WO2015105160A1 - 内燃機関の制御装置 - Google Patents
内燃機関の制御装置 Download PDFInfo
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- WO2015105160A1 WO2015105160A1 PCT/JP2015/050406 JP2015050406W WO2015105160A1 WO 2015105160 A1 WO2015105160 A1 WO 2015105160A1 JP 2015050406 W JP2015050406 W JP 2015050406W WO 2015105160 A1 WO2015105160 A1 WO 2015105160A1
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- Prior art keywords
- fuel ratio
- air
- rich
- oxygen
- purification catalyst
- Prior art date
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- 238000002485 combustion reaction Methods 0.000 title claims abstract description 65
- 239000000446 fuel Substances 0.000 claims abstract description 1547
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims abstract description 355
- 239000001301 oxygen Substances 0.000 claims abstract description 355
- 229910052760 oxygen Inorganic materials 0.000 claims abstract description 355
- 238000012937 correction Methods 0.000 claims abstract description 233
- 238000000746 purification Methods 0.000 claims abstract description 207
- 239000003054 catalyst Substances 0.000 claims abstract description 206
- 239000007789 gas Substances 0.000 claims abstract description 163
- 230000001133 acceleration Effects 0.000 claims abstract description 12
- 238000011144 upstream manufacturing Methods 0.000 claims description 249
- 230000007812 deficiency Effects 0.000 claims description 127
- 230000001186 cumulative effect Effects 0.000 claims description 92
- 238000012423 maintenance Methods 0.000 claims description 40
- 230000003247 decreasing effect Effects 0.000 claims description 19
- MWUXSHHQAYIFBG-UHFFFAOYSA-N nitrogen oxide Inorganic materials O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 41
- 230000007423 decrease Effects 0.000 description 36
- 238000000034 method Methods 0.000 description 36
- 238000002347 injection Methods 0.000 description 31
- 239000007924 injection Substances 0.000 description 31
- 230000008569 process Effects 0.000 description 30
- 230000009467 reduction Effects 0.000 description 16
- 238000010586 diagram Methods 0.000 description 10
- 230000008859 change Effects 0.000 description 6
- 206010021143 Hypoxia Diseases 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 3
- 230000006835 compression Effects 0.000 description 3
- 238000007906 compression Methods 0.000 description 3
- 230000003111 delayed effect Effects 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 3
- 238000013459 approach Methods 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 230000009471 action Effects 0.000 description 1
- 230000004913 activation Effects 0.000 description 1
- 230000002457 bidirectional effect Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000004904 shortening Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Images
Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2451—Methods of calibrating or learning characterised by what is learned or calibrated
- F02D41/2454—Learning of the air-fuel ratio control
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
- F01N11/007—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
- F01N13/008—Mounting or arrangement of exhaust sensors in or on exhaust apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
- F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
- F01N3/0864—Oxygen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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- F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
- F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
- F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
- F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
- F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N9/00—Electrical control of exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/021—Introducing corrections for particular conditions exterior to the engine
- F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
- F02D41/0295—Control according to the amount of oxygen that is stored on the exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1439—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the position of the sensor
- F02D41/1441—Plural sensors
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1444—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases
- F02D41/1454—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the characteristics of the combustion gases the characteristics being an oxygen content or concentration or the air-fuel ratio
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
- F02D41/1475—Regulating the air fuel ratio at a value other than stoichiometry
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2441—Methods of calibrating or learning characterised by the learning conditions
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/2406—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using essentially read only memories
- F02D41/2425—Particular ways of programming the data
- F02D41/2429—Methods of calibrating or learning
- F02D41/2477—Methods of calibrating or learning characterised by the method used for learning
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/24—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means
- F02D41/26—Electrical control of supply of combustible mixture or its constituents characterised by the use of digital means using computer, e.g. microprocessor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
- F01N2570/16—Oxygen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
- F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
- F01N2900/06—Parameters used for exhaust control or diagnosing
- F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
- F01N2900/1624—Catalyst oxygen storage capacity
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D2200/00—Input parameters for engine control
- F02D2200/02—Input parameters for engine control the parameters being related to the engine
- F02D2200/08—Exhaust gas treatment apparatus parameters
- F02D2200/0814—Oxygen storage amount
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- F02D41/00—Electrical control of supply of combustible mixture or its constituents
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/14—Introducing closed-loop corrections
- F02D41/1438—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor
- F02D41/1473—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method
- F02D41/1474—Introducing closed-loop corrections using means for determining characteristics of the combustion gases; Sensors therefor characterised by the regulation method by detecting the commutation time of the sensor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/12—Improving ICE efficiencies
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present invention relates to a control device for an internal combustion engine.
- control devices for internal combustion engines are widely known in which an air-fuel ratio sensor is provided in the exhaust passage of the internal combustion engine and the amount of fuel supplied to the internal combustion engine is controlled based on the output of the air-fuel ratio sensor.
- an air-fuel ratio sensor provided upstream of an exhaust purification catalyst provided in an engine exhaust passage and an oxygen sensor provided downstream is known (for example, Patent Documents 1 to 4). etc).
- JP 2012-017694 A JP 2013-060927 A JP 2008-274895 A JP 2002-364427 A JP 2009-036024 A JP-A-4-231636
- the oxygen storage amount of the exhaust purification catalyst becomes equal to or higher than the switching reference storage amount while the target air-fuel ratio is the lean air-fuel ratio
- the target air-fuel ratio is richer than the stoichiometric air-fuel ratio (hereinafter, “ It is set to “rich air-fuel ratio”.
- the switching reference storage amount is set to an amount smaller than the maximum storable oxygen amount in a new state.
- the target air-fuel ratio is switched from the lean air-fuel ratio to the rich air-fuel ratio before the oxygen storage amount of the exhaust purification catalyst reaches the maximum storable oxygen amount. Therefore, according to such control, the exhaust gas having a lean air-fuel ratio hardly flows out from the exhaust purification catalyst, and as a result, the outflow of NOx from the exhaust purification catalyst can be suppressed.
- the control when the control is performed to alternately switch the target air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio, the control is performed so that the target air-fuel ratio becomes a constant air-fuel ratio such as the stoichiometric air-fuel ratio.
- the learning value cannot be updated by the same method as in the case where it is performed.
- the learning value update rate cannot be changed in the same manner as when control is performed so that the target air-fuel ratio becomes a constant air-fuel ratio.
- the control for alternately switching the target air-fuel ratio between the rich air-fuel ratio and the lean air-fuel ratio it is necessary to consider a new method for changing the learning value update speed.
- the method for changing the learning value update rate is used as a method for changing the learning value update rate. It is possible to do.
- the update speed of the learning value is changed by such a method, the learning value may be excessively captured in some cases, and as a result, the convergence of the learning value may be delayed.
- an object of the present invention is to appropriately update the learning value update speed even when the target air-fuel ratio is controlled to alternately switch between the rich air-fuel ratio and the lean air-fuel ratio. It is to provide an internal combustion engine that can be changed.
- an exhaust purification catalyst that is disposed in an exhaust passage of an internal combustion engine and that can store oxygen
- an exhaust purification catalyst that is disposed downstream of the exhaust purification catalyst in the exhaust flow direction
- a control device for an internal combustion engine comprising a downstream air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing out from an exhaust purification catalyst, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio.
- the target air-fuel ratio is alternately switched between a rich set air-fuel ratio richer than the stoichiometric air-fuel ratio and a lean set air-fuel ratio leaner than the stoichiometric air-fuel ratio.
- Learning priority condition is satisfied when it is necessary to promote the correction of the parameters by the learning control to when satisfied, the degree of richness of the rich set air-fuel ratio is made to increase, the control device of the internal combustion engine is provided.
- the target air-fuel ratio is switched to the lean set air-fuel ratio when the air-fuel ratio detected by the downstream air-fuel ratio sensor becomes equal to or less than the rich determination air-fuel ratio.
- the exhaust purification catalyst is switched to the rich set air-fuel ratio when the oxygen storage amount of the exhaust purification catalyst is equal to or greater than a predetermined switching reference storage amount smaller than the maximum storable oxygen amount, and when the learning promotion condition is satisfied, the switching is performed. The standard occlusion amount is reduced.
- an exhaust purification catalyst that is disposed in the exhaust passage of the internal combustion engine and that can store oxygen, and is disposed downstream of the exhaust purification catalyst in the exhaust flow direction and
- a control device for an internal combustion engine comprising a downstream air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas flowing out from an exhaust purification catalyst, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst becomes a target air-fuel ratio.
- the target air-fuel ratio is leaner than the stoichiometric air-fuel ratio when the air-fuel ratio detected by the downstream air-fuel ratio sensor becomes equal to or less than the rich determination air-fuel ratio.
- the rich set air-fuel ratio that is richer than the stoichiometric air-fuel ratio when the oxygen storage amount of the exhaust purification catalyst becomes equal to or greater than a predetermined switching reference storage amount that is less than the maximum storable oxygen amount.
- the lean degree of the lean set air-fuel ratio is increased.
- the lean set air-fuel ratio is maintained as it is even when the learning promotion condition is satisfied.
- the oxygen storage amount of the exhaust purification catalyst is changed to the switching reference amount after the target air-fuel ratio is switched to a lean set air-fuel ratio.
- the first oxygen amount integrated value which is the absolute value of the cumulative oxygen excess / deficiency in the first period until the above is reached, and the downstream air-fuel ratio sensor detected after switching the target air-fuel ratio to the rich set air-fuel ratio.
- the learning promotion condition is such that a difference between the first oxygen amount integrated value and the second oxygen amount integrated value is equal to or greater than a predetermined acceleration determination reference value. Is established.
- the learning promotion condition is detected by the downstream air-fuel ratio sensor when the target air-fuel ratio is a rich set air-fuel ratio.
- the learning promotion condition is that, when the target air-fuel ratio is a rich air-fuel ratio, the air-fuel ratio detected by the downstream air-fuel ratio sensor is the stoichiometric air-fuel ratio. This is established when the air-fuel ratio is maintained leaner than the lean determination air-fuel ratio over the lean air-fuel ratio maintenance determination time shorter than the acceleration determination time.
- the learning control detects the downstream air-fuel ratio sensor when the target air-fuel ratio is a rich set air-fuel ratio.
- the learning control detects the downstream air-fuel ratio sensor when the target air-fuel ratio is a rich set air-fuel ratio.
- the parameter related to the air-fuel ratio is corrected so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst changes to the rich side.
- the oxygen storage amount of the exhaust purification catalyst is changed to the switching reference amount after the target air-fuel ratio is switched to a lean set air-fuel ratio.
- the absolute value of the cumulative oxygen excess / deficiency after the target air-fuel ratio is switched to the rich set air-fuel ratio with respect to the first oxygen amount integrated value, which is the absolute value of the cumulative oxygen excess / deficiency in the first period until the above is reached.
- the parameter relating to the air-fuel ratio is corrected so that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst changes to the rich side in the feedback control.
- the parameter relating to the air-fuel ratio is any one of the target air-fuel ratio, the fuel supply amount, and the air-fuel ratio serving as a control center.
- the upstream side of the exhaust purification catalyst that is disposed upstream of the exhaust flow direction and detects the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- the parameter is an output value of the upstream air-fuel ratio sensor.
- an internal combustion engine capable of appropriately changing the update speed of the learning value even when the target air-fuel ratio is controlled to alternately switch between the rich air-fuel ratio and the lean air-fuel ratio. Provided.
- FIG. 1 is a diagram schematically showing an internal combustion engine in which a control device of the present invention is used.
- FIG. 2 is a graph showing the relationship between the oxygen storage amount of the exhaust purification catalyst and the NOx concentration or HC, CO concentration in the exhaust gas flowing out from the exhaust purification catalyst.
- FIG. 3 is a diagram showing the relationship between the sensor applied voltage and the output current at each exhaust air-fuel ratio.
- FIG. 4 is a diagram showing the relationship between the exhaust air-fuel ratio and the output current when the sensor applied voltage is made constant.
- FIG. 5 is a time chart of the air-fuel ratio correction amount when the air-fuel ratio control is performed.
- FIG. 6 is a time chart of the air-fuel ratio correction amount when the air-fuel ratio control is performed.
- FIG. 7 is a time chart of the air-fuel ratio correction amount and the like when there is a deviation in the output value of the upstream air-fuel ratio sensor.
- FIG. 8 is a time chart of the air-fuel ratio correction amount and the like when there is a deviation in the output value of the upstream air-fuel ratio sensor.
- FIG. 9 is a time chart of the air-fuel ratio correction amount and the like when performing normal learning.
- FIG. 10 is a time chart of the air-fuel ratio correction amount when the output value of the upstream air-fuel ratio sensor has a large deviation.
- FIG. 11 is a time chart of the air-fuel ratio correction amount when the output value of the upstream air-fuel ratio sensor has a large deviation.
- FIG. 12 is a time chart of the air-fuel ratio correction amount and the like when performing theoretical air-fuel ratio sticking learning.
- FIG. 13 is a time chart of the air-fuel ratio correction amount and the like when performing lean stuck learning or the like.
- FIG. 14 is a time chart of the air-fuel ratio correction amount and the like when performing learning promotion control.
- FIG. 15 is a functional block diagram of the control device.
- FIG. 16 is a flowchart showing a control routine for calculation control of the air-fuel ratio correction amount.
- FIG. 17 is a flowchart showing a control routine of normal learning control.
- FIG. 18 is a flowchart showing a control routine for sticking learning control.
- FIG. 19 is a flowchart showing a control routine for learning promotion control.
- FIG. 16 is a flowchart showing a control routine for calculation control of the air-fuel ratio correction amount.
- FIG. 17 is a flowchart showing a control routine of normal learning control.
- FIG. 18 is a flowchart
- FIG. 20 is a diagram showing the relationship between the exhaust air-fuel ratio and the output current when the sensor applied voltage is made constant.
- FIG. 21 is a time chart of the air-fuel ratio correction amount and the like when a reduction deviation occurs in the output air-fuel ratio of the downstream air-fuel ratio sensor.
- FIG. 22 is a time chart of the air-fuel ratio correction amount and the like when a reduction deviation occurs in the output air-fuel ratio of the downstream air-fuel ratio sensor.
- FIG. 23 is a flowchart showing a control routine of sticking learning control according to the second embodiment.
- FIG. 1 is a diagram schematically showing an internal combustion engine in which a control device according to a first embodiment of the present invention is used.
- 1 is an engine body
- 2 is a cylinder block
- 3 is a piston that reciprocates in the cylinder block
- 4 is a cylinder head fixed on the cylinder block 2
- 5 is between the piston 3 and the cylinder head 4.
- 6 is an intake valve
- 7 is an intake port
- 8 is an exhaust valve
- 9 is an exhaust port.
- the intake valve 6 opens and closes the intake port 7, and the exhaust valve 8 opens and closes the exhaust port 9.
- a spark plug 10 is disposed at the center of the inner wall surface of the cylinder head 4, and a fuel injection valve 11 is disposed around the inner wall surface of the cylinder head 4.
