FR2848157A1 - Vehicle baby seat mounting has support with curved guide rails that tilt and slide seat into safe position in event of impact - Google Patents

Abstract

The baby seat has a curved back (26) with channels (46) for guide rails (66) on a base plate (54). The seat is tensioned by a belt (76) and pulley (78) system while being held in the upright position by a shearing pin thriough the base. In the event of a front or rear impact the pin shears and the belt, actuated by a pyrotechnic device (86), tilts the seat into a safe position with the baby's back towards the direction of travel. A second pyrotechnic device (98) and pulley system (88, 92) rotates the seat before tilting it in the event of a side impact.

Description

i

  "Arrangement of a child seat capable of tilting towards a protective position in an automobile" The present invention relates to an arrangement for mounting a child seat in a motor vehicle.

  The invention relates more particularly to an arrangement for mounting a child seat in the passenger compartment of a motor vehicle of the type comprising a fixed support structure on which the seat is mounted so that it occupies a so-called position circulation: - in which its backrest element extends generally vertically upwards, with respect to the vehicle floor, so as to comprise a bearing surface, for the child's head, which is oriented towards the forward, or backward, considering the direction of travel of the vehicle in forward; - and in which the child's bodily axis, defined by the alignment of the child's bust with his neck, extends in a longitudinal and vertical plane and is oriented in an initial position inclined relative to the vertical .

  Motor vehicle child seats are generally designed for young children, that is, children who are 6 months to 4 years of age, and who weigh less than about 18 kg. This type of seat keeps the child's body in a so-called circulation position inside the vehicle cabin.

  The child seat is generally fixed on an adult seat in the passenger compartment.

  In the most frequent case of a longitudinal frontal impact directed towards the rear, considering the direction of movement of the vehicle in forward gear, the vehicle undergoes a sudden longitudinal deceleration. Because of this sudden deceleration, the child undergoes a longitudinal acceleration directed forwards, or antero-posterior acceleration, relative to the vehicle, which tends to throw the child out of his seat forward, when the child sits facing forward.

  To prevent the child from being thrown forward, the seat has a harness that keeps the child in the seat, mainly at the level of his abdomen, chest, and shoulders. The harness possibly includes a pelvic strap 5, that is to say a strap that passes between the legs of the child, so as to remedy the risk of submarining, that is to say the risk of slipping of the child's body under the ventral part of the harness, during a frontal impact.

  However, in the event of a frontal impact, it is noted that the child 10 is subjected to hyper flexion of the neck which often leads to cervical lesions.

  Reconstructions of accidents with child mannequins have shown that in the event of an impact at 40 km / h, a horizontal inertia force of 1000 to 2000 Newtons could be generated at the child's neck. This critical situation stems from the relative importance of the mass of the head compared to the mass of the whole body, the ratio between these masses being 25% in a young child, when it is only 7% in an adult.

  In the event of a violent frontal impact, there is also a significant risk of lesions by deflection of the child's thorax.

  To limit the risk of cervical and thoracic injuries, it has been proposed to mount the rear-facing child seat, so that, in the event of a frontal impact, the child is pressed against the back of the seat and the neck is not subject to hyper flexion. Finally, the thorax is also less stressed.

  This type of assembly has drawbacks.

  Indeed, when the vehicle comprises an airbag, or airbag, frontal, associated with the adult seat on which the child seat is fixed, it is then necessary to provide a device to deactivate the airbag.

  In addition, rearward-facing mounting only displaces the problem, since the risk of hyper flexion of the neck then arises in the case of an opposite direction shock or rear impact, that is to say when the child tends to be thrown back from his seat. The invention aims to remedy these drawbacks by proposing an arrangement for mounting the child seat which significantly improves the safety of the child by reducing the risk of cervical and thoracic injuries during a frontal impact.

  To this end, the invention provides an arrangement of the type described above, characterized in that it comprises means which, when the vehicle is subjected to a generally longitudinal frontal impact directed towards the rear, respectively a rear impact directed towards the front, cause, at the latest during the impact, the tilting of the seat, generally around a substantially transverse and horizontal geometric axis, to a so-called front protection position, rear protection respectively, in which the orientation of the child's body axis is between a substantially horizontal position in which the child's head is essentially biased forward, respectively rearward, along its body axis, and a maximum inclined position , opposite the initial position, in which the child's head is essentially biased forward, respectively backward, against the bearing surface of the folder item.

