JP4665830B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Exhaust gas purification system for internal combustion engine Download PDF

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JP4665830B2
JP4665830B2 JP2006143948A JP2006143948A JP4665830B2 JP 4665830 B2 JP4665830 B2 JP 4665830B2 JP 2006143948 A JP2006143948 A JP 2006143948A JP 2006143948 A JP2006143948 A JP 2006143948A JP 4665830 B2 JP4665830 B2 JP 4665830B2
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reducing agent
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catalyst
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佳久 塚本
伸基 大橋
孝充 浅沼
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Toyota Motor Corp
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Description

本発明は、内燃機関の排気通路に設けられ且つ触媒を含んで構成される排気浄化装置と、該排気浄化装置よりも上流側の排気通路に設けられ且つ酸化機能を有する前段触媒と、を備える内燃機関の排気浄化システムに関する。   The present invention includes an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst, and a pre-stage catalyst that is provided in an exhaust passage upstream of the exhaust purification device and has an oxidation function. The present invention relates to an exhaust gas purification system for an internal combustion engine.

内燃機関の排気システムにおいては、内燃機関の排気通路に設けられ且つ触媒を含んで構成される排気浄化装置と、該排気浄化装置よりも上流側の排気通路に設けられ且つ酸化機能を有する前段触媒と、を備えたものが知られている。このような構成においては、排気浄化装置の性能を回復すべく前段触媒よりも上流側の排気中に還元剤を供給することで該排気浄化装置に還元剤を供給する場合がある。   In an exhaust system of an internal combustion engine, an exhaust purification device provided in an exhaust passage of the internal combustion engine and including a catalyst, and a pre-stage catalyst provided in an exhaust passage upstream of the exhaust purification device and having an oxidation function The thing equipped with these is known. In such a configuration, there is a case where the reducing agent is supplied to the exhaust gas purification device by supplying the reducing agent into the exhaust gas upstream of the upstream catalyst in order to recover the performance of the exhaust gas purification device.

この場合、排気中に供給された還元剤が排気浄化装置に到達する前に前段触媒において酸化されることになる。   In this case, the reducing agent supplied into the exhaust is oxidized in the pre-stage catalyst before reaching the exhaust purification device.

また、特許文献１には、内燃機関の排気通路に設けられた触媒の上流側の排気温度と該触媒の下流側の排気温度との差に基づいて、排気中のＨＣが触媒において酸化することで発生した発熱量を推定し、この推定された発熱量が判定値よりも小さいときに触媒が劣化状態にあると判定する技術が開示されている。
特開２００３−１０６１４０号公報 Further, Patent Document 1 discloses that HC in the exhaust is oxidized in the catalyst based on the difference between the exhaust temperature upstream of the catalyst provided in the exhaust passage of the internal combustion engine and the exhaust temperature downstream of the catalyst. A technique is disclosed in which the amount of generated heat is estimated and the catalyst is determined to be in a deteriorated state when the estimated amount of generated heat is smaller than a determination value.
JP 2003-106140 A

本発明は、内燃機関の排気通路に設けられ且つ触媒を含んで構成される排気浄化装置と、該排気浄化装置よりも上流側の排気通路に設けられ且つ酸化機能を有する前段触媒と、を備えた内燃機関の排気浄化システムにおいて、排気浄化装置の性能を回復すべく該排気浄化装置に還元剤を供給するときに、該排気浄化装置に実際に供給される還元剤の量をより好適に制御することが可能な技術を提供することを目的とする。   The present invention includes an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst, and a pre-stage catalyst that is provided in an exhaust passage upstream of the exhaust purification device and has an oxidation function. In the exhaust gas purification system for an internal combustion engine, when the reducing agent is supplied to the exhaust gas purification device in order to restore the performance of the exhaust gas purification device, the amount of the reducing agent actually supplied to the exhaust gas purification device is more preferably controlled. It aims at providing the technology which can be done.

本発明は、還元剤供給の実行時に、前段触媒において酸化された還元剤の量である還元剤酸化量を算出すると共に、該還元剤酸化量と還元剤供給量との差に基づいて、排気浄化装置に到達している還元剤の量である還元剤到達量を算出する。そして、還元剤到達量が目標供給量となるように還元剤の供給方法および／または還元剤の供給量を制御する。   The present invention calculates a reducing agent oxidation amount, which is the amount of reducing agent oxidized in the preceding catalyst at the time of execution of reducing agent supply, and based on the difference between the reducing agent oxidation amount and the reducing agent supply amount, A reducing agent reaching amount, which is an amount of the reducing agent reaching the purification device, is calculated. Then, the reducing agent supply method and / or the reducing agent supply amount are controlled so that the reducing agent reaching amount becomes the target supply amount.

