JP2012031787A - Device and method for exhaust emission control of internal combustion engine - Google Patents

Device and method for exhaust emission control of internal combustion engine Download PDF

Info

Publication number
JP2012031787A
JP2012031787A JP2010172142A JP2010172142A JP2012031787A JP 2012031787 A JP2012031787 A JP 2012031787A JP 2010172142 A JP2010172142 A JP 2010172142A JP 2010172142 A JP2010172142 A JP 2010172142A JP 2012031787 A JP2012031787 A JP 2012031787A
Authority
JP
Japan
Prior art keywords
reaction
ratio
selective reduction
exhaust
bed temperature
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.)
Withdrawn
Application number
JP2010172142A
Other languages
Japanese (ja)
Inventor
Taiga Hagimoto
大河 萩本
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 JP2010172142A priority Critical patent/JP2012031787A/en
Publication of JP2012031787A publication Critical patent/JP2012031787A/en
Withdrawn legal-status Critical Current

Links

Images

Landscapes

  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

PROBLEM TO BE SOLVED: To provide a technique avoiding the problem of insufficient or excessive supply of NHwhile securing a NOx purification rate required in a selective reduction type NOx catalyst.SOLUTION: By utilizing the difference among activity degrees of three reactions, i.e. first reaction R1 consuming both NO and NO, second reaction R2 consuming NO, and third reaction R3 consuming NO in each region acquired by dividing SCR catalyst into a plurality of regions in order from an exhaust flow upstream side when a bed temperature in each region is different, a ratio range between NO and NOflowing into the SCR catalyst for reaching a target purification rate is calculated on the basis of a bed temperature of each region derived from the bed temperature of the SCR catalyst acquired by an exhaust temperature sensor and an assumed ratio range between NO and NOflowing into the SCR catalyst (S101), and the ratio between NO and NOflowing into the SCR catalyst is controlled so as to be within the calculated ratio range (S102).

Description

本発明は、内燃機関の排気浄化装置及び内燃機関の排気浄化方法に関する。   The present invention relates to an exhaust gas purification apparatus for an internal combustion engine and an exhaust gas purification method for the internal combustion engine.

内燃機関の排気通路に上流から順に、酸化触媒、還元剤添加弁、選択還元型ＮＯｘ触媒（以下、ＳＣＲ触媒という）を配置し、還元剤添加弁から添加した還元剤から生成されるＮＨ３（アンモニア）を用いて、ＳＣＲ触媒に流入する排気中のＮＯｘを浄化することが行われている。ここで、酸化触媒におけるＮＯ２吸着量の増減を推定し、推定したＮＯ２吸着量の増減に基づいて酸化触媒をバイパスする排気流量を調整し、ＳＣＲ触媒へ流入するＮＯとＮＯ２との比率を１対１に近付ける技術が開示されている（例えば特許文献１参照）。特許文献１の技術によれば、酸化触媒におけるＮＯ２吸着量を制御することで、ＳＣＲ触媒に流入するＮＯとＮＯ２との比率をできるだけ１対１に近付けて必要な還元剤量を添加し、ＮＨ３の不足や過剰供給といった問題を回避しようとしている。 An oxidation catalyst, a reducing agent addition valve, and a selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) are arranged in this order from the upstream in the exhaust passage of the internal combustion engine, and NH 3 (generated from the reducing agent added from the reducing agent addition valve ( Ammonia) is used to purify NOx in the exhaust gas flowing into the SCR catalyst. Here, the increase / decrease in the NO 2 adsorption amount in the oxidation catalyst is estimated, the exhaust gas flow rate bypassing the oxidation catalyst is adjusted based on the estimated increase / decrease in the NO 2 adsorption amount, and the ratio of NO and NO 2 flowing into the SCR catalyst Has been disclosed (see, for example, Patent Document 1). According to the technique of Patent Document 1, by controlling the NO 2 adsorption amount in the oxidation catalyst, the ratio of NO and NO 2 flowing into the SCR catalyst is made as close as possible to 1: 1, and the necessary reducing agent amount is added. , Trying to avoid problems such as lack of NH 3 and excessive supply.

特開２００９−２１６０１９号公報JP 2009-216019 A

上記特許文献１の技術においては、ＳＣＲ触媒では、基本的にＮＯとＮＯ２との比率が１対１であるとＮＯｘ浄化率が最も良くなるとの考え方に基づいて制御を行っている。これは、低温域では、ＮＯ及びＮＯ２とＮＨ３との反応（ＮＯ＋ＮＯ２＋２ＮＨ３→２Ｎ２＋３Ｈ２Ｏ：第１反応）が他の反応に比べて進行し易いからである。しかしながら、ＳＣＲ触媒での反応は、ＳＣＲ触媒床温の変化に伴い、ＮＯ２のみが浄化する反応（２ＮＯ２＋２ＮＨ３→Ｎ２＋ＮＨ４ＮＯ３＋Ｈ２Ｏ：第２反応）や、ＮＯのみが浄化する反応（４ＮＯ＋４ＮＨ３＋Ｏ２→４Ｎ２＋６Ｈ２Ｏ：第３反応）も同時に起こる。また、ＳＣＲ触媒の排気流れ上流側から順に複数に分けた際の各領域で、床温が異なる。これは、ＳＣＲ触媒の上流側の箇所ほど流入する排気の温度の影響を受け易い等、各領域の床温について影響を受ける要因が種々存在するからである。このように、各領域の床温が異なることから、各領域では第１〜第３反応の活性度合いが夫々異なる。よって、各領域での第１〜第３反応の活性度合いを考慮してＳＣＲ触媒に流入するＮＯとＮＯ２との比率を制御すれば、ＳＣＲ触媒での必要なＮＯｘ浄化率を確保し易く、ＮＨ３の不足や過剰供給といった問題を回避し易いと考えられた。 In the technique of Patent Document 1, the SCR catalyst performs control based on the idea that the NOx purification rate is best when the ratio of NO to NO 2 is basically 1: 1. This is because the reaction of NO and NO 2 with NH 3 (NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O: first reaction) is likely to proceed in comparison with other reactions at low temperatures. However, the reaction with the SCR catalyst is a reaction in which only NO 2 purifies with changes in the SCR catalyst bed temperature (2NO 2 + 2NH 3 → N 2 + NH 4 NO 3 + H 2 O: second reaction), or only NO The reaction to be purified (4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O: third reaction) also occurs at the same time. Further, the bed temperature is different in each region when the SCR catalyst is divided into a plurality in order from the exhaust gas upstream side. This is because there are various factors that affect the bed temperature in each region, such as being more susceptible to the temperature of the exhaust gas flowing into the upstream side of the SCR catalyst. Thus, since the bed temperature of each region is different, the activity levels of the first to third reactions are different in each region. Therefore, if the ratio of NO and NO 2 flowing into the SCR catalyst is controlled in consideration of the activity level of the first to third reactions in each region, it is easy to ensure the required NOx purification rate in the SCR catalyst, It was thought that it was easy to avoid problems such as shortage of NH 3 and excessive supply.

本発明は上記問題点に鑑みてなされたもので、本発明の目的は、選択還元型ＮＯｘ触媒での必要なＮＯｘ浄化率を確保しつつ、ＮＨ３の不足や過剰供給といった問題を回避する技術を提供することにある。 The present invention has been made in view of the above problems, and an object of the present invention is a technique for avoiding problems such as shortage and excessive supply of NH 3 while ensuring a necessary NOx purification rate in a selective reduction type NOx catalyst. Is to provide.

本発明にあっては、以下の構成を採用する。すなわち、本発明は、
内燃機関の排気通路に配置された選択還元型ＮＯｘ触媒と、
前記選択還元型ＮＯｘ触媒よりも上流の前記排気通路に配置され、前記選択還元型ＮＯｘ触媒へＮＨ３を供給するための還元剤を添加する還元剤添加部と、
前記選択還元型ＮＯｘ触媒の床温を、検出又は推定することにより取得する床温取得部と、
を備えた内燃機関の排気浄化装置であって、
前記選択還元型ＮＯｘ触媒を排気流れ上流側から順に複数の領域に分けた際の各領域での床温が異なると、各領域での、ＮＯとＮＯ２との両方を消費する第１反応、ＮＯ２を消費する第２反応、及びＮＯを消費する第３反応という３つの反応の活性度合いが異なることを利用して、前記床温取得部が取得した前記選択還元型ＮＯｘ触媒の床温により導かれる各領域の床温と、前記選択還元型ＮＯｘ触媒へ流入すると想定されるＮＯとＮＯ２との比率と、に基づいて、目標浄化率に到達するための前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率範囲を算出する比率範囲算出部と、
前記比率範囲算出部によって算出された比率範囲内に収まるように、前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御するＮＯｘ比率制御部と、
を備えたことを特徴とする内燃機関の排気浄化装置である。 In the present invention, the following configuration is adopted. That is, the present invention
A selective reduction type NOx catalyst disposed in an exhaust passage of the internal combustion engine;
A reducing agent addition unit that is disposed in the exhaust passage upstream of the selective reduction type NOx catalyst and adds a reducing agent for supplying NH 3 to the selective reduction type NOx catalyst;
A bed temperature acquisition unit which acquires the bed temperature of the selective catalytic reduction NOx catalyst by detecting or estimating;
An exhaust purification device for an internal combustion engine comprising:
When the selective reduction type NOx catalyst is divided into a plurality of regions in order from the exhaust flow upstream side and the bed temperature in each region is different, a first reaction that consumes both NO and NO 2 in each region, By utilizing the fact that the degree of activity of the three reactions of the second reaction that consumes NO 2 and the third reaction that consumes NO is different, the bed temperature of the selective reduction type NOx catalyst acquired by the bed temperature acquisition unit is used. Based on the derived bed temperature of each region and the ratio of NO and NO 2 that is assumed to flow into the selective reduction NOx catalyst, the flow into the selective reduction NOx catalyst to reach the target purification rate A ratio range calculation unit for calculating a ratio range of NO and NO 2 to be performed;
And said ratio range calculation section so as to fall within a ratio range calculated by, NOx ratio controller for controlling the ratio between NO and NO 2 which flows into the selective reduction type NOx catalyst,
An exhaust emission control device for an internal combustion engine, comprising:

本発明によると、選択還元型ＮＯｘ触媒の各領域での第１〜第３反応という３つの反応の活性度合いが異なることを利用して、目標浄化率に到達するための選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率範囲内に収まるように、選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御する。これにより、選択還元型ＮＯｘ触媒では目標浄化率以上のＮＯｘ浄化率を確保して、ＮＨ３の不足や過剰供給といった問題を回避することができる。 According to the present invention, the selective reduction type NOx catalyst for reaching the target purification rate is obtained by utilizing the different degrees of activity of the first to third reactions in each region of the selective reduction type NOx catalyst. The ratio of NO and NO 2 flowing into the selective reduction NOx catalyst is controlled so as to be within the ratio range of NO and NO 2 flowing in. Thereby, in the selective reduction type NOx catalyst, a NOx purification rate equal to or higher than the target purification rate can be secured, and problems such as shortage of NH 3 and excessive supply can be avoided.

