VEHICLE SEAT FILE

Abstract

This disclosure relates to a vehicle seat back (11) comprising a backrest frame and a backrest height adjustment device including: - a support member (20) for receiving the upper back of a seat occupant against its front face, pivotally mounted on the backrest frame; - at least one first connecting rod (30) pivotally articulated relative to the backrest frame (11); - an intermediate piece (40) between the support member (20) and the first connecting rod (30), pivotally articulated relative to the support member and relative to the first connecting rod (30); - an actuator for adjusting the position of the support member (20) between a rearward and a forward position, the actuator comprising a connecting piece (50) pivotally articulated relative to the intermediate piece (40). Figure 4

Description

Description Title of the invention: VEHICLE SEAT BACKREST Technical field

[0001] — The present description relates to a vehicle seat back. The present description also relates to a vehicle seat comprising such a backrest. Prior art

[0002] = To improve the comfort of the occupant of a vehicle seat 10, in particular of motor vehicle, the seat 10 can have several adjustments allowing it to be better adapted to the occupant's morphology. Thus, the position of the seat 10 can be adjusted in relation to the steering wheel, depending on the size of the occupant. The backrest 11 of the seat can be more or less reclined in relation to the seat base. The seat can still be equipped with a headrest 15 whose height position, relative to the backrest 11 of the seat, can be adjusted by the occupant.

[0003] — More recently, there have appeared devices for adjusting the top of the backrest 11 of vehicle seat such as the position of the occupant's upper back support area on the top of the backrest 11 can be changed. To do this, the devices in question com- take a support member 20, pivoting relative to a backrest frame 12 of seat around a first transverse axis B1 between a retracted position and a position advanced. In the retracted position, the support member 20 extends generally parallel- attached to the backrest frame 12, while in the forward position the organ is pivoted forwards relative to the backrest frame 12 as seen in [Fig.1].

[0004] — The support member 20 can be pivoted about the first transverse axis B1 ma- nually. However, preferably, the high backrest adjustment device comprises an actuator, for controlling the rotation of the support member 20 around the first transverse axis B1.

[0005] — To do this, the actuator generally comprises a motor fixed to the body of the support member 20 and which drives a rod 102 in translation in a direction sen- possibly vertical, corresponding to the main direction of extension of the screw without END.

[0006] — The upper backrest adjustment device comprises a connecting rod 101. The connecting rod 101 is pivoting articulated relative to the backrest frame 12 around a second axis B2 transverse and relative to the rod 102 around a third transverse axis B3.

