JP5142052B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Exhaust gas purification device for internal combustion engine Download PDF

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JP5142052B2
JP5142052B2 JP2009192243A JP2009192243A JP5142052B2 JP 5142052 B2 JP5142052 B2 JP 5142052B2 JP 2009192243 A JP2009192243 A JP 2009192243A JP 2009192243 A JP2009192243 A JP 2009192243A JP 5142052 B2 JP5142052 B2 JP 5142052B2
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正訓 横山
淳 川村
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Denso Corp
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Description

本発明は内燃機関の排気浄化装置に関する。   The present invention relates to an exhaust emission control device for an internal combustion engine.

ディーゼルエンジン等では、排気中の窒素酸化物（ＮＯｘ）を浄化する目的で排気管の途中に吸蔵還元型ＮＯｘ触媒（ＮＯｘ触媒、Ｌｅａｎ ＮＯｘ Ｔｒａｐ、ＬＮＴ）を配置する場合がある。ＬＮＴには、ディーゼルエンジンにおいて基本となるリーン雰囲気でＮＯｘが吸蔵され、間隔を置いてリッチ雰囲気に切り替えることにより吸蔵されていたＮＯｘが無害な窒素に還元されて放出される。   In a diesel engine or the like, a storage reduction type NOx catalyst (NOx catalyst, Lean NOx Trap, LNT) may be disposed in the middle of an exhaust pipe for the purpose of purifying nitrogen oxide (NOx) in exhaust gas. In the LNT, NOx is occluded in a basic lean atmosphere in a diesel engine, and the occluded NOx is reduced to harmless nitrogen and released by switching to a rich atmosphere at intervals.

リッチ雰囲気を形成する手法として排気燃料添加と呼ばれる手法がある。この手法では排気管に燃料添加弁（添加弁）を設置して、燃料添加弁から排気管に燃料を噴射（添加）することによりリッチ雰囲気を形成してＬＮＴに還元剤である未燃燃料が供給される。   There is a technique called exhaust fuel addition as a technique for forming a rich atmosphere. In this method, a fuel addition valve (addition valve) is installed in the exhaust pipe, and fuel is injected (added) from the fuel addition valve to the exhaust pipe to form a rich atmosphere, and unburned fuel as a reducing agent is added to the LNT. Supplied.

添加弁が装備されている場合、添加弁において燃料を噴射する噴孔が詰まる場合がある。詰まりの原因としては排気中の煤や、燃料中のデポジット成分がある。下記特許文献１では、排気中の煤は燃焼の適合で減らし、デポジット成分による詰まりが発生しないように燃料添加弁から燃料を噴射して噴孔の温度を低下させている。   When the addition valve is equipped, the injection hole for injecting fuel may be clogged in the addition valve. Causes of clogging include soot in the exhaust and deposit components in the fuel. In Patent Document 1 below, soot in exhaust gas is reduced due to the suitability of combustion, and fuel is injected from a fuel addition valve so as to prevent clogging due to deposit components, thereby lowering the temperature of the injection hole.

特開２００５−１０６０４７号公報JP 2005-106047 A

従来技術において燃料添加弁の劣化（詰まり）程度を検出する場合、ＮＯｘ還元中において燃料添加弁への噴射量の指令値から想定されるＡ／Ｆ値と、実際のＡ／Ｆ計測値とを取得して、この２数値から劣化程度を検出していた。   When detecting the degree of deterioration (clogging) of the fuel addition valve in the prior art, the A / F value assumed from the command value of the injection amount to the fuel addition valve during the NOx reduction and the actual A / F measurement value are obtained. The degree of deterioration was detected from these two values.

しかし、この手法には以下の問題がある。まず、Ａ／Ｆがリッチのときは、排ガス成分の影響によりＡ／Ｆセンサの精度が低減する。またＡ／Ｆがリーンである期間中にＮＯｘ触媒に吸着した酸素がリッチ期間中に排気中に放出されることにより、Ａ／Ｆ値が影響を受ける。したがって、こうした精度の低いＡ／Ｆ計測値を用いて算出された劣化程度も低精度となる。このような問題点を回避して高精度に燃料添加弁の劣化（詰まり）程度を検出する手法の開発が必要である。   However, this method has the following problems. First, when the A / F is rich, the accuracy of the A / F sensor is reduced due to the influence of exhaust gas components. Further, the oxygen adsorbed on the NOx catalyst during the period when the A / F is lean is released into the exhaust gas during the rich period, so that the A / F value is affected. Therefore, the degree of deterioration calculated using such an A / F measurement value with low accuracy also becomes low accuracy. It is necessary to develop a technique for avoiding such problems and detecting the degree of deterioration (clogging) of the fuel addition valve with high accuracy.

そこで本発明が解決しようとする課題は、上記問題点に鑑み、排気管に、ＮＯｘの吸蔵及び還元を行うＮＯｘ触媒と、そのＮＯｘ触媒の上流に燃料を添加する燃料添加弁とを備える構成において、燃料添加弁の劣化程度を高精度に検出できる内燃機関の排気浄化装置を提供することである。   In view of the above problems, the problem to be solved by the present invention is that the exhaust pipe is provided with a NOx catalyst for storing and reducing NOx, and a fuel addition valve for adding fuel upstream of the NOx catalyst. Another object of the present invention is to provide an exhaust purification device for an internal combustion engine that can detect the degree of deterioration of the fuel addition valve with high accuracy.

