US2034186A - Muffler - Google Patents

Description

March 17, 1936. L R HEATH 2,034,186

MUFFLER Filed Oct, 15, 1952 Patented Miu'.v 17, 1936l UNITED STATES PATENT OFFICE MUFFLER Laurence R. Heath, Arlington," Mass. Application October 15, 1932, Serial No. 637,946

13 Claims.

'I'his invention relates to improvements in mufilers of the' type commonly employed for silencing noises resulting from the discharge of exhaust gases from an internal combustion engine. The objects of this invention are to provide a muiiler of this kind of improved construction, by means of which the back pressure caused by the muiller is materially less than in muiiiers heretofore commonly employed; also to provide a muiiler of this kind in which the pulsations in the pressure and flow of exhaust gases are reduced to such' an extent that a substantially uniform or only slightly pulsating flow of exhaust gas is discharged from the muffler; also to provide a mumer of this kind in which the pulsating gases entering the muiiler are permitted to expand in certain chambers formed about the mumer and to again join the current of gas going through the muiller during low pressure intervals or between the pulsations; also to pro vide a mufiier of this kind in which noise due to the exhaust is reduced by producing a substantially uniform flow of exhaust gas through the discharge passage of the muiller; also to produce a muilier of this kind inlwhich the chambers surrounding the inner passage through the muiiler are designed to permit gases to ilow back and forth into and out of the chambers in accordance with the pulsations of the gas in the inner passage, and also to cause some gas to ow through the chambers fromthe inlet to the discharge of the muiller; also to improve muiilers of this kind in other respects hereinafter specifled.

I have found that when a muiiler is designed in i such a manner as to smooth out the pulsating flow of the exhaust gases from an internal combustion engine, such a muiiler will at the same time remove the objectionable exhaust noises. Even the simplest types of muiliers of the kind heretofore employed will transmit very little of the initial sound of the exhaust of an engine, but in such muillers the waves of gases leaving the mufliers create noises or sounds which are objectlonable.` In accordance with my invention,

I, therefore, reduce the intensity of the pulsations of the exhaust gases, and I have found -that when a muffler is designed to remove these pressure or flow pulsations `:from the exhaust gases, the objectionable noise of the exhaust is f also eliminated. The muillers shown in the accompanying drawing are, therefore, designed to remove the crests from the impulse waves of exhaust gases entering the muiiler and to em- 55 'ploy the gas from these crests to fill up subsequent troughs or low pressure -spaces between these waves. thus producing a flow oi' gas at the discharge end of the mumer which has very lit- Wf'tleevanationwin pressure. I have alsoaccom# 00 plished this by producing a niumer having va passage extending straight through the same so that the gases passing through the muiiler encounter a minimum resistance to ilow and, consequently, result in very little back pressure."

In the accompanying drawing, I 'have illus- 5 trated some forms of muiliers capable of producing the desiredl results, but it will be understood that the muillers shown in the drawing are merely illustrative, since Wide variations in the numbers of baiiles and in the passage of gases l0 through shells may be made in order to accommodate muiilers to engines of diierent kinds. In this drawing:

Fig. 1 represents a longitudinal sectional elevationfof a muffler embodying this invention. l5

Figs. 2, 3 and 4 are similar sectional elevations of muiers of modified constructions.

Fig. 5 is a transverse sectional elevation on line 5-5, Fig. 2.

Fig. 1 embodies the simplest form of my in- 20 Vention and in this form, the muiller is provided with an outer shell I0 having heads II and I2 secured to the ends thereof, the head I I at the inlet side of the muffler Abeing provided with a tubular extension I 4 constituting the inlet of the 25 muiiler and with which the exhaust pipe from the engine may connect, and the head I2 at the discharge end of the muierbeing formed with a tubular extension I5 to which a tail pipe may be secured. The heads II and I2 may also be 30 provided with shoulders with which an intermediate shell I6 engages. The muffler also has an inner shell or conduit I'I which may be suitably mounted on the muiiler in any desired manner,

` and which, in the construction shown, is sup- 35 ported on the inner shell4 by means of baiiies I8 and I9. A ny other means for supporting the shells and heads relatively to each other may be provided.

