JP3788315B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

ところで、還元剤噴射弁２８は、フィルタ２０の昇温時だけではなく、フィルタ２０に担持された吸蔵還元型ＮＯx触媒からＮＯxを還元させるときにも燃料の噴射を行う。このときの燃料添加量も、フィルタ２０の昇温時と同様の理由により、目標添加量と実際の添加量との間に差異を生じる。フィルタ２０の昇温時とＮＯx還元時とでは、燃料添加量は異なるが還元剤噴射弁２８の開弁時間に比例した量の燃料が噴射される点では同一である。従って、フィルタ２０昇温時に算出された補正係数により、還元剤噴射弁２８から噴射される還元剤の量を補正することが可能となり、ＮＯx還元等に必要となる還元剤の量を算出することが可能となる。以上より、この補正係数を用いてＮＯx還元用の燃料添加量を補正した値は、次式により求めることができる。
【０１２１】
ＮＯx還元用添加量＝基本噴射量指令値×補正係数×反映係数ａ
ここで、基本噴射量指令値は、前記したリッチスパイク制御で算出される燃料添加量である。また、反映係数ａは運転状態等からマップにより算出される値である。
【０１２２】
ここで、図６は、補正係数と反映係数との関係を示した図である。補正係数が１よりも大きいとき、即ち、目標温度よりも実際の温度が低い場合は、実際に添加される燃料量が目標添加量に達していない場合である。このような場合には、単位時間あたりの燃料添加量が減少しているので、還元剤噴射弁２８の開弁時間を延長することにより燃料添加量を増加することができる。しかし、基本噴射量指令値に単に補正係数を乗じた値では、新たに追加される還元剤の量は還元剤噴射弁２８の噴射量が減少している分だけ不足してしまう。この不足分を補うために反映係数ａが用いられる。ここで、図６に示されるマップを予めＲＯＭ３５２に記憶させておき、該マップへ補正係数を代入することにより反映係数ａが算出される。また、補正係数及び反映係数ａは、バックアップＲＡＭ３５４に記憶され、次回からの燃料添加の際にＣＰＵ３５１がこの値を用いて燃料添加を行う。
【０１２３】
このようにして求められたＮＯx還元用添加量に基づいて、還元剤噴射弁２８から燃料が噴射されるが、実際に還元剤噴射弁２８から噴射される燃料量は基本噴射量と略等しい量となる。このようにしてＮＯx還元等に必要となる空燃比を得ることができる。
【０１２４】
尚、このような燃料添加量の補正は、燃料添加後例えば１分３０秒乃至２分程度の期間が経過した後に行うと、フィルタ２０の温度が安定した状態で補正係数を算出することができ、ＮＯx還元時の燃料添加量の精度を向上させることができる。
【０１２５】
以上述べたように、本実施の形態による内燃機関の排気浄化装置によれば、目標昇温量と実際の昇温量とに基づいてフィルタ２０からＮＯxを還元させるため等の燃料添加量を補正することができ、フィルタ２０に目標空燃比の排気を供給することが可能となる。
【０１２６】
尚、本実施の形態では、吸蔵還元型ＮＯx触媒からのＮＯx還元時の燃料添加量の補正方法について述べたが、吸蔵還元型ＮＯx触媒昇温後のＳＯx被毒回復制御における燃料添加量についても同様に補正することが可能である。
＜第２の実施の形態＞
本実施の形態は、第１の実施の形態と比較して以下の点で相違する。
【０１２７】
即ち、第１の実施の形態では、燃料添加後フィルタ２０の温度の上昇が完了した後に燃料添加量の補正係数を算出するが、本実施の形態では、昇温途中の任意の期間中にフィルタ２０が温度上昇したときの昇温量に着目し、燃料添加量の補正係数を算出する。即ち、第１の実施の形態の図５の状態に到達する前のフィルタ２０の温度に基づいて燃料添加量を補正する。
【０１２８】
尚、本実施の形態においては、第１の実施の形態と比較して、燃料添加量の補正時期がフィルタ２０の昇温途中であるという点で異なるものの、対用対象となるエンジン１やその他ハードウェアの基本構成については、第１の実施の形態と共通なので説明を割愛する。
【０１２９】
ここで、図７は、燃料添加開始からのフィルタ２０の温度推移を示したタイムチャート図である。
【０１３０】
本実施の形態では、燃料添加開始からフィルタ２０の温度が目標温度に到達するまでの期間（以下、目標期間とする）であって、例えば燃料添加開始からの所定の期間（以下、対象期間とする）のフィルタ２０の昇温量に着目する。
【０１３１】
先ず、ＣＰＵ３５１は、対象期間中の目標昇温量を算出する。対象期間中の目標昇温量は、目標期間に対する対象期間の割合を最終的な目標となるフィルタ２０の昇温量に乗じて求められる。
【０１３２】
次に、対象期間中にフィルタ２０が実際に温度上昇した昇温量を求める。ここで、ＣＰＵ３５１は、排気温度センサ２４の出力信号を読み込み、フィルタ２０の温度を推定する。また、フィルタ２０の温度は、吸入空気量（エアフローメータ１１の出力信号）、回転数、負荷、燃料噴射量等から推定することもできる。更に、予め実験により求めた値をマップ化してフィルタ２０の温度を求めても良く、フィルタ２０に温度センサを設けて直接該フィルタ２０の温度を測定するようにしても良い。
【０１３３】
このようにして求めた対象期間中の目標昇温量を実際の昇温量で除することにより求められる値は、第１の実施の形態において算出される燃料添加量の補正係数と略同一となる。従って、第１の実施の形態と同様にして以後の燃料添加量を補正することが可能である。
【０１３４】
このように、本実施の形態では、フィルタ２０の昇温途中であっても燃料添加量の補正係数を算出することが可能となる。
【０１３５】
尚、図８は、対象期間をフィルタ２０の昇温途中であって図７とは異なる期間に対象期間を設定した図である。図８に示すように燃料添加量の補正係数を算出するための対象期間は、目標期間内であれば、任意の期間を設定することができ、対象期間の長さも任意に設定可能である。
【０１３６】
また、本実施の形態では、吸蔵還元型ＮＯx触媒からのＮＯx還元時の燃料添加量の補正方法について述べたが、吸蔵還元型ＮＯx触媒昇温後のＳＯx被毒回復制御における燃料添加量についても同様に補正することが可能である。
【０１３７】
【発明の効果】
本発明に係る内燃機関の排気浄化装置では、触媒の実際の温度と目標温度とに基づいて触媒昇温時の還元剤添加量を補正することができる。従って、ＮＯx還元、ＳＯx被毒回復等を行うときに目標となる還元剤の量と実際に供給される還元剤の量との差異を小さくすることが可能となり、空燃比を精度良く制御することができる。
【図面の簡単な説明】
【図１】 本発明の実施の形態に係る内燃機関の排気浄化装置を適用するエンジンとその吸排気系とを併せ示す概略構成図である。
【図２】 （Ａ）は、パティキュレートフィルタの横方向断面を示す図である。（Ｂ）は、パティキュレートフィルタの縦方向断面を示す図である。
【図３】 ＥＣＵの内部構成を示すブロック図である。
【図４】 フィルタの昇温量と単位吸入空気量あたりの燃料添加量との関係を示す図である。
【図５】 フィルタの目標温度、実際の温度、及びベース温度の時間推移を示すタイムチャート図である。
【図６】 補正係数と反映係数との関係を示した図である。
【図７】 第２の実施の形態による目標昇温量と実際の昇温量との関係を示した図である。
【図８】 第２の実施の形態による目標昇温量と実際の昇温量との関係を示した図である。
【符号の説明】
１・・・・エンジン
１ａ・・・クランクプーリ
２・・・・気筒
３・・・・燃料噴射弁
４・・・・コモンレール
４ａ・・・コモンレール圧センサ
５・・・・燃料供給管
６・・・・燃料ポンプ
６ａ・・・ポンププーリ
８・・・・吸気枝管
９・・・・吸気管
１８・・・排気枝管
１９・・・排気管
２０・・・パティキュレートフィルタ
２１・・・排気絞り弁
２４・・・排気温度センサ
２５・・・ＥＧＲ通路
２６・・・ＥＧＲ弁
２７・・・ＥＧＲクーラ
２８・・・還元剤噴射弁
２９・・・還元剤供給路
３１・・・遮断弁
３３・・・クランクポジションセンサ
３５・・・ＥＣＵ
３６・・・アクセル開度センサ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
As a technique for purifying nitrogen oxide (NOx) contained in the exhaust gas of an internal combustion engine, a technique for arranging a lean NOx catalyst in an exhaust system of the internal combustion engine has been proposed. As one of the lean NOx catalysts, for example, when the oxygen concentration of the inflowing exhaust gas is high, nitrogen oxide (NOx) in the exhaust gas is occluded (absorbed and adsorbed), and the oxygen concentration of the inflowing exhaust gas decreases and the reducing agent Nitrogen oxide (NOx) that has been occluded when nitrogen is present₂The NOx storage reduction catalyst is known to reduce to (3).
