U.S. patent application number 10/590172 was filed with the patent office on 2007-07-19 for highly insulated exhaust manifold.
Invention is credited to Bruce O. Budinger, Scott A. Churby, James L. Eucker, Dan T. III Moore, Ajit Y. Sane.
Application Number | 20070163250 10/590172 |
Document ID | / |
Family ID | 35056674 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163250 |
Kind Code |
A1 |
Sane; Ajit Y. ; et
al. |
July 19, 2007 |
Highly insulated exhaust manifold
Abstract
An exhaust manifold (10, 110) is provided having a ceramic inner
layer (22, 32) defining an exhaust gas passageway (20), and a
composite insulation zone (24, 26) that is highly thermally
insulating. In one embodiment, the composite insulation zone (24)
includes a plurality of metallic foils (31, 32) in alternating
arrangement with layers having insulating qualities. In the
composite insulation zone, the layers having insulating qualities
can include ceramic layers (26), evacuated spaces, microsphere
layers (37) including substantially evacuated microspheres, or a
combination of these. A novel sealing arrangement also is provided
for sealing the ceramic inner and metallic outer layers of a
metal-encased-ceramic exhaust manifold at a location adjacent the
inlet port (14, 15, 16) of a runner of the manifold. A sealing
gasket (140) is substantially completely encased within or shielded
by the metallic outer layer, so as not to contact the cylinder head
(115) when assembled to an internal combustion engine.
Inventors: |
Sane; Ajit Y.; (Medina,
OH) ; Budinger; Bruce O.; (Chagrin Falls, OH)
; Churby; Scott A.; (Lodi, OH) ; Moore; Dan T.
III; (Cleveland Heights, OH) ; Eucker; James L.;
(North Ridgeville, OH) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET
SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Family ID: |
35056674 |
Appl. No.: |
10/590172 |
Filed: |
March 2, 2005 |
PCT Filed: |
March 2, 2005 |
PCT NO: |
PCT/US05/06510 |
371 Date: |
August 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60549793 |
Mar 3, 2004 |
|
|
|
60559119 |
Apr 2, 2004 |
|
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Current U.S.
Class: |
60/323 ;
60/320 |
Current CPC
Class: |
F01N 13/148 20130101;
F01N 13/16 20130101; F01N 2310/00 20130101; F01N 2510/06 20130101;
F01N 13/102 20130101; F01N 3/20 20130101; F01N 2370/02 20130101;
F01N 2310/06 20130101 |
Class at
Publication: |
060/323 ;
060/320 |
International
Class: |
F01N 5/02 20060101
F01N005/02; F01N 7/10 20060101 F01N007/10; F01N 3/02 20060101
F01N003/02 |
Claims
1. An exhaust manifold comprising a ceramic inner layer defining an
exhaust gas passageway, a composite insulation zone disposed
exterior to and adjacent said inner layer, a strain isolation layer
disposed between said composite insulation zone and said outer
structural layer, and an outer structural layer disposed exterior
to said composite insulation zone, said composite insulation zone
comprising at least one metallic foil layer.
2. An exhaust manifold according to claim 1, said composite
insulation zone comprising a plurality of said metallic foil layers
and at least one ceramic insulating layer disposed between adjacent
ones of said metallic foil layers.
3. An exhaust manifold according to claim 1, said composite
insulation zone comprising a plurality of said metallic foil layers
and at least one substantially evacuated annular space disposed
between adjacent ones of said metallic foil layers.
4. An exhaust manifold according to claim 1, said composite
insulation zone comprising a plurality of said metallic foil layers
and at least one microsphere layer disposed between adjacent ones
of said metallic foil layers.
5. (canceled)
6. An exhaust manifold according to claim 1, said strain isolation
layer being an intumescent mat.
7. An exhaust manifold according to claim 6, said intumescent mat
comprising, by weight, 20-60 percent ceramic fibers, and 35-75
percent expandable material.
8. An exhaust manifold according to claim 7, said expandable
material being vermiculite, perlite, or a mixture thereof.
9. An exhaust manifold according to claim 7, said intumescent mat
further comprising an organic binder material effective to bind
said ceramic fibers together to provide a coherent fibrous mat.
10. An exhaust manifold according to claim 6, said intumescent mat
exhibiting the property of expanding on heating of said mat, and
contracting on cooling thereof.
11. An exhaust manifold according to claim 6, said intumescent mat
having a crossover temperature below which said mat exhibits the
property of expanding on heating and contracting on cooling, and
above which said mat no longer exhibits the property of contracting
on cooling.
12. An exhaust manifold according to claim 1, wherein said inner
layer is 0.05-10 mm thick, said composite insulation zone is 1-40
mm thick and said outer layer is 1-25 mm thick.
13. An exhaust manifold according to claim 1, wherein said inner
layer comprises a catalyst effective to convert at least a portion
of CO and NO.sub.x in an exhaust gas flowing through said exhaust
passageway to CO.sub.2, and N.sub.2 and O.sub.2 respectively.
14. An exhaust manifold according to claim 13, wherein said
catalyst has the form ABO.sub.z and is selected from the group
consisting of a) a perovskite catalyst, wherein A is a rare earth
element and an alkaline earth element, and B is a transition metal
element; and b) a fluorite catalyst, wherein A is a rare earth
element and B is Ce or Zr.
15. An exhaust manifold according to claim 14, said catalyst being
a perovskite metal oxide catalyst, wherein A is lanthanum and
strontium, and B is selected from the group consisting of iron,
cobalt, manganese, titanium, gallium, chromium, and nickel.
16. An exhaust manifold according to claim 14, said catalyst being
a fluorite metal oxide catalyst, wherein A is a rare earth element,
B is either Ce or Zr.
17. An exhaust manifold comprising a ceramic inner layer defining
an exhaust gas passageway, an outer structural layer disposed
exterior to said ceramic inner layer, and a strain isolation layer
disposed intermediate said ceramic inner layer and said outer
structural layer, said strain isolation layer comprising an
intumescent mat.
18. An exhaust manifold according to claim 17, said intumescent mat
comprising, by weight, 20-60 percent ceramic fibers, and 35-75
percent expandable material.
19. An intumescent mat according to claim 18, said expandable
material being vermiculite, perlite, or a mixture thereof.
20. An exhaust manifold according to claim 18, said intumescent mat
further comprising an organic binder material effective to bind
said ceramic fibers together to provide a coherent fibrous mat.
21. An exhaust manifold according to claim 18, said intumescent mat
exhibiting the property of expanding on heating of said mat, and
contracting on cooling thereof.
22. An exhaust manifold according to claim 17, said intumescent mat
having a crossover temperature below which said mat exhibits the
property of expanding on heating and contracting on cooling, and
above which said mat no longer exhibits the property of contracting
on cooling.
23. An exhaust manifold according to claim 1, said manifold having
a main tube portion and at least one runner extending from said
main tube portion with an inlet port located at a terminal end of
the runner, wherein the layers and the composite insulation zone
described in claim 1 are provided in the main tube portion of the
manifold, the runner comprising a ceramic inner layer that is
substantially encased within and spaced apart from a metallic outer
layer thereof, said ceramic inner layer defining an exhaust gas
passageway therein for conducting exhaust gas from said inlet port
toward and into said main tube portion of said manifold, wherein a
sealing gasket is disposed and compressed between said ceramic
inner and metallic outer layers of the runner at or adjacent the
terminal end thereof, said sealing gasket being shielded by the
metallic outer layer.
24. An exhaust manifold according to claim 23: said metallic outer
layer of said runner comprising a metallic extruded portion that
extends from the main tube portion of the manifold, and an inwardly
extending flange portion located at the terminal end of the
metallic extruded portion, said ceramic inner layer of said runner
having an extruded configuration and extending from the main tube
portion of the manifold, wherein the ceramic extruded layer
approaches but does not contact the flange portion of the metallic
outer layer of the runner, leaving a small gap between a terminal
end of the ceramic extruded layer of the runner and the flange
portion, said sealing gasket being at least partially expanded in
the gap between the terminal end of the ceramic extruded layer and
the flange portion of the metallic outer layer, thereby shielding
the terminal edge of the ceramic extruded layer from direct contact
with said flange portion.
25. An exhaust manifold having a main tube portion and at least one
runner extending from said main tube portion and having an inlet
port located at a terminal end of the runner, the runner comprising
a ceramic inner layer that is substantially encased within and
spaced apart from a metallic outer layer, said ceramic inner layer
defining an exhaust gas passageway therein for conducting exhaust
gas from said inlet port toward and into said main tube portion of
said manifold, wherein a sealing gasket is disposed and compressed
between said ceramic inner and metallic outer layers at or adjacent
the terminal end of said runner, said sealing gasket being shielded
by the metallic outer layer.
26. An exhaust manifold according to claim 25: said metallic outer
layer of said runner comprising a metallic extruded portion that
extends from the main tube portion of the manifold, and an inwardly
extending flange portion located at the terminal end of the
metallic extruded portion, said ceramic inner layer of said runner
having an extruded configuration and extending from the main tube
portion of the manifold, wherein the ceramic extruded layer
approaches but does not contact the flange portion of the metallic
outer layer of the runner, leaving a small gap between a terminal
end of the ceramic extruded layer of the runner and the flange
portion, said sealing gasket being at least partially expanded in
the gap between the terminal end of the ceramic extruded layer and
the flange portion of the metallic outer layer, thereby shielding
the terminal edge of the ceramic extruded layer from direct contact
with said flange portion.
27. An exhaust manifold comprising a ceramic inner layer encased
within and spaced apart from a metallic outer layer thus defining
an annular space therebetween, said manifold having a main tube
portion and at least one runner extending from said main tube
portion, wherein at least one O-ring gasket is provided and
compressed in said annular space at a location in said main tube
portion of said exhaust manifold.