- the spark plug 10 is configured to generate a spark in response to the ignition signal.
- the fuel injection valve 11 injects a predetermined amount of fuel into the combustion chamber 5 according to the injection signal.
- the fuel injection valve 11 may be arranged so as to inject fuel into the intake port 7.
- gasoline having a theoretical air-fuel ratio of 14.6 is used as the fuel.
- the internal combustion engine of the present embodiment may use other fuels.
- the intake port 7 of each cylinder is connected to a surge tank 14 via a corresponding intake branch pipe 13, and the surge tank 14 is connected to an air cleaner 16 via an intake pipe 15.
- the intake port 7, the intake branch pipe 13, the surge tank 14, and the intake pipe 15 form an intake passage.
- a throttle valve 18 driven by a throttle valve drive actuator 17 is disposed in the intake pipe 15. The throttle valve 18 is rotated by a throttle valve drive actuator 17 so that the opening area of the intake passage can be changed.
- the exhaust port 9 of each cylinder is connected to an exhaust manifold 19.
- the exhaust manifold 19 has a plurality of branches connected to the exhaust ports 9 and a collective part in which these branches are assembled.
- a collecting portion of the exhaust manifold 19 is connected to an upstream casing 21 containing an upstream exhaust purification catalyst 20.
- the upstream casing 21 is connected to a downstream casing 23 containing a downstream exhaust purification catalyst 24 via an exhaust pipe 22.
- the exhaust port 9, the exhaust manifold 19, the upstream casing 21, the exhaust pipe 22, and the downstream casing 23 form an exhaust passage.
- An electronic control unit (ECU) 31 comprises a digital computer, and is connected to each other via a bidirectional bus 32, a RAM (Random Access Memory) 33, a ROM (Read Only Memory) 34, a CPU (Microprocessor) 35, and an input.
- a port 36 and an output port 37 are provided.
- An air flow meter 39 for detecting the flow rate of air flowing through the intake pipe 15 is disposed in the intake pipe 15, and the output of the air flow meter 39 is input to the input port 36 via the corresponding AD converter 38.
- an upstream air-fuel ratio sensor (upstream air-fuel ratio detection) that detects an air-fuel ratio of exhaust gas flowing through the exhaust manifold 19 (that is, exhaust gas flowing into the upstream-side exhaust purification catalyst 20) is provided at a collecting portion of the exhaust manifold 19.
- Device 40 is arranged in the exhaust pipe 22 in the exhaust pipe 22, the downstream side that detects the air-fuel ratio of the exhaust gas that flows in the exhaust pipe 22 (that is, the exhaust gas that flows out of the upstream side exhaust purification catalyst 20 and flows into the downstream side exhaust purification catalyst 24).
- An air-fuel ratio sensor (downstream air-fuel ratio detection device) 41 is arranged. The outputs of these air-fuel ratio sensors 40 and 41 are also input to the input port 36 via the corresponding AD converter 38.
- a load sensor 43 that generates an output voltage proportional to the amount of depression of the accelerator pedal 42 is connected to the accelerator pedal 42, and the output voltage of the load sensor 43 is input to the input port 36 via the corresponding AD converter 38.
- the crank angle sensor 44 generates an output pulse every time the crankshaft rotates 15 degrees, and this output pulse is input to the input port 36.
- the CPU 35 calculates the engine speed from the output pulse of the crank angle sensor 44.
- the output port 37 is connected to the spark plug 10, the fuel injection valve 11, and the throttle valve drive actuator 17 via the corresponding drive circuit 45.
- the ECU 31 functions as a control device that controls the internal combustion engine.
- the internal combustion engine which concerns on this embodiment is a non-supercharging internal combustion engine which uses gasoline as a fuel
- the structure of the internal combustion engine which concerns on this invention is not limited to the said structure.
- an internal combustion engine according to the present invention is different from the above internal combustion engine in terms of cylinder arrangement, fuel injection mode, intake / exhaust system configuration, valve mechanism configuration, presence / absence of a supercharger, and supercharging mode. There may be.
- the exhaust purification catalysts 20 and 24 are three-way catalysts having an oxygen storage capacity.
- the exhaust purification catalysts 20 and 24 are made of a noble metal having a catalytic action (for example, platinum (Pt)) and a substance having an oxygen storage capacity (for example, ceria (CeO 2 )) on a base material made of ceramic. It is supported.
- the exhaust purification catalysts 20 and 24 When the exhaust purification catalysts 20 and 24 reach a predetermined activation temperature, the exhaust purification catalysts 20 and 24 exhibit an oxygen storage capability in addition to the catalytic action of simultaneously purifying unburned gas (HC, CO, etc.) and nitrogen oxides (NOx).
- HC, CO, etc. unburned gas
- NOx nitrogen oxides
- the exhaust purification catalysts 20, 24 are such that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalysts 20, 24 is leaner than the stoichiometric air-fuel ratio (lean air-fuel ratio). Sometimes it stores oxygen in the exhaust gas. On the other hand, the exhaust purification catalysts 20, 24 release the oxygen stored in the exhaust purification catalysts 20, 24 when the air-fuel ratio of the inflowing exhaust gas is richer than the stoichiometric air-fuel ratio (rich air-fuel ratio).
- the exhaust purification catalysts 20 and 24 have a catalytic action and an oxygen storage capacity, and thus have a NOx and unburned gas purification action according to the oxygen storage amount. That is, when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalysts 20, 24 is a lean air-fuel ratio, as shown in FIG. 2A, the exhaust gas is exhausted by the exhaust purification catalysts 20, 24 when the oxygen storage amount is small. The oxygen inside is occluded. Along with this, NOx in the exhaust gas is reduced and purified.
- the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalysts 20, 24 is a rich air-fuel ratio, as shown in FIG. 2B
- the exhaust purification catalysts 20, 24 store the exhaust gas.
- the released oxygen is released and the unburned gas in the exhaust gas is oxidized and purified.
- the oxygen storage amount decreases, the concentration of unburned gas in the exhaust gas flowing out from the exhaust purification catalysts 20 and 24 sharply increases with a certain storage amount in the vicinity of zero (Crowlim in the figure) as a boundary.
- exhaust purification catalysts 20 and 24 used in the present embodiment, NOx and unburned in the exhaust gas according to the air-fuel ratio and oxygen storage amount of the exhaust gas flowing into the exhaust purification catalysts 20 and 24. Gas purification characteristics change.
- the exhaust purification catalysts 20 and 24 may be different from the three-way catalyst as long as they have a catalytic action and an oxygen storage capacity.
- FIG. 3 is a diagram showing the voltage-current (VI) characteristics of the air-fuel ratio sensors 40 and 41 in the present embodiment
- FIG. 4 shows the air-fuel ratio sensors 40 and 41 when the applied voltage is kept constant.
- 2 is a diagram showing a relationship between an air-fuel ratio (hereinafter referred to as “exhaust air-fuel ratio”) of exhaust gas flowing around and an output current I;
- exhaust air-fuel ratio an air-fuel ratio (hereinafter referred to as “exhaust air-fuel ratio”) of exhaust gas flowing around and an output current I;
- exhaust air-fuel ratio sensors having the same configuration are used as the air-fuel ratio sensors 40 and 41.
- the output current I increases as the exhaust air-fuel ratio increases (lean).
- the VI line at each exhaust air-fuel ratio has a region substantially parallel to the V-axis, that is, a region where the output current hardly changes even when the sensor applied voltage changes. This voltage region is referred to as a limiting current region, and the current at this time is referred to as a limiting current.
- the limit current region and limit current when the exhaust air-fuel ratio is 18 are indicated by W 18 and I 18 , respectively. Therefore, it can be said that the air-fuel ratio sensors 40 and 41 are limit current type air-fuel ratio sensors.
- FIG. 4 is a diagram showing the relationship between the exhaust air-fuel ratio and the output current I when the applied voltage is kept constant at about 0.45V.
- the air-fuel ratio sensors 40 and 41 the exhaust air-fuel ratio becomes higher so that the output current I from the air-fuel ratio sensors 40 and 41 becomes larger as the exhaust air-fuel ratio becomes higher (that is, the leaner the air-fuel ratio).
- the output current changes linearly (in proportion).
- the air-fuel ratio sensors 40 and 41 are configured such that the output current I becomes zero when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio. Further, when the exhaust air-fuel ratio becomes larger than a certain value or when it becomes smaller than a certain value, the ratio of the change in the output current to the change in the exhaust air-fuel ratio becomes smaller.
- limit current type air-fuel ratio sensors are used as the air-fuel ratio sensors 40 and 41.
- any air-fuel ratio sensor such as an air-fuel ratio sensor that is not a limit current type may be used as the air-fuel ratio sensors 40 and 41.
- the air-fuel ratio sensors 40 and 41 may be air-fuel ratio sensors having different structures.
- target air-fuel ratio setting control is performed to set the target air-fuel ratio based on the output air-fuel ratio of the downstream air-fuel ratio sensor 41 and the like.
- the target air-fuel ratio setting control when the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes a rich air-fuel ratio, the target air-fuel ratio is set to the lean set air-fuel ratio, and then maintained at that air-fuel ratio.
- the lean set air-fuel ratio is a predetermined air-fuel ratio that is somewhat leaner than the stoichiometric air-fuel ratio (the air-fuel ratio serving as the control center), and is, for example, 14.65 to 20, preferably 14.65 to 18, more preferably about 14.65 to 16.
- the lean set air-fuel ratio can also be expressed as an air-fuel ratio obtained by adding a lean correction amount to an air-fuel ratio (in this embodiment, the theoretical air-fuel ratio) serving as a control center.
- the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes less than the rich determination air-fuel ratio (for example, 14.55) that is slightly richer than the stoichiometric air-fuel ratio, the downstream air-fuel ratio is reduced. It is determined that the output air-fuel ratio of the sensor 41 has become a rich air-fuel ratio.
- the oxygen excess / deficiency is defined as an excess oxygen amount or an insufficient oxygen amount (excess unburned gas, etc.) when the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is set to the stoichiometric air-fuel ratio. Amount).
- the target air-fuel ratio is the lean set air-fuel ratio
- oxygen in the exhaust gas flowing into the upstream side exhaust purification catalyst 20 becomes excessive, and this excess oxygen is stored in the upstream side exhaust purification catalyst 20. Therefore, it can be said that the integrated value of oxygen excess / deficiency (hereinafter referred to as “accumulated oxygen excess / deficiency”) represents the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20.
- the oxygen excess / deficiency amount is calculated by estimating the intake air amount into the combustion chamber 5 calculated based on the output air-fuel ratio of the upstream air-fuel ratio sensor 40, the output of the air flow meter 39, or the like, or the fuel injection valve. 11 is performed based on the amount of fuel supplied from 11 or the like. Specifically, the oxygen excess / deficiency OED is calculated by, for example, the following formula (1).
- ODE 0.23 ⁇ Qi / (AFup-AFR) (1)
- 0.23 is the oxygen concentration in the air
- Qi is the fuel injection amount
- AFup is the output air-fuel ratio of the upstream air-fuel ratio sensor 40
- AFR is the air-fuel ratio that is the control center (the theoretical air-fuel ratio in this embodiment).
- the lean set empty is used until then.
- the target air-fuel ratio that was the fuel ratio is made the rich set air-fuel ratio, and then maintained at that air-fuel ratio.
- the rich set air-fuel ratio is a predetermined air-fuel ratio that is somewhat richer than the stoichiometric air-fuel ratio (the air-fuel ratio that becomes the control center), for example, 12 to 14.58, preferably 13 to 14.57, More preferably, it is about 14 to 14.55.
- the rich set air-fuel ratio is set to be richer than the rich determination air-fuel ratio described above.
- the rich set air-fuel ratio can also be expressed as an air-fuel ratio obtained by subtracting the rich correction amount from the air-fuel ratio that is the control center (the theoretical air-fuel ratio in the present embodiment).
- the difference (rich degree) of the rich set air-fuel ratio from the stoichiometric air-fuel ratio is set to be equal to or less than the difference (lean degree) of the lean set air-fuel ratio from the stoichiometric air-fuel ratio.
- the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is alternately set to the lean set air-fuel ratio and the rich set air-fuel ratio.
- the actual oxygen storage amount of the upstream side exhaust purification catalyst 20 reaches the maximum storable oxygen amount before the cumulative oxygen excess / deficiency amount reaches the switching reference value.
- the maximum storable oxygen amount of the upstream side exhaust purification catalyst 20 is decreased, or the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 temporarily changes abruptly.
- the oxygen storage amount reaches the maximum storable oxygen amount, the exhaust gas having a lean air-fuel ratio flows out from the upstream side exhaust purification catalyst 20.
- the target air-fuel ratio is switched to the rich set air-fuel ratio.
- the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes equal to or higher than the lean determination air-fuel ratio (for example, 14.65) that is slightly leaner than the stoichiometric air-fuel ratio, the downstream air-fuel ratio. It is determined that the output air-fuel ratio of the sensor 41 has become a lean air-fuel ratio. Note that the lean determination air-fuel ratio is made richer than the lean set air-fuel ratio described above.
- FIG. 5 shows the air-fuel ratio correction amount AFC, the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20, the cumulative oxygen excess when the air-fuel ratio control of this embodiment is performed.
- 4 is a time chart of a shortage ⁇ OED, an output air-fuel ratio AFdwn of a downstream air-fuel ratio sensor 41, and a NOx concentration in exhaust gas flowing out from an upstream side exhaust purification catalyst 20.
- the air-fuel ratio correction amount AFC is a correction amount related to the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20.
- the target air-fuel ratio is set to an air-fuel ratio (in this embodiment, the theoretical air-fuel ratio) equal to the air-fuel ratio serving as the control center (hereinafter referred to as “control center air-fuel ratio”).
- the target air-fuel ratio is leaner than the control center air-fuel ratio (in this embodiment, the lean air-fuel ratio), and when the air-fuel ratio correction amount AFC is a negative value, the target air-fuel ratio is Is richer than the control center air-fuel ratio (in this embodiment, the rich air-fuel ratio).
- the “control center air-fuel ratio” is a reference when the target air-fuel ratio is changed according to the air-fuel ratio to which the air-fuel ratio correction amount AFC is added according to the engine operating state, that is, the air-fuel ratio correction amount AFC. It means air / fuel ratio.
- the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich (corresponding to the rich set air-fuel ratio) before the time t 1 . That is, the target air-fuel ratio is a rich air-fuel ratio, and accordingly, the output air-fuel ratio of the upstream air-fuel ratio sensor 40 becomes the rich air-fuel ratio. Unburned gas contained in the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is purified by the upstream side exhaust purification catalyst 20, and accordingly, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 gradually increases. It will decrease to. Therefore, the cumulative oxygen excess / deficiency ⁇ OED also gradually decreases.
