JP4179386B2 - NOx purification system and control method of NOx purification system - Google Patents

NOx purification system and control method of NOx purification system Download PDF

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JP4179386B2
JP4179386B2 JP2007103530A JP2007103530A JP4179386B2 JP 4179386 B2 JP4179386 B2 JP 4179386B2 JP 2007103530 A JP2007103530 A JP 2007103530A JP 2007103530 A JP2007103530 A JP 2007103530A JP 4179386 B2 JP4179386 B2 JP 4179386B2
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哲也 藤田
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Isuzu Motors Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • F01N3/208—Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9495—Controlling the catalytic process
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
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    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/105—General auxiliary catalysts, e.g. upstream or downstream of the main catalyst
    • F01N3/106—Auxiliary oxidation catalysts
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/206—Ammonium compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/91—NOx-storage component incorporated in the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
    • B01D53/9477—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on separate bricks, e.g. exhaust systems
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/02—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor
    • F01N2560/026—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics the means being an exhaust gas sensor for measuring or detecting NOx
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2560/00—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics
    • F01N2560/14—Exhaust systems with means for detecting or measuring exhaust gas components or characteristics having more than one sensor of one kind
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/14—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust gas
    • F01N2900/1402—Exhaust gas composition
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00—Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06—Parameters used for exhaust control or diagnosing
    • F01N2900/16—Parameters used for exhaust control or diagnosing said parameters being related to the exhaust apparatus, e.g. particulate filter or catalyst
    • F01N2900/1622—Catalyst reducing agent absorption capacity or consumption amount
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

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  • Engineering & Computer Science (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
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  • Environmental & Geological Engineering (AREA)
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  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
  • Treating Waste Gases (AREA)

Description

本発明は、排気ガス通路の上流側に酸化触媒を下流側に選択還元型ＮＯｘ触媒（ＳＣＲ触媒）を備えたＮＯｘ浄化システム及びＮＯｘ浄化システムの制御方法に関する。   The present invention relates to a NOx purification system including an oxidation catalyst upstream of an exhaust gas passage and a selective reduction type NOx catalyst (SCR catalyst) downstream, and a control method of the NOx purification system.

従来の選択還元型ＮＯｘ触媒（ＳＣＲ触媒）を備えたＮＯｘ浄化システムは、選択還元型ＮＯｘ触媒と、この選択還元型ＮＯｘ触媒にアンモニア（ＮＨ3 ）を供給するために、その上流側に尿素水等のアンモニア源となるアンモニア系溶液を排気ガス通路の排気ガス中に供給するアンモニア系溶液供給装置を備えると共に、このアンモニア系溶液供給措置よりも上流側に酸化触媒を配置している。また、選択還元型ＮＯｘ触媒の下流側にアンモニアの大気中への流出を防止するための酸化触媒を配置する場合もある。 A conventional NOx purification system equipped with a selective reduction type NOx catalyst (SCR catalyst) includes a selective reduction type NOx catalyst and urea water upstream thereof to supply ammonia (NH 3 ) to the selective reduction type NOx catalyst. An ammonia-based solution supply device that supplies an ammonia-based solution serving as an ammonia source into the exhaust gas of the exhaust gas passage is provided, and an oxidation catalyst is disposed upstream of the ammonia-based solution supply measure. In some cases, an oxidation catalyst for preventing the outflow of ammonia into the atmosphere is disposed downstream of the selective reduction type NOx catalyst.

このＮＯｘ浄化システムの選択還元型ＮＯｘ触媒は、アンモニア発生化合物（尿素水溶液等）を吸着して貯蔵する機能を有するので、排気ガス中のＮＯｘを浄化するため以外でも、アンモニア発生化合物を供給して選択還元型ＮＯｘ触媒に溜め込んで、ＮＯｘを浄化する時に、この溜め込んだアンモニア発生化合物を徐々に放出させて、排気ガス中のＮＯｘを浄化する内燃機関の排気浄化装置が提案されている（例えば、特許文献１参照。）。   The selective reduction type NOx catalyst of this NOx purification system has a function of adsorbing and storing an ammonia generating compound (such as an aqueous urea solution), so it can supply an ammonia generating compound other than for purifying NOx in exhaust gas. There has been proposed an exhaust purification device for an internal combustion engine that purifies NOx in exhaust gas by gradually releasing the accumulated ammonia-generating compound when purifying NOx by accumulating in a selective reduction type NOx catalyst (for example, (See Patent Document 1).

この選択還元型ＮＯｘ触媒は、酸素過剰雰囲気ではアンモニアを還元剤として、ＮＯｘを浄化する触媒であるが、条件によりアンモニアを、この触媒内に貯蔵する機能も有している。   This selective reduction type NOx catalyst is a catalyst that purifies NOx using ammonia as a reducing agent in an oxygen-excess atmosphere, but also has a function of storing ammonia in the catalyst depending on conditions.

このアンモニア系溶液の供給方法については、次の二通りの方法が用いられている。第１の方法は、内燃機関からのＮＯｘ排出量や選択還元型ＮＯｘ触媒の温度条件で変化するＮＯｘ浄化能力に対応したアンモニア量になるように、つまり、ＮＯｘとアンモニアの当量比が１になるように計算して、アンモニア系溶液の供給量を制御しながら供給する方法である。   The following two methods are used for supplying the ammonia-based solution. The first method is such that the ammonia amount corresponds to the NOx purification capacity that changes depending on the NOx emission amount from the internal combustion engine and the temperature condition of the selective reduction type NOx catalyst, that is, the equivalent ratio of NOx and ammonia becomes 1. This is a method of supplying the ammonia-based solution while controlling the supply amount of the ammonia-based solution.

この方法の場合には、アンモニア系溶液の供給制御の応答遅れ（タイムラグ）等により、ＮＯｘ排出量が急激に変化した場合に対応が間に合わず、的確な添加量とすることが難しい。そのため、アンモニアが大気中に放出されるアンモニアスリップやアンモニア系溶液の供給不足により、ＮＯｘの浄化が不十分になるという問題がある。   In the case of this method, due to a response delay (time lag) in the supply control of the ammonia-based solution, when the NOx emission amount changes abruptly, it is not possible to keep up with it, and it is difficult to make an accurate addition amount. Therefore, there is a problem that the purification of NOx becomes insufficient due to an ammonia slip in which ammonia is released into the atmosphere or an insufficient supply of the ammonia-based solution.

第２の方法は、選択還元型ＮＯｘ触媒のアンモニア保持機能を利用し、一定範囲のアンモニア量を選択還元型ＮＯｘ触媒に保持させておき、ＮＯｘの還元により消費されたアンモニア量に相当する量のアンモニア系溶液を供給して、選択還元型ＮＯｘ触媒が保持するアンモニア量を所定の範囲内に保つ方法である。   The second method uses the ammonia retention function of the selective reduction type NOx catalyst, holds an ammonia amount within a certain range in the selective reduction type NOx catalyst, and has an amount corresponding to the amount of ammonia consumed by the reduction of NOx. In this method, an ammonia-based solution is supplied to keep the amount of ammonia held by the selective reduction type NOx catalyst within a predetermined range.

この第２の方法の場合には、第１の方法に比べて、アンモニア系溶液の供給制御の応答遅れやＮＯｘが急激に増加した場合に対応し易いという利点がある。なお、この場合でも、内燃機関のＮＯｘ排出量は、選択還元型ＮＯｘ触媒に保持されているアンモニアの消費量を求めるために必要である。   Compared to the first method, the second method has an advantage that it is easy to cope with a response delay in the supply control of the ammonia-based solution and when NOx increases rapidly. Even in this case, the NOx emission amount of the internal combustion engine is necessary for obtaining the consumption amount of ammonia held in the selective reduction type NOx catalyst.

しかしながら、この選択還元型ＮＯｘ触媒は、炭化水素（ＨＣ）が共存すると、ＮＯｘ浄化性能が低下し、また、この触媒自体は酸化機能が低いため、炭化水素や一酸化炭素（ＣＯ）の浄化については期待できないという問題がある。   However, when this selective reduction type NOx catalyst coexists with hydrocarbons (HC), the NOx purification performance is lowered, and since the catalyst itself has a low oxidation function, the hydrocarbons and carbon monoxide (CO) are purified. There is a problem that cannot be expected.

そのため、選択還元型ＮＯｘ触媒の上流側（前段）に、酸化触媒を配置して炭化水素や一酸化炭素を処理することにより、選択還元型ＮＯｘ触媒のＮＯｘ浄化機能を低下させる炭化水素等を低減させることが行われている。   Therefore, by arranging an oxidation catalyst upstream of the selective reduction type NOx catalyst (previous stage) to treat hydrocarbons and carbon monoxide, hydrocarbons that reduce the NOx purification function of the selective reduction type NOx catalyst are reduced. Has been done.

この酸化触媒は、ＮＯｘ、炭化水素の酸化以外に、ＮＯｘを吸着する性質を併せ持っている。つまり、酸化触媒は、炭化水素、一酸化炭素を酸化する能力が高いが、同時に一酸化窒素（ＮＯ）を二酸化窒素（ＮＯ2 ）に酸化する能力も高く、生成した二酸化窒素は吸着性が高いため、通常は、酸化触媒に吸着し保持される。この酸化触媒に保持された二酸化窒素は排気ガス温度が上昇し、ある一定の温度以上になると脱離して放出される。この酸化触媒のＮＯｘ飽和吸着量は、図５に示すように、触媒温度が上昇すると少なくなる。例えば、触媒温度がＴａではＮＯｘがＡａ量吸着しているが、酸化触媒の温度がＴｂに上昇すると、ＮＯｘ飽和吸着量はＡｂに減少するため、Ａａ−Ａｂの量のＮＯｘが放出されることになる。 This oxidation catalyst has the property of adsorbing NOx in addition to the oxidation of NOx and hydrocarbons. In other words, the oxidation catalyst has a high ability to oxidize hydrocarbons and carbon monoxide, but at the same time has a high ability to oxidize nitric oxide (NO) to nitrogen dioxide (NO 2 ), and the produced nitrogen dioxide has a high adsorptivity. Therefore, it is normally adsorbed and held by the oxidation catalyst. Nitrogen dioxide held in this oxidation catalyst is desorbed and released when the exhaust gas temperature rises and exceeds a certain temperature. As shown in FIG. 5, the NOx saturation adsorption amount of the oxidation catalyst decreases as the catalyst temperature rises. For example, when the catalyst temperature is Ta, NOx is adsorbed by the amount of Aa, but when the temperature of the oxidation catalyst rises to Tb, the saturated adsorption amount of NOx decreases to Ab, so that the amount of NOx of Aa-Ab is released. become.

