JP2014005742A - Exhaust cleaning device of internal combustion engine - Google Patents

Exhaust cleaning device of internal combustion engine Download PDF

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JP2014005742A
JP2014005742A JP2012140010A JP2012140010A JP2014005742A JP 2014005742 A JP2014005742 A JP 2014005742A JP 2012140010 A JP2012140010 A JP 2012140010A JP 2012140010 A JP2012140010 A JP 2012140010A JP 2014005742 A JP2014005742 A JP 2014005742A
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exhaust
urea water
addition
amount
catalyst
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Ataru Ichikawa
中 市川
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Denso Corp
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Denso Corp
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Priority to US13/900,693 priority patent/US20130340412A1/en
Priority to DE102013106205A priority patent/DE102013106205A1/en
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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
    • 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
    • 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
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/02—Adding substances to exhaust gases the substance being ammonia or urea
    • 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
    • F01N2900/0601—Parameters used for exhaust control or diagnosing being estimated
    • 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
    • F01N2900/1411—Exhaust gas flow rate, e.g. mass flow rate or volumetric flow rate
    • 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
    • F01N2900/1602—Temperature of exhaust gas apparatus
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • 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

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust cleaning device of an internal combustion engine which prevents an additive added into an exhaust pipe from an adding means from being stuck to an exhaust pipe wall surface, in the exhaust cleaning device of the internal combustion engine which selectively cleans specified harmful components such as NOx in exhaust by means of a catalyst disposed on an exhaust pipe.SOLUTION: An urea water addition valve 2 for adding urea water into an exhaust pipe 13 is disposed on an exhaust pipe 13 of an engine 101 of a vehicle. On the downstream side from the urea water addition valve 2 of the exhaust pipe 13, an SCR catalyst 1 which converts the added urea water into ammonia and stores the ammonia to reduce NOx in exhaust by the use of the ammonia is disposed. An ECU 11 as an exhaust cleaning device of the internal combustion engine calculates a space speed of the exhaust in the SCR catalyst 1 as exhaust flow velocity based on exhaust flow rate, catalyst temperature and atmospheric pressure. When the calculated exhaust flow velocity is low, the ECU 11 controls the urea water addition valve 2 such that the addition amount of the urea water per unit time becomes less than that when the calculated exhaust flow velocity is high.

Description

本発明は、内燃機関の排気浄化装置に関し、詳細には尿素ＳＣＲシステムなどの排気浄化システムに備えられ、排気管に設けられた触媒により排気中の所定の有害成分（ＮＯｘ等）を選択的に浄化する内燃機関の排気浄化装置に関する。   The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more specifically, is provided in an exhaust gas purification system such as a urea SCR system, and selectively removes predetermined harmful components (NOx, etc.) in the exhaust gas by a catalyst provided in an exhaust pipe. The present invention relates to an exhaust emission control device for an internal combustion engine to be purified.

従来、内燃機関の排気浄化システムの一つに尿素ＳＣＲシステムが知られている。その尿素ＳＣＲシステムでは排気管に排気中のＮＯｘを選択的に還元浄化する触媒（ＳＣＲ触媒、ＮＯｘ選択還元触媒）が設けられる。その触媒より上流側には、排気管内に尿素水（添加剤）を添加する添加弁（添加手段）が設けられる。触媒は、尿素水添加弁から添加された尿素水をアンモニアに変換して貯蔵し、貯蔵したアンモニアで排気中のＮＯｘを窒素と水とに分解（還元）する。   Conventionally, a urea SCR system is known as one of exhaust gas purification systems for internal combustion engines. In the urea SCR system, a catalyst (SCR catalyst, NOx selective reduction catalyst) that selectively reduces and purifies NOx in the exhaust is provided in the exhaust pipe. An addition valve (addition means) for adding urea water (additive) into the exhaust pipe is provided upstream of the catalyst. The catalyst converts urea water added from the urea water addition valve into ammonia and stores it, and decomposes (reduces) NOx in the exhaust gas into nitrogen and water with the stored ammonia.

触媒でのアンモニアの貯蔵可能量は触媒温度によって変化する。そのため、触媒でのＮＯｘ浄化率を高めるには触媒に貯蔵するアンモニアの貯蔵量を触媒温度に応じて最適にする必要がある。例えばアンモニア貯蔵量が少ないと十分なＮＯｘ還元が行えない。反対にアンモニア貯蔵量が多すぎて触媒温度の急激な変化で貯蔵可能量を超えてしまうと、超えた分のアンモニアが触媒から放出されるアンモニアスリップという現象が発生する。このような不具合の発生を防止するためには、触媒に貯蔵されているアンモニアの貯蔵量を正確に推定し、推定した貯蔵量に応じて添加弁による尿素水の添加を適切に行う必要がある。   The amount of ammonia that can be stored in the catalyst varies depending on the catalyst temperature. Therefore, in order to increase the NOx purification rate in the catalyst, it is necessary to optimize the amount of ammonia stored in the catalyst according to the catalyst temperature. For example, if the amount of ammonia stored is small, sufficient NOx reduction cannot be performed. On the other hand, if the amount of ammonia stored is too large and exceeds the storable amount due to a rapid change in the catalyst temperature, a phenomenon called ammonia slip occurs in which the excess ammonia is released from the catalyst. In order to prevent the occurrence of such problems, it is necessary to accurately estimate the storage amount of ammonia stored in the catalyst and appropriately add urea water using the addition valve according to the estimated storage amount. .

そして従来、触媒でのアンモニア貯蔵量は、内燃機関（エンジン）から排出されたＮＯｘの排出量、添加弁から添加された尿素水量（ＮＨ３量）、触媒で消費したアンモニア量の収支に基づき推定されていた（例えば特許文献１参照）。   Conventionally, the amount of ammonia stored in the catalyst is estimated based on the amount of NOx discharged from the internal combustion engine (engine), the amount of urea water added from the addition valve (NH3 amount), and the balance of the amount of ammonia consumed by the catalyst. (For example, refer to Patent Document 1).

特許第３９５１７７４号公報Japanese Patent No. 3951774

ところで、触媒での添加剤（アンモニア）の貯蔵量を正確に推定するには、添加弁から添加された添加剤（尿素水）を排気に乗せて触媒まで到達させる必要がある。しかし、排気流速が低いときには、排気のエネルギー不足により添加弁からの添加剤が触媒に到達しないで排気管壁面に付着することがある。この場合、触媒での貯蔵量の推定値に誤差が生じるため、最適な添加剤添加を行うことができず、その結果、触媒での浄化率が低下するという問題が発生する。   By the way, in order to accurately estimate the storage amount of the additive (ammonia) in the catalyst, it is necessary to allow the additive (urea water) added from the addition valve to reach the catalyst on the exhaust. However, when the exhaust gas flow rate is low, the additive from the addition valve may not reach the catalyst and adhere to the exhaust pipe wall surface due to insufficient exhaust energy. In this case, since an error occurs in the estimated value of the storage amount in the catalyst, the optimum additive cannot be added, resulting in a problem that the purification rate in the catalyst is lowered.

本発明は上記事情に鑑みてなされたものであり、排気管に設けられた触媒により排気中の所定の有害成分（ＮＯｘ等）を選択的に浄化する内燃機関の排気浄化装置において、添加手段から排気管内に添加された添加剤が排気管壁面に付着してしまうのを防止することを課題とする。   The present invention has been made in view of the above circumstances. In an exhaust gas purification apparatus for an internal combustion engine that selectively purifies predetermined harmful components (NOx and the like) in exhaust gas by a catalyst provided in an exhaust pipe, It is an object to prevent the additive added in the exhaust pipe from adhering to the wall surface of the exhaust pipe.

上記課題を解決するために、本発明の内燃機関の排気浄化装置は、内燃機関の排気管に設けられ、前記排気管に所定の添加剤を添加する添加手段と、
前記排気管の前記添加手段より下流側に設けられ、前記添加手段で添加された添加剤を貯蔵しその添加剤で排気中の所定の有害成分を浄化する触媒とを備えた排気浄化システムに備えられ、
前記添加手段で添加すべき添加剤の添加量を決定する添加量決定手段と、
その添加量決定手段が決定した添加量である総添加量ぶんの添加剤が前記排気管に添加されるように前記添加手段を制御する添加制御手段と、
排気流速を算出する流速算出手段とを備え、
前記添加制御手段は、前記流速算出手段が算出した排気流速が低いほど単位時間当たりの添加剤の添加量が小さくなるように前記添加手段を制御することを特徴とする。 In order to solve the above problems, an exhaust emission control device for an internal combustion engine of the present invention is provided in an exhaust pipe of the internal combustion engine, and an adding means for adding a predetermined additive to the exhaust pipe;
Provided in an exhaust purification system provided with a catalyst provided downstream of the adding means of the exhaust pipe and storing an additive added by the adding means and purifying predetermined harmful components in the exhaust gas with the additive. And
An addition amount determining means for determining the amount of additive to be added by the adding means;
An addition control means for controlling the addition means so that the total addition amount of additive which is the addition amount determined by the addition amount determination means is added to the exhaust pipe;
A flow velocity calculating means for calculating the exhaust flow velocity,
The addition control means controls the addition means so that the additive addition amount per unit time becomes smaller as the exhaust flow velocity calculated by the flow velocity calculation means is lower.

