JP2010025015A - Exhaust gas purifier for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely prevent deactivation of catalyst caused by hydrocarbon (HC) poisoning, as well as to reduce an influence on fuel consumption, regarding an exhaust gas purifier for internal combustion engine. <P>SOLUTION: The exhaust gas purifier includes a catalyst for exhaust emission purification, and a NOx sensor for detecting NOx concentrations of exhaust gas flowing out of the catalyst. An internal combustion engine switches between a lean operation to make exhaust air-fuel ratio larger than theoretical air-fuel ratio and a rich operation to make the exhaust air-fuel ratio equal to or smaller than the theoretical air-fuel ratio. ECU performs deactivation determination of catalysts based on values of the NOx sensor during the rich operation. If it is determined that a catalyst has been deactivated, the HC poisoning is resolved by supplying active oxygen to the catalyst. The supply of the active oxygen is performed during the lean operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  Japanese Patent Application Laid-Open No. 2007-154755 discloses an exhaust gas purification system for an internal combustion engine that includes a pre-stage catalyst having an oxidizing ability and a NOx catalyst arranged downstream thereof. In this system, based on the result of actually measuring the bed temperature of the front catalyst, it is determined whether or not the front catalyst is active, and the supply of the reducing agent is controlled based on the determination result. In this system, when it is determined that the pre-stage catalyst is not active, a catalyst activation process is performed to activate the pre-stage catalyst by raising the temperature. This catalyst activation treatment is selected from low temperature combustion operation, post injection, and exhaust fuel addition.

JP 2007-154755 A JP 2005-133656 A JP 2008-38890 A JP 2008-31927 A

  In the above conventional technology, the deactivation of the pre-stage catalyst is determined, but deactivation can also occur in the NOx catalyst. In addition, the catalyst is deactivated not only because the catalyst bed temperature is low, but also accompanied by HC poisoning. HC poisoning is a phenomenon in which the purification reaction is hindered as a result of exhaust gas not being able to come into contact with the active sites by liquefying HC, which is an unburned fuel component, and adhering (adsorbing) to the active sites (noble metals) of the catalyst. It is. When the catalyst is deactivated due to HC poisoning, the activity of the catalyst cannot be recovered unless HC attached to the active sites is removed.

  The present invention has been made to solve the above-described problems, and can effectively suppress the deactivation of the catalyst due to the HC poisoning, and has little influence on the fuel consumption. The purpose is to provide.

In order to achieve the above object, a first invention is an exhaust gas purification apparatus for an internal combustion engine,
An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine;
Deactivation determination means for determining deactivation of the catalyst;
Active oxygen supply means for supplying active oxygen for recovering the activity of the catalyst to the catalyst when the deactivation determination means determines that the catalyst is deactivated;
It is characterized by providing.

The second invention is the first invention, wherein
A detecting means for detecting a concentration of a predetermined component in the exhaust gas flowing out from the catalyst;
The deactivation determination unit performs deactivation determination based on a detection result of the detection unit.

The third invention is the second invention, wherein
The detection means is a NOx sensor that detects a NOx concentration.

Moreover, 4th invention is 2nd invention.
The detection means is an oxygen sensor that detects an oxygen concentration.

According to a fifth invention, in any one of the first to fourth inventions,
Switching means for switching between a lean operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is larger than the stoichiometric air-fuel ratio and a rich operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is less than the stoichiometric air-fuel ratio;
The deactivation determination unit performs deactivation determination during execution of the rich operation.

According to a sixth invention, in any one of the first to fifth inventions,
Switching means for switching between a lean operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is larger than the stoichiometric air-fuel ratio and a rich operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is less than the stoichiometric air-fuel ratio;
The active oxygen supply means supplies active oxygen to the catalyst during execution of the lean operation.

The seventh invention is the sixth invention, wherein
The active oxygen supply means supplies active oxygen to the catalyst in the second half of the lean operation period.

  According to the first aspect of the present invention, it is possible to determine the deactivation of the catalyst, and when it is determined that the catalyst is deactivated, active oxygen for recovering the activity of the catalyst can be supplied to the catalyst. By supplying active oxygen, HC poisoning of the catalyst can be quickly and reliably eliminated, and the activity of the catalyst can be recovered. For this reason, even in situations where the catalyst is easily poisoned by HC, such as immediately after the start of the internal combustion engine or during low-load operation, emission of harmful components to the atmosphere can be reliably suppressed. Further, according to the first invention, since active oxygen is supplied after determining the deactivation of the catalyst, the active oxygen can be used effectively without waste, and the amount of use can be reduced. Therefore, power consumption for generating active oxygen can be reduced, and adverse effects on fuel consumption can be minimized.

