JP2005113801A - Exhaust emission control device for internal combustion engine - Google Patents

Exhaust emission control device for internal combustion engine Download PDF

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JP2005113801A
JP2005113801A JP2003349739A JP2003349739A JP2005113801A JP 2005113801 A JP2005113801 A JP 2005113801A JP 2003349739 A JP2003349739 A JP 2003349739A JP 2003349739 A JP2003349739 A JP 2003349739A JP 2005113801 A JP2005113801 A JP 2005113801A
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exhaust gas
storage catalyst
air
catalyst
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JP4039349B2 (en
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Koichiro Nakatani
好一郎 中谷
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Toyota Motor Corp
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02T10/40—Engine management systems

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  • Exhaust Gas After Treatment (AREA)
  • Electrical Control Of Air Or Fuel Supplied To Internal-Combustion Engine (AREA)
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Abstract

<P>PROBLEM TO BE SOLVED: To properly set regeneration time for an NOx storage catalyst in relation to an exhaust emission control device for an internal combustion engine. <P>SOLUTION: A reforming catalyst 13 is disposed in an engine exhaust passage, and downstream of the reforming catalyst 13, the NOx storage catalyst 15 is disposed to store NOx when an air-fuel ratio is lean, and emit stored NOx when the air-fuel ratio is rich. Relation between necessary regeneration time for regenerating the NOx storage catalyst 15 and exhaust gas quantity is preliminarily determined. An SOx emission process from the NOx storage catalyst 15 is executed through a regeneration period determined based on the relation. <P>COPYRIGHT: (C)2005,JPO&NCIPI

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.

流入する排気ガスの空燃比がリーンのときには排気ガス中に含まれるＮＯxを吸蔵し流入する排気ガスの空燃比が理論空燃比又はリッチになると吸蔵したＮＯxを放出するＮＯxトラップ触媒を機関排気通路内に配置し、ＮＯxトラップ触媒上流の排気通路から排気ガスを取込んでこの排気ガス中に燃料を供給することにより燃料を改質するようにした改質装置を具備し、ＮＯxトラップ触媒にトラップされているＮＯx量を推定し、ＮＯxトラップ触媒にトラップされているＮＯxを還元すべきときにはＮＯxトラップ触媒にトラップされていると推定されるＮＯxを還元するのに必要な量の改質燃料をＮＯxトラップ触媒に送り込むようにした内燃機関が公知である（特許文献１を参照）。
特開２００２−１６１７３５号公報 NO x trap catalyst an engine air-fuel ratio of the exhaust gas when the lean of releasing NO x air-fuel ratio of the exhaust gas which is occluded becomes the stoichiometric air-fuel ratio or rich for occluding NO x contained in the exhaust gas flowing into the inflowing was disposed in the exhaust passage, comprising a reformer which is adapted to reform the fuel by supplying the fuel from the NO x trap catalyst upstream of the exhaust passage to the exhaust gas by captures and exhaust gas, NO x estimating the amount of NO x trapped in the trapping catalyst, for the reduction of NO x which is the time to reduce the NO x trapped in the NO x trap catalyst is estimated to have been trapped in the NO x trap catalyst An internal combustion engine in which a required amount of reformed fuel is fed into a NO x trap catalyst is known (see Patent Document 1).
JP 2002-161735 A

ところで機関排気通路内に炭化水素を改質することのできる改質触媒を配置し、流入する排気ガスの空燃比がリーンのときには排気ガス中に含まれるＮＯxを吸蔵し流入する排気ガスの空燃比が理論空燃比又はリッチになると吸蔵したＮＯxを放出するＮＯx吸蔵触媒を改質触媒下流の機関排気通路内に配置し、ＮＯx吸蔵触媒に吸蔵されたＳＯxを放出すべきときには排気ガスの空燃比がリッチにされ、このとき排気ガス中に含まれる炭化水素が改質触媒により改質されるようにした場合には、機関の運転状態に応じて炭化水素の改質の程度が異なるために上述の公知の内燃機関におけるＮＯxの還元と同様な方法でもってＳＯxをＮＯx吸蔵触媒から放出させることはできない。 Meanwhile arranged reforming catalyst capable of reforming the hydrocarbon into the engine exhaust passage, empty the exhaust gas air-fuel ratio of the inflowing exhaust gas when the lean to occlude the NO x contained in the exhaust gas inflow ratio is arranged to the stoichiometric air-fuel ratio or the NO x storage catalyst and a reforming catalyst downstream of the engine exhaust passage that releases becomes rich the occluded NO x, exhaust the time to release the SO x occluded in the NO x storage catalyst When the air-fuel ratio of the gas is made rich, and the hydrocarbons contained in the exhaust gas are reformed by the reforming catalyst at this time, the degree of reforming of the hydrocarbons depends on the operating state of the engine. Due to the difference, SO x cannot be released from the NO x storage catalyst by the same method as the reduction of NO x in the known internal combustion engine.

即ち、改質触媒における炭化水素の改質率が高いほどＮＯx吸蔵触媒からのＳＯxの放出量が増大し、ＳＯxの放出に要する時間、即ちＮＯx吸蔵触媒の再生期間が短かくなる。ところで、排気ガス量が少なくなるほど炭化水素と改質触媒との接触時間が長くなるため炭化水素の改質率が高くなり、従ってこの点からみるとＮＯx吸蔵触媒の再生期間は排気ガス量が少なくなるにつれて短かくなる。 That is, the higher the hydrocarbon reforming rate in the reforming catalyst, the more the amount of SO x released from the NO x storage catalyst increases, and the shorter the time required for SO x release, that is, the regeneration period of the NO x storage catalyst. . By the way, the smaller the exhaust gas amount, the longer the contact time between the hydrocarbon and the reforming catalyst, and the higher the reforming rate of the hydrocarbon. Therefore, from this point of view, the exhaust gas amount is increased during the regeneration period of the NO x storage catalyst. It becomes shorter as it decreases.

一方、単位時間当りにＮＯx吸蔵触媒に送り込まれる炭化水素の量が少なくなるほどＮＯx吸蔵触媒からのＳＯx放出量は減少し、ＮＯx吸蔵触媒の再生期間が長くなる。この場合、排気ガス量が少なくなるほどＮＯx吸蔵触媒に送り込まれる炭化水素の量が少なくなり、この点からみるとＮＯx吸蔵触媒の再生期間は排気ガス量が少なくなるにつれて長くなる。このようにＳＯxの再生期間は排気ガス量に依存しており、従ってＮＯx吸蔵触媒からＳＯxを放出させるに当っては排気ガス量を考慮しなければならないことになる。 On the other hand, as the amount of hydrocarbons fed into the NO x storage catalyst per unit time decreases, the SO x release amount from the NO x storage catalyst decreases, and the regeneration period of the NO x storage catalyst becomes longer. In this case, the smaller the amount of exhaust gas, the smaller the amount of hydrocarbons sent to the NO x storage catalyst. From this point of view, the regeneration period of the NO x storage catalyst becomes longer as the amount of exhaust gas decreases. Thus, the regeneration period of SO x depends on the amount of exhaust gas, and therefore, the amount of exhaust gas must be taken into account when releasing SO x from the NO x storage catalyst.

