Automotive exhaust system

An improved exhaust system (24) uses the entire length of the system in which to perform the essential functions of muffling noise and converting unburned hydrocarbons. The improved exhaust system (24) performs these functions with a relatively uniform minimum diameter along its length. The exhaust system (24) includes a uniform outer diameter pipe (26) and elements (44) of porous material (46) forming a plurality of filters (50) through which the exhaust gas flows and which attenuates sonic frequency sound waves in the exhaust. The elements (44) are preferably elongate strips which may be folded into rectangular filters (60) or elliptical filters (90). The rectangular filters can be folded sufficiently to form squares and the elliptical filters to form circles. The rectangular filters define passageways (62-68) between the edges of the filters and inner wall (70) of the pipe (26) which further attenuates exhaust noise through imbalances in the gas flow. The elliptical filters maintain continuous contact with the inner surface of the pipe. In a second embodiment, an exhaust system (110) includes a liner (112) having a plurality of airfoil baffles (114) extending into the gas flow to muffle the exhaust. A third embodiment is formed by an exhaust system (130) having a woven wire fabric (132) along its interior to attenuate the exhaust sounds. All of the filters or elements can be coated with alumina and a platinum group metal for catalytic converting.

TECHNICAL FIELD 
This invention relates to systems for exhausting combusted gases from 
internal combustion engines, and in particular for exhausting combusted 
gases from internal combustion engines in vehicles. 
BACKGROUND ART 
The exhaust gases generated by internal combustion engines such as found in 
vehicles are exhausted through an exhaust system. The typical exhaust 
system includes a relatively small diameter pipe extending from the 
exhaust manifold to an opening to the atmosphere with one or more muffler 
sections along the pipe. The typical muffler is a heavy, bulky device of 
much larger diameter than the remainder of the system. 
The muffler is employed to break down within a relatively short distance 
the sonic shock waves generated by the explosive release of the combusted 
air/fuel mixture from the cylinders. The shock waves include sound waves 
of various frequencies. The muffler is designed to break up the sound 
waves of various frequencies by structure well understood in the art. 
The large size of the muffler results in a greater likelihood of road 
damage and imposes space limitations which must be designed for in the 
vehicle. When the exhaust system cools, the large, confined space within 
the muffler condenses moisture, which contributes to rusting and 
deterioration of the muffler. A muffler is relatively complex in 
construction and requires several different pieces of metal to be 
processed in different techniques. The muffler is therefore relatively 
expensive and heavy. 
In recent years, the exhaust system has also been required to eliminate 
unburned hydrocarbons from the exhaust gases. This function has been 
performed by a separate catalytic converter. The converter is essentially 
an add on to the conventional exhaust system and again forms a relatively 
bulky container. The exhaust gases with unburned hydrocarbons flow into 
the converter and are passed over catalysts from the precious metals of 
the platinum group, including platinum, palladium and rhodium, all plated 
over alumina. The alumina can be in pellet form or carried on a substrate 
of extruded ceramics. The converter acts to oxidize the hydrocarbons to 
reduce the pollutants in the atmosphere. Again, the converter's bulk 
requires the design of the vehicle to be specially adapted to accept the 
converter. The oxidation of the unburned hydrocarbons generates a great 
deal of heat and the converter reaches a high temperature. The vehicle 
must also be designed to insure no damage results from this high 
temperature. 
The conventional muffler, converter, interconnecting pipe, exhaust pipe and 
tail pipe are connected by clamps and mounted on the vehicle through 
mounting brackets. The various components must be assembled and positioned 
on the vehicle on the assembly line. The relative complexity of the design 
results in a lengthy and costly assembly operation. 
A need exists for an improved exhaust system which retains the muffling and 
oxidation features of the conventional muffler and converter with 
reduction of the size, cost and weight of the system. This would increase 
the flexibility of vehicle design. There is also a need to develop an 
improved exhaust system which reduces assembly time and material cost with 
equivalent or improved durability during use. A recent attempt to achieve 
some of these goals is the device in U.S. Pat. No. 3,746,126 issued July 
17, 1973 to de Cardenas. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the present invention, an exhaust system 
for exhausting gases from an internal combustion engine having an exhaust 
manifold on a vehicle is provided. The system includes a uniform diameter 
pipe extending from the engine exhaust manifold to an opening to the 
atmosphere. The pipe carries the exhaust gases within from the engine to 
the atmosphere. A plurality of porous filters are positioned within the 
pipe along its length to muffle the noise of the exhaust. The porous 
filters are formed of at least one section of expanded metal. Each section 
is folded at preselected positions along its length to form individual 
filters between the folds with each filter spaced a predetermined distance 
from the filters formed by a common fold. 
