Spark Arrester And Muffler Construction

Abstract

A combined muffle and spark arrester for use with small internal combustion engines. The muffler includes two expansion chambers through which engine exhaust is passed and a hat-shaped spark-arresting screen positioned within the second chamber. The screen removes particles from the exhaust having a size greater than the screen mesh to prevent the discharge of potentially dangerous sparks. A curved heat shield is supported on the muffler by a plurality of U-shaped brackets which are projection welded to the two chambers. The muffler construction is particularly rigid and the muffler is provided with a removable end cap to provide convenient access for removing the screen for cleaning.

Description

This invention relates to a muffler and spark arrester construction for use with small internal combustion engines.

The increasing use of such engines in a wide variety of applications has occasioned a need for a mass-produced muffler which can accommodate various sizes of engines within the small horsepower range. When such an engine is installed on a mini-bike and operated where combustible material is present, such as in forests and fields, the engine must be prevented from discharging sparks which could ignite the combustible material. A spark-arresting muffler can be connected to the engine exhaust to prevent the discharge of sparks in addition to reducing the noise level of the engine. In small engines, such a spark-arresting muffler must perform the aforementioned functions without seriously reducing the engine efficiency. An effective spark arrester must achieve a satisfactory arresting efficiency at various exhaust flow rates. Consequently, from time to time the arrester must be cleaned so that the engine efficiency is not unduly impaired.

An object of the invention is to provide a spark-arresting muffler construction suitable for mass production which can accommodate various sizes of engines with a minimum number of unique parts.

Another object of the invention is to provide a spark arrester for a muffler which may be very easily cleaned when it becomes clogged.

It is also an object of the invention to provide a rigidly constructed spark-arresting muffler which is well suited for severe operating conditions.

A further object of the invention is the provision of a simple, sturdy and versatile attaching structure for mounting a heat shield on a muffler.

Additional objects, features and advantages of the invention will become apparent from the following detailed description and drawings in which:

FIG. 1 is a vertical sectional view through the longitudinal axis of an exemplary but preferred form of a spark-arresting muffler constructed in accordance with the present invention.

FIG. 2 is a right-hand end elevational view of the muffler of FIG. 1.

FIG. 3 is an end elevational view of an interior baffle taken in the direction of arrow 3 in FIG. 1 but showing the baffle by itself.

FIG. 4 is a left-hand end elevational view of the muffler of FIG. 1.

FIG. 5 is an exploded view of a portion of the spark arrester structure of the muffler of FIG. 1 shown apart from the muffler.

FIG. 6 is a perspective view of an attachment bracket of the muffler of FIG. 1 shown by itself.

Referring in more detail to the accompanying drawings, muffler 10 (FIG. 1) comprises a first cylindrical expansion chamber 12 and a second cylindrical expansion chamber 14 which are communicated by a connecting pipe 16. Chambers 12 and 14 are in the shape of cylindrical shells which are coaxially aligned in spaced-apart relation, chamber 12 being upstream of chamber 14. Chamber 12 is constructed from two half shells 18 and 20 which are crimped together and, if desired, brazed as at 22 along the open circular edges thereof. A circular baffle plate 24 is supported within chamber 12 by the attachment of the two shell halves 18 and 20, so as to lie perpendicular to the chamber axis. The solid central portion 23 of baffle 24 (FIG. 3) is surrounded by a plurality of variously-sized orifices 25 which are generally circularly arranged around the outer margin of baffle 24. The ends of chamber 12 are circularly centrally apertured and flanged as at 26 and 28. An inlet pipe 30 is inserted into aperture 26 to conduct exhaust into chamber 12. Connecting pipe 16 is coaxial with chambers 12 and 14 and one end thereof is inserted into aperture 28 to conduct exhaust from chamber 12 into chamber 14. The opposite end of pipe 16 is inserted into a central flanged aperture 32 at the inlet to chamber 14. Brazed, leak-proof joints connect pipes 16 and 30 to chambers 12 and 14. Preferably pipes 16 and 30 are cut from the same tubular stock. Chamber 14 is defined by a half shell 34 and a cover or end cap 36. Half shell 34 is preferably a deep draw stamping made from the same tooling used to stamp shells 18 and 20. The end of cap 36 is provided with openings 37 and the diameter thereof is enlarged as at 38 to slidably fit snugly over the outside of the large open end of half shell 34.

