Muffler

Oct. 1, 1935. q. g. noblitt et al 2,016,253

MUFFLER

Filed Aug. 3, 1931 2 Sheets-Sheet 1

<img file="US2016253A_D0001.tif" />

Oct. 1, 1935.

Q. G. NOBL1TT ET AL

2,016,253

MUFFLER

Filed Aug. 3, 1931

Sheets-Sheet 2

<img file="US2016253A_D0002.tif" />

<img file="US2016253A_D0003.tif" />

<img file="US2016253A_D0004.tif" />

<img file="US2016253A_D0005.tif" />

<img file="US2016253A_D0006.tif" />

EpMUNf) Ludlow,

Patented Oct. 1, 1935

2,016,253

UNITED STATES PATENT OFFICE

2,016,253

MUFFLER

Quintin G. Noblitt, Earl C. Booth, and Edmund

Ludlow, Indianapolis, Ind., assignors to NoblittSparks Industries, Inc., Indianapolis, Ind., a corporation of Indiana

Application August 3,1931, Serial No. 554,722

Claims. (Cl. 137—160)

Our invention is concerned with silencers for silencing the sound of flowing gases, particularly where such gases are subjected to abrupt changes in pressure as are the exhaust gases discharged 5 from the cylinders of an internal combustion engine. It is our object to produce a silencer or muffler which will adequately silence the exhaust gases and which will perform this function without imposing a substantial back-pres10 sure on the flowing gases. A further object of our invention is to produce a muffler which can be simply and economically constructed of sheetmetal parts. Still another object of our invention is to produce a muffler of a type which, with 15 structural variations of a simple character, can be made suitable for use with engines of widely varying characteristics.

In carrying out our invention we form the muffler with an exterior casing and an inner tube, 20 the latter receiving the gases at one end and discharging them at the other and being unrestricted throughout its length. The tube is provided with a multiplicity of openings providing at each of a series of longitudinally spaced points re25 stricted communication between the interior of the tube and the space surrounding it. The space within the casing and surrounding the tube is divided into a series of chambers by means of partitions located at longitudinally spaced points 30 along the muffler. The muffler is preferably formed of two similar halves each of which is conical in form, the large ends of the conical halves being joined together to form a unitary casing.

The accompanying drawings illustrate the invention: Fig. 1 is a longitudinal section through one form of muffler embodying our invention; Fig. 2 is a section similar to Fig. 1, but on an enlarged scale, on the line 2—2 of Fig. 3; Fig. 3 is a transverse section on the line 3—3 of Fig. 1, Fig. 4 is a fragmental isometric view showing one end of the inner tube; Fig. 5 is a fragmental plan showing a portion of one of the pieces which make up the inner tube; Fig. 6 is a fragmental 45 isometric view illustrating the construction of the ferrule by which the inner tube is secured to the central partition; Figs. 7 and 8 are sections similar to Fig. 1 showing modified arrangements; Fig. 9 is a fragmental section similar to Fig. 7, 50 but on an enlarged scale; and Fig. 10 is a fragmental longitudinal section showing the construction at one end of the muffler.

In the muffler illustrated in Figs. 1 and 2, the outer muffler casing is formed of two conical 55 halves 15 joined together at their bases. The inner tube previously referred to is preferably also formed of two halves 16 each of which extends from one end of the muffler to a central partition Π that is disposed between the two casing-halves 15 and divides the space surround- t ing the tube 16 into two parts.

In the muffler shown in Fig. 1, the two halves 15 of the casing are not right-angle cones; but instead are oblique to such an extent that the two halves of the inner tube (6 may be secured 10 at one side of the casing in substantial alinement with each other. As will be pointed out hereinafter, this form of muffler casing has certain advantages which make it desirable, although it is not necessary to our invention in its 15 broad aspects.

