WO2010146717A1 - Exhaust cleaner for internal combustion engine - Google Patents

Exhaust cleaner for internal combustion engine Download PDF

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Publication number
WO2010146717A1
WO2010146717A1 PCT/JP2009/061250 JP2009061250W WO2010146717A1 WO 2010146717 A1 WO2010146717 A1 WO 2010146717A1 JP 2009061250 W JP2009061250 W JP 2009061250W WO 2010146717 A1 WO2010146717 A1 WO 2010146717A1
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Prior art keywords
exhaust gas
air
fuel ratio
amount
regeneration process
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PCT/JP2009/061250
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French (fr)
Japanese (ja)
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浅沼孝充
吉田耕平
西岡寛真
今井大地
梅本寿丈
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トヨタ自動車株式会社
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Priority to PCT/JP2009/061250 priority Critical patent/WO2010146717A1/en
Publication of WO2010146717A1 publication Critical patent/WO2010146717A1/en

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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
    • F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the present invention relates to an exhaust purification device for an internal combustion engine.
  • a NO X catalyst device for purifying NO X in exhaust gas is disposed.
  • NO X catalyst device the exhaust gas when a lean air-fuel ratio, i.e., when a high oxygen concentration in the exhaust gas, NO X catalyst device which NO X is better retained in the exhaust gas has been proposed .
  • the exhaust gas purification apparatus for an internal combustion engine described above reduces the oxygen concentration of the exhaust gas during the regeneration process, assuming that if the oxygen concentration in the exhaust gas during the regeneration process is high, the amount of N 2 O produced increases. However, if the air-fuel ratio of the exhaust gas is made too small in order to reduce the oxygen concentration of the exhaust gas during the regeneration process, the flow amount of N 2 O from the NO X catalyst device may increase and exceed the allowable value. is there.
  • an object of the present invention when a high concentration of oxygen in the exhaust gas satisfactorily hold the NO X in the exhaust gas, as the reproduction process, if lower the oxygen concentration in the exhaust gas, the held NO X withdrawal, and thus the exhaust gas purification apparatus for an internal combustion engine having a NO X catalyst device which is capable of reduce and purify NO X in which is disengaged to N 2 by reducing substances in the exhaust gas, the NO X catalyst device accompanying the regeneration process This is to reduce the outflow amount of N 2 O to an allowable value or less.
  • An exhaust purification system of an internal combustion engine according to claim 1 according to the present invention when a high concentration of oxygen in the exhaust gas satisfactorily hold the NO X in the exhaust gas, as the reproduction process, reduce the oxygen concentration in the exhaust gas if brought into, it leaves the held NO X, thus the exhaust purification system of an internal combustion engine having a NO X catalyst device which is capable of reduce and purify NO X in which is disengaged to N 2 by reducing substances in the exhaust gas, the air-fuel ratio of the exhaust gas to flow into the NO X catalyst device at the time of reproduction processing, the following first air-fuel ratio and the second air-fuel ratio or more, the air-fuel ratio of the exhaust gas by more than the first air-fuel ratio, regeneration the N 2 O production amount generated by insufficient reduction of the NO X during the process as follows the first set amount, by the air-fuel ratio of the exhaust gas to the second air-fuel ratio or more, of the NO X in the reproduction process Produced by reduction NH 2 (ammonia) produced is oxidized by oxygen
  • the exhaust gas purification apparatus for an internal combustion engine according to claim 2 according to the present invention is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio of the exhaust gas in the second half of the regeneration process is the exhaust gas in the first half of the regeneration process. It is characterized by being made larger than the air-fuel ratio.
  • the air-fuel ratio of the exhaust gas to flow into the NO X catalyst device at the time of reproduction processing, the second air-fuel ratio or below the first air-fuel ratio, the exhaust By setting the air / fuel ratio of the gas to be equal to or lower than the first air / fuel ratio, the amount of N 2 O generated due to insufficient reduction of NO X during the regeneration process can be made equal to or lower than the first set amount.
  • the air-fuel ratio of the exhaust gas is made excessively small, the amount of N 2 O produced due to insufficient reduction can be greatly reduced, but a large amount of NH 3 is produced due to NO X reduction during the regeneration process. End up.
  • the air-fuel ratio of the exhaust gas is the second air-fuel ratio or more
  • N 2 to NH 3 produced by the reduction of the NO X in the regeneration process is produced is oxidized by oxygen in the exhaust gas after regeneration treatment
  • the O generation amount is set to be equal to or less than the second set amount
  • the N 2 O outflow amount from the NO X catalyst device accompanying the regeneration process is set to be an allowable value or less.
  • the exhaust purification system of an internal combustion engine according to claim 2 leaving the exhaust gas control apparatus according to claim 1, reproduction processing second half from NO X catalyst device compared to the reproduction process early for the amount of NO X is decreased to, the air-fuel ratio of the exhaust gas in the second half reproduction process, by greater than the air-fuel ratio of the exhaust gas regeneration process early, NO X catalyst, including leaving the amount of NO X during the reproduction process
  • the air-fuel ratio of the exhaust gas in the apparatus can be maintained almost constant.
  • FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
  • Figure 2 is the change of the NO X reduction rate of the NO X catalyst device with respect to the air-fuel ratio of the exhaust gas at the time of reproduction processing, the change of the NH 3 produced amount, and is a graph showing changes in N 2 O runoff.
  • FIG. 3 is a flowchart showing the control during the reproduction process.
  • FIG. 1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
  • reference numeral 1 denotes an exhaust passage of an internal combustion engine that performs lean combustion such as a diesel engine or an in-cylinder spark ignition internal combustion engine.
  • the exhaust gas of such an internal combustion engine in order to contain a relatively large amount of NO X, in the exhaust passage 1, NO X catalyst device 2 for purifying NO X is arranged.
  • a fuel supply device 3 for supplying fuel (or a reducing agent) is disposed upstream of the NO X catalyst device 2 in the exhaust passage 1.
  • 4 is an air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2.
  • the NO X catalyst device 2 carries a NO X holding agent and a noble metal catalyst such as platinum Pt.
  • the NO X retention agent is at least one selected from an alkali metal such as potassium K, sodium Na, lithium Li and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and a rare earth such as lanthanum La and yttrium Y.
  • an alkali metal such as potassium K, sodium Na, lithium Li and cesium Cs
  • an alkaline earth such as barium Ba and calcium Ca
  • a rare earth such as lanthanum La and yttrium Y.
  • NO X cannot be held indefinitely, and as a regeneration process, the air-fuel ratio of the exhaust gas is reduced before the NO X hold amount reaches the NO X holdable amount and can no longer hold NO X.
  • the stoichiometric air-fuel ratio or rich air-fuel ratio is set, that is, the oxygen concentration in the exhaust gas is reduced.
  • the retained NO X is desorbed, that is, the absorbed NO X is released, and the adsorbed NO 2 is desorbed, and the desorbed NO X is reduced and purified to N 2 by the reducing substance in the exhaust gas.
  • N 2 O dinitrogen monoxide or nitrous oxide
  • Figure 2 is a variation of the NO X reduction rate with respect to the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 in the regeneration process, the change of the NH 3 produced amount, and is a graph showing changes in N 2 O runoff.
