JP2010209771A - Malfunction diagnosis device for exhaust emission control system, and exhaust emission control system - Google Patents

Malfunction diagnosis device for exhaust emission control system, and exhaust emission control system Download PDF

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JP2010209771A
JP2010209771A JP2009055860A JP2009055860A JP2010209771A JP 2010209771 A JP2010209771 A JP 2010209771A JP 2009055860 A JP2009055860 A JP 2009055860A JP 2009055860 A JP2009055860 A JP 2009055860A JP 2010209771 A JP2010209771 A JP 2010209771A
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amount
reducing agent
abnormality
catalyst
purification rate
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JP4737312B2 (en
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Kazuharu Tochikawa
和治 栩川
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Denso Corp
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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
    • 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
    • F01N11/00—Monitoring or diagnostic devices for exhaust-gas treatment apparatus, e.g. for catalytic activity
    • 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
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
    • F01N2550/02—Catalytic activity of catalytic converters
    • 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
    • F01N2550/00—Monitoring or diagnosing the deterioration of exhaust systems
    • F01N2550/05—Systems for adding substances into exhaust
    • 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
    • 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
    • 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
    • Y02T10/40—Engine management systems

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a malfunction diagnosis device for an exhaust emission control system having a simple hardware construction for diagnosing the malfunction of the exhaust emission control system such as the quality of a reducing agent. <P>SOLUTION: The malfunction diagnosis device includes conversion rate calculating means S14, S27 for calculating a NOx conversion rate, and quality diagnosing means S28, S32 (diagnosing means) for diagnosing the quality of urea water (reducing agent) in accordance with a degree of the deviation of an conversion rate ηstart at current start of an internal combustion engine from an conversion rate ηlast calculated by the conversion rate calculating means at previous stop of the internal combustion engine. From the fact that there should be no great change of the conversion rate between before and after an engine stopping period unless the quality of the urea water is changed during the engine stopping period, the quality of the urea water (the malfunction of the exhaust emission control system) can be diagnosed without the need for a sensor to detect the concentration of the urea water, in accordance with a degree of the deviation of the starting conversion rate ηstart from the stopping conversion rate ηlast. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

本発明は、排気浄化システムの異常を診断する装置に関するものであり、特に、還元剤として尿素水を用いた場合において、尿素濃度の異常に起因したシステム異常について診断するものである。   The present invention relates to an apparatus for diagnosing an abnormality of an exhaust purification system, and particularly to diagnosing a system abnormality caused by an abnormal urea concentration when urea water is used as a reducing agent.

従来、内燃機関の排気中に含まれるＮＯｘ（窒素酸化物）を浄化する手法として、内燃機関の排気中に還元剤を添加し、添加した還元剤を用いて排気中のＮＯｘを触媒で浄化する技術が知られている。還元剤の一例としては尿素が挙げられ、この場合には、尿素を水に溶解させてなる尿素水を排気中に添加する。ちなみに、添加された尿素水からは加水分解によりアンモニア（ＮＨ3）が生成され、このアンモニアが触媒上でＮＯｘを還元する。 Conventionally, as a method for purifying NOx (nitrogen oxide) contained in exhaust gas of an internal combustion engine, a reducing agent is added to the exhaust gas of the internal combustion engine, and NOx in the exhaust gas is purified by a catalyst using the added reducing agent. Technology is known. An example of the reducing agent is urea. In this case, urea water obtained by dissolving urea in water is added to the exhaust gas. Incidentally, ammonia (NH 3 ) is generated from the added urea water by hydrolysis, and this ammonia reduces NOx on the catalyst.

ここで、タンクに貯蔵されている尿素水（還元剤）は、内燃機関の停止中に品質変化することが有りうる。例えば、正規の尿素水以外の液体（例えば水や軽油等）をタンクへ補給してしまうことで、尿素の濃度が著しく低下するといった品質変化が懸念される。また、内燃機関を長期間停止させておくことで尿素水中の水分が蒸発してしまい、尿素の濃度が高くなるといった品質変化が懸念される。そして、このような低濃度の尿素水を添加して用いるとアンモニアの供給不足によるＮＯｘ浄化率の低下が生じ、また、高濃度の尿素水を用いるとアンモニアの供給過剰により触媒からアンモニアの過剰分が排出されるといったアンモニアスリップが生じる。   Here, the quality of the urea water (reducing agent) stored in the tank may change while the internal combustion engine is stopped. For example, there is a concern about quality changes such that the concentration of urea is significantly reduced by replenishing the tank with a liquid other than regular urea water (for example, water or light oil). In addition, there is a concern about quality changes that the water in the urea water evaporates by keeping the internal combustion engine stopped for a long period of time and the concentration of urea becomes high. When such low concentration urea water is added and used, the NOx purification rate is reduced due to insufficient supply of ammonia, and when high concentration urea water is used, excess ammonia is supplied from the catalyst due to excessive supply of ammonia. Causes ammonia slip.

このような問題に対し従来では、尿素水の濃度を検出する濃度センサをタンク内に設置し、濃度センサの検出値に基づき尿素水の濃度（品質）を診断し、品質異常と診断された場合にはその旨をユーザに警告している。なお、濃度センサの具体例として、各々離間して配置された発熱体及び温度計測部を備えるセンサが挙げられる（特許文献１参照）。このセンサによれば、発熱体の発熱量及び温度計測部の計測値に基づき尿素水の熱伝達特性を算出でき、算出した熱伝達特性に基づき尿素水の濃度を検出できる。   Conventionally, when a concentration sensor that detects the concentration of urea water is installed in the tank and the concentration (quality) of the urea water is diagnosed based on the detection value of the concentration sensor, a quality abnormality is diagnosed. Warns the user to that effect. In addition, as a specific example of the density sensor, a sensor including a heating element and a temperature measurement unit that are spaced apart from each other can be cited (see Patent Document 1). According to this sensor, the heat transfer characteristic of urea water can be calculated based on the calorific value of the heating element and the measured value of the temperature measurement unit, and the concentration of urea water can be detected based on the calculated heat transfer characteristic.

特開２００５−１２７２６２号公報JP 2005-127262 A

しかしながら、上述の如く濃度センサの検出値に基づき尿素水（還元剤）の品質を診断する装置では、品質診断専用の濃度センサを必要とする。しかも特許文献１記載の濃度センサでは、発熱体及び温度計測部を備えることに起因したセンサ体格の大型化やコスト高、発熱体で電力消費が生じるといった問題を抱えている。   However, an apparatus for diagnosing the quality of urea water (reducing agent) based on the detection value of the concentration sensor as described above requires a concentration sensor dedicated to quality diagnosis. In addition, the concentration sensor described in Patent Document 1 has problems such as an increase in size and cost of the sensor due to the provision of the heating element and the temperature measurement unit, and power consumption in the heating element.

本発明は、上記課題を解決するためになされたものであり、その目的は、還元剤の品質等の排気浄化システムの異常を、簡素なハード構成で診断可能にした排気浄化システムの異常診断装置を提供することにある。   The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an abnormality diagnosis device for an exhaust purification system that can diagnose an abnormality of the exhaust purification system such as the quality of the reducing agent with a simple hardware configuration. Is to provide.

以下、上記課題を解決するための手段、及びその作用効果について記載する。   Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

請求項１記載の発明では、還元剤添加手段及び触媒を備える排気浄化システムに適用されており、内燃機関の停止時におけるＮＯｘの浄化率及び内燃機関の始動時におけるＮＯｘの浄化率を算出する（浄化率算出手段）。そして、前回停止時の浄化率に対する今回始動時の浄化率の乖離度に基づいて、排気浄化システムの異常有無を診断する（診断手段）ことを特徴とする。   According to the first aspect of the present invention, the present invention is applied to an exhaust purification system including a reducing agent addition means and a catalyst, and calculates a NOx purification rate when the internal combustion engine is stopped and a NOx purification rate when the internal combustion engine is started ( Purification rate calculation means). Then, based on the degree of deviation of the purification rate at the current start from the purification rate at the previous stop, the presence or absence of an abnormality in the exhaust purification system is diagnosed (diagnostic means).

内燃機関の停止期間中に還元剤の品質が変化していなければ、停止期間の前後においてその浄化率は大きくは変化しないはずである。換言すれば、停止期間の前後における浄化率を比較すれば、停止期間中に還元剤の品質が変化したか否かを診断できるはずである。この点に着目し、本発明では、前回停止時の浄化率に対する今回始動時の浄化率の乖離度に基づいて、還元剤の品質を診断する。よって、特許文献１等に記載の診断専用の濃度センサを不要にしつつ還元剤の品質を診断できる。   If the quality of the reducing agent does not change during the stop period of the internal combustion engine, the purification rate should not change significantly before and after the stop period. In other words, if the purification rates before and after the stop period are compared, it should be possible to diagnose whether the quality of the reducing agent has changed during the stop period. Focusing on this point, in the present invention, the quality of the reducing agent is diagnosed on the basis of the degree of divergence of the purification rate at the current start with respect to the purification rate at the previous stop. Therefore, the quality of the reducing agent can be diagnosed without using the dedicated concentration sensor described in Patent Document 1 or the like.

また、本発明において前記乖離度に基づけば、還元剤の品質を診断することの他に、排気浄化システムのハード構成に異常が生じているか否かを診断できる。例えば後述する触媒（請求項１０参照）の異常有無について診断できる。 なお、本発明にかかる浄化率算出手段により浄化率を算出する具体例としては、触媒に流入したＮＯｘ量と触媒から流出したＮＯｘ量との差分をＮＯｘ浄化量として算出し、ＮＯｘ流入量に対する浄化量の割合を「浄化率」として算出することが挙げられる。ＮＯｘ流入量及び流出量の算出には、触媒の上流側に位置するＮＯｘセンサ及び下流側に位置するＮＯｘセンサの検出値に基づき算出してもよいし、内燃機関の運転状態に基づき算出してもよい。   Further, in the present invention, based on the degree of deviation, in addition to diagnosing the quality of the reducing agent, it is possible to diagnose whether or not an abnormality has occurred in the hardware configuration of the exhaust purification system. For example, the presence or absence of abnormality of a catalyst (see claim 10) described later can be diagnosed. As a specific example of calculating the purification rate by the purification rate calculating means according to the present invention, the difference between the NOx amount flowing into the catalyst and the NOx amount flowing out from the catalyst is calculated as the NOx purification amount, and the purification with respect to the NOx inflow amount is performed. The ratio of the amount can be calculated as “purification rate”. The NOx inflow and outflow may be calculated based on the detected values of the NOx sensor located upstream and the NOx sensor located downstream of the catalyst, or based on the operating state of the internal combustion engine. Also good.