本発明によれば、添加量決定手段が決定した総添加量ぶんの添加剤を添加手段で添加する際に、排気流速が低いほど単位時間当たりの添加量を小さくしている。排気流速が低いときには添加剤を触媒まで搬送する排気のエネルギーが小さくなるが、この場合には単位時間当たりの添加量を小さくしているので、添加された添加剤を排気に効率良く乗せることができ、触媒に効率良く到達させることができる。つまり、添加された添加剤が排気管壁面に付着してしまうのを防止できる。   According to the present invention, when adding the total addition amount of additive determined by the addition amount determining means by the adding means, the addition amount per unit time is made smaller as the exhaust gas flow rate is lower. When the exhaust gas flow rate is low, the energy of the exhaust gas that conveys the additive to the catalyst becomes small. In this case, since the additive amount per unit time is reduced, the added additive can be efficiently put on the exhaust gas. And can reach the catalyst efficiently. That is, it is possible to prevent the added additive from adhering to the exhaust pipe wall surface.

排気浄化システム１００の構成図である。1 is a configuration diagram of an exhaust purification system 100. FIG. 第１実施形態におけるＥＣＵ１１が実行する処理のフローチャートである。It is a flowchart of the process which ECU11 in 1st Embodiment performs. 排気流速としての空間速度ＳＶの算出方法の第１例を説明する図である。It is a figure explaining the 1st example of the calculation method of space velocity SV as exhaust flow velocity. 排気流速としての空間速度ＳＶの算出方法の第２例を説明する図である。It is a figure explaining the 2nd example of the calculation method of space velocity SV as exhaust flow velocity. 触媒温度に対する最大ＮＨ３貯蔵量を示した図である。It is the figure which showed the largest NH3 storage amount with respect to catalyst temperature. 触媒温度に対する最大ＮＨ３貯蔵量のライン２０３及び目標ＮＨ３貯蔵量のライン２０４を示した図である。It is the figure which showed the line 203 of the maximum NH3 storage amount with respect to catalyst temperature, and the line 204 of the target NH3 storage amount. 排気流速Ｖｅｘが低くなるにしたがって連続的に分割回数Ｎ（尿素水添加するときの添加回数）を大きくしていくマップ３０１である。This is a map 301 in which the number of divisions N (the number of times of addition when urea water is added) is continuously increased as the exhaust flow velocity Vex decreases. 排気流速Ｖｅｘが低くなるにしたがって段階的に分割回数Ｎを大きくしていくマップ３０２である。The map 302 increases the number of divisions N stepwise as the exhaust flow velocity Vex decreases. 排気流速Ｖｅｘが閾値Ｖｔｈ以上の高いときと、閾値Ｖｔｈ以下の低いときとで択一的に分割回数Ｎを切り替えるマップ３０３を示している。A map 303 is shown in which the number of divisions N is alternatively switched between when the exhaust flow velocity Vex is higher than the threshold Vth and when it is lower than the threshold Vth. 第１実施形態において、排気流速が高いか低いかで、尿素水添加がどのように変わるか、それによってＳＣＲ触媒１へのＮＨ３貯蔵量がどのように変わるかを説明する図である。In 1st Embodiment, it is a figure explaining how urea water addition changes depending on whether the exhaust gas flow rate is high or low, and how NH3 storage amount to the SCR catalyst 1 changes by it. 第２実施形態におけるＥＣＵ１１が実行する処理のフローチャートを示している。The flowchart of the process which ECU11 in 2nd Embodiment performs is shown. 排気流速Ｖｅｘに対する駆動デューティＤのマップ４０１である。It is the map 401 of the drive duty D with respect to the exhaust flow velocity Vex. 第２実施形態において、排気流速が高いか低いかで、尿素水添加がどのように変わるか、それによってＳＣＲ触媒１へのＮＨ３貯蔵量がどのように変わるかを説明する図である。In a 2nd embodiment, it is a figure explaining how urea water addition changes depending on whether an exhaust gas flow rate is high or low, and how NH3 storage amount to SCR catalyst 1 changes by it. 第３実施形態におけるＥＣＵ１１が実行する処理のフローチャートを示している。The flowchart of the process which ECU11 in 3rd Embodiment performs is shown. 排気流速Ｖｅｘに対する駆動周期Ｆのマップ５０１である。It is the map 501 of the driving period F with respect to the exhaust flow velocity Vex. 第３実施形態において、排気流速が高いか低いかで、尿素水添加がどのように変わるか、それによってＳＣＲ触媒１へのＮＨ３貯蔵量がどのように変わるかを説明する図である。In 3rd Embodiment, it is a figure explaining how urea water addition changes by the exhaust gas flow rate being high or low, and how NH3 storage amount to the SCR catalyst 1 changes by it.

（第１実施形態）
以下、本発明に係る内燃機関の排気浄化装置の第１実施形態を図面を参照しながら説明する。図１は、車両に搭載された排気浄化システム１００の構成図である。排気浄化システム１００は、内燃機関としてのディーゼルエンジン１０１から排出される排気中のＮＯｘを浄化する尿素ＳＣＲシステムとして構築されている。排気浄化システム１００では、エンジン１０１に排気管１３が接続されており、エンジン１０１からの排気はその排気管１３を通って車両外に排出されるようになっている。排気管１３には、排気中のＮＯｘを選択的に還元するＳＣＲ触媒１（ＮＯｘ選択還元触媒）が設けられている。そのＳＣＲ触媒１は、後述する尿素水添加弁２から添加された尿素水（添加剤、還元剤）を加水分解によりアンモニア（ＮＨ３）に変換してそのアンモニアを貯蔵する。そして、ＳＣＲ触媒１は、貯蔵したアンモニア（ＮＨ３）と排気中のＮＯｘとを例えば下記式１、式２の反応を行わせることで、ＮＯｘを水や窒素に分解（浄化）する。
４ＮＯ＋４ＮＨ３＋Ｏ２→４Ｎ２＋６Ｈ２Ｏ ・・・（式１）
６ＮＯ２＋８ＮＨ３→７Ｎ２＋３Ｈ２Ｏ ・・・（式２） (First embodiment)
Hereinafter, a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram of an exhaust purification system 100 mounted on a vehicle. The exhaust purification system 100 is constructed as a urea SCR system that purifies NOx in exhaust discharged from a diesel engine 101 as an internal combustion engine. In the exhaust purification system 100, an exhaust pipe 13 is connected to the engine 101, and exhaust from the engine 101 is discharged outside the vehicle through the exhaust pipe 13. The exhaust pipe 13 is provided with an SCR catalyst 1 (NOx selective reduction catalyst) that selectively reduces NOx in the exhaust. The SCR catalyst 1 converts urea water (additive, reducing agent) added from a urea water addition valve 2 described later into ammonia (NH 3) by hydrolysis and stores the ammonia. Then, the SCR catalyst 1 decomposes (purifies) NOx into water or nitrogen by causing the stored ammonia (NH3) and NOx in the exhaust to react, for example, by the following formulas 1 and 2.
4NO + 4NH3 + O2 → 4N2 + 6H2O (Formula 1)
6NO2 + 8NH3 → 7N2 + 3H2O (Formula 2)

なお、ＳＣＲ触媒１は無尽蔵にアンモニアを貯蔵できるわけではなく、ＳＣＲ触媒１に貯蔵できるアンモニアの最大貯蔵量（最大ＮＨ３貯蔵量）は、図５に示すように、ＳＣＲ触媒１の温度（触媒温度）によって変化する。具体的には、触媒温度が高いほど最大ＮＨ３貯蔵量は低下する。   In addition, the SCR catalyst 1 cannot store ammonia inexhaustably, and the maximum storage amount of ammonia that can be stored in the SCR catalyst 1 (maximum NH3 storage amount) is the temperature of the SCR catalyst 1 (catalyst temperature) as shown in FIG. ). Specifically, the maximum NH3 storage amount decreases as the catalyst temperature increases.

排気管１３のＳＣＲ触媒１より上流側には尿素水を排気管１３内に添加する尿素水添加弁２が設けられている。その尿素水添加弁２は、エンジン１０１の筒内に燃料を噴射するインジェクタ（図示外）と同様の構造を有している。具体的には、尿素水添加弁２は、電磁ソレノイド等からなる駆動部と、尿素水を流通させる尿素水通路や先端噴出口を開閉するためのニードルを有する弁本部とを備えた電磁式開閉弁として構成されており、ＥＣＵ１１からの駆動信号に基づき開弁又は閉弁する。すなわち、駆動信号に基づき電磁ソレノイドが通電されると、その通電に伴いニードルが開弁方向に移動し、そのニードルの移動に伴い先端噴出口から尿素水が添加（噴射）される。   A urea water addition valve 2 for adding urea water into the exhaust pipe 13 is provided upstream of the SCR catalyst 1 in the exhaust pipe 13. The urea water addition valve 2 has the same structure as an injector (not shown) that injects fuel into the cylinder of the engine 101. Specifically, the urea water addition valve 2 is an electromagnetic opening / closing provided with a drive unit composed of an electromagnetic solenoid or the like, and a valve main unit having a needle for opening and closing a urea water passage through which urea water flows and a tip jet port. It is comprised as a valve and opens or closes based on the drive signal from ECU11. That is, when the electromagnetic solenoid is energized based on the drive signal, the needle moves in the valve opening direction along with the energization, and urea water is added (injected) from the tip ejection port as the needle moves.

尿素水添加弁２に対しては、尿素水タンク７から尿素水が逐次供給される。以下、尿素水供給系の構成について説明する。なお、以下の説明では便宜上、尿素水タンク７から尿素水添加弁２に対して尿素水が供給される場合を基準として、尿素水タンク７側を上流側、尿素水添加弁２側を下流側として記載する。   The urea water is sequentially supplied from the urea water tank 7 to the urea water addition valve 2. Hereinafter, the configuration of the urea water supply system will be described. In the following description, for convenience, the urea water tank 7 side is the upstream side and the urea water addition valve 2 side is the downstream side, based on the case where urea water is supplied from the urea water tank 7 to the urea water addition valve 2. It describes as.

