Abstract:
A unitary contact with a box-like contact part, in which two spring legs are oppositely arranged that extend to respective free ends in the direction of the mating face of the contact spring where one of the spring legs is formed by a reverse inward bend and the other spring leg is formed through separation from an opposite wall.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a unitary contact spring comprising a box-like contact part and two oppositely arranged spring legs extending to free ends in the direction of a mating face of the contact spring. 
     DESCRIPTION OF THE PRIOR ART 
     A contact spring of this type is known, for example, from U.S. Pat. No. 4,834,681. 
     As can be seen from FIGS. 1 and 2 of this patent, the spring legs in the layout are attached laterally along the longitudinal axis of the contact spring and are folded inwards. The spring legs are therefore arranged on the inside of the sidewalls. The top wall, as a result of this folding technique, is divided in the middle and formed as a double wall. 
     Contact springs are needed in large quantities for use in industry as well as in the automotive field. It is therefore important to be able to manufacture a contact spring with controlled bending operations allowing a high number of strokes and requiring a minimum of consumption of material. The cost of the material for the contact springs of the prior art amounts to about 20% of the manufacturing costs. 
     The contact spring known from U.S. Pat. No. 4,834,681 has the disadvantage that, as a result of the double wall construction of the top wall as well as the lateral attachment of the spring legs in the layout, a high consumption of material is entailed. Furthermore the split top wall must be separately connected. 
     A further unitary contact spring having spring legs pointing towards the mating face is known from DE 19704311 A1. However, the spring legs of this contact spring are arranged side-by-side and not opposite one another. 
     As shown in FIG. 4A of DE19704311 A1, the spring legs are also laterally attached in the layout, resulting again in a high consumption of material. A layout which saves some material is shown in FIG. 1, where the spring legs are attached laterally and slightly obliquely to the longitudinal axis of the contact. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a contact spring of the type set out above which, despite well-controlled bending operations allowing a high number of strokes, minimizes the consumption of material. 
     It is further required that, even at the end of its service life, the contact force does not fall below 2 Newton and that the contact spring, as a whole, is robust. 
     According to the invention this object is obtained in that one of the spring legs is formed by inward bending over 180° and the other spring leg by separation out of the opposite wall. 
     This method of forming spring legs results in a very narrow layout per contact. The spring leg which is bent inwards over 180° is preferably attached in the layout to the extension of the wall on the inner side of which it is attached in its unbent state. 
     Compared with a lateral attachment in the layout, this configuration has the advantage that the layouts of the individual contacts can be arranged more closely, thereby achieving a higher utilization factor when stamping from the continuous strip of material. 
     The material utilization can be further increased by attaching the spring leg, which is to be bent inwardly over 180°, obliquely to the longitudinal axis of the wall on the inner side of which it is arranged in its bent state. 
     Further advantageous embodiments of the contact spring are disclosed in the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows part of a continuous strip with the stamped layout of one contact as well as a partially represented layout of its adjacent contact; 
     FIG. 2 shows a top view of the box-like contact part of the unitary contact spring; 
     FIG. 3 shows section BB of FIG. 2; 
     FIG. 4 shows a box-like contact part as seen from the mating face; and 
     FIG. 5 shows section AA of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a strip  1 , onto which layouts for the contact spring according to the invention are attached. A complete layout of one contact spring as well as the layout in part of its adjacent contact spring is shown. The contact spring essentially consists of a terminal part  2   a  and a contact part  2   b . In the embodiment shown, the terminal part  2   a  is formed as a crimp terminal with crimp tabs  3   a  and  3   b  as well as  4   a  and  4   b.    
     In the layout, the contact part  2   b  comprises a bottom wall  5 , laterally thereto side walls  6  and  7  and on the underside, top wall  8 . A spring leg  9  is separated out of the bottom wall  5 , such that its free end points towards the mating face of the contact part. A further spring leg  10  is attached slightly obliquely to the longitudinal axis of the contact to the top wall  8  in the direction of the terminal part  2   a.    
     Both spring legs  9  and  10  are provided with stampings or through-cracks  11 . These serve to increase the stiffness of the spring legs and, in the case of spring leg  10 , are arranged centrally inside the spring leg. In the case of spring leg  9 , the stamping  11  from the bottom wall  5  into the leg  9  is also arranged centrally to the spring leg  9 . A latching hook  12  is separated out of the top wall  8  by means of an L-shaped separation cut. 
