U.S. patent application number 11/318932 was filed with the patent office on 2006-05-25 for exhaust gas after-treatment unit with countercurrent housing and corresponding process for exhaust gas after-treatment.
This patent application is currently assigned to Emitec Gesellschaft fur Emissions Technologie MBH. Invention is credited to Rolf Bruck.
Application Number | 20060107656 11/318932 |
Document ID | / |
Family ID | 33546685 |
Filed Date | 2006-05-25 |
United States Patent
Application |
20060107656 |
Kind Code |
A1 |
Bruck; Rolf |
May 25, 2006 |
Exhaust gas after-treatment unit with countercurrent housing and
corresponding process for exhaust gas after-treatment
Abstract
An exhaust gas after-treatment unit, in particular for use close
to an internal combustion engine of an automobile, includes a
housing which contains at least one catalytic converter surrounded
by at least one substantially free flow-through return flow region.
The catalytic converter has first and second end surfaces and
hollow spaces through which a fluid can flow in an inflow
direction. The first end surface is connected to at least one gas
feed line and at least one gas removal line is substantially
gas-tightly connected to the return flow region. At least one flow
deflector effects a deflection of the fluid from the catalytic
converter into the return flow region of the housing. The exhaust
gas after-treatment unit has a compact construction, improved
start-up properties and lower thermal alternating stresses as
compared with conventional exhaust gas after-treatment units.
Inventors: |
Bruck; Rolf;
(Bergisch-Gladbach, DE) |
Correspondence
Address: |
LERNER GREENBERG STEMER LLP
P O BOX 2480
HOLLYWOOD
FL
33022-2480
US
|
Assignee: |
Emitec Gesellschaft fur Emissions
Technologie MBH
|
Family ID: |
33546685 |
Appl. No.: |
11/318932 |
Filed: |
December 27, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/EP04/06204 |
Jun 9, 2004 |
|
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11318932 |
Dec 27, 2005 |
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Current U.S.
Class: |
60/288 ;
60/299 |
Current CPC
Class: |
F01N 2470/14 20130101;
F01N 3/2889 20130101; F01N 13/017 20140601; Y02A 50/20 20180101;
F01N 2240/20 20130101; F01N 3/2842 20130101; F01N 3/2825 20130101;
Y02A 50/2322 20180101; F01N 2470/16 20130101; F01N 13/10 20130101;
F01N 3/281 20130101; F01N 13/0097 20140603; F01N 2470/24 20130101;
F01N 2470/08 20130101; F01N 3/2892 20130101; F01N 2470/22
20130101 |
Class at
Publication: |
060/288 ;
060/299 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/10 20060101 F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 2003 |
DE |
103 29 000.1 |
Claims
1. An exhaust gas after-treatment unit, comprising: a housing; at
least one catalytic converter disposed in said housing and defining
at least one substantially free flow-through return flow region
disposed within said housing and surrounding said at least one
catalytic converter, said at least one catalytic converter having a
first end surface, a second end surface and hollow spaces through
which a fluid can flow in an inflow direction; at least one gas
feed line connected to said first end surface of said at least one
catalytic converter; at least one gas removal line substantially
gas-tightly connected to said at least one return flow region; and
at least one flow deflector effecting a deflection of the fluid
from said at least one catalytic converter into said substantially
free flow-through return flow region of said housing.
2. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one gas feed line and said at least one gas
removal line are disposed in vicinity of said first end surface of
said at least one catalytic converter.
3. The exhaust gas after-treatment unit according to claim 1,
wherein said housing is a manifold.
4. The exhaust gas after-treatment unit according to claim 1,
wherein said housing is a collector.
5. The exhaust gas after-treatment unit according to claim 1,
wherein at least one of said at least one gas removal line or said
at least one gas feed line has a connection for a turbocharger.
6. The exhaust gas after-treatment unit according to claim 1,
wherein said housing and said at least one catalytic converter are
concentric.
7. The exhaust gas after-treatment unit according to claim 1,
wherein said housing and said at least one catalytic converter are
coaxial.
8. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one return flow region is disposed outside
said at least one catalytic converter.
9. The exhaust gas after-treatment unit according to claim 1,
wherein said hollow spaces of said at least one catalytic converter
each have a first through-flow cross-section, said return flow
region is an inner region within said at least one catalytic
converter having a second through-flow cross-section, and said
second cross-section is significantly greater than said first
cross-section.
10. The exhaust gas after-treatment unit according to claim 9,
wherein said second flow-through cross-section of said return flow
region is substantially the same size as a sum of said first
flow-through cross-sections of said at least one catalytic
converter.
11. The exhaust gas after-treatment unit according to claim 1,
wherein said housing has a first length, said at least one
catalytic converter has a second length, and said first length of
said housing and said second length of said at least one catalytic
converter are substantially identical.
12. The exhaust gas after-treatment unit according to claim 11,
wherein said housing has a diameter, and a quotient of said first
length and said diameter of said housing is at least 0.3 and at
most 1.5.
