JP2008303815A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of recovering catalyst activity, when a catalyst is an inactive state, by detecting active state of the catalyst. <P>SOLUTION: This exhaust emission control device of the internal combustion engine is suitably used when using alcohol mixed fuel as fuel. The exhaust emission control device of the internal combustion engine has a catalyst active state determining means having an NOx storage-reduction catalyst on an exhaust passage and a control means. The catalyst active state determining means determines whether or not an active state of the NOx storage-reduction catalyst is in the inactive state. The control means reduces a fuel injection quantity of a cylinder of causing rich combustion of the internal combustion engine, when determining that the active state of the NOx storage-reduction catalyst is in the inactive state by the catalyst active state determining means, when performing enriching control for enriching the air-fuel ratio of exhaust gas from the internal combustion engine. With such a constitution, cooling of the NOx storage-reduction catalyst can be restrained, and the catalyst activity of the NOx storage-reduction catalyst can be recovered. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine that performs exhaust gas purification.

  2. Description of the Related Art Conventionally, there has been proposed an exhaust purification device that provides a NOx storage reduction catalyst on an exhaust passage and purifies NOx using this catalyst. For example, Patent Document 1 discloses a purification action by making the rate of change of the air-fuel ratio feedback correction amount after activation of the NOx absorption reduction catalyst smaller than the rate of change of the feedback correction amount before activation of the catalyst. Techniques for improving the performance are described. Patent Document 2 describes a technique for performing control that periodically repeats rich and lean in accordance with the catalyst activation state.

JP 2000-220503 A Japanese Patent Laid-Open No. 2001-50086

  However, for example, in Patent Document 1, when alcohol fuel is supplied, the feedback correction coefficient is corrected so that the required air-fuel ratio is richer than gasoline, and thus the fuel injection amount increases. As described above, as a result of the increase in the fuel injection amount, the activity of the catalyst is reduced, NOx reduction or sulfur desorption is not performed, and emission may be deteriorated. Patent Document 1 does not discuss this point at all. Also, Patent Document 2 does not discuss this point at all.

  The present invention has been made to solve the above-described problems, and detects the active state of a catalyst. When the catalyst is in an inactive state, the exhaust purification of an internal combustion engine that can recover the catalytic activity is achieved. It is an object to provide an apparatus.

  In one aspect of the present invention, an exhaust purification device for an internal combustion engine having a NOx storage reduction catalyst on an exhaust passage determines whether or not the active state of the NOx storage reduction catalyst is in an inactive state. And when the enrichment control for enriching the air-fuel ratio of the exhaust gas from the internal combustion engine is executed, it is determined by the catalyst active state determination means that the active state of the NOx storage reduction catalyst is in an inactive state. And a control means for reducing the fuel injection amount of the cylinder for rich combustion of the internal combustion engine.

  The exhaust gas purification apparatus for an internal combustion engine is preferably used when an alcohol mixed fuel is used as the fuel. The above exhaust gas purification apparatus for an internal combustion engine has a NOx occlusion reduction catalyst on an exhaust passage, and includes a catalyst activation state determination unit and a control unit. The catalyst activation state determination unit and the control unit are realized by, for example, an ECU (Electric Control Unit). The catalyst active state determining means determines whether or not the active state of the NOx storage reduction catalyst is in an inactive state. When the enrichment control for enriching the air-fuel ratio of the exhaust gas from the internal combustion engine is executed, the control means determines that the active state of the NOx storage reduction catalyst is in an inactive state by the catalyst active state determination means. If it is determined, the fuel injection amount of the cylinder in which the rich combustion is performed in the internal combustion engine is reduced. By doing so, cooling of the NOx storage reduction catalyst can be suppressed, and the catalytic activity of the NOx storage reduction catalyst can be recovered.

  In another aspect of the exhaust gas purification apparatus for an internal combustion engine, the control means executes bank control that makes the air-fuel ratio of one cylinder group rich and makes the air-fuel ratio of the other cylinder group lean or stoichiometric. On the other hand, when the catalyst active state determining means determines that the active state of the NOx storage reduction catalyst is in an inactive state, the rich degree of the one cylinder group is corrected to be shallow and the bank control is executed. Correct the time longer. As a result, the catalytic activity of the NOx storage reduction catalyst can be recovered, and the sulfur poisoning recovery can be prevented from becoming insufficient.

  In another aspect of the exhaust gas purification apparatus for an internal combustion engine, the control means performs an active state of the NOx occlusion reduction catalyst when performing the rich spike control for reducing NOx occluded in the NOx occlusion reduction catalyst. Is determined to be in an inactive state by the catalyst active state determination means, the rich degree of the cylinder of the internal combustion engine at the time of rich combustion is corrected shallowly, and the execution time of rich spike control is corrected to be longer. . Thereby, it is possible to recover the catalytic activity of the NOx storage reduction catalyst and to prevent the NOx reduction from becoming insufficient.

  In another aspect of the exhaust gas purification apparatus for an internal combustion engine, the catalyst activation state determination means determines that the activation state of the NOx occlusion reduction catalyst is higher when the temperature rise of the catalyst temperature of the NOx occlusion reduction catalyst is a predetermined value or less. Determined to be in an inactive state. Thereby, it can be determined whether the active state of the NOx storage reduction catalyst is in an inactive state.

  In another preferred embodiment of the exhaust gas purification apparatus for an internal combustion engine, the catalyst activation state determining means is configured such that the air-fuel ratio downstream of the NOx storage reduction catalyst is a predetermined value within a predetermined time after the rich spike control is started. When it is below, it determines with the active state of the said NOx storage reduction catalyst being in an inactive state. The predetermined value here is, for example, the value of the air-fuel ratio at the time of stoichiometric. This is because it is considered that the air-fuel ratio becomes rich immediately after the start of rich spike control because the reducing agent is not consumed by the NOx storage reduction catalyst when the active state of the NOx storage reduction catalyst is in an inactive state. It is.

