US3119459A - Sound attenuating gas conduit - Google Patents

Sound attenuating gas conduit Download PDF

Info

Publication number
US3119459A
US3119459A US88977A US8897761A US3119459A US 3119459 A US3119459 A US 3119459A US 88977 A US88977 A US 88977A US 8897761 A US8897761 A US 8897761A US 3119459 A US3119459 A US 3119459A
Authority
US
United States
Prior art keywords
pipe
gas
elements
silencing
conduit
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US88977A
Inventor
Ludlow Edmund
Benjamin H Irwin
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Meritor Inc
Original Assignee
Arvin Industries Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Arvin Industries Inc filed Critical Arvin Industries Inc
Priority to US88977A priority Critical patent/US3119459A/en
Priority to GB26727/61A priority patent/GB989061A/en
Priority to DEA38596A priority patent/DE1299647B/en
Priority to DEA17848U priority patent/DE1856343U/en
Application granted granted Critical
Publication of US3119459A publication Critical patent/US3119459A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00Silencing apparatus characterised by method of silencing
    • F01N1/02Silencing apparatus characterised by method of silencing by using resonance
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N1/00Silencing apparatus characterised by method of silencing
    • F01N1/08Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling
    • F01N1/10Silencing apparatus characterised by method of silencing by reducing exhaust energy by throttling or whirling in combination with sound-absorbing materials
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2490/00Structure, disposition or shape of gas-chambers
    • F01N2490/20Chambers being formed inside the exhaust pipe without enlargement of the cross section of the pipe, e.g. resonance chambers