13. The exhaust gas after-treatment unit according to claim 11,
wherein said housing has a diameter, and a quotient of said first
length and said diameter of said housing is at least 0.3 and at
most 1.
14. The exhaust gas after-treatment unit according to claim 11,
wherein said housing has a diameter, and a quotient of said first
length and said diameter of said housing is approximately 0.5.
15. The exhaust gas after-treatment unit according to claim 1,
wherein said hollow spaces form an inflow region, and said return
flow region has a pressure loss being at most equal to a pressure
loss of said inflow region.
16. The exhaust gas after-treatment unit according to claim 11,
wherein said return flow region has a pressure loss being at most
equal to a pressure loss of a pipe having said first length and a
diameter corresponding to a diameter of said at least one feed
line.
17. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one gas feed line has a first longitudinal
axis, said at least one gas removal line has a second longitudinal
axis, and a projection of said first and second longitudinal axes
onto a plane including said first end surface of said at least one
catalytic converter encloses an angle greater than 60.degree..
18. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one gas feed line and said first end surface
of said at least one catalytic converter are connected to one
another with a push-fit.
19. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one catalytic converter is formed of
ceramic.
20. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one catalytic converter is extruded.
21. The exhaust gas after-treatment unit according to claim 1,
wherein said at least one catalytic converter is formed of at least
one metallic layer.
22. The exhaust gas after-treatment unit according to claim 21,
wherein said at least one catalytic converter is constructed by
winding up at least one at least partly structured metallic
layer.
23. The exhaust gas after-treatment unit according to claim 21,
wherein said at least one catalytic converter is constructed by
winding up at least one substantially smooth and at least one at
least partly structured metallic layer.
24. The exhaust gas after-treatment unit according to claim 21,
wherein said at least one catalytic converter is constructed by
stacking a plurality of substantially smooth and at least partly
structured metallic layers and subsequently winding a plurality of
stacks.
25. The exhaust gas after-treatment unit according to claim 1,
wherein said housing is disposed close to an internal combustion
engine of an automobile.
26. A process for exhaust gas after-treatment, which comprises the
following steps: a) providing an exhaust gas after-treatment unit;
b) guiding an exhaust gas flow through an inflow region of the
exhaust gas after-treatment unit in an inflow direction and
catalytically converting at least parts of the exhaust gas in the
inflow region; c) deflecting a direction of flow of the exhaust gas
from the inflow direction into a return flow direction; and d)
guiding the exhaust gas flow through a substantially free
flow-through return flow region in a return flow direction.
27. A process for exhaust gas after-treatment, which comprises the
following steps: a) guiding an exhaust gas flow through an inflow
region of an exhaust gas after-treatment unit according to claim 1
in an inflow direction and catalytically converting at least parts
of the exhaust gas in the inflow region; b) deflecting a direction
of flow of the exhaust gas from the inflow direction into a return
flow direction; and c) guiding the exhaust gas flow through a
substantially free flow-through return flow region in a return flow
direction.
28. The process according to claim 26, which further comprises
supplying the exhaust gas from an internal combustion engine of an
automobile.
29. The process according to claim 27, which further comprises
supplying the exhaust gas from an internal combustion engine of an
automobile.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This is a continuing application, under 35 U.S.C. .sctn.
120, of copending International Application No. PCT/EP2004/006204,
filed Jun. 9, 2004, which designated the United States; this
application also claims the priority, under 35 U.S.C. .sctn. 119,
of German Patent Application 103 29 000.1, filed Jun. 27, 2003; the
prior applications are herewith incorporated by reference in their
entirety.
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
[0002] The invention relates to an exhaust gas after-treatment unit
with a countercurrent housing. The invention also relates to a
corresponding process for exhaust gas after-treatment.
[0003] Legal limits which must not be exceeded by the pollutant
load of the exhaust gas of automobiles have been adopted in
numerous countries throughout the world, due to the constantly
increasing extent of automobile traffic. Those limits are lowered
on a regular basis, so that there must be an increased expenditure
for conversion of pollutants in exhaust gas to comply with the
limits. It has become accepted in that context to subject the
exhaust gas to a catalytic conversion, in which noxious contents of
the exhaust gas are converted into harmless contents. Such a
catalytic conversion requires the largest possible reaction
surface, but the component used therefor should not be so large
that it exceeds the space conventionally available in an
automobile. Honeycomb bodies used as a catalyst carrier body offer
a solution to that problem. Honeycomb bodies have hollow spaces,
for example channels, over or through which the exhaust gas can
flow. A large reaction surface for the catalytic conversion can be
provided by the construction of walls which separate the hollow
spaces and can be provided with a layer, e.g. a washcoat layer,
which includes a catalyst, for example a noble metal catalyst.
[0004] Such honeycomb bodies or catalytic converters can be
constructed, for example, from ceramic materials, from metallic
layers or as an extruded component. A distinction is made above all
between two typical structural forms for metallic honeycomb bodies.