従って、排気ガス温度が脱離温度に達しない温度域で内燃機関の運転が連続した場合には、酸化触媒にＮＯｘが多量に堆積されることになる。このような状況下では、選択還元型ＮＯｘ触媒へのＮＯｘ流入量は、上流側に配置された酸化触媒における吸着があるため、内燃機関の運転状態から算出されるＮＯｘ排出量の推定値だけでは決まらず、アンモニア系溶液の最適な供給量を決定することが難しい。   Accordingly, when the operation of the internal combustion engine continues in a temperature range where the exhaust gas temperature does not reach the desorption temperature, a large amount of NOx is deposited on the oxidation catalyst. Under such circumstances, the NOx inflow amount to the selective reduction type NOx catalyst is adsorbed by the oxidation catalyst disposed on the upstream side, so that only the estimated value of the NOx emission amount calculated from the operating state of the internal combustion engine is used. Regardless, it is difficult to determine the optimum supply amount of the ammonia-based solution.

その結果、選択還元型ＮＯｘ触媒への実際のＮＯｘ流入量が推定したＮＯｘ流入量よりも少ない場合には、アンモニア系溶液が供給過剰になり、選択還元型ＮＯｘ触媒に保持されるアンモニア量が予測した値よりも多くなるため、アンモニアスリップが発生するという問題が生じる。また、酸化触媒に保持されたＮＯｘが、酸化触媒の急激な温度上昇により多量に脱離した場合には、選択還元型ＮＯｘ触媒におけるアンモニア量が不足し、ＮＯｘを浄化処理できなくなるという問題が生じる。   As a result, when the actual NOx inflow amount to the selective reduction type NOx catalyst is smaller than the estimated NOx inflow amount, the ammonia-based solution is excessively supplied, and the amount of ammonia retained in the selective reduction type NOx catalyst is predicted. Therefore, there is a problem that ammonia slip occurs. In addition, when a large amount of NOx held in the oxidation catalyst is desorbed due to a rapid increase in temperature of the oxidation catalyst, there is a problem that the amount of ammonia in the selective reduction type NOx catalyst is insufficient and the NOx cannot be purified. .

これらの問題に関連して、発明者は次のような知見を得た。上流側の酸化触媒のＮＯｘ吸着量がＮＯｘ飽和吸着量よりも少ない場合は、酸化触媒が温度上昇しても、ＮＯｘの放出は起こらないか、起こっても少ないため、選択還元型ＮＯｘ触媒におけるアンモニア保持量を比較的少なくしておけばよい。一方、選択還元型ＮＯｘ触媒におけるアンモニア保持量を多い状態にしておくと、酸化触媒の温度上昇時にアンモニアスリップが発生する恐れが高い。そのため、酸化触媒におけるＮＯｘ吸着量が増えて、ＮＯｘ飽和吸着量に近づいてくると、酸化触媒の僅かな温度上昇でＮＯｘの放出が発生する。従って、この場合は、選択還元型ＮＯｘ触媒におけるアンモニア保持量を比較的多くしておけばよい。
特許第３６８５０６３号公報 In relation to these problems, the inventors have obtained the following knowledge. When the NOx adsorption amount of the upstream oxidation catalyst is smaller than the NOx saturation adsorption amount, the NOx release does not occur or does not occur even if the temperature of the oxidation catalyst rises. Therefore, ammonia in the selective reduction type NOx catalyst The holding amount may be relatively small. On the other hand, if the amount of ammonia retained in the selective reduction type NOx catalyst is kept large, there is a high risk that ammonia slip will occur when the temperature of the oxidation catalyst rises. For this reason, when the NOx adsorption amount in the oxidation catalyst increases and approaches the NOx saturation adsorption amount, NOx release occurs with a slight temperature increase of the oxidation catalyst. Therefore, in this case, the ammonia retention amount in the selective reduction type NOx catalyst may be relatively large.
Japanese Patent No. 3685063

本発明は、上記の知見を得て、上記の問題を解決するためになされたものであり、その目的は、上流側の酸化触媒と下流側の選択的還元ＮＯｘ触媒を備え、選択還元型ＮＯｘ触媒にＮＯｘの還元に用いるアンモニア系溶液を供給して排気ガス中のＮＯｘを浄化する場合に、アンモニア系溶液を選択還元型ＮＯｘ触媒に対して過不足なく供給して、アンモニアとＮＯｘの両方の大気中への排出を防止することができるＮＯｘ浄化システム及びＮＯｘ浄化システムの制御方法を提供することにある。   The present invention has been made in order to solve the above problems by obtaining the above knowledge, and an object thereof is to provide an upstream oxidation catalyst and a downstream selective reduction NOx catalyst, and a selective reduction type NOx. When purifying NOx in exhaust gas by supplying an ammonia-based solution used for NOx reduction to the catalyst, the ammonia-based solution is supplied to the selective reduction-type NOx catalyst without excess or deficiency, and both ammonia and NOx are supplied. It is an object of the present invention to provide a NOx purification system and a control method for the NOx purification system that can prevent discharge into the atmosphere.

上記のような目的を達成するためのＮＯｘ浄化システムは、排気ガス通路の上流側から順に、酸化触媒と、排気ガス通路にアンモニア系溶液を供給するアンモニア系溶液供給装置と、選択還元型ＮＯｘ触媒とを備えると共に、前記アンモニア系溶液の供給量を制御する供給量制御装置とを備えて、排気ガス中のＮＯｘを還元するＮＯｘ浄化システムにおいて、前記供給量制御装置が、前記酸化触媒におけるＮＯｘの吸着量の推定値であるＮＯｘ吸着推定量を算出し、該ＮＯｘ吸着推定量に応じて、前記アンモニア系溶液の供給量を制御すると共に、前記供給量制御装置が、前記ＮＯｘ吸着推定量が所定の第１判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を所定の第１制御目標範囲内とし、前記ＮＯｘ吸着推定量が所定の第１判定値より大きく所定の第２判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第１制御目標範囲よりも大きい所定の第２制御目標範囲内とし、前記ＮＯｘ吸着推定量が前記所定の第２判定値より大きい場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第２制御目標範囲よりも大きい所定の第３制御目標範囲内として、前記アンモニア系溶液の供給量を制御するように構成される。 A NOx purification system for achieving the above object includes an oxidation catalyst, an ammonia-based solution supply device for supplying an ammonia-based solution to the exhaust gas passage, and a selective reduction type NOx catalyst in order from the upstream side of the exhaust gas passage. And a supply amount control device that controls the supply amount of the ammonia-based solution, wherein the supply amount control device is configured to reduce NOx in the oxidation catalyst. An estimated NOx adsorption amount, which is an estimated value of the adsorption amount, is calculated, and the supply amount of the ammonia-based solution is controlled according to the estimated NOx adsorption amount, and the supply amount control device determines that the estimated NOx adsorption amount is predetermined. When the target value of the ammonia-based solution supply amount is within a predetermined first control target range, the estimated NOx adsorption amount is a predetermined first value. When the value is larger than the determination value and equal to or less than the predetermined second determination value, the target amount of the supply amount of the ammonia-based solution is set within the predetermined second control target range that is larger than the predetermined first control target range, and the NOx When the estimated adsorption amount is larger than the predetermined second determination value, the target amount of the ammonia-based solution supply amount is set within a predetermined third control target range that is larger than the predetermined second control target range. It is configured to control the supply amount of the ammonia-based solution .

この構成によれば、上流側の酸化触媒に吸着されるＮＯｘ量を考慮した制御となるので、酸化触媒にＮＯｘが吸着されたときには、アンモニア系溶液供給装置から供給され、ＮＯｘ還元で余ったアンモニアを下流側の選択還元型ＮＯｘ触媒で吸着及び保持してアンモニアの大気中への放出（アンモニアスリップ）を防止でき、また、排気ガス温度の急上昇などで酸化触媒からＮＯｘが放出されたときには、選択還元型ＮＯｘ触媒で保持したアンモニアを使用してＮＯｘを十分に還元処理でき、ＮＯｘの大気中への放出（ＮＯｘスリップ）を防止できる。   According to this configuration, the control takes into account the amount of NOx adsorbed on the upstream side oxidation catalyst. Therefore, when NOx is adsorbed on the oxidation catalyst, it is supplied from the ammonia-based solution supply device and the remaining ammonia is reduced by NOx reduction. Can be adsorbed and retained by the selective reduction-type NOx catalyst on the downstream side to prevent ammonia from being released into the atmosphere (ammonia slip), and when NOx is released from the oxidation catalyst due to a sudden rise in exhaust gas temperature, etc. NOx can be sufficiently reduced using ammonia held by the reduced NOx catalyst, and release of NOx into the atmosphere (NOx slip) can be prevented.

この構成によれば、酸化触媒におけるＮＯｘ吸着推定量が少ない場合には、選択還元型ＮＯｘ触媒に保持されるアンモニア保持量が少なくなるように制御し、ＮＯｘ吸着推定量が中程度の場合には、アンモニア保持量が中程度になるように制御し、ＮＯｘ吸着推定量が多い場合には、アンモニア保持量が多くなるように制御するので、アンモニア系溶液の供給量を適切な量にすることができ、アンモニアスリップとＮＯｘスリップを防止できる。   According to this configuration, when the estimated amount of NOx adsorption in the oxidation catalyst is small, control is performed so that the amount of ammonia retained in the selective reduction type NOx catalyst is reduced, and when the estimated amount of NOx adsorption is medium The ammonia holding amount is controlled to be moderate, and when the estimated NOx adsorption amount is large, the ammonia holding amount is controlled to increase. Therefore, the supply amount of the ammonia-based solution can be set to an appropriate amount. It is possible to prevent ammonia slip and NOx slip.