  In another preferred embodiment of the exhaust gas purification apparatus for an internal combustion engine, the catalyst activation state determining means is configured such that the NOx concentration on the downstream side of the NOx storage reduction catalyst does not decrease within a predetermined time after the rich spike control is started. In this case, it is determined that the active state of the NOx storage reduction catalyst is in an inactive state. This is because the NOx concentration on the downstream side of the NOx storage reduction catalyst does not decrease despite the rich spike control being started, which means that NOx reduction is not performed in the NOx storage reduction catalyst. Because it can.

  Preferred embodiments of the present invention will be described below with reference to the drawings.

[System configuration]
First, an exhaust purification system according to each embodiment of the present invention will be described.

(overall structure)
FIG. 1 shows an exhaust gas purification system 100 to which an exhaust gas purification apparatus for an internal combustion engine according to each embodiment of the present invention is applied. The exhaust purification system 100 is mainly composed of an internal combustion engine 1, an exhaust passage 4, and a NOx storage reduction catalyst 7. The internal combustion engine 1 is mounted on a vehicle such as an automobile as a driving power source, and can be operated with an alcohol mixed fuel containing alcohol such as ethanol.

  The internal combustion engine 1 is configured as a V-type 6-cylinder gasoline engine in which three cylinders 3 are provided in each of the left and right banks 2L and 2R. Hereinafter, the internal combustion engine 1 is simply referred to as the engine 1. In the engine 1, one cylinder group is constituted by the three cylinders 3 in the left bank 2L, and another cylinder group is constituted by the three cylinders 3 in the right bank 2R. In the following, when the left and right banks 2L and 2R are not distinguished, they are simply referred to as “bank 2”.

  The engine 1 includes an exhaust passage 4 connected to the exhaust side of each cylinder 3. The exhaust passage 4 includes branch portions 5L and 5R provided for each bank, and a common exhaust passage 6 extending downstream from a junction where the branch portions 5L and 5R merge. A NOx occlusion reduction catalyst 7 is provided in the exhaust passage 6. The NOx occlusion reduction catalyst 7 is leaner than stoichiometric, that is, stores NOx in the exhaust gas in an oxygen-excess oxidizing atmosphere, and richer than stoichiometric, that is, the NOx occluded in a reducing atmosphere or stoichiometric excess of fuel. The NOx is reduced and purified while being released. Specifically, when the NOx occlusion rate of the NOx occlusion reduction catalyst 7 decreases to a predetermined value (95%) or less, rich spike control (RS control) for forcibly enriching the air-fuel ratio is executed by the ECU 20. As a result, the stored NOx is reduced.

  The engine 1 also includes a fuel supply device 10. The fuel supply device 10 includes an injector 11 and a fuel tank 12 provided in each cylinder 3. Each injector 11 is supplied with fuel pressurized by a fuel pump (not shown) from a fuel tank 12. An alcohol concentration sensor 13 is attached to the fuel tank 12. The alcohol concentration sensor 13 detects the alcohol concentration in the fuel and supplies a detection signal corresponding to the detected alcohol concentration to the ECU 20.

The exhaust passage 6, the air-fuel ratio (A / F) sensor 22,0 ₂ sensor 23, exhaust gas temperature sensor 24 is attached. The A / F sensor 22 is attached to the upstream side of the NOx storage reduction catalyst 7, detects the air-fuel ratio of the exhaust gas upstream of the NOx storage reduction catalyst 7, and sends a detection signal corresponding to the detected air-fuel ratio to the ECU 20. Supply. The O ₂ sensor 23 and the exhaust temperature sensor 24 are attached to the downstream side of the NOx storage reduction catalyst 7. The O ₂ sensor 23 detects the oxygen concentration of the exhaust gas downstream of the NOx storage reduction catalyst 7 and supplies a detection signal corresponding to the detected oxygen concentration to the ECU 20. The exhaust temperature sensor 24 detects the exhaust temperature of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 and supplies a detection signal corresponding to the detected exhaust temperature to the ECU 20. Instead of the exhaust temperature sensor 24 being attached, a catalyst temperature sensor for detecting the catalyst temperature of the NOx storage reduction catalyst 7 may be attached.

The ECU (Electric Control Unit) 20 includes a CPU, a ROM, a RAM, an A / D converter, and the like (not shown). The ECU 20 controls the operating state of the engine 1 based on detection signals supplied from various sensors in the vehicle. For example, ECU 20, the alcohol concentration sensor 13, the air-fuel ratio (A / F) sensor 22,0 ₂ sensor 23, based on the detection signal from the exhaust temperature sensor 24, calculates the fuel injection quantity to be injected from the injectors 11 Then, the operation of each injector 11 is controlled so that the calculated fuel injection amount is supplied to each cylinder 3. Specifically, when the ECU 20 executes the enrichment control for enriching the air-fuel ratio of the exhaust gas from the engine 1, the active state of the NOx storage reduction catalyst 7 is in an inactive state based on these detection signals. If the active state of the NOx storage reduction catalyst 7 is determined to be in an inactive state, the NOx storage reduction catalyst 7 is compared with the case where it is determined that the active state is not in an inactive state. Then, control is performed to reduce the fuel injection amount of the cylinder 3 for rich combustion. The enrichment control is executed, for example, when rich spike control or bank control is executed. Thereby, the catalytic activity of the NOx occlusion reduction catalyst 7 can be recovered. Therefore, the ECU 20 functions as a catalyst activity determination unit and a control unit in the present invention. A specific control method will be described below.

