US1957012A - Silencing device for internal combustion engines - Google Patents

Description

May l, 1934.

A. J, L. HAYNEs SILENCING DEVICE FOR INTERNAL COMBUSTION ENGINES Filed OC'C. 25, 1930 3mm/vbo@ A JL. Haynes www Patented May 1, 1934 UNlTED STATES SILENCING DEVICE FOR INTERNAL COllBUSTION ENGINES arthur J. L. Haynes, Por: Haney, British Columbia, Canada Application October 23, 1930, Serial No. 490,792 In Canada November 21, 1929 1 Claim.

This invention relates to a silencing device for internal combustion engines. Its object is to absorb, mufe, destroy or dissipate the noise of the exhaust gases emerging from the engine into the atmosphere.

With this and other objects in view I adopt a novel form of construction which by reason of the simplicity and repetition of its components lends itself to factory production in mass while ensuring a highly ecient operative principle which forms a new departure in devices of this class.

In the practical exeniplification of my ideas I make use of the usual cylindrical casing as commonly adopted for muliiers on internal combustion engines and similarly coupled up to the outlet of the exhaust manifold, with the exception, however, that the emergence aperture of the casing in my case may be equal in cross sectional area with that of the intake end, instead of being reduced as in the common practice, and with, of course, in my device a corresponding reduction in the back pressure on the manifold and exhaust valves.

The interior of the casing has secured therein at spaced apart intervals a series of similar helical formations of thin metal, the helix being of a slightly increasing pitch, the rate of increase being based upon the well known exponential curve used in connection with acoustic instruments whereby the resistance of the passage to the gas flow is reduced to the minimum. In other words the inertia passages of my silencer increase in cross section throughout their length and the rate of increase is continually doubling; i. e., if a passage is 1" in diameter at its beginning it increases to lg in the first ten inches of its length, 11% in twenty inches of its length, and 1% at thirty inches. This, of course, makes it a long Venturi tube or, in other words, an internal streamline. This is solely to reduce the skin friction of the passages and consequently the back-pressure of the silencer. For example, for a two cylinder 25 B. H. P. engine the silencer may consist of three expansion chambers and two helical passages, each passage being approximately 18 long, 1 square inch in area at its entrance, 11/8 square inches nine inches therefrom, and 1% square inches at its exit.

The space between the helical members forms an expansion chamber which tends to absorb the momentum of the stream of exhaust gases.

The theory underlying the device is, rstly, to reduce the violent pulsations of the exhaust gas to as nearly a steady stream as possible by directing it through a series of alternate expansion chambers and passages through which the gas moves as a column. The purpose of the expansion chambers is to utilize the elasticity of the gas to absorb the sharp increase of pressure occasioned by the surge of gas from the exhaust valve. The purpose of the passages is to form the issuing gas into a column (thereby making the mest of its mass) to utilize its inertia to oppose sudden changes in the rate of its ow.

Silence is attained in vthis device by (a) the inertia of the gas columns opposing any change in the rate ci flow through them; (b) the complementary action of the expansion chambers in absorbing or storing the sudden rises in pressure and feeding the in a steadier stream to the succeeding passage.

By the of an inertia passage the preceding chamber held up to its work and compelled to absorb a iarge percentage of the fluctuations in the flow oi the exhaust gas. This arrangement ci' components takes advantage of the erkable functional affinity existing between eiastmity and inertia. This may be explained as follows. When a single pulsation of gas is offered the option of I'iowing into an expansion chamber or through a relatively long passage to the atmosphere it will invariably flow iirst into the chamber and afterwards through the passage.

At the beginning of the pulsation the attitude o the chamber and of the passage will be exactly opposite. Due to the elasticity of its enclosed gas the chamber wili immediately accept and accommodate it, whilst owing to its inertia, the column of gas in the passage will resist any acceleration.

Each component begins at once to reverse its attitude. The pressure in the chamber rises and increasingly opposes the influx, whilst its inertia yielding, the gas column in the passage gradually accelerates.

After a certain interval, depending on the size of the chamber and the length of the passage, each component will complete this reversal of attitude. The chamber will now expel its contents, and the momentum of the moving gas column will assist and prolong the flow of. gas through the passage until there is actually a depression in the chamber. The peak of this depression will be equal to the previous pressure peak, minus the loss due to the friction of the gas column against the walls of the passage. Thus the elasticity of a gas in a compact chamber and the inertia of a swiftly moving gas column are properties which are distinct to the point oi opposition, yeiJ paradoxically these properties are reciprocal, giving us a splendid example of team work. The same is true of the analogous properties in the electrical realm-inductance and capacity, and in mechanics, the properties of a weight and a spring In this silencer the passages and chambers separately develop the inertia and elasticity of the gas and the said passages and chambers are so arranged that the effects or functions of these properties are co-ordinated to smooth out the pulsations in the flow of the gas.

