Abstract:
An electrical switching device comprises a contact point having two double-break contacts, a contact link having a width, a contact pressure spring exerting a pressure on the contact link, a striker pin configured to act on the contact link counter to the pressure of the contact pressure spring during a switch-off operation so as to move the contact link into an open position, and a thruster actuatable by a switching mechanism and configured to guide the striker pin, the thruster having two limbs projecting in the same direction towards a free end of the thruster so as to form a slot there between, wherein a distance between the two limbs tapers towards the free end such that the distance at the free end is smaller than the width of the contact link, so that the contact link is clamped between the two limbs during the switch-off operation.

Description:
[0001]    Priority is claimed to German Patent Application DE 10 2008 016 036.9 filed on Mar. 28, 2008, the entire disclosure of which is incorporated by reference herein. 
         [0002]    The invention relates to a service switching device with double-break contacts, a contact link which is brought by a striker pin, counter to the pressure of a contact pressure spring, during a switch-off operation into the open position, for at least one pole current path, with a thruster, which can be actuated by a switching mechanism and in which the striker pin is guided, the contact link being accommodated in a slot in the thruster, which slot is formed by two limbs projecting in the same direction. 
       BACKGROUND 
       [0003]    Generic service switching devices, for example motor circuit breakers, have at least one pole current path with a double contact point and two fixed contact pieces and two moveable contact pieces arranged on a moveable contact link. 
         [0004]    In this case, the contact link is acted on by means of a thruster in the opening direction and by means of a contact pressure spring in the closing direction. 
         [0005]    Furthermore, generic service switching devices comprise an electromagnetic release, whose armature, in the event of the occurrence of a short-circuit current in the pole current path, both acts on the contact link in the opening direction via the thruster and unlatches the latching point of a switching mechanism, with the result that the switching mechanism acts on the contact link permanently counter to the force of the contact pressure spring so as to open said contact link via an active lever. 
         [0006]    Directly after the contact link has been acted upon and therefore directly after the interruption of the short-circuit current in the pole current path, the electrodynamic reaction of the electromagnetic release breaks down and the contact link is acted upon again in the direction towards its closing position by the force of the contact pressure spring. 
         [0007]    Owing to the relatively high level of mechanical inertia of the switching mechanism, compared with that of the system comprising the armature and the thruster, the active lever lags the thruster movement in order to keep the contacts permanently open by means of the switching mechanism. 
         [0008]    Under unfavourable conditions it may arise that the contacts have already been closed again by the contact pressure spring before the switching mechanism can bring about a permanent opening via the active lever and the thruster. This is then referred to as an occurrence of contact bounce, which is undesirable. 
         [0009]    In order to avoid contact bounce, DE 10 2006 055 007.2 proposes using a slide and a striker pin as thruster, of which the striker pin is guided within the slide, the arrangement comprising the slide, the striker pin, the contact link, the active lever and the armature being designed such that, in the event of a short circuit, the armature accelerates the striker pin very rapidly owing to the small mass thereof and therefore acts very quickly on the contact link. In this case, the slide lags the striker pin before the active lever, via the slide, keeps the contact link permanently in the open position counter to the contact pressure force. 
         [0010]    If the contact link has been acted upon and, as a result, the short-circuit current has been interrupted, the force effect of the armature on the striker pin also ends. The contact link is now pushed in the closing direction again by the force of the contact pressure spring. 
         [0011]    The slide, which lags the striker pin, can brake this countermovement of the contact link, with the result that the contact link is prevented from closing the contacts before the active lever, which still continues to lag the striker pin owing to the relatively high level of mechanical inertia of the switching mechanism, finally keeps the contact link permanently in the open position via the slide. 
         [0012]    In this case, the inertia of the striker pin and a low level of friction between the mechanical striker pin and the slide are utilized such that the striker pin keeps the contact link open for a sufficient period of time until the effect of the slide sets in during the triggering of the switching mechanism. 
       SUMMARY OF THE INVENTION 
       [0013]    An aspect of the present invention is to provide a generic service switching device with further improved dynamic response for the interruption of short circuits whilst avoiding contact bounce. 
         [0014]    The present invention provides a generic switching device wherein a distance between two limbs tapers towards a free end, the distance at the free end being smaller than the width of a contact link, with the result that said contact link can be clamped between the limbs in the event of a switch-off operation. This results in a clamping region at the free end of the limbs and a guide region being produced in the region between the free end of the limbs and the attachment point of the limbs to a thruster, in which guide region the contact link is guided moveably. 
