Reduced head path seat

Abstract: A seat assembly for commercial aircraft or other vehicles has features that reduce head excursion in high impact events such as crashes or collisions. These include the use of low-elongation seatbelt material and high seatbelt anchor location. Another feature which reduces head excursion is an articulating seatpan. The bottom seat cushion (24) is guided by rollers (26,27) in tracks (28) to follow a prescribed motion under forward inertial load. As the inertial load is applied, the seatpan travels forward and tilts upward. This reduces forward pelvic rotation which, in turn, reduces head excursion. Other features which limit pelvic rotation are the use of dynamically stiff foam for the seat cushion, and a relatively steep initial cushion angle/cushion contour.

Description: The present invention relate to seat assemblies and restraint systems for passengers in moving vehicles such as commercial airplanes. Reduction of head injuries to commercial aircraft passengers in the event of an emergency is of great concern for obvious safety reasons, and also is the goal of certain Government regulations. In commercial aircraft, the seats immediately behind the bulkhead are of special concern because of the possibility of a passenger's head striking the bulkhead in a high impact event such as a crash or emergency landing. While the chance of head injury for occupants of these seats could be reduced by increasing the distance between the seat and bulkhead, this would also significantly reduce floor space available for seating and therefore have a significant adverse impact on revenue in commercial aircraft. What is needed is a seating and restraint system which reliably reduces head excursion (i.e., the forward distance traversed by an occupant's head during a high impact event) so as to prevent or minimize the chance for head impact on the bulkhead. This would have the same beneficial effect in reducing head injuries as would increasing the distance between the seat and bulkhead, without the loss of seating space. Such a reduced head path seat should ideally have little impact on aircraft interiors, cause no reduction in seating density, and preferably involve passive technology needing no triggering devices. The features which contribute to reduction of head excursion should be imperceptible to the passenger during normal operation, so as not to affect his or her comfort. FR-A-2 419 079 describes a seat assembly comprising a frame to be mounted to a substantially horizontal floor, a seat back mounted to said frame, a seatpan pivotally mounted to said frame and provided with a seat cushion thereon, a lap type seat belt for passing over the pelvis of the occupant of the seat assembly, and means for allowing the seatpan to move forward and tilt upwards in an impact event. In this know seat assembly the seat back and seatpan are pivoted in an impact event, while a seatbelt anchor is moved downwardly to tighten the seatbelt. During a high impact event, such as a crash or collision, head excursion could lead to head injuries. It is an object of the present invention to reduce head excursion. The present invention provides a seat assembly comprising: a frame to be mounted to a substantially horizontal floor, a seat back mounted to said frame, a seatpan pivotally mounted to said frame and provided with a bottom seat cushion thereon; a lap type seat belt; and means for allowing the seatpan to move forward and tilt upwards in an impact event, characterized in that the front surface of the seat back extends to a point (SRP) where it meets the upper surface of the bottom seat cushion, said seat back being fixedly mounted to said frame, in that said means include a seatpan articulation mechanism for allowing the seatpan to move relative to said fixed seat back, in that a seat belt anchor for anchoring said seat belt is fixedly mounted to said frame at a level above said meeting point (SRP), and in that said seat belt is configured so as to be wearable by the seat occupant in a position where said seat belt restrains forward rotation of the occupant's pelvis. In EP-A-0 323 758 also both the seatpan and the seat back are moved, while no indication of a seatbelt anchor is shown. According to the present invention the seat belt anchor point is positioned to allow the belt to be worn in a position where it exerts a relatively large horizontal force on the pelvis. The seat belt is configured so as to be wearable by an occupant in the position where said seatbelt tends to restrain forward rotation of the pelvis, contrary to seatbelts of prior art seats, wherein a relatively large downward force on the pelvis is exerted. Further the present invention provides a seat, especially suited for a