U.S. patent application number 10/065650 was filed with the patent office on 2004-05-06 for diesel aftertreatment systems.
This patent application is currently assigned to Ford Global Technologies, Inc.. Invention is credited to Ketcher, David Arthur, Ruona, William Charles.
Application Number | 20040083721 10/065650 |
Document ID | / |
Family ID | 29731621 |
Filed Date | 2004-05-06 |
United States Patent
Application |
20040083721 |
Kind Code |
A1 |
Ketcher, David Arthur ; et
al. |
May 6, 2004 |
Diesel aftertreatment systems
Abstract
A method for improving NOx conversion efficiency of a
NOx-reducing catalyst by determining an accurate amount of
reductant required is presented. The method includes calculating an
initial reductant injection amount based on a steady state amount
of NOx in the engine feedgas and adjusting the initial amount to
compensate for transient NOx emissions. The compensation is
initiated in response to an engine transient, such as impending
acceleration or deceleration. This method further results in
improved vehicle fuel economy.
Inventors: |
Ketcher, David Arthur;
(Chelmsford, GB) ; Ruona, William Charles;
(Farmington Hills, MI) |
Correspondence
Address: |
FORD GLOBAL TECHNOLOGIES, LLC.
SUITE 600 - PARKLANE TOWERS EAST
ONE PARKLANE BLVD.
DEARBORN
MI
48126
US
|
Assignee: |
Ford Global Technologies,
Inc.
Dearborn
MI
|
Family ID: |
29731621 |
Appl. No.: |
10/065650 |
Filed: |
November 6, 2002 |
Current U.S.
Class: |
60/286 ; 60/285;
60/301 |
Current CPC
Class: |
F01N 2250/04 20130101;
F02D 2200/1012 20130101; F01N 2610/03 20130101; Y02T 10/24
20130101; Y02A 50/20 20180101; Y02A 50/2325 20180101; B01D 53/9495
20130101; F01N 2610/02 20130101; F01N 2250/12 20130101; F02D
41/0275 20130101; B01D 53/9431 20130101; F01N 13/009 20140601; F02B
3/06 20130101; F01N 2900/0404 20130101; Y02T 10/12 20130101; F02D
41/107 20130101; F01N 3/208 20130101 |
Class at
Publication: |
060/286 ;
060/285; 060/301 |
International
Class: |
F01N 003/00; F01N
003/10 |
Claims
1. A method for controlling a NOx-reducing catalyst coupled
downstream of an internal combustion engine, comprising:
calculating a desired amount of reductant based on a measure of
engine transient behavior; and injecting said calculated desired
amount of reductant into the lean exhaust gas aftertreatment
device.
2. The method as set forth in claim 1 wherein the engine is a
diesel engine.
3. The method as set forth in claim 1 wherein the NOx-reducing
catalyst is an ALNC.
4. The method as set forth in claim 3 wherein said reductant is
hydrocarbon.
5. The method as set forth in claim 1 wherein the NOx-reducing
catalyst is an SCR catalyst.
6. The method as set forth in claim 5 wherein said reductant is
urea.
7. The method as set forth in claim 1 wherein said measure of
engine transient behavior comprises a measure of engine
deceleration.
8. The method a set forth in claim 1 wherein said measure of engine
transient behavior is based on a rate of change of pedal
position.
9. The method as set forth in claim 1 wherein said measure of
engine transient behavior is based a rate of change of engine
speed.
10. The method as set forth in claim 1 wherein said measure of
engine transient behavior is based a rate of change of engine fuel
injection amount.
11. The method as set forth in claim 1 wherein said measure of
engine transient behavior is based a rate of change of engine
load.
12. The method as set forth in claim 1 wherein said measure of
engine transient behavior is filtered.
13. A method for controlling a NOx-reducing catalyst coupled
downstream of an internal combustion engine, comprising:
calculating an initial reductant amount; adjusting said initial
reductant amount to compensate for engine transient behavior; and
injecting said adjusted initial amount of reductant into the
exhaust gas aftertreatment device.
14. The method as set forth in claim 13 wherein the NOx-reducing
catalyst is an ALNC.
15. The method as set forth in claim 14 wherein said reductant is
hydrocarbon.
