U.S. patent application number 09/873205 was filed with the patent office on 2002-02-21 for air/fuel ratio control system of internal combustion engine.
Invention is credited to Kakuyama, Masatomo, Matsuno, Osamu, Tayama, Akira, Tsuchida, Hirofumi.
Application Number | 20020020170 09/873205 |
Document ID | / |
Family ID | 26396600 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020020170 |
Kind Code |
A1 |
Kakuyama, Masatomo ; et
al. |
February 21, 2002 |
AIR/FUEL RATIO CONTROL SYSTEM OF INTERNAL COMBUSTION ENGINE
Abstract
In an automotive vehicle with at least one catalyst located in
an exhaust passage for adsorbing oxygen contained within exhaust
gases entering the catalyst, and an air/fuel ratio sensor located
in the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, an air/fuel ratio control system controls an air/fuel
mixture ratio of the engine at as close to stoichiometric as
possible, an air/fuel ratio control system calculates a quantity of
oxygen stored in the catalyst on the basis of a deviation of the
air/fuel ratio detected by the air/fuel ratio sensor from a
stoichiometric air/fuel ratio to produce informational data
indicative of a calculated value of the quantity of oxygen stored.
The control system controls the air/fuel mixture ratio of the
engine so that the calculated value of the quantity of oxygen
stored is adjusted to a desired value. The control system has a
limiter capable of preventing the calculated value of the quantity
of oxygen stored from exceeding a specified level.
Inventors: |
Kakuyama, Masatomo;
(Yokohama, JP) ; Tayama, Akira; (Kanagawa, JP)
; Tsuchida, Hirofumi; (Kanagawa, JP) ; Matsuno,
Osamu; (Kanagawa, JP) |
Correspondence
Address: |
Richard L. Schwaab
FOLEY & LARDNER
Washington Harbour
3000 K Street, N.W., Suite 500
Washington
DC
20007-5109
US
|
Family ID: |
26396600 |
Appl. No.: |
09/873205 |
Filed: |
June 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09873205 |
Jun 5, 2001 |
|
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|
09516498 |
Mar 1, 2000 |
|
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6282889 |
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Current U.S.
Class: |
60/285 ; 60/274;
60/277 |
Current CPC
Class: |
F02D 2200/0814 20130101;
F02D 2200/0816 20130101; F02D 41/1456 20130101; F02D 41/0295
20130101 |
Class at
Publication: |
60/285 ; 60/274;
60/277 |
International
Class: |
F01N 003/00; F01N
007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 3, 1999 |
JP |
11-55693 |
Feb 22, 2000 |
JP |
2000-44723 |
Claims
What is claimed is:
1. An air/fuel ratio control system of an internal combustion
engine, comprising: a catalyst located in an exhaust passage, for
adsorbing oxygen contained within exhaust gases entering the
catalyst; an air/fuel ratio sensor located in the exhaust passage
upstream of the catalyst, for detecting an air/fuel ratio based on
a percentage of oxygen contained within the exhaust gases flowing
through the exhaust passage and entering the catalyst; and a
control unit configured to be electronically connected to the
air/fuel ratio sensor, for controlling an air/fuel mixture ratio at
as close to stoichiometric as possible, said control unit
comprising: (a) an arithmetic-calculation section which calculates
a quantity of oxygen stored in the catalyst on the basis of a
deviation of the air/fuel ratio detected by the air/fuel ratio
sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, (b) a control section which controls the air/fuel
mixture ratio so that the calculated value of the quantity of
oxygen stored is adjusted to a desired value, and (c) a limiter
which prevents the calculated value of the quantity of oxygen
stored from exceeding a specified level.
2. The air/fuel ratio control system as claimed in claim 1, wherein
the specified level is set at a predetermined limit value of the
catalyst.
3. The air/fuel ratio control system as claimed in claim 2, wherein
the predetermined limit value of the catalyst is set at a maximum
allowable quantity of oxygen stored in the catalyst, and the
desired value is set at substantially one-half of the maximum
allowable quantity of oxygen stored.
4. An air/fuel ratio control system of an internal combustion
engine, comprising: a catalyst located in an exhaust passage, for
adsorbing oxygen contained within exhaust gases entering the
catalyst; an air/fuel ratio sensor located in the exhaust passage
upstream of the catalyst, for detecting an air/fuel ratio based on
a percentage of oxygen contained within the exhaust gases flowing
through the exhaust passage and entering the catalyst; and a
control unit configured to be electronically connected to the
air/fuel ratio sensor, for controlling an air/fuel mixture ratio at
as close to stoichiometric as possible, said control unit
comprising (a) an arithmetic-calculation section which calculates a
quantity of oxygen stored in the catalyst on the basis of a
deviation of the air/fuel ratio detected by the air/fuel ratio
sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, (b) a control section which controls an air/fuel
mixture ratio so that the calculated value of the quantity of
oxygen stored is adjusted to a desired value, and (c) a limiter
which prevents the calculated value of the quantity of oxygen
stored from exceeding a predetermined limit value of the quantity
of oxygen stored in the catalyst, said limiter comprising (1) a
determination section which determines whether the engine operates
at a fuel cutoff operating mode, and (2) an update section which,
when the calculated value of the quantity of oxygen stored is above
the predetermined limit value during the fuel cutoff operating
mode, terminates arithmetic-operation for the quantity of oxygen
stored, executed by the arithmetic-calculation section, and updates
the calculated value by the predetermined limit value.
5. The air/fuel ratio control system as claimed in claim 4, wherein
the predetermined limit value of the catalyst is set at a maximum
allowable quantity of oxygen stored in the catalyst, and the
desired value is set at substantially one-half of the maximum
allowable quantity of oxygen stored.
6. An air/fuel ratio control system of an internal combustion
engine, comprising: a catalyst located in an exhaust passage, for
adsorbing oxygen contained within exhaust gases entering the
catalyst; an upstream air/fuel ratio sensor located in the exhaust
passage upstream of the catalyst, for detecting an air/fuel ratio
based on a percentage of oxygen contained within the exhaust gases
flowing through the exhaust passage and entering the catalyst; a
downstream air/fuel ratio sensor located in the exhaust passage
downstream of the catalyst, for detecting an air/fuel ratio based
on a percentage of oxygen contained within the exhaust gases
flowing through the exhaust passage and leaving the catalyst; and a
control unit configured to be electronically connected to the
upstream and downstream air/fuel ratio sensors, for controlling an
air/fuel mixture ratio at as close to stoichiometric as possible,
said control unit comprising (a) an arithmetic-calculation section
which calculates a quantity of oxygen stored in the catalyst on the
basis of a deviation of the air/fuel ratio detected by the upstream
air/fuel ratio sensor from a stoichiometric air/fuel ratio, to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, (b) a control section which controls an
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, and (c) a limiter
which prevents the calculated value of the quantity of oxygen
stored from exceeding a specified level, said limiter comprising a
determination section which determines whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is leaner than a
predetermined lean air/fuel ratio criterion.
7. The air/fuel ratio control system as claimed in claim 6, wherein
said limiter comprising an update section which, when the
determination section determines that the air/fuel ratio detected
by the downstream air/fuel ratio sensor is leaner than the
predetermined lean air/fuel ratio criterion, terminates
arithmetic-operation for the quantity of oxygen stored, executed by
the arithmetic-calculation section, and updates the calculated
value by a predetermined limit value.
8. An air/fuel ratio control system of an internal combustion
engine, comprising: a catalyst located in an exhaust passage, for
adsorbing oxygen contained within exhaust gases entering the
catalyst; an upstream air/fuel ratio sensor located in the exhaust
passage upstream of the catalyst, for detecting an air/fuel ratio
based on a percentage of oxygen contained within the exhaust gases
flowing through the exhaust passage and entering the catalyst; a
downstream air/fuel ratio sensor located in the exhaust passage
downstream of the catalyst, for detecting an air/fuel ratio based
on a percentage of oxygen contained within the exhaust gases
flowing through the exhaust passage and leaving the catalyst; and a
control unit configured to be electronically connected to the
upstream and downstream air/fuel ratio sensors, for controlling an
air/fuel mixture ratio at as close to stoichiometric as possible,
said control unit comprising (a) an arithmetic-calculation section
which calculates a quantity of oxygen stored in the catalyst on the
basis of a deviation of the air/fuel ratio detected by the upstream
air/fuel ratio sensor from a stoichiometric air/fuel ratio, to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, (b) a control section which controls an
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, and (c) a limiter
which prevents the calculated value of the quantity of oxygen
stored from exceeding a predetermined limit value of the quantity
of oxygen stored in the catalyst, said limiter comprising (1) a
determination section which determines whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is a leaner
air/fuel ratio than the stoichiometric air/fuel ratio, and (2) an
update section which, when the determination section determines
that the air/fuel ratio detected by the downstream air/fuel ratio
sensor is the leaner air/fuel ratio and the calculated value of the
quantity of oxygen stored is above the predetermined limit value,
terminates arithmetic-operation for the quantity of oxygen stored,
executed by the arithmetic-calculation section, and updates the
calculated value by the predetermined limit value.