また、本発明にかかる「浄化率算出手段」は、浄化率そのものを算出することに限定されず、浄化率と相関性が高い物理量を浄化率に置き換えて算出するようにしてもよい。例えば、触媒に吸着された還元剤の吸着量は浄化率と相関性が高い。よって、浄化率算出手段では前記吸着量を浄化率に置き換えて算出してもよい。   Further, the “purification rate calculating means” according to the present invention is not limited to calculating the purification rate itself, but may be calculated by replacing a physical quantity having a high correlation with the purification rate with the purification rate. For example, the amount of reducing agent adsorbed on the catalyst is highly correlated with the purification rate. Therefore, the purification rate calculation means may calculate by replacing the adsorption amount with the purification rate.

次に、例えば、還元剤を貯蔵するタンクに水を供給する等により還元剤の濃度が低下していれば、還元剤の添加量が同じであっても触媒に供給される還元剤の供給量は減少することとなり、その結果、浄化率が低下することとなる。   Next, for example, if the concentration of the reducing agent is reduced by supplying water to a tank for storing the reducing agent, the supply amount of the reducing agent supplied to the catalyst even if the addition amount of the reducing agent is the same. As a result, the purification rate decreases.

この点に着目した請求項２記載の発明では、前回停止時の浄化率に対する今回始動時の浄化率が低下側へ所定量以上乖離している場合に、還元剤の還元剤濃度が低下している低濃度異常と診断することを特徴とする。これによれば、還元剤濃度センサを用いることなく、還元剤の品質異常の内容（低濃度である旨）を診断結果として取得できる。   In the invention according to claim 2 which pays attention to this point, the reducing agent concentration of the reducing agent decreases when the purification rate at the current start relative to the purification rate at the time of the previous stop deviates more than a predetermined amount toward the lower side. It is characterized by diagnosing a low concentration abnormality. According to this, the content of the quality abnormality of the reducing agent (that is, the low concentration) can be acquired as a diagnosis result without using the reducing agent concentration sensor.

また、例えば、内燃機関を長期間停止させておくことで還元剤の水分が蒸発する等により、還元剤の濃度が上昇していれば、還元剤の添加量が同じであっても触媒に供給される還元剤の供給量は増大することとなり、その結果、供給過剰分の還元剤が触媒から流出するほどに、浄化率が上昇する場合がある。   Further, for example, if the concentration of the reducing agent is increased by evaporating the moisture of the reducing agent by keeping the internal combustion engine stopped for a long period of time, the reducing agent is supplied to the catalyst even if the amount of the reducing agent is the same. The supply amount of the reducing agent to be increased increases, and as a result, the purification rate may increase as the excessive supply amount of the reducing agent flows out of the catalyst.

この点に着目した請求項３記載の発明では、前回停止時の浄化率に対する今回始動時の浄化率が上昇側へ所定量以上乖離している場合に、還元剤の還元剤濃度が上昇している高濃度異常と診断することを特徴とする。これによれば、還元剤濃度センサを用いることなく、還元剤の品質異常の内容（高濃度である旨）を診断結果として取得できる。   In the invention according to claim 3 which pays attention to this point, the reducing agent concentration of the reducing agent increases when the purification rate at the current start with respect to the purification rate at the time of the previous stop deviates by a predetermined amount or more. It is characterized by diagnosing a high concentration abnormality. According to this, the content of the reducing agent quality abnormality (high concentration) can be acquired as a diagnosis result without using the reducing agent concentration sensor.

次に、内燃機関の停止時点において触媒に吸着されている還元剤は、内燃機関の停止期間中に触媒から放出されて減少していく。したがって、停止期間中に還元剤の品質が変化していなかったとしても、前記放出の分を加味すると、停止時浄化率に比べて始動時浄化率は低下するはずである。   Next, the reducing agent adsorbed on the catalyst when the internal combustion engine is stopped is released from the catalyst and decreases during the stop period of the internal combustion engine. Therefore, even if the quality of the reducing agent has not changed during the stop period, the start-up purification rate should be lower than the stop-time purification rate when the release amount is taken into account.

この点を鑑みた請求項４記載の発明では、触媒で吸着されている還元剤が内燃機関の停止期間中に減少した量と相関のある情報を吸着減少量情報として取得する吸着減少量取得手段を備え、前記診断手段は、前記乖離度に加え前記吸着減少量情報に基づき、排気浄化システムの異常（特に還元剤の品質）を診断することを特徴とする。これによれば、停止前後の浄化率の乖離度に基づき還元剤の品質を診断するにあたり、停止期間中に触媒から放出されて減少量を加味して診断するので、診断精度を向上できる。   In view of this point, in the invention according to claim 4, the adsorption reduction amount acquisition means for acquiring, as the adsorption reduction amount information, information correlating with the amount of reducing agent adsorbed by the catalyst during the stop period of the internal combustion engine. The diagnostic means diagnoses an abnormality (particularly, the quality of the reducing agent) of the exhaust purification system based on the adsorption reduction amount information in addition to the degree of deviation. According to this, when diagnosing the quality of the reducing agent based on the degree of divergence of the purification rate before and after the stop, the diagnosis is performed taking into account the reduction amount released from the catalyst during the stop period, so that the diagnosis accuracy can be improved.

なお、前記吸着減少量情報として用いる好適な具体例として、請求項５記載の如く、内燃機関の停止期間長さ、及び停止期間における外気温度が挙げられる。   Note that preferred specific examples used as the adsorption reduction amount information include the length of the stop period of the internal combustion engine and the outside air temperature during the stop period.

請求項６記載の発明では、前記浄化率算出手段は、前記触媒の温度が所定温度に達して触媒暖機期間が終了した時点での浄化率を、始動時の浄化率として算出し、前記触媒に吸着されていた還元剤が前記触媒暖機期間中にＮＯｘ浄化に使用された量を、暖機時使用量として算出する使用量算出手段を備え、前記診断手段は、前記乖離度に加え前記暖機時使用量に基づき、排気浄化システムの異常（特に還元剤の品質）を診断することを特徴とする。   In the invention according to claim 6, the purification rate calculation means calculates a purification rate at the time when the temperature of the catalyst reaches a predetermined temperature and the catalyst warm-up period ends as a purification rate at start-up, and the catalyst The amount of the reducing agent adsorbed on the catalyst is used for NOx purification during the catalyst warm-up period, and is used as a warm-up use amount. It is characterized by diagnosing abnormalities of the exhaust purification system (particularly the quality of the reducing agent) based on the amount used during warm-up.

ここで、内燃機関の始動時に触媒に吸着されている還元剤は、触媒暖機期間中におけるＮＯｘ浄化に使用されるため減少していく。したがって、停止期間中に還元剤の品質が変化していなかったとしても、前記使用した分を加味すると、停止時浄化率に比べて始動時（触媒暖機終了時）の浄化率は低下するはずである。   Here, the reducing agent adsorbed on the catalyst at the start of the internal combustion engine decreases because it is used for NOx purification during the catalyst warm-up period. Therefore, even if the quality of the reducing agent has not changed during the stop period, the purification rate at start-up (at the end of catalyst warm-up) should be lower than the stop-time purification rate when taking into account the amount used. It is.

この点を鑑みた上記請求項６記載の発明によれば、停止前後の浄化率の乖離度に基づき排気浄化システムの異常を診断するにあたり、始動時に吸着されている還元剤のうち触媒暖機期間中にＮＯｘ浄化に使用されて減少した分を加味して診断するので、診断精度を向上できる。なお、暖機時使用量を算出する例としては、例えば触媒暖機期間の長さ、触媒暖機期間中のエンジン回転速度及びエンジン負荷等に基づき算出することが挙げられる。   According to the sixth aspect of the invention in view of this point, when diagnosing an abnormality of the exhaust purification system based on the degree of divergence of the purification rate before and after the stop, the catalyst warm-up period among the reducing agents adsorbed at start-up Since the diagnosis is made by taking into account the reduced amount used for NOx purification, the diagnostic accuracy can be improved. An example of calculating the warm-up usage amount is, for example, calculation based on the length of the catalyst warm-up period, the engine speed during the catalyst warm-up period, the engine load, and the like.

次に、前回停止時の浄化率が同じであっても、内燃機関の停止時点において触媒に吸着されている還元剤の量（吸着量）が異なってくる場合がある。そして、前回停止時での吸着量が異なれば、前回停止時の浄化率が同じであり、かつ、停止期間中に還元剤の品質が変化していない場合であっても、始動時の浄化率は変化する。また、前回停止時の吸着量は、前回での内燃機関の運転状態に応じて異なる。例えば、燃焼室からのＮＯｘ排出量が多い状態で継続して運転していた場合には、停止時の吸着量は少なくなっている。   Next, even if the purification rate at the previous stop is the same, the amount of reducing agent (adsorption amount) adsorbed on the catalyst when the internal combustion engine is stopped may differ. And, if the adsorption amount at the previous stop is different, the purification rate at the previous stop is the same, and even if the quality of the reducing agent has not changed during the stop period, the purification rate at the start Will change. Further, the amount of adsorption at the previous stop varies depending on the previous operating state of the internal combustion engine. For example, when continuously operating with a large amount of NOx discharged from the combustion chamber, the amount of adsorption at the time of stoppage is small.

この点を鑑みた請求項７記載の発明では、前記内燃機関の運転履歴のうち前回停止時点における還元剤吸着量と相関のある履歴情報を、運転履歴情報として取得する吸着量取得手段を備え、前記診断手段は、前記乖離度に加え前記運転履歴情報に基づき、排気浄化システムの異常（特に還元剤溶液の品質）を診断することを特徴とする。これによれば、停止前後の浄化率の乖離度に基づき還元剤の品質を診断するにあたり、停止時の吸着量を加味して診断するので、診断精度を向上できる。   In view of this point, the invention according to claim 7, further comprising adsorption amount acquisition means for acquiring, as operation history information, history information correlated with the reducing agent adsorption amount at the previous stop point in the operation history of the internal combustion engine, The diagnostic means diagnoses an abnormality (particularly, the quality of the reducing agent solution) of the exhaust purification system based on the operation history information in addition to the degree of deviation. According to this, in diagnosing the quality of the reducing agent based on the degree of divergence of the purification rate before and after the stop, the diagnosis is performed in consideration of the adsorption amount at the stop, so that the diagnosis accuracy can be improved.

なお、前記運転履歴情報として用いる好適な具体例として、請求項８記載の如く、前回停止時までの還元剤の添加量履歴、前回停止時までの前記触媒からのＮＯｘ流出量履歴、及び前回停止時点における前記触媒の温度が挙げられる。   As a preferable specific example used as the operation history information, as described in claim 8, a reducing agent addition amount history until the previous stop, a NOx outflow history from the catalyst until the previous stop, and a previous stop The temperature of the catalyst at the time is mentioned.