前記選択還元型ＮＯｘ触媒よりも上流の前記排気通路に配置された酸化触媒と、
排気に前記酸化触媒を迂回させるバイパス通路と、
前記酸化触媒を流通する排気流量と前記バイパス通路を流通する排気流量とを調節する排気流量調節部と、
を更に備え、
前記ＮＯｘ比率制御部は、前記排気流量調節部で前記酸化触媒を流通する排気流量と前記バイパス通路を流通する排気流量とを調節することにより、前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御するとよい。 An oxidation catalyst disposed in the exhaust passage upstream of the selective reduction NOx catalyst;
A bypass passage for bypassing the oxidation catalyst to exhaust,
An exhaust flow rate adjusting unit for adjusting an exhaust flow rate flowing through the oxidation catalyst and an exhaust flow rate flowing through the bypass passage;
Further comprising
The NOx ratio control unit adjusts an exhaust flow rate through which the oxidation catalyst is circulated and an exhaust flow rate through which the bypass passage is circulated by the exhaust flow rate adjustment unit, whereby NO and NO 2 flowing into the selective reduction type NOx catalyst are adjusted. It is good to control the ratio.

本発明によると、目標浄化率に到達するための選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率範囲内に収まるように、選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御することができる。 According to the present invention so as to fall within a ratio range of between NO and NO 2 which flows into the selective reduction type NOx catalyst to reach the target purification rate, the ratio of NO and NO 2 which flows into the selective reduction type NOx catalyst Can be controlled.

また、本発明は、
内燃機関の排気通路に配置された選択還元型ＮＯｘ触媒よりも上流の前記排気通路に配置された還元剤添加部から還元剤を添加して、前記選択還元型ＮＯｘ触媒へＮＨ３を供給し、前記選択還元型ＮＯｘ触媒でＮＯｘを浄化させる内燃機関の排気浄化方法であって、
前記選択還元型ＮＯｘ触媒を排気流れ上流側から順に複数の領域に分けた際の各領域での床温が異なると、各領域での、ＮＯとＮＯ２との両方を消費する第１反応、ＮＯ２を消費する第２反応、及びＮＯを消費する第３反応という３つの反応の活性度合いが異なることを利用して、前記選択還元型ＮＯｘ触媒の床温を、検出又は推定することにより取得する床温取得部が取得した前記選択還元型ＮＯｘ触媒の床温により導かれる各領域の床温と、前記選択還元型ＮＯｘ触媒へ流入すると想定されるＮＯとＮＯ２との比率と、に基づいて、目標浄化率に到達するための前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率範囲を算出し、
算出された比率範囲内に収まるように、前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御することを特徴とする内燃機関の排気浄化方法である。 The present invention also provides:
Adding a reducing agent from a reducing agent addition section arranged in the exhaust passage upstream of the selective reduction type NOx catalyst arranged in the exhaust passage of the internal combustion engine, and supplying NH 3 to the selective reduction type NOx catalyst; An exhaust purification method for an internal combustion engine that purifies NOx with the selective reduction type NOx catalyst,
When the selective reduction type NOx catalyst is divided into a plurality of regions in order from the exhaust flow upstream side and the bed temperature in each region is different, a first reaction that consumes both NO and NO 2 in each region, Obtained by detecting or estimating the bed temperature of the selective reduction-type NOx catalyst using the fact that the activity levels of the three reactions, the second reaction consuming NO 2 and the third reaction consuming NO, are different. Based on the bed temperature of each region derived from the bed temperature of the selective reduction NOx catalyst acquired by the bed temperature acquisition unit and the ratio of NO and NO 2 that is assumed to flow into the selective reduction NOx catalyst. Calculating a ratio range of NO and NO 2 flowing into the selective catalytic reduction NOx catalyst to reach the target purification rate,
An exhaust gas purification method for an internal combustion engine, wherein a ratio between NO and NO 2 flowing into the selective reduction type NOx catalyst is controlled so as to be within a calculated ratio range.

本発明によっても、選択還元型ＮＯｘ触媒では目標浄化率以上のＮＯｘ浄化率を確保して、ＮＨ３の不足や過剰供給といった問題を回避することができる。 According to the present invention, the selective reduction type NOx catalyst can secure a NOx purification rate that is equal to or higher than the target purification rate, and can avoid problems such as shortage and excessive supply of NH 3 .

本発明によると、選択還元型ＮＯｘ触媒での必要なＮＯｘ浄化率を確保しつつ、ＮＨ３の不足や過剰供給といった問題を回避することができる。 According to the present invention, it is possible to avoid problems such as shortage and excessive supply of NH 3 while ensuring the necessary NOx purification rate in the selective reduction type NOx catalyst.

本発明の実施例１に係る内燃機関の概略構成を示す図である。1 is a diagram illustrating a schematic configuration of an internal combustion engine according to Embodiment 1 of the present invention. ＳＣＲ触媒床温と３つの反応の活性度合いとの関係を示す図である。It is a figure which shows the relationship between SCR catalyst bed temperature and the activity degree of three reaction. ＳＣＲ触媒の各領域の床温に応じた各領域の出入りするＮＯとＮＯ２との比率及びＮＯｘ浄化率を示す図である。Depending on the bed temperature of each region of the SCR catalyst is a diagram showing a ratio and NOx purification rate of NO and NO 2 into and out of each region. ＳＣＲ触媒全体が一定温度の場合におけるＮＯ２比率の目標比率範囲を求めるモデルを示す図である。Entire SCR catalyst is a diagram illustrating a model for determining the target ratio range of NO 2 ratio in the case of a constant temperature. ＳＣＲ触媒が温度の異なる２つの領域に分けられる場合におけるＮＯ２比率の目標比率範囲を求めるモデルを示す図である。SCR catalyst is a diagram illustrating a model for determining the target ratio range of NO 2 ratio in the case is divided into two regions having different temperatures. 実施例１に係るＮＯｘ比率制御ルーチンを示すフローチャートである。3 is a flowchart showing a NOx ratio control routine according to the first embodiment.

以下に本発明の具体的な実施例を説明する。   Specific examples of the present invention will be described below.

＜実施例１＞
（内燃機関）
図１は、本発明の実施例１に係る内燃機関の概略構成を示す図である。図１に示す内燃機関１は、４つの気筒を有する車両駆動用の４ストロークサイクル・ディーゼルエンジンである。内燃機関１には、内燃機関１から排出された排気を流通させる排気通路２が接続されている。 <Example 1>
(Internal combustion engine)
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine according to Embodiment 1 of the present invention. The internal combustion engine 1 shown in FIG. 1 is a four-stroke cycle diesel engine for driving a vehicle having four cylinders. Connected to the internal combustion engine 1 is an exhaust passage 2 through which the exhaust discharged from the internal combustion engine 1 flows.

排気通路２の途中には、選択還元型ＮＯｘ触媒（以下、ＳＣＲ触媒という）３が配置されている。ＳＣＲ触媒３は、ＮＨ３（アンモニア）を用いて排気中のＮＯｘを還元浄化する。ＳＣＲ触媒３は、尿素やＮＨ３を吸着する機能を有する。 A selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) 3 is disposed in the middle of the exhaust passage 2. The SCR catalyst 3 reduces and purifies NOx in the exhaust gas using NH 3 (ammonia). The SCR catalyst 3 has a function of adsorbing urea and NH 3 .

ＳＣＲ触媒３よりも上流の排気通路２には、ＳＣＲ触媒３に供給するＮＨ３に加水分解される還元剤として尿素水溶液（以下、尿素水という）を添加する尿素水添加弁４が配置されている。尿素水添加弁４からは、尿素水タンク５に蓄えられた尿素水が指令に基づいて排気通路２内に噴射される。噴射された尿素水は、（ＮＨ２）２ＣＯ＋Ｈ２Ｏ→２ＮＨ３＋ＣＯ２のような反応で排気熱を用いて加水分解され、ＮＨ３が生成される。噴射された尿素水の尿素やＮＨ３は、ＳＣＲ触媒３に吸着される。尿素水添加弁４が、本発明の還元剤添加部に対応する。還元剤としては、尿素水以外にもアンモニア水溶液等のアンモニア系溶液を用いることができる。 In the exhaust passage 2 upstream of the SCR catalyst 3, a urea water addition valve 4 for adding a urea aqueous solution (hereinafter referred to as urea water) as a reducing agent hydrolyzed to NH 3 supplied to the SCR catalyst 3 is arranged. Yes. From the urea water addition valve 4, urea water stored in the urea water tank 5 is injected into the exhaust passage 2 based on a command. The injected urea water is hydrolyzed using exhaust heat in a reaction such as (NH 2 ) 2 CO + H 2 O → 2NH 3 + CO 2 , and NH 3 is generated. The urea and NH 3 thus injected are adsorbed on the SCR catalyst 3. The urea water addition valve 4 corresponds to the reducing agent addition part of the present invention. As the reducing agent, an ammonia-based solution such as an aqueous ammonia solution can be used in addition to the urea water.