9. The air/fuel ratio control system as claimed in claim 8, wherein
the predetermined limit value of the catalyst is set at a maximum
allowable quantity of oxygen stored in the catalyst, and the
desired value is set at substantially one-half of the maximum
allowable quantity of oxygen stored.
10. In an internal combustion engine having a catalyst located in
an exhaust passage for adsorbing oxygen contained within exhaust
gases entering the catalyst, and an air/fuel ratio sensor located
in the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, an air/fuel ratio control system for controlling an
air/fuel mixture ratio of the internal combustion engine at as
close to stoichiometric as possible, comprising: (a) an
arithmetic-calculation means for calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the air/fuel ratio sensor from a stoichiometric
air/fuel ratio, to produce informational data indicative of a
calculated value of the quantity of oxygen stored; (b) a control
means for controlling the air/fuel mixture ratio so that the
calculated value of the quantity of oxygen stored is adjusted to a
desired value; and (c) a limiter means for preventing the
calculated value of the quantity of oxygen stored from exceeding a
specified level.
11. In an internal combustion engine having a catalyst located in
an exhaust passage for adsorbing oxygen contained within exhaust
gases entering the catalyst, and an air/fuel ratio sensor located
in the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, an air/fuel ratio control system for controlling an
air/fuel mixture ratio of the internal combustion engine at as
close to stoichiometric as possible, comprising: (a) an
arithmetic-calculation means for calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the air/fuel ratio sensor from a stoichiometric
air/fuel ratio, to produce informational data indicative of a
calculated value of the quantity of oxygen stored, (b) a control
means for controlling an air/fuel mixture ratio so that the
calculated value of the quantity of oxygen stored is adjusted to a
desired value, and (c) a limiter means for preventing the
calculated value of the quantity of oxygen stored from exceeding a
predetermined limit value of the quantity of oxygen stored in the
catalyst, said limiter means comprising (1) a determination means
for determining whether the engine operates at a fuel cutoff
operating mode, and (2) an update means for terminating
arithmetic-operation for the quantity of oxygen stored, executed by
the arithmetic-calculation means and for updating the calculated
value by the predetermined limit value, when the calculated value
of the quantity of oxygen stored is above the predetermined limit
value during the fuel cutoff operating mode.
12. In an internal combustion engine having a catalyst located in
an exhaust passage for adsorbing oxygen contained within exhaust
gases entering the catalyst, an upstream air/fuel ratio sensor
located in the exhaust passage upstream of the catalyst for
detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and entering the catalyst, and a downstream air/fuel ratio
sensor located in the exhaust passage downstream of the catalyst
for detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and leaving the catalyst, an air/fuel ratio control system
for controlling an air/fuel mixture ratio of the internal
combustion engine at as close to stoichiometric as possible,
comprising: (a) an arithmetic-calculation means for calculating a
quantity of oxygen stored in the catalyst on the basis of a
deviation of the air/fuel ratio detected by the upstream air/fuel
ratio sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, (b) a control means for controlling an air/fuel
mixture ratio so that the calculated value of the quantity of
oxygen stored is adjusted to a desired value, and (c) a limiter
means for preventing the calculated value of the quantity of oxygen
stored from exceeding a specified level, said limiter comprising a
determination means for determining whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is leaner than a
predetermined lean air/fuel ratio criterion.
13. The air/fuel ratio control system as claimed in claim 12,
wherein said limiter means comprises an update means for
terminating arithmetic-operation for the quantity of oxygen stored,
executed by the arithmetic-calculation means and for updating the
calculated value by a predetermined limit value, when the
determination means determines that the air/fuel ratio detected by
the downstream air/fuel ratio sensor is leaner than the
predetermined lean air/fuel ratio criterion.
14. In an internal combustion engine having a catalyst located in
an exhaust passage for adsorbing oxygen contained within exhaust
gases entering the catalyst, an upstream air/fuel ratio sensor
located in the exhaust passage upstream of the catalyst for
detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and entering the catalyst, and a downstream air/fuel ratio
sensor located in the exhaust passage downstream of the catalyst
for detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and leaving the catalyst, an air/fuel ratio control system
for controlling an air/fuel mixture ratio of the internal
combustion engine at as close to stoichiometric as possible,
comprising: (a) an arithmetic-calculation means for calculating a
quantity of oxygen stored in the catalyst on the basis of a
deviation of the air/fuel ratio detected by the upstream air/fuel
ratio sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, (b) a control means for controlling an air/fuel
mixture ratio so that the calculated value of the quantity of
oxygen stored is adjusted to a desired value, and (c) a limiter
means for preventing the calculated value of the quantity of oxygen
stored from exceeding a predetermined limit value of the quantity
of oxygen stored in the catalyst, said limiter comprising (1) a
determination means for determining whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is a leaner
air/fuel ratio than the stoichiometric air/fuel ratio, and (2) an
update means for terminating arithmetic-operation for the quantity
of oxygen stored, executed by the arithmetic-calculation means and
for updating the calculated value by the predetermined limit value,
when the determination section determines that the air/fuel ratio
detected by the downstream air/fuel ratio sensor is the leaner
air/fuel ratio and the calculated value of the quantity of oxygen
stored is above the predetermined limit value.
15. A method for controlling an air/fuel mixture ratio of an
internal combustion engine, wherein the engine includes a catalyst
located in an exhaust passage for adsorbing oxygen contained within
exhaust gases entering the catalyst, and an air/fuel ratio sensor
located in the exhaust passage upstream of the catalyst for
detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and entering the catalyst, the method comprising:
calculating a quantity of oxygen stored in the catalyst on the
basis of a deviation of the air/fuel ratio detected by the air/fuel
ratio sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored; controlling the air/fuel mixture ratio so that
the calculated value of the quantity of oxygen stored is adjusted
to a desired value; and preventing the calculated value of the
quantity of oxygen stored from exceeding a specified level.
16. A method for controlling an air/fuel mixture ratio of an
internal combustion engine, wherein the engine includes a catalyst
located in an exhaust passage for adsorbing oxygen contained within
exhaust gases entering the catalyst, and an air/fuel ratio sensor
located in the exhaust passage upstream of the catalyst for
detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and entering the catalyst, the method comprising:
calculating a quantity of oxygen stored in the catalyst on the
basis of a deviation of the air/fuel ratio detected by the air/fuel
ratio sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, controlling an air/fuel mixture ratio so that the
calculated value of the quantity of oxygen stored is adjusted to a
desired value, determining whether the engine operates at a fuel
cutoff operating mode, terminating arithmetic-operation for the
quantity of oxygen stored and updating the calculated value by a
predetermined limit value of the quantity of oxygen stored in the
catalyst, when the calculated value of the quantity of oxygen
stored is above the predetermined limit value during the fuel
cutoff operating mode.
17. A method for controlling an air/fuel mixture ratio of an
internal combustion engine, wherein the engine includes a catalyst
located in an exhaust passage for adsorbing oxygen contained within
exhaust gases entering the catalyst, an upstream air/fuel ratio
sensor located in the exhaust passage upstream of the catalyst for
detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and entering the catalyst, and a downstream air/fuel ratio
sensor located in the exhaust passage downstream of the catalyst
for detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and leaving the catalyst, the method comprising:
calculating a quantity of oxygen stored in the catalyst on the
basis of a deviation of the air/fuel ratio detected by the upstream
air/fuel ratio sensor from a stoichiometric air/fuel ratio, to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, controlling an air/fuel mixture ratio so
that the calculated value of the quantity of oxygen stored is
adjusted to a desired value, determining whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is leaner than a
predetermined lean air/fuel ratio criterion, and terminating
arithmetic-operation for the quantity of oxygen stored and updating
the calculated value by a predetermined limit value of the quantity
of oxygen stored in the catalyst, when the air/fuel ratio detected
by the downstream air/fuel ratio sensor is leaner than the
predetermined lean air/fuel ratio criterion.
