Abstract:
A device for maintaining a hinge of a seat in an unlocked position, that includes a locking mechanism that can be declutched by rotation of an axis of the hinge, and a cam connected to a back of the seat and having a profile adapted to act on a forced-rotation driving mechanism of the hinge axis from a first inclination angle of the back of the seat towards the front, and to stop acting on the driving mechanism from a second inclination angle towards the front.

Description:
BACKGROUND 
     The present invention relates to a motor vehicle seat, the backrest of which is hinged to the seat cushion, it being possible to adjust and lock the inclination of the backrest in particular angular ranges with respect to the seat cushion by virtue of a special mechanism commonly known as a “hinge”. 
     The general principle of a seat hinge has been known for a long time, for example from the documents FR 2 599 684 or EP 0 770 514. It is based on the meshing, with a toothed ring, of three sprags at an angular spacing of 120°, it being possible to disengage this meshing by virtue of a hinge pin actuated by a handle. In the disengaged position, the sprags approach the center of the hinge and no longer mesh in the toothed ring. 
     As an adjustable inclination is only useful in an angular range which is more limited than 120°, and since it is furthermore expedient not to be able to lock the seat outside this angular range, it is known, for example from the document FR 2 659 604, to provide sectors on the toothed ring of the hinge which are not cogged and thus where the sprags cannot mesh. For example, it is known practice to divide each 120° sector of the toothed ring into a cogged 75° sector and a smooth 45° sector. The upper cogged sector is split on either side of the vertical, for example between 65° toward the rear and 10° toward the front; this cogged sector is thus followed toward the front by the smooth 45° sector which is itself followed, at an inclination of 35° to the horizontal, by the start of the next cogged sector. 
     In some vehicles it is desirable to be able to retract the seat by moving the backrest in folded-flat form toward the front, horizontally. The user in this case has to maneuver the handle of the hinge pin and simultaneously pivot the backrest forward; once the inclination of the latter causes it to enter the sectors of the hinge which are not cogged, that is to say between 10° and 55° beyond the vertical, the user can release the handle since it is no longer possible to lock the seat. However, this locking becomes possible again (beyond 55° in the example given) before reaching the horizontal, such that the user must actuate the maneuvering handle again in the last part of the folding-flat operation in order to prevent the seat from locking before it reaches the retracted position. Moreover, it is difficult for the user to estimate this horizontal position exactly, such that the backrest may in the end be immobilized in a position which is not the absolutely ideal position. 
     BRIEF SUMMARY 
     The aim of the invention is to remedy this difficulty and to enable the user to release the maneuvering handle again when he is retracting the backrest, at least through the whole of the final part of the maneuver and to enable locking exactly in the position desired for retracting, in principle the horizontal position. 
     This aim is achieved according to the invention by virtue of a device for keeping a seat hinge unlocked, comprising a locking mechanism that can be disengaged by the rotation of a hinge pin, characterized in that the device comprises a cam connected to the backrest, the profile of which is intended to act on means for forced rotation of the hinge pin forward of a first inclination angle of the backrest, and is intended to stop acting on said rotation means forward of a second inclination angle. Thus, the user can release the maneuvering handle again as soon as it has passed the first angle and the backrest will incline without locking as far as the second angle. 
     The first angle can be chosen to be less than or equal to 10°, or else it can be chosen to have any value equal to or greater than the start of the sector of the hinge which is not cogged (but less than the start of the next cogged sector). 
     The second angle is advantageously chosen to be equal to 90° for precise retraction horizontally. In this manner, the backrest is positioned directly at the end of forward travel in the ideal retracted position without the user having to take hold of the maneuvering handle again. 
     The device of the invention and the forced rotation means are outside the hinge such that a conventional hinge can be used and the means of the invention can be adapted thereto. 
     According to one embodiment, the forced rotation means comprise a set of link rods, the end of one of which is connected in rotation to the hinge pin and the end of the other of which is connected to a member moved by the cam of the device. 
     The member moved by the cam advantageously travels in a guide slot. The latter is formed in the wall of a guide piece attached to the seat; this wall may be located at a slight distance from the surface of application to the seat in order for the set of link rods to be housed between it and the seat. 
