JP2008303816A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of suppressing discharge quantity of ammonia by controlling difference of air fuel ratio between a rich air cylinder group and a lean air cylinder group. <P>SOLUTION: The exhaust emission control device for the internal combustion engine is suitably used for sulfur poisoning recovery with raising temperature of a NOx storage reduction catalyst. In particular, the exhaust emission control device for the internal combustion engine raises temperature of the NOx storage reduction catalyst and executes sulfur poisoning recovery control, namely S regeneration control by keeping air fuel ratios of one cylinder group and another cylinder group different. A control means corrects difference of air fuel ratios of one air cylinder group and another air cylinder group small when ammonia concentration at a downstream side of the NOx storage reduction catalyst is not less than a first predetermined value. Consequently, increase of discharge quantity of ammonia leaking out of the NOx storage reduction catalyst can be suppressed. <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, in Patent Document 1, ammonia is generated by disposing a NOx occlusion reduction catalyst in a part of exhaust ports and making the upstream cylinder rich, and in the exhaust purification catalyst on the downstream side, other cylinders Describes a technique for purifying NOx discharged from the atmosphere.

  By the way, in this NOx occlusion reduction catalyst, substances other than NOx, for example, sulfur (S) and its compounds (SOx) are actually attached, and so-called sulfur (S) poisoning occurs. Such substances other than NOx adhere to the place where NOx should be adsorbed instead of NOx, and as a result, the NOx purification performance of the NOx storage reduction catalyst is reduced.

  As a method for recovering the NOx purification performance of the NOx storage reduction catalyst, sulfur (S) desorption is performed by increasing the catalyst temperature of the NOx storage reduction catalyst and controlling the air-fuel ratio to stoichiometric or rich. A “reproduction control method” is known. Further, as a method for increasing the catalyst temperature of the NOx storage reduction catalyst, it is divided into a rich cylinder group and a lean cylinder group, and a NOx storage reduction catalyst is disposed at the junction between the two, and the rich gas and lean gas are catalyzed. A “bank control method” for burning is known. For example, Patent Document 2 describes a bank control technique for controlling the catalyst temperature by increasing or decreasing the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine for each cylinder.

Japanese Patent Laid-Open No. 10-47041 JP-A-8-189388

However, in the bank control method, since the rich degree of the rich cylinder group is large, there is a possibility that the discharge amount of ammonia (NH ₃ ) may increase. In Patent Document 1, no consideration is given to a case where ammonia leaks from an exhaust purification catalyst on the downstream side or a more effective purification method. In addition, Patent Document 2 has not been studied at all from the viewpoint of ammonia emission.

  The present invention has been made to solve the above-described problems, and it is possible to suppress the discharge amount of ammonia by controlling the difference in air-fuel ratio between the rich cylinder group and the lean cylinder group. It is an object of the present invention to provide an exhaust purification device for an internal combustion engine.

  In one aspect of the present invention, an exhaust gas purification apparatus for an internal combustion engine that performs sulfur poisoning recovery control by increasing the temperature of the NOx storage reduction catalyst by making the air-fuel ratio different between one cylinder group and the other cylinder group. Is a control means for correcting the difference in air-fuel ratio between the one cylinder group and the other cylinder group to be small when the ammonia concentration on the downstream side of the NOx storage reduction catalyst is equal to or higher than a first predetermined value. Is provided.

The exhaust gas purification apparatus for an internal combustion engine is suitably used for recovering sulfur poisoning by raising the temperature of the NOx storage reduction catalyst. Specifically, the exhaust gas purification apparatus for an internal combustion engine raises the NOx storage reduction catalyst by making the air-fuel ratio different between one cylinder group and the other cylinder group, thereby controlling sulfur poisoning recovery, that is, S Perform playback control. The exhaust gas purification apparatus for an internal combustion engine includes control means such as an ECU (Electric Control Unit). The control means corrects the difference in air-fuel ratio between the one cylinder group and the other cylinder group to be small when the ammonia concentration downstream of the NOx storage reduction catalyst is equal to or higher than the first predetermined value. . Here, the first predetermined value is a value by which it can be estimated that, for example, when the ammonia concentration is equal to or higher than this value, the amount of ammonia discharged from the NOx storage reduction catalyst is increased. By doing so, the concentration of hydrogen (H ₂ ) and hydrocarbon (HC) in the exhaust gas discharged from the richly burned cylinder group is made lower than before the correction of the air-fuel ratio difference. And increase in the amount of ammonia produced can be suppressed. Thereby, the increase in the discharge | emission amount of ammonia leaking out from the said NOx storage reduction catalyst can be suppressed.