In accordance with another aspect of the present invention, the 
predetermined distance between filters is varied along the pipe to enhance 
the muffling of a range of sonic frequencies. The exhaust system can also 
include at least one section along the length of the pipe without filters 
to form a mixing chamber in which the separated portions of the shock wave 
cancel one another. 
The filters can have a rectangular (including square) cross section, 
forming four arcuate channels between the filters and inner wall of the 
pipe which assist in dissipating the shock waves. The filters can have an 
elliptical (including circular) cross section between the folds to permit 
the filters to contact the inner wall of the pipe substantially about its 
inner circumference. The element can be twisted in a spiral shape to form 
the filters with the edges of the elements contacting the inner surface of 
the pipe. 
In accordance with yet another aspect of the present invention, the porous 
material can be selected from the group comprising metal, ceramics or high 
temperature plastics. The openings in the porous material can be of varied 
dimensions to enhance muffling of a range of sonic frequencies and can 
include airfoil sections to enhance muffling. The openings can be created 
by expanding the material, by weaving material of linear form or by other 
suitable methods. 
In accordance with yet another aspect of the present invention, portions of 
the porous material are coated with alumina and with metals from the 
platinum group located along the length within the pipe to oxidize 
unburned hydrocarbons in the exhaust. The pipe may be a continuous piece 
along its entire length with the porous material extending within 
substantially along the entire length of the pipe or with material 
concentrated in one or more areas. 
In accordance with another aspect of the present invention, an exhaust 
system for exhausting gases from an internal combustion engine having an 
exhaust manifold on a vehicle is provided. The exhaust system includes a 
uniform diameter pipe extending from the engine exhaust manifold to an 
opening to the atmosphere. The pipe carries exhaust gases therein to the 
opening. At least one section of liner is positioned within the pipe as 
the pipe is formed, the section includes a plurality of airfoil baffles 
extending into the gas flow for muffling the exhaust. 
In accordance with another aspect, the airfoil baffles may be selected from 
the group including metal, high temperature plastic and ceramics. The 
liner can be constructed from a continuous strip with the airfoil baffles 
stamped from the strip and the strip folded to form a cylinder welded 
along its edges within the exhaust pipe as the pipe itself is being formed 
and welded. 
The airfoil baffles can be varied in length, section, thickness, angle of 
attack and frequency along the length of the liner to enhance the muffling 
of the exhaust system. 
In yet another embodiment of the present invention, an exhaust system is 
provided which includes a uniform diameter pipe with woven wire fabric 
therein to muffle the exhaust. The wire can be of various diameters and 
cross sections with the resulting fabric extending along the length of the 
pipe to enhance muffling of a range of sonic frequencies in the exhaust.

DETAILED DESCRIPTION 
Referring now to the Drawings, wherein like reference characters designate 
like or corresponding parts throughout several views, FIG. 1 illustrates a 
vehicle 10 incorporating an internal combustion engine 12 for propulsion. 
The engine 12 includes an exhaust manifold 14 which collects combusted 
exhaust gases from the engine from one or more cylinders for disposal in 
the atmosphere. 
The components illustrated in dotted line represent a conventional muffler 
20, a conventional catalytic converter 18 and conventional clamps 21. The 
converter and muffler are interconnected by pipe 22. It can be readily 
seen that the design of the vehicle 10 must be especially adapted to 
accommodate the relative bulk of the converter 18 and muffler 20. It can 
also be seen that the conventional system is made up of many parts which 
must be assembled concurrently or before the vehicle is assembled on the 
assembly line. 
