Muffler assembly for internal combustion engines

May 10, 1955 _H _ _BACKM._{M 0}

n. r. BACKMAN 2

MUFFLER ASSEMBLY FOR INTERNAL COMBUSTION ENGINES Filed Nov. 5, 1953

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United States Patent Office „ . _M²’^708,e°⁶

Patented May 10, 1955

2,708,006

MUFFLER ASSEMBLY FOR INTERNAL COMBUSTION ENGINES

Hans Fredrik Backman, Alby, Sweden

Application November 5, 1953, Serial No. 390,377

Claims. (Cl. 181—55)

The present invention broadly relates to mufflers for internal combustion engines, and more particularly to certain new and useful improvements in muffler assemblies for four-cycle type internal combustion engines.

The muffler is of the kind composed by three aligned sections in series arrangement, the intermediate section consisting of at least three tubular elements coaxially nested in space interrelation, and the invention is mainly characterised by the fact that, firstly, for coaxially locating said tubular elements relative to each other, the innermost tubular element and the intermediate tubular element or elements is or are provided externally with a circumferential series of radial ribs arranged in uniformly spaced interrelation and longitudinally coextensive with said tubular elements, both said ribs and said intermediate tubular element or elements being made of perforated sheet-metal and said ribs dividing the annular interspaces into a plurality of longitudinally extending gas passages, secondly, the upstream or inlet section, which is connectable at its upstream end to the exhaust pipe of said engine, is provided at its downstream end adjacent to said intermediate section with an insert element comprising a plurality of radially inwardly extending webs provided at their radially outer ends with projections extending axially upstream along, and in contact with, the conically tapering internal casing wall of said inlet section, said insert element being adapted to cause uniform distribution of the exhaust gases into said longitudinal passages, and, thirdly, the rear or outlet section comprises a plurality of axially but slightly helically extending gas passages connecting to said longitudinal passages and opening towards the outlet end of the muffler assembly.

It has been found that, in practice, the muffler assembly according to the present invention provides an excellent silencing effect, and at the same time the operating efficiency of the engine will be improved which, in its turn, involves improved fuel economies.

According to a further feature of the invention, a still better operation characteristic of the muffler assembly may be obtained by resiliently axially displaceably and rotatably mounting an exhaust driven rotor element on a shaft coaxially secured within the innermost tubular element of the intermediate section and having its upstream end projecting into the upstream or inlet section for carrying said rotor at the upstream side of said insert element.

Such an arrangement entails, inter alia, a further improved distribution of the exhaust gases into the longitudinal passages, involving improved efficiency of the muffler assembly.

A spring is arranged to urge the rotor yieldingly toward the smaller diameter inlet end of the conically convergent inlet section against the flow direction of the exhaust gases. At low engine speeds substantially all of the exhaust gases are thus constrained to flow through the rotor blades. At high engine speeds the increased flow of exhaust gases forces the rotor in a downstream direction against the action of the spring and allows a substantial portion of the exhaust gases to flow past the peripheral edges of the rotor without passing through its blades. The rotor thus provides a variable throttling ac5 tion with respect to the exhaust gases which automatically accommodates itself to the flow rate of the exhaust gases through the muffler.

The invention will now be described more fully in conjunction with the accompanying drawing illustrating by 10 way of example a muffler assembly according to a preferred embodiment of the invention, and in which:

Fig. 1 is a longitudinal section through the muffler assembly according to this embodiment,

Fig. 2 is a cross-sectional view thereof taken on line 15 Π—II in Fig. 1,

Fig. 3 is a cross-sectional view thereof taken on line HI—HI in Fig. 1, and

Fig. 4 is a cross-sectional view of the same taken on line IV—IV in Fig. 1.

Referring now to the accompanying drawing, the muffler assembly illustrated therein consists of three sections A, B, and C arranged in series and of which the intermediate section B is composed by a plurality of, and in the present example five, tubular elements 1, 2, 3, 4, 15 and 5 coaxially nested one within the other in radially spaced interrelation. For centering the tubular elements relative to each other the innermost tubular element 1 and the intervening tubular elements 2, 3, and 4 are provided externally with a plurality of radial ribs 6 circum30 ferentially spaced in uniform distribution and coextensive with the tubular elements 1 to 5, said ribs 6 being, as well as the intermediate tubular elements 2, 3, and 4, made of perforated sheet-metal. The axially extending gas passages 7 formed by these tubular elements and the 35 associated radial ribs 6 are open at both ends at which they communicate with the front or inlet section A and the rear or outlet section C, respectively.

