U.S. patent application number 12/281132 was filed with the patent office on 2009-08-20 for exhaust gas aftertreatment system and exhaust gas cleaning method.
This patent application is currently assigned to Daimler AG. Invention is credited to Tillmann Braun, Christoph Espey, Andreas Gorbach, Axel Zuschlag.
Application Number | 20090205322 12/281132 |
Document ID | / |
Family ID | 38121768 |
Filed Date | 2009-08-20 |
United States Patent
Application |
20090205322 |
Kind Code |
A1 |
Braun; Tillmann ; et
al. |
August 20, 2009 |
Exhaust Gas Aftertreatment System and Exhaust Gas Cleaning
Method
Abstract
An exhaust gas aftertreatment system, and a method for exhaust
gas purification, has a first oxidation catalyst device, a NOx
catalyst device for removing nitrogen from the exhaust gas, a
device for actively increasing an exhaust gas temperature with at
least one second oxidation catalyst device, and a device for
removing particles. The devices are arranged one behind the other
in the flow direction of the exhaust gas of an internal combustion
engine, so that the exhaust gas flows through them. A respective
operating temperature of the NOx catalyst device and of the device
for removing particles can be set independently of an exhaust gas
temperature at an outlet of the internal combustion engine.
Inventors: |
Braun; Tillmann; (Berglen,
DE) ; Espey; Christoph; (Esslingen, DE) ;
Gorbach; Andreas; (Reutlingen, DE) ; Zuschlag;
Axel; (Stuttgart, DE) |
Correspondence
Address: |
CROWELL & MORING LLP;INTELLECTUAL PROPERTY GROUP
P.O. BOX 14300
WASHINGTON
DC
20044-4300
US
|
Assignee: |
Daimler AG
Stuttgart
DE
|
Family ID: |
38121768 |
Appl. No.: |
12/281132 |
Filed: |
March 1, 2007 |
PCT Filed: |
March 1, 2007 |
PCT NO: |
PCT/EP2007/001742 |
371 Date: |
January 7, 2009 |
Current U.S.
Class: |
60/286 ; 60/297;
60/299 |
Current CPC
Class: |
F01N 3/106 20130101;
F01N 2560/14 20130101; F01N 2610/03 20130101; F01N 13/009 20140601;
F01N 2250/14 20130101; F01N 3/2006 20130101; F01N 3/103 20130101;
F01N 2560/026 20130101; F01N 3/0253 20130101; F01N 2610/04
20130101; Y02T 10/24 20130101; F01N 2610/02 20130101; Y02T 10/26
20130101; F01N 2560/06 20130101; F01N 13/0093 20140601; F01N
2240/02 20130101; F01N 2560/021 20130101; F01N 2610/1453 20130101;
Y02T 10/12 20130101; F01N 13/011 20140603; F01N 2560/08 20130101;
F01N 2240/40 20130101; F01N 3/023 20130101; F01N 3/2066 20130101;
F01N 3/035 20130101 |
Class at
Publication: |
60/286 ; 60/297;
60/299 |
International
Class: |
F01N 9/00 20060101
F01N009/00; F01N 3/035 20060101 F01N003/035; F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 2006 |
DE |
10 2006 009 934.6 |
Claims
1-24. (canceled)
25. An exhaust-gas aftertreatment system having, arranged in series
in the flow direction of exhaust gas of an internal combustion
engine, and traversed by exhaust gas, a first oxidation catalytic
converter device, a NOx catalytic converter device for the
denitrogenization of the exhaust gas, a device for actively raising
an exhaust-gas temperature with at least one second oxidation
catalytic converter device, and a device for particle removal,
wherein a respective operating temperature of the NOx catalytic
converter device and of the device for particle removal can be set
independently of an exhaust-gas temperature at an outlet of the
internal combustion engine.
26. The exhaust-gas aftertreatment system of claim 25, further
comprising a unit for generating a heat tone to control the
temperature of the NOx catalytic converter device.
