Patent Publication Number: US-6710277-B1

Title: Electrical switch

Description:
BACKGROUND OF THE INVENTION 
     An electrical switch of the kind concerned typically has a casing, a fixed contact and a moving contact, and an actuator for moving the moving contact into contact with the fixed contact. The actuator is movable to an opposite position for permitting the moving contact to move out of contact from the fixed contact under the action of a spring. 
     In a faulty situation, the moving contact may be hindered from departing from the fixed contact while the switch is intended to be opened. This may occur, particularly but not exclusively, when the load current is large and the two contacts are welded together as a result of arcing and/or flashover across them. 
     The invention seeks to provide an improved electrical switch of this type in general. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided an electrical switch comprising a casing, a fixed contact and a moving contact in the scaning, and an actuator supported by the casing for movement to a first position thereby moving the moving contact into contact with the fixed contact. The actuator is movable to a second position for permitting the moving contact to move out of contact from the fixed contact. Resilient means biases the moving contact out of contact from the fixed contact. The switch includes a remover having a part provided adjacent the fixed contact and movable by the actuator moving to the second position for removing the moving contact from the fixed contact in case the moving contact stays in contact with the fixed contact. 
     Preferably, the remover part is provided on the same side as the fixed contact relative to the moving contact for pushing the moving contact away from the fixed contact. 
     It is preferred that the remover is supported for sliding movement to remove the moving contact from the fixed contact. 
     It is further preferred that the electrical switch includes a pivotal member provided between the actuator and the remover for pivoting by the actuator to slide the remover. 
     In a preferred embodiment, the electrical switch includes a contact lever having a first end about which the lever is pivotably supported and an opposite second end supporting the moving contact. The remover part is arranged to act upon the second lever end for removing the moving contact from the fixed contact. 
     More preferably, the remover part faces the moving contact as the fixed contact and is slidable in a direction substantially perpendicular to the contact lever for hitting its second end to push the moving contact away from the fixed contact. 
     More preferably, the electrical switch includes a pivotal member provided between the actuator and the remover for pivoting by the actuator to move the remover, the pivotal member extending substantially parallel to the contact lever. 
     More preferably, the electrical switch includes a pivotal lever having a first end for pivoting by the actuator and a second end for moving the remover. The actuator includes a slider slidable by the actuator through a cam action, and the slider is positioned between the first ends of the contact lever and the pivotal lever. 
     Further more preferably, the actuator includes an inclined slot through which the slider extends at substantially right angles, such that the slider will be slid by the actuator through a cam action in a direction substantially perpendicular to the direction in which the actuator moves. 
     In a specific construction, the resilient means comprises a first spring biassing the actuator towards its second position and a second spring biassing the moving contact away from the fixed contact. 
     As an example, the electrical switch is a normally-open pushbutton switch. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of an embodiment of an electrical switch in accordance with the invention; 
     FIG. 2 is an exposed perspective view the switch of FIG. 1, showing all its components; 
     FIG. 3 is a cross-sectional side view of the switch of FIG. 1 in an open condition i.e. switched off; and 
     FIG. 4 is a cross-sectional side view of the switch of FIG. 1 in a closed condition i.e. switched on. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring to the drawings, there is shown an electrical switch in the form of a pushbutton switch  100  embodying the invention. The switch  100  has a rectangular box-like plastic casing  110  including an open top side sealed by a plastic lid  120 , which contains a pair of left and right switching mechanisms  210  operated by a single pushbutton actuator  300 . Each mechanism  210  is associated with a pair of switch terminals  410  and  420  and includes a moving contact lever  500  for making and breaking electrical connection between the two terminals  410  and  420 , together constituting a switch unit  200 . The terminals  410  and  420  are located on opposite front and rear sides of the casing  110 , and the contact lever  500  inside the casing  110 . 
     Each switch unit  200  includes a plastic frames  220  that supports components of the corresponding switching mechanism  210 , and the two frames  220  are located side-by-side within the casing  110 . Only one switch unit  200  is shown in the drawings and described herein for clarity, while the other unit  200  is simply a mirror image thereof in terms of design and construction. 
