Abstract:
The invention concerns an electromechanical protective relay comprising deformable bimetal switches in the event of overload in power lines. A triggering mechanism acts on a flexible blistering segment ( 20 ) which can pivot by means of a support ( 30 ) on a fixed rest ( 17 ) and whereof the stem ( 21 ) has an extension ( 27 ) formed along the length of the segment and folded back in U- or V-shape to press elastically against a bearing surface ( 36 ) of the box so as to cause the segment to exert pressure on the pivot.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an electromechanical thermal protection relay comprising in a case, components such as thermally deformable bimetal strips in the case of overcurrent in power current lines, as well as switch contacts associated with power lines and able to be actuated by a command element which may be stressed through deformable components. 
     Usually, the command element acts on a middle point of a thin and flexible blade which has a foot fixed or resting on the case and a head cooperating with a contact maneuvering component. In response to the displacement of the control element resulting from an overcurrent, the stress to which the blade is subject at its middle point causes a sudden displacement of the head from a stable rest position to a working stable position, whereas the foot of the blade substantially remains in its initial position. The blade is designed, made and mounted in order to be able to bow from one stable position to the other, i.e. able to suddenly flex and for this purpose, it has, in its middle portion and for forming an application range for the control element, a protruding finger in a cutout area. 
     A relay of this type is described in document FR-1 274 608. The prestressing required for bowing the blade is then produced by stiffly fixing and tightening legs provided at the foot of the blade. This embodiment is difficult to reproduce and does not allow the positions of the head to be adjusted. 
     Another thermal relay of this type is described in document EP-360 215. The prestressing required for bowing the blade is then produced by a bridge of material embossed in the foot of the blade, whereas a stiff support, which may be pivotally applied on a support and stressed by an adjustment screw, is fixed at the foot of the blade. The making of the embossed bridge is particularly difficult to reproduce industrially. Further, the overall dimensions of the blade are observed to be too large in height. Finally the device is not satisfactory since, as the prop of the support is located away in height from the area where the control element is applied on the finger of the blade, it causes, a misadjustment of the control element during an adjustment operation made by means of the screw. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to find a remedy to the aforementioned drawbacks and to make the manufacturing characteristics reliable and reproducible, notably the adjustment conditions for a thermal relay of the described type, while providing it with small dimensions. 
     According to the invention, the foot of the flexible blade has a folded back extension so as to be applied elastically against a span of the case in order to cause the blade to be pressed against the prop. 
     The extension may notably extend from the foot of the blade in the direction of its length and be folded, beyond the area for fixing the stiff support on the blade, into the shape of a V or U with respect to the main plane of the blade, wherein the free leg of the V or the U is applied against the span of the case. When the blade is symmetrical, the extension may comprise two symmetrical legs. 
     Preferably, the pivoting rest point of the support of the blade is located along the length of the blade, substantially at the level of the area of application of the control element on the blade. 
     The adjustment element may have a cam applied on the stiff support of the blade on the side of the pivoting rest point, wherein this cam is able to rotate around an axis parallel to the main plane of the blade. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The description of an embodiment of the invention is made hereafter, as a non-limiting example and with reference to the appended drawings. 
     FIG. 1 illustrates a section of the thermal protection relay according to the invention. 
     FIG. 2 is a perspective view of the bowing elastic blade of the relay. 
     FIGS. 3 and 4 illustrate the blade, as seen in elevation, from the front and from the side, respectively; 
    
    
     DETAILED DESCRIPTION 
     The illustrated electromechanical thermal protection relay comprises an insulating case  10  which offers a front face  10   a  provided with maneuvering and adjustment elements  10   b  and which contains bimetal strips not shown, deformable in the case of overcurrent in the power current lines, also not shown. 
     Case  10  houses pairs of normally closed (NC) switched contacts  11  and normally open (NO) switch contacts  12 , the mobile contacts of which are located at the ends of respective elastic blades  13 ,  14  controllable by a triggering mechanism  15  in response to the deformation of at least a bimetal strip. The triggering mechanism  15  comprises a control element  16  acting on a flexible bowing blade  20  which will act on the contacts. The control element  16  is for example a lever pivoting around an axis X 1  and a portion of which is formed by a room temperature compensation bimetal strip. 
     The flexible blade  20  extends in the direction of its length over a distance h and is symmetrical with respect to a plane Q which defines a main directrix X 2  at rest and X′ 2  in the working position. The general surface of the blade is slightly curved and will be subsequently designated as the main plane P. The blade has a foot  21  resting, via a support  30 , on a span  17  of the case, as well as a head  22  and a middle portion  23 . 
     Head  22  of the blade cooperates with a slide  18  for maneuvering the contacts  11 ,  12  in order to move it along a direction Y 1  parallel to the front face  10   a  of the case. The middle portion  23  of the blade, located between the foot  21  and the head  22 , is provided with a finger  24 , protruding in a cutout region  25 . The finger  24  forms an area  24   a  for applying the control lever  16 , wherein the latter in the case of an overcurrent, exerts a stress in a direction Y 2  parallel to the front face  10   a  of the case and opposite to Y 1 . 
     The stiff support  30 , as a small plate or analogous element, is fixed by any suitable means to the foot  21  of blade  20 . The small plate is positioned on the side of the blade opposite to lever  16  and it has, in its lower portion, a fixing area  31 , associated with an area  26  for fixing the foot  21  of the blade, and at its upper portion, a rest point  32  in order to pivot on the fixed span  17  of the case. 
     Near its lower end  33  and below its fixing area  31 , the blade  20  or preferably the small plate  30  is stressed by an adjustment element  34  capable of displacing it along Y 1  or Y 2 . The adjustment element  34  rotates around an axis X 3  and offers a cam surface  35  applied on the end  33  of the small plate  30  in order to cause the small plate  30  together with the flexible blade  20  to rotate around the pivot axis X 4  defined by the span  17  and the rest point  32 , in order to adjust the position of the head  22  of the blade which cooperates with the slide. The adjustment element  34  is easily accessible through the opening of the case before fitting a lid, not shown. Axes X 1 , X 3 , X 4  are parallel to one another and are perpendicular to Y 1 , Y 2  as well as to the symmetry plane Q of the blade. 
     According to the invention, foot  21  of the blade  20  is provided with an extension  27  consisting either of a leg, or preferably of two elastic legs  28 ,  29 . The extension  27  is directed from the foot along the length of the blade. Legs  28 ,  29  are symmetrical with respect to plane Q. Legs  28 ,  29  are folded back as a V or U through folding, with a fold back angle greater than 135° and here close to 180°, and their free end rests on a span  36  of the case. It is seen that this configuration of the blade reduces the overall dimensions in the length of the blade while producing the targeted pressing of pivot  32  on span  17 . 
     The pivot axis X 4  is located, in the direction of the height of the blade, substantially at the level of the rest area  24   a  for finger  24  of the blade, so that adjustment of the position of the head  22  has a very small effect on the rest position of lever  16  and so on the initial condition of the control mechanism. Distance e between axis X 4  and area  24   a  may for example be less than 10%, preferably 7%, of the length h of the blade. 
     Upon assembly, blade  20  is introduced into the case between the pivot prop  17  and span  36  which ensures the compression on prop  17 ; leg  21  is applied against the adjustment cam  35 , whereas the head engages into the slide  18 . Lever  16  is applied on area  24   a . To adjust the position of the head, the operator causes element  34  to rotate until it reaches the desired position, without disturbing the mechanism  15 , through the provisions of the invention.