referring now to the drawings , the safety binding according to the invention constitutes a stop for the front of a ski boot 13 . it comprises a body or casing 1 which is movably mounted on a fixed piece 2 on which it is maintained elastically in abutment . this support means 2 is fast with a base plate 3 which is fixed on the top surface of a ski 4 , for example by means of screws 5 . the body 1 is maintained elastically in abutment on the fixed means 2 due to an elastic device comprising a piston 6 urged by a compression spring 7 and which is permanently applied under pressure by this spring against the front face 2b of the support means 2 . the compression spring 7 which extends axially inside the body 1 , abuts furthermore , at its front end , on the end 8 of an adjusting plug 9 screwed at the front of the body . the piston 6 is mounted to slide in a bore 10 disposed in the front part of the body 1 , along the longitudinal axis thereof . it should be noted that all the embodiments shown a one - piece assembly formed by a casing plus jaw but this is not necessarily the case , provided that the jaw and the casing , if they are made of a plurality of elements , are fast in displacement whenever there is a disconnection . the piston 6 is preferably constituted by a cylindrical sleeve of revolution comprising a rear support face 11 which is applied against the front face 2b of the support means 2 . a jaw 12 which is fast with the body 1 and in fact constitutes the rear part thereof , holds the front of the ski boot 13 . the boot is held laterally due to the substantially vertical faces 14 and 15 of the wings of the jaw 12 and vertically due to a horizontal flange 16 of this jaw . as may be seen in fig1 and 2 , the body 1 comprises a central recess 17 in which the support means is engaged . this recess 17 is substantially parallelepipedic in form and it is downwardly open , i . e . in the direction of the ski 4 . the dimensions of this recess 17 are such that the body 1 may tip on both sides , as may be seen in particular in fig7 and 8 . the inner , rear face 17 &# 39 ; of the recess 17 , i . e . the one located towards the jaw 12 , presents two forwardly projecting sections 18 and 19 ( fig3 and 4 ). these two projecting sections constitute two ribs which converge at a point located above the ski . when the body 1 is in normal position of use or position of rest , the two ribs ( projecting sections ) 18 and 19 take their place in two corresponding grooves or recessed sections 20 and 21 provided in the rear face 2a of the support means 2 and which converge at a point a located above the ski ( fig5 ), point where the two ribs 18 and 19 also converge . the two ribs 18 and 19 engaged in the two grooves 20 and 21 thus define two lines of support x -- x &# 39 ; and y -- y &# 39 ; converging at point a . a sufficient space is provided between the rear face 17 &# 39 ; of the recess 17 and the rear face 2a of the support means 2 to allow the tipping movement of the ribs 18 , 19 . the body 1 is maintained in abutment on the rear face 2a of the support means 2 due to the elastic device which is disposed towards the front with respect to the fixed support means 2 and which comprises the piston 6 urged rearwardly by the spring 7 . this piston 6 is thus permanently in elastic abutment against the front transverse face 2b of the support means 2 , which face is flat and rectangular in shape for example . this transverse front face 2b is included in a plane parallel to the transverse plane defined by the lines of support x -- x &# 39 ; and y -- y &# 39 ;. on this face abuts the rear transverse face 11 of the piston 6 which has the form of an isosceles triangle or trapezium with the vertex directed downwardly ( fig5 and 10 ), and / of which the vertices are indicated by 23 , 24 , 25 . according to the invention , the edge 35 which is included between a top vertex 24 and the bottom vertex 23 of the triangular rear face 11 is parallel to the line of support y -- y &# 39 ;, whilst the other edge 36 , included between the other top vertex 25 and the lower vertex 23 , is parallel to the line of support x -- x &# 39 ;. it should be noted that the line of support x -- x &# 39 ; and the edge 36 are located on either side of the longitudinal plane of symmetry a - b perpendicular to the ski and that the same applies to the other line of support y -- y &# 39 ; and the edge 35 . the piston 6 may be mounted to rotate freely about its axis , in the bore 10 . however , it is preferable if it is guided longitudinally so as always to be maintained in correct position , during its movement of longitudinal slide in the bore 10 . to this end , guide members may be provided on the lateral surface of the piston 6 , which cooperate with other members extending longitudinally in the bore 10 . these guide members may be constituted for example by longitudinal ribs 6a provided on the lateral surface of the piston 6 and sliding in corresponding grooves made in the wall of the bore 10 . the position of the ribs 6a and of the corresponding guide grooves is determined so that the two edges 35 , 36 or the rear support face 11 are symmetrical with respect to a vertical and longitudinal plane . the body 1 is retained vertically with respect to the fixed support means 