U.S. patent application number 13/439917 was filed with the patent office on 2013-10-10 for system and method for controlling an exhaust system having a selective catalyst reduction component.
This patent application is currently assigned to GM GLOBAL TECHNOLOGY OPERATIONS LLC. The applicant listed for this patent is Min Sun. Invention is credited to Min Sun.
Application Number | 20130263575 13/439917 |
Document ID | / |
Family ID | 49210096 |
Filed Date | 2013-10-10 |
United States Patent
Application |
20130263575 |
Kind Code |
A1 |
Sun; Min |
October 10, 2013 |
SYSTEM AND METHOD FOR CONTROLLING AN EXHAUST SYSTEM HAVING A
SELECTIVE CATALYST REDUCTION COMPONENT
Abstract
A method for controlling operation of an SCR component includes
receiving a signal reflecting a sensed condition of an exhaust
stream associated with the SCR component, estimating an apparent
aging time of the SCR component based on the sensed condition of
the exhaust stream, and setting an operating condition of the SCR
component based on the apparent aging time of the SCR
component.
Inventors: |
Sun; Min; (Troy,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sun; Min |
Troy |
MI |
US |
|
|
Assignee: |
GM GLOBAL TECHNOLOGY OPERATIONS
LLC
Detroit
MI
|
Family ID: |
49210096 |
Appl. No.: |
13/439917 |
Filed: |
April 5, 2012 |
Current U.S.
Class: |
60/274 ; 60/276;
60/301 |
Current CPC
Class: |
F01N 11/00 20130101;
F01N 2900/0412 20130101; Y02T 10/12 20130101; Y02T 10/47 20130101;
Y02T 10/40 20130101; F01N 3/106 20130101; F01N 3/035 20130101; F01N
9/005 20130101; F01N 2560/026 20130101; F01N 2550/02 20130101; F01N
2560/021 20130101; F01N 2900/1402 20130101; F01N 13/009 20140601;
Y02T 10/24 20130101; F01N 3/2066 20130101 |
Class at
Publication: |
60/274 ; 60/301;
60/276 |
International
Class: |
F01N 11/00 20060101
F01N011/00; F01N 3/20 20060101 F01N003/20 |
Claims
1. A method for controlling operation of an SCR component
comprising: receiving a signal reflecting a sensed condition of an
exhaust stream associated with the SCR component; estimating an
apparent aging time of the SCR component based on the sensed
condition of the exhaust stream; and setting an operating condition
of the SCR component based on the apparent aging time of the SCR
component.
2. A method as described in claim 1, wherein said receiving a
signal reflecting a sensed condition of an exhaust stream
associated with the SCR component comprises receiving a signal
reflecting a sensed NOx content of the exhaust stream.
3. A method as described in claim 1, wherein said receiving a
signal reflecting a sensed condition of an exhaust stream
associated with the SCR component comprises receiving a signal
reflecting a sensed NH3 content of the exhaust stream.
4. A method as described in claim 1, wherein said receiving a
signal reflecting a condition of an exhaust stream associated with
the SCR component comprises receiving a signal reflecting a sensed
condition of the exhaust stream downstream from the SCR
component.
5. A method as described in claim 1, wherein said estimating an
apparent aging time of the SCR component comprises: setting a model
input SCR aging time; executing an SCR reaction model comprising:
determining a predicted SCR reaction efficiency based on the model
input SCR aging time; and determining a predicted condition of the
exhaust stream based on the predicted SCR reaction efficiency;
adjusting the model input SCR aging time and subsequently executing
the SCR reaction model until the predicted condition of the exhaust
stream is within a predetermined tolerance of the sensed condition
of the exhaust stream; and setting an apparent SCR aging time equal
to the model input SCR aging time when the predicted condition of
the exhaust stream is within the predetermined tolerance of the
sensed condition of the exhaust stream.
6. A method as described in claim 5, wherein said sensed condition
of the exhaust stream comprises a sensed NOx content of the exhaust
stream.
