Peripheral return flow muffler

A muffler for attenuating sound in internal combustion engine exhaust systems comprises an inner shell subdivided into an inlet chamber and an outlet chamber, inlet and outlet tubes for the muffler opening into the respective chambers, and an outer shell surrounding the inner shell but spaced transversely from it to provide a passage between the outer periphery of the inner shell and the inner periphery of the outer shell through which gas flows toward the inlet end of the muffler from the inlet chamber to the outlet chamber.

SUMMARY OF THE INVENTION 
It is the purpose of this invention to provide a return flow or tri-flow 
type muffler structure for exhaust systems (or other pulsating gas flow 
systems) that is effective in reducing the sound level of the system from 
both the objective and subjective standpoints, produces an acceptable 
backpressure and horsepower loss, and is small enough to be packageable on 
the vehicle for which it is intended. 
The invention achieves this purpose by utilizing the space between inner 
and outer shells as a return flow gas passage connecting inlet and outlet 
chambers that are formed within the inner shell and that communicate, 
respectively, with the open ends of inlet and outlet gas flow tubes.

DETAILED DESCRIPTION OF THE INVENTION 
The muffler 1 has an oval tubular outer shell 3 that is closed at its 
opposite ends by an inlet header 5 and an outlet header 7, the headers 
having outer edges that are interlocked with the ends of the shell in gas 
tight joints 9. An oval, open-ended inner tubular shell 11 is 
symmetrically positioned inside the outer shell and has an outer surface 
which is in contact with the inner surface of the outer shell, the 
contacting areas of the respective surfaces preferably being rather large 
as can be seen in FIG. 2. The two shells are preferably spotwelded to each 
other, as indicated at "x" in FIG. 2, along a midplane bisecting the major 
diameters of the shells 3 and 11. The open inlet and outlet ends 13 and 
15, respectively, of the inner shell are spaced inwardly from the inlet 
and outlet headers 5 and 7. A transverse partition 17, located at 
substantially the longitudinal midpoint of shell 11, has a peripheral 
flange 19 that is spotwelded to the shell 11. The wall of partition 17 has 
a collar 21 formed in it which is coaxial with an inlet collar 23 formed 
in the inlet header 5 and also a collar 25 which is coaxial with an outlet 
collar 27 formed in the outlet header. Except for the collars, the 
partition 17 is preferably imperforate. 
An inlet bushing 29 is mounted in and spot welded to the collar 23 and has 
a reduced diameter inner portion 31 which receives and is spotwelded to 
the outer end of an inlet tube member 33, the other end of the tube being 
supported in and spot welded to the partition collar 21. 
An outlet tube member 35 comprises a tubular outlet shell 36 which has a 
bushing portion 37 mounted in and spotwelded to the collar 27 in header 7. 
The outer shell 36 has reduced diameter portions 39 which provide annular 
inner surfaces that engage and support a gas flow tube 41. The tube 41 has 
an inner end that fits within the collar 25 and is spotwelded to it and an 
outer end which opens into the bushing 37 and is spotwelded to the 
outermost of the reduced diameter portions 39. 
In the embodiment illustrated, the outlet tube 41 has a pair of louver 
patches or sets of openings 43 and 45 which open, respectively, into 
closed annular chambers 47 and 49 that are formed between the tube 41 and 
the outer shell 36 and between the reduced diameter portions 39. The 
louver patches 43 and 45 with the chambers form high frequency attenuating 
spit chambers as is well known. In the embodiment shown, the inlet tube 33 
also has a patch of louvers 51 extending over a major part of its length 
and opening into a chamber 53 formed on the inlet side of the partition 
17. These louvers in combination with the fairly large chamber 53 serve to 
attenuate medium to high frequency sounds. 
While the inlet tube is shown as perforated because of the louver patch 51, 
it is within the broad purview of this invention for it to be imperforate. 
Similarly, modifications can be made in the outlet tube member, such as 
the use of only a single tube, such as tube 41, either with or without 
perforations opening directly into chamber 55 that is between the 
partition 17 and the outlet header 7. Various combinations and 
arrangements of perforate and/or imperforate inlet and outlet tube members 
can be utilized within the broad framework of the invention. 
The inner shell 11 has a smaller major diameter than the outer shell 3 and, 
therefore, is transversely spaced inwardly from it on each side to form 
longitudinal extending peripheral passages 57 and 59 running the full 
length of the inner shell 11. The ends of the inner shell are spaced from 
the inlet and outlet headers 5 and 7 to form, respectively, cross chambers 
61 and 63 that connect the ends of the peripheral passages 57 and 59 with 
the chambers 53 and 55 inside of the shell 11. 
In operation, gas enters the inlet bushing 29 and flows through the inlet 
tube 33 into the enlarged chamber 55 which may, therefore, be considered 
as an inlet chamber. Gas in the chamber 55 enters the crossover chamber 63 
and reverses its direction of flow to enter peripheral passages 57 and 59 
and return toward the inlet end of the muffler. As it leaves the passages 
57 and 59, it enters the crossover chamber 61 and then flows to the 
enlarged chamber 53 which may be considered to be an outlet chamber. From 
there it flows into the outlet tube 41 and leaves the muffler through the 
outlet bushing 35. Some bypass flow through louvers 51 into the outlet 
chamber 53 can occur in the arrangement illustrated. Similarly, if the 
outlet tube member shell 36 were omitted some bypass flow could take place 
in the chamber 55 directly to the outlet tube. 
In addition to the sound attenuation that occurs as a result of the louver 
patches 43, 45, and 51, there is attenuation due to the changes in cross 
sectional size of the passages through which the gas must flow. The inlet 
chamber 55 and the outlet chamber 53 act as relatively large volume 
compliance chambers. The chambers 61 and 63 will tend to function in 
combination with the adjacent chambers 55 and 53 as compliance volumes. 
The peripheral passages 57 and 59 are considerably smaller in cross 
section than the chambers and serve as inertance passages connecting the 
compliance volumes. Preferably, the longitudinal mid plane of the muffler 
1, and therefore the midpoints of the peripheral inertance passages 57 and 
59, is located substantially at a point of maximum compliance in the 
exhaust system for reasons set forth in U.S. Pat. No. 3,807,527 issued 
Apr. 3, 1974. When so located, the muffler 1 functions to attenuate sound 
in accordance with classic acoustic principles and also will tend to 
convert high energy exhaust pulses into lower energy pulses as described 
in U.S. Pat. No. 3,807,527. 
Thus, the invention provides a relatively small and packageable muffler of 
the tri-flow or return flow type (return flow taking place through 
passages 57 and 59) that is effective in the objective and subjective 
attenuation of sound and in reducing the sound level of a pulsating gas 
system, and yet does not have restrictions or contours that produce an 
excessive back pressure or horsepower loss. 
Modifications, some of which have been mentioned above, may be made in the 
specific structure shown without departing from the spirit and scope of 
the invention.