従って１番目の発明では、機関排気通路内に炭化水素を改質することのできる改質触媒を配置し、流入する排気ガスの空燃比がリーンのときには排気ガス中に含まれるＮＯxを吸蔵し流入する排気ガスの空燃比が理論空燃比又はリッチになると吸蔵したＮＯxを放出するＮＯx吸蔵触媒を改質触媒下流の機関排気通路内に配置し、ＮＯx吸蔵触媒に吸蔵されたＳＯx量が予め定められた許容値を越えたときにＮＯx吸蔵触媒からＳＯxを放出させてＮＯx吸蔵触媒を再生させるのに必要な再生期間中、ＮＯx吸蔵触媒の温度をＳＯx放出温度に維持すると共に排気ガスの空燃比をリッチに維持するようにした内燃機関の排気浄化装置において、排気ガス量を推定する排気ガス量推定手段と、排気ガス量と再生期間との関係を記憶している記憶手段とを具備し、この関係から求められた再生期間中、ＮＯx吸蔵触媒の温度をＳＯx放出温度に維持すると共に排気ガスの空燃比をリッチに維持するようにしている。
２番目の発明では１番目の発明において、再生期間中に上述の関係に基づいて各排気ガス量におけるＮＯx吸蔵触媒の再生割合を求め、求められた再生割合を順次積算して再生割合の積算合計が１．０になったときに再生期間が完了したと判断される。
３番目の発明では１番目の発明において、排気ガス量を最小排気ガス量から増大させると、再生期間は減少して最小値に達した後に増大する。
４番目の発明では１番目の発明において、排気ガス温が高いほど再生期間は短かくなる。
５番目の発明では１番目の発明において、排気ガスの空燃比のリッチの度合が大きいほど再生期間は短かくなる。 Accordingly, in the first invention, a reforming catalyst capable of reforming hydrocarbons is disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, NO x contained in the exhaust gas is stored. air-fuel ratio of the inflowing exhaust gas is disposed in the stoichiometric air-fuel ratio or the NO x storage catalyst and a reforming catalyst downstream of the engine exhaust passage that releases becomes rich the occluded NO x, the NO x storage catalyst occluded SO x During the regeneration period required to regenerate the NO x storage catalyst by releasing SO x from the NO x storage catalyst when the amount exceeds a predetermined allowable value, the temperature of the NO x storage catalyst is changed to the SO x release temperature. The exhaust gas amount estimating means for estimating the exhaust gas amount and the relationship between the exhaust gas amount and the regeneration period are stored in the exhaust gas purification apparatus for an internal combustion engine that maintains the air-fuel ratio of the exhaust gas at a rich level. Storage means Provided, so as to maintain the air-fuel ratio of the exhaust gas rich while maintaining playing time obtained based on this relationship, the temperature of the NO x storage catalyst release SO x temperature.
In the second invention, in the first invention, during the regeneration period, the regeneration ratio of the NO x storage catalyst in each exhaust gas amount is obtained based on the above-mentioned relationship, and the obtained regeneration ratio is sequentially integrated to integrate the regeneration ratio. When the total reaches 1.0, it is determined that the playback period has been completed.
In the third invention, in the first invention, when the exhaust gas amount is increased from the minimum exhaust gas amount, the regeneration period decreases and increases after reaching the minimum value.
In the fourth invention, in the first invention, the regeneration period becomes shorter as the exhaust gas temperature becomes higher.
According to the fifth aspect, in the first aspect, the regeneration period becomes shorter as the degree of richness of the air-fuel ratio of the exhaust gas is larger.

ＮＯx吸蔵触媒の再生期間を適切に定めることができる。 The regeneration period of the NO x storage catalyst can be determined appropriately.

図１は本発明を圧縮着火式内燃機関に適用した場合を示している。
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 a case where the present invention is applied to 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の集合部は排気通路１２を介して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、この排気通路１２内に排気ガス中に含まれる炭化水素を軽質のＨＣや、ＣＯや、Ｈ2に改質することができる改質触媒１３が配置される。この改質触媒１３は例えば金属薄板からなる担体上に白金Ｐｔのような貴金属触媒を担持した酸化触媒からなる。また、排気タービン７ｂ下流の排気通路１４内には改質触媒１３よりも容量の大きい第２の触媒１５が配置されている。 On the other hand, the collective portion of the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7b of the exhaust turbocharger 7 through the exhaust passage 12, and the hydrocarbons contained in the exhaust gas in the exhaust passage 12 are converted into light HC and CO. Alternatively, a reforming catalyst 13 that can be reformed to H 2 is disposed. The reforming catalyst 13 is made of an oxidation catalyst in which a noble metal catalyst such as platinum Pt is supported on a carrier made of a thin metal plate, for example. A second catalyst 15 having a capacity larger than that of the reforming catalyst 13 is disposed in the exhaust passage 14 downstream of the exhaust turbine 7b.

排気マニホルド５と吸気マニホルド４とは排気ガス再循環（以下、ＥＧＲと称す）通路１６を介して互いに連結され、ＥＧＲ通路１６内には電子制御式ＥＧＲ制御弁１７が配置される。また、ＥＧＲ通路１６周りにはＥＧＲ通路１６内を流れるＥＧＲガスを冷却するための冷却装置１８が配置される。図１に示される実施例では機関冷却水が冷却装置１８内に導びかれ、機関冷却水によってＥＧＲガスが冷却される。一方、各燃料噴射弁３は燃料供給管１９を介してコモンレール２０に連結される。このコモンレール２０内へは電子制御式の吐出量可変な燃料ポンプ２１から燃料が供給され、コモンレール２０内に供給された燃料は各燃料供給管１９を介して燃料噴射弁３に供給される。   The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 16, and an electronically controlled EGR control valve 17 is disposed in the EGR passage 16. Further, a cooling device 18 for cooling the EGR gas flowing in the EGR passage 16 is disposed around the EGR passage 16. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 18, 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 20 through a fuel supply pipe 19. Fuel is supplied into the common rail 20 from an electronically controlled fuel pump 21 having a variable discharge amount, and the fuel supplied into the common rail 20 is supplied to the fuel injection valve 3 via each fuel supply pipe 19.

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。吸入空気量検出器８は吸入空気量を表す出力信号を発生し、この出力信号が対応するＡＤ変換器３７を介して入力ポート３５に入力される。改質触媒１３には改質触媒１３の温度を検出するための温度センサ２２が取付けられ、この温度センサ２２の出力信号は対応するＡＤ変換器３７を介して入力ポート３５に入力される。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、スロットル弁駆動用ステップモータ１０、ＥＧＲ制御弁１７、および燃料ポンプ２１に接続される。   The electronic control unit 30 is composed of a digital computer and includes 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 connected to each other by a bidirectional bus 31. It comprises. The intake air amount detector 8 generates an output signal representing the intake air amount, and this output signal is input to the input port 35 via the corresponding AD converter 37. A temperature sensor 22 for detecting the temperature of the reforming catalyst 13 is attached to the reforming catalyst 13, and an output signal of the temperature sensor 22 is input to the input port 35 via the corresponding AD converter 37. 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 throttle valve driving step motor 10, the EGR control valve 17, and the fuel pump 21 through corresponding drive circuits 38.