7. A method as described in claim 5, wherein said sensed condition
of the exhaust stream comprises a sensed NH3 content of the exhaust
stream.
8. A method as described in claim 5, wherein said sensed condition
of the exhaust stream comprises a sensed condition downstream from
the SCR component.
9. A method as described in claim 5, wherein said determining a
predicted SCR reaction efficiency comprises interpolating one or
more empirical data tables representing an efficiency of an SCR
reaction as a function of SCR aging time.
10. A method as described in claim 5, wherein said determining a
predicted SCR reaction efficiency comprises evaluating one or more
polynomial expressions characterizing reaction efficiency as a
function of SCR aging time.
11. A system for controlling operation of an SCR component
comprising: a selective catalyst reduction (SCR) component
diagnostic module that is configured for receiving a signal
reflecting a sensed condition of an exhaust stream associated with
the SCR component and for estimating an apparent aging time of the
SCR component based on the sensed condition of the exhaust stream;
and an SCR component management module that is configured for
selectively adjusting an operating condition of the SCR component
based on the apparent aging time of the SCR component.
12. A system as described in claim 11, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for receiving a signal reflecting a sensed NOx content of the
exhaust stream.
13. A system as described in claim 11, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for receiving a signal reflecting a sensed NH3 content of the
exhaust stream.
14. A system as described in claim 11, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for receiving a signal reflecting a sensed condition of the exhaust
stream downstream from the SCR component.
15. A system as described in claim 11, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for: setting a model input SCR aging time; executing an SCR
reaction model comprising: determining a predicted SCR reaction
efficiency based on the model input SCR aging time; and determining
a predicted condition of the exhaust stream based on the predicted
SCR reaction efficiency; adjusting the model input SCR aging time
and subsequently executing the SCR reaction model until the
predicted condition of the exhaust stream is within a predetermined
tolerance of the sensed condition of the exhaust stream; and
setting an apparent SCR aging time equal to the model input SCR
aging time when the predicted condition of the exhaust stream is
within the predetermined tolerance of the sensed condition of the
exhaust stream.
16. A system as described in claim 15, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for receiving a signal reflecting a sensed NOx content of the
exhaust stream.
17. A system as described in claim 15, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for receiving a signal reflecting a sensed NH3 content of the
exhaust stream.
18. A system as described in claim 15, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for receiving a signal reflecting a sensed condition of the exhaust
stream downstream from the SCR component.
19. A system as described in claim 15, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for interpolating one or more empirical data tables representing an
efficiency of an SCR reaction as a function of SCR aging time.
20. A system as described in claim 15, wherein said selective
catalyst reduction (SCR) component diagnostic module is configured
for evaluating one or more polynomial expressions characterizing
reaction efficiency as a function of SCR aging time.
Description
FIELD OF THE INVENTION
[0001] The subject invention relates to vehicle exhaust systems,
and more particularly to systems and methods for controlling
exhaust systems that include a selective catalyst reduction (SCR)
components.
BACKGROUND
[0002] The background description provided herein is for the
purpose of generally presenting the context of the disclosure. Work
of the presently named inventors, to the extent it is described in
this background section, as well as aspects of the description that
may not otherwise qualify as prior art at the time of filing, are
neither expressly nor impliedly admitted as prior art against the
present disclosure.
[0003] During combustion in a diesel engine, an air/fuel mixture is
delivered through an intake valve to cylinders and is compressed
and combusted therein. After combustion, the piston forces the
exhaust gas in the cylinders into an exhaust system. The exhaust
gas may contain oxides of nitrogen (NOx) and carbon monoxide
(CO).
