JP2008231950A - Exhaust emission control device for internal combustion engine - Google Patents

Exhaust emission control device for internal combustion engine Download PDF

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Publication number
JP2008231950A
JP2008231950A JP2007068966A JP2007068966A JP2008231950A JP 2008231950 A JP2008231950 A JP 2008231950A JP 2007068966 A JP2007068966 A JP 2007068966A JP 2007068966 A JP2007068966 A JP 2007068966A JP 2008231950 A JP2008231950 A JP 2008231950A
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exhaust gas
engine
oxidation catalyst
selective reduction
ratio
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Japanese (ja)
Inventor
Toshisuke Toshioka
俊祐 利岡
Tomihisa Oda
富久 小田
Kazuhiro Ito
和浩 伊藤
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Toyota Motor Corp
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Toyota Motor Corp
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Priority to JP2007068966A priority Critical patent/JP2008231950A/en
Priority to PCT/JP2008/055151 priority patent/WO2008114834A1/en
Publication of JP2008231950A publication Critical patent/JP2008231950A/en
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • 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
    • F01N3/033—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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
    • F01N3/106—Auxiliary oxidation catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2053—By-passing catalytic reactors, e.g. to prevent overheating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/06—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being a temperature sensor
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
    • F02B37/00—Engines characterised by provision of pumps driven at least for part of the time by exhaust
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
    • F02M26/02—EGR systems specially adapted for supercharged engines
    • F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
    • F02M26/05—High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
    • 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
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
    • 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

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Mechanical Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Materials Engineering (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Combined Controls Of Internal Combustion Engines (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To approximate a ratio of NO to NO<SB>2</SB>in exhaust gas 1:1. <P>SOLUTION: A NOx selective reduction catalyst 15 is disposed in an engine exhaust passage, an oxidation catalyst 12 is disposed in the engine exhaust passage upstream of the NOx selective reduction catalyst 15, and urea water is supplied to the NOx selective reduction catalyst 15 to reduce NOx. In an engine operation state where a conversion ratio from NO to NOx in the oxidation catalyst 12 suffers a loss, combustion is controlled so that the ratio of NO<SB>2</SB>to NOx in exhaust gas delivered from a combustion chamber 2 becomes 50% or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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 emission control device for an internal combustion engine.

機関排気通路内にＮＯx選択還元触媒を配置し、ＮＯx選択還元触媒上流の機関排気通路内に酸化触媒を配置してこの酸化触媒により排気ガス中に含まれるＮＯをＮＯ2に変換し、ＮＯx選択還元触媒に尿素を供給して尿素から発生するアンモニアにより排気ガス中に含まれるＮＯxを選択的に還元するようにした内燃機関が公知である（例えば特許文献１を参照）。 A NO x selective reduction catalyst is arranged in the engine exhaust passage, an oxidation catalyst is arranged in the engine exhaust passage upstream of the NO x selective reduction catalyst, and NO contained in the exhaust gas is converted into NO 2 by this oxidation catalyst, An internal combustion engine in which urea is supplied to a NO x selective reduction catalyst and NO x contained in exhaust gas is selectively reduced by ammonia generated from the urea is known (see, for example, Patent Document 1).

ところでアンモニアを用いてＮＯxを還元するようにした場合には排気ガス中のＮＯxに対するＮＯ2の比率が５０パーセントのときに最も良好にＮＯxを浄化できることが知られている。ところがＮＯx選択還元触媒の上流に酸化触媒を配置した場合には酸化触媒において多量のＮＯ2が生成されてＮＯx選択還元触媒に流入する排気ガス中のＮＯ2の量が過剰になる場合があり、この場合にはＮＯxの良好な浄化作用が得られなくなる。 Meanwhile when so as to reduce NO x with ammonia is known to be the ratio of NO 2 with respect to NO x in the exhaust gas can be purified to best NO x at 50%. However if in the case of arranging the oxidation catalyst upstream of the NO x selective reduction catalyst is the amount of NO 2 in the exhaust gas flowing into a large amount of NO 2 is produced by the NO x selective reduction catalyst in the oxidation catalyst becomes excessive In this case, a good NO x purification action cannot be obtained.

そこで上述の内燃機関では酸化触媒を迂回するバイパス通路を設け、酸化触媒において生成されるＮＯ2の量が過剰になるときには排気ガスの一部をバイパス通路内に分流させ、それによって酸化触媒において過剰なＮＯ2が生成されないようにしている。
特開２００５−２３９２１号公報 Therefore, in the above-described internal combustion engine, a bypass passage that bypasses the oxidation catalyst is provided, and when the amount of NO 2 generated in the oxidation catalyst becomes excessive, a part of the exhaust gas is diverted into the bypass passage, thereby causing an excess in the oxidation catalyst. NO 2 is not generated.
Japanese Patent Laid-Open No. 2005-23921

ところが機関の運転状態によっては酸化触媒においてＮＯ2がＮＯに還元させる場合、即ち酸化触媒におけるＮＯからＮＯ2への転換率がマイナスになる場合もあり、この場合にもＮＯxの良好な浄化が得られなくなる。しかしながら上述の内燃機関では酸化触媒におけるＮＯからＮＯ2への転換率がマイナスとなる場合については何ら対処しておらず、従って上述の内燃機関ではこのような場合にＮＯxの良好な浄化が得られないという問題がある。 However, depending on the operating state of the engine, NO 2 may be reduced to NO in the oxidation catalyst, that is, the conversion rate from NO to NO 2 in the oxidation catalyst may be negative. In this case as well, good purification of NO x is achieved. It can no longer be obtained. However, the above-described internal combustion engine does not deal with the case where the conversion rate from NO to NO 2 in the oxidation catalyst becomes negative. Therefore, the above-described internal combustion engine can obtain a good purification of NO x in such a case. There is a problem that can not be.