seat assembly as defined above, comprising: a frame to be mounted to a substantially horizontal floor, a seat back mounted to said frame, a seatpan pivotally mounted to said frame and provided with a bottom seat cushion thereon; an anchor for mounting a lap type seat; means for allowing the seatpan to move forward and tilt upward in an impact event, wherein the front surface of the seat back extends to a point where it meets the upper surface of the bottom seat cushion, said seat back being fixedly mounted to said frame, wherein said means include a seat pan articulation mechanism, for allowing the seatpan to move relative to said fixed seat back, wherein said seat belt anchor is fixedly mounted to said frame at a level above said meeting point, and wherein said seat belt is mounted so as to be wearable in a position where it restrains forward rotation of the pelvis. Brief Description of the Drawings Figure 1 is a side view of a passenger in a vehicle seat with arrows to indicate the path of travel of the head. Figure 2 is a side view of a passenger in a prior art vehicle seat in a vehicle which is undergoing a frontal impact. Figure 3 is a side view of a passenger in a vehicle seat according to a preferred embodiment of the invention in a vehicle which is undergoing a frontal impact. Figures 4a and 4b schematically show the action of seat belt restraining forces and impact forces on the pelvis of an occupant of a prior art seat. Figures 5a and 5b schematically show the action of seat belt restraining forces and impact forces on the pelvis of an occupant of a seat according to a preferred embodiment of the invention. Figure 6 illustrates the seatpan structure of a preferred embodiment of the invention. Figure 7 illustrates the frame and seatpan mounting structure of a preferred embodiment of the invention. Figure 8 illustrates the seatpan of Figure 6 mounted on the frame of Figure 7. Figure 9 is a side view of a seat with an X-Z coordinate system superimposed thereon to show the location of various points on a seat assembly according to a preferred embodiment. Detailed Description of the Preferred Embodiments Resisting forward rotation of the pelvis is key to reducing head excursion. When a seated person leans forward, the pelvis tends to rotate with the upper body. Pelvic rotation in this direction is hereinafter referred to as forward pelvic rotation. As shown in Figures 1 and 2, the upper body of a seated person 1 subjected to an inertial load like that experienced in a high impact event in a conventional aircraft seat 2 with a conventional lap belt 3 rotates primarily about the upper femur/pelvic joint 4, with a great deal of forward pelvic rotation. The path of travel of the top of the head 6 is shown in Figure 1 by arrow A, which describes a circle of radius R 1. Referring to Figures 1 and 3, if the pelvis 16 is restrained from rotating forward, the upper body rotates forward primarily by spinal flexure, rotating about a point 8 (shown in Figure 1) in the lower abdomen. The head excursion path in this case is shown in Figure 1 by arrow B which describes a circle of radius R 2. Head excursion is reduced because the distance from this point 8 in the lower abdomen to the top of the head 6 is less than the distance from the femur/pelvic joint 4 to the top of the head 6, so the radius R 2 of the resulting head path B is consequently shorter than radius R 1 of head path A. Figure 2 shows the overall operation of a conventional, prior art seat 2, while Figure 3 shows the operation of a reduced head path seat 7 according to a preferred embodiment of the present invention. Several features of the preferred embodiment work to resist forward pelvic rotation, and thereby reduce head excursion. A first feature which limits pelvic rotation is a high seatbelt anchor location. Figures 4a, 4b, 5a, and 5b show the effect of seatbelt mounting location. Figure 4a shows conventional prior art placement of the seatbelt relative to the pelvis 16 before impact. The angle α between the seatbelt and the horizontal when the seatbelt is secured around the seat occupant in conventional seats is usually recommended to be about 45° to 55°, although in practice, angles of around 70° are not uncommon. Figure 5a shows the angle of seatbelt placement in the preferred embodiment. This angle β is preferably in the range of 10° to 20°, with an angle of 15° being preferable. Figure 3 illustrates a seatbelt 18 mounted in this high anchor position. The mounting point is above the plane where the seatpan and seat back meet, and preferably is on that part of the seat frame which supports the seat back. A comparison of Figures 2 and 3 will show how this positioning of the seatbelt anchor 20 at a higher point, so that the belt forms