Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02414160 2002-12-12
Title
MULTI-LAYER EMBOSSED HEAT SHIELD FOR A VEHICLE
EXHAUST SYSTEM AND OTHER HEAT INSULATION
APPLICATIONS
Scope of the Invention
[0001] This invention relates to a heat shield with thermal, acoustical and/or
vibrational abatement properties and, in particular, to a heat shield for an
exhaust system
of an internal combustion engine.
Background of the Invention
[0002] Heat shields for exhaust systems of internal combustion engines are
known,
for example, as described in U.S. Patent No. 5,590,524 to Moore et al. issued
January 7,
1997, U.S Patent No. 6,177,157 to Cota issued January 23, 2001, and U.S.
Patent No.
6,231,944 to Holt issued May 15, 2001. These shields are useful to prevent
heat
transmitted from an engine's high temperature components, such as the exhaust
manifold,
from reaching and damaging adjacent non-metal components. Examples of
operating
apparatus having non-metal components in need of protection include
alternators, starter
motors, turbo chargers, plastic storage containers for water and brake
cylinder reservoirs
wiring and tubing. These shields are also useful to reduce the transfer of
noise and
vibrations coming from the engine and various components of the exhaust
system,
including the manifold.
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[0003] It is desirable that a heat shield for exhaust systems of internal
combustion
engines to meet the following criteria:
(a) to provide thermal shielding;
(b) to abate noise;
(c) to abate vibrations;
(d) strength to resist damage;
(e) to protect the engine/manifold from mechanical damage;
(f) recyclable;
(g) easy and inexpensive to manufacture;
(h) easy to cut the edges of the shield into the desired shape.
[0004] Known heat shields for exhaust systems of internal combustion engines
include those formed of a single metal layer. Among the disadvantages of such
shields
are that they do not efficiently reduce noise, they have a tendency to
vibrate, and that they
are the least effective of all heat shield types in reducing conductive heat
transfer.
Known heat shields for exhaust systems of internal combustion engines include
those
formed of two metal layers of either equal or unequal thickness. Such shields
tend to be
superior in terms of ability to abate transfer of heat, noise and vibrations
over shields
formed of a single metal layer. However, the present inventor has appreciated
that the
ability of these shields to abate transfer of heat, noise and vibrations can
be further
improved.
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[0005] Known heat shields for exhaust systems of internal combustion engines
include those formed of two metal layers of either equal or unequal thickness,
and a layer
of insulating material (e.g. fiberglass, ceramic, aramid or air) sandwiched
between the
two metal layers. Such shields are, for example, described in U.S. Patent Nos.
5,590,524
and 6,231,944. The present inventor has appreciated that such shields suffer
from several
disadvantages. For example, such shields are not easily recyclable because of
the non-
recyclable layer of insulating material. Such shields are relatively costly
and
inconvenient to manufacture because of the process steps required to insert
the layer of
insulating material between the two metal layers. Also, after the layer of
insulating
material is inserted between the two metal layers, the edges of such shields
are difficult to
cut into the desired shape because the layer of insulating material tends to
tear in an
uncontrollable fashion instead of shear exactly along the shear edge of the
blanking die or
other cutting tool used in heat shield manufacturing. In addition, it is very
problematic to
blank or cut mufti-layer sandwich compositions that incorporate different
layers of
metallic and/or non-metallic materials having different mechanical properties
sand
different layer thickness. Furthermore, the manufacturing process of any fiber
materials
pose respiratory health hazards because of the airborne ceramic or glass or
other micro
particles they release to the environment. Also, such shields are usually
heavy, due to the
thick metal outer layer or layers. Further, the present inventor has
appreciated that the
layer of insulating material is susceptible to damage, which is caused by
periodic heat
shock and vibration loads of the environment and by the moisture it can
absorb, thus
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resulting in the disintegration of the fibers and reducing the serviceable
life of such
shields.
[0006] U.S. Patent No. 5,590,524 describes a shield comprising two metal
layers
which have substantially different thicknesses and a layer of insulating
material between
the two metal layers. This patent is a good illustration of the approach that
persons
skilled in the art have taken in attempting to improve the thermal, acoustical
and
vibrational abatement properties of such shields. Persons skilled in the art
expect that by
providing layers which are different as in having substantially different
thicknesses, these
two layers would have mismatched resonant frequencies resulting in more
efficient
damping and absorption of acoustical and vibrational energy. Persons skilled
in the art
also expect that providing a third layer of insulating material would improve
the damping
properties of the shield by increasing the friction resisting the relative
movement between
the two metal sheets. Further, persons skilled in the art also expect that a
third layer of
insulating material would provide more shielding to thermal transmission by
increasing
the number of interface surface barriers within the shield. The present
inventor has
appreciated that, surprisingly, the use of two metal layers with a layer of
insulating
material sandwiched in between is not the best approach for producing shields
with
superior thermal, acoustical and vibrational abatement properties.
Summary of the Invention
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[0007] To at least partially overcome the disadvantages of previous heat
shields,
especially for applications where heat management, damage protection,
vibration control,
noise emittance, recyclability, and geometrical restrictions are given high
priority, the
present invention provides a heat shield with improved thermal, acoustical
and/or
vibrational abatement properties. The present invention also provides a shield
which has
strength to resist damage, is recyclable, and is relatively easy and
inexpensive to
manufacture.