An early structural form, for which German Published,
Non-Prosecuted Patent Application 29 02 779 A1, corresponding to
U.S. Pat. No. 4,273,681, shows typical examples, is the spiral
structural form, in which substantially a smooth and a corrugated
sheet metal layer are laid on one another and are wound up
spirally. In another structural form the honeycomb body is
constructed from a plurality of alternately disposed smooth and
corrugated or differently corrugated sheet metal layers. The sheet
metal layers initially form one or more stacks, which are
intertwined with one another. In that construction, the ends of all
of the sheet metal layers come to lie on the outside and can be
connected to a housing or casing tube, as a result of which
numerous connections are made which increase the stability of the
honeycomb body. Typical examples of those structural forms are
described in European Patent 0 245 737 B1, corresponding to U.S.
Pat. Nos. 4,946,822; 4,923,109; 4,803,189; and 4,832,998, or
International Publication No. WO 90/03220, corresponding to U.S.
Pat. Nos. 5,139,844; 5,135,794; and 5,105,539. It has also been
known for a long time to equip the sheet metal layers with
additional structures in order to influence the flow and/or to
achieve a transverse mixing between the individual flow channels.
Typical examples of such structures are in International
Publication No. WO 91/01178, corresponding to U.S. Pat. No.
5,403,559, International Publication No. WO 91/01807, corresponding
to U.S. Pat. Nos. 5,130,208 and 5,045,403, and International
Publication No. WO 90/08249, corresponding to U.S. Pat. No.
5,157,010. Finally, there are also honeycomb bodies in a conical
structural form, optionally also having further additional
structures to influence the flow. Such a honeycomb body is
described, for example, in International Publication No. WO
97/49905, corresponding to U.S. Pat. No. 6,190,784. It is moreover
also known to leave open a recess for a sensor in a honeycomb body,
in particular for accommodating a lambda probe. An example thereof
is described in German Utility Model 88 16 154 U1. Honeycomb bodies
which render possible a flow of a fluid in the radial direction
from the inside outwards are furthermore known. An example thereof
which is described in International Publication No. WO 96/09893,
corresponding to U.S. Pat. Nos. 5,902,558 and 5,795,658, is formed
from discs which lie adjacent one another and have a macrostructure
that forms channels which run in an arc shape outwards from a
central channel. A further possibility for the construction of
honeycomb bodies which have a through-flow radially from the inside
outwards is described in International Publication No. WO 98/57050,
corresponding to U.S. Pat. No. 6,277,784.
[0005] In order to achieve the highest possible rate of conversion
and a rapid start-up of the catalytic conversion, it is
advantageous to charge the honeycomb body with exhaust gas which is
as hot as possible, since upon cold starting in this way it
relatively rapidly reaches its start-up temperature from which the
catalytic conversion proceeds. This can be achieved by installing
the catalytic converter as close to the engine as possible.
However, the spaces available for installing a catalytic converter
precisely in the region close to the engine are often only very
limited. On the other hand, installation close to the engine causes
high thermal stress on the catalytic converter because of the
thermal gradients formed and the highly pulsatile gas stream.
SUMMARY OF THE INVENTION
[0006] It is accordingly an object of the invention to provide an
exhaust gas after-treatment unit with a countercurrent housing and
a corresponding process for exhaust gas after-treatment, which
overcome the hereinafore-mentioned disadvantages of the
heretofore-known devices and processes of this general type and in
which the exhaust gas after-treatment can be carried out in a
compact manner and rapid start-up properties are ensured, with a
simultaneous long life of the exhaust gas after-treatment unit.
[0007] With the foregoing and other objects in view there is
provided, in accordance with the invention, an exhaust gas
after-treatment unit, in particular to be used close to an internal
combustion engine of an automobile. The exhaust gas after-treatment
unit comprises a housing and at least one catalytic converter
disposed in the housing and defining at least one substantially
free flow-through return flow region disposed within the housing
and surrounding the at least one catalytic converter. The at least
one catalytic converter has a first end surface, a second end
surface and hollow spaces through which a fluid can flow in an
inflow direction. At least one gas feed line is connected to the
first end surface of the at least one catalytic converter. At least
one gas removal line is substantially gas-tightly connected to the
at least one return flow region. At least one flow deflector
effects a deflection of the fluid from the at least one catalytic
converter into the substantially free flow-through return flow
region of the housing.
[0008] A substantially free through-flow return flow region is
understood herein as meaning in particular that the return flow
region is not constructed as a honeycomb structure, i.e. is
substantially not divided into through-flow channels or hollow
spaces. In particular, it is possible according to the invention
for there to be a completely free through-flow return flow region,
where appropriate with the exception of fixing devices for fixing
the catalytic converter, which is, for example, a honeycomb
structure in a casing tube, in the housing. In the case of an
internal cylindrical catalytic converter in a cylindrical housing,
the return flow region therein is constructed as an annular
cylindrical gap between the casing tube of the catalytic converter
and the inner wall of the housing. The exhaust gas after-treatment
unit according to the invention has the advantage that due to the
deflection of the direction of flow, for example, pocket holes in
the vicinity of the engine can be used to accommodate the exhaust
gas after-treatment unit. It is not possible to use such pocket
holes in the case of catalytic converters having a conventional
construction--i.e. without deflection of the direction of flow.
