Abstract:
A seat base length adjustment device including a seat nose plate assembled on a carriage movable with respect to the seating frame, means for slidably guiding the carriage, and means for maintaining the carriage in position with respect to said frame. The sliding guide means comprises a guide rail located in a middle portion of the carriage, the carriage supports a toothed wheel, rotatably assembled on the carriage along an axis perpendicular to the seating frame and to the sliding direction, and meshing with a rack arranged close to the guide rail, and the means for maintaining the carriage in position comprises a lock acting on the rotation of the toothed wheel.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to motor vehicle seats which comprise a seat base that can be adjusted to the user&#39;s morphology. Such seats enable to adapt the length provided by the seat base to the user&#39;s leg length, to provide a better comfort by supporting the thighs all the way to the knee bend. 
     2. Discussion of Prior Art 
     For this purpose, known seats comprise a seat base in which only the central portion of the seat cushion has an adjustable length, the stuffed lateral sides of the seat base remaining fixed. To be able to adjust this cushion length, it is known to move only the front portion of the cushion, or seat nose, backwards or forwards. 
     Known systems comprise a seat nose support plate assembled to slide backwards or forwards on a seating frame front crosspiece. The plate is assembled on a carriage sliding in a guide rail placed on the crosspiece. 
     DE19826823 discloses an adjustment system in which the opposite edges of the carriage are guided in lateral grooves of the guide rail. Said grooves are thus very distant from each other, especially as compared with their length. The system described in this document aims at avoiding for the sliding carriage supporting the seat nose to block by buttressing between the guide rail edges, due to the small length of the guide rail as compared with its width. This system uses a set of four toothed wheels meshing with one another, rotatably assembled on the carriage and aligned transversely to the sliding direction. The two end toothed wheels, which have the same dimension, also mesh with racks respectively provided on each edge of the guide rail. Thus, the displacements of the carriage are necessarily identical on both sides and the carriage thus cannot get stuck by buttressing in the guide rail. The locking in position is ensured by a pivoting lock located towards the back and engaging with one of the intermediary toothed wheels. 
     A disadvantage of such a system especially is the relatively large number of wheels, required to avoid the above-mentioned buttressing. Further, the unlocking requires operating the pivoting lock located towards the back with complementary control means enabling to control the pivoting of the lock from an offset driving member accessible to the user, which complicates the system manufacturing. 
     DE-A-102004030363 describes a system for setting the seat base length which comprises a carriage ( 1 ) slidably driven by a motor ( 27 ) which drives a pinion meshing with a rack ( 21 ) fixed on the seat frame. The carriage is guided on guide rails located laterally on either side of the seat. 
     The present invention especially aims at solving the above-discussed problems. It more specifically aims at providing a system which is easier to form and to use, while suppressing buttressing risks. It also aims at enabling to keep the largest possible seat nose cushioning thickness, by limiting to a minimum the thickness of the adjustment system. It further aims at enabling to use the largest possible number of common parts for a manually-operated adjustment system or a motor-driven adjustment system. 
     SUMMARY OF THE INVENTION 
     To achieve these objects, the present invention provides a device for adjusting the seat base length for a motor vehicle seat, comprising a seat nose plate assembled on a carriage movable with respect to the seating frame, means for slidably guiding the carriage, and means for maintaining the carriage in position with respect to said frame. 
     According to the present invention, the adjustment device is characterized in that the sliding guide means comprise a guide rail located in a middle portion of the carriage, the carriage supports a toothed wheel rotatably assembled on the carriage on an axis perpendicular to the seating frame and to the sliding direction, and meshing with a rack arranged close to the guide rail, and the means for maintaining the carriage in position comprise a lock acting on the rotation of the toothed wheel. 
     Thus, the use of a guide rail which is narrow with respect to its length and located in a middle portion of the carriage suppresses almost any risk for the carriage to get stuck by buttressing in the guide rail. The loads tending to immobilize the translation of the carriage, transmitted between the toothed wheel and the rack, are also exerted in a middle portion and do not risk generating a buttressing effect. The number of parts, and thus the cost, are decreased and, as will be better seen hereafter, many of the parts can be indifferently used in the manually-operated version and in the electric control version. 
