Vehicle Design for Passenger Protection from High-Speed Rear-End Collisions

Severy, Derwyn M.; Brink, Harrison M.; Baird, J D

doi:10.4271/680774

Cited by 31 publications

(2 citation statements)

References 6 publications

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“…Based on sled testing with the Hybrid III dummy, Viano (2002) determined that the effective mass (m) loaded by the seatback was 70% of the total dummy mass, or 52.5 kg for the 50th percentile Hybrid III dummy. This agrees with the estimate by Severy (1968b) using an earlier vintage dummy. The mass of the head-neck is 5.5 kg, based on 4.5 kg for the head plus two-thirds of the neck mass or 1.0 kg (Backaitis & Mertz, 1994); so torso mass is 47.0 kg.…”

Section: Occupant Dynamicssupporting

confidence: 89%

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Influence of Seat Properties on Occupant Dynamics in Severe Rear Crashes

Viano¹

2003

Traffic Injury Prevention

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Seat performance in retaining an occupant, transferring energy, and controlling neck responses is often questioned after severe rear crashes when fatal or disabling injury occur. It is argued that a stiffer seat would have improved occupant kinematics. However, there are many factors in occupant interactions with the seat. This study evaluates four different seat types in 26 and 32 mph (42 and 51 km/h), rear crash delta Vs. Two seats were yielding with k = 20 kN/m occupant load per displacement. One represented a 1970s yielding seat with j = 3.4 degrees /kN frame rotation per occupant load, and 3 kN maximum load (660 Nm moment), and the other a high retention seat phased into production since 1997 with j = 1.4 degrees /kN, and 10 kN maximum load (2200 Nm). Two seats were stiff with k = 40 kN/m. One represented a 1990s foreign benchmark with j = 1.8 degrees /kN and a 7.7 kN maximum load (1700 Nm), and the other an all belts to seat (ABTS) with j = 1.0 degrees /kN and 20 kN maximum load (4400 Nm). The crash was a constant acceleration of 11.8 g, or 14.5 g for 100 ms. Occupant interactions with the seat were modeled using a torso mass, flexible neck and head mass. By analysis of the equations of motion, the initial change in seatback angle (Deltatheta) is proportional to jk(y - x), the product jk and the differential motion between the vehicle (seat cushion) and occupant. The transition from 1970s-80s yielding seats to stronger seats of the 1990s involved an increase in k stiffness; however, the jk property did not change as frame structures became stronger. The yielding seats of the 1970s had jk = 68 degrees /m, while the stiff foreign benchmark seat had jk = 72 degrees /m. The foreign benchmark rotated about the same as the 1970s seat up to 50 ms in the severe rear crashes. While it was substantially stronger, it produced higher loads on the occupant, and the higher loads increased seatback rotations and neck responses. The ABTS seat had the lowest rotations but also caused high neck responses because of the greater loads on the torso. Neck displacement (d) is initially proportional to (k/m(T)) integral integral y, seat stiffness times the second integral of vehicle displacement divided by torso mass. As seat stiffness increases, head-torso acceleration, velocity, and neck displacement increase. This study shows that the jk seat property determines the initial seatback rotation in rear crashes. If a stronger seat has a higher stiffness, it rotates at higher loads on the occupant, reducing the overall benefit of the stronger frame, while increasing neck responses related to whiplash or neck extension prior to subsequent impacts. The aim of seat designs should be to reduce jk, provide pocketing of the pelvis, and give head-neck support for the best protection in severe rear crashes. For low-speed crashes, a low k is important to reduce early neck responses related to whiplash.

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Section: Occupant Dynamicssupporting

confidence: 89%

“…Stiff or rigidized seats were one aspect of the pioneering work of Severy et al (1967aSevery et al ( , 1967bSevery et al ( , 1968aSevery et al ( , 1968b on occupant dynamics in rear crashes. These studies showed the need for controlled deformation of the seatback and support of the head.…”

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confidence: 99%