Note: Descriptions are shown in the official language in which they were submitted.
CA 02377027 2001-12-19
Device for the Treatment of Exhaust Gas
A catalytic converter for the exhaust flow of an
internal combustion engine is described in DE-C-43 03 850. The
catalytic converter consists of knit mineral fibers. The knit
material is arranged in layers in that it is either folded in
an accordion- like manner or rolled up. The flow through the
body obtained in this way takes place in a direction parallel
l0 with the individual layers. The fibers from which the knit
material has been produced are coated with an appropriate
catalytic material, for example platinum.
The great advantage of this arrangement lies in a highly
effective purification of the exhaust flow while, on the other
hand, because of the inherently resilient knit material, there
is no danger of its destruction. Since the knit material is
furthermore produced as a tubular fabric, there are no exposed
edges where the knit material might start to unravel. Even if
yarn breaks should occur within the body formed by the knit
material, the structure of the knit material is still preserved
because the broken yarn is held fast by means of the mesh on
both sides of the break.
So-called monoliths are another embodiment of catalytic
converters, wherein a porous, gas-permeable ceramic body is
covered with the catalytic material. These ceramic bodies have
the disadvantage that they possibly might be shattered in the
exhaust gas flow.
Independently of the manner how the carrier for the
catalytic material is embodied, the known catalytic converters
encounter difficulties in their reaction under partial load
conditions and at a low output of the internal combustion
engine. The reason for this lies in that the exhaust gas flow
has too small a volume at these low engine outputs and is not
capable of bringing the catalytic converter up to the process
temperature at which the catalytic material is capable of
splitting the nitrogen monoxide. The low-volume exhaust gas
flow is cooled too extensively in the exhaust pipe.
In order to be able to start the catalytic process
CA 02377027 2001-12-19
perfectly at low engine output, the catalytic converter would
have to be moved closer to the outlet openings of the internal
combustion engine, so that cooling in the exhaust pipe does not
become too strong. But this has the result that at a high
S engine output the catalytic converter is destroyed thermally.
The large volume exhaust gas flow is not cooled so much. With
a short distance between the outlet opening of the cylinder and
the catalytic converter when they are connected in a way
required for partial load operations, the exhaust gas flow of a
large mass would heat the catalytic converter to relatively
high temperatures, which are still further increased because of
the catalytic decay of the NOX. Because of this, temperatures
are reached inside the catalytic converter which will destroy
it thermally, or at least damage the catalytic material.
1S Basically similar conditions are encountered with self-
regenerating soot filters. Too large a distance of the soot
filter from the outlet opening of the cylinder leads to low
temperatures in the partial load range of the engine. Higher
temperatures would be necessary so that the soot is burned
catalytically in the filter. Too short a distance of the soot
filter from the outlet opening results in too high temperatures
at high engine output.
Based on the foregoing, it is the object of the
invention to create a device for the exhaust gas treatment of
internal combustion engines which also operates dependably in
the lower output range, or partial load range, of internal
combustion engines without there being the danger of it being
thermally destroyed under full load operations of the engine.
In accordance with the invention, this object is
attained by means of the device having the characteristics of
claim i.
Flat textile str~~ctures, which are stacked in layers,
are also used for the catalytic converter material with the
device in accordance with the invention. In this case the body
formed in this way is composed of two different types of
layers, namely layers consisting exclusively of wire and layers
which are either formed of mineral fibers alone, or of a
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combination of wires and mineral fibers. The layers consisting
exclusively of wire are arranged in such a way that, on the
inflow side, they protrude for a short distance, for example 3
to 10 mm, past the other layers.
In comparison with mineral fibers, wire is a very good
heat conductor and it~is assumed that the protruding wire
layers will heat up very rapidly in the exhaust gas flow and
will convey the high temperatures into the interior, or between
the layers made of mineral fibers. The catalytic process is
i0 started by this and further heats the catalytic converter
correspondingly. It is therefore possible to arrange the novel
catalytic converter at such a distance from the outlet opening
of the cylinder that there is no danger of overheating the
catalytic converter, even if the engine is operated under full
load.
Similar conditions basically exist in connection with a
self-regenerating soot filter, wherein the soot deposited on
the wire or the fibers with or without a catalytic coating can
burn off, even if the vehicle is only operated under partial
load.