[0007] — The upper backrest adjustment device then operates as follows. The rotation of the motor causes the rod 102 to move up or down. The de- placement of the rod 102 then causes a rotation of the connecting rod 101 relative to the rod 102, around the third transverse axis B3, on the one hand, and / or with respect to the backrest frame 12, around the second transverse axis B2, on the other hand. Finally, the rotation of the connecting rod 101 causes a rotation of the support member 20 relative to the backrest frame 12, around the first transverse axis B1. However, it has been found by the inventors that in order to drive the support member 20 in rotation about the first axis B1 forward (i.e. from the retracted position to the advanced position), the motor must generate a much greater torque when the support member 20 is at the retracted position than when it is at the advanced position. In addition, the motor used must allow its integration into the backrest 11 of the seat 10 and must therefore have reduced dimensions for this purpose. However, the reduction in the dimensions of the motor is generally accompanied by a reduction in the torque that it can produce. Thus, the motors for driving the support member 20 whose dimensions are suitable for being arranged in the backrest 11 are generally in an overloaded state when the support member 20 is at the retracted position, which can lead to premature wear of the electrical and mechanical components of the motor.Furthermore, the upper backrest adjustment device as described above has a degree of hyperstaticity which makes its assembly complex. Also, according to the inventors' findings, a collision can generate significant forces on the kinematics of the upper backrest adjustment device and in particular on the actuator, which can cause the actuator worm screw to bend due to the degree of hyperstaticism. It has also been found that during a rear collision, the forces transmitted to the kinematics and to the actuator are maximum when the support member 20 is in the rearward position. Summary There is provided a backrest for a vehicle seat, the backrest comprising a backrest frame and a top backrest adjustment device, the top backrest adjustment device comprising: - a support member comprising a body intended to receive the upper back of an occupant of the seat in support on a front face, the support member being pivotally mounted around a first transverse axis on the backrest frame; - at least one first articulated connecting rod pivoting relative to the backrest frame around a second transverse axis: - an intermediate part between the support member and the first connecting rod, the intermediate part being pivotally articulated relative to the support member around a third transverse axis and relative to the first connecting rod around a fourth transverse axis, - an actuator for adjusting the position of the support member around the first transverse axis between a retracted position and an advanced position, the actuator comprising an articulated connecting piece pivoting relative to the intermediate piece around a fifth transverse axis, the actuator being adapted to move the connecting piece in translation along a first axis perpendicular to the transverse direction. Advantageously, the upper backrest adjustment device has kinematics which make it possible to reduce the variation in the force required by the actuator during the forward rotation of the support member around the first transverse axis between the retracted position and the advanced position (i.e. from the retracted position to the advanced position). In particular, the maximum observed relative variation in the force required by the actuator to drive the support member in rotation around the first transverse axis towards the front is less than 20%. Furthermore, the kinematics of the upper backrest adjustment device allows a reduction in the force required by the actuator to drive the support member around the first transverse axis forward when it is close to the rearward position compared to known upper backrest adjustment devices. Thus, the motor can have reduced dimensions allowing its integration into the backrest while limiting, or even avoiding, it being subjected to excessive load. This makes it possible to protect the motor from premature wear and to maintain a compact upper backrest adjustment device. Also, the kinematics of the upper backrest adjustment device allows a reduction in the maximum force transmitted to the kinematics and to the actuator during a collision. In particular, a reduction of around 40% of the force transmitted to the kinematics and to the actuator during a collision was measured when the support member is in the retracted position. The kinematics of the upper backrest adjustment device also allows a reduction in the relative variation of the force transmitted to the actuator during a collision over the angular range of rotation of the support member around the first transverse axis. The backrest frame may comprise a first upright and a second upright. The backrest frame may comprise at least one crossbar that extends transversely between the first upright and the second upright. The crossbar may be connected on each side in the transverse direction respectively to the first upright and the second upright. The body of the support member may be intended to be in contact, possibly by means of a lining and / or a cover at least partially covering the body of the support member, with the upper back of the occupant of the seat, in particular with the shoulders and / or the shoulder blades of the occupant. The body may have a front face, intended to be oriented towards the upper back of an occupant of the seat. The front face may be flat or concave. The body may further comprise a rear face opposite the front face. The rear face may comprise ribs of reinforcement. The