A VEHICLE SEAT

Abstract: A vehicle seat (1) comprises a squab (2) and a back (4) which is mounted for pivotal movement relative to the squab. The seat incorporates energy absorbing force limiting means (11) adapted to absorb energy as the back of the seat moves rearwardly when subjected to a force from the torso of an occupant of the seat, for example, during a rear impact. The energy absorbing force limiting means (11) provides a first resistive force resisting the pivotal movement during a first predetermined pivotal movement, and a second resistive force during a second subsequent pivotal movement. The resistive force provided during the first pivotal movement is dependent upon the energy of the rear impact. If the rear impact is a low energy rear impact, the resistive force is relatively low whereas if the rear impact is a high energy rear impact, the resistive force is relatively high.

Description: A VEHICLE SEAT THE PRESENT INVENTION relates to a vehicle seat and more particularly, relates to a vehicle seat intended for use in a motor vehicle such as a motor car. It has been appreciated that if a motor vehicle, such as a motor car, is involved in a rear-end collision or rear impact - that is to say if a following vehicle runs into the back of the car - the occupants of the struck car often suffer from neck injuries. It is to be understood that during a rear-end collision of this type, the vehicle that is struck is subjected to a forward acceleration. This imparts a forward acceleration to the seats of the vehicle. The squab and the back of each occupied seat engage the posterior and torso of the occupant of the seat and impart a substantial acceleration to the posterior and torso of the occupant. However, no corresponding acceleration is immediately imparted to the head of the occupant. The head is a part of the body that has substantial mass, and consequently the head has substantial inertia. Thus, whilst the posterior and torso of the occupant of the vehicle are accelerated forwardly as a result of the rear-end collision, the head of the occupant of the vehicle initially remains stationary. This causes the neck initially to adopt a "S"-shaped configuration as the lower part of the neck moves forwardly, whilst "S"-shaped configuration as the lower part of the neck moves forwardly, whilst remaining vertical, and the upper part of the neck remains in its initial position. Subsequently, the head begins to rotate, and the neck then occupies a curved configuration. The head subsequently moves forwardly. Research has shown that "whiplash" injuries may occur when the neck adopts the "S"-shaped configuration, if the head is moving, relative to the torso, at a substantial speed. The present invention seeks to provide an improved vehicle seat in which the risk of "whiplash" injuries occurring to the occupant of the seat during a rear-end collision are reduced. According to this invention there is provided a vehicle seat, the seat comprising a squab and a back, the back being mounted for pivotal movement relative to the squab of the seat incorporating energy absorbing force limiting means adapted to absorb energy as the back of the seat moves rearwardly when subjected to a force from the torso of an occupant of the seat, if a vehicle in which the seat is mounted is involved in a rear impact, the energy absorbing force limiting means providing a first resistive force resisting the pivotal movement during a first predetermined pivotal movement, and second resistive force during a second subsequent pivotal movement, the resistive force provided during the first pivotal movement being dependent upon the energy of the rear impact. Preferably the energy absorbing force limiting mean comprise elements to provide the first resistive force comprising an energy absorbing force limiting device and a damped spring. Conveniently the energy absorbing force limiting device and the damped spring are connected in series between the back of the seat and an element mounted on the squab of the seat. Advantageously the damped spring comprises a spring connected in parallel with a fluid-filled cylinder containing a double acting piston, the opposed ends of the cylinder being inter-connected by a parallel connection of a non-return valve and a constriction. Preferably the energy absorbing force limiting means comprise a framework present within the back of the set adapted to deform when subjected to a predetermined force. Advantageously the energy absorbing force limiting means comprise an energy absorbing force limiting device adapted to provide said second resistive force during the second subsequent pivotal movement. Conveniently the back of the seat is mounted for pivotal movement between predetermined limits relative to a support, the support being pivotally mounted to the squab of the seat, the said energy absorbing force limiting device providing the second resistive force during the second subsequent pivotal movement being adapted to provide the resistive support on pivotal movement of said