  • the N 2 O outflow amount is the sum of the outflow amount of N 2 O during the regeneration process and the outflow amount of N 2 O immediately after the regeneration process, that is, indicates the outflow amount of N 2 O accompanying the regeneration process. . As shown in FIG.
  • the air-fuel ratio of the exhaust gas during the regeneration process is slightly higher than the first air-fuel ratio A1 (for example, 14.3) slightly richer than the theoretical air-fuel ratio S (14.7). If it is (for example, 13.3) or less, the outflow amount of N 2 O can be set to an allowable value M or less.
  • the air-fuel ratio of the exhaust gas at the time of regeneration processing close to the third air-fuel ratio (for example, 13.8) between the first air-fuel ratio A1 and the second air-fuel ratio A2
  • the outflow amount of N 2 O is minimized. can do.
  • the smaller the air-fuel ratio of the exhaust gas during regeneration treatment the reducing action of playing action becomes active, NO X reduction rate gradually increases.
  • the smaller the air-fuel ratio of the exhaust gas in the regeneration process the smaller the amount of N 2 O (NO + N ⁇ N 2 O) generated due to insufficient reduction of NO X , and the air-fuel ratio of the exhaust gas in the regeneration process is reduced.
  • the air-fuel ratio is set to 1 or less, the N 2 O generation amount during the regeneration process can be set to the first set amount or less.
  • the air-fuel ratio of the exhaust gas is excessively reduced, the amount of N 2 O produced due to insufficient reduction can be reduced very much, but the amount of NH 3 (ammonia amount) produced during the regeneration process is very small.
  • the air-fuel ratio of the exhaust gas during the regeneration process is set to be equal to or higher than the second air-fuel ratio A2, so that not much NH 3 is generated by the reduction of NO X during the regeneration process, and the generated NH 3 is regenerated.
  • the amount of N 2 O produced by oxidation with oxygen in the later exhaust gas is set to a second set amount or less.
  • the amount of N 2 O generated during the regeneration process is set to be equal to or less than the first set amount by setting the air-fuel ratio of the exhaust gas during the regeneration process to be the first air-fuel ratio A1 or more and the second air-fuel ratio A2 or less.
  • the amount of N 2 O produced when the NH 3 produced by the reduction of NO X during the regeneration process is oxidized by the oxygen in the exhaust gas after the regeneration process is set to be equal to or less than the second set amount.
  • the NO X reduction rate indicated by the solid line includes the N 2 O outflow amount (including the N 2 O generation amount after the regeneration process), and the NO X reduction rate not including the N 2 O outflow amount is defined as the NO X purification rate.
  • FIG. 3 is a flowchart showing the regeneration timing control performed by the electronic control unit. First, at step 101, whether the current is the playback time of the NO X catalyst device 2 is determined.
  • the exhaust gas provided downstream NO X concentration sensor immediately downstream of the NO X catalyst device provided with the upstream NO X concentration sensor immediately upstream of the NO X catalyst device 2 flows into the NO X catalyst device 2 detecting the concentration of NO X in the exhaust gas flowing out from NO X concentration and the NO X catalyst device 2 in and out of NO X concentration and the NO X catalyst device 2 in the exhaust gas flowing into the NO X catalyst device 2 when the difference between the concentration of NO X in the exhaust gas is below the set value, the NO X holding amount of the NO X catalyst device 2, and reaches the vicinity of the NO X holding amount, with sufficiently retaining the NO X in the exhaust gas It can be determined that it is time to regenerate as it is no longer possible.
  • downstream NO X concentration sensor detects the concentration of NO X in the exhaust gas flowing into the NO X catalyst device 2 by the upstream NO X concentration sensor, exhaust gas per unit time determined from NO X concentration Assuming that the set ratio of the NO X amount contained in the NO X catalyst device 2 is held per unit time, the current NO X hold amount is estimated by integrating the hold amount per unit time, and this is the set amount It may be determined that the playback time is reached.
  • the upstream NO X concentration sensor even without providing, in advance set the amount of NO X contained in the exhaust gas per unit time for each engine operating state, NO X catalyst that setting percentage per unit time as it is held to the apparatus 2, to estimate the current of the NO X holding amount by integrating the amount retained per unit time, which may be determined that the regeneration timing when reaching the set amount.
  • the fuel supply by the fuel supply device 3 is stopped in step 107 and the process is terminated.
  • step 101 determines whether the NO X catalyst device 2 is a timing regeneration.
  • step 102 to implement the regeneration process, the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2, the theoretical The current combustion air-fuel ratio and the amount of exhaust gas are set so that the air-fuel ratio becomes a preset air-fuel ratio A (for example, 13.8) that is slightly higher than the first air-fuel ratio A1 and slightly lower than the second air-fuel ratio A2.
  • the fuel supply amount Q per unit time supplied by the fuel supply device 3 is determined.
  • step 103 it is determined whether or not an elapsed time t since the start of the reproduction process has reached a predetermined second set time t2 corresponding to the completion of the reproduction process. Initially, this determination is denied and the routine proceeds to step 104, where it is determined whether or not the elapsed time t has reached the first set time t1 set to half of the second set time. Initially, this determination is denied and the routine proceeds to step 106 where fuel supply is performed by the fuel supply device 3 based on the fuel supply amount Q per unit time determined in step 102. Thereby, the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 as a setting an air-fuel ratio A, reproduction process is performed.
  • the amount of N 2 O outflow associated with the regeneration process does not necessarily exceed the allowable value, but in the flowchart shown in FIG. 3, the elapsed time t from the start of the regeneration process in the latter half of the regeneration process is
  • the fuel supply amount Q per unit time determined in step 102 is reduced by a predetermined set amount ⁇ Q. Based on the fuel supply amount Q, fuel is supplied in step 106.
  • the air-fuel ratio of the exhaust gas in the second half reproduction process by greater than the air-fuel ratio of the exhaust gas of the reproduction process the first half, the air-fuel ratio of the exhaust gas in the NO X catalyst device, including a detachment NO X during the reproduction process It is kept almost constant to ensure that the N 2 O efflux amount associated with the regeneration process does not exceed the allowable value. If the elapsed time from the start of the regeneration process reaches the second set time t2, the determination in step 103 is affirmed, the fuel supply by the fuel supply device 3 is stopped in step 107, and the regeneration process ends.
  • the fuel supply system in order to set the air-fuel ratio A between the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 at the time of reproduction processing from the first air-fuel ratio A1 and the second air-fuel ratio A2, the fuel supply system Although the fuel is supplied to the exhaust gas having a lean air-fuel ratio according to No. 3, this does not limit the present invention.
  • the air-fuel ratio of the air-fuel mixture burned in the cylinder of the internal combustion engine may be set to a rich set air-fuel ratio A, and the exhaust gas that is discharged from the cylinder by supplying additional fuel into the cylinder in the expansion stroke and the exhaust stroke
  • the air-fuel ratio of the gas may be set to a rich set air-fuel ratio A.
  • playback if processing late and become, as slightly larger than the NO X catalyst set the air-fuel ratio of the exhaust gas flowing into the device 2 air A may be controlled combustion air or additional fuel amount.
  • the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 by detecting the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 by the air-fuel ratio sensor 4, so that the desired air-fuel ratio, the fuel supply amount of the fuel supply device 3, combustion air-fuel ratio, or The additional fuel amount can be feedback controlled.