18. A method for controlling an air/fuel mixture ratio of an
internal combustion engine, wherein the engine includes a catalyst
located in an exhaust passage for adsorbing oxygen contained within
exhaust gases entering the catalyst, an upstream air/fuel ratio
sensor located in the exhaust passage upstream of the catalyst for
detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and entering the catalyst, and a downstream air/fuel ratio
sensor located in the exhaust passage downstream of the catalyst
for detecting an air/fuel ratio based on a percentage of oxygen
contained within the exhaust gases flowing through the exhaust
passage and leaving the catalyst, the method comprising:
calculating a quantity of oxygen stored in the catalyst on the
basis of a deviation of the air/fuel ratio detected by the upstream
air/fuel ratio sensor from a stoichiometric air/fuel ratio, to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, controlling an air/fuel mixture ratio so
that the calculated value of the quantity of oxygen stored is
adjusted to a desired value, determining whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is a leaner
air/fuel ratio than the stoichiometric air/fuel ratio, and
terminating arithmetic-operation for the quantity of oxygen stored
and updating the calculated value by a predetermined limit value of
the quantity of oxygen stored in the catalyst, when the air/fuel
ratio detected by the downstream air/fuel ratio sensor is the
leaner air/fuel ratio and the calculated value of the quantity of
oxygen stored is above the predetermined limit value.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the improvements of an
air/fuel ratio control system of an internal combustion engine with
an emission control system having at least a catalyst, and
specifically to an air/fuel ratio control system capable of
controlling an air/fuel mixture ratio so that the quantity of
oxygen stored in the catalyst is adjusted toward a desired
quantity.
[0003] 2. Description of the Prior Art
[0004] In recent years, an automotive vehicle often uses a
three-way catalyst to reduce oxides of nitrogen (NOx), unburned
hydrocarbons (HC), and carbon monoxide (CO). On automotive vehicles
employing a three-way catalytic converter (a three-way catalyst) in
the exhaust passage, in order to detect an air/fuel mixture ratio
(often abbreviated to "A/F ratio"), an A/F ratio sensor, such as an
O.sub.2 sensor, is usually provided in the exhaust passage upstream
of the three-way catalyst. As is generally known, the purpose of
the A/F sensor such as oxygen sensor is to monitor the percentage
of oxygen contained within the exhaust gases at all times when the
engine is running, so that the ECU can maintain the A/F ratio at as
close to stoichiometric as possible. A voltage signal from the A/F
ratio sensor varies depending on the air/fuel mixture ratio. In
automotive vehicles with both a three-way catalyst and an A/F ratio
sensor located upstream of the three-way catalyst, an electronic
engine control unit (ECU) or an electronic engine control module
(ECM) generally utilizes the deviation of an A/F ratio sensed by
the A/F ratio sensor from a stoichiometric air/fuel ratio to
arithmetically calculate or estimate the quantity of oxygen stored
in the three-way catalyst. The ECU controls the A/F ratio such that
the estimate (the calculated value) of the quantity of air (oxygen)
stored in the catalyst is adjusted to a desired value (for example,
one-half of a limit value of the quantity of oxygen stored in the
three-way catalyst). When the A/F ratio is lean (excess air), air
(oxygen) is adsorbed or trapped by the three-way catalyst and
stored in the catalyst. Conversely, when the A/F ratio is rich (too
much fuel), air (oxygen) is desorbed or released from the three-way
catalyst. Generally, an oxygen desorption speed at which oxygen is
desorbed from the three-way catalyst is lower than an oxygen
adsorption speed at which oxygen is adsorbed by the three-way
catalyst. For the reasons discussed above, the ECU increasingly
compensates for the quantity of oxygen stored in the three-way
catalyst, which quantity will be hereinafter referred to as an
"oxygen storage quantity", by increasing an increment for a
calculated value (or an estimate) of oxygen storage quantity, when
the sensed A/F ratio is lean (excess air). To the contrary, when
the sensed A/F ratio is rich (too much fuel), the ECU decreasingly
compensates for the oxygen storage quantity, by decreasing a
decrement for the calculated value (or the estimate) of oxygen
storage quantity. Such A/F ratio control systems have been
disclosed in Japanese Patent Provisional Publication Nos. 9-310635
and 6-249028.
SUMMARY OF THE INVENTION
[0005] In an automotive vehicle having an A/F ratio control system
as described previously, if the actual air/fuel ratio becomes ultra
lean, for example during deceleration fuel-cutoff operation, the
actual oxygen storage quantity of the three-way catalyst will reach
its limit value soon. However, the arithmetic-calculation section
of the ECU continues arithmetic operation for the oxygen storage
quantity based on the A/F sensor signal. In such a case, there is a
possibility that the calculated value (or the estimate) of oxygen
storage quantity is estimated or calculated as an excessive value
greater than the limit value of oxygen storage quantity, even when
the actual oxygen storage quantity of the three-way catalyst is
kept at the limit value of oxygen storage quantity. As discussed
above, there is a problem of a remarkable difference between the
calculated value of oxygen storage quantity produced by the ECU and
the actual oxygen storage quantity, when the A/F ratio is reduced
to below an excessively lean A/F ratio less than a predetermined
threshold, such as during deceleration fuel-cutoff operation.
Assuming that the engine/vehicle operating condition is recovered
from the previously-noted deceleration fuel-cutoff operating mode
to a normal operating mode, there is a possibility of a malfunction
in the A/F ratio control system owing to such an undesirably
excessive rise in the calculated value of oxygen storage quantity.
Also, the excessive rise in the calculated value of oxygen storage
quantity may degrade the performance of the A/F ratio control
system.
[0006] Accordingly, it is an object of the invention to provide an
air/fuel mixture ratio control system of an internal combustion
engine which avoids the aforementioned disadvantages of the prior
art.
[0007] In order to accomplish the aforementioned and other objects
of the present invention, an air/fuel ratio control system of an
internal combustion engine comprises a catalyst located in an
exhaust passage, for adsorbing oxygen contained within exhaust
gases entering the catalyst, an air/fuel ratio sensor located in
the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, and a control unit configured to be electronically
connected to the air/fuel ratio sensor for controlling an air/fuel
mixture ratio at as close to stoichiometric as possible, the
control unit comprising an arithmetic-calculation section which
calculates a quantity of oxygen stored in the catalyst on the basis
of a deviation of the air/fuel ratio detected by the air/fuel ratio
sensor from a stoichiometric air/fuel ratio to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, a control section which controls the air/fuel
mixture ratio so that the calculated value of the quantity of
oxygen stored is adjusted to a desired value, and a limiter which
prevents the calculated value of the quantity of oxygen stored from
exceeding a specified level.
[0008] According to another aspect of the invention, an air/fuel
ratio control system of an internal combustion engine comprises a
catalyst located in an exhaust passage, for adsorbing oxygen
contained within exhaust gases entering the catalyst, an air/fuel
ratio sensor located in the exhaust passage upstream of the
catalyst for detecting an air/fuel ratio based on a percentage of
oxygen contained within the exhaust gases flowing through the
exhaust passage and entering the catalyst, and a control unit
configured to be electronically connected to the air/fuel ratio
sensor for controlling an air/fuel mixture ratio at as close to
stoichiometric as possible, the control unit comprising an
arithmetic-calculation section which calculates a quantity of
oxygen stored in the catalyst on the basis of a deviation of the
air/fuel ratio detected by the air/fuel ratio sensor from a
stoichiometric air/fuel ratio to produce informational data
indicative of a calculated value of the quantity of oxygen stored,
a control section which controls an air/fuel mixture ratio so that
the calculated value of the quantity of oxygen stored is adjusted
to a desired value, and a limiter which prevents the calculated
value of the quantity of oxygen stored from exceeding a
predetermined limit value of the quantity of oxygen stored in the
catalyst, the limiter comprising a determination section which
determines whether the engine operates at a fuel cutoff operating
mode, and an update section which, when the calculated value of the
quantity of oxygen stored is above the predetermined limit value
during the fuel cutoff operating mode, terminates
arithmetic-operation for the quantity of oxygen stored, executed by
the arithmetic-calculation section, and updates the calculated
value by the predetermined limit value.
