Design Of Child Restraint System And Decrease Of Head Displacement

Child passenger safety has become an important topic in vehicle crash. Childrenare vulnerable groups in the traffic accidents compared with the adults, even a slightcollision will lead to injury. According to the statistic results by some foreignauthorities, using child safety seat can effectively reduce child injury risk by70%, theproportion of casualties from11.5%down to3.5%. In China, research anddevelopment of child seat is still at early stage, most of the seats are less secure.Therefore, it is necessary for the research on the safety of child seat.Data from NASS-CDS database showed that head injury was the leading reasonfor the child serious injury.20.5%of the head injury was caused by the seat back ofits frontal seat. In this study, a lot of child seat sled tests were conducted to provehead displacement was the major representation leading to the failure of the child seat.Meanwhile, the structure of child seats was analyzed to summarize the typical failureforms of child seats.A MADYMO simulation model of child restraint system was established. TheMADYMO model was validated against in chest acceleration and head displacementfrom sled test. Some conclusions on the sensitivity of design parameters wereobtained: the stiffness of child seat has significant influence on the head displacementand chest acceleration of child dummy. When the seat belt stiffness increased, thehead displacement would decrease while the acceleration would increase. Thus, thegroups of design parameters were very important for the safety performance.In order to get CRS’s design parameters, an orthogonal experiment was designed.According to the orthogonal table, the sensitivity parameters were taken asindependent variables. The result showed that several groups of parameters couldmeet the regulation. In order to decrease the head displacement, a modeFRONTIERsingle objective optimization model coupling with MADYMO was established. Thehead displacement was set as the single object, using SIMPLEX Algorithm to get theminimum value of head displacement. After about12iterations, the result of theoptimization was503mm, which was smaller than the value of orthogonal method. The conclusion showed that the orthogonal method was a faster method to find outthe solutions for some objects. SIMPLEX Algorithm needed more times of simulationto get the solution for a single object to get it’s maximum or minimum value. Theconclusions by this thesis provided some guiding significance for CRS design.