Heat shielded exhaust system component

An exhaust muffler and heat shield assembly and a method for producing the assembly are provided The muffler includes a pair of stamp formed external shells. At least one external shell is stamped to include a plurality of tabs extending outwardly from the peripheral flange of the external shell. The tabs preferably are disposed at locations that otherwise would have defined wastage to be trimmed from the stamp formed external shell The heat shield is configured to be mounted to the muffler by crimping the tabs. In particular, peripheral regions of the heat shield may be engaged between the peripheral flange of the muffler and the crimped tabs. Alternatively, the heat shield may include slots through which the tabs extend for mechanical engagement with the heat shield.

BACKGROUND OF THE INVENTION 
Exhaust mufflers formed at least in part from stamped components have been 
available for many years. The typical prior art stamped muffler includes 
at least a pair of stamp formed external shells. These shells include 
peripheral flanges dimensioned and configured to be placed generally in 
register with one another. Portions of each shell intermediate the 
peripheral flanges are formed to define at least one chamber. The prior 
art stamp formed muffler further includes one or more internal components 
between the external shells to define a flow path for exhaust gas through 
the muffler. In some prior art mufflers, the flow path has been defined by 
an array of conventional tubes. Examples of mufflers of this general type 
are shown in U.S. Pat. No. 4,901,816 which issued to David Garey on Feb. 
20, 1990 and in U.S. Pat. No. 4,905,791 which issued to David Garey on 
Mar. 6, 1990. These prior art patents are assigned to the assignee of the 
subject invention. It will be noted that the external shells of the 
mufflers shown in U.S. Pat. No. 4,901,816 and in U.S. Pat. No. 4,905,791 
include baffles formed from the external shells for supporting the 
conventional tubes within the muffler. Other prior art mufflers have 
employed conventional tubes supported by separate transverse baffles and 
disposed within a stamp formed external shell. A muffler of this general 
type is shown in published U.K. Patent Application No. 2,120,318A. 
Many other prior art mufflers include stamp formed external shells and one 
or more stamped internal plates formed to define the flow path for exhaust 
gas through the muffler. An extremely effective muffler of this general 
type is shown in re-issue Pat. No. Re. 33,370 which was re-issued on Oct. 
9, 1990. Re-issue Patent No. Re. 33,370 also is assigned to the assignee 
of the subject invention. It will be noted that Re. 33,370 shows a muffler 
with a pair of formed internal plates defining an array of tubes through 
which exhaust gas in the muffler flows. At least one of the tubes defined 
by the plates is a tuning tube which communicates with a low frequency 
resonating chamber. The pair of formed internal plates shown in Re. 33,370 
is disposed between the pair of external shells that define the chambers 
of the muffler. 
Other patents assigned to the assignee of the subject invention show still 
other advances in stamp formed exhaust mufflers. For example, U.S. Pat. 
No. 4,860,853 which issued to Walter G. Moring, III on Aug. 29, 1989 shows 
a muffler that can be formed with only three stamped components, but still 
defining an efficient flow path for exhaust gases and a plurality of 
chambers for attenuating the noise associated with the flowing exhaust 
gases. U.S. Pat. No. 4,894,987 issued to Jon Harwood et. al. on Jan. 23, 
1990 and covers a stamp formed muffler and catalytic converter assembly. 
A vehicular exhaust system generally must travel an extremely circuitous 
route from one end of the vehicle to the other, and the various components 
of the exhaust system often must be disposed in closely nested 
relationship to other parts of the vehicle. Components of the exhaust 
system, including the muffler, become very hot when the vehicle is 
operating due to the flow of heated exhaust gas therethrough. In many 
situations, it is necessary to employ a shield in proximity to the muffler 
or some other component of the vehicular exhaust system. The shield 
generally is slightly spaced from the heated exhaust system component and 
hence provides an insulating layer of air between the shield and the hot 
exhaust system component. In some situations, the shield is disposed on 
the side of the muffler or pipe facing away from the vehicle to prevent 
the heated exhaust system component from igniting dried leaves or grass 
near the vehicle. Hence, shields mounted on the side away from the vehicle 
may be referred to as grass shields. In many other situations, the shield 
is disposed between the muffler or pipe and the vehicle to prevent 
overheating of floor boards or other parts of the vehicle disposed near 
the exhaust system component. Shields mounted between the exhaust 
component and the vehicle generally are referred to as heat shields. The 
term heat shield will be used herein to refer to any shield regardless of 
its orientation on the muffler. 