[0009] According to another aspect of the invention, an air/fuel
ratio control system of an internal combustion engine comprises a
catalyst located in an exhaust passage for adsorbing oxygen
contained within exhaust gases entering the catalyst, an upstream
air/fuel ratio sensor located in the exhaust passage upstream of
the catalyst for detecting an air/fuel ratio based on a percentage
of oxygen contained within the exhaust gases flowing through the
exhaust passage and entering the catalyst, a downstream air/fuel
ratio sensor located in the exhaust passage downstream of the
catalyst for detecting an air/fuel ratio based on a percentage of
oxygen contained within the exhaust gases flowing through the
exhaust passage and leaving the catalyst, and a control unit
configured to be electronically connected to the upstream and
downstream air/fuel ratio sensors, for controlling an air/fuel
mixture ratio at as close to stoichiometric as possible, the
control unit comprising an arithmetic-calculation section which
calculates a quantity of oxygen stored in the catalyst on the basis
of a deviation of the air/fuel ratio detected by the upstream
air/fuel ratio sensor from a stoichiometric air/fuel ratio, to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, a control section which controls an
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, and a limiter
which prevents the calculated value of the quantity of oxygen
stored from exceeding a specified level, the limiter comprising a
determination section which determines whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is leaner than a
predetermined lean air/fuel ratio criterion. The limiter may
further comprise an update section which, when the determination
section determines that the air/fuel ratio detected by the
downstream air/fuel ratio sensor is leaner than the predetermined
lean air/fuel ratio criterion, terminates arithmetic-operation for
the quantity of oxygen stored, executed by the
arithmetic-calculation section, and updates the calculated value by
a predetermined limit value.
[0010] According to a further aspect of the invention, an air/fuel
ratio control system of an internal combustion engine comprises a
catalyst located in an exhaust passage for adsorbing oxygen
contained within exhaust gases entering the catalyst, an upstream
air/fuel ratio sensor located in the exhaust passage upstream of
the catalyst for detecting an air/fuel ratio based on a percentage
of oxygen contained within the exhaust gases flowing through the
exhaust passage and entering the catalyst, a downstream air/fuel
ratio sensor located in the exhaust passage downstream of the
catalyst for detecting an air/fuel ratio based on a percentage of
oxygen contained within the exhaust gases flowing through the
exhaust passage and leaving the catalyst, and a control unit
configured to be electronically connected to the upstream and
downstream air/fuel ratio sensors for controlling an air/fuel
mixture ratio at as close to stoichiometric as possible, the
control unit comprising an arithmetic-calculation section which
calculates a quantity of oxygen stored in the catalyst on the basis
of a deviation of the air/fuel ratio detected by the upstream
air/fuel ratio sensor from a stoichiometric air/fuel ratio to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, a control section which controls an
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, and a limiter
which prevents the calculated value of the quantity of oxygen
stored from exceeding a predetermined limit value of the quantity
of oxygen stored in the catalyst, the limiter comprising a
determination section which determines whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is a leaner
air/fuel ratio than the stoichiometric air/fuel ratio, and an
update section which, when the determination section determines
that the air/fuel ratio detected by the downstream air/fuel ratio
sensor is the leaner air/fuel ratio and the calculated value of the
quantity of oxygen stored is above the predetermined limit value,
terminates arithmetic-operation for the quantity of oxygen stored,
executed by the arithmetic-calculation section, and updates the
calculated value by the predetermined limit value.
[0011] According to another aspect of the invention, in an internal
combustion engine having a catalyst located in an exhaust passage
for adsorbing oxygen contained within exhaust gases entering the
catalyst, and an air/fuel ratio sensor located in the exhaust
passage upstream of the catalyst for detecting an air/fuel ratio
based on a percentage of oxygen contained within the exhaust gases
flowing through the exhaust passage and entering the catalyst, an
air/fuel ratio control system for controlling an air/fuel mixture
ratio of the internal combustion engine at as close to
stoichiometric as possible comprises an arithmetic-calculation
means for calculating a quantity of oxygen stored in the catalyst
on the basis of a deviation of the air/fuel ratio detected by the
air/fuel ratio sensor from a stoichiometric air/fuel ratio to
produce informational data indicative of a calculated value of the
quantity of oxygen stored, a control means for controlling the
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, and a limiter
means for preventing the calculated value of the quantity of oxygen
stored from exceeding a specified level.
[0012] According to a further aspect of the invention, in an
internal combustion engine having a catalyst located in an exhaust
passage for adsorbing oxygen contained within exhaust gases
entering the catalyst, and an air/fuel ratio sensor located in the
exhaust passage upstream of the catalyst for detecting an air/fuel
ratio based on a percentage of oxygen contained within the exhaust
gases flowing through the exhaust passage and entering the
catalyst, an air/fuel ratio control system for controlling an
air/fuel mixture ratio of the internal combustion engine at as
close to stoichiometric as possible comprises an
arithmetic-calculation means for calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the air/fuel ratio sensor from a stoichiometric
air/fuel ratio to produce informational data indicative of a
calculated value of the quantity of oxygen stored, a control means
for controlling an air/fuel mixture ratio so that the calculated
value of the quantity of oxygen stored is adjusted to a desired
value, and a limiter means for preventing the calculated value of
the quantity of oxygen stored from exceeding a predetermined limit
value of the quantity of oxygen stored in the catalyst, the limiter
means comprising a determination means for determining whether the
engine operates at a fuel cutoff operating mode, and an update
means for terminating arithmetic-operation for the quantity of
oxygen stored, executed by the arithmetic-calculation means and for
updating the calculated value by the predetermined limit value,
when the calculated value of the quantity of oxygen stored is above
the predetermined limit value during the fuel cutoff operating
mode.
[0013] According to another aspect of the invention, in an internal
combustion engine having a catalyst located in an exhaust passage
for adsorbing oxygen contained within exhaust gases entering the
catalyst, an upstream air/fuel ratio sensor located in the exhaust
passage upstream of the catalyst for detecting an air/fuel ratio
based on a percentage of oxygen contained within the exhaust gases
flowing through the exhaust passage and entering the catalyst, and
a downstream air/fuel ratio sensor located in the exhaust passage
downstream of the catalyst for detecting an air/fuel ratio based on
a percentage of oxygen contained within the exhaust gases flowing
through the exhaust passage and leaving the catalyst, an air/fuel
ratio control system for controlling an air/fuel mixture ratio of
the internal combustion engine at as close to stoichiometric as
possible, comprises an arithmetic-calculation means for calculating
a quantity of oxygen stored in the catalyst on the basis of a
deviation of the air/fuel ratio detected by the upstream air/fuel
ratio sensor from a stoichiometric air/fuel ratio, to produce
informational data indicative of a calculated value of the quantity
of oxygen stored, a control means for controlling an air/fuel
mixture ratio so that the calculated value of the quantity of
oxygen stored is adjusted to a desired value, and a limiter means
for preventing the calculated value of the quantity of oxygen
stored from exceeding a specified level, the limiter comprising a
determination means for determining whether the air/fuel ratio
detected by the downstream air/fuel ratio sensor is leaner than a
predetermined lean air/fuel ratio criterion. The limiter means may
further comprise an update means for terminating
arithmetic-operation for the quantity of oxygen stored, executed by
the arithmetic-calculation means and for updating the calculated
value by a predetermined limit value, when the determination means
determines that the air/fuel ratio detected by the downstream
air/fuel ratio sensor is leaner than the predetermined lean
air/fuel ratio criterion.
[0014] According to a still further aspect of the invention, in an
internal combustion engine having a catalyst located in an exhaust
passage for adsorbing oxygen contained within exhaust gases
entering the catalyst, an upstream air/fuel ratio sensor located in
the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, and a downstream air/fuel ratio sensor located in the
exhaust passage downstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and leaving the
catalyst, an air/fuel ratio control system for controlling an
air/fuel mixture ratio of the internal combustion engine at as
close to stoichiometric as possible comprises an
arithmetic-calculation means for calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the upstream air/fuel ratio sensor from a
stoichiometric air/fuel ratio to produce informational data
indicative of a calculated value of the quantity of oxygen stored,
a control means for controlling an air/fuel mixture ratio so that
the calculated value of the quantity of oxygen stored is adjusted
to a desired value, and a limiter means for preventing the
calculated value of the quantity of oxygen stored from exceeding a
predetermined limit value of the quantity of oxygen stored in the
catalyst, the limiter comprising a determination means for
determining whether the air/fuel ratio detected by the downstream
air/fuel ratio sensor is a leaner air/fuel ratio than the
stoichiometric air/fuel ratio, and an update means for terminating
arithmetic-operation for the quantity of oxygen stored, executed by
the arithmetic-calculation means and for updating the calculated
value by the predetermined limit value, when the determination
section determines that the air/fuel ratio detected by the
downstream air/fuel ratio sensor is the leaner air/fuel ratio and
the calculated value of the quantity of oxygen stored is above the
predetermined limit value.
