JP2009281290A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifier for an internal combustion engine capable of effectively utilizing a NOx catalyst by supplying active oxygen to an upstream side of the storage reduction type NOx catalyst. <P>SOLUTION: This exhaust gas purifier for the internal combustion engine is provided with the storage reduction type NOx catalyst 21 arranged in an exhaust passage 15 of the internal combustion engine 10, an active oxygen supplying device 27 for supplying the active oxygen to the upstream side of the NOx catalyst 21, and a control means for controlling supply of the active oxygen by the active oxygen supplying device 27 based on a state of the NOx catalyst 21. The control means recovers HC poisoning of the NOx catalyst 21 by supplying the active oxygen by the active oxygen supplying device 27 before execution of reduction of NOx stored in the NOx catalyst 21. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine.

  As an exhaust gas purification device for an internal combustion engine, an NOx storage reduction catalyst (hereinafter referred to as “NSR catalyst”) is known. The NSR catalyst occludes NOx when the air-fuel ratio of the exhaust gas is lean. On the other hand, when a reducing agent is added to the exhaust gas, the NSR catalyst desorbs the stored NOx and performs reduction purification.

  Japanese Patent Application Publication No. 2005-538295 discloses a technique of adding ozone as an oxidizing aid immediately before the NSR catalyst. According to this technique, the nitrogen dioxide component in the exhaust gas flowing into the NSR catalyst can be increased. Nitrogen dioxide is well occluded by the NSR catalyst.

JP 2005-538295 A

  The NSR catalyst is useful as an exhaust gas purification device for a diesel engine or a lean burn engine. However, this technique is not necessarily completed and there is still room for improvement. For example, there are the following problems.

  In general, the NSR catalyst includes a noble metal catalyst and a NOx storage material. During NOx reduction, NOx desorbed from the NOx storage material reacts with the reducing agent by the action of the noble metal catalyst. However, when NOx is occluded, HC (unburned fuel component) may be adsorbed on the noble metal catalyst, reducing its activity. In such a case, when the reducing agent is added, there is a problem that a part of the NOx desorbed from the NOx storage material flows to the downstream side of the NSR catalyst without being purified.

  The present invention has been made in view of the above points, and by supplying active oxygen to the upstream side of the NOx storage reduction catalyst, exhaust gas of an internal combustion engine that can more effectively utilize the NOx catalyst. An object is to provide a purification device.

In order to achieve the above object, a first invention is an exhaust gas purification apparatus for an internal combustion engine,
An NOx storage reduction catalyst disposed in the exhaust passage of the internal combustion engine;
An active oxygen supply device for supplying active oxygen to the upstream side of the NOx catalyst;
Control means for controlling the supply of active oxygen by the active oxygen supply device based on the state of the NOx catalyst;
It is characterized by providing.

The second invention is the first invention, wherein
NOx reduction means for reducing NOx stored in the NOx catalyst by supplying a reducing agent to the NOx catalyst;
The control means includes means for supplying active oxygen by the active oxygen supply device before the reduction of NOx stored in the NOx catalyst is executed.

The third invention is the first invention, wherein
The control means includes
A slipping NOx determining means for determining the amount of NOx slipping downstream of the NOx catalyst;
Means for starting the supply of active oxygen or increasing the supply amount by the active oxygen supply device when it is determined that the amount of NOx passing through the downstream side of the NOx catalyst exceeds a predetermined value;
It is characterized by including.

Moreover, 4th invention is set in 1st invention,
The control means includes means for controlling the amount of NOx desorbed by reducing the amount of active oxygen supplied by the active oxygen supply device when desorbing NOx stored in the NOx catalyst. It is characterized by.

The fifth invention is the fourth invention, wherein
A second NOx catalyst disposed on the downstream side of the NOx catalyst and having a function of purifying NOx;
The control means controls the reduction amount of the active oxygen supply amount so that the amount of desorbed NOx becomes an amount that can be purified by the second NOx catalyst.

According to a sixth invention, in any one of the first to fifth inventions,
The active oxygen supply device supplies ozone as active oxygen.

  According to the first invention, the supply of active oxygen to the upstream side of the NOx catalyst can be controlled based on the state of the NOx storage reduction catalyst. Thereby, the NOx catalyst can be utilized more effectively by utilizing the characteristics of active oxygen. In addition, since the amount of active oxygen used can be appropriately controlled to a necessary and sufficient amount, the electric power necessary for generating active oxygen can be saved, which contributes to improvement in fuel efficiency.