A housing insert, which is very resistant to mechanical
damage by the exhaust gas flow is achieved if at least the
first and/or second layer consists of a knit fabric. One
skilled in the art understands a knit fabric to be a material
produced by knitting. The knit fabric is also very strong if
it has been produced in the form of a tubular fabric or as a
ribbon with a firm edge, because it is".then possible, for one,
to create a double-layered structure, and furthermore, because
no exposed borders occur at the edges where there would be a
danger of the knit material beginning to unravel. The tubular
fabric is endless in the circumferential direction, so that ro
Wales are created which are not tied up between the neighboring
wares.
The first layers are usefully connected in one piece
with each other, which also applies to the second layers. To
achieve this, the basic materials for the first and the second
layers are placed on top of each other. The double-layered
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material obtained in this way is either pleated in an accordion
fold or is rolled up. First and second layers then
respectively alternate in the stack. Depending on the type of
internal combustion engine with which the device is to be
employed, the catalytic material is either a catalytic material
for nitrogen monoxide, or a catalytic material for the
oxidation of soot. Finally, the novel device can also be used
as a self-regenerating filter arrangement for superfine
particles which occur in connection with a Diesel engine as
well as with a gasoline engine.
Further developments are the subject of the dependent
claims. Exemplary embodiments of the subject of the invention
are represented in the drawings; shown are in
Fig. 1, the device in accordance with the invention in
schematic longitudinal section,
Fig. 2, the insert in accordance with Fig. 1 in a
perspective schematic representation, and
Fig. 3, a further embodiment of the insert of the device
in accordance with Fig. 1, also in a partial schematic
representation.
Fig. 1 shows in schematic form a device 1 for treating
the exhaust gas from an internal combustion engine, for example
a Diesel or gasoline engine.
The device 1 has a housing 2, which is provided with an
inlet connector 3 and an outlet connector 4. The inlet
connector 3 is provided, for example, for a connection to the
exhaust manifold of the internal combustion engine, while the
exhaust pipe is connected at 4.
An insert 5 is located in the interior of the housing 2.
As shown, the insert 5 completely fills the cross section of
the housing 2. On the side facing the inlet connector 3, the
insert S is secured by means of an annular collar 6, which is
fastened on the housing 2. A perforated plate 7 is fastened in
the housing 2 at a distance from the annular collar 6, which is
used as a contact surface for the insert 5 and is intended to
prevent the exhaust gas flow from displacing the insert 5 in
the direction toward the outlet connector 4.
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The perforated plate 7 contains a plurality of holes 8
and can also be constituted by a narrow-meshed screen, which is
welded to the inside of the housing 2.
The flow through the device 1 occurs from the inlet
S connector 3 to the outlet connector 4 in the direction of an
arrow 9. In this way; an inflow side 11 and an outflow side 12
is created on the insert 5.
The structure of the insert 5 can be seen in Fig. 2.
The insert 5 consists of two knit tubes 13 and 14, wound
in a drum-like manner. The knit tube 13 consists of metal wire
15, which is knit so that a mesh is formed. This results in a
structure which, is endless in the circumferential direction, in
which the wales 17 formed in the course of knitting extend in
the direction of the generator line of the knit tube. The rows
of mesh iie in the circumferential direction.
The second knit tube 14 also consists of a mesh 18,
wherein the fibers from which the knit tube 14 is formed are
mineral fibers. Depending on the type of use, these mineral
fibers are coated with a catalytic material for soot, or with a
catalytic material for NOx. Moreover, in the case of glass
fibers, the latter are also thinned out, if required.
The created tubes 13, 14 of material are laid flat,
which can be seen in Fig. 2, and have been wound together over
the broad side. The drum-like structure 2 represented in Fig.
2S 2 is created in this way. The width of the knit tube 13 has
been selected in respect to the width of the knit tube 14 in
such a way that, when both knit tubes_1_3, 14 are pressed flat,
the width of the knit tube 13 made of the metal wire 15 is
slightly greater than the width of the knit tube 14 made of
mineral fibers. Because of this, the knit tube 13 protrudes
past the edge of the knit tube 14 at the one side of the insert
S.
