Abstract:
A low-voltage switching device includes a guide insert for receiving the bridge contact of the device. The guide insert can be fixed without play inside the housing of the switching device. The bridge contact is mounted in the guide insert in a manner that permits it to linearly move counter to a spring force.

Description:
[0001]    This is a continuation of International Application No. PCT/EP00/08337, with an international filing date of Aug. 26, 2000. 
     
    
     
       BACKGROUND  
         [0002]    The present invention relates to a low-voltage switching device having a housing, a double-break bridge contact, two arcing chambers allocated to contact separation points, a plunger for actuating the bridge contact, and a drive unit.  
           [0003]    A switching device of this type is described in European Patent Document No. EP 0 647 350 B1. This switching device has a housing in which a double-break bridge contact is arranged for each pole. In this context, the contact bridge is supported in an actuating plunger in known manner. The actuating plunger, in turn, is supported in a cage, the cage having slotted-hole shaped windows for the passage of the linearly movable contact bridge. Furthermore, the cage features lateral insulating wings for bounding the arcing chamber. This system can be preassembled and fixedly arranged in the housing of the switching device.  
           [0004]    In prior devices, in which the bridge contact is movably supported in an actuating plunger and the actuating plunger is supported in a linearly movable manner in the switch housing itself or in a cage which can be inserted into the housing of the switching device, at least two guide plays are present (bridge contact/plunger and plunger/housing or bridge contact/plunger and plunger/cage).  
         SUMMARY OF THE INVENTION  
         [0005]    An object of the present invention is to provide a low-voltage switching device in which the guide play of the bridge contact is markedly reduced and thus the guidance of bridge contact is more precise.  
           [0006]    The present invention provides a low-voltage switching device. The device includes: a housing having an upper housing part and a lower housing part; a double-break bridge contact; a pair of arcing chambers associated contact separation points of the bridge contact; a plunger configured for actuating the bridge contact; a drive unit; and a guide insert configured for receiving the bridge contact. The bridge contact is supported in the guide insert so as to be linearly movable against a spring force. The guide insert is capable of being fixed without play in the housing.  
           [0007]    The guide play of the bridge contact is minimized by designing a separate guide insert according to the present invention which is supported without play in the housing of the switching device, preferably being pressed in, and in which the bridge contact is supported in such a manner that it is linearly movable against a spring force, it being possible to actuate the bridge contact via a separate plunger. In this manner, it is achieved that a guide play occurs just between the guide insert and the bridge contact supported therein. Via the guidance, according to the present invention, of the bridge contact in the guide unit, which can be fixed without play in the housing, the bridge contact guidance is markedly improved. Unlike the related art, where the bridge contact is guided in the actuating plunger, the present invention eliminates the play which otherwise occurs between plunger and bridge contact. Due to the more precise bridge contact guidance, it is possible to build a switching device in which the bridge contact can be placed closer to the arcing chamber without having to fear a welding of the bridge contact to the arc splitter plates. Because of this, an electric arc occurring, in particular in the case of short circuits, is guided into the arcing chamber earlier so that the quenching performance of a switching device designed in this manner is improved. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    Further details and advantages of the present invention will be explained based on an exemplary embodiment with reference to the drawings.  
         [0009]    [0009]FIG. 1 is an exploded view of a lower part of a switching device according to the present invention;  
         [0010]    [0010]FIG. 2 depicts a possible embodiment of the guide insert according to the present invention with spring and bridge contact; and  
         [0011]    [0011]FIG. 3 shows the lower part of the switching device according to FIG. 1 in the assembled condition. 
     
