Abstract:
The invention relates to a relay comprising a coil bobbin, a core penetrating the coil bobbin and a yoke. To achieve a high switching force with a low overall height, the cross-sectional area of the core is greater in the region toward the transition to the yoke than in the central region of the coil bobbin. Increased magnetic flux can be conveyed from the core owing to the cross-sectional enlargement and at the same time more coil windings can be arranged in the central region owing to the reduced cross-section there. Both measures act together and allow high switching forces with low overall height.

Description:
FIELD OF THE INVENTION 
   The invention relates to a relay with a coil bobbin, a core penetrating the coil bobbin and a yoke. 
   BACKGROUND 
   Relays with a coil bobbin, a core penetrating the coil bobbin and a yoke are known, for example, from EP-A-202 651, EP-B-363 176, EP-B-691 667 and DE-C-42 32 228. 
   In all of these relays the coil bobbin, the core and the yoke form a magnetic system that induces a switching process when the coil is excited or energized. During the switching process, the excited coil, generates a magnetic switching force that moves an armature. The movement of the armature is transmitted to a spring contact which then closes (makes) or opens (breaks) electrical contact with one or more fixed contacts. 
   One disadvantage of the relays from these known references is that it is difficult to provide adequate switching force with a compact construction. 
   The object of the invention is therefore to improve a switching relay such that large switching forces are achieved with a small overall volume. 
   SUMMARY OF THE INVENTION 
   This and other objects are achieved by a relay according to an embodiment of the invention having a core with a greater cross-sectional area in the region of the transition to the yoke than in the central region of the core surrounded by the coil bobbin. 
   This solution is simple in terms of construction and leads to smaller overall constructions of the relay with a constantly high switching force. 
   According to an exemplary embodiment of the invention, the central region of the core, which is surrounded by the coil bobbin, has a reduced cross-section providing space for additional coil windings, so the coil can generate a higher magnetic force. In the transition region between the yoke and core the cross-section is, on the other hand, designed so as to widen, so high magnetic flux can be conveyed from the core to the yoke. Both measures—the cross-sectional enlargement in the transition region between core and yoke and the cross-sectional reduction and the increased winding space for the coil bobbin—optimally supplement one another when a higher switching force is generated. 
   The invention will be described by way of example hereinafter with reference to various embodiments and to the accompanying drawings. The various features in the individual embodiments can be combined here independently of one another, as has already been illustrated above in the individual advantageous designs. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Exemplary embodiments of the invention will next be described with reference to the drawings, in which: 
       FIG. 1  is a perspective view of a relay according to an exemplary embodiment of the invention; 
       FIG. 2  shows a coil bobbin, a core and a yoke of a relay according to an exemplary embodiment of the invention; 
       FIG. 3  shows the core and the yoke of the embodiment of  FIG. 2 ; 
       FIG. 4  shows an exemplary core element for a relay according to the invention; 
       FIG. 5  shows an alternative exemplary core element for a relay according to the invention; 
       FIG. 6  shows a further alternative exemplary core element for a relay according to the invention; 
       FIG. 7  shows an exemplary coil bobbin for a relay according to the invention; 
       FIG. 8  shows the coil bobbin of  FIG. 7  in a view from the direction of arrow VIII; and 
       FIG. 9  shows an exemplary coil bobbin with inserted core element according to an embodiment of the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The general construction of a relay will firstly be described with reference to  FIG. 1 . 
   A relay  1  comprises a coil (not shown in  FIG. 1 ) wound on a coil bobbin  2 , a yoke  3 , and a core (not shown in  FIG. 1 ) penetrating the coil bobbin  2 . The yoke  3  ends in a pole face  4  adjoining a working air gap  5 . In other designs the pole face  4  can also be formed on the core. 
   The working air gap  5  is arranged between the pole face  4  and a movable armature  6 . The armature  6  is connected to a spring contact  8  so as to transmit movement, via a connecting element  7  guided along the coil bobbin  2 , so that a movement of the armature  6  inevitably leads to a movement of the spring contact  8 . 