reinforcing ribs here form cells. The rotation of the support member around the first transverse axis between a retracted position and a forward position can correspond to a 15° rotation of the support member around the first transverse axis. The support member and the uprights of the backrest frame may comprise associated reliefs, in particular by complementarity of shape, to guide the support member in rotation around the first transverse axis, relative to the first upright and second upright of the backrest frame. The reliefs of the support member may project transversely from the body of the support member, the reliefs of the support member preferably extending from lateral faces of the body of the support member, the reliefs of the support member being each received respectively in a housing of the first upright and a housing of the second upright of the backrest frame. The actuator may comprise a motor and a worm screw extending along the first axis perpendicular to the transverse direction, the connecting piece being secured to one end of the worm screw, the motor being adapted to move the worm screw in translation along the direction of the first axis perpendicular to the transverse direction. The upper backrest adjustment device comprising such an actuator allows linearity between the translation of the worm screw in the direction of the first axis perpendicular to the transverse direction and the rotation of the support member around the first transverse axis. Adjusting the position of the support member around the first transverse axis is thus easier and more comfortable for an occupant seated on the seat. The motor can move the worm screw in translation along the first axis perpendicular to the transverse axis by means of a gear. The motor and the worm screw can be pivotally articulated relative to the support member around a sixth transverse axis. This makes it possible to reduce the isostatic constraints of the upper backrest adjustment device. Thus, the upper backrest adjustment device is advantageously isostatic, which facilitates assembly and reduces, or even eliminates, the risks of bending of the worm screw in the event of a vehicle collision. The angular movement around the sixth transverse axis of the motor and the worm screw relative to the support member can be less than or equal to 4°. The second transverse axis, the fourth transverse axis and the fifth transverse axis may be substantially aligned when the support member is in the forward position or in the vicinity of the forward position. Thus, when an occupant has the upper back resting on the body of the support member, the force induced on the support member is transmitted to the first connecting rod and then to the backrest frame instead of being transmitted to the actuator, which protects the actuator from premature wear. The upper backrest adjustment device may comprise a second articulated connecting rod pivoting relative to the backrest frame about the second transverse axis. The intermediate part may comprise a first flange and a second flange spaced apart from each other in the transverse direction, the first flange being pivotally articulated relative to the first connecting rod about the fourth transverse axis and the second flange being pivotally articulated relative to the second connecting rod about the fourth transverse axis. The arrangement of two connecting rods makes it possible to reinforce the structure of the upper backrest adjustment device in the event of a vehicle collision, in particular this makes it possible to prevent the upper backrest adjustment device from twisting. The intermediate piece may comprise a transversely extending spar connecting the first flange and the second flange to each other. The spar maintains the spacing in the transverse direction between the first flange and the second flange. The first connecting rod and the second connecting rod may each comprise a first end and a second end. The first connecting rod and the second connecting rod may each be pivotally articulated relative to the backrest frame at their first end. In particular, the first connecting rod and the second connecting rod may each be pivotally articulated relative to a respective branch of a U-shaped guide which is integral with the crosspiece. The first connecting rod and the second connecting rod may each be pivotally articulated respectively relative to the first flange and the second flange at their second end. For this purpose, the first flange and the second flange may each comprise a first hole centered on the fourth transverse axis and through which a pivot member extends. The first flange and the second flange may each extend perpendicularly to the transverse direction, the first flange and the second flange each having a substantially triangular shape whose vertices are respectively in the vicinity of the third transverse axis, the fourth transverse axis and the fifth transverse axis. The upper backrest adjustment device may comprise a first shaft extending along the third transverse axis, the first shaft being integral with the support member, the intermediate part being pivotally mounted on the first shaft. The first Mask and the second (mask may each include a second hole centered on the third transverse axis and through which the first shaft extends. The support member may include a first leg and a second leg each extending from the rear face of the body. The first shaft may extend transversely from the first leg to the second leg. The first shaft may comprise a first retention portion relative to the support member in a first direction of the third transverse axis and a second retention portion relative to the support member in a second direction of the third transverse axis, the second direction being opposite to the first direction. The first retention portion and the second retention portion may bear