support. In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings in which: FIGURE 1 is a diagrammatic view comprising four illustrations showing the condition of head and neck of an occupant of a vehicle in rear collision situation where a conventional seat is used, FIGURE 2 is a diagrammatic view of a seat in accordance with the invention, FIGURE 3 is an enlarged view of part of the seat of Figure 2, FIGURE 4 is a graphical figure provided for purposes of explanation, FIGURE 5 is a view of an energy absorbing force limiter , and FIGURE 6 is a view of an alternative energy absorbing force limiter. Referring initially to Figure 1 of the accompanying drawings, illustration A shows the position of the head 1 and neck 2 of the occupant of a motor vehicle during ordinary conditions. The head and neck would occupy this position if, for example, the vehicle were stationary. Assuming that the vehicle was then subjected to a rear impact, the posterior and torso of the occupant of the vehicle would be moved forwardly, as a consequence of the forward movement of the vehicle and the forward movement of the seat mounted in the vehicle. The head 1 of the occupant would tend to remain stationary. A neck 2 of the occupant would then have the condition shown in illustration B. The neck here has a "S" configuration. Subsequently, as shown in illustration C, the head 1 moves rearwardly, thus giving the neck 2 an arcuate configuration and, if the head does not impinge on the head-rest, the head can move to the tilted back position shown in illustration D where the neck 2 is bent back (hyperextension) with a very significant degree of curvature. It is believed that if the neck is subject to the distortions shown in illustrations A to D, the hydro-dynamic pressure of the fluid within the spine can rise suddenly, when the neck adopts the "S"-shaped configuration, thus imparting pressure shocks to parts of the central nervous system in contact with that fluid. Also, injuries may well be imparted to the ganglia. It is believed that this is why patients with so-called "whiplash" injuries may suffer from the effects of those injuries for a long time. Even though a typical rear impact collision occurs with a relatively low impact speed, these colhsions are responsible for a large number of relatively serious injuries each year. Whilst it has been proposed previously to provide a seat having a seat back which moves rearwardly, against a retarding force, in the event that a rear impact should occur, such prior proposals have not differentiated between a low speed or low intensity rear impact, and a high speed or high intensity rear impact. Referring to Figure 2 of the accompanying drawings, a seat 1 for use in a vehicle such as a motor car is illustrated. The seat 1 comprises a squab 2 adapted to be secured to the floor 3 of the motor vehicle. The squab 2 may be secured to the floor 3 by means of a carriage slideable along rails mounted in the floor. The seat 1 is provided with a back 4, the back 4 carrying a head-rest 5. The back 4 incorporates a frame, one are 6 of which is visible in Figure 1. The arm 6 is pivotally connected by means of a pivot 7 to a support plate 8 which is secured to the squab of the seat. The frame member 6 can pivot about the pivot 7 between a forward-most position as illustrated in Figure 2 in which the frame element contacts a stop 9, and a rear-most position when the frame element contacts a stop 10. A force limiter assembly 11, which will be described hereinafter in greater detail, is connected between the frame element 6 and the support plate 8. The support plate 8 is actually connected to the squab of the seat by means of a pivotal connection 12. The support plate 8 can thus effect a pivotal motion about the axis defined by the pivotal connection 12. The support plate 8 is associated with an energy absorbing force limiting device 13 connected between the support plate 8 and the squab 2 of the seat. Thus, if the combination of the seat back 4 and the support plate 8 pivot about the pivot axis 12, the energy absorbing force limiting device 13 resists the movement, absorbing energy. Referring now to Figure 3, the force limiter assembly 11 is illustrated in greater detail. The force limiter assembly 11 is connected, by appropriate connection means 14 to the support plate 8 and is also connected, by appropriate connection means 15 to the frame member 6 forming part of the back 4 of the seat. The force limiter assembly 11 comprises a series connection of an energy absorbing force limiting device 16, and a damped spring 17. The damped spring comprises the combination of a spring 18 connected in parallel with a fluid-filled cylinder 19 containing a double acting piston 20, the opposed ends of the cylinder being connected by the parallel connection of a non-return valve 21 and a constriction 22. If a seat as illustrated, and described with reference to Figures 2 and 3 is in a vehicle which is subjected to a low speed or low energy rear impact, the squab of the seat will be accelerated