Abstract:
A switch includes a casing having a bottom to which first and second conductive blades are mounted. The second blade has a top edge forming a notch for receiving a see saw plat and allowing seesawing of the seesaw plate. A conductive strip made of a material that bends when subject to a temperature rise has an end fixed to the first blade and an opposite, free end forming a cantilever. The seesaw plate is movable between an engaged position where a first end of the seesaw plate engages the free end of the conductive strip thereby forming an electrical connection between the first and second blades and a disengaged position where the seesaw plate disengages from the conductive strip thereby electrically disconnecting the second blade from the first blade. A control button is movably received in a top opening of the casing and has a driver assembly mounted thereto. The control button is movable between a first position wherein the driver assembly drives the seesaw plate toward the engaged position and a second position where the driver assembly drives the seesaw plate toward the disengaged position. When an excessive current flows through the conductive strip, causing a temperature rise in the conductive strip, the conductive strip bends and separates the free end thereof from the seesaw plate thereby breaking the electrical connection between the first and second blades.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a switch, and in particular to a switch having an overload protection mechanism for operation safety. 
     BACKGROUND OF THE INVENTION 
     A switch is operable between an ON (connected) state and an OFF (disconnected) state for control of power supply or electrical signal transmission. For a power switch, overheating and burning caused by overload resulting from undesired shorting is one of the major concerns of operation safety. Some switches available in the market are provided with safety mechanism that automatically cuts off power supplied therethrough in order to eliminate the potential risk of overheating and burning. Such switches, however, have complicated structures, making costs high and manufacture difficult. 
     It is thus desirable to have a switch structure that is simple in structure but possesses operation safety feature. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a switch having a simple structure while capable of operation safety. 
     Another object of the present invention is to provide a switch of low costs while having overload protection. 
     A further object of the present invention is to provide a switch which is easy to manufacture. 
     To achieve the above objects, in accordance with the present invention, there is provided a switch comprising a casing having a bottom to which first and second conductive blades are mounted. The second blade has a top edge forming a notch for receiving a seesaw plate and allowing seesawing of the seesaw plate. A conductive strip made of a material that bends when subject to a temperature rise has an end fixed to the first blade and an opposite, free end forming a cantilever. The seesaw plate is movable between an engaged position where a first end of the seesaw plate engages the free end of the conductive strip thereby forming an electrical connection between the first and second blades and a disengaged position where the seesaw plate disengages from the conductive strip thereby electrically disconnecting the second blade from the first blade. A control button is movably received in a top opening of the casing and has a driver assembly mounted thereto. The control button is movable between a first position wherein the driver assembly drives the seesaw plate toward the engaged position and a second position where the driver assembly drives the seesaw plate toward the disengaged position. When an excessive current flows through the conductive strip, causing a temperature rise in the conductive strip, the conductive strip bends and separates the free end thereof from the seesaw plate thereby breaking the electrical connection between the first and second blades. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be apparent to those skilled in the art by reading the following description of preferred embodiments thereof, with reference to the attached drawings, in which: 
     FIG. 1 is an exploded perspective view of a switch constructed in accordance with a first embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of the switch in an OFF condition; 
     FIG. 3 is a cross-sectional view of the switch in an ON condition; 
     FIG. 4 is a cross-sectional view of the switch in a breaking condition; 
     FIG. 5 is an exploded view of a switch constructed in accordance with a second embodiment of the present invention; 
     FIG. 6 is a cross-sectional view of the switch in an OFF condition; 
     FIG. 7 is a cross-sectional view of the switch in an ON condition; and 
     FIG. 8 is a cross-sectional view of the switch in a breaking condition. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings and in particular to FIGS. 1-3, a switch constructed in accordance with the present invention comprises a casing  1  forming an interior space (not labeled) and having opposite side walls (not labeled) defining a top opening  11  in communication with the interior space. Aligned holes  111  arc defined in the sidewalls. A rotation button  2  is partially received in the opening  11  and has opposite pivot pins  21  rotatably received in the holes  111  of the casing  1  whereby the button  2  is rotatable between first and second positions respectively associated with ON and OFF conditions of the switch as shown in FIGS. 3 and 2. 