図１に示す実施例では第２の触媒１５がＮＯx吸蔵触媒からなる。このＮＯx吸蔵触媒１５は三次元網目構造のモノリス担体或いはペレット状担体上に担持されているか、又はハニカム構造をなすパティキュレートフィルタ上に担持されている。 In the embodiment shown in FIG. 1, the second catalyst 15 is composed of a NO x storage catalyst. The NO x storage catalyst 15 is supported on a monolith support or pellet support having a three-dimensional network structure, or is supported on a particulate filter having a honeycomb structure.

モノリス担体、ペレット状担体、或いはパティキュレートフィルタ上には例えばアルミナからなる触媒担体が担持されており、図２（Ａ）および（Ｂ）はこの触媒担体４５の表面部分の断面を図解的に示している。図２（Ａ）および（Ｂ）に示されるように触媒担体４５の表面上には貴金属触媒４６が分散して担持されており、更に触媒担体４５の表面上にはＮＯx吸収剤４７の層が形成されている。 A catalyst carrier made of alumina, for example, is supported on a monolithic carrier, a pellet-like carrier, or a particulate filter. FIGS. 2A and 2B schematically show a cross-section of the surface portion of the catalyst carrier 45. ing. As shown in FIGS. 2A and 2B, a noble metal catalyst 46 is dispersedly supported on the surface of the catalyst carrier 45, and a layer of NO x absorbent 47 is further provided on the surface of the catalyst carrier 45. Is formed.

本発明による実施例では貴金属触媒４６として白金Ｐｔが用いられており、ＮＯx吸収剤４７を構成する成分としては例えばカリウムＫ、ナトリウムＮａ、セシウムＣｓのようなアルカリ金属、バリウムＢａ、カルシウムＣａのようなアルカリ土類、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が用いられている。 In the embodiment according to the present invention, platinum Pt is used as the noble metal catalyst 46, and the constituents of the NO x absorbent 47 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, calcium Ca. At least one selected from alkaline earths such as these, lanthanum La, and rare earths such as yttrium Y is used.

機関吸気通路、燃焼室２およびＮＯx吸蔵触媒１５上流の排気通路内に供給された空気および燃料（炭化水素）の比を排気ガスの空燃比と称するとＮＯx吸収剤４７は排気ガスの空燃比がリーンのときにはＮＯxを吸収し、排気ガス中の酸素濃度が低下すると吸収したＮＯxを放出するＮＯxの吸放出作用を行う。なお、ＮＯx吸蔵触媒１５上流の排気通路内に燃料（炭化水素）或いは空気が供給されない場合には排気ガスの空燃比は燃焼室２内における空燃比に一致し、従ってこの場合にはＮＯx吸収剤４７は燃焼室２内における空燃比がリーンのときにはＮＯxを吸収し、燃焼室２内における酸素濃度が低下すると吸収したＮＯxを放出することになる。 When the ratio of air and fuel (hydrocarbon) supplied into the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NO x storage catalyst 15 is referred to as the air-fuel ratio of the exhaust gas, the NO x absorbent 47 is exhausted from the exhaust gas. ratio absorbs NO x when the lean, the oxygen concentration in the exhaust gas performs the absorbing and releasing action of the NO x that releases NO x absorbed to decrease. When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NO x storage catalyst 15, the air-fuel ratio of the exhaust gas coincides with the air-fuel ratio in the combustion chamber 2. Therefore, in this case, the NO x absorbent 47 absorbs NO x when the air-fuel ratio is lean in the combustion chamber 2, the oxygen concentration in the combustion chamber 2 will release the NO x absorbed to decrease.

即ち、ＮＯx吸収剤４７を構成する成分としてバリウムＢａを用いた場合を例にとって説明すると、排気ガスの空燃比がリーンのとき、即ち排気ガス中の酸素濃度が高いときには排気ガス中に含まれるＮＯは図２（Ａ）に示されるように白金Ｐｔ４６上において酸化されてＮＯ2となり、次いでＮＯx吸収剤４７内に吸収されて酸化バリウムＢａＯと結合しながら硝酸イオンＮＯ3 -の形でＮＯx吸収剤４７内に拡散する。このようにしてＮＯxがＮＯx吸収剤４７内に吸収される。排気ガス中の酸素濃度が高い限り白金Ｐｔ４６の表面でＮＯ2が生成され、ＮＯx吸収剤４７のＮＯx吸収能力が飽和しない限りＮＯ2がＮＯx吸収剤４７内に吸収されて硝酸イオンＮＯ3 -が生成される。 That is, the case where barium Ba is used as a component constituting the NO x absorbent 47 will be described as an example. When the air-fuel ratio of the exhaust gas is lean, that is, when the oxygen concentration in the exhaust gas is high, it is contained in the exhaust gas. As shown in FIG. 2 (A), NO is oxidized on platinum Pt 46 to become NO 2 , then absorbed into the NO x absorbent 47 and combined with barium oxide BaO in the form of nitrate ions NO 3 −. x Diffuses in the absorbent 47. In this way, NO x is absorbed in the NO x absorbent 47. Oxygen concentration in the exhaust gas, NO 2 is produced on the surface as long as the platinum Pt46 high, the NO x absorbent 47 of the NO x absorbing capability as long as NO 2 not to saturate been absorbed in the NO x absorbent 47 nitrate ions NO 3 - is generated.

これに対し、燃焼室２内における空燃比をリッチ或いは理論空燃比にすることによって、又は排気マニホルド５内に還元剤を供給することによって排気ガスの空燃比をリッチ或いは理論空燃比にすると排気ガス中の酸素濃度が低下するために反応が逆方向（ＮＯ3 -→ＮＯ2）に進み、斯くして図２（Ｂ）に示されるようにＮＯx吸収剤４７内の硝酸イオンＮＯ3 -がＮＯ2の形でＮＯx吸収剤４７から放出される。次いで放出されたＮＯxは排気ガス中に含まれる未燃ＨＣ，ＣＯによって還元される。 On the other hand, if the air-fuel ratio in the combustion chamber 2 is made rich or stoichiometric, or if the reducing agent is supplied into the exhaust manifold 5 to make the air-fuel ratio rich or stoichiometric, the exhaust gas The reaction proceeds in the reverse direction (NO 3 − → NO 2 ) due to a decrease in the oxygen concentration therein, so that the nitrate ions NO 3 − in the NO x absorbent 47 are formed as shown in FIG. 2 (B). It is released from the NO x absorbent 47 in the form of NO 2 . Next, the released NO x is reduced by unburned HC and CO contained in the exhaust gas.