[Control Method According to First Embodiment]
First, the control method according to the first embodiment will be described. As described above, the NOx occlusion reduction catalyst 7 is leaner than stoichiometric, that is, in an oxygen excess oxidizing atmosphere, stores NOx in the exhaust gas, and is richer than stoichiometric, that is, a reducing atmosphere with excess fuel. Or, in stoichiometry, the stored NOx is released and this NOx is reduced and purified. Therefore, rich spike control (RS control) for forcibly enriching the air-fuel ratio is executed by the ECU 20. Specifically, in order to enrich the air-fuel ratio, the ECU 20 causes the cylinder group of the bank 2 to perform rich combustion, that is, increases the fuel injection amount injected from each injector 11.

  Here, consider a case where an alcohol mixed fuel in which alcohol is mixed with gasoline is used as fuel. Alcohol fuel has a smaller stoichiometric air-fuel ratio than gasoline fuel. Therefore, the fuel injection amount injected from each injector 11 when the cylinder group of the bank 2 is richly burned is larger when alcohol mixed fuel is used as fuel than when gasoline fuel is used as fuel. . Therefore, when the alcohol control fuel is used as the fuel during the execution of the RS control, the NOx occlusion reduction catalyst 7 is cooled because the fuel is excessive as compared with the case where the gasoline fuel is used as the fuel. It becomes easy to become inactive.

  Therefore, in the first embodiment, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state during the execution of the RS control, the active state of the NOx storage reduction catalyst 7 is inactive. Compared to when it is determined that the engine is not in the state, the rich degree of the cylinder group of the bank 2 at the time of rich combustion is corrected to be shallow, that is, the fuel injection amount of the cylinder group of the bank 2 at the time of rich combustion is set. Decrease weight. By doing so, the cooling of the NOx storage reduction catalyst 7 can be suppressed, so that the catalytic activity of the NOx storage reduction catalyst 7 can be recovered.

  Note that if the rich degree is corrected to be shallow during execution of RS control, NOx reduction may be insufficient. Therefore, when the RS 20 performs the RS control, when the rich degree is corrected to be shallow, the execution time of the RS control is compared with a case where it is determined that the active state of the NOx storage reduction catalyst 7 is not in the inactive state. May be corrected longer. By doing in this way, it can prevent that NOx reduction | restoration becomes inadequate because a rich degree becomes shallow. In the process described below, when the rich degree is corrected to be shallow, the RS control execution time is corrected to be longer.

(Processing according to the first embodiment)
The processing according to the first embodiment will be described with reference to the flowchart shown in FIG.

  First, in step S101, the ECU 20 detects the operating state of the engine 1 based on detection signals from various sensors. Next, in step S102, the ECU 20 determines whether or not the engine 1 is in a lean operation. If it is determined that the engine 1 is not in a lean operation (step S102; No), the present process is terminated. On the other hand, when the ECU 20 determines that the engine 1 is in the lean operation (step S102: Yes), the ECU 20 proceeds to step S103.

  In step S103, the ECU 20 calculates the rich spike execution time (RS time), the interval, and the rich degree based on the operating state of the engine 1. For example, the ECU 20 obtains the NOx storage amount of the NOx storage reduction catalyst 7 based on the engine speed and the engine load, and uses the map or the like based on the input NOx amount to execute the rich spike execution time (RS time). ), The interval, and the richness are calculated and recorded in a RAM or the like. The execution time (RS time) and interval of rich spikes and the rich degree recorded in the RAM or the like may be referred to as RS control variables below.

  In step S104, the ECU 20 determines whether or not a rich spike execution condition (RS execution condition) is satisfied. The fact that the RS execution condition is satisfied includes, for example, that the lean operation has continued for a predetermined time. When it is determined that the RS execution condition is not satisfied (step S104: No), the ECU 20 ends this process. On the other hand, if the ECU 20 determines that the RS execution condition is satisfied (step S104: Yes), the ECU 20 proceeds to step S105.

  In step S105, the ECU 20 reads the RS control variable recorded in step S104, that is, the RS time and interval, and the rich degree from the RAM or the like. In step S106, the ECU 20 determines whether RS control is being performed. The ECU 20 can determine whether or not the RS control is in progress, for example, by setting a flag in advance when the RS control is started. When the ECU 20 determines that the RS control is not being performed (step S106: No), the ECU 20 starts the RS control with the RS control variable read in the step S105 (step S114), and ends this process. On the other hand, when the ECU 20 determines that the RS control is being performed (step S106: Yes), the ECU 20 proceeds to step S107.

  In step S107, the ECU 20 detects the active state of the NOx storage reduction catalyst 7. In step S108, the ECU 20 determines whether the active state of the NOx storage reduction catalyst 7 is in an inactive state based on the detected active state of the NOx storage reduction catalyst 7. A method for determining whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state will be described in detail later. If the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state, the ECU 20 proceeds to step S109, and if it determines that the active state of the NOx storage reduction catalyst 7 is not in an inactive state, Proceed to step S112.

  In step S109, the ECU 20 reads the catalyst deactivation correction coefficient from the RAM. In the first embodiment, the catalyst deactivation correction coefficient is a coefficient for correcting the values of the rich spike execution time (RS time), interval, and richness. That is, the ECU 20 can change the rich spike execution time (RS time), the interval, and the rich degree by correcting the catalyst deactivation correction coefficient. In step S110, the ECU 20 corrects the catalyst deactivation correction coefficient. Specifically, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state, the ECU 20 compares it with a determination that the active state of the NOx storage reduction catalyst 7 is not in an inactive state. Thus, the catalyst deactivation correction coefficient is corrected so that the rich degree of the cylinder group of the bank 2 during the rich combustion becomes shallower and the RS time becomes longer. In step S111, the ECU 20 actually corrects the rich spike execution time (RS time), interval, and richness based on the corrected catalyst deactivation correction coefficient. Specifically, the ECU 20 corrects the degree of richness based on the corrected catalyst deactivation correction coefficient, that is, reduces the fuel injection amount and corrects the RS time longer. Thus, by correcting the rich degree to be shallow, the catalytic activity of the NOx storage reduction catalyst 7 can be recovered, and by correcting the RS time longer, it is possible to prevent the NOx reduction from becoming insufficient. .

