JP4285193B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

Info

Publication number
JP4285193B2
JP4285193B2 JP2003364865A JP2003364865A JP4285193B2 JP 4285193 B2 JP4285193 B2 JP 4285193B2 JP 2003364865 A JP2003364865 A JP 2003364865A JP 2003364865 A JP2003364865 A JP 2003364865A JP 4285193 B2 JP4285193 B2 JP 4285193B2
Authority
JP
Japan
Prior art keywords
nox
temperature
storage catalyst
catalyst
exhaust gas
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Fee Related
Application number
JP2003364865A
Other languages
Japanese (ja)
Other versions
JP2005127248A (en
Inventor
孝充 浅沼
信也 広田
泰彰 仲野
俊祐 利岡
耕平 吉田
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Toyota Motor Corp
Original Assignee
Toyota Motor Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyota Motor Corp filed Critical Toyota Motor Corp
Priority to JP2003364865A priority Critical patent/JP4285193B2/en
Publication of JP2005127248A publication Critical patent/JP2005127248A/en
Application granted granted Critical
Publication of JP4285193B2 publication Critical patent/JP4285193B2/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

Links

Images

Classifications

    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Landscapes

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

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.

リーン空燃比のもとで燃焼が行われている時に排気ガス中に含まれるＮＯｘを浄化するための触媒として、アルミナからなる担体の表面上にアルカリ金属あるいはアルカリ土類からなるＮＯｘ吸収剤の層を形成し、更に白金のような貴金属触媒を担体表面上に担持した触媒が公知である（例えば特許文献１参照）。この触媒では触媒が活性化すると排気ガスの空燃比がリーンの時には排気ガス中に含まれるＮＯｘがＮＯｘ吸収剤内に吸蔵され、排気ガスの空燃比がリッチにされるとＮＯｘ吸収剤に吸蔵されていたＮＯｘが放出され、還元される。   As a catalyst for purifying NOx contained in exhaust gas when combustion is performed under a lean air-fuel ratio, a layer of NOx absorbent made of alkali metal or alkaline earth on the surface of a carrier made of alumina. And a catalyst in which a noble metal catalyst such as platinum is supported on the surface of the support is known (see, for example, Patent Document 1). In this catalyst, when the catalyst is activated, NOx contained in the exhaust gas is stored in the NOx absorbent when the air-fuel ratio of the exhaust gas is lean, and is stored in the NOx absorbent when the air-fuel ratio of the exhaust gas is made rich. The NOx that has been released is released and reduced.

ところでこのようなＮＯｘの吸放出作用は触媒が活性化していないと行われないと考えられており、したがってこの特許文献１に記載された内燃機関では触媒が活性化していない時には電気ヒータにより触媒を加熱するようにしている。   By the way, it is considered that such NOx absorption / release action is not performed unless the catalyst is activated. Therefore, in the internal combustion engine described in Patent Document 1, when the catalyst is not activated, the catalyst is activated by an electric heater. I try to heat it.

特開平６−１０８８２６JP-A-6-108826 特開２００２−８９２４６JP 2002-89246

しかしながらこのようにＮＯｘの吸放出作用を行うようにした触媒について本発明者が研究を重ねた結果、排気ガス中に含まれる一酸化窒素ＮＯは触媒が活性化しないとＮＯｘ吸収剤に吸蔵されないが排気ガス中に含まれる二酸化窒素ＮＯ2は触媒が活性化しなくても、触媒活性時に一酸化窒素ＮＯが吸蔵されるのとは異なるメカニズムでＮＯｘ吸収剤に吸蔵（低温吸蔵）されることが判明したのである。 However, as a result of repeated studies by the present inventors on the catalyst that performs the NOx absorption / release action as described above, the nitric oxide NO contained in the exhaust gas is not stored in the NOx absorbent unless the catalyst is activated. It turns out that nitrogen dioxide NO 2 contained in the exhaust gas is stored in the NOx absorbent (stored at low temperature) by a mechanism different from that in which NO is stored when the catalyst is activated even if the catalyst is not activated. It was.

そして、このような本発明者により見出された事実、すなわち触媒が活性化していない状態においてもＮＯ2がＮＯｘ吸収剤に低温吸蔵されるということを利用すれば、従来よりも効率的に排気ガス中のＮＯｘを除去することが可能になる。しかしながらその一方で、このような場合において、触媒のＮＯｘ浄化能力（触媒の不活性時における低温吸蔵に基づくＮＯｘ浄化能力も含む）が、触媒状態すなわち触媒の劣化や硫黄被毒の程度によって大きく異なるために意図した通りの充分なＮＯｘの除去が行えない場合があることが判明した。そして更に、このような問題は、触媒の不活性時におけるＮＯｘ浄化能力が上記触媒状態によって大きな影響を受けることから、触媒の不活性時において特に顕著であることも判明した。 And by utilizing such facts found by the present inventors, that is, that NO 2 is stored in the NOx absorbent at a low temperature even when the catalyst is not activated, the exhaust gas can be exhausted more efficiently than before. It becomes possible to remove NOx in the gas. However, on the other hand, in such a case, the NOx purification capacity of the catalyst (including NOx purification capacity based on low-temperature occlusion when the catalyst is inactive) varies greatly depending on the catalyst state, that is, the degree of catalyst deterioration and sulfur poisoning. Therefore, it has been found that there is a case where sufficient NOx removal cannot be performed as intended. Further, it has been found that such a problem is particularly remarkable when the catalyst is inactive, since the NOx purification ability when the catalyst is inactive is greatly influenced by the catalyst state.

そこで、本発明では、触媒が活性化しない状態においても二酸化窒素ＮＯ2がＮＯｘ吸収剤に低温吸蔵されることを利用して排気ガスを浄化するようにした排気浄化装置において、上記触媒状態を考慮して排気ガスの浄化を行うことができる排気浄化装置を提供することを目的とする。 Therefore, in the present invention, in the exhaust purification device that purifies exhaust gas by utilizing the low temperature storage of nitrogen dioxide NO 2 in the NOx absorbent even when the catalyst is not activated, the catalyst state is considered. An object of the present invention is to provide an exhaust emission control device capable of purifying exhaust gas.

請求項１に記載の発明は、機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒と、該ＮＯｘ吸蔵触媒の活性状態に基づいて上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力を推定する手段と、を具備した内燃機関の排気浄化装置において、上記ＮＯｘ浄化能力推定手段は上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、該酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を大きく推定する排気浄化装置を提供する。 The invention according to claim 1 is a NOx storage catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and is activated when the air-fuel ratio of the inflowing exhaust gas is lean. when non will cold occlude nitrogen dioxide nO 2 contained in the exhaust gas in the NOx absorbent, a NOx storage catalyst to a high temperature storage of nitrogen oxides NOx in the exhaust gas in the NOx absorbent when being activated Means for estimating the NOx purification capacity of the NOx storage catalyst based on the active state of the NOx storage catalyst, wherein the NOx purification capacity estimation means is the oxidation performance of the NOx storage catalyst. comprise means for estimating the reduction degree of, as reduction degree of oxidation performance estimated by the oxidation degradation degree estimating means is high above NOx storage catalyst Serial to provide an exhaust purification device of the NOx purification capacity based on cold storage large estimates.

ＮＯｘ吸蔵触媒、すなわち貴金属触媒が活性化していない状態から完全に活性化している状態に移る過程においては、貴金属触媒における炭化水素ＨＣの酸化反応の際に二酸化窒素ＮＯ2の一酸化窒素ＮＯへの還元反応が起こる。また、排気ガス中に含まれる二酸化窒素ＮＯ2はＮＯｘ吸蔵触媒、すなわち貴金属触媒が活性化していなくてもＮＯｘ吸収剤に低温吸蔵されるが、排気ガス中に含まれる一酸化窒素ＮＯはＮＯｘ吸蔵触媒が活性化して二酸化窒素ＮＯ2に酸化されないとＮＯｘ吸収剤に高温吸蔵されない。 In the process of shifting from a state in which the NOx storage catalyst, that is, the precious metal catalyst is not activated to a fully activated state, during the oxidation reaction of hydrocarbon HC in the precious metal catalyst, nitrogen dioxide NO 2 is converted to nitric oxide NO. A reduction reaction occurs. Nitrogen dioxide NO 2 contained in the exhaust gas is occluded in the NOx absorbent at a low temperature even if the NOx occlusion catalyst, that is, the noble metal catalyst is not activated, but nitrogen monoxide NO contained in the exhaust gas is occluded in the NOx occlusion. Unless the catalyst is activated and oxidized to nitrogen dioxide NO 2 , it is not stored in the NOx absorbent at high temperature.

以上のようなことから、上記のような二酸化窒素ＮＯ2の一酸化窒素ＮＯへの還元反応が起こるとＮＯｘ吸蔵触媒が活性化されていない時におけるＮＯｘ浄化能力（すなわち、上記低温吸蔵に基づくＮＯｘ浄化能力）が低下することになる。一方、上述したように上記二酸化窒素ＮＯ2の一酸化窒素ＮＯへの還元反応は、貴金属触媒における炭化水素ＨＣの酸化反応に伴って生じるので、ＮＯｘ吸蔵触媒が劣化し貴金属触媒がシンタリングする等してその酸化性能が低下すると起こり難くなる。そして上記二酸化窒素ＮＯ2の一酸化窒素ＮＯへの還元反応が減少すれば、その結果として、上記ＮＯｘ吸蔵触媒が活性化されていない時における上記ＮＯｘ浄化能力の低下が抑制される。つまり、ＮＯｘ吸蔵触媒の酸化性能が低下すると上記ＮＯｘ吸蔵触媒が活性化されていない時における上記ＮＯｘ浄化能力の低下が抑制される。 As described above, when the reduction reaction of nitrogen dioxide NO 2 to nitric oxide NO occurs as described above, the NOx storage capacity when the NOx storage catalyst is not activated (that is, NOx based on the low temperature storage). (Purification capacity) will decrease. On the other hand, as described above, the reduction reaction of nitrogen dioxide NO 2 to nitric oxide NO occurs with the oxidation reaction of hydrocarbon HC in the noble metal catalyst, so that the NOx storage catalyst deteriorates and the noble metal catalyst is sintered, etc. If the oxidation performance is lowered, it is difficult to occur. If the reduction reaction of the nitrogen dioxide NO 2 to nitric oxide NO decreases, as a result, the decrease in the NOx purification capacity when the NOx storage catalyst is not activated is suppressed. In other words, reduction of the NOx purifying ability at the time when the oxidation performance of the NOx storage catalyst decreases Then the NOx storage catalyst is not activated can be suppressed.

請求項１に記載の発明によれば、上記ＮＯｘ吸蔵触媒の活性状態、例えば温度に基づいて上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力を推定する手段が、上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、推定された酸化性能の低下度合が高い程上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を大きく推定するようにされている。このようにすると結果的には、推定された酸化性能の低下度合が高い程、ＮＯｘ吸蔵触媒の活性の比較的低い状態（低活性側）におけるＮＯｘ浄化能力、すなわち例えばＮＯｘ吸蔵触媒の温度の低い場合におけるＮＯｘ浄化能力をより大きく推定することになる。より具体的には、例えばＮＯｘ吸蔵触媒の温度が酸化性能の低下度合によって定まる所定温度以下である範囲についてＮＯｘ浄化能力をより大きく推定するようにする。 According to the first aspect of the present invention, the means for estimating the NOx purification capacity of the NOx storage catalyst based on the active state of the NOx storage catalyst, for example, the temperature, estimates the degree of decrease in the oxidation performance of the NOx storage catalyst. The NOx purification ability based on the said low temperature storage of the said NOx storage catalyst is estimated largely, so that the fall degree of the estimated oxidation performance is high. As a result, as a result, the higher the estimated degree of decrease in the oxidation performance, the lower the NOx purification capacity in the state where the activity of the NOx storage catalyst is relatively low (low activity side), that is, for example, the lower the temperature of the NOx storage catalyst. In this case, the NOx purification capacity is estimated to be larger. More specifically, for example, the NOx purification capacity is estimated to be larger in a range where the temperature of the NOx storage catalyst is equal to or lower than a predetermined temperature determined by the degree of reduction in oxidation performance .

そして、このようにすることで、上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力、特にＮＯｘ吸蔵触媒の酸化性能の低下度合に影響を受け易い上記ＮＯｘ吸蔵触媒の活性の比較的低い状態におけるＮＯｘ浄化能力をより正確に推定することができる。そのため、このように推定されるＮＯｘ浄化能力に基づいて排気ガスの浄化を行うことで、意図した通りの充分なＮＯｘの除去を効率的に行うことが可能となる。
なお、本明細書においてＮＯｘ浄化能力とは例えば、ＮＯｘ吸蔵速度（単位時間当たりにＮＯｘ吸収剤に吸蔵されるＮＯｘ量）を意味する。 By doing so, the NOx purification ability of the NOx storage catalyst, in particular, the NOx purification ability in a relatively low activity state of the NOx storage catalyst that is easily affected by the degree of decrease in the oxidation performance of the NOx storage catalyst is further improved. It can be estimated accurately. Therefore, by performing exhaust gas purification based on the NOx purification capacity estimated in this way, it is possible to efficiently remove sufficient NOx as intended.
In this specification, the NOx purification capacity means, for example, the NOx occlusion speed (the amount of NOx occluded in the NOx absorbent per unit time).

請求項２に記載の発明は、機関排気通路内に配置された、貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒と、該ＮＯｘ吸蔵触媒の活性状態に基づいて上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力を推定する手段と、を具備した内燃機関の排気浄化装置において、上記ＮＯｘ浄化能力推定手段は上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、該硫黄被毒度合推定手段によって推定された硫黄被毒の度合が高い程、上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を小さく推定するようにした排気浄化装置を提供する。 The invention according to claim 2 is an NOx storage catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and activated when the air-fuel ratio of the inflowing exhaust gas is lean. NOx storage catalyst that stores nitrogen dioxide NO 2 contained in the exhaust gas in the NOx absorbent at a low temperature when it is not activated and stores NOx absorbent in the NOx absorbent at a high temperature when the NOx absorbent is activated And an NOx purification capacity of the NOx storage catalyst based on an active state of the NOx storage catalyst, wherein the NOx purification capacity estimation means is a sulfur of the NOx storage catalyst. Means for estimating the degree of poisoning, and the higher the degree of sulfur poisoning estimated by the sulfur poisoning degree estimating means, the lower the temperature of the NOx storage catalyst. To provide an exhaust purifying apparatus that estimates reduce the NOx purifying capability-based built.

上記ＮＯｘ吸蔵触媒が硫黄被毒されると上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力が低下することになるが、特に上記ＮＯｘ吸蔵触媒が活性化されていない時における上記ＮＯｘ浄化能力（すなわち、上記低温吸蔵に基づくＮＯｘ浄化能力）の低下が顕著である。   When the NOx occlusion catalyst is poisoned with sulfur, the NOx occlusion capacity of the NOx occlusion catalyst is reduced. In particular, the NOx occlusion capacity when the NOx occlusion catalyst is not activated (that is, the low temperature occlusion catalyst). The reduction in the NOx purification capacity based on the above is remarkable.

請求項２に記載の発明によれば、上記ＮＯｘ吸蔵触媒の活性状態、例えば温度に基づいて上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力を推定する手段が、上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、推定された硫黄被毒の度合が高い程上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を小さく推定するようにされている。このようにすると結果的には、推定された硫黄被毒の度合が高い程、ＮＯｘ吸蔵触媒の活性の比較的低い状態（低活性側）におけるＮＯｘ浄化能力、すなわち例えばＮＯｘ吸蔵触媒の温度の低い場合におけるＮＯｘ浄化能力をより小さく推定することになる。より具体的には、例えばＮＯｘ吸蔵触媒の温度が硫黄被毒度合によって定まる所定温度以下である範囲についてＮＯｘ浄化能力をより小さく推定するようにする。   According to the second aspect of the present invention, the means for estimating the NOx purification capacity of the NOx storage catalyst based on the active state of the NOx storage catalyst, for example, the temperature, estimates the degree of sulfur poisoning of the NOx storage catalyst. The NOx purification ability based on the said low temperature occlusion of the said NOx occlusion catalyst is estimated to be smaller as the estimated degree of sulfur poisoning is higher. Consequently, as a result, the higher the estimated degree of sulfur poisoning, the lower the NOx purification capacity in the state where the activity of the NOx storage catalyst is relatively low (low activity side), that is, for example, the temperature of the NOx storage catalyst is lower. In this case, the NOx purification capacity is estimated to be smaller. More specifically, for example, the NOx purification capacity is estimated to be smaller in a range where the temperature of the NOx storage catalyst is equal to or lower than a predetermined temperature determined by the degree of sulfur poisoning.