Definitions

  • This invention relates to a sound attenuating gas conduit for conveying, and attenuating the noise level of, a moving gas stream, and which is well adapted for use with an internal combustion engine for conveying the exhaust gases therefrom and silencing the noise level of said exhaust gases.
  • silencing elements may be used individually or in combination with other silencing means, and, in such applications as automotive exhaust silencing, our invention contemplates a system embodying a number of silencing elements in interrelated arrangement.
  • the exhaust manifold is connected to a pipe to convey the exhaust gases to the desired discharge point, as at the rear of the vehicle.
  • sound attenuating elements are placed at or adjacent to these pressure points, and are respectively made to attenuate the particular harmonic frequencies or bands of frequencies having pressure points at or adjacent such locations.
  • the silencing elements are arranged in direct and close thermal coupling relation with the gas stream, as
  • the silencing elements may include resonance cavities or volumes and one or more throats for acoustically coupling the volumes with the gas stream. These thermal and acoustical coupling relationships with the gas stream are desirably made maximal as by disposing the volumes and throats within, and axially symmetrical with, the gas stream.
  • silencing elements may also be used.
  • units for suppressing relatively wide bands of high sound wave frequencies may be placed at pointsnot occupied by specifically tuned elements.
  • FIG. 1 is a fragmentary isometric view partially in section showing a sound attenuating exhaust system embodying our invention
  • FIG. 2 is an enlarged fragmentary longitudinal section of the exhaust system shown in FIG. 1, but with the outer pipe shown as interfitting pipe sections;
  • FIG. 3 is an enlarged vertical section taken on the line 33 of FIG. 2;
  • FIG. 4 is an enlarged fragmentary longitudinal section of another portion of the exhaust system shown in FIG. 1;
  • FIG. 5 is a fragmentary longitudinal section showing a different form of silencing element
  • FIG. 6 is an enlarged vertical section taken on the line 66 Otf FIG. 5;
  • FIG. 7 is a fragmentary longitudinal section showing another form of silencing element
  • FIG. 8 is an enlarged vertical section taken on the line 8-8 of FIG. 7;
  • FIG. 9 is a vertical section of a modified embodiment of our invention.
  • Our invention is particularly well adapted for use with an internal combustion engine in an automobile to silence the exhaust gases emanating from said engine and to convey them to a suitable discharge point.
  • it completely replaces a conventional exhaust system in which all of the silencing effect is lumped in specific locations determined by the structural requirements of the vehicle, as in a muffler connected between an exhaust pipe joined to the exhaust manifold of the engine and a tail pipe leading from the mufi ler to a gas discharge point.
  • Such a muffier conventionally comprises an outer shell having an elliptically or circularly shaped cross-section many times larger than the cross-section of the exhaust and tail pipes, and has a relatively small number of large resonators, each adapted to attenuate a wide band of sound frequencies in the exhaust gases passing through the system.
  • All of the resonator chambers are baflled one from another, and are arranged within the mufiler shell in staggered patterns which, combined with the large size of the resonator chambers for the exhaust and tail pipes, result in the mufiler being large and difficult to mount in the limited space available on the underside of an automotive vehicle.
  • Our invention avoids the need for such large mufliers in specific locations by the employment of a series of small silencing elements in in-line relationship Within the gas stream in a pipe extending from the manifold to the gas discharge point.
  • the different silencing elements may be designed to attenuate different and/or overlapping bands of wave frequencies, and may be located in the pipe with respect to the harmonic characteristics of the pipe so that they will effect sound attenuation without the use of any large bulky resonator chambers,
  • Our invention thus provides an exhaust system which has a substantially smaller size and a lighter weight than a conventional muffler-type system, while still effecting at least the same degree of attenuation as a conventional muflleratype system.
  • the muffier silencers used provide in the flow passage of the system a substantial, abrupt enlargement of the cross-sectional area of the passage, with an abrupt increase in area at the upstream end of the silencing structure and an-abrupt decrease in area at the downstream end.
  • this produces a velocity decrease and an abrupt gas expansion which reduces the temperature of the gas and tends to condense exhaust vapors in position to be trapped and corrode the muffler structure.
  • our invention avoids such enlargement of the gas-flow passage, and desirably uses an outer pipe of substantially uniform cross-section with the silencing elements; disposed Wholly within such cross-section, which produces a reduction instead of an enlargement of the flow passage area at the location of a silencing element. While we avoid the abrupt enlargement of prior systems, and conveniently have reductions instead, we may form the structure to give a flow passage of generally uniform area.
  • Our invention is adapted to attenuate the noise level of the exhaust gases over a wide range of frequencies, including the troublesome frequencies below 200 cycles/ sec., by passing said gases through an exhaust conduit having a series of silencing elements mounted within it along its length.
  • the silencing elements may take several forms. For example, one form may be used to attenuate frequencies up to 300 cycles/see, another form to attenuate frequencies in the range of 100 cycles/see, to 700 cycles/sec, another form to attenuate frequencies in the range of 300 cycles/ sec. to 1,500 cycles/see, and still another form to attenuate those frequencies above 1,500 cycles/sec.-
  • silencing elements in accordance with our invention may be used alone to effect attenuation of the exhaust gas noises, they may be used in combination with conventional mufiiers, or may be incorporated within otherwise conventional mufflers as acoustical muffler components, or used in combination with acoustical liners lining axial sections of the conduit.
  • the embodiment shown in FIG. 1 comprises a pipe 10 adapted to be connected at one end to an exhaust manifold 12 by a conventional mounting flange 14, with its opposite end open to the atmosphere.
  • the pipe 10 may have the same outer diameter as the exhaust and tail pipes used in conventional exhaust systems. For example, it may have a diameter of about one and three-quarters to two and one-half inches, the diameters normally used in conventional exhaust pipes and tail pipes on automobiles; but it may have a larger diameter, say as large as four inches, the diameter of conventional exhaust and tail pipes in trucks, buses, and other large vehicles.
  • the pipe 10 may be a unitary length, it may be formed from a plurality of short interconnected lengths of pipe, as indicated in FIG. 2, to facilitate the installation and replacement of the silencing elements.
  • each of the elements 16 comprises an elongated wall, conveniently in the form of a length of metal-tubing 20, closed at its opposite ends as by inturned flanges forming end walls 22.
  • a baflle plate 24 is mounted within the tubing 20 intermediate its ends to divide the tubing 20 into a pair of elongated cavities or resonator volumes 26.
  • Each of the volumes 26 has associated with it a resonator throat-forming tube 28 having one of its ends open to its respective volume 26 and its opposite end open to the gas-flow passage formed by the pipe ll). In this manner, each of the volumes 26 is directly coupled by means of its throat 28 with the gas stream moving through the pipe 10 so that the resonators formed by said throats and volumes will attenuate the noise level of sound waves in the exhaust gases.
  • the elements 16 are supported in the pipe 10 by brackets 30, conveniently in the form of sheet-metal stampings.
  • the brackets 30 are rigidly secured to each of the sound attenuating elements 16 and to the wall of the pipe 10, and support the element 16 in spaced relation to the wall of the pipe 10.
  • the elements 16 are maintained out of contact with the wall of the pipe 10 and out of contact with any corrosive liquids condensed out of the exhaust gases onto the pipe wall, said liquids thus being free to drain out of the pipe.
  • the brackets 30 support the elements directly in the gas stream so that said elements are thermally coupled to the gas stream and will assume the temperature changes of said gas stream.
  • each resonator While each resonator attenuates to the maximum degree the particular frequency to which it is tuned, it will, of course, attenuate to a lesser extent a limited band of frequencies on either side of that particular frequency, and will effect some attenuation of substantially all frequencies.
  • the fundamental resonant frequency of the exhaust conduit depends upon the speed of sound.
  • the frequency of a resonator likewise depends upon the speed of sound. Since the speed of sound varies with temperature, differences between the temperatures of the resonators and the exhaust gases will interfere with the coordination necessary for the resonators to achieve their maximum attenuation.
  • the harmonic frequencies of the pipe 10 are subject to wide changes in the lower frequency ranges.
  • the resonators in the silencing elements 16 are respectively tuned to attenuate the objectionable harmonics in the gases in the conduit.
  • Each harmonic will have specifically located maximum sound-pressure points along the length of the conduit, the number of such pressure points and their location being a function of the particular harmonic involved.
  • the second overtone (third harmonic) will have three maximum pressure points along the conduit which will occur at points spaced from either end of the conduit by distances of onesixth, one-half, and five-sixths of the conduit-length.
  • Each of the resonators will attenuate to the maximum degree the particular harmonic for which it is tuned if its throat opening is coupled into the gas stream at any one of the points of maximum pressure of the harmonic for which it is tuned.
  • resonators While the resonators will effect maximum attenuation if their throats are located precisely at their maximum pressure points, they will, of course, still operate at high attenuating efficiencies if their throats are located adjacent such pressure points. For example, we have found that a resonator will operate at not less than 90% efficiency if its throat opening is placed at any point within a distance from the true maximum pressure point equal to one-twentieth of the length of the sound wave producing the pressure point.
  • n is the harmonic number for which the resonator is tuned, and m is every integer between and including 1 and n.
  • two or more resonators may be employed to attenuate a particular harmonic; indeed, in certain cases, substantially improved results may be obtained by using the same total resonator capacity in two or more resonators rather than in a single resonator. If two resonators are employed to attenuate a particular harmonic, they should be spaced along the conduit either so that their throats open to the conduit adjacent to the appropriate pressure points, or mounted in the conduit so that the throats of both open to the gas stream adjacent one of such pressure points.
  • each of the silencing elements 16 is mounted only in a straight section of the outer pipe 10, but the maximum pressure point of a harmonic frequency for which its resonator is tuned may be in a curved section of the pipe.
  • the silencing element may be constructed with the resonator throat projecting outwardly therefrom so that with the element mounted adjacent the curved section, the throat will project into said curved section to dispose its open end at the desired maximum pressure point location, as indicated at 27 in FIG. 1.
  • the relative positioning of the elements 16 with respect to each other also influences the action of the resonators with respect to the frequencies which they attenuate.
  • the resonators are spaced too close together, the space between their opposed end walls will be insufficient for the necessary acoustic coupling and will substantially reduce the attenuation efiiciencies of the resonators.
  • the silencing element 16 shown in FIG. 2 with the elongated tubular throats 28 is particularly well adapted for attenuating the troublesome sound wave frequencies "elow 300 cycles/sec.
  • the silencing element 18 is employed.
  • the element 18 comprises an elongated tube 34, conveniently a length of metal-tubing, closed at each of its ends, and supported on a bracket 36 mounted in the pipe 10 to thus dispose the element 13 directly in the path of the gas stream moving through the conduit.
  • the cavity within the tube 34- contains a porous fibrous material 38, such as asbestos fibers, stainless steel wool, or the like. This material may be in the form of a porous wadding filling the cavity, a hollow sleeve lining the cavity walls, or any other suitable configuration.
  • a plurality of perforations 39 are formed in the tube 34 to render it at least 30% open, and thus dispose the cavity containing the porous material 38 in operative acoustical communication with the sound waves in the gas stream.
  • the perforations 39 correspond to the throats 28 shown in FIG. 2 in that they operatively interconnect the cavity of the tube 34 with the gas stream.
  • the conductivity of 7 the perforations 39 is extremely high to thus cause the element 18 to preferentially attenuate the extremely high frequency sound waves above 1,500 cycles/sec.
  • silencing element shown in FIG. 4 will attenuate broad bands of high frequency sound waves having large numbers of relatively closely spaced maximum pressure points. Therefore, the axial positioning of these elements along the conduit is less critical than the placement of silencing elements for attenuating the lOWer frequency sound waves, and the type of element shown in FIG. 4 may thus be disposed immediately adjacent the discharge end of the conduit downstream from the silencing elements for the lower frequency sound waves. This leaves the other parts of the conduit free for mounting the lower frequency silencing elements at the maximum pressure points of the frequencies for which they are tuned.