Secondly, to reduce backward pressure to a minimum by (a) causing the gas to assume a rotary motion as soon as it enters the silencer and continuing this motion in the same direction all the way through; (o) refraining from constricting the gas passage at any point to any smaller crees sectional area than is possessed in the inlet pipe; (c) giving each passage an increasing cross section according to the well known exponential law or in other words making it an internal streamline.

The theory has its practically exact counterpart in the well known ltering operation used in connection with radio apparatus in which an electrical impulse or current having a marked amplitude is subject to the effect of successive `pairs of condensers and choke coils, the combined and resultant effect of which is the production of a practically direct current to the radio tube.

Similarly in this device the violent pulsations of the engine exhaust are guided into a helical passage which directs the gas but restricts 'the fluctuation and corresponds with the choke coil, while the expansion chambers, which correspond to the condensers, cushion the impulses, each stage tending to reduce their amplitude and promote a more continuous flow of the gas.

Turning now to a considera-tion of the actual exhaust of a running engine, we see at once that it is made up of a series of sharp, almost explosive, pulsations. Directed through the streamline silencer these pulsations are progressively opposed by the inertia of the gas columns in the passages. rIhis inertia opposes and delays their deceleration equally with their acceleration.

The inertia, however, of the gas columns is not suilicient to resist successfully the pressure developed by these pulsations, were the passages joined together and connected directly to the exhaust port.

In order, therefore, that the limited inertia of the gas columns may successfully cope with the fluctuations of the exhaust stream each inertia passage is preceded by an expansion chamber.

Eventually the expansion chamber may be said to act as a shock absorber. Analysis shows that its function is that of converting brief, high pressure surges into those of longer duration and correspondingly lower pressure. This reduces the stress and enables the gas column to fulfil its function which is that of storing power during acceleration and returning it during the deceleration of the gas column, thereby opposing andreducing the fluctuations in its rate of flow and tending to produce a stream in which the successive pulsations merge one into the other.

By this arrangement there is no direct baflling eect tending to produce back pressure, but the entire operation is of a continuous and more efficient character.

The drawing accompanying and forming a part of this application shows the essential features of the device, in which:

Figure l is a side elevation of a silencer with the end portion in section.

Figure 2 shows a portion of Figure 1 to an enlarged scale, the casing being shown in section.

Figure 3 is a transverse section on the line 3-3 of Figure 1.

Figure 4 is a transverse section on the line 4 4 of Figure 1.

Figure 5 is a transverse section on the line 5 5 of Figure l.

In this drawing the numeral 6 indicates the cylindrical casing of a silencer or mulller such as may be applied to the internal combustion engine of an automobile; 7 the exhaust pipe from the engine and having a branched nozzle 8 by which the gases are deflected to take an approximately helical path.

At spaced apart intervals within and secured to the casing 6 are a series of helical members 9 disposed around a central core member 16. The character of the helix in these members is such that its pitch is slightly but continuously increasing, so that the enclosed space within the casing 6 takes the form of a helical chamber of gradually increasing volume from its intake, the rate of increase being determined on the same lines as that of the well known exponential curve as applied to acoustics, and for the same purpose.

Between the helical members 9 are vacant spaces l0, ll, l2 which form expansion chambers for the traversing exhaust gases.

The operation of the device may he summarized thus:-

The exhaust gases traverse the manifold pipe 7 and enter the end chamber 13 within the casing 6 through the deilecting nozzle 8 which imparts an approximate helical and swirling motion to the flow which then enters the helical path at la, the direction of which is indicated by the arrow. This stream of gas after traversing the helical enclosure becomes slightly increased in volume by the time it emerges at the arrow l5 to traverse the first expansion chamber 1G.

In traversing this latter the acquired helical motion of the gas stream-now unconstrained` loses a measure of its form and expands, thus consolidating its flow and reducing the sharpnessof its pulsations, and this effect is repeated and accumulated as the gases traverse the jremaining portion' of the device, until the final chamber l2 is reached when they are discharged at the pipe 17.

Owing to the fact that a continuous traverse towardsthe exhaust outlet 17 has been effected without the use of abrupt baffles and the conse-- quent setting' up of wasteful eddies resisting the flow of the gases, the outlet pipe 17 may be of the same bore as the inlet 7 with the consequent considerable reduction of back pressure as compared withusual practice in this type of device.

Having now particularly described my invention, what I claim and desire to be protected in by Letters Patent, is:

A silencer comprising a cylindrical casing divided intoa series of separate expansion chambers by a`series of helical partitions each forming interiorly a helical passage from one chamber to the next adjacent one, the diameter of said helical partitions being that of the casing whereby each expansion chamber is completely isolated from the next, save for said helical passages, each helical passage being of gradually increasing crosssectionalarea from its inlet to its outlet in virtue of which'the functional affinity existing between the elasticity and inertia of a gas is utilized through a series of stages cumulatively to reduce the amplitude of its pulsations', said helical passages all winding in the same direction.

ARTHUR J. L. H'AYNES.

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