forwardly whilst the torso of an occupant of the seat will tend to remain stationary due to inertia. The back 4 of the seat will thus be brought into contact with the torso of the occupant of the seat, and will start to accelerate the torso of the occupant of the seat. Effectively, the torso of the occupant of the seat will apply a rearwardly directed force to the back of the seat causing, initially, the back 4 of the seat to pivot about the pivot 7. The back of the seat thus executes a first pivotal movement. Because the force is a relatively low force, the piston 20 moved to the right within cylinder 19 as shown in Figure 3, against a resisting bias provided by spring 18 causing fluid present within the cylinder to flow through the constriction 22. The resisting force is thus a relatively low substantially constant resistive force as the back of the seat moves rearwardly, as illustrated by the solid line 23 in Figure 4, which is a graphical figure showing resistive force plotted against the distance of pivotal movement of the back 4 of the seat. The resistivity force is a combination of the force provided by the spring and the effect of fluid flowing through the constriction 22. When the frame member 6 has pivoted about the pivot 7 to such an extent that the frame member 6 engages the stop 10, (shown as point S on the axis of the graph of Figure 4) if the force applied to the back of the seat is sufficient, the back of the seat executes a second pivot movement during which the support plate 8 pivots about the pivot axis 12, and energy is absorbed by energy absorbing force limiting device 13, as shown in the solid line 24 in Figure 4. It is to be understood that following the impact, the spring 18 will contract, thus moving the piston 20 towards the left within the cylinder 19. The fluid within the cylinder may easily flow through the non-return valve 21 to facilitate this movement of the piston. Thus, if the vehicle is involved in a mild rear impact, only the spring loaded damper unit 15 will operate, and, if the impact is great enough, the energy absorbing force limiting device 13 will also operate. If, in contrast, the vehicle is involved in a high speed, high energy rear impact, a very substantial acceleration will be imparted to the squab 2 of the seat, and to the back 4 of the seat. The torso of the occupant, because of its inertia, will impart a substantial force against the back 4 of the seat. The force will tend to move the piston 20 very rapidly towards the right within the cylinder as shown in Figure 3. This will tend to cause fluid to flow very swiftly through the constriction 22. The constriction 22 will prevent the flow of fluid and consequently the spring biased damped unit 17 will become substantially rigid. The energy absorbing force limiter 16 will consequently extend, absorbing a substantial amount of energy, and thus providing a very substantial force limiting effect as the frame element 6 of the seat back moves pivotally about the pivot 7 to engage the stop 10. When the stop 10 has been engaged, the support plate 8 will pivot about the pivot axis 12. During this pivoting movement energy will be absorbed by the energy absorbing force limiter 13. The resisting force will thus be high during the first pivotal movement as the frame member 6 moves from stop 9 to stop 10, because the energy absorbing force limiter 16 is operating. This is shown as the dashed line 23 in Figure 4. Should the vehicle be involved in an intermediate energy and intermediate speed rear impact, the force limiter 11 assembly may operate so that during the movement of the frame element 6 between the stop 9 and the stop 10, part of the energy is absorbed by the force limiter 14 and pare of the energy is absorbed by the gas spring unit 15. This is shown by the dotted line 27 in Figure 4. It is to be appreciated that, in a vehicle seat as described above, the reaction of the seat to a rear impact depends upon the energy of the rear impact. In a low energy rear impact, the torso of the occupant is effectively accelerated very gradually by the back of the seat, thus minimising the risk of injury to the torso. However, in a high energy or high speed rear impact, it is not practicable to accelerate the torso of the occupant with only a relatively low acceleration, by permitting the back of the seat to move rearwardly in an appropriate manner, since there would be a grave risk that the back of the seat would be substantially horizontal before the occupant of the seat had been given a sufficient acceleration. This would be clearly disadvantageous since if the back of the seat did approach the horizontal condition, the occupant of the seat would tend to slide rearwardly out of the seat, due to inertia, with a very grave risk of severe injuries occurring. Thus, in the seat of the present invention, if the vehicle in which the seat is mounted is subjected to a high energy rear impact, the seat responds by giving the torso of the occupant a relatively high acceleration whilst still minimising that