The exhaust system 24 illustrated in FIG. 1 forms a first embodiment of the 
present invention. As can be readily seen, the exhaust system includes a 
continuous pipe 26 having a uniform outer diameter with a flange 28 at one 
end for connection to the exhaust manifold 14. The opposite end of the 
pipe 26 has an opening 30 proximate the rear of the vehicle for exhausting 
the combusted gases from the engine to the atmosphere. The pipe 26 can 
have bends 32, 34, 36, 38, 40, 42 and 43 along its length to accommodate 
the construction of the vehicle, including the rear axle and other 
structures. As will be described in greater detail, the exhaust system 24 
acts to muffle the exhaust of the engine and can also include catalytic 
converting elements to oxidize the unburned hydrocarbons to reduce 
atmospheric pollution. 
The interior details of the exhaust system are best described in reference 
to FIGS. 2-4. FIG. 2 illustrates an element 44 of expanded porous material 
46. The element 44 is folded along folds 48 to form individual spaced 
rectangular filters 50. The rectangular filters can be folded sufficiently 
to form square filters as shown. The webbing 52 of each filter 50 defines 
a plurality of holes 54 which permit the exhaust gases to pass through the 
filters. The webbing breaks up and destroys the sonic frequency shock 
waves in the exhaust generated by the explosive release of the combusted 
air/fuel mixture from the engine 12. 
The bending angle 56 of the folds 48 is selected to provide an optimal 
cross section to the filters 50. In the embodiment in FIGS. 2-4, the 
material is folded at angle 56 approaching 180.degree. to provide square 
filters 50 transverse to the exhaust gas flow represented by the arrow 58. 
In a modification illustrated in FIGS. 6A-C, the bending angle 56 is 
folded through an angle less than 180.degree. to provide an expanded 
element with rectangular filters 60 which are not transverse to the 
direction of gas flow. The bending angle 56 can be varied along the length 
of the element to enhance the muffling of a range of sonic frequencies in 
the exhaust flow. Steel forms the preferred material which forms the 
expanded material 46. However, a high temperature plastic, ceramic or 
other material may be used. One exhaust system constructed in accordance 
with the teachings of the invention employed holes 54 having a measurement 
of one-quarter inch by one-eighth inch and was found to satisfactorily 
muffle the exhaust with acceptable back pressure. 
With rectangular filters 50 (including the square filters 50 shown), four 
arcuate passageways 62, 64, 66 and 68 are formed between the inner wall 70 
of the pipe 26 and the outer edges 72 of the filters. Portions of the 
shock waves in the exhaust enter the passageways. The turbulent imbalances 
in the gas flow between the passageways and gas filtering through filters 
50 enhance the disintegration of the sonic frequency shock waves and 
enhance the muffling. 
While element 44 can fill the entire length of the pipe 26, the preferred 
construction is to incorporate one or more mixing chambers 74 along the 
length of the pipe as illustrated in FIG. 5. The mixing chamber can be 
formed between two elements 44 or a single continuous element may have a 
portion 76 extending linearly along the mixing chamber as shown in FIG. 5. 
The mixing chambers mix the separated portions of the disintegrating shock 
waves so that they cancel one another to further enhance the muffling. By 
having a linear section 76, the element 44 may extend through the entire 
length of the pipe in one continuous strip to ease manufacture. Ideally, 
to attenuate the maximum range of sonic frequencies, the exhaust system 24 
will have a series of filters and mixing chambers, with the filters having 
varied hole sizes to provide attenuation of the shock waves. The pattern 
may be repeated along the length of the exhaust system to form several 
stages of targeted sonic disintegration for each frequency. The webbing 52 
can also be formed with various airfoil cross-sectional shapes to move the 
gas within the pipe to enhance attenuation. 
The exhaust system 24 can also act as a catalytic converter. Conventional 
catalytic converters are constructed in two basic modes. One mode is to 
provide a number of alumina pellets coated with a platinum group metal. 
The platinum group includes platinum, paladium and rhodium. In the second 
mode, a ceramic is coated with alumina and then with a catalyst from the 
platinum group. The catalyst facilitates the oxidation of the unburned 
hydrocarbons in the exhaust gas to reduce hydrocarbon pollution. 
The webbing 52 is coated with alumina 78 and a platinum group metal 80 as 
best seen in FIG. 3A to perform the catalytic converting function in 
exhaust system 24. If steel forms expanded material 46, it is desirable to 
coat the steel with ceramic prior to coating with alumina and platinum 
group metal 80. 
