JP2007231862A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To more quickly raise temperature of an exhaust emission control catalyst to activation temperature and inhibit deterioration of exhaust emission in an exhaust control device for an internal combustion engine provided with an exhaust emission control catalyst provided in an exhaust gas passage of the internal combustion engine. <P>SOLUTION: When temperature of the exhaust emission control catalyst 3 is lower than activation temperature, steam in exhaust gas is removed by a steam removing means 4 provided in an exhaust gas passage 2 on an upstream side of the exhaust emission control catalyst 3, and the removed steam is stored in a condensed water storing means 5 provided separately from the exhaust gas passage 2 as condensed water. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine provided with an exhaust gas purification catalyst provided in an exhaust passage of the internal combustion engine.

  An exhaust gas purification apparatus for an internal combustion engine having an exhaust gas purification catalyst provided in an exhaust gas passage of the internal combustion engine is provided with a collision plate for collision of exhaust gas with an exhaust gas passage upstream of the exhaust gas purification catalyst, A technique is known in which a recess is provided in a portion located below (see, for example, Patent Document 1). According to such a configuration, moisture in the exhaust is captured by the collision plate, and the captured moisture is accumulated in the recess. Thereby, the supply of moisture to the exhaust purification catalyst is suppressed. Therefore, it is possible to raise the temperature of the exhaust purification catalyst more quickly.

However, in the case of the configuration as described above, when the exhaust gas temperature rises, the water accumulated in the recesses evaporates and becomes steam again and flows into the exhaust purification catalyst. When the steam flows into the exhaust purification catalyst, a steam reforming reaction of HC in the exhaust occurs in the exhaust purification catalyst, so that there is a possibility that the temperature rise of the exhaust purification catalyst is hindered. Further, if the steam reforming reaction of HC occurs in a state where the temperature of the exhaust purification catalyst is not sufficiently increased, there is a risk of deteriorating exhaust emission.
JP-A-5-65819 Japanese Patent Laid-Open No. 10-311215 JP 2001-259415 A

  The present invention provides an internal combustion engine exhaust gas purification apparatus provided with an exhaust gas purification catalyst provided in an exhaust passage of an internal combustion engine, which can quickly raise the temperature of the exhaust gas purification catalyst to the activation temperature and reduce exhaust emission. It is an object to provide a technique that can be suppressed.

  The present invention removes water vapor in the exhaust in the exhaust passage upstream of the exhaust purification catalyst when the temperature of the exhaust purification catalyst is lower than the activation temperature, and the removed water vapor is condensed water provided separately from the exhaust passage. It is stored as condensed water in the storage means.

More specifically, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
Water vapor removal means for removing water vapor in the exhaust gas provided in the exhaust passage upstream of the exhaust purification catalyst;
Condensate water storage means that is provided separately from the exhaust passage and stores the water vapor removed by the water vapor removal means as condensed water;
Temperature detecting means for detecting the temperature of the exhaust purification catalyst,
The water vapor removing means removes water vapor in the exhaust when the temperature of the exhaust purification catalyst detected by the temperature detecting means is lower than the activation temperature.

  In the present invention, the condensed water storage means is provided separately from the exhaust passage. Therefore, it is possible to prevent the condensed water once stored in the condensed water storage means from evaporating as the exhaust gas temperature rises and flowing again into the exhaust purification catalyst as water vapor.

  Therefore, according to the present invention, when the temperature of the exhaust purification catalyst is lower than the activation temperature, it is possible to further suppress the inflow of water vapor into the exhaust purification catalyst. As a result, it is possible to suppress the occurrence of the steam reforming reaction of HC in the exhaust in the exhaust purification catalyst in a state where the temperature of the exhaust purification catalyst has not risen to the activation temperature. Therefore, the temperature of the exhaust purification catalyst can be raised more quickly to the activation temperature, and deterioration of exhaust emission can be suppressed.

  In the present invention, a cooling water passage through which cooling water flows via the exhaust purification catalyst may be further provided. In such a case, when the temperature of the exhaust purification catalyst is equal to or higher than a first predetermined temperature that is higher than the lower limit value of the activation temperature, the condensed water stored in the condensed water storage means may flow as cooling water in the cooling water passage. .

