ENERGY ABSORBING AIRCRAFT SEAT FRAME STRUCTURE

Abstract: An improved energy absorbing seat frame structure (10) for an aircraft seat has leg structures which com­ prise a pair of generally U-shaped front and rear leg members (34, 36) which are joined back to back in a gener­ ally X-shaped configuration. A curved die member (44) is held in contact with the forward facing concave portion of the front leg member (34) by a strap member (48) which surrounds the rear leg member (36). In a crash situation, the front leg can bend about the die member (44) to lower the centre of gravity. In a preferred embodiment, strap type clamps (54) on the upper ends of each leg member permit the leg members to rotate relative to tubular stretcher members(14, 16) of the seat. The ability of the front leg members to be deformed downwardly permits a portion of the excess loading on one front leg member to be transferred through the front stretcher member (14) to the other leg member which is less heavily loaded. Pin joint connections of each leg member to front and rear track fittings (24, 28) enables the structure to accommodate, and to uniformly transfer, loading to seat tracks (26) which have been deformed vertically. A modi­ fied fitting (see Figure 8) also accommodates twisting deformation of the seat tracks. The seat can have its front and rear legs positioned closer together than con­ ventional seats for a given "G" loading, so as to increase passenger leg room behind the seat. Alternatively, for a given front to rear leg spacing distance, the "G" load­ ing capacity of a particular seat can be significantly increased without increasing the loading on the seat tracks.

Description: The invention relates to vehicle seats and particularly to aircraft seats. A critical aspect of survivable aircraft crashes has been the ability of the seats to remain attached to the floor structure. In certain accidents, the seat track in the floor of the aircraft has fractured when overloaded by forces applied to it by a seat. It is well known that a given seat design having a predetermined distance between its front and rear legs can be made to absorb more "G" loading than the amount currently specified by the United States Federal Aviation Administration (FAA), which is noted below. However, to do so, the seat tracks and other supports in the aircraft floor would probably have to be replaced with much stronger and heavier members. Furthermore, any modification of the basic airframe structure of existing aircraft would be extremely expensive. Also, the additional weight of stronger supports would cause a significant increase in the operating cost. It is also known that increasing the spacing between the front and rear support fittings for the front and rear legs of a seat will reduce the bending load exerted on the seat track in a crash situation. This is because the load applied to the rear fitting tends to lift the seat track while the load applied to the front fitting tends to depress the track. Typically, a seat is designed to fail by having its front legs collapse in a controlled mode after the design load is reached. Additional loading generally causes the rear track fittings to tear out of the seat track or causes the seat track to tear out of the floor. As increased operating costs have forced carriers to reduce the pitch distance between seats from about 86.4 cm (34 inches) to as little as 71-74 cm (28 or 29 inches) to accommodate more passengers, it has become quite desirable to minimize the front to rear leg spacing in order to preserve as much passenger foot and leg access room behind the seat as possible. However, as previously noted, the strength of existing seat tracks places a distinct limit on how closely the legs can be spaced for a given seat and seat frame configuration. Under current FAA regulations, using an NAS 809 dummy block (National Aircraft Standard promulgated by the Aircraft Industries Association of America, Inc.), a seat must be able to withstand, in a static test, a force of 6 "G's" with no permanent deformation. The seat can yield, but must not fail, when subjected to loads in the range 6 to 9 "G's". The desired failure mode is to have the front legs start to collapse at 9 "G's" so that the rear studs will not pull out of the track, or lift the track from the floor supports, at loads of less than 12 "G's". To permit a particular existing seat, which has a 40.6 cm (16 inch) leg spacing, to resist failure at higher loads, for example, at 16 "G's" rather than 9 "G's", without altering the seat track or aircraft, the leg spacing must typically be increased to about 48.3 cm (19 inches). However, such 48.3 cm spacing is quite undesirable since it greatly reduces passenger access room behind the seat. It is further known that seats can be manufactured with portions thereof adapted to absorb energy so as to decrease the "G" forces applied to a seat and its occupant in the rapid deceleration conditions of a crash landing. For example, US-A-2,959,207 discloses a telescoping rear leg