US Patent 8002081 Exhaust system for combustion engine

An exhaust system includes a tubular inner shell for passing therethrough exhaust gases from a combustion engine, and a tubular outer shell enclosing the tubular inner shell and cooperating therewith to define a sound silencing chamber into which the exhaust gases are introduced. The tubular inner shell forms an inner peripheral wall of the sound silencing chamber, and an upstream portion of the inner peripheral wall is formed with a perforated wall area having a plurality of communicating perforations for communicating between an interior of the tubular inner shell and the sound silencing chamber, and a downstream portion of the inner peripheral wall has a non-perforated wall area having no communicating perforation defined therein.