JP4333612B2 - Exhaust gas purification device and exhaust gas purification catalyst - Google Patents
Exhaust gas purification device and exhaust gas purification catalyst Download PDFInfo
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本発明は理論空燃比よりも燃料が希薄なリーンバーン状態で運転される内燃機関の排ガス浄化装置と排ガス浄化触媒に関する。 The present invention relates to an exhaust gas purification device and an exhaust gas purification catalyst for an internal combustion engine that is operated in a lean burn state in which fuel is leaner than the stoichiometric air-fuel ratio.
近年、空燃比を燃料希薄とするリーンバーンエンジンが注目されている。ここで空燃比とは、ガス中の空気と燃料の比を表す。排ガスの空燃比がリーンである場合、理論空燃比（ストイキ）用エンジンの排ガス浄化に従来使用されてきた三元触媒ではＮＯｘを浄化するのが難しい。この為、リーンバーンエンジン用の排ガス浄化触媒が検討されている。その一つに特開平１１−３１９５６４号公報（特許文献１）に記載された触媒がある。該公報には、多孔質担体にアルカリ金属，アルカリ土類金属及び希土類金属の中から選ばれた少なくとも１種のＮＯｘ吸蔵元素の酸化物と触媒貴金属とを担持してなる排ガス浄化触媒が記載されている。 In recent years, a lean burn engine in which the air-fuel ratio is a lean fuel has attracted attention. Here, the air-fuel ratio represents the ratio of air to fuel in the gas. When the air-fuel ratio of the exhaust gas is lean, it is difficult to purify NOx with a three-way catalyst that has been conventionally used for exhaust gas purification of a stoichiometric engine. For this reason, exhaust gas purification catalysts for lean burn engines have been studied. One of them is a catalyst described in JP-A-11-319564 (Patent Document 1). This publication describes an exhaust gas purifying catalyst comprising a porous carrier supporting an oxide of at least one NOx storage element selected from alkali metal, alkaline earth metal and rare earth metal and a catalyst noble metal. ing.
上記公報によれば、該公報に示された触媒を用いることにより、空燃比がリーン時においてもＮＯｘを効率良く浄化できるとしている。該触媒の浄化機構は、リーン時は排ガス中のＮＯｘを一旦酸化して触媒に捕捉し、一定量のＮＯｘが捕捉されると、排ガス中の酸素濃度を低下させてＮＯｘ吸蔵剤より吸収ＮＯｘを放出させるものである。 According to the above publication, NOx can be efficiently purified even when the air-fuel ratio is lean by using the catalyst disclosed in the publication. The purification mechanism of the catalyst oxidizes NOx in the exhaust gas once when it is lean and traps it in the catalyst. When a certain amount of NOx is trapped, the oxygen concentration in the exhaust gas is reduced to absorb the absorbed NOx from the NOx storage agent. It is what is released.
また、特開２００２−７０６１１号公報(特許文献２)には、トラップしたＮＯｘを適切に放出，還元するため、ＮＯｘトラップ触媒の上流に設けられた排ガス浄化触媒とＮＯｘトラップ触媒にストレージされている酸素量に対して過不足のない量の還元剤をＮＯｘトラップ触媒に供給するエンジンの空燃比制御装置が提案されている。 Japanese Patent Laid-Open No. 2002-70611 (Patent Document 2) stores the trapped NOx in an exhaust gas purification catalyst and a NOx trap catalyst provided upstream of the NOx trap catalyst in order to appropriately release and reduce the trapped NOx. There has been proposed an air-fuel ratio control device for an engine that supplies an amount of reducing agent that is not excessive or insufficient with respect to the amount of oxygen to a NOx trap catalyst.
上記特許文献１に開示された内容は、吸収ＮＯｘを一旦触媒から放出させるものであり、文献２に開示された内容は放出ＮＯｘの効率的な還元装置に関するものである。何れの文献においても、放出させたＮＯｘが適切に浄化できなければ却って排ガス浄化能の低下を引き起こす恐れがある。
The content disclosed in
本発明の目的は、上記課題を解消し、高いＮＯｘ浄化性能を示す排ガス浄化装置及び排ガス浄化触媒を提供することにある。 An object of the present invention is to provide an exhaust gas purification apparatus and an exhaust gas purification catalyst that solve the above-described problems and exhibit high NOx purification performance.
本発明は、空燃比がリーンの排ガスと空燃比がリッチ或いはストイキの排ガスとが流入する内燃機関排ガス流路にＮＯｘを捕捉可能な排ガス浄化触媒を備えた内燃機関の排ガス浄化装置において、排ガス中の酸素濃度,ＣＯ濃度,炭化水素濃度及び水素濃度が０％の時に捕捉できるＮＯｘ量を予め求めておき、リーンでのＮＯｘ捕捉量が該予め求めたＮＯｘ量を超えないようにリーン運転を制御することにある。リーンでのＮＯｘ捕捉量はＮＯｘセンサなどにより推算することができる。 The present invention relates to an exhaust gas purification apparatus for an internal combustion engine having an exhaust gas purification catalyst capable of capturing NOx in an exhaust gas flow path of an internal combustion engine into which an exhaust gas having a lean air-fuel ratio and a rich or stoichiometric exhaust gas flows. The NOx amount that can be captured when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration of 0% are determined in advance, and the lean operation is controlled so that the NOx trapping amount in lean does not exceed the previously determined NOx amount There is to do. The amount of NOx trapped in lean can be estimated by a NOx sensor or the like.
また、本発明は排ガス浄化触媒を少なくとも２つ用いて、リーンにおいて最初に排ガスを流通させる排ガス浄化触媒（前段排ガス浄化触媒）が排ガス中の酸素濃度及びＣＯ濃度、炭化水素濃度及び水素濃度が０％において捕捉できるＮＯｘ量を超えない所定値に捕捉量が達したとリーン運転制御装置が判断すると、該前段排ガス浄化触媒へ排ガスを通過させずに次の排ガス浄化触媒（後段排ガス浄化触媒）へと排ガスを流通させることを特徴とする内燃機関の排ガス浄化装置にある。 In the present invention, at least two exhaust gas purification catalysts are used, and the exhaust gas purification catalyst (the first stage exhaust gas purification catalyst) that first circulates the exhaust gas in lean has zero oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas. When the lean operation control device determines that the trapped amount has reached a predetermined value that does not exceed the amount of NOx that can be trapped in%, the exhaust gas does not pass through the preceding exhaust gas purification catalyst, and the next exhaust gas purification catalyst (the latter exhaust gas purification catalyst). And an exhaust gas purifying apparatus for an internal combustion engine, characterized in that the exhaust gas is circulated.
