JP5488493B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device for an internal combustion engine that includes a NOx storage reduction catalyst and a NOx selective reduction catalyst.

Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2009-97469, a three-way catalyst (TWC), a NOx storage reduction catalyst (NSR catalyst), and a NOx selective reduction catalyst (SCR) are provided in an exhaust passage of an internal combustion engine. A system arranged in this order from the upstream side is known. In this system, ammonia (NH ₃ ) is generated in the three-way catalyst and the NSR catalyst by executing bank control or rich spike. The produced ammonia (NH ₃ ) is supplied to the SCR and used when NOx flowing into the SCR is selectively reduced.

The NOx reduction reaction using ammonia (NH ₃ ) as a reducing agent in the SCR is an exothermic reaction and progresses more easily in a low-frequency environment. Conversely, if the temperature of the SCR becomes too high, even if NH3 as a reducing agent is supplied to the SCR, the NOx reduction reaction by the NH3 becomes difficult to proceed, and a sufficient NOx purification rate may not be obtained in the SCR. . In this regard, in the above-described conventional system, when the temperature of the exhaust gas flowing into the SCR exceeds the upper limit value of the temperature at which the NOx reduction reaction proceeds with NH3 as a reducing agent in the SCR, the exhaust path from the NSR catalyst to the SCR is , The shortest path from the NSR catalyst to the SCR is switched to the path via the U-shaped tube. Thereby, since the temperature of SCR falls, NOx reduction reaction advances suitably in this SCR.

JP 2009-97469 A Japanese Patent Laid-Open No. 2005-214098

  By the way, SCR generally tends to be deteriorated with time more than a three-way catalyst or a NSR catalyst containing a noble metal. This is because the zeolite structure in the SCR tends to be relatively easily destroyed by water vapor and de-Al reaction. As the SCR deteriorates over time, the NOx purification rate decreases due to the decrease in NOx reduction performance. The above conventional system does not take into account a decrease in NOx purification performance due to aging degradation of the SCR. For this reason, the above-described conventional system leaves room for further improvement in terms of always realizing a high NOx purification rate by the combination of the NSR catalyst and the SCR.

  The present invention has been made to solve the above-described problems. In an internal combustion engine including an NSR catalyst and an SCR, a high NOx purification rate is achieved by a combination of the NSR catalyst and the SCR regardless of the degree of deterioration of the SCR. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can be realized.

In order to achieve the above object, a first invention is an exhaust purification device for an internal combustion engine capable of lean operation,
A NOx occlusion reduction catalyst (NSR catalyst) disposed in the exhaust passage of the internal combustion engine;
A NOx selective reduction catalyst (SCR) disposed downstream of the NSR catalyst;
Deterioration determining means for determining whether the SCR has deteriorated;
A bed temperature changing means capable of changing the bed temperature of the NSR catalyst;
When it is determined that the SCR is not deteriorated, the bed temperature of the NSR catalyst is controlled to a predetermined reference temperature range, and when it is determined that the SCR is deteriorated, Control means for varying the bed temperature of the NSR catalyst to a predetermined low temperature range lower than the reference temperature range;
It is characterized by having.

According to a second invention, in the first invention,
Further comprising engine load detecting means for detecting the engine load of the internal combustion engine,
The control means determines the bed temperature of the NSR catalyst in the reference temperature range when the deterioration determination means determines that the SCR has deteriorated and the engine load is equal to or higher than a predetermined reference load. To the low temperature range.

According to a third invention, in the first or second invention,
The reference temperature range is a temperature range of 350 to 450 ° C., and the low temperature range is a temperature range of 250 to 350 ° C.

A fourth invention is the invention according to any one of the first to third aspects,
The deterioration determining means determines that deterioration has occurred in the SCR when the total travel distance of the internal combustion engine exceeds a predetermined reference distance.

According to a fifth invention, in any one of the first to fourth inventions,
Obtaining means for obtaining information on the degree of deterioration of the NSR catalyst;
Degradation recovery processing means for performing degradation recovery processing of the NSR catalyst when the degradation degree of the NSR catalyst grasped by the information reaches a predetermined reference value;
Secondly, the bed temperature of the NSR catalyst is varied from the reference temperature range to the low temperature range by using the bed temperature variable means during a predetermined period before the deterioration recovery process by the deterioration recovery processing means is started. Control means,
Is further provided.

According to a sixth invention, in the fifth invention,
The acquisition means acquires the travel distance of the internal combustion engine as the information.

