TECHNICAL FIELD
The subject matter disclosed herein relates to emissions control in
internal combustion engine and more particularly to the control of CO and NOx
emissions in an internal combustion engine.
BACKGROUND
^ P Internal combustion engines are ideally operated in a way that the
combustion mixture contains air and fuel in the exact relative proportions required for
a stoichiometric combustion reaction. A rich burn engine may operate with a
stoichiometric amount of fuel or a slight excess fuel, while a lean-burn engine
operates with excess oxygen (O2) compared to the amount required for stoichiometric
combustion. The operation of an internal combustion engine in lean mode may reduce
throttling losses and can take advantage of higher compression ratios thereby
providing improvements in performance and efficiency. Rich burn engines, on the
other hand are relatively simple, reliable and stable, and adapt well to changing loads.
In order to comply with emissions standards, many rich burn internal
combustion engines utilize non-selective catalytic reduction (NSCR) subsystems also
known as 3-way catalyst. These subsystems reduce emissions of nitrogen oxides NO
j ^ and NO2 (collectively NOx), carbon monoxide (CO) and volatile organic compounds
(VOC), along with other regulated emissions. 3-way catalysts have high reduction
efficiencies and are economical but require tight control of the air fuel ratio of the
engine in order to meet emissions standards. These standards are sometimes stated in
terms of grams of emissions per brake horsepower hour (g/bhp-hr).
Previously, rich burn emissions control with a catalyst was only
possible using O2 sensing at both the input and output locations of the catalyst
subsystem. In those systems a control subsystem adjusted the air fuel ratio
continuously to maintain a constant O2 content in the exhaust. The target value for the
constant O2 content (the O2 voltage setpoint) was static. Occasionally, these control
2
systems allowed greater variation of emissions than is optimal over varying operating
and environmental conditions as well as shifts in the catalyst operating window. The
reason is that to reach low NOx and CO emissions levels one cannot simply set the 02
voltage setpoint to a single value. The optimal 02 voltage setpoint for emissions
compliance varies depending on load, speed, ambient conditions, among other
conditions.
BRIEF DESCRIPTION OF THE INVENTION
According to one aspect of the invention, a method of operating an
internal combustion engine over a range of operating conditions, the internal
^ P combustion engine having at least one O2 sensor is provided. The method of this
aspect includes operating the engine at an initial 02 voltage setpoint and
automatically adjusting the 02 voltage setpoint to a new 02 voltage setpoint to reduce
emissions.
According to another aspect of the present invention a system for
improving emission performance of an internal combustion engine over a range of
operating conditions is provided. The system of this aspect includes a catalyst
subsystem for treating exhaust from the internal combustion engine; an 02 sensor
disposed upstream from the catalyst subsystem; and a NOx sensor disposed in the
exhaust. The system of this aspect also includes a control subsystem that receives
data from the 02 sensor and the NOx sensor, and automatically adjusts an 02 voltage
setpoint to a new voltage setpoint to reduce emissions.
£ k According to another aspect of the present invention, a control
system for controlling emissions in an internal combustion engine exhaust is
provided. The control system of this aspect includes at least one subsystem that
controls an 02 voltage setpoint; at least one subsystem that measures NOx emissions
in the engine exhaust; and at least one subsystem that initiates a lambda sweep to
determine an optimal 02 voltage setpoint.
According to another aspect of the present invention, a method for
controlling emissions in an internal combustion engine exhaust is provided. The
method of this aspect includes measuring NOx emissions; initiating a lambda sweep
to determine an 02 voltage setpoint at which NOx emissions at the new operating
3
condition comply with NOx emissions standards; and operating the internal
combustion engine at the new 02 voltage setpoint.
According to another aspect of the present invention, computerreadable
media is provided. The computer readable media of this aspect provides
instructions that, when executed by a control module that controls emissions in an
internal combustion engine exhaust, cause the control module to measure NOx
emissions; initiate a lambda sweep to determine an 02 voltage setpoint at which NOx
emissions at the new operating condition comply with NOx emissions standards; and
operate the internal combustion engine at the new 02 voltage setpoint.
