U.S. patent application number 12/302540 was filed with the patent office on 2009-06-18 for method and device for operating an exhaust-gas after-treatment system.
This patent application is currently assigned to FEV MOTORENTECHNIK GMBH. Invention is credited to Juergen Schnitzler, Christopher Severin, Andreas Wiartalla.
Application Number | 20090151323 12/302540 |
Document ID | / |
Family ID | 38461838 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090151323 |
Kind Code |
A1 |
Severin; Christopher ; et
al. |
June 18, 2009 |
METHOD AND DEVICE FOR OPERATING AN EXHAUST-GAS AFTER-TREATMENT
SYSTEM
Abstract
The invention relates to a method for operating a motor vehicle
exhaust-gas aftertreatment system (1), in which oxygen is fed to
and removed from the oxygen tank (8) of an exhaust-gas
aftertreatment component (7). According to the invention, the
oxygen quantity in the oxygen tank (8) is determined and a
rich-lean cycle is influenced in accordance with the determined
oxygen quantity. The invention also relates to a motor vehicle
exhaust-gas aftertreatment system (1), which permits a temperature
regulation of the oxygen tank (8) and/or an uninterrupted
desulphation during the transition between a rich operation and a
lean operation.
Inventors: |
Severin; Christopher;
(Aachen, DE) ; Schnitzler; Juergen;
(Herzogenrath-Kohlscheid, DE) ; Wiartalla; Andreas;
(Wuerselen, DE) |
Correspondence
Address: |
GIFFORD, KRASS, SPRINKLE,ANDERSON & CITKOWSKI, P.C
PO BOX 7021
TROY
MI
48007-7021
US
|
Assignee: |
FEV MOTORENTECHNIK GMBH
AACHEN
DE
|
Family ID: |
38461838 |
Appl. No.: |
12/302540 |
Filed: |
May 25, 2008 |
PCT Filed: |
May 25, 2008 |
PCT NO: |
PCT/EP2007/004676 |
371 Date: |
November 26, 2008 |
Current U.S.
Class: |
60/276 ; 60/295;
60/297 |
Current CPC
Class: |
F01N 3/0885 20130101;
F02D 2200/0802 20130101; F01N 3/0842 20130101; F01N 2560/02
20130101; F01N 11/007 20130101; F01N 3/023 20130101; Y02T 10/47
20130101; F01N 3/0821 20130101; F01N 11/002 20130101; F02D 41/027
20130101; F02D 41/1408 20130101; Y02T 10/40 20130101; F01N 3/0814
20130101; F01N 3/0871 20130101; F02D 2200/0814 20130101; F01N
3/0828 20130101; F01N 3/0864 20130101; F02D 41/0295 20130101; F01N
13/0097 20140603 |
Class at
Publication: |
60/276 ; 60/295;
60/297 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
May 27, 2006 |
DE |
10 2006 025 050.8 |
Claims
1. A method for operating a motor-vehicle exhaust-gas
after-treatment system in which oxygen is fed to or removed from an
oxygen accumulator of an exhaust-gas after-treatment component,
wherein at least one changing parameter defined by the oxygen
accumulator and its oxygen content is determined and is used in the
operation of the motor-vehicle exhaust-gas after-treatment
system.
2. The method according to claim 1, wherein an oxygen quantity in
the oxygen accumulator is defined.
3. The method according to claim 1, wherein the oxygen quantity in
the oxygen accumulator is incorporated as a parameter for setting a
rich-lean cycle.
4. The method according to claim 1, wherein a cyclical change of a
stored oxygen quantity is used for the defined influence of a
temperature of the exhaust gas or the oxygen accumulator.
5. The method according to claim 1, wherein an additional oxygen
supply in the motor-vehicle exhaust-gas after-treatment system is
performed as a function of the determined oxygen quantity.
6. The method according to claim 1, wherein the oxygen quantity is
calculated by means of an oxygen balancing across the oxygen
accumulator.
7. The method according to claim 6, wherein a first probe
determines a continuous measurement of an oxygen content before the
oxygen accumulator, while a second probe determines whether an
exhaust gas is a rich mix or lean mix.
8. The method according to claim 1, wherein for a regeneration of a
particulate filter and/or an NOx-accumulating catalytic converter,
the determined oxygen quantity is included as a parameter.
9. The method according to claim 1, wherein for desulfurization of
an oxide accumulator, the determined oxygen quantity is included as
a parameter.
10. The method according to claim 8, wherein for determining a
beginning of the desulfurization and/or the regeneration, the
determined oxygen quantity is included as a parameter.
11. The method according to claim 8, wherein for determining a time
period of the desulfurization and/or the regeneration, the
determined oxygen quantity is included as a parameter.
12. The method according to claim 1, wherein a cyclical use of the
oxygen accumulator is used for increasing the temperature before a
diesel particulate filter regeneration.
13. The method according to claim 1, wherein at least one threshold
is set with respect to the determined stored oxygen quantity, and
when this threshold is exceeded, a cycle change between lean
operation and rich operation is triggered.
14-15. (canceled)
16. The method according to claim 1, wherein an internal combustion
engine is operated in a rich-lean cycle, wherein a temperature of
the oxygen accumulator is determined and an operating parameter
influencing the stored oxygen quantity is changed as a function of
the determined temperature.
17. The method according to claim 1, wherein a temperature
regulation or temperature control system, with respect to the
exhaust-gas after-treatment component having the oxygen accumulator
changes an oxygen quantity discharged from or absorbed in the
oxygen accumulator per unit time for adjusting the temperature of
the exhaust-gas after-treatment component.