28. An exhaust manifold according to claim 27, said ceramic inner
layer comprising a ceramic main tube portion and a ceramic extruded
portion that extends from and is in fluid communication with said
ceramic main tube portion, said ceramic extruded portion defining
an exhaust gas passageway therein for said at least one runner,
said metallic outer layer comprising a metallic main tube portion
and a metallic extruded portion that extends from said metallic
main tube portion, said metallic extruded portion substantially
enclosing said ceramic extruded portion therein, thereby forming
said at least one runner extending from said main tube portion of
said manifold, wherein said at least one O-ring gasket is located
in said main tube portion adjacent said at least one runner.
29. An exhaust manifold according to claim 28, comprising a pair of
O-ring gaskets located in said main tube portion adjacent opposite
sides of said at least one runner.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/549,793 filed Mar. 3, 2004, and U.S.
Provisional Patent Application Ser. No. 60/559,119 filed Apr. 2,
2004, the contents of both of which are incorporated herein by
reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an exhaust manifold, and
more particularly to a highly insulated exhaust manifold for an
internal combustion engine.
[0004] 2. Description of Related Art
[0005] Catalytic converters in motorized vehicles, particularly
passenger automobiles, must reach a certain temperature before they
"light off." Light off occurs when the catalytic converter begins
to convert harmful pollutants by oxidizing carbon monoxide and
hydrocarbons to CO.sub.2, and reducing NO.sub.x to N.sub.2 and
O.sub.2. It is important to minimize the time to light off once a
car is started to minimize the amount of harmful pollutants emitted
to the atmosphere.
[0006] Catalytic converters typically are heated to light off by
the high temperature engine exhaust gas itself. Unfortunately, the
catalytic converter normally is mounted downstream of the exhaust
manifold which conducts the heated exhaust gas from the engine. A
typical exhaust manifold is made of metal, or substantially made of
metal. Metal exhaust manifolds conduct and disperse thermal energy
away from exhaust gas to the outside atmosphere. This loss in
thermal energy reduces the exhaust gas temperature before it
reaches the catalytic converter and delays light off.
[0007] Various techniques for insulating exhaust manifolds and/or
for providing other means to speed up light off have been suggested
and attempted. Cast iron exhaust manifolds are useful but heavy.
Also, the mass (large thermal mass) of iron drains heat from the
exhaust gas. Welded tubing exhaust manifolds have less mass, but
are complicated and expensive. Double-walled welded tubing exhaust
manifolds have been suggested, with an air gap between the walls,
but the two walls have the same thickness and are both
structural.
[0008] U.S. Pat. No. 5,419,127 teaches an exhaust manifold having
inner and outer metal walls enclosing a layer of insulating
material. Because the inner layer is metal and defines the wall of
the exhaust gas pathway (i.e. it contacts the traveling exhaust
gas), it conducts heat from the traveling exhaust gas thus delaying
light off. In addition, the metal inner layer is subject to erosion
or loss of integrity over time from thermal cycling.
[0009] U.S. Pat. No. 6,725,656 describes an insulated exhaust
manifold having a ceramic inner layer and a ceramic insulation
layer encased in a metallic outer structural layer. This
arrangement has proven effective at substantially reducing the
amount of heat conducted away from exhaust gases while traveling
through the exhaust manifold on the way to the catalytic converter,
resulting in reduced skin (outer surface) temperature for the
manifold. However, it is desirable to reduce even further the skin
temperature of the manifold.
SUMMARY OF THE INVENTION
[0010] An exhaust manifold is provided having a ceramic inner layer
defining an exhaust gas passageway, a composite insulation zone
disposed exterior to and adjacent the inner layer, and an outer
structural layer disposed exterior to the composite insulation
zone. The composite insulation zone includes at least one metallic
foil layer.
[0011] An exhaust manifold also is provided having a main tube
portion and at least one runner extending from the main tube
portion, which has an inlet port located in a terminal end of the
runner. The runner has a ceramic inner layer that is substantially
encased within and spaced apart from a metallic outer layer,
wherein the ceramic inner layer defines an exhaust gas passageway
therein for conducting exhaust gas from the inlet port toward and
into the main tube portion of the manifold. A sealing gasket is
disposed and compressed between the ceramic inner and metallic
outer layers at or adjacent the terminal end of the runner. The
sealing gasket is encased within the metallic outer layer.
[0012] An exhaust manifold also is provided having a ceramic inner
layer defining an exhaust gas passageway, an outer structural layer
disposed exterior to the ceramic inner layer, and a strain
isolation layer disposed intermediate the ceramic inner layer and
the outer structural layer, wherein the strain isolation layer
includes an intumescent mat.
[0013] An exhaust manifold also is provided having a ceramic inner
layer encased within and spaced apart from a metallic outer layer
thus defining an annular space therebetween. The manifold has a
main tube portion and at least one runner extending from the main
tube portion, wherein at least one O-ring gasket is provided and
compressed in the annular space at a location in the main tube
portion of the exhaust manifold.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a top view of an exhaust manifold for conducting
exhaust gas away from one side of a typical V-6 engine.
[0015] FIG. 2 is a cross-sectional view taken along line 2-2 in
FIG. 1, showing an embodiment of the manifold having an inner
layer, a composite insulation zone, a strain isolation layer, and
an outer structural layer.
[0016] FIG. 3 is a cross-sectional view as in FIG. 2, wherein the
composite insulation zone is composed of alternating discrete
metallic foil and ceramic layers.
[0017] FIG. 4 is a cross-sectional view as in FIG. 2, wherein the
composite insulation zone is composed of a plurality of metallic
foil layers, with adjacent ones of the foil layers enclosing and
defining substantially evacuated annular spaces therebetween.
[0018] FIG. 4a is a longitudinal cross-section of the composite
insulation zone of FIG. 4 shown apart from the manifold, showing
the individual metallic foils joined together along the
circumference of their respective terminal edges, thereby defining
the annular spaces in between adjacent foils.
[0019] FIG. 5 is a cross-sectional view as in FIG. 2, wherein the
composite insulation zone is composed of at least one pair of
opposing metallic foil layers enclosing and defining an annular
space therebetween, wherein the annular space is filled with
substantially evacuated glass or ceramic microspheres.
[0020] FIG. 6 is a cross-sectional view taken along line 6-6 in
FIG. 1, showing an embodiment of the manifold having an inner
layer, a composite insulation zone and an outer structural layer,
where the composite insulation zone has been provided with a
plurality of intumescent tabs in openings made at discrete
locations through the layers of the composite insulation zone.
[0021] FIG. 7 shows a schematic diagram, in cross-section, of a
testing apparatus for testing the insulative properties of sample
disc composites as further described in the examples
hereinbelow.
[0022] FIG. 8 is a lateral cross-sectional view, shown partially in
perspective, of an exhaust manifold runner mated or mounted to an
associated cylinder head of an internal combustion engine for
receiving exhaust gases therefrom, having a separate sealing gasket
disposed internally of the metallic outer layer.
[0023] FIG. 9 shows a slip cast ceramic inner layer having an
appropriate configuration as it is being enclosed within opposing
metal clamshell halves to provide a metal-encased-ceramic exhaust
manifold. O-ring gaskets are provided at strategic locations along
the main tube portion of the ceramic inner layer.
[0024] FIG. 10 shows a slip cast ceramic inner layer as in FIG. 9,
but having a ceramic rope wrapped in a helical configuration around
the main tube of the ceramic inner layer as a spacer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0025] In the description that follows, when a range such as 5 to
25 (or 5-25) is given, this means preferably at least 5 and,
separately and independently, preferably not more than 25. Also, as
used herein an "extruded" portion of a layer, for example of a
metallic or ceramic layer, refers to a portion of that layer that
has the form of a hollow extruded solid. When referred to as a
"circumferential portion," this means the extruded portion
preferably has a circular or substantially circular cross-section.
It is to be noted an "extruded" portion need not (and most likely
will not) have been formed by the process of extrusion; it may be
formed, e.g., via slip casting, metal casting or other suitable
technique effective to produce hollow solids having a generally
extruded form. Also, an "extruded" portion need not have a
perfectly extruded form, such as a closed polygon or circle that
has been extruded to form a perfect prism or cylinder; the term
"extruded" portion is used merely for convenience to indicate a
generally elongate portion of a layer of an exhaust manifold as
hereinafter described. Also as used herein, an "annular" space
refers to the space defined between adjacent but spaced apart
concentric layers of an exhaust manifold. It is not necessary that
the "annular" space be ring-shaped or cylindrical as for a true
annulus, or that the concentric layers be truly parallel.
[0026] The term ceramic includes any inorganic compound, typically
(though not necessary) crystalline, formed between a metallic (or
semimetallic) and a nonmetallic element, and mixtures thereof; for
example, alumina (Al.sub.2O.sub.3), titania (TiO.sub.2), and boron
nitride (BN), where Al and Ti are metallic elements, B is
semimetallic, and O and N are both nonmetallic. Ceramics also
include mixtures of ceramic compounds; i.e. soda-lime-silica glass
is a ceramic composed of sodium oxide, calcium oxide and silicon
oxide. As used herein, a ceramic (such as a ceramic layer, ceramic
fibers or filler material, or any other ceramic component or
material) can be and preferably is substantially ceramic;
preferably comprising at least 80, preferably at least 85,
preferably at least 90, preferably at least 92, preferably at least
94, preferably at least 96, preferably at least 98, wt. % ceramics
as described in the preceding sentence, with the balance being
additives and/or contaminants. Ceramics or ceramic materials
include glasses, such as borosilicate glass, aluminosilicate glass,
calcium aluminoborate glass, calcium aluminoborosilicate, and other
known or conventional glass materials. Glasses are a special
subclass of ceramic materials having an amorphous structure.