請求項９記載の発明では、前記排気浄化システムは、前記触媒から流出したＮＯｘの量を検出するＮＯｘセンサと、前記ＮＯｘセンサにより検出されたＮＯｘ量に基づき前記還元剤添加手段による還元剤添加量を制御する手段と、を備えており、前記ＮＯｘセンサ及び前記還元剤添加手段の少なくとも１つについて異常の有無を判定するハード異常判定手段を備え、前記診断手段は、前記ハード異常判定手段により異常が発生していないと判定されていることを条件として、還元剤が品質異常であるとの診断結果を出力することを特徴とする。   According to a ninth aspect of the present invention, the exhaust purification system includes a NOx sensor that detects the amount of NOx flowing out from the catalyst, and a reducing agent addition amount by the reducing agent addition means based on the NOx amount detected by the NOx sensor. And a hardware abnormality determining means for determining whether or not there is an abnormality in at least one of the NOx sensor and the reducing agent adding means, and the diagnostic means detects an abnormality by the hardware abnormality determining means. On the condition that it has been determined that no occurrence of oxidization occurs, a diagnostic result that the quality of the reducing agent is abnormal is output.

ＮＯｘセンサや還元剤添加手段に異常が生じていると、浄化率算出手段により算出した浄化率が誤った値となり、正常な還元剤に対して品質異常との診断結果を出力（誤診断）することが懸念される。この懸念に対し上記請求項９記載の発明によれば、ＮＯｘセンサや還元剤添加手段に異常が生じていないことを条件として品質異常診断結果を出力するので、上記誤診断を回避できる。   If an abnormality occurs in the NOx sensor or the reducing agent addition means, the purification rate calculated by the purification rate calculation means becomes an incorrect value, and a diagnosis result indicating that the quality is abnormal is output (incorrect diagnosis) to a normal reducing agent. There is concern. With respect to this concern, according to the invention described in claim 9, since the quality abnormality diagnosis result is output on the condition that no abnormality has occurred in the NOx sensor and the reducing agent addition means, the above-mentioned erroneous diagnosis can be avoided.

次に、触媒が経年劣化して浄化性能が低下してくると、正常な還元剤を添加しても想定（期待）されるＮＯｘ浄化性能が発揮されなくなり、診断手段は還元剤の品質悪化を誤診断する場合が生じる。   Next, if the catalyst deteriorates with age and the purification performance decreases, the expected (expected) NOx purification performance will not be exhibited even if a normal reducing agent is added, and the diagnostic means will deteriorate the quality of the reducing agent. Misdiagnosis may occur.

この点を鑑みた請求項１０記載の発明では、前記乖離度が所定量以上であるとの診断結果が所定回数以上出力された場合には、前記触媒の浄化性能が低下している異常状態であると判定する触媒異常判定手段を備えることを特徴とするので、触媒の異常状態を検知できる。   In the invention according to claim 10 in view of this point, when the diagnosis result that the degree of divergence is a predetermined amount or more is output a predetermined number of times or more, an abnormal state in which the purification performance of the catalyst is deteriorated. Since it has a catalyst abnormality determining means for determining that there is a catalyst, an abnormal state of the catalyst can be detected.

請求項１１記載の発明は、上述した排気浄化システムの異常診断装置と、前記還元剤添加手段、前記触媒、及び前記触媒から流出したＮＯｘの量を検出するＮＯｘセンサの少なくとも１つと、を備えることを特徴とする排気浄化システムである。この排気浄化システムによれば、上述の各種効果を同様に発揮することができる。   An eleventh aspect of the invention includes the above-described abnormality diagnosis device of the exhaust purification system, and at least one of the reducing agent addition unit, the catalyst, and a NOx sensor that detects the amount of NOx flowing out of the catalyst. An exhaust purification system characterized by the above. According to this exhaust gas purification system, the various effects described above can be exhibited in the same manner.

排気浄化システムの概要を示す構成図。The block diagram which shows the outline | summary of an exhaust gas purification system. 停止時浄化率算出の処理手順を示すフローチャート。The flowchart which shows the process sequence of purification rate at the time of a stop. 尿素水品質診断の処理手順を示すフローチャート。The flowchart which shows the process sequence of urea water quality diagnosis. 低濃度異常時における浄化率変化を示す図。The figure which shows the purification rate change at the time of low concentration abnormality. 高濃度異常時における浄化率変化を示す図。The figure which shows the purification rate change at the time of abnormal high concentration.

以下、本発明を具体化した排気浄化システムの一実施形態について図面を参照しつつ説明する。本実施形態の排気浄化システムは、選択還元型触媒を用いて排気中のＮＯｘを浄化するものであり、尿素ＳＣＲ（Selective Catalytic Reduction）システムとして構築されている。はじめに、図１を参照してこのシステムの構成について詳述する。図１は、本実施形態に係る尿素ＳＣＲシステムの概要を示す構成図である。本システムは、自動車に搭載されたディーゼルエンジン（図示略）により排出される排気を浄化対象として、排気を浄化するための各種アクチュエータ及び各種センサ、並びに電子制御ユニット（ＥＣＵ４０）等を有して構築されている。   Hereinafter, an embodiment of an exhaust purification system embodying the present invention will be described with reference to the drawings. The exhaust purification system of this embodiment purifies NOx in exhaust using a selective reduction catalyst, and is constructed as a urea SCR (Selective Catalytic Reduction) system. First, the configuration of this system will be described in detail with reference to FIG. FIG. 1 is a configuration diagram showing an outline of a urea SCR system according to the present embodiment. This system is constructed with various actuators and various sensors for purifying exhaust, and an electronic control unit (ECU 40), etc., for purifying exhaust discharged by a diesel engine (not shown) mounted on an automobile. Has been.

図１のエンジン排気系において、エンジン本体に接続され排気通路を形成する排気管１１が設けられており、その排気管１１に、排気上流側から順にＤＰＦ１２（Diesel Particulate Filter）、選択還元型触媒（以下、ＳＣＲ触媒という）１３が配設されている。また、排気管１１においてＤＰＦ１２とＳＣＲ触媒１３との間には、還元剤としての尿素水を排気管１１内に添加供給するための尿素水添加弁１５（還元剤添加手段）が設けられている。   In the engine exhaust system of FIG. 1, an exhaust pipe 11 connected to the engine body and forming an exhaust passage is provided. In the exhaust pipe 11, a DPF 12 (Diesel Particulate Filter), a selective reduction catalyst ( (Hereinafter referred to as SCR catalyst) 13 is provided. Further, a urea water addition valve 15 (reducing agent adding means) for adding and supplying urea water as a reducing agent into the exhaust pipe 11 is provided between the DPF 12 and the SCR catalyst 13 in the exhaust pipe 11. .

排気管１１においてＳＣＲ触媒１３の上流側には、上流側ＮＯｘセンサ１６が設けられている。この上流側ＮＯｘセンサ１６により、同ＳＣＲ触媒１３の上流側にて、排気中のＮＯｘ量（ＳＣＲ触媒１３へ流入するＮＯｘ量）が検出される。   An upstream NOx sensor 16 is provided on the upstream side of the SCR catalyst 13 in the exhaust pipe 11. The upstream NOx sensor 16 detects the amount of NOx in the exhaust (the amount of NOx flowing into the SCR catalyst 13) on the upstream side of the SCR catalyst 13.

排気管１１においてＳＣＲ触媒１３の下流側には、下流側ＮＯｘセンサ１７が設けられている。この下流側ＮＯｘセンサ１７により、同ＳＣＲ触媒１３の下流側にて、排気中のＮＯｘ量（ＳＣＲ触媒１３から流出したＮＯｘ量）が検出される。なお、これらのＮＯｘセンサ１６，１７に排気温度を検出する温度センサを内蔵させてもよい。   A downstream NOx sensor 17 is provided downstream of the SCR catalyst 13 in the exhaust pipe 11. The downstream NOx sensor 17 detects the amount of NOx in the exhaust (the amount of NOx flowing out of the SCR catalyst 13) on the downstream side of the SCR catalyst 13. Note that a temperature sensor for detecting the exhaust gas temperature may be incorporated in these NOx sensors 16 and 17.

排気管１１においてＳＣＲ触媒１３の更に下流側には、アンモニア除去装置としての酸化触媒１９が設けられている。この酸化触媒１９により、ＳＣＲ触媒１３から排出されるアンモニア（ＮＨ3）、すなわち余剰のアンモニアが除去される。 An oxidation catalyst 19 as an ammonia removing device is provided further downstream of the SCR catalyst 13 in the exhaust pipe 11. The oxidation catalyst 19 removes ammonia (NH 3 ) discharged from the SCR catalyst 13, that is, excess ammonia.

なお、上述したＤＰＦ１２、ＳＣＲ触媒１３、尿素水添加弁１５、上流側ＮＯｘセンサ１６、下流側ＮＯｘセンサ１７、及び酸化触媒１９は、「排気浄化システム」を構成する手段に相当する。   The DPF 12, the SCR catalyst 13, the urea water addition valve 15, the upstream side NOx sensor 16, the downstream side NOx sensor 17, and the oxidation catalyst 19 described above correspond to means constituting the “exhaust purification system”.

次に、本システムを構成する上記各部の構成についてそれぞれ説明する。   Next, the configuration of each of the above parts constituting the system will be described.

ＤＰＦ１２は、排気中のＰＭ（粒子状物質）を捕集するＰＭ除去用フィルタである。ＤＰＦ１２は白金系の酸化触媒を担持しており、この酸化触媒により、ＰＭ成分の１つである可溶性有機成分（ＳＯＦ）とともにＨＣやＣＯが除去される。このＤＰＦ１２に捕集されたＰＭは、ディーゼルエンジンにおけるメイン燃料噴射後のポスト噴射等により燃焼除去でき（再生処理に相当）、これによりＤＰＦ１２の継続使用が可能となっている。   The DPF 12 is a PM removal filter that collects PM (particulate matter) in the exhaust gas. The DPF 12 carries a platinum-based oxidation catalyst, and this oxidation catalyst removes HC and CO together with a soluble organic component (SOF) that is one of the PM components. The PM collected in the DPF 12 can be removed by combustion by post-injection after the main fuel injection in the diesel engine or the like (corresponding to a regeneration process), and thus the DPF 12 can be used continuously.