つまり、上流側の酸化触媒のＮＯｘ吸着量が少なく、温度上昇によるＮＯｘの放出が殆ど無いと推定される場合は、選択還元型ＮＯｘ触媒におけるアンモニア保持量が比較的少な範囲になるように制御するので、選択還元型ＮＯｘ触媒に必要以上に保持したアンモニアが大気中へ放出されることを防止できる。また、上流側の酸化触媒のＮＯｘ吸着量が増加して、温度上昇により急激にＮＯｘ放出が起こる可能性が高くなったと推定される場合は、選択還元型ＮＯｘ触媒におけるアンモニア保持量が比較的多い範囲になるように制御するので、急激な温度上昇によりＮＯｘの放出が起こっても対応でき、ＮＯｘが大気中へ放出されることを防止できる。   In other words, when it is estimated that the NOx adsorption amount of the upstream side oxidation catalyst is small and NOx is hardly released due to the temperature rise, the ammonia retention amount in the selective reduction type NOx catalyst is controlled to be in a relatively small range. Therefore, it is possible to prevent ammonia held more than necessary in the selective reduction type NOx catalyst from being released into the atmosphere. In addition, when it is estimated that the NOx adsorption amount of the upstream oxidation catalyst has increased and the possibility of abrupt NOx release due to the temperature rise is increased, the ammonia retention amount in the selective reduction type NOx catalyst is relatively large. Since the control is performed so as to be within the range, it is possible to cope with the release of NOx due to a rapid temperature rise, and it is possible to prevent the release of NOx into the atmosphere.

また、上記のＮＯｘ浄化システムにおいて、前記所定の第１判定値と前記所定の第２判定値とを前記酸化触媒の触媒温度に対応して算出すると共に、前記第１制御目標範囲と前記第２制御目標範囲と前記第３制御目標範囲とを前記選択還元型ＮＯｘ触媒の触媒温度に対応して算出するように構成される。   In the NOx purification system, the predetermined first determination value and the predetermined second determination value are calculated corresponding to the catalyst temperature of the oxidation catalyst, and the first control target range and the second control value are calculated. The control target range and the third control target range are calculated corresponding to the catalyst temperature of the selective reduction type NOx catalyst.

この構成によれば、酸化触媒の触媒温度によって酸化触媒が吸着可能なＮＯｘ量が変化するが、この変化に効率よく対応できる。また、選択還元型ＮＯｘ触媒の触媒温度によって選択還元型ＮＯｘ触媒が保持可能なアンモニア量が変化するが、この変化に効率よく対応できる。   According to this configuration, although the amount of NOx that can be adsorbed by the oxidation catalyst varies depending on the catalyst temperature of the oxidation catalyst, it is possible to efficiently cope with this change. In addition, the amount of ammonia that can be held by the selective reduction type NOx catalyst varies depending on the catalyst temperature of the selective reduction type NOx catalyst, but this change can be handled efficiently.

また、上記のＮＯｘ浄化システムにおいて、前記所定の第１判定値と前記所定の第２判定値を前記酸化触媒の触媒温度に対応したＮＯｘ飽和吸着量を基にして算出すると共に、前記第１制御目標範囲と前記第２制御目標範囲と前記第３制御目標範囲を前記選択還元型ＮＯｘ触媒の触媒温度に対応したアンモニア飽和保持量を基にして算出するように構成される。   In the NOx purification system, the predetermined first determination value and the predetermined second determination value are calculated based on a NOx saturated adsorption amount corresponding to a catalyst temperature of the oxidation catalyst, and the first control is performed. The target range, the second control target range, and the third control target range are calculated based on the ammonia saturation retention amount corresponding to the catalyst temperature of the selective reduction type NOx catalyst.

この構成によれば、酸化触媒の触媒温度によって酸化触媒が吸着可能なＮＯｘ量の限界であるＮＯｘ飽和吸着量が変化するが、この変化への対応を比較的単純なアルゴリズムでできるようになる。また、選択還元型ＮＯｘ触媒の触媒温度によって選択還元型ＮＯｘ触媒が保持可能なアンモニア量の限界であるアンモニア飽和保持量が変化するが、この変化への対応を比較的単純なアルゴリズムでできるようになる。   According to this configuration, the NOx saturation adsorption amount, which is the limit of the NOx amount that can be adsorbed by the oxidation catalyst, varies depending on the catalyst temperature of the oxidation catalyst, but this change can be handled with a relatively simple algorithm. In addition, the ammonia saturation retention amount, which is the limit of the ammonia amount that can be held by the selective reduction NOx catalyst, varies depending on the catalyst temperature of the selective reduction NOx catalyst, so that this change can be handled with a relatively simple algorithm. Become.

更に、上記のＮＯｘ浄化システムにおいて、前記酸化触媒における前記ＮＯｘ吸着推定量の算出に際して、前記酸化触媒の下流側に配置したＮＯｘセンサーの検出値を用いるように構成される。この構成によれば、内燃機関の吸気量と燃料量とから算出される排気ガス量と、ＮＯｘセンサーで検出されたＮＯｘ濃度とから、酸化触媒の下流側に流出したＮＯｘ流出量を容易に算出できるようになる。従って、酸化触媒の上流側のＮＯｘ量（内燃機関からのＮＯｘ排出量）とこのＮＯｘ流出量の差からＮＯｘ吸着推定量を容易に算出できるようになる。   Further, the NOx purification system is configured to use a detected value of a NOx sensor disposed downstream of the oxidation catalyst when calculating the estimated NOx adsorption amount in the oxidation catalyst. According to this configuration, the NOx outflow amount that flows out downstream of the oxidation catalyst is easily calculated from the exhaust gas amount calculated from the intake air amount and fuel amount of the internal combustion engine and the NOx concentration detected by the NOx sensor. become able to. Therefore, the estimated NOx adsorption amount can be easily calculated from the difference between the NOx amount upstream of the oxidation catalyst (NOx emission amount from the internal combustion engine) and the NOx outflow amount.

そして、上記の目的を達成するためのＮＯｘ浄化システムの制御方法は、排気ガス通路の上流側から順に、酸化触媒と、排気ガス通路にアンモニア系溶液を供給するアンモニア系溶液供給装置と、選択還元型ＮＯｘ触媒とを備えると共に、前記アンモニア系溶液の供給量を制御する供給量制御装置とを備えて、排気ガス中のＮＯｘを還元するＮＯｘ浄化システムの制御方法において、前記酸化触媒におけるＮＯｘの吸着量の推定値であるＮＯｘ吸着推定量を算出し、該ＮＯｘ吸着推定量に応じて、前記アンモニア系溶液の供給量を制御すると共に、前記ＮＯｘ吸着推定量が所定の第１判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を所定の第１制御目標範囲内とし、前記ＮＯｘ吸着推定量が所定の第１判定値より大きく所定の第２判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第１制御目標範囲よりも大きい所定の第２制御目標範囲内とし、前記ＮＯｘ吸着推定量が前記所定の第２判定値より大きい場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第２制御目標範囲よりも大きい所定の第３制御目標範囲内として、前記アンモニア系溶液の供給量を制御する方法である。この方法によれば、アンモニア系溶液を選択還元型ＮＯｘ触媒に対して過不足なく供給して、アンモニアとＮＯｘの両方の大気中への排出を防止することができる。 And the control method of the NOx purification system for achieving the above-mentioned object is the oxidation catalyst, the ammonia-based solution supply device for supplying the ammonia-based solution to the exhaust gas passage, the selective reduction, in order from the upstream side of the exhaust gas passage. NOx adsorption in the oxidation catalyst in a control method of a NOx purification system that includes a NOx catalyst and a supply amount control device that controls the supply amount of the ammonia-based solution and reduces NOx in exhaust gas A NOx adsorption estimated amount that is an estimated value of the amount is calculated, the supply amount of the ammonia-based solution is controlled according to the NOx adsorption estimated amount, and the NOx adsorption estimated amount is equal to or less than a predetermined first determination value The target amount of the supply amount of the ammonia-based solution is set within a predetermined first control target range, and the estimated NOx adsorption amount is larger than a predetermined first determination value. When the value is equal to or smaller than the second determination value, the target amount of the supply amount of the ammonia-based solution is set within a predetermined second control target range that is larger than the predetermined first control target range, and the NOx adsorption estimation amount is the predetermined amount. Is greater than the second determination value, the supply amount of the ammonia-based solution is set to a predetermined third control target range that is larger than the predetermined second control target range. It is a method to control . According to this method, the ammonia-based solution can be supplied to the selective reduction-type NOx catalyst without excess or deficiency to prevent both ammonia and NOx from being discharged into the atmosphere.

本発明に係るＮＯｘ浄化システム及びＮＯｘ浄化システムの制御方法によれば、上流側の酸化触媒におけるＮＯｘ吸着推定量を考慮して、アンモニア系溶液の供給量を制御するので、内燃機関の運転条件によるＮＯｘの増減のみならず、酸化触媒の温度変化によるＮＯｘ放出量にも対応して、選択還元型ＮＯｘ触媒へ供給するアンモニア系溶液の供給量を適切に制御することが可能とになる   According to the NOx purification system and the control method of the NOx purification system according to the present invention, the supply amount of the ammonia-based solution is controlled in consideration of the estimated NOx adsorption amount in the upstream side oxidation catalyst. It is possible to appropriately control the supply amount of the ammonia-based solution supplied to the selective reduction type NOx catalyst in response to not only the increase / decrease in NOx but also the NOx release amount due to the temperature change of the oxidation catalyst.

従って、上流側の酸化触媒において、ＮＯｘの吸着とこの吸着されたＮＯｘの放出とが起こっても、アンモニアスリップを抑えながらＮＯｘを浄化することが可能となる。その結果、大気中へのアンモニアの放出とＮＯｘの放出を共に低減することができる。   Therefore, even if adsorption of NOx and release of this adsorbed NOx occur in the upstream oxidation catalyst, it is possible to purify NOx while suppressing ammonia slip. As a result, both ammonia release and NOx release into the atmosphere can be reduced.