As is clear from Fig. 4, each half 16 of the Inner, tube is conveniently formed of two sheet-metal stampings each formed in generally semi-cylindrical shape and provided at its longitudinal 20 edges with flanges 18. The flanges on the two tube-parts may be secured together as by spotwelding to form a complete tube-half. At a point circumferentially intermediate the flanges 18, each tube-part is formed with a longitudinally 25 extending ridge 19. The openings which afford restricted communication between the interior of the tube and the space surrounding it are preferably formed by providing each tube-part with a “ series of circumferentially extending slits which 30 extend between the ridge 19 and each of the flanges 18, the material at one side of each of such slits being displaced radially as indicated at 21, to provide an opening 22. This radial displacement of the tube-material at one side of 35 each of the slits may be either inward or outward, but we prefer to displace the material outward, as such displacement does not decrease the effective interior cross-sectional area of the tube.

The ridge 19 is provided on the lower part of 40 the inner-tube for the purpose of affording a surface which may contact with the interior of the muffler casing 15 and be secured thereto as by spot-welding. Aside from its stiffening effect, the ridge 19 on the upper part of the inner tube has 45 no function and is not necessary; but it is provided in order that both tube-parts may be the same and the cost of production thus decreased.

At each end of the muffler casing, one of the tube-halves 16 fits closely within it, the flanges 50 18 being trimmed diagonally, as is clear from Fig. 10. At its inner end, each of the tube-halves 16 is received within a ferrule 25 which is notched at angularly spaced points to provide for the flanges 18 and the ridges 19 on the tube. The M

2,010,253 ferrule >1 has a flange 28 which may be secured to the partition II as by spot-welding.

Between the center partition 11 and each end of the muffler there are one or more auxiliary * partitions 21, shown in the drawings as three in number, which serve to divide each half of the casing Into separate chambers. The partitions 28 are preferably arranged to provide restricted communication between adjacent chambers, as 10 by providing each of them with an opening which receives the tube 18, such opening being slightly larger than the tube to provide an annular passage 29 (Fig. 2). The openings provided in the partitions 28 by the passages 28 are not essential, U but we find that their presence has a tendency to inhibit the production of secondary noises. The partitions 28 may be located approximately as Indicated in the drawings so that the chambers into which they divide the interior of the muffler M are of progressively increasing volume toward the center of the muffler.

In use, the muffler is connected at one end to the pipe through which exhaust gases are led from the engine, and at the other end to a tailM pipe, if such a tail-pipe is desired. The gases entering the muffler enter the tube 16, which is uninterrupted from one end of the muffler to the other. The slots 22 provide for flow from the interior of the tube to the space surrounding it, 80 or in the reverse direction, as localized instantaneous pressure conditions necessitate. The exhaust gases from the engine enter the muffler under periodically varying pressure conditions, and emerge therefrom silently with pressure M variations materially reduced in extent. Because the tube 16 has no obstructions within it, the muffler does not build up a material back pressure. In fact, we find by tests that our muffler creates substantially no more back-pres40 sure than does a plain tube of equal length. The silencing action we believe to be due to the flow of gases back and forth through the restricted openings 22.

In the prior patent of Q. G. Noblitt, No. 45 1,972,065, there is shown a muffler somewhat similar to that above described, the chief difference between the muffler of this application and the muffler of such earlier application, except for certain details of construction, being in M the presence of the partitions 28 in the muffler above described. We have found that the presence of the partitions 28 very materially increases the silencing action of the muffler.

Our invention is not limited to the specific argg rangement so far described and illustrated in Hgs. 1 to 3 Inclusive. Instead of disposing the tube-halves 16 in alinement with each other along the straight side of the muffler casing, we may dispose them on the opposite side of the 80 curing, as indicated in Fig. 8, in which position they are at a slight angle to each other. A still further modification is illustrated in Fig. 7, where the two halves II of the muffler-casing are rightangle cones and the tubes 16 are disposed axially 65 and in alinement with each other.

In the muffler illustrated in Figs. 1 and 2, the two halves of the casing are secured to each other and to the center partition IT by forming the casing-halves 16 with annular flanges 30 TO which receive the partition IT between them. After assembly, the three parts are secured together by seam-welding along the circumference of the flanges 80 and the partition IT. This same method pt assembly may be used with the muffler n of Fig. 8.