in the direction of the third transverse axis respectively on a face of the first leg and a face of the second leg which are opposite each other in the direction of the third transverse axis. The first leg and the second leg may each include a hole centered on the third transverse axis through which the first shaft extends. The second retention portion may be elastically deformable so as to be insertable into the hole of each of the legs and the second hole of each flange, and to cooperate by elastic return with the bearing face of the second leg. The upper backrest adjustment device may comprise a second shaft extending along the fifth transverse axis, the second shaft being integral with the intermediate part, the connecting part being pivotally mounted on the second shaft. The first flange and the second flange may each include a third hole centered on the fifth transverse axis and through which the second shaft extends. The second shaft may comprise a first retention portion relative to the intermediate piece in a first direction of the fifth transverse axis and a second retention portion relative to the intermediate piece in a second direction of the third transverse axis, the second direction being opposite the first direction. The first retention portion and the second retention portion may bear in the direction of the fifth transverse axis respectively on a face of the first flange and a face of the second flange which are opposite each other in the direction of the fifth transverse axis. The second retention portion may be elastically deformable so as to be able to be inserted into the third hole of each flange, and to cooperate by elastic return with the bearing face of the second flange. The connecting piece may comprise a tubular portion through which the second shaft extends freely to rotate about the fifth transverse axis. The body of the support member may form at a rear face a recess in which the intermediate part, said at least one first connecting rod and the actuator are received, in whole or in part. The upper backrest adjustment device advantageously has a small footprint. According to another aspect, there is provided a vehicle seat comprising a seat with a seat frame, and a backrest as described above, the backrest frame being fixed to the seat frame, the backrest frame preferably being pivotally mounted about a seventh axis transverse to the seat frame. The vehicle seat may include a headrest. The body of the support member can be adapted to receive pins from the headrest, preferably so that the height position relative to the support member can be adjusted. Brief description of the drawings Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which: [Fig.1] schematically represents a backrest for a vehicle seat comprising a top backrest adjustment device according to the state of the art; [Fig.2] includes figures 2a and 2b which schematically represent the kinematics of the upper backrest adjustment device of the backrest of [Fig.1], respectively in a retracted position and a forward position; [Fig.3] schematically represents a side view of a vehicle seat according to the present description; [Fig.4] includes Figures 4a and 4b which represent a partial sectional view of a backrest of the seat of [Fig.3], with a backrest top adjustment device in a rearward position in Figure 4a and in a forward position in Figure 4b; [Fig.5] represents a partial rear view of the backrest of [Fig.4] in which the crossbar has been removed; [Fig.6] represents a partial perspective view of the backrest of [Fig.4] in which the crossbar has been removed and in which the upper backrest adjustment device is in the retracted position; [Fig.7] represents a partial perspective view of the backrest of [Fig.4] in which the crossbar has been removed and in which the upper backrest adjustment device is in the forward position; [Fig.8] includes figures 8a to 8c which respectively represent an intermediate part, a first shaft and a second shaft connected to a connecting part, each belonging to the upper backrest adjustment device of the backrest of [Fig.4]; [Fig.9] comprises Figures 9a to 9c: Figure 9a is a graph comparing the high backrest adjustment device of the prior art (called known UBA) and according to the present description (called UBA according to the present description) in terms of actuator force; Figure 9b is a graph comparing the high backrest adjustment device of the prior art and according to the present description in terms of kinematic parameters; Figure 9c is a graph comparing the high backrest adjustment device of the prior art and according to the present description with respect to resistance following a collision. Description of the embodiments In the following description, when referring to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right ", etc., or relative, such as the terms "above", "below", "upper", "lower", etc., or to orientation qualifiers, such as "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures or of a seat in its normal position of use. In the following, the longitudinal direction X means the longitudinal direction of the seat. The longitudinal direction X of the seat is considered to be the same as the longitudinal direction of the motor vehicle in which the seat is mounted. This longitudinal direction X corresponds to the normal direction of travel of the vehicle. The longitudinal direction X is preferably horizontal. The transverse direction Y is the transverse direction of the seat. The transverse direction of the seat thus corresponds to the transverse or lateral direction of the motor vehicle. This transverse direction corresponds to a direction perpendicular to the normal direction of travel of the vehicle. The transverse direction Y is preferably horizontal. Finally, the vertical direction Z is a vertical direction of the seat, perpendicular to the longitudinal