[0015] According to another aspect of the invention, a method for
controlling an air/fuel mixture ratio of an internal combustion
engine, wherein the engine includes a catalyst located in an
exhaust passage for adsorbing oxygen contained within exhaust gases
entering the catalyst, and an air/fuel ratio sensor located in the
exhaust passage upstream of the catalyst for detecting an air/fuel
ratio based on a percentage of oxygen contained within the exhaust
gases flowing through the exhaust passage and entering the
catalyst, the method comprises calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the air/fuel ratio sensor from a stoichiometric
air/fuel ratio, to produce informational data indicative of a
calculated value of the quantity of oxygen stored, controlling the
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, and preventing the
calculated value of the quantity of oxygen stored from exceeding a
specified level.
[0016] According to another aspect of the invention, a method for
controlling an air/fuel mixture ratio of an internal combustion
engine, wherein the engine includes a catalyst located in an
exhaust passage for adsorbing oxygen contained within exhaust gases
entering the catalyst, and an air/fuel ratio sensor located in the
exhaust passage upstream of the catalyst for detecting an air/fuel
ratio based on a percentage of oxygen contained within the exhaust
gases flowing through the exhaust passage and entering the
catalyst, the method comprises calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the air/fuel ratio sensor from a stoichiometric
air/fuel ratio, to produce informational data indicative of a
calculated value of the quantity of oxygen stored, controlling an
air/fuel mixture ratio so that the calculated value of the quantity
of oxygen stored is adjusted to a desired value, determining
whether the engine operates at a fuel cutoff operating mode,
terminating arithmetic-operation for the quantity of oxygen stored
and updating the calculated value by a predetermined limit value of
the quantity of oxygen stored in the catalyst, when the calculated
value of the quantity of oxygen stored is above the predetermined
limit value during the fuel cutoff operating mode.
[0017] According to another aspect of the invention, a method for
controlling an air/fuel mixture ratio of an internal combustion
engine, wherein the engine includes a catalyst located in an
exhaust passage for adsorbing oxygen contained within exhaust gases
entering the catalyst, an upstream air/fuel ratio sensor located in
the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, and a downstream air/fuel ratio sensor located in the
exhaust passage downstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and leaving the
catalyst, the method comprising calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the upstream air/fuel ratio sensor from a
stoichiometric air/fuel ratio, to produce informational data
indicative of a calculated value of the quantity of oxygen stored,
controlling an air/fuel mixture ratio so that the calculated value
of the quantity of oxygen stored is adjusted to a desired value,
determining whether the air/fuel ratio detected by the downstream
air/fuel ratio sensor is leaner than a predetermined lean air/fuel
ratio criterion, and terminating arithmetic-operation for the
quantity of oxygen stored and updating the calculated value by a
predetermined limit value of the quantity of oxygen stored in the
catalyst, when the air/fuel ratio detected by the downstream
air/fuel ratio sensor is leaner than the predetermined lean
air/fuel ratio criterion.
[0018] According to another aspect of the invention, a method for
controlling an air/fuel mixture ratio of an internal combustion
engine, wherein the engine includes a catalyst located in an
exhaust passage for adsorbing oxygen contained within exhaust gases
entering the catalyst, an upstream air/fuel ratio sensor located in
the exhaust passage upstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and entering the
catalyst, and a downstream air/fuel ratio sensor located in the
exhaust passage downstream of the catalyst for detecting an
air/fuel ratio based on a percentage of oxygen contained within the
exhaust gases flowing through the exhaust passage and leaving the
catalyst, the method comprises calculating a quantity of oxygen
stored in the catalyst on the basis of a deviation of the air/fuel
ratio detected by the upstream air/fuel ratio sensor from a
stoichiometric air/fuel ratio, to produce informational data
indicative of a calculated value of the quantity of oxygen stored,
controlling an air/fuel mixture ratio so that the calculated value
of the quantity of oxygen stored is adjusted to a desired value,
determining whether the air/fuel ratio detected by the downstream
air/fuel ratio sensor is a leaner air/fuel ratio than the
stoichiometric air/fuel ratio, and terminating arithmetic-operation
for the quantity of oxygen stored and updating the calculated value
by a predetermined limit value of the quantity of oxygen stored in
the catalyst, when the air/fuel ratio detected by the downstream
air/fuel ratio sensor is the leaner air/fuel ratio and the
calculated value of the quantity of oxygen stored is above the
predetermined limit value.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a system diagram illustrating the general system
layout of a computer-controlled internal combustion engine equipped
with an air/fuel mixture ratio (A/F ratio) control system and an
emission control system.
[0020] FIG. 2 is a flow chart illustrating one example of a
sub-routine (a control procedure) executed by an electronic control
unit (ECU) included in the A/F ratio control system of the
embodiment.
[0021] FIGS. 3A through 3C are timing charts illustrating the
operation of the A/F ratio control system (related to the flow
chart shown in FIGS. 2 and 4).
[0022] FIG. 4 is a flow chart illustrating another example of a
sub-routine (a control procedure) executed by the electronic
control unit (ECU) included in the A/F ratio control system of the
embodiment.
[0023] FIG. 5 is a flow chart illustrating a further example of a
sub-routine (a control procedure) executed by the electronic
control unit (ECU) included in the A/F ratio control system of the
embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] Referring now to the drawings, particularly to FIG. 1, the
A/F ratio control system of the invention is exemplified in case of
an internal combustion engine equipped with a three-way catalytic
converter (a three-way catalyst). In FIG. 1, an engine cylinder
block is denoted by reference sign 1. Fresh air is introduced into
each engine cylinder through an intake-air duct (or an intake-air
passage) 2 and an intake manifold (not numbered). An intake-air
quantity sensor 13, such as an air-flow meter, is located on the
intake-air passage 2 for detecting a quantity of air flowing
through the intake-air quantity sensor and drawn into the engine. A
hot-wire mass air flow meter is commonly used as the intake-air
quantity sensor which detects air flow (air quantity Qa) through
the intake-air passage 2. A throttle valve 5 of a throttle body
assembly (an electronically-controlled throttle unit) is provided
in the intake-air passage 2. Reference sign 14 denotes a throttle
opening sensor usually located on the throttle body and connected
to the throttle linkage, for detecting a throttle opening TVO of
the throttle valve 5. Fuel injectors 4 are provided at each of
branched portions of the intake manifold. A spark plug (not
numbered) is screwed into a tapped hole of the cylinder head for
each combustion chamber to ignite the air fuel mixture in the
combustion chamber. Hot burned gases from the engine cylinders are
exhausted through an exhaust valve (not numbered) and an exhaust
manifold (not numbered) into an exhaust passage 3. The three-way
catalytic converter (the three-way catalyst 6) is located in the
exhaust passage 3, to convert harmful exhaust gases (HC, CO, NOx)
into harmless gases (H.sub.2O, CO.sub.2, N.sub.2), and to reduce
oxides of nitrogen (generally termed NOx), unburned hydrocarbons
(HC), and carbon monoxide (CO). An upstream air/fuel ratio sensor
(simply, an upstream A/F ratio sensor) 11 is located in the exhaust
passage 3 upstream of the three-way catalyst 6, for monitoring or
detecting an air/fuel mixture ratio (simply, an A/F ratio) AFSABF
based on the percentage of oxygen contained within the engine
exhaust gases flowing through the exhaust passage 3 and entering
the catalyst 6, at all times when the engine is running, so that an
electronic control module (ECM) or an electronic engine control
unit (ECU) 10 can maintain the A/F ratio at as close to
stoichiometric as possible, for complete combustion and minimum
exhaust emissions. In the system of the embodiment, the upstream
A/F ratio sensor 11 has a linear characteristic that an output
voltage signal from the upstream A/F ratio sensor 11 varies
linearly with an actual air/fuel mixture ratio. Thus, the output
voltage signal from the upstream A/F ratio sensor 11 tends to
change in proportion to the actual A/F ratio all over a measurement
range. That is, a high voltage signal from the upstream A/F ratio
sensor 11 means that the air/fuel mixture is rich, whereas a low
voltage signal from the sensor 11 means that the air/fuel mixture
is lean. Generally, when the A/F ratio is lean (excess air), air is
adsorbed or trapped by the three-way catalyst 6 and stored in the
catalyst 6. Conversely, when the A/F ratio is rich (too much fuel),
air is desorbed or released from the three-way catalyst 6. By
virtue of such catalytic actions, that is, adsorption and
desorption of oxygen by and from the three-way catalyst 6, the
exhaust gas leaving the catalyst 6 contains less HC, CO, and NOx
than the exhaust gas entering, and as a result of the exhaust gases
are cleared or purified. In the system of the embodiment, a
downstream air/fuel ratio sensor (simply, a downstream A/F ratio
sensor) 20 is further located in the exhaust passage 3 downstream
of the three-way catalyst 6, for monitoring or detecting an A/F
ratio AFSABF2 based on the percentage of oxygen contained within
the engine exhaust gases flowing through the exhaust passage 3 and
leaving the catalyst 6, at all times when the engine is running. In
the system of the embodiment, the downstream A/F ratio sensor 20
has a non-linear characteristic that an output voltage signal from
the downstream A/F ratio sensor 20 varies, in a non-linear fashion,
with an actual air/fuel mixture ratio, such that the output voltage
signal value of the sensor 20 rapidly increases from the vicinity
of the stoichiometric ratio. Alternatively, the downstream A/F
ratio sensor 20 may be constructed as a sensor having a linear
characteristic in the same manner as the upstream A/F ratio sensor.
