GB1567437A - Engine silencer and spark arrester - Google Patents

Description

(54) ENGINE SILENCER AND SPARK ARRESTER O(71) We, DISCOJET CORPORA TION, a corporation organised and existing under the laws of the State of California, of 920 3rd Street, Davis, California, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to an engine silencer and spark arrester.

In connection with the exhaust from an internal combustion engine, there is always the desideratum to provide a relatively low level of exhaust noise without seriously interfering with exhaust outflow. In fact, it is preferred to reduce the back pressure of the exhaust, if possible, while attenuating the inherent exhaust sound. In addition, for some environments, particularly on forest trails and the like, there is a strict requirement that emission of glowing particles from the exhaust be restricted to particles of such a small size that they are virtually extinguished or are absolutely extinguished after leaving the engine and before being able to touch the grounds or any of the surroundings.

There is a requirement for continued improvement in this field as there is greater and greater emphasis on the retention of carbon particles and there are wider prohibitions of emission of such particles at any time as might be likely to start fires. There is also the general requirement that a silencing and spark arresting device be relatively simple and inexpensive so that it can be widely used and so that it can easily be maintained and cared for, as many users are technically or mechanically unskilled.

In earlier devices used on engines burning leaded fuels, it has been noted that lead often builds up on muffler surfaces to an extent to impede the flow of the exhaust gases. It is a desideratum or even a requirement to overcome such deleterious build-up of lead from the fuel.

Another requirement is to provide an arrangement so that sparks which otherwise would be emitted are retained but the residue particles can periodically be removed without substantial difficulty.

It is therefore an object of the invention to provide an engine silencer and spark arrester which meets all of the foregoing requirements and is a substantial advance over devices heretofore available.

In accordance with this invention there is provided an engine muffler and spark arrester comprising an outer tube extending along an axis between an inlet and an outlet; a perforate inner tube disposed coaxially within said outer tube and substantially merging therewith adjacent said inlet; a partially toroidal end wall (as herein defined) engaging said outer tube and said inner tube adjacent said outlet; sound absorbing material disposed around said inner tube; a central tube disposed coaxially within a portion of said inner tube and extending substantially through a plurality of coaxial nested, partially toroidal cups disposed adjacent said end wall; a resonator-spark arrester chamber disposed coaxially with said cups beyond said outlet; and means for securing said inner and outer tubes, said central tube. said cups and said resonator-spark arrester chamber together.

Preferably a gas flow barrier is radially interposed between said inner tube and said central tube.

The features and objects of the present invention will be best understood from the following description of the accompanying drawings. in which: Figure 1 is a cross-section on a longitudinal plane through one form of an engine silencer and spark arrester constructed pursuant to the invention: Figure 2 is a cross-section to an enlarged scale, the plane of which is indicated by the line 2-2 of Figure 1, Figure 3 is an enlarged detail showing the arrangement of the partially toroidal cups; Figure 4 is a cross-section, the plane of which is indicated by the line 4-4 of Figure 2; Figure 5 is a partial side view, the plane of the view being indicated by the line 5-5 of Figure 4, and Figure 6 is a longitudinal cross-section, like Figure 1, but showing a modified form of the device.

In a preferred form of the arrangement, as shown particularly in Figures 1-5 inclusive, there is afforded a silencer and spark arrester which has an outer tube 6 symmetrical about a longitudinal axis 7 and of generally tapering configuration or frustoconical in aspect. At one end, the inlet end 8, the device has a substantially circularcylindrical portion 9 designed to interfit with the exhaust pipe of an internal combustion engine. The manner of attachment of the muffler to the engine is presently immaterial, except that it should be without any substantial leaks, an appropriate joint including a clamp or the like normally being provided. The outer tube 6 is largely frustoconical and expands from a region adjacent the inlet to a generally circular-cylindrical outlet portion 11.

Within the tube 6 there is an inner tube 12 of generally circular-cylindrical form symmetrical about the axis 7 and at its inlet end having a diameter only slightly less than that of the outer tube so that the two fit together well. The inner tube makes a close fit with or is secured to the outer tube near the inlet.

Near the outlet the inner tube overlies an end wall 13 spanning the annular space between the inner tube and the outer tube.

The end wall has inturned flanges 14 and 16 for close interfitting or even fastening of the tubes and end wall. The end wall 13 is an annulus symmetrical about the axis 7 and having a partially toroidal form, including a concave intermediate section. The term "partially toroidal" is not an exact mathematical designation but is intended to define a configuration which is similar to or like that of a portion of a torus on one side of a median plane normal to the axis of the torus or like a ring having an annular groove.