尿素水タンク７は、給液キャップ付きの密閉容器にて構成されており、その内部に所定の規定濃度の尿素水が貯蔵されている。尿素水タンク７と尿素水添加弁２とは尿素水供給管１５により接続されており、尿素水供給管１５内に尿素水通路が形成されている。尿素水供給管１５のうち尿素水タンク７側の先端部には、尿素水を吸い込むための吸込口が形成されており、その吸込口が尿素水タンク７内に尿素水が貯留された状態において尿素水に浸漬した状態になっている。   The urea water tank 7 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined specified concentration is stored therein. The urea water tank 7 and the urea water addition valve 2 are connected by a urea water supply pipe 15, and a urea water passage is formed in the urea water supply pipe 15. A suction port for sucking urea water is formed at the end of the urea water supply pipe 15 on the urea water tank 7 side, and the suction port is in a state where urea water is stored in the urea water tank 7. It is in a state immersed in urea water.

尿素水供給管１５の途中には、尿素水ポンプ６が設けられている。尿素水ポンプ６は、ＥＣＵ１１からの駆動信号により回転駆動されるインライン式の電動ポンプである。本実施形態では、尿素水ポンプ６は尿素水タンク７内の尿素水に浸漬した状態で設けられているが、尿素水タンク７外に設けられたとしても良い。   A urea water pump 6 is provided in the middle of the urea water supply pipe 15. The urea water pump 6 is an in-line electric pump that is rotationally driven by a drive signal from the ECU 11. In this embodiment, the urea water pump 6 is provided so as to be immersed in the urea water in the urea water tank 7, but it may be provided outside the urea water tank 7.

尿素水供給管１５の途中には、尿素水を濾過する多孔質状の尿素水フィルタ３が設けられている。この尿素水フィルタ３によって尿素水内の異物が除去され、尿素水添加弁２や尿素水タンク７内に異物が入り込むのが抑制される。   In the middle of the urea water supply pipe 15, a porous urea water filter 3 for filtering the urea water is provided. Foreign substances in the urea water are removed by the urea water filter 3, and foreign substances are prevented from entering the urea water addition valve 2 and the urea water tank 7.

また、尿素水ポンプ６よりも下流側には、尿素水添加圧が所定の圧力となるように調整する尿素水圧レギュレータ５が設けられている。尿素水圧レギュレータ５にて圧力調整の結果、余剰となった尿素水は尿素水タンク７に戻される。また、尿素水供給管１５の途中には、尿素水供給管１５内の尿素水の圧力を検出する尿素水圧センサ４が設けられている。尿素水添加圧を尿素水圧レギュレータ５で機械的に制御する方法に代えて、尿素水圧センサ４の検出値に基づきＥＣＵ１１が尿素水ポンプ６の駆動を制御することで、尿素水添加圧を調整する方法を採用しても良い。   A urea water pressure regulator 5 that adjusts the urea water addition pressure to a predetermined pressure is provided downstream of the urea water pump 6. As a result of pressure adjustment by the urea water pressure regulator 5, surplus urea water is returned to the urea water tank 7. A urea water pressure sensor 4 that detects the pressure of the urea water in the urea water supply pipe 15 is provided in the middle of the urea water supply pipe 15. Instead of the method of mechanically controlling the urea water addition pressure with the urea water pressure regulator 5, the ECU 11 controls the drive of the urea water pump 6 based on the detected value of the urea water pressure sensor 4, thereby adjusting the urea water addition pressure. A method may be adopted.

排気管１３のＳＣＲ触媒１より上流側にはエンジン１０１からの排気流量を検出する排気流量センサ９が設けられている。なお、排気流量センサ９は、尿素水添加弁２よりも上流側に設けられている。また、排気管１３のＳＣＲ触媒１よりも上流側（尿素水添加弁２とＳＣＲ触媒１の間）には、ＳＣＲ触媒１の上流側の排気温度を検出する排気温センサ１２と、ＳＣＲ触媒１の上流側のＮＯｘ濃度を検出する上流側ＮＯｘセンサ８１とが設けられている。排気管１３のＳＣＲ触媒１よりも下流側には、ＳＣＲ触媒１の下流側のＮＯｘ濃度を検出する下流側ＮＯｘセンサ８２が設けられている。また、大気圧を検出する大気圧センサ１０が設けられている。各センサ９、１２、８１、８２、１０とＥＣＵ１１１とは接続されており、各センサ９、１２、８１、８２、１０の検出値はＥＣＵ１１に入力されるようになっている。   An exhaust flow rate sensor 9 for detecting the exhaust flow rate from the engine 101 is provided upstream of the SCR catalyst 1 in the exhaust pipe 13. The exhaust flow sensor 9 is provided on the upstream side of the urea water addition valve 2. Further, on the upstream side of the exhaust pipe 13 from the SCR catalyst 1 (between the urea water addition valve 2 and the SCR catalyst 1), an exhaust temperature sensor 12 for detecting the exhaust temperature upstream of the SCR catalyst 1, and the SCR catalyst 1 And an upstream NOx sensor 81 for detecting the upstream NOx concentration. A downstream NOx sensor 82 that detects the NOx concentration on the downstream side of the SCR catalyst 1 is provided downstream of the SCR catalyst 1 in the exhaust pipe 13. An atmospheric pressure sensor 10 that detects atmospheric pressure is provided. The sensors 9, 12, 81, 82, 10 and the ECU 111 are connected to each other, and the detection values of the sensors 9, 12, 81, 82, 10 are input to the ECU 11.

ＥＣＵ１１は、周知のマイクロコンピュータを備え、各種センサの検出値に基づいて尿素水添加弁２による排気管１３内への尿素水添加を制御する。また、ＥＣＵ１１はメモリ１１１を備え、そのメモリ１１１にはＥＣＵ１１が実行する処理に必要な各種データ（後述する各種マップなど）が記憶されている。なお、ＥＣＵ１１が本発明に係る「内燃機関の排気浄化装置」に相当する。以下、ＥＣＵ１１が実行する処理の詳細を説明する。図２はＥＣＵ１１が実行する処理のフローチャートを示している。図２の処理は例えばエンジン１０１の始動と同時に開始され、以後、エンジン１０１が停止するまで一定間隔で繰り返し実行される。   The ECU 11 includes a known microcomputer, and controls urea water addition into the exhaust pipe 13 by the urea water addition valve 2 based on detection values of various sensors. The ECU 11 includes a memory 111, and various data (such as various maps described later) necessary for processing executed by the ECU 11 are stored in the memory 111. The ECU 11 corresponds to an “exhaust gas purification device for an internal combustion engine” according to the present invention. Hereinafter, details of processing executed by the ECU 11 will be described. FIG. 2 shows a flowchart of processing executed by the ECU 11. The processing in FIG. 2 is started at the same time as the engine 101 is started, for example, and thereafter repeatedly executed at regular intervals until the engine 101 stops.

図２の処理が開始されると、先ず、排気温度Ｔｅｘ（℃）、大気圧Ｐａ（Ｐａ）及び排気流量Ｍｆ（ｋｇ／ｓ）を、排気温センサ１２、大気圧センサ１０、排気流量センサ９から取り込む（Ｓ１１）。本実施形態では、排気流量Ｍｆは、質量流量（ｋｇ／ｓ）として取り込んでいる。なお、排気流量センサ９の検出値の代わりに、エンジン１０１への空気吸入量を検出するエアフロメーター（図示外）の検出値で、排気流量を代用しても良い。   When the processing of FIG. 2 is started, first, the exhaust temperature Tex (° C.), the atmospheric pressure Pa (Pa), and the exhaust flow rate Mf (kg / s) are set to the exhaust temperature sensor 12, the atmospheric pressure sensor 10, and the exhaust flow rate sensor 9. (S11). In the present embodiment, the exhaust flow rate Mf is taken in as a mass flow rate (kg / s). Instead of the detection value of the exhaust flow sensor 9, the detection value of an air flow meter (not shown) that detects the amount of air sucked into the engine 101 may be used instead.

次いで、排気流速Ｖｅｘを算出する（Ｓ１２）。本実施形態では、排気流速Ｖｅｘとして、ＳＣＲ触媒１における排気の空間速度ＳＶを算出している（Ｓ１２）。排気の空間速度ＳＶの算出の考え方を説明すると、先ずＳＣＲ触媒１の上流の排気密度（ｋｇ／ｍ３）を算出する。排気密度は、例えばＳＣＲ触媒１の温度Ｔｃ（触媒温度）や排気の圧力を理想気体の状態方程式に代入して算出する。ここでは、触媒温度Ｔｃは排気温度Ｔｅｘで代用している。なお、排気温度Ｔｅｘに対する触媒温度Ｔｃの関係を示したマップを予め用意しておき、そのマップに基づき排気温度Ｔｅｘから触媒温度Ｔｃを算出しても良い。また、ＳＣＲ触媒１の前後差圧は無視して、ここではＳ１１で取り込んだ大気圧Ｐａを排気の圧力としている。排気密度を算出した後、Ｓ１１で取り込んだ排気流量Ｍｆ（ｋｇ／ｓ）を排気密度（ｋｇ／ｍ３）で除算して、排気の体積流量（ｍ３／ｓ）を算出する。そして、その体積流量（ｍ３／ｓ）をＳＣＲ触媒１の体積（ｍ３）で除算して、空間速度ＳＶ（１／ｓ）を算出する。なお、メモリ１１１には、ＳＣＲ触媒１の体積が予め記憶されている。 Next, the exhaust flow velocity Vex is calculated (S12). In the present embodiment, the exhaust space velocity SV in the SCR catalyst 1 is calculated as the exhaust flow velocity Vex (S12). Explaining the concept of calculating the exhaust space velocity SV, first, the exhaust density (kg / m 3 ) upstream of the SCR catalyst 1 is calculated. The exhaust density is calculated by, for example, substituting the temperature Tc (catalyst temperature) of the SCR catalyst 1 and the exhaust pressure into the ideal gas equation of state. Here, the exhaust gas temperature Tex is substituted for the catalyst temperature Tc. A map showing the relationship of the catalyst temperature Tc to the exhaust temperature Tex may be prepared in advance, and the catalyst temperature Tc may be calculated from the exhaust temperature Tex based on the map. Further, the differential pressure across the SCR catalyst 1 is ignored, and the atmospheric pressure Pa taken in S11 is used as the exhaust pressure here. After calculating the exhaust density, the exhaust flow rate Mf (kg / s) captured in S11 is divided by the exhaust density (kg / m 3 ) to calculate the exhaust volume flow rate (m 3 / s). Then, the volumetric flow rate (m 3 / s) is divided by the volume (m 3 ) of the SCR catalyst 1 to calculate the space velocity SV (1 / s). In the memory 111, the volume of the SCR catalyst 1 is stored in advance.