In accordance with my invention, the inner 4o tube or shell Il is preferably constructed to pass theflow of 'exhaust gas therethrough, and the discharge end of this tube or shell may be made slightly smaller than the inlet opening. In the particular construction shown in Fig. l, this 45 result is obtained by constructing the inner shell so vthat the same tapers slightly from the receiving end thereof to the discharge end. This causes the gases entering the muler from the inlet opening therein to build up a pressure near 50 the inlet end of the inner shell I1 which is slightly greater than the pressure at the discharge end of this shell.

In accordance with my invention. this shell is made of perforated metal substantially throughout the length thereof. 'I'he perforation;

may be of any suitable or desired form, but I 2 obtained, and that a whistling sound which sometimes results if perforations of circular shape are used, does not occur. While such rectangular perforations are preferably employed, it will be understood that perforations ofany other form may be used, since the object of these perforations is mainly to permit gases to pass out of the inner. shell through these perforations into a chamber 22 formed between the inner and intermediate shells of the mufiier. In the construction illustrated in Fig. 1, apertures 23 are formed in the intermediate shell near the inlet end of the muiiler so that gases may pass through these apertures 23 into the outer chamber 24 of the muliler which is arranged between the intermediate and outer shells thereof. The inter` mediate shell is provided with a second series of apertures or openings 25 which, in the particular constructions shown, are arrangedin rear ofa the baiiie I9, and the dischargevend of the inner shell terminates -at a distance' from the discharge duct I of the muier so that the discharge end of the shell I1 has an ejector action which tends to draw gases through the apertures 25 to mix With the gases discharged from the innershell, and thus to enter into the tail pipe of the muiiier. The discharge end of th inner shell extending beyond the baiiie I9 is preferably not perforated, to increase the ejector action. Y

In the operation of this muffler, when a charge of exhaust gas enters into the inner shell I'i thereof, asa result of the opening of an exhaust valve of the engine, the pressure wave orpulsation of this gas will have a relatively high peak caused by the' gas leaving the engine at considerable pressure immediately after the opening of the exhaust valve. 'Ihis wave or pulsation of exhaust gas entering into the inner shell Il will, of course, tend to expand as rapidly as possible and upon reaching the inner (shell, thisK gas will immediately expand through the perforations 20 therein and enter into the inner chamber 22. Because of the high pressure peak, some of the gas enteringvthechamber 22 will immediately ow through the apertures 23 into the outer chamber 24. Immediately after the peak of the wave, there will be a depression inthe wave or pulsation, so that gases in the chambers' 22 and .24 will again tend to flow in the reverse direction through the apertures 22 of the inner shell I1, thus adding this amount of gas to the trough or depression of; the pulsation. It will be evident, therefore, that by removing the peak of a wave or pulsation of exhaust gas and again returning the gas Aof the peak thus removed into the trough, both the peak and the depression or .trough of the waveor pulsation have been removed, so that when this exhaust gas nally enters'the tail pipe, it will iow at a fairly uniform rate and with greatly reduced variation in pressurev between the peak and the trough of the wave of exhaust gas. uniform ow orJ discharge of the gas fromx the tail pipe into the air, consequently, takes place Without the. objectionable from the inner shell also have a silencing effect f upon sound waves in the muier because of the refraction of these sound waves in passing through gases of diierent temperatures.

It will bek understood that the apertures 25, which, in the construction shown, are arranged in rear of the bale I9, may be located in front of this baille, in which case, the ejector action will be replaced by a drawing of gas throughthese apertures due to the fact that the pressure of gas at the discharge end of the inner shell IT, due to the taper of thisshell, is .less than at the inlet end thereof. In either case, cool gas will iiow crosswise of the inner-shell resulting in the well known silencing effect upon sound waves. f