£ BRIEF DESCRIPTION OF THE DRAWINGS
The following description of the Figures is not intended to be, and
should not be interpreted to be, limiting in any way.
Figure 1 is a diagram of an example of an internal combustion engine
system in accordance with an embodiment.
Figure 2 is a chart illustrating the impact of operating conditions on a
NOx compliance window.
Figure 3 is a flowchart showing a process of an embodiment.
Figure 4 is a chart illustrating the principle of operation of an
embodiment.
Figure 5 is a flowchart showing a process of an embodiment.
Figure 6 is a chart illustrating the principle of operation of an
J ^ embodiment.
DETAILED DESCRIPTION OF THE INVENTION
Illustrated in Figure 1 is an internal combustion engine system 1 with
improved emissions control capabilities according to one embodiment of the present
invention. The internal combustion engine system 1 includes a left cylinder bank 3
and a right cylinder bank 5. The left cylinder bank 3 includes a plurality of cylinders
7, 9, 11, 13, 15, and 17. The right cylinder bank 5 includes a plurality of cylinders, 19,
21, 23, 25, 27 and 29. Although the internal combustion engine system 1 in this
embodiment is illustrated with 12 cylinders, any number of cylinders, (1, 2, 4, 8, 14,
4
16 etc.) may be used. The internal combustion engine system 1 also includes a fly
wheel 31.
The internal combustion engine system 1 also includes a right
regulator 33 associated with the right cylinder bank 5, and a left regulator 35
associated with the left cylinder bank 3. The right regulator 33 controls the flow of
air and fuel to the right cylinder bank 5, and the left regulator 35 controls the flow of
air and fuel to the left cylinder bank 3. A regulator is a device that determines and
maintains the operating parameters of a system, usually within certain prescribed or
preset limits. The right regulator 33 and left regulator 35 adjust the air fuel ratio in
^ ^ the right cylinder bank 5 and the left cylinder bank 3 respectively. Although the
^ ^ embodiment illustrated in Figure 1 refers to a regulator, any device or combination of
devices that can be used to control the air fuel ratio may be included, such as for
example electronic fuel injection devices, carburetors, and the like.
Associated with the right cylinder bank 5 and the left cylinder bank 3
is a manifold 37 that conveys the exhaust gases from internal combustion engine
system 1. The manifold 37 includes a left manifold tube 38 into which is placed at
least one left O2 sensor 39, and a right manifold tube 40 into which is placed at least
one right O2 sensor 41. The left O2 sensor 39 and right O2 sensor 41 (also known as
lambda sensors) are electronic devices that measure the proportion of O2 in the
exhaust inside the manifolds 38,40 and determine, in real time, if the air fuel ratio of
a combustion engine is rich or lean. Information from the left O2 sensor 39 and the
right O2 sensor 41 may be used to indirectly determine the air fuel ratio. In some
^fc embodiments only one O2 sensor may be used. Among the types of O2 sensors
available are concentration cell (zirconia sensors), oxide semiconductor (TiC>2
sensors) and electrochemical O2 sensors (limiting current sensors). The sensors do not
typically measure O2 concentration directly, but rather the difference between the
amount of O2 in the exhaust gas and the amount of O2 in a reference sample. Rich
mixtures cause an O2 demand. This demand results in a build-up of voltage due to
transportation of O2 ions through a sensor layer. Lean mixture result in low voltage,
since there is an O2 excess.
Exhaust gases from the internal combustion engine system 1 are
conveyed through the right manifold tube 40 and the left manifold tube 38 into a
5
catalytic chamber 43 that contains a catalyst for the reduction of NOx and CO
emissions. In a preferred embodiment the catalyst may be a 3-way catalyst commonly
used for internal combustion engine applications. The catalyst converts CO, NOx and
VOC emissions through reduction and oxidation to produce carbon dioxide, nitrogen,
and water. Three-way catalysts are effective when the engine is operated within a
narrow band of air-fuel ratios near stoichiometry. The conversion efficiency of the
catalyst declines significantly when the engine is operated outside of that band of airfuel
ratios. Under lean engine operation, there is excess O2 and the reduction of NOx
is not favored. Under rich conditions, excess fuel consumes all of the available O2 in
^ ^ the exhaust prior to the catalyst, thereby making oxidation reactions less likely.
