行人死亡在總交通意外事故死亡中，佔有相當大的比例。先前的研究指出，50%以上的行人死亡是由於頭部傷害所造成，而傷害多因頭部撞擊至車體的引擎蓋與擋風玻璃處。為降低行人碰的傷害，近年來業界開始積極推動行人碰撞的被動安全性設計，諸如彈出式引擎蓋與車體外部安全氣囊等。本研究主要將針對現有的彈出式引擎蓋進行改良設計。
彈出式引擎蓋的作用在於當行人碰撞發生時，將引擎蓋後緣抬升一段高度並加以固定，以提供引擎蓋下足夠的自由空間，並在行人頭部碰撞到引擎蓋時，以彈出式引擎蓋的整體結構形變吸收衝擊的能量，進而降低頭部碰撞所造成的傷害。然而，當引擎蓋彈出並固定後，某些剛性較高之區域，如引擎蓋後緣兩端的支撐處等，卻無法以結構形變的方式有效降低頭部傷害，並且造成頭部碰撞時有較高的頭部受傷準則值。本研究針對該現象加以探討分析，以Euro-NCAP的引擎蓋劃分與測試方式進行引擎蓋全區域的碰撞模擬與評估，並提出降低高頭部傷害準則值區域之新型彈出式引擎蓋系統，該系統包含一組新型的引擎蓋抬升機構，並以彈簧阻尼器作為結構支撐以降低原本彈出式引擎蓋的結構剛性。
本研究可概分為三階段。第一階段中，首先建立車體與頭部衝擊器的有限元素模型，並加以驗證；第二階段則以所建立的有限元素模型進行Euro-NCAP各碰撞測試點的碰撞模擬，分析並比較現有與新型的彈出式引擎蓋，並且針對新型彈出式引擎蓋的三個主要的設計參數：引擎蓋抬升高度、支撐彈簧剛性與阻尼常數進行分析設計；第三階段則針對新型彈出式引擎蓋進行機構設計，並以剛體動力學加以驗證。
本論文於最後對本研究的進行總結，並且針對未來本研究可能的改善方向給予建議。

Fatalities related to pedestrian accidents contribute a large proportion of all traffic accidental deaths. Previous studies show that more than 50% of pedestrian fatalities are caused by head injuries and most of them are impacted by engine hood or windshield. In order to prevent the human life loss due to car-pedestrian collisions, passive safety devices to lower the possibility of head injury has been proposed in industry recently. Among them are pop-up hood systems and outside airbags, etc. In this study, the improvement of the current pop-up hood is our main focus.
The pop-up hood system lifts up the rear part of the hood for a distance at the time when the car-pedestrian impact happens and provides a free space between the hood and the hard components underneath the hood. As the head of pedestrian impacts to the hood, free space of pop-up hood allows the hood to deform and absorb most of the impact energy through structural deformation. The system, as a result, is capable of reducing the head injury with its structural deformation. However, some area of the structure, such as supports, still keeps its high stiffness after the hood is popped up, and it might still cause high risk of head injury. Therefore, such phenomenon is analyzed and a new pop-up hood system to improve the high-HIC-valued area is developed in this thesis. This pop-up system is designed with a newly driving mechanism and spring-damper system to reduce the high stiffness of the original hood structural support. For validation, the numerical tests based on Euro-NCAP are conducted to evaluate the performance over the complete area of the hood system.
The study is departed into 3 stages. In the first stage, the finite element model of the headform impactor and the car front structure are created and validated. In the second stage, the numerical tests based on Euro-NCAP are simulated and the performance of the original and the new pop-up hood system are analyzed and compared. The three design parameters for the new pop-up hood systems, hood lift-up height, supporting spring stiffness and damping coefficient, are also analyzed. In the last stage, pop-up mechanism for the new pop-up hood system is designed and tested with rigid-body dynamics. Finally, conclusions and suggestions of this study are summarized in the last part of the thesis.

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