Automotive Seat Design and Collision Performance
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760810 Automotive Seat Design and Collision Performance D. M. Severy, D. M. Blaisdell, and J. F. Kerkhoff Severy, Inc. ALTHOUGH SAFETY IS A BASIC CONSIDERATION research up to that time. Although some research in all aspects of automotive engineering, it is a has been conducted since that time, the development fact of life that safety advances are not uniformly of a safety seat still has not been accomplished. In accomplished. Some essential aspects of motorist the same study special devices, including the air protection have in the past, and probably will in the bag, were rated as only of moderate relative im- future, continue to be greatly outstripped by advances portance. made in other areas. In some instances, the design After 10 years of government regulated safety challenge simply exceeds current technology; on standards and nearly that many years of intensive other occasions an adequate safety standard and con- air bag development sponsored by both government certed industry interest can correct obvious safety and industry, the consensus of many automotive deficiencies. For example, although improved safety researchers in Europe (2), (3) and elsewhere tires resulted only after new materials evolved, a is to change the emphasis back to development of greatly improved motorist restraining system active restraint systems and to increase effective- resulted from industry initiated research that cul- ness by means of mandatory use laws. Air bags, minated in a standard requiring installation of com- if used, would serve a supplementary function in bination cross chest lap belts for all outboard front conjunction with active systems. Progress in seat locations. safer seat design has been impeded throughout a During the past 20 years, new materials and decade of automotive safety standard making, and techniques have improved the comfort and wear many lives have been lost that could have been fully resistance of automotive seats while simultaneously protected with a fraction of the inventive genius and reducing their weight and cost; however, significant funding lost to air bag development. A basic common safety related improvement in seat design during sense approach to motorist protection from collision this period has not been accomplished. A summary trauma calls for special attention to design of the of findings from prior research (l)* published in critically important structure nearest the motorist, 1966 classified a structurally redesigned Integral his seat. Seat with built-in S-point belt restraint as critically A vital consideration of seat design is its cap- important for reduction of motorist injuries; this acity to protect motorists, to the extent practical, summary also pointed out the lack of safety-seat from all types of collision injury exposures. This paper provides basic design data for crashworthy *Number in parentheses designate References automotive seat systems with integral active re- at end of paper. Eighty-five laboratory full-scale force-deflec- tive significance to the requirements of automotive tion tests were conducted on passenger vehicle seat collision performance. seats, foreign and domestic, for purposes of evaluat- The foregoing research provided foundation for ing specific resistance to a collision environment modification of a production automobile seat into an and mechanisms of collision induced seat distortion. integral safety seat, based on a design concept that These tests evaluated seats that span the past thirty minimizes bending moments during collision. The years; additionally, seat design studies were con- modified seat was subjected to the same laboratory ducted evaluating basic features of automotive seat- test procedure applied to the 85 non-modified pro- ing during the past eighty years. duction seats and results of its performance is Data from full-scale collision experiments and given. from a large number of actual accidents facilitated Design concepts are presented that would serve the establishment of seat design criteria for greatly to mitigate undesirable seat distortions during col- improved collision performance. Evolution of seat lision and thus improve seat restraint capabilities and head support standards in the United States and without compromising the important factors of com- Europe are presented with evaluation of their rela- fort and cost. 2551 2552 D. M. SEVERY straints, as determined from the authors’ collision a seat also should have adequate structure for research and laboratory studies as well as experi- housing safety and convenience accessories. Trade- ence gained from investigation of relevant accidents. offs are imposed by this complex mix of require- ments; however, in seat design we should