FR2973748A1 - Seat for e.g. car such as two-door car, has elastic restoring connection including two ends, and anchoring unit movable relative to fixed rail so as to vary position of one of ends of elastic restoring connection relative to fixed rail - Google Patents

Abstract

The seat has a fixed rail (10) equipped with a fixing unit (12) for fixing to a frame of a car. A movable rail (20) is slidingly mounted on the fixed rail between a rear extreme position and a front extreme position. An elastic restoring connection includes an end, which is fixed on the movable rail or on one of seat elements such as seat base and backrest, and another end that is fixed at an anchoring unit (60) mounted on the fixed rail. The anchoring unit is movable relative to the fixed rail so as to vary a position of the latter end of the connection relative to the fixed rail.

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates generally to the automotive field. It relates more particularly to a motor vehicle seat, comprising: - a fixed rail equipped with fastening means to a motor vehicle frame, - a movable rail which is slidably mounted on the fixed rail between an extreme rear position and a front extreme position - seat elements, including at least one seat and backrest, which are supported by said movable rail, and - a resilient return link of said movable rail in extreme rear position, comprising a first end which is fixed on said movable rail or on one of said seat members, and a second end which is attached to an anchoring means mounted on said fixed rail. It also relates to a motor vehicle equipped with such a seat. BACKGROUND ART In such a seat as mentioned above, the ability of the movable rail to slide on the fixed rail makes it possible to adjust the position of the seat and the backrest towards the front or towards the rear of the motor vehicle. In a vehicle with two doors and two rows of seats (in the first row of seats) or in a vehicle with four doors and three rows of seats (in the second row of seats), the movement of this seat towards the front allows in particular to release a passage of access to the rear seats. The elastic link allows for him to recall the movable rail backwards. The disadvantage of such an elastic link is that the effort required to push the movable rail forward increases proportionally with the moving distance of the movable rail on the fixed rail. Therefore, when a long fixed rail is provided to provide better access to the rear seats, there comes a time when the effort that the user has to exert to push the movable rail forward is too important to be ergonomic.

OBJECT OF THE INVENTION The present invention then proposes a seat in which there is provided means for disengaging the elastic link, so as to reduce its tension if necessary.

More particularly, it is proposed according to the invention a seat as defined in the introduction, wherein said anchoring means is movably mounted relative to the fixed rail so as to vary the position of the second end of the return link. elastic with respect to the fixed rail. Thanks to the invention, the movable stowage of the second end of the elastic link reduces on demand the tension of the elastic link. In this way, it is possible to provide that the movable rail has a large clearance on the fixed rail, without this travel requires the user to exert too much effort on the seat to access the rear seats.

Other advantageous and non-limiting characteristics of the seat according to the invention are the following: said anchoring means is rotatably mounted with respect to said fixed rail; said movable rail comprises an abutment element which is adapted, on the one hand, to retain said anchoring means in a locked position when said movable rail is situated between its rearmost position and an intermediate position which is distinct from the rearmost and frontmost positions. and, on the other hand, to release said anchoring means when said movable rail is located between the intermediate position and the extreme forward position; said stop element comprises a plate which is, on the one hand, arranged to slide on a retaining tab in order to retain said anchoring means in a locked position when said movable rail is situated between its rearmost position and its intermediate position and which, on the other hand, delimits a release passage to release said anchoring means when said movable rail is located between the intermediate position and the forward end position; - There is provided a return spring of said anchoring means in the released position; the fixed rail comprises a notched rear section and a notched front section; - The movable rail is equipped with a locking member movably mounted between a locked position in which it cooperates with the notches of the rear section so as to lock the movable rail relative to the fixed rail, and an unlocked position in which it releases the sliding of the movable rail on the fixed rail; - The junction between said front and rear sections of the fixed rail is positioned such that, when said locking member is up to this junction, the movable rail is located intermediate to the fixed rail; - The movable rail is equipped with a clipping member which is movable between an abutment position in which it forms a stop of the movable rail in the intermediate position and a release position in which it leaves the movable rail free to slide between the positions. extreme front and back; - The position of said clipping member is controlled in such a way that the clipping member is in the stop position when the backrest is in the upright position and in the release position when the backrest is in the tilted position; said clipping member comprises a return face which is adapted to come into contact with said anchoring means in favor of the sliding of the movable rail from its foremost position towards its intermediate position, in order to return this anchoring means to a locked position ; - The backrest is adapted to tilt relative to the fixed rail between three stable positions including a straight position in which the backrest is slightly inclined backwards, an inclined position in which the backrest is slightly inclined forward, and a position folded in which the backrest is brought against the seat; when the backrest is in an inclined position and the movable rail is in the extreme forward position, the elastic return link is not stretched; and the movable rail has an amplitude of displacement between the extreme front and rear positions which is greater than 200 millimeters.

