US3318412A

US3318412A - Muffler with reed valve

Info

Publication number: US3318412A
Application number: US535185A
Authority: US
Inventors: Jay R Bailey
Original assignee: Mcculloch Corp
Current assignee: Mcculloch Corp
Priority date: 1966-03-17
Filing date: 1966-03-17
Publication date: 1967-05-09
Anticipated expiration: 1984-05-09
Also published as: SE318585B; DE1476582A1; FR1507576A; GB1126657A

Description

May 9, 1967 J. R. BAILEY MUFFLER WITH REED VALVE Filed March 17, 1966 '3c l' Q l",

INVENTOR WHA NN I Mc MAN/GAL United States Patent Office 3,318,412 Patented May 9, 1967 3,318,412 MUFFLER WITH REED VALVE Jay R. Bailey, Woodland Hills, Calif., assignor to McCulloch Corporation, Los Angeles, Calif., a corporation of Wisconsin Filed Mar. 17, 19,66, Ser. No. 535,185 Claims. (Cl. 181-65) This invention relates to mufflers, and more particularly, to mufllers for internal combustion engines.

The example shown and described is a muffler for use on a small internal combustion engine. However, the principles involved are applicable for any size engine and for any size muffler.

The traditional approach of using an acoustic filter to attenuate two cycle gasoline engine exhaust noise in small engines has not been successful. For a small engine, as may -be used for a chain saw, the ymuffler must be restricted in size and this results i'n the filter cut-'off frequency not being low enough. The sound level' of a two cycle engine is high over a broad band o f frequencies, and thus, even the noise in the low frequency bands must be attenuated. In addition, the sound waves emitted from a two cycle gasoline engine are trains of discrete sharpfronted pressure pulses of shock-wave severity. Hence, the laws used for ordinary acoustical phenomena do not fully apply.

It has been found, according to the invention, that by introducing a reed into theexhaust stream the sharp fronted pressure pulses are smoothed out, that is, blunted and the noise energy is spread over a longer period. The net effect of this is to attenuate the sharp high noise peaks. Further, the high intermittentv pulses of very short duration are reacted by the inertia and the spring force of the thin reed, cantilevered on the muffler to act as a valve on the exhaust discharge opening. Thereed in turn returns the energyV to the exhaust stream. The metal reed must be designed to be thick enough to avoid resonance which could cause loads high enough to destroy the reed and thin enough to avoid back pressure which could create a horsepower loss.

The reed dimensions are such that its resonant frequency is above the highest exhaust pulse frequency of the engine and its stiffness is aslow as possible in order to avoid excessive `back pressure. The deflection of the reed must be limited by a reed stop. The shape of the reed stop and its distance from the exhaust opening, over which it extends, is determined by the exhaust exit requirements and the allowable stress levels for the reed. The configuration of the reed stop matches the fully deflected shape of the reed. Since the exhaust kacts as an equally distributed load on the reed, the configuration of the reed stop is determined by the deflection curve of a beam loaded by its own weight. The exhaust discharge opening at the reed and the engine exhaust outlet or muffler inlet are designed to be of substantially the same area.

It is an object of the present invention to provide an improved muffler for noise attenuation.`

It is another object of the present invention to provide a muffler for internal combustion engines having a reed valve on the muffler exhaust discharge outlet, the reed deflection being determined by a stop having a deflection curve of a beam loaded by its own weight.

It is still another object of the invention to provide a muffler in which the sharp-fronted pressure pulses are smoothed out and blunted and in which the noise energy is spread over a longer period by means of a reed Valve on the muffler exhaust opening.

It is a further object of the invention to provide a muffler in which the high intermittent pulses of very short wave duration are reacted bythe inertia and spring force of a thin cantilevered metal reed on the exhaust opening discharge of the muffler and in which the reed returns the energy to the exhaust stream.

It is a still further object of the present invention to provide ya muffler in -which the sound level is approximately eight decibels lower than that of a cavity tail pipe muffler of identical size and shape. It should be noted that a six decibel drop is equivalent to reducing the sound level by 50%.

