Acoustics – Sound-modifying means – Muffler – fluid conducting type
Patent
1997-04-17
1999-05-11
Dang, Khanh
Acoustics
Sound-modifying means
Muffler, fluid conducting type
181252, 181272, F01N1/02
Patent
active
059029706
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an exhaust muffler for internal combustion engines, especially for aircraft.
BACKGROUND OF THE INVENTION
There are presently several baffle plate muffler systems, by absorption by expansion, which permit attenuating the level of noise emitted to bring into compliance with the standards in force. These systems have the disadvantages of causing overheating and turbine blade counter pressures.
SUMMARY OF THE INVENTION
To alleviate these disadvantages the invention proposes a simple device using a particular geometry, and secondarily, components of austenite stainless steel. Besides the substantial reduction of the level of noise emitted in comparison with the existing systems, as will be described in an application example later, the proposed device is easy to install and to remove; its maintenance is easy and its durability over time is improved.
It was not obvious that the proposed geometry and the selection of an austenite stainless steel would permit obtaining the important advantages of the invention, and especially a gain greater than 5 dB minimum compared to mufflers of the former type. Nor was it obvious that baffle plate devices should be rejected, which are used often in numerous types of mufflers, in various types of industries.
Briefly, the muffler according to the invention, according to a preferred but not limiting mode of implementation, comprises a perforated tube extending throughout its length, and this muffler is characterized by the fact that the tube forms a geometry with several cones whose function is that of forming a substantial volume, of creating at least one system known under the term "venturi" to accelerate the flow of exhaust gas by the fact that the gas passing in the annular space between the tube and the envelope and escaping by the outlet parts whose shape and geometry prevent the formation of turbulence generating back pressures. Secondarily, according to a preferred mode of implementation, the muffler is made of austenite stainless steel. The space between the tube and the envelope is filled with steel wool likewise of austenite stainless steel.
An important advantage of the invention is that it permits the treatment of a more substantial volume of gas with a greater contact surface, the unit reducing the noise in a very significant degree, while permitting, which is surprising, the rapid exhaust of this greater volume without generating the major disadvantage which can be anticipated, of back pressure.
The geometry of the invention will be understood by a specialist in the field upon reading the enclosed drawings, without it being necessary to explain it in greater detail. A specialist in the field will moreover be able to imagine without difficulty the variants and derivatives of this geometry, observing the above general concept.
It is likewise surprising to note that the disagreeable noise well known to professionals using stainless steel (caused by ultrasonic frequencies) is not produced by the device according to the invention. It is known, for example, that the use of copper gives a "felt" sound but copper is naturally heavier. It is surprising to obtain an agreeable sound with a material sought for its qualities but likewise notorious for its disagreeable sound.
Other features and advantages of the invention will be clearly evident in the following description given by way of non-limiting example in regard to the enclosed figures, in which represent:
DESCRIPTION OF THE DRAWINGS
FIG. 1: a longitudinal cutaway view of the device according to the invention,
FIG. 2: a longitudinal cutaway view of a variant of the device according to the invention,
FIGS. 3 and 4: longitudinal cutaway views of variants of the device according to the invention,
FIGS. 5 and 6: respective transverse views of FIGS. 3 and 4 along A--A (representing the perforated partitions (6a),
FIG. 7: detail of a device represented in FIG. 1 or 2,
FIGS. 8 and 9: details of a device represented in FIG. 3 or 4.
DETAILED DESCRIPTION OF THE INVENTION
In reference to
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