Sound protection panel for a motor vehicle engine compartment

A sound protection panel for a motor vehicle engine compartment, the panel comprising:

• a porous shell having a front face and a back face, the shell being based on polyurethane foam,
• a spring layer made from elastically compressible moulded polyurethane foam overmoulding the porous shell by the back face, part of the foam of the spring layer entering the porous shell over a proportion of the thickness of the porous shell, the porous shell is provided on its back face with an integrated sealed barrier,
• the panel provides sound protection
• by insulation, according to a “mass-spring” principle, the mass of which is formed by the porous shell,
• and by absorption through the porosity of the porous shell,
• the panel wherein
• the foam of the porous shell is an integral skinned foam the porous shell having
• a core with substantially homogeneous density,
• and a porous skin corresponding to the proportion of thickness where the density of the foam is greater than that of the core,
• the overall density of the shell is between 150 and 350 kg/m3, the shell has a mass per unit surface area that is sufficient for fulfilling its role of a mass,
• the skin has, on said front face, to optimise the absorption of the medium-frequency sound waves
• a thickness of between 0.3 and 2 mm,
• and a permeability such that a 2 mm thick strip of foam cut into the porous shell and integrating the skin exhibits air flow resistance of between 250 and 2000 N.s.m−3.