directions X and transverse directions Y. [Fig. 3] schematically represents a motor vehicle seat 10. This is mounted here on a sliding mechanism allowing the seat 10 to slide in the longitudinal direction X. The seat 10 comprises a seat 13 with a seat frame 14. The seat 10 also comprises a backrest 11 with a backrest frame 12. The backrest frame 12 is mounted on the seat frame 14, pivoting about a transverse articulation axis A7 (also called seventh transverse axis A7 in the present description with reference to the other transverse axes described below), by at least one articulation mechanism. Such articulation mechanisms are known. Consequently, these articulation mechanisms are not described in further detail here. The seat 10 also comprises a headrest 15. In the following, the backrest 11 of the seat 10 is described in more detail with reference to FIGS. 4 to 9. Here, the backrest 11 comprises an upper backrest adjustment device (commonly referred to by the acronym UBA for “Upper Backrest Adjustment” in English). The backrest frame 12 comprises a first upright 16 and a second upright 16'. In the example illustrated, the backrest frame 12 further comprises a crosspiece 17. The crosspiece 17 is here a high crosspiece 17. Indeed, the crosspiece 17 is fixed on high end portions of the first upright 16 and of the second upright 16' of the backrest frame 12. The high ends of the first upright 16 and of the second upright 16° are for example the ends of the first and second uprights 16, 16°, opposite their respective end, intended to receive a hinge mechanism. The upper backrest adjustment device firstly comprises a support member 20. The support member 20 comprises a body 21 intended to receive, in support on a front face, the upper back of an occupant of the seat 10, in particular with the shoulders and / or the shoulder blades of the occupant. The body 21 of the support member 20 may be intended to be in contact, possibly by means of a lining and / or a cover covering it at least partially. The body 21 has a front face, intended to be oriented towards the upper back of an occupant of the seat 10. The front face may be flat or concave. The body 21 also comprises a rear face opposite the front face. The rear face here comprises reinforcing ribs visible in figures S to 7, these forming cells. The body 21 of the support member 20 is located opposite in the longitudinal direction X and in front of the crossmember 17.Finally, the body 21 of the support member 20 can be adapted to receive pins of the headrest 15, preferably so as to be able to adjust the height position relative to the support member 20. The support member 20 is pivotally mounted about a first transverse axis A1 on the backrest frame 12. In particular, the support member 20 is movable about the first transverse axis A1 between a retracted position shown in Figures 4a and 6 and a forward position shown in Figures 4b and 7. The rotation of the support member 20 about the first transverse axis A1 between the retracted position and the forward position may correspond to a rotation of an angle Omax equal to 15° of the support member 20 about the first transverse axis A1. The support member 20 is moved into the forward position after a forward rotation from the retracted position. In other words, the support member 20 is further away from the crosspiece 17 in the forward position than in the retracted position. The forward position can provide support between the upper back of an occupant of the seat 10 and the support member 20, thereby improving the comfort of the occupant. To allow the rotation of the support member 20 around the first transverse axis A1, the support member 20 and the uprights 16, 16° of the backrest frame 12 may comprise associated reliefs, in particular by complementarity of shape, to guide 18 the support member 20 in rotation around the first transverse axis A1, relative to the first upright 16 and second upright 16° of the backrest frame 12. The reliefs 22 of the support member 20 here project transversely from the body 21 of the support member 20. The reliefs 22 of the support member 20 extend from lateral faces of the body 21 of the support member 20 and are each received respectively in a housing of the first upright 16 and a housing of the second upright 16° of the backrest frame 12. The backrest top adjustment device comprises a first connecting rod 30 and a second connecting rod 30'. The first connecting rod 30 and the second connecting rod 30° are each pivotally articulated relative to the backrest frame 12 around a second axis. transverse A2. The first connecting rod 30 and the second connecting rod 30” each comprise a first end and a second end. The first connecting rod 30 and the second connecting rod 30” are each pivotally articulated relative to the backrest frame 12 at their first end. In particular, the first connecting rod 30 and the second connecting rod 30” may each be pivotally articulated relative to a respective branch of a U-shaped guide 18 which is secured to the crosspiece 17. The backrest top adjustment device comprises an intermediate piece 40 between the support member 20 and each of the first connecting rod 30 and second connecting rod 30'. The intermediate piece 40 comprises a first flange 41 and a second flange 41° spaced apart from each other in the transverse direction Y. The first flange 41 and the second flange 41' each extend perpendicular to the transverse direction Y. The intermediate piece 40 further comprises a longitudinal member 42 which extends transversely and which connects the first flange 41 and the second flange 41' to each other. The longitudinal member 42 makes it possible to maintain the spacing in the transverse direction Y between the first flange 41 and the second flange 41'. More particularly visible in figure Ba, the first flange 41 and the second flange 41' each comprise a first