  Here, the first predetermined temperature is a temperature that becomes a threshold at which it can be determined that the exhaust purification catalyst may overheat.

  According to the above, when the temperature of the exhaust purification catalyst is equal to or higher than the first predetermined temperature, the exhaust purification catalyst is cooled by the condensed water stored in the condensed water storage means. Accordingly, it is possible to suppress an excessive temperature rise of the exhaust purification catalyst, and thus it is possible to suppress the exhaust purification catalyst from being excessively deteriorated.

  In the present invention, water addition means for adding water into the exhaust gas may further be provided in the exhaust passage upstream from the exhaust purification catalyst and downstream from the water vapor removal means. Further, an air-fuel ratio detecting means for detecting the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst may be further provided. When the exhaust purification catalyst is a catalyst having an oxidation function, the exhaust purification catalyst temperature is equal to or higher than a second predetermined temperature higher than the lower limit value of the activation temperature, and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is When the air / fuel ratio is equal to or lower than the predetermined air / fuel ratio, the condensed water stored in the condensed water storage means may be added to the exhaust gas by the water addition means.

  Here, the second predetermined temperature is a temperature that becomes a threshold at which it can be determined that the exhaust purification catalyst is sufficiently active. The second predetermined temperature is a temperature lower than a threshold at which it can be determined that the exhaust purification catalyst may overheat. Further, the predetermined air-fuel ratio is an air-fuel ratio that becomes a threshold at which it can be determined that oxygen in exhaust gas for oxidizing HC in the exhaust purification catalyst is insufficient.

  In the present invention, when the temperature of the exhaust purification catalyst is equal to or higher than the second predetermined temperature and the air-fuel ratio of the exhaust flowing into the exhaust purification catalyst is equal to or lower than the predetermined air-fuel ratio, the condensed water stored in the condensed water storage means is water. It is added to the exhaust by an adding means. The added condensed water becomes steam and flows into the exhaust purification catalyst together with the exhaust gas.

  When the temperature of the exhaust purification catalyst is equal to or higher than the second predetermined temperature, even if the steam purification reaction of HC occurs in the exhaust purification catalyst, the possibility that the temperature of the exhaust purification catalyst decreases excessively is low. Further, when the temperature of the exhaust purification catalyst is equal to or higher than the second predetermined temperature, oxidation of the HC is promoted when a steam reforming reaction of HC occurs in the exhaust purification catalyst. As a result, the amount of HC discharged downstream from the exhaust purification catalyst is reduced.

  Therefore, according to the above, it is possible to suppress the deterioration of exhaust emission even when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is equal to or lower than the predetermined air-fuel ratio.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, it is possible to raise the temperature of the exhaust gas purification catalyst to the activation temperature more quickly and to suppress the deterioration of exhaust emission.

  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.

<Schematic configuration of 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 exhaust system of an internal combustion engine according to the present embodiment.

  The internal combustion engine 1 is a diesel engine for driving a vehicle. An exhaust passage 2 is connected to the internal combustion engine 1. A three-way catalyst 3 is provided in the exhaust passage 2. The three-way catalyst 3 is provided with a temperature sensor 8 for detecting the temperature.

  A centrifuge 4 that rotates around the exhaust passage 2 as a central axis is provided upstream of the three-way catalyst 3 in the exhaust passage 2. One end of a condensed water recovery passage 6 is connected to the centrifugal separator 4, and the other end of the condensed water recovery passage 6 is connected to a water tank 5.

  When the centrifuge 4 is operated, water vapor is removed from the exhaust gas flowing through the exhaust passage 2. The removed water vapor becomes condensed water and is stored in the water tank 5 through the condensed water recovery passage 6. A check valve 7 is installed in the condensed water recovery passage 6 so that the condensed water flows only in the direction from the centrifuge 4 side to the water tank 5 side.

  In this embodiment, the three-way catalyst 3 corresponds to the exhaust purification catalyst according to the present invention, and the temperature sensor 8 corresponds to the temperature detecting means according to the present invention. The centrifuge 4 corresponds to the water vapor removing means according to the present invention, and the water tank 5 corresponds to the condensed water storage means according to the present invention.