- the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is substantially equal to the theoretical air-fuel ratio. Become. Since the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio, the NOx emission amount from the upstream side exhaust purification catalyst 20 becomes substantially zero.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 gradually decreases, the oxygen storage amount OSA approaches zero at time t 1 , and accordingly, a part of the unburned gas flowing into the upstream side exhaust purification catalyst 20. Begins to flow out without being purified by the upstream side exhaust purification catalyst 20.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 gradually decreases after time t 1 .
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich.
- the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean (lean set air amount) to increase the oxygen storage amount OSA. Equivalent to the fuel ratio). Therefore, the target air-fuel ratio is switched from the rich air-fuel ratio to the lean air-fuel ratio. At this time, the cumulative oxygen excess / deficiency ⁇ OED is reset to zero.
- the air-fuel ratio correction amount AFC is switched after the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich. This is because even if the oxygen storage amount of the upstream side exhaust purification catalyst 20 is sufficient, the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 may slightly deviate from the stoichiometric air-fuel ratio. is there. Conversely, the rich determination air-fuel ratio is such that the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 does not reach when the oxygen storage amount of the upstream side exhaust purification catalyst 20 is sufficient. It is said.
- the switch the target air-fuel ratio to the lean air-fuel ratio the air-fuel ratio of the exhaust gas flowing into the upstream exhaust purification catalyst 20 is changed to a lean air-fuel ratio from the rich air-fuel ratio. Accordingly, the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 becomes a lean air-fuel ratio (actually, the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 after switching the target air-fuel ratio)
- the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 changes to the stoichiometric air-fuel ratio, and the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 also converges to the stoichiometric air-fuel ratio.
- the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a lean air-fuel ratio.
- the oxygen storage capacity of the upstream side exhaust purification catalyst 20 has a sufficient margin, the inflowing exhaust gas The oxygen therein is stored in the upstream side exhaust purification catalyst 20, and NOx is reduced and purified. For this reason, the NOx emission from the upstream side exhaust purification catalyst 20 becomes substantially zero.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 increases, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 reaches the switching reference storage amount Cref at time t 3 . For this reason, the cumulative oxygen excess / deficiency ⁇ OED reaches the switching reference value OEDref corresponding to the switching reference storage amount Cref.
- the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich so as to stop storing oxygen in the upstream side exhaust purification catalyst 20. . Therefore, the target air-fuel ratio is set to a rich air-fuel ratio. At this time, the cumulative oxygen excess / deficiency ⁇ OED is reset to zero.
- the oxygen storage amount OSA decreases at the same time as the target air-fuel ratio is switched at time t 3 , but actually the oxygen storage amount OSA decreases after the target air-fuel ratio is switched. There will be a delay. Further, when the engine load increases due to acceleration of the vehicle equipped with the internal combustion engine and the intake air amount deviates momentarily, the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is unintentionally instantaneous. In some cases, the target air-fuel ratio deviates greatly.
- the switching reference storage amount Cref is set sufficiently lower than the maximum storable oxygen amount Cmax when the upstream side exhaust purification catalyst 20 is new.
- the oxygen storage amount OSA is the maximum storable oxygen amount even when the above-described delay occurs or the actual air-fuel ratio of the exhaust gas deviates instantaneously from the target air-fuel ratio unintentionally. Cmax is not reached.
- the switching reference storage amount Cref is set to a sufficiently small amount so that the oxygen storage amount OSA does not reach the maximum storable oxygen amount Cmax even if the above-described delay or unintended air-fuel ratio shift occurs. Is done.
- the switching reference storage amount Cref is set to 3/4 or less, preferably 1/2 or less, more preferably 1/5 or less of the maximum storable oxygen amount Cmax when the upstream side exhaust purification catalyst 20 is new.
- the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes from the lean air-fuel ratio to the rich air-fuel ratio.
- the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 becomes a rich air-fuel ratio (actually, the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes after the target air-fuel ratio is switched). (In the example shown in the figure, it is assumed that it changes simultaneously for the sake of convenience).
- the oxygen storage amount of the upstream exhaust purification catalyst 20 OSA is gradually decreased at time t 4, the time Similar to t 1 , the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 starts to decrease. Also at this time, since the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is a rich air-fuel ratio, the NOx emission from the upstream side exhaust purification catalyst 20 is substantially zero.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich.
- the air-fuel ratio correction amount AFC is switched to a value AFClean that corresponds to the lean set air-fuel ratio. Thereafter, the cycle from the time t 1 to t 5 described above is repeated.
- the NOx emission amount from the upstream side exhaust purification catalyst 20 can always be suppressed. That is, as long as the above-described control is performed, basically, the NOx emission amount from the upstream side exhaust purification catalyst 20 can be made substantially zero.
- the integration period when calculating the integrated oxygen excess / deficiency ⁇ OED is short, a calculation error is less likely to occur than when integrating over a long period of time. For this reason, NOx is prevented from being discharged due to a calculation error of the cumulative oxygen excess / deficiency ⁇ OED.
- the oxygen storage amount of the exhaust purification catalyst decreases. That is, in order to keep the oxygen storage capacity of the exhaust purification catalyst high, it is necessary that the oxygen storage amount of the exhaust purification catalyst fluctuates.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 always fluctuates up and down, so that the oxygen storage capacity is prevented from being lowered. Is done.
- the air-fuel ratio correction amount AFC is maintained at the lean set correction amount AFClean from time t 2 to t 3 .
- the air-fuel ratio correction amount AFC does not necessarily have to be kept constant, and may be set so as to fluctuate, for example, gradually decrease.
- the air-fuel ratio correction amount AFC may be temporarily set to a value smaller than 0 (for example, a rich setting correction amount). That is, the target air-fuel ratio may be temporarily set to the rich air-fuel ratio during the period from time t 2 to t 3 .
- the air-fuel ratio correction amount AFC is maintained at the rich set correction amount AFCrich from time t 3 to t 5 .
- the air-fuel ratio correction amount AFC does not necessarily have to be kept constant, and may be set to vary, for example, gradually increase.
- the air-fuel ratio correction amount AFC may be temporarily set to a value larger than 0 (for example, a lean set correction amount) (FIG. 6). of the time t 6, t 7, etc.). That is, the target air-fuel ratio may be temporarily set to the lean air-fuel ratio during the period from time t 3 to time t 5 .
- the air-fuel ratio correction amount AFC is at time t 2 ⁇ t 3, the difference between the average value and the stoichiometric air-fuel ratio the target air-fuel ratio in the period, the target air at time t 3 ⁇ t 5 It is set to be larger than the difference between the average value of the fuel ratio and the stoichiometric air-fuel ratio.
- the setting of the air-fuel ratio correction amount AFC in this embodiment is performed by the ECU 31. Accordingly, when the air-fuel ratio of the exhaust gas detected by the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio, the ECU 31 determines that the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is equal to the switching reference storage amount Cref. Until the target air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is set to the lean air-fuel ratio continuously or intermittently, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is equal to or higher than the switching reference storage amount Cref.
- the rich air-fuel ratio is made continuously or intermittently.
- the ECU 31 switches the target air-fuel ratio to the lean air-fuel ratio when the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 is equal to or lower than the rich determination air-fuel ratio, and the upstream side. It can be said that the target air-fuel ratio is switched to the rich air-fuel ratio when the oxygen storage amount OSA of the exhaust purification catalyst 20 becomes equal to or greater than the switching reference storage amount Cref.
- the cumulative oxygen excess / deficiency ⁇ OED is calculated based on the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40, the estimated value of the intake air amount into the combustion chamber 5, and the like.
- the oxygen storage amount OSA may be calculated based on other parameters in addition to these parameters, or may be estimated based on parameters different from these parameters.
- the target air-fuel ratio is switched from the lean set air-fuel ratio to the rich set air-fuel ratio.
- the timing of switching the target air-fuel ratio from the lean set air-fuel ratio to the rich set air-fuel ratio is, for example, the engine operation time after switching the target air-fuel ratio from the rich set air-fuel ratio to the lean set air-fuel ratio, the integrated intake air amount, etc.
- Other parameters may be used as a reference.
- the target air-fuel ratio is changed from the lean set air-fuel ratio to the rich set air-fuel ratio while the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is estimated to be smaller than the maximum storable oxygen amount. It is necessary to switch.
- the air-fuel ratio of the exhaust gas discharged from each cylinder may vary between the cylinders.
- the upstream side air-fuel ratio sensor 40 is disposed at the collection portion of the exhaust manifold 19, but the extent to which the exhaust gas discharged from each cylinder is exposed to the upstream side air-fuel ratio sensor 40 according to the position of the upstream manifold 19 is determined. It is different. As a result, the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is strongly influenced by the air-fuel ratio of the exhaust gas discharged from a specific cylinder.
- the average air-fuel ratio and the upstream air-fuel ratio There is a deviation from the output air-fuel ratio of the sensor 40. That is, the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is shifted to the rich side or the lean side from the actual average air-fuel ratio of the exhaust gas.
- FIG. 7 is a time chart of the oxygen storage amount OSA and the like of the upstream side exhaust purification catalyst 20, similar to FIG. FIG. 7 shows a case where the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is shifted to the rich side.
- the solid line in the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 indicates the actual output air-fuel ratio of the upstream air-fuel ratio sensor 40.
- the broken line indicates the actual air-fuel ratio of the exhaust gas flowing around the upstream air-fuel ratio sensor 40.
- the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich, and thus the target air-fuel ratio is set to the rich set air-fuel ratio. Accordingly, the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 becomes an air-fuel ratio equal to the rich set air-fuel ratio.
- the actual air-fuel ratio of the exhaust gas is on the lean side of the rich set air-fuel ratio.
- the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is lower (rich side) than the actual air-fuel ratio (broken line in the figure). For this reason, the decrease rate of the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is slow.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich. Therefore, as described above, at time t 2, the air-fuel ratio correction quantity AFC is switched to the lean set correction amount AFClean. That is, the target air-fuel ratio is switched to the lean set air-fuel ratio.
- the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 becomes an air-fuel ratio equal to the lean set air-fuel ratio.
- the actual air-fuel ratio of the exhaust gas is leaner than the lean set air-fuel ratio. That is, the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is lower (rich side) than the actual air-fuel ratio (broken line in the figure).
- the increase rate of the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is increased, and the actual oxygen amount supplied to the upstream side exhaust purification catalyst 20 is switched while the target air-fuel ratio is set to the lean set air-fuel ratio. It becomes larger than the reference oxygen amount Cref.
- ⁇ Normal learning control> Therefore, in the embodiment of the present invention, in order to compensate for the deviation in the output air-fuel ratio of the upstream side air-fuel ratio sensor 40, during normal operation (that is, when feedback control is performed based on the target air-fuel ratio as described above). Learning control is performed. First, normal learning control will be described.
- the period from when the target air-fuel ratio is switched to the lean air-fuel ratio until the cumulative oxygen excess / deficiency ⁇ OED becomes equal to or higher than the switching reference value OEDref is defined as an oxygen increase period (first period).
- a period from when the target air-fuel ratio is switched to the rich air-fuel ratio until the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio is defined as an oxygen reduction period (second period).
- the lean oxygen amount integrated value (first oxygen amount integrated value) is calculated as the absolute value of the cumulative oxygen excess / deficiency ⁇ ODE during the oxygen increase period.
- a rich oxygen amount integrated value (second oxygen amount integrated value) is calculated as an absolute value of the cumulative oxygen excess / deficiency amount during the oxygen reduction period. Then, the control center air-fuel ratio AFR is corrected so that the difference between the lean oxygen amount integrated value and the rich oxygen amount integrated value becomes small.
- FIG. 9 shows this state.
- FIG. 9 shows the control center air-fuel ratio AFR, the air-fuel ratio correction amount AFC, the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20, the cumulative oxygen excess / deficiency ⁇ OED, 4 is a time chart of an output air-fuel ratio AFdwn of a fuel ratio sensor 41 and a learned value sfbg.
- FIG. 9 shows a case where the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 is shifted to the low side (rich side) as in FIG.
- the learned value sfbg is a value that changes in accordance with the deviation of the output air-fuel ratio (output current) of the upstream air-fuel ratio sensor 40, and is used to correct the control center air-fuel ratio AFR in this embodiment.
- the solid line at the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 indicates the air-fuel ratio corresponding to the output detected by the upstream air-fuel ratio sensor 40, and the broken line circulates around the upstream air-fuel ratio sensor 40.
- the actual air-fuel ratio of exhaust gas is shown.
- the alternate long and short dash line indicates the target air-fuel ratio, that is, the air-fuel ratio corresponding to the air-fuel ratio correction amount AFC.
- the control center air-fuel ratio is the stoichiometric air-fuel ratio
- the air-fuel ratio correction amount AFC is the rich set correction amount AFCrich.
- the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 becomes an air-fuel ratio corresponding to the rich set air-fuel ratio as shown by the solid line.
- the actual air-fuel ratio of the exhaust gas is leaner than the rich set air-fuel ratio (broken line in FIG. 9).
- the actual air-fuel ratio of the exhaust gas before time t 1 is leaner than the rich set air-fuel ratio, but is a rich air-fuel ratio. Therefore, the oxygen storage amount of the upstream side exhaust purification catalyst 20 gradually decreases.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich.
- the air-fuel ratio correction amount AFC is switched to the lean set correction amount AFClean.
- the output air-fuel ratio of the upstream air-fuel ratio sensor 40 becomes an air-fuel ratio corresponding to the lean set air-fuel ratio.
- the actual air-fuel ratio of the exhaust gas becomes an air-fuel ratio that is leaner than the lean set air-fuel ratio, that is, an air-fuel ratio with a large lean degree (the broken line in FIG. See). For this reason, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 increases rapidly.
- the oxygen excess / deficiency amount is calculated based on the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 (more precisely, the difference between the output air-fuel ratio AFup and the control center air-fuel ratio AFR).
- the calculated oxygen excess / deficiency is a value smaller than the actual oxygen excess / deficiency (that is, the amount of oxygen is small).
- the calculated cumulative oxygen excess / deficiency ⁇ OED is smaller than the actual value.
- the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich. Therefore, the target air-fuel ratio is set to a rich air-fuel ratio.
- the actual oxygen storage amount OSA is larger than the switching reference storage amount Cref as shown in FIG.
- the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich, and thus the target air-fuel ratio is set to the rich air-fuel ratio. Also at this time, the actual air-fuel ratio of the exhaust gas is leaner than the rich set air-fuel ratio. As a result, the decrease rate of the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 becomes slow. In addition, as described above, at time t 2, the actual oxygen storage amount of the upstream exhaust purification catalyst 20 is made larger than the switching reference occlusion amount Cref. For this reason, it takes time until the actual oxygen storage amount of the upstream side exhaust purification catalyst 20 reaches zero.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich.
- the air-fuel ratio correction amount AFC is switched to the lean set correction amount AFClean. Therefore, the target air-fuel ratio is switched from the rich set air-fuel ratio to the lean set air-fuel ratio.
- the cumulative oxygen excess / deficiency ⁇ OED is calculated from time t 1 to time t 2 .