[0003]
When this storage reduction type NOx catalyst is arranged in the exhaust system of the internal combustion engine, when the internal combustion engine is operated with lean combustion and the air-fuel ratio of the exhaust gas becomes high, nitrogen oxides (NOx) in the exhaust gas are stored in the NOx storage reduction catalyst. When the air-fuel ratio of the exhaust gas that has been occluded and flows into the occlusion reduction type NOx catalyst becomes low, the nitrogen oxide (NOx) occluded in the occlusion reduction type NOx catalyst becomes nitrogen (N₂).
[0004]
By the way, since the NOx storage capacity of the NOx storage reduction catalyst is limited, when the internal combustion engine is operated for lean combustion over a long period of time, the NOx storage capacity of the NOx storage reduction catalyst is saturated and nitrogen oxides in the exhaust ( NOx) is released into the atmosphere without being removed by the NOx storage reduction catalyst.
[0005]
Therefore, when the NOx storage reduction catalyst is applied to a lean combustion internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is reduced for a short period before the NOx storage capacity of the NOx storage reduction catalyst is saturated. Therefore, it is necessary to reduce nitrogen oxide (NOx) stored in the NOx storage reduction catalyst.
[0006]
As a method for lowering the air-fuel ratio of the exhaust in this way, a method of adding fuel as a reducing agent to the exhaust flowing upstream from the NOx storage reduction catalyst can be exemplified.
[0007]
In addition, when such a reducing agent is added, it is also important to accurately control the amount of reducing agent added according to the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst.
[0008]
This is because if the amount of reducing agent added is excessive with respect to nitrogen oxide (NOx) stored in the NOx storage reduction catalyst, excess reducing agent will be released into the atmosphere, If the amount of addition of the reducing agent is insufficient with respect to the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst, the NOx storage capacity of the NOx storage reduction catalyst is saturated and the nitrogen oxide (NOx) in the exhaust gas is exhausted. ) Will be released into the atmosphere without being purified.
[0009]
With respect to such a problem, the exhaust gas purification apparatus for an internal combustion engine described in Japanese Patent No. 2845056 considers the amount of air sucked into the internal combustion engine and the oxygen concentration detected by the air-fuel ratio sensor, and reduces the amount of reducing agent. By determining the addition amount, it is intended to prevent excessive supply and supply shortage of the reducing agent, and thereby suppress the deterioration of exhaust emission due to the release of the reducing agent and nitrogen oxide (NOx) into the atmosphere. .
[0010]
[Problems to be solved by the invention]
However, in the invention described in the above publication, a fuel injection valve for supplying fuel, a fuel pump for sending high-pressure fuel to the fuel injection valve, an air flow meter for measuring the amount of air taken into the internal combustion engine, etc. Variation in fuel injection amount due to the difference was not taken into account. If there is such a variation in the fuel injection amount, the required amount of reducing agent added cannot be obtained, and therefore the air-fuel ratio required for NOx reduction or the like may not be obtained. In such a case, the air-fuel ratio cannot be optimized due to excess or shortage of fuel, and exhaust emission may deteriorate.
[0011]
The present invention has been made in view of the above-described problems, and in an exhaust gas purification apparatus for an internal combustion engine, the amount of reducing agent required when NOx occluded in the NOx occlusion agent is reduced and actually is reduced. An object of the present invention is to provide a technique for eliminating the difference from the amount of reducing agent supplied, and to accurately control the air-fuel ratio during NOx reduction.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the first invention is
NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Target temperature rise determination means for determining a temperature rise amount of the NOx storage agent based on the operation state detected by the operation state detection means;
Reducing agent supply means for supplying a reducing agent to the NOx storage agent to reduce NOx stored in the NOx storage agent;
A temperature raising means for supplying a reducing agent corresponding to the target temperature raising amount determined by the target temperature raising amount determining means to the NOx storage agent to increase the temperature of the NOx storage agent;
A temperature rise estimation means for estimating the actual temperature rise of the NOx storage agent;
Correction coefficient calculating means for calculating a ratio between the temperature rise determined by the target temperature rise determining means and the temperature rise estimated by the temperature rise estimation means;
Reducing agent supply amount correction means for correcting the amount of reducing agent supplied by the reducing agent supply means based on the value calculated by the correction coefficient calculation means when reducing NOx stored in the NOx storage agent;
It is provided with.
[0013]
The most significant feature of the present invention is that, in an exhaust gas purification apparatus for an internal combustion engine, a ratio between a target temperature increase amount and an actual temperature increase amount is obtained as a correction coefficient, and the supply amount of the reducing agent multiplied by the correction coefficient is corrected. By supplying to the NOx storage agent as the supply amount of the reducing agent, excess or deficiency of the reducing agent is eliminated and NOx is reduced from the NOx storage agent.
[0014]
  In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the NOx stored in the NOx storage agent needs to be reduced, the reducing agent supply means supplies the reducing agent to the NOx storage agent.As the reducing agent supply means, there is a method of injecting fuel into exhaust gas by a reducing agent injection valve and adding fuel, but in addition, the fuel is supplied from the fuel injection valve to the expansion stroke or exhaust stroke of the engine. Examples include a method of adding fuel by injection.On the other hand, when it is necessary to raise the temperature of the NOx storage agent, the target temperature rise amount determining means determines the target temperature rise amount.Where NO x There is a correlation between the temperature rise of the occluding agent and the required fuel amount per unit intake air amount. Therefore, by obtaining the required fuel amount per unit intake air amount from the target temperature rise, and further multiplying the required fuel amount per unit intake air amount by, for example, the intake air amount that is an output signal of the air flow meter, It is possible to calculate the amount of reducing agent to be supplied.Based on the target temperature increase amount, the temperature raising means supplies a reducing agent to the NOx storage agent to increase the temperature of the NOx storage agent. However, the supply amount of the reducing agent may vary due to deterioration of the reducing agent supply means, individual differences, and the like. When the supply amount of the reducing agent fluctuates in this way, there is a difference between the amount of reducing agent that the reducing agent supply means tried to supply and the amount of reducing agent that was actually supplied to the catalyst, which is required during NOx reduction. There is a risk that the air-fuel ratio cannot be obtained.