  In step S112, the ECU 20 determines whether it is a rich spike end time (RS end time), that is, whether the RS time has elapsed. If the ECU 20 determines that it is not the RS end time, that is, if it is determined that the RS time has not elapsed (step S112: No), the process ends. On the other hand, when it is determined that the RS end time is reached, that is, when it is determined that the RS time has elapsed (step S112: Yes), the ECU 20 ends the RS control (step S113) and ends the process. To do. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

  According to the above processing, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state when the RS control is executed, the active state of the NOx storage reduction catalyst 7 is inactive. The rich degree of the cylinder group of the bank 2 at the time of rich combustion is corrected to be shallower than when it is determined that it is not in the active state. Thereby, the catalytic activity of the NOx occlusion reduction catalyst 7 can be recovered. Further, when reducing the rich degree during the execution of the RS control, the ECU 20 sets the execution time of the RS control as compared to when determining that the active state of the NOx storage reduction catalyst 7 is not in the inactive state. It will be corrected for a long time. By doing in this way, it can prevent that NOx reduction | restoration becomes inadequate.

[Control Method According to Second Embodiment]
Next, a control method according to the second embodiment will be described. In actuality, the NOx occlusion reduction catalyst 7 is so-called sulfur (S) poisoning, in which substances other than NOx, for example, sulfur (S) and its compounds (SOx) also adhere. Such substances other than NOx adhere to the place where NOx should be adsorbed instead of NOx. As a result, the NOx purification performance of the NOx storage reduction catalyst is reduced.

  Therefore, the ECU 20 executes bank control in order to recover sulfur poisoning of the NOx storage reduction catalyst 7. Specifically, the ECU 20 performs control to make the air-fuel ratio different between one bank 2 and the other bank 2. Specifically, control is performed so that one bank 2 (for example, the left bank 2L) is richly burned and the other bank 2 (for example, the right bank 2R) is lean-burned. Thereby, a gas in which a gas containing a lot of fuel and a gas containing a lot of oxygen are mixed is supplied to the NOx occlusion reduction catalyst 7, the NOx occlusion reduction catalyst 7 is heated, and sulfur is desorbed from the NOx occlusion reduction catalyst 7. Thus, sulfur poisoning of the NOx storage reduction catalyst 7 is recovered.

  As described in the first embodiment, the fuel injection amount injected from each injector 11 when the cylinder group of the bank 2 is richly burned is obtained by using alcohol-mixed fuel as fuel, rather than using gasoline fuel as fuel. When used, it becomes larger. Therefore, even when the bank control is executed, when the alcohol mixed fuel is used as the fuel, the NOx occlusion reduction catalyst 7 is cooled because the fuel is excessive as compared with the case where the gasoline fuel is used as the fuel. Easily become inactive.

  Therefore, also in the second embodiment, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state during execution of bank control, the active state of the NOx storage reduction catalyst 7 is inactive. Compared to the case where it is determined that the engine is not in the active state, the rich degree of the cylinder group of the bank 2 to be richly burned is corrected to be shallow, that is, the fuel injection amount of the cylinder group of the bank 2 to be richly burned is reduced. And Specifically, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state, the ECU 20 compares it with a determination that the active state of the NOx storage reduction catalyst 7 is not in an inactive state. Thus, the air-fuel ratio difference between the cylinder group of the bank 2 that performs rich combustion and the cylinder group of the bank 2 that performs lean combustion is corrected to be small so that the rich degree of the cylinder group of the bank 2 that performs rich combustion becomes shallow. By doing so, the fuel injection amount of the cylinder group of the bank 2 to be richly burned can be reduced and the cooling of the NOx storage reduction catalyst 7 can be suppressed, so that the catalytic activity of the NOx storage reduction catalyst 7 is recovered. Can be made.

  When the bank control is executed, the rich degree of the cylinder group of the bank 2 that performs rich combustion is corrected to be shallow, that is, the air-fuel ratio difference between the cylinder group of the bank 2 that performs rich combustion and the cylinder group of the bank 2 that performs lean combustion. If it is corrected to a small value, S poison recovery may be insufficient. Therefore, when executing the bank control, when the rich degree of the cylinder group of the bank 2 to be richly burned is made shallower, the ECU 20 is compared with the case where it is determined that the active state of the NOx storage reduction catalyst 7 is not in the inactive state. Thus, the bank control execution time may be corrected to be longer. By doing in this way, it can prevent that S poison recovery becomes inadequate. In the processing described below, when the rich degree is corrected to be shallow, the bank control execution time is corrected to be longer.

(Processing according to the second embodiment)
Processing according to the second embodiment will be described with reference to the flowchart shown in FIG.

  First, in step S121, the ECU 20 detects the operating state of the engine 1 based on detection signals from various sensors. Next, in step S122, the ECU 20 determines whether or not the engine 1 is in a lean operation. If it is determined that the engine 1 is not in a lean operation (step S122; No), the process is terminated. On the other hand, when the ECU 20 determines that the engine 1 is in the lean operation (step S122: Yes), the ECU 20 proceeds to step S123.

  In step S123, the ECU 20 estimates the sulfur (S) poisoning amount of the NOx storage reduction catalyst 7 based on the operating state of the engine 1. For example, the ECU 20 estimates the S poisoning amount of the NOx occlusion reduction catalyst 7 based on the accumulated fuel consumption and the running time since the most recent bank control is executed.