上記問題を解決するために本発明によれば、機関排気通路内にＮＯx選択還元触媒を配置し、ＮＯx選択還元触媒に尿素を供給して尿素から発生するアンモニアにより排気ガス中に含まれるＮＯxを選択的に還元するようにした内燃機関の排気浄化装置において、ＮＯx選択還元触媒上流の機関排気通路内に酸化触媒を配置し、この酸化触媒におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときには燃焼室から排出される排気ガス中のＮＯxに対するＮＯ2の比率が５０パーセント以上になるように燃焼を制御するようにしている。 In order to solve the above problem, according to the present invention, a NO x selective reduction catalyst is disposed in the engine exhaust passage, urea is supplied to the NO x selective reduction catalyst, and is contained in the exhaust gas by ammonia generated from the urea. in the exhaust purification system of an internal combustion engine so as to selectively reduce the NO x, placing the oxidation catalyst in the NO x selective reduction catalyst in the engine exhaust passage upstream of the conversion rate from NO in the oxidation catalyst to NO 2 is Combustion is controlled so that the ratio of NO 2 to NO x in the exhaust gas discharged from the combustion chamber is 50% or more when the engine is in a negative engine operating state.

更に、本発明によれば上記問題を解決するために、機関排気通路内にＮＯx選択還元触媒を配置し、ＮＯx選択還元触媒に尿素を供給して尿素から発生するアンモニアにより排気ガス中に含まれるＮＯxを選択的に還元するようにした内燃機関の排気浄化装置において、ＮＯx選択還元触媒上流の機関排気通路内に酸化触媒を配置すると共にこの酸化触媒を迂回するバイパス通路を設け、酸化触媒におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときには燃焼室から排出された排気ガスをバイパス通路内に導びいて酸化触媒を経由せずにＮＯx選択還元触媒に流入させるようにしている。 Furthermore, according to the present invention, in order to solve the above problem, a NO x selective reduction catalyst is disposed in the engine exhaust passage, urea is supplied to the NO x selective reduction catalyst, and ammonia generated from the urea enters the exhaust gas. in the exhaust purification system of an internal combustion engine which is adapted to selectively reduce NO x contained, a bypass passage which bypasses the oxidation catalyst together with arranging an oxidation catalyst in the NO x selective reduction catalyst in the engine exhaust passage upstream of, When the engine is in an engine operating state in which the conversion rate from NO to NO 2 in the oxidation catalyst is negative, exhaust gas discharged from the combustion chamber is introduced into the bypass passage and flows into the NO x selective reduction catalyst without passing through the oxidation catalyst. I try to let them.

１番目の発明では燃焼を制御することによってＮＯx選択還元触媒に流入する排気ガス中のＮＯxに対するＮＯ2の比率が増大せしめられる。
２番目の発明では酸化触媒を迂回して排気ガスをＮＯx選択還元触媒に送り込むことによってＮＯx選択還元触媒に流入する排気ガス中のＮＯxに対するＮＯ2の比率が増大せしめられる。 In the first invention, the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst is increased by controlling the combustion.
In the second invention, the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst is increased by bypassing the oxidation catalyst and sending the exhaust gas to the NO x selective reduction catalyst.

図１に圧縮着火式内燃機関の全体図を示す。
図１を参照すると、１は機関本体、２は各気筒の燃焼室、３は各燃焼室２内に夫々燃料を噴射するための電子制御式燃料噴射弁、４は吸気マニホルド、５は排気マニホルドを夫々示す。吸気マニホルド４は吸気ダクト６を介して排気ターボチャージャ７のコンプレッサ７ａの出口に連結され、コンプレッサ７ａの入口は吸入空気量検出器８を介してエアクリーナ９に連結される。吸気ダクト６内にはステップモータにより駆動されるスロットル弁１０が配置され、更に吸気ダクト６周りには吸気ダクト６内を流れる吸入空気を冷却するための冷却装置１１が配置される。図１に示される実施例では機関冷却水が冷却装置１１内に導かれ、機関冷却水によって吸入空気が冷却される。 FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.

一方、排気マニホルド５は排気ターボチャージャ７の排気タービン７ｂの入口に連結され、排気タービン７ｂの出口は酸化触媒１２の入口に連結される。この酸化触媒１２の下流には酸化触媒１２に隣接して排気ガス中に含まれる粒子状物質を捕集するためのパティキュレートフィルタ１３が配置され、このパティキュレートフィルタ１３の出口は排気管１４を介してＮＯx選択還元触媒１５の入口に連結される。このＮＯx選択還元触媒１５の出口には酸化触媒１６が連結される。 On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the inlet of the oxidation catalyst 12. Downstream of the oxidation catalyst 12, a particulate filter 13 for collecting particulate matter contained in the exhaust gas is disposed adjacent to the oxidation catalyst 12, and the outlet of the particulate filter 13 passes through the exhaust pipe 14. To the inlet of the NO x selective reduction catalyst 15. An oxidation catalyst 16 is connected to the outlet of the NO x selective reduction catalyst 15.