a shallower angle with the horizontal, restrains forward rotation of the pelvis. As shown in Figures 4b and 5b, in an impact situation, the direction of action of the conventionally mounted seatbelt, indicated by arrow 10, has only a small component opposing the direction of force of impact, indicated by arrow 12, as compared to the direction of action of the high-mounted seatbelt of the preferred embodiment, indicated by arrow 14. The high mounted seatbelt applies a strong rearward moment on the pelvis 16, as indicated by arrow 15. The seatbelt line of action 14 is more directly opposite the inertial load imposed on the occupant. Also, the seatbelt forces are applied higher on the pelvis 16 and the seatbelt anchor position is preferably chosen so as to have the belt maximally apply a moment resisting forward pelvic rotation. The seatbelt material is preferably a material characterized by low elongation when loaded, such as polyester, rather than nylon as has been customary on commercial aircraft. When nylon webbing is loaded to 2500 pounds, the elongation is typically 15%-20%. Polyester webbing is stiffer, elongating about half as much when equally loaded. With less stretch, the occupant does not slip as far forward in the seat, and head excursion is thereby further reduced. Another feature which reduces pelvic rotation is an articulating seatpan. As shown in Figure 3, the front of the seatpan 22 of a preferred embodiment pivots upward while the seatpan moves slightly forward in an impact event. Referring to Figures 6, 7 and 8, the seatpan 22, which holds the bottom seat cushion 24, is guided by rollers 26, 27 in tracks 28 on the rear of the seat frame 23 and up ramps 29 on the front of the seat frame 23 to follow a prescribed motion under forward inertial load. As the inertial load is applied, the seatpan 22 travels forward and tilts upward. The forward travel resists forward pelvic rotation by reducing or reversing the direction of the frictional force the seatpan applies to the thighs and buttocks, while the upwards tilt of the seatpan 22 imparts a rearward rotation to the upper legs to further resist forward pelvic rotation. The upward tilting of the seatpan 22 also keeps the lower body planted in the cushion 24, directly opposing the forward motion of the occupant 1. The trajectory of the seatpan 22 will be determined by the length and angles of the tracks 28 and ramps 29. In choosing these dimensions, those skilled in the art will appreciate that a steep trajectory rotates more for a given forward seatpan displacement than a shallow trajectory. The trajectory is chosen so as not to be too steep (in which case the seatpan will not rotate at all), and not too shallow (in which case the seatpan will move too far forward toward the bulkhead or other obstacle to be avoided). Figure 9 shows a schematic side view of a seat 7 according to a preferred embodiment with an X-Z coordinate system having its origin at the Seat Reference Point (SRP), the point where the bottom seat cushion and seat back meet. X coordinates are positive in a forward position (toward the left as illustrated); Z coordinates are positive in a downward direction. In the illustrated embodiment, the rear ramp is at an angle  1 of 15 degrees to the horizontal, and the trajectory of the rear roller is indicated by line 30. The total forward motion of the seat is 3.35 inches, and the initial seat cushion angle  2 is 2.7 degrees. In this illustrated embodiment, the surface of the front ramp is a circular arc 31 of radius 27.136 inches beginning at the application point AP. The coordinates of various points on this seat assembly are given in the chart below. All coordinates are given in inches. X Z Rear roller initial position (RR) 0.525 3.007 Front roller initial position (FR) 11.59 2.508 Application point (AP) 12.27 1.03 Belt anchor (BA) -0.9646 -2.378 Center of ramp surface arc (C) 30.646 20.996 The seatpan articulation mechanism of the preferred embodiment operates smoothly with little friction. Seat articulation is preferably achieved by four roller bearing track rollers 26, 27 mounted on the seatpan 22. Each roller runs on tracks 28, 29 in spreaders 30 which are supported by the front and rear lateral structural tubes 32, 34, with short load paths from the rollers to the tubes. This lateral tube and spreader construction allows single, double, triple, quadruple or quintuple seats to be built with a high degree of part commonalty. The seat legs 36, 38 support the lateral tubes, allowing for different seat track spacings and locations. In an accident or emergency landing, the airplane floor may deform. The articulated seatpan 22 must not jam under yaw or seat track pitch due to deformation of the airplane floor. To assure jam-free