18. The method according to claim 1, wherein during desulfurization
of an oxide-accumulating catalytic converter, a rich-lean cycle is
at least partially performed and an air ratio is detected before
and after the oxide-accumulating catalytic converter, wherein the
oxygen quantity is determined and the oxygen accumulator is used to
avoid substoichiometry and/or hyperstoichiometry of the air ratio
after the oxide-accumulating catalytic converter.
19. An exhaust-gas after-treatment system with a connected internal
combustion engine, wherein the internal combustion engine has a
motor control system, and the exhaust-gas after-treatment system
has at least one regulated catalytic converter and an oxygen
accumulator, wherein a first probe is arranged before the oxygen
accumulator and a second probe is arranged after the oxygen
accumulator, wherein at least the first probe determines a first
parameter characterizing the oxygen content, and a signal
transmission of the parameter recorded by the first and the second
probes to an evaluation unit is provided, and the evaluation unit
is coupled with a motor control system with a regulation or control
unit that takes into account a rich-lean cycle based on the
determined parameter.
20. The exhaust-gas after-treatment system according to claim 19,
wherein the second probe is a temperature probe whose parameter is
included in a control or regulation system of a lambda value of the
motor control system.
21. The exhaust-gas after-treatment system according to claim 20,
wherein a rich-lean cycle is included as a desired value in a
lambda regulation of the internal combustion engine.
22. The exhaust-gas after-treatment system according to claim 19,
wherein the first and the second probes each determine a first
parameter characterizing an oxygen content, and a signal
transmission of the first parameter from the first and the second
probes to an evaluation unit is provided, and the evaluation unit
determines, from the first parameters, a second parameter
characterizing the oxygen content of the oxygen accumulator, and
the motor control system is coupled with a device for setting an
air ratio in the exhaust-gas after-treatment system, wherein an
adaptation of the air ratio is provided as a function of the second
parameter by means of the device.
23. The exhaust-gas after-treatment system according to claim 19,
wherein the first probe is a broadband lambda probe and the second
probe is a transition probe.
24. The exhaust-gas after-treatment system according to claim 19,
wherein the oxygen accumulator has a first part and a second part
that are arranged in one or at least two different exhaust-gas
after-treatment components.
25. The exhaust-gas after-treatment system according to claim 19,
wherein the oxygen accumulator is a component of an NOx catalytic
converter or a particulate filter.
26. (canceled)
27. The exhaust-gas after-treatment system according to claim 19,
wherein a measurement probe is provided for determining a
temperature of the oxygen accumulator.
28. The exhaust-gas after-treatment system according to claim 22,
wherein at least one of a control system or a regulation system is
included and is geared toward the second parameter, in order to
trigger a change between rich and lean operation.
29-32. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is the U.S. national phase of international
patent application PCT/EP2007/004676 filed May 25, 2007, which
claims priority to German patent application DE 10 2006 025 050.8
filed May 27, 2006.
FIELD OF THE INVENTION
[0002] The present invention relates to a method for operating a
motor vehicle exhaust-gas after-treatment system and also to an
exhaust-gas after-treatment system with a connected internal
combustion engine.
BACKGROUND OF THE INVENTION
[0003] From U.S. Pat. No. 6,843,052, it is known that a rich-lean
cycle can be used so that the oxygen accumulator of an exhaust-gas
after-treatment component is used for the oxidation of H.sub.sS.
The accumulator is filled during a lean phase and at least
partially emptied during a rich phase. For regulating O.sub.2
content, a lambda probe placed downstream of the exhaust-gas
after-treatment component is used. Here, if a substoichiometric air
ratio is detected, a lean transition is triggered. For a
hyperstoichiometric air ratio, a rich transition is triggered. In
EP 0 893 154 B1, an oxygen accumulator connected downstream of an
NOx-accumulating catalytic converter (NAC) is used for supplying
oxygen for the H.sub.2S oxidation.
[0004] From DE 197 47 222 C1, an internal combustion engine system
with NAC and secondary air injection with a method for
desulfurization of the NAC is known. In this system, the
desulfurization control system is regulated by the output signal of
a lambda probe placed downstream.
[0005] From DE 198 27 195 A1, it is known that for a lean-rich
transition, initially SO.sub.2 is produced for a short time and
formation of H.sub.2S follows with a time delay. Therefore,
H.sub.2S emission can be suppressed by an early rich-lean
transition.
[0006] In DE 101 26 455 A1, a method for the desulfurization of an
NAC is described that follows the regeneration of a particulate
filter, whereby the heating to a desulfurization temperature is
eliminated or shortened.
[0007] From DE 199 22 962 C2, it is known that the air ratio in the
exhaust gas can be set by supplying secondary air during NAC
desulfurization.
[0008] The regulation or control system concepts emerging from the
above documents relate to a lambda probe signal downstream of an
oxygen-storing component in the exhaust-gas train. Especially at
high temperatures, the lambda probe here shows a value that is not
equal to one only when an oxygen accumulator is completely filled
(.lamda.>1) or is completely empty (.lamda.<1). Therefore,
e.g., for desulfurization, rich breakthroughs with accompanying
H.sub.2S emission can appear.
SUMMARY OF THE INVENTION
[0009] The task of the present invention is to create an
improvement in the operating behavior of an exhaust-gas
after-treatment system that takes into account, in particular, the
actual conditions in an exhaust-gas after-treatment system and
allows a rapid and also reliable reaction.