このように排気ガスの空燃比がリーンであるとき、即ちリーン空燃比のもとで燃焼が行われているときには排気ガス中のＮＯxがＮＯx吸収剤４７内に吸収される。しかしながらリーン空燃比のもとでの燃焼が継続して行われるとその間にＮＯx吸収剤４７のＮＯx吸収能力が飽和してしまい、斯くしてＮＯx吸収剤４７によりＮＯxを吸収できなくなってしまう。そこで本発明による実施例ではＮＯx吸収剤４７の吸収能力が飽和する前に排気ガスの空燃比を一時的にリッチにし、それによってＮＯx吸収剤４７からＮＯxを放出させるようにしている。 In this way, when the air-fuel ratio of the exhaust gas is lean, that is, when combustion is performed under the lean air-fuel ratio, NO x in the exhaust gas is absorbed into the NO x absorbent 47. However becomes saturated the absorption of NO x capacity of the NO x absorbent 47 during the combustion of the fuel under a lean air-fuel ratio is continued, no longer able to absorb NO x by the NO x absorbent 47 and thus End up. Therefore, in this embodiment of the present invention to temporarily make the air before the absorbing capability of the NO x absorbent 47 becomes saturated, thereby so that to release the NO x from the NO x absorbent 47.

一方、排気ガス中にはＳＯ2も含まれており、このＳＯ2は白金Ｐｔ４６において酸化されてＳＯ3となる。次いでこのＳＯ3はＮＯx吸収剤４７内に吸収されて酸化バリウムＢａＯと結合しながら、硫酸イオンＳＯ4 2-の形でＮＯx吸収剤４７内に拡散し、安定した硫酸塩ＢａＳＯ4を生成する。しかしながらＮＯx吸収剤４７が強い塩基性を有するためにこの硫酸塩ＢａＳＯ4は安定していて分解しづらく、排気ガスの空燃比を単にリッチにしただけでは硫酸塩ＢａＳＯ4は分解されずにそのまま残る。従ってＮＯx吸収剤４７内には時間が経過するにつれて硫酸塩ＢａＳＯ4が増大することになり、斯くして時間が経過するにつれてＮＯx吸収剤４７が吸収しうるＮＯx量が低下することになる。 On the other hand, SO 2 is also contained in the exhaust gas, and this SO 2 is oxidized in platinum Pt 46 to become SO 3 . Next, this SO 3 is absorbed in the NO x absorbent 47 and bonded to the barium oxide BaO, while diffusing into the NO x absorbent 47 in the form of sulfate ions SO 4 2− to produce stable sulfate BaSO 4 . To do. However, since the NO x absorbent 47 has a strong basicity, this sulfate BaSO 4 is stable and difficult to decompose, and if the air-fuel ratio of the exhaust gas is simply made rich, the sulfate BaSO 4 is not decomposed and remains as it is. Remain. Thus will be sulfates BaSO 4 increases as NO x time to absorbent 47 has elapsed, that the amount of NO x the NO x absorbent 47 can absorb as thus to time has elapsed is reduced Become.

ところが、ＮＯx吸蔵触媒１５の温度をＳＯx放出温度まで上昇させた状態で排気ガスの空燃比をリッチにするとＮＯx吸収剤４７からＳＯxが放出される。従って本発明による実施例ではＮＯx吸収剤４７に吸収されているＳＯx量が増大したときにはＮＯx吸蔵触媒１５の温度をＳＯx放出温度まで上昇させて排気ガスの空燃比をリッチにするようにしている。 However, if the air-fuel ratio of the exhaust gas is made rich while the temperature of the NO x storage catalyst 15 is raised to the SO x release temperature, SO x is released from the NO x absorbent 47. Therefore, in the embodiment according to the present invention, when the amount of SO x absorbed in the NO x absorbent 47 increases, the temperature of the NO x storage catalyst 15 is raised to the SO x release temperature to make the air-fuel ratio of the exhaust gas rich. I have to.

図３はＮＯxおよびＳＯxの放出制御のタイムチャートを示している。図３に示されるようにＮＯx吸収剤４７に吸収されているＮＯx吸収量の積算値ΣＮＯＸが許容値ＮＸを越える毎にＮＯx吸蔵触媒１５に流入する排気ガスの空燃比Ａ／Ｆがリーンからリッチに一時的に切換えられる。このときＮＯxがＮＯx吸収剤４７から放出され、還元される。 FIG. 3 shows a time chart of NO x and SO x release control. As shown in FIG. 3, the air-fuel ratio A / F of the exhaust gas flowing into the NO x storage catalyst 15 is calculated every time the integrated value ΣNOX of the NO x absorption amount absorbed by the NO x absorbent 47 exceeds the allowable value NX. Temporarily switched from lean to rich. At this time, NO x is released from the NO x absorbent 47 and reduced.

一方、ＮＯx吸収剤４７に吸収されているＳＯx量の積算値ΣＳＯＸも算出されており、このＳＯx量の積算値ΣＳＯＸが許容値ＳＸを越えるとＮＯx吸収剤４７からのＳＯx放出作用が行われる。即ち、まず初めにＮＯx吸蔵触媒１５の温度ＴＣがＳＯx放出温度ＴＸに達するまで上昇せしめられる。このＳＯx放出温度ＴＸは６００℃以上である。 On the other hand, the integrated value ΣSOX of the SO x amount absorbed in the NO x absorbent 47 is also calculated. If the integrated value ΣSOX of the SO x amount exceeds the allowable value SX, the SO x release from the NO x absorbent 47 is performed. The action is performed. That is, first, the temperature TC of the NO x storage catalyst 15 is raised until it reaches the SO x release temperature TX. The SO x release temperature TX is 600 ° C. or higher.

ＮＯx吸蔵触媒１５の温度ＴＣがＳＯx放出温度ＴＸに達するとＮＯx吸蔵触媒１５に流入する排気ガスの空燃比がリーンからリッチに切換えられ、ＮＯx吸収剤４７からのＳＯxの放出が開始される。ＳＯxが放出されている間、ＮＯx吸蔵触媒１５の温度ＴＣはＳＯx放出温度ＴＸに保持され、排気ガスの空燃比はリッチに維持される。次いでＳＯx放出作用が完了するとＮＯx吸蔵触媒１５の昇温作用は停止され、排気ガスの空燃比がリーンに戻される。 Air-fuel ratio of the exhaust gas temperature TC of the NO x storing catalyst 15 flows into the NO x storage catalyst 15 reaches the release of SO x temperature TX is switched from lean to rich, the release of the SO x from the NO x absorbent 47 Be started. While SO x is released, the temperature TC of the NO x storage catalyst 15 is maintained at the SO x release temperature TX, and the air-fuel ratio of the exhaust gas is maintained rich. Next, when the SO x releasing action is completed, the temperature raising action of the NO x storage catalyst 15 is stopped, and the air-fuel ratio of the exhaust gas is returned to lean.

上述したようにＮＯx吸蔵触媒１５からＳＯxを放出すべきときにはＮＯx吸蔵触媒１５の温度がＳＯx放出温度ＴＸに達するまで上昇せしめられる。次にこのようにＮＯx吸蔵触媒１５の温度ＴＣを上昇させる方法について図４を参照しつつ説明する。 When as described above from the NO x storage catalyst 15 should be released SO x is the temperature of the NO x storing catalyst 15 is raised until it reaches the release of SO x temperature TX. Next, a method for increasing the temperature TC of the NO x storage catalyst 15 will be described with reference to FIG.

