Acoustics – Sound-modifying means – Muffler – fluid conducting type
Patent
1995-10-10
1997-12-30
Dang, Khanh
Acoustics
Sound-modifying means
Muffler, fluid conducting type
181268, 181281, F01N 108
Patent
active
057033382
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a sound absorber consisting of one or a plurality of sound absorbing elements which are installed in a round or oval guidance channel through which a flow acted upon by sound extends.
BACKGROUND OF THE INVENTION
Such devices are, for instance, known as exhaust systems on engines or air guides of air conditioning systems. In such systems a sound insulation is achieved by arranging "baffle plates" in the guidance channel (reflection damping) or by perforating the guidance channel and simultaneous covering with sound-absorbing materials (such as rock wool) between perforated guide pipe and another gas-tight covering (absorption damping).
In these systems a satisfactory sound absorption can only be accomplished at great overall lengths and thus at great amounts of material and great weights.
The present invention is based on the utility model registered under Register No. G 92 10 988.8 for a sound absorbing device for rectangular cross-sections.
SUMMARY OF THE INVENTION
It is the object of the present invention to improve a sound absorber in such a manner that an increased sound absorption can be achieved with the efforts spent on space, material and weight being small.
It is also the object of the present invention to provide a sound absorber of the above-mentioned type which avoids the drawbacks of the prior art and nevertheless has a small size under optimized flow conditions, at a high absorbing performance and at an optimized exhaust gas counterpressure.
In accordance with the invention, the object is attained by providing a sound absorber with a housing having inflow and outflow openings and sound absorbing elements therebetween. The sound absorbing elements define parallel entrance and exit planes inclined at an angle of less than 90.degree. with respect to a flow through the inflow opening.
The invention is especially suited for sound absorbing measures in systems in which there is little space available and whose weights are restricted and in which, at the same time, the maximum pressure is limited at a given throughput.
The sound absorber known from utility model 92 10 988.8 has only a limited absorbing effect, since the entrance flow impinges at a right angle onto the entrance plane. This may lead to undesired reflections of the sound waves and may be detrimental to the flow characteristics. Another disadvantage is that only rectangular cross-sections can be realized in the prior-art sound absorber. By contrast, the invention makes it possible to guide the entrance flow at a flat angle against the entrance plane. This will effect substantially improved sound absorbing characteristics which are above all due to the improved flow characteristics. In addition, it is possible to give the sound absorber a smaller size or to install a larger number of sound absorbing elements within a given volume.
These demands are, for instance, made on sound absorbers of aircraft engines which have a critical weight and in which there is only a very limited space available within the engine covering. Moreover, the sound absorber should only produce a limited back-pressure towards the engine.
Conventional systems (absorption dampers) must be mounted outside of the engine covering because of their large dimensions, they are very objectionable from an aerodynamic point of view and heavy.
Making use of the present invention on the sound absorber of an aircraft and integrating an absorbing element with a weight of 0.5 kg, a diameter of 95 mm, and a length of 200 mm into the existing exhaust system, one will achieve an absorbing performance which is improved by 1.5 dB(A) in comparison with a conventional external sound absorbing system having a weight of about 6 kg and a diameter of about 15 cm and a length of 1 m.
This comparison is based on officially acknowledged measurement results.
The improved sound-absorbing effect of the invention is due to the design of the gas guiding channels which respectively unite acoustically identical gas flows in the opposite dir
REFERENCES:
patent: 1081348 (1913-12-01), Unke et al.
patent: 4167987 (1979-09-01), Turner
patent: 4890691 (1990-01-01), Chingho
patent: 5123502 (1992-06-01), Flugger
patent: 5492195 (1996-02-01), Zink et al.
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