尿素水添加弁４の上流の排気通路２には、酸化触媒６及びディーゼルパティキュレートフィルタ（以下、ＤＰＦという）７が配置されている。酸化触媒６は、排気中の物質を酸化させる。ＤＰＦ７は、排気中の粒子状物質（以下、ＰＭという）を捕集する。また、ＤＰＦ７にＰＭが規定量を超えて堆積すると、内燃機関１でポスト噴射して酸化触媒６に燃料を供給し、この燃料の酸化によりＤＰＦ７を昇温させてＤＰＦ７に堆積したＰＭを強制的に酸化除去する。   An oxidation catalyst 6 and a diesel particulate filter (hereinafter referred to as DPF) 7 are disposed in the exhaust passage 2 upstream of the urea water addition valve 4. The oxidation catalyst 6 oxidizes substances in the exhaust. The DPF 7 collects particulate matter (hereinafter referred to as PM) in the exhaust gas. Further, when PM accumulates in the DPF 7 exceeding a specified amount, the post-injection is performed by the internal combustion engine 1 and fuel is supplied to the oxidation catalyst 6. The oxidation of the fuel raises the temperature of the DPF 7 and forcibly accumulates the PM accumulated in the DPF 7. To oxidize and remove.

排気に酸化触媒６を迂回させるバイパス通路８が配置されている。バイパス通路８は、酸化触媒６の上流の排気通路２と、酸化触媒６の下流且つＤＰＦ７の上流の排気通路２と、を接続している。   A bypass passage 8 for bypassing the oxidation catalyst 6 to the exhaust is disposed. The bypass passage 8 connects the exhaust passage 2 upstream of the oxidation catalyst 6 and the exhaust passage 2 downstream of the oxidation catalyst 6 and upstream of the DPF 7.

バイパス通路８との分岐下流且つ酸化触媒６の上流の排気通路２には、酸化触媒６を流通する排気流量を調節する第１流量調節弁９が設けられている。また、バイパス通路８に
は、バイパス通路８を流通する排気流量を調節する第２流量調節弁１０が設けられている。第１流量調節弁９及び第２流量調節弁１０が、本発明の排気流量調節部に対応する。 In the exhaust passage 2 downstream of the bypass passage 8 and upstream of the oxidation catalyst 6, a first flow rate control valve 9 for adjusting the exhaust flow rate flowing through the oxidation catalyst 6 is provided. The bypass passage 8 is provided with a second flow rate adjusting valve 10 that adjusts the exhaust flow rate flowing through the bypass passage 8. The first flow rate adjusting valve 9 and the second flow rate adjusting valve 10 correspond to the exhaust flow rate adjusting unit of the present invention.

ＳＣＲ触媒３の直下流の排気通路２には、排気の温度を検出する排気温度センサ１１が配置されている。排気温度センサ１１が、本発明のＳＣＲ触媒３の床温を、推定することにより取得する床温取得部に対応する。排気温度センサ１１によって推定されるＳＣＲ触媒３の床温からは、後述するＳＣＲ触媒３の各領域の床温を導くことができる。なお、床温取得部は、ＳＣＲ触媒３に設けられ、ＳＣＲ触媒３の床温を、直接検出することにより取得するものでもよい。排気温度センサ１１の直下流の排気通路２には、ＳＣＲ触媒３から流出する排気中のＮＯｘ濃度を検出するＮＯｘセンサ１２が配置されている。   An exhaust temperature sensor 11 for detecting the temperature of the exhaust is disposed in the exhaust passage 2 immediately downstream of the SCR catalyst 3. The exhaust temperature sensor 11 corresponds to a bed temperature acquisition unit that acquires the bed temperature of the SCR catalyst 3 of the present invention by estimating. From the bed temperature of the SCR catalyst 3 estimated by the exhaust temperature sensor 11, the bed temperature of each region of the SCR catalyst 3 described later can be derived. The bed temperature acquisition unit may be provided in the SCR catalyst 3, and may be acquired by directly detecting the bed temperature of the SCR catalyst 3. A NOx sensor 12 that detects the NOx concentration in the exhaust gas flowing out from the SCR catalyst 3 is disposed in the exhaust passage 2 immediately downstream of the exhaust temperature sensor 11.

以上述べたように構成された内燃機関１には電子制御ユニット（以下、ＥＣＵという）１３が併設されている。ＥＣＵ１３には、排気温度センサ１１及びＮＯｘセンサ１２並びに不図示のクランクポジションセンサ及びアクセル開度センサが電気的に接続されている。これらの出力信号がＥＣＵ１３に入力される。また、ＥＣＵ１３には、尿素水添加弁４、第１流量調節弁９及び第２流量調節弁１０が電気的に接続されており、ＥＣＵ１３によってこれらが制御される。ＥＣＵ１３は、ＳＣＲ触媒３でＮＨ３を用いてＮＯｘを還元浄化するよう尿素水添加弁４から尿素水を添加する。 The internal combustion engine 1 configured as described above is provided with an electronic control unit (hereinafter referred to as ECU) 13. The ECU 13 is electrically connected to an exhaust temperature sensor 11 and a NOx sensor 12, and a crank position sensor and an accelerator opening sensor (not shown). These output signals are input to the ECU 13. Further, the urea water addition valve 4, the first flow rate adjustment valve 9, and the second flow rate adjustment valve 10 are electrically connected to the ECU 13, and these are controlled by the ECU 13. The ECU 13 adds urea water from the urea water addition valve 4 so that the SCR catalyst 3 reduces and purifies NOx using NH 3 .

（ＳＣＲ触媒でのＮＯｘ浄化制御）
排気エミッションの悪化を防止するため、ＳＣＲ触媒３のＮＯｘ浄化率を目標浄化率に到達させるよう、尿素水添加弁４からの尿素水添加制御と、ＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率を制御するＮＯｘ比率制御と、を行う。尿素水添加制御は、ＳＣＲ触媒３でＮＯｘを浄化するために必要なＮＯｘ量に対応した尿素水量を尿素水添加弁４から添加する制御である。ＮＯｘ比率制御は、ＳＣＲ触媒３のＮＯｘ浄化率が目標浄化率に到達するよう、第１流量調節弁９及び第２流量調節弁１０で酸化触媒６を流通する排気流量とバイパス通路８を流通する排気流量とを調節することにより、ＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率を変更する制御である。 (NOx purification control with SCR catalyst)
In order to prevent the exhaust emission from deteriorating, the urea water addition control from the urea water addition valve 4 and the NO and NO 2 flowing into the SCR catalyst 3 are controlled so that the NOx purification rate of the SCR catalyst 3 reaches the target purification rate. NOx ratio control for controlling the ratio is performed. The urea water addition control is a control in which the urea water amount corresponding to the NOx amount necessary for purifying NOx by the SCR catalyst 3 is added from the urea water addition valve 4. In the NOx ratio control, the exhaust flow rate through the oxidation catalyst 6 and the bypass passage 8 are circulated by the first flow rate control valve 9 and the second flow rate control valve 10 so that the NOx purification rate of the SCR catalyst 3 reaches the target purification rate. In this control, the ratio of NO and NO 2 flowing into the SCR catalyst 3 is changed by adjusting the exhaust gas flow rate.

（ＮＯｘ比率制御）
ＮＯｘ比率制御では、目標浄化率に到達するためのＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率範囲を算出し、算出された比率範囲内に収まるようにＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率を制御する。このようなＮＯｘ比率制御を正確に行うためには、目標浄化率に到達するためのＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率範囲を正確に算出する必要がある。 (NOx ratio control)
In the NOx ratio control, a ratio range of NO and NO 2 flowing into the SCR catalyst 3 for reaching the target purification rate is calculated, and NO and NO flowing into the SCR catalyst 3 so as to be within the calculated ratio range. 2 to control the ratio. In order to perform such accurately NOx ratio control, it is necessary to accurately calculate the ratio range of NO and NO 2 flowing into the SCR catalyst 3 to reach the target purification rate.

ところで、本発明者らの知見によると、ＳＣＲ触媒３を排気流れ上流側から順に複数の領域に分けた際の各領域での床温が異なると、各領域でのＮＯｘ浄化率が異なることが判明した。これは、各領域での床温が異なると、各領域での、ＮＯとＮＯ２との両方を消費する第１反応（ＮＯ＋ＮＯ２＋２ＮＨ３→２Ｎ２＋３Ｈ２Ｏ）Ｒ１、ＮＯ２を消費する第２反応（２ＮＨ３＋２ＮＯ２→Ｎ２＋ＮＨ４ＮＯ３＋Ｈ２Ｏ）Ｒ２、及びＮＯを消費する第３反応（４ＮＯ＋４ＮＨ３＋Ｏ２→４Ｎ２＋６Ｈ２Ｏ）Ｒ３というＲ１〜Ｒ３の３つの反応の活性度合いが異なるからである。よって、上記比率範囲を正確に算出するためには、各領域でのこれら３つの反応の活性度合いを考慮しなければならない。 By the way, according to the knowledge of the present inventors, if the bed temperature in each region when the SCR catalyst 3 is divided into a plurality of regions in order from the exhaust flow upstream side is different, the NOx purification rate in each region may be different. found. This is because when the bed temperature in each region is different, the first reaction (NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O) R 1 and NO 2 is consumed in each region, which consumes both NO and NO 2. The second reaction (2NH 3 + 2NO 2 → N 2 + NH 4 NO 3 + H 2 O) R2, and the third reaction (4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O) R3 that consumes NO, R3 to R3 This is because the degree of activity differs. Therefore, in order to accurately calculate the above ratio range, it is necessary to consider the activity levels of these three reactions in each region.