[0004] Exhaust gas treatment systems may employ catalysts in one or
more components configured for accomplishing an SCR process such as
reducing nitrogen oxides (NOx) to produce more tolerable exhaust
constituents of nitrogen (N2) and water (H2O). Reductant may be
added to the exhaust gas upstream from an SCR component, and, for
example only, the reductant may include anhydrous ammonia (NH3),
aqueous ammonia or urea, any or all of which may be injected as a
fine mist into the exhaust gas. When the ammonia, mixed with
exhaust gases, reaches the SCR component, the NOx emissions break
down. A Diesel Particulate Filter (DPF) may then capture soot, and
that soot may be periodically incinerated during regeneration
cycles. Water vapor, nitrogen and reduced emissions exit the
exhaust system.
[0005] To maintain efficient NOx reduction in the SCR component, a
control may be employed so as to maintain a desired quantity of the
reductant (i.e., reductant load) in the SCR component. As exhaust
gas containing NOx passes through the SCR component, the reductant
is consumed, and the load is depleted. A model may be employed by
the control to track and/or predict how much reductant is loaded in
the SCR component and to maintain an appropriate reductant load for
achieving a desired effect such as reduction of NOx in the exhaust
stream. The model may also be employed to determine aging of the
SCR component so as to facilitate periodic servicing or to adapt
control over the engine and SCR systems so as to achieve selected
objectives. Proper assessment of aging of the SCR component can
facilitate advantageous control over the SCR component so as to
achieve desirable SCR efficiencies and beneficial trade-offs
between engine operability, power output, fuel consumption, and NOx
emission, resulting in improved performance and/or fuel economy and
reduced urea consumption.
[0006] Unfortunately, determining aging of an SCR component onboard
a vehicle can be costly and unreliable. For example, conventional
methods may rely upon correlations between SCR aging rates and
engine-related parameters sensed upstream from the SCR component.
Yet, SCR aging may actually be more closely related to substrate
temperatures in the SCR component and to other conditions internal
to the SCR component, conditions that can be difficult to determine
with suitable accuracy. Therefore, aging methods that are based on
correlations with engine parameters that can be sensed can be
costly, can require significant time to develop correlation data to
fully characterize aging as a function of the numerous parameters
affecting aging, and can be inaccurate if all significant variables
are not considered.
[0007] Accordingly, it is desirable to provide a system and method
for predicting SCR aging time onboard the vehicle without relying
on sensed engine parameters and costly correlations. It is also
desirable to have an improved system and method for controlling
exhaust systems that include an SCR component, wherein SCR
component aging may be determined based on one or more parameters
directly affected by operation of the SCR component.
SUMMARY OF THE INVENTION
[0008] In one exemplary embodiment of the invention, a method for
controlling operation of an SCR component includes receiving a
signal reflecting a sensed condition of an exhaust stream
associated with the SCR component, estimating an apparent aging
time of the SCR component based on the sensed condition of the
exhaust stream, and setting an operating condition of the SCR
component based on the apparent aging time of the SCR
component.
[0009] In another exemplary embodiment of the invention, a system
for controlling operation of an SCR component comprises a selective
catalyst reduction (SCR) component diagnostic module that is
configured for receiving a signal reflecting a sensed condition of
an exhaust stream associated with the SCR component and for
estimating an apparent aging time of the SCR component based on the
sensed condition of the exhaust stream. A system for controlling
operation of an SCR component also comprises an SCR component
management module that is configured for selectively adjusting an
operating condition of the SCR component based on the apparent
aging time of the SCR component.
[0010] The above features and advantages and other features and
advantages of the invention are readily apparent from the following
detailed description of the invention when taken in connection with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other features, advantages and details appear, by way of
example only, in the following detailed description of embodiments,
the detailed description referring to the drawings in which:
[0012] FIG. 1 is a functional block diagram of an engine control
system including an exhaust diagnostic system that automatically
predicts SCR aging time according to the present disclosure;
[0013] FIG. 2 is a functional block diagram of an exemplary
implementation of a control module of the exhaust diagnostic system
of FIG. 1; and
[0014] FIG. 3 illustrates a method for resetting an exhaust
diagnostic system after operating with poor diesel reductant
quality according to the present disclosure.
