Abstract:
Seat back rapidly deflates on occurrence of a rear end impact to permit upper torso of vehicle occupant to sink into the seat rather than be propelled forward. This permits his head to meet the headrest. Particulate material in headrest absorbs energy.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is related to the provisional application Ser. No. 60/093,799 filed Jul. 23, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a vehicle safety seat assembly. More specifically, the invention relates to such an assembly having means to prevent whiplash injuries. 
     BACKGROUND OF THE INVENTION 
     A significant number of auto accidents involve one vehicle colliding into the rear of another at relatively low velocities. The passengers in the rear car are subjected to the sudden deceleration resulting from a front end collision, and are protected by belts, bags, and compliant steering wheels. On the other hand, the impacted vehicle is accelerated forward, subjecting the passengers to impact forces to their backs and heads. In this collision mode, the seat back and headrest are supposed to restrain the passenger and absorb the impact energy. 
     An objective of the invention is to prevent relative horizontal motion between the passenger&#39;s upper body and head during the collision process. 
     A further objective is to absorb the energy of impact between the head and the headrest by means of entropic heat generation. 
     SUMMARY OF THE INVENTION 
     The invention is a vehicle safety seat assembly comprising a seat portion, a backrest portion and a headrest portion, the backrest including a frame secured to the seat portion and having an upper portion defined by a cover portion adapted to be engaged by the shoulders and upper torso of a vehicle occupant and a pressurized bladder or bag disposed between the frame and the cover portion and supporting the occupant away from the frame to a given level. The headrest is secured to the frame and positioned above the backrest, the headrest having a cover adapted to be engaged by the head of an occupant, the cover being at a level away from the frame less far toward the occupant than the cover of the backrest so that the head of the occupant is normally spaced from the headrest. The invention also comprises a rear end collision detecting means, and means activated by the detecting means for promptly evacuating the pressure in the bag. 
     The evacuation reduces the level of the backrest to the same level as the cover of the headrest to avoid injury to the neck of the occupant. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further objects and features of the invention will be clear to those skilled in the art from a review of the following specification and drawings, all of which present a non-limiting form of the invention. In the drawings: 
     FIG. 1 is a side elevation showing schematically the rider sitting in a conventional vehicle seat; 
     FIG. 2 is a side elevation showing the rider&#39;s head thrown back against the headrest in a rear end collision in a conventional vehicle seat; 
     FIG. 3 is a side elevation showing the rider sitting on a seat embodying the invention; 
     FIG. 4 is a side elevation showing the seat upon deflation at an instant after collision; 
     FIG. 5 is a side elevation showing the rider&#39;s back and head sinking back against the deflated seat. 
     FIG. 6 is an exploded perspective view showing the structure of a seat back embodying the invention; 
     FIG. 7 is a front elevation of a seat back embodying the invention and showing the deflating wire in phantom; 
     FIGS. 8 a ,  8   b  and  8   c  are sectional views taken on the line  8 — 8  of FIG. 7 as the seat back progressively deflates; and 
     FIGS. 9 a  and  9   b  are schematic views comparing the bounce of an object having the approximate size and weight of a human head onto foam rubber or buckwheat husks respectively. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of a vehicle seat embodying the invention is shown in FIG.  3  and generally designated  10  and comprises a seat back  12  and headrest  14 . 
     As shown in FIG. 6, the seat back comprises metal supporting frame  20 . Supported by the frame is an air bladder  22  having separate cells  24  defined by transverse walls  26 . The proposed air bladder, or bag, thus has an interconnected cellular construction so that it can be inflated after insertion into the seat back, and has cell walls  26  that connect the front to the back in order to retain its shape. Preferably, the bladder is tapered having greater thickness at the top, approximately  3 ″, than at the bottom (FIG.  6 ). 
     A number of means for suddenly deflating the bladder are envisioned. One involves a nichrome heating wire  28  which is attached to the rear side of the bladder so that it passes through all the individual cells. This is shown schematically in FIG. 7. A suitable “g” trigger switch  30  containing a time fuse (not shown) is connected in series with the wire to a power source. Upon an impact above some pre-determined “g” threshold, the switch closes, causing a current to flow through the fuse and wire, bringing the wire to a white heat in milliseconds. This melts slits into the cells, releasing the trapped air. The fuse melts slightly later, opening the circuit. 
     As shown in FIG. 6, the seat assembly also comprises a thin layer of batting  40  and suitable upholstery covering  42 . 
     The headrest  14  consists of an upholstery fabric cover, a metal frame, and is filled with particulate. More specifically, the headrest is filled with particulate such as buckwheat husks or irregular plastic particles. FIGS. 9 a  and  9   b  demonstrate the difference in the bounce of an object when landing on a sack filled with buckwheat husks as opposed to foam rubber as is often used for headrests. In some cases it is necessary to create compartments within the structure to prevent the particulate from sagging towards the bottom. 
     In any case, upon impact by the head after the backrest reduces, the headrest deforms into the shape of the back and partial sides of the passenger&#39;s head, and in so doing, the particulate has to shear, generating heat due to friction. This heat represents dynamic energy converted into entropic thermal energy. Depending on the design, it may be possible to reuse the headrest without any service. 
     It is important to understand that the air bladder in the seat back and the particulate in the headrest work in concert to prevent arching of the neck and rebound of the head. If the gap (FIG. 1) between the head and the headrest is normally 2″, the bladder should deflate to a higher value, perhaps 3″. This difference allows the head to deform the headrest 1″ before the upper body bottoms out on the deflated seat back. The head may continue to further deform the headrest, but the difference will bend the neck to a much smaller degree when compared to many back and seat rests in use today. 
     A variation of the backrest structure of FIG. 6 involves filling alternate cells with particulate (FIG. 7) similar to that suggested for the headrest. Upon triggering, the air cells comprising the bladder will collapse, allowing the particulate-filled cells to flatten, thus absorbing some of the upper body impact energy. There are many other schemes that could accomplish the same result, i.e., allowing the backrest to collapse rapidly and yet provide some energy absorption when the upper body bottoms out. 
     In another embodiment, the headrest itself contains an air bladder. The bladder can be suddenly deflated upon engagement of the head with the headrest, after deflation of the backrest. 
     The seat back can be so designed to allow the bladder and associated trigger system to be readily replaced, or the entire back can be replaced. 
     While this invention has been disclosed in limited embodiments, it is not so limited but is of a scope defined by the following claim language which may be broadened by an extension of the right to exclude others from making, using or selling the invention as is appropriate under the doctrine of equivalents.