which includes a cylindrical tube which absorbs energy when it is reduced in diameter by being drawn over a die. A somewhat similar arrangement for a front leg is disclosed in US-A-3,059,966. It is among the aims of the present invention to provide a seat frame structure which, for a particular seat design: permits the various pairs of front and rear legs of the seat: 1) to be positioned closer together than in conventional designs of seats which are constructed to withstand, in static testing, a given "G" loading force; or, 2) permits the "G" loading ability of the seat to be increased while maintaining a predetermined leg spacing; or, 3) permits a combination of closer leg spacing and improved "G" loading capability It is another aim of the invention to provide a seat frame structure which can absorb energy by means of a controlled deformation of the legs. A still further aim is to provide a seat with a front leg member which is shaped to permit a forward stretcher tube or equivalent support structure to move lower in a crash load situation so as to lower the centre of gravity of the seat and its occupants and also to shift excess loading of one front leg member through the stretcher tube or equivalent support structure to another front leg member. These and other aims and advantages are achieved by the improved seat frame structure of the present invention which is defined in claim 1. Although various structures could be used for retaining the curved die member in place, a U-shaped strap member which passes around the rearwardly facing concave bend portion of the rear support leg member and has its legs fastened to flat side portions of the curved die member is preferred. Such a U-shaped strap member can hold the front and rear leg members in tight contact and support the die member so that the front leg member can bend uniformly around it should crash forces be applied to the seat. The bending of the front leg member will lower the centre of gravity of the seat and its occupants, thus reducing the "G" loading on the seat track even more than it is reduced by the energy absorbed by the deformation of the front leg member. A connecting member, having an enlarged diameter flat intermediate bearing portion with a pair of pin portions projecting normal to the flat portion can be provided between the leg members so that the pins are located in small openings in the convex portions of each seat leg member which are adjacent to each other. Such a connecting member serves as a bearing surface between the respective convex portions of the seat leg members and prevents relative vertical movement between the respective front and rear leg members while permitting the upper end of the rear leg member to move up as the upper end of the front leg member moves down. The upper ends of the front and rear seat leg members are preferably pivotally mounted to laterally-extending fore and aft stretcher members by sheet metal clamp rings which surround the stretcher members. The pivotal mounting allows the leg members to deform under crash loads and rotate relative to the stretcher members without affecting the integrity of the stretcher members which are normally rigidly attached to each other by at least one fore and aft support member. In the case of a seat such as that disclosed in US-A-4,526,421 which uses a moulded panel for lateral and fore and aft support, the upper ends of the seat leg members can be pivotally mounted to brackets attached to the panel. Since the upper ends of the U-shaped front leg members are designed to bend around the die members and move downwardly under a crash load, the front leg member which sees the most force will start to move down first and will naturally cause the stretcher member or other support structure which is attached to it to move down with it, thereby transferring some of the excess loading through the stretcher tube or other support structure to the other leg member. This feature is especially valuable in the case of a seat, such as a triple seat, wherein there are usually only two legs, and where, due to the location of the seat tracks in the aircraft, it is necessary that at least one seat position be supported in a cantilever fashion and/or where at least one seat position extends much further beyond the legs than another seat position. The advantages of this feature can be even more pronounced in a situation where a triple seat is occupied by only two passengers, but wherein those passengers are seated next to each other on the longest overhanging portion of the seat. The latter loading situation could generate higher loads with respect to certain frame members, such as a leg member, than the situation where three passengers occuplied all of the positions of the triple seat. In the usual construction of a seat frame, the front legs are straight and rigidly affixed to stretcher tubes. Thus, they will tend to remain straight when loaded and will not permit any lowering of the centre of gravity until they start to collapse. Also, such straight legs