  In another aspect of the exhaust gas purification apparatus for an internal combustion engine, the control means has an ammonia concentration on the downstream side of the NOx storage reduction catalyst that is equal to or higher than a second predetermined value that is greater than the first predetermined value. If so, the sulfur poisoning recovery control is stopped for a predetermined time. Here, the predetermined time is, for example, a time until the ammonia concentration becomes equal to or lower than the second predetermined value. Thereby, since the increase in the production amount of ammonia can be further suppressed, the increase in the discharge amount of ammonia leaking from the NOx storage reduction catalyst can be further suppressed.

In another aspect of the exhaust gas purification apparatus for an internal combustion engine, the control means corrects the difference in air-fuel ratio between the one cylinder group and the other cylinder group so that the sulfur poisoning recovery control is performed. Correct the execution time of. By doing this, the temperature of the NOx occlusion reduction catalyst is lowered, and the amount of H ₂ and HC components that are reduced and the sulfur poisoning recovery rate is lowered can be sufficiently increased by increasing the sulfur poisoning recovery control time. Sulfur desorption can be promoted while warming, and sulfur poisoning of the NOx storage reduction catalyst can be recovered.

  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 may be 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 the reducing atmosphere or stoichiometric excess of fuel. The NOx is reduced and purified while being released.

  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.

The exhaust passage 6, the air-fuel ratio (A / F) sensor 22,0 ₂ sensor 23, NH ₃ 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 NH ₃ 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 NH ₃ sensor 24 detects the ammonia concentration of the exhaust gas downstream of the NOx storage reduction catalyst 7 and supplies a detection signal corresponding to the detected ammonia concentration to the ECU 20. Further, a catalyst temperature sensor (not shown) for detecting the catalyst temperature of the NOx storage reduction catalyst 7 is attached to the exhaust passage 6. The catalyst temperature sensor supplies a detection signal corresponding to the detected catalyst temperature to the ECU 20. Instead of the catalyst temperature sensor, an exhaust temperature sensor may be attached to the exhaust passage 6 on the downstream side of the NOx storage reduction catalyst 7.

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. Fuel For example, ECU 20 is an air-fuel ratio (A / F) sensor 22,0 ₂ sensor 23, NH ₃ sensor 24, a detection signal from the catalyst temperature sensor (or exhaust temperature sensor) based on, to be injected from the injectors 11 The amount is calculated, and the operation of each injector 11 is controlled so that the calculated fuel amount is supplied to each cylinder 3.

[Control Method According to First Embodiment]
Next, a control method according to the first embodiment will be described. In fact, substances other than NOx, for example, sulfur (S) and its compounds (SOx) are also attached to the NOx occlusion reduction catalyst 7, and so-called sulfur (S) poisoning occurs. 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. Such bank control is also referred to as “S regeneration control” and corresponds to the sulfur poisoning recovery control in the present invention.

In the S regeneration control, the richness of the cylinder group of the bank 2 that has been richly burned increases, so in the exhaust gas discharged from the cylinder group of the bank 2 that has been richly burned, hydrogen (H ₂ ) and hydrocarbons ( The concentration of HC) increases. When the concentration of hydrogen (H ₂ ) or hydrocarbon (HC) in the exhaust gas increases, generation of ammonia (NH ₃ ) generated by reducing NOx by hydrogen or hydrocarbon in the NOx occlusion reduction catalyst 7. The amount also increases, and the amount of ammonia that leaks out from the NOx storage reduction catalyst 7 may increase.