^ ^ A NOx sensor 45 is disposed downstream from the catalytic chamber
43. In alternative embodiments, the NOx sensor may be located upstream of the
catalytic chamber 43 (if a catalyst is used), or multiple NOx sensors may be used.
NOx sensors are devices that detect nitrogen oxides in combustion environments such
as internal combustion engine system 1. A variety of different sensors are available
for adaptation to use in an internal combustion engine system 1. For example, there
are a variety of solid-state electrochemical sensors including solid electrolyte
(potentiometric and amperometric) and semiconducting types.
The NOx sensor 45, right O2 sensor 41 and left O2 sensor 39, right
regulator 33 and left regulator 35 are all coupled to an emission control module 47.
The emission control module 47 may be provided as a microprocessor and a memory,
or as software otherwise provided or embedded within other processors or electronic
i B systems associated with the internal combustion engine system 1 or in any other
known forms. Emissions control module 47 in various embodiments may include
instructions executable by one or more computing devices. Such instructions may be
compiled or interpreted from computer programs created using a variety of known
programming languages and/or technologies, including, without limitation, and either
alone or in combination, Java™, C, C++, Visual Basic, Java Script, Perl, etc. In
general, a processor (e.g., a microprocessor) receives instructions, e.g., from a
memory, a computer-readable medium, etc., and executes these instructions, thereby
performing one or more processes, including one or more of the processes described
6
herein. Such instructions and other data may be stored and transmitted using a variety
of known computer readable media.
A computer-readable medium includes any medium that participates
in providing data (e.g., instructions), which may be read by a computer. Such a
medium may take many forms, including, but not limited to, non-volatile media,
volatile media, and transmission media. Non-volatile media include, for example,
optical or magnetic disks and other persistent memory. Volatile media include
dynamic random access memory (DRAM), which typically constitutes a main
memory. Transmission media include coaxial cables, copper wire and fiber optics,
^ ^ including the wires that comprise a system bus coupled to the processor. Transmission
media may include or convey acoustic waves, light waves and electromagnetic
emissions, such as those generated during radio frequency (RF) and infrared (IR) data
communications. Common forms of computer-readable media include, for example, a
floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a
CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other
physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASHEEPROM,
any other memory chip or cartridge, a carrier wave as described
hereinafter, or any other medium from which a computer can read.
The internal combustion engine system 1 with improved emissions
control capabilities may be operated over a range of operating conditions by
automatically adjusting a setpoint of one or more O2 sensors, such as left O2 sensor
30, right O2 sensor 41, or both. An 0 2 voltage setpoint is the target value for O2 that
^ F the emission control module 47 will aim to reach by controlling the amount of fuel
that enters the engine relative to the amount of air. The amount of fuel that enters the
engine relative to air is called the air fuel ratio (AFR), and sometimes expressed as
Lambda (X) which is the engine's AFR relative to a stoichiometric AFR. The internal
combustion engine system 1 accomplishes an improved emissions performance by
adjusting the pre-catalyst O2 voltage setpoints from a calibrated high setpoint at a
calibrated sweep rate downwards to a low O2 voltage setpoint until NOx
measurements become unstable or spike (i.e. stability level threshold is breached). In
one embodiment, stability may be determined by measuring NOx concentration over a
given period of time." The sweep rate may be in milli-volts per second and may be
7
specifically calibrated for each engine. Once the stability threshold is breached the O2
voltage setpoint is adjusted upward at a calibrated sweep rate until the stability level is
achieved (NOx readings NOX sensor 45 become stable again).
The principles behind the process for automatically adjusting the
setpoints is best understood with reference to Figure 2. Figure 2 illustrates a typical
catalyst window characteristic in respect to NOx and CO emissions in a rich burn
engine. In the chart, emissions measured in g/bhp-hr.volts are plotted against X. In
Stoichiometric mixtures X =1, in rich mixtures X < 1, and in lean mixtures X > 1.