will act as fulcrums for the stretcher tubes so that the cantilevered loads which are applied laterally outwardly of the legs at each end of the seat will tend to act independently. By making the front leg members so that they can deform, and thereby allow the excess load on one leg member to be shifted by means of the stretcher member or other support structure, it is possible to either eliminate the need for using reinforcements in the stretcher member in the region of the leg locations or permit thinner tubes to be used for the stretcher members to accommodate a given loading. The lower ends of the set of front and rear leg members which make up each leg assembly are attached to each other by a generally channel-shaped track covering connector tension member. The connector tension member is desirably pivotally connected to a rear track fitting member by a horizontal pin which is mounted in a bearing aperture in the fitting member. In a modification, each of the ends of the aperture are tapered so that the fitting can tilt from side to side relative to the pin and seat. This ability to tilt can accommodate twisting rotation of the track in a crash situation. Normally, a rear track fitting has at least two studs having enlarged heads which are adapted to engage the under surface of the seat track. Conventional track covering connector members are normally tension members in the form of a strap or of a channel shape having relatively short flanges. Such conventional connecting members are adapted to be retained to the rear track fitting by a vertical bolt which passes through a hole in the top surface of the strap or channel at one end thereof. The advantage of mounting the rear track fitting to the track covering connector member with a horizontal pivot, as described hereinabove, is to permit the rear fitting to self align with the seat track when the seat track is deformed in a vertical direction so that the loading applied to the fitting by the rear seat leg member will be distributed uniformly to the seat track by each of the pair of studs. This self alignment feature is of great value and is enhanced further by the fitting of the modification embodiment disclosed herein which permits side to side tilting, since it has been determined that seat tracks can be distorted both laterally and fore and aft in a crash so that one portion might be lifted or rotated relative to another portion. For example the specially shaped cargo containers that are designed to be placed in the belly of an aircraft lie directly under the floor which supports the seat tracks. In a crash, these containers get compressed and can move upwardly into engagement with the floor of the passenger compartment where that can distort the seat tracks. By providing pin joints on the seat and track fittings, as described, it is possible to cause the seat to remain in firm engagement with the seat tracks even after the seat tracks have been distorted. The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective view showing a seat frame structure according to the present invention attached to fore and aft stretcher tubes and fore and aft support members of a triple seat, Figure 2 is a side view illustrating the energy absorbing leg assembly of the frame structure, with the crash position of the legs shown in phantom lines, Figure 3 is a section view taken on line 3-3 of Figure 2 and illustrating a double-ended pin connector member that acts as a bearing between the front and rear legs, Figure 4 is an enlarged view showing in detail the joint between the upper rear leg member and the rear stretcher tube, Figure 5 is a front cross-sectional view of the front leg taken on line 5-5 of Figure 2, Figure 6 is a cross-sectional view of a track covering connector member taken on line 6-6 of Figure 2, Figure 7 is a cross-sectional view of the rear leg and track fitting taken on line 7-7 of Figure 1, Figure 8 is a cross-sectional view similar to Figure 7 but illustrating a modified track fitting which supports the seat leg even when the floor track and fitting become tilted sideways relative to the leg, Figure 9 is a side view illustrating a modification of the assembly shown in Figure 1 in which the "X"-leg structure is used to support a panel type seat, and Figure 10 is a perspective view illustrating the rear leg and rear track fitting. Referring to Figure 1, one embodiment of improved energy absorbing seat frame structure according to the present invention is indicated generally at 10 and includes a pair of X-shaped leg assemblies 12 which are shown as being mounted to a pair of conventional forward and rearward tubular stretcher members 14, 16, respectively. Although varying numbers of seat positions could be provided, the drawing illustrates the tubular stretcher members 14, 16 as being sized so as to provide fore and aft support for three seat cushion support panels, not shown, which support three seat cushions, not shown, for three seating positions. The stretcher members are rigidly fixed relative to each