2 by means of a projection 26 , which extends forwardly from the rear face 17 &# 39 ; of the recess 17 , and which is engaged in a corresponding housing 27 made in the rear face 2a of the support means 2 . the projection 26 comprises , in fact , two projecting sections corresponding respectively to the ribs 18 and 19 . these projecting sections extend substantially perpendicularly to the axes of the ribs 18 and 19 , i . e . to the lines of support x -- x &# 39 ; and y -- y &# 39 ;, so that the projection 26 is generally in the form of a v very widely open towards the top . the projection 26 defines upper retaining flanges located in planes respectively perpendicular to the axes of the ribs 18 and 19 . the recessed section 27 made in the rear face 2a of the support means 2 and with which the projection 26 cooperates , defines two upper flanges 33 and 34 for vertical retention , the upper flange 33 being perpendicular to the line of support x -- x &# 39 ; and the flange 34 being perpendicular to the other line of support y -- y &# 39 ;. upon lateral disconnection , the assembly formed by the jaw 12 and casing or body 1 pivots either on one of the lines of support x -- x &# 39 ; or on the other y -- y &# 39 ;, depending on the direction of disconnection . this pivoting is effected elastically against the action of the elastic device acting , by action of the piston 6 , against the front face 2b of the support means 2 , along a line of reaction . fig7 and 8 illustrate a lateral disconnection towards the right in the direction of arrow f ( anticlockwise direction ). in the course of this movement , the assembly formed by the jaw 12 and the body 1 pivots about the line of support x -- x &# 39 ;. in rest or starting position , the piston 6 is applied against the front face 2b of the support means 2 by its triangular rear face 11 . from the beginning the tipping movement about the line of support x -- x &# 39 ;, the piston 6 pivots with respect to the support means 2 so that it bears thereon only by its edge 36 defining a line of reaction . this edge is then in the position 36 1 indicated in fig7 and in this position the piston 6 exerts on the front face 2b of the support piece 2 an effort f 1 perpendicular to the face 2b along an axis located at a distance d 1 from the line of support x -- x &# 39 ;. the assembly formed by the jaw 12 and th body 1 is therefore subjected , in the position illustrated in fig7 to a return moment , in clockwise direction , of value f 1 × d 1 . when the pivoting movement corresponding to the lateral disconnection continues , the binding may reach a position as illustrated in fig8 in which it is tipped further towards the outside . in this case , the edge 36 of the piston 6 is displaced further towards the outside and is in position 36 2 on the front face 2b of the support means 2 . in this position , due to the tipping movement , the piston 6 has been pushed further into the bore 10 , bringing about an additional compression of the return spring 7 , so that the piston 6 exerts on the support means 2 an effort f 2 greater than the effort f 1 . furthermore , the point of application of this effort is more to the outside , so that the leverage d 2 of the effort f 2 is greater than the leverage d 1 of the leverage d 1 of the effort f 1 . this results in that the return moment of the binding f 2 × d 2 when it is in the position illustrated in fig8 is much greater than the moment of return f 1 × d 1 . fig9 illustrates the approximate variation of the effort p before being exerted on the end of the boot as a function of the lateral displacement 1 of this end . curve a shown in solid lines represents the variation of the effort p obtained with a binding according to the invention , during the movement of lateral disconnection , and curve a 1 corresponds to the variation of this effort during the return of the binding to its rest position . fig9 shows in dashed lines another curve b giving the variation of the effort p in the course of the disconnection of a binding of prior known type and in which the piston 6 presents a circular rear face 11 applied against a front face 2 b of the support means 2 presenting a triangular form with downwardly directed vertex . curve b 1 indicates the variation of the effort during the return of the known binding into rest position . the curves of fig9 show that the binding according to the invention offers the advantage that the effort exerted on the end of the boot is maintained at a high level , even for a fairly considerable lateral displacement 1 , which gives much more energy for the return of the boot and of the binding into rest position than in the case of the prior known binding . in fact , the curve b shows that with a binding of this type , although the effort exerted on the end of the boot increases progressively at the beginning of the lateral disconnection , it then decreases very substantially , this being due to a notable reduction of the return moment itself provoked by a considerable reduction of the leverage . this is not the case with the binding according to the invention since , as has been seen previously , the effort exerted by the piston 6 increases as well as the leverage as the lateral disconnection movement progresses . fig1 illustrates a