Vehicle seat adapted to protect occupant from injury in rear end collision

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.

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'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.

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.
 9a and 9b 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'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.