課題を解決するための手段及び発明の効果Means for Solving the Problems and Effects of the Invention

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、内燃機関からの排気を流通する排気通路に配置された、ＮＯｘを吸蔵し還元するための触媒と、前記排気通路における前記触媒よりも上流に配置されて前記排気通路内へ燃料を添加する添加弁と、前記排気通路における前記触媒の上流または下流に配置されて排気中の空燃比を検出する検出手段と、リーン期間中に、排気の空燃比がリッチとならない範囲で前記添加弁から燃料の添加を１回または連続的に複数回行い、前記検出手段によって検出された空燃比の計測値のうちで所定の収束条件を満たす計測値を用いて前記添加弁からの燃料添加量を推定する推定手段と、その推定手段による推定値と、前記添加弁への燃料添加量の指令値とから、前記添加弁の劣化程度を算出する算出手段と、前記算出手段により算出された前記劣化程度が大きい程、前記添加弁への燃料添加量の指令値を増加側に補正する補正手段と、を備えたことを特徴とする。
In order to solve the above problems, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes a catalyst for storing and reducing NOx disposed in an exhaust passage through which exhaust from the internal combustion engine flows, and the exhaust passage in the exhaust passage. An addition valve arranged upstream of the catalyst to add fuel into the exhaust passage; a detecting means arranged upstream or downstream of the catalyst in the exhaust passage to detect an air-fuel ratio in the exhaust; and during a lean period In addition, fuel is added from the addition valve once or continuously several times within a range in which the air-fuel ratio of the exhaust gas does not become rich, and a predetermined convergence condition among the measured values of the air-fuel ratio detected by the detection means is set. An estimation means for estimating the amount of fuel added from the addition valve using a measured value that satisfies, an estimated value by the estimation means, and a command value for the amount of fuel addition to the addition valve, the degree of deterioration of the addition valve Calculation A calculation unit that, the greater the degree of deterioration calculated by the calculation means, characterized by comprising a correction means for correcting the increase side command value of the fuel addition amount to the addition valve.

これにより本発明の内燃機関の排気浄化装置では、ＮＯｘ触媒でのＮＯｘ還元のために、その上流の排気管中に燃料を添加するための添加弁を備える構成において、リーン期間中に、排気の空燃比がリッチとならない範囲で添加弁から燃料添加を行い、空燃比を計測して燃料添加量を推定し、その推定値と添加量の指令値とから添加弁の劣化程度を算出するので、リッチ期間中に劣化程度を算出する場合のように、排ガス成分の影響による空燃比の計測値の精度低減や、リーン期間中に吸蔵された酸素の放出の影響を受けて、劣化程度の精度が低減するとの不具合を回避できる。したがって高精度に添加弁の劣化程度を算出できる内燃機関の排気浄化装置が実現できる。   Thus, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, in the configuration including the addition valve for adding fuel to the exhaust pipe upstream of the NOx reduction by the NOx catalyst, the exhaust gas is reduced during the lean period. Fuel is added from the addition valve in a range where the air-fuel ratio does not become rich, the fuel addition amount is estimated by measuring the air-fuel ratio, and the degree of deterioration of the addition valve is calculated from the estimated value and the command value of the addition amount. As in the case of calculating the degree of deterioration during the rich period, the accuracy of the degree of deterioration is affected by the reduction in the accuracy of the air-fuel ratio measurement due to the effect of exhaust gas components and the effect of the release of oxygen stored during the lean period. The problem of reduction can be avoided. Therefore, an exhaust gas purification apparatus for an internal combustion engine that can calculate the deterioration degree of the addition valve with high accuracy can be realized.

また前記算出手段により算出された前記劣化程度が大きい程、前記添加弁への燃料添加量の指令値を増加側に補正する補正手段を備えたとしてもよい。   Further, it may be provided with correction means for correcting the command value of the fuel addition amount to the addition valve to the increase side as the degree of deterioration calculated by the calculation means is larger.

これにより添加弁の劣化程度が大きいほど添加弁への添加量指令値を増加側に補正する、つまり詰まり程度が大きい（小さい）ほど指令値を大きく（小さく）するので、高精度に算出された劣化程度を用いて、噴孔の詰まりにも関わらず、実際の添加量を所望の値に近づけることができる。   As a result, as the deterioration degree of the addition valve is larger, the addition amount command value to the addition valve is corrected to an increase side, that is, as the degree of clogging is larger (smaller), the command value is larger (smaller). Using the degree of deterioration, it is possible to bring the actual addition amount close to a desired value despite the clogging of the nozzle hole.

また前記推定手段による前記推定のために行われる前記添加弁からの燃料の添加は１回または連続的に複数回行われるとしてもよい。   The addition of fuel from the addition valve performed for the estimation by the estimation unit may be performed once or a plurality of times continuously.

これにより添加弁からの燃料の添加は連続的に複数回行うので、添加された燃料の触媒への吸着や酸化等の影響を低減して、高精度に添加弁の劣化程度を算出できる。   As a result, the addition of fuel from the addition valve is continuously performed a plurality of times, so that the influence of adsorption or oxidation of the added fuel on the catalyst can be reduced, and the deterioration degree of the addition valve can be calculated with high accuracy.

また前記推定手段による前記推定のために用いられる前記空燃比の計測値は、前記計測値のうちで、所定の収束条件を満たす計測値が用いられるとしてもよい。   The measured value of the air-fuel ratio used for the estimation by the estimating means may be a measured value satisfying a predetermined convergence condition among the measured values.

これにより空燃比の計測値が所定の収束条件を満たす計測値を添加弁の劣化程度の算出に用いるので、添加された燃料の排気管への付着と、排気管へ付着した燃料の蒸発が釣り合う状態まで待つこととなって、触媒まで到達する燃料の量が添加された燃料と同量となる。したがって付着と蒸発とが一致しないことによる誤差の影響が低減されて、高精度に添加弁の劣化程度を算出できる。   As a result, the measured value of the air-fuel ratio that satisfies the predetermined convergence condition is used to calculate the deterioration degree of the addition valve, so that the adhesion of the added fuel to the exhaust pipe and the evaporation of the fuel attached to the exhaust pipe are balanced. The amount of fuel that reaches the catalyst is the same as that of the added fuel. Therefore, the influence of the error due to the fact that adhesion and evaporation do not match is reduced, and the deterioration degree of the addition valve can be calculated with high accuracy.