  • the air-fuel ratio of the exhaust gas in the second half of the regeneration process is made larger than the air-fuel ratio of the exhaust gas in the first half of the regeneration process.
  • NO X withdrawal amount from the NO X catalyst device decreases gradually as the elapsed time t becomes longer, it may be gradually increased air-fuel ratio of the exhaust gas flowing into the NO X catalyst device.

Abstract

An exhaust cleaner for internal combustion engines, the cleaner being equipped with an NOX catalyst device which, when the exhaust gas has a high oxygen concentration, satisfactorily holds the NOX contained in the exhaust gas and which, when the oxygen concentration of the exhaust gas is reduced in order to conduct regeneration, releases the NOX held and enables the released NOX to be reduced to N2 with a reducing substance contained in the exhaust gas, thereby purifying the exhaust gas.  During the regeneration, the air-fuel ratio of the exhaust gas to be introduced into the NOX catalyst device is regulated to a value not higher than a first air-fuel ratio and not lower than a second air-fuel ratio.  By regulating the air-fuel ratio of the exhaust gas so as to be not higher than the first air-fuel ratio, the amount of N2O to be generated by insufficient NOX reduction during the regeneration is regulated to or below a first set value.  By regulating the air-fuel ratio of the exhaust gas so as to be not lower than the second air-fuel ratio, the amount of N2O to be generated when the NH3 generated by NOX reduction during the regeneration is oxidized with the oxygen contained in the exhaust gas after the regeneration is regulated to or below a second set value.  As a result, the amount of N2O to be discharged from the NOX catalyst device due to the regeneration is reduced to or below an acceptable limit.

Description

内燃機関の排気浄化装置Exhaust gas purification device for internal combustion engine
　本発明は、内燃機関の排気浄化装置に関する。 The present invention relates to an exhaust purification device for an internal combustion engine.
　ディーゼルエンジンのような希薄燃焼を実施する内燃機関の排気系には、排気ガス中のＮＯＸを浄化するためのＮＯＸ触媒装置が配置されている。このようなＮＯＸ触媒装置として、排気ガスがリーン空燃比である時、すなわち、排気ガス中の酸素濃度が高い時に、排気ガス中のＮＯＸ良好に保持するＮＯＸ触媒装置が提案されている。このＮＯＸ触媒装置は、再生処理として、排気ガスの空燃比を理論空燃比又はリッチ空燃比とすれば、すなわち、排気ガス中の酸素濃度を低下させれば、保持したＮＯＸを離脱し、こうして離脱させたＮＯＸを排気ガス中の還元物質によりＮ２へ還元浄化することができる。
　しかしながら、このようなＮＯＸ触媒装置の再生処理においてＮ２Ｏ（一酸化二窒素又は亜酸化窒素）が生成されることがあり、Ｎ２Ｏも大気中へ放出することは好ましくない。それにより、再生処理時においてＮＯＸ触媒装置からのＮ２Ｏの流出量を減少させることを意図した内燃機関の排気浄化装置が提案されている（例えば、特許文献１参照）。 In an exhaust system of an internal combustion engine that performs lean combustion such as a diesel engine, a NO X catalyst device for purifying NO X in exhaust gas is disposed. Such NO X catalyst device, the exhaust gas when a lean air-fuel ratio, i.e., when a high oxygen concentration in the exhaust gas, NO X catalyst device which NO X is better retained in the exhaust gas has been proposed . In this NO X catalyst device, if the air-fuel ratio of the exhaust gas is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio as a regeneration process, that is, if the oxygen concentration in the exhaust gas is reduced, the retained NO X is released, The NO X thus released can be reduced and purified to N 2 by the reducing substance in the exhaust gas.
However, N 2 O (dinitrogen monoxide or nitrous oxide) may be generated in such regeneration processing of the NO X catalyst device, and it is not preferable to release N 2 O into the atmosphere. Thereby, an exhaust gas purification apparatus for an internal combustion engine intended to reduce the outflow amount of N 2 O from the NO X catalyst apparatus during the regeneration process has been proposed (see, for example, Patent Document 1).
特開２００４−２１１６７６Japanese Patent Application Laid-Open No. 2004-211676
　前述の内燃機関の排気浄化装置は、再生処理時の排気ガス中の酸素濃度が高いと、Ｎ２Ｏの生成量が増加するとして、再生処理時の排気ガスの酸素濃度を低下させている。しかしながら、再生処理時の排気ガスの酸素濃度を低下させるために、排気ガスの空燃比を小さくし過ぎると、ＮＯＸ触媒装置からのＮ２Ｏの流出量が増大して許容値を超えることがある。
　従って、本発明の目的は、排気ガス中の酸素濃度が高い時には排気ガス中のＮＯＸを良好に保持し、再生処理として、排気ガス中の酸素濃度を低下させれば、保持したＮＯＸを離脱し、こうして離脱させたＮＯＸを排気ガス中の還元物質によりＮ２へ還元浄化することができるＮＯＸ触媒装置を具備する内燃機関の排気浄化装置において、再生処理に伴うＮＯＸ触媒装置からのＮ２Ｏの流出量を許容値以下に減少させることである。 The exhaust gas purification apparatus for an internal combustion engine described above reduces the oxygen concentration of the exhaust gas during the regeneration process, assuming that if the oxygen concentration in the exhaust gas during the regeneration process is high, the amount of N 2 O produced increases. However, if the air-fuel ratio of the exhaust gas is made too small in order to reduce the oxygen concentration of the exhaust gas during the regeneration process, the flow amount of N 2 O from the NO X catalyst device may increase and exceed the allowable value. is there.
Accordingly, an object of the present invention, when a high concentration of oxygen in the exhaust gas satisfactorily hold the NO X in the exhaust gas, as the reproduction process, if lower the oxygen concentration in the exhaust gas, the held NO X withdrawal, and thus the exhaust gas purification apparatus for an internal combustion engine having a NO X catalyst device which is capable of reduce and purify NO X in which is disengaged to N 2 by reducing substances in the exhaust gas, the NO X catalyst device accompanying the regeneration process This is to reduce the outflow amount of N 2 O to an allowable value or less.