A seventh invention is the fifth or sixth invention, wherein
The second control means is characterized in that the bed temperature of the NSR catalyst is gradually changed to a lower temperature in accordance with the degree of deterioration of the NSR catalyst grasped by the information.

According to an eighth invention, in any one of the fifth to seventh inventions,
The deterioration recovery processing means is a process for recovering the NSR catalyst from sulfur poisoning.

According to the first invention, when the SCR is not deteriorated, the bed temperature of the NSR catalyst is controlled within a predetermined reference temperature range. In this case, since the NOx purification rate in the NSR catalyst can be maintained high, a high NOx purification rate can be maintained by the combination of the NSR catalyst and the SCR. On the other hand, when it is determined that the SCR is deteriorated, the bed temperature of the NSR catalyst is changed to a predetermined low temperature range lower than the reference temperature range. In this case, the amount of ammonia (NH ₃ ) generated in the NSR catalyst increases as compared with the case of the reference temperature range, so that a large amount of NH ₃ is supplied to the deteriorated SCR. Thereby, since the fall of the NOx purification rate in SCR is suppressed, a high NOx purification rate can be maintained by the combination of the NSR catalyst and SCR. Thus, according to the present invention, a high NOx purification rate can be realized by a combination of the NSR catalyst and the SCR regardless of whether the SCR is deteriorated or not.

  According to the second invention, when it is determined that the SCR has deteriorated and the engine load of the internal combustion engine is equal to or higher than a predetermined reference load, the bed temperature of the NSR catalyst is within a predetermined reference temperature range. It is variable to a predetermined low temperature range. From the standpoint of poisoning of the NSR catalyst, the bed temperature of the NSR catalyst is preferably controlled within the reference temperature range. On the other hand, if the amount of NOx generated is low and the load is low, the NOx purification rate can be maintained high even if the NOx purification rate of the SCR is lowered due to deterioration. For this reason, according to the present invention, it is possible to suppress the poisoning of the NSR catalyst and achieve a high NOx purification rate by combining the NSR catalyst and the SCR regardless of whether the SCR is deteriorated or not.

According to the third aspect, the predetermined reference temperature range is controlled to 350 to 450 ° C., and the predetermined low temperature range is controlled to 250 to 350 ° C. Therefore, according to the present invention, the NOx purification rate of the NSR catalyst can be maintained high in a predetermined reference temperature range, and a large amount of NH ₃ can be generated in a predetermined low temperature range.

  As the total travel distance becomes longer, the degree of SCR degradation progresses. For this reason, according to the fourth invention, it is possible to effectively determine the deterioration of the SCR based on the total travel distance.

According to the fifth aspect of the present invention, the bed temperature of the NSR catalyst is varied from the reference temperature range to the low temperature range during a predetermined period before executing the NSR catalyst deterioration recovery process. For this reason, according to the present invention, when the NOx purification rate of the NSR catalyst is decreasing, the amount of NH ₃ generated is increased, so the NOx purification rate in the SCR is increased, and the combination of the NSR catalyst and SCR is high. A NOx purification rate can be realized.

  According to the sixth aspect of the invention, the travel distance of the internal combustion engine is acquired as information regarding the degree of deterioration of the NSR catalyst. The travel distance of the internal combustion engine is an indicator of the degree of deterioration of the NSR catalyst. Therefore, according to the present invention, it is possible to appropriately determine the execution timing of the NSR catalyst deterioration recovery process based on the travel distance.

  According to the seventh aspect, the bed temperature of the NSR catalyst is gradually changed to a lower temperature value in accordance with the degree of deterioration of the NSR catalyst. For this reason, according to the present invention, as the NOx purification rate of the NSR catalyst decreases, the NOx purification rate of the SCR can be increased. Therefore, a combination of the NSR catalyst and the SCR can always achieve a high NOx purification rate. .

  According to the eighth invention, the sulfur poisoning of the NSR catalyst can be effectively recovered by the deterioration recovery processing means.