より詳しくは、本発明に係る内燃機関の排気浄化システムによれば、
内燃機関の排気通路に設けられ且つ触媒を含んで構成される排気浄化装置と、
該排気浄化装置よりも上流側の排気通路に設けられ且つ酸化機能を有する前段触媒と、
該前段触媒に流入する排気の温度である流入排気温度を検出する流入排気温度検出手段と、
該前段触媒の温度を検出する前段触媒温度検出手段と、
前記排気浄化装置の性能を回復させるときに前記前段触媒よりも上流側の排気中に還元剤を供給することで該還元剤を前記排気浄化装置に供給する還元剤供給手段と、
該還元剤供給手段による還元剤の供給が実行されたときに前記流入排気温度と前記前段触媒の温度との差に基づいて前記前段触媒で酸化された還元剤の量である還元剤酸化量を算出する還元剤酸化量算出手段と、
還元剤供給手段によって排気中に供給された還元剤の供給量と前記還元剤酸化量算出手
段によって算出される還元剤酸化量との差に基づいて前記排気浄化装置に到達している還元剤の量である還元剤到達量を算出する還元剤到達量算出手段と、を備え、
前記還元剤供給手段による還元剤の供給の実行時に、前記還元到達量算出手段によって算出される還元剤到達量が目標供給量となるように前記還元剤供給手段を制御することを特徴とする。 More specifically, according to the exhaust gas purification system for an internal combustion engine according to the present invention,
An exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst;
A pre-stage catalyst provided in the exhaust passage upstream of the exhaust purification device and having an oxidation function;
Inflow exhaust gas temperature detection means for detecting an inflow exhaust gas temperature that is the temperature of the exhaust gas flowing into the front catalyst,
A pre-catalyst temperature detecting means for detecting the temperature of the pre-catalyst;
Reducing agent supply means for supplying the reducing agent to the exhaust purification device by supplying the reducing agent into the exhaust upstream of the preceding catalyst when recovering the performance of the exhaust purification device;
When the reducing agent is supplied by the reducing agent supply means, a reducing agent oxidation amount, which is the amount of reducing agent oxidized by the preceding catalyst based on the difference between the inflow exhaust gas temperature and the temperature of the preceding catalyst. A reducing agent oxidation amount calculating means for calculating;
Based on the difference between the supply amount of the reducing agent supplied into the exhaust gas by the reducing agent supply means and the reducing agent oxidation amount calculated by the reducing agent oxidation amount calculation means, the amount of the reducing agent that has reached the exhaust purification device A reducing agent reaching amount calculating means for calculating a reducing agent reaching amount that is an amount,
The reducing agent supply unit is controlled so that the reducing agent arrival amount calculated by the reduction arrival amount calculation unit becomes a target supply amount when the reducing agent supply unit executes the reducing agent supply.

前段触媒において還元剤が酸化されると酸化熱によって該前段触媒の温度が上昇する。そのため、流入排気温度と前段触媒の温度との差から該前段触媒での還元剤酸化量を算出することが出来る。   When the reducing agent is oxidized in the pre-stage catalyst, the temperature of the pre-stage catalyst rises due to the heat of oxidation. Therefore, the reducing agent oxidation amount at the upstream catalyst can be calculated from the difference between the inflow exhaust gas temperature and the temperature of the upstream catalyst.

また、還元剤供給手段によって供給される還元剤供給量と前段触媒での還元剤酸化量との差から、排気浄化装置に到達する還元剤到達量、即ち、排気浄化触媒に実際に供給される還元剤の供給量を算出することが出来る。   Further, from the difference between the reducing agent supply amount supplied by the reducing agent supply means and the reducing agent oxidation amount at the pre-stage catalyst, the reducing agent arrival amount reaching the exhaust purification device, that is, actually supplied to the exhaust purification catalyst. The supply amount of the reducing agent can be calculated.

そして、本発明によれば、還元剤到達量が目標供給量となるように還元剤供給手段が制御される。これにより、排気浄化装置に実際に供給される還元剤の供給量をより高精度で目標供給量に制御することが出来る。   And according to this invention, a reducing agent supply means is controlled so that the reducing agent arrival amount becomes the target supply amount. Thereby, the supply amount of the reducing agent actually supplied to the exhaust gas purification device can be controlled to the target supply amount with higher accuracy.

尚、本発明においては、還元剤供給手段からの還元剤供給量を制御することで、排気浄化装置に到達する還元剤到達量を制御してもよい。また、還元剤供給手段による還元剤の供給方法を制御することで、排気浄化装置に到達する還元剤到達量を制御してもよい。   In the present invention, the amount of reducing agent that reaches the exhaust emission control device may be controlled by controlling the amount of reducing agent supplied from the reducing agent supply means. Further, the amount of reducing agent that reaches the exhaust gas purification device may be controlled by controlling the method of supplying the reducing agent by the reducing agent supply means.

排気浄化装置の性能を回復させるべく該排気浄化装置に還元剤を供給する場合、排気浄化装置に実際に供給される還元剤の供給量が比較的少ないときは該還元剤の供給量の増加に伴ってその回復率が上昇する。   When supplying a reducing agent to the exhaust purification device in order to restore the performance of the exhaust purification device, if the supply amount of the reducing agent actually supplied to the exhaust purification device is relatively small, the supply amount of the reducing agent is increased. Along with this, the recovery rate increases.

