FIELD OF THE INVENTION

The present invention relates to adjustable seats, and more particularly to adjustable seats having at least first and second movable parts, a worm screw and a rotating mechanism adapted to rotate the worm screw, said worm screw having a first thread which drives said first movable part.

BACKGROUND OF THE INVENTION

An example of such adjustable seat is disclosed in particular in document US-A-2008/157578, wherein said first movable part is a movable front frame supporting the foremost part of a seat and the second movable part is the trim supported by said movable front frame. The trim is rolled around the front end of the movable front frame and the lower free end of said trim undergoes a linear displacement which is substantially twice the displacement of the movable front frame, both movements being synchronized.

In this prior art document, the displacement of the trim around the front end of the movable front frame is merely obtained by the fact that the lower end of the trim cover is pulled rearward by elastic means. But such elastic means do not enable to control precisely the movement of the trim, so that the foam padding belonging to the trim may be subject to local deformations due in particular to friction between the movable front frame and the foam padding.

SUMMARY One object of the present invention is to enable a better control of the movement of the second movable part, in a seat of the kind defined above.

To this end, according to the invention, a seat of the kind in question is characterized in that the worm screw further has a second thread driving the second movable part in synchronism with the first movable part.

Thus, a precise control of the movement of the second movable part is obtained, to ensure excellent synchronism of the movements of the first and second movable parts. As used herein, the word "synchronism" does not mean that the first and second movable parts move at the same speed or in the same direction, but only that they move simultaneously in a coordinated way.

Besides, one should note that the first and second movable parts according to the invention may be various parts of a seat and are therefore not limited to a movable front frame and a trim borne by said movable front frame.

In various embodiments of the invention, one may further have recourse to one and/or other of the following features: the second thread is external and is screwed in a nut which is immobilized in rotation but free to move axially along the worm screw, the worm screw having an axial bore and the first thread being internal to said bore and being screwed on a stem which is immobilized in rotation but free in axial movement; the first and second threads have different pitches; the seat includes a seat part having a main portion and a front portion which is movable at least forward and backward relative to the main portion in a longitudinal direction to adjust a length of the seat part, said front portion of the seat part including a movable front frame which bears a trim, the movable front frame and the trim constituting respectively said first and second movable parts of the seat, said trim being fixed to the main portion of the seat part and being rolled around a front end of said movable front frame, said trim extending from said front end up to a free end of said trim which is driven by the second thread of the worm screw, said first and second threads having respectively first and second pitches, the second pitch being substantially twice the first pitch, and the first and second threads being such that the nut and the threaded stem are moved in the same direction when the wonn screw is rotated; - the worm screw is connected to the main portion of the seat part, the second thread being external and being screwed in a nut which is connected to the free end of the trim, said nut being immobilized in rotation but free to move axially along the worm screw, the worm screw having an axial bore and the second thread being internal to said bore and being screwed on a stem which is immobilized in rotation but free in axial movement, said stem being attached to the movable front frame; the nut bears a transverse rod which is attached to the free end of the trim; - the trim includes a foam padding and a cover covering the foam padding, the nut being connected to the cover at the free end of said trim; the movable front frame is further connected to the main portion of the seat part by two parallel slides extending in the longitudinal direction; the rotating mechanism includes an electric motor which is fixed to the main portion of the seat part.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention appear from the following description of one embodiment thereof, given by way of non limiting example in regard of the drawings. In the drawings: figure 1 is a lateral view of an adjustable seat according to one embodiment of the invention, figure 2 shows a vertical section of the front portion of the seat of figure 1 , in the retracted position, figures 3 and 4 are perspective views, viewed respectively from above and from the underside, showing the armature of the seat part of the seat of figure 1 , in the retracted position, figures 5 and 6 are perspective views, viewed respectively from above and from the underside, showing a movable front frame belonging to the armature of figures 3-4 and of the adjusting mechanism for moving said movable front frame, in the retracted position, and figures 7-10 show respectively views similar to figures 2-4 and 6, in the extended position of the front portion of the seat part.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the drawings, the same reference numerals denote identical or similar elements.

Figure 1 shows a vehicle seat 1, e.g. a front seat for an automobile, having a backrest 2 borne a seat part 3. The seat is mounted on the vehicle floor 5, e.g. through slides 4 which enable to adjust the position of the seat 1 in a horizontal direction X.

The seat part 3 has a main portion 6 extending in the longitudinal direction X between the backrest 2 and a front portion 7 of the seat part. The front portion 7 is movable forward and backward relative to the main portion in a longitudinal direction L which is parallel or nearly parallel to direction X, in order to adjust the length of the seat part 3.

As shown in figure 2, the seat part 3 has a rigid frame 8 which is covered by a trim 9. The frame 8 may be mostly composed of metallic parts. It comprises a main frame 10 belonging to the main portion of the seat part, and a movable front frame 11 which is slidably mounted on the main frame in the longitudinal direction L. The trim 9 may comprise for instance a foam padding 12 covered by an outer trim cover 13, made out of textile, leather or other supple material. The foam padding 12 may be adhered or not to the trim cover 13. The trim 9 of the seat part extends on both the main portion 6 and the front portion 7 of the seat part, and is fixed to the main portion 6. Said trim is supported by the movable front frame 11 without being fixed thereto, so that said trim may slide on said movable front frame 11. The trim 9 is rolled around the foremost edge 14 of the movable front frame and has a lower portion 15 which extends under said movable front frame, rearward in the longitudinal direction X, up to a free end 16. As shown in figures 2-4, the movable front frame may include a substantially horizontal upper support plate 17 which supports the trim 9 in the front portion 7 of the seat part, and which covers the front end 1 Oa of the main frame 10. This support plate 17 is extended downward by the foremost end 14 of the movable front frame, which may have a rounded shape in vertical cross section, to facilitate sliding of the trim 9 around said foremost end 14 when the front portion 7 of the seat part is moved forward or backward in the direction L, as will be explained later.

