U.S. patent application number 10/301361 was filed with the patent office on 2004-05-27 for diesel aftertreatment systems.
Invention is credited to Goebelbecker, Michael, Ruona, William Charles, Upadhyay, Devesh, van Nieuwstadt, Michiel J..
Application Number | 20040098976 10/301361 |
Document ID | / |
Family ID | 32312170 |
Filed Date | 2004-05-27 |
United States Patent
Application |
20040098976 |
Kind Code |
A1 |
van Nieuwstadt, Michiel J. ;
et al. |
May 27, 2004 |
Diesel aftertreatment systems
Abstract
A method for controlling a temperature of a heated element of a
reductant delivery system for a lean exhaust gas aftertreatment
device coupled downstream of an internal combustion engine is
presented. The method teaches achieving a desired temperature of a
heating element by selecting a control signal to the heating
element from a predetermined temperature map based on engine
operating conditions, such as exhaust gas temperature, engine
speed, load, etc. Therefore, durability of the heating element and
its power consumption are improved by, for example, controlling its
temperature to prevent overheating, and having the ability to turn
the heating element off when the exhaust gas temperatures are
sufficiently high.
Inventors: |
van Nieuwstadt, Michiel J.;
(Ann Arbor, MI) ; Upadhyay, Devesh; (Dearborn,
MI) ; Goebelbecker, Michael; (Dearborn Heights,
MI) ; Ruona, William Charles; (Farmington Hills,
MI) |
Correspondence
Address: |
FORD GLOBAL TECHNOLOGIES, LLC.
SUITE 600 - PARKLANE TOWERS EAST
ONE PARKLANE BLVD.
DEARBORN
MI
48126
US
|
Family ID: |
32312170 |
Appl. No.: |
10/301361 |
Filed: |
November 21, 2002 |
Current U.S.
Class: |
60/286 ;
60/295 |
Current CPC
Class: |
F01N 2610/107 20130101;
F01N 2610/02 20130101; F01N 2610/03 20130101; F01N 3/0231 20130101;
Y02T 10/12 20130101; F01N 3/2066 20130101; F01N 2610/08 20130101;
F01N 2250/02 20130101; F01N 3/035 20130101; F01N 3/106 20130101;
F01N 2240/16 20130101; F01N 2390/02 20130101; Y02T 10/24 20130101;
F01N 13/009 20140601; F01N 2610/10 20130101; F01N 3/36
20130101 |
Class at
Publication: |
060/286 ;
060/295 |
International
Class: |
F01N 003/00 |
Claims
1. A reductant delivery system, comprising: an evaporator unit
including at least a heating device; a mixing device having at
least one inlet and at least one outlet coupled to said evaporator
unit; and a controller for introducing reductant and air into said
mixing device through said inlet, injecting a mixture of said
reductant and said air through said outlet into said evaporator
unit, said controller adjusting a temperature of said heating
device to evaporate said mixture.
2. The system as set forth in claim 1 wherein said reductant is
urea.
3. The system as set forth in claim 1 wherein said reductant is
hydrocarbon.
4. The system as set forth in claim 1 wherein said reductant
delivery system further comprises a container for housing said
injected reductant and air mixture, wherein said reductant and air
mixture evaporates inside said container without coming in direct
contact with a surface of said heating element.
5. The system as set forth in claim 1 wherein said heating device
is an electrically heated elongated heater plug.
6. The system as set forth in claim 5 wherein said heater plug is
cylindrically shaped.
7. The system as set forth in claim 5 wherein said heater plug is
rectangular in shape.
8. The system as set forth in claim 2 wherein said evaporator unit
further comprises a hydrolyzing catalyst.
9. The system as set forth in claim 3 wherein said evaporator unit
further comprises an oxidation catalyst.
10. The system as set forth in claim 1 wherein said controller
supplies a pulse-width modulated signal of a predetermined duty
cycle to adjust said heating device temperature.
11. The system as set forth in claim 10 wherein said controller
turns off power to said heating device when said heating device
temperature is above a predetermined temperature.
12. A method for controlling a temperature of a heating element of
a reductant delivery system for an exhaust gas aftertreatment
device, the device coupled downstream of an internal combustion
engine, the method comprising: estimating operating conditions; and
adjusting the temperature of the heating element based on said
operating conditions.
