Abstract:
An electromagnetic drive for an electrical switch such as a circuit breaker, has at least one movable armature that can implement a lifting movement along a pushing direction for moving a movable switching contact of the switch. In a closed armature position, the armature closes a magnetic circuit through first and second magnetically conductive yoke parts. A permanent magnet produces a magnetic field for the magnetic circuit and a holding force for holding the armature in the closed position. A coil is disposed to generate a magnetic flux in the same or opposite direction as the magnetic flux of the permanent magnet. The electromagnetic drive can be readjusted after installation, where the first and second yoke parts are moved relative to one another by the permanent magnet into the adjusted state, whereupon they are fixed in position.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an electromagnetic drive for an electrical switch. 
     A drive of this kind is known by way of example from unexamined patent application EP 0 321 664. This drive has a movable armature which can implement a lifting movement along a predetermined pushing direction and can be connected to a movable switching contact of a switch. The drive also has a permanent magnet which produces a magnetic field and a holding force for holding the armature in a predetermined position. A coil is arranged in such a way that the drive can be actuated and the armature can be moved by a flow of current. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention is based on the object of disclosing a drive which enables subsequent adjustment of the components and subsequent correction of manufacturing tolerances. 
     This object is achieved according to the invention by a switch as claimed. Advantageous embodiments of the inventive switch are disclosed in the dependent claims. 
     According to the invention an electromagnetic drive is then provided for an electrical switch, in particular an electrical circuit breaker, with at least one movable armature, which can implement a lifting movement along a predetermined pushing direction, can be connected indirectly or directly to a movable switching contact of the switch, and, in a closed position, closes a magnetic; circuit of the drive at a first armature-side stop face with a first magnetically conductive yoke part of the drive and at a second armature-side stop face with a second magnetically conductive yoke part of the drive, at least one permanent magnet, which produces a magnetic field for the magnetic circuit and a holding force for holding the armature in the closed position, and at least one coil, which is arranged in such a way that a magnetic flux can be brought about by a current flow through the coil, which magnetic flux is directed in the same direction as or in opposition to the magnetic flux of the permanent magnet in the magnetic circuit, wherein the electromagnetic drive provides the possibility of a readjustment state after installation by virtue of self-adjustment of the position of the first yoke part and the second yoke part relative to one another being possible as a result of the magnetic force of the permanent magnet, and wherein the yoke parts can be brought into a fixedly installed state, in which the alignment of the yoke parts is fixed independently of the further positioning of the armature. 
     A fundamental advantage of the inventive drive is that, due to the possibility of subsequent self-adjustment, it may be simply installed even with components produced with relatively high manufacturing tolerances because, following installation, the electromagnetic drive, as a result of the magnetic self-adjustment provided according to the invention, can be readjusted with respect to the arrangement of the first and second yoke parts with very little effort. Readjustment occurs automatically due to the magnetic force of the permanent magnet in such a way that the first and second yoke parts are aligned at an optimum spacing from each other. 
     The at least one permanent magnet is preferably arranged in such a way that it adjoins at least one of the yoke parts of the drive. 
     Automatic readjustment is possible particularly easily and therefore advantageously if, in the readjustment state, the magnetic circuit is closed by the armature and at least two yoke parts of the drive can be displaced relative to one another along the pushing direction of the armature, so—driven by the magnetic force of the permanent magnet—the yoke-side stop face of the first yoke part is brought in a self-adjusting manner to a spacing from the yoke-side stop face of the second yoke part which is identical to the spacing between the first and the second armature-side stop face along the predetermined pushing direction. 
     The at least two yoke parts, which can be displaced relative to one another along the pushing direction of the armature, are screwed together, wherein one screw is led through a hole in one of the two yoke parts and is screwed to the other of the two yoke parts. The diameter of the hole along the pushing direction of the armature is preferably greater than the diameter of the screw. With a loose screw connection and closed position of the armature the yoke parts are in the readjustment state in this arrangement and can be displaced relative to one another along the pushing direction of the armature; with a tight screw connection the yoke parts are, by contrast, in a fixedly installed state. 