acceleration as much as practicable. In an intermediate situation, the seat provides an intermediate response. It is to be appreciated that in the described embodiments of the invention the back of the seat effects the two movements, the first movement being a pivotal movement about the pivot point 7 and the second movement being a pivotal movement about the pivotal connection 12, with both movements being against appropriate force limiting means. It is to be understood that the second movement could, instead of being moved about a pivot such as the pivotal connection 12, comprise a deformation of the frame forming the back of the seat. It is also to be understood that whilst in the described embodiment there are two pivotal movements about two pivot axes, the two pivotal movements could be about a single pivot axis. In Figures 2 and 3, energy absorbing force limiters have been illustrated in a totally schematic way. Different types of energy absorbing force limiters could be utilised. Figure 5 illustrates one type of force limiter that can be used, comprising a cylinder 40 formed of an appropriate material which defines an outlet orifice 41. A piston 42 is present within the cylinder. The space between the piston and the outlet orifice 41 is filled with a deformable material. The deformable material may comprise lead or a plastic material. The cylinder 40 is fixed in position and the piston 42 is connected to the movable element. Thus, for example, the cylinder 40 may be connected to the outer frame, with the piston 42 being connected to the inner frame. Alternatively, the cylinder 40 may be connected to the side piece 18, with the piston 42 being connected to the side element 14 of the main frame. The arrangement is such that as the movable element moves, this piston 42 is driven into the cylinder 40, thus ejecting the material 43 that is initially inside the cylinder through the outlet orifice 41. This provides a force limiting effect. An alternative form of force limiter is shown in Figure 6. A plate 45 is provided which supports two upwardly extending posts 46,47. A metal strip 48 is located to substantially surround one post 47, then to pass through the gap between the post 47 and 46, subsequently lying adjacent another part of the strip 48. If the free end 48 of the strip is pulled, the metal strip will shde through the posts 46 and 47, with the metal strip being deformed. This will absorb energy.

Claims: CLAIMS: 1. A vehicle seat, the seat comprising a squab and a back, the back being mounted for pivotal movement relative to the squab of the seat incorporating energy absorbing force limiting means adapted to absorb energy as the back of the seat moves rearwardly when subjected to a force from the torso of an occupant of the seat, if a vehicle in which the seat is mounted is involved in a rear impact, the energy absorbing force limiting means providing a first resistive force resisting the pivotal movement during a first predetermined pivotal movement, and second resistive force during a second subsequent pivotal movement, the resistive force provided during the first pivotal movement being dependent upon the energy of the rear impact. 2. A vehicle seat according to Claim 1 wherein the energy absorbing force limiting mean comprise elements to provide the first resistive force comprising an energy absorbing force limiting device and a damped spring. 3. A vehicle seat according to Claim 2 wherein the energy absorbing force limiting device and the damped spring are connected in series between the back of the seat and an element mounted on the squab of the seat. 4. A vehicle seat according to Claim 2 or 3 wherein the damped spring comprises a spring connected in parallel with a fluid-filled cylinder containing a double acting piston, the opposed ends of the cylinder being inter-connected by a parallel connection of a non-return valve and a constriction. 5. A seat according to any one of the preceding Claims wherein the energy absorbing force limiting means comprise a framework present within the back of the seat adapted to deform when subjected to a predetermined force. 6. A vehicle seat according to any one of Claims 1 to 4 wherein the energy absorbing force limiting means comprise an energy absorbing force limiting device adapted to provide said second resistive force during the second subsequent pivotal movement. 7. A vehicle seat according to Claim 6 wherein the back of the seat is mounted for pivotal movement between predetermined limits relative to a support, the support being pivotally mounted to the squab of the seat, the said energy absorbing force limiting device providing the second resistive force during the second subsequent pivotal movement being adapted to provide the resistive support on pivotal movement of said support.

Inventors: BOSTROEM OLA, HAALAND YNGVE, BOSTROEM, OLA, HAALAND, YNGVE
Applicants: AUTOLIV DEV, BOSTROEM OLA, HAALAND YNGVE, AUTOLIV DEVELOPMENT AB, BOSTROEM, OLA, HAALAND, YNGVE
Application year: 1998
Main classification: B60N2
IPC codes: B60N2