[0008] An object of the present invention is to provide a shield with improved
thermal abatement properties compared to the previous double-layer metallic
heat shields
of identical overall thickness and comparable metallic materials.
[0009] A further object of the present invention is to provide a shield with
improved
acoustical abatement properties compared to the previous double-layer metallic
heat
shields of identical overall thickness and comparable metallic materials.
[0010] A further object of the present invention is to provide a shield with
improved
vibrational abatement properties through increased stiffness.
[0011] A further object of the present invention is to provide a shield which
has
strength to resist damage better than prior art heat shields, including the
ones with a layer
of insulating material.
[0012] A further object of the present invention is to provide a shield which
is
recyclable.
[0013] A further object of the present invention is to provide a shield which
has a
longer serviceable life due to better vibration management.
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[0014] A further object of the present invention is to provide a shield which
has
improved corrosion resistance without changing its base material and/or its
coating.
[0015] A further object of the present invention is to provide a shield which
is
relatively easy and inexpensive to manufacture.
[0016] A further object of the present invention is to provide a shield which
is
relatively easy to cut to the desired shape at its edges.
[0017] A further object of the present invention is to provide a shield that
is
manufacturable without the health hazard that non-metallic insulators pose. A
further
object of the present invention is to provide a shield that has much less
weight and can
contribute to savings in fuel consumption.
[0018] Accordingly, in one aspect, the present invention provides a heat
shield for an
exhaust system of an internal combustion engine, comprising three metal layers
shaped to
conform generally to the shape of a high temperature portion of said exhaust
system; said
metal layers having substantially the same shape and extending in face-to-face
adjacency
with one layer positioned between the other two layers; said three metal
layers being
substantially identical.
[0019] Preferably, said three metal layers are substantially identical in
being of
substantially the same thickness and composition.
[0020] Preferably, one of said three metal layers may differ in thickness from
the
other two metal layers by not greater than 20%, more preferably not greater
than 15%, or
10%, or 5%.
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[0021] Preferably, two of said three metal layers have an identical thickness,
and
more preferably, all said three metal layers have an identical thickness.
[0022] Preferably, each of said metal layers has a thickness of between about
0.1 mm
and about 0.5 mm, more preferably between about 0.1 mm and about 0.3 mm, or
between
about 0.1 mm and about 0.2 mm.
[0023] Preferably, each of said metal layers has a thickness of about 0.34 mm.
[0024] Preferably, each of said three metal layers comprise the same base
metals; or
two of said three metal layers comprise the same base metals and the remaining
layer
comprises material that is an alloy of the material of the other two layers;
or each of said
three metal layers comprises material that is an alloy of the material in at
least one of the
other two layers.
[0025] Preferably, each of said metal layers comprises materials selected from
the
group consisting of aluminized steel, aluminum coated steel, aluminum cladded
steel,
galvanized steel, and aluminum.
[0026] Preferably, said heat shield is manufactured by a process under which
said
metal layers are compressed together under pressure.
[0027] Preferably, each of said metal layers has a non-planar shape.
[0028] Preferably, each of said metal layers is deep drawn to a ratio of depth
to
thickness of from about S:1 to about 100:1, more preferably from about 10:1 to
about
75:1, or from about 15:1 to about 50:1.
[0029] Preferably, hems are provided along at least some edges of said heat
shield to
maintain said metal layers nested together.
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[0030] Preferably, the exterior surface of said shield is coated with a
coating effective
to provide corrosion-resistant protection to said shield.
[0031] Preferably, the exterior surface of said shield is coated with a
coating effective
to provide heat reflection.
[0032] Preferably, said coating is high temperature resistant.
[0033] Preferably, said high temperature portion of said exhaust system is an
exhaust
manifold.
[0034] Preferably, said high temperature portion of said exhaust system is
selected
from the group consisting of a catalytic converter, a muffler, and an exhaust
pipe.
[0035] Preferably, the shield is spaced away from the exhaust system by an air
gap,
with preferably, a significant portion of said air gap being between about 1
mm and about
30 mm, more preferably between about 3 mm and about 15 mm wide.
[0036] In another aspect, the present invention provides a heat shield for an
exhaust
system of an internal combustion engine, comprising at least two metal layers
shaped to
conform generally to the shape of a high temperature portion of said exhaust
system; said
metal layers having substantially the same shape and extending in face-to-face
adjacency;
wherein at least one of said metal layers has a surface comprising raised
bosses.
[0037] Preferably, said heat shield comprises two metal layers, wherein one of
said
two metal layers is to be positioned proximal to said high temperature portion
of said
exhaust system and the other of said two metal layers is to be positioned
distal to said
high temperature portion of said exhaust system.
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[0038] Preferably, the metal layer which is to be positioned distal to said
high
temperature portion of said exhaust system has a surface comprising raised
bosses.
[0039] Preferably, the metal layer which is to be positioned proximal to said
high
temperature portion of said exhaust system has a surface without raised
bosses.