図２は、ＳＣＲ触媒床温と３つの反応の活性度合いとの関係を示す図である。図３は、ＳＣＲ触媒３の各領域の床温に応じた各領域の出入りするＮＯとＮＯ２との比率及びＮＯｘ浄化率を示す図である。図２に示すように、Ｒ１〜Ｒ３の３つの反応の活性度合いは、ＳＣＲ触媒３の床温に応じて異なる。例えば図２に示すＡ点では、図３（ａ）に示すように第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合
いは０％である。このため、Ａ点では、第１反応Ｒ１のみが８０％の活性度合いで行われ、図示するＮＯとＮＯ２との比率及びＮＯｘ浄化率となる。図２に示すＢ点では、図３（ｂ）に示すように第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％である。このため、Ｂ点では、第１反応Ｒ１が９０％の活性度合いで行われ、第２反応Ｒ２が４０％の活性度合いで行われ、図示するＮＯとＮＯ２との比率及びＮＯｘ浄化率となる。図２に示すＣ点では、図３（ｃ）に示すように第１反応Ｒ１の活性度合いが１００％であり、第２反応Ｒ２の活性度合いが６０％であり、第３反応Ｒ３の活性度合いが３０％である。このため、Ｃ点では、第１反応Ｒ１が１００％の活性度合いで行われ、第２反応Ｒ２が６０％の活性度合いで行われ、第３反応Ｒ３が３０％の活性度合いで行われ、図示するＮＯとＮＯ２との比率及びＮＯｘ浄化率となる。 FIG. 2 is a graph showing the relationship between the SCR catalyst bed temperature and the activity levels of the three reactions. FIG. 3 is a diagram showing the ratio of NO and NO 2 entering and exiting each region and the NOx purification rate according to the bed temperature of each region of the SCR catalyst 3. As shown in FIG. 2, the activity levels of the three reactions R <b> 1 to R <b> 3 vary depending on the bed temperature of the SCR catalyst 3. For example, at the point A shown in FIG. 2, the activity level of the first reaction R1 is 80% and the activity levels of the second reaction R2 and the third reaction R3 are 0% as shown in FIG. For this reason, at the point A, only the first reaction R1 is performed with the degree of activity of 80%, and the illustrated ratio of NO to NO 2 and the NOx purification rate are obtained. At point B shown in FIG. 2, as shown in FIG. 3B, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, and the activity level of the third reaction R3. Is 0%. Therefore, at the point B, the first reaction R1 is performed with a degree of activity of 90%, the second reaction R2 is performed with a degree of activity of 40%, and the ratio of NO to NO 2 and the NOx purification rate shown in the figure are obtained. . At the point C shown in FIG. 2, as shown in FIG. 3C, the activity level of the first reaction R1 is 100%, the activity level of the second reaction R2 is 60%, and the activity level of the third reaction R3. Is 30%. Therefore, at the point C, the first reaction R1 is performed with a degree of activity of 100%, the second reaction R2 is performed with a degree of activity of 60%, and the third reaction R3 is performed with a degree of activity of 30%. The ratio of NO to NO 2 and the NOx purification rate are obtained.

以上のことから、ＳＣＲ触媒３を排気流れ上流側から順に複数の領域に分けた際の各領域の床温が、上記で例示したＡ点、Ｂ点、Ｃ点のように異なると、各領域でのＲ１〜Ｒ３の３つの反応の活性度合いが異なることになる。   From the above, if the bed temperature of each region when the SCR catalyst 3 is divided into a plurality of regions in order from the upstream side of the exhaust flow is different as in the points A, B, and C illustrated above, The activity levels of the three reactions R1 to R3 are different.

図４（ａ）は、ＳＣＲ触媒３の床温がＡ点の温度で一定の場合の、ＳＣＲ触媒３内で浄化されて行くＮＯとＮＯ２との濃度分布（以下、ＮＯｘ濃度分布ともいう）及び目標浄化率に到達するためのＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率範囲（以下、目標比率範囲ともいう）を示す図である。ここでは、目標浄化率として９０％を求めるものである。 FIG. 4A shows the concentration distribution of NO and NO 2 that is purified in the SCR catalyst 3 when the bed temperature of the SCR catalyst 3 is constant at point A (hereinafter also referred to as NOx concentration distribution). 2 is a diagram showing a ratio range (hereinafter also referred to as a target ratio range) of NO and NO 2 flowing into the SCR catalyst 3 for reaching the target purification rate. Here, 90% is obtained as the target purification rate.

図４（ａ）のＡ１は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯとＮＯ２との内ＮＯ２の比率（ＮＯ２／（ＮＯ＋ＮＯ２）：以下、ＮＯ２比率という）が５０％の場合を想定している。Ａ１の場合には、第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合いは０％であるので、５０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用い尽くされる。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は１００％である。 A1 in FIG. 4A has a NO 2 ratio of NO to NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 (NO 2 / (NO + NO 2 ): hereinafter referred to as NO 2 ratio). % Is assumed. In the case of A1, since the activity level of the first reaction R1 is 80% and the activity levels of the second reaction R2 and the third reaction R3 are 0%, 50% NO and NO 2 are all 1 One pair is used up for the first reaction R1. Thereby, the NOx purification rate of the SCR catalyst 3 is 100%.

図４（ａ）のＡ２は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が４５％の場合を想定している。Ａ２の場合には、第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合いは０％であるので、４５％ずつのＮＯとＮＯ２とが１対１で第１反応Ｒ１に用いられ、１０％の余りのＮＯが反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 A2 in FIG. 4A assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 45%. In the case of A2, the activity degree of the first reaction R1 is 80%, since the degree of activation of the second reaction R2 and the third reaction R3 is 0%, one by 45% NO and NO 2 and a pair 1 is used for the first reaction R1, and 10% of the excess NO is released without being able to react. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

図４（ａ）のＡ３は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が５５％の場合を想定している。Ａ３の場合には、第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合いは０％であるので、４５％ずつのＮＯとＮＯ２とが１対１で第１反応Ｒ１に用いられ、１０％の余りのＮＯ２が反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 A3 in FIG. 4A assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 55%. In the case of A3 is the degree of activation of the first reaction R1 is 80%, since the degree of activation of the second reaction R2 and the third reaction R3 is 0%, one by 45% NO and NO 2 and a pair 1 is used for the first reaction R1, and 10% of the excess NO 2 cannot be reacted and is released. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

以上の図４（ａ）のＡ１〜Ａ３では、目標浄化率である９０％のＮＯｘ浄化率に到達するためには、Ａ１を含みＡ２からＡ３までの範囲が許容できるので、ＮＯ２比率の目標比率範囲が４５％〜５５％となる。 In A1~A3 above of FIG. 4 (a), in order to reach 90% of the NOx purification rate is the target purification rate, since the range from A2 include A1 to A3 are acceptable, NO 2 ratio objectives of The ratio range is 45% to 55%.

また、図４（ｂ）は、ＳＣＲ触媒３の床温がＢ点の温度で一定の場合の、ＳＣＲ触媒３内のＮＯｘ濃度分布及び目標比率範囲を示す図である。ここでも、目標浄化率として９０％を求めるものである。   FIG. 4B is a diagram showing the NOx concentration distribution and the target ratio range in the SCR catalyst 3 when the bed temperature of the SCR catalyst 3 is constant at the point B temperature. Again, 90% is obtained as the target purification rate.

図４（ｂ）のＢ１は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が５
０％の場合を想定している。Ｂ１の場合には、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、５０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用い尽くされる。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は１００％である。 In B1 of FIG. 4B, the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 5
The case of 0% is assumed. In the case of B1, the activity degree of the first reaction R1 is 90%, the activity degree of the second reaction R2 is 40%, the activity degree of the third reaction R3 is 0%, and the first reaction R1 is Since it is performed preferentially over the second reaction R2, 50% of NO and NO 2 are all used up for the first reaction R1 on a one-to-one basis. Thereby, the NOx purification rate of the SCR catalyst 3 is 100%.

図４（ｂ）のＢ２は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が４５％の場合を想定している。Ｂ２の場合には、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、４５％ずつのＮＯとＮＯ２とが１対１で第１反応Ｒ１に用いられ、１０％の余りのＮＯが反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 B2 in FIG. 4B assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 45%. In the case of B2, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, the activity level of the third reaction R3 is 0%, and the first reaction R1 is Since the reaction is preferentially performed over the second reaction R2, 45% of NO and NO 2 are used in the first reaction R1 on a one-to-one basis, and 10% of the excess NO is released without being reacted. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

図４（ｂ）のＢ３は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が７０％の場合を想定している。Ｂ３の場合には、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、まず３０％ずつのＮＯとＮＯ２とが１対１で第１反応Ｒ１に用いられ、次に３０％のＮＯ２が第２反応Ｒ２に用いられ、残りの１０％の余りのＮＯ２が反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 B3 in FIG. 4B assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 70%. In the case of B3, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, the activity level of the third reaction R3 is 0%, and the first reaction R1 is Since the reaction is preferentially performed over the second reaction R2, 30% NO and NO 2 are first used in the first reaction R1 in a one-to-one relationship, and then 30% NO 2 is used in the second reaction R2. And the remaining 10% of the remaining NO 2 cannot be reacted and is released. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

以上の図４（ｂ）のＢ１〜Ｂ３では、目標浄化率である９０％のＮＯｘ浄化率に到達するためには、Ｂ１を含みＢ２からＢ３までの範囲が許容できるので、ＮＯ２比率の目標比率範囲が４５％〜７０％となる。 In B1~B3 above in FIG. 4 (b), in order to reach 90% of the NOx purification rate is the target purification rate, since the range from B2 includes B1 to B3 are acceptable, NO 2 ratio objectives of The ratio range is 45% to 70%.

以上では、図４を用いＳＣＲ触媒３の床温が一定温度の場合を説明した。しかし、上述のように、ＳＣＲ触媒３を排気流れ上流側から順に複数の領域に分けた際の各領域の床温が異なる場合もある。以下に、ＳＣＲ触媒３の各領域の床温が異なる場合を説明する。   The case where the bed temperature of the SCR catalyst 3 is constant has been described above with reference to FIG. However, as described above, the bed temperature in each region may be different when the SCR catalyst 3 is divided into a plurality of regions in order from the exhaust flow upstream side. Below, the case where the bed temperature of each area | region of the SCR catalyst 3 differs is demonstrated.