  According to the second aspect of the present invention, active oxygen can be added to the upstream side of the NOx catalyst before NOx reduction is performed. By adding this active oxygen, HC adsorbed on the active point of the NOx catalyst can be removed, so that HC poisoning can be reliably recovered. For this reason, when a reducing agent is supplied to the NOx catalyst, NOx desorbed from the NOx catalyst can be reliably reacted with the reducing agent. For this reason, it can suppress reliably that unpurified NOx is discharge | released downstream of a NOx catalyst.

  According to the third invention, when it is determined that the amount of NOx passing through the downstream side of the NOx catalyst exceeds a predetermined value, the supply of active oxygen to the upstream side of the NOx catalyst is started or the supply amount is increased. it can. By adding active oxygen to the upstream side of the NOx catalyst, the NOx occlusion capacity can be expanded. Therefore, according to the third invention, a large amount of NOx can be stored in the NOx catalyst. Further, according to the third aspect of the invention, since the start of supply of active oxygen or the increase in supply amount can be controlled based on the amount of NOx that passes through, the use amount of active oxygen can be reduced. For this reason, electric power required for the production | generation of active oxygen can be reduced, and a fuel consumption performance can be improved.

  According to the fourth aspect of the present invention, when NOx occluded in the NOx catalyst is desorbed, the amount of NOx desorbed is controlled by decreasing the amount of active oxygen supplied to the upstream side of the NOx catalyst. Can do. According to the fourth aspect of the present invention, it is possible to reliably avoid a situation in which a large amount of NOx is desorbed from the NOx catalyst at a stretch so that the purification process cannot be completed. For this reason, it can suppress reliably that unpurified NOx is discharge | released in air | atmosphere.

  According to the fifth aspect of the invention, when NOx stored in the NOx catalyst is desorbed, the amount of NOx desorbed is an amount that can be purified by the second NOx catalyst disposed downstream of the NOx catalyst. Thus, the reduction amount of the active oxygen supply amount can be controlled. Therefore, it is possible to reliably avoid a situation in which a large amount of NOx is desorbed from the NOx catalyst at a stretch so that the second NOx catalyst cannot be completely purified. For this reason, it can suppress reliably that unpurified NOx is discharge | released in air | atmosphere.

  According to the sixth aspect of the present invention, the above effect can be exhibited more remarkably by using ozone as active oxygen.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration according to the first embodiment of the present invention. As shown in FIG. 1, the system of the present embodiment includes an internal combustion engine 10 that is used as a power source for a vehicle or the like. In the present embodiment, the internal combustion engine 10 is a four-cylinder compression ignition internal combustion engine (diesel engine) including four cylinders 13. The internal combustion engine 10 of this embodiment includes a turbocharger 19. The intake air compressed by the compressor of the turbocharger 19 flows into each cylinder 13 through the intake manifold 11. Each cylinder 13 is provided with a fuel injector 14 for injecting fuel directly into the cylinder. The high pressure fuel stored in the common rail 18 is supplied to each fuel injector 14. Fuel in a fuel tank (not shown) is pressurized by the supply pump 17 and supplied to the common rail 18. Exhaust gas discharged from each cylinder 13 joins at the exhaust manifold 12 and flows into the turbine of the turbocharger 19. The exhaust gas that has passed through the turbine flows through the exhaust passage 15.

  In the exhaust passage 15, a NOx storage reduction type NOx catalyst (hereinafter referred to as “NSR catalyst”) 21 is installed. The NSR catalyst 21 will be described later. An ozone supply nozzle 22 is installed on the upstream side of the NSR catalyst 21. The ozone supply nozzle 22 is provided with a plurality of ozone supply ports 23. An ozone generator 25 is connected to the ozone supply nozzle 22 via an ozone supply passage 24. In the configuration shown in the figure, the ozone supply nozzle 22 is disposed inside the casing 26 that houses the NSR catalyst 21 and on the front side (upstream side) of the NSR catalyst 21. In the present embodiment, the ozone generator 25, the ozone supply passage 24, and the ozone supply nozzle 22 constitute an ozone supply device 27.

  As the ozone generator 25, a mode in which ozone is generated while flowing dry air or oxygen as a raw material in a discharge tube to which a high voltage can be applied, or any other type can be used. The dry air or oxygen used as a raw material here is a gas taken from outside the exhaust passage 15, for example, a gas contained in the outside air.

