JP7206756B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Exhaust gas purification system for internal combustion engine Download PDF

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JP7206756B2
JP7206756B2 JP2018184010A JP2018184010A JP7206756B2 JP 7206756 B2 JP7206756 B2 JP 7206756B2 JP 2018184010 A JP2018184010 A JP 2018184010A JP 2018184010 A JP2018184010 A JP 2018184010A JP 7206756 B2 JP7206756 B2 JP 7206756B2
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大治 長岡
隆行 坂本
輝男 中田
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Description

本発明は、内燃機関の排気ガス浄化システムに関する。 The present invention relates to an exhaust gas purification system for internal combustion engines.

自動車業界では、近年の排気ガス規制の強化により、市街地走行や高速道路走行での大気に排出される排気ガスに含まれるNOx量の低減が求められている。従来のNOx量低減技術としては、LNT(NOx吸蔵還元型触媒装置)や尿素SCR(尿素系選択還元型触媒装置)があるが、各装置単独では自動車の走行状態全域をカバーできないため、LNTとSCRを組み合わせた構成の自動車への搭載が検討されている(例えば、特許文献1参照)。 In the automobile industry, due to the tightening of exhaust gas regulations in recent years, there is a demand for reducing the amount of NOx contained in the exhaust gas emitted into the atmosphere during city driving and highway driving. Conventional technologies for reducing the amount of NOx include LNT (NOx storage reduction catalyst) and urea SCR (urea selective reduction catalyst). Mounting on automobiles having a configuration in which SCRs are combined is under consideration (see Patent Document 1, for example).

特開2017-36700号公報Japanese Patent Application Laid-Open No. 2017-36700

ところで、NOx吸蔵還元型触媒装置は、排気ガスの空燃比がリーン空燃比のときにその内部に排気ガスに含まれるNOxを蓄積し、リッチ空燃比のときにこの蓄積したNOxを放出して、この放出したNOxを排気ガスに含まれる炭化水素や一酸化炭素により窒素に還元して浄化する装置である。このNOxから窒素への還元反応時に、排気ガスの空燃比が1より小さいと、副生成物としてアンモニアが生成される場合がある。副生成物として生成されたアンモニアはNOx吸蔵還元型触媒装置から下流側の選択還元型触媒装置に向って流出する。 By the way, the NOx storage reduction type catalyst device accumulates NOx contained in the exhaust gas when the air-fuel ratio of the exhaust gas is a lean air-fuel ratio, and releases the accumulated NOx when the air-fuel ratio is a rich air-fuel ratio. This device purifies the released NOx by reducing it to nitrogen with hydrocarbons and carbon monoxide contained in the exhaust gas. If the air-fuel ratio of the exhaust gas is less than 1 during the reduction reaction of NOx to nitrogen, ammonia may be produced as a by-product. Ammonia produced as a by-product flows out from the NOx storage reduction catalyst device toward the downstream selective reduction catalyst device.

一方、選択還元型触媒装置には、その内部にアンモニアが所定量蓄積され、排気ガスに含まれるNOxの浄化に使用されているが、尿素水供給制御時におけるこのアンモニアの蓄積量は推定値であるので、実際の蓄積量とは少し異なる。そのため、アンモニアの蓄積量の推定値よりも実際の蓄積量が大きい場合、NOx吸蔵還元型触媒装置で生成されたアンモニアが選択還元型触媒装置に流入すると、この流入したアンモニアを選択還元型触媒装置に蓄積することができず、選択還元型触媒装置から下流側の排気通路にアンモニアを流出させる虞がある。 On the other hand, in the selective reduction catalyst device, a predetermined amount of ammonia is accumulated inside and used to purify NOx contained in the exhaust gas. Therefore, it is slightly different from the actual accumulated amount. Therefore, when the actual accumulated amount of ammonia is larger than the estimated accumulated amount of ammonia and the ammonia generated in the NOx storage reduction catalyst device flows into the selective reduction catalyst device, the ammonia that has flowed into the selective reduction catalyst device is Therefore, there is a risk that the ammonia may flow out from the selective reduction catalyst device into the exhaust passage on the downstream side.

本発明の目的は、選択還元型触媒装置のアンモニアの蓄積量の推定精度を向上して、選択還元型触媒装置から下流側の排気通路に流出するアンモニアの量を抑制できる内燃機関の排気ガス浄化システム及び内燃機関の排気ガス浄化方法を提供することにある。 An object of the present invention is to improve the accuracy of estimating the accumulated amount of ammonia in a selective reduction catalyst device, and to suppress the amount of ammonia flowing out of the selective reduction catalyst device into the exhaust passage on the downstream side. An object of the present invention is to provide a system and a method for purifying an exhaust gas of an internal combustion engine.

