Viano David C
ProBiomechanics LLC, Bloomfield Hills, Michigan 48304-2952, USA.
Traffic Inj Prev. 2003 Dec;4(4):324-36. doi: 10.1080/714040490.
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.
在严重的追尾碰撞导致致命或致残伤害后，座椅在固定乘客、传递能量和控制颈部反应方面的性能常常受到质疑。有人认为，更硬的座椅会改善乘客的运动学表现。然而，乘客与座椅相互作用存在许多因素。本研究评估了四种不同类型的座椅在26英里/小时和32英里/小时（42公里/小时和51公里/小时）追尾碰撞时的情况，碰撞速度变化量为ΔV。其中两个座椅具有屈服特性，每单位位移的乘客负载下k = 20 kN/m。一个代表20世纪70年代的屈服座椅，每单位乘客负载下框架旋转角度j = 3.4度/kN，最大负载为3 kN（660 Nm力矩），另一个是自1997年开始量产的高固定性座椅，j = 1.4度/kN，最大负载为10 kN（2200 Nm）。另外两个座椅较硬，k = 40 kN/m。一个代表20世纪90年代的国外基准座椅，j = 1.8度/kN，最大负载为7.7 kN（1700 Nm），另一个是全带至座椅（ABTS），j = 1.0度/kN，最大负载为20 kN（4400 Nm）。碰撞时的加速度为恒定的11.8 g，或者在100毫秒内为14.5 g。使用躯干质量、柔性颈部和头部质量对乘客与座椅的相互作用进行建模。通过对运动方程的分析，座椅靠背角度的初始变化量（Δθ）与jk(y - x)成正比，即jk的乘积以及车辆（座垫）与乘客之间的差动。从20世纪70年代 - 80年代的屈服座椅过渡到90年代更强的座椅，涉及k刚度的增加；然而，随着框架结构变强，jk特性并未改变。20世纪70年代的屈服座椅jk = 68度/m，而较硬的国外基准座椅jk = 72度/m。在严重的追尾碰撞中，国外基准座椅在高达50毫秒的时间内与20世纪70年代的座椅旋转情况大致相同。虽然它强度大得多，但对乘客产生了更高的负载，而更高的负载增加了座椅靠背的旋转和颈部反应。ABTS座椅的旋转最小，但由于躯干上的负载更大，也导致了较高的颈部反应。颈部位移（d）最初与(k/m(T))∫∫y成正比，即座椅刚度乘以车辆位移的二阶积分再除以躯干质量。随着座椅刚度增加，头部 - 躯干加速度、速度和颈部位移都会增加。本研究表明，jk座椅特性决定了追尾碰撞中座椅靠背的初始旋转。如果更强的座椅具有更高的刚度，它会在对乘客更高的负载下旋转，降低更强框架的整体益处，同时增加与鞭打或后续碰撞前颈部伸展相关的颈部反应。座椅设计的目标应该是降低jk，提供骨盆的凹陷，并在严重的追尾碰撞中为头部 - 颈部提供支撑以实现最佳保护。对于低速碰撞，低k对于减少与鞭打相关的早期颈部反应很重要。