図５（ａ）は、ＳＣＲ触媒３を排気流れ上流側から順に２つの上流側領域と下流側領域とに分けた際の上流側領域の床温がＡ点の温度であり、下流側領域の床温がＢ点の温度である場合の、ＳＣＲ触媒３内のＮＯｘ濃度分布及び比率範囲を示す図である。ここでも、目標浄化率として９０％を求めるものである。   FIG. 5A shows that the bed temperature in the upstream region when the SCR catalyst 3 is divided into two upstream regions and a downstream region in order from the exhaust flow upstream side is the temperature at point A, and It is a figure which shows NOx density | concentration distribution and ratio range in the SCR catalyst 3 in case a bed temperature is the temperature of B point. Again, 90% is obtained as the target purification rate.

図５（ａ）のＣ１は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が５０％の場合を想定している。Ｃ１の場合には、上流側領域では、第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合いは０％であるので、３０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられる。下流側領域では、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、残りの２０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用い尽くされる。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は１００％である。 C1 in FIG. 5A assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 50%. In the case of C1, in the upstream region, the degree of activity of the first reaction R1 is 80%, and the degree of activity of the second reaction R2 and the third reaction R3 is 0%. 2 are all used in the first reaction R1 on a one-to-one basis. In the downstream region, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, the activity level of the third reaction R3 is 0%, and the first reaction R1 is Since the reaction is performed preferentially over the two reactions R2, the remaining 20% NO and NO 2 are all used up for the first reaction R1 in a one-to-one relationship. Thereby, the NOx purification rate of the SCR catalyst 3 is 100%.

図５（ａ）のＣ２は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が４５％の場合を想定している。Ｃ２の場合には、上流側領域では、第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合いは０％であるので、３０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられる。下流側領域では、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、残りの１５％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられ、
１０％の余りのＮＯが反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 C2 in FIG. 5A assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 45%. In the case of C2, in the upstream region, the degree of activity of the first reaction R1 is 80%, and the degree of activity of the second reaction R2 and the third reaction R3 is 0%. 2 are all used in the first reaction R1 on a one-to-one basis. In the downstream region, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, the activity level of the third reaction R3 is 0%, and the first reaction R1 is Since it is preferentially performed over the two reactions R2, the remaining 15% NO and NO 2 are all used in the first reaction R1 in a one-to-one relationship.
More than 10% of NO is released without being able to react. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

図５（ａ）のＣ３は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が６０％の場合を想定している。Ｃ３の場合には、上流側領域では、第１反応Ｒ１の活性度合いが８０％であり、第２反応Ｒ２及び第３反応Ｒ３の活性度合いは０％であるので、３０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられる。下流側領域では、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、残りの１０％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられ、次に１０％のＮＯ２が第２反応Ｒ２に用いられ、残りの１０％の余りのＮＯ２が反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 C3 in FIG. 5A assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 60%. In the case of C3, in the upstream region, the degree of activity of the first reaction R1 is 80%, and the degree of activity of the second reaction R2 and the third reaction R3 is 0%. 2 are all used in the first reaction R1 on a one-to-one basis. In the downstream region, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, the activity level of the third reaction R3 is 0%, and the first reaction R1 is Since the second reaction R2 is preferentially performed, the remaining 10% of NO and NO 2 are all used one-to-one for the first reaction R1, and then 10% of NO 2 is supplied to the second reaction R2. Used, the remaining 10% of the remaining NO 2 is released without being able to react. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

以上の図５（ａ）のＣ１〜Ｃ３では、目標浄化率である９０％のＮＯｘ浄化率に到達するためには、Ｃ１を含みＣ２からＣ３までの範囲が許容できるので、ＮＯ２比率の目標比率範囲が４５％〜６０％となる。 In C1~C3 above of FIG. 5 (a), in order to reach 90% of the NOx purification rate is the target purification rate, because allowable range from C2 includes a C1 to C3, NO 2 ratio objectives of The ratio range is 45% to 60%.

図５（ｂ）は、ＳＣＲ触媒３を排気流れ上流側から順に２つの上流側領域と下流側領域とに分けた際の上流側領域の床温がＢ点の温度であり、下流側領域の床温がＣ点の温度である場合の、ＳＣＲ触媒３内のＮＯｘ濃度分布及び比率範囲を示す図である。ここでも、目標浄化率として９０％を求めるものである。   FIG. 5B shows that the bed temperature in the upstream region when the SCR catalyst 3 is divided into two upstream regions and a downstream region in order from the upstream side of the exhaust flow is the temperature of the point B. It is a figure which shows NOx density | concentration distribution and ratio range in the SCR catalyst 3 in case a bed temperature is the temperature of C point. Again, 90% is obtained as the target purification rate.

図５（ｂ）のＤ１は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が５０％の場合を想定している。Ｄ１の場合には、上流側領域では、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、３５％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられる。下流側領域では、第１反応Ｒ１の活性度合いが１００％であり、第２反応Ｒ２の活性度合いが６０％であり、第３反応Ｒ３の活性度合いが３０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、残りの１５％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用い尽くされる。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は１００％である。 D1 in FIG. 5B assumes a case where the NO 2 ratio discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 50%. In the case of D1, in the upstream region, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, and the activity level of the third reaction R3 is 0%, Since the first reaction R1 is preferentially performed over the second reaction R2, 35% NO and NO 2 are all used in the first reaction R1 in a one-to-one relationship. In the downstream region, the activity level of the first reaction R1 is 100%, the activity level of the second reaction R2 is 60%, the activity level of the third reaction R3 is 30%, and the first reaction R1 is 2 so performed preferentially over reaction R2, it is exhausted used in the first reaction R1 is and the NO 2 remaining one by 15% NO by all one-to-one. Thereby, the NOx purification rate of the SCR catalyst 3 is 100%.

図５（ｂ）のＤ２は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が３５％の場合を想定している。Ｄ２の場合には、上流側領域では、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、３５％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられる。下流側領域では、第１反応Ｒ１の活性度合いが１００％であり、第２反応Ｒ２の活性度合いが６０％であり、第３反応Ｒ３の活性度合いが３０％であるので、残りの２０％のＮＯが第３反応Ｒ３に用いられ、１０％の余りのＮＯが反応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 D2 in FIG. 5B assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 35%. In the case of D2, in the upstream region, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, and the activity level of the third reaction R3 is 0%, Since the first reaction R1 is preferentially performed over the second reaction R2, 35% NO and NO 2 are all used in the first reaction R1 in a one-to-one relationship. In the downstream region, the activity level of the first reaction R1 is 100%, the activity level of the second reaction R2 is 60%, and the activity level of the third reaction R3 is 30%, so that the remaining 20% NO is used for the third reaction R3, and 10% of the excess NO is not reacted and is released. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

図５（ｂ）のＤ３は、内燃機関１から排出されＳＣＲ触媒３に流入するＮＯ２比率が７５％の場合を想定している。Ｄ３の場合には、上流側領域では、第１反応Ｒ１の活性度合いが９０％であり、第２反応Ｒ２の活性度合いが４０％であり、第３反応Ｒ３の活性度合いが０％であり、第１反応Ｒ１が第２反応Ｒ２よりも優先的に行われるので、まず２５％ずつのＮＯとＮＯ２とが全て１対１で第１反応Ｒ１に用いられ、次に５％のＮＯ２が第２反応Ｒ２に用いられる。下流側領域では、第１反応Ｒ１の活性度合いが１００％であり、第２反応Ｒ２の活性度合いが６０％であり、第３反応Ｒ３の活性度合いが３０％であるので、残りの３５％のＮＯ２が第２反応Ｒ２に用いられ、残りの１０％の余りのＮＯ２が反
応できずに放出される。これにより、ＳＣＲ触媒３のＮＯｘ浄化率は９０％である。 D3 in FIG. 5B assumes a case where the ratio of NO 2 discharged from the internal combustion engine 1 and flowing into the SCR catalyst 3 is 75%. In the case of D3, in the upstream region, the activity level of the first reaction R1 is 90%, the activity level of the second reaction R2 is 40%, and the activity level of the third reaction R3 is 0%, Since the first reaction R1 is preferentially performed over the second reaction R2, 25% NO and NO 2 are all used one-to-one for the first reaction R1, and then 5% NO 2 is used. Used in second reaction R2. In the downstream region, the activity level of the first reaction R1 is 100%, the activity level of the second reaction R2 is 60%, and the activity level of the third reaction R3 is 30%, so the remaining 35% NO 2 is used for the second reaction R2, and the remaining 10% of the remaining NO 2 cannot be reacted and is released. Thereby, the NOx purification rate of the SCR catalyst 3 is 90%.

以上の図５（ｂ）のＤ１〜Ｄ３では、目標浄化率である９０％のＮＯｘ浄化率に到達するためには、Ｄ１を含みＤ２からＤ３までの範囲が許容できるので、ＮＯ２比率の目標比率範囲が３５％〜７５％となる。 In D1~D3 above in FIG. 5 (b), in order to reach 90% of the NOx purification rate is the target purification rate, since the range from D2 include D1 to D3 is acceptable, NO 2 ratio objectives of The ratio range is 35% to 75%.