The prior art heat shield for an exhaust system component generally has 
been a flat or slightly curved piece of sheet metal that is strapped to 
the muffler or pipe. The heat shield may further be formed with stand-offs 
to achieve the desired spacing from the exhaust system component An 
extremely effective heat shield of this general type is shown in U.S. Pat. 
No. 4,478,310 which issued to Donald Harter on Oct. 23, 1984 and which is 
assigned to the assignee of the subject invention. 
Heat shields may be stamp formed efficiently and employed with stamp formed 
mufflers For example, a heat shielded stamped formed exhaust muffler is 
shown in U.S. Pat. No. 4,759,423 which issued to Harwood et. al. on Jul. 
26, 1988 and which also is assigned to the assignee of the subject 
invention. The muffler shown in U.S. Pat. No. 4,759,423 employs a pair of 
stamped internal plates and a pair of stamped external shells to achieve a 
tri-flow pattern of exhaust gas which in many respects resembles the flow 
pattern formed with conventional mufflers One embodiment of the muffler 
shown in U.S. Pat. No. 4,759,423 further employs a heat shield generally 
conforming to the shape of one of the external shells to nest over the 
external shell for attachment around the periphery of the muffler. This 
design provides extremely effective heat shielding. However, the welding 
or mechanical attachment of five thicknesses of metal around the periphery 
of the muffler can be difficult. Additionally, the heat shield will not 
become as hot as the muffler and hence will expand and contract 
differently. This differential expansion and contraction can damage the 
welded connection of the heat shield to the muffler. Furthermore, the heat 
shield often will perform its shielding function if formed from a thinner 
grade of metal. However, thinner metal is easily damaged by the heat of 
welding. Thus, it has been necessary to make the heat shield from a 
thicker metal and thereby incur a cost and weight penalty. As an 
alternative to the welding or mechanical attachment around the periphery 
of the muffler, straps could be employed as in the above referenced U.S. 
Pat. No. 4,478,310. However, straps require additional material, 
additional weight and an assembly process that is not well suited to 
automation. 
FIGS. 1 and 2 show a prior art stamp formed external shell for an exhaust 
muffler. The prior art external shell shown in FIGS. 1 and 2 is identified 
generally by the numeral 10, and is stamped from an initially rectangular 
flat sheet of metal. A peripheral flange 12 generally will retain its 
initial planar configuration. However, a central region of the external 
shell 10 is formed to define at least one chamber 14 The prior art 
external shell 10 typically will be formed in a progressive stamping die 
wherein the initially planar rectangular sheet is sequentially worked into 
the shape of the external shell 10 depicted in FIGS. 1 and 2. As part of 
this formation process, the metal material of the external shell 10 will 
deform and stretch to enable the formation of the chamber 14. As shown 
most clearly in FIG. 2, the external shell 10 will achieve a 
non-rectangular peripheral configuration due to the stretching and 
deformation of the metal. In particular, portions of the metal 
intermediate the corners will be drawn inwardly to enable the formation of 
the chamber 14. A final step of the progressive stamping operation 
typically will be to cut the peripheral flange 12 of the external shell 10 
into a uniform width as shown by the edge 16 in FIG. 2, which, in this 
instance is rectangular. Metallic material disposed outwardly from the 
final edge shape 16 will be accumulated and resold for scrap. However, 
there is a substantial loss in value in the metal material sold for scrap. 
Although the above described stamped mufflers and heat shields are 
extremely effective, it is desired to provide further efficiencies and 
improvements in the manufacture of heat shielded mufflers. As a result, it 
is an object of the subject invention to provide a more efficient heat 
shield and exhaust muffler combination. 
It is another object of the subject invention to provide efficient methods 
for manufacturing and assembling a heat shielded exhaust muffler. 
It is still another object of the subject invention to provide a muffler 
and heat shield combination with an efficient attachment between the 
muffler and the heat shield. 
Still an additional object of the subject invention is to provide a muffler 
and heat shield assembly with an efficient means for achieving a desired 
stand-off therebetween 
SUMMARY OF THE INVENTION 
The subject invention is directed to a heat shielded exhaust system 
component, such as a catalytic converter or a muffler or a combined 
catalytic converter and muffler The converter and/or muffler includes at 
least one internal component defining a passage for exhaust gas flowing 
therethrough. The internal components may comprise at least one 
conventional tube. The internal components may further comprise at least 
one baffle for supporting the tube and/or for defining more than one 
chamber within a muffler. In a preferred embodiment as described further 
below, a muffler is provided with internal flow passages defined by a pair 
of internal plates that are formed to define an array of tubes within the 
muffler. The array of tubes comprises at least one inlet to the muffler 
and at least one outlet from the muffler. 