[0040] Preferably, said heat shield comprises three metal layers, wherein one
of said
three metal layers is to be positioned proximal to said high temperature
portion of said
exhaust system, one of said three metal layers is to be positioned distal to
said high
temperature portion of said exhaust system, and one of said three metal layers
is
positioned between the proximal metal layer and the distal metal layer.
[0041] Preferably, the metal layer which is to be positioned proximal to said
high
temperature portion of said exhaust system has a surface comprising raised
bosses, and
the metal layer which is to be positioned distal to said high temperature
portion of said
exhaust system has a surface comprising raised bosses.
[0042] Preferably, the metal layer positioned between the proximal metal layer
and
the distal metal layer has a surface without raised bosses.
[0043] Preferably, said heat shield comprises four metal layers, wherein one
of said
four metal layers is to be positioned proximal to said high temperature
portion of said
exhaust system, one of said four metal layers is to be positioned distal to
said high
temperature portion of said exhaust system, one of said four metal layers is
positioned
adjacent to the proximal metal layer, and one of said four metal layers is
positioned
adjacent to the distal metal layer.
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[0044] Preferably, the metal layer which is to be positioned distal to said
high
temperature portion of said exhaust system has a surface comprising raised
bosses, and
the metal layer which is positioned adjacent to the proximal metal layer has a
surface
comprising raised bosses.
[0045] Preferably, the metal layer which is to be positioned proximal to said
high
temperature portion of said exhaust system has a surface without raised
bosses, and the
metal layer which is positioned adjacent to the distal metal layer has a
surface without
raised bosses.
[0046] Preferably, the raised bosses have a height of between about 0.25 mm
and 2.5
mm.
Brief Description of the Drawings
[0047] Further aspects and advantages will become apparent from the following
description taken together with the accompanying drawings in which:
[0048] FIG. 1 is a perspective view of a shield in accordance with a first
preferred
embodiment of the present invention;
[0049] FIG. 2 is an inside view of the shield shown in FIG. 1;
[0050] FIG. 3 is an exploded cross-sectional view of the portion identified as
12 in
FIG. 1;
[0051] FIG. 4 is an enlarged view of the portion identified as 20 in FIG. 2
illustrating
the structural detail at peripheral edge portions of the shield where a hem is
formed;
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[0052] FIG. 5 is a perspective view of a shield in accordance with a second
preferred
embodiment of the present invention;
[0053] FIG. 6 is a cross-sectional view of the portion identified as 112 in
FIG. S;
[0054] FIG. 7 is a cross-sectional view of a shield in accordance with a third
preferred embodiment of the present invention at a location similar to the
cross-section of
FIG. 6; and
[0055] FIG. 8 is a cross-sectional view of a shield in accordance with a
fourth
preferred embodiment of the present invention at a location similar to the
cross-section of
FIG. 6.
[0056] Throughout all the drawings and the disclosure, similar parts are
indicated by
the same reference numerals.
Description of First Preferred Embodiment
[0057] Reference is made to FIGS. 1 to 4 which show a first preferred
embodiment of
the present invention.
[0058] As illustrated in FIG. 1, the present invention is a heat shield 10.
FIG. 3
illustrates an exploded cross-sectional view of the portion identified as 12
in FIG. 1. As
shown in FIG. 3, the shield 10 comprises three metal layers: an inner metal
layer 14, a
middle metal layer 16, and an outer metal layer 18. All three metal layers 14,
16 and 18
of the preferred embodiment are identical in being of identical thickness and
composition.
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[0059] In the preferred embodiment, each of the three metal layers 14, 16 and
18 has
a thickness of between about 0.1 mm to 0.50 mm. The total thickness of the
three metal
layers 14, 16 and 18 together is between about 0.3 mm and 1.5 mm.
[0060] The shield 10 must generally be capable of surviving exposure to
extreme
temperature conditions caused by heat transmitted from high temperature
portions of an
exhaust system. For example, shield 10 shown in FIGS. 1 to 4 is intended to be
used
with an exhaust manifold of an internal combustion engine. An exhaust manifold
directly
receives exhaust gases, for example at temperatures of about 1550 degrees F.,
from the
engine causing the exterior surface of the exhaust manifold to reach high
temperatures,
for example of about 1400 degrees F and the shield 10 to reach temperatures in
the range
of about 1000 degrees F. In practice, the inner metal layer 14 generally does
not exceed
1000 degrees F. to 1200 degrees F. because it is spaced apart from the exhaust
manifold
by an air gap. Therefore, the shield 10 comprises material that can withstand
a
temperature of 1000 degrees F., and more preferably 1200 degrees F without
significant
degradation.
[0061] In the preferred embodiment, all three metal layers 14, 16 and 18 have
identical compositions in that they comprise the same base metals. This
ensures similar
thermal expansion rate in order to avoid building up frictional and
compression stress
among layers if exposed to heat. Specifically, the three metal layers 14, 16
and 18 of the
preferred embodiment are all made from aluminized steel.
[0062] Generally, aluminized steel is produced by contacting liquid aluminum
with a
solid steel surface such as a steel sheet. For example, a steel sheet may be
dipped in an
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aluminum bath. Alternatively, it is believed that vacuum deposition aluminum-
coated
steel may be used. Vacuum deposition aluminum-coated steel is produced by a
process
also referred to as vacuum metalizing or aluminum vapor deposition, where
aluminum is
vaporized, typically by applying an electric arc current to aluminum wire, and
the
vaporized aluminum is deposited as a thin coat or film on a relatively cool
sheet steel
substrate in close proximity, in a vacuum environment. In the preferred
embodiment, the
steel is coated with a thin coating or film of aluminum on both sides of each
metal layer.
