US2958390A - Sound muffling device - Google Patents

Description

v- 1960 c. H. MONTAGUE 2,953,390

SOUND MUFFLING DEVICE Filed March 18, 1957 INVENTOR (israswwqw [pom via? .5

ATTORNEYS United States Patent SOUND MUFFLING DEVICE Charles H. Montague, Toledo, Ohio, assignor to Owens- Illinois Glass Company, a corporation of Ohio Filed Mar. 18, 1957, Ser. No. 646,664

8 Claims. (Cl. 18157) This invention relates to a sound muffler device, and more specifically to an internal baffle arrangement or construction for such muffler device.

It is well known that the exhaust from engines produces a disagreeable noise in the nature of an explosion. Other industrial machines either create gases or require the dissipation of large amounts of gases including air and are, consequently, beset with similar noise problems. To overcome this objection, various kinds of mufflers and baffle arrangements have been provided which reduce the sound to a certain extent. However, the known mufflers and baffles have not proved completely satisfactory in that the sound remains disagreeably loud to the ear. Furthermore, the known muffiers, and particularly the baffle arrangements therefor, are quite complicated and devious in their construction and are usually accompanied by the creation of material back pressures reducing the etficiency of the engine to which attached, or otherwise interfering with the dissipation of the gases. In addition, the complexity of the construction makes these arrangements difiicult to fabricate and, therefore, costly.

Accordingly, it is an object of the present invention to provide an improved muffier device which efficiently reduces the sound accompanying the rapid issuance of gases without the attendant creation of material efficiency-reducing back pressures.

It is also an object of this invention to provide a mulfier device incorporating a novel baflle construction which is of simple design and is easily and economically fabricated and assembled.

These and other objects of this invention will become apparent from the following detailed description, taken in conjunction with the annexed sheet of drawings, on which is presented for purposes of illustration only, a preferred embodiment of this invention.

In the drawings:

Fig. l is a cross-sectional side elevational view of an expansion chamber having mounted therein the mufiier device of this invention.

Fig. 2 is an enlarged side elevational view partly in section of the muffier device of this invention.

Fig. 3 is a view taken on the line 33' of Fig. 2.

Fig. 4 is a view taken on the line 4-4 of Fig. 2.

In its simplest form, the device of this invention comprises an open-ended tubular casing and an interiorly positioned bafiie comprising a conical spiral having its apex disposed to meet the flow of exhaust gases.

Referring now more specifically to the drawings:

There is shown in Fig. l, a hollow chamber 11 consisting of a horizontally positioned, thin-walled cylinder 11a having circular end members 13 and 15 serving to confine an interior 11b. The end 13 contains a circular port 13a located in the upper portion thereof and tangent to the wall of the cylinder. A relatively short inlet tube 12 is sealably mounted within the port 13a in such fashion that a portion 12a thereof projects without the chamher 11 for suitable conduit connection to an engine (not shown) or the like. The other end of the inlet tube within the chamber 11 has a bias-cut portion 120. The inlet tube provides a cylindrical passageway 12b permitting entry of gases to the interior 1112 of the chamher. The end member 15 at the opposite end of the cylinder contains a circular aperture 15a diametrically opposite the aperture 13a, e.g., located at the lowermost portion of the end member 15. The device of this invention 16 is sealably mounted in the aperture 15a. This device comprises a tubular or cylindrical casing 17 having an open inlet end 19 and an open outlet end 20, and containing therewithin a baffle 21 in the form of a generally conical spiral having an apex 22 facing the inlet end of the tubular casing.

The conical spiral is most conveniently considered as the structure resulting from a deformation of a triangular piece of sheet material so that one edge describes a spiral. In Fig. 3, the edge of the spiral is designated 22a, and the vertex 22 opposite this edge constitutes the apex of the cone-like baffle. The other vertices of the triangle, 24 and 26, become, respectively, the outer terminus and the inner terminus of the spiral formed by the edge 22a. The edge 26a, opposite the vertex 26, connects the apex 22 and the outer terminus 24, while the edge 24a, opposite the vertex 26, connects the apex 22 and the inner terminus 26.

In the embodiment illustrated on the drawings, the outer terminus 24 is tangent to the inner surface 18 of the tubular casing 17 near the outlet end 20. As can be seen, the outer terminus 24, in effect, has been wrapped about the inner terminus 26 to cause overlapping with respect to certain portions of the surface extending from the edge 22a to the apex 22. This movement of the terminus 24 causes the edges 26:: and 24a to be more than 360 disposed with respect to each other and, in the embodiment illustrated in the drawings, almost 540", e.g., almost 1 /2 turns.

In Fig. 2, the numeral 31 designates the line of surface of an inner portion of the spiral overlapped by the outer portion terminating in the edge 26a. The distance therebetween is greatest in the plane of the base edge 22:: and diminishes uniformly in the direction of the apex 22. These reference points define, in section, a triangular aperture through which some of the gases pass. The triangular aperture is substantially uniform in size on any section considered so long as the base edge 22:: describes a substantially uniform spiral.