Since the catalytic conversion as a rule proceeds exothermically,
after starting or start-up of the catalytic conversion, the exhaust
gas is heated up. This causes severe thermal gradients over the
catalytic converter in the case of conventional catalytic
converters. Since in an exhaust gas after-treatment unit according
to the invention the converted stream of exhaust gas is deflected
in its direction of flow, is inverted in a through-flow catalytic
converter in the axial direction, and flows back in the return flow
region of the housing, but this housing also contains the catalytic
converter, the catalytic converter is heated up uniformly, so that
thermal gradients are avoided and the service life of the catalytic
converter is increased in this way. Heating up of the catalytic
converter with the aid of the hot exhaust gas furthermore leads to
a faster start-up of the catalytic conversion in the catalytic
converter in the cold start phase and thus to significantly
accelerated start-up properties as compared with conventional
exhaust gas after-treatment units without a countercurrent
housing.
[0009] In accordance with another feature of the invention, the gas
feed line and the gas removal line are provided in the region of
the first end surface of the catalytic converter.
[0010] The placement of the gas feed line and the gas removal line
on only one side of the housing and of the catalytic converter
allows a space-saving construction of the exhaust gas
after-treatment unit according to the invention. In particular, the
gas feed and removal lines are not constructed in parallel, in
particular not coaxially. In a catalytic converter through which
the exhaust gas flows substantially radially, a deflection of the
exhaust gas occurs upon emergence from the catalytic converter,
while in an axial through-flow catalytic converter, the deflection
of the gas stream represents an inversion of the gas stream, that
is to say a deflection of substantially 180.degree. (degrees).
[0011] In accordance with a further feature of the invention, the
housing is constructed as a manifold or elbow. A further
advantageous construction of the exhaust gas after-treatment unit
is directed at the construction of the housing as a collector. Both
in a construction of the housing as a manifold and in its
construction as a collector, it is possible to employ the exhaust
gas after-treatment unit as close to the engine as possible.
[0012] In accordance with an added feature of the invention, the
gas removal line and/or the gas feed line is connected to a
turbocharger.
[0013] A turbocharger serves to boost the engine, i.e. it is used
to increase the performance of an internal combustion engine, and
is used in particular in connection with diesel engines. During
boosting the air required for the engine combustion process is
compressed by a power engine so that a larger mass of air enters
the cylinder or combustion chamber per work cycle of the internal
combustion engine. For this purpose, the compressor is driven, for
example, by a turbocharger which utilizes the exhaust gas energy.
The coupling with the engine in this context is not mechanical, but
proceeds purely thermally, with the principle of dynamic boosting
chiefly being used in automobile construction. The configuration of
the exhaust gas after-treatment unit upstream of such a
turbocharger ensures that the operating temperature of the
catalytic converter contained therein is reached very rapidly,
since a removal of heat from the exhaust gas due to contact with
components of the turbocharger is avoided in this manner.
[0014] The respective configuration of the turbocharger directly
connected with or directly upstream of the feed line is, however,
particularly preferred. In this construction it is particularly
advantageous to provide the feed line with a cone, which conducts
the exhaust gas directly to the first end surface of the honeycomb
body. This cone advantageously has an opening angle of at least
20.degree., in particular of at least 30.degree. and particularly
preferably of at least 40.degree..
[0015] Advantageously, only a very short or no tubular feed line
section is at the same time upstream of the cone towards the
turbocharger, but rather the cone is optionally directly connected
to the turbocharger. Should a tubular feed line section be
provided, however, for example in order to make available a
sufficiently large return flow area for the exhaust gas with a
cup-shaped component, this section should not exceed a length of 20
mm (millimeters), in particular it should not be longer than 10 mm
or even only 8 mm. With such a construction, notably the exhaust
gas stream generated by the turbocharger is used for an effective
flow towards the honeycomb body. The turbocharger generates a type
of swirl-stream, which is advantageously maintained and thus
results in an intensive contact of the uniformly mixed exhaust gas
stream.
[0016] In accordance with an additional feature of the invention,
the housing and the at least one catalytic converter are
constructed concentrically, preferably coaxially. The concentric or
coaxial structure of the catalytic converter and housing
advantageously allows the exhaust gas after-treatment unit to be
constructed in a particularly simple manner, in particular
catalytic converters in cylindrical construction which are
conventional per se can thus be used. The coaxial structure
advantageously offers only low pressure losses in the return flow
region, with a simultaneous simple structure of the exhaust gas
after-treatment unit. Furthermore, the concentric or coaxial
structure of the catalytic converter and housing simplifies the
construction of the flow deflector. If the housing and catalytic
converter have substantially a cylinder geometry and if the exhaust
gas flows axially through the catalytic converter, the flow
deflector can be constructed in a particularly simple manner by
formation of a torus with the smallest possible internal radius, in
the ideal case of zero. If the exhaust gas flows through the
catalytic converter substantially radially, the housing itself
forms the flow deflector, which ensures deflection of the exhaust
gas from the radial flow direction into the return flow
direction.