  In step S124, the ECU 20 determines whether or not a bank control execution condition (S regeneration condition) is satisfied. Specifically, the ECU 20 determines that the S regeneration condition is satisfied when the estimated S poisoning amount of the NOx storage reduction catalyst 7 is equal to or greater than a predetermined value. The predetermined value here is, for example, a value estimated that the NOx occlusion reduction catalyst 7 cannot occlude NOx when the sulfur poisoning amount becomes equal to or greater than this value. If the ECU 20 determines that the S regeneration condition is not satisfied (step S124: No), the process is terminated. On the other hand, when the ECU 20 determines that the S regeneration condition is satisfied (step S124: Yes), the ECU 20 proceeds to step S125.

  In step S125, the ECU 20 reads the basic value of the S regeneration condition. The basic value of the S regeneration condition is a basic value for performing the bank control. Specifically, when performing the bank control, the air-fuel ratio of the cylinder group of the bank 2 that performs rich combustion, the bank that performs lean combustion The air-fuel ratio of the second cylinder group and the execution time for executing bank control. The basic value of the S reproduction condition is a preset value and is recorded in a ROM or the like. The ECU 20 reads from the ROM or the like the air-fuel ratio of the cylinder group of the bank 2 for rich combustion, the air-fuel ratio of the cylinder group of the bank 2 for lean combustion, and the execution time for executing the bank control, and then proceeds to step S126.

  In step S126, the ECU 20 determines whether bank control is being performed. Specifically, the ECU 20 can determine whether or not the bank control is being performed, for example, by setting a flag in advance when the bank control is started. If it is determined that the bank control is not being performed (step S126: No), the ECU 20 starts the bank control with the basic value of the S reproduction condition read in step S125 (step S135), and measures the execution time of the bank control. In order to do this, a timer is set (step S136). Thereafter, the ECU 20 ends this process. On the other hand, if the ECU 20 determines that bank control is being performed (step S126: Yes), the process proceeds to step S127.

  In step S127, the ECU 20 detects the active state of the NOx storage reduction catalyst 7. In step S128, the ECU 20 determines whether the active state of the NOx storage reduction catalyst 7 is in an inactive state based on the active state of the NOx storage reduction catalyst 7. The processing of step S127 and step 128 is the same processing as step S107 and step S108 in the first embodiment, and will be described in detail later. If the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state, the ECU 20 proceeds to step S129, and if it determines that the active state of the NOx storage reduction catalyst 7 is not in an inactive state, The process proceeds to step S133.

  In step S129, the ECU 20 reads the catalyst deactivation correction coefficient from the RAM. In the second embodiment, the catalyst deactivation correction coefficient is a coefficient for correcting the basic value of the S regeneration condition. The ECU 20 changes the values of the air-fuel ratio of the cylinder group of the bank 2 for rich combustion, the air-fuel ratio of the cylinder group of the bank 2 for lean combustion, and the execution time of the bank control by correcting the catalyst deactivation correction coefficient. be able to. In step S130, the ECU 20 corrects the catalyst deactivation correction coefficient. Specifically, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state, the ECU 20 compares it with a determination that the active state of the NOx storage reduction catalyst 7 is not in an inactive state. Thus, the catalyst deactivation correction coefficient is corrected so that the rich degree of the cylinder group of the bank 2 that performs rich combustion becomes shallow and the execution time of the bank control becomes longer.

  In step S131, the ECU 20 determines, based on the corrected catalyst deactivation correction coefficient, the air-fuel ratio of the cylinder group of the bank 2 that performs rich combustion, the air-fuel ratio of the cylinder group of the bank 2 that performs lean combustion, and the execution time of the bank control, respectively. The value of is actually corrected. Specifically, the ECU 20 makes the rich degree of the richly burned cylinder group of the bank 2 based on the corrected catalyst deactivation correction coefficient, that is, the fuel of the richly burned cylinder group of the bank 2. The air-fuel ratio difference between the richly burned bank 2 cylinder group and the lean burned bank 2 cylinder group is corrected so as to reduce the injection amount. For example, when the air-fuel ratio of the cylinder group of the bank 2 that is richly burned is 12 and the air-fuel ratio of the cylinder group of the bank 2 that is lean-burned is 18, the active state of the NOx storage reduction catalyst 7 is the inactive state. When it is determined that the air-fuel ratio is in the range, for example, the ECU 20 corrects the air-fuel ratio of the cylinder group of the bank 2 in rich burn to 13 and the air-fuel ratio of the cylinder group of the bank 2 in lean burn to 16, for example. When the fuel is alcohol fuel, the theoretical air-fuel ratio becomes a small value, so these corrected air-fuel ratios also become a small value. Further, at this time, the ECU 20 corrects the execution time of the bank control longer than when it is determined that the active state of the NOx storage reduction catalyst 7 is not in the inactive state. Thus, by correcting the rich degree of the cylinder group of the bank 2 that has been richly burned, the catalytic activity of the NOx storage reduction catalyst 7 can be recovered, and by correcting the execution time of the bank control longer, S Poor recovery from poisoning can be prevented. Thereafter, the ECU 20 proceeds to step S132.

  In step S132, the ECU 20 reads the time measured by the timer. In step S133, the ECU 20 determines whether or not it is the bank control end time, that is, whether or not the time measured by the timer has passed the bank control execution time. When the ECU 20 determines that it is not the bank control end time (step S133: No), that is, when it is determined that the time measured by the timer has passed the execution time of the bank control, this process is terminated. To do. On the other hand, if the ECU 20 determines that it is the bank control end time (step S133: Yes), that is, if it is determined that the time measured by the timer has passed the execution time of the bank control, After the control is finished (step S134), this process is finished. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

  According to the above processing, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state when the bank control is executed, the active state of the NOx storage reduction catalyst 7 is inactive. The rich degree of the cylinder group of the bank 2 to be richly burned is corrected to be shallower than when it is determined that it is not in the active state. Thereby, the catalytic activity of the NOx occlusion reduction catalyst 7 can be recovered. When the ECU 20 performs the bank control and corrects the rich degree of the cylinder group of the bank 2 to be richly burned, when the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is not in the inactive state. In comparison, the bank control execution time is corrected to be longer. By doing in this way, it can prevent that S poison recovery becomes inadequate.

