Greater safety, less noise

WOCO acoustic covers made of polyurethane foam (PUF) increase pedestrian safety and reduce engine noise

The subject of pedestrian safety plays an increasingly important role for carmakers. Various types of acoustic covers, designed by Woco recently, and made of flexible, soft-integral polyurethane foam, help to optimise passive safety features involving pedestrians. During impact, they – in addition to the hood – absorb kinetic energy and hence prevent pedestrians making direct impact with the solid engine block. In this way, PUF covers help to improve the degree of fulfilment of the so-called Head Injury Criterion (HIC). As determined by crash tests, the HIC rating gives a measure of the severity of a head injury following a collision.

More space in the engine compartment

The single-part solution made of polyurethane foam allows for better use of the engine compartment space, compared to hard plastic covers. In order to protect the head and upper body of pedestrians against impact, carmakers have to keep a minimum clearance of 60 to 80 millimetres between the hood and the first hard component, depending on the type of vehicle. This is to ensure that there is sufficient space for the deformation of the hood so as to absorb kinetic energy. In contrast to hard plastic covers, the recently designed Woco acoustic covers perform exceptionally well in the area of pedestrian safety due to the fact that they are made exclusively from relatively soft polyurethane foam. Vehicle design engineers can thus utilise a larger design space by fitting engine components with dimensions matching the prescribed limits. This advantage of PUF covers is significant with regard to the steadily increasing number of technical components accommodated by the engine compartment and flatter hoods that have been optimised in terms of aerodynamics.

Optimal design, quiet & quick to assemble

The aspect of design played an important part during the development phase since the PUF covers are attached within the field of view of the engine. The engine trim panel therefore completely satisfies all OEM requirements with respect to logo integration and script nameplates from carmakers. By the same token, freedom of design is essential for optimal vibration insulation and it also affects the thermal management of the engine in a positive way. The foam is aligned with virtually all contours of the engine block on the inner side and by resting directly on the engine it completely encloses the upper section of the engine.

The trim panel thus reduces the noise level by up to five decibels. This improves the degree of acoustic comfort of passengers; however, the engine sound level is also important for obtaining type approval. The general maximum limit for motor vehicles in Europe is 74 decibels, which must not be exceeded when driving the vehicle. The acoustic cover dampens the ticking of the injectors in modern direct fuel-injected vehicles and, with diesel engines it reduces the so-called “rattle”. When conventional plastic covers are applied, special functional solutions involving foamed material are required. The perfect fit of the PUF cover allows the engine more time to cool down when shut off, so that it is still warm when started at a much later time; this, in turn, helps to reduce the emission of pollutants when restarting the vehicle.

There is yet another advantage for carmakers in using PUF covers: Only one component has to be installed and no additional fixtures are required to fit it at the engine. The fasteners are moulded in the foam during the production process. The cover snaps into place at the prepared recesses without the need for bolts or other tools.