A spark-arresting screen 40 and the structure for supporting the same within chamber 14 are illustrated more clearly in FIG. 5. Screen 40 is in the shape of a hat having a brim 42 and a crown 44 supported on brim 42. In the illustrated embodiment, crown 44 comprises a flat circular top or end 46 spaced axially downstream from brim 42 and a cylindrical side wall 48 supporting top 46 on brim 42. The plane of top 46 is parallel to the plane of brim 42 and the axis of side 48 is perpendicular to these two planes. An annular mounting ring 50 supports screen 40 within chamber 14. Brim 42 is fixedly secured to an inturned circular flange 52 of ring 50. Attachment is preferably performed by resistance welding brim 42 to flange 52 with the aid of a plurality of circularly arranged weld projections 54 protruding from the upstream side of flange 52. Such attachment prevents exhaust leakage between brim 42 and flange 52 and insures that the exhaust can pass only through screen 40. The cylindrical side wall of ring 50 is provided with a pair of diametrically opposed extruded holes 56 which receive self-threading sheet metal screws 58 (FIG. 1) for detachably mounting ring 50 within chamber 14. Screws 58 extend through suitable clearance holes in cover 36 and half shell 34 to threadably engage holes 56. The axial positioning of ring 50 and cover 36 is facilitated for assembly purposes by an outturned circular flange 60 on ring 50 and a circular offset 62 formed in cover 36.

Four identical U-shaped brackets 64 are welded to the outside of chambers 12 and 14 and are used to attach a curved heat shield 66 in outwardly spaced enveloping relation about chambers 12 and 14. The shape of bracket 64 is best seen in FIG. 6. Bracket 64 comprises a top 68 curved to closely match the curvature of heat shield 66 and a pair of flat sides or legs 70 projecting downwardly from top 68 from opposite side edges thereof. An extruded hole 72 is centrally provided in top 68 and receives a sheet metal screw 73 for attaching heat shield 66. A pair of semi-circular weld projections 74 are formed at the lower opposite ends of each side 70.

The edge 76 of side 70, which extends between projections 74, is provided with a curvature having a radius of curvature not substantially greater than and preferably equal to the radius of chambers 12 and 14. This construction permits brackets 64 to be attached to chambers 12 and 14 in the following way. Brackets 64 are positioned by a suitable welding fixture on chambers 12 and 14 oriented as shown in FIGS. 1 and 2 so that projections 74 abut the curved outside surfaces thereof, edges 76 being spaced radially outwardly from said surfaces. Brackets 64 are then projection welded to chambers 12 and 14, causing projections 74 to fuse into shells 12 and 14 as the brackets are pressed thereagainst until edges 76 abut the outer surface of chambers 12 and 14. If the curvature of edge 76 is equal to the curvature of chambers 12 and 14, abutment will be substantially along the entire length thereof; if less than, then contact will be only at the portions immediately adjacent projections 74; if slightly greater than, then only the center of edge 76 will abut the chamber. Thus, edge 76 may then be readily brazed along its length to chambers 12 and 14, despite curvature mismatch, to complete the attachment.

Heat shield 66, in the illustrated embodiment, surrounds the muffler for approximately 270 degrees rather than a full 360.degree. to allow close clearance mounting of muffler 10 with the gap in shield 66 oriented inboard of the mini-bike. Heat shield 66 extends for substantially the full length of the muffler and thus serves to prevent a riding operator or passenger from being accidentally burned by the muffler when hot. Heat shield 66 is provided with a plurality of rows of staggered elongated slots 78 (FIG. 1) which facilitate the circulation of air over the outside surfaces of chambers 12 and 14, help cool the shield and vent radiant heat. Shield 66 is made sufficiently thick so that it also rigidifies the muffler structure. Because heat shield 66 is supported only by four small brackets 64, conductive transfer of heat from chambers 12 and 14 to heat shield 66 is minimized.