本発明の排ガス浄化方法，排ガス浄化装置及び排ガス浄化触媒によれば、理論空燃比よりも燃料が希薄なリーンバーン状態で運転される内燃機関において、ストイキまたはリッチに切り替える際に生じるＮＯｘ浄化性能の低下を抑制することができ、内燃機関からのＮＯｘの排出量を抑制することができる。 According to the exhaust gas purification method, the exhaust gas purification device, and the exhaust gas purification catalyst of the present invention, in an internal combustion engine that is operated in a lean burn state where the fuel is leaner than the stoichiometric air-fuel ratio, the NOx purification performance that occurs when switching to stoichiometric or rich is achieved. The decrease can be suppressed, and the amount of NOx emitted from the internal combustion engine can be suppressed.
通常、空燃比をリーンからストイキまたはリッチに切り替えると排ガス浄化触媒に流入する。酸素濃度は数％（例えば、７％）からほぼ０％まで低下する。ＮＯｘ吸蔵元素を用いた排ガス浄化触媒では捕捉ＮＯｘの放出が起こるため、放出ＮＯｘの還元浄化ができなければＮＯｘが排出されてしまう。しかしながら、酸素濃度は数％（例えば、７％）から０％に低下しても捕捉ＮＯｘの放出が回避できれば、捕捉された状態でＮＯｘが還元されるのでＮＯｘの排出が防止されて効果的である（なお、本願明細書においては本発明では排ガス浄化触媒に捕捉されたＮＯｘが気相の酸素濃度低下で該触媒から離れる現象を放出と記載している。）。 Normally, when the air-fuel ratio is switched from lean to stoichiometric or rich, it flows into the exhaust gas purification catalyst. The oxygen concentration decreases from a few percent (eg, 7%) to almost 0%. In the exhaust gas purification catalyst using the NOx occlusion element, trapped NOx is released. Therefore, NOx is discharged if the released NOx cannot be reduced and purified. However, if the release of trapped NOx can be avoided even if the oxygen concentration is reduced from several percent (for example, 7%) to 0%, NOx is reduced in the trapped state, so that NOx emission is prevented and effective. In the present specification, the present invention describes that the NOx trapped in the exhaust gas purification catalyst is released from the catalyst due to a decrease in the oxygen concentration in the gas phase.
本発明者が鋭意検討した結果、リーン時にＮＯｘを捕捉し、空燃比をストイキまたはリッチに切り替えて捕捉ＮＯｘを浄化しようとした時、排ガスの空燃比がリーンの間に捕捉させるＮＯｘ量が排ガス中の酸素濃度，ＣＯ濃度，炭化水素濃度及び水素濃度が０％の時に捕捉できるＮＯｘ量を超えないようにすることでＮＯｘの離脱を防止できることが判った。 As a result of intensive studies by the inventor, when NOx is captured during lean and the air-fuel ratio is switched to stoichiometric or rich to purify the captured NOx, the amount of NOx that is captured while the air-fuel ratio of the exhaust gas is lean is in the exhaust gas. It was found that NOx detachment can be prevented by not exceeding the amount of NOx that can be captured when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration are 0%.
即ち、空燃比がリーンの排ガスと空燃比がリッチ或いはストイキの排ガスとが流入する内燃機関排ガス流路にＮＯｘを捕捉可能な排ガス浄化触媒を備え、空燃比がリーンの場合には排ガス中のＮＯｘを触媒に捕捉し、空燃比がストイキまたはリッチの場合に該捕捉
ＮＯｘを還元浄化する排ガス浄化装置において、排ガスの空燃比がリーンの間に捕捉させるＮＯｘ量が排ガス中の酸素濃度，ＣＯ濃度，炭化水素濃度及び水素濃度が０％の時に捕捉できるＮＯｘ量を超えないようにリーン運転を制御するリーン運転制御装置を備えることを特徴とする内燃機関の排ガス浄化装置が好適である。
That is, an exhaust gas purification catalyst capable of capturing NOx is provided in an exhaust gas flow path of an internal combustion engine into which an exhaust gas having a lean air-fuel ratio and a rich or stoichiometric exhaust gas flows, and when the air-fuel ratio is lean, the NOx in the exhaust gas In the exhaust gas purification device that captures NOx when the air-fuel ratio is stoichiometric or rich, the amount of NOx that is captured while the air-fuel ratio of the exhaust gas is lean is the oxygen concentration, CO concentration, An exhaust gas purification apparatus for an internal combustion engine is preferable, which includes a lean operation control device that controls the lean operation so as not to exceed the NOx amount that can be captured when the hydrocarbon concentration and the hydrogen concentration are 0%.
空燃比がリーンの間に捕捉させるＮＯｘ量を決める具体的な方法として、例えば、予め排ガス中の酸素濃度を０％としたときの排ガス浄化触媒のＮＯｘ捕捉量を調べておくことができる。ＣＯ，炭化水素及び水素などの還元剤が含まれているとＮＯｘ還元が起きるため、酸素濃度を０％としたときの排ガス浄化触媒のＮＯｘ捕捉量を調べる場合には、これらの還元剤濃度も０％としておく。さらに、ＮＯｘ捕捉量は温度に依存するため、内燃機関で利用する排ガス温度領域について該ＮＯｘ捕捉量を調べ、マッピングまたは数式化してリーン運転制御装置に備えておくことが好ましい。 As a specific method for determining the amount of NOx to be captured while the air-fuel ratio is lean, for example, the amount of NOx trapped by the exhaust gas purification catalyst when the oxygen concentration in the exhaust gas is set to 0% can be examined in advance. NOx reduction occurs when reducing agents such as CO, hydrocarbons, and hydrogen are included. Therefore, when examining the NOx trapping amount of the exhaust gas purification catalyst when the oxygen concentration is 0%, these reducing agent concentrations are also Set to 0%. Furthermore, since the NOx trapping amount depends on the temperature, it is preferable to investigate the NOx trapping amount in the exhaust gas temperature region used in the internal combustion engine, and map or formulate it to prepare for the lean operation control device.
リーン時のＮＯｘ捕捉量を該排ガス中の酸素濃度，ＣＯ濃度，炭化水素濃度及び水素濃度が０％の時のＮＯｘ捕捉量以下とすることとは、具体的には、例えば排ガス浄化触媒の劣化などを考慮して触媒劣化前の該ＮＯｘ捕捉量の１／４に設定すること等である。 Specifically, when the lean NOx trapping amount is less than or equal to the NOx trapping amount when the oxygen concentration, CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%, specifically, for example, deterioration of the exhaust gas purification catalyst In consideration of the above, etc., it may be set to 1/4 of the NOx trapping amount before catalyst deterioration.
ここで、リーンでのＮＯｘ捕捉量を推定する手段の例としては、以下の方法がある。 Here, examples of means for estimating the lean NOx trapping amount include the following methods.