The muffler or converter further comprises at least one external shell that 
may be stamped or otherwise formed to define at least one chamber 
surrounding the internal components. The external shell may be defined by 
a pair of shells formed to define peripheral flanges that are secured to 
one another to substantially enclose the internal components. 
At least one of the components of the muffler or catalytic converter 
defines at least one heat shield mounting means. For example, at least one 
external shell of the muffler or converter may be stamped to define a 
plurality of heat shield mounting tabs. The heat shield mounting tab may 
extend outwardly from the periphery of a formed component of the muffler 
or converter. The tab may include a non-planar portion for rigidity, and 
preferably is formed on a portion of a formed component of the muffler or 
converter that would otherwise define scrap. For example, one or more tabs 
may be disposed adjacent corner regions of the formed component which 
otherwise would have been trimmed to achieve a specified configuration for 
the muffler or converter. 
The assembly of the subject invention further comprises at least one heat 
shield which may generally conform to the shape of an external shell of 
the exhaust system component. The heat shield may be formed from a thinner 
gage metal than the shell of the exhaust system component. The heat shield 
may be provided with mounting means for engagement with the exhaust system 
component The mounting means of the heat shield may comprise at least one 
mounting flange at a peripheral location on the heat shield for crimped 
engagement with a peripheral flange of the exhaust system component or for 
crimped engagement by a mounting tab of the exhaust system component. More 
particularly, the heat shield may be provided with a plurality of mounting 
flanges extending from spaced apart locations thereon for engagement by a 
corresponding plurality of tabs on the exhaust system component. The 
mounting tabs of the muffler may be crimped or otherwise mechanically 
deformed to engage the corresponding mounting flanges of the heat shield. 
Preferably, the heat shield is biased prior to or during mounting to be 
preloaded against the exhaust system component. The preload prevents 
relative movement between the heat shield and the exhaust system component 
and hence avoids rattles during use. 
Alternatively, the mounting means on the heat shield may comprise at least 
one slot on the heat shield through which one or more mounting tabs of the 
exhaust system component may extend. The mounting tabs of the exhaust 
system component may be passed through corresponding mounting slots of the 
heat shield, and may be secured to the heat shield by crimping. In this 
embodiment, the heat shield may be employed to shield an edge region of 
the exhaust system component defined by the securely affixed peripheral 
flanges of the exhaust system component. This latter embodiment is 
particularly effective in embodiments where a plane defined by the 
peripheral flanges of the exhaust system component is not horizontally 
disposed on the vehicle. The heat shield may be dimensioned to achieve a 
preload against the exhaust system component in this embodiment as well. 
The subject invention is further directed to a method of manufacturing a 
heat shielded component. The method comprises forming at least one 
component of the muffler or catalytic converter from a sheet of metal. The 
formed component may define at least one external shell of the muffler or 
catalytic. The forming is carried out to define a peripheral flange for 
the formed component of the muffler or catalytic converter. The method 
further comprises trimming the peripheral flange into a specified 
peripheral configuration, including the trimming of at least one heat 
shield mounting tab on the formed component of the muffler or catalytic 
converter. The method further may comprise the step of forming the heat 
shield mounting tab into a selected non-planar configuration to ensure 
rigidity. The heat shield may then be mounted to the muffler or catalytic 
converter by crimping the mounting tabs. Preferably, the heat shield is 
biased and deformed during mounting to achieve a preload against the 
muffler or catalytic converter. 
The non-welded connection of the heat shield to the muffler or catalytic 
converter in accordance with the subjection invention achieves several 
significant advantages. First, the problems that could be encountered in 
attempting to weld through several thicknesses of metal are entirely 
avoided Second, a thinner gage metal and a less expensive metal that might 
not be weldable to the muffler or catalytic converter can be used on the 
heat shield. Third, the preload of the heat shield against the muffler or 
catalytic converter entirely avoids the relative movement of components 
that exists with prior art mechanical engagement means for heat shields.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
An external shell for a muffler in accordance with the subject invention is 
identified generally by the numeral 20 in FIG. 3. The external shell 20 
preferably is formed from an initially planar sheet of metal in a transfer 
stamping apparatus. However, other metal forming techniques may be 
employed In its final formed configuration, the external shell 20 is of 
generally rectangular configuration with opposed longitudinal ends 22 and 
24 and opposed sides 26 and 28. The external shell 20 includes a 
substantially planar peripheral flange 30 from which a chamber 32 extends. 
