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01/04/2005
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With regulatory pressure now firmly on vehicle OEMs and suppliers for vehicle front ends to meet pedestrian impact targets, some increasingly novel systems are being developed, writes Roger Bishop.
Two organisations at the forefront of delivering pedestrian protection solutions are HBPO, an independent supplier owned jointly by Hella, Behr and Plastic Omnium, and GE Advanced Materials.
In last month’s issue (page 31) we briefly described a new front end beam developed by GE Advanced Materials, and this is more fully explained below. HBPO, meanwhile, has been developing a multi-system approach to lower and upper leg protection based on two components—a lower leg stiffener called SFuse and a fascia armature—along with a strategy for protecting pedestrians from the hard points of the front lighting system.
For the IAA Frankfurt Motor Show in September, HBPO is developing a demonstration front-end module integrating these features and proposals for reducing the size and packaging of cooling parts.
S-Fuse, a product of the company’s experience with VW Touran and Citroën C4 components, is designed to ensure that a pedestrian slides over the bonnet of the vehicle rather than being run over. The part is injection moulded in one piece from unfilled polypropylene and integrates four functions: an air guide for engine cooling, an air guide for brake cooling, the lower crashbox for meeting the low speed (15km/h) crash requirement and the lower stiffener for pedestrian protection.
According to Ralf Schmidt, director of R&D at HBPO, the laws of physics suggest that to meet the targets for intrusion, bending angle (<15º) and shear (<6mm), front overhang of a vehicle would have to increase by around 70mm, “completely contrary to the desire of OEMs who want to reduce the front overhang to give the car a more sporty dynamic outfit.”
To overcome the conflict, his team integrated a secondary load path specifically to meet the low speed crash requirements. “This allowed us to reduce the front overhang by roughly 50mm resulting in a total additional overhang to just 20mm,” he says. The part also exceeds the other principal requirements with a bending angle of <13º and a shear figure of 2mm.
The fascia armature component, also unfilled polypropylene, has an influence on both lower and upper leg protection. It includes foamed elements for energy absorption.
For optimal lower leg protection the lower leg stiffener and the armature have to be designed as a ‘tuned’ package, particularly with regard to stiffness. For upper leg impact protection, the fascia armature has to absorb impact energy of between 200 and 700J and intrusion of between 60 and 190mm. Early consultation between stylists, engineers and suppliers is crucial to achieving the best performance. An ideal illustration of this is the influence of moving the first contact point with the upper leg. “There is a direct link between the style of a car and the impact energy of a upper leg impact on the body,” says Schmidt. Moving the contact point 30mm downwards and 10mm forwards reduced the impact energy by 130J.
A simulation of the HBPO armature at impact showed all the hard components—radiator, condenser and air ducting—sliding backwards out of the impact zone. The company is confident of ‘under-running’ the regulatory requirements that says the reacting force should be smaller than 5000N and the resulting moment smaller than 300Nm.
Headlamp systems are being developed jointly by Hella and HBPO. Engineers are working on projector modules that absorb impact energy. “Rather than a solution that moves the headlamp, it is more efficient to absorb the energy within the headlamp by designing it like a crash box,” says Schmidt.
The behaviour of a headlamp can be compared with a tennis racket, soft in the middle and hard at the edges. This is why greater value must be placed on space for controlled displacement to absorb impact energy. Hella’s aim is to improve the energy absorption of headlamps via design changes. As a result of these design the maximum force arising in the case of thigh impact in accordance with Directive EEVC WG 17 stays below 5kN in relation to the overall vehicle.
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Author
Roger bishop
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