Abstract:
A switch assembly comprises a switch knob, a contact control member, a resilient contact piece and a bimetal alloy leaf for automatically cutting off power supply when current overload occurs. The switch knob is depressed to drive a protuberance to directly press or release the contact control member and the resilient contact piece to connect or cut off the power supply in normal operation. When current overload occurs, the bimetal alloy leaf deformed to push a moveable rod of the contact control member to release the resilient contact piece for cutting off the power supply. The switch assembly also includes a resilient member for restoring the contact control member to a normal off state after cutting off the power supply.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a switch assembly and, more particularly, it relates to a switch assembly built with a simple control circuit and an associated thermal-sensitive alloy leaf for cutting off power supply automatically in case of overload so as to ensure safety. 
     2. Description of the Prior Art 
     A power switch is a widely used electronic component for ON/OFF control of a power supply, and is highlighted in its structural complexity in consideration of cost, and particularly, of its reliability of safety. 
     A generic power switch is a manipulative switch. In some districts where electric power lacks stability, unexpected overload may occur occasionally to bring about overheat that could possibly result in public dangers. 
     For the improvement of a switch assembly, many patents, such as U.S. Pat. No. 5,786,742, 5,223,813, 4,937,548, 4,661,667, 4,931,762, 5,451,729, and 4,709,594 have been disclosed, wherein a bimetal thermal-sensitive element is implemented for cutting off power supply automatically in case of overload. 
     For example, the U.S. Pat. No. 4,937,548 has disclosed a mechanism including a bimetal piece, a lever controlled by the bimetal piece, and a cam associated with a see-saw member for controlling contact or separation of two conductive plates and for displacing the lever when the bimetal is heated and deformed to thereby remove the support of the cam to cut off the power supply. Whereas, the bimetal is to react to the overload current directly while the conductive plates are separated by indirect interaction through the bimetal, the cam, and the see-saw member in a somewhat abrupt response with possible malfunctions. Hence, there is still some time for the overload current to pass through an electric appliance and destroy it instantaneously. In addition, it requires an extra wire for connection of the conductive plate and the bimetal to complicate the structure. 
     In the U.S. Pat. No. 5,786,742, deformation of an overheated alloy leaf drives a limit seat to have a switch knob escaped and reset. However, the contact points could probably contact with each other when overloading occurs because the switch knob drives one of the contact points directly. Therefore, there is a need in improving the abrupt response and complicated structure of a switch although the above patents can solve the overload problem in one way or another. 
     SUMMARY OF THE INVENTION 
     The primary object of this invention is to provide a switch assembly comprising a switch knob, a contact control member, and an alloy leaf for cutting off power supply rapidly to ensure safety in the event of overload. 
     Another object of this invention is to provide a switch assembly with simple interactive mechanism by means of a protuberance of a switch knob, wherein the protuberance oppresses or release a contact control member directly to enable the latter to in turn oppress or release a resilient member to connect or cut off a power supply. 
     For more detailed information regarding this invention together with further advantages or features thereof, at least an example of preferred embodiment will be elucidated below with reference to the annexed drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The related drawings in connection with the detailed description of this invention, which is to be made later, are described briefly as follows, in which: 
     FIG. 1 is an exploded view of an embodiment of this invention in three dimensions; 
     FIG. 2 is a cutaway sectional view showing the embodiment of this invention under OPEN (OFF) state; 
     FIG. 3 is a cutaway sectional view showing the embodiment of this invention under CLOSE (ON) state; 
     FIG. 4 is a cutaway sectional view of the embodiment of this inventiion showing response of an alloy leaf in case of overload; and 
     FIG. 5 is a cutaway sectional view of the embodiment of this invention illustrating that a contact control member drops to cut off power supply in case of overload. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As illustrated in FIG. 1, a switch assembly of this invention mainly comprises a switch knob  1 , a casing  2 , a contact control member  3 , a resilient contact piece  4 , an alloy leaf  5 , and a resilient member  6 . 