According to the ozone supply device 27 as described above, ozone (O ₃ ) can be generated by the ozone generator 25, and this ozone can be injected from the ozone supply port 23 of the ozone supply nozzle 22. Thereby, ozone can be added to the exhaust gas on the upstream side of the NSR catalyst 21.

  A temperature sensor 28 that detects the temperature (bed temperature) of the NSR catalyst 21 and a NOx sensor 29 that detects the NOx concentration in the exhaust gas that has exited the NSR catalyst 21 are further installed in the exhaust passage 15.

  The system of the present embodiment further includes an ECU (Electronic Control Unit) 50. The ECU 50 includes a fuel injector 14, an ozone generator 25, a temperature sensor 28, a NOx sensor 29, a crank angle sensor 46, an air flow meter 47, an accelerator position sensor 48, and the like for controlling the internal combustion engine 10. The sensors and actuators are electrically connected.

FIG. 2 is a diagram illustrating a state in which NOx is occluded in the NSR catalyst 21. As shown in FIG. 2, the NSR catalyst 21 has, for example, a catalyst component in which a noble metal such as platinum Pt and a storage material capable of storing NOx are supported on the surface of alumina (Al ₂ O ₃ ). Yes. Examples of the occlusion material include at least one selected from an alkali metal such as potassium K, sodium Na, lithium Li, and cesium Cs, an alkaline earth such as barium Ba and calcium Ca, and a rare earth such as lanthanum La and yttrium Y. One can be used. In this specification, the term “occlusion” includes all concepts similar to “holding”, “adsorption”, “absorption”, and the like.

The storage material of the NSR catalyst 21 absorbs NOx by forming a nitrate such as Ba (NO ₃ ) ₂ , for example. The storage material can well absorb NO ₂ , NO ₃ or N ₂ O ₅ in NOx. On the other hand, most of NOx originally contained in the exhaust gas is NO (nitrogen monoxide). NO cannot be absorbed by the occlusion material as it is. Therefore, in the NSR catalyst 21, NO and oxygen O ₂ in the exhaust gas are reacted with each other by a noble metal catalyst such as Pt to convert to NO ₂ , and this NO ₂ is absorbed by the storage material (FIG. 2). reference).

  There is a limit to the amount of NOx that can be stored in the NSR catalyst 21. Therefore, in this system, before the NOx occlusion amount of the NSR catalyst 21 reaches the limit, NOx reduction control is executed to reduce and purify the occluded NOx by supplying a reducing agent to the NSR catalyst 21. .

The method for supplying the reducing agent to the NSR catalyst 21 is not particularly limited, and for example, any of the following methods can be employed.
(1) A method of injecting fuel as a reducing agent from the fuel injector 14 in an expansion stroke or an exhaust stroke (post injection).
(2) A method of injecting fuel as a reducing agent from a fuel addition valve (not shown) provided in the exhaust passage 15 (exhaust system fuel addition).
(3) A method in which the air-fuel ratio in the cylinder is greatly enriched from the normal time by performing a large amount of exhaust gas recirculation (EGR), and combustion is performed at a low temperature so as not to generate soot (low temperature rich combustion).

When the reducing agent is supplied to the NSR catalyst 21, the oxygen concentration in the NSR catalyst 21 decreases, so that NOx is desorbed from the storage material. Then, the desorbed NOx reacts with the reducing agent by the action of the noble metal catalyst. Thereby, NOx can be reduced and purified to N ₂ .

  However, when the reducing agent is supplied to the NSR catalyst 21, a part of the stored NOx may flow out to the downstream side of the NSR catalyst 21 without being purified. This is considered to be caused by HC poisoning described below. When the temperature of the NSR catalyst 21 is not sufficiently high, HC (unburned fuel component) that has not been completely purified while the NSR catalyst 21 is absorbing NOx is a precious metal that is an active point. May adsorb. When HC is adsorbed on the noble metal, the activity of the noble metal is inhibited. For this reason, when the reducing agent is supplied, NOx desorbed from the storage material cannot be sufficiently reacted with the reducing agent. As a result, it is considered that a part of NOx is released without being reduced.

