US2554032A - Silencer with toroidal expansion chambers - Google Patents

Description

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May 22, 1951 J. F. JOHNSTON SI-LENCER WITH TOIEOIDAL EXPANSION CHAMBERS Filed March 31, 1949 Patented May 22, 1951 .SILENCER WITH TOROIDAL EXPANSION ERS CHAMB J. FordJohnstonQHampton, Va., assignor of onevhalf to John R. Anthony, Jr., Takoma Park, Md.

vApplication March 31, 1949, Serial No. 84,573

Claims. 1

This invention relates-to a silencer or muliler for suppressing .the noise caused by the sudden exit of gas from or entrance of gas into a reciprocating pump, compressor, engine or other device which may transmit or otherwise handle gas With periodic pulsations.

Mufflers of conventional design employ charnbers equipped With bailles, slots, holes, and like devices for creating turbulence in the flow of gas, all of which convert the kinetic energy of the gas into heat energy which results in an increased back Ipressure at the exhaust valve or a decreased induction pressure at the inlet valve The .primary object of this invention is to suppress the noise attendant upon pulsating flow of vgas by providing suitable chambers for transforming the pulsations into relatively continuous viiow Withoutconverting kinetic energy into heat energy. This may be achieved by the application of commonly known aerodynamic and acoustic principles relating-to the handling of flowing gases.

The secondary object is to produce such a mui-- Viler havingphysical characteristics which render it readilyadaptable to'loW-cost, high-volume production, and which will .be comparatively much smaller ,in size than muillers of known construcber tothe other, the peripheral chamber being so shaped as to maintain a smooth now of gas. It'is a Well-known principle of acoustics that a sudden reduction of area in a'gas conductor will materiallyreduce the intensity of noise transmitted along the conductor, but past designs using thisprinciple have always failed to maintain the kinetic yenergy of the gas, so that a high pressure differential rWas required to maintain the gas oW.

Thelvelocityvof exhaust gas leaving a valve port at beginning of 'exhaust is supersonic. The function of-a muffler -is to ysuppress the noise of the V.supersonic Wave front by reducing its velocity as much as possible. inthe silencer of the present invention, ythe gas expands as Vit leaves the inlet pipe, and the expansion causes the conversion of pressure energy into velocity energy With the gas rotating at a high velocity around the inlet. This rotation causes a partial vacuum at the.center of rotation, due to centrifugal force. The creation of the partial vacuum occurs after the supersonic Wave has passed, and is maintained during the remainder oi the exhaust stroke. Therefore, since the exhaust strokeis completed during a time when the pressure is low, the weight of exhaust gas remaining in the cylinder from one cycle to the next is minimized. In essence, the energy of the initial supersonic blast is utilized to provide a ylow pressure chamber into which the scavenging operation can discharge during the end of the stroke, whichis the most important part of the stroke.

It will be obvious, of course, that the same design is effective as an intake silencer.

The invention is illustrated in the form of a two-piece casting, with parts riveted together. Using all the above-mentioned principles, the silencer takes in the gas at its center, lets the gas escape into the central expansion chamber through diffuser vanes which impart to the gas a whirling motion about the axis of the inlet pipe, and then permits the gas to escape into a peripheral collection chamber through a peripheral slot. While the pressure Waves causing objectionable noise will spread to the Walls of the central chamn ber, only a small portion of them will escape through the slot into the peripheral collection chamber. The collection chamber preferably is designed so that its cross section area at any point is proportional to the position of the point vbetween the beginning and end of the peripheral slot, in order to achieve the maximum smoothness of iloW.

The small part of the pressure wave which escapes from the central expansion chamber through the 4peripheral slot Will enter all parts of the peripheral collection chamber at approximately the same time. Therefore, the Wave front Will not be concentrated at one point in the collection chamber, and its exit will be spread over the time required for sound to travel the circumferential length of the collection chamber. Most of the energy of the pressure waves will be absorbed by the walls of the two chambers as they are reflected from side to side.

The pulsations in pressure of the incoming gas are smoothed out by the iactthat the gas in any given pulsation enters the central chamber without striking against any baille, but makes a gentle transitional curve in vchanging its direction, so

that a new pulsation meets no resistance except the gas in the central chamber, which is already whirling rapidly in the same direction as the new pulsation.