しかしながら、該還元剤の供給量がある程度の量以上となると排気浄化装置の性能の回復率が上限値に達し、それ以上の量の還元剤が供給されても回復率が上昇しない状態となる。   However, when the supply amount of the reducing agent exceeds a certain level, the recovery rate of the performance of the exhaust gas purification device reaches the upper limit value, and even when an additional amount of reducing agent is supplied, the recovery rate does not increase.

そこで、本発明においては、目標供給量を、排気浄化装置の性能の回復率が上限値近傍となる還元剤量の下限値近傍の値としてもよい。   Therefore, in the present invention, the target supply amount may be a value in the vicinity of the lower limit value of the reducing agent amount at which the recovery rate of the performance of the exhaust purification device is in the vicinity of the upper limit value.

これにより、排気浄化装置の性能を可及的に回復させることが出来ると共に、還元剤供給手段からの還元剤の供給量を抑制することが出来る。   As a result, the performance of the exhaust emission control device can be restored as much as possible, and the amount of reducing agent supplied from the reducing agent supply means can be suppressed.

本発明によれば、内燃機関の排気通路に設けられ且つ触媒を含んで構成される排気浄化装置と、該排気浄化装置よりも上流側の排気通路に設けられ且つ酸化機能を有する前段触媒と、を備えた内燃機関の排気浄化システムにおいて、排気浄化装置の性能を回復すべく該排気浄化装置に還元剤を供給するときに、該排気浄化装置に実際に供給される還元剤の量をより好適に制御することが出来る。   According to the present invention, an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst, a pre-stage catalyst that is provided in an exhaust passage upstream of the exhaust purification device and has an oxidation function, In the exhaust gas purification system for an internal combustion engine having the above, when the reducing agent is supplied to the exhaust gas purification device so as to restore the performance of the exhaust gas purification device, the amount of the reducing agent actually supplied to the exhaust gas purification device is more suitable Can be controlled.

以下、本発明に係る内燃機関の排気浄化システムの具体的な実施形態について図面に基づいて説明する。   Hereinafter, specific embodiments of an exhaust gas purification system for an internal combustion engine according to the present invention will be described with reference to the drawings.

＜内燃機関の吸排気系の概略構成＞
ここでは、本発明を車両駆動用のディーゼルエンジンに適用した場合を例に挙げて説明する。図１は、本実施例に係る内燃機関の吸排気系の概略構成を示す図である。 <Schematic configuration of intake and exhaust system of internal combustion engine>
Here, a case where the present invention is applied to a diesel engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an intake / exhaust system of an internal combustion engine according to the present embodiment.

内燃機関１は車両駆動用のディーゼルエンジンである。この内燃機関１には、吸気通路３および排気通路２が接続されている。排気通路２には、酸化触媒４および吸蔵還元型ＮＯｘ触媒５（以下、単にＮＯｘ触媒５と称する）が設けられている。   The internal combustion engine 1 is a diesel engine for driving a vehicle. An intake passage 3 and an exhaust passage 2 are connected to the internal combustion engine 1. The exhaust passage 2 is provided with an oxidation catalyst 4 and an NOx storage reduction catalyst 5 (hereinafter simply referred to as NOx catalyst 5).

ＮＯｘ触媒５は、周囲雰囲気が酸化雰囲気のときに排気中のＮＯｘを吸蔵し周囲雰囲気が還元雰囲気のときに吸蔵していたＮＯｘを還元する触媒である。該ＮＯｘ触媒５は排気通路２における酸化触媒４より下流側に設けられている。尚、本実施例においては、酸化触媒４が本発明に係る前段触媒に相当し、ＮＯｘ触媒が本発明に係る排気浄化装置に相当する。前段触媒は酸化機能を有する触媒であればよく、例えば、酸化触媒４をＮＯｘ触媒とし、ＮＯｘ触媒５をＮＯｘ触媒を担持したパティキュレートフィルタとしてもよい。   The NOx catalyst 5 is a catalyst that stores NOx in the exhaust when the ambient atmosphere is an oxidizing atmosphere and reduces the NOx that is stored when the ambient atmosphere is a reducing atmosphere. The NOx catalyst 5 is provided downstream of the oxidation catalyst 4 in the exhaust passage 2. In this embodiment, the oxidation catalyst 4 corresponds to the pre-stage catalyst according to the present invention, and the NOx catalyst corresponds to the exhaust purification device according to the present invention. The pre-stage catalyst may be a catalyst having an oxidation function. For example, the oxidation catalyst 4 may be a NOx catalyst, and the NOx catalyst 5 may be a particulate filter carrying a NOx catalyst.

酸化触媒４より上流側の排気通路２には排気中に還元剤として燃料を添加する燃料添加弁６が設けられている。   A fuel addition valve 6 is provided in the exhaust passage 2 upstream of the oxidation catalyst 4 to add fuel as a reducing agent into the exhaust.