[0017] In accordance with yet another feature of the invention, the
at least one return flow region is constructed outside the at least
one catalytic converter. The construction of the return flow region
outside the at least one catalytic converter advantageously ensures
rapid starting up properties of the catalytic converter, uniform
heating up of the catalytic converter with prevention of the
formation of thermal gradients and a simple structural layout both
of the catalytic converter and of the housing, since a conventional
catalytic converter with a honeycomb structure of ceramic or metal,
optionally an extruded honeycomb structure, can be employed inside
the housing. In an advantageous manner, it is possible to fix the
catalytic converter with holding devices, for example thin bars,
which point radially from the catalytic converter outwards in the
direction of the housing, without the pressure loss in the return
flow region being considerably increased. Other holding devices are
also possible according to the invention, in particular it is also
advantageous to fix the catalytic converter only through the use of
the gas feed line.
[0018] In accordance with yet a further feature of the invention,
the hollow spaces of the at least one catalytic converter each have
a first through-flow cross-section, and an inner region E-81181
with a second through-flow cross-section is constructed as the
return flow region within the catalytic converter. In this case the
second through-flow cross-section is significantly greater than the
first through-flow cross-section. This allows, for example, the use
of catalytic converters in the form of hollow cylinders, the
flow-through cross-section of which is an annulus with hollow
spaces of a first through-flow cross-section.
[0019] In accordance with yet an added feature of the invention,
the second flow-through cross-section of the return flow region is
substantially the same size as the sum of the first flow-through
cross-sections of the catalytic converter. This advantageously
prevents a pressure loss during the deflection of the flow.
However, it is equally as advantageous to construct the second
through-flow cross-section to be greater than the sum of the first
flow-through cross-sections, in order to thus slow down the flow in
the return flow region and to increase the heat transfer to the
catalytic converter in the cold starting phase.
[0020] In accordance with yet an additional feature of the
invention, the housing has a first length L1, the catalytic
converter has a second length L2, and the first length of the
housing and the second length of the catalytic converter are
substantially identical. The construction of the catalytic
converter in an identical length to the length of the housing
allows holding of the catalytic converter in the housing in a
simple manner and a simple construction both of the flow deflector
and of the gas removal and feed line.
[0021] In accordance with again another feature of the invention,
the housing has a diameter D, the quotient of the first length L1
and the diameter D of the housing is greater than or equal to 0.3
and less than or equal to 1.5, preferably greater than or equal to
0.3 and less than or equal to 1, and particularly preferably about
0.5. That is to say, the following equation applies to the first
length L1 and the diameter D of the housing:
0.3.ltoreq.L1/D.ltoreq.1.5
[0022] In accordance with again a further feature of the invention,
the return flow region has a pressure loss which is less than or
equal to the pressure loss of the inflow region, in particular less
than or equal to the pressure loss of a pipe of the first length
and a diameter which corresponds to the diameter of the feed
line.
[0023] In accordance with again an added feature of the invention,
the at least one gas feed line has a first longitudinal axis, the
at least one gas removal line has a second longitudinal axis, and a
projection of the first and the second longitudinal axis onto a
plane which includes the first end surface of the catalytic
converter encloses an angle which is greater than 60.degree.
(degrees). Such an angle constellation between the gas removal line
and the gas feed line advantageously allows the utilization of even
the smallest free hollow spaces upon installation close to the
engine, for example of very narrow pocket holes.
[0024] In accordance with again an additional feature of the
invention, the gas feed line and the first end surface of the at
least one catalytic converter are connected to one another in the
form of a push-fit. The construction of the connection between the
gas feed line and the first end surface in the form of a push-fit
advantageously allows the construction of a substantially gas-tight
connection, and at the same time allows a different thermal
expansion, which in the case of a simple weld connection can easily
lead to severing of the connection. A substantially gas-tight
connection between the gas feed line and the first end surface of
the at least one catalytic converter can thus be ensured in an
advantageous manner even in the case of different thermal expansion
properties.
[0025] In accordance with a concomitant feature of the invention,
the catalytic converter is constructed of ceramic. Construction of
the catalytic converter as an extruded component is also
advantageous. According to a further advantageous construction, the
catalytic converter can also be constructed from at least one
metallic layer. In this connection, it is particularly advantageous
that the catalytic converter is constructed: [0026] a) by winding
up at least one at least partly structured metallic layer or at
least one substantially smooth and at least one at least partly
structured metallic layer, or [0027] b) by stacking a plurality of
substantially smooth and at least partly structured metallic layers
and subsequently winding a plurality of stacks.
[0028] This allows the construction both of spiral honeycomb bodies
and of metallic honeycomb bodies with stacks intertwined in
S-shaped or involuted form. In particular, in the case of metallic
catalytic converters it is advantageous according to the invention
for them to be provided with structures constructed transversally
to the extension of the hollow space or longitudinally to the
extension of the hollow space, to provide holes in the metallic
layers, as well as to construct at least a part of the metallic
layers of material which is at least partly permeable to a
fluid.