other by a pair of conventional fore and aft extending support frame members 18 which are attached to each stretcher member in a conventional fashion. An additional pair of such frame members, not shown, would be mounted at the ends of the seat to support the outer arms and seat belts. The rear stretcher member 16 has a thicker wall and smaller diameter than the front stretcher member 14 so as to maximise the foot space and stowage space under the seat. A short insert sleeve 17 in the ends of the rear stretcher member provides additional support for the aforementioned pair of end mounted frame members. The members 18 divide the seating unit which is defined by the frame structure 10 into three seating positions and provide support for the seat backs, not shown, and other conventional seat elements such as the recline locks and seat belts. The seat frame 10 is adapted to be anchored to the floor of an aircraft by an enlarged diameter stud portion 22 of a front leg fitting member 24. The enlarged diameter stud portion 22 is adapted to pass through one of the spaced slotted holes, not shown, in a conventional seat track 26, and be retained against upward movement by one of the sets of lips, not shown, which are positioned between adjacent holes. Similarly, a rear track fitting 28, which includes a pair of stud portions 30, is adapted to engage the seat track. The rear track fitting includes a conventional shear pin 32 (Figure 10), which is adapted to fit into one of the holes in the seat track and be retained thereby against fore and aft movement. Each of the X-shaped leg assemblies 12 includes a U-shaped front leg member 34 and a U-shaped rear leg member 36 which are preferably formed of rectangular metal tubing but which could be of other materials or shapes. The upper end portion 34′ of the front leg member 34 diverges relative to the lower end portion 34″. Similarly, the upper end portion 36′ of the rear leg member 36 diverges relative to the lower end portion 36″. The U-shaped intermediate portions 38 of the front leg member and 40 of the rear leg member have convex portions 38′, 40′ which contact each other and are retained against vertical movement relative to each other, by an intermediate connecting pin member 42 having a flat bearing portion 42′ and a pair of pins 42″ which engage apertures in the convex portions, as best seen in Figure 3. A die member 44, having a curved rear surface 44′, contacts the concave inner surface 38″ of the front leg 34 and is retained in tight engagement with it by a U-shaped metal strap member 48 which is attached to the die member by fasteners 50. The upper end portions 34′ and 36′ of the front and rear legs 34, 36 are preferably clamped to the tubular stretcher members 14, 16 by sheet metal clamp members 54 which frictionally engage the stretcher members. The clamp members 54 should be free to rotate relative to the stretcher members so as to not cause the stretcher members to twist or rotate relative to the fore and aft extending support frame members 18 to which the stretcher members are rigidly attached, when the legs 34, 36 have their upper end portions 34′, 36′ lowered or lifted, respectively, in a crash situation. To prevent lateral relative movement, it is preferable to provide the strap portion of each clamp member 54 with a short peripheral slot 54′ in which a pin 55 located on the tubular stretcher member may move. Figure 2 illustrates the X-shaped leg structure 12 in its normal configuration by means of solid lines. The configuration of the X-shaped leg structure which might be expected following a crash is indicated at 12′. In such a situation, the loading of the seat is assumed to be downward and forward and such loading would cause the upper rear leg portion 36′ to be lifted up while the upper portion 34′ of the front leg would move down. Since the weight of the seat is a quite small fraction of the weight of a typical occupant, the centre of gravity of the combined seat and occupant will move down considerably as the occupant's head and torso tend to be thrown forward and downwardly to a generally horizontal position. The lowering of the centre of gravity causes a substantial decrease in the loading applied by the seat to the seat track, thus permitting the seat to absorb much higher "G" forces than prior art seats which do not have as much reduction in their centre of gravity in a crash. As previously discussed, the typical prior art seat has a generally straight front leg which would tend to maintain its height above the track until it started to collapse. As the rear leg portion 36′ rises to its Figure 2 crash position indicated by phantom lines, the rear clamp member or strap 54 will rotate counter-clockwise relative to the stretcher member 16. This movement will cause the pin 55 which is mounted in the member 16 (Figure 1) to end up at the lower end of the slot 54′. The die member 44, being strapped to the legs 36, 34, will also be translated to a new position but will move with the legs and will function as a fulcrum