The insert 5 is produced in the following manner:
The knit tube 13 is knit from metal wire 15 on
appropriate circular knitting machines. The knit tube 14 is
created from mineral fiber yarn, also on a circular knitting
machine. Then the knit tube 14 made of mineral fibers is
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placed on top of the knit tube made of metal wire in such a way
that the knit tube 14, laid flat, is flush at the one edge with
the corresponding edge of the knit tube 13 made of metal wire,
also laid flat.
Because of the difference in width, one edge of the knit
tube 13 made of metal'wire protrudes past the edge of the knit
tube 14, as can be schematically seen in Fig. 2. Then the
double- layered structure made of the two knit tubes 13 and 14,
laid flat, is wound up over the broad side, as also seen in
Fig. 2. Winding is continued until a lap roll of a diameter
equal to the interior diameter of the housing 2 is created.
Thereafter the created lap roll is cut off from the supply of
knit tunes 13 and 14. The lap roll which has been created now
represents the insert 5, which is arranged in the housing 2.
1S It is placed into the housing 2 in such a way that the front of
the lap roll at which the knit tube 13 of metal wire protrudes
faces the inlet connector 3, i.e. constitutes the inflow side
11 of the insert 5.
As can be seen from the explanation of the invention, a
first layer formed by the knit tube 14 respectively alternates,
viewed in relation to the radial direction of the insert S,
with a second layer formed from the knit tube 13 of metal wire.
Because of the arrangement of the lap roll, or of the insert
5, the flow through the insert 5 essentially takes place in a
direction parallel with the approximately cylindrical (or more
correctly helical) surfaces defined by the layers of the
flattened knit tubes 13, 14. In relation to the main.
direction, namely the connection between the inlet connector 3
and the outlet connector 4, the flow takes place approximately
parallel with the rows of the mesh 17, wherein in this
definition of the flow-through direction only the macroscopic
flow is considered. In a microscopical view it can easily
occur that a thread of a stream passes through a layer because
of turbulence.
Because the knit tube 13 made of metal wire protrudes
past the knit tube 14 on the inflow side 11, the structure in
this area is quite a bit looser. Moreover, the metal wire has
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better heat conducting properties than mineral fibers. The
metal wire can absorb heat much faster on the flow-in side and
convey this heat between the layers of mineral fibers, namely
the layers formed by the knit tube 14. Because of this it also
becomes possible in the partial load range of the engine to
bring the insert 5 up to temperatures at which it can perform
its catalytic functions. This occurs at a spatial distance
from the outlet opening which prevents the thermal destruction
of the insert 5.
The catalytic effects can possibly even be increased if,
in addition the metal wire of the knit tube 13 is also coated
with a catalytic material.
Instead of producing a cylindrical lap roll, such as
represented in Fig. 2, there is also the option of producing a
lap roll which has the shape of an oval in a view from above,
so that the extension of the housing 2 matched to this is of
different size in two directions placed perpendicularly on top
of each other. Such a configuration has advantages, for
example, when the arrangement must be placed underneath a
vehicle.
With the previously explained exemplary embodiment the
two knit tubes 13, 14 are wound in every case, i.e. they more
or less follow a spiral.
Fig. 3 shows an embodiment wherein the two knit tubes
2S 13, 14 are folded in an accordion-like manner into a stack.
Because of the accordion-like arranged folds, respectively two
layers constituted by the knit tube 14_rest directly on top of
each other, which are followed, viewed in the stack direction,
by two layers of a knit tube 13 placed directly on top of each
other. The same effect as with the arrangement in accordance
with rig. 2 can also be achieved with such a configuration of
the insert 5.
A device 1 for treating exhaust gases from internal
combustion engines has a housing 2, in which an insert 5 is
located, which is composed of two types of knit tubes 13, 14.
One knit tube 13 consists exclusively of metal wire, while the
other knit tube 14 is made completely of mineral fibers, or
CA 02377027 2001-12-19
primarily consists of mineral fibers. The knit tube 13 made of
metal wire forms a mesh, which protrudes on the inflow side
past the knit tube 14 made of mineral fibers in order to absorb
additional heat and to convey it into the interior of the
insert 5. Because of this it is possible to arrange the insert
5 at such a distance~from the outlet of the engine, that
overheating in the full load range is prevented while, on the
other hand, the response of the catalytic material is also
assured when employed in the partial load range of the internal
combustion engine.
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