[0063] To manufacture a heat shield in accordance with the preferred
embodiment,
blanks, consisting of the three metal layers 14, 16 and 18 are obtained from a
supply of
aluminized steel. The three layers 14, 16 and 18 are positioned relative to
one another
such that they are in face-to-face adjacency. Preferably, the three layers 14,
16 and 18
are mechanically secured to maintain a unitary assembly by means such as, but
not
limited to, tabs, hems, rivets or welding along scrap edge portions. The inner
metal layer
14, middle metal layer 16 and outer metal layer 18 are then compressed
together between
two dies and formed into the desired shape in one or several forming stages
using an
amount of pressure of preferably from about 1200 psi to about 1400psi.
Consequently, all
three layers 14, 16 and 18 have the same shape and extend in face-to-face
adjacency.
[0064] In the preferred embodiment, the shield 10 is to be used with an
exhaust
manifold of an internal combustion engine. Therefore, the shield 10 is shaped
to conform
generally to the shape of an exhaust manifold of an internal combustion engine
as shown
in FIGS. l and 2.
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[0065] Deep drawing techniques are used in the shaping operation to prevent
unwanted folds and wrinkles from developing in the metal layers 14, 16 and 18.
The
inventor has surprisingly and unexpectedly found that it is possible to
effectively deep
draw the three metal layers 14, 16 and 18 together. The inventor has also
found that, by
using metal layers of the same thickness and composition, it is easier to deep
draw and
avoid folds and wrinkles than with metal layers of different thickness and
composition.
As shown in FIG. 2, the preferred embodiment is deep drawn to a ratio of depth
to
thickness of from about 15:1, at D1, to about 50:1, at D2.
[0066] As illustrated in FIG. 2, the edge portions of the shield 10 are
provided with
hems 22 which maintain the three metal layers 14, 16 and 18 nested together.
FIG. 4 is
an enlarged view of the portion identified as 20 in FIG. 2 illustrating the
structural detail
at an edge portion of the shield 10 where a hem 22 is formed. The three metal
layers 14,
16 and 18 of the preferred embodiment are nested together such that the
peripheral edges
of each of the metal layers are conterminous. The inner metal layer 14 is bent
back upon
itself at 24 to form a reverse bend and extends to a free end at 26.
Similarly, the middle
metal layer 16 is bent back upon itself at 28 and extends to a free end at 30.
Finally, the
outer metal layer 18 is bent back upon itself at 32 and extends to a free end
at 34.
[0067] To help minimize the transmission of thermal and vibrational energy
from the
high temperature portion of the exhaust system to the shield 10, there is
minimal physical
contact between them. Preferably, the only points of physical contact are
bolts which fix
the shield 10 in relation to the high temperature portion of the exhaust
system such that
an air gap is provided. As shown in FIGS. 1 and 2, holes 24 are provided at
various
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points in the preferred embodiment for use with such bolts. The width of the
air gap
varies due to manufacturing considerations. Preferably, the air gap is about 1
mm to 30
mm wide, and more preferably, 3 mm to 15 mm wide, or 6mm to 12 mm wide.
Alternatives to First Embodiment
[0068] In alternative embodiments to the preferred embodiment described above,
each of the three metal layers 14, 16 and 18 has substantially the same
thickness in that
one of the three metal layers may differ in thickness from the other two metal
layers by
not greater than 20%. More preferably, one of the three metal layers may
differ in
thickness from the other two metal layers by not greater than 15%, or not
greater than
10%, or not greater than 5%. Preferably, at least two of the three metal
layers have an
identical thickness.
[0069] Preferably, each of the three metal layers 14, 16 and 18 has a
thickness of
between about 0.25 mm and about 0.5 mm. More preferably, each of the three
metal
layers 14, 16 and 18 has a thickness of between about 0.30 mm and about 0.45
mm, still
more preferably between about 0.35 mm and about 0.40 mm.
[0070] The total thickness of the three metal layers 14, 16 and 18 together
will vary
depending upon the intended application and can be selected by a person
skilled in the art
to meet the requirements for thermal, acoustical and/or vibrational abatement.
[0071 ] Preferably, each of the three metal layers 14, 16 and 18 have
substantially the
same composition in that either:
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(a) all three metal layers 14, 16 and 18 comprise the same base metals;
or
(b) two metal layers comprise the same base metals and the remaining
metal layer comprises material that is an alloy of the material of
the other two layers; or
(c) each of the three metal layers 14, 16, 18 comprises material that is
an alloy of the material in at least one of the other two layers.
[0072] Preferably, each of the three metal layers 14, 16 and 18 is obtained
from the
same roll of metal sheeting.
[0073] The three metal layers 14, l6 and 18 may be made from a range of
materials
which can be selected by a person skilled in the art. Preferably, the three
metal layers 14,
16 and 18 are made from corrosion-resistant materials. More preferably, the
three metal
layers 14, 16 and 18 are made from steel or aluminum, and still more
preferably from
materials selected from the group consisting of aluminized steel, aluminum
coated steel,
aluminum cladded steel and galvanized steel.