A second modification of exhaust system 24 is illustrated in FIGS. 7A-C. 
The modified exhaust system includes an element 82 formed of expanded 
material 46 having circular filters 84. The folds 48 between each filter 
84 have been folded approximately 180.degree. so that the circular filters 
are approximately transverse to the gas flow. The edges 86 of the circular 
filters contact the inner wall 70 so that each filter extends over the 
entire internal cross section of the pipe. The arcuate passageways 62-68 
are therefore eliminated. 
In a fourth modification of the exhaust system 24, an element 88 formed of 
expanded material 46 is provided which defines elliptical filters 90. The 
material at each fold 48 is folded less than 180.degree. to expand the 
element. However, the elliptical shape of filters 90 permit each 
elliptical filter 90 to contact the inner wall 70 of the pipe 26 along an 
interior circumference oblique to the length of the pipe. Therefore, the 
filters are not traverse to the direction of flow. The passageways 62-68 
are eliminated so that the entire gas flow must pass through each filter. 
The distance between the filters 90 can also be adjusted according to the 
length of the ellipse. 
A fifth modification of exhaust system 24 is illustrated in FIGS. 9A-C and 
FIGS. 15 and 16. In this embodiment, an element 94 of a continuous strip 
of expanded material 46 having a uniform width is twisted into a spiral so 
that the outer edges 96 of the element contact the inner wall 70 of the 
pipe 26 along helical lines 98 and 100. The gas will flow through each 
filter 102 defined by the helical element 94 to present a plurality of 
porous cross sections to the gas flow extending about the entire 
circumference of the inner wall. 
FIG. 15 is an accurate representation of the placement of a portion of the 
element 94 within the pipe 26. FIG. 16 is an end view of the exhaust 
system having one filter 102 formed by a sufficient length of the element 
94 to complete a full circumference of the inner wall. 
Many advantages are achieved by the exhaust system 24. The pipe 26 in the 
system 24 forms a continuous muffling pipe. Experiments have shown that a 
pipe 26 having substantially the same outer diameter as connecting pipe 22 
in a conventional system 16 and which extends the length of a conventional 
exhaust system 16 achieves substantially the same muffling effect as the 
conventional exhaust system 16. Therefore, the bulky muffler is 
eliminated. If the exhaust system 24 includes a catalytic converter 
function, the catalytic converter 18 can also be eliminated. The exhaust 
system 24 therefore reduces the size and weight of the exhaust system 
which permits increased flexibility in vehicle design including a lower 
profile and more streamlined and lighter vehicle. This can result in fuel 
savings. The smoother, less bulky profile of the system 24 also means it 
is less exposed to road damage. 
In addition, the continuous length pipe 26 does not require the clamps 
typically employed in the conventional exhaust system 16. The simplicity 
of the exhaust system 24 can provide saving on the assembly line, reduced 
material costs and can result in lower back pressure for a desired 
muffling level. 
When designed to have a catalytic converter function, the exhaust system 24 
further has the advantage of dispersing the heat generation from the 
catalytic action along that length of the exhaust system 24 which includes 
the catalytic converter action. This reduces the heat build up in any 
particular part of the vehicle again providing more flexibility in the 
vehicle design. The exhaust system 24 can achieve three functions within a 
given length and minimum diameter while the pipe 22 of the conventional 
system 16 of similar diameter only carries gases. The section of pipe 26 
can not only carry away gases, but muffle the exhaust sounds and remove 
pollutants as well. 
The presence of passageway 62-68 can enhance ventilation within the exhaust 
system when the system is not operating. This will reduce the corrosion 
level below that found in conventional mufflers and permit the exhaust 
system 24 to be more durable in operation. The exhaust system 24 also 
provides great flexibility in bending to conform to the structure of the 
vehicle. For example, FIG. 14 illustrates the interior cross section of 
the exhaust system 24 at bends 40 and 42. Since the muffling action occurs 
over a substantial length of the exhaust system, any limited distortion or 
disintegration of the filters at a particular bend do not significantly 
effect the operation of the exhaust system. The distortion of the few 
filters 60 which are pressed closer together at the inner radius of the 
curve and fanned apart at the outer radius of the curve have no practical 
ill effect on the operation of the exhaust system. A few filters 59 are 
pressed closer together by the shortening of the pipe when the flange 53 
is formed which again has no practical ill effect. 
