U.S. patent application number 10/836656 was filed with the patent office on 2005-11-03 for method and apparatus for an optimized fuel control based on outlet oxygen signal to reduce vehicle missions.
Invention is credited to Anilovich, Igor, Avallone, Louis A., Draper, Daniel M., Emmorey, Michael S., Wallace, Brian M., Wang, Wenbo.
Application Number | 20050241297 10/836656 |
Document ID | / |
Family ID | 35185648 |
Filed Date | 2005-11-03 |
United States Patent
Application |
20050241297 |
Kind Code |
A1 |
Wang, Wenbo ; et
al. |
November 3, 2005 |
Method and apparatus for an optimized fuel control based on outlet
oxygen signal to reduce vehicle missions
Abstract
A control system and method for optimizing fuel control in an
internal combustion engine utilizes a signal from an oxygen sensor
disposed in an exhaust downstream of a catalytic converter. An
air/fuel mixture introduced into the engine is compensated based on
the signal exceeding predetermined enabling thresholds. The
predetermined rich or lean condition enable threshold represents an
oxygen content so less or greater than desired that the normal
closed loop control including regular secondary fuel trim is not
sufficient enough to bring the outlet oxygen sensor signal back to
the desired window quickly. A reduced or increased amount of fuel
is introduced into the engine based on the signal exceeding the
predetermined rich or lean enable threshold respectively.
Inventors: |
Wang, Wenbo; (Novi, MI)
; Anilovich, Igor; (Walled Lake, MI) ; Avallone,
Louis A.; (Linden, MI) ; Draper, Daniel M.;
(Fenton, MI) ; Emmorey, Michael S.; (Brighton,
MI) ; Wallace, Brian M.; (Grand Blanc, MI) |
Correspondence
Address: |
CHRISTOPHER DEVRIES
General Motors Corporation
Legal Staff, Mail Code 482-C23-B21
P.O. Box 300
Detroit
MI
48265-3000
US
|
Family ID: |
35185648 |
Appl. No.: |
10/836656 |
Filed: |
April 30, 2004 |
Current U.S.
Class: |
60/276 ; 60/274;
60/285 |
Current CPC
Class: |
F02D 41/149 20130101;
F02D 41/1487 20130101 |
Class at
Publication: |
060/276 ;
060/285; 060/274 |
International
Class: |
F01N 003/00 |
Claims
What is claimed is:
1. A control system for optimizing fuel control in an internal
combustion engine, comprising: an exhaust connected to said engine
and having a catalytic converter disposed therein; an oxygen sensor
disposed in said exhaust downstream of said catalytic converter
that generates an oxygen signal; and a controller that communicates
with said oxygen sensor and that modifies an air/fuel mixture
introduced into said engine based on said oxygen signal from said
oxygen sensor.
2. The control system of claim 1 wherein said controller compares
said signal to a predetermined lean condition enable threshold that
represents an oxygen content that is greater than desired, and
wherein said controller introduces an increased amount of fuel into
said engine based on said signal dropping below said predetermined
lean condition enable threshold.
3. The control system of claim 1 wherein said controller compares
said signal to a predetermined rich condition enable threshold that
represents an oxygen content that is less than desired, and wherein
said controller introduces a reduced amount of fuel into said
engine based on said signal exceeding said predetermined rich
condition enable threshold.
4. The control system of claim 2 wherein said controller compares
said signal to a predetermined lean condition disable threshold
that represents an oxygen content that is greater than a desired
level, but appropriate to return to normal closed loop fueling, and
wherein said controller returns fuel delivery to a normal operation
based on said signal satisfying said lean condition disable
threshold.
5. The control system of claim 3 wherein said controller compares
said signal to a predetermined rich condition disable threshold
that represents an oxygen content that is less than a desired
level, but appropriate to return to normal closed loop fueling, and
wherein said controller returns fuel delivery to a normal operation
based on said signal satisfying said rich condition disable
threshold.
6. The control system of claim 2 wherein said controller initiates
an accumulated engine airflow variable and concludes introducing
increased amounts of fuel to said engine based on said accumulated
engine airflow reaching a predetermined condition.
7. The control system of claim 3 wherein said controller initiates
an accumulated engine airflow variable and concludes introducing
reduced amounts of fuel to said engine based on said accumulated
engine airflow reaching a predetermined condition.
8. A method for optimizing fuel control in an internal combustion
engine, comprising: utilizing a signal from an oxygen sensor
disposed in an exhaust downstream of a catalytic converter;
determining whether said signal exceeds predetermined thresholds;
compensating an air/fuel mixture introduced into the engine based
on said signal exceeding said predetermined thresholds.