The chamber 32 is formed with an array of substantially parallel 
reinforcing grooves which may be similar to those disclosed in U.S. Pat. 
No. 4,924,968 which issued to Moring et. al. on May 15, 1990 and which is 
assigned to the assignee of the subject invention. The formation of the 
chamber 32 causes a stretching and drawing of the initially rectangular 
planar sheet of metal from which the external shell 20 is formed. In 
particular, the shape of the metal from which the external shell 20 is 
formed prior to final trimming is shown in phantom lines in FIG. 3 and is 
identified generally by the numeral 34. It will be noted that the sheet of 
metal 34 prior to trimming defines greater lengths and widths in proximity 
to the corners of the external shell 20. 
In contrast to the prior art external shell shown in FIG. 2, the external 
shell 20 of the subject invention is trimmed to include heat shield 
mounting tabs 36-42. In particular, tabs 36 and 38 extend from the first 
longitudinal side 26 in proximity to the first and second ends 22 and 24 
respectively. Similarly, the tabs 40 and 42 extend from the second 
longitudinal side 28 in proximity to the first and second longitudinal 
ends 22 and 24 respectively. The tabs 36-42 are characterized by 
corrugations 46-52 respectively. The corrugations 46-52 are provided to 
make the tabs 36-42 rigid. 
The external shell 20 defines a portion of a muffler/heat shield assembly 
identified generally by the numeral 54 in FIGS. 4- 6. The assembly 54 
includes a muffler 55 having a first external shell 20, as described and 
illustrated above, and an opposed second external shell 56 which is 
depicted as being substantially identical to the first external shell 20. 
However, such identity is not required, and the actual shape of the second 
external shell 56 will be determined, in part, by the acoustical 
requirements of the muffler and the available space on the underside of 
the vehicle. The muffler 55 further includes at least one internal 
component defining a flow passage for exhaust gas. In the embodiment 
depicted in FIGS. 4-6, the flow passage is defined by first and second 
stamp formed internal plates 58 and 60 respectively. The internal plates 
58 and 60 preferably are stamped with arrays of opposed channels defining 
tubes therebetween through which exhaust gas may flow. The arrays of tubes 
may be structurally and functionally similar to those described in the 
above referenced patents that are assigned to the assignee of the subject 
invention. However, in other embodiments the flow passage may be defined 
by an array of conventional tubes and associated baffles. The internal 
plates 58 and 60 and the external shells 20 and 56 are further stamped to 
define at least one inlet 62 to the muffler 55 and at least one outlet 64. 
The inlet 62 and outlet 64 will be connected respectively to the exhaust 
pipe and tail pipe (not shown) on a vehicle. 
The muffler/heat shield assembly 54 further includes a stamp formed heat 
shield identified generally by the numeral 65 in FIGS. 4-6. The heat 
shield 65 generally conforms to the shape of the first external shell 20. 
The heat shield 65 is stamped to include mounting flanges 66-72 
respectively. The mounting flanges 66-72 are disposed and dimensioned to 
be placed generally in register with and to mount approximately adjacent 
to the peripheral flange 30 of the first external shell 20. However, the 
heat shield 65 preferably is dimensioned to require a slight biasing of 
opposed longitudinal sides to achieve perfect registration and alignment. 
The heat shield 65 may be secured in the biased or preloaded position 
shown in FIGS. 4-6 by crimping the respective mounting tabs 36-42 of the 
first external shell 20 into secure engagement with the respective 
mounting flanges on the heat shield 65. This crimped mounting of the heat 
shield 65 permits differential thermal expansion and avoids the above 
described problems with welding. The biasing or preload prevents vibration 
related movement between the heat shield 65 and the first external shell 
20 The heat shield 65 is held by the tabs 36-42 in spaced relationship to 
the first external shell 20 to achieve an insulating air space 
therebetween as shown most clearly in FIGS. 4 and 5. The spacing between 
the heat shield 65 and the first external shell 20 is determined by the 
geometry of the mounting flanges 66-72 of the heat shield 65. 