     The diameter of the hole along the pushing direction of the armature is preferably at least  10 % greater than the diameter of the screw. The hole can be by way of example a slot whose longitudinal direction is oriented along the pushing direction of the armature. 
     The yoke parts and the permanent magnet (s) preferably form a magnetically conductive hollow body with an opening slit through which the armature can plunge into the interior of the hollow body. 
     In the closed position of the armature the first armature-side stop face rests externally on the outer side of the hollow body and the second armature-side stop face rests internally on the inner side of the hollow body. 
     It is also regarded as advantageous if the hollow body is tubular or channel-shaped and extends along a longitudinal axis which is oriented perpendicularly to the predetermined pushing direction of the armature, and the opening slit extends parallel to the longitudinal axis and the armature closes the opening slit. The hollow body is preferably closed, an least in certain sections, at its leading and trailing tubular or channel end by a metal sheet in each case, preferably made from magnetically non-conductive material. 
     The armature is preferably a plunger armature with a T-shaped cross-section. 
     The armature is preferably connected to a spring device which exerts a spring force in the direction of the open position of the armature in which the magnetic circuit is opened. 
     The invention also relates to a method for installing an electromagnetic drive for an electrical switch, in particular an electrical circuit breaker. According to the invention it is provided in relation to a method of this kind that the drive is pre-installed and the magnetic circuit is then closed by the armature in that the armature is brought into its closed position, the drive is brought into the readjustment state and self-adjustment of the position of the yoke parts relative to one another occurs due to the magnetic force of the permanent magnet, and after self-adjustment the yoke parts are brought into a fixedly installed state in which the alignment of the yoke parts remains fixed independently of the further positioning of the armature. 
     Reference is made with respect to the advantages of the inventive method to the above statements in connection with the inventive electrical switch since the advantages of the inventive method substantially match those of the electrical switch. 
     It is regarded as advantageous if, in the readjustment state, at least two yoke parts—driven by the magnetic force of the permanent magnet—are displaced relative to one another along the pushing direction of the armature until the yoke-side stop face of the first yoke part has been brought in a self-adjusting manner to a spacing from the yoke-side stop face of the second yoke part, which spacing is identical to the spacing between the first and second armature-side stop face along the predetermined pushing direction. 
     According to a particularly preferred embodiment it is provided that the drive is brought into the readjustment state by loosening a screw connection between at least two yoke parts which can be displaced relative to one another, within a predetermined region, along the pushing direction of the armature, and after self-adjustment the yoke parts are screwed tight again. 
     The invention will be explained in more detail below with reference to exemplary embodiments. In the drawings, by way of example: 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         FIG. 1  shows an exemplary embodiment for an arrangement with an electromagnetic drive and an electrical switch which is connected to the electromagnetic drive, 
         FIG. 2  shows a plunger armature of the electromagnetic drive according to  FIG. 1  in an open position and in more detail, 
         FIG. 3  shows the plunger armature according to  FIG. 2  in a closed position, 
         FIG. 4  shows a second exemplary embodiment for an electromagnetic drive in which the plunger armature is slightly too large for the hollow body into which it should plunge, 
         FIG. 5  shows the plunger armature according to  FIG. 4  after a readjustment of the drive,  FIG. 6  shows an exemplary embodiment for an inventive electromagnetic drive in a three-dimensional exploded drawing and 
         FIG. 7  shows the electromagnetic drive according to  FIG. 6  in the installed state. 
     
    
    
     For the sake of clarity the same reference numerals are always used in the figures for identical or comparable components. 
     DESCRIPTION OF THE INVENTION 
     An electromagnetic drive  10  for an electrical switch  20 , which can be by way of example a circuit breaker, can be seen in  FIG. 1 . The electrical switch  20  includes a movable switching contact  21  and a fixed switching contact  22 . 
     The movable switching contact  21  is connected to a drive stem  30  of the electromagnetic drive  10  which cooperates with a spring device  40  of the electromagnetic drive  10 . A further drive stem  50  is also coupled to the spring device  40  and this is connected to a plunger armature  60  of the electromagnetic drive  10 . 
