A Study of an Integrated Safety System for the Protection of Adult Pedestrians from Car Collisions

Doctoral thesis, 2010

This study aimed to evaluate and improve the performance of a newly developed safety system intended to protect pedestrians during frontal car collisions. This system includes a remote sensor system, a contact sensor, a reversible bumper system (RBS), and a reversible hood (RH). The remote sensor system was evaluated for its ability to detect pedestrians at risk in a vehicular traffic environment. In this assessment, car-pedestrian accident scenarios were analyzed based on the cases selected from the Swedish TRaffic Accident Data Acquisition (STRADA) database. The two most common scenarios were identified as cars entering and leaving intersections, and colliding with pedestrians crossing the road. The accident data for these two scenarios were then investigated in terms of specific factors, such as the trajectory and velocity of the pedestrians and cars involved. Based on the accident data, a mathematical model was presented, and the remote pedestrian sensor system was evaluated using this model. The contact sensor was analyzed for the temperature-independent measurement of pedestrian impacts. A baseline bumper finite element (FE) model was initially developed and validated using the European New Car Assessment Program (EuroNCAP) lower legform impact tests performed on the production bumper. Based on the baseline bumper model, an improved bumper model was subsequently developed to meet the acceptance requirements of the European Enhanced Vehicle–safety Committee Working Group 17 (EEVC WG17) lower legform impact tests. A lower limb FE model was then developed and used to evaluate further the protective performance of the baseline and improved bumper models. Finally, the contact sensor was incorporated into the improved bumper model, and a performance study was conducted to evaluate its performance in terms of temperature stability and mass sensitivity of the sensor output. The performance of the RBS was investigated for the protection of pedestrians’ lower limbs during bumper collisions. The detailed FE model of a production car front was developed and validated based on the EuroNCAP lower legform impact tests performed on the production car front. Next, a model RBS was developed to replace the original bumper in the car front model. In order to investigate the performance of the RBS, the lower limb model and the EEVC WG17 lower legform model were used to collide with the RBS model of different design configurations under various impact conditions. Finally, the effects of the design parameters on the protective performance of the RBS were calculated using the statistical method for factorial experiment design. The RH was evaluated and optimized for the prevention of head injuries among adult pedestrians from hood collisions. The car front FE model was validated based on the EuroNCAP adult headform impact tests conducted on the car hood. The baseline RH was subsequently developed from the original hood of the validated car front model. The FE models of a 50th percentile human head and the EEVC WG17 adult headform were used in parallel to evaluate the protective performance of the baseline RH. In order to minimize the Head Injury Criterion (HIC) values of the headform model, the response surface method was applied to optimize the RH in terms of material stiffness, lifting speed and lifted height. Finally, the headform and human head models were once again used to evaluate the protective performance of the optimized RH. The results of this study indicated that the remote sensor system can detect almost all visible pedestrians in the two most common scenarios in a timely manner when the detection angle is greater than 60 degrees. The contact sensor can also identify pedestrian impacts with the car bumper. Moreover, enhanced sensor output stability and mass sensitivity can be achieved by using a 25 mm rather than 50 mm sensor tube. The RBS performance can be improved by reducing bumper stiffness; however, such performance is impaired in the bumper-deploying process at speeds of 2.5 m/s or greater. Less than 150 mm, the deployment distance of the RBS has no influence on the bumper protective performance. Compared with the retracted and lifting baseline RH, the lifted baseline RH can definitely minimize the injury parameters of the headform and human head models. When the optimized RH is lifted, the Head Injury Criterion (HIC) values of the headform and human head models are reduced to much lower than 1,000. Thus, the risk of pedestrian head injuries can be prevented as required by EEVC WG17.