ＳＣＲ触媒１３は、ＮＯｘの還元反応（排気浄化反応）を促進するものであり、例えば、
４ＮＯ＋４ＮＨ3＋Ｏ2→４Ｎ2＋６Ｈ2Ｏ …（式１）
６ＮＯ2＋８ＮＨ3→７Ｎ2＋１２Ｈ2Ｏ …（式２）
ＮＯ＋ＮＯ2＋２ＮＨ3→２Ｎ2＋３Ｈ2Ｏ …（式３）
といった反応を促進して排気中のＮＯｘを還元する。そして、これらの反応においてＮＯｘの還元剤となるアンモニア（ＮＨ3）を添加供給するものが、同ＳＣＲ触媒１３の上流側に設けられた尿素水添加弁１５である。 The SCR catalyst 13 promotes a NOx reduction reaction (exhaust purification reaction).
4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O (Formula 1)
6NO 2 + 8NH 3 → 7N 2 + 12H 2 O (Formula 2)
NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O (Formula 3)
Such a reaction is promoted to reduce NOx in the exhaust gas. A urea water addition valve 15 provided on the upstream side of the SCR catalyst 13 is additionally supplied with ammonia (NH 3 ) as a NOx reducing agent in these reactions.

尿素水添加弁１５は、既存の燃料噴射弁（インジェクタ）とほぼ同様の構成を有するものであり、公知の構成が採用できるためここでは構成を簡単に説明する。尿素水添加弁１５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１５ａを開閉するためのニードルを有する弁体部とを備えた電磁式開閉弁として構成されており、ＥＣＵ４０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、そのニードル移動に伴い先端噴出口１５ａから尿素水が添加（噴射）される。   The urea water addition valve 15 has substantially the same configuration as an existing fuel injection valve (injector), and since a known configuration can be adopted, the configuration will be briefly described here. The urea water addition valve 15 is configured as an electromagnetic on-off valve provided with a drive unit composed of an electromagnetic solenoid or the like, and a valve body unit having a urea water passage through which urea water flows and a needle for opening and closing the tip jet port 15a. The valve is opened or closed based on a drive signal from the ECU 40. 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 15a as the needle moves.

尿素水添加弁１５に対しては、尿素水タンク２１から尿素水が逐次供給される。尿素水タンク２１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ＣＮＨ（例えば３２．５％）の尿素水が貯蔵されている。この尿素水タンク２１と尿素水添加弁１５とは尿素水供給管２２により接続されており、尿素水供給管２２内に尿素水通路（還元剤通路）が形成されている。尿素水供給管２２の途中には、ＥＣＵ４０からの駆動信号により回転駆動する電動の尿素水ポンプ２３が設けられている。   Urea water is sequentially supplied from the urea water tank 21 to the urea water addition valve 15. The urea water tank 21 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined specified concentration CNH (for example, 32.5%) is stored therein. The urea water tank 21 and the urea water addition valve 15 are connected by a urea water supply pipe 22, and a urea water passage (reducing agent passage) is formed in the urea water supply pipe 22. In the middle of the urea water supply pipe 22, an electric urea water pump 23 that is rotationally driven by a drive signal from the ECU 40 is provided.

尿素水ポンプ２３を駆動させると、尿素水タンク２１内の尿素水は、フィルタ装置２５を通過した後、圧力調整弁２６により所定の供給圧力に調整され、尿素水添加弁１５へ圧送される。なお、圧力調整弁２６により圧力調整した結果、余剰となった尿素水はリターン配管２７を通じて尿素水タンク２１に戻される。   When the urea water pump 23 is driven, the urea water in the urea water tank 21 passes through the filter device 25, is adjusted to a predetermined supply pressure by the pressure adjustment valve 26, and is pumped to the urea water addition valve 15. As a result of pressure adjustment by the pressure adjustment valve 26, surplus urea water is returned to the urea water tank 21 through the return pipe 27.

その他、本システムには、エンジン回転速度やエンジン水温、燃料残量、尿素水残量など車両に関する各種情報を表示する表示パネル３３が運転席前に設けられており、ＥＣＵ４０により各種の表示制御が行われる。   In addition, this system is provided with a display panel 33 in front of the driver's seat for displaying various information relating to the vehicle such as the engine speed, engine water temperature, fuel remaining amount, urea water remaining amount, and the ECU 40 performs various display controls. Done.

上記システムの中で電子制御ユニットとして主体的に排気浄化に係る制御を行う部分がＥＣＵ４０である。ＥＣＵ４０は、周知のマイクロコンピュータ（図示略）を備え、各種センサの検出値に基づいて所望とされる態様で尿素水添加弁１５等の各種アクチュエータを操作することにより、排気浄化に係る各種の制御を実施する。具体的には、例えば上述した上流側ＮＯｘセンサ１６や下流側ＮＯｘセンサ１７等の各種センサから検出信号を入力し、その入力信号に基づいて尿素水添加弁１５の通電時間や尿素水ポンプ２３の駆動量等を制御する。これにより、排気管１１内に、適切な時期に適正な量の尿素水を添加供給する。   In the system, the ECU 40 is a part that mainly performs control related to exhaust gas purification as an electronic control unit. The ECU 40 includes a known microcomputer (not shown), and operates various actuators such as the urea water addition valve 15 in a desired mode based on detection values of various sensors, thereby performing various controls related to exhaust purification. To implement. Specifically, for example, detection signals are input from various sensors such as the upstream NOx sensor 16 and the downstream NOx sensor 17 described above, and the energization time of the urea water addition valve 15 and the urea water pump 23 are based on the input signals. Control the driving amount. Thereby, an appropriate amount of urea water is added and supplied into the exhaust pipe 11 at an appropriate time.

本実施形態に係る上記システムでは、エンジン運転時において、尿素水ポンプ２３の駆動により尿素水タンク２１内の尿素水が尿素水供給管２２を通じて尿素水添加弁１５に圧送され、尿素水添加弁１５により排気管１１内に尿素水が添加供給される。すると、排気管１１内において排気と共に尿素水がＳＣＲ触媒１３に供給され、ＳＣＲ触媒１３においてＮＯｘの還元反応によりその排気が浄化される。ＮＯｘの還元に際しては、例えば、
（ＮＨ2）2ＣＯ＋Ｈ2Ｏ→２ＮＨ3＋ＣＯ2 …（式４）
といった反応により、排気熱による高温下で尿素水が加水分解される。これにより、アンモニア（ＮＨ3）が生成され、そのアンモニアがＳＣＲ触媒１３に吸着するとともに同ＳＣＲ触媒１３において排気中のＮＯｘがアンモニアにより選択的に還元除去される。すなわち、同ＳＣＲ触媒１３上で、アンモニアに基づく還元反応（上記反応式（式１）〜（式３））が行われることによってＮＯｘが還元、浄化されることとなる。 In the system according to this embodiment, during operation of the engine, the urea water in the urea water tank 21 is pumped to the urea water addition valve 15 through the urea water supply pipe 22 by driving the urea water pump 23, and the urea water addition valve 15. Thus, urea water is added and supplied into the exhaust pipe 11. Then, urea water is supplied to the SCR catalyst 13 in the exhaust pipe 11 together with the exhaust gas, and the exhaust gas is purified by the NOx reduction reaction in the SCR catalyst 13. When reducing NOx, for example,
(NH 2 ) 2 CO + H 2 O → 2NH 3 + CO 2 (Formula 4)
As a result, urea water is hydrolyzed at a high temperature due to exhaust heat. As a result, ammonia (NH 3 ) is generated, and the ammonia is adsorbed to the SCR catalyst 13, and NOx in the exhaust is selectively reduced and removed by the ammonia in the SCR catalyst 13. That is, NOx is reduced and purified by performing a reduction reaction based on ammonia (the above reaction formulas (Formula 1) to (Formula 3)) on the SCR catalyst 13.

尿素水添加弁１５による排気中への尿素添加量は、下流側ＮＯｘセンサ１７により検出される排気中のＮＯｘ量に応じてアンモニアの過不足が生じないよう算出される。例えば、下流側ＮＯｘセンサ１７により検出されるＮＯｘ量がゼロとなるよう、尿素添加量はフィードバック制御されている。   The amount of urea added to the exhaust gas by the urea water addition valve 15 is calculated according to the amount of NOx in the exhaust gas detected by the downstream side NOx sensor 17 so as not to cause excess or deficiency of ammonia. For example, the urea addition amount is feedback controlled so that the NOx amount detected by the downstream NOx sensor 17 becomes zero.

ところが、尿素水タンク２１内に貯留されている尿素水の濃度が規定濃度ＣＮＨからずれていたり、あるいは尿素水タンク２１内に尿素水以外の液体が混入されていたりすると、排気中のＮＯｘ量に対して適正な量のアンモニアを供給することができず、結果としてＮＯｘ浄化率の低下やアンモニアスリップが生じることが考えられる。   However, if the concentration of urea water stored in the urea water tank 21 deviates from the specified concentration CNH or if a liquid other than urea water is mixed in the urea water tank 21, the amount of NOx in the exhaust gas is increased. On the other hand, it is conceivable that an appropriate amount of ammonia cannot be supplied, resulting in a decrease in the NOx purification rate and ammonia slip.

すなわち、例えばエンジンが停止状態のまま長期間放置された場合、尿素水タンク２１内の尿素水のうち水成分が蒸発し、尿素水の濃度が規定濃度ＣＮＨよりも高くなることが考えられる。かかる場合、排気中へのアンモニア供給量がＮＯｘ排出量に対して過剰になり、結果としてアンモニアスリップが発生することが懸念される。一方、使用者が、尿素水タンク２１内に規定濃度ＣＮＨの尿素水の代わりに水を補給したり規定濃度ＣＮＨよりも低い尿素濃度の尿素水を補給したりした場合、尿素水の濃度が規定濃度ＣＮＨよりも低くなることが考えられる。かかる場合、排気中へのアンモニア供給量が不足し、結果として排気中のＮＯｘ浄化率が低下してしまうことが懸念される。あるいは、尿素水タンク２１内への尿素水補給の際に、使用者が尿素水以外の液体（例えば軽油など）を誤って又は故意に補給した場合、その異物により尿素水の品質低下を招き、その結果、ＮＯｘ浄化率の低下やシステム故障の発生が懸念される。   That is, for example, when the engine is left in a stopped state for a long time, the water component of the urea water in the urea water tank 21 evaporates, and the concentration of the urea water may be higher than the specified concentration CNH. In such a case, there is a concern that the ammonia supply amount into the exhaust gas becomes excessive with respect to the NOx emission amount, and as a result, ammonia slip occurs. On the other hand, when the user replenishes the urea water tank 21 with water instead of the urea water with the specified concentration CNH or supplies urea water with a urea concentration lower than the specified concentration CNH, the concentration of the urea water is specified. It is conceivable that the concentration is lower than CNH. In such a case, there is a concern that the amount of ammonia supplied into the exhaust gas is insufficient, and as a result, the NOx purification rate in the exhaust gas decreases. Alternatively, when the user mistakenly or intentionally replenishes a liquid other than urea water (for example, light oil) when replenishing urea water into the urea water tank 21, the quality of the urea water is reduced due to the foreign matter, As a result, there are concerns about a decrease in the NOx purification rate and the occurrence of a system failure.