  According to other characteristics of the invention - the arrangement comprises means capable of producing a signal for detecting a frontal impact, respectively of a rear impact, and actuation means which control the tilting of the seat towards its position of frontal protection, respectively of rear protection, when they receive the signal of frontal impact, respectively of rear impact; - the center of gravity of the assembly formed by the seat and the child is offset in a vertical longitudinal plane, with respect to the tilt axis so that, in a situation of frontal impact, respectively of rear impact, the seat switches to its front protection position, rear protection respectively, under the effect of the longitudinal acceleration due to the shock and under the effect of the moment of inertia of the assembly, and the seat includes angular retaining means in circulation position which are capable of being retracted in the event of a frontal impact or a rear impact respectively; the arrangement comprises means which, when the vehicle is subjected to a generally transverse lateral impact, directed towards one side, cause, at the latest during the lateral impact, the pivoting of the seat, generally around a substantially geometric axis vertical, generally a quarter turn to the side, so that the seat comes to occupy a position called lateral protection in which the bearing surface of the backrest element is oriented towards the side; - The arrangement comprises means capable of producing a signal for detecting a side impact, and actuation means which control the pivoting of the seat towards its lateral protection position when they receive the signal of side impact; - the actuating means comprise pyrotechnic means which propel the seat towards its frontal protection position, respectively rear protection position, or its lateral protection position, when a signal of frontal impact, respectively of rear impact, respectively a signal of side impact is produced; the arrangement comprises elastic means which are prestressed when the seat occupies its circulation position, and the actuation means command the release of the elastic means which propel the seat towards its position of frontal protection, respectively of rear protection, or its lateral protection position, when a front impact signal, respectively rear impact signal, respectively a side impact signal, is produced;

HAVE

  - The arrangement comprises a damping device which stops the tilting, or the pivoting, of the seat when it reaches its frontal protection position, respectively rear protection, respectively its lateral protection position, during s the frontal impact, respectively rear impact, respectively during the side impact; the damping device comprises friction braking means; the seat is slidably mounted on at least one guide rail with a radius of curvature determined in a vertical longitudinal plane, so as to be guided in tilting; - The arrangement comprises means for adjusting the angular position of movement of the seat relative to the tilting axis, and these adjustment means are capable of being retracted in a situation of frontal impact, respectively of rear impact; the support structure is designed to be fixed to a seat of the vehicle by means of a standard Isofix type fastening device and / or by means of seat belts.

  Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: - Figure 1 is a side view with cutaway which schematically represents the arrangement of a child seat in a vehicle in accordance with the teachings of the invention; Figure 2 is an exploded perspective view which shows the arrangement of Figure 1; - Figure 3 is a partial longitudinal sectional view which schematically shows the seat of Figure 1 in a circulation position; - Figure 4 is a view similar to that of Figure 3 which shows the seat of Figure 1 in an intermediate angular position of frontal protection; - Figure 5 is a view similar to that of Figure 3 which 5 shows the seat of Figure 1 in a final angular position of frontal protection; - Figure 6 is a view similar to that of Figure 3 which shows the seat of Figure 1 in a lateral protective position. For the description of the invention, the vertical, longitudinal and transverse orientations will be adopted, without limitation, according to the reference V, L, T indicated in the figures.

  In the description which follows, identical, similar or analogous elements will be designated by the same reference numerals.

  FIG. 1 shows an arrangement 10 for mounting a child seat 12 in the passenger compartment 14 of a motor vehicle 16 in accordance with the teachings of the invention.

  The child seat 12 is mounted on a support structure 18 which is fixed relative to the floor 20 of the vehicle 16.

  According to the embodiment shown diagrammatically here, the support structure 18 is mounted on the seat element 22 of an adult seat 24 of the passenger compartment 14.

  The support structure 18 can be held on the adult seat 25 in the same way as the child seats according to the prior art, for example by using hooking means (not shown) carried by the support structure 18 which cooperate with anchoring means (not shown) fixed to the floor 20.

  Generally, these means for attaching and anchoring a child seat are standardized, for example according to the international standard "ISOFIX" (ISO WG 13216).