On the right-hand side of the chart in Figure 2, values for NOx
' ^ ^ emissions for a specific set of conditions CI are illustrated by a continuous double
^ ^ line with superimposed triangles. On the left-hand side of the chart values for CO
emissions for condition CI are illustrated as a solid line with superimposed
rectangles. A compliance window is represented by a shaded rectangular area.
Highlighted with a circle denoted as A is the area where CO emissions begin to rise
rapidly as lambda is decreased. This is referred to as the rich knee of the lambda
curve. Highlighted with a circle denoted as B is the area where NOx emissions begin
to rise rapidly as the lambda values increase. This is referred to as the lean knee of the
lambda curve. The preferred operation window usually resides between the rich knee
and the lean knee of the lambda curve.
When, for example, engine load, fuel quality, or engine ambient
conditions change, conditions CI may shift as shown in C2, C3, or shift in other
ways. When conditions change from conditions CI to conditions C2 the area between
^ B the NOx curve (shown as dashed double lines on the right hand side of the chart) and
the CO curve (shown as solid double lines on the left hand side of the chart) narrows.
When conditions change from conditions CI to conditions C3 the area between the
NOx curve and the CO curve widens. Additionally, with changing conditions the
NOx and CO curves may be shifted left or right. This phenomenon makes it very
difficult to control emissions with a static O2 voltage setpoint.
Figure 3 illustrates an embodiment of a method for setting a new O2
voltage setpoint for NOx compliance 50. The internal combustion engine system 1 is
in operation with a starting O2 voltage setpoint (method element 51). A change of
condition is detected (method element 53), such as, for example, a change in the load,
8
a change in the operating speed, a change in ambient conditions, elapsing of a
specified time increment, and the like. At that point the emission control module 47
instructs a decrease of the O2 voltage setpoint by a predetermined increment. The
incremental decrease of the O2 voltage setpoint may be determined from a calibrated
sweep rate determined for each internal combustion engine system 1. The calibrated
sweep rate may be determined for the engine based on the period of time required for
the 02 sensor(s) (left O2 sensor 39, right 0 2 sensor 41, or both) and the NOx sensor 45
to be stabilized. NOx emissions and O2 concentrations may then be measured
(method elements 57 and 59). A determination of whether the NOx stability threshold
^ ^ has been breached is then made (method element 61) based on the values from
^ ^ method element 57. If the NOx stability threshold has not been breached then the O2
voltage setpoint may be decreased again by a predetermined amount (method element
55). Once the NOx stability threshold is breached, the O2 voltage setpoint may be
increased by a predetermined increment (method element 63). A determination of the
change in NOx emissions may then be made (method element 65) and the O2
concentration may be measured (method element 67). A determination may then be
made as to whether the NOx levels have become stable (i.e. the rate of change of NOx
levels as close to 0), (method element 69). If the NOx levels are not stable the 02
voltage setpoint may be increased again by a predetermined amount (method element
63), until the NOx levels are stable. To perform the stability portion of the algorithm
it may be necessary to run a scheme that uses filtering and debounce timers to indicate
when the NOx knee or the CO knee are being approached. The new O2 voltage
^ B setpoint at which the NOx levels are stable may then be saved (method element 71).
The O2 voltage setpoint may be skewed a calibrated value either upward or downward
to maintain a setpoint just rich of the NOx knee in the lambda curve (method element
73). The calibrated value may be determined for each engine. At that point the
process may end (method element 75) and may be restarted upon the detection of a
change in condition or after a predetermined period of time has elapsed. Method
elements 55-69 comprise a lean lambda sweep 77.
The principle behind the method for setting a new O2 voltage setpoint
for NOx compliance 50. is best illustrated with reference to Figure 4. Figure 4 is a
chart that plots measurements of NOx concentrations (double line) for varying O2
9
voltage setpoints (solid line) over time. The O2 voltage setpoint is decreased at a
predetermined rate from a starting O2 voltage setpoint in the downward sweep of the
method. As the O2 voltage setpoint is decreased, a stability threshold is breached
when the NOx concentration spikes upward. At that point the O2 voltage setpoint is
increased at a pre-determined rate in the upward sweep until the NOx levels decrease
and become stable. The new O2 voltage setpoint is set at the level where the NOx
emissions are stable.
