Sankt Augustin, Germany -- Three companies, Magna Steyr, Rühl Puromer and Hennecke have developed an engine bonnet with a honeycomb core, which meets automotive specifications, is substantially lighter and provides superior thermal and acoustic insulation to conventional bonnets made from steel or aluminium, Hennecke said.
In 2009, the EU published Global Technical Regulation (GTR) no. 9 on pedestrian protection, this is driving automotive innovation at a number of automotive manufacturers and suppliers around the world, said Hennecke. Pedestrian protection is also assuming greater importance in redefining of Euro NCAP ratings, a non-manufacturer-specific crash test programme.
Hennecke said that to receive 4-star or 5- star ratings for their vehicles, manufacturers must make greater efforts to ensure pedestrian protection. The engine bonnet is critical. It should be designed to absorb as much energy as possible in a collision with the body. This requires free space underneath the bonnet. In current motor vehicles, all of the space in the engine compartment is filled.
Henneck added that as a result, manufacturers have developed quick-acting systems that raise the bonnet in a collision, some are fitted with additional airbags. These are expensive, technically complex and need maintenance. They also take up more space and need design compromises to work.
Magna Steyr is part of Magna International used its expertise in sandwich technology to develop and produce exterior parts in series, said Hennecke.
The resulting fibre composite bonnet has been produced with support from Rühl Puromer and Hennecke. It is based on using fibre-reinforced polyurethane on an interlaced paper honeycomb structure.
The bonnet needed to meet Class A surface standard.
Rühl Puromer GmbH from Friedrichsdorf, Germany, developed the PU system and Puropreg system to make honeycomb sandwich support structures. Rhul also developed Purorim that uses Reaction Injection Moulding (RIM) process to ensure the required surface quality.
Hennecke's PURSeite PU mixing and metering system was chosen to process the materials
After the development period, series production of the bonnet is now imminent.
Hennecke said that, in principle, the sandwich structure of the bonnet resembles the design of a load-floor for luggage compartment system. A honeycomb core is used for the production of the bonnet, with glass fibre reinforcement applied from above and below. To achieve the different compression hardnesses and stability required in the bonnet, as might be needed for hinges, the honeycomb core is designed as a reinforced structure at the relevant points, Hennecke said.
Afterwards, the PU matrix is applied using the PUR-CSM spraying process. In this patented spray-up approach, the semi-finished fibre products are wetted on both sides with a thermally activated PU system. This makes it possible to apply a thicker layer of material in specific, targeted areas of the component. The part is then compressed and cured inside a mould. In the next stage, the RIM process is used on the outside and around the outer edge of the bonnet to produce the paintable class-A surface.
The polyurethane spray coat creates a durable connection between the glass fibre and the honeycomb core. This ensures extremely high stability and torsional rigidity. The thickness and structure of the honeycomb core allows the crash performance of the bonnet to be adjusted as needed. If the bonnet is designed to extend down to the radiator grille at the front, this area then also corresponds to the regulations for pedestrian protection, and allows the designers almost total freedom to design the front section of a vehicle.
The structural design also includes other positive effects. In addition to the substantially lower weight, the bonnet has excellent insulating properties thanks to its honeycomb core. A noise-absorbent mat, which is almost inevitable in conventional bonnets,is not needed.
It also thermally insulates the engine and means that cold starts can be reduced with lower CO2 emissions.
The bonnet has passed all of the comprehensive approval tests for use in the automotive industry - and naturally also the new requirements for pedestrian protection.