The invention also proposes a motor vehicle comprising a chassis and a seat as mentioned above, whose fixed rail is fixed to the chassis. DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT The following description, with reference to the accompanying drawings, given by way of non-limiting example, will make it clear what the invention consists of and how it can be achieved. In the accompanying drawings: - Figures 1 to 3 are side views of a seat according to the invention, respectively shown in a straight, inclined and folded position; - Figure 4 is an exploded schematic view of the fixed rail, the movable rail and the anchoring means of the seat of Figure 1; and FIG. 5 is a diagrammatic cross-sectional view of the fixed rail, the movable rail and the means for anchoring the seat of FIG. 1. FIG. 1 diagrammatically shows a seat 1 for a motor vehicle. The motor vehicle here considered will be the four-door type and three rows of seats. The seat shown in Figure 1 will then be one of the seats of the second row.

In the description, the terms front and rear will be defined with respect to this motor vehicle, the front designating the side of the seat facing the hood of the vehicle and the rear designating the side facing the trunk. The longitudinal and transverse terms will be used to define the direction of the axes, a longitudinal axis being a horizontal axis (when the vehicle is on a horizontal ground) directed according to the direction of circulation of the vehicle and a transverse axis being a horizontal axis perpendicular to the longitudinal axes. As represented in FIG. 1, this seat 1 comprises: two identical fixed rails 10, equipped with means for attaching to the chassis of the motor vehicle, a movable coupling 20, 30, 40 slidably mounted on the fixed rails 10, and comprises in particular a seat 30 and a backrest 40, and - an elastic return link 50 designed to automatically return the movable linkage to the rear.

The mobile hitch comprises in particular two identical movable rails 20 which are respectively slidably mounted on the two fixed rails 10, between an extreme rear position and an extreme forward position, and which support the seat 30 and the backrest 40. In the following of the description, we will focus on one of these fixed rails 10 and the corresponding movable rail 20. To automatically return the movable rail 20 to the extreme rear position, the elastic return link 50 has a first end 51 which is fixed on a member of the movable coupling and a second end 52 which is fixed to an anchoring means 60 mounted on the fixed rail 10. According to a particularly advantageous characteristic of the invention, this anchoring means 60 is disengageable to allow to change the position of the second end 52 of the elastic return link 50. The anchoring means 60 is more precisely mounted movable relative to the fixed rail 10 between two extreme positions, called "locked position" and "relaxed position", between which the length of the path taken by the elastic return link 50 varies. Thanks to the mobility of this anchoring means 60, it is therefore possible to vary the tension of the elastic link 50.

In the embodiment of the invention shown in the figures, the fixed rail 10 is formed by a profiled beam section generally U-shaped (see Figure 4). It thus has a bottom 13 to bring against the chassis of the vehicle, along a longitudinal axis A1, and two flanks 14.

This fixed rail 10 is formed of two sections 10A, 10B located in the extension of one another. One of these two sections, the rear section 10A, is notched while the other section, the front section 10B, is devoid of detents. With its notches, the rear leg 10A is designed to hold the movable hitch in a fixed position on the fixed rail 10 when the vehicle is in motion. The front section 10B makes it possible to increase the travel of the mobile hitch forward. This section before 10B thus makes it possible to momentarily advance the mobile coupling so as to release a space at the rear of the seat 1, in particular to facilitate access to the rear seats of the motor vehicle. The bottom 13 of each section 10A; 10B here two openings 12 for the passage of two fixing screws (not shown) of the fixed rail 10 on the vehicle frame.

The rear section 10A has a length of 150 millimeters, while the front section 10B has a length of 200 millimeters. The movable rail 20 is also formed by a profiled beam, of generally U-shaped section reversed.

It thus has a front wall 24 on which is fixed the movable coupling, and two sidewalls 25. This movable rail 20 has a width greater than that of the fixed rail 10, so that its front wall 24 is applied against the slices of flanks 14 of the fixed rail 10 and that its flanks 25 slide on either side of the flanks 14 of the fixed rail 10. These fixed rails 10 and movable 20 comprise complementary interlocking means 15, 26, which are designed to block all the degrees of mobility of the movable rail 20 relative to the fixed rail 10, except for the sliding mobility of the movable rail 20 along the fixed rail 10 along the longitudinal axis A1.

