US 1144306 A
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Description (OCR text may contain errors)
F. c. MOCK.
APPARATUS FOR MUFFLING SOUND.
APPLICATION FILED JUNE 15. 1910.
Patentd June 22, 1915.
2 SHEETSSHEET 1.
F. C. MOCK.
APPARATUS FOR MUFFLING SOUND.
APPLICATION FILED JUNE 15. 1910.
Patented June 22, 1915.
2 SHEETS-SHEET 2.'
UN TED STATES-PATENT OFFICE. J
ran-N1: c.- Mo-cx. Ore-CLEVELAND, onro.
arranarus ren mnrF-Lme sounn.
Specification 5: Letters Patent.
Patented June 22, 1915.
a n ationilea June 15, 1910. Serial No. 566,917.
To all whom it may concern;
Be it known that I, FRANK C. Moox, a citizen of the United States, and a resident of Cleveland, county," of Cuyahoga, and
5 State of Ohio, have. invented a new and useful Improvement in Apparatus for Muffling Sound, of which the following is a specification, the principle of the invention being herein explained and the best mode in v which I have contemplated applying that principle, so as to distinguish it from other.
"The present invention relates to an improved apparatus for muflling sounds, which may find application in a variety ,of uses but for illustrative purposes is shown in the form of a mufiier to silence the explosion," of an. internal combustion engine.
The object of the present improvements is to provide such an apparatus or device which will be adapted to diminish the sound resulting from the exhaust of the motor or similar source to any desired degree without interposing' obstructions of any sort in the path of the discharged gases. Although ape paratus designed for this purpose are at present in general use, and in appearance are somewhat similar ,to my improved ap-' paratus, yet they differ in details which are most important and operate upon an entirely different principle.
To the accomplishment of the foregoing and related ends, said invention, then, consists of the steps; and means hereinafter lfully described and particularly pointed out a in the claims.
The annexed drawings and the folldwing.
- i4, 4, and 5 respectively illustrate in broken:
section different forms of muflier designed primarily for use with explosive motors.
As of probable assistance in understanding my invention as illustrated in the a lratus shown herewith, I should first further explain the principle ofoperation involved. 1
There are two theories commonly advanced in explanation of the manner in which a sound wave is generated from the pressure energy of confined gas suddenly released from confinement, as in'the case of an ex-- plosion motor,- a gun or the like, both of which. I believe, can be shown to be erroneous. The first of such theories is that the sound heard from an unmuflied motor for example, is produced by the exhaust issuing from the mouth of the pipe and striking the,
atmosphere, thus generating the sound wave.
Hence it is assumed that by obstructing and constricting the flow of the gas it may be retarded so that it will strike the atmosphere with generally decreased velocity and diminished sound effect. Now, in order to produce an audible impulse, such escaping gas would have to possess the velocity of sound when it strikes the outside air furthermore, this air should come to rest after each blow or the sounds will become less and or frequency less as the speed of the motor, of discharge, increases. As a matter of fact, the sounds are known-to be individual' for each explosion up to the highest motor speed, and to accelerate a column of air of of sound in the small interval between two explosions, one-twentieth of a second apart, would require so much power that" this hypothesis would seem obviously wrong. Another theory not requiring discussion, is that the discharge of gas into the exhaust pipe sets up some sort of sound waves which, if properly handled, may be made to interfere with each other and so dampen out the noise of the exhaust.
It is believed that a truer explanation of any appreciable volume up tothe velocity the phenomenon is that there is but a single wave impulse for each explosion and that such impulse is generated when the gas from the cylinder, rushing through the exhaust Y valve orifice at a greater velocity than that of. sound in air, strikes the first molecules of air in the pipe; that such wave passes-out of the exhaust pipe with-the velocity of sound. (or greater atfirst) and thenspreads through the air as does any wave impulse through any elastic medium. The travel'of this wave impulse, however, is not quite I similar to the flow of gas which it initiates, but differs therefrom in several important particulars. It is by taking advantage of subtract from, the energy....of the original thesedifierences that I am able greatlyto sound impulse, while allowing a free passage for the escaping gas. To present this action clearly, recourse may be had to the analogous action occurring where a body of liquid, such as water is suddenly released. Thus, in Fig. 1, I have represented a reservoir 1 opening by means of gates 2 into a channel 3 having an unobstructed discharge. If the gates, now, be suddenly thrown open, the height or weight of water in the reservoir representing the potential energy of the body of escaping gas in the case of a motor, will first form a wall of water which will travel down the channel as a tidal wave with a nearly perpendicular front; following this the hydraulic gradient, as determined by the continuous flow, will be established, the .tidal Wave meanwhile spreading at the discharge end of the channel. The
travel of such a tidal wave as that just described, requires no energy beyond that which starts it, this energy being passed from one molecule to the next, as in a row of billiard balls, if the one on the end be struck. Moreover, the energy of the wave being constant, as its front grows greater and greater, the energy is passed to a greater number ofmolecules, so that the amount of energy received by each successive molecule grows correspondingly less. The motion of the molecules in the wave front itself, as such front passes down the channel, may be illustrated by assuming a body afloat as at B; it will remain at rest until the movement of the tidal wave strikes it, because the velocity of the wave is limited only by the elasticity and density of the medium. When the water around the body receives the force of the wave, it is not instantaneously able to escape on account of the inertia of the water farther down the channel, so it rises in height (pressure) and becomes part of the wave front, partaking of the forward motion of the latter and traveling in a path indicated in dotted outline in Fig. 2.