    
     DETAILED DESCRIPTION  
       [0012]    [0012]FIG. 1 depicts an exploded view of components of the switching device according to the present invention. The switching device includes a housing featuring a lower housing part  2  and an upper housing part as well as a double-break bridge contact  4  for each pole, and two stationary contacts interacting with bridge contact  4 , two arcing chambers  6  allocated to the contact points of each bridge contact, in each case one plunger  8  for actuating a bridge contact  4 , and a drive unit for acting upon plunger  8  or bridge contact  4 , it being preferred for the drive unit to be operable at least electromagnetically.  
         [0013]    Each arcing chamber  6  includes at least one arc splitter plate stack  6   a  and a holding device  6   b  for accommodating arc splitter plate stack  6   a . To form an arcing chamber  6 , a unit including an arc splitter plate stack  6   a  and a holding device  6   b  is then inserted into an opening  6   c  of lower housing part  2  provided for this.  
         [0014]    Also shown is a preassembled unit including a guide insert  10 , a spring element  12  (see FIG. 2) and bridge contact  4  which is supported inside guide insert  10  in a manner that it is linearly movable against a spring force. This preassembled unit can be fixed without play in lower housing part  2 , preferably by a force fit. In this connection, the force fit is achieved by an exact, mutually matched dimensional accuracy of guide insert  10  and of the receptacle provided for the guide insert in the housing of the switching device. The force fit can, of course, also be achieved by tapering the interacting surfaces of guide insert  10  and the housing receptacle for the guide insert.  
         [0015]    A preferred embodiment of guide insert  10  is shown in FIG. 2. In this connection, guide insert  10  is preferably designed as a one-piece, injection-molded part composed of insulating material. Guide insert  10  is substantially composed of a plate-like (or ring-shaped or the like) base part  10   a  from where preferably four guide columns  10   b  extend perpendicularly. In this connection, guide columns  10   b  are arranged, in particular, in such a manner that two neighboring guide columns  10   b  lie in one plane, respectively, and the planes run parallel to each other. It is preferred for the columns to form the corners of a square as viewed from above. Guide insert  10  can be preassembled with a spring element  12  and bridge contact  4  to from a unit. To this end, guide insert  10  is advantageously open from one of its end faces so that spring element  12 , here a spiral spring, can be inserted from one end face in a simple manner. Moreover, bridge contact  4  can also be inserted from above so that it is supported in a linearly movable manner between two pairs of guide columns. To simplify the assembly and to be able to preassemble the individual components in the form of a unit, it is required for bridge contact  4 , which is biased by spring element  12 , to be retained in guide unit  10 . To this end, bridge contact  4  preferably has two projecting guide lugs  4   a  at each of its long sides. Guide insert  10 , in turn, preferably features guide shoulders  14  which extend along guide columns  10   b  and which are limited at the free ends of guide columns  10   b  by stop extensions  16  which are directed outward.  
         [0016]    Thus, for assembling this unit, spring element  12  is to be inserted into guide insert  10  and, subsequently, bridge contact  4  has to be slightly rotated about its longitudinal axis so that it can be introduced between guide columns  10   b  against the spring force and there be rotated into its original position again in such a way it makes contact against guide shoulders  14  with its guide lugs  4   a  and is pushed by spring element  12  in the direction of the free guide column ends and is retained there in guide insert  10  by limiting extensions  16 .  
         [0017]    Moreover, the edges of guide columns  10   b  facing the interior of the guide insert are preferably beveled so that plunger  8 , in adaptation thereto, is reliably guided between guide columns  10   b  with its plunger body  8   a  for actuating bridge contact  4 . To improve the plunger guidance, plunger  8  has elongated guide flanks  8   b  at opposite sides of its essentially cuboidal plunger body  8   a . To accommodate guide flanks  8   b  of plunger  8 , lower housing part  2  has corresponding recesses  9 .  
         [0018]    In order for plunger  8  to be limited in its actuator travel, it has at least one extension  8   c  at the top end which cooperates with at least one end face of a free end of a guide column  10   b.    
         [0019]    The present invention is not limited to the specific embodiments described above but is intended to be defined in scope by the appended claims. Thus, guide insert  10  can also be designed, for example, in the form of a closed cuboidal block which then has suitable clearance windows for receiving bridge contact  4 , which is supported in a linearly movable manner, and for receiving spring element  12 . Then, it would be possible for bridge contact  4  to be actuated via a plunger which acts upon bridge contact  4  via an opening at the end face of the block or which acts immediately thereon via the bridge contact ends laterally projecting from the clearance window. Moreover, all features shown in the drawing belong to the present invention. In particular, the geometric designs as shown.