上記の目的を達成するための本発明の内燃機関の排気ガス浄化システムは、内燃機関の排気通路に上流側より順に、NOx吸蔵還元型触媒装置、選択還元型触媒装置を備えて構成される内燃機関の排気ガス浄化システムにおいて、前記選択還元型触媒装置より上流側の前記排気通路に排気ガスの酸素濃度を取得する酸素濃度取得装置を備え、前記NOx吸蔵還元型触媒装置と前記選択還元型触媒装置の間の前記排気通路に排気ガスのNOx濃度を取得するNOx濃度取得装置とを備えるとともに、前記酸素濃度取得装置及び前記NOx濃度取得装置と電気的に接続された制御装置を備え、前記制御装置が、前記NOx吸蔵還元型触媒装置のリッチ還元制御を行っている場合で、前記酸素濃度取得装置の取得値と前記NOx濃度取得装置の取得値とに基づいて、前記NOx吸蔵還元型触媒装置でアンモニアが生成されていると判定するときには、前記NOx吸蔵還元型触媒装置で生成されるアンモニア量を算出するとともに、この算出値を基に前記選択還元型触媒装置のアンモニアの蓄積量を補正する制御を行うように構成されており、かつ、前記制御装置が、前記酸素濃度取得装置の取得値が予め設定された設定酸素濃度閾値を下回り、かつ、前記NOx濃度取得装置の取得値が予め設定された設定NOx濃度閾値以上となるときに、前記NOx吸蔵還元型触媒装置でアンモニアが生成されていると判定する制御を行うように構成されていることを特徴とする。
また、本発明の内燃機関の排気ガス浄化システムは、内燃機関の排気通路に上流側より順に、NOx吸蔵還元型触媒装置、選択還元型触媒装置を備えて構成される内燃機関の排気ガス浄化システムにおいて、
前記選択還元型触媒装置より上流側の前記排気通路に排気ガスの酸素濃度を取得する酸素濃度取得装置を備え、前記NOx吸蔵還元型触媒装置と前記選択還元型触媒装置の間の前記排気通路に排気ガスのNOx濃度を取得するNOx濃度取得装置とを備えるとともに、前記酸素濃度取得装置及び前記NOx濃度取得装置と電気的に接続された制御装置を備え、
前記制御装置が、前記NOx吸蔵還元型触媒装置のリッチ還元制御を行っている場合で、前記酸素濃度取得装置の取得値と前記NOx濃度取得装置の取得値とに基づいて、前記NOx吸蔵還元型触媒装置でアンモニアが生成されていると判定するときには、前記NOx吸蔵還元型触媒装置で生成されるアンモニア量を算出するとともに、この算出値を基に前記選択還元型触媒装置のアンモニアの蓄積量を補正する制御を行うように構成されており、かつ、前記内燃機関から排気される排気ガスのNOx濃度を取得するエンジン出口NOx濃度取得装置を備え、このエンジン出口NOx濃度取得装置を前記制御装置に電気的に接続するとともに、前記制御装置が、前記エンジン出口NOx濃度取得装置の取得値と前記NOx濃度取得装置の取得値との差に基づいて、あるいは、前記リッチ還元制御の開始時の前記NOx吸蔵還元型触媒装置のNOx吸蔵量に基づいて、前記NOx吸蔵還元型触媒装置で生成されるアンモニア量を算出する制御を行うように構成されていることを特徴とする。
In order to achieve the above objects, an exhaust gas purification system for an internal combustion engine according to the present invention comprises an internal combustion engine exhaust gas passage comprising a NOx storage reduction catalyst device and a selective reduction catalyst device in this order from the upstream side in the exhaust passage of the internal combustion engine. In an exhaust gas purification system for an engine, an oxygen concentration acquiring device for acquiring an oxygen concentration of exhaust gas is provided in the exhaust passage upstream of the selective catalytic reduction device, the NOx storage reduction catalytic device and the selective catalytic reduction catalyst. a NOx concentration acquiring device for acquiring the NOx concentration of the exhaust gas in the exhaust passage between the devices, and a control device electrically connected to the oxygen concentration acquiring device and the NOx concentration acquiring device, When the device is performing rich reduction control of the NOx storage reduction type catalyst device, the NOx storage reduction type catalyst device is controlled based on the acquired value of the oxygen concentration acquisition device and the acquired value of the NOx concentration acquisition device. When it is determined that ammonia is generated in the NOx storage reduction catalyst device, the amount of ammonia generated in the NOx storage reduction catalyst device is calculated, and the accumulated amount of ammonia in the selective reduction catalyst device is corrected based on this calculated value. and the control device determines that the value acquired by the oxygen concentration acquisition device is below a preset oxygen concentration threshold and the value acquired by the NOx concentration acquisition device is preset. control is performed to determine that ammonia is being generated in the NOx storage reduction type catalyst device when the NOx concentration exceeds the set NOx concentration threshold .
Further, the exhaust gas purification system for an internal combustion engine of the present invention comprises a NOx storage reduction catalyst device and a selective reduction catalyst device in this order from the upstream side in an exhaust passage of the internal combustion engine. in
An oxygen concentration acquiring device for acquiring an oxygen concentration of exhaust gas is provided in the exhaust passage upstream of the selective catalytic reduction device, and the exhaust passage between the NOx storage reduction catalytic device and the selective catalytic reduction catalytic device is provided with an oxygen concentration acquisition device for acquiring an oxygen concentration of exhaust gas. a NOx concentration acquisition device for acquiring the NOx concentration of exhaust gas, and a control device electrically connected to the oxygen concentration acquisition device and the NOx concentration acquisition device,
When the control device is performing rich reduction control of the NOx storage reduction type catalyst device, the NOx storage reduction type When it is determined that ammonia is being generated in the catalyst device, the amount of ammonia generated in the NOx storage reduction catalyst device is calculated, and based on this calculated value, the accumulated amount of ammonia in the selective reduction catalyst device is calculated. An engine outlet NOx concentration acquisition device is configured to perform correction control and acquires the NOx concentration of exhaust gas discharged from the internal combustion engine, and the engine outlet NOx concentration acquisition device is attached to the control device. While electrically connecting, the control device controls the NOx concentration based on the difference between the acquired value of the engine outlet NOx concentration acquiring device and the acquired value of the NOx concentration acquiring device, or the NOx concentration at the start of the rich reduction control. It is characterized in that control is performed to calculate the amount of ammonia generated in the NOx storage reduction type catalyst device based on the NOx storage amount of the NOx storage reduction type catalyst device.

選択還元型触媒装置の前段に設けたNOx濃度センサ(NOx濃度取得装置)は、このセンサの性質上、排気ガスに含まれるNOxの他に、アンモニアも検出する。本発明では、このセンサの性質を利用して、NOx吸蔵還元型触媒装置のリッチ還元制御時に、NOx吸蔵還元型触媒装置でアンモニアが生成されているか否かを判定する。 The NOx concentration sensor (NOx concentration acquisition device) provided at the front stage of the selective reduction catalyst device detects ammonia as well as NOx contained in the exhaust gas due to the nature of this sensor. In the present invention, the property of this sensor is utilized to determine whether or not ammonia is being generated in the NOx storage reduction type catalyst device during rich reduction control of the NOx storage reduction type catalyst device.