It is a figure for demonstrating the structure of embodiment of this invention. It is a figure for demonstrating the structure of an exhaust heat recovery device. NH ₃ amount exhausted from the NSR catalyst and SCR and NOx emissions is a diagram showing respectively. It is a figure which shows the relationship between the catalyst bed temperature of SCR of this Embodiment, and a NOx purification rate. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the relationship between a travel distance and the NOx purification rate of an NSR catalyst. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a figure for demonstrating the modification of the system of this Embodiment 2. FIG.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted. The present invention is not limited to the following embodiments.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining the configuration of the embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10. The internal combustion engine 10 is configured as a V-type gasoline engine including a right bank 101 and a left bank 102. The cylinder group belonging to the right bank 101 communicates with the exhaust passage 121. The cylinder group belonging to the left bank 102 communicates with the exhaust passage 122. The exhaust passages 121 and 122 communicate with one end of the exhaust passage 123 after joining downstream. Hereinafter, when the exhaust passages 121, 122, and 123 are not particularly distinguished, they are simply referred to as “exhaust passage 12”.

  In the exhaust passages 121 and 122, start catalysts (hereinafter referred to as “SC”) 141 and 142, which are three-way catalysts, are arranged, respectively. Further, a NOx storage reduction catalyst (NSR catalyst) 16 is disposed in the exhaust passage 123. Further, a NOx selective reduction catalyst (SCR) 18 is disposed downstream of the NSR catalyst 16 in the exhaust passage 123. Hereinafter, when the SCs 141 and 142 are not particularly distinguished, these are simply referred to as “SC 14”.

The internal combustion engine 10 easily discharges HC and CO when the air-fuel ratio is rich. Further, it is easy to exhaust NOx when the air-fuel ratio is lean. The SC 14 reduces NOx (purifies to N ₂ ) while adsorbing oxygen (O ₂ ) in a lean atmosphere. On the other hand, in a rich atmosphere, HC and CO are oxidized (purified to H ₂ O, CO ₂ ) while releasing oxygen. In a rich atmosphere, ammonia (NH ₃ ) is generated by the reaction of nitrogen and hydrogen or HC and NOx contained in the exhaust gas.

The NSR catalyst 16 occludes NOx contained in the exhaust gas under a lean atmosphere. Further, the NSR catalyst 16 releases NOx stored in a rich atmosphere. NOx released in a rich atmosphere is reduced by HC and CO. At this time, NH ₃ is also generated in the NSR 16 as in the case of the SC 14.

The SCR 18 is configured as a Cu-based zeolite catalyst, and the SC 14 and the NSR catalyst 16 occlude NH ₃ produced in a rich atmosphere. Under a lean atmosphere, the NO ₃ in the exhaust gas is selectively used with NH ₃ as a reducing agent. It has the function of reducing to According to the SCR 18, it is possible to effectively prevent a situation in which NH ₃ and NOx blown downstream of the NSR catalyst 16 are released into the atmosphere.

  An exhaust heat recovery device 20 is disposed upstream of the NSR catalyst in the exhaust passage 123. FIG. 2 is a view for explaining the structure of the exhaust heat recovery unit 20. As shown in this figure, the exhaust heat recovery device 20 includes a U-turn pipe 22 and a flow path switching valve 24. The flow path switching valve 24 is a valve for switching the outlet of the exhaust gas flowing into the apparatus between the U-turn pipe 22 and the exhaust passage 123 in conjunction with ON / OFF of the exhaust heat recovery device 20. is there. According to such a configuration, when the exhaust heat recovery device is OFF, the exhaust gas that has flowed directly flows into the exhaust passage 123 as shown in FIG. As a result, the high-temperature exhaust gas can be led directly into the NSR catalyst 16, so that the bed temperature of the NSR catalyst can be controlled within a predetermined reference temperature range (350 to 450 ° C.). On the other hand, when the exhaust heat recovery device is ON, the exhaust gas flowing in is guided to the U-turn pipe 22 as shown in FIG. Thereby, since the exhaust heat of the high-temperature exhaust gas is recovered, the bed temperature of the NSR catalyst can be controlled to a low temperature range (250 to 350 ° C.) lower than a predetermined reference temperature range.

  The system according to the present embodiment includes an ECU (Electronic Control Unit) 30 as shown in FIG. Various actuators such as the above-described exhaust heat recovery device 20 and a fuel injection device (not shown) are connected to the output portion of the ECU 30. Various sensors such as a crank angle sensor for detecting the engine speed and a throttle opening sensor (none of which are shown) for detecting the throttle opening are connected to the input portion of the ECU 30. The ECU 30 can control the state of the system shown in FIG. 1 based on various types of input information.