27. The exhaust-gas aftertreatment system of claim 26, wherein the
unit for generating a heat tone is arranged upstream of the NOx
catalytic converter device and downstream of the first oxidation
catalytic converter device.
28. The exhaust-gas aftertreatment system of claim 26, wherein the
unit for generating a heat tone is arranged upstream of the first
oxidation catalytic converter device.
29. The exhaust-gas aftertreatment system of claim 25, wherein the
device for actively raising an exhaust-gas temperature comprises at
least one fuel metering apparatus upstream of the second oxidation
catalytic converter device.
30. The exhaust-gas aftertreatment system of claim 29, wherein the
oxidation catalytic converter device has a twin-strand
configuration.
31. The exhaust-gas aftertreatment system of claim 30, wherein a
fuel metering apparatus is provided separately for each oxidation
catalytic converter.
32. The exhaust-gas aftertreatment system of claim 30, wherein a
single fuel metering apparatus supplies all of the oxidation
catalytic converters of the device for actively raising an
exhaust-gas temperature together.
33. The exhaust-gas aftertreatment system of claim 25, wherein the
NOx catalytic converter device has a twin-strand configuration.
34. The exhaust-gas aftertreatment system of claim 25, wherein the
device for particle removal has at least one particle filter.
35. The exhaust-gas aftertreatment system of claim 34, wherein the
device for particle removal has a twin-strand configuration.
36. The exhaust-gas aftertreatment system of claim 35, wherein the
oxidation catalytic converter of the device for actively raising
the exhaust-gas temperature or the first oxidation catalytic
converter is integrated into the device for particle removal.
37. The exhaust-gas aftertreatment system of claim 36, wherein a
third oxidation catalytic converter device is provided downstream
of the device for particle removal.
38. The exhaust-gas aftertreatment device of claim 37, wherein the
third oxidation catalytic converter device has a single-strand
configuration.
39. The exhaust-gas aftertreatment device of claim 37, wherein the
third oxidation catalytic converter device has a twin-strand
configuration.
40. The exhaust-gas aftertreatment device of claim 25 wherein at
least one temperature sensor is provided upstream of the first
oxidation catalytic converter unit or downstream of the unit for
generating a heat tone or upstream of the NOx catalytic converter
device or downstream of the NOx catalytic converter device or
upstream of the device for actively raising the exhaust-gas
temperature or upstream of the device for particle removal or
downstream of the device for particle removal.
41. The exhaust-gas aftertreatment device of claim 25, wherein an
ammonia sensor is provided downstream of the NOx catalytic
converter device.
42. The exhaust-gas aftertreatment device of claim 25, wherein a
NOx sensor is provided downstream of the NOx catalytic converter
device or upstream of the first oxidation catalytic converter
unit.
43. The exhaust-gas aftertreatment device of claim 25, wherein one
pressure sensor is arranged upstream and downstream of the device
for particle removal.
44. A method for exhaust-gas purification in an exhaust-gas
aftertreatment system having, arranged in series in the flow
direction of exhaust gas of an internal combustion engine, a first
oxidation catalytic converter device, a NOx catalytic converter
device for the denitrogenization of the exhaust gas, a device for
actively raising an exhaust-gas temperature with at least one
second oxidation catalytic converter device, and a device for
particle removal, said method comprising the steps of: operating
the NOx catalytic converter device and the device for particle
removal independently of the exhaust-gas temperature at an outlet
of the internal combustion engine and according to demand.
45. The method of claim 44, further comprising the steps of
activating the unit for generating a heat tone to control the
temperature of the NOx catalytic converter device if regulated
operation of a metering of reducing agent into the NOx catalytic
converter device or regulated operation of the device for actively
raising an exhaust-gas temperature is required and the NOx
catalytic converter device or one or more oxidation catalytic
converters of the device for actively raising an exhaust-gas
temperature are outside a respective preferred temperature
range.
