GB989061A - Improvements in or relating to a sound attenuating gas conduit - Google Patents

Abstract

989,061. Exhaust silencers. ARVIN INDUSTRIES Inc. July 24, 1961 [Feb. 13, 1961], No. 26727/61. Heading F1B. In a sound attenuating gas conduit, an openended pipe forming a gas-flow passage is free from substantial abrupt changes in its diameter and has an unrestricted flow at its ends, and mounted within the pipe is at least one silencing element comprising an elongated enclosed wall forming a sound attenuating cavity interconnected by throat-forming means with the interior of the pipe and having all or substantially all of its wall spaced from the pipe, the cross-sectional area of the gas passage within the axial extent of the element being smaller than the average cross-sectional area of the gas passage elsewhere. The cross-sectional area of the element is from about 25% to 75% of the cross-sectional area of the pipe within the axial extent of the element. The invention is described in connection with an exhaust system of an I.C. engine but it may be used on the intake side of an I.C. engine. An exhaust pipe 10, Fig. 1, is provided with low frequency (below 300 cycles/sec.) silencing elements 16 and high frequency (above 1500 cycles/sec.) silencing elements 18. Each element 16 has a tube 28 at each end interconnecting the gas stream with noise attenuating resonator volumes 26 separated by a baffle 24. Sheet metal support brackets 30 keep the elements clear of any condensed corrosive liquids. Alternatively, the elements may be suspended -from the pipe wall with one or more lines of contact therewith. In Fig. 9 (not shown) the elements are supported by two lines of contact with the wall of a pipe of elliptical cross-section. The pipe 10 may be in sections to facilitate replacement of corroded elements. Preferably the resonator volumes 26 are tuned to attenuate one of the objectionable harmonics and placed at or adjacent one of the maximum pressure points of that harmonic. If one of the maximum pressure points occurs at a bend a curved tube 27 may be provided. The elements 16 may be positioned closely adjacent one another so that the opposing tubes 28 thereof form a greater effective length and attenuate lower frequency waves. The elements 18 which are closed at their ends are perforated to render them at least 30% open. They contain a porous fibrous material, such as asbestos fibres or stainless steel wool, in the form of a wadding filling the cavity or a hollow sleeve lining the cavity walls. Another form of silencing element 42, Figs. 5 and 6 for frequencies of 300 to 1500 cycles/secs., is divided by baffle plates 45 into chambers 46 associated with openings 48 formed by shearing the tube to provide tongues 49. In another form of silencing element a plain cylinder closed at its ends has perforations in its side wall or in one end. In the latter case two such elements may be arranged perforated end to perforated end and suitably spaced to provide an effective throat length which will attenuate sound waves having frequencies of 100 to 700 cycles/sec. Alternatively, a perforated end may be arranged adjacent an unperforated one. The different forms of elements described may be used in combination and with conventional silencers.