16. The method as set forth in claim 13 wherein the NOx-reducing
catalyst is an SCR catalyst.
17. The method as set forth in claim 16 wherein said reductant is
urea.
18. The method as set forth in claim 13 wherein the engine is a
diesel engine.
19. The method as set forth in claim 13 wherein said initial amount
of reductant is based on a steady state estimate of an amount of
NOx in an engine exhaust gas.
20. The method as set forth in claim 13 wherein said engine
transient behavior is measured by calculating a rate of change of
pedal position.
21. The method as set forth in claim 13 wherein said engine
transient behavior is measured by calculating a rate of change of
engine fuel injection amount.
22. The method as set forth in claim 13 wherein said engine
transient behavior is measured by calculating a rate of change of
engine speed.
23. The method as set forth in claim 13 wherein said engine
transient behavior is measured by calculating a rate of change of
engine load.
24. A system for reducing NOx emissions in an engine exhaust gas
mixture, comprising: a NOx-reducing catalyst coupled downstream of
the engine; and a controller injecting reductant into said
NOx-reducing catalyst wherein said amount of injected reductant is
based on a measure of engine transient behavior.
25. A method for improving efficiency of a NOx reducing catalyst
coupled downstream of an internal combustion engine, comprising:
providing an indication of an impending engine transient; and
adjusting an amount of reductant injection into the NOx-reducing
catalyst to compensate for variations in engine feedgas NOx caused
by said engine transient.
26. A system for reducing transient and steady-state NOx emissions
in the exhaust gases of a vehicle powered by a diesel fueled
internal combustion engine comprising: a) a NOx-reducing catalyst
downstream of said engine; b) a source of liquid hydrocarbons; c) a
valve for introducing predetermined quantities of said hydrocarbons
from said source into said exhaust gases upstream of said
NOx-reducing catalyst pursuant to a command signal; d) a plurality
of vehicle sensors generating sensor signals indicative of at least
one operating condition of said engine, said sensors including at
least one transient operation sensor generating a signal prior to a
transient operating condition of said engine and predictive of said
transient operating condition; e) an engine control unit having a
plurality of programmed routines for controlling said engine in
response to said plurality of sensor signals, said routines
including at least (1) a first routine for generating a first
command signal for introducing a first predetermined quantity of
said hydrocarbons through said valve when said engine is operating
at a steady state condition sufficient to reduce a portion of NOx
emissions produced at the steady state condition, and (2) a second
routine activated when said at least one transient operating sensor
generates said signal predictive of said transient operating
condition, said second routine comprising: i) calculating a second
quantity of hydrocarbons sufficient to reduce a portion of the NOx
emissions generated during a period in which said engine is
operating in said transient operating condition and ii) generating
a second command signal for introducing said second predetermined
quantity of said hydrocarbons through said valve during at least a
portion of the period in which said engine is operating in said
transient operating condition.
27. The system of claim 26 wherein said source of hydrocarbons
comprises a diesel fuel tank of said vehicle.
28. The system of claim 26 wherein said transient operation sensor
comprises an engine speed sensor.
29. The system of claim 26 wherein said transient operation sensor
comprises a pedal position sensor.
30. The system of claim 26 wherein said transient operation sensor
is indicative of a change in speed of said engine.
31. The system of claim 26 wherein said transient operation sensor
is indicative of deceleration of said engine.
32. The system of claim 26 wherein said transient operation sensor
is indicative of a change in load of said engine.
33. The system of claim 26 wherein said transient operating
condition is controlled by the operator of said vehicle.