The operation of 'this muler is believed to be as follows: Whena wave or pulsation of gas enters into the inlet end, gas flows rapidly out through the perforations in the inner shell into the intermediate space or chamber of the mufer located between the inner and intermediate shells, and a portion of this gas flows through the apertures 23 into the outer chamber of the muiiier. Immediately reduction of the pressure in the inner shell results, and when the pressure wave or pulsation reaches the discharge end of the muflier, its pressure is so reduced that no objectionable sound results when this pulsation is discharged' from the end of the tail pipe.` A considerable portion of the gas from the intermediate and outer shells will flow back into the inner shell when the peak of the pressure wave has passed and will then pass outwardly through the tail pipe in a comparatively steady or uniform flow, and without producing objectionable noise. By this construction, the flow of gas from the inner shell during the peak or high pressure portion of the pressure wave, reduces or flattens out this `peak and-materially reduces the pressure in the inner shell, and when the trough or portion of low pressure of the. wave passes. into the inner shell, this gas in the intermediate and outer chambers is returned and lls in this trough, -with the result that afairly uniform discharge of gas takes place through the discharge end of the muilier.

In addition to this alternating -movement of gas in the chambers of this muiiler, there will also be a movement in the outer chamber toward v the discharge end of the muilier, this movement being produced b y the ejector action of the discharge end of the muier, resulting 'in the mixing ofgases of different temperatures. which has been described. Probably a similar movement of gas takes place inthe inner chamber because of the fact 'that the pressure in the inner shell is greater at the inlet. end thereof than at the discharge end., 'I'his passage of gas lengthwise of the muiiierqthrough the chambers surround ing the inner shell has a further equalizing eti'ect on the gas discharged from the mufller, and also reduces back pressure by cooling the gases by contact with the outer shell. thus reducing the volume of the gas to be discharged. The resulting mixture of gases of varying temperatures results in a turbulence and refraction and absorption of sound waves. Furthermore, by maintaining a now of rgases through the several chambers, a deposit and accumulation of other foreign material in the chambers is prevented.

tween the outer and intermediate shells intermediate of the heads of the muffler, and a pair of bailles 3| and 32 are provided between the inner and intermediate shells and spaced at intervals; This arrangement of the bailles 3| and 32 results in the formation of` chambers 35, 36 and 31 between the inner and intermediate shells, and the baille 30 results in the formation of outer chambers 384 and 39 between the outer and intermediate shells. The intermediate shell is provided near the inlet end of the muiller with a plurality of apertures 48 through which gases passing through the perforations of the inner shell into the chamber 35 may pass into the chamber 38, and additional perforations 4 I, fewer in number than the perforations 40, establish communication between the chamber 38 and the chamber 36. Similarly a relatively1 small number of 4perforations 42 are provided in the intermediate shell between the bailles 30 and 32 to establish communication between the chamber 36 and the chamber 39, and a larger number of perforations or apertures 43 are formed to establish communication between the chambers 39 and 31.

In the operation of this muiller, gas from the pealrs of the pulsations passes out through the perforations of the inner shell and successively enters the chambers 35, 36 and 31. Gases from the chamber 35 may pass through apertures 4U into the outer chamber 38, and when the trough of the pressure wave is reached, a part of these l gases may again pass in the reverse direction through the openings 40 and perforations in the inner shell. Other gases from the outer chamber 38 will pass into the intermediate chamber 36 through the eapertures 4|, it being borne in mind that the pressures along the tapered inner shell vary, being highest at the inlet end of the muffier and lowest at the discharge end. Gases from the chamber 36 may also pass outwardly through the apertures 42 into the chamber 39, and then through apertures 43 into the chamber 31, and thence back to the inner shell. In this case, the

. inner shell does not have the ejector action described in connection with Fig. 1, but by slight l rearrangement of the` baille supporting the dis- 1 can be readily changed to charge end of the inner shell from the intermediate shell and the apertures 43, the muiller producethe ejector acti/Jn, if the sameis desired.

In the construction shown in Fig.`2, in addition to the eiect of producing an evenl ilow of f gas through the muiller, the chamber'36 has a decided silencing action on vsound waves because of the fact that hot and cold gases ilow into and out of this chamber and set up a turbulence in this chamber, which has been round to deaden sound. The muiller shown in Fig. 2 is of conshells shown in Figs. 1 and 2. Baines siderably larger capacity than the one shown in Fig. 1, and-because oi the plurality oi chambers provided lengthwise of the inner shell, a greater equalization of pressure is produced by this muiller, than by the one shown in Fig. 1, which greater equalization would be necessary in connection withiarger engines because of greater pressure variations of the exhaust gases. It will be obvious that the number of chambers in a muiiler can be readily varied as desired by in` creasing or decreasing the number of bailles and the length of the shells, but preferably the chambers are so arranged that the gases passing lengthwise through the chambers about the inner shell will pass alternately from an intermediate chamber to an outer chamber and from such outer chamber to another intermediate chamber located nearer to the discharge end of the muifier. 'This reversal of directions or alternate inward and outward flow of gases helps materially in eliminating sound waves from the gases discharged by the muffler. It will, 'of course,'be understood that dead chambers, or chambers into and out of which gases flow only through the same set of openings may'be used, if desired,

in connection with the interconnected chambers.