[0015]
Therefore, the correction coefficient calculation means obtains the target temperature rise that is the deviation between the target temperature of the catalyst and the temperature before the supply of the reducing agent and the temperature rise that is the deviation of the catalyst temperature before and after the catalyst temperature rise. The ratio between the amount and the actual temperature rise is calculated. Since there is a correlation between the supply amount of the reducing agent and the temperature increase amount of the catalyst, the ratio between the target temperature increase amount and the actual temperature increase amount is the reducing agent required to raise the catalyst temperature to the target temperature. It is equal to the ratio between the amount and the amount of reducing agent actually supplied. This ratio is equal to the ratio between the amount of reducing agent required during NOx reduction and the amount of reducing agent actually supplied.
[0016]
Thus, when the reducing agent supply amount correcting means supplies the reducing agent to the NOx storage agent and reduces NOx from the NOx storage agent, the reducing agent amount after correction is based on the ratio calculated by the correction coefficient calculating means. Is calculated.
[0017]
In this way, it is possible to eliminate the difference between the amount of the reducing agent to be supplied by the reducing agent supply means and the amount of the reducing agent that is actually supplied to the catalyst.
[0018]
In the present invention, occlusion includes absorption and adsorption.
[0019]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the second invention is
NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Target temperature rise determination means for determining a target temperature rise of the NOx storage agent based on the operation state detected by the operation state detection means;
Reducing agent supply means for supplying a reducing agent to the NOx storage agent to reduce NOx stored in the NOx storage agent;
A temperature raising means for supplying a reducing agent corresponding to the target temperature raising amount determined by the target temperature raising amount determining means to the NOx storage agent to increase the temperature of the NOx storage agent;
A temperature rise amount estimation means within a predetermined period for estimating an actual temperature rise amount of the NOx storage agent in a predetermined period;
A target temperature increase amount calculating means for calculating a target temperature increase amount of the NOx storage agent in the predetermined period;
Correction coefficient calculating means for calculating a ratio between the target temperature increase amount of the NOx storage agent calculated by the target temperature increase amount calculation means within the predetermined period and the actual temperature increase amount in the predetermined period;
Reducing agent supply amount correction means for correcting the amount of reducing agent supplied by the reducing agent supply means based on the value calculated by the correction coefficient calculation means when reducing NOx stored in the NOx storage agent;
It is provided with.
[0020]
The most significant feature of the present invention is that, in an exhaust gas purification apparatus for an internal combustion engine, a ratio between a target temperature increase amount and an actual temperature increase amount within a predetermined period is obtained as a correction coefficient, and the supply amount of the reducing agent multiplied by the correction coefficient Is supplied to the NOx storage agent as the supply amount of the reducing agent after correction, thereby eliminating excess and deficiency of the reducing agent and reducing NOx from the NOx storage agent.
[0021]
  In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the NOx stored in the NOx storage agent needs to be reduced, the reducing agent supply means supplies the reducing agent to the NOx storage agent.As the reducing agent supply means, there is a method of injecting fuel into exhaust gas by a reducing agent injection valve and adding fuel, but in addition, the fuel is supplied from the fuel injection valve to the expansion stroke or exhaust stroke of the engine. Examples include a method of adding fuel by injection.On the other hand, when it is necessary to raise the temperature of the NOx storage agent, the target temperature rise amount determining means determines the target temperature rise amount.Where NO x There is a correlation between the temperature rise of the occluding agent and the required fuel amount per unit intake air amount. Therefore, by obtaining the required fuel amount per unit intake air amount from the target temperature rise, and further multiplying the required fuel amount per unit intake air amount by, for example, the intake air amount that is an output signal of the air flow meter, It is possible to calculate the amount of reducing agent to be supplied.Based on the target temperature increase amount, the temperature raising means supplies a reducing agent to the NOx storage agent to increase the temperature of the NOx storage agent. However, the supply amount of the reducing agent may vary due to deterioration of the reducing agent supply means, individual differences, and the like. When the supply amount of the reducing agent fluctuates in this way, a difference occurs between the amount of the reducing agent that the reducing agent supply means tries to supply and the amount of the reducing agent that is actually supplied to the catalyst, which is required for NOx reduction. There is a risk that the air-fuel ratio cannot be obtained. This applies even within a predetermined period during which the temperature of the catalyst is raised.
[0022]
Accordingly, the correction coefficient calculation means obtains a target temperature increase amount that is a deviation between the target temperature of the catalyst within a predetermined period and a temperature before the supply of the reducing agent, and a temperature increase amount that is a deviation of the catalyst temperature before and after the catalyst temperature increase, Further, the ratio between the target temperature increase amount and the actual temperature increase amount within a predetermined period is calculated. Since there is a correlation between the supply amount of the reducing agent and the temperature increase amount of the catalyst, the ratio between the target temperature increase amount and the actual temperature increase amount is the reducing agent required to raise the catalyst temperature to the target temperature. It is equal to the ratio between the amount and the amount of reducing agent actually supplied. This ratio is also equal to the ratio between the amount of reducing agent required during NOx reduction and the amount of reducing agent actually supplied.
[0023]
Thus, when the reducing agent supply amount correcting means supplies the reducing agent to the NOx storage agent and reduces NOx from the NOx storage agent, the reducing agent amount after correction is based on the ratio calculated by the correction coefficient calculating means. Is calculated.
[0024]
In this way, it is possible to eliminate the difference between the amount of the reducing agent to be supplied by the reducing agent supply means and the amount of the reducing agent that is actually supplied to the catalyst.
[0025]
In the present invention, occlusion includes absorption and adsorption.
[0026]
  In the first and second aspects of the invention, the reducing agent supply means supplies the reducing agent to the NOx storage agent to release SOx stored in the NOx storage agent, and the reducing agent supply amount correction means includes the When releasing the SOx stored in the NOx storage agent,The amount of reducing agent supplied by the reducing agent supply means can be multiplied by the ratio calculated by the correction coefficient calculating means to correct the amount of reducing agent supplied.
[0027]
In the exhaust gas purification apparatus for an internal combustion engine thus configured, when it becomes necessary to release the SOx stored in the NOx storage agent, the reducing agent supply means supplies the reducing agent after the temperature of the NOx storage agent is raised. To release SOx. However, the supply amount of the reducing agent fluctuates for the same reason as when NOx is released, resulting in a difference between the amount of the reducing agent that the reducing agent supply means tried to supply and the amount of the reducing agent that was actually supplied to the catalyst, There is a risk that the air-fuel ratio required when releasing SOx cannot be obtained. Such fluctuations in the amount of reducing agent during SOx release can be corrected in the same manner as the method for correcting the amount of reducing agent during NOx reduction.
[0028]
In the first and second aspects of the invention, the reducing agent supply means includes a reducing agent injection valve that injects the reducing agent into the exhaust gas, and is required to inject an amount of the reducing agent according to the operating state. The time is calculated, and the reducing agent supply amount correcting means multiplies the opening time of the reducing agent injection valve calculated by the reducing agent supplying means by the ratio calculated by the correction coefficient calculating means, and further calculated by the correction coefficient calculating means. When the ratio is 1 or more, an amount of reducing agent multiplied by a correction coefficient that increases in accordance with the ratio can be supplied to the NOx storage agent.
[0029]
If the amount of reducing agent injected is reduced with respect to the opening time of the reducing agent injection valve, even if the opening time is extended, the extended amount of reducing agent also decreases. If correction is performed in anticipation of the decrease, the accuracy of the reducing agent supply amount can be further improved. Therefore, when the opening time of the reducing agent injection valve is extended, a valve opening time corresponding to the amount of reducing agent that is insufficient due to the reduction of the reducing agent injection amount during the extended time is further added. In this way, it is possible to supply the reducing agent amount necessary for NOx reduction or the like even when the injection amount of the reducing agent injection valve is reduced.
[0030]
In the first and second aspects of the invention, the temperature raising means can supply the reducing agent based on the intake air amount taken into the internal combustion engine and the target temperature raising amount.