以下、本発明に係る実施の形態のＮＯｘ浄化システム及びＮＯｘ浄化システムの制御方法について、ディーゼルエンジンの排気通路を通過する排気ガスのＮＯｘを浄化するＮＯｘ浄化システムを例にして図面を参照しながら説明する。図１に、本発明の実施の形態のＮＯｘ浄化システム１の構成を示す。   Hereinafter, the NOx purification system and the control method of the NOx purification system according to the embodiments of the present invention will be described with reference to the drawings, taking as an example a NOx purification system that purifies NOx of exhaust gas passing through an exhaust passage of a diesel engine. To do. FIG. 1 shows a configuration of a NOx purification system 1 according to an embodiment of the present invention.

このＮＯｘ浄化システム１では、ディーゼルエンジン２の排気ガス通路３に、上流側から順に、酸化触媒（ＤＯＣ）４、アンモニア系溶液供給装置５、選択還元型ＮＯｘ触媒（ＳＣＲ触媒）６が配設される。   In this NOx purification system 1, an oxidation catalyst (DOC) 4, an ammonia-based solution supply device 5, and a selective reduction type NOx catalyst (SCR catalyst) 6 are arranged in the exhaust gas passage 3 of the diesel engine 2 in order from the upstream side. The

酸化触媒４は、コージェライトハニカム等の多孔質のセラミックのハニカム構造等の担持体に、パラジウム、酸化セリウム、白金、酸化アルミニウム等を担持して形成される。この酸化触媒４は、排気ガス中に未燃燃料（炭化水素：ＨＣ）や一酸化炭素（ＣＯ）等があるとこれを酸化して、この酸化で発生する熱により排気ガスを昇温し、この昇温した排気ガスで下流側の選択還元型ＮＯｘ触媒６を昇温させることができる。   The oxidation catalyst 4 is formed by supporting palladium, cerium oxide, platinum, aluminum oxide or the like on a support such as a porous ceramic honeycomb structure such as a cordierite honeycomb. This oxidation catalyst 4 oxidizes unburned fuel (hydrocarbon: HC), carbon monoxide (CO), etc. in the exhaust gas, and raises the temperature of the exhaust gas by the heat generated by this oxidation. The temperature of the selective reduction-type NOx catalyst 6 on the downstream side can be increased by the exhaust gas whose temperature has been increased.

この酸化触媒４は、ＮＯｘ、炭化水素の酸化以外に、ＮＯｘを吸着する性質を併せ持っている。つまり、一酸化窒素（ＮＯ）を二酸化窒素（ＮＯ2 ）に酸化し、この二酸化窒素を吸着し保持する。この酸化触媒に保持された二酸化窒素は排気ガス温度が上昇し、ある一定の温度以上になると脱離して放出される。この酸化触媒のＮＯｘ飽和吸着量は、図３及び図５に示すように、触媒温度が上昇すると少なくなる。 This oxidation catalyst 4 has the property of adsorbing NOx in addition to the oxidation of NOx and hydrocarbons. That is, nitric oxide (NO) is oxidized to nitrogen dioxide (NO 2 ), and this nitrogen dioxide is adsorbed and retained. Nitrogen dioxide held in this oxidation catalyst is desorbed and released when the exhaust gas temperature rises and exceeds a certain temperature. As shown in FIGS. 3 and 5, the NOx saturation adsorption amount of the oxidation catalyst decreases as the catalyst temperature rises.

アンモニア系溶液供給装置５は、選択還元型ＮＯｘ触媒に、ＮＯｘを還元する際の還元剤となるアンモニア（ＮＨ3 ）を供給するためのもので、尿素水溶液やアンモニア水溶液等のアンモニア系溶液を、アンモニア系溶液タンク７から排気ガス通路３に噴射する噴射弁等で形成される。 The ammonia-based solution supply device 5 is for supplying ammonia (NH 3 ) as a reducing agent when reducing NOx to a selective reduction-type NOx catalyst. An ammonia-based solution such as an aqueous urea solution or an aqueous ammonia solution It is formed by an injection valve or the like that injects into the exhaust gas passage 3 from the ammonia solution tank 7.

選択還元型ＮＯｘ触媒６は、コージェライトや酸化アルミニウムや酸化チタン等で形成されるハニカム構造等の担持体に、チタニアーバナジウム、ゼオライト、酸化クロム、酸化マンガン、酸化モリブデン、酸化チタン、酸化タングステン等を担持して形成される。この構成により、ＮＯｘをアンモニアで還元浄化する機能に加えて、アンモニアを吸着して保持する機能も有する。このアンモニア飽和保持量は、図４の曲線Ｅで示すように、触媒温度によって変化し、触媒温度が上昇する程少なくなる。   The selective reduction type NOx catalyst 6 is formed on a carrier such as a honeycomb structure formed of cordierite, aluminum oxide, titanium oxide, etc., titania-vanadium, zeolite, chromium oxide, manganese oxide, molybdenum oxide, titanium oxide, tungsten oxide, etc. Is formed. With this configuration, in addition to the function of reducing and purifying NOx with ammonia, it also has a function of adsorbing and holding ammonia. As shown by the curve E in FIG. 4, the ammonia saturation retention amount varies depending on the catalyst temperature and decreases as the catalyst temperature increases.

また、酸化触媒４の下流側に、酸化触媒４で吸着されたＮＯｘ量を推定するために第１のＮＯｘセンサー（ＮＯｘ濃度検出センサー）８ａが配置される。また、図示しないが、酸化触媒４の触媒温度と選択還元型ＮＯｘ触媒６の触媒温度とを検出する温度センサー等の触媒温度検出手段も配置される。   In addition, a first NOx sensor (NOx concentration detection sensor) 8 a is disposed downstream of the oxidation catalyst 4 in order to estimate the amount of NOx adsorbed by the oxidation catalyst 4. Although not shown, a catalyst temperature detecting means such as a temperature sensor for detecting the catalyst temperature of the oxidation catalyst 4 and the catalyst temperature of the selective reduction type NOx catalyst 6 is also arranged.

なお、エンジン２からのＮＯｘ排出量をＮＯｘ排出量マップデータから推定する場合には不要であるが、エンジン２から排出されるＮＯｘを酸化触媒４の上流側のＮＯｘ濃度から算出する場合には、酸化触媒４の上流側に、第２のＮＯｘセンサー（ＮＯｘ濃度検出センサー）８ｂが配置される。   Note that this is not necessary when the NOx emission amount from the engine 2 is estimated from the NOx emission map data, but when NOx emitted from the engine 2 is calculated from the NOx concentration on the upstream side of the oxidation catalyst 4, A second NOx sensor (NOx concentration detection sensor) 8 b is disposed upstream of the oxidation catalyst 4.

更に、供給量制御装置９が設けられ、この供給量制御装置９によりアンモニア系溶液供給装置５で供給するアンモニア系溶液の供給量を制御する。この供給量制御装置９は、通常はエンジン２の運転全般を制御するＥＣＵ（エンジンコントロールユニット）と呼ばれる制御装置に組み込まれる。この供給量制御装置９には、エンジン２の運転状態（例えば、エンジン回転数Ｎｅ，負荷（燃料噴射量）Ｑなど）と第１のＮＯｘセンサー８ａの検出ＮＯｘ濃度や酸化触媒４の検出温度や図示しない選択還元型ＮＯｘ触媒６の検出温度等が入力される。また、必要に応じて、第２のＮＯｘセンサー８ｂの検出ＮＯｘ濃度が入力される。   Further, a supply amount control device 9 is provided, and the supply amount control device 9 controls the supply amount of the ammonia-based solution supplied by the ammonia-based solution supply device 5. The supply amount control device 9 is usually incorporated in a control device called an ECU (engine control unit) that controls the overall operation of the engine 2. The supply amount control device 9 includes the operation state of the engine 2 (for example, the engine speed Ne, the load (fuel injection amount) Q, etc.), the detected NOx concentration of the first NOx sensor 8a, the detected temperature of the oxidation catalyst 4, The detected temperature of the selective reduction type NOx catalyst 6 (not shown) is input. Further, the detected NOx concentration of the second NOx sensor 8b is input as necessary.

このＮＯｘ浄化システム１では、エンジン２から排出された排気ガスＧ中のＮＯｘは、一部が酸化触媒４に吸着され、酸化触媒４を通過した残りのＮＯｘや酸化触媒４から放出されたＮＯｘが、選択還元型ＮＯｘ触媒６において、アンモニア系溶液供給装置５から供給（排気ガスＧ中に添加）されたアンモニア系溶液から発生するアンモニアを還元剤にして還元浄化される。この浄化された排気ガスＧｃは、排気ガス通路３を通過して大気中に放出される。このアンモニアの一部は選択還元型ＮＯｘ触媒６に保持されるが、この保持されたアンモニアは選択還元型ＮＯｘ触媒６の条件によって放出され、ＮＯｘの還元に消費される。   In this NOx purification system 1, a part of the NOx in the exhaust gas G discharged from the engine 2 is adsorbed by the oxidation catalyst 4, and the remaining NOx that has passed through the oxidation catalyst 4 and the NOx released from the oxidation catalyst 4 are removed. The selective reduction type NOx catalyst 6 is reduced and purified using ammonia generated from the ammonia-based solution supplied (added into the exhaust gas G) from the ammonia-based solution supply device 5 as a reducing agent. The purified exhaust gas Gc passes through the exhaust gas passage 3 and is released into the atmosphere. A part of this ammonia is held in the selective reduction type NOx catalyst 6, but this held ammonia is released under the conditions of the selective reduction type NOx catalyst 6 and consumed for the reduction of NOx.

本発明においては、これらのＮＯｘ浄化システム１で、アンモニア系溶液供給装置５は、図２に例示するような制御フローに従って、次のように制御される。この図２の制御フローは、エンジン２の運転が開始されると、エンジン２の運転制御を行う制御フローから、アンモニア系溶液の供給が必要になった時に繰り返し呼ばれて実行され、エンジン２の運転が終了すると、エンジン２の運転制御を行う制御フローと共に終了するものとして示してある。   In the present invention, in these NOx purification systems 1, the ammonia-based solution supply device 5 is controlled as follows according to the control flow illustrated in FIG. The control flow of FIG. 2 is repeatedly called and executed when the supply of the ammonia-based solution is required from the control flow for controlling the operation of the engine 2 when the operation of the engine 2 is started. When the operation is completed, it is shown that the operation is completed together with a control flow for controlling the operation of the engine 2.

