Seat with an adjustable fold-down back
BACKGROUND OF THE INVENTION 
     Since the comfort of passengers and the saving of space are constant preoccupations of the manufacturers of vehicles, especially motor vehicles, there are many types of seats of which the back can be folded down onto the sitting surface, and it is increasingly desirable that there should also be the possibility of adjusting the inclination of this back during use, in order to ensure that the user is truly comfortable. 
     However, it can be seen that the devices allowing this adjustment of inclination are complex and mostly employ an auxiliary pivoting mechanism which comprises numerous components and which is therefore costly. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to overcome these disadvantages by providing a seat of which the back can be both adjusted and folded down, but which is produced in an especially simple way, is of absolute reliability and has a relatively low cost price. 
     In fact, the subject of this invention is a seat comprising a backframe and a sitting-surface frame which are connected to one another by means of two mutually spaced axles, namely a tilting axle and a folding-down axle, fixed to one of the frames and locked on the other, and means for releasing each of these axles for the purpose of pivoting the back about the other. 
     According to a preferred embodiment, the backframe has a serrated slot engaged on a folding-down axle fixed to the sitting-surface frame and carries a tilting axle which is locked on the end of the sitting-surface frame. 
     The releasing means consist of a releasing lever integral with the tilting axle and having a finger intended for retention in a notch of the end of the sitting surface and offset relative to the tilting axle. 
     As a result of this arrangement, the pivoting of the releasing lever in one direction makes the retention finger rock in the notch, causes a lifting of the tilting axle and of the backframe as a whole and frees the latter from the folding-down axle, thus allowing it to assume the desired inclination. Conversely, a pivoting of the releasing lever in the opposite direction causes the retention finger to come out of the notch and frees the tilting axle, so that the back can be folded down onto the sitting surface. The frames thus themselves form the means for guiding the pivoting of the back, thus avoiding the need to use auxiliary devices. 
     According to a preferred embodiment, the sitting-surface frame and the backframe each comprise a U-shaped tube, the lateral branches of which are bent upwards at their end, the lateral branches of the backframe also being flattened, starting from the tilting axle. Production is further simplified, whilst the rigidity of the seat is increased. 
     Moreover, the following description of an embodiment, given as a non-limiting example and illustrated in the accompanying drawings, will highlight the advantages and characteristics of the invention. In these drawings: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagrammatic side view of a seat according to the invention in the position of use. 
     FIG. 2 is a sectional view along the line 2--2 of FIG. 1. 
     FIG. 3 is a partial view on a larger scale, taken from the side opposite that of FIG. 1 and showing the connection between the releasing lever and the sitting-surface frame. 
     FIG. 4 is a sectional view along the line 4--4 of FIG. 3. 
     FIG. 5 is a view, similar to that of FIG. 1, of the seat in the position for adjustment of the inclination of the back. 
     FIGS. 6 and 7 are views, similar to that of FIG. 5, of the released seat before and after the folding down of the back onto the sitting surface respectively. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The seat which is the subject of the invention comprises a backframe 1 preferably formed by an element bent in a U-shaped manner, the lateral branches 11 of which are flattened in their lower part. These lower parts are also curved upwards and forwards, so that each of the lateral branches of the frame 1 terminates in an upwardly directed flat portion 2. This end portion 2 has an elongate and slightly curved longitudinal slot 4, the upper edge of which has rounded teeth 6, between two of which is engaged an axle 8 fixed to a sitting-surface frame 10. 
     This sitting-surface frame 10 possesses, above a base or mounting 12, two lateral arms 14 which, towards the rear of the seat, are curved downwards and then upwards so as to have a form closely resembling that of the flattened portion of the adjacent lateral branch 11 of the backframe. The axle 8 thus passes through a descending portion 16 of the corresponding branch 14. 
     Furthermore, each of the branches 14 terminates in a flattened and slightly widened portion 18 which forms two flat lugs, 20 and 22 respectively, separated by a notch 24 and terminating in bearing surfaces 25 and 26 respectively. These two bearing surfaces are inclined downwards, and preferably the front bearing surface 26 is slightly curved and centred on the axle 8. The central notch 24 is widened outwards and is joined to each of the bearing surfaces 25 and 26 by means of a rounded angle 27 and 28 respectively (FIG. 3). 