さらに、排気通路２における酸化触媒４より上流側および酸化触媒４とＮＯｘ触媒５との間には排気の温度を検出する第一温度センサ８および第二温度センサ９がそれぞれ設けられている。   Further, a first temperature sensor 8 and a second temperature sensor 9 for detecting the temperature of the exhaust gas are provided upstream of the oxidation catalyst 4 in the exhaust passage 2 and between the oxidation catalyst 4 and the NOx catalyst 5, respectively.

以上述べたように構成された内燃機関１には、この内燃機関１を制御するための電子制御ユニット（ＥＣＵ）１０が併設されている。ＥＣＵ１０には第一温度センサ８および第二温度センサ９が電気的に接続されている。そして、これらの出力信号がＥＣＵ１０に入力される。ＥＣＵ１０は、第二温度センサ９の出力値に基づいて酸化触媒４の温度を推定する。   The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 10 for controlling the internal combustion engine 1. A first temperature sensor 8 and a second temperature sensor 9 are electrically connected to the ECU 10. These output signals are input to the ECU 10. The ECU 10 estimates the temperature of the oxidation catalyst 4 based on the output value of the second temperature sensor 9.

また、ＥＣＵ１０には燃料添加弁６が電気的に接続されている。ＥＣＵ１０によってこれが制御される。   Further, the fuel addition valve 6 is electrically connected to the ECU 10. This is controlled by the ECU 10.

＜ＮＯｘ還元制御＞
本実施例では、ＮＯｘ触媒５に吸蔵されたＮＯｘを還元させて該ＮＯｘ触媒５のＮＯｘ吸蔵能力を回復させるべくＮＯｘ還元制御が行われる。本実施例に係るＮＯｘ還元制御は、ＮＯｘ触媒５の温度が活性温度であるときに燃料添加弁６から間欠的に燃料を添加することで実行される。燃料添加弁６から燃料が添加されることで該燃料が酸化触媒４を介してＮＯｘ触媒５に供給される。これにより、ＮＯｘ触媒５の周囲雰囲気の空燃比が低下し該周囲雰囲気が還元雰囲気となるためＮＯｘ触媒５に吸蔵されたＮＯｘが還元される。また、燃料添加弁６からの燃料添加を間欠的に行うことで、酸化触媒４やＮＯｘ触媒５の過度な昇温を抑制することが出来る。 <NOx reduction control>
In this embodiment, NOx reduction control is performed to reduce the NOx stored in the NOx catalyst 5 and restore the NOx storage capability of the NOx catalyst 5. The NOx reduction control according to this embodiment is executed by intermittently adding fuel from the fuel addition valve 6 when the temperature of the NOx catalyst 5 is the activation temperature. By adding fuel from the fuel addition valve 6, the fuel is supplied to the NOx catalyst 5 via the oxidation catalyst 4. As a result, the air-fuel ratio of the ambient atmosphere of the NOx catalyst 5 decreases and the ambient atmosphere becomes a reducing atmosphere, so that NOx stored in the NOx catalyst 5 is reduced. Further, by intermittently adding fuel from the fuel addition valve 6, it is possible to suppress an excessive increase in temperature of the oxidation catalyst 4 or the NOx catalyst 5.

また、上記のように、燃料添加弁６から添加された燃料はＮＯｘ触媒５に到達する前に酸化触媒４に供給される。そのため、燃料添加弁６から添加された燃料のうち少なくとも一部は酸化触媒４において酸化される。従って、ＮＯｘ触媒５に実際に供給される燃料の量である到達燃料量は燃料添加弁６から添加された燃料添加量よりも少なくなる。そこで、本実施例では、到達燃料量が目標供給量となるように燃料添加弁６からの燃料添加量を制御する。   Further, as described above, the fuel added from the fuel addition valve 6 is supplied to the oxidation catalyst 4 before reaching the NOx catalyst 5. Therefore, at least a part of the fuel added from the fuel addition valve 6 is oxidized in the oxidation catalyst 4. Therefore, the amount of fuel reached, which is the amount of fuel actually supplied to the NOx catalyst 5, becomes smaller than the amount of fuel added from the fuel addition valve 6. Therefore, in this embodiment, the amount of fuel added from the fuel addition valve 6 is controlled so that the amount of fuel reached becomes the target supply amount.

ここで、ＮＯｘ還元制御の実行時における、ＮＯｘ触媒５に実際に供給される燃料の供給量とＮＯｘ還元率との関係について図２に基づいて説明する。尚、ここで、ＮＯｘ還元率とは、ＮＯｘ触媒５に吸蔵されたＮＯｘの量に対する還元されるＮＯｘの量の割合を示す値である。図２において、縦軸はＮＯｘ還元率を表しており、ＮＯｘ触媒５に実際に供給される燃料の量を表している。   Here, the relationship between the amount of fuel actually supplied to the NOx catalyst 5 and the NOx reduction rate when the NOx reduction control is executed will be described with reference to FIG. Here, the NOx reduction rate is a value indicating the ratio of the amount of NOx to be reduced to the amount of NOx stored in the NOx catalyst 5. In FIG. 2, the vertical axis represents the NOx reduction rate, and represents the amount of fuel actually supplied to the NOx catalyst 5.