ＮＯx選択還元触媒１５上流の排気管１４内には尿素水溶液供給弁１７が配置され、この尿素水溶液供給弁１７は供給管１８、供給ポンプ１９を介して尿素水溶液タンク２０に連結される。尿素水溶液タンク２０内に貯蔵されている尿素水溶液を供給ポンプ１９によって尿素水溶液供給弁１７から排気管１４内を流れる排気ガス中に噴射され、尿素から発生したアンモニア（（ＮＨ2）2ＣＯ＋Ｈ2Ｏ→２ＮＨ3＋ＣＯ2）によって排気ガス中に含まれるＮＯxがＮＯx選択還元触媒１５において還元される。 A urea aqueous solution supply valve 17 is disposed in the exhaust pipe 14 upstream of the NO x selective reduction catalyst 15, and this urea aqueous solution supply valve 17 is connected to a urea aqueous solution tank 20 via a supply pipe 18 and a supply pump 19. The urea aqueous solution stored in the urea aqueous solution tank 20 is injected by the supply pump 19 into the exhaust gas flowing through the exhaust pipe 14 from the urea aqueous solution supply valve 17, and ammonia ((NH 2 ) 2 CO + H 2 O generated from urea. → 2NH 3 + CO 2 ), NO x contained in the exhaust gas is reduced in the NO x selective reduction catalyst 15.

排気マニホルド５と吸気マニホルド４とは排気ガス再循環（以下、ＥＧＲと称す）通路２１を介して互いに連結され、ＥＧＲ通路２１内には電子制御式ＥＧＲ制御弁２２が配置される。また、ＥＧＲ通路２１周りにはＥＧＲ通路２１内を流れるＥＧＲガスを冷却するための冷却装置２３が配置される。図１に示される実施例では機関冷却水が冷却装置２３内に導かれ、機関冷却水によってＥＧＲガスが冷却される。一方、各燃料噴射弁３は燃料供給管２４を介してコモンレール２５に連結され、このコモンレール２５は電子制御式の吐出量可変な燃料ポンプ２６を介して燃料タンク２７に連結される。燃料タンク２７内に貯蔵されている燃料は燃料ポンプ２６によってコモンレール２５内に供給され、コモンレール２５内に供給された燃料は各燃料供給管２４を介して燃料噴射弁３に供給される。   The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 21, and an electronically controlled EGR control valve 22 is disposed in the EGR passage 21. A cooling device 23 for cooling the EGR gas flowing in the EGR passage 21 is disposed around the EGR passage 21. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 23, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 25 via a fuel supply pipe 24, and this common rail 25 is connected to a fuel tank 27 via an electronically controlled fuel pump 26 with variable discharge amount. The fuel stored in the fuel tank 27 is supplied into the common rail 25 by the fuel pump 26, and the fuel supplied into the common rail 25 is supplied to the fuel injection valve 3 through each fuel supply pipe 24.

電子制御ユニット３０はデジタルコンピュータからなり、双方向性バス３１によって互いに接続されたＲＯＭ（リードオンリメモリ）３２、ＲＡＭ（ランダムアクセスメモリ）３３、ＣＰＵ（マイクロプロセッサ）３４、入力ポート３５および出力ポート３６を具備する。酸化触媒１２には酸化触媒１２の床温を検出するための温度センサ２８が取付けられ、この温度センサ２８および吸入空気量検出器８の出力信号は夫々対応するＡＤ変換器３７を介して入力ポート３５に入力される。また、アクセルペダル４０にはアクセルペダル４０の踏込み量Ｌに比例した出力電圧を発生する負荷センサ４１が接続され、負荷センサ４１の出力電圧は対応するＡＤ変換器３７を介して入力ポート３５に入力される。更に入力ポート３５にはクランクシャフトが例えば１５°回転する毎に出力パルスを発生するクランク角センサ４２が接続される。一方、出力ポート３６は対応する駆動回路３８を介して燃料噴射弁３、スロットル弁１０の駆動用ステップモータ、尿素水溶液供給弁１７、供給ポンプ１９、ＥＧＲ制御弁２２および燃料ポンプ２６に接続される。   The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. A temperature sensor 28 for detecting the bed temperature of the oxidation catalyst 12 is attached to the oxidation catalyst 12, and output signals of the temperature sensor 28 and the intake air amount detector 8 are input to the input port via corresponding AD converters 37. 35. A load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the urea aqueous solution supply valve 17, the supply pump 19, the EGR control valve 22, and the fuel pump 26 through corresponding drive circuits 38. .

酸化触媒１２は例えば白金のような貴金属触媒を担持しており、この酸化触媒１２は排気ガス中に含まれるＮＯをＮＯ2に転換する作用と排気ガス中に含まれるＨＣを酸化させる作用をなす。即ち、ＮＯ2はＮＯよりも酸化性が強く、従ってＮＯがＮＯ2に転換されるとパティキュレートフィルタ１３上に捕獲された粒子状物質の酸化反応が促進され、またＮＯx選択還元触媒１５でのアンモニアによる還元作用が促進される。一方、アンモニアが吸着するタイプのＮＯx選択還元触媒１５ではＨＣが吸着するとアンモニアの吸着量が減少するためにＮＯx浄化率が低下する。従ってこのようなＮＯx選択還元触媒を用いた場合には酸化触媒１２によりＨＣを酸化することによってＮＯx浄化率が低下するのが阻止される。 The oxidation catalyst 12 carries a noble metal catalyst such as platinum, for example. The oxidation catalyst 12 functions to convert NO contained in the exhaust gas into NO 2 and oxidize HC contained in the exhaust gas. . That is, NO 2 is more oxidizable than NO. Therefore, when NO is converted to NO 2 , the oxidation reaction of the particulate matter captured on the particulate filter 13 is promoted, and the NO x selective reduction catalyst 15 The reduction action by ammonia is promoted. On the other hand, in the NO x selective reduction catalyst 15 of the type that adsorbs ammonia, the adsorption amount of ammonia decreases when HC adsorbs, so the NO x purification rate decreases. Thus the NO x purification rate is prevented from dropping by oxidizes HC by the oxidation catalyst 12 in the case of using such the NO x selective reduction catalyst.