     The first terminal  410  has a vertical limb  412  lying on a front wall  112  of the casing  110 , and a horizontal limb  414  that extends from a lower end of the first limb  412  to underlie a casing bottom wall  113 . The horizontal limb  414  turns upwards into the casing  110  and in there it mounts, at its free end on the bottle wall  113 , a vertical fixed contact plate  416  facing rearwards. 
     The second terminal  420  has a vertical limb  422  located within a double rear wall  114  of the casing  110 , and a horizontal limb  424  that extends from a U-turned upper end of the first limb  422  into the casing  110 . The free end of the limb  424  terminates into a horizontal palm  426  that lies on a lower platform  222  of the support frame  220 . The palm  426  has a cutout  427  and a pair of bottom recesses  428  an opposite sides of the cutout  427 . The platform  222  is situated immediately above the fixed contact plate  416 . 
     The contact lever  500  extends generally upright, having a bifurcate upper end or portion  502  and including a lower end  504  that supports a moving contact knob  506  for movement into and out of contact with the fixed contact plate  416  to perform a switching action. The contact lever  500  is supported for pivotal movement by a generally upright copper lever holder  510 , which is in turn hinged by the palm  426  of the second terminal  420  for simultaneous pivotal movement, both about a horizontal axis. 
     The lever holder  510  has a T-shaped lower end  512 , and includes a trifurcate upper end providing a pair of left and right side fingers  514  bent through 90° outwards and a straight middle finger  516  pointing upwards. The crooked fingers  514  have respective notches engaging the contact lever  500  by its upper end  502 , whereby the lever holder  510  hingedly supports the contact lever  500 . The T-shaped lower end  512  is anchored through the cutout  427  by the recesses  428  of the palm  426 , whereby the lever holder  510  is hinged to the palm  428 . 
     The contact lever  500  lies alongside in front of the lever holder  510 , and an extension coil spring  530  co-extends with the contact lever  500  through its the upper portion  502 . The spring  530  is stretched across the lower end  504  of the contact lever  500  and an upper pin  532  of the support frame  220 , thereby holding the contact lever  500  and in turn the lever holder  510  in position, while the latter is anchored to the palm  426 . The spring  530  is hooked at its lower end to a small hole  505  of the contact lever end  504  immediately above the contact knob  506 . In particular, the spring  530  resiliently biasses the contact lever  500  into an inclined stable position (FIG.  3 ). 
     While the lever holder  510  is hinged about the palm  426  below it, its upper end fingers  514  may be pivoted to swing the upper end  502  of the contact lever  500  about generally its lower end  504  from the stable position to a less inclined second position (FIG.  4 ). As the spring  530  is stretched longer given that the second position is less inclined, this position is unstable. The lever holder  510  is to be pivoted by the actuator  300  acting upon its upper middle finger  516  (as hereinafter described). Upon release of the lever holder  510 , the spring  530  reacts to return the contact lever  500  to the stable position. 
     In the stable position (FIG.  3 ), the moving contact knob  506  separates from the fixed contact plate  416 , whereby the switch unit  200  is normally open (switched off). In the second position (FIG.  4 ), the moving contact knob  506  bears against the fixed contact plate  416 , whereby the switch unit  200  is closed (switched on). 
     The actuator  300  has a plastic body  310  sandwiched by the two support frames  220 , which is resiliently biassed upwards by a pair of compression coil springs  320  also between the frames  220 . The body  310  protrudes out of the lid  120  through an aperture  122  thereof, and has an uppermost end  312  to which a press knob (not shown) is snapped on. The space between the end  312  and the aperture  122  is sealed off by a frusto-conical rubber bellow  314  for dust protection. The body  310  is formed with an inclined slot  316  as shown, which has upper and lower ends  317  and  318 . 