operation, all sliding surfaces of the tracks 28 and ramps 29 are preferably covered with a friction-reducing material such as PTFE to minimize friction generated by yaw-induced side loads. Lateral seatpan play is preferably incorporated to allow for spreader sliding surface misalignment. Lateral play on the order of .125 inches is preferable for smooth, jam-free operation even in the event of considerable floor deformation. To further assure jam-free operation, sufficient bearing-to-slot clearance is incorporated to allow for bearing skew caused by floor deformation. Preferably, this is in the range of about .03 inches clearance. Low friction roller bearing track rollers are preferable so deformation-increased loading does not result in unacceptably high frictional forces. The seatpan 22 is preferably designed to easily flex in transverse torsion as shown by the arrows C in Figure 6, allowing the four rollers to go out of plane without developing large contact loads when the ramps and slots are misaligned due to floor deformation. This can be achieved by using an open section (low torsional stiffness) lateral beam 40 at the front of the seatpan 22, and jointed compression links 42, 44 in the rear. The two side plates 46, 47 can then be twisted with respect to each other without jamming the operation of the articulated seatpan. Another feature which serves to limit pelvic rotation is the use of dynamically stiff foam cushion. The cushion in the seat is preferably made from a polyurethane foam which flows to the occupant's shape over time but stiffens and absorbs energy when rapidly deformed. The weight and pressure of the occupant in the seat forms a pocket conforming to the occupant's shape. During sudden impact, however, the stiffness of the foam resists plowing of the occupant on the cushion and increases the friction between the occupant and the cushion, so the occupant and seatpan tend to move together to a greater degree than is the case with a conventional seat cushion. When a significant downward inertial load is present, the cushion reduces spinal compressive forces by absorbing energy and by stiffening so acceleration of the occupant into the seat structure does not occur, thereby reducing the likelihood of injury due to spinal compression. The use of such foam also prevents the occupant from sinking into the cushion under a download or from seatbelt forces. Such sinking can allow the lap belt to ride up and off the anterior superior iliac crests of the pelvis, allowing pelvic submarining and abdominal injury. Prevention of downward occupant motion is especially important when a high seatbelt anchor location is used, because the lap belt starts out riding higher on the pelvis, and therefore cannot rise as far. Although the dynamically stiff cushion has the above beneficial effects, it will be understood that an effective reduced head path seat can be designed using conventional foam. Still another feature of a preferred embodiment which reduces head excursion is a relatively steep initial cushion angle. A steeper initial cushion angle reduces head excursion in two ways. First, it directly adds to the initial rearward pelvic rotation. Second, the longitudinal inertial load more directly pushes the thighs and buttocks into the cushion, increasing the friction between the occupant and the cushion, and more directly opposing the forward motion of the occupant., can be seen in Figure 2. While an initial cushion angle of 12.7 º with the horizontal can reduce head excursion by 3 to 4 inches, those skilled in the art will weigh the beneficial results of increased initial cushion angle against passenger comfort considerations to achieve the desired result. A hybrid dynamically stiff/conventional foam cushion may be used to provide the advantages of a steep initial seat cushion angle with greater comfort. A cushion with a dynamically stiff thigh bolster and conventional foam under the buttocks would effectively change shape under a longitudinal inertial load, with the rear of the cushion compressing more than the front, effectively increasing the cushion angle while maintaining passenger comfort under non-emergency conditions. Although the invention has been described above with respect to certain specific embodiments, the scope of the invention is not limited to the specific embodiments disclosed. Other designs within the spirit and scope of the invention will be apparent to those skilled in the field after receiving the above teachings, and it will be apparent that various combinations of all or some of the above-described features may result in a reduced head path seat within the scope of the invention. The scope of the invention, therefore, is defined by reference to the following claims.