The material 46 may be formed of extruded ceramic of varying porosity and 
shapes which can be produced in sizes and designs to fit into the pipe 26 
prior to forming of the pipe and welding of a seam on the pipe. When the 
pipe is bent, the ceramic elements can be broken at the flanges and bends 
without significant deterioration of the muffling capacity of the exhaust 
system. 
The exhaust system 24 can be manufactured in various grades to suit the 
displacement of the internal combustion engine with which it is to be 
used, the length of pipe to be installed, the muffling characteristics 
desired, the degree of back pressure which will be tolerated and the level 
of pollution control required. Since the muffling and catalytic converter 
functions are separate, the exhaust system 24 can be used solely for 
muffling or solely for pollution control. However, both muffling and 
catalytic conversion can be combined in the same exhaust system 24. 
It can also be desirable to construct the exhaust system 24 in more than 
one section. This may be desirable for ease of assembly. In addition, this 
permits the assembly of one section of the exhaust system employed solely 
for muffling with another section employed solely as a catalytic 
converter. The muffling and conversion sections can then be replaced 
independently. It is also possible that the muffling and catalytic 
converting sections will not occupy the entire length of pipe 26. The 
weight of the exhaust system may be reduced by eliminating unnecessary 
material within the pipe. It is also possible to provide expanded material 
within the exhaust system 24 which is comprised of more than one material. 
For example, steel may be used in the muffling section while ceramic 
employed in the catalytic converter section. The ideal mode of production 
is one in which the pipe for muffling and catalytic converting can be 
manufactured in a continuous manner and in a continuous form, or in a 
continuously repeating series of forms, and designed so that all parts 
would reach the end of their service life at the same time. 
Sound level tests were made to compare the muffling effects of a 
conventional exhaust system, an exhaust system incorporating a muffler as 
disclosed in U.S. Pat. No. 3,746,126, issued July 17, 1973 to de Cardenas 
and an exhaust system constructed in accordance with the teachings of the 
present invention. Sound level tests were also made with a single five 
foot length of empty pipe and with no muffler or pipe whatsoever. All 
tests were made on a General Motors V8 engine having a displacement of 283 
cubic inches. A Genrad Model 1983 sound level meter was used in all 
measurements on the "fast" response mode. 
All tests were conducted under identical conditions in a home garage. The 
sound level meter was mounted on a tripod approximately midway between the 
side of the automobile and one wall of the garage, about four feet from 
the open end of the exhaust system. In every case, the exhaust systems 
tested were mounted after the Y or cross over junction which joins exhaust 
pipe sections from the two exhaust manifolds into a common pipe 
immediately ahead of the position of the conventional muffler. 
The muffler constructed under the teachings of the de Cardenas patent was 
constructed of a length of galvanized sheet steel such as used in roof 
flashing from which a strip was cut of width equal to the inside diameter 
of a two inch OD exhaust pipe. The sheet steel was twisted into a helix 
five feet in length and inserted into a five foot length of two inch OD 
pipe. 
Table 1 summarizes the sound level readings from a conventional muffler at 
various engine speeds with the automatic transmission provided on the test 
vehicle in park and drive positions. 
TABLE 1 
______________________________________ 
CONVENTIONAL MUFFLER 
R.P.M. dB (A) in park 
dB (A) in drive 
______________________________________ 
500 -- 68 
600 70 71 
800 72 73 
1000 73 78 
1200 77 -- 
2000 80 -- 
2500 84 -- 
______________________________________ 
The sound readings for the muffler constructed in accordance with the 
teachings of the de Cardenas patent are recorded in Table 2. 
TABLE 2 
______________________________________ 
De CARDENAS MUFFLER 
R.P.M. dB (A) in park 
dB (A) in drive 
______________________________________ 
500 -- 78 
600 76 81 
800 80 88 
1000 82 94 
1200 84 -- 
2000 88 -- 
2500 90 -- 
______________________________________ 
The sound level results with a muffling pipe constructed in accordance with 
the present invention are tabulated in Table No. 3. 