Therefore, in this embodiment, when supplying the reducing agent to the NSR catalyst 21, prior to that, ozone is added to the upstream side of the NSR catalyst 21 by the ozone supply device 27, thereby recovering the HC poisoning of the noble metal. We decided to plan. FIG. 3 is a view for explaining a mechanism for recovering the HC poisoning of the noble metal of the NSR catalyst 21 by addition of ozone. The left diagram in FIG. 3 shows a state where noble metal HC poisoning occurs. Prior to supplying the reducing agent to the NSR catalyst 21, when ozone is added by the ozone supply device 27, ozone flows into the NSR catalyst 21 as shown in the center diagram in FIG. 3. Ozone has a strong oxidizing power. For this reason, this ozone easily reacts with HC adsorbed on the noble metal. By this reaction, HC is removed from the noble metal catalyst as CO, CO ₂ or H ₂ O, and HC poisoning is recovered. As a result, as shown in the diagram on the right side of FIG. 3, when the reducing agent is added to the NSR catalyst 21, the catalytic activity of the noble metal is sufficiently exerted, so that NOx desorbed from the occlusion material is used as the reducing agent. It can be reliably reacted and purified.

The present inventors performed the following test in order to confirm the effect of ozone addition before NOx reduction as described above. In this test, 3 grams of 1 mm square pellets composed of 100 grams of γAl ₂ O ₃ , 1 gram of Pt, and 0.2 moles of Ba were used as the catalyst. A model gas was passed through the catalyst at 200 ° C., and the NOx concentration in the catalyst downstream was measured. For 30 minutes after the start, NOx was occluded in the catalyst by flowing a model gas with a lean composition, and then the NOx was reduced and purified by switching to a model gas with a rich composition. The composition of the lean gas was 400 ppm NO, 10% O ₂ , 3% H ₂ O, and the rest N ₂ . The composition of the rich gas was 400 ppm NO, 1% CO, 3% H ₂ O, and the remaining N ₂ . Ozone was added for 1 minute before switching to rich gas (that is, before NOx reduction). As a comparative example, the same test was performed without adding this ozone.

  FIG. 4 is a diagram showing a test result when ozone addition before NOx reduction was not performed (comparative example). As shown in this figure, when the ozone addition before the NOx reduction is not performed, the NOx concentration in the catalyst downstream is temporarily significantly increased immediately after the start of the NOx reduction. This indicates that a part of the stored NOx was discharged without being purified.

  On the other hand, FIG. 5 is a figure which shows the test result at the time of implementing ozone addition before NOx reduction | restoration. As shown in this figure, when ozone addition before NOx reduction is performed, after the start of NOx reduction, the NOx concentration in the catalyst downstream immediately decreases without increasing. This indicates that the stored NOx is reliably purified without slipping downstream of the catalyst.

  From the results of the tests as described above, by adding ozone before NOx reduction, HC poisoning of precious metals can be reliably recovered, and unpurified NOx is released into the atmosphere during NOx reduction. It has become clear that this can be reliably suppressed.

  FIG. 6 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to perform ozone addition before NOx reduction. According to the routine shown in FIG. 6, it is first determined whether or not NOx reduction needs to be executed (step 100). In step 100, the determination can be made as follows, for example. The ECU 50 stores a map created by examining the relationship between the operating state (engine speed, load, etc.) of the internal combustion engine 10 and the amount of NOx discharged from the internal combustion engine 10 in advance. The ECU 50 calculates the total NOx inflow amount into the NSR catalyst 21 after the previous NOx reduction by sequentially integrating the NOx emission amount calculated based on the map. When the total NOx inflow amount reaches a predetermined reference value, it is determined that it is necessary to perform NOx reduction. Alternatively, when the NOx concentration detected by the NOx sensor 29, that is, the NOx concentration downstream of the NSR catalyst 21, exceeds a predetermined concentration, it may be determined that it is necessary to perform NOx reduction.

  If it is determined in step 100 that it is not necessary to perform NOx reduction, the following process does not need to be performed, and the process of this routine is terminated as it is. On the other hand, when it is determined that it is necessary to perform NOx reduction, ozone is first added to the upstream side of the NSR catalyst 21 by the ozone supply device 27 (step 102). Here, the ozone supply device 27 is driven so that ozone is added for a predetermined time or a predetermined amount. The ozone added here flows into the NSR catalyst 21, and the HC poisoning can be recovered by oxidizing and removing the HC adsorbed on the noble metal.

  When the ozone addition in step 102 is completed, NOx reduction is performed (step 104). That is, the reducing agent is supplied to the NSR catalyst 21 by a predetermined method such as post injection, exhaust system fuel addition, low temperature rich combustion, or the like. At this time, according to this embodiment, the HC poisoning of the noble metal is reliably recovered by the addition of ozone before the start of the NOx reduction. Therefore, the activity of the noble metal is sufficiently exhibited from the beginning of the NOx reduction. For this reason, NOx desorbed from the occlusion material can be reliably reacted with the reducing agent, and NOx can be reliably prevented from slipping downstream of the NSR catalyst 21 without being purified.