     The guide piece may have a surface which swivels in a piece attached to the backrest and covers the guide piece close to the hinge pin. This piece advantageously forms said cam at a tab. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the invention will become apparent from the following description of an exemplary embodiment. Reference will be made to the attached drawings, in which: 
         FIG. 1  is an exploded perspective view of one embodiment of the invention, 
         FIGS. 2 to 5  are four side views close to the hinge of side members of an inclinable seat equipped with the device of  FIG. 1 ,  FIGS. 2 to 5  corresponding to four stages of inclination, and 
         FIG. 6  is a schematic view of the hinge angles provided according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     In a manner known per se, in particular from the documents cited at the beginning of this description, the hinge between the backrest and the seat cushion is obtained by means of a hinge mechanism consisting of two round plates able to rotate with respect to one another, one of the plates being attached to a fitting connected to the seat cushion and known as the seat side member  1 , and the other plate being attached to a fitting  6  connected to the backrest. The relative rotation of the two plates is normally prevented by a locking system consisting of serrated radial sprags borne by one of the plates and pressing radially against a toothed ring formed in a circular shoulder borne by the other plate and provided with cogged sectors and sectors which are not cogged. The radial sprags may be disengaged simultaneously from their meshing with the circular shoulder by actuating a mechanism controlled by a hinge pin  2  bearing a maneuvering handle (or connected to actuating means). The maneuvering of the hinge pin  2  therefore allows one of the two plates to be pivoted with respect to the other and thus inclines the backrest of the seat to a greater or lesser degree with respect to the seat cushion, and releasing the hinge pin again causes the sprags to mesh once again in the circular shoulder and sets a new position of the backrest unless the sprags are then opposite a part which is not cogged, in which case the backrest inclines further until the sprags are once again in front of a cogged part, the arrival and blocking position moreover being approximate. 
     The device of the invention aims, as the backrest is inclined into particular positions, to exert positive action automatically on the hinge pin in order to prevent locking in position. 
     The device of the invention fits on the side member  1  which is in the form of an L with a horizontal leg intended for fastening to the seat cushion (not shown) and a vertical leg, the rounded upper part  3  of which, having a rim, houses the hinge mechanism of known type which is approximately in the form of a disk. Holes enable said mechanism to be fastened securely. The hinge pin or rod  2  passes through the side member  3  in order to form a terminal part  4  having a noncircular (for example square) cross section in order to be able to have an element for maneuvering the hinge pin  2  fitted onto it. 
     A guide piece  10  is fastened to the outer surface of the vertical leg of the side member  1 , being held on the one hand by holding means  36 , which will be described hereinbelow and hold the piece  10  around the end piece protruding from the pin  2  which penetrates into an opening  11  in the guide piece, and on the other hand by an assembly rivet  12  passing into the holes  5  and  13  of the side member  1  and of the guide piece  10 . Around the opening  11 , a circular rib  14  is formed in order to receive in rotation a cam member  30  described hereinbelow. Finally, the guide piece  10  has in its middle a guide slot  15  in the form of a pistol, the point of which points toward the opening  11 . The slot  15 , surrounded by an area  15 ′, is formed in a wall  16  of the guide piece  10  which is offset toward the front with respect to the wall in which the fastening hole  13  is made, such that when the guide piece  10  is fastened on the side member  1  there is enough room behind the wall  16  for other flat members of the mechanism of the invention to be housed and moved, namely a rear link rod  20  and a front link rod  21 . The front link rod  21  is a simple short arm having toward one end a slot  22  intended to engage with play with the end piece  4  of the hinge pin  2  so as to be fixed in rotation therewith, and having a hole  23  toward the other end. The rear link rod  20  is circularly arcuate and has holes  24  and  25  at its ends. A holding rivet  26  passes through the slot  15  in the guide piece  10  and is fastened behind the hole  24  in the link rod  20 ; the rivet  26  is held protruding from the front of the slot  15  by virtue of a friction ring  27  which rubs against the area  15 ′ surrounding the slot  15 . A rivet  28  and a washer  29  assemble the link rod  20  and the link rod  21  in the manner of a hinge through their respective holes  25  and  23 . 