The internal combustion engine system 1 may be used for operating
an engine at an optimum O2 voltage setpoint for NOx and CO compliance. NOx
sensor 45 may be used to provide an indication of CO concentration that is
^ ^ represented as an increase in the NOx ppm output as the rich knee of the lambda
curve is approached. The CO concentration in on the rich side appear to create stable
interference in the NOx sensor 45resulting in a NOx reading. This anomaly is caused
by ammonia creation at extreme rich levels which is reported as NOx concentration
by the NOx sensor 45.
Using both a lean and rich stability detection algorithm with this
anomaly, it is possible to develop a method for setting a new O2 voltage setpoint for
NOx and CO compliance. This is accomplished by performing a lambda sweep (i.e.
sweeping the 02 voltage setpoint))to verify both locations of the lean and rich knees
on the lambda curve. The O2 voltage setpoint may then be readjusted to a value at a
point between the lean and rich knees to achieve lower NOx and CO catalyst out
emissions in the optimal part of the emissions curve.
^k. Figure 5 illustrates an embodiment of a method for setting a new O2
voltage setpoint for NOx and CO compliance 80 that may be carried out by the
emission control module 47. In this method it is assumed that the internal combustion
engine system 1 is operating at a starting O2 voltage setpoint (method element 81).
Upon the detection of a condition change (method element 83), the emission control
module 47 may initiate a lean a lambda sweep (method element 85) (e.g. sweeping the
operation of the engine to a lean 02 voltage setpoint in the direction of the lean knee
of Figure 2, resulting in a lean engine lambda). The lean lambda sweep is more
specifically described as reference 77 in Figure 3. The lean O2 voltage setpoint is
saved in method element 87, and a rich lambda sweep is initiated (e.g. sweeping the
10
operation of the engine to a rich 02 voltage setpoint in the direction of the rich knee
of Figure 2, resulting in a rich engine lambda) with the increase of the 02 voltage
setpoint by a predetermined increment (method element 89). The NOx emissions and
O2 concentrations are measured in method element 91 and 93 respectively. A
determination of whether the NOx stability threshold on the rich side of the lambda
curve has been breached is then made (method element 95). As described before the
stability threshold is breached when the NOx levels spike. If the NOx stability level
has not been breached then the O2 voltage setpoint is increased again by a
predetermined increment (method element 89). If the NOx stability level has been
^ ^ breached then a downward sweep of the O2 voltage setpoint is initiated by decreasing
^~ the O2 voltage setpoint a predetermined increment (method element 97). NOx
emissions and O2 concentrations are measured in method element 99 and 101
respectively. The emissions control module 47 then determines whether the NOx
levels have become stable (method element 103). If the NOx levels are not stable, the
emissions control module 47 again instructs a decrease of the O2 voltage setpoint by a
predetermined increment (method element 97). If the NOx levels are stable the rich
O2 voltage setpoint is saved (method element 105), and the 02 voltage setpoint is set
at a level between the saved lean and rich O2 voltage setpoints (method element 107).
The iteration of the method is then completed (method element 109. The method
elements 89 through 105 may be designated as the rich lambda sweep 111. The 02
voltage setpoint increments and decrements described herein may be changed by a
predetermined amount or by a predetermined sweep rate or until the NOx sensor reads
flfc a predetermined threshold concentration, or some other method.
The principle of a method for setting a new O2 voltage setpoint for
NOx and CO compliance 80 is best illustrated with reference to Figure 6. Figure 6 is a
chart that plots measurements of NOx concentrations (the bottom curve) and the O2
voltage setpoint is (top solid curve). Also illustrated in the chart in Figure 6 are the
engine RPM and the signals to the right regulator 33 and the left regulator 35, denoted
as stepper RB and stepper LB. A new search is initiated by decreasing the O2
voltage setpoint until the stability threshold is breached (spike in NOx for lean
search), and then increasing the O2 voltage setpoint until the NOx readings become
stable again. The O2 voltage setpoint is increased until the stability threshold is
11
breached, and then decreased until the NOx levels become stable again. At that point
the emission control module has an 02 voltage setpoint value determined by the lean
search and an 02 voltage setpoint value determined by the rich search. These values
correspond the rich knee and the lean knee of the lambda curve. The desired O2
voltage setpoint for the operation of the internal combustion engine system 1 would
typically fall between the two 02 voltage setpoints, and optionally may be set at the
midpoint between these O2 voltage setpoints to achieve the lowest NOx and CO
catalyst out emissions in the optimal part of the emissions curve.