ＮＯx吸蔵触媒１５の温度ＴＣを上昇させるのに有効な方法の一つは燃料噴射時期を圧縮上死点以後まで遅角させる方法である。即ち、通常主燃料Ｑmは図４において、（Ｉ）に示されるように圧縮上死点付近で噴射される。この場合、図４の（II）に示されるように主燃料Ｑmの噴射時期が遅角されると後燃え期間が長くなり、斯くして排気ガス温が上昇する。排気ガス温が高くなるとそれに伴ってＮＯx吸蔵触媒１５の温度ＴＣが上昇する。 One effective method for increasing the temperature TC of the NO x storage catalyst 15 is to retard the fuel injection timing until after the compression top dead center. That is, normally the main fuel Q m in FIG. 4, it is injected near compression top dead center as shown in (I). In this case, the main injection timing of fuel Q m is burning period becomes longer after the is retarded as shown in (II) of FIG. 4, the exhaust gas temperature rises in thus. As the exhaust gas temperature increases, the temperature TC of the NO x storage catalyst 15 increases accordingly.

また、ＮＯx吸蔵触媒１５の温度ＴＣを上昇させるために図４の（III）に示されるように主燃料Ｑmに加え、吸気上死点付近において補助燃料Ｑvを噴射することもできる。このように補助燃料Ｑvを追加的に噴射すると補助燃料Ｑv分だけ燃焼せしめられる燃料が増えるために排気ガス温が上昇し、斯くしてＮＯx吸蔵触媒１５の温度ＴＣが上昇する。
一方、このように吸気上死点付近において補助燃料Ｑvを噴射すると圧縮行程中に圧縮熱によってこの補助燃料Ｑvからアルデヒド、ケトン、パーオキサイド、一酸化炭素等の中間生成物が生成され、これら中間生成物によって主燃料Ｑmの反応が加速される。従ってこの場合には図４の（III）に示されるように主燃料Ｑmの噴射時期を大巾に遅らせても失火を生ずることなく良好な燃焼が得られる。即ち、このように主燃料Ｑmの噴射時期を大巾に遅らせることができるので排気ガス温はかなり高くなり、斯くしてＮＯx吸蔵触媒１５の温度ＴＣをすみやかに上昇させることができる。 Further, in order to increase the temperature TC of the NO x storage catalyst 15, it is possible to inject the auxiliary fuel Q v in the vicinity of the intake top dead center in addition to the main fuel Q m as shown in FIG. Thus the auxiliary fuel Q v additionally inject auxiliary fuel Q v amount corresponding exhaust gas temperature for the fuel to be burned increases rises, the temperature TC of the NO x storing catalyst 15 rises and thus.
On the other hand, in this way the intake top dead center near the aldehyde from this auxiliary fuel Q v due to the heat of compression in the auxiliary fuel Q v compressed and injects stroke in, ketones, peroxides, intermediate products such as carbon monoxide is generated, these intermediate products cause the reaction of the main fuel Q m is accelerated. Therefore, in this case it is good combustion without causing a misfire even delaying the injection timing of the main fuel Q m to greatly as shown in (III) of FIG. 4 is obtained. That is, in this way be mainly because the fuel Q m injection timing of the can be delayed by a large margin the exhaust gas temperature is considerably high, it is possible to quickly raise the temperature TC of the NO x storing catalyst 15 and thus.

また、ＮＯx吸蔵触媒１５の温度ＴＣを上昇させるために図４の（IV）に示されるように主燃料Ｑmに加え、膨張行程中又は排気行程中に補助燃料Ｑpを噴射することもできる。即ち、この場合、大部分の補助燃料Ｑpは燃焼することなく未燃ＨＣの形で排気通路内に排出される。この未燃ＨＣはＮＯx吸蔵触媒１５上において過剰酸素により酸化され、このとき発生する酸化反応熱によってＮＯx吸蔵触媒１５の温度ＴＣが上昇せしめられる。 Further, in order to increase the temperature TC of the NO x storage catalyst 15, in addition to the main fuel Q m as shown in FIG. 4 (IV), the auxiliary fuel Q p may be injected during the expansion stroke or the exhaust stroke. it can. That is, in this case, most of the auxiliary fuel Q p is discharged into the exhaust passage in the form of unburned HC without burning. The unburned HC is oxidized on the NO x storage catalyst 15 by excess oxygen, and the temperature TC of the NO x storage catalyst 15 is raised by the oxidation reaction heat generated at this time.

図５は、ＮＯx吸蔵触媒１５からＳＯxを放出させてＮＯx吸蔵触媒１５を再生させるのに必要な再生時期間Ｒtと空間速度ＳＶとの関係を示している。なお、図５において太い実線は改質触媒１３が基準温度である場合を示しており、細い実線は改質触媒１３の温度が基準温度よりも高い場合を示している。また、図５において各破線Ｒ1，Ｒ2，Ｒ3，Ｒ4は改質触媒１３における改質率が等しい等改質率曲線を表わしており、Ｒ1からＲ4に向けて改質率が次第に高くなる（Ｒ1＜Ｒ2＜Ｒ3＜Ｒ4）。 Figure 5 shows the relationship between the NO x from storing catalyst 15 to release the SO x regeneration time period required to reproduce the NO x storage catalyst 15 R t and space velocity SV. In FIG. 5, a thick solid line indicates a case where the reforming catalyst 13 is at the reference temperature, and a thin solid line indicates a case where the temperature of the reforming catalyst 13 is higher than the reference temperature. In FIG. 5, each broken line R 1 , R 2 , R 3 , R 4 represents an equal reforming rate curve in which the reforming rate in the reforming catalyst 13 is equal, and the reforming rate from R 1 to R 4. Gradually increases (R 1 <R 2 <R 3 <R 4 ).

空間速度ＳＶは（単位時間当りに触媒を流通する排気ガスの容積流量／触媒の容積）で表される。本発明による実施例ではいずれの触媒１３，１５における空間速度ＳＶを用いても再生期間の変化パターンは同様の形状となるので図５の横軸としてはいずれの触媒１３，１５における空間速度ＳＶを用いてもよい。なお、触媒１３，１５の容積は一定であるので空間速度ＳＶは排気ガスの容積流量で代表することができ、従って図５は排気ガスの容積流量（以下、単に排気ガス量という）と再生期間Ｒtとの関係を示しているとも言える。なお、排気ガス量はほぼ吸入空気量に比例するので吸入空気量検出器８により検出された吸入空気量から排気ガス量を推定することができる。 The space velocity SV is expressed by (volumetric flow rate of exhaust gas flowing through the catalyst per unit time / volume of catalyst). In the embodiment according to the present invention, the change pattern of the regeneration period has the same shape regardless of the space velocity SV in any of the catalysts 13 and 15, so the horizontal axis in FIG. 5 shows the space velocity SV in any of the catalysts 13 and 15. It may be used. Since the volumes of the catalysts 13 and 15 are constant, the space velocity SV can be represented by the exhaust gas volume flow rate. Therefore, FIG. 5 shows the exhaust gas volume flow rate (hereinafter simply referred to as the exhaust gas amount) and the regeneration period. it can be said that shows the relationship between the R t. Since the exhaust gas amount is substantially proportional to the intake air amount, the exhaust gas amount can be estimated from the intake air amount detected by the intake air amount detector 8.