As discussed above, note that, in the system of the embodiment, the
upstream A/F ratio sensor 11 is provided to detect the A/F ratio
AFSABF based on the percentage of oxygen contained within the
engine exhaust gases entering the catalyst 6, while the downstream
A/F ratio sensor 20 is provided to detect the A/F ratio AFSABF2
based on the percentage of oxygen contained within the engine
exhaust gases leaving the catalyst 6. In FIG. 1, reference sign 12
denotes a crank angle sensor which is usually mounted on the engine
for monitoring engine speed Ne as well as a relative position of
the engine crankshaft. Reference sign 15 denotes an engine
temperature sensor (a coolant temperature sensor) which is mounted
on the engine and usually screwed into one of top coolant passages
for monitoring engine temperature (operating temperature of the
engine) Te. Generally, engine coolant temperature is used as the
engine temperature Te. Reference sign 16 denotes a vehicle speed
sensor which is usually located at either the transmission or
transaxle (on front-wheel drive vehicles) for monitoring the output
shaft speed to the road wheels. The output shaft speed is relayed a
pulsing voltage signal to the input interface of the of the ECU 10
and converted into the vehicle speed data vsp. Input information
from the previously-noted engine/vehicle sensors 11, 12, 13, 14,
15, 16, and 20 is transmitted into the input interface of the
electronic control unit (ECU) 10. The ECU 10 usually comprises a
microcomputer. Although it is not clearly shown in FIG. 1, the ECU
10 includes a central processing unit (CPU) that performs necessary
arithmetic calculations, processes informational data, compares
input signals from engine/vehicle sensors to predetermined or
preprogrammed threshold values, and makes necessary decisions of
acceptance, and memories (RAM, ROM), an input/output interface, and
driver circuits for amplification of output signals from the output
interface. The ECU 10 performs data processing actions shown in
FIGS. 2 or 4 which will be fully described later. The output
interface of the ECU 10 is configured to be electronically
connected often through the driver circuits to various electrical
loads, such as the electronically-controlled throttle valve 5, fuel
injector solenoids of the fuel injectors 4, and the spark plugs,
for generating control command signals to operate these electrical
loads. Particularly, in the system of the embodiment, as detailed
in reference to the flow charts shown in FIGS. 2 and 4, the
processor of the ECU 10 arithmetically calculates or estimates the
oxygen storage quantity OSQH (exactly, the quantity of oxygen
stored in the three-way catalyst 6), on the basis of the signals
(AFSABF, (AFSABF2), Ne, Qa, TVO, Te, vsp) from the previously-noted
sensors, and an oxygen adsorption speed ADS.sub.speed of the
three-way catalyst 6. In order to properly control the A/F ratio,
the ECU 10 determines the fuel-injection amount of the injector 4
(the amount of fuel delivered to the cylinder), so that the oxygen
storage quantity OSQH of the three-way catalyst 6 is adjusted to a
desired value (for example, substantially one-half of a limit value
OSQH.sub.LIMIT of the oxygen storage quantity). Also, under a
specified condition (described later), the ECU 10 terminates the
arithmetic operation for the oxygen storage quantity OSQH and then
limits the calculated value (OSQH) of the oxygen storage quantity
to a predetermined limit value OSQH.sub.LIMIT of the quantity of
oxygen stored in the three-way catalyst 6.
[0025] Referring now to FIG. 2, there is shown the first control
routine executed by the ECU 10 incorporated in the A/F ratio
control system of the embodiment. The first control routine shown
in FIG. 2 is executed as time-triggered interrupt routines to be
triggered every predetermined time intervals such as 10
milliseconds.
[0026] At step 1, parameters needed to arithmetically calculate the
oxygen storage quantity OSQH, namely the output AFSABF from the
upstream A/F ratio sensor 11, the oxygen adsorption speed
ADS.sub.speed of the three-way catalyst 6, and the intake-air
quantity Qa (regarded as engine load), and conditional-decision
parameters needed to determine whether specified conditions are
satisfied, namely the engine speed Ne, the throttle opening TVO,
the engine temperature Te, and the vehicle speed vsp, are read.
[0027] At step 2, a test is made to determine whether a specified
arithmetic-calculation initiation condition needed to calculate or
estimate the oxygen storage quantity OSQH of the three-way catalyst
6 is satisfied. In the system of the embodiment, the ECU 10
determines that the specified arithmetic-calculation initiation
condition is met when the three-way catalyst 6 is in its activated
state. In order for the computer to determine or estimate whether
the catalyst 6 reaches a sufficient activation level, there are
various ways, for example, direct temperature measurement of a
temperature of the three-way catalyst 6, or estimation of the
catalyst temperature from the engine temperature Te. In the shown
embodiment, the ECU 10 determines the activated state of the
catalyst 6, depending on whether the engine temperature Te is above
a predetermined temperature value. When the answer to step 2 is in
the negative (NO), the routine proceeds to step 6. Conversely, when
the answer to step 2 is in the affirmative (YES), the routine
proceeds to step 3.
[0028] At step 3, a test is made to determine whether the engine is
out of a fuel-cutoff operating mode (a deceleration fuel-cutoff
operating mode). The presence or absence of the fuel-cutoff
operating mode is determined on the basis of the engine speed Ne,
the throttle opening TVO, and the vehicle speed vsp. The
deceleration fuel-cutoff operating mode is usually executed for
example during down-hill driving or during engine speed limitation
when the maximum allowable engine speed is reached. When the answer
to step 3 is negative (NO), that is, during the fuel cutoff
operating mode, step 8 occurs. Conversely, when the answer to step
3 is affirmative (YES), the routine proceeds to step 4.
[0029] At step 4, the oxygen storage quantity OSQH is
arithmetically calculated or estimated on the basis of the
deviation (divergency) of the A/F ratio AFSABF detected by the
upstream A/F ratio sensor 11 from the stoichiometric A/F ratio
AFSM, by way of the following expression (1).
OSQH={(AFSABF-AFSM)/AFSM}.times.Qa.times.ADS.sub.speed+HSOSQ
(1)
[0030] where AFSABF denotes a current value AFSABF.sub.(n) of the
A/F ratio detected by the upstream A/F sensor 11, AFSM denotes the
stoichiometric A/F ratio, Qa denotes the intake-air quantity,
ADS.sub.speed denotes the oxygen adsorption speed of the three-way
catalyst 6, and HSOSQ means AFSABF.sub.(n-1) and denotes a previous
value of the oxygen storage quantity calculated one cycle
before.