It has been found through experimentation that the peripheral slot area, for best performance, will generally be approximately one-twentieth to one-thirtieth of a square inch per brake horsepower of the engine.

The invention as illustrated in the drawings takes the form of a muffler and is shown, generally, in a two-part casting.

In the drawings, Figure 1 is a top plan view of the assembled muiiier;

Figure 2 is a sectional View tak-en on the line 2--2 of Figure 3;

Figure 3 is a side view of the assembled muffler wherein certain portions of the inner construction are illustrated in dotted lines; while Figure 4 is a sectional view taken on the line 4-4 of Figure 1.

The upper casting is indicated generally by reference numeral A, while the lower casting is indicated generally by reference numeral B. The upper casting A is provided with an annular extension I6 having a screw-threaded bore II formed therein, for attachment to the manifold pipe of an internal combustion engine or the like, wherein the pulsating gases to be muffled originate. The upper casting A is in the general form of a hemisphere, as indicated by reference numeral I2, while the outer periphery of the sphere is generally arcuately shaped, as indicated at i3, and an annular flange I4 is provided for attachment through suitable bolts I to the lower casting B. A substantially annular pipe I5 is formed integrally with the casting A, the pipe IE having a plurality of angularly positioned diffuser vanes I1 formed therein.

The lower casting B, as illustrated particularly in Figures 2 and 4, is formed in substantially the shape of a hemisphere 20 and has a generally arcuately shaped outer periphery 2| with a flange 22 formed thereabout, the ange 22 cooperating with the flange I4 of the casting A, and bolts I5 extending through the two flanges to secure the two castings together. An annular pipe 24 extends upwardly from the bottom of casting B, the pipe 24 being so positioned to register with pipe I6 so as to form a continuation thereof, pipes I5 and 24 being positioned substantially centrally of the castings A and B. Pipe 24 is also provided with a plurality of angularly positioned diffuser vanes 25 so as to form a continuous slot with the vanes I'I formed in pipe I6. When the two castings are assembled through their flanges I4 and 22, as shown particularly in Figs. 3 and 4, the hemispheres I2 and 2G form a substantially spherical inner chamber 3B. While this chamber 3i) has been generally indicated as being spherical, it will, of course, be understood that it need not necessarily take the same shape as a sphere, although the same should be substantially toroidal. The arcuate extensions I3 and 2| form a substantially annular collection chamber 32, when Viewed in cross section, the collection chamber 32 taking the form of a spiral, as indicated in the drawings, the area of chamber 32 gradually increasing from the point indicated at X as Zero to the outlet opening 33.

The castings A and B are so shaped, at a point intermediate the expansion and collection chambers, as to provide a peripheral restricted slot 35 when the castings are positioned together, as seen particularly in Fig. 4 in order to act upon the gases passing therethrough in a manner similar to a venturi. As the castings are subjected to certain heat and pressure, it is possible that the same may in time warp and, accordingly, suitable spacer elements 36 are positioned about the peripheral slot 35 so as to prevent the castings from closing which would in turn close the Venturi slot.

The bottom central portion of casting B is provided with a cone-shaped indentation 4D for purposes later to be described.

In operation, the assembled unit as illustrated in Figs. 3 and 4 is secured at the opening I I to the source of pulsating gases. The gases enter the pipes IE and 24 and through the aid of the cone 4U and angularly positioned diffuser vanes II and 25 pass into the expansion chamber 30 in a whirlingl motion. The gases will continue their whirling motion and hence be thrown outwardly within the expansion chamber 30 and pass through the peripheral slot 35 into the collection chamber 32 which, as has been noted, is generally in the shape of a spiral and gradually spreads from zero, as indicated at point X, to full area at the outlet port 33.