- the estimated value of the oxygen storage amount OSA of the upstream exhaust purification catalyst 20 from the time of switching the target air-fuel ratio to the lean air-fuel ratio (time t 1) is equal to or higher than the switching reference occlusion amount Cref (time t 2)
- the cumulative oxygen excess / deficiency ⁇ OED is calculated in the oxygen increase period Tinc.
- the absolute value of the cumulative oxygen excess / deficiency ⁇ OED in the oxygen increase period Tinc from time t 1 to time t 2 is indicated by R 1 .
- the cumulative oxygen excess / deficiency ⁇ OED (R 1 ) in the oxygen increase period Tinc corresponds to the oxygen storage amount OSA at time t 2 .
- the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is used for estimating the oxygen excess / deficiency, and there is a deviation in this output air-fuel ratio AFup. Therefore, in the example shown in FIG. 9, the cumulative oxygen excess / deficiency ⁇ OED in the oxygen increase period Tinc from time t 1 to time t 2 is smaller than the value corresponding to the actual oxygen storage amount OSA at time t 2 . It has become.
- the cumulative oxygen excess / deficiency ⁇ OED is also calculated from time t 2 to time t 3 .
- a period from when the target air-fuel ratio is switched to the rich air-fuel ratio (time t 2 ) to when the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich (time t 3 ) is set.
- the cumulative oxygen excess / deficiency ⁇ OED is calculated during the oxygen reduction period Tdec when referred to as the oxygen reduction period Tdec.
- the absolute value of the cumulative oxygen excess / deficiency ⁇ OED in the oxygen decrease period Tdec from time t 2 to time t 3 is indicated by F 1 .
- the cumulative oxygen excess / deficiency ⁇ OED (F 1 ) in the oxygen reduction period Tdec corresponds to the total oxygen amount released from the upstream side exhaust purification catalyst 20 from time t 2 to time t 3 .
- the integrated oxygen deficiency amount ⁇ OED in the oxygen reduction period Tdec time t 2 ⁇ time t 3 is from time t 2 to time t 3 actually from the upstream side exhaust purification catalyst 20 It is less than the value corresponding to the total amount of oxygen released.
- oxygen is stored in the upstream side exhaust purification catalyst 20 during the oxygen increase period Tinc, and all of the stored oxygen is released during the oxygen decrease period Tdec. Therefore, it is ideal that the absolute value R 1 of the cumulative oxygen excess / deficiency in the oxygen increase period Tinc and the absolute value F 1 of the cumulative oxygen excess / deficiency in the oxygen decrease period Tdec are basically the same value. .
- the integrated value when there is a deviation in the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40, the integrated value also changes in accordance with this deviation.
- the control center air-fuel ratio AFR is corrected based on the excess / deficiency error ⁇ OED.
- the control center air-fuel ratio is set such that the difference ⁇ OED between the absolute value R 1 of the cumulative oxygen excess / deficiency amount during the oxygen increase period Tinc and the absolute value F 1 of the cumulative oxygen excess / deficiency amount during the oxygen decrease period Tdec becomes small.
- AFR is corrected.
- the learning value sfbg is calculated by the following equation (2), and the control center air-fuel ratio AFR is corrected by the following equation (3).
- sfbg (n) sfbg (n ⁇ 1) + k 1 ⁇ ⁇ OED (2)
- AFR AFRbase + sfbg (n) (3)
- n represents the number of calculations or time. Therefore, sfbg (n) is the current calculation or the current learning value.
- k 1 in the above equation (2) is a gain representing the degree to which the excess / deficiency error ⁇ OED is reflected in the control center air-fuel ratio AFR.
- the correction amount of the control center air-fuel ratio AFR increases as the value of the gain k 1 increases.
- the basic control center air-fuel ratio AFRbase is the basic control center air-fuel ratio, and in this embodiment, is the theoretical air-fuel ratio.
- the learning value sfbg is calculated based on the absolute values R 1 and F 1 .
- the absolute value F 1 of the cumulative oxygen excess / deficiency during the oxygen decrease period Tdec is greater than the absolute value R 1 of the cumulative oxygen excess / deficiency during the oxygen increase period Tinc.
- the learning value sfbg is decreased at t 3 .
- control center air-fuel ratio AFR is corrected based on the learned value sfbg using the above equation (3).
- the control center air-fuel ratio AFR is smaller than the basic control center air-fuel ratio AFRbase, that is, a rich value.
- the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 is corrected to the rich side.
- the target air-fuel ratio is switched from the lean set air-fuel ratio to the rich set air-fuel ratio. Then, at time t 5, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches a rich determination air AFrich, again, the target air-fuel ratio is switched to a lean set air-fuel ratio.
- the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 gradually departs from the target air-fuel ratio, but the exhaust gas flowing into the upstream side exhaust purification catalyst 20 The actual air-fuel ratio of the gas gradually approaches the target air-fuel ratio. Thereby, the deviation in the output air-fuel ratio of the upstream air-fuel ratio sensor 40 can be compensated.
- the target air-fuel ratio is switched before the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 reaches the maximum storable oxygen amount Cmax. Therefore, when the target air-fuel ratio is switched after the oxygen storage amount OSA reaches the maximum storable oxygen amount, that is, after the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 becomes equal to or greater than the lean determination air-fuel ratio AFlean. In comparison, the update frequency of the learning value can be increased. Further, the cumulative oxygen excess / deficiency ⁇ OED is more likely to have an error as the calculation period becomes longer.
- the calculation period can be shortened. For this reason, the error in the calculation of the cumulative oxygen excess / deficiency ⁇ OED can be reduced.
- the update of the learned value sfbg is based on the cumulative oxygen excess / deficiency ⁇ OED in the oxygen increase period Tinc and the cumulative oxygen excess / deficiency ⁇ OED in the oxygen decrease period Tdec immediately after the oxygen increase period Tinc. Is preferably performed. As described above, this is because the total amount of oxygen stored in the upstream side exhaust purification catalyst 20 during the oxygen increase period Tinc and the total amount of oxygen released from the upstream side exhaust purification catalyst 20 during the oxygen decrease period Tdec that follows immediately after this increase. This is because they are equal.
- the learning value sfbg is updated based on the cumulative oxygen excess / deficiency ⁇ OED in one oxygen increase period Tinc and the cumulative oxygen excess / deficiency ⁇ OED in one oxygen decrease period Tdec. ing. However, the learning value is based on the total value or average value of the cumulative oxygen excess / deficiency ⁇ OED in the plurality of oxygen increase periods Tinc and the total value or average value of the cumulative oxygen excess / deficiency ⁇ OED in the plurality of oxygen decrease periods Tdec. You may update sfbg.
- control center air-fuel ratio AFR (that is, the target air-fuel ratio) is corrected based on the learned value sfbg.
- other parameters relating to the air-fuel ratio may be corrected based on the learned value sfbg. Examples of other parameters include the amount of fuel supplied into the combustion chamber 5, the output air-fuel ratio of the upstream air-fuel ratio sensor 40, the air-fuel ratio correction amount, and the like.
- the target air-fuel ratio in the basic air-fuel ratio control, is switched to the lean air-fuel ratio when the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio. Further, the target air-fuel ratio is switched to the rich air-fuel ratio when the cumulative oxygen excess / deficiency ⁇ OED becomes equal to or greater than a predetermined switching reference value OEDref.
- another control may be used as the basic air-fuel ratio control.
- control for example, when the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes equal to or higher than the lean determination air-fuel ratio, the target air-fuel ratio is switched to the rich air-fuel ratio, and the output air-fuel ratio of the downstream air-fuel ratio sensor 41 is changed.
- Control that switches the target air-fuel ratio to a lean air-fuel ratio when the fuel ratio becomes equal to or lower than the rich determination air-fuel ratio can be considered.
- the rich oxygen amount as an absolute value of the cumulative oxygen excess / deficiency in the oxygen reduction period from when the target air-fuel ratio is switched to the rich air-fuel ratio until the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio.
- An integrated value is calculated.
- the lean oxygen amount as an absolute value of the cumulative oxygen excess / deficiency during the oxygen increase period from when the target air-fuel ratio is switched to the lean air-fuel ratio until the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes equal to or greater than the lean determination air-fuel ratio.
- An integrated value is calculated. Then, the control center air-fuel ratio or the like is corrected so that the difference between the rich oxygen amount integrated value and the lean oxygen amount integrated value becomes small.
- the target air-fuel ratio is switched to the lean air-fuel ratio when the output air-fuel ratio of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio.
- the target air-fuel ratio is set when the oxygen storage amount of the upstream side exhaust purification catalyst 20 exceeds a predetermined switching reference amount or when the output air-fuel ratio of the downstream side air-fuel ratio sensor 41 reaches the lean determination air-fuel ratio.
- the rich air-fuel ratio is switched.
- the target air-fuel ratio is switched between a plurality of air-fuel ratios that are richer and leaner than the stoichiometric air-fuel ratio.
- the learning means switches from the target air-fuel ratio to the lean air-fuel ratio until the amount of change in the oxygen storage amount reaches or exceeds the switching reference amount or until the output air-fuel ratio of the downstream air-fuel ratio sensor 41 reaches the lean determination air-fuel ratio.
- the first oxygen amount integrated value that is the absolute value of the accumulated oxygen excess / deficiency in the first period of time, and the output air-fuel ratio of the downstream air-fuel ratio sensor 41 after the target air-fuel ratio is switched to the rich air-fuel ratio is less than or equal to the rich determination air-fuel ratio.
- the difference between the first oxygen amount integrated value and the second oxygen amount integrated value is reduced based on the second oxygen amount integrated value, which is the absolute value of the integrated oxygen excess / deficiency in the second period until It can be said that the normal learning control in which the parameter relating to the air-fuel ratio is corrected is performed.
- the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean. Accordingly, the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 becomes the lean set air-fuel ratio. However, since the output air-fuel ratio of the upstream side air-fuel ratio sensor 40 is greatly shifted to the rich side, the actual air-fuel ratio of the exhaust gas is leaner than the lean set air-fuel ratio (broken line in the figure). .
- the air-fuel ratio correction amount AFC becomes the rich set correction amount AFCrich.
- the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 becomes an air-fuel ratio corresponding to the rich set air-fuel ratio.
- the actual air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio (broken line in the figure).
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is maintained at a constant value without changing. Therefore, unburned gas is not discharged from the upstream side exhaust purification catalyst 20 even after a long time has elapsed since the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich.
- the output air-fuel ratio AFdwn of the sensor 41 is maintained substantially at the theoretical air-fuel ratio.
- the air-fuel ratio correction amount AFC is switched from the rich set correction amount AFCrich to the lean set correction amount AFClean when the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich. .
- the air-fuel ratio correction amount AFC becomes the rich set correction amount AFCrich over a long period of time. Will be maintained.
- the above-described normal learning control is based on the premise that the air-fuel ratio correction amount AFC is alternately switched between the rich setting correction amount AFCrich and the lean setting correction amount AFClean. Therefore, when the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is greatly deviated, the air-fuel ratio correction amount AFC is not switched, and thus the normal learning control described above cannot be performed.
- FIG. 11 is a view similar to FIG. 10 showing a case where the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is extremely large and deviates to the rich side.
- the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich at time t 1 as in the example shown in FIG. That is, the target air-fuel ratio is set to the rich set air-fuel ratio at time t 1 .
- the actual air-fuel ratio of the exhaust gas becomes the lean air-fuel ratio (broken line in the figure).
- the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich
- the lean air-fuel ratio exhaust gas flows into the upstream side exhaust purification catalyst 20. Therefore, the oxygen storage amount of the upstream exhaust purification catalyst 20 OSA is gradually increased, eventually reaching the maximum storable oxygen amount Cmax at time t 2.
- the upstream side exhaust purification catalyst 20 can no longer store oxygen in the exhaust gas any more. For this reason, oxygen and NOx contained in the exhaust gas flowing in from the upstream side exhaust purification catalyst 20 flow out as they are, and as a result, the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 increases.
- the air-fuel ratio correction amount AFC is switched from the rich set correction amount AFCrich to the lean set correction amount AFClean when the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich. For this reason, even when the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is greatly deviated, the air-fuel ratio correction amount AFC is not switched, and thus the above-described normal learning control cannot be performed.
- the stoichiometric air-fuel ratio sticking learning control is a learning control that is performed when the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 is stuck to the stoichiometric air-fuel ratio as in the example shown in FIG. .
- an intermediate region M a region between the rich determination air-fuel ratio AFrich and the lean determination air-fuel ratio AFlean is referred to as an intermediate region M.
- This intermediate region M corresponds to a region near the stoichiometric air-fuel ratio, which is an air-fuel ratio region between the rich determination air-fuel ratio and the lean determination air-fuel ratio.
- the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich, that is, after the target air-fuel ratio is switched to the rich set air-fuel ratio, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is changed. Is maintained in the intermediate region M for a predetermined theoretical air-fuel ratio maintenance determination time or longer.
- the learned value sfbg is set so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side. Is reduced.
- FIG. 12 shows this state.
- FIG. 12 is a view similar to FIG. 9 showing a time chart of the air-fuel ratio correction amount AFC and the like.
- FIG. 12 shows a case where the output air-fuel ratio AFup of the upstream side air-fuel ratio sensor 40 is greatly shifted to the low side (rich side), as in FIG.
- the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean before time t 1 as in FIG. Thereafter, at time t 1 , the cumulative oxygen excess / deficiency ⁇ OED reaches the switching reference value OEDref, and the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich.
- the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is greatly shifted to the rich side, the actual air-fuel ratio of the exhaust gas is almost the stoichiometric air-fuel ratio as in the example shown in FIG. Therefore, after time t 1, the oxygen storage amount OSA of the upstream exhaust purification catalyst 20 is maintained at a constant value.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained in the vicinity of the theoretical air-fuel ratio over a long period of time, and is thus maintained in the intermediate region M.
- the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is intermediate for a predetermined theoretical air-fuel ratio maintenance determination time Tsto after the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich.
- the control center air-fuel ratio AFR is corrected.
- the learning value sfbg is updated so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side.
- the learning value sfbg is calculated by the following equation (4), and the control center air-fuel ratio AFR is corrected by the above equation (3).
- sfbg (n) sfbg (n ⁇ 1) + k 2 ⁇ AFCrich (4)
- k 2 is a gain representing the degree of correction of the control center air-fuel ratio AFR (0 ⁇ k 2 ⁇ 1). As the value of the gain k 2 is large, the correction amount of the control center air-fuel ratio AFR is large.
- the deviation in the upstream air-fuel ratio sensor 40 is approximately the same as the difference between the control center air-fuel ratio (theoretical air-fuel ratio) and the target air-fuel ratio (in this case, the rich set air-fuel ratio).
- the learning value sfbg is updated based on the air-fuel ratio correction amount AFC corresponding to the difference between the control center air-fuel ratio and the target air-fuel ratio as shown in the above equation (4). The deviation in the output air-fuel ratio of the upstream air-fuel ratio sensor 40 can be compensated appropriately.
