Mazda Motor Corporation has developed a “Shock Cone Aluminium Hood [bonnet],” which has an all-new impact-absorbing structure aimed at enhancing pedestrian protection. Compared to conventional framed aluminium bonnets, this new structure has the potential to significantly reduce the severity of head injuries that can result when a pedestrian is struck by a car. The all-new bonnet will be used on the new RX-8 sports coupe due to appear in showrooms this spring, and will be gradually incorporated into other Mazda products.
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Framed bonnets, which are conventionally used for vehicles, have an inner panel with a bone structure to act as reinforcement. For pedestrian protection, safety engineers traditionally control impact absorption by adjusting the way the bone structure crumples. However, the framed inner panel inevitably leaves some hard points that may not fully absorb the forces of an impact.
Instead of a framed structure, the bonnet on the RX-8 has an inner panel that is uniquely shaped with numerous craters, similar to cones. The structure with these craters, called “shock cone,” yields effective impact absorption across the entire surface of the bonnet. This is the first time that this structure has been applied to bonnets with the aim of enhancing impact absorption to improve pedestrian protection.
The new bonnet is claimed to dramatically reduce the severity of head injuries sustained by pedestrians in accident. The shock cone structure achieves consistent impact absorption capacity across the entire bonnet surface. This reduces the extent of head injuries sustained by pedestrians who hit the bonnet after being struck by a car. In internal tests conducted under European NCAP pedestrian head protection test conditions, the new bonnet was shown to reduce the degree of head injury by as much as 50% when compared to a conventional aluminium bonnet structure.
The new panel also allows a reduced gap between bonnet and engine. The gap between the bonnet and engine is designed by taking into account the degree of intrusion into the engine compartment in a collision. The relatively even intrusion level and effective impact-absorbing properties of the new bonnet structure allowed engineers to reduce the gap between the engine and bonnet by one-third (approximately 30mm). This configuration, along with the low centre of gravity and compact size of the rotary engine, made it possible to employ a low bonnet design for the RX-8.
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By GlobalDataEnhanced rigidity and substantial weight reduction are additional benefits. Despite a 22% reduction in the thickness of the inner panel, the new bonnet structure is 1.5 times stronger in torsional rigidity than bonnets made using traditional construction. With a weight per unit area of 4.87kg/m2, the new aluminium bonnet is 23% lighter than that of the Mazda RX-7, and 9% lighter than that of the MX-5/Miata.
While car makers have been working very hard to enhance vehicle safety in the event of collisions through the introduction of new technologies, improvements to pedestrian protection are urgently needed. According to a report provided by the Institute for Traffic Accident Research and Data Analysis, around 30% of deaths resulting from traffic accidents are pedestrians, 60% of whom died from fatal head injuries.