[Operation of Embodiment 1]
(Function and operation of NSR catalyst 16)
First, the function and operation of the NSR catalyst 16 will be described. The ECU 30 normally operates the internal combustion engine 10 at a lean air-fuel ratio (lean operation). During lean operation, oxidizers such as NOx are discharged in a larger amount than reducing agents such as HC and CO. For this reason, even if it is going to purify the exhaust gas using a three-way catalyst, it is not possible to purify all NOx due to a shortage of reducing agent. Therefore, the system according to the first embodiment is provided with the NSR catalyst 16 in the exhaust passage 12. The NSR catalyst 16 has a function of storing NOx as nitrates such as Ba (NO ₃ ) ₂ . For this reason, according to the system of the first embodiment, it is possible to effectively suppress the situation where the NOx is released into the atmosphere even during the lean operation.

However, the NOx storage performance of the NSR catalyst 16 decreases as the storage amount increases. For this reason, if the lean operation is continued for a long time, NOx that has not been occluded will blow through downstream of the catalyst. Therefore, in the system of the first embodiment, rich spike control is performed in which NOx occluded in the NSR catalyst 16 is periodically desorbed and processed. More specifically, the exhaust air-fuel ratio of the internal combustion engine 10 is temporarily made rich (for example, A / F = 12) at a predetermined timing when the storage performance of the NSR catalyst 16 is lowered. The exhaust gas during execution of rich spike contains a large amount of reducing agent such as HC, CO, H _{2 and the} like. For this reason, when these reducing agents are introduced into the NSR catalyst 16, NOx stored as nitrate is reduced to NO and desorbed from the base. The desorbed NOx is purified to N ₂ or the like on the catalyst in the NSR catalyst 16 and processed. Thus, by executing the rich spike during the lean operation, the NOx occluded in the NSR catalyst 16 can be desorbed, so that the NOx occlusion performance can be effectively recovered.

(NOx purification operation by SCR)
Next, the function of the SCR 18 will be described. As described above, the NOx storage performance of the NSR catalyst 16 can be effectively recovered by executing the rich spike. However, when the rich spike is executed, part of the NOx desorbed from the NSR catalyst 16 is blown downstream without being purified. Further, as described above, there is also NOx that is blown downstream without being stored in the NSR catalyst 16 during the lean operation. If these blow-by NOx are released into the atmosphere as they are, emissions will be deteriorated.

Therefore, the system according to the first embodiment includes an SCR 18 for processing NOx blown through the downstream side of the NSR catalyst 16. As described above, the SCR 18 occludes therein NH ₃ produced by the SC 14 and the NSR catalyst 16 in a rich atmosphere. For this reason, according to the SCR 18, NOx blown downstream of the NSR catalyst 16 can be selectively reduced and purified by NH ₃ . Thereby, the situation where NOx is released into the atmosphere and the emission deteriorates can be effectively prevented.

[Features of Embodiment 1]
(Relationship between NSR catalyst bed temperature and NOx purification rate)
First, the relationship between the bed temperature of the NSR catalyst 16 and the NOx purification rate will be described with reference to FIG. The inventor of the present application has made extensive studies focusing on the relationship between the bed temperature of the NSR catalyst 16 and the amount of NH ₃ produced. FIG. 3 is a diagram showing the amount of NH ₃ and NOx discharged from the NSR catalyst 16 and the SCR 18, respectively. Note that (a) in the figure shows the case where the exhaust heat recovery unit 20 is turned off and the bed temperature of the NSR catalyst 16 is controlled to 450 ° C., and (b) in the figure shows that the exhaust heat recovery unit 20 is turned on and NSR. The cases where the bed temperature of the catalyst 16 is controlled to 300 ° C. are shown.

As shown in this figure, the amount of NH ₃ produced in the NSR catalyst 16 is greatly related to the bed temperature of the NSR catalyst 16. More specifically, as shown in (a) of this figure, when the bed temperature of the NSR catalyst 16 is 450 ° C., the NSR storage performance of the NSR catalyst 16 is high, but the amount of NH ₃ produced is small. . According to such a configuration, although the NOx purification rate of the SCR 18 is reduced due to the lack of NH ₃ , the NOx purification rate of the NSR catalyst 16 is high in this temperature range. As a result, the combination of the NSR catalyst and the SCR 18 A high NOx purification rate can be maintained.

On the other hand, as shown in (b) in the figure, when the bed temperature of the NSR catalyst 16 is 300 ° C., the amount of NH ₃ produced by the NSR catalyst 16 increases dramatically, but the NOx occlusion performance decreases. According to such a configuration, although the NOx purification rate of the NSR catalyst 16 is reduced, the NOx purification rate of the SCR 18 that is supplied with a large amount of NH ₃ is high. As in the case of 450 ° C., a high NOx purification rate can be maintained by the combination of the NSR catalyst and the SCR 18.