パティキュレートフィルタ１３としては触媒を担持していないパティキュレートフィルタを用いることもできるし、例えば白金のような貴金属触媒を担持したパティキュレートフィルタを用いることもできる。一方、ＮＯx選択還元触媒１５は低温で高いＮＯx浄化率を有するアンモニア吸着タイプのＦｅゼオライトから構成することもできるし、アンモニアの吸着機能がないチタニア・バナジウム系の触媒から構成することもできる。酸化触媒１６は例えば白金からなる貴金属触媒を担持しており、この酸化触媒１６はＮＯx選択還元触媒１５から漏出したアンモニアを酸化する作用をなす。 As the particulate filter 13, a particulate filter not supporting a catalyst can be used, or a particulate filter supporting a noble metal catalyst such as platinum can be used. On the other hand, the NO x selective reduction catalyst 15 can be composed of an ammonia adsorption type Fe zeolite having a high NO x purification rate at a low temperature, or can be composed of a titania / vanadium catalyst having no ammonia adsorption function. . The oxidation catalyst 16 carries a noble metal catalyst made of platinum, for example, and this oxidation catalyst 16 has an action of oxidizing ammonia leaked from the NO x selective reduction catalyst 15.

図２に圧縮着火式内燃機関の別の実施例を示す。この実施例ではパティキュレートフィルタ１３が酸化触媒１６の下流に配置され、従ってこの実施例では酸化触媒１２の出口が排気管１４を介してＮＯx選択還元触媒１５の入口に連結される。 FIG. 2 shows another embodiment of the compression ignition type internal combustion engine. In this embodiment, the particulate filter 13 is arranged downstream of the oxidation catalyst 16. Therefore, in this embodiment, the outlet of the oxidation catalyst 12 is connected to the inlet of the NO x selective reduction catalyst 15 through the exhaust pipe 14.

さて、機関運転中に燃焼室２から排出されるＮＯxの大部分はＮＯかＮＯ2であり、これらＮＯとＮＯ2との比率は機関の運転状態に応じて変化する。 Now, most of the NO x discharged from the combustion chamber 2 during engine operation is NO or NO 2, the ratio of these NO and NO 2 will vary in accordance with the engine operating state.

一方、ＮＯx選択還元触媒１５では尿素から発生したアンモニアＮＨ3によって排気ガス中に含まれるＮＯxが選択的に還元され、このとき最も速度の速い反応式が次式で示される。
ＮＯ＋ＮＯ2＋２ＮＨ3→２Ｎ2＋３Ｈ2Ｏ
上式から、排気ガス中のＮＯとＮＯ2との比率が１：１のとき、即ち排気ガス中の（ＮＯ＋ＮＯ2）に対するＮＯ2の比率、言い換えると排気ガス中のＮＯxに対するＮＯ2の比率が５０パーセントのときに反応速度が最も速くなり、斯くしてＮＯx浄化率が最も高くなることがわかる。 On the other hand, in the NO x selective reduction catalyst 15, NO x contained in the exhaust gas is selectively reduced by ammonia NH 3 generated from urea. At this time, the fastest reaction formula is shown by the following formula.
NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O
From the above equation, the ratio of NO and NO 2 in the exhaust gas 1: When 1, i.e. the ratio of NO 2 with respect to the exhaust gas (NO + NO 2), in other words the ratio of NO 2 with respect to NO x in the exhaust gas There kinetics at 50% is the fastest, thus to the NO x purification rate is seen that the most becomes higher.

因みに、排気ガス中のＮＯ2が過剰の場合には例えばＮＯ2の過剰分は反応速度の遅い次式に従って反応が行われ、
６ＮＯ2＋８ＮＨ3→７Ｎ2＋１２Ｈ2Ｏ
排気ガス中のＮＯが過剰の場合には例えばＮＯの過剰分は反応速度の遅い次式に従って反応が行われる。
６ＮＯ＋４ＮＨ3→５Ｎ2＋６Ｈ2Ｏ
このように反応速度が遅くなるとＮＯx浄化率が低下する。 Incidentally, when NO 2 in the exhaust gas is excessive, for example, the excess of NO 2 is reacted according to the following equation with a slow reaction rate,
6NO 2 + 8NH 3 → 7N 2 + 12H 2 O
When the NO in the exhaust gas is excessive, for example, the excess NO is reacted according to the following equation with a slow reaction rate.
6NO + 4NH 3 → 5N 2 + 6H 2 O
Thus when the reaction rate the NO x purification rate decreases.