46. The method as claimed in claim 44, further comprising
activating a regulated operation of the device for actively raising
an exhaust-gas temperature if the device for particle removal
exceeds a pressure loss increase or a temperature to be expected in
the device for particle removal when the device for raising the
exhaust-gas temperature is active exceeds a limit value, or if a
loading of the device for particle removal exceeds an admissible
limit value.
47. The method as claimed in claim 45, further comprising
activating regulated operation of the device for actively raising
an exhaust-gas temperature if the device for particle removal
exceeds a pressure loss increase or a temperature to be expected in
the device for particle removal when the device for raising the
exhaust-gas temperature is active exceeds a limit value, or a
loading of the device for particle removal exceeds an admissible
limit value.
48. The method as claimed in claim 44, further comprising
activating the unit for generating a heat tone to control the
temperature of the NOx catalytic converter device if regulated
operation of a metering of reducing agent into the NOx catalytic
converter device or regulated operation of the device for actively
raising an exhaust-gas temperature is required and the NOx
catalytic converter device or one or more oxidation catalytic
converters of the device for actively raising an exhaust-gas
temperature are outside a respective preferred temperature range;
and activating regulated operation of the device for actively
raising an exhaust-gas temperature if the device for particle
removal exceeds a pressure loss increase or a temperature to be
expected in the device for particle removal when the device for
raising the exhaust-gas temperature is active exceeds a limit
value, or a loading of the device for particle removal exceeds an
admissible limit value; wherein when the device for raising an
exhaust-gas temperature is active, a mean temperature of the device
for particle removal is between 550.degree. C. and 850.degree. C.,
preferably between 600.degree. C. and 800.degree. C.
49. The method as claimed in claim 44, wherein in regulated
operation of the device for raising an exhaust-gas temperature, the
temperature of its oxidation catalytic converter device is higher
than 250.degree. C., preferably higher than 300.degree. C.
Description
RELATED APPLICATIONS
[0001] This application is a National Phase Entry under 35 U.S.C.
.sctn. 371 of international application number PCT/EP2007/001742,
filed Mar. 1, 2007, which claims priority under 35 U.S.C. .sctn.
120 to German patent application number 10 2006 009 934.6, filed
Mar. 3, 2006. The disclosures of each of which are expressly
incorporated by reference herein.
BACKGROUND AND SUMMARY OF THE INVENTION
[0002] The invention relates to an exhaust-gas aftertreatment
system and a method for exhaust-gas purification in an exhaust-gas
aftertreatment system, having, arranged in series in the flow
direction of exhaust gas of an internal combustion engine, and
traversed by exhaust gas, a first oxidation catalytic converter
device, a NOx catalytic converter device for the denitrogenization
of the exhaust gas, a device for actively raising an exhaust-gas
temperature with at least one second oxidation catalytic converter
device, and a device for particle removal.
[0003] Exhaust-gas aftertreatment serves to convert and retain
statutorily limited pollutant components in the exhaust gas of
internal combustion engines.
[0004] U.S. Pat. No. 6,467,257 B1 discloses an exhaust-gas
aftertreatment system having, arranged downstream of a catalytic
converter for the selective catalytic reduction (SCR) of nitrogen
oxides (NOx), a particle filter for removing soot particles in the
exhaust gas.
[0005] EP 1 469 173 A1 discloses an exhaust-gas aftertreatment
system in which an oxidation catalytic converter is arranged
upstream of an SCR catalytic converter and a subsequent particle
filter. Arranged between the oxidation catalytic converter and the
SCR catalytic converter is a heat exchanger. Exhaust gas can be
cooled therein or can bypass the heat exchanger. A separate burner
supplies the particle filter with thermal energy in order to
regenerate the particle filter by burning off the accumulated
soot.