In the present embodiment, the internal combustion engine 10 is described as being of the compression ignition type, but the present invention can also be applied to a spark ignition type internal combustion engine. Further, the ozone supply device 27 of the present embodiment is configured to supply the ozone generated by the ozone generator 25 as it is into the exhaust passage 15, but in the present invention, ozone is generated and stored in advance. The stored ozone may be supplied into the exhaust passage 15 when necessary. In the present embodiment, ozone is added to the exhaust gas as active oxygen. However, in the present invention, other types of active oxygen (for example, O ⁻ , O ²⁻ , O ₂ ⁻⁾ are used instead of ozone. , O ₃ ⁻ , O _n ^−, etc.) may be added to the exhaust gas. The same applies to the embodiments described later.

  In the first embodiment described above, the ozone supply device 27 corresponds to the “active oxygen supply device” in the first invention. Further, when the ECU 50 executes the processing of the steps 100 and 102, the “control means” in the first and second inventions executes the processing of the step 104, and thereby the “NOx” in the second invention. Each “reducing means” is realized.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 7 and FIG. 8. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Simplify or omit. The present embodiment can be realized by causing the ECU 50 to execute a routine shown in FIG. 8 to be described later using the same hardware configuration (FIG. 1) as that of the first embodiment described above.

As a result of intensive studies to improve the performance of the NSR catalyst 21, the inventors of the present invention increase the amount of NOx that can be stored by storing NOx while adding ozone to the upstream side of the NSR catalyst 21. I found that I can do it. With respect to this finding, the present inventors conducted the following test. In this test, 3 grams of 1 mm square pellets composed of 100 grams of γAl ₂ O ₃ , 1 gram of Pt, and 0.2 moles of Ba were used as the catalyst. A model gas having a lean composition was passed through the catalyst at 200 ° C., and the NOx concentration in the catalyst downstream was measured. The composition of this model gas was 400 ppm NO, 10% O ₂ , 3% H ₂ O, and the rest N ₂ . From 30 minutes after the start, ozone was added by converting a part of O _{2 in} the model gas into ozone by discharge. The composition of the model gas after the start of ozone addition was 400 ppm NO, 1000 ppm ozone, 8.5% O ₂ , 3% H ₂ O and the rest N ₂ .

  FIG. 7 is a diagram showing the results of the above test, in which the solid line is the NOx concentration in the catalyst downstream, and the broken line is the ozone concentration in the model gas flowing into the catalyst. As shown in FIG. 7, after the test is started, the NOx concentration in the catalyst downstream increases. This is because, as the amount of NOx occluded in the catalyst approaches the limit, the equilibrium reaction that converts NOx to nitrate is less likely to proceed, so that NOx is less likely to be absorbed. However, when the addition of ozone is started, the NOx concentration in the catalyst downstream is rapidly reduced to near zero. This indicates that the NOx occlusion capacity of the catalyst was expanded by the addition of ozone, and NOx began to be well absorbed by the catalyst again.

The mechanism by which the storage capacity of the NSR catalyst 21 is expanded by the addition of ozone is not necessarily clear, but is estimated to be as follows. Since ozone has a strong oxidizing power, it has a high reactivity with NO, easily reacts with NO in the gas phase, and is oxidized to change to NO ₂ . Furthermore, a part of the NO ₂ reacts with ozone to generate NO ₃ , or NO ₂ and NO ₃ react to generate N ₂ O ₅ . Since NO ₃ and N ₂ O ₅ have a stronger action to advance the equilibrium reaction in the direction of forming nitrates than NO ₂ , the absorption of NOx into the storage material is further promoted. As a result, it is considered that the storage capacity of the NSR catalyst 21 is expanded.

  As described above, by adding ozone to the upstream side of the NSR catalyst 21, the storage capacity is expanded, and a larger amount of NOx can be stored in the NSR catalyst 21. Therefore, in order to reduce the amount of NOx that slips downstream of the NSR catalyst 21 as much as possible, it is desirable to cause the NSR catalyst 21 to store NOx while continuing the supply of ozone by the ozone supply device 27. However, when the amount of ozone used increases, a large amount of electric power is required to generate ozone, which may lead to deterioration in fuel efficiency.