[0010] This task is achieved with a method with the features of
claim 1 and also with an exhaust-gas after-treatment system with
the features of Claim 19. Other advantageous configurations are
specified in each subordinate claim.
[0011] According to the invention, a method for operating a
motor-vehicle exhaust-gas after-treatment system is proposed in
which oxygen is fed to and removed from an oxygen accumulator of an
exhaust-gas after-treatment system, wherein at least one variable
parameter influenced by the oxygen accumulator and its oxygen
content is determined and is used for operation of the
motor-vehicle exhaust-gas after-treatment system.
[0012] Advantageously, the oxygen quantity in the oxygen
accumulator is determined and, according to one improvement, a
rich-lean cycle is influenced as a function of the determined
oxygen quantity. For example, an oxygen quantity in the oxygen
accumulator can be included as a parameter for setting a rich-lean
cycle. An example configuration provides that the oxygen quantity
is used as a regulating or control parameter for a rich-lean cycle.
Another example configuration provides that an oxygen quantity in
the oxygen accumulator is regulated by means of at least one
rich-lean cycle, advantageously by means of different rich-lean
cycles. One possible realization has a motor control system that
controls or regulates the rich-lean cycles, wherein the oxygen
content in the oxygen accumulator is controlled or regulated. For
this purpose, the motor control system can use, for example, a
plurality of characteristic engine maps or an oxygen calculation
that is performed continuously or discontinuously.
[0013] In particular, a fill level of the oxygen accumulator is
taken into account. Thus, for control or regulation systems with
respect to individual components or all of the components of the
exhaust-gas after-treatment system, not only is a lambda probe
signal taken into account, but the current state of the oxygen
accumulator is detected and taken into account insofar as this is
in the position, for example, to discharge oxygen for operation in
a rich section of the rich-lean cycle or, conversely, to be able to
store oxygen in a lean range of the rich-lean cycle.
[0014] In addition, an additional oxygen supply into the
motor-vehicle exhaust-gas after-treatment system can be provided as
a function of the determined oxygen quantity of the oxygen
accumulator. Such an oxygen supply can be performed, for example,
by means of an air supply, also like an oxygen supply into the
exhaust-gas after-treatment system. There is also the possibility,
for example, to change the air supply in the exhaust-gas
after-treatment system additionally or also independently through
corresponding valve overlap in a connected internal-combustion
engine.
[0015] Preferably, the oxygen quantity is calculated by means of an
oxygen balance across the oxygen accumulator. This can be realized,
for example, by means of a first probe and a second probe. The
first probe is preferably arranged in the flow direction before the
oxygen accumulator, advantageously at least directly before the
oxygen accumulator. The second probe is preferably arranged in the
immediate vicinity downstream of the oxygen accumulator. In
addition, there is the possibility that at least one of the two
probes is arranged directly on an opening of the oxygen
accumulator. There is also the possibility that at least one of the
probes is arranged in the oxygen accumulator. For example, the
entire accumulation behavior of the entire oxygen accumulator can
be determined from the partial behavior of the oxygen
accumulator.
[0016] Preferably, a first probe for a continuous measurement of
the oxygen content before the oxygen accumulator is used. Here,
instead of the oxygen content, the air content before the oxygen
accumulator can also be determined, and the oxygen content can be
determined from this. The second probe preferably determines the
oxygen content after the oxygen accumulator, at least at time
intervals. It is preferred that a continuous measurement of the
oxygen content or the air ratio is performed. For example, it is
provided that, of the two probes, at least the probe in front in
the flow direction is a broadband lambda probe. In contrast, the
other of the two probes can be a transition probe. However, two
broadband lambda probes can also be used. Advantageously, at least
one of the probes is in a position to also record the
temperature.
[0017] According to one improvement, the exhaust-gas
after-treatment system is equipped with a separate control device.
The control device stores, advantageously, not only a control or
regulation system with respect to the oxygen accumulator.
Advantageously, other components of the exhaust-gas after-treatment
components are also included in the control device. In addition to
the oxygen accumulator, this can be additional catalysts,
particulate filters, injection devices in the exhaust-gas
after-treatment system, for example, ammonia-containing means or
the like. A configuration provides that such functionality is
implemented in a motor control device. Another configuration
provides that the control device is arranged separately from the
motor control system.
[0018] According to one configuration, the method is used to
achieve a targeted influence on the rich-lean cycle with the oxygen
quantity stored in the oxygen accumulator. For example, it is
possible through targeted filling and emptying of the oxygen
accumulator to be able to change a quantity of heat released per
unit of time. Thus there is the possibility to be able to
influence, for example, the temperature of the oxygen accumulator
or a component that has the oxygen accumulator.
[0019] For example, it is provided that regeneration of an
exhaust-gas purification component of the motor vehicle has to be
performed within a certain temperature range. This is the case, for
example, for a regeneration of a diesel particulate filter, as well
as for a desulfurization of a nitrogen oxide-accumulating catalytic
converter. For example, in a particulate filter, if an internal
combustion engine is operated in a lean mode, then soot collects.
For burning off soot, advantageously a temperature greater than
500.degree. C. is set. If, for example, an uncoated particulate
filter is used, a temperature greater than 600.degree. C. is used.