     A driver assembly  22  is formed on an underside of the button  2  and extends into the interior space of the casing  1 . The driver assembly  22  comprises a cylinder  221  extending from the underside of the button  2  inside which a cap  23  is partially and movably received. A biasing element  231 , such as a helical spring, is mounted between the cylinder  221  and the cap  23  for biasing the cap  23  away from the cylinder  221 . The helical spring  231  is received and retained in both the cylinder  221  and the cap  23 . 
     Two slots  12 ,  13  are defined in a bottom (not labeled) of the casing  1 . First and second conductive blades  14 ,  15  are fit and fixed in the slots  12 ,  13  and having tails (not labeled) extending beyond the bottom of the casing  1  for external connection. An opening  151  is defined in the second blade  15 . A conductive strip  4  made of a conductive material, such as an alloy or a bimetal, that bends when subject to heat and thus having a temperature rise is arranged inside the casing  1  and has an end attached to the first blade  14  and a second, free end extending through the opening  151 , forming a cantilever beam. The opening  151  is large enough to accommodate the bending and deformation of the conductive strip  4  without any physical engagement therebetween. 
     The second blade  15  defines a notch  152  in a top edge (not labeled) thereof. A seesaw plate  3  made of a conductive material is arranged inside the casing  1  and has a concave configuration and forms a bottom projection (not labeled) fit in the notch  152  of the second blade  15  whereby the seesaw plate  3  seesaws about the top edge of the second blade  15 . The bottom projection of the seesaw plate  3  is formed by pressing the plate  3  which forms a recess  31  on a top side thereof and the recessed portion of the plate  3  forms the projection. A hole  32  is defined at a first end of the seesaw plate  3  to which a first contact  33  is received and fixed. A second contact  42  is mounted to a hole  41  defined in the conductive strip  4  to correspond to the first contact  33 . 
     The cap  23  of the button  2  engages the top side of the seesaw plate  3  and is slidable along the seesaw plate  3  to seesaw the seesaw plate  3 . When the button  2  is rotated to the first position (the ON condition, FIG.  3 ), the cap  23  is moved to the first end of the seesaw plate  3  close to the first contact  33  whereby the seesaw plate  3  is moved to an engaged position where the first contact  33  is brought into engagement with the second contact  42  of the conductive strip  4 . Thus, an electrical connection between the first and second blades  14 ,  15 , through the conductive strip  4 , the second and first contacts  42 ,  33  and the seesaw plate  3 , is formed. 
     When the button  2  is rotated to the second position (the OFF condition, FIG.  2 ), the cap  23  is moved to a second end of the seesaw plate  3  away from the first contact  33  whereby the seesaw plate  3  is moved to a disengaged position by rotation about the notch  152  of the second blade  15  to separate the first contact  33  from the second contact  42 . Thus, the electrical connection between the first and second blades  14 ,  15  is broken. 
     In sliding along the seesaw plate  3  between the first and second ends thereof, the cap  23  is forced toward the button  2  when the cap  23  passes the edge of the second blade  15  by deforming the biasing element  231 . If desired, the cap  23  may be partially received in the recess  31  defined in the top side of the seesaw plate  3  to be guided thereby. 
     The rotation of the button  2  between OFF and ON conditions causes the seesaw plate  3  to seesaw between the disengaged and engaged positions. When the seesaw plate  3  is moved to the disengaged position, to ensure correctly positioning of the seesaw plate  3  and to prevent undesired engagement between the seesaw plate  3  and the first blade  14  (noting that the seesaw plate  3  is always in engagement with the second blade  15 ), a partition  16  is formed inside the casing  1  and extending above the conductive strip  4  and the first blade  14 . Thus, when the seesaw plate  3  is moved to the disengaged position, the second end of the seesaw plate  3  is stopped by the partition  16  thereby ensuring the correct positioning of the seesaw plate  3  at the disengaged position. 
     Similarly, when the seesaw plate  3  is moved to the engaged position, the casing  1  forms a first stop  17  located between the first end of the seesaw plate  3  and the conductive strip  4 . When the first contact  33  engages the second contact  42 , the first stop  17  engages the seesaw plate  3  and thus fixing the seesaw plate  3  at the engaged position. Overturning of the seesaw plate  3  is prevented. An additional second stop  18  may be formed inside the casing  1  spaced from and substantially opposite to the partition  16  for engaging the second end of the seesaw plate  3  and thus further fixing the seesaw plate  3  at the engaged position. 