そして、このようにすることで、上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力、特にＮＯｘ吸蔵触媒の硫黄被毒の度合に影響を受け易い上記ＮＯｘ吸蔵触媒の活性の比較的低い状態におけるＮＯｘ浄化能力をより正確に推定することができる。そのため、このように推定されるＮＯｘ浄化能力に基づいて排気ガスの浄化を行うことで、意図した通りの充分なＮＯｘの除去を効率的に行うことが可能となる。   By doing so, the NOx purification capacity of the NOx storage catalyst, particularly the NOx purification capacity in a relatively low state of activity of the NOx storage catalyst that is easily affected by the degree of sulfur poisoning of the NOx storage catalyst is further improved. It can be estimated accurately. Therefore, by performing exhaust gas purification based on the NOx purification capacity estimated in this way, it is possible to efficiently remove sufficient NOx as intended.

請求項３に記載の発明では請求項１に記載の発明において、上記ＮＯｘ浄化能力推定手段が更に上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、推定された硫黄被毒の度合が高い程上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を小さく推定する。   According to a third aspect of the present invention, in the first aspect of the invention, the NOx purification capacity estimating means further includes means for estimating the degree of sulfur poisoning of the NOx storage catalyst, and the estimated sulfur poisoning. The higher the degree is, the smaller the NOx purification capacity of the NOx storage catalyst based on the low temperature storage is estimated.

請求項３に記載の発明によっても、特に上記ＮＯｘ吸蔵触媒の活性の比較的低い状態、すなわち例えば低温時におけるＮＯｘ浄化能力を正確に推定することができ、推定されるＮＯｘ浄化能力に基づいて排気ガスの浄化を行うことで、意図した通りの充分なＮＯｘの除去を効率的に行うことが可能となる。   According to the third aspect of the present invention, it is possible to accurately estimate the NOx purification capacity at a relatively low activity of the NOx storage catalyst, that is, for example, at a low temperature, and exhaust gas based on the estimated NOx purification capacity. By purifying the gas, it is possible to efficiently remove sufficient NOx as intended.

請求項４に記載の発明は、機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、機関の始動後に上記ＮＯｘ吸蔵触媒の温度を予め定めた目標温度以上に上昇させる昇温制御が実施される内燃機関の排気浄化装置において、更に上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、該酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記昇温制御の開始時期が遅れるようにされる、または、機関の始動から上記ＮＯｘ吸蔵触媒の温度が上記目標温度になるまでの時間が長くなるようにされる排気浄化装置を提供する。 The invention according to claim 4 is a NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and is activated when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx storage catalyst that stores nitrogen dioxide NO 2 contained in the exhaust gas in the NOx absorbent at a low temperature when it is not activated, and stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature when activated. In an exhaust gas purification apparatus for an internal combustion engine, in which temperature rise control is performed to increase the temperature of the NOx storage catalyst to a predetermined target temperature or higher after the engine is started, the degree of reduction in the oxidation performance of the NOx storage catalyst is further reduced . comprise means for estimating, as the degree of reduction in oxidation performance estimated by the oxidation degradation degree estimating means is high, is to start time of the temperature increase control is delayed Or the temperature of the NOx storage catalyst from the start of the engine to provide an exhaust purification device to be so that the time until the target temperature becomes longer.

請求項４に記載の発明によると、ＮＯｘ吸蔵触媒の酸化性能が低下している場合にはＮＯｘ吸蔵触媒の昇温が遅くなりＮＯｘ吸蔵触媒の温度の低い状態が長くされる。そして上述したようにＮＯｘ吸蔵触媒の酸化性能が低下している場合には低温側でのＮＯｘ浄化能力が上昇するので、本発明のようにＮＯｘ吸蔵触媒の温度の低い状態を長くすることで、効率的且つ充分なＮＯｘの除去が可能となる。 According to the fourth aspect of the present invention, when the oxidation performance of the NOx occlusion catalyst is lowered, the temperature rise of the NOx occlusion catalyst is delayed, and the low temperature state of the NOx occlusion catalyst is lengthened. And, as described above, when the oxidation performance of the NOx storage catalyst is lowered , the NOx purification ability on the low temperature side increases, so by increasing the low temperature state of the NOx storage catalyst as in the present invention, Efficient and sufficient removal of NOx becomes possible.

請求項５に記載の発明は、機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、機関の始動後に上記ＮＯｘ吸蔵触媒の温度を予め定めた目標温度以上に上昇させる昇温制御が実施される内燃機関の排気浄化装置において、更に上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、該硫黄被毒度合推定手段によって推定された硫黄被毒の度合が高い程、上記昇温制御の開始時期が早まるようにされる、または、機関の始動から上記ＮＯｘ吸蔵触媒の温度が上記目標温度になるまでの時間が短くなるようにされる排気浄化装置を提供する。 The invention according to claim 5 is a NOx storage catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and is activated when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx storage catalyst that stores nitrogen dioxide NO 2 contained in the exhaust gas in the NOx absorbent at a low temperature when it is not activated, and stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature when activated. In an exhaust gas purification apparatus for an internal combustion engine, in which temperature rise control is performed to increase the temperature of the NOx storage catalyst to a predetermined target temperature or higher after the engine is started, the degree of sulfur poisoning of the NOx storage catalyst is further increased. Means for estimating, and the higher the degree of sulfur poisoning estimated by the sulfur poisoning degree estimating means, the earlier the start timing of the temperature increase control, or Temperature from the start of the NOx storage catalyst related to provide an exhaust purification device which is as time until the target temperature is shortened.

請求項５に記載の発明によると、ＮＯｘ吸蔵触媒が硫黄被毒された場合にはＮＯｘ吸蔵触媒の昇温が速くなりＮＯｘ吸蔵触媒の温度の低い状態が短くされる。そして上述したようにＮＯｘ吸蔵触媒が硫黄被毒された場合には低温側でのＮＯｘ浄化能力が特に低下するので、本発明のようにＮＯｘ吸蔵触媒の温度の低い状態を短くすることで、充分なＮＯｘの除去の実現を図ることができる。   According to the fifth aspect of the present invention, when the NOx occlusion catalyst is poisoned with sulfur, the temperature rise of the NOx occlusion catalyst is accelerated and the low temperature state of the NOx occlusion catalyst is shortened. As described above, when the NOx storage catalyst is poisoned with sulfur, the NOx purification ability on the low temperature side is particularly lowered. Therefore, it is sufficient to shorten the low temperature state of the NOx storage catalyst as in the present invention. It is possible to realize the removal of NOx.

請求項６に記載の発明は、機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒と、該ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段とを具備し、機関の始動後に上記酸化性能低下度合推定手段によって推定された酸化性能の低下度合が所定の低下度合以上であれば上記ＮＯｘ吸蔵触媒の温度を低く維持するための低温維持制御が実施される内燃機関の排気浄化装置において、上記酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記低温維持制御の実施時間を長くする、または上記低温維持制御において維持する温度を低くするようにした排気浄化装置を提供する。 The invention according to claim 6 is a NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and is activated when the air-fuel ratio of the inflowing exhaust gas is lean. when non will cold occlude nitrogen dioxide nO 2 contained in the exhaust gas in the NOx absorbent, a NOx storage catalyst to a high temperature storage of nitrogen oxides NOx in the exhaust gas in the NOx absorbent when being activated , and means for estimating the reduction degree of the oxidation performance of the NOx storage catalyst, the long deterioration degree of oxidation performance estimated after the start of the engine by the oxidation degradation degree estimating means is equal to or greater than a predetermined reduction degree in the exhaust purification apparatus for an internal combustion engine cryostat control is performed for maintaining a low temperature of the NOx storage catalyst, which is estimated by the oxidation degradation degree estimating means The higher the degree of reduction of performance, to increase the execution time of the low temperature maintenance control, or to provide an exhaust gas purification apparatus adapted to lower the temperature to maintain in the cryostat control.

請求項６に記載の発明によると、ＮＯｘ吸蔵触媒の酸化性能が低下している場合にはＮＯｘ吸蔵触媒が温度の低い状態に長く維持されることになる。そして上述したようにＮＯｘ吸蔵触媒の酸化性能が低下している場合には低温側でのＮＯｘ浄化能力が上昇するので、本発明のようにＮＯｘ吸蔵触媒を温度の低い状態に長く維持することで、効率的且つ充分なＮＯｘの除去が可能となる。 According to the sixth aspect of the present invention, when the oxidation performance of the NOx storage catalyst is lowered , the NOx storage catalyst is maintained at a low temperature for a long time. As described above, when the oxidation performance of the NOx storage catalyst is lowered , the NOx purification capacity on the low temperature side is increased, so that the NOx storage catalyst can be maintained at a low temperature for a long time as in the present invention. Thus, efficient and sufficient removal of NOx becomes possible.

請求項７に記載の発明は、機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、上記ＮＯｘ吸蔵触媒の温度が所定温度未満である時には、リーン空燃比のもとで燃焼を行った際に発生する一酸化窒素ＮＯに対する二酸化窒素ＮＯ2の割合を、ＮＯｘ吸蔵触媒の温度が上記所定温度以上である時の同一の機関運転状態の場合に比べて増大させるようにしている排気浄化装置において、更に上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、該酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記所定温度が高く設定されるようになっている排気浄化装置を提供する。 The invention according to claim 7 is a NOx storage catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and is activated when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx storage catalyst that stores nitrogen dioxide NO 2 contained in the exhaust gas in the NOx absorbent at a low temperature when it is not activated, and stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature when activated. And when the temperature of the NOx storage catalyst is lower than a predetermined temperature, the ratio of nitrogen dioxide NO 2 to nitrogen monoxide NO generated when combustion is performed under a lean air-fuel ratio is expressed as the temperature of the NOx storage catalyst. In the exhaust emission control device that is increased as compared with the case of the same engine operating state when the temperature is equal to or higher than the predetermined temperature, the degree of reduction in the oxidation performance of the NOx storage catalyst Comprise means for estimating the case, the higher the degree of reduction in oxidation performance estimated by the oxidation degradation degree estimating means, to provide an exhaust purification device that is adapted to the predetermined temperature is set high.

上述したように排気ガス中に含まれる二酸化窒素ＮＯ2はＮＯｘ吸蔵触媒が活性化しなくてもＮＯｘ吸収剤に低温吸蔵されるが、排気ガス中に含まれる一酸化窒素ＮＯはＮＯｘ吸蔵触媒が活性化して二酸化窒素ＮＯ2に酸化されないとＮＯｘ吸収剤に高温吸蔵されない。このため、ＮＯｘ吸蔵触媒が活性化していない、または低活性であるＮＯｘ吸蔵触媒の低温時には、排気ガス中の一酸化窒素ＮＯの量を減らし、排気ガス中の二酸化窒素ＮＯ2の量を増大することが好ましい。そこで、上記所定温度を例えば、ＮＯｘ吸収剤に単位時間当たりに低温吸蔵される二酸化窒素ＮＯ2の量と単位時間当たりに高温吸蔵される窒素酸化物ＮＯｘの量とが等しくなる温度に設定すれば、二酸化窒素ＮＯ2の低温吸蔵がより期待できる温度域で排気ガス中の二酸化窒素ＮＯ2の量を増大することになり、ＮＯｘ浄化率の向上を図ることができる。 As described above, nitrogen dioxide NO 2 contained in the exhaust gas is occluded at a low temperature by the NOx absorbent even if the NOx occlusion catalyst is not activated. However, nitrogen monoxide NO contained in the exhaust gas is activated by the NOx occlusion catalyst. If it is not oxidized to nitrogen dioxide NO 2, it will not be stored in the NOx absorbent at high temperature. For this reason, when the NOx storage catalyst is not activated or has a low activity, the amount of nitrogen monoxide NO in the exhaust gas is reduced and the amount of nitrogen dioxide NO 2 in the exhaust gas is increased when the NOx storage catalyst is low in temperature. It is preferable. Therefore, for example, if the predetermined temperature is set to a temperature at which the amount of nitrogen dioxide NO 2 stored in the NOx absorbent at a low temperature per unit time is equal to the amount of nitrogen oxide NOx stored at a high temperature per unit time. In addition, the amount of nitrogen dioxide NO 2 in the exhaust gas is increased in a temperature range where low-temperature storage of nitrogen dioxide NO 2 can be expected, and the NOx purification rate can be improved.

そして、上述したように低温吸蔵に基づくＮＯｘ浄化能力はＮＯｘ吸蔵触媒の酸化性能が低下している場合に結果的に増加するので、本発明のようにＮＯｘ吸蔵触媒の酸化性能の低下度合が高い程、上記所定温度を高くし、低温吸蔵に期待する温度範囲を広げることで、効率的且つ充分なＮＯｘの除去が可能となる。 Since NOx purification performance based on the low-temperature storage as described above is consequently increased when the oxidation performance of the NOx storage catalyst is reduced, a higher degree of decrease of the oxidation performance of the NOx storage catalyst as in the present invention As the predetermined temperature is increased and the temperature range expected for low-temperature storage is increased, efficient and sufficient removal of NOx becomes possible.

請求項８に記載の発明は、機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、上記ＮＯｘ吸蔵触媒の温度が所定温度未満である時には、リーン空燃比のもとで燃焼を行った際に発生する一酸化窒素ＮＯに対する二酸化窒素ＮＯ2の割合を、ＮＯｘ吸蔵触媒の温度が上記所定温度以上である時の同一の機関運転状態の場合に比べて増大させるようにしている排気浄化装置において、更に上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、該硫黄被毒度合推定手段によって推定された硫黄被毒の度合が高い程、上記所定温度が低く設定されるようになっている排気浄化装置を提供する。 The invention according to claim 8 is a NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and is activated when the air-fuel ratio of the inflowing exhaust gas is lean. A NOx storage catalyst that stores nitrogen dioxide NO 2 contained in the exhaust gas in the NOx absorbent at a low temperature when it is not activated, and stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature when activated. And when the temperature of the NOx storage catalyst is lower than a predetermined temperature, the ratio of nitrogen dioxide NO 2 to nitrogen monoxide NO generated when combustion is performed under a lean air-fuel ratio is expressed as the temperature of the NOx storage catalyst. In the exhaust emission control device that is increased as compared with the same engine operating state when the temperature is equal to or higher than the predetermined temperature, the degree of sulfur poisoning of the NOx storage catalyst is further increased. Provided is an exhaust emission control device provided with a means for estimating, wherein the predetermined temperature is set lower as the degree of sulfur poisoning estimated by the sulfur poisoning degree estimating means is higher.

上述したように低温吸蔵に基づくＮＯｘ浄化能力はＮＯｘ吸蔵触媒が硫黄被毒された場合に大きな影響を受ける。つまり、ＮＯｘ吸蔵触媒が硫黄被毒されると低温吸蔵に基づくＮＯｘ浄化能力は極めて低くなってしまう。そのため、本発明のようにＮＯｘ吸蔵触媒の硫黄被毒の度合が高い程、上記所定温度を低くし、低温吸蔵に期待する温度範囲を縮小することで、充分なＮＯｘの除去の実現を図ることができる。   As described above, the NOx purification capacity based on low-temperature storage is greatly affected when the NOx storage catalyst is poisoned with sulfur. That is, when the NOx storage catalyst is poisoned with sulfur, the NOx purification ability based on the low temperature storage becomes extremely low. Therefore, as the degree of sulfur poisoning of the NOx storage catalyst is higher as in the present invention, the predetermined temperature is lowered, and the temperature range expected for low temperature storage is reduced, thereby realizing sufficient removal of NOx. Can do.