以上のように、図５を用いＳＣＲ触媒３を排気流れ上流側から順に２つの領域に分けた際の各領域の床温が異なる場合を説明した。このように、ＳＣＲ触媒３の各領域の床温が異なると、Ｒ１〜Ｒ３の３つの反応の活性度合いが各領域で異なるので、各領域でのＲ１〜Ｒ３の３つの反応の活性度合いが異なることを利用することにより、比率範囲を正確に算出することができる。すなわち、比率範囲は、図２及び図３のような各領域の床温とＲ１〜Ｒ３の３つの反応の活性度合いとを関連付けたマップと、各領域の床温と、ＳＣＲ触媒３へ流入すると想定されるＮＯとＮＯ２との比率と、に基づいて算出することができる。つまり、ＳＣＲ触媒３へ流入すると仮に想定されるＮＯとＮＯ２との比率に対して、各領域の床温をマップに取り込んで導出したＲ１〜Ｒ３の３つの反応の活性度合いを考慮して、各領域でのＮＯｘ浄化反応を推定してＮＯｘ浄化率を算出することができる。そして、算出したＮＯｘ浄化率が目標浄化率を達成できる限界の上限と下限のＳＣＲ触媒３へ流入すると想定されるＮＯとＮＯ２との比率を求め、この上限から下限までの範囲を比率範囲として特定することができる。なお、本実施例では、ＳＣＲ触媒３を排気流れ上流側から順に２つの領域に分けた場合を例示しているが、各領域はＳＣＲ触媒を３つ以上に分けるものでもよい。 As described above, the case where the bed temperature of each region is different when the SCR catalyst 3 is divided into two regions in order from the exhaust flow upstream side has been described with reference to FIG. Thus, when the bed temperature of each region of the SCR catalyst 3 is different, the activity levels of the three reactions R1 to R3 are different in each region, so the activity levels of the three reactions R1 to R3 in each region are different. By utilizing this, the ratio range can be accurately calculated. That is, when the ratio range flows into the SCR catalyst 3, the map associating the bed temperature of each region as shown in FIGS. 2 and 3 with the activity levels of the three reactions R1 to R3, the bed temperature of each region, and the SCR catalyst 3. the ratio between NO and NO 2 which is assumed, can be calculated based on. That is, for a ratio between NO and NO 2 provisionally envisaged when flowing into the SCR catalyst 3, in consideration of the degree of activation of the three reactions of R1~R3 derived captures bed temperature of each area on the map, The NOx purification rate can be calculated by estimating the NOx purification reaction in each region. Then, a ratio between NO and NO 2 that is assumed to flow into the upper limit and lower limit SCR catalysts 3 at which the calculated NOx purification rate can achieve the target purification rate is obtained, and the range from the upper limit to the lower limit is defined as the ratio range. Can be identified. In the present embodiment, the case where the SCR catalyst 3 is divided into two regions in order from the exhaust flow upstream side is illustrated, but each region may be divided into three or more SCR catalysts.

そこで本実施例では、ＳＣＲ触媒３を排気流れ上流側から順に複数の領域に分けた際の各領域での床温が異なると、各領域での、ＮＯとＮＯ２との両方を消費する第１反応Ｒ１、ＮＯ２を消費する第２反応Ｒ２、及びＮＯを消費する第３反応Ｒ３という３つの反応の活性度合いが異なることを利用して、排気温度センサ１１が取得したＳＣＲ触媒３の床温により導かれる各領域の床温と、ＳＣＲ触媒３へ流入すると想定されるＮＯとＮＯ２との比率と、に基づいて、目標浄化率に到達するためのＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率範囲を算出する。このように比率範囲を算出するＥＣＵ１３が、本発明の比率範囲算出部に対応する。 Therefore, in this embodiment, if the bed temperature in each region when the SCR catalyst 3 is divided into a plurality of regions in order from the exhaust flow upstream side is different, both NO and NO 2 in each region are consumed. The floor of the SCR catalyst 3 acquired by the exhaust gas temperature sensor 11 by utilizing the fact that the activity levels of the three reactions of the first reaction R1, the second reaction R2 consuming NO 2 and the third reaction R3 consuming NO are different. NO and NO flowing into the SCR catalyst 3 for reaching the target purification rate based on the bed temperature of each region guided by the temperature and the ratio of NO and NO 2 assumed to flow into the SCR catalyst 3 A ratio range of 2 is calculated. Thus, ECU13 which calculates a ratio range respond | corresponds to the ratio range calculation part of this invention.

そして、算出された比率範囲内に収まるように、ＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率を、第１流量調節弁９及び第２流量調節弁１０によって制御する。酸化触媒６は、ＮＯをＮＯ２に酸化させる機能を有するので、内燃機関１から排出されるＮＯ２比率が目標比率範囲よりも低ければ、第１流量調節弁９を開き側に調整し、第２流量調節弁１０を閉じ側に調整し、酸化触媒６を流通する排気流量を多くすることで、ＮＯ２比率を高くする。内燃機関１から排出されるＮＯ２比率が目標比率範囲内であれば、第１流量調節弁９を全閉し、第２流量調節弁１０を全開し、バイパス通路８だけに排気を流通させることで、ＮＯ２比率を維持する。または、内燃機関１から排出されるＮＯ２比率が目標比率範囲内であり、排気が酸化触媒６を流通してもＮＯ２比率が目標比率範囲内に収まるようであれば、第１流量調節弁９を全開し、第２流量調節弁１０を全閉し、酸化触媒６を流通するように排気を流通させることで、ＮＯ２比率が変動しても目標比率範囲内に維持できる。内燃機関１から排出されるＮＯ２比率が目標比率範囲よりも高ければ、内燃機関１の運転状態をＮＯ２比率が低くなる運転状態に変更し、第１流量調節弁９を全閉し、第２流量調節弁１０を全開し、バイパス通路８だけに排気を流通させることで、ＮＯ２比率を低くする。また、このように比率を制御するＥＣＵ１３が、本発明のＮＯｘ比率制御部に対応する。 Then, the ratio of NO and NO 2 flowing into the SCR catalyst 3 is controlled by the first flow rate control valve 9 and the second flow rate control valve 10 so as to be within the calculated ratio range. The oxidation catalyst 6, because it has a function of oxidizing NO to NO 2, the NO 2 ratio discharged from the internal combustion engine 1 is lower than the target ratio range, and adjusted to the open side of the first flow rate control valve 9, the 2 The flow rate adjusting valve 10 is adjusted to the closed side, and the exhaust gas flow rate flowing through the oxidation catalyst 6 is increased to increase the NO 2 ratio. If the NO 2 ratio discharged from the internal combustion engine 1 is within the target ratio range, the first flow rate control valve 9 is fully closed, the second flow rate control valve 10 is fully opened, and the exhaust gas is allowed to flow only through the bypass passage 8. Thus, the NO 2 ratio is maintained. Or is in the NO 2 ratio target ratio range to be discharged from the internal combustion engine 1, the exhaust is equal so that NO 2 ratio also flows through the oxidation catalyst 6 falls within the target ratio range, the first flow rate control valve 9 is fully opened, the second flow rate control valve 10 is fully closed, and the exhaust gas is circulated so as to circulate through the oxidation catalyst 6, so that the NO 2 ratio can be maintained within the target ratio range. If the ratio of NO 2 discharged from the internal combustion engine 1 is higher than the target ratio range, the operating state of the internal combustion engine 1 is changed to an operating state in which the NO 2 ratio becomes low, the first flow rate control valve 9 is fully closed, 2 The flow rate adjusting valve 10 is fully opened and the exhaust gas is allowed to flow only through the bypass passage 8 to reduce the NO 2 ratio. The ECU 13 that controls the ratio in this way corresponds to the NOx ratio control unit of the present invention.

本実施例によると、ＳＣＲ触媒３では目標浄化率以上のＮＯｘ浄化率を確保して、ＮＨ３の不足や過剰供給といった問題を回避することができる。 According to the present embodiment, the SCR catalyst 3 can secure a NOx purification rate that is equal to or higher than the target purification rate, thereby avoiding problems such as shortage and excessive supply of NH 3 .

（ＮＯｘ比率制御ルーチン）
ＥＣＵ１３が行うＮＯｘ比率制御ルーチンについて、図６に示すフローチャートに基づいて説明する。図６は、本実施例に係るＮＯｘ比率制御ルーチンを示すフローチャートである。本ルーチンは、所定の時間毎にＥＣＵ１３によって実行される。 (NOx ratio control routine)
The NOx ratio control routine performed by the ECU 13 will be described based on the flowchart shown in FIG. FIG. 6 is a flowchart showing a NOx ratio control routine according to the present embodiment. This routine is executed by the ECU 13 every predetermined time.

図６に示すルーチンが開始されると、Ｓ１０１では、ＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率範囲を算出する。比率範囲は以下のようにして特定する。まず、ＳＣＲ触媒３へ流入すると想定されるＮＯとＮＯ２との比率（ＮＯ２比率）に５０％を設定する。排気温度センサ１１の出力値からは、ＳＣＲ触媒３の床温が推定される。このＳＣＲ触媒３の床温を推定する際には、内燃機関１の運転状態等を加味してもよい。この排気温度センサ１１の出力値から推定されたＳＣＲ触媒３の床温により、内燃機関１の運転状態等を加味することでＳＣＲ触媒３の各領域の床温を推定する。推定されたＳＣＲ触媒３の各領域の床温を、図２及び図３のような各領域の床温とＲ１〜Ｒ３の３つの反応の活性度合いとを関連付けたマップに取り込んで、各領域のＲ１〜Ｒ３の３つの反応の活性度合いを導出する。そして、ＮＯ２比率５０％に対する、各領域のＲ１〜Ｒ３の３つの反応の活性度合いを考慮して、各領域でのＮＯｘ反応を推定してＮＯｘ浄化率を算出する。このようなＮＯｘ浄化率の算出を、算出したＮＯｘ浄化率が目標浄化率を達成できる限界となるＳＣＲ触媒３へ流入すると想定されるＮＯ２比率が特定できるまで行う。つまり、ＮＯ２比率５０％から上方の比率及び下方の比率へ想定されるＮＯ２比率を変更してＮＯｘ浄化率を算出する。そして、算出したＮＯｘ浄化率が目標浄化率を達成できる限界の上限と下限のＮＯ２比率を求め、この上限から下限の範囲を比率範囲として特定する。本ステップの処理を行うＥＣＵ１３が、本発明の比率範囲算出部に対応する。 When the routine shown in FIG 6 is started, the S101, and calculates the ratio range of NO and NO 2 flowing into the SCR catalyst 3. The ratio range is specified as follows. First, 50% is set as the ratio of NO to NO 2 (NO 2 ratio) that is assumed to flow into the SCR catalyst 3. From the output value of the exhaust temperature sensor 11, the bed temperature of the SCR catalyst 3 is estimated. When estimating the bed temperature of the SCR catalyst 3, the operating state of the internal combustion engine 1 may be taken into consideration. Based on the bed temperature of the SCR catalyst 3 estimated from the output value of the exhaust temperature sensor 11, the bed temperature of each region of the SCR catalyst 3 is estimated by taking into account the operating state of the internal combustion engine 1 and the like. The estimated bed temperature of each region of the SCR catalyst 3 is taken into a map in which the bed temperature of each region and the activity levels of the three reactions R1 to R3 are associated with each other as shown in FIGS. The degree of activity of the three reactions R1 to R3 is derived. Then, considering the activity level of the three reactions R1 to R3 in each region with respect to the NO 2 ratio of 50%, the NOx purification rate is calculated by estimating the NOx reaction in each region. Such calculation of the NOx purification rate is performed until the NO 2 ratio that is assumed to flow into the SCR catalyst 3 at which the calculated NOx purification rate becomes the limit at which the target purification rate can be achieved can be specified. In other words, change the NO 2 ratio estimated from NO 2 ratio of 50% above the ratio and lower ratio calculating a NOx purification ratio. Then, the upper limit and lower limit NO 2 ratios at which the calculated NOx purification rate can achieve the target purification rate are obtained, and the lower limit range from this upper limit is specified as the ratio range. The ECU 13 that performs the processing of this step corresponds to the ratio range calculation unit of the present invention.