34. A method for reducing NOx emissions present in the exhaust
gases of an internal combustion engine comprising the steps of: a)
providing a source of liquid hydrocarbons; b) providing a reducing
catalytic converter downstream of said engine through which said
exhaust gases pass; c) sensing a set of engine operating parameters
including at least a space velocity of the exhaust gases and a
temperature of the exhaust gases; d) calculating a first
concentration of hydrocarbon and NOx emissions present in said
exhaust gases based on said sensed engine operating parameters
during a steady state operation of said engine; e) determining an
amount of said hydrocarbons sufficient to reduce a desired
percentage of said NOx emissions when said exhaust gases leave said
reducing catalytic converter during said steady state operation of
said engine; f) metering a quantity of said hydrocarbons into said
exhaust gases upstream of said reducing catalytic converter
sufficient to reduce said desired percentage of said NOx emissions
during said steady state operation of said engine; g) sensing a
signal predictive of a transient operation state of said engine; h)
calculating the expected concentration of NOx emissions present in
said exhaust gases while the engine is in said transient operation
state based on said signal predictive of said transient operation
state; and i) metering an additional quantity of said hydrocarbons
into said exhaust gases upstream of said reducing catalytic
converter sufficient to reduce said expected concentration of NOx
emissions during said transient engine operation state.
35. The method of claim 34 in which said internal combustion engine
is a lean operating gasoline engine.
36. The method of claim 34 wherein said lean operating gasoline
engine operates at an air-to-fuel ratio of at least 1.03.
37. The method of claim 34 wherein said signal predictive of a
transient operating state of said engine indicates a change in
engine fuel demand.
38. The method of claim 34 wherein said signal predictive of a
transient operating state of said engine indicates a change in
engine fueling rate.
39. The method of claim 34 wherein said signal predictive of a
transient operating state of said engine indicates a change in a
pedal position.
40. The method of claim 34 wherein said signal predictive of a
transient operating state of said engine indicates a change in
engine speed.
41. The method of claim 34 wherein said signal predictive of a
transient operating state of said engine indicates a change in
engine load.
42. The method of claim 34 wherein said signal predictive of a
transient operating state of said engine indicates deceleration of
said engine.
43. The method of claim 34 wherein said transient operating state
of said engine is responsive to an operator inputted command.
44. The method of claim 34 wherein said sensed operating conditions
include the air-to-fuel ratio of the engine.
45. A method for reducing NO.sub.x emissions produced by a vehicle
powered by a diesel engine having an active lean NOx catalyst
through which the exhaust gases pass and sensors for determining
NO.sub.x concentrations at steady state engine operating
conditions, the improvement comprising the steps of: a)sensing a
pedal position sensor signal prior to an engine transient; and
b)injecting a set quantity of diesel fuel reductant into the
exhaust gases of the engine sufficient to substantially react with
transient emissions produced by the engine during said transient,
the injection occurring at a time in advance of and not later than
the time the engine produces the transient emissions.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a system and a method for
improving performance of a NOx-reducing catalyst and, more
particularly, to controlling an amount of reductant injection to
achieve optimum NOx conversion efficiency while minimizing the fuel
economy penalty.
[0003] 2. Background of the Invention
[0004] Current emission control regulations necessitate the use of
catalysts in the exhaust systems of automotive vehicles in order to
convert carbon monoxide (CO), hydrocarbons (HC), and nitrogen
oxides (NOx) produced during engine operation into harmless exhaust
gasses. Vehicles equipped with diesel or lean gasoline engines
offer the benefits of increased fuel economy. Such vehicles have to
be equipped with lean exhaust aftertreatment devices, such as, for
example, an Active Lean NOx Catalysts (ALNC) or Selective Catalytic
Reduction (SCR) catalysts, which continuously reduce NOx emissions,
even in an oxygen rich environment, through active injection of
reductant, such as fuel (HC) or urea, into the exhaust gas entering
these devices. Further, it is important to precisely control the
amounts of reductant in order to achieve maximum NOx conversion
efficiency.
[0005] The inventors herein have recognized that transient changes
in engine operating conditions cause changes in engine feedgas NOx
production. For example, NOx production usually increases during
engine acceleration, and decreases during deceleration. Since the
amount of reductant injection is typically calculated based on
steady state engine operating conditions, these transient NOx
variations result in over or under-injection of reductant and
negatively impact fuel economy and emission standards.
SUMMARY OF INVENTION
[0006] In accordance with the present invention, a system and a
method for controlling an amount of reductant to be delivered to a
NOx-reducing catalyst are presented. The method includes
calculating a desired amount of reductant based on a measure of
engine transient behavior; and injecting said calculated desired
amount of reductant into the NOx-reducing catalyst.