  Thus, according to the system of the present embodiment, even if the bed temperature of the NSR catalyst 16 is in the reference temperature range or a low temperature range lower than the reference temperature range, the NSR catalyst and the SCR 18 A high NOx purification rate can be realized by the combination. However, in a low temperature range of 250 to 350 ° C., a phenomenon (sulfur poisoning) in which sulfur components adhere to the NSR catalyst 16 is likely to occur. For this reason, it is preferable to control the bed temperature of the NSR catalyst 16 to a reference temperature range (for example, 450 ° C.) during normal lean operation.

(Characteristic operation of this embodiment)
Next, a characteristic operation of the system according to the present embodiment will be described with reference to FIG. As described above, in the system of the present embodiment, a high NOx purification rate can be realized by controlling the bed temperature of the NSR catalyst 16 during the lean operation to the reference temperature range. However, SCR 18 is susceptible to aging because zeolite is the main component. For this reason, if deterioration occurs in the SCR 18, it is assumed that the NOx purification rate of the entire system cannot be maintained high due to a decrease in the NOx purification rate of the SCR 18.

Therefore, in the system of the first embodiment, when it is determined that the SCR 18 has deteriorated, the bed temperature of the NSR catalyst 16 is controlled to a low temperature range. More specifically, when the total travel distance of the internal combustion engine 10 exceeds a predetermined reference distance, the exhaust heat recovery device 20 is turned on and the exhaust gas is circulated to the U-turn pipe 22 side. When the bed temperature of the NSR catalyst 16 is controlled to a predetermined low temperature range, the amount of NH ₃ produced in the NSR catalyst 16 increases dramatically. Thereby, since a large amount of NH3 can be supplied to the deteriorated SCR 18, it is possible to increase the NOx purification rate of the SCR 18.

  In addition, the NOx purification rate of the SCR changes with the change of the bed temperature. FIG. 4 is a diagram showing the relationship between the catalyst bed temperature of the SCR 18 and the NOx purification rate of the present embodiment. The dotted line in the figure indicates the NOx purification rate of the SCR 18 before deterioration, and the solid line in the figure indicates the NOx purification rate of the SCR 18 after deterioration. Also, (1) in the figure shows the SCR bed temperature when the bed temperature of the NSR catalyst 16 is controlled in the reference temperature range, and (2) in the figure shows the bed temperature of the NSR catalyst 16 in the low temperature range. The floor temperature of the SCR when controlled is shown.

  As shown in this figure, the SCR 18 composed of Cu-based zeolite has a high NOx purification rate in a relatively low temperature range. Therefore, if the bed temperature of the NSR catalyst 16 is reduced from the reference temperature range to the low temperature range, the reduction in the NOx purification rate due to the deterioration of the SCR 18 can be effectively suppressed. As described above, by reducing the bed temperature of the NSR catalyst 16 from the reference temperature range to the low temperature range, even if the NOx purification rate of the NSR catalyst 16 is reduced, the reduction of the NOx purification rate of the entire system is effectively suppressed. can do.

  Even when it is determined that the SCR 18 is deteriorated, it is assumed that a desired NOx purification rate can be satisfied, for example, when the internal combustion engine 10 is lightly loaded. Therefore, in the system according to the present embodiment, when the load of the internal combustion engine 10 is equal to or less than the predetermined reference load, even if it is determined that the SCR 18 has deteriorated, the floor of the NSR catalyst 16 The temperature may be controlled to the reference temperature range. Thereby, the sulfur poisoning resulting from the bed temperature fall of the NSR catalyst 16 can be suppressed effectively.

[Specific Processing in Embodiment 1]
Next, with reference to FIG. 5, the specific content of the process performed in this Embodiment is demonstrated. FIG. 5 is a flowchart of a routine in which the ECU 30 executes the bed temperature control of the NSR catalyst 16. Note that the routine shown in FIG. 5 is repeatedly executed during the lean operation of the internal combustion engine 10.

