Patent Publication Number: US-7723632-B2

Title: Electrical switch

Description:
The present invention relates to an electrical switch. 
   BACKGROUND OF THE INVENTION 
   An electrical switch of the kind concerned typically has a casing, two fixed contacts, and a moving contact which is resiliently biased towards contacting the fixed contacts, whereby the switch is closed. A spring-loaded actuator is used to bring about movement of the moving contact relative to the fixed contacts, and in particular to move the moving contact out of contact from the fixed contacts for opening the switch. 
   During opening of the switch, it is unpredictable as to which one of the fixed contacts the moving contact is to leave last. This is a concern in the design of heavy-current switches as arcing and/or flashover often occur at where the circuit is opened i.e. across the moving contact and the fixed contact it departs last. Of course, both fixed contacts together with the moving contact can be enhanced for better performance, for example made larger and/or coated with platinum, but production cost will escalate. Another consideration is the speed at which the moving contact is separated from the fixed contacts. 
   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, two fixed contacts and a moving contact in the casing, a first spring resiliently biasing the moving contact towards contacting the fixed contacts to thereby close the switch, and an actuating mechanism for causing movement of the moving contact relative to the fixed contacts. The actuating mechanism is operable between a first operating condition in which the moving contact is moved out of contact from the fixed contacts against the action of the first spring and a second operating condition in which the moving contact is allowed to come into contact with the fixed contacts under the action of the first spring. The actuating mechanism has an engaging member for engaging and retaining the moving contact from contacting the fixed contacts in the first operating condition and includes a second spring acting on the engaging member for moving the moving contact out of contact from the fixed contacts through an instant spring-release action. At least one of the engaging member and the contacts is configured such that the moving contact will be engaged and moved by the engaging member out of contact from a predetermined first of the fixed contacts earlier than the second fixed contact. 
   Preferably, the engaging member is arranged to engage the moving contact at a position on one side of the moving contact about the first spring relatively closer to the first fixed contact than the second fixed contact. 
   More preferably, the engaging member has a first region arranged to initially engage the moving contact at said position on one side of the moving contact about the first spring relatively closer to the first fixed contact than the second fixed contact, and includes a second region arranged to subsequently engage the moving contact at another position on the opposite side of the moving contact about the first spring. 
   Further more preferably, the first and second regions lie on a plane which is inclined at a small angle relative to the two fixed contacts. 
   Yet further more preferably, the first and second regions are provided by a flat surface of the engaging member on said plane. 
   It is preferred that the moving contact has a straight body. 
   In a preferred embodiment, the actuating mechanism includes a first actuating member for manual movement and a second actuating member comprising the engaging member and movable by the first actuating member via the second spring past a maximum strain condition thereof to perform said instant spring-release action. 
   More preferably, the first and second actuating members comprise separate sliders. 
   Further more preferably, the first and second actuating members are slidable linearly in parallel directions. 
   It is further preferred that the second spring comprises a compression coil spring co-acting between the first and the second actuating members, with said maximum strain condition being the condition of the coil spring at shortest length. 
   Preferably, the electrical switch includes a contact separator provided adjacent to the moving contact and movable by the actuating mechanism, upon the actuating mechanism operating towards the first operating condition, to engage and move the moving contact away from the fixed contacts. 
   More preferably, the separator comprises a pivotable lever. 
   Further more preferably, the separator has one end engageable and movable by the actuating mechanism and an opposite end for in turn engaging and moving the moving contact. 
   The electrical switch is preferably 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 a partially-broken perspective view showing certain internal components of the switch of  FIG. 1 ; 
       FIG. 3  is a side view of the switch of  FIG. 2 ; 
       FIG. 4  is a simplified side view corresponding to  FIG. 3 , showing the switch in an open condition; and 
       FIG. 5  is a simplified side view similar to  FIG. 4 , showing the switch in a closed condition. 