These interlocking means cooperate by form cooperation. As shown in FIG. 5, these interlocking means comprise: on the fixed rail 10, two flanges 15 which extend at right angles to the slices of the flanks 14 of this fixed rail 10, in the direction of one of the and, - on the movable rail 20, two longitudinal ribs 26 which project from the front wall 24 of the movable rail 20, parallel to the longitudinal axis A1, to form two rails in which the two can slide. flanges 15 of the fixed rail 10. There is further provided a means for blocking the sliding of the movable rail 20 on the fixed rail 10. This locking means comprises a notching member (not visible in the figures) which is intended to cooperate with the notches of the rear section 10A of the fixed rail 10, and an operating lever 29 which is rotatably mounted on the movable rail 20 about a transverse axis A9, and which is accessible to the user to lock or unlock the organ of notching. This operating lever 29 thus makes it possible to block the sliding of the movable rail 20 in a plurality of positions on the rear section 10A of the fixed rail 10. On the other hand, it does not make it possible to block the sliding of the movable rail 20 when its detent member is located at the height of the front section 10B of the fixed rail .10, since the latter is devoid of detents. As shown in Figure 1, for fixing the seat 30 and the backrest 40 to the movable rail 20, there is provided a support plate 16 which is screwed on the front wall of the movable rail 20, so as to extend in parallel to the flanks 25 of this movable rail 20. As shown in Figure 1, the backrest 40 is rotatably mounted on the support plate 16. It is for that equipped with a rear rod 17, a first end is rotatably mounted on the backrest 40 about a transverse axis A2 and a second end of which is rotatably mounted on the support plate 16 about a transverse axis A3 located below the transverse axis A2 (when the seat 1 is in position d 'use). The seat 30 is rotatably mounted at the rear, on the backrest 40, and at the front, on the movable rail 20 by means of a front link 18. This seat 30 is more precisely rotatably mounted on the backrest 40 about a transverse axis A4 located above the transverse axis A2. The forward link 18 has a first end rotatably mounted on the seat 30 about a transverse axis A5, and a second end rotatably mounted on a movable rail 20 about a transverse axis A6 located below the transverse axis A5. Thus, the backrest 40 is free to swing relative to the movable rail 20 between three stable positions, including: a substantially vertical upright position (FIG. 1), in which the seat 1 can accommodate a passenger, and a substantially horizontal folded position ( Figure 3), wherein the seat 1 frees a loading space in the motor vehicle, and - an inclined position (Figure 2), intermediate between the right and folded positions, wherein the seat 1 allows access to the rear seats of the vehicle. Two modes of tilting the backrest 40 are then provided. In a first tilting mode enabling the backrest 40 to move from its straight position to its folded position, the rear connecting rod 17 is locked in rotation on the support plate 16, so that the back 40 pivots around the only transverse axis A2. In this tilting mode, the front link 18 tilts forward, which allows the seat 30 to sag downward. This kinematics thus makes it possible to benefit from an increased loading space in the vehicle. In a second tilting mode allowing the backrest 40 to move from its upright position to its inclined position, the rear link 17 is locked in rotation on the backrest 40, so that the backrest 40 pivots about the only transverse axis A3. In this tilting mode, the rear link 7 allows the bottom of the back 40 to advance, which facilitates access to the rear seats. As shown in Figure 1, the first end 51 of the elastic return link 50 is fixed in a clamp 41 provided at the low end of the backrest 40, halfway up the transverse axes A2 and A3. The elastic return link 50 is then passed through a return zone 54 (for example a pulley) situated at the front end of the seat 30. Finally, the second end 52 is fixed in a clamp 70 provided on the means 60. The elastic return link 50 is here designed to remain relaxed when the back 40 is in the upright position, regardless of the position of the movable rail 20 on the fixed rail 10. It is also designed to remain relaxed when the The backrest 40 is in an inclined position, regardless of the position of the movable rail 20 on the fixed rail 10. In this way, it does not exert a return force when a passenger accesses the rear seats of the vehicle. It is finally designed to stretch when the backrest 40 is in the tilted position, regardless of the position of the movable rail 20 on the fixed rail 10. This link 25 allows, before the folder 40 is returned to the upright position, to force the movable rail 20 back to prevent the top of the backrest 40 abuts against the front seat of the vehicle. In this case, the kinematics of the seat 1 is such that the elastic return link 50 does not stretch more when the backrest 40 is in an inclined position than 30 when the folder 40 is in the upright position. This kinematics could allow itself to leave the link relaxed when the folder 40 is upright or inclined, regardless of the position of the movable rail 20 on the fixed rail 10, if the fixed rail 10 had a reduced length.