Therefore, in the first embodiment, the ECU 20 calculates the difference between the air-fuel ratios of one cylinder group and the other cylinder group when the ammonia concentration downstream of the NOx storage reduction catalyst 7 is equal to or greater than the predetermined value α. The correction will be made small. That is, when executing the S regeneration control, the ECU 20 reduces the rich degree of the richly burned bank 2 cylinder group and the richly burned bank 2 cylinder group and the lean burned cylinder 2 cylinder group. Correct the air-fuel ratio difference with. 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 ammonia concentration on the downstream side of the NOx storage reduction catalyst 7 is When the value is equal to or greater than the predetermined value α, the ECU 20 corrects the air-fuel ratio of the cylinder group of the bank 2 in rich combustion to 14 and the air-fuel ratio of the cylinder group of the bank 2 in lean combustion to 16, for example. Here, the predetermined value α is a value by which it can be estimated that, for example, when the ammonia concentration becomes equal to or higher than this value, the amount of ammonia discharged from the NOx storage reduction catalyst 7 increases. By doing so, the concentration of hydrogen (H ₂ ) and hydrocarbon (HC) in the exhaust gas discharged from the cylinder group of the bank 2 that is richly burned is compared with that before the correction of the air-fuel ratio difference, It can be lowered, and an increase in the amount of ammonia produced can be suppressed. Thereby, the increase in the discharge amount of ammonia leaking from the NOx storage reduction catalyst 7 can be suppressed.

  If the difference between the air-fuel ratios of one cylinder group and the other cylinder group is corrected to be small, the NOx occlusion reduction catalyst 7 becomes harder to raise the temperature accordingly. Therefore, the ECU 20 may correct the execution time of the S regeneration control to be longer when correcting the difference in the air-fuel ratio between the one cylinder group and the other cylinder group to be small. By doing in this way, the NOx occlusion reduction catalyst 7 can be sufficiently heated, and the sulfur poisoning of the NOx occlusion reduction catalyst 7 can be recovered. The process described below includes correction of the execution time of this S regeneration control.

(Processing according to the first embodiment)
The processing according to the first embodiment will be described with reference to the flowchart shown in FIG. This process is repeatedly executed at a predetermined cycle by the ECU 20 described above.

  First, in step S101, the ECU 20 detects the operating state of the engine 1 based on detection signals from various sensors. In step S102, for example, the ECU 20 determines whether or not the NOx storage reduction catalyst 7 is in a catalyst active state based on the catalyst temperature of the NOx storage reduction catalyst 7. When the ECU 20 determines that the NOx occlusion reduction catalyst 7 is not in the catalyst active state (step S102: No), the present process is terminated. On the other hand, when the ECU 20 determines that the NOx occlusion reduction catalyst 7 is in the catalyst active state (step S102: Yes), the ECU 20 proceeds to step S103.

  In step S103, the ECU 20 determines whether or not the NOx storage reduction catalyst 7 is in a sulfur poisoning state. Specifically, the ECU 20 estimates the sulfur poisoning amount of the NOx occlusion reduction catalyst 7 based on, for example, the accumulated fuel consumption and the travel time after the most recent S regeneration process is executed, and the estimated sulfur When the poisoning amount is a predetermined value or more, it is determined that the NOx storage reduction catalyst 7 is in a sulfur poisoning state. 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. When the ECU 20 determines that the NOx occlusion reduction catalyst 7 is not in the sulfur poisoning state (step S103: No), the present process is terminated. On the other hand, when the ECU 20 determines that the NOx storage reduction catalyst 7 is in the sulfur poisoning state (step S103: Yes), the ECU 20 proceeds to step S104.

  In step S104, 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 S regeneration control. Specifically, when performing the S regeneration control, the air-fuel ratio of the cylinder group of the bank 2 that performs rich combustion, lean combustion The air-fuel ratio of the cylinder group of bank 2 to be executed, and the execution time for executing the S regeneration control. When performing the S regeneration control, the air-fuel ratio of the cylinder group of the bank 2 for rich combustion and the air-fuel ratio of the cylinder group of the bank 2 for lean combustion are set in advance and recorded in a ROM or the like. The execution time for executing the S regeneration control is also set in advance as a map corresponding to the difference between the air-fuel ratio of the cylinder group of the bank 2 for rich combustion and the air-fuel ratio of the cylinder group of the bank 2 for lean combustion. It is recorded in ROM. The ECU 20 reads from the ROM or the like 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 for executing the S regeneration control, and proceeds to step S105.

  In step S105, the ECU 20 determines whether or not the S regeneration control is being performed. Specifically, the ECU 20 can determine whether or not the S regeneration control is being performed, for example, by setting a flag in advance when the most recent S regeneration control is performed. If it is determined that the S regeneration control is not being performed (step S105: No), the ECU 20 proceeds to step S113 and starts the S regeneration control with the basic value of the S regeneration condition read in step S104. On the other hand, when the ECU 20 determines that the S regeneration control is being performed (step S105: Yes), the ECU 20 proceeds to step S106.