  The support structure 18 can be maintained on the adult seat 24 in particular by means of the seat belts (not shown) of the adult seat 24.

  In accordance with the teachings of the invention, as shown in FIGS. 2 and 3, the seat 12 is mounted to tilt, relative to the support structure 18, around a geometric axis AI generally transverse and horizontal .

  With particular reference to FIG. 3, the child seat 12 is described when it occupies its angular position known as the circulation Pc, in which the back element 26 of the seat 12 extends generally vertically upwards, relative to the floor 20 of the vehicle 16, so as to include a bearing surface 28, for the head 30 of the child 32, which is oriented towards the front by considering the direction of movement of the vehicle 16 in forward motion.

  The forward direction of traffic corresponds to a longitudinal direction oriented from left to right, in particular considering Figures 1 and 3.

  In the circulation position Pc, the body axis AC of the child 32, which is defined by the alignment of the bust 34 of the child 32 with its neck 36, extends in a longitudinal and vertical plane and is oriented in an initial inclined position.

  According to the embodiment shown here, the child seat 12 generally has the shape of a bucket which can be molded at least partly in a plastic material.

  The backrest element 26 of the seat 12 is extended by a seat element 38, which here extends generally longitudinally forward.

  The rear face 40 of the backrest element 26 and the lower face 42 of the seat element 38 here form a continuous curved face by which the seat 12 is mounted on its support 18.

  To this end, the curved face 40, 42 comprises two generally parallel grooves 44, 46 or slides, which have a determined radius of curvature corresponding to the tilt axis AI of the seat 12.

  Each groove 44, 46 is generally contained in a vertical longitudinal plane.

  The support structure 18 here comprises a base 48 in the form of a housing which comprises an upper planar main wall 50 and a lower planar main wall 52.

  Of course, the main walls 50, 52 can have different shapes. In particular, the lower main wall 52 10 can be curved so as to best match the shape of the adult seat 24, in particular the shape of the adjacent face of its seating element 22.

  In accordance with the teachings of the invention, the support structure 18 comprises a support plate 54, here in the form of a disc, which is contained in a generally horizontal plane, and which is rotatably mounted on the base 48, by the intermediate of a vertical shaft 56.

  The support plate 54 has, on its upper face 58, two vertical longitudinal plates 60, 62. Each plate 20 60, 62 has, at its upper end, a support shoe 64, 66, forming a guide rail, which is provided to cooperate with an associated groove 44, 46 of the seat 12, so as to guide the seat 12 in tilting.

  According to the embodiment shown here, each shoe 25 64, 66 has the shape of a T-profile which is received in a complementary manner inside the associated groove 44, 46.

  Each shoe 64, 66 has a curved shape whose radius of curvature corresponds to the tilt axis AI.

  Advantageously, the arrangement 10 according to the invention 30 comprises retractable means for the angular blocking of the seat 12 in the circulation position Pc.

  The angular locking means here comprise a transverse rod 68 which is screwed through one of the support plates 66. An end section 70 of the rod 68 is received in a hole 72 which is produced in a blocking plate 74 carried by the lower face 42 of the seat element 38 of the child seat 12.

  The blocking plate 74 here has the form of an angular sector 5, contained in a generally longitudinal and vertical plane, and it comprises several holes 72, which makes it possible to choose the angular position of circulation Pc according to the choice of the hole 72 .

  To make the angular locking means 10 retractable, in the event of a frontal impact, the rod 68 comprises for example a primer of rupture.

  Of course, the angular locking means can be produced differently, without departing from the scope of the invention. In particular, it is possible to provide, in place of the rod 68 and the locking plate 74, notches in the grooves 44, 46 and a movable stop which is capable of cooperating with these notches to angularly block the seat 12.

  The stop can be controlled by a lever arranged at the base of the seat 12, for example between the child's feet 32.

  In accordance with the teachings of the invention, means are provided which, when the vehicle 16 is subjected to a frontal impact, that is to say a generally longitudinal impact directed towards the rear, cause, at the latest during the impact, tilting of the seat 12 around its axis AI, up to an angular position called frontal protection Pf.

  The frontal protection position Pf aims to allow the child 32 to withstand the significant acceleration due to the frontal impact, in particular by avoiding hyper-flexion of the neck, damaging to the cervical spine of the child 32, and by avoiding crushing the child's rib cage 32.