For a catalytically- coated filter, for example, a temperature
greater than 550.degree. C. exhaust gas temperature is set on the
particulate filter. According to one configuration, a rich-lean
cycle is used for increasing temperature during regeneration. Here,
an oxygen accumulator is at least partially filled and emptied
cyclically. Reactions performed in this way in the oxygen
accumulator generate heat that is used for increasing the
temperature. The temperature increase can be performed, for
example, before the actual regeneration, so that for triggering the
actual regeneration, advantageously only little enthalpy must still
be provided. For example, the oxygen quantity present in the oxygen
accumulator can be used to generate, at least partially, a required
temperature and/or temperature increase for regeneration. For this
purpose, the oxygen accumulator stores oxygen accordingly in phases
of an oxygen excess supply, wherein this oxygen can be output in
phases of regeneration.
[0020] Such an operation of the oxygen accumulator in interaction
with regeneration is supported, for example, in various ways by
means of the motor control system and/or the separate control
device. For example, the temperature increase can be achieved in
such a way that an exhaust-gas temperature is detected at the
internal combustion engine or else also for operation of a turbine
at the outlet of the turbine. For example, in an internal
combustion engine, this can be realized by a reduction of the air
ratio, for example, by post injection, through a change of an
injection angle and also through throttling of the air fed to the
engine or a turbine. To allow an amplification of the temperature
increase, fuel that has not combusted or that has combusted only
incompletely can be fed to the oxygen accumulator. For example, for
this purpose, a delayed post injection of fuel can be used in an
expansion cycle of the internal combustion engine. Furthermore,
there is the possibility to provide an injection of the fuel into a
displacement cycle. In addition there is the possibility of direct
fuel supply into the exhaust-gas flow, for example, by means of an
additional injection. There is also the possibility of reforming
fuel and supplying it as synthesis gas. For example, there is also
the possibility that, in a motor vehicle that has a bivalent drive,
for example, a liquid gas accumulator, a natural gas accumulator,
or the like is used in addition, in order to allow a corresponding
fluid inflow into the exhaust-gas after-treatment system.
[0021] The oxygen to be stored in the oxygen accumulator is fed,
for example, from residual oxygen from the engine combustion.
However, there is also the possibility of providing an external air
supply into the exhaust gas. For this purpose, for example, a
secondary air fan can be used. There is also the possibility of
being able to use a charging device of an internal combustion
engine for this purpose. In addition there is the possibility of
using oxygen stored at other locations of the exhaust-gas
after-treatment system for enriching the oxygen output from this
system in the oxygen accumulator.
[0022] A combustible gas component can be converted in the
exhaust-gas after-treatment system through sufficient oxygen made
available, for example, by means of oxygen fed exclusively from the
oxygen accumulator or additionally from the oxygen accumulator, in
particular, as a supplement from the oxygen accumulator. For the
operation of the motor vehicle exhaust-gas after-treatment system,
it is geared in a targeted way to the use of the present oxygen
accumulator in a controlled way. For example, there is the
possibility of performing a temperature control or regulation of
the particulate filter, in particular, when the particulate filter
itself has the ability to act as an oxygen accumulator.
[0023] According to another configuration, the determined oxygen
quantity of the oxygen accumulator is included as a parameter in a
desulfurization process of an oxide accumulator advantageously for
influencing a rich-lean cycle. The oxide accumulator can be, for
example, a nitrogen oxide-accumulating catalytic converter and/or a
sulfur oxide accumulator. In desulfurization, an oxygen supply from
the oxygen accumulator is used to oxidize, for example, H.sub.2S
created during substoichiometric operation into SO.sub.2. By
determining the current oxygen content in the oxygen accumulator,
it is advantageously implemented in the corresponding operating
strategy that complete emptying of the oxygen accumulator is
avoided especially during rich operation. Thus, a risk of H.sub.2S
output is prevented. In particular, if it is provided as an
operating strategy that the oxygen accumulator may never be
completely emptied, then instead of a lambda probe after the oxygen
accumulator, in particular, a transition probe can also be
provided.
[0024] Advantageously, not just a determination of a beginning of a
desulfurization process and/or a regeneration process can be
determined by means of the considered oxygen quantity. There is
also the possibility that the determined oxygen quantity is
incorporated as a parameter for determining a time period of the
desulfurization and/or the regeneration.
[0025] Advantageously, not just a determination of a beginning of a
desulfurization process and/or a regeneration process can be
determined by means of the considered oxygen quantity. There is
also the possibility that the determined oxygen quantity is
incorporated as a parameter for determining a time period of the
desulfurization and/or regeneration. [sic; repeated paragraph
(except for one "the")]
[0026] The oxygen quantity required for the method in the oxygen
accumulator is determined, according to one configuration, through
integration of the oxygen mass flow exchanged with the accumulator.
The oxygen mass flow is here calculated with reference to a
difference in the probes, in particular, the lambda probes, and
also the exhaust-gas mass flow. For this purpose, the following
formula is used:
{dot over (m)}.sub.02={dot over
(m)}.sub.AL(.lamda..sub.beforeCat-.lamda..sub.afterCat)
m.sub.02=.intg. {dot over (m)}.sub.02dt where
m.sub.02--stored oxygen mass m.sub.02--exchanged oxygen mass flow
m.sub.02--exhaust-gas mass flow L--stoichiometric factor
.lamda.--air ratio
[0027] The result of such a calculation or another may be
incorrect, for example, due to inaccurate lambda signals or an
inaccurate exhaust-gas mass flow, so that the calculated oxygen
content does not correspond to the actual oxygen content. Also,
through integration, an error can continue to grow over time. It is
then possible that undesired rich or lean breakthroughs are
realized. If such a breakthrough should occur, with reference to
this breakthrough the actual state of the accumulator can be
identified and the calculation can be reset to a certain value. In
addition, a targeted breakthrough situation can be created, in
order to also achieve a calibration of the measurement. There is
also the possibility for initiating a calibration from the
operating behavior of the oxygen accumulator. For example, a
maximum storage state can also be tested through corresponding air
or oxygen supply and advantageously a calibration for the storage
capacity and the storage state of the oxygen accumulator can be
determined.