     In the switch knob  1 , a dipped arcuate face is formed on the top end  101 . An axle-supporting groove  11  concavely and centrally disposed at the bottom end  102  of the switch knob  1  serves as a pivot center to enable the switch knob  1  to rotate. The bottom end  102  of the switch knob  1  is further extended downwardly to form at least a protuberance  12 , which, in this case, is substantially a triangular protrusion with a through hole  13 . 
     The case  2  is a hollow housing having an open lateral wall, wherein an opening  21  is formed at the top end of the casing  2 . An axle-supporting rod  201  is protrusively formed on an inner wall under the opening  21  for assembling and disposing the switch knob  1  to the axle-supporting groove  11 . First and second slots  23 , 25  are arranged in the bottom end of the casing  2  for plugging first and second terminals  24 , 26  respectively. A hollow combination column  202 , a stopper  22 , a stationary supporting pin  27 , and a protruding post  28  are protrusively fitted on the inner wall. A plurality of combination holes  203  is distributed to corners of the inner wall. Moreover, a cover  29  is provided to the casing  2 , wherein an assembling post  291  in a position corresponding to the hollow combination column  202  is protuberantly disposed on an inner wall of the cover  29 . A plurality of combination holes  292  in positions corresponding to the combination holes  203  of the casing  2  is distributed to the corners of the cover  29  that is riveted to joint with the casing  2  with a plurality of rivets  293 . 
     In the contact control member  3 , at least an upper lump  31  is located on the top end  30  of the contact control member  3 . The top end  30  is extended to form a hook portion  32 . At least a lower lump  33  is formed at the bottom end of the contact control member  3  in a position substantially corresponding to the upper lump  31 . A first slot  34  having a slot opening  341  at a tail end is concavely disposed in a lateral face of the contact control member  3  and a movable rod  35  is assembled in the slot opening  341 . Furthermore, a flange  351  annularly encloses the pillar body of the movable rod  35  at a nearer end  353 , and the farther end is a propping end  352 . The end face of the movable rod  35  is slightly smaller than the mouth area of the slot opening  341 . A resilient component  36  (a compressible spring in this case) is assembled and disposed in the first slot  34  to enable the movable rod  35  to relatively stretch or shrink in the slot opening  341  within a range limited by the flange  351 . A upright longitudinal second slot  37  is trenched in an opposite lateral face  38  of the contact control member  3  for assembling and jointing the contact control member  3  to the stationary supporting pin  27  of the casing  2 . 
     The resilient contact piece  4  is provided with a jointing hole  41  at its upper free end for combining with an upper contact dot  42  which is located right above a lower contact dot  521  of an L-shaped second-circuit link rod  52 . The lower end  43  of the contact piece  4  is a flat sheet coupled with an upper end  44  of the second terminal  26 , and is fixedly clamped between a fixing plate  251  and a sole plate of the casing  2 . 
     The alloy leaf  5  (thermal-sensitive element) is a metallic sheet  5  with a slit  57  at its top end, wherein two top ends  58 ,  59  standing aside the slit  57  are joint terminals. The lower part of the alloy leaf  5  is a free end  50 , wherein one top end  58  beside the slit  57  is fixedly jointed with an upper end  53  of a first circuit link member  51 . A lower end of the link member  51  is coupled with the first terminal  24  and a top end  59  beside the slit  57  is fixedly jointed to the top end  54  of the second circuit link member  52 . 
     Moreover, one end of the resilient member  6  (a stretchable spring in this case) is connected with the protruding post  28  and the other end is hooked in the through hole  13  of the protuberance  12 . 
     The operational states of the switch assembly of this invention include OPEN (OFF) state, CLOSE (ON) state, and automatic cutoff in case of OVERLOAD, which are to be described below. 
     As shown in FIG. 2, an assembled cutaway sectional view of an embodiment of this invention under OPEN (OFF) state controlled by a user is illustrated. When the user depresses the right end of the switch knob  1 , the resilient member  6  is pressed leftward at the moment the switch knob  1  is forced to rotate clockwise around the axle-supporting rod  201  which is taken as a pivot. Simultaneously, taking the axle-supporting rod  201  as a pivot, the protuberance  12  rotates clockwise in an arcuate movement (leftward in this case), and the bottom end of the protuberance  12  slides from the right side of the upper lump  31  of the contact control member  3  to the left side of the upper lump  31 . Therefore, the resilient contact piece  4  is freed from constraint of the lower lump  33  of the contact control member  3  to bounce upwardly and allow the upper contact dot  42  to depart from the lower contact dot  521  so as to separate the first terminal  24  from the second terminal  26  and cut off the power supply accordingly. 