It is another object of the invention to provide a muffler of small size in which the noise level is substantially lower than was heretofore possible in a muffler of equivalent size. For example, the rule of thumb for muffler volume is that the muffler be ten times the cubic inch displacement of the engine. Thus, where an engine has a displacement of 3.3 cubic inches, the prior art mufflers are required to have a volume of 33.3 cubic inches. An equivalent muffler, according to the present invention, has a volume of seven cubic inches. It is very important that the noise level of internal combustion engines be decreased, as for example in chain saws, where the prior art noise level has been damaging to the hearing of the operators.

Further objects and advantages of the invention may be brought out in the following part of the specification wherein small details have been described for the competence of disclosure, without intending to limit the scope of the invention which is set forth in the appendedV claims.

Referring to the accompanying drawings, which are for illustrative purposes:

FIG. l is a side elevational view, partially in cross section, of a two cycle internal combustion engine having a muffler according to the present invention;

FIG. 2 is a plan view of the muffler shown in FIG. 1;

FIG. 3 is a fragmentary cross-sectional view, take along the line 3 3 in FIG. 2; and

FIG. 4 is a diagram illustrating a deflection curve of a beam loaded by its own weight, used to determine the curve of the reed stop for the muffler reed valve.

Referring again to the drawings, there is shown in FIG. l a two cycle internal combustion engine, generally designated as 10 having an exhaust opening 11. Secured t0 the engine is .a metallic muffler, generally designated as 12, and having the configuration of a rectangular prism. The muffler has an exhaust inlet 13 in register with .and having the same area as the exhaust opening 11 of the engine.

The muffler is made of two pan-'shaped parts, a botJ tom 17 and a top 18, the top having a marginal portion fitting over the bottom and by which the two parts are secured together.

As best seen in FIGS. 2 and 3, the top 18 has a circular exhaust discharge opening 19 and which has substantially the same area as the openings 11 and 13. Forming part of the opening is a supporting boss 20. Externally of the top and extending diagonally across are a reed valve 23 and a reed stop 24. In plan, as shown in FIG. A2, the reed and its stop have the same configuration and are coextensive. They are both secured to the top 18 by means of three cap screws 25 extending through the top and which are threadedly engaged in a supporting iblock 26.

The reed 23 is very flexible having a thickness of 0.014 inch and is 11A; inches Wide.4 The length of its lever portion, that is, the part extending from the point of holding by the two screws nearest its free end 29, is 1% inches. The reed should be made of a high-strength alloy, such as a cobalt-chrome-nickel alloy, which can withstand bending fatigue stresses of as high as 150,000 pound-s per square inch at l000 F. As shown in FIG. 3, the reed is flat and normally covers the exhaust discharge outlet. The reed stop 24 is relatively rigid so as to not be moved by the vibrations of the reed during operation.

For a two cycle engine, as shown, having 31/2 horsepower and an engine displacement of 3.3 cubic inches, a muffler, as 12, having a volume of 7 cubic inches, has been successfully tested for use. This volume includes the exhaust inlet 13 and the specific measurements of the can-shaped part of the muffler are approximately 2 inches by 2.75 inches by 1.3 inches. This is in contrast to a muffler in the prior art made according to the rule of thumb which is to the effect that the volume of the muffler should be ten times the displacement of the engine, or in this case 33.3 cubic inches. The exhaust inlet 13 in the mufer described has an area of 0.484 square inch and the exhaust discharge outlet has an area of 0.442 square inch.

It has been found that the maximum deflection of the reed stop at its free end 30 required to permit the reed valve to open sufficiently to accommodate the exhaust discharge is 0.300 inch. That is, the distance of the inner face of the free end 30 must be positioned the latter distance from the face of the top 18 of the mufler. From this dimension, the curve of the reed stop may be determined.

Since it has been found that the exhaust acts on the reed as an equally distributed load, the deflection curve of the reed is that of a beam loaded by its own weight, as shown in FIG. 4. The reed must be limited in its movement and this is accomplished by the reed stop. In order that the movement of the reed be effectively -controlled against breakage, the deflection curve of the reed stop should be that of the reed, that is, that of a beam fixed at one end and loaded by its own weight.