[0031]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
<First Embodiment>
FIG. 1 is a diagram showing a schematic configuration of an engine 1 and an intake / exhaust system to which the exhaust purification apparatus according to the present embodiment is applied.
[0032]
An engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0033]
The engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 that accumulates fuel to a predetermined pressure. A common rail pressure sensor 4 a that outputs an electrical signal corresponding to the fuel pressure in the common rail 4 is attached to the common rail 4.
[0034]
The common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5. This fuel pump 6 is a pump that operates using the rotational torque of the output shaft (crankshaft) of the engine 1 as a drive source, and a pump pulley 6 a attached to the input shaft of the fuel pump 6 is connected to the output shaft (crankshaft) of the engine 1. ) And the belt pulley 7 are connected to each other.
[0035]
In the fuel injection system configured as described above, when the rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 transmits the rotational torque transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure according to the pressure.
[0036]
The fuel discharged from the fuel pump 6 is supplied to the common rail 4 via the fuel supply pipe 5, accumulated in the common rail 4 up to a predetermined pressure, and distributed to the fuel injection valves 3 of each cylinder 2. When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2.
[0037]
Next, an intake branch pipe 8 is connected to the engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0038]
The intake branch pipe 8 is connected to an intake pipe 9, and the intake pipe 9 is connected to an air cleaner box 10. An air flow meter 11 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake pipe 9 is attached to the intake pipe 9 downstream of the air cleaner box 10.
[0039]
An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 13 is provided with an intake throttle actuator 14 that is configured by a step motor or the like and that drives the intake throttle valve 13 to open and close.
[0040]
The intake pipe 9 positioned between the air flow meter 11 and the intake throttle valve 13 is provided with a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using the thermal energy of exhaust as a drive source. The intake pipe 9 downstream of the housing 15a is provided with an intercooler 16 for cooling the intake air that has been compressed in the compressor housing 15a and has reached a high temperature.
[0041]
In the intake system configured as described above, the intake air that has flowed into the air cleaner box 10 is removed through the intake pipe 9 after dust or dust in the intake air is removed by an air cleaner (not shown) in the air cleaner box 10. It flows into the compressor housing 15a.
[0042]
The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel built in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has reached a high temperature is cooled by the intercooler 16, and then the flow rate is adjusted by the intake throttle valve 13 as necessary to flow into the intake branch pipe 8. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chambers of the respective cylinders 2 through the respective branch pipes, and is burned using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0043]
On the other hand, an exhaust branch pipe 18 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with a combustion chamber of each cylinder 2 via an exhaust port (not shown).
[0044]
The exhaust branch pipe 18 is connected to the turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected to a muffler (not shown) downstream.
[0045]
In the middle of the exhaust pipe 19, a particulate filter (hereinafter simply referred to as a filter) 20 carrying an NOx storage reduction catalyst is provided. An exhaust gas temperature sensor 24 that outputs an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20.
[0046]
The exhaust pipe 19 downstream of the filter 20 is provided with an exhaust throttle valve 21 that adjusts the flow rate of the exhaust gas flowing through the exhaust pipe 19. The exhaust throttle valve 21 is provided with an exhaust throttle actuator 22 that is configured by a step motor or the like and that drives the exhaust throttle valve 21 to open and close.
[0047]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then centrifugally supercharged from the exhaust branch pipe 18. Flows into the turbine housing 15b of the machine 15. The exhaust gas flowing into the turbine housing 15b rotates a turbine wheel that is rotatably supported in the turbine housing 15b using the thermal energy of the exhaust gas. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.
[0048]
Exhaust gas discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19, and particulate matter (hereinafter simply referred to as PM) in the exhaust gas is collected and harmful gas components are removed or purified. The Exhaust gas from which PM has been collected by the filter 20 and from which harmful gas components have been removed or purified is adjusted in flow rate by the exhaust throttle valve 21 as necessary, and then released into the atmosphere via the muffler.
[0049]
Further, the exhaust branch pipe 18 and the intake branch pipe 8 have an exhaust recirculation passage (hereinafter referred to as an EGR passage) 25 for recirculating a part of the exhaust gas flowing through the exhaust branch pipe 18 to the intake branch pipe 8. It is communicated through. In the middle of the EGR passage 25, a flow rate adjusting valve is configured with an electromagnetic valve or the like, and changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) flowing through the EGR passage 25 in accordance with the magnitude of applied power. (Hereinafter referred to as an EGR valve) 26 is provided.
[0050]
An EGR cooler 27 that cools the EGR gas flowing in the EGR passage 25 is provided in the middle of the EGR passage 25 and upstream of the EGR valve 26. The EGR cooler 27 is provided with a cooling water passage (not shown), and a part of the cooling water for cooling the engine 1 circulates.
[0051]
In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe 18 flows into the EGR passage 25. Then, it is guided to the intake branch pipe 8 through the EGR cooler 27.
[0052]
At that time, in the EGR cooler 27, heat exchange is performed between the EGR gas flowing in the EGR passage 25 and the cooling water of the engine 1 to cool the EGR gas.
[0053]
The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 through the EGR passage 25 is guided to the combustion chamber of each cylinder 2 while being mixed with fresh air flowing from the upstream side of the intake branch pipe 8.
[0054]
Here, the EGR gas contains water (H₂O) and carbon dioxide (CO₂) And the like, and since an inert gas component having a high heat capacity is not included, if the EGR gas is contained in the air-fuel mixture, the combustion temperature of the air-fuel mixture is lowered. Therefore, the amount of nitrogen oxide (NOx) generated is suppressed.
[0055]
Further, when the EGR gas is cooled in the EGR cooler 27, the temperature of the EGR gas itself is reduced and the volume of the EGR gas is reduced. Therefore, when the EGR gas is supplied into the combustion chamber, the atmospheric temperature in the combustion chamber is reduced. Is not increased unnecessarily, and the amount of fresh air (volume of fresh air) supplied into the combustion chamber is not unnecessarily reduced.
[0056]
Next, the filter 20 according to the present embodiment will be described.
[0057]
FIG. 2 is a cross-sectional view of the filter 20. FIG. 2A is a diagram illustrating a cross-section in the horizontal direction of the filter 20. FIG. 2B is a view showing a longitudinal section of the filter 20.
[0058]
As shown in FIGS. 2A and 2B, the filter 20 is a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Therefore, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by four exhaust inflow passages 50.
[0059]
The filter 20 is made of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust inflow passage 50 is adjacent to the surrounding partition wall 54 as shown by an arrow in FIG. To the exhaust outlet passage 51.
[0060]
In the embodiment according to the present invention, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of each exhaust inflow passage 50 and each exhaust outflow passage 51, that is, on both side surfaces of each partition wall 54 and on the pore inner wall surface in each partition wall 54. A NOx storage reduction catalyst as a NOx storage agent is supported on the carrier.
[0061]
Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to the present embodiment will be described.
[0062]
The filter 20 uses, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), and barium (Ba) or calcium (Ca). ), An alkaline earth such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). In this embodiment, barium (Ba) and platinum (Pt) are supported on a support made of alumina, and O 2 is further supported.₂Ceria with storage capability (Ce₂O_ThreeThe NOx storage reduction catalyst is added.
[0063]
The NOx catalyst configured in this way occludes (absorbs and adsorbs) nitrogen oxides (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high.
[0064]
On the other hand, the NOx catalyst releases the stored nitrogen oxide (NOx) when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, the NOx catalyst converts nitrogen oxide (NOx) released from the NOx catalyst to nitrogen (N₂).
[0065]
By the way, when the engine 1 is operated with lean combustion, the air-fuel ratio of the exhaust discharged from the engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high, so that nitrogen oxide (NOx) contained in the exhaust is NOx. When the lean combustion operation of the engine 1 is continued for a long period of time, the NOx storage capacity of the NOx catalyst is saturated, and nitrogen oxides (NOx) in the exhaust gas are removed by the NOx catalyst. Without being released into the atmosphere.