variant embodiment of the piston 6 in which the rear support face 11 thereof has the form of an isosceles trapezium . the small base 37 and the large base 38 of this isosceles trapezium are respectively located in the lower part and in the upper part of the support face 11 and they are connected by two edges 39 and 40 which are symmetrical with respect to the vertical and longitudinal plane and constituting lines of reaction coming into contact with the front face 2b of the support means 2 in the course of the lateral disconnection movement . fig1 and 12 show another variant embodiment of the piston 6 . in the embodiments which have been described hereinabove , the edges 35 , 36 ( fig6 ) or 39 , 40 ( fig1 ) of the piston 6 are fixed with respect to this piston but they constitute with respect to the front face 2b of the support means 2 lines of reaction which move over this front face 2 b in the course of a lateral disconnection movement . in the variant embodiment illustrated in fig1 and 12 , the lines of reaction in the course of a movement of disconnection move over the piston 6 . to this end , this piston 6 has two reaction surfaces 41 and 42 which are symmetrical with respect to the vertical and longitudinal plane of symmetry . these reaction surfaces 41 and 42 connect the flat rear transverse face 11 , in the form of an isosceles triangle or trapezium with vertex or small base directed downwardly , and the cylindrical lateral surface of the piston 6 . the reaction surface 41 is a cylindrical surface which is produced by a line of reaction moving over a curve 43 , whilst remaining parallel to the line of support x -- x &# 39 ;. in the same way , the reaction surface 42 is also a cylindrical surface produced by a line of reaction moving over a curve 44 whilst remaining parallel to the line of support y -- y &# 39 ;. with such an arrangement , in the course of a disconnection , the piston 6 is in abutment on the front face 2b of the support means 2 along a line of reaction , constituting a generatrix of the cylindrical surfaces 41 and 42 , this line of reaction moving , in the course of the movement of disconnection , over the cylindrical surface 41 or 42 whilst always remaining parallel to the corresponding line of support x -- x &# 39 ; or y -- y &# 39 ;. in a binding of this type , it should be noted that the lines of reaction which are constituted by the edges 35 , 36 or 39 , 40 or by generatrices of the surfaces of reaction 41 , 42 have a constant length used whatever the height of the piston with respect to the plane of the ski . in other words , the piston 6 is applied on the flat front face 2b of the support means 2 , always along a section of straight line of invariable length whatever the adjustment of the binding in height . this constitutes a noteworthy advantage with respect to the known binding in which the converging lines of reaction are fixed on the support means . in this latter case , the length of the portion of reaction line formed on the fixed support means decreases as the piston moves vertically . it should be noted that the features of the invention may be used in a binding of the type such as the one described in french patent application no . 79 14484 of june 6 , 1979 and in which the upper support is effected on a screw for adjustment in height , moving the assembly constituted by the jaw and the casing with respect to the support means . the fact of making the support means of a plurality of independent elements would , or course , not depart from the scope of the invention . for example , the support means may comprise a front element fixed to the ski and comprising the support face for the piston , and another independent outer element also fixed to the ski and comprising the lines of support . it should also be noted that the lines of support are at least two in number , but this is not necessarily the case , as is described in french patent application no . 78 08342 of mar . 22 , 1978 .
a safety binding for a ski including a body having a jaw for holding a ski boot and a support fixed to the ski . the support has a rear transverse face with two recesses therein , and a front transverse face . the body includes a transverse face having two projections thereon , each adapted to engage one of the recesses of the support . the recesses and projections define two lines of support converging at a point above the ski and disposed , respectively , on either side of the longitudinal plane of symmetry of the ski , so that the body can pivot along either one of the lines of support . a spring urges the rear face of a piston against the front transverse face of the support so that the rear traverse face of the support is urged against the transverse face of the body . the rear face of the piston includes two lines of reaction converging toward the ski . because the two lines of reaction are on the rear face of the piston , the return moment of the binding increases continuously as the binding pivots further away from a central retaining position , thereby ensuring the rapid return of the binding whatever the displacement of the boot . in addition , because lines of reaction are on the rear face of the piston , the line of contact between the rear face of the piston and the support is constant .