The standard formula for determining the deflection of a beam loaded by its own weight is W 4 24EIL(X where capital E is the modulus of elasticity, I is the moment of inertia, W is the total weight in pounds of the beam, L is the total length of the lever portion of the beam, that is, the length from the fixed point to the free end, Y is the amount of the deflection from the horizontal, and X is the horizontal distance from the free end to any point of deflection Y. For a known L, 1.75 inches in the muler shown, it has been found that the D (delta)mx, that is, the maximum value of Y, where X is 0, is 0.30 inch. This value for Y is that required to permit the proper exit of exhaust out of the exhaust discharge without creating excessive back pressure. Then, solving the above equation, inserting X as and the lmaximum Y, 0.3,

then W/EI=2.4/L3, and substituting this into the first for-mula,

X 4 4X Lil@ TSl Iand when various values .are substituted for X in the lat, ter equation, solving for Y, the following is determined:

X=l.75 1.5 1.25 1.00 .75 .50 .25 0 Y=0 .011 .041 .081 .132 .187 .243 .300A

When the foregoing values are applied to the reed stop 24 to determine its configuration, it is properly curved so that when the reed 23 is vibrated by the exhaust, the reed moves so as to be in full contact with the reed stop along its entire length. This permits the reed to operate properly and without damage to it. Where the reed is not so limited so as to deflect properly .according to the shape of the reed stop, there is a strong tendency toward breakage.

The invention and its attendant advantages will be understood from the foregoing description and it will be ,apparent that various changes may be made in the form, construction and arrangement of the parts of the invention without departing from the spirit and scope thereof or sacrificing its material advantages, the arrangement herein-before described being merely by way of example. I do not wish to be restricted to the specific form shown or uses mentioned except as defined in the accompanying claims, wherein various portions have been separated for clarity of reading and not for emphasis.

I claim:

1. A m-ufller for an internal combustion engine comprising:

(a) a closed walled structure forming an expansion chamber and having an exhaust inlet and an exhaust outlet;

(b) a relatively thin, elongated flexible metallic reed having one end xed at a point to ka wall of said structure and extending externally over a wall of said structure;

(c) a free end of said reed, `opposite said fixed end, extending over said exhaust outlet and terminating 'adjacent the distal end of said outlet with respect to said xed end; and

(d) a rigid reed stop outwardly of said reed and having substantially the elongated configuration of said reed,

(e) said stop having one end fixed at a point to said xed end of said reed and to the wall thereunder and having an opposite free end extending over said reed `and said outlet,

(f) said fixed end of said stop being spaced from said outlet a distance sufficient to permit the reed to deflect away from the outlet to permit adequate ex haust discharge,

(g) said stop being curved gradually outwardly from its xed end and the chamber wall over which it extends so that its free end is spaced said suicient distance from said outlet and so that the exhaust will cause the reed to deect against said stop as it deflects away from said outlet.

2. The invention according to claim 1 in which:

(a) the curve of said stop from the 4fixed point is substantially that of a beam loaded by lits own weight,

(b) said reed being ada-pted to be deflected by the exhaust force to make contact along its entire length with said stop.

3. The invention laccording to claim 1 in which:

said reed is dimensioned so that its resonant frequency is above the -highest exhaust pulse frequency of the engine and its vstiffness is as low as possible to avoid excessive back pressure that would create a horsepower loss.

4. The invention according to claim 2 in which:

`said reed and stop are coextensive when said reed is -defiected against said stop by the exhaust pressure.

5. The invention according to claim 4 in which:

said reed is dimensioned so that its resonant frequency is above the highest exhaust pulse frequency of the engine and its stiffness is as low as possible to avoid excessive back pressure that would create a horsepower loss.