DESCRIPTION OF THE EMBODIMENTS
[0015] The following description is merely exemplary in nature and
is in no way intended to limit the disclosure, its application, or
uses. For purposes of clarity, the same reference numbers will be
used in the drawings to identify similar elements. As used herein,
the phrase at least one of A, B, and C should be construed to mean
a logical (A or B or C), using a non-exclusive logical or. It
should be understood that steps within a method may be executed in
different order without altering the principles of the present
disclosure.
[0016] As used herein, the term "module" refers to an Application
Specific Integrated Circuit (ASIC), an electronic circuit, a
processor (shared, dedicated, or group) and memory that execute one
or more software or firmware programs, a combinational logic
circuit, and/or other suitable components that provide the
described functionality.
[0017] While the following disclosure involves diesel engines,
other types of engines such as gasoline engines, including direct
injection engines, may benefit from the teachings herein.
[0018] In accordance with an exemplary embodiment of the invention,
the present disclosure provides a system and method for predicting
SCR aging time onboard the vehicle without relying on sensed engine
parameters and/or correlations between SCR aging and engine-related
parameters. The present disclosure also provides improved systems
and methods for controlling exhaust systems that include a
selective catalyst reduction (SCR) component. These improved
systems and methods are enabled by the capability to determine SCR
component aging, in real time, based on one or more on-board
parameters that are directly affected by operation of the SCR
component (e.g., NOx content of the exhaust stream downstream from
the SCR component).
[0019] With SCR aging time established, control over operation of
the engine system, including the SCR component, can be executed
with improved accuracy and reliability. For example, dosing can be
controlled to provide a suitable load of reductant on the SCR
catalyst. Similarly, the exhaust diagnostic system according to the
present disclosure may elevate the exhaust temperature using
intrusive exhaust gas temperature management so that a temperature
of the SCR catalyst is at a suitable level to facilitate desirable
operation of the SCR component or, in some situations, to allow
testing of the efficiency of the SCR catalyst. In some situations,
it may be desirable to exercise control over the vehicle speed
and/or other operating parameters.
[0020] Referring now to FIG. 1, a diesel engine system 10 is
schematically illustrated. The diesel engine system 10 includes a
diesel engine 12 and an exhaust treatment system 13. The exhaust
treatment system 13 further includes an exhaust system 14 and a
dosing system 16. The diesel engine 12 includes a cylinder 18, an
intake manifold 20, a mass air flow (MAF) sensor 22 and an engine
speed sensor 24. Air flows into the diesel engine 12 through the
intake manifold 20 and is monitored by the MAF sensor 22. The air
is directed into the cylinder 18 and is combusted with fuel to
drive pistons (not shown). Although a single cylinder 18 is
illustrated, it can be appreciated that the diesel engine 12 may
include additional cylinders 18. For example, diesel engines having
2, 3, 4, 5, 6, 8, 10, 12 and 16 cylinders are anticipated.
[0021] Exhaust gas 19 is produced inside the cylinder 18 as a
result of the combustion process. The exhaust system 14 treats the
exhaust gas before the exhaust gas is released to atmosphere. The
exhaust system 14 includes an exhaust manifold 26 and a diesel
oxidation catalyst (DOC) 28. The exhaust manifold 26 directs
exhaust exiting the cylinder through the DOC 28. The exhaust is
treated within the DOC 28 to reduce the emissions. The exhaust
system 14 further includes an SCR component 30, a DOC inlet
temperature sensor 31, an SRC inlet temperature sensor 32, an SRC
outlet temperature sensor 34 and a particulate filter (PF) 36.
[0022] The DOC inlet temperature sensor 31 may be positioned
between the engine and the DOC 28. The SRC inlet temperature sensor
32 is located upstream from the SCR component 30 to monitor
temperatures at the inlet of the SCR component 30. The SRC outlet
temperature sensor 34 is located downstream from the SCR component
30 to monitor temperatures at the outlet of the SCR component 30.
