Abstract:
Enhancing efficiency in assembling a waterproof switch, and enhance flexibility of seal design. The waterproof switch  7  includes a plunger  11  accommodated in a cylindrical case  10  capable of moving in the longitudinal direction, and to which a spring  17  applies a force in a direction. One end of the plunger  11  is provided with a common contact point  16  which contacts with contact point terminals  18  and  19  when predetermined amount of displacement to the spring  17  which applies the force to the plunder  11  is provided. A concave portion  10   a  is that to which a seal  13  for a sliding part of the plunger  11  is attached, and this concave portion  10   a  is provided to an end portion of the case  10 . Assembling is proceeded while recognizing how the seal  13  is attached thereto from the appearance in the assembling process.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a waterproof switch, and particularly to a waterproof switch suitable for enhancing its waterproof functions and for improving workability with which to attach a sealing member for waterproofness to the waterproof switch.  
         [0003]     2. Description of the Related Art  
         [0004]     A rear stop switch has been known as a switch which detects brake operations in response to a movement of a foot brake of a motorcycle or the like, and which thus lights a stop lamp. In a case of a rear stop switch of a conventional type, for example, a plunger is accommodated in a cylindrical case in a state where an end of the plunger penetrates through a sealing member and juts out of the case, and a spring member applies a force to the plunger toward the interior of the case. Lead contact points are configured to be capable of engaging with a contact point provided to the other end of the plunger, that is, a contact point provided to a portion in the interior of the case. This configuration makes the lead contact points engage (come into contact) with the contact point, and thus causes a detection signal indicating a stop operation to be outputted, if the stop operation draws the plunger out of the case against the spring. A switch of this type is disclosed, for example, in the specification of Utility Model Application Sho. 57-166347 (Unexamined Utility Model Application Publication Sho. 59-70884).  
         [0005]     In a case of a rear stop switch of a conventional type described in Patent Document 1, when assembling the rear stop switch, first of all, a seal and a spring member (a coil spring) are attached to the bottom portion of a cylindrical case. Subsequently, a plunger is caused to penetrate through the coil spring and the seal. During this work, it is likely that the seal may be out of place because the plunger and the coil spring interferes with the seal. For this reason, in the conventional practice, it takes a long time to carry out the assembling work.  
         [0006]     In addition, it is difficult to visibly check on the bottom portion of the cylindrical case. For this reason, as well, it takes much labor to make the visible check in some cases. With this taken in consideration, there has been a demand that the seal be attached to the rear stop switch efficiently by improving the time- and labor-consuming work.  
         [0007]     On the other hand, the seal is used for making the rear stop switch not only waterproof but also dust-resistant. For this reason, that has been a demand that latitude of design be enlarged by using a larger seal for the purpose of enhancing the waterproofness and dust-resistance of the rear stop switch. If, however, the outer diameter of the seal is made larger than the outer diameter of the coil in the coil spring, this enlargement affects the expansion and contraction of the coil spring. This makes it impossible to enlarge the size of the seal.  
       SUMMARY OF THE INVENTION  
       [0008]     An object of the present invention is to provide a waterproof switch which realizes an improved workability with which to attach a seal to the switch and an enhanced waterproofness, and which can be provided with an independent dust-resistance function.  
         [0009]     The present invention made for the purpose of fulfilling the foregoing object is carried out as a waterproof switch which includes a plunger, a spring, and electric contact point terminals. The plunger is provided to the interior of a cylindrical case by being movably supported in a cylindrical case, and by protruding an end of the plunger out of the case, in order that the plunger can receives an external force. The spring is accommodated in the case for the purpose of applying a force to the plunger. The electrical contact point terminals are provided respectively to the plunger and the case. The waterproof switch is configured to close the electrical contact point terminals when the external force causes the plunger to provide a predetermined amount of displacement against the spring. The waterproof switch has a first characteristic that the waterproof switch includes a concave portion and a seal. The concave portion is open to the end portion of the case, and forms a space in the circumference of the plunger. The seal is provided to the concave portion for the purpose of sealing the interstice between the case and the circumference of the plunger.  
         [0010]     The present invention has a second characteristic that the seal is a rubber seal configured of an anti-fluid sealing part and an anti-dust sealing part.  
         [0011]     In addition, the present invention has a third characteristic that the anti-fluid sealing part is arranged inward of the anti-dust sealing part.  
         [0012]     Moreover, the present invention has a fourth characteristic that the waterproof switch is that used for a rear stop switch for a vehicle.  
         [0013]     In the case of the present invention having the first characteristic, the spring for applying a force to the plunger is accommodated in the case, and the concave portion which is open to the outside of the case, and in which to accommodate the seal, is formed as an entity separated from a space in which to accommodate this spring. This configuration makes it possible to assemble the waterproof switch while visibly checking with the appearance on whether or not the seal is arranged in the case properly. This makes it possible to enhance efficiency for assembling work. In addition, this brings about an effect that latitude of designing the seal can be increased. That is because the formation of the concave portion in the end portion of the case makes dimensional tolerance larger.  