  According to the second invention, it is possible to detect the concentration of the predetermined component in the exhaust gas flowing out from the catalyst, and perform the deactivation determination based on the detection result. Thereby, the deactivation determination of the catalyst can be performed with higher accuracy.

  According to the third aspect, the deactivation determination can be performed based on the value of the NOx sensor that detects the NOx concentration in the exhaust gas flowing out from the catalyst. Thereby, the deactivation determination of the catalyst can be performed with higher accuracy.

  According to the fourth invention, the deactivation determination can be performed based on the value of the oxygen sensor that detects the oxygen concentration in the exhaust gas flowing out from the catalyst. Thereby, the deactivation determination of the catalyst can be performed with higher accuracy.

  According to the fifth aspect, the deactivation determination can be performed during execution of the rich operation. The influence of the catalyst deactivation on the exhaust gas component appears more greatly in the rich operation than in the lean operation. For this reason, the determination accuracy can be further improved by performing the deactivation determination during execution of the rich operation.

  According to the sixth aspect of the invention, when supplying active oxygen for recovering the activity of the catalyst, the supply can be performed during the execution of the lean operation. If active oxygen is supplied during the rich operation, the reducing atmosphere in the catalyst is returned to the oxidation direction, and the purification reaction may be hindered. According to the sixth aspect, by supplying active oxygen during the lean operation, it is possible to reliably prevent adverse effects on the purification reaction.

  According to the seventh aspect, when supplying active oxygen for recovering the activity of the catalyst, the supply can be performed in the latter half of the lean operation period. Thus, the rich operation is performed immediately after the HC adsorbed on the catalyst is removed. For this reason, the HC adsorption amount of the catalyst is extremely small, and the harmful component can be purified in a state where the original catalytic activity is sufficiently expressed, and particularly excellent purification efficiency can be obtained.

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 a compression ignition type internal combustion engine (diesel engine) 10 used as a power source for a vehicle or the like. Although the internal combustion engine 10 shown in FIG. 1 is an in-line four-cylinder type, the number of cylinders and the cylinder arrangement of the internal combustion engine are not particularly limited in the present invention. In FIG. 1, for convenience, the size of the exhaust passage is drawn larger than the actual size with respect to the size of the internal combustion engine 10.

  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 via the intake manifold 11. Each cylinder 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. The exhaust gas discharged from each cylinder 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 into the exhaust passage 15.

  A NOx storage reduction type NOx catalyst 21 is installed in the exhaust passage 15. The NOx catalyst 21 will be described later. An ozone supply nozzle 22 is installed on the upstream side of the NOx catalyst 21. The ozone supply nozzle 22 is provided with a plurality of ozone supply ports 23. The ozone supply nozzle 22 is connected to an ozone generator 25 through an ozone supply passage 24. In the illustrated configuration, the ozone supply nozzle 22 is disposed inside the casing 26 that houses the NOx catalyst 21 and on the front side (upstream side) of the NOx catalyst 21.

  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 above configuration, 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 NOx catalyst 21.

  A NOx sensor 29 that detects the NOx concentration in the exhaust gas flowing out from the NOx catalyst 21 is installed in the exhaust passage 15 on the downstream side of the NOx catalyst 21. The system of the present embodiment further includes an ECU (Electronic Control Unit) 50. The ECU 50 includes various sensors and actuators for controlling the internal combustion engine 10 such as the fuel injector 14, the ozone generator 25, the NOx sensor 29, the crank angle sensor 46, the air flow meter 47, and the accelerator position sensor 48. Are electrically connected.

  In the cylinder of the internal combustion engine 10 of this embodiment, combustion is usually performed at an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. Therefore, a large amount of oxygen usually remains in the exhaust gas of the internal combustion engine 10. As is well known, when a large amount of oxygen remains in the exhaust gas, NOx cannot be purified by a three-way reaction. Therefore, in the present embodiment, NOx contained in the exhaust gas is absorbed by the NOx catalyst 21 to suppress NOx emission into the atmosphere.