[0031] The previously-noted oxygen adsorption speed ADS.sub.speed
is a variable. That is, the leaner the A/F ratio AFSABF detected by
the upstream A/F ratio sensor 11, the higher the oxygen adsorption
speed ADS.sub.speed. In other words, the richer the A/F ratio
AFSABF detected by the upstream A/F ratio sensor 11, the lower the
oxygen adsorption speed ADS.sub.speed. As can be appreciated from
the expression (1), when the A/F ratio AFSABF detected by the
upstream A/F ratio sensor is a leaner ratio (AFSABF-AFSM >0) in
comparison with the stoichiometric ratio AFSM, the calculated
oxygen storage quantity OSQH tends to increase. To the contrary,
when the A/F ratio AFSABF detected by the upstream A/F ratio sensor
is a richer ratio (AFSABF-AFSM<0) in comparison with the
stoichiometric ratio AFSM, the calculated oxygen storage quantity
OSQH tends to decrease. Then, the calculated value of oxygen
storage quantity, obtained through step 4, is stored in a
predetermined memory address as a current value OSQH.sub.(n).
[0032] At step 5, a deviation (TGOSQH-OSQH) of the calculated
oxygen storage quantity OSQH from a desired value or a
predetermined target oxygen storage quantity TGOSQH is calculated.
The predetermined target oxygen storage quantity TGOSQH is set at a
substantially one-half of the limit value OSQH.sub.LIMIT of oxygen
storage quantity.
[0033] At step 6, a desired A/F ratio ALPHA is arithmetically
calculated on the basis of the deviation (TGOSQH-OSQH) obtained
through step 5, from the following expression (2) for PID control
(proportional-plus-integral-- plus-derivative control). As may be
appreciated from the above, in the system of the embodiment,
proportional-plus-integral-plus-derivative (PID) control in which
the control signal from the ECU is a linear combination of the
error signal, its integral and its derivative, is used as the
feedback control for the A/F ratio.
ALPHA=[AFSM/{1-(TGOSQH-OSQH).times.PID/Qa}-AFSABF]/AFSABF.times.PID
(2)
[0034] where PID denotes a
proportional-plus-integral-plus-derivative gain.
[0035] As can be appreciated from the expression (2), when the
calculated oxygen storage quantity OSQH of the three-way catalyst 6
is greater than the predetermined target oxygen storage quantity
TGOSQH, that is, in case of TGOSQH-OSQH<0, the desired A/F ratio
ALPHA is controlled toward a richer ratio. To the contrary, when
the calculated oxygen storage quantity OSQH of the three-way
catalyst 6 is less than the predetermined target oxygen storage
quantity TGOSQH, that is, in case of TGOSQH-OSQH>0, the desired
A/F ratio ALPHA is controlled toward a leaner ratio.
[0036] At step 7, a fuel-injection amount is determined on the
basis of engine speed Ne, engine load (e.g., the intake-air
quantity Qa), and the desired A/F ratio ALPHA. First, a basic
fuel-injection amount is calculated as K.times.Qa/Ne, where K
denotes a predetermined constant. Second, the fuel-injection amount
is calculated as the product (ALPHA.times.K.times.Qa/Ne) of the
basic fuel-injection amount and the desired A/F ratio ALPHA.
[0037] On the other hand, during the deceleration fuel cutoff mode,
at step 8, a limit check is made to determine whether the
calculated oxygen storage quantity (exactly, a previous value
OSQH.sub.(n-1) of the calculated oxygen storage quantity,
calculated one cycle before) is less than the predetermined limit
value OSQH.sub.LIMIT (the maximum allowable oxygen storage
quantity). When the answer to step 8 is affirmative (YES), that is,
in case of OSQH.sub.LIMIT>OSQH.sub.(n-1), the routine proceeds
to step 9. At step 9, the oxygen storage quantity OSQH is
arithmetically calculated or estimated in the same manner as step
4, and then the calculated value of oxygen storage quantity is
stored in the memory address as the current value OSQH.sub.(n).
Conversely, when the answer to step 8 is negative (NO), that is, in
case of OSQH.sub.LIMIT.ltoreq.OSQH.sub.(n-1), the routine proceeds
to step 10. At step 10, the ECU 10 operates to terminate arithmetic
calculation for the oxygen storage quantity OSQH of the three-way
catalyst 6, for the purpose of estimate limitation of the oxygen
storage quantity. Then, the calculated value of oxygen storage
quantity is limited to or updated by the predetermined limit value
OSQH.sub.LIMIT. In other words, the flow from step 3 via step 8 to
step 10 functions as a limiter (or a limiter circuit) which
prevents the calculated oxygen storage quantity OSQH from exceeding
a specified level, that is, the predetermined limit value
OSQH.sub.LIMIT. After step 10, the routine flows to step 6. During
the fuel cutoff mode, the desired A/F ratio ALPHA is set at "0" at
step 6, and the fuel-injection amount is also set at "0" at step
7.
[0038] With the previously-discussed arrangement, during the
deceleration fuel cutoff where the oxygen storage quantity of the
three-way catalyst will rapidly rise and the limit value (the
maximum allowable oxygen storage quantity) will be reached soon, as
indicated by the vertical arrow in FIGS. 3A-3C, the ECU 10
terminates the arithmetic operation for the oxygen storage quantity
immediately when the calculated value OSQH.sub.(n-1) of oxygen
storage quantity reaches the predetermined limit value
OSQH.sub.LIMIT. As a result of this, during the deceleration fuel
cutoff, the ECU 10 preserves the current value OSQH.sub.(n) of
oxygen storage quantity at the limit value OSQH.sub.LIMIT. FIG. 3A
shows variations in the A/F ratio AFSABF2 based on the percentage
of oxygen contained within the engine exhaust gases leaving the
catalyst 6 and detected by the downstream A/F ratio sensor 20. In
FIG. 3A, a horizontal line indicated by lambda=1 shows the
stoichiometric ratio. In FIG. 3B, the upper horizontal straight
broken line indicates the predetermined limit value OSQH.sub.LIMIT
of oxygen storage quantity, the solid polygonal line indicates
variations in the calculated value OSQH.sub.(n) of oxygen storage
quantity OSQH, and the one-dotted line indicates variations in the
desired A/F ratio ALPHA. In FIG. 3B, the (trapezoidal) hypothetical
line above the upper horizontal straight broken line indicating the
predetermined oxygen-storage-quantity limit value OSQH.sub.LIMIT
shows variations in the calculated value of the oxygen storage
quantity OSQH, produced by the conventional system, during the
deceleration fuel shutoff. In FIG. 3C, the central pulsed area
indicates the deceleration fuel cutoff operating-mode zone. As
discussed above, even during the deceleration fuel cutoff, there is
no difference between the calculated oxygen storage quantity
OSQH.sub.(n) and the limit value OSQH.sub.LIMIT of oxygen storage
quantity of the three-way catalyst 6. This ensures very precise
control of A/F ratio, even when the engine/vehicle operating
condition is recovered from a specific engine/vehicle operating
condition containing during deceleration fuel cutoff to a normal
operating mode.
[0039] Referring now to FIG. 4, there is shown the second control
routine executed by the ECU 10 incorporated in the A/F ratio
control system of the embodiment. The second control routine shown
in FIG. 4 is executed as time-triggered interrupt routines to be
triggered every predetermined time intervals such as 10
milliseconds. The second routine is aimed at executing proper and
precise A/F control not only during fuel cutoff, but also when the
calculated oxygen storage quantity (exactly, the previous value
OSQH.sub.(n-1) of the calculated oxygen storage quantity) is above
the predetermined limit value OSQH.sub.LIMIT of the three-way
catalyst 6.
[0040] At step 21, parameters needed to arithmetically calculate
the oxygen storage quantity OSQH, namely the output AFSABF from the
upstream A/F ratio sensor 11, the oxygen adsorption speed
ADS.sub.speed of the three-way catalyst 6, and the intake-air
quantity Qa (regarded as engine load), and conditional-decision
parameters needed to determine whether specified conditions are
satisfied, namely the engine speed Ne, the throttle opening TVO,
the engine temperature Te, the vehicle speed vsp and the output
AFSABF2 from the downstream A/F ratio sensor 20 are read.