[0007] In one aspect of the present invention, the device is an
ALNC and the reductant is hydrocarbon. In another aspect of the
present invention, the device is an SCR catalyst and the reductant
is urea. In yet another aspect of the present invention, the
measure of engine transient behavior is a measure of engine
acceleration. In another aspect of the present invention, the
measure further includes engine deceleration. In another aspect of
the present invention, the measure of engine transient behavior is
based on a rate of change of pedal position. In yet another aspect
of the present invention, the measure of engine transient behavior
is based on a rate of change of engine fuel injection amount. In
yet another aspect of the present invention, the measure of engine
transient behavior is based on a rate of change of engine
speed.
[0008] In another aspect of the present invention, a method for
improving efficiency of a NOx-reducing catalyst coupled downstream
of an internal combustion engine includes: providing an indication
of an impending engine transient; and adjusting an amount of
reductant injection into the NOx-reducing catalyst to compensate
for variations in engine feedgas NOx caused by said impending
engine transient.
[0009] The present invention provides a number of advantages. In
particular, NOx conversion efficiency of the NOx-reducing catalyst
is improved by adjusting the injected reductant amounts to
compensate for transient increases or decreases in the engine
feedgas NOx amounts. Further, monitoring the rate of change of
pedal position provides a quick and accurate indication of an
impending engine transient and the associated change in engine
feedgas NOx. Thus, reductant injection amount can be timely
adjusted to compensate for NOx variations. Another advantage of the
present invention is improved fuel economy due to optimized
reductant usage. For example, reductant injection amount can be
reduced in anticipation of engine deceleration to compensate for a
reduction in engine feedgas NOx.
[0010] The above advantages and other advantages, objects and
features of the present invention will be readily apparent from the
following detailed description of the preferred embodiments when
taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0011] The objects and advantages described herein will be more
fully understood by reading an example of an embodiment in which
the invention is used to advantage, referred to herein as the
Description of Preferred Embodiment, with reference to the
drawings, wherein:
[0012] FIGS. 1A and 1B are schematic diagrams of an engine wherein
the invention is used to advantage;
[0013] FIG. 2 is an example of a reductant delivery system used to
advantage with the present invention;
[0014] FIGS. 3 and 4 describe an exemplary routine and a
modification curve for determining an amount of reductant to be
delivered to the exhaust gas aftertreatment device in accordance
with the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS(S)
[0015] Internal combustion engine 10, comprising a plurality of
cylinders, one cylinder of which is shown in FIG. 1A, is controlled
by electronic engine controller 12. Engine 10 includes combustion
chamber 30 and cylinder walls 32 with piston 36 positioned therein
and connected to crankshaft 40. Combustion chamber 30 is shown
communicating with intake manifold 44 and exhaust manifold 48 via
respective intake valve 52 and exhaust valve 54. Intake manifold 44
is also shown having fuel injector 80 coupled thereto for
delivering liquid fuel in proportion to the pulse width of signal
FPW from controller 12. Both fuel quantity, controlled by signal
FPW and injection timing are adjustable. Fuel is delivered to fuel
injector 80 by a fuel system including a fuel tank, fuel pump, and
fuel rail (not shown).
[0016] Controller 12 is shown in FIG. 1A as a conventional
microcomputer including:
[0017] microprocessor unit 102, input/output ports 104, read-only
memory 106, random access memory 108, and a conventional data bus.
Controller 12 is shown receiving various signals from sensors
coupled to engine 10, in addition to those signals previously
discussed, including: engine coolant temperature (ECT) from
temperature sensor 112 coupled to cooling sleeve 114; a measurement
of manifold pressure (MAP) from pressure sensor 116 coupled to
intake manifold 44; a measurement (AT) of manifold temperature from
temperature sensor 117; an engine speed signal (RPM) from engine
speed sensor 118 coupled to crankshaft 40.
