Damped heat shield

DETAILED DESCRIPTION The present invention provides a novel and improved damped heat shield.
The illustrated embodiment is an exhaust manifold heat shield.
However, the invention is applicable to other shielding applications where the shield must combine high temperature heat shielding with efficient vibration damping.
Illustratively, the heat shield may shield other portions of the exhaust system such as the exhaust pipe, the catalytic converter, and the muffler.
An illustrated embodiment provides two very thin metal layers of steel having different thicknesses positioned on opposite sides of a sheet of non-ferrous metal.
The two steel layers are formed of uncoated material which, in its initial state, does not have good corrosion resistance.
After the three layers are formed to the desired shape, at least some edges are hemmed to maintain the layers in nested substantial abutting contact.
The assembly is then coated with a high temperature corrosion-resistant coating that not only provides corrosion resistance to the exposed surface of the shield, but also forms a seal between the layers along the edges of the shield.
Although the inner surfaces of the three layers remain substantially uncoated, the entry of corrosion producing substances into the interior of the shield is prevented by the high temperature coating.
Consequently, significant corrosion of the interior surfaces of the shield does not occur.
Damping and vibration absorption is improved by utilizing sheets of thin steel having different thicknesses for the inner and outer metal layers.
Because the two layers have the same shape but different thicknesses, they have mismatched resonant frequencies.
When the frequency of vibration created by engine operation or from other sources is in resonance with one steel layer, it is not in resonance with the other steel layer.
Therefore, the two layers move relative to each other.
The friction resisting such relative movement results in an efficient damping and absorption of the vibrational energy resulting in the radiation of less sound energy and noise