  According to the invention, the child 32 occupies a frontal protection position Pf when the orientation of its body axis AC is between a substantially horizontal position, in which the head 30 of the child 32 is essentially biased forward along its body axis AC, and a maximum inclined position, opposite to the initial position Pc, in which the head 30 of the child 32 is essentially biased forward against the bearing surface 28 of the backrest element 26 of the seat 12. According to the embodiment shown here, the arrangement according to the invention comprises means capable of producing a signal for detecting a frontal impact, and an actuation system which controls the tilting of the seat 12 towards its 10 frontal protection position Pf when it receives the frontal shock signal. Advantageously, the front impact detection signal is produced by a front impact sensor (not shown). One can use, for example, the sensor which is used to control the triggering of airbags on the dashboard of the vehicle 16. Such a type of sensor generally comprises multidirectional accelerometers which are arranged under the front adult seats of the vehicle 16. A front impact sensor dedicated to the child seat 20 12 can also be used.

  The actuation system here comprises a belt 76, a first end of which is connected to a reel 78 and a second end of which 80 is attached to the upper part of the backrest element 26.

  A return pulley 82 is here inserted between the second end 80 and the reel 78, in line with a window 84 which is arranged in the upper wall 50 of the base 48.

  The reel 78 is arranged inside the base 48 and is fitted with a pyrotechnic device 86 capable of pulling the belt 76 downwards by winding so as to propel the seat 12 towards its frontal protection position Pf, by causing it to tilt here counterclockwise.

  The tilting of the seat 12 is guided by the relative sliding of the pads 64, 66 in the grooves 44, 46.

  The pyrotechnic device 86 and the retractor 78 may be of the same type as those used as a seat belt "pretensioner". Thus, the tilting movement towards the frontal protection position Pf can be triggered, thanks in particular to the frontal impact sensor, even before the inertial forces come into play, as already exists for the pretensioning of seat belts.

  It is noted that the tilting movement can be initiated by an impulse transmitted by the pyrotechnic device 86, and then continue under the effect of the kinetic energy stored by the child seat assembly.

  Advantageously, according to the embodiment shown here, the arrangement 10 according to the invention is equipped with a system for protecting the child 32 in a side impact situation.

  Indeed, in a seat 12 according to the state of the art, although the head 30 of the child 32 seems to be well maintained laterally, we often deplore, in the event of a lateral impact, lesions of the cervical spine or even head trauma from the impact of the head 30 against the interior surfaces 20 of the passenger compartment 14 (side window or the like).

  This observation is explained by the fact that the so-called lateral shocks are rarely "pure" and that there are therefore anteroposterior components. A further explanation may be the effect of sudden braking before the side impact, which would have the effect of extracting the child's head 30 from its lateral supports, just before the side impact itself.

  To remedy this problem, the arrangement 10 according to the invention comprises means which, when the vehicle 16 is subjected to a generally transverse lateral impact, directed towards a side, cause pivoting, at the latest during the lateral impact of the seat 12 around a vertical geometric axis A2, generally by a quarter turn to the side, so that the seat 16 comes to occupy a position called lateral protection PI in which the bearing surface 28 of the element backrest 26 is oriented towards the side opposite the origin of the side impact.

  This is why the arrangement 10 according to the invention here comprises a support plate 54 which is rotatably mounted around the shaft 56, relative to the base 48.

  According to the invention, the child 32 occupies a lateral protection position PI when the head 30 of the child 32 is essentially biased transversely towards the impact against the bearing surface 28 of the backrest element 26 of the seat 12, that is to say that the seat 12 "turns back" at the origin of the side impact.

  According to the embodiment shown here, the arrangement according to the invention comprises means capable of producing a signal for detecting a side impact, and an actuation system which controls the pivoting of the seat 12 towards its protective position lateral PI when it receives the side impact signal. Advantageously, the side impact detection signal is produced by a side impact sensor (not shown), such as that which is used to control the triggering of 20 airbags, or curtain type airbags, in the vicinity of the passenger compartment side walls 14. The same sensor can be used to trigger the airbags and seat pivoting 12.

  According to the embodiment shown here, the shaft 56 extends inside the base 48, through its upper wall 50, and it has on its lower section a pulley 88 integral with rotation of the shaft 56.