太い実線上の白丸は改質率Ｒ1，Ｒ2，Ｒ3，Ｒ4は表す各破線との交点を示している。従って各白丸に注目すると空間速度ＳＶが低くなるほど、即ち排気ガス量が少なくなるほど改質率が高くなっていくことがわかる（Ｒ1→Ｒ2→Ｒ3→Ｒ4）。即ち、空間速度ＳＶが低くなるほど、即ち排気ガス量が少なくなるほど排気ガス中に含まれる炭化水素と改質触媒１３との接触時間が長くなり、従って空間速度ＳＶが低くなるほど改質率が高くなる。 The white circles on the thick solid line indicate the intersections with the respective broken lines that represent the reforming rates R 1 , R 2 , R 3 , and R 4 . Accordingly, when attention is paid to each white circle, it can be seen that the lower the space velocity SV, that is, the smaller the exhaust gas amount, the higher the reforming rate (R 1 → R 2 → R 3 → R 4 ). That is, the lower the space velocity SV, that is, the smaller the amount of exhaust gas, the longer the contact time between the hydrocarbons contained in the exhaust gas and the reforming catalyst 13, and the lower the space velocity SV, the higher the reforming rate. .

このように空間速度ＳＶが低くなると改質率が高くなるが図５の白丸からわかるように改質率が高くなっても必ずしも再生時間Ｒtは短かくはならない。これはＮＯx吸蔵触媒１５に送り込まれる炭化水素の絶対量がＳＯxの放出量に大きな影響を与えるからである。即ち、ＮＯx吸蔵触媒１５に送り込まれる炭化水素の絶対量が多くなるほどＳＯxの放出量が多くなるからである。この場合、ＮＯx吸蔵触媒１５に送り込まれる炭化水素の量は空間速度ＳＶ、即ち排気ガス量に比例し、空間速度ＳＶが高くなるほど、即ち排気ガス量が増大するほどＳＯxの放出量が多くなる。 Having thus the space velocity SV is the modification rate increases lower necessarily reproduction time R t be modified rate becomes high as can be seen from the white circle in FIG. 5 is not short. This is because the absolute amount of hydrocarbons sent to the NO x storage catalyst 15 greatly affects the amount of SO x released. That is, as the absolute amount of hydrocarbons sent to the NO x storage catalyst 15 increases, the amount of released SO x increases. In this case, the amount of hydrocarbons fed into the NO x storage catalyst 15 is proportional to the space velocity SV, that is, the exhaust gas amount, and the higher the space velocity SV, that is, the greater the exhaust gas amount, the greater the amount of SO x released. Become.

このように空間速度ＳＶが高くなるほど、即ち排気ガス量が増大するほどＳＯxの放出量が増大するので再生時間Ｒtは短かくなるはずである。しかしながら空間速度ＳＶが高くなると、即ち排気ガス量が増大すると改質率が低下するので図５に示されるように排気ガス量を最小排気ガス量から増大させると、再生期間Ｒtは減少して最小値に達した後に増大することになる。即ち、再生時間Ｒtの変化は下に凸の曲線で表されることになる。 Thus, the higher the space velocity SV, that is, the greater the amount of exhaust gas, the greater the amount of SO x released, so the regeneration time R t should be shorter. However, as the space velocity SV increases, that is, the amount of exhaust gas increases, the reforming rate decreases. Therefore, when the exhaust gas amount is increased from the minimum exhaust gas amount as shown in FIG. 5, the regeneration period R t decreases. It will increase after reaching the minimum value. That is, the change of the reproduction time R t will be expressed by the downward convex curve.

また、図５において細い実線で示されるように改質触媒１３の温度が高い場合には再生時間Ｒtはあらゆる空間速度ＳＶに対して短かくなる。なお、本発明による実施例では改質触媒１５の種々の温度について再生時間Ｒtと排気ガス量との関係が予めＲＯＭ３２内に記憶されている。また、図５は排気ガスのリッチの度合が基準度合のとき、例えば排気ガスの空燃比が１４．０のときの再生時間Ｒtを示している。排気ガスの空燃比をリッチにしたときにはリッチの度合が大きくなるほど、即ち空燃比Ａ／Ｆが小さくなるほど再生時間Ｒtは短かくなり、実際の再生時間Ｒtは図５から求められた再生時間Ｒtに図６に示される補正係数Ｋを乗算した値となる。 Further, reproduction time R t in the case the temperature of the reforming catalyst 13 as indicated by the thin solid line in FIG. 5 is high short nucleating for any space velocity SV. In the embodiment according to the present invention, the relationship between the regeneration time R t and the exhaust gas amount is stored in advance in the ROM 32 for various temperatures of the reforming catalyst 15. FIG. 5 shows the regeneration time R t when the exhaust gas rich degree is the reference degree, for example, when the air-fuel ratio of the exhaust gas is 14.0. When the air-fuel ratio of the exhaust gas is made rich, the regeneration time R t becomes shorter as the degree of richness increases, that is, as the air-fuel ratio A / F decreases, and the actual regeneration time R t is the regeneration time obtained from FIG. to R t becomes a value obtained by multiplying the correction coefficient K shown in FIG.

図５および図６を用いて実際の再生時間Ｒtが求まると機関が定常運転をしているときであればこの再生時間ＲtだけＮＯx吸蔵触媒１５の温度をＳＯx放出温度ＴＸに保持しかつ排気ガスの空燃比をリッチに維持すればＮＯx吸蔵触媒１５を再生することができる。しかしながら実際には再生中に機関の運転状態が変化し、排気ガス量や改質触媒１３の温度が変化する。従って本発明による実施例では次のようにして再生が完了したか否かを判断するようにしている。 When the actual regeneration time R t is obtained using FIG. 5 and FIG. 6, the temperature of the NO x storage catalyst 15 is maintained at the SO x release temperature TX only during the regeneration time R t when the engine is in steady operation. In addition, if the air-fuel ratio of the exhaust gas is maintained rich, the NO x storage catalyst 15 can be regenerated. In practice, however, the operating state of the engine changes during regeneration, and the amount of exhaust gas and the temperature of the reforming catalyst 13 change. Therefore, in the embodiment according to the present invention, it is determined whether or not the reproduction is completed as follows.

即ち、今或る運転状態が継続していてこの運転状態のときの再生時間をＲtとする。この運転状態がΔｔ時間継続すればこの間にΔｔ／Ｒtだけ再生が完了したことになる。従って順次行われる運転状態において夫々再生割合Δｔ／Ｒtを求め、この再生割合Δｔ／Ｒtを順次積算して再生割合Δｔ／Ｒtの積算合計を求め、この積算合計が１．０になると全てのＳＯxが放出されたことになる。従って再生割合Δｔ／Ｒtの積算合計が１．０になったときに再生期間が完了したと判断される。 That is, let R t be the regeneration time when a certain operating state is continuing and in this operating state. If this operating state continues for Δt time, regeneration is completed during this time by Δt / R t . Thus calculated respectively playback ratio Delta] t / R t in the operating state sequentially performed, the reproduction rate Delta] t / R t by sequentially integrating seeking a running total of the reproduction rate Delta] t / R t, this running total of 1.0 All SO x has been released. Accordingly, it is determined that the reproduction period is completed when the total sum of the reproduction ratios Δt / R t reaches 1.0.