There is thus formed a convoluted, curvilinear plane extending from the apex 22 in partially overlapping, spaced-apart relationship to define a generally spiral passageway for gases passing therethrough. In the embodiment illustrated in the drawings, the span of the conical spiral measured at the base portion extends across a major part of the inner diameter of the tubular casing. This leaves a passageway, designated as 29 in Figs. 2 and 3, through which some of the gases might proceed without passing through the aperture defined between the overlapping wall portions of the spiral discussed hereinhefore. In the embodiment as illustrated, there is also left an unintercepted portion, identified by the numeral 32 in Figs. 3 and 4. As can be readily appreciated, gases entering the inlet end 19 will encounter the surface 28 (Fig. 4) and will be propelled in a radial fashion through the length of the tubular casing. The surface 28 may be conveniently considered as generated by the line 26a, held substantially fixed at the end 22, while moving the end 24 in a spiral line of travel of uniformly decreasing diameter through a path of more than 360 and, in fact, until this line assumes the position designated in Fig. 4 as 24a. Thus, although there are uninterrupted portions of the sectional area of the casing 17, the construction, as described, will establish a controlling pattern of swirling gas movement. Furthermore, this pattern will exert an influence on the total volume of gas entering the tubular casing without undue obstruction of the linear path of the gases therethrough.

A device according to this invention was constructed, utilizing as the tubular casing 17 a 2" diameter pipe nipple, in length. The baffle was constructed out of a triangular piece of l8-gauge sheet metal by deforming one edge into a spiral configuration of about 1 /2 turns. The conical spiral thus formed had an altitude of about 4", while the distance formed by the overlapping measured A3" across the base portion. The distance was greatest at the base portion and diminished in size in the direction of the apex formed by the vertex opposite the edge deformed in the originally triangular piece of metal. The outermost vertex forming the outermost terminus of the spiral was welded to the inner wall of the 2" pipe in such a way that the cone-like baffle was essentially axially aligned with the tubular casing, and with the apex and base equidistant the ends of the casing. The effectiveness of the thus-described muffler device was determined by mounting the tubular casing containing the described baffle in one end of a cylindrical expansion chamber, having a diameter of 6" and a length of in the manner illustrated in Fig. l of the drawings. A short length of 2" diameter pipe was mounted in the opposite end of the cylindrical expansion chamber, likewise in the manner illustrated in Pig. 1 of the drawings. The expansion chamber was closed except for the two openings provided. by the above. To the latter was connected, by a flexible hose about 18 long, the exhaust manifold of a 6-cylinder internal combustion gasoline engine. In this fashion, the exhaust would enter the expansion chamber through the pipe containing no bafiie and leave the expansion chamber through the baffled device of the invention. The above assembly was then set up in a large room in order to measure the noise level effected by the muffler device of the invention. For the measurement of the sound level, there was utilized a general radio sound level meter and an octave band analyzer. A microphone (a Brush sound cell) to pick up the sound and transmit it to the aforesaid apparatus was positioned 9 feet from the assembly, incorporating the apparatus of the invention, and with the line of the microphone located at right angles to the line of centers of the described muffler assembly. The room gave a measurement of background noise level of 70 db (decibels) at a re (reference level) of 0.0002 microbar.

Measurements were made of the noise level in total (Table I) and in each of eight octave bands (Table II) for the engine idling and running fast. Measurements were also made in the manner described above, but wherein no muffler was employed and where an expansion chamber only was employed.

Table I.-0verall noise level An electrical attenuation scheme which weights the different frequencies to approximate the response of the average normal human ear for loud noise.

The back pressure at the exhaust manifold outlet with the engine running at high speed measured only X of mercury for the muffler device of the invention, which pressure is practically insignificant insofar as the utility of the device is concerned.

Table II.--0ctave band level, db re 0.0002 microbar 20 to to 150 to Engine Idling:

No expansion chamber" 76 78 79-80 79 Expansion chamber only Device constituting invention 75 87 84 79 1 Reference level.

As can be seen from an examination of the data appearing in the foregoing tables, the noise level expressed in decibels for the device constituting the invention was less than that measured with the other noted conditions. Of particular significance is the sound reading measured under sudden acceleration conditions with the B weighting (most closely approximating the response of the average human ear), wherein the device constituting the invention effected a sound level of 91 db as compared to 97 db for the other two arrangements.

It has been determined that there are several controlling factors which materially aifect the function of the mufiler device of this invention. These factors are (a) the effective span of the base portion of the spiral in relation to the inner diameter of the cylindrical casing, (b) the distance, measured at the base portion of the conelike spiral baffle, between overlapping wall portions thereof, and (c) the amount of overlap, expressed as degrees of displacement, between the edges extending from the apex. It has been found that the most advantageous results, in terms of noise reduction coupled with the least amount of created back pressures, are accomplished with the construction of the baflle conforming to the drawings. In particular, it has been found that the amount of overlap is that elfected by a displacement of the edges extending from the apex of at least 360 and, preferably, not substantially more than 540.