  • silencing element in accordance with our invention is shown in FIGS. and 6, and comprises an outer pipe 40 having suspended within it one or more silencing elements, each comprising an elongated tube 42 closed at its ends and mounted on a channeled bracket 44 mounted in the pipe 40 to thus suspend the tube 42 in the gas stream in spaced relation to the pipe 40.
  • a plurality of baffle plates 45 are mounted within the tube 42 to divide it in a plurality of axially spaced resonator volumes 46.
  • a plurality of throat-forming openings 48 are formed in the tube 42 around its circumference within the axial extent of each of said volumes.
  • the openings are formed by shearing the tube 42 to provide tongues 49 bent to project from the tube wall.
  • the openings 48 with their adjacent tongues 49 constitute resonator throats which, because of their sheared construction, have a conductivity such that the silencing element will attenuate sound wave frequencies in the range of 300 cycles/ sec. to 1,500 cycles/ sec.
  • FIGS. 7 and 8 Still another form of silencing element in accordance with our invention is shown in FIGS. 7 and 8, in which there is an outer pipe 52 forming the gas-flow passage and having suspended within it pairs of silencing elements 54.
  • each of the elements 54 comprises an elongated tube 56 having one of its ends closed as at 58, and its opposite end provided with one or more perforations 60 which constitute throat-forming means for the resonator volume formed by the tube 56.
  • Each of the elements 54 is mounted on a bracket 62 mounted in the pipe 52 to thus dispose said elements in spaced relation to the pipe 52.
  • the elements 54 may be arranged in opposed pairs with their perforated end faces immediately adjacent each other. In such a closely spaced relationship, the space between the opposed end faces forms a common extension of the throat-forming means in the two resonators to increase the effective length of said means and cause the elements 54 to act upon a lower range of sound wave frequencies than the frequencies for which they are individually tuned.
  • the elements 54 When the elements 54 are disposed in their opposed relationship, they will attenuate sound wave frequencies in the range of 100 cycles/sec. to 700 cycles/sec, with their preferential frequency response in said range depending upon the size of the volumes of the tubes 56, the size and number of their perforations 6t), and the spacing between their opposed end faces.
  • the pair of elements are mounted in alignment with the perforated end face of one of said elements being disposed adjacent the nonperforated end face of the other.
  • either of the elements 54 may be employed without the use of the other and/or the throat-forming perforations in said elements may be disposed around the side walls of said elements instead of in their end faces.
  • the degree to which the elements 54 are perforated will normally be very small in comparison with the large degree of perfora' tion present in the silencing element 18 shown in FIGS. 1 and 4.
  • our silencing elements are carried within an outer pipe forming the gas-flow passage whereby the gases moving through said pipe will have to pass through the space between said pipe and the silencing elements.
  • the pipe forming said passage has a generally uniform cross-section with no substantial, abrupt changes in its diameter adjacent said silencing elements, and the average cross-sectional area of the gas-flow passage bctween said elements and the pipe within the axial extents of said elements is smaller than the average cross* sectional area of the gas-flow passage in the open portions of the pipe outside the extent of the silencing elements.
  • the cross-sectional area of the silencing elements is in the range of from about 25% to about 75% of the cross-sectional area of the pipe within the axial C71LHt of said elements so that said elements will effect the necessary degree of attenuation but will not unduly obstruct gas flow through the pipe and create excessive back pressures.
  • FIGS. 2 and 4 may be employed to attenuate extremely low and high ranges of frequencies, respectively, and elements of the type shown in FIGS. 5 and 7 may be used in combination therewith to attenuate the intermediate range frequencies.
  • FIGS. 5 and 7 may be used in combination therewith to attenuate the intermediate range frequencies.
  • FIGS. 2, 4, and 5 may be incorporated in an axially spaced relationship in the same length of tubing, and that length of tubing mounted in an outer pipe.
  • the silencing elements are located in the path of the gas stream movement. This permits our silencing elements to be intimately acoustically and thermally coupled to said gas stream so that said elements will not only achieve their maximum acoustic efficiencies through such direct coupling, but in addition, their resonant frequencies will adjust directly with the frequency changes in the gas stream due to temperature changes. Further, such suspension positions the silencing elements out of contact with the outer pipe to reduce their susceptibility to corrosion. However, should such corrosion occur, the silencing elements may be easily replaced by simply removing the corroded element and replacing it with a new element. As previously described, such replacement may be facilitated by forming the outer pipe from a plurality of short interfitting sections of pipe so that the defective silencing element and its respective pipe section may be replaced as a unit.
  • brackets may be omitted and the elements may contact the outer pipe along one or more lines of contact.
  • the elements may be suspended from one line of contact along the wall of the outer pipe, or the pipe and elements may have different cross-sectional configurations which permit the elements to contact, and be supported from, the pipe along two or more lines of contact.
  • FIG. 9 An example of the latter situation is shown in FIG. 9, in which the outer pipe indicated at it? is flattened into an eliptical cross-section, and the silencing element indicated at 16" abuts it along two lines of contact and is secured thereto by welds '13.
  • the means supporting the elements therein may comprise welded interconnections between the pipe and silencing elements along their lines of contact.
  • the major portions of the walls of said elements are disposed wholly out of contact with the outer pipe to provide a high degree of coupling between the elements and the gas stream, and to cause the gases to move through the space between the elements and the p1pe.
  • our invention for purposes of simplicity of description, we have only described our invention for use in an exhaust system for an engine. However, it may, of course, also be used on the intake side of an internal combustion engine for transporting and silencing the gas, intake flow to the engine, or for many other silencing applications.
  • an open-ended pipe free from substantial abrupt changes in its diameter forming a gas-flow passage having unrestricted flow at its ends, at least one silencing element mounted within said pipe inwardly from the ends thereof and comprisingan elongated enclosed wall forming a sound attenuating cavity, and throat-forming means in direct communication with the interior of said pipe operatively interconnecting said cavity and gas-flow passage whereby said element will silence the gases moving through said passage, the cross-sectional area of the gas passage within the axial extent of said element being smaller than the average cross-sectional area of the gas passage outside the axial extent of said element, said silencing element being mounted within said pipe in said gas-flow passage on a bracket secured to said pipe to support said silencing element wholly out of contact with said pipe whereby said gas stream must pass through the space between said element and pipe during its movement through the conduit.
  • an open-ended pipe free from substantial abrupt changes in its diameter forming a gas-flow passage having unrestricted flow at its ends, at least one silencing element mounted within said pipe inwardly from the ends thereof and comprising an elongated enclosed Wall forming a sound attenuating cavity, and throat-forming means in direct communication with the interior of said pipe operatively interconnecting said cavityand gas-flow passage whereby said element will silence the gases moving through said passage, said element having a cross-sectional area in a range of from about 25% to about 75% of the crosasectional area of the pipe within the axial extent of said silencing element with at least substantially all of said wall in spaced relation to said pipe whereby said gas stream must pass through the space between said element and pipe during its movement through the conduit.
  • said wall comprises a first length of tubing having enclosed ends
  • said throat-forming means comprises a second length of tubing mounted on said first length of tubing, said second length of tubing having a smaller crosssectional area than said first length of tubing and having one of its ends open to said gas-flow passage and its opposite end open to the cavity formed by said first length of tubing.
  • said wall comprises a length of tubing having enclosed ends
  • said throat-forming means comprises a plurality of axially and circumferentially spaced openings formed in said tubing, the portions of the tubing defining the edges of said openings being deformed out of the general plane of said tubing.
  • said wall comprises a length of tubing having enclosed ends, and said tubing is provided with one or more perforations comprising said throat-forming means.
  • said wall comprises a length of tubing having enclosed ends and containing a porous, fibrous sound-absorbing material
  • said throat-forming means comprises a plurality of perforations formed in said tubing to render the same at least 30% open.
  • said Wall comprises an elongated length of tubing having enclosed ends and provided with a plurality of axially spaced bafile plates mounted on its interior to divide said cavity into a plurality of cavities, and said throat-forming means forms a plurality of passages each of which is open to said gas-flow passage and one of said plurality of cavities.
  • a pipe forming a gas-flow passage for said gas stream, a plurality of silencing elements mounted within said gas stream, each of said silencing elements comprising an elongated wall closed at its ends and forming a sound attenuating cavity, and throat-forming means operatively interconnecting said cavity and gas-flow passage whereby each of said elements will attenuate the noise level of the gases moving through said passage, at least one pair of said elements being mounted in the gas stream in opposed relationship with the throat-forming means of each of said pair of elements being disposed in their opposed end faces and said opposed end faces being disposed closely adjacent each other to define a common extension for the throat-forming means of said pair of elements, and means supporting each of saidelements in said gas-flow passage with at least substantially all its wall in spaced relation to said pipe whereby said gas stream will have to pass between said silencing elements and the pipe during its movement through the conduit.
  • an open-ended elongated pipe forming a gas-fiow passage wherein a sound source will produce standing waves having pluralities of harmonic frequencies, and a plurality of silencing elements mounted within said pipe along the length thereof with their adjacent ends in axially spaced relationship, said pipe being free from substantial, abrupt changes in its diameter adjacent said silencing elements, each of said silencing elements comprising means disposed in said gas-flow passage forming a closed resonator volume, said means being positioned in said gas-flow passage with at least a major portion of said volume spaced from said pipe whereby said gas stream must pass between said means and the pipe during its movement through the gas-flow passage, and means on said first mentioned means forming a resonator volume throat operatively interconnecting said volume and gasflow passage whereby said plurality of silencing elements will be acoustically coupled to said gas stream at points along the length of said
  • each of said one or more silencing elements has a throat formed from an elongated tubular element, and each :of said one or more silencing elements is responsive to a predetermined sound wave frequency constituting one of the standing harmonic frequencies of the conduit with its associated throat operatively connected tosaid gas flow passage adjacent a position along the length of the conduit where the harmonic frequency for which the silencing element is responsive reaches its maximum pressure.
  • ⁇ An exhaust silencing system for an internal com bustion engine comprising an open-ended pipe for connection to the engine to receive the exhaust gases thereof and to convey such gases to a discharge point, said pipe forming a gas conduit wherein the exhaust sound produces one or more distinct harmonic sound-pressure points at particular locations along the length of the conduit equal to fractional lengths thereof according to the formula where n is a harmonic number and m is every integer between and including 1 and n, and a plurality of silencing elements moiuited in said conduit along the length thereof with their adjacent ends in axially spaced relationship and in close thermal coupling relationship with the gas stream, one or more of said silencing elements comprising a resonator volume formed from a closed end pipe and an elongated tubular throat operatively associated with said volume, each of said one or more silencing elements having volume and throat construction to cause said silencing element to have a frequency response according to the formula where C is the speed of sound at the temperature of the gas stream, V is the capacity of the resonator
  • each of the silencing elements in said second set comprises a plurality of perforations formed in said tubing to render the same at least 30% open, and all of said second set of silencing elements are mounted in said pipe downstream of said first set of silencing elements.