[0074] The shape of the shield 10 will vary depending on the environment in
which it
is intended to be used and can be selected by a person skilled in the art. The
three metal
layers 14, 16 and 18 are compressed together and formed into the desired shape
using
conventional tools and techniques known to those skilled in the art. For
example,
stamping techniques may be used. Consequently, all three layers 14, 16 and 18
have the
same shape and extend in face-to-face adjacency.
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[0075] Deep drawing techniques which are known to those skilled in the art may
be
used in the shaping operation to prevent unwanted fold and wrinkles from
developing in
the metal layers 14, 16 and 18. Preferably, the shield 10 is deep drawn to a
ratio of depth
to thickness of from about 5:1 to about 100:1. More preferably, the shield 10
is deep
drawn to a ratio of depth to thickness of from about 10:1 to about 75:1.
[0076] In alternative embodiments to the preferred embodiment, the shield 10
may be
coated along its exterior surfaces with a high temperature resistant paint-
type coating.
This coating is applied preferably by dipping the uncoated shield 10 into a
bath of the
temperature-resistive paint coating to ensure that all exterior surfaces,
including the
edges, are fully coated. Alternatively, the coating may be applied by
spraying. After
removing the shield 10 from the bath and allowing excess material to drip off,
the coated
shield 10 is allowed to dry. Then, to provide a full cure of the coating, the
shield 10 is
baked, for example, at about 400 degrees F. for one hour. The coating material
penetrates into the edge portions between the metal layers 14, 16 and 18 and
forms an
effective seal to prevent corrosion producing substances from entering into
the interior of
the shield 10. Similarly, a full seal is formed along the edges of the hems
22. The cured
coating is about 0.001 inch thick. Two metal layers are still considered to
have
substantially the same composition where:
(a) one metal layer has a coating while the other metal layer does not;
and
(b) one metal layer has a coating that is different in thickness and/or
composition from the coating of the other metal layer.
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[0077] The present inventor has found that, surprisingly, the thermal,
acoustical and
vibrational abatement properties of such shields are further improved by
replacing the
layer of insulating material from prior art with a middle metal layer 16 which
is
substantially identical in thickness and material composition to the inner
metal layer 14
and the outer metal layer 18 and by embossing either the middle or inner or
outer layers.
By producing a shield 10 with three metal layers 14, 16 and 18 which are
substantially
identical in chemical composition and thickness, the present invention has the
following
additional enhanced features:
(a) The shield 10 of the present invention has a longer serviceable life
than prior art shields which have a layer of insulating material.
This is because the layer of insulating material is often more
susceptible to damage due to repeated heat shock, vibration and
moisture than the metal layers.
(b) The shield 10 of the present invention has better corrosion
resistance due to the increased number of corrosion resistant
surfaces and encapsulated mill oil films in the material sandwich.
(c) The entire shield 10 of the present invention is recyclable. In
contrast, the layer of insulating material in prior art shields is often
made from materials, such as fiberglass, silica fiber, ceramic fiber,
rock wool, and refractory materials in a blanket or paper form
which are not recyclable.
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(d) The shield 10 of the present invention is more environmentally
friendly to manufacture than prior art shields having a layer of
insulating material, because there are no airborne fiber particles
present to cause respiratory hazards.
(e) The shield 10 of the present invention is more environmentally
friendly to operate and service than prior art shields having a layer
of insulating material, because there are no airborne fiber particles
can be released from damaged shields.
(f) The shield 10 of the present invention is more environmentally
friendly to operate and service than prior art shields having a layer
of insulating material, because there are no chemical bonding
agents present which, when exposed to service temperatures of the
shield, could transform and result in degasing and could also
release smoke.
(g) The shield 10 of the present invention is easier and less expensive
to manufacture than prior art shields having a layer of insulating
material. Manufacturing the above-mentioned prior art shields
includes the inconvenience of having to work with more than one
type of material and additional process steps required to insert the
layer of insulating material between the two metal layers.
(h) The shield 10 of the present invention is easier and less expensive
to manufacture than prior art shields which have metal layers of
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different thicknesses. The metal layers 14, 16 and 18 of the
present invention can be cut from the same coil .
[0078] The present inventor conducted extensive tests on the thermal,
acoustical and
vibrational abatement properties of the following types of heat shields:
(a) Various thicknesses of a single metal layer;
(b) Various thicknesses of two metal layers which are identical in
thickness;
(c) Various thicknesses of two metal layers which differ in thickness
by between 25% and 150%;
(d) Various thicknesses of two layers which differ in thickness and
having the thinner layer facing the heat source;
(e) Various thicknesses of two layers which differ in thickness and
having the thicker layer facing the heat source;
(f) Two metal layers which are identical in thickness with various
types of insulating materials with various layer thicknesses
sandwiched between the two metal layers;
(g) Two metal layers which differ in thickness by greater than 25%
with a layer of insulating material sandwiched between the two
metal layers;
(h) Three metal layers which are each different in thickness;
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(i) Three metal layers which have two layers of identical thickness as
the exposed layers and a third layer of different thickness as the
encapsulated layer;
(j) Three metal layers which are identical in thickness and
composition; and
(k) Two, three and four layers where layers are identical in thickness
and composition but different in having or not having embosses.