     Also referring to FIG. 4, when an overload happens, an excessive current flows through the conductive strip  4 , causing a significant temperature rise. The conducive strip  4  thus bends in a direction away from the seesaw plate  3  to separate the first and second contacts  33 ,  42  thereby breaking the electrical connection between the first and second blades  14 ,  15  and cutting off the current. The stop  17  that is located between the seesaw plate  3  and the conductive strip  4  also functions to prevent the conductive strip  4  from bending toward the seesaw plate  3 . Thus, the conductive strip  4  is only allowed to bend, due to temperature rise, in a direction away from the seesaw plate  3  in order to properly disengage the contacts  33 ,  42 . 
     Preferably, one or more stops are formed inside the casing for preventing over-bending of the conductive strip  4  when the conductive strip  4  is subject to a temperature rise. This is to ensure that the conductive strip  4  does not contact the second blade  15  even when it is subject to a significant temperature rise. 
     To return to the normal operation from the breaking condition, the button  2  is moved to the OFF condition. The conductive strip  4  restores its original position when the temperature thereof lowers down. The button  2  may then be moved to the ON condition to engage the first contact  33  with the second contact  42  for resuming electrical connection between the first and second blades  14 ,  15 . 
     FIGS. 5-7 show a switch constructed in accordance with a second embodiment of the present invention, comprising a casing  1  forming an interior space (not labeled) and having opposite side walls (not labeled) defining a top opening  11  and a side opening  112  both in communication with the interior space. A cover  19  is fit into the top opening  11  and is fixed to the casing  1 . A hole  190  is defined in an inside surface (not labeled) of the cover  19 . A Z-shaped bar  191  has a major central section and two minor end sections extending from opposite ends of the central section in opposite directions. An end section of the bar  191  is fit into the hole  190  whereby the bar  191  is attached to the inner surface of the cover  19 . 
     A push button  2 ′ is movably received in the interior space of the casing  1  through the side opening  112 . A guide block  25  having a polygonal configuration is formed on a top side of the pushbutton  2 ′ defining a multi-section channel  24  surrounding the block  25 . The channel  24  forms a closed loop path or route having stop points A and B. The second end section of the bar  191  is movably received in the channel  24  and is guided to move along the route. The pushbutton  2 ′ is linearly movable with respect to the casing  1  between an outer position (FIG. 6) and an inner position FIG.  7 . By repeatedly pushing the pushbutton  2 ′, the end section of the bar  191  is moved along the channel  24  between the stop points A and B. When the pushbutton  2 ′ is pushed once and moved to the inner position, the end section of the bar  191  is moved to the stop point B and trapped there for retaining the pushbutton  2 ′ at the inner position. When the pushbutton  2 ′ is pushed again and is thus moved to the outer position, the end section of the bar  191  is moved to the stop point A. The outer and inner positions of the pushbutton  2 ′ respectively associated with OFF and ON conditions of the switch as shown in FIGS. 6 and 7. The pushbutton  2 ′ is spring-biased for helping movement between the stop points A and B. 
     A driver assembly  22  is formed on an underside of the pushbutton  2 ′ and extends into the interior space of the casing  1 . The driver assembly  22  comprises a cylinder  221  extending from the underside of the pushbutton  2 ′ inside which a cap  23  is movably received. A biasing element  231 , such as a helical spring, is mounted between the cylinder  221  and the cap  23  for biasing the cap  23  away from the cylinder  221 . The helical spring  231  is received and retained in both the cylinder  221  and the cap  23 . 
     Two slots  12 ,  13  are defined in a bottom (not labeled) of the casing  1 . First and second conductive plates  14 ,  15  are fit and fixed in the slots  12 ,  13  and having tails (not labeled) extending beyond the bottom of the casing  1  for external connection. An opening  151  is defined in the second blade  15 . A conductive strip  4  made of a conductive material, such as an alloy and a bimetal, that bends when subject to heat and thus having a temperature rise has an end attached to the first blade  14  and a second, free end extending through the opening  151  forming a cantilever beam. The opening  151  is large enough to accommodate the deformation of the conductive strip  4  without any physical engagement therebetween. 
