Research On General Layout Parameters Of I-SIZE Child Safety Seat In Front Impact

With the implementation of the national standard of CRS（child restraint system）in motor vehicles in China,more and more attention has been paid to the safety of children in vehicles.The development of ECE R129 regulation in Europe and other national legislation around the world has also driven the innovation of CRS industry.So there are more and more researches on the advanced child restraint system all around the world.In this paper,the relevant literatures at home and abroad in recent years are introduced in detail,but there are few studies on the general layout of child safety seats.So the main purpose of this paper is to study the influence of general layout parameters of CRS on children’s injury in frontal collision,so as to explore the general layout scheme with the best protection performance for children.This paper introduces the development of ECE R129 and the relevant regulations of frontal impact in detail,and a frontal impact sled test was carried out in accordance with regulations.At the same time,an I-Size simulation model of child safety seat was built in MADYMO software.The method of combining multi-rigid body and finite element is used to carry out the simulation calculation,and the validity of the model is verified by comparison with the actual experiment.In order to shorten the simulation time and improve the efficiency of following research,a concept model which is suitable for the study of general layout parameters was built based on the original model and also was verified.Using the verified concept model as the research object,the general layout parameters of CRS were studied.The influence of the angles between the back and cushion with the horizontal plane on the injury of children was studied.12 simulation tests were uniformly and comprehensively arranged within the design range and constraint conditions of parameter variables.And then three approximate formulas were obtained by using Matlab polynomial fitting program for the test results,which can better represent the relationship between head excursion,head cumulative 3ms resultant acceleration,chest cumulative 3ms resultant acceleration with the two angels.NSGA-II genetic algorithm multi-objective optimization was realized by Matlab gamultiobj function.The final optimization scheme is that the angel between the seatback and horizontal plane is 62°,the angel between cushion and horizontal plane is 23°.The optimized model can reduce HPC₁₅by 32.86%,head cumulative 3ms resultant acceleration by 18.87%,and chest cumulative 3ms resultant acceleration by 6.34%,which means the child protection performance of the optimized model was improved obviously.At the same time,factors those influence the head horizontal excursion relative to Cr point and the relationship between them are summarized.In addition,the study on stiffness of backrest shows that the change in stiffness of backrest has great impact on HPC₁₅ and the chest cumulative 3ms resultant acceleration.And when backrest stiffness increases,the chest 3ms resultant acceleration rises while the head injury decreases.The outlet position of the shoulder strap and lap belt of five-point harness is taken as research parameters.Take 5 levels for the height of the shoulder strap outlet and 3 levels for the front and rear positions of the lap belt outlet,refer to the child dummy comprehensive injury criterion C₁₂₉,and carry out DOE full factor experiment.As a result,the optimal solution is that the shoulder strap outlet is 40mm higher than the original model,and the center point of lap belt outlet moves 25mm forward relative to the original model.The optimized model can reduce HPC₁₅ by 28.32%,head cumulative 3ms resultant acceleration by 18.07%,and chest cumulative3ms resultant acceleration by 10.24%,comprehensive injury criterion C₁₂₉ by 15.89%.So after optimization,the injury of child decreased significantly.In addition,the study on stiffness of harness shows that the change in stiffness of backrest has great impact on HPC₁₅ and the pelvis cumulative 3ms resultant acceleration.And when harness stiffness increases,the head injury and head displacement rises while the chest and pelvis resultant acceleration decreases.At the same time,it is determined that the stiffness of the safety belt is 0.75 times of the original stiffness as the optimization scheme,which can minimize the value of the comprehensive evaluation index C₁₂₉.