以上説明したように、空間速度ＳＶは排気流量Ｍｆ、大気圧Ｐａ及び触媒温度Ｔｃ（排気温度Ｔｅｘ）と相関がある。そこで、Ｓ１２では、図３に示すように、排気流量Ｍｆ、大気圧Ｐａ及び触媒温度Ｔｃをパラメータとした空間速度ＳＶの算出式ＳＶ（Ｍｆ、Ｐａ、Ｔｃ）をメモリ１１１に記憶しておく。そして、その算出式ＳＶ（Ｍｆ、Ｐａ、Ｔｃ）に、今回の排気流量Ｍｆ、大気圧Ｐａ及び触媒温度Ｔｃを代入して、空間速度ＳＶを算出すれば良い。又は、図４に示すように、触媒温度Ｔｃ、排気流量Ｍｆ及び大気圧Ｐａに対応する空間速度ＳＶのマップ２０１をメモリ１１１に記憶しておき、そのマップ２０１に基づいて空間速度ＳＶを算出するようにしても良い。なお、図４では、触媒温度Ｔｃごとに、排気流量Ｍｆ及び大気圧Ｐａに対する空間速度ＳＶのマップ２０１を設けた例を示している。   As described above, the space velocity SV is correlated with the exhaust gas flow rate Mf, the atmospheric pressure Pa, and the catalyst temperature Tc (exhaust temperature Tex). Therefore, in S12, as shown in FIG. 3, the calculation formula SV (Mf, Pa, Tc) of the space velocity SV using the exhaust gas flow rate Mf, the atmospheric pressure Pa, and the catalyst temperature Tc as parameters is stored in the memory 111. Then, the space velocity SV may be calculated by substituting the exhaust flow rate Mf, the atmospheric pressure Pa, and the catalyst temperature Tc of this time into the calculation formula SV (Mf, Pa, Tc). Alternatively, as shown in FIG. 4, a map 201 of the space velocity SV corresponding to the catalyst temperature Tc, the exhaust gas flow rate Mf, and the atmospheric pressure Pa is stored in the memory 111, and the space velocity SV is calculated based on the map 201. You may do it. FIG. 4 shows an example in which a map 201 of the space velocity SV with respect to the exhaust gas flow rate Mf and the atmospheric pressure Pa is provided for each catalyst temperature Tc.

図２の説明に戻り、Ｓ１２の後、現在の触媒温度Ｔｃにおける最大ＮＨ３貯蔵量を算出する（Ｓ１３）。具体的には、図５に示す触媒温度Ｔｃと最大ＮＨ３貯蔵量との関係を示したマップ２０３をメモリ１１１に記憶しておく。そして、そのマップ２０３に基づいて今回の最大ＮＨ３貯蔵量を算出する。なお、ここでは、Ｓ１１で取り込んだ排気温度Ｔｅｘを触媒温度Ｔｃに代用し、その排気温度Ｔｅｘに対する最大ＮＨ３貯蔵量ＳＴｍａｘ（Ｔｅｘ）を算出している。   Returning to FIG. 2, after S12, the maximum NH3 storage amount at the current catalyst temperature Tc is calculated (S13). Specifically, a map 203 showing the relationship between the catalyst temperature Tc and the maximum NH 3 storage amount shown in FIG. Based on the map 203, the current maximum NH3 storage amount is calculated. Here, the exhaust temperature Tex taken in S11 is substituted for the catalyst temperature Tc, and the maximum NH3 storage amount STmax (Tex) with respect to the exhaust temperature Tex is calculated.

次いで、ＳＣＲ触媒１に貯蔵するアンモニアの目標貯蔵量（目標ＮＨ３貯蔵量）ＳＴｔｇ（Ｔｅｘ）を算出する（Ｓ１４）。ここで、図６は、目標ＮＨ３貯蔵量の算出の考え方を説明するための図であり、詳細には、触媒温度に対する最大ＮＨ３貯蔵量のライン２０３（図５のマップ２０３と同じ）及び目標ＮＨ３貯蔵量のライン２０４を示している。ある触媒温度Ｔ１での最大ＮＨ３貯蔵量をＳＴｍａｘ（Ｔ１）としたとき、その貯蔵量ＳＴｍａｘ（Ｔ１）自体又は貯蔵量ＳＴｍａｘ（Ｔ１）に近い貯蔵量２０２を目標ＮＨ３貯蔵量に設定したとする。この場合、例えばエンジン１０１がアイドル状態から加速状態に移行したときのように、触媒温度（排気温度）が急激に上昇したときには、最大ＮＨ３貯蔵量が急激に低下する。その結果、最大ＮＨ３貯蔵量を超えた分のアンモニアがＳＣＲ触媒１から放出されてしまう（ＮＨ３スリップ）。   Next, a target storage amount (target NH3 storage amount) STtg (Tex) of ammonia stored in the SCR catalyst 1 is calculated (S14). Here, FIG. 6 is a diagram for explaining the concept of calculation of the target NH3 storage amount. Specifically, the line 203 of the maximum NH3 storage amount with respect to the catalyst temperature (same as the map 203 in FIG. 5) and the target NH3. A storage line 204 is shown. When the maximum NH3 storage amount at a certain catalyst temperature T1 is STmax (T1), it is assumed that the storage amount STmax (T1) itself or the storage amount 202 close to the storage amount STmax (T1) is set as the target NH3 storage amount. In this case, for example, when the catalyst temperature (exhaust temperature) increases abruptly, such as when the engine 101 shifts from the idle state to the acceleration state, the maximum NH3 storage amount rapidly decreases. As a result, ammonia in excess of the maximum NH3 storage amount is released from the SCR catalyst 1 (NH3 slip).

そこで、Ｓ１４では、触媒温度が急激に上昇したときにもＮＨ３スリップが発生しないように、最大ＮＨ３貯蔵量に対してある程度余裕を持った貯蔵量を、目標ＮＨ３貯蔵量に設定する。具体的には例えば、目標ＮＨ３貯蔵量は、最大ＮＨ３貯蔵量の６０％〜７０％の値に設定する。なお、実際は、最大ＮＨ３貯蔵量を超えた分のアンモニアの全部が無駄に放出されるわけではなく、放出されたアンモニアのうちのいくらかはＮＯｘの還元に消費される。その消費される分も見越して設定された触媒温度と目標ＮＨ３貯蔵量の関係が、ライン２０４である。Ｓ１４では、触媒温度と目標ＮＨ３貯蔵量の関係を示したマップ２０４（ライン）を予めメモリ１１１に記憶しておき、マップ２０４から（最大ＮＨ３貯蔵量の算出を経ないで）直接目標ＮＨ３貯蔵量を算出しても良い。この場合には、Ｓ１３の処理を省略できる。   Therefore, in S14, the storage amount having a certain margin with respect to the maximum NH3 storage amount is set as the target NH3 storage amount so that NH3 slip does not occur even when the catalyst temperature rapidly increases. Specifically, for example, the target NH3 storage amount is set to a value of 60% to 70% of the maximum NH3 storage amount. Actually, not all of the ammonia exceeding the maximum NH3 storage amount is wasted and some of the released ammonia is consumed for the reduction of NOx. The relationship between the catalyst temperature set in anticipation of the consumed amount and the target NH 3 storage amount is a line 204. In S14, a map 204 (line) showing the relationship between the catalyst temperature and the target NH3 storage amount is stored in the memory 111 in advance, and the target NH3 storage amount is directly calculated from the map 204 (without calculating the maximum NH3 storage amount). May be calculated. In this case, the process of S13 can be omitted.