各請求項に記載の発明は、ＮＯｘ吸蔵触媒が活性化しない状態においても二酸化窒素ＮＯ2がＮＯｘ吸収剤に低温吸蔵されることを利用して排気ガスを浄化するようにした排気浄化装置において、意図した通りの充分なＮＯｘの除去を行うことを可能にするという共通の効果を奏する。 The invention described in each claim is an exhaust purification apparatus that purifies exhaust gas by utilizing low-temperature storage of nitrogen dioxide NO 2 in the NOx absorbent even in a state where the NOx storage catalyst is not activated. There is a common effect that it is possible to remove sufficient NOx as intended.

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。なお、本発明は火花点火式内燃機関に適用することもできる。   FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a spark ignition internal combustion engine.

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内にそれぞれ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それぞれ示す。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の入口はエアクリーナ８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９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（インタークーラ）１０が配置される。図１に示される実施形態では機関冷却水がインタークーラ１０内に導かれ、機関冷却水によって吸入空気が冷却される。一方、排気マニホルド５は排気ターボチャージャ７の排気タービン７ｂの入口に連結され、排気タービン７ｂの出口はＮＯｘ吸蔵触媒１１を内蔵したケーシング１２に連結される。排気マニホルド５の集合部出口には排気マニホルド５内を流れる排気ガス中に例えば炭化水素からなる還元剤を供給するための還元剤供給弁１３が配置される。   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 through the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 8. A throttle valve 9 driven by a step motor is arranged in the intake duct 6, and a cooling device (intercooler) 10 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. . In the embodiment shown in FIG. 1, the engine cooling water is guided into the intercooler 10 and the intake air is cooled by the engine cooling water. 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 casing 12 containing the NOx storage catalyst 11. A reducing agent supply valve 13 for supplying a reducing agent made of, for example, hydrocarbons into the exhaust gas flowing through the exhaust manifold 5 is disposed at the outlet of the collecting portion of the exhaust manifold 5.

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１４を介して互いに連結され、ＥＧＲ通路１４内には電子制御式ＥＧＲ制御弁１５が配置される。また、ＥＧＲ通路１４周りにはＥＧＲ通路１４内を流れるＥＧＲガスを冷却するための冷却装置（ＥＧＲクーラ）１６が配置される。図１に示される実施形態では機関冷却水がＥＧＲクーラ１６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１７を介して燃料リザーバ、いわゆるコモンレール１８に連結される。このコモンレール１８内へは電子制御式の吐出量可変な燃料ポンプ１９から燃料が供給され、コモンレール１８内に供給された燃料は各燃料供給管１７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 14, and an electronically controlled EGR control valve 15 is disposed in the EGR passage 14. A cooling device (EGR cooler) 16 for cooling the EGR gas flowing in the EGR passage 14 is disposed around the EGR passage 14. In the embodiment shown in FIG. 1, the engine cooling water is guided into the EGR cooler 16, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a fuel reservoir, so-called common rail 18 via a fuel supply pipe 17. Fuel is supplied into the common rail 18 from an electronically controlled fuel pump 19 with variable discharge amount, and the fuel supplied into the common rail 18 is supplied to the fuel injection valve 3 via each fuel supply pipe 17.

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及び出力ポート３６を具備する。ＮＯｘ吸蔵触媒１１にはＮＯｘ吸蔵触媒１１の温度を検出するための温度センサ２０が取付けられ、この温度センサ２０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９駆動用ステップモータ、還元剤供給弁１３、ＥＧＲ制御弁１５、及び燃料ポンプ１９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 20 for detecting the temperature of the NOx storage catalyst 11 is attached to the NOx storage catalyst 11, and an output signal of the temperature sensor 20 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 9 driving step motor, the reducing agent supply valve 13, the EGR control valve 15, and the fuel pump 19 through corresponding drive circuits 38.

図１に示すＮＯｘ吸蔵触媒１１はモノリス触媒からなり、このＮＯｘ吸蔵触媒１１の基体上には例えばアルミナからなる触媒担体が担持されている。図２（Ａ）から（Ｃ）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）から（Ｃ）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。   The NOx storage catalyst 11 shown in FIG. 1 is composed of a monolith catalyst, and a catalyst carrier made of alumina, for example, is supported on the base of the NOx storage catalyst 11. 2A to 2C schematically show a cross section of the surface portion of the catalyst carrier 45. FIG. As shown in FIGS. 2A to 2C, a noble metal catalyst 46 is dispersedly supported on the surface of the catalyst carrier 45, and a layer of NOx absorbent 47 is further formed on the surface of the catalyst carrier 45. Is formed.

本発明の実施形態では、貴金属触媒４６としては例えば白金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 of the present invention, for example, platinum Pt is used as the noble metal catalyst 46, and the components constituting the NOx absorbent 47 are, for example, alkali metals such as potassium K, sodium Na, cesium Cs, barium Ba, calcium. At least one selected from alkaline earth such as Ca, rare earth such as lanthanum La and yttrium Y is used.

機関吸気通路、燃焼室２及びＮＯｘ吸蔵触媒１１上流の排気通路内に供給された空気及び燃料（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、貴金属触媒４６が活性化していれば、すなわちＮＯｘ吸蔵触媒１１が活性化していれば排気ガスの空燃比がリーンの時にはＮＯｘを高温吸蔵し、排気ガス中の酸素濃度が低下すると高温吸蔵したＮＯｘを放出するＮＯｘの吸放出作用を行う。なお、ＮＯｘ吸蔵触媒１１上流の排気通路内に燃料（炭化水素）ある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内における混合気の空燃比に一致し、したがってこの場合にはＮＯｘ吸収剤４７は燃焼室２内における混合気の空燃比がリーンの時にはＮＯｘを高温吸蔵し、燃焼室２内における混合気中の酸素濃度が低下すると高温吸蔵したＮＯｘを放出することになる。   When the ratio of air and fuel (hydrocarbon) supplied to the engine intake passage, the combustion chamber 2 and the exhaust passage upstream of the NOx storage catalyst 11 is called the air-fuel ratio of the exhaust gas, the NOx absorbent 47 is activated by the noble metal catalyst 46. If the NOx occlusion catalyst 11 is activated, NOx is occluded at a high temperature when the air-fuel ratio of the exhaust gas is lean, and NOx occlusion that releases the NOx occluded at a high temperature when the oxygen concentration in the exhaust gas decreases. Performs release action. When fuel (hydrocarbon) or air is not supplied into the exhaust passage upstream of the NOx storage catalyst 11, the air-fuel ratio of the exhaust gas matches the air-fuel ratio of the air-fuel mixture in the combustion chamber 2. Therefore, in this case The NOx absorbent 47 stores NOx at a high temperature when the air-fuel ratio of the mixture in the combustion chamber 2 is lean, and releases the NOx stored at a high temperature when the oxygen concentration in the mixture in the combustion chamber 2 decreases.

すなわち、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時、すなわち排気ガス中の酸素濃度が高い時には貴金属触媒４６が活性化していれば排気ガス中に含まれるＮＯは図２（Ａ）に示されるように貴金属触媒４６上において酸化されてＮＯ2となり、次いでＮＯｘ吸収剤４７内に高温吸蔵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内に高温吸蔵される。すなわち、このような硝酸イオンＮＯ3 -の形での吸蔵を高温吸蔵と称する。排気ガス中の酸素濃度が高い限り貴金属触媒４６の表面でＮＯ2が生成され、ＮＯｘ吸収剤４７の高温吸蔵能力が飽和しない限りＮＯ2がＮＯｘ吸収剤４７内に高温吸蔵されて硝酸イオンＮＯ3 -が生成される。 That is, the case where barium Ba is used as a component constituting the NOx 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, the noble metal catalyst 46 is activated. Then, the NO contained in the exhaust gas is oxidized on the noble metal catalyst 46 to become NO 2 as shown in FIG. 2 (A), and then stored in the NOx absorbent 47 at a high temperature and combined with the barium oxide BaO. It diffuses into the NOx absorbent 47 in the form of nitrate ions NO 3 − . In this way, NOx is occluded in the NOx absorbent 47 at a high temperature. That is, such occlusion in the form of nitrate ions NO 3 − is referred to as high-temperature occlusion. NO 2 on the surface as long as the precious metal catalyst 46 a high oxygen concentration in the exhaust gas is generated, as long as NO 2 to a high temperature storage capacity is not saturated in the NOx absorbent 47 is a high temperature occluded in the NOx 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あるいは理論空燃比にすることによって、または還元剤供給弁１３から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ある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に進み、斯くしてＮＯｘ吸収剤４７内の硝酸イオンＮＯ3 -がＮＯ2またはＮＯ等の形でＮＯｘ吸収剤４７から放出される。そしてこの場合、排気ガス中に還元剤（未燃ＨＣ，ＣＯ等）が存在する状態になっているため、放出されたＮＯｘは次いで排気ガス中に含まれる還元剤（未燃ＨＣ，ＣＯ等）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 the reducing agent is supplied from the reducing agent supply valve 13 to make the air-fuel ratio rich or stoichiometric, the exhaust gas is exhausted. Since the oxygen concentration in the gas decreases, the reaction proceeds in the reverse direction, and thus nitrate ions NO 3 − in the NOx absorbent 47 are released from the NOx absorbent 47 in the form of NO 2 or NO. In this case, since the reducing agent (unburned HC, CO, etc.) is present in the exhaust gas, the released NOx is then contained in the exhaust gas (unburned HC, CO, etc.). Reduced by

さて、排気ガス中の窒素酸化物ＮＯｘは一酸化窒素ＮＯの形ではＮＯｘ吸収剤４７に高温吸蔵されず、二酸化窒素ＮＯ2の形にならなければＮＯｘ吸収剤４７に高温吸蔵されない。すなわち、排気ガス中に含まれる一酸化窒素ＮＯは二酸化窒素ＮＯ2にならないと、すなわち酸化されないとＮＯｘ吸収剤４７に高温吸蔵されない。貴金属触媒４６、すなわち例えば白金Ｐｔは本来的に低温での活性を有しているが、ＮＯｘ吸収剤４７の塩基性はかなり強く、そのために貴金属触媒４６の低温での活性、すなわち酸化性が弱められてしまう。その結果、ＮＯｘ吸蔵触媒１１の温度ＴＣが低下すると、一酸化窒素ＮＯを二酸化窒素ＮＯ2に酸化する作用が弱まってしまう。このため、一酸化窒素ＮＯを酸化するには貴金属触媒４６の温度が高く活性化していること、すなわちＮＯｘ吸蔵触媒１１が活性化していることが必要であり、したがってこれまでＮＯｘを浄化するためには貴金属触媒４６が活性化していること、すなわちＮＯｘ吸蔵触媒１１が活性化していることが必要であると考えられてきた。 Now, the nitrogen oxides NOx in the exhaust gas is not hot stored in the NOx absorbent 47 in the form of nitrogen monoxide NO, are not hot stored in the NOx absorbent 47 unless not in the form of nitrogen dioxide NO 2. That is, nitrogen monoxide NO contained in the exhaust gas does not become nitrogen dioxide NO 2 , that is, is not stored in the NOx absorbent 47 unless it is oxidized. The noble metal catalyst 46, for example, platinum Pt inherently has activity at a low temperature, but the basicity of the NOx absorbent 47 is quite strong, and therefore the activity at a low temperature of the noble metal catalyst 46, that is, the oxidizing property is weakened. It will be. As a result, when the temperature TC of the NOx storage catalyst 11 decreases, the action of oxidizing nitric oxide NO to nitrogen dioxide NO 2 is weakened. For this reason, in order to oxidize nitric oxide NO, it is necessary that the temperature of the noble metal catalyst 46 is high and activated, that is, that the NOx storage catalyst 11 is activated. Has been considered to require that the noble metal catalyst 46 is activated, that is, that the NOx storage catalyst 11 is activated.

ところがこのＮＯｘ吸蔵触媒１１について本発明者が研究を重ねた結果、排気ガス中に含まれる一酸化窒素ＮＯは貴金属触媒４６が活性化しないと、すなわちＮＯｘ吸蔵触媒１１が活性化しないとＮＯｘ吸収剤４７に吸蔵されないが排気ガス中に含まれる二酸化窒素ＮＯ2はＮＯｘ吸蔵触媒１１が活性化しなくても図２（Ｂ）に示されるように亜硝酸ＮＯ2 -の形でＮＯｘ吸収剤４７に低温吸蔵されることが判明したのである。なお、本明細書ではこのような亜硝酸ＮＯ2 -の形での吸蔵を上述の高温吸蔵と区別して低温吸蔵と称する。また、高温吸蔵と低温吸蔵とを特に区別する必要の無い場合にはこれらをまとめて単に吸蔵という。 However, as a result of the inventor's repeated research on the NOx storage catalyst 11, the NOx absorbent contained in the exhaust gas does not activate the noble metal catalyst 46, that is, the NOx storage catalyst 11 does not activate. Nitrogen dioxide NO 2 that is not stored in the exhaust gas but is contained in the exhaust gas is low in the NOx absorbent 47 in the form of nitrous acid NO 2 − as shown in FIG. 2B even if the NOx storage catalyst 11 is not activated. It was found that it was occluded. In the present specification, such occlusion in the form of nitrous acid NO 2 − is referred to as low-temperature occlusion to distinguish it from the above-described high-temperature occlusion. Further, when it is not necessary to distinguish between high temperature storage and low temperature storage, these are collectively referred to simply as storage.

このようにＮＯｘ吸蔵触媒１１が活性化していなくても二酸化窒素ＮＯ2が低温吸蔵されるので、本発明の実施形態では、例えばリーン空燃比のもとで燃焼が行われている場合等、流入する排気ガスの空燃比がリーンである場合において、ＮＯｘ吸蔵触媒１１が活性化されていない状態で排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵させるようにしている。すなわち、図１に示されるような圧縮着火式内燃機関では、通常運転時の排気ガス空燃比はリーンである。そして例えば、機関の冷間始動後しばらくの間は、ＮＯｘ吸蔵触媒１１は活性化していない状態にある。このため、例えば、このような機関始動後しばらくの間等には、ＮＯｘ吸蔵触媒１１のＮＯｘ吸収剤４７が排気ガス中に含まれる二酸化窒素ＮＯ2を低温吸蔵する。 Thus, even if the NOx storage catalyst 11 is not activated, nitrogen dioxide NO 2 is stored at a low temperature. Therefore, in the embodiment of the present invention, for example, when combustion is performed under a lean air-fuel ratio, the inflow In the case where the air-fuel ratio of the exhaust gas being lean is lean, nitrogen dioxide NO 2 contained in the exhaust gas is stored in the NOx absorbent at a low temperature while the NOx storage catalyst 11 is not activated. That is, in the compression ignition type internal combustion engine as shown in FIG. 1, the exhaust gas air-fuel ratio during normal operation is lean. For example, the NOx storage catalyst 11 is not activated for a while after the cold start of the engine. For this reason, for example, for a while after the engine is started, the NOx absorbent 47 of the NOx storage catalyst 11 stores nitrogen dioxide NO 2 contained in the exhaust gas at a low temperature.

ところで、図２（Ｂ）で示されたようなＮＯｘ吸蔵触媒１１が活性化していない状態から図２（Ａ）で示されたようなＮＯｘ吸蔵触媒１１が活性化している状態への移行は、実際にはＮＯｘ吸蔵触媒１１の温度ＴＣの上昇に伴って徐々に起こる。そして、これら二つの状態の間には図２（Ｃ）で示されるような中間的な状態（以下、「中間状態」と称す）が存在する。   By the way, the transition from the state where the NOx storage catalyst 11 as shown in FIG. 2 (B) is not activated to the state where the NOx storage catalyst 11 as shown in FIG. Actually, this gradually occurs as the temperature TC of the NOx storage catalyst 11 increases. An intermediate state (hereinafter referred to as “intermediate state”) as shown in FIG. 2C exists between these two states.