  Further, in this embodiment, a water circulation passage 11 is provided through which condensed water stored in the water tank 5 circulates via the three-way catalyst 3. The water circulation passage 11 is provided with a circulation control valve 12 for blocking or opening the water circulation passage 11 and a pump 13. When the circulation control valve 12 is opened and the pump 13 is operated, condensed water is circulated through the three-way catalyst 3. The condensed water acts as cooling water to cool the three-way catalyst 3.

  In this embodiment, the water circulation passage 11 corresponds to the cooling water passage according to the present invention.

  A water injection valve 15 and an air-fuel ratio sensor 14 are installed in the exhaust passage 2 downstream of the centrifugal separator 4 and upstream of the three-way catalyst 3. The water injection valve 15 injects the condensed water stored in the water tank 5 into the exhaust gas. The air-fuel ratio sensor 14 detects the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 3.

  In this embodiment, the water injection valve 15 corresponds to the water addition means according to the present invention, and the air-fuel ratio sensor 14 corresponds to the air-fuel ratio detection means according to the present invention.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 10. A temperature sensor 8 and an air-fuel ratio sensor 14 are electrically connected to the ECU 10. Those output signals are input to the ECU 10. In addition, the centrifugal separator 4, the circulation control valve 12, the pump 13, and the water injection valve 15 are electrically connected to the ECU 10. These are controlled by the ECU 10.

<HC steam reforming reaction>
The exhaust gas discharged from the internal combustion engine 1 contains water vapor. When the steam flows into the three-way catalyst 3, a steam reforming reaction of HC in the exhaust occurs. Here, the composition of the product resulting from the steam reforming reaction of HC will be described based on the graph shown in FIG. FIG. 2 is a diagram showing the relationship between the composition of the product and the temperature of the three-way catalyst 3 when the HC steam reforming reaction occurs in the three-way catalyst 3. In FIG. 2, the vertical axis represents the composition of the product resulting from the steam reforming reaction of HC, and the horizontal axis represents the temperature of the three-way catalyst 3.

When the temperature of the three-way catalyst 3 is relatively low and the activation of the three-way catalyst 3 is insufficient (that is, when the temperature is equal to or lower than the temperature indicated by Ta in FIG. 2), When the steam reforming reaction occurs, as shown in FIG. 2, a relatively large amount of CH ₄ or CO ₂ is generated. If these substances are produced excessively, exhaust emission may be deteriorated.

On the other hand, when the temperature of the three-way catalyst 3 is relatively high and the three-way catalyst 3 is sufficiently active (that is, when the temperature is equal to or higher than Tb in FIG. 2), the three-way catalyst 3 has HC. When the steam reforming reaction occurs, a relatively large amount of H ₂ or CO is generated as shown in FIG. When these substances are generated, the oxidation of HC in the three-way catalyst 3 is promoted.

  Further, since the steam reforming reaction is an endothermic reaction, when the steam reforming reaction occurs due to the flow of steam into the three-way catalyst 3, the temperature increase of the three-way catalyst 3 is suppressed.

  Therefore, in this embodiment, water vapor removal control, catalyst cooling control, and water injection control are performed according to the temperature of the three-way catalyst 3 and the air-fuel ratio of the exhaust. Hereinafter, each control according to the present embodiment will be described.

<Water vapor removal control>
In the present embodiment, when the temperature of the three-way catalyst 3 is lower than the lower limit value of the activation temperature as in the cold start of the internal combustion engine 1, water vapor should be removed from the exhaust gas flowing into the three-way catalyst 3. Water vapor removal control is executed. Here, the control routine of the water vapor removal 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 repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 10 first determines in S101 whether or not the temperature of the three-way catalyst 3 is lower than the lower limit value T0 of the activation temperature. If an affirmative determination is made in S101, the ECU 10 proceeds to S102, and if a negative determination is made, the ECU 10 ends the execution of this routine.

  In S <b> 101, the ECU 10 operates the centrifuge 4. When the centrifuge 4 is operated, water vapor in the exhaust gas is removed. The removed water vapor is stored in the water tank 5 as condensed water.

  Next, the ECU 10 proceeds to S103 and determines whether or not the temperature of the three-way catalyst 3 is equal to or higher than the lower limit value T0 of the activation temperature. If an affirmative determination is made in S103, the ECU 10 proceeds to S104. If a negative determination is made, the ECU 10 returns to S102 and continues the operation of the centrifuge 4.