図７にＮＯxおよびＳＯxの放出処理ルーチンを示す。
図７を参照するとまず初めにステップ５０においてＮＯx吸蔵触媒１５のＮＯx吸収剤４７に単位時間当り吸収されるＮＯx吸収量Ａが算出される。単位時間当りに機関から排出されるＮＯx量は要求トルクＴＱと機関回転数Ｎの関数であり、従って単位時間当りにＮＯx吸収剤４７に吸収されるＮＯx吸収量Ａは要求トルクＴＱと機関回転数Ｎの関数となる。本発明による実施例では要求トルクＴＱと機関回転数Ｎに応じた単位時間当りのＮＯx吸収量Ａが予め実験により求められており、このＮＯx吸収量Ａが要求トルクＴＱと機関回転数Ｎの関数として図８に示すようにマップの形で予めＲＯＭ３２内に記憶されている。 FIG. 7 shows the NO x and SO x release processing routine.
Absorption of NO x amount A to be absorbed per unit time in the NO x absorbent 47 of the NO x storing catalyst 15 is calculated first, at step 50 and reference to FIG. Amount of NO x discharged from the engine per unit time is a function of the required torque TQ and the engine rotational speed N, hence absorption of NO x amount A is absorbed in the NO x absorbent 47 per unit time and the required torque TQ It is a function of the engine speed N. In the embodiment according to the present invention, the NO x absorption amount A per unit time corresponding to the required torque TQ and the engine speed N is obtained in advance by experiment, and this NO x absorption amount A is obtained from the required torque TQ and the engine speed N. As shown in FIG. 8, it is stored in the ROM 32 in advance in the form of a map.

次いでステップ５１ではＮＯx吸収量ΣＮＯＸにＡが加算される。次いでステップ５２ではＮＯx吸収量ΣＮＯＸが許容値ＮＸを越えたか否かが判別される。ΣＮＯＸ＞ＮＸになるとステップ５３に進み、排気ガスの空燃比を一時的にリッチにするリッチ処理が行われる。このときＮＯxがＮＯx吸蔵触媒１５から放出される。次いでステップ５４ではΣＮＯＸがクリアされる。 Next, at step 51, A is added to the NO x absorption amount ΣNOX. Next, at step 52, it is judged if the NO x absorption amount ΣNOX has exceeded the allowable value NX. When ΣNOX> NX, the routine proceeds to step 53 where rich processing for temporarily enriching the air-fuel ratio of the exhaust gas is performed. At this time, NO x is released from the NO x storage catalyst 15. Next, at step 54, ΣNOX is cleared.

次いでステップ５５では燃料噴射量Ｑに定数ｋＫを乗算した値ｋＫ・ＱがΣＳＯＸに加算される。燃料中には一定量のイオウが含まれており、従って単位時間当りにＮＯx吸蔵触媒１５に吸蔵されるＳＯx量はｋＫ・Ｑで表わすことができる。従ってｋＫ・ＱにΣＳＯＸを加算することによって得られるΣＳＯＸはＮＯx吸蔵触媒１５に吸蔵されたＳＯx量の積算値を表わしている。次いでステップ５６ではＳＯx量の積算値ΣＳＯＸが許容値ＳＸを越えたか否かが判別される。ΣＳＯＸ≦ＳＸのときには処理サイクルを完了し、ΣＳＯＸ＞ＳＸになるとステップ５７に進んでＳＯx放出処理が行われる。このＳＯx放出処理を行うためのルーチンが図９に示されている。 Next, at step 55, a value kK · Q obtained by multiplying the fuel injection amount Q by a constant kK is added to ΣSOX. The fuel contains a certain amount of sulfur. Therefore, the amount of SO x stored in the NO x storage catalyst 15 per unit time can be expressed by kK · Q. Therefore, ΣSOX obtained by adding ΣSOX to kK · Q represents an integrated value of the amount of SO x stored in the NO x storage catalyst 15. Next, at step 56, it is judged if the integrated value ΣSOX of the SO x amount exceeds the allowable value SX. When ΣSOX ≦ SX, the processing cycle is completed, and when ΣSOX> SX, the routine proceeds to step 57 where SO x releasing processing is performed. A routine for performing this SO x releasing process is shown in FIG.

図９を参照するとまず初めにステップ６０においてＮＯx吸蔵触媒１５の昇温制御が行われる。次いでステップ６１ではＮＯx吸蔵触媒１５の温度ＴＣがＳＯx放出温度ＴＸ以上であるか否かが判別される。ＴＣ＜ＴＸのときにはステップ６０に戻る。一方、ＴＣ≧ＴＸになると、即ちＮＯx吸蔵触媒１５の温度ＴＣがＳＯx放出温度ＴＸ以上になるとステップ６２に進んでＳＯxの放出作用が開始される。 Referring to FIG. 9, first, in step 60, the temperature increase control of the NO x storage catalyst 15 is performed. Next, at step 61, it is judged if the temperature TC of the NO x storage catalyst 15 is equal to or higher than the SO x release temperature TX. When TC <TX, the process returns to step 60. On the other hand, when TC ≧ TX, that is, when the temperature TC of the NO x storage catalyst 15 becomes equal to or higher than the SO x release temperature TX, the routine proceeds to step 62 where the SO x release action is started.

即ち、ステップ６２では排気ガスの空燃比をリッチにするリッチ処理が行われ、それによってＳＯxの放出作用が開始される。次いでステップ６３では予め定められた一定時間Δｔが経過したか否かが判別される。一定時間Δｔが経過していないときにはステップ６３に戻り、一定時間Δｔが経過したときにはステップ６４に進む。即ち、Δｔ時間が経過する毎にステップ６４に進む。 That is, in step 62, a rich process for enriching the air-fuel ratio of the exhaust gas is performed, and thereby the SO x releasing action is started. Next, at step 63, it is judged if a predetermined time Δt has elapsed. When the fixed time Δt has not elapsed, the process returns to step 63, and when the fixed time Δt has elapsed, the process proceeds to step 64. That is, the process proceeds to step 64 every time Δt time elapses.

ステップ６４では吸入空気量検出器８により検出された吸入空気量から空間速度ＳＶが算出される。次いでステップ６５ではこの空間速度ＳＶと温度センサ２２により検出された改質触媒１３の温度とに基づいて図５に示す関係から排気ガス量に応じた再生期間Ｒtが算出される。次いでステップ６６では図６から空燃比Ａ／Ｆに応じた補正係数Ｋが求められ、この補正係数Ｋを再生期間Ｒtに乗算することによって最終的な再生時間Ｒtが算出される。 In step 64, the space velocity SV is calculated from the intake air amount detected by the intake air amount detector 8. Then the playback period R t corresponding to the amount of exhaust gas from the relationship shown in FIG. 5 on the basis of the temperature of the reforming catalyst 13 detected by the step 65 and the space velocity SV temperature sensor 22 is calculated. Then the correction coefficient K in accordance with the air-fuel ratio A / F is obtained from FIG. 6, step 66, the final reproduction time R t by multiplying the correction coefficient K in the reproduction period R t is calculated.