     The plunger armature  60  can implement a lifting movement along a predetermined pushing direction P and plunge into a magnetic hollow body  70  of the drive  10  in the process. With solid lines  FIG. 1  shows the plunger armature  60  in an open position in which it projects from the hollow body  70 . Broken lines and the reference numeral  61  show the closed position of the plunger armature in which it is completely introduced into the magnetic hollow body  70 . 
     The function of the spring device  40  is to press the additional drive stem  50  in  FIG. 1  upwards, so the plunger armature  60  is subjected to a spring force which is designed to bring it into the open position. In the open position of the plunger armature  60  the movable switching contact  21  is in an open position which is shown in  FIG. 1  by solid lines. 
     As will be explained in more detail below, by feeding a current through a coil  80  of the electromagnetic drive  10  a magnetic force can be produced with which the plunger armature  60  is brought into its closed position counter to the spring force of the spring device  40 . In this closed position the plunger armature is held by the magnetic hollow body  70  even if no current is conducted through the coil  80 . The magnetic force, which the magnetic hollow body  70  requires to hold the plunger armature  60  in the closed position, is produced by two permanent magnets  90  and  95  which form components of the magnetic hollow body  70 . Apart from the two permanent magnets  90  and  95  the magnetic hollow body  70  in the exemplary embodiment of  FIG. 1  includes five yoke parts, namely a first yoke part  100 , a second yoke part  105 , a third yoke part  110 , a fourth yoke part  115  and a fifth yoke part  120 . The arrangement of the five yoke parts  100 ,  105 ,  110 ,  115  and  120  is chosen such that the magnetic hollow body  70  forms an opening slit  130  through which the plunger armature  60 , which is substantially T-shaped in cross-section, can plunge into the hollow body. The five yoke parts  100 ,  105 ,  110 ,  115  and  120  are made from a magnetizable material, by way of example a material containing iron. 
     Once the plunger armature  60  has reached its closed position the two drive stems  30  and  50  press the movable switching contact  21  in  FIG. 1  downwards, so this also reaches its closed position and closes the electrical switch  20 . The movable position of the switching contact  21  is identified in  FIG. 1  by broken lines and reference numeral  21   a.    
     It may also be seen in  FIG. 1  that the plunger armature  60  has a first armature-side stop face  62  and a second armature-side contact face  63 . In the closed position of the plunger armature  60  the first armature-side contact face  62  rests on the outer side  71  of the magnetic hollow body  70  and on the outer side of the first yoke part  100  and the third yoke part  110 . In the closed position of the plunger armature  60  the second armature-side stop face  63  rests on the inner side  72  of the hollow body  70  and, more precisely, on the inner side of the second yoke part  105 . 
     In the closed position of the plunger armature  60  two magnetic circuits are closed whose magnetic flux is created by the two permanent magnets  90  and  95 . The magnetic flux of the first magnetic circuit flows from the permanent magnet  90 , via the fourth yoke part  115 , the first yoke part  100 , the plunger armature  60  and the second yoke part  105  back to the permanent magnet  90 . The magnetic flux of the second permanent magnet  95  flows via the fifth yoke part  120 , the third yoke part  110 , the plunger armature  60  and the second yoke part  105 . 
     The plunger armature  60  is held in its closed position by the magnetic force of the two magnetic circuits, although the spring force of the spring device  40  wants to bring the plunger armature  60  into the open position. The spring force of the spring device  40  is therefore smaller than the magnetic force of the magnetic circuits of the two permanent magnets  90  and  95 . 
     If the electrical switch  20  is to be opened by the electromagnetic drive  10  then a current, which is opposed to the two magnetic circuits of the two permanent magnets  90  and  95 , is fed through the coil  80 . The magnetic holding force of the two magnetic circuits of the two permanent magnets  90  and  95  is reduced as a result, so the spring force of the spring device  40  is sufficient to press the plunger armature  60  into its open position. In the open position of the plunger armature  60  the spacing between the first armature-side stop face  62  and the outer side  71  of the hollow body and the spacing between the second armature stop face  63  and the inner side  72  of the hollow body is so large that the magnetic force of the permanent magnets  90  and  95  is no longer sufficient to close the plunger armature  60  counter to the spring force of the spring device  40 . 