すなわち、本発明によれば、NOx吸蔵還元型触媒装置のリッチ還元制御時に、NOx吸蔵還元型触媒装置を通過する排気ガスの空燃比がNOx吸蔵還元型触媒装置でアンモニアが生成される虞のある空燃比であり、かつ、選択還元型触媒装置に流入する排気ガスのNOx濃度の実測値がアンモニアの誤検出を含む値と推定される場合に、NOx吸蔵還元型触媒装置で生成されるアンモニアの量を算出して、この算出値を基に選択還元型触媒装置のアンモニアの蓄積量を補正する。これにより、選択還元型触媒装置のアンモニアの蓄積量の推定精度を向上して、選択還元型触媒装置から下流側の排気通路に流出するアンモニアの量を抑制できる。 That is, according to the present invention, during the rich reduction control of the NOx storage reduction type catalyst device, the air-fuel ratio of the exhaust gas passing through the NOx storage reduction type catalyst device may cause ammonia to be generated in the NOx storage reduction type catalyst device. is the air-fuel ratio, and the measured value of the NOx concentration of the exhaust gas flowing into the selective reduction catalyst device is estimated to be a value including erroneous detection of ammonia, the amount of ammonia generated in the NOx storage reduction catalyst device The amount of ammonia is calculated, and the accumulated amount of ammonia in the selective reduction catalyst device is corrected based on this calculated value. As a result, it is possible to improve the accuracy of estimating the accumulated amount of ammonia in the selective reduction catalyst device, and to suppress the amount of ammonia flowing out from the selective reduction catalyst device into the exhaust passage on the downstream side.

本発明の内燃機関の排気ガス浄化システムの構成を例示する図である。1 is a diagram illustrating the configuration of an exhaust gas purification system for an internal combustion engine according to the present invention; FIG. リッチ還元制御時におけるNOx濃度の推移と空燃比の推移を例示する図である。FIG. 5 is a diagram illustrating changes in NOx concentration and changes in air-fuel ratio during rich reduction control; 本発明の内燃機関の排気ガス浄化方法の制御フローを例示する図である。1 is a diagram illustrating a control flow of a method for purifying exhaust gas of an internal combustion engine according to the present invention; FIG.

以下、本発明の内燃機関の排気ガス浄化システムについて図に示した実施形態に基づいて説明する。本発明の内燃機関の排気ガス浄化システム1は、図1に示すように、エンジン(内燃機関)2の排気通路3に上流側より順にNOx吸蔵還元型触媒装置(LNT)4、ディーゼル微粒子捕集フィルター装置(CSF)5、選択還元型触媒装置(SCR)6が配置される。また、NOx吸蔵還元型触媒装置4より上流側の排気通路3には燃料噴射装置7が配置される。また、ディーゼル微粒子捕集フィルター装置5と選択還元型触媒装置6の間の排気通路3(選択還元型触媒装置6より上流側の排気通路3)には尿素水噴射装置8が配置される。 Hereinafter, an exhaust gas purification system for an internal combustion engine according to the present invention will be described based on embodiments shown in the drawings. As shown in FIG. 1, an exhaust gas purification system 1 for an internal combustion engine according to the present invention includes a NOx storage reduction catalyst device (LNT) 4 and a diesel particulate collector installed in an exhaust passage 3 of an engine (internal combustion engine) 2 in this order from the upstream side. A filter device (CSF) 5 and a selective catalytic reduction device (SCR) 6 are arranged. A fuel injection device 7 is arranged in the exhaust passage 3 on the upstream side of the NOx storage reduction type catalyst device 4 . A urea water injection device 8 is arranged in the exhaust passage 3 between the diesel particulate filter device 5 and the selective catalytic reduction device 6 (the exhaust passage 3 on the upstream side of the selective catalytic reduction device 6).

NOx吸蔵還元型触媒装置4は、NOx吸蔵材と貴金属触媒を担持しており、排気ガスGの空燃比がリーン状態であるときに排気ガスGに含まれるNOxをこのNOx吸蔵材により吸蔵する。吸蔵したNOxは、排気ガスGの空燃比をリッチ状態とすることで放出され、この放出されたNOxは、貴金属触媒により還元処理される。排気ガスGの空燃比をリッチ状態に移行することで、NOx吸蔵還元型触媒装置4に吸蔵したNOxを放出して還元処理する制御をリッチ還元制御という。排気ガスGの空燃比のリッチ状態への移行は、エンジン2の気筒(シリンダ)内燃料噴射でポスト噴射したり、燃料噴射装置7から排気通路3に燃料Fを噴射したりすることにより行う。また、NOx吸蔵還元型触媒装置4は酸化触媒装置(DOC)の機能も有しており、排気ガスGに含まれる一酸化炭素(CO)や炭化水素(HC)を酸化処理する。 The NOx storage reduction catalyst device 4 carries a NOx storage material and a noble metal catalyst, and stores NOx contained in the exhaust gas G with this NOx storage material when the air-fuel ratio of the exhaust gas G is lean. The stored NOx is released by making the air-fuel ratio of the exhaust gas G rich, and the released NOx is reduced by the noble metal catalyst. The control for releasing the NOx stored in the NOx storage reduction type catalyst device 4 for reduction treatment by shifting the air-fuel ratio of the exhaust gas G to a rich state is called rich reduction control. The transition to the rich state of the air-fuel ratio of the exhaust gas G is performed by post-injecting the fuel in the cylinder of the engine 2 or by injecting the fuel F from the fuel injection device 7 into the exhaust passage 3 . The NOx storage reduction type catalyst device 4 also has a function of an oxidation catalyst device (DOC), and oxidizes carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas G.

ディーゼル微粒子捕集フィルター装置5は、排気ガスGに含まれる微粒子状物質(PM)を捕集する。この捕集したPMは、通常、高温の排気ガスGをディーゼル微粒子捕集フィルター装置5に通過させることで燃焼除去される。排気ガスGを高温化して、捕集したPMを高温の排気ガスGで燃焼除去する制御を強制PM再生制御という。高温の排気ガスGは、エンジン2の気筒内燃料噴射でポスト噴射したり、燃料噴射装置7から燃料Fを噴射したりして、この燃料Fに含まれる一酸化炭素や炭化水素をNOx吸蔵還元型触媒装置4で酸化処理(発熱反応)することにより得られる。 The diesel particulate filtering device 5 collects particulate matter (PM) contained in the exhaust gas G. The collected PM is generally removed by combustion by passing the high-temperature exhaust gas G through the diesel particulate filter device 5 . A control in which the temperature of the exhaust gas G is raised and the trapped PM is removed by combustion with the high temperature exhaust gas G is called forced PM regeneration control. The high-temperature exhaust gas G is post-injected in the in-cylinder fuel injection of the engine 2, or the fuel F is injected from the fuel injection device 7, and the carbon monoxide and hydrocarbons contained in this fuel F are absorbed and reduced by NOx absorption. It is obtained by oxidation treatment (exothermic reaction) in the type catalyst device 4 .