In step S <b> 106, the ECU 20 obtains the ammonia concentration (V _NH3 ) of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 based on the detection signal supplied from the NH ₃ sensor 24. In step S107, the ECU 20 determines whether or not the ammonia concentration (V _NH3 ) is equal to or greater than a predetermined value α. If the ECU 20 determines that the ammonia concentration (V _NH3 ) is less than the predetermined value α (step S107: No), the ECU 20 proceeds to step S110. On the other hand, when the ECU 20 determines that the ammonia concentration (V _NH3 ) is equal to or greater than the predetermined value α (step S107: Yes), the ECU 20 proceeds to step S108.

In step S108, the ECU 20 performs control to correct the difference between the air-fuel ratio of the cylinder group of the bank 2 for rich combustion and the air-fuel ratio of the cylinder group of the bank 2 for lean combustion. By doing so, the concentration of hydrogen (H ₂ ) and hydrocarbon (HC) in the exhaust gas discharged from the cylinder group of the bank 2 to be richly burned is lower than before the correction of the air-fuel ratio difference. And increase in the amount of ammonia produced can be suppressed. Thereby, the increase in the discharge amount of ammonia leaking from the NOx storage reduction catalyst 7 can be suppressed.

In step S109, the ECU 20 corrects the execution time of the S regeneration control to be longer. Specifically, the ECU 20 is based on the difference between the corrected value of the air-fuel ratio of the cylinder group of the bank 2 that performs rich combustion and the corrected value of the air-fuel ratio of the cylinder group of the bank 2 that performs lean combustion. The execution time of the S reproduction control is obtained again from the map recorded in the ROM or the like described above, and is corrected to the obtained execution time. In the map, the execution time of the S regeneration control is set to be longer as the difference between the air-fuel ratio of the cylinder group of the bank 2 for lean combustion and the air-fuel ratio of the cylinder group of the bank 2 for rich combustion becomes smaller. . Therefore, if the ECU 20 corrects the difference between the air-fuel ratio of the cylinder group of the bank 2 for lean combustion and the air-fuel ratio of the cylinder group of the bank 2 for rich combustion, the ECU 20 corrects the execution time of the S regeneration control longer by that amount. It becomes. By doing so, even if the difference between the air-fuel ratio of the cylinder group of the bank 2 for lean combustion and the air-fuel ratio of the cylinder group of the bank 2 for rich combustion is corrected to be small, the temperature of the NOx occlusion reduction catalyst 7 decreases. and while sufficiently heated by H ₂ and HC components is reduced sulfur poisoning recovery rate to increase the amount of sulfur poisoning recovery control time reduced can be promoted sulfur desorption, NOx storage reduction The sulfur poisoning of the catalyst 7 can be recovered. Thereafter, the ECU 20 proceeds to step S110.

  In step S110, the ECU 20 determines whether it is the S regeneration end time, that is, whether the execution time of the S regeneration control has elapsed. When the ECU 20 determines that the S regeneration end time is reached (step S110: Yes), the ECU 20 ends the execution of the S regeneration control (step S111) and determines that the S regeneration end time is not reached. (Step S110: No), the execution of the S regeneration control is continued (Step S112), and this process is terminated.

According to the above processing, by correcting the difference between the air-fuel ratio of the cylinder group of the bank 2 that performs rich combustion and the air-fuel ratio of the cylinder group of the bank 2 that performs lean combustion, the ammonia leaking from the NOx storage reduction catalyst 7 is corrected. An increase in the amount of discharge can be suppressed. At this time, by correcting the execution time of the S regeneration control to be longer, the amount of sulfur covered by the reduction of the sulfur poisoning recovery rate due to a decrease in the temperature of the NOx storage reduction catalyst 7 and a decrease in the H ₂ and HC components. By extending the poison recovery control time, sulfur desorption can be promoted while sufficiently raising the temperature, and sulfur poisoning of the NOx storage reduction catalyst 7 can be recovered.