FIG. 2 is a diagram illustrating a state in which NOx is absorbed by the NOx catalyst 21. As shown in FIG. 2, the NOx catalyst 21 includes, for example, a noble metal such as platinum Pt and an occlusion material capable of occluding NOx (in this embodiment, barium Ba) on the surface of alumina (Al ₂ O ₃ ). It has a supported catalyst component. As the occlusion material, for example, alkali metal such as potassium K, sodium Na, lithium Li and cesium Cs, alkaline earth such as calcium Ca, rare earth such as lanthanum La and yttrium Y, and the like are used in addition to barium Ba. You can also. In this specification, the term “occlusion” includes all concepts similar to “holding”, “adsorption”, “absorption”, and the like.

The storage material of the NOx 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 NOx 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 NOx catalyst 21. For this reason, in this system, the control for temporarily setting the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 21 to be equal to or lower than the stoichiometric air-fuel ratio is executed intermittently (periodically). When the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 21 becomes equal to or lower than the stoichiometric air-fuel ratio, NOx is desorbed from the storage material, and the desorbed NOx and surplus fuel (reducing agent) react via the noble metal catalyst. NOx is reduced and purified to N ₂ .

  In the present specification, the above-described control, that is, the operation control for temporarily setting the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 21 to be equal to or lower than the stoichiometric air-fuel ratio (including when it is equal to the stoichiometric air-fuel ratio) is referred to as “rich operation”. Called. The operation control (that is, normal operation control) for making the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 21 larger than the stoichiometric air-fuel ratio is referred to as “lean operation”.

In the present embodiment, the method for performing the rich operation is not particularly limited. For example, any of the following methods can be employed.
(1) A method of additionally injecting fuel from the fuel injector 14 in the expansion stroke or the exhaust stroke (post injection).
(2) A method of adding fuel to exhaust gas from an exhaust fuel addition injector (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 by performing mass EGR (Exhaust Gas Recirculation), and combustion is performed at a low temperature so as not to generate soot (low temperature rich combustion).

  By the way, the timing for switching from lean operation to rich operation can be determined, for example, as follows. The ECU 50 stores a map created by examining in advance the relationship between the operating state of the internal combustion engine 10 (engine speed, load, etc.) and the amount of NOx discharged from the internal combustion engine 10. The ECU 50 calculates the integrated value of the NOx inflow amount to the NOx catalyst 21 by sequentially integrating the NOx emission amount calculated based on the map. When the integrated value reaches a predetermined threshold value, it is determined that it is necessary to perform NOx reduction by rich operation. In addition, the determination method of the timing which performs rich operation is not limited to the above. For example, in the present embodiment, when the NOx concentration detected by the NOx sensor 29 exceeds a predetermined concentration, it may be determined that it is necessary to execute the rich operation.

  As described above, in both cases where the NOx catalyst 21 absorbs NOx in the lean operation and NOx of the NOx catalyst 21 is reduced in the rich operation, the noble metal catalyst (hereinafter referred to as “active” in the NOx catalyst 21. The catalyst activity is sometimes required. However, when the exhaust gas temperature is low, such as immediately after starting the internal combustion engine 10 or during low load operation, the HC flowing into the NOx catalyst 21 is liable to be liquefied, and the liquefied HC is adsorbed (attached) to the active point. May end up. This phenomenon is generally called “HC poisoning”. When HC poisoning occurs, contact between the active sites and the exhaust gas is hindered, so that the original catalytic activity cannot be obtained. The fact that the original catalytic activity cannot be obtained is referred to as “deactivation” in the present specification. If the NOx catalyst 21 is deactivated, NOx absorption during lean operation and NOx reduction during rich operation cannot be performed efficiently, and the amount of harmful components discharged into the atmosphere increases.

Therefore, in this embodiment, when it is determined that the NOx catalyst 21 is deactivated due to HC poisoning, ozone is supplied into the NOx catalyst 21 to eliminate the HC poisoning and to increase the catalytic activity. It was decided to recover. FIG. 3 is a diagram showing a mechanism for recovering HC poisoning of the NOx catalyst 21 by adding ozone. Ozone has a strong oxidizing power. For this reason, the ozone supplied to the NOx catalyst 21 easily reacts with the HC adsorbed on the active sites, and can oxidize the HC quickly and reliably. That is, as shown in FIG. 3, by supplying ozone to the NOx catalyst 21, HC adsorbed on the active sites is quickly oxidized by ozone and removed as CO, CO ₂ or H ₂ O. Thereby, HC poisoning of the NOx catalyst 21 is eliminated, and the catalyst activity can be recovered.

