US2881851A - Apparatus for silencing the exhaust of internal combustion engines - Google Patents

Description

April 14, 1959 w s 2,881,851

J. APPARATUS FOR SILENCING THE EXHAUST OF INTERNAL COMBUSTION ENGINES Filed Sept. 24, 1954 BY M a fF- INVENTOR.

United States Patent APPARATUS FOR SILENCING THE EXHAUST OF INTERNAL COMBUSTION ENGINES Jasper Willsea, Webster, NY. Application September 24, 1954, Serial No. 458,084 2 Claims. (Cl. 181-40) The present invention relates to sound mufllers such as are used to silence noises developed in the operation of internal combustion engines, air compressors, and the like.

It is well known, for instance, that the rotational inertia of an internal combustion engine is the power that enables an automotive vehicle to accelerate. Any force working against the rotational inertia of the engine will tend to retard acceleration thereof. When the exhaust valves of the respective engine cylinders are open, however, any resistance to the outflow of the exhaust gases from the cylinders through the exhaust pipe to free air at the rear of the car will react as back pressure against the pistons in the several cylinders during the whole time that the exhaust ports of these cylinders are open. The effect of any such back-pressure is proportionately greatest at the beginning of acceleration of the engine when the rotational inertia thereof is the least, and least when the engine has been accelerated to full speed for delivering maximum horse power. At any speed of the engine, however, any reduction in the resistance to the outflow of exhaust gases from the several cylinders will increase the eificiency of the engine, the increased efiiciency being most pronounced at the beginning of acceleration. Consequently, the silencing of the exhaust from an internal combustion engine should be eflfected with minimum back pressure so that there will be minimum reduction in engine efficiency.

Much of the back pressure in the conventional exhaust-silencing systems of internal combustion engines arises from the fact that the exhaust valves of the several cylinders discharge into an exhaust manifold which includes pipes having relatively small internal diameters approximately the size of the exhaust valve ports. The exhaust gases are discharged through the exhaust valve of each cylinder in the form of pulse masses of exhaust gases; and they tend, if unrestrained, to expand in all directions; but because of the small piping of a conventional manifold the pulse masses can expand only by crowding their way at high velocity through the small and crooked manifold pipes with resulting back pressure. The higher the velocity of gas flow through small pipes, depending on their lengths, the greater the resistance there is to such flow and consequently the greater the back pressure on the pistons in the respective cylinders.

In my pending patent application Serial No. 403,162, filed January 11, 1954, I have disclosed an arrangement for increasing the elficiency of engines and at the same time largely reducing exhaust noises, by allowing the exhaust gases from a multi-cylinder engine to expand into a relatively large common manifold which is connected with the tail pipe leading to the atmosphere. However, a certain residual volume of airborne sound will still be communicated through the tail pipe in such an arrangement.

A primary object of the present invention is to provide means which, when combined with the plenum chamber,

or large common manifold, of my prior application, will eliminate the residual tail-pipe noise.

Another object of the invention is to provide an improved tail-pipe construction usable either with the plenum chamber, or large common manifold, of my prior application, or with a conventional automobile manifold, to reduce tail-pipe noises and increase the eificiency of the engine operation.

Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims.

The present invention achieves its purposes by a tailpipe construction including two tail pipes of exactly the same length instead of the conventional single tail pipe. The two tail pipes act as two open ended pipes in a harmonic sense, for both will have the same frequency of vibration because of their identical length. The natural frequency of a pipe itself always dominates the frequency of a sound from a closely coupled source. With the construction of the present invention, the two tail pipes coupled to the same noise source, will both be set into vibration with a slight deviation from their own natural frequency produced by the frequency of the originating sound, and the nodes and loops of the sound waves in the two pipes will offset one another dampering to all practical purposes the sound in the exhaust pipes.