Ｓ１４の後、ＳＣＲ触媒１に現在貯蔵されているアンモニアの貯蔵量を推定ＮＨ３貯蔵量ＳＴｒとして算出する（Ｓ１５）。具体的には例えば、エンジン１０１から排出されたＮＯｘ排出量を、例えばエンジン回転数及び燃料噴射量に対するＮＯｘ排出量のマップに基づき算出する。また、ＳＣＲ触媒１の上流側及び下流側に設けられたＮＯｘセンサ８１、８２からの検出値に基づいて、ＳＣＲ触媒１によるＮＯｘ浄化率を算出する。これらＮＯｘ排出量、ＮＯｘ浄化率から、ＳＣＲ触媒１で浄化されたＮＯｘ量（浄化ＮＯｘ量）を算出する。その浄化ＮＯｘ量からＳＣＲ触媒１で消費されたアンモニアの消費量を算出する。なお、浄化ＮＯｘ量とアンモニアの消費量とは相関があるので、その相関データを予めメモリ１１１に記憶しておき、その相関データに基づいてアンモニアの消費量を算出すれば良い。算出したアンモニアの消費量をこれまでの推定ＮＨ３貯蔵量から引くことで、現在の推定ＮＨ３貯蔵量を算出する。なお、推定ＮＨ３貯蔵量ＳＴｒの推定方法としては、上記の特許文献１（特許第３９５１７７４号公報）の方法など従来の各種方法を採用することができる。   After S14, the storage amount of ammonia currently stored in the SCR catalyst 1 is calculated as the estimated NH3 storage amount STr (S15). Specifically, for example, the NOx emission amount discharged from the engine 101 is calculated based on, for example, a map of the NOx emission amount with respect to the engine speed and the fuel injection amount. Further, the NOx purification rate by the SCR catalyst 1 is calculated based on the detected values from the NOx sensors 81 and 82 provided on the upstream side and the downstream side of the SCR catalyst 1. From the NOx emission amount and the NOx purification rate, the NOx amount purified by the SCR catalyst 1 (purified NOx amount) is calculated. The consumption amount of ammonia consumed by the SCR catalyst 1 is calculated from the purified NOx amount. Since the purified NOx amount and the ammonia consumption amount have a correlation, the correlation data may be stored in the memory 111 in advance, and the ammonia consumption amount may be calculated based on the correlation data. The current estimated NH3 storage amount is calculated by subtracting the calculated ammonia consumption from the estimated NH3 storage amount thus far. In addition, as a method for estimating the estimated NH 3 storage amount STr, various conventional methods such as the method described in Patent Document 1 (Japanese Patent No. 3951774) can be employed.

次に、目標ＮＨ３貯蔵量ＳＴｔｇと推定ＮＨ３貯蔵量ＳＴｒとの偏差ΔＳＴを算出する（Ｓ１６）。つまり、ＳＴｔｇ−ＳＴｒ＝ΔＳＴを計算する。次に、Ｓ１６で算出した偏差ΔＳＴに基づいて、尿素水添加弁２に添加させる尿素水の添加量（尿素水添加量）Ｑｕ（ΔＳＴ）を算出する（Ｓ１７）。なお、ＮＯｘの還元として、ＳＣＲ触媒１に貯蔵されたアンモニアで行われる還元と、尿素水添加弁２から添加された尿素水（アンモニア）により直接行われる還元（以下、直接還元という）とがある。それら２つの還元の比率は触媒温度など各種条件によって変化する。Ｓ１７では、直接還元で消費される尿素水の量（２つの還元の比率）を考慮して、目標ＮＨ３貯蔵量ＳＴｔｇを満足するように尿素水添加量Ｑｕを算出する。具体的には、偏差ΔＳＴ、触媒温度などの各種条件をパラメータとした尿素水添加量Ｑｕの算出式を予めメモリ１１１に持っておき、その算出式に基づき尿素水添加量Ｑｕを算出する。   Next, a deviation ΔST between the target NH3 storage amount STtg and the estimated NH3 storage amount STr is calculated (S16). That is, STtg−STr = ΔST is calculated. Next, based on the deviation ΔST calculated in S16, the urea water addition amount (urea water addition amount) Qu (ΔST) to be added to the urea water addition valve 2 is calculated (S17). Note that the reduction of NOx includes a reduction performed with ammonia stored in the SCR catalyst 1 and a reduction performed directly with urea water (ammonia) added from the urea water addition valve 2 (hereinafter referred to as direct reduction). . The ratio of these two reductions varies depending on various conditions such as the catalyst temperature. In S17, the urea water addition amount Qu is calculated so as to satisfy the target NH3 storage amount STtg in consideration of the amount of urea water consumed by the direct reduction (the ratio of the two reductions). Specifically, a calculation formula for the urea water addition amount Qu using various conditions such as deviation ΔST and catalyst temperature as parameters is stored in the memory 111 in advance, and the urea water addition amount Qu is calculated based on the calculation formula.

次に、Ｓ１７で算出した尿素水添加量Ｑｕの分の尿素水を尿素水添加弁２に添加させるときの、尿素水の添加回数（分割回数）Ｎを算出する（Ｓ１８）。具体的には、Ｓ１２で算出した排気流速Ｖｅｘ（空間速度ＳＶ）が低いほど大きい分割回数Ｎを算出する。より具体的には、例えば図７〜図９に示すように、排気流速Ｖｅｘに対する分割回数Ｎのマップ３０１（図７）、３０２（図８）、３０３（図９）を予めメモリ１１１に記憶しておき、それらマップ３０１、３０２、３０３のいずれかに基づいて分割回数Ｎを算出する。図７は、閾値Ｖｔｈ以上の排気流速Ｖｅｘのときには分割回数Ｎ＝１（添加を分割しないで１回で添加すること）とし、閾値Ｖｔｈ以下の排気流速Ｖｅｘのときには排気流速Ｖｅｘが低くなるにしたがって連続的に分割回数Ｎを大きくしていくマップ３０１を示している。このマップ３０１に基づき分割回数Ｎを算出することで、排気流速に応じたきめ細かい尿素水添加が可能となる。   Next, the number of times of urea water addition (number of divisions) N when adding urea water corresponding to the urea water addition amount Qu calculated in S17 to the urea water addition valve 2 is calculated (S18). Specifically, the lower the exhaust flow velocity Vex (space velocity SV) calculated in S12, the larger the division number N is calculated. More specifically, for example, as shown in FIGS. 7 to 9, maps 301 (FIG. 7), 302 (FIG. 8), and 303 (FIG. 9) of the division number N with respect to the exhaust flow velocity Vex are stored in the memory 111 in advance. In addition, the division number N is calculated based on one of the maps 301, 302, and 303. FIG. 7 shows that when the exhaust flow velocity Vex is equal to or higher than the threshold Vth, the number of divisions is N = 1 (addition is performed once without dividing), and when the exhaust flow velocity Vex is lower than the threshold Vth, the exhaust flow velocity Vex decreases. A map 301 in which the number of divisions N is continuously increased is shown. By calculating the number N of divisions based on this map 301, it is possible to add fine urea water according to the exhaust flow rate.

また、図８は、閾値Ｖｔｈ以上の排気流速Ｖｅｘのときには分割回数Ｎ＝１とし、閾値Ｖｔｈ以下の排気流速Ｖｅｘのときには排気流速Ｖｅｘが低くなるにしたがって段階的に分割回数Ｎを大きくしていくマップ３０２を示している。なお、添加した尿素水が排気管１３の壁面に付着しないでＳＣＲ触媒１に到達できるのであれば、マップ３０２の隣り合う２つの分割回数Ｎの間隔ΔＮや、排気流速Ｖｅｘの間隔ΔＶｅｘは適宜に設定することができる。このマップ３０２に基づき分割回数Ｎを算出することで、排気流速Ｖｅｘが変わる度に頻繁に分割回数Ｎを変更しなくてもすむ。   FIG. 8 shows that the number of divisions N = 1 when the exhaust flow velocity Vex is equal to or higher than the threshold Vth, and the number of divisions N is increased stepwise as the exhaust flow velocity Vex decreases when the exhaust flow velocity Vex is equal to or lower than the threshold Vth. A map 302 is shown. If the added urea water can reach the SCR catalyst 1 without adhering to the wall surface of the exhaust pipe 13, the interval ΔN between two adjacent divisions N of the map 302 and the interval ΔVex of the exhaust flow velocity Vex are appropriately set. Can be set. By calculating the division number N based on the map 302, it is not necessary to frequently change the division number N every time the exhaust flow velocity Vex changes.

また、図９は、排気流速Ｖｅｘが閾値Ｖｔｈ以上の高いときと、閾値Ｖｔｈ以下の低いときとで択一的に分割回数Ｎを切り替えるマップ３０３を示している。マップ３０３では、排気流速Ｖｅｘが閾値Ｖｔｈ以上のときには分割回数Ｎ＝Ｎ１（例えばＮ１＝１）、閾値Ｖｔｈ以下のときには分割回数Ｎ＝Ｎ２（Ｎ２＞Ｎ１）となっている。このマップ３０３に基づき分割回数Ｎを算出することで、排気流速Ｖｅｘが高いか低いかを択一的に判定するだけでよいので、分割回数Ｎの算出処理が簡単になる。   FIG. 9 shows a map 303 that selectively switches the division number N between when the exhaust flow velocity Vex is higher than the threshold value Vth and when it is lower than the threshold value Vth. In the map 303, the division number N = N1 (for example, N1 = 1) when the exhaust flow velocity Vex is equal to or higher than the threshold value Vth, and the division number N = N2 (N2> N1) when the exhaust flow rate Vex is equal to or lower than the threshold value Vth. By calculating the number of divisions N based on this map 303, it is only necessary to alternatively determine whether the exhaust flow velocity Vex is high or low, so that the calculation process of the number of divisions N is simplified.