Claims: A seat assembly (7) comprising: a frame (30, 32, 34, 36, 38) to be mounted to a substantially horizontal floor, a seat back (25) mounted to said frame, a seatpan (22) pivotally mounted to said frame and provided with a bottom seat cushion (24) thereon; a lap type seat belt (3); and means for allowing the seatpan (22) to move forward and tilt upwards in an impact event, characterized in that the front surface of the seat back (25) extends to a point (SRP) where it meets the upper surface of the bottom seat cushion (24), said seat back (25) being fixedly mounted to said frame (30, 32, 34, 36, 38), in that said means include a seatpan articulation mechanism (26 - 29) for allowing the seatpan (22) to move relative to said fixed seat back (25), in that a seat belt anchor (BA) for anchoring said seat belt (3) is fixedly mounted to said frame at a level above said meeting point (SRP), in that said seat belt (3) is configured so as to be wearable by the seat occupant in a position where said seat belt restrains forward rotation of the occupant's pelvis. The seat assembly of claim 1 wherein said seatpan articulation mechanism includes slots (28, 29) formed in frame parts (30) and a plurality of rollers (26, 27) attached to said seatpan, said slots and rollers being configured to direct said seatpan in a forward and upwardly tilting path relative to said seat back. The seat assembly (7) of claim 1 or 2, wherein said seat belt (3) comprises a polyester material. The seat assembly (7) of claim 1, 2 or 3 further comprising a seat cushion (24) on said seatpan (22), said cushion being formed of a dynamically stiff foam. The seat assembly (7) of claim 4 wherein said foam is a polyurethane foam. The seat assembly (7) of any of claims 1-5, wherein said forward movement of said seatpan is about 7.5 cm (three inches). The seat assembly (7) of any of claims 1-6, wherein said seat belt forms an angle of about 15 degrees with the horizontal. The seat assembly (7) of any of claims 2-7, further comprising a ramp assembly (29) on said frame which cooperates with said rollers (26, 27) to impart said upward tilting motion to said seatpan (22). The seat assembly (7) of any of claims 2-8, further comprising a low friction coating on the surfaces of said slots (28) and ramps (29) which contact said rollers (26, 27). The seat assembly (7) of claim 8, wherein said ramp (29) defines a circular arc. A seat, especially suited for a seat assembly according to any of claims 1 - 10, comprising: a frame (30, 32, 34, 36, 38) to be mounted to a substantially horizontal floor, a seat back (25) mounted to said frame, a seatpan (22) pivotally mounted to said frame and provided with a bottom seat cushion (24) thereon; an anchor for mounting a lap type seat belt (3); and means for allowing the seatpan (22) to move forward and tilt upward in an impact event, wherein the front surface of the seat back (25) extends to a point (SRP) where it meets the upper surface of the bottom seat cushion (24), said seat back (25) being fixedly mounted to said frame (30, 32, 34, 36, 38), wherein said means include a seat pan articulation mechanism, for allowing the seatpan (22) to move relative to said fixed seat back, wherein said seat belt anchor (BA) is fixedly mounted to said frame at a level above said meeting point (SRP), and wherein said seat belt anchor (BA) is mounted so that a seat belt to be mounted is wearable in a position where it restrains forward rotation of the pelvis.

Inventors: WITTMANN THOMAS E, WITTMANN, THOMAS E.
Applicants: BOEING CO, THE BOEING COMPANY
Application year: 1995
Main classification: B64D25
IPC codes: B60N2, B64D25, B60R22