[0028] One improvement provides that, in the scope of a control or
regulation system, the oxygen accumulator, advantageously also its
oxygen storage capacity and, in particular, the current, determined
stored oxygen quantity are used to set at least one threshold
value. When this threshold is exceeded, a cycle change is triggered
between lean and rich operation. The threshold value can be fixed.
However, there is also the possibility that the threshold value can
be adapted, for example, due to aging of the oxygen accumulator.
For example, for a calibration of the oxygen storage capacity or
the calculation of the oxygen storage capacity, the threshold value
can be increased or decreased. For example, the threshold value is
stored in the control device of the exhaust-gas after-treatment
system. However, it can also be provided, for example, in the motor
control system. Preferably it is provided that a lower and an upper
threshold are set with respect to the oxygen quantity and a cycle
change between lean and rich operation is triggered when the
threshold is exceeded. A trigger time point for the cycle change
can here be provided when the threshold is reached but also only
after the threshold is exceeded. Preferably, a hysteresis response
can be triggered for a cycle change. This means that after a
threshold is reached, the oxygen accumulator either continues to
store oxygen in a slowed manner before discharging the oxygen or,
in the inverse case, a discharge of the oxygen is performed in a
slowed manner before oxygen is stored again in the oxygen
accumulator. Advantageously it is provided that the threshold with
respect to the oxygen quantity in the oxygen accumulator can be
exceeded once the threshold is reached and then after the cycle
change has been completed and the operating behavior with respect
to the oxygen discharge or absorption of the oxygen accumulator has
been reversed.
[0029] In addition, it can be provided that an internal combustion
engine is operated in a rich-lean cycle, wherein a temperature of
the oxygen accumulator is determined and an operating parameter
influencing the stored oxygen quantity is changed as a function of
the determined temperature. In particular, there is also the
possibility that temperature control of the exhaust-gas
after-treatment component having the oxygen accumulator changes an
oxygen quantity discharged per unit time from the oxygen
accumulator for adjusting the temperature of the exhaust-gas
after-treatment component. In the case of temperature regulation
through the use of the oxygen accumulator, for example, a PI
regulator can be used.
[0030] In addition, as well as also separately, an operation of the
motor-vehicle exhaust-gas after-treatment system can be provided in
which a rich-lean cycle is performed at least partially during
desulfurization of an oxide, in particular, a nitrogen
oxide-accumulating catalytic converter, and an air ratio is stored
after the oxide, in particular, the nitrogen oxide-accumulating
catalytic converter, wherein the oxygen quantity is determined and
used to prevent substoichiometry and/or hyperstoichiometry of the
air ratio after the oxide, in particular, the nitrogen
oxide-accumulating catalytic converter. Here, reference is made, in
particular, to one or more thresholds that can be set with respect
to the storage quantity of oxygen in the oxygen accumulator. For
example, there is the possibility that not just one threshold
value, but several threshold values are provided. Here there is the
possibility to be able to operate the oxygen accumulator with
different temperatures or oxygen discharge or oxygen
absorption.
[0031] The operation of the oxygen accumulator is integrated into
the exhaust-gas after-treatment concept of the motor vehicle.
Therefore, the oxygen accumulator can be arranged as an individual
component in the exhaust-gas after-treatment system. It is
preferred, however, that the oxygen accumulator is a part of a
component of the exhaust-gas after-treatment system. This can be a
catalytic converter, a particulate filter, or some other element in
the exhaust-gas after-treatment system.
[0032] According to another concept of the invention, an
exhaust-gas after-treatment system with a connected internal
combustion engine is proposed, wherein the internal combustion
engine has a motor control system and the exhaust-gas
after-treatment system has at least one regulated catalytic
converter and an oxygen accumulator, wherein a first probe is
arranged before the oxygen accumulator and a second probe is
arranged after the oxygen accumulator, wherein the first probe
detects a first parameter characterizing an oxygen content, a
signal transmission of the parameter recorded by the first and
second probes to an evaluation unit is provided, and the evaluation
unit is coupled with a motor control system with a regulation or
control unit that takes into account a rich-lean cycle based on the
determined parameter.
[0033] By means of such an exhaust-gas after-treatment system with
connected internal combustion engine, the method described above is
preferably performed for operating a motor-vehicle exhaust-gas
after-treatment system.
[0034] One improvement provides that the second probe is a
temperature probe whose parameter is included in a control or
regulation system of a lambda value of the motor control system.
Advantageously, a rich-lean cycle is included as a desired value in
a lambda regulation of the internal combustion engine.
[0035] Another configuration of the exhaust-gas after-treatment
system provides that the first and the second probes each determine
a first parameter characterizing an oxygen content, and a signal
transmission of the first parameter from the first and the second
probes to an evaluation unit is provided; the evaluation unit
determines, from the first parameters, a second parameter
characterizing an oxygen content of the oxygen accumulator, and the
motor control system is coupled with a device for setting an air
ratio in the exhaust-gas after-treatment system, wherein an
adaptation of the air ratio as a function of the second parameter
is provided by means of the device.