まず、リーンにおいて排ガス浄化触媒に流入するＮＯｘ量を積算する方法がある。通常、ＮＯｘ量の積算値は排ガス中のＮＯｘ濃度と空気量の積の積分から得られる。また、排ガス中のＮＯｘ濃度は空燃比から推算でき、空気量はエアフローセンサーまたはエンジン回転数とエンジン排気量から推算できる。予め排ガス浄化触媒に流入するＮＯ量に対するＮＯｘ捕捉量を調べておくことで、リーンにおいて排ガス浄化触媒に流入するＮＯｘ量積算値から排ガス浄化触媒に捕捉されるＮＯｘ量を推算することができる。 First, there is a method of integrating the amount of NOx flowing into the exhaust gas purification catalyst in lean. Usually, the integrated value of the NOx amount is obtained by integrating the product of the NOx concentration in the exhaust gas and the air amount. Further, the NOx concentration in the exhaust gas can be estimated from the air-fuel ratio, and the air amount can be estimated from the air flow sensor or the engine speed and the engine exhaust amount. By examining the NOx trapping amount with respect to the NO amount flowing into the exhaust gas purification catalyst in advance, the NOx amount trapped by the exhaust gas purification catalyst can be estimated from the integrated value of the NOx amount flowing into the exhaust gas purification catalyst in lean.
また、ＮＯｘセンサを利用し、排ガス浄化触媒に捕捉されたＮＯｘ量を直接調べる方法がある。具体的にはＮＯｘセンサを排ガス浄化触媒の上流と下流に設置し、上流と下流のＮＯｘセンサーが検出するＮＯｘ濃度の差分から排ガス浄化触媒に捕捉されたＮＯｘ量を求めることができる。なお、ＮＯｘセンサは上流と下流の何れか一方に設定しても推算は可能であるが、両方に設置すれば正確な推測が可能となる。 There is also a method for directly examining the amount of NOx trapped in the exhaust gas purification catalyst using a NOx sensor. Specifically, NOx sensors can be installed upstream and downstream of the exhaust gas purification catalyst, and the amount of NOx trapped by the exhaust gas purification catalyst can be determined from the difference in NOx concentration detected by the upstream and downstream NOx sensors. The NOx sensor can be estimated even if it is set on either the upstream or downstream side, but if it is installed on both, accurate estimation is possible.
他に簡便な方法として、リーン運転時間をカウントして排ガス浄化触媒に捕捉された
ＮＯｘ量を推算する方法がある。
Another simple method is to estimate the amount of NOx trapped in the exhaust gas purification catalyst by counting the lean operation time.
さらに、ＮＯｘ捕捉量は排ガス温度に依存する場合がある。そこで、リーン運転終了判断装置は流入する排ガス温度を反映させて切り替え制御を行わせることが好ましい。具体的には排ガス温度と排ガス浄化触媒に流入するＮＯｘ濃度から排ガス浄化触媒に捕捉されるＮＯｘ量を推算して排ガス中の酸素濃度が０％の時に捕捉できるＮＯｘ量以下の所定量（例えば、１／４量）に達したと判断すると、リッチ運転に切り替える制御を実行させることが好ましい。 Furthermore, the NOx trapping amount may depend on the exhaust gas temperature. Therefore, it is preferable that the lean operation end determination device performs the switching control by reflecting the inflowing exhaust gas temperature. Specifically, the amount of NOx trapped in the exhaust gas purification catalyst is estimated from the exhaust gas temperature and the NOx concentration flowing into the exhaust gas purification catalyst, and a predetermined amount below the NOx amount that can be captured when the oxygen concentration in the exhaust gas is 0% (for example, When it is determined that the ¼ amount has been reached, it is preferable to execute control to switch to rich operation.
なお、排ガス温度は、排ガス温度センサを排ガス浄化触媒の上流，触媒内部または触媒下流の何れかに設置することで調べることができる。排ガス浄化触媒内部に設置されていれば触媒自身の温度を直接知ることができて好適である。排ガス温度は車速とエンジン回転数から推算することも可能であるが、排ガス温度センサを用いる方が温度情報を正確に得られるので好ましい。 The exhaust gas temperature can be examined by installing an exhaust gas temperature sensor either upstream of the exhaust gas purification catalyst, inside the catalyst, or downstream of the catalyst. If it is installed inside the exhaust gas purification catalyst, it is preferable that the temperature of the catalyst itself can be directly known. The exhaust gas temperature can be estimated from the vehicle speed and the engine speed, but it is preferable to use an exhaust gas temperature sensor because temperature information can be obtained accurately.
ストイキないしリッチにおいて炭化水素及びＣＯなどの還元剤が排ガス浄化触媒へ供給されるが、還元剤を有効利用し燃費改善するためには、リーンで捕捉するＮＯｘ量をできるだけ多くすることが望ましい。 In stoichiometric or rich, reducing agents such as hydrocarbons and CO are supplied to the exhaust gas purification catalyst. However, in order to effectively use the reducing agent and improve fuel consumption, it is desirable to increase the amount of NOx captured by lean as much as possible.
これらの還元剤の量はリーンで捕捉されたＮＯｘを還元するのに必要な量より多い場合がある。また、排ガス浄化触媒のリーンでのＮＯｘ捕捉量を排ガス中の酸素濃度及びＣＯ濃度，炭化水素濃度及び水素濃度が０％においても補足できるＮＯｘ量以下とすることで、場合によってはリーン時間が短くなりすぎ、ストイキないしリッチとリーンとが頻繁に繰り返されてしまい、排ガス浄化性能は良いが、燃費が悪化する可能性がある。 The amount of these reducing agents may be greater than the amount required to reduce lean trapped NOx. In addition, the lean time of the exhaust gas purification catalyst can be reduced by making the NOx trapping amount in the lean of the exhaust gas purification catalyst less than the NOx amount that can be supplemented even when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0%. It becomes too much, and stoichiometric or rich and lean are frequently repeated, and although the exhaust gas purification performance is good, there is a possibility that the fuel consumption deteriorates.
一方、リーン時間を長くすると、リーンにおける排ガス浄化触媒のＮＯｘ捕捉量は、排ガス中の酸素濃度及びＣＯ濃度，炭化水素濃度及び水素濃度が０％においても捕捉できるＮＯｘ量を超えてしまう結果、ストイキないしリッチ切り替え時に排ガス浄化触媒からのＮＯｘ放出が起こり、ＮＯｘが還元浄化されずに排出されてしまう恐れがある。 On the other hand, when the lean time is lengthened, the NOx trapping amount of the exhaust gas purification catalyst in lean exceeds the NOx trapping amount that can be trapped even when the oxygen concentration, CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%. In addition, NOx release from the exhaust gas purification catalyst occurs during rich switching, and NOx may be discharged without being reduced and purified.