Description

1964 E. LUDLOW ETAL SOUND ATTENUATING GAS coNnuI'r 2 Sheets-Sheet 1 Filed Feb. 13, 1961 i'illl hllll iP "6.0.:
INVENTORS. {UNI/N0 Luoww AND BYBE/VJ'AM/N M I ,ewuv w OOQOOOGO A TTORNE ys.
E. LUDLOW ETAL SOUND ATTENUATING GAS CONDUIT Jan. 28, 1964 2 Sheets-Sheet 2 Filed Feb. 13, 1961 INVENTORS. ZZJMUND L001. ow Am: BY 35mm M/IV H. Imam United States Patent 3,119,459 SOUND ATTENUATING GAS CONDUIT Edmund Ludlow and Benjamin H. Irwin, Columbus, Ind, assignors to Arvin Industries, Inc., Columbus, Ind., a corporation of Indiana Filed Feb. 13, 1961, Ser. No. 88,977 Claims. (Cl. 181-59) This invention relates to a sound attenuating gas conduit for conveying, and attenuating the noise level of, a moving gas stream, and which is well adapted for use with an internal combustion engine for conveying the exhaust gases therefrom and silencing the noise level of said exhaust gases.
It is an object of our invention to provide such a sound attenuating gas conduit which will meet limited space requirements, which can be easily manufactured largely from inexpensive metal-tubing, and which can be of lightweight construction with its weight substantially uniformly distributed along its length. It is a further object of our invention to provide such a sound attenuating gas conduit which can be made to effect sound attenuation over a wide range of frequencies, which may be tuned to attenuate undesired frequencies, and which will remain substantially in tune with said frequencies irrespective of temperature changes of the gas stream in which'the sound waves are carried. It is still a further object of our invention to provide such a sound attenuating gas conduit which will be less susceptible to certain types of corrosion than conventional gas-silencing systems, and which may employ replaceable sound attenuating units.
it is a special object of our invention to provide a sound attenuating gas conduit for the exhaust gas stream of an automotive vehicle, which will eliminate the need for the bulky, expensive, and troublesome muffiers which are required in conventional automotive exhaust silencing systems.
We have discovered that it is possible to attenuate the noise level of individual sound frequencies by suitably located tuned elements of much smaller physical size than the structures required in prior muffler-type systems, and that by the use of a combination of such elements we can provide a complete and practical automotive exhaust silencing system within the configuration of a simple pipe extending from the usual automotive engine to the usual point of discharge of the exhaust gases.
Our silencing elements may be used individually or in combination with other silencing means, and, in such applications as automotive exhaust silencing, our invention contemplates a system embodying a number of silencing elements in interrelated arrangement.
In accordance with our invention as applied to an automotive exhaust system, the exhaust manifold is connected to a pipe to convey the exhaust gases to the desired discharge point, as at the rear of the vehicle. Acoustically, such pipe, usually with at least part of the exhaust manifold, forms a conduit in which the exhaust sound produces standing wave pressure patterns, wherein each of the several harmonic components of the standing waves has one or more distinct pressure points, that is, points of maximum sound pressure, at particular locations along the conduit. In accordance with our invention, sound attenuating elements are placed at or adjacent to these pressure points, and are respectively made to attenuate the particular harmonic frequencies or bands of frequencies having pressure points at or adjacent such locations.
In order to maintain effective attenuation under the varying temperature conditions and gradients which will occur, the silencing elements are arranged in direct and close thermal coupling relation with the gas stream, as
I 3,119,459 Patented Jan. '28, 1964 within and surrounded by the gas stream. The silencing elements may include resonance cavities or volumes and one or more throats for acoustically coupling the volumes with the gas stream. These thermal and acoustical coupling relationships with the gas stream are desirably made maximal as by disposing the volumes and throats within, and axially symmetrical with, the gas stream.
Other forms and locations of silencing elements may also be used. For example, units for suppressing relatively wide bands of high sound wave frequencies may be placed at pointsnot occupied by specifically tuned elements.
Other objects and features of our invention will become apparent from the more detailed description which follows and from the accompanying drawings, in which:
FIG. 1 is a fragmentary isometric view partially in section showing a sound attenuating exhaust system embodying our invention;
FIG. 2 is an enlarged fragmentary longitudinal section of the exhaust system shown in FIG. 1, but with the outer pipe shown as interfitting pipe sections;
FIG. 3 is an enlarged vertical section taken on the line 33 of FIG. 2;
FIG. 4 is an enlarged fragmentary longitudinal section of another portion of the exhaust system shown in FIG. 1;
FIG. 5 is a fragmentary longitudinal section showing a different form of silencing element;
FIG. 6 is an enlarged vertical section taken on the line 66 Otf FIG. 5;
FIG. 7 is a fragmentary longitudinal section showing another form of silencing element;
FIG. 8 is an enlarged vertical section taken on the line 8-8 of FIG. 7; and
FIG. 9 is a vertical section of a modified embodiment of our invention.
Our invention is particularly well adapted for use with an internal combustion engine in an automobile to silence the exhaust gases emanating from said engine and to convey them to a suitable discharge point. In such usage, it completely replaces a conventional exhaust system in which all of the silencing effect is lumped in specific locations determined by the structural requirements of the vehicle, as in a muffler connected between an exhaust pipe joined to the exhaust manifold of the engine and a tail pipe leading from the mufi ler to a gas discharge point. Such a muffier conventionally comprises an outer shell having an elliptically or circularly shaped cross-section many times larger than the cross-section of the exhaust and tail pipes, and has a relatively small number of large resonators, each adapted to attenuate a wide band of sound frequencies in the exhaust gases passing through the system. In such muffiers, there are normally provided two large resonator chambers respectively tuned to attenuate the harmonic frequencies of the exhaust and tail pipes. All of the resonator chambers are baflled one from another, and are arranged within the mufiler shell in staggered patterns which, combined with the large size of the resonator chambers for the exhaust and tail pipes, result in the mufiler being large and difficult to mount in the limited space available on the underside of an automotive vehicle.
Our invention, however, avoids the need for such large mufliers in specific locations by the employment of a series of small silencing elements in in-line relationship Within the gas stream in a pipe extending from the manifold to the gas discharge point. The different silencing elements may be designed to attenuate different and/or overlapping bands of wave frequencies, and may be located in the pipe with respect to the harmonic characteristics of the pipe so that they will effect sound attenuation without the use of any large bulky resonator chambers,
as are required in a conventional mufller-type system. Our invention thus provides an exhaust system which has a substantially smaller size and a lighter weight than a conventional muffler-type system, while still effecting at least the same degree of attenuation as a conventional muflleratype system.
In muffler-type silencing systems, the muffier silencers used provide in the flow passage of the system a substantial, abrupt enlargement of the cross-sectional area of the passage, with an abrupt increase in area at the upstream end of the silencing structure and an-abrupt decrease in area at the downstream end. Among other things, this produces a velocity decrease and an abrupt gas expansion which reduces the temperature of the gas and tends to condense exhaust vapors in position to be trapped and corrode the muffler structure. In contrast to this, our invention avoids such enlargement of the gas-flow passage, and desirably uses an outer pipe of substantially uniform cross-section with the silencing elements; disposed Wholly within such cross-section, which produces a reduction instead of an enlargement of the flow passage area at the location of a silencing element. While we avoid the abrupt enlargement of prior systems, and conveniently have reductions instead, we may form the structure to give a flow passage of generally uniform area.
In the operation of a conventional internal combustion engine in an automobile, the combustion of fuel within the cylinders produces a substantial volume of hot exhaust gases which are exhausted with substantial noise into the exhaust manifolds mounted on the engine in communication with the cylinder exhaust ports. The frequencies of the sound waves in such exhaust gases extend over a wide range, such as from about 30 cycles/sec. to about 5,000 cycles/see, with the lower frequencies largely representing the fundamental and lower harmonics determined by the length of the exhaust conduit. In many exhaust systems it is the lower range of frequencies, i.e., frequencies below 200 cycles/sec. that are the most difficult to attenuate and produce the most objectionable noises, especially since it is in this low frequency range that the firing frequencies of the engine coincide with and augment the natural resonant frequencies of the exhaust system itself. In many conventional mufilers these low frequencies are not adequately attenuated because the large size of the mufilers prevents them from being positioned on the underside of a vehicle in the proper positions with respect to the exhaust system to act upon and attenuate these low frequencies.
Our invention is adapted to attenuate the noise level of the exhaust gases over a wide range of frequencies, including the troublesome frequencies below 200 cycles/ sec., by passing said gases through an exhaust conduit having a series of silencing elements mounted within it along its length. The silencing elements may take several forms. For example, one form may be used to attenuate frequencies up to 300 cycles/see, another form to attenuate frequencies in the range of 100 cycles/see, to 700 cycles/sec, another form to attenuate frequencies in the range of 300 cycles/ sec. to 1,500 cycles/see, and still another form to attenuate those frequencies above 1,500 cycles/sec.-
While silencing elements in accordance with our invention may be used alone to effect attenuation of the exhaust gas noises, they may be used in combination with conventional mufiiers, or may be incorporated within otherwise conventional mufflers as acoustical muffler components, or used in combination with acoustical liners lining axial sections of the conduit.
The embodiment shown in FIG. 1 comprises a pipe 10 adapted to be connected at one end to an exhaust manifold 12 by a conventional mounting flange 14, with its opposite end open to the atmosphere. Conveniently, the pipe 10 may have the same outer diameter as the exhaust and tail pipes used in conventional exhaust systems. For example, it may have a diameter of about one and three-quarters to two and one-half inches, the diameters normally used in conventional exhaust pipes and tail pipes on automobiles; but it may have a larger diameter, say as large as four inches, the diameter of conventional exhaust and tail pipes in trucks, buses, and other large vehicles. While the pipe 10 may be a unitary length, it may be formed from a plurality of short interconnected lengths of pipe, as indicated in FIG. 2, to facilitate the installation and replacement of the silencing elements.
In the exhaust system illustrated in FIG. 1, a plurality of low frequency silencing elements 16 and high frequency silencing elements 18 are mounted in the pipe 10 in the path of the gas stream moving through said pipe. As shown in FIG. 2, each of the elements 16 comprises an elongated wall, conveniently in the form of a length of metal-tubing 20, closed at its opposite ends as by inturned flanges forming end walls 22. A baflle plate 24 is mounted within the tubing 20 intermediate its ends to divide the tubing 20 into a pair of elongated cavities or resonator volumes 26. Each of the volumes 26 has associated with it a resonator throat-forming tube 28 having one of its ends open to its respective volume 26 and its opposite end open to the gas-flow passage formed by the pipe ll). In this manner, each of the volumes 26 is directly coupled by means of its throat 28 with the gas stream moving through the pipe 10 so that the resonators formed by said throats and volumes will attenuate the noise level of sound waves in the exhaust gases.
In the embodiment of FIGS. 1 and 2, the elements 16 are supported in the pipe 10 by brackets 30, conveniently in the form of sheet-metal stampings. The brackets 30 are rigidly secured to each of the sound attenuating elements 16 and to the wall of the pipe 10, and support the element 16 in spaced relation to the wall of the pipe 10. Thus, the elements 16 are maintained out of contact with the wall of the pipe 10 and out of contact with any corrosive liquids condensed out of the exhaust gases onto the pipe wall, said liquids thus being free to drain out of the pipe. Further, the brackets 30 support the elements directly in the gas stream so that said elements are thermally coupled to the gas stream and will assume the temperature changes of said gas stream.