　本発明による請求項１に記載の内燃機関の排気浄化装置は、排気ガス中の酸素濃度が高い時には排気ガス中のＮＯＸを良好に保持し、再生処理として、排気ガス中の酸素濃度を低下させれば、保持したＮＯＸを離脱し、こうして離脱させたＮＯＸを排気ガス中の還元物質によりＮ２へ還元浄化することができるＮＯＸ触媒装置を具備する内燃機関の排気浄化装置において、再生処理時に前記ＮＯＸ触媒装置へ流入させる排気ガスの空燃比を、第一空燃比以下で第二空燃比以上とし、前記排気ガスの空燃比を前記第一空燃比以下とすることにより、再生処理中にＮＯＸの還元不足により生成されるＮ２Ｏ生成量を第一設定量以下とし、前記排気ガスの空燃比を前記第二空燃比以上とすることにより、再生処理中にＮＯＸの還元により生成されたＮＨ３（アンモニア）が再生処理後の排気ガス中の酸素により酸化されて生成されるＮ２Ｏ生成量を第二設定量以下とし、再生処理に伴うＮＯＸ触媒装置からのＮ２Ｏ流出量を許容値以下とすることを特徴とする。
　本発明による請求項２に記載の内燃機関の排気浄化装置は、請求項１に記載の内燃機関の排気浄化装置において、再生処理後半の前記排気ガスの空燃比は、再生処理前半の前記排気ガスの空燃比より大きくされることを特徴とする。 An exhaust purification system of an internal combustion engine according to claim 1 according to the present invention, when a high concentration of oxygen in the exhaust gas satisfactorily hold the NO X in the exhaust gas, as the reproduction process, reduce the oxygen concentration in the exhaust gas if brought into, it leaves the held NO X, thus the exhaust purification system of an internal combustion engine having a NO X catalyst device which is capable of reduce and purify NO X in which is disengaged to N 2 by reducing substances in the exhaust gas, the air-fuel ratio of the exhaust gas to flow into the NO X catalyst device at the time of reproduction processing, the following first air-fuel ratio and the second air-fuel ratio or more, the air-fuel ratio of the exhaust gas by more than the first air-fuel ratio, regeneration the N 2 O production amount generated by insufficient reduction of the NO X during the process as follows the first set amount, by the air-fuel ratio of the exhaust gas to the second air-fuel ratio or more, of the NO X in the reproduction process Produced by reduction NH 2 (ammonia) produced is oxidized by oxygen in the exhaust gas after the regeneration treatment, and the N 2 O production amount produced is made equal to or less than the second set amount, and N 2 O from the NO X catalyst device accompanying the regeneration treatment It is characterized in that the outflow amount is less than the allowable value.
The exhaust gas purification apparatus for an internal combustion engine according to claim 2 according to the present invention is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the air-fuel ratio of the exhaust gas in the second half of the regeneration process is the exhaust gas in the first half of the regeneration process. It is characterized by being made larger than the air-fuel ratio.
　本発明による請求項１に記載の内燃機関の排気浄化装置によれば、再生処理時にＮＯＸ触媒装置へ流入させる排気ガスの空燃比を、第一空燃比以下で第二空燃比以上とし、排気ガスの空燃比を第一空燃比以下とすることにより、再生処理中にＮＯＸの還元不足により生成されるＮ２Ｏ生成量を第一設定量以下とすることができる。しかしながら、排気ガスの空燃比を過剰に小さくすると、還元不足により生成されるＮ２Ｏ生成量を非常に少なくすることはできるが、再生処理中にＮＯＸの還元により多量のＮＨ３が生成されてしまう。それにより、排気ガスの空燃比は第二空燃比以上とされ、再生処理中にＮＯＸの還元により生成されたＮＨ３が再生処理後の排気ガス中の酸素により酸化されて生成されるＮ２Ｏ生成量を第二設定量以下とし、再生処理に伴うＮＯＸ触媒装置からのＮ２Ｏ流出量を許容値以下としている。
　本発明による請求項２に記載の内燃機関の排気浄化装置によれば、請求項１に記載の内燃機関の排気浄化装置において、再生処理後半は再生処理前半に比較してＮＯＸ触媒装置から離脱するＮＯＸ量が減少するために、再生処理後半の排気ガスの空燃比を、再生処理前半の排気ガスの空燃比より大きくすることにより、再生処理中において離脱ＮＯＸ量を含めたＮＯＸ触媒装置内の排気ガスの空燃比をほぼ一定に維持することができる。 According to the exhaust purification system of an internal combustion engine according to claim 1 according to the present invention, the air-fuel ratio of the exhaust gas to flow into the NO X catalyst device at the time of reproduction processing, the second air-fuel ratio or below the first air-fuel ratio, the exhaust By setting the air / fuel ratio of the gas to be equal to or lower than the first air / fuel ratio, the amount of N 2 O generated due to insufficient reduction of NO X during the regeneration process can be made equal to or lower than the first set amount. However, if the air-fuel ratio of the exhaust gas is made excessively small, the amount of N 2 O produced due to insufficient reduction can be greatly reduced, but a large amount of NH 3 is produced due to NO X reduction during the regeneration process. End up. Thereby, the air-fuel ratio of the exhaust gas is the second air-fuel ratio or more, N 2 to NH 3 produced by the reduction of the NO X in the regeneration process is produced is oxidized by oxygen in the exhaust gas after regeneration treatment The O generation amount is set to be equal to or less than the second set amount, and the N 2 O outflow amount from the NO X catalyst device accompanying the regeneration process is set to be an allowable value or less.
According to the exhaust purification system of an internal combustion engine according to claim 2 according to the present invention, leaving the exhaust gas control apparatus according to claim 1, reproduction processing second half from NO X catalyst device compared to the reproduction process early for the amount of NO X is decreased to, the air-fuel ratio of the exhaust gas in the second half reproduction process, by greater than the air-fuel ratio of the exhaust gas regeneration process early, NO X catalyst, including leaving the amount of NO X during the reproduction process The air-fuel ratio of the exhaust gas in the apparatus can be maintained almost constant.
　図１は本発明による内燃機関の排気浄化装置の実施形態を示す概略図である。
　図２は再生処理時の排気ガスの空燃比に対するＮＯＸ触媒装置におけるＮＯＸ還元率の変化、ＮＨ３生成量の変化、及び、Ｎ２Ｏ流出量の変化を示すグラフである。
　図３は再生処理時の制御を示すフローチャートである。 FIG. 1 is a schematic view showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention.
Figure 2 is the change of the NO X reduction rate of the NO X catalyst device with respect to the air-fuel ratio of the exhaust gas at the time of reproduction processing, the change of the NH 3 produced amount, and is a graph showing changes in N 2 O runoff.
FIG. 3 is a flowchart showing the control during the reproduction process.
