行人小腿保护（基于-腿型）

2013年以后，Euro-NCAP要求使用FLEX-PLI行人保护柔性腿型，同时GTR（全球性法规）也要求在2013年后使用该腿型。与传统腿型相比，FLEX-PLI腿型的优势在于：

（1）采用多段可变形骨骼连接结构；

（2）形状采用类人设计，符合人体腿部形状，变形模式复杂多样，受外界载荷作用后柔性很强；

（3）伤害模式更接近实际人体生物力学响应，测量全面。

车辆前端造型直接决定着行人保护实施对策的难易程度，如果前期造型设计没有充分考虑行人保护性能要求，将会给后期的结构设计和布置带来很大挑战。

车辆造型与行人小腿保护性能相关的参数主要有：发动机前缘参考线距离地面的高度H1、小腿支撑离地高度H2、发动机前缘参考线与保险杠上参考线的水平距离B1、小腿支撑与蒙皮的水平距离B2（见图3.81）。各参数与FLEX-PLI腿型的影响关系如下：

图3.81　小腿保护相关尺寸

发动机前缘参考线与保险杠上参考线的水平距离B1：影响车辆前脸造型特征，B1越小，越有利于控制小腿膝部十字韧带拉长量和股骨弯矩伤害。

小腿支撑离地高度H2：影响车辆前脸下部造型特征，H2越小，越有利于控制腿型的运动姿态，能够有效降低膝部韧带PCL、ACL、MCL及胫骨弯矩伤害；

小腿支撑与蒙皮的水平距离B2：影响碰撞时小腿支撑起作用的时间，B2越小，小腿支撑起作用的时间越早，一般建议B2≤40mm；

前伸吸能结构：前伸吸能结构不仅影响车辆的造型特征，还影响小腿膝关节韧带拉长量，其厚度可根据能量原理和牛顿第二定律计算得出：

得：

式中，E小腿为小腿腿型冲击器动能，m为小腿腿型冲击器质量。

以FLEX-PLI柔性腿为例，m=12.95kg，令a=150g，则由公式（3.90）得保险杠横梁前端面与蒙皮之间的最小可变形空间为：

图3.82　小腿保护相关尺寸

考虑到在碰撞过程中动能并不能被完全吸收，现假设吸收了60%，那么有效吸能空间xΔ应为43.3/0.6=72（mm）。

结构布置时应尽可能将刚度大的零部件（如拖钩、雷达等）布置在小腿碰撞区域内、外。此外，车辆的造型对小腿区域范围也有较大影响，合理的前脸造型能有效减小小腿碰撞区域。如图3.82所示，其采用凸角结构，缩小了120°试验范围。

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