ＮＯｘ還元制御の実行時において、ＮＯｘ触媒５に実際に供給される燃料が比較的少ないときは該燃料の量の増加に伴ってＮＯｘ還元率が上昇する。しかしながら、図２に示すように、ＮＯｘ触媒５に実際に供給される燃料がある程度の量以上となるとＮＯｘ還元率が上限値に達し、それ以上の量の燃料が供給されてもＮＯｘ還元率が上昇しない状態となる。   When the NOx reduction control is executed and the amount of fuel actually supplied to the NOx catalyst 5 is relatively small, the NOx reduction rate increases as the amount of fuel increases. However, as shown in FIG. 2, when the amount of fuel actually supplied to the NOx catalyst 5 exceeds a certain amount, the NOx reduction rate reaches the upper limit value, and even if more fuel is supplied, the NOx reduction rate is increased. It will not rise.

そこで、本実施例に係るＮＯｘ還元制御においては、到達燃料量の目標値である目標供給量を、ＮＯｘ還元率が上限値近傍となる燃料量の下限値近傍の範囲（図２にＡで示す範囲）内の値に設定する。   Therefore, in the NOx reduction control according to this embodiment, the target supply amount, which is the target value of the reached fuel amount, is set in a range near the lower limit value of the fuel amount where the NOx reduction rate is in the vicinity of the upper limit value (indicated by A in FIG. 2). Set to a value within the range.

＜ＮＯｘ還元制御のルーチン＞
以下、本実施例に係るＮＯｘ還元制御のルーチンについて図３に示すフローチャートに基づいて説明する。本ルーチンは、ＥＣＵ１０に予め記憶されており、所定の間隔で繰り返されるルーチンである。 <NOx reduction control routine>
Hereinafter, the routine for NOx reduction control according to the present embodiment will be described based on the flowchart shown in FIG. This routine is stored in advance in the ECU 10 and is repeated at a predetermined interval.

本ルーチンでは、ＥＣＵ１０は、先ずＳ１０１において、ＮＯｘ還元制御の実行条件が成立したか否かを判別する。ここで、ＮＯｘ還元制御の実行条件としては、ＮＯｘ触媒５におけるＮＯｘ吸蔵量の推定値がＮＯｘ還元制御実行の閾値以上となり且つ酸化触媒４およびＮＯｘ触媒５の温度が活性温度にある場合を例示することが出来る。このＳ１０１において、肯定判定された場合、ＥＣＵ１０はＳ１０２に進み、否定判定された場合、本ルーチンの実行を一旦終了する。   In this routine, the ECU 10 first determines in S101 whether or not an execution condition for NOx reduction control is satisfied. Here, the execution condition of the NOx reduction control is exemplified when the estimated value of the NOx occlusion amount in the NOx catalyst 5 is equal to or higher than the threshold value for executing the NOx reduction control and the temperatures of the oxidation catalyst 4 and the NOx catalyst 5 are at the activation temperature. I can do it. If an affirmative determination is made in S101, the ECU 10 proceeds to S102, and if a negative determination is made, the execution of this routine is once terminated.

Ｓ１０２において、ＥＣＵ１０は、吸入空気量および内燃機関１での燃料噴射量、第一温度センサ８によって検出される流入排気温度等に基づいて、燃料添加弁６による燃料添加を実行するときの基準燃料添加量Ｑｆｂａｓｅを算出する。この基準燃料添加量Ｑｆｂａｓｅは、燃料添加弁６や酸化触媒４が初期状態であるときは、ＮＯｘ触媒５への到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔとなると予測される燃料添加量である。   In S <b> 102, the ECU 10 performs reference fuel when fuel addition by the fuel addition valve 6 is performed based on the intake air amount, the fuel injection amount in the internal combustion engine 1, the inflow exhaust gas temperature detected by the first temperature sensor 8, and the like. The addition amount Qfbase is calculated. This reference fuel addition amount Qfbase is a fuel addition amount that is predicted to reach the target supply amount Qfnt when the fuel addition valve 6 and the oxidation catalyst 4 are in the initial state.

次に、ＥＣＵ１０は、Ｓ１０３に進み、燃料添加量Ｑｆｉを基準燃料添加量Ｑｆｂａｓｅとして燃料添加弁６による燃料添加を実行する。   Next, the ECU 10 proceeds to S103 and executes fuel addition by the fuel addition valve 6 with the fuel addition amount Qfi as the reference fuel addition amount Qfbase.

しかしながら、燃料添加量Ｑｆｉを基準燃料添加量Ｑｆｂａｓｅとして燃料添加を実行しても、燃料添加弁６や酸化触媒４の製造誤差や劣化等に起因してＮＯｘ触媒５への到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔよりも多くなったり少なくなったりする虞がある。そこで、本ルーチンにおいては以下の方法で燃料添加量Ｑｆｉを補正する。   However, even if the fuel addition is executed with the fuel addition amount Qfi as the reference fuel addition amount Qfbase, the target fuel amount Qfn reaching the NOx catalyst 5 due to manufacturing errors or deterioration of the fuel addition valve 6 or the oxidation catalyst 4 is the target. There is a possibility that it may be larger or smaller than the supply amount Qfnt. Therefore, in this routine, the fuel addition amount Qfi is corrected by the following method.