If at any time the lambda sweep routine is not able to detect the
^. knee(s) on the curve(s), a new sweep may be performed to retry the setpoint
^ ^ optimization. Reasons for not detecting optimal setpoints could include; changes in
fuel composition, large changes in humidity, other environmental conditions, or
degrading of catalyst performance. Optionally emission control module 47 may be
programmed to periodically re-establish the optimum setpoint to the left of the knee.
This is done as these optimum points will shift due to changes in operating and/or
j environmental conditions.
The internal combustion engine system 1 provides NOx and CO
compliance over a wider range of operating conditions, including environmental and
catalyst window shift conditions by providing periodic automatic resetting of the O2
setpoints. Additionally, because of the continuous measurements taken over time,
emission control module 47 may log emissions performance and emissions
compliance status. Another option that may be added to the emission control module
^fc 47 would include the addition of shut down instructions if the internal combustion
engine system 1 is not in compliance with emission regulations.
While the methods and apparatus described above and/or claimed
herein are described above with reference to an exemplary embodiment, it will be
understood by those skilled in the art that various changes may be made and
equivalence may be substituted for elements thereof without departing from the scope
of the methods and apparatus described above and/or claimed herein. In addition,
many modifications may be made to the teachings of above to adapt to a particular
situation without departing from the scope thereof. Therefore, it is intended that the
methods and apparatus described above and/or claimed herein not be limited to the
12
embodiment disclosed for carrying out this invention, but that the invention includes
all embodiments falling with the scope of the intended claims. Moreover, the use of
the term's first, second, etc. does not denote any order of importance, but rather the
term's first, second, etc. are used to distinguish one element from another.
Furthermore, it should be emphasized that a variety of computer platforms and control
modules and operating systems are contemplated.
13
APPARATUS AND METHOD FOR CONTROLLING EMISSIONS IN
AN INTERNAL COMBUSTION ENGINE
Ref Component Figures
No.
1 Internal combustion engine system
2
3 Left cylinder Bank
4
5 Right cylinder bank
6
7 Left Cylinder
8
^ 9 Left Cylinder
• 10
11 Left Cylinder
12
13 Left Cylinder
14
15 Left Cylinder
16
17 Left Cylinder
18
19 Right Cylinder
20
21 Right Cylinder
22
23 Right Cylinder
24
25 Right Cylinder
^ 26
W 27 Right Cylinder
28
29 Right Cylinder
30
31 Flywheel
32
33 Right regulator
34
35 Left regulator
36
37 Manifold
38 Left manifold tube
39 left Q2 sensor
40 1 Right manifold tube 1 I
41 Right Q2 sensor
42
43 Catalytic chamber
44
45 NOx Sensor
46
47 Emission control module
48
49
50 A method for setting an 0 2 setpoint
for NOx compliance
51 Starting Q2 setpoint
52
53 detect condition change
m 54
55 decreased 0 2 setpoint predetermined
increment
56
57 Determine change in NOx emissions
58
59 measure Q2 concentration
60
61 NOx stability threshold breached?
62
63 Increase 0 2 setpoint a predetermined
increment
64
65 measure NOx emissions
66
67 measure Q2 concentration
68
£ 69 NOx level stable?
70
71 Save new Q2 setpoint
72
73 skew new Q2 setpoint
74
75 end
76
77 Lean lambda sweep
78
79
80 Method for Setting an 0 2 setpoint for
NOx and CO compliance
81 I Starting Q2 set point | I
1ST
1 82 1 I I
83 Detect conditions change
84
85 Conduct lean lambda sweep
86
87 Save lean Q2 setpoint
88
89 Increase 02 setpoint predetermined
increment
90
91 Measure NOx emissions
92
93 Measure Q2 concentration
94
9 95 NOx stability threshold breached?