この懸念を解消すべく本発明者は次の点に着目した。すなわち、エンジン停止期間中に尿素水の品質が変化していなければ、停止期間の前後においてその浄化率は大きくは変化しないはずである。換言すれば、停止期間の前後における浄化率に変化が生じていれば、停止期間中に、水や軽油の補給行為や水成分蒸発等に起因した尿素水の品質変化が生じたと診断できるはずである。そこで本実施形態では、エンジン停止時（図４中のｔ１時点）の浄化率ηlastに対するエンジン始動時（厳密にはエンジン始動の直後ｔ３）の浄化率ηstartの乖離度に基づき、その乖離度が大きければ尿素水の品質異常と診断する。   In order to eliminate this concern, the present inventor has focused on the following points. That is, if the quality of urea water does not change during the engine stop period, the purification rate should not change greatly before and after the stop period. In other words, if there is a change in the purification rate before and after the stop period, it should be possible to diagnose that the quality of urea water has changed during the stop period due to water or light oil replenishment or water component evaporation. is there. Therefore, in this embodiment, the degree of divergence is large based on the degree of divergence of the purification rate ηstart at the time of engine start (strictly, t3 immediately after engine start) with respect to the purification rate ηlast at the time of engine stop (time t1 in FIG. 4). Diagnosed as abnormal quality of urea water.

但し、エンジン停止期間中において、ＳＣＲ触媒１３に吸着されているアンモニアの一部は、エンジンの停止期間中にＳＣＲ触媒１３から放出されていく（図４中のｔ１〜ｔ２参照）。そのため、停止期間中に尿素水の品質が変化していなかったとしても、前記放出によりＮＨ3吸着量が減少した分、始動時の浄化率ηstartは低下するはずである。よって、このような停止期間中に生じる浄化率の低下分（以下、「吸着減少量」と記載）を加味して尿素水の品質を診断する。 However, part of the ammonia adsorbed on the SCR catalyst 13 during the engine stop period is released from the SCR catalyst 13 during the engine stop period (see t1 to t2 in FIG. 4). Therefore, even if the quality of the urea water does not change during the stop period, the purification rate ηstart at the start should decrease by the amount of decrease in the NH 3 adsorption amount due to the release. Therefore, the quality of urea water is diagnosed by taking into account the decrease in the purification rate (hereinafter referred to as “adsorption reduction amount”) that occurs during such a stop period.

また、エンジン始動直後はＳＣＲ触媒１３の暖機運転が必要であり、その触媒暖機が終了するまでは尿素水添加弁１５からの尿素水添加は停止されている。そのため、エンジン始動時（燃焼開始時）にＳＣＲ触媒１３に吸着されているアンモニアは、触媒暖機期間中におけるＮＯｘ浄化に使用されるため減少していく（図４中のｔ２〜ｔ３参照）。したがって、停止期間中に尿素水の品質が変化していなかったとしても、触媒暖機期間に使用した分、停止時浄化率に比べて始動時（触媒暖機終了時）の浄化率は低下するはずである。よって、このような触媒暖機期間中に生じる浄化率の低下分（以下、「暖機時使用量」と記載）を加味して尿素水の品質を診断する。   Further, immediately after the engine is started, the SCR catalyst 13 needs to be warmed up, and the urea water addition from the urea water addition valve 15 is stopped until the catalyst warm-up is completed. Therefore, ammonia adsorbed to the SCR catalyst 13 at the time of engine start (at the start of combustion) decreases because it is used for NOx purification during the catalyst warm-up period (see t2 to t3 in FIG. 4). Therefore, even if the quality of the urea water does not change during the stop period, the purification rate at the start time (at the end of catalyst warm-up) is lower than the stop-time purification rate by the amount used during the catalyst warm-up period. It should be. Therefore, the quality of urea water is diagnosed by taking into account the reduction in the purification rate that occurs during the catalyst warm-up period (hereinafter referred to as “amount used during warm-up”).

以下、上述の如く尿素水の品質を診断するための処理について、図２及び図３のフローチャートを用いて説明する。   Hereinafter, the process for diagnosing the quality of urea water as described above will be described with reference to the flowcharts of FIGS.

まず、エンジン停止時の浄化率を算出する処理（停止時浄化率算出処理）について説明する。図２は、停止時浄化率算出処理の処理手順を示すフローチャートである。この処理は、ＥＣＵ４０が有するマイコンによりエンジン運転中に所定の時間周期で繰り返し実行される。   First, the process for calculating the purification rate when the engine is stopped (stop-time purification rate calculation process) will be described. FIG. 2 is a flowchart showing a processing procedure of the stoppage purification rate calculation processing. This process is repeatedly executed at a predetermined time period during engine operation by the microcomputer of the ECU 40.

図２において、まずステップＳ１１（ハード異常判定手段）では、排気浄化システムのハード系が正常であるか否かを判定する。例えば、尿素水添加弁１５、上流側ＮＯｘセンサ１６、下流側ＮＯｘセンサ１７、尿素水ポンプ２３等のシステム構成部品に対して、断線や短絡等の異常判定を実施する。ハード系に異常有りと判定されれば、続くステップＳ１２において、ハード系に異常が有る旨を車両運転者に報知すべく、例えば表示パネル３３（図１参照）にて警告表示や警告音発生を行い、図２の処理を終了する。   In FIG. 2, first, in step S11 (hard abnormality determination means), it is determined whether or not the hardware system of the exhaust purification system is normal. For example, abnormality determination such as disconnection or short circuit is performed on system components such as the urea water addition valve 15, the upstream NOx sensor 16, the downstream NOx sensor 17, and the urea water pump 23. If it is determined that there is an abnormality in the hardware system, in a subsequent step S12, for example, a warning display or a warning sound is generated on the display panel 33 (see FIG. 1) in order to notify the vehicle driver that there is an abnormality in the hardware system. 2 to complete the process of FIG.

一方、ステップＳ１１にてハード系に異常が無く正常と判定されれば、続くステップＳ１３において、現時点でのエンジン運転状態が触媒暖機が完了した状態であるか否かを判定する。なお、燃焼室での燃焼を開始した後、ＳＣＲ触媒１３の温度が所定温度に達した時点を触媒暖機完了時点とする。   On the other hand, if it is determined in step S11 that the hardware system is normal and normal, it is determined in subsequent step S13 whether or not the current engine operating state is a state in which catalyst warm-up has been completed. The time when the temperature of the SCR catalyst 13 reaches a predetermined temperature after starting combustion in the combustion chamber is defined as the catalyst warm-up completion time.

触媒暖機完了状態でないと判定されれば（Ｓ１３：ＮＯ）図２の処理を終了し、触媒暖機完了状態であると判定されれば（Ｓ１３：ＹＥＳ）、続くステップＳ１４（浄化率算出手段）において、上流側ＮＯｘセンサ１６及び下流側ＮＯｘセンサ１７の検出値に基づき現時点での浄化率ηlastを算出する。この算出結果は逐次記憶更新されるので、エンジン停止時点（図４中のｔ１時点）で記憶されている浄化率ηlastがエンジン停止時の浄化率に相当することとなる。   If it is determined that the catalyst is not warmed up (S13: NO), the process of FIG. 2 is terminated, and if it is determined that the catalyst is warmed up (S13: YES), the following step S14 (purification rate calculating means) ), The current purification rate ηlast is calculated based on the detected values of the upstream NOx sensor 16 and the downstream NOx sensor 17. Since this calculation result is sequentially stored and updated, the purification rate ηlast stored at the time of engine stop (time t1 in FIG. 4) corresponds to the purification rate at the time of engine stop.

ここで言う「浄化率」について説明すると、ＳＣＲ触媒１３に流入したＮＯｘの量（ＮＯｘ流入量）とＳＣＲ触媒１３から流出したＮＯｘの量（ＮＯｘ流出量）との差分をＮＯｘ浄化量とした場合において、ＮＯｘ流入量に対する浄化量の割合を「浄化率」としている。そして、ＮＯｘ流入量については上流側ＮＯｘセンサ１６の検出値に基づき算出し、ＮＯｘ流出量については下流側ＮＯｘセンサ１７の検出値に基づき算出する。   Explaining the “purification rate” here, the difference between the amount of NOx flowing into the SCR catalyst 13 (NOx inflow amount) and the amount of NOx flowing out of the SCR catalyst 13 (NOx outflow amount) is defined as the NOx purification amount. , The ratio of the purification amount to the NOx inflow amount is referred to as “purification rate”. The NOx inflow amount is calculated based on the detection value of the upstream NOx sensor 16, and the NOx outflow amount is calculated based on the detection value of the downstream NOx sensor 17.

なお、「エンジン停止時」とは、例えば内燃機関が実際に停止した時点又は停止されることが推測された時点とし、具体的には、イグニッションスイッチのオンからオフへの切替時、又はエンジン回転速度がゼロもしくはその近傍になった時点とする。後述する図４の例では、エンジン回転速度がゼロとなった時点ｔ１をエンジン停止時としている。   Note that “when the engine is stopped” is, for example, the time when the internal combustion engine is actually stopped or when it is estimated that the engine is stopped, and specifically, when the ignition switch is switched from on to off, or when the engine rotates. When the speed is zero or close to it. In the example of FIG. 4 to be described later, the time point t1 when the engine rotation speed becomes zero is the time when the engine is stopped.

続くステップＳ１５（吸着量取得手段）では、エンジンの運転履歴のうちＮＨ3吸着量と相関のある履歴情報（運転履歴情報）を取得する。取得した情報は逐次記憶更新されるので、エンジン停止時点で記憶されている情報がエンジン停止時の運転履歴情報に相当することとなる。運転履歴情報の具体例としては、尿素水の添加量履歴、ＳＣＲ触媒１３からのＮＯｘ流出量履歴、及びＳＣＲ触媒１３の温度等が挙げられる。 In subsequent step S15 (adsorption amount acquisition means), history information (operation history information) correlated with the NH 3 adsorption amount is acquired from the engine operation history. Since the acquired information is sequentially stored and updated, the information stored when the engine is stopped corresponds to the operation history information when the engine is stopped. Specific examples of the operation history information include the urea water addition amount history, the NOx outflow history from the SCR catalyst 13, the temperature of the SCR catalyst 13, and the like.