When assembly 10 is installed in its intended application on a mini-bike engine or the like, the pulsating flow of hot exhaust gases from the engine enters chamber 12 through pipe 30 as indicated by arrow 79 (FIG. 1). The solid central portion 23 of baffle 24 blocks any direct flow from pipe 30 to pipe 16. Consequently, the flow follows the direction of arrows 80 through orifices 25 in baffle 24. In turn, the exhaust follows the path of arrows 82 from chamber 12 through pipe 16 and into chamber 14. The exhaust passes through top 46 and side 48 of screen 40 as illustrated by arrows 84. Screen 40 traps carbon particles having a size greater than the openings in the screen to thereby prevent the discharge of potentially dangerous sparks from the muffler. The exhaust gases finally exit through openings 37 in cover 36 as indicated by arrows 86.

A muffler 10 constructed in accordance with the present invention is operable to limit the noise of a running engine to a tolerable level and achieves satisfactory spark-arresting efficiency for all running conditions of the engine. Due to carbon accumulation caused by the relatively fine mesh of the spark-arresting screen, it is necessary to periodically remove such collected contaminants from the screen. Screen 40 is readily accessible for such cleaning by unfastening screws 58 and removing cover 36. Preferably, tool clearance or openings (not shown) are provided in heat shield 66 so that heat shield 66 does not have to be removed to render screws 58 accessible for removal. Screen 40 may then be removed from the large open end of half shell 34 for cleaning. The screen may continue to be used so long as it is neither torn nor punctured. By way of example, a stainless steel screen having rectangular openings of 0.023 inch by 0.023 inch and a wire diameter of 0.014 inch has been successfully used with the disclosed assembly. Preferably, the flow through area of screen 40 is approximately 200 percent greater than the exhaust port area of the engine with which the muffler is used.

The structure of the present invention is susceptible to a variety of modifications which enhance the adaptability thereof to numerous applications while still retaining many common parts. A first modification may be made to the dimensions of screen 40. More specifically, the axial dimension of side wall 48 may be increased and/or its diameter decreased to change the relative proportions of screen 40. In a second modification, a circular disk 88, shown only in FIG. 5, may be positioned within crown 44 of screen 40 and attached to top 46 by welding projections 90 provided thereon. While disk 88 improves muffler attenuation, the size thereof relative to screen 40 is such that satisfactory arresting efficiency is maintained at all flow rates. In a third modification, the length of connecting pipe 16 may be changed to thereby vary the tonal quality of the muffler. In a fourth modification, the diameter of chambers 12 and 14 may be varied while still using brackets 64 so long as the curvature of edge 76 is not substantially greater than that of the chambers. In a fifth modification, the length of either one of the chambers may be varied while still retaining the use of the other chamber. In a sixth modification, various types of heat shields, which may be decorative as well as functional, may be used. In a seventh modification, screen 40 may be turned around 180.degree. from its position shown in FIG. 1 so that crown 44 of the screen is positioned upstream of brim 42. With either orientation, the hat shape of screen 40 provides an increase in total screen area which in turn decreases power loss due to screen clogging as well as improving screen life and efficiency. Therefore, without further elaboration, it can be seen that the spark-arresting muffler of the present invention can be mass produced to accommodate various sizes of engines with the use of a minimum number of unique parts and a maximum number of interchangeable parts.

Claims

I claim:

1. A spark-arresting muffler comprising a first expansion chamber adapted to communicate with an engine for receiving exhaust therefrom, a second expansion chamber spaced axially of said first chamber and adapted to communicate with the atmosphere for discharging exhaust thereto, means communicating the first chamber with the second chamber for conducting exhaust from the former to the latter, a spark-arresting screen positioned within the second chamber so as to be disposed in the path of engine exhaust passing through the second chamber for removing particles of selected size from the exhaust, means for removably mounting the screen within said second chamber, heat shield means axially overlapping and at least partially surrounding said chambers and means for securing said heat shield means to said chambers to thereby structurally rigidify the muffler.

2. The muffler of claim 1 wherein said first and second chambers are cylindrically shaped and substantially coaxial, said means communicating said first and second chambers comprising a pipe coaxial with said chambers and having a diameter less than the diameter of said chambers.

3. The muffler of claim 2 further including baffle means within said first chamber having a solid central portion disposed about the chamber axis for preventing entering exhaust gas from traveling in a straight line to said connecting pipe and having aperture means radially spaced from said central portion through which exhaust may be passed.