9. The method of claim 8 wherein determining if said signal exceeds
predetermined thresholds comprises: comparing said signal to a
predetermined lean condition enable threshold that represents an
oxygen content that is greater than desired; and introducing an
increased amount of fuel into said engine based on said signal
dropping below said predetermined lean condition enable
threshold.
10. The method of claim 8 wherein determining if said signal
exceeds predetermined thresholds comprises: comparing said signal
to a predetermined rich condition enable threshold that represents
an oxygen content less than desired; and introducing a reduced
amount of fuel into said engine based on said signal exceeding said
predetermined rich condition enable threshold.
11. The method of claim 9, further comprising: comparing said
signal to a predetermined lean condition disable threshold that
represents an oxygen content greater than a desired level, but
appropriate for the return to normal closed loop fueling; and
returning fuel delivery to a normal operation based on said signal
satisfying said lean condition disable threshold.
12. The method of claim 10, further comprising: comparing said
signal to a predetermined rich condition disable threshold that
represents an oxygen content less than a desired level, but
appropriate for the return to normal closed loop fueling; and
returning fuel delivery to a normal operation based on said signal
satisfying said rich condition disable threshold.
13. The method of claim 9, wherein introducing an increased amount
of fuel comprises introducing an increased amount of fuel into said
engine for a predetermined maximum accumulated airflow.
14. The method of claim 10, wherein introducing a reduced amount of
fuel further comprises introducing a reduced amount of fuel into
said engine for a predetermined maximum accumulated airflow.
15. A method for optimizing fuel control in an internal combustion
engine comprising: determining whether said engine is operating in
closed loop control; utilizing a signal from an oxygen sensor
disposed in an exhaust system downstream of a catalytic converter;
determining if said signal exceeds predetermined thresholds; and
introducing a modified amount of fuel into said engine based on
said signal exceeding said predetermined thresholds.
16. The method of claim 15 wherein determining if said engine is
meeting closed loop control conditions further comprises:
determining whether diagnostic trouble codes are inactive; and
determining whether said oxygen sensor has reached operating
temperature and been ready for use; and determining whether other
open loop fueling or intrusive diagnostic modes are inactive.
17. The method of claim 15 wherein determining if said signal
exceeds predetermined thresholds comprises: comparing said signal
to a predetermined lean condition enable threshold that represents
an oxygen content greater than desired; and introducing an
increased amount of fuel into said engine based on said signal
below said predetermined lean condition enable threshold.
18. The method of claim 15 wherein determining if said signal
exceeds predetermined thresholds comprises: comparing said signal
to a predetermined rich condition enable threshold that represents
an oxygen content less than desired; and introducing a reduced
amount of fuel into said engine based on said signal above said
predetermined rich condition enable threshold.
19. The method of claim 17, further comprising: comparing said
signal to a predetermined lean condition disable threshold that
represents an oxygen content greater than a desired level, but
appropriate for the return to normal closed loop fueling; and
returning fuel delivery to a normal operation based on said signal
satisfying said lean condition disable threshold.
20. The method of claim 18, further comprising: comparing said
signal to a predetermined rich condition disable threshold that
represents an oxygen content less than a desired level, but
appropriate for the return to normal closed loop fueling; and
returning fuel delivery to a normal operation based on said signal
satisfying said rich condition disable threshold.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to fuel control systems for
gasoline vehicles, and more particularly to engine fuel control
systems including an oxygen sensor that is located downstream from
a three-way catalytic converter.
BACKGROUND OF THE INVENTION
[0002] Three-way catalytic converters reduce exhaust gas emissions
in vehicles using an internal combustion engine. The catalytic
converter includes a substrate with a coating of catalyst materials
that stimulate the oxidation of hydrocarbon and carbon monoxide
molecules, and the reduction of nitrogen oxides, in the vehicle
exhaust gas. The catalysts operate optimally when the temperature
of the catalysts is above a minimum level and when the air/fuel
ratio is stoichiometric. Stoichiometry is defined as an ideal
air/fuel ratio, which is 14.7 to 1 for gasoline.
[0003] Fuel delivery is managed by an engine control system using
either open loop or closed loop feedback control. Open loop control
is typically initiated during specific operating conditions such as
start up, cold engine operation, heavy load conditions, wide open
throttle, and intrusive diagnostic events, etc.