In the drawing:

Fig. 1 is a more or less diagrammatic view showing in side elevation, with parts broken away, a silencing system constructed according to one embodiment of the present invention;

Fig. 2 is a view, partially broken away, showing the plenum chamber, or large common manifold of this system and one way of connecting this plenum chamber or manifold with the tail pipes of the silencing system; and

Fig. 3 is a view, also partially broken away, showing another way of connecting the plenum chamber or manifold with the tail pipes.

In Fig. 1, 10 denotes a plenum chamber, or large common exhaust manifold, such as disclosed in my prior application, Serial No. 403,162 above mentioned. This chamber is secured to one side of the internal combustion engine, air-compressor, or other noise source, to receive the exhaust gases therefrom. In an automotive vehicle it is mounted in communication with the exhaust valves of the several motor cylinders.

The chamber 10 is preferably in the form of a closed box or manifold made of cast aluminum to give rigidity to its walls and to dissipate some of the heat from the exhaust gases introduced therein. This box is conveniently lined with a layer or coating 11 of asbestos or other sound cushioning heat-proof material. The box 10 is imperforate except for an exhaust outlet 12 and except for lateral openings 14 which register in gas-tight relation with exhaust ports of the several cylinders. The chamber, which approximates the length of the motor block, has a depth and width to fit under the hood of the automotive vehicle. Ideally the chamber should be of a size such that the expanding mass of gas issuing from an exhaust port of the engine, as well as the masses of gases exhausting from all the exhaust ports of the engine, is lost in the general volume of gas in the chamber, which is filled with gas under average or uniform pressure greater than atmospheric pressure. In the instance illustrated, the cham ber 10 is shown as provided with four ports 14 for entry therein of the exhaust gases from the engine. This chamber illustrated is for a four cylinder engine, although, of course, the invention may be used with engines of any number of cylinders. With a four cylinder engine, the volume of the chamber 10 is at least four times the volume of each cylinder discharging into it, so that the exhaust gases resulting from the individual explosions in 3 the separate cylinders are almost completely expanded and at least partially transformed from velocity pressure gases into lower, substantially static pressure gases.

The most important dimension of the chamber 10, as explained in my pending application above mentioned, is its horizontal width, which ideally should be wide enough to permit the pulses of exhaust gases from the successive engine explosions, which issue from the exhaust valves as high pressure, high velocity jets, to expand and be dissipated in the chamber without substantial impact against the opposite chamber wall. Practically this horizontal dimension may be reduced, with some sacrifice in the desired results, in the event that the need for space under an automobile hood becomes a factor.

The vertical height of the chamber ideally should be such that it will accommodate the expansion of the explosive jet of gases from each exhaust valve while the jet is expanding radially with respect to its axis of travel so that the jet cannot strike a chamber wall until it has become an expanded body of gas. The convenient rectangular shape of the chamber provides a volumetric capacity large enough for the exhaust gases, so that they can expand readily, and so that the only back pressure on the piston is from pushing the expanded gases through the tail pipe which is a minimum requirement. The whole engine can be designed for large exhaust port open ings because when the plenum chamber or large common manifold is used, the exhaust gases from each cylinder are not being sent into separate individual manifold pipes as in conventional construction. With larger port openings there is, of course, greater immediate expansion of the exhaust gases at the exhaust valves themselves. This makes it possible to effect immediate, natural cooling of the exhaust valves themselves due to this expansion. The plenum chamber therefore makes for a cooler running engine.

The distance between valve ports will allow enough space for lateral expansion between explosion jets other than where two exhaust ports are adjacent each other but this last situation will not be harmful since the purpose is to avoid having the jets hit a metal wall; and an adjacent exhaust port does not have an immediately consecutive explosive jet in the course of the normal order of firing the cylinders. Furthermore, the two adjacent ports will not be discharging simultaneously, or even without considerable sequential spacing in the consecutive order of firing. In this manner, the noise from the walls of the box arising from the impacts thereagainst of the individual explosion jets will be greatly reduced since these jets are largely dissipated or disintegrated in the great volume of the chamber.