図２の説明に戻り、Ｓ１８の後、Ｓ１７で算出した尿素水添加量Ｑｕ（本発明の総添加量に相当）の分の尿素水が排気管１３内に添加されるように、尿素水添加弁２を駆動制御する（Ｓ１９）。これによって、尿素水添加弁２から添加された尿素水がＳＣＲ触媒１にてアンモニアに変換され、そのアンモニアがＳＣＲ触媒１に貯蔵されていく。そして、ＳＣＲ触媒１でのアンモニア貯蔵量をＳ１４で算出した目標ＮＨ３貯蔵量にできる。また、Ｓ１９では、分割回数Ｎ＝１のときには、尿素水添加量Ｑｕの分の尿素水を１回で添加し、分割回数Ｎ≧２のときには、尿素水添加量Ｑｕを分割回数Ｎで等分して複数回Ｎに分けて尿素水を添加する。ここで、図１０は、排気流速が高いか低いかで、尿素水添加がどのように変わるか、それによってＳＣＲ触媒１へのＮＨ３貯蔵量がどのように変わるかを説明する図である。図１０（Ａ）は排気流速が高いときを、図１０（Ｂ）は排気流速が低いときを示している。詳細には、図１０は、尿素水添加後のＮＨ３貯蔵量の時間変化を示しており、図１０（Ａ）、（Ｂ）それぞれには、目標ＮＨ３貯蔵量の時間変化２１と、実際のＮＨ３貯蔵量（推定ＮＨ３貯蔵量）の時間変化２２、２４とを示している。また、図１０（Ａ）、（Ｂ）それぞれには、時間ｔの経過に対する尿素水添加の回数及び１回当たりの添加量をパルス２３、２５で図示している。パルス２３、２５の個数が尿素水添加の回数を示しており、パルス２３、２５の大きさが１回当たりの添加量を示している。なお、図１０（Ａ）では、尿素水を１回で添加する例を示している。図１０（Ｂ）では、尿素水を５回に分けて添加する例を示している。   Returning to the description of FIG. 2, after S18, urea water addition is performed so that the urea water addition amount Qu (corresponding to the total addition amount of the present invention) calculated in S17 is added into the exhaust pipe 13. The valve 2 is driven and controlled (S19). As a result, the urea water added from the urea water addition valve 2 is converted into ammonia by the SCR catalyst 1, and the ammonia is stored in the SCR catalyst 1. Then, the ammonia storage amount in the SCR catalyst 1 can be made the target NH3 storage amount calculated in S14. In S19, when the number of times of division N = 1, urea water corresponding to the amount of added urea water Qu is added once, and when the number of times of division N ≧ 2, the amount of urea water added Qu is equally divided by the number of times of division N. Then, urea water is added in a plurality of N times. Here, FIG. 10 is a diagram for explaining how the urea water addition changes depending on whether the exhaust gas flow rate is high or low, and how the NH3 storage amount in the SCR catalyst 1 changes accordingly. FIG. 10A shows when the exhaust flow rate is high, and FIG. 10B shows when the exhaust flow rate is low. Specifically, FIG. 10 shows the time change of the NH3 storage amount after the urea water addition, and FIGS. 10A and 10B respectively show the time change 21 of the target NH3 storage amount and the actual NH3 amount. Time changes 22 and 24 of the storage amount (estimated NH 3 storage amount) are shown. 10A and 10B respectively show the number of urea water additions and the addition amount per pulse with pulses 23 and 25 over time t. The number of pulses 23 and 25 indicates the number of times of urea water addition, and the magnitude of the pulses 23 and 25 indicates the amount of addition per one time. Note that FIG. 10A shows an example in which urea water is added once. FIG. 10B shows an example in which urea water is added in five portions.

図１０（Ａ）に示すように、排気流速が高いときには、図１０（Ｂ）の排気流速が低いときに比べて添加回数Ｎ（図１０（Ａ）では１回）が少なく１回当たりの添加量が多いので、推定ＮＨ３貯蔵量２２を迅速に（短時間で）目標ＮＨ３貯蔵量２１に近づけることができる。これに対し、図１０（Ｂ）に示すように、排気流速が低いときには、図１０（Ａ）の排気流速が高いときに比べて添加回数Ｎ（図１０（Ｂ）では５回）が多く１回当たりの添加量が少ないので、添加された尿素水が排気管１３の壁面に付着してしまうのを防止でき、尿素水をＳＣＲ触媒１に効率良く到達させることができる。ただし、図１０（Ｂ）では、図１０（Ａ）に比べて、推定ＮＨ３貯蔵量２４が目標ＮＨ３貯蔵量２１に近づくのに時間が掛かっている。なお、Ｓ１９では、尿素水を複数回に分けて添加するときの添加間隔Δｔ（図１０（Ｂ）参照）は例えば分割回数Ｎにかかわらず一定となっている。Ｓ１９の後、図２のフローチャートの処理を終了する。   As shown in FIG. 10 (A), when the exhaust gas flow rate is high, the number of additions N (one time in FIG. 10 (A)) is smaller than when the exhaust gas flow rate is low in FIG. 10 (B). Since the amount is large, the estimated NH 3 storage amount 22 can be brought close to the target NH 3 storage amount 21 quickly (in a short time). On the other hand, as shown in FIG. 10 (B), when the exhaust gas flow rate is low, the number of times of addition N (5 times in FIG. 10 (B)) is larger than when the exhaust gas flow rate in FIG. Since the addition amount per rotation is small, it is possible to prevent the added urea water from adhering to the wall surface of the exhaust pipe 13 and to make the urea water reach the SCR catalyst 1 efficiently. However, in FIG. 10B, it takes time for the estimated NH 3 storage amount 24 to approach the target NH 3 storage amount 21 as compared with FIG. 10A. In S19, the addition interval Δt (see FIG. 10B) when urea water is added in a plurality of times is constant regardless of the division number N, for example. After S19, the process of the flowchart of FIG.

以上説明したように、本実施形態では、触媒温度に応じた目標ＮＨ３貯蔵量となるように尿素水添加が行われるので、触媒温度が変わったとしてもＮＯｘ浄化率が低下するのを防止できるとともに、ＮＨ３スリップも防止できる。また、尿素水添加の際に、排気流速が低いときには、尿素水の添加回数を増やして１回当たりの添加量を少なくしているので、排気管壁面に付着する尿素水を抑制できる。その結果、ＳＣＲ触媒に貯蔵されているアンモニアの貯蔵量（推定ＮＨ３貯蔵量）を推定するときの誤差を小さくできるので、高いＮＯｘ浄化率を維持することができる。   As described above, in the present embodiment, urea water is added so as to achieve the target NH3 storage amount corresponding to the catalyst temperature, so that it is possible to prevent the NOx purification rate from decreasing even if the catalyst temperature changes. NH3 slip can also be prevented. In addition, when the urea water is added, when the exhaust gas flow rate is low, the urea water added to the exhaust pipe wall surface can be suppressed because the number of urea water additions is increased to reduce the addition amount per time. As a result, an error in estimating the amount of ammonia stored in the SCR catalyst (estimated NH3 storage amount) can be reduced, and a high NOx purification rate can be maintained.

（第２実施形態）
次に、本発明に係る内燃機関の排気浄化装置の第２実施形態を第１実施形態と異なる部分を中心にして説明する。この第２実施形態では、尿素水添加弁による尿素水の添加方法が第１実施形態と異なっており、具体的には、尿素水添加弁をデューティ制御することで、尿素水添加弁に駆動デューティに応じた尿素水添加を行わせている。 (Second Embodiment)
Next, a second embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with a focus on differences from the first embodiment. In the second embodiment, the urea water addition method using the urea water addition valve is different from that in the first embodiment. Specifically, the urea water addition valve is controlled by duty control so that the urea water addition valve has a drive duty. The urea water addition according to is performed.

本実施形態の排気浄化システムの構成は、図１に示す第１実施形態の構成と同じである。図１１は、ＥＣＵ１１が実行する処理のフローチャートを示している。図１１において、図２と同じ処理には同一符号を付している。図１１では、図２の処理に比べて、Ｓ１８１、Ｓ１９１の処理が異なっている。すなわち、Ｓ１７の後、尿素水添加弁２を駆動するときの駆動デューティＤ（添加周期Ｔに対する駆動時間τ、Ｄ＝τ／Ｔ）を算出する（Ｓ１８１）。具体的には、Ｓ１２で算出した排気流速Ｖｅｘ（空間速度ＳＶ）が低いほど小さい駆動デューティＤを算出する。より具体的には、例えば図１２に示すように、排気流速Ｖｅｘに対する駆動デューティＤのマップ４０１を予めメモリ１１１に記憶しておき、そのマップ４０１に基づいて駆動デューティＤを算出する。図１２では、排気流速Ｖｅｘが低くなるにしたがって連続的に駆動デューティＤを小さくしていくマップ４０１を示している。なお、Ｓ１８１では、第１実施形態の図８、図９と同様に、排気流速Ｖｅｘが低くなるにしたがって段階的に駆動デューティを小さくしても良いし、排気流速Ｖｅｘが高いときと低いときとで択一的に駆動デューティを切り替えても良い。   The configuration of the exhaust purification system of this embodiment is the same as that of the first embodiment shown in FIG. FIG. 11 shows a flowchart of processing executed by the ECU 11. In FIG. 11, the same processes as those in FIG. In FIG. 11, the processing of S181 and S191 is different from the processing of FIG. That is, after S17, a drive duty D (drive time τ with respect to the addition period T, D = τ / T) when the urea water addition valve 2 is driven is calculated (S181). Specifically, the smaller the exhaust flow velocity Vex (space velocity SV) calculated in S12, the smaller the drive duty D is calculated. More specifically, for example, as shown in FIG. 12, a map 401 of the drive duty D with respect to the exhaust flow velocity Vex is stored in the memory 111 in advance, and the drive duty D is calculated based on the map 401. FIG. 12 shows a map 401 in which the drive duty D is continuously reduced as the exhaust flow velocity Vex decreases. In S181, as in FIGS. 8 and 9 of the first embodiment, the drive duty may be reduced stepwise as the exhaust flow velocity Vex decreases, and when the exhaust flow velocity Vex is high and low. Alternatively, the drive duty may be switched.