[0004] An engine control system typically employs closed loop
control to maintain the air/fuel mixture at or close to the ideal
stoichiometric air/fuel ratio. Closed loop fuel control commands a
desired fuel delivery based on the oxygen content in the exhaust.
The oxygen level in the exhaust is determined by oxygen sensors
that are located both upstream and downstream from the catalytic
converter. A three-way catalytic converter and the upstream and
downstream oxygen sensors are used in gasoline vehicles for
emission reduction. The upstream (inlet oxygen sensor) and
downstream oxygen sensor (outlet oxygen sensor) are also used for
catalytic converter efficiency monitoring.
[0005] Primary closed loop fuel control using an oxygen sensor
upstream from a catalytic converter has been widely used, driven by
fuel economy and emission reduction. The fundamental idea is to try
to maintain catalytic converter inlet oxygen sensor signals
toggling around a reference voltage to provide engine combustion at
or close to stoichiometric air/fuel ratios.
[0006] Secondary fuel trim using an oxygen sensor after a catalytic
converter is also widely used and is mainly driven by trying to
meet increasingly stringent emission regulations. The outlet oxygen
sensor signal correlates to air/fuel ratios or rich/lean conditions
in the catalyst-out gas flow. A three-way catalytic converter has
the capacity to store or release oxygen, and thus can maintain good
catalyst efficiency despite small or short duration fueling errors
from the ideal stoichiometric air/fuel ratio. However, large or
long duration fueling errors from stoichiometric, will make
emissions break through the catalytic converter, which can be
observed by the outlet oxygen sensor signals going to very low or
very high voltages. Secondary fuel trim works to maintain the
catalytic converter outlet oxygen sensor signal within a window
identified as providing optimal catalytic converter efficiency.
[0007] Given the primary closed loop fuel control and secondary
fuel trim as designed, there still exists several normal maneuvers
as well as intrusive diagnostic tests that could saturate the
converter and lead to increased emissions break through. The
intrusive diagnostic tests for performance monitoring of the
catalytic converters, outlet oxygen sensors and secondary air
injection are a few examples of diagnostic tests that can leave the
converter in a lower efficiency state. The invention is to minimize
these negative impacts and reduce catalyst-out emissions by quickly
taking fuel control actions that force outlet oxygen signals back
toward the normal or desired zone to get optimum catalyst
efficiency. The methodology is to add four new thresholds in
addition to the existing target window for the outlet oxygen sensor
signal to further optimize engine fuel control strategy.
SUMMARY OF THE INVENTION
[0008] A control system and method for optimizing fuel control in
an internal combustion engine utilizes a signal from an oxygen
sensor disposed in an exhaust downstream of a catalytic converter.
Control determines whether the signal exceeds predetermined
thresholds. An air/fuel mixture introduced into the engine is
compensated based on the signal exceeding the predetermined
thresholds.
[0009] To enable rich fuel compensation for a lean downstream
condition, control compares the downstream oxygen sensor signal to
a predetermined lean condition enable threshold that represents an
oxygen content so greater than desired that the normal closed loop
control including regular secondary fuel trim is not sufficient
enough to bring the outlet oxygen sensor signal back to the desired
window quickly. An increased amount of fuel is introduced into the
engine based on the signal exceeding (dropping lower than) the
predetermined lean condition enable threshold. Similarly, to enable
lean fuel compensation for a rich downstream condition, control
compares the signal to a predetermined rich condition enable
threshold that represents an oxygen content so less than desired
that the normal closed loop control including regular secondary
fuel trim is not sufficient enough to bring the outlet oxygen
sensor signal back to the desired window quickly. A reduced amount
of fuel is introduced into the engine based on the signal exceeding
the predetermined rich condition enable threshold.
[0010] Once rich fuel compensation for a lean downstream condition
has been enabled, control compares the signal to a predetermined
lean condition disable threshold that represents an oxygen content
greater than a desired level, but appropriate for providing normal
closed loop fueling once again. Fuel delivery is returned to normal
closed loop operation based on the signal satisfying or rising
above the lean condition disable threshold. Similarly, once lean
fuel compensation for a rich downstream condition has been enabled,
control compares the signal to a predetermined rich condition
disable threshold that represents an oxygen content less than a
desired level, but appropriate for providing normal closed loop
fueling once again. Fuel delivery is returned to normal closed loop
operation based on the signal satisfying or dropping lower than the
rich condition disable threshold.
[0011] According to other features, this control is only used while
meeting closed loop conditions with normally functioning oxygen
sensors and while not in an intrusive diagnostic test or any other
open loop fuel.