Further, the lower end of the foremost end 14 may be extended rearward by a horizontal lower gliding plate 18 (see figure 2), for example made out of plasties. The lower gliding plate 18, also facilitates sliding of the trim 9 around the foremost end 14 of the movable front frame 1 1.

As shown in figures 2, and 4-6, the movable from frame 1 1 may be moved forward and backward by a driving mechanism 19 including a woiτn screw 20 which extends in the longitudinal direction L. The worm screw 20 is rotatably mounted on a support bracket 21 which is fixed (e.g. welded) to the underside of the main frame 10. This support bracket 21 may further bear a rotating mechanism including an electric motor 22 and a transmission gear 23 connected to the rear end of the worm screw 20 for driving said worm screw in rotation.

The worm screw 20 has first and second threads 24, 25. In the present case, the first thread 24 is an internal thread and is made in a blind bore 26 which opens at the front end of the worm screw 20.

More precisely, the first thread may be formed inside a hollow sleeve 24a, belonging to the worm screw 20 and fixed inside the blind bore

26 which is hollowed out in a main body 20a of the worm screw 20. This main body 20a of the worm screw 20 may be for instance made out of metal and the hollow sleeve 24a may be made out of plastics. The sleeve

24a is fixed to the main body 20a so that it cannot move axially and that it cannot rotate relative to said main body 20a. The sleeve 24a is fixed to the main body 20a by any known means, e.g. by fitting combined with the use of a snap spring or by fitting combined with gluing, and so on.

A threaded stem 27, which extends in the longitudinal direction L, is screwed in the first thread 24 through the open front end of the worm screw 20. It should be noted that, in a variant (not shown), the stem 27 might be composed of a non-threaded member fixed to a intermediate threaded part, in which case the stem would still be screwed in the first thread 24 through this intermediate part. The front end 28 of the threaded stem 27 protrudes out of the open front end of the worm screw and is fixed to a bracket 29 which is in turn fixed (e.g. welded) to the movable front frame 1 1. More precisely, the support bracket 29 may be fixed to the underside of the support plate 17 of the movable front frame. The threaded screw 27 is immobilized in rotation by the bracket 29, so that rotation of the worm screw 20 generates a linear movement of the threaded stem 27 with the movable front frame 1 1 in direction L, forward or backward.

Besides, the second thread 25 of the worm screw is an external thread which is made on the external surface of the worm screw. This external thread is screwed in a nut 30 which bears a transverse rigid rod 31 (e.g. a rigid metallic wire) extending in a transverse direction Y which is perpendicular to direction X. This transverse rod 31 is fixed to the free end 16 of the trim and may be fixed in particular to a free end 32 of the trim cover 13. the rod 31 may be retained on the nut for instance by snap fitting in a rearwardly open hook member 30a formed on the underside of the nut. The nut 30 is immobilized in rotation by a guide 33 which may be fixed for instance to the casing of the transmission gear 23. This guide 33 may include for instance two longitudinal lateral sections 34 which extend parallel to the worm screw 20 on both sides thereof, and which are connected at their back and front ends by two spacers 35, 36.

The nut 30 is matingly received between the lateral sections 34, so that said nut 30 may be moved along the worm screw in the longitudinal direction L without rotating with the worm screw 20.

Besides, the movable front frame 1 1 is slidably guided relative to the main frame 10 by two parallel slides 38 which extend parallel to the longitudinal direction L and which connect the movable front frame 1 1 to the main frame 10. In the example shown in the drawings, each slide may include a cylinder 39 fixed through a bracket 39a to the underside of the main frame 10, and a stem 40 fixed through a bracket 40a to the underside of the movable front frame 1 1.

The pitch of the second thread 25 is substantially twice the pitch of the first thread 24 in the example considered here and the two threads 24, 25 have the same direction, so that, when the worm screw 20 is rotated by the motor 22 upon actuation of a control bottom (not shown) by the user of the seat, the nut 30 is moved longitudinally twice as quickly as the movable front frame 11 and in the same direction. Since the trim 9 is rolled around the foremost end 14 and slides on the movable front frame 1 1, this difference of speed enables to move the trim 9 in synchronism with the movable front frame 11, without generating tensile stresses of compressions of the trim, as illustrated in figures 7-10 which show the extended position of the movable front frame. It should be noted that the front frame 1 1 might be driven by the driving mechanism 19 in a more complex movement than just a sliding movement (for instance, a composite movement including a rotation and an axial displacement). It should also be noted that the worm screw 20 of the invention might drive first and second movable parts of a seat which would be other than a front frame and a trim.

Besides, the motor could drive several similar worm screws, e.g.

2 similar worm screws extending opposite to one another. Also, the worm screw as described above could be used in a telescopic worm gear, and/or the stem 27 might go through the entire length of the worm screw 20.