ところで前述したように酸化触媒１２は排気ガス中のＮＯをＮＯ2に変換する作用をなす。しかしながらこの点について詳細に検討するとＮＯがＮＯ2に変換されるのは酸化触媒１２が活性化しているときであり、酸化触媒１２が活性化していないときには逆にＮＯ2がＮＯに変換されることが判明したのである。即ち、排気ガス中にはＮＯ，ＮＯ2に加えてＨＣ，ＣＯが含まれており、酸化触媒１２が活性化するとＨＣ，ＣＯに加えてＮＯも酸化されるためにＮＯ2が生成される。ところが酸化触媒１２が活性化していないと排気ガス中にはＨＣ，ＣＯが残存しているためにこれらＨＣ，ＣＯによってＮＯ2が還元され、斯くしてＮＯが生成されることになる。 Incidentally, as described above, the oxidation catalyst 12 functions to convert NO in the exhaust gas into NO 2 . However, when this point is examined in detail, NO is converted to NO 2 when the oxidation catalyst 12 is activated, and NO 2 is converted to NO when the oxidation catalyst 12 is not activated. It turned out. That is, in the exhaust gas NO, in addition to NO 2 HC, contains the CO, NO 2 is produced in the oxidation catalyst 12 is NO is also oxidized by adding HC, the CO upon activation. However, if the oxidation catalyst 12 is not activated, HC and CO remain in the exhaust gas, so that NO 2 is reduced by these HC and CO, thus generating NO.

図３に酸化触媒１２におけるＮＯからＮＯ2へのＮＯ2転換率を示す。図３に示されるように酸化触媒１２の床温ＴＣが活性化温度Ｔ0を越えることにより酸化触媒１２が活性化するとＮＯ2転換率はプラスとなり、酸化触媒１２の床温ＴＣが活性化温度Ｔ0以下であって酸化触媒１２が活性化していないときにはＮＯ2転換率はマイナスとなる。 FIG. 3 shows the NO 2 conversion rate from NO to NO 2 in the oxidation catalyst 12. As shown in FIG. 3, when the oxidation catalyst 12 is activated when the bed temperature TC of the oxidation catalyst 12 exceeds the activation temperature T 0 , the NO 2 conversion rate becomes positive, and the bed temperature TC of the oxidation catalyst 12 becomes the activation temperature. When T 0 or less and the oxidation catalyst 12 is not activated, the NO 2 conversion rate becomes negative.

また、図３には燃焼室２から排出される排気ガス中のＮＯxに対するＮＯ2の目標ＮＯ2比率が示されており、本発明では排気ガス中のＮＯxに対するＮＯ2の比率は燃焼室２内における燃焼を制御することによって行われる。従って図３からわかるように本発明では酸化触媒１２が活性化していないときには、即ち、ＮＯ2転換率がマイナスとなる機関運転状態のときには燃焼室２から排出される排気ガス中のＮＯxに対するＮＯ2の比率が５０パーセント以上になるように燃焼が制御される。 FIG. 3 shows the target NO 2 ratio of NO 2 to NO x in the exhaust gas discharged from the combustion chamber 2. In the present invention, the ratio of NO 2 to NO x in the exhaust gas is the combustion chamber. This is done by controlling the combustion in 2. Therefore, as can be seen from FIG. 3, according to the present invention, when the oxidation catalyst 12 is not activated, that is, when the engine is operating at a negative NO 2 conversion rate, NO with respect to NO x in the exhaust gas discharged from the combustion chamber 2 is reduced. Combustion is controlled so that the ratio of 2 is 50% or more.

なお、図３に示される目標ＮＯ2比率ＮＲＯは本発明による第１の実施例における目標ＮＯ2比率を示しており、本発明による第１の実施例ではこの目標ＮＯ2比率ＮＲＯはＮＯx選択還元触媒１５に流入する排気ガス中のＮＯxに対するＮＯ2の比率をほぼ５０パーセントとするのに必要なＮＯ2比率を示している。従ってこの第１実施例ではほぼ全ての機関運転状態においてＮＯx選択還元触媒１５に流入する排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるように燃焼が制御されることになる。 The target NO 2 ratio NRO shown in FIG. 3 shows a target NO 2 ratio in the first embodiment according to the present invention, this objective NO 2 ratio NRO in the first embodiment according to the present invention the NO x selective It shows the NO 2 ratio required to make the ratio of NO 2 to NO x in the exhaust gas flowing into the reduction catalyst 15 approximately 50 percent. Therefore, in this first embodiment, the combustion is controlled so that the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst 15 is almost 50% in almost all engine operating states. .

この場合、具体的にはＮＯx選択還元触媒１５に流入する排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるようにＥＧＲ率および燃料噴射時期のいずれか一方又は双方が制御される。次にこのことについて図４および図５を参照しつつ説明する。 In this case, specifically, one or both of the EGR rate and the fuel injection timing are controlled so that the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst 15 is approximately 50%. The Next, this will be described with reference to FIGS.

図４に、ＥＧＲ率を変化させたときの燃焼室２から排出されるＮＯとＮＯ2の排出量の変化を示す。図４に示されるようにＥＧＲ率を高くしていくとＮＯ2の排出量はほとんど変化しないがＮＯの排出量は徐々に減少し、従って燃焼室２から排出される排気ガス中のＮＯxに対するＮＯ2の比率ＮＲは図４に示されるようにＥＧＲ率が高くなるほど増大する。従ってこの実施例ではこのＮＯ2比率ＮＲが図３に示される目標ＮＯ2比率ＮＲＯとなるようにＥＧＲ率が制御される。 FIG. 4 shows changes in the NO and NO 2 emission amounts discharged from the combustion chamber 2 when the EGR rate is changed. As shown in FIG. 4, when the EGR rate is increased, the NO 2 emission amount hardly changes, but the NO emission amount gradually decreases, so that the NO x amount in the exhaust gas discharged from the combustion chamber 2 is reduced. As shown in FIG. 4, the NO 2 ratio NR increases as the EGR rate increases. Therefore, in this embodiment, the EGR rate is controlled so that the NO 2 ratio NR becomes the target NO 2 ratio NRO shown in FIG.