[0066]
In particular, in a diesel engine such as the engine 1, a lean air-fuel ratio mixture is combusted in most operating regions, and the exhaust air-fuel ratio becomes lean air-fuel ratio in most operating regions accordingly. The NOx occlusion capacity is easily saturated. Here, the lean air-fuel ratio means, for example, 20 to 50 in a diesel engine, and a region in which NOx cannot be purified by a three-way catalyst.
[0067]
Therefore, when the engine 1 is in lean burn operation, before the NOx occlusion capacity of the NOx catalyst is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is lowered and the concentration of the reducing agent is increased and occluded in the NOx catalyst. It is necessary to reduce the formed nitrogen oxides (NOx).
[0068]
As a method for reducing the oxygen concentration in this way, after adding fuel in the exhaust gas or increasing the amount of recirculated EGR gas to increase the amount of soot generation to a maximum, the amount of EGR gas is further increased. Methods such as low-temperature combustion (Japanese Patent No. 3116876) and fuel injection during the expansion stroke into the cylinder 2 are conceivable. In the present embodiment, a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust pipe 19 upstream from the filter 20 is provided, and the fuel is added from the reducing agent supply mechanism into the exhaust gas. As a result, the oxygen concentration of the exhaust gas flowing into the filter 20 is decreased and the concentration of the reducing agent is increased.
[0069]
As shown in FIG. 1, the reducing agent supply mechanism is attached so that its injection hole faces the exhaust branch pipe 18, and is opened by a signal from the ECU 35 to inject fuel and a reducing agent injection valve 28. A reducing agent supply path 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and a shutoff that is provided in the reducing agent supply path 29 and blocks the flow of fuel in the reducing agent supply path 29. And a valve 31.
[0070]
In such a reducing agent supply mechanism, high-pressure fuel discharged from the fuel pump 6 is applied to the reducing agent injection valve 28 via the reducing agent supply path 29. Then, the reducing agent injection valve 28 is opened by a signal from the ECU 35 and fuel as a reducing agent is injected into the exhaust branch pipe 18.
[0071]
The reducing agent injected into the exhaust branch pipe 18 from the reducing agent injection valve 28 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust branch pipe 18.
[0072]
The exhaust gas having a low oxygen concentration thus formed flows into the filter 20 and releases nitrogen oxide (NOx) stored in the filter 20 while nitrogen (N₂).
[0073]
Thereafter, the reducing agent injection valve 28 is closed by a signal from the ECU 35, and the addition of the reducing agent into the exhaust branch pipe 18 is stopped.
[0074]
In the present embodiment, fuel is injected into the exhaust gas to add the fuel. Alternatively, low-temperature combustion may be performed, and the fuel is used for the expansion stroke or exhaust stroke of the engine 1. Fuel may be injected from the injection valve 3.
[0075]
The engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the engine 1. The ECU 35 is a unit that controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.
[0076]
Various sensors such as the common rail pressure sensor 4a, the air flow meter 11, the exhaust temperature sensor 24, the crank position sensor 33, the accelerator opening sensor 36, and the like are connected to the ECU 35 through electric wiring, and output signals of the various sensors described above are transmitted to the ECU 35. To be input.
[0077]
On the other hand, the ECU 35 is connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the reducing agent injection valve 28, the EGR valve 26, the shutoff valve 31 and the like via electrical wiring, The ECU 35 can be controlled.
[0078]
Here, as shown in FIG. 3, the ECU 35 includes a CPU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357, which are connected to each other by a bidirectional bus 350. , An A / D converter (A / D) 355 connected to the input port 356 is provided.
[0079]
The input port 356 receives an output signal from a sensor that outputs a digital signal format signal, such as the crank position sensor 33, and transmits the output signal to the CPU 351 and the RAM 353.
[0080]
The input port 356 is input via an A / D 355 of a sensor that outputs an analog signal format signal such as the common rail pressure sensor 4a, the air flow meter 11, the exhaust gas temperature sensor 24, the accelerator opening sensor 36, and the like. Are output to the CPU 351 and the RAM 353.
[0081]
The output port 357 is connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the reducing agent injection valve 28, the shutoff valve 31, etc. via electrical wiring, and is output from the CPU 351. The control signal is transmitted to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the reducing agent injection valve 28, or the shutoff valve 31.
[0082]
The ROM 352 controls a fuel injection control routine for controlling the fuel injection valve 3, an intake throttle control routine for controlling the intake throttle valve 13, an exhaust throttle control routine for controlling the exhaust throttle valve 21, and an EGR valve 26. EGR control routine, NOx purification control routine for reducing the stored NOx by adding a reducing agent to the filter 20, poisoning recovery control routine for recovering SOx poisoning of the filter 20, trapped by the filter 20 An application program such as a PM combustion control routine for burning and removing PM is stored.
[0083]
The ROM 352 stores various control maps in addition to the application programs described above. The control map is, for example, a fuel injection amount control map indicating the relationship between the operating state of the engine 1 and the basic fuel injection amount (basic fuel injection time), and the fuel indicating the relationship between the operating state of the engine 1 and the basic fuel injection timing. The injection timing control map, the intake throttle valve opening control map showing the relationship between the operating state of the engine 1 and the target opening of the intake throttle valve 13, the relationship between the operating state of the engine 1 and the target opening of the exhaust throttle valve 21 Exhaust throttle valve opening control map, EGR valve opening control map showing the relationship between the operating state of the engine 1 and the target opening of the EGR valve 26, the operating state of the engine 1 and the target addition amount of reducing agent (or the exhaust gas A reducing agent addition amount control map showing the relationship with the target air-fuel ratio), a reducing agent injection valve control map showing the relationship between the target addition amount of the reducing agent and the opening time of the reducing agent injection valve 28, and the like.
[0084]
The RAM 353 stores output signals from the sensors, calculation results of the CPU 351, and the like. The calculation result is, for example, the engine speed calculated based on the time interval at which the crank position sensor 33 outputs a pulse signal. These data are rewritten to the latest data every time the crank position sensor 33 outputs a pulse signal.
[0085]
The backup RAM 354 is a non-volatile memory capable of storing data even after the engine 1 is stopped.
[0086]
The CPU 351 operates in accordance with an application program stored in the ROM 352, and executes fuel injection valve control, intake throttle control, exhaust throttle control, EGR control, NOx purification control, poisoning recovery control, PM combustion control, and the like.
[0087]
For example, in the NOx purification control, the CPU 351 executes so-called rich spike control in which the oxygen concentration in the exhaust gas flowing into the filter 20 is reduced in a spike manner (short time) in a relatively short cycle.
[0088]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. As this rich spike control execution condition, for example, the filter 20 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value, poisoning recovery control is not executed, Etc. can be exemplified.
[0089]
When it is determined that the rich spike control execution condition as described above is satisfied, the CPU 351 controls the reducing agent injection valve 28 to inject fuel as a reducing agent from the reducing agent injection valve 28 in a spike manner. As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to a predetermined target rich air-fuel ratio.
[0090]
Specifically, the CPU 351 stores the engine speed stored in the RAM 353, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), and the output of the air-fuel ratio sensor. Read signal, fuel injection amount, etc.
[0091]
The CPU 351 accesses the reducing agent addition amount control map in the ROM 352 using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the air-fuel ratio of the exhaust to a preset target air-fuel ratio. The amount of addition of the reducing agent (target addition amount) required above is calculated.
[0092]
Subsequently, the CPU 351 accesses the reducing agent injection valve control map of the ROM 352 using the target addition amount as a parameter, and the reducing agent injection valve 28 necessary for injecting the reducing agent with the target addition amount from the reducing agent injection valve 28. The valve opening time (target valve opening time) is calculated.