[0006] DE 103 47 133 A1 discloses an exhaust-gas aftertreatment
system in which an oxidation catalytic converter with a fuel
metering apparatus is arranged downstream of an SCR catalytic
converter. The oxidation catalytic converter is followed by a
particle filter. A further oxidation catalytic converter is
arranged upstream of the SCR catalytic converter.
[0007] One object of the invention is to specify an exhaust-gas
aftertreatment system and a method for exhaust-gas purification by
means of which functionally optimized operation of the components
is possible.
[0008] The exhaust-gas aftertreatment system according to the
invention is designed such that a respective operating temperature
of the NOx catalytic converter device and of the device for
particle removal can be set independently of an exhaust-gas
temperature at an outlet of the internal combustion engine. The
functionally optimized arrangement of the NOx catalytic converter
device, which preferably comprises at least one SCR catalytic
converter, and of the device for particle removal, differs from
known exhaust-gas aftertreatment systems, which arrangement is
substantially dependent on the components by means of which the
respective operating temperature can be set. Said components are
preferably a unit for generating a heat tone at the inlet side of
the NOx catalytic converter device and of the device for actively
raising the exhaust-gas temperature at the inlet of the device for
particle removal.
[0009] A unit for generating a heat tone to control the temperature
of a NOx catalytic converter device is preferably also up, in
addition to the device for actively raising an exhaust-gas
temperature, upstream of a device for particle removal, wherein the
NOx catalytic converter device can be decoupled from the
exhaust-gas temperature of the internal combustion engine. Both the
device for particle removal and also the NOx catalytic converter
device can be operated in a functionally optimized manner. The unit
for generating a heat tone permits optimized operation of the
preferred SCR catalytic converter with regard to its conversion of
nitrogen oxides (NOx). For this purpose, the temperature of the SCR
catalytic converter can be regulated. In addition, the temperature
of the second oxidation catalytic converter can be set so as to
permit the use of a fuel metering apparatus. The functionalities of
the NOx catalytic converter device and of the device for particle
removal are therefore no longer coupled to the exhaust-gas
temperatures of the internal combustion engine. The exhaust-gas
aftertreatment system can consequently be operated in a manner
decoupled from the internal combustion engine.
[0010] The unit for generating a heat tone is preferably arranged
upstream of the NOx catalytic converter device and downstream of
the first oxidation catalytic converter device.
[0011] Alternatively, the unit for generating a heat tone can also
be arranged upstream of the first oxidation catalytic converter
unit.
[0012] Furthermore, the device for actively raising an exhaust-gas
temperature can comprise at least one fuel metering apparatus in
addition to a second oxidation catalytic converter device with at
least one oxidation catalytic converter. Here, the oxidation
catalytic converter device can be of single-strand or twin-strand
design, wherein the fuel metering apparatus can be provided
separately for each oxidation catalytic converter. Alternatively, a
single fuel metering apparatus can be provided for commonly
supplying all of the oxidation catalytic converters of the device
for actively raising an exhaust-gas temperature.
[0013] The NOx catalytic converter device can likewise be of
single-strand or twin-strand design.
[0014] Furthermore, the device for particle removal can have at
least one particle filter, wherein the device for particle removal
can be of single-strand or twin-strand design.
[0015] It is possible for a third oxidation catalytic converter
device to be provided downstream of the device for particle
removal.
[0016] Here, the third oxidation catalytic converter device can be
of single-strand or twin-strand design.
[0017] The second and/or third oxidation catalytic converter unit
can be dispensed with if the device for particle removal has a
suitable catalytic coating of the particle filter, or the particle
filters.
[0018] At least one temperature sensor can be provided upstream of
the first oxidation catalytic converter unit and/or downstream of
the unit for generating a heat tone and/or upstream of the NOx
catalytic converter device and/or downstream of the NOx catalytic
converter device and/or upstream of the second oxidation catalytic
converter device and/or upstream of the device for particle removal
and/or downstream of the device for particle removal.