         [0015]    In accordance with an advantageous embodiment, the limbs are designed to be spring-elastic. In this case, in accordance with a further advantageous embodiment, the limbs can be bent towards one another towards the free end. They could also be bent back towards one another in the form of a V in the region of their free ends. 
         [0016]    The advantageous effect of the configuration according to the invention of a generic service switching device consists in the fact that, when the contact link is acted upon, said contact link is clamped between the limbs of the thruster and, as a result, premature bouncing-back of the contact link in the direction of the closing position is prevented. If the contact link is fixedly clamped, it can only continue to move together with the thruster. 
         [0017]    In an advantageous development of the invention, means are provided which, owing to a movement of the thruster, can bring the contact link free from the limbs again. This is helpful if, once the contact link has been acted upon, for example if the short circuit has died out, the service switching device is intended to be switched on again by a renewed switch-on operation. 
         [0018]    In an advantageous embodiment of the invention, the abovementioned means are a web or a journal, against which the contact link rests in the switch-off position, with the result that, during a further movement of the thruster, the web or the journal brings the contact link free from the limbs in the switch-off direction again. 
         [0019]    This further movement of the thruster can take place during resetting, for example, by virtue of the fact that the thruster is pushed a bit further in the direction of the switch-off position by the active lever. Owing to the fact that it rests on the web or journal, the contact link can no longer follow this further movement of the thruster and is thus brought into the guide region of the slot again, counter to the clamping and frictional force relative to the longitudinal extent direction of the limbs, in which guide region it can then be pushed into its closing position again by the contact pressure spring. 
         [0020]    In a further advantageous embodiment, it is also possible for the means to be a spring, which, during a further movement of the thruster, moves the contact link in the switch-off position from the clamping region between the limbs, with the result that the contact link is brought free from the limbs into the guide region. The unclamping of the contact link by the spring takes place when the restoring force of the compressed spring is greater than the clamping force which the limbs exert on the contact link. 
         [0021]    Further advantageous configurations and improvements of the invention are described in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The invention and further advantageous configurations and improvements and further advantages of the invention will be explained and described in more detail with reference to the drawing, which illustrates two exemplary embodiments of the invention and in which: 
           [0023]      FIG. 1   a  shows a function schematic diagram of a service switching device with a thruster in the rest position, 
           [0024]      FIG. 1   b  shows a longitudinal sectional view of the thruster shown in  FIG. 1   a  in the rest position, 
           [0025]      FIG. 2   a  shows the function schematic diagram of the service switching device with the thruster, as shown in  FIG. 1   a , shortly after the occurrence of a short-circuit current, 
           [0026]      FIG. 2   b  shows a sectional view of the thruster shown in  FIG. 2   a , similar to that shown in  FIG. 1   b,    
           [0027]      FIG. 3   a  shows the function schematic diagram of the service switching device with the thruster shown in  FIGS. 1   a ,  2   a  given a maximum deflection of the contact link in the opening direction, 
           [0028]      FIG. 3   b  shows a sectional view of the thruster similar to that in  FIGS. 1   b  and  2   b  as shown in  FIG. 3   a , and 
           [0029]      FIG. 4  shows a sectional view of the thruster of a further configuration of a service device. 
       
    
    
       [0030]    In  FIGS. 1 to 4 , identical or functionally identical elements or assemblies have each been denoted by the same reference numerals. 
       DETAILED DESCRIPTION 
       [0031]      FIG. 1  shows a service switching device  1  according to the invention with a pole current path  2  between an input terminal  3  and an output terminal  4 . It could be, for example, a pole current path of a three-pole motor circuit breaker, whose other two pole current paths are constructed correspondingly but are not illustrated here. 
         [0032]    The pole current path  2  comprises two fixed contact pieces  5 ,  6  and two moveable contact pieces  8 ,  9 , which are arranged on a moveable contact link  7  and which form a contact point  10  with double-break contacts. The contact link  7  is acted upon by a contact pressure spring  11  in the closing direction, see direction arrow S. The contact link  7  can be acted upon in the opening direction, see direction arrow O, by a thruster  12 , which acts on that side of said contact link  7  which is opposite the contact pressure spring  11 . 