[0029] With the objects of the invention in view, there is also
provided a process for exhaust gas after-treatment, in particular
close to an internal combustion engine of an automobile. The
process comprises the following steps:
[0030] a) An exhaust gas flow is guided through an inflow region of
an exhaust gas after-treatment unit according to the invention in
an inflow direction and at least parts of the exhaust gas are
catalytically converted in the inflow region.
[0031] b) A direction of flow of the exhaust gas is deflected from
the inflow direction into a return flow direction.
[0032] c) The exhaust gas flow is guided through a substantially
free flow-through return flow region in a return flow
direction.
[0033] The advantages and details described above for the exhaust
gas after-treatment unit according to the invention can be applied
in the same manner to the process according to the invention for
exhaust gas after-treatment.
[0034] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0035] Although the invention is illustrated and described herein
as embodied in an exhaust gas after-treatment unit with a
countercurrent housing and a corresponding process for exhaust gas
after-treatment, it is nevertheless not intended to be limited to
the details shown, since various modifications and structural
changes may be made therein without departing from the spirit of
the invention and within the scope and range of equivalents of the
claims.
[0036] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a diagrammatic, longitudinal-sectional view of an
exhaust gas after-treatment unit according to the invention;
[0038] FIG. 2 is a cross-sectional view of a honeycomb body;
[0039] FIG. 3 is a perspective view of a housing with a honeycomb
body installed;
[0040] FIG. 4 is a perspective view of a second embodiment of an
exhaust gas after-treatment unit according to the invention;
[0041] FIG. 5 is a cross-sectional view of a section through the
second embodiment of the exhaust gas after-treatment unit; and
[0042] FIG. 6 is an enlarged, longitudinal-sectional view of a
third embodiment of an exhaust gas after-treatment unit according
to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] Referring now to the figures of the drawings in detail and
first, particularly, to FIG. 1 thereof, there is seen a
longitudinal section through a first embodiment of an exhaust gas
after-treatment unit 1 according to the invention. The exhaust gas
after-treatment unit 1 has a housing 2 with a honeycomb body 3,
which serves as a catalytic converter. The honeycomb body 3 is
surrounded by a casing tube 4 and is fixed in the housing 2 with
holding devices 5. These holding devices 5 are predominantly
constructed as bars which do not substantially reduce the size of a
free through-flow cross-section of a return flow region 6. The
phrase free through-flow cross-section, means in particular that no
honeycomb structure is placed in the return flow region. The
honeycomb body 3 can be constructed both as a ceramic and as a
metallic honeycomb body 3. An example of a metallic honeycomb body
can be seen in FIG. 2. A feed line 13 is provided with a cone 35,
which conducts exhaust gas directly to a first end surface 14 of
the honeycomb body 3. This cone 35 has an opening angle 33 of at
least 20.degree.. A very short tubular feed line section which is
disposed upstream of the cone 35 towards a non-illustrated
turbocharger, does not exceed a length 34 of 20 mm
(millimeters).
[0044] FIG. 2 shows the honeycomb body 3 which has the casing tube
4. A honeycomb structure 7 is fixed in the casing tube 4. The
structure 7 is formed of metallic layers 8, 9. In order to form the
honeycomb structure 7, substantially smooth metallic layers 8 and
at least partly structured metallic layers 9 are stacked
alternately and several stacks are joined to one another in the
same direction. For simplicity, the at least partly structured
metallic layers 9 are shown only in a partial region. The
substantially smooth metallic layers 8 and the at least partly
structured metallic layers 9 form hollow spaces or channels 10.
[0045] Sheet metal layers having a thickness of less than 80 .mu.m,
preferably less than 40 .mu.m, particularly preferably less than 25
.mu.m, can be used as the metallic layers. It is equally possible
for the substantially smooth metallic layers 8 and/or the at least
partly structured metallic layers 9 to be constructed at least
partly from a material through which a fluid can at least partially
flow, for example a metallic sintered non-woven. It is furthermore
possible, according to the invention, to introduce holes and/or
structures of any type into the substantially smooth metallic
layers 8 and/or the at least partly structured metallic layers 9.
In particular, it is also possible to close some of the channels
10. The introduction of holes having dimensions greater than the
structurally recurring length of the at least partly structured
metallic layers 9 is also possible according to the invention.
[0046] FIG. 1 shows that the housing 2 of the exhaust gas
after-treatment unit 1 according to the invention has two flow
regions. The channels 10 of the honeycomb body 3 form an inflow
region 11, while a region of the housing between the casing tube 4
and walls of the housing 2 forms the return flow region 6. The
honeycomb body 3 serves as a catalytic converter, i.e. it is as a
rule provided with a catalytically active coating, for example a
washcoat, which includes, for example, noble metal catalyst
particles, such as platinum or rhodium. In the present embodiment,
the exhaust gas flows axially through the honeycomb body 3. An
exhaust gas stream flowing through the honeycomb body 3 is at least
partly catalytically converted in the honeycomb body 3. In
contrast, an exhaust gas stream flowing through the return flow
region 6 is not catalytically converted.