However, here, the fixed rail 10 has a great length, allowing a large clearance of the movable rail 20 on the fixed rail 10. As a result, the kinematics of the seat 1 alone does not allow the link relaxed when the record 40 is in the upright or inclined position and that the movable rail 20 is returned to its extreme forward position. More specifically, given the length of the fixed rail, when the backrest 40 is upright and inclined, the elastic return link 50 remains relaxed as the movable rail 20 slides on the rear section 10A of the fixed rail 10, then it starts to be stretched when the movable rail 20 arrives on the front section 10B of the fixed rail 10 (that is to say as soon as the detent member exceeds the junction between the sections 10A, 10B). The mobility of the anchoring means 60 is then provided to prevent that, when the movable rail 20 slides on the front section 10B of the fixed rail 10, the link is stretched when the folder 40 is in the upright or inclined position.

The mobility of the anchoring means 60 is also provided to prevent the elastic return link 50 from being stretched excessively when the backrest 40 is in the folded position and the movable rail 20 slides on the front section 10B of the fixed rail 10, benefit of the ergonomics of the use of the seat 1. As shown in Figures 4 and 5, the anchoring means 60 comprises for this purpose an elongate plate 80, a first end is rotatably mounted on a lug 11 fixed to the fixed rail 10 and a second end carries the clamp 70 in which is blocked the second end 52 of the elastic return link 50. The tab 11 is here formed by a metal plate folded L. It has a first branch 11A which is fixed under the fixed rail 10, for example by screwing, welding or riveting, and which projects on one side of this fixed rail 10. It has a second branch 11B, bent with respect to the first, which extends parallel to the flanks 14 of the fixed rail 10, at a distance from the latter, and which is pierced with a threaded orifice 11C.

The first end of the wafer 80 is pierced in correspondence of an orifice 81 through which is engaged a screw 92 screwed into the tapped hole 11C of the lug 11. Thus, the wafer 80 is left free to pivot around it. a transverse axis A10, between its locked position and its relaxed position. Of course, alternatively, it could be provided that the orifice 11C is smooth and not tapped and that the screw 92 is replaced by a stepped and riveted axis. Anyway, the locked position is then defined as the position of the wafer 80 when it extends horizontally. The relaxed position is defined as the position of the wafer 80 when it extends along an inclined axis, which passes through the transverse axis Al0 and the axis of the pulley 54. A stop (not visible on the figures) is provided to limit the movement of this plate 80 forward. The anchoring means 60 is here designed to remain inactive (that is to say to immobilize the wafer 80 in "locked position") when the movable rail 20 slides on the rear section 10A of the fixed rail 10, and for activate (that is to say to release the wafer 80 so that it can pivot to its "relaxed position") when the movable rail 20 slides on the front section 10B of the fixed rail 10. The wafer 80 carries for this, on its second end, a retaining tab 82 which is retained under a flange 22 of the movable rail 20 when the latter slides on the rear section 10A of the fixed rail 10, and which is released when the movable rail 20 slides on the front portion 10B of the fixed rail 10. The retaining tab 82 extends more precisely projecting from the face of the wafer which is located opposite the movable rail 20. It is oriented so that it extends horizontally when the wafer 80 is in the locked position. The rim 22 extends in turn protruding from the outer face of one of the flanks 25 of the movable rail 20, the one located opposite the wafer 80. It is located horizontally.