13. The method as set forth in claim 12 wherein said operating
conditions are engine operating conditions.
14. The method as set forth in claim 12 wherein said engine
operating conditions comprise at least engine speed.
15. The method as set forth in claim 12 wherein said operating
conditions comprise at least an exhaust gas mixture
temperature.
16. The method as set forth in claim 12 wherein said operating
conditions comprise at least engine load.
17. The method as set forth in claim 12 wherein said engine is a
diesel engine.
18. The method as set forth in claim 17 wherein the exhaust gas
aftertreatment device is an ALNC.
19. The method as set forth in claim 17 wherein the exhaust gas
aftertreatment device is an SCR catalyst.
20. A method for operating a reductant delivery system for an
exhaust gas aftertreatment device, the system including at least a
heating element, the method comprising: operating in a first mode
where a reductant and air mixture is injected into the reductant
delivery system and the heating element is turned on; and operating
in a second mode where said reductant and air mixture is injected
into the reductant delivery system, and the heating element is
turned off.
21. The method as set forth in claim 20 wherein said reductant is
urea.
22. The method as set forth in claim 21 wherein the exhaust gas
aftertreatment device is an SCR catalyst.
23. The method as set forth in claim 20 wherein said reductant is
hydrocarbon.
24. The method as set forth in claim 23 wherein the exhaust gas
aftertreatment device is an ALNC.
25. The method as set forth in claim 20 wherein the heating element
is turned off when a temperature of the exhaust gas aftertreatment
device is above a predetermined threshold.
26. A method for controlling a reductant delivery system for an
exhaust gas aftertreatment device coupled downstream of an internal
combustion engine exhaust, comprising: injecting a mixture of
reductant and air into the reductant delivery system; adjusting a
temperature of a heating element housed inside the reductant
delivery system thereby causing said mixture to evaporate; and
introducing said evaporated mixture into the exhaust gas
aftertreatment device.
27. The method as set forth in claim 26 wherein the engine is a
diesel engine.
28. The method as set forth in claim 27 wherein the exhaust gas
aftertreatment device is an ALNC.
29. The method as set forth in claim 28 wherein said mixture of
reductant and air is a mixture of hydrocarbon and air.
30. The method as set forth in claim 27 wherein the exhaust gas
aftertreatment device is an SCR catalyst.
31. The method as set forth in claim 30 wherein said mixture of
reductant and air is a mixture of urea and air.
32. A method for operating a reductant delivery system for an
exhaust gas aftertreatment device coupled downstream of an internal
combustion engine, the system including at least a heating element,
the method comprising: operating the system in a first mode by
injecting a reductant and air mixture into the system and adjusting
a temperature of said heating element to evaporate said reductant
and air mixture; and operating the system in a second mode by
injecting said reductant and air mixture into the system, and
adjusting said temperature of said heating element to combust said
reductant and air mixture.
Description
FIELD OF INVENTION
[0001] The present invention relates to a system and a method for
improving performance of an exhaust gas aftertreatment device and,
more particularly, to using an air assist heated reductant delivery
system to enhance system performance and reduce fuel penalty.
BACKGROUND OF THE INVENTION
[0002] 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, Active Lean NOx Catalysts (ALNC), which are capable of
continuously reducing NOx emissions, even in an oxygen rich
environment. In order to maximize NOx reduction in the ALNC, a
hydrocarbon-based reductant, such as fuel (HC), has to be added to
the exhaust gas entering the device. However, introducing fuel as a
reductant reduces overall vehicle fuel economy. Therefore, in order
to achieve high levels of NOx conversion in the ALNC while
concurrently minimizing the fuel penalty, it is important to
optimize usage of injected reductant.
[0003] In this regard, it is known that improved NOx conversion can
be achieved by introducing the reductant in vapor rather than
liquid form. Introducing the reductant in vapor form allows better
distribution and mixing of the reductant with the exhaust gas
entering the NOx reduction device.
[0004] One such system is described in U.S. Pat. No. 5,771,689,
wherein a reductant is introduced into the exhaust system via an
evaporator device that has a hollow body with a heating element
protruding into its interior. The evaporator device protrudes into
the wall of the exhaust pipe upstream of the catalyst. The
reductant is introduced so that it flows through the narrow space
between the hollow body and the heating element until it reaches
the tip of the heating element from where it enters the exhaust
pipe in vapor form and mixes with the exhaust gas entering the
catalyst.