[Control Method According to Second Embodiment]
Next, a control method according to the second embodiment will be described. In the first embodiment, the ECU 20 corrects the difference in air-fuel ratio between one cylinder group and the other cylinder group to be small when the ammonia concentration downstream of the NOx storage reduction catalyst 7 is equal to or greater than the predetermined value α. On the other hand, in the second embodiment, when the ammonia concentration on the downstream side of the NOx storage reduction catalyst 7 is equal to or higher than the predetermined value β, the ECU 20 performs the S regeneration control for a predetermined time. Is stopped until the ammonia concentration becomes less than the predetermined value β.

That is, in the second embodiment, the ECU 20 does not cause the rich combustion of the cylinder group of the bank 2 by stopping the S regeneration control itself, so that hydrogen (H ₂ ) in the exhaust gas is compared with the first embodiment. The amount of decrease in the concentration of hydrocarbons (HC) becomes larger. Therefore, in the second embodiment, compared to the first embodiment, an increase in the amount of ammonia generated can be further suppressed, and an increase in the amount of ammonia leaking out from the NOx storage reduction catalyst 7 can also be suppressed. .

  Here, the predetermined value β is, for example, a value larger than the predetermined value α. That is, when the ammonia concentration becomes the predetermined value β, it is considered that the ammonia emission amount is increased more than when the ammonia concentration becomes the predetermined value α. There is a need. Therefore, in the second embodiment, the ECU 20 stops the S regeneration control for a predetermined time, thereby further suppressing an increase in the amount of ammonia leaked from the NOx storage reduction catalyst 7 as compared with the first embodiment. To do.

  When the S regeneration control is stopped for a predetermined time, it takes time until the NOx storage reduction catalyst 7 is sufficiently heated. Therefore, when the S regeneration control is stopped for a predetermined time, the ECU 20 may correct the execution time of the S regeneration control to be longer when the S regeneration control is resumed. By doing in this way, the NOx occlusion reduction catalyst 7 can be sufficiently heated, and the sulfur poisoning of the NOx occlusion reduction catalyst 7 can be recovered. Note that the processing described below includes correction of the execution time of the S regeneration control.

(Processing according to the second embodiment)
Processing according to the second embodiment will be described with reference to the flowchart shown in FIG. This process is repeatedly executed at a predetermined cycle by the ECU 20 described above.

  The processing from step S121 to S126 is the same as the processing from step S101 to step S106 described in the first embodiment, and a description thereof will be omitted. Moreover, since the process of step S136 is the same process as the process of step S113 described in 1st Embodiment, description is abbreviate | omitted.

In step S127, the ECU 20 determines whether or not the ammonia concentration (V _NH3 ) of the exhaust gas on the downstream side of the NOx storage reduction catalyst 7 is equal to or higher than a predetermined value β. If the ECU 20 determines that the ammonia concentration (V _NH3 ) is equal to or greater than the predetermined value β (step S127: Yes), the ECU 20 proceeds to step S128.

  In step S128, the ECU 20 determines whether or not the S regeneration control is temporarily stopped. Specifically, the ECU 20 can determine whether or not the S regeneration control is being performed, for example, by setting a flag in advance when the most recent S regeneration control is stopped. When the ECU 20 determines that the S regeneration control is temporarily stopped (step S128: Yes), the ECU 20 ends the process. On the other hand, when the ECU 20 determines that the S regeneration control is not temporarily stopped (step S128: No), the ECU 20 proceeds to step S129, stops the execution of the S regeneration control, and then proceeds to step S130. By doing this, the cylinder group of the bank 2 is not richly burned, so that an increase in the amount of ammonia generated can be suppressed, and an increase in the amount of ammonia leaking from the NOx storage reduction catalyst 7 can be suppressed. Can do.

  In step S130, the ECU 20 corrects the execution time of the S regeneration control when the S regeneration control is resumed using a map or the like, and then ends the present process. Thus, when the S regeneration control is resumed (step S132 described later), the S regeneration control is performed with the corrected execution time.

Returning to step S127, the case where the ECU 20 determines that the ammonia concentration (V _NH3 ) is less than the predetermined value β (step S127: No) will be described. If the ECU 20 determines that the ammonia concentration (V _NH3 ) is less than the predetermined value β (step S127: No), the ECU 20 proceeds to step S131.