選択還元型触媒装置6は、排気ガスGに含まれるNOxを還元剤で窒素に還元して浄化する装置である。本実施形態では、この還元剤としてアンモニア(NH3)を使用する。尿素水噴射装置8より排気ガスGに向けて噴射された尿素水Uが排気ガスGの熱によりアンモニアに変化して、このアンモニアが選択還元型触媒装置6に流入することで、アンモニアは選択還元型触媒装置6に吸着され、排気ガスGが通過する際に排気ガスG中のNOxと反応してNOxを還元する。 The selective reduction catalyst device 6 is a device that purifies NOx contained in the exhaust gas G by reducing it to nitrogen with a reducing agent. In this embodiment, ammonia (NH 3 ) is used as this reducing agent. The urea water U injected toward the exhaust gas G from the urea water injection device 8 is changed into ammonia by the heat of the exhaust gas G, and this ammonia flows into the selective reduction catalyst device 6, whereby the ammonia is selectively reduced. It is adsorbed by the type catalyst device 6 and reacts with NOx in the exhaust gas G to reduce the NOx when the exhaust gas G passes.

また、NOx吸蔵還元型触媒装置4より上流側の排気通路3に温度センサ9と前段酸素濃度センサ10を備え、NOx吸蔵還元型触媒装置4と選択還元型触媒装置6の間の排気通路3に後段酸素濃度センサ11とNOx濃度センサ(NOx濃度取得装置)12を備える。温度センサ9は、NOx吸蔵還元型触媒装置4に流入する排気ガスGの温度Tを取得するセンサである。NOx濃度センサ12は、NOx吸蔵還元型触媒装置4と選択還元型触媒装置6の間の排気通路3を通過する排気ガスGのNOx濃度を取得するセンサである。 In addition, a temperature sensor 9 and a pre-stage oxygen concentration sensor 10 are provided in the exhaust passage 3 on the upstream side of the NOx storage reduction type catalyst device 4, and in the exhaust passage 3 between the NOx storage reduction type catalyst device 4 and the selective reduction type catalyst device 6 A post-stage oxygen concentration sensor 11 and a NOx concentration sensor (NOx concentration acquisition device) 12 are provided. The temperature sensor 9 is a sensor that acquires the temperature T of the exhaust gas G flowing into the NOx storage reduction type catalyst device 4 . The NOx concentration sensor 12 is a sensor that acquires the NOx concentration of the exhaust gas G passing through the exhaust passage 3 between the NOx storage reduction catalyst device 4 and the selective reduction catalyst device 6 .

本発明の酸素濃度取得装置としては、NOx吸蔵還元型触媒装置4を通過する排気ガスGの酸素濃度を取得できればよいので、前段酸素濃度センサ10、後段酸素濃度センサ11、前段酸素濃度センサ10と後段酸素濃度センサ11の両方、のいずれかで構成すればよい。本実施形態では、後段酸素濃度センサ11を酸素濃度取得装置とする。なお、酸素濃度取得装置を前段酸素濃度センサ10と後段酸素濃度センサ11の両方で構成する場合には、酸素濃度取得装置の取得値は、前段酸素濃度センサ10の取得値と後段酸素濃度センサ11の取得値の平均値とすることが好ましい。 As the oxygen concentration acquisition device of the present invention, it is sufficient to acquire the oxygen concentration of the exhaust gas G passing through the NOx storage reduction type catalyst device 4. It may be composed of either both of the post-stage oxygen concentration sensors 11 . In this embodiment, the post-stage oxygen concentration sensor 11 is used as an oxygen concentration acquisition device. When the oxygen concentration acquisition device is composed of both the front oxygen concentration sensor 10 and the rear oxygen concentration sensor 11, the values acquired by the oxygen concentration acquisition device are the values acquired by the front oxygen concentration sensor 10 and the values acquired by the rear oxygen concentration sensor 11. is preferably the average value of the acquired values.

制御装置13は、各種情報処理を行うCPU、その各種情報処理を行うために用いられるプログラムや、情報処理結果を読み書き可能な内部記憶装置、及び各種インターフェースなどから構成されるソフトウエアとハードウェアの組み合わせである。制御装置13は、上記した後段酸素濃度センサ11やNOx濃度センサ12等の各種センサに信号線を介して電気的に接続されている。 The control device 13 consists of a CPU that performs various types of information processing, a program used to perform the various types of information processing, an internal storage device capable of reading and writing information processing results, and various interfaces. It's a combination. The control device 13 is electrically connected to various sensors such as the post-stage oxygen concentration sensor 11 and the NOx concentration sensor 12 via signal lines.

制御装置13は、NOx吸蔵還元型触媒装置4のNOx吸蔵量Nが予め設定されたリッチ要求閾値N1以上であるときに、NOx吸蔵還元型触媒装置4のリッチ還元制御を行う必要があると判定して、燃料噴射装置7からの燃料噴射等により、後段酸素濃度センサ11の取得値λが予め設定された設定酸素濃度閾値λ1を下回るように、すなわち、排気ガスGの空燃比がリッチ状態に移行するように制御する。この設定酸素濃度閾値λ1は、例えば、ストイキ空燃比である1.0に設定する。 The control device 13 determines that it is necessary to perform rich reduction control of the NOx storage reduction type catalyst device 4 when the NOx storage amount N of the NOx storage reduction type catalyst device 4 is equal to or greater than a preset rich request threshold value N1. Then, fuel injection from the fuel injection device 7 or the like is performed so that the acquired value λ of the post-stage oxygen concentration sensor 11 falls below the preset set oxygen concentration threshold value λ1, that is, the air-fuel ratio of the exhaust gas G becomes rich. Control to migrate. This set oxygen concentration threshold λ1 is set to 1.0, which is the stoichiometric air-fuel ratio, for example.