- the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich from time t 1 to time t 2 when the theoretical air-fuel ratio maintenance determination time Tsto has elapsed. Therefore, the use of Equation (4), the learning value sfbg at time t 2 is used to lower. As a result, the actual air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side. Thus, after time t 2 , the deviation of the actual air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 from the target air-fuel ratio becomes smaller than before time t 2 . Therefore, after time t 2 , the difference between the broken line representing the actual air-fuel ratio and the one-dot chain line representing the target air-fuel ratio is smaller than the difference before time t 2 .
- the gain k 2 is set to a relatively small value. For this reason, even if the learned value sfbg is updated at time t 2 , there still remains a deviation of the actual air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 from the target air-fuel ratio. For this reason, the actual air-fuel ratio of the exhaust gas becomes an air-fuel ratio leaner than the rich set air-fuel ratio, that is, an air-fuel ratio with a small rich degree (see the broken line in FIG. 12). For this reason, the decreasing rate of the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is slow.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained in the vicinity of the theoretical air-fuel ratio from time t 2 until time t 3 when the stoichiometric air-fuel ratio maintenance determination time Tst has elapsed, and thus is maintained in the intermediate region M.
- the learning value sfbg is updated using Expression (4) also at time t 3 .
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio AFrich.
- the air-fuel ratio correction amount AFC is alternately set to the lean set correction amount AFClean and the rich set correction amount AFCrich as described above.
- the above-described normal learning control is performed.
- the learning value can be updated even when the deviation of the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is large. it can. Thereby, the deviation in the output air-fuel ratio of the upstream air-fuel ratio sensor 40 can be compensated.
- the theoretical air-fuel ratio maintenance determination time Tsto is a predetermined time.
- the stoichiometric air-fuel ratio maintenance determination time reaches the maximum storable oxygen amount of the upstream side exhaust purification catalyst 20 when the absolute value of the cumulative oxygen excess / deficiency ⁇ OED after switching the target air-fuel ratio to the rich air-fuel ratio is new. It usually takes more time to complete. Specifically, the time is preferably about 2 to 4 times.
- the theoretical air-fuel ratio maintenance determination time Tsto may be changed according to other parameters such as the cumulative oxygen excess / deficiency ⁇ OED after the target air-fuel ratio is switched to the rich air-fuel ratio. Specifically, for example, as the cumulative oxygen excess / deficiency ⁇ OED increases, the theoretical air-fuel ratio maintenance determination time Tsto is shortened.
- the learning value sfbg as described above is updated when the cumulative oxygen excess / deficiency ⁇ OED after the target air-fuel ratio is switched to the rich air-fuel ratio becomes a predetermined amount (for example, OEDsw in FIG. 12). It can also be.
- the predetermined amount in the cumulative oxygen excess / deficiency ⁇ OED is equal to or greater than the maximum storable oxygen amount of the upstream side exhaust purification catalyst 20 when new.
- the amount is preferably about 2 to 4 times the maximum storable oxygen amount.
- the stoichiometric air-fuel ratio stuck learning control can also be applied to the case where another control described above is used as the basic air-fuel ratio control, as in the case of the normal learning control described above.
- the target air-fuel ratio is switched to the lean air-fuel ratio, and then the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 exceeds the stoichiometric air-fuel ratio maintenance determination time Tsto.
- learning is performed so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side or the lean side according to the target air-fuel ratio at that time.
- the value sfbg will be increased or decreased.
- the learning means switches the target air-fuel ratio to an air-fuel ratio that is shifted to one side of the theoretical air-fuel ratio (corresponding to the rich side in the example shown in FIG. 9).
- the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 is maintained in the stoichiometric air-fuel ratio vicinity air-fuel ratio region over the stoichiometric air-fuel ratio maintenance determination time Tsto, the upstream side exhaust purification is performed in feedback control. It can be said that the theoretical air-fuel ratio sticking learning is performed to correct the parameter relating to the air-fuel ratio so that the air-fuel ratio of the exhaust gas flowing into the catalyst 20 changes to the one side.
- the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 after switching the target air-fuel ratio to the lean air-fuel ratio exceeds the stoichiometric air-fuel ratio maintenance determination time Tsto.
- the learning value is updated when it is maintained within the vicinity air-fuel ratio region.
- the theoretical air-fuel ratio sticking learning may be performed based on parameters other than time.
- the change amount of the oxygen storage amount is changed to the switching reference amount after the target air-fuel ratio is switched to the lean air-fuel ratio.
- a first oxygen amount integrated value for example, the absolute value of the accumulated oxygen excess / deficiency in the first period until the output air-fuel ratio of the downstream air-fuel ratio sensor 41 reaches the lean determination air-fuel ratio until the above value is reached (for example, FIG. 14).
- the absolute value of the cumulative oxygen excess / deficiency after switching the target air-fuel ratio to the rich air-fuel ratio (however, before the output air-fuel ratio of the downstream air-fuel ratio sensor 41 becomes equal to or less than the rich determination air-fuel ratio) That is, the integrated oxygen amount after rich switching becomes extremely large. Therefore, when the absolute value of the cumulative oxygen excess / deficiency after switching the target air-fuel ratio to the rich air-fuel ratio with respect to the first oxygen amount integrated value becomes greater than a predetermined value, learning as described above is performed.
- the value may be updated. That is, when the value obtained by subtracting the first oxygen amount integrated value from the rich integrated oxygen value after the rich switching is equal to or greater than a predetermined value, the learning value described above is updated.
- lean stuck learning control the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 is stretched to the lean air-fuel ratio even though the target air-fuel ratio is set to the rich air-fuel ratio as in the example shown in FIG. It is a learning control performed when it is attached.
- lean stuck learning control after the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich, that is, after the target air-fuel ratio is switched to the rich set air-fuel ratio, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is set in advance.
- the learned value sfbg is set so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side. It can be reduced.
- FIG. 13 shows this state.
- FIG. 13 is a view similar to FIG. 9 showing a time chart of the air-fuel ratio correction amount AFC and the like.
- FIG. 13 shows a case where the output air-fuel ratio AFup of the upstream-side air-fuel ratio sensor 40 is significantly shifted to the low side (rich side), as in FIG.
- the air-fuel ratio correction amount AFC is switched from the lean set correction amount AFClean to the rich set correction amount AFCrich.
- the actual air-fuel ratio of the exhaust gas is a lean air-fuel ratio, as in the example shown in FIG.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained at the lean air-fuel ratio.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is equal to or longer than the predetermined lean air-fuel ratio maintenance determination time Tlean after the air-fuel ratio correction amount AFC is set to the rich set correction amount AFCrich. Is maintained at a lean air-fuel ratio, the air-fuel ratio correction amount AFC is corrected.
- the learning value sfbg is corrected so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side.
- the learning value sfbg is calculated by the following equation (5), and the control center air-fuel ratio AFR is corrected based on the learning value sfbg by the above equation (3).
- sfbg (n) sfbg (n ⁇ 1) + k 3 ⁇ (AFCrich ⁇ (AFdwn ⁇ 14.6)) (5)
- k 3 is a gain indicating the degree of correction of the control center air-fuel ratio AFR (0 ⁇ k 3 ⁇ 1). As the value of the gain K 3 is large, the correction amount of the control center air-fuel ratio AFR is large.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained at the lean air-fuel ratio.
- the deviation in the upstream air-fuel ratio sensor 40 corresponds to the difference between the target air-fuel ratio and the output air-fuel ratio of the downstream air-fuel ratio sensor 41.
- the deviation in the upstream air-fuel ratio sensor 40 is the difference between the target air-fuel ratio and the theoretical air-fuel ratio (corresponding to the rich set correction amount AFCrich), the theoretical air-fuel ratio, and the output air-fuel ratio of the downstream air-fuel ratio sensor 41.
- the learning value is based on the value obtained by adding the difference between the output air-fuel ratio of the downstream air-fuel ratio sensor 41 and the theoretical air-fuel ratio to the rich set correction amount AFCrich. sfbg is updated.
- the learning value is corrected by an amount corresponding to the rich set correction amount AFCrich.
- the output air flow of the downstream air-fuel ratio sensor 41 is corrected.
- the learning value is corrected by an amount corresponding to the fuel ratio AFdwn.
- the gain k 3 is set to be approximately the same as the gain k 3 . For this reason, the correction amount in lean stuck learning is larger than the correction amount in theoretical air-fuel ratio stuck learning.
- the learning value sfbg is decreased at the time t 1 by using the equation (5).
- the actual air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the rich side.
- the deviation of the actual air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 from the target air-fuel ratio becomes smaller than before time t 1 . Therefore, after time t 1 , the difference between the broken line representing the actual air-fuel ratio and the one-dot chain line representing the target air-fuel ratio is smaller than the difference before time t 1 .
- FIG. 13 shows an example in which the gain k 3 is set to a relatively small value. For this reason, even if the learning value sfbg is updated at time t 1 , a deviation in the output air-fuel ratio of the upstream air-fuel ratio sensor 40 remains. In particular, in the illustrated example, the actual air-fuel ratio of the exhaust gas remains the lean air-fuel ratio even after time t 1 . As a result, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor is maintained at the lean air-fuel ratio from the time t 1 over the lean air-fuel ratio maintenance determination time Tlean. For this reason, in the illustrated example, the learning value sfbg is corrected using lean equation learning at time t 2 using the above equation (5).
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is substantially the stoichiometric air-fuel ratio, that is, within the intermediate region M, over the stoichiometric air-fuel ratio maintenance determination time Tsto from time t 2 to time t 3 . Maintained. For this reason, at the time t 3 , the learning value sfbg is corrected by the theoretical air-fuel ratio sticking learning using the above equation (4).
- the learning value sfbg By updating the learning value sfbg in this way by lean stuck learning control, the learning value can be updated even when the deviation of the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is extremely large. . Thereby, the shift
- the lean air-fuel ratio maintenance determination time Tlean is set to a predetermined time.
- the lean air-fuel ratio maintenance determination time Tlean is a response of the downstream air-fuel ratio sensor that is normally applied from when the target air-fuel ratio is switched to the rich air-fuel ratio until the output air-fuel ratio of the downstream air-fuel ratio sensor 41 changes accordingly. It is assumed that the delay time is exceeded. Specifically, the time is preferably about 2 to 4 times.
- the lean air-fuel ratio maintenance determination time Tlean is set so that the absolute value of the cumulative oxygen excess / deficiency ⁇ OED after switching the target air-fuel ratio to the rich air-fuel ratio becomes the maximum storable oxygen amount of the upstream side exhaust purification catalyst 20 at the time of new contact It takes less time than usual to reach. Accordingly, the lean air-fuel ratio maintenance determination time Tlean is shorter than the above-described theoretical air-fuel ratio maintenance determination time Tsto.
- the lean air-fuel ratio maintenance determination time Tlean may be changed according to other parameters such as the exhaust gas flow rate integrated after switching the target air-fuel ratio to the rich air-fuel ratio. Specifically, for example, the lean air-fuel ratio maintenance determination time Tlean is shortened as the integrated exhaust gas flow rate ⁇ Ge increases.
- the learning value sfbg as described above is updated when the cumulative exhaust gas flow rate after switching the target air-fuel ratio to the rich air-fuel ratio becomes a predetermined amount (for example, ⁇ Gesw in FIG. 13).
- the predetermined amount needs to be equal to or greater than the total flow rate of the exhaust gas required from when the target air-fuel ratio is switched to when the output air-fuel ratio of the downstream air-fuel ratio sensor 41 changes accordingly. .
- the amount is preferably about 2 to 4 times the total flow rate.
- the rich stuck learning control is the same control as the lean stuck learning control, and the air-fuel ratio detected by the downstream air-fuel ratio sensor 41 is the rich air-fuel ratio even though the target air-fuel ratio is set to the lean air-fuel ratio. This is the learning control that is performed when it is stuck to.
- the rich sticky learning control after the air-fuel ratio correction amount AFC is switched to the lean set correction amount AFClean, that is, after the target air-fuel ratio is switched to the lean set air-fuel ratio, the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is set in advance.
- the rich air-fuel ratio maintenance determination time (similar to the lean air-fuel ratio maintenance determination time) or longer.
- the learned value sfbg is set so that the air-fuel ratio of the exhaust gas flowing into the upstream side exhaust purification catalyst 20 changes to the lean side. Increased. That is, in rich sticky learning control, rich and lean control is reversed from the lean sticky learning control described above.
- the rich degree of the rich set air-fuel ratio is increased compared to when it is not necessary to promote the update.
- the switching reference storage amount is reduced compared to when it is not necessary to promote.
- the difference ⁇ OED of the value) F 1 is greater than or equal to a predetermined acceleration determination reference value, it is determined that it is necessary to promote the update of the learning value sfbg by learning control.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is When it is maintained in the intermediate region M for a predetermined theoretical air-fuel ratio promotion determination time (preferably less than the theoretical air-fuel ratio maintenance determination time), the learning value sfbg is updated by learning control. It is judged that it is necessary to do.
- the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is lean over a predetermined lean air-fuel ratio maintenance determination time. Even when the air-fuel ratio is maintained, it is determined that it is necessary to promote the update of the learning value sfbg by the learning control.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained at the rich air-fuel ratio for a predetermined rich air-fuel ratio maintenance determination time or more. Even in the case where it is determined, it is determined that it is necessary to promote the update of the learning value sfbg by the learning control.
- FIG. 14 shows the control center air-fuel ratio AFR, the air-fuel ratio correction amount AFC, the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40, the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20, the cumulative oxygen excess / deficiency ⁇ OED, 10 is a time chart similar to FIG. 9 and the like of the output air-fuel ratio AFdwn and the learning value sfbg of the fuel ratio sensor 41.
- FIG. 14 shows a case where the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is shifted to the low side (rich side), as in FIG.
- the control center air-fuel ratio is set to the stoichiometric air-fuel ratio, and the air-fuel ratio correction amount AFC is set to the rich setting correction amount AFCrich 1 (the rich setting correction amount AFCrich in the example shown in FIG. 9). The same value).
- the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 is an air-fuel ratio corresponding to the rich set air-fuel ratio.
- the actual air-fuel ratio of the exhaust gas is leaner than the rich set air-fuel ratio (broken line in FIG. 14).
- the absolute value of the cumulative oxygen excess / deficiency ⁇ OED in the oxygen increase period Tinc (time t 1 to time t 2 ) is calculated as R 1 .
- the absolute value of the cumulative oxygen excess / deficiency ⁇ OED in the oxygen decrease period Tdec (time t 2 to time t 3 ) is calculated as F 1 .
- the difference between the absolute value R 1 of the cumulative oxygen excess / deficiency amount during the oxygen increase period Tinc and the absolute value F 1 of the cumulative oxygen excess / deficiency amount during the oxygen decrease period Tdec (excess / deficiency error).
- ⁇ OED is greater than or equal to a predetermined acceleration determination reference value. For this reason, in the example illustrated in FIG. 14, it is determined that it is necessary to promote the update of the learning value sfbg by learning control at time t 3 .