         [0014]     The second and the third characteristics makes it possible for the waterproof switch to exhibit better performance of sealing itself off water, dirt, dust and the like.  
         [0015]     The fourth characteristic makes it possible to bring a remarkable waterproof and anti-dust effect to vehicles used while exposed to the severe external environment, particularly to vehicles of saddle-riding type including motor cycles.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a cross-sectional view of a waterproof switch according to an embodiment of the present invention.  
         [0017]      FIG. 2  is a front elevation of the waterproof switch according to the embodiment of the present invention.  
         [0018]      FIG. 3  is a perspective view of a main part of a vehicle to which the waterproof switch according to the embodiment of the present invention is applied.  
         [0019]      FIG. 4  is a partial cross-sectional view of a seal used for the waterproof switch according to the embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]     Descriptions will be provided below for an embodiment of the present invention by referring to the drawings.  FIG. 3  is a perspective view of a main part of a vehicle which includes a rear stop switch, and for which waterproof and anti-dust performance is highly required. A brake arm  1  is arranged adjacent to, and at the right side of, a crank case  2 . The brake arm  1  is swingably supported by a pivot  3  attached to a vehicle body frame. A latch  5  which protrudes upward is arranged in the brake arm  1  between the front end part  4  and the pivot  3  of the brake arm  1 . A rear stop switch  7  is attached to the vehicle body frame  6 . A plunger (described later) of the rear stop switch  7  is linked to the latch  5  by use of a return spring  8 . A rear end of the brake arm  1  is linked to a hydraulic piston  9  for generating a hydraulic pressure to be applied to the brake in response to a step on the brake arm  1 .  
         [0021]     With this configuration, once the brake arm  1  is stepped on, a hydraulic pressure is applied to a rear brake caliper, which is not illustrated, by the hydraulic piston  9 , and thereby an arresting force works on a rear wheel of the vehicle. In conjunction with the arresting force, the plunger of the rear stop switch  7  is pulled via the return spring  8 . This operation closes the contact points of the rear stop switch  7 , and thus lights a rear stop lamp (not illustrated) of a rear portion of the vehicle.  
         [0022]      FIG. 2  is a diagram showing an external appearance of the rear stop switch.  FIG. 1  is a cross-sectional view of the rear stop switch taken along the A-A line of  FIG. 2 . The rear stop switch  7  includes a cylindrical case  10 , which is a main body of the rear stop switch  7 , and the plunger  11  which is fitted in the case  10 . It is preferable that a material of the case  10  be polypropylene, and that a material of the plunger  11  be a stainless steel. The plunger  11  is supported by a journal  12  of the case  10  in a way that the plunger  11  is capable of sliding relative to the case  10 . A concave portion  10   a  is formed in an extremity (shown as a lower end in  FIG. 1 ) of the case  10 . A seal  13  is inserted in this concave portion  10   a . The plunger  11  passes through the journal  12 , and a part of the plunger  11  protrudes out of the extremity of the case  10 . A hole  11   a  into which to hook an end portion of the return spring  8  is formed in the protruding part of the plunger  11 .  
         [0023]     The extremity of the case  10  is covered with a lower cover  14  for protecting the seal  13 . The lower cover  14  includes a through-hole which allows the extremity of the plunger  11  to penetrate through the lower cover  14 , and to extend outwards. It is preferable that a material of the lower cover  14  be rubber. An insulating cylinder  15  is fixed to an upper portion of the plunger  11 . In addition, a cylindrical contact point (common contact point)  16  is inserted and fitted to a part of the circumference of the insulating cylinder  15 . It is preferable that a material of the insulating cylinder  15  be nylon.  
         [0024]     A compression coil spring  17  is provided thereto in order for the plunger  11  to be pulled into the case  10 , that is, in order for the plunger  11  to be pulled upward in  FIG. 1 . A washer  26  is interposed between the lower end surface of the compression coil spring  17  and the bottom portion of the case  10 . Lead contact points  18  and  19  are provided to the circumference of the insulating cylinder  15 . The lead contact points  18  and  19  are extended from above in order that the extremities of the respective lead contact points  18  and  19  can contact the circumference of the insulating cylinder  15 . Positions of the respective lead contact points  18  and  19  are set in order that the lead contact points  18  and  19  can be brought into contact with the cylindrical contact point  16  when the plunger  11  provides a displacement in a direction in which the plunger  11  is pulled out of the case  10  against a repulsive force of the compression coil spring  17 . The lead contact points  18  and  19  are connected respectively to lead wires  20  and  21 . A connecting portion between the lead wire  20  and the contact point  18  and a connecting portion between the lead wire  21  and the contact point  19  are held in the case  10  by means of a terminal stage  22 . An o-ring  27  is provided to the interstice between the terminal stage  22  and the case  10 . The upper portion of the case  10  in which the terminal stage  22  is inserted is covered with an upper cover  23  made of rubber.  