この図２の制御フローが呼ばれると、スタートし、ステップＳ１１で、アンモニア系溶液の供給量Ｙの制御に必要なデータを入力する。このデータとしては、エンジン２の運転状態を示すような、エンジン回転数、負荷（又は燃料噴射量）、吸気量等とＮＯｘ排出量マップデータと図３に示すようなＮＯｘ吸着量マップデータと図４に示すようなアンモニア保持量マップデータ等が入力される。更に、第１のＮＯｘセンサー８ａの検出値（ＮＯｘ濃度）が入力される。なお、ＮＯｘ排出量マップデータを使用せずに、第２のＮＯｘセンサー８ｂの検出値（ＮＯｘ濃度）を用いるときは、この検出値が入力される。   When the control flow of FIG. 2 is called, the process starts, and in step S11, data necessary for controlling the supply amount Y of the ammonia-based solution is input. This data includes engine speed, load (or fuel injection amount), intake air amount, NOx emission map data, NOx adsorption amount map data as shown in FIG. Ammonia retention amount map data as shown in FIG. Further, the detection value (NOx concentration) of the first NOx sensor 8a is input. Note that, when the detected value (NOx concentration) of the second NOx sensor 8b is used without using the NOx emission map data, this detected value is input.

次のステップＳ１２で、酸化触媒４におけるＮＯｘ吸着推定量Ｎｅを算出する。この算出は、エンジン２から排出されるＮＯｘ排出量Ｎ１を、エンジン２の運転状態を示すデータ（エンジン回転数、負荷など）と、これらのデータをベースにしたＮＯｘ排出量を示すＮＯｘ排出量マップデータを参照して算出する。このＮＯｘ排出量マップデータは、予め、実験などにより求めておき、供給量制御装置９に記憶させておく。   In the next step S12, an estimated NOx adsorption amount Ne in the oxidation catalyst 4 is calculated. This calculation is based on the NOx emission amount N1 discharged from the engine 2, data indicating the operating state of the engine 2 (engine speed, load, etc.), and the NOx emission amount map indicating the NOx emission amount based on these data. Calculate with reference to the data. This NOx emission amount map data is obtained in advance by experiments or the like and stored in the supply amount control device 9.

このＮＯｘ排出量Ｎ１を算出すると共に、エンジン２の運転状態（燃料噴射量や吸気量等）から算出される排気ガス流量と第１のＮＯｘセンサー８ａの検出ＮＯｘ濃度値とから、酸化触媒４を通過した後の排気ガスＧ中のＮＯｘ流出量Ｎ２を算出する。そして、このＮＯｘ排出量Ｎ１とＮＯｘ流出量Ｎ２との差を、時間Δｔに関して積算してＮＯｘ吸着推定量Ｎｅ（＝Σ（Ｎ１−Ｎ２）×Δｔ）を算出する。   The NOx emission amount N1 is calculated, and the oxidation catalyst 4 is determined from the exhaust gas flow rate calculated from the operating state of the engine 2 (fuel injection amount, intake air amount, etc.) and the detected NOx concentration value of the first NOx sensor 8a. The NOx outflow amount N2 in the exhaust gas G after passing through is calculated. Then, the difference between the NOx emission amount N1 and the NOx outflow amount N2 is integrated with respect to the time Δt to calculate the NOx adsorption estimated amount Ne (= Σ (N1−N2) × Δt).

なお、酸化触媒４におけるＮＯｘ吸着推定値Ｎｅの算出に、ＮＯｘ排出量マップデータを使用せずに、第２のＮＯｘセンサー８ｂの検出ＮＯｘ濃度値を用いるときは、エンジン２の運転状態（燃料噴射量や吸気量等）から算出される排気ガス流量と第２のＮＯｘセンサー８ｂの検出ＮＯｘ濃度値とから、エンジン２から排出され、酸化触媒４を通過する前の排気ガスＧ中のＮＯｘ排出量Ｎ１を算出する。   When the detected NOx concentration value of the second NOx sensor 8b is used for calculating the estimated NOx adsorption value Ne in the oxidation catalyst 4 without using the NOx emission map data, the operating state of the engine 2 (fuel injection) NOx emission amount in the exhaust gas G before being discharged from the engine 2 and passing through the oxidation catalyst 4 from the exhaust gas flow rate calculated from the exhaust gas flow rate calculated from the exhaust gas flow rate and the intake air amount) and the detected NOx concentration value of the second NOx sensor 8b N1 is calculated.

次のステップＳ１３とステップＳ１４により、ＮＯｘ吸着推定量Ｎｅがどの範囲にあるかをチェックする。このＮＯｘ吸着推定量Ｎｅの範囲は、この図２の制御フローでは、酸化触媒４の触媒温度をベースにした図３に示すように、３つの曲線Ｎａ，Ｎｂ，Ｎｃによって３つの領域Ｒａ１，Ｒａ２，Ｒａ３に分割される。   In the next step S13 and step S14, it is checked in which range the NOx adsorption estimated amount Ne is. In the control flow of FIG. 2, the range of the estimated NOx adsorption amount Ne is shown in FIG. 3, which is based on the catalyst temperature of the oxidation catalyst 4, and is divided into three regions Ra1, Ra2 by three curves Na, Nb, Nc. , Ra3.

この曲線Ｎｃは酸化触媒４のＮＯｘ飽和吸着量を示す曲線である。第１の領域Ｒａ１は曲線Ｎａ以下の領域であり、第２の領域Ｒａ２は曲線Ｎａよりも上で曲線Ｎｂ以下の領域である。また、第３の領域Ｒａ３は曲線Ｎｂよりも上で曲線Ｎｃ以下の領域である。   This curve Nc is a curve showing the NOx saturated adsorption amount of the oxidation catalyst 4. The first region Ra1 is a region below the curve Na, and the second region Ra2 is a region above the curve Na and below the curve Nb. The third region Ra3 is a region above the curve Nb and below the curve Nc.

このＮＯｘ吸着推定量Ｎｅのチェックは、酸化触媒４の触媒温度を直接測定するか、酸化触媒４の前後の排気ガス温度、前方の排気ガス温度、又は、後方の排気ガス温度等から推定する。そして、所定の第１判定値Ｎａと所定の第２判定値Ｎｂとを酸化触媒４の触媒温度に対応させて、この触媒温度に対応したＮＯｘ飽和吸着量を基にして算出する。この触媒温度における３つの曲線の値、Ｎａ、Ｎｂ、Ｎｃと、ステップＳ１２で算出されたＮＯｘ吸着推定量Ｎｅとを比較して、ＮＯｘ吸着推定量Ｎｅが３つの領域Ｒａ１，Ｒａ２，Ｒａ３のいずれの領域にあるかを判定する。   This NOx adsorption estimation amount Ne is checked by directly measuring the catalyst temperature of the oxidation catalyst 4, or estimating it from the exhaust gas temperature before and after the oxidation catalyst 4, the front exhaust gas temperature, the rear exhaust gas temperature, or the like. Then, the predetermined first determination value Na and the predetermined second determination value Nb are made to correspond to the catalyst temperature of the oxidation catalyst 4 and calculated based on the NOx saturated adsorption amount corresponding to the catalyst temperature. The three curve values Na, Nb, and Nc at the catalyst temperature are compared with the estimated NOx adsorption amount Ne calculated in step S12, and the estimated NOx adsorption amount Ne is one of the three regions Ra1, Ra2, and Ra3. It is determined whether it is in the area.

図２の制御フローでは、ステップＳ１３で、ＮＯｘ吸着推定量ＮｅがＮａ（所定の第１判定値）以下であるか否かを判定し、Ｎａ以下であれば、ステップＳ１５に行き、Ｎａ以下でなければ、ステップＳ１４に行く。ステップＳ１４で、ＮＯｘ吸着推定量ＮｅがＮｂ（所定の第２判定値）以下であるか否かを判定し、Ｎｂ以下であれば、ステップＳ１６に行き、Ｎｂ以下でなければ、ステップＳ１７に行く。これらの判定により、Ｎｅ≦Ｎａであれば、ステップＳ１５に、Ｎａ＜Ｎｅ≦Ｎｂであれば、ステップＳ１６に、Ｎｂ＜Ｎｅ（≦Ｎｃ）であれば、ステップＳ１７に行くことになる。   In the control flow of FIG. 2, it is determined in step S13 whether or not the NOx adsorption estimated amount Ne is equal to or less than Na (predetermined first determination value). If it is equal to or less than Na, the process goes to step S15. If not, go to step S14. In step S14, it is determined whether or not the NOx adsorption estimation amount Ne is equal to or less than Nb (predetermined second determination value). If it is equal to or less than Nb, the process goes to step S16, and if it is not less than Nb, the process goes to step S17. . From these determinations, if Ne ≦ Na, go to step S15, if Na <Ne ≦ Nb, go to step S16, and if Nb <Ne (≦ Nc), go to step S17.

ステップＳ１５〜Ｓ１７では、選択還元型ＮＯｘ触媒６のアンモニア保持量Ｘの制御目標範囲の算出を行う。つまり、制御目標範囲の下限Ｘｄと上限Ｘｕを算出する。この制御目標範囲は、この図２の制御フローでは、選択還元型ＮＯｘ触媒６の触媒温度をベースにした図４に示すように、５つの曲線Ａ，Ｂ，Ｃ，Ｄ，Ｅによって５つの領域Ｒｂ１，Ｒｂ２，Ｒｂ３，Ｒｂ４，Ｒｂ５に分割される。この曲線Ｅは選択還元型ＮＯｘ触媒６のアンモニア飽和保持量を示す曲線である。   In steps S15 to S17, the control target range of the ammonia retention amount X of the selective reduction type NOx catalyst 6 is calculated. That is, the lower limit Xd and the upper limit Xu of the control target range are calculated. In the control flow of FIG. 2, this control target range is divided into five regions by five curves A, B, C, D, E as shown in FIG. 4 based on the catalyst temperature of the selective reduction type NOx catalyst 6. It is divided into Rb1, Rb2, Rb3, Rb4 and Rb5. This curve E is a curve showing the ammonia saturation retention amount of the selective reduction type NOx catalyst 6.