What it is desired to illustrate by the foregoing is that there is a region of static energy forming the front of a wave impulse of this sort; also that the energy of the wave front is a constant after the wave has separated from the main discharge. These points of distinction lead to diiferences between the mode of travel of an impulse in a fluid and a steady flow in that fluid; such, for instance, as that a sound wave has no momentum, but travels as readily at right angles to, as in the original direction of flow; and is subject tono contraction when passing through a sharp-edged orifice. Pursuing the tidal wave analogy further, if it be assumed that the channel through which.
the wave passes is provided with a number of alternately projecting piers 4 as shown in Fig. 3, it will be obvious that such wave will arrive at the mouth of the channel with as high a front except for energy lost by friction and at the bends, as when it started. If, however, these pieces 4 should be pierced with a number of holes 5 and the wave started down the channel as before, suchwave will lose a portion of its energy through the holes in the first of such piers, then through those in the second and so on, so that when it passes around to the lower side of each successive pier, the level there will already have been raised somewhat, and the energy of the wave front, as represented by its height, will be correspondingly decreased. Further, each little wave front as it progresses down the channel ahead of the main wave, is subjected to the same process of diminution, the general result being that the rise in pressure at the mouth of the channel is gradual and the spreading waves will be small, irregular and quickly dampened out. The applicability of this method of diminishing wave impulses to the mufliing of the sound of a motor exhaust, may be best understood from a reference to Fig. 4 of the drawings where I illustrate one approved construction of mufiler suited for use in connection with an ordinary automobile engine. As there shown, such muffler is outwardly of the usual elongated cylindrical form, while internally it is formed into a continuous spiral chamber 6 (see Fig. 4), that winds about the axis of the mufiler so that the gases discharged into the center of the muffler will travel spirally about the center until they reach the outer portion 7 of such chamber, which opens at the farther end of the muflier substantially freely to the atmosphere through apertures 8. The walls of the spiral chamber are moreover pierced with numerous smaller perforations 9 similarly located in successive convolutions of said chamber, so that in addition to the main impulse traveling spirally through the winding passage thus formed in the mufller, there will be formed a succession of smaller wave impulses that find their way through the series of openings 9. These smaller waves correspondingly diminishing the main wave impulse, so that a gradual discharge results through the apertures 8 without any impediment being placed in the way of the travel in the gases, but rather their escape being rendered freer by reason of the bypasses in the walls of the spiral passage.
In addition to the advantage obtained by the free exhaust, the foregoing construction allows .he escaping gas to retain nearly all of the kinetic energy of its discharge velocity which is obtained when the gas under pressure expands through the orifice of the exhaust valve of the engine. In other words, the gasis discharged from my improved silencer cool but at a high speed. By reason of such high speed and the high inertia of the gas, at the close of the disinches,
tion is perforated as at 18,
ordinary gas charge from the valve a considerable vacuum is caused at the upper end of the exhaust pipe which, owing to the length of the passage persists longer than where the velocity of the discharge has been dampened by constrict'ion of the discharge orifice,,or the interposition of actual barriers in the path of the discharge.
In Fig. 5 a helical passage is provided by arranging a partition 17 in the form of a which partiscrew, within the mufller body,
in the same fashion as are the partitions construction shown in Fig. 4
The foregoing features of improvement, although apparently simple,.have been demonstrated in eliminate the noise of the explosions in the engine such as is used on automobiles and the like; so that, for example, withla minimum cross-sectional area of 7.5
the sound of the exhaust is. not audible to a passenger in the car above the ordinary noise. of the latter when running. At the same time the power absorption is greatly reduced by providing a much freer outlet for the escape of the exhaust gases.
Other modes of applyingthe principle of my inventionxmaybe employed instead of the one explained, change being made as regards the mechanism herein disclosed, provided the means stated by any of the following claims -or the equivalent of such stated means be employed.
I therefore particularly point out and distinctly claim as my invention 1. Apparatus for muflling sound, comprispassage, and a shownin the practice to almost entirely ing a chamberhaving an unobstructed spiral passage, and a plurality of openings disposed in the walls 9f said passage adapted to by-pass gases from said portion of such passage to a portion farther advanced, substantially as described.
2. Apparatus for mufiling sound, comprising a chamber having an unobstructed spiral plurality of openings disposed throughout the length of said spiral, passage adapted to successively by-pass gases from one portion of such passage to a portion farther advanced,substantially as described.
3. Apparatus for muflling sound, comprising a chamber having an unobstructed spiral passage adapted to receive the gases at one end thereof, and a plurality of openings in l the spiral walls disposed throughout the length of said spiral passage and adapted to. successively by-pass gases from one portion to a portion farther advanced, substantially as described. f
4. Apparatus for muflling sound, comprising a cylindrical chamber having a rod disposed centrally therein and a helical plate disposed about such rod forming an unobstructed helical passage, said plate having a plurality of openings disposed throughout its length adapted to by-pass gases from one portion of such passa e to a portion farther advanced, substantial y as described. I
Signed by me this 10th day of June, 1910.
- FRANK O. MOCK.
Attested by- ANNA L.- G JTNO. F. OBEZLJN.