US20020189246A1 - Method and system for reducing lean-burn vehicle emissions using a downstream reductant sensor - Google Patents
Method and system for reducing lean-burn vehicle emissions using a downstream reductant sensor Download PDFInfo
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- US20020189246A1 US20020189246A1 US09/884,760 US88476001A US2002189246A1 US 20020189246 A1 US20020189246 A1 US 20020189246A1 US 88476001 A US88476001 A US 88476001A US 2002189246 A1 US2002189246 A1 US 2002189246A1
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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
- F01N3/0842—Nitrogen oxides
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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
- F01N13/009—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 having two or more separate purifying devices arranged in series
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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
- F01N13/009—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 having two or more separate purifying devices arranged in series
- F01N13/0093—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 having two or more separate purifying devices arranged in series the purifying devices are of the same type
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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
- F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
- F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
- F02D41/028—Desulfurisation of NOx traps or adsorbent
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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
- 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
- F01N2570/04—Sulfur or sulfur oxides
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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
- 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
- F02D41/30—Controlling fuel injection
- F02D41/38—Controlling fuel injection of the high pressure type
- F02D2041/389—Controlling fuel injection of the high pressure type for injecting directly into the cylinder
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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
- F02D2200/0806—NOx storage amount, i.e. amount of NOx stored on NOx trap
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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
- F02D2200/0808—NOx storage capacity, i.e. maximum amount of NOx that can be stored on NOx trap
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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
- F02D41/1446—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 exhaust temperatures
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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
- F02D41/1456—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 with sensor output signal being linear or quasi-linear with the concentration of oxygen
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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
- F02D41/02—Circuit arrangements for generating control signals
- F02D41/18—Circuit arrangements for generating control signals by measuring intake air flow
- F02D41/187—Circuit arrangements for generating control signals by measuring intake air flow using a hot wire flow sensor
Definitions
- the invention relates to methods and systems for the treatment of exhaust gas generated by “lean burn” operation of an internal combustion engine which are characterized by reduced tailpipe emissions of a selected exhaust gas constituent.
- engine exhaust that includes a variety of constituent gases, including carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO x ).
- CO carbon monoxide
- HC hydrocarbons
- NO x nitrogen oxides
- the rates at which the engine generates these constituent gases are dependent upon a variety of factors, such as engine operating speed and load, engine temperature, ignition (“spark”) timing, and EGR.
- such engines often generate increased levels of one or more constituent gases, such as NO x , when the engine is operated in a lean-burn cycle, i.e., when engine operation includes engine operating conditions characterized by a ratio of intake air to injected fuel that is greater than the stoichiometric air-fuel ratio, for example, to achieve greater vehicle fuel economy.
- Such systems often employ open-loop control of device storage and release times (also respectively known as device “fill” and “purge” times) so as to maximize the benefits of increased fuel efficiency obtained through lean engine operation without concomitantly increasing tailpipe emissions as the device becomes “filled.”
- each purge event must be controlled so that the device does not otherwise exceed its capacity to store the selected exhaust gas constituent, because the selected constituent would then pass through the device and effect an increase in tailpipe emissions. Further, the timing of the purge event is preferably controlled to avoid the purging of only partially filled devices, due to the fuel penalty associated with the purge event's enriched air-fuel mixture. Moreover, when plural emission control devices are deployed in series, excess feedgas HC and CO during the purge event are typically initially consumed in the upstream device to release stored oxygen, whereupon the excess feedgas HC and CO ultimately “break through” the upstream device and enter the downstream device to thereby effect a both an initial release of oxygen previously stored in the downstream device and then a release of stored selected exhaust gas constituent.
- 5,437,153 teaches use of a nominal NO x -retaining capacity for its disclosed device which is significantly less than the actual NO x -storage capacity of the device, to thereby provide the device with a perfect instantaneous NO x -absorbing efficiency, that is, so that the device is able to absorb all engine-generated NO x as long as the cumulative stored NO x remains below this nominal capacity.
- a purge event is scheduled to rejuvenate the device whenever accumulated estimates of engine-generated NO x reach the device's nominal capacity.
- the use of such a fixed nominal NO x capacity necessarily requires a larger device, because this prior art approach relies upon a partial, e.g., fifty-percent NO x fill in order to ensure retention of engine-generated NO x .
- the amount of the selected constituent gas that is actually stored in a given emission control device during vehicle operation depends on the concentration of the selected constituent gas in the engine feedgas, the exhaust flow rate, the ambient humidity, the device temperature, and other variables including the “poisoning” of the device with certain other constituents of the exhaust gas.
- concentration of the selected constituent gas in the engine feedgas the concentration of the selected constituent gas in the engine feedgas
- the exhaust flow rate the ambient humidity
- the device temperature and other variables including the “poisoning” of the device with certain other constituents of the exhaust gas.
- sulfur may be stored in the device and may correlatively cause a decrease in both the device's absolute capacity to store the selected exhaust gas constituent, and the device's instantaneous constituent-storing efficiency.
- U.S. Pat. No. 5,746,049 teaches a device desulfation method which includes raising the device temperature to at least 650° C. by introducing a source of secondary air into the exhaust upstream of the device when operating the engine with an enriched air-fuel mixture and relying on the resulting exothermic reaction to raise the device temperature to the desired level to purge the device of SO x .
- a method for controlling an engine operating over a range of operating conditions including those characterized by combustion of air-fuel mixtures that are both lean and rich of a stoichiometric air-fuel ratio, and wherein exhaust gas generated during engine operation is directed through an exhaust purification system including an upstream emission control device and a downstream sensor operative to generate an output signal representing a concentration of reductants, i.e., excess hydrocarbons, in the exhaust gas exiting the device.
- the method includes determining a first value representing a cumulative amount of a selected constituent of the engine feedgas, such as NO x , generated during an engine operating condition characterized by combustion of an air-fuel mixture lean of the stoichiometric air-fuel ratio (“a lean operating condition”).
- the method also includes determining a second value representing an instantaneous capacity of the device to store the selected constituent, wherein the second value is determined as a function of a characteristic of the output signal generated by the reductant sensor during an engine operating condition characterized by combustion of an air-fuel mixture having an air-fuel ratio rich of the stoichiometric air-fuel ratio (“a rich air-fuel ratio”), and a predetermined reference value.
- the method further includes selecting an engine operating condition as a function of the first and second values.
- the first value is estimated using a lookup table containing mapped values for engine-generated NO x as a function of engine operating conditions, such as instantaneous engine speed and load, air-fuel ratio, spark and EGR.
- the lean operating condition is discontinued, and a rich operating condition suitable for purging the device of stored feedgas NO x is scheduled, when the first value representing accumulated feedgas NO x exceeds the second value representing the instantaneous device NO x -storage capacity.
- the second value is a previously stored value which is periodically adaptively updated based upon a comparison of the amplitude of the reductant sensor's output signal with the predetermined reference value during a subsequent device purge event. In this manner, the storage of NO x by the device and, hence, the “fill time” during which the engine is operated in a lean operating condition, is optimized.
