Acoustics – Sound-modifying means – Muffler – fluid conducting type
Reexamination Certificate
2001-02-07
2002-10-01
Hsieh, Shih-Yung (Department: 2837)
Acoustics
Sound-modifying means
Muffler, fluid conducting type
C181S238000, C181S248000, C181S249000, C181S250000, C181S251000, C181S268000
Reexamination Certificate
active
06457552
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is in the field of muffling apparatus used to reduce the sound emitted by internal combustion engines. More particularly, the present invention involves methods and systems for muffling the sound emitted by internal combustion engines while maintaining low back pressure for improved power and fuel economy. The methods and systems employ a bed of silica, alumina or other appropriate particulate material for absorbing and/or disrupting sound waves.
2. Review of the Relevant Technology
Internal combustion engines are ubiquitous in modern life but have the drawback of producing considerable noise, particularly from the exhaust pipe. To effectively muffle and reduce engine noise to within acceptable levels, exhaust pipes are typically equipped with sophisticated channeling and baffling schemes. Because muffling systems typically involve restricting the free flow of exhaust gasses in order to disrupt or otherwise dampen the sound waves generated by the operation of the engine, mufflers can create significant “back pressure”, known to reduce fuel economy and power. The use of catalytic converters in-line with conventional muffling systems further increases back pressure.
Back pressure inherently reduces fuel economy and engine power by increasing the amount of work that the engine must perform just to emit the waste exhaust gases into the air. It also reduces power by generally requiring an increase in the fuel to air ratio that is fed into the cylinders in order for the engine to run properly. Conversely, reducing back pressure, such as by the use of expensive “headers” or other muffling systems rather than conventional mufflers allows for a leaner fuel/air mixture, thus resulting in greater generation of power per quantity of fuel used. Reducing back pressure also reduces the amount of work that the engine must perform to emit waste exhaust gases. Unfortunately, headers or other low back pressure muffling systems are costly and generally not approved for conventional vehicles, but are reserved for racing vehicles, because they do not meet present noise reduction standards.
In view of the requirement that vehicles with internal combustion engines must be equipped with muffling systems which meet relevant government noise reduction standards, but in view of other standards relating to the need to reduce pollution and improve fuel economy, there is inherently a tension or conflict with noise reduction goals, on the one hand, and fuel economy and emissions reduction, on the other. The result of this tradeoff is generally reduced power and vehicular performance.
It is obvious that improving fuel economy generally reduces the quantity of emissions produced by a vehicle. It is also true that deriving more power per quantity of fuel generally translates into better fuel economy and reduced emissions. One way to do this would be to reduce the back pressure resulting from conventional muffling systems. The problem with this strategy is that there are presently no reasonably priced or sized muffling systems that are capable of significantly reducing back pressure while satisfying present vehicle noise standards.
Another source of back pressure are in-line catalytic converters, which are required in order to reduce emissions from gasoline powered vehicles. Although catalytic converters themselves might not create as much back pressure as conventional mufflers, the back pressure imparted by a catalytic converter is cumulative to the back pressure created by the muffler in the same exhaust system, thus further reducing fuel economy and engine power.
In view of the foregoing, it would be an significant advancement in the art to provide improved methods and systems for effectively and inexpensively muffling the sound emitted by internal combustion engines while substantially reducing back pressure compared to conventional mufflers.
It would be a further advancement in the art to provide methods and systems for muffling the sound emitted by internal combustion engines which were simultaneously capable of substantially reducing back pressure compared to conventional mufflers while meeting or exceeding present noise reduction standards.
It would be a tremendous advancement in the art if such methods and systems for muffling the sound emitted by internal combustion engines were capable of reducing back pressure so as to improve fuel efficiency and increase engine power, while also providing equal or greater muffling of engine sounds compared to conventional mufflers.
Finally, it would be an enormous advancement in the art if such methods and systems for muffling the sound emitted by internal combustion engines were adaptable so as to also be capable of reducing pollutants found in exhaust emissions such that they provided the duel purpose of reducing engine noise and engine pollution.
Such methods and systems for muffling the sound emitted by internal combustion engines while reducing back pressure, increasing engine power and, optionally, reducing engine emissions are disclosed and claimed herein.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention encompasses improved methods and systems for muffling engine sounds emanating from the exhaust system of internal combustion engines. Such muffling methods and systems employ a muffling chamber filled with an appropriate particulate media capable of absorbing or otherwise disrupting the sound waves found in the exhaust stream corresponding to engine noise. Because moving exhaust gases are able to more freely pass through the spaces between the individual particles comprising the particulate media than through baffling and dampening devices found in conventional mufflers, the muffling systems of the present invention are able to muffle sound while reducing back pressure compared to conventional mufflers. In turn, greatly reducing the back pressure substantially improves the power and fuel efficiency of the engine.
The inventive muffling systems according to the invention preferably include one or more exhaust muffling chambers, which include muffling particles disposed therein, in gaseous communication with an internal combustion engine. The sound waves generated by the explosions within the cylinders of internal combustion engines are concentrated within and directed through the exhaust pipes or conduits connected to the engine. As the exhaust gases pass through the one or more exhaust muffling chambers the sound waves contained therein and propagated thereby are widely scattered, and thus dissipated and muted, by the surrounding particulate media. More particularly, a diffusion pipe is at least partially sunk beneath a volume of muffling particles so that the exhaust gases are passed from the diffusion pipe into the surrounding muffling particles. It is believed that the particulate muffling particles act to scatter and redistribute the sound waves throughout the muffling chamber in a manner that causes a substantial portion of the sound waves to become substantially out of phase and thus able to cancel each other out. This reduces the amplitude and, hence, the volume of the sound represented by the at least partially cancelled out sound waves.
An example of an appropriate particulate material capable of muffling sound from an internal combustion engine is silica sand. Another is alumina. Silica and alumina are preferred because they are also capable of catalytically degrading waste gases and particulates found in the exhaust gases from internal combustion engines, as more fully explained: in U.S. Pat. No. 5,928,618 and co-pending U.S. application Ser. Nos. 09/257,458 and 09/307,145. For purposes of disclosing methods and systems for catalytically degrading unburnt particulates and hydrocarbons in waste exhaust gases from an internal combustion engine and other systems that burn fossil fuels, the foregoing patent and applications are incorporated herein by specific reference.
In addition to providing catalytic degradation of unburnt hydrocarbons in waste exhaust gases, sil
Harrington Alan L.
Maganas Thomas C.
Hsieh Shih-Yung
Workman & Nydegger & Seeley
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