[0093]
When the target valve opening time of the reducing agent injection valve 28 is calculated, the CPU 351 opens the reducing agent injection valve 28.
[0094]
When the target valve opening time has elapsed from the time when the reducing agent injection valve 28 is opened, the CPU 351 closes the reducing agent injection valve 28.
[0095]
Thus, when the reducing agent injection valve 28 is opened for the target valve opening time, a target addition amount of fuel is injected into the exhaust branch pipe 18 from the reducing agent injection valve 28. The reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust gas flowing from the upstream side of the exhaust branch pipe 18 to form an air-fuel mixture having a target air-fuel ratio and flows into the filter 20.
[0096]
As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 changes its oxygen concentration in a relatively short cycle, and thus the filter 20 alternately shortens the storage and reduction of nitrogen oxides (NOx). It will repeat periodically.
[0097]
Next, in the poisoning recovery control, the CPU 351 performs a poisoning recovery process to recover the poisoning due to the oxide of the filter 20.
[0098]
Here, the fuel of the engine 1 may contain sulfur (S), and when such fuel is burned in the engine 1, sulfur dioxide (SO₂) And sulfur trioxide (SO_Three) And other sulfur oxides (SOx).
[0099]
Sulfur oxide (SOx) flows into the filter 20 together with the exhaust gas, and is stored in the filter 20 by the same mechanism as nitrogen oxide (NOx).
[0100]
Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 20 is high, sulfur dioxide (SO₂) And sulfur trioxide (SO_Three) And other sulfur oxides (SOx) are oxidized on the surface of platinum (Pt), and sulfate ions (SO_Four ^2-) Is stored in the filter 20. Further, sulfate ions (SO_Four ^2-) Combines with barium oxide (BaO) to form sulfate (BaSO)._Four).
[0101]
By the way, sulfate (BaSO_Four) Is barium nitrate (Ba (NO_Three)₂) And is difficult to decompose, and even if the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered, it remains in the filter 20 without being decomposed.
[0102]
Sulfate (BaSO_Four) Increases accordingly, the amount of barium oxide (BaO) that can participate in the storage of nitrogen oxides (NOx) decreases accordingly, so that the NOx storage capacity of the filter 20 decreases, so-called SOx poisoning. Occurs.
[0103]
As a method for recovering the SOx poisoning of the filter 20, the atmospheric temperature of the filter 20 is raised to a high temperature range of approximately 600 to 650 ° C., and the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered to reduce the filter 20 Barium sulfate (BaSO_Four) SO_Three ^-And SO_Four ^-Pyrolyzed, and then SO_Three ^-And SO_Four ^-Reacts with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust to produce gaseous SO₂ ^-An example of the method for reduction is shown.
[0104]
Therefore, in the poisoning recovery process according to the present embodiment, the CPU 351 first performs the catalyst temperature increase control for increasing the bed temperature of the filter 20 and then reduces the oxygen concentration of the exhaust gas flowing into the filter 20. .
[0105]
In the catalyst temperature increase control, the CPU 351 oxidizes the fuel in the filter 20 by injecting the fuel from the reducing agent injection valve 28, and increases the temperature increase of the filter 20 by the heat generated at that time. At this time, the injection amount of the fuel injected from the reducing agent injection valve 28 is set so that the injection interval is shorter than the fuel injection performed at the time of NOx reduction, and the air-fuel ratio at that time is higher.
[0106]
However, if the temperature of the filter 20 is excessively increased, thermal deterioration of the filter 20 may be induced. Therefore, it is preferable that the amount of added fuel is feedback controlled based on the output signal value of the exhaust temperature sensor 24. .
[0107]
When the bed temperature of the filter 20 rises to a high temperature range of, for example, 630 ° C. by the catalyst temperature raising process as described above, the CPU 351 injects fuel from the reducing agent injection valve 28 to reduce the oxygen concentration of the exhaust gas flowing into the filter 20. Let
[0108]
When excessive fuel is injected from the reducing agent injection valve 28, the fuel is burnt rapidly in the filter 20 and the filter 20 is overheated, or the excess fuel injected from the reducing agent injection valve 28 filters the fuel. Therefore, it is preferable that the CPU 351 feedback-controls the fuel injection amount from the reducing agent injection valve 28 based on an output signal of an air-fuel ratio sensor (not shown).
[0109]
When the poisoning recovery process is performed in this manner, the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low under the condition where the bed temperature of the filter 20 is high, so that barium sulfate (BaSO) stored in the filter 20 is stored._Four) Is SO_Three ^-And SO_Four ^-They are pyrolyzed into SO_Three ^-And SO_Four ^-Reacts with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and is reduced, so that SOx poisoning of the filter 20 is recovered.
[0110]
By the way, the PM collected by the filter 20 is burned and removed by the high-temperature exhaust discharged when the engine 1 is operated in a high-rotation and high-load region, but some time is required for PM combustion. Therefore, if the engine operating region deviates from the high rotation / high load region before PM is completely burned and removed, the PM may remain unburned. In some cases, the engine operating state suitable for PM combustion cannot be maintained for a long time, and unburned PM gradually accumulates on the filter, which may cause clogging of the filter.
[0111]
The addition of fuel into the exhaust is also effective as one method for effectively removing unburned PM.
[0112]
When fuel is added into the exhaust gas, the active oxygen is released by the fuel that has flowed into the filter 20, so that the PM is easily oxidized and the amount that can be removed by oxidation per unit time is improved. Further, the addition of fuel removes oxygen poisoning of the catalyst and increases the activity of the catalyst, so that active oxygen is easily released. Then, PM is oxidized and burned by active oxygen and removed.
[0113]
By the way, the amount of fuel injected from the reducing agent injection valve during NOx reduction and SOx poisoning recovery may vary due to deterioration of the reducing agent injection valve, individual differences, and the like. In this case, the air-fuel ratio required for NOx reduction and SOx poisoning recovery may not be obtained. Further, even if the air flow meter 11 and the fuel pump 6 are deteriorated or have individual differences, the target air-fuel ratio may not be obtained. Then, even if NOx reduction, SOx poisoning recovery, PM regeneration, and the like are performed, sufficient effects cannot be obtained, and exhaust emission may be deteriorated.
[0114]
Therefore, in this embodiment, paying attention to the temperature increase amount of the filter 20 at the time of fuel addition, the fuel addition amount is determined based on the ratio of the target temperature increase amount of the filter 20 and the actual temperature increase amount of the filter 20. Correct and solve the above problem.
[0115]
Next, a method for correcting the reducing agent addition amount according to the present embodiment will be described.
[0116]
Here, FIG. 4 is a diagram showing the relationship between the temperature increase required for the filter 20 and the required fuel amount per unit intake air amount. This map is stored in the ROM 352 in advance. Here, the temperature increase required for the filter 20 (hereinafter referred to as a target temperature increase) is a temperature required for SOx poisoning (for example, 600 to 650 ° C.) or a temperature required for PM regeneration (for example, 600 to 650 ° C.). For example, it is a deviation between the temperature of the filter 20 and the temperature before the temperature rise. Here, the temperature of the filter 20 before the temperature rise is obtained by mapping the rotation speed when the fuel is not added, the load and the temperature of the filter 20 in advance, and mapping the current rotation speed (crank position sensor). 33) and the load (the output signal of the accelerator opening sensor 36 or the fuel injection amount) and the temperature of the filter 20 (hereinafter referred to as the base temperature) obtained by substituting it.