[0079] Surprisingly, the present inventor found that the heat shield of the
present
invention has improved acoustical and vibrational abatement properties over
the other
metallic heat shields.
Description of Second Preferred Embodiment
[0080] Reference is made to FIGS. 5 to 10 which show second, third and fourth
preferred embodiments of the present invention.
[0081] FIG. 5 illlustrates a second embodiment of the heat shield 110 of the
present
invention. FIG. 6 illustrates a cross-sectional view of the portion identified
as 112 in
FIG. 5.
[0082] As shown in FIG. 6, the shield 110 of the second preferred embodiment
comprises two metal layers: an inner metal layer 114 and an outer metal layer
116. The
inner metal layer 114 is to be positioned proximal to the high temperature
portion of the
exhaust system while the outer metal layer 116 is to be positioned distal to
the high
temperature portion of the exhaust system.
21
CA 02414160 2002-12-12
[0083] The outer metal layer 116 has a surface comprising raised bosses 118.
The
raised bosses 118 are preferably hemispherical, cone or pyramid-shaped, more
preferably
hemispherical-shaped. . In the second preferred embodiment, the inner metal
layer 114
has a planar surface without any raised bosses.
[0084] Air pockets 120 are created between the inner metal layer 114 and the
outer
metal layer 116 at the location beneath each raised boss 118.
[0085] The heat shield 110 of the second embodiment is shown as having a C-
shape
in the end view and being, for example, like a segment of a wall of a
cylinder. A heat
shield of this shape could be used in certain individual applications
depending on the
configuration of a motor and its manifold. The shape shown is also used for
testing
performance. More typically, the heat shield 110 will need to be formed to
adopt a more
complex 3-dimensional shape such as illustrated in Figure 1. However, the
second
embodiment is shown in a simplified configuration for ease of illustration.
Similarly, the
layers of the heat shield 110 are to be secured together by many known methods
as
discussed, for example, with the first embodiment. Preferably, the layers of
the heat
shield 110 are secured together by rolled-up or curled-up edges.
Description of Third Preferred Embodiment
[0086] FIG. 7 illustrates a cross-section of a third embodiment of the heat
shield of
the present invention at a location similar to the cross-section in FIG. 6.
[0087] As shown in FIG. 7, the heat shield 210 of the third preferred
embodiment
comprises three metal layers: an inner metal layer 214, a middle metal layer
216, and an
22
CA 02414160 2002-12-12
outer metal layer 218. The inner metal layer 214 is to be positioned proximal
to the high
temperature portion of the exhaust system while the outer metal layer 218 is
to be
positioned distal to the high temperature portion of the exhaust system. The
middle metal
layer 216 is positioned between the inner metal layer 214 and the outer metal
layer 218.
[0088] The inner metal layer 214 has a surface comprising raised bosses 220.
Similarly, the outer metal layer 218 has a surface comprising raised bosses
222. The
raised bosses 220 and 222 are preferably pyramid-shaped. In the third
preferred
embodiment, the middle metal layer 216 has a planar surface without any raised
bosses.
[0089] Inner air pockets 224 are created between the inner metal layer 214 and
the
middle metal layer 216 at the location above and between raised bosses 220.
[0090] Also, outer air pockets 226 are created between the outer metal layer
218 and
the middle metal layer 216 at the location beneath each raised boss 222.
Description of Fourth Preferred Embodiment
[0091 ] FIG. 8 illustrates a cross-sectional view of a fourth embodiment of
the heat
shield of the present invention at a location similar to the cross-section
shown in FIG. 6.
[0092] As shown in FIG. 8, the heat shield of the fourth preferred embodiment
comprises four metal layers: an inner metal layer 314, a first middle metal
layer 316, a
second middle metal layer 318, and an outer metal layer 320. The inner metal
layer 314
is to be positioned proximal to the high temperature portion of the exhaust
system while
the outer metal layer 320 is to be positioned distal to the high temperature
portion of the
exhaust system. The first middle metal layer 316 is positioned adjacent to the
inner metal
23
CA 02414160 2002-12-12
layer 314. The second middle metal layer 318 is positioned adjacent to the
outer metal
layer 320.
[0093] The first middle metal layer 316 has a surface comprising raised bosses
322.
Similarly, the outer metal layer 320 has a surface comprising raised bosses
324. The
raised bosses 322 and 324 are preferably pyramid-shaped. In the fourth
preferred
embodiment, both the inner metal layer 314 and the second middle metal layer
318 have
planar surfaces without any raised bosses.
[0094] Inner air pockets 326 are created between the inner metal layer 314 and
the
first middle metal layer 316 at the location below each raised boss 322.
[0095] Middle air pockets 328 are created between the first middle metal layer
316
and the second middle metal layer 318 at the location above and between raised
bosses
322.
[0096] Outer air pockets 330 are created between the outer metal layer 320 and
the
second middle metal layer 318 at the location beneath each raised boss 324.