The inner tube 12 is not solid or continuous, as is the outer tube, but rather is provided with a number of perforations 18 therein. These are evenly spaced over most of its extend and afford communication between the interior of the inner tube and the interior of the outer tube. The intervening space 19 is preferably filled with sound attenuating or sound absorbing material; for example, fiber glass or the like. Overlying at the end wall 13 is a plurality of nested, partially torodial cups 21. as illustrated to larger scale in Figure 3. These cups are arranged partly to nest one within the other and to have a concave portion 22 substantially matching the concave portion of the end wall 13. Adjacent their radial inner peripheries 26 the cups are provided with inclined flanges 23 so arranged that the edge 24 of one flange is spaced from the adjacent wall of the adjacent flange.This leaves an annular opening 27 therebeween of a predetermined dimension. This size is substantially that of the largest particle that is to be permitted to escape from the device. Particles that are larger cannot pass through the opening 27, whereas particles that are smaller can freely pass therethrough. The flanges 23 are turned in the general directionof the inlet to the silencer, whereas the outer peripheral edges 28 of the cups are inclined toward the direction of the outlet of the silencer, the spaces between the individual discs at the outlet or adjacent the outer edges being much larger than the openings 27 near the inlet edges.

The thickness of the flange material and the upstream direction of the edges 24 of the cups are such that whatever entrained lead in the exhaust gas is intercepted is deposited on the edges 24 themselves and only thereon for they form substantially the only impact surfaces. It has been noted that the lead erosion rate by passing gases usually equals the lead deposit rate, after some build-up, so this arrangement does not suffer from lead blocking and the gas passages remain free and of substantially original dimensions.

The space relationship is maintained, as especially shown in Figure 2, 4 and 5, by a number of dimples 31 indenting the outer edges 28 of the individual cups and arranged, as shown in Figure 5, to nest in a wedging fashing. That is, a number of partially toroidal cups can be arranged coaxially with the dimples interengaging or interlocking so that a packet is made of the desired array and with the desired spacing between cups and with the cups held against shifting transversely. Since each one of the cups is just like the others it is possible to assemble an array of any number of cups, depending upon the desired capacity of the muffler and depending upon the amount of exhaust area required.

As shown particularly in Figure 2, the cups may also have a number of apertures 33 through them, especially through the concavities 22, so that there can be some straight flow or pressure equalization in the cup region. However, there is no possiblity of large solid particles passing therethrough because there is interposed between the end wall 13 and the first adjacent cup 21 a gas flow barrier 36. This is a solid, imperforate member. The barrier 36 has an outer por tion 37 of the same general configuration as the partial toroids nested on either side of it and has an interior flange 38 designed to be fastened to and support a coaxially arranged central tube 39.This central tube has a relatively small entrance end 41 with an out-turned or flared flange 42, next has a cylindrical portion, then has an intermediate enlargement 43 and has a generally circularcylindrical larger end 44 passing substantially entirely through the nested group of discs or cups. The central tube 39 is relatively long and narrow to provide gas flow inertia and also incorporates a flared or diffusing section 43 so that most of the kinetic energy in the gas is recovered in one direction of flow. This is not true for the backward direction of flow, so back flow is inhibited by the central tube, and there is a resulting reduction of dissipated sound. As an example only, the configuration of Figure 1 is especially effective as a sound attenuator between about 250-750 Hertz.

Coaxially arranged and surrounding the outlet of the central tube 39 is a resonatorarrester chamber 46 having at one end a wall 47 shaped very much like an adjacent one of the cups 21 and designed to interfit therewith. This is joined by welding, for example, to the chamber wall 46. The wall 46 is preferably necked down at its outer end 48 to receive the flange 49 of the closure cap 51.

To hold all of these parts in the proper axially spaced and concentrically arranged position, there is a fastening means including a through bolt 52. At its inner or upstream end, this bolt passes through a gap 53 in a split, diametricaly extending vane 54 having ears 56 lodged in small slits 57 in the tube 6. The central rod is secured in the vane 54 against axial movement and at this opposite end is provided with threads 58 receptive of a nut 59. With this arrangement all of the parts can be assembled coaxially, the nesting portions of the cups, the end wall 13 and the barrier well 47 as well as the gas barrier 36 substantially aligning themselves. When the nut 59 is tightened on the rod 52, the entire silencer and spark arrester is maintained firmly in position.

In use, exhaust gas with its attendant particles, usually glowing carbon, comes in through the inlet, travels through the inner tube and has some of the sound attenuated by passage through the openings into fiber glass in the surrounding space 19. The gas then exhausts through the narrow portion of the central tube 39 and passes into the resonator-arrester 46. The light gas makes a sharp U-turn back upon itself, whereas the relatively heavy glowing particles or sparks are deposited in the chamber 46. The exhausting gases then travel in a reverse direction through the interior of the nested cups, being prevented from travelling farther backward by the intervening gas barrier wall 36. The gases then must pass through the relatively narrow annular openings 27 between the successive discs 21, only very small particles being passed along with the gas.The gases then expand radially outwardly and travel through the sinuous pathway afforded by the nested, partially toroid cups and finally discharge in conical patterns from the outer openings between the outer edges 28 of the nested cups.