[0036] One improvement of the exhaust-gas after-treatment system
provides that the oxygen accumulator has a first part and a second
part that are arranged in at least two different exhaust-gas
after-treatment components. For example, the oxygen accumulator can
be formed from an NOx catalytic converter and also from a
particulate filter. These can also be provided separate from each
other. In addition, there is the possibility that a three-way
catalytic converter also includes an oxygen accumulator or a part
of this oxygen accumulator. It is preferred when a measurement
probe is provided for determining a temperature of the oxygen
accumulator. This permits a direct coupling of the measured
temperature for a calculation of the oxygen content of the oxygen
accumulator. For example, this determined temperature value can be
used for testing the oxygen content set, for example, by means of
the oxygen balance. Alternatively or additionally, the
determination of the temperature of the oxygen accumulator also
allows one or more of the thresholds named above to change to
influence the rich-lean cycle according to the
temperature-dependent oxygen storage capacity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Other advantageous configurations and improvements are
specified in the following drawings. The resulting features,
however, are not limited to the individual configurations. Instead,
to form improvements, individual features can be combined with
those of other configurations of the drawings and also with
features of the above description. Shown are:
[0038] FIG. 1, a first schematic view of a first exhaust-gas
after-treatment system,
[0039] FIG. 2, a schematic view of a second exhaust-gas
after-treatment system with temperature regulation,
[0040] FIG. 3, a schematic diagram of a temperature change through
a change in the operation of an internal combustion engine under
consideration of the oxygen quantity stored per unit time in an
oxygen accumulator of the exhaust-gas after-treatment system
connected to the internal combustion engine,
[0041] FIG. 4, a schematic view of a control loop for setting a
temperature change through a change in the use of an oxygen
accumulator,
[0042] FIG. 5, a schematic view of a third exhaust-gas
after-treatment system that allows, for example, the prevention of
a rich breakthrough by means of calculating a stored oxygen
quantity,
[0043] FIG. 6, a schematic diagram of a conventional regulation of
a conventional catalytic converter with an oxygen accumulator by
means of a lambda probe arranged at an outlet of the catalytic
converter, and
[0044] FIG. 7, a changed operation of the catalytic converter from
FIG. 6 that acts as an oxygen accumulator under consideration of a
calculated oxygen content based on a two-point regulation according
to the proposed operating method.
DETAILED DESCRIPTION OF THE INVENTION
[0045] FIG. 1 shows, in a schematic view, a first exhaust-gas
after-treatment system 1 in an example configuration. The
exhaust-gas after-treatment system 1 is arranged after an internal
combustion engine 2. This system has an exhaust-gas train 3 in
which, for example, an additional air feed 4 and also an additional
fuel feed 5 are provided. Both feeds 4, 5 are arranged before a
first probe 6, in particular, a lambda probe. The first probe 6 is
connected in front of an exhaust-gas after-treatment component 7
viewed in the flow direction. The exhaust-gas after-treatment
component 7 has an oxygen accumulator 8. In addition, the
exhaust-gas after-treatment component 7 can have a catalytic
converter, in particular, a regulated catalytic converter, an
NOx-accumulating catalytic converter, a particulate trap, a sulfur
trap, and/or some other component that is in the position to change
an exhaust gas originating from the internal combustion engine 2.
The oxygen accumulator 8 has a first part 9 and a second part 10.
These are arranged, for example, separately from each other in
different areas of the exhaust-gas after-treatment component 7. For
example, the first part of the oxygen accumulator 8 can be arranged
in a particulate filter, while the second part 10 of the oxygen
accumulator 8 is arranged in an NOx-accumulating catalytic
converter. The particulate filter and the NOx-accumulating
catalytic converter together form, for example, the exhaust-gas
after-treatment component 7. A second probe 11 is arranged after
this component, wherein this probe can also be, for example, a
lambda probe. After the second probe 11, viewed in the flow
direction, there can be another exhaust-gas after-treatment
component that can also have an oxygen accumulator. For example,
the second probe 11 can be used for more than balancing the oxygen
content for the exhaust-gas after-treatment component 7 by
determining the corresponding air ratio or the oxygen content after
the exhaust-gas after-treatment component 7. The second probe 11
can use, preferably simultaneously, the same signal as an input
parameter for the oxygen content or the air ratio for the
subsequent exhaust-gas after-treatment component in the scope of a
calculation or balancing. For this purpose, another probe, not
shown here in more detail, is arranged after the following
exhaust-gas after-treatment component. Furthermore, there is the
possibility that one or more other probes are provided in the
exhaust-gas after-treatment component 7. For example, one or more
of these probes can also form a replacement of the second probe 11
if, by means of the determined balancing, the oxygen content of the
region outside of the balancing limits can be determined. By means
of a motor control system 12, in particular, the air ratio in the
exhaust-gas train can be changed under consideration of the oxygen
accumulator 8. The motor control system 12 is connected, for
example, to a separate control device 13 of the first exhaust-gas
after-treatment system 1. The control device 13 records, for
example, the measurement values provided by the different probes
and uses these values in a separate evaluation unit 14. By means of
this unit, the currently stored oxygen quantity can be determined,
for example, by means of oxygen balancing across the oxygen
accumulator 8. This value can be forwarded, for example, to the
motor control system 12. The control device 13 is in the position,
in turn, to be able to adapt, for example, also under consideration
of the determined current oxygen quantity, an exhaust-gas strategy
in connection with the motor control system 12. This can be
incorporated, for example, in such a way that an ammonia-containing
medium is fed in a targeted way by means of the control device 13.