[0097] The air pockets described in the second, third and fourth embodiments
enhance the thermal abatement properties of the heat shield. Specifically, the
air pockets
help to dissipate the heat that is transmitted from the high temperature
portions of the
exhaust system. This causes a greater temperature drop from the metal layer
that is most
proximal to the high temperature portions of the exhaust system to the metal
layer that is
most distal to the high temperature portions of the exhaust system. Generally,
the larger
the air pocket, the more heat that can be dissipated.
24
CA 02414160 2002-12-12
[0098] An embossed metal layer, or a layer having a surface with raised
bosses, can
be produced by methods known to persons skilled in the art. For example, the
embossed
metal layer can be produced after decoding a planar sheet of metal and before
the metal
sheet is fed to a shaping press. The embossing equipment may comprise one or
more sets
of rollers. The sets of rollers may comprise pins, ballbearing balls or the
like embedded
into the rollers. The metal sheet is passed through each roller and the pins,
ballbearing
balls or the like are applied to the metal layer under pressure, thus forming
raised bosses
on the surface of the metal sheet. The embossed metal layer is then placed in
a stack with
other metal layers to form the heat shield. They are typically cut in a
blanking process
and then stamped in a stamping press so as to adopt a desired shape such as,
for example,
shown in Figure 1. In the stamping press, the layers will be shaped and/or
drawn. The
action of the shaping press will typically cause alterations to the shape or
height of the
raised bosses, however, such alterations typically will not significantly
affect the shield's
thermal abatement efficiency. Further, the stamping press can be configured to
minimize
reduction of the raised bosses at least over areas of the heat shield.
[0099] The three-dimensional shape of the raised bosses is not limited to any
particular shape. In the second, third and fourth preferred embodiments, the
raised bosses
are pyramid-shaped. In alternative embodiments, the raised bosses are
preferably
spherical-shaped or box-shaped.
[00100] The height of the raised bosses can be selected by a person skilled in
the art.
The greater the height of the raised bosses, the larger the air pockets formed
between
CA 02414160 2002-12-12
adjacent metal layers of the shield. In the second, third and fourth preferred
embodiments, the height of the raised bosses is preferably between about 0.25
mm to 2.5
mm.
[00101] The pattern and spacing of the raised bosses on the surface of the
metal layer
is not limited and can be selected by a person skilled in the art. In the
second, third and
fourth preferred embodiments, the raised bosses are evenly spaced away from
each other.
However, in alternative embodiments, there may be no spacing between the
raised
bosses, and the bosses need not be evenly spaced. In a particularly preferred
embodiment, the bosses may be non-uniformly distributed over the metal layers
so as to
provide greater density and/or size of bosses over areas where the bosses are
not to be
compressed by the stamping process.
[00102] In the second, third and fourth preferred embodiments, all of the
metal layers
preferably comprise aluminum-clad steel. The use of aluminum-clad steel
provides
several advantages. First, aluminum-clad steel has a greater degree of
stretchability than
stainless steel which is often used for applications where corrosion
resistance is
important. This greater degree of stretchability allows for the formation of
raised bosses
with a greater height, and therefore, deeper air pockets. Further, aluminum-
clad steel has
a shinier surface than most other steels and does not go through decoloration
after
exposed to heat cycles as most stainless steels do. Decoloration would degrade
shininess
and thus degrade emissivity properties and heat reflective capability.
Therefore, the
aluminum-clad steel metal layers have less mass than stainless steel layers of
identical
thickness, and would itself radiate less heat as a secondary heat source.
Preferred
26
CA 02414160 2002-12-12
aluminum-clad steel is of thickness of 0.1 to 0.5 mm, more preferably between
0.1 and
0.3 mm, more preferably between 0.1 and 0.2 mm. Such aluminum-clad steel is
available
from WICKEDER WESTFALENSPAHiL under the trade name FERAN.
[00103] Generally, aluminum-clad steel is produced using a system of three
decoders.
The middle decoder provides the base steel sheet while the other two decoders
each
provide one aluminum foil sheet. The base steel sheet and two aluminum foil
sheets are
cold rolled together under pressure to produce physical bonds between the
steel and
aluminum. The three physically bonded metal sheets are then rolled on a single
coil.
Subsequent treatment in a heating furnace produces chemical bonds between the
steel and
aluminum such that the three sheets are fused together into a single metal
layer of
aluminum-clad steel. Aluminum-clad steel is advantageous since it is more
resistant to
rusting and corrosion than plated steels, and is available in smaller gauges.
[00104] The present inventor has also found that, surprisingly, the use of an
embossed
metal layer, or a metal layer have a surface with raised bosses, results in
either equal or
greater thermal abatement properties as the prior art shields which comprise a
layer of
insulating material sandwiched between two metal layers. The air pockets
created by the
presence of the raised bosses increase the efficiency of thermal abatement by
dissipating
heat and therefore, causing a greater temperature drop from the metal layer
that is most
proximal to the high temperature portions of the exhaust system to the metal
layer that is
most distal to the high temperature portions of the exhaust system. By
producing a shield
27
CA 02414160 2002-12-12
with at least one metal layer having a surface comprising raised bosses, the
present
invention has the following enhanced features:
(a) The shield of the present invention has a longer serviceable life than
prior art shields which have a layer of insulating material. This is
because the layer of insulating material is often more susceptible to
damage due to repeated heat shock, vibration and moisture than the
metal layers.