     The actuator  300  includes a horizontal rod  330  inside the support frames  220 , which extends through the slot  316  at right angles and whose opposite ends carry a pair of knobs  332  disposed thereon. The rod  330  is slidable sideways back-and-forth along a linear passage  228  formed by a pair of opposed horizontal tracks inside the frames  220 . There is a cam action between the rod  330  and the slot  316 , which causes the rod  330  to slide rearwards (to the right in FIG. 3) or forwards (to the left in FIG. 4) when the body  310  is lifted by the springs  320  or lowered upon depression respectively. 
     The upper end middle finger  516  of the lever holder  510  is positioned in front of and aligned with the corresponding knob  332  of the rod  330 . When the rod  330  slides forwards, each of its knobs  332  will pivot the corresponding lever holder  510  by pushing its upper middle finger  516 , thereby closing both switch units  200 . Upon rearward sliding of the rod  330 , its two knobs  332  will release the corresponding lever holders  510 , thereby allowing both switch units  200  to return to the normally-open condition. 
     The platform  222  includes a central tunnel  224  which has front and rear ends  225  and  226  and extends horizontally from back to front through the support frame  220 . The tunnel front end  225  is positioned adjacent and immediately above the fixed contact plate  416 , together facing the moving contact knob  506 . 
     A plunger  250  is received in the tunnel  224  for sliding movement therealong. Immediately behind the plunger  250 , a generally upright kick lever  260  is hinged at mid-length by a horizontal pin  266  of the support frame  220  for pivotal motion. The lever  260  has upper and lower ends  262  and  264  and is provided between the actuator  300  and the plunger  250 . 
     The upper lever end  262  is positioned behind and aligned with the corresponding knob  332  of the rod  330 , for movement by the knob  332  when the rod  330  slides rearwards (to the right in FIG. 3) during opening of the switch unit  200 , whereby the lever  260  is pivoted. The lower lever end  264  is aligned with the rear plunger end  254  for kicking the plunger  250  forwards to protrude its front end  252  out of the front tunnel end  225 , or to protrude it further out, simultaneously upon said pivoting of the lever  260 . 
     The rear plunger end  254  is enlarged to stop the plunger  250  over protruding from the tunnel end  225 . Upon closing of the switch unit  200 , the knob  332  slides forwards (to the left in FIG. 4) away from the upper lever end  262 , whereby the lever  262  and in turn the plunger  250  is released. While the plunger  250  is free (to a limited but sufficient extent), it will not obstruct pivoting close of the contact lever  500 . 
     The front tunnel end  225  is positioned on the same side as the contact plate  416  relative to the contact knob  506  such that the associated plunger end  252  faces or points at the contact lever  500 . The plunger end  252  will, upon protruding, reach out to the position where the small hole  505  of the contact lever  500  was previously. In normal circumstances, given that the lower end  504  of the contact lever  500  will simultaneously be leaving this position under the action of the spring  530 , the plunger end  252  will not hit or touch the lever  500  (FIG.  3 ). 
     The plunger  250  acts as a contact remover and is deployed as a safety measure for action in a faulty situation during intended opening of the switch unit  200 , where the contact lever  500  is hindered from pivoting its contact knob  506  away from the fixed contact plate  416 . This may occur, particularly but not exclusively, when the load current is large and the two contact members  506  and  416  are welded together by arcing and/or flashover across them. The plunger  250  is useful to hit the contact lever  500  in the region of its lower end small hole  505 , or the lower end of the spring  530  engaged thereat, thereby striking off or removing the contact knob  506  from the contact plate  416 . 
     It is important to note that the precise form of the contact remover  250 , including the lever  260  therefor, is not essential. For example, these two components may be replaced by a single lever, or a simple linkage, arranged to transmit the self-return movement of the actuator  300  to the moving contact  500 / 506 . Also, the contact remover  250  may act upon the moving contact  500 / 506  from behind, i.e. pulling instead of pushing. 
     In general, the subject electrical switch may not need to be a pushbutton switch and can be, for example, a rocker or toggle switch. It is also not necessarily a normally-open switch. 
     The invention has been given by way of example only, and various other modifications of and/or alterations to the described embodiment may be made by persons skilled in the art without departing from the scope of the invention as specified in the appended claims.