`6. In combination with a two cycle internal combustion engine which produces a high sound level over a broad band of frequencies and produces sound waves in trains of discrete sharp-fronted pressure pulses of shock-wave severity, a mufller comprising:

(a) a walled structure forming an expansion chamber rand having an exhaust inlet connected to the engine exhaust;

(b) -an exhaust outlet in a wall of said structure;

(c) a relatively thin, elongated flexible metallic reed having one end fixed at a point to a wall of said structure and extending externally over a wall of said structure;

(d) a free end of said reed, opposite said xed end, eX- tending over said exhaust outlet and terminating adjacent thedistal end of said outlet with respect to ,said fixed end; and

(e) a rigid reed stop outwardly of said reed and having substantially the elongated configuration of said reed,

(f) said stop having one end xed at a point to said xed end of said reed and to the wall thereunder and having an opposite free end extending over said reed and said outlet,

(g) said xed end of said stop being spaced from said outlet a distance suicient to permit the reed to deect away from the outlet to permit adequate eX- haust discharge,

(h) said stop being curved gradually outwardly from its xed end and the chamber Wall over which it extends so that its free end is spaced said sucient distance from said outlet and so that the exhaust will cause the reed to deflect against said stop as it de- -ects away from said outlet.

7. The invention according to claim 6 in which:

(a) the curve of said stop from the xed point is substantially that of a beam loaded by its own weight,

(b) said reed being adapted to be deected by the exhaust force to make contact along its entire length with said stop.

8. The invention according to claim 6 in which:

said reed is dimensioned so that its resonant frequency is labove the highest exhaust pulse frequency of the engine and its stiffness is as low as possible to avoid excessive back pressure that would create a horsepower loss.

9. The invention according to claim 7 in which:

said reed land stop are coextensive when said reed is deflected against said stop by the exhaust pressure.

10. The invention according to claim 9 in which:

References Cited by the Examiner UNITED STATES PATENTS 3,006,l60 10/1961 Heidorn 181-64 3,132,716 5/1964 Williams 181--40 FOREIGN PATENTS 278,857 lO/ 1927 Great Britain. 177,359 8/1935 Sweden.

RICHARD B. WILKINSON, Primary Examiner. R. S. WARD, Assistant Examiner.

Claims

1. A MUFFLER FOR AN INTERNAL COMBUSTION ENGINE COMPRISING: (A) A CLOSED WALLED STRUCTURE FORMING AN EXPANSION CHAMBER AND HAVING AN EXHAUST INLET AND AN EXHAUST OUTLET; (B) A RELATIVELY THIN, ELONGATED FLEXIBLE METALLIC REED HAVING ONE END FIXED AT A POINT TO A WALL OF SAID STRUCTURE AND EXTENDING EXTERNALLY OVER A WALL OF SAID STRUCTURE; (C) A FREE END OF SAID REED, OPPOSITE SAID FIXED END, EXTENDING OVER SAID EXHAUST OUTLET AND TERMINATING ADJACENT THE DISTAL END OF SAID OUTLET WITH RESPECT TO SAID FIXED END; AND (D) A RIGID REED STOP OUTWARDLY OF SAID REED AND HAVING SUBSTANTIALLY THE ELONGATED CONFIGURATION OF SAID REED, (E) SAID STOP HAVING ONE END FIXED AT A POINT TO SAID FIXED END OF SAID REED AND TO THE WALL THEREUNDER AND HAVING AN OPPOSITE FREE END EXTENDING OVER SAID REED AND SAID OUTLET, (F) SAID FIXED END OF SAID STOP BEING SPACED FROM SAID OUTLET A DISTANCE SUFFICIENT TO PERMIT THE REED TO DEFLECT AWAY FROM THE OUTLET TO PERMIT ADEQUATE EXHAUST DISCHARGE, (G) SAID STOP BEING CURVED GRADUALLY OUTWARDLY FROM ITS FIXED END AND THE CHAMBER WALL OVER WHICH IT EXTENDS SO THAT ITS FREE END IS SPACED SAID SUFFICIENT DISTANCE FROM SAID OUTLET AND SO THAT THE EXHAUST WILL CAUSE THE REED TO DEFLECT AGAINST SAID STOP AS IT DEFLECTS AWAY FROM SAID OUTLET.