to ensure that the bending of the front leg 34 will be uniform and that it will take place over an extended area of the leg. As best seen in Figure 4, the upper end portions 36′ of the rear legs are preferably clamped to the stretcher member 16 by sheet metal clamp members 54 which surround the tubular member 16. The front stretcher member 14 is similarly mounted. The ends of the legs are preferably finished off with a curved plate 56 which helps spread the loading and also ensures that the outer ends of the tubular legs do not dig into the stretcher members and prevent the relative rotation which must take place during a crash. Figure 5 illustrates the pivotal attachment of the lower end 34″ of the front leg to a threaded upper portion 22′ of the stud 22 on the front fitting member 24 by means of an intermediate U-shaped bracket 62 and a pivot pin 64. The pin 64 also anchors a bracket 66 which supports a baggage bar 67. The upper stud portion 22′ also forms a forward anchor point for an elongated connector tension channel member 68 which is joined at its opposite end to the rear lower leg portion 36″ and also to a rear fitting member 28 by means of a horizontal pin 72 (Figure 7). The channel member 68 has a considerable height at its rear end so as to permit it to form the bearings for the horizontal pivot pin 72. A short U-shaped reinforcing channel member 74, best seen in Figure 6, is attached to the channel member 68 near its rear end to provide additional strength. As compared to the usual connector tension member which is fastened at each end to a vertical fitting stud, the rear end of channel member 68 is attached to the rear leg portion 36″ and to a bearing aperture 70 within the fitting 28 with a horizontal pivot pin 72. This type of mounting leaves the rear fitting free to rock in a vertical plane relative to the channel member 68 so as to uniformly distribute the loading applied to it by the seat through each of its two track studs 30 in a crash situation. For example, a crash might cause the section of the seat track under one fitting to be moved up or down relative to the section under the other fitting. If the channel member 68 was flat, and held to the rear fitting by a vertical stud, it would reinforce the attachment between the fitting and track and prevent self-alignment. Figure 8 illustrates a modified form of rear fitting 128 which would accommodate vertical movement of the seat track 26 while distributing the loading between its two studs exactly in the same manner as the fitting 28 in Figure 7. However, the bearing aperture 170 within the modified fitting has tapered end portions 170′. The tapered end portions 170′ and curved outside wall surfaces 128′ cooperate to permit the fitting 128 to tilt sideways by some predetermined amount, such as about 10°, for example, in either direction. This additional tilting capability would allow the fitting to tilt with a seat track that got twisted in a crash while still remaining firmly attached to the seat leg and tension channel member 68. Figure 9 illustrates how the X-shaped support system of the invention can be used with a seat that does not include fore and aft stretcher members 14, 16 or a fore and aft support member 18. The seat assembly 210 which is shown, includes a fibre reinforced panel member 213 of the type disclosed in US-A-4,526,421. Although the referenced patent shows the front seat leg members 234 of the seat being rigidly attached to the seat panel, in this embodiment the leg members 234, 236 are each capable of pivoting relative to the forward and rearward portions of the seat frame. To accommodate this pivotal movement, the seat panel 213 has brackets 215, 217 attached to its forward and rearward portion. The upper leg portions 234′, 236′ are attached to the brackets 215, 217 by pivot pin means 219, 221, respectively. The lower leg portions 234″, 236″ are pivotally attached to a channel-shaped connector member 268 in the same manner as described for the embodiment of Figures 1 to 7 or 8. A die member 244 secured by a U-shaped strap 248 to the rear leg member 236 bears against the concave surface 238″ of the front leg member 234 as in the embodiment of Figure 1. Figure 10 is an enlarged perspective view which more clearly illustrates the design of the rear fitting 28 and its connection to the tension channel member 68 and the lower rear leg portion 36″ by means of the horizontal bolt 72. From the foregoing it will be seen that the invention provides an improved seat frame structure which is designed so that the front and rear support leg members are each of a generally "U" shape with diverging upper and lower leg portions and with the bends of each "U" in contact under the seat so that the overall appearance of the assembly of the front and rear legs, as viewed from the side of the seat is in the shape of an "X". A curved die member is mounted in the forward facing concave bend portion of the front leg and a retaining element is provided for retaining the die member relative to the rear leg.