In the muffler illustrated in Figs. 7 and 9, the two halves 16 of the muffler-casing are buttwelded together, the central partition IT being eliminated and its function being performed by two partitions 31 each of which is secured in 5 place in its associated casing-half 16 at a distance from the large end of such casing-half. The two partitions 31 fit substantially tightly within the muffler casing and about the inner ends of the two tube-halves 16 in order to pre- 10 vent gas-flow from one side of either partition to the other side except through the tube. In the assembled muffler, the two partitions 31 define an expansion chamber having an inlet opening through one of the two tube-halves 16 and 15 an outlet opening through the other. We have found that such an expansion chamber located near the center, in spite of the enlargement and contraction which it provides in the gas passage, does not produce any appreciable Increase in back 20 pressure.

It will be noted that as a result of the manner in which the openings 22 in the tube 16 are shown as formed the gases passing through the muffler from inlet to outlet thereof will flow through C5 such openings more readily in one direction than the other. That is, if the tube 16 is disposed so that the louvers 21 slope outwardly in the general direction of gas-flow through the muffler, gases can pass outwardly through the openings 22 w with but a slight change of direction and will flow from the tube to the space surrounding it more readily than they will flow in the reverse direction. In the claims we have described such an arrangement as providing openings arranged M to open outwardly in the general direction of gas-flow through the tube, and we mean by that expression to include any opening so arranged that the direction of outward gas-flow through it has a substantial component in the direction of 40 gas-flow through the tube. On the other hand, and for the same reason, if the tube 16 is disposed in such a way that the louvers 21 slope inwardly in the general direction of gas flow through the muffler, the gases will pass into the tube more _4areadily than they will pass out into the surrounding space. In the claims we have described the openings provided by the louvers so disposed as opening inwardly in the general direction of gasflow through the tube. This expression is in- go tended to include an opening so arranged that the direction of inward gas-flow through it has a substantial component in the direction of gasflow through the tube.

We find that better silencing of the exhaust can 55 be obtained by arranging some of the louvers so that they slope outwardly In the general direction of gas flow and others so that they slope Inwardly. The best and preferred arrangement is that Illustrated in the drawings, where each tube- go half 16 is disposed so that its louvers slope outwardly toward the center partition IT. In this arrangement, the gases enter the muffler into a tube the louvers of which are disposed to favor outflow of gases from the tube and leave the muf- 66 fler through a tube having louvers disposed to favor inflow of the gases. In addition to providing better silencing, the arrangement of louvers just described makes the muffler reversible if the two tube-halves 16 are of the same diameter. Ordinarily, however, it will be found advisable to make the tube-half 16 in the inlet half of the muffler of slightly larger diameter than the other tube-half, as the gases when entering the muf- y.

2,016,253 fler have higher temperature and greater volume thari when leaving.

.In all the mufflers herein specifically illustrated an&lt;J described there is but a single tube or gas5 passage extending between the inlet and discharge openings of the jnuffler. It is not essential that there be a single tube, however. In our copending application Serial No. 554,523, filed August 3,1931, we have illustrated a muffler hav10 ing a plurality of gas-passages formed by sheetmetal, louvered stampings which extend through a cylindrical casing having interior baffles.

The mufflers illustrated in Figs. 1 and 8 are unsymmetrical about the axis of the inlet and dis15 charge openings. We have found mufflers of this shape to have a wide range of application because of the small amount of room they require on one side of such axis.

The practical design of a muffler for use with 20 a given engine is a compromise between cost and silencing efficiency, the object being to make the smallest, simplest, and most economical muffler which will adequately silence the exhaust of that engine. To an extent the size of the muffler de25 pends upon the size of the engine, larger engines generally requiring larger mufflers. A muffler which will produce adequate silencing of the exhaust gases from a large engine will frequently be found satisfactory for use with a smaller en30 gine; but if a smaller muffler proves satisfactory with the smaller engine, considerations of economy usually demand that such a smaller muffler be used.