[0005] The inventors herein have recognized several disadvantages
with this approach. Namely, if delivery of the reductant has been
shut off, or reduced, as dictated by the operating conditions, some
reductant may remain in the annular space, in contact with the
heating element, and may therefore clog up the annular opening
around the heating device by carbonation of the residual fuel. Such
carbon build up may lead to a blockage of the passage at the tip by
which the vaporized fuel enters the exhaust stream. Further, there
is a delay in introducing the reductant into the exhaust gas stream
due to the time it takes for the reductant to travel down the
length of the heating element. Additionally, durability of the
heating element is reduced because its temperature is not
controlled and adjusted based on operating conditions, and due to
soot contamination. Yet another disadvantage of the prior art
approach is that extra power is consumed due to the above-mentioned
lack of temperature control.
SUMMARY OF THE INVENTION
[0006] The present invention teaches a system and a method for
introducing evaporated reductant into an exhaust gas stream
entering a lean exhaust gas aftertreatment device while eliminating
the above-mentioned disadvantages of the prior art approaches.
[0007] In accordance with the present invention, a reductant
delivery system includes: an evaporator unit including at least a
heating element; a mixing device having at least one inlet and at
least one outlet, said outlet coupled to said evaporator unit; and
a controller for introducing reductant and air into said mixing
device through said inlet, injecting a mixture of said reductant
and said air through said outlet into said evaporator unit, said
controller adjusting a temperature of said heating device to
evaporate said mixture.
[0008] In another aspect of the present invention, a method for
operating a reductant delivery system for an exhaust gas
aftertreatment device, the system including at least a heating
element, includes: operating in a first mode where a reductant and
air mixture is injected into the reductant delivery system and the
heating element is turned on; and operating in a second mode where
said reductant and air mixture is injected into the reductant
delivery system, and the heating element is turned off.
[0009] The present invention provides a number of advantages. In
particular, creating a mixture of reductant and air improves the
exhaust gas aftertreatment device efficiency, due to the enhanced
mixing of the reductant with the bulk exhaust flow and improved
catalytic action relative to the use of liquid phase reductant.
Additionally, mixing reductant with air breaks up the reductant in
small particles, thus resulting in faster evaporation process.
Additionally, injecting air into the vaporizer unit prevents
lacquering and soot deposits on the surface of the heating element.
Further, the inventors have recognized that dynamically controlling
the temperature of the heating element to take advantage of the
heat supplied by the exhaust gasses prevents overheating, improves
the heating element durability and reduces power consumption.
[0010] Yet another advantage of the present invention is that the
heating element temperature can be controlled to ignite the
injected reductant and air mixture, and thus produce carbon
monoxide (CO), which further improves NOx reduction in the
ALNC.
[0011] It is a further advantage of this invention that CO
generation is increased (and thus NOx conversion efficiency
increased) by placing an oxidizing catalyst in the path of the
reductant and air mixture prior to its mixing with the exhaust
gasses.
[0012] 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 THE DRAWINGS
[0013] 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:
[0014] FIGS. 1A and 1B are schematic diagrams of an engine wherein
the invention is used to advantage;
[0015] FIG. 2 is a an example of one embodiment of an emission
control system wherein the present invention is used to
advantage;
[0016] FIGS. 3A, 3B and 3C are examples of reductant delivery
systems in accordance with the present invention;
[0017] FIG. 4 is a high level flowchart of an exemplary routine for
controlling a temperature of the heating element of the reductant
delivery system in accordance with the present invention;
[0018] FIGS. 5 and 6 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 EMBODIMENT(S)
[0019] Internal combustion engine 10, comprising a plurality of
cylinders, one cylinder of which is shown in FIG. 1, 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 (not shown) including a fuel tank,
fuel pump, and fuel rail (not shown).
[0020] Controller 12 is shown in FIG. 1 as a conventional
microcomputer including: 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.
[0021] An emission control system 20, coupled to an exhaust
manifold 48, is described in detail in FIG. 2 below.
[0022] 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.
[0023] Referring now to FIG. 2, an example of an emission control
system in accordance with the present invention is described.
Emission control system 20 is coupled downstream of an internal
combustion engine 10 described with particular reference in FIG. 1.