     Engaged in the notch 24 is a flat finger 30 which is formed at the end of a releasing lever 32 integral with an axle 34 passing through the branch 11 of the frame 1. In fact, near the finger 30, the lever 32 has a boss 35 (FIG. 4), from which the axle 34 starts and which forms a washer 36, against which the branch 11 of the frame 1 is retained axially by means of a washer 38, whilst at the same time being free to rotate relative to the axle 34. The boss 35 also possesses a notch 40, into which engages the lug 22 of the sitting-surface frame when the seat is in the position of use. The bottom 42 of the notch 40 constitutes an extension of the lateral face of the finger 30 which has a form substantially matching that of the edge of the lug 22 and which constitutes the lower face of a nose 44 projecting laterally on the lever 32. The finger 30, on its other side, is extended by a plane face 46 inclined upwards, that is to say in the opposite direction to the bearing surface 25. 
     The flat finger 30 is thus offset relative to the tilting axle 34 of the releasing lever 32. However, it is strictly immobilized in the notch 24 when this lever is in the raised position, shown in FIGS. 1 and 3, because of its contact with the two lugs 20 and 22, the action of the weight of the back 1 tending to press it into the notch 24 and the action of the restoring spring 48. 
     However, when the user wishes to change the inclination of the back 1, it is sufficient for him to cause the releasing lever 32 to pivot towards the rear of the seat, as shown in FIG. 5. This pivoting lays the lever onto the rounded angle 27 of the lug 20 and makes it pivot about this angle, in such a way that the face 46 comes to bear on the bearing surface 25, whilst the finger 30 rocks in the notch 24 and causes a lifting of the axle 34 which moves outwards away from its initial position, and the notch 40 slides on the lug 22, but maintains the connection between the two frames. The axle 34, in its movement, takes with it the backframe 1 and consequently the upwardly curved flattened portion 2, the slot 4 and particularly the toothing 6. This toothing disengages from the axle 8, so that the back is no longer connected to the sitting-surface frame 10 by means of this axle 8. The user can then shift the upper part of the frame 1 forwards or rearwards, that is to say according to the arrow F1 or the arrow F2 of FIG. 5, in order to change the inclination of the back in relation to the sitting surface and especially to move the toothing 6 relative to the axle 8 about the axle 34 which performs the function of a tilting axle. 
     When the desired position has been reached, the lever 32 is returned to its initial position, that is to say it pivots in the opposite direction about the rounded angle 27, until, when the notch 40 has slid over the lug 22 of the sitting surface, the finger 30 is once again retained in the notch 24. At this moment, the axle 34 has descended again and the toothing 6 has engaged onto the axle 8, although the latter is not between the same teeth as before. Moreover, this return to the locked position becomes easier as a result of the action of a spring 48 which is mounted between the end of the curved portion 2 of the backframe 1 and a fixed point 50 of the supporting cradle 12 of the sitting surface and which at any moment tends to return the end of the backframe downwards, that is to say the toothing 6 into its position of engagement on the axle 8. 
     Furthermore, if it is necessary to increase the space available behind the seat and therefore fold the back 1 down, the releasing lever 32 is pushed forwards, as shown in FIG. 6. It then pivots, together with the axle 34, in relation to the backframe 1, in such a way that its profiled face 42 engages onto the edge of the lug 22 of the sitting-surface frame, whilst the finger 30 comes out of the notch 24, thus breaking the connection between the sitting surface and the back at this point. Because the nose 44 comes to bear on the front edge of the lug 22 of the sitting surface, no rearward movement of the back is possible. In contrast, force simply exerted forwards on the upper part of the backframe 1 is sufficient to cause the latter to pivot about the axle 8 which performs the function of a folding-down axle. The seat then assumes the position shown in FIG. 7. 
     The back 1 is returned to the normal position by pivoting the frame 1 about the axle 8 in the opposite direction, the profiled face 42 once again engaging on the bearing surface 26 of the lug 22, particularly because this bearing surface is centred on the axle 8. When the nose 44 is once more in contact with the lug 22, the lever 32 can be raised in order to retain the finger 30 once again in the notch 24. The seat resumes its locked position. 
     This operation, like the preceding one, is therefore carried out extremely simply without the need for a special external mechanism, purely by virtue of the form of the sitting-surface and backframes. The control of the inclination of the back and that of its folding down thus have an especially small bulk, although they are of unfailing reliability, so that the seat obtained is extremely resistant, especially comfortable and inexpensive. 
     Of course, the lateral branches of the backframe, like those of the sitting-surface frame, are formed in an identical way, a folding-down axle 8 and the slot 4 being provided on each of the sides of the seat. Likewise, a tilting axle 34, a retention finger 30 and a boss 35 are mounted on each of the lateral branches 11 of the backframe 1, so as to interact with two identical notches 24 of the sitting-surface frame. It is nevertheless generally preferable to use only a single release control lever 32 integral with one of the bosses 35 and connect the two axles 34 to one another by means of a transverse rod. The two sides of the seat are thus shifted simultaneously and pivot together about the tilting axle 34 of the folding-down axle 8.