次いでステップ６７では一定時間Δｔを再生時間Ｒtで除した値、即ちΔｔ時間経過する間にＮＯx吸蔵触媒１５を再生した割合（Δｔ／Ｒt）が算出され、この再生割合（Δｔ／Ｒt）がΣ（Δｔ／Ｒt）に加算される。従ってΣ（Δｔ／Ｒt）は再生割合（Δｔ／Ｒt）の積算合計を表している。次いでステップ６８において再生割合の積算合計Σ（Δｔ／Ｒt）が１．０に達したか否かが判別される。Σ（Δｔ／Ｒt）＜１．０のときにはステップ６３に戻り、Σ（Δｔ／Ｒt）≧１．０となるとステップ６９に進んでＳＯxの放出作用が停止される。即ち、ステップ６９において昇温制御およびリッチ処理が停止され、次いでステップ７０においてΣＳＯＸおよびΣ（Δｔ／Ｒt）がクリアされる。 Next, at step 67, a value obtained by dividing the constant time Δt by the regeneration time R t , that is, a ratio (Δt / R t ) of regenerating the NO x storage catalyst 15 during the time Δt has elapsed, is calculated, and this regeneration ratio (Δt / R t ) is added to Σ (Δt / R t ). Therefore, Σ (Δt / R t ) represents the total sum of the reproduction ratios (Δt / R t ). Next, at step 68, it is judged if the total sum Σ (Δt / R t ) of the reproduction ratio has reached 1.0. When Σ (Δt / R t ) <1.0, the process returns to step 63. When Σ (Δt / R t ) ≧ 1.0, the routine proceeds to step 69 where the SO x releasing action is stopped. That is, the temperature increase control and the rich process are stopped in step 69, and then ΣSOX and Σ (Δt / R t ) are cleared in step 70.

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. ＮＯxの吸放出作用を説明するための図である。It is a diagram for explaining the absorbing and releasing action of NO x. ＮＯx吸収量ΣＮＯＸ、ＳＯx吸収量ΣＳＯＸ等を示すタイムチャートである。3 is a time chart showing NO x absorption amount ΣNOX, SO x absorption amount ΣSOX, and the like. 噴射制御を示す図である。It is a figure which shows injection control. 再生時間Ｒtと空間速度ＳＶの関係を示す図である。It is a figure which shows the relationship between reproduction time Rt and space velocity SV. 補正係数Ｋを示す図である。It is a figure which shows the correction coefficient K. ＮＯx、ＳＯx放出処理を行うためのフローチャートである。It is a flowchart for performing NO x and SO x release processing. ＮＯx吸収量のマップを示す図である。It is a diagram showing a map of the NO x absorption amount. ＳＯx放出処理を行うためのフローチャートである。It is a flow chart for performing the release of SO x treatment.

符号の説明Explanation of symbols

５…排気マニホルド
１３…改質触媒
１５…ＮＯx吸蔵触媒 5 ... exhaust manifold 13 ... reforming catalyst 15 ... NO x storage catalyst

Claims (5)

機関排気通路内に炭化水素を改質することのできる改質触媒を配置し、流入する排気ガスの空燃比がリーンのときには排気ガス中に含まれるＮＯxを吸蔵し流入する排気ガスの空燃比が理論空燃比又はリッチになると吸蔵したＮＯxを放出するＮＯx吸蔵触媒を該改質触媒下流の機関排気通路内に配置し、該ＮＯx吸蔵触媒に吸蔵されたＳＯx量が予め定められた許容値を越えたときにＮＯx吸蔵触媒からＳＯxを放出させてＮＯx吸蔵触媒を再生させるのに必要な再生期間中、ＮＯx吸蔵触媒の温度をＳＯx放出温度に維持すると共に排気ガスの空燃比をリッチに維持するようにした内燃機関の排気浄化装置において、排気ガス量を推定する排気ガス量推定手段と、排気ガス量と再生期間との関係を記憶している記憶手段とを具備し、該関係から求められた再生期間中、ＮＯx吸蔵触媒の温度をＳＯx放出温度に維持すると共に排気ガスの空燃比をリッチに維持するようにした内燃機関の排気浄化装置。 A reforming catalyst capable of reforming hydrocarbons is disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, the air-fuel ratio of the inflowing exhaust gas is occluded by storing NO x contained in the exhaust gas. There is arranged the stoichiometric air-fuel ratio or the NO x storage catalyst and reforming catalyst downstream of the engine exhaust passage that releases becomes rich the occluded NO x, SO x amount occluded in the the NO x storage catalyst is predetermined During the regeneration period required to regenerate the NO x storage catalyst by releasing SO x from the NO x storage catalyst when the allowable value is exceeded, the temperature of the NO x storage catalyst is maintained at the SO x release temperature and exhausted. In an exhaust gas purification apparatus for an internal combustion engine configured to maintain a rich air-fuel ratio of gas, exhaust gas amount estimating means for estimating an exhaust gas amount, and storage means for storing a relationship between the exhaust gas amount and a regeneration period From the relationship During Because was play duration, exhaust gas purification apparatus for an internal combustion engine so as to maintain the air-fuel ratio of the exhaust gas rich while maintaining the temperature of the NO x storage catalyst release SO x temperature. 再生期間中に上記関係に基づいて各排気ガス量におけるＮＯx吸蔵触媒の再生割合を求め、求められた再生割合を順次積算して再生割合の積算合計が１．０になったときに再生期間が完了したと判断される請求項１に記載の内燃機関の排気浄化装置。 During the regeneration period, the regeneration ratio of the NO x storage catalyst in each exhaust gas amount is obtained based on the above relationship, and the regeneration period is obtained when the obtained regeneration ratio is sequentially integrated and the cumulative total of the regeneration ratio reaches 1.0. The exhaust emission control device for an internal combustion engine according to claim 1, wherein it is determined that is completed. 排気ガス量を最小排気ガス量から増大させると、上記再生期間は減少して最小値に達した後に増大する請求項１に記載の内燃機関の排気浄化装置。   2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein when the exhaust gas amount is increased from the minimum exhaust gas amount, the regeneration period decreases and increases after reaching a minimum value. 排気ガス温が高いほど再生期間は短かくなる請求項１に記載の内燃機関の排気浄化装置。   The exhaust emission control device for an internal combustion engine according to claim 1, wherein the regeneration period becomes shorter as the exhaust gas temperature is higher. 排気ガスの空燃比のリッチの度合が大きいほど再生期間は短かくなる請求項１に記載の内燃機関の排気浄化装置。   The exhaust emission control device for an internal combustion engine according to claim 1, wherein the regeneration period becomes shorter as the richness of the air-fuel ratio of the exhaust gas becomes larger.
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