第１の領域Ｒｂ１は、曲線Ａよりも下の領域であり、第２の領域Ｒｂ２は曲線Ａよりも上で曲線Ｂよりも下の領域である。また、第３の領域Ｒｂ３は曲線Ｂよりも上で曲線Ｃよりも下の領域であり、第４の領域Ｒｂ４は曲線Ｃよりも上で曲線Ｄよりも下の領域である。更に、第５の領域Ｒｂ５は曲線Ｄよりも上で曲線Ｅよりも下の領域である。   The first region Rb1 is a region below the curve A, and the second region Rb2 is a region above the curve A and below the curve B. The third region Rb3 is a region above the curve B and below the curve C, and the fourth region Rb4 is a region above the curve C and below the curve D. Further, the fifth region Rb5 is a region above the curve D and below the curve E.

ここで、アンモニア保持量が少ない第１の領域Ｒｂ１は、排気ガス中のＮＯｘ排出量の増減や酸化触媒４の温度上昇によるＮＯｘ増加への対応には不十分であるので、この実施の形態では、制御目標範囲から除外する。また、アンモニア保持量が多くアンモニア飽和保持量Ｅに近い第５の領域Ｒｂ５も、排気ガス中のＮＯｘ排出量の増減や酸化触媒４の温度上昇によるＮＯｘ増加への対応に応じてアンモニア系溶液の供給量Ｙを増加したときに、アンモニアを選択還元型ＮＯｘ触媒６で保持できなくなって、アンモニアスリップが発生し易いので、この実施の形態では、制御目標範囲から除外する。   Here, the first region Rb1 having a small ammonia retention amount is insufficient to cope with the increase / decrease in the NOx emission amount in the exhaust gas and the increase in NOx due to the temperature increase of the oxidation catalyst 4, so in this embodiment. Exclude from the control target range. In addition, the fifth region Rb5 having a large ammonia retention amount and close to the ammonia saturation retention amount E is also used for the ammonia-based solution according to the increase / decrease in the NOx emission amount in the exhaust gas or the increase in NOx due to the temperature increase of the oxidation catalyst 4. When the supply amount Y is increased, ammonia cannot be held by the selective reduction type NOx catalyst 6 and ammonia slip easily occurs. Therefore, in this embodiment, it is excluded from the control target range.

そして、このステップＳ１５〜Ｓ１７においては、選択還元型ＮＯｘ触媒６の触媒温度を直接測定するか、選択還元型ＮＯｘ触媒６の前後又は前方又は後方の排気ガス温度から推定し、この触媒温度における５つの曲線の値、Ａ，Ｂ，Ｃ，Ｄ，ＥのうちのＡ，Ｂ，Ｃ，Ｄから３つの領域のＲｂ２，Ｒｂ３，Ｒｂ４のいずれかの領域に設定する。つまり、第１制御目標範囲Ｒｂ２と第２制御目標範囲Ｒｂ３と第３制御目標範囲Ｒｂ４とを選択還元型ＮＯｘ触媒６の触媒温度に対応させて、この触媒温度に対応したアンモニア飽和保持量を基にして算出する。   In Steps S15 to S17, the catalyst temperature of the selective reduction type NOx catalyst 6 is directly measured or estimated from the exhaust gas temperatures before, after, or in front of or behind the selective reduction type NOx catalyst 6, and 5 at this catalyst temperature. Of the values of the two curves, A, B, C, D, and E, A, B, C, and D are set to one of the three regions Rb2, Rb3, and Rb4. That is, the first control target range Rb2, the second control target range Rb3, and the third control target range Rb4 are made to correspond to the catalyst temperature of the selective reduction type NOx catalyst 6, and the ammonia saturation retention amount corresponding to this catalyst temperature is used as a basis. To calculate.

そして、Ｎｅ≦Ｎａであれば、ステップＳ１５で、下限Ｘｄを曲線Ａの値に，上限Ｘｕを曲線Ｂの値にし、Ｎａ＜Ｎｅ≦Ｎｂであれば、ステップＳ１６で、下限Ｘｄを曲線Ｂの値に、上限Ｘｕを曲線Ｃの値にし、更に、Ｎｂ＜Ｎｅ（≦Ｎｃ）であれば、ステップＳ１７で下限Ｘｄを曲線Ｃの値に，上限Ｘｕを曲線Ｄの値にする。言い換えれば、選択還元型ＮＯｘ触媒６のアンモニア保持量Ｘの制御目標範囲（Ｘｄ＜Ｘ＜Ｘｕ）を、Ｎｅ≦Ｎａであれば、第２の領域（第１制御目標範囲）Ｒｂ２に、Ｎａ＜Ｎｅ≦Ｎｂであれば、第３の領域（第２制御目標範囲）Ｒｂ３に、Ｎｂ＜Ｎｅ（≦Ｎｃ）であれば、第４の領域（第３制御目標範囲）Ｒｂ４に設定する。   If Ne ≦ Na, the lower limit Xd is set to the value of curve A and the upper limit Xu is set to the value of curve B in step S15. If Na <Ne ≦ Nb, the lower limit Xd is set to the value of curve B in step S16. The upper limit Xu is set to the value of the curve C, and if Nb <Ne (≦ Nc), the lower limit Xd is set to the value of the curve C and the upper limit Xu is set to the value of the curve D in step S17. In other words, if the control target range (Xd <X <Xu) of the ammonia retention amount X of the selective reduction type NOx catalyst 6 is Ne ≦ Na, the second region (first control target range) Rb2 has Na < If Ne ≦ Nb, the third region (second control target range) Rb3 is set. If Nb <Ne (≦ Nc), the fourth region (third control target range) Rb4 is set.

そして、ステップＳ１８で、選択還元型ＮＯｘ触媒６のアンモニア保持量Ｘが、これらの設定した制御目標範囲（Ｘｄ＜Ｘ＜Ｘｕ）になるように、アンモニア系溶液供給装置５で供給するアンモニア系溶液の供給量Ｙを調整及び制御する。   In step S18, the ammonia-based solution supplied by the ammonia-based solution supply device 5 so that the ammonia retention amount X of the selective reduction type NOx catalyst 6 falls within the set control target range (Xd <X <Xu). Is adjusted and controlled.

この供給量Ｙの制御では、エンジンの運転状態によるＮＯｘ排出量と選択還元型ＮＯｘ触媒６の（推定）温度における（予想）ＮＯｘ浄化率から選択還元型ＮＯｘ触媒６において保持されているアンモニアがＮＯｘ浄化に消費された量を算出して残っているアンモニア保持量を推察し、このアンモニア保持量Ｘが、選択還元型ＮＯｘ触媒６のその温度における制御目標範囲（Ｘｄ＜Ｘ＜Ｘｕ）になるようにする。アンモニア保持量Ｘが上限Ｘｕを超えそうになった場合はアンモニア系溶液の供給を停止し、下限Ｘｄを下回りそうになった場合はアンモニア系溶液の供給を行い制御する。   In the control of the supply amount Y, the ammonia held in the selective reduction NOx catalyst 6 is NOx from the NOx emission amount according to the operating state of the engine and the (predicted) NOx purification rate at the (estimated) temperature of the selective reduction NOx catalyst 6. The amount of ammonia retained is calculated by calculating the amount consumed for purification, and the ammonia retained amount X is set to be within the control target range (Xd <X <Xu) at the temperature of the selective reduction type NOx catalyst 6. To. When the ammonia holding amount X is about to exceed the upper limit Xu, the supply of the ammonia-based solution is stopped, and when the ammonia holding amount X is about to fall below the lower limit Xd, the ammonia-based solution is supplied and controlled.

この制御に基づく供給を所定の時間（この図２の制御フローが呼ばれて戻るインターバルに関係する時間）の間行う。その後、リターンして、図２の制御フローを呼んだ上級の制御フローに戻り、再度、この上級の制御フローから呼ばれて、図２制御フローが繰り返し実行される。   Supply based on this control is performed for a predetermined time (time related to the return interval when the control flow of FIG. 2 is called). Thereafter, the process returns to the upper control flow that called the control flow of FIG. 2, and is called again from this higher control flow, and the control flow of FIG. 2 is repeatedly executed.

この上記の図２の制御フローに従ったＮＯｘ浄化システム１の制御方法により、酸化触媒４に吸着しているＮＯｘ量が少ない場合、即ち、ＮＯｘ吸着推定量Ｎｅが領域Ｒａ１にある場合には、選択還元型ＮＯｘ触媒６のアンモニア保持量Ｘの制御目標範囲（Ｘｄ＜Ｘ＜Ｘｕ）を、アンモニア保持量Ｘが比較的少なくなる領域Ｒｂ２とする。この酸化触媒４におけるＮＯｘ吸着量が少なく、排気ガスの温度上昇によるＮＯｘの多量の放出が殆ど無いと推定される場合は、選択還元型ＮＯｘ触媒６におけるアンモニア保持量Ｘを、エンジン２の運転条件によるＮＯｘ排出量Ｎ１の増減に対応した比較的少ない量に制御して、アンモニアスリップを防止する。   When the amount of NOx adsorbed on the oxidation catalyst 4 is small by the control method of the NOx purification system 1 according to the control flow of FIG. 2 described above, that is, when the estimated NOx adsorption amount Ne is in the region Ra1, A control target range (Xd <X <Xu) of the ammonia retention amount X of the selective reduction type NOx catalyst 6 is defined as a region Rb2 where the ammonia retention amount X is relatively small. When it is estimated that the NOx adsorption amount in the oxidation catalyst 4 is small and a large amount of NOx is not released due to the temperature rise of the exhaust gas, the ammonia retention amount X in the selective reduction type NOx catalyst 6 is set as the operating condition of the engine 2. Therefore, the ammonia slip is prevented by controlling to a relatively small amount corresponding to the increase / decrease of the NOx emission amount N1.