- the method preferably includes calculating a third value representing the amount of fuel, in excess of a stoichiometric amount, which is necessary to purge the device of both stored selected exhaust gas constituent and stored oxygen, based on the first value representing accumulated exhaust gas constituent present in the engine feedgas and a previously stored fourth value representing the amount of excess fuel necessary to purge only stored oxygen from the device.
- the method also preferably includes determining a fifth value representing a cumulative amount of fuel, in excess of the stoichiometric amount, which has been supplied to the engine during a given rich operating condition; and discontinuing the purge event when the fifth value representing the supplied excess fuel exceeds the third value representing the necessary excess fuel to purge the device of all stored selected constituent and stored oxygen.
- the invention optimizes the amount of excess fuel used to purge the device and, indirectly, the device purge time.
- the method preferably includes selecting an engine operating condition suitable for desulfating the device when the second value representing the device's instantaneous capacity to store the selected exhaust gas constituent falls below a minimum threshold value.
- the method further preferably includes indicating a deteriorated device if a predetermined number of device-desulfating engine operating conditions are performed without any significant increase in the second value.
- the fourth value representing the oxygen-only excess fuel amount is periodically updated using an adaption value which is itself generated by comparing the amplitude of the reductant sensor's output signal to a threshold value during a scheduled purge.
- FIG. 1 is a schematic of an exemplary system for practicing the invention
- FIG. 2 is a flowchart illustrating the main control process employed by the exemplary system.
- FIGS. 3 - 5 are flowcharts illustrating the control process for three adaptive algorithms for updating previously stored values utilized by the exemplary system.
- an exemplary control system 10 for a four-cylinder, direct-injection, spark-ignition, gasoline-powered engine 12 for a motor vehicle includes an electronic engine controller 14 having ROM, RAM and a processor (“CPU”) as indicated.
- the controller 14 controls the operation of a set of fuel injectors 16 , each of which is positioned to inject fuel into a respective cylinder 18 of the engine 12 in precise quantities as determined by the controller 14 .
- the controller 14 similarly controls the individual operation, i.e., timing, of the current directed through each of a set of spark plugs 20 in a known manner.
- the controller 14 also controls an electronic throttle 22 that regulates the mass flow of air into the engine 12 .
- An air mass flow sensor 24 positioned at the air intake of engine's intake manifold 26 , provides a signal regarding the air mass flow resulting from positioning of the engine's throttle 22 .
- the air flow signal from the air mass flow sensor 24 is utilized by the controller 14 to calculate an air mass value which is indicative of a mass of air flowing per unit time into the engine's induction system.
- a first oxygen sensor 28 coupled to the engine's exhaust manifold detects the oxygen content of the exhaust gas generated by the engine 12 and transmits a representative output signal to the controller 14 .
- the first oxygen sensor 28 provides feedback to the controller 14 for improved control of the air-fuel ratio of the air-fuel mixture supplied to the engine 12 , particularly during operation of the engine 12 at or near the stoichiometric air-fuel ratio which, for a constructed embodiment, is about 14.65.
- a plurality of other sensors, including an engine speed sensor and an engine load sensor, indicated generally at 29 also generate additional signals in a known manner for use by the controller 14 .
- An exhaust system 30 transports exhaust gas produced from combustion of an air-fuel mixture in each cylinder 18 through an upstream catalytic emission control device 32 and, then, through a downstream catalytic emission control device 34 , both of which function in a known manner to reduce the amount of engine-generated exhaust gas constituents, such as NO x , that reach the vehicle tailpipe 36 .
- a second oxygen sensor 38 is positioned in the exhaust system 30 between the upstream and downstream devices 32 , 34 .
- the first and second oxygen sensors 28 , 38 are “switching” heated exhaust gas oxygen (HEGO) sensors; however, the invention contemplates use of other suitable sensors for generating a signal representing the oxygen concentration in the exhaust manifold and exiting the upstream device 32 , respectively, including but not limited to exhaust gas oxygen (EGO) type sensors, and linear-type sensors such as universal exhaust gas oxygen (UEGO) sensors.
- EGO exhaust gas oxygen
- UEGO universal exhaust gas oxygen
- a reductant sensor 40 is positioned in the exhaust system 30 downstream of the downstream device 34 .
- the reductant sensor 40 generates an output signal RECON which is representing the instantaneous concentration of reductants, i.e., excess hydrocarbons, in the exhaust gas exiting the downstream device 34 .
- FIG. 2 A flowchart illustrating the steps of the control process 100 employed by the exemplary system 10 is shown in FIG. 2.
- the controller 14 sets both a fill-purge cycle counter PCNT and a desulfation flag DSOXFLG to logical zero (blocks 104 and 106 ).
- the controller 14 initializes lean-burn operation, i.e., enables selection by the controller 14 of a lean engine operating condition, at block 110 by resetting the following stored values to zero: a value MNOx representing cumulative feedgas NO x generated during a given lean operating condition; a value XSF representing an amount of fuel in excess of the stoichiometric amount that has been supplied to the engine 12 during a purge event; and values AML1 and AML2 representing cumulative air mass flow into the engine's intake manifold 26 during a given lean operating condition.
- the controller 14 also resets (at block 110 ) a flag ADFLG 1 indicative of the state of a plurality of adaption algorithms, the operation of each of which is described below in connection with FIGS. 4, 5, and 6 .
- the controller 14 then checks to see if a lean flag LFLG is set to logical “1” (block 112 ). If the lean flag LFLG is set to “1,” indicating that lean engine operating condition has been specified, the controller 14 initiates lean engine operation (at block 114 ) by adjusting the fuel injectors 16 and electronic throttle 22 so as to achieve a lean air-fuel mixture having an air-fuel ratio greater than about 18 while further responding to instantaneous vehicle power requirements, as derived from sensed values for engine speed, engine load, vehicle speed and vehicle acceleration.
- the controller 14 After updating values AML1 and AML2 with the current air mass flow rate AM, as obtained from the system's air mass flow sensor 24 (at block 116 , later used to define a time period within which the adaptive algorithms look for a slow response from the reductant sensor 40 ), the controller 14 determines a value FGNOx representing the instantaneous concentration of “feedgas” NO x , i.e., the concentration of NO x in the engine exhaust as a result of the combustion of the air-fuel mixture within the engine 12 (at block 118 ).
- the value FGNOx is determined in a known manner from instantaneous engine operating conditions, which may include, without limitation, engine speed, engine load, EGR, air-fuel ratio, and spark.
- the controller 14 retrieves a stored estimate for instantaneously feedgas NO x concentration from a lookup table stored in ROM, originally obtained from engine mapping data.
- the controller 14 updates the value MNOx representing the cumulative amount of feedgas NO x which has been generated by the engine 12 during the lean operating condition.