  In S <b> 104, the ECU 10 stops the operation of the centrifuge 4. Thereafter, the ECU 10 ends the execution of this routine.

According to the water vapor removal control, when the temperature of the three-way catalyst 3 is lower than the activation temperature, the inflow of water vapor into the three-way catalyst 3 can be further suppressed. As a result, it is possible to suppress the occurrence of the steam reforming reaction of HC in the exhaust gas in the three-way catalyst 3 in a state where the temperature of the three-way catalyst 3 does not rise to the activation temperature. Therefore, the temperature of the three-way catalyst 3 can be raised more quickly to the activation temperature. Further, CH ₄ and CO ₂ exhaust emission since it is possible to suppress the generated can be prevented from deteriorating.

<Catalyst cooling control>
In this embodiment, when it is determined that the three-way catalyst 3 may be overheated, catalyst cooling control is executed to cool the three-way catalyst 3. Here, the control routine of the catalyst cooling 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 repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, first, in S201, the ECU 10 determines whether or not the temperature of the three-way catalyst 3 is equal to or higher than a first predetermined temperature T1. Here, the first predetermined temperature T1 is a temperature that becomes a threshold at which it can be determined that the three-way catalyst 3 may overheat. The first predetermined temperature T1 is determined in advance by experiments or the like. If an affirmative determination is made in S201, the ECU 10 proceeds to S202, and if a negative determination is made, the ECU 10 ends the execution of this routine.

  In S202, the ECU 10 opens the circulation control valve 12 and activates the pump 13. As a result, the condensed water stored in the water tank 5 circulates through the water circulation passage 11 via the three-way catalyst 3. As a result, the three-way catalyst 3 is cooled by the condensed water.

  Next, the ECU 10 proceeds to S203 and determines whether or not the temperature of the three-way catalyst 3 has become lower than the second predetermined temperature T2. Here, the second predetermined temperature T2 is a temperature that becomes a threshold at which it can be determined that the three-way catalyst 3 is sufficiently active. The second predetermined temperature T2 is a temperature lower than the first predetermined temperature T1. The second predetermined temperature T2 is the same temperature as the temperature Tb in FIG. The second predetermined temperature T2 is determined in advance by experiments or the like. If an affirmative determination is made in S203, the ECU 10 proceeds to S204, and if a negative determination is made, the ECU 10 returns to S202 and continues to circulate condensed water in the water circulation passage 11.

  In S204, the ECU 10 closes the circulation control valve 12 and stops the operation of the pump 13. Thereby, the circulation of the condensed water in the water circulation passage 11 is stopped. Thereafter, the ECU 10 ends the execution of this routine.

  According to the catalyst cooling control, the three-way catalyst 3 is cooled by the condensed water stored in the water tank 5 when the temperature of the three-way catalyst 3 is equal to or higher than the first predetermined temperature T1. Therefore, the excessive temperature rise of the three-way catalyst 3 can be suppressed, and thus the three-way catalyst 3 can be prevented from being excessively deteriorated.

<Water injection control>
In this embodiment, when it is determined that the three-way catalyst 3 is sufficiently active and oxygen in the exhaust gas for oxidizing HC in the three-way catalyst 3 is insufficient, the three-way catalyst 3 Water injection control is executed to promote the oxidation of HC. Here, the control routine of the water injection 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 repeatedly executed at predetermined intervals during the operation of the internal combustion engine 1.

  In this routine, the ECU 10 first determines in S301 whether or not the temperature of the three-way catalyst 3 is equal to or higher than a second predetermined temperature T2. If an affirmative determination is made in S202, the ECU 10 determines that the three-way catalyst 3 is sufficiently active and proceeds to 302. If a negative determination is made, the ECU 10 ends the execution of this routine.

  In S302, the ECU 10 determines whether or not the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 3 is equal to or less than a predetermined air-fuel ratio R0. Here, the predetermined air-fuel ratio R0 is an air-fuel ratio that becomes a threshold at which it can be determined that oxygen in the exhaust gas for oxidizing HC in the three-way catalyst 3 is insufficient. The predetermined air-fuel ratio R0 is determined in advance by experiments or the like. For example, the predetermined air-fuel ratio R0 may be the theoretical air-fuel ratio. If an affirmative determination is made in S302, the ECU 10 proceeds to 303, and if a negative determination is made, the ECU 10 ends the execution of this routine.