[0019] An ammonia sensor can expediently be provided downstream of
the NOx catalytic converter device, by means of which ammonia
sensor it is possible to provide improved regulation of the
addition of reducing agent, in particular aqueous urea solution, to
the NOx catalytic converter device.
[0020] A NOx sensor can advantageously be provided downstream of
the NOx catalytic converter device and/or upstream of the first
oxidation catalytic converter unit. The arrangement downstream of
the NOx catalytic converter device permits improved regulation of
the addition of the reducing agent and/or of any on-board diagnosis
(OBD). On-board diagnosis means the monitoring of
exhaust-gas-relevant components and systems during driving,
detecting malfunctions and for example displaying said malfunctions
by means of a warning lamp and transferring said malfunctions to a
scanning tool in the workshop. Furthermore, it is intended to
protect vulnerable components such as catalytic converters. The
arrangement upstream of the first oxidation catalytic converter
device can serve for quantifying untreated emissions and the
resulting demands on the NOx catalytic converter device.
[0021] In each case one pressure sensor can be provided upstream
and downstream of the device for particle removal. It is thereby
possible to provide an estimation of the soot and/or ash content in
the device for particle removal and therefore to control the fuel
metering apparatus.
[0022] The method according to the invention for exhaust-gas
purification provides that, in addition to the device for particle
removal, the NOx catalytic converter device can, according to
demand, be operated independently of the exhaust-gas temperature of
the internal combustion engine.
[0023] The unit for generating a heat tone to control the
temperature of the NOx catalytic converter device can preferably be
activated if regulated operation of a metering of reducing agent
into the NOx catalytic converter device and/or regulated operation
of the device for actively raising an exhaust-gas temperature is
required and the NOx catalytic converter device and/or one or more
oxidation catalytic converter(s) of the device for actively raising
an exhaust-gas temperature are/is outside a respective preferred
temperature range.
[0024] Furthermore, regulated operation of the device for actively
raising an exhaust-gas temperature takes place if the device for
particle removal exceeds a pressure loss increase and/or a
temperature to be expected in the device for particle removal when
the device for raising the exhaust-gas temperature is active
exceeds a limit value, and/or a loading of the device for particle
removal exceeds an admissible limit value.
[0025] When the device for raising an exhaust-gas temperature is
active, a mean temperature of the device for particle removal can
expediently be between 550.degree. C. and 850.degree. C.,
preferably between 600.degree. C. and 800.degree. C.
[0026] In regulated operation of the device for raising an
exhaust-gas temperature, the temperature of its oxidation catalytic
converter device can advantageously be higher than 250.degree. C.,
preferably higher than 300.degree. C.
[0027] Other objects, advantages and novel features of the present
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The invention will be explained in more detail below with
reference to the exemplary embodiments shown in the drawings, in
which:
[0029] FIG. 1 is a first embodiment of the exhaust-gas
aftertreatment system with single-strand exhaust-gas guidance,
[0030] FIG. 2 is a further embodiment of the exhaust-gas
aftertreatment system with single-strand exhaust-gas guidance,
[0031] FIG. 3 is a further embodiment of the exhaust-gas
aftertreatment system with partially twin-strand exhaust-gas
guidance,
[0032] FIG. 4 is a further embodiment of the exhaust-gas
aftertreatment system with partially twin-strand exhaust-gas
guidance,
[0033] FIG. 5 is a first embodiment of a preferred exhaust-gas
aftertreatment system with partially twin-strand exhaust-gas
guidance and a single-strand outlet-side oxidation catalytic
converter.
DETAILED DESCRIPTION OF THE DRAWINGS
[0034] In the figures, functionally equivalent components are
denoted by the same reference symbols.