- learning promotion control is started at time t 3 .
- the rich set correction amount AFCrich is increased from AFCrich 1 to AFCrich 2 , and thus the rich degree of the rich set air-fuel ratio is increased.
- the switching reference storage amount Cref is decreased from Cref 1 to Cref 2 . Accordingly, the switching reference value OEDref is also decreased from OEDref 1 corresponding to Cref 1 to OEDref 2 corresponding to Cref 2 .
- the control center air-fuel ratio AFR is corrected by the above formula (3)
- the learning value sfbg is decreased at time t 3 and the control center air-fuel ratio AFR is corrected to the rich side.
- the air-fuel ratio correction amount AFC is switched to the lean set correction amount AFClean at time t 3 , the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 increases, and accordingly, the cumulative oxygen excess / deficiency ⁇ OED also increases. I will do it.
- the air-fuel ratio correction amount AFC is switched to the increased rich set correction amount AFCrich 2 (time t 4 ).
- the switching reference value OEDref is reduced to ⁇ OEDref 2 . Therefore, the integrated oxygen deficiency amount ⁇ OED at time t 4 after switching the air-fuel ratio correction quantity AFC to lean setting correction amount AFClean is the time to reach the switching reference value OEDref 2 at time t 3 becomes short.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 decreases.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich.
- the rich set correction amount AFCrich is increased to AFCrich 2 . For this reason, the decreasing rate of the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 is increased.
- the cycle until the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 reaches the rich determination air-fuel ratio AFrich or less and then reaches the rich determination air-fuel ratio AFrich again (for example, the time t in FIG. 14).
- the cycle from 3 to t 5 ) is repeated after a predetermined number of times, and then finished.
- the learning promotion control may be terminated after a predetermined time has elapsed from the start of the learning promotion control.
- the rich set correction amount AFCrich is made to decrease from AFCrich 2 to AFCrich 1, thus the degree of richness of the rich set air-fuel ratio is made to decrease.
- the switching reference value OEDref is also increased from OEDref 2 to OEFref 1 .
- the switching reference value OEDref is decreased to OEDref 2 , thereby shortening the time from time t 3 to time t 4 .
- the time from time t 4 to time t 5 is shortened by increasing the rich setting correction amount AFCrich to increase the rich degree of the rich setting air-fuel ratio. Therefore, considering these together, the time from time t 3 to time t 5 is shortened.
- a cycle including the oxygen increase period Tinc and the oxygen decrease period Tdec is required to update the learning value sfbg. Therefore, in the present embodiment, the time of one cycle (for example, time t 3 to time t 5 ) necessary for updating the learning value sfbg can be shortened, and updating of the learning value can be promoted.
- the switching reference value OEDref is decreased and the rich set correction amount AFCrich is increased.
- the rich setting correction amount AFCrich may not be changed by reducing only the switching reference value OEDref as compared with the case where the learning promotion control is not performed.
- only the rich setting correction amount AFCrich may be increased and the switching reference value OEDref may not be changed as compared to when the learning promotion control is not executed.
- the lean setting correction amount AFCrich is not changed even when the learning promotion control is performed, and the learning promotion control is not performed even when the learning promotion control is not performed. It is maintained at the same value as when.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 reaches the maximum storable oxygen amount Cmax unintentionally for some reason, and the upstream side.
- the exhaust gas having a lean air-fuel ratio flows out from the exhaust purification catalyst 20.
- Increasing the lean set correction amount AFCrich that is, increasing the lean degree of the lean set air-fuel ratio increases the amount of NOx contained in the exhaust gas flowing out in such a case. For this reason, in the above embodiment, the lean setting correction amount AFCrich is not increased even during the learning promotion control.
- the lean setting correction amount AFCrich may be increased during the learning promotion control.
- the gains k 1 , k 2 , and k 3 in the equations (2), (4), and (5) are not changed when the learning promotion control is performed.
- the gains k 1 , k 2 , and k 3 may be increased as compared to when learning promotion control is not performed.
- the switching reference value and the rich setting correction amount are changed, so that only the gains k 1 , k 2 , and k 3 are increased.
- the degree of increasing the gains k 1 , k 2 , and k 3 can be kept low. Therefore, a delay in the final convergence of the learning value sfbg is suppressed.
- FIG. 15 which is a functional block diagram
- the control device in the present embodiment is configured to include each functional block of A1 to A11.
- each functional block will be described with reference to FIG. Operations in these functional blocks A1 to A11 are basically executed in the ECU 31.
- the in-cylinder intake air amount calculation means A1 calculates the intake air amount Mc to each cylinder based on the intake air flow rate Ga, the engine speed NE, and a map or calculation formula stored in the ROM 34 of the ECU 31.
- the intake air flow rate Ga is measured by the air flow meter 39, and the engine speed NE is calculated based on the output of the crank angle sensor 44.
- the target air-fuel ratio AFT is calculated by target air-fuel ratio setting means A8 described later.
- An injection instruction is issued to the fuel injection valve 11 so that the fuel of the fuel injection amount Qi calculated in this way is injected from the fuel injection valve 11.
- the oxygen excess / deficiency calculation means A4 calculates the integrated oxygen excess / deficiency ⁇ OED based on the fuel injection quantity Qi calculated by the fuel injection quantity calculation means A3 and the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40.
- the oxygen excess / deficiency calculation means A4 for example, multiplies the difference between the output air-fuel ratio of the upstream air-fuel ratio sensor 40 and the control center air-fuel ratio by the fuel injection amount Qi and integrates the obtained value to integrate the excess oxygen excess.
- the deficiency ⁇ OED is calculated.
- the air-fuel ratio of the target air-fuel ratio is calculated based on the integrated oxygen excess / deficiency amount ⁇ OED calculated by the oxygen excess / deficiency amount calculation means A4 and the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41.
- a correction amount AFC is calculated. Specifically, the air-fuel ratio correction amount AFC is calculated based on the flowchart shown in FIG. 16 and the flowchart shown in FIG.
- the learning value sfbg is calculated based on the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41, the integrated oxygen excess / deficiency ⁇ OED calculated by the oxygen excess / deficiency calculation means A4, and the like. Specifically, the learning value sfbg is calculated based on the normal learning control flowchart shown in FIG. 17 and the sticky learning control flowchart shown in FIG. The learning value sfbg calculated in this manner is stored in a storage medium in the RAM 33 of the ECU 31 that is not erased even if the ignition key of the vehicle equipped with the internal combustion engine is turned off.
- control center air-fuel ratio calculating means A7 the control center air-fuel ratio AFR is calculated based on the basic control center air-fuel ratio AFRbase (for example, the theoretical air-fuel ratio) and the learned value sfbg calculated by the learned value calculating means A6. Specifically, the control center air-fuel ratio AFR is calculated by adding the learned value sfbg to the basic control center air-fuel ratio AFRbase, as shown in the above-described equation (3).
- the target air-fuel ratio setting means A8 adds the air-fuel ratio correction amount AFC calculated by the air-fuel ratio correction amount calculation means A5 to the control center air-fuel ratio AFR calculated by the control center air-fuel ratio calculation means A7, so that the target air-fuel ratio setting means A8 is added.
- the fuel ratio AFT is calculated.
- the target air-fuel ratio AFT calculated in this way is input to the basic fuel injection amount calculating means A2 and an air-fuel ratio deviation calculating means A9 described later.
- This air-fuel ratio deviation DAF is a value that represents the excess or deficiency of the fuel supply amount with respect to the target air-fuel ratio AFT.
- the F / B correction amount calculation means A10 supplies fuel based on the following equation (6) by subjecting the air-fuel ratio deviation DAF calculated by the air-fuel ratio deviation calculation means A9 to proportional / integral / derivative processing (PID processing).
- PID processing proportional / integral / derivative processing
- An F / B correction amount DFi for compensating for the excess or deficiency of the amount is calculated.
- the F / B correction amount DFi calculated in this way is input to the fuel injection amount calculation means A3.
- DFi Kp / DAF + Ki / SDAF + Kd / DDAF (6)
- Kp is a preset proportional gain (proportional constant)
- Ki is a preset integral gain (integral constant)
- Kd is a preset differential gain (differential constant).
- DDAF is a time differential value of the air-fuel ratio deviation DAF, and is calculated by dividing the deviation between the air-fuel ratio deviation DAF updated this time and the air-fuel ratio deviation DAF updated last time by the time corresponding to the update interval. Is done.
- FIG. 16 is a flowchart showing a control routine for calculation control of the air-fuel ratio correction amount AFC.
- the illustrated control routine is performed by interruption at regular time intervals.
- step S11 it is determined whether or not a calculation condition for the air-fuel ratio correction amount AFC is satisfied.
- the case where the calculation condition of the air-fuel ratio correction amount AFC is satisfied includes that the normal control in which feedback control is performed, for example, that the fuel cut control is not being performed, and the like. If it is determined in step S11 that the target air-fuel ratio calculation condition is satisfied, the process proceeds to step S12.
- step S12 the cumulative oxygen excess / deficiency ⁇ OED is calculated based on the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 and the fuel injection amount Qi.
- step S13 it is determined whether or not the lean setting flag Fr is set to zero.
- the lean setting flag Fr is set to 1 when the air-fuel ratio correction amount AFC is set to the lean setting correction amount AFClean, and is set to 0 otherwise. If the lean setting flag Fr is set to 0 in step S13, the process proceeds to step S14.
- step S14 it is determined whether or not the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is equal to or less than the rich determination air-fuel ratio AFrich. When it is determined that the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is larger than the rich determination air-fuel ratio AFrich, the control routine is ended.
- step S14 when the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 decreases and the air-fuel ratio of the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 decreases, the output air-fuel ratio of the downstream side air-fuel ratio sensor 41 in step S14. It is determined that AFdwn is equal to or less than the rich determination air-fuel ratio AFrich. In this case, the process proceeds to step S15, and the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean. Next, at step S16, the lean setting flag Fr is set to 1, and the control routine is ended.
- step S13 it is determined in step S13 that the lean setting flag Fr is not set to 0, and the process proceeds to step S17.
- step S17 it is determined whether or not the cumulative oxygen excess / deficiency ⁇ OED calculated in step S12 is smaller than the determination reference value OEDref. If it is determined that the cumulative oxygen excess / deficiency ⁇ OED is smaller than the determination reference value OEDref, the process proceeds to step S18, and the air-fuel ratio correction amount AFC is continuously set to the lean set correction amount AFClean.
- step S17 when the oxygen storage amount of the upstream side exhaust purification catalyst 20 increases, it is determined in step S17 that the cumulative oxygen excess / deficiency ⁇ OED is equal to or greater than the determination reference value OEDref, and the process proceeds to step S19.
- step S19 the air-fuel ratio correction amount AFC is set to the rich setting correction amount AFCrich.
- step S20 the lean setting flag Fr is reset to 0, and the control routine is ended.
- FIG. 17 is a flowchart showing a control routine of normal learning control. The illustrated control routine is performed by interruption at regular time intervals.
- step S21 it is determined whether or not an update condition for the learning value sfbg is satisfied.
- the case where the update condition is satisfied includes, for example, that normal control is being performed. If it is determined in step S21 that the update condition for the learning value sfbg is satisfied, the process proceeds to step S22.
- step S22 it is determined whether or not the lean flag Fl is set to zero. If it is determined in step S22 that the lean flag Fl is set to 0, the process proceeds to step S23.
- step S23 it is determined whether the air-fuel ratio correction amount AFC is greater than 0, that is, whether the target air-fuel ratio is a lean air-fuel ratio. If it is determined in step S23 that the air-fuel ratio correction amount AFC is greater than 0, the process proceeds to step S24. In step S24, the current oxygen excess / deficiency amount OED is added to the integrated oxygen excess / deficiency amount ⁇ OED.
- step S23 the air-fuel ratio correction amount AFC is 0 or less, and the process proceeds to step S25.
- step S25 the lean flag Fl is set to 1.
- step S26 Rn is made the absolute value of the current cumulative oxygen excess / deficiency ⁇ OED.
- step S27 the cumulative oxygen excess / deficiency ⁇ OED is reset to 0, and the control routine is ended.
- step S28 it is determined whether or not the air-fuel ratio correction amount AFC is smaller than 0, that is, whether or not the target air-fuel ratio is a rich air-fuel ratio. If it is determined in step S28 that the air-fuel ratio correction amount AFC is smaller than 0, the process proceeds to step S29. In step S29, the current oxygen excess / deficiency amount OED is added to the integrated oxygen excess / deficiency amount ⁇ OED.
- step S28 it is determined in step S28 that the air-fuel ratio correction amount AFC is 0 or more, and the process proceeds to step S30.
- step S30 the lean flag Fl is set to 0.
- step S31 Fn is made the absolute value of the current cumulative oxygen excess / deficiency ⁇ OED.
- step S32 the cumulative oxygen excess / deficiency ⁇ OED is reset to zero.
- step S33 the learning value sfbg is updated based on Rn calculated in step S26 and Fn calculated in step S31, and the control routine is terminated.
- FIG. 18 is a flowchart showing a control routine of sticking learning control (theoretical air-fuel ratio sticking control, rich sticking control, and lean sticking control).
- the illustrated control routine is performed by interruption at regular time intervals.
- step S41 it is determined whether or not the lean flag Fl is set to zero. If it is determined in step S41 that the lean flag Fl is set to 0, the process proceeds to step S42. In step S42, it is determined whether or not the air-fuel ratio correction amount AFC is greater than 0, that is, whether or not the target air-fuel ratio is a lean air-fuel ratio. If it is determined in step S42 that the air-fuel ratio correction amount AFC is 0 or less, the process proceeds to step S43.
- step S43 it is determined whether or not the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is larger than the lean determination air-fuel ratio AFlean.
- step S44 the output air-fuel ratio AFdwn is rich determination air-fuel ratio AFrich and lean determination air-fuel ratio. It is determined whether or not the value is between AFlean.
- Steps S43 and S44 when it is determined that the output air-fuel ratio AFdwn is smaller than the rich determination air-fuel ratio AFrich, that is, when it is determined that the output air-fuel ratio is the rich air-fuel ratio, the control routine is ended.
- step S43 and S44 determines whether the output air-fuel ratio AFdwn is greater than the lean determination air-fuel ratio AFlean, that is, if it is determined that the output air-fuel ratio is the lean air-fuel ratio. If it is determined in steps S43 and S44 that the output air-fuel ratio AFdwn is greater than the lean determination air-fuel ratio AFlean, that is, if it is determined that the output air-fuel ratio is the lean air-fuel ratio, the process proceeds to step S45. .
- step S45 a value obtained by adding the current exhaust gas flow rate Ge to the integrated exhaust gas flow rate ⁇ Ge is set as a new integrated exhaust gas flow rate ⁇ Ge.
- the exhaust gas flow rate Ge is calculated based on the output of the air flow meter 39, for example.