[0012] Further areas of applicability of the present invention will
become apparent from the detailed description provided hereinafter.
It should be understood that the detailed description and specific
examples, while indicating the preferred embodiment of the
invention, are intended for purposes of illustration only and are
not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The present invention will become more fully understood from
the detailed description and the accompanying drawings,
wherein:
[0014] FIG. 1 is a functional block diagram of an engine control
system according to the present invention for a vehicle;
[0015] FIG. 2 illustrates outlet oxygen sensor thresholds according
to the present invention;
[0016] FIG. 3 is a flow diagram illustrating steps for optimizing
fuel control; and
[0017] FIG. 4 is a flow diagram illustrating steps for implementing
the fuel correction of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] The following description of the preferred embodiment is
merely exemplary in nature and is in no way intended to limit the
invention, its application, or uses.
[0019] Referring to FIG. 1, an exemplary engine control system 8 is
shown. A throttle 10 and a fuel system 12 control the air/fuel
mixture that is delivered to an engine 14 through an intake 16. An
ignition system 18 ignites the fuel and air mixture in the engine
14. Exhaust gas that is created by the combustion of the air/fuel
mixture is expelled through an exhaust manifold 20. A catalytic
converter 22 receives the exhaust gas from the exhaust manifold 20
and reduces the emissions levels of the exhaust gas.
[0020] A controller 30 communicates with various components of the
engine control system 8, including but not limited to a throttle
position sensor 32 (TPS), the fuel system 12, the ignition system
18, and a mass airflow sensor 36 (MAF). The controller 30 receives
a throttle position signal from the TPS 32 and a mass air flow
signal from the MAF 36. The throttle position signal and the mass
air flow signal are used to determine air flow into the engine 14.
The air flow data is then used to calculate the corresponding fuel
to be delivered by the fuel system 12 to the engine 14. The
controller 30 further communicates with the ignition system 18 to
determine ignition spark timing. Oxygen sensors 46 and 48 are
disposed in the exhaust 20 upstream and downstream, respectively,
of the catalytic converter 22. The oxygen sensors 46 and 48 output
signals to the controller 30 that represent the oxygen content
before and after the catalytic converter 22 in the exhaust 20.
[0021] The controller 30 may receive additional feedback from other
components in the engine control system 8, including but not
limited to coolant temperature from a coolant temperature sensor 50
and engine speed from the engine speed sensor 34 (RPM). These and
other variables may affect the overall performance and behavior of
the engine control system 8. The controller 30 utilizes data
gathered from the various engine components to monitor and optimize
engine performance.
[0022] With continued reference to FIG. 1 and further reference to
FIG. 2, the controller 30 according to the present invention
establishes a plurality of thresholds during closed loop fuel
control to maintain optimum catalyst efficiency. The thresholds are
defined as rich condition enable, rich condition disable, lean
condition enable and lean condition disable. The control method is
active only when normal closed loop fuel control conditions are
met. The control method is inactive during other open loop fuel
control or intrusive diagnostic modes. The controller 30 receives
the oxygen signal generated by the downstream oxygen sensor 48.
Based on the signal from the oxygen sensor 48, the controller 30
determines whether the established enable thresholds have been
exceeded. For example, if the downstream oxygen sensor 48 generates
a voltage signal below a predetermined threshold 70, control will
enter an open loop rich control strategy. The open loop rich
control strategy includes delivering an increased amount of fuel to
the engine 14. An increased amount of fuel is delivered to return
the downstream oxygen sensor 48 to a desired window 68. For
example, increasing the amount of fuel delivered to the engine 14
may include increasing the fuel injection duration. The desired
window 68 is defined as a predetermined optimum range of oxygen
measured by the downstream oxygen sensor 48. The open loop rich
control continues until accumulated airflow reaches its
predetermined value or until a lean condition disable threshold 72
is met.
[0023] Similarly, if the downstream oxygen sensor 48 generates a
voltage signal above a predetermined threshold 60, control will
enter an open loop lean control strategy. The open loop lean
control strategy includes delivering a reduced amount of fuel to
the engine 14. A reduced amount of fuel is desired to return the
downstream oxygen sensor 48 to the desired window 68. For example,
decreasing the amount of fuel delivered to the engine 14 may
include decreasing the fuel injection duration. The open loop lean
control continues for a predetermined accumulated airflow or until
a rich condition disable threshold 62 is met.
[0024] Referring now to FIG. 3, steps for optimizing fuel control
in an internal combustion engine are shown generally at 100.