In order that the system of resonators formed by the volumes 26 and throats 28 will attenuate a substantial range of sound wave frequencies in the exhaust gases, it is necessary that individual resonators be tuned to given frequencies or frequency ranges at least approximately coordinated with the fundamental resonant frequency of the exhaust conduit. Such tuning may be effected by adjusting the conductivity of the resonator throat with respect to the size or capacity of the resonator volume. For resonators with tubular throats, the formula for calculating the tuning may be represented by the formula:
C C 21r V where f is the frequency to which the resonator is to be tuned, C is the speed of sound in inches per second at the temperature of the medium, V is the capacity of the resonator volume, and C is the conductivity of the resonator throat calculated from the formula:
While each resonator attenuates to the maximum degree the particular frequency to which it is tuned, it will, of course, attenuate to a lesser extent a limited band of frequencies on either side of that particular frequency, and will effect some attenuation of substantially all frequencies.
As will be understood from well known principles of acoustics, the fundamental resonant frequency of the exhaust conduit, with which the frequncies of the resonators are to be coordinated, depends upon the speed of sound. As shown by the first formula set forth above, the frequency of a resonator likewise depends upon the speed of sound. Since the speed of sound varies with temperature, differences between the temperatures of the resonators and the exhaust gases will interfere with the coordination necessary for the resonators to achieve their maximum attenuation.
These changes in the speed of sound resulting from changes in the temperature of the medium in which the sound waves are carried will also cause the frequencies of the sound waves to change, the degree of frequency change depending upon the temperatures and frequencies involved. For example, we have found that in the temperature range of 72 F. to 500 F., each 100 F. change in temperature will produce the following frequency changes in a conduit whose fundamental wave frequency is 37.7 cycles/sec: its fundamental wave frequency of 37.7 cycles/sec. will change 3 cycles/see; its second harmonic of 75.4 cycles/sec. will change 6 cycles/see; its third harmonic of 113.1 cycles/sec. will change 9 cycles/sec; etc. Thus, in the normal operation of an automobile where the exhaust gases may range from a temperature of about 200 F. when the engine is cold to a temperature of about 1,700 F. when the engine is hot, the harmonic frequencies of the pipe 10 are subject to wide changes in the lower frequency ranges. In our system, we place the silencing elements directly in the gas stream so that the resonators are subjected to the same temperature changes as the gas stream at the points where the resonators are located in said gas stream. This maintains the temperature difference between the resonators and the gas stream at a minimum, irrespective of gas stream temperature changes, and the resonators will thus remain coordinated with the resonant harmonic pipe frequencies which they are to attenuate.
Preferably, the resonators in the silencing elements 16 are respectively tuned to attenuate the objectionable harmonics in the gases in the conduit. Each harmonic will have specifically located maximum sound-pressure points along the length of the conduit, the number of such pressure points and their location being a function of the particular harmonic involved. For example, the second overtone (third harmonic) will have three maximum pressure points along the conduit which will occur at points spaced from either end of the conduit by distances of onesixth, one-half, and five-sixths of the conduit-length. Each of the resonators will attenuate to the maximum degree the particular harmonic for which it is tuned if its throat opening is coupled into the gas stream at any one of the points of maximum pressure of the harmonic for which it is tuned. While the resonators will effect maximum attenuation if their throats are located precisely at their maximum pressure points, they will, of course, still operate at high attenuating efficiencies if their throats are located adjacent such pressure points. For example, we have found that a resonator will operate at not less than 90% efficiency if its throat opening is placed at any point within a distance from the true maximum pressure point equal to one-twentieth of the length of the sound wave producing the pressure point.
In general, such maximum pressure points are spaced from an end of the conduit by fractions L of the conduitlength according to the formula:
2m 1 L- 2n where n is the harmonic number for which the resonator is tuned, and m is every integer between and including 1 and n. Thus, if a particular resonator is tuned to attenuate the second harmonic frequency of the gases in the conduit, the above formula may be employed to determine that the throat opening for the resonator should be spaced from one end of the conduit by a distance equal to one-fourth or three-fourths of the length of the conduit.
It is to be understood that instead of a single resonator, two or more resonators may be employed to attenuate a particular harmonic; indeed, in certain cases, substantially improved results may be obtained by using the same total resonator capacity in two or more resonators rather than in a single resonator. If two resonators are employed to attenuate a particular harmonic, they should be spaced along the conduit either so that their throats open to the conduit adjacent to the appropriate pressure points, or mounted in the conduit so that the throats of both open to the gas stream adjacent one of such pressure points.
For ease of construction, each of the silencing elements 16 is mounted only in a straight section of the outer pipe 10, but the maximum pressure point of a harmonic frequency for which its resonator is tuned may be in a curved section of the pipe. To overcome this difficulty and to permit the resonator to operate at its maximum efliciency, the silencing element may be constructed with the resonator throat projecting outwardly therefrom so that with the element mounted adjacent the curved section, the throat will project into said curved section to dispose its open end at the desired maximum pressure point location, as indicated at 27 in FIG. 1.
The relative positioning of the elements 16 with respect to each other also influences the action of the resonators with respect to the frequencies which they attenuate. We have found that by positioning a pair of elements 16 closely adjacent each other as in the relationship shown in FIG. 7, the space between the opposed end walls 22 forms a common annular extension of the throats 28. This increases the effective length of the throats 28 with the result that the opposed resonators attenuate lower frequencies than they would attenuate if their walls 22 are spaced relatively farther apart. Of course, if the resonators are spaced too close together, the space between their opposed end walls will be insufficient for the necessary acoustic coupling and will substantially reduce the attenuation efiiciencies of the resonators. Conversely, if the opposed end walls are spaced substantially apart, there will be no mutual throat action between the resonators and they will act independently of each other.
The silencing element 16 shown in FIG. 2 with the elongated tubular throats 28 is particularly well adapted for attenuating the troublesome sound wave frequencies "elow 300 cycles/sec. To attenuate those frequencies occurring above 1,500 cycles/sec, the silencing element 18 is employed. As shown in FIG. 4, the element 18 comprises an elongated tube 34, conveniently a length of metal-tubing, closed at each of its ends, and supported on a bracket 36 mounted in the pipe 10 to thus dispose the element 13 directly in the path of the gas stream moving through the conduit. The cavity within the tube 34- contains a porous fibrous material 38, such as asbestos fibers, stainless steel wool, or the like. This material may be in the form of a porous wadding filling the cavity, a hollow sleeve lining the cavity walls, or any other suitable configuration.
A plurality of perforations 39 are formed in the tube 34 to render it at least 30% open, and thus dispose the cavity containing the porous material 38 in operative acoustical communication with the sound waves in the gas stream. The perforations 39 correspond to the throats 28 shown in FIG. 2 in that they operatively interconnect the cavity of the tube 34 with the gas stream. However, because of their negligible length, the conductivity of 7 the perforations 39 is extremely high to thus cause the element 18 to preferentially attenuate the extremely high frequency sound waves above 1,500 cycles/sec.
The type of silencing element shown in FIG. 4 will attenuate broad bands of high frequency sound waves having large numbers of relatively closely spaced maximum pressure points. Therefore, the axial positioning of these elements along the conduit is less critical than the placement of silencing elements for attenuating the lOWer frequency sound waves, and the type of element shown in FIG. 4 may thus be disposed immediately adjacent the discharge end of the conduit downstream from the silencing elements for the lower frequency sound waves. This leaves the other parts of the conduit free for mounting the lower frequency silencing elements at the maximum pressure points of the frequencies for which they are tuned.
Another form of silencing element in accordance with our invention is shown in FIGS. and 6, and comprises an outer pipe 40 having suspended within it one or more silencing elements, each comprising an elongated tube 42 closed at its ends and mounted on a channeled bracket 44 mounted in the pipe 40 to thus suspend the tube 42 in the gas stream in spaced relation to the pipe 40. Conveniently, a plurality of baffle plates 45 are mounted within the tube 42 to divide it in a plurality of axially spaced resonator volumes 46.
To operatively interconnect each of the volumes 46 with the gas stream, a plurality of throat-forming openings 48 are formed in the tube 42 around its circumference within the axial extent of each of said volumes. Desirably, the openings are formed by shearing the tube 42 to provide tongues 49 bent to project from the tube wall. In this manner, the openings 48 with their adjacent tongues 49 constitute resonator throats which, because of their sheared construction, have a conductivity such that the silencing element will attenuate sound wave frequencies in the range of 300 cycles/ sec. to 1,500 cycles/ sec.
Still another form of silencing element in accordance with our invention is shown in FIGS. 7 and 8, in which there is an outer pipe 52 forming the gas-flow passage and having suspended within it pairs of silencing elements 54. As shown, each of the elements 54 comprises an elongated tube 56 having one of its ends closed as at 58, and its opposite end provided with one or more perforations 60 which constitute throat-forming means for the resonator volume formed by the tube 56. Each of the elements 54 is mounted on a bracket 62 mounted in the pipe 52 to thus dispose said elements in spaced relation to the pipe 52.
As previously described in connection with the silencing elements 16, the elements 54 may be arranged in opposed pairs with their perforated end faces immediately adjacent each other. In such a closely spaced relationship, the space between the opposed end faces forms a common extension of the throat-forming means in the two resonators to increase the effective length of said means and cause the elements 54 to act upon a lower range of sound wave frequencies than the frequencies for which they are individually tuned. When the elements 54 are disposed in their opposed relationship, they will attenuate sound wave frequencies in the range of 100 cycles/sec. to 700 cycles/sec, with their preferential frequency response in said range depending upon the size of the volumes of the tubes 56, the size and number of their perforations 6t), and the spacing between their opposed end faces. If it is desired to modify the effective throat length of only one of the silencing elements, the pair of elements are mounted in alignment with the perforated end face of one of said elements being disposed adjacent the nonperforated end face of the other.
It is to be understood, of course, that either of the elements 54 may be employed without the use of the other and/or the throat-forming perforations in said elements may be disposed around the side walls of said elements instead of in their end faces. However, the degree to which the elements 54 are perforated will normally be very small in comparison with the large degree of perfora' tion present in the silencing element 18 shown in FIGS. 1 and 4.
In all of the modifications shown, our silencing elements are carried within an outer pipe forming the gas-flow passage whereby the gases moving through said pipe will have to pass through the space between said pipe and the silencing elements. The pipe forming said passage has a generally uniform cross-section with no substantial, abrupt changes in its diameter adjacent said silencing elements, and the average cross-sectional area of the gas-flow passage bctween said elements and the pipe within the axial extents of said elements is smaller than the average cross* sectional area of the gas-flow passage in the open portions of the pipe outside the extent of the silencing elements. However, the cross-sectional area of the silencing elements is in the range of from about 25% to about 75% of the cross-sectional area of the pipe within the axial C71LHt of said elements so that said elements will effect the necessary degree of attenuation but will not unduly obstruct gas flow through the pipe and create excessive back pressures.