   

   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  includes a cuboidal plastic casing  110  which has an open top side sealed by a lid  111  and houses a pair of switching mechanisms  210  and a central press actuator  310  therefor. Each mechanism  210  involves a pair of switch terminals  410  and  420  and 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 right and left sides of the casing  110 , and the contact lever  500  inside the casing  110 . 
   The two switch units  200  are operated by the actuator  310  in tandem. They are arranged on opposite left and right sides of the actuator  310 , having practically the same construction but arranged as mirror images of each other. Only one switch unit  200  is shown in the drawings and described herein for clarity. 
   The right terminal  410  is formed by two, lower and upper L-shaped copper strips  411  and  414 , with the lower strip  411  situated upright and the upper strip  414  inverted, having respective vertical limbs  412  and  415  overlapped in contact alongside a right side wall  112  of the casing  110 . A horizontal bottom limb  413  of the lower strip  411  extends and underlies a casing bottom wall  113  for connection of an electric cable for example. A horizontal top limb  416  of the upper strip  414  overhangs inside the casing  110 , at the free end of which there is mounted a fixed contact pad  417 . 
   The left terminal  420  is formed by a single inverted L-shaped copper strip  424 , which has a vertical limb  425  alongside a left side wall  114  of the casing  110  and a horizontal top limb  426  overhanging inside the casing  110 . The bottom end of the vertical limb  425  is exposed for connection of an electric cable for example. A fixed contact pad  427  is mounted at the free end of the top limb  426 , at the same horizontal level as the other contact  417 . 
   The contact lever  500  has a straight body provided by a straight copper strip that extends generally horizontally, having opposite ends bearing respective contact pads  501  and  502  which are aligned with the aforesaid fixed contacts  417  and  427  respectively for contact making therewith or contact breaking therefrom to perform switching. A vertical compression coil spring  510  acts upon the contact lever  500  at mid-length thereof, from a fixed support  115  of the casing  110 , such that the contact lever  500  is resiliently biased upwardly towards the fixed contacts  417  and  427 . 
   The actuator  310  is part of an actuating mechanism  300  inside the casing  110 , which includes a first vertical slider  320  integrally formed with the actuator  310  on the left side of the casing  110 , and a separate second vertical slider  330  on the right casing side. The actuator  310  is resiliently biased upwards to stay normally uppermost, i.e. while not being pressed ( FIG. 4 ), by a compression coil spring  321  that acts upon the first slider  320  from below. Thus, the first slider  320  also normally stays uppermost. 
   There is a relatively strong coil spring  340  which is compressed, extending at an acute angle, between the two sliders  320  and  330 . Opposite ends of the spring  340  engage respective lateral projections  322  and  332  of the sliders  320  and  330  via individual pivoting bearings  342  and  343 . The spring  340  co-acts between the sliders  320  and  330  to resiliently force them apart such that they tend to slide and stay at opposite uppermost and lowermost positions. Consequently, the second slider  330  normally stays lowermost ( FIG. 4 ). 
   In such a normal operating condition of the actuating mechanism  300 , while in the lowermost position, the second slider  330  engages upon the contact lever  500  from above by means of an integral hook  333  thereof situated right over the contact lever  500 , at mid-length thereof. The hook  333  is provided by a thickened portion of a top end of the second slider  330 , having a slightly inclined flat surface  334  engaging the contact lever  500  such that the contact lever  500  is retained downwardly, against the action of the spring  510 , at a correspondingly inclined position ( FIG. 4 ). 
   The subject switch  100  is thus normally-open, in that the contact lever  500  is retained at a slightly inclined position by the second slider  330 , counteracting the spring  510 , from contacting the fixed contacts  417  and  427  or short-circuiting the switch terminals  410  and  420  ( FIG. 4 ). 
   In operation, during pressing of the actuator  310  (from  FIG. 4 ), upon sufficient lowering of the first slider  320  causing the spring  340  to pivot, or bend, past its shortest length condition in the horizontal position i.e. maximum strain condition, the spring  340  is instantly released and hence flicks the second slider  330  upwards to its uppermost position ( FIG. 5 ). 