　図１は本発明による内燃機関の排気浄化装置を示す概略図である。同図において、１はディーゼルエンジン又は筒内噴射式火花点火内燃機関のような希薄燃焼を実施する内燃機関の排気通路である。このような内燃機関の排気ガス中には、比較的多くのＮＯＸが含まれるために、排気通路１には、ＮＯＸを浄化するためのＮＯＸ触媒装置２が配置されている。排気通路１のＮＯＸ触媒装置２の上流側には、燃料（又は還元剤）を供給するための燃料供給装置３が配置されている。４はＮＯＸ触媒装置２へ流入する排気ガスの空燃比を検出するための空燃比センサである。
　ＮＯＸ触媒装置２には、ＮＯＸ保持剤と白金Ｐｔのような貴金属触媒とが担持されている。ＮＯＸ保持剤は、カリウムＫ、ナトリウムＮａ、リチウムＬｉ、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、ランタンＬａ、イットリウムＹのような希土類から選ばれた少なくとも一つである。
　ＮＯＸ触媒装置２は、排気ガスがリーン空燃比である時、すなわち、排気ガス中の酸素濃度が高い時に、排気ガス中のＮＯＸを良好に保持し、すなわち、硝酸塩として良好に吸収したり、ＮＯ２として良好に吸着したりする。しかしながら、無制限にＮＯＸを保持することはできず、ＮＯＸ保持量がＮＯＸ保持可能量に達してさらにＮＯＸを保持することができなくなる前に、再生処理として、排気ガスの空燃比を理論空燃比又はリッチ空燃比とし、すなわち、排気ガス中の酸素濃度を低下させる。それにより、保持ＮＯＸは離脱され、すなわち、吸収ＮＯＸは放出され、また、吸着ＮＯ２は脱離され、これら離脱ＮＯＸは排気ガス中の還元物質によりＮ２へ還元浄化される。
　しかしながら、このような再生処理に伴って、Ｎ２Ｏ（一酸化二窒素又は亜酸化窒素）が生成されてＮＯＸ触媒装置２から流出することがある。Ｎ２Ｏの大気放出は好ましくないために、Ｎ２Ｏの流出量を許容値以下にすることが必要である。
　図２は、再生処理においてＮＯＸ触媒装置２へ流入する排気ガスの空燃比に対するＮＯＸ還元率の変化、ＮＨ３生成量の変化、及び、Ｎ２Ｏ流出量の変化を示すグラフである。Ｎ２Ｏ流出量は、再生処理中のＮ２Ｏの流出量と再生処理直後のＮ２Ｏの流出量との合計であり、すなわち、再生処理に伴うＮ２Ｏの流出量を示している。図２に示すように、再生処理時の排気ガスの空燃比を理論空燃比Ｓ（１４．７）より僅かにリッチ側の第一空燃比Ａ１（例えば１４．３）以上で第二空燃比Ａ２（例えば１３．３）以下とすれば、Ｎ２Ｏの流出量を許容値Ｍ以下とすることができる。再生処理時の排気ガスの空燃比を第一空燃比Ａ１と第二空燃比Ａ２との間の第三空燃比（例えば１３．８）近傍とすることにより、Ｎ２Ｏの流出量を最少にすることができる。
　再生処理時の排気ガスの空燃比を小さくするほど、再生処置中の還元作用が活発となり、ＮＯＸ還元率は徐々に大きくなる。それにより、再生処理の排気ガスの空燃比を小さくするほど、ＮＯＸの還元不足により生成されるＮ２Ｏ量（ＮＯ＋Ｎ→Ｎ２Ｏ）は少なくなり、再生処理の排気ガスの空燃比を第一空燃比Ａ１以下とすれば、再生処理中のＮ２Ｏ生成量を第一設定量以下とすることができる。
　しかしながら、排気ガスの空燃比を過剰に小さくすると、還元不足により生成されるＮ２Ｏ生成量を非常に少なくすることはできるが、再生処理中に生成されるＮＨ３量（アンモニア量）が非常に多くなり、こうして生成されたＮＨ３は、ＮＯＸ触媒装置２の担体に吸着される等してＮＯＸ触媒装置２から流出することなく留まる。次いで、再生処理が完了して排気ガスの空燃比がリーンとなると、排気ガス中の含まれる酸素がＮＨ３を酸化してＮ２Ｏが生成される（２ＮＨ３を＋２Ｏ２→Ｎ２Ｏ＋３Ｈ２Ｏ）。こうして、排気ガスの空燃比を小さくするほど、再生処理中のＮ２Ｏ生成量を少なくすることはできるが、再生処理中のＮＨ３生成量が多くなり、再生処理中のＮＨ３生成量が多いほど再生処理直後のＮ２Ｏ生成量が多くなる。
　それにより、再生処理時の排気ガスの空燃比は第二空燃比Ａ２以上とされ、再生処理中にＮＯＸの還元によりそれほど多くのＮＨ３が生成されないようにし、生成されたＮＨ３が再生処理後の排気ガス中の酸素により酸化されて生成されるＮ２Ｏ生成量を第二設定量以下とする。
　このように、再生処理時の排気ガスの空燃比を第一空燃比Ａ１以上で第二空燃比Ａ２以下とすることにより、再生処理中のＮ２Ｏ生成量を第一設定量以下とすることができ、また、再生処理中にＮＯＸの還元により生成されたＮＨ３が再生処理後の排気ガス中の酸素により酸化されて生成されるＮ２Ｏ生成量を第二設定量以下とすることができ、再生処理に伴うＮＯＸ触媒装置からのＮ２Ｏ流出量、すなわち、再生処理中のＮ２Ｏ生成量と再生処理後のＮ２Ｏの生成量との合計を許容値以下とすることができる。
　実線で示すＮＯＸ還元率は、Ｎ２Ｏ流出量（再生処理後のＮ２Ｏ生成量を含む）を含んでおり、Ｎ２Ｏ流出量を含めないＮＯＸ還元率をＮＯＸ浄化率とすれば、ＮＯＸ浄化率は、図２に点線で示すように再生処理時の排気ガスの空燃比に応じて変化する。再生処理時の排気ガスの空燃比を第一空燃比Ａ１以上で第二空燃比Ａ２以下とすることにより、ＮＯＸ浄化率を高くすることができる。
　図３は、電子制御装置により実施される再生時期の制御を示すフローチャートである。先ず、ステップ１０１において、現在がＮＯＸ触媒装置２の再生時期であるか否かが判断される。例えば、ＮＯＸ触媒装置２の直上流側に上流側ＮＯＸ濃度センサを設けると共にＮＯＸ触媒装置の直下流側に下流側ＮＯＸ濃度センサを設けて、ＮＯＸ触媒装置２へ流入する排気ガス中のＮＯＸ濃度とＮＯＸ触媒装置２から流出する排気ガス中のＮＯＸ濃度とを検出し、ＮＯＸ触媒装置２へ流入する排気ガス中のＮＯＸ濃度とＮＯＸ触媒装置２から流出する排気ガス中のＮＯＸ濃度との差が設定値を下回る時に、ＮＯＸ触媒装置２のＮＯＸ保持量は、ＮＯＸ保持可能量近傍に到達して、排気ガス中のＮＯＸを十分に保持することができなくなったとして、再生時期と判断することができる。
　また、下流側ＮＯＸ濃度センサを設けることなく、上流側ＮＯＸ濃度センサによりＮＯＸ触媒装置２へ流入する排気ガス中のＮＯＸ濃度を検出し、ＮＯＸ濃度から定まる単位時間当たりの排気ガス中に含まれるＮＯＸ量の設定割合が単位時間当たりにＮＯＸ触媒装置２へ保持されるとして、単位時間当たりの保持量を積算して現在のＮＯＸ保持量を推定し、これが設定量に達した時に再生時期と判断するようにしても良い。また、上流側ＮＯＸ濃度センサも設けることなく、機関運転状態毎の単位時間当たりの排気ガス中に含まれるＮＯＸ量を予め設定しておいて、その設定割合が単位時間当たりにＮＯＸ触媒装置２へ保持されるとして、単位時間当たりの保持量を積算して現在のＮＯＸ保持量を推定し、これが設定量に達した時に再生時期と判断するようにしても良い。
　再生時期でない時にはステップ１０７において燃料供給装置３による燃料供給は停止されたままとして終了する。一方、ＮＯＸ触媒装置２が再生時期である時には、ステップ１０１の判断が肯定され、ステップ１０２において、再生処理を実施するために、ＮＯＸ触媒装置２へ流入する排気ガスの空燃比を、理論空燃比Ｓより僅かにリッチ側の第一空燃比Ａ１以上で第二空燃比Ａ２以下の予め設定した空燃比Ａ（例えば１３．８）となるように、現在の燃焼空燃比と排気ガス量とに基づき、燃料供給装置３により供給する単位時間当たりの燃料供給量Ｑを決定する。
　次いで、ステップ１０３において、再生処理を開始してからの経過時間ｔが再生処理の完了に対応する予め定められた第二設定時間ｔ２に達したか否かが判断される。当初、この判断は否定されてステップ１０４へ進み、経過時間ｔが第二設定時間の半分に設定された第一設定時間ｔ１に達したか否かが判断される。当初、この判断は否定されてステップ１０６に進み、ステップ１０２において決定された単位時間当たりの燃料供給量Ｑに基づき燃料供給装置３により燃料供給を実施する。それにより、ＮＯＸ触媒装置２へ流入する排気ガスの空燃比を設定空燃比Ａとして、再生処理が実施される。
　リッチな設定空燃比Ａの排気ガスがＮＯＸ触媒装置２へ流入すると、再生処理前半では、ＮＯＸ触媒装置２から多量のＮＯＸが離脱する。しかしながら、再生処理後半では、ＮＯＸ触媒装置２に保持されているＮＯＸ量が少なくなるために、ＮＯＸ触媒装置２から離脱するＮＯＸ量も少なくなり、ＮＯＸ触媒装置２へ流入する排気ガスの空燃比を設定空燃比Ａとままとしていると、ＮＯＸ触媒装置２内において離脱ＮＯＸを含めた空燃比は再生処理前半よりリッチ側となってしまう。
　それにより、再生処理中のＮＨ３生成量が増大して再生処理終了後のＮ２Ｏ生成量が増大してしまう。その結果として、再生処理に伴うＮ２Ｏ流出量が必ずしも許容値を超えるとは限らないが、図３に示すフローチャートでは、再生処理後半となって再生処理を開始してからの経過時間ｔが第一設定時間ｔ１に達し、ステップ１０４の判断が肯定されると、ステップ１０５において、ステップ１０２において決定された単位時間当たりの燃料供給量Ｑは予め定められた設定量ΔＱだけ少なくされ、少なくされた燃料供給量Ｑに基づきステップ１０６において燃料供給が実施される。こうして、再生処理後半の排気ガスの空燃比を、再生処理前半の排気ガスの空燃比より大きくすることにより、再生処理中において離脱ＮＯＸを含めたＮＯＸ触媒装置内の排気ガスの空燃比をほぼ一定に維持して、再生処理に伴うＮ２Ｏ流出量が確実に許容値を越えないようにしている。