As will be apparent, by employing several of the illustrated types of silencing elements in combination, a wide range of sound wave frequencies may be attenuated, For example, elements of the type shown in FIGS. 2 and 4 may be employed to attenuate extremely low and high ranges of frequencies, respectively, and elements of the type shown in FIGS. 5 and 7 may be used in combination therewith to attenuate the intermediate range frequencies. It is also possible to combine several types of elements in a single combination structure carried within the outer pipe. For example, elements of the type shown in FIGS. 2, 4, and 5 may be incorporated in an axially spaced relationship in the same length of tubing, and that length of tubing mounted in an outer pipe.
As shown in the drawings, the silencing elements are located in the path of the gas stream movement. This permits our silencing elements to be intimately acoustically and thermally coupled to said gas stream so that said elements will not only achieve their maximum acoustic efficiencies through such direct coupling, but in addition, their resonant frequencies will adjust directly with the frequency changes in the gas stream due to temperature changes. Further, such suspension positions the silencing elements out of contact with the outer pipe to reduce their susceptibility to corrosion. However, should such corrosion occur, the silencing elements may be easily replaced by simply removing the corroded element and replacing it with a new element. As previously described, such replacement may be facilitated by forming the outer pipe from a plurality of short interfitting sections of pipe so that the defective silencing element and its respective pipe section may be replaced as a unit.
While we have shown our silencing elements as disposed concentrically within an outer pipe on brackets, it is to be understood that such brackets may be omitted and the elements may contact the outer pipe along one or more lines of contact. To this end, the elements may be suspended from one line of contact along the wall of the outer pipe, or the pipe and elements may have different cross-sectional configurations which permit the elements to contact, and be supported from, the pipe along two or more lines of contact. An example of the latter situation is shown in FIG. 9, in which the outer pipe indicated at it? is flattened into an eliptical cross-section, and the silencing element indicated at 16" abuts it along two lines of contact and is secured thereto by welds '13. However, as in the embodiments of our invention, there are no substantial, abrupt changes made in the general crosssection of the pipe. Where the silencing elements are in line contact with the pipe, the means supporting the elements therein may comprise welded interconnections between the pipe and silencing elements along their lines of contact. However, even where the silencingelements contact the pipe, the major portions of the walls of said elements are disposed wholly out of contact with the outer pipe to provide a high degree of coupling between the elements and the gas stream, and to cause the gases to move through the space between the elements and the p1pe.
For purposes of simplicity of description, we have only described our invention for use in an exhaust system for an engine. However, it may, of course, also be used on the intake side of an internal combustion engine for transporting and silencing the gas, intake flow to the engine, or for many other silencing applications.
We claim as our invention:
1. In a sound attenuating gas conduit for conveying, and attenuating the noise level of, a moving gas stream, an open-ended pipe free from substantial abrupt changes in its diameter forming a gas-flow passage having unrestricted flow at its ends, at least one silencing element mounted within said pipe inwardly from the ends thereof and comprisingan elongated enclosed wall forming a sound attenuating cavity, and throat-forming means in direct communication with the interior of said pipe operatively interconnecting said cavity and gas-flow passage whereby said element will silence the gases moving through said passage, the cross-sectional area of the gas passage within the axial extent of said element being smaller than the average cross-sectional area of the gas passage outside the axial extent of said element, said silencing element being mounted within said pipe in said gas-flow passage on a bracket secured to said pipe to support said silencing element wholly out of contact with said pipe whereby said gas stream must pass through the space between said element and pipe during its movement through the conduit.
2. In a sound attenuating gas conduit for conveying, and attenuating the noise level of, a moving gas stream, an open-ended pipe free from substantial abrupt changes in its diameter forming a gas-flow passage having unrestricted flow at its ends, at least one silencing element mounted within said pipe inwardly from the ends thereof and comprising an elongated enclosed Wall forming a sound attenuating cavity, and throat-forming means in direct communication with the interior of said pipe operatively interconnecting said cavityand gas-flow passage whereby said element will silence the gases moving through said passage, said element having a cross-sectional area in a range of from about 25% to about 75% of the crosasectional area of the pipe within the axial extent of said silencing element with at least substantially all of said wall in spaced relation to said pipe whereby said gas stream must pass through the space between said element and pipe during its movement through the conduit.
3. The invention as set forth in claim 2 in which said wall comprises a first length of tubing having enclosed ends, and said throat-forming means comprises a second length of tubing mounted on said first length of tubing, said second length of tubing having a smaller crosssectional area than said first length of tubing and having one of its ends open to said gas-flow passage and its opposite end open to the cavity formed by said first length of tubing.
4. The invention as set forth in claim 2 in which said wall comprises a length of tubing having enclosed ends, and said throat-forming means comprises a plurality of axially and circumferentially spaced openings formed in said tubing, the portions of the tubing defining the edges of said openings being deformed out of the general plane of said tubing.
5. The invention as set forth in claim 2 in which said wall comprises a length of tubing having enclosed ends, and said tubing is provided with one or more perforations comprising said throat-forming means.
6. The invention as set forth in claim 2 in which said wall comprises a length of tubing having enclosed ends and containing a porous, fibrous sound-absorbing material, and said throat-forming means comprises a plurality of perforations formed in said tubing to render the same at least 30% open.
7. The invention as set forth in claim 6 in which said sound-absorbing material is in the form of a porous wadding filling said tubing.
8. The invention as set forth in claim 2 in which said Wall comprises an elongated length of tubing having enclosed ends and provided with a plurality of axially spaced bafile plates mounted on its interior to divide said cavity into a plurality of cavities, and said throat-forming means forms a plurality of passages each of which is open to said gas-flow passage and one of said plurality of cavities.
9. The invention as set forth in claim 2 in which said wall abuts the inner face of said pipe along one or more lines of contact, and said element and pipe are rigidly secured together along at least one of said lines of contact.
10. In a sound attenuating gas conduit for conveying, and attenuating the noise level of, a moving gas stream, a pipe forming a gas-flow passage for said gas stream, a plurality of silencing elements mounted within said gas stream, each of said silencing elements comprising an elongated wall closed at its ends and forming a sound attenuating cavity, and throat-forming means operatively interconnecting said cavity and gas-flow passage whereby each of said elements will attenuate the noise level of the gases moving through said passage, at least one pair of said elements being mounted in the gas stream in opposed relationship with the throat-forming means of each of said pair of elements being disposed in their opposed end faces and said opposed end faces being disposed closely adjacent each other to define a common extension for the throat-forming means of said pair of elements, and means supporting each of saidelements in said gas-flow passage with at least substantially all its wall in spaced relation to said pipe whereby said gas stream will have to pass between said silencing elements and the pipe during its movement through the conduit.
'11. In a sound attenuating gas conduit for conveying, and attenuating the noise level of, a moving gas stream, an open-ended elongated pipe forming a gas-fiow passage wherein a sound source will produce standing waves having pluralities of harmonic frequencies, and a plurality of silencing elements mounted within said pipe along the length thereof with their adjacent ends in axially spaced relationship, said pipe being free from substantial, abrupt changes in its diameter adjacent said silencing elements, each of said silencing elements comprising means disposed in said gas-flow passage forming a closed resonator volume, said means being positioned in said gas-flow passage with at least a major portion of said volume spaced from said pipe whereby said gas stream must pass between said means and the pipe during its movement through the gas-flow passage, and means on said first mentioned means forming a resonator volume throat operatively interconnecting said volume and gasflow passage whereby said plurality of silencing elements will be acoustically coupled to said gas stream at points along the length of said conduit to attenuate the noise level of the gas stream moving through the conduit, one or more of said silencing elements having a volume and throat construction to cause said silencing element to have a frequency response according to the formula 2h+(mean radius of the throat cross section) and h is the length of the throat.
12. The invention as set forth in claim 11in which each of said one or more silencing elements has a throat formed from an elongated tubular element, and each :of said one or more silencing elements is responsive to a predetermined sound wave frequency constituting one of the standing harmonic frequencies of the conduit with its associated throat operatively connected tosaid gas flow passage adjacent a position along the length of the conduit where the harmonic frequency for which the silencing element is responsive reaches its maximum pressure.
13. \An exhaust silencing system for an internal com bustion engine, comprising an open-ended pipe for connection to the engine to receive the exhaust gases thereof and to convey such gases to a discharge point, said pipe forming a gas conduit wherein the exhaust sound produces one or more distinct harmonic sound-pressure points at particular locations along the length of the conduit equal to fractional lengths thereof according to the formula where n is a harmonic number and m is every integer between and including 1 and n, and a plurality of silencing elements moiuited in said conduit along the length thereof with their adjacent ends in axially spaced relationship and in close thermal coupling relationship with the gas stream, one or more of said silencing elements comprising a resonator volume formed from a closed end pipe and an elongated tubular throat operatively associated with said volume, each of said one or more silencing elements having volume and throat construction to cause said silencing element to have a frequency response according to the formula where C is the speed of sound at the temperature of the gas stream, V is the capacity of the resonator volume, and C is the conductivity of the resonator throat equal to 2(cross sectional area of the throat) Zh-i-(means radius of the throat cross section) bustion engine, an elongated open-ended pipe constituting a main gas-flow passage and formed from a plurality of axially extending interconnected shorter lengths of pipe, said pipe being free from substantial abrupt changes in its diameter and being adapted to be connected to said engine for transferring the exhaust gases therefrom, and a plurality of axially spaced siliencing elements mounted within said elongated pipe along the length thereof and having at least the major portion of their outwardly presented surfaces in spaced relation to said elongated pipe whereby gases moving through said conduit must pass through the spaces between said silencing elements and said elongated pipe, each of said silencing elements comprising a length of tubing forming a sound attenuating cavity, and throat-forming means in direct communication with said gas-flow passage operatively interconnecting each cavity to the gas-flow passage, 3. first set of said silencing elements having hollow sound attenuating cavities and a second set of said silencing elements having a porous fibrous sound attenuating material carried in their sound attenuating cavities.
15. The invention as set forth in claim 14 in which the throat-forming means in each of the silencing elements in said second set comprises a plurality of perforations formed in said tubing to render the same at least 30% open, and all of said second set of silencing elements are mounted in said pipe downstream of said first set of silencing elements.
References Cited in the file of this patent UNITED STATES PATENTS 1,811,762 Schnell June 23, 1931 1,847,830 Hills Mar. 1, 1932 1,910,672 Bourne May 23, 1933 1,947,987 Hathorn Feb. 20, 1934 2,014,666 Peik Sept. 17, 1935 2,038,309 Oldberg Apr. 21, 1936 2,056,608 Jack Oct. 6, 1936 2,099,887 Heath Nov. 23, 1937 2,184,891 Bourne Dec. 26, 1939 2,297,046 Bourne Sept. 29, 1942 2,671,523 Walker Mar. 9, 1954 2,694,462 Robbins et al. Nov. 16, 1954 2,748,883 Ralph June 5, 1956 2,795,374 Isakofi June 11, 1957 FOREIGN PATENTS 415,446 Great Britain Aug. 27, 1934 678,344 Great Britain Sept. 3, 1952 317,630 Switzerland Ian. 15, 1957 559,326 Belgium Aug. 14, 1957