そこで、排ガス浄化触媒を少なくとも２つ用いて、それぞれのリーンでのＮＯｘ捕捉量を排ガス中の酸素濃度及びＣＯ濃度，炭化水素濃度及び水素濃度が０％時のＮＯｘ捕捉量以下とする方法を採用可能である。 Therefore, a method of using at least two exhaust gas purification catalysts and setting the NOx trapping amount in each lean to be equal to or less than the NOx trapping amount when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0% is adopted. Is possible.
即ち、排ガス中の酸素濃度及びＣＯ濃度，炭化水素濃度及び水素濃度が０％においても排ガス中のＮＯｘを捕捉する排ガス浄化触媒を少なくとも２つ用いて、リーンにおいて最初に排ガスを流通させる排ガス浄化触媒（前段排ガス浄化触媒）が排ガス中の酸素濃度及びＣＯ濃度，炭化水素濃度及び水素濃度が０％において捕捉できるＮＯｘ量を超えるとリーン運転制御装置が判断すると、該前段排ガス浄化触媒への排ガスを通過せずに次の排ガス浄化触媒（後段排ガス浄化触媒）へと排ガスを流通させることを特徴とする内燃機関の排ガス浄化装置となる。 That is, an exhaust gas purification catalyst that first circulates exhaust gas in lean using at least two exhaust gas purification catalysts that capture NOx in exhaust gas even when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0% When the lean operation control device determines that the (pre-stage exhaust gas purification catalyst) exceeds the NOx amount that can be captured when the oxygen concentration and CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%, the exhaust gas to the pre-stage exhaust gas purification catalyst is reduced. An exhaust gas purification apparatus for an internal combustion engine, characterized in that the exhaust gas is circulated to the next exhaust gas purification catalyst (second-stage exhaust gas purification catalyst) without passing through.
具体例としては、該前段排ガス浄化触媒の上流に切り替えバルブを設け、リーンにおいて前段排ガス浄化触媒が所定値以上のＮＯｘを補足したとリーン運転制御装置が判断すると、該切り替えバルブは該前段排ガス浄化触媒へ排ガスを通過させずに後段排ガス浄化触媒へと排ガスを流通させることを特徴とする内燃機関の排ガス浄化装置である。このようにすることで、リーン運転時間を長くし、かつストイキ及びリッチガス中の還元剤を有効に利用することができるので、排ガス浄化と共に燃費の改善の両立が可能となる。 As a specific example, a switching valve is provided upstream of the upstream exhaust gas purification catalyst, and when the lean operation control device determines that the upstream exhaust gas purification catalyst has supplemented NOx of a predetermined value or more in lean, the switching valve is switched to the upstream exhaust gas purification catalyst. An exhaust gas purification apparatus for an internal combustion engine, characterized in that exhaust gas is circulated to a subsequent exhaust gas purification catalyst without passing the exhaust gas through the catalyst. By doing so, the lean operation time can be lengthened, and the reducing agent in the stoichiometric and rich gas can be used effectively, so that it is possible to achieve both the purification of exhaust gas and the improvement of fuel consumption.
本発明に用いられる排ガス浄化触媒は、ＮＯｘ捕捉材を有している。ＮＯｘ捕捉材は、排ガス中の酸素濃度及びＣＯ濃度，炭化水素濃度及び水素濃度が０％においても排ガス中のＮＯｘを捕捉する機能を有しており、ＮＯｘを硝酸化合物として吸収する吸収剤またはＮＯ2 として化学吸着する吸着材など何れも利用できる。 The exhaust gas purification catalyst used in the present invention has a NOx trap. The NOx trapping material has a function of trapping NOx in the exhaust gas even when the oxygen concentration and CO concentration, hydrocarbon concentration and hydrogen concentration in the exhaust gas are 0%, and it absorbs NOx as a nitric acid compound or NOx Any adsorbent that chemically adsorbs as 2 can be used.
ＮＯｘ捕捉材としては、アルカリ金属又はアルカリ土類金属の少なくともいずれかを含み、かつ、リーン時のＮＯｘ酸化材及びストイキ（リッチ）時の捕捉ＮＯｘを還元するためにＰｔ，Ｐｄ，Ｒｈの少なくともいずれかを含むことが好ましい。また、触媒に含有されるアルカリ金属及びアルカリ土類金属は１種でも良いが、捕捉する温度領域に応じて２種類以上を組み合わせるのが好適である。更に貴金属をＰｔとＰｄとＲｈとすることで、リーン及びストイキまたはリッチ時において効果的にＮＯｘを浄化できる。Ｐｔは主にリーン時のＮＯの酸化反応に効果があり、Ｐｄ，Ｒｈは主にストイキ（リッチ）時の捕捉
ＮＯｘ還元反応に効果があるためと考えられる。さらに、希土類元素として、Ｃｅが含まれるとストイキ近傍での酸素吸蔵放出によりＮＯｘに加えて炭化水素及びＣＯも浄化されて好適である。
The NOx trapping material includes at least one of an alkali metal or an alkaline earth metal, and at least any of Pt, Pd, and Rh for reducing the NOx oxide during lean and the trapped NOx during stoichiometric (rich) It is preferable that these are included. Moreover, although the alkali metal and alkaline-earth metal contained in a catalyst may be 1 type, it is suitable to combine 2 or more types according to the temperature range to capture | acquire. Furthermore, NOx can be effectively purified at the time of lean, stoichiometric or rich by using noble metals as Pt, Pd and Rh. It is considered that Pt is mainly effective in the NO oxidation reaction during lean, and Pd and Rh are mainly effective in the trapped NOx reduction reaction during stoichiometric (rich). Further, when Ce is contained as a rare earth element, hydrocarbons and CO are preferably purified in addition to NOx by oxygen storage and release in the vicinity of stoichiometry.
排ガス浄化触媒の調製方法は、含浸法，混練法，共沈法，ゾルゲル法，イオン交換法，蒸着法等の物理的調製方法や化学反応を利用した調製方法等いずれも適用可能である。排ガス浄化触媒の出発原料としては、硝酸化合物，酢酸化合物，錯体化合物，水酸化物，炭酸化合物，有機化合物などの種々の化合物や金属及び金属酸化物を用いることができる。 As the method for preparing the exhaust gas purification catalyst, any of a physical preparation method such as an impregnation method, a kneading method, a coprecipitation method, a sol-gel method, an ion exchange method, and a vapor deposition method and a preparation method using a chemical reaction can be applied. As starting materials for the exhaust gas purification catalyst, various compounds such as nitric acid compounds, acetic acid compounds, complex compounds, hydroxides, carbonic acid compounds, organic compounds, metals, and metal oxides can be used.