- the controller 14 compares the current value PCNT for the fill-purge cycle counter to a reference value PCNT_MAX (at block 122 ).
- the purpose of the fill-purge cycle counter is to enable the controller 14 to periodically break-out of a lean operating condition with only a partially-filled downstream device 34 , in order to adaptively update a previously stored maximum threshold value MNOx_MAX representing the instantaneous NO x -storage capacity of the downstream device 34 (as described more fully below).
- the controller 14 compares the cumulative feedgas NO x value MNOx to the maximum threshold value MNOx_MAX (at block 124 ). If the cumulative feedgas NO x value MNOx is not greater than the maximum threshold value MNOx_MAX, the controller 14 determines (at block 126 ) whether an adaption flag ADFLG 1 is set to logical “1.” If the adaption flag ADFLG 1 is set to logical “1,” the controller 14 continues to enable the selection of a lean engine operating condition, by returning to block 112 as illustrated in FIG. 2.
- the controller 14 then executes either of two adaption algorithms 174 , 176 based upon the current value of the purge cycle counter PCNT, as discussed below in connection with FIGS. 5 and 6.
- the controller 14 determines the cumulative feedgas NO x value MNOx is greater than the maximum threshold value MNOx_MAX, the controller 14 discontinues the lean operating condition and then compares the cumulative feedgas NO x value MNOx to a first minimum threshold value MNOx_THR (at block 128 ).
- the first minimum threshold value MNOx_THR represents a minimum acceptable level of NO x storage and, hence, a failure of the cumulative feedgas NO x value MNOx to exceed the first minimum threshold value MNOx_THR is indicative of a threshold level of device deterioration requiring a response, such as the scheduling of a desulfation event (the control process for which is generally illustrated in FIG. 3, described below). If the cumulative feedgas NO x value MNOx is greater than the first minimum threshold value MNOx_THR (at block 128 ), the controller 14 schedules a downstream device purge event at the first opportunity.
- the controller 14 When initiating a purge event, the controller 14 first updates the value PCNT representing the number of downstream device fill-purge cycles since the last downstream device desulfation event (at block 130 ). The controller 14 then operates the fuel injectors 16 and the electronic throttle 22 so as to switch the air-fuel ratio of the air-fuel mixture supplied to one or more cylinders 18 to a selected purge air-fuel ratio (at block 132 ). The controller 14 then updates the value XSF representing the amount by which the fuel flow F supplied during the purge event exceeds that which is required for stoichiometric engine operation (at block 134 ).
- the controller 14 compares the output signal RECON generated by the reductant sensor 40 to a predetermined maximum threshold value RECON_MAX (at block 136 ).
- the sensor output signal RECON is representative of the instantaneous concentration of reductants, e.g., excess CO, H 2 and HC, in the exhaust gas exiting the downstream device 34 . If the sensor output signal RECON is greater than the maximum threshold value RECON_MAX, indicating an excess amount of hydrocarbons in the exhaust gas exiting the downstream device 34 , the downstream device 34 must already be substantially purged of both stored NO x and stored oxygen, thereby further indicating that the previously stored maximum threshold value MNOx_MAX is too low. Accordingly, the controller 14 increases the stored maximum threshold value MNOx_MAX by a predetermined increment (at block 138 ) and reenables lean engine operation (by looping back to block 110 of FIG. 2).
- the controller 14 determines (at block 136 ) that the reductant sensor output signal RECON is not greater than the maximum threshold value RECON_MAX, the controller 14 compares (at block 140 ) the value XSF representing the supplied excess purge fuel to a calculated reference value XSF_MAX representing the amount of purge fuel, in excess of the stoichiometric amount, necessary to release both stored NO x and stored oxygen from the downstream device 34 . More specifically, the excess fuel reference value XSF_MAX is directly proportional to the quantity of NO x previously calculated to have been stored in the downstream device 34 (represented by the value MNOx achieved in the immediately preceding fill)and is determined according to the following expression:
- XSF_MAX K ⁇ MNOx ⁇ EFF — DES+XSF — OSC
- K is a proportionality constant between the quantity of NO x stored and the amount of excess fuel
- MNOx is a value for cumulative feedgas NO x generated in an immediately preceding lean operating condition
- EFF_DES is a desired device absorption efficiency, for example, eighty to ninety percent of the NO x passing through the downstream device 34 ;
- XSF_OSC is a previously calculated value representing the quantity of excess fuel required to release oxygen stored within the downstream device 34 , as discussed further below.
- the controller 14 loops back (to block 132 ) to continue the purge event. If, however, the supplied excess fuel value XSF exceeds the calculated excess fuel reference value XSF_MAX, the downstream device purge event is deemed to have been completed, and the controller 14 reenables lean engine operation (by looping back to block 110 ).
- the control process 142 for a desulfation event is generally illustrated in FIG. 3. Specifically, the controller 14 initially checks the value of a desulfation flag DSOXFLG (at block 144 ) to determine whether the subject desulfation event is one of several, immediately-successive downstream device desulfating events (the latter condition suggesting that the downstream device 34 has irrevocably deteriorated and, hence, needs servicing).
- DSOXFLG the controller 14 initially checks the value of a desulfation flag DSOXFLG (at block 144 ) to determine whether the subject desulfation event is one of several, immediately-successive downstream device desulfating events (the latter condition suggesting that the downstream device 34 has irrevocably deteriorated and, hence, needs servicing).
- the controller 14 initiates a desulfation event, during which the controller 14 enriches the air-fuel mixture supplied to each engine cylinder 18 at a time when the controller 14 has otherwise operated to raise the temperature T of the downstream device 34 above a minimum desulfating temperature of perhaps about 625° C.
- the controller 14 sets the desulfation flag DSOXFLG to logical “1.”
- the controller 14 then operates the fuel injectors 16 and the electronic throttle 22 to return engine operation to either a near-stoichiometric operating condition or-, preferably, a lean operating condition to achieve greater vehicle fuel economy.
- the controller 14 determines, during a lean operating condition, that the counter PCNT equals a reference value PCNT_MAX (at block 122 )
- the controller 14 compares the cumulative feedgas NO x value MNOx to a second minimum threshold value MNOx_MIN (at block 154 ) which is typically substantially less than the first minimum threshold value MNOx_THR and, most preferably, is selected such that stored oxygen predominates over stored NO x within the downstream device 34 .
- the downstream device 34 has not yet been partially filled to the level represented by the second minimum threshold value MNOx_MIN, which fill level is required to adaptively update the previously stored value XSF_OSC representing the quantity of excess fuel required to release oxygen stored within the downstream device 34 , and the controller 14 loops back to block 112 for further lean engine operation, if desired (as indicated by flag LFLG being equal to logical “1”).