[0027] An exhaust manifold has at least one inlet and at least one
outlet. With reference to FIG. 1, an exhaust manifold 10 is shown
having three inlets or runners 5, 6 and 7 and one collector or
outlet tube 8. Preferably, runners 5, 6, and 7 have inlet flanges
14, 15 and 16 respectively for mounting to exhaust ports in the
engine block, and outlet tube 8 preferably has an outlet flange 12
for mounting to the exhaust pipe of an exhaust system. The manifold
pictured in FIG. 1 is configured to conduct exhaust gas away from
one side of a typical V-6 internal combustion engine. Exhaust gas
from each of three cylinders on one side of the engine (not shown)
enters that cylinder's corresponding runner 5, 6 or 7 in the
exhaust manifold and exits the manifold through outlet tube 8. The
outer surfaces of the inlet flanges preferably define a plane of
assembly for mounting the exhaust manifold 10 to the head of the
internal combustion engine. The inlet flanges 14, 15, and 16, and
outlet flange 12 are all preferably made from cast iron or
steel.
[0028] It will be understood that a manifold can be configured
having, for example, 2, 4, 6, or any number of runners to
accommodate engines having different numbers of cylinders (e.g. 4,
8, 12, etc.) and different configurations (e.g. in-line instead of
V-oriented cylinders).
[0029] Referring to FIG. 2, manifold 10 is composed of multiple
layers. In one embodiment, all the runners and the outlet tube have
the same multiple layer construction. The manifold 10 has at least
the following layers: inner layer 22, composite insulation zone 24,
and outer structural layer (or outer layer) 28. Optionally and
preferably, manifold 10 also has a strain isolation layer 26
disposed between outer layer 28 and insulation zone 24. The
compositions and physical characteristics of each of the above
layers will now be described.
[0030] Inner layer 22 defines an exhaust gas passageway 20
preferably having a diameter of 1-3 inches. Inner layer 22 is a
dense ceramic layer or glaze that provides a smooth, nonporous or
substantially nonporous, thermally resistant inner surface 21 for
contacting hot exhaust gas as it passes through the manifold 10.
The inner layer 22 is preferably composed of non-fibrous thermal
shock resistant and erosion resistant dense ceramic, less
preferably of ceramic fibers and a non-fibrous ceramic filler
material. It is preferred that the non-fibrous dense ceramic is
chosen from one or more of phases belonging to ceramic
multi-component systems comprising
alumina-silica-calcia-magnesia-titania. While oxide materials are
usually cheaper to fabricate, it is also possible to consider a
combination of non-oxide or oxide and non-oxide systems such as
Si.sub.3N.sub.4, SiC, Si/SiC, Si/Si.sub.3N.sub.4 (e.g., the
notation Si/SiC means silicon bonded SiC) and
SiC--Si.sub.3N.sub.4--Al.sub.2O.sub.3--Y.sub.2O.sub.3. The primary
selection criterion is the thermal shock resistance under cyclic
conditions when the engine is quickly turned to fall power after it
is allowed to be at ambient temperature. In the case of fibrous
materials, the ceramic filler material preferably fills the void or
interstitial space between the fibers, and coats the fibers. The
ceramic fibers are preferably aluminosilicate fibers, less
preferably silica fibers, less preferably alumina (such as Saffil
from DuPont) or zirconia fibers, less preferably
alumina-borosilicate fibers (such as Nextel from 3M), less
preferably a mixture thereof. The above ranking of ceramic fibers
is largely based on material cost and/or shrinkage under operating
and processing conditions. Aluminosilicate fibers are presently the
most widely available ceramic fibers (they are less expensive than
alumina or zirconia) that are suitable to withstand the temperature
ranges for many exhaust manifolds, typically 1600-1800.degree. F.
Any of the above fibers will perform adequately for most exhausts
having a temperature of about 1600-1800.degree. F. (i.e. automobile
exhausts). Silica can withstand exhaust temperatures up to about
2100.degree. F., while the more expensive alumina and zirconia
fibers can withstand exhaust temperatures up to 2300.degree. F. and
beyond but are more expensive.
[0031] The ceramic filler material in inner layer 22 is selected to
be stable or substantially stable against oxidation in strong
oxidizing environments up to 1600, 1800, 2000, 2100, or
2300,.degree. F., or greater, as the application requires. Material
preference can be based on factors other than but not excluding
performance. Such additional factors may include cost, ease of
fabrication or incorporation into a particular manufacturing
scheme, and thermo-mechanical compatibility with other
constituents. Preferred ceramic filler materials suitable to
withstand oxidation up to 2100.degree. F. are alumina, mullite
(aluminosilicate), silica, other metal oxides (e.g. titania,
magnesia, or ceria), partially stabilized zirconia (PSZ), silicon
carbide, silicon nitride, aluminum nitride, silicon boride,
molybdenum disilicide, as well as borides, carbides, nitrides and
oxides of refractory metals, and mixtures thereof. Included in
these materials is a glass or glass-ceramic frit constituent of
some of these components: alumina, silica, B.sub.2O.sub.3,
P.sub.2O.sub.5, TiO.sub.2 and an alkaline earth oxide such as MgO,
CaO or a mixture thereof. Less preferably, the ceramic filler
material can be an alkaline oxide or transition metal oxide.
Alkaline oxides and transition metal oxides may provide similar
performance to alumina or silica filler materials in inner layer
22. Less preferably, the ceramic filler material in inner layer 22
is SiC, SiB.sub.4, Si.sub.3N.sub.4, or a mixture thereof. Such
materials are even less preferred when the ceramic filler material
in inner layer 22, particularly non-fibrous and crystalline
ceramic, is in the sintered form. Less preferably, the ceramic
filler material can be those glasses that may cause unacceptable
dimensional changes in ceramic fibers, for example, when used in
conjunction with silica or high silica fibers: glasses such as
alkali containing calcium borosilicate glass, aluminosilicate
glass, calcium aluminoborate glass, less preferably any other glass
material capable of withstanding exhaust temperatures of 1200,
preferably 1400, preferably 1600, preferably 1800, preferably
2100,.degree. F. Less preferably, ceramic filler material in inner
layer 22 can be any other highly refractive ceramic material known
in the art. The ceramic filler material preferably is provided as a
ceramic powder (preferably colloidal when used as an inorganic
binder) which, once it is fired, preferably forms into and fills
the spaces between, preferably coating, the ceramic fibers. The
ceramic fibers can be short fibers, long fibers, or a mixture
thereof. Short fibers have a length of about 10-1000, preferably
20-100, .mu.m, and long fibers have a length greater than 10,000
.mu.m (10 mm). Both long and short fibers preferably have a
diameter of 0.1-20, preferably 0.15-10, preferably 0.2-5,
.mu.m.
[0032] Inner layer 22 is preferably 40-98, preferably 50-96,
preferably 60-94, preferably 70-92, preferably 75-90, wt. % ceramic
filler material, balance ceramic fibers. Inner layer 22 preferably
has a porosity less than 20%, preferably less than 15%, preferably
less than about 10%, with the localized porosity at the inner
surface 21 of inner layer 22 being near zero or substantially zero,
in any event less than 5, preferably less than 3, preferably less
than 1, percent. It is important to have a very low or as low as
possible (near zero) localized porosity at the inner surface 21 in
order to provide a gas-tight or substantially gas-tight exhaust
passageway 20, and further to provide a highly smooth surface to
minimize frictional losses and pressure drop across the manifold
10. Inner layer 22 has a thickness of 0.05-8, preferably 0.08-3,
preferably 0.1-2, mm. In the case of non-fibrous composition, inner
layer 22 has a thickness of 0.05-10 mm, preferably 0.1-8 mm,
preferably 1-6 mm.
[0033] The inner layer has low thermal conductivity and thermal
diffusivity compared to metal. In addition, it is backed up by a
highly insulating zone 24 as shown in FIG. 2 and described below.
Consequently, the passing exhaust gas in passageway 20 retains a
much greater proportion of its thermal energy rather than
conducting/convecting it to the outer layers as heat.
[0034] In the embodiment illustrated in FIG. 3, the composite
insulation zone 24 is a multi-layer zone composed of alternating
layers of thin metallic foils 31 having ceramic insulating layers
32 disposed between adjacent ones of the foils 31. The foils 31
preferably are made from a highly reflecting or low emissivity
metal or metal alloy, most preferably aluminum. By "highly
reflecting," it is meant that majority of infra-red radiation is
reflected and not transmitted. The most preferred case is 100%
reflectance of infra-red radiation and 0% transmission or
absorption. The next most preferred is at least 80% reflectance. By
"low emissivity," it is meant that emissivity is less than 0.5 and
preferably less than 0.3. According to published literature,
polished aluminum typically has emissivity in the range of 0.1 to
0.2 even if it is oxidized at 1100.degree. F. The presence of the
foils 31 facilitates a substantial reduction in radiative heat
transfer. The use of multiple foils 31 in the composite insulation
zone 24 assures their effectiveness in the case of degradation of
their properties under excessive heat, specifically for those foils
at a temperature above 1100.degree. F. The metallic foils
preferably are 0.005-0.2 mm, preferably 0.01-0.1, preferably about
0.02-0.05, mm thick. Though it is preferred (for simplicity) that
all the metallic foils 31 in the insulation zone 24 are made from
the same material and have the same thickness, it is contemplated
that different metallic foils 31 can be made from different metals
or have different thicknesses. For example, based on the
reflectance and/or emissivity properties of different metals, one
may select combinations of foils 31 to provide an insulating zone
24 having insulating properties that are particularly suited or
adapted to a specific application, exhaust gas temperature, or
desired outer surface or "skin" temperature. Foils 31 closer to the
inner layer 22 may be selected from high temperature oxidation
resistant alloys such as polished nickel or cobalt alloys, while
foils closer to outer layer 28 may be aluminum or aluminum alloys.
Determination and selection of further combinations of metallic
foils 31 as described herein can be made for a specific application
by persons of ordinary skill in the art without undue
experimentation.