排ガス浄化触媒にＴｉが含有されると更にストイキ（リッチ）切り替え時のＮＯｘ浄化性能が向上する。捕捉ＮＯｘ還元反応に効果があるためと考えられる。用いるＴｉ量は排ガス浄化触媒に含有されているアルカリ金属及びアルカリ土類金属の総量に対してモル比で０.０５以上１以下であることが望ましい。０.０５より少ないとＴｉの効果が表れず、多すぎると、ＮＯｘ捕捉材及び貴金属等の活性点を覆ってしまう為と考えられる。 When Ti is contained in the exhaust gas purification catalyst, the NOx purification performance at the time of stoichiometric (rich) switching is further improved. This is thought to be because the trapped NOx reduction reaction is effective. The amount of Ti to be used is desirably 0.05 or more and 1 or less in molar ratio with respect to the total amount of alkali metal and alkaline earth metal contained in the exhaust gas purification catalyst. If the amount is less than 0.05, the effect of Ti does not appear. If the amount is too large, the active points of the NOx trapping material and the noble metal are covered.
排ガス浄化触媒は、活性成分のみを用いても良いが多孔質担体上に活性成分を担持しても良い。多孔質担体上に担持されることで活性成分の高分散化が進むものと考えられる。その結果ストイキ（リッチ）切り替え時のＮＯｘ浄化性能が向上するためである。多孔質担体はさらに基材上に担持しても良く、その場合基材１Ｌに対し多孔質担体の担持量を
５０ｇ以上４００ｇ以下とするとストイキ（リッチ）切り替え時のＮＯｘ浄化性能にとって好ましい。多孔質担体の担持量が５０ｇより少ないと多孔質担体の効果は不十分となり、４００ｇより多いと多孔質担体自体の比表面積が低下し、更には基材がハニカム形状の場合、目詰まりが生じやすくなり好ましくないためである。多孔質担体としては、アルミナのほかにチタニア，シリカ，シリカ−アルミナ，ジルコニア，マグネシア等の金属酸化物や複合酸化物等を用いることができる。特にアルミナが最適である。アルミナは耐熱性が高く、更にＮＯｘ捕捉材，貴金属等の活性成分の分散を高める機能を持つと考えられる。
The exhaust gas purification catalyst may use only the active component, but may support the active component on a porous carrier. It is considered that the active ingredient is highly dispersed by being supported on the porous carrier. As a result, the NOx purification performance at the time of stoichiometric (rich) switching is improved. The porous carrier may be further supported on the substrate. In this case, the amount of the porous carrier supported on 1 L of the substrate is preferably 50 g or more and 400 g or less, which is preferable for NOx purification performance at stoichiometric (rich) switching. If the loading amount of the porous carrier is less than 50 g, the effect of the porous carrier is insufficient, and if it is more than 400 g, the specific surface area of the porous carrier itself is reduced, and further, when the substrate is in a honeycomb shape, clogging occurs. It is because it becomes easy and is not preferable. As the porous carrier, in addition to alumina, metal oxides such as titania, silica, silica-alumina, zirconia, and magnesia, composite oxides, and the like can be used. Alumina is particularly optimal. Alumina is considered to have high heat resistance and a function of enhancing dispersion of active components such as NOx trapping materials and noble metals.
本発明による排ガス浄化触媒の形状は、用途に応じ各種の形状で適用できる。コージェライト，ＳｉＣ，ステンレス等の各種材料からなるハニカム構造体に各種成分を担持した排ガス浄化触媒をコーティングして得られるハニカム形状を始めとし、ペレット状，板状，粒状，粉末状等として適用できる。ハニカム形状の場合、その基材はコージェライトが最適であるが、触媒温度が高まるおそれがある場合、触媒成分と反応しにくい基材、例えば金属製のものを用いても良好な結果を得ることができる。また排ガス浄化触媒のみからなるハニカムを形成しても良好な結果が得られる。 The shape of the exhaust gas purifying catalyst according to the present invention can be applied in various shapes depending on applications. It can be applied to pellets, plates, granules, powders, etc., including honeycomb shapes obtained by coating exhaust gas purification catalysts carrying various components on honeycomb structures made of various materials such as cordierite, SiC, and stainless steel . In the case of a honeycomb shape, cordierite is optimal as the base material. However, if there is a risk that the catalyst temperature may increase, good results can be obtained even if a base material that is difficult to react with the catalyst component, such as a metal base, is used. Can do. In addition, good results can be obtained even when a honeycomb composed only of an exhaust gas purification catalyst is formed.
〔実施例〕
以下、具体的な本発明の実施例を説明する。尚、本発明はこれらの実施例により制限されるものではない。
〔Example〕
Specific examples of the present invention will be described below. In addition, this invention is not restrict | limited by these Examples.
（ＮＯｘ浄化触媒調製法）
アルミナ粉末及びアルミナの前駆体からなり硝酸酸性に調製したスラリーをコージェライト製ハニカム（４００セル／Inc2）にコーティングした後、乾燥焼成して、ハニカムの見掛けの容積１リットルあたり１.９molのアルミナをコーティングしたアルミナコートハニカムを得た。該アルミナコートハニカムに、硝酸Ｃｅ溶液を含浸し、２００℃で乾燥、続いて６００℃で１時間焼成した。次に、該Ｃｅを担持したアルミナに、ジニトロジアンミンＰｔ硝酸溶液とジニトロジアンミンＰｄ硝酸溶液と硝酸Ｒｈ溶液と硝酸Ｎａと硝酸
Ｍｇとチタニアゾルの混合溶液を含浸し、２００℃で乾燥、続いて６００℃で１時間焼成した。
(NOx purification catalyst preparation method)
A cordierite honeycomb (400 cells / Inc 2 ) was coated with a slurry made of alumina powder and an alumina precursor and made nitric acid acidic, and then dried and fired to obtain 1.9 mol of alumina per liter of apparent volume of the honeycomb. A coated alumina coated honeycomb was obtained. The alumina-coated honeycomb was impregnated with a Ce nitrate solution, dried at 200 ° C., and then fired at 600 ° C. for 1 hour. Next, the alumina supporting Ce is impregnated with a mixed solution of dinitrodiammine Pt nitric acid solution, dinitrodiammine Pd nitric acid solution, Rh nitrate solution, Na nitrate, Mg nitrate and titania sol, dried at 200 ° C., and subsequently 600 ° C. For 1 hour.
以上により、ハニカム１Ｌに対してアルミナが１９０ｇ、及び元素換算でＣｅ：２７ｇ，Ｎａ：１８ｇ，Ｍｇ：１.８ｇ，Ｔｉ：４ｇ，Ｒｈ：０.１３９ｇ ，Ｐｔ：２.７９２ｇを含有する触媒Ａを得た。 Thus, catalyst A containing 190 g of alumina with respect to 1 L of honeycomb, and Ce: 27 g, Na: 18 g, Mg: 1.8 g, Ti: 4 g, Rh: 0.139 g, Pt: 2.792 g in terms of elements. Got.