- the controller 14 executes a first adaptive algorithm 156 , whose control process is illustrated in greater detail in FIG. 4. Specifically, the controller 14 immediately discontinues the lean operating condition and schedules a downstream device purge event, in the manner described above. During the immediately following purge event, in which the air-fuel ratio is set to the selected purge air-fuel ratio (at block 158 ) and the fuel flow F is summed to obtain the desired excess fuel value XSF (at block 160 ), the controller 14 again compares the sensor output signal RECON with the maximum threshold value RECON_MAX (at block 162 ).
- the controller 14 compares the excess fuel value XSF to the excess fuel reference value XSF_MAX (at block 164 ). When the excess fuel value XSF is greater than the excess fuel reference value XSF_MAX, the downstream device 34 is deemed to have been substantially purged of both stored NO x and stored oxygen. The purge cycle counter PCNT is then incremented (at block 166 ) and the controller 14 returns to the main control process 100 of FIG. 2.
- the controller 14 determines whether the purge cycle counter PCNT is greater than the reference value PCNT_MAX. If the counter PCNT exceeds the reference value PCNT_MAX, the controller 14 executes the second adaption algorithm 174 whose control process is generally illustrated in FIG. 5. Otherwise, the controller 14 executes the third adaption algorithm 176 whose control process is generally illustrated in FIG. 6.
- the controller 14 determines at block 178 that the sensor output signal RECON is not greater than the maximum reference value RECON_MAX, indicating that the downstream device 34 has not been substantially purged both of stored NO x and of stored oxygen, the controller 14 then confirms that both the sensor output signal RECON is less than a minimum reference value RECON_MIN and that the second cumulative air mass flow measure AML2 is greater than a minimum threshold AML2_MIN at blocks 180 and 182 , respectively (the latter serving to ensure that there has not been an inordinate delay between a change in the air-fuel mixture delivered to each cylinder 18 and the point in time when the resulting exhaust reaches the downstream reductant sensor 40 ).
- the controller 14 immediately discontinues the purge event and increases the stored value XSF_OSC by a predetermined increment (at block 184 ). If either condition of blocks 180 and 182 is not met, however, the controller 14 immediately loops back to the main control process 100 .
- the controller 14 if the controller 14 otherwise determines at block 178 that the sensor output signal RECON is greater than the maximum reference value RECON_MAX, indicating that the downstream device 34 has been substantially purged both of stored NO x and of stored oxygen, the controller 14 immediately discontinues the purge event and further decreases the stored value XSF_OSC by a predetermined increment (at block 186 ). Then, after the controller 14 has either increased or decreased the stored value XSF_OSC at blocks 184 or 186 , the controller 14 sets the adaption flag ADFLG to logical “1,” resets the counter PCNT to zero (both at block 188 ), and returns to the main control process 100 .
- the controller 14 determines at block 178 that the sensor output signal RECON is not greater than the maximum reference value RECON_MAX, indicating that the downstream device 34 has not been substantially purged both of stored NO x and of stored oxygen, the controller 14 then confirms that both the sensor output signal RECON is less than a minimum reference value RECON_MIN and that the first cumulative air mass flow measure AML1 is greater than a minimum threshold AML1_MIN at blocks 190 and 192 , respectively (the latter similarly serving to ensure that there has not been an inordinate delay between a change in the air-fuel mixture delivered to each cylinder 18 and the point in time when the resulting exhaust reaches the downstream reductant sensor 40 ).
- the actual device efficiency may be assumed to be less than the is a desired device absorption efficiency value EFF_DES used in the calculation of the excess fuel reference value XSF_MAX, and the controller 14 immediately discontinues the purge event and decreases the stored maximum threshold value MNOx_MAX by a predetermined increment (at block 194 ). If either condition of blocks 190 and 192 is not met, however, the controller 14 immediately loops back to the main control process 100 .
- the controller 14 if the controller 14 otherwise determines at block 190 that the sensor output signal RECON is greater than the maximum reference value RECON MAX, indicating that the downstream device 34 has been substantially purged both of stored NO x and of stored oxygen, the controller 14 immediately discontinues the purge event and further decreases the stored maximum threshold value MNOx_MAX value by a predetermined increment (at block 200 ). Then, after the controller 14 has either increased or decreased the stored value XSF_OSC at blocks 184 or 186 , the controller 14 sets the adaption flag ADFLG to logical “1” (at block 198 ), and returns to the main control process 100 .
- the controller 14 determines, at block 112 , that lean operating flag LFLG is not set to logical “1,” the controller 14 compares the first cumulative air mass flow value AML1 to a minimum threshold value AML1_MIN (at block 202 ) representing a minimum engine operating time. If the first cumulative air mass flow value AML1 exceeds the threshold value AML1_MIN, a purge event is immediately scheduled to ensure maximum device operating efficiency.
Abstract
Description
- 1. Field of the Invention
- The invention relates to methods and systems for the treatment of exhaust gas generated by “lean burn” operation of an internal combustion engine which are characterized by reduced tailpipe emissions of a selected exhaust gas constituent.
- 2. Background Art
- Generally, the operation of a vehicle's internal combustion engine produces engine exhaust that includes a variety of constituent gases, including carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). The rates at which the engine generates these constituent gases are dependent upon a variety of factors, such as engine operating speed and load, engine temperature, ignition (“spark”) timing, and EGR. Moreover, such engines often generate increased levels of one or more constituent gases, such as NOx, when the engine is operated in a lean-burn cycle, i.e., when engine operation includes engine operating conditions characterized by a ratio of intake air to injected fuel that is greater than the stoichiometric air-fuel ratio, for example, to achieve greater vehicle fuel economy.
- In order to control these vehicle tailpipe emissions, the prior art teaches vehicle exhaust treatment systems that employ one or more three-way catalysts, also referred to as emission control devices, in an exhaust passage to store and release selected exhaust gas constituents, such as NOx, depending upon engine operating conditions. For example, U.S. Pat. No. 5,437,153 teaches an emission control device which stores exhaust gas NOx when the exhaust gas is lean, and releases previously-stored NOx when the exhaust gas is either stoichiometric or “rich” of stoichiometric, i.e., when the ratio of intake air to injected fuel is at or below the stoichiometric air-fuel ratio. Such systems often employ open-loop control of device storage and release times (also respectively known as device “fill” and “purge” times) so as to maximize the benefits of increased fuel efficiency obtained through lean engine operation without concomitantly increasing tailpipe emissions as the device becomes “filled.”
- The timing of each purge event must be controlled so that the device does not otherwise exceed its capacity to store the selected exhaust gas constituent, because the selected constituent would then pass through the device and effect an increase in tailpipe emissions. Further, the timing of the purge event is preferably controlled to avoid the purging of only partially filled devices, due to the fuel penalty associated with the purge event's enriched air-fuel mixture. Moreover, when plural emission control devices are deployed in series, excess feedgas HC and CO during the purge event are typically initially consumed in the upstream device to release stored oxygen, whereupon the excess feedgas HC and CO ultimately “break through” the upstream device and enter the downstream device to thereby effect a both an initial release of oxygen previously stored in the downstream device and then a release of stored selected exhaust gas constituent.