[0035] The ceramic insulating layers 32 in the composite insulation
zone 24 preferably are composed of ceramic fibers and/or
non-fibrous (preferably colloidal) ceramic filler material
similarly to the inner layer 22. In the insulating layers 32,
ceramic fibers can be provided in the form of a ceramic paper as
known in the art; non-fibrous or colloidal ceramic particles can be
provided, e.g., in the form of a suitable particle suspension such
as a ceramic paste. The ceramic fibers and filler material used in
the ceramic insulating layers 32 can be the same materials as inner
layer 22, except for a given insulating layer 32 they are combined
in different ratios compared to the inner layer 22. In the
insulating layers 32, fibers make up 65-99, preferably 70-96,
preferably 75-94, preferably 80-92, preferably 85-90, wt. % of the
layer, with the balance being ceramic filler material.
Alternatively, the ceramic insulating layers 32 can be provided
having substantially 100% ceramic fibers with no or substantially
no filler material.
[0036] Preferably, the ceramic fibers in each of the insulating
layers 32 are silica fibers, alumina fibers, or aluminosilicate (or
boroaluminosilicate) fibers of sufficiently high alumina content,
preferably 40-99, more preferably 50-90, more preferably 55-80,
most preferably 60-75, wt. % alumina. High alumina content in the
insulating layers 32 enables the composite insulation zone 24 to
resist shrinkage at high temperature. Alternatively, high purity
silica fibers may be used if the manifold 10 is to be used with
lower temperature exhaust such that the resulting shrinkage of
insulation zone 24 will not be greater than 0.5%. The insulating
layers 32 preferably have a porosity of 20-95, preferably 40-90,
preferably 60-90, preferably 70-90, preferably about 75-85,
percent. This high porosity is achieved by increasing the ratio of
ceramic fibers to filler material as compared to inner layer
22.
[0037] It is possible to use ceramic filler material having a high
level of microporosity, thereby increasing the thermal resistance,
and consequent insulation capacity, of the layers 32. For example,
silica in the form of silica aerogel particles can be used to fill
interfiber spaces to improve insulating characteristics of the
layer. The composite insulation zone 24 preferably has an overall
thickness of 1-40, preferably 2-30, preferably 2-20, mm, including
all of the metallic foil 31 and ceramic insulating layers 32
therein.
[0038] The ceramic insulating layers 32 preferably are rigidized to
promote dimensional stability and erosion resistance. Rigidization
is preferably achieved with one of the following rigidizers:
colloidal silica or silica precursor, colloidal alumina or alumina
precursor, finely divided glass frit, or a mixture thereof. Where
one of the above (or another) rigidizer is used as the ceramic
filler material in a layer 32, no additional rigidizer is required.
Where a non-rigidizer is used as the ceramic filler material in a
layer 32, that layer preferably also contains 1-15, preferably
3-12, preferably 4-10, preferably 5-8, preferably about 6, wt. %
rigidizer. In a further embodiment illustrated in FIG. 4, each pair
of metallic foils 31 in the insulation zone 24 encloses and defines
a substantially evacuated annular space 35 between the adjacent
foils. As seen in the figure, adjacent pairs of foil layers can
share a foil layer in common, e.g., yielding the illustrated
construction: [foil][evacuated space][foil][evacuated space][foil]
In this embodiment, spacers, e.g. in the form of periodically
spaced annular rings of suitable thickness, may be provided in the
evacuated spaces 35 to maintain the separation of adjacent metallic
foil layers and the integrity of the respective evacuated annular
spaces 35. Cylindrical sections of the insulation zone 24 can be
made according to this embodiment by joining cylindrical metallic
foils 31 around the circumference of their respective terminal
edges as shown in FIG. 4a, and then evacuating the thus-defined
annular spaces between the foils via known or conventional
techniques. The foils can be joined, e.g., by brazing or welding
their circumferentially extending terminal ends 42 together to
create a circumferential weld-seam between the foils that is
substantially air-tight and effective to maintain a vacuum in the
annular spaces 35. Each space 35 preferably is filled with
insulating ceramic material selected from those materials described
for the inner layer 22. In addition, the spaces 35 may also be
filled with loose ceramic powder (the term "loose" means no binder
is provided, the powder particles are uncohered) with low intrinsic
thermal conductivity such as aerogel particle of silica, fumed
silica, stabilized and expanded vermiculite having fine pores,
etc.
[0039] FIG. 5 illustrates a further embodiment in which a
microsphere layer 37 is disposed between adjacent metallic foil 31
layers. Each pair of opposing metallic foil 31 layers defines an
annular space 35a between the foils. The annular space is filled
with substantially evacuated hollow glass or ceramic microspheres
to provide the highly evacuated microsphere layer 37 in between
adjacent metallic foils 31 in the composite insulation zone 24. As
discussed below, the use of evacuated microspheres makes it easier
to provide substantially evacuated spaces in the composite
insulation zone 24 without having to evacuate annular spaces
between metallic foil 31 layers. Such an arrangement results in the
effective thermal conductivity of the microsphere layer 37 being
less than that of a stagnant air layer of equivalent dimensions.
Such a layer of stagnant air has been reported to have thermal
conductivity of about 0.02 BTU/hr-ft-.degree. F. Preferably, the
microspheres are in the range of 10-1000, preferably 100-500
(+/-10%) microns in diameter having a composition substantially
belonging to the system of Al.sub.2O.sub.3--SiO.sub.2-Alkaline
Earth Oxide (CaO, MgO, etc) including fused silica with a softening
point greater than 2000.degree. F. and preferably 25000.degree. F.
Suitable microspheres are commercially available from Hy-Tech
Thermal Solutions, L.L.C., Melbourne, Fla., USA. The microspheres
in the microsphere layer 37 can be, and preferably are, loosely
packed in the annular space 35a between adjacent foils 31. By
loosely packed, it is meant that the microspheres essentially are
poured or injected into the annular space 35a sufficient to fill
the space between the foils, but are not adhesively bound to one
another or to the foils 31, e.g. using any sort of binder. Loosely
packed does not necessarily mean that the microspheres are not
packed tightly or crammed in the annular space 35a (they can be),
only that no adhesive or binder is used to cohere them. Less
preferably, the microsphere layer 37 can include a binder, such as
a ceramic binder material, effective to provide a cohesive
microsphere layer 37 in the annular space 35a. Use of a binder is
less preferred because the binder itself may reduce flowability of
microspheres, making it more difficult to pack them in the annular
space 35a. Preferably, to ensure maximum evacuated volume,
microspheres are packed as tightly as possible into the annular
space 35a to provide the microsphere layer 37.
[0040] The evacuated annular space 35 described above and
illustrated in FIG. 4 has better insulating properties than the
microsphere layer 37 described in the preceding paragraph because
the evacuated annular space 35 has a lower thermal mass than the
microsphere layer 37. However, the microsphere layer 37 may be
preferred because it is easier to make and provide in the manifold
10 from a manufacturing standpoint; i.e. it is not required to join
the metallic foils 31 circumferentially at their terminal edges
because the microsphere layer 37 does not depend on a hermetic air
tight seal. Instead, the microsphere layer 37 approximates an
evacuated space or layer because the internal volumes of the
microspheres themselves are evacuated or at substantially reduced
pressure as a result of the process by which they are manufactured.
Thus, a substantial proportion of the volume of the microsphere
layer 37 is evacuated or maintained at substantially reduced
pressure. Further, the microsphere walls are made from ceramic
material and consequently are poor conductors of heat.
[0041] The composite insulation zone 24 can be or comprise a
combination of any or all of the above-described layers having
insulating properties, in alternating arrangement with the metallic
foils 31. For example, the composite insulation zone 24 can include
a ceramic insulating layer 32, a microsphere layer 37, an evacuated
annular space 35, or any combination of these in alternating
arrangement with and separated by metallic foils 31. Appropriate
combinations of these layers in the composite insulation zone 24
can be determined and selected by a person of ordinary skill in the
art without undue experimentation based on a particular
application.
[0042] The composite insulation zone 24 is effective to insulate
the exhaust gas traveling through passageway 20 adjacent inner
layer 22 such that the gas retains at least 80 preferably 85,
preferably 90, preferably 95, percent of its initial thermal energy
(or temperature) on exiting the manifold 10.
[0043] The strain isolation layer 26 is an optional layer is
disposed exterior to and adjacent, preferably in direct contact
with, the outer surface of the composite insulation zone 24. Strain
isolation layer 26 is disposed between the composite insulation
zone 24 and the outer layer 28. Strain isolation layer 26 is a very
thin layer, preferably 0.05-3, more preferably 0.1-2, mm thick, and
is preferably made of ceramic fibers and/or ceramic filler
material. Preferably, strain isolation layer 26 is composed of the
same or similar ceramic fibers as the inner layer 22. However, the
ceramic filler material in isolation layer 26 is chosen to be metal
resistant; i.e. to resist seepage of molten metal during
application or casting of outer structural layer 28 which is
preferably a metal layer as will be described. The preferred metal
resistant ceramic filler material in strain isolation layer 26
depends on the metal used for outer layer 28. If outer layer 28 is
a ferrous metal layer (i.e. steel), then zirconia, alumina, boron
nitride, zircon (zirconium silicate ZrSiO.sub.4), or a mixture
thereof is the preferred ceramic filler material for layer 26. If
aluminum or an aluminum alloy is used for outer layer 28, then the
preferred ceramic filler material for isolation layer 26 is
alumina, boron nitride, calcium aluminoborate glass, calcium
aluminoborosilicate, calcium aluminate cement or a mixture thereof.
When boron nitride is used (preferably with a ferrous metal outer
layer 28), the boron nitride is preferably applied via spray
coating, dipping, or other similar means. Boron nitride is
preferably applied as a slurry of boron nitride and a liquid such
as water, preferably having ceramic fibers as described above
dispersed therein. Strain isolation layer 26 has 70-99, preferably
80-90, wt. % ceramic fibers, balance filler material. When boron
nitride, zircon, alumina and mixtures containing them are used for
the isolation layer, ceramic fibers may not be required but are
preferred. Layer 26 is a compliant layer and is not rigidized.
