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. Typical types of uses for these systems are on automobiles, trucks, snowmobiles, motorcycles, boats, motorized scooters, railroad engines, electrical generators, golf carts, tractors, lawn mowers, and other motorized agricultural, industrial, and landscaping equipment. Virtually any internal combustion engine includes a muffler (system) as a component. Because of the high temperatures of the exhaust gases, and the corrosive nature of those gases, metals, particularly steel, have traditionally been used for mufflers. Corrosion is a problem with these metals, but that has partially been solved by using more expensive alloys such as stainless steel or steel alloys such as aluminized steel. Nevertheless mufflers have tended to be bulky (needed to reduce the noise sufficiently), and heavy because of the high density of metals.
More recently it has been proposed to use mufflers in which the muffler body is a polymer with good high temperature resistance, see for instance U.S. Pat. Nos. 5,321,214; 5,340,952; 5,052,513; 6,543,577; and European Patent 446,064A2.
Today, with emissions regulations tightening every year, especially when related to carbon dioxide (CO2) emissions, and increasing demands for improved fuel economy, weight reduction has become a necessity for all applications related to internal combustion engines, especially for automobiles, commercial trucks, and other vehicles. In addition to emissions requirements, the ability to package exhaust system components to be as compact as possible is attractive, especially for non-automotive applications, such as small engines for lawn and garden, power tools, generators and generator sets.
Due to the extremely high temperatures involved with the exhaust gases produced during the combustion process, previous attempts to reduce weight in exhaust system components by using polymeric materials relied heavily upon thermoset polymers, thermoset composite materials, and thinner gauge steel or steel alloys. Exhaust system components made using thermoplastic polymers require considerable insulation to protect them from the hot gases and the hot exhaust pipes used to channel those gases. Previous embodiments of polymeric mufflers, for example, have used copious amounts of glass fiber matting, glass fiber fabrics, or glass fiber roving to provide thermal as well as acoustic insulation, infusible polymer or high melting temperature polymers bushings, or other insulating materials, such as ceramic, cleverly designed metal adaptors, metallic wire mesh, and even thermoset rubbers.
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.
However, there is still a need for polymeric exhaust mufflers having improved acoustic tuning capabilities than can be achieved using previous designs. What is needed is a muffler that utilizes a reflective tuning technique, similar to what is done in most metal mufflers on the market today.