Fig. 3 shows a muffler which is quite similar to the one shown in Fig. 1, except that in Fig. 3 the inner sleeve is formed of two parts of dinerent diameters, the part of the smaller diameter being nearer the discharge end of the muiller, and the two parts being held in place by shoulders formed on an intermediate head 46. The portion 41 of the inner shell or tube is of larger diameter than the portion 48, so that there will be a slightly greater pressure at the inlet end of the muiiler than at the discharge end. The intermediate head 46 divides the chamber between the inner and intermediate shells into two intermediate chambers, and a similar intermediate head could, of course, be employed on the muiller shown in Fig. 1. This arrangement causes gases to pass irom.one of these chambers through apertures 49 into the outer chamber between the -outer and intermediate shells and then through apertures 50 from the outer chamber into the other intermediate chamber, and finally back to the inner shell.

It will be noted that in all of the constructions shown, none Vof the chambers formed in the oi' the muiller in preventing corrosion or rusting of the same, and maintains the eiiiciency of the muiller at its highest point throughout its life by preventing the filling up of any chamber with liquid, soot', or other foreign materiali. This mufiler can vbe readily changed to produce the ejector action by arranging the apertures 5.0 and the baille which supports the discharge end loi' the inner shell in lthe manner shown in Fig. 1, this change also being possible with the other constructions herein illustrated.

'I'he construction shown in Fig. 4 is intended for use where a materially greater amount oi' silencing is required, than can be obtained from the use of the muiller shown in Fl'gs. 1 and 3, and in this case, the inner shell comprises three sections or parts 55, 56 and 51, which are of successively smaller diameters, and thus produce a stepped arrangement in the inner shell which may be used interchangeably with the tapering 4 vided between the irner and intermediate shells at the ends of the several sections or parts of ythe inner shell, and an additional baille 58 is provided intermediate of the ends of the section 5l o f the inner shell. Bailies are also provided between the intermediate and theouter shells and arranged alternately with baiiies between the inner and intermediate shells. This forms intermediate chambers or compartments 59, 60, 6| and 62 between the inner and intermediate shells, and 'outer chambers 63, 64 and 65 between the intermediate and outer shells. The apertures in the intermediateshell are so arranged that gases may pass from the intermediate chamber 59 into the outer chamber 63 and through this chamber 63 into the intermediate chamber 60. In the chamber\60, the gases may Iiow either into the intermediate shell or into the chamber 64 and gases cooled in the outer chamber 63 will mix with the hot gases enteringy through the perforations of= the portion 56 of the inner shell, and thus produce the turbulence referred to in connection with the description of Fig. 2. ,The presence of gases of diiierent temperatures in diierent parts of the chamber 60 produces refraction and absorpton of sound waves. Gases from the chamber 64 enter into the' chamber 6I, and consequently, turbulence is again set up in this chamber with the result of further deadening of sound waves. Some gases from the chamber 6I will enter into theouter chamber 65, and thus into a chamber.

-62, this flow being induced by the decreased pressure at the discharge end of the inner shell, or

' if desired, the baille and apertures at' the discharge end of the intermediate shell -may be rearranged as shown in Fig. 1, to produce an ejector action.