[0044] Alternatively, the strain isolation layer is an intumescent
mat. The intumescent mat is composed of ceramic fibers, an
expandable material and a binder material, wherein the basic
construction is that of a highly porous, compliant and resilient
fibrous mat. The binder is present in an amount effective to bind
the ceramic fibers and the expandable material together in the mat
construction to provide a coherent fibrous mat. Suitable binder
materials include organic binders such as methyl cellulose ether,
less preferably starch, less preferably polyvinyl acetate or
polyvinyl butyrol, less preferably another known organic binder,
less preferably a mixture thereof. Less preferably the binder can
be a mixture of organic and inorganic binders. The expandable
material preferably is in the form of embedded particles of
vermiculite, perlite, or combinations thereof, which are dispersed
throughout the fibrous mat. Vermiculite is a naturally occurring
mineral, a member of the phyllosilicate group. Perlite is a
naturally occurring siliceous rock or volcanic glass. Each of these
materials exhibits the unique property of expanding many (i.e.
4-20) times on heating. Preferably, the fibrous mat has the
following composition by weight: 20-60, preferably 25-50,
preferably 30-45 weight percent ceramic fibers, 35-75, preferably
40-65, preferably 45-60 weight percent vermiculite or perlite (or
combination) particles, balance ceramic filler or binder material.
The binder has the effect of constraining the fibers in their
resting orientation or state, resulting in the intumescent mat
being resilient (or rebounding) following external compression or
expansion of the mat. Conversely, the vermiculite particles expand
in volume on being heated, and the expansion of the dispersed
vermiculite particles tends to cause the intumescent mat to expand
on heating. The result of these competing effects is a compliant,
resilient intumescent mat that expands on heating, and contracts or
rebounds substantially back to its initial (unexpanded or
substantially unexpanded) state on cooling. The
expanding/rebounding property of the intumescent mat will be
maintained so long as the mat is not heated above the temperature
at which the binder is baked off. Once this temperature (referred
to as the crossover temperature) has been reached, the binder is
depleted from the mat and the force tending to constrain the
expansion of the ceramic fibers is removed. Therefore, above the
crossover temperature the intumescent mat irreversibly expands from
the heat-induced expansion of the dispersed vermiculite (or
perlite) particles; on cooling the mat will no longer contract or
rebound to its initial state because the contracting/binding
influence of the binder material has been removed. Once the
intumescent mat has been cycled once above the crossover
temperature, it will no longer rebound from an expanded state.
[0045] If the crossover temperature is likely to be exceeded (e.g.
during operation of the manifold 10) then the thickness of the
intumescent mat should be adjusted so that after binder bum-off and
consequent expansion of the vermiculite, the inner layer 22 is
subjected to a modest compression so that it will not be damaged.
Under these conditions, if the metallic outer layer 28 expands
relative to ceramic inner layer 22, expansion of the intumescent
mat is accommodated by the expanded outer layer 28 resulting in
reduced compression at the inner layer 22. It is important to
select the temperature (the reference temperature) at which the
metallic outer layer 28 and the ceramic inner layer 22 are
assembled, and their relative expansion coefficients. By judicious
selection of materials and adjusting effective expansion
coefficients, thermal mismatch can be reduced. For example, a cast
manifold undergoes a large temperature excursion during fabrication
(as determined by the melting point of the metal) and hence there
is a greater likelihood of expansion/contraction mismatch once the
cast outer layer 28 cools. On the other hand, if the outer layer 28
is provided as an assembly of two split-molded or clamshell molded
halves assembled around the inner layers at or near room
temperature, the outer layer 28 is less likely to exhibit so great
a thermal mismatch with the inner layer 22.
[0046] For example, aluminum is cast at a temperature in the range
of 600-650.degree. C., while its temperature during use as the
outer layer in a manifold disclosed herein would be much less, e.g.
200-300.degree. C. Therefore, for a manifold whose metal outer
layer 28 is assembled at room temperature, the outer layer 28 is
likely to be expanding by 200-300.degree. C. (operating temperature
for the outer layer 28); whereas for a cast metallic outer layer
28, the outer layer would not exhibit any substantial thermal
expansion below the casting temperature of 600-650.degree. C.,
which it will not reach due to the highly insulative properties of
the composite insulation zone 24.
[0047] Therefore, when an intumescent mat is used for the strain
isolation layer 26, its expansion-contraction properties and its
thickness relative to (a) the gap between the concentric outer
layer 28 and the insulation zone 24 and (b) the anticipated thermal
excursions due to the fabrication process for the outer layer and
the manifold operating conditions, should be taken into account in
intumescent material selection.
[0048] The intumescent (expansion-contraction) property of the
intumescent mat is advantageous because as the manifold heats up or
cools down with respect to a reference temperature determined by
the fabrication process, expansion of the metallic outer layer 28
and the various ceramic inner layers (22 and 32) can occur at
different rates. The intumescent mat allows for and can accommodate
large changes in the relative displacement of these layers through
its reversible expansion-contraction characteristics over a large
fraction of the mat's original thickness. For example, a 2 mm thick
intumescent mat layer 26 that exhibits a 50% reversible change in
displacement on heating/cooling can fill the space between the
outer layer 28 and insulation zone 24, and provide effective
support even if the spacing between the layer 28 and zone 24 varies
from 1 to 3 mm due to thermal mismatch.
[0049] Strain isolation layer 26 absorbs or dampens vibrational
stresses from the engine and from road harshness. Layer 26 also
accommodates the unmatched thermal expansion characteristics of
outer layer 28 and insulation zone 24. Because layer 28 is
preferably made of metal, and the insulation zone 24 can include
ceramic layers 32, the outer layer 28 has a much higher coefficient
of thermal expansion than insulation zone 24 (typically about or at
least twice as high). Consequently, the expansion and contraction
of outer layer 28 due to thermal cycling may cause the ceramic
layers in the composite insulation zone 24 to fracture in the
absence of a compliant strain isolation layer 26. Even when ceramic
insulating layers 32 are not used, the strain isolation layer 26
still prevents or minimizes mechanical stresses from the outer
layer 28 from being transferred ultimately to the ceramic inner
layer 22 which may be damaged or crack under mechanical stress.
[0050] In the absence of a strain isolation layer 26, intumescent
tabs 38 can be provided in openings 44 made at discrete locations
through the layers of the composite insulation zone 24 (see FIG. 6)
in order to stabilize the inner layer 22 relative to the outer
layer 28 through thermal cycling of the exhaust manifold 10. In
addition, if a strain isolation layer 26 is absent, the intumescent
tabs 38 dampen mechanical vibrations or stresses between the outer
layer 28 and the inner layer 22. Such damping helps ensure the
inner layer 22 of the manifold is not damaged or cracked from
mechanical stresses as described in the preceding paragraph. The
intumescent tabs 38 can be made or cut from the same material as
the intumescent mat previously described.
[0051] As indicated above, outer layer 28 is a structural layer and
preferably is made from metal. Layer 28 can be a metal-containing
layer or a metal composite layer. Metal-containing materials and
metal composites are generally known in the art. Preferably, a
metal composite layer contains ceramic filler material such as SiC,
alumina, or a mixture thereof. Outer layer 28 is disposed exterior
to and adjacent the strain isolation layer 26 if present. In the
absence of a strain isolation layer, outer layer 28 is disposed
exterior to and adjacent the insulation zone 24. An outer metal
layer provides mechanical and impact strength, and ensures
gas-tightness of the exhaust manifold. Preferably, outer layer 28
is made of a ferrous metal, preferably cast ferrous metal or metal
alloy such as steel. Less preferably, outer layer 28 is made from
aluminum, less preferably any other suitable metal or metal alloy
known in the art. Aluminum conserves weight, but may be subjected
to creeping under stress from an applied load. This is why a
ferrous metal (such as steel) outer layer 28 is preferred. However,
aluminum can be used advantageously if steps are taken to avoid
excess loading of the manifold to maintain stresses below the creep
threshold, i.e. with brackets to support the manifold. Preferably,
the outer layer 28 is 1-25, preferably 2-20, preferably 5-15, mm
thick.
[0052] An exhaust manifold having a ceramic inner layer 22, a
composite insulation zone 24, a strain isolation layer 26 and a
metal outer layer 28 can be made as follows. The inner layer 22 is
made first by slip casting the inner layer 22 in the appropriate
configuration for the desired manifold; i.e. having the appropriate
piping configuration, number and placement of runners, etc. Slip
casting techniques are very well known in the art and will not be
described further here, except to describe the preferred slip
casting composition. The slip casting composition, also called
"slip" preferred for use herein is a fused silica based slip
composition. Such a fused silica slip composition is available from
Industrial Ceramic Products, Marysville, Ohio. The slip composition
is used to produce the layer 22 such that after firing, it is
resistant to thermal shock, dimensional changes at elevated
temperatures and high velocity gases.
[0053] The metallic outer layer 28 is prepared as two clamshell
halves that can be suitably joined, e.g. along mating perimeter
flanges 40 provided on each half (see FIGS. 9 and 10).
Alternatively, the halves can be suitably joined by welding as
known in the art. Prior to joining the clamshell halves, the strain
isolation layer 26 (if present), composite insulation zone 24 and
previously slip cast inner layer 22 are prepared and assembled
together in the appropriate order, and placed within the volume of
one of the clamshell halves such that the other clamshell half of
the outer layer 28 can be fit thereover, enclosing all the
constituent layers to form the manifold 10. Then the clamshell
halves are suitably joined by a conventional technique to provide
the finished exhaust manifold 10. Alternatively, if a metal
seepage-resistant strain isolation layer is used, the inner layer
22, insulation zone 24 and strain isolation layer 26 can be
constructed and assembled, and then used as a mold core for casting
the outer metal layer 28 directly thereto.