  In the routine shown in FIG. 5, it is first determined whether or not the SCR 18 has deteriorated (step 100). Specifically, it is determined whether or not the travel distance of the internal combustion engine 10 has reached a predetermined threshold value K. As the threshold value K, a preset value is used as a reference distance for determining that the SCR 18 has deteriorated to such an extent that the desired NOx purification rate cannot be maintained. As a result, when the mileage> threshold value K is not established, it is determined that the SCR 18 has not yet deteriorated and the desired NOx purification rate can be maintained by the combination of the NSR catalyst 16 and the SCR 18. Then, the process proceeds to the next step, and the exhaust heat recovery device 20 is controlled to be OFF (step 102). Here, specifically, the flow path switching valve 24 of the exhaust heat recovery device 20 is switched to a flow path that discharges to the exhaust passage 123 without going through the U-turn pipe 22. Thereby, the bed temperature of the NSR catalyst 16 is controlled to a predetermined reference temperature range (350 to 450 ° C.).

  On the other hand, if it is determined in step 100 that the travel distance> threshold value K is established, it is determined that the SCR 18 has already deteriorated, the process proceeds to the next step, and the load KL of the internal combustion engine 10 becomes the threshold value K. It is determined whether it is larger than '(step 104). As the threshold value K ′, a preset value is used as a reference load in which the deteriorated SCR 18 cannot maintain a desired NOx purification rate. As a result, when the establishment of KL> K ′ is not recognized, it is determined that the desired NOx purification rate can be maintained by the deteriorated SCR 18, the process proceeds to step 102, and the exhaust heat recovery device 20 is controlled to be turned off. Is done.

  On the other hand, if the establishment of KL> K ′ is recognized in step 104, it is determined that the desired NOx purification rate cannot be maintained due to the deteriorated SCR 18, and the routine proceeds to the next step, where the exhaust heat recovery device 20 Is controlled to be ON (step 108). Specifically, the flow path switching valve 24 of the exhaust heat recovery unit 20 is switched to a flow path that discharges to the exhaust passage 123 via the U-turn pipe 22. Thereby, the bed temperature of the NSR catalyst 16 is controlled to a low temperature range (250 to 350 ° C.) lower than a predetermined reference temperature range.

  As described above, according to the system of the present embodiment, when the SCR 18 deteriorates and the desired NOx purification rate cannot be maintained, the bed temperature of the NSR catalyst 16 is controlled from the reference temperature range to the low temperature range. Thereby, since the NOx purification rate of SCR18 can be raised, it becomes possible to maintain a NOx purification rate high with the combination of NSR catalyst 16 and SCR18.

  By the way, in the first embodiment described above, the deterioration determination of the SCR 18 is performed based on the total travel distance of the internal combustion engine 10. However, the method for determining the deterioration of the SCR 18 is not limited to this. For example, the total number of revolutions of the internal combustion engine 10 may be used as another parameter reflecting the degree of aging deterioration of the SCR 18. Alternatively, a NOx sensor, a temperature sensor, or the like may be provided to directly detect the presence or absence of deterioration.

  Moreover, in Embodiment 1 mentioned above, it is supposed that the apparatus comprised by the U turn pipe 22 and the flow-path switching valve 24 is used as the exhaust heat recovery device 20, However, The bed temperature of an NSR catalyst is made into reference | standard temperature range. For example, a method of changing the air-fuel ratio A / F or a method of retarding the ignition timing may be used as long as it can be switched between the low temperature range and the low temperature range.

  In Embodiment 1 described above, the charging efficiency KL is used as the load of the internal combustion engine 10, but the air amount Ga may be used instead of KL.

  In the first embodiment described above, the NSR catalyst 16 is the “NSR catalyst” in the first invention, the SCR 18 is the “SCR” in the first invention, and the exhaust heat recovery device 20 is the first invention. It corresponds to “floor temperature variable means” in the invention. In the first embodiment described above, the ECU 30 executes the process of step 100, so that the “deterioration determination means” in the first invention executes the processes of steps 102 and 104. The “control means” in the first invention is realized.

  In the first embodiment described above, the ECU 30 executes the process of step 104, so that the “engine load detecting means” in the second aspect of the invention executes the processes of steps 102 and 104. Thus, the “control means” in the second invention is realized.

Embodiment 2. FIG.
[Features of Embodiment 2]
Next, a second embodiment of the present invention will be described with reference to FIGS. The second embodiment can be realized by executing a routine shown in FIG. 7 to be described later using the system shown in FIG.

As described above, during normal lean operation, the exhaust heat recovery device 20 is turned off, and the bed temperature of the NSR catalyst 16 is controlled to be in the normal temperature range (350 to 450 ° C.). However, in such a temperature range, sulfur poisoning of the NSR catalyst 16 proceeds, so that the NOx purification performance and the NH ₃ generation performance gradually deteriorate.