  Therefore, in this embodiment, NOx is initially absorbed by the NSR catalyst 21 without adding ozone, and the addition of ozone is started when the amount of NOx passing through the NSR catalyst 21 exceeds a predetermined allowable value. It was. As a result, the NSR catalyst 21 can absorb a large amount of NOx while saving the amount of ozone used as much as possible.

  FIG. 8 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is executed when the NSR catalyst 21 is absorbing NOx without adding ozone. According to the routine shown in FIG. 8, it is first determined whether or not the amount of NOx passing through the NSR catalyst 21 (hereinafter referred to as “passing NOx amount”) exceeds a predetermined allowable limit (step 110). Specifically, it is determined whether or not the NOx concentration in the downstream of the NSR catalyst 21 detected by the NOx sensor 29 exceeds a predetermined value.

  As the NSR catalyst 21 continues to absorb NOx, the amount of slipping NOx gradually increases. If it is determined in step 110 that the NOx concentration at the outlet of the NSR catalyst 21 does not exceed the predetermined value, it can be determined that the amount of slipped NOx is still below the allowable limit. In this case, it is not yet necessary to start adding ozone, and the current execution of this routine is terminated as it is.

  On the other hand, if it is determined in step 110 that the NOx concentration at the outlet of the NSR catalyst 21 exceeds the predetermined value, it can be determined that the slip-through NOx amount has reached the allowable limit. Therefore, in this case, by adding the ozone supply device 27, the addition of ozone to the upstream side of the NSR catalyst 21 is started (step 112). When the addition of ozone is started, the storage capacity of the NSR catalyst 21 is expanded, so that the amount of slipping NOx can be reduced as shown in the test results of FIG. For this reason, absorption of NOx into the NSR catalyst 21 can be further continued.

  Thereafter, when NOx absorption into the NSR catalyst 21 is continued while ozone is added, the stored amount approaches the limit and the slip-through NOx amount increases again. As a result, when the slip-through NOx amount reaches the allowable limit again, the ozone supply amount by the ozone supply device 27 may be controlled to be increased, although omitted in the routine shown in FIG. According to the knowledge of the present inventor, the occlusion capacity of the NSR catalyst 21 can be further expanded as the amount of ozone added is increased. For this reason, by increasing the ozone addition amount, the slip-through NOx amount can be reduced again. Therefore, absorption of NOx into the NSR catalyst 21 can be further continued.

  In the routine shown in FIG. 8 described above, the determination of the slipping NOx amount is performed based on the output of the NOx sensor 29. However, in the present invention, the method of determining the slipping NOx amount is not limited to this. For example, the determination may be made by the following method. As the NSR catalyst 21 continues to absorb NOx, the slip-through NOx amount gradually increases. That is, the slip-through NOx amount correlates with the total NOx inflow amount into the NSR catalyst 21. Therefore, the total NOx inflow amount into the NSR catalyst 21 is calculated based on the operating state of the internal combustion engine 10 and the NOx emission amount map as described in the first embodiment, and the slipping NOx amount is estimated from the calculated value. You may do it.

  In the second embodiment described above, the ECU 50 executes the process of the routine shown in FIG. 8 so that the “control means” in the third invention executes the process of step 110 described above. The “passing NOx determining means” in the third invention realizes the “means for starting supply or increasing the supply amount” in the third invention by executing the processing of step 112 described above.

Embodiment 3 FIG.
Next, the third embodiment of the present invention will be described with reference to FIG. 9 to FIG. 11. The description will focus on the differences from the above-described embodiment, and the description of the same matters will be simplified. Or omit.

  As described in the second embodiment, by adding ozone to the upstream side of the NSR catalyst 21, the storage capability of the NSR catalyst 21 is expanded, and a large amount of NOx can be stored in the NSR catalyst 21. When a large amount of NOx is occluded in the NSR catalyst 21, if the NOx is desorbed all at once in order to reduce and purify the occluded NOx, the amount of desorbed NOx is too large and the reduction process is completed. There is a risk of not. For this reason, when desorbing NOx from the NSR catalyst 21 in which a large amount of NOx has been occluded, it is desirable to desorb NOx in several batches rather than desorbing NOx all at once.