この中間状態においては、図２（Ｃ）に示されているように二酸化窒素ＮＯ2が貴金属触媒４６上で排気ガス中の炭化水素ＨＣと反応して一酸化窒素ＮＯに還元される反応が起こる。すなわち、ＮＯｘ吸蔵触媒１１が完全に活性化し貴金属触媒４６の酸化性が充分である時に炭化水素ＨＣが存在する場合には、二酸化窒素ＮＯ2は貴金属触媒４６上で排気ガス中の炭化水素ＨＣと反応して窒素Ｎ2に還元される（換言すれば、炭化水素ＨＣが二酸化窒素ＮＯ2の酸素によって酸化される）が、上記中間状態ではＮＯｘ吸蔵触媒１１は活性化の過程にあり貴金属触媒４６の酸化性が不充分であるため二酸化窒素ＮＯ2は一酸化窒素ＮＯまでにしか還元されないのである。 In this intermediate state, as shown in FIG. 2C, a reaction occurs in which nitrogen dioxide NO 2 reacts with hydrocarbon HC in the exhaust gas on the noble metal catalyst 46 and is reduced to nitric oxide NO. . That is, when hydrocarbon HC is present when the NOx storage catalyst 11 is fully activated and the noble metal catalyst 46 is sufficiently oxidized, nitrogen dioxide NO 2 and hydrocarbon HC in the exhaust gas on the noble metal catalyst 46. It reacts and is reduced to nitrogen N 2 (in other words, hydrocarbon HC is oxidized by oxygen of nitrogen dioxide NO 2 ). However, in the intermediate state, the NOx storage catalyst 11 is in the process of activation and the noble metal catalyst 46. Nitrogen dioxide NO 2 can only be reduced up to nitrogen monoxide NO.

そして、このように中間状態では排気ガス中の二酸化窒素ＮＯ2が一酸化窒素ＮＯに還元されるので、排気ガス中の二酸化窒素ＮＯ2の割合が減り、一酸化窒素ＮＯの割合が増えることになる。中間状態において二酸化窒素ＮＯ2はＮＯｘ吸収剤４７に低温吸蔵され得るのであるが、上述したように排気ガス中の二酸化窒素ＮＯ2の割合が減り、一酸化窒素ＮＯの割合が増えるので、結果としてこの中間状態におけるＮＯｘ浄化能力、例えばＮＯｘ吸蔵速度は低下すると考えられる。 In this intermediate state, nitrogen dioxide NO 2 in the exhaust gas is reduced to nitrogen monoxide NO, so that the proportion of nitrogen dioxide NO 2 in the exhaust gas decreases and the proportion of nitrogen monoxide NO increases. Become. In the intermediate state, nitrogen dioxide NO 2 can be stored in the NOx absorbent 47 at a low temperature, but as described above, the ratio of nitrogen dioxide NO 2 in the exhaust gas decreases and the ratio of nitrogen monoxide NO increases. It is considered that the NOx purification capacity in this intermediate state, for example, the NOx occlusion speed is lowered.

なお、更に詳細には、図２（Ａ）から（Ｃ）を参照して説明した上記ＮＯｘ吸蔵触媒１１における各反応が、ＮＯｘ吸蔵触媒１１の活性状態の変化、すなわち温度変化に伴ってそれぞれの割合を変化させながら起きることになる。換言すれば、ＮＯｘ吸蔵触媒１１の温度ＴＣに応じてＮＯｘ吸蔵触媒１１の活性状態が定まり、その活性状態に応じて上記の各反応が割合を変えて起きることになる。つまり、ＮＯｘ吸蔵触媒１１の温度ＴＣが次第に上昇する場合を例にとると、初めのうちはＮＯｘ吸蔵触媒１１が低温であるため図２（Ｂ）を参照して説明したＮＯｘ吸蔵触媒１１が活性化されていない場合の反応（すなわち二酸化窒素ＮＯ2の低温吸蔵）の割合が大きいが、ＮＯｘ吸蔵触媒１１の温度ＴＣが上昇してくると次第に図２（Ｃ）を参照して説明した中間状態での反応（すなわち二酸化窒素ＮＯ2の一酸化窒素ＮＯへの還元反応等）の割合が増加してくる。更に温度ＴＣが上昇すると、上記中間状態での反応の割合が低下し図２（Ａ）を参照して説明したＮＯｘ吸蔵触媒１１が活性化されている場合の反応（すなわち窒素酸化物ＮＯｘの高温吸蔵）の割合が大きくなる。 In more detail, each reaction in the NOx storage catalyst 11 described with reference to FIGS. 2A to 2C is changed according to the change in the active state of the NOx storage catalyst 11, that is, the temperature change. It happens while changing the ratio. In other words, the active state of the NOx storage catalyst 11 is determined according to the temperature TC of the NOx storage catalyst 11, and each of the reactions described above occurs at different rates according to the active state. That is, taking the case where the temperature TC of the NOx storage catalyst 11 gradually increases as an example, the NOx storage catalyst 11 described with reference to FIG. 2B is active because the NOx storage catalyst 11 is initially at a low temperature. In the intermediate state described with reference to FIG. 2 (C) when the temperature TC of the NOx storage catalyst 11 rises, the ratio of the reaction (ie, the low temperature storage of nitrogen dioxide NO 2 ) is large. The ratio of the reaction (ie, the reduction reaction of nitrogen dioxide NO 2 to nitric oxide NO) increases. When the temperature TC further increases, the reaction rate in the intermediate state decreases, and the reaction when the NOx storage catalyst 11 described with reference to FIG. 2A is activated (that is, the high temperature of the nitrogen oxide NOx). (Occlusion) ratio increases.

そして、以上のようなＮＯｘ吸蔵触媒１１の温度変化とＮＯｘ吸蔵触媒１１の活性状態（すなわち活性状態に応じた上記の各反応）との関係から、ＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係は図３に示すようになると考えられる。図中のＴｍ、Ｔａ、Ｔｋはそれぞれ、上述したＮＯｘ吸蔵触媒１１が活性化されていない場合の反応、中間状態である場合の反応、活性化されている場合の反応の各反応の割合が多い活性状態に対応するＮＯｘ吸蔵触媒１１の温度ＴＣの例を表している。   Then, from the relationship between the temperature change of the NOx storage catalyst 11 and the active state of the NOx storage catalyst 11 (that is, each of the reactions according to the active state) as described above, the NOx storage capability Nc of the NOx storage catalyst 11 and the NOx storage are stored. It is considered that the relationship with the temperature TC of the catalyst 11 is as shown in FIG. Each of Tm, Ta, and Tk in the figure has a large proportion of each reaction of the reaction when the above-described NOx storage catalyst 11 is not activated, the reaction when it is in an intermediate state, and the reaction when it is activated. The example of temperature TC of the NOx storage catalyst 11 corresponding to an active state is represented.

以下、ＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔｍから温度Ｔｋまで徐々に上昇していく場合を例にとって図３について説明する。ＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔｍである場合にはＮＯｘ吸蔵触媒１１が活性化されていない状態にあるので、この場合のＮＯｘ浄化能力Ｎｃは殆どが二酸化窒素ＮＯ2の低温吸蔵に基づくものである。そのため、ＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔｍから上昇していくとＮＯｘ浄化能力Ｎｃは次第に低下する。すなわち、ＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔｍから上昇していくと、上述した中間状態における二酸化窒素ＮＯ2から一酸化窒素ＮＯへの還元反応が徐々に多くなるため低温吸蔵できる二酸化窒素ＮＯ2が減少する。その結果としてＮＯｘ浄化能力Ｎｃが次第に低下するのである。 Hereinafter, the case where the temperature TC of the NOx storage catalyst 11 gradually increases from the temperature Tm to the temperature Tk will be described with reference to FIG. When the temperature TC of the NOx storage catalyst 11 is the temperature Tm, the NOx storage catalyst 11 is not activated, so the NOx purification capacity Nc in this case is mostly based on the low temperature storage of nitrogen dioxide NO 2. It is. Therefore, as the temperature TC of the NOx storage catalyst 11 increases from the temperature Tm, the NOx purification capability Nc gradually decreases. That is, as the temperature TC of the NOx storage catalyst 11 rises from the temperature Tm, the reduction reaction from nitrogen dioxide NO 2 to nitrogen monoxide NO in the intermediate state described above gradually increases, so nitrogen dioxide NO 2 that can be stored at a low temperature. Decrease. As a result, the NOx purification capacity Nc gradually decreases.

一方、更にＮＯｘ吸蔵触媒１１の温度ＴＣが上昇して温度Ｔａに近づいてくると、ＮＯｘ吸蔵触媒が徐々に活性化し始めてＮＯｘの高温吸蔵が可能になってくる。そしてＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔａを超えると低温吸蔵に基づくＮＯｘ浄化能力Ｎｃの低下度合を高温吸蔵に基づくＮＯｘ浄化能力Ｎｃの上昇度合が上回り、ＮＯｘ吸蔵触媒１１の温度上昇に伴って全体のＮＯｘ浄化能力Ｎｃが上昇するようになる。つまり、ＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔａとなった時にＮＯｘ浄化能力Ｎｃが極小値をとる。   On the other hand, when the temperature TC of the NOx occlusion catalyst 11 further increases and approaches the temperature Ta, the NOx occlusion catalyst gradually starts to be activated and high temperature occlusion of NOx becomes possible. When the temperature TC of the NOx storage catalyst 11 exceeds the temperature Ta, the degree of increase in the NOx purification capacity Nc based on the low temperature storage exceeds the degree of decrease in the NOx purification capacity Nc based on the high temperature storage, and as the temperature of the NOx storage catalyst 11 increases. The overall NOx purification capacity Nc increases. That is, when the temperature TC of the NOx storage catalyst 11 reaches the temperature Ta, the NOx purification capacity Nc takes a minimum value.

ＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔａを超えると、ＮＯｘ吸蔵触媒１１の温度ＴＣの上昇に伴って一酸化窒素ＮＯを酸化して二酸化窒素ＮＯ2とする酸化反応が活発化し、その結果として次第に多くのＮＯｘが高温吸蔵されるようになってＮＯｘ浄化能力Ｎｃは上昇していく。そして、ＮＯｘ吸蔵触媒１１の温度ＴＣが温度ＴｋとなるころにはＮＯｘ吸蔵触媒１１が完全に活性化され、この場合のＮＯｘ浄化能力Ｎｃの殆どが窒素酸化物ＮＯｘの高温吸蔵に基づくものとなる。 When the temperature TC of the NOx storage catalyst 11 exceeds the temperature Ta, as the temperature TC of the NOx storage catalyst 11 increases, the oxidation reaction of oxidizing nitric oxide NO to nitrogen dioxide NO 2 is activated, and as a result, gradually. A large amount of NOx is occluded and the NOx purification capacity Nc increases. When the temperature TC of the NOx storage catalyst 11 reaches the temperature Tk, the NOx storage catalyst 11 is completely activated, and in this case, most of the NOx purification capacity Nc is based on the high temperature storage of the nitrogen oxide NOx. .

ところで、図３に示されるようなＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を把握することは、ＮＯｘ吸蔵触媒１１の温度ＴＣを制御して排気ガス中のＮＯｘを浄化する際に重要である。すなわち、ＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を正確に把握していればＮＯｘ吸蔵触媒１１の温度ＴＣを制御することで排気ガス中のＮＯｘを効率的且つ充分に除去することが可能になる。   By the way, ascertaining the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 as shown in FIG. 3 is controlled by controlling the temperature TC of the NOx storage catalyst 11 in the exhaust gas. This is important when purifying NOx. That is, if the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 is accurately grasped, the temperature TC of the NOx storage catalyst 11 is controlled to efficiently reduce NOx in the exhaust gas. And it becomes possible to remove sufficiently.

一方、上述したように、ＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係は、ＮＯｘ吸蔵触媒１１が各温度ＴＣの場合においてＮＯｘ吸蔵触媒１１において生じる各反応（すなわち、図２（Ａ）から（Ｃ）を参照して説明した各反応）のバランスによって決定される。したがって、このＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係は、ＮＯｘ吸蔵触媒１１における上記各反応に影響を与える要因、すなわち例えばＮＯｘ吸蔵触媒１１の触媒状態によっても影響を受ける。ここで、上記触媒状態の例としては、ＮＯｘ吸蔵触媒１１の劣化度合や硫黄被毒の度合が挙げられる。   On the other hand, as described above, the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 is such that each reaction occurring in the NOx storage catalyst 11 when the NOx storage catalyst 11 is at each temperature TC (that is, Each reaction described with reference to FIGS. 2 (A) to 2 (C) is determined by the balance. Therefore, the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 depends on factors affecting the above reactions in the NOx storage catalyst 11, that is, for example, the catalyst state of the NOx storage catalyst 11. to be influenced. Here, examples of the catalyst state include the degree of deterioration of the NOx storage catalyst 11 and the degree of sulfur poisoning.

すなわち、ＮＯｘ吸蔵触媒１１が劣化すると、貴金属触媒４６がシンタリングしてその表面積が低下する等して酸化性能の低下が生じる。そのため、上述した中間状態における二酸化窒素ＮＯ2から一酸化窒素ＮＯへの還元反応が抑制されると共に、ＮＯｘ吸蔵触媒１１が活性化されている状態における一酸化窒素ＮＯから二酸化窒素ＮＯ2への酸化反応が抑制される。その結果、ＮＯｘ吸蔵触媒１１が劣化している場合、ＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係は図４に示したようになる。 That is, when the NOx occlusion catalyst 11 deteriorates, the noble metal catalyst 46 is sintered and its surface area is reduced. Therefore, the reduction reaction from nitrogen dioxide NO 2 to nitrogen monoxide NO in the intermediate state described above is suppressed, and oxidation from nitrogen monoxide NO to nitrogen dioxide NO 2 in a state where the NOx storage catalyst 11 is activated. The reaction is suppressed. As a result, when the NOx storage catalyst 11 is deteriorated, the relationship between the NOx purification capability Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 is as shown in FIG.

すなわち、図４において、実線が、ＮＯｘ吸蔵触媒１１が劣化している場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表しており、点線が、ＮＯｘ吸蔵触媒１１が劣化していない場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表している。つまり、ＮＯｘ吸蔵触媒１１が劣化している場合は劣化していない場合に比べ、低温側でのＮＯｘ浄化能力Ｎｃが上昇し高温側でのＮＯｘ浄化能力Ｎｃが低下する。また、その結果として、ＮＯｘ吸蔵触媒１１が劣化している場合にＮＯｘ浄化能力Ｎｃが極小となる温度Ｔｂは、ＮＯｘ吸蔵触媒１１が劣化していない場合（温度Ｔａ）に比べ高くなっている。そしてこのような傾向は、ＮＯｘ吸蔵触媒１１の劣化度合が高い程大きくなる。   That is, in FIG. 4, the solid line represents the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the NOx storage catalyst 11 has deteriorated, and the dotted line represents the NOx storage catalyst. The relationship between the NOx purification capability Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the catalyst 11 is not deteriorated is shown. That is, when the NOx storage catalyst 11 is deteriorated, the NOx purification capability Nc on the low temperature side is increased and the NOx purification capability Nc on the high temperature side is decreased compared to the case where the NOx storage catalyst 11 is not deteriorated. As a result, the temperature Tb at which the NOx purification capacity Nc is minimized when the NOx storage catalyst 11 is deteriorated is higher than that when the NOx storage catalyst 11 is not deteriorated (temperature Ta). Such a tendency increases as the degree of deterioration of the NOx storage catalyst 11 increases.

なお、ここで、低温側においてＮＯｘ浄化能力Ｎｃが上昇するのは、上記中間状態における二酸化窒素ＮＯ2から一酸化窒素ＮＯへの還元反応が抑制されることにより、低温吸蔵に基づくＮＯｘ浄化能力の低下が抑制されるためである。 Here, the NOx purification capacity Nc increases on the low temperature side because the reduction reaction from nitrogen dioxide NO 2 to nitrogen monoxide NO in the intermediate state is suppressed, so that the NOx purification capacity based on low temperature storage is reduced. This is because the decrease is suppressed.