It win be understood in connecten with autor these mufliers which have been described, that the iiow of gasesthrough the chambers about the inner shell is not necessarily continuous in -a direction from the receiving to the discharge end of the muiiler, since this iiow varies with varia,-v tions in pressure in the inner shell. For example,

when the peak of a pressure or pulsation wave of exhaust gas reaches the inner shell, there will be a very rapid ow of gas from the perforations of the inner shell and a corresponding iiow into the chamber between the intermediate and outer shells. When the peak has passed, there will be greater pressure in the chambers surrounding the inner. shell than in the inner shell, and consequently, there will-be an immediate return of the gases from the chambers to the inner shell. By the time the trough of the wave or pulsation is reachedfthe larger volumes or gas temporarily stored in the outer chambers of the muiiler will reach the inner shell,l the return of `these gases 'to the inner shell being delayed because .of the greater distance which they have to travel. In tlf-is manner, the impulse yorgas ypressureV waves -will be to a very large extent smoothed out by the action of the 'chambers of the mumer, and consequently, a much more uniform flow of gas will discharge from the tail pipe, and consequently, objectionable noises ordinarily caused by the discharge of gases from. the end of the tail pipe 'into the atmosphere will be eliminated.A Inaddition to the alternating flow of gases into andv outof the chambers, there will be a more or less constant now through these chambers in the general direction toward the discharge end' of the muiller, ,which ow results in the drawing of the fcooled gases, back into the innershell for mixture with' the hot gases and for producing the rechambers.

fraction and absorption of sound waves in this shell. Without this continuous 110W,` the cooled gases in the outer chambers would not be mixed to any appreciable extent with the gases in the inner shell, since these cooled gases would act more or less as buffers or cushions in the outer chambers without actually passing out of these 'Ihe passing of gases through the chambers about the inner shell also reduces the volume of gases whichl must pass through the in-l ner shell and, consequently, reduces back pressure in the muilier. I have found it particularly eiective in silencing the exhaust to provide imperforate bailles and passing the gases in opposite directions into and out of an outer chamber through apertures in the inner shell.A

It will be understood that the`constructions shown in the drawing are merely illustrative of theprinciple of my linvention and numerous changes in'the details of construction may be made. I While the best results are obtained when the inner shell is of lesser diameter at its discharge end than at its receiving end, yet I have found that in certain cases good results can be obtained if the inner shell is of uniform diameter throughout, if other meansare employed vfor slightly reducing the pressure near the discharge end of the muiiler.

I claim as my invention:

l.' A muiller havinginlet and outlet openings, an inner perforate shell extending from said inlet toward Lsaid outlet opening, intermediate and outer shells arranged concentrically about said inner shell, bailies lconnectingsaid inner and intermediate shells and dividing the space between Y said inner and'intermediate shells into a plurality of turbulence chambers, a baffle extending from lessen the intensity of sounds emitted by the A muiiler.

2. A muiiler includingv inner, intermediate, and

outer shells, the inner shell vbeing perforate and forming a substantially direct passage through said muier, said inner and intermediate shells forming between themv an inner chamber, the perforations in said inner shell establishingcommunication between the interior thereof and said inner chamber, an outer chamber formed between said intermediate and outer shells, and substan- `tially imperforate baiiies disposed crosswise of said shells and subdividing the Vinner 'chamber into separate turbulence chambers and said outer chamber i'ntocooling compartments, said intermediate shell being perforate solely in limited minor zones, with the perforations connecting cach outer cooling compartment through one-of said zones with one of said turbulence chambers and throughanother of said zoneswith another v of saidI turbulence chambers, said perforations also connecting one of said turbulence chambers with both of said cooling compartments whereby gases may enter eachcooling compartment from through said muiller, and being formed of portions of varying diameters, the portions ofl said inner shell nearer to the discharge end of said muiilerbeing of less diameter than the portion near the gas receiving end of said inner shell, said intermediate and inner shells forming between them a sound eliminating chamber, a plurality of imperforate, transverse baille means disposed across said chamber at intervals along its length and subdividing it into' turbulence chambers, the space between said intermediate and outer shells forming a cooling chamber, imperforate partition means disposed across said cooling chamber at a point between two of said baffle means to subdivide said cooling chamber into compartments, said intermediate shell having a periorate zone connecting one end portion of each compartment to one turbulence chamber and another perforate zone connecting the other end portion of that compartment to another turbulence chamber, said intermediate shell being otherwise substantially imperforate.