Although at low engine speeds, there is sulficient volume in the chamber for the complete expansion of each successive mass of gas exhausting from the engine, which eliminates variation in pressure in the exhaust gases and consequently the noise therefrom, at high engine speeds the rapid succession of explosions and consequent volumes of exhausting gases does not allow sutncient time between pulse masses of gas for complete expansion of each pulse mass. It is not convenient, however, to make the chamber large enough to completely expand the exhausting gas masses generated at high engine speed. The present invention, though provides further means for efficient reduction of the pressure in the exhaust gases as they leave the confined space of the plenum chamber, or manifold, 10.

The chamber 10 discharges into the atmosphere at a remote point through a tail pipe system constructed according to the present invention. This tail pipe system, which is open at its remote end, is connected to the chamber 10 in sealed relation thereto through the exhaust outlet 12, preferably located in the bottom of the box or chamber 10.

The inlet portion (Fig. 2) of the tail pipe system, which is connected to chamber 10, can be made integral with the chamber, but it is preferably made of a separate removable piece as shown. Thus a variety of different inlet portions can be used as desired. The inlet portion shown in Fig. 2 consists of a pipe provided with a plurality of lateral openings 16 conveniently arranged according to a preferably symmetrical pattern. These openings constitute a series of vena eontracta or small openings connecting the chamber with the tail pipe system. The more openings 16 that are provided in the inlet section 15, the more the pressure pulses of the explosions are broken up or disintegrated before they are carried to the discharge end of the tail pipe where exhaust noises can be heard. The large number of small openings 16 in the inlet section 15 constitute orifices for passage from the expansion chamber 10 to the discharge or tail pipe system of the exhaust gases, thereby filling the tail pipe system with exhaust gas more efliciently than were a small number of large openings employed.

The inlet section 15 extends vertically through chamber 10 and its upper end is closed by a gasket 18 carried on the underside of a removable cap 19 which seals an opening in the top of the box 10. This cap permits the substitution of various inlet sections 15 and serves to hold a selected inlet section in registry with tail pipe section 20 at the discharge outlet of the chamber.

By extending the inlet section 15 of the tail pipe into the confined space of the chamber, the tail pipe inlet section 15 can be filled efiiciently through its round holes 16 exactly and efiiciently without substantial turbulence. The greater the pressure in the confined space, the faster the tail pipe section 15 will be filled, thus relieving pressure by almost completely converting the energy of pressure into velocity so efficiently that minimum back pressure will be applied against the engine pistons.

The tail pipe section 20 is connected by a T 21 (Fig. l), or other suitable coupling, with two axially-aligned identical pipe sections 22 of equal length, which, in turn, are connected by identical elbows 23 with the two parallel, identical tail, or discharge, pipes 24, which at their rear ends, or in the case of vertical discharge, at their upper ends, open into the atmosphere.

The two pipe sections 22 are of considerable length. (It should be noted that they are shown broken in Fig. 1.) Moreover, as clearly shown in the drawing they are of larger diameter than the two tail pipes 24. These two pipe sections 22 with the connecting portion of the T 21 constitute, therefore, a second chamber or chest which is connected to the first plenum chamber or chest by the T 21 and the pipe section 20.

With this identical two-pipe system, the vibrations emitted by the two pipe systems, which singly would produce sound, will match each other as to phase, that is, a rarefaction phase in one pipe system will be neutralized by a compression phase in the other pipe system, thereby producing silence instead.

A pipe open at both ends has a natural frequency of vibration; and sound waves therein moving inwardly from opposite ends thereof meet at a node midway of the pipe from which the waves move outwardly toward the ends of the pipe. The reaction against the atmosphere at each of the two open ends of the pipes causes the sound waves to rebound inwardly against the rarefaction phase that follows a compression phase of a wave. Because of the speed of sound waves, the length of the pipe determines the node midway of the pipe and the anti-nodes of the reaction at the pipe ends. The length of the pipe therefore determines the number of complete wave travels within the pipe every second, which determines the pitch of the pipe.