また、ＮＯｘ吸蔵触媒１１の劣化は、例えばＮＯｘ吸蔵触媒１１の温度が高い程、または、触媒種によって定まる上限温度以上の温度となっている時間が長い程、あるいは、流入する排気ガスの酸素濃度が高い程、その進行が速くなることが判明している。したがって、このことを利用してＮＯｘ吸蔵触媒１１の劣化の度合を推定することができる。すなわち、例えば、新品のＮＯｘ吸蔵触媒１１を取り付けた時からのＮＯｘ吸蔵触媒１１の温度履歴に基づいてＮＯｘ吸蔵触媒１１の劣化度合を推定することができる。   The deterioration of the NOx storage catalyst 11 is caused by, for example, the higher the temperature of the NOx storage catalyst 11, the longer the time when the temperature is higher than the upper limit temperature determined by the catalyst type, or the oxygen concentration of the inflowing exhaust gas. It has been found that the higher the value, the faster the progression. Therefore, the degree of deterioration of the NOx storage catalyst 11 can be estimated using this fact. That is, for example, the degree of deterioration of the NOx storage catalyst 11 can be estimated based on the temperature history of the NOx storage catalyst 11 since the new NOx storage catalyst 11 is attached.

一方、ＮＯｘ吸蔵触媒１１の硫黄被毒は、排気ガス中の硫黄酸化物ＳＯｘが窒素酸化物ＮＯｘを高温吸蔵するのと同じメカニズムでＮＯｘ吸収剤４７に吸蔵され、ＮＯｘ吸収剤４７内に硫酸塩、例えば硫酸バリウムＢａＳＯ4を生成することによって生じる。このような硫酸塩は塩基度が低いため、ＮＯｘ吸蔵触媒１１が硫黄被毒されるとＮＯｘ吸収剤４７上の塩基点が減少し二酸化窒素ＮＯ2の低温吸蔵が起こり難くなる。また、上記のように硫酸塩は窒素酸化物ＮＯｘを高温吸蔵するのと同じメカニズムで硫黄酸化物ＳＯｘを吸蔵することによって生じるため、ＮＯｘ吸収剤４７内に硫酸塩が増える分だけ高温吸蔵できるＮＯｘ量が減少してしまう。そのため、ＮＯｘ吸蔵触媒１１が硫黄被毒されると窒素酸化物ＮＯｘの高温吸蔵も起こり難くなる。以上のようなことから、ＮＯｘ吸蔵触媒１１が硫黄被毒された場合、ＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係は図５に示したようになる。 On the other hand, sulfur poisoning of the NOx storage catalyst 11 is stored in the NOx absorbent 47 by the same mechanism as the sulfur oxide SOx in the exhaust gas stores the nitrogen oxide NOx at a high temperature, and sulfate is contained in the NOx absorbent 47. For example, by producing barium sulfate BaSO 4 . Since such a sulfate has a low basicity, when the NOx storage catalyst 11 is poisoned with sulfur, the base point on the NOx absorbent 47 is reduced, and low temperature storage of nitrogen dioxide NO 2 is difficult to occur. Further, as described above, since sulfate is stored by storing sulfur oxide SOx by the same mechanism as storing nitrogen oxide NOx at a high temperature, NOx can be stored at a high temperature by the amount of sulfate in the NOx absorbent 47. The amount will decrease. Therefore, when the NOx storage catalyst 11 is poisoned with sulfur, high temperature storage of nitrogen oxides NOx hardly occurs. From the above, when the NOx storage catalyst 11 is poisoned with sulfur, the relationship between the NOx purification capability Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 is as shown in FIG.

すなわち、図５において、実線が、ＮＯｘ吸蔵触媒１１が硫黄被毒されている場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表しており、点線が、ＮＯｘ吸蔵触媒１１が硫黄被毒されていない場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表している。つまり、ＮＯｘ吸蔵触媒１１が硫黄被毒されている場合は硫黄被毒されていない場合に比べて、全温度域でＮＯｘ浄化能力Ｎｃが低下する。但し、その影響は低温側で大きく、その結果としてＮＯｘ吸蔵触媒１１が硫黄被毒されている場合にＮＯｘ浄化能力Ｎｃが極小となる温度Ｔｓは、ＮＯｘ吸蔵触媒１１が硫黄被毒されていない場合（温度Ｔａ）に比べ低くなっている。そしてこのような傾向は、ＮＯｘ吸蔵触媒１１の硫黄被毒の度合が高い程大きくなる。   That is, in FIG. 5, the solid line represents the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the NOx storage catalyst 11 is poisoned with sulfur, and the dotted line represents The relationship between the NOx purification capability Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the NOx storage catalyst 11 is not sulfur-poisoned is shown. That is, when the NOx storage catalyst 11 is sulfur-poisoned, the NOx purification capacity Nc is reduced in the entire temperature range as compared to the case where the NOx-occlusion catalyst 11 is not sulfur-poisoned. However, the effect is large on the low temperature side, and as a result, the temperature Ts at which the NOx purification capacity Nc is minimized when the NOx storage catalyst 11 is sulfur poisoned is the case where the NOx storage catalyst 11 is not sulfur poisoned. It is lower than (temperature Ta). Such a tendency increases as the degree of sulfur poisoning of the NOx storage catalyst 11 increases.

なお、ＮＯｘ吸蔵触媒１１の硫黄被毒の度合は、例えば前回の硫黄被毒解消制御実施後の燃料消費量から推定することができる。すなわち、ＮＯｘ吸蔵触媒１１の硫黄被毒は、ＮＯｘ吸蔵触媒１１を６００℃程度に昇温すると共にＮＯｘ吸蔵触媒１１に流入する排気ガスの空燃比を理論空燃比またはリッチにすると、硫黄酸化物ＳＯｘがＮＯｘ吸収剤４７から放出されて解消されることがわかっている。したがって、上記のようなＮＯｘ吸蔵触媒を備えた排気浄化装置では通常、ＮＯｘ吸蔵触媒１１を６００℃程度に昇温すると共にＮＯｘ吸蔵触媒１１に流入する排気ガスの空燃比を理論空燃比またはリッチにする硫黄被毒解消制御が定期的に実施される。このような硫黄被毒解消制御が実施されれば硫黄被毒は基本的には解消されるので、燃料の硫黄含有量を予め求めておけば、硫黄被毒解消制御実施後の燃料消費量から現在の硫黄被毒の度合を推定することができる。更に、オイルの硫黄含有量も求めておきオイル消費量も考慮して硫黄被毒の度合を求めるようにしてもよい。   The degree of sulfur poisoning of the NOx storage catalyst 11 can be estimated from, for example, the fuel consumption after the previous sulfur poisoning elimination control. That is, the sulfur poisoning of the NOx storage catalyst 11 is caused by raising the temperature of the NOx storage catalyst 11 to about 600 ° C. and making the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 11 the stoichiometric air-fuel ratio or rich. Has been found to be released from the NOx absorbent 47 and eliminated. Therefore, in the exhaust gas purification apparatus provided with the NOx storage catalyst as described above, the NOx storage catalyst 11 is usually heated to about 600 ° C. and the air-fuel ratio of the exhaust gas flowing into the NOx storage catalyst 11 is made the stoichiometric air-fuel ratio or rich. Sulfur poisoning elimination control is regularly implemented. If such sulfur poisoning elimination control is carried out, sulfur poisoning is basically eliminated. Therefore, if the sulfur content of the fuel is obtained in advance, the fuel consumption after the sulfur poisoning elimination control is implemented. The current degree of sulfur poisoning can be estimated. Further, the sulfur content of the oil may be obtained, and the degree of sulfur poisoning may be obtained in consideration of the oil consumption.

あるいは、ＮＯｘ吸蔵触媒１１の下流側に排気ガス中のＮＯｘ濃度を検出するＮＯｘセンサを設けておき、ＮＯｘセンサの出力値に基づいて硫黄被毒の度合を推定するようにしてもよい。すなわち、この場合には例えば、硫黄被毒されていない時の基準出力を予め求めておき、その基準出力と実際のＮＯｘセンサ出力値とを比較して硫黄被毒の度合を推定するようにする。   Alternatively, a NOx sensor that detects the NOx concentration in the exhaust gas may be provided on the downstream side of the NOx storage catalyst 11, and the degree of sulfur poisoning may be estimated based on the output value of the NOx sensor. That is, in this case, for example, a reference output when sulfur poisoning is not performed is obtained in advance, and the degree of sulfur poisoning is estimated by comparing the reference output with the actual NOx sensor output value. .

以上、説明したように、ＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃはＮＯｘ吸蔵触媒１１の温度ＴＣ（すなわち、活性状態）の他、ＮＯｘ吸蔵触媒１１の劣化度合や硫黄被毒の度合等の触媒状態にも影響を受ける。そこで本発明の実施形態では、上記触媒状態を考慮して、すなわち上述したような上記触媒状態のＮＯｘ浄化能力Ｎｃへの影響を考慮して排気ガスの浄化を行うようにしている。   As described above, the NOx purification ability Nc of the NOx storage catalyst 11 is not limited to the temperature TC (that is, the active state) of the NOx storage catalyst 11, but the catalyst state such as the degree of deterioration of the NOx storage catalyst 11 and the degree of sulfur poisoning. Also affected. Therefore, in the embodiment of the present invention, the exhaust gas is purified in consideration of the catalyst state, that is, in consideration of the influence of the catalyst state on the NOx purification ability Nc as described above.

すなわち、例えば本発明の一実施形態においては、機関の始動から所定時間ｔｓ経過後にＮＯｘ吸蔵触媒１１の温度ＴＣが所定の目標温度Ｔｏ未満であればＮＯｘ吸蔵触媒１１の活性化を目的としてＮＯｘ吸蔵触媒１１の温度ＴＣを上記目標温度Ｔｏまで上昇させる昇温制御を実施するようにしている排気浄化装置において、推定されたＮＯｘ吸蔵触媒１１の劣化度合が高い程、始動からＮＯｘ吸蔵触媒１１の温度ＴＣが上記目標温度Ｔｏになるまでの時間が長くなるようにされている。より具体的には例えば、上記所定時間ｔｓを長くしたり、昇温のペースを遅く（単位時間当たりの温度上昇を小さく）したりする。また、例えば上記昇温制御において上記の最終的な目標温度Ｔｏまでの間に段階的にターゲット温度を設定し各ターゲット温度に維持する時間ｔｉを定めることで昇温のペースを決定している場合には、ＮＯｘ吸蔵触媒１１の劣化度合が高い程、各ターゲット温度における上記維持時間ｔｉを長くするようにする。   That is, for example, in one embodiment of the present invention, if the temperature TC of the NOx storage catalyst 11 is less than the predetermined target temperature To after a predetermined time ts has elapsed since the start of the engine, the NOx storage catalyst 11 is activated for the purpose of activating the NOx storage catalyst 11. In the exhaust gas purification apparatus that performs the temperature rise control for raising the temperature TC of the catalyst 11 to the target temperature To, the higher the estimated deterioration degree of the NOx storage catalyst 11, the higher the temperature of the NOx storage catalyst 11 from the start. The time until TC reaches the target temperature To is increased. More specifically, for example, the predetermined time ts is lengthened, or the rate of temperature rise is slowed (temperature rise per unit time is made small). Further, for example, in the temperature increase control, when the target temperature is set stepwise until the final target temperature To and the time ti for maintaining each target temperature is determined, the rate of temperature increase is determined. In other words, the higher the degree of deterioration of the NOx storage catalyst 11, the longer the maintenance time ti at each target temperature.

このようにすると、ＮＯｘ吸蔵触媒１１が劣化された場合にはＮＯｘ吸蔵触媒１１の昇温が遅くなりＮＯｘ吸蔵触媒１１の温度ＴＣの低い状態が長くされる。そして上述したようにＮＯｘ吸蔵触媒１１が劣化された場合には低温側でのＮＯｘ浄化能力Ｎｃが上昇するので、上記のようにしてＮＯｘ吸蔵触媒１１の温度ＴＣの低い状態を長くすることで、より効率的なＮＯｘの除去が可能となる。   In this way, when the NOx storage catalyst 11 is deteriorated, the temperature rise of the NOx storage catalyst 11 is delayed, and the state where the temperature TC of the NOx storage catalyst 11 is low is lengthened. As described above, when the NOx storage catalyst 11 is deteriorated, the NOx purification ability Nc on the low temperature side increases, so by increasing the low temperature TC state of the NOx storage catalyst 11 as described above, More efficient removal of NOx becomes possible.

なお、始動からＮＯｘ吸蔵触媒１１の温度ＴＣが上記目標温度Ｔｏになるまでの時間をどの程度長くするか（より具体的には、例えば上記所定時間ｔｓをどの程度長くするか、あるいは昇温ペースをどの程度遅くするか等）については、事前にマップを作成しておき、そのマップに基づいて求めるようにする。すなわち、ＮＯｘ吸蔵触媒１１の劣化度合と低温側でのＮＯｘ浄化能力Ｎｃの上昇との関係を事前に求め、それに基づいてＮＯｘ吸蔵触媒１１の劣化度合に対応して必要な制御パラメータ（例えば、上記所定時間ｔｓ等）の適切な値が求められるマップを作成しておき、そのマップに基づいて求めるようにする。なお、このマップには、複数の劣化度合に対応して複数の値が規定されていてもよいし、劣化している場合と劣化していない場合の二つの値のみが規定されていてもよい。   It should be noted that how long the time from the start until the temperature TC of the NOx storage catalyst 11 reaches the target temperature To is increased (more specifically, for example, how long the predetermined time ts is increased, or the rate of temperature increase) For example, how much late is to be made), a map is prepared in advance, and the map is obtained based on the map. That is, the relationship between the degree of deterioration of the NOx storage catalyst 11 and the increase in the NOx purification capacity Nc on the low temperature side is obtained in advance, and based on this, control parameters necessary for the degree of deterioration of the NOx storage catalyst 11 (for example, the above-mentioned) A map for which an appropriate value for a predetermined time ts or the like is obtained is created and obtained based on the map. In this map, a plurality of values may be defined corresponding to a plurality of degrees of deterioration, or only two values, that is, a case where deterioration is caused and a case where deterioration is not caused may be prescribed. .

また、本発明の別の実施形態においては、機関の始動から所定時間ｔｓ経過後にＮＯｘ吸蔵触媒１１の温度ＴＣが所定の目標温度Ｔｏ未満であればＮＯｘ吸蔵触媒１１の活性化を目的としてＮＯｘ吸蔵触媒１１の温度ＴＣを上記目標温度Ｔｏまで上昇させる昇温制御を実施するようにしている排気浄化装置において、推定されたＮＯｘ吸蔵触媒１１の硫黄被毒の度合が高い程、始動からＮＯｘ吸蔵触媒１１の温度ＴＣが上記目標温度Ｔｏになるまでの時間が短くなるようにされている。より具体的には例えば、上記所定時間ｔｓを短くしたり、昇温のペースを速く（単位時間当たりの温度上昇を大きく）したりする。また、例えば上記昇温制御において上記の最終的な目標温度Ｔｏまでの間に段階的にターゲット温度を設定し各ターゲット温度に維持する時間ｔｉを定めることで昇温のペースを決定している場合には、ＮＯｘ吸蔵触媒１１の硫黄被毒の度合が高い程、各ターゲット温度における上記維持時間ｔｉを短くするようにする。   In another embodiment of the present invention, if the temperature TC of the NOx storage catalyst 11 is lower than a predetermined target temperature To after a predetermined time ts has elapsed from the start of the engine, the NOx storage catalyst 11 is activated for the purpose of activating the NOx storage catalyst 11. In the exhaust gas purification apparatus that performs the temperature raising control for raising the temperature TC of the catalyst 11 to the target temperature To, the higher the estimated degree of sulfur poisoning of the NOx storage catalyst 11, the more the NOx storage catalyst from the start. The time until the temperature TC 11 becomes the target temperature To is shortened. More specifically, for example, the predetermined time ts is shortened, or the rate of temperature increase is increased (the temperature increase per unit time is increased). Further, for example, in the temperature increase control, when the target temperature is set stepwise until the final target temperature To and the time ti for maintaining each target temperature is determined, the rate of temperature increase is determined. First, the higher the degree of sulfur poisoning of the NOx storage catalyst 11, the shorter the maintenance time ti at each target temperature.