[0047] Each of the channels 10 has a first through-flow
cross-section, while the return flow region 6 has a second free
through-flow cross-section. The phrase "free flow-through" means
that the second flow-through cross-section of the return flow
region 6 is significantly greater than the first flow-through
cross-section of a channel 10.
[0048] During operation of the exhaust gas after-treatment unit 1,
an exhaust gas stream 12 is introduced through the gas feed line 13
into the exhaust gas after-treatment unit 1. The gas feed line 13
is connected in a substantially gas-tight manner to the casing tube
4 of the honeycomb body 3 in the region of the first end surface 14
of the honeycomb body, so that there is a substantially gas-tight
connection between the gas feed line 13 and the inflow region 11.
The exhaust stream 12 thus enters the honeycomb body 3
substantially completely. The exhaust gas stream 12 flows through
this honeycomb body 3 in an inflow direction 15. During this flow,
an at least partial conversion of at least parts of the exhaust gas
stream 12 takes place. The exhaust gas stream 12 leaves the
honeycomb body 3 through a second end surface 16. A flow deflector
17 is adjacent the region of the second end surface 16 in the
inflow direction 15. The flow deflector 17 is connected to the
housing 2 in a substantially gas-tight manner. The flow deflector
17 has a depression 18 and a torus-shaped elevation 19. The highest
elevations each lie in the axial direction of the honeycomb body 3
opposite the center of the return flow region 6, while the
depression 18 lies opposite the center of the cylindrical honeycomb
body 3 in the axial direction. Other constructions of the flow
deflector 17 are also possible according to the invention. The flow
deflector 17 leads to a deflection 20 of the exhaust gas stream 12
from the inflow direction 15 into a return flow direction 21. In
the present case, this is even an inversion of the exhaust gas
stream, i.e. a deflection by substantially 180.degree.. During this
inversion, the exhaust gas stream 12 is deflected from the inflow
region 11 into the return flow region 6. The flow deflector 17 can
optionally have a thermal insulation 22.
[0049] A collector 23 is furthermore connected to the housing 2
with a connection that is substantially gas-tight in construction.
The collector 23 includes a cup-shaped component 24 and a gas
removal line 25. An at least partly converted gas stream 26 leaves
the exhaust gas after-treatment unit 1 through the gas removal line
25. The gas removal line 25 and/or the gas feed line 13 have a
connection for a turbocharger.
[0050] As mentioned above, during operation, the exhaust gas stream
12 flows through the gas feed line 13 into the honeycomb body 3. An
at least partial catalytic conversion of at least a part of the
exhaust gas stream 12 takes place in this manner. After flowing
through the honeycomb body 3 in the inflow direction 15, the
deflection 20 in the direction of flow takes place in the flow
deflector 17. The exhaust gas stream 12 then flows in the return
flow direction 21 through the return flow region 6. No catalytic
conversion takes place in the return flow region 6, which is
substantially an undivided flow chamber. The gas stream flowing
through the return flow region 6 as a rule is heated as compared
with the exhaust gas stream 12 flowing in, since the catalytic
conversion in the honeycomb body 3 as a rule takes place
exothermically. The gas stream flowing through the return flow
region 6 is thus advantageously used for heating the honeycomb body
3. In the cold start phase as well, in which no heating of the gas
stream in the honeycomb body 3 takes place because the exothermic
reaction has not yet started up, the recycling of the exhaust gas
stream can advantageously be used for heating up the honeycomb body
3, since upon cold start of an internal combustion engine elevated
temperatures are rapidly achieved which, although below the
starting up temperature of the catalytic conversion in the
catalytic converter 3, are above the ambient temperature of the
environment of the honeycomb body 3. This leads to significantly
shorter starting up times of the catalytic reaction in the
honeycomb body 3. The optional thermal insulation 22 of the flow
deflector 17 also prevents heat losses and therefore improves the
starting up properties of the honeycomb body 3. Furthermore, the
return flow of the hot exhaust gas means that lower thermal
gradients build up over the honeycomb body as compared with
conventional exhaust gas after-treatment units. This results in an
improved service life of the honeycomb body.
[0051] A push-fit or sliding-fit can advantageously be used for the
connection between the gas feed line 13 and the casing tube 4. This
renders possible a gas-tight connection even in the case of
different thermal expansions of the two components.
[0052] Through the use of the return flow principle, in particular
due to the fact that the gas feed line 13 and the gas removal line
25 are both constructed in the region of the first end surface 14
of the honeycomb body 3, the utilization of even small free spaces
in the region of the engine compartment of an automobile, for
example pocket holes, is possible. The exhaust gas after-treatment
unit 1 can thus be installed as close to the engine as possible. In
this way, higher temperatures are reached more quickly in the
exhaust gas, so that in this way the starting up properties of the
honeycomb body 3 are also improved. The gas feed line 13 has a
first longitudinal axis 27. The gas removal line 25 has a second
longitudinal axis 28. In order to render possible an installation
of the exhaust gas after-treatment unit 1 which is as space-saving
as possible, it is advantageous if the angle of the projections of
the first longitudinal axis 27 and the second longitudinal axis 28
onto a plane which includes the first end surface 14 is greater
than 60 degrees.