  Two winders 90, 92 are arranged inside the base 48, respectively to the left and to the right of a longitudinal axis 30 passing through the shaft 56.

  A cable 94 is wound on the pulley 88 and it is connected to each reel 90, 92.

  Each reel 90, 92 comprises a pyrotechnic device 96, 98 which is capable of causing an abrupt winding of the cable 94 so as to cause the seat 12 to pivot on the side of the winding.

  Of course, when the cable 94 is wound on one of the reels 90, 92, the opposite reel 90, 92 is provided to allow the unwinding of the cable 94.

  According to an alternative embodiment (not shown) of the invention, the cable 94 can be replaced by a toothed belt which cooperates with complementary notches made on the pulley 88.

  The operation of the arrangement 10 according to the invention is as follows.

  The vehicle 16 travels forward and the seat 12 occupies its circulation position Pc (FIG. 3). The vehicle 16 undergoes a frontal impact, for example coming into abutment against a 1s obstacle located at the front of the vehicle 16.

  The frontal impact sensor then produces a frontal impact signal. The frontal impact signal is transmitted to the pyrotechnic device 86 which is triggered by exerting an abrupt pulling force on the belt 76, so that the belt 76 pulls the seat 12.

  Under the effect of the significant tensile force, the locking rod 68 retracts by breaking at the level of the primer, which releases the seat 12 in tilting.

  The traction exerted on the belt 76 therefore causes an abrupt tilting of the seat 12 around its axis AI.

  From its circulation position Pc, which is represented in FIG. 3, the seat 12 successively occupies an intermediate angular position Pi, which is represented in FIG. 4, in which the body axis AC of the child 32 is substantially longitudinal, then its final position of frontal protection Pf, which is represented in FIG. 5, in which the bodily axis AC of the child 32 is inclined relative to the longitudinal direction. Note that, when the seat 12 occupies the intermediate angular position Pi, which is shown in FIG. 4, the child 32 is protected against hyper-bending of the neck 36 since the body axis AC of the child 32 is substantially aligned with the longitudinal direction of the impact.

  In the angular positions of the seat 12 located between the intermediate position Pi and the final protective position Pf, the body axis AC is inclined relative to the longitudinal direction so that the head 30 is urged longitudinally forward, against the bearing surface 28 of the backrest element 26.

  When the seat 12 occupies its final frontal protection position Pf, the pads 64, 66 are located in the end section of the associated grooves 44, 46, on the side of the backrest element 15.

  Advantageously, each groove 44, 46 comprises, in its end section, a stop (not shown) which stops the tilting of the seat 12 when it reaches its final frontal protection position Pf during the frontal impact.

  It is preferable that the stops are not simply elastic, otherwise they would cause a "rebound" of the seat 12 against the stops. Each stop may be, for example, of the elastoplastic type, which allows it to dampen the movement of the seat 12 at the end of the stroke, by plastic deformation.

  Depending on the position chosen for the stops in the grooves 44, 46, it is therefore possible to choose beforehand the final position of frontal protection Pf. For example one can choose as final position of frontal protection Pf the intermediate position Pi of the figure 4.

  The final position of frontal protection Pf can in particular be chosen as a function of the space available in the passenger compartment 14 around the seat 12 and as a function of the size of the seat 12, when it occupies said position of frontal protection Pf.

  Advantageously, a damping device (not shown) slows down the seat 12 at the end of the tilting stroke towards its final position Pf. This damping device can for example include friction braking means which are arranged in each groove 44 , 46 and which cooperate with the guide shoes 64, 66.

  Throughout the duration of the frontal impact, the seat 12 is biased towards its final position of frontal protection Pf, so that the seat 12 retains its position of frontal protection Pf as long as it is necessary.

  At the end of the frontal impact, the seat 12 can either remain locked in its protective position Pf, or return to an intermediate position of equilibrium, which is a function of the position of the center of gravity of the seat-child assembly relative to to the support structure 15, tilting clockwise to its initial position of circulation Pc. It is noted that, when the vehicle 16 is subjected to a longitudinal impact

  directed forwards, called rear impact, therefore in the opposite direction to the frontal impact, it is not necessary to tilt the seat 12 since the child's head 30 is biased longitudinally rearward, against the surface support 28.