For the tubular casing having a diameter of 2", it was found preferable that the base portion of the cone span a major part of the diameter of the tubular casing, thereby effecting an interception by the curvilinear plane of a substantial proportion of the sectional area of the casing. It is further preferable that the distance between the overlapping portions of the wall measure at the base by about /s" for a conical spiral fabricated to have an altitude of about 4". The above values for a tubular casing member having a diameter of 2 may be conveniently expressed as a ratio of (distance) :4" (altitude) 2" (diameter of casing). The foregoing ratio converted to whole numbers becomes the ratio 5 32: 16.

It is readily apparent that an increase in the amount of overlap will effect an increase in the amount of back pressure. Furthermore, a smaller distance between the overlapping portions of the wall forming the cone will likewise increase the amount of back pressure. Conversely, a lesser amount of overlap and an increase in the distance will decrease the amount of back pressure. In any event, as indicated hereinbefore, the most advantageous results are accomplished when the device of this invention is constructed in a manner to satisfy the ratio discussed hereinbefore or their obvious equivalents.

The location of the apex has been found to be of critical importance. It has been found essential that the apex of the cone-like, spiral bafile be disposed to face the inlet and meet the incoming gases. An attempt to utilize the device in the reverse manner, that is, with the base of the cone meeting the flow of gases, resulted in no reduction in noise.

Modifications may be made without departing from the spirit and scope of this invention, it being understood that the invention is not limited to the specific embodiment illustrated, except as defined in the appended claims.

I claim:

1. A sound muflier device for exhaust gases, said device comprising a tubular casing having an inlet end and an outlet end, and a unitary internally positioned, conelike baflle having its apex disposed toward said inlet end, said baflle comprising a convoluted, curvilinear wall surface described between two edges extending from said apex in partially and radially overlapping, spaced-apart relationship to thereby define a spiral passageway for exhaust gases and leave a portion of the sectional area of said casing uninterrupted by said bafile.

2. A sound mufller device for exhaust gases, said device comprising a tubular casing having an inlet end and an outlet end, and an internal, cone-like baflie member having its apex disposed toward said inlet end, said member comprising a convoluted wall extending between two edges extending longitudinally and radially from said apex and disposed circumferentially more than 360, and a third edge connecting the said two edges at a point away from said apex, said third edge describing a spiral in a plane normal to the longitudinal axis of said casing.

3. A sound mufller device for exhaust gases, said device comprising a tubular casing having an inlet end and an outlet end, and an internal, cone-like baflie having its apex disposed toward said inlet end, said cone-like baflie being constructed to define a convoluted wall structure bounded by two edges extending linearly and radially from said apex, and a third edge connecting said two edges, said two edges being circumferentially disposed more than 360 apart, said third edge describing a spiral in a plane normal to the longitudinal axis of said casing, said spiral being such as to define a distance between overlapping portions thereof which satisfies a ratio, with respect to the altitude of said cone and the diameter of said casing, of about 5 32 16.

4. A sound mufller device for exhaust gases, said device comprising a tubular casing having an inlet end and an outlet end, and an internal, convoluted, cone-like baffle 6 having its apex disposed toward said inlet end, said bathe comprising a conical, spiral wall generated by the movement of a line having one end substantially fixed at said apex and the other end moving in a spiral path of generally uniformly varying radius through a circumferential distance of more than 360.

5. A sound mufiler device for exhaust gases said device comprising a tubular casing having an inlet end and an outlet end, and an internal, cone-like bafile having its apex disposed toward said inlet end, and comprising a rigid sheet of material of generally triangular configuration having one vertex located substantially concentrically with respect to said casing to form said apex, and the edge opposite said vertex deformed into spiral configuration, said spiral describing an arc of at least 360.

6. The sound mufiler device of claim 5, wherein one terminus of the edge deformed into spiral configuration is tangent to the inner wall of said casing.

7. The sound muffler device of claim 5, wherein the maximum span of said spiral is less than the inner diameter of said casing.

8. A sound mufller device for exhaust gases, said device comprising a tubular casing having an inlet end and an outlet end and a unitary internal cone-like baflle having its apex disposed toward said inlet end, said battle comprising a convoluted, curvilinear plane described between two edges extending from said apex in overlapping, spaced-apart relationship to define a slot extending throughout the axial length of said batfle, said slot being of gradually increasing size in a direction away from said apex.

References Cited in the file of this patent UNITED STATES PATENTS 1,842,921 Van Dyke Jan, 26, 1932 1,922,848 Harley Aug. 15, 1933 2,205,024 Zinsitz June 18, 1940 2,552,615 Baltzer May 15, 1951

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