本発明では、NOx吸蔵還元型触媒装置4のリッチ還元制御を行うときに、制御装置13により、NOx吸蔵還元型触媒装置4でアンモニアが生成されているか否かを、後段酸素濃度センサ11の取得値λとNOx濃度センサ12の取得値Dとに基づいて判定する。より具体的には、図2に示すように、後段酸素濃度センサ11の取得値λが予め設定された設定酸素濃度閾値λ1(=1.0)を下回り(判定A)、かつ、NOx濃度センサ12の取得値Dが予め設定された設定濃度閾値D1以上となる(判定B)ときに、制御装置13により、NOx吸蔵還元型触媒装置4でアンモニアが生成されていると判定する。これ以外のときでは、NOx吸蔵還元型触媒装置4でアンモニアが生成されていないと判定する。設定濃度閾値D1は、リッチ還元制御時にエンジン2より排出される排気ガスGのNOx濃度より大きく、NOx濃度センサ12がアンモニアを誤検出していると判定可能な値(例えば、500ppm)に設定される。 In the present invention, when the rich reduction control of the NOx storage reduction type catalyst device 4 is performed, the control device 13 detects whether or not ammonia is being generated in the NOx storage reduction type catalyst device 4 by acquiring the post-stage oxygen concentration sensor 11. The determination is made based on the value λ and the acquired value D of the NOx concentration sensor 12 . More specifically, as shown in FIG. 2, the acquired value λ of the post-stage oxygen concentration sensor 11 is below a preset set oxygen concentration threshold value λ1 (=1.0) (determination A), and the NOx concentration sensor 12 obtained value D is greater than or equal to a preset concentration threshold value D1 (determination B), the control device 13 determines that the NOx storage reduction catalyst device 4 is generating ammonia. At times other than this, it is determined that ammonia is not generated in the NOx storage reduction type catalyst device 4 . The set concentration threshold value D1 is set to a value (for example, 500 ppm) that is larger than the NOx concentration of the exhaust gas G emitted from the engine 2 during rich reduction control and that allows determination that the NOx concentration sensor 12 has erroneously detected ammonia. be.

なお、上記の判定Bに関しては、NOx濃度センサ12の取得値Dと設定濃度閾値D1の比較による判定の代わりに、以下の判定としてもよい。すなわち、制御装置13に組み込まれたエンジン出口NOx濃度取得装置によりエンジン2から排出される排気ガスGのNOx濃度をエンジン2の運転状態から演算するとともに、この演算値D2とNOx濃度センサ12の取得値Dを比較する。判定Aが成立し、かつ、NOx濃度センサ12の取得値Dが演算値D2以上となるときに、制御装置13により、NOx吸蔵還元型触媒装置4でアンモニアが生成されていると判定する。 As for the determination B described above, the following determination may be made instead of the determination by comparing the acquired value D of the NOx concentration sensor 12 and the set concentration threshold value D1. That is, the NOx concentration of the exhaust gas G emitted from the engine 2 is calculated from the operating state of the engine 2 by the engine outlet NOx concentration acquisition device incorporated in the control device 13, and the calculated value D2 and the NOx concentration sensor 12 are acquired. Compare the value D. When determination A is established and the acquired value D of the NOx concentration sensor 12 is equal to or greater than the calculated value D2, the control device 13 determines that the NOx storage reduction catalyst device 4 is producing ammonia.

NOx吸蔵還元型触媒装置4を通過する排気ガスGの空燃比がリッチ状態となると、リッチ還元制御時にNOxの還元反応の副生成物としてアンモニアが生成される。また、リッチ還元制御時にNOx吸蔵還元型触媒装置4から放出されるNOxはその場で還元処理されるため、選択還元型触媒装置6に流入する排気ガスGのNOx濃度は、リッチ還元制御の開始時から時間が経過するにつれて小さくなる。しかしながら、NOx濃度センサ12は、センサの性質上NOxの他にアンモニアも誤検出してしまうため、副生成物としてアンモニアが生成されていると、NOx濃度センサ12の取得値は、リッチ還元制御の開始時から時間が経過するにつれて小さくならず、リッチ還元制御の実施期間中に急上昇してしまう。 When the air-fuel ratio of the exhaust gas G passing through the NOx storage reduction type catalyst device 4 becomes rich, ammonia is produced as a by-product of the NOx reduction reaction during the rich reduction control. In addition, since the NOx released from the NOx storage reduction type catalyst device 4 during rich reduction control is reduced on the spot, the NOx concentration of the exhaust gas G flowing into the selective reduction type catalyst device 6 is reduced to the level at which rich reduction control starts. It gets smaller as time goes on. However, the NOx concentration sensor 12 erroneously detects not only NOx but also ammonia due to the nature of the sensor. Therefore, if ammonia is produced as a by-product, the value obtained by the NOx concentration sensor 12 will be different from that of the rich reduction control. It does not decrease as time elapses from the start, and it rises sharply during the execution period of the rich reduction control.

本発明では、制御装置13により、NOx吸蔵還元型触媒装置4でアンモニアが生成される状態であるか否かを後段酸素濃度センサ11の取得値λで判定するとともに、実際にNOx吸蔵還元型触媒装置4からアンモニアが流出しているか否かをNOx濃度センサ12の取得値Dで判定する。すなわち、後段酸素濃度センサ11の取得値λによる判定とNOx濃度センサ12の取得値Dによる判定の二重の判定を経て、リッチ還元制御時にNOx吸蔵還元型触媒装置4でアンモニアが生成されていることを確認する。 In the present invention, the control device 13 determines whether or not the NOx storage reduction catalyst device 4 is in a state where ammonia is generated based on the acquired value λ of the post-stage oxygen concentration sensor 11, and actually determines whether the NOx storage reduction catalyst device 4 is in a state where ammonia is generated. A value D acquired by the NOx concentration sensor 12 is used to determine whether or not ammonia is flowing out from the device 4 . That is, through double determination based on the acquired value λ of the post-stage oxygen concentration sensor 11 and determination based on the acquired value D of the NOx concentration sensor 12, ammonia is generated in the NOx storage reduction catalyst device 4 during rich reduction control. Confirm that

そして、リッチ還元制御時にNOx吸蔵還元型触媒装置4でアンモニアが生成されていると判定したときに、制御装置13により、NOx吸蔵還元型触媒装置4で生成されるアンモニア量Naを算出するとともに、この算出値Naを基に選択還元型触媒装置6のアンモニアの蓄積量Nsを補正する制御を行う。 Then, when it is determined that ammonia is being generated in the NOx storage reduction type catalyst device 4 during rich reduction control, the control device 13 calculates the ammonia amount Na generated in the NOx storage reduction type catalyst device 4, Based on this calculated value Na, control is performed to correct the accumulated amount Ns of ammonia in the selective catalytic reduction catalyst device 6 .

