US 2109220 A
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Feb. 22, 1938. Q G, NOBLlTT ET AL 2,109,220
MUFFLER Filed April ll, 1956 Patented Feb. 22, 1938 UNITED STATES MUFFLEB Quintin G. Noblitt and Edmund Ludlow. Columbus, Ind.. assigner! to Noblitt-Sparks lndustries, Inc., Columbus, Ind., a corporation of Indiana Application April 11, 1936, Serial No. 73,819
This invention relates to muiilers for silencing flowing gases, such as the exhaust gases from internal combustion engines, and is primarily concerned with a muiiler of the type in which the sound waves in the flowing gases, during their passage through the muiller, are divided and subdivided, compelled to now over paths of different lengths, and then re-combined and discharged from the muiller. When two components 10 or fractions of a sound wave which have traveled paths of different lengths are re-combined they will, at the point of re-combination, differ in phase, thus creating an interference which results in lessened amplitudes and which therel5 fore silences or tends to silence the noise which would otherwise occur. When a large number of such sound-wave fractions, each having traveled over its own path, are re-combined, the possibilities of individual interferences arising from 90 phase differences are multiplied enormously, with the result that the silencing action extends over a range or band of frequency which, given a muiiler of adequate size, can be made wide enough to include those frequencies whose presence in the stream of emerging gases is responsible for disagreeable sounds. In a muiuer of this type, the longest sound wave which can be completely silenced by a simple division into and re-combination of two fractions has a wave length equal $0 to twice the difference between the lengths of the two paths which the separate fractions respectively follow.
Our co-pending application Serial No. 632, filed January "I, 1935, illustrates a muiller of this general type, and the present invention is a development of that muilier. The object of the present invention is to increase the width of the band of frequencies which can be adequately silenced by a muiller of the type set forth in our prior application. It is also our object to pro- -duce more effective silencing of sounds of any given frequency, and to do this without building up an excessive back-pressure. Still another object of our invention is to produce a muiiier which can be simply and economically constructed and in which such variations and inaccuracies as inevitably occur in high-quantity production will not adversely ailect the silencing action.
In carrying out our invention we employ the same general arrangement as that shown' in our prior application above referred to-namely, a generally cylindrical shell provided interiorly with three longitudinally co-extensive, perforated silencing tubes through which the gases may successively pass, each of such silencing tubes being located in an individual compartment separated from the compartments for the other tubes by perforated partitions and the whole being arranged so as to provide at least one unrestricted path, including the silencing tubes, through 5 which gases can ow from the inlet of the muilier to the outlet. For lconvenience of description, we shall refer to those gases which remain in this unrestricted path during the entire extent of their passage through the muilier l0 as the main body of gases; although it is believed immaterial, and we do not know, whether that fraction -of the gases constitutes a major or a minor part of the whole. In the muffler Y of our prior application, as the main body of l5 flowing gases left the discharge end of either of the first two silencing tubes, it entered a transverse passage by which it was directly conducted into the next succeeding silencing tube. In the present invention, instead of permitting the gases 20 discharged from the end of the first silencing tube to enter immediately the second silencing tube, we so construct the muiller that the first silencing tube discharges into the compartment in which it is located, and we close the adjacent 25 end of that compartment, so that the main body of gases will flow backwardly through the annular space between the first silencing tube and the walls of the compartment. Upon being discharged from this annular space, the gasesenter 0 a transverse passage conveying them to the intermediate silencing tube through which they flow into a second transverse passage communicating with the open end of the compartment in which the third silencing tube is located. The gases flow through the annular space between thewalls of this compartment and the third silencing tube to the. remote end of the compartment, where they enter the third silencing tube and pass therethrough into the tail pipe. The walls of the compartments in `which the nrst and third perforated silencing tubes are located are provided with a multiplicity of well distributed openings which, coupled with the perfora- 45 tions in the tubes, provide a vast number of paths over which fractions of the exhaust gases, and fractions of divided sound waves in such gases, can flow.
The accompanying drawing illustrates our in- 50 vention: Fig. 1 is a side elevation of a muiller with parts thereof broken away to illustrate the interior construction; Fig. 2 is a transverse section on the line 2 2 of Fig. 1; and Fig. 3 is, in somewhat idealized and diagrammatic form, a 55 developed section on the broken line 3 3 of Fig. 2.
'I'he muiiler shown in the drawing comprises a cylindrical shell I il provided with end heads II and I2. A transverse interior partition I3 mounted near the head I2 serves to define, in co-operation with saidhead, a transverse gas passage I4. A second transverse partition IE, similar to but spaced from the partition I2, serves in part to denne a second transverse passage I6.
If, as is usually desirable, the muiller is to include a resonating chamber adapted to silence sounds of a rather definite frequency, the passage I6 may lie between the partition I5 and a diaphragm I1 which, in co-operation with the muiller shell and head II, defines a resonating chamber I8.
