Viano David C
ProBiomechanics LLC, Bloomfield Hills, Michigan 48304-2952, USA.
Traffic Inj Prev. 2003 Sep;4(3):214-27. doi: 10.1080/15389580309877.
Whiplash has increased over the past two decades. This study compares occupant dynamics with three different seat types (two yielding and one stiff) in rear crashes. Responses up to head restraint contact are used to describe possible reasons for the increase in whiplash as seat stiffness increased in the 1980s and 1990s. Three exemplar seats were defined by seat stiffness (k) and frame rotation stiffness (j) under occupant load. The stiff seat had k=40 kN/m and j=1.8 degrees /kN representing a foreign benchmark. One yielding seat had k=20 kN/m and j=1.4 degrees /kN simulating a high-retention seat. The other had k=20 kN/m and j=3.4 degrees /kN simulating a typical yielding seat of the 1980s and 1990s. Constant vehicle acceleration for 100 ms gave delta-V of 6, 10, 16, 24, and 35 km/h. The one-dimensional model included a torso mass loading the seatback, head motion through a flexible neck, and head restraint drop and rearward displacement with seatback rotation. Neck displacement was greatest with the stiff seat due to higher loads on the torso. It peaked at 10 km/h rear delta-V and was lower in higher-severity crashes. It averaged 32% more than neck displacements with the 1980s yielding seat. The high-retention seat had 67% lower neck displacements than the stiff seat because of yielding into the seatback, earlier head restraint contact and less seatback rotation, which involved 16 mm drop in head restraint height due to seatback rotation in the 16 km/h rear delta-V. This was significantly lower than 47 mm with the foreign benchmark and 73 mm with the 1980s yielding seat. Early in the crash, neck responses are proportional to ky/mT, seat stiffness times vehicle displacement divided by torso mass, so neck responses increase with seat stiffness. The trend toward stiffer seats increased neck responses over the yielding seats of the 1980s and 1990s, which offers one explanation for the increase in whiplash over the past two decades. This is a result of not enough seat suspension compliance as stronger seat frames were introduced. As seat stiffness has increased, so have neck displacements and the Neck Injury Criterion (NIC). High-retention seats reduce neck biomechanical responses by allowing the occupant to displace into the seatback at relatively low torso loads until head restraint contact and then transferring crash energy. High-retention seats resolve the historic debate between stiff (rigid) and yielding seats by providing both a strong frame (low j) for occupant retention and yielding suspension (low k) to reduce whiplash.
在过去二十年中，挥鞭伤的发生率有所上升。本研究比较了在追尾碰撞中三种不同座椅类型（两种可变形座椅和一种刚性座椅）上乘客的动力学响应。使用直到头枕接触时的响应来描述在20世纪80年代和90年代随着座椅刚度增加挥鞭伤增加的可能原因。根据乘客负载下的座椅刚度（k）和框架旋转刚度（j）定义了三个示例座椅。刚性座椅的k = 40 kN/m，j = 1.8度/kN，代表一个国外基准。一种可变形座椅的k = 20 kN/m，j = 1.4度/kN，模拟高固定性座椅。另一种可变形座椅的k = 20 kN/m，j = 3.4度/kN，模拟20世纪80年代和90年代的典型可变形座椅。车辆持续100毫秒的加速度产生的速度变化量分别为6、10、16、24和35公里/小时。一维模型包括一个加载在座椅靠背上的躯干质量、通过柔性颈部的头部运动以及随着座椅靠背旋转头枕的下落和向后位移。由于躯干上的负载更高，刚性座椅上的颈部位移最大。它在追尾碰撞速度变化量为10公里/小时时达到峰值，在更严重的碰撞中较低。与20世纪80年代的可变形座椅相比，其平均颈部位移多32%。高固定性座椅的颈部位移比刚性座椅低67%，这是因为它会向座椅靠背变形、更早地接触头枕且座椅靠背旋转较小，在追尾碰撞速度变化量为16公里/小时时，由于座椅靠背旋转，头枕高度下降16毫米。这明显低于国外基准的47毫米和20世纪80年代可变形座椅的73毫米。在碰撞早期，颈部响应与ky/mT成正比（ky为座椅刚度，mT为躯干质量，y为车辆位移），即座椅刚度乘以车辆位移除以躯干质量，所以颈部响应随座椅刚度增加。座椅刚度增加的趋势使得颈部响应比20世纪80年代和90年代的可变形座椅有所增加，这为过去二十年中挥鞭伤增加提供了一种解释。这是由于引入更坚固的座椅框架时座椅悬架的柔顺性不足导致的。随着座椅刚度增加，颈部位移和颈部损伤标准（NIC）也增加。高固定性座椅通过允许乘客在相对较低的躯干负载下向座椅靠背位移直到接触头枕，然后传递碰撞能量，从而降低颈部生物力学响应。高固定性座椅通过提供一个用于固定乘客的坚固框架（低j）和可变形悬架（低k）来减少挥鞭伤，解决了刚性（硬）座椅和可变形座椅之间长期存在的争论。