次に、尿素水の品質を診断する処理（尿素水品質診断処理）について図３を用いて説明する。図３は、尿素水品質診断処理の処理手順を示すフローチャートである。この処理は、ＥＣＵ４０（品質診断装置）が有するマイコンにより実行され、触媒暖機が完了した直後においてのみ、その実行を開始する。例えば、触媒暖機が完了したことをトリガとして図３の処理を１回だけ実施してもよいし、触媒暖機完了から所定時間が経過するまでの期間を「触媒暖機完了の直後」として図３の処理を繰り返し実行してもよい。 図３において、まずステップＳ２１（ハード異常判定手段）では、排気浄化システムのハード系が正常であるか否かを判定する。例えば、尿素水添加弁１５、上流側ＮＯｘセンサ１６、下流側ＮＯｘセンサ１７、尿素水ポンプ２３等のシステム構成部品に対して、断線や短絡等の異常判定を実施する。ハード系に異常有りと判定されれば、続くステップＳ２２において、ハード系に異常が有る旨を車両運転者に報知すべく、例えば表示パネル３３（図１参照）にて警告表示や警告音発生を行い、図３の処理を終了する。   Next, a process for diagnosing the quality of urea water (urea water quality diagnostic process) will be described with reference to FIG. FIG. 3 is a flowchart showing a processing procedure of the urea water quality diagnosis processing. This process is executed by a microcomputer included in the ECU 40 (quality diagnostic device), and the execution is started only immediately after the catalyst warm-up is completed. For example, the process shown in FIG. 3 may be performed only once with the completion of the catalyst warm-up as a trigger, or the period from when the catalyst warm-up is completed until a predetermined time has elapsed is “immediately after the catalyst warm-up is completed”. The process of FIG. 3 may be repeatedly executed. In FIG. 3, first, in step S21 (hardware abnormality determination means), it is determined whether or not the hardware system of the exhaust purification system is normal. For example, abnormality determination such as disconnection or short circuit is performed on system components such as the urea water addition valve 15, the upstream NOx sensor 16, the downstream NOx sensor 17, and the urea water pump 23. If it is determined that there is an abnormality in the hardware system, in a subsequent step S22, for example, a warning display or a warning sound is generated on the display panel 33 (see FIG. 1) to notify the vehicle driver that there is an abnormality in the hardware system. 3 to complete the process of FIG.

一方、ステップＳ２１にてハード系に異常が無く正常と判定されれば、続くステップＳ２３（吸着減少量取得手段）において、エンジンの停止期間中にＳＣＲ触媒１３から放出されていくアンモニア放出量（ＮＨ3吸着の減少量）と相関のある情報（吸着減少量情報）として、前回エンジン停止時から今回エンジン始動時までの停止期間長さ、及びその停止期間における外気温度の履歴を取得する。 On the other hand, if it is determined in step S21 that the hardware system is normal and normal, the ammonia release amount (NH) released from the SCR catalyst 13 during the engine stop period in subsequent step S23 (adsorption reduction amount acquisition means). (3 Adsorption decrease amount) As information (adsorption decrease amount information), the length of the stop period from the previous engine stop to the current engine start and the history of the outside air temperature during the stop period are acquired.

続くステップＳ２４では、ステップＳ２３で取得した停止期間長さ及び外気温度履歴に基づき、先述した吸着減少量を算出する。ちなみに、停止期間が長く外気温度が高いほど、吸着減少量は多くなるよう算出される。   In subsequent step S24, the above-described adsorption decrease amount is calculated based on the stop period length and the outside air temperature history acquired in step S23. Incidentally, the amount of decrease in adsorption is calculated so that the longer the stop period and the higher the outside air temperature, the greater the amount of decrease in adsorption.

続くステップＳ２５（使用量算出手段）では、触媒暖機期間における上流側ＮＯｘセンサ１６及び下流側ＮＯｘセンサ１７の検出履歴に基づき、先述した暖機時使用量を算出する。例えば、触媒暖機期間の長さ、触媒暖機期間中のエンジン回転速度及びエンジン負荷等に基づき暖機時使用量を算出する。   In the subsequent step S25 (usage amount calculating means), the aforementioned warm-up use amount is calculated based on the detection history of the upstream NOx sensor 16 and the downstream NOx sensor 17 during the catalyst warm-up period. For example, the usage amount during warm-up is calculated based on the length of the catalyst warm-up period, the engine rotation speed during the catalyst warm-up period, the engine load, and the like.

続くステップＳ２６では、エンジン停止期間中に尿素水の品質変化がなく正常であると仮定した場合における、エンジン始動時点（厳密にはエンジン始動の直後ｔ３）での浄化率の推定値（推定浄化率ηest）を算出する。この算出では、ステップＳ１４で算出した停止時浄化率ηlast、ステップＳ２４で算出した吸着減少量、ステップＳ２５で算出した暖機時使用量、及びステップＳ１５で取得した運転履歴情報に基づき推定浄化率ηestを算出する。具体的には、先ず、運転履歴情報に基づき停止時浄化率ηlastを補正する。次に、補正された停止時浄化率ηlastから、吸着減少量に相当する浄化率の減少分、及び暖機時使用量に相当する浄化率の減少分を減算し、その減算結果を推定浄化率ηestとする。   In the subsequent step S26, the estimated value of the purification rate (estimated purification rate at the time of engine start (strictly, t3 immediately after engine start) when it is assumed that the quality of the urea water does not change during the engine stop period and is normal. ηest) is calculated. In this calculation, the estimated purification rate ηest calculated based on the stoppage purification rate ηlast calculated in step S14, the adsorption reduction amount calculated in step S24, the warm-up usage amount calculated in step S25, and the operation history information acquired in step S15. Is calculated. Specifically, first, the stop purification rate ηlast is corrected based on the operation history information. Next, from the corrected stop-time purification rate ηlast, the decrease in the purification rate corresponding to the adsorption reduction amount and the decrease in the purification rate corresponding to the warm-up usage amount are subtracted, and the subtraction result is the estimated purification rate. Let ηest.

続くステップＳ２７（浄化率算出手段）では、上流側ＮＯｘセンサ１６及び下流側ＮＯｘセンサ１７の検出値に基づき、現時点での浄化率、つまり始動直後のｔ３時点における始動時浄化率ηstartを算出する。具体的には、ステップＳ１４での停止時浄化率ηlastの算出と同様にして、ＮＯｘ流入量に対する浄化量の割合を浄化率として算出する。そして、ＮＯｘ流入量については上流側ＮＯｘセンサ１６の検出値に基づき算出し、ＮＯｘ流出量については下流側ＮＯｘセンサ１７の検出値に基づき算出する。   In the subsequent step S27 (purification rate calculating means), based on the detected values of the upstream NOx sensor 16 and the downstream NOx sensor 17, the current purification rate, that is, the startup purification rate ηstart at time t3 immediately after startup is calculated. Specifically, similarly to the calculation of the stop-time purification rate ηlast in step S14, the ratio of the purification amount to the NOx inflow amount is calculated as the purification rate. The NOx inflow amount is calculated based on the detection value of the upstream NOx sensor 16, and the NOx outflow amount is calculated based on the detection value of the downstream NOx sensor 17.

続くステップＳ２８，Ｓ３２では、ステップＳ２７で算出した始動時浄化率ηstartと、ステップＳ２６で算出した推定浄化率ηestとを比較して、これらの浄化率の乖離度が予め設定した所定値αよりも大きいか否かを判定するとともに、推定浄化率ηestに対する始動時浄化率ηstartの乖離が、浄化率の低下側及び上昇側のいずれであるかを判定する。すなわち、ステップＳ２８（診断手段）では、始動時浄化率ηstartが推定浄化率ηestに対して所定値αを超えて浄化率低下側に乖離しているか否かを判定する。また、ステップＳ３２（診断手段）では、始動時浄化率ηstartが推定浄化率ηestに対して所定値αを超えて浄化率上昇側に乖離しているか否かを判定する。   In subsequent steps S28 and S32, the starting purification rate ηstart calculated in step S27 is compared with the estimated purification rate ηest calculated in step S26, and the degree of divergence between these purification rates is greater than a predetermined value α set in advance. It is determined whether or not it is large, and it is determined whether the deviation of the startup purification rate ηstart from the estimated purification rate ηest is the decrease side or the increase side of the purification rate. That is, in step S28 (diagnostic means), it is determined whether or not the startup purification rate ηstart exceeds the predetermined value α with respect to the estimated purification rate ηest and deviates to the purification rate lowering side. In step S32 (diagnostic means), it is determined whether or not the starting purification rate ηstart exceeds the predetermined value α with respect to the estimated purification rate ηest and deviates to the purification rate increasing side.

図４は、低下側に乖離していると判定される場合の浄化率変化の一例であり、図５は、上昇側に乖離していると判定される場合の浄化率変化の一例である。図中の実線は実際のＮＯｘ浄化率の推移を示す。そして、前回運転の停止時点ｔ１での実線の値が、ステップＳ１４で算出される停止時浄化率ηlastに相当し、今回運転の始動直後の時点ｔ３での実線の値が、ステップ２５で算出される始動時浄化率ηstartに相当する。また、図中の点線は、停止期間中に尿素水の品質が変化しなかった場合における浄化率、つまり推定浄化率ηestの推移を示す。   FIG. 4 is an example of the purification rate change when it is determined that the deviation is on the lower side, and FIG. 5 is an example of the purification rate change when it is determined that the deviation is on the increase side. The solid line in the figure shows the transition of the actual NOx purification rate. Then, the value of the solid line at the time t1 when the previous operation is stopped corresponds to the stop purification rate ηlast calculated at step S14, and the value of the solid line at the time t3 immediately after the start of the current operation is calculated at step 25. This corresponds to the starting purification rate ηstart. Also, the dotted line in the figure shows the transition of the purification rate, that is, the estimated purification rate ηest when the quality of the urea water does not change during the stop period.

低下側に乖離していると判定した場合には（Ｓ２８：ＹＥＳ）、続くステップＳ２９にて尿素水濃度が異常に低下している低濃度異常と診断し、低濃度異常である旨を車両運転者に警告報知する。また、上昇側に乖離していると判定した場合には（Ｓ３２：ＹＥＳ）、続くステップＳ３３にて尿素水濃度が異常に上昇している高濃度異常と診断し、高濃度異常である旨を車両運転者に警告報知する。これらの警告報知は、例えば表示パネル３３（図１参照）にて警告表示や警告音により行う。また、いずれの側にも乖離していないと判定した場合には（Ｓ２８：ＮＯ，Ｓ３２：ＮＯ）、尿素水の品質は正常であると診断して図３の処理を終了する。   If it is determined that there is a divergence to the lower side (S28: YES), in the subsequent step S29, it is diagnosed as a low concentration abnormality in which the urea water concentration is abnormally decreased, and the vehicle is operated to indicate that the concentration is abnormal. Warning to the person. If it is determined that there is a deviation from the rising side (S32: YES), in the subsequent step S33, it is diagnosed that the urea water concentration is abnormally high, and a high concentration abnormality is indicated. A warning is given to the vehicle driver. These warning notifications are performed by warning display or warning sound on the display panel 33 (see FIG. 1), for example. Moreover, when it determines with not having deviated to any side (S28: NO, S32: NO), it diagnoses that the quality of urea water is normal, and complete | finishes the process of FIG.