This flange 22 extends over only a portion of the length of the movable rail 20, so that its rear end edge 23 is located at the height of the retaining tab 82 when the movable rail 20 is at the junction between the two sections 10A, 10B of the fixed rail 10. Thus, once the movable rail 20 has passed this junction, the flange 22 releases the wafer 80, which can then pivot to its relaxed position. When the movable rail 20 is brought back, it is necessary that the plate 80 returns to the locked position to allow its retaining tab 82 to slide under the flange 22 of the movable rail 20. It is then provided a spring of torsion which, engaged on the screw 92, remembers the wafer 80 in the locked position. Advantageously, the seat 1 further comprises a stop 83 and a clipping member 28 which cooperate together to allow the user to perceive the passage of the movable rail 20 from the rear section 10A to the front section 10B of the fixed rail 10. Here , this abutment 83 and this clipping member 28 are further adapted to cooperate together to limit the displacement of the movable rail 20 on the only rear portion 10A of the fixed rail 10 when the backrest 40 is in the upright position, and to release the sliding of the movable rail 20 on the entire fixed rail 10 when the backrest 40 is in the tilted or inclined position. As shown in FIG. 4, the abutment 83 comes into formation with the wafer 80 and is located at a reduced distance from the retaining tab 82. It could of course also be fixed to the wafer 80, by welding or by any other means. . This stop 83 is formed by a V-folded plate, one of whose slices is fixed to the wafer 80, and whose apex points upwards when the wafer 80 is retained in the locked position. As shown in Figures 4 and 5, the clipping member comprises a blade 28 curved in a circular arc, one end is rotatably mounted on the movable rail 20 about a transverse axis A11, and the Another is rounded and rests on the rim 22. This clipping member also comprises a return spring (not shown in the figures) of the rounded end of the blade 28 bearing against the movable rail 20. When the movable rail 20 slides forward, the rounded end of the blade 28 is arranged to come into contact with the clip 23 just before the retaining tab 82 is released by the flange 22 of the movable rail 20. The user thus feels the stop 83 ,. which signals the attempt of passage of the movable rail 20 from the rear section 10A to the front section 10B of the fixed rail 10. At this stage, if the back 40 is in the upright or folded position, the free end of the blade 28 bears against the stop 83, which prevents the movable rail 20 from sliding towards the front section 10B of the fixed rail 10. On the other hand, when the backrest 40 is in an inclined position (FIG. 2), a projection of the connecting rod 17 comes press against a tab 28B provided correspondingly on the blade 28. In this way, the blade 28 is slightly raised and can slide on one of the sides of the stop 83, which allows the movable rail 20 to slide towards the front section 10B of the fixed rail 10. With its kinematics, the seat 1 operates in the following manner. Initially, the movable rail 20 is in extreme rear position and the backrest 40 is in the upright position, so that the seat 1 can accommodate a passenger. When a passenger wishes to access the rear seats, it tilts the backrest 40 to its inclined position, which pushes the movable rail 20 to its extreme forward position. The tilting of the backrest 40 makes it possible to release the pivoting of the blade 28. During the sliding of the movable rail 20 on the rear section 10A of the fixed rail 10, the flange 22 slides over the retaining tab 82 of the wafer 80, which keeps it in a locked position. The elastic return link 50 remains relaxed however (see Figure 2).

Then, the blade 28 slides against one of the sides of the abutment 83, which allows the user to perceive the passage of the movable rail 20 on the front section 10B of the fixed rail 10. Finally, the flange 22 of the rail mobile 20 releases the retaining tab 82 of the wafer 80. Then, during the sliding of the movable rail 20 on the front section 10B of the fixed rail 10, the elastic return link 50 is stretched slightly, which causes the wafer to pivot. 80 to his relaxed position. The mobility of this wafer 80 thus makes it possible to artificially lengthen the elastic return link 50, so that the latter does not return the movable rail 20 towards the rear.

Once arrived in extreme forward position, the flexible elastic link 50 is further relaxed, so that the movable rail 20 naturally remains in extreme forward position, which facilitates the access of the passenger to the rear seats. To return the seat to the initial position, the user rotates the backrest 40 towards the rear, which causes the sliding of the movable rail 20 towards the rear.

During this sliding, the blade 28 slides by its lower portion 28A on the retaining tab 82 and on the stop 83 of the wafer 80, which helps the torsion spring to bring the wafer 80 in the locked position. Then, the rim 22 engages above this retaining tab 82, which allows the movable rail 20 to return to its rearmost position.

During this sliding, the blade 28 slides by its lower portion 28A on the retaining tab 82 and on the stop 83 of the wafer 80, which helps the torsion spring to bring the wafer 80 in the locked position. Then, the rim 22 engages above this retaining tab 82, which allows the movable rail 20 to return to its rearmost position. When a user wishes to release a storage space above the seat 1, it tilts the back 40 to its folded position and pushes the movable rail 20. The tilting of the backrest 40 does not release the pivoting of the blade 28 .

