an illustration of a car on which switch  20  is mounted on a part of car body  17  facing door  18 . Car body  17  is held by driving wheels  19  that are driven by an engine or a motor (not shown). Switch  20  is attached to a part of the chassis (not shown) of car body  17  facing an end of door  18  by a screw (not shown) through mounting hole  9 A. 
   Hereinafter will be described the workings of switch  20  with reference to  FIGS. 1 through 4  and FIG.  6 . Contact hooks  7 A and  7 B make contact with fixed contacts  12 A and  12 B in a resilient manner, respectively. While the electrical connection is maintained (i.e., during the ON-state), fixed contacts  12 A and  12 B carry, for example, a current of 1-10 mA at 12 volts d. c. via movable piece  7 . When door  18  is closed, the edge of door  18  pushes operation head  2 A covered with waterproof cover  10  as shown in FIG.  3 . Operation component  2  moves downwardly and compresses coil spring  8 . By the downward movement, movable piece  7  held by operation component  2  also moves downwardly as shown in  FIG. 4A , a perspective view of the essential part of the vehicle switch. As shown in  FIG. 4B , contact hook  7 A thus slides on fixed contacts  12 A in a resilient manner, and contact hook  7 B leaves from fixed contact  12 B and slides on substrate  11  in a resilient manner. At this moment, the electrical connections between fixed contacts  12 A and  12 B are broken (i.e., the fixed contacts are in the OFF-state). The signal indicating the OFF-state between contacts  12 A and  12 B is sent to the electronic circuit of the car, so that the components controlled by the circuit carry out an operation that should be done in the OFF-state-turning OFF the room light, enabling the automatic door lock system, a burglar alarm system, etc. 
   When door  18  gets opened, the edge of door  18  leaves operation head  2 A, and accordingly, operation component  2  urged by coil spring  8  moves upwardly. The upward movement brings movable piece  7  up, so that the contact hooks of movable piece  7  make contact with corresponding fixed contacts, i.e., the contacts are in the ON-state, as shown in FIG.  1 . The signal thus indicating the ON-state is sent to the electronic circuit of the car, so that the room light is turned ON, and other relating components carry out each predetermined operation. 
   By opening or closing door  18 , operation component  2  moves up or down, accordingly, the contacts of movable piece  7  make contact with fixed contacts  12 A and  12 B or move away from them. In this way, the ON-state and the OFF-state of electrical connections are repeated. As contact hooks  7 A,  7 B are repeatedly rubbed against fixed contacts  12 A,  12 B over and over again, metallic abrasion powders of movable piece  7  and fixed contacts  12 A,  12 B tend to accumulate on substrate  11  between fixed contacts  12 A and  12 B. At about the midpoint section between fixed contacts  12 A and  12 B, there is a clearance formed by slit  14 . That is, the creeping distance between fixed contacts  12 A and  12 B is kept large enough. 
   As described above, slit  14  is disposed between fixed contacts  12 A and  12 B. Therefore, insulation characteristics between fixed contacts  12 A and  12 B can be properly maintained, even in the case that metallic abrasion powders accumulate between the fixed contacts. That is, a switch with reliable electrical connections can be obtained. Furthermore, even if substrate  11  becomes wet because of an accidental intrusion of water, degradation of insulation characteristics between the fixed contacts due to moisture absorption is unlikely to occur, since fixed contact  12 A and  12 B are separated by the clearance of slit  14 . Besides, the structure can suppress a phenomenon known as migration-when a DC voltage is applied between the fixed contacts, metal atoms of one of the contacts are ionized and deposit on the other contact. 
   Fixed contact  12 A has a length greater than fixed contact  12 B. Slit  14  is so formed that both ends of the slit exceed outwardly the upper and the lower ends of fixed contact  12 B. By virtue of the structure, fixed contacts  12 A and  12 B have a satisfactory creeping distance therebetween, even if slit  14  has a shorter length. Hence, there is little affection on strength of substrate  11 . 
   Although the description above introduces the structure in which substrate  11  has slit  14  between fixed contacts  12 A and  12 B, it is not limited thereto; when substrate  11  is formed of insulation resin moldings, the present invention is also applicable to the substrate having a groove  15  with a predetermined depth. Furthermore, instead of a dent portion including slit  14  and groove  15 , forming projection  16  between the fixed contacts  12 A and  12 B, as shown in  FIG. 5 , can offer the same effect. In this case, projection  16  should have a length and be positioned similar to slit  14 . 
   The vehicle switch of the present invention, as described above, has a simple structure and can suppress degradation of insulation characteristics between the fixed contacts, thereby providing reliable electrical connections. The switch is therefore suitable for detecting opening/closing of a vehicle door.