（触媒性能評価方法）
触媒の性能を評価する為、次の条件でＮＯｘ浄化性能試験を行った。容量６ccのハニカム触媒を石英ガラス製反応管中に固定した。この反応管を電気炉中に導入し、反応管に導入されるガス温度が４５０℃となるように加熱制御した。反応管に導入されるガスは、
ＳＶ５０,０００／ｈ とし、自動車のエンジンがリッチで運転されているときの排ガスを想定したモデルガス（以下、リッチモデルガス）と、自動車のエシジンがリーンバーン運転を行っているときの排ガスを想定したモデルガス（以下、リーンモデルガス），排ガス中の酸素，炭化水素及び水素濃度を０％としたモデルガス（以下、酸素濃度０％モデルガス）を用いた。
(Catalyst performance evaluation method)
In order to evaluate the performance of the catalyst, a NOx purification performance test was conducted under the following conditions. A 6 cc honeycomb catalyst was fixed in a quartz glass reaction tube. This reaction tube was introduced into an electric furnace, and the heating was controlled so that the temperature of the gas introduced into the reaction tube was 450 ° C. The gas introduced into the reaction tube is
SV50,000 / h, model gas assuming exhaust gas when the car engine is operating rich (hereinafter rich model gas), and exhaust gas when the car Ecidin is performing lean burn operation The model gas (hereinafter referred to as lean model gas), the model gas in which the oxygen, hydrocarbon and hydrogen concentrations in the exhaust gas were set to 0% (hereinafter referred to as oxygen concentration 0% model gas) were used.
リッチモデルガスの組成は、ＮＯｘ：１０００ppm，Ｃ3Ｈ6：０.２％，ＣＯ：２％，
ＣＯ2：１２％，Ｈ2Ｏ：１０％，Ｎ2：残差とした。
The composition of the rich model gas is NOx: 1000 ppm, C 3 H 6 : 0.2%, CO: 2%,
CO 2 : 12%, H 2 O: 10%, N 2 : residual.
リーンモデルガスの組成は、ＮＯｘ：６００ppm，ＣＯ2：１２％，Ｏ2：７％，Ｈ2Ｏ：１０％，Ｎ2：残差とした。
The composition of the
酸素濃度０％モデルガスの組成は、ＮＯ：６００ppm，ＣＯ2：１２％，Ｈ2Ｏ ：１０％，Ｎ2：残差とした。 The composition of the model gas having an oxygen concentration of 0% was NO: 600 ppm, CO 2 : 12%, H 2 O: 10%, N 2 : residual.
また、パージガスの組成は、ＣＯ2：１２％，Ｈ2Ｏ：１０％，Ｎ2：残差とした。 The composition of the purge gas was CO 2 : 12%, H 2 O: 10%, N 2 : residual.
測定手順は、リッチモデルガスを１０分間流通させた後、パージガスを１０分間流通させてＣＯ及びＣ3Ｈ6を除去した。次に、酸素濃度０％モデルガスを流通させて６０分間保持した。触媒流入前の各モデルガス中のＮＯｘ濃度（以下、入口ＮＯｘ濃度）と触媒流通後各モデルガス中のＮＯｘ濃度（以下、出口ＮＯｘ濃度）をＮＯｘ計にて計測し、入口
ＮＯｘ濃度と出口ＮＯｘ濃度との差（入口ＮＯｘ濃度−出口ＮＯｘ濃度）の経時変化を調べた。該差が負値である間は、ＮＯｘは捕捉されている。従って、負値の積算値がＮＯｘ捕捉量となる。
In the measurement procedure, after rich model gas was circulated for 10 minutes, purge gas was circulated for 10 minutes to remove CO and C 3 H 6 . Next, an oxygen concentration 0% model gas was circulated and held for 60 minutes. The NOx concentration in each model gas (hereinafter referred to as inlet NOx concentration) before the catalyst inflow and the NOx concentration in each model gas (hereinafter referred to as outlet NOx concentration) after the catalyst flow are measured with a NOx meter, and the inlet NOx concentration and outlet NOx are measured. The change with time (inlet NOx concentration−outlet NOx concentration) with time was examined. While the difference is negative, NOx is captured. Therefore, the negative integrated value becomes the NOx trapping amount.
以上の方法で触媒の性能を評価する方法を評価方法ａとする。 The method for evaluating the performance of the catalyst by the above method is referred to as an evaluation method a.
（ＮＯｘ捕捉量）
ＮＯｘ浄化触媒Ａを評価方法ａにより評価した。リーンモデルガスにおける４５０℃でのＮＯｘ捕捉量は、酸素濃度０％モデルガスにおけるＮＯｘ捕捉量を求めると、触媒単位容積当り０.０４mol／Ｌとなった。この値が、４５０℃において排ガス中の酸素濃度，
ＣＯ濃度，炭化水素濃度及び水素濃度が０％においてＮＯｘを捕捉できる限界量（以下、酸素０％時のＮＯｘ捕捉量）となる。
(NOx trapping amount)
The NOx purification catalyst A was evaluated by the evaluation method a. The NOx trapping amount at 450 ° C. in the lean model gas was found to be 0.04 mol / L per catalyst unit volume when the NOx trapping amount in the 0% oxygen concentration model gas was determined. This value is the oxygen concentration in the exhaust gas at 450 ° C,
It becomes the limit amount (hereinafter referred to as NOx trapping amount when oxygen is 0%) at which the CO concentration, hydrocarbon concentration and hydrogen concentration are 0%.
なお、酸素濃度０％時のＮＯｘ捕捉量（０.０４mol／Ｌ）は、リーンモデルガスを２分間弱流通させた時のＮＯｘ量に相当した。そこで、リーンモデルガスを３０秒流通させた後にリッチガスを流通すると、ＮＯｘの放出が無く還元浄化された。 Note that the NOx trapping amount (0.04 mol / L) when the oxygen concentration was 0% corresponded to the NOx amount when lean model gas was allowed to flow slightly for 2 minutes. Therefore, when the rich gas was circulated after the lean model gas was circulated for 30 seconds, NOx was not released and the gas was reduced and purified.