Catalyst 14 is an Active Lean NOx Catalyst (ALNC) capable of
reducing NOx in an oxygen rich environment. Oxidation catalyst 13
is coupled upstream of the ALNC and may be a precious metal
catalyst, preferably one containing platinum. The oxidation
catalyst exothermically combusts hydrocarbons (HC) in the incoming
exhaust gas from the engine thus supplying heat to rapidly warm up
the Active Lean NOx Catalyst (ALNC) 14. Additionally, carbon
monoxide (CO) produced as a result of HC combustion in the
oxidation catalyst 13 improves NOx reduction in the ALNC.
Particulate filter 15 is coupled downstream of the ALNC and is
capable of storing carbon particles from the exhaust.
[0024] A reductant delivery system 16 is coupled to the exhaust gas
manifold between the oxidation catalyst and the ALNC. Alternative
embodiments of the reductant delivery system are described later
herein with particular reference to FIGS. 3A-3C.
[0025] The diagram of FIG. 3A 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. In this example, the
heating element is an electrically heated cylindrically shaped
heating element. Alternatively, the heating element could be
rectangular shaped to increase its surface contact area with the
injected reductant and air mixture.
[0026] In yet another alternative embodiment, an oxidizing
catalytic coating may be added to the evaporator unit such as, for
example, a coating on the inner surface of the heating element
housing and a catalytic cap at the point where the evaporated
reductant and air mixture enters the exhaust gas manifold, to
facilitate CO generation. The catalytic coating may be a precious
metal coating, preferably one containing Platinum or Palladium.
Controller 12 controls the temperature of the heating element by
providing a PWM signal of varying duty cycles. The duty cycle of
the PWM control signal to the heating element is determined from a
prestored table based on operating conditions to achieve desired
heating element temperature. 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.
[0027] In an alternative embodiment (not shown), 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. The outlet
24 is configured so that it delivers the reductant and air mixture
to a specific area on the surface of the heating element.
Alternatively, outlet 24 could be configured to deliver the
reductant and air mixture to more than one area on the surface of
the heating element. The 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.
[0028] FIG. 3B shows an alternate design for the heating element
housing. As can be seen in the drawing, the heating element is
surrounded by a delivery tube the inner diameter of which is wide
enough to allow the heating element to be housed. The delivery tube
has a narrow channel drilled into it, which serves as a passage for
the air and reductant mixture. The air and reductant mixture is
injected into the narrow channel and is rapidly vaporized by the
heat provided by the enclosed heating element without coming into
direct contact with its surface. In this embodiment, the durability
of the heating element is further improved since the reductant and
air mixture never comes into direct contact its surface. The
delivery tube has one or more holes at its tip through which the
evaporated reductant and air mixture enters the exhaust gas
manifold.
[0029] FIG. 3C shows an alternative embodiment of the heating
element housing shown in FIG. 3B wherein a porous oxidizing
catalytic plug, preferably one containing Platinum or Palladium, is
placed at the tip of the delivery tube to facilitate conversion of
the vaporized hydrocarbons to carbon monoxide. Additionally, one or
more ports may be drilled into the delivery tube along its length
and plugged up with porous oxidizing catalytic material to further
facilitate conversion of hydrocarbons into carbon monoxide.
[0030] Therefore, according to the present invention, an improved
reductant delivery system and method are presented. Mixing
reductant with air causes the reductant to be well distributed
inside the reductant delivery system and thus speeds up the
vaporization process. Also, system durability is improved by
reducing lacquering and soot deposits through better distribution
of the reductant and faster evaporation process. The system
performance is further improved through the addition of an
oxidizing catalytic coating.
[0031] As will be appreciated by one of ordinary skill in the art,
the routines described in FIGS. 4 and 5 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.
[0032] Referring now to FIG. 4, an exemplary routine for
controlling the temperature of the heating element of the reductant
delivery system in accordance with the present invention is
described. First, in step 100, desired heating element temperature,
T.sub.des, is determined. This determination is based on what
function the reductant evaporator system is performing such as
whether the mixture is to be evaporated or combusted. Next, the
routine proceeds to step 200 wherein operating conditions known to
have an effect on the heating element temperature, such as the
exhaust gas temperature upstream of the ALNC, are evaluated. The
exhaust gas temperature can be determined from a temperature sensor
coupled in the exhaust gas manifold, or estimated based on
parameters such as engine speed, load, engine temperature, ignition
timing, etc. Next, in step 300, optimal duty cycle to achieve
desired heating element temperature is determined from a prestored
experimentally determined temperature map of the heating element
based on operating conditions such as the exhaust gas temperature
in this example. The routine then proceeds to step 400 wherein the
duty cycle of the heating element control signal is adjusted to
achieve desired heating element temperature. The routine then
exits.