  The operation of the invention is now explained in the event of a side impact.

  The vehicle 16 travels forward and the seat 12 occupies its circulation position Pc (FIG. 3). The vehicle 16 undergoes a lateral impact oriented transversely towards the left side, for example when the vehicle is struck on its right side. The right side impact sensor then produces a right side impact signal oriented to the left.

  The side impact signal is transmitted to the left pyrotechnic device 96 which is triggered by causing the cable 94 to be wound on the left reel 90, so that the cable 94 pulls the support plate 54, therefore the seat 12, towards the left. During the winding of the cable 94 on the left winder 90, the right winder 92 releases the cable 94.

  The traction exerted on the cable 94 therefore causes an abrupt pivoting of the seat 12 around its shaft 56, up to 5 the lateral protection position Pl which is shown in FIG. 6, in which the seat 12 has pivoted by a quarter in turn, here to the left, around its vertical axis A2.

  Of course, depending on the direction of the side impact, indicated by the side impact signal, the seat 12 pivots to the left or 10 to the right, under the effect of the triggering of one or the other of the pyrotechnic devices 96 , 98 associated with the reels 90, 92.

  According to an alternative embodiment (not shown) of the invention, the seat 12 can tilt towards its frontal protection position Pf under the effect of its only inertial force and of the acceleration due to the frontal impact.

  To this end, the center of gravity of the assembly formed by the seat 12 and the child 32 is offset in a vertical longitudinal plane, relative to the tilting axis AI, so that in a frontal impact situation, the seat 12 switches to its position 20 of frontal protection Pf under the effect of the longitudinal acceleration due to the shock and under the effect of the moment of inertia of the assembly. The offset of the center of gravity of the child seat assembly can be increased by arranging a mass (not shown) in the seat 12.

  According to this embodiment, it is no longer necessary to provide pyrotechnic triggering means, nor a frontal impact sensor, the frontal impact being detected "automatically" by the presence of inertial forces, which apply to the seat 12 , and automatically causing the tilting to the frontal protection position Pf.

  According to another alternative embodiment (not shown) of the invention, other means for actuating the seat 12 to cause it to tilt or pivot can be provided. For example, the actuating means may comprise elastic means which are prestressed when the seat 12 occupies its circulation position Pc and which are released when a frontal or lateral impact is detected, and the connection by belt 76 and / or the cable connection 94 can be replaced by connections comprising at least one jack and possibly a link for returning the movement of the jack. The pivoting of the seat 12 around its vertical axis A2 can also be caused by a device, such as a piston, providing a 1o impulse to a stud secured to rotation of the support plate 54. Of course, the invention is applies symmetrically to the case where the mounting of the child seat 12 in the passenger compartment 14 is of the "rearward facing" type, that is to say that the bearing face 28 of the seat 12 is oriented towards the 'back.

  In this case, the situation equivalent to frontal impact is a rear impact situation, in which the head 30 of the child 32 undergoes a longitudinal acceleration directed towards the rear, which tends to move the head 30 away from the bearing surface. 28. The arrangement 20 according to the invention then uses a rear impact sensor which causes the seat 12 to tilt towards an angular position of rear impact which is substantially symmetrical to the angular position of front impact Pf, with respect to a plane vertical transverse. It is noted that, in the case of mounting the seat 12 "rearward facing", for a side impact, the seat 12 will have to pivot in the opposite direction around its vertical axis A2, relative to the direction of pivoting in the case of mounting "facing the road" described above.

Claims (10)

