Wuppertal, Germany -- Acoustics specialists at Happich Division, Pelzer Acoustic Products, said 11 Jan that have yet again put their motto-- 'Creating Silence' -- into practice, by developing a new "double-sided sound-absorbing engine cover."
This component, made of perforated aluminium foil with a sound absorbent foam or glass fibre filling, cuts noise emissions in the engine compartment by 4 decibels compared with standard engine covers, and simultaneously halves the weight, a Happich statement said.
A prototype of this new method is already being used successfully by Volvo Penta Diesel for ships' engines.
Pointing out that standard engine covers offer barely any noise reduction, Happich notes that their main aim is to improve the appearance of the engine compartment.
"Look under the bonnet and the first thing you see is an immaculate plastic cover with an appealing manufacturer's logo. However, almost nobody knows that these attractive engine covers are made of a so-called 'reverberant' material." Despite the insulation underneath, an annoying residual noise remains that is not absorbed, said Happich.
Instead of "locking in" the noise emissions in this kind of reverberant plastic cover and thus even increasing them, it is more effective to absorb the sound directly at and outside the engine, in the engine compartment.
With this concept, it is not even necessary to fully cover the engine: Partial cladding is enough to reduce noise levels. And, because vibration isolators and rubber seals are redundant, the weight is also reduced by around 2 kilos.
This is the highly effective method of sound absorption is achieved with a special material, 'Versapanel,' used as a flexible engine cover. Its surface is made of aluminium foil, microperforated on both sides, and it contains a highly absorbent filling.
Asked for specific details of the construction, Alan Franks, managing director of Happich UK Ltd, said the engine cover is a thermoplastic, and the acoustic insulation uses aluminium foil, christened VariFoil, with either polyurethane foam or glass fibre core. Which core is used will depend on the application, specifically on the temperature demand upon the panel, Franks said.
The Llightweight and flexible construction can be easily adjusted even for complicated engine compartments. It also provides mechanical protection and is highly heat and liquid-resistant.
PIC: The new cover in Volvo Penta Diesel engine for ships' engines.