As a result of continual research in view of the above matters, the present inventors have partially desorbed NOx occluded in the NSR catalyst 21 by reducing the amount of ozone added to the upstream side of the NSR catalyst 21. I found out that I can make it. The present inventors conducted the following tests regarding this finding. In this test, 3 grams of 1 mm square pellets composed of 100 grams of γAl ₂ O ₃ , 1 gram of Pt, and 0.2 moles of Ba were used as the catalyst. The catalyst was placed in a model gas stream, and the NOx concentration in the subsequent stream was measured. The temperature of the catalyst and model gas was 200 ° C., and the flow rate of the model gas was 15 liters per minute. The composition of the model gas was 200 ppm NO, 10% O ₂ , 3% H ₂ O and the remaining N ₂ , and a part of O ₂ was converted to ozone by discharge. After the catalyst was sufficiently occluded with NOx in this model gas stream, the ozone concentration was lowered and the change in the NOx concentration was recorded.

  FIG. 9 is a diagram showing the measurement results of the NOx concentration in the catalyst downstream and the ozone concentration in front of the catalyst in the above test. At the start point at the left end of the measurement data shown in FIG. 9, the catalyst is in a state of sufficiently storing NOx. As shown in FIG. 9, the ozone concentration was decreased twice from this state. Then, after the ozone concentration decreased, the NOx concentration in the catalyst downstream increased rapidly. This is presumably because when the amount of ozone flowing into the catalyst decreases, the stability of nitrate that has been increased by ozone decreases, so that part of the nitrate decomposes and NOx is desorbed.

  In the present embodiment, in view of the above findings, when NOx is desorbed from the NSR catalyst 21, the amount of NOx desorbed is controlled by reducing the amount of ozone added. FIG. 10 is a diagram showing a system configuration of the present embodiment. As shown in FIG. 10, in the system of the present embodiment, a selective catalytic reduction NOx catalyst (hereinafter referred to as “SCR catalyst”) 30 is installed downstream of the NSR catalyst 21. As the catalyst component of the SCR catalyst 30, for example, a material in which Fe is supported on the surface of zeolite can be preferably used. A reducing agent adder 31 for adding a reducing agent such as urea water is installed on the upstream side of the SCR catalyst 30. In the SCR catalyst 30, NOx can be reduced and purified by reacting the reducing agent added by the reducing agent adder 31 with NOx. The SCR catalyst 30 is provided with a temperature sensor 32 for detecting the bed temperature.

  In the present embodiment, for example, immediately after the internal combustion engine 10 is started, NOx is prevented from being released into the atmosphere when the temperatures of the NSR catalyst 21 and the SCR catalyst 30 are not sufficiently increased. Control like this. When the temperature of the NSR catalyst 21 or the SCR catalyst 30 is low, NOx is absorbed by the NSR catalyst 21 while ozone is added to the upstream side of the NSR catalyst 21 by the ozone supply device 27. At this time, the occlusion ability of the NSR catalyst 21 can be expanded by adding ozone, so that NOx can be absorbed by the NSR catalyst 21 for a long time. For this reason, during this time, the temperature of the SCR catalyst 30 can be sufficiently increased (to the activation temperature or higher). When the SCR catalyst 30 reaches the activation temperature or higher, NOx is desorbed from the NSR catalyst 21 by decreasing the amount of ozone added. The desorbed NOx can be purified by the SCR catalyst 30. In this case, if the amount of NOx desorbed from the NSR catalyst 21 is too large, the SCR catalyst 30 cannot completely purify the NOx. Therefore, when the ozone addition amount is decreased, the ozone reduction amount is adjusted so that the amount of NOx desorbed from the NSR catalyst 21 becomes an amount that can be purified by the SCR catalyst 30.

  FIG. 11 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. This routine is executed when NOx is absorbed by the NSR catalyst 21 while ozone is added to the upstream side of the NSR catalyst 21 by the ozone supply device 27. According to this routine, first, it is determined whether or not a condition for starting to desorb NOx from the NSR catalyst 21 (hereinafter referred to as “NOx desorption start condition”) is established (step 120).

  In the present embodiment, in step 120 described above, the success or failure of the NOx desorption start condition is determined based on the temperature of the SCR catalyst 30 detected by the temperature sensor 30. That is, when the temperature of the SCR catalyst 30 becomes equal to or higher than a predetermined activation temperature, NOx desorbed from the NSR catalyst 21 can be purified by the SCR catalyst 30, so it is determined that the NOx desorption start condition is satisfied. The On the other hand, when the temperature of the SCR catalyst 30 has not yet reached the activation temperature, it is determined that the NOx desorption start condition is not satisfied because the SCR catalyst 30 cannot purify NOx.