     According to a specific configuration, the edges of the carriage are also guided in lateral grooves, which essentially only provide a guiding in the vertical plane, to avoid for the carriage edges to move away from the frame, but without taking part in the guiding in the horizontal plane, and thus without risking to cause a buttressing. 
     According to another specific configuration, return springs are arranged between the carriage and the guide rail on either side of the rack, to push the carriage towards the front of the seat base. These springs facilitate the seat nose adjustment manipulation by acting in such a way as to always push towards the front, thus avoiding for the user to have to pull the seat nose towards the front to increase the seat base length. Further, since the springs are placed on the guide rail edges, they contribute to balancing the sliding load and avoid a jamming. 
     As a variation, a spiral return spring may be assembled between the toothed wheel and the carriage, to exert on the toothed wheel a torque capable of pushing the carriage towards the front of the seat base by meshing of the toothed wheel with the rack. 
     According to a preferred configuration, the lock is slidably assembled on the carriage in the sliding direction of the carriage and has a notched locking end cooperating with the teeth of the toothed wheel. 
     Preferably, the teeth of the toothed wheel cooperating with the end of the lock are specific teeth different from the teeth cooperating with the rack. 
     According to a specific embodiment, the end of the lock and said specific teeth are made to form a ratchet enabling the toothed wheel to rotate without having to unlock the lock, when the carriage is pushed backwards against the thrust of the return springs. 
     According to a specific configuration, the sliding of the lock to ensure its unlocking is driven by a control handle acting on the lock against resilient return means tending to engage the lock with the teeth of the toothed wheel. Preferentially, the control handle is hinged at the front of the carriage. This configuration enables to ease the unlocking manipulation, while simplifying the forming of the device, the control handle directly acting on the lock. 
     According to another specific configuration, the toothed wheel and the lock are arranged under the carriage, between the carriage and a guide plate placed on the frame, the guide plate comprising an element of the middle guide rail and the lateral grooves for guiding the carriage edges. This arrangement especially enables to pre-assemble the device, and to ease its subsequent installation on the frame, while protecting the mechanical locking elements housed between the carriage and said plate. 
     In a motor-driven adjustment version, the device comprises a motor driving the toothed wheel in rotation. 
     The motor is preferentially attached under the frame and drives the toothed wheel via a flexible drive running through a port made in said frame. 
     According to another specific embodiment, the device comprises pins attached to the seat nose plate and extending downwards from said plate, each pin comprising a lower end portion arranged to engage under a rib attached to the seating frame, permanently during the sliding of the carriage. Thus, if the plate is submitted to lifting loads, these loads are directly transmitted to the seating frame, via the pins and said ribs, and thus without for the carriage itself to have to withstand such loads. This is particularly advantageous when the seat nose is placed in forward position. Indeed, as will be better seen hereafter, the load then exerted by the user on the front of the seat nose may generate a significant torque thereon, while the carriage is only maintained in its guide means over a short length. A significant load on the means for guiding the carriage edges would result from this situation, which would be particularly prejudicial if these parts are made of plastic. The previously-mentioned embodiment avoids this problem by transmitting this load almost directly from the plate to the seating frame. Further, for this purpose, the pins are arranged on the plate, by being preferably welded thereto, to be immediately next to the means for attaching the rib to the frame in end positions of the carriage sliding travel, since the carriage is most currently in these end sliding positions, and the previously-mentioned load may be the strongest in the forward end position. 
     Preferentially still, the rib forms a branch of a T guide rail having its other branch forming the lateral rib intended to guide the carriage edges, and the T guide rail is fastened to the frame by bolts having their head embedded in the transverse bar of the T. Thus, especially in the forward end sliding position, the heads of the pins attached to the plate are substantially in correspondence with the bolt heads and the loads tending to lift the plate are then almost directly borne by said bolts, and thus by the frame. 
     The present invention also aims at a motor vehicle seat having a seat base of adjustable length, characterized in that it comprises a device for adjusting the seat base length such as defined hereabove. 