     For an improved overview  FIG. 2  shows the plunger armature  60  in a larger diagram in its open position again. It can be seen that the spacing A 2  between the first armature-side stop face  62  and the second armature-side stop face  63  matches the spacing A 1  between the outer side of the first yoke part  100  and the inner side of the second yoke part  105 . For this reason the two magnetic circuits of the two permanent magnets  90  and  95  are closed so as to be gap-free, or at least approximately gap-free, if the plunger armature  60  is introduced fully into the hollow body  70 .  FIG. 3  shows this in more detail. 
     It can be seen in  FIG. 3  that the first armature-side stop face  62  rests on the outer side of the two yoke parts  100  and  110  and the two magnetic circuits M 1  and M 2  are closed at this location. In a corresponding manner the two magnetic circuits M 1  and M 2  are also closed at the second armature-side stop face  63 , because this rests completely on the inner side of the second yoke part  105 . 
     The complete closure, shown in  FIG. 3 , of the two magnetic circuits M 1  and M 2  is only possible in the case of the electromagnetic drive  10  according to  FIGS. 1 to 3  because the spacing A 1  between the two armature-side stop faces  62  and  63  is identical to the spacing A 2  between the outer side of the two yoke parts  100  and  110  and the inner side of the second yoke part  105 . 
     There is preferably a readjustment option in the exemplary embodiment according to  FIGS. 1 to 3 , with which the position of the yoke parts can subsequently be automatically relatively readjusted. The mode of operation of a readjustment option of this kind will be explained below by way of example with reference to exemplary embodiments in which the length of the plunger armature  60  is not optimum. 
       FIG. 4  shows a case in which the spacing A 1  between the two armature-side stop faces  62  and  63  is slightly larger than the spacing A 2 . As may be seen:
 
 A 1= A 2+dx here.
 
     The difference in length dx can be based on manufacturing tolerances in the production of the yoke parts, in particular the fourth yoke part  115  and the fifth yoke part  120 , or on manufacturing tolerances in the production of the plunger armature  60 . 
     To nevertheless ensure that, in its closed position, the plunger armature  60  can close the two magnetic circuits M 1  and M 2  (cf.  FIG. 3 ) without air gaps having to be bridged, in the exemplary embodiment according to  FIG. 4  a readjustment option is provided in the fourth yoke part  115  and in the fifth yoke part  120  with which the manufacturing tolerances can be subsequently corrected. 
     It can be seen in  FIG. 4  that the fourth yoke part  115  and the fifth yoke part  120  are each fitted with holes  200  and  205  whose diameter d is slightly greater than the diameter of the associated fastening screws  210  and  215  which are screwed into the first yoke part  100  and the third yoke part  110  and fixedly hold the fourth yoke part  115  and the fifth yoke part  120 . Due to the over-dimensioned size of the holes  200  and  205  it is accordingly possible to subsequently correct the difference in length dx by loosening the two fastening screws  210  and  215  in the closed position of the plunger armature  60 . Due to the magnetic force of the two permanent magnets  90  and  95  the first yoke part  100  and the third yoke part  110  are pulled upwards, so they abut with their outer side on the first armature-side stop face  62 .  FIG. 5  shows this by way of example. Pulling-up of the first yoke part  100  and the third yoke part  110  is based on the magnetic force of the two magnetic circuits M 1  and M 2  which always exert a magnetic force such that the magnetic circuit M 1  or M 2  is closed so as to be gap-free. The air gap, shown in  FIG. 4 , between the plunger armature  62  and the two yoke parts  105  and  110  is therefore closed by the magnetic force of the two permanent magnets  90  and  95  by the two yoke parts being pulled upwards by the difference in length dx. 
     The diameter d of the holes  200  and  205  along the pushing direction of the armature is preferably at least 10% greater than the diameter of the fastening screws  210  and  215 . The holes  200  and  205  can be slots by way of example whose longitudinal direction is oriented along the pushing direction of the armature. 