A source of vibration, such as chamber 10 or such as the chamber comprising the pipe sections 22 and the communicating portion of the T 21, which has a vibration rate quite different from the pipe itself, may be coupled to a pipe at one end of the pipe, but when the vibration emanating from the source 10 or 22-2122 passes through the pipe, causing a general distribution of sound waves from the reaction node at the other end of the pipe, the frequency of the vibration will be almost completely changed to the frequency of the pipe itself. When another pipe is connected to this same source, however, where the two pipes have the same length and are otherwise identical, both pipes will have the same vibration rates but they will compensate each other, that is, when one pipe is in the compression phase at the end of the pipe at the common chamber, the other pipe will be in the rarefaction phase, and the two pipes will vibrate in alternate phases which will neutralize the sound. Thus, with the dual pipe exhaust system of the present invention, sounds due to exhaust gases will be substantially completely mufiled. Thus, with the present invention automobiles, air compressors, and the like, materially improved as to quietness can be obtained.

It is not necessary that the inlet end of the tail pipe system extend through the plenum chamber or manifold 10. Instead the tail pipe section 20 can be replaced by a section 20', as explained in my prior application abovementioned, which at its juncture with the bottom of the box 10 at exhaust port 12, is formed into a flared funnellike shape similar to a Venturi tube throat. A tapering pointed plug 25 of the contour shown in Fig. 3, is adjustably mounted with its point directed toward the center of the opening in the tail pipe section 20' thereby defining an annular discharge orifice. The plug 25 is carried on a threaded stein which is threaded in an opening in the top of the box 10 and is locked by the nut 27. The stem 26 terminates in a hexagonal head 28, whereby the tapered plug 25 can be adjusted toward and away from the opening in pipe 20, to vary the size of the discharge orifice. The discharge orifice construction functions as an adjustable Venturi nozzle which smooths the successive explosive pulses of exhaust gases from the several cylinders into a continuous swift emission of gases into the tail pipe. Pipe 20' discharges into two identical tail pipes, similar to the pipes 22 2324 of Fig. 1, so that, save for the Venturi effect of plug 25 and opening 12, the apparatus of Fig. 3 may operate in the same way as the mufiling apparatus described with reference to Figs. 1 and 2.

While the invention has been described in connection with different embodiments thereof, it will be understood that it is capable of further modification, and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention, and including such departures from the 6 present disclosure as come within known or' customary practice in the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

1. Sound-mufiling apparatus for internal combustion engines having a plurality of cylinders, each provided with an exhaust port, comprising a box defining a confined chamber in immediate sealed communication with all said exhaust ports whereby all said exhaust ports discharge directly freely into said chamber, said chamber having a volume several times greater than that of a cylinder, and a chest communicating with said chamber and a pair of identical, equal length tail pipes connected to opposite ends of said chest, said tail pipes extending to points remote with respect to said cylinders and being open to atmosphere at their distal ends.

2. Sound-mufiling apparatus for internal combustion engines having a plurality of cylinders, each provided with an exhaust port, comprising a box defining a confined chamber in immediate sealed communication with all said exhaust ports whereby all said exhaust ports discharge directly freely into said chamber, said chamber having a volume greater than that of all the cylinders whose exhaust ports communicate with said chamber, an elongate, tubular chest, connecting means having a restricted entrance connecting said chamber with said chest, and a pair of identical, equal length tail pipes connected to said chest and extending to points remote with respect to said cylinders, said tail pipes being open at their distal ends.

References Cited in the file of this patent UNITED STATES PATENTS 1,949,667 Transiskus Mar. 6, 1934 2,078,754 Day Apr. 27, 1937 2,353,036 Hoyle July 4, 1944 2,513,229 Bourne et al June 27, 1950 2,660,257 Bourne et a1 Nov. 24, 1953 FOREIGN PATENTS 679,940 Great Britain Sept. 24, 1952 OTHER REFERENCES Publication: Harrison Wholesale Co., Chicago, Ill., Catalog #580, dated 1951.

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