即ち、ＮＯ2比率の制御ルーチンを示す図５を参照すると、まず初めにステップ５０において温度センサ２８により検出された酸化触媒１２の床温ＴＣから図３に示す目標ＮＯ2比率ＮＲＯが算出される。次いでステップ５１ではＮＯ2比率を目標ＮＯ2比率ＮＲＯとするのに必要な目標ＥＧＲ率が算出される。次いでステップ５２ではＥＧＲ率が目標ＥＧＲ率となるようにＥＧＲ制御弁２２の開度が制御される。 That is, referring to FIG. 5 showing the control routine of the NO 2 ratio, first, the target NO 2 ratio NRO shown in FIG. 3 is calculated from the bed temperature TC of the oxidation catalyst 12 detected by the temperature sensor 28 in step 50. . Then the target EGR rate required to bring the NO 2 ratio in step 51 the target NO 2 ratio NRO is calculated. Next, at step 52, the opening degree of the EGR control valve 22 is controlled so that the EGR rate becomes the target EGR rate.

図６に、燃料噴射時期を変化させたときの燃焼室２から排出されるＮＯとＮＯ2の排出量の変化を示す。図６に示されるように燃料噴射時期を進角していくとＮＯ2の排出量はほとんど変化しないがＮＯの排出量は徐々に減少し、従って燃焼室２から排出される排気ガス中のＮＯxに対するＮＯ2の比率ＮＲは図６に示されるように燃料噴射時期が進角されるほど増大する。従ってこの実施例ではこのＮＯ2比率ＮＲが図３に示される目標ＮＯ2比率ＮＲＯとなるように燃料噴射時期が制御される。 FIG. 6 shows changes in the NO and NO 2 emission amounts discharged from the combustion chamber 2 when the fuel injection timing is changed. As the fuel injection timing is advanced as shown in FIG. 6, the NO 2 emission amount hardly changes, but the NO emission amount gradually decreases. Therefore, the NO in the exhaust gas discharged from the combustion chamber 2 is reduced. The ratio NR of NO 2 to x increases as the fuel injection timing is advanced as shown in FIG. Therefore, in this embodiment, the fuel injection timing is controlled so that the NO 2 ratio NR becomes the target NO 2 ratio NRO shown in FIG.

即ち、ＮＯ2比率の制御ルーチンを示す図７を参照すると、まず初めにステップ６０において温度センサ２８により検出された酸化触媒１２の床温ＴＣから図３に示す目標ＮＯ2比率ＮＲＯが算出される。次いでステップ６１ではＮＯ2比率を目標ＮＯ2比率ＮＲＯとするのに必要な目標噴射時期が算出される。次いでステップ６２ではこの目標噴射時期において燃料噴射が行われる。なお、ＮＯ2比率を目標ＮＯ2比率に制御する際にＥＧＲ率と燃料噴射時期の双方を制御することもできる。 That is, referring to FIG. 7 showing the control routine of the NO 2 ratio, first, the target NO 2 ratio NRO shown in FIG. 3 is calculated from the bed temperature TC of the oxidation catalyst 12 detected by the temperature sensor 28 in step 60. . Next, at step 61, the target injection timing necessary for setting the NO 2 ratio to the target NO 2 ratio NRO is calculated. Next, at step 62, fuel injection is performed at this target injection timing. Note that both the EGR rate and the fuel injection timing can be controlled when controlling the NO 2 ratio to the target NO 2 ratio.

図８に圧縮着火式内燃機関の更に別の実施例を示す。この実施例では酸化触媒１２を迂回するバイパス通路４５が設けられ、バイパス通路４５の入口部に流路切換弁４６が配置される。この実施例では通常図８において実線で示されるように流路切換弁４６がバイパス通路４５を閉鎖しており、このとき排気ガスは酸化触媒１２内を流通する。これに対し、図８の破線で示すように流路制御弁４６が酸化触媒１２の入口を閉鎖したときには排気ガスはバイパス通路４５内を流れてパティキュレートフィルタ１３に流入する。   FIG. 8 shows still another embodiment of the compression ignition type internal combustion engine. In this embodiment, a bypass passage 45 that bypasses the oxidation catalyst 12 is provided, and a flow path switching valve 46 is disposed at the inlet of the bypass passage 45. In this embodiment, the flow path switching valve 46 normally closes the bypass passage 45 as indicated by the solid line in FIG. 8, and at this time, the exhaust gas flows through the oxidation catalyst 12. On the other hand, as shown by a broken line in FIG. 8, when the flow path control valve 46 closes the inlet of the oxidation catalyst 12, the exhaust gas flows through the bypass passage 45 and flows into the particulate filter 13.