ここで、ステップＳ２９で低濃度異常と診断した場合には、その異常診断した回数をカウントアップしている。図３の処理はエンジン始動直後においてのみ実行される処理であるため、異常診断した回数は、１トリップ毎に１回ずつカウントアップされ得る。そして、続くステップＳ３０では、低濃度異常との診断回数が所定回数Ｎ以上であるか否かを判定する。所定回数Ｎ以上であると判定された場合には（Ｓ３０：ＹＥＳ）、続くステップＳ３１にてＳＣＲ触媒１３の浄化性能が劣化等により低下している異常状態であると判定し、触媒性能低下異常である旨を車両運転者に警告報知する。なお、触媒性能低下異常と判定された場合には、尿素水品質診断処理の実行フラグをオフに設定することで、尿素水品質の誤診断回避を図ることが望ましい。   Here, when a low concentration abnormality is diagnosed in step S29, the number of times of abnormality diagnosis is counted up. Since the process of FIG. 3 is a process executed only immediately after the engine is started, the number of times of abnormality diagnosis can be counted up once for each trip. In the subsequent step S30, it is determined whether or not the number of diagnoses of low concentration abnormality is a predetermined number N or more. If it is determined that the predetermined number of times is N or more (S30: YES), it is determined in the following step S31 that the purification performance of the SCR catalyst 13 is deteriorated due to deterioration or the like, and the catalyst performance deterioration is abnormal. A warning is given to the vehicle driver. If it is determined that the catalyst performance is deteriorated abnormally, it is desirable to avoid an erroneous diagnosis of the urea water quality by setting the execution flag of the urea water quality diagnostic process to OFF.

以上詳述した本実施形態によれば、以下の効果が得られるようになる。   According to the embodiment described in detail above, the following effects can be obtained.

（１）尿素水の品質がエンジン停止期間中に変化したか否かを診断するにあたり、停止時浄化率ηlastに対する始動時浄化率ηstartの乖離度に基づいて、尿素水の品質を診断する。そして、この診断に用いる浄化率ηlast，ηstartは、尿素水添加量の制御に用いられているＮＯｘセンサ１６，１７の検出値を利用して算出できるので、特許文献１等に記載の診断専用の濃度センサを不要にしつつ尿素水の品質を診断できる。   (1) In diagnosing whether or not the quality of the urea water has changed during the engine stop period, the quality of the urea water is diagnosed based on the degree of deviation of the start-time purification rate ηstart from the stop-time purification rate ηlast. The purification rates ηlast and ηstart used for the diagnosis can be calculated using the detection values of the NOx sensors 16 and 17 used for controlling the urea water addition amount. The quality of urea water can be diagnosed while eliminating the need for a concentration sensor.

（２）エンジン停止前後の浄化率の乖離度を算出するにあたり、停止時浄化率ηlastの値を乖離度算出にそのまま用いるのではなく、停止時浄化率ηlastから吸着減少量に相当する浄化率の減少分、及び暖機時使用量に相当する浄化率の減少分を減算し、その減算により得られた値（推定浄化率ηest）を乖離度算出に用いる。そのため、エンジン停止期間中にＮＨ3吸着量が減少した分と、ＮＨ3吸着量のうち触媒暖機期間中にＮＯｘ浄化に使用された分とを加味して尿素水の品質が診断されるので、その診断精度を向上できる。 (2) When calculating the degree of divergence of the purification rate before and after the engine is stopped, the value of the purification rate ηlast at the time of stop is not used as it is for calculating the degree of divergence. The reduction amount and the reduction amount of the purification rate corresponding to the warm-up usage amount are subtracted, and the value (estimated purification rate ηest) obtained by the subtraction is used for calculating the divergence degree. Therefore, the quality of urea water is diagnosed by taking into account the amount of decrease in NH 3 adsorption during the engine stop period and the amount of NH 3 adsorption that was used for NOx purification during the catalyst warm-up period. The diagnostic accuracy can be improved.

（３）エンジン停止時におけるＮＨ3吸着量に影響を及ぼす運転履歴情報、つまり尿素水の添加量履歴、ＳＣＲ触媒１３からのＮＯｘ流出量履歴、及びＳＣＲ触媒１３の温度に応じて、前記乖離度算出に用いる停止時浄化率ηlastの値を補正するので、尿素水の品質診断の精度を向上できる。 (3) The deviation degree according to the operation history information that affects the NH 3 adsorption amount when the engine is stopped, that is, the urea water addition amount history, the NOx outflow history from the SCR catalyst 13, and the temperature of the SCR catalyst 13. Since the value of the stop purification rate ηlast used for the calculation is corrected, the accuracy of the quality diagnosis of urea water can be improved.

（４）尿素水添加弁１５、上流側ＮＯｘセンサ１６、下流側ＮＯｘセンサ１７、尿素水ポンプ２３等の排気浄化システムのハード系に異常が無いことを条件として、尿素水品質診断処理を実行するので、例えば異常状態の下流側ＮＯｘセンサ１７の検出値に基づき浄化率を算出することを回避でき、ひいては尿素水の品質を誤って診断することを回避できる。   (4) The urea water quality diagnosis process is executed on condition that there is no abnormality in the hardware system of the exhaust gas purification system such as the urea water addition valve 15, the upstream side NOx sensor 16, the downstream side NOx sensor 17, and the urea water pump 23. Therefore, for example, it is possible to avoid calculating the purification rate based on the detected value of the downstream side NOx sensor 17 in an abnormal state, and to avoid erroneously diagnosing the quality of the urea water.

（５）低濃度異常との診断回数が所定回数Ｎ以上になると、その場合にはＳＣＲ触媒１３の浄化性能が低下している異常状態であると判定する。よって、尿素水品質の診断結果を利用して、ＳＣＲ触媒１３の異常状態を検知することができる。   (5) When the number of diagnoses of low concentration abnormality is equal to or greater than the predetermined number N, in this case, it is determined that the abnormal state in which the purification performance of the SCR catalyst 13 is degraded. Therefore, the abnormal state of the SCR catalyst 13 can be detected using the diagnosis result of the urea water quality.

（他の実施形態）
本発明は上記実施形態の記載内容に限定されず、以下のように変更して実施してもよい。 (Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows.

・上述したステップＳ１４，Ｓ２７では、ＮＯｘセンサ１６，１７の検出値に基づき浄化率を算出しているが、ＮＯｘセンサ１６，１７の検出値及び尿素水の添加量に基づきＮＨ3吸着量を算出し、エンジン停止前後のＮＨ3吸着量を比較することで尿素水の品質を診断するようにしてもよい。 In steps S14 and S27 described above, the purification rate is calculated based on the detected values of the NOx sensors 16 and 17, but the NH 3 adsorption amount is calculated based on the detected values of the NOx sensors 16 and 17 and the added amount of urea water. Then, the quality of the urea water may be diagnosed by comparing the NH 3 adsorption amounts before and after the engine is stopped.

・上述したステップＳ１４，Ｓ２７では、浄化率の算出に用いるＮＯｘ流入量を、上流側ＮＯｘセンサ１６の検出値に基づき算出しているが、エンジン回転速度、エンジン負荷、燃料噴射量、ＥＧＲ率、加給圧等のエンジン運転状態に基づき算出してもよい。この場合には、上流側ＮＯｘセンサ１６を不要にできる。   In steps S14 and S27 described above, the NOx inflow amount used for calculating the purification rate is calculated based on the detected value of the upstream NOx sensor 16, but the engine speed, engine load, fuel injection amount, EGR rate, You may calculate based on engine operating conditions, such as a boost pressure. In this case, the upstream NOx sensor 16 can be dispensed with.

・上記実施形態では、ＳＣＲ触媒１３の温度が所定温度に達した触媒暖機完了時点を「始動時」として、その時点での浄化率をステップＳ２６，Ｓ２７にて推定、算出しているが、触媒暖機完了時点での浄化率を推定、算出することに替え、触媒暖機が完了してから所定時間が経過した時点での浄化率を推定、算出するようにしてもよいし、尿素水の添加を開始した時点での浄化率を推定、算出するようにしてもよい。   In the above embodiment, the catalyst warm-up completion time when the temperature of the SCR catalyst 13 has reached a predetermined temperature is set as “starting time”, and the purification rate at that time is estimated and calculated in steps S26 and S27. Instead of estimating and calculating the purification rate at the time of catalyst warm-up completion, the purification rate at the time when a predetermined time has elapsed after completion of catalyst warm-up may be estimated and calculated, or urea water It is also possible to estimate and calculate the purification rate at the time when the addition of is started.

・上述したステップＳ２８，Ｓ３２では、停止時浄化率ηlast（正確には停止時浄化率ηlastを用いて算出した推定浄化率ηest）からの始動時浄化率ηstartの乖離度を、推定浄化率ηestから始動時浄化率ηstartを差し引いた値としているが、停止時浄化率ηlast又は停止時浄化率ηlastを用いて算出した推定浄化率ηestに対する、始動時浄化率ηstartの比率としてもよい。   In steps S28 and S32 described above, the degree of deviation of the startup purification rate ηstart from the stop purification rate ηlast (more precisely, the estimated purification rate ηest calculated using the stoppage purification rate ηlast) is calculated from the estimated purification rate ηest. Although the value is obtained by subtracting the start-up purification rate ηstart, it may be the ratio of the start-up purification rate ηstart to the estimated purification rate ηest calculated using the stop-time purification rate ηlast or the stop-time purification rate ηlast.

・車載ディーゼルエンジン用の尿素ＳＣＲシステムとして実用化する以外に、例えばガソリンエンジン、特にリーンバーンエンジン用の尿素ＳＣＲシステムとして実用化することも可能である。また、尿素水以外の還元剤を用いる排気浄化システムにおいても本発明を同様に適用することが可能である。例えば、還元剤として、アンモニア含有の水溶液を用いることが考えられる。   -Besides being put into practical use as a urea SCR system for in-vehicle diesel engines, it can also be put into practical use as a urea SCR system for gasoline engines, particularly lean burn engines. Further, the present invention can be similarly applied to an exhaust purification system using a reducing agent other than urea water. For example, it is conceivable to use an aqueous solution containing ammonia as the reducing agent.