     FIG. 3 shows an assembled cutaway sectional view of the embodiment of this invention under CLOSE (ON) state. When a user depresses the left end of the switch knob  1 , the resilient member  6  is stretched rightward to build a leftward restoring force at the moment the switch knob  1  is forced to rotate counterclockwise. The protuberance  12  also has counterclockwise movement (rightward in this case) by taking the axlesupporting rod  201  as a pivot. Simultaneously, the bottom end of the protuberance  12  slides from the left side of the upper lump  31  of the contact control member  3  to the right side to depress the contact control member  3  downwardly to have the lower lump  33  push against the resilient contact piece  4 . Consequently, the upper contact dot  42  at the bottom face of the free end of the resilient contact piece  4  contacts the lower contact dot  521  to thereby form a current path for the power supply to go through the first terminal  24 , the first circuit link member  51 , the alloy leaf  5 , the second circuit link member  52 , the lower contact dot  521 , the upper contact dot  42 , the resilient contact piece  4 , and the second terminal  26 . 
     A highlight to be stressed herein is that under OPEN (OFF) state of the switch, the propping end  352  of the movable rod  35  of the contact control member  3  is located exactly over the top face of the stopper  22  of the casing  2 . On the contrary, the propping end  352  props against the top face of the stopper  22  under CLOSE (ON) state, and the movable rod  35  itself does not stretch or shrink at all to keep its bottom face always on or above the top face of the stopper  22 . 
     According to a diagram of an alloy leaf of this invention in case of overload shown in FIG. 4, the free end  50  of the alloy leaf  5  will extend in a predetermined direction constantly (leftward in this case) because of the heat created when overloading occurs. The alloy leaf pushes the propping end  352  of the movable rod  35  to retreat and depart from the top face of the stopper  22  until the movable rod  35  together with the right end of the contact control member  3  drops downward in lack of support of the stopper  22 . As soon as the movable rod  35  leaves the stopper  22 , the lower lump  33  under the contact control member  3  rotates clockwise by taking the stationary supporting pin  27  in the second slot  37  as a pivot to allow the upper contact dot  42  at the free end of the resilient contact piece  4  to escape from the lower contact dot  521  and thereby cut off the power supply. 
     Meanwhile, at the moment the movable rod  35  drops, the resilient component (the compressible spring)  36  in the first slot  34  of the contact control member  3  is restored to stretch until it is stopped by the flang  351  of the movable rod  35  so that the movable rod  35  is reset to have its farther end emerged form the slot opening  341  as usual. 
     Under this circumstance, if no external force is applied onto the left end of the switch knob  1 , the resilient member (the stretchable spring) retreats to pull the lower end of the protuberance  12  leftward, and the switch knob  1  is driven to rotate clockwise by taking the axle-supporting rod  201  as a pivot and stop at the OPEN (OFF) position as shown in FIG.  2 . At this moment, the farther end of the resilient contact piece  4  is propping upwardly against the contact control member  3 . After the alloy leaf  5  is cooled, the free end  50  is restored to its initial state and the bottom face of the propping end  352  of the movable rod  35  will again rest on or above the top face of the stopper  22  to enter the OPEN (OFF) state shown in FIG. 2 pending a next triggering. 
     In summary, the present invention takes advantage of the alloy leaf  5  and the contact control member  3  for automatic control of power supply cutoff in case of overload. The switch assembly also returns to stand-by state and direct contact between the switch knob  1  and the contact control member  3  without malfunction. The switch assembly of this invention can be operated reliably with a simple structure and relatively lower cost. 
     Although, this invention has been described in terms of preferred embodiments, it is apparent that numerous variations and modifications may be made without departing from the true spirit and scope thereof, as set forth in the following claims.