この実施例では図９に示されるように酸化触媒１２におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときにはバイパス通路４５が開通せしめられ、即ち酸化触媒１２の入口が閉鎖され、このとき燃焼室２から排出された排気ガスはバイパス通路４５内に導びかれて酸化触媒１２を経由せずにパティキュレートフィルタ１３およびＮＯx選択還元触媒１５に流入する。即ち、この実施例ではＮＯ2転換率がマイナスのときにはＮＯがＮＯ2に変換されるのを回避するようにしている。 In this embodiment, as shown in FIG. 9, the bypass passage 45 is opened when the conversion rate from NO to NO 2 in the oxidation catalyst 12 is negative, that is, the inlet of the oxidation catalyst 12 is closed, At this time, the exhaust gas discharged from the combustion chamber 2 is guided into the bypass passage 45 and flows into the particulate filter 13 and the NO x selective reduction catalyst 15 without passing through the oxidation catalyst 12. That is, in this embodiment, NO is converted to NO 2 when the NO 2 conversion rate is negative.

具体的に言うとこの実施例では図９に示されるように酸化触媒１２が活性化していないときには、即ち酸化触媒１２におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときには燃焼室２から排出される排気ガス中のＮＯxに対するＮＯ2の目標ＮＯ2比率がほぼ５０パーセントになるように燃焼が制御される。このとき、排気ガスはバイパス通路４５内に送り込まれるのでＮＯx選択還元触媒１５に流入する排気ガス中のＮＯxに対するＮＯ2の比率はほぼ５０パーセントになる。 Specifically, in this embodiment, as shown in FIG. 9, when the oxidation catalyst 12 is not activated, that is, when the engine operating state in which the conversion rate of NO to NO 2 in the oxidation catalyst 12 is negative, the combustion chamber. Combustion is controlled so that the target NO 2 ratio of NO 2 to NO x in the exhaust gas discharged from 2 is approximately 50%. At this time, since the exhaust gas is sent into the bypass passage 45, the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst 15 becomes approximately 50%.

一方、酸化触媒１２が活性化しているとき、即ち酸化触媒１２におけるＮＯからＮＯ2への転換率がプラスとなる機関運転状態のときにはバイパス通路４５が閉鎖されて燃焼室２から排出された排気ガスが酸化触媒１２に流入される。このときにはＮＯx選択還元触媒１５に流入する排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるように燃焼が制御される。 On the other hand, when the oxidation catalyst 12 is activated, that is, in an engine operating state in which the conversion rate from NO to NO 2 in the oxidation catalyst 12 is positive, the bypass passage 45 is closed and the exhaust gas discharged from the combustion chamber 2 Flows into the oxidation catalyst 12. At this time, the combustion is controlled so that the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst 15 is approximately 50%.

次に図１０を参照しつつＥＧＲ率を制御することによってＮＯ2比率を制御するようにした場合のＮＯ2比率制御ルーチンについて説明する。
図１０を参照すると、まず初めにステップ７０において温度センサ２８により検出された酸化触媒１２の床温ＴＣが活性化温度Ｔ0よりも高いか否かが判別される。ＴＣ＞Ｔ0のときにはステップ７１に進んでバイパス通路４５が閉鎖される。次いでステップ７２では図３に示す目標ＮＯ2比率ＮＲＯが算出される。次いでステップ７３ではＮＯ2比率を目標ＮＯ2比率ＮＲＯとするのに必要な目標ＥＧＲ率が算出される。次いでステップ７４ではＥＧＲ率が目標ＥＧＲ率となるようにＥＧＲ制御弁２２の開度が制御される。 Next NO 2 ratio control routine will be described in the case of so controlling the NO 2 ratio by controlling the EGR rate with reference to FIG. 10.
Referring to FIG. 10, first, at step 70, it is judged if the bed temperature TC of the oxidation catalyst 12 detected by the temperature sensor 28 is higher than the activation temperature T 0 . When TC> T 0, the routine proceeds to step 71 where the bypass passage 45 is closed. Next, at step 72, the target NO 2 ratio NRO shown in FIG. 3 is calculated. Then the target EGR rate required to bring the NO 2 ratio in step 73 the target NO 2 ratio NRO is calculated. Next, at step 74, the opening degree of the EGR control valve 22 is controlled so that the EGR rate becomes the target EGR rate.

これに対し、ステップ７０においてＴＣ≦Ｔ0であると判別されたときにはステップ７５に進んでバイパス通路４５が開通せしめられる。次いでステップ７６では目標ＮＯ2比率ＮＲＯが０．５、即ち５０パーセントとされ、次いでステップ７３に進む。従ってこのときには燃焼室２から排出される排気ガス中のＮＯxに対するＮＯ2の比率はほぼ５０パーセントとなる。 On the other hand, when it is determined at step 70 that TC ≦ T 0 , the routine proceeds to step 75 where the bypass passage 45 is opened. Next, at step 76, the target NO 2 ratio NRO is set to 0.5, that is, 50%, and then the routine proceeds to step 73. Accordingly, at this time, the ratio of NO 2 to NO x in the exhaust gas discharged from the combustion chamber 2 is approximately 50 percent.

圧縮着火式内燃機関の全体図である。1 is an overall view of a compression ignition type internal combustion engine. 圧縮着火式内燃機関の別の実施例を示す全体図である。It is a general view which shows another Example of a compression ignition type internal combustion engine. ＮＯ2転換率等の変化を示す図である。Is a graph showing changes in NO 2 conversion, and the like. ＮＯ2比率等を示す図である。It is a diagram illustrating a NO 2 ratio like. ＮＯ2比率を制御するためのフローチャートである。It is a flowchart for controlling a NO 2 ratio. ＮＯ2比率等を示す図である。It is a diagram illustrating a NO 2 ratio like. ＮＯ2比率を制御するためのフローチャートである。It is a flowchart for controlling a NO 2 ratio. 圧縮着火式内燃機関の更に別の実施例を示す全体図である。It is a general view which shows another Example of a compression ignition type internal combustion engine. ＮＯ2転換率等の変化を示す図である。Is a graph showing changes in NO 2 conversion, and the like. ＮＯ2比率を制御するためのフローチャートである。It is a flowchart for controlling a NO 2 ratio.