  In step S <b> 303, the ECU 10 injects the condensed water stored in the water tank 5 from the water injection valve 15 into the exhaust gas. The injected condensed water becomes steam and flows into the three-way catalyst 3 together with the exhaust gas. Thereafter, the ECU 10 ends the execution of this routine.

  According to the water injection control, when the temperature of the three-way catalyst 3 is equal to or higher than the second predetermined temperature T2 and the air-fuel ratio of the exhaust gas is equal to or lower than the predetermined air-fuel ratio R0, steam is supplied to the three-way catalyst 3, The steam reforming reaction of HC in the catalyst 3 is promoted. When the temperature of the three-way catalyst 3 is equal to or higher than the second predetermined temperature T2, even if the steam reforming reaction of HC occurs in the three-way catalyst 3, it is unlikely that the temperature of the three-way catalyst 3 is excessively lowered. Further, as described above, when the steam reforming reaction of HC occurs when the three-way catalyst 3 is sufficiently active, the oxidation of HC is accelerated unlike the case where the activation of the three-way catalyst 3 is insufficient. Will be. As a result, the amount of HC discharged downstream from the three-way catalyst 3 is reduced.

  Therefore, according to the present embodiment, it is possible to suppress the deterioration of the exhaust emission even when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 3 is not more than the predetermined air-fuel ratio R0.

  In this embodiment, the exhaust purification catalyst is a three-way catalyst. However, this is not limited to a three-way catalyst, and any catalyst having an oxidation function such as an oxidation catalyst or a NOx storage reduction catalyst may be used. It ’s fine. Further, instead of the temperature sensor 8, an exhaust temperature sensor may be provided on the downstream side of the three-way catalyst 3, and the temperature of the three-way catalyst 3 may be estimated based on a detection value of the exhaust temperature sensor.

The figure which shows schematic structure of the exhaust system of the internal combustion engine which concerns on an Example. The figure which shows the relationship between the composition of a product when the steam reforming reaction of HC occurs in a three-way catalyst, and the temperature of a three-way catalyst. The flowchart which shows the control routine of the water vapor removal control which concerns on an Example. The flowchart which shows the control routine of the catalyst cooling control which concerns on an Example. The flowchart which shows the control routine of the water-injection control which concerns on an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Three-way catalyst 4 ... Centrifuge 5 ... Water tank 8 ... Temperature sensor 10 ... ECU
11..Water circulation passage 14..Air-fuel ratio sensor 15..Water injection valve

Claims (3)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
Water vapor removal means for removing water vapor in the exhaust gas provided in the exhaust passage upstream of the exhaust purification catalyst;
Condensate water storage means that is provided separately from the exhaust passage and stores the water vapor removed by the water vapor removal means as condensed water;
Temperature detecting means for detecting the temperature of the exhaust purification catalyst,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the water vapor removing means removes water vapor in the exhaust gas when the temperature of the exhaust purification catalyst detected by the temperature detecting means is lower than an activation temperature. A cooling water passage through which cooling water flows via the exhaust purification catalyst;
When the temperature of the exhaust purification catalyst detected by the temperature detection means is equal to or higher than a first predetermined temperature that is higher than the lower limit value of the activation temperature, the condensed water stored in the condensed water storage means is cooled to the cooling water passage. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus flows as water. The exhaust purification catalyst is a catalyst having an oxidation function,
Water addition means for adding water to the exhaust gas, provided in the exhaust passage upstream from the exhaust purification catalyst and downstream from the water vapor removal means;
Air-fuel ratio detection means for detecting the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst,
The temperature of the exhaust purification catalyst detected by the temperature detection means is equal to or higher than a second predetermined temperature higher than the lower limit value of the activation temperature, and the air-fuel ratio of the exhaust detected by the air-fuel ratio detection means is less than a predetermined air-fuel ratio. 3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the condensed water stored in the condensed water storage means is added to the exhaust gas by the water addition means.

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