以上のことから、予め酸素濃度０％時のＮＯｘ捕捉量を調べておき、リーン運転時の
ＮＯｘ捕捉量を該酸素０％時のＮＯｘ捕捉量以下にすることで、気相の酸素濃度が低下してもリーンで捕捉したＮＯｘを離脱させることなく還元浄化することができる。また、リーンでの運転状況（入口ＮＯｘ濃度やＳＶなど）の情報を逐次収集することによりリーン運転終了を判断することができる。
From the above, the NOx trapping amount when the oxygen concentration is 0% is examined in advance, and the NOx trapping amount during the lean operation is made equal to or less than the NOx trapping amount when the oxygen is 0%, thereby reducing the oxygen concentration in the gas phase. Even in this case, the NOx trapped by the lean can be reduced and purified without leaving. Further, it is possible to determine the end of the lean operation by sequentially collecting information on the lean operation status (inlet NOx concentration, SV, etc.).
（内燃機関の構成図）
図１は本発明の排ガス浄化装置を備えた内燃機関の一実施態様を示す全体構成図である。本発明の浄化装置はリーンバーン可能なエンジン９９，エアフローセンサー２，スロットバルブ３等を擁する吸気系、酸素濃度センサ(又はＡ／Ｆセンサー)７，触媒入ロガス温度センサ８，触媒入口ＮＯｘセンサ９，触媒出口ＮＯｘセンサ１０，排ガス浄化触媒１２、等を擁する排気系及び制御ユニット(ＥＣＵ：Engine Control Unit) １１等から構成される。ＥＣＵは入出力インターフェイスとしてのＩ／Ｏ，ＬＳＩ，演算処理装置ＭＰＵ，多数の制御プログラムを記憶させた記憶装置ＲＡＭ及びＲＯＭ，タイマーカウンター等により構成される。
(Configuration diagram of internal combustion engine)
FIG. 1 is an overall configuration diagram showing an embodiment of an internal combustion engine equipped with an exhaust gas purification apparatus of the present invention. The purifying apparatus of the present invention includes a lean
以上の排気浄化装置は下記のように機能する。エンジンヘの吸入空気はエアクリーナー１によりろ過された後エアフローセンサー２により計量され、スロットバルブ３を経て、さらにインジェクター５から燃料噴射を受け混合気としてエンジン９９に供給される。エアフローセンサー信号その他のセンサ信号はＥＣＵ１１へ入力される。ＥＣＵ１１では内燃機関の運転状態及び排ガス浄化触媒の状態を評価して運転空燃比を決定し、インジェクター５の噴射時間等を制御して混合気の燃料濃度を所定値に設定する。シリンダーに吸入された混合気はＥＣＵ１１からの信号で制御される点火プラグ６により着火され燃焼する。燃焼排ガスは排気浄化系に導かれる。排気浄化系には三元触媒１３の後流に排ガス浄化触媒１２が設けられている。排ガス浄化触媒は、ストイキ運転時には排ガス浄化触媒に備えられた三元触媒機能により排ガス中のＮＯｘ，ＨＣ，ＣＯを浄化し、また、リーン運転時にはＮＯｘ捕捉能によりＮＯｘを浄化すると同時に併せ持つ燃焼機能により、ＨＣ，
ＣＯを浄化する。
The above exhaust purification device functions as follows. The intake air to the engine is filtered by the
Purify CO.
ＥＣＵ１１には予め、排ガスの空燃比がリーンの間に捕捉させるＮＯｘ量の情報や、排ガス中の酸素濃度，ＣＯ濃度，炭化水素濃度及び水素濃度が０％の時に捕捉できるＮＯｘ量の情報が組み込まれている。
Information on the amount of NOx to be captured while the air-fuel ratio of the exhaust gas is lean and information on the amount of NOx that can be captured when the oxygen concentration, CO concentration, hydrocarbon concentration, and hydrogen concentration in the exhaust gas are 0% are incorporated in the
リーン運転時には、ＥＣＵ１１は、触媒入口ＮＯｘセンサ９と触媒出口ＮＯｘセンサ
１０にて計測されるＮＯｘ濃度の差分値とエアフローセンサー２にて計量される空気量から排ガス浄化触媒に捕捉されているＮＯｘ量を推算する。そして、該ＮＯｘ量が排ガス中の酸素０％のＮＯｘ捕捉量を超えないように予め設定された値（例えば、排ガス中の酸素濃度，ＣＯ濃度，炭化水素濃度及び水素濃度が０％の時に捕捉できるＮＯｘ量の１／４）に達したとＥＣＵ１１にて判断されると、ＥＣＵ１１の判定及び制御信号により、ストイキ（リッチ）運転に切り替える。このようにすることで、排ガス中のＮＯｘの排出量を効果的に低減することができる。
During the lean operation, the
（切り替えバルブを用いた排ガス浄化装置の構成図）
前段排ガス浄化触媒の上流に、ＮＯｘセンサ，切り替えバルブをこの順に排ガスが流通するように設ける（図２）。リーン時において、ＮＯｘセンサからの情報に基づきＥＣＵに前段排ガス浄化触媒に捕捉されるＮＯｘ量を推算させる。その後ＥＣＵが、該推算値が酸素０％時のＮＯｘ捕捉量の所定値（例えば、酸素０％時のＮＯｘ捕捉量の２／３）を超えたと判断すると、切り替えバルブにて前段排ガス浄化触媒から後段排ガス浄化触媒へ排ガスが流れるように切り替えをさせる。そして、ＥＣＵは前記ＮＯｘセンサの情報に基づき、後段排ガス浄化触媒にて捕捉されるＮＯｘ量の推算を始める。ＥＣＵは、後段排ガス浄化触媒のＮＯｘ捕捉量が酸素０％時のＮＯｘ捕捉量の所定値を超えたと判断すると、再度切り替えバルブを切り替えて排ガスが前段排ガス浄化触媒及び後段排ガス浄化触媒の順に流れるようにし、空燃比をストイキまたはリッチに切り替える。結果、ＣＯなどの還元剤により前段排ガス浄化触媒及び後段排ガス浄化触媒に捕捉されたＮＯｘが放出されることなく、還元浄化される。
(Configuration diagram of exhaust gas purification device using switching valve)
An NOx sensor and a switching valve are provided upstream of the upstream exhaust gas purification catalyst so that the exhaust gas flows in this order (FIG. 2). At the lean time, the ECU estimates the amount of NOx trapped by the upstream exhaust gas purification catalyst based on information from the NOx sensor. Thereafter, when the ECU determines that the estimated value exceeds a predetermined value of the NOx trapping amount when oxygen is 0% (for example, 2/3 of the NOx trapping amount when oxygen is 0%), the changeover valve causes the upstream exhaust gas purification catalyst to The exhaust gas is switched to the downstream exhaust gas purification catalyst so that the exhaust gas flows. Then, the ECU starts estimating the amount of NOx captured by the post-exhaust gas purification catalyst based on the information of the NOx sensor. When the ECU determines that the NOx trapping amount of the rear exhaust gas purification catalyst exceeds a predetermined value of the NOx trapping amount when oxygen is 0%, the ECU switches the switching valve again so that the exhaust gas flows in the order of the front exhaust gas purification catalyst and the rear exhaust gas purification catalyst. And switch the air-fuel ratio to stoichiometric or rich. As a result, the NOx trapped by the upstream exhaust gas purification catalyst and the downstream exhaust gas purification catalyst is reduced and purified by a reducing agent such as CO.