　再生処理を開始してからの経過時間が第二設定時間ｔ２に達すれば、ステップ１０３の判断が肯定され、ステップ１０７において燃料供給装置３による燃料供給は停止され、再生処理を終了する。
　本実施形態において、再生処理時のＮＯＸ触媒装置２へ流入する排気ガスの空燃比を第一空燃比Ａ１と第二空燃比Ａ２との間の設定空燃比Ａとするために、燃料供給装置３によるリーン空燃比の排気ガスへ燃料供給を実施するようにしたが、これは本発明を限定するものではない。例えば、内燃機関の気筒内で燃焼させる混合気の空燃比をリッチな設定空燃比Ａとしても良く、また、膨張行程及び排気行程において気筒内へ追加燃料を供給して気筒内から排出される排気ガスの空燃比をリッチな設定空燃比Ａとするようにしても良い。もちろん、再生処理後半となれば、ＮＯＸ触媒装置２へ流入する排気ガスの空燃比を設定空燃比Ａより僅かに大きくするように、燃焼空燃比又は追加燃料量を制御すれば良い。
　再生処理時において、空燃比センサ４によりＮＯＸ触媒装置２へ流入する排気ガスの空燃比を検出すれば、所望空燃比となるように、燃料供給装置３による燃料供給量、燃焼空燃比、又は、追加燃料量をフィードバック制御することができる。
　図３に示すフローチャートでは、再生処理後半の排気ガスの空燃比を、再生処理前半の排気ガスの空燃比より大きくしたが、再生処理において、再生処理を開始してからの経過時間ｔが長くなるほど、ＮＯＸ触媒装置からのＮＯＸ離脱量が徐々に減少するために、経過時間ｔが長くなるほど、ＮＯＸ触媒装置へ流入する排気ガスの空燃比を徐々に大きくするようにしても良い。 FIG. 1 is a schematic view showing an exhaust gas purification apparatus for an internal combustion engine according to the present invention. In the figure, reference numeral 1 denotes an exhaust passage of an internal combustion engine that performs lean combustion such as a diesel engine or an in-cylinder spark ignition internal combustion engine. The exhaust gas of such an internal combustion engine, in order to contain a relatively large amount of NO X, in the exhaust passage 1, NO X catalyst device 2 for purifying NO X is arranged. A fuel supply device 3 for supplying fuel (or a reducing agent) is disposed upstream of the NO X catalyst device 2 in the exhaust passage 1. 4 is an air-fuel ratio sensor for detecting an air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2.
The NO X catalyst device 2 carries a NO X holding agent and a noble metal catalyst such as platinum Pt. The NO X retention agent is at least one selected from an alkali metal such as potassium K, sodium Na, lithium Li and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and a rare earth such as lanthanum La and yttrium Y. One.
When the exhaust gas has a lean air-fuel ratio, that is, when the oxygen concentration in the exhaust gas is high, the NO X catalyst device 2 holds the NO X in the exhaust gas well, that is, absorbs it well as nitrate. , NO 2 adsorbs well. However, NO X cannot be held indefinitely, and as a regeneration process, the air-fuel ratio of the exhaust gas is reduced before the NO X hold amount reaches the NO X holdable amount and can no longer hold NO X. The stoichiometric air-fuel ratio or rich air-fuel ratio is set, that is, the oxygen concentration in the exhaust gas is reduced. As a result, the retained NO X is desorbed, that is, the absorbed NO X is released, and the adsorbed NO 2 is desorbed, and the desorbed NO X is reduced and purified to N 2 by the reducing substance in the exhaust gas.
However, with such regeneration treatment, N 2 O (dinitrogen monoxide or nitrous oxide) may be generated and flow out of the NO X catalyst device 2. Since release of N 2 O into the atmosphere is not preferable, it is necessary to make the outflow amount of N 2 O below an allowable value.
Figure 2 is a variation of the NO X reduction rate with respect to the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 in the regeneration process, the change of the NH 3 produced amount, and is a graph showing changes in N 2 O runoff. The N 2 O outflow amount is the sum of the outflow amount of N 2 O during the regeneration process and the outflow amount of N 2 O immediately after the regeneration process, that is, indicates the outflow amount of N 2 O accompanying the regeneration process. . As shown in FIG. 2, the air-fuel ratio of the exhaust gas during the regeneration process is slightly higher than the first air-fuel ratio A1 (for example, 14.3) slightly richer than the theoretical air-fuel ratio S (14.7). If it is (for example, 13.3) or less, the outflow amount of N 2 O can be set to an allowable value M or less. By making the air-fuel ratio of the exhaust gas at the time of regeneration processing close to the third air-fuel ratio (for example, 13.8) between the first air-fuel ratio A1 and the second air-fuel ratio A2, the outflow amount of N 2 O is minimized. can do.