- The prior art has recognized that the storage capacity of a given emission control device is itself a function of many variables, including device temperature, device history, sulfation level, and the presence of any thermal damage to the device. Moreover, as the device approaches its maximum capacity, the prior art teaches that the incremental rate at which the device continues to store the selected constituent, also referred to as the instantaneous efficiency of the device, may begin to fall. Accordingly, U.S. Pat. No. 5,437,153 teaches use of a nominal NOx-retaining capacity for its disclosed device which is significantly less than the actual NOx-storage capacity of the device, to thereby provide the device with a perfect instantaneous NOx-absorbing efficiency, that is, so that the device is able to absorb all engine-generated NOx as long as the cumulative stored NOx remains below this nominal capacity. A purge event is scheduled to rejuvenate the device whenever accumulated estimates of engine-generated NOx reach the device's nominal capacity. Unfortunately, however, the use of such a fixed nominal NOx capacity necessarily requires a larger device, because this prior art approach relies upon a partial, e.g., fifty-percent NOx fill in order to ensure retention of engine-generated NOx.
- The amount of the selected constituent gas that is actually stored in a given emission control device during vehicle operation depends on the concentration of the selected constituent gas in the engine feedgas, the exhaust flow rate, the ambient humidity, the device temperature, and other variables including the “poisoning” of the device with certain other constituents of the exhaust gas. For example, when an internal combustion engine is operated using a fuel containing sulfur, the prior art teaches that sulfur may be stored in the device and may correlatively cause a decrease in both the device's absolute capacity to store the selected exhaust gas constituent, and the device's instantaneous constituent-storing efficiency. When such device sulfation exceeds a critical level, the stored SOx must be “burned off” or released during a desulfation event, during which device temperatures are raised above perhaps about 650° C. in the presence of excess HC and CO. By way of example only, U.S. Pat. No. 5,746,049 teaches a device desulfation method which includes raising the device temperature to at least 650° C. by introducing a source of secondary air into the exhaust upstream of the device when operating the engine with an enriched air-fuel mixture and relying on the resulting exothermic reaction to raise the device temperature to the desired level to purge the device of SOx.
- Thus, it will be appreciated that both the device capacity to store the selected exhaust gas constituent, and the actual quantity of the selected constituent stored in the device, are complex functions of many variables that prior art accumulation-model-based systems do not take into account. The inventors herein have recognized a need for a method and system for controlling an internal combustion engine whose exhaust gas is received by an emission control device which can more accurately determine the amount of the selected exhaust gas constituent, such as NOx, stored in an emission control device during lean engine operation and which, in response, can more closely regulate device fill and purge times to optimize tailpipe emissions.
- Under the invention, a method is provided for controlling an engine operating over a range of operating conditions including those characterized by combustion of air-fuel mixtures that are both lean and rich of a stoichiometric air-fuel ratio, and wherein exhaust gas generated during engine operation is directed through an exhaust purification system including an upstream emission control device and a downstream sensor operative to generate an output signal representing a concentration of reductants, i.e., excess hydrocarbons, in the exhaust gas exiting the device. The method includes determining a first value representing a cumulative amount of a selected constituent of the engine feedgas, such as NOx, generated during an engine operating condition characterized by combustion of an air-fuel mixture lean of the stoichiometric air-fuel ratio (“a lean operating condition”). The method also includes determining a second value representing an instantaneous capacity of the device to store the selected constituent, wherein the second value is determined as a function of a characteristic of the output signal generated by the reductant sensor during an engine operating condition characterized by combustion of an air-fuel mixture having an air-fuel ratio rich of the stoichiometric air-fuel ratio (“a rich air-fuel ratio”), and a predetermined reference value. The method further includes selecting an engine operating condition as a function of the first and second values.
- More specifically, in a preferred embodiment in which the selected exhaust gas constituent is NOx, the first value is estimated using a lookup table containing mapped values for engine-generated NOx as a function of engine operating conditions, such as instantaneous engine speed and load, air-fuel ratio, spark and EGR. The lean operating condition is discontinued, and a rich operating condition suitable for purging the device of stored feedgas NOx is scheduled, when the first value representing accumulated feedgas NOx exceeds the second value representing the instantaneous device NOx-storage capacity. The second value is a previously stored value which is periodically adaptively updated based upon a comparison of the amplitude of the reductant sensor's output signal with the predetermined reference value during a subsequent device purge event. In this manner, the storage of NOx by the device and, hence, the “fill time” during which the engine is operated in a lean operating condition, is optimized.
- In accordance with another feature of the invention, the method preferably includes calculating a third value representing the amount of fuel, in excess of a stoichiometric amount, which is necessary to purge the device of both stored selected exhaust gas constituent and stored oxygen, based on the first value representing accumulated exhaust gas constituent present in the engine feedgas and a previously stored fourth value representing the amount of excess fuel necessary to purge only stored oxygen from the device. The method also preferably includes determining a fifth value representing a cumulative amount of fuel, in excess of the stoichiometric amount, which has been supplied to the engine during a given rich operating condition; and discontinuing the purge event when the fifth value representing the supplied excess fuel exceeds the third value representing the necessary excess fuel to purge the device of all stored selected constituent and stored oxygen. In this manner, the invention optimizes the amount of excess fuel used to purge the device and, indirectly, the device purge time.
- In accordance with another feature of the invention, the method preferably includes selecting an engine operating condition suitable for desulfating the device when the second value representing the device's instantaneous capacity to store the selected exhaust gas constituent falls below a minimum threshold value. The method further preferably includes indicating a deteriorated device if a predetermined number of device-desulfating engine operating conditions are performed without any significant increase in the second value.
- In accordance with a further feature of the invention, the fourth value representing the oxygen-only excess fuel amount is periodically updated using an adaption value which is itself generated by comparing the amplitude of the reductant sensor's output signal to a threshold value during a scheduled purge.
- The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.
- FIG. 1 is a schematic of an exemplary system for practicing the invention;
- FIG. 2 is a flowchart illustrating the main control process employed by the exemplary system; and
- FIGS.3-5 are flowcharts illustrating the control process for three adaptive algorithms for updating previously stored values utilized by the exemplary system.