また前記所定の収束条件は、前記計測値の局所的な最小値のなかで、前回の最小値と今回の最小値とのずれが所定範囲内であるとの条件であるとしてもよい。   Further, the predetermined convergence condition may be a condition that a deviation between a previous minimum value and a current minimum value is within a predetermined range among local minimum values of the measurement values.

これにより空燃比の計測値の局所的な最小値のなかで、前回の最小値と今回の最小値とのずれが所定範囲内であるとの条件を収束条件とすることにより、適切に排気管への付着と蒸発とが一致しない場合の誤差の影響を低減して、高精度に添加弁の劣化程度を算出できる。   As a result, among the local minimum values of the measured values of the air-fuel ratio, the condition that the deviation between the previous minimum value and the current minimum value is within a predetermined range is set as the convergence condition, so that the exhaust pipe is appropriately The degree of deterioration of the addition valve can be calculated with high accuracy by reducing the influence of the error in the case where the adhesion to the ink does not coincide with the evaporation.

また前記所定の収束条件は、前記計測値の局所的な最小値を用いて、その平均値を算出し、その平均値と前記局所的な最小値とのずれが所定範囲内であるとの条件であるとしてもよい。   Further, the predetermined convergence condition is a condition that a local minimum value of the measured value is used to calculate an average value, and a deviation between the average value and the local minimum value is within a predetermined range. It may be.

これにより空燃比の計測値の局所的な最小値を用いて、その平均値を算出し、その平均値と前記局所的な最小値とのずれが所定範囲内であるとの条件を収束条件とすることにより、適切に排気管への付着と蒸発とが一致しない場合の誤差の影響を低減して、高精度に添加弁の劣化程度を算出できる。   Accordingly, the average value is calculated using the local minimum value of the measured value of the air-fuel ratio, and the condition that the deviation between the average value and the local minimum value is within a predetermined range is defined as the convergence condition. By doing so, it is possible to reduce the influence of the error when the attachment to the exhaust pipe and the evaporation do not coincide with each other properly, and to calculate the deterioration degree of the addition valve with high accuracy.

また前記所定の収束条件は、前記計測値が得られるにつれて周期的に前記添加弁からの燃料添加量を推定し、前回の燃料添加量の推定値と今回の燃料添加量の推定値とのずれが所定範囲内であるとの条件であるとしてもよい。   In addition, the predetermined convergence condition is that the fuel addition amount from the addition valve is periodically estimated as the measurement value is obtained, and the difference between the estimated value of the previous fuel addition amount and the estimated value of the current fuel addition amount is estimated. May be within a predetermined range.

これにより空燃比の計測値が得られるにつれて周期的に添加弁からの燃料添加量を推定し、前回の燃料添加量の推定値と今回の燃料添加量の推定値とのずれが所定範囲内であるとの条件を収束条件とすることにより、適切に排気管への付着と蒸発とが一致しない場合の誤差の影響を低減して、高精度に添加弁の劣化程度を算出できる。   As a result, the fuel addition amount from the addition valve is periodically estimated as the measured value of the air-fuel ratio is obtained, and the deviation between the estimated value of the previous fuel addition amount and the estimated value of the current fuel addition amount is within a predetermined range. By setting the certain condition as the convergence condition, it is possible to reduce the influence of the error when the attachment to the exhaust pipe and the evaporation do not match appropriately, and to calculate the deterioration degree of the addition valve with high accuracy.

また前記所定の収束条件は、前記計測値が得られるにつれて周期的に前記添加弁からの燃料添加量を推定し、その燃料添加量の推定値の平均値を算出し、その平均値と前記燃料添加量とのずれが所定範囲内であるとの条件であるとしてもよい。   The predetermined convergence condition is that the fuel addition amount from the addition valve is periodically estimated as the measurement value is obtained, an average value of the estimated value of the fuel addition amount is calculated, and the average value and the fuel are calculated. The condition may be that the deviation from the addition amount is within a predetermined range.

これにより空燃比の計測値が得られるにつれて周期的に添加弁からの燃料添加量を推定し、その燃料添加量の推定値の平均値を算出し、その平均値と燃料添加量とのずれが所定範囲内であるとの条件を収束条件とすることにより、適切に排気管への付着と蒸発とが一致しない場合の誤差の影響を低減して、高精度に添加弁の劣化程度を算出できる。   As a result, the fuel addition amount from the addition valve is periodically estimated as the measured value of the air-fuel ratio is obtained, the average value of the estimated value of the fuel addition amount is calculated, and the deviation between the average value and the fuel addition amount is calculated. By setting the condition of being within a predetermined range as the convergence condition, it is possible to reduce the influence of the error when the adhesion to the exhaust pipe and the evaporation do not match properly, and to calculate the deterioration degree of the addition valve with high accuracy. .

本発明に係る内燃機関の排気浄化装置の実施例での装置構成図。The apparatus block diagram in the Example of the exhaust gas purification apparatus of the internal combustion engine which concerns on this invention. 燃料添加弁の劣化度に対処する処理手順を示すフローチャート。The flowchart which shows the process sequence which copes with the deterioration degree of a fuel addition valve. Ａ／Ｆ計測値と添加量算出値を示す図。The figure which shows A / F measurement value and addition amount calculation value. 複数回の燃料添加を説明する図。The figure explaining the fuel addition of multiple times.