- step S46 it is determined whether or not the integrated exhaust gas flow rate ⁇ Ge calculated in step S45 is greater than or equal to a predetermined amount ⁇ Gesw. If it is determined in step S46 that ⁇ Ge is smaller than ⁇ Gesw, the control routine is terminated.
- step S46 if the integrated exhaust gas flow rate ⁇ Ge increases and it is determined in step S46 that ⁇ Ge is equal to or greater than ⁇ Gesw, the process proceeds to step S47.
- step S47 the learning value sfbg is corrected using the above equation (5).
- step S48 a value obtained by adding the current oxygen excess / deficiency amount OED to the cumulative oxygen excess / deficiency amount ⁇ OED is set as a new cumulative oxygen excess / deficiency amount ⁇ OED.
- step S49 it is determined whether or not the cumulative oxygen excess / deficiency ⁇ OED calculated in step S48 is greater than or equal to a predetermined amount OEDsw.
- step S49 If it is determined in step S49 that ⁇ OED is smaller than OEDsw, the control routine is terminated. On the other hand, if the cumulative oxygen excess / deficiency ⁇ OED increases and it is determined in step S49 that ⁇ OED is equal to or greater than OEDsw, the process proceeds to step S50. In step S50, the learning value sfbg is corrected using the above equation (4).
- step S51 the accumulated exhaust gas flow rate ⁇ Ge and the accumulated oxygen excess / deficiency ⁇ OED are reset to zero.
- step S52 the lean flag Fl is set to 1.
- step S53 it is determined whether the air-fuel ratio correction amount AFC is smaller than 0, that is, whether the target air-fuel ratio is a rich air-fuel ratio. If it is determined in step S53 that the air-fuel ratio correction amount AFC is 0 or more, the process proceeds to step S54.
- step S54 it is determined whether or not the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is smaller than the rich determination air-fuel ratio AFrich. If it is determined in step S54 that the output air-fuel ratio AFdwn is greater than or equal to the rich determination air-fuel ratio AFrich, that is, if it is determined that the output air-fuel ratio is a lean air-fuel ratio, the control routine is terminated. On the other hand, if it is determined in step S54 that the output air-fuel ratio AFdwn is smaller than the rich determination air-fuel ratio AFrich, that is, if it is determined that the output air-fuel ratio is the rich air-fuel ratio, the process proceeds to step S55.
- step S55 a value obtained by adding the current exhaust gas flow rate Ge to the integrated exhaust gas flow rate ⁇ Ge is set as a new integrated exhaust gas flow rate ⁇ Ge.
- step S56 it is determined whether or not the integrated exhaust gas flow rate ⁇ Ge calculated in step S55 is greater than or equal to a predetermined amount ⁇ Gesw. If it is determined in step S56 that ⁇ Ge is smaller than ⁇ Gesw, the control routine is terminated. On the other hand, when the integrated exhaust gas flow rate ⁇ Ge increases and it is determined in step S56 that ⁇ Ge is equal to or greater than ⁇ Gesw, the process proceeds to step S57. In step S57, the learning value sfbg is corrected using the above equation (5).
- step S58 the cumulative exhaust gas flow rate ⁇ Ge and the cumulative oxygen excess / deficiency ⁇ OED are reset to zero.
- step S59 the lean flag Fl is set to 0, and the control routine is ended.
- FIG. 19 is a flowchart showing a control routine for learning promotion control.
- the control routine shown in FIG. 19 is performed by interruption at regular time intervals.
- step S71 it is determined whether or not the learning promotion flag Fa is set to 1.
- the learning promotion flag Fa is a flag that is set to 1 when learning promotion control is performed, and is set to 0 in other cases. If it is determined in step S71 that the learning promotion flag Fa is set to 0, the process proceeds to step S72.
- step S72 it is determined whether or not a learning promotion condition is satisfied.
- the learning promotion condition is satisfied when it is necessary to promote the update of the learning value by learning control. Specifically, when the above-described excess / deficiency error ⁇ OED is equal to or greater than the acceleration determination reference value, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained in the intermediate region M for the theoretical air-fuel ratio acceleration determination time. When the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained at the lean air-fuel ratio or the rich air-fuel ratio over the lean air-fuel ratio maintenance determination time or the rich air-fuel ratio maintenance determination time, etc. Learning promotion conditions are established. Alternatively, the learning promotion condition is learned when the learning value update amount added to sfbg (n ⁇ 1) in the above formulas (2), (4), and (5) is equal to or greater than a predetermined reference value. The promotion condition may be satisfied.
- step S72 If it is determined in step S72 that the learning promotion condition is not satisfied, the process proceeds to step S73.
- step S73 the rich set correction amount AFCrich is set to AFCrich 1.
- step S74 the switching reference value OEDref is set to OEDref 1 and the control routine is ended.
- step S72 determines whether or not the learning promotion condition is satisfied. If it is determined in step S72 that the learning promotion condition is satisfied, the process proceeds to step S75.
- step S75 the learning promotion flag Fa is set to 1.
- step S76 it is determined whether or not the inversion counter CT is N or more.
- the inversion counter CT is a counter that is incremented by 1 every time the target air-fuel ratio is inverted between the rich air-fuel ratio and the lean air-fuel ratio.
- step S76 When it is determined in step S76 that the reversal counter CT is less than N, that is, when it is determined that the number of reversals of the target air-fuel ratio is less than N, the process proceeds to step S77.
- the rich set correction amount AFCrich is set to AFCrich 2 greater than AFCrich 1.
- step S78 the switching reference value OEDref is set to OEDref 2 which is smaller than OEDref 1 , and the control routine is ended.
- step S76 it is determined in step S76 that the inversion counter CT is N or more, and the process proceeds to step S79.
- step S79 the rich set correction amount AFCrich is set to AFCrich 1 .
- step S80 the switching reference value OEDref is set to OEDref 1 .
- the learning promotion flag Fa is reset to 0 in step S81, and the inversion counter CT is reset to 0 in step S82, and the control routine is terminated.
- control device for an internal combustion engine according to a second embodiment of the present invention will be described with reference to FIGS.
- the configuration and control of the control device according to the second embodiment are the same as the configuration and control of the control device according to the first embodiment except for the points described below.
- the first embodiment described above has a problem that the output air-fuel ratio of the upstream air-fuel ratio sensor 40 is shifted to the rich side or the lean side as a whole.
- the exhaust gas flowing out from the upstream side exhaust purification catalyst 20 circulates around the downstream air-fuel ratio sensor 41, it is affected by the deviation of the air-fuel ratio of the exhaust gas between the cylinders and the hydrogen in the exhaust gas. Hateful. Therefore, compared with the upstream air-fuel ratio sensor 40, the downstream air-fuel ratio sensor 41 is less likely to shift the output air-fuel ratio to the rich side or the lean side as a whole.
- FIG. 20 shows the output current of the air-fuel ratio sensor when such a reduction deviation occurs.
- the solid line in the figure indicates the output current of the air-fuel ratio sensor in which the reduction deviation has occurred, and the broken line in the figure indicates the output current of the normal air-fuel ratio sensor.
- the output current of the air-fuel ratio sensor in which the reduction deviation has occurred is reduced as a whole.
- the output air-fuel ratio of the air-fuel ratio sensor becomes an air-fuel ratio closer to the theoretical air-fuel ratio than the actual air-fuel ratio.
- FIG. 21 is a view similar to FIG. 12 showing a time chart of the air-fuel ratio correction amount AFC and the like.
- FIG. 21 shows a case where there is no deviation in the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40 and there is a reduction deviation in the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41.
- the air-fuel ratio correction amount AFC is set to the lean set correction amount AFClean before time t 1 . Thereafter, at time t 1 , the cumulative oxygen excess / deficiency ⁇ OED reaches the switching reference value OEDref, and the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich. Accordingly, since the air-fuel ratio of the exhaust gas flowing into the upstream exhaust purification catalyst 20 becomes rich air-fuel ratio, the oxygen storage amount of the upstream exhaust purification catalyst 20 OSA is gradually decreased, almost zero at time t 2 It becomes. As a result, the exhaust gas having a rich set air-fuel ratio corresponding to the rich set correction amount AFCrich flows out from the upstream side exhaust purification catalyst 20.
- the rich determination air-fuel ratio is made leaner than the rich set air-fuel ratio. Therefore, if there is no deviation in the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41, if the exhaust gas having the rich set air-fuel ratio flows out from the upstream side exhaust purification catalyst 20, the output air-fuel ratio AFdwn becomes the rich judgment air.
- the fuel ratio is equal to or less than AFrich. However, if the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is reduced, the output air-fuel ratio AFdwn becomes the rich determination air-fuel ratio even though the actual air-fuel ratio is less than or equal to the rich determination air-fuel ratio.
- the air / fuel ratio becomes larger than that.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 becomes almost zero, and the exhaust gas having a rich set air-fuel ratio flows out from the upstream side exhaust purification catalyst 20. Nevertheless, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 remains higher than the rich determination air-fuel ratio AFrich. Therefore, the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is also a time t 2 after being maintained in an intermediate region M.
- the output air-fuel ratio sensor 41 outputs the air-fuel ratio correction amount AFC at the time t 1 from the rich set correction amount AFCrich to the theoretical air-fuel ratio maintenance determination time Tsto or longer.
- the fuel ratio AFdwn is maintained in the intermediate region M. Therefore, as described above, the stoichiometric air-fuel ratio Zhang with learning control, the learning value sfbg is changed so that the air-fuel ratio of the exhaust gas flowing into the upstream exhaust purification catalyst 20 is changed to the rich side at time t 3 .
- the air-fuel ratio of the exhaust gas control center air-fuel ratio AFR is flowing when shifted to the rich side from the upstream side exhaust purification catalyst 20 at time t 4 is also changed to the rich side, therefore at time t 5
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is equal to or less than the rich determination air-fuel ratio AFrich. Therefore, air-fuel ratio correction quantity AFC is switched to the lean set correction amount AFClean at time t 5, then the air-fuel ratio correction amount AFC is switched alternately between the rich set correction amount AFC and lean setting correction amount AFClean.
- the learning value sfbg is not decreased even if the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained in the intermediate region M over the theoretical air-fuel ratio maintenance determination time Tsto. ing.
- the rich set air-fuel ratio is rich as in the above-described learning promotion control. The degree is increased.
- FIG. 22 is a view similar to FIG. 21 showing a time chart of the air-fuel ratio correction amount AFC and the like.
- FIG. 22 as in FIG. 21, there is no deviation in the output air-fuel ratio AFup of the upstream air-fuel ratio sensor 40, and there is a reduction deviation in the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41. Is shown.
- the time t 2 before a similar control in the example shown in FIG. 21 is performed.
- the air-fuel ratio correction amount AFC is switched from the lean setting the correction amount AFClean rich set correction amount AFCrich.
- the oxygen storage amount OSA of the upstream side exhaust purification catalyst 20 becomes substantially zero at time t 2 , and thereafter, the exhaust gas having a rich set air-fuel ratio corresponding to the rich set correction amount AFCrich flows out of the upstream side exhaust purification catalyst 20.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 has reduced the deviation occurs, the output air-fuel ratio AFdwn also time t 2 after being maintained in an intermediate region M.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is maintained in the intermediate region M from the time t 1 to the time t 3 over the theoretical air-fuel ratio maintenance determination time Tsto. It will be.
- the learning value sfbg is not changed by the theoretical air-fuel ratio stuck learning control even at time t 3 .
- the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is intermediate over the theoretical air-fuel ratio maintenance determination time Tsto after the air-fuel ratio correction amount AFC is switched to the rich set correction amount AFCrich at time t 1 . since it was maintained in the area M, the rich set correction amount AFCrich is made to increase from AFCrich 1 to AFCrich 2 at time t 3 by the learning acceleration control. Therefore, the rich degree of the rich set air-fuel ratio is increased.
- the air-fuel ratio of the exhaust gas flowing into and out of the upstream side exhaust purification catalyst 20 changes to the rich side, so that the output air-fuel ratio AFdwn of the downstream side air-fuel ratio sensor 41 is increased. Also changes to the rich side.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 becomes equal to or lower than the rich determining the air-fuel ratio AFrich at time t 4. Therefore, air-fuel ratio correction quantity AFC is switched to the lean set correction amount AFClean at time t 4, then the air-fuel ratio correction amount AFC is switched alternately between the rich set correction amount AFC and lean setting correction amount AFClean.
- the stoichiometric air-fuel ratio sticking control is not executed, so that when the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 has a reduction deviation, the learned value sfbg is erroneously set. It is prevented from being reduced.
- the output air-fuel ratio AFdwn of the downstream air-fuel ratio sensor 41 is within the intermediate region M without executing the theoretical air-fuel ratio sticking control. It is prevented from being maintained.
- FIG. 23 is a flowchart showing a control routine of sticking learning control in the present embodiment.
- the illustrated control routine is performed by interruption at regular time intervals.
- steps S44 and S8 to S50 of the sticky learning control shown in FIG. 18 are not performed.
- steps S91 to S93, S95 to S97, and S101 to S109 in FIG. 23 are the same as steps S41 to S43, S45 to S47, and S51 to S59 in FIG.
- the same learning promotion control as the learning promotion control shown in FIG. 19 is performed.