ＥＣＵ１０は、Ｓ１０３の次にＳ１０４に進む。Ｓ１０４において、ＥＣＵ１０は、第二温度センサ９の検出値から推定される酸化触媒４の温度から流入排気温度を減算することで温度差ΔＴｇｃを算出する。   The ECU 10 proceeds to S104 after S103. In S104, the ECU 10 calculates the temperature difference ΔTgc by subtracting the inflow exhaust gas temperature from the temperature of the oxidation catalyst 4 estimated from the detection value of the second temperature sensor 9.

ここで、内燃機関１の運転状態が定常状態であれば流入排気温度はほぼ一定であるが、燃料添加弁６による燃料添加は間欠的に行われるため酸化触媒４の温度は変動する。つまり、燃料添加弁６から添加された燃料が酸化触媒４に到達したときは該酸化触媒４の温度は上昇し、該燃料が酸化触媒４に到達していないときは該酸化触媒４の温度は下降する。そこで、Ｓ１０４において、ＥＣＵ１０は、燃料添加弁６による間欠的な燃料添加が実行されている間、温度差ΔＴｇｃの履歴を記憶する。   Here, if the operating state of the internal combustion engine 1 is in a steady state, the inflow exhaust gas temperature is substantially constant, but since the fuel addition by the fuel addition valve 6 is performed intermittently, the temperature of the oxidation catalyst 4 varies. That is, when the fuel added from the fuel addition valve 6 reaches the oxidation catalyst 4, the temperature of the oxidation catalyst 4 rises, and when the fuel does not reach the oxidation catalyst 4, the temperature of the oxidation catalyst 4 is Descend. Therefore, in S104, the ECU 10 stores the history of the temperature difference ΔTgc while intermittent fuel addition by the fuel addition valve 6 is being executed.

次に、ＥＣＵ１０は、Ｓ１０５に進み、記憶された温度差ΔＴｇｃの履歴に基づいて、酸化触媒４において酸化された燃料の量である酸化燃料量Ｑｆｏを算出する。ここでは、
温度差ΔＴｇｃが大きいほど酸化燃料量Ｑｆｏが多いと判断出来る。 Next, the ECU 10 proceeds to S105, and calculates an oxidized fuel amount Qfo, which is the amount of fuel oxidized in the oxidation catalyst 4, based on the stored history of the temperature difference ΔTgc. here,
It can be determined that the greater the temperature difference ΔTgc, the greater the amount of oxidized fuel Qfo.

次に、ＥＣＵ１０は、Ｓ１０６に進み、基準燃料添加量Ｑｆｂａｓｅから酸化燃料量Ｑｆｏを減算することでＮＯｘ触媒５への到達燃料量Ｑｆｎを算出する。   Next, the ECU 10 proceeds to S106, and calculates the fuel amount Qfn that reaches the NOx catalyst 5 by subtracting the oxidized fuel amount Qfo from the reference fuel addition amount Qfbase.

次に、ＥＣＵ１０は、Ｓ１０７に進み、Ｓ１０５において算出された到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔより小さいか否かを判別する。Ｓ１０７において、肯定判定された場合、ＥＣＵ１０はＳ１０８に進み、否定判定された場合、ＥＣＵ１０はＳ１０９に進む。   Next, the ECU 10 proceeds to S107, and determines whether or not the reached fuel amount Qfn calculated in S105 is smaller than the target supply amount Qfnt. If an affirmative determination is made in S107, the ECU 10 proceeds to S108, and if a negative determination is made, the ECU 10 proceeds to S109.

Ｓ１０８において、ＥＣＵ１０は、到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔとなるよう燃料添加弁６からの燃料添加量Ｑｆｉを増量補正する。その後、ＥＣＵ１０は本ルーチンの実行を一旦終了する。   In S108, the ECU 10 increases and corrects the fuel addition amount Qfi from the fuel addition valve 6 so that the reached fuel amount Qfn becomes the target supply amount Qfnt. Thereafter, the ECU 10 once terminates execution of this routine.

一方、Ｓ１０９において、ＥＣＵ１０は、Ｓ１０５において算出された到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔより大きいか否かを判別する。Ｓ１０９において、肯定判定された場合、ＥＣＵ１０はＳ１１０に進む。一方、Ｓ１０９において、否定判定された場合、ＥＣＵ１０は本ルーチンの実行を一旦終了する。この場合、燃料添加弁６からの燃料添加量Ｑｆｉは基準燃料添加量Ｑｆｂａｓｅに維持される。   On the other hand, in S109, the ECU 10 determines whether or not the reached fuel amount Qfn calculated in S105 is larger than the target supply amount Qfnt. If an affirmative determination is made in S109, the ECU 10 proceeds to S110. On the other hand, if a negative determination is made in S109, the ECU 10 once ends the execution of this routine. In this case, the fuel addition amount Qfi from the fuel addition valve 6 is maintained at the reference fuel addition amount Qfbase.