hole 43, a second hole 44 and a third hole 45 whose positioning and function are described in more detail below. The intermediate part 40 is first pivotally articulated relative to the support member 20 around a third transverse axis A3. For this purpose, the upper backrest adjustment device comprises a first shaft 81 which extends along the third transverse axis A3. The first shaft 81 is integral with the support member 20 and the intermediate part 40 is pivotally mounted on the first shaft 81. For this purpose, the second hole 44 of the first flange 41 and the second flange 41' are each centered on the third transverse axis A3 and the first shaft 81 extends through the second hole 44 of each of the first flange 41 and the second flange 41'. The support member 20 here comprises a first leg 23 and a second leg 23” each extending from the rear face of the body 21. The first shaft 81 extends transversely from the first leg 23 to the second leg 23'. The first leg 23 and the second leg 23' may each comprise a hole centered on the third transverse axis A3 through which the first shaft 81 extends. More particularly visible in Figure 8b, the first shaft 81 comprises a first retention portion 83 relative to the support member 20 in a first direction of the third transverse axis A3 and a second retention portion 84 relative to the support member 20 in a second direction of the third transverse axis A3, the second direction being opposite to the first direction.The first retention part 83 and the second retention part 84 bear in the direction of the third transverse axis A3 respectively on a face of the first leg 23 and a face of the second leg 23° which are opposite each other. of the other according to the direction of the third transverse axis A3. The second retention part 84 is elastically deformable so as to be able to be inserted into the hole of each of the tabs 23, 23° and the second hole 44 of each flange, and to cooperate by elastic return with the bearing face of the second tab 23°. The intermediate part 40 is also pivotally articulated relative to the first connecting rod 30 and the second connecting rod 30° about a fourth transverse axis A4. In particular, the first flange 41 is pivotally articulated relative to the first connecting rod 30 about the fourth transverse axis A4 and the second flange 41' is pivotally articulated relative to the second connecting rod 30' about the fourth transverse axis A4. The first connecting rod 30 and the second connecting rod 30' are each pivotally articulated respectively relative to the first flange 41 and the second flange 41° at their second end. For this purpose, the first hole 43 of each of the first flange 41 and the second flange 41' is centered on the fourth transverse axis A4 and a pivot member extends through the first hole 43 of each flange.Advantageously, the arrangement of the two connecting rods 30, 30” makes it possible to reinforce the structure of the upper backrest adjustment device in the event of a vehicle collision, in particular this makes it possible to prevent the upper backrest adjustment device from twisting. The upper backrest adjustment device finally comprises an actuator which makes it possible to adjust the position of the support member 20 around the first transverse axis A1 between a rearward position and a forward position. The actuator firstly comprises a connecting piece 50 pivoting relative to the intermediate piece 40 about a fifth transverse axis A5. To do this, the upper backrest adjustment device comprises a second shaft 82 which extends along the fifth transverse axis A5. The second shaft 82 is secured to the intermediate piece 40 and the connecting piece 50 is pivotally mounted on the second shaft 82. The third hole 45 of each of the first flange 41 and the second flange 41' is centered on the fifth transverse axis AS and the second shaft 82 extends through the third of each of the first flange 41 and the second flange 41'. The connecting piece 50 comprises a tubular part S1 with the fifth transverse axis AS and through which the second shaft 82 extends freely in rotation about the fifth transverse axis AS. The second shaft 82 is of a similar shape to the first shaft 81. Thus, as more particularly visible in FIG. 8c, the second shaft 82 comprises a first retention portion 83 relative to the intermediate piece 40 in a first direction of the fifth transverse axis A5 and a second retention portion 84 relative to the intermediate piece 40 in a second direction of the third transverse axis A3, the second direction being opposite to the first direction. The first retention portion 83 and the second retention portion 84 are supported in the direction of the fifth transverse axis A5 respectively on one face of the first flange 41 and one face of the second flange 41” which are opposite each other in the direction of the fifth transverse axis AS. The second retention part 84 of the second shaft 81 is elastically deformable so as to be able to be inserted into the third hole of each flange 41, 41', and to cooperate by elastic return with the bearing face of the second flange 41'. Remarkably, the first flange 41 and the second flange 41' each have a substantially triangular shape whose apexes are respectively in the vicinity of the third transverse axis A3, the fourth transverse axis A4 and the fifth transverse axis A5. The actuator is furthermore adapted to move the connecting piece 50 in translation along a first axis C1 perpendicular to the transverse direction Y. The actuator here comprises a motor 60 and a worm screw 70 extending along the first axis perpendicular C1 to the transverse direction Y. The connecting piece 50 is secured, for example by embedding, to one end of the worm screw 70. The motor 60 is adapted to move the worm screw 70 in translation along the direction of the first axis perpendicular C1 to the transverse direction