  If it is determined in step 120 that the NOx desorption start condition is satisfied, then, a target value of the NOx desorption amount is calculated (step 122). The target value of the NOx desorption amount corresponds to the amount of NOx that can be purified by the SCR catalyst 30. In the present embodiment, the target value of the NOx desorption amount is calculated based on the temperature of the SCR catalyst 30 and the like.

  Subsequently, control is performed to reduce the amount of ozone added by the ozone supply device 27 so that the amount of NOx corresponding to the target value calculated in step 122 is desorbed from the NSR catalyst 21 (step 124). In the present embodiment, the ECU 50 stores a map created by examining the relationship between the reduction amount of the ozone addition amount and the NOx desorption amount from the NSR catalyst 21 in advance. In step 124, a reduction amount of the ozone addition amount is calculated based on the map, and the ozone supply device 27 is controlled so that the reduction amount is realized.

  Following the processing of step 124, it is determined whether or not the current ozone addition amount is zero (step 126). In this step 126, when the ozone addition amount is not zero, the processing from step 122 onward is executed again. According to the control as described above, in the present embodiment, the ozone addition amount is reduced stepwise. Along with this, NOx stored in the NSR catalyst 21 can be desorbed stepwise. That is, it is possible to reliably prevent a large amount of NOx that cannot be completely processed by the SCR catalyst 30 from being desorbed at once. For this reason, NOx can be reliably suppressed from being released into the atmosphere without being purified.

  In the third embodiment described above, the SCR catalyst 30 corresponds to the “second NOx catalyst” in the fifth aspect of the invention. Further, the “control means” in the fourth and fifth aspects of the present invention is realized by the ECU 50 executing the routine processing shown in FIG.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows a mode that NOx is occluded by the NSR catalyst. It is a figure for demonstrating the mechanism which recovers HC poisoning of the noble metal of an NSR catalyst by ozone addition. It is a figure which shows the result of the test implemented in Embodiment 1 of this invention. It is a figure which shows the result of the test implemented in Embodiment 1 of this invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the result of the test implemented in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention. It is a figure which shows the result of the test implemented in Embodiment 3 of this invention. It is a figure for demonstrating the system configuration | structure of Embodiment 3 of this invention. It is a flowchart of the routine performed in Embodiment 3 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Intake manifold 12 Exhaust manifold 13 Cylinder 14 Fuel injector 15 Exhaust passage 17 Supply pump 18 Common rail 19 Turbocharger 21 NSR catalyst 22 Ozone supply nozzle 23 Ozone supply port 24 Ozone supply passage 25 Ozone generator 26 Casing 27 Ozone supply device 28 Temperature sensor 29 NOx sensor 30 SCR catalyst 31 Reductant adder 32 Temperature sensor 50 ECU

Claims (6)

An NOx storage reduction catalyst disposed in the exhaust passage of the internal combustion engine;
An active oxygen supply device for supplying active oxygen to the upstream side of the NOx catalyst;
Control means for controlling the supply of active oxygen by the active oxygen supply device based on the state of the NOx catalyst;
An exhaust gas purifying device for an internal combustion engine, comprising: NOx reduction means for reducing NOx stored in the NOx catalyst by supplying a reducing agent to the NOx catalyst;
2. The exhaust gas of an internal combustion engine according to claim 1, wherein the control means includes means for supplying active oxygen by the active oxygen supply device before the reduction of NOx stored in the NOx catalyst is executed. Gas purification device. The control means includes
A slipping NOx determining means for determining the amount of NOx slipping downstream of the NOx catalyst;
Means for starting the supply of active oxygen or increasing the supply amount by the active oxygen supply device when it is determined that the amount of NOx passing through the downstream side of the NOx catalyst exceeds a predetermined value;
The exhaust gas purification device for an internal combustion engine according to claim 1, comprising:   The control means includes means for controlling the amount of NOx desorbed by reducing the amount of active oxygen supplied by the active oxygen supply device when desorbing NOx stored in the NOx catalyst. The exhaust gas purifying device for an internal combustion engine according to claim 1. A second NOx catalyst disposed on the downstream side of the NOx catalyst and having a function of purifying NOx;
5. The internal combustion engine according to claim 4, wherein the control unit controls a reduction amount of the active oxygen supply amount so that the amount of desorbed NOx becomes an amount that can be purified by the second NOx catalyst. Engine exhaust gas purification device.   The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 5, wherein the active oxygen supply device supplies ozone as active oxygen.

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