The smaller the air-fuel ratio of the exhaust gas during regeneration treatment, the reducing action of playing action becomes active, NO X reduction rate gradually increases. As a result, the smaller the air-fuel ratio of the exhaust gas in the regeneration process, the smaller the amount of N 2 O (NO + N → N 2 O) generated due to insufficient reduction of NO X , and the air-fuel ratio of the exhaust gas in the regeneration process is reduced. If the air-fuel ratio is set to 1 or less, the N 2 O generation amount during the regeneration process can be set to the first set amount or less.
However, if the air-fuel ratio of the exhaust gas is excessively reduced, the amount of N 2 O produced due to insufficient reduction can be reduced very much, but the amount of NH 3 (ammonia amount) produced during the regeneration process is very small. increases to, NH 3 thus generated will remain without flowing out from the NO X catalyst device 2 and the like are adsorbed on the carrier of the NO X catalyst device 2. Next, when the regeneration process is completed and the air-fuel ratio of the exhaust gas becomes lean, oxygen contained in the exhaust gas oxidizes NH 3 to generate N 2 O (2NH 3 becomes + 2O 2 → N 2 O + 3H 2 O). Thus, the smaller the air-fuel ratio of the exhaust gas, although it is possible to reduce the N 2 O production of playing process, the number of NH 3 generated content in the regeneration process, NH 3 generated content in the reproduction process The greater the amount, the greater the amount of N 2 O produced immediately after the regeneration process.
Thereby, the air-fuel ratio of the exhaust gas during the regeneration process is set to be equal to or higher than the second air-fuel ratio A2, so that not much NH 3 is generated by the reduction of NO X during the regeneration process, and the generated NH 3 is regenerated. The amount of N 2 O produced by oxidation with oxygen in the later exhaust gas is set to a second set amount or less.
As described above, the amount of N 2 O generated during the regeneration process is set to be equal to or less than the first set amount by setting the air-fuel ratio of the exhaust gas during the regeneration process to be the first air-fuel ratio A1 or more and the second air-fuel ratio A2 or less. In addition, the amount of N 2 O produced when the NH 3 produced by the reduction of NO X during the regeneration process is oxidized by the oxygen in the exhaust gas after the regeneration process is set to be equal to or less than the second set amount. can be, N 2 O outflow from NO X catalyst device accompanying the regeneration process, i.e., the sum of the generation quantity of N 2 O after regeneration treatment and N 2 O produced amount in the regeneration process than the allowable value be able to.
The NO X reduction rate indicated by the solid line includes the N 2 O outflow amount (including the N 2 O generation amount after the regeneration process), and the NO X reduction rate not including the N 2 O outflow amount is defined as the NO X purification rate. if, NO X purification rate will vary according to the air-fuel ratio of the exhaust gas during regeneration treatment as indicated by a dotted line in FIG. By the second air-fuel ratio A2 below the air-fuel ratio of the exhaust gas at the time of reproduction processing in the first air-fuel ratio A1 or more, it is possible to increase the NO X purification rate.
FIG. 3 is a flowchart showing the regeneration timing control performed by the electronic control unit. First, at step 101, whether the current is the playback time of the NO X catalyst device 2 is determined. For example, the exhaust gas provided downstream NO X concentration sensor immediately downstream of the NO X catalyst device provided with the upstream NO X concentration sensor immediately upstream of the NO X catalyst device 2, flows into the NO X catalyst device 2 detecting the concentration of NO X in the exhaust gas flowing out from NO X concentration and the NO X catalyst device 2 in and out of NO X concentration and the NO X catalyst device 2 in the exhaust gas flowing into the NO X catalyst device 2 when the difference between the concentration of NO X in the exhaust gas is below the set value, the NO X holding amount of the NO X catalyst device 2, and reaches the vicinity of the NO X holding amount, with sufficiently retaining the NO X in the exhaust gas It can be determined that it is time to regenerate as it is no longer possible.
Moreover, without providing the downstream NO X concentration sensor detects the concentration of NO X in the exhaust gas flowing into the NO X catalyst device 2 by the upstream NO X concentration sensor, exhaust gas per unit time determined from NO X concentration Assuming that the set ratio of the NO X amount contained in the NO X catalyst device 2 is held per unit time, the current NO X hold amount is estimated by integrating the hold amount per unit time, and this is the set amount It may be determined that the playback time is reached. Further, the upstream NO X concentration sensor even without providing, in advance set the amount of NO X contained in the exhaust gas per unit time for each engine operating state, NO X catalyst that setting percentage per unit time as it is held to the apparatus 2, to estimate the current of the NO X holding amount by integrating the amount retained per unit time, which may be determined that the regeneration timing when reaching the set amount.
When it is not the regeneration time, the fuel supply by the fuel supply device 3 is stopped in step 107 and the process is terminated. On the other hand, when the NO X catalyst device 2 is a timing regeneration, the determination in step 101 is affirmative, at step 102, to implement the regeneration process, the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2, the theoretical The current combustion air-fuel ratio and the amount of exhaust gas are set so that the air-fuel ratio becomes a preset air-fuel ratio A (for example, 13.8) that is slightly higher than the first air-fuel ratio A1 and slightly lower than the second air-fuel ratio A2. Based on the above, the fuel supply amount Q per unit time supplied by the fuel supply device 3 is determined.
Next, in step 103, it is determined whether or not an elapsed time t since the start of the reproduction process has reached a predetermined second set time t2 corresponding to the completion of the reproduction process. Initially, this determination is denied and the routine proceeds to step 104, where it is determined whether or not the elapsed time t has reached the first set time t1 set to half of the second set time. Initially, this determination is denied and the routine proceeds to step 106 where fuel supply is performed by the fuel supply device 3 based on the fuel supply amount Q per unit time determined in step 102. Thereby, the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 as a setting an air-fuel ratio A, reproduction process is performed.
When exhaust gas rich set air-fuel ratio A flows into the NO X catalyst device 2, in the regeneration process early, NO X catalyst from the apparatus 2 multimers NO X is disengaged. However, in the second half regeneration process, in order to the amount of NO X held in the NO X catalyst device 2 is reduced, the amount of NO X becomes fewer leaves the NO X catalyst device 2, flows into the NO X catalyst device 2 exhaust If the air-fuel ratio of the gas remains at the set air-fuel ratio A, the air-fuel ratio including the separated NO X in the NO X catalyst device 2 becomes richer than the first half of the regeneration process.
As a result, the amount of NH 3 generated during the regeneration process increases and the amount of N 2 O generated after the regeneration process ends increases. As a result, the amount of N 2 O outflow associated with the regeneration process does not necessarily exceed the allowable value, but in the flowchart shown in FIG. 3, the elapsed time t from the start of the regeneration process in the latter half of the regeneration process is When the first set time t1 is reached and the determination in step 104 is affirmed, in step 105, the fuel supply amount Q per unit time determined in step 102 is reduced by a predetermined set amount ΔQ. Based on the fuel supply amount Q, fuel is supplied in step 106. Thus, the air-fuel ratio of the exhaust gas in the second half reproduction process, by greater than the air-fuel ratio of the exhaust gas of the reproduction process the first half, the air-fuel ratio of the exhaust gas in the NO X catalyst device, including a detachment NO X during the reproduction process It is kept almost constant to ensure that the N 2 O efflux amount associated with the regeneration process does not exceed the allowable value.