Y. For example, the motor 60 can move the worm screw 70 in translation along the first axis perpendicular C1 to the transverse axis by means of a gear. Such means for driving the worm screw 70 by the motor 60 are known and are therefore not described in more detail. As visible in Figures 6 and 7, the body 21 of the support member 20 forms at the rear face a recess in which is, in part, received the intermediate part 40, said at least one first connecting rod 30 and the actuator whatever the angular position of the support member 20 around the first axis. The upper backrest adjustment device thus advantageously has a small footprint. Reference is now made to Figure 9a which represents a graph illustrating the variation in the force required by the actuator to pivot the support member 20 forwards as a function of the angular position of the support member 20 between the retracted position and the advanced position, for a high backrest adjustment device of the state of the art and according to the present description. The high backrest adjustment device advantageously has kinematics which makes it possible to reduce the variation in the force required by the actuator during the forward rotation of the support member 20 around the first transverse axis A1 between the retracted position and the advanced position. In particular, the maximum observed relative variation in the force required by the actuator to drive the support member 20 in rotation around the first transverse axis A1 forwards is less than 20%. Furthermore, the kinematics of the upper backrest adjustment device allows a reduction in the force required by the actuator to drive the support member 20 around the first transverse axis A1 forward when the latter is in the vicinity of the rearward position relative to known upper backrest adjustment devices. Thus, the motor 60 can have reduced dimensions allowing its integration into the backrest 11 while limiting, or even avoiding, the latter being subjected to excessive load. This makes it possible to protect the motor 60 from premature wear and to maintain a compact upper backrest adjustment device. Reference is now made to Figure 9b which represents a graph illustrating the variation of the angular position of the support member 20 between the retracted position and the advanced position as a function of the translational movement of the endless screw 70, for a high backrest adjustment device of the state of the art and according to the present description. It can be seen that, unlike the device of the prior art, the high backrest adjustment device according to the present description allows a linear relationship between the translation of the endless screw 70 in the direction of the first perpendicular axis C1 and the rotation of the support member 20 around the first transverse axis A1. Adjusting the position of the support member 20 around the first transverse axis A1 is thus easier and more comfortable for an occupant seated on the seat 10. Furthermore, the motor 60 and the worm screw 70 are pivotally articulated relative to the support member 20 around a sixth transverse axis A6. This makes it possible to reduce the isostatic constraints of the upper backrest adjustment device. Thus, the upper backrest adjustment device is advantageously isostatic, which facilitates its assembly and reduces, or even eliminates, the risks of bending of the worm screw 70 in the event of a vehicle collision. The angular movement around the sixth transverse axis A6 of the motor 60 and the worm screw 70 relative to the support member 20 may be less than or equal to 4°. Figure 9c represents a graph illustrating the variation of the force transmitted to the actuator in the event of a vehicle collision as a function of the angular position of the support member 20 between the retracted position and the advanced position, for a high backrest adjustment device of the state of the art and according to the present description. The graph of Figure 9c corresponds in this case to a rear collision with the vehicle of the order of 32 G. The kinematics of the high backrest adjustment device according to the present description firstly allows a reduction in the maximum force transmitted to the kinematics and to the actuator during a collision (i.e. when the support member 20 is in the retracted position). In particular, a reduction of the order of 40% of the force transmitted to the kinematics and to the actuator during a collision was measured when the support member 20 is in the retracted position.The kinematics of the upper backrest adjustment device also allows a reduction in the relative variation of the force transmitted to the actuator during a collision over the angular range of rotation of the support member 20 around the first transverse axis A1. Remarkably in Figure 4b, the second transverse axis A2, the fourth transverse axis A4 and the fifth transverse axis AS are substantially aligned when the support member 20 is in the advanced position or in the vicinity of the advanced position. Thus, when an occupant has the upper back resting on the body 21 of the support member 20, the force induced on the support member 20 is transmitted to the first connecting rod 30 and then to the backrest frame 12 instead of being transmitted to the actuator, which protects the actuator from premature wear. The numerical designation (first, second, third, etc.) of the transverse axes is purely a matter of editorial choice. Thus, the numerical designation of the transverse axes can be reversed in any order. The invention is not limited to the examples described above and is susceptible to numerous variants. Also, according to a variant not shown, the connecting piece 50 can be integral with a rod moved in translation along the first axis perpendicular C1 to the transverse direction by a hydraulic, pneumatic or electric cylinder for example.