[0035] A first embodiment of the invention is shown in FIG. 1. In a
first embodiment, a preferred exhaust-gas aftertreatment system 10
of an internal combustion engine (not illustrated) has, in series
in the flow direction 70 of the exhaust gas, firstly a first
oxidation catalytic converter device 20, a NOx catalytic converter
device 30 for the denitrogenization of the exhaust gas, a device 40
for actively raising an exhaust-gas temperature, a device 50 for
particle removal, and a third oxidation catalytic converter device
60.
[0036] Between the two first components, the first oxidation
catalytic converter device 20 and the NOx catalytic converter
device 30 for the denitrogenization of the exhaust gas, an infusive
unit 22 for generating a heat tone to control the temperature of
the NOx catalytic converter device 30 introduces heat. The energy
input by the infusive unit 22 can take place by means of the
combustion of a liquid and/or gaseous substance, and/or by
radiation and/or by means of electrical energy and/or by means of a
heat exchanger and/or by means of a hot gas flow. The unit 22
serves to set a temperature expedient for the NOx reduction in the
NOx catalytic converter device 30 and to provide a temperature,
which is suitable for an active regeneration of the unit 50 for
particle removal, of the device 40 for actively raising the
exhaust-gas temperature with the oxidation catalytic converter
42.
[0037] A further infusive unit 36 conducts a reducing agent, for
example a precursor of a reducing agent, for example an aqueous
urea solution, hydrocarbon or the like, to the SCR catalytic
converter 32. In the first oxidation catalytic converter 20,
unburned hydrocarbons, carbon monoxide and particles are oxidized
as completely as possible to form nitrogen monoxide (NO) and
partially to form nitrogen dioxide (NO2). The unit 36 sprays the
reducing agent, for example urea solution, into the hot exhaust-gas
flow whose temperature is suitably controlled by means of the unit
22, where said reducing agent is hydrolyzed to form ammonia (NH3)
and carbon dioxide (CO2). In the selective reduction itself, the
NH3 then reacts with the NO/NO2 mixture to form nitrogen and water.
The reaction takes place on a catalyst which is conventionally
composed of transition metal compounds on a ceramic substrate.
Unused NH3 proportions can be converted in a downstream second
oxidation catalytic converter 42 of a unit 40 for actively raising
an exhaust-gas temperature.
[0038] The unit 40 for actively raising the exhaust-gas temperature
comprises, in addition to the oxidation catalytic converter 42, a
fuel metering apparatus 46, by means of which fuel can be metered
according to demand into the exhaust-gas duct in order to set a
suitable temperature in the oxidation catalytic converter 42 by
means of the oxidation of said fuel. The resulting heat tone can be
utilized for the active, regulated regeneration of the particle
filter 52 of the subsequent, downstream device 50 for particle
removal, without it being necessary for the internal combustion
engine to be adapted in terms of its present operating conditions
for a regeneration phase of said type. The oxidation catalytic
converter 42 can be replaced or supplemented by a suitable
catalytic coating of the particle filter 52.
[0039] The particle filter 52 is preferably composed of a unit for
retaining the soot particles contained in the exhaust gas, which
soot particles can be burned off by means of the unit 40 in the
event of a corresponding exhaust-gas temperature increase. The
particle filter 52 can be formed with or without a catalytic
converter coating.
[0040] The third oxidation catalytic converter device 60 with its
oxidation catalytic converter 62 serves to oxidize components in
the exhaust gas which are not fully oxidized during operation of
the unit 40 for actively increasing an exhaust-gas temperature. The
oxidation catalytic converter device 60 can be replaced or
supplemented by a suitable catalytic converter coating of the
particle filter 52.
[0041] Not illustrated are any present, suitably positioned
temperature sensors, ammonia sensors, NOx sensors, pressure
sensors.