- Referring to FIG. 1, an
exemplary control system 10 for a four-cylinder, direct-injection, spark-ignition, gasoline-poweredengine 12 for a motor vehicle includes anelectronic engine controller 14 having ROM, RAM and a processor (“CPU”) as indicated. Thecontroller 14 controls the operation of a set offuel injectors 16, each of which is positioned to inject fuel into arespective cylinder 18 of theengine 12 in precise quantities as determined by thecontroller 14. Thecontroller 14 similarly controls the individual operation, i.e., timing, of the current directed through each of a set ofspark plugs 20 in a known manner. - The
controller 14 also controls anelectronic throttle 22 that regulates the mass flow of air into theengine 12. An airmass flow sensor 24, positioned at the air intake of engine'sintake manifold 26, provides a signal regarding the air mass flow resulting from positioning of the engine'sthrottle 22. The air flow signal from the airmass flow sensor 24 is utilized by thecontroller 14 to calculate an air mass value which is indicative of a mass of air flowing per unit time into the engine's induction system. - A
first oxygen sensor 28 coupled to the engine's exhaust manifold detects the oxygen content of the exhaust gas generated by theengine 12 and transmits a representative output signal to thecontroller 14. Thefirst oxygen sensor 28 provides feedback to thecontroller 14 for improved control of the air-fuel ratio of the air-fuel mixture supplied to theengine 12, particularly during operation of theengine 12 at or near the stoichiometric air-fuel ratio which, for a constructed embodiment, is about 14.65. A plurality of other sensors, including an engine speed sensor and an engine load sensor, indicated generally at 29, also generate additional signals in a known manner for use by thecontroller 14. - An
exhaust system 30 transports exhaust gas produced from combustion of an air-fuel mixture in eachcylinder 18 through an upstream catalyticemission control device 32 and, then, through a downstream catalyticemission control device 34, both of which function in a known manner to reduce the amount of engine-generated exhaust gas constituents, such as NOx, that reach thevehicle tailpipe 36. Asecond oxygen sensor 38 is positioned in theexhaust system 30 between the upstream anddownstream devices second oxygen sensors upstream device 32, respectively, including but not limited to exhaust gas oxygen (EGO) type sensors, and linear-type sensors such as universal exhaust gas oxygen (UEGO) sensors. - In accordance with the invention, a
reductant sensor 40 is positioned in theexhaust system 30 downstream of thedownstream device 34. Thereductant sensor 40 generates an output signal RECON which is representing the instantaneous concentration of reductants, i.e., excess hydrocarbons, in the exhaust gas exiting thedownstream device 34. - A flowchart illustrating the steps of the
control process 100 employed by theexemplary system 10 is shown in FIG. 2. Upon engine startup, indicated atblock 102, thecontroller 14 sets both a fill-purge cycle counter PCNT and a desulfation flag DSOXFLG to logical zero (blocks 104 and 106). Then, after checking the value of the desulfation flag DSOXFLG against a reference value indicative of an irrecoverably-deteriorated downstream device 34 (at block 108), thecontroller 14 initializes lean-burn operation, i.e., enables selection by thecontroller 14 of a lean engine operating condition, atblock 110 by resetting the following stored values to zero: a value MNOx representing cumulative feedgas NOx generated during a given lean operating condition; a value XSF representing an amount of fuel in excess of the stoichiometric amount that has been supplied to theengine 12 during a purge event; and values AML1 and AML2 representing cumulative air mass flow into the engine'sintake manifold 26 during a given lean operating condition. Thecontroller 14 also resets (at block 110) a flag ADFLG1 indicative of the state of a plurality of adaption algorithms, the operation of each of which is described below in connection with FIGS. 4, 5, and 6. - The
controller 14 then checks to see if a lean flag LFLG is set to logical “1” (block 112). If the lean flag LFLG is set to “1,” indicating that lean engine operating condition has been specified, thecontroller 14 initiates lean engine operation (at block 114) by adjusting thefuel injectors 16 andelectronic throttle 22 so as to achieve a lean air-fuel mixture having an air-fuel ratio greater than about 18 while further responding to instantaneous vehicle power requirements, as derived from sensed values for engine speed, engine load, vehicle speed and vehicle acceleration. After updating values AML1 and AML2 with the current air mass flow rate AM, as obtained from the system's air mass flow sensor 24 (atblock 116, later used to define a time period within which the adaptive algorithms look for a slow response from the reductant sensor 40), thecontroller 14 determines a value FGNOx representing the instantaneous concentration of “feedgas” NOx, i.e., the concentration of NOx in the engine exhaust as a result of the combustion of the air-fuel mixture within the engine 12 (at block 118). The value FGNOx is determined in a known manner from instantaneous engine operating conditions, which may include, without limitation, engine speed, engine load, EGR, air-fuel ratio, and spark. By way of example only, in a preferred embodiment, thecontroller 14 retrieves a stored estimate for instantaneously feedgas NOx concentration from a lookup table stored in ROM, originally obtained from engine mapping data. - At
block 120 of FIG. 2, thecontroller 14 updates the value MNOx representing the cumulative amount of feedgas NOx which has been generated by theengine 12 during the lean operating condition. Thecontroller 14 compares the current value PCNT for the fill-purge cycle counter to a reference value PCNT_MAX (at block 122). The purpose of the fill-purge cycle counter is to enable thecontroller 14 to periodically break-out of a lean operating condition with only a partially-filleddownstream device 34, in order to adaptively update a previously stored maximum threshold value MNOx_MAX representing the instantaneous NOx-storage capacity of the downstream device 34 (as described more fully below). - If the counter PCNT does not equal the reference value PCNT_MAX, the
controller 14 compares the cumulative feedgas NOx value MNOx to the maximum threshold value MNOx_MAX (at block 124). If the cumulative feedgas NOx value MNOx is not greater than the maximum threshold value MNOx_MAX, thecontroller 14 determines (at block 126) whether an adaption flag ADFLG1 is set to logical “1.” If the adaption flag ADFLG1 is set to logical “1,” thecontroller 14 continues to enable the selection of a lean engine operating condition, by returning to block 112 as illustrated in FIG. 2. If the adaption flag ADFLG is not set to logical “1,” thecontroller 14 then executes either of twoadaption algorithms - If, at
block 124, thecontroller 14 determines the cumulative feedgas NOx value MNOx is greater than the maximum threshold value MNOx_MAX, thecontroller 14 discontinues the lean operating condition and then compares the cumulative feedgas NOx value MNOx to a first minimum threshold value MNOx_THR (at block 128). The first minimum threshold value MNOx_THR represents a minimum acceptable level of NOx storage and, hence, a failure of the cumulative feedgas NOx value MNOx to exceed the first minimum threshold value MNOx_THR is indicative of a threshold level of device deterioration requiring a response, such as the scheduling of a desulfation event (the control process for which is generally illustrated in FIG. 3, described below). If the cumulative feedgas NOx value MNOx is greater than the first minimum threshold value MNOx_THR (at block 128), thecontroller 14 schedules a downstream device purge event at the first opportunity. - When initiating a purge event, the