[0054] To make the composite insulation zone, at least one metallic
foil 31 is coated on one of its surfaces with ceramic fibers,
hollow micro-spheres, ceramic binder, ceramic particulates etc.,
depending on the desired construction for the insulation zone 24.
The coating can be provided as an appropriate slurry or paste
having the desired combination or ratio of fibers to filler
material or other insulating components as described above. Such
ceramic slurries are well known in the art, and typically contain
from 1 to 2 percent by weight solids, balance water. A second
metallic foil is then provided over the coating on the first foil
surface to provide a sandwich composite. This composite is then
folded to conform to the proper shape and contour within the outer
layer 28 clamshell half, between the inner layer 22 and strain
isolation layer 26 (if present) prior to fitting the second outer
layer 28 clamshell half to complete the manifold. Additional layers
of foil/ceramic can be provided if it is desired to provide a
composite insulation zone 24 having multiple ceramic insulating
layers 32. Once the manifold is assembled, it is heated to bake off
the water or other volatiles from the ceramic slurries thus leaving
behind the insulating material. If evacuated annular spaces 35 are
to be used, the metallic foils are formed into concentric
cylindrical forms and their terminal circumferential edges are
joined as described above and illustrated in FIG. 4a, around the
inner layer 22. For simplicity of construction in this embodiment,
the composite insulation zone can be made in a plurality of
discrete sections which are separately and adjacently fitted around
the slip cast inner layer 22. If a microsphere layer 37 is to be
used, then adjacent metallic foils 31 can be assembled to provide
the composite insulation zone 24, and then microspheres injected
into the intermediate annular space 35a between adjacent metallic
foils.
[0055] In a further embodiment, a catalyst belonging to a family of
inorganic compounds, ABO.sub.z where O is oxygen, is added to the
inner surface 21 of the inner layer 22. Preferably the catalyst has
either a perovskite structure (with A being a rare earth element
and an alkaline earth element, and B being a transition metal
element), or a fluorite structure (with A being a rare earth
element and B being Ce or Zr). For a perovskite catalyst, A is
preferably La and Sr, and B is preferably Fe, Co or Mn, less
preferably Ti, Ga, Cr, or Ni. For a fluorite catalyst, A is
preferably a rare earth metal such as Gd or Y and less preferably
alkaline earth metal such as Ca or Mg. When the ABO.sub.z catalyst
has a perovskite structure z is 2-5; when it has a fluorite
structure z is 1-4.
[0056] Other known catalysts, such as partially substituted
BiMoO.sub.3 and Gd-doped CeO.sub.2, also can be used. Such a
catalyst preferably is activated at a lower temperature than the
platinum and palladium catalysts typical of most catalytic
converters, and can begin to convert CO and NO.sub.x to CO.sub.2
and N.sub.2 and O.sub.2 during the period prior to light off after
a vehicle is started. The catalyst preferably is provided as finely
divided (preferably colloidal) particles, and can be added to the
inner layer slip prior to slip casting thereof. Preferably, the
catalyst particles are 0.1-5, preferably 0.5-4, preferably 1-3, wt.
% of the total solids in the inner layer slip.
[0057] In addition to unmatched thermal expansion, another issue
related to metal-encased-ceramic type exhaust manifolds is the need
to provide an appropriate gas-tight seal between the inner ceramic
and outer metallic layers. This is particularly important adjacent
the manifold inlet and exit ports, for example at the lip of the
runner inlets where high temperature exhaust gas flows at high
pressure out from the cylinder head of an engine and into the
manifold. At these locations, an improper or low integrity seal
between the metallic and inner ceramic layers will permit hot
exhaust gases to enter the annular space between those layers where
the gases can damage or potentially oxidize insulation material. In
addition, exhaust gas in this annular space may not be conducted
into the catalytic converter before being emitted to the
atmosphere, thus increasing harmful emissions.
[0058] FIG. 8 shows, in cross-section, a runner 106 of an exhaust
manifold 110 mated or mounted to an associated exhaust port of a
cylinder head 115 (shown schematically in FIG. 8) in order to
receive hot exhaust gases therefrom during engine operation. In
this embodiment, the runner 106 is formed from metallic outer layer
128 and ceramic inner layer 122 generally as described above,
except that they are dimensioned and configured as follows. To form
the runner 106, the outer layer 128 has a metallic extruded portion
131 (preferably in the form of a circumferential portion) that
extends radially from the main tube portion 130 of the outer metal
layer of the manifold, with an inwardly extending (preferably
circular) flange portion 132 located at its terminal end. The
inwardly extending flange portion 132 can be formed integrally with
extruded portion 131 when the outer layer 128 (or its clamshell
half) is cast. The flange portion 132 extends inward and defines a
preferably circular opening or inlet port 133 for the runner
106.
[0059] The ceramic inner layer 122 of the runner 106 also has a
substantially extruded configuration, and extends from the main
tube portion of the ceramic inner layer, extending concentrically
within the metallic extruded portion 131 of the outer layer 128
toward the inlet port 133 or flange portion 132. The ceramic
extruded inner layer 122 of the runner 106 approaches but does not
contact the flange portion 132, leaving a small gap 135 between the
terminal end of the inner layer 122 and the flange portion 132. In
the illustrated embodiment, the extruded (preferably
circumferential) portions of both the outer and ceramic inner
layers 131 and 122 are conically shaped, with the reduced diameter
portions located distal from the main tube of the manifold 110
adjacent the inlet port 133. This construction may be preferred,
for example, when the exhaust port in the cylinder head 115 has a
smaller diameter than the exhaust gas passageway 20 of the main
tube of the manifold 110, and it is desired to taper the diameter
of the runner 106 (inner layer 122) between these two diameters.
Ideally, the ceramic extruded inner layer 122 of the runner 106 has
the same or substantially the same diameter as the main tube
portion of the ceramic inner layer at the point where the two
portions are joined.
[0060] It is desirable that the terminal edge of the ceramic inner
layer 122 and the inlet port 133 are substantially round because
this configuration results in a substantially circular inlet port
133 which permits the highest possible flux of exhaust gas per
area, and also permits the greatest amount of compressive force to
be uniformly exerted against the intermediately located sealing
gasket 140 (described below).
[0061] In one embodiment, the entire ceramic inner layer (main tube
portion and the depending extruded portion(s) 122 for the runner or
runners 106) is slip cast as a single, integral structure wherein
the interior passages of the main tube portion and the extruded
portion(s) 122 have continuous fluid communication therebetween.
See, e.g., FIG. 9 (discussed more fully below) showing a complete
and integrally formed ceramic inner layer that has been slip cast
into an appropriate configuration, which is then enclosed within
opposing metal clamshell halves to provide the manifold.
[0062] A sealing gasket 140 is provided and compressed against the
flange portion 132 adjacent the terminal end of the ceramic
extruded inner layer 122. To achieve this construction, an O-ring
gasket having an annular width equal to or somewhat less than that
of the flange portion 132, and suitable thickness, can be laid down
on the inner surface of the flange portion 132. Subsequently, the
ceramic inner layer 122 can be inserted into position such that its
terminal edge compresses the sealing gasket 140 thereby forming a
seal between the ceramic inner layer 122 and the metallic outer
layer 128 adjacent the runner inlet port 133. Preferably, the
sealing gasket 140 is appropriately dimensioned and is made from a
suitably flexible material such that when compressed as described
in this paragraph, it is caused to expand into the gap 135 thereby
shielding the terminal edge of the ceramic inner layer 122 from
direct contact with the flange portion 132. In this manner, the
fragile terminal edge of the ceramic inner layer 122 never contacts
the metal flange portion 132, and the gasket material provided in
the gap 135 protects the ceramic layer from damage due to unmatched
thermal expansion through thermal cycling of the manifold. Also, a
perimeter extending rib 142 can be provided that extends inward
from the inner surface of the metal extruded portion 131. The rib
142 extends toward the ceramic inner layer 122, but not far enough
that it will contact that layer during cyclic expansion/compression
which may be expected from thermal cycling. This rib 142 limits the
expansion of the sealing gasket 140 away from the flange portion
132 on compression, thereby forcing the gasket 140 into greater and
more intimate contact with the ceramic layer surface resulting in a
more robust seal. The rib 142 can be formed integrally with and as
part of the metal outer layer, or it can be separately provided and
adhered at an appropriate location.
[0063] As seen in FIG. 8, the sealing gasket 140 is entirely
shielded from direct contact with the cylinder head 115, as it is
substantially completely contained in the space between the outer
and ceramic inner layers 128 and 122. Insulation material, e.g. in
the form of a composite insulation zone 124 or other insulating
material or layer as herein described (e.g. similar to the ceramic
insulating layers 32 described above), can be provided in the space
between the outer and ceramic inner layers 128 and 122.
[0064] When installed, the runner 106 is coupled to the cylinder
head 115 such that the exhaust port is aligned with the inlet port
133 of the runner 106. The runner 106 and cylinder head 115 can be
mechanically coupled via suitable or conventional structure used
for that purpose. Conventionally, a washer gasket 150 is provided
and compressed in between the exhaust port and the inlet port 133
mating surfaces to prevent exhaust gas from leaking out from the
exhaust port and around the runner 106 ("blow-by" leakage).
However, as will be evident from the foregoing description and the
associated figures, the washer gasket 150 is only responsible for
preventing blow-by leakage of hot exhaust gases. The separate
sealing gasket 140, which is provided substantially entirely within
the metallic outer layer 128, is separately responsible for
preventing hot exhaust gases from entering the annular space
between the metallic outer and ceramic inner layers 128 and 122 of
the runner 106. Thus, the sealing gasket 140 does not experience
the abrasive sliding action that occurs between the inlet and
exhaust port surfaces, and is not subject to being worn down
thereby, even after a significant period of use and repeated
thermal cycling.