Therefore, in such a system including the NSR catalyst 16 and the SCR 18, a regeneration process for desorbing the sulfur component adhering to the NSR catalyst 16 is executed at a predetermined cycle (for example, once every 3000 km). Thereby, the NOx purification performance and the NH ₃ generation performance of the NSR catalyst 16 can be periodically recovered. still. In the regeneration process, it is necessary to raise the bed temperature of the NSR catalyst 16 to about 700 ° C. and to expose the inside of the NSR catalyst 16 to a rich atmosphere, but various methods are already known for these operations. Therefore, detailed description thereof is omitted.

  FIG. 6 is a diagram showing the relationship between the travel distance and the NOx purification rate of the NSR catalyst 16. As shown in this figure, the NOx purification rate of the NSR catalyst 16 that has decreased with traveling can be recovered by the regeneration process of sulfur poisoning. However, the NOx purification rate of the NSR catalyst 16 has decreased immediately before the regeneration process is executed. For this reason, it is assumed that a high NOx purification rate cannot be realized by the combination of the NSR catalyst 16 and the SCR 18 at this time.

Therefore, in the system of the second embodiment, the bed temperature of the NSR catalyst 16 is controlled to a low temperature range immediately before the execution of the sulfur poisoning regeneration process of the NSR catalyst 16. More specifically, when the travel distance of the internal combustion engine 10 is the distance immediately before the travel distance for executing the regeneration process, the exhaust heat recovery device 20 is turned on and the exhaust gas is circulated to the U-turn pipe 22 side. I will do it. When the bed temperature of the NSR catalyst 16 is controlled to a predetermined low temperature range, the amount of NH ₃ produced in the NSR catalyst 16 increases dramatically. Thereby, since a large amount of NH3 can be supplied to the SCR 18, it is possible to effectively increase the NOx purification rate of the SCR 18 and effectively compensate for the decrease in the NOx purification rate of the NSR catalyst 16.

[Specific Processing in Embodiment 1]
Next, with reference to FIG. 7, the specific content of the process performed in this Embodiment is demonstrated. FIG. 7 is a flowchart of a routine in which the ECU 30 executes the bed temperature control of the NSR catalyst 16. Note that the routine shown in FIG. 7 is repeatedly executed during the lean operation of the internal combustion engine 10.

  In the routine shown in FIG. 7, first, it is determined whether or not the sulfur poisoning regeneration process of the NSR catalyst 16 is just prior to execution (step 200). Specifically, it is determined whether or not the travel distance of the internal combustion engine 10 is just before the travel distance for executing the sulfur poisoning regeneration process. As a result, when it is determined that it is not immediately before the execution of the sulfur poisoning regeneration process of the NSR catalyst 16, the NOx purification rate of the NSR catalyst 16 has not yet deteriorated, and a desired combination is obtained depending on the combination of the NSR catalyst 16 and the SCR 18. When it is determined that the NOx purification rate can be maintained, the process proceeds to the next step, and the exhaust heat recovery device 20 is controlled to be OFF (step 202). Here, specifically, the same processing as in step 102 is executed.

  On the other hand, if it is determined in step 200 that it is not immediately before the sulfur poisoning regeneration process of the NSR catalyst 16 is performed, it is determined that the NOx purification rate of the NSR catalyst 16 has decreased, and the next step is performed. Then, the exhaust heat recovery unit 20 is controlled to be ON (step 204). Here, specifically, the same processing as in step 108 is executed.

  Next, it is determined whether or not the sulfur poisoning regeneration process of the NSR catalyst 16 has been completed (step 206). As a result, when it is determined that the sulfur poisoning regeneration process of the NSR catalyst 16 has not been completed yet, it is determined that the NOx purification rate of the NSR catalyst 16 has not yet decreased, and the process of step 204 is performed. Repeatedly executed. On the other hand, if it is determined in step 206 that the sulfur poisoning regeneration process of the NSR catalyst 16 has been completed, it is determined that the NOx purification rate of the NSR catalyst 16 has recovered, the process proceeds to step 202, and the exhaust gas is exhausted. The heat recovery unit 20 is controlled to be OFF.