[0117]
First, the CPU 351 determines the required fuel amount per unit intake air amount by substituting the target temperature increase amount into FIG. Next, the CPU 351 calculates the fuel addition amount that can obtain the target temperature increase amount from the output signal of the air flow meter 11 and the required fuel amount per unit intake air amount. Based on the fuel addition amount calculated in this way, the CPU 351 causes the reducing agent injection valve 28 to add fuel. At this time, the fuel required by the filter 20 may not actually be added due to deterioration and individual differences of the reducing agent injection valve 28, the fuel pump 6, the air flow meter 11, and the like. Such excess or deficiency of the added fuel affects the temperature increase of the filter 20.
[0118]
Here, FIG. 5 is a time chart showing the time transition of the relationship between the target temperature, the actual temperature, and the base temperature of the filter 20. From this figure, it can be seen that the relationship between the target temperature, the actual temperature, and the base temperature of the filter 20 changes at a constant rate. Further, the fuel addition amount and the temperature increase amount of the filter 20 have a correlation as shown in FIG. Therefore, by calculating the relationship between the target temperature of the filter 20, the actual temperature, and the base temperature, the fuel addition amount required to raise the filter 20 to the target temperature can be calculated from the current fuel addition amount. It becomes possible.
[0119]
As described above, the correction coefficient for correcting the fuel addition amount can be obtained by the following equation.
[0120]

Incidentally, the reducing agent injection valve 28 injects fuel not only when the temperature of the filter 20 is raised but also when NOx is reduced from the NOx storage reduction catalyst carried on the filter 20. The fuel addition amount at this time also differs between the target addition amount and the actual addition amount for the same reason as when the filter 20 is heated. The amount of fuel added is different between the temperature rise of the filter 20 and NOx reduction, but the fuel is injected in an amount proportional to the opening time of the reducing agent injection valve 28. Therefore, the amount of reducing agent injected from the reducing agent injection valve 28 can be corrected by the correction coefficient calculated when the filter 20 is heated, and the amount of reducing agent required for NOx reduction or the like is calculated. Is possible. As described above, a value obtained by correcting the fuel addition amount for NOx reduction using this correction coefficient can be obtained by the following equation.
[0121]
NOx reduction addition amount = basic injection amount command value × correction coefficient × reflection coefficient a
Here, the basic injection amount command value is the fuel addition amount calculated by the rich spike control described above. The reflection coefficient a is a value calculated from a map based on the driving state.
[0122]
Here, FIG. 6 is a diagram showing the relationship between the correction coefficient and the reflection coefficient. When the correction coefficient is larger than 1, that is, when the actual temperature is lower than the target temperature, the amount of fuel actually added does not reach the target addition amount. In such a case, since the fuel addition amount per unit time is decreasing, the fuel addition amount can be increased by extending the opening time of the reducing agent injection valve 28. However, if the basic injection amount command value is simply multiplied by the correction coefficient, the amount of newly added reducing agent will be insufficient as the injection amount of the reducing agent injection valve 28 is reduced. The reflection coefficient a is used to compensate for this shortage. Here, the map shown in FIG. 6 is stored in the ROM 352 in advance, and the reflection coefficient a is calculated by substituting the correction coefficient into the map. The correction coefficient and the reflection coefficient a are stored in the backup RAM 354, and the CPU 351 uses this value to add fuel at the next fuel addition.
[0123]
Based on the NOx reduction addition amount thus determined, fuel is injected from the reducing agent injection valve 28. The amount of fuel actually injected from the reducing agent injection valve 28 is an amount substantially equal to the basic injection amount. It becomes. In this way, the air-fuel ratio required for NOx reduction or the like can be obtained.
[0124]
If the fuel addition amount is corrected after, for example, a period of about 1 minute 30 seconds to 2 minutes after the fuel addition, the correction coefficient can be calculated while the temperature of the filter 20 is stable. In addition, the accuracy of the amount of fuel added during NOx reduction can be improved.
[0125]
As described above, according to the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the amount of fuel addition for reducing NOx from the filter 20 is corrected based on the target temperature increase amount and the actual temperature increase amount. This makes it possible to supply exhaust gas having a target air-fuel ratio to the filter 20.
[0126]
In this embodiment, the correction method of the fuel addition amount during NOx reduction from the NOx storage reduction catalyst has been described. However, the fuel addition amount in the SOx poisoning recovery control after the temperature increase of the NOx storage reduction catalyst is also described. It is possible to correct similarly.
<Second Embodiment>
This embodiment is different from the first embodiment in the following points.
[0127]
That is, in the first embodiment, the correction coefficient for the fuel addition amount is calculated after the temperature increase of the post-fuel addition filter 20 is completed. In this embodiment, the filter is added during an arbitrary period during the temperature increase. Paying attention to the temperature rise when the temperature rises, the fuel addition amount correction coefficient is calculated. That is, the fuel addition amount is corrected based on the temperature of the filter 20 before reaching the state of FIG. 5 of the first embodiment.
[0128]
In the present embodiment, compared with the first embodiment, the correction timing of the fuel addition amount is different in that the temperature of the filter 20 is being raised. Since the basic configuration of the hardware is the same as that of the first embodiment, a description thereof will be omitted.
[0129]
Here, FIG. 7 is a time chart showing the temperature transition of the filter 20 from the start of fuel addition.
[0130]
In the present embodiment, the period from the start of fuel addition until the temperature of the filter 20 reaches the target temperature (hereinafter referred to as the target period), for example, a predetermined period from the start of fuel addition (hereinafter referred to as the target period). Pay attention to the temperature rise amount of the filter 20.
[0131]
First, the CPU 351 calculates a target temperature increase amount during the target period. The target temperature increase amount during the target period is obtained by multiplying the ratio of the target period to the target period by the temperature increase amount of the filter 20 that is the final target.
[0132]
Next, the amount of temperature rise by which the filter 20 has actually increased during the target period is obtained. Here, the CPU 351 reads the output signal of the exhaust temperature sensor 24 and estimates the temperature of the filter 20. The temperature of the filter 20 can also be estimated from the intake air amount (output signal of the air flow meter 11), the rotation speed, the load, the fuel injection amount, and the like. Furthermore, the temperature of the filter 20 may be obtained by mapping a value obtained in advance by experiment, or the temperature of the filter 20 may be directly measured by providing a temperature sensor in the filter 20.
[0133]
The value obtained by dividing the target temperature increase amount during the target period obtained in this way by the actual temperature increase amount is substantially the same as the fuel addition amount correction coefficient calculated in the first embodiment. Become. Accordingly, it is possible to correct the subsequent fuel addition amount in the same manner as in the first embodiment.
[0134]
As described above, in the present embodiment, it is possible to calculate the correction coefficient of the fuel addition amount even during the temperature increase of the filter 20.
[0135]
FIG. 8 is a diagram in which the target period is set to a period different from that of FIG. 7 during the temperature increase of the filter 20. As shown in FIG. 8, the target period for calculating the correction coefficient of the fuel addition amount can be set as long as it is within the target period, and the length of the target period can also be set arbitrarily.
[0136]
Further, in this embodiment, the correction method of the fuel addition amount at the time of NOx reduction from the NOx storage reduction catalyst has been described, but the fuel addition amount in the SOx poisoning recovery control after the temperature increase of the NOx storage reduction catalyst is also described. It is possible to correct similarly.
[0137]
【The invention's effect】
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, it is possible to correct the amount of reducing agent added when the catalyst is heated based on the actual temperature of the catalyst and the target temperature. Accordingly, it is possible to reduce the difference between the target amount of reducing agent and the amount of reducing agent actually supplied when performing NOx reduction, SOx poisoning recovery, and the like, and accurately control the air-fuel ratio. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.
FIG. 2A is a diagram showing a transverse cross section of a particulate filter. (B) is a figure which shows the longitudinal direction cross section of a particulate filter.
FIG. 3 is a block diagram showing an internal configuration of an ECU.