   The spring contact  8  is in turn arranged between two fixed contacts  9 ,  10  arranged at a distance from one another in the movement direction of the spring contact, wherein the spring contact can preferably only touch one of the two fixed contacts  9 ,  10  respectively. The spring contact  8  is conventionally biased such that in the force-free state it rests against one of the fixed contacts, for example contact  10 . 
   If an excitation current is passed through the coil, a magnetic force is produced at the pole face  4 , which force attracts the armature  6  and attempts to reduce the working air gap. As a result, the armature  6  moves out of its resting position. This movement is transmitted to the spring contact  8  via the connecting element  7 . The spring contact  8  consequently also moves from its resting position and is pressed against the contact  9 . 
   The spring contact  8  and fixed contacts  9 ,  10  are each provided with contact pins  11 ,  13 ,  12 , respectively, extending to the outside of the relay. The contact pins  11 ,  12 ,  13  can each be present in pairs. 
   The contacts  11 ,  12 ,  13  form contact pairs  11 ,  13  and  11 ,  12  that are opened and closed as a function of the position of the spring contact  8 . For example in the exemplary resting position of the spring contact  8  shown in  FIG. 1 , the contacts  11  and  12  are electrically connected to one another via the spring contact  8  and the fixed contact  10 . 
   To provide defined contact points at the fixed contacts  9 ,  10  and the spring contact  8 , contact points or projections  14 ,  15 ,  16  are provided at the contacts  9 ,  10  and/or the spring contact  8 . 
     FIG. 2  shows an embodiment of the coil bobbin  2  with the yoke  3  and with the core  17  penetrating the coil, the viewing direction being oriented obliquely onto the pole face  4 . 
   For clarity, the coil, which is held by the coil bobbin  2  in the recess  18 , winding around the coil bobbin  2  and extending in the axial direction of the coil bobbin  2 , has been omitted in  FIG. 2 . 
   As can be seen in  FIG. 2 , the core  17  comprises two core elements  19 ,  20  located abutting one another along a parting plane  26  (shown in  FIG. 3 ) and extending transversely to the coil winding direction. 
   The core  17  projects from the coil bobbin  2  in the longitudinal direction thereof. 
     FIG. 3  shows the yoke  3  and the core  17  in the perspective of  FIG. 2  with the coil bobbin  2  removed. 
   It can be seen that the one core element  20  is designed integrally with the yoke  3  while the other core element  19  abuts the yoke  3  and the core  20 . The two core elements  19 ,  20  terminate flush with each other, toward the armature, to form a substantially level end face  21  which can also be used as the pole face  4 . 
   In the exemplary embodiment, the core elements  20  is integral with the yoke  3 , and is substantially uniformly rectangular in cross-section and does not have any projections and/or undercuts. 
   The other, separate core element  19  is provided with cross-sectional enlargements  22 ,  23  at the respective end faces in the longitudinal direction L of the coil. The cross-sectional enlargements  22 ,  23  can engage on the ends of the coil bobbin  2 . 
   In the central region of the core  17 , which is surrounded by the coil bobbin  2 , the cross-section of the core is reduced with respect to the two end regions located in the longitudinal direction of the coil bobbin. As a result, a recess  25  is produced in the core  17  which can be used as additional winding space for the coil, so the coil has a higher number of windings and/or density of windings. 
   If the core  17  does not adjoin the working air gap  5  of the relay  1  (because the pole face  4  is formed by the yoke), the cross-sectional enlargement  23  can be dispensed with although, as a consequence, the flux of the magnetic field from the core into the armature is affected. Of course, the pole face  4  formed by the yoke  3  can also have a cross-sectional enlargement. 
   As can also be seen in  FIG. 3  the parting plane  26  between the two core elements  19 ,  20  extends in the longitudinal direction L of the coil parallel to the yoke  3 . The faces located one on top of the other at the parting plane  26 , and at the abutment face  27  between the cross-sectional enlargement  22  and the yoke  3  are designed so as to be as flat and smooth as possible. As a result, air gaps in the transitional regions and losses in the magnetic flux are minimized or avoided. 
     FIG. 4 to 6  show further embodiments of the core element  19 . In all of these core elements  19  the cross-section at the two ends  22 ,  23  located in the longitudinal direction is enlarged in a cross-sectional plane perpendicular to the longitudinal direction L. 