(b) The entire shield of the present invention is recyclable. In contrast, the
layer of insulating material in prior art shields is often made from
materials, such as fiberglass, silica fiber, ceramic fiber, rock wool, and
refractory materials in a blanket or paper form which are not
recyclable.
(c) The shield of the present invention is more environmentally friendly to
manufacture than prior art shields having a layer of insulating material,
because there are no airborne fiber particles present to cause
respiratory hazards.
(d) The shield of the present invention is more environmentally friendly to
operate and service than prior art shields having a layer of insulating
material, because there are no airborne fiber particles can be released
from damaged shields.
(e) The shield of the present invention is more environmentally friendly to
operate and service than prior art shields having a layer of insulating
28
CA 02414160 2002-12-12
material, because there are no chemical bonding agents present which,
when exposed to service temperatures of the shield, could transform
and result in degasing and could also release smoke.
(f) The shield of the present invention is easier and less expensive to
manufacture than prior art shields having a layer of insulating material.
Manufacturing the above-mentioned prior art shields includes the
inconvenience of having to work with more than one type of material
and additional process steps required to insert the layer of insulating
material between the two metal layers.
(g) The shield of the present invention has enhanced thermal abatement
properties due to the raised bosses on the surface of at least one of the
metal layers. The presence of the raised bosses creates air pockets
between adjacent metal layers which increase the efficiency of thermal
abatement.
(h) The shield of the present invention is relatively easy to cut at the edges
into the desired shape. Unlike prior art shields which include a layer
of insulating material that tends to shear when a cutting instrument is
applied, the shield of the present invention can be easily cut at the
edges without the problem of shearing.
[00105] The embossing of the metal layers may be carned out by various methods
including rolling. Alternatively, the metal layer to be embossed could have
embossing
29
CA 02414160 2002-12-12
applied in a press to adopt a shape which continues to be substantially flat
yet embossed
or to adopt a shape which confirms as close as possible to a desired final
shape yet
permits press halves to be opened after the press step. Such press embossed
sheet could
then be placed in a further press with other metal layers for a final pressing
to a desired
shape.
[00106] The multiple layers of the thermal shields of the second, third and
fourth
embodiment are schematically shown as having a C-shape in cross-section.
Various
known methods may be used to secure the layers together including crimping
their edges,
rivets, fasteners, and forming a perimeter folded over or rolled-up or curled-
up edges as
shown. The shield would typically have openings through it for fastening to an
engine.
[00107] The metal layer which is referred to as embossed has a plurality of
raised
bosses or protuberances. Such an embossed metal layer is intended to include
many
forms in which the metal sheet is not planar, but has been deformed to provide
a
thickness greater than the thickness of the metal sheet, as preferred to
provide air pockets
intermediate an adjacent sheet. Metal sheets with various wrinkles or folds or
furrows or
alternating ridges and grooves as in a corrugated form fall within the
intended meaning of
embossed as used in this application.
[00108] The embossed metal layer has significantly increased rigidity and
dimensional
stability over a non-embossed planar sheet and improved thermal radiation
properties. A
planar sheet has improved thermal reflective properties. Generally it is
preferred to have
an outer layer as embossed and an inner layer as planar.
CA 02414160 2002-12-12
[00109] The combination of one embossed layer and one planar layer when joined
significantly improves the rigidity of the resultant product and such rigidity
is further
increased with three layers where one or two layers are embossed.
[00110) The term planar, as used to refer to a metal layer, generally refers
to the metal
layer having its surfaces substantially lying in the same plane which plane
may be flat or
curved. Preferably, the metal layer which is to be planar may comprise a flat
sheet of
metal rolled in a coil and which is unrolled for use in manufacture. The
different metal
layers in the heat shield may have different degrees of embossing and in the
case of a
planar layer, no embossing. However, to have some embossing in all sheets is
within the
scope of the invention, preferably provided the bosses and adjacent sheets do
not match
so as to avoid air pockets therebetween. Unembossed planar sheets have an
advantage of
generally greatest reflectance of thermal radiation. For example, a three-
layer heat shield
might have an inner layer which is not embossed, an intermediate layer of
greatest
embossing, and an outer layer of some less embossing than the intermediate
layer, with
the outer Iayer embossing being of a different geometric spacing in plan view
to always
be out of phase with the embossing on the intermediate layer.
[00111] Embossing may be symmetrical about a sheet that is equally towards
both
sides or asymmetrical, merely to one side. Locating adjacent embossed sheets
so that
their bosses extend away from the other sheet can increase air pockets
therebetween.
[00112] Preferably, the heat shields of the second, third or fourth
embodiments will
have all their layers formed from the same metal sheetings, preferably
aluminum-clad
steel.
31
CA 02414160 2002-12-12
[00113] Although this disclosure has described and illustrated several
preferred
embodiments of the invention, it is to be understood that the invention is not
restricted to
these particular embodiments. Rather, the invention includes all embodiments
which are
functional or mechanical equivalents of the specific embodiment and features
that have
been described and illustrated herein. Many modifications and variations will
now occur
to those skilled in the art. For a definition of the invention, reference is
made to the
following claims.
32