[0041] At step 22, a test is made to determine whether a specified
arithmetic-calculation initiation condition needed to calculate or
estimate the oxygen storage quantity OSQH of the three-way catalyst
6 is satisfied. The ECU 10 determines that the specified
arithmetic-calculation initiation condition is met when the
three-way catalyst 6 is in its activated state. Actually, the ECU
10 determines the activated state of the catalyst 6, depending on
whether the engine temperature Te is above a predetermined
temperature value. When the answer to step 22 is in the negative
(NO), the routine proceeds to step 26. Conversely, when the answer
to step 22 is in the affirmative (YES), the routine proceeds to
step 23.
[0042] At step 23, a check is made to determine whether the A/F
ratio AFSABF2, which is detected by the downstream A/F ratio sensor
20 and based on the percentage of oxygen contained within the
engine exhaust gases leaving the three-way catalyst 6, is a lean
A/F ratio. When the answer to step 23 is affirmative (YES), that
is, when the A/F ratio AFSABF2 detected by the downstream A/F ratio
sensor 20 is a lean A/F ratio, the routine proceeds to step 28.
Conversely, when the answer to step 23 is negative (NO), that is,
when the A/F ratio AFSABF2 is a stoichiometric A/F ratio or a rich
A/F ratio, the routine proceeds to step 24.
[0043] At step 24, in the same manner as step 4, the oxygen storage
quantity OSQH is arithmetically calculated or estimated on the
basis of the deviation of the A/F ratio AFSABF detected by the
upstream A/F ratio sensor 11 and based on the percentage of oxygen
contained within the engine exhaust gases entering the three-way
catalyst 6 from the stoichiometric air/fuel ratio AFSM, by way of
the previously-discussed expression
OSQH={(AFSABF-AFSM)/AFSM}.times.Qa.times.ADS.sub.speed+HSOSQ.
[0044] Thereafter, at step 25, in the same manner as step 5, a
deviation (TGOSQH-OSQH) of the calculated oxygen storage quantity
OSQH from a predetermined target oxygen storage quantity TGOSQH is
calculated.
[0045] At step 26, in the same manner as step 6, a desired A/F
ratio ALPHA is arithmetically calculated on the basis of the
deviation (TGOSQH-OSQH) obtained through step 25, from the
previously-discussed expression
ALPHA=[AFSM/{1-(TGOSQH-OSQH).times.PID/Qa}-AFSABF]/AFSABF.times.PID,
where PID denotes a proportional-plus-integral-plus-derivative
gain.
[0046] At step 27, in the same manner as step 7, a fuel-injection
amount is determined on the basis of engine speed Ne, engine load
(e.g., the intake-air quantity Qa), and the desired A/F ratio
ALPHA. First, a basic fuel-injection amount is calculated as
K.times.Qa/Ne, where K denotes a predetermined constant. Second,
the fuel-injection amount is calculated as the product
(ALPHA.times.K.times.Qa/Ne) of the basic fuel-injection amount and
the desired A/F ratio ALPHA.
[0047] In contrast to the above, when the A/F ratio AFSABF2, which
is detected by the downstream A/F ratio sensor 20 and based on the
percentage of oxygen contained within the engine exhaust gases
leaving the three-way catalyst 6, is a lean A/F ratio, the routine
proceeds from step 23 to step 28. At step 28, a limit check is made
to determine whether the calculated oxygen storage quantity
(exactly, a previous value OSQH.sub.(n-1) of the calculated oxygen
storage quantity, calculated one cycle before) is less than the
predetermined limit value OSQH.sub.LIMIT (the maximum allowable
oxygen storage quantity). When the answer to step 28 is affirmative
(YES), that is, in case of OSQH.sub.LIMIT>OSQH.sub.(- n-1), the
routine flows to step 24 at which the oxygen storage quantity OSQH
is calculated or estimated by way of the previously-discussed
expression (1), and then the calculated value of oxygen storage
quantity is stored in the memory address as the current value
OSQH.sub.(n). Conversely, when the answer to step 28 is negative
(NO), that is, in case of OSQH.sub.LIMIT.ltoreq.OSQH.sub.(n-1), the
routine proceeds to step 29. At step 29, the ECU 10 operates to
terminate arithmetic calculation for the oxygen storage quantity
OSQH of the three-way catalyst 6, for the purpose of estimate
limitation of the oxygen storage quantity. Then, the calculated
value of oxygen storage quantity is limited to or updated by the
predetermined limit value OSQH.sub.LIMIT. In other words, the flow
from step 23 via step 28 to step 29 functions as a limiter circuit
which prevents the calculated oxygen storage quantity OSQH from
exceeding a specified level, that is, the predetermined limit value
OSQH.sub.LIMIT. After step 29, the routine flows to step 25.
[0048] As set forth above, according to the second routine shown in
FIG. 4, as seen in FIGS. 3A-3C, when the A/F ratio AFSABF2 based on
the percentage of oxygen contained within the engine exhaust gases
leaving the three-way catalyst 6 becomes a lean A/F ratio, and then
the calculated value (the previous value OSQH.sub.(n-1)) of the
oxygen storage quantity reaches the limit value OSQH.sub.LIMIT, the
ECU 10 terminates the arithmetic operation for the oxygen storage
quantity at once. As a consequence, when the necessary conditions,
namely a lean A/F ratio AFSABF2 and OSQH.sub.LIMIT.ltoreq.OSQH, are
met, the ECU 10 preserves the current value OSQH.sub.(n) of oxygen
storage quantity at the limit value OSQH.sub.LIMIT. Thus, when the
previously-noted necessary conditions are met, there is no
difference between the calculated oxygen storage quantity
OSQH.sub.(n) and the limit value OSQH.sub.LIMIT of oxygen storage
quantity of the three-way catalyst 6. This ensures very precise
control of A/F ratio, based on the estimated or calculated value of
oxygen storage quantity of the catalyst, even when the
engine/vehicle operating condition is recovered from the lean
operating condition to a correct (stoichiometric) operating
condition, after a lean operating condition continues for a while
due to some factor.
[0049] Referring now to FIG. 5, there is shown the third control
routine executed by the ECU 10 incorporated in the A/F ratio
control system of the embodiment. The third control routine shown
in FIG. 5 is similar to the second control routine shown in FIG. 4,
except that steps 23 and 28 included in the routine shown in FIG. 4
are replaced with step 30 included in the routine shown in FIG. 5.
Thus, the same step numbers used to designate steps in the routine
shown in FIG. 4 will be applied to the corresponding step numbers
used in the modified arithmetic processing shown in FIG. 5, for the
purpose of comparison of the two different interrupt routines. Step
30 will be hereinafter described in detail with reference to the
accompanying drawings, while detailed description of steps 21, 22,
and 24-29 will be omitted because the above description thereon
seems to be self-explanatory. The third routine is aimed at
executing proper and precise A/F control not only during fuel
cutoff, but also when the A/F ratio AFSABF2 is leaner than a
predetermined lean A/F criterion.
[0050] At step 30, a check is made to determine whether the A/F
ratio AFSABF2, which is detected by the downstream A/F ratio sensor
20 and based on the percentage of oxygen contained within the
engine exhaust gases leaving the three-way catalyst 6, is leaner
than a predetermined lean A/F criterion. When the answer to step 30
is in the negative (NO), the routine proceeds to step 24, and then
flows through steps 25 and 26 to step 27. Conversely, when the
answer to step 30 is in the affirmative (YES), the routine proceeds
to step 29 where the ECU 10 operates to terminate arithmetic
calculation for the oxygen storage quantity OSQH, and then the
calculated value of oxygen storage quantity is limited to or
updated by a predetermined limit value OSQH.sub.LIMIT. That is to
say, the flow from step 30 to step 29 serves as a limiter circuit
which prevents the calculated oxygen storage quantity OSQH from
exceeding a specified level. Thereafter, the routine proceeds from
step 29 to step 25. The third routine shown in FIG. 5 provides the
same effects as the second routine shown in FIG. 4.
[0051] The entire contents of Japanese Patent Application Nos.
P11-55693 (filed Mar. 3, 1999) and P2000-44723 (filed Feb. 22,
2000) are incorporated herein by reference.
[0052] While the foregoing is a description of the preferred
embodiments carried out the invention, it will be understood that
the invention is not limited to the particular embodiments shown
and described herein, but that various changes and modifications
may be made without departing from the scope or spirit of this
invention as defined by the following claims.
* * * * *