Size, however, is not the only characteristic of 35 an engine which may influence muffler design. Number of cylinders, speed, bore-and-stroke ratio, compression ratio, valve timing, spark timing, and the length and diameter of the exhaust pipe are other factors which appear to influence 40 the silencing efficiency of an exhaust-muffler. Due to variation in these or other factors, we have found that for two engines of the same number of cylinders, the engine with the smaller piston displacement may require a larger muffler than 45 the other.

As an example of a muffler found suitable for use with a specific engine, we may mention a muffler which has proven satisfactory with the present Ford engine of four cylinders and approx50 imately 200 cubic inches piston displacement. Such a muffler was 35 inches in length and 5½ inches in diameter at the center. The tube 16 in the inlet half of the muffler was one and seveneighths inches in diameter, and in the outlet half 55 one and five-eighths inches in diameter, and each half of the muffler contained three auxiliary partitions 28. The slots forming the openings 22 were spaced one-half inch apart, and the louvers 21 were struck up to make such openings an av60 erage of about 0.025 inches in width.

Decreasing the spacing of the slots 22 has a tendency to increase silencing efficiency, and a spacing of three-eighths, or even one-quarter, of an inch may be used if desired. The width of the 65 openings 22 we have found to be susceptible of comparatively wide variation without materially influencing the silencing efficiency of the muffler; but with a width of much less than 0.010 Inches the openings are prone to become clogged, 70 while if the width is increased much over 0.040 inches an adverse effect or silencing becomes noticeable.

Because of the large number of factors external to the muffler which influence silencing effi75 ciency, as well as because the design of a muffler is in practice a compromise between cost and the degree of silencing desired, we find that no general rule for determining the size and other characteristics of a muffler intended for use with a given engine is applicable. The simplest and 5 most effective way to develop a muffler for use with a particular engine is to test with that engine a muffler which is known to give satisfactory results with a generally similar engine. If the degree of silencing produced is not all that is de- 10 sired, there are two ways in which it may be increased: The number of auxiliary partitions 21 may be increased, or the size of the muffler may be made larger. There is a practical limit, largely from the standpoint of cost, to the number of 15 auxiliary partitions 28 which may be used, and we find it seldom worth while to space such partitions less than about two inches apart, especially near the ends of the muffler. If the desired degree of silencing is not attained by increasing the 20 number of auxiliary partitions, the size of the muffler may be increased.

If a muffler, when first tested with an engine, proves adequate to silence the exhaust, the number of auxiliary partitions 28 or the size of the 25 muffler, or both, may be reduced with a view to lowering the cost of the muffler.

As examples of mufflers suitable for use with engines larger than the Ford engine above referred to, we might mention that a muffler 42 30 inches in length by six inches in diameter, with a two inch tube 16 in the inlet half and a one and three-quarter inch tube in the outlet half and with four auxiliary partitions 28 in each half proved satisfactory for use with the eight-cyl- 35 inder, 235 cubic inch engine of the Hudson automobile; while a muffler adequate to silence the exhaust of the eight-cylinder, 345 cubic inch Buick engine was 48 inches long, six inches in diameter, and had two auxiliary partitions 22. In 40 both mufflers just mentioned, the openings in the walls of the tube 16 were approximately 0.025 inches in width and spaced one-half inch apart, as in the case of the Ford muffler. We have found width of opening and spacing of this order to be 45 generally applicable.

To avoid the creation of excessive back pressure, the tube 16 in the inlet half of the muffler should have a diameter not materially less than that of the exhaust pipe which supplies gases to 50 it. The tube 16 in the other half of the muffler may be somewhat smaller in diameter than the exhaust pipe, as previously indicated.

Our muffler is to be distinguished from a muffler such as is shown in the Mason Patent No. 55 1,874,326 and which demands for maximum silencing efficiency that the openings in the center tube be arranged in spaced groups with a section of unperforated tube separating adjacent groups and with a rather definite relation be- 60 tween the lengths of perforated and imperforated tube-portions. To distinguish from such a muffler, we refer in the claims to our center tube as being provided with a “continuous series of openings”. 65