A KNEE AIRBAG FOR ENHANCING FRONTAL IMPACT PROTECTION

摘要

The field accident data shows that the number of severe crash injuries to the head and chest has decreased in the last years due to improvements in vehicle crash-worthiness as well as the use of safety devices such as airbags, seat belt pretensioners and load limiters. Despite these achievements, there is still a long way to go to reduce injuries in other parts of the body such as the lower extremities. While these injuries are less critical because they are usually not life threatening, they may require very long recovery periods and also may often result in long-term or permanent disability. Knee airbags have been developed in order to improve the overall occupant restraint performance of the safety systems and also to help to reduce the injuries in the lower extremity area. In this study, the restraint performance of a safety system with and without knee airbag is compared through testing, under belted and unbelted conditions. Preliminary simulations with MADYMO were done to define the best position of the knee airbag optimizing its performance to make it work in the best conditions, together with the rest of frontal restraint systems (driver airbag, seatbelt pretensioner and load limiter). Many previous studies evaluating the performance of knee airbag systems have already been made. However, the efficiency of these systems have been usually assessed by testing, using the family of Hybrid III dummies who have some limitations when reproducing the occupant injuries. In this study, the THUMS simulation model has been used. This human model allows a better assessment of the potential injuries (such as ligament and bone injuries) from which the occupants might suffer. The study shows a potential reduction of occupant injuries by using a knee airbag, especially regarding loads in the knee area and the chest deflection. Recent crash test results (e.g. Euro NCAP) have also demonstrated an overall performance improvement in vehicles equipped with knee airbags. In addition, through the study of the THUMS model, a significant decrease in the injury level sustained by the lower extremities (patella and ligaments) in unbelted conditions was observed.