・上記実施形態では、前記乖離度に基づいて、尿素水の濃度異常を診断することに加えＳＣＲ触媒１３の異常を診断しているが、尿素水の濃度異常診断及びＳＣＲ触媒１３の異常診断のいずれかのみを診断するようにしてもよい。   In the above embodiment, the abnormality of the SCR catalyst 13 is diagnosed in addition to diagnosing the urea water concentration abnormality based on the degree of divergence. However, the urea water concentration abnormality diagnosis and the SCR catalyst 13 abnormality diagnosis are performed. Only one of them may be diagnosed.

・排気浄化システムの異常のうち、尿素水の品質、ＳＣＲ触媒１３の劣化、及びステップＳ１１，Ｓ２１で判定されるハード異常の他の異常についても、前記乖離度に基づけば簡素なハード構成で診断できる。例えば、尿素水の濃度を検出する濃度センサを設け、その濃度センサにより還元剤の濃度（品質）が正常である旨が検出されているにも拘わらず、前記乖離度が所定量異常であれば、排気浄化システムのハード構成に異常があると診断できる。   -Among the abnormalities of the exhaust purification system, the quality of urea water, the deterioration of the SCR catalyst 13, and other abnormalities of the hardware abnormality determined in steps S11 and S21 are also diagnosed with a simple hardware configuration based on the degree of deviation. it can. For example, if a concentration sensor that detects the concentration of urea water is provided and the concentration sensor detects that the concentration (quality) of the reducing agent is normal, the deviation degree is abnormal for a predetermined amount. It can be diagnosed that there is an abnormality in the hardware configuration of the exhaust purification system.

１３…ＳＣＲ触媒、１５…尿素水添加弁（還元剤添加手段）、１７…下流側ＮＯｘセンサ、４０…ＥＣＵ（品質診断装置）、Ｓ１１，Ｓ２１…ハード異常判定手段、Ｓ１４，Ｓ２７…浄化率算出手段、Ｓ１５…吸着量取得手段、Ｓ２３…吸着減少量取得手段、Ｓ２５…使用量算出手段、Ｓ２８，Ｓ３２…診断手段。   DESCRIPTION OF SYMBOLS 13 ... SCR catalyst, 15 ... Urea water addition valve (reducing agent addition means), 17 ... Downstream side NOx sensor, 40 ... ECU (quality diagnostic device), S11, S21 ... Hard abnormality determination means, S14, S27 ... Purification rate calculation Means, S15 ... Adsorption amount acquisition means, S23 ... Adsorption decrease amount acquisition means, S25 ... Use amount calculation means, S28, S32 ... Diagnostic means.

Claims (11)

内燃機関の排気通路に設けられて還元剤を添加する還元剤添加手段と、添加された還元剤を用いて排気中のＮＯｘを浄化する触媒と、を備える排気浄化システムに適用され、
ＮＯｘの浄化率を算出する浄化率算出手段と、
前記浄化率算出手段により算出された、前記内燃機関の前回停止時の浄化率に対する、前記内燃機関の今回始動時の浄化率の乖離度に基づいて、前記排気浄化システムの異常有無を診断する診断手段と、
を備えることを特徴とする排気浄化システムの異常診断装置。 Applied to an exhaust purification system comprising a reducing agent adding means provided in an exhaust passage of an internal combustion engine for adding a reducing agent, and a catalyst for purifying NOx in exhaust gas using the added reducing agent;
A purification rate calculating means for calculating a NOx purification rate;
Diagnosis for diagnosing the presence or absence of abnormality in the exhaust purification system based on the degree of deviation of the purification rate at the current start of the internal combustion engine from the purification rate at the previous stop of the internal combustion engine calculated by the purification rate calculation means Means,
An abnormality diagnosis device for an exhaust purification system, comprising: 前記診断手段は、前回停止時の浄化率に対する今回始動時の浄化率が低下側へ所定量以上乖離している場合に、還元剤の還元剤濃度が低下している低濃度異常と診断することを特徴とする請求項１に記載の排気浄化システムの異常診断装置。   The diagnostic means diagnoses a low-concentration abnormality in which the reducing agent concentration of the reducing agent is reduced when the purification rate at the current start relative to the purification rate at the time of the previous stop deviates by a predetermined amount or more. The abnormality diagnosis device for an exhaust purification system according to claim 1. 前記診断手段は、前回停止時の浄化率に対する今回始動時の浄化率が上昇側へ所定量以上乖離している場合に、還元剤の還元剤濃度が上昇している高濃度異常と診断することを特徴とする請求項１又は２に記載の排気浄化システムの異常診断装置。   The diagnostic means diagnoses a high concentration abnormality in which the reducing agent concentration of the reducing agent is increasing when the purification rate at the current start relative to the purification rate at the time of the previous stop deviates by a predetermined amount or more. The abnormality diagnosis device for an exhaust purification system according to claim 1 or 2. 前記触媒で吸着されている還元剤が前記内燃機関の停止期間中に減少した量と相関のある情報を吸着減少量情報として取得する吸着減少量取得手段を備え、
前記診断手段は、前記乖離度に加え前記吸着減少量情報に基づき、排気浄化システムの異常を診断することを特徴とする請求項１〜３のいずれか１つに記載の排気浄化システムの異常診断装置。 An adsorption reduction amount acquisition means for acquiring, as the adsorption reduction amount information, information correlated with the amount of reducing agent adsorbed by the catalyst decreased during the stop period of the internal combustion engine;
The abnormality diagnosis of the exhaust gas purification system according to any one of claims 1 to 3, wherein the diagnosis unit diagnoses an abnormality of the exhaust gas purification system based on the adsorption reduction amount information in addition to the degree of deviation. apparatus. 前記吸着減少量情報には、前記内燃機関の停止期間長さ、及び前記停止期間における外気温度の少なくとも１つが含まれていることを特徴とする請求項４に記載の排気浄化システムの異常診断装置。   The abnormality diagnosis device for an exhaust purification system according to claim 4, wherein the adsorption reduction amount information includes at least one of a length of a stop period of the internal combustion engine and an outside air temperature during the stop period. . 前記浄化率算出手段は、前記触媒の温度が所定温度に達して触媒暖機期間が終了した時点での浄化率を、始動時の浄化率として算出し、
前記触媒に吸着されていた還元剤が前記触媒暖機期間中にＮＯｘ浄化に使用された量を、暖機時使用量として算出する使用量算出手段を備え、
前記診断手段は、前記乖離度に加え前記暖機時使用量に基づき、排気浄化システムの異常を診断することを特徴とする請求項１〜５のいずれか１つに記載の排気浄化システムの異常診断装置。 The purification rate calculation means calculates the purification rate at the time when the catalyst temperature reaches a predetermined temperature and the catalyst warm-up period ends as the purification rate at the start,
Use amount calculating means for calculating the amount of the reducing agent adsorbed on the catalyst used for NOx purification during the catalyst warm-up period as the warm-up use amount,
The abnormality of the exhaust purification system according to any one of claims 1 to 5, wherein the diagnosis unit diagnoses an abnormality of the exhaust purification system based on the warm-up usage amount in addition to the degree of deviation. Diagnostic device. 前記内燃機関の運転履歴のうち前回停止時点における還元剤吸着量と相関のある履歴情報を、運転履歴情報として取得する吸着量取得手段を備え、
前記診断手段は、前記乖離度に加え前記運転履歴情報に基づき、排気浄化システムの異常を診断することを特徴とする請求項１〜６のいずれか１つに記載の排気浄化システムの異常診断装置。 An adsorption amount acquisition means for acquiring history information correlated with the reducing agent adsorption amount at the previous stop time among the operation history of the internal combustion engine as operation history information,
The abnormality diagnosis device for an exhaust purification system according to any one of claims 1 to 6, wherein the diagnosis unit diagnoses an abnormality of the exhaust purification system based on the operation history information in addition to the degree of deviation. . 前記運転履歴情報には、前回停止時までの還元剤の添加量履歴、前回停止時までの前記触媒からのＮＯｘ流出量履歴、及び前回停止時点における前記触媒の温度の少なくとも１つが含まれていることを特徴とする請求項７に記載の排気浄化システムの異常診断装置。   The operation history information includes at least one of a reducing agent addition amount history until the previous stop, a NOx outflow history from the catalyst until the previous stop, and a temperature of the catalyst at the previous stop time. The abnormality diagnosis device for an exhaust purification system according to claim 7. 前記排気浄化システムは、前記触媒から流出したＮＯｘの量を検出するＮＯｘセンサと、前記ＮＯｘセンサにより検出されたＮＯｘ量に基づき前記還元剤添加手段による還元剤添加量を制御する手段と、を備えており、
前記ＮＯｘセンサ及び前記還元剤添加手段の少なくとも１つについて異常の有無を判定するハード異常判定手段を備え、
前記診断手段は、前記ハード異常判定手段により異常が発生していないと判定されていることを条件として、還元剤が品質異常であるとの診断結果を出力することを特徴とする請求項１〜８のいずれか１つに記載の排気浄化システムの異常診断装置。 The exhaust purification system includes a NOx sensor that detects the amount of NOx that has flowed out of the catalyst, and a unit that controls the amount of reducing agent added by the reducing agent addition unit based on the amount of NOx detected by the NOx sensor. And
Hardware abnormality determination means for determining the presence or absence of abnormality for at least one of the NOx sensor and the reducing agent addition means,
The diagnostic means outputs a diagnostic result that the reducing agent is abnormal in quality on the condition that it is determined that no abnormality has occurred by the hardware abnormality determining means. The abnormality diagnosis device for an exhaust gas purification system according to any one of 8. 前記乖離度が所定量以上であるとの診断結果が所定回数以上出力された場合には、前記触媒の浄化性能が低下している異常状態であると判定する触媒異常判定手段を備えることを特徴とする請求項１〜９のいずれか１つに記載の排気浄化システムの異常診断装置。   And a catalyst abnormality determining unit that determines that the catalyst purification performance is in an abnormal state when the diagnosis result that the degree of divergence is a predetermined amount or more is output a predetermined number of times or more. An abnormality diagnosis device for an exhaust purification system according to any one of claims 1 to 9. 請求項１〜１０のいずれか１つに記載の排気浄化システムの異常診断装置と、
前記還元剤添加手段、前記触媒、及び前記触媒から流出したＮＯｘの量を検出するＮＯｘセンサの少なくとも１つと、
を備えることを特徴とする排気浄化システム。 An abnormality diagnosis device for an exhaust purification system according to any one of claims 1 to 10,
At least one of the reducing agent adding means, the catalyst, and a NOx sensor for detecting the amount of NOx flowing out of the catalyst;
An exhaust purification system comprising:
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