CN110945218B - Exhaust gas purification system - Google Patents

Exhaust gas purification system Download PDF

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Publication number
CN110945218B
CN110945218B CN201880047889.5A CN201880047889A CN110945218B CN 110945218 B CN110945218 B CN 110945218B CN 201880047889 A CN201880047889 A CN 201880047889A CN 110945218 B CN110945218 B CN 110945218B
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Prior art keywords
nox
exhaust gas
catalyst
vehicle
sensor
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CN110945218A (en
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坂本隆行
长冈大治
中田辉男
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Isuzu Motors Ltd
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Isuzu Motors Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • 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
    • 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
    • F01N3/10—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
    • 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
    • F01N3/10—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
    • F01N3/24—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 constructional aspects of converting apparatus
    • 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
    • F02D41/04—Introducing corrections for particular operating conditions
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D45/00—Electrical control not provided for in groups F02D41/00 - F02D43/00
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

An exhaust gas purification system comprising: a NOx absorption-reduction catalyst (32) that is provided in an exhaust system of an internal combustion engine (10) mounted in a vehicle (1), absorbs NOx in exhaust gas in an exhaust gas lean combustion state, and reduces and purifies the absorbed NOx in an exhaust gas rich combustion state; acceleration travel acquisition units (42, 47) that acquire whether or not the vehicle (1) is in an acceleration travel state; and a control unit (60) that performs a catalyst regeneration process in which the NOx occlusion reduction catalyst (32) reduces and purifies the occluded NOx by bringing the exhaust gas into a rich state when the acceleration travel state of the vehicle (1) is acquired.

Description

Exhaust gas purification system
Technical Field
The present disclosure relates to an exhaust gas purification system.
Background
Conventionally, an NOx occlusion reduction type catalyst is known as a catalyst for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from an internal combustion engine. The NOx occlusion reduction catalyst occludes NOx contained in the exhaust gas when the exhaust gas is in a lean environment, and detoxifies and releases the occluded NOx by reducing and purifying hydrocarbons contained in the exhaust gas when the exhaust gas is in a rich environment. Therefore, when a predetermined condition such as the amount of NOx absorbed by the catalyst reaching a predetermined amount is satisfied, it is necessary to periodically perform so-called NOx purification in which the exhaust gas is brought into a rich state by exhaust pipe injection or after injection in order to recover the NOx absorption capacity (see, for example, patent documents 1 and 2).
[ Prior art documents ]
[ patent document ]
Patent document 1 Japanese laid-open patent application No. 2008-202425
Patent document 2 Japanese laid-open patent application No. 2007-16713
[ problem to be solved by the invention ]
The NOx purification described above is performed for the purpose of recovering the NOx absorbing ability. Therefore, the conditions for carrying out NOx purification include that a predetermined amount or more of NOx is absorbed in the NOx occlusion reduction catalyst. The conditions for carrying out NOx purification generally include a catalyst temperature equal to or higher than an activation temperature, a stable output torque of an engine in a predetermined operating state, and the like. Therefore, there are problems as follows: even if the excess air ratio of the exhaust gas is in a state in which NOx purification is suitably performed, if the NOx storage amount of the NOx occlusion reduction catalyst does not reach a predetermined amount, NOx purification is not performed, and a chance that the NOx occlusion ability can be efficiently recovered is missed.
The disclosed technology aims to efficiently recover the NOx absorption capacity of a NOx absorption reduction catalyst.
[ means for solving the problems ]
The disclosed technique is characterized by comprising: a NOx occlusion reduction catalyst that is provided in an exhaust system of an internal combustion engine mounted in a vehicle, that occludes NOx in exhaust gas in an exhaust gas lean combustion state, and that reduces and purifies the occluded NOx in an exhaust gas rich combustion state; an acceleration travel acquisition means that acquires whether or not the vehicle is in an acceleration travel state; and a catalyst regeneration unit that performs a catalyst regeneration process in which the exhaust gas is brought into a rich state when the acceleration travel state of the vehicle is acquired by the acceleration travel acquisition unit, thereby reducing and purifying the NOx absorbed by the NOx absorption reduction catalyst.
Preferably, the vehicle further includes catalyst temperature estimating means for estimating a catalyst temperature of the NOx absorption reduction catalyst, and the catalyst regenerating means performs the catalyst regeneration process when the catalyst temperature estimated by the catalyst temperature estimating means is equal to or higher than a catalyst activation temperature of the NOx absorption reduction catalyst and the acceleration running state of the vehicle is acquired by the acceleration running acquiring means.
In addition, the acceleration travel acquiring means may acquire a vehicle speed of the vehicle, and acquire whether or not the vehicle is in an acceleration travel state based on a change amount of the vehicle speed.
Further, the acceleration travel acquiring means may include: a first sensor that detects information of a fuel injection quantity of an injector for injecting high-pressure fuel into a cylinder of the internal combustion engine; and a second sensor that acquires a vehicle speed of the vehicle, wherein the acceleration travel acquisition means performs the catalyst regeneration process when the fuel injection amount acquired based on the detection information of the first sensor is equal to or greater than a predetermined injection amount threshold value and the acceleration of the vehicle based on the vehicle speed acquired by the second sensor is equal to or greater than a predetermined acceleration threshold value.
[ Effect of the invention ]
According to the technique of the present disclosure, the NOx storage capacity of the NOx storage reduction catalyst can be recovered efficiently.
Drawings
Fig. 1 is a diagram showing an overall configuration of an exhaust gas purification system according to the present embodiment.
Fig. 2 is a functional block diagram showing the NOx purification control unit of the present embodiment.
Fig. 3 is a timing chart for explaining the NOx purification control according to the present embodiment.
Fig. 4 is a block diagram showing a MAF target value setting process used in the NOx purification lean burn control according to the present embodiment.
Fig. 5 is a block diagram showing a process of setting a target injection amount used in the NOx purification rich control according to the present embodiment.
Fig. 6 is a block diagram showing an implementation determination process of the NOx purification control according to the present embodiment.
Fig. 7 is a timing chart illustrating the NOx purification control performed when the third embodiment condition is satisfied.
Fig. 8 is a block diagram showing a process of learning and correcting the injection quantity of the in-cylinder injector according to the present embodiment.
Fig. 9 is a flowchart for explaining the processing for calculating the learning correction coefficient according to the present embodiment.
Fig. 10 is a block diagram showing the MAF correction coefficient setting process according to the present embodiment.
Detailed Description
Hereinafter, an exhaust gas purification system and a control method thereof according to an embodiment of the present disclosure will be described with reference to the drawings.
Fig. 1 is a schematic overall configuration diagram showing an intake/exhaust system of a diesel engine (hereinafter, simply referred to as an engine) 10 mounted on a vehicle 1 according to the present embodiment. In each cylinder of engine 10, an in-cylinder injector 11 is provided for directly injecting high-pressure fuel accumulated in a common rail, not shown, into each cylinder. The fuel injection amount or the fuel injection timing of each of these in-cylinder injectors 11 is controlled in accordance with an instruction signal input from an electronic control unit (hereinafter, referred to as ECU) 50.
An intake passage 12 for introducing fresh air is connected to an intake manifold 10A of the engine 10, and an exhaust passage 13 for discharging exhaust gas to the outside is connected to an exhaust manifold 10B. In the intake passage 12, an air cleaner 14, an intake air amount sensor (hereinafter, referred to as MAF sensor) 40, a compressor 20A of a supercharger 20, an intercooler 15, an intake throttle valve 16, and the like are provided in this order from the intake upstream side. In the exhaust passage 13, a turbine 20B of the supercharger 20, an exhaust aftertreatment device 30, and the like are provided in this order from the exhaust upstream side.
In fig. 1, reference numeral 41 denotes an engine speed sensor for acquiring an engine speed Ne from an unillustrated crankshaft of the engine 10, reference numeral 42 denotes an accelerator opening degree sensor (one example of a first sensor) (one example of an acceleration running acquiring means) for detecting an unillustrated depression amount (accelerator opening degree) of an accelerator pedal in order to acquire the instruction fuel injection quantity Q to the in-cylinder injector 11, reference numeral 46 denotes a boost pressure sensor for acquiring an intake air pressure boosted by the compressor 20A, and reference numeral 47 denotes a vehicle speed sensor (one example of a second sensor) (one example of an acceleration running acquiring means) for acquiring a vehicle speed of the vehicle 1 from an unillustrated drive shaft. ECU10 obtains an instruction fuel injection quantity Q to in-cylinder injector 11 based on the detection information of accelerator opening sensor 46.
The EGR (Exhaust Gas Recirculation) device 21 includes: an EGR passage 22 connecting the exhaust manifold 10B and the intake manifold 10A; an EGR cooler 23 that cools EGR gas; an EGR valve 24 for adjusting the EGR amount.
The exhaust aftertreatment device 30 is configured such that an oxidation catalyst 31, a NOx occlusion reduction catalyst 32, and a particulate filter (hereinafter, simply referred to as a filter) 33 are arranged in this order from the exhaust upstream side in a casing 30A. Further, an exhaust injector 34 is provided in the exhaust passage 13 on the upstream side of the oxidation catalyst 31, and the exhaust injector 34 injects unburned fuel (mainly HC) into the exhaust passage 13 in accordance with an instruction signal input from the ECU 50.
The oxidation catalyst 31 is formed by placing an oxidation catalyst component on the surface of a ceramic support such as a honeycomb structure. If unburned fuel is supplied to oxidation catalyst 31 by exhaust pipe injection of exhaust injector 34 or remote injection of in-cylinder injector 11, oxidation catalyst 31 oxidizes it to raise the exhaust gas temperature.
The NOx occlusion reduction catalyst 32 is formed by, for example, placing an alkali metal or the like on the surface of a ceramic support such as a honeycomb structure. The NOx occlusion reduction catalyst 32 occludes NOx in the exhaust gas when the exhaust gas air-fuel ratio is in a lean state, and reduces and purifies the occluded NOx with a reducing agent (HC or the like) contained in the exhaust gas when the exhaust gas air-fuel ratio is in a rich state.
The filter 33 is formed by arranging a plurality of cells partitioned by, for example, a porous partition wall in the flow direction of the exhaust gas, and alternately closing the upstream side and the downstream side of the cells. The filter 33 traps Particulate Matter (PM) in the exhaust gas on the pores or the surface of the partition wall, and if the estimated amount of PM accumulation reaches a predetermined amount, so-called forced filter regeneration is performed in which the PM is burned off. The filter forced regeneration is performed by supplying unburned fuel to the upstream side oxidation catalyst 31 by exhaust pipe injection or after injection, and raising the temperature of the exhaust gas flowing into the filter 33 to the PM combustion temperature.
The first exhaust temperature sensor 43 is provided upstream of the oxidation catalyst 31, and detects the temperature of the exhaust gas flowing into the oxidation catalyst 31. The second exhaust gas temperature sensor 44 is provided between the NOx adsorption-reduction catalyst 32 and the filter 33, and detects the temperature of the exhaust gas flowing into the filter 33. The NOx/λ sensor 45 is provided downstream of the filter 33, and detects the NOx value and the λ value (hereinafter also referred to as the excess air ratio) of the exhaust gas passing through the NOx occlusion reduction catalyst 32.
The ECU50 performs various controls of the engine 10 and the like, and is configured to include a known CPU, ROM, RAM, input ports, output ports, and the like. In order to perform these various controls, the sensor values of the sensors 40 to 47 are input to the ECU 50. The ECU50 includes functional elements that are part of the NOx purification control unit 60, the MAF tracking control unit 80, the injection amount learning correction unit 90, and the MAF correction coefficient calculation unit 95. These functional elements are described as components of the ECU50 which is integrated hardware, but any of them may be provided as separate hardware.
[ NOx purge control ]
The NOx purification control portion 60 is an example of the catalyst regeneration means of the present disclosure, and performs a catalyst regeneration process in which the exhaust gas is brought into a rich state, and NOx absorbed by the NOx occlusion reduction catalyst 32 is detoxified and released by reduction purification, thereby recovering the NOx absorption capacity of the NOx occlusion reduction catalyst 32 (hereinafter, this control is referred to as NOx purification control). If the NOx purge execution determination processing unit 70, which will be described later, determines that the NOx purge execution condition is satisfied, the NOx purge flag F is turned onNP(FNP1) to start NOx purification control (refer toTime t of fig. 31)。
As shown in fig. 2, the NOx purification control portion 60 includes functional elements of the NOx purification lean control portion 60A, NOx purification rich control portion 60B and the NOx purification implementation determination processing portion 70 as a part. In the present embodiment, the exhaust gas is made rich under the NOx purification control by a combination of the NOx purification lean control in which the air excess ratio is reduced from the steady operation time (for example, about 1.5) to the first target air excess ratio (for example, about 1.3) on the lean side of the stoichiometric air-fuel ratio equivalent value (about 1.0) by the air system control and the NOx purification rich control in which the air excess ratio is reduced from the first target air excess ratio to the second target air excess ratio (for example, about 0.9) on the rich side by the injection system control. The following describes details of the NOx purification lean burn control and the NOx purification rich burn control.
[ NOx purge lean burn control ]
FIG. 4 shows MAF target value MAF performed by NOx purge lean burn control unit 60ANPL＿TrgtA block diagram of the setting process of (1). The first target excess air ratio setting map 61 is a map referred to based on the engine rotation speed Ne and the accelerator opening Q, and an excess air ratio target value λ at the time of NOx purification lean burn control corresponding to the engine rotation speed Ne and the accelerator opening Q is set in advance based on experiments or the likeNPL＿Trgt(first target excess air ratio).
First, the engine speed Ne and the accelerator opening Q are input signals, and the air excess ratio target value λ at the time of NOx purification lean burn control is read from the first target air excess ratio setting map 61NPL＿TrgtAnd then input to the MAF target value calculation unit 62. Then, the MAF target value calculation unit 62 calculates the MAF target value MAF in the NOx purification lean burn control based on the following equation (1)NPL＿Trgt。
MAFNPL＿Trgt＝λNPL＿Trgt×Qfnl＿corrd×RoFuel×AFRsto/Maf＿corr···(1)
In the formula (1), Qfnl＿corrdShows the fuel injection quantity (excluding the far post injection), Ro, of in-cylinder injector 11 after learning correction described laterFuelIndicating specific gravity of fuel, AFRstoRepresenting the theoretical air-fuel ratio, Maf＿corrThe MAF correction coefficient is shown below.
If NOx purge flag FNPOn (refer to time t in FIG. 3)1) The MAF target value MAF calculated by the MAF target value calculation unit 62 is input to the gradient processing unit 63NPL＿Trgt. The gradient processing unit 63 reads a gradient coefficient from each gradient coefficient map 63A, B using the engine speed Ne and the accelerator opening Q as input signals, and adds the gradient coefficient to a MAF target gradient value MAFNPL＿Trgt＿RampAnd is input to the valve control section 64.
The valve control unit 64 performs feedback control for throttling the intake throttle valve 16 to the closed side and opening the EGR valve 24 to the lower open side so that the actual MAF value MAF inputted from the MAF sensor 40 is controlledActBecome the MAF target slope value MAFNPL＿Trgt＿Ramp。
As described above, in the present embodiment, the target value λ of the excess air ratio read from the first target excess air ratio setting map 61 is based onNPL＿TrgtAnd the fuel injection amount of each in-cylinder injector 11 to set the MAF target value MAFNPL＿TrgtAnd based on the MAF target value MAFNPL＿TrgtThe air system operation is feedback controlled. Thus, the exhaust gas can be effectively reduced to a desired excess air ratio necessary for the NOx purification lean burn control without providing a λ sensor on the upstream side of the NOx occlusion reduction catalyst 32 or without using the sensor value of the λ sensor even when the λ sensor is provided on the upstream side of the NOx occlusion reduction catalyst 32.
In addition, the fuel injection quantity Q after correction by using learningfnl＿corrdThe MAF target value MAF can be set by feedforward control as the fuel injection amount of each in-cylinder injector 11NPL＿TrgtThe influence of deterioration, characteristic change, or the like of each in-cylinder injector 11 can be effectively eliminated.
In addition, by applying a MAF target value MAFNPL＿TrgtIn addition to the basisThe gradient coefficient set according to the operating state of the engine 10 can effectively prevent the engine 10 from stalling due to a rapid change in the intake air amount, and the drivability from deteriorating due to a torque variation.
[ Fuel injection quantity setting for NOx purge rich control ]
FIG. 5 shows a target injection quantity Q of the exhaust pipe injection or the after-rich injection by the NOx purification rich control portion 60BNPR＿Trgt(injection amount per unit time) setting process. The second target excess air ratio setting map 65 is a map referred to based on the engine rotation speed Ne and the accelerator opening Q, and the target excess air ratio value λ during the NOx purification rich control corresponding to the engine rotation speed Ne and the accelerator opening Q is set in advance based on experiments or the likeNPR＿Trgt(second target excess air ratio).
First, the air excess ratio target value λ at the time of NOx purification rich control is read from the second target air excess ratio setting map 65 using the engine speed Ne and the accelerator opening Q as input signalsNPR＿TrgtThis is input to the injection amount target value calculation unit 66. Then, the target injection amount Q in the NOx purification rich control is calculated by the injection amount target value calculation unit 66 based on the following formula (2)NPR＿Trgt。
QNPR＿Trgt＝MAFNPL＿Trgt×Maf＿corr/(λNPR＿Trgt×RoFuel×AFRsto)－Qfnl＿corrd···(2)
In the formula (2), MAFNPL＿TrgtThe NOx purification lean MAF target value is input from the MAF target value calculation unit 62. In addition, QfnlRaw＿corrdShows the fuel injection quantity (except for the far after injection), Ro, of in-cylinder injector 11 before the application of the after-mentioned learning corrected MAF tracking controlFuelIndicating specific gravity of fuel, AFRstoRepresenting the theoretical air-fuel ratio, Maf＿corrThe MAF correction coefficient is shown below.
If NOx purge flag FNPWhen ON, the target injection quantity Q calculated by the injection quantity target value calculation part 66 is setNPR＿TrgtSent to exhaust as an injection indication signalInjector 34 or in-cylinder injectors 11 (time t in fig. 3)1). The transmission of the injection instruction signal is continued until the NOx purification flag F is turned off due to the establishment of the NOx purification end condition described laterNP(time t of FIG. 32) Until now.
As described above, in the present embodiment, the excess air ratio target value λ read from the second target excess air ratio setting map 65 is used as the basisNPR＿TrgtAnd the fuel injection amount of each in-cylinder injector 11 to set a target injection amount QNPR＿Trgt. Thus, the exhaust gas can be effectively reduced to a desired excess air ratio necessary for the NOx purification rich combustion control without providing a λ sensor on the upstream side of the NOx occlusion reduction catalyst 32 or without using the sensor value of the λ sensor even when the λ sensor is provided on the upstream side of the NOx occlusion reduction catalyst 32.
In addition, the fuel injection quantity Q after correction by using learningfnl＿corrdAs the fuel injection amount of each in-cylinder injector 11, the target injection amount Q can be set by the feedforward controlNPR＿TrgtAnd the influence of deterioration, characteristic change, and the like of each in-cylinder injector 11 can be effectively eliminated.
[ NOx purification implementation determination processing ]
Fig. 6 is a block diagram showing the determination process performed by the NOx purification implementation determination processing unit 70. The NOx purification implementation determination processing unit 70 includes an implementation determination unit 71, a NOx absorption amount estimation unit 72, an absorption amount threshold map 73, a catalyst temperature estimation unit (an example of a catalyst temperature estimation means) 74, an absorption amount threshold correction unit 75, a purification rate calculation unit 76, and a degradation degree estimation unit 77 as a part of functional elements.
When any of the following conditions (1) to (3) is satisfied, the implementation determination unit 71 determines that the NOx purification control is implemented and sets the NOx purification flag FNPIs set to be on (F)NP＝1)。
The implementation conditions determined by the implementation determination unit 71 are the following three: (1) under the first embodiment conditions, the catalyst temperature of the NOx occlusion reduction catalyst 32 is equal to or higher than the predetermined activation temperature, and the estimated NOx occlusion amount of the NOx occlusion reduction catalyst 32m＿NOxReaches a predetermined absorption threshold STR＿thr＿NOxThe above; (2) under the second embodiment condition, the catalyst temperature of the NOx occlusion reduction catalyst 32 is equal to or higher than the predetermined activation temperature, and the NOx purification rate NOx by the NOx occlusion reduction catalyst 32 is set to be higher than the predetermined activation temperature＿pur％Decreasing to below a predetermined purge rate threshold; (3) under the third embodiment, the catalyst temperature of the NOx occlusion reduction catalyst 32 is equal to or higher than the predetermined activation temperature, and the vehicle 1 is in the acceleration running state. If any of the three execution conditions is satisfied, the execution determination unit 71 turns on the NOx purification flag FNP(FNP1) to start the NOx purification control.
NOx storage amount estimation value m used for determination under the first embodiment＿NOxThe NOx storage amount estimation unit 72 estimates the NOx storage amount. The NOx storage amount estimated value m is calculated based on, for example, a map or a model equation including the operating state of the engine 10 and the sensor value of the NOx/λ sensor 45 as input signals＿NOxAnd (4) finishing. Catalyst estimated temperature Temp using NOx occlusion reduction catalyst 32＿LNTAnd the reference threshold value map 73 sets the threshold value STR of the NOx absorption amount＿thr＿NOx. Catalyst temperature estimated temperature Temp is estimated by catalyst temperature estimating unit 74＿LNT. The catalyst estimated temperature Temp is estimated, for example, based on the inlet temperature of the oxidation catalyst 31 detected by the first exhaust temperature sensor 43, the HC and CO heat generation amounts in the oxidation catalyst 31 and the NOx occlusion reduction catalyst 32, and the like＿LNTAnd (4) finishing. NOx purification flag F turned on by satisfaction of first embodiment conditionNPAt the estimated NOx absorption amount m＿NOxClosed when the NOx removal rate is reduced to a predetermined value indicating that NOx removal is successful (F)NP＝0)。
Further, the NOx absorption threshold STR set based on the absorption threshold map 73 is corrected by the absorption threshold correction unit 75＿thr＿NOx. The absorption threshold correction unit 75 corrects the NOx absorption threshold STR＿thr＿NOxThe deterioration correction coefficient (deterioration degree) obtained by the deterioration degree estimating unit 77 is multiplied. For example, the heat generation amount of HC and CO in the NOx occlusion reduction catalyst 32 is reduced, and the NOx occlusion reduction catalyst 32 is usedThe deterioration correction coefficient is determined based on the thermal history, the decrease in the NOx purification rate of the NOx occlusion reduction catalyst 32, the vehicle travel distance, and the like.
NOx purification rate NOx used for determination of second embodiment condition＿pur％The purification rate calculating unit 76 calculates the purification rate. NOx purification Rate NOx＿pur％For example, the NOx amount on the downstream side of the catalyst detected by the NOx/λ sensor 45 is divided by the NOx emission amount on the upstream side of the catalyst estimated from the operating state of the engine 10 and the like. NOx purification flag F turned on by satisfaction of second embodiment conditionNPAt NOx purifying rate NOx＿pur％Closed when the purification rate rises to a predetermined value indicating recovery of the purification rate (F)NP＝0)。
The third implementation condition is determined depending on whether or not the fuel injection quantity of in-cylinder injector 11 is increased by the driver's operation of depressing the accelerator pedal, and the vehicle 1 is in a state of acceleration running along with this. Specifically, when the acceleration of vehicle 1 obtained by differentiating the sensor value of vehicle speed sensor 47 is equal to or greater than a predetermined acceleration threshold value indicating acceleration running of vehicle 1 in a state where the catalyst temperature of NOx absorption reduction catalyst 32 is equal to or greater than a predetermined activation temperature, and the fuel injection quantity to in-cylinder injector 11 indicated by the sensor value of accelerator opening sensor 42 is equal to or greater than a predetermined injection quantity threshold value indicating the load operation state of engine 10, execution determination unit 71 determines that vehicle 1 is in a predetermined acceleration running state (including start acceleration from a stopped state and reacceleration from a decelerated state), and turns on NOx purification flag FNP(FNP1). The NOx purification control performed by the establishment of the third embodiment condition may be performed by using both the air system control and the injection system control, or may be performed by using only the injection system control in accordance with the load state of the engine 10.
When the acceleration of vehicle 1 obtained from the sensor value of vehicle speed sensor 47 is reduced to a predetermined value, when the fuel injection quantity instructed from in-cylinder injector 11 based on the sensor value of accelerator opening sensor 42 is reduced to a predetermined threshold value or less, or from NOx purification flag FNPIs turned on for a prescribed upper threshold timeWhen the third condition is satisfied, the NOx purge flag F that is turned on is turned offNP(FNP＝0)。
In this way, regardless of the NOx storage amount of the NOx storage reduction catalyst 32, the NOx purification control is performed every time the vehicle 1 accelerates in a state where the catalyst temperature is equal to or higher than the activation temperature, and as shown by T in fig. 71～TnAs shown, the execution frequency of NOx purification is effectively ensured. This enables the NOx storage capacity of the NOx storage reduction catalyst 32 to be recovered efficiently.
In addition, by carrying out NOx purification at the time of acceleration of the vehicle (which is likely to become a rich environment) in which exhaust gas λ is likely to decrease due to an increase in the fuel injection quantity of in-cylinder injector 11, the amount of consumption of fuel used in NOx purification is effectively suppressed, and fuel economy performance can be reliably improved.
Further, in the conventional technology in which NOx purification is performed in a state in which vibration or noise is small and the output torque of the engine 10 is stable, there is a possibility that a sense of incongruity may be given to the driver due to a variation in the engine rotational speed (output torque) or the like associated with the rich combustion of the exhaust gas, but as in the present embodiment, by performing NOx purification control during acceleration running of the vehicle 1 in which the output torque of the engine 10 varies, the sense of incongruity of the driver due to the torque variation or the like is effectively reduced, and deterioration of drivability can be reliably prevented.
[ MAF tracking control ]
Returning to fig. 1, the MAF tracking control unit 80 executes MAF tracking control for correcting the fuel injection timing and the fuel injection amount of each in-cylinder injector 11 based on the MAF change during (1) the period for switching from the lean state in the normal operation to the rich state in the NOx purification control and (2) the period for switching from the rich state in the NOx purification control to the lean state in the normal operation.
[ injection quantity learning correction ]
As shown in fig. 8, the injection amount learning correction unit 90 includes a learning correction coefficient calculation unit 91 and an injection amount correction unit 92.
The learning correction coefficient calculation unit 91 calculates the learning correction coefficient based on the actual NOx/λ sensor 45 detected during the lean operation of the engine 10Lambda value lambdaActAnd the estimated lambda value lambdaEstThe error Delta lambda between the correction coefficients is used to calculate the learning correction coefficient F of the fuel injection quantityCorr. When the exhaust gas is in a lean state, since the HC concentration in the exhaust gas is very low, the change in the exhaust gas λ value due to the oxidation reaction of HC in the oxidation catalyst 31 is very small and can be ignored. Therefore, it is considered that the actual λ value λ in the exhaust gas which has passed through the oxidation catalyst 31 and is detected by the downstream NOx/λ sensor 45 isActWith an estimated lambda value lambda in exhaust gas discharged from the engine 10EstAnd (5) the consistency is achieved. I.e. at these actual lambda values lambdaActAnd the estimated lambda value lambdaEstWhen the error Δ λ occurs therebetween, it can be assumed that the error is caused by a difference between the indicated injection amount and the actual injection amount for each in-cylinder injector 11. The following describes a learning correction coefficient calculation process performed by the learning correction coefficient calculation unit 91 using the error Δ λ, based on the flow of fig. 9.
In step S300, it is determined whether the engine 10 is in a lean operation state based on the engine rotation speed Ne and the accelerator opening Q. If the engine is in the lean operation state, the routine proceeds to step S310 to start learning the correction coefficient.
In step S310, the lambda value lambda is estimated from the obtained valuesEstAn error Δ λ obtained by subtracting the actual λ value λ Act detected by the NOx/λ sensor 45 is multiplied by a learning value gain K1And correcting the sensitivity coefficient K2Thereby calculating a learning value FCorrAdpt(FCorrAdpt＝(λEst－λAct)×K1×K2). The estimated lambda value lambda is estimated and calculated from the operating state of the engine 10 corresponding to the engine rotation speed Ne or the accelerator opening QEst. In addition, the actual lambda value lambda detected by the NOx/lambda sensor 45 is measuredActAs an input signal, a correction sensitivity coefficient K is read from a correction sensitivity coefficient map 91A shown in fig. 72。
In step S320, the learning value F is determinedCorrAdptAbsolute value of | FCorrAdptIf | is within the specified correction limit value a. At absolute value | FCorrAdptIf | exceeds the correction limit A, the control returnsAnd then the study is stopped.
In step S330, the learning prohibition flag F is judgedProWhether it is off. As learning prohibition flag FProFor example, this corresponds to the transient operation of the engine 10 or the NOx purification control (F)NP1) and the like. This is because, in a state where such a condition is satisfied, the error Δ λ is due to the actual λ value λActThe variation of (a) increases, and accurate learning cannot be performed. For the engine 10 in the transient operation state, for example, based on the actual lambda value lambda detected by the NOx/lambda sensor 45ActWhen the time variation amount of (a) is larger than a predetermined threshold value, it is determined that the transient operation state is sufficient.
In step S340, the learning value map 91B (see fig. 8) referred to based on the engine rotation speed Ne and the accelerator opening Q is updated to the learning value F calculated in step S310CorrAdpt. More specifically, a plurality of learning regions divided according to the engine rotation speed Ne and the accelerator opening Q are set in the learning value map 91B. It is preferable that the learning regions are set to be narrower as the frequency of use increases, and to be wider as the frequency of use decreases. Thus, the learning accuracy can be improved in a region with a high frequency of use, and the non-learning can be effectively prevented in a region with a low frequency of use.
In step S350, a learning correction coefficient F is calculated by adding "1" to the learning value read from the learning value map 91B using the engine speed Ne and the accelerator opening Q as input signalsCorr(FCorr＝1+FCorrAdpt). Correcting the learning coefficient FCorrThe injection amount is input to an injection amount correction unit 92 shown in fig. 7.
Injection quantity correction unit 92 injects pilot injection QPilotPilot injection QPreMain injection QMainPost injection QAfterRemote post injection QPostIs multiplied by a learning correction coefficient FCorrAnd correction of these fuel injection amounts is thereby performed.
Thus, by using the estimated lambda value lambdaEstWith the actual lambda value lambdaActError in betweenThe learning value corresponding to the difference Δ λ corrects the fuel injection amount for each in-cylinder injector 11, and thus variation in the deterioration over time, characteristic change, individual difference, and the like of each in-cylinder injector 11 can be effectively eliminated.
[ MAF correction coefficient ]
Returning to fig. 1, the MAF correction coefficient calculation unit 95 calculates a MAF target value MAF for setting the NOx purification controlNPL＿TrgtOr target injection quantity QNPR＿TrgtMAF correction coefficient MAF＿corr。
In the present embodiment, the actual lambda value lambda detected by the NOx/lambda sensor 45 is used as the basisActAnd the estimated lambda value lambdaEstThe error Δ λ therebetween corrects the fuel injection amount of each in-cylinder injector 11. However, since λ is the ratio of air to fuel, the cause of the error Δ λ is not necessarily limited to the influence of the difference between the indicated injection amount and the actual injection amount for each in-cylinder injector 11. That is, there is a possibility that not only the error of each in-cylinder injector 11 but also the error of the sensor 40 affects the error Δ λ of λ.