Ｓ１１０において、ＥＣＵ１０は、到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔとなるよう燃料添加弁６からの燃料添加量Ｑｆｉを減量補正する。その後、ＥＣＵ１０は本ルーチンの実行を一旦終了する。   In S110, the ECU 10 corrects the fuel addition amount Qfi from the fuel addition valve 6 so as to decrease so that the reached fuel amount Qfn becomes the target supply amount Qfnt. Thereafter, the ECU 10 once terminates execution of this routine.

以上説明したルーチンによれば、燃料添加弁６からの燃料添加が実行されることでＮＯｘ触媒５に実際に供給される到達燃料量Ｑｆｎが算出される。そして、この到達燃料量Ｑｆｎが目標供給量Ｑｆｎｔとなるよう燃料添加弁６からの燃料添加量Ｑｆｉが制御される。   According to the routine described above, the fuel amount Qfn that is actually supplied to the NOx catalyst 5 is calculated by performing fuel addition from the fuel addition valve 6. Then, the fuel addition amount Qfi from the fuel addition valve 6 is controlled so that the reached fuel amount Qfn becomes the target supply amount Qfnt.

従って、ＮＯｘ還元制御の実行時において、ＮＯｘ触媒５に実際に供給される燃料の供給量（到達燃料量Ｑｆｎ）をより高精度で目標供給量Ｑｆｎｔに制御することが出来る。その結果、ＮＯｘ触媒５に吸蔵されたＮＯｘを可及的に還元することが出来ると共に、ＮＯｘ還元制御の実行時における燃料添加弁６からの燃料添加量を抑制することが出来る。   Therefore, when the NOx reduction control is executed, the amount of fuel actually supplied to the NOx catalyst 5 (reached fuel amount Qfn) can be controlled to the target supply amount Qfnt with higher accuracy. As a result, the NOx stored in the NOx catalyst 5 can be reduced as much as possible, and the amount of fuel added from the fuel addition valve 6 when the NOx reduction control is executed can be suppressed.

尚、上記ルーチンにおいては、燃料添加弁６からの燃料添加量Ｑｆｉを制御することで到達燃料量Ｑｆｎを目標供給量Ｑｆｎｔに制御する。本実施例においては、これに代えて、燃料添加弁６による燃料添加方法を制御することによって到達燃料量Ｑｆｎを目標供給量Ｑｆｎｔに制御してもよい。   In the above routine, the reached fuel amount Qfn is controlled to the target supply amount Qfnt by controlling the fuel addition amount Qfi from the fuel addition valve 6. In this embodiment, instead of this, the reached fuel amount Qfn may be controlled to the target supply amount Qfnt by controlling the fuel addition method by the fuel addition valve 6.

例えば、燃料添加弁６から間欠的に燃料を添加する際の燃料添加のインターバルを長くすることで到達燃料量Ｑｆｎを増加させることが出来、該燃料添加のインターバルを短くすることで到達燃料量Ｑｆｎを減量させることが出来る。また、燃料添加弁６から間欠的に燃料を添加する際の一回の燃料添加当たりの燃料添加量を増加させることで到達燃料量Ｑｆｎを増加させることが出来、該一回の燃料添加当たりの燃料添加量を減少させることで到達燃料量Ｑｆｎを減少させることが出来る。   For example, the reached fuel amount Qfn can be increased by lengthening the fuel addition interval when fuel is intermittently added from the fuel addition valve 6, and the reached fuel amount Qfn can be increased by shortening the fuel addition interval. Can be reduced. Further, the amount of fuel reached Qfn can be increased by increasing the amount of fuel added per fuel addition at the time of intermittently adding fuel from the fuel addition valve 6, and the amount per fuel addition can be increased. By reducing the fuel addition amount, the reached fuel amount Qfn can be reduced.

また、本実施例に係るＮＯｘ還元制御おいては、燃料添加弁６による燃料添加に代えて、内燃機関１において排気行程時に副燃料噴射を実行することで排気中に燃料を供給し、該燃料をＮＯｘ触媒５に供給してもよい。   In addition, in the NOx reduction control according to the present embodiment, instead of fuel addition by the fuel addition valve 6, fuel is supplied into the exhaust gas by executing sub fuel injection in the internal combustion engine 1 during the exhaust stroke, and the fuel May be supplied to the NOx catalyst 5.

本実施例においては、ＮＯｘ還元制御の実行時に本発明を適用した場合を例に挙げて説明したが、ＮＯｘ触媒５に吸蔵されたＳＯｘを還元する、所謂ＳＯｘ被毒回復制御の実行時に本発明を適用してもよい。この場合、ＳＯｘ被毒回復制御の実行時において、ＮＯｘ触媒５に実際に供給される燃料の量をより好適な量に制御することが出来る。   In the present embodiment, the case where the present invention is applied at the time of executing the NOx reduction control has been described as an example. However, the present invention is performed at the time of performing the so-called SOx poisoning recovery control that reduces the SOx stored in the NOx catalyst 5. May be applied. In this case, when the SOx poisoning recovery control is executed, the amount of fuel actually supplied to the NOx catalyst 5 can be controlled to a more suitable amount.