In particular, the control device 13 is in the position, together
with the motor control system 12, to be able to set a turnover
between rich operation and lean operation in the first exhaust-gas
after-treatment system 1 under consideration of the oxygen
accumulator 8. According to another configuration, however,
functionality of the control device 13, shown separately, can also
be implemented in a motor control device of the motor control
system 12.
[0046] FIG. 2 shows, in a schematic view, a second exhaust-gas
after-treatment system 15. A control/regulation unit 16 that is
coupled, in turn, to the internal combustion engine 2 is connected
to this system. The control/regulation unit 16 is preferably a
motor control device, but can also be a control device arranged
separately from the motor control device. Control signals 17 and
sensor signals 18 can be exchanged between the control/regulation
unit 16 and the internal combustion engine 2. A lambda probe 19 is
connected upstream in the direction of flow between the internal
combustion engine 2 and a catalytic converter 20 that contains an
oxygen accumulator 8. By means of the lambda probe 19, a signal
characterizing an oxygen content before the catalytic converter 20
is fed to the control/regulation unit 16. By means of a temperature
sensor 21 that is arranged after the catalytic converter 20, viewed
in the direction of flow, a temperature signal is also fed to the
control/regulation unit 16. By means of this device, showing the
most important components of an exhaust-gas after-treatment system
15 only schematically, it is possible to perform temperature
regulation of the oxygen accumulator 8. In particular, this device
made from second exhaust-gas after-treatment system 15 and internal
combustion engine 2 allows that a rich-lean cycle can be performed
that is influenced by a change of an air ratio and/or a time, a
rich phase, and/or a lean phase so that the oxygen quantity
originating from the oxygen accumulator 8 per unit time can be
changed and therefore a temperature of the oxygen accumulator 8 and
thus also the catalytic converter 20 is regulated or
controlled.
[0047] FIG. 3 shows, in a schematic view, an example of the use of
the oxygen accumulator from FIG. 2 for setting a temperature change
of the oxygen accumulator 8 from FIG. 1 or FIG. 2. In an upper
first diagram of FIG. 3, the air ratio lambda is shown, plotted on
the y-axis, versus time, which is plotted on the x-axis. Under
this, the profile of a stored oxygen quantity in the oxygen
accumulator is specified, wherein the solid line running parallel
to the x-axis, the time axis, specifies a maximum oxygen storage
capacity of the oxygen accumulator. Under this, a converted oxygen
quantity from the oxygen accumulator is also recorded versus time
on the x-axis. Under this, a temperature profile of the oxygen
accumulator or the catalytic converter that contains, for example,
the oxygen accumulator, is specified, in turn, versus time. In the
diagrams of FIG. 3 are two different rich-lean cycles set in
comparison. A first rich-lean cycle A is characterized with the
dashed line in the uppermost diagram of FIG. 3. A second rich-lean
cycle B is shown with a dash-dot line. A thin line running parallel
to the x-axis specifies the air ratio lambda=1 in the uppermost
diagram of FIG. 3. The two rich-lean cycles A, B differ by an
amplitude of a change of the respective air ratio delta lambda.
Both cycles have in common that the oxygen accumulator is neither
completely filled nor completely emptied. This starts from the
profile of the stored oxygen quantity in the oxygen accumulator
that at no time exceeds the maximum oxygen storage capacity. In a
lean phase, a stored oxygen quantity increases. This takes place in
time period I. In a subsequent rich phase, the oxygen present in
the oxygen accumulator is converted with combustible exhaust-gas
components. This is shown in time phase II. By setting a high
amplitude as shown, for example, in the second rich-lean cycle B,
more oxygen is converted in each rich phase II. Therefore, there is
a higher heat flux, so that a higher temperature increase is set by
means of the oxygen accumulator. This is reproduced in the
lowermost diagram of FIG. 3. While a temperature at an inlet of the
oxygen accumulator remains constant, this changes at the outlet as
a function of the set air ratio or the change in the air ratio, as
emerges from the uppermost diagram of FIG. 3. Taking advantage of
this relationship, the temperature of the oxygen accumulator and
thus, for example, a catalytic converter can be controlled or
regulated.
[0048] In a schematic view, FIG. 4 shows a possibility for
implementing temperature regulation with reference to an action
diagram for using the oxygen accumulator. The action diagram
provides the internal combustion engine 2 that delivers a
time-varying air ratio lambda as a current state. The value of the
current state of the air ratio is included, on one hand, in an
oxygen accumulator 8. By this, a temperature T is detected by means
of a corresponding temperature sensor. Here, the temperature of the
oxygen accumulator 8 and/or a temperature of an exhaust-gas flow
can be detected at an outlet from the oxygen accumulator 8, for
example, a catalytic converter, a particulate trap, or another
exhaust-gas after-treatment component. The temperature value is
used as a control parameter. This allows a temperature value to be
set that specifies a desired value of the temperature to be set in
the oxygen accumulator or in the exhaust-gas after-treatment
component. This desired value is set, for example, by means of the
motor control system or by means of a separate control device. From
the comparison of the control parameter with the desired value, the
control difference can be determined that is fed as an input
parameter to a regulator 15. From this, the regulator generates an
amplitude of the air ratio, advantageously in the form of an air
ratio change. By means of a corresponding generator, for example,
by means of a pulse-width modulation generator, a desired value of
the air ratio can be formed from the change of air ratio delta
lambda. This means the corresponding rich-lean cycle delivers the
desired value of the air ratio that is included together with the
current value of the air ratio in a lambda regulator 16 of the
internal combustion engine 2.