FIG. 4 is a diagram showing a relationship between a temperature increase amount of a filter and a fuel addition amount per unit intake air amount.
FIG. 5 is a time chart showing a time transition of a target temperature, an actual temperature, and a base temperature of the filter.
FIG. 6 is a diagram showing a relationship between a correction coefficient and a reflection coefficient.
FIG. 7 is a diagram showing a relationship between a target temperature increase amount and an actual temperature increase amount according to the second embodiment.
FIG. 8 is a diagram showing a relationship between a target temperature increase amount and an actual temperature increase amount according to the second embodiment.
[Explanation of symbols]
1 ... Engine
1a ... Crank pulley
2. Cylinder
3. Fuel injection valve
4 ... Common rail
4a ... Common rail pressure sensor
5. Fuel supply pipe
6. Fuel pump
6a ... Pump pulley
8 ... Intake branch pipe
9. Intake pipe
18 ... Exhaust branch pipe
19 ... Exhaust pipe
20 ... Particulate filter
21 ... Exhaust throttle valve
24 ... Exhaust temperature sensor
25 ... EGR passage
26 ... EGR valve
27 ... EGR cooler
28 ... Reducing agent injection valve
29 ... Reducing agent supply path
31 ... Shut-off valve
33 ... Crank position sensor
35 ... ECU
36 Accelerator opening sensor

Claims (5)

NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Target temperature rise determination means for determining a temperature rise amount of the NOx storage agent based on the operation state detected by the operation state detection means;
The NO than x catalyst comprising a reducing agent injection valve for injecting a reducing agent into the exhaust pipe upstream, reducing agent supply means for reducing the NOx occluded in the NOx occluding agent by supplying the reducing agent to the NOx occluding agent When,
The required fuel amount per unit intake air amount is obtained from the target temperature increase amount determined by the target temperature increase amount determining means, and the intake air amount sucked into the internal combustion engine is further calculated as the required fuel amount per unit intake air amount. A temperature raising means for supplying the NOx storage agent with an amount of the reducing agent calculated by multiplication to increase the temperature of the NOx storage agent;
A temperature rise estimation means for estimating the actual temperature rise of the NOx storage agent;
Correction coefficient calculation means for calculating a ratio between the temperature rise amount determined by the target temperature rise amount determination means and the temperature rise amount estimated by the temperature rise amount estimation means;
A reducing agent that corrects the supply amount of the reducing agent by multiplying the amount of the reducing agent supplied by the reducing agent supply means when the NOx stored in the NOx storage agent is reduced by the ratio calculated by the correction coefficient calculating means. Supply amount correction means;
An exhaust emission control device for an internal combustion engine, comprising: NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Target temperature rise determination means for determining a target temperature rise of the NOx storage agent based on the operation state detected by the operation state detection means;
The NO than x catalyst comprising a reducing agent injection valve for injecting a reducing agent into the exhaust pipe upstream, reducing agent supply means for reducing the NOx occluded in the NOx occluding agent by supplying the reducing agent to the NOx occluding agent When,
The required fuel amount per unit intake air amount is obtained from the target temperature increase amount determined by the target temperature increase amount determining means, and the intake air amount sucked into the internal combustion engine is further calculated as the required fuel amount per unit intake air amount. A temperature raising means for supplying the NOx storage agent with an amount of the reducing agent calculated by multiplication to increase the temperature of the NOx storage agent;
A temperature rise amount estimation means within a predetermined period for estimating an actual temperature rise amount of the NOx storage agent in a predetermined period;
A target temperature increase amount calculating means for calculating a target temperature increase amount of the NOx storage agent in the predetermined period;
Correction coefficient calculating means for calculating a ratio between the target temperature increase amount of the NOx storage agent calculated by the target temperature increase amount calculation means within the predetermined period and the actual temperature increase amount in the predetermined period;
A reducing agent that corrects the supply amount of the reducing agent by multiplying the amount of the reducing agent supplied by the reducing agent supply means when the NOx stored in the NOx storage agent is reduced by the ratio calculated by the correction coefficient calculating means. Supply amount correction means;
An exhaust emission control device for an internal combustion engine, comprising: NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Target temperature rise determination means for determining a temperature rise amount of the NOx storage agent based on the operation state detected by the operation state detection means;
Reducing agent supply means for supplying a reducing agent to the NOx storage agent to reduce NOx stored in the NOx storage agent;
A temperature raising means for supplying a reducing agent corresponding to the target temperature raising amount determined by the target temperature raising amount determining means to the NOx storage agent to increase the temperature of the NOx storage agent;
A temperature rise estimation means for estimating the actual temperature rise of the NOx storage agent;
Correction coefficient calculation means for calculating a ratio between the temperature rise amount determined by the target temperature rise amount determination means and the temperature rise amount estimated by the temperature rise amount estimation means;
Reducing agent supply amount correction means for correcting the amount of reducing agent supplied by the reducing agent supply means based on the value calculated by the correction coefficient calculation means when reducing NOx stored in the NOx storage agent;
With
The reducing agent supply means includes a reducing agent injection valve that injects the reducing agent into the exhaust gas, calculates a valve opening time required to inject an amount of reducing agent according to an operating state, and supplies the reducing agent supply amount. The correcting means multiplies the opening time of the reducing agent injection valve calculated by the reducing agent supply means by the ratio calculated by the correction coefficient calculating means, and when the ratio calculated by the correction coefficient calculating means is 1 or more, An exhaust emission control device for an internal combustion engine, characterized in that an amount of reducing agent multiplied by a correction coefficient that increases in proportion to the ratio is supplied to the NO x storage agent . NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
An operating state detecting means for detecting an operating state of the internal combustion engine;
Target temperature rise determination means for determining a target temperature rise of the NOx storage agent based on the operation state detected by the operation state detection means;
Reducing agent supply means for supplying a reducing agent to the NOx storage agent to reduce NOx stored in the NOx storage agent;
A temperature raising means for supplying a reducing agent corresponding to the target temperature raising amount determined by the target temperature raising amount determining means to the NOx storage agent to increase the temperature of the NOx storage agent;
A temperature rise amount estimation means within a predetermined period for estimating an actual temperature rise amount of the NOx storage agent in a predetermined period;
A target temperature increase amount calculating means for calculating a target temperature increase amount of the NOx storage agent in the predetermined period;
Correction coefficient calculating means for calculating a ratio between the target temperature increase amount of the NOx storage agent calculated by the target temperature increase amount calculation means within the predetermined period and the actual temperature increase amount in the predetermined period;
Reducing agent supply amount correction means for correcting the amount of reducing agent supplied by the reducing agent supply means based on the value calculated by the correction coefficient calculation means when reducing NOx stored in the NOx storage agent;
With
The reducing agent supply means includes a reducing agent injection valve that injects the reducing agent into the exhaust gas, calculates a valve opening time required to inject an amount of reducing agent according to an operating state, and supplies the reducing agent supply amount. The correcting means multiplies the opening time of the reducing agent injection valve calculated by the reducing agent supply means by the ratio calculated by the correction coefficient calculating means, and when the ratio calculated by the correction coefficient calculating means is 1 or more, An exhaust emission control device for an internal combustion engine, characterized in that an amount of reducing agent multiplied by a correction coefficient that increases in proportion to the ratio is supplied to the NO x storage agent . The reducing agent supply means supplies the reducing agent to the NOx storage agent to release SOx stored in the NOx storage agent, and the reducing agent supply amount correction means releases the SOx stored in the NOx storage agent. 5. The supply amount of the reducing agent is corrected by multiplying the amount of the reducing agent supplied by the reducing agent supply unit when the ratio is calculated by the correction coefficient calculating unit . 2. An exhaust gas purification apparatus for an internal combustion engine according to 1.

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