以下、本発明の実施例を図面を参照しつつ説明する。まず図１は、本発明に係る内燃機関の排気浄化装置１の実施例１の装置構成の概略図である。図１の排気浄化装置１はディーゼルエンジン２（エンジン）に対して構成され、吸気管３、排気管４を備える。図１の構成は車両に装備されているとすればよい。   Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 1 is a schematic diagram of a device configuration of Embodiment 1 of an exhaust gas purification device 1 for an internal combustion engine according to the present invention. An exhaust emission control device 1 in FIG. 1 is configured for a diesel engine 2 (engine) and includes an intake pipe 3 and an exhaust pipe 4. The configuration shown in FIG. 1 may be installed in a vehicle.

吸気管３を通ってエンジン２に空気（新気、吸気）が供給され、エンジン２からの排気は排気管４へ排出される。エンジン２には図示しないインジェクタが装備され、インジェクタから筒内へ燃料が噴射される。吸気管３にはエアフロメータ３１が設置されている。エアフロメータ３１によって（単位時間当たりの）吸気量が計測される。   Air (fresh air, intake air) is supplied to the engine 2 through the intake pipe 3, and the exhaust from the engine 2 is discharged to the exhaust pipe 4. The engine 2 is equipped with an injector (not shown), and fuel is injected from the injector into the cylinder. An air flow meter 31 is installed in the intake pipe 3. The air flow meter 31 measures the amount of intake air (per unit time).

排気管４には上流側から順に、燃料添加弁４１（添加弁）、吸蔵還元型ＮＯｘ触媒６（ＮＯｘ触媒、Ｌｅａｎ ＮＯｘ Ｔｒａｐ、ＬＮＴ）、Ａ／Ｆセンサ４２が配置されている。ＮＯｘ還元の際に添加弁４１からはリッチ雰囲気を形成するために燃料が添加（噴射）される。Ａ／Ｆセンサ４２によってＡ／Ｆ値が計測される。Ａ／Ｆセンサ４２は、排気中のＨＣ（炭化水素）によってＡ／Ｆの計測値が影響を受けることを抑制するためにＬＮＴ６の下流位置に配置されている。なおＡ／Ｆセンサ４２はＬＮＴ６の上流位置に配置してもよい。   A fuel addition valve 41 (addition valve), an occlusion reduction type NOx catalyst 6 (NOx catalyst, Lean NOx Trap, LNT), and an A / F sensor 42 are arranged in the exhaust pipe 4 in order from the upstream side. During the NOx reduction, fuel is added (injected) from the addition valve 41 to form a rich atmosphere. The A / F value is measured by the A / F sensor 42. The A / F sensor 42 is arranged at a downstream position of the LNT 6 in order to suppress the measurement value of A / F from being affected by HC (hydrocarbon) in the exhaust gas. The A / F sensor 42 may be disposed at an upstream position of the LNT 6.

ＬＮＴ６は例えばセラミック製の基材上に担体の層が形成されて、担体上に吸蔵剤と触媒とが担持された構造であるとすればよい。担体としては例えばガンマアルミナを用いれば表面の凹凸による大きな表面積によって多くの吸蔵剤、触媒が担持できて好適である。また吸蔵剤としては例えばバリウム、リチウム、カリウムなどを用いればよい。触媒としては例えば白金などを用いればよい。   The LNT 6 may have a structure in which, for example, a carrier layer is formed on a ceramic substrate, and a storage agent and a catalyst are supported on the carrier. As the carrier, for example, gamma alumina is suitable because it can carry a large amount of storage agent and catalyst due to its large surface area due to surface irregularities. For example, barium, lithium, potassium, or the like may be used as the storage agent. For example, platinum or the like may be used as the catalyst.

ＬＮＴ６においては、理論空燃比（ストイキ）よりも燃料が希薄な（通常、Ａ／Ｆ値（空燃比値）は１７以上）リーン雰囲気時に排気中のＮＯｘが吸蔵剤に吸蔵される。そして理論空燃比よりも燃料が過剰な（通常、Ａ／Ｆ値は１４．５以下）リッチ雰囲気に空燃比が調節され、所定の温度条件（例えば触媒が機能するために摂氏３００度以上）が満たされると、吸蔵剤に吸蔵されていたＮＯｘが、燃料中の成分から生成された還元剤によって還元されて無害な窒素となって排出される。   In the LNT6, the fuel is leaner than the stoichiometric air fuel ratio (stoichiometric) (normally, the A / F value (air fuel ratio value) is 17 or more), and NOx in the exhaust is occluded in the occlusion agent in a lean atmosphere. The fuel is more than the stoichiometric air-fuel ratio (usually A / F value is 14.5 or less), the air-fuel ratio is adjusted to a rich atmosphere, and a predetermined temperature condition (for example, 300 degrees Celsius or more for the catalyst to function) When it is satisfied, the NOx stored in the storage agent is reduced by the reducing agent generated from the components in the fuel and discharged as harmless nitrogen.

上で述べたエアフロメータ３１、Ａ／Ｆセンサ４２の計測値は電子制御装置７（ＥＣＵ：Ｅｌｅｃｔｒｏｎｉｃ Ｃｏｎｔｒｏｌ Ｕｎｉｔ）へ送られる。またＥＣＵ７によりインジェクタによるエンジン２への燃料噴射量や噴射時期、添加弁４１による燃料噴射における噴射量や噴射時期が制御される。ＥＣＵ７は通常のコンピュータの構造を有するとし、各種演算をおこなうＣＰＵや各種情報の記憶を行うメモリを備えるとすればよい。また車室内には表示部９が装備されて乗員に各種情報を報知する。   The measured values of the air flow meter 31 and the A / F sensor 42 described above are sent to an electronic control unit 7 (ECU: Electronic Control Unit). Further, the ECU 7 controls the fuel injection amount and injection timing to the engine 2 by the injector, and the injection amount and injection timing in the fuel injection by the addition valve 41. The ECU 7 may have a normal computer structure, and may include a CPU that performs various calculations and a memory that stores various types of information. In addition, a display unit 9 is provided in the passenger compartment to notify the passengers of various information.