つまり、選択還元型ＮＯｘ触媒６におけるアンモニア保持量Ｘを多くしておいた場合に、排気ガス中のＮＯｘの増加に対応してアンモニア系溶液の供給量Ｙを増加すると、ＮＯｘ還元で余ったアンモニアを選択還元型ＮＯｘ触媒６で保持できなくなって、アンモニアが大気中に放出される可能性が高い。このアンモニアスリップを、予め、選択還元型ＮＯｘ触媒６におけるアンモニア保持量Ｘを少なくしておくことで防止する。   That is, when the ammonia retention amount X in the selective reduction type NOx catalyst 6 is increased, if the supply amount Y of the ammonia-based solution is increased in response to the increase in NOx in the exhaust gas, the remaining ammonia due to NOx reduction Cannot be held by the selective reduction type NOx catalyst 6 and ammonia is likely to be released into the atmosphere. This ammonia slip is prevented by decreasing the ammonia retention amount X in the selective reduction type NOx catalyst 6 in advance.

また、酸化触媒４に吸着しているＮＯｘ量が中程度の場合、、即ち、ＮＯｘ吸着推定量Ｎｅが領域Ｒａ２にある場合には、制御目標範囲（Ｘｄ＜Ｘ＜Ｘｕ）を、アンモニア保持量が中程度の領域Ｒｂ３とする。この場合は、アンモニアスリップの発生の可能性も、次に述べるＮＯｘスリップの発生の可能性も低いので、特にアンモニア保持量を大きく増減させることはしない。   When the amount of NOx adsorbed on the oxidation catalyst 4 is medium, that is, when the estimated NOx adsorption amount Ne is in the region Ra2, the control target range (Xd <X <Xu) is set to the ammonia retention amount. Is a medium region Rb3. In this case, since the possibility of occurrence of ammonia slip and the possibility of occurrence of NOx slip described below are low, the ammonia retention amount is not particularly increased or decreased.

更に、酸化触媒４に吸着しているＮＯｘ量が増加して、ＮＯｘ飽和吸着量Ｎｃに近づいた場合、即ち、ＮＯｘ吸着推定量Ｎｅが領域Ｒａ３に入った場合には、制御目標範囲（Ｘｄ＜Ｘ＜Ｘｕ）を、アンモニア保持量が比較的多い領域Ｒｂ４とする。これにより、選択還元型ＮＯｘ触媒６で保持しているアンモニア量を増加し、排気ガス温度が上昇した場合に酸化触媒４から多量のＮＯｘが放出されて、選択還元型ＮＯｘ触媒６に流入しても、選択還元型ＮＯｘ触媒６で保持しているアンモニア量で十分にＮＯｘを還元できるようにしておく。つまり、酸化触媒４におけるＮＯｘ吸着量が増加してＮＯｘ飽和吸着量Ｎｃに近づいてくると、酸化触媒４の僅かな温度上昇でＮＯｘが放出されるため、選択還元型ＮＯｘ触媒６におけるアンモニア保持量を高めに維持して、この急激なＮＯｘ放出に備える。これにより、排気ガス温度の急上昇によるＮＯｘの大気中への放出（ＮＯｘスリップ）を防止できる。   Further, when the amount of NOx adsorbed on the oxidation catalyst 4 increases and approaches the NOx saturated adsorption amount Nc, that is, when the NOx adsorption estimated amount Ne enters the region Ra3, the control target range (Xd < X <Xu) is defined as a region Rb4 having a relatively large ammonia retention amount. As a result, the amount of ammonia held in the selective reduction type NOx catalyst 6 is increased, and when the exhaust gas temperature rises, a large amount of NOx is released from the oxidation catalyst 4 and flows into the selective reduction type NOx catalyst 6. Also, NOx can be sufficiently reduced by the amount of ammonia retained by the selective reduction type NOx catalyst 6. That is, when the NOx adsorption amount in the oxidation catalyst 4 increases and approaches the NOx saturated adsorption amount Nc, NOx is released with a slight temperature rise of the oxidation catalyst 4, so the ammonia retention amount in the selective reduction type NOx catalyst 6. Is kept high to prepare for this rapid NOx release. Thereby, it is possible to prevent the release of NOx into the atmosphere (NOx slip) due to a sudden rise in the exhaust gas temperature.

上記のように、このＮＯｘ浄化システム１及びＮＯｘ浄化システムの制御方法では、排気ガス通路３に上流側から順に、酸化触媒４と、排気ガス通路３にアンモニア系溶液を供給するアンモニア系溶液供給装置５と、選択還元型ＮＯｘ触媒６とを備えると共に、アンモニア系溶液の供給量Ｙを制御する供給量制御装置９とを備えて、排気ガスＧ中のＮＯｘを還元するＮＯｘ浄化システム１において、酸化触媒４におけるＮＯｘ吸着推定量Ｎｅを算出し、このＮＯｘ吸着推定量Ｎｅに応じて、アンモニア系溶液の供給量Ｙを制御する。   As described above, in the NOx purification system 1 and the control method for the NOx purification system, the oxidation catalyst 4 and the ammonia-based solution supply device that supplies the ammonia-based solution to the exhaust gas passage 3 sequentially from the upstream side to the exhaust gas passage 3. 5 and a selective reduction type NOx catalyst 6 and a supply amount control device 9 for controlling the supply amount Y of the ammonia-based solution to reduce the NOx in the exhaust gas G. An estimated NOx adsorption amount Ne in the catalyst 4 is calculated, and the supply amount Y of the ammonia-based solution is controlled according to the estimated NOx adsorption amount Ne.

また、供給量制御装置９は、ＮＯｘ吸着推定量Ｎｅが所定の第１判定値Ｎａ以下の場合には、アンモニア系溶液の供給量Ｙの目標量Ｘを所定の第１制御目標範囲Ｒｂ２内とし、ＮＯｘ吸着推定量Ｎｅが所定の第１判定値Ｎａより大きく所定の第２判定値Ｎｂ以下の場合には、アンモニア系溶液の供給量Ｙの目標量Ｘを前記所定の第１制御目標範囲Ｒｂ２よりも大きい所定の第２制御目標範囲Ｒｂ３内とし、ＮＯｘ吸着推定量Ｎｅが所定の第２判定値Ｎｂより大きい場合には、アンモニア系溶液の供給量Ｙの目標量Ｘを所定の第２制御目標範囲Ｒｂ３よりも大きい所定の第３制御目標範囲Ｒｂ４内として、アンモニア系溶液の供給量Ｙを制御する。 Further, when the estimated NOx adsorption amount Ne is equal to or less than the predetermined first determination value Na, the supply amount control device 9 sets the target amount X of the ammonia-based solution supply amount Y within the predetermined first control target range Rb2. When the estimated NOx adsorption amount Ne is greater than the predetermined first determination value Na and equal to or less than the predetermined second determination value Nb, the target amount X of the ammonia-based solution supply amount Y is set to the predetermined first control target range Rb2. If the NOx adsorption estimated amount Ne is larger than the predetermined second determination value Nb, the target amount X of the ammonia-based solution supply amount Y is set to the predetermined second control. The supply amount Y of the ammonia-based solution is controlled within a predetermined third control target range Rb4 that is larger than the target range Rb3.

また、供給量制御装置９は、酸化触媒４におけるＮＯｘ吸着推定量ＮｅとＮＯｘ飽和吸着量Ｎｃとの比較に基づいて、選択還元型ＮＯｘ触媒６におけるアンモニア飽和保持量Ｅを基にアンモニア系溶液の供給量Ｙを算出し、更に、酸化触媒４の触媒温度に対応するＮＯｘ吸着推定量ＮｅとＮＯｘ飽和吸着量Ｎｃとの比較に基づいて、選択還元型ＮＯｘ触媒６の触媒温度に対応するアンモニア飽和保持量Ｅを基にアンモニア系溶液の供給量Ｙを算出する。   Further, the supply amount control device 9 determines the ammonia-based solution based on the ammonia saturation retention amount E in the selective reduction type NOx catalyst 6 based on the comparison between the NOx adsorption estimated amount Ne and the NOx saturated adsorption amount Nc in the oxidation catalyst 4. The supply amount Y is calculated, and further, based on the comparison between the NOx adsorption estimated amount Ne corresponding to the catalyst temperature of the oxidation catalyst 4 and the NOx saturated adsorption amount Nc, the ammonia saturation corresponding to the catalyst temperature of the selective reduction type NOx catalyst 6 Based on the holding amount E, the supply amount Y of the ammonia-based solution is calculated.

従って、上流側の酸化触媒４におけるＮＯｘ吸着推定量Ｎｅを考慮して、アンモニア系溶液の供給量Ｙを制御することができるので、エンジン２の運転条件によるＮＯｘの増減のみならず、酸化触媒４の温度変化によるＮＯｘ放出量にも対応して、選択還元型ＮＯｘ触媒６へ供給するアンモニア系溶液の供給量Ｙを適切に制御することができる。その結果、上流側の酸化触媒４において、ＮＯｘの吸着とこの吸着されたＮＯｘの放出とが起こっても、アンモニアスリップを抑えながら、ＮＯｘを浄化することができ、大気中へのアンモニアの放出とＮＯｘの放出の両方を共に低減することができる。   Accordingly, the supply amount Y of the ammonia-based solution can be controlled in consideration of the estimated NOx adsorption amount Ne in the upstream side oxidation catalyst 4, so that not only the increase / decrease of NOx depending on the operating conditions of the engine 2 but also the oxidation catalyst 4. The supply amount Y of the ammonia-based solution to be supplied to the selective reduction type NOx catalyst 6 can be appropriately controlled in response to the NOx release amount due to the temperature change. As a result, even if adsorption of NOx and release of this adsorbed NOx occur in the upstream oxidation catalyst 4, NOx can be purified while suppressing ammonia slip, and release of ammonia into the atmosphere. Both NOx emissions can be reduced together.