[0042] It is thus possible for at least one temperature sensor to
be provided upstream of the first oxidation catalytic converter
unit 20 and/or downstream of the unit 22 for generating a heat tone
and/or upstream of the NOx catalytic converter device 30 and/or
downstream of the NOx catalytic converter device 30 and/or upstream
of the device 40 for actively raising the exhaust-gas temperature
and/or upstream of the device 50 for particle removal and/or
downstream of the device 50 for particle removal. The placement
upstream of the first oxidation catalytic converter unit 20 permits
an estimation of the NO2 proportion in the exhaust gas at the
outlet of the oxidation catalytic converter unit 20. By means of
the placement downstream of the unit 22 for generating a heat tone,
it is possible to check the functionality of the latter, and if
appropriate detect a malfunction. The placement upstream of the NOx
catalytic converter device 30 and/or downstream of the NOx
catalytic converter device 30 permits regulation of the addition of
the reducing agent by means of the unit 36.
[0043] The placement of an ammonia sensor downstream of the NOx
catalytic converter device 30 permits improved regulation of the
addition of the reducing agent by means of the unit 36.
[0044] The placement of a NOx sensor downstream of the NOx
catalytic converter device 30 permits improved regulation of the
addition of the reducing agent by means of the unit 36 and/or
improved diagnosis (on-board diagnosis). The placement upstream of
the first oxidation catalytic converter device 20 permits
quantification of untreated emissions, and of the resulting demands
on the subsystem of the NOx catalytic converter device 30.
[0045] By placing in each case one pressure sensor upstream and
downstream of the device 50 for particle removal, it is possible
for an estimation of the soot or ash content in the particle filter
52, and therefore a regulation of the fuel metering apparatus 46,
to take place.
[0046] Also provided is a control unit (not illustrated in the
drawing) which is connected to sensors and which serves for
regulating the unit 22 for generating a heat tone, the unit 36 for
metering a reducing agent, and the fuel metering apparatus 46, and
for communicating with a conventional engine control unit which
controls the internal combustion engine.
[0047] FIG. 2 shows an alternative embodiment of the exhaust-gas
aftertreatment system 10 in FIG. 1, in which the unit 22 for
generating a heat tone is arranged upstream of the first oxidation
catalytic converter device 20. The arrangement of the components is
otherwise identical. The unit 22 can, in the following exemplary
embodiments, be arranged upstream or downstream of the first
oxidation catalytic converter device 20.
[0048] The exemplary embodiment of FIG. 3 illustrates a further
preferred variant of the exhaust-gas aftertreatment system 10, in
which the NOx catalytic converter device 30, the unit 40 for
actively raising the exhaust-gas temperature, the device 50 for
particle removal and the third oxidation catalytic converter device
60 are each of twin-strand design. The functionalities, embodiments
and alternatives explained for the single-strand embodiment of the
individual components apply analogously to the components of the
twin-strand designs.
[0049] The first oxidation catalytic converter device 20 is
arranged, in a single-strand design, upstream of the strand
division. The unit 36, by means of which the reducing agent is
metered, is common to the two SCR catalytic converters 32, 34.
[0050] Here, the NOx catalytic converter device 30 comprises two
SCR catalytic converters 32, 34 which are connected in parallel in
terms of flow. The device 40 for actively raising the exhaust-gas
temperature comprises two oxidation catalytic converters 42, 44
which are connected in parallel in terms of flow, the device 50 for
particle removal comprises two particle filters 52, 54 which are
connected in parallel in terms of flow, and the oxidation catalytic
converter device 60 comprises two oxidation catalytic converters
62, 64 which are connected in parallel in terms of flow.
[0051] Arranged at the inlet of the first oxidation catalytic
converter device 20, as in the exemplary embodiment of FIG. 2, is
the infusive unit 22 for supplying a heat tone, and the unit 36 for
supplying reducing agent for the SCR catalytic converters 32, 34 of
the NOx catalytic converter device 30 is arranged between the first
oxidation catalytic converter device 20 and upstream of a strand
division 72 upstream of the NOx catalytic converter device 30.