Ｓ１０２では、Ｓ１０１で算出された比率範囲内に収まるように、ＳＣＲ触媒３へ流入するＮＯとＮＯ２との比率（ＮＯ２比率）を制御する。内燃機関１から排出されるＮＯ２比率が目標比率範囲よりも低ければ、第１流量調節弁９を開き側に調整し、第２流量調節弁１０を閉じ側に調整し、酸化触媒６を流通する排気流量を多くすることで、ＮＯ２比率を高くする。内燃機関１から排出されるＮＯ２比率が目標比率範囲内であれば、第１流量調節弁９を全閉し、第２流量調節弁１０を全開し、バイパス通路８だけに排気を流通させることで、ＮＯ２比率を維持する。または、内燃機関１から排出されるＮＯ２比率が目標比率範囲内であり、排気が酸化触媒６を流通してもＮＯ２比率が目標比率範囲内に収まるようであれば、第１流量調節弁９を全開し、第２流量調節弁１０を全閉し、酸化触媒６を流通するように排気を流通させることで、ＮＯ２比率が変動しても目標比率範囲内に維持できる。内燃機関１から排出されるＮＯ２比率が目標比率範囲よりも高ければ、内燃機関１の運転状態をＮＯ２比率が低くなる運転状態に変更し、第１流量調節弁９を全閉し、第２流量調節弁１０を全開し、バイパス通路８だけに排気を流通させることで、ＮＯ２比率を低くする。本ステップの処理を行うＥＣＵ１３が、本発明のＮＯｘ比率制御部に対応する。本ステップの処理の後、本ルーチンを一旦終了する。 In S102, so as to fall within a ratio range calculated in S101, controlling the ratio (NO 2 ratio) of NO and NO 2 flowing into the SCR catalyst 3. If the NO 2 ratio discharged from the internal combustion engine 1 is lower than the target ratio range, the first flow rate control valve 9 is adjusted to the open side, the second flow rate control valve 10 is adjusted to the close side, and the oxidation catalyst 6 is circulated. By increasing the exhaust flow rate to be increased, the NO 2 ratio is increased. If the NO 2 ratio discharged from the internal combustion engine 1 is within the target ratio range, the first flow rate control valve 9 is fully closed, the second flow rate control valve 10 is fully opened, and the exhaust gas is allowed to flow only through the bypass passage 8. Thus, the NO 2 ratio is maintained. Or is in the NO 2 ratio target ratio range to be discharged from the internal combustion engine 1, the exhaust is equal so that NO 2 ratio also flows through the oxidation catalyst 6 falls within the target ratio range, the first flow rate control valve 9 is fully opened, the second flow rate control valve 10 is fully closed, and the exhaust gas is circulated so as to circulate through the oxidation catalyst 6, so that the NO 2 ratio can be maintained within the target ratio range. If the ratio of NO 2 discharged from the internal combustion engine 1 is higher than the target ratio range, the operating state of the internal combustion engine 1 is changed to an operating state in which the NO 2 ratio becomes low, the first flow rate control valve 9 is fully closed, 2 The flow rate adjusting valve 10 is fully opened and the exhaust gas is allowed to flow only through the bypass passage 8 to reduce the NO 2 ratio. The ECU 13 that performs the processing of this step corresponds to the NOx ratio control unit of the present invention. After the processing of this step, this routine is once ended.

また、Ｓ１０２で決定されたＮＯ２比率の場合に得られるＮＯｘ浄化率、内燃機関１から排出されるＮＯｘ量、ＮＯｘセンサ１２の検出値、さらにはＳＣＲ触媒３に吸着された尿素やＮＨ３の量を考慮して、必要な尿素水の量を算出し、尿素水添加制御を行う。このようにして尿素水が算出されると尿素水はＮＯｘの浄化に最適な量となるので、ＮＨ３の不足や過剰供給といった問題を回避することができる。 Further, the NOx purification rate obtained in the case of the NO 2 ratio determined in S102, the NOx amount discharged from the internal combustion engine 1, the detected value of the NOx sensor 12, and further, the urea and NH 3 adsorbed on the SCR catalyst 3 The amount of urea water required is calculated in consideration of the amount, and urea water addition control is performed. When the urea water is calculated in this way, the urea water becomes an optimum amount for the purification of NOx, so that problems such as insufficient NH 3 and excessive supply can be avoided.

以上説明した本ルーチンによると、ＳＣＲ触媒３の各領域での床温が異なると、各領域でのＲ１〜Ｒ３という３つの反応の活性度合いが異なることを利用して、排気温度センサ１１が取得したＳＣＲ触媒３の床温により導かれる各領域の床温と、ＳＣＲ触媒３へ流入すると想定されるＮＯ２比率と、に基づいて、目標浄化率に到達するためのＳＣＲ触媒３
へ流入するＮＯとＮＯ２との比率範囲を算出することができる。そして、算出された比率範囲内に収まるように、ＳＣＲ触媒３へ流入するＮＯ２比率を制御することができる。よって、ＳＣＲ触媒３では目標浄化率以上のＮＯｘ浄化率を確保して、ＮＨ３の不足や過剰供給といった問題を回避することができる。 According to this routine described above, the exhaust temperature sensor 11 acquires the fact that the activity levels of the three reactions R1 to R3 in each region differ when the bed temperature in each region of the SCR catalyst 3 differs. The SCR catalyst 3 for reaching the target purification rate based on the bed temperature of each region guided by the bed temperature of the SCR catalyst 3 and the NO 2 ratio assumed to flow into the SCR catalyst 3
The ratio range between NO and NO 2 flowing into the engine can be calculated. Then, the NO 2 ratio flowing into the SCR catalyst 3 can be controlled so as to be within the calculated ratio range. Therefore, the SCR catalyst 3 can secure a NOx purification rate that is equal to or higher than the target purification rate, thereby avoiding problems such as shortage and excessive supply of NH 3 .

＜その他＞
上記実施例では、ＮＯとＮＯ２との比率を目標比率範囲内に収めるために、バイパス通路８と第１流量調節弁９と第２流量調節弁１０とを用いて内燃機関１から排出されるＮＯとＮＯ２との比率を変更していた。しかしこれに限られない。例えば、内燃機関１の運転状態を変更することで内燃機関１から排出されるＮＯとＮＯ２との比率を変更するものでもよいし、他の手法であってもよい。 <Others>
In the above embodiment, the exhaust gas is discharged from the internal combustion engine 1 using the bypass passage 8, the first flow rate control valve 9, and the second flow rate control valve 10 in order to keep the ratio of NO and NO 2 within the target ratio range. I had to change the ratio of NO and NO 2. However, it is not limited to this. For example, the ratio of NO and NO 2 discharged from the internal combustion engine 1 may be changed by changing the operating state of the internal combustion engine 1, or another method may be used.

本発明に係る内燃機関の排気浄化装置は、上述の実施例に限定されるものではなく、本発明の要旨を逸脱しない範囲内において種々の変更を加えてもよい。また、上記実施例は、本発明に係る内燃機関の排気浄化方法の実施例をも兼ねるものである。   The exhaust gas purification apparatus for an internal combustion engine according to the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the gist of the present invention. Further, the above embodiment also serves as an embodiment of the exhaust gas purification method for an internal combustion engine according to the present invention.