     The foregoing and other objects, features, and advantages of the present invention will be discussed in detail in the following non-limiting description of two embodiments of a device for adjusting the seat base length of a motor vehicle seat according to the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Reference will be made to the appended drawings, among which: 
         FIG. 1  is a perspective view of the seating frame provided with the manually-operated adjustment device, 
         FIG. 2  is a view of the device at larger scale, in a forward position of the seat nose, the carriage being shown by its contour only, to better show the guiding and locking system, 
         FIG. 3  is a similar view, the central portion of the carriage being cut away, when the carriage is in a backward position, with a detail of the lock sliding drive, 
         FIG. 4  is a half cross-section view along line IV-IV of  FIG. 3 , 
         FIG. 5  is a bottom perspective view of the pre-assembled device, 
         FIG. 6  is a perspective view of the adjustment device, in the case of the motor-driven version, 
         FIG. 7  is a transverse cross-section view of the device in the embodiment comprising pins attached to the plate, 
         FIGS. 8 and 9  are bottom perspective views of this embodiment, in the back and front end sliding positions, respectively. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows seating frame  1 , typically made of dished plate, having two edges  11  intended to support the lateral stuffing of the seat cushion, not shown, and a crosspiece  12  connecting these edges, and supporting the central portion of the cushion. Plate  13  supporting the seat nose is schematically shown in this view by dotted lines, and fastened to adjustment device  10 , which is itself fastened to crosspiece  12 . 
     The adjustment device, which can be better seen in  FIGS. 2 and 3 , comprises:
         a guide plate  2     a carriage  3     a lock  4         

     Guide plate  2  comprises lugs  21  for attaching it to crosspiece  12 . 
     Carriage  3  is guided in translation on guide plate  2  by a guide rail located in a middle area, formed by a rib  37  formed on the bottom surface of the carriage and sliding in a groove  27  made in guide plate  2 . Guide plate  2  also comprises two parallel grooves  22  in which lateral edges  31  of carriage  3  are slidably inserted, with a clearance in the horizontal plane, visible in  FIG. 4 . Grooves  22  are only used to maintain the carriage in the vertical direction against guide plate  2 . 
     Guide plate  2  also comprises, in its central portion between grooves  22  immediately next to groove  27 , a rack  23  extending along the sliding direction. 
     Guide plate  2  also comprises two housings  24  of partially cylindrical cross-section, extending parallel to the sliding direction and intended to receive compression springs  25  used to push back the carriage towards the front of the seat. 
     Springs  25  are held in their housings  24  between the guide plate and the carriage, bearing against stops respectively attached to the carriage and to the guide plate. 
     Carriage  3  comprises on its upper surface housings  32  for the fastening of plate  13 , for example, by insertion and clenching in the housings of lugs provided on plate  13 . 
     A toothed wheel  33  is clenched on a pivot  34  attached to the carriage, extending downwards perpendicularly to the general plane of the carriage. Toothed wheel  33  comprises first teeth  331  which mesh with rack  23  when the carriage slides in the guide rail and second asymmetrical teeth  332 , such as in a ratchet wheel. 
     Lock  4  is slidably assembled on carriage  3 , and guided to slide along the sliding direction of the carriage by a guide rail element  35  formed on the lower surface of the carriage and substantially aligned with the rotation axis of toothed wheel  33 . It comprises at its rear end a locking notch  41  having a shape adapted to engage with the second teeth  332  of toothed wheel  33 . 
     A control handle  42  is pivotally assembled to the front of carriage  3  along a horizontal axis  43  supported at the end of two arms  38  extending from the carriage. The handle further comprises a stud  44  which engages into an oblong bore  45  formed at the front end of lock  4 , so that an upward rotation of the handle around its axis  43  causes a longitudinal forward motion of lock  4 , to unlock toothed wheel  33 . A spring  46  placed on axis  43  pulls back handle  42  and thus pulls lock  4  back to its locked position, notch  41  being in mesh with teeth  332  of toothed wheel  33 . 