The inlet section A, the outer casing wall of which, 8, is, in the embodiment illustrated, a continuous extension 40 of the outermost tubular element 5 of the intermediate section B, and consists of an outlet end portion tapering conically in the upstream direction and merging into a cylindrical inlet end portion 9 adapted, in any suitable manner, to be connected to the exhaust pipe (not shown) of the internal combustion engine. The front or inlet section A is provided in its outlet end adjacent to the intermediate section B with an insert element consisting of a plurality of inwardly extending radial webs 10 having at their outer upstream ends axially directed extensions 11 which project upstream along, and in contact with, the inner walls of the tapering end portion 8, said webs 10 together with their extensions or projections 11 being made of perforated sheet-metal. This insert element 10, 11 has for its purpose to cause an even dis55 tribution of the exhaust gases into the passages 7 of the intermediate section B.

Within the innermost tubular element 1 of the intermediate section B a shaft 12 is coaxially secured, said shaft being extended into the inlet section A. Onto this 60 shall 12 is slipped a socket member 13 having its upstream end closed and which, through the intermediary of a conically divergent portion 14, merges into a sleeve or skirt 15 of larger diameter, said sleeve or skirt being loosely slipped over the innermost tube 1 of the inter05 mediate section B and both axially slidably and rotatably supported on the shaft 12 by means of a ball bearing 16. On these parts 13, 14, 15 forming a hub a rotor 17 comprising a plurality of radial vanes is mounted to be rotated by the action of the engine exhaust gases. Between the 70 axially siidable ball bearing 16 and a collar 18 on the shaft 12 a compression coil spring 19 is positioned and is arranged to urge the hub 13—14—15 and rotor 17

3.708,006 yieldingly towards the convergent inlet end of the muffler assembly. In order to enable the sleeve 15 of the hub to move freely over and around the tubular element 1, as will appear from Fig. 1, the ribs 6 are cut away axially at their bases, adjacent the tubular element 1.

The rotor 17 has for its purpose, firstly, to provide a uniform distribution of the exhaust gases, and, secondly, in response to a reduction in the engine speed, to move in the upstream direction under the yielding influence of the helical compression spring 19 and thereby bring the periphery of the rotor 17 into closer proximity to the conically tapering inner wall surfaces of the outer casing 8 of the inlet section A. The periphery of the rotor 17 acting in cooperation with the convergent casing 8 constrains a greater portion of the exhaust gases at low engine speeds to pass through the vanes of the rotor 17 than at higher engine speeds when the rotor is forced downstream against the action of spring 19 by the increased pressure of the exhaust gases. As the rotor 17 moves downstream, a greater portion of the exhaust gases are permitted to flow past the periphery of rotor 17 as the diameter of the casing 8 progressively increases. An automatic variable throttling action is thus obtained. In order to take up axial thrust when the rotor 17 is in its extreme downstream position, as shown in Fig. 1, a ball 26 is disposed in the socket 13 between the upstream ends of shaft 12 and socket 13, the ball 26 serving to limit the downstream movement of the rotor 17.

The rear or outlet section C of the muffler assembly consists, in part, of a conical outer casing 20 having its end portion adjacent to and communicating with the intermediate muffler section B, the casing 20 being slipped over the tubular element 5 thereof and secured thereto by bolts 21, and in part by an interiorly disposed cylindrical part 22 in the form of a rearward extension of the tubular member 1. Between these two parts 20 and 22 helically extending partitions 23 are interposed forming helical passages 24 which receive the gases discharged from the passages 7 of the intermediate section B and impart to said gases a vortex motion. In the embodiment illustrated, the outer casing 20 of the rear section C is provided externally with two diametrically disposed radially and longitudinally extending fins 25 serving as handles for use when assembling and dismantling the muffler assembly.

It will be understood that the invention is not restricted to the embodiment specifically described in the foregoing and illustrated in the accompanying drawing since the same is susceptible of various modifications without departing from its scope as defined in the appended claims.