[0049] As an alternative to the schematic temperature regulation
from FIG. 4 in a closed control loop with the required temperature
measurement, there is also the possibility of using a pure control
system in which a change in the air ratio is stored in a
characteristic map or a characteristic line.
[0050] In an example schematic view, FIG. 5 shows a third
exhaust-gas after-treatment system 22 with an internal combustion
engine 2 and also a control/regulation unit 16, between which
control signals 17 and sensor signals 18 can be exchanged. A
broadband lambda probe 23 is arranged before an oxygen accumulator
8, for example, in the form of a catalytic converter. Viewed in the
direction of flow, a control probe 24 is located after the oxygen
accumulator 8. The control probe 24 can be a broadband lambda probe
or a transition probe. By means of the broadband lambda probe 23,
an air ratio or an oxygen content in the exhaust-gas flow is
transmitted with reference to a characterizing parameter to the
control/regulation unit 16. From the control probe 24, an air ratio
or an oxygen-characterizing signal value is also forwarded to the
control/regulation unit 16. This signal can also represent a
transition signal on the basis of the probe that is used. This
configuration allows, on one hand, a determination of the stored
oxygen quantity in the oxygen accumulator 8 by means of balancing
across the oxygen accumulator 8. On the other hand, the
configuration is suitable for preventing a rich breakthrough by the
oxygen accumulator 8 and thus, for example, the connected catalytic
converter, with the resulting H.sub.2S emissions, in particular,
for desulfurization.
[0051] In a schematic diagram, FIG. 6 shows a conventional
regulation of a catalytic converter that uses a lambda probe
arranged at an outlet. In the upper diagram of FIG. 6, the air
ratio is shown, and in the lower diagram of FIG. 6, the stored
oxygen quantity in the catalytic converter is reproduced. All
values are plotted versus time. If it is determined by means of the
lambda probe that the air ratio after the catalytic converter is
greater than 1, then a switch point is set at which a transition
from lean operation to rich operation is performed. In contrast, if
it is determined by means of the lambda probe that there is an air
ratio less than 1 after the catalytic converter, then the control
system is switched from rich operation to lean operation. From the
lower diagram, the respective switch points are drawn using dotted
lines downward from the upper diagram. The substoichiometric or
hyperstoichiometric air ratios are advantageously set so that the
respectively stored oxygen quantities in the oxygen accumulator
have been completely removed from the oxygen accumulator or else
the storage capacity of the oxygen accumulator was exceeded.
Starting from the upper diagram of FIG. 6, the desired value of the
air ratio before the catalytic converter emerges as a solid line c.
In the dotted diagram a, the actual value of the air ratio before
the catalytic converter is shown, while the air ratio after the
catalytic converter b is also recorded with dashed lines. From this
emerges the following relationship with respect to the rich-lean
cycle that is controlled with respect to the lambda signal after
the catalytic converter: in the lean phase I with lambda greater
than 1 before the catalytic converter, this and thus the oxygen
accumulator are filled. If accumulation of oxygen in this phase is
not controlled, no oxygen is led through the accumulator and the
lambda signal that is recorded after the catalytic converter as the
oxygen accumulator remains at the value of 1. Only when the oxygen
accumulator is completely filled can an oxygen breakthrough be
detected with reference to the lambda signal and a rich transition
can be triggered. In this rich phase II, the accumulator empties.
If a sufficiently high temperature is provided here, nearly all of
the reduction agent is converted, so that the lambda signal again
remains at 1. After complete emptying of the oxygen accumulator,
however, a reduction agent breakthrough is realized that is
indicated by means of the probe. Only when this has been detected
by the lambda probe can a lean transition be realized. Through the
inertia provided in the control path and in the respective
actuators, reduction agent is discharged for a certain time. During
desulfurization, this can mean that H.sub.2S is discharged. In
contrast, with the device emerging from FIG. 5, there is the
possibility of preventing such discharge and allowing, in
particular, another type of regulation.
[0052] FIG. 7 shows the configuration of 2-point regulation of the
oxygen accumulator that is possible relative to the catalytic
converter emerging from FIG. 6. Here, the rich-lean cycle is
controlled with reference to the stored oxygen quantity, for
example, in the catalytic converter. This allows rich and also lean
breakthroughs to be prevented. Here, preferably, for example, a
2-point regulation with hysteresis is used. When a certain oxygen
threshold is exceeded, a rich transition is triggered. When the
value falls below another threshold, a lean transition is realized.
In the case of desulfurization, at any time there is sufficient
oxygen that can be used for the oxidation of H.sub.2S. The upper
threshold 25 and lower threshold drawn in the lower diagram from
FIG. 7 can thus be guaranteed for sufficient spacing relative to a
maximum oxygen absorption capacity of the oxygen accumulator or a
safe operation in all operating points of the exhaust-gas
after-treatment system for an emptied state of the oxygen
accumulator. From the upper diagram of FIG. 7 it is to be taken
that, in turn, the desired value before the catalytic converter,
shown as a solid line c, and also the current value of the air
ratio before the catalytic converter, shown as a dotted line a, can
lead to an air ratio of lambda=1 after the catalytic converter for
consideration of the oxygen quantity in the oxygen accumulator and
thus in the exhaust-gas after-treatment component. In particular,
this permits a constant air ratio b of lambda =1 to be reliably set
after the catalytic converter or the exhaust-gas after-treatment
component.
* * * * *