Exhaust system components of internal combustion and other types of engines are principally designed to reduce the noise exiting the engine with the exhaust gases. A typical exhaust system includes an exhaust pipe to carry exhaust gases and sound away from an engine, and a muffler to attenuate the sound propagated through the exhaust pipe. Mufflers include two general types according to the mode by which noise is attenuated. Reflection mufflers attenuate noise by reflection of sound waves in a series of structures. Mufflers that attenuate noise by absorption of sound waves using absorptive materials such as glass roving are known as dissipative or absorption mufflers.
Reflection mufflers use resonators or changes in exhaust flow direction by labyrinth-like baffling in the muffler. Reflection mufflers usually include a hollow steel housing defining an expansion chamber and one or more baffles and/or resonates chambers in flow communication with the expansion chamber, and inlet and outlet pipes. Sound waves enter and reflect off internal surfaces to cancel each other out and thereby reduce noise.
High temperature of exhaust gas and the corrosive nature of the gas typically have led designers to use metals, particularly steel, in fabrication of mufflers. Corrosion is a problem and has been addressed by using more expensive alloys such as stainless steel or steel alloys. Nevertheless mufflers typically remain bulky and heavy because of the high density of metals.
In effort to reduce the weight of mufflers, polymeric muffler housings with high temperature resistance have been designed, see for instance U.S. Pat. Nos. 5,321,214, 5,340,952 and 5,052,513, 6,543,577 and European Patent 446,064. However, polymeric muffler housings must, in some manner, interface and seal at very hot exhaust pipes. Much attention has been given to the issue of insulating polymeric muffler housings from the very hot exhaust temperatures.
U.S. Pat. No. 7,810,609 teaches an absorption muffler comprising a metallic exhaust pipe including a plurality of perforations, a polymeric housing carried by the exhaust pipe and enclosing the plurality of perforations, and including axially opposed ends. The acoustic insulation is carried between the thermal insulation and the polymeric housing. The muffler comprises flanges to seal the muffler assembly at the interface of the polymeric housing and the exhaust pipe.
U.S. Pat. No. 5,468,923 discloses a polymeric muffler including two halves, each with baffle walls and gas flow openings integrally molded therein. The gas flow openings do not intersect with the mating edges of the baffle walls. The muffler halves are joined along the mating edges of the baffle walls and the outer walls of the two muffler halves.
JP61077544 teaches a silencer material with silencing properties by attaching a viscous elastic body made of synthetic resin to the back of a plate-like non-woven cloth formed of synthetic resin fibers.
JP61034310 discloses a foamed and shaped body to be used as a silencing member by forming a skin layer. The skin layer has higher heat resisting characteristics than that of the foamed part.
US20070240932 teaches composite muffler systems formed of a long fiber thermoplastic. One suitable muffler structure is a multi-piece muffler assembly including at least one long fiber thermoplastic shell section.
EP394451B1 teaches a light-weight muffler having a high noise deadening effect. The outer shell may be a single layer of a thermotropic liquid crystal polyester or of a multiple layer structure comprising a first layer of a thermotropic liquid crystal polyester and a second layer of another structural material such as stainless steel.
US20100269344 discloses a process for making muffler systems wherein the muffler polymeric bodies have a cross section that is constant over the length of the muffler polymeric body.
US20090194364 discloses mufflers having polymeric bodies that are protected from being overheated from the exhaust pipe by having an air gap between the exhaust pipe and the polymeric body.
There is still a need for muffler assemblies having polymeric housings having improved acoustic tuning capabilities, reduction in overall weight, and ease of manufacturing especially addressing the issues of insulating and sealing the polymeric housing at the housing-exhaust pipe or a housing-mounting adapter interface.