[Method for judging catalyst inactive state]
Next, a method for determining the inactive state of the catalyst will be described. In steps S107 and S108 in the process according to the first embodiment and steps S127 and S128 in the process according to the second embodiment, the ECU 20 detects the active state of the NOx storage reduction catalyst 7 and detects the detected NOx storage reduction catalyst. On the basis of the active state of 7, the NOx storage reduction catalyst 7 is determined whether or not the active state is in an inactive state. Below, the determination method of the inactive state of this NOx storage reduction catalyst 7 is demonstrated concretely.

(First determination method of inactive state of catalyst)
First, the first determination method for the inactive state of the catalyst will be described. The NOx occlusion reduction catalyst 7 becomes inactive when the fuel becomes excessive and is cooled. Therefore, in the first catalyst inactive state determination method, the ECU 20 has no exothermic reaction of the NOx storage reduction catalyst 7, that is, the temperature increase of the catalyst temperature of the NOx storage reduction catalyst 7 is not more than a predetermined value (the temperature increase). Is a negative value, that is, when the catalyst temperature of the NOx storage reduction catalyst 7 is low), the active state of the NOx storage reduction catalyst 7 is in an inactive state. It is determined that there is. This predetermined value is obtained in advance by experiments or the like and recorded in a ROM or the like.

  Processing related to the first determination method of the inactive state of the catalyst will be described with reference to the flowchart shown in FIG.

  In step S141, the ECU 20 detects the operating state of the engine 1 based on detection signals from various sensors. Next, in step S142, the ECU 20 determines whether or not the engine 1 is in a lean operation. If it is determined that the engine 1 is not in a lean operation (step S142; No), the process is terminated. On the other hand, when the ECU 20 determines that the engine 1 is in the lean operation (step S142: Yes), the ECU 20 proceeds to step S143.

  In step S143, the ECU 20 determines whether or not an activity determination condition is satisfied. Specifically, the ECU 20 determines that the activity determination condition is satisfied when the RS control or the bank control is being executed. When it is determined that the activity determination condition is not satisfied (step S143: No), the ECU 20 ends this process. On the other hand, when the ECU 20 determines that the activity determination condition is satisfied (step S143: Yes), the ECU 20 proceeds to step 144.

  In step S144, the ECU 20 determines the catalyst temperature of the NOx storage reduction catalyst 7. Specifically, the ECU 20 obtains the exhaust temperature of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 based on the output from the exhaust temperature sensor 24, and based on the obtained exhaust temperature, the NOx storage reduction catalyst 7 is obtained. The catalyst temperature Tcc is estimated. The ECU 20 may directly detect the catalyst temperature Tcc of the NOx storage reduction catalyst 7 using a catalyst temperature sensor that detects the catalyst temperature of the NOx storage reduction catalyst 7 instead of using the exhaust temperature sensor 24.

  In step S145, the ECU 20 calculates a difference Tdiff (= Tcc-To) between the catalyst temperature Tcc and the previously determined catalyst temperature To of the NOx storage reduction catalyst 7. This difference Tdiff corresponds to the rising temperature of the NOx storage reduction catalyst 7. In step S146, the ECU 20 determines whether or not the difference Tdiff is equal to or less than a predetermined value α. When the ECU 20 determines that the difference Tdiff is equal to or less than the predetermined value α (step S146: Yes), the active state of the NOx storage reduction catalyst 7 is assumed to be in an inactive state. An inactive flag indicating that the state is in an inactive state is set (step S147), and the process proceeds to step S149. On the other hand, when the ECU 20 determines that the difference Tdiff is larger than the predetermined value α (step S146: No), the active state of the NOx storage reduction catalyst 7 is not in an inactive state, and an inactive flag is set. Reset (step S148), the process proceeds to step S149. In this way, the ECU 20 can determine whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state based on whether or not the inactive flag is set. The predetermined value α is obtained in advance by experiments or the like and recorded in a ROM or the like.

  In step S149, the ECU 20 updates the catalyst temperature To of the NOx storage reduction catalyst 7 obtained last time. Specifically, the ECU 20 sets the catalyst temperature Tcc obtained this time as a new catalyst temperature To. Thereafter, the ECU 20 ends this process. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

  According to the above processing, the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state when the rising temperature of the catalyst temperature of the NOx storage reduction catalyst 7 is not more than the predetermined value α. judge. In this way, the ECU 20 can determine whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state.

(Second determination method of catalyst inactive state)
Next, a second determination method for the inactive state of the catalyst will be described. In the second determination method of the inactive state of the catalyst, when the ECU 20 determines that the air-fuel ratio on the downstream side of the NOx storage reduction catalyst 7 is rich within a predetermined time after the RS control is started. Determines that the active state of the NOx storage reduction catalyst 7 is in an inactive state.

  FIG. 5 is a graph showing the transition of the air-fuel ratio of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 during the RS control. During the RS control, when the active state of the NOx storage reduction catalyst 7 is not in an inactive state, the reducing agent is consumed by the NOx storage reduction catalyst 7 for NOx reduction. As shown in the graph 31, the air-fuel ratio of the exhaust gas in FIG. 3 becomes rich after showing a slight lean from the stoichiometry for a while after the start of the RS control. However, during the RS control, when the active state of the NOx storage reduction catalyst 7 is in an inactive state, NOx reduction is not performed. Therefore, the reducing agent is not consumed by the NOx storage reduction catalyst 7, and the NOx storage reduction catalyst. As shown in the graph 32, the air-fuel ratio of the exhaust gas on the downstream side of 7 shows rich immediately after the start of the RS control. That is, when the predetermined time has elapsed since the start of the RS control, when the active state of the NOx storage reduction catalyst 7 is not in the inactive state, as shown at a point 31p, the downstream side of the NOx storage reduction catalyst 7 While the air-fuel ratio of the exhaust gas at the exhaust gas is slightly leaner than stoichiometric, when the active state of the NOx storage reduction catalyst 7 is in an inactive state, as shown at point 32p, the NOx storage reduction catalyst 7 The air-fuel ratio of the exhaust gas on the downstream side is rich.