このようにすることで、リーン運転時間を長くし、かつストイキ及びリッチガス中の還元剤を有効に利用することができるので、排ガス浄化と共に燃費の改善の両立が可能となる。 By doing so, the lean operation time can be lengthened, and the reducing agent in the stoichiometric and rich gas can be used effectively, so that it is possible to achieve both the purification of exhaust gas and the improvement of fuel consumption.
１…エアクリーナー、２…エアフローセンサー、３…スロットバルブ、５…インジェクター、６…点火プラグ、７…酸素濃度センサ（またはＡ／Ｆセンサー）、８…触媒入ロガス温度センサ、９…触媒入口ＮＯｘセンサ、１０…触媒出口ＮＯｘセンサ、１１…ＥＣＵ、１２…排ガス浄化触媒、１３…三元触媒、９９…エンジン。
DESCRIPTION OF
Claims (6)
前記排ガス浄化装置はリーン運転制御装置を備え、前記リーン運転制御装置は、前記リーン運転時に、前記浄化触媒に捕捉されたＮＯｘの量が排ガス中の酸素，ＣＯ，炭化水素，水素濃度がそれぞれ０％の時に捕捉可能なＮＯｘ量以下の値となった場合にリッチ運転に切り替える制御を実行することを特徴とする内燃機関の排ガス浄化装置。 An exhaust gas purification catalyst capable of capturing NOx is provided in the exhaust gas flow path of the internal combustion engine in which the exhaust gas having a lean air-fuel ratio and the exhaust gas having a rich or stoichiometric air-fuel ratio alternately flows, and the NOx in the exhaust gas when the air-fuel ratio is lean An exhaust gas purifying device that reduces and purifies the captured NOx when the air-fuel ratio is rich or stoichiometric,
The exhaust gas purification device includes a lean operation control device, and the lean operation control device is configured such that, during the lean operation , the amount of NOx trapped by the purification catalyst is 0 in oxygen, CO, hydrocarbon, and hydrogen concentrations in the exhaust gas. An exhaust gas purifying apparatus for an internal combustion engine, wherein control for switching to rich operation is executed when the value becomes equal to or less than the NOx amount that can be captured at the time of% .
前記リーン運転制御装置は、リーン運転時間を積算し、前記排ガス浄化触媒に捕捉されたＮＯｘ量を推算することを特徴とする内燃機関の排ガス浄化装置。 An exhaust gas purification device according to claim 1 ,
The lean operation control device integrates the lean operation time and estimates the amount of NOx trapped by the exhaust gas purification catalyst.
前記排ガス流路内に前記排ガス浄化触媒に流入する排ガスの温度を計測する排ガス温度測定装置と、前記排ガス浄化触媒に流入する排ガスのＮＯｘ濃度を計測する排ガス濃度測定装置とを有し、
前記リーン運転制御装置は、前記排ガス温度測定装置で計測された排ガス温度と、前記排ガス中のＮＯｘ濃度とより排ガス浄化触媒に捕捉されるＮＯｘ濃度を推算することを特徴とする内燃機関の排ガス浄化装置。 An exhaust gas purification device according to claim 1 ,
An exhaust gas temperature measuring device for measuring the temperature of the exhaust gas flowing into the exhaust gas purification catalyst in the exhaust gas flow path, and an exhaust gas concentration measuring device for measuring the NOx concentration of the exhaust gas flowing into the exhaust gas purification catalyst,
The lean operation control device estimates the NOx concentration captured by the exhaust gas purification catalyst from the exhaust gas temperature measured by the exhaust gas temperature measuring device and the NOx concentration in the exhaust gas, apparatus.
前記排ガス浄化触媒はアルカリ金属またはアルカリ土類金属の少なくともいずれかと、Ｐｔ，Ｐｄ，Ｒｈの少なくともいずれかとを含むことを特徴とする内燃機関の排ガス浄化装置。 An exhaust gas purifying device according to any one of claims 1 to 3 ,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the exhaust gas purifying catalyst includes at least one of alkali metal or alkaline earth metal and at least one of Pt, Pd, and Rh.
前記排ガス浄化触媒として排ガス中の酸素濃度，ＣＯ濃度，炭化水素濃度、および水素濃度が０％の雰囲気下でＮＯｘを捕捉する触媒を採用していることを特徴とする内燃機関の排ガス浄化装置。 An exhaust gas purification device according to any one of claims 1 to 4 ,
An exhaust gas purification apparatus for an internal combustion engine, wherein a catalyst that captures NOx in an atmosphere having an oxygen concentration, a CO concentration, a hydrocarbon concentration, and a hydrogen concentration of 0% in the exhaust gas is employed as the exhaust gas purification catalyst.
前記排ガス浄化装置は前記複数のＮＯｘを捕捉可能な排ガス浄化触媒のうち最も内燃機関に近い第一の浄化触媒を迂回するバイパス排ガス流路を有し、
前記排ガス浄化装置はリーン運転制御装置を備え、
前記リーン運転制御装置は、前記リーン運転時に、前記第一の浄化触媒に捕捉されたＮＯｘの量が排ガス中の酸素，ＣＯ，炭化水素，水素濃度がそれぞれ０％の時に捕捉可能なＮＯｘ量以下の値となった場合に、排ガス流路を前記バイパス流路に切り替える制御を実行することを特徴とする内燃機関の排ガス浄化装置。 An exhaust gas purification catalyst capable of capturing a plurality of NOx is provided in the exhaust gas flow path of the internal combustion engine in which the exhaust gas having a lean air-fuel ratio and the rich or stoichiometric exhaust gas alternately flows, and in the exhaust gas when the air-fuel ratio is lean An exhaust gas purifying apparatus that supplements NOx of the catalyst to the catalyst and reduces and purifies the captured NOx when the air-fuel ratio is rich or stoichiometric.
The exhaust gas purification apparatus has a bypass exhaust gas flow path that bypasses the first purification catalyst closest to the internal combustion engine among the exhaust gas purification catalysts capable of capturing the plurality of NOx,
The exhaust gas purification device includes a lean operation control device,
In the lean operation control device, the NOx amount trapped by the first purification catalyst during the lean operation is less than the NOx amount that can be captured when the oxygen, CO, hydrocarbon, and hydrogen concentrations in the exhaust gas are 0%, respectively. The exhaust gas purifying apparatus for an internal combustion engine, wherein control for switching the exhaust gas flow path to the bypass flow path is executed when the value becomes.
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