     The device may be pre-assembled by engaging carriage  3  provided with toothed wheel  33  and with lock  4  into grooves  22  and  27  of guide plate  2  after having placed return springs  25  inside of it, a stop, not shown, preventing the carriage from coming out of the guide rail. For the assembly on the seat base, preassembled device  10  just has to be attached by screwing or riveting of lugs  21  on frame crosspiece  12 . When the seat base is being upholstered, plate  13  of the pre-upholstered seat nose is positioned on the carriage and clenched into housings  32  of carriage  3  provided for this purpose, this final assembly operation thus requiring no tool. 
     The use of the device will be easily deduced from the foregoing. After unlocking by upward pulling of handle  42 , the seat nose may be pushed backwards, against the thrust of springs  25 . As soon as the handle is released, end notch  41  of lock  4  engages with toothed wheel  33 , which blocks its rotation and thus maintains the seat nose in position. It should be noted that, to decrease the length of the seat base, due to the ratchet effect between lock  4  and teeth  332  of the toothed wheel, it may also be sufficient to push the seat nose backwards without necessarily actuating the unlocking handle. To increase the seat base length, it is necessary to unlock the device before letting it slide forward under the effect of the return springs all the way to the desired position, where it will be blocked as soon as the unlocking control handle is released. 
     In the version shown in  FIG. 5 , the sliding of the carriage is controlled by an electric gear motor  5 , attached under crosspiece  12 , and driving toothed wheel  33  in rotation by means of a flexible connection  51  connecting the motor to the wheel and running through a port  26  formed in guide plate  2  and also, correspondingly, in the frame crosspiece, to enable the flexible drive to follow the motion of the carriage, as schematically shown in  FIG. 5 . Guide plate  2  and carriage  4  are similar to the previously-described version. The holding of the carriage in position may result from the sole stopping of gear motor  5 , or may be achieved by a lock as in the previously-described manual version, the motor control being then coupled with the lock unlocking control. 
     In the embodiment illustrated in  FIGS. 7 to 9 , two pins  6  are attached on plate  13 , for example by welding, and extend downwards from said plate. The pins comprise a lower portion forming a head  61  which is engaged under a rib  71  forming a branch of a guide rail  7  of T-shaped cross-section, the other branch  72  of this T determining, under it, one of parallel grooves  22  in which lateral edges  31  of carriage  3  are slidably inserted. 
     T-shaped guide rails  7  form the lateral edges of guide plate  2  and are attached to frame crosspiece  12  by four bolts  8  having their head  81  embedded in the transverse bar of the T, as shown in  FIG. 7 . 
     Pins  6  are located towards the back of plate  13 , to be immediately next to bolts  8  in the sliding end positions of the carriage, as can be seen in  FIGS. 8 and 9 . In particular, when the seat nose is moved forward, as illustrated in  FIG. 9 , pins  6  are close to the forwardmost bolts  8 , so that heads  61  of the pins are engaged under a portion of rib  71  close to head  81  of said bolts. It can thus be seen that forces F 1  tending to lift the back of the plate, under the effect of the tilting torque appearing when the seat nose is moved forward, are almost directly transmitted via head  61  of the pin to head  81  of the bolt, and from there to frame crosspiece  12 , while avoiding to create a significant load on edges  31  of the carriage in grooves  22  of the guide plate. 
     As compared with above-mentioned document DE-A-102004030363, the described embodiments provide a specific positioning of the guide rail and of the rack to avoid buttressing risks. In this document, the guide rail is not positioned in a middle portion and the rack is not positioned close to the guide rail. Further, there is no lock acting on the toothed wheel since the motor ensures the rotation of the pinion. 
     The present invention is not limited to the above-described embodiment, which has been described as an example only. 
     In particular, springs  25  for pulling back the carriage to the forward position may be replaced with a spiral spring  28  assembled between toothed wheel  33  and pivot  34 , as can be seen in  FIG. 5 , said spiral spring exerting on the toothed wheel a torque tending to rotate the wheel in a direction causing a forward displacement of the carriage by meshing with rack  23 . 
     The lock may also directly act upon the teeth of the toothed wheel which meshes with the rack. 
     Of course, the present invention is likely to have various alterations, modifications, and improvements which will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. The present invention is limited only as defined in the following claims and the equivalents thereto.