  Therefore, in the second determination method of the catalyst inactive state, the ECU 20 causes the air-fuel ratio downstream of the NOx storage reduction catalyst 7 to fall below a predetermined value within a predetermined time after the start of the RS control. That is, when it is determined that the engine is rich, it is determined that the active state of the NOx storage reduction catalyst 7 is in an inactive state. Here, the predetermined value is, for example, the value of the air-fuel ratio when stoichiometric. The range of time that can be taken as the predetermined time is the time Tr from the start of RS control until the air-fuel ratio becomes rich when the active state of the NOx storage reduction catalyst 7 is not in the inactive state (graph 31).

  Processing related to the second determination method of the inactive state of the catalyst will be described with reference to the flowchart shown in FIG.

  In step S151, the ECU 20 detects the operating state of the engine 1 based on detection signals from various sensors. Next, in step S152, the ECU 20 determines whether or not the engine 1 is in the lean operation. If it is determined that the engine 1 is not in the lean operation (step S152; No), the process is terminated. On the other hand, when the ECU 20 determines that the engine 1 is in the lean operation (step S152: Yes), the ECU 20 proceeds to step S153.

  In step S153, the ECU 20 determines whether or not the RS control is being performed. When it is determined that the RS control is not being performed (step S153: No), the present process is terminated, and when it is determined that the RS control is being performed. (Step S153: Yes), the process proceeds to Step S154.

  In step S154, the ECU 20 determines whether or not a predetermined time has elapsed since the start of the RS control. If it is determined that the predetermined time has not elapsed (step S154: No), the process is terminated. If it is determined that the predetermined time has elapsed (step S154: Yes), the process proceeds to step S155.

In step S155, the ECU ₂₀ obtains the oxygen concentration Vcc of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 based on the output from the 02 sensor 23. In step S156, when the ECU 20 determines that the obtained oxygen concentration Vcc is equal to or less than the predetermined value β (step S156: Yes), the exhaust gas empty on the downstream side of the NOx storage reduction catalyst 7 is determined. Assume that the fuel ratio is rich, and after setting the inactive flag (step S157), this process is terminated. On the other hand, when the ECU 20 determines that the obtained oxygen concentration Vcc is larger than the predetermined value β (step S156: No), the air-fuel ratio of the exhaust gas on the downstream side of the Ox storage reduction catalyst 7 is lean. If the inactive flag is reset (step S158), the process is terminated. In this way, the ECU 20 can determine whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state based on whether or not the inactive flag is set. Here, the predetermined value β is, for example, the value of the oxygen concentration of the exhaust gas when stoichiometric. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

Note that, in step S155, ECU 20 is ₀ instead of using _two sensors 23 may be used A / F sensor provided at the downstream side of the NOx occluding and reducing catalyst 7. That is, the ECU 20 may obtain the air-fuel ratio (Fcc) of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 based on the output from the A / F sensor provided on the downstream side of the NOx storage reduction catalyst 7. .

  In step S156, when the ECU 20 determines that the obtained air-fuel ratio (Fcc) of the exhaust gas is equal to or less than the predetermined value βa, the air-fuel ratio of the exhaust gas downstream of the NOx storage reduction catalyst 7 is determined. Is set to rich (step S157), the process is terminated. On the other hand, when the ECU 20 determines that the obtained air-fuel ratio (Fcc) of the exhaust gas is greater than the predetermined value βa (step S156: No), the exhaust gas downstream of the NOx storage reduction catalyst 7 is determined. Assuming that the air-fuel ratio is lean, the inactive flag is reset (step S158), and then this process is terminated. Here, the predetermined value βa is, for example, the value of the air-fuel ratio at the time of stoichiometric.

  According to the above processing, the ECU 20 determines that the air-fuel ratio on the downstream side of the NOx storage reduction catalyst 7 is equal to or less than a predetermined value within a predetermined time after the RS control is started, that is, is rich. If it is determined, it is determined that the active state of the NOx storage reduction catalyst 7 is in an inactive state. In this way, the ECU 20 can determine whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state.

(Third determination method of catalyst inactive state)
Next, a third determination method for the inactive state of the catalyst will be described. In the third determination method of the inactive state of the catalyst, when the ECU 20 determines that the NOx concentration on the downstream side of the NOx storage reduction catalyst 7 has not decreased within a predetermined time after the start of the RS control, It is determined that the active state of the NOx storage reduction catalyst 7 is in an inactive state. This is because the NOx concentration on the downstream side of the NOx occlusion reduction catalyst 7 does not decrease despite the RS control being started. This means that the NOx occlusion reduction catalyst 7 is not performing NOx reduction. Because you can think. Specifically, the ECU 20 determines the activity of the NOx storage reduction catalyst 7 when the NOx concentration on the downstream side of the NOx storage reduction catalyst 7 is equal to or higher than a predetermined value within a predetermined time after the RS control is started. It is determined that the state is in an inactive state. Here, the predetermined value is, for example, the NOx concentration on the downstream side of the NOx storage reduction catalyst 7 before the RS control is started.

  Processing related to the third determination method of the inactive state of the catalyst will be described with reference to the flowchart shown in FIG.

  In step S161, the ECU 20 detects the operating state of the engine 1 based on detection signals from various sensors. Next, in step S162, the ECU 20 determines whether or not the engine 1 is in the lean operation. If it is determined that the engine 1 is not in the lean operation (step S162; No), the process is terminated. On the other hand, when the ECU 20 determines that the engine 1 is in the lean operation (step S162: Yes), the ECU 20 proceeds to step S163.