         [0025]     A circumference of the extremity of the case  10  is provided with a screw part  24 . An adjustment nut  25  is screwed into the screw part  24 . The adjustment nut  25  is configured of a thumb section  25   a  and an engagement section  25   b  extending downward from the thumb section  25   a . The engagement section  25   b  is caused to engage with an attachment rib which is provided to the vehicle body frame  6  (see  FIG. 3 ), and thus plays a function of holding the rear stop switch  7  to the vehicle body. For this reason, when the adjustment nut  25  is turned relative to the case  10 , this turn makes it possible to adjust the distance between the rear stop switch  7  and the brake arm  1 .  
         [0026]      FIG. 4  is a partial cross-sectional view of the seal  13 . The seal  13  has both an anti-fluid function and an anti-dust function. The seal  13  is configured of a main body  131  and a reinforcement ring  132 . An internal circumference of the main body  131  is provided with lips  133  which jut out. The lips  133  include an anti-fluid sealing part  134  and an anti-dust sealing part  135 . The anti-fluid sealing part  134  is suitable for preventing oil and water from entering the inside. The anti-dust sealing part  135  is that for preventing sand, dust and the like from entering the inside. The anti-fluid sealing part  134  and the anti-dust sealing part  135  are attached to the seal  13  in a way that the anti-fluid sealing part  134  is located closer to the interior of the case  10 , and in a way that the anti-dust sealing part  135  is located closer to the exterior of the case  10 , that is, in a way that the anti-dust sealing part  135  is located opposite to the inner surface of the lower cover  14 .  
         [0027]     Because the seal  13  has the anti-fluid sealing part  134  and the anti-dust sealing part  135 , when sand and dust containing fluids enter the interior of the lower cover  14 , first of all, the anti-dust sealing part  135  prevents the fluids, the sand and the dust from entering the interior of the switch. Even if there are fluids which the anti-dust sealing part  135  cannot prevent from entering the interior of the switch, the anti-fluid sealing part  134  located closer to the interior of the switch blocks the fluids from entering beyond the ant-fluid sealing part  134 . As a result, the fluids can be securely prevented from entering the deeper interior of the switch.  
         [0028]     When the foregoing rear stop switch  7  is intended to be assembled, first of all, a washer  26  is placed in the bottom portion of the case  10 . Subsequently, the compression coil spring  27  is fitted into the bottom portion thereof. Thereafter, the plunger  11  to which the insulating cylinder  15  and the cylindrical contact point  16  have been beforehand fixed is caused to penetrate through the compression coil spring  17  and the journal  12 , and thus the plunger  11  is held in the case  10 . After that, the lead contact points  18  and  19  along with the terminal stage  22  are inserted in the case  10  from above. The terminal stage  22  is brought into intimate contact with the inner surface of the case  10  with the O-ring  27  interposed in between, and thus the terminal stage  22  and the case  10  are fixed to each other. Subsequently, the seal  13  is fitted into the interstice between the part of the plunger  11  which protrudes out of the case  10  and the concave portion  10   a  of the case  10 , and thereafter these fitting arrangements are covered with the lower cover  14 . The adjustment nut  25  is screwed into the screw part  24  at an appropriate time before the fitting arrangements are covered with the lower cover  14 .  
         [0029]     As described above, the seal  13  is designed to be fitted in an opening at the end portion of the case  10 , that is, the concave portion  10   a  of the case  10 . This makes it possible to visibly check with ease on whether or not the seal  13  is properly fitted into the concave portion  10   a  while assembling the rear stop switch  7 . As a result, this makes it possible to enhance efficiency for assembling work.  
         [0030]     Furthermore, the seal  13  is designed to be capable of being accommodated in the concave portion  10   a , which is an accommodation part independent of the compression coil spring  17 . This makes it possible to optimally determine the dimensions of the seal  13  regardless of the dimensions of the compression coil spring  17 . As a result, this makes it possible to provide a switch suitable for detecting operations of the rear brake in an off-road motorcycle, a rough terrain vehicle of a saddle-riding type and the like, which run while affected by sand and water.  
         [0031]     Note that, although what is obtained by forming the anti-dust sealing part and the anti-fluid sealing part integrally into a unit has been described as the seal  13 , the present invention does not limit the seal  13  to the seal of the foregoing type. The anti-fluid sealing part and the anti-dust sealing part may be arranged independently of each other in the seal  13 . In sum, it suffices if the seal is configured to be capable of being attached from outside to the accommodation part provided to the end portion of the case which is the switch main body.  
         [0032]     Furthermore, although the present invention is suitable as the stop switch for a vehicle, the present invention can be widely applied to not only the switch for a vehicle, but also a switch having a configuration in which: a plunger with contact points is included in a cylindrical main body of the switch; a spring is arranged in the cylindrical main body in a way that the spring is movable manually; the spring applies a force to the plunger in a direction; and the interstice between this plunger and the cylindrical main body is sealed with a seal.