In step S131, the ECU 20 determines whether or not the S regeneration control is temporarily stopped. If the ECU 20 determines that the S regeneration control is not temporarily stopped (step S131: No), the ECU 20 proceeds to step S133. On the other hand, when the ECU 20 determines that the S regeneration control is temporarily stopped (step S131: Yes), the ECU 20 proceeds to step S132 and resumes the execution of the S regeneration control. The execution time of the S regeneration control at this time is the corrected execution time corrected in step S130. As a result, even when the execution of the S regeneration control is temporarily stopped, the amount of sulfur covered by the reduction of the sulfur poisoning recovery rate due to the decrease in the temperature of the NOx occlusion reduction catalyst 7 and the decrease in H ₂ and HC components. By extending the poison recovery control time, sulfur desorption can be promoted while sufficiently raising the temperature, and sulfur poisoning of the NOx storage reduction catalyst 7 can be recovered. Thereafter, the ECU 20 proceeds to step S133.

  In step S133, the ECU 20 determines whether it is the S regeneration end time, that is, whether the execution time of the S regeneration control has elapsed. When the ECU 20 determines that the S regeneration end time is reached (step S133: Yes), the ECU 20 ends the execution of the S regeneration control (step S134), and determines that the S regeneration end time is not reached. (Step S133: No), the execution of the S regeneration control is continued (step S135), and this process is terminated.

According to the above processing, the S regeneration control is stopped for a predetermined time, specifically, until the ammonia concentration becomes less than the predetermined value β, thereby suppressing an increase in the amount of ammonia leaking from the NOx storage reduction catalyst 7. be able to. At this time, by correcting the execution time of the S regeneration control at the time of resuming the S regeneration control, the temperature of the NOx occlusion reduction catalyst 7 is lowered, and the H ₂ and HC components are reduced, so that the sulfur poisoning recovery rate By increasing the sulfur poisoning recovery control time for the reduced amount, the sulfur desorption can be promoted while sufficiently raising the temperature, and the sulfur poisoning of the NOx storage reduction catalyst 7 can be recovered. In the second embodiment described above, the predetermined value β is, for example, larger than the predetermined value α. However, the predetermined value β is not limited to this. Needless to say, it is possible to obtain the same effects as those of [Control method according to the third embodiment]
Next, a control method according to the third embodiment will be described. In the first embodiment, the ECU 20 corrects the difference in air-fuel ratio between one cylinder group and the other cylinder group to be small when the ammonia concentration downstream of the NOx storage reduction catalyst 7 is equal to or greater than the predetermined value α. In contrast, in the third embodiment, the ECU 20 determines that the ammonia concentration at the downstream side of the NOx storage reduction catalyst 7 when the catalyst temperature of the NOx storage reduction catalyst 7 is equal to or higher than the predetermined temperature γ. Only when the value is equal to or greater than the predetermined value α, the difference in air-fuel ratio between one cylinder group and the other cylinder group is corrected to be small. Here, the predetermined temperature γ is a temperature at which sulfur cannot be desorbed unless the catalyst temperature of the NOx storage reduction catalyst 7 is equal to or higher than this temperature. is there.

  When the catalyst temperature of the NOx occlusion reduction catalyst 7 is lower than the predetermined temperature γ, when the oxygen and fuel are reduced by correcting the difference in air-fuel ratio between one cylinder group and the other cylinder group to be small, The catalyst temperature of the NOx occlusion reduction catalyst 7 does not increase to such an extent that the sulfur poisoning of the NOx occlusion reduction catalyst 7 can be sufficiently recovered.

  Therefore, in the third embodiment, the ECU 20 determines that the ammonia concentration at the downstream side of the NOx storage reduction catalyst 7 is equal to or higher than the predetermined value α when the catalyst temperature of the NOx storage reduction catalyst 7 is equal to or higher than the predetermined temperature γ. Only when the difference between the air-fuel ratios of one cylinder group and the other cylinder group is corrected to be small, and when the catalyst temperature of the NOx storage reduction catalyst 7 is lower than the predetermined temperature γ, The difference in air-fuel ratio between this cylinder group and the other cylinder group is not corrected small. By doing so, even when the catalyst temperature of the NOx storage reduction catalyst 7 is lower than the predetermined temperature γ, the sulfur poisoning of the NOx storage reduction catalyst 7 can be sufficiently recovered. The catalyst temperature of the NOx storage reduction catalyst 7 can be raised.

(Processing according to the third embodiment)
The process according to the second embodiment will be described with reference to the flowchart shown in FIG. This process is repeatedly executed at a predetermined cycle by the ECU 20 described above.