[0065] In the embodiment illustrated in FIG. 8, a baffle washer 160
can be provided adjacent the facing surface of the flange portion
132 extending within the inlet port 133. The baffle washer 160
includes a flat circular portion that is provided or abutted
against the outer or facing surface of the flange portion 132, and
a cylindrical portion extending from the flat circular portion
through the inlet port 133 of the runner 106, past the gap 135 and
at least partially within the ceramic extruded inner layer 122. The
baffle washer 160 is made from Inconel, less preferably stainless
steel or other suitable high strength and oxidation resistant
alloy. The baffle washer 160 is provided to shield the sealing
gasket 140 compressed within the gap 135 from the turbulent flow of
exhaust gas as it enters the inlet port 133. This may increase the
useful life of the manifold by protecting the integrity of the
gasket seal between the metal and ceramic layers located adjacent
the inlet port 133. In addition, because the flat circular portion
of the baffle washer, and not the flange portion 132 of the metal
layer 128, contacts the washer gasket 150 and forms the seal
therewith, the baffle washer 160 also may protect the integrity of
the metallic outer layer of the manifold against oxidation from the
turbulent exhaust gases. This is an advantage because although the
cylinder head 115 typically is equipped with a water cooling
jacket, the runner 106 has no such cooling capability. The
presently described structure minimizes contact between high
temperature exhaust gases and the outer metal layer adjacent the
inlet port 133, which is particularly desirable if that layer is
made of aluminum.
[0066] In an alternative construction, the washer gasket 150 that
provides the seal between the flange portion 132 and the cylinder
head 115 can be provided with a sleeve portion extending upward and
through the inlet port 133 of the runner 106, substantially lining
the inlet port 133. This construction also will prevent turbulent
exhaust gases from impinging on the sealing gasket 140.
[0067] The sealing gasket 140 is made from a suitably flexible
material that is effective to maintain a gas-tight seal as
described above. The sealing gasket 140 can be made, for example,
from Grafoil.RTM. which is a well known compressible and resilient
graphite material having a crystalline structure. In a preferred
embodiment, when such a graphite material is used it is impregnated
or formulated with additives to render it oxidation resistant. For
example, Grafoil.RTM. can be impregnated with a substantially
amorphous material selected from or containing (but not limited to)
borate, silicate and/or phosphate glass of a transition metallic
element, alkaline earth elements, alkali metals, Group III elements
such as zinc, calcium, magnesium, and aluminum, and ceramic fillers
such as TiB.sub.2, SiB.sub.6 and TiC. Such materials can be chosen
so as to obtain a protective layer separating the Grafoil and hot
exhaust. Alternatively, the sealing gasket 140 also can be made out
of ceramic fibers. In this case, one should select fiber
compositions that will not undergo slow shrinkage or fracture
during operating conditions. In this case it is desirable to
compress the gasket seal 140 so that under any operating
conditions, the movement between opposing surfaces of the gasket
seal 140 will exhibit elastic deformation.
[0068] In a further alternative, the gasket seal 140 can be
constructed having two parts or layers; for example with one layer
that faces the hot exhaust gas being made out of ceramic fibers
(which are substantially oxidation resistant), and another layer
located distally from the exhaust gases (more proximate the
insulating material provided between the ceramic inner layer 122
and the metal outer layer 128) being made of a carbon or graphite
based composition such as Grafoil.RTM.. Such a design combines the
oxidation resistance of ceramic fibers with the excellent sealing
capability of flexible graphite based materials like
Grafoil.RTM..
[0069] In addition to oxidation resistant additives, the gasket
seal material also can include additives to enhance its thermal
conductivity. Suitable conductivity enhancing additives include,
e.g., Ag, BN, AlN, alumina, magnesia, SiC. By enhancing the thermal
conductivity of the seal gasket 140, the gasket 140 exhibits more
efficient heat transfer properties enabling it to dissipate more
heat. As a result, its temperature can be kept as low as possible
to prevent or slow or minimize oxidation from the hot exhaust
gases.
[0070] In the construction illustrated in FIG. 8, the
metal-to-ceramic seal is provided by a sealing gasket 140 located
in a position in between the respective layers adjacent the inlet
port 133 for the associated runner 106, yet it is substantially
entirely shielded from contact with the cylinder head 115 by the
metallic outer layer 128 (flange portion 132). Also in this design,
the terminal end of the ceramic inner layer 122 is completely
encased within the metallic outer layer 128 adjacent the inlet port
133 of the runner, and does not come into contact with the cylinder
head. This design has multiple advantages. Because the ceramic
layer is not exposed, the ceramic layer is protected from damage
during handling and assembly of the manifold to the engine. Also,
more precise compression of the gasket seal 140 can be achieved
between the spaced terminal ends of the respective ceramic and
metallic layers adjacent the inlet port 133 of the runner 106.
[0071] Selection of gasket materials having suitable flexibility,
compressibility, stiffness, etc., can be employed to achieve a
precisely defined degree of compression or compressive force in the
final installation, depending on manifold-specific design criteria
such as the strength and/or brittleness of the particular ceramic
composition used for the inner layer. Also, the gasket seal 140 can
be made from a relatively soft material compared to the washer
gasket 150 used to prevent blow-by leakage, which is an advantage
because softer materials are more suitable for sealing against
ceramic layers because they exert less stress on the ceramic while
ensuring a gas-tight seal. Use of a soft gasket material would not
be practical were the ceramic layer to be sealed directly against
the cylinder head as in conventional constructions, because a soft
gasket would wear very quickly due to manifold-to-cylinder head
abrasion from thermal cycling because the head and the manifold
will experience different rates of expansion and contraction. In a
conventional manifold-to-cylinder head surface seal, the gasket is
extremely hard and compresses only slightly, perhaps 10-15%. The
sealing gasket 140 in the present embodiment preferably is
compressed at least 20%, more preferably at least 30% between the
concentric ceramic and metallic layers 122 and 128.
[0072] As a result, manifold longevity is improved because the
insulation layer (or composite insulation zone 124) located between
these layers will not be subjected to turbulent exhaust gases as a
result of a degraded seal between the ceramic and metallic layers
from manifold-to-cylinder head abrasion. Even if the washer gasket
150 were to become damaged or its integrity breached, this would
not affect the integrity of the sealing gasket 140 which prevents
turbulent exhaust gases from entering the annular insulation space
between the ceramic and metallic layers. A further advantage of
using the separate sealing gasket 140 is that the integrity of the
resulting seal can be tested during the manufacturing process of
the manifold itself, and no longer is left to the final engine
assembly operation.
[0073] After the manifold has been assembled, in particular after
the construction of the runner 106 as described above has been
completed, it may be desirable for certain high temperature
applications (e.g. exhaust gas temperatures about or greater than
1850.degree. F.) to further seal the gap 135 between the ceramic
and metallic layers via methods that may include brazing, dip
coating or thermal spray coating.
[0074] Referring now to FIG. 9, a further embodiment is shown where
O-ring gaskets 170 are provided at strategic locations in the
annular space between the ceramic inner layer 22 and the metallic
outer layer 28 of the main tube portion of the exhaust manifold 10.
In particular, a pair of O-ring gaskets 170 are provided in the
main tube portion located on opposite sides of each runner 106.
These O-ring gaskets 170 are or can be made from the same or
similar materials as the sealing gasket 140 previously described,
and are provided to prevent turbulent exhaust gases from traveling
through the insulation space between the ceramic and metallic
layers. The O-ring gaskets 170 are optional components, and are
provided as a failsafe in the unlikely event the sealing gasket 140
described above should fail. In that event, the O-ring gaskets 170
will confine any exhaust gas that may be permitted to enter the
insulation space to only that space adjacent the associated runner
106 where the gas entered; turbulent exhaust gases will not be
permitted to flow through the remainder of the manifold insulation,
and any loss of insulating capacity due to damage from these gases
will be confined to only the runner 106 whose sealing gasket 140
might have failed.
[0075] An additional benefit of the O-ring gaskets 170 is that the
spacing between the ceramic inner and metallic outer layers 22 and
28 can be very precisely controlled based on the thickness and
compression of the O-ring gaskets, so that this spacing is no
longer dependent on the insulation material (such as insulation
zone 24 described in detail above) to provide the spacing. If the
O-ring gaskets are to be provided solely for spacing purposes, then
alternatively a ceramic rope 180 can be wrapped around the main
tube of the ceramic inner layer 22 of the manifold 10 in a
generally helical configuration as shown in FIG. 10 as a spacer.
This configuration will not prevent the travel of exhaust gases in
the insulation space or zone 24 because of the helical pathway of
the rope 180, but it can be used as an effective spacer. The O-ring
gaskets 170 or ceramic rope 180 are made from a compressible,
compliant material, similar as that described for the sealing
gasket 140 above. Therefore, these gaskets 170 or rope 180 also are
able to absorb relative expansions/contractions between the
concentric metallic outer and ceramic inner layers 28 and 22 of the
manifold 10. Thus, when either the O-ring gaskets 170 or the
ceramic rope 180 is/are used as spacers, these elements can take
the place of a strain isolation layer 26 as described above.
Alternatively, if a strain isolation layer 26 is to be used, then
it is laid into the metallic clamshell halves for the outer layer
28 along the inner surface thereof prior to installing the inner
layer 22 structure therein as shown in FIGS. 9-10 (discussed
below).
[0076] When either the O-ring gaskets 170 or ceramic rope 180
is/are used as described above, the manifold can be assembled as
follows. First, the ceramic inner layer 22/122 is slip cast as a
unitary structure in the appropriate configuration for the desired
manifold; i.e. having appropriately shaped and oriented main tube
portion, depending extruded portions for runners, etc. Next, the
O-ring gaskets 170 or ceramic rope 180 is/are provided around the
main tube portion of the slip cast inner layer 22 in the
appropriate configuration or at appropriate locations. The O-rings
may be fashioned out of a ceramic rope that is cut to exact length
so that when the rope is wrapped around the inner layer and the
metallic clamshells are closed, resultant compression forces the
two ends of the rope to join and effectively act as an O-ring.