符号の説明Explanation of symbols

４ 吸気マニホルド
５ 排気マニホルド
７ 排気ターボチャージャ
１２，１６ 酸化触媒
１３ パティキュレートフィルタ
１５ ＮＯx選択還元触媒
１７ 尿素水溶液供給弁 4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 12, 16 Oxidation catalyst 13 Particulate filter 15 NO x selective reduction catalyst 17 Urea aqueous solution supply valve

Claims (5)

機関排気通路内にＮＯx選択還元触媒を配置し、該ＮＯx選択還元触媒に尿素を供給して該尿素から発生するアンモニアにより排気ガス中に含まれるＮＯxを選択的に還元するようにした内燃機関の排気浄化装置において、上記ＮＯx選択還元触媒上流の機関排気通路内に酸化触媒を配置し、該酸化触媒におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときには燃焼室から排出される排気ガス中のＮＯxに対するＮＯ2の比率が５０パーセント以上になるように燃焼を制御するようにした内燃機関の排気浄化装置。 The the NO x selective reduction catalyst arranged in the engine exhaust passage and adapted to selectively reduce NO x contained in the exhaust gas by the ammonia generated from the urea to supply urea to the the NO x selective reduction catalyst In the exhaust gas purification apparatus for an internal combustion engine, an oxidation catalyst is disposed in the engine exhaust passage upstream of the NO x selective reduction catalyst, and the combustion chamber is in an engine operating state in which the conversion rate from NO to NO 2 in the oxidation catalyst becomes negative. An exhaust purification device for an internal combustion engine, in which combustion is controlled so that the ratio of NO 2 to NO x in the exhaust gas discharged from the engine becomes 50% or more. ほぼ全ての機関運転状態において上記ＮＯx選択還元触媒に流入する排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるように燃焼を制御する請求項１に記載の内燃機関の排気浄化装置。 The exhaust purification of an internal combustion engine according to claim 1, wherein the combustion is controlled so that the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst is substantially 50% in almost all engine operating states. apparatus. 上記ＮＯx選択還元触媒に流入する排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるようにＥＧＲ率および燃料噴射時期のいずれか一方又は双方を制御するようにした請求項２に記載の内燃機関の排気浄化装置。 3. The EGR rate and / or fuel injection timing are controlled so that the ratio of NO 2 to NO x in the exhaust gas flowing into the NO x selective reduction catalyst is approximately 50%. An exhaust gas purification apparatus for an internal combustion engine as described. 機関排気通路内にＮＯx選択還元触媒を配置し、該ＮＯx選択還元触媒に尿素を供給して該尿素から発生するアンモニアにより排気ガス中に含まれるＮＯxを選択的に還元するようにした内燃機関の排気浄化装置において、上記ＮＯx選択還元触媒上流の機関排気通路内に酸化触媒を配置すると共に該酸化触媒を迂回するバイパス通路を設け、該酸化触媒におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときには燃焼室から排出された排気ガスをバイパス通路内に導びいて酸化触媒を経由せずにＮＯx選択還元触媒に流入させるようにした内燃機関の排気浄化装置。 The the NO x selective reduction catalyst arranged in the engine exhaust passage and adapted to selectively reduce NO x contained in the exhaust gas by the ammonia generated from the urea to supply urea to the the NO x selective reduction catalyst In the exhaust gas purification apparatus for an internal combustion engine, an oxidation catalyst is disposed in the engine exhaust passage upstream of the NO x selective reduction catalyst and a bypass passage is provided to bypass the oxidation catalyst, so that the conversion rate from NO to NO 2 in the oxidation catalyst An exhaust gas purification apparatus for an internal combustion engine in which exhaust gas discharged from a combustion chamber is introduced into a bypass passage and flows into a NO x selective reduction catalyst without passing through an oxidation catalyst when the engine is in a negative state. 上記酸化触媒におけるＮＯからＮＯ2への転換率がマイナスとなる機関運転状態のときには燃焼室から排出される排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるように燃焼を制御し、該酸化触媒におけるＮＯからＮＯ2への転換率がプラスとなる機関運転状態のときにはバイパス通路を閉鎖して燃焼室から排出された排気ガスを該酸化触媒に流入させると共に、上記ＮＯx選択還元触媒に流入する排気ガス中のＮＯxに対するＮＯ2の比率がほぼ５０パーセントになるように燃焼を制御する請求項４に記載の内燃機関の排気浄化装置。 Combustion is controlled so that the ratio of NO 2 to NO x in the exhaust gas discharged from the combustion chamber is approximately 50% when the engine is in an engine operating state in which the conversion rate of NO to NO 2 in the oxidation catalyst is negative. When the engine is in an engine operating state in which the conversion rate of NO to NO 2 in the oxidation catalyst is positive, the bypass passage is closed and the exhaust gas discharged from the combustion chamber flows into the oxidation catalyst, and the NO x selective reduction is performed. The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein combustion is controlled so that a ratio of NO 2 to NO x in the exhaust gas flowing into the catalyst is approximately 50%.
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