Mounted in and extending between the partitions I3 and I5 is an elongated cup-like chamber 20 disposed in substantial alinement with an inlet nipple 2| and having its open end communieating with the transverse passage I6. A similar cup-like chamber 22 also extends between the partitions I3 and I5 and is disposed in substantial alinement with an outlet pipe 23 with its open end communicating with the transverse passage II.
Within the cup 20 there is disposed a silencing -tube 25 connected to the inlet nipple 2| to receive rearwardly flowing gases therefrom. The rear end of the tube 25 is open and is spaced from the adjacent closed end of the cup 2Il so as to permit gases discharged from the end of the tube to enter and flow forwardly through the annular space between the tube and the walls of the cup, and thence into the transverse passage I6.
- The second silencing tube 26 is mounted be- -tween the partitions I3 and I5 and serves to interconnect the transverse passage I6 at the front end of the muiiler with the other transverse passage I4 at the rear end.
The third and last silencing tube 21 is disposed within the cup 22 and communicates with the outlet passage 23, as by being a forwardly projecting continuation thereof. The front end of the silencing tube 2l is open and spaced from the adjacent closed end of the cup 22, so that gases owing forwardly through the nannular space between the tube 21 and cup 22 may enter the open front end of the tube to ow rearwardly therethrough into the outlet pipe.
Between the partitions I3 and I5, each of the silencing tubes 25, 26, and 21 is provided with a multiplicity of perforations forming restricted gas-passing openings. Similar perforations, also located between the partitions I3 and I5, are provided in the cups 20 and 22.
To conserve space longitudinally of the muiller, the rear end of the cup 20 may project rearwardly beyond the partition I3 into the passage I4, and the front end of the cup 22 may project similarly through the partition I5 into the passage I6. We find it desirable in some instances to provide for direct communication between these projecting cup-ends and the passages Il and I6 into which they respectively project. As shown, this communication isafforded by perforating the member which closes the projecting cup-end.
The silencing tubes, especially the tubes 25 and 21, and the cups 20 and 22 are conveniently formed of perforated flat stock rolled into cylindrical form. If this is done, we find it convenient to bend the longitudinal edges of the silencing tubes 25 and 21 and of the cups 20 and 22 into flanges which project radially outwardly and which are nested together, as indicated in Fig. 2, with the anges of each silencing tube received between the flanges of its associated cup. The four superposed flanges may then be secured together, as by spot-welding, to hold the tube and cup in proper relative position.
If, as shown in the drawing, the muiiier includes a partition I1 in part defining a resonating chamber I8. the partition I1 is provided with an opening aifording communication between the resonatlng chamber and the passage I6. In the arrangement illustrated in the drawing this opening, indicated at 30, receives the inlet nipple 2| but is materially larger in diameter than such nipple and has its edges bent into a short cylindrical flange to form a neck the length and efi'ective cross-sectional area ot which will be factors in the determination ofthe frequency of the sound wave which the resonating chamber I8 is to absorb.
As is clear from the drawing, the silencing tube, the space between each of the silencing tubes 20 and 22 and its associated cup, and the transverse passages I4 and I5 afford an unrestricted path through which gases can flow from the inlet and outlet of the muiller. Not all the gases will follow this path, however, as the perforations in the silencing tubes and in the walls of the cups provide a vast number of transversely or obliquely extending paths over which fractions of the gases and fractions of sound waves may travel. In the last silencing tube 21 all the fractions are re-coxnbined and, as there is a wide variation in the lengths of the paths respectively traversed by them,vv there will be a great number of possibilities of interference between fractions resulting in the smoothing out or attenuation of sound waves. That fraction of the gases, or of a sound wave, which follows the unrestricted path through the muiller will flow ve times across the space between the partitions I3 and I5, and thus will follow a p'ath materially longer than the shortest and most direct path through the mutller. Since the longest sound wave which can be silenced as the result of interference phenomena depends upon the dinerence in the effective lengths of the paths followed by the two fractions which combine to produce the interference, it will be apparent that our muiiier can silence sound waves of relatively great length in comparison to the over-all dimensions of the muffler. Not only does our mumer produce silencing of such relatively long waves, but it also,v because of the tremendous number of possible paths of `diiferent length, effectively silences sounds of shorter wave length. In addition to the possibilities of interference between gas-fractions or wave-fractions some of which have traversed transverse or oblique paths between the cups or between either and the intermediate silencing tube, there are also possibilities of interference within each cup; for each of the openings in either of the tubes 25 and 21 will pass a gas-fraction or wave-fraction interfering with another fraction which has passed around the end of the tube.