During sliding of the movable rail 20 on the rear section 10A of the fixed rail 10, the flange 22 covers the retaining tab 82 of the wafer 80, which holds it in the locked position. The elastic return link 50 then becomes progressively tighter (see FIG. 3). Thanks to the kinematics of the seat, the flexible elastic link 50 is then tightened, so that the movable rail 20 is automatically returned to its rearmost position, which prevents the top of the backrest 40 from abutting against the front seat of the vehicle when it pivots to its upright position. To return the seat to the initial position, the user rotates the backrest 40 backwards.

The present invention is not limited to the embodiment described and shown, but the art can apply any variant within his mind. In particular, it can be provided that the wafer (80) is rotatably mounted about an axis not transverse, but vertical.

Alternatively, it may also be provided that the wafer is movably mounted in translation along a longitudinal axis. In this variant, the translation of the wafer will be blocked as long as the movable rail will slide on the rear section of the fixed rail, and will be released when the movable rail will slide on the front section of the fixed rail.

Alternatively, it can be provided that the anchoring means is devoid of torsion spring, in which case only the blade (28) will bring the wafer in the locked position.

Claims (10)

REVENDICATIONS1. Seat (1) for a motor vehicle, comprising: - a fixed rail (10) equipped with fastening means (12) to a frame (100) of a motor vehicle, - a movable rail (20) which is slidably mounted on the fixed rail (10) between an extreme rear position and an extreme forward position, - seat elements, including at least one seat (30) and a backrest (40) ', which are supported by said movable rail (20), and - a elastic return link (50) of said movable rail (20) at the rear end position, comprising a first end (51) which is fixed on said movable rail (20) or on one of said seat members (30, 40), and a second end (52) which is attached to an anchoring means (60) mounted on said fixed rail (10), characterized in that said anchoring means (60) is movably mounted relative to said fixed rail (10). ) so as to vary the position of the second end (52) of the elastic return link (50) relative to the fixed rail (10). 2. Seat (1) according to the preceding claim, wherein said anchoring means (60) is rotatably mounted relative to said fixed rail (10). Seat (1) according to one of the preceding claims, wherein said movable rail (20) comprises an abutment element (22) which is adapted, on the one hand, to retain said anchoring means (60) in a locked position when said movable rail (20) is located between its rearmost position and an intermediate position distinct from the rear and front extreme positions, and secondly to release said anchoring means (60) when said movable rail ( 20) is located between the intermediate position and the extreme forward position. 4. Seat (1) according to the preceding claim, wherein said stop element comprises a plate (22) which is, on the one hand, arranged to slide on a retaining tab (82) to retain said anchoring means (60) in the locked position when said movable rail (20) is located between its rearmost position and its intermediate position, and which, on the other hand, delimits a release passage (23) to release said anchoring means ( 60) when said movable rail (20) is located between the intermediate position and the extreme forward position. 5. Seat (1) according to one of the two preceding claims, wherein there is provided a return spring of said anchoring means (60) in the locked position. 6. Seat (1) according to one of the three preceding claims, wherein - the fixed rail (10) comprises a notched rear section (10A) and a notched front section (10B), and - the movable rail (20). is equipped with a locking member (29) movably mounted between a locked position in which it cooperates with the notches of the rear section (10A) so as to lock the movable rail (20) with respect to the fixed rail (10), and an unlocked position in which it releases the sliding of the movable rail (20) on the fixed rail (10). 7. Seat (1) according to the preceding claim, wherein the junction between said front sections (10B) and rear (10A) of the fixed rail (10) is positioned so that when said locking member (29) is at height of this junction, the movable rail (20) is' located intermediate to the fixed rail (10). 8. Seat (1) according to one of the two preceding claims, wherein the movable rail (20) is equipped with a clipping member (28) which is movable between an abutment position in which it forms a stop of the rail movable (20) in an intermediate position and a release position in which it leaves the movable rail (20) free to slide between the extreme front and rear positions. 9. Seat (1) according to the preceding claim, wherein the position of said clipping member (28) is controlled in such a way that the clipping member (28) is in abutment position when the backrest (40) is in position. right and in the release position when the backrest (40) is in the tilted position. 10. Seat (1) according to one of the two preceding claims, wherein said clipping member (28) comprises a return face (28A) which is adapted to come into contact with said anchoring means (60) in favor sliding of the movable rail (20) from its extreme forward position to its intermediate position, to return the anchoring means (60) to the locked position.