controller 14 first updates the value PCNT representing the number of downstream device fill-purge cycles since the last downstream device desulfation event (at block 130). Thecontroller 14 then operates thefuel injectors 16 and theelectronic throttle 22 so as to switch the air-fuel ratio of the air-fuel mixture supplied to one ormore cylinders 18 to a selected purge air-fuel ratio (at block 132). Thecontroller 14 then updates the value XSF representing the amount by which the fuel flow F supplied during the purge event exceeds that which is required for stoichiometric engine operation (at block 134). - The
controller 14 then compares the output signal RECON generated by thereductant sensor 40 to a predetermined maximum threshold value RECON_MAX (at block 136). As noted above, the sensor output signal RECON is representative of the instantaneous concentration of reductants, e.g., excess CO, H2 and HC, in the exhaust gas exiting thedownstream device 34. If the sensor output signal RECON is greater than the maximum threshold value RECON_MAX, indicating an excess amount of hydrocarbons in the exhaust gas exiting thedownstream device 34, thedownstream device 34 must already be substantially purged of both stored NOx and stored oxygen, thereby further indicating that the previously stored maximum threshold value MNOx_MAX is too low. Accordingly, thecontroller 14 increases the stored maximum threshold value MNOx_MAX by a predetermined increment (at block 138) and reenables lean engine operation (by looping back to block 110 of FIG. 2). - If the
controller 14 determines (at block 136) that the reductant sensor output signal RECON is not greater than the maximum threshold value RECON_MAX, thecontroller 14 compares (at block 140) the value XSF representing the supplied excess purge fuel to a calculated reference value XSF_MAX representing the amount of purge fuel, in excess of the stoichiometric amount, necessary to release both stored NOx and stored oxygen from thedownstream device 34. More specifically, the excess fuel reference value XSF_MAX is directly proportional to the quantity of NOx previously calculated to have been stored in the downstream device 34 (represented by the value MNOx achieved in the immediately preceding fill)and is determined according to the following expression: - XSF_MAX=K×MNOx×EFF — DES+XSF — OSC,
- where: K is a proportionality constant between the quantity of NOx stored and the amount of excess fuel;
- MNOx is a value for cumulative feedgas NOx generated in an immediately preceding lean operating condition;
- EFF_DES is a desired device absorption efficiency, for example, eighty to ninety percent of the NOx passing through the
downstream device 34; and - XSF_OSC is a previously calculated value representing the quantity of excess fuel required to release oxygen stored within the
downstream device 34, as discussed further below. - If the supplied excess fuel value XSF does not exceed the calculated excess fuel reference value XSF_MAX (as determined at
block 140 of FIG. 2), thecontroller 14 loops back (to block 132) to continue the purge event. If, however, the supplied excess fuel value XSF exceeds the calculated excess fuel reference value XSF_MAX, the downstream device purge event is deemed to have been completed, and thecontroller 14 reenables lean engine operation (by looping back to block 110). - As noted above, after the
controller 14 determines that lean operating condition should be discontinued atblock 124 of FIG. 2, if thecontroller 14 also determines that the cumulative feedgas NOx value MNOx is greater than the first minimum threshold value MNOx_THR representing the minimum acceptable level of NOx storage (the latter being determined at block 128), thecontroller 14 schedules a purge event. However, if thecontroller 14 determines (at block 128) that the cumulative feedgas NOx value MNOx is not greater than the first minimum threshold value MNOx_THR after discontinuing a lean operating condition, thecontroller 14 schedules a downstream device desulfating event, as indicated atblock 142 of FIG. 2. - The
control process 142 for a desulfation event is generally illustrated in FIG. 3. Specifically, thecontroller 14 initially checks the value of a desulfation flag DSOXFLG (at block 144) to determine whether the subject desulfation event is one of several, immediately-successive downstream device desulfating events (the latter condition suggesting that thedownstream device 34 has irrevocably deteriorated and, hence, needs servicing). If the desulfation flag DSOXFLG is set to logical zero, thecontroller 14 initiates a desulfation event, during which thecontroller 14 enriches the air-fuel mixture supplied to eachengine cylinder 18 at a time when thecontroller 14 has otherwise operated to raise the temperature T of thedownstream device 34 above a minimum desulfating temperature of perhaps about 625° C. Upon completion of the desulfation event, thecontroller 14 sets the desulfation flag DSOXFLG to logical “1.” Thecontroller 14 then operates thefuel injectors 16 and theelectronic throttle 22 to return engine operation to either a near-stoichiometric operating condition or-, preferably, a lean operating condition to achieve greater vehicle fuel economy. - As noted above, if the
controller 14 determines, during a lean operating condition, that the counter PCNT equals a reference value PCNT_MAX (at block 122), thecontroller 14 compares the cumulative feedgas NOx value MNOx to a second minimum threshold value MNOx_MIN (at block 154) which is typically substantially less than the first minimum threshold value MNOx_THR and, most preferably, is selected such that stored oxygen predominates over stored NOx within thedownstream device 34. If the cumulative feedgas NOx value MNOx is not greater than the second minimum threshold value MNOx_MIN (as determined at block 154), thedownstream device 34 has not yet been partially filled to the level represented by the second minimum threshold value MNOx_MIN, which fill level is required to adaptively update the previously stored value XSF_OSC representing the quantity of excess fuel required to release oxygen stored within thedownstream device 34, and thecontroller 14 loops back to block 112 for further lean engine operation, if desired (as indicated by flag LFLG being equal to logical “1”). - If the cumulative feedgas NOx value MNOx is greater than the second minimum threshold value MNOx_MIN (as determined at
block 154 of FIG. 2), thecontroller 14 executes a firstadaptive algorithm 156, whose control process is illustrated in greater detail in FIG. 4. Specifically, thecontroller 14 immediately discontinues the lean operating condition and schedules a downstream device purge event, in the manner described above. During the immediately following purge event, in which the air-fuel ratio is set to the selected purge air-fuel ratio (at block 158) and the fuel flow F is summed to obtain the desired excess fuel value XSF (at block 160), thecontroller 14 again compares the sensor output signal RECON with the maximum threshold value RECON_MAX (at block 162). If thecontroller 14 determines that the sensor output signal RECON is greater than the maximum threshold value RECON_MAX, thereby indicating an excess amount of hydrocarbons in the exhaust gas exiting thedownstream device 34, thedownstream device 34 is deemed to already be substantially purged of both stored NOx and stored oxygen. And, since oxygen storage predominates when thedownstream device 34 is filled to the level represented by the second minimum threshold value MNOx_MIN, the previously stored value XSF_OSC representing the quantity of excess fuel required to release stored oxygen is likely too high. Accordingly, thecontroller 14 immediately discontinues the purge event and further decreases the stored value XSF_OSC by a predetermined increment (at block 168). Thecontroller 14 also resets both the counter PCNT and the adaption flag ADFLG to logical-zero (at block 170). - If the
