Impactor Development for the Assessment of Active Pedestrian Protection Systems

Although pedestrian protection regulation does not yet cover the complete testing of active protection systems, Euro NCAP introduced in 2011 a pop-up hood test protocol. Part of this assessment is a physical impact of a leg impactor against the vehicle front-end at the system’s lower deployment threshold speed to test the sensing systems’ response. As the leg impactors used for injury assessment are not suitable for sensor testing, some first generation "sensor assessment impactors" were developed. Three of them can be selected within the Euro NCAP testing: IEE lower limit impactor, PDI, TRL SensorLeg. But as each of these impactors has certain limitations, further research was needed to develop an impactor reproducing a representative human impact. This paper describes the development of an enhanced impactor with the highest possible level of abstraction, representing an appropriate effective mass not depending on the vehicle front-end geometry, showing human-like material properties and suitable for testing the "lower limit" case. The "lower limit" is defined as the lowest possible impact imprint that a sensing system must detect in a pedestrian-vehicle collision. A first step in the development is based on LSDYNA MADYMO coupled simulations where collisions between various MADYMO model statures (six-year-old child, 5% female, slim tall male, 50% male) and a variable test rig are evaluated. The test rig consists of variable load paths representing hood leading edge, lower bumper stiffener and the crossbeam area. In a second step, calculations are performed with an IEE in-house finite element human pedestrian model that is based on a driver knee-thigh-hip model which was further developed to a pedestrian model. This model was also scaled to represent the same adult pedestrian statures as mentioned above. Both simulation results were cross-checked and resulting differences were elaborated in a sensitivity analysis regarding knee-joint bending, knee-joint shear stiffness and contact stiffness of the MADYMO models. The resulting impactor with a mass of approximately 6.6 kg at maximum abstraction level represents the lower limit against a wide range of different vehicle front-end designs. Omitting the knee joint allows the representation of the lower limit stature, which can be the 5th percentile female, the slim tall male or the six-year-old child, depending on the front end geometry. The impactor has a flexible robust core and the tissue is made of PU material replicating human tissue characteristics. The impactor can be shot with a propulsion system or used in driving tests. The applicability of the impactor may be restricted for low bumper vehicles with a sensor mounting height below 400 mm above road level. As the development of active protection systems including A-pillar airbags is ongoing, there is a pressing need for defining procedures testing the sensors triggering these systems. A "lower limit" impactor properly reproducing pedestrian-bumper interaction in a realistic way is a crucial element within such tests.