Ｓ１８１の後、Ｓ１７で算出した尿素水添加量Ｑｕの分の尿素水が排気管１３内に添加されるように、尿素水添加弁２を駆動制御する（Ｓ１９１）。具体的には、Ｓ１８１で算出した駆動デューティＤの駆動パルスを尿素水添加弁２に供給する。ここで、図１３は、図１０と同様の図であり、尿素水添加後のＮＨ３貯蔵量の時間変化を示している。図１３（Ａ）は排気流速が高いときを、図１３（Ｂ）は排気流速が低いときを示している。また、図１３（Ａ）、（Ｂ）それぞれには、尿素水添加弁２に供給する駆動パルスのパルス列２６、２７を図示している。なお、図１３（Ａ）のパルス列２６における周期Ｔ（添加周期）と図１３（Ｂ）のパルス列２７における周期Ｔは同じである。また、図１３（Ａ）の駆動時間τ１よりも図１３（Ｂ）の駆動時間τ２のほうが小さくなっている。つまり、図１３（Ａ）の駆動デューティよりも図１３（Ｂ）の駆動デューティのほうが小さくなっている。なお、尿素水添加弁２から添加される尿素水の総添加量は、図１３（Ａ）と図１３（Ｂ）とで同じとなっている。   After S181, the urea water addition valve 2 is driven and controlled so that urea water corresponding to the urea water addition amount Qu calculated in S17 is added into the exhaust pipe 13 (S191). Specifically, the drive pulse with the drive duty D calculated in S181 is supplied to the urea water addition valve 2. Here, FIG. 13 is the same diagram as FIG. 10 and shows the time change of the NH 3 storage amount after the addition of urea water. FIG. 13A shows when the exhaust flow rate is high, and FIG. 13B shows when the exhaust flow rate is low. FIGS. 13A and 13B respectively show pulse trains 26 and 27 of drive pulses supplied to the urea water addition valve 2. Note that the period T (addition period) in the pulse train 26 in FIG. 13A and the period T in the pulse train 27 in FIG. 13B are the same. Further, the drive time τ2 in FIG. 13B is shorter than the drive time τ1 in FIG. That is, the drive duty in FIG. 13B is smaller than the drive duty in FIG. Note that the total amount of urea water added from the urea water addition valve 2 is the same in FIG. 13A and FIG.

図１３（Ａ）に示すように、排気流速が高いときには、図１３（Ｂ）の排気流速が低いときに比べて駆動デューティが大きく単位時間当たりの添加量が多くなるので、推定ＮＨ３貯蔵量２２を迅速に目標ＮＨ３貯蔵量２１に近づけることができる。これに対し、図１３（Ｂ）に示すように、排気流速が低いときには、図１３（Ａ）の排気流速が高いときに比べて駆動デューティが小さく単位時間当たりの添加量が少なくなるので、添加された尿素水が排気管１３の壁面に付着してしまうのを防止でき、尿素水をＳＣＲ触媒１に効率良く到達させることができる。ただし、図１３（Ｂ）では、図１３（Ａ）に比べて、推定ＮＨ３貯蔵量２４が目標ＮＨ３貯蔵量２１に近づくのに時間が掛かっている。Ｓ１９１の後、図１１のフローチャートの処理を終了する。   As shown in FIG. 13A, when the exhaust gas flow rate is high, the drive duty is large and the amount of addition per unit time is larger than when the exhaust gas flow rate is low in FIG. Can be quickly brought close to the target NH 3 storage amount 21. On the other hand, as shown in FIG. 13B, when the exhaust flow rate is low, the drive duty is small and the amount of addition per unit time is smaller than when the exhaust flow rate is high in FIG. The urea water thus made can be prevented from adhering to the wall surface of the exhaust pipe 13, and the urea water can efficiently reach the SCR catalyst 1. However, in FIG. 13B, it takes time for the estimated NH 3 storage amount 24 to approach the target NH 3 storage amount 21 as compared with FIG. 13A. After S191, the process of the flowchart of FIG.

以上説明したように、尿素水添加弁をデューティ制御する場合にも本発明を適用でき、第１実施形態と同様の効果を得ることができる。   As described above, the present invention can be applied to the case where the urea water addition valve is duty-controlled, and the same effect as that of the first embodiment can be obtained.

（第３実施形態）
次に、本発明に係る内燃機関の排気浄化装置の第３実施形態を第１、第２実施形態と異なる部分を中心にして説明する。この第３実施形態では、尿素水添加弁による尿素水の添加方法が第１、第２実施形態と異なっており、具体的には、尿素水添加弁を周期的に駆動する周波数制御をすることで、尿素水添加弁に駆動周期（駆動周波数）に応じた尿素水添加を行わせている。この周波数制御では、駆動周期（駆動周波数）にかかわらず１回の駆動で添加される尿素水の量は一定となっている。 (Third embodiment)
Next, a description will be given of a third embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention, focusing on portions different from the first and second embodiments. In the third embodiment, the urea water addition method using the urea water addition valve is different from those in the first and second embodiments. Specifically, the frequency control for periodically driving the urea water addition valve is performed. Therefore, the urea water addition valve is caused to add urea water according to the driving cycle (driving frequency). In this frequency control, the amount of urea water added by one driving is constant regardless of the driving cycle (driving frequency).

本実施形態の排気浄化システムの構成は、図１に示す第１実施形態の構成と同じである。図１４は、ＥＣＵ１１が実行する処理のフローチャートを示している。図１１において、図２と同じ処理には同一符号を付している。図１４では、図２の処理に比べて、Ｓ１８２、Ｓ１９２の処理が異なっている。すなわち、Ｓ１７の後、尿素水添加弁２を駆動するときの駆動周期Ｆを算出する（Ｓ１８２）。具体的には、Ｓ１２で算出した排気流速Ｖｅｘ（空間速度ＳＶ）が低いほど長い駆動周期Ｆを算出する。駆動周波数（駆動周期Ｆの逆数）で考えると、排気流速Ｖｅｘ（空間速度ＳＶ）が低いほど小さい駆動周波数を算出する。より具体的には、例えば図１５に示すように、排気流速Ｖｅｘに対する駆動周期Ｆのマップ５０１を予めメモリ１１１に記憶しておき、そのマップ５０１に基づいて駆動周期Ｆを算出する。図１５では、排気流速Ｖｅｘが低くなるにしたがって連続的に駆動周期Ｆを長くしていくマップ５０１を示している。なお、Ｓ１８２では、第１実施形態の図８、図９と同様に、排気流速Ｖｅｘが低くなるにしたがって段階的に駆動周期を長くしても良いし、排気流速Ｖｅｘが高いときと低いときとで択一的に駆動周期を切り替えても良い。   The configuration of the exhaust purification system of this embodiment is the same as that of the first embodiment shown in FIG. FIG. 14 shows a flowchart of processing executed by the ECU 11. In FIG. 11, the same processes as those in FIG. In FIG. 14, the processes of S182 and S192 are different from those of FIG. That is, after S17, the driving cycle F when the urea water addition valve 2 is driven is calculated (S182). Specifically, a longer drive cycle F is calculated as the exhaust flow velocity Vex (space velocity SV) calculated in S12 is lower. Considering the drive frequency (reciprocal of the drive cycle F), the lower the exhaust flow velocity Vex (space velocity SV), the smaller the drive frequency is calculated. More specifically, for example, as shown in FIG. 15, a map 501 of the driving cycle F with respect to the exhaust flow velocity Vex is stored in the memory 111 in advance, and the driving cycle F is calculated based on the map 501. FIG. 15 shows a map 501 in which the drive cycle F is continuously increased as the exhaust flow velocity Vex decreases. In S182, as in FIGS. 8 and 9 of the first embodiment, the drive cycle may be increased stepwise as the exhaust flow velocity Vex decreases, and when the exhaust flow velocity Vex is high and low. Alternatively, the driving cycle may be switched.

Ｓ１８２の後、Ｓ１７で算出した尿素水添加量Ｑｕの分の尿素水が排気管１３内に添加されるように、尿素水添加弁２を駆動制御する（Ｓ１９２）。具体的には、Ｓ１８２で算出した駆動周期Ｆの駆動パルスを尿素水添加弁２に供給する。ここで、図１６は、図１０と同様の図であり、尿素水添加後のＮＨ３貯蔵量の時間変化を示している。図１６（Ａ）は排気流速が高いときを、図１６（Ｂ）は排気流速が低いときを示している。また、図１６（Ａ）、（Ｂ）それぞれには、尿素水添加弁２に供給する駆動パルスのパルス列２８、２９を図示している。パルス列２８、２９における各駆動パルスのパルス幅は一定となっている。つまり、各駆動パルスで添加される尿素水の量は各駆動パルス間で一定となっている。また、図１６（Ａ）の駆動周期Ｆ１よりも図１６（Ｂ）の駆動周期Ｆ２のほうが長くなっている。   After S182, the urea water addition valve 2 is driven and controlled so that the urea water corresponding to the urea water addition amount Qu calculated in S17 is added into the exhaust pipe 13 (S192). Specifically, the drive pulse of the drive cycle F calculated in S182 is supplied to the urea water addition valve 2. Here, FIG. 16 is the same diagram as FIG. 10, and shows the time change of the NH 3 storage amount after the addition of urea water. FIG. 16A shows when the exhaust flow rate is high, and FIG. 16B shows when the exhaust flow rate is low. 16A and 16B show pulse trains 28 and 29 of drive pulses supplied to the urea water addition valve 2, respectively. The pulse width of each drive pulse in the pulse trains 28 and 29 is constant. That is, the amount of urea water added with each drive pulse is constant between the drive pulses. In addition, the driving cycle F2 in FIG. 16B is longer than the driving cycle F1 in FIG.