NOx吸蔵還元型触媒装置4で生成されるアンモニア量Naは、例えば、リッチ還元制御の開始時のNOx吸蔵還元型触媒装置4のNOx吸蔵量に実験等により定まる補正係数を乗算することで算出する。あるいは、エンジン2から排出される排気ガスGのNOx濃度とNOx濃度センサ12の取得値(選択還元型触媒装置6に流入する排気ガスのNOx濃度とアンモニア濃度の合算値)Dとの差に基づいて、NOx吸蔵還元型触媒装置4で生成されるアンモニア量Naを算出する。より具体的には、エンジン出口NOx濃度取得装置に記憶されたエンジン2の運転状態に応じたNOx量マップを基本として、このマップにおけるNOx量をエンジン冷却水温やエンジン2の過渡運転時におけるエンジン2の吸気内酸素濃度及びブースト圧力等により補正することで、エンジン2から排出される排気ガスGのNOx濃度を算出する。 The ammonia amount Na generated in the NOx storage reduction type catalyst device 4 is calculated, for example, by multiplying the NOx storage amount of the NOx storage reduction type catalyst device 4 at the start of the rich reduction control by a correction coefficient determined by experiments or the like. . Alternatively, based on the difference between the NOx concentration of the exhaust gas G emitted from the engine 2 and the acquired value of the NOx concentration sensor 12 (the sum of the NOx concentration and the ammonia concentration of the exhaust gas flowing into the selective reduction catalyst device 6) D Then, the ammonia amount Na generated by the NOx storage reduction type catalyst device 4 is calculated. More specifically, based on the NOx amount map corresponding to the operating state of the engine 2 stored in the engine outlet NOx concentration acquisition device, the NOx amount in this map is used as the engine cooling water temperature or during the transient operation of the engine 2. NOx concentration of the exhaust gas G emitted from the engine 2 is calculated by correcting with the oxygen concentration in the intake air, the boost pressure, and the like.

そして、上述のようにして算出されたNOx吸蔵還元型触媒装置4で生成されるアンモニア量の算出値Naを基に、制御装置13により、選択還元型触媒装置6のアンモニアの蓄積量Nsを補正する制御を行う。より具体的には、補正前の選択還元型触媒装置6のアンモニアの蓄積量NsにNOx吸蔵還元型触媒装置4で生成されるアンモニア量の算出値Naを加算することで、補正後の選択還元型触媒装置6のアンモニアの蓄積量Nscを算出する。 Then, based on the calculated value Na of the amount of ammonia generated in the NOx storage reduction catalyst device 4 calculated as described above, the control device 13 corrects the accumulated amount Ns of ammonia in the selective reduction catalyst device 6. to control. More specifically, by adding the calculated value Na of the amount of ammonia generated in the NOx storage reduction catalyst device 4 to the accumulated amount Ns of ammonia in the selective reduction catalyst device 6 before correction, the selective reduction after correction The accumulated amount Nsc of ammonia in the type catalyst device 6 is calculated.

補正前の選択還元型触媒装置6のアンモニアの蓄積量Nsは、尿素水噴射装置8から噴射された尿素水量と、選択還元型触媒装置6に流入する排気ガスGの温度(温度センサ9等により検出)毎に設定されるアンモニアの蓄積効率と、に基づいて算出される。 The accumulated amount Ns of ammonia in the selective catalytic reduction catalyst device 6 before correction is the amount of urea water injected from the aqueous urea injection device 8 and the temperature of the exhaust gas G flowing into the selective catalytic reduction catalyst device 6 (detected by the temperature sensor 9 or the like). detection), and the ammonia storage efficiency set for each detection.

本発明の内燃機関の排気ガス浄化方法の制御フローの一例について、図3の制御フローを基に説明する。図3に示す制御フローは、NOx吸蔵還元型触媒装置4のリッチ還元制御時に周期的に実施される制御フローである。 An example of the control flow of the exhaust gas purification method for an internal combustion engine of the present invention will be described based on the control flow of FIG. The control flow shown in FIG. 3 is a control flow that is periodically executed during rich reduction control of the NOx storage reduction type catalyst device 4 .

図3に示す制御フローがスタートすると、ステップS10にて、NOx吸蔵還元型触媒装置4を通過する排気ガスGの酸素濃度λと、NOx吸蔵還元型触媒装置4と選択還元型触媒装置6の間の排気通路3を通過する排気ガスGのNOx濃度を取得するNOx濃度センサ12の取得値Dを取得する。ステップS10を実施後、ステップS20に進む。 When the control flow shown in FIG. 3 starts, in step S10, the oxygen concentration λ of the exhaust gas G passing through the NOx storage reduction type catalyst device 4 and the oxygen concentration λ between the NOx storage reduction type catalyst device 4 and the selective reduction type catalyst device 6 Acquisition value D of NOx concentration sensor 12 for acquiring NOx concentration of exhaust gas G passing through exhaust passage 3 is acquired. After performing step S10, the process proceeds to step S20.

ステップS20にて、ステップS10で取得した2つの取得値λ、Dを基にNOx吸蔵還元型触媒装置4でアンモニアが生成されているか否かを判定する。判定方法は上述したので、ここでは説明を省略する。この判定で、NOx吸蔵還元型触媒装置4でアンモニアが生成されていないと判定する場合(NO)には、リターンに進んで、本制御フローを終了する。一方、この判定で、NOx吸蔵還元型触媒装置4でアンモニアが生成されていると判定する場合(YES)には、ステップS30に進む。 In step S20, it is determined whether or not ammonia is being generated in the NOx storage reduction catalyst device 4 based on the two acquired values λ and D acquired in step S10. Since the determination method has been described above, the description is omitted here. In this determination, if it is determined that ammonia is not generated in the NOx storage reduction type catalyst device 4 (NO), the process proceeds to RETURN and ends this control flow. On the other hand, if it is determined that ammonia is being generated in the NOx storage reduction catalyst device 4 (YES), the process proceeds to step S30.

ステップS30にて、NOx吸蔵還元型触媒装置4で生成されるアンモニア量(アンモニアの生成量)Naを算出する。算出方法は上述したので、ここでは説明を省略する。ステップS30を実施後、ステップS40に進む。ステップS40にて、ステップS30で算出したアンモニアの生成量Naを基に、選択還元型触媒装置6のアンモニアの蓄積量Nsを補正する。補正方法は上述したので、ここでは説明を省略する。ステップS40の制御を実施後、リターンに進んで、本制御フローを終了する。 In step S30, the amount of ammonia (the amount of ammonia generated) Na generated by the NOx storage reduction type catalyst device 4 is calculated. Since the calculation method has been described above, the explanation is omitted here. After performing step S30, the process proceeds to step S40. In step S40, the accumulated amount Ns of ammonia in the selective catalytic reduction catalytic converter 6 is corrected based on the amount Na of ammonia produced calculated in step S30. Since the correction method has been described above, the description is omitted here. After executing the control in step S40, the process proceeds to RETURN and terminates this control flow.