以上の構成のもとで本実施例では、リーン期間中に燃料添加弁の劣化（詰まり）程度の検出のために燃料添加を実行して劣化程度を高精度に検出する。その処理手順は図２のフローチャートに示されている。図２の処理手順はプログラム化されてＥＣＵ７に記憶しておき、ＥＣＵ７が自動的に実行するとすればよい。   With this configuration, in this embodiment, fuel addition is executed to detect the degree of deterioration (clogging) of the fuel addition valve during the lean period, and the degree of deterioration is detected with high accuracy. The processing procedure is shown in the flowchart of FIG. The processing procedure in FIG. 2 may be programmed and stored in the ECU 7 and automatically executed by the ECU 7.

ＥＣＵ７はまず手順Ｓ１０で劣化度検出要求が出ているかを判断する。劣化度検出要求とは、ＥＣＵ７が、添加弁４１の使用期間等から劣化度を検出する必要があると判断した場合に出す要求である。同要求が出ている場合（Ｓ１０：ＹＥＳ）は、Ｓ２０へ進み、出ていない場合（Ｓ１０：ＮＯ）は、図２の処理を終了する。   The ECU 7 first determines in step S10 whether a deterioration degree detection request has been issued. The deterioration level detection request is a request issued when the ECU 7 determines that it is necessary to detect the deterioration level from the usage period of the addition valve 41 or the like. When the request is issued (S10: YES), the process proceeds to S20. When the request is not issued (S10: NO), the process of FIG.

次にＳ２０でＥＣＵ７は、添加弁４１からの燃料添加を開始する。ただし、この添加はＮＯｘ還元とは異なる期間、つまりリーン期間中に、添加弁４１の劣化度（劣化程度、詰まりの程度）を検出することのみを目的として実行する。次にＳ３０でＥＣＵ７は、波形が安定（収束）しているか否かを判定する。ここで波形とは、Ａ／Ｆ計測値の波形としてもよく、それから算出された燃料添加量の推定値の波形としてもよい。   Next, in S <b> 20, the ECU 7 starts adding fuel from the addition valve 41. However, this addition is executed only for the purpose of detecting the degree of deterioration of the addition valve 41 (deterioration degree, clogging degree) during a period different from NOx reduction, that is, during the lean period. Next, in S30, the ECU 7 determines whether or not the waveform is stable (converged). Here, the waveform may be a waveform of an A / F measurement value or a waveform of an estimated value of the fuel addition amount calculated therefrom.

波形の安定（収束）に関して図３を参照して説明する。図３には上から順に添加弁駆動信号、Ａ／Ｆ計測値、添加量推定値の時間波形が示されている。以下、時間はｔで示す。添加弁駆動信号とは、ＥＣＵ７から送られる添加弁４１の駆動指令の信号であり、ＯＮである期間（通電期間）、添加弁４１の噴射部が通電されて燃料が排気管４に添加される。   Waveform stability (convergence) will be described with reference to FIG. FIG. 3 shows an addition valve drive signal, an A / F measurement value, and an addition amount estimated value time waveform in order from the top. Hereinafter, the time is indicated by t. The addition valve drive signal is a drive command signal for the addition valve 41 sent from the ECU 7, and the injection portion of the addition valve 41 is energized and fuel is added to the exhaust pipe 4 during the ON period (energization period). .

図３に示されたとおり、駆動信号は時点Ｔ０、Ｔ１、Ｔ２、・・・で通電期間が始まる周期的な波形とすればよい。本実施例では、通電期間、添加インターバル（通電しない期間）は全て同じとする。これにより連続的に複数回燃料が添加される。なお燃料の添加は１回としてもよい。   As shown in FIG. 3, the drive signal may be a periodic waveform in which the energization period starts at time points T0, T1, T2,. In this embodiment, the energization period and the addition interval (non-energization period) are all the same. As a result, the fuel is continuously added a plurality of times. The fuel may be added once.

このような周期的な燃料添加により、Ａ／Ｆセンサ４２によるＡ／Ｆ計測値ＡＦ（ｔ）は、図３のような過渡応答を有し、徐々に定常波形へと収束する波形となる。Ａ／Ｆ計測値ＡＦ（ｔ）の過渡応答及び定常応答は、添加弁駆動信号と同じ周期の周期性を有する波形となる。ｉ番目の周期におけるＡ／Ｆ計測値のピーク値（Ａ／Ｆ計測値の各周期内での最小値）をＡＦｐ（ｉ）で表記する。また添加弁４１からの燃料添加がない場合の時間ｔでのＡ／Ｆ値をＡＦ０（ｔ）とする。   By such periodic fuel addition, the A / F measurement value AF (t) by the A / F sensor 42 has a transient response as shown in FIG. 3 and gradually becomes a waveform that converges to a steady waveform. The transient response and steady state response of the A / F measurement value AF (t) have a waveform having the same periodicity as the addition valve drive signal. The peak value of the A / F measurement value in the i-th cycle (the minimum value in each cycle of the A / F measurement value) is expressed as AFp (i). The A / F value at time t when no fuel is added from the addition valve 41 is AF0 (t).

図３に示されているように、本実施例における燃料添加はＡ／Ｆがリッチにならない範囲で行われる。この条件を満たすように通電期間、添加インターバルを予め設定すればよい。ＡＦ０（ｔ）は、運転条件が定常状態であるとみなされる場合は、添加開始以前（図３ではＴ０以前）のＡ／Ｆ計測値と同じとみなしてもよい。またエアフロメータ３１で計測した吸気量を、ＥＣＵ７からエンジン２のインジェクタへの筒内噴射量の指令値で除算した時々刻々の値としてもよい。   As shown in FIG. 3, the fuel addition in the present embodiment is performed within a range where A / F does not become rich. The energization period and the addition interval may be set in advance so as to satisfy this condition. AF0 (t) may be regarded as the same as the A / F measurement value before the addition start (before T0 in FIG. 3) when the operation condition is considered to be a steady state. Alternatively, the intake air amount measured by the air flow meter 31 may be an instantaneous value obtained by dividing the intake air amount from the ECU 7 into the in-cylinder injection amount command value to the injector of the engine 2.