     During the manufacture of the contact spring, after the formation of all the separation cuts, the stampings  11  are formed in the spring leg  10  and the latter is subsequently folded over by 180° onto the top wall  8  and aligned parallel to the longitudinal direction of the contact spring. 
     In the next step, the crimp tabs  3   a ,  3   b  as well as  4   a  and  4   b , in addition to side walls  6  and  7  are bent upwards over 90° from the bottom wall  5 . The stamping  11  is subsequently formed in spring leg  9 . Finally the top wall  8  with the spring leg  10  lying on its inner side is bent over 90° to close the box-like contact part. A connecting tab  13  is formed in the top wall  8  and the latching hook  12 , which are inserted into the side wall  6  through corresponding apertures  14 . 
     FIG. 2 shows a top view of the box-like contact part. In this view, the connecting tabs  13  are already inserted into apertures  14  and slightly protrude on the outside beyond the side walls  6 . 
     As can be seen from FIG. 5, which shows section AA of FIG. 3, the protruding connecting tabs  13  are subsequently pressed flat against the outside of side wall  6 . As can be seen from the dashed lines in FIG. 2, the connecting tabs  13  comprise a lower chamfered edge in the protruding region. 
     Likewise, a chamfered edge  16  is formed in the region of the apertures  16  on the part of the side wall  6 , which protrudes beyond the top wall  8  and which forms at the same time a continuous polarization  15 . The closing of the box during the bending operation is facilitated by the chamfered edge  16  as well as by the chamfered edges on the connecting tabs  13 . 
     FIG. 3 shows section BB of FIG.  2 . The latching hook  12  is bent upwards out of the top wall  8 . The upper spring leg  10  is bent over inwardly in a first region A over 180° parallel to the top wall  8  and in a second region B is bent slightly inwardly in the direction of the opposite spring leg  9 . In the third region C, the spring leg  10  is again bent upwards in order to facilitate the introduction of a contact blade (not shown). The free end of the spring leg  10  is formed as a point  17 . 
     In order to prevent insertion of the contact blade behind spring leg  10 , a tab  18  is provided on the frontal side of the top wall  8 , which is bent over, over 180°, to receive the point  17  of the spring leg  10  between itself and the top wall  8 . Side parts  19   a  and  19   b  are formed on tab  18  and are bent over by more than 180° and thereby also guide point  17  laterally. 
     In order to enable the displacement of the spring leg  10  during the insertion of a contact blade, a window  20  is provided in the top wall  8 , into which point  17  can deflect. The spring leg  9 , which has been separated out from the bottom wall  5 , also comprises a point  21  which, as shown in FIG. 1, is formed in the bottom wall  5  by means of a waste-free separation cut. The point  21  is also fixed via a tab  22  bent over inwardly over 180° between tab  22  and bottom wall  5 , whereby side parts  23   a  and  23   b , which are bent over inwardly by more than 180° also assure a lateral fixing. The spring leg  9  is also bent inwards, in the region opposite to section B of spring leg  10 , and comprises at its free end, a bulge  24  pointing in the direction of the opposite spring leg  10  for making contact with the contact blade to be inserted. The stampings or the through-cracks  11  extend, in the case of spring leg  10 , from section A to approximately the middle of section B and, in the case of spring leg  9 , from the bottom wall  5  to approximately the middle of spring leg  9 . 
     As can be seen from FIG. 5, the size of the through-crack  11  at the location of section AA is approximately equal to the thickness of the material of the spring leg  9  or  10 . The stamping or through-crack  11  on spring leg  10  is somewhat wider than on the spring leg  9 , whereby a higher contact force is obtained. In order to facilitate the frontal insertion of the contact blade, the side walls also comprise guide tabs  25 ,  26  which are slightly bent inwardly (see FIG. 2) for forming a guide funnel. 
     In order to facilitate the bending processes, prestampings V are foreseen between guide tabs  25 ,  26  (as well as between tabs  18 ,  22 ) and adjacent walls as well as between the top wall  8  and the side wall  7  as well as between the spring leg  10  and the top wall  8 . 
     The invention is not limited to the embodiment shown. For instance, the terminal part  2   a  can also be formed as an IDC or as a flexible terminal. It is furthermore also possible to connect the top walls  8  with the side wall  6  by laser soldering instead of pressing the tabs  13  into apertures  14 .