The present inventors performed the following test in order to confirm the effect of HC poisoning recovery by adding ozone as described above.
(HC poisoning test)
As a catalyst sample, 2 grams of pellets made of Pt / γ alumina were used. First, in order to poison this catalyst sample with HC, a model gas containing HC was flowed to the catalyst sample. The gas conditions at this time are as follows.
Total gas flow: 15L / min
Gas composition: C ₃ H ₆ 1000 ppm, N ₂ balance Temperature: 100 ° C.

  FIG. 4 is a diagram comparing the HC concentration of the inlet gas upstream of the catalyst sample and the HC concentration of the outlet gas downstream of the catalyst sample in the HC poisoning test. As shown in this figure, the HC concentration of the exit gas is lower than that of the entrance gas. This reduced amount of HC is adsorbed on the catalyst sample. By such an HC poisoning test, the catalyst sample was brought into an HC poisoning state.

(HC purification performance evaluation test)
Next, a model gas containing HC was passed through the catalyst sample that became HC poisoned by the above treatment, and the HC purification performance was evaluated. The gas conditions at this time are as follows.
Total gas flow: 15L / min
Gas composition: C ₃ H ₆ 1000 ppm, O ₂ 8%, N ₂ balance Temperature conditions: 100 ° C. to 500 ° C. (heating rate 50 ° C. per minute)

  The HC purification performance evaluation test was performed twice, and once, ozone was added at a rate of 1000 ppm for 1 minute from the start of the evaluation. 5 and 6 are diagrams showing the test results. FIG. 5 shows the relationship between the gas temperature and the HC concentration downstream of the catalyst sample, and FIG. 6 shows the gas temperature when the HC purification rate is 50%. As shown in these figures, in the case where ozone was added, excellent HC purification performance was obtained even at a low temperature compared to the case where ozone was not added. From such a test result, it became clear that HC poisoning can be surely eliminated and the original catalytic activity can be restored by supplying ozone to the catalyst poisoned by HC.

  By the way, in order to generate ozone in the ozone generator 25, electric power is required. In the system of the present embodiment, a battery (not shown) is charged by driving a generator (not shown) in the internal combustion engine 10, and electric power is supplied from the battery to the ozone generator 25. Therefore, when the power consumption in the ozone generator 25 increases, the fuel consumption of the internal combustion engine 10 is adversely affected. For this reason, from the viewpoint of improving the fuel efficiency of the internal combustion engine 10, it is desirable to effectively use ozone without waste. In order to effectively use ozone without waste, it is important to accurately determine whether ozone supply is necessary, that is, whether the NOx catalyst 21 is deactivated due to HC poisoning. In view of such points, in the present embodiment, it is determined whether the NOx catalyst 21 is deactivated based on the value of the NOx sensor 29 that detects the NOx concentration downstream of the NOx catalyst 21.

  FIG. 7 is a graph showing a change in the value of the NOx sensor 29 when the internal combustion engine 10 repeats the lean operation and the rich operation. The value of the NOx sensor 29 represents the NOx concentration on the downstream side of the NOx catalyst 21. In FIG. 7, a broken line waveform indicates a case where the NOx catalyst 21 is deactivated due to HC poisoning, and a solid line waveform indicates a case where the NOx catalyst 21 is normal.

  During the execution of the lean operation, the amount of NOx stored in the NOx catalyst 21 gradually increases and approaches the limit. Along with this, the amount of NOx passing through the NOx catalyst 21 gradually increases. For this reason, as shown in FIG. 7, during the lean operation, the NOx concentration on the downstream side of the NOx catalyst 21 gradually increases.

As described above, in order for NO emitted from the internal combustion engine 10 to be absorbed by the NOx catalyst 21, NO is reacted with O ₂ and converted to NO ₂ by the activity of the noble metal catalyst in the NOx catalyst 21. is necessary. When the NOx catalyst 21 is deactivated due to HC poisoning, NO cannot be sufficiently converted to NO ₂ . For this reason, as shown in FIG. 7, when the NOx catalyst 21 is deactivated, more NOx passes through the NOx catalyst 21 than when it is normal.