Claims: A seat frame structure (10) for supporting a plurality of seats in a multi-passenger seating unit which has both laterally extending (14, 16: 213) and fore and aft extending support means (18: 213) for supporting seat cushion means, said seating unit including front (34) and rear (36) support leg members attached at their upper ends (34′, 36′: 234′, 236′) at spaced locations to fore and aft located portions of said laterally extending support means (14, 16: 213) so that said upper ends will be maintained at a fixed distance from each other, said front and rear support leg members (34, 36) having their lower ends (34″, 36″) connected to each other by a connector member (68: 268) and to a seating track (26) on the floor by at least one track fitting member (24, 28) which includes locking portions (22, 30) which are adapted to engage complementary shaped openings in said seating track (26); characterised in that said front and rear support leg members (34, 36) are each bent into a generally "U" shape with the leg portions of each "U" being divergent from each other and with the outer surface (38′) of the bend portion (38) of the "U" of one support leg member (34) being in engagement with the outer surface (40′) of the bend portion (40) of the "U" of the other support leg member (36); said front and rear support leg members (34, 36) each, respectively, having the upper and lower leg portions thereof directed generally forwardly and rearwardly; means (48 : 248) for maintaining the front and rear leg support members (34, 36: 234, 236) in engagement with each other at their bend portions; and a curved die member (44: 244) mounted in contact with the curved inside surface of the forward facing bend (38″: 238″) of the front support leg member (34: 234), said curved die member (44: 244) serving to guide and control the bending movement of the upper and lower leg portions of said front support leg member (34: 234) toward one another when a sufficient downward and forward force is applied to said seating unit to cause the upper and lower ends of said front support leg member (34: 234) to move toward each other. A seat frame structure according to claim 1, characterised in that said curved die member (44: 244) is maintained in engagement with said front support leg member by a retaining element (48: 248) which is carried by the rear support leg member (36: 236). A seat frame structure according to claim 2, characterised in that said retaining element (48: 248) comprises a U-shaped strap member. A seat frame structure according to any one of the preceding claims, characterised in that vertical relative movement between the front and rear support leg members (34, 36: 234, 236) is prevented by a connecting member (42) which has a generally flat bearing portion (42′) which is positioned between and is engaged by each of said leg members, and pins (42″) extending from said generally flat bearing portion (42′) and into apertures in each of said leg members (34, 36). A seat frame structure according to any preceding claim, characterised in that said laterally extending support means comprise front and rear stretcher tubular members (14, 16) and each of said front and rear support leg members (34, 36) have their upper ends (34′, 36′) attached to said stretcher members (14, 16) by a clamp member (54) which comprises a bent length of sheet metal which has a curved intermediate portion which surrounds the major portion of the circumference of the respective stretcher member (14, 16) and has its free ends fastened to the front and rear surfaces of the support leg members (34, 36), said clamp members (54) being maintained in frictional engaging contact with said stretcher members but being rotatable relative to said stretcher members so that, when sufficient force is applied to said seat to cause said support leg members to deform, said clamp members (54) and support leg members (34, 36) will be able to pivot to a limited degree relative to said stretcher members (14, 16). A seat frame structure according to claim 5, characterised in that at least one of said clamp members (54) includes an elongated peripheral slot (54′) which is engaged by a pin (55) mounted in at least one of said stretcher members. A seat frame structure according to claim 1, characterised in that said connector member (68: 268) which is connected to the lower ends of said leg members (34, 36: 234, 236) is a generally channel-shaped member which is attached to a rear track fitting (28: 128) and also to the lower end of the rear leg member (36: 236) by means of a horizontally disposed pin (72) which passes through a bearing aperture in said rear track fitting (28: 128) and engages vertically extending walls of the connector member (68: 268) which straddle said rear track fitting (28: 128). A seat frame structure according to claim 7, characterised in that said bearing aperture (170) is tapered at each of its ends (170′) so as to permit a sideways tilting movement of said rear track fitting (128) relative to said horizontally disposed pin (72). A seat frame structure according to claim 8, characterised in that said bearing aperture (170) is tapered sufficiently to allow said track fitting (128) to tilt about +/-10° relative to said horizontally disposed pin. A seat frame structure (210) according to claim 1, characterised in that said laterally extending and fore and aft extending support means comprise a fibre reinforced panel member (213) which has fore and aft positioned bracket elements (215, 217) affixed thereto, said bracket elements being pivotally attached, respectively, to the upper ends (234′, 236′) of the front and rear support leg members (234, 236).

Inventors: BRENNAN, EDWARD JOSEPH
Applicants: PTC AEROSPACE INC.
Application year: 1987
Main classification: B64D11
IPC codes: B60R22, B60N2, B64D11, B64D25