If the elapsed time from the start of the regeneration process reaches the second set time t2, the determination in step 103 is affirmed, the fuel supply by the fuel supply device 3 is stopped in step 107, and the regeneration process ends.
In the present embodiment, in order to set the air-fuel ratio A between the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 at the time of reproduction processing from the first air-fuel ratio A1 and the second air-fuel ratio A2, the fuel supply system Although the fuel is supplied to the exhaust gas having a lean air-fuel ratio according to No. 3, this does not limit the present invention. For example, the air-fuel ratio of the air-fuel mixture burned in the cylinder of the internal combustion engine may be set to a rich set air-fuel ratio A, and the exhaust gas that is discharged from the cylinder by supplying additional fuel into the cylinder in the expansion stroke and the exhaust stroke The air-fuel ratio of the gas may be set to a rich set air-fuel ratio A. Of course, playback if processing late and become, as slightly larger than the NO X catalyst set the air-fuel ratio of the exhaust gas flowing into the device 2 air A, may be controlled combustion air or additional fuel amount.
During reproduction process, by detecting the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device 2 by the air-fuel ratio sensor 4, so that the desired air-fuel ratio, the fuel supply amount of the fuel supply device 3, combustion air-fuel ratio, or The additional fuel amount can be feedback controlled.
In the flowchart shown in FIG. 3, the air-fuel ratio of the exhaust gas in the second half of the regeneration process is made larger than the air-fuel ratio of the exhaust gas in the first half of the regeneration process. , to NO X withdrawal amount from the NO X catalyst device decreases gradually as the elapsed time t becomes longer, it may be gradually increased air-fuel ratio of the exhaust gas flowing into the NO X catalyst device.
　１　　排気通路
　２　　ＮＯＸ触媒装置
　３　　燃料供給装置 DESCRIPTION OF SYMBOLS 1 Exhaust passage 2 NO X catalyst apparatus 3 Fuel supply apparatus

Claims (2)

  1. 　排気ガス中の酸素濃度が高い時には排気ガス中のＮＯＸを良好に保持し、再生処理として、排気ガス中の酸素濃度を低下させれば、保持したＮＯＸを離脱し、こうして離脱させたＮＯＸを排気ガス中の還元物質によりＮ２へ還元浄化することができるＮＯＸ触媒装置を具備する内燃機関の排気浄化装置において、再生処理時に前記ＮＯＸ触媒装置へ流入させる排気ガスの空燃比を、第一空燃比以下で第二空燃比以上とし、前記排気ガスの空燃比を前記第一空燃比以下とすることにより、再生処理中にＮＯＸの還元不足により生成されるＮ２Ｏ生成量を第一設定量以下とし、前記排気ガスの空燃比を前記第二空燃比以上とすることにより、再生処理中にＮＯＸの還元により生成されたＮＨ３が再生処理後の排気ガス中の酸素により酸化されて生成されるＮ２Ｏ生成量を第二設定量以下とし、再生処理に伴うＮＯＸ触媒装置からのＮ２Ｏ流出量を許容値以下とすることを特徴とする内燃機関の排気浄化装置。 When a high oxygen concentration in the exhaust gas is satisfactorily hold the NO X in the exhaust gas, as the reproduction process, if lower the oxygen concentration in the exhaust gas, leaves the held NO X, thus is detached NO In an exhaust gas purification apparatus for an internal combustion engine having a NO X catalyst device capable of reducing and purifying X to N 2 with a reducing substance in the exhaust gas, the air-fuel ratio of the exhaust gas flowing into the NO X catalyst device during the regeneration process is set. The amount of N 2 O generated due to insufficient reduction of NO X during the regeneration process by setting the air-fuel ratio below the first air-fuel ratio and above the second air-fuel ratio and the air-fuel ratio of the exhaust gas below the first air-fuel ratio Is less than the first set amount, and the air-fuel ratio of the exhaust gas is greater than or equal to the second air-fuel ratio, so that NH 3 produced by NO X reduction during the regeneration process is oxygen in the exhaust gas after the regeneration process. Oxidized by Is the N 2 O production amount generated in the following second set amount, the exhaust gas purifying apparatus for an internal combustion engine, characterized in that the N 2 O outflow from NO X catalyst device accompanying the regeneration process than the allowable value .
  2. 　再生処理後半の前記排気ガスの空燃比は、再生処理前半の前記排気ガスの空燃比より大きくされることを特徴とする請求項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 air-fuel ratio of the exhaust gas in the second half of the regeneration process is made larger than the air-fuel ratio of the exhaust gas in the first half of the regeneration process.
PCT/JP2009/061250 2009-06-15 2009-06-15 Exhaust cleaner for internal combustion engine WO2010146717A1 (en)

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US20120073273A1 (en) * 2009-06-16 2012-03-29 Toyota Jidosha Kabushiki Kaisha Exhaust purification system of internal combustion engine
JP2016532055A (en) * 2013-09-11 2016-10-13 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフトＵｍｉｃｏｒｅ ＡＧ ＆ Ｃｏ．ＫＧ Reduction of N2O in exhaust gas from lean-burn petroleum engines
JP2017515032A (en) * 2014-04-03 2017-06-08 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフトＵｍｉｃｏｒｅ ＡＧ ＆ Ｃｏ．ＫＧ Regeneration method of exhaust gas aftertreatment system

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JPH04232359A (en) * 1990-12-28 1992-08-20 Yanmar Diesel Engine Co Ltd Air-fuel ratio control device of internal combustion engine
JP2002195025A (en) * 2000-12-27 2002-07-10 Toyota Motor Corp Exhaust emission control device for internal combustion engine
JP2004211676A (en) * 2002-11-11 2004-07-29 Toyota Motor Corp Exhaust gas cleaner for internal combustion engine
JP2006289211A (en) * 2005-04-07 2006-10-26 Ne Chemcat Corp Ammonia oxidation catalyst

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JPH04232359A (en) * 1990-12-28 1992-08-20 Yanmar Diesel Engine Co Ltd Air-fuel ratio control device of internal combustion engine
JP2002195025A (en) * 2000-12-27 2002-07-10 Toyota Motor Corp Exhaust emission control device for internal combustion engine
JP2004211676A (en) * 2002-11-11 2004-07-29 Toyota Motor Corp Exhaust gas cleaner for internal combustion engine
JP2006289211A (en) * 2005-04-07 2006-10-26 Ne Chemcat Corp Ammonia oxidation catalyst

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20120073273A1 (en) * 2009-06-16 2012-03-29 Toyota Jidosha Kabushiki Kaisha Exhaust purification system of internal combustion engine
US9109492B2 (en) * 2009-06-16 2015-08-18 Toyota Jidosha Kabushiki Kaisha Exhaust purification system of internal combustion engine
JP2016532055A (en) * 2013-09-11 2016-10-13 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフトＵｍｉｃｏｒｅ ＡＧ ＆ Ｃｏ．ＫＧ Reduction of N2O in exhaust gas from lean-burn petroleum engines
JP2017515032A (en) * 2014-04-03 2017-06-08 ユミコア・アクチエンゲゼルシャフト・ウント・コムパニー・コマンディットゲゼルシャフトＵｍｉｃｏｒｅ ＡＧ ＆ Ｃｏ．ＫＧ Regeneration method of exhaust gas aftertreatment system

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