   The cross-sectional plane Q is shown in  FIG. 4 , once in the central region as the cross-sectional plane Q 1  and once in the end region as the cross-sectional plane Q 2 . As can be seen, the area of the core element  19  in the cross-sectional plane Q 2  is greater than the area in the cross-sectional plane Q 1 . 
   The core element  19  of  FIG. 4  is economically produced from one piece and comprises bent ends  22 ,  23 . The bending process is facilitated by a recess  28  in the vicinity of the bending radius  29  and extending over the entire width of the core element  19 . 
     FIG. 5  shows a core element  19  constructed from a plurality of individual elements  19   a ,  19   b , etc. arranged side-by-side. The number of core elements  19   a ,  19   b , etc. arranged side-by-side and preferably touching may be varied;  FIG. 5  shows, merely as an example, four elements located side-by-side. The cross-sectional areas or contours of the individual core elements  20   a ,  20   b , etc. are identical in a plane located in the longitudinal direction L. To be able to easily handle the core element  19  in the embodiment of  FIG. 5 , the core elements  19   a ,  19   b , etc. may be connected to one another into one piece, for example by gluing, soldering, or welding. 
   In the embodiment of  FIG. 6  the core element  19  is a stamped part made of a metal material in which the two cross-sectional enlargements  22 ,  23  are designed in the form of impressed ramps extending obliquely in the longitudinal direction L of the coil. Alternatively, the core element  19  with oblique ramps can also be produced by injection moulding. 
     FIG. 7  shows the coil bobbin  2  with the core  17  and the yoke  3  omitted. The coil bobbin  2  has a passage  30  extending in the longitudinal direction L of the coil and open at both ends. 
   In the central region  31  of the coil bobbin  2 , which substantially coincides with the recess  18  for the coil, the internal cross-section is reduced in a plane perpendicular to the longitudinal direction L of the passage  30  in order to create space for additional coil windings. The passage  30  widens in a region  32  located toward the two ends of the coil bobbin  2 . The form of the region  32  is adapted to the form of the respective cross-sectional enlargement  22 ,  23  so the core element  19  can be received in the passage  30  with the cross-sectional enlargements  22 ,  23 . The cross-section of the passage  30  is dimensioned at its smallest point such that the cross-sectional enlargement  22  of the core element  20  can still be pushed through the passage  30 . In the inserted state, the cross-sectional enlargements  22 ,  23  engage behind the coil bobbin  2  so the core element  19  is held substantially non-displaceably by the coil bobbin. 
   As shown in  FIG. 8 , in which the coil bobbin  2  of  FIG. 7  is illustrated in the viewing direction VIII, the cross-sectional enlargement of the passage  30  can be differently designed at the two open ends in order, for example, to allow a flush termination of the core with the coil bobbin  2  at the one end and protrusion of the core  17  at the other end. 
   When the core element  19  with cross-sectional enlargements  22  and  23  is inserted into the passage  30 , the cross-sectional enlargements  22 ,  23  are received in enlarged regions  32  and a free space  33  extending through the coil bobbin  2  and of substantially constant internal width remains. The other core element  20  can then be inserted into the free space  33 . Held by the cross-sectional enlargements  22 ,  23 , the core element  19  can no longer be removed from the passage  30  as long as the other core element  20  is inserted. The core can be rigidly held in the coil member by a press fit of the core element  20 . For this purpose, the cross-section of the core element  20  is somewhat larger than the cross-section of the free space  33 . 
   The assembly process of a relay according to the invention will be briefly described hereinafter. 
   First, the core element  19  provided with at least one cross-sectional enlargement  22 ,  23  is inserted into the passage  30  in the coil bobbin  2 . As soon as the cross-sectional enlargements  22 ,  23  are received in the enlarged region  32  of the passage  30 , the other core element  20  can be inserted into the space  33  still free. 
   Depending on whether the cross-sectional enlargements  22 ,  23  are designed in one piece on the yoke  3  or on the separate core element  19 , the yoke  3  or the core element  19  is firstly placed in the passage  30 . The core element  20  with substantially uniform rectangular cross-section is then inserted.