Control begins with step 102. In step 104, control determines
whether any applicable active faults are identified. The applicable
active faults are those that may prevent the control from correct
performance. Active faults may include component diagnostic trouble
codes such as catalytic converter fault codes, oxygen sensor fault
codes, cylinder misfire codes, and secondary fuel trim fault codes,
etc. If one or more active fault codes are identified in step 104,
control returns in step 124. If no active faults are identified in
step 104, control determines whether the downstream oxygen sensor
48 is ready to support closed loop operation in step 108. If the
oxygen sensor 48 is not ready to support closed loop operation,
control returns in step 124. If the oxygen sensor 48 is ready,
control determines whether other open loop fuel or intrusive
diagnostic modes having higher priority are active in step 112.
[0025] If other open loop fuel or intrusive diagnostic modes are
active, control returns in step 124. If there are no other open
loop fuel or intrusive diagnostic modes active, control determines
whether the engine 14 is operating correctly in closed loop mode in
step 118. If the closed loop operation conditions are not met,
control returns in step 124. If all the entire enable conditions
are true, control runs a correction routine in step 120.
[0026] With reference now to FIG. 4, the correction routine 120
will be described in greater detail. The correction routine 120, as
previously described, implements a brief open loop rich or lean
control if the oxygen sensor 48 communicates a signal exceeding the
enable conditions 60 or 70 (FIG. 2). The correction routine 120
begins in step 140. In step 144, control determines if the oxygen
sensor signal 48 has dropped below the lean condition enable
threshold 70 or if the signal has exceeded the rich condition
enable threshold 60 in step 148.
[0027] If the oxygen sensor signal 48 is below the lean condition
enable threshold 70 in step 144, then an intrusive air/fuel ratio
(AFR) control is implemented in step 150 having a rich fuel mixture
of air/fuel (a ratio less than 14.7 to 1 for gasoline). An
accumulated engine airflow variable is also set to zero in step 150
upon initiation of intrusive AFR control. In step 152 control
determines if the oxygen sensor 48 communicates a signal satisfying
the lean condition disable threshold 72. If the oxygen sensor 48
communicates a signal satisfying the lean condition disable
threshold 72, control returns to normal closed loop control mode in
step 156 and control returns in step 158. If the lean condition
disable threshold 72 is not satisfied in step 152, control
determines if intrusive AFR control has been running beyond one or
more predetermined applicable criteria in step 160. The applicable
criteria can be an accumulated airflow, lapsed time or other
variables. For an example, the accumulated airflow is used for
demonstration. If the AFR control has exceeded the predetermined
accumulated engine airflow calibration in step 160, control returns
to normal closed loop control mode in step 156 and control returns
in step 158. If the AFR control has not exceeded the calibration,
the accumulated engine airflow is incremented in step 164 and
control loops to step 152.
[0028] In step 148, control determines whether the oxygen sensor 48
communicates a signal exceeding the rich condition enable threshold
60. If the rich condition enable threshold 60 is not exceeded in
step 148, control returns to normal closed loop control in step 156
and control returns in step 158.
[0029] If the rich condition enable threshold 60 is exceeded in
step 148, an intrusive air/fuel ratio (AFR) control is implemented
in step 170 having a lean fuel mixture of air/fuel (a ratio greater
than 14.7 to 1 for gasoline). An accumulated engine airflow
variable is also set to zero in step 170 upon initiation of
intrusive AFR control. In step 172, control determines whether the
oxygen sensor 48 communicates a signal satisfying the rich
condition disable threshold 62. If the oxygen sensor 48
communicates a signal satisfying the rich condition disable
threshold 62, control returns to normal closed loop control mode in
step 156 and control returns in step 158. If the rich condition
disable threshold 62 is not satisfied in step 172, control
determines whether intrusive AFR control has been running beyond
one or more predetermined applicable criteria in step 180. The
applicable criteria can be an accumulated airflow, lapsed time or
other variables. For an example, the accumulated airflow is used
for demonstration. If the AFR control has exceeded the
predetermined accumulated engine airflow calibration in step 180,
control returns to normal closed loop control mode in step 156 and
control returns in step 158. If the AFR control has not exceeded
the calibration, the accumulated engine airflow is incremented in
step 184 and control loops to step 172.
[0030] Those skilled in the art can now appreciate from the
foregoing description that the broad teachings of the present
invention can be implemented in a variety of forms. Therefore,
while this invention has been described in connection with
particular examples thereof, the true scope of the invention should
not be so limited since other modifications will become apparent to
the skilled practitioner upon a study of the drawings, the
specification and the following claims.
* * * * *