１：内燃機関、２：排気通路、３：ＳＣＲ触媒、４：尿素水添加弁、５：尿素水タンク、６：酸化触媒、７：ＤＰＦ、８：バイパス通路、９：第１流量調節弁、１０：第２流量調節弁、１１：排気温度センサ、１２：ＮＯｘセンサ、１３：ＥＣＵ 1: internal combustion engine, 2: exhaust passage, 3: SCR catalyst, 4: urea water addition valve, 5: urea water tank, 6: oxidation catalyst, 7: DPF, 8: bypass passage, 9: first flow control valve, 10: second flow control valve, 11: exhaust temperature sensor, 12: NOx sensor, 13: ECU

Claims (3)

内燃機関の排気通路に配置された選択還元型ＮＯｘ触媒と、
前記選択還元型ＮＯｘ触媒よりも上流の前記排気通路に配置され、前記選択還元型ＮＯｘ触媒へＮＨ３を供給するための還元剤を添加する還元剤添加部と、
前記選択還元型ＮＯｘ触媒の床温を、検出又は推定することにより取得する床温取得部と、
を備えた内燃機関の排気浄化装置であって、
前記選択還元型ＮＯｘ触媒を排気流れ上流側から順に複数の領域に分けた際の各領域での床温が異なると、各領域での、ＮＯとＮＯ２との両方を消費する第１反応、ＮＯ２を消費する第２反応、及びＮＯを消費する第３反応という３つの反応の活性度合いが異なることを利用して、前記床温取得部が取得した前記選択還元型ＮＯｘ触媒の床温により導かれる各領域の床温と、前記選択還元型ＮＯｘ触媒へ流入すると想定されるＮＯとＮＯ２との比率と、に基づいて、目標浄化率に到達するための前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率範囲を算出する比率範囲算出部と、
前記比率範囲算出部によって算出された比率範囲内に収まるように、前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御するＮＯｘ比率制御部と、
を備えたことを特徴とする内燃機関の排気浄化装置。 A selective reduction type NOx catalyst disposed in an exhaust passage of the internal combustion engine;
A reducing agent addition unit that is disposed in the exhaust passage upstream of the selective reduction type NOx catalyst and adds a reducing agent for supplying NH 3 to the selective reduction type NOx catalyst;
A bed temperature acquisition unit which acquires the bed temperature of the selective catalytic reduction NOx catalyst by detecting or estimating;
An exhaust purification device for an internal combustion engine comprising:
When the selective reduction type NOx catalyst is divided into a plurality of regions in order from the exhaust flow upstream side and the bed temperature in each region is different, a first reaction that consumes both NO and NO 2 in each region, By utilizing the fact that the degree of activity of the three reactions of the second reaction that consumes NO 2 and the third reaction that consumes NO is different, the bed temperature of the selective reduction type NOx catalyst acquired by the bed temperature acquisition unit is used. Based on the derived bed temperature of each region and the ratio of NO and NO 2 that is assumed to flow into the selective reduction NOx catalyst, the flow into the selective reduction NOx catalyst to reach the target purification rate A ratio range calculation unit for calculating a ratio range of NO and NO 2 to be performed;
And said ratio range calculation section so as to fall within a ratio range calculated by, NOx ratio controller for controlling the ratio between NO and NO 2 which flows into the selective reduction type NOx catalyst,
An exhaust emission control device for an internal combustion engine, comprising: 前記選択還元型ＮＯｘ触媒よりも上流の前記排気通路に配置された酸化触媒と、
排気に前記酸化触媒を迂回させるバイパス通路と、
前記酸化触媒を流通する排気流量と前記バイパス通路を流通する排気流量とを調節する排気流量調節部と、
を更に備え、
前記ＮＯｘ比率制御部は、前記排気流量調節部で前記酸化触媒を流通する排気流量と前記バイパス通路を流通する排気流量とを調節することにより、前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御することを特徴とする請求項１に記載の内燃機関の排気浄化装置。 An oxidation catalyst disposed in the exhaust passage upstream of the selective reduction NOx catalyst;
A bypass passage for bypassing the oxidation catalyst to exhaust,
An exhaust flow rate adjusting unit for adjusting an exhaust flow rate flowing through the oxidation catalyst and an exhaust flow rate flowing through the bypass passage;
Further comprising
The NOx ratio control unit adjusts an exhaust flow rate through which the oxidation catalyst is circulated and an exhaust flow rate through which the bypass passage is circulated by the exhaust flow rate adjustment unit, whereby NO and NO 2 flowing into the selective reduction type NOx catalyst are adjusted. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the ratio is controlled. 内燃機関の排気通路に配置された選択還元型ＮＯｘ触媒よりも上流の前記排気通路に配置された還元剤添加部から還元剤を添加して、前記選択還元型ＮＯｘ触媒へＮＨ３を供給し、前記選択還元型ＮＯｘ触媒でＮＯｘを浄化させる内燃機関の排気浄化方法であって、
前記選択還元型ＮＯｘ触媒を排気流れ上流側から順に複数の領域に分けた際の各領域での床温が異なると、各領域での、ＮＯとＮＯ２との両方を消費する第１反応、ＮＯ２を消費する第２反応、及びＮＯを消費する第３反応という３つの反応の活性度合いが異なることを利用して、前記選択還元型ＮＯｘ触媒の床温を、検出又は推定することにより取得する床温取得部が取得した前記選択還元型ＮＯｘ触媒の床温により導かれる各領域の床温と、前記選択還元型ＮＯｘ触媒へ流入すると想定されるＮＯとＮＯ２との比率と、に基づいて、目標浄化率に到達するための前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率範囲を算出し、
算出された比率範囲内に収まるように、前記選択還元型ＮＯｘ触媒へ流入するＮＯとＮＯ２との比率を制御することを特徴とする内燃機関の排気浄化方法。 Adding a reducing agent from a reducing agent addition section arranged in the exhaust passage upstream of the selective reduction type NOx catalyst arranged in the exhaust passage of the internal combustion engine, and supplying NH 3 to the selective reduction type NOx catalyst; An exhaust purification method for an internal combustion engine that purifies NOx with the selective reduction type NOx catalyst,
When the selective reduction type NOx catalyst is divided into a plurality of regions in order from the exhaust flow upstream side and the bed temperature in each region is different, a first reaction that consumes both NO and NO 2 in each region, Obtained by detecting or estimating the bed temperature of the selective reduction-type NOx catalyst using the fact that the activity levels of the three reactions, the second reaction consuming NO 2 and the third reaction consuming NO, are different. Based on the bed temperature of each region derived from the bed temperature of the selective reduction NOx catalyst acquired by the bed temperature acquisition unit and the ratio of NO and NO 2 that is assumed to flow into the selective reduction NOx catalyst. Calculating a ratio range of NO and NO 2 flowing into the selective catalytic reduction NOx catalyst to reach the target purification rate,
An exhaust gas purification method for an internal combustion engine, wherein a ratio between NO and NO 2 flowing into the selective reduction type NOx catalyst is controlled so as to be within a calculated ratio range.
JP2010172142A 2010-07-30 2010-07-30 Device and method for exhaust emission control of internal combustion engine Withdrawn JP2012031787A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP2010172142A JP2012031787A (en) 2010-07-30 2010-07-30 Device and method for exhaust emission control of internal combustion engine

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP2010172142A JP2012031787A (en) 2010-07-30 2010-07-30 Device and method for exhaust emission control of internal combustion engine

Publications (1)

Publication Number Publication Date
JP2012031787A true JP2012031787A (en) 2012-02-16

Family

ID=45845489

Family Applications (1)

Application Number Title Priority Date Filing Date
JP2010172142A Withdrawn JP2012031787A (en) 2010-07-30 2010-07-30 Device and method for exhaust emission control of internal combustion engine

Country Status (1)

Country Link
JP (1) JP2012031787A (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014073408A1 (en) 2012-11-07 2014-05-15 トヨタ自動車株式会社 Exhaust gas purification device for internal-combustion engine
JP2016532810A (en) * 2013-07-29 2016-10-20 マン・ディーゼル・アンド・ターボ・エスイー Operation method of internal combustion engine
JP2018525565A (en) * 2015-08-27 2018-09-06 スカニア シーブイ アクチボラグ Method and system for exhaust gas treatment
US11007481B2 (en) 2015-08-27 2021-05-18 Scania Cv Ab Exhaust treatment system and method for treatment of an exhaust gas stream

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2014073408A1 (en) 2012-11-07 2014-05-15 トヨタ自動車株式会社 Exhaust gas purification device for internal-combustion engine
US9593611B2 (en) 2012-11-07 2017-03-14 Toyota Jidosha Kabushiki Kaisha Exhaust gas control apparatus for internal combustion engine
JP2016532810A (en) * 2013-07-29 2016-10-20 マン・ディーゼル・アンド・ターボ・エスイー Operation method of internal combustion engine
US9803575B2 (en) 2013-07-29 2017-10-31 Man Diesel & Turbo Se Method for operating an internal combustion engine
JP2018525565A (en) * 2015-08-27 2018-09-06 スカニア シーブイ アクチボラグ Method and system for exhaust gas treatment
US10920632B2 (en) 2015-08-27 2021-02-16 Scania Cv Ab Method and exhaust treatment system for treatment of an exhaust gas stream
US11007481B2 (en) 2015-08-27 2021-05-18 Scania Cv Ab Exhaust treatment system and method for treatment of an exhaust gas stream

Similar Documents

Publication Publication Date Title
JP5880731B2 (en) Exhaust gas purification device for internal combustion engine
US8978367B2 (en) Exhaust gas purifying system of internal combustion engine
US8656702B2 (en) Exhaust gas after treatment system
JP4702318B2 (en) Exhaust gas purification system for internal combustion engine
JP5272455B2 (en) NOx purification system control method and NOx purification system
US8161731B2 (en) Selective catalytic reduction using controlled catalytic deactivation
JP5002040B2 (en) Exhaust gas purification device for internal combustion engine
JP5127052B2 (en) Exhaust treatment device control device
JP2008163856A (en) Exhaust emission control device of internal combustion engine
EP2940267B1 (en) Exhaust gas purification apparatus for internal combustion engine
WO2010087005A1 (en) Exhaust purifying device
JP5560089B2 (en) Exhaust gas purification device for internal combustion engine
WO2010134189A1 (en) Exhaust emission controler device for internal combustion engine
US10364727B2 (en) Exhaust gas purification apparatus for an internal combustion engine
JP2012031787A (en) Device and method for exhaust emission control of internal combustion engine
JP2009293605A (en) Control device for exhaust treatment device
JP2012082703A (en) DEVICE AND METHOD FOR DETECTING DEGRADATION OF SELECTIVE REDUCTION TYPE NOx CATALYST
JP2010185369A (en) Fuel supply device of engine
JP2010185434A (en) Exhaust emission control device for internal combustion engine
US8307635B2 (en) Exhaust purification system of internal combustion engine
JP2023113032A (en) Exhaust emission control system
JP6453702B2 (en) Abnormality diagnosis device for exhaust purification mechanism
JP2013238164A (en) Exhaust emission control apparatus of internal combustion engine
JP2013234624A (en) Abnormality determination system for exhaust emission control device of internal combustion engine
JP2018035766A (en) Exhaust emission control device for internal combustion engine

Legal Events

Date Code Title Description
A300 Withdrawal of application because of no request for examination

Free format text: JAPANESE INTERMEDIATE CODE: A300

Effective date: 20131001