no longer BACKGROUND overlook the requirement for a reasonably safe, collision resistive structure with built-in active The first automotive seat, like the first restraint system. automobile was an adaptation from the horse-drawn SEATING CATEGORIES - Automotive seats carriage. Springs to absorb road shocks were for passenger vehicles have a number of basic primitive, effective padding was non-existent and configurations and sizes depending on intended use seat adjustability had not yet been considered. Com- and location. Position adjustment depends on mencing around 1900, motorist safety while travel- factors such as location (front or rear): availability ling over rough roads was improved by development of comfort features, including center armrests, of deeply contoured seats that reduced the likeli- depends on vehicle price, type, purpose and country hood of motorist ejection as the car body pitched of origin. and rolled. Generally, however, little considera- BENCH SEAT - SOLID BACK - Standard and tion was given for the safety of the occupants, compact 4-doer sedans are frequently equipped with Fig. 1. solid-back berth seats, front and rear. The front Front seat fore-and-aft adjustment was not seat has a single adjustment mechanism and the available until about 1929 when adjustable front entire seat is usually adjusted according to the seats for the driver became a feature of higher priced automobiles. Occupant comfort was given increased attention as engineering problems con- cerning motor vehicle performance and reliability became more effectively managed. Improvements in seat design continued and by the mid 1930’s, seats, tracks and runners closely resembled those of the mid 1960’s. During the period between the thirties and the sixties, the only significant in- novation in seat design was the introduction of power seats and adjustable reclining backrests during the early 1950’s, Table 1. Seatback height reached reasonable levels in the late 1960’s but by the mid- seventies the height of backrests on many models had declined to levels less effective than thirty v” years ago. Seatback strength has not increased BJtLAWt significantly over the past thirty years and remains Fig. 1 - Driver’s seat, horseless carriage inadequate to resist even moderate collision forces. The remarkable safety improvement facilitated by - the backrest head support standard FMVSS 202 has TABLE 1 been compromised through failure to upgrade cri- teria to maintain performance commensurate with SEAT DESIGN EVOLUTION intent. Seventy percent of adjustable head restraints are used in the downmost position (4). Little ef- INTRODUCED ITEM EXAMPLE fective protection is afforded the motorist unless 1890 - 1900 Automotive Bench Seats Philion* the head restraint is positioned behind or slightly 1900 - 1910 Deep Bucket Seats Thomas* 1910 - 1915 Fold-forward Backrests [Model-T Ford* above the head and remains in such support posi- 1910 - 1915 Console Between Seats Wescott* tion during collision. 1910 - 1915 Pedestal Seat Argo Electric* 1915 - 1920 Swivel Seat Cole* SEAT FUNCTION AND CONFIGURATIONS 1920 - 1925 Fold-down Armrest Dusenberg* 1925 - 1930 Fore-and-aft Adjustment Viking* 1950 - 1952 Power Seats Packard It is not a simple engineering task to design a 1960 - 1963 Optional Head Restraints All U.S. good automotive seat; it must provide comfort, 1968 Integrated Head Restraint Volkswagen style and safety, and yet be sufficiently light weight 1969 Standard Head Restraints All U.S. to facilitate vehicle fuel economy and to minimize collision inertial stresses. Seat designs and mater- _ ____ -- .----- - ials must be affordable and durable to give accept- *Based on authors’ study of vehicles made available through coopera- able service over the life of the car. In addition to tion of Harrah’s Automotive Museum, Reno, Nevada. provisions for comfort and position adjustments, AUTOMOTIVE SEAT DESIGN AND COLLISION PERFORMANCE 2553 needs of the driver. A bench seat, if adequately their elevation, direct restraint system attachment designed for three occupants, must be capable of requires special design considerations. sustaining a rearward static moment, calculated FIXED, BUS-TYPE BENCH SEATS - Although about the H-point of the seat, equal to three times similar to the rear seats of passenger sedans these that of a single seat. seats are elevated and generally provide open BENCH SEAT - SPLIT BACK - Fold-forward space beneath; structural limitations and remoteness backrests provide access to the rear seat of 2-doer of seat from floor increase the difficulty of direct vehicles. Since only the upper portion of the seat restraint attachment. Seats used in buses that is divided, the fore-and-aft adjustment can accom- transport children require special considerations, modate only one person. Backrest angle,