[0053] In a honeycomb body 3 according to the invention, the return
flow region 6 has a pressure loss which is less than or equal to
the pressure loss in the inflow region 11. It is preferable in this
case for the pressure loss in the return flow region 6 to be less
than or equal to a pressure loss encountered by a pipe having a
first length L1 and a diameter which corresponds to the diameter 32
of a feed line 31.
[0054] FIG. 3 shows a housing 2 according to the invention with the
honeycomb body 3 inserted. The honeycomb body 3 is constructed to
be coaxial with the housing 2. The casing tube 4 of the honeycomb
body 3 is connected to the housing 2 by the holding devices 5. The
channels 10 of the honeycomb body 3, which are not drawn in for
clarity, form the inflow region 11, while the region of the housing
between the housing wall and the casing tube 4 forms the return
flow region 6. The housing 2 has a first length L1 and a diameter
D. The honeycomb body 3 has a second length L2. In the present
embodiment, the first length L1 is identical to the second length
L2. A so-called pancake shape is preferred for the exhaust gas
after-treatment unit according to the invention, i.e. for the ratio
of L1/D, the equation 0.3.ltoreq.L1/D.ltoreq.1 preferably applies.
It is particularly preferable in this case for the ratio of L1/D to
be about 0.5. However, other ratios of L1/D are also possible
according to the invention.
[0055] FIG. 4 shows a diagrammatic illustration of a second
embodiment of an exhaust gas after-treatment unit 1 according to
the invention. In this case, four non-illustrated honeycomb bodies
3 which are charged with exhaust gas through four gas feed lines 13
are fixed in the housing 2 of the exhaust gas after-treatment unit
1. A gas removal line 25 is furthermore provided, so that this
embodiment of an exhaust gas after-treatment unit according to the
invention can be employed as a collector. It is likewise possible
according to the invention to provide two or more gas removal lines
25 instead of one gas removal line 25, in order to thus be able to
realize, for example, multi-lane or multi-tract exhaust gas units.
The cup-shaped components 24 are accordingly connected to one
another. The flow deflector 17 is constructed in such a way that an
effective non-illustrated deflection 20 from the inflow regions 11
into the particular return flow regions 6 also takes place in this
embodiment. In this case as well, the flow deflector 17 is
constructed with depressions 18 and elevations 19. The depressions
18 in each case are constructed centrally with respect to the
honeycomb body 3.
[0056] FIG. 5 shows a diagrammatic view of a section through the
embodiment shown in FIG. 4, which is taken along a line V-V. This
cross-section shows the housing 2 with the four honeycomb bodies 3
fixed thereto. In this cross-section, the casing tubes 4 form the
boundary between the inflow regions 11 and the return flow region
6.
[0057] FIG. 6 shows a third embodiment of an exhaust gas
after-treatment unit 1 according to the invention, which has a
radial flow-through honeycomb body 3. As is known from the prior
art, this honeycomb body 3 is constructed from discs 29 with
non-illustrated macrostructures which form channels 10 that lead in
an arc shape from a central flow region 30 to the return flow
region 6. The exhaust gas stream 12 to be converted flows axially
through the gas feed line 13 and through the first end surface 14
into the central flow region 30. As a result of the second end
surface 16 of the honeycomb body 3 being closed, the gas stream is
deflected into the radial flow channels 10, as is indicated by
arrows. The inflow direction 15 of the inflow region 11 formed by
the channels 10 is thus directed radially from the inside outwards.
The housing 2 serves as the flow deflector 17 and, after exiting of
the gas from the channels 10, effects a deflection 20 of the gas
stream in the return flow direction 21 in the return flow region 6.
In contrast to an axial flow-through honeycomb body in which a
deflection of, for example, substantially 180.degree. takes place,
in a radial flow-through honeycomb body 3 the gas stream is
deflected by about 90.degree..
[0058] The exhaust gas flows from the return flow region 6 into the
cup-shaped component 24. From there, the converted gas stream 26
leaves the exhaust gas after-treatment unit 1 through the gas
removal line 25. In this embodiment also, the gas feed line 13 and
the gas removal line 25 are in the region of the first end surface
14 of the honeycomb body.
[0059] With an exhaust gas after-treatment unit 1 according to the
invention, at least partial catalytic conversion of exhaust gases
can advantageously take place even in the event of very limited
free space for accommodating an exhaust gas after-treatment unit 1.
This is possible on the basis of the countercurrent principle in
the housing 2. An exhaust gas after-treatment unit 1 according to
the invention is furthermore distinguished by improved starting up
properties and lower thermal alternating stresses as compared with
conventional exhaust gas after-treatment units.
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