Beyond the fact that the over-all dimensions of a muilier and the cross-sectional area of the main gas-passages in it will in general vary roughly with the piston-displacement of the engine with which the mumer is to be used, few if any general rules can be\ laid down for determining exact dimensions of a muiiier. The
ultimate design, where factors of cost, silencing emciency, and back-pressure are regarded as important involves considerable experimentation. As an example of a satisfactory mui'iier of the type set forth in this application, we refer to one found suitable for use with the engines of the 1936 and 1937 Chevrolet automobiles. The general proportions of that muiller were roughly as indicated in Figs. l and 2. The silencing tubes were 1% inches inside diameter, and the cups 2| and 2l were 21'; inches; the partitions i3 and Ilwere 71. inches apart; each silencing tube was provided with '15 holes s', inch in diameter; each of the cups 20 and 22 had, distributed between the partitions I3 and Ii, 130 holes inch in diameter; and the extreme end wall of each cup was provided with 2l holes s', inch in diameter.
We claim as our invention:
1. A muiiler, comprising a hollow shell, spaced transverse partitions within said shell, end heads for said shell spaced outwardly from said partitions to provide passages for transversely flowing gases, a pair of cups extending longitudinally of the shell between said partitions and opening respectively into said transverse passages, openended silencing tubes disposed respectively within said cups and connected throughvthe open ends thereof one with a gas-supply conduit and the other with an outlet pipe, and a third silencing tube extending between said partitions and interconnecting said transverse passages, each of said silencing tubes being provided with a multiplicity of distributed openings each providing restricted communication between the interior of the tube and the space around it, each of said cups being provided between said partitions with a plurality of distributed openings each a'ording restricted communication between its interior and the space within the shell, at least one of said cups being additionally provided near itsA closed end with perforations interconnecting the interior of the.,
cup with the adjacent transverse passage.
2. A muilller, comprising a hollow shell, spaced transverse partitions within said shell, end heads for said shell spaced outwardly from said partitions to provide passages for transversely flowing gases, a pairof cups extending longitudinally of the shell between said partitions and opening respectively into said transverse passages, openended silencing tubes disposed respectively within said cups and connected through the open ends thereof one with a gas-supply conduitv and the other with an outlet pipe, and a third silencing tube extending between said partitions and interconnecting said transiverse passages, each of said silencing tubes being provided with a multiplicity of distributed openings each providing restricted communication between the interior of the tube and the space around it, each of said cups being provided between said partitions with a plurality of distributed openings each affording restricted communication between its interior and the space within the shell each of said cups being additionally provided near its closed end with perforations interconnecting the interior of the cup with the adjacent transverse passage.
3. A muiller, comprising a hollow shell, spaced transverse partitions within said shell, end heads for said shell spaced outwardly from said partitions to provide passages for transversely flowing gases, a pair of cups extending longitudinally of the shell between said partitions and opening respectively into said transverse passages, openended silencing tubes disposed respectively within said cups and connected through the open ends thereof one with a gas-supply conduit and the otherwith an outlet pipe, and a third silencing tube extending between said partitions and interconnecting said transverse passages, each of said silencing tubes being provided with a multiplicity of distributed openings each providing restricted communication between the interior of the tube and the space around it, each of said cups being provided between said partitions with a plurality of distributed openings each affording restricted communication between its interior and the space within the shell.
4. A muiller as set forth in claim 3 with the addition that the closed end of at least one of said cups projects through the adjacent partition into the transverse passage in part defined by that partition.
5. A muiiler, comprising a shell, partition means within said shell defining two longitudinally spaced transverse passages and three longitudinally extending compartments located between said passages, two of said compartments opening respectively into said two transverse passages, a silencing tube disposed in the third compartment and interconnecting said two transverse passages, and open ended silencing tubes disposed respectively in the other two compartments and adapted one for connection to a supply conduit and the other with an outlet pipe, each of said silencing tubes being provided with a multiplicity of distributed openings each providing restricted communication between the interior of the tube and the compartment in which it is located, and the side walls oi' said compartments being provided with a multiplicity of distributed openings each providing restricted communication between two of such compartments.
6. A muiller for silencing a flowing gas, comprising a shell having an inlet and an outlet, perforated now-directing means arranged within said shell to provide a multiplicity of restricted paths of varying lengths over which fractions of the gas may flow between said inlet and outlet and also to provide at least one unrestricted gas passage between the inlet and outlet, said iinrestricted passage being retroverted with one of two immediately successive stretches being located within the other.
'1. A muiiler for silencing flowing gases, comprising a shell having an inlet and an outlet, partition means within said' shell defining a retroverted and substantially unrestricted gas e between said inlet and outlet, said partition means including a wall separating and at least partially dening two parallel stretches of said passage through which gases flow in opposite directions, and said wall being provided with a multiplicity of longitudinally spaced perforations.
EDMUND LUDLOW. QUENTIN G. NOBLITI.