[0018] Oxidation catalyst 13 is coupled to the exhaust manifold 48
downstream of engine 10 and may be a precious metal catalyst,
preferably one containing platinum. Catalyst 14, a NOx-reducing
catalyst capable of reducing NOx in an oxygen rich environment, is
coupled downstream of the oxidation catalyst. In a preferred
embodiment Catalyst 14 is an Active Lean NOx Catalyst (ALNC)
comprising a precious metal or a combination of precious metals,
such as Platinum or Palladium, an acidic support material, such as
the one containing alumina and silica, and a zeolite material. In
an alternative embodiment, catalyst 14 may be a urea-based
Selective Catalytic Reduction (SCR) catalyst, which is a device
comprising some or all of the features of the ALNC catalyst and
optimized for use with urea or other ammonia-based compounds as
reductant. The oxidation catalyst 13 exothermically combusts
hydrocarbons (HC) in the incoming exhaust gas from the engine thus
supplying heat to rapidly warm up catalyst 14. Additionally, carbon
monoxide (CO) produced as a result of HC combustion in the
oxidation catalyst 13 improves NOx reduction in the catalyst
14.
[0019] A reductant delivery system 16 is coupled to the exhaust gas
manifold between the oxidation catalyst and the NOx-reducing
catalyst and is described in more detail in FIG. 2 below.
Alternatively, reductant delivery system 16 may be any system known
to those skilled in the art capable of supplying reductant to the
NOx-reducing catalyst. In a preferred embodiment, reductant
delivery system injects fuel (hydrocarbon) into the exhaust gas
mixture entering catalyst 14. Alternatively, reductant delivery
system 16 may supply aqueous urea to the NOx-reducing catalyst.
[0020] Referring now to FIG. 1B, an alternative embodiment is shown
where engine 10 is a direct injection engine with injector 80
located to inject fuel directly into cylinder 30.
[0021] The diagram of FIG. 2 generally represents an example of one
embodiment of a reductant delivery system according to the present
invention. The system comprises an evaporator unit 21 housing an
elongated heating element 22. The mixing unit 23 has a reductant
inlet and an air inlet and an outlet 24 coupled to the evaporator
unit 21 through which a mixture of reductant and air is injected
into the housing and subsequently comes into contact with the
surface of the heating element 22. Alternatively, both air and
reductant can be injected through a single input. The reductant can
be supplied to the mixing unit 23 from the fuel tank or from a
storage vessel. Air pump 25 supplies pressurized air to the mixing
unit 23 thereby creating a mixture of reductant and air. Outlet 24
is configured to deliver the reductant and air mixture to more than
one area on the surface of the heating element. Controller 12 can
selectively enable and disable injection of the mixture to these
areas depending on operating conditions, such as engine speed,
load, exhaust gas temperature, etc. For example, when the amount of
reductant required is high, such as at high load conditions, it may
be necessary to enable delivery of the reductant and air mixture to
more than one area on the surface of the heating element.
Alternatively, outlet 24 may be configured to deliver the reductant
and air mixture to a specific area on the surface of the heating
element.
[0022] As will be appreciated by one of ordinary skill in the art,
the routines described in FIGS. 3 and 4 below may represent one or
more of any number of processing strategies such as event-driven,
interrupt-driven, multi-tasking, multi-threading, and the like. As
such, various steps or functions illustrated may be performed in
the sequence illustrated, in parallel, or in some cases omitted.
Likewise, the order of processing is not necessarily required to
achieve the objects, features and advantages of the invention, but
is provided for ease of illustration and description. Although not
explicitly illustrated, one of ordinary skill in the art will
recognize that one or more of the illustrated steps or functions
may be repeatedly performed depending on the particular strategy
being used.