Claims (1)

1. IN A SOUND ATTENUATING GAS CONDUIT FOR CONVEYING, AND ATTENUATING THE NOISE LEVEL OF, A MOVING GAS STREAM, AN OPEN-ENDED PIPE FREE FROM SUBSTANTIAL ABRUPT CHANGES IN ITS DIAMETER FORMING A GAS-FLOW PASSAGE HAVING UNRESTRICTED FLOW AT ITS ENDS, AT LEAST ONE SILENCING ELEMENT MOUNTED WITHIN SAID PIPE INWARDLY FROM THE ENDS THEREOF AND COMPRISING AN ELONGATED ENCLOSED WALL FORMING A SOUND ATTENUATING CAVITY, AND THROAT-FORMING MEANS IN DIRECT COMMUNICATION WITH THE INTERIOR OF SAID PIPE OPERATIVELY INTERCONNECTING SAID CAVITY AND GAS-FLOW PASSAGE WHEREBY SAID ELEMENT WILL SILENCE THE GASES MOVING THROUGH SAID PASSAGE, THE CROSS-SECTIONAL AREA OF THE GAS PASSAGE WITHIN THE AXIAL EXTENT OF SAID ELEMENT BEING SMALLER THAN THE AVERAGE CROSS-SECTIONAL AREA OF THE GAS PASSAGE OUTSIDE THE AXIAL EXTENT OF SAID ELEMENT, SAID SILENCING ELEMENT BEING MOUNTED WITHIN SAID PIPE IN SAID GAS-FLOW PASSAGE ON A BRACKET SECURED TO SAID PIPE TO SUPPORT SAID SILENCING ELEMENT WHOLLY OUT OF CONTACT WITH SAID PIPE WHEREBY SAID GAS STREAM MUST PASS THROUGH THE SPACE BETWEEN SAID ELEMENT AND PIPE DURING ITS MOVEMENT THROUGH THE CONDUIT.
US88977A 1961-02-13 1961-02-13 Sound attenuating gas conduit Expired - Lifetime US3119459A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
US88977A US3119459A (en) 1961-02-13 1961-02-13 Sound attenuating gas conduit
GB26727/61A GB989061A (en) 1961-02-13 1961-07-24 Improvements in or relating to a sound attenuating gas conduit
DEA38596A DE1299647B (en) 1961-02-13 1961-10-18 Sound-absorbing gas pipe
DEA17848U DE1856343U (en) 1961-02-13 1962-02-12 SOUND-ATTENUATING GAS DUCT.