以上より、本発明によれば、NOx吸蔵還元型触媒装置4のリッチ還元制御時に、NOx吸蔵還元型触媒装置4を通過する排気ガスGの空燃比λがNOx吸蔵還元型触媒装置4でアンモニアが生成される虞のある空燃比であり、かつ、NOx吸蔵還元型触媒装置4と選択還元型触媒装置6の間の排気通路3を通過する排気ガスGのNOx濃度のNOx濃度センサ12による実測値Dがアンモニアの誤検出を含む値と推定される場合に、NOx吸蔵還元型触媒装置4で生成されるアンモニアの量Naを算出して、この算出値を基に選択還元型触媒装置6のアンモニアの蓄積量Nsを補正する。これにより、選択還元型触媒装置6のアンモニアの蓄積量Nsの推定精度を向上して、選択還元型触媒装置6から下流側の排気通路3に流出するアンモニアの量を抑制できる。 As described above, according to the present invention, during the rich reduction control of the NOx storage reduction type catalyst device 4, the air-fuel ratio λ of the exhaust gas G passing through the NOx storage reduction type catalyst device 4 becomes The NOx concentration sensor 12 actually measures the NOx concentration of the exhaust gas G passing through the exhaust passage 3 between the NOx storage reduction catalyst device 4 and the selective reduction catalyst device 6 at an air-fuel ratio that may be generated. When D is estimated to be a value including erroneous detection of ammonia, the amount Na of ammonia generated in the NOx storage reduction catalyst device 4 is calculated, and based on this calculated value, ammonia in the selective reduction catalyst device 6 is corrected. As a result, the accuracy of estimating the accumulated amount Ns of ammonia in the selective catalytic reduction catalyst device 6 can be improved, and the amount of ammonia flowing out from the selective catalytic reduction catalytic device 6 into the exhaust passage 3 on the downstream side can be suppressed.

また、NOx吸蔵還元型触媒装置4でアンモニアが生成されているか否かを、NOx吸蔵還元型触媒装置4を通過する排気ガスGの酸素濃度λによる判定とNOx吸蔵還元型触媒装置4と選択還元型触媒装置6の間の排気通路3を通過する排気ガスGに対するNOx濃度センサ12の取得値Dによる判定の二重の判定を経て行うことで、NOx吸蔵還元型触媒装置4でのアンモニア生成の検出精度を向上させることができる。 Further, whether or not ammonia is generated in the NOx storage reduction type catalyst device 4 is determined based on the oxygen concentration λ of the exhaust gas G passing through the NOx storage reduction type catalyst device 4, and the NOx storage reduction type catalyst device 4 and selective reduction are performed. The exhaust gas G passing through the exhaust passage 3 between the type catalyst devices 6 is subjected to a double determination based on the acquired value D of the NOx concentration sensor 12, so that the ammonia generation in the NOx storage reduction type catalyst device 4 is reduced. Detection accuracy can be improved.

さらに、NOx吸蔵還元型触媒装置4で生成されるアンモニア量Naを、エンジン2より排出される排気ガスGのNOx量と選択還元型触媒装置6に流入する排気ガスGに対するNOx濃度センサ12の取得値(NOx量とアンモニア量)Dとの差に基づいて算出すると、NOx吸蔵還元型触媒装置4で生成されるアンモニア量Naの算出精度を向上させることができる。 Furthermore, the ammonia amount Na generated by the NOx storage reduction type catalyst device 4 is obtained by obtaining the NOx amount of the exhaust gas G discharged from the engine 2 and the NOx concentration sensor 12 for the exhaust gas G flowing into the selective reduction type catalyst device 6. If calculated based on the difference between the values (the amount of NOx and the amount of ammonia) D, the calculation accuracy of the amount of ammonia Na generated by the NOx storage reduction catalyst device 4 can be improved.

また、リッチ還元制御の開始時のNOx吸蔵還元型触媒装置4のNOx吸蔵量に基づいて算出する方法を用いてもよい。NOx吸蔵還元型触媒装置4のNOx吸蔵量Nは、エンジン2より排出される排気ガスGのNOx量とNOx濃度センサ12の取得値Dとの差を制御装置13により時間で積分して得られる値である。制御装置13は、NOx吸蔵還元型触媒装置4のリッチ還元制御を行う必要があると判定した時点でのNOz吸蔵還元型触媒装置4のNOx吸蔵量Nを算出して記憶する。 Alternatively, a method of calculating based on the NOx storage amount of the NOx storage reduction type catalyst device 4 at the start of the rich reduction control may be used. The NOx storage amount N of the NOx storage reduction catalyst device 4 is obtained by integrating the difference between the NOx amount of the exhaust gas G discharged from the engine 2 and the acquired value D of the NOx concentration sensor 12 by the controller 13 over time. value. The control device 13 calculates and stores the NOx storage amount N of the NOx storage reduction type catalyst device 4 at the time when it is determined that the rich reduction control of the NOx storage reduction type catalyst device 4 needs to be performed.

1 内燃機関の排気ガス浄化システム
2 エンジン(内燃機関)
3 排気通路
4 NOx吸蔵還元型触媒装置
5 ディーゼル微粒子捕集フィルター装置
6 選択還元型触媒装置
7 燃料噴射装置
8 尿素水噴射装置
9 温度センサ
10 前段酸素濃度センサ
11 後段酸素濃度センサ
12 NOx濃度センサ
13 制御装置
1 Exhaust gas purification system for internal combustion engine 2 Engine (internal combustion engine)
3 exhaust passage 4 NOx storage reduction catalyst device 5 diesel particulate filter device 6 selective reduction catalyst device 7 fuel injection device 8 urea water injection device 9 temperature sensor 10 front stage oxygen concentration sensor 11 rear stage oxygen concentration sensor 12 NOx concentration sensor 13 Control device

Claims (2)