添加量推定値は、各周期での合計の燃料添加量の推定値であり、Ａ／Ｆ計測値ＡＦ（ｔ）を用いて次の式（Ｅ１）により算出する。ただしｉ番目の周期での添加量算出値をＱ（ｉ）で表記する。またエアフロメータによって計測された時間ｔにおける単位時間あたりの吸気量をＧ（ｔ）で表記する。式（Ｅ１）の右辺での積分区間は時間Ｔｉ−２からＴｉ−１である。なお式（Ｅ１）の積分は実際に行う場合は適当に差分（和分）近似すればよい。
Ｑ（ｉ）＝∫｛（Ｇ（ｔ）／ＡＦ（ｔ）−Ｇ（ｔ）／ＡＦ０（ｔ））｝ｄｔ
（ｉ＝２、３、４、・・・） （Ｅ１） The added amount estimated value is an estimated value of the total fuel added amount in each cycle, and is calculated by the following equation (E1) using the A / F measured value AF (t). However, the addition amount calculated value in the i-th cycle is denoted by Q (i). Further, the intake air amount per unit time at the time t measured by the air flow meter is expressed as G (t). The integration interval on the right side of equation (E1) is from time Ti-2 to Ti-1. It should be noted that the integration of equation (E1) may be appropriately approximated by a difference (sum) when actually performed.
Q (i) = ∫ {(G (t) / AF (t) −G (t) / AF0 (t))} dt
(I = 2, 3, 4,...) (E1)

式（Ｅ１）の意味を以下で説明する。まず式（Ｅ１）の被積分関数のうちＧ（ｔ）／ＡＦ（ｔ）は、Ａ／Ｆセンサ４２の計測値から算出される、時間ｔにおける単位時間当たりの燃料添加量の推定値である。またＧ（ｔ）／ＡＦ０（ｔ）は、燃料添加がなされない場合における、時間ｔにおける単位時間当たりの燃料添加量の推定値である。したがって、この２項の差分は、燃料添加弁からの単位時間当たりの燃料添加量の推定値となる。よって、これを１周期分積分すれば、１周期分の燃料添加弁からの燃料添加量の合計値となる。   The meaning of the formula (E1) will be described below. First, G (t) / AF (t) in the integrand of the equation (E1) is an estimated value of the amount of fuel added per unit time at time t calculated from the measured value of the A / F sensor 42. . G (t) / AF0 (t) is an estimated value of the amount of fuel added per unit time at time t when no fuel is added. Therefore, the difference between the two terms is an estimated value of the amount of fuel added per unit time from the fuel addition valve. Therefore, if this is integrated for one cycle, the total amount of fuel addition from the fuel addition valve for one cycle is obtained.

図２に戻り、手順Ｓ３０において、以上のような図３のＡＦｐ（ｉ）あるいはＱ（ｉ）の波形が安定（あるいは収束）したかどうかを判定する。安定（収束）の判定方法の詳細は後述する。   Returning to FIG. 2, in step S30, it is determined whether the AFp (i) or Q (i) waveform of FIG. 3 as described above is stable (or converged). Details of the stability (convergence) determination method will be described later.

安定の判定を行う理由は次のとおりである。一般に添加弁４１から添加された燃料のうち排気管４に付着する部分があり、逆に排気管４に付着していた燃料が排気管４へ蒸発する。ＡＦｐ（ｉ）あるいはＱ（ｉ）の波形が安定化する以前は上記付着が蒸発よりも多く、安定化した時点で上記付着と蒸発とが釣り合う（同量となる）と考えられる。付着と蒸発とが釣り合えば、添加弁４１から添加された燃料とＬＮＴ６に到着する燃料とが同量であるとみなされる。したがってＡＦｐ（ｉ）あるいはＱ（ｉ）の波形が安定化するまで待つことにより、Ａ／Ｆ計測値から添加された燃料量が高精度に推定できることとなる。   The reason for determining the stability is as follows. Generally, there is a portion of the fuel added from the addition valve 41 that adheres to the exhaust pipe 4, and conversely, the fuel that has adhered to the exhaust pipe 4 evaporates to the exhaust pipe 4. Before the AFp (i) or Q (i) waveform is stabilized, the adhesion is more than the evaporation, and it is considered that the adhesion and the evaporation are balanced (same amount) at the time of stabilization. If the adhesion and evaporation are balanced, it is considered that the fuel added from the addition valve 41 and the fuel arriving at the LNT 6 are the same amount. Therefore, by waiting until the AFp (i) or Q (i) waveform is stabilized, the amount of fuel added from the A / F measurement value can be estimated with high accuracy.

波形が安定（収束）している場合（Ｓ３０：ＹＥＳ）は、Ｓ４０へ進み、安定（収束）していない場合（Ｓ３０：ＮＯ）は、安定（収束）するまでＳ３０を繰り返す。   When the waveform is stable (converged) (S30: YES), the process proceeds to S40. When the waveform is not stable (converged) (S30: NO), S30 is repeated until the waveform is stable (converged).

