WO2012108062A1 - Internal combustion engine exhaust purification device - Google Patents
Internal combustion engine exhaust purification device Download PDFInfo
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- WO2012108062A1 WO2012108062A1 PCT/JP2011/053065 JP2011053065W WO2012108062A1 WO 2012108062 A1 WO2012108062 A1 WO 2012108062A1 JP 2011053065 W JP2011053065 W JP 2011053065W WO 2012108062 A1 WO2012108062 A1 WO 2012108062A1
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- catalyst
- exhaust gas
- upstream
- exhaust
- hydrocarbon
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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
- F02D41/40—Controlling fuel injection of the high pressure type with means for controlling injection timing or duration
- F02D41/402—Multiple injections
- F02D41/405—Multiple injections with post injections
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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
- 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
- F01N13/0097—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 arranged in a single housing
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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
- F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
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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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- 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
- F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
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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
- F01N3/10—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
- F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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- 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
- F01N3/28—Construction of catalytic reactors
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- 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
- F01N3/28—Construction of catalytic reactors
- F01N3/2892—Exhaust flow directors or the like, e.g. upstream of catalytic device
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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
- F01N3/10—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
- F01N3/36—Arrangements for supply of additional fuel
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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
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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
- F02D41/1401—Introducing closed-loop corrections characterised by the control or regulation method
- F02D41/1408—Dithering techniques
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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
- 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
- F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
- F01N2240/30—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being a fuel reformer
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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
- F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
- F01N2560/06—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being a temperature sensor
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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
- F01N2610/00—Adding substances to exhaust gases
- F01N2610/03—Adding substances to exhaust gases the substance being hydrocarbons, e.g. engine fuel
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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
- F02D2041/0265—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to decrease temperature of the exhaust gas treating apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- 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
- F02D2200/0802—Temperature of the exhaust gas treatment apparatus
- F02D2200/0804—Estimation of the temperature of the exhaust gas treatment apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02D—CONTROLLING COMBUSTION ENGINES
- 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
- F02D2250/00—Engine control related to specific problems or objectives
- F02D2250/36—Control for minimising NOx emissions
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T10/00—Road transport of goods or passengers
- Y02T10/10—Internal combustion engine [ICE] based vehicles
- Y02T10/40—Engine management systems
Definitions
- the present invention relates to an exhaust purification device for an internal combustion engine.
- An internal combustion engine in which the air-fuel ratio of the exhaust gas flowing into the NO x storage catalyst is made rich is known (see, for example, Patent Document 1).
- An object of the present invention is to provide an exhaust purification device for an internal combustion engine that can obtain a high NO x purification rate even when the temperature of the exhaust purification catalyst becomes high.
- a hydrocarbon supply valve for supplying hydrocarbons is disposed in the engine exhaust passage, and reformed with NO x contained in the exhaust gas in the engine exhaust passage downstream of the hydrocarbon supply valve.
- An exhaust purification catalyst for reacting with hydrocarbons is arranged, and the exhaust purification catalyst is composed of an upstream catalyst and a downstream catalyst arranged in series at a distance from each other, and the upstream catalyst is at least from the hydrocarbon supply valve. It has a function of reforming the supplied hydrocarbon, and the upstream catalyst has a contour shape that expands from the upstream end to the downstream end, and in the upstream catalyst, from the upstream end to the downstream end.
- a plurality of exhaust gas passages extending radially are formed.
- a noble metal catalyst is supported on the exhaust gas flow surface of at least one of the upstream catalyst and the downstream catalyst, and around the noble metal catalyst.
- Basic exhaust gas flow chart The exhaust purification catalyst is included in the exhaust gas when the hydrocarbon concentration flowing into the upstream catalyst is vibrated with an amplitude within a predetermined range and a period within a predetermined range.
- FIG. 1 is an overall view of a compression ignition type internal combustion engine.
- FIG. 2 is a view schematically showing the surface portion of the catalyst carrier.
- FIG. 3 is a view for explaining an oxidation reaction in the exhaust purification catalyst.
- FIG. 4 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- Figure 5 is a diagram showing the NO x purification rate.
- 6A, 6B and 6C are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
- 7A and 7B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
- FIG. 8 is a diagram showing a change in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 9 is a diagram showing the NO x purification rate.
- FIG. 10 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 11 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 12 is a diagram showing the relationship between the oxidizing power of the exhaust purification catalyst and the required minimum air-fuel ratio X.
- FIG. 13 is a diagram showing the relationship between the oxygen concentration in the exhaust gas and the amplitude ⁇ H of the hydrocarbon concentration, with which the same NO x purification rate can be obtained.
- Figure 14 is a diagram showing a relationship between an amplitude ⁇ H and the NO x purification rate of the hydrocarbon concentration.
- FIG. 10 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 11 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
- FIG. 15 is a graph showing the relationship between the vibration period ⁇ T of the hydrocarbon concentration and the NO x purification rate.
- FIG. 16 is a diagram showing a map of the hydrocarbon feed amount W.
- FIG. 17 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
- Figure 18 is a diagram illustrating a map of exhaust NO x amount NOXA.
- FIG. 19 shows the fuel injection timing.
- FIG. 20 is a diagram showing a map of the hydrocarbon supply amount WR. 21A to 21D are enlarged views of the exhaust purification catalyst.
- FIG. 22 is a flowchart for performing NO x purification control.
- FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
- 1 is an engine body
- 2 is a combustion chamber of each cylinder
- 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber
- 4 is an intake manifold
- 5 is an exhaust manifold.
- the intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8.
- a throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6.
- a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6.
- the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.
- the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the exhaust purification catalyst 13 via the exhaust pipe 12.
- the exhaust purification catalyst 13 includes an upstream side catalyst 14a and a downstream side catalyst 14b arranged in series at a distance from each other, and the upstream side catalyst 14a expands from the upstream end toward the downstream end. Has a contoured shape.
- a hydrocarbon supply valve 15 for supplying hydrocarbons composed of light oil and other fuels used as fuel for the compression ignition internal combustion engine is disposed.
- light oil is used as the hydrocarbon supplied from the hydrocarbon supply valve 15.
- the present invention can also be applied to a spark ignition type internal combustion engine in which combustion is performed under a lean air-fuel ratio.
- the hydrocarbon supply valve 15 supplies hydrocarbons made of gasoline or other fuel used as fuel for the spark ignition internal combustion engine.
- the exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 16, and an electronically controlled EGR control valve 17 is disposed in the EGR passage 16.
- EGR exhaust gas recirculation
- a cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed around the EGR passage 16.
- the engine cooling water is guided into the cooling device 18, and the EGR gas is cooled by the engine cooling water.
- each fuel injection valve 3 is connected to a common rail 20 via a fuel supply pipe 19, and this common rail 20 is connected to a fuel tank 22 via an electronically controlled fuel pump 21 having a variable discharge amount.
- the fuel stored in the fuel tank 22 is supplied into the common rail 20 by the fuel pump 21, and the fuel supplied into the common rail 20 is supplied to the fuel injection valve 3 through each fuel supply pipe 19.
- the electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31.
- a temperature sensor 23 for estimating the temperature of the upstream catalyst 14a and the temperature of the upstream end of the upstream catalyst 14a is attached downstream of the upstream catalyst 14a. Output signals of the temperature sensor 23 and the intake air amount detector 8 are input to the input port 35 via the corresponding AD converters 37, respectively.
- a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the hydrocarbon supply valve 15, the EGR control valve 17, and the fuel pump 21 through corresponding drive circuits 38.
- the base of the upstream catalyst 14a is formed from a thin metal plate, and the base of the downstream catalyst 14b is formed from a ceramic such as cordierite.
- the bases of the upstream catalyst 14a and the downstream catalyst 14b are different, but the same catalyst carrier and the same catalyst are supported on the upstream catalyst 14a and the downstream catalyst 14b.
- FIG. 2 schematically shows the surface portions of the catalyst carrier supported on the bases of the upstream catalyst 14a and the downstream catalyst 14b. In the upstream catalyst 14a and the downstream catalyst 14b, as shown in FIG.
- noble metal catalysts 51 and 52 are supported on a catalyst carrier 50 made of alumina, for example, and potassium K, sodium Na, cesium Cs, barium Ba, alkaline earth metals such as calcium Ca, rare earth and silver Ag, such as lanthanides, copper Cu, iron Fe, donate electrons to NO x, such as iridium Ir
- a basic layer 53 containing at least one selected from possible metals is formed. Since the exhaust gas flows along the catalyst carrier 50, it can be said that the noble metal catalysts 51 and 52 are supported on the exhaust gas flow surfaces of the upstream catalyst 14a and the downstream catalyst 14b. Further, since the surface of the basic layer 53 is basic, the surface of the basic layer 53 is referred to as a basic exhaust gas flow surface portion 54.
- the noble metal catalyst 51 is made of platinum Pt
- the noble metal catalyst 52 is made of rhodium Rh. That is, the noble metal catalysts 51 and 52 carried on the catalyst carrier 50 are composed of platinum Pt and rhodium Rh.
- palladium Pd can be supported on the catalyst carrier 50 of the upstream catalyst 14a and downstream catalyst 14b, or palladium Pd can be supported instead of rhodium Rh. it can. That is, the noble metal catalysts 51 and 52 supported on the catalyst carrier 50 are composed of platinum Pt and at least one of rhodium Rh and palladium Pd.
- FIG. 3 schematically shows the reforming action performed in the upstream catalyst 14a at this time.
- the hydrocarbon HC injected from the hydrocarbon feed valve 15 is converted into a radical hydrocarbon HC having a small number of carbons by the catalyst 51.
- FIG. 4 shows the supply timing of hydrocarbons from the hydrocarbon supply valve 15 and the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the upstream catalyst 14a.
- FIG. 5 shows a change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the upstream catalyst 14a as shown in FIG. 4 by periodically changing the concentration of hydrocarbons flowing into the upstream catalyst 14a.
- the concentration of hydrocarbons flowing into the upstream side catalyst 14a is set to an amplitude within a predetermined range and a predetermined range. As shown in FIG. 5, it was found that an extremely high NO x purification rate can be obtained even in a high temperature region of 400 ° C. or higher when the vibration is made with the internal period.
- FIGS. 6A, 6B and 6C schematically illustrate the surface portion of the catalyst carrier 50 of the upstream catalyst 14a
- FIG. 6C schematically illustrates the surface portion of the catalyst carrier 50 of the downstream catalyst 14b.
- 6A, 6B and 6C it is estimated that the hydrocarbon concentration flowing into the upstream catalyst 14a is generated when it is vibrated with an amplitude within a predetermined range and a period within the predetermined range.
- the reaction is shown. 6A shows a case where the concentration of hydrocarbons flowing into the upstream catalyst 14a is low, and FIG. 6B shows that the concentration of hydrocarbons supplied from the hydrocarbon supply valve 15 and flowing into the upstream catalyst 14a is high. It shows when As can be seen from FIG. 4, since the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 14a is maintained lean except for a moment, the exhaust gas flowing into the upstream catalyst 14a is usually in an oxygen excess state.
- the NO contained in the exhaust gas is oxidized on the platinum 51 to become NO 2 as shown in FIG. 6A, and then this NO 2 is further oxidized to become NO 3 .
- a part of the NO 2 is NO 2 - and becomes.
- the amount of NO 3 produced is much larger than the amount of NO 2 ⁇ produced. Therefore, a large amount of NO 3 and a small amount of NO 2 ⁇ are generated on the platinum Pt 51.
- These NO 3 and NO 2 ⁇ are highly active, and hereinafter these NO 3 and NO 2 ⁇ will be referred to as active NO x * .
- active NO x * When hydrocarbon is supplied from the hydrocarbon supply valve 15, as shown in FIG. 3, this hydrocarbon is reformed in the upstream catalyst 14a to become radicals.
- the hydrocarbon concentration around the active NO x * increases.
- the active NO x * is oxidized and enters the basic layer 53 in the form of nitrate ions NO 3 ⁇ . Absorbed.
- radical hydrocarbons HC activity NO x * is as hydrocarbon concentration is shown to be high in FIG. 6B on the platinum 51 around before the lapse of this period of time, whereby A reducing intermediate is generated on the surface of the basic layer 53.
- the first produced reducing intermediate this time is considered to be a nitro compound R-NO 2.
- this nitro compound R-NO 2 becomes a nitrile compound R-CN, but since this nitrile compound R-CN can only survive for a moment in that state, it immediately becomes an isocyanate compound R-NCO.
- This isocyanate compound R—NCO becomes an amine compound R—NH 2 when hydrolyzed.
- the reducing intermediates R-NCO and R-NH 2 produced in these upstream catalysts 14a are sent to the downstream catalyst 14b.
- the cross-sectional area of the downstream catalyst 14b is larger than the cross-sectional area of the upstream end of the upstream catalyst 14a. Therefore, even if the air-fuel ratio of the exhaust gas flowing out to the upstream side catalyst 14a is instantaneously made rich, this rich gas diffuses before flowing into the downstream side catalyst 14b, and thus flows into the downstream side catalyst 14b. The air-fuel ratio of the exhaust gas is always kept lean. Accordingly, as shown in FIG. 6C, active NO x * is actively generated on the downstream catalyst 14b.
- the concentration of hydrocarbons flowing into the upstream catalyst 14a is temporarily increased to generate a reducing intermediate, whereby the active NO x * reacts with the reducing intermediate, and NO. x is purified.
- NO. x reacts with the reducing intermediate
- NO. x is purified.
- to purify NO x by the exhaust purification catalyst 13 is necessary to vary the concentration of hydrocarbon flowing into the upstream catalyst 14a periodically.
- the active NO x * is reduced to the reducing intermediate. Without being generated in the basic layer 53 in the form of nitrate. In order to avoid this, it is necessary to vibrate the concentration of hydrocarbons flowing into the exhaust purification catalyst 13 with a period within a predetermined range. Incidentally, in the example shown in FIG. 4, the injection interval is 3 seconds. As described above, when the oscillation period of the hydrocarbon concentration, that is, the supply period of the hydrocarbon HC is longer than the period within a predetermined range, the active NO x * generated on the platinum Pt 53 is as shown in FIG.
- FIG. 7A when the air-fuel ratio of the exhaust gas flowing into the upstream catalysis 14a when being absorbed in this way in the basic layer 53 NO x is in the form of nitrates is the stoichiometric air-fuel ratio or rich Is shown.
- FIG. 7B shows a case where absorption of NO x capacity of the basic layer 53 is to be temporarily rich air-fuel ratio (A / F) in of the exhaust gas flowing into the upstream catalyst 14a shortly before saturation Yes.
- the time interval of this rich control is 1 minute or more.
- the basic layer 53 when the air-fuel ratio (A / F) in of the exhaust gas is lean, the NO x absorbed in the basic layer 53 temporarily makes the air-fuel ratio (A / F) in of the exhaust gas rich. When released, it is released from the basic layer 53 at once and reduced. Therefore, in this case, the basic layer 53 serves as an absorbent for temporarily absorbing NO x . Incidentally, at this time, sometimes the basic layer 53 temporarily adsorbs NO x, thus using term of storage as a term including both absorption and adsorption In this case the basic layer 53 temporarily the NO x It plays the role of a NO x storage agent for storage.
- FIG. 9 shows the NO x purification rate when the exhaust purification catalyst 13 is made to function as a NO x storage catalyst in this way.
- the horizontal axis in FIG. 9 indicates the catalyst temperature TC of the upstream catalyst 14a.
- the exhaust purification catalyst 13 When the exhaust purification catalyst 13 is made to function as a NO x storage catalyst, as shown in FIG. 9, a very high NO x purification rate can be obtained when the catalyst temperature TC is 300 ° C. to 400 ° C., but the catalyst temperature TC is 400 ° C. the NO x purification rate decreases when a high temperature of more. Thus, when the catalyst temperature TC becomes 400 ° C. or higher, the NO x purification rate decreases. When the catalyst temperature TC becomes 400 ° C. or higher, the nitrate is thermally decomposed and released from the exhaust purification catalyst 13 in the form of NO 2. Because.
- the hydrocarbon supply valve 15 for supplying hydrocarbons is disposed in the engine exhaust passage, and NO contained in the exhaust gas in the engine exhaust passage downstream of the hydrocarbon supply valve 15.
- the hydrocarbon flowing into the medium 14a When the concentration of the hydrocarbon flowing into the medium 14a is vibrated with an amplitude within a predetermined range and a period within the predetermined range, the hydrocarbon has a property of reducing NO x contained in the exhaust gas, and a hydrocarbon If the concentration oscillation period is longer than this predetermined range, the storage amount of NO x contained in the exhaust gas increases, and the concentration of hydrocarbons flowing into the upstream catalyst 14a during engine operation. Is vibrated with an amplitude within a predetermined range and a period within a predetermined range, whereby NO x contained in the exhaust gas is reduced by the exhaust purification catalyst 13. That is, the NO x purification methods shown in FIGS.
- FIG. 10 shows an enlarged view of the change in the air-fuel ratio (A / F) in shown in FIG.
- the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the upstream catalyst 14a simultaneously indicates the change in the concentration of hydrocarbons flowing into the upstream catalyst 14a.
- ⁇ H indicates the amplitude of the change in the concentration of hydrocarbon HC flowing into the upstream catalyst 14a
- ⁇ T indicates the oscillation cycle of the concentration of hydrocarbon flowing into the upstream catalyst 14a.
- (A / F) b represents the base air-fuel ratio indicating the air-fuel ratio of the combustion gas for generating the engine output.
- this base air-fuel ratio (A / F) b represents the air-fuel ratio of the exhaust gas flowing into the upstream side catalyst 14a when the hydrocarbon supply is stopped.
- X is the air-fuel ratio (A / F) used for generating the reducing intermediate without the generated active NO x * being occluded in the basic layer 53 in the form of nitrate.
- the upper limit of in is expressed, and in order to generate a reducing intermediate by reacting active NO x * and the reformed hydrocarbon, the air-fuel ratio (A / F) in is set to be higher than the upper limit X of the air-fuel ratio. It needs to be lowered.
- the hydrocarbon concentration needs to be higher than the lower limit X.
- whether or not the reducing intermediate is generated is determined by the ratio of the oxygen concentration around the active NO x * to the hydrocarbon concentration, that is, the air-fuel ratio (A / F) in, and the reducing intermediate is generated.
- the above-described upper limit X of the air-fuel ratio necessary for this is hereinafter referred to as a required minimum air-fuel ratio.
- the required minimum air-fuel ratio X is rich.
- the air-fuel ratio (A / F) in is instantaneously required to generate the reducing intermediate.
- the following is made rich:
- the required minimum air-fuel ratio X is lean.
- the reducing intermediate is generated by periodically reducing the air-fuel ratio (A / F) in while maintaining the air-fuel ratio (A / F) in lean.
- whether the required minimum air-fuel ratio X becomes rich or lean depends on the oxidizing power of the upstream catalyst 14a. In this case, for example, if the amount of the precious metal 51 supported is increased, the upstream catalyst 14a becomes stronger in oxidizing power, and if it becomes more acidic, the oxidizing power becomes stronger.
- the oxidizing power of the upstream catalyst 14a varies depending on the amount of the noble metal 51 supported and the acidity.
- the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG.
- the air-fuel ratio (A / F) in is lowered, the hydrocarbon is completely oxidized, and as a result, a reducing intermediate cannot be generated.
- the upstream side catalyst 14a having a strong oxidizing power is used, if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, the air-fuel ratio (A / F) in is rich.
- the hydrocarbons are partially oxidized without being completely oxidized, i.e., the hydrocarbons are reformed, thus producing a reducing intermediate. Therefore, when the upstream catalyst 14a having a strong oxidizing power is used, the required minimum air-fuel ratio X needs to be made rich. On the other hand, when the upstream side catalyst 14a having a weak oxidizing power is used, the air-fuel ratio (A / F) in is periodically decreased while maintaining the air-fuel ratio (A / F) in lean as shown in FIG. In this case, the hydrocarbon is not completely oxidized but partially oxidized, that is, the hydrocarbon is reformed, and thus a reducing intermediate is produced.
- the upstream catalyst 14a having a weak oxidizing power when the upstream catalyst 14a having a weak oxidizing power is used, if the air-fuel ratio (A / F) in is periodically made rich as shown in FIG. 10, a large amount of hydrocarbons are not oxidized. It is simply discharged from the upstream side catalyst 14a, and thus the amount of hydrocarbons that are wasted is increased. Therefore, when the upstream catalyst 14a having a weak oxidizing power is used, the required minimum air-fuel ratio X needs to be made lean. That is, it can be seen that the required minimum air-fuel ratio X needs to be lowered as the oxidizing power of the upstream catalyst 14a becomes stronger, as shown in FIG.
- the required minimum air-fuel ratio X becomes lean or rich due to the oxidizing power of the upstream catalyst 14a.
- the case where the required minimum air-fuel ratio X is rich will be described as an example in the upstream catalyst 14a.
- the amplitude of the concentration change of the inflowing hydrocarbon and the vibration period of the concentration of the hydrocarbon flowing into the upstream side catalyst 14a will be described.
- the base air-fuel ratio (A / F) b increases, that is, when the oxygen concentration in the exhaust gas before the hydrocarbons are supplied increases, the air-fuel ratio (A / F) in is made equal to or less than the required minimum air-fuel ratio X. This increases the amount of hydrocarbons required for this.
- the predetermined range of the amplitude of the hydrocarbon concentration is set to 200 ppm to 10,000 ppm. Further, when the vibration period ⁇ T of the hydrocarbon concentration becomes longer, the oxygen concentration around the active NO x * becomes higher while the hydrocarbon is supplied after the hydrocarbon is supplied.
- the vibration period ⁇ T of the hydrocarbon concentration becomes longer than about 5 seconds, the active NO x * starts to be absorbed in the basic layer 53 in the form of nitrate, and therefore the vibration of the hydrocarbon concentration as shown in FIG.
- the vibration period ⁇ T of the hydrocarbon concentration needs to be 5 seconds or less.
- the vibration period ⁇ T of the hydrocarbon concentration becomes approximately 0.3 seconds or less, the supplied hydrocarbon begins to accumulate on the exhaust gas flow surface of the upstream catalyst 14a, and therefore the hydrocarbon concentration as shown in FIG. the NO x purification rate decreases the vibration period ⁇ T approximately 0.3 seconds becomes below.
- the vibration period of the hydrocarbon concentration is set to be between 0.3 seconds and 5 seconds.
- the hydrocarbon supply amount and the injection timing from the hydrocarbon supply valve 15 are controlled so that the amplitude ⁇ H and the vibration period ⁇ T of the hydrocarbon concentration become optimum values according to the operating state of the engine.
- the hydrocarbon supply amount W capable of obtaining the optimum hydrocarbon concentration amplitude ⁇ H is shown in FIG. 16 as a function of the injection amount Q from the fuel injection valve 3 and the engine speed N. Such a map is stored in the ROM 32 in advance.
- the vibration amplitude ⁇ T of the optimum hydrocarbon concentration is also stored in the ROM 32 in advance in the form of a map as a function of the injection amount Q and the engine speed N.
- the NO x purification method in the case where the exhaust purification catalyst 13 functions as a NO x storage catalyst will be specifically described with reference to FIGS.
- the NO x purification method when the exhaust purification catalyst 13 functions as the NO x storage catalyst is referred to as a second NO x purification method. In this second NO x purification method, as shown in FIG.
- occluded amount of NO x ⁇ NOX is calculated from the discharge amount of NO x NOXA.
- the period during which the air-fuel ratio (A / F) in of the exhaust gas is made rich is usually 1 minute or more.
- the air / fuel ratio (A / F) in of the gas is made rich.
- the horizontal axis in FIG. 19 indicates the crank angle.
- This additional fuel WR is injected when it burns but does not appear as engine output, that is, slightly before ATDC 90 ° after compression top dead center.
- This fuel amount WR is stored in advance in the ROM 32 as a function of the injection amount Q and the engine speed N in the form of a map as shown in FIG.
- the air-fuel ratio (A / F) in of the exhaust gas can be made rich by increasing the amount of hydrocarbons supplied from the hydrocarbon supply valve 15 in this case.
- 21A shows an enlarged view around the exhaust purification catalyst 13 of FIG. 1, FIG.
- the exhaust purification catalyst 13 is used to reduce the amount of hydrocarbons required to make the air-fuel ratio (A / F) in of the exhaust gas not more than the required minimum air-fuel ratio X.
- a plurality of exhaust gas flow passages 56 extending radially from the upstream end toward the downstream end are formed in the upstream catalyst 14a.
- the base of the upstream catalyst 14a is formed of a metal thin plate, and the metal thin plate pieces arranged in the radial direction from the central axis of the upstream catalyst 14a and the central axis of the upstream catalyst 14a.
- a plurality of exhaust gas flow passages 56 surrounded by the metal thin plate are formed by joining the metal thin plate pieces arranged along the conical surface in FIG.
- the contour shape of the upstream catalyst 14a has a truncated cone shape, and each exhaust gas flow passage 56 has a cross-sectional area from the upstream end surface to the downstream end surface of the upstream catalyst 14a. Extending radially.
- each exhaust gas flow passage 56 is expanded toward the downstream side.
- the diameter of the upstream end of the upstream catalyst 14a is smaller than the diameter of the downstream catalyst 14b, and the diameter of the downstream end of the upstream catalyst 14a is made equal to the diameter of the downstream catalyst 14b. ing. It should be noted that “equal” here also includes a case where they are substantially equal.
- the radicalization action of the hydrocarbon supplied from the hydrocarbon feed valve 15, that is, the reforming action mainly occurs on the upstream side of the upstream side catalyst 14 a.
- the upstream side It is necessary to prevent the feed hydrocarbons from dispersing on the upstream side of the catalyst 14a.
- FIG. 21A to FIG. 21C if a plurality of exhaust gas flow passages 56 extending radially from the upstream end to the downstream end of the upstream catalyst 14a are formed, The inflowing exhaust gas flows along the exhaust gas flow passage 56 without being stirred. Therefore, the degree of diffusion of the supplied hydrocarbons in the exhaust gas flowing into the upstream catalyst 14a is weak, and thus the hydrocarbons required to make the air-fuel ratio (A / F) in of the exhaust gas be less than the required minimum air-fuel ratio X. The supply amount of can be reduced.
- the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 14b does not need to be lower than the required minimum air-fuel ratio X, and in order to generate NO x * , that is, to increase the NO x purification rate. Needs to maintain the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 14b lean. Accordingly, as shown in FIG. 21A, the upstream catalyst 14a is formed in a truncated cone shape so that its cross section expands toward the downstream catalyst 14b. Further, in order not to diffuse the hydrocarbons injected from the hydrocarbon supply valve 15, it is necessary that the exhaust gas flow flowing into the upstream side catalyst 14a is not disturbed as much as possible.
- the downstream catalyst 14b for example, a NO x purification catalyst in which a metal having a lower oxidizing power than a noble metal is supported on a catalyst carrier can be used.
- the catalyst support is made of alumina or zeolite, and the metal supported on the catalyst support is silver Ag, copper Cu, iron Fe, vanadium V, molybdenum Mo, cobalt Co, nickel Ni, manganese It consists of at least one transition metal selected from Mn. Therefore, in the present invention, the noble metal catalysts 51 and 52 are supported on the exhaust gas flow surface of at least one of the upstream catalyst 14a and the downstream catalyst 14b, and the basic exhaust around the noble metal catalysts 54 and 52 is provided.
- a gas flow surface portion 54 is formed.
- the oxidation reaction of hydrocarbons flowing into the upstream catalyst 14a is most actively performed at the upstream end of the upstream catalyst 14a, and therefore the upstream catalyst 14a has the highest temperature at the upstream end.
- the generated active NO x * begins to be desorbed, and as a result, the amount of reducing intermediate produced begins to decrease, and the NO x purification rate begins to decrease.
- TC max predetermined to cause a reduction of the NO x purification rate temperature TCA at the upstream end of the upstream catalyst 14a.
- This limit temperature TC max is about 500 ° C.
- One method of reducing the temperature TCA at the upstream end of the upstream catalyst 14a is a method of increasing the amount of hydrocarbons supplied to enrich the atmosphere in the upstream catalyst 14a. When the atmosphere in the upstream catalyst 14a is made rich, the oxidation reaction is suppressed, and the temperature TCA at the upstream end of the upstream catalyst 14a is lowered by the heat of vaporization of the supplied hydrocarbon.
- FIG. 22 shows the NO x purification control routine. This routine is executed by interruption every predetermined time. Referring to FIG. 22, first, at step 60, it is judged from the output signal of the temperature sensor 23 whether or not the temperature TC of the upstream catalyst 14a exceeds the activation temperature TX.
- step 61 It is determined whether or not a predetermined limit temperature TC max has been exceeded.
- TCA ⁇ TC max it is determined that the first NO x purification method should be used.
- step 62 supply control of hydrocarbons from the hydrocarbon supply valve 15 is performed. At this time, the NO x purification action by the first NO x purification method is executed.
- step 61 when it is determined in step 61 that TCA ⁇ TC max , the routine proceeds to step 63, where a temperature lowering process for decreasing the temperature TCA at the upstream end of the upstream catalyst 14a is performed.
- a temperature lowering process for decreasing the temperature TCA at the upstream end of the upstream catalyst 14a is performed.
- the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 14a is lean, the air-fuel ratio of the exhaust gas becomes rich, and when the air-fuel ratio of the exhaust gas flowing into the upstream catalyst 14a is rich, the exhaust gas empty
- the concentration of hydrocarbons flowing into the upstream catalyst 14a is increased so that the fuel ratio becomes richer.
- the vibration period of the concentration of hydrocarbons flowing into the upstream catalyst 14a is lengthened, or the supply of hydrocarbons from the hydrocarbon supply valve 15 is stopped.
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Abstract
Description
この内燃機関ではNOx吸蔵触媒からNOxを放出すべきときに供給された炭化水素が酸化触媒においてガス状の炭化水素とされ、ガス状の炭化水素がNOx吸蔵触媒に送り込まれる。その結果、NOx吸蔵触媒から放出されたNOxが良好に還元せしめられることになる。 The engine exhaust passage, NO x storage catalyst air-fuel ratio of the inflowing exhaust gas when the lean of releasing NO x air-fuel ratio of the exhaust gas which is occluded becomes rich for occluding NO x contained in the exhaust gas inflow It was placed, an oxidation catalyst is arranged having an adsorbing function in the NO x storage catalyst in the engine exhaust passage upstream of the feed hydrocarbon into the engine exhaust passage an oxidation catalyst upstream in when releasing the NO x from the NO x storage catalyst An internal combustion engine in which the air-fuel ratio of the exhaust gas flowing into the NO x storage catalyst is made rich is known (see, for example, Patent Document 1).
In this internal combustion engine, hydrocarbons supplied when NO x should be released from the NO x storage catalyst are turned into gaseous hydrocarbons in the oxidation catalyst, and gaseous hydrocarbons are sent to the NO x storage catalyst. As a result, the the NO x storage NO x released from the catalyst is caused to favorably reduced.
本発明の目的は、排気浄化触媒の温度が高温になっても高いNOx浄化率を得ることのできる内燃機関の排気浄化装置を提供することにある。 However, the NO x storage catalyst has a problem that the NO x purification rate decreases at a high temperature.
An object of the present invention is to provide an exhaust purification device for an internal combustion engine that can obtain a high NO x purification rate even when the temperature of the exhaust purification catalyst becomes high.
図2は触媒担体の表面部分を図解的に示す図である。
図3は排気浄化触媒における酸化反応を説明するための図である。
図4は排気浄化触媒への流入排気ガスの空燃比の変化を示す図である。
図5はNOx浄化率を示す図である。
図6A,6Bおよび6Cは排気浄化触媒における酸化還元反応を説明するための図である。
図7Aおよび7Bは排気浄化触媒における酸化還元反応を説明するための図である。
図8は排気浄化触媒への流入排気ガスの空燃比の変化を示す図である。
図9はNOx浄化率を示す図である。
図10は排気浄化触媒への流入排気ガスの空燃比の変化を示すタイムチャートである。
図11は排気浄化触媒への流入排気ガスの空燃比の変化を示すタイムチャートである。
図12は排気浄化触媒の酸化力と要求最小空燃比Xとの関係を示す図である。
図13は同一のNOx浄化率の得られる、排気ガス中の酸素濃度と炭化水素濃度の振幅ΔHとの関係を示す図である。
図14は炭化水素濃度の振幅ΔHとNOx浄化率との関係を示す図である。
図15は炭化水素濃度の振動周期ΔTとNOx浄化率との関係を示す図である。
図16は炭化水素供給量Wのマップを示す図である。
図17は排気浄化触媒への流入排気ガスの空燃比の変化等を示す図である。
図18は排出NOx量NOXAのマップを示す図である。
図19は燃料噴射時期を示す図である。
図20は炭化水素供給量WRのマップを示す図である。
図21Aから21Dは排気浄化触媒の拡大図を示す図である。
図22はNOx浄化制御を行うためのフローチャートである。 FIG. 1 is an overall view of a compression ignition type internal combustion engine.
FIG. 2 is a view schematically showing the surface portion of the catalyst carrier.
FIG. 3 is a view for explaining an oxidation reaction in the exhaust purification catalyst.
FIG. 4 is a diagram showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
Figure 5 is a diagram showing the NO x purification rate.
6A, 6B and 6C are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
7A and 7B are diagrams for explaining the oxidation-reduction reaction in the exhaust purification catalyst.
FIG. 8 is a diagram showing a change in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 9 is a diagram showing the NO x purification rate.
FIG. 10 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 11 is a time chart showing changes in the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst.
FIG. 12 is a diagram showing the relationship between the oxidizing power of the exhaust purification catalyst and the required minimum air-fuel ratio X.
FIG. 13 is a diagram showing the relationship between the oxygen concentration in the exhaust gas and the amplitude ΔH of the hydrocarbon concentration, with which the same NO x purification rate can be obtained.
Figure 14 is a diagram showing a relationship between an amplitude ΔH and the NO x purification rate of the hydrocarbon concentration.
FIG. 15 is a graph showing the relationship between the vibration period ΔT of the hydrocarbon concentration and the NO x purification rate.
FIG. 16 is a diagram showing a map of the hydrocarbon feed amount W.
FIG. 17 is a diagram showing changes in the air-fuel ratio of exhaust gas flowing into the exhaust purification catalyst.
Figure 18 is a diagram illustrating a map of exhaust NO x amount NOXA.
FIG. 19 shows the fuel injection timing.
FIG. 20 is a diagram showing a map of the hydrocarbon supply amount WR.
21A to 21D are enlarged views of the exhaust purification catalyst.
FIG. 22 is a flowchart for performing NO x purification control.
図1を参照すると、1は機関本体、2は各気筒の燃焼室、3は各燃焼室2内に夫々燃料を噴射するための電子制御式燃料噴射弁、4は吸気マニホルド、5は排気マニホルドを夫々示す。吸気マニホルド4は吸気ダクト6を介して排気ターボチャージャ7のコンプレッサ7aの出口に連結され、コンプレッサ7aの入口は吸入空気量検出器8を介してエアクリーナ9に連結される。吸気ダクト6内にはステップモータにより駆動されるスロットル弁10が配置され、更に吸気ダクト6周りには吸気ダクト6内を流れる吸入空気を冷却するための冷却装置11が配置される。図1に示される実施例では機関冷却水が冷却装置11内に導かれ、機関冷却水によって吸入空気が冷却される。
一方、排気マニホルド5は排気ターボチャージャ7の排気タービン7bの入口に連結され、排気タービン7bの出口は排気管12を介して排気浄化触媒13に連結される。図1に示されるようにこの排気浄化触媒13は互いに間隔を隔てて直列に配置された上流側触媒14aと下流側触媒14bからなり、上流側触媒14aは上流端から下流端に向けて拡開する輪郭形状を有する。
排気浄化触媒13上流の排気管12内には圧縮着火式内燃機関の燃料として用いられる軽油その他の燃料からなる炭化水素を供給するための炭化水素供給弁15が配置される。図1に示される実施例では炭化水素供給弁15から供給される炭化水素として軽油が用いられている。なお、本発明はリーン空燃比のもとで燃焼の行われる火花点火式内燃機関にも適用することができる。この場合、炭化水素供給弁15からは火花点火式内燃機関の燃料として用いられるガソリンその他の燃料からなる炭化水素が供給される。
一方、排気マニホルド5と吸気マニホルド4とは排気ガス再循環(以下、EGRと称す)通路16を介して互いに連結され、EGR通路16内には電子制御式EGR制御弁17が配置される。また、EGR通路16周りにはEGR通路16内を流れるEGRガスを冷却するための冷却装置18が配置される。図1に示される実施例では機関冷却水が冷却装置18内に導かれ、機関冷却水によってEGRガスが冷却される。一方、各燃料噴射弁3は燃料供給管19を介してコモンレール20に連結され、このコモンレール20は電子制御式の吐出量可変な燃料ポンプ21を介して燃料タンク22に連結される。燃料タンク22内に貯蔵されている燃料は燃料ポンプ21によってコモンレール20内に供給され、コモンレール20内に供給された燃料は各燃料供給管19を介して燃料噴射弁3に供給される。
電子制御ユニット30はデジタルコンピュータからなり、双方向性バス31によって互いに接続されたROM(リードオンリメモリ)32、RAM(ランダムアクセスメモリ)33、CPU(マイクロプロセッサ)34、入力ポート35および出力ポート36を具備する。上流側触媒14aの下流には上流側触媒14aの温度および上流側触媒14aの上流端の温度を推定するための温度センサ23が取付けられている。この温度センサ23および吸入空気量検出器8の出力信号は夫々対応するAD変換器37を介して入力ポート35に入力される。また、アクセルペダル40にはアクセルペダル40の踏込み量Lに比例した出力電圧を発生する負荷センサ41が接続され、負荷センサ41の出力電圧は対応するAD変換器37を介して入力ポート35に入力される。更に入力ポート35にはクランクシャフトが例えば15°回転する毎に出力パルスを発生するクランク角センサ42が接続される。一方、出力ポート36は対応する駆動回路38を介して燃料噴射弁3、スロットル弁10の駆動用ステップモータ、炭化水素供給弁15、EGR制御弁17および燃料ポンプ21に接続される。
本発明による第1実施例では上流側触媒14aの基体は金属薄板から形成されており、下流側触媒14bの基体はコージライトのようなセラミックから形成されている。このようにこの第1実施例では上流側触媒14aおよび下流側触媒14bの基体は夫々異なるが上流側触媒14aおよび下流側触媒14b上には同じ触媒担体と同じ触媒とが担持されている。
図2は上流側触媒14aおよび下流側触媒14bの基体上に担持された触媒担体の表面部分を図解的に示している。これら上流側触媒14aおよび下流側触媒14bでは図2に示されるように例えばアルミナからなる触媒担体50上には貴金属触媒51,52が担持されており、更にこの触媒担体50上にはカリウムK、ナトリウムNa、セシウムCsのようなアルカリ金属、バリウムBa、カルシウムCaのようなアルカリ土類金属、ランタノイドのような希土類および銀Ag、銅Cu、鉄Fe、イリジウムIrのようなNOxに電子を供与しうる金属から選ばれた少くとも一つを含む塩基性層53が形成されている。排気ガスは触媒担体50上に沿って流れるので貴金属触媒51,52は上流側触媒14aおよび下流側触媒14bの排気ガス流通表面上に担持されていると言える。また、塩基性層53の表面は塩基性を呈するので塩基性層53の表面は塩基性の排気ガス流通表面部分54と称される。
一方、図2において貴金属触媒51は白金Ptからなり、貴金属触媒52はロジウムRhからなる。即ち、触媒担体50に担持されている貴金属触媒51,52は白金PtおよびロジウムRhから構成されている。なお、上流側触媒14aおよび下流側触媒14bの触媒担体50上には白金PtおよびロジウムRhに加えて更にパラジウムPdを担持させることができるし、或いはロジウムRhに代えてパラジウムPdを担持させることができる。即ち、触媒担体50に担持されている貴金属触媒51,52は白金Ptと、ロジウムRhおよびパラジウムPdの少なくとも一方とにより構成される。
炭化水素供給弁15から排気ガス中に炭化水素が噴射されるとこの炭化水素は上流側触媒14aにおいて改質される。本発明ではこのとき改質された炭化水素を用いて下流側触媒14bにおいてNOxを浄化するようにしている。図3はこのとき上流側触媒14aにおいて行われる改質作用を図解的に示している。図3に示されるように炭化水素供給弁15から噴射された炭化水素HCは触媒51によって炭素数の少ないラジカル状の炭化水素HCとなる。
図4は炭化水素供給弁15からの炭化水素の供給タイミングと上流側触媒14aへの流入排気ガスの空燃比(A/F)inの変化とを示している。なお、この空燃比(A/F)inの変化は上流側触媒14aに流入する排気ガス中の炭化水素の濃度変化に依存しているので図4に示される空燃比(A/F)inの変化は炭化水素の濃度変化を表しているとも言える。ただし、炭化水素濃度が高くなると空燃比(A/F)inは小さくなるので図4においては空燃比(A/F)inがリッチ側となるほど炭化水素濃度が高くなっている。
図5は、上流側触媒14aに流入する炭化水素の濃度を周期的に変化させることによって図4に示されるように上流側触媒14aへの流入排気ガスの空燃比(A/F)inを変化させたときの排気浄化触媒13によるNOx浄化率を上流側触媒14aの各触媒温度TCに対して示している。本発明者は長い期間に亘ってNOx浄化に関する研究を重ねており、その研究課程において、上流側触媒14aに流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させると、図5に示されるように400℃以上の高温領域においても極めて高いNOx浄化率が得られることが判明したのである。
更にこのときには窒素および炭化水素を含む多量の還元性中間体が上流側触媒14aの塩基性層53の表面上において、即ち上流側触媒14aの塩基性排気ガス流通表面部分54上において生成され、この還元性中間体が高いNOx浄化率を得る上で中心的役割を果していることが判明したのである。次にこのことについて図6A,6Bおよび6Cを参照しつつ説明する。なお、図6Aおよび6Bは上流側触媒14aの触媒担体50の表面部分を図解的に示しており、図6Cは下流側触媒14bの触媒担体50の表面部分を図解的に示している。これら図6A,6Bおよび6Cには上流側触媒14aに流入する炭化水素の濃度が予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動せしめたときに生ずると推測される反応が示されている。
図6Aは上流側触媒14aに流入する炭化水素の濃度が低いときを示しており、図6Bは炭化水素供給弁15から炭化水素が供給されて上流側触媒14aに流入する炭化水素の濃度が高くなっているときを示している。
さて、図4からわかるように上流側触媒14aに流入する排気ガスの空燃比は一瞬を除いてリーンに維持されているので上流側触媒14aに流入する排気ガスは通常酸素過剰の状態にある。従って排気ガス中に含まれるNOは図6Aに示されるように白金51上において酸化されてNO2となり、次いでこのNO2は更に酸化されてNO3となる。また、NO2の一部はNO2 −となる。この場合、NO3の生成量の方がNO2 −の生成量よりもはるかに多い。従って白金Pt51上には多量のNO3と少量のNO2 −が生成されることになる。これらNO3およびNO2 −は活性が強く、以下これらNO3およびNO2 −を活性NOx *と称する。
一方、炭化水素供給弁15から炭化水素が供給されると図3に示されるようにこの炭化水素は上流側触媒14a内において改質され、ラジカルとなる。その結果、図6Bに示されるように活性NOx *周りの炭化水素濃度が高くなる。ところで活性NOx *が生成された後、活性NOx *周りの酸素濃度が高い状態が一定時間以上継続すると活性NOx *は酸化され、硝酸イオンNO3 −の形で塩基性層53内に吸収される。しかしながらこの一定時間が経過する前に活性NOx *周りの炭化水素濃度が高くされると図6Bに示されるように活性NOx *は白金51上においてラジカル状の炭化水素HCと反応し、それにより塩基性層53の表面上において還元性中間体が生成される。
なお、このとき最初に生成される還元性中間体はニトロ化合物R−NO2であると考えられる。このニトロ化合物R−NO2は生成されるとニトリル化合物R−CNとなるがこのニトリル化合物R−CNはその状態では瞬時しか存続し得ないのでただちにイソシアネート化合物R−NCOとなる。このイソシアネート化合物R−NCOは加水分解するとアミン化合物R−NH2となる。ただしこの場合、加水分解されるのはイソシアネート化合物R−NCOの一部であると考えられる。従って図6Bに示されるように塩基性層53の表面上において生成される還元性中間体の大部分はイソシアネート化合物R−NCOおよびアミン化合物R−NH2であると考えられる。これら上流側触媒14aにおいて生成された還元性中間体R−NCOやR−NH2は下流側触媒14bに送り込まれる。
一方、下流側触媒14bの断面積は上流側触媒14aの上流端の断面積よりも大きい。従って上流側触媒14aに流出する排気ガスの空燃比が瞬時的にリッチにされたとしてもこのリッチなガスは下流側触媒14bに流入する前に拡散し、斯くして下流側触媒14bに流入する排気ガスの空燃比は常時リーンに維持されている。従って図6Cに示されるように下流側触媒14b上では活性NOx *が活発に生成される。また、上流側触媒14aにおいて生成された活性NOx *の一部は上流側触媒14aから流出し、下流側触媒14b内に流入して下流側触媒14bの塩基性層53の表面上に付着又は吸着される。従って下流側触媒14b内には多量の活性NOx *が保持されていることになる。
一方、前述したように上流側触媒14aからは下流側触媒14b内に多量の還元性中間体が送り込まれる。これらの還元性中間体R−NCOやR−NH2は図6Cに示されるように下流側触媒14b内に保持されている活性NOx *と反応してN2,CO2,H2Oとなり、斯くしてNOxが浄化されることになる。
このように排気浄化触媒13では、上流側触媒14aに流入する炭化水素の濃度を一時的に高くして還元性中間体を生成することにより活性NOx *が還元性中間体と反応し、NOxが浄化される。即ち、排気浄化触媒13によりNOxを浄化するには上流側触媒14aに流入する炭化水素の濃度を周期的に変化させる必要がある。
無論、この場合、還元性中間体を生成するのに十分高い濃度まで炭化水素の濃度を高める必要がある。即ち、上流側触媒14aに流入する炭化水素の濃度を予め定められた範囲内の振幅で振動させる必要がある。
一方、炭化水素の供給周期を長くすると炭化水素が供給された後、次に炭化水素が供給されるまでの間において酸素濃度が高くなる期間が長くなり、従って活性NOx *は還元性中間体を生成することなく硝酸塩の形で塩基性層53内に吸収されることになる。これを回避するためには排気浄化触媒13に流入する炭化水素の濃度を予め定められた範囲内の周期でもって振動させることが必要となる。因みに図4に示される例では噴射間隔が3秒とされている。
上述したように炭化水素濃度の振動周期、即ち炭化水素HCの供給周期を予め定められた範囲内の周期よりも長くすると白金Pt53上において生成された活性NOx *は図7Aに示されるように硝酸イオンNO3 −の形で塩基性層53内に拡散し、硝酸塩となる。即ち、このときには排気ガス中のNOxは硝酸塩の形で塩基性層53内に吸収されることになる。
一方、図7BはこのようにNOxが硝酸塩の形で塩基性層53内に吸収されているときに上流側触媒14a内に流入する排気ガスの空燃比が理論空燃比又はリッチにされた場合を示している。この場合には排気ガス中の酸素濃度が低下するために反応が逆方向(NO3 −→NO2)に進み、斯くして塩基性層53内に吸収されている硝酸塩は順次硝酸イオンNO3 −となって図7Bに示されるようにNO2の形で塩基性層53から放出される。次いで放出されたNO2は排気ガス中に含まれる炭化水素HCおよびCOによって還元される。
図8は塩基性層53のNOx吸収能力が飽和する少し前に上流側触媒14aに流入する排気ガスの空燃比(A/F)inを一時的にリッチにするようにした場合を示している。なお、図8に示す例ではこのリッチ制御の時間間隔は1分以上である。この場合には排気ガスの空燃比(A/F)inがリーンのときに塩基性層53内に吸収されたNOxは、排気ガスの空燃比(A/F)inが一時的にリッチにされたときに塩基性層53から一気に放出されて還元される。従ってこの場合には塩基性層53はNOxを一時的に吸収するための吸収剤の役目を果している。
なお、このとき塩基性層53がNOxを一時的に吸着する場合もあり、従って吸収および吸着の双方を含む用語として吸蔵という用語を用いるとこのとき塩基性層53はNOxを一時的に吸蔵するためのNOx吸蔵剤の役目を果していることになる。即ち、この場合には、機関吸気通路、燃焼室2および上流側触媒14a上流の排気通路内に供給された空気および燃料(炭化水素)の比を排気ガスの空燃比と称すると、排気浄化触媒13は、排気ガスの空燃比がリーンのときにはNOxを吸蔵し、排気ガス中の酸素濃度が低下すると吸蔵したNOxを放出するNOx吸蔵触媒として機能している。
図9は、排気浄化触媒13をこのようにNOx吸蔵触媒として機能させたときのNOx浄化率を示している。なお、図9の横軸は上流側触媒14aの触媒温度TCを示している。排気浄化触媒13をNOx吸蔵触媒として機能させた場合には図9に示されるように触媒温度TCが300℃から400℃のときには極めて高いNOx浄化率が得られるが触媒温度TCが400℃以上の高温になるとNOx浄化率が低下する。
このように触媒温度TCが400℃以上になるとNOx浄化率が低下するのは、触媒温度TCが400℃以上になると硝酸塩が熱分解してNO2の形で排気浄化触媒13から放出されるからである。即ち、NOxを硝酸塩の形で吸蔵している限り、触媒温度TCが高いときに高いNOx浄化率を得るのは困難である。しかしながら図4から図6A,6Bに示される新たなNOx浄化方法では図6A,6Bからわかるように硝酸塩は生成されず或いは生成されても極く微量であり、斯くして図5に示されるように触媒温度TCが高いときでも高いNOx浄化率が得られることになる。
そこで本発明による第1実施例では、炭化水素を供給するための炭化水素供給弁15を機関排気通路内に配置し、炭化水素供給弁15下流の機関排気通路内に排気ガス中に含まれるNOxと改質された炭化水素とを反応させるための排気浄化触媒13を配置し、排気浄化触媒13は互いに間隔を隔てて直列に配置された上流側触媒14aと下流側触媒14bからなり、上流側触媒14aは下流側に向けて拡開する輪郭形状を有すると共に炭化水素供給弁15から供給された炭化水素を改質する機能を有しており、上流側触媒14aと下流側触媒14bの排気ガス流通表面上には貴金属触媒51,52が担持されていると共に貴金属触媒51,52周りには塩基性の排気ガス流通表面部分54が形成されており、排気浄化触媒13は、上流側触媒14aに流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させると排気ガス中に含まれるNOxを還元する性質を有すると共に、炭化水素濃度の振動周期をこの予め定められた範囲よりも長くすると排気ガス中に含まれるNOxの吸蔵量が増大する性質を有しており、機関運転時に上流側触媒14aに流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させ、それにより排気ガス中に含まれるNOxを排気浄化触媒13において還元するようにしている。
即ち、図4から図6A,6Bに示されるNOx浄化方法は、貴金属触媒を担持しかつNOxを吸収しうる塩基性層を形成した排気浄化触媒を用いた場合において、ほとんど硝酸塩を形成することなくNOxを浄化するようにした新たなNOx浄化方法であると言うことができる。実際、この新たなNOx浄化方法を用いた場合には排気浄化触媒13をNOx吸蔵触媒として機能させた場合に比べて、塩基性層53から検出される硝酸塩は極く微量である。なお、この新たなNOx浄化方法を以下、第1のNOx浄化方法と称する。
次に図10から図15を参照しつつこの第1のNOx浄化方法についてもう少し詳細に説明する。
図10は図4に示される空燃比(A/F)inの変化を拡大して示している。なお、前述したようにこの上流側触媒14aへの流入排気ガスの空燃比(A/F)inの変化は同時に上流側触媒14aに流入する炭化水素の濃度変化を示している。なお、図10においてΔHは上流側触媒14aに流入する炭化水素HCの濃度変化の振幅を示しており、ΔTは上流側触媒14aに流入する炭化水素濃度の振動周期を示している。
更に図10において(A/F)bは機関出力を発生するための燃焼ガスの空燃比を示すベース空燃比を表している。言い換えるとこのベース空燃比(A/F)bは炭化水素の供給を停止したときに上流側触媒14aに流入する排気ガスの空燃比を表している。一方、図10においてXは、生成された活性NOx *が硝酸塩の形で塩基性層53内に吸蔵されることなく還元性中間体の生成のために使用される空燃比(A/F)inの上限を表しており、活性NOx *と改質された炭化水素とを反応させて還元性中間体を生成させるには空燃比(A/F)inをこの空燃比の上限Xよりも低くすることが必要となる。
別の言い方をすると図10のXは活性NOx *と改質された炭化水素とを反応させて還元性中間体を生成させるのに必要な炭化水素の濃度の下限を表しており、還元性中間体を生成するためには炭化水素の濃度をこの下限Xよりも高くする必要がある。この場合、還元性中間体が生成されるか否かは活性NOx *周りの酸素濃度と炭化水素濃度との比率、即ち空燃比(A/F)inで決まり、還元性中間体を生成するのに必要な上述の空燃比の上限Xを以下、要求最小空燃比と称する。
図10に示される例では要求最小空燃比Xがリッチとなっており、従ってこの場合には還元性中間体を生成するために空燃比(A/F)inが瞬時的に要求最小空燃比X以下に、即ちリッチにされる。これに対し、図11に示される例では要求最小空燃比Xがリーンとなっている。この場合には空燃比(A/F)inをリーンに維持しつつ空燃比(A/F)inを周期的に低下させることによって還元性中間体が生成される。
この場合、要求最小空燃比Xがリッチになるかリーンになるかは上流側触媒14aの酸化力による。この場合、上流側触媒14aは例えば貴金属51の担持量を増大させれば酸化力が強まり、酸性を強めれば酸化力が強まる。従って上流側触媒14aの酸化力は貴金属51の担持量や酸性の強さによって変化することになる。
さて、酸化力が強い上流側触媒14aを用いた場合に図11に示されるように空燃比(A/F)inをリーンに維持しつつ空燃比(A/F)inを周期的に低下させると、空燃比(A/F)inが低下せしめられたときに炭化水素が完全に酸化されてしまい、その結果還元性中間体を生成することができなくなる。これに対し、酸化力が強い上流側触媒14aを用いた場合に図10に示されるように空燃比(A/F)inを周期的にリッチにさせると空燃比(A/F)inがリッチにされたときに炭化水素は完全に酸化されることなく部分酸化され、即ち炭化水素が改質され、斯くして還元性中間体が生成されることになる。従って酸化力が強い上流側触媒14aを用いた場合には要求最小空燃比Xはリッチにする必要がある。
一方、酸化力が弱い上流側触媒14aを用いた場合には図11に示されるように空燃比(A/F)inをリーンに維持しつつ空燃比(A/F)inを周期的に低下させると、炭化水素は完全に酸化されずに部分酸化され、即ち炭化水素が改質され、斯くして還元性中間体が生成される。これに対し、酸化力が弱い上流側触媒14aを用いた場合に図10に示されるように空燃比(A/F)inを周期的にリッチにさせると多量の炭化水素は酸化されることなく単に上流側触媒14aから排出されることになり、斯くして無駄に消費される炭化水素量が増大することになる。従って酸化力が弱い上流側触媒14aを用いた場合には要求最小空燃比Xはリーンにする必要がある。
即ち、要求最小空燃比Xは図12に示されるように上流側触媒14aの酸化力が強くなるほど低下させる必要があることがわかる。このように要求最小空燃比Xは上流側触媒14aの酸化力によってリーンになったり、或いはリッチになったりするが、以下要求最小空燃比Xがリッチである場合を例にとって、上流側触媒14aに流入する炭化水素の濃度変化の振幅や上流側触媒14aに流入する炭化水素濃度の振動周期について説明する。
さて、ベース空燃比(A/F)bが大きくなると、即ち炭化水素が供給される前の排気ガス中の酸素濃度が高くなると空燃比(A/F)inを要求最小空燃比X以下とするのに必要な炭化水素の供給量が増大する。従って、炭化水素が供給される前の排気ガス中の酸素濃度が高いほど炭化水素濃度の振幅を大きくする必要がある。
図13は同一のNOx浄化率が得られるときの、炭化水素が供給される前の排気ガス中の酸素濃度と炭化水素濃度の振幅ΔHとの関係を示している。図13から同一のNOx浄化率を得るためには炭化水素が供給される前の排気ガス中の酸素濃度が高いほど炭化水素濃度の振幅ΔHを増大させる必要があることがわかる。即ち、同一のNOx浄化率を得るにはベース空燃比(A/F)bが高くなるほど炭化水素濃度の振幅ΔTを増大させることが必要となる。別の言い方をすると、NOxを良好に浄化するためにはベース空燃比(A/F)bが低くなるほど炭化水素濃度の振幅ΔTを減少させることができる。
ところでベース空燃比(A/F)bが最も低くなるのは加速運転時であり、このとき炭化水素濃度の振幅ΔHが200ppm程度あればNOxを良好に浄化することができる。ベース空燃比(A/F)bは通常、加速運転時よりも大きく、従って図14に示されるように炭化水素濃度の振幅ΔHが200ppm以上であれば良好なNOx浄化率を得ることができることになる。
一方、ベース空燃比(A/F)bが最も高いときには炭化水素濃度の振幅ΔHを10000ppm程度にすれば良好なNOx浄化率が得られることがわかっている。従って本発明では炭化水素濃度の振幅の予め定められた範囲が200ppmから10000ppmとされている。
また、炭化水素濃度の振動周期ΔTが長くなると炭化水素が供給された後、次に炭化水素が供給される間、活性NOx *周りの酸素濃度が高くなる。この場合、炭化水素濃度の振動周期ΔTが5秒程度よりも長くなると活性NOx *が硝酸塩の形で塩基性層53内に吸収され始め、従って図15に示されるように炭化水素濃度の振動周期ΔTが5秒程度よりも長くなるとNOx浄化率が低下することになる。従って炭化水素濃度の振動周期ΔTは5秒以下とする必要がある。
一方、炭化水素濃度の振動周期ΔTがほぼ0.3秒以下になると供給された炭化水素が上流側触媒14aの排気ガス流通表面上に堆積し始め、従って図15に示されるように炭化水素濃度の振動周期ΔTがほぼ0.3秒以下になるとNOx浄化率が低下する。そこで本発明では炭化水素濃度の振動周期が0.3秒から5秒の間とされている。
さて、本発明では炭化水素供給弁15からの炭化水素供給量および噴射時期を変化させることによって炭化水素濃度の振幅ΔHおよび振動周期ΔTが機関の運転状態に応じた最適値となるように制御される。この場合、本発明による実施例ではこの最適な炭化水素濃度の振幅ΔHを得ることのできる炭化水素供給量Wが燃料噴射弁3からの噴射量Qおよび機関回転数Nの関数として図16に示すようなマップの形で予めROM32内に記憶されている。また、最適な炭化水素濃度の振動振幅ΔT、即ち炭化水素の噴射周期ΔTも同様に噴射量Qおよび機関回転数Nの関数としてマップの形で予めROM32内に記憶されている。
次に図17から図20を参照しつつ排気浄化触媒13をNOx吸蔵触媒として機能させた場合のNOx浄化方法について具体的に説明する。このように排気浄化触媒13をNOx吸蔵触媒として機能させた場合のNOx浄化方法を以下、第2のNOx浄化方法と称する。
この第2のNOx浄化方法では図17に示されるように塩基性層53に吸蔵された吸蔵NOx量ΣNOxが予め定められた許容量MAXを越えたときに上流側触媒14aに流入する排気ガスの空燃比(A/F)inが一時的にリッチにされる。排気ガスの空燃比(A/F)inがリッチにされると排気ガスの空燃比(A/F)inがリーンのときに塩基性層53内に吸蔵されたNOxが塩基性層53から一気に放出されて還元される。それによってNOxが浄化される。
吸蔵NOx量ΣNOXは例えば機関から排出されるNOx量から算出される。本発明による実施例では機関から単位時間当り排出される排出NOx量NOXAが噴射量Qおよび機関回転数Nの関数として図18に示すようなマップの形で予めROM32内に記憶されており、この排出NOx量NOXAから吸蔵NOx量ΣNOXが算出される。この場合、前述したように排気ガスの空燃比(A/F)inがリッチにされる周期は通常1分以上である。
この第2のNOx浄化方法では図19に示されるように燃焼室2内に燃料噴射弁3から燃焼用燃料Qに加え、追加の燃料WRを噴射することによって上流側触媒14aに流入する排気ガスの空燃比(A/F)inがリッチにされる。なお、図19の横軸はクランク角を示している。この追加の燃料WRは燃焼はするが機関出力となって現われない時期に、即ち圧縮上死点後ATDC90°の少し手前で噴射される。この燃料量WRは噴射量Qおよび機関回転数Nの関数として図20に示すようなマップの形で予めROM32内に記憶されている。無論、この場合炭化水素供給弁15からの炭化水素の供給量を増大させることによって排気ガスの空燃比(A/F)inをリッチにすることもできる。
図21Aは図1の排気浄化触媒13の周りの拡大図を示しており、図21Bは図21Aにおいて左側からみた上流側触媒14aの正面図を示しており、図21Cは上流側触媒14aの斜視図を示している。また、図21Dは図21Aから図21Cに示される本発明による排気浄化触媒13の機能を説明するための図である。
さて、前述したように還元性中間体を生成するには排気浄化触媒13に流入する排気ガスの空燃比(A/F)inを要求最小空燃比X以下にする必要がある。この場合、図21Dに示されるように排気浄化触媒13の前方に排気通路の断面拡張部55が形成されるいるとこの断面拡張部55において排気ガス流が乱れるために炭化水素供給弁15から噴射された炭化水素が半径方向および流れ方向に拡散してしまう。その結果、排気浄化触媒13に流入する排気ガスの空燃比は排気管12内における空燃比よりも大巾にリーン側にずれてしまう。従ってこの場合、排気浄化触媒13に流入する排気ガスの空燃比(A/F)inを要求最小空燃比X以下にするには多量の炭化水素を供給する必要がある。
本発明では、排気ガスの空燃比(A/F)inを要求最小空燃比X以下とするのに必要な炭化水素の供給量を低減するために図21Aに示される如く、排気浄化触媒13は互いに間隔を隔てて直列に配置された上流側触媒14aと下流側触媒14bからなり、図21Aから図21Cに示されるように上流側触媒14aは上流端から下流端に向けて拡開する輪郭形状を有すると共に上流側触媒14a内には上流端から下流端に向けて放射状に延びる複数個の排気ガス流通路56が形成されている。
即ち、前述したように上流側触媒14aの基体は金属薄板から形成されており、上流側触媒14aの中心軸線から半径方向に向かうように配列された金属薄板片と上流側触媒14aの中心軸線周りにおいて円錐面に沿って配列された金属薄板片とを接合することによって金属薄板により包囲された複数個の排気ガス流通路56が形成されている。図21Aから図21Cに示される実施例では上流側触媒14aの輪郭形状は円錐台形をなしており、各排気ガス流通路56は上流側触媒14aの上流側端面から下流側端面に向けて断面積を増大させつつ放射状に延びている。即ち、各排気ガス流通路56は下流側に向けて拡開している。
図21Aから図21Cに示される実施例では上流側触媒14aの上流端の径は下流側触媒14bの径よりも小さく、上流側触媒14aの下流端の径は下流側触媒14bの径と等しくされている。なお、ここで等しいというのはほぼ等しい場合も当然に含まれている。
炭化水素供給弁15から供給された炭化水素のラジカル化作用、即ち改質作用は主に上流側触媒14aの上流側で生じ、このとき炭化水素の改質作用を良好に行うためには上流側触媒14aの上流側において供給炭化水素が分散しないようにする必要がある。この場合、図21Aから図21Cに示されるように上流側触媒14aの上流端から下流端に向けて放射状に延びる複数個の排気ガス流通路56が形成されていると排気ガス流通路56内に流入した排気ガスは掻き混ぜられることなく排気ガス流通路56に沿って流れる。従って上流側触媒14aに流入した排気ガス中における供給炭化水素の拡散度合は弱く、斯くして排気ガスの空燃比(A/F)inを要求最小空燃比X以下とするのに必要な炭化水素の供給量を低減することができることになる。
一方、本発明では下流側触媒14bに流入する排気ガスの空燃比は要求最小空燃比X以下にする必要がなく、NOx *を生成するためには、即ち、NOx浄化率を高めるためには下流側触媒14bに流入する排気ガスの空燃比をリーンに維持する必要がある。従って図21Aに示されるように上流側触媒14aは下流側触媒14bに向けて断面が拡大するように円錐台形に形成されている。
また、炭化水素供給弁15から噴射された炭化水素を拡散させないためには上流側触媒14aに流入する排気ガス流にできる限り乱れを与えないことが必要である。そこで本発明による実施例では図21Aに示されるように炭化水素供給弁15と上流側触媒14aとの間の機関排気通路がまっすぐに延びる一様な径の排気管12内に形成されている。
なお、本発明では上流側触媒14aを酸化触媒から構成し、上流側触媒14aでは炭化水素の部分酸化作用、即ち炭化水素の改質作用のみを行わせることもできる。この場合には還元性中間体の生成とNOxの浄化作用は下流側触媒14bにおいて行われる。従って本発明では上流側触媒14aは少くとも炭化水素供給弁15から供給された炭化水素を改質する機能を有していることになる。
また、本発明では下流側触媒14bとして、例えば触媒担体上に貴金属よりも酸化力の低い金属を担持したNOx浄化触媒を用いることもできる。このNOx浄化触媒では例えば、触媒担体がアルミナ又はゼオライトからなり、この触媒担体上に担持されている金属が銀Ag、銅Cu、鉄Fe、バナジウムV、モリブデンMo、コバルトCo、ニッケルNi、マンガンMnから選ばれた少くとも一つの遷移金属からなる。従って本発明では、上流側触媒14aと下流側触媒14bの少くとも一方の触媒の排気ガス流通表面上に貴金属触媒51,52が担持されていると共にこれら貴金属触媒54,52周りに塩基性の排気ガス流通表面部分54が形成されていることになる。
さて、上流側触媒14aに流入する炭化水素の酸化反応は上流側触媒14aの上流端で最も活発に行われ、従って上流側触媒14aはその上流端の温度が最も高くなる。上流側触媒14aの上流端の温度が高くなると生成された活性NOx *が脱離しはじめ、その結果還元性中間体の生成量が低下しはじめるためにNOx浄化率が低下しはじめる。即ち、上流側触媒14aの上流端の温度TCAにはNOx浄化率の低下をひき起す予め定められた限界温度TCmaxが存在することになる。この限界温度TCmaxは500℃程度である。
そこで本発明による実施例では、上流側触媒14aの上流端の温度TCAがNOx浄化率の低下をひき起す予め定められた限界温度TCmaxを越えたときには上流側触媒14aの上流端の温度TCAを低下させるようにしている。上流側触媒14aの上流端の温度TCAを低下させる一つの方法は、炭化水素の供給量を増量して上流側触媒14a内における雰囲気をリッチにする方法である。上流側触媒14a内における雰囲気をリッチにすると酸化反応が抑制され、供給炭化水素の気化熱により上流側触媒14aの上流端の温度TCAは低下することになる。
また、上流側触媒14aの上流端の温度TCAを低下させる他の方法は上流側触媒14aに流入する炭化水素の濃度の振動周期ΔTを長くする、即ち炭化水素の噴射周期を長くするか、又は炭化水素の供給を停止することである。本発明ではこれらのいずれかの方法が用いられる。
図22にNOx浄化制御ルーチンを示す。このルーチンは一定時間毎に割込みによって実行される。
図22を参照するとまず初めにステップ60において温度センサ23の出力信号から上流側触媒14aの温度TCが活性化温度TXを越えているか否かが判別される。TC≧TXのとき、即ち上流側触媒14aが活性化しているときにはステップ61に進んで温度センサ23の出力信号から上流側触媒14aの上流端の温度TCAがNOx浄化率の低下をひき起す予め定められた限界温度TCmaxを越えたか否かが判別される。TCA<TCmaxのときには第1のNOx浄化方法を用いるべきであると判断され、このときにはステップ62に進む。ステップ62では炭化水素供給弁15からの炭化水素の供給制御が行われる。このとき第1のNOx浄化方法によるNOx浄化作用が実行される。
一方、ステップ61においてTCA≧TCmaxであると判別されたときにはステップ63に進んで上流側触媒14aの上流端の温度TCAを低下させる温度低下処理が行われる。例えば、上流側触媒14aに流入する排気ガスの空燃比がリーンのときには排気ガスの空燃比がリッチになるように、上流側触媒14aに流入する排気ガスの空燃比がリッチのときには排気ガスの空燃比が更にリッチになるように上流側触媒14aに流入する炭化水素の濃度が高められる。或いは、上流側触媒14aに流入する炭化水素の濃度の振動周期が長くされるか、又は炭化水素供給弁15からの炭化水素の供給が停止される。
一方、ステップ60においてTC<TXであると判断されたときには第2のNOx浄化方法を用いるべきであると判断され、ステップ64に進む。ステップ64では図18に示すマップから単位時間当りの排出NOx量NOXAが算出される。次いでステップ65ではΣNOXに排出NOx量NOXAを加算することによって吸蔵NOx量ΣNOXが算出される。次いでステップ66では吸蔵NOx量ΣNOXが許容値MAXを越えたか否かが判別される。ΣNOX>MAXになるとステップ67に進んで図20に示すマップから追加の燃料量WRが算出され、追加の燃料の噴射作用が行われる。次いでステップ68ではΣNOXがクリアされる。 FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each
On the other hand, the
In the
On the other hand, the
The
In the first embodiment according to the present invention, the base of the
FIG. 2 schematically shows the surface portions of the catalyst carrier supported on the bases of the
On the other hand, in FIG. 2, the
When hydrocarbons are injected into the exhaust gas from the
FIG. 4 shows the supply timing of hydrocarbons from the
FIG. 5 shows a change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the
Further, at this time, a large amount of a reducing intermediate containing nitrogen and hydrocarbons is generated on the surface of the
6A shows a case where the concentration of hydrocarbons flowing into the
As can be seen from FIG. 4, since the air-fuel ratio of the exhaust gas flowing into the
On the other hand, when hydrocarbon is supplied from the
Incidentally, the first produced reducing intermediate this time is considered to be a nitro compound R-NO 2. When this nitro compound R-NO 2 is produced, it becomes a nitrile compound R-CN, but since this nitrile compound R-CN can only survive for a moment in that state, it immediately becomes an isocyanate compound R-NCO. This isocyanate compound R—NCO becomes an amine compound R—NH 2 when hydrolyzed. However, in this case, it is considered that a part of the isocyanate compound R-NCO is hydrolyzed. Therefore, as shown in FIG. 6B, most of the reducing intermediates generated on the surface of the
On the other hand, the cross-sectional area of the downstream catalyst 14b is larger than the cross-sectional area of the upstream end of the
On the other hand, as described above, a large amount of reducing intermediate is sent from the
Thus, in the
Of course, in this case, it is necessary to increase the concentration of the hydrocarbon to a concentration high enough to produce the reducing intermediate. That is, it is necessary to vibrate the concentration of hydrocarbons flowing into the
On the other hand, if the supply cycle of the hydrocarbon is lengthened, the period during which the oxygen concentration becomes high after the hydrocarbon is supplied and before the next hydrocarbon is supplied, and therefore, the active NO x * is reduced to the reducing intermediate. Without being generated in the
As described above, when the oscillation period of the hydrocarbon concentration, that is, the supply period of the hydrocarbon HC is longer than the period within a predetermined range, the active NO x * generated on the
On the other hand, FIG. 7B when the air-fuel ratio of the exhaust gas flowing into the
Figure 8 shows a case where absorption of NO x capacity of the
Incidentally, at this time, sometimes the
FIG. 9 shows the NO x purification rate when the
Thus, when the catalyst temperature TC becomes 400 ° C. or higher, the NO x purification rate decreases. When the catalyst temperature TC becomes 400 ° C. or higher, the nitrate is thermally decomposed and released from the
Therefore, in the first embodiment according to the present invention, the
That is, the NO x purification methods shown in FIGS. 4 to 6A and 6B almost form nitrates when an exhaust purification catalyst carrying a noble metal catalyst and forming a basic layer capable of absorbing NO x is used. It can be said that this is a new NO x purification method that purifies NO x without any problems. In fact, when this new NO x purification method is used, the amount of nitrate detected from the
Next, the first NO x purification method will be described in a little more detail with reference to FIGS. 10 to 15.
FIG. 10 shows an enlarged view of the change in the air-fuel ratio (A / F) in shown in FIG. As described above, the change in the air-fuel ratio (A / F) in of the exhaust gas flowing into the
Further, in FIG. 10, (A / F) b represents the base air-fuel ratio indicating the air-fuel ratio of the combustion gas for generating the engine output. In other words, this base air-fuel ratio (A / F) b represents the air-fuel ratio of the exhaust gas flowing into the
In other words, X in FIG. 10 represents the lower limit of the concentration of hydrocarbons required for reacting active NO x * with the reformed hydrocarbon to produce a reducing intermediate, which is reducible. In order to produce the intermediate, the hydrocarbon concentration needs to be higher than the lower limit X. In this case, whether or not the reducing intermediate is generated is determined by the ratio of the oxygen concentration around the active NO x * to the hydrocarbon concentration, that is, the air-fuel ratio (A / F) in, and the reducing intermediate is generated. The above-described upper limit X of the air-fuel ratio necessary for this is hereinafter referred to as a required minimum air-fuel ratio.
In the example shown in FIG. 10, the required minimum air-fuel ratio X is rich. Therefore, in this case, the air-fuel ratio (A / F) in is instantaneously required to generate the reducing intermediate. The following is made rich: On the other hand, in the example shown in FIG. 11, the required minimum air-fuel ratio X is lean. In this case, the reducing intermediate is generated by periodically reducing the air-fuel ratio (A / F) in while maintaining the air-fuel ratio (A / F) in lean.
In this case, whether the required minimum air-fuel ratio X becomes rich or lean depends on the oxidizing power of the
Now, when the
On the other hand, when the
That is, it can be seen that the required minimum air-fuel ratio X needs to be lowered as the oxidizing power of the
When the base air-fuel ratio (A / F) b increases, that is, when the oxygen concentration in the exhaust gas before the hydrocarbons are supplied increases, the air-fuel ratio (A / F) in is made equal to or less than the required minimum air-fuel ratio X. This increases the amount of hydrocarbons required for this. Therefore, it is necessary to increase the amplitude of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher.
FIG. 13 shows the relationship between the oxygen concentration in the exhaust gas before the hydrocarbon is supplied and the amplitude ΔH of the hydrocarbon concentration when the same NO x purification rate is obtained. FIG. 13 shows that in order to obtain the same NO x purification rate, it is necessary to increase the amplitude ΔH of the hydrocarbon concentration as the oxygen concentration in the exhaust gas before the hydrocarbon is supplied is higher. That is, in order to obtain the same NO x purification rate, it is necessary to increase the amplitude ΔT of the hydrocarbon concentration as the base air-fuel ratio (A / F) b increases. In other words, in order to remove the NO x well it can reduce the amplitude ΔT of the hydrocarbon concentration as the base air-fuel ratio (A / F) b becomes lower.
By the way, the base air-fuel ratio (A / F) b becomes the lowest during the acceleration operation. At this time, if the amplitude ΔH of the hydrocarbon concentration is about 200 ppm, NO x can be purified well. The base air-fuel ratio (A / F) b is usually larger than that during acceleration operation. Therefore, as shown in FIG. 14, if the hydrocarbon concentration amplitude ΔH is 200 ppm or more, a good NO x purification rate can be obtained. become.
On the other hand, when the base air-fuel ratio (A / F) b is the highest is found that good the NO x purification rate when the amplitude ΔH of the hydrocarbon concentration of about 10000ppm is obtained. Therefore, in the present invention, the predetermined range of the amplitude of the hydrocarbon concentration is set to 200 ppm to 10,000 ppm.
Further, when the vibration period ΔT of the hydrocarbon concentration becomes longer, the oxygen concentration around the active NO x * becomes higher while the hydrocarbon is supplied after the hydrocarbon is supplied. In this case, when the vibration period ΔT of the hydrocarbon concentration becomes longer than about 5 seconds, the active NO x * starts to be absorbed in the
On the other hand, when the vibration period ΔT of the hydrocarbon concentration becomes approximately 0.3 seconds or less, the supplied hydrocarbon begins to accumulate on the exhaust gas flow surface of the
In the present invention, the hydrocarbon supply amount and the injection timing from the
Next, the NO x purification method in the case where the
In this second NO x purification method, as shown in FIG. 17, the occluded NO x amount ΣNO x occluded in the
Occluded amount of NO x ΣNOX is calculated from the amount of NO x exhausted from the engine, for example. In the embodiment according to the present invention is stored in advance in the ROM32 in the form of a map as shown in FIG. 18 as a function of the discharge amount of NO x NOXA the injection quantity Q and the engine speed N which is discharged from the engine per unit time, occluded amount of NO x ΣNOX is calculated from the discharge amount of NO x NOXA. In this case, as described above, the period during which the air-fuel ratio (A / F) in of the exhaust gas is made rich is usually 1 minute or more.
In this second NO x purification method, as shown in FIG. 19, the exhaust gas flowing into the
21A shows an enlarged view around the
As described above, to generate the reducing intermediate, it is necessary to set the air-fuel ratio (A / F) in of the exhaust gas flowing into the
In the present invention, as shown in FIG. 21A, the
That is, as described above, the base of the
In the embodiment shown in FIGS. 21A to 21C, the diameter of the upstream end of the
The radicalization action of the hydrocarbon supplied from the
On the other hand, in the present invention, the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 14b does not need to be lower than the required minimum air-fuel ratio X, and in order to generate NO x * , that is, to increase the NO x purification rate. Needs to maintain the air-fuel ratio of the exhaust gas flowing into the downstream catalyst 14b lean. Accordingly, as shown in FIG. 21A, the
Further, in order not to diffuse the hydrocarbons injected from the
In the present invention, the
In the present invention, as the downstream catalyst 14b, for example, a NO x purification catalyst in which a metal having a lower oxidizing power than a noble metal is supported on a catalyst carrier can be used. In this NO x purification catalyst, for example, the catalyst support is made of alumina or zeolite, and the metal supported on the catalyst support is silver Ag, copper Cu, iron Fe, vanadium V, molybdenum Mo, cobalt Co, nickel Ni, manganese It consists of at least one transition metal selected from Mn. Therefore, in the present invention, the
The oxidation reaction of hydrocarbons flowing into the
Therefore, in this embodiment of the present invention, the temperature TCA at the upstream end of the
Another method for reducing the temperature TCA at the upstream end of the
FIG. 22 shows the NO x purification control routine. This routine is executed by interruption every predetermined time.
Referring to FIG. 22, first, at
On the other hand, when it is determined in
On the other hand, when it is determined at
5…排気マニホルド
7…排気ターボチャージャ
12…排気管
13…排気浄化触媒
14a…上流側触媒
14b…下流側触媒
15…炭化水素供給弁 4 ...
Claims (9)
- 炭化水素を供給するための炭化水素供給弁を機関排気通路内に配置し、炭化水素供給弁下流の機関排気通路内に排気ガス中に含まれるNOxと改質された炭化水素とを反応させるための排気浄化触媒を配置し、該排気浄化触媒は互いに間隔を隔てて直列に配置された上流側触媒と下流側触媒からなり、該上流側触媒は少くとも炭化水素供給弁から供給された炭化水素を改質する機能を有しており、該上流側触媒は上流端から下流端に向けて拡開する輪郭形状を有すると共に該上流側触媒内には上流端から下流端に向けて放射状に延びる複数個の排気ガス流通路が形成されており、該上流側触媒と下流側触媒の少くとも一方の触媒の排気ガス流通表面上には貴金属触媒が担持されていると共に該貴金属触媒周りには塩基性の排気ガス流通表面部分が形成されており、該排気浄化触媒は、該上流側触媒に流入する炭化水素の濃度を予め定められた範囲内の振幅および予め定められた範囲内の周期でもって振動させると排気ガス中に含まれるNOxを還元する性質を有すると共に、該炭化水素濃度の振動周期を該予め定められた範囲よりも長くすると排気ガス中に含まれるNOxの吸蔵量が増大する性質を有しており、機関運転時に該上流側触媒に流入する炭化水素の濃度を上記予め定められた範囲内の振幅および上記予め定められた範囲内の周期でもって振動させ、それにより排気ガス中に含まれるNOxを排気浄化触媒において還元するようにした内燃機関の排気浄化装置。 The hydrocarbon feed valve for feeding hydrocarbons is arranged in the engine exhaust passage, reacting NO x and reformed hydrocarbons contained in the exhaust gas to the hydrocarbon feed valve engine exhaust passage downstream of An exhaust purification catalyst is provided, and the exhaust purification catalyst comprises an upstream catalyst and a downstream catalyst arranged in series at a distance from each other, and the upstream catalyst is at least carbonized from a hydrocarbon feed valve. It has a function of reforming hydrogen, and the upstream catalyst has a contour shape that expands from the upstream end to the downstream end, and radially in the upstream catalyst from the upstream end to the downstream end. A plurality of exhaust gas flow passages extending are formed. A noble metal catalyst is supported on the exhaust gas flow surface of at least one of the upstream catalyst and the downstream catalyst, and around the noble metal catalyst. Basic exhaust gas flow surface And the exhaust purification catalyst causes the concentration of hydrocarbons flowing into the upstream catalyst to oscillate with an amplitude within a predetermined range and a period within a predetermined range. which has a property for reducing the NO x contained in, have a property of absorbing the amount of the NO x contained the vibration period in the exhaust gas to be longer than the range defined the advance of the hydrocarbon concentration is increased And the hydrocarbon concentration flowing into the upstream catalyst during engine operation is vibrated with an amplitude within the predetermined range and a period within the predetermined range, whereby NO contained in the exhaust gas An exhaust purification device for an internal combustion engine, wherein x is reduced by an exhaust purification catalyst.
- 上記排気ガス流通路が下流側に向けて拡開している請求項1に記載の内燃機関の排気浄化装置。 The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas flow passage is expanded toward the downstream side.
- 該上流側触媒の上流端の径は下流側触媒の径よりも小さく、上流側触媒の下流端の径は下流側触媒の径と等しくされる請求項1に記載の内燃機関の排気浄化装置。 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the diameter of the upstream end of the upstream catalyst is smaller than the diameter of the downstream catalyst, and the diameter of the downstream end of the upstream catalyst is equal to the diameter of the downstream catalyst.
- 上記上流側触媒の上流端の温度がNOx浄化率の低下をひき起す予め定められた限界温度を越えたときには該上流側触媒の上流端の温度を低下させるために、上流側触媒に流入する排気ガスの空燃比がリーンのときには該排気ガスの空燃比がリッチになるように、上流側触媒に流入する排気ガスの空燃比がリッチのときには該排気ガスの空燃比が更にリッチになるように上流側触媒に流入する炭化水素の濃度が高められる請求項1に記載の内燃機関の排気浄化装置。 For the lowering of the temperature of the upstream end of the upstream side catalyst when the temperature of the upstream end of the upstream catalyst exceeds a predetermined limit temperature cause a reduction of the NO x purification rate, and flows into the upstream catalyst When the air-fuel ratio of the exhaust gas is lean, the air-fuel ratio of the exhaust gas becomes rich. When the air-fuel ratio of the exhaust gas flowing into the upstream catalyst is rich, the air-fuel ratio of the exhaust gas becomes further rich. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the concentration of hydrocarbons flowing into the upstream catalyst is increased.
- 上記上流側触媒の上流端の温度がNOx浄化率の低下をひき起す予め定められた限界温度を越えたときには該上流側触媒の上流端の温度を低下させるために、上流側触媒に流入する炭化水素の濃度の振動周期を長くするか、又は炭化水素供給弁からの炭化水素の供給を停止する請求項1に記載の内燃機関の排気浄化装置。 For the lowering of the temperature of the upstream end of the upstream side catalyst when the temperature of the upstream end of the upstream catalyst exceeds a predetermined limit temperature cause a reduction of the NO x purification rate, and flows into the upstream catalyst The exhaust emission control device for an internal combustion engine according to claim 1, wherein the vibration cycle of the hydrocarbon concentration is lengthened or the supply of hydrocarbons from the hydrocarbon supply valve is stopped.
- 上記排気浄化触媒内において排気ガス中に含まれるNOxと改質された炭化水素とが反応して窒素および炭化水素を含む還元性中間体が生成され、上記炭化水素濃度の振動周期は還元性中間体を生成し続けるのに必要な振動周期である請求項1に記載の内燃機関の排気浄化装置。 In the exhaust purification catalyst, NO x contained in the exhaust gas reacts with the reformed hydrocarbon to produce a reducing intermediate containing nitrogen and hydrocarbons, and the oscillation cycle of the hydrocarbon concentration is reducible. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the vibration period is required to continue producing the intermediate.
- 上記炭化水素濃度の振動周期が0.3秒から5秒の間である請求項6に記載の内燃機関の排気浄化装置。 The exhaust gas purification apparatus for an internal combustion engine according to claim 6, wherein the vibration period of the hydrocarbon concentration is between 0.3 seconds and 5 seconds.
- 上記貴金属触媒は白金Ptと、ロジウムRhおよびパラジウムPdの少くとも一方とにより構成される請求項1に記載の内燃機関の排気浄化装置。 The exhaust purification device for an internal combustion engine according to claim 1, wherein the noble metal catalyst is composed of platinum Pt and at least one of rhodium Rh and palladium Pd.
- 上記排気ガス流通表面上にアルカリ金属又はアルカリ土類金属又は希土類又はNOxに電子を供与しうる金属を含む塩基性層が形成されており、該塩基性層の表面が上記塩基性の排気ガス流通表面部分を形成している請求項1に記載の内燃機関の排気浄化装置。 The are the basic layer is formed containing a metal capable of donating electrons to the alkali metal or alkaline earth metal or rare earth or NO x in the exhaust gas flow on the surface, an exhaust gas surface of the base layer is the basic The exhaust emission control device for an internal combustion engine according to claim 1, wherein a flow surface portion is formed.
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DE112011104856.4T DE112011104856B4 (en) | 2011-02-08 | 2011-02-08 | Emission control system for an internal combustion engine |
PCT/JP2011/053065 WO2012108062A1 (en) | 2011-02-08 | 2011-02-08 | Internal combustion engine exhaust purification device |
CN201180001926.7A CN103328781B (en) | 2011-02-08 | 2011-02-08 | The Exhaust gas purifying device of internal-combustion engine |
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JP2015025434A (en) * | 2013-07-29 | 2015-02-05 | 三菱自動車工業株式会社 | Exhaust emission control device of internal combustion engine |
JPWO2015092941A1 (en) * | 2013-12-20 | 2017-03-16 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
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WO2005054637A1 (en) * | 2003-12-01 | 2005-06-16 | Toyota Jidosha Kabushiki Kaisha | Exhaust emission purification apparatus of compression ignition internal combustion engine |
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JP4155320B2 (en) * | 2006-09-06 | 2008-09-24 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
JP2009024642A (en) * | 2007-07-20 | 2009-02-05 | Toyota Motor Corp | Exhaust emission control system of internal combustion engine |
-
2011
- 2011-02-08 WO PCT/JP2011/053065 patent/WO2012108062A1/en active Application Filing
- 2011-02-08 CN CN201180001926.7A patent/CN103328781B/en not_active Expired - Fee Related
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JP2009168031A (en) * | 2001-12-03 | 2009-07-30 | Eaton Corp | System and method for improved emission control of internal combustion engine |
JP2005113801A (en) * | 2003-10-08 | 2005-04-28 | Toyota Motor Corp | Exhaust emission control device for internal combustion engine |
JP2008002451A (en) * | 2006-05-23 | 2008-01-10 | Honda Motor Co Ltd | Exhaust emission control device for diesel engine and exhaust emission control method for diesel engine |
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JPWO2015092941A1 (en) * | 2013-12-20 | 2017-03-16 | トヨタ自動車株式会社 | Exhaust gas purification device for internal combustion engine |
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JPWO2012108062A1 (en) | 2014-07-03 |
CN103328781B (en) | 2015-09-09 |
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CN103328781A (en) | 2013-09-25 |
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DE112011104856T8 (en) | 2014-01-16 |
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