また、ＮＯｘ触媒５に代えて、ＮＯｘ触媒を担持したパティキュレートフィルタを設けた場合においては、該パティキュレートフィルタに捕集された粒子状物質を除去するフィルタ再生制御に本発明を適用してもよい。この場合、フィルタ再生制御の実行時において、パティキュレートフィルタに実際に供給される燃料の量をより好適な量に制御するが出来る。   Further, when a particulate filter carrying a NOx catalyst is provided in place of the NOx catalyst 5, the present invention can be applied to filter regeneration control for removing particulate matter collected on the particulate filter. Good. In this case, when the filter regeneration control is executed, the amount of fuel actually supplied to the particulate filter can be controlled to a more suitable amount.

実施例に係る内燃機関の吸排気系の概略構成を示す図。The figure which shows schematic structure of the intake / exhaust system of the internal combustion engine which concerns on an Example. ＮＯｘ触媒に実際に供給される燃料の供給量とＮＯｘ還元率との関係を示す図。The figure which shows the relationship between the supply amount of the fuel actually supplied to a NOx catalyst, and a NOx reduction rate. 実施例に係るＮＯｘ還元制御のルーチンを示すフローチャート。The flowchart which shows the routine of NOx reduction control which concerns on an Example.

符号の説明Explanation of symbols

１・・・内燃機関
２・・・排気通路
３・・・吸気通路
４・・・酸化触媒
５・・・吸蔵還元型ＮＯｘ触媒
６・・・燃料添加弁
８・・・第一温度センサ
９・・・第二温度センサ
１０・・ＥＣＵ DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Intake passage 4 ... Oxidation catalyst 5 ... NOx storage reduction catalyst 6 ... Fuel addition valve 8 ... First temperature sensor 9・ ・ Second temperature sensor 10 ・ ・ ECU

Claims (2)

内燃機関の排気通路に設けられ且つ触媒を含んで構成される排気浄化装置と、
該排気浄化装置よりも上流側の排気通路に設けられ且つ酸化機能を有する前段触媒と、
該前段触媒に流入する排気の温度である流入排気温度を検出する流入排気温度検出手段と、
該前段触媒の温度を検出する前段触媒温度検出手段と、
前記排気浄化装置の性能を回復させるときに前記前段触媒よりも上流側の排気中に還元剤を供給することで該還元剤を前記排気浄化装置に供給する還元剤供給手段と、
該還元剤供給手段による還元剤の供給が実行されたときに前記流入排気温度と前記前段触媒の温度との差に基づいて前記前段触媒で酸化された還元剤の量である還元剤酸化量を算出する還元剤酸化量算出手段と、
還元剤供給手段によって排気中に供給された還元剤の供給量と前記還元剤酸化量算出手段によって算出される還元剤酸化量との差に基づいて前記排気浄化装置に到達している還元剤の量である還元剤到達量を算出する還元剤到達量算出手段と、を備え、
前記還元剤供給手段による還元剤の供給の実行時に、前記還元到達量算出手段によって算出される還元剤到達量が目標供給量となるように前記還元剤供給手段を制御することを特徴とする内燃機関の排気浄化システム。 An exhaust purification device that is provided in an exhaust passage of an internal combustion engine and includes a catalyst;
A pre-stage catalyst provided in the exhaust passage upstream of the exhaust purification device and having an oxidation function;
Inflow exhaust gas temperature detection means for detecting an inflow exhaust gas temperature that is the temperature of the exhaust gas flowing into the front catalyst,
A pre-catalyst temperature detecting means for detecting the temperature of the pre-catalyst;
Reducing agent supply means for supplying the reducing agent to the exhaust purification device by supplying the reducing agent into the exhaust upstream of the upstream catalyst when recovering the performance of the exhaust purification device;
When the reducing agent is supplied by the reducing agent supply means, the reducing agent oxidation amount, which is the amount of reducing agent oxidized by the preceding catalyst, based on the difference between the inflow exhaust gas temperature and the temperature of the preceding catalyst. A reducing agent oxidation amount calculating means for calculating;
Based on the difference between the supply amount of the reducing agent supplied into the exhaust gas by the reducing agent supply means and the reducing agent oxidation amount calculated by the reducing agent oxidation amount calculation means, the amount of the reducing agent that has reached the exhaust purification device A reducing agent reaching amount calculating means for calculating a reducing agent reaching amount that is an amount,
An internal combustion engine characterized by controlling the reducing agent supply means so that the reducing agent arrival amount calculated by the reduction arrival amount calculating means becomes a target supply amount when the reducing agent supply means executes the reducing agent supply. Engine exhaust purification system. 前記目標供給量が、前記排気浄化装置の性能の回復率が上限値近傍となる還元剤量の下限値近傍の値であることを特徴とする請求項１記載の内燃機関の排気浄化システム。   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the target supply amount is a value in the vicinity of a lower limit value of a reducing agent amount at which a performance recovery rate of the exhaust gas purification apparatus is in the vicinity of an upper limit value.
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