図１６（Ａ）に示すように、排気流速が高いときには、図１６（Ｂ）の排気流速が低いときに比べて駆動周期が短いので、推定ＮＨ３貯蔵量２２を迅速に目標ＮＨ３貯蔵量２１に近づけることができる。これに対し、図１６（Ｂ）に示すように、排気流速が低いときには、図１６（Ａ）の排気流速が高いときに比べて駆動周期が長く単位時間当たりの添加量が少なくなるので、添加された尿素水が排気管１３の壁面に付着してしまうのを防止でき、尿素水をＳＣＲ触媒１に効率良く到達させることができる。ただし、図１６（Ｂ）では、図１６（Ａ）に比べて、推定ＮＨ３貯蔵量２４が目標ＮＨ３貯蔵量２１に近づくのに時間が掛かっている。Ｓ１９２の後、図１４のフローチャートの処理を終了する。   As shown in FIG. 16 (A), when the exhaust gas flow rate is high, the drive cycle is shorter than when the exhaust gas flow rate is low in FIG. 16 (B), so the estimated NH3 storage amount 22 is quickly changed to the target NH3 storage amount 21. You can get closer. On the other hand, as shown in FIG. 16B, when the exhaust flow rate is low, the drive cycle is longer and the addition amount per unit time is smaller than when the exhaust flow rate is high in FIG. The urea water thus made can be prevented from adhering to the wall surface of the exhaust pipe 13, and the urea water can efficiently reach the SCR catalyst 1. However, in FIG. 16B, it takes time for the estimated NH 3 storage amount 24 to approach the target NH 3 storage amount 21 as compared to FIG. 16A. After S192, the process of the flowchart of FIG.

以上説明したように、尿素水添加弁を周波数制御する場合にも本発明を適用でき、第１、第２実施形態と同様の効果を得ることができる。   As described above, the present invention can also be applied when the frequency of the urea water addition valve is controlled, and the same effects as those of the first and second embodiments can be obtained.

なお、本発明の内燃機関の排気浄化装置は上記実施形態に限定されるものではなく、特許請求の範囲の記載を逸脱しない限度で種々の変更が可能である。例えば、上記第２実施形態のデューティ制御と第３実施形態の周波数制御とを併用したシステムにも本発明を適用できる。この場合には例えば、排気流速が低いときには、排気流速が高いときよりも、尿素水添加弁の駆動デューティを小さくするとともに、駆動周期を長くする。また、ガソリンエンジン、特にリーンバーンエンジン用の尿素ＳＣＲシステムシステムに本発明を適用しても良い。また、尿素水以外の還元剤（例えば、アンモニア含有の水溶液）を用いる排気浄化システムに本発明を適用しても良い。   The exhaust emission control device for an internal combustion engine of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the claims. For example, the present invention can also be applied to a system using both the duty control of the second embodiment and the frequency control of the third embodiment. In this case, for example, when the exhaust gas flow rate is low, the drive duty of the urea water addition valve is made smaller and the drive cycle is made longer than when the exhaust gas flow rate is high. Further, the present invention may be applied to a urea SCR system system for a gasoline engine, particularly a lean burn engine. Further, the present invention may be applied to an exhaust purification system that uses a reducing agent other than urea water (for example, an aqueous solution containing ammonia).

１ ＳＣＲ触媒
２ 尿素水添加弁
１１ ＥＣＵ
１３ 排気管
１００ 排気浄化システム（尿素ＳＣＲシステム）
１０１ ディーゼルエンジン 1 SCR catalyst 2 Urea water addition valve 11 ECU
13 Exhaust pipe 100 Exhaust gas purification system (urea SCR system)
101 diesel engine

Claims (8)

内燃機関（１０１）の排気管（１３）に設けられ、前記排気管に所定の添加剤を添加する添加手段（２）と、
前記排気管の前記添加手段より下流側に設けられ、前記添加手段で添加された添加剤を貯蔵しその添加剤で排気中の所定の有害成分を浄化する触媒（１）とを備えた排気浄化システム（１００）に備えられ、
前記添加手段で添加すべき添加剤の添加量を決定する添加量決定手段（Ｓ１７）と、
その添加量決定手段が決定した添加量である総添加量ぶんの添加剤が前記排気管に添加されるように前記添加手段を制御する添加制御手段（Ｓ１８、Ｓ１９、Ｓ１８１、Ｓ１９１、Ｓ１８２、Ｓ１９２）と、
排気流速を算出する流速算出手段（Ｓ１２）とを備え、
前記添加制御手段は、前記流速算出手段が算出した排気流速が低いほど単位時間当たりの添加剤の添加量が小さくなるように前記添加手段を制御することを特徴とする内燃機関の排気浄化装置（１１）。 An adding means (2) provided in the exhaust pipe (13) of the internal combustion engine (101) for adding a predetermined additive to the exhaust pipe;
Exhaust gas purification provided with a catalyst (1) provided downstream of the addition means of the exhaust pipe and storing the additive added by the addition means and purifying predetermined harmful components in the exhaust gas with the additive Provided in the system (100),
An addition amount determining means (S17) for determining an addition amount of the additive to be added by the adding means;
Addition control means (S18, S19, S181, S191, S182, S192) for controlling the addition means so that a total addition amount of additive which is the addition amount determined by the addition amount determination means is added to the exhaust pipe. )When,
A flow rate calculation means (S12) for calculating an exhaust flow rate,
The addition control means controls the addition means so that the addition amount of the additive per unit time becomes smaller as the exhaust flow velocity calculated by the flow velocity calculation means is lower. 11). 前記添加制御手段（Ｓ１８、Ｓ１９）は、前記総添加量ぶんの添加剤を１回で又は複数回に分割して前記排気管に添加し、前記排気流速が低いほど前記総添加量ぶんの添加剤の分割回数を大きくすることを特徴とする請求項１に記載の内燃機関の排気浄化装置。   The addition control means (S18, S19) adds the total added amount of additive to the exhaust pipe at one time or divided into a plurality of times, and the lower the exhaust flow rate, the more the added amount of the added amount is added. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the number of times the agent is divided is increased. 前記添加制御手段（Ｓ１８１、Ｓ１９１）は、前記添加手段をデューティ制御することで前記添加手段に前記添加剤の添加を行わせ、前記排気流速が低いほど前記添加手段の駆動デューティを小さくすることを特徴とする請求項１に記載の内燃機関の排気浄化装置。   The addition control means (S181, S191) causes the addition means to add the additive by duty-controlling the addition means, and decreases the drive duty of the addition means as the exhaust gas flow rate decreases. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is an internal combustion engine. 前記添加制御手段（Ｓ１８２、Ｓ１９２）は、前記添加手段を周期的に駆動する周波数制御により前記添加手段に前記添加剤の添加を行わせ、前記排気流速が低いほど前記添加手段の駆動周期を長くすることを特徴とする請求項１に記載の内燃機関の排気浄化装置。   The addition control means (S182, S192) causes the addition means to add the additive by frequency control for periodically driving the addition means, and the drive cycle of the addition means is increased as the exhaust flow rate is lower. The exhaust emission control device for an internal combustion engine according to claim 1, wherein: 前記添加量決定手段は、
前記触媒の温度を取得する温度取得手段（Ｓ１１）と、
その温度取得手段が取得した温度に応じた、前記触媒に貯蔵する前記添加剤の目標量を目標貯蔵量として算出する第１算出手段（Ｓ１３、Ｓ１４）と、
前記触媒に現在貯蔵されている前記添加剤の量を推定貯蔵量として算出する第２算出手段（Ｓ１５）と、
前記第１算出手段が算出した前記目標貯蔵量と前記第２算出手段が算出した前記推定貯蔵量との偏差を算出する第３算出手段（Ｓ１６）とを含み、その第３算出手段が算出した前記偏差に基づき前記総添加量を決定することを特徴とする請求項１〜４のいずれか１項に記載の内燃機関の排気浄化装置。 The addition amount determining means includes
Temperature acquisition means (S11) for acquiring the temperature of the catalyst;
First calculation means (S13, S14) for calculating a target storage amount of the additive stored in the catalyst according to the temperature acquired by the temperature acquisition means as a target storage amount;
Second calculation means (S15) for calculating the amount of the additive currently stored in the catalyst as an estimated storage amount;
Third calculation means (S16) for calculating a deviation between the target storage amount calculated by the first calculation means and the estimated storage amount calculated by the second calculation means; The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 4, wherein the total addition amount is determined based on the deviation. 前記第１算出手段（Ｓ１４）は、前記温度で前記触媒に貯蔵できる前記添加剤の最大貯蔵量より小さい貯蔵量を前記目標貯蔵量として算出することを特徴とする請求項５に記載の内燃機関の排気浄化装置。   6. The internal combustion engine according to claim 5, wherein the first calculation means (S14) calculates a storage amount smaller than a maximum storage amount of the additive that can be stored in the catalyst at the temperature as the target storage amount. Exhaust purification equipment. 前記流速算出手段は、前記触媒における排気の空間速度を前記排気流速として算出することを特徴とする請求項１〜６のいずれか１項に記載の内燃機関の排気浄化装置。   The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the flow velocity calculation means calculates an exhaust space velocity of the catalyst as the exhaust gas flow velocity. 前記添加手段は尿素水を前記添加剤として添加し、
前記触媒は、前記添加手段からの尿素水をアンモニアに変換してそのアンモニアを貯蔵し、貯蔵したアンモニアで排気中のＮＯｘを還元するＮＯｘ選択還元触媒であることを特徴とする請求項１〜７のいずれか１項に記載の内燃機関の排気浄化装置。 The adding means adds urea water as the additive,
The catalyst is a NOx selective reduction catalyst that converts urea water from the adding means into ammonia, stores the ammonia, and reduces NOx in the exhaust with the stored ammonia. The exhaust gas purification apparatus for an internal combustion engine according to any one of the above.
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