このようにすると、ＮＯｘ吸蔵触媒１１が硫黄被毒された場合にはＮＯｘ吸蔵触媒１１の昇温が速くなりＮＯｘ吸蔵触媒１１の温度ＴＣの低い状態が短くされる。そして上述したようにＮＯｘ吸蔵触媒１１が硫黄被毒された場合には低温側でのＮＯｘ浄化能力Ｎｃが特に低下するので、上記のようにしてＮＯｘ吸蔵触媒１１の温度ＴＣの低い状態を短くすることで、充分なＮＯｘの除去の実現を図ることができる。   In this way, when the NOx storage catalyst 11 is poisoned with sulfur, the temperature rise of the NOx storage catalyst 11 is accelerated, and the state where the temperature TC of the NOx storage catalyst 11 is low is shortened. As described above, when the NOx storage catalyst 11 is poisoned with sulfur, the NOx purification ability Nc on the low temperature side is particularly lowered, so that the low temperature TC state of the NOx storage catalyst 11 is shortened as described above. Thus, it is possible to achieve sufficient removal of NOx.

なお、始動からＮＯｘ吸蔵触媒１１の温度ＴＣが上記目標温度Ｔｏになるまでの時間をどの程度短くするか（より具体的には、例えば上記所定時間ｔｓをどの程度短くするか、あるいは昇温ペースをどの程度速くするか等）については、上述した劣化度合の場合と同様にして事前にＮＯｘ吸蔵触媒１１の硫黄被毒の度合と必要な制御パラメータ（例えば、上記所定時間ｔｓ等）の適切な値とを対応させたマップを作成しておき、そのマップに基づいて求めるようにする。   It should be noted that how much time is required from the start until the temperature TC of the NOx storage catalyst 11 reaches the target temperature To (more specifically, how much the predetermined time ts is reduced, for example, or the rate of temperature increase) As to the degree of deterioration, the degree of sulfur poisoning of the NOx storage catalyst 11 and the appropriate control parameters (for example, the predetermined time ts) are appropriately set in advance. A map in which values are associated with each other is created and obtained based on the map.

また、ここでの昇温制御は、例えば、以下のように燃料噴射パターンを制御することによって実施できる。すなわち、図６は図１に示した内燃機関で実施し得る燃料噴射パターンのうちの四つの例について示した概略図であるが、通常時には主燃料ｑｍは図６において（Ｉ）で示されるように圧縮上死点付近で噴射される。これに対し、昇温制御が開始されると、例えば図６の（ＩＩ）に示されるような燃料噴射パターンとされる。つまり、主燃料ｑｍの噴射時期が圧縮上死点以後まで遅角せしめられる。このように主燃料ｑｍの噴射時期を圧縮上死点以後まで遅角させ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１１の温度ＴＣが上昇する。   Further, the temperature increase control here can be performed by controlling the fuel injection pattern as follows, for example. That is, FIG. 6 is a schematic diagram showing four examples of fuel injection patterns that can be implemented in the internal combustion engine shown in FIG. 1, but the main fuel qm is normally indicated by (I) in FIG. Is injected near the compression top dead center. On the other hand, when the temperature raising control is started, a fuel injection pattern as shown in FIG. That is, the injection timing of the main fuel qm is retarded until after the compression top dead center. Thus, if the injection timing of the main fuel qm is retarded until after the compression top dead center, the afterburning period becomes longer, and thus the exhaust gas temperature rises. As the exhaust gas temperature increases, the temperature TC of the NOx storage catalyst 11 increases accordingly.

また、ＮＯｘ吸蔵触媒１１の温度ＴＣを上昇させるために図６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１１の温度ＴＣが上昇する。   Further, in order to increase the temperature TC of the NOx storage catalyst 11, in addition to the main fuel qm as shown in FIG. 6 (III), the auxiliary fuel qv can be injected near the intake top dead center. When the auxiliary fuel qv is additionally injected in this manner, the amount of fuel combusted by the amount corresponding to the auxiliary fuel qv increases, so that the exhaust gas temperature rises, and thus the temperature TC of the NOx storage catalyst 11 rises.

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。したがってこの場合には図６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。すなわち、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１１の温度ＴＣをすみやかに上昇させることができる。   On the other hand, when the auxiliary fuel qv is injected in the vicinity of the intake top dead center, intermediate products such as aldehyde, ketone, peroxide, and carbon monoxide are generated from the auxiliary fuel qv by the compression heat during the compression stroke. The product accelerates the reaction of the main fuel qm. Therefore, in this case, as shown in FIG. 6 (III), even if the injection timing of the main fuel qm is greatly delayed, good combustion can be obtained without causing misfire. That is, since the injection timing of the main fuel qm can be greatly delayed in this way, the exhaust gas temperature becomes considerably high, and thus the temperature TC of the NOx storage catalyst 11 can be quickly raised.

また、ＮＯｘ吸蔵触媒１１の温度ＴＣを上昇させるために図６の（IV）に示されるように主燃料ｑｍに加え、膨張行程中または排気行程中に補助燃料ｑｐを噴射することもできる。すなわち、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１１上において過剰酸素により酸化され、この時発生する酸化反応熱によってＮＯｘ吸蔵触媒１１の温度ＴＣが上昇せしめられる。   Further, in order to increase the temperature TC of the NOx storage catalyst 11, in addition to the main fuel qm as shown in FIG. 6 (IV), the auxiliary fuel qp can be injected during the expansion stroke or the exhaust stroke. That is, in this case, most of the auxiliary fuel qp is discharged into the exhaust passage in the form of unburned HC without burning. The unburned HC is oxidized on the NOx storage catalyst 11 by excess oxygen, and the temperature TC of the NOx storage catalyst 11 is raised by the oxidation reaction heat generated at this time.

そして、以上のような燃料噴射パターンにおいて、主噴射ｑｍの遅角量、補助燃料ｑｖ及びｑｐの噴射時期及び噴射量等を調節することによってＮＯｘ吸蔵触媒１１の昇温のペースを制御することができる。   In the fuel injection pattern as described above, the rate of temperature increase of the NOx storage catalyst 11 can be controlled by adjusting the retard amount of the main injection qm, the injection timing and the injection amount of the auxiliary fuels qv and qp, and the like. it can.

本発明の更に他の実施形態においては、機関の冷間始動後等において、ＮＯｘ吸蔵触媒１１の温度ＴＣが上昇して所定温度Ｔｄになった時にＮＯｘ吸蔵触媒１１の活性化を目的としてＮＯｘ吸蔵触媒１１の温度ＴＣを所定の目標温度Ｔｏまで昇温する昇温制御を実施するようにしている排気浄化装置において、推定されたＮＯｘ吸蔵触媒１１の劣化度合が高い程、上記所定温度Ｔｄが高く設定されるようになっている。   In still another embodiment of the present invention, for example, after the cold start of the engine, the NOx occlusion catalyst 11 is activated for the purpose of activating the NOx occlusion catalyst 11 when the temperature TC of the NOx occlusion catalyst 11 rises to a predetermined temperature Td. In the exhaust gas purification apparatus that performs the temperature raising control for raising the temperature TC of the catalyst 11 to a predetermined target temperature To, the higher the estimated degree of deterioration of the NOx storage catalyst 11, the higher the predetermined temperature Td. It is set up.

このようにすると、ＮＯｘ吸蔵触媒１１が劣化された場合にはＮＯｘ吸蔵触媒１１がその温度ＴＣの低い状態に長く維持されることになる。そして上述したようにＮＯｘ吸蔵触媒１１が劣化された場合には低温側でのＮＯｘ浄化能力Ｎｃが上昇するので、上記のようにしてＮＯｘ吸蔵触媒１１をその温度ＴＣの低い状態に長く維持することで、より効率的なＮＯｘの除去が可能となる。   In this way, when the NOx storage catalyst 11 is deteriorated, the NOx storage catalyst 11 is maintained for a long time at a low temperature TC. As described above, when the NOx storage catalyst 11 is deteriorated, the NOx purification ability Nc on the low temperature side increases, so that the NOx storage catalyst 11 is maintained at a low temperature TC for a long time as described above. Thus, more efficient removal of NOx becomes possible.

更に、この場合において、ＮＯｘ吸蔵触媒１１の劣化度合がＮＯｘ浄化能力Ｎｃへ与える影響を考慮して昇温制御の開始温度（すなわち上記所定温度Ｔｄ）と終了温度（すなわち上記目標温度Ｔｏ）を設定することで、ＮＯｘ浄化能力Ｎｃが不足する時間を効率的に短縮することができる。これについて図７を参照しつつ説明する。すなわち図７においては、実線が、ＮＯｘ吸蔵触媒１１が劣化している場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表し、点線が、ＮＯｘ吸蔵触媒１１が劣化していない場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表していて、Ｎｒが必要なＮＯｘ浄化能力を表している。図７で示された例において、ＮＯｘ吸蔵触媒１１が劣化していない場合には、昇温制御はＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔ1になった時に開始され、温度Ｔ2になった時に終了せしめられる。そして、ＮＯｘ吸蔵触媒１１が劣化している場合には、昇温制御はＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔ3になった時に開始され、温度Ｔ4になった時に終了せしめられる。 Further, in this case, the start temperature (that is, the predetermined temperature Td) and the end temperature (that is, the target temperature To) of the temperature increase control are set in consideration of the influence of the deterioration degree of the NOx storage catalyst 11 on the NOx purification ability Nc. By doing so, the time when the NOx purification capacity Nc is insufficient can be efficiently shortened. This will be described with reference to FIG. That is, in FIG. 7, the solid line represents the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the NOx storage catalyst 11 has deteriorated, and the dotted line represents the NOx storage catalyst 11. The relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when NO is not deteriorated represents the NOx purification capacity that requires Nr. In the example shown in FIG. 7, when the NOx storage catalyst 11 is not deteriorated, the temperature increase control is started when the temperature TC of the NOx storage catalyst 11 reaches the temperature T 1 and reaches the temperature T 2 . Sometimes it ends. When the NOx storage catalyst 11 is deteriorated, the temperature rise control is started when the temperature TC of the NOx storing catalyst 11 becomes the temperature T 3, is caused to exit when it becomes the temperature T 4.

このようにＮＯｘ吸蔵触媒１１の劣化度合がＮＯｘ浄化能力Ｎｃへ与える影響を考慮して昇温制御の開始温度（すなわち上記所定温度Ｔｄ）と終了温度（すなわち上記目標温度Ｔｏ）を設定することで、昇温制御が劣化度合に応じた適切な温度範囲に対して実施されるようになり、ＮＯｘ浄化能力Ｎｃが必要ＮＯｘ浄化能力Ｎｒ以下になる時間を効率的に短縮することができる。すなわち、例えばＮＯｘ吸蔵触媒１１が劣化している場合にも昇温制御がＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔ1になった時に開始され、温度Ｔ2になった時に終了せしめられたとすると、ＮＯｘ吸蔵触媒１１の温度ＴＣが機関の通常運転によって温度Ｔ2から温度Ｔ4に上昇するまでＮＯｘ浄化能力Ｎｃが不足している状態が続いてしまう。 In this way, the temperature rise control start temperature (ie, the predetermined temperature Td) and end temperature (ie, the target temperature To) are set in consideration of the influence of the deterioration degree of the NOx storage catalyst 11 on the NOx purification capacity Nc. Thus, the temperature rise control is performed over an appropriate temperature range according to the degree of deterioration, and the time during which the NOx purification capability Nc is equal to or less than the required NOx purification capability Nr can be efficiently shortened. That is, for example, even when the NOx storage catalyst 11 is deteriorated, the temperature increase control is started when the temperature TC of the NOx storage catalyst 11 reaches the temperature T 1 and is ended when the temperature T 2 reaches the temperature T 2 . temperature TC of the NOx storing catalyst 11 will continue to be a state where the NOx purifying ability Nc is insufficient to increase the temperature T 2 to the temperature T 4 by the normal operation of the engine.

なお、上述したようなＮＯｘ吸蔵触媒１１の劣化度合に応じた昇温制御の開始温度及び終了温度の設定を行うためには、ＮＯｘ吸蔵触媒１１の劣化度合とそれに対応する適切な昇温制御の開始温度及び終了温度との関係を事前に求め、マップ化しておくとよい。   In order to set the start temperature and the end temperature of the temperature increase control according to the deterioration degree of the NOx storage catalyst 11 as described above, the deterioration degree of the NOx storage catalyst 11 and an appropriate temperature increase control corresponding thereto are performed. The relationship between the start temperature and the end temperature may be obtained in advance and mapped.

更に、本発明の他の実施形態においては、機関の冷間始動後等において、ＮＯｘ吸蔵触媒１１の温度ＴＣが上昇して所定温度Ｔｄになった時にＮＯｘ吸蔵触媒１１の活性化を目的としてＮＯｘ吸蔵触媒１１の温度ＴＣを所定の目標温度Ｔｏまで昇温する昇温制御を実施するようにしている排気浄化装置において、推定されたＮＯｘ吸蔵触媒１１の硫黄被毒の度合が高い程、上記所定温度Ｔｄが低く設定されるようになっている。   Furthermore, in another embodiment of the present invention, for example, for the purpose of activating the NOx storage catalyst 11 when the temperature TC of the NOx storage catalyst 11 rises to a predetermined temperature Td after a cold start of the engine or the like. In the exhaust gas purification apparatus in which the temperature raising control for raising the temperature TC of the storage catalyst 11 to the predetermined target temperature To is performed, the higher the estimated degree of sulfur poisoning of the NOx storage catalyst 11, the higher the predetermined value. The temperature Td is set low.

このようにすると、ＮＯｘ吸蔵触媒１１が硫黄被毒された場合には昇温制御がＮＯｘ吸蔵触媒１１の温度ＴＣのより低い時から開始されるようになり、結果としてＮＯｘ吸蔵触媒の温度ＴＣの低い状態が短くされる。そして上述したようにＮＯｘ吸蔵触媒１１が硫黄被毒された場合には低温側でのＮＯｘ浄化能力Ｎｃが特に低下するので、上記のようにして昇温制御をＮＯｘ吸蔵触媒１１の温度ＴＣのより低い時から開始するようにすることで、充分なＮＯｘの除去の実現を図ることができる。   In this way, when the NOx storage catalyst 11 is poisoned with sulfur, the temperature increase control is started when the temperature TC of the NOx storage catalyst 11 is lower, and as a result, the temperature TC of the NOx storage catalyst 11 is increased. The low state is shortened. As described above, when the NOx storage catalyst 11 is poisoned with sulfur, the NOx purification ability Nc on the low temperature side is particularly reduced. Therefore, the temperature increase control is performed by the temperature TC of the NOx storage catalyst 11 as described above. By starting from a low time, it is possible to realize sufficient removal of NOx.

そして、この場合においても、ＮＯｘ吸蔵触媒１１の硫黄被毒度合がＮＯｘ浄化能力Ｎｃへ与える影響を考慮して昇温制御の開始温度（すなわち上記所定温度Ｔｄ）と終了温度（すなわち上記目標温度Ｔｏ）を設定することで、ＮＯｘ浄化能力Ｎｃが不足する時間を効率的に短縮することができる。これについて図８を参照しつつ説明する。すなわち図８においては、実線が、ＮＯｘ吸蔵触媒１１が硫黄被毒している場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表し、点線が、ＮＯｘ吸蔵触媒１１が硫黄被毒されていない場合のＮＯｘ吸蔵触媒１１のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒１１の温度ＴＣとの関係を表していて、Ｎｒが必要なＮＯｘ浄化能力を表している。図８で示された例において、ＮＯｘ吸蔵触媒１１が硫黄被毒されていない場合には、昇温制御はＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔ1になった時に開始され、温度Ｔ2になった時に終了せしめられる。そして、ＮＯｘ吸蔵触媒１１が硫黄被毒されている場合には、昇温制御はＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔ5以下である時は常に実施され、温度Ｔ5になった時に終了せしめられる。 In this case also, the temperature rise control start temperature (that is, the predetermined temperature Td) and end temperature (that is, the target temperature To) are considered in consideration of the influence of the sulfur poisoning degree of the NOx storage catalyst 11 on the NOx purification capability Nc. ) Can be set to efficiently reduce the time for which the NOx purification capacity Nc is insufficient. This will be described with reference to FIG. That is, in FIG. 8, the solid line represents the relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the NOx storage catalyst 11 is poisoned with sulfur, and the dotted line represents the NOx storage catalyst. The relationship between the NOx purification capacity Nc of the NOx storage catalyst 11 and the temperature TC of the NOx storage catalyst 11 when the catalyst 11 is not poisoned with sulfur is shown, and the NOx purification capacity that requires Nr is shown. In the example shown in FIG. 8, when the NOx storage catalyst 11 is not poisoned with sulfur, the temperature increase control is started when the temperature TC of the NOx storage catalyst 11 reaches the temperature T 1, and reaches the temperature T 2 . It is finished when it becomes. When the NOx storage catalyst 11 is sulfur poisoning, the temperature increase control is always performed when the temperature TC of the NOx storing catalyst 11 is the temperature T 5 less, allowed ends when it becomes the temperature T 5 It is done.