TABLE 3 
______________________________________ 
PRESENT INVENTION 
R.P.M. dB (A) in park 
dB (A) in drive 
______________________________________ 
500 -- 71 
600 72 74 
800 75 78 
1000 77 84 
1200 78 -- 
2000 81 -- 
2500 84 -- 
______________________________________ 
The sound level measurements with a hollow or empty five foot length of 
pipe are tabulated in Table No. 4. 
TABLE NO. 4 
______________________________________ 
EMPTY FIVE FOOT LENGTH OF PIPE 
R.P.M. dB (A) in park 
dB (A) in drive 
______________________________________ 
500 -- 80 
600 77 83 
800 80 89 
1000 85 95 
1200 85 -- 
2000 89 -- 
2500 90 -- 
______________________________________ 
The sound level measurements when no pipe or muffler is provided after the 
Y junction are tabulated in Table No. 5. 
TABLE NO. 5 
______________________________________ 
NO PIPE OR MUFFLER 
R.P.M. dB (A) in park 
dB (A) in drive 
______________________________________ 
500 -- 79 
600 78 84 
800 80 90 
1000 81 96 
1200 83 -- 
2000 90 -- 
2500 92 -- 
______________________________________ 
Sound levels measured in rapid acceleration to 3,000 R.P.M. are recorded 
below. 
______________________________________ 
Conven- de- Empty five 
No pipe 
Sound tional Present Cardenas 
Foot Length 
or 
Level Muffler Invention 
Muffler 
of Pipe Muffler 
______________________________________ 
dB (A) 
93 96 103 103 106 
______________________________________ 
The exhaust system 110 illustrated in FIGS. 10-13 forms a second embodiment 
of the present invention. The exhaust system 110 includes the pipe 26 
having a substantially uniform outer diameter over its entire length. 
However, a liner 112 is positioned inside the pipe 26 which includes a 
plurality of airfoil baffles 114 projecting inwardly from the liner 112 
into the gas flow to break up and disintegrate the sonic shock waves. The 
liner 112 is preferably constructed of a metal such as steel. The airfoil 
baffles 114 can be stamped from the continuous strip of liner material 112 
shown in FIG. 11 by cutting the material along edges 116, 118 and 120 and 
bending the baffle 114 created thereby in one direction so that all the 
baffles extend from one side 122 of the liner 112. 
The pipe 26 and liner 112 can then be simultaneously rolled into tube form 
as shown in FIG. 10. When rolled, the pipe is welded along seam 124 to 
form a gas tight exhaust system. If desired, both the pipe and liner can 
be welded. 
The baffles 114 in the rolled liner extend radially inward toward the 
center of the exhaust system as best seen in FIG. 12. The baffles can 
extend entirely across the inner diameter of the rolled liner or any 
lesser distance desired. 
The individual baffles 114 are shaped to form an airfoil surface as best 
seen in FIG. 13. The airfoil surface breaks up the gas flow to attenuate 
the sonic frequencies of the shock wave. The baffles can vary in their 
airfoil sections, their lengths, their thickness and their angle of attack 
8 to the gas flow as well as their frequency along the length of the 
exhaust system. If a catalytic conversion function is desired, the baffles 
can be coated with alumina and a platinum group metal to perform the 
converting function. 
The exhaust system 110 includes the advantages noted above with regard to 
exhaust system 24. Exhaust system 110 can also be used in substantially 
the same manner as the exhaust system 24 described above. 
In FIG. 17, exhaust system 130 forms a third embodiment of the present 
invention. In the exhaust system 130, the pipe 26 is filled with woven 
wire fabric 132. The woven wire fabric acts to attenuate the sonic 
frequencies of the shock wave in the exhaust in a manner similar to the 
systems 24 and 110 described above. The warp of the woven fabric can be of 
wires of varying diameters and cross sections. The weft in the fabric can 
also be similarly varied. Open spaces between the wires in the fabric can 
be varied in size and shape along the length thereof to increase the 
attenuation across a range of sonic frequencies. The exhaust system 130 
also provides the advantages and uses of systems 24 and 110 mentioned 
above. 
While several embodiments of the present invention have been illustrated in 
the accompanying Drawings and described in the foregoing Detailed 
Description, it will be understood that the invention is not limited to 
the embodiment disclosed, but is capable of numerous rearrangements, 
modifications and substitutions of parts and elements without departing 
from the spirit of the invention.