  When the lean operation is switched to the rich operation and the reducing agent flows into the NOx catalyst 21, NOx is released from the NOx catalyst 21, and the reducing agent and NOx react via the noble metal catalyst, thereby purifying NOx. Therefore, as shown in FIG. 7, when the noble metal catalyst is active, the NOx concentration on the downstream side of the NOx catalyst 21 rapidly decreases after switching to the rich operation.

  However, when the NOx catalyst 21 is deactivated due to HC poisoning, even if the reducing agent flows into the NOx catalyst 21, NOx cannot sufficiently react with the reducing agent. For this reason, as shown in FIG. 7, when the NOx catalyst 21 is deactivated, the NOx concentration downstream of the NOx catalyst 21 during the rich operation is significantly higher than that during normal operation.

  Therefore, in this embodiment, the deactivation of the NOx catalyst 21 is determined based on the value of the NOx sensor 29 during the rich operation. There is a difference in the value of the NOx sensor 29 between when the NOx catalyst 21 is normal and when it is deactivated. As shown in FIG. 7, the difference is larger during the rich operation than during the lean operation. Therefore, the determination accuracy can be made higher when the deactivation determination is performed during the rich operation than when the deactivation determination is performed during the lean operation.

  If it is determined that the NOx catalyst 21 is deactivated, ozone is supplied to the NOx catalyst 21 in order to eliminate HC poisoning and restore the original activity. This ozone supply is preferably performed during lean operation rather than during rich operation. This is because if ozone is supplied during the rich operation, the reducing agent in the NOx catalyst 21 is consumed by the ozone, leading to a reduction in NOx reduction efficiency.

  In addition, ozone supply is more preferably performed in the latter half of the lean operation period, and most preferably in the final stage of the lean operation period. By doing so, since the rich operation is performed immediately after the HC adsorbed on the active sites is removed by the supply of ozone, NOx reduction can be performed in a state where the amount of HC adsorbed on the active sites is very small. Therefore, the original medium activity can be expressed more reliably, and particularly excellent NOx reduction efficiency can be obtained.

  Therefore, in this embodiment, when ozone is supplied to the NOx catalyst 21 in order to recover HC poisoning, the supply is performed at the end of the lean operation period. That is, in the present embodiment, the deactivation determination of the NOx catalyst 21 is executed during the rich operation (the timing indicated by the arrow A in FIG. 7), and if it is determined that the NOx catalyst 21 is deactivated, It was decided to supply ozone at the end of the lean operation period (timing indicated by arrow B in FIG. 7).

[Specific Processing in Embodiment 1]
FIG. 8 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the above function. According to the routine shown in FIG. 8, it is first determined whether or not the rich operation is being executed (step 100). In the present embodiment, as described above, the deactivation determination of the NOx catalyst 21 is performed during execution of the rich operation. For this reason, when the rich operation is not being executed in step 100, that is, when the lean operation is being executed, the system waits for switching to the rich operation.

If it is determined in step 100 that the rich operation is being performed, the deactivation determination of the NOx catalyst 21 is performed (step 102). In step 102, first, the value N of the NOx sensor 29 is read. The ECU 50 stores a determination value N ₀ in advance. The determination value N ₀ is the value of the upper limit NOx sensor 29 that can determine that the NOx catalyst 21 is normal (not deactivated). In step 102, the determination value N ₀ is compared with the read sensor value N. As a result, when N ≦ N ₀ , it can be determined that the NOx catalyst 21 is not deactivated. In this case, since it is not necessary to supply ozone to the NOx catalyst 21, the addition of ozone from the ozone supply port 23 is prohibited (step 104).

On the other hand, if N> N ₀ in step 102, it can be determined that the NOx catalyst 21 is deactivated. In this case, it is necessary to supply ozone in order to eliminate HC poisoning of the NOx catalyst 21. In the present embodiment, as described above, ozone is supplied at the end of the lean operation period. Therefore, in this case, it waits for switching to the lean operation, and further determines whether or not the end of the lean operation period has come (step 106). As described above, in the present embodiment, the integrated value of the NOx inflow amount to the NOx catalyst 21 is calculated, and the rich operation is executed when the integrated value reaches a predetermined threshold value. Therefore, in step 106, it is possible to determine the end of the lean operation period by determining whether or not the integrated value of the NOx inflow amount has approached the threshold value.