Alternatively, ceramic rope can be wrapped around tightly for
multiple turns so that the contacting faces and sides are pressed
against each other to form O-ring type seal. Grooves may be
provided in the metallic shell to facilitate positioning and
constraining the ceramic rope or O-ring gaskets for sealing
purposes.
[0077] Then, ceramic inner layer 22/122 is inserted into one of a
pair of clamshell halves for the metallic outer layer 28/128 of the
exhaust manifold. In the embodiments shown in FIGS. 9 and 10, the
clamshell halves are made such that all the runners are provided in
one clamshell half. The ceramic inner layer 22/122 having the
O-ring gaskets 170 or ceramic rope 180 thereon is inserted into one
of the clamshell halves so that the respective runner portions of
the ceramic inner and metallic outer layers 122 and 128 are
appropriately aligned. Once the appropriate alignment has been
achieved, the ceramic layer 22/122 is seated in the respective
clamshell half and then the second clamshell half is aligned and
assembled to the first clamshell half, thereby enclosing the
ceramic inner layer 22/122 therebetween. The O-ring gaskets 170 or
ceramic rope 180 is/are designed so that they are compressed in the
space between the ceramic layer 22/122 and the opposing clamshell
halves of the metallic outer layer 28/128 when the clamshell halves
are pressed together. Uniform compression across the entire
manifold can be achieved by measuring the compressive force at
periodic locations, e.g., using conventional load cells mounted to
a fixture for compressing the clamshell halves together.
Compressive load can be measured, for example, at four locations on
the manifold, preferably corresponding to locations where O-ring
gaskets 170 or the ceramic rope 180 is/are compressed between the
clamshell halves and the ceramic inner layer 22/122. The clamshell
halves can be selectively compressed together and fastened at
selected locations such that the compressive force across the
entire manifold as determined by the load cells is substantially
uniform. It will be understood that adjustments can be made to the
fastening means to ensure uniform compression. The clamshell halves
can be secured together via any conventional or suitable fastening
means, including welding, bolting or other suitable fasteners.
[0078] In this embodiment, it is preferred that a series of small
access holes 190 be drilled through the wall of at least one of the
clamshell halves so that insulating material can be provided or
injected into the annular space between the respective ceramic and
metallic layers once the manifold has been assembled. The
insulating material can be in any suitable form that will permit
injection through these access holes 190 that will substantially
fill up the aforementioned annular space to thereby provide an
appropriate insulating layer. Suitable insulating materials include
ceramic fibers and filler materials, as well as glass or ceramic
microspheres discussed above, or slurries of any of these or
combinations of these. If a slurry is used, preferably the
continuous phase is a highly volatile material such as alcohol,
less preferably water. The slurry can be used to fill the annular
space and then the volatile carrier baked or flashed off such that
the flashed vapor can escape through the access holes 190 before
they are sealed (described in next paragraph). If a separate strain
isolation layer 26 is to be used in this embodiment, then it is
laid down on the inner surface of each clamshell half prior to
assembling around the ceramic layer 22 as shown in FIGS. 9-10, and
the access holes 190 must be drilled completely through the outer
layer 28 and the strain isolation layer 26 to permit injection of
insulating material.
[0079] A metallic foil layer also can be provided in this
embodiment. If a metallic foil layer is to be provided, it should
be wrapped around the ceramic inner layer 22/122 prior to encasing
that layer within the metallic outer layer 28/128, and preferably
it is wrapped against the ceramic inner layer 22/122 prior to
placing the O-rings 170 or ceramic rope 180 thereon. If the
metallic foil is provided over the O-rings 170 or ceramic rope 180,
then it will interfere with uniformly filling the space between the
ceramic and metallic layers with insulation material through the
access holes 190. Once this space has been filled, the access holes
190 can be closed as by welding a plug therein. Alternatively, the
holes 180 can be threaded to accommodate threaded bolts or plugs
(not shown).
[0080] Yet another method may be used to place ceramic insulation
layers and metal foils between the space created by ceramic inner
layer (22/122), metallic outer layer (28/128) and seals such as
O-rings 170 or ceramic rope 180. Specifically, insulation
components can be fabricated into modular fashion so that
individual insulation modules can be inserted into and fitted
within the annular sections defined radially between the ceramic
inner and metallic outer layers, and longitudinally between
adjacent O-rings 170 or turns of the ceramic rope 180. Since the
contacting area of seals is much smaller than the contacting area
of the modular ceramic insulation, the net effect on heat transfer
due to slightly different thermal resistance of the seals will be
very small. For example, two "C" sections or insulation modules may
be placed in opposing relationship in the annular spaces defined
for respective clamshell halves prior to assembly thereof, such
that upon closing of the clamshell the opposed "C" shaped modules
join to form a complete annular insulating layer. Similarly in cone
shaped regions of the manifold (such as runner 106), a suitable
cone shaped insulation package can be made for easy placement. It
is understood that there are several methods to achieve the
manifold architecture described in FIGS. 1-10 and the methods
listed above are examples illustrating basic principles of
assembly.
[0081] An exhaust manifold disclosed herein facilitates faster
light off of the catalytic converter because the exhaust gas
retains a greater proportion of its initial thermal energy on
exiting the manifold and entry into the catalytic converter. Also,
because heat loss to the exhaust manifold is significantly reduced,
lighter metal such as aluminum can be used in the manifold provided
operational stresses to the manifold are minimized as described
above. The need for heat shields and for other high temperature
resistant materials such as silicone-coated wires in the engine
compartment also may be reduced or eliminated. Further, manifolds
disclosed herein resist erosion and corrosion because the ceramic
inner layer 22 effectively resists these effects.
EXAMPLES
[0082] A series of 4-inch diameter disc composites were prepared in
order to simulate the composite structure of an exhaust manifold
having a composite insulation zone as described herein, and to
demonstrate the improved insulative properties of such a composite
structure. In all, four disc composites were prepared, three
samples incorporating a composite insulation zone and a fourth
sample that did not have a composite insulation zone. All four
samples included an inner ceramic layer made by pouring a fused
silica slip composition on a Plaster of Paris mold. The slip
composition was product ICP-3 available from Industrial Ceramic
Products, Marysville, Ohio. After the slip was dried each dried
piece was fired in a ceramic kiln to cure the piece and form a
finished inner ceramic layer. All four of the inner ceramic layers
had a thickness of 0.265 inch.
[0083] Three separate composite insulation zones also were
prepared. The first two consisted of alternating layers of aluminum
foil and ceramic paper but were of different overall thickness (see
table 1 for thicknesses). The third layer consisted of alternating
layers of aluminum foil and thin layers of Zyalite.TM. ceramic
paste from Vesuvius-McDanel, Beaver Falls, Pa. Each of these
composite layers was then laminated on one side to an inner ceramic
layer, and on the other side to a layer of cold rolled steel to
produce an overall composite structure of:
[0084] [ceramic inner layer][composite insulation zone][cold rolled
steel layer]This composite structure was meant to simulate the
composite structure of an exhaust manifold having the analogous
layers as described hereinabove.
[0085] The fourth ceramic inner layer was laminated directly to a
cold rolled steel layer to simulate the laminate construction of a
conventional ceramic-lined exhaust manifold, and resulted the
following composite construction: [ceramic inner layer][cold rolled
steel layer]
[0086] A test apparatus illustrated schematically in FIG. 7 was
used to test the insulative properties of each of the four-above
described sample composites. As seen in FIG. 7, one-inch thick
Fiberfrax insulation boards 50 were used to create a vertically
oriented enclosed channel 52. Each of the four disc composite test
pieces (ref. num. 55 in FIG. 7) was suspended at the top of the
channel 52 with the ceramic inner layer facing downward and exposed
to the channel 52, and the steel layer facing upward away from the
channel. An oxy-acetylene torch 54 was inserted through the
Fiberfrax wall at the base of the channel 52 and ignited to heat
the ceramic inner layer and simulate a hot exhaust gas condition.
For each of the four samples the exposed surface temperatures of
the inner ceramic layer and the steel layer were monitored by
thermocouples, and the steady state values are reported below in
table 1. For sample 2, data were collected for two ceramic inner
layer surface temperatures which is the reason for the notation
"#1" and "#2" for that sample. TABLE-US-00001 TABLE 1 Sample 1
Sample 2 Sample 3 Comparative Ceramic 0.265 inch 0.265 inch 0.265
inch 0.265 inch inner layer thickness Composite 0.105 inch 0.120
inch 0.120 inch None insulation zone thickness Cold rolled 0.187
inch 0.187 inch 0.187 inch 0.187 inch steel layer thickness
Insulation Aluminum Aluminum Aluminum None zone foil/ foil/ foil/
composition Ceramic Zyalite Zyalite paper Ceramic 1875.degree. F.
#1: 1856.degree. F. 1906.degree. F. 1851.degree. F. inner layer #2:
1882.degree. F. surface T Steel 340.degree. F. #1: 325.degree. F.
212.degree. F. 878.degree. F. surface T #2: 384.degree. F. Ambient
71.degree. F.; 71.degree. F.; 72.degree. F.; 71.degree. F.;
Conditions 20% RH; Air 20% RH; Air 20% RH; Air 20% RH; Air speed =
0 speed = 0 speed = speed = 0 8.9 MPH
[0087] From the above it will be seen that a composite insulation
zone including layers of highly reflective material such as
aluminum foil greatly improves the insulative properties of the
overall composite structure. Thus the outer metal surface or "skin"
of the overall composite structure exhibits a greatly reduced
surface temperature compared to a conventional construction where
no composite insulation zone is provided.
[0088] Although the hereinabove described embodiments of the
invention constitute the preferred embodiments, it should be
understood that modifications can be made thereto without departing
from the spirit and scope of the invention as set forth in the
appended claims.
* * * * *