このようにＮＯｘ吸蔵触媒１１の硫黄被毒度合がＮＯｘ浄化能力Ｎｃへ与える影響を考慮して昇温制御の開始温度（すなわち上記所定温度Ｔｄ）と終了温度（すなわち上記目標温度Ｔｏ）を設定することで、昇温制御が硫黄被毒度合に応じた適切な温度範囲に対して実施されるようになり、ＮＯｘ浄化能力Ｎｃが必要ＮＯｘ浄化能力Ｎｒ以下になる時間を効率的に短縮することができる。すなわち、例えばＮＯｘ吸蔵触媒１１が硫黄被毒されている場合にも昇温制御がＮＯｘ吸蔵触媒１１の温度ＴＣが温度Ｔ1になった時に開始され、温度Ｔ2になった時に終了せしめられるとすると、ＮＯｘ吸蔵触媒１１の温度ＴＣが機関の通常運転によって温度Ｔ1に上昇するまでの間及び温度Ｔ2から温度Ｔ5に上昇するまでの間はＮＯｘ浄化能力Ｎｃが不足している状態が続いてしまう。 As described above, the start temperature (that is, the predetermined temperature Td) and the end temperature (that is, the target temperature To) of the temperature increase control are set in consideration of the influence of the degree of sulfur poisoning of the NOx storage catalyst 11 on the NOx purification ability Nc. As a result, the temperature increase control is performed over an appropriate temperature range corresponding to the degree of sulfur poisoning, and the time during which the NOx purification capability Nc is equal to or less than the required NOx purification capability Nr can be efficiently shortened. it can. That is, for example, when the NOx storage catalyst 11 is poisoned with sulfur, the temperature increase control is started when the temperature TC of the NOx storage catalyst 11 reaches the temperature T 1 and is ended when the temperature TC reaches the temperature T 2. then, the state between the between and temperature T 2 to the temperature TC of the NOx storage catalyst 11 is raised to the temperature T 1 of the normal operation of the engine until the rise in the temperature T 5 is the NOx purifying ability Nc is insufficient It will continue.

なお、上述したようなＮＯｘ吸蔵触媒１１の硫黄被毒度合に応じた昇温制御の開始温度及び終了温度の設定を行うためには、劣化度合に関する場合と同様、ＮＯｘ吸蔵触媒１１の硫黄被毒度合とそれに対応する適切な昇温制御の開始温度及び終了温度との関係を事前に求め、マップ化しておくとよい。   In order to set the start temperature and the end temperature of the temperature increase control according to the sulfur poisoning degree of the NOx storage catalyst 11 as described above, the sulfur poisoning of the NOx storage catalyst 11 is the same as in the case of the deterioration degree. The relationship between the degree and the start temperature and end temperature of appropriate temperature increase control corresponding to the degree is preferably obtained in advance and mapped.

また、本発明の更に別の実施形態においては、機関の始動後等において、推定されたＮＯｘ吸蔵触媒１１の劣化度合に応じてＮＯｘ吸蔵触媒１１の温度ＴＣを低く維持するための低温維持制御が実施されるようになっている。すなわち、ＮＯｘ吸蔵触媒１１の劣化度合が高い場合（例えば予め定めた基準の劣化度合より高い場合）に低温維持制御が行われる。また、この場合に劣化度合が高い程、低温維持制御の時間を長くする、あるいは維持する温度を低くするようにしてもよい。この時、制御パラメータ（例えば、低温維持制御の時間等）の具体的な値は、ＮＯｘ吸蔵触媒１１の劣化度合と低温側でのＮＯｘ浄化能力Ｎｃの上昇との関係に基づいて事前にＮＯｘ吸蔵触媒１１の劣化度合と必要な制御パラメータの適切な値とを対応させたマップを作成しておき、それに基づいて求めるようにすることができる。なお、ここでの低温維持制御は、例えば、燃料噴射時期を進角すること、ＥＧＲ量を減少すること、ＮＯｘ吸蔵触媒１１の上流に空気を導入することの少なくとも何れか一つを実施することで実現することができる。   In yet another embodiment of the present invention, low temperature maintenance control for keeping the temperature TC of the NOx occlusion catalyst 11 low according to the estimated degree of deterioration of the NOx occlusion catalyst 11 after engine startup or the like is performed. To be implemented. That is, the low temperature maintenance control is performed when the deterioration degree of the NOx storage catalyst 11 is high (for example, when the deterioration degree is higher than a predetermined reference deterioration degree). In this case, the higher the degree of deterioration, the longer the time for low temperature maintenance control, or the lower the temperature to be maintained. At this time, the specific value of the control parameter (for example, the time for maintaining the low temperature) is stored in advance based on the relationship between the degree of deterioration of the NOx storage catalyst 11 and the increase in the NOx purification capacity Nc on the low temperature side. A map in which the degree of deterioration of the catalyst 11 is associated with an appropriate value of a necessary control parameter can be created and obtained based on the map. Note that the low temperature maintenance control here includes, for example, at least one of advancing the fuel injection timing, reducing the EGR amount, and introducing air upstream of the NOx storage catalyst 11. Can be realized.

このような実施形態によれば、ＮＯｘ吸蔵触媒１１が劣化している場合にＮＯｘ吸蔵触媒１１がその温度ＴＣの低い状態に長く維持される。そして上述したようにＮＯｘ吸蔵触媒１１が劣化された場合には低温側でのＮＯｘ浄化能力Ｎｃが上昇するので、上記のようにしてＮＯｘ吸蔵触媒１１をその温度ＴＣの低い状態に長く維持することで、より効率的なＮＯｘの除去が可能となる。   According to such an embodiment, when the NOx storage catalyst 11 is deteriorated, the NOx storage catalyst 11 is maintained at a low temperature TC for a long time. As described above, when the NOx storage catalyst 11 is deteriorated, the NOx purification ability Nc on the low temperature side increases, so that the NOx storage catalyst 11 is maintained at a low temperature TC for a long time as described above. Thus, more efficient removal of NOx becomes possible.

更に、本発明の他の実施形態においては、ＮＯｘ吸蔵触媒１１の温度ＴＣが所定温度Ｔｆ未満である時には、リーン空燃比のもとで燃焼を行った際に発生する一酸化窒素ＮＯに対する二酸化窒素ＮＯ2の割合を、ＮＯｘ吸蔵触媒１１の温度ＴＣが所定温度Ｔｆ以上である時の同一の機関運転状態、すなわち同一回転数、同一トルクの場合に比べて増大させるようにしている排気浄化装置において、推定されたＮＯｘ吸蔵触媒１１の劣化度合が高い程、上記所定温度Ｔｆが高く設定されるようになっている。 Furthermore, in another embodiment of the present invention, when the temperature TC of the NOx storage catalyst 11 is less than the predetermined temperature Tf, nitrogen dioxide with respect to nitrogen monoxide NO generated when combustion is performed under a lean air-fuel ratio. In the exhaust gas purification apparatus in which the ratio of NO 2 is increased compared to the same engine operating state when the temperature TC of the NOx storage catalyst 11 is equal to or higher than the predetermined temperature Tf, that is, the same rotational speed and the same torque. The predetermined temperature Tf is set higher as the estimated degree of deterioration of the NOx storage catalyst 11 is higher.

上述したように排気ガス中に含まれる二酸化窒素ＮＯ2はＮＯｘ吸蔵触媒１１が活性化しなくてもＮＯｘ吸収剤４７に低温吸蔵されるが、排気ガス中に含まれる一酸化窒素ＮＯはＮＯｘ吸蔵触媒１１が活性化して二酸化窒素ＮＯ2に酸化されないとＮＯｘ吸収剤４７に高温吸蔵されない。このため、ＮＯｘ吸蔵触媒１１が活性化していない、または低活性であるＮＯｘ吸蔵触媒１１の低温時には、排気ガス中の一酸化窒素ＮＯの量を減らし、排気ガス中の二酸化窒素ＮＯ2の量を増大することが好ましい。そこで、上記所定温度Ｔｆを例えば、ＮＯｘ吸収剤４７に単位時間当たりに低温吸蔵される二酸化窒素ＮＯ2の量と単位時間当たりに高温吸蔵される窒素酸化物ＮＯｘの量とが等しくなる温度に設定すれば、二酸化窒素ＮＯ2の低温吸蔵がより期待できる温度域で排気ガス中の二酸化窒素ＮＯ2の量を増大することになり、ＮＯｘ浄化率の向上を図ることができる。 As described above, nitrogen dioxide NO 2 contained in the exhaust gas is stored in the NOx absorbent 47 at a low temperature even if the NOx storage catalyst 11 is not activated, but nitrogen monoxide NO contained in the exhaust gas is stored in the NOx storage catalyst. The NOx absorbent 47 is not occluded at high temperature unless 11 is activated and oxidized to nitrogen dioxide NO 2 . Therefore, when the NOx storage catalyst 11 is not activated or has a low activity, the NOx storage catalyst 11 has a low temperature, the amount of nitrogen monoxide NO in the exhaust gas is reduced, and the amount of nitrogen dioxide NO 2 in the exhaust gas is reduced. It is preferable to increase. Therefore, for example, the predetermined temperature Tf is set to a temperature at which the amount of nitrogen dioxide NO 2 stored in the NOx absorbent 47 at a low temperature per unit time is equal to the amount of nitrogen oxide NOx stored at a high temperature per unit time. In this case, the amount of nitrogen dioxide NO 2 in the exhaust gas is increased in a temperature range where low-temperature storage of nitrogen dioxide NO 2 can be expected, and the NOx purification rate can be improved.

そして、上述したように低温吸蔵に基づくＮＯｘ浄化能力ＮｃはＮＯｘ吸蔵触媒１１が劣化された場合に結果的に増加するので、上記のようにＮＯｘ吸蔵触媒１１の劣化度合が高い程、上記所定温度Ｔｆを高くし、低温吸蔵に期待する温度範囲を広げることで、より効率的なＮＯｘの除去が可能となる。   As described above, the NOx purification capacity Nc based on the low-temperature storage increases as a result when the NOx storage catalyst 11 is deteriorated. Therefore, the higher the degree of deterioration of the NOx storage catalyst 11 as described above, the higher the predetermined temperature. By increasing Tf and expanding the temperature range expected for low-temperature storage, more efficient removal of NOx becomes possible.

また、本発明の他の実施形態においては、ＮＯｘ吸蔵触媒１１の温度ＴＣが所定温度Ｔｆ未満である時には、リーン空燃比のもとで燃焼を行った際に発生する一酸化窒素ＮＯに対する二酸化窒素ＮＯ2の割合を、ＮＯｘ吸蔵触媒１１の温度ＴＣが所定温度Ｔｆ以上である時の同一の機関運転状態、すなわち同一回転数、同一トルクの場合に比べて増大させるようにしている排気浄化装置において、推定されたＮＯｘ吸蔵触媒１１の硫黄被毒の度合が高い程、上記所定温度Ｔｆが低く設定されるようになっている。 In another embodiment of the present invention, when the temperature TC of the NOx storage catalyst 11 is lower than the predetermined temperature Tf, nitrogen dioxide with respect to nitrogen monoxide NO generated when combustion is performed under a lean air-fuel ratio. In the exhaust gas purification apparatus in which the ratio of NO 2 is increased compared to the same engine operating state when the temperature TC of the NOx storage catalyst 11 is equal to or higher than the predetermined temperature Tf, that is, the same rotational speed and the same torque. The predetermined temperature Tf is set lower as the estimated degree of sulfur poisoning of the NOx storage catalyst 11 is higher.

上述したように低温吸蔵に基づくＮＯｘ浄化能力ＮｃはＮＯｘ吸蔵触媒１１が硫黄被毒された場合に大きな影響を受ける。つまり、ＮＯｘ吸蔵触媒１１が硫黄被毒されると低温吸蔵に基づくＮＯｘ浄化能力Ｎｃは極めて低くなってしまう。そのため、上記のようにＮＯｘ吸蔵触媒１１の硫黄被毒の度合が高い程、上記所定温度Ｔｆを低くし、低温吸蔵に期待する温度範囲を縮小することで、充分なＮＯｘの除去の実現を図ることができる。   As described above, the NOx purification capacity Nc based on low-temperature storage is greatly affected when the NOx storage catalyst 11 is poisoned with sulfur. That is, when the NOx storage catalyst 11 is poisoned with sulfur, the NOx purification ability Nc based on the low temperature storage becomes extremely low. Therefore, the higher the degree of sulfur poisoning of the NOx storage catalyst 11 as described above, the lower the predetermined temperature Tf and the lower the temperature range expected for low temperature storage, thereby realizing sufficient removal of NOx. be able to.

なお、上記のＮＯ2の割合（＝ＮＯ2の量／ＮＯの量）は、緩慢な燃焼を行わせると増大することが判明しており、例えば燃料噴射時期を遅角するか、ＥＧＲガス量を増大するか、パイロット噴射を行うか、または予混合気燃焼を行うかの少なくとも何れか一つを行うと燃焼が緩慢となる。そこで本発明による実施形態のうち上記のような排気ガス中の二酸化窒素ＮＯ2量の増大を図るものでは、二酸化窒素ＮＯ2量の増大の必要がある時に上記の燃焼を緩慢にする方法の少なくとも何れか一つを実施して緩慢な燃焼を行わせるようにしている。 It has been found that the ratio of NO 2 (= NO 2 amount / NO amount) increases when slow combustion is performed. For example, the fuel injection timing is retarded or the EGR gas amount is increased. When at least one of the above is increased, pilot injection is performed, or premixed gas combustion is performed, the combustion becomes slow. Therefore, in the embodiment according to the present invention, in order to increase the amount of nitrogen dioxide NO 2 in the exhaust gas as described above, at least the method of slowing down the combustion when the amount of nitrogen dioxide NO 2 needs to be increased is required. Either one is implemented to cause slow combustion.

なお、以上の説明では、昇温制御は燃料噴射パターンを制御することによって行われたが、本発明はこれに限定されるものではなく、例えば電気ヒータを用いる等、他の手段によってＮＯｘ吸蔵触媒１１を昇温するようにしてもよい。   In the above description, the temperature raising control is performed by controlling the fuel injection pattern. However, the present invention is not limited to this, and the NOx occlusion catalyst is used by other means such as using an electric heater. 11 may be heated.

また、以上の説明では理解を容易にするためにＮＯｘ吸蔵触媒１１の劣化度合に応じて行われる制御とＮＯｘ吸蔵触媒１１の硫黄被毒度合に応じて行われる制御とを別々に説明したが、これら両方の度合を考慮して実施する制御を決定するようにしてもよい。この場合、例えばＮＯｘ吸蔵触媒１１が劣化し且つ硫黄被毒されていると、低温側でのＮＯｘ浄化能力Ｎｃは劣化度合に応じた分だけ上昇し、硫黄被毒度合に応じた分だけ低下するものとして実施する制御が決定される。したがって、上述した機関の冷間始動後に昇温制御を開始するまでの所定時間ｔｓを例にとると、劣化度合に応じた分だけ長くされた後、硫黄被毒度合に応じた分だけ短くされて実際の制御に用いられる最終的な所定時間ｔｓが決定される。   Moreover, in the above description, in order to facilitate understanding, the control performed according to the deterioration degree of the NOx storage catalyst 11 and the control performed according to the sulfur poisoning degree of the NOx storage catalyst 11 are separately described. The control to be performed may be determined in consideration of both of these degrees. In this case, for example, if the NOx storage catalyst 11 is deteriorated and sulfur-poisoned, the NOx purification capacity Nc on the low temperature side increases by the amount corresponding to the degree of deterioration and decreases by the amount corresponding to the degree of sulfur poisoning. The control to be implemented is determined. Therefore, taking as an example the predetermined time ts until the temperature raising control is started after the cold start of the engine described above, it is increased by an amount corresponding to the degree of deterioration and then reduced by an amount corresponding to the degree of sulfur poisoning. Thus, a final predetermined time ts used for actual control is determined.