Claims

Claims

1. Backrest (11) for a vehicle seat (10), the backrest (11) comprising a backrest frame (12) and a backrest top adjustment device, the upper backrest adjustment device comprising: - a support member (20) comprising a body (21) intended to receive in support on a front face the upper back of a seat occupant, the organ support (20) being pivotally mounted around a first transverse axis {A1) on the backrest frame (12); - at least one first connecting rod (30) pivoting relative to the backrest frame (11) around a second transverse axis (A2); - an intermediate piece (40) between the support member (20) and the first connecting rod (30), the intermediate part (40) being pivotally articulated by relative to the support member (20) around a third transverse axis (A3) and relative to the first connecting rod (30) around a fourth axis transverse (A4), - an actuator for adjusting the position of the support member (20) around of the first transverse axis (A1) between a retracted position and a advanced position, the actuator comprising a connecting piece (50) pivotally articulated relative to the intermediate part (40) around a fifth transverse axis (A5), the actuator being adapted to move the connecting part (50) in translation along a first axis perpen- dicular (C1) to the transverse direction (Y).

2. Backrest (11) according to the preceding claim, in which the actuator comprises a motor (60) and a worm screw (70) extending according to the first axis perpendicular (C1) to the transverse direction (Y), the part connecting member (50) being secured to one end of the worm screw (70), the motor (60) being adapted to move the worm screw (70) in translation according to the direction of the first axis perpendicular (C1) to the direction transverse (Y).

3. File (11) according to the preceding claim, in which the motor (60) and the worm screw (70) are pivotally articulated relative to the member support (20) around a sixth transverse axis (A6).

4. File (11) according to any one of the preceding claims, in which the second transverse axis (A2), the fourth axis transverse (A4) and the fifth transverse axis (A5) are substantially aligned when the support member (20) is in the advanced position or at vicinity of the advanced position.

5. File (11) according to any one of the preceding claims, wherein the upper backrest adjustment device comprises a second connecting rod (30°) articulated pivoting relative to the frame of backrest (12) around the second transverse axis (A2), and in which the intermediate part (40) comprises a first flange (41) and a second flange (41') spaced apart from each other in the transverse direction (Y), the first flange (41) being pivotally articulated relative to the first connecting rod (30) around the fourth transverse axis (A4) and the second flange (41') being pivotally articulated relative to the second connecting rod (30') around of the fourth transverse axis (a4).

6. A folder (11) according to any one of claim 5, wherein the first flange (41) and the second flange (41') each extend per- pendicular to the transverse direction (Y), the first flange (41) and the second flange (41') each having a substantially tri- angular whose vertices are respectively in the vicinity of the third transverse axis (A3), the fourth transverse axis (A4) and the fifth transverse axis (A5).

7. File (11) according to any one of the preceding claims, wherein the upper backrest adjustment device comprises a first shaft (81) extending along the third transverse axis (A3), the first shaft (81) being integral with the support member (20), the part in- intermediate (40) being pivotally mounted on the first shaft (81).

8. Backrest (11) according to any one of the preceding claims, wherein the upper backrest adjustment device comprises a second shaft (82) extending along the fifth transverse axis (A5), the second shaft (82) being integral with the intermediate part (40), the part connecting member (40) being pivotally mounted on the second shaft (82).

9. Backrest (11) according to any one of the preceding claims, in which the body (21) of the support member (20) forms at a rear face a recess in which is, in whole or in part, received the intermediate part (40), said at least one first connecting rod (30) and the actuator.

10. Vehicle seat (10) comprising a seat (13) with a frame seat (14), and a backrest (11) according to any one of the re- preceding indications, the backrest frame (12) being fixed to the frame seat (14), the backrest frame (11) being preferably mounted pivoting around a seventh transverse axis (A7) relative to the seat frame (14).

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