     A cam piece  30  is secured to the fitting  6  of the seat backrest by virtue of assembly rivets  31  and holes  32  in the cam  30 . The piece  30  has a flat form folded in the form of a Z so as to form a part  33  in contact with the fitting  6  of the backrest located at a different level from the opposite parallel part  35 , these two parts  33  and  35  which are parallel to the fitting  6  being separated by a perpendicular part  34 . The part  35  covers the guide member  10  and holds it in position by virtue of the engagement of the circular rib  14  and an orifice  36  into which it is introduced with play. The part  35  has a cam tab  37  defining a cam profile intended to engage with the holding rivet  26  located in the slot  15  in the guide member. The form and function of this cam page will become apparent from the explanations which will be given in connection with  FIGS. 2 to 5 . 
       FIG. 2  shows the seat in the comfort position, as shown by the slight rearward inclination (25°) of the backrest fitting  6  with respect to the seat side member  1 . In this position, the cam tab  37  points downward and does not interfere with the holding rivet  26  located at the right-hand end of the slot  15  in the guide piece  10 . 
     In  FIG. 3 , the seat is in the end locking position toward the front, with the fitting  6  inclined forward (for example 10°). The holding rivet  26  is housed in a hollow  38  in the left-hand profile of the cam tab  37 , just before reaching a ramp  39  which runs away from the pin  4  in the piece  30 . In order to reach this ramp, the hinge mechanism must first be maneuvered by the rod  4 , the effect of which is to send the holding rivet  26 , by means of the set of link rods  20 ,  21 , to the opposite end of the slot  15 , to the left, as shown in  FIG. 4 , and to make it possible to rotate the seat. 
     When the mechanism is unlocked, the seat can be hinged down further forward as is shown in  FIG. 4 ; in this way, a circular part  40  of the cam tab  37  follows the ramp  39  and holds the rivet  26  in the left-hand position in the slot  15 , that is to say in the unlocked position of the hinge, even if the sprags of the latter are in front of a cogged sector of the hinge. The sprags do not mesh since the mechanism is unlocked and the seat is not blocked in this position but may follow its path as far as the position shown in  FIG. 5  where the seat is horizontal. 
     In this position, the cam tab  37  suddenly offers a hollow profile  41  to the rivet  26  which, as it leaves the flat part  40 , then falls into this hollow profile and passes back to the right-hand end of the slot  15  under the effect of the elasticity of the hinge mechanism, and thus relocks the hinge mechanism. The sprags can then mesh with the toothed sector opposite them and the seat is locked in this folded-flat position, exactly horizontally. 
     In order to return the seat to the right-hand position, all that is necessary is to maneuver the rod  4  in order to unlock the mechanism and, with the maneuvering of the rod  4  having pushed by way of the link rods  20 ,  21  the holding rivet toward the left, to freely straighten up the seat. 
       FIG. 6  summarizes the possibilities of seat inclination and locking in position according to the invention. The sleeper-seat position of the seat at an inclination of 65° rearward with respect to the vertical axis Y (maximum inclination limited by a mechanical stop) can be seen at A, the so-called comfort position at 25° toward the rear can be seen at B, and the retracted or hinged-flat position toward the front can be seen at X, coincident with the horizontal axis. 
     Moreover, the hinge mechanism used, known per se, has three 120° sectors engaging with three sprags, each 120° sector being divided into a cogged sector C, C′, C″ of 75° and a sector NC, NC′, NC″ which is not cogged and makes up the remaining 45°. 
     The user adjusts the position of the seat in the angular zone “beta”. If he wishes to retract the seat backrest to position X, he must maneuver the hinge mechanism, which unmeshes the sprags from the cogged sectors C, C′ and C″. However, having passed through the 10° of angular zone “gamma” toward the front, he can release the maneuvering handle again since, in the following 45°, the sprags will be in front of sectors NC, NC′, NC″ which are not cogged, and, starting from the terminal zone “alpha” of 35°, the device of the invention will force the maneuvering rod, by virtue of the cam  37 , into the unlocked position, preventing the sprags meshing until the position X has actually been reached, and the cam profile  41  returns the maneuvering rod  4  into the locked position with the sprags thus meshed with the cogged zone. 
     It goes without saying that other angular configurations can be chosen to define the cogged sectors and the sectors which are not cogged. Thus, if desired, the angular zone “gamma” of 10° toward the front, where the backrest can be locked, can be avoided, or by another cam mechanism or an appropriate cam profile which eclipses the locking in this zone or more simply by rotating the toothed ring of the hinge 10° toward the rear in order to move the cogged zones further away.