4. A muiller including an inner shell and intermediate and outer shells arrangedabout said inner shell, the space between the intermediate and outer shells forming a cooling chamber, means cooperating with said shells to divide the space between said inner and intermediate shells into a plurality of non-communicating intermediate chambers, imperforate means disposed transversely across saidcooling chamber and dlviding it into compartments disposed end to end, said inner shell communicating directly with y each of said intermediate chambers, and passages in said intermediate shell solely in zones thereof spaced substantially apart lengthwise of that shell for connecting each cooling compartment at diierent zones thereof directly with two adjacent intermediate chambers, one' of which intermediate chambers is connected to both of said compartments, said passages having an aggregate area which is very materially less than the area of communication between said inner shell and said intermediate chambers.

5. A muffler having inlet and discharge openings in opposite ends thereof, an inner shell open at its opposite ends and extending substantially from the inlet to the discharge opening of said muiiler, said shell being provided with perforations substantially throughout the length thereof and being of smaller diameter at the discharge end thereof than at the inlet end, intermediate and outer shells arranged in spaced relation to each other about said inner shell, means for closing the ends of the spaces between said inner, intermediate and outer shells, imperiorate bailles arranged between said inner and intermediate shells and forming a plurality'ofv intermedate chambers disposed endto end, an imperforate wal arranged between and connecting the intermedate and outer shells at a point between two intermediate bailles in a direction along the length of the shells and dlvidimr the space between said intermedate and outer shells into outer chambers disposed end to end, each outer chamber being arranged in overlapped relation to the two adjacent intermediate chambers, and perforatio'ns in said intermediate shell to establlish communication of each outer chamber with the two adjacent intermediate chambers, one of said intermediate chambers establishing communication between the two outer chambers separately from the passage through the inner shell.

6. A muiiier having inlet r`and outlet openings, an inner perforate shell extending from said inlet toward said outlet opening, intermediate and outer shells arranged concentrically about said inner shell, a plurality of substantially imper-V forate baiiles connecting said inner and intermediate shells and dividing the space between said inner and intermediate shells into a plurality of chambers, a substantially imperforate wall extending from said intermediate to said outer shell at a point between two of said ballles, andA dividing the space between said intermediate and outer shels into separate compartments having no direct communication with one another, said intermediate shell being apertured solely in relatively small zones spaced apart along tne length of said intermediate shell but with said zones at opposite sides of each of said bailles connecting said inner and intermediate yshells and connecting each intermediate chamber directly with two different and adjacent compartments, and each compartment with two different and adjacent chambers.

7. A muiller including inner, intermediate, and outer shells, the inner shell being perforate and forming a substantially direct passage through said muiller, said inner and intermediate shells forming lbetween them an inner chamber, the perforations in said inner shell establishing communication between the interior thereof and said inner chamber, separate and non-communicating outer compartments formed between said intermediate and outer shells and disposed in a row along the length of said outer shell, and substantially imperforate bailies disposed crosswlse of said inner and intermediate shells, each at a point between the ends of an adjacent compartment, and subdividing said inner chamber into separate non-communicating lsub-chambers, each overlapping with'an adjacent compartment, said intermediate shell being perforate solely in limited minor z'ones spaced apart in a direction endwis'e of the shells, with each outer compartment communicating directly through one of said zones with one of the inner sub-chambers, and through another of said zones with another of said subchambers, and with each sub-chamber between the `end sub-chambers communicating directly with a plurality of adjacent compartments, the total areas of the perforations in the zone of the intermediate shell leading to one inner subchamber from one compartment being less than for the zone leading from the same compartment into another inner sub-chamber.

8. A muiller for internal combustion engines and the like comprising a casing subdivided by imperforate walls into a direct passage therethrough from end to end, and a plurality o! separate chambers, onev group of said chambers being disposed along and communicating directly and freely with said direct passage, but' having substantially no direct communication with one another, and another group of said chambers being disposed along the chambers of said one group and having substantially no direct communication with one anothen'each of the chambers of said, another group having restricted direct communication with two diil'erent chambers of said one group, and at least one chamber oi said one group having direct communication separately of the other chambers of that group and of said passage, with a plurality of the chambers of said another group, whereby t e chambers of said another group may all communicate with one aning disposed along ,and communicating directlyI and freely with said direct passage, but having substantially no direct communication with one another, and another group of said chambers bej ing disposed along the chambers of said one group and having substantially no direct communication with one another, each of the chambers of said another group having restricted` direct communication with two different chambers of said one group, and at least one chamber o f said one group havingdirect communication separately of the other chambers of that group and of said passage, with a plurality of the chambers o! saidanother group, whereby the /chambers of said another group may all communicate with f one another through the chambers of said one group, so asA to provide for restricted and local communication 4between chambers of said one group by means of a chamber 'of said another group, some of the chambers of said one group having different volumes; A