本発明に係る実施の形態のＮＯｘ浄化システムの構成を模式的に示す図である。It is a figure showing typically composition of a NOx purification system of an embodiment concerning the present invention. 本発明に係るＮＯｘ浄化システムの制御方法を示す制御フローの図である。It is a figure of the control flow which shows the control method of the NOx purification system which concerns on this invention. 酸化触媒におけるＮＯｘ吸着量の領域分割を示す模式的な図である。It is a schematic diagram which shows the area | region division | segmentation of the NOx adsorption amount in an oxidation catalyst. 選択還元型ＮＯｘ触媒におけるアンモニア保持量の領域分割を示す模式的な図である。FIG. 3 is a schematic diagram showing region division of ammonia retention amount in a selective reduction type NOx catalyst. 酸化触媒におけるＮＯｘの放出を説明するための模式的な図である。It is a schematic diagram for demonstrating discharge | release of NOx in an oxidation catalyst.

符号の説明Explanation of symbols

１ ＮＯｘ浄化システム
２ ディーゼルエンジン（内燃機関）
３ 排気ガス通路
４ 酸化触媒（ＤＯＣ）
５ アンモニア系溶液供給装置
６ 選択還元型ＮＯｘ触媒（ＳＣＲ触媒）
８ａ 第１のＮＯｘセンサー（ＮＯｘ濃度検出センサー）
８ｂ 第２のＮＯｘセンサー（ＮＯｘ濃度検出センサー）
９ 供給量制御装置
Ａ，Ｂ，Ｃ，Ｄ アンモニア保持量を示す曲線
Ｅ アンモニア飽和保持量を示す曲線
Ｎａ ＮＯｘ吸着量を示す曲線（所定の第１判定値）
Ｎｂ ＮＯｘ吸着量を示す曲線（所定の第２判定値）
Ｎｃ ＮＯｘ飽和吸着量を示す曲線
Ｎｅ ＮＯｘ吸着推定量
Ｒａ１ ＮＯｘ吸着量の第１の領域
Ｒａ２ ＮＯｘ吸着量の第２の領域
Ｒａ３ ＮＯｘ吸着量の第３の領域
Ｒｂ１ アンモニア保持量の第１の領域
Ｒｂ２ アンモニア保持量の第２の領域（第１制御目標範囲）
Ｒｂ３ アンモニア保持量の第３の領域（第２制御目標範囲）
Ｒｂ４ アンモニア保持量の第４の領域（第３制御目標範囲）
Ｒｂ５ アンモニア保持量の第５の領域
Ｘ アンモニア保持量
Ｘｄ 制御目標範囲の下限
Ｘｕ 制御目標範囲の上限
Ｙ アンモニア系溶液の供給量 1 NOx purification system 2 Diesel engine (internal combustion engine)
3 Exhaust gas passage 4 Oxidation catalyst (DOC)
5 Ammonia-based solution supply device 6 Selective reduction type NOx catalyst (SCR catalyst)
8a First NOx sensor (NOx concentration detection sensor)
8b Second NOx sensor (NOx concentration detection sensor)
9 Supply amount control device A, B, C, D Curve showing ammonia retention amount E Curve showing ammonia saturation retention amount Curve showing Na NOx adsorption amount (predetermined first judgment value)
Curve showing Nb NOx adsorption amount (predetermined second determination value)
Curve showing Nc NOx saturated adsorption amount Ne NOx adsorption estimation amount Ra1 NOx adsorption amount first region Ra2 NOx adsorption amount second region Ra3 NOx adsorption amount third region Rb1 Ammonia retention amount first region Rb2 Second region of ammonia retention amount (first control target range)
Rb3 Ammonia retention amount third region (second control target range)
Rb4 Fourth region of ammonia retention amount (third control target range)
Rb5 Fifth region of ammonia retention amount X Ammonia retention amount Xd Lower limit of control target range Xu Upper limit of control target range Y Supply amount of ammonia-based solution

Claims (5)

排気ガス通路の上流側から順に、酸化触媒と、排気ガス通路にアンモニア系溶液を供給するアンモニア系溶液供給装置と、選択還元型ＮＯｘ触媒とを備えると共に、前記アンモニア系溶液の供給量を制御する供給量制御装置とを備えて、排気ガス中のＮＯｘを還元するＮＯｘ浄化システムにおいて、
前記供給量制御装置が、前記酸化触媒におけるＮＯｘの吸着量の推定値であるＮＯｘ吸着推定量を算出し、該ＮＯｘ吸着推定量に応じて、前記アンモニア系溶液の供給量を制御すると共に、
前記供給量制御装置が、前記ＮＯｘ吸着推定量が所定の第１判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を所定の第１制御目標範囲内とし、前記ＮＯｘ吸着推定量が所定の第１判定値より大きく所定の第２判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第１制御目標範囲よりも大きい所定の第２制御目標範囲内とし、前記ＮＯｘ吸着推定量が前記所定の第２判定値より大きい場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第２制御目標範囲よりも大きい所定の第３制御目標範囲内として、前記アンモニア系溶液の供給量を制御することを特徴とするＮＯｘ浄化システム。 In order from the upstream side of the exhaust gas passage, an oxidation catalyst, an ammonia solution supply device that supplies the ammonia solution to the exhaust gas passage, and a selective reduction type NOx catalyst are provided, and the supply amount of the ammonia solution is controlled. In a NOx purification system that includes a supply amount control device and reduces NOx in exhaust gas,
The supply amount control device calculates an estimated NOx adsorption amount that is an estimated value of the NOx adsorption amount in the oxidation catalyst, and controls the supply amount of the ammonia-based solution according to the estimated NOx adsorption amount .
When the estimated amount of NOx adsorption is less than or equal to a predetermined first determination value, the supply amount control device sets the target amount of the ammonia-based solution supply amount within a predetermined first control target range, and estimates the NOx adsorption. When the amount is greater than the predetermined first determination value and equal to or less than the predetermined second determination value, the target amount of the supply amount of the ammonia-based solution is set to a predetermined second control target that is larger than the predetermined first control target range. When the estimated NOx adsorption amount is larger than the predetermined second determination value, the target amount of the supply amount of the ammonia-based solution is set to a predetermined third control larger than the predetermined second control target range. A NOx purification system , wherein the supply amount of the ammonia-based solution is controlled within a target range . 前記所定の第１判定値と前記所定の第２判定値とを前記酸化触媒の触媒温度に対応して算出すると共に、前記第１制御目標範囲と前記第２制御目標範囲と前記第３制御目標範囲とを前記選択還元型ＮＯｘ触媒の触媒温度に対応して算出することを特徴とする請求項１記載のＮＯｘ浄化システム。 The predetermined first determination value and the predetermined second determination value are calculated corresponding to the catalyst temperature of the oxidation catalyst, and the first control target range, the second control target range, and the third control target are calculated. 2. The NOx purification system according to claim 1 , wherein the range is calculated corresponding to the catalyst temperature of the selective reduction type NOx catalyst . 前記所定の第１判定値と前記所定の第２判定値を前記酸化触媒の触媒温度に対応したＮＯｘ飽和吸着量を基にして算出すると共に、前記第１制御目標範囲と前記第２制御目標範囲と前記第３制御目標範囲を前記選択還元型ＮＯｘ触媒の触媒温度に対応したアンモニア飽和保持量を基にして算出することを特徴とする請求項１又は２記載のＮＯｘ浄化システム。 The predetermined first determination value and the predetermined second determination value are calculated based on a NOx saturated adsorption amount corresponding to the catalyst temperature of the oxidation catalyst, and the first control target range and the second control target range 3. The NOx purification system according to claim 1 , wherein the third control target range is calculated based on an ammonia saturation retention amount corresponding to a catalyst temperature of the selective reduction type NOx catalyst . 前記酸化触媒における前記ＮＯｘ吸着推定量の算出に際して、前記酸化触媒の下流側に配置したＮＯｘセンサーの検出値を用いることを特徴とする請求項１、２又は３記載のＮＯｘ浄化システム。 4. The NOx purification system according to claim 1, wherein a detection value of a NOx sensor disposed downstream of the oxidation catalyst is used for calculating the estimated amount of NOx adsorption in the oxidation catalyst . 排気ガス通路の上流側から順に、酸化触媒と、排気ガス通路にアンモニア系溶液を供給するアンモニア系溶液供給装置と、選択還元型ＮＯｘ触媒とを備えると共に、前記アンモニア系溶液の供給量を制御する供給量制御装置とを備えて、排気ガス中のＮＯｘを還元するＮＯｘ浄化システムの制御方法において、In order from the upstream side of the exhaust gas passage, an oxidation catalyst, an ammonia solution supply device that supplies the ammonia solution to the exhaust gas passage, and a selective reduction type NOx catalyst are provided, and the supply amount of the ammonia solution is controlled. In a control method of a NOx purification system comprising a supply amount control device and reducing NOx in exhaust gas,
前記酸化触媒におけるＮＯｘの吸着量の推定値であるＮＯｘ吸着推定量を算出し、該ＮＯｘ吸着推定量に応じて、前記アンモニア系溶液の供給量を制御すると共に、Calculating an NOx adsorption estimated amount that is an estimated value of the NOx adsorption amount in the oxidation catalyst, and controlling the supply amount of the ammonia-based solution according to the NOx adsorption estimated amount;
前記ＮＯｘ吸着推定量が所定の第１判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を所定の第１制御目標範囲内とし、前記ＮＯｘ吸着推定量が所定の第１判定値より大きく所定の第２判定値以下の場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第１制御目標範囲よりも大きい所定の第２制御目標範囲内とし、前記ＮＯｘ吸着推定量が前記所定の第２判定値より大きい場合には、前記アンモニア系溶液の供給量の目標量を前記所定の第２制御目標範囲よりも大きい所定の第３制御目標範囲内として、前記アンモニア系溶液の供給量を制御することを特徴とするＮＯｘ浄化システムの制御方法。When the estimated NOx adsorption amount is equal to or smaller than a predetermined first determination value, the target amount of the ammonia-based solution supply amount is set within a predetermined first control target range, and the estimated NOx adsorption amount is a predetermined first determination. If the value is less than a predetermined second determination value, the target amount of the ammonia-based solution supply is set within a predetermined second control target range larger than the predetermined first control target range, and the NOx adsorption is performed. When the estimated amount is larger than the predetermined second determination value, the target amount of the supply amount of the ammonia-based solution is set within a predetermined third control target range that is larger than the predetermined second control target range, and the ammonia A control method for a NOx purification system, wherein the supply amount of the system solution is controlled.
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