  The processing from step S141 to S145 is the same processing as the processing from step S101 to S105 described in the first embodiment, and a description thereof will be omitted.

  If it is determined in step S145 that the S regeneration control is being performed (step S145: Yes), the ECU 20 proceeds to step S146. In step S146, the ECU 20 obtains the catalyst temperature (Tcat) of the NOx storage reduction catalyst 7 based on the detection signal from the catalyst temperature sensor, and advances the process to step S147. Note that the ECU 20 does not rely on the detection signal from the catalyst temperature sensor, but based on the detection signal from the exhaust temperature sensor downstream of the NOx storage reduction catalyst 7, the catalyst temperature (Tcat) of the NOx storage reduction catalyst 7. You may ask for. That is, the ECU 20 obtains the exhaust temperature of the exhaust gas downstream of the NOx storage reduction catalyst 7 based on the detection signal from the exhaust temperature sensor downstream of the NOx storage reduction catalyst 7, and based on the exhaust temperature, the NOx The catalyst temperature (Tcat) of the storage reduction catalyst 7 may be estimated.

  In step S147, the ECU 20 determines whether or not the catalyst temperature (Tcat) is equal to or higher than a predetermined temperature γ. When the ECU 20 determines that the catalyst temperature (Tcat) is lower than the predetermined temperature γ (step S147: No), the ECU 20 proceeds to step S152. On the other hand, if the ECU 20 determines that the catalyst temperature (Tcat) is equal to or higher than the predetermined temperature γ (step S147: Yes), the process proceeds to step S148. After step S148, the ECU 20 corrects the difference between the air-fuel ratios of one cylinder group and the other cylinder group to be small when the ammonia concentration downstream of the NOx storage reduction catalyst 7 is equal to or greater than the predetermined value α. At the same time, the execution time of the S regeneration control is corrected to be longer. Since the processing from step S148 to step S155 is the same as the processing from step S106 to step 113 described in the first embodiment, detailed description thereof is omitted.

  According to the above processing, when the catalyst temperature of the NOx storage reduction catalyst 7 is lower than the predetermined temperature γ, the difference between the air-fuel ratios of one cylinder group and the other cylinder group is not corrected small. By doing so, even when the catalyst temperature of the NOx storage reduction catalyst 7 is lower than the predetermined temperature γ, the sulfur poisoning of the NOx storage reduction catalyst 7 can be sufficiently recovered. The catalyst temperature of the NOx storage reduction catalyst 7 can be raised.

[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 the cylinder group of one bank 2 (for example, bank 2L) is richly burned, and the other bank Although it is assumed that the cylinder group of 2 (for example, the bank 2R) is subjected to lean combustion, the present invention is not limited to this. Instead, the internal combustion engine 1 may include, for example, a cylinder that performs rich combustion and a cylinder that performs lean combustion in the same bank 2. In short, regardless of the banks 2L and 2R, the present invention can be applied if one cylinder group is richly burned and the other cylinder group is lean burned. 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 3rd Embodiment.

Explanation of symbols

1 Internal combustion engine
2 Bank 4, 6 Exhaust passage 7 NOx storage reduction catalyst 20 ECU
24 NH ₃ sensor

Claims (3)

In an exhaust gas purification apparatus for an internal combustion engine that performs sulfur poisoning recovery control by raising the temperature of the NOx storage reduction catalyst by making the air-fuel ratio different between one cylinder group and the other cylinder group,
When the ammonia concentration on the downstream side of the NOx storage reduction catalyst is equal to or higher than a first predetermined value, there is provided control means for correcting the difference in air-fuel ratio between the one cylinder group and the other cylinder group to be small. An exhaust emission control device for an internal combustion engine.   The control means stops the sulfur poisoning recovery control for a predetermined time when the ammonia concentration on the downstream side of the NOx storage reduction catalyst is equal to or higher than a second predetermined value larger than the first predetermined value. The exhaust emission control device for an internal combustion engine according to claim 1, wherein:   2. The control unit according to claim 1, wherein when the difference in air-fuel ratio between the one cylinder group and the other cylinder group is corrected to be small, the execution time of the sulfur poisoning recovery control is corrected to be long. Or an exhaust gas purification apparatus for an internal combustion engine according to 2 or 2,

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