controller 14 otherwise determined, atblock 162, that the sensor output signal RECON does not exceed the maximum threshold value RECON_MAX, thecontroller 14 compares the excess fuel value XSF to the excess fuel reference value XSF_MAX (at block 164). When the excess fuel value XSF is greater than the excess fuel reference value XSF_MAX, thedownstream device 34 is deemed to have been substantially purged of both stored NOx and stored oxygen. The purge cycle counter PCNT is then incremented (at block 166) and thecontroller 14 returns to themain control process 100 of FIG. 2. - Returning to the decision made by the
controller 14 atblock 126 of FIG. 2, if thecontroller 14 determines that the adaption flag ADFLG is not set to logical “1,” thecontroller 14 then determines whether the purge cycle counter PCNT is greater than the reference value PCNT_MAX. If the counter PCNT exceeds the reference value PCNT_MAX, thecontroller 14 executes thesecond adaption algorithm 174 whose control process is generally illustrated in FIG. 5. Otherwise, thecontroller 14 executes thethird adaption algorithm 176 whose control process is generally illustrated in FIG. 6. - As seen in FIG. 5, in the
second adaption algorithm 174, if thecontroller 14 determines atblock 178 that the sensor output signal RECON is not greater than the maximum reference value RECON_MAX, indicating that thedownstream device 34 has not been substantially purged both of stored NOx and of stored oxygen, thecontroller 14 then confirms that both the sensor output signal RECON is less than a minimum reference value RECON_MIN and that the second cumulative air mass flow measure AML2 is greater than a minimum threshold AML2_MIN atblocks cylinder 18 and the point in time when the resulting exhaust reaches the downstream reductant sensor 40). If so, thecontroller 14 immediately discontinues the purge event and increases the stored value XSF_OSC by a predetermined increment (at block 184). If either condition ofblocks controller 14 immediately loops back to themain control process 100. - Continuing with FIG. 5, if the
controller 14 otherwise determines atblock 178 that the sensor output signal RECON is greater than the maximum reference value RECON_MAX, indicating that thedownstream device 34 has been substantially purged both of stored NOx and of stored oxygen, thecontroller 14 immediately discontinues the purge event and further decreases the stored value XSF_OSC by a predetermined increment (at block 186). Then, after thecontroller 14 has either increased or decreased the stored value XSF_OSC atblocks controller 14 sets the adaption flag ADFLG to logical “1,” resets the counter PCNT to zero (both at block 188), and returns to themain control process 100. - Referring to the
third adaption algorithm 176 illustrated in FIG. 6, if thecontroller 14 determines atblock 178 that the sensor output signal RECON is not greater than the maximum reference value RECON_MAX, indicating that thedownstream device 34 has not been substantially purged both of stored NOx and of stored oxygen, thecontroller 14 then confirms that both the sensor output signal RECON is less than a minimum reference value RECON_MIN and that the first cumulative air mass flow measure AML1 is greater than a minimum threshold AML1_MIN atblocks cylinder 18 and the point in time when the resulting exhaust reaches the downstream reductant sensor 40). If so, the actual device efficiency may be assumed to be less than the is a desired device absorption efficiency value EFF_DES used in the calculation of the excess fuel reference value XSF_MAX, and thecontroller 14 immediately discontinues the purge event and decreases the stored maximum threshold value MNOx_MAX by a predetermined increment (at block 194). If either condition ofblocks controller 14 immediately loops back to themain control process 100. - Continuing with FIG. 6, if the
controller 14 otherwise determines atblock 190 that the sensor output signal RECON is greater than the maximum reference value RECON MAX, indicating that thedownstream device 34 has been substantially purged both of stored NOx and of stored oxygen, thecontroller 14 immediately discontinues the purge event and further decreases the stored maximum threshold value MNOx_MAX value by a predetermined increment (at block 200). Then, after thecontroller 14 has either increased or decreased the stored value XSF_OSC atblocks controller 14 sets the adaption flag ADFLG to logical “1” (at block 198), and returns to themain control process 100. - Finally, returning to the
main control process 100 illustrated in FIG. 2, if thecontroller 14 determines, atblock 112, that lean operating flag LFLG is not set to logical “1,” thecontroller 14 compares the first cumulative air mass flow value AML1 to a minimum threshold value AML1_MIN (at block 202) representing a minimum engine operating time. If the first cumulative air mass flow value AML1 exceeds the threshold value AML1_MIN, a purge event is immediately scheduled to ensure maximum device operating efficiency. - While an exemplary embodiment of the invention has been illustrated and described, it is not intended that the disclosed embodiment illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.
Claims (22)
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
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US09/884,760 US6487853B1 (en) | 2001-06-19 | 2001-06-19 | Method and system for reducing lean-burn vehicle emissions using a downstream reductant sensor |
DE10223494A DE10223494A1 (en) | 2001-06-19 | 2002-05-27 | Method and system for reducing emissions from a lean-burn engine in a motor vehicle using a downstream reductant sensor |
GB0213524A GB2380694B (en) | 2001-06-19 | 2002-06-13 | A method and system for reducing vehicle emissions |
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US09/884,760 US6487853B1 (en) | 2001-06-19 | 2001-06-19 | Method and system for reducing lean-burn vehicle emissions using a downstream reductant sensor |
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US6487853B1 US6487853B1 (en) | 2002-12-03 |
US20020189246A1 true US20020189246A1 (en) | 2002-12-19 |
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US09/884,760 Expired - Fee Related US6487853B1 (en) | 2001-06-19 | 2001-06-19 | Method and system for reducing lean-burn vehicle emissions using a downstream reductant sensor |
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US (1) | US6487853B1 (en) |
DE (1) | DE10223494A1 (en) |
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US20050072406A1 (en) * | 2003-10-02 | 2005-04-07 | Cullen Michael J. | Engine control advantageously using humidity |
US7246604B2 (en) * | 2003-10-02 | 2007-07-24 | Ford Global Technologies, Llc | Engine control advantageously using humidity |
US20050109208A1 (en) * | 2003-11-25 | 2005-05-26 | Driscoll J. J. | Method and apparatus for regenerating NOx adsorbers |
US7018442B2 (en) * | 2003-11-25 | 2006-03-28 | Caterpillar Inc. | Method and apparatus for regenerating NOx adsorbers |
GB2475320A (en) * | 2009-11-16 | 2011-05-18 | Gm Global Tech Operations Inc | Method for controlling fluid injected quantity in a NOx reduction system |
US20110120092A1 (en) * | 2009-11-16 | 2011-05-26 | Gm Global Technology Operations, Inc. | Method for controlling fluid injected quantity in a nox reduction system employing a scr catalyist |
US8615987B2 (en) | 2009-11-16 | 2013-12-31 | GM Global Technology Operations LLC | Method for controlling fluid injected quantity in a NOx reduction system employing a SCR catalyst |
GB2475320B (en) * | 2009-11-16 | 2016-09-28 | Gm Global Tech Operations Llc | Method for controlling a diesel emission fluid injected quantity in a NOx reduction system employing a SCR catalyist |
US8689544B2 (en) | 2011-07-15 | 2014-04-08 | GM Global Technology Operations LLC | Emission control system for a vehicle |
Also Published As
Publication number | Publication date |
---|---|
GB2380694A (en) | 2003-04-16 |
DE10223494A1 (en) | 2003-01-09 |
US6487853B1 (en) | 2002-12-03 |
GB2380694B (en) | 2004-11-24 |
GB0213524D0 (en) | 2002-07-24 |
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