Although the exhaust treatment system 13 is illustrated as
including the SRC inlet and SRC outlet temperature sensors 32, 34
arranged outside the SCR component 30, the SRC inlet and SRC outlet
temperature sensors 32, 34 can be located inside the SCR component
30 to monitor temperatures of the exhaust 19 at the inlet and
outlet of the SCR component 30. The PF 36 further reduces emissions
by trapping particulates (i.e., soot) in the exhaust gas 19.
[0023] The dosing system 16 includes a dosing injector 40 that
injects reductant from a reductant supply 38 into the exhaust gas
19. The reductant mixes with the exhaust gas and further reduces
the emissions when the mixture is exposed to the SCR component 30.
A mixer 41 may be used to mix the reductant with the exhaust gas
upstream from the SCR component 30. A control module 42 regulates
and controls the operation of the engine system 10.
[0024] An exhaust gas flow rate sensor 44 may generate a signal
corresponding to the flow of exhaust 19 in the exhaust system.
Although the sensor is illustrated between the SCR component 30 and
the PF 36, various other locations within the exhaust system may be
used for measurement including downstream from the exhaust manifold
and upstream from the SCR component 30.
[0025] A temperature sensor 46 generates a particulate filter
temperature corresponding to a measured particulate filter
temperature. The temperature sensor 46 may be disposed on or within
the PF 36. The temperature sensor 46 may also be located upstream
or downstream from the PF 36.
[0026] Other sensors in the exhaust system may include an upstream
NOx sensor 50 that generates a NOx signal based on a concentration
of NOx present in the exhaust system. A downstream NOx sensor 52
may be positioned downstream from the PF 36 to measure a
concentration of NOx leaving the PF 36 or may be positioned
downstream from the SCR component 30, such as in a close-coupled
arrangement. In addition, an ammonia (NH3) sensor 54 generates a
signal corresponding to the amount of ammonia within the exhaust
gas. The NH3 sensor 54 is optional, but can be used to simplify the
control system due to the ability to discern between NOx and NH3.
The downstream NH3 sensor 54 may be positioned downstream from the
PF 36 to measure a concentration of NH3 leaving the PF 36 or may be
positioned downstream from the SCR component 30, such as in a
close-coupled arrangement. Alternately and/or in addition, a
hydrocarbon (HC) supply 56 and a HC injector 58 may be provided to
supply HC in the exhaust gas 19 reaching the DOC catalyst.
[0027] Referring now to FIG. 2, the control module 42 may include
an SCR component diagnostic module 60 that is used to determine a
conversion efficiency of NOx at the SCR component 30. The control
module 42 further includes an SCR component management module 62
that intrusively controls a temperature or other parameters of the
SCR component 30. In an exemplary embodiment, the SCR component
diagnostic module 60 includes a signal receiver 70 and an SCR
reaction simulation module 72. The signal receiver 70 is configured
for receiving a signal reflecting a sensed condition of an exhaust
stream associated with the SCR component. The SCR reaction
simulation module 72 is configured for estimating an apparent aging
time of the SCR component based on the sensed condition of the
exhaust stream. In an exemplary embodiment, the signal receiver 70
of the SCR component diagnostic module 60 receives one or more
signals reflecting conditions of the exhaust stream, such as a
sensed NOx content of the exhaust stream and/or a sensed NH3
content of the exhaust stream downstream from the SCR
component.
[0028] In an exemplary embodiment, the SCR reaction simulation
module 72 of the SCR component diagnostic module 60 is configured
to determine SCR component aging (e.g., through a recursive
algorithm or an iterative process). For example, the SCR reaction
simulation module 72 may set a model input SCR aging time and
subsequently execute an SCR reaction simulation model by first
determining a predicted SCR reaction efficiency based on the model
input SCR aging time and then determining a predicted condition of
the exhaust stream 19 based on the predicted SCR reaction
efficiency. In accordance with such embodiments, the SCR reaction
simulation module 72 is driven to iterate as a solution module 74
adjusts the model input SCR aging time and subsequently causes the
SCR reaction simulation module 72 to predict SCR reaction
efficiency based on the incremented input SCR aging time and the
corresponding predicted condition of the exhaust stream. The
solution module 74 continues this process until the predicted
condition of the exhaust stream 19 is within a predetermined
tolerance of the sensed condition of the exhaust stream 19. When
the predicted condition of the exhaust stream is within the
predetermined tolerance of the sensed condition of the exhaust
stream (i.e., the model is converged, a solution is achieved), the
solution module 74 sets an apparent SCR aging time to be equal to
the model input SCR aging time.
[0029] In an exemplary embodiment, the SCR component management
module 62 includes an SCR component manager 78 that is configured
for selectively adjusting an operating condition of the SCR
component based on the apparent aging time of the SCR component.
For example, operating conditions of the SCR component may include
SCR temperature, dosing rate, reductant load, EGR, and/or other
pertinent operating conditions. To accomplish this, the SCR
component management module 62 includes an SCR efficiency module 76
that is configured for determining an efficiency of an SCR
reaction. The SCR efficiency module 76 may accomplish this, for
example, by interpolating one or more empirical data tables
representing an efficiency of an SCR reaction as a function of SCR
aging time. Alternatively, the SCR efficiency module 76 may
determine efficiency by evaluating one or more polynomial
expressions characterizing reaction efficiency as a function of SCR
aging time.
[0030] The SCR efficiency module 76 of the SCR component management
module 62 also calculates a temperature of the SCR component. The
SCR efficiency module 76 may calculate the temperature of the SCR
component based on the SRC inlet temperature sensor 32, the SRC
outlet temperature sensor 34, a model or any other suitable method.
For example only, the SCR efficiency module 76 may calculate the
SCR component temperature based on values from both the SRC inlet
and SRC outlet temperature sensors 32, 34. For example only, the
SCR efficiency module 76 may calculate the temperature based on an
average or a weighted average of the SRC inlet and SRC outlet
temperature sensors 32, 34.
[0031] The control module 42 includes a vehicle speed control
module 80 that controls vehicle speed based on the SCR component
efficiency (e.g., limits vehicle speed when efficiency falls below
a predetermined threshold). The control module 42 further includes
a fueling control module 82 that determines fuel quantity, fuel
injection timing, post injection, etc. When in the intrusive SCR
component test mode, the SCR component management module 62 adjusts
fueling. The fueling adjustment increases a temperature of the SCR
component. Alternately, a hydrocarbon injection module 84 injects
fuel into the exhaust upstream from the DOC catalyst 28 to generate
an exotherm to increase the temperature in the SCR component.
[0032] Referring now to FIG. 3, a method for controlling operation
of an SCR component begins by determining whether it is necessary
or desirable to determine an aging of the SCR component (step 100).
If so, a method for controlling operation of an SCR component
includes receiving a signal reflecting a sensed condition of an
exhaust stream 19 associated with the SCR component (step 110). The
signal may reflect a sensed NOx content of the exhaust stream (step
112) and/or a sensed NH3 content of the exhaust stream (step 114),
and the signal may originate downstream from the SCR component
(step 116).
[0033] A method for controlling operation of an SCR component also
includes estimating an apparent aging time of the SCR component
based on the sensed condition of the exhaust stream (step 120). A
method for estimating an apparent aging time of the SCR component
may include first setting a model input SCR aging time (step 130),
and then executing an SCR reaction model (step 140). Executing an
SCR reaction model may include determining a predicted SCR reaction
efficiency based on the model input SCR aging time (step 142) and
then determining a predicted condition of the exhaust stream based
on the predicted SCR reaction efficiency (step 144). The predicted
condition of the exhaust stream is compared to the sensed condition
of the exhaust stream to determine whether they are sufficiently
close, or within an acceptable tolerance (step 146). If not, the
model input SCR aging time is adjusted (step 148) and the SCR
reaction model is again executed (step 140) until the predicted
condition of the exhaust stream is within a predetermined tolerance
of the sensed condition of the exhaust stream. When the predicted
condition of the exhaust stream is within the predetermined
tolerance of the sensed condition of the exhaust stream (or when
another appropriate convergence criteria) is achieved, an apparent
SCR aging time is set equal to the model input SCR aging time (step
150).