内燃機関の排気通路に上流側より順に、NOx吸蔵還元型触媒装置、選択還元型触媒装置を備えて構成される内燃機関の排気ガス浄化システムにおいて、
前記選択還元型触媒装置より上流側の前記排気通路に排気ガスの酸素濃度を取得する酸素濃度取得装置を備え、前記NOx吸蔵還元型触媒装置と前記選択還元型触媒装置の間の前記排気通路に排気ガスのNOx濃度を取得するNOx濃度取得装置とを備えるとともに、前記酸素濃度取得装置及び前記NOx濃度取得装置と電気的に接続された制御装置を備え、
前記制御装置が、
前記NOx吸蔵還元型触媒装置のリッチ還元制御を行っている場合で、
前記酸素濃度取得装置の取得値と前記NOx濃度取得装置の取得値とに基づいて、前記NOx吸蔵還元型触媒装置でアンモニアが生成されていると判定するときには、
前記NOx吸蔵還元型触媒装置で生成されるアンモニア量を算出するとともに、この算出値を基に前記選択還元型触媒装置のアンモニアの蓄積量を補正する制御を行うように構成されており、かつ、
前記制御装置が、
前記酸素濃度取得装置の取得値が予め設定された設定酸素濃度閾値を下回り、かつ、前記NOx濃度取得装置の取得値が予め設定された設定NOx濃度閾値以上となるときに、前記NOx吸蔵還元型触媒装置でアンモニアが生成されていると判定する制御を行うように構成されていることを特徴とする内燃機関の排気ガス浄化システム。
An exhaust gas purification system for an internal combustion engine, comprising a NOx storage reduction catalyst device and a selective reduction catalyst device in this order from the upstream side in an exhaust passage of the internal combustion engine,
An oxygen concentration acquiring device for acquiring an oxygen concentration of exhaust gas is provided in the exhaust passage upstream of the selective catalytic reduction device, and the exhaust passage between the NOx storage reduction catalytic device and the selective catalytic reduction catalytic device is provided with an oxygen concentration acquisition device for acquiring an oxygen concentration of exhaust gas. a NOx concentration acquisition device for acquiring the NOx concentration of exhaust gas, and a control device electrically connected to the oxygen concentration acquisition device and the NOx concentration acquisition device,
The control device
When rich reduction control is being performed on the NOx storage reduction type catalyst device,
When determining that ammonia is generated in the NOx storage reduction catalyst device based on the acquired value of the oxygen concentration acquisition device and the acquired value of the NOx concentration acquisition device,
The amount of ammonia generated in the NOx storage reduction catalyst device is calculated, and based on the calculated value, control is performed to correct the accumulated amount of ammonia in the selective reduction catalyst device , and
The control device
When the acquired value of the oxygen concentration acquisition device is lower than a preset set oxygen concentration threshold and the acquired value of the NOx concentration acquisition device is equal to or higher than a preset set NOx concentration threshold, the NOx storage reduction type An exhaust gas purification system for an internal combustion engine, characterized in that it is configured to perform control to determine that ammonia is being generated in a catalytic device .
内燃機関の排気通路に上流側より順に、NOx吸蔵還元型触媒装置、選択還元型触媒装置を備えて構成される内燃機関の排気ガス浄化システムにおいて、
前記選択還元型触媒装置より上流側の前記排気通路に排気ガスの酸素濃度を取得する酸素濃度取得装置を備え、前記NOx吸蔵還元型触媒装置と前記選択還元型触媒装置の間の前記排気通路に排気ガスのNOx濃度を取得するNOx濃度取得装置とを備えるとともに、前記酸素濃度取得装置及び前記NOx濃度取得装置と電気的に接続された制御装置を備え、
前記制御装置が、
前記NOx吸蔵還元型触媒装置のリッチ還元制御を行っている場合で、
前記酸素濃度取得装置の取得値と前記NOx濃度取得装置の取得値とに基づいて、前記NOx吸蔵還元型触媒装置でアンモニアが生成されていると判定するときには、
前記NOx吸蔵還元型触媒装置で生成されるアンモニア量を算出するとともに、この算出値を基に前記選択還元型触媒装置のアンモニアの蓄積量を補正する制御を行うように構成されており、かつ、
前記内燃機関から排気される排気ガスのNOx濃度を取得するエンジン出口NOx濃度取得装置を備え、このエンジン出口NOx濃度取得装置を前記制御装置に電気的に接続するとともに、
前記制御装置が、
前記エンジン出口NOx濃度取得装置の取得値と前記NOx濃度取得装置の取得値との差に基づいて、あるいは、前記リッチ還元制御の開始時の前記NOx吸蔵還元型触媒装置のNOx吸蔵量に基づいて、前記NOx吸蔵還元型触媒装置で生成されるアンモニア量を算出する制御を行うように構成されていることを特徴とする内燃機関の排気ガス浄化システム。
An exhaust gas purification system for an internal combustion engine, comprising a NOx storage reduction catalyst device and a selective reduction catalyst device in this order from the upstream side in an exhaust passage of the internal combustion engine,
An oxygen concentration acquiring device for acquiring an oxygen concentration of exhaust gas is provided in the exhaust passage upstream of the selective catalytic reduction device, and the exhaust passage between the NOx storage reduction catalytic device and the selective catalytic reduction catalytic device is provided with an oxygen concentration acquisition device for acquiring an oxygen concentration of exhaust gas. a NOx concentration acquisition device for acquiring the NOx concentration of exhaust gas, and a control device electrically connected to the oxygen concentration acquisition device and the NOx concentration acquisition device,
The control device
When rich reduction control is being performed on the NOx storage reduction type catalyst device,
When determining that ammonia is generated in the NOx storage reduction catalyst device based on the acquired value of the oxygen concentration acquisition device and the acquired value of the NOx concentration acquisition device,
The amount of ammonia generated in the NOx storage reduction catalyst device is calculated, and based on the calculated value, control is performed to correct the accumulated amount of ammonia in the selective reduction catalyst device, and
An engine outlet NOx concentration acquiring device for acquiring the NOx concentration of exhaust gas discharged from the internal combustion engine is provided, and the engine outlet NOx concentration acquiring device is electrically connected to the control device,
The control device
Based on the difference between the acquired value of the engine outlet NOx concentration acquiring device and the acquired value of the NOx concentration acquiring device, or based on the NOx storage amount of the NOx storage reduction type catalyst device at the start of the rich reduction control 1. An exhaust gas purification system for an internal combustion engine, characterized in that it is configured to perform control for calculating the amount of ammonia generated by said NOx storage reduction type catalyst device.
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