[0023] Referring now to FIG. 3, an exemplary routine for
controlling injection of a reductant into exhaust flow is
presented. First, in step 500, the amount of NOx in the exhaust gas
mixture entering the device, NOx.sub.fg, is estimated based on
engine operating conditions. These conditions may include engine
speed, engine load, exhaust temperatures, exhaust gas
aftertreatment device temperatures, injection timing, engine
temperature, and any other parameter know to those skilled in the
art to indicate the amount of NOx produced by the combustion
presses. Alternatively, a NOx sensor may be used to measure the
amount of NOx in the exhaust gas mixture. Next, in step 600, the
steady-state reductant injection amount,
RA.sub.inj.sub..sub.--.sub.1, is calculated based on the following
equation: 1 ( RA fg + RA inj_ 1 ) NOx fg = R des
[0024] wherein
RA.sub.fg
[0025] is the amount of reductant in the engine feedgas, which can
be determined based on engine operating conditions. This initial
reductant amount,
RA.sub.inj.sub..sub.--.sub.1,
[0026] is evaluated at steady state and yields a base reductant
quantity to be injected for each engine speed and load point. The
amount is calibrated to achieve a certain feedgas reductant to NOx
ratio, R.sub.des. The ratio is typically obtained as a trade-off
between NOx conversion and the fuel penalty due to reductant
injection, and in this example is set at approximately 10. Next, in
step 700, the steady-state base reductant injection amount,
RA.sub.inj.sub..sub.--.sub.1,
[0027] is modified to account for engine operating conditions, such
as engine coolant temperature,
T.sub.e,
[0028] exhaust gas temperature,
T.sub.eg,
[0029] EGR valve position,
EGR.sub.pos,
[0030] start of injection,
SOI,
[0031] and other parameters:
RA.sub.inj.sub..sub.--.sub.2=RA.sub.inj.sub..sub.--.sub.1.multidot.f.sub.1-
(T.sub.c).multidot.f.sub.2(T.sub.eg).multidot.f.sub.3(SOI).multidot.f.sub.-
4(EGR.sub.pos)
[0032] The routine then proceeds to step 800 wherein the rate of
change of pedal position is computed as follows: 2 pps_diff ( t ) =
( pps ( t ) - pps ( t - 1 ) ) T s
[0033] where T.sub.S is the sampling rate, and
pps(t)
[0034] denotes the pedal position at time
t.
[0035] Next, in step 900, a low pass filter is applied to smooth
out the noise:
pps_diff.sub.--lp(t)=(1-k.sub.f).multidot.pps_diff.sub.--lp(t-1)+k.sub.f.m-
ultidot.pps_diff(t-1)
[0036] where
k.sub.f
[0037] controls the rate of filtering. The routine then proceeds to
step 1000 wherein the reductant amount is further modified to
account for engine transient behaviors as represented by the
changes in the pedal position:
RA.sub.inj 3=RA.sub.inj 2.multidot.f.sub.5(pps_diff.sub.--lp)
[0038] where function
f.sub.5
[0039] is shaped to allow overinjection of reductant during pedal
position tip-in and underinjection of reductant during pedal
position tip-out. An example of
f.sub.5
[0040] is shown with particular reference to FIG. 6. In an
alternative embodiment, rate of change of engine speed, rate of
change of engine fuel injection amount, rate of change of engine
load, rate of change of engine fuel demand or any other parameter
known to those skilled in the art to provide a measure of engine
transient behavior may be used to obtain
RA.sub.inj.sub..sub.--.sub.3.
[0041] The routine then exits.
[0042] In an alternative embodiment (not shown), the modified
steady-state reductant injection amount,
RA.sub.inj 2.
[0043] calculated in step 700, is further modified to account for
engine transient behavior only if the rate of change of pedal
position is greater than a predetermined calibratable value.
[0044] Therefore, according to the present invention, in order to
achieve a more efficient NOx-reducing catalyst performance, the
amount of reductant to be injected should be adjusted to account
for increases and decreases in the amount of NOx in the exhaust gas
entering the catalyst. This can be accomplished by continuously
monitoring engine parameters that are capable of providing a
measure of engine transient behaviors, and continuously adjusting
the amount of reductant to be injected as a function of these
parameters. Since NOx production typically increases at tip-in and
decreases at tip-out, the result of such operation would be to
increase thee base injected amount in the former case, and decrease
the base injected amount in the latter case. By monitoring
parameters that are capable of providing very quick indication of
engine transients, such as, for example, rate of change of pedal
position, rate of change of engine fuel injection amount, or rate
of change of engine speed or load, it is possible optimize system
response and ensure that optimal reductant amount is timely
injected into the device in response to a change in engine feedgas
NOx.
[0045] This concludes the description of the invention. The reading
of it by those skilled in the art would bring to mind many
alterations and modifications without departing from the spirit and
the scope of the invention. Accordingly, it is intended that the
scope of the invention be defined by the following claims:
* * * * *