  If it is determined in step 106 that the end of the lean operation period has come, ozone supply to the NOx catalyst 21 is executed (step 108). That is, a process for operating the ozone generator 25 is performed so that ozone is added from the ozone supply port 23.

  According to the routine processing shown in FIG. 8 described above, it is possible to reliably suppress the NOx catalyst 21 from being deactivated by HC poisoning. For this reason, it can suppress reliably that the harmful | toxic component in exhaust gas passes through the NOx catalyst 21, and is discharged | emitted in air | atmosphere. Further, the deactivation of the NOx catalyst 21 can be determined with high accuracy, and ozone can be supplied when it is deemed necessary. For this reason, since ozone can be effectively utilized without waste, the power consumed for ozone generation can be reduced, and adverse effects on fuel consumption can be minimized.

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. In the present embodiment, the case where the deactivation determination and the activity recovery process are performed on the NOx catalyst 21 has been described. However, the catalyst targeted in the present invention is not limited to this, and the oxidation catalyst, the ternary It may be a catalyst or the like. In the present embodiment, the deactivation determination is performed during execution of the rich operation. However, in the present invention, the deactivation determination may be performed during execution of the lean operation. In the present embodiment, the ozone generated by the ozone generator 25 is added to the exhaust gas as it is. However, in the present invention, ozone is generated and stored in advance, and the stored ozone is stored. May be added to the exhaust gas when necessary. In the present embodiment, the ozone generator 25 is outside the exhaust gas flow path. However, the present invention is not limited to this configuration, and the ozone generator may be in the exhaust gas flow path. In other words, ozone may be generated by discharging by applying a high voltage in the exhaust gas flow path. In the present embodiment, ozone is supplied as the active oxygen into the exhaust gas. 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 supplied to the exhaust gas.

  In the first embodiment described above, the NOx catalyst 21 is the “catalyst” in the first invention, NOx is the “predetermined component” in the second invention, and the NOx sensor 29 is the “detection” in the second invention. It corresponds to “means”. Further, when the ECU 50 executes the process of step 102, the “deactivation determination means” in the first and fifth aspects of the invention executes the process of step 108, so that the first, sixth and sixth steps are executed. The “switching means” according to the fifth or sixth invention is configured such that the “active oxygen supply means” in the seventh invention switches between lean operation and rich operation (post injection, exhaust fuel addition, low temperature rich combustion, etc.), Each is realized.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIG. 9. The description will focus on the differences from the first embodiment described above, and the same matters will be simplified or described. Omitted.

  In this embodiment, it is assumed that an oxygen sensor capable of detecting the oxygen concentration in the exhaust gas is provided in place of the NOx sensor 29 of the first embodiment. The hardware configuration other than this point is the same as that of the first embodiment. Therefore, illustration of the hardware configuration is omitted, and reference numeral 29 in FIG. 1 is an oxygen sensor in the present embodiment.

  The present embodiment is the same as the first embodiment described above except that the method for determining the deactivation of the NOx catalyst 21 is different. In the present embodiment, it is determined whether the NOx catalyst 21 is deactivated based on the value of the oxygen sensor 29 during the rich operation.

  FIG. 9 is a graph showing a change in the value of the oxygen sensor 29 when the internal combustion engine 10 repeats the lean operation and the rich operation. The value of the oxygen sensor 29 represents the oxygen concentration on the downstream side of the NOx catalyst 21. In FIG. 9, the broken line graph shows a case where the NOx catalyst 21 is deactivated due to HC poisoning, and the solid line graph shows a case where the NOx catalyst 21 is normal.

  During execution of the lean operation, exhaust gas leaner than the stoichiometric air-fuel ratio flows into the NOx catalyst 21. Therefore, a large amount of oxygen remains in the exhaust gas flowing out from the NOx catalyst 21. For this reason, as shown in FIG. 9, during the execution of the lean operation, the value of the oxygen sensor 29 is maintained at a high value.

  On the other hand, during execution of the rich operation, exhaust gas richer than the stoichiometric air-fuel ratio, that is, exhaust gas containing a reducing agent (surplus fuel) flows into the NOx catalyst 21. For this reason, almost all of the oxygen remaining in the exhaust gas is consumed by reacting with the reducing agent via the noble metal catalyst of the NOