WO2014136832A1 - 排ガス後処理装置の制御方法 - Google Patents

排ガス後処理装置の制御方法 Download PDF

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Publication number
WO2014136832A1
WO2014136832A1 PCT/JP2014/055607 JP2014055607W WO2014136832A1 WO 2014136832 A1 WO2014136832 A1 WO 2014136832A1 JP 2014055607 W JP2014055607 W JP 2014055607W WO 2014136832 A1 WO2014136832 A1 WO 2014136832A1
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Prior art keywords
exhaust gas
nox
rich
exhaust pipe
urea water
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PCT/JP2014/055607
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English (en)
French (fr)
Inventor
長岡　大治
輝男 中田
裕之 遊座
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いすゞ自動車株式会社
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Application filed by いすゞ自動車株式会社 filed Critical いすゞ自動車株式会社
Priority to EP14760529.9A priority Critical patent/EP2966277B1/en
Priority to CN201480010796.7A priority patent/CN105189964B/zh
Priority to US14/771,847 priority patent/US9562463B2/en
Publication of WO2014136832A1 publication Critical patent/WO2014136832A1/ja

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • F01N9/002—Electrical control of exhaust gas treating apparatus of filter regeneration, e.g. detection of clogging
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
    • F01N11/002—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity the diagnostic devices measuring or estimating temperature or pressure in, or downstream of the exhaust apparatus
    • 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
    • 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
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
    • F01N3/0232—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles removing incombustible material from a particle filter, e.g. ash
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
    • F01N3/025—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using fuel burner or by adding fuel to exhaust
    • F01N3/0253—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using fuel burner or by adding fuel to exhaust adding fuel to exhaust gases
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
    • F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
    • F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
    • F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/0807—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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    • 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
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    • 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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    • 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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    • 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
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    • F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
    • F01N3/0885—Regeneration of deteriorated absorbents or adsorbents, e.g. desulfurization of NOx traps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/103—Oxidation catalysts for HC and CO only
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/2073—Selective catalytic reduction [SCR] with means for generating a reducing substance from the exhaust gases
    • 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
    • F01N3/18—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
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
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    • F01N9/00—Electrical control of exhaust gas treating apparatus
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
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    • 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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    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
    • F01N2900/1602—Temperature of exhaust gas apparatus
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    • F01N2900/1606—Particle filter loading or soot amount
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
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    • 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
    • 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
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    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Definitions

  • the present invention relates to a method for controlling an exhaust gas aftertreatment device after performing PM regeneration and S purge in the exhaust gas aftertreatment device.
  • DOC Diesel Oxidation Catalyst
  • DPF Diesel Particulate Filter
  • NOx occlusion reduction catalyst LNT: Lean NOx Trap or NSR: NOx Storage ReductionCriticalRectRectCureC)
  • DOC and DPF system are effective means for PM reduction.
  • the DOC provided in the front stage of the exhaust gas stream cannot oxidize solid soot itself, but it oxidizes most of the soluble organic component (SOF) that accounts for 30 to 70% of the total PM, and simultaneously removes HC and CO.
  • the DPF provided in is formed of a porous ceramic or the like having a pore diameter and captures most of the PM in the exhaust gas.
  • the NOx occlusion reduction type catalyst includes a catalyst carrier such as alumina (Al 2 O 3 ), a noble metal catalyst such as Pt and Pd, an alkali metal such as Na, K and Cs, an alkaline earth metal such as Ca and Ba, Y , La and other rare earths and other storage materials having NOx storage function are supported, and exhibit two functions of NOx storage and NOx release / purification depending on the oxygen concentration in the exhaust gas.
  • a catalyst carrier such as alumina (Al 2 O 3 )
  • a noble metal catalyst such as Pt and Pd
  • an alkali metal such as Na, K and Cs
  • an alkaline earth metal such as Ca and Ba, Y , La and other rare earths and other storage materials having NOx storage function are supported, and exhibit two functions of NOx storage and NOx release / purification depending on the oxygen concentration in the exhaust gas.
  • NO in exhaust gas is converted to NO 2 by a noble metal catalyst such as Pt and Pd under conditions of high oxygen concentration in the exhaust gas (lean air-fuel ratio) as in the normal operation state.
  • a noble metal catalyst such as Pt and Pd
  • Oxidized and the occlusion material occludes it as nitrate (Ba (NO 3 ) 2 ) to purify NOx.
  • EGR Exhaust Gas Recirculation
  • fuel post-injection are performed under conditions of low oxygen concentration by changing the operating conditions.
  • exhaust pipe injection is performed to form a rich state, and the fuel is reduced on the noble metal catalyst, so that CO, HC, H 2 is generated in the exhaust gas, NOx is reduced, and NOx is released and purified.
  • the purification system using the NOx occlusion reduction catalyst is a system that occludes NOx when the air-fuel ratio is lean (conditions where the oxygen concentration is high) and reduces and purifies NOx occluded when rich.
  • the NOx occlusion reduction type catalyst adsorbs and occludes SOx in the exhaust gas simultaneously with NOx.
  • SOx is not easily desorbed, and in order to release S accumulated in the storage material, control the catalyst so that the ambient temperature of the catalyst is higher than 650 ° C. and the air-fuel ratio becomes rich.
  • Ba 2 SO 4 becomes carbonate + SO 2 and sulfur is desulfurized. Therefore, the NOx occlusion reduction type catalyst needs to be regenerated by performing desulfurization control (S purge) at a constant travel interval.
  • S purge desulfurization control
  • the EGR amount is increased more than usual and the air / fuel ratio is close to the stoichiometric ratio. Therefore, the NOx emission amount is small due to the decrease in the NOx concentration at the engine outlet and the three-way function, and there is no problem of NOx deterioration.
  • urea SCR selective reduction catalyst
  • Patent Document 1 In LNT (Lean NOx Trap) catalyst, there is Patent Document 1 in which rich reduction is not performed until after a specified time interval after S purge, but in Patent Document 1, due to disturbances such as outside air temperature, vehicle speed, traveling wind, etc. Since the amount of heat released from the catalyst changes and the catalyst temperature changes, appropriate control cannot be performed. For example, in high-speed traveling, the catalyst temperature decreases early, but in low-speed traveling, the catalyst temperature requires more time to decrease.
  • an object of the present invention is to provide a control method for an exhaust gas aftertreatment device capable of solving the above-described problems and accurately controlling the timing for returning to a rich state after S purge and the urea water injection timing after PM regeneration.
  • an exhaust gas aftertreatment device control method includes an exhaust pipe injector provided in an engine exhaust pipe, and a DOC, NOx occlusion reduction type catalyst provided in an exhaust pipe downstream of the exhaust pipe injector.
  • DPF is connected to constitute an exhaust gas aftertreatment device, NOx in the exhaust gas is occluded by the NOx occlusion reduction type catalyst with the air-fuel ratio being lean, and NOx occluded with the air-fuel ratio being rich is reduced and purified
  • the exhaust gas temperature is raised to regenerate PM, and then the exhaust gas temperature is further raised to perform S purge of sulfur stored in the NOx storage reduction catalyst,
  • the rich regeneration is prohibited during the S purge period from the PM regeneration period, and after the completion of the S purge, the difference between the DOC inlet temperature and the NOx storage reduction catalyst outlet temperature is a set threshold value. It is intended to continue the rich prohibited until the bottom.
  • This set threshold is set in the range of 80 to 100 ° C., is less than the set threshold, and after the minimum rich prohibition time has elapsed, rich reduction is performed, and when the set threshold is exceeded and exceeded, the maximum rich It is preferable to perform rich reduction after elapse of the prohibited time.
  • the temperature setting threshold is a value obtained by experiments, and normal control is possible within this range. If it is higher than this, the NOx storage capacity is not completely recovered, and if it is lower than this, the rich prohibition period becomes longer than necessary.
  • the exhaust gas aftertreatment device control method of the present invention includes an exhaust pipe injector provided in an exhaust pipe of an engine, a DPF connected to an exhaust pipe downstream of the exhaust pipe injector, and an exhaust pipe downstream of the DPF.
  • the exhaust gas aftertreatment device is configured by connecting the SCR and DOC to the upstream side of the SCR and providing a urea water injection nozzle in the upstream exhaust pipe of the SCR, and reducing and purifying NOx by the SCR.
  • the set threshold value is set in the range of 80 to 100 ° C., the urea solution is injected after the shortest urea solution injection prohibition time has elapsed, and the time that exceeds the set threshold value and exceeds the set threshold value It is preferable to perform urea water injection after elapse of the longest urea water injection prohibition time or longer.
  • Hours limit values are set for the rich prohibition period and the urea water injection prohibition period. This is to cope with the case where the temperature difference before and after the catalyst does not easily fall below the threshold value due to the operating conditions.
  • the present invention prohibits the rich reduction immediately after performing the S purge of the NOx storage reduction catalyst, and permits the rich after waiting for the temperature of the exhaust gas at the inlet / outlet of the NOx storage reduction catalyst to fall to the set threshold value. This can improve the fuel economy during that time. Further, even during PM regeneration by SCR, an excellent effect of preventing ammonia slip is exhibited by injecting urea water after waiting for the temperature of the exhaust gas before and after the SCR to fall to the set threshold value.
  • FIG. 1 It is a figure which shows the apparatus structure of the control method of the waste gas aftertreatment apparatus using the NOx storage reduction type catalyst of this invention. It is a figure which shows the time-dependent change of the exhaust gas temperature of each part at the time of PM reproduction
  • FIG. 1 shows an exhaust gas aftertreatment device 10 using a NOx occlusion reduction type catalyst.
  • a turbocharger 11 and an EGR pipe 12 are connected to the intake / exhaust system of the engine E, and the air sucked from the air cleaner 13 is compressed by the compressor 14 of the turbocharger 11 and is pumped to the intake passage 15.
  • E is supplied into the engine E from the intake manifold 16 of E.
  • An intake valve 17 for adjusting the amount of air to the engine E is provided in the intake passage 15.
  • Exhaust gas discharged from the engine E is discharged from the exhaust manifold 18 to the turbine 19 of the turbocharger 11, drives the turbine 19, and is discharged to the exhaust pipe 20.
  • An EGR pipe 12 is connected to the intake manifold 16 and the exhaust manifold 18, and an EGR cooler 21 for cooling the exhaust gas from the exhaust manifold 18 to the intake manifold 16 is connected to the EGR pipe 12, and the EGR amount is adjusted.
  • An EGR valve 22 is connected.
  • an exhaust pipe injector 23 is provided in an exhaust pipe 20 on the downstream side of the turbine 19, and a DOC 25, NOx is placed in a canning container 24 formed in the exhaust pipe 20 on the downstream side of the exhaust pipe injector 23.
  • the storage reduction catalyst 26 and the DPF 27 are sequentially canned.
  • An exhaust gas temperature sensor 28 is provided upstream of the DOC 25, a catalyst inlet temperature sensor 29 is provided on the inlet side of the NOx storage reduction catalyst 26, and a catalyst outlet temperature sensor 30 is provided on the outlet side.
  • the engine E is generally controlled by the ECU 32.
  • a temperature detection means 33 In the ECU 32, a temperature detection means 33, an air-fuel ratio control means 34, and an injection control means 35 are formed.
  • the detected values of the exhaust gas temperature sensor 28, the catalyst inlet temperature sensor 29, and the catalyst outlet temperature sensor 30 are input to the temperature detection means 33 of the ECU 32 that controls the operation of the engine E.
  • the air-fuel ratio control means 34 controls the EGR valve 22 and the intake valve 17, and the injection control means 35 controls the combustion injection amount of the engine E, controls multi-injection such as post-injection by the injector, and further exhaust pipe injector
  • the fuel HC injected from 23 is controlled.
  • the exhaust gas aftertreatment device 10 using the NOx occlusion reduction catalyst normally stores NOx by the NOx occlusion reduction catalyst 26 in an air-fuel ratio lean state, and in the meantime, the exhaust gas injector 23 pulsates the fuel HC in a pulsed manner. NOx reduction purification is performed in the fuel-rich state.
  • PM in the exhaust gas is captured by the DPF 27. If a predetermined amount of PM accumulated on the DPF 27 accumulates, for example, when the differential pressure before and after the DPF 27 reaches a constant value, or travels a predetermined travel distance. At this time, the ECU 32 performs automatic regeneration control of PM. At the time of this PM regeneration, post-injection or fuel injection by the exhaust pipe injector 23 is performed to raise the exhaust gas temperature to 600 ° C., thereby burning the PM deposited on the DPF 27.
  • the exhaust gas temperature is set to purge SOx adsorbed and stored in the NOx storage reduction catalyst 26 following the end of PM regeneration.
  • the temperature is raised to, for example, about 700 ° C. above 605 ° C., and the S purge is performed.
  • the temperature detection means 33 detects the exhaust gas temperature directly detected by the exhaust gas temperature sensor 28, the catalyst inlet temperature sensor 29, and the catalyst outlet temperature sensor 30, particularly the catalyst inlet temperature.
  • a set threshold value a value set in the range of 80 to 100 ° C.
  • the temperature of the exhaust gas at the inlet / outlet of the NOx storage reduction catalyst 26 is directly detected and the rich prohibition period is determined, so that it is less affected by disturbance than setting the rich prohibition period after S purge in terms of time. It is possible to control appropriately. Therefore, it is possible to prevent excessive richness and more appropriately prevent deterioration of fuel consumption and exhaust gas due to HC slip.
  • the catalyst inlet / outlet temperature difference as the rich start threshold, the state in which the catalyst has generated heat due to PM regeneration or S purge has been settled, and the NOx occlusion ability has been restored to enable richness. Can be monitored accurately.
  • the set threshold value of the temperature is a value obtained through experiments, and normal control is possible within this range. If it is higher than this, the NOx storage capacity is not completely recovered, and if it is lower than this, the rich prohibition period becomes longer than necessary.
  • FIG. 2 shows the change with time of the temperature of the exhaust gas at the inlet / outlet of the NOx storage reduction catalyst 26 from the start of PM regeneration to immediately after the end of the S purge.
  • FIG. 2 also shows changes over time in the vehicle speed (0 to 70 km / h).
  • the pre-catalyst exhaust gas temperature is the temperature detected by the catalyst inlet temperature sensor 29
  • the post-catalyst exhaust gas temperature is the temperature detected by the catalyst outlet temperature sensor 30
  • the exhaust gas temperature difference before and after the catalyst is the catalyst inlet temperature sensor 29.
  • the temperature difference detected by the catalyst outlet temperature sensor 30 is shown.
  • the exhaust gas temperature is raised to 600 ° C. by post injection or exhaust pipe injection, and the PM deposited on the DPF 27 is burned and regenerated. After the regeneration is completed, the exhaust gas temperature is raised to 700 ° C. and the NOx occlusion reduction type catalyst 26 is recovered. The SOx adsorbed and occluded in the gas is purged.
  • a rich prohibition period is set. If the exhaust gas temperature difference before and after the catalyst falls to the set threshold when the S purge is completed, NOx is reduced under the air-fuel ratio rich condition as a rich permission. I do.
  • FIG. 3 shows a flowchart of the control method of the exhaust gas aftertreatment device of the present invention.
  • step S10 Control is started in step S10, and in step S11, the pre-catalyst exhaust gas temperature and the post-catalyst exhaust gas temperature are measured, and the difference is calculated.
  • step S12 PM regeneration is started, and thereafter S purge is started, and the S purge is ended by the S purge end determination.
  • rich is prohibited.
  • step S13 it is determined whether the exhaust gas temperature difference before and after the catalyst is equal to or less than the threshold while continuing the rich prohibition. If the condition is met below the threshold, the minimum rich prohibition time (for example, 1) is determined in step S14. Min)), it is determined whether or not the minimum rich prohibition time has elapsed, and if the condition is met, rich reduction permission is performed in step S16.
  • the minimum rich prohibition time for example, 1
  • step S13 If it is determined in step S13 that the condition is not satisfied without being less than the threshold value, it is determined in step S15 whether or not the maximum rich prohibition time (for example, 5 minutes) has elapsed. If so, rich reduction permission is performed in step S16, and then control is terminated in step S17.
  • the maximum rich prohibition time for example, 5 minutes
  • the rich prohibition period is selected by dividing the rich prohibition time into the minimum rich time and the maximum rich time.
  • FIG. 4 shows the exhaust gas aftertreatment device 10 using the SCR catalyst.
  • the basic configuration of the engine E is the same as that in FIG. 1 except for the exhaust gas aftertreatment device 10, and this will be described again.
  • the turbocharger 11 and the EGR pipe 12 are connected to the intake / exhaust system of the engine E, and the air from the air cleaner 13 is compressed by the compressor 14 of the turbocharger 11 and is pumped to the intake passage 15, and passes through the intake valve 17 to the engine.
  • E is supplied into the engine E from the intake manifold 16 of E.
  • the exhaust gas discharged from the engine E is discharged from the exhaust manifold 18 to the turbine 19 of the turbocharger 11, drives the turbine 19, and is discharged to the exhaust pipe 20.
  • the EGR pipe 12 is connected to the intake manifold 16 and the exhaust manifold 18, and an EGR cooler 21 and an EGR valve 22 are connected to the EGR pipe 12.
  • an exhaust pipe injector 23 is provided in the exhaust pipe 20 on the downstream side of the turbine 19, and a DPF device 41 and an SCR device 42 are provided in the exhaust pipe 20 on the downstream side of the exhaust pipe injector 23.
  • the DPF device 41 is configured by canning a DOC 44 and a DPF 45 in a DPF canning container 43 formed in the exhaust pipe 20.
  • the SCR device 42 is provided with a SCR catalyst 47 and a DOC 48 for preventing ammonia slip in an SCR canning container 46 formed in the exhaust pipe 20, and a urea water injection nozzle in the exhaust pipe 20 upstream of the SCR canning container 46. 49 is provided.
  • An exhaust gas temperature sensor 50 is provided upstream of the DOC 44 of the DPF device 41, a DPF temperature sensor 51 is provided on the inlet side of the DPF 45, and an SCR catalyst inlet temperature sensor 52 is provided on the inlet side of the SCR catalyst 47 of the SCR device 42.
  • the SCR catalyst outlet temperature sensor 53 is provided on the outlet side.
  • the engine E is generally controlled by the ECU 32.
  • a temperature detection means 33 In the ECU 32, a temperature detection means 33, an air-fuel ratio control means 34, and an injection control means 35 are formed.
  • the detection value of each temperature sensor 50, 51, 52, 53 of the exhaust gas aftertreatment device 10 is input to the temperature detection means 33 of the ECU 32 that controls the operation of the engine E.
  • the air-fuel ratio control means 34 controls the EGR valve 22 and the intake valve 17, and the injection control means 35 controls the combustion injection amount of the engine E, controls multi-injection such as post-injection by the injector, and further exhaust pipe injector The fuel injected from 23 is controlled.
  • the urea water injection nozzle 49 is controlled by a DCU (Dosing Control Unit) 55 connected to the ECU 32. Although the urea water injection by the urea water injection nozzle 49 is omitted in the drawing, the supply module controlled by the DCU 55 sucks the urea water in the urea water tank and raises it to a predetermined pressure, thereby injecting the urea water.
  • the DCU 55 controls the on-off valve in the nozzle 49 so that a predetermined amount of urea water corresponding to the NOx concentration in the exhaust gas is injected from the urea water injection nozzle 49.
  • the injected urea water generates ammonia by hydrolysis while flowing into the SCR device 42 from the exhaust pipe 20, and the generated ammonia and NOx in the exhaust gas are reacted by the SCR catalyst 47 to denitrate. Excess ammonia is adsorbed on the DOC 48 to prevent ammonia slip.
  • the catalyst inlet / outlet temperature of the SCR device 42 is monitored by monitoring the temperature of each of the temperature sensors 50-53, in particular the sensor SCR catalyst inlet temperature sensor 52 and the SCR catalyst inlet temperature sensor 53, and the catalyst canning inlet temperature.
  • the urea water injection by the urea water injection nozzle 49 is prohibited until the difference in the outlet temperature with respect to is equal to or less than the set threshold value (a value set in the range of 80 to 100 ° C.).
  • the urea water injection prohibition period is determined directly at the temperature of the urea water injection timing, the urea water injection prohibition period after PM regeneration is appropriately controlled without being affected by disturbance rather than setting the urea water injection prohibition period in time. Is possible. Therefore, excessive urea water injection can be prevented and ammonia slip can be more appropriately prevented.
  • Control starts in step S20, and in step S21, the pre-catalyst exhaust gas temperature and the post-catalyst exhaust gas temperature are measured, and the difference is calculated.
  • step S22 PM regeneration is started, and thereafter PM regeneration is terminated by PM regeneration end determination.
  • step S23 it is determined whether the exhaust gas temperature difference before and after the catalyst is equal to or less than a threshold while continuing prohibition of urea water injection. If the condition is met below the threshold, the shortest urea water injection is performed in step S24. It is determined whether or not the prohibition time (for example, 1 minute) or more has passed, and if the minimum urea water injection prohibition time has passed and the conditions are met, the urea water injection is permitted in step S26.
  • the prohibition time for example, 1 minute
  • step S23 If it is determined in step S23 that the condition is not satisfied without being less than the threshold value, it is determined in step S25 whether or not the longest urea water injection prohibition time (for example, 5 minutes) has elapsed, and the longest urea water injection prohibition time has elapsed. If the conditions are met, the urea water injection is permitted in step S26, and then the control is terminated in step S27.
  • the longest urea water injection prohibition time for example, 5 minutes
  • the urea water injection prohibition time is set to the shortest urea water injection prohibition time and the longest urea water injection prohibition time.
  • Hours limit values are set for the rich prohibition period and the urea water injection prohibition period. This is to cope with the case where the temperature difference before and after the catalyst does not easily fall below the threshold value due to the operating conditions.

Abstract

　Ｓパージ後にリッチ状態に戻す時期やＰＭ再生後に尿素水噴射時期を的確に制御できる排ガス後処理装置の制御方法を提供する。　エンジンＥの排気管２０に設けた排気管インジェクタ２３の下流側の排気管２０に、ＤＯＣ２５、ＮＯｘ吸蔵還元型触媒２６、ＤＰＦ２７を接続し、空燃比がリーン条件で排ガス中のＮＯｘをＮＯｘ吸蔵還元型触媒２６で吸蔵し、空燃比がリッチ条件で吸蔵したＮＯｘを還元・浄化するに際し、ＤＰＦ２７にＰＭが所定量堆積したとき排ガス温度を上昇させてＰＭ再生し、その後、排ガス温度をさらに上昇させてＮＯｘ吸蔵還元型触媒２６に吸蔵した硫黄のＳパージを行い、そのＰＭ再生期間からＳパージ期間中リッチ禁止を行い、Ｓパージ完了後、ＤＯＣ２５の入口温度とＮＯｘ吸蔵還元型触媒２６の出口温度の差が設定閾値以下になるまでリッチ禁止を継続するものである。

Description

排ガス後処理装置の制御方法
　本発明は、排ガス後処理装置で、ＰＭ再生やＳパージを行った後の排ガス後処理装置の制御方法に関するものである。
　ディーゼルエンジンの排ガス後処理装置としてＤＯＣ（Ｄｉｅｓｅｌ　Ｏｘｉｄａｔｉｏｎ　Ｃａｔａｌｙｓｔ；酸化触媒）、ＤＰＦ（Ｄｉｅｓｅｌ　Ｐａｒｔｉｃｕｌａｔｅ　Ｆｉｌｔｅｒ）、ＮＯｘ吸蔵還元型触媒（ＬＮＴ：Ｌｅａｎ　ＮＯｘ　ＴｒａｐもしくはＮＳＲ：ＮＯｘ　Ｓｔｒａｇｅ　Ｒｅｄｕｃｔｉｏｎ）、尿素ＳＣＲ（Ｓｅｌｅｃｔｉｖｅ　Ｃａｔａｌｙｓｔｉｃ　Ｒｅｄｕｃｔｉｏｎ）システム等が実用化されている。
　ＤＯＣとＤＰＦシステムは、ＰＭ低減のための有力な手段である。排ガス流の前段に設けられるＤＯＣは、固体のＳｏｏｔ自体は酸化できないが、ＰＭ全体の３０～７０％を占める可溶性有機成分（ＳＯＦ）の大部分を酸化し、ＨＣやＣＯも同時に除去し、後段に設けられるＤＰＦは、細孔径を有する多孔質セラミック等で形成され、排ガス中のＰＭの大部分を捕捉する。
　ＮＯｘ吸蔵還元型触媒は、アルミナ（Ａｌ2Ｏ3）等の触媒担体に、ＰｔやＰｄなどの貴金属触媒と、Ｎａ、Ｋ、Ｃｓ等のアルカリ金属やＣａ、Ｂａ等のアルカリ土類金属、Ｙ、Ｌａ等の希土類等のＮＯｘ吸蔵機能をもつ吸蔵材を担持したもので、排ガス中の酸素濃度によって、ＮＯｘ吸蔵とＮＯｘ放出・浄化の二つの機能を発揮する。
　このＮＯｘ吸蔵還元型触媒による浄化システムは、通常運転状態のように排ガス中の酸素濃度が高い条件（リーン空燃比）では、排ガス中のＮＯが、ＰｔやＰｄなどの貴金属触媒等でＮＯ2に酸化され、これを吸蔵材が、硝酸塩（Ｂａ（ＮＯ3）2）として吸蔵しＮＯｘを浄化する。
　しかし、ＮＯｘの吸蔵が継続すると、硝酸塩が飽和して吸蔵材の吸蔵機能を失うため、運転条件を変え、低酸素濃度の条件で、ＥＧＲ（Ｅｘｈａｕｓｔ　Ｇａｓ　Ｒｅｃｉｒｃｕｌａｔｉｏｎ：排ガス再循環）、燃料のポスト噴射や、排気管噴射を行って、リッチ状態を形成し、燃料を貴金属触媒上で還元することで、排ガス中にＣＯ、ＨＣ、Ｈ2を生成させてＮＯｘを還元してＮＯｘを放出・浄化する。
　このようにＮＯｘ吸蔵還元型触媒による浄化システムは、空燃比リーン時（酸素濃度が高い条件）にＮＯｘを吸蔵し、リッチ時に吸蔵されたＮＯｘを還元・浄化するシステムである。
　ところでＮＯｘ吸蔵還元型触媒は、ＮＯｘと同時に、排ガス中のＳＯｘも吸着、吸蔵する。ＳＯｘはＮＯｘと異なり、容易に脱離できず、吸蔵材に蓄積したＳを放出させるために、触媒の雰囲気温度を６５０℃以上の高温とし、かつ空燃比がリッチ雰囲気になるように制御することで、Ｂａ2ＳＯ4が炭酸塩＋ＳＯ2となって、硫黄の脱硫が行われる。よって、ＮＯｘ吸蔵還元型触媒は、一定の走行間隔で脱硫制御（Ｓパージ）を行って再生を行う必要がある。Ｓパージ中は、ＥＧＲ量を通常よりも多くして、かつストイキに近い空燃比となるので、エンジン出口のＮＯｘ濃度の低下と三元機能によりＮＯｘ排出量は少なく、ＮＯｘ悪化の問題は無い。
　また選択還元式触媒（尿素ＳＣＲ）でも、ＰＭ再生時は、吸入空気量を減らしてエンジン出口のＮＯｘ排出量を減らしているので、ＮＯｘ悪化の問題は無い。
特許第４４７４７７５号公報 特開２０１０－２２９９２９号公報
　しかしながら、ＰＭ再生やＳパージが終了すると、通常の空気系制御に戻るので、エンジン出口のＮＯｘ排出量は、通常レベルに増加する。ＮＯｘ吸蔵の効果でＮＯｘ悪化は一時的には防止できるが、Ｓパージ直後のＮＯｘ吸蔵還元型触媒は高温のため、吸蔵能力が低く、リッチ処理が通常よりも頻繁に入り、燃費悪化やリッチ時のＨＣスリップによる排ガス悪化を招く問題がある。
　また、選択還元式触媒（尿素ＳＣＲ）でも、ＰＭ再生直後は、ＳＣＲ触媒が高温のためにＮＯｘ還元能力は低下しており、通常時と同様の尿素水噴射を行うと還元に使用されないＮＨ3がスリップする等の問題が生じる。
　従来、この問題が発生するのは、ＳパージやＰＭ再生直後で、発生する期間としては非常に短いので、対処されていなかった。
　しかし、排気ガス規制値が厳しくなり、この様な僅かな問題でもＫｉ（ＰＭ再生等により排ガスが悪化する割合を、触媒の劣化係数に反映する値）の改善の為に見過ごすことができなくなっており、瞬間的には排ガスや燃費の悪化を招くこの問題の対処が必要となってきた。
　ＬＮＴ（Ｌｅａｎ　ＮＯｘ　Ｔｒａｐ）触媒では、Ｓパージ後に指定の時間インターバル後まではリッチ還元を行わないようにする特許文献１があるが、特許文献１では、外気温や車速、走行風等の外乱により、触媒からの放熱量が変化して触媒温度が変化するので、適切な制御をすることができない。例えば、高速走行では触媒温度は、早期に温度低下するが、低速走行では触媒温度は、温度低下に、より多くの時間を要する。
　また尿素ＳＣＲ触媒について、特許文献２では、ＰＭ再生時にアンモニアスリップの発生を防止するためにＳＣＲ触媒のアンモニア吸着量が所定の閾値より下がったときにＤＰＦの再生を行うようにしているが、ＰＭ再生終了後の尿素水噴射によるアンモニアスリップについては考慮されていない。
　そこで、本発明の目的は、上記課題を解決し、Ｓパージ後にリッチ状態に戻す時期やＰＭ再生後に尿素水噴射時期を的確に制御できる排ガス後処理装置の制御方法を提供することにある。
　上記目的を達成するために本発明の排ガス後処理装置の制御方法は、エンジンの排気管に、排気管インジェクタを設け、その排気管インジェクタの下流側の排気管に、ＤＯＣ、ＮＯｘ吸蔵還元型触媒、ＤＰＦを接続して排ガス後処理装置を構成し、空燃比がリーン条件で排ガス中のＮＯｘをＮＯｘ吸蔵還元型触媒で吸蔵し、空燃比がリッチ条件で吸蔵したＮＯｘを還元・浄化する排ガス後処理装置の制御方法において、ＤＰＦにＰＭが所定量堆積したとき排ガス温度を上昇させてＰＭ再生し、その後、排ガス温度をさらに上昇させてＮＯｘ吸蔵還元型触媒に吸蔵した硫黄のＳパージを行い、そのＰＭ再生期間からＳパージ期間中リッチ禁止を行い、Ｓパージ完了後、前記ＤＯＣの入口温度とＮＯｘ吸蔵還元型触媒の出口温度の差が設定閾値以下になるまでリッチ禁止を継続するものである。
　触媒の出入り口温度差をリッチ開始の閾値とする事で、ＰＭ再生やＳパージで触媒が発熱した状態が収まり、ＮＯｘの吸蔵能力が回復してリッチが可能な状態となった事を正確にモニターができる。この設定閾値は８０～１００℃の範囲で設定し、その設定閾値以下となり、かつ最小リッチ禁止時間以上経過後に、リッチ還元を行い、また、前記設定閾値を超え、かつその超える時間が、最大リッチ禁止時間以上経過後に、リッチ還元を行うことが好ましい。温度の設定閾値は実験により得られた値であり、この範囲であれば正常な制御が可能である。これよりも高いと完全にＮＯｘ吸蔵能力が回復しておらず、これよりも低いとリッチ禁止期間が必要以上に長くなってしまう。
　また本発明の排ガス後処理装置の制御方法は、エンジンの排気管に、排気管インジェクタを設け、その排気管インジェクタの下流側の排気管に、ＤＰＦを接続し、そのＤＰＦの下流側の排気管にＳＣＲ、ＤＯＣを接続し、前記ＳＣＲの上流側排気管に尿素水噴射ノズルを設けて排ガス後処理装置を構成し、前記ＳＣＲでＮＯｘを還元・浄化する排ガス後処理装置の制御方法において、ＤＰＦにＰＭが所定量堆積したとき排ガス温度を上昇させてＰＭ再生を行うと共に前記尿素水噴射ノズルでの尿素水噴射を禁止し、ＰＭ再生終了後、ＳＣＲの出入口温度の差が設定閾値以下になるまで尿素水噴射禁止を継続するものである。
　前記設定閾値を８０～１００℃の範囲で設定し、その設定閾値以下となり、かつ最短尿素水噴射禁止時間以上経過後に、尿素水噴射を行い、また、前記設定閾値を超え、かつその超える時間が、最長尿素水噴射禁止時間以上経過後に、尿素水噴射を行うことが好ましい。
　上記のリッチ禁止期間と、尿素水噴射禁止期間には時間のリミット値を設定する。これは運転条件により触媒前後温度差が閾値以下になかなか下がらない場合に対処するためである。
　本発明は、ＮＯｘ吸蔵還元型触媒のＳパージを行った後、直ちにリッチ還元するのを禁止し、そのＮＯｘ吸蔵還元型触媒の出入口の排ガスの温度が設定閾値まで下がるのを待ってリッチ許可することでその間の燃費を改善できる。またＳＣＲによるＰＭ再生時にもそのＳＣＲ前後の排ガスの温度が設定閾値まで下がるのを待って尿素水噴射を行うことで、アンモニアスリップを防止できるという優れた効果を発揮する。
本発明のＮＯｘ吸蔵還元型触媒を用いた排ガス後処理装置の制御方法の装置構成を示す図である。 図１におけるＰＭ再生とＳパージ時の各部の排ガス温度の経時変化を示す図である。 図１における排ガス後処理装置の制御方法のフローチャートを示す図である。 本発明のＳＣＲ触媒を用いた排ガス後処理装置の制御方法の装置構成を示す図である。 図４における排ガス後処理装置の制御方法のフローチャートを示す図である。
　以下、本発明の好適な一実施の形態を添付図面に基づいて詳述する。
　図１は、ＮＯｘ吸蔵還元型触媒による排ガス後処理装置１０を示したものである。
　エンジンＥの吸排気系には、ターボチャージャ１１とＥＧＲ管１２が接続されており、エアクリーナ１３から吸入される空気は、ターボチャージャ１１のコンプレッサ１４で圧縮されると共に吸気通路１５に圧送され、エンジンＥの吸気マニホールド１６からエンジンＥ内に供給される。吸気通路１５には、エンジンＥへの空気量を調節するための吸気バルブ１７が設けられる。
　エンジンＥから排出された排ガスは、排気マニホールド１８からターボチャージャ１１のタービン１９に排出されると共にタービン１９を駆動し、排気管２０に排気される。
　吸気マニホールド１６と排気マニホールド１８にはＥＧＲ管１２が接続され、ＥＧＲ管１２に、排気マニホールド１８から吸気マニホールド１６に至る排ガスを冷却するためのＥＧＲクーラ２１が接続されると共に、ＥＧＲ量を調節するＥＧＲバルブ２２が接続される。
　排ガス後処理装置１０は、タービン１９の下流側の排気管２０に排気管インジェクタ２３が設けられ、その排気管インジェクタ２３の下流側の排気管２０に形成されたキャニング容器２４内に、ＤＯＣ２５、ＮＯｘ吸蔵還元型触媒２６、ＤＰＦ２７が順次キャニングされて構成される。
　ＤＯＣ２５の上流側には、排ガス温度センサ２８、ＮＯｘ吸蔵還元型触媒２６の入口側には触媒入口温度センサ２９、出口側には触媒出口温度センサ３０が設けられる。
　エンジンＥは、ＥＣＵ３２により運転の全般的な制御がなされる。ＥＣＵ３２には、温度検出手段３３、空燃比制御手段３４、噴射制御手段３５が形成される。
　排ガス温度センサ２８、触媒入口温度センサ２９、触媒出口温度センサ３０の各検出値は、エンジンＥの運転を制御するＥＣＵ３２の温度検出手段３３に入力される。
　空燃比制御手段３４は、ＥＧＲバルブ２２、吸気バルブ１７を制御し、噴射制御手段３５は、エンジンＥの燃焼噴射量を制御すると共にインジェクタによるポスト噴射などのマルチ噴射を制御し、さらに排気管インジェクタ２３から噴射する燃料ＨＣを制御する。
　このＮＯｘ吸蔵還元型触媒による排ガス後処理装置１０は、通常は空燃比リーン状態でＮＯｘをＮＯｘ吸蔵還元型触媒２６で吸蔵し、その間に排気管インジェクタ２３で燃料ＨＣをパルス的に噴射して空燃比リッチ状態でＮＯｘ還元浄化を行う。
　また排ガス中のＰＭは、ＤＰＦ２７で捕捉されるが、ＤＰＦ２７へのＰＭ堆積量が所定量溜まったならば、例えば、ＤＰＦ２７前後の差圧が一定に達したときや、所定の走行距離を走行したとき、ＥＣＵ３２がＰＭの自動再生制御を行う。このＰＭ再生の際には、ポスト噴射や排気管インジェクタ２３による燃料噴射を行って排ガス温度を６００℃に上げることで、ＤＰＦ２７へ堆積したＰＭを燃焼させる。
　このＰＭ再生では、排ガス温度が高く（約６００℃）、リッチ禁止で行われるため、ＰＭ再生終了に引き続いて、ＮＯｘ吸蔵還元型触媒２６に吸着、吸蔵されたＳＯｘをパージするために排ガス温度を、排気管インジェクタ２３による燃料噴射で、６０５℃以上の例えば約７００℃に昇温してＳパージを行う。
　この際、ＮＯｘ吸蔵還元型触媒２６のＳパージ処理直後に、温度検出手段３３が、排ガス温度センサ２８、触媒入口温度センサ２９、触媒出口温度センサ３０で直接検出される排ガス温度、特に触媒入口温度センサ２９と触媒出口温度センサ３０によるＮＯｘ吸蔵還元型触媒２６の出入り口温度を監視して、入口温度に対して出口温度の差が設定閾値（８０～１００℃の範囲で設定した値）以下になるまで、リッチ還元制御を停止した状態を継続（リッチ禁止）し、その後、設定閾値以下になったとき、リッチ還元を許可する。
　これにより、ＮＯｘ吸蔵還元型触媒２６の出入り口の排ガスの温度を直接検出して、リッチ禁止期間を判定するので、Ｓパージ後のリッチ禁止期間を時間で設定するよりも、外乱の影響を受けずに適切に制御が可能である。よって、過剰なリッチを防止し、燃費の悪化やＨＣスリップによる排ガスの悪化をより適切に防止できる。
　このように、触媒の出入り口温度差をリッチ開始の閾値とする事で、ＰＭ再生やＳパージで触媒が発熱した状態が収まり、ＮＯｘの吸蔵能力が回復してリッチが可能な状態となった事を正確にモニターができる。またこの温度の設定閾値は実験により得られた値であり、この範囲であれば正常な制御が可能である。これよりも高いと完全にＮＯｘ吸蔵能力が回復しておらず、これよりも低いとリッチ禁止期間が必要以上に長くなってしまう。
　図２は、ＰＭ再生開始からＳパージ終了直後までのＮＯｘ吸蔵還元型触媒２６の出入り口の排ガスの温度の経時変化を示したものである。なお図２には車速（０～７０ｋｍ／ｈ）の経時変化も示している。
　図２において、触媒前排ガス温度は、触媒入口温度センサ２９で検出した温度、触媒後排ガス温度は、触媒出口温度センサ３０で検出した温度で、触媒前後の排ガス温度差は、触媒入口温度センサ２９と触媒出口温度センサ３０で検出した温度差を示す。
　ＰＭ再生は、ポスト噴射や排気管噴射で排ガス温度を６００℃に上げ、ＤＰＦ２７に堆積したＰＭを燃焼させて再生し、再生完了後は、排ガス温度を７００℃に上げてＮＯｘ吸蔵還元型触媒２６に吸着、吸蔵したＳＯｘのパージを行う。
　このＰＭ再生期間とＳパージ期間中は、リッチ禁止期間とし、そのＳパージが終了したときに触媒前後の排ガス温度差が設定閾値まで下がったならば、リッチ許可として空燃比リッチ条件でＮＯｘの還元を行う。
　図３は、本発明の排ガス後処理装置の制御方法のフローチャートを示したものである。
　ステップＳ１０で制御が開始され、ステップＳ１１で、触媒前排ガス温度と、触媒後排ガス温度を測定し、その差を算出する。次にステップＳ１２で、ＰＭ再生を開始し、その後、Ｓパージを開始し、Ｓパージ終了判定により、Ｓパージを終了する。このステップＳ１２の処理の間はリッチ禁止とする。
　次に、ステップＳ１３の判断で、リッチ禁止を継続しながら触媒前後の排ガス温度差が閾値以下かどうかを判断し、閾値以下に条件適合したならば、ステップＳ１４で、最小リッチ禁止時間（例えば１分）以上経過したかどうかを判断し、最小リッチ禁止時間以上経過して、条件適合したならば、ステップＳ１６でリッチ還元許可を行う。
　またステップＳ１３の判断で、閾値以下にならず条件不適合のときは、ステップＳ１５で最大リッチ禁止時間（例えば５分）以上経過かどうかを判断し、その最大リッチ禁止時間以上経過して、条件適合したならば、ステップＳ１６でリッチ還元許可を行い、その後ステップＳ１７で制御を終了する。
　このように、Ｓパージ終了後に触媒前後の排ガス温度差が閾値以下かどうかを判断し、その温度差を基にリッチ禁止時間を最小リッチ時間と最大リッチ時間に分けてリッチ禁止期間を選択することで、無駄な燃料の噴射をなくし、その間の燃費を改善することができる。
　次に、図４により本発明の他の実施の形態を説明する。
　図４は、ＳＣＲ触媒による排ガス後処理装置１０を示したものであり、排ガス後処理装置１０を除いてエンジンＥの基本構成は図１と同じであり、これを再度説明する。
　エンジンＥの吸排気系には、ターボチャージャ１１とＥＧＲ管１２が接続され、エアクリーナ１３からの空気は、ターボチャージャ１１のコンプレッサ１４で圧縮されると共に吸気通路１５に圧送され、吸気バルブ１７を通してエンジンＥの吸気マニホールド１６からエンジンＥ内に供給される。エンジンＥから排出された排ガスは、排気マニホールド１８からターボチャージャ１１のタービン１９に排出されると共にタービン１９を駆動し、排気管２０に排気される。
　吸気マニホールド１６と排気マニホールド１８にはＥＧＲ管１２が接続され、そのＥＧＲ管１２に、ＥＧＲクーラ２１が接続されると共にＥＧＲバルブ２２が接続される。
　排ガス後処理装置１０は、タービン１９の下流側の排気管２０に排気管インジェクタ２３が設けられ、その排気管インジェクタ２３の下流側の排気管２０に、ＤＰＦ装置４１とＳＣＲ装置４２が設けられる。ＤＰＦ装置４１は、排気管２０に形成されたＤＰＦ用キャニング容器４３内に、ＤＯＣ４４、ＤＰＦ４５がキャニングされて構成される。ＳＣＲ装置４２は、排気管２０に形成されたＳＣＲキャニング容器４６内に、ＳＣＲ触媒４７とアンモニアスリップを防止するＤＯＣ４８が設けられ、さらにＳＣＲキャニング容器４６の上流側の排気管２０に尿素水噴射ノズル４９が設けられて構成される。
　ＤＰＦ装置４１のＤＯＣ４４の上流側には、排ガス温度センサ５０、ＤＰＦ４５の入口側にはＤＰＦ温度センサ５１が設けられ、またＳＣＲ装置４２のＳＣＲ触媒４７の入口側には、ＳＣＲ触媒入口温度センサ５２、出口側には、ＳＣＲ触媒出口温度センサ５３が設けられる。
　エンジンＥは、ＥＣＵ３２により運転の全般的な制御がなされる。ＥＣＵ３２には、温度検出手段３３、空燃比制御手段３４、噴射制御手段３５が形成される。
　排ガス後処理装置１０の各温度センサ５０、５１、５２、５３の検出値は、エンジンＥの運転を制御するＥＣＵ３２の温度検出手段３３に入力される。
　空燃比制御手段３４は、ＥＧＲバルブ２２、吸気バルブ１７を制御し、噴射制御手段３５は、エンジンＥの燃焼噴射量を制御すると共にインジェクタによるポスト噴射などのマルチ噴射を制御し、さらに排気管インジェクタ２３から噴射する燃料を制御する。
　尿素水噴射ノズル４９は、ＥＣＵ３２と接続されたＤＣＵ（ドージングコントロールユニット）５５で制御される。尿素水噴射ノズル４９による尿素水の噴射は、図示では省略しているが、ＤＣＵ５５で制御されるサプライモジュールが尿素水タンク内の尿素水を吸い込むと共にこれを所定の圧に昇圧し、尿素水噴射ノズル４９内の開閉弁をＤＣＵ５５が制御することで、排ガス中のＮＯｘ濃度に応じた所定量の尿素水を尿素水噴射ノズル４９から噴射するようになっている。
　噴射された尿素水は排気管２０からＳＣＲ装置４２に流入する間に加水分解によりアンモニアが生成され、生成したアンモニアと排ガス中のＮＯｘとをＳＣＲ触媒４７で反応させて脱硝する。また余剰のアンモニアはＤＯＣ４８に吸着されアンモニアスリップが防止される。
　このＳＣＲ触媒４７による排ガス後処理装置１０では、前段のＤＰＦ装置４１で排ガス中のＰＭを捕捉し、後段のＳＣＲ装置４２で排ガス中のＮＯｘを脱硝する。
　この際、排ガス中のＰＭは、ＤＰＦ４５で捕捉されるが、ＤＰＦ４５へのＰＭ堆積量が所定量溜まったならば、ＥＣＵ３２がＰＭの自動再生制御を行う。
　このＰＭ再生の際には、ポスト噴射や排気管インジェクタ２３による燃料噴射を行って排ガス温度を６００℃に上げることで、ＤＰＦ４５へ堆積したＰＭを燃焼させる。
　このＰＭ再生直後に、ＳＣＲ装置４２の触媒の出入り口温度を、各温度センサ５０～５３、特にセンサＳＣＲ触媒入口温度センサ５２とＳＣＲ触媒入口温度センサ５３の温度を監視して、触媒キャニングの入口温度に対する出口温度の差が設定閾値（８０～１００℃の範囲で設定した値）以下になるまで、尿素水噴射ノズル４９による尿素水噴射を禁止する。
　すなわち、ＰＭ再生直後の排ガス温度は高く、ＳＣＲ触媒４７にアンモニアを供給してもＮＯｘ還元反応が起きずにアンモニアスリップが発生しやすくなるため、出入口の温度がある幅に入るまで、尿素水噴射制御を停止する。
　これにより、尿素水噴射時期を、直接温度で尿素水噴射禁止期間を判定するので、ＰＭ再生後の尿素水噴射禁止期間を時間で設定するよりも、外乱の影響を受けずに適切に制御が可能である。よって、過剰な尿素水噴射を防止し、アンモニアスリップをより適切に防止できる。
　このＳＣＲ触媒を用いた排ガス後処理装置１０におけるＰＭ再生と再生直後の尿素水噴射禁止と許可のフローを図５により説明する。
　ステップＳ２０で制御が開始され、ステップＳ２１で、触媒前排ガス温度と、触媒後排ガス温度を測定し、その差を算出する。次にステップＳ２２で、ＰＭ再生を開始し、その後、ＰＭ再生終了判定により、ＰＭ再生を終了する。
　次に、ステップＳ２３の判断で、尿素水噴射の禁止を継続しながら触媒前後の排ガス温度差が閾値以下かどうかを判断し、閾値以下に条件適合したならば、ステップＳ２４で、最短尿素水噴射禁止時間（例えば１分）以上経過したかどうかを判断し、最短尿素水噴射禁止時間以上経過して、条件適合したならば、ステップＳ２６で尿素水噴射許可を行う。
　またステップＳ２３の判断で、閾値以下にならず条件不適合のときは、ステップＳ２５で最長尿素水噴射禁止時間（例えば５分）以上経過かどうかを判断し、その最長尿素水噴射禁止時間以上経過して、条件適合したならば、ステップＳ２６で尿素水噴射許可を行い、その後ステップＳ２７で制御を終了する。
　このように、ＰＭ再生直後に触媒前後の排ガス温度差が閾値以下かどうかを判断し、その温度差を基に尿素水噴射禁止時間を、最短尿素水噴射禁止時間と最長尿素水噴射禁止時間に分けて尿素水噴射禁止期間を選択することで、無駄な尿素水の噴射をなくし、その間のアンモニアスリップを防止することができる。
　上記のリッチ禁止期間と、尿素水噴射禁止期間には時間のリミット値を設定する。これは運転条件により触媒前後温度差が閾値以下になかなか下がらない場合に対処するためである。
　１０　排ガス後処理装置
　２０　排気管
　２３　排気管インジェクタ
　２５　ＤＯＣ
　２６　ＮＯｘ吸蔵還元型触媒
　２７、４５　ＤＰＦ
　４１　ＤＰＦ装置
　４２　ＳＣＲ装置
　４７　ＳＣＲ触媒
　４９　尿素水噴射ノズル
　Ｅ　エンジン

Claims (6)

  1. 　エンジンの排気管に、排気管インジェクタを設け、その排気管インジェクタの下流側の排気管に、ＤＯＣ、ＮＯｘ吸蔵還元型触媒、ＤＰＦを接続して排ガス後処理装置を構成し、空燃比がリーン条件で排ガス中のＮＯｘをＮＯｘ吸蔵還元型触媒で吸蔵し、空燃比がリッチ条件で吸蔵したＮＯｘを還元・浄化する排ガス後処理装置の制御方法において、ＤＰＦにＰＭが所定量堆積したとき排ガス温度を上昇させてＰＭ再生し、その後、排ガス温度をさらに上昇させてＮＯｘ吸蔵還元型触媒に吸蔵した硫黄のＳパージを行い、そのＰＭ再生期間からＳパージ期間中リッチ禁止を行い、Ｓパージ完了後、前記ＤＯＣの入口温度とＮＯｘ吸蔵還元型触媒の出口温度の差が設定閾値以下になるまでリッチ禁止を継続することを特徴とする排ガス後処理装置の制御方法。
  2. 　前記設定閾値を８０～１００℃の範囲で設定し、その設定閾値以下となり、かつ最小リッチ禁止時間以上経過後に、リッチ還元を行う請求項１記載の排ガス後処理装置の制御方法。
  3. 　前記設定閾値を超え、かつその超える時間が、最大リッチ禁止時間以上経過後に、リッチ還元を行う請求項２記載の排ガス後処理装置の制御方法。
  4. 　エンジンの排気管に、排気管インジェクタを設け、その排気管インジェクタの下流側の排気管に、ＤＰＦを接続し、そのＤＰＦの下流側の排気管にＳＣＲ、ＤＯＣを接続し、前記ＳＣＲの上流側排気管に尿素水噴射ノズルを設けて排ガス後処理装置を構成し、前記ＳＣＲでＮＯｘを還元・浄化する排ガス後処理装置の制御方法において、ＤＰＦにＰＭが所定量堆積したとき排ガス温度を上昇させてＰＭ再生を行うと共に前記尿素水噴射ノズルでの尿素水噴射を禁止し、ＰＭ再生終了後、ＳＣＲの出入口温度の差が設定閾値以下になるまで尿素水噴射禁止を継続することを特徴とする排ガス後処理装置の制御方法。
  5. 　前記設定閾値を８０～１００℃の範囲で設定し、その設定閾値以下となり、かつ最短尿素水噴射禁止時間以上経過後に、尿素水噴射を行う請求項４記載の排ガス後処理装置の制御方法。
  6. 　前記設定閾値を超え、かつその超える時間が、最長尿素水噴射禁止時間以上経過後に、尿素水噴射を行う請求項５記載の排ガス後処理装置の制御方法。
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