4. The muffler of claim 1 wherein said second chamber comprises a removable cap through which exhaust is discharged from said second chamber, said screen being manually accessible for removal when said cap is removed from the muffler.

5. The muffler of claim 1 wherein said means for mounting the heat shield means to said first and second chambers comprises a plurality of U-shaped brackets each having a central portion providing a heat-shield-engaging surface spaced radially outwardly of the periphery of said chambers and supported thereon by axially spaced-apart legs extending from said central portion, said legs each having a radially inner edge attached by fusion metal to said chambers, and means for securing said heat shield means to said heat-shield-engaging surface.

6. The muffler of claim 1 wherein said spark-arresting screen comprises a hat-shaped screen having crown and brim portions, said brim portion lying substantially in a plane perpendicular to the axis of said muffler and said crown portion being supported on said brim portion radially inwardly thereof and extending axially of the muffler.

7. The muffler of claim 6 wherein said means for removably mounting said screen within said second chamber comprises a ring permanently attached to said brim portion and means for removably mounting said ring on said chamber.

8. The muffler of claim 7 wherein said ring comprises a circular flange extending radially of the muffler axis and an axially extending cylindrical portion connected to the outer periphery of said radial flange, said second chamber being cylindrically shaped and having an inside diameter slightly greater than the outside diameter of said cylindrical portion, said means for removably mounting said screen comprising sheet metal screws extending radially through the wall of said chamber and threadably engaging said ring cylindrical portion.

9. The muffler of claim 7 wherein said crown projects axially through said ring.

10. The muffler of claim 6 wherein said crown comprises an end portion spaced axially of said brim and extending perpendicular to the muffler axis and connected to said brim by a cylindrical side wall portion coaxial with the muffler axis.

11. The muffler of claim 6 further including a disk centrally mounted in said crown perpendicular to the muffler axis for limiting exhaust flow through the central portion of the crown.

12. A bracket for mounting a heat shield to a curved peripheral outer surface of an axially-extending muffler comprising a central portion having a heat-shield-engaging surface and a pair of axially spaced-apart legs adapted to extend radially between said central portion and said peripheral muffler surface when said bracket is attached to said muffler, each of said legs having a radially inner edge at its free end shaped for preliminary engagement with the muffler surface, said inner edge being defined by a pair of projections arcuately spaced apart about the muffler axis and adapted to be projection welded to said muffler surface and a curved intermediate edge extending arcuately between said projections about the muffler axis.

13. The bracket of claim 12 wherein said intermediate edge has a radius of curvature not substantially greater than the radius of said curved peripheral muffler surface.

14. The bracket of claim 12 wherein said heat-shield-engaging surface of said central portion of said bracket is arcuately curved about the muffler axis.

15. The bracket of claim 14 further including means on said heat-shield-engaging portion for attaching said heat shield thereto.

16. The bracket of claim 15 wherein said legs are perpendicular to the axis of said muffler.

17. A spark arrester for interchangeable tandem installation in series downstream of a muffler or a tailpipe comprising a hat-shaped screen member having wire mesh crown and brim portions, said crown portion being supported on said brim portion radially inwardly thereof and extending axially thereof, a cylindrical shell having a closed end with a central aperture adapted to coaxially receive the tailpipe or a muffler outlet pipe of the same size, said shell having an axially opposite open end defined by a cylindrical wall larger in diameter than said aperture and removably receiving said screen therein, and a perforated cap having outlet means at one end thereof and having a cylindrical flange at the other opposite end thereof with said flange receiving said cylindrical wall of said shell therein, said screen member having a cylindrical outer flange radially aligned with said cylindrical wall of said shell and said flange of said cap, and detachable fastener means extending radially through said cap and screen flanges and said shell wall.

18. The arrester as set forth in claim 17 wherein said cap has a tubular portion concentric with said cap flange and said cap flange is enlarged diametrically relative to said tubular portion to slidable fit snugly over the outside of said cylindrical wall of said shell, said outlet means being spaced axially downstream from said crown of said screen at the end of said tubular portion remote form said cap flange.

19. The arrester as set forth in claim 20 wherein said outlet means comprises an end wall of said cap having a plurality of perforations therethrough.