[0052] The fuel metering apparatus 46 for the two oxidation
catalytic converters 42, 44 of the unit 40 for actively raising the
exhaust-gas temperature is arranged in the strand confluence 74
downstream of the NOx catalytic converter device 30.
[0053] Downstream of the third oxidation catalytic converter device
60, the twin-strand exhaust-gas guidance of the NOx catalytic
converter device 30, of the unit 40 for actively raising the
exhaust-gas temperature and of the third oxidation catalytic
converter device 60 opens out into a strand confluence 76.
[0054] FIG. 4 shows an embodiment of the exhaust-gas aftertreatment
system 10 corresponding to FIG. 3, with the difference that the
fuel metering apparatus 46 is provided separately in each strand
for the respective oxidation catalytic converter 42, 44 of the unit
40 for actively raising the exhaust-gas temperature. Said twin
design of the fuel metering apparatus 46 permits regulation of the
temperature downstream of the strand confluence 74.
[0055] FIG. 5 shows a further variant of the exhaust-gas
aftertreatment system 10 according to the invention, which
corresponds largely to the twin-strand design in FIG. 4. In the
embodiment shown, however, the third oxidation catalytic converter
unit 60 is now of single-strand design downstream of a strand
confluence 76.
[0056] For all of the twin-strand arrangements shown in the
exemplary embodiments, it is also possible to dispense with a
strand confluence 76 downstream of the third oxidation catalytic
converter unit 60; if appropriate, it is also possible to dispense
with a strand confluence 74 downstream of the NOx catalytic
converter unit 30.
[0057] For regulated operation of the unit 36 for supplying
reducing agent, an SCR catalytic converter temperature of at least
150.degree. C., preferably at least 200.degree. C. and a maximum of
500.degree. C., preferably the maximum of 500.degree. C., is
preferable. The unit 36 is active when the untreated NOx emissions
of the internal combustion engine are higher than the statutorily
demanded limit value.
[0058] For the operation of the NOx reduction arrangement, a
temperature of the first oxidation catalytic converter device 20 of
at least 120.degree. C., preferably of at least 150.degree. C., and
an SCR catalytic converter temperature of at least 180.degree. C.,
preferably at least 200.degree. C., are preferable.
[0059] For the regulated operation of the fuel metering apparatus
46, a temperature of the second oxidation catalytic converter 42 or
of the second oxidation catalytic converters 42, 44 of over
280.degree. C., preferably over 300.degree. C. is preferable. The
fuel metering apparatus is active if the loading of the unit 50 for
particle removal with soot and/or ash exceeds a threshold value of
the resulting pressure loss increase across the particle filter(s)
52, 54, for example in the range from 50 to 200 mbar, and/or if the
temperature to be expected in the particle filter(s) 52, 54 exceeds
a certain threshold value, for example in the range from
700.degree. C. to 800.degree. C. and/or if the loading of the
particle filter(s) 52, 54 exceeds a certain threshold value, for
example 2 g/l to 15 g/l.
[0060] During operation of the fuel metering apparatus 46, a mean
temperature of the particle filter(s) 52, 54 of at least
550.degree. C., preferably of at least 600.degree. C., and a
maximum of 850.degree. C., preferably a maximum of 800.degree. C.,
is preferable.
[0061] The unit 22 for generating a heat tone is expediently
designed so as to permit operation over the entire state space of
the engine system variables. The unit 22 is activated if regulated
operation of the unit 36 for metering reducing agent and/or
regulated operation of the fuel metering apparatus 46 is required,
and the SCR catalytic converter temperature or the temperature of
the oxidation catalytic converter 42 or of the oxidation catalytic
converters 42, 44 are not in the respective preferred range.
[0062] The foregoing disclosure has been set forth merely to
illustrate the invention and is not intended to be limiting. Since
modifications of the disclosed embodiments incorporating the spirit
and substance of the invention may occur to persons skilled in the
art, the invention should be construed to include everything within
the scope of the appended claims and equivalents thereof.
* * * * *