[0034] In an exemplary embodiment, a predicted SCR reaction
efficiency may be determined (step 160) by interpolating one or
more empirical data tables representing an efficiency of an SCR
reaction as a function of SCR aging time (step 162) or by
evaluating one or more polynomial expressions characterizing
reaction efficiency as a function of SCR aging time (step 164).
Finally, a method for controlling operation of an SCR component
also includes setting an operating condition of the SCR component
based on the apparent aging time of the SCR component (step 170).
Having improved knowledge of SCR component aging, operation of the
engine and the SCR can be more advantageously controlled such as by
improving SCR efficiency and optionally balancing engine fuel
consumption, NOx emission, and urea consumption (step 172). The
control may, for example, increase or decrease the exhaust
temperature by altering fueling (fuel quantity, fuel injection
timing, post injection, etc.) and/or by starting, stopping,
increasing, or decreasing HC injection.
[0035] In some situations, such as when an SCR component has been
determined to be of sufficient aging, control may undertake
remedial measures such as disabling exhaust gas recirculation (EGR)
(step 180). The control may also activate a process for depleting a
reductant load to establish a reliable reductant load on the SCR
component (step 182). After the reductant load has been depleted,
dosing can be re-commenced to re-establish a known (i.e., reliably
predictable by the reductant load model) load on the SCR component
(step 184). With a known reductant load, the control may measure an
efficiency of the SCR conversion process (step 186), for example,
by comparing an efficiency based on upstream and downstream
accumulated masses as well as upstream NOx and SCR component
temperature. The control may assess quality of the reductant by
comparing the measured efficiency to the efficiency determined
based on aging as described above (step 188). If reductant quality
is insufficient, additional remedial measures may be undertaken
(step 190). These may include illumination of a warning light,
imposition of vehicle speed limiting, intrusive exhaust gas
temperature management, and adjustments to EGR.
[0036] Thus, an exemplary method for controlling operation of an
SCR component enables use of an onboard recursive optimization
algorithm to determine SCR aging time in real-time by matching
output from an SCR model with signals dispatched from a NOx sensor
positioned at the outlet of the SCR component or downstream from
the SCR component. The SCR model determines a predicted
concentration of NOx and NH3 at the outlet of the SCR component
based on SCR reaction efficiency values which are determined by
interpolating SCR efficiency tables with SCR aging time. An SCR
aging input is floated until the predicted concentrations of NOx
and/or NH3 match, with sufficient accuracy, signals dispatched from
the sensors. A model may employ interpolation between data points
of predetermined (e.g., based on empirical data or developed
theoretically) SCR NH3 reaction efficiency tables and NH3
desorption and absorption tables covering a range of aging
stages.
[0037] Accordingly, SCR aging time can be determined on-board, and
adaptively, eliminating the need for the system to have knowledge
of the relationship between SCR aging rate and engine parameters.
By obviating the need to correlate SCR aging rate with engine
parameters, substantial time and cost associated with calibration
can be eliminated. In addition, the systems and methods described
herein enable determination of SCR aging after a vehicle SCR is
changed (e.g., due to damage). Finally, having improved knowledge
of SCR component aging, operation of the engine and the SCR can be
more advantageously controlled such as by improving SCR efficiency
and optionally balancing engine fuel consumption, NOx emission, and
urea consumption.
[0038] While the invention has been described with reference to
exemplary embodiments, it will be understood by those skilled in
the art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the invention. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiments disclosed, but that the invention will
include all embodiments falling within the scope of the
application.
* * * * *