After prolonged use a number of particles may be trapped within the chamber 46. If that is true then the nut 59 is easily removed, and the end cap 51 is taken off. If the particles cannot then be easily discharged, the wall 46 itself is removed and shaken out and emptied. The parts are then reassembled in their initial condition, and when the nut 59 is again tightened the silencer is availabe for further sound attenuation and spark gathering duties.

As shown in Figure 6, there is a modification of this arrangement in that similar parts are utilized with somewhat different proportions or scales for sound attenuation in engines of different character. In addition, the inner tube 61 has a special configuration. This allows for higher gas velocity and additional attenuating material. The gas flows toward a specially provided central tube 62 somewhat shorter than before, terminating within the axial extent of the nested cups 21. Furthermore, the wall 63 which closes the inner end of the resonatorarrester chamber 64 is extended to provide a short resonator tube 66.

While the general function and operation of the Figure 6 device is the same as the device of Figures 1-5, the Figure 6 device is designed for greater or different frequency rejection, being, for example, particularly effective between 500-2000 Hertz. The gas inflow is as previously described, through the perforated inner tube 61 and then through the relatively short central tube 62.

Some of the gas can virtually short circuit into the nested cups. Some of the sound reverberates within the interior of the chamber 64 but is attenuated. Any particles that flow into the chamber 64 with substantial velocity deposit therein and do not flow back toward the outlet. The cups are previously described and permit the passage only of particles under the maximum size permitted for exhaust.

In both instances there is provided an engine silencer and spark arrester effective substantially to attenuate the exhaust sound of an internal combusion engine without providing back pressure thereon and often allowing a lower exhaust pressure than without the silencer. Furthermore. exhaust particles are retained and are not permitted to discharge to the outside unless they are well under the size limit permitted to discharge without endangering the environment.

WHAT WE CLAIM IS: 1. An engine muffler and spark arrester comprising an outer tube extending along an axis between an inlet and an outlet; a perforate inner tube disposed coaxially within said outer tube and substantially merging therewith adjacent said inlet; a partially toroidal end wall (as herein defined) engaging said outer tube and said inner tube adjacent said outlet; sound absorbing material disposed around said inner tube; a central tube disposed coaxially within a portion of said inner tube and extending substantially through a plurality of coaxial nested, partially toroidal cups disposed adjacent said end wall; a resonator-spark arrester chamber disposed coaxially with said cups beyond said outlet; and means for securing said inner and outer tubes, said central tube, said cups and said resonator-spark arrester chamber together.

2. A device as in claim 1, including a gas flow barrier radially interposed between said inner tube and said central tube.

3. A device as in claim 2, in which said gas flow barrier is nested with said end wall and with said cups.

4. A device as in claim 2 or 3, in which said gas flow barrier and said central tube are secured together.

5. A device as in any of the preceding claims, in which said cups are axially spaced apart at their inner periphery to define annular gaps between successive cups.

6. A device as in claim 5, in which said cups at their radial inner periphery have inturned flanges directed upstream.

7. A device as in claim 5 or 6, in which each said cups has dimples at its outer periphery which are arranged to contactingly nest with dimples on adjacent cups.

8. A device as in any of the preceding claims, in which said central tube has a tapered internal diameter with the decreased diameter adjacent said inlet.

9. An engine silencer and spark arrester substantially as herein described with reference to. and as illustrated in, Figures 1 to 5 and Figure 6 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. to discharge to the outside unless they are well under the size limit permitted to discharge without endangering the environment. WHAT WE CLAIM IS:

1. An engine muffler and spark arrester comprising an outer tube extending along an axis between an inlet and an outlet; a perforate inner tube disposed coaxially within said outer tube and substantially merging therewith adjacent said inlet; a partially toroidal end wall (as herein defined) engaging said outer tube and said inner tube adjacent said outlet; sound absorbing material disposed around said inner tube; a central tube disposed coaxially within a portion of said inner tube and extending substantially through a plurality of coaxial nested, partially toroidal cups disposed adjacent said end wall; a resonator-spark arrester chamber disposed coaxially with said cups beyond said outlet; and means for securing said inner and outer tubes, said central tube, said cups and said resonator-spark arrester chamber together.

2. A device as in claim 1, including a gas flow barrier radially interposed between said inner tube and said central tube.

3. A device as in claim 2, in which said gas flow barrier is nested with said end wall and with said cups.

4. A device as in claim 2 or 3, in which said gas flow barrier and said central tube are secured together.

5. A device as in any of the preceding claims, in which said cups are axially spaced apart at their inner periphery to define annular gaps between successive cups.

6. A device as in claim 5, in which said cups at their radial inner periphery have inturned flanges directed upstream.

7. A device as in claim 5 or 6, in which each said cups has dimples at its outer periphery which are arranged to contactingly nest with dimples on adjacent cups.

8. A device as in any of the preceding claims, in which said central tube has a tapered internal diameter with the decreased diameter adjacent said inlet.

9. An engine silencer and spark arrester substantially as herein described with reference to. and as illustrated in, Figures 1 to 5 and Figure 6 of the accompanying drawings.