[0033] Therefore, by generating a map of the heating element
temperature based on operating conditions, such as the exhaust gas
temperature, or any parameter known to affect the temperature of
the heated element, it is possible to dynamically control the
temperature of the heated element to achieve optimal reductant and
air mixture delivery while minimizing power consumption and
preventing overheating of the heating element. In other words, it
is possible to take advantage of the heat provided by the exhaust
gas passing through the reductant delivery system when controlling
the temperature of the heating element. For example, higher exhaust
gas temperature result in less power requirements, while lower
exhaust gas temperatures result in higher power requirements. It is
also possible to completely turn off power supply when the exhaust
gas temperature is high enough to keep the heating element at
desired temperature such as at high engine load conditions.
[0034] Referring now to FIG. 5, an exemplary routine for
controlling injection of a reductant into exhaust flow using a
reductant vaporizer system as described in FIG. 3A 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
[0035] wherein RA.sub.fg is the amount of reductant in the exhaust
gas mixture entering the device, which can be determined based on
engine operating conditions. This initial reductant amount,
RA.sub.inj.sub..sub.--.sub.1, 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, is
modified to account for engine operating conditions, such as engine
coolant temperature, T.sub.c, exhaust gas temperature, T.sub.eg,
EGR valve position, EGR.sub.pos, start of injection, SOI, 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)
[0036] The routine then proceeds to step 800 wherein the
instantaneous change in the pedal position is computed as follows:
2 pps_diff ( t ) = ( pps ( t ) - pps ( t - 1 ) ) T s
[0037] where T.sub.B is the sampling rate, and pps(t) denotes the
pedal position at time t. Next, in step 900, a low pass filter is
applied to smooth out the noise:
pps.sub.--diff.sub.--lp(t)=(1-k.sub.f).multidot.pps.sub.--diff.sub.--lp(t--
1)+k.sub.f.multidot.pps.sub.--diff(t-1)
[0038] where k.sub.f 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.sub..sub.--.sub.3=RA.sub.inj.sub..sub.--.sub.2.multidot.f.sub.5-
(pps.sub.--diff.sub.--p)
[0039] where function f.sub.5 is shaped to allow overinjection of
reductant during pedal position tip-in and underinjection of
reductant during pedal position tip-out. In an alternative
embodiment, instead of pedal position, engine speed or fuel demand
sensor, 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.--.su- b.3 Next, in step 1100, the
desired temperature of the heating element is obtained as described
with particular reference to FIG. 4, thus achieving optimum
temperature for reductant and air mixture evaporation. The routine
then proceeds to step 1200 wherein the areas on the surface of the
heating element to which a reductant and air mixture is injected
are selected basedlon operating conditions. These areas are
selected from a prestored map based on such parameters as the
amount of reductant to be delivered, engine load, speed, exhaust
gas temperature, catalyst temperature, throttle position, etc. For
example, at high engine loads it may be desirable to inject the
reductant and air mixture faster than at low engine loads, and
delivery to more than one area will therefore be enabled. The
routine then exits. An example of f.sub.5 is shown with particular
reference to FIG. 6.
[0040] Therefore, according to the present invention, in order to
achieve more efficient exhaust aftertreatment device 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 device. This can be accomplished by
continuously monitoring engine parameters that are capable of
providing a measure of engine transient behaviors, such as a pedal
position sensor, and continuously adjusting the amount of reductant
to be injected as a function of filtered instantaneous changes in
these parameters. Since NOx production typically increases at
tip-in and decreases at tip-out, the result of such operation would
be to increase the base injected amount in the former case, and
decrease the base injected amount in the latter case. Further,
using a reductant vaporizer unit ensures fast system response, more
efficient system operation, better emission control, and improved
fuel economy.
[0041] 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 is defined by the following claims:
* * * * *