     Once this self-adjustment, which is based on the magnetic force of the permanent magnets  90  and  95 , is complete the two fastening screws  210  and  215  can be tightened again, so the position of the first yoke part  100  and that of the third yoke part  110  relative to the fourth yoke part  115  and the fifth yoke part  120  is fixed again by clamping. After fixing the spacing between the two armature-side stop faces  62  and  63  matches the spacing between the outer side of the two yoke parts  100  and  110  and the inner side of the second yoke part  105 . 
       FIG. 6  shows by way of example the mechanical construction of an electromagnetic drive in a three-dimensional exploded view. The first yoke part  100  can be seen, and this is screwed to the fourth yoke part  115  by means of screws which are led through over-dimensioned holes  200 . Located between the fourth yoke part  115  and the second yoke part  105  is the permanent magnet  90  which is fixed with the aid of two fastening plates  300  and  305  to the yoke parts. The two fastening plates  300  and  305  also fix the other permanent magnet  95  which is positioned between the second yoke part  105  and the fifth yoke part  120 . The third yoke part  110  is fixed to the firth yoke part  120  by means of fastening screws which are led through over-dimensioned holes  205 . 
     As already explained, the holes  200  and  205  are slightly larger than the fastening screws used, so automatic self-adjustment can occur if the plunger armature  60  is too large or too small and undesirable air gaps occur in the closed position of the plunger armature. In the exemplary embodiment according to  FIG. 6  the plunger armature  60  is formed by an upper armature plate  64  and a guide plate  65  which are screwed to an armature center piece  66 . 
     The additional drive stem  50 , which is guided through a hole  105   a  in the second yoke part  105  can also be seen in  FIG. 6 . 
     It may also be seen in the diagram according to  FIG. 6  that the yoke parts  100 ,  105 ,  110 ,  115  and  120  and the two permanent magnets  90  and  95  form a hollow body which is tubular or channel-shaped and extends along a longitudinal axis L. The longitudinal axis L is perpendicular to the predetermined pushing direction P with which the plunger armature  60  implements its lifting movement. The leading and trailing tube or channel end of the tubular or channel-shaped hollow body is closed by a metal sheet in each case, of which one is shown by way of example in  FIG. 6  and is identified by reference numeral  310 . 
       FIG. 7  shows the electromagnetic drive according to  FIG. 6  in the installed state. Two metal sheets  310  and  320  can be seen which complete the tubular or channel-shaped hollow body  70  at the two tube or channel ends. The additional drive stem  50  can also be seen, and this is lead out of the hollow body  70  and can be connected to the spring device  40  according to  FIG. 1 . 
     The fourth yoke part  115  and the second yoke part  105 , the two fastening plates  300  and  305  and the coil  80  can also be seen, and this can project out of the hollow body  70  through recesses in the two metal sheets  310  and  320 . The fastening screws  210 , with which the first yoke part is screwed to the fourth yoke part  115  in such a way that automatic readjustment, as has been described above, is possible, can also be seen. 
     Although the invention has been illustrated and described in more detail by preferred exemplary embodiments it is not restricted by the disclosed examples and a person skilled in the art can derive other variations therefrom without departing from the scope of the invention. 
     List of Reference Numerals 
     
         
           10  electromagnetic drive 
           20  electrical switch 
           21  movable switching contact 
           21   a  movable position 
           22  fixed switching contact 
           30  drive stem 
           40  spring device 
           50  drive stem 
           60  plunger armature 
           61  closed position of the plunger armature 
           62  first armature-side stop face 
           63  second armature-side stop face 
           64  armature plate 
           65  guide plate 
           66  armature center piece 
           70  hollow body 
           71  outer side 
           72  inner side 
           80  coil 
           90  permanent magnet 
           95  permanent magnet 
           100  first yoke part 
           105  second yoke part 
           105   a  hole 
           110  third yoke part 
           115  fourth yoke part 
           120  fifth yoke part 
           130  opening slit 
           200  hole 
           205  hole 
           210  fastening screw 
           215  fastening screw 
           300  fastening plate 
           305  fastening plate 
           310  metal sheet 
           320  metal sheet 
         A 1  spacing 
         A 2  spacing 
         d diameter 
         dx difference in length 
         L longitudinal axis 
         M 1  magnetic circuit 
         M 2  magnetic circuit 
         P pushing direction