The heat shield 65 includes a peripheral flange 74 extending intermediate 
the mounting flanges 66-72. The peripheral flange 74 is disposed and 
configured to be substantially spaced from the peripheral flange 30 of the 
first external shell 20. The spacing between the peripheral flange 74 of 
the heat shield 65 and the peripheral flange 30 of the first external 
shell 20 facilitates a flow of air between the first external shell 20 and 
the heat shield 65. This flow of air enhances the cooling and insulating 
function carried out by the heat shield 65. 
As shown in FIGS. 4-6, the heat shield 65 is disposed to be positioned 
between the muffler 55 and the vehicle to which the muffler 55 is 
attached. In other embodiments, however, it may be preferable to have the 
heat shield 65 positioned intermediate the muffler 55 and the surface on 
which the vehicle is supported, and to function as a grass shield. This 
can readily be achieved by providing the second external shell 56 with 
heat shield mounting tabs 36'-42' comparable to the tabs 36-42 on the 
first external shell 20. Thus, the muffler 55 could be provided with a top 
heat shield 65 and/or a substantially similar opposed bottom heat shield 
or grass shield (not shown) mounted to tabs 36'-42' extending from the 
second external shell 56. The tabs 36-42 or 36'-42' normally would be 
wastage or offage, as noted above. Consequently, tabs 36-42 and 36'-42' 
may always be provided on both external shells 20 and 56 at all times. The 
tabs 36'-42' may always be crimped ove even in situations where a heat 
shield is not present. 
An alternate muffler and heat shield assembly is shown in FIGS. 7-9 and is 
identified generally by the numeral 75. The assembly 75 includes a muffler 
55 which is substantially identical to the muffler 55 described above and 
illustrated in FIGS. 4-6. In particular, the muffler 55 shown in FIGS. 4 6 
includes first and second external shells 20 and 56 respectively and first 
and second internal plates 58 and 60. However, the available space on the 
underside of the vehicle with which the muffler 55 is used requires the 
peripheral flanges of the first and second external shells 20 and 56 and 
the planes defined by the first and second internal plates 58 and 60 to be 
orientated substantially vertically with respect to the surface on which 
the vehicle is supported. 
The assembly 75 further includes a heat shield 82 disposed to be positioned 
between the muffler 55 and the surface on which the vehicle is supported. 
The heat shield 82 is intended to prevent inadvertent contact with the 
heated muffler 55 and further to prevent the heated muffler 55 from 
contacting any combustible material that may be disposed on the ground. 
The heat shield 82 is of elongated configuration generally conforming to 
the profile of the muffler 55. In particular, the heat shield 82 includes 
a peripheral flange 84 disposed and dimensioned to be in spaced 
relationship to the muffler 55. The heat shield 82 is further 
characterized by a pair of aligned slots 86 and 88 respectively disposed 
and dimensioned to receive the tabs 36, 38, 36' and 38' of the muffler 55. 
More particularly, the tabs 36 and 36' of the muffler 55 are disposed and 
dimensioned to pass through the slot 86 in the heat shield 82. Similarly, 
the slot 88 is disposed and dimensioned to receive the tabs 38 and 38' of 
the muffler 55. The tabs 36, 38, 36' and 38' may be folded over to 
securely engage the heat shield 82 and thereby mechanically ret in the 
heat shield to the muffler 55. 
The heat shield 82 is further characterized by lateral support surfaces 90 
and 92 extending from opposite sides of the slot 86 and toward the 
peripheral flange 84. Similarly, lateral support surfaces 94 and 96 extend 
from the slot B8 toward the peripheral flange 84. The lateral support 
surfaces 90-96 are configured to be preloaded against and supportingly 
engage the respective external shells 20 and 56 on the muffler 55. In 
particular, the mechanical engagement of the tabs 36, 38, 36' and 38' with 
the heat shield 82 preloads the lateral support surfaces 90-96 of the heat 
shield 82 firmly against the external shells 20 and 56 of the muffler 55, 
thereby preventing rattling and avoiding the need to manually affix straps 
around the muffler and heat shield assembly 75. 
While the invention has been described with respect to certain preferred 
embodiments, it is apparent that various changes can be made without 
departing from the scope of the invention as defined by the appended 
claims. In particular, the respective mufflers and heat shields may assume 
configurations other than the rectangular shapes depicted in the attached 
figures. Additionally, more then one heat shield may be employed with each 
muffler. Furthermore, the relative position of the heat shield to the 
muffler is not restricted to any particular gravitational orientation, but 
rather is dictated by design and safety considerations for the exhaust 
system and the associated vehicle.