As before indicated, the incoming pulsating gases expand in the expansion chamber, which expansion causes the conversion of pressure energy into velocity energy and the expanding gases rotate at high velocity within the expansion chamber. A partial vacuum is thereby formed in the central portion of the expansion chamber, the partial vacuum occurring after the supersonic wave has passed. As the exhaust stroke of the engine is completed during the formation of this partial vacuum, the weight of exhaust gases remaining in the cylinder from one cycle to the next is materially decreased. While the pressure waves, which cause the objectionable noises, will spread to the walls of the expansion chamber, only a small portion of the pressure waves will escape through the peripheral slot into the peripheral collection chamber. The small percentage of the pressure waves which thus escape from the expansion chamber into the spiral collection chamber will escape at approximately the same time and, therefore, the wave front will not be concentrated in the collection chamber and its exit will be spread over the time required for sound waves to travel the circumferential length of the collection chamber. Also, most of the energy of the pressure waves will be absorbed by the walls of the two chambers as they are reflected from side to side.

While the invention has been illustrated in the form of castings, it will be obvious that the same may be formed of sheet metal or the like and the various elements riveted or otherwise secured together. Also, the whirling motion may be imparted by other means than diffuser vanes. Sufcient whirl can be imparted to the gas in planes parallel to the inlet axis by placing a tall cone in the path of the incoming gas, which gently turns the gas from its linear flow path without reflecting an appreciable pressure rise to the inlet pipe.

I claim:

1. A silencer comprising a hollow substantially toroidal expansion chamber, an inlet therefor, a collection chamber positioned about the outer periphery of said expansion chamber for receiving gases from said expansion chamber, a peripheral slot formed between said chambers to provide communication therebetween, and an outlet for said collection chamber, said collection chamber being formed by a substantially annular inner wall portion and a spiral outer wall portion whereby said collection chamber gradually increases in cross-section from substantially zero to substantially the cross-sectional area of said outlet.

2. A silencer -comprising a hollow substantially toroidal expansion chamber, an inlet therefor, means for imparting whirlingI motion to the inlet gas in said expansion chamber, a collection chamber positioned about the outer periphery of said expansion chamber for receiving gases from said expansion chamber, a peripheral slot formed between said chambers to provide communication therebetween, and an outlet for said collection chamber, said collection chamber being formed by a substantially annular inner wall portion and a spiral outer wall portion whereby said collection chamber gradually increases in crosssection from substantially zero to substantially the cross-sectional area of said outlet.

3. An exhaust gas muler for internal com bustion engines comprising a hollow substantially toroidal expansion chamber, an exhaust gas inlet conduit connected to said chamber, a substantially annular collection chamber positioned on the outer periphery of said expansion chamber and having a gas outlet, a substantially continuous annular slot formed between said expansion chamber and said collection chamber providing communication therebetween, said slot being less than 360, and an outlet for said collection chamber, said collection chamber being formed by a substantially annular inner wall portion and a spiral outer wall portion whereby said collection chamber gradually increases in cross-section from subtantially zero to substantially the crosssectional area of said outlet.

4. An exhaust gas muiiler for internal combustion engines comprising a hollow substantially toroidal expansion chamber, an exhaust gas inlet conduit connected to said chamber and extending therein, said inlet conduit having diffuser vanes therein to cause the gases to rotate within said chamber, a substantially annular collection chamber positioned on the outer periphery of said expansion chamber and having a gas outlet, said collection chamber being formed by a substantially annular inner wall portion and a spiral outer` wall portion whereby said collection chamber gradually increases in cross-section from substantially zero to substantially the cross-sectional area of said outlet, a substantially continuous annular slot formed between said expansion chamber and said collection chamber` providing communication therebetween, said slot being less than 360.

5. An exhaust gas muiller for internal combustion engines comprising a hollow substantially toroidal expansion chamber, an exhaust gas inlet conduit connected to said chamber, a cone in said expansion chamber for causing the gases to rotate within said chamber, a substantially annular collection chamber positioned on the outer periphery of said expansion chamber and having a gas outlet, said collection chamber being formed by a substantially annular inner wall portion and a spiral outer wall portion whereby said collection chamber gradually increases in cross-section from substantially zero to substantially the crosssectional area of said outlet, a substantially continuous annular slot formed between said expansion chamber and said collection chamber providing communication therebetween, said slot being less than 360,

J. FORD JOHNSTON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number

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