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Abstract
Description
図1は、本発明の第一実施形態に係る制御装置が用いられる内燃機関を概略的に示す図である。図1において、1は機関本体、2はシリンダブロック、3はシリンダブロック2内で往復動するピストン、4はシリンダブロック2上に固定されたシリンダヘッド、5はピストン3とシリンダヘッド4との間に形成された燃焼室、6は吸気弁、7は吸気ポート、8は排気弁、9は排気ポートをそれぞれ示す。吸気弁6は吸気ポート7を開閉し、排気弁8は排気ポート9を開閉する。
上流側排気浄化触媒20及び下流側排気浄化触媒24は、いずれも同様な構成を有する。排気浄化触媒20、24は、酸素吸蔵能力を有する三元触媒である。具体的には、排気浄化触媒20、24は、セラミックから成る基材に、触媒作用を有する貴金属(例えば、白金(Pt))及び酸素吸蔵能力を有する物質(例えば、セリア(CeO2))を担持させたものである。排気浄化触媒20、24は、所定の活性温度に達すると、未燃ガス(HCやCO等)と窒素酸化物(NOx)とを同時に浄化する触媒作用に加えて、酸素吸蔵能力を発揮する。
次に、図3及び図4を参照して、本実施形態における空燃比センサ40、41の出力特性について説明する。図3は、本実施形態における空燃比センサ40、41の電圧-電流(V-I)特性を示す図であり、図4は、印加電圧を一定に維持したときの、空燃比センサ40、41周りを流通する排気ガスの空燃比(以下、「排気空燃比」という)と出力電流Iとの関係を示す図である。なお、本実施形態では、両空燃比センサ40、41として同一構成の空燃比センサが用いられる。
次に、本実施形態の内燃機関の制御装置における基本的な空燃比制御の概要を説明する。本実施形態の空燃比制御では、上流側空燃比センサ40の出力空燃比に基づいて上流側空燃比センサ40の出力空燃比が目標空燃比となるように燃料噴射弁11からの燃料噴射量を制御するフィードバック制御が行われる。なお、「出力空燃比」は、空燃比センサの出力値に相当する空燃比を意味する。
ODE=0.23・Qi/(AFup-AFR) …(1)
ここで、0.23は空気中の酸素濃度、Qiは燃料噴射量、AFupは上流側空燃比センサ40の出力空燃比、AFRは制御中心となる空燃比(本実施形態では、理論空燃比)をそれぞれ表している。
図5を参照して、上述したような操作について具体的に説明する。図5は、本実施形態の空燃比制御を行った場合における、空燃比補正量AFC、上流側空燃比センサ40の出力空燃比AFup、上流側排気浄化触媒20の酸素吸蔵量OSA、積算酸素過不足量ΣOED、下流側空燃比センサ41の出力空燃比AFdwn及び上流側排気浄化触媒20から流出する排気ガス中のNOx濃度のタイムチャートである。
ところで、機関本体1が複数の気筒を有する場合、各気筒から排出される排気ガスの空燃比には気筒間でずれが生じる場合がある。一方、上流側空燃比センサ40は排気マニホルド19の集合部に配置されるが、その配置位置に応じて各気筒から排出された排気ガスが上流側空燃比センサ40に曝される程度が気筒間で異なる。この結果、上流側空燃比センサ40の出力空燃比は、或る特定の気筒から排出された排気ガスの空燃比の影響を強く受けることになる。このため、この或る特定の気筒から排出された排気ガスの空燃比が全気筒から排出される排気ガスの平均空燃比とは異なる空燃比となっている場合、平均空燃比と上流側空燃比センサ40の出力空燃比との間にはずれが生じる。すなわち、上流側空燃比センサ40の出力空燃比は実際の排気ガスの平均空燃比よりもリッチ側又はリーン側にずれることになる。
そこで、本発明の実施形態では、上流側空燃比センサ40の出力空燃比におけるずれを補償すべく、通常運転中(すなわち、上述したような目標空燃比に基づいてフィードバック制御を行っているとき)に学習制御が行われる。このうち、まず、通常学習制御について説明する。
sfbg(n)=sfbg(n-1)+k1・ΔΣOED …(2)
AFR=AFRbase+sfbg(n) …(3)
なお、上記式(2)において、nは計算回数又は時間を表している。したがって、sfbg(n)は今回の計算又は現在の学習値である。加えて、上記式(2)におけるk1は、過不足量誤差ΔΣOEDを制御中心空燃比AFRに反映させる程度を表すゲインである。ゲインk1の値が大きいほど制御中心空燃比AFRの補正量が大きくなる。さらに、上記式(3)において、基本制御中心空燃比AFRbaseは、基本となる制御中心空燃比であり、本実施形態では理論空燃比である。
ところで、図7及び図8に示した例では、上流側空燃比センサ40の出力空燃比にずれが生じているが、その程度はそれほど大きくない場合を示している。したがって、図7及び図8の破線からもわかるように、目標空燃比がリッチ設定空燃比に設定されている場合において、実際の排気ガスの空燃比は、リッチ設定空燃比よりもリーンながらも、リッチ空燃比となっている。
そこで、本実施形態では、上流側空燃比センサ40の出力空燃比におけるずれが大きな場合であってもそのずれを補償すべく、上述した通常学習制御に加えて、理論空燃比張付き学習制御、リーン張付き学習制御及びリッチ張付き学習制御が行われる。
まず、理論空燃比張付き学習制御について説明する。理論空燃比張付き学習制御は、図10に示した例のように、下流側空燃比センサ41によって検出される空燃比が理論空燃比に張り付いてしまっている場合に行われる学習制御である。
sfbg(n)=sfbg(n-1)+k2・AFCrich …(4)
なお、上記式(3)において、k2は、制御中心空燃比AFRを補正する程度を表すゲインである(0<k2≦1)。ゲインk2の値が大きいほど、制御中心空燃比AFRの補正量が大きくなる。
次に、リーン張付き学習制御について説明する。リーン張付き学習制御は、図11に示した例のように、目標空燃比をリッチ空燃比にしているにもかかわらず、下流側空燃比センサ41によって検出される空燃比がリーン空燃比に張り付いてしまっている場合に行われる学習制御である。リーン張付き学習制御では、空燃比補正量AFCをリッチ設定補正量AFCrichに切り替えてから、すなわち目標空燃比をリッチ設定空燃比に切り替えてから、下流側空燃比センサ41の出力空燃比AFdwnが予め定められたリーン空燃比維持判定時間以上に亘ってリーン空燃比に維持されているかを判断する。そして、リーン空燃比維持判定時間以上に亘ってリーン空燃比に維持されている場合には、上流側排気浄化触媒20に流入する排気ガスの空燃比がリッチ側に変化するように学習値sfbgが減少せしめられる。図13にこの様子を示す。
sfbg(n)=sfbg(n-1)+k3・(AFCrich-(AFdwn-14.6)) …(5)
なお、上記式(5)において、k3は、制御中心空燃比AFRを補正する程度を表すゲインである(0<k3≦1)。ゲインK3の値が大きいほど、制御中心空燃比AFRの補正量が大きくなる。
ところで、上流側空燃比センサ40の出力空燃比AFupに大きなずれが生じている場合には、このずれを迅速に解消するために、学習制御による学習値sfbgの更新を促進することが必要になる。
次に、図15~図19を参照して、上記実施形態における制御装置について具体的に説明する。本実施形態における制御装置は、機能ブロック図である図15に示したように、A1~A11の各機能ブロックを含んで構成されている。以下、図15を参照しながら各機能ブロックについて説明する。これら各機能ブロックA1~A11における操作は、基本的にECU31において実行される。
まず、燃料噴射量の算出について説明する。燃料噴射量の算出に当たっては、筒内吸入空気量算出手段A1、基本燃料噴射量算出手段A2、及び燃料噴射量算出手段A3が用いられる。
次に、目標空燃比の算出について説明する。目標空燃比の算出に当たっては、酸素過不足量算出手段A4、空燃比補正量算出手段A5、学習値算出手段A6、制御中心空燃比算出手段A7、目標空燃比設定手段A8が用いられる。
次に、上流側空燃比センサ40の出力空燃比AFupに基づいたF/B補正量の算出について説明する。F/B補正量の算出に当たっては、空燃比偏差算出手段A9、F/B補正量算出手段A10が用いられる。
DFi=Kp・DAF+Ki・SDAF+Kd・DDAF …(6)
図16は、空燃比補正量AFCの算出制御の制御ルーチンを示すフローチャートである。図示した制御ルーチンは一定時間間隔の割り込みによって行われる。
図17は、通常学習制御の制御ルーチンを示すフローチャートである。図示した制御ルーチンは一定時間間隔の割り込みによって行われる。
図18は、張付き学習制御(理論空燃比張付き制御、リッチ張付き制御及びリーン張付き制御)の制御ルーチンを示すフローチャートである。図示した制御ルーチンは一定時間間隔の割り込みによって行われる。
図19は、学習促進制御の制御ルーチンを示すフローチャートである。図19に示した制御ルーチンは一定時間間隔の割り込みによって行われる。図19に示したように、まず、ステップS71において、学習促進フラグFaが1にセットされているか否かが判定される。学習促進フラグFaは、学習促進制御を行う場合に1にセットされ、それ以外の場合に0にセットされるフラグである。ステップS71において、学習促進フラグFaが0にセットされていると判定された場合には、ステップS72へと進む。
図23は、本実施形態における張付き学習制御の制御ルーチンを示すフローチャートである。図示した制御ルーチンは一定時間間隔の割り込みによって行われる。図23から分かるように、本実施形態における張付き学習制御では、図18に示した張付き学習制御のステップS44及びS8~ステップS50が行われない。なお、図23のステップS91~S93、S95~S97及びS101~S109は、図18のステップS41~S43、S45~S47及びS51~S59と同一であるため、説明を省略する。なお、本実施形態では、図19に示した学習促進制御と同一の学習促進制御が行われる。
5 燃焼室
7 吸気ポート
9 排気ポート
19 排気マニホルド
20 上流側排気浄化触媒
24 下流側排気浄化触媒
31 ECU
40 上流側空燃比センサ
41 下流側空燃比センサ
Claims (13)
- 内燃機関の排気通路に配置されると共に酸素を吸蔵可能な排気浄化触媒と、前記排気浄化触媒の排気流れ方向下流側に配置されると共に該排気浄化触媒から流出する排気ガスの空燃比を検出する下流側空燃比センサとを具備する内燃機関の制御装置において、
前記排気浄化触媒に流入する排気ガスの空燃比が目標空燃比となるように内燃機関の燃焼室に供給される燃料供給量をフィードバック制御すると共に、前記下流側空燃比センサによって検出された排気ガスの空燃比に基づいて該フィードバック制御に関するパラメータを補正する学習制御を行い、
前記目標空燃比は、理論空燃比よりもリッチなリッチ設定空燃比と理論空燃比よりもリーンなリーン設定空燃比との間で交互に切り替えられ、
前記学習制御による前記パラメータの補正を促進する必要があるときに成立する学習促進条件が成立したときには、前記リッチ設定空燃比のリッチ度合いが増大せしめられる、内燃機関の制御装置。 - 前記目標空燃比は、前記下流側空燃比センサによって検出された空燃比がリッチ判定空燃比以下になったときに前記リーン設定空燃比に切り替えられると共に、前記排気浄化触媒の酸素吸蔵量が最大吸蔵可能酸素量よりも少ない所定の切替基準吸蔵量以上になったときに前記リッチ設定空燃比に切り替えられ、
前記学習促進条件が成立したときには、前記切替基準吸蔵量が減少せしめられる、請求項1に記載の内燃機関の制御装置。 - 内燃機関の排気通路に配置されると共に酸素を吸蔵可能な排気浄化触媒と、前記排気浄化触媒の排気流れ方向下流側に配置されると共に該排気浄化触媒から流出する排気ガスの空燃比を検出する下流側空燃比センサとを具備する内燃機関の制御装置において、
前記排気浄化触媒に流入する排気ガスの空燃比が目標空燃比となるように内燃機関の燃焼室に供給される燃料供給量をフィードバック制御すると共に、前記下流側空燃比センサによって検出された排気ガスの空燃比に基づいて該フィードバック制御に関するパラメータを補正する学習制御を行い、
前記目標空燃比は、前記下流側空燃比センサによって検出された空燃比がリッチ判定空燃比以下になったときに理論空燃比よりもリーンなリーン設定空燃比に切り替えられると共に、前記排気浄化触媒の酸素吸蔵量が最大吸蔵可能酸素量よりも少ない所定の切替基準吸蔵量以上になったときに理論空燃比よりもリッチなリッチ設定空燃比に切り替えられ、
前記学習制御による前記パラメータの補正を促進する必要があるときに成立する学習促進条件が成立したときには、前記切替基準吸蔵量が減少せしめられる、内燃機関の制御装置。 - 前記学習促進条件が成立したときには、前記リーン設定空燃比のリーン度合いが増大せしめられる、請求項2又は3に記載の内燃機関の制御装置。
- 前記学習促進条件が成立したときであっても、前記リーン設定空燃比はそのままの値に維持される、請求項2又は3に記載の内燃機関の制御装置。
- 前記学習制御では、前記目標空燃比をリーン設定空燃比に切り替えてから前記排気浄化触媒の酸素吸蔵量が前記切替基準量以上になるまでの第1期間における積算酸素過不足量の絶対値である第1酸素量積算値と、前記目標空燃比をリッチ設定空燃比に切り替えてから前記下流側空燃比センサによって検出された空燃比が前記リッチ判定空燃比以下になるまでの第2期間における積算酸素過不足量の絶対値である第2酸素量積算値とに基づいて、これら第1酸素量積算値と第2酸素量積算値との差が小さくなるように空燃比に関するパラメータが補正される、請求項2~5のいずれか1項に記載の内燃機関の制御装置。
- 前記学習促進条件は、前記第1酸素量積算値と前記第2酸素量積算値との差が予め定められた促進判定基準値以上であった場合に成立する、請求項6に記載の内燃機関の制御装置。
- 前記学習促進条件は、前記目標空燃比がリッチ設定空燃比とされているときに、前記下流側空燃比センサによって検出された空燃比が所定の理論空燃比促進判定時間以上に亘って理論空燃比よりもリッチなリッチ判定空燃比と理論空燃比よりもリーンなリーン判定空燃比との間の理論空燃比近傍空燃比領域内に維持されている場合に成立する、請求項2~7のいずれか1項に記載の内燃機関の制御装置。
- 前記学習促進条件は、前記目標空燃比がリッチ空燃比とされているときに、前記下流側空燃比センサによって検出された空燃比が前記理論空燃比促進判定時間よりも短いリーン空燃比維持判定時間以上に亘って前記リーン判定空燃比よりもリーンな空燃比に維持されている場合に成立する、請求項8に記載の内燃機関の制御装置。
- 前記学習制御では、前記目標空燃比がリッチ設定空燃比とされているときに、前記下流側空燃比センサによって検出された空燃比が所定の理論空燃比維持判定時間以上に亘って理論空燃比よりもリッチなリッチ判定空燃比と理論空燃比よりもリーンなリーン判定空燃比との間の理論空燃比近傍空燃比量内に維持されている場合には、前記フィードバック制御において前記排気浄化触媒に流入する排気ガスの空燃比がリッチ側に変化するように前記空燃比に関するパラメータが補正される、請求項2~9のいずれか1項に記載の内燃機関の制御装置。
- 前記学習制御では、前記目標空燃比をリーン設定空燃比に切り替えてから前記排気浄化触媒の酸素吸蔵量が前記切替基準量以上になるまでの第1期間における積算酸素過不足量の絶対値である第1酸素量積算値に対して、前記目標空燃比をリッチ設定空燃比に切り替えてからの積算酸素過不足量の絶対値が予め定められた所定値以上大きくなった場合には、前記フィードバック制御において前記排気浄化触媒に流入する排気ガスの空燃比がリッチ側に変化するように前記空燃比に関するパラメータが補正される、請求項2~9のいずれか1項に記載の内燃機関の制御装置。
- 前記空燃比に関するパラメータは、前記目標空燃比、燃料供給量及び制御中心となる空燃比のいずれかである、請求項1~11のいずれか1項に記載の内燃機関の制御装置。
- 前記排気浄化触媒の排気流れ方向上流側に配置されると共に該排気浄化触媒に流入する排気ガスの空燃比を検出する上流側空燃比センサを更に具備し、
前記上流側空燃比センサによって検出される空燃比が目標空燃比となるように内燃機関の燃焼室に供給される燃料供給量をフィードバック制御し、
前記空燃比に関するパラメータは、前記上流側空燃比センサの出力値である、請求項1~12のいずれか1項に記載の内燃機関の制御装置。
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