  1. Arrangement (10) for mounting a child seat (12) in the passenger compartment (14) of a motor vehicle (16) of the type comprising a fixed support structure (18) on which the seat 5 (12) is mounted so that it occupies a so-called circulation position (Pc): - in which its back element (26) extends generally vertically upwards, relative to the floor (20) of the vehicle (16 ), so as to include a bearing surface 10 (28), for the head (30) of the child (32), which is oriented towards the front, or towards the rear, considering the direction of circulation the vehicle (16) in forward; - And in which the body axis (AC) of the child (32), defined by the alignment of the bust (34) of the child (32) with his neck 15 (36), extends in a plane longitudinal and vertical and is oriented in an initial inclined position (Pc) relative to the vertical; characterized in that it comprises means (76, 78, 86) which, when the vehicle (16) is subjected to a generally longitudinal frontal impact directed towards the rear, respectively a rear impact directed towards the front, cause , at the latest during the impact, the tilting of the seat (12), generally around a geometric axis (Ai) substantially transverse and horizontal, to a position called front protection (Pf), rear protection respectively, in wherein the orientation 25 of the body axis (AC) of the child (32) is between a substantially horizontal position (Pi) in which the head (30) of the child (32) is essentially biased towards the forward, backward respectively, along its body axis (AC), and a maximum inclined position, opposite to the initial position (Pc), in which the head (30) of the child (32) is essentially biased towards front, rear respectively against the bearing surface (28) of the backrest element (26).   2. Arrangement (10) according to the preceding claim, characterized in that it comprises means capable of producing a signal for detecting a frontal impact, respectively of a rear impact, and actuating means (76, 78 , 86) which control the tilting of the seat (12) to its front protection position (Pf), respectively rear protection, 5 when they receive the front impact signal, respectively rear impact.   3. Arrangement (10) according to claim 1, characterized in that the center of gravity of the assembly formed by the seat (12) and the child (32) is offset in a vertical longitudinal plane, 10 relative to the tilt axis (AI) so that, in the event of a frontal impact or a rear impact respectively, the seat (12) switches to its front protection position (Pf), respectively rear protection, under the effect of the longitudinal acceleration due to shock and under the effect of the moment of inertia of the assembly, and in that the seat (12) comprises means (68, 74) of angular retention in the circulation position (Pc) which are likely to retract in the event of a frontal impact or rear impact respectively.   4. Arrangement (10) according to any one of the preceding claims, characterized in that it comprises means (56, 88, 90, 92, 94, 96, 98) which, when the vehicle (12) is subjected to a generally transverse lateral impact, directed towards a side, cause, at the latest during the lateral impact, the pivoting of the seat (12), generally around a geometric axis (A2) substantially vertical, generally by a quarter of turn to the side, so that the seat (12) comes to occupy a position called lateral protection (PI) in which the bearing surface (28) of the backrest element (26) is oriented towards the side.   5. Arrangement (10) according to the preceding claim, characterized in that it comprises means capable of producing a signal for detecting a side impact, and actuating means (90, 92, 94, 96, 98) which control the pivoting of the seat (12) to its lateral protection position (Pl) when they receive the side impact signal.   6. Arrangement (10) according to claim 2 or 5, characterized in that the actuating means (76, 78, 86, 90, 5 92, 94, 96, 98) comprise pyrotechnic means (86, 96, 98 ) which propel the seat (12) towards its frontal protection position (Pf), respectively rear protection, or its lateral protection position (PI), when a signal of frontal impact, respectively of rear impact, respectively a signal of side impact, is produced.   7. Arrangement (10) according to claim 2 or 5, characterized in that it comprises elastic means which are prestressed when the seat (12) occupies its circulation position (Pc), and in that the actuating means 15 control the release of the elastic means which propel the seat (12) towards its frontal protection position (Pf), rear protection respectively, or its lateral protection position (Pl), when a frontal shock signal, respectively shock rear, respectively a side impact signal, is produced.   8. Arrangement (10) according to any one of the preceding claims, characterized in that it comprises a damping device which stops the tilting, or the pivoting, of the seat (12) when it reaches its protective position. frontal (Pf), respectively rear protection, respectively its lateral protection position (PI), during the frontal impact, respectively the rear impact, respectively during the lateral impact. 9. Arrangement (10) according to the preceding claim, characterized in that the damping device comprises friction braking means.   10. Arrangement (10) according to any one of the preceding claims, characterized in that the seat (12) is slidably mounted on at least one guide rail (64, 66) of radius of curvature determined in a vertical longitudinal plane, so as to be guided in tilting.   He. Arrangement (10) according to any one of the preceding claims, characterized in that it comprises means for adjusting (68, 74) the angular position of circulation (Pc) of the seat (12) relative to the axis tilting (AI), and in that these adjustment means (68, 74) are capable of being retracted in a frontal impact situation, respectively rear impact. 12. Arrangement (10) according to any one of the preceding claims, characterized in that the support structure (18) is designed to be fixed on a seat (24) of the vehicle (16) by means of a device Isofix type fastening system and / or by means of seat belts.