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US88977A US3119459A (en) 1961-02-13 1961-02-13 Sound attenuating gas conduit

Publications (1)

Publication Number Publication Date
US3119459A true US3119459A (en) 1964-01-28

Family

ID=22214619

Family Applications (1)

Application Number Title Priority Date Filing Date
US88977A Expired - Lifetime US3119459A (en) 1961-02-13 1961-02-13 Sound attenuating gas conduit

Country Status (3)

Country Link
US (1) US3119459A (en)
DE (2) DE1299647B (en)
GB (1) GB989061A (en)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3263772A (en) * 1964-06-17 1966-08-02 Arvin Ind Inc Sound attenuating gas conduit with one-quarter wave-length side branch chambers
US4979587A (en) * 1989-08-01 1990-12-25 The Boeing Company Jet engine noise suppressor
US5109950A (en) * 1989-01-27 1992-05-05 Glaenzer Spicer Silencer for exhaust gases and part of an exhaust line having such a silencer
US5123501A (en) * 1988-10-21 1992-06-23 Donaldson Company, Inc. In-line constricted sound-attenuating system
US5449866A (en) * 1991-11-26 1995-09-12 Ab Volvo Arrangement for damping sound in a pipe system
US20080190689A1 (en) * 2007-02-12 2008-08-14 Ballard Ebbin C Inserts for engine exhaust systems
WO2010085695A1 (en) * 2009-01-23 2010-07-29 Dresser-Rand Company Fluid-carrying conduit and method with noise attenuation
US20110108358A1 (en) * 2009-11-06 2011-05-12 Jason Michael Edgington Noise attenuator and resonator
US9121329B2 (en) * 2012-04-24 2015-09-01 Faurecia Emissions Control Technologies, Usa, Llc Tailpipe diffuser
CN107461231A (en) * 2017-09-29 2017-12-12 武汉理工大学 A kind of model muffler
CN112443433A (en) * 2019-09-05 2021-03-05 上海索菲玛汽车滤清器有限公司 Air filter

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE461290B (en) * 1982-06-01 1990-01-29 Neil Lawrence Currie EXHAUST SYSTEM FOR MOTOR VEHICLE

Citations (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE559326A (en) *
US1811762A (en) * 1929-05-08 1931-06-23 Burgess Lab Inc C F Exhaust muffler
US1847830A (en) * 1929-08-10 1932-03-01 Hills Horace Gastineau Exhaust silencer
US1910672A (en) * 1932-05-13 1933-05-23 Maxim Silencer Co Acoustic wave filter
US1947987A (en) * 1929-03-26 1934-02-20 Curtiss Aeroplane & Motor Co Combined exhaust manifold and muffler
GB415446A (en) * 1931-11-25 1934-08-27 Daimler Benz Ag Method of and means for stabilising the flow of gas in pipes connected to reciprocating piston machines
US2014666A (en) * 1932-10-31 1935-09-17 Halsey W Taylor Company Muffler
US2038309A (en) * 1934-07-25 1936-04-21 Oldberg Sidney Silencer
US2056608A (en) * 1933-12-22 1936-10-06 C F Burges Lab Inc Silencer
US2099887A (en) * 1934-05-26 1937-11-23 Buffalo Pressed Steel Company Muffler
US2184891A (en) * 1937-12-13 1939-12-26 Maxim Silencer Co Silencer
US2297046A (en) * 1939-08-25 1942-09-29 Maxim Silencer Co Means for preventing shock excitation of acoustic conduits or chambers
GB678344A (en) * 1950-10-12 1952-09-03 Vokes Ltd Improvements in silencers
US2671523A (en) * 1950-07-14 1954-03-09 Walker George Bromhead Silencer or muffler for engine exhausts or the like
US2694462A (en) * 1951-09-19 1954-11-16 Robbins Frank Acoustic system for loud-speakers
US2748883A (en) * 1952-12-03 1956-06-05 Millard J Ralph Muffler unit
CH317630A (en) * 1953-04-17 1956-11-30 Dehais Lucien Clement Georges Silencer for internal combustion engine
US2795374A (en) * 1953-08-13 1957-06-11 Du Pont Fluid flow pulsation damping

Family Cites Families (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE511490C (en) * 1930-10-31 Paul Barringhaus Silencer for motor vehicles and. Like. With one behind the other and directly abutting nozzles
AT124595B (en) * 1928-06-02 1931-09-25 Burgess Lab Inc C F Silencer.
DE650784C (en) * 1931-11-26 1937-10-01 Daimler Benz Akt Ges A device used to steady intermittently flowing gaseous fluids in pipelines
CH285576A (en) * 1949-12-12 1952-09-15 Wayth Cullum Douglas Jack Noise damping device, especially for jet engine testing.
DE1712462U (en) * 1954-06-02 1955-12-08 Auto Union Gmbh EXHAUST SYSTEM FOR TWO-STROKE COMBUSTION MACHINES.
FR1215262A (en) * 1958-11-13 1960-04-15 Device for attenuating the noise of a moving fluid

Patent Citations (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
BE559326A (en) *
US1947987A (en) * 1929-03-26 1934-02-20 Curtiss Aeroplane & Motor Co Combined exhaust manifold and muffler
US1811762A (en) * 1929-05-08 1931-06-23 Burgess Lab Inc C F Exhaust muffler
US1847830A (en) * 1929-08-10 1932-03-01 Hills Horace Gastineau Exhaust silencer
GB415446A (en) * 1931-11-25 1934-08-27 Daimler Benz Ag Method of and means for stabilising the flow of gas in pipes connected to reciprocating piston machines
US1910672A (en) * 1932-05-13 1933-05-23 Maxim Silencer Co Acoustic wave filter
US2014666A (en) * 1932-10-31 1935-09-17 Halsey W Taylor Company Muffler
US2056608A (en) * 1933-12-22 1936-10-06 C F Burges Lab Inc Silencer
US2099887A (en) * 1934-05-26 1937-11-23 Buffalo Pressed Steel Company Muffler
US2038309A (en) * 1934-07-25 1936-04-21 Oldberg Sidney Silencer
US2184891A (en) * 1937-12-13 1939-12-26 Maxim Silencer Co Silencer
US2297046A (en) * 1939-08-25 1942-09-29 Maxim Silencer Co Means for preventing shock excitation of acoustic conduits or chambers
US2671523A (en) * 1950-07-14 1954-03-09 Walker George Bromhead Silencer or muffler for engine exhausts or the like
GB678344A (en) * 1950-10-12 1952-09-03 Vokes Ltd Improvements in silencers
US2694462A (en) * 1951-09-19 1954-11-16 Robbins Frank Acoustic system for loud-speakers
US2748883A (en) * 1952-12-03 1956-06-05 Millard J Ralph Muffler unit
CH317630A (en) * 1953-04-17 1956-11-30 Dehais Lucien Clement Georges Silencer for internal combustion engine
US2795374A (en) * 1953-08-13 1957-06-11 Du Pont Fluid flow pulsation damping

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3263772A (en) * 1964-06-17 1966-08-02 Arvin Ind Inc Sound attenuating gas conduit with one-quarter wave-length side branch chambers
US5123501A (en) * 1988-10-21 1992-06-23 Donaldson Company, Inc. In-line constricted sound-attenuating system
US5109950A (en) * 1989-01-27 1992-05-05 Glaenzer Spicer Silencer for exhaust gases and part of an exhaust line having such a silencer
US4979587A (en) * 1989-08-01 1990-12-25 The Boeing Company Jet engine noise suppressor
US5449866A (en) * 1991-11-26 1995-09-12 Ab Volvo Arrangement for damping sound in a pipe system
US20080190689A1 (en) * 2007-02-12 2008-08-14 Ballard Ebbin C Inserts for engine exhaust systems
WO2010085695A1 (en) * 2009-01-23 2010-07-29 Dresser-Rand Company Fluid-carrying conduit and method with noise attenuation
US20110108358A1 (en) * 2009-11-06 2011-05-12 Jason Michael Edgington Noise attenuator and resonator
US9121329B2 (en) * 2012-04-24 2015-09-01 Faurecia Emissions Control Technologies, Usa, Llc Tailpipe diffuser
CN107461231A (en) * 2017-09-29 2017-12-12 武汉理工大学 A kind of model muffler
CN112443433A (en) * 2019-09-05 2021-03-05 上海索菲玛汽车滤清器有限公司 Air filter
CN112443433B (en) * 2019-09-05 2024-02-27 上海索菲玛汽车滤清器有限公司 Air filter

Also Published As

Publication number Publication date
DE1299647B (en) 1969-07-24
GB989061A (en) 1965-04-14
DE1856343U (en) 1962-08-09

Similar Documents

Publication Publication Date Title
US5365025A (en) Low backpressure straight-through reactive and dissipative muffler
US5350888A (en) Broad band low frequency passive muffler
US2070543A (en) Muffler
US3388769A (en) Dual inlet and outlet muffler
US3212603A (en) Muffler with tuned silencing chambers
US3119459A (en) Sound attenuating gas conduit
US8136627B2 (en) Exhaust silencer device for internal combustion engine
US2940538A (en) Silencer
US2841237A (en) Muffler structure
US3114432A (en) Sound attenuating gas conduit
US3338331A (en) Exhaust system with plural silencing units
US2099887A (en) Muffler
US2652128A (en) Retroverted passage type muffler with expansion chambers
US3512607A (en) Co-axial tuning tubes for muffler
US3382948A (en) Mufflers with side branch tuning chambers
CA1083486A (en) Louver flow muffler
US3104732A (en) Acoustically treated gas pipe
US2656005A (en) Retroverted passage type muffler with resonator chambers
US3498406A (en) Triflow muffler for exhaust gases
US2960179A (en) Exhaust muffler
US3118517A (en) Sound attenuating gas conduit
US3495680A (en) Exhaust silencing system
US2151470A (en) Muffler
US3146851A (en) Sound attenuating gas conduit and resonators therefor
US3146850A (en) Sound attenuating gas conduit