  In step S163, the ECU 20 determines whether or not the RS control is being performed. When it is determined that the RS control is not being performed (step S163: No), the present process is terminated, and when it is determined that the RS control is being performed. (Step S163: Yes), the process proceeds to Step S164.

  In step S164, the ECU 20 determines whether or not a predetermined time has elapsed since the start of the RS control. If it is determined that the predetermined time has not elapsed (step S164: No), the process is terminated. If it is determined that the predetermined time has elapsed (step S164: Yes), the process proceeds to step S165.

  In step S165, the ECU 20 obtains the NOx concentration Ncc of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 based on the output from the NOx sensor provided on the downstream side of the NOx storage reduction catalyst 7. In step S166, when the ECU 20 determines that the obtained NOx concentration Ncc is equal to or greater than the predetermined value γ (step S166: Yes), the active state of the NOx storage reduction catalyst 7 is in an inactive state. If there is, the inactive flag is set (step S167), and then this process is terminated. On the other hand, when the ECU 20 determines that the obtained NOx concentration Ncc is less than the predetermined value γ (step S166: No), the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is not in an inactive state. After resetting the activation flag (step S168), this process is terminated. Here, the predetermined value γ is, for example, the NOx concentration on the downstream side of the NOx storage reduction catalyst 7 before the RS control is started, for example. In this way, the ECU 20 can determine whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state based on whether or not the inactive flag is set. This process is repeatedly executed by the ECU 20 at a predetermined cycle.

  According to the above processing, when the NOx concentration on the downstream side of the NOx storage reduction catalyst 7 does not decrease within a predetermined time from the execution of the RS control, the ECU 20 determines that the active state of the NOx storage reduction catalyst 7 is inactive. Determined to be in an active state. Even in this way, the ECU 20 can determine whether or not the active state of the NOx storage reduction catalyst 7 is in an inactive state.

[Modification]
In each of the above-described embodiments, the engine 1 is provided with three cylinders 3 in each of the left and right banks 2L and 2R, and when executing the bank control, the cylinders in one bank 2 (for example, the bank 2L) Although the group is richly burned and the cylinder group of the other bank 2 (for example, bank 2R) is lean burned, the invention is not limited to this. Instead, the internal combustion engine 1 may include, for example, a rich combustion cylinder and a lean combustion cylinder in the same bank 2 when performing bank control. In short, when executing the bank control, the present invention can be applied if one cylinder group is richly burned and the other cylinder group is lean burned regardless of the banks 2L and 2R. Therefore, the internal combustion engine 1 is not limited to using a V-type 6-cylinder engine in which two banks 5 are configured by three cylinders 5c. For example, an in-line engine may be used.

1 is an exhaust purification system to which an exhaust gas purification apparatus for an internal combustion engine according to each embodiment is applied. It is a flowchart which shows the process which concerns on 1st Embodiment. It is a flowchart which shows the process which concerns on 2nd Embodiment. It is a flowchart which shows the process which concerns on the 1st determination method of the inactive state of a catalyst. It is a graph which shows the transition of the air fuel ratio of the exhaust gas during RS control. It is a flowchart which shows the process which concerns on the 2nd determination method of the inactive state of a catalyst. It is a flowchart which shows the process which concerns on the 3rd determination method of the inactive state of a catalyst.

Explanation of symbols

1 Internal combustion engine
2 Bank 4, 6 Exhaust passage 7 NOx storage reduction catalyst 20 ECU
22 A / F sensor 23 0 ₂ sensor 24 Exhaust temperature sensor

Claims (6)

In an exhaust gas purification apparatus for an internal combustion engine having a NOx storage reduction catalyst on an exhaust passage,
Catalyst active state determining means for determining whether or not the active state of the NOx storage reduction catalyst is in an inactive state;
When performing the enrichment control for enriching the air-fuel ratio of the exhaust gas from the internal combustion engine, when the active state of the NOx storage reduction catalyst is determined to be in an inactive state by the catalyst active state determination means Comprises a control means for reducing the fuel injection amount of the cylinder for rich combustion of the internal combustion engine.   When the control means executes the bank control that makes the air-fuel ratio of one cylinder group rich and makes the air-fuel ratio of the other cylinder group lean or stoichiometric, the active state of the NOx storage reduction catalyst becomes an inactive state. 2. The control according to claim 1, wherein if it is determined by the catalyst activation state determination means, the rich degree of the one cylinder group is corrected to be shallow and the execution time of the bank control is corrected to be longer. Exhaust gas purification device for internal combustion engine.   The control means determines by the catalyst active state determination means that the active state of the NOx storage reduction catalyst is in an inactive state when performing rich spike control for reducing NOx stored in the NOx storage reduction catalyst. 2. The exhaust of the internal combustion engine according to claim 1, wherein when the rich combustion is performed, the richness of the cylinder of the internal combustion engine is corrected to be shallow and the execution time of the rich spike control is corrected to be longer. Purification equipment.   The catalyst active state determining means determines that the active state of the NOx storage reduction catalyst is in an inactive state when the rising temperature of the catalyst temperature of the NOx storage reduction catalyst is a predetermined value or less. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3.   When the air-fuel ratio on the downstream side of the NOx storage reduction catalyst is equal to or less than a predetermined value within a predetermined time after the rich spike control is started, the catalyst active state determination means determines the NOx storage reduction catalyst. The exhaust emission control device for an internal combustion engine according to claim 3, wherein the active state is determined to be in an inactive state.   When the NOx concentration on the downstream side of the NOx occlusion reduction catalyst does not decrease within a predetermined time after the rich spike control is started, the catalyst activation state determination means determines that the activation state of the NOx occlusion reduction catalyst is inactive. The exhaust emission control device for an internal combustion engine according to claim 3, wherein it is determined that the engine is in a state.

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