10. A muiller for internal combustion engines and the` like comprising a casing subdivided by imperforate walls into a direct passage therethrough from end to end, and a plurality of separate'ch'ambers, one group of said chambers being disposed in a rowalong and communicating directly and freely with said direct passage, but

having substantially no direct communication withUone another, and another group-of said' chambers being disposed along the chambers of said one group and having substantially no direct communication with one another, each of the chambers of said another group having restricted communication, solely at kzones spaced substantially apart ln a direction lengthwise ofl said direct passage, with two chambers of said one group, and each intermediate chamber in said row of said one group having restricted communication with two f the chambers of said another group solely at said zones. so as to provide for restricted and local Acommunication between chambers of said one group by means of a chamber or said another group.

11. A munier for internal combustion engines and the like comprising a casing subdivided by imperforate walls into a dirct passage therethrough from end to end, and a plurality of sep'- arate chambers, one group of said chambers being disposed in a row along and communicating 'directly and freely with said direct passage, but

having substantially no' direct communicationwith one another, and another group of said chambers being disposed in a -row along theV chambers of said one group and having substantially no Ydirectcommunication with one another, each of the chambers of said another group having restricted /communication, solely at zones spaced .substantially apart in a direction length-v wise et said direct passage, with two chambers of said one group, and each intermediate chamber in said row'o! said one group having re- Aaos-4,186

stricted communication with two of the chambers yof said another group solely at said zones, so as to provide for restrictedV and local communication between chambers of said one group by means of a chamber of said another group, the aggregate areas of communication between each chamber of said another group with the chambers of said one group, being greater at' the zone nearer the inlet end of said direct passage than at the other zone of the same chamber of said another group.

12. A muiier having inlet and outlet openings, an inner perforate shell extending from. said inlet toward said outlet opening, intermediate and outer shells arranged concentrically about said inner shell, baiiies connecting said inner and intermediate shells and dividing the space between said inner and intermediate shells into a plurality of chambers, a wall extending from said intermediateto said outer shell, approximately mid` way between the two nearest battles and dividing the space between said intermediate and outer j shells into separate chambers, perforations in said intermediate shell at opposite sides of each of said baiiles connecting said inner and intermediate shells, at least one of said inner chambers between said inner and intermediate shells receiving cool gases from one of said outer chambers and discharging gases to said other outer chamber through said perforations in said intermediate shell, and also being arranged to receive hot gases through the perforations of said inner shell, to set up a'turbulence of gases within said intermediate chamber to retract sound waves.

13. A, muler including inner, intermediate and outer shells, said inner shell being perforate and through said manier, and being formed of portions of varying diameters, the portion of said inner shell nearer. to the discharge end of said muiiier being of less diameter than the portion f near the gas receiving .end of said inner shell,v said intermediate and inner shells forming beforming a substantially direct passage for gases tween them asound eliminating chamber, im-

sage, the space between said intermediate and.v

outer shells forming a cooling chamber, an im- -perforate wall connecting the outer and intermediate shells at a point intermediate said baille means and dividing said cooling chamber intov compartments disposed end to end lengthwisel l along said shells, with each compartment overlapping with a common turbulence chamber with which the 'other compartment overlaps, said interlmediate shell having perlorate zones to provide lcommunication from said common turbulence perforate zones of said intermediate shell having a less aggregate perforate area than the asgref gate perforate areas oi the section oi' said passage through those turbulence chambers, and the aggregate perforate area of the zone connecting said common chamber to the compartment nearest the gas inlet end of said passagebeing greater than f orthe zone connecting said common chamber to the othercompartment, substantially all of the gases'from said chambersbeing returned LAURENCE R. HEATH.

to said inner shell for `discharge from said muiier."

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