  As described above, according to the system of the present embodiment, the bed temperature of the NSR catalyst 16 is controlled from the reference temperature range to the low temperature range immediately before the sulfur poisoning regeneration process of the NSR catalyst 16 is executed. Is done. Thereby, since the NOx purification rate of the SCR 18 can be increased, it is possible to effectively compensate for the decrease in the NOx purification rate of the NSR catalyst 16.

  Incidentally, in Embodiment 2 described above, the exhaust heat recovery machine 20 is turned on immediately before the sulfur poisoning recovery process of the NSR catalyst 16 is executed. The opening degree of the flow path switching valve 24 of the exhaust heat recovery machine 20 may be gradually varied in accordance with the degree of decrease in the exhaust heat recovery machine 20. FIG. 8 is a diagram for explaining a modification of the system according to the second embodiment. As shown in FIG. 6 described above, during the period until the sulfur poisoning regeneration process is executed, the NOx purification rate of the NSR catalyst 16 decreases as the travel distance increases. Therefore, as shown in FIG. 8A, for example, in the period until the sulfur poisoning regeneration process is executed, the opening degree of the flow path switching valve 24 may be controlled to the ON side as the travel distance becomes longer. Good. Thereby, since the bed temperature of the NSR catalyst 16 can be varied linearly, as shown in FIG. 8 (as shown in FIG. 8B), it becomes possible to realize a high NOx purification rate by the combination of the NSR catalyst 16 and the SCR 18. .

  In the second embodiment described above, the ECU 30 executes the process of step 200, so that the “acquiring means” in the fifth aspect of the invention executes the processes of steps 402 and 206. The “second control means” in the fifth aspect of the present invention is realized.

10 Internal combustion engine
12 Exhaust passage 14 Start catalyst (SC)
16 NOx storage reduction catalyst (NSR catalyst)
18 NOx selective reduction catalyst (SCR)
20 Exhaust heat recovery device 22 U-turn pipe 24 Flow path switching valve 30 ECU (Electronic Control Unit)

Claims (8)

An exhaust purification device for an internal combustion engine capable of lean operation,
A NOx occlusion reduction catalyst (hereinafter referred to as NSR catalyst) disposed in the exhaust passage of the internal combustion engine;
A NOx selective reduction catalyst (hereinafter referred to as SCR) disposed downstream of the NSR catalyst;
Deterioration determining means for determining whether the SCR has deteriorated;
A bed temperature changing means capable of changing the bed temperature of the NSR catalyst;
When it is determined that the SCR is not deteriorated, the bed temperature of the NSR catalyst is controlled to a predetermined reference temperature range, and when it is determined that the SCR is deteriorated, Control means for varying the bed temperature of the NSR catalyst to a predetermined low temperature range lower than the reference temperature range;
An exhaust emission control device for an internal combustion engine, comprising: Further comprising engine load detecting means for detecting the engine load of the internal combustion engine,
The control means determines the bed temperature of the NSR catalyst in the reference temperature range when the deterioration determination means determines that the SCR has deteriorated and the engine load is equal to or higher than a predetermined reference load. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is variable from the low temperature range to the low temperature range.   The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the reference temperature range is a temperature range of 350 to 450 ° C, and the low temperature range is a temperature range of 250 to 350 ° C.   4. The deterioration determination unit according to claim 1, wherein the deterioration determining unit determines that the SCR has deteriorated when a total travel distance of the internal combustion engine exceeds a predetermined reference distance. The exhaust emission control device for an internal combustion engine according to claim 1. Obtaining means for obtaining information on the degree of deterioration of the NSR catalyst;
Degradation recovery processing means for performing degradation recovery processing of the NSR catalyst when the degradation degree of the NSR catalyst grasped by the information reaches a predetermined reference value;
Secondly, the bed temperature of the NSR catalyst is varied from the reference temperature range to the low temperature range by using the bed temperature variable means during a predetermined period before the deterioration recovery process by the deterioration recovery processing means is started. Control means,
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4, further comprising:   6. The exhaust gas purification apparatus for an internal combustion engine according to claim 5, wherein the acquisition means acquires a travel distance of the internal combustion engine as the information.   The said 2nd control means changes the bed temperature of the said NSR catalyst to the low temperature gradually according to the deterioration degree of the said NSR catalyst grasped | ascertained by the said information, The Claim 5 or 6 characterized by the above-mentioned. Exhaust gas purification device for internal combustion engine.   The exhaust purification device for an internal combustion engine according to any one of claims 5 to 7, wherein the deterioration recovery processing means is processing for recovering the NSR catalyst from sulfur poisoning.

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