次にＳ４０では、添加弁４１からの燃料添加量を算出（推定）する。この算出は上で説明したＱ（ｉ）の算出と同じである。すなわちＳ３０で安定になったと判定されたのがｉ−１番目の周期だった場合は、Ｓ４０でＱ（ｉ）を算出する。Ｓ３０で安定（収束）を判定した波形がＱ（ｉ）の波形の場合は、手順Ｓ４０を省略して次のＳ５０に進めばよい。   Next, in S40, the amount of fuel added from the addition valve 41 is calculated (estimated). This calculation is the same as the calculation of Q (i) described above. That is, if it is determined that the stable period is S-1 in S30, Q (i) is calculated in S40. If the waveform for which stability (convergence) is determined in S30 is a waveform of Q (i), step S40 may be omitted and the process proceeds to the next S50.

Ｓ５０では劣化度（劣化程度）を算出する。例えば劣化度は、添加弁４１への添加量指令値と、Ｓ３０あるいはＳ４０で求めたＱ（ｉ）（ただし安定だと判定されたのがｉ−１番目の周期のとき）との比と定義する。次にＳ６０では、Ｓ５０で算出した劣化度が所定値以下であるか否かを判定する。所定値以下の場合（Ｓ６０：ＹＥＳ）はＳ７０に進み、所定値より大きい場合（Ｓ６０：ＮＯ）はＳ８０に進む。   In S50, the degree of deterioration (deterioration degree) is calculated. For example, the degree of deterioration is defined as a ratio between an addition amount command value to the addition valve 41 and Q (i) obtained in S30 or S40 (however, when it is determined that the cycle is the i−1th cycle). To do. Next, in S60, it is determined whether or not the degree of deterioration calculated in S50 is a predetermined value or less. If it is equal to or smaller than the predetermined value (S60: YES), the process proceeds to S70, and if it is larger than the predetermined value (S60: NO), the process proceeds to S80.

Ｓ７０では添加弁４１の劣化度が相対的に小さいので、添加パラメータを補正することで対処する。添加パラメータは、図３に示された通電期間、添加インターバルである。上記劣化度の値が例えばＡならば、添加弁４１からの実際の添加量がＡ倍となるように通電期間、添加インターバルを調節する。例えば通電期間を調節する場合は、通電期間をＡ倍にする。また添加インターバルを調節する場合は、通電期間と添加インターバルとの和が１／Ａ倍になるように添加インターバルを調節する。   In S70, since the deterioration degree of the addition valve 41 is relatively small, this is dealt with by correcting the addition parameter. The addition parameter is the energization period and the addition interval shown in FIG. If the value of the deterioration degree is A, for example, the energization period and the addition interval are adjusted so that the actual addition amount from the addition valve 41 is A times. For example, when adjusting the energization period, the energization period is set to A times. When adjusting the addition interval, the addition interval is adjusted so that the sum of the energization period and the addition interval is 1 / A times.

Ｓ８０では、添加弁４１の劣化度が相対的に大きいので、運転者あるいは乗員に「排気管に装備された添加弁の修理が必要です」との内容の報知を行う。これは例えば車室内に装備された表示部９を用いて行えばよい。以上が図２の処理である。   In S80, since the deterioration degree of the addition valve 41 is relatively large, the driver or the passenger is notified of the content that “the repair of the addition valve installed in the exhaust pipe is necessary”. This may be performed using, for example, the display unit 9 installed in the passenger compartment. The above is the processing of FIG.

次に上記Ｓ３０での波形の安定（収束）の判定方法を説明する。以下ではＡＦｐ（ｉ）を用いて説明するが、Ｑ（ｉ）を用いて収束判定する場合は、単に以下でＡＦｐ（ｉ）をＱ（ｉ）に置き替えればよい。判定方法を２つ説明する。第１の判定方法では、ＡＦｐ（ｉ）の今回値と前回値との差分、すなわちＡＦｐ（ｉ）−ＡＦｐ（ｉ−１）の絶対値が所定値以下となったら安定（収束）したと判定する。第２の判定方法では、今回（現在）の時点までの過去の所定個のＡＦｐ（ｉ）の平均値を求め、その平均値から所定範囲内に過去の所定個のＡＦｐ（ｉ）が全て含まれたら安定（収束）したと判定する。第１の判定方法はより簡易である。第２の判定方法はより確実に収束が検出できる。   Next, a method for determining the stability (convergence) of the waveform in S30 will be described. In the following, description will be made using AFp (i). However, when convergence is determined using Q (i), AFp (i) may simply be replaced with Q (i) below. Two determination methods will be described. In the first determination method, when the difference between the current value of AFp (i) and the previous value, that is, the absolute value of AFp (i) −AFp (i−1) is equal to or less than a predetermined value, it is determined that the state is stable (converged). To do. In the second determination method, an average value of a predetermined number of past AFp (i) up to the current (current) time point is obtained, and the past predetermined number of AFp (i) is included within a predetermined range from the average value. If it is, it is determined that it is stable (converged). The first determination method is simpler. The second determination method can detect convergence more reliably.

上記実施例では添加弁４１からの燃料添加を図３のとおり複数回行った。この効果が図４に示されている。図４（ａ）のように１回のみ添加する場合は、図のとおりＡ／Ｆ計測値とＡ／Ｆ真値とのずれ（図における斜線部）が相対的に大きくなる。これに対して（ｂ）のように複数回添加する場合には、１回当たりの添加量を相対的に少量とするので、Ａ／Ｆ計測値とＡ／Ｆ真値とのずれ（個々の斜線部）が相対的に小さくできる。したがってＡ／Ｆ計測値の精度が相対的に高くできるので、劣化度も高精度に算出できる。   In the above embodiment, the fuel addition from the addition valve 41 was performed a plurality of times as shown in FIG. This effect is illustrated in FIG. When added only once as shown in FIG. 4A, the difference between the A / F measurement value and the A / F true value (shaded portion in the figure) becomes relatively large as shown in the figure. On the other hand, in the case of adding a plurality of times as shown in (b), since the amount added per time is relatively small, the deviation between the A / F measured value and the A / F true value (individual The hatched portion can be made relatively small. Therefore, since the accuracy of the A / F measurement value can be relatively high, the degree of deterioration can also be calculated with high accuracy.