         [0033]    The pole current path  2  also comprises a thermal release  113 , which is only illustrated for reasons of completeness, and an electromagnetic release  13  with a moveable armature, which acts on the contact link  7  in the opening direction in the case of a short-circuit current occurring in the pole current path  2  as a result of electrodynamic forces via the thruster  12 , as is indicated by the line of action  14 . At the same time, the armature of the electromagnetic release  13  also acts in the event of a short circuit on a switching mechanism  15  and unlatches the latching point thereof, indicated by the line of action  16 , with the result that the switching mechanism  15  in the unlatched state acts on the thruster  12  permanently in the opening direction of the contact link  7  via an active lever  17 , indicated by the line of action  18 . In the event of high short-circuit currents, electrodynamic opening of the double contact point  10  as a result of the current flow in the pole current path can also take place. 
         [0034]    The function of the thermal release  113  which, in the event of an excess current, likewise acts on the switching mechanism  15 , indicated by the line of action  114 , is known in principle and is not the subject matter of the present invention. 
         [0035]    The mechanical system comprising the switching mechanism  15  and the active lever  17  may be, for example, a toggle system with two-stage latching. The active lever  17  is in the form of a double-arm lever, whose first lever arm  171 , which is acted upon by the switching mechanism  15 , and whose second lever arm  172 , which interacts with the thruster  12 , form an obtuse angle with one another, and is mounted rotatably in a stationary rotary spindle  173 , as a result of which the active lever  17  acts as a deflecting lever. However, the active lever could also have a different shape. 
         [0036]    This just-described mechanical system has a certain mechanical inertia, as a result of which a certain amount of time, for example 3 ms, passes after unlatching before the active lever  17  meets the thruster  12  in order to act upon said thruster permanently in the opening direction. 
         [0037]    In contrast, the time until the armature, which in this case acts as a striking armature, of the electromagnetic release  13  directly hits the contact link  7  is much shorter; it is, for example, only 1 ms. 
         [0038]    As a result, it could arise, if no further measures are taken, that the contact link  7 , owing to the restoring force of the contact pressure spring  11 , is already pushed back into its initial position in the closing position again and the contact point  10  is as a result closed again before the active lever  17  with the free end of its second arm  171  can act on the thruster and therefore act on the contact link  7  permanently in the opening position. 
         [0039]    The thruster  12  is formed in two parts, corresponding to the configuration in accordance with DE 10 2006 055 007.2, and comprises a slide  19  and a striker pin  20 . As can be seen in the sectional illustration in  FIG. 1   b , the thruster  12  is an elongate component part with an approximately cylindrical basic shape. 
         [0040]    In a first, slot-like opening  21  in the slide  19 , which is open at the bottom towards the narrow side of the slide  19 , the contact link  7  is guided displaceably in its closing or in its opening direction. 
         [0041]    The striker pin  20  is guided moveably in a second, channel-like opening  22  in the slide  19  likewise in the closing or opening direction of the contact link  7 . It protrudes beyond the slide  19  upwards in the direction of the point of action of the striking armature. 
         [0042]    A first shoulder  23 , which acts as an upper stop for the contact link  7 , is formed in the first opening  21  of the slide  19 . A second shoulder  24 , which acts as a point of action for the active lever  17 , is formed on the slide  19  at the end opposite the contact link  7 . 
         [0043]    The first opening  21  is formed by two fork-like projections or limbs  30 ,  31  which project in the longitudinal direction of the slide  19  and take the contact link  7  between them. The free ends  32 ,  33  of the prongs  30 ,  31  have a smaller distance A between them than the distance A W  at the shoulder  23 . The distance A is also smaller than the width B of the contact link  7 . In the drawing, the shape of the limbs  30 ,  31  is represented as being slightly curved; it is naturally also possible for the limbs  30 ,  31  to be bent back towards one another for example in their centre, with the result that they form a V shape in the region of the free ends. 
         [0044]    A clamping region for fixedly clamping the contact link  7  is therefore produced at the free ends  33 ,  32  of the limbs  30 ,  31 , and a guide region for the contact link, in which guide region said contact link can be guided moveably, is produced between the free ends  33 ,  32  and the first shoulder  23  at which the limbs  30 ,  31  are attached to the thruster body. 