96
97 Decrease 02 setpoint predetermined
increment
98
99 Measure NOx emission
100
| 101 Measure Q2 concentration
102
103 NOx levels stable?
104
105 Save rich Q2 setpoint
106
107 Set 02 setpoint between lean and rich
Q2 setpoints
108
109 End
0 110
111 Rich Lambda Sweep
112
113
114
115
116
117
118
119
120
121
122
123 I I I
»4>
124 I I 1
125
126
127
128
129
130
131
132
133
134
135
136
137
0 138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
% 155
156
157
158
159
160
161
162
163
164
165
166
167
168 I I I
\1
1 6 9 I I 1
170
171
172
173
174
175
176
177
178
179
180
181
182
f 183
184
185 I 1 I
IS

WE CLAIM :
1. A method of operating an internal combustion engine over a range of
operating conditions, the internal combustion engine having at least one O2 sensor, the
method comprising:
operating the engine at an initial O2 voltage setpoint;
automatically adjusting the O2 voltage setpoint to a new O2 voltage setpoint to
reduce emissions.
1 9 2. The method of claim 1 wherein the method element of automatically
adjusting the O2 voltage setpoint to reduce emissions comprises incrementally
decreasing the 02 voltage setpoint from a high setpoint to a low setpoint until
measurements of NOx become unstable and incrementally increasing the O2 voltage
setpoint imtil measurements of NOx become stable.
3. The method of claim 2 wherein the method element of incrementally
decreasing the O2 voltage setpoint comprises decreasing the O2 voltage setpoint at a
predetermined sweep rate.
4. The method of claim 2 wherein the method element of incrementally
increasing the O2 voltage setpoint comprises increasing the O2 voltage setpoint at one
^ of a predetermined sweep rate and a predetermined O2 voltage setpoint amount.
5. The method of claim 1 further comprising adjusting the O2 voltage
setpoint in response to one of a change in operating conditions and a timer.
6. The method of claim 5 wherein the change in operating conditions
comprises a change in operating conditions chosen from the group including a new
load on the engine, a new engine speed, new ambient conditions; degradation of the
catalyst and an operating time interval.
7. The method of claim 1 further comprising:
19
sensing an O2 content of the exhaust;
sensing a NOx content of the exhaust; and
wherein the method element of automatically adjusting the O2 voltage setpoint
comprises:
incrementally decreasing the O2 voltage setpoint until the NOx content
becomes unstable; and
incrementally increasing the O2 voltage setpoint until the NOx content
^ 1 becomes stable.
8. A system for improving emission performance of an internal
combustion engine over a range of operating conditions, comprising:
a catalyst subsystem for treating exhaust from the internal combustion engine;
an O2 sensor disposed upstream fi^om the catalyst subsystem;
a NOx sensor disposed in the exhaust; and
a control subsystem that receives data from the O2 sensor and the NOx sensor,
and automatically adjusts an O2 voltage setpoint to a new setpoint to
reduce emissions.
^ F 9. The system of claim 8 wherein the control subsystem further comprises
a control subsystem that incrementally adjusts the O2 voltage setpoint from a high
setpoint to a low setpoint until a NOx stability level is breached; and incrementally
increases the O2 voltage setpoint until NOx measurements become stable.
10. The system of claim 8 wherein the control subsystem that
incrementally adjust the O2 voltage setpoint comprises a control subsystem that
adjusts the O2 voltage setpoint at one of a predetermined sweep rate and a
predetermined 02 setpoint amount.
11. The system of claim 8 wherein control subsystem automatically adjusts
the 02 voltage setpoint in response to a change in the operating conditions the
change in operating conditions comprising at least one of anew load on the engine; a
new engine speed; new ambient conditions; a new fiiel quality and an operating time
interval.