     The second blade  15  defines a notch  152  at a top edge (not labeled) thereof. A seesaw plate  3  made of a conductive material has a concave configuration and forms a bottom projection (not labeled) fit in the notch  152  of the second blade  15  whereby the seesaw plate  3  seesaws about the top edge of the second blade  15 . The bottom projection of the seesaw plate  3  is formed by pressing the plate  3  which forms a recess  31  on a top side thereof and the recessed portion of the plate  3  forms the projection. A hole  32  is defined at a first end of the seesaw plate  3  to which a first contact  33  is received and fixed. A second contact  42  is mounted to a hole  41  defined in the conductive strip  4  to correspond to the first contact  33 . 
     The cap  23  of the button  2  engages the top side of the seesaw plate  3  and is slidable along the seesaw plate  3  to seesaw the seesaw plate  3 . When the pushbutton  2 ′ is moved to the inner position (the ON condition, FIG.  7 ), the cap  23  is moved to the first end of the seesaw plate  3  close to the first contact  33  whereby the seesaw plate  3  is driven to an engaged position where the first contact  33  is brought into engagement with the second contact  42  of the conductive strip  4 . Thus, an electrical connection between the first and second blades  14 ,  15 , through the conductive strip  4 , the second and first contacts  42 ,  33  and the seesaw plate  3 , is formed. 
     When the pushbutton  2 ′ is moved to the outer position (the OFF condition, FIG.  6 ). The cap  23  is moved to a second end of the seesaw plate  3  away from the first contact  33  whereby the seesaw plate  3  is driven to a disengaged position by rotation about the notch  152  of the second blade  15  to separate the first contact  33  from the second contact  42 . Thus, the electrical connection between the first and second blades  14 ,  15  is broken. 
     In sliding along the seesaw plate  3  between the first and second ends thereof, the cap  23  is forced toward the button  2  when the cap  23  passes the edge of the second blade  15  by deforming the biasing element  231 . If desired, the cap  23  may be partially received in the recess  31  defined in the top side of the seesaw plate  3  to be guided thereby. 
     The movement of the pushbutton  2 ′ between the outer and inner positions (the OFF and ON conditions) causes the seesaw plate  3  to seesaw between the disengaged and engaged positions. When the seesaw plate  3  is moved to the disengaged position, to ensure correctly positioning of the seesaw plate  3  and to prevent undesired engagement between the seesaw plate  3  and the first blade  14  (noting that the seesaw plate  3  is always in engagement with the second blade  15 ), a partition  16  is formed inside the casing  1  and extending above the conductive strip  4  and the first blade  14 . Thus, when the seesaw plate  3  is moved to the disengaged position, the second end of the seesaw plate  3  is stopped by the partition  16  thereby ensuring the correct positioning of the seesaw plate  3  at the disengaged position. 
     Similarly, when the seesaw plate  3  is moved to the engaged position, the casing  1  forms a stop  17  located between the seesaw plate  3  and the conductive strip  4 . When the first contact  33  engages the second contact  42 , the stop  17  engages the seesaw plate  3  and thus fixing the seesaw plate  3  at the engaged position. Overturning of the seesaw plate  3  is prevented. 
     Also referring to FIG. 8, when an overload happens, an excessive current flows through the conductive strip  4 , causing a significant temperature rise. The conducive strip  4  thus bends in a direction away from the seesaw plate  3  to separate the first and second contacts  33 ,  42  thereby breaking the electrical connection between the first and second blades  14 ,  15  and cutting off the current. The stop  17  that is located between the seesaw plate  3  and the conductive strip  4  also functions to prevent the conductive strip  4  from bending toward the seesaw plate  3 . Thus, the conductive strip  4  is only allowed to bend, due to temperature rise, in a direction away from the seesaw plate  3  in order to properly disengage the contacts  33 ,  42 . 
     To return to the normal operation from the breaking condition, the pushbutton  2 ′ is moved to the outer position (the OFF condition). The conductive strip  4  restores its original position when the temperature thereof lowers down. The pushbutton  2 ′ may then be moved to the inner position (the ON condition) to engage the first contact  33  with the second contact  42  for resuming electrical connection between the first and second blades  14 ,  15   
     Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the is intended to be defined by the appended claims.