なお図２の処理は車両の運転状態が定常的であると判断できる場合にのみ実行するとしてもよい。その場合、図３におけるＡＦ０（ｔ）が（ほぼ）定常値であるとみなせるので、ＡＦ０（ｔ）を添加前（時点Ｔ０以前）のＡ／Ｆ計測値と同じとみなすことができ、より簡易な処理となる。上記実施例でのエンジン２はディーゼルエンジンでなく、リーンバーンガソリンエンジンとしても上で述べた効果が同様に得られる。   The process of FIG. 2 may be executed only when it can be determined that the driving state of the vehicle is steady. In that case, since AF0 (t) in FIG. 3 can be regarded as a (substantially) steady value, AF0 (t) can be regarded as the same as the A / F measurement value before the addition (before time T0), which is simpler. Processing. The engine 2 in the above embodiment is not a diesel engine but a lean burn gasoline engine.

１ 排気浄化装置
２ ディーゼルエンジン（エンジン、内燃機関）
３ 吸気管
４ 排気管（排気通路）
６ 吸蔵還元型ＮＯｘ触媒（ＮＯｘ触媒、触媒、ＬＮＴ）
７ ＥＣＵ
４１ 燃料添加弁
４２ Ａ／Ｆセンサ 1 Exhaust purification device 2 Diesel engine (engine, internal combustion engine)
3 Intake pipe 4 Exhaust pipe (exhaust passage)
6 NOx storage reduction catalyst (NOx catalyst, catalyst, LNT)
7 ECU
41 Fuel addition valve 42 A / F sensor

Claims (5)

内燃機関からの排気を流通する排気通路に配置された、ＮＯｘを吸蔵し還元するための触媒と、
前記排気通路における前記触媒よりも上流に配置されて前記排気通路内へ燃料を添加する添加弁と、
前記排気通路における前記触媒の上流または下流に配置されて排気中の空燃比を検出する検出手段と、
リーン期間中に、排気の空燃比がリッチとならない範囲で前記添加弁から燃料の添加を１回または連続的に複数回行い、前記検出手段によって検出された空燃比の計測値のうちで所定の収束条件を満たす計測値を用いて前記添加弁からの燃料添加量を推定する推定手段と、
その推定手段による推定値と、前記添加弁への燃料添加量の指令値とから、前記添加弁の劣化程度を算出する算出手段と、
前記算出手段により算出された前記劣化程度が大きい程、前記添加弁への燃料添加量の指令値を増加側に補正する補正手段と、
を備えたことを特徴とする内燃機関の排気浄化装置。 A catalyst for storing and reducing NOx disposed in an exhaust passage through which exhaust from the internal combustion engine flows;
An addition valve that is arranged upstream of the catalyst in the exhaust passage and adds fuel into the exhaust passage;
A detecting means that is arranged upstream or downstream of the catalyst in the exhaust passage and detects an air-fuel ratio in the exhaust;
During the lean period, fuel is added from the addition valve once or continuously several times within a range in which the air-fuel ratio of the exhaust gas does not become rich, and a predetermined value among the measured values of the air-fuel ratio detected by the detection means Estimating means for estimating the amount of fuel added from the addition valve using a measured value that satisfies a convergence condition ;
Calculating means for calculating the degree of deterioration of the addition valve from the estimated value by the estimation means and the command value of the fuel addition amount to the addition valve;
Correction means for correcting the command value of the amount of fuel added to the addition valve to an increase side as the degree of deterioration calculated by the calculation means increases;
An exhaust emission control device for an internal combustion engine, comprising: 前記所定の収束条件は、前記計測値の局所的な最小値のなかで、前回の最小値と今回の最小値とのずれが所定範囲内であるとの条件である請求項１に記載の内燃機関の排気浄化装置。 2. The internal combustion engine according to claim 1 , wherein the predetermined convergence condition is a condition that a deviation between a previous minimum value and a current minimum value is within a predetermined range among local minimum values of the measurement values. Engine exhaust purification system. 前記所定の収束条件は、前記計測値の局所的な最小値を用いて、その平均値を算出し、その平均値と前記局所的な最小値とのずれが所定範囲内であるとの条件である請求項１に記載の内燃機関の排気浄化装置。 The predetermined convergence condition is a condition that a local minimum value of the measurement value is used to calculate an average value, and a deviation between the average value and the local minimum value is within a predetermined range. The exhaust emission control device for an internal combustion engine according to claim 1 . 前記所定の収束条件は、前記計測値が得られるにつれて周期的に前記添加弁からの燃料添加量を推定し、前回の燃料添加量の推定値と今回の燃料添加量の推定値とのずれが所定範囲内であるとの条件である請求項１に記載の内燃機関の排気浄化装置。 The predetermined convergence condition periodically estimates the fuel addition amount from the addition valve as the measurement value is obtained, and there is a difference between the estimated value of the previous fuel addition amount and the estimated value of the current fuel addition amount. The exhaust emission control device for an internal combustion engine according to claim 1 , wherein the exhaust gas purification device is in a predetermined range. 前記所定の収束条件は、前記計測値が得られるにつれて周期的に前記添加弁からの燃料添加量を推定し、その燃料添加量の推定値の平均値を算出し、その平均値と前記燃料添加量とのずれが所定範囲内であるとの条件である請求項１に記載の内燃機関の排気浄化装置。 The predetermined convergence condition is that the fuel addition amount from the addition valve is periodically estimated as the measurement value is obtained, an average value of the estimated value of the fuel addition amount is calculated, and the average value and the fuel addition amount are calculated. 2. The exhaust emission control device for an internal combustion engine according to claim 1 , wherein the deviation from the amount is within a predetermined range.
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