12. A control system for controlling emissions in an internal combustion
engine exhaust comprising:
at least one subsystem that controls an O2 voltage setpoint;
^ ^ at least one subsystem that measures NOx emissions in the engine exhaust;
and
at least one subsystem that initiates a lambda sweep to determine an optimal
O2 voltage setpoint.
13. The control system of claim 12 wherein the subsystem that initiates the
lambda sweep comprises:
a subsystem that decreases the O2 voltage setpoint until a NOx stability
threshold is breached; and
a subsystem that increases the O2 voltage setpoint until NOx emissions in the
^ ^ engine exhaust become stable.
14. The control system of claim 12 further comprising at least one
subsystem that sets the O2 voltage setpoint to the optimal setpoint.
15. The control system of claim 12 wherein the subsystem that initiates a
lambda sweep comprises at least one subsystem that initiates a lean lambda sweep;
and at least one subsystem that initiates a rich lambda sweep.
16. The control subsystem of claim 15 wherein the subsystem that initiates
a lean lambda sweep comprises:
a;
at least one subsystem that incrementally decreases the O2 voltage setpoint
until the NOx emissions become unstable; and
at least one subsystem that incrementally increases the O2 voltage setpoint
until the NOx emissions become stable.
17. The control subsystem of claim 15 wherein the subsystem that initiates
a rich lambda sweep comprises:
at least one subsystem that incrementally increases the O2 voltage setpoint
^ ^ until the NOx emissions become unstable; and
at least one subsystem that incrementally decreases the O2 voltage setpoint
until the NOx emissions become stable.
18. The control subsystem of claim 12 wherein the subsystem that initiates
a lambda sweep comprises:
at least one subsystem that initiates a lean lambda sweep to determine a lean
O2 voltage setpoint
at least one subsystem that initiates a rich lambda sweep to determine a rich O2
voltage setpoint; and
at least one subsystem that determines an O2 voltage setpoint between the lean
^ r O2 voltage setpoint and the rich O2 voltage setpoint.
19. A method for controlling emissions in an internal combustion engine
exhaust comprising"
measuring NOx emissions;
initiating a lambda sweep to determine an O2 voltage setpoint at which NOx
emissions at the new operating condition comply with NOx emissions
standards; and
operating the internal combustion engine at the new O2 voltage setpoint.
20. The method of Claim 19 further comprising initiating a lambda sweep
to determine an O2 voltage setpoint at which CO emissions at the new operating
condition comply with CO emissions standards
21. The method of claim 19 wherein the method element of initiating a
lambda sweep comprises
incrementally decreasing the O2 voltage setpoint imtil the NOx emissions
^ ^ become unstable; and
incrementally increasing the O2 voltage setpoint until the NOx emissions
become stable.
22. The method of claim 20 wherein the method element of initiating a
lambda sweep comprises incrementally increasing the O2 voltage setpoint until the
NOx emissions become unstable ; and a incrementally decreasing the O2 voltage
setpoint until the NOx emissions become stable
23. One or more computer-readable media having computer-readable
instructions thereon which, when executed by a control module that controls
emissions in an internal combustion engine exhaust, cause the control module to:
^ ^ measure NOx emissions;
initiate a lambda sweep to determine an O2 voltage setpoint at which NOx
emissions at the new operating condition comply with NOx emissions
standards; and
operate the internal combustion engine at the new O2 voltage setpoint.
24. The one or more computer readable media of claim 23, which further
cause the control module to initiate a lambda sweep to determine an O2 voltage
setpoint at which CO emissions at the new operating condition comply with CO
emissions standards
25. The one or more computer readable media of claim 24 wherein the
instructions that cause the control module to initiate a lambda sweep comprises
instructions that cause the control module to
incrementally decrease the O2 voltage setpoint until the NOx emissions
become unstable; and
incrementally increase the O2 voltage setpoint until the NOx emissions
^ P become stable.
26. The one or more computer readable media of claim 24 wherein the
instructions that cause the control module to initiate a lambda sweep comprises
instructions that cause the control module to
incrementally increase the O2 voltage setpoint until the NOx emissions
become unstable; and
incrementally decrease the O2 voltage setpoint until the NOx emissions
become stable.