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。FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. 図２は、ＮＯｘ吸蔵触媒の担体表面部分の断面を図解的に示す図である。FIG. 2 is a diagram schematically showing a cross-section of the carrier surface portion of the NOx storage catalyst. 図３は、ＮＯｘ吸蔵触媒のＮＯｘ浄化能力ＮｃとＮＯｘ吸蔵触媒の温度ＴＣとの関係を示す図である。FIG. 3 is a diagram showing the relationship between the NOx purification capacity Nc of the NOx storage catalyst and the temperature TC of the NOx storage catalyst. 図４は、図３と同様の図であり、ＮＯｘ吸蔵触媒が劣化している場合と劣化していない場合とを比較して示している。FIG. 4 is a view similar to FIG. 3 and shows a comparison between a case where the NOx storage catalyst is deteriorated and a case where the NOx storage catalyst is not deteriorated. 図５は、図３と同様の図であり、ＮＯｘ吸蔵触媒が硫黄被毒されている場合と硫黄被毒されていない場合とを比較して示している。FIG. 5 is a view similar to FIG. 3 and shows a comparison between a case where the NOx storage catalyst is sulfur-poisoned and a case where it is not sulfur-poisoned. 図６は、種々の燃料噴射パターンを示す図である。FIG. 6 is a diagram showing various fuel injection patterns. 図７は、本発明の一実施形態において、ＮＯｘ吸蔵触媒の昇温制御の開始温度と終了温度を決定する方法を説明するための図である。FIG. 7 is a diagram for explaining a method for determining the start temperature and the end temperature of the temperature increase control of the NOx storage catalyst in an embodiment of the present invention. 図８は、本発明の他の実施形態において、ＮＯｘ吸蔵触媒の昇温制御の開始温度と終了温度を決定する方法を説明するための図である。FIG. 8 is a diagram for explaining a method for determining the start temperature and the end temperature of the temperature rise control of the NOx storage catalyst in another embodiment of the present invention.

符号の説明Explanation of symbols

３…燃料噴射弁
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
１１…ＮＯｘ吸蔵触媒
１３…還元剤供給弁 3 ... Fuel injection valve 4 ... Intake manifold 5 ... Exhaust manifold 7 ... Exhaust turbocharger 11 ... NOx storage catalyst 13 ... Reductant supply valve

Claims (8)

機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒と、
該ＮＯｘ吸蔵触媒の活性状態に基づいて上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力を推定する手段と、を具備した内燃機関の排気浄化装置において、
上記ＮＯｘ浄化能力推定手段は上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、該酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を大きく推定する排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated NOx storage catalyst that stores nitrogen dioxide NO 2 in the NOx absorbent at a low temperature and, when activated, stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature;
Means for estimating the NOx purification capacity of the NOx storage catalyst based on the active state of the NOx storage catalyst,
The above NOx purification ability estimation means comprise means for estimating the reduction degree of the oxidation performance of the NOx storage catalyst, as degree of reduction in oxidation performance estimated by the oxidation degradation degree estimating means is high, the NOx storage catalyst An exhaust gas purification apparatus that largely estimates the NOx purification capacity based on the low temperature storage. 機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒と、
該ＮＯｘ吸蔵触媒の活性状態に基づいて上記ＮＯｘ吸蔵触媒のＮＯｘ浄化能力を推定する手段と、を具備した内燃機関の排気浄化装置において、
上記ＮＯｘ浄化能力推定手段は上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、該硫黄被毒度合推定手段によって推定された硫黄被毒の度合が高い程、上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を小さく推定するようにした排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated NOx storage catalyst that stores nitrogen dioxide NO 2 in the NOx absorbent at a low temperature and, when activated, stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature;
Means for estimating the NOx purification capacity of the NOx storage catalyst based on the active state of the NOx storage catalyst,
The NOx purification capacity estimation means includes means for estimating the degree of sulfur poisoning of the NOx storage catalyst, and the higher the degree of sulfur poisoning estimated by the sulfur poisoning degree estimation means, the higher the NOx storage catalyst. An exhaust gas purification apparatus in which the NOx purification capacity based on the low-temperature storage is estimated to be small. 上記ＮＯｘ浄化能力推定手段が更に上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、推定された硫黄被毒の度合が高い程上記ＮＯｘ吸蔵触媒の上記低温吸蔵に基づくＮＯｘ浄化能力を小さく推定する請求項１に記載の排気浄化装置。   The NOx purification capacity estimating means further includes means for estimating the degree of sulfur poisoning of the NOx storage catalyst, and the higher the estimated degree of sulfur poisoning, the more the NOx purification based on the low temperature storage of the NOx storage catalyst. The exhaust emission control device according to claim 1, wherein the capacity is estimated to be small. 機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、機関の始動後に上記ＮＯｘ吸蔵触媒の温度を予め定めた目標温度以上に上昇させる昇温制御が実施される内燃機関の排気浄化装置において、
更に上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、該酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記昇温制御の開始時期が遅れるようにされる、または、機関の始動から上記ＮＯｘ吸蔵触媒の温度が上記目標温度になるまでの時間が長くなるようにされる排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated A NOx storage catalyst that stores nitrogen dioxide NO 2 in the NOx absorbent at a low temperature and, when activated, stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature, is provided after the engine is started. In the exhaust gas purification apparatus for an internal combustion engine in which the temperature raising control for raising the temperature of the storage catalyst to a predetermined target temperature or higher is performed
Further comprise means for estimating the reduction degree of the oxidation performance of the NOx storage catalyst, as degree of reduction in oxidation performance estimated by the oxidation degradation degree estimating means is high, so that the starting time of the temperature increase control is delayed Or an exhaust purification device in which the time from the start of the engine until the temperature of the NOx storage catalyst reaches the target temperature is lengthened. 機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、機関の始動後に上記ＮＯｘ吸蔵触媒の温度を予め定めた目標温度以上に上昇させる昇温制御が実施される内燃機関の排気浄化装置において、
更に上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、該硫黄被毒度合推定手段によって推定された硫黄被毒の度合が高い程、上記昇温制御の開始時期が早まるようにされる、または、機関の始動から上記ＮＯｘ吸蔵触媒の温度が上記目標温度になるまでの時間が短くなるようにされる排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated A NOx storage catalyst that stores nitrogen dioxide NO 2 in the NOx absorbent at a low temperature and, when activated, stores nitrogen oxide NOx contained in the exhaust gas in the NOx absorbent at a high temperature, is provided after the engine is started. In the exhaust gas purification apparatus for an internal combustion engine in which the temperature raising control for raising the temperature of the storage catalyst to a predetermined target temperature or higher is performed
Furthermore, a means for estimating the degree of sulfur poisoning of the NOx storage catalyst is provided, so that the higher the degree of sulfur poisoning estimated by the sulfur poisoning degree estimating means, the earlier the start timing of the temperature increase control. Or an exhaust purification device in which the time from the start of the engine until the temperature of the NOx storage catalyst reaches the target temperature is shortened. 機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒と、該ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段とを具備し、機関の始動後に上記酸化性能低下度合推定手段によって推定された酸化性能の低下度合が所定の低下度合以上であれば上記ＮＯｘ吸蔵触媒の温度を低く維持するための低温維持制御が実施される内燃機関の排気浄化装置において、
上記酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記低温維持制御の実施時間を長くする、または上記低温維持制御において維持する温度を低くするようにした排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated Nitrogen dioxide NO 2 is stored in the NOx absorbent at a low temperature, and when activated, the NOx storage catalyst that stores NOx absorbent in the exhaust gas at a high temperature is stored in the NOx absorbent, and the oxidation performance of the NOx storage catalyst And a means for estimating the degree of decrease, and the temperature of the NOx occlusion catalyst is kept low if the degree of decrease in oxidation performance estimated by the degree of decrease in oxidation performance estimated after starting the engine is equal to or greater than a predetermined degree of decrease. In an exhaust gas purification apparatus for an internal combustion engine in which low temperature maintenance control is performed for
The exhaust gas purification apparatus in which the lower the oxidation performance estimated by the oxidation performance degradation degree estimation means, the longer the duration of the low temperature maintenance control, or the lower the temperature maintained in the low temperature maintenance control. 機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、上記ＮＯｘ吸蔵触媒の温度が所定温度未満である時には、リーン空燃比のもとで燃焼を行った際に発生する一酸化窒素ＮＯに対する二酸化窒素ＮＯ2の割合を、ＮＯｘ吸蔵触媒の温度が上記所定温度以上である時の同一の機関運転状態の場合に比べて増大させるようにしている排気浄化装置において、
更に上記ＮＯｘ吸蔵触媒の酸化性能の低下度合を推定する手段を備えていて、該酸化性能低下度合推定手段によって推定された酸化性能の低下度合が高い程、上記所定温度が高く設定されるようになっている排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated nitrogen dioxide NO 2 is cold stored in the NOx absorbent, when being activated comprising the NOx storage catalyst to a high temperature storage of nitrogen oxides NOx in the exhaust gas in the NOx absorbent, the temperature of the NOx storage catalyst Is lower than the predetermined temperature, the ratio of nitrogen dioxide NO 2 to nitrogen monoxide NO generated when combustion is performed at a lean air-fuel ratio is determined when the temperature of the NOx storage catalyst is equal to or higher than the predetermined temperature. In the exhaust emission control device that is increased compared to the case of the same engine operating state,
Further comprise means for estimating the reduction degree of the oxidation performance of the NOx storage catalyst, the higher the degree of reduction in oxidation performance estimated by the oxidation degradation degree estimating means, so that the predetermined temperature is set high Exhaust gas purification device. 機関排気通路内に配置された貴金属触媒とＮＯｘ吸収剤とからなるＮＯｘ吸蔵触媒であって、流入する排気ガスの空燃比がリーンである場合において、活性化されていない時には排気ガス中に含まれる二酸化窒素ＮＯ2をＮＯｘ吸収剤に低温吸蔵し、活性化されている時には排気ガス中に含まれる窒素酸化物ＮＯｘをＮＯｘ吸収剤に高温吸蔵するＮＯｘ吸蔵触媒を具備し、上記ＮＯｘ吸蔵触媒の温度が所定温度未満である時には、リーン空燃比のもとで燃焼を行った際に発生する一酸化窒素ＮＯに対する二酸化窒素ＮＯ2の割合を、ＮＯｘ吸蔵触媒の温度が上記所定温度以上である時の同一の機関運転状態の場合に比べて増大させるようにしている排気浄化装置において、
更に上記ＮＯｘ吸蔵触媒の硫黄被毒の度合を推定する手段を備えていて、該硫黄被毒度合推定手段によって推定された硫黄被毒の度合が高い程、上記所定温度が低く設定されるようになっている排気浄化装置。 A NOx occlusion catalyst comprising a noble metal catalyst and a NOx absorbent disposed in the engine exhaust passage, and when the air-fuel ratio of the inflowing exhaust gas is lean, it is included in the exhaust gas when it is not activated nitrogen dioxide NO 2 is cold stored in the NOx absorbent, when being activated comprising the NOx storage catalyst to a high temperature storage of nitrogen oxides NOx in the exhaust gas in the NOx absorbent, the temperature of the NOx storage catalyst Is lower than the predetermined temperature, the ratio of nitrogen dioxide NO 2 to nitrogen monoxide NO generated when combustion is performed at a lean air-fuel ratio is determined when the temperature of the NOx storage catalyst is equal to or higher than the predetermined temperature. In the exhaust emission control device that is increased compared to the case of the same engine operating state,
Further, a means for estimating the degree of sulfur poisoning of the NOx storage catalyst is provided, and the predetermined temperature is set lower as the degree of sulfur poisoning estimated by the sulfur poisoning degree estimating means is higher. Exhaust gas purification device.
JP2003364865A 2003-10-24 2003-10-24 Exhaust gas purification device for internal combustion engine Expired - Fee Related JP4285193B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2003364865A JP4285193B2 (en) 2003-10-24 2003-10-24 Exhaust gas purification device for internal combustion engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2003364865A JP4285193B2 (en) 2003-10-24 2003-10-24 Exhaust gas purification device for internal combustion engine

Publications (2)

Publication Number Publication Date
JP2005127248A JP2005127248A (en) 2005-05-19
JP4285193B2 true JP4285193B2 (en) 2009-06-24

Family

ID=34643716

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2003364865A Expired - Fee Related JP4285193B2 (en) 2003-10-24 2003-10-24 Exhaust gas purification device for internal combustion engine

Country Status (1)

Country Link
JP (1) JP4285193B2 (en)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4706404B2 (en) * 2005-09-13 2011-06-22 トヨタ自動車株式会社 Exhaust gas purification device for internal combustion engine
JP4739104B2 (en) * 2006-04-21 2011-08-03 日本特殊陶業株式会社 Sensor control device
JP2010255531A (en) * 2009-04-24 2010-11-11 Honda Motor Co Ltd Exhaust emission control system for internal combustion engine

Also Published As

Publication number Publication date
JP2005127248A (en) 2005-05-19

Similar Documents

Publication Publication Date Title
JP4158697B2 (en) Exhaust gas purification device and exhaust gas purification method for internal combustion engine
JP2004068700A (en) Exhaust gas purification method
JP4039349B2 (en) Exhaust gas purification device for internal combustion engine
JP5056725B2 (en) Control device for internal combustion engine
JPWO2003069137A1 (en) Exhaust gas purification system and exhaust gas purification method
JP4935928B2 (en) Exhaust gas purification device for internal combustion engine
JP5748005B2 (en) Exhaust gas purification device for internal combustion engine
JP3912354B2 (en) Exhaust purification device and exhaust purification method for internal combustion engine
JP3536733B2 (en) Exhaust gas purification device for internal combustion engine
JP4285193B2 (en) Exhaust gas purification device for internal combustion engine
JP4556364B2 (en) Exhaust gas purification device for internal combustion engine
JP4357917B2 (en) Exhaust gas purification device for internal combustion engine
JP2001003782A (en) Exhaust emission control device for internal combustion engine
JP3512064B2 (en) Exhaust gas purification device for internal combustion engine
JP4269919B2 (en) Exhaust gas purification device for internal combustion engine
JP4254505B2 (en) Exhaust gas purification device for internal combustion engine
JP4003730B2 (en) Exhaust gas purification device for internal combustion engine
JP4329378B2 (en) Exhaust gas purification device for internal combustion engine
JP2003214152A (en) Exhaust emission control device for internal combustion engine
JP2005090310A (en) NOx CLEANING DEVICE
JPH11294152A (en) Compression ignition type internal combustion engine
JP5088298B2 (en) Exhaust gas purification method and exhaust gas purification system
JP2005188387A (en) Exhaust emission control device for internal combustion engine
JP2003083115A (en) Exhaust emission control device for internal combustion engine
JP2003065108A (en) Exhaust emission control device for internal combustion engine

Legal Events

Date Code Title Description
A621 Written request for application examination

Free format text: JAPANESE INTERMEDIATE CODE: A621

Effective date: 20061002

A977 Report on retrieval

Free format text: JAPANESE INTERMEDIATE CODE: A971007

Effective date: 20080910

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20081007

A131 Notification of reasons for refusal

Free format text: JAPANESE INTERMEDIATE CODE: A131

Effective date: 20081202

A521 Written amendment

Free format text: JAPANESE INTERMEDIATE CODE: A523

Effective date: 20090116

TRDD Decision of grant or rejection written
A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

Effective date: 20090303

A01 Written decision to grant a patent or to grant a registration (utility model)

Free format text: JAPANESE INTERMEDIATE CODE: A01

A61 First payment of annual fees (during grant procedure)

Free format text: JAPANESE INTERMEDIATE CODE: A61

Effective date: 20090316

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20120403

Year of fee payment: 3

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20120403

Year of fee payment: 3

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20130403

Year of fee payment: 4

FPAY Renewal fee payment (event date is renewal date of database)

Free format text: PAYMENT UNTIL: 20140403

Year of fee payment: 5

LAPS Cancellation because of no payment of annual fees