FIG. 10 shows a MAF correction coefficient MAF calculated by the MAF correction coefficient calculation unit 95＿corrA block diagram of the setting process of (1). The correction coefficient setting map 96 is a setting table referred to based on the engine rotation speed Ne and the accelerator opening Q, and the MAF correction coefficient MAF indicating the sensor characteristics of the sensor 40 corresponding to the engine rotation speed Ne and the accelerator opening Q is set in advance based on experiments or the like＿corr。
The MAF correction coefficient calculation unit 95 reads the MAF correction coefficient MAF from the correction coefficient setting map 96 using the engine speed Ne and the accelerator opening Q as input signals＿corrAnd correcting the MAF by a coefficient Maf＿corrThe MAF target value calculation unit 62 and the injection amount target value calculation unit 66. This enables the sensor characteristics of the sensor 40 to be effectively reflected on the MAF target value MAF during NOx purification controlNPL＿TrgtOr target injection quantity QNPR＿TrgtIn the setting of (1).
[ others ]
The present disclosure is not limited to the above-described embodiments, and can be appropriately modified and implemented without departing from the scope of the present disclosure.
The present application is based on the japanese patent application filed on 19/7/2017 (japanese application 2017-140371), the contents of which are hereby incorporated by reference.
[ Industrial Applicability ]
The present invention has an effect of efficiently recovering the NOx storage capacity of the NOx storage reduction catalyst, and is useful in an exhaust gas purification system or the like.
[ description of reference numerals ]
10 Engine
11 in-cylinder injector
12 air inlet channel
13 exhaust channel
16 air intake throttle valve
24 EGR valve
31 oxidation catalyst
32 NOx occlusion reduction catalyst
33 Filter
34 exhaust gas injector
40 MAF sensor
42 accelerator opening degree sensor
45 NOx/lambda sensor
47 vehicle speed sensor
50 ECU
60 NOx purification control section

Claims (2)

1. An exhaust gas purification system, characterized by comprising:
a NOx occlusion-reduction catalyst that is provided in an exhaust system of an internal combustion engine mounted in a vehicle, adsorbs NOx in exhaust gas in an exhaust gas lean combustion state, and reduces and purifies the adsorbed NOx in an exhaust gas rich combustion state,
an acceleration travel acquisition means that acquires whether the vehicle is in an acceleration travel state, an
Catalyst regeneration means for performing a catalyst regeneration process in which the exhaust gas is brought into a rich state when the acceleration travel state of the vehicle is acquired by the acceleration travel acquisition means, thereby reducing and purifying the NOx absorbed by the NOx absorption reduction catalyst,
the acceleration travel acquiring means includes:
a catalyst temperature estimating means for estimating the catalyst temperature of the NOx absorption-reduction catalyst,
a first sensor that detects information on a fuel injection quantity of an injector for injecting high-pressure fuel into a cylinder of the internal combustion engine, an
A second sensor that acquires a vehicle speed of the vehicle;
the catalyst regeneration means performs the catalyst regeneration process regardless of the NOx absorption amount of the NOx absorption reduction catalyst when the catalyst temperature estimated by the catalyst temperature estimation means is equal to or higher than the catalyst activation temperature of the NOx absorption reduction catalyst, the fuel injection amount acquired based on the detection information of the first sensor is equal to or higher than a predetermined injection amount threshold, and the acceleration of the vehicle acquired based on the vehicle speed by the second sensor is equal to or higher than a predetermined acceleration threshold.
2. The exhaust gas purification system according to claim 1,
the acceleration travel acquisition means acquires a vehicle speed of the vehicle, and acquires whether the vehicle is in an acceleration travel state or not, based on a variation amount of the vehicle speed.
CN201880047889.5A 2017-07-19 2018-07-17 Exhaust gas purification system Active CN110945218B (en)

Applications Claiming Priority (3)

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JP2017-140371 2017-07-19
JP2017140371A JP7019983B2 (en) 2017-07-19 2017-07-19 Exhaust purification system
PCT/JP2018/026647 WO2019017316A1 (en) 2017-07-19 2018-07-17 Exhaust purification system

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JP3509502B2 (en) * 1997-10-20 2004-03-22 日産自動車株式会社 Exhaust gas purification control device for internal combustion engine
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