   Given that the second slider  330  will move upwards with its hook  333  beyond the fixed contacts  417  and  427 , the contact lever  500  will follow the hook  333  to rise under the action of its own spring  510 . The lever  500  will first move into contact with the left fixed contact  417  and then turn horizontal to engage the right fixed contact  427 , thereby completing the electrical circuit across the terminals  410  and  420 . 
   The subject switch  100  is then closed in this alternative operating condition of the actuating mechanism  300 , temporarily for as long as the actuator  310  remains depressed. 
   On release of the actuator  310  (from  FIG. 5 ), upon rising of the first slider  320  (by the spring  321 ) pivoting, or bending, the spring  340  past its shortest length condition in the horizontal position i.e. maximum strain condition, the spring  340  is instantly released and hence flicks the second slider  330  downwards back to its original lowermost position ( FIG. 4 ). En route to the lowermost position, the second slider  330  has its hook  333  hit and pull the contact lever  500  downwardly, against the action of the spring  510 , away from the fixed contacts  417  and  427 , whereby the subject switch  100  is re-opened. 
   With its planar surface  334  inclined at a small angle of about 3° to 5° from horizontal, the hook  333  has a bottom right corner  333 A that is slightly lower than a bottom left corner  333 B thereof, on opposite sides about the axis of the lever spring  510 . During switch opening, the right corner  333 A will initially engage the contact lever  500  at one position on the right side about the spring  510 , with the left corner  333 B subsequently engaging the contact lever  500  at another position on the opposite left side about the spring  510 . 
   As the contact lever  500  is initially engaged on the right side of the axis of its supporting spring  510 , it will first be pivoted clockwise about the left fixed contact  427 , thereby coming out of contact from the right fixed contact  417  first. On continual pivoting, the contact lever  500  will lie flat against the hook surface  334  and be further pressed downwards at the inclined position to also break away from the left fixed contact  427 . 
   This arrangement ensures that the contact lever  500  will make contact with the left fixed contact  427  first, and more importantly to break contact from the other, right fixed contact  417  first. It is therefore possible to make only the right fixed contact pad  417  and the associated contact pad  501  of the lever  500  more robust to withstand contact arcing and/or flashover that are inevitable, thereby rendering the switching action weld-safe and/or non-tease. 
   The surface  334  of the actuator hook  333  inclined relative to the two fixed contacts  417  and  427  ensures that the contact lever  500  makes contact with and, more importantly, breaks contact from the fixed contacts  417  and  427  at different moments in time. The same result can be achieved in several other ways that can be taken instead or concurrently, for example by inclining the two fixed contacts (i.e. located at different levels) relative to the contact lever, or using a slightly folded or angled contact lever to incline its opposite end contact pads relative to the fixed contacts. 
   The aforesaid flicking of the second slider  330  by the first slider  320  or the actuator  310  via the spring  340  upon release is rapid and ensures instant contact making and, in particular, contact breaking to alleviate the problem associated with contact arcing and/or flashover. 
   For double precaution, the subject switch  100  includes a contact separator in the form of a plastic lever  600  for actively separating the contact lever  500  from the fixed contacts  417  and  427 . The separator  600  is supported at mid-length by a hinge pin  610  located in the casing  110 , for limited pivotal movement. 
   Opposite ends  601  and  602  of the separator  600  are positioned above a side projection  311  of the actuator  310  and the left end of the contact lever  500  (adjacent to the left contact pad  502 ) respectively. Upon rising of the actuator  310  on release, its projection  311  hits the right end  601  of the separator  600  from below to thereby pivot the other end  602  downwards, which in turn hits the contact lever  500  (at its left end) from above to assist or ensure separation of the contact lever  500  from the fixed contacts  417  and  427 . 
   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.