Development and Validation of Mathematical Model to Optimize a New Pedestrian Sensor Concept

Abstract

ABSTRACT - EEVC proposed the pedestrian headform impact test procedure to minimize the risk of head injuries in passenger car to pedestrian collisions. To meet the test requirements one protective system was developed and named Active Hood. It consists of a hood that is lifted in the rear end in case of a pedestrian impact. To activate it a contact sensor placed in the bumper is needed. An important issue of the sensor system to be solved is the temperature sensitivity arising from the unstable stiffness of bumper foam with the variety of environment temperature. A new concept pedestrian sensor has thus been developed and it should be less temperature dependent. This study aims at development of mathematical model of a new bumper system. Then the model will be used to optimize the new pedestrian sensor concept so as to solve the temperature sensitivity issue. Based on physical tests with simplified experimental bumpers in Autoliv Research, three Finite Element (FE) experimental bumper models have been developed in a first phase. Using these experimental bumper models, 11 physical tests were simulated to obtain the valid material parameters for a production bumper. Then a detailed production bumper FE model has been developed using validated material parameters. The standard production bumper model was evaluated according to EEVC WG17 test procedure requirements. Two aspects of improvement were then made on this model for the purpose that the improved FE bumper model can meet the requirements of the EEVC WG17 legform test procedure. Based on the improved bumper FE model, the new pedestrian sensor has been introduced in bumper foam and optimization has been carried out with varying concept sensor parameters. According to the optimization analysis, the smaller sensor tube diameter will lead to a better result. In all the tested parameters, the 25 mm diameter of sensor tube with 2.5 bars initial air pressure can give a high distinction of sensor signals when impact with objects of different masses. The signals from this FE model are less temperature dependent, which provided a mathematical model and background knowledge for a pedestrian sensing system design.