         [0045]    The function of the arrangement according to the invention in the event of the occurrence of a short-circuit current will now be explained below. If a short-circuit current occurs, see  FIG. 2   a , the armature of the release  13  strikes the striker pin  20  of the thruster  12 , indicated by the pulse arrow I in  FIG. 2   a . The striker pin  20  is accelerated downwards in the opening direction O, with it carrying along the contact link  7  in the opening direction O and moving it away from the stop  23 . As a result, the moveable contact pieces  8 ,  9  are separated from the fixed contact pieces  5 ,  6  and the double contact point  10  is opened. As a result of this downward movement of the striker pin  20 , the contact link  7  enters the tapered region and is held fixedly between the prongs  30 ,  31  by being clamped, since the distance A between the projections or the prongs  30 ,  31  is reduced. As it moves into the tapered region, the contact link  7  carries along the slide  19  for a certain distance, the slide  19  then being fixedly held by the active lever  17 , even if said slide  19  is carried along owing to the return movement of the contact link  7  by said contact link  7  owing to the friction (the fact that it is clamped). In any case, the double contact point  10  remains open. It is essential that the distance between the tapering of the prongs or the opening  21  and the shoulder  23  is sufficiently great. 
         [0046]    A journal  41 , which engages partially in the slot  21 , is integrally formed, fixed in position, on the housing  40 , of which only part is illustrated. The contact link  7  enters the immediate vicinity of the end of the journal  41  and the contact link  7  can come free from the projections by the slide  19  being pushed lower still (for example by a reset button), with the result that the contact link  7  is brought back into the switch-on position by the contact spring. 
         [0047]    Instead of a journal  41 , a pressure spring  45  can also be provided (see  FIG. 4 ), the pressure spring being correspondingly dimensioned such that it can overcome the frictional force if a switch-on operation is performed. 
         [0048]    A further advantageous effect of the configuration according to the invention also arises when the striking movement of the contact link is insufficient for it to be pushed into the clamping region to such an extent that it is clamped there fixedly. This is because, owing to the curved inner contour of the slot which is produced by the curved shape of the limbs, there is also already a certain amount of friction between the contact link  7  and the inner sides of the limbs  30 ,  31  in a region which is still just above the clamping region. This is a transition region between the guide region and the clamping region. Owing to the friction between the contact link  7  and the limbs  30 ,  31  in the intermediate region, the movement of the contact link  7  relative to the limbs  30 ,  31  there is already slowed down. A delay in the movement of the contact link therefore also already results when said contact link should not be pushed completely into the clamping region. The delay achieved in this way can also already be sufficient for effectively avoiding contact bounce. 
         [0049]    It should also be mentioned that the above-described effect according to the invention also occurs when the opening of the contact link first takes place not by the striker pin but as a result of an electrodynamic repelling action between the fixed and moveable contact pieces. In particular in the case of high current levels of a short-circuit current, the electrodynamic repelling effect is more rapid than the response time of the electromagnetic release  13 . The armature of the electromagnetic release  13  therefore lags the electrodynamic repelling effect of the contact point  10 . Even if the contact link  7  is pushed downwards into the clamping region of the slot  21  as a result of an electrodynamic repelling effect, the fixedly clamping effect in the clamping region occurs, and therefore the advantageous effect of the delay of the bounce-back of the contact link. 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  Service switching device 
           2  Pole current path 
           3  Input terminal 
           4  Output terminal 
           5 , 6  Fixed contact pieces 
           7  Moveable contact link 
           8 , 9  Moveable contact pieces 
           10  Contact point 
           11  Contact pressure spring 
           12  Thruster 
           13  Electromagnetic release 
           14  Line of action 
           15  Switching mechanism 
           16  Line of action 
           17  Active lever 
           18  Line of action 
           19  Slide 
           20  Striker pin 
           21  First opening, slot 
           22  Second opening 
           23  First shoulder 
           24  Second shoulder 
           25  Web 
           26  Shoulder 
           27  Bevelled side faces 
           30 , 31  Fork-like projection, limb 
           32 , 33  Free end of limbs 
           41  Journal, web 
           40  Housing 
           45  Pressure spring 
           113  Thermal release 
           114  Line of action 
           171  First lever arm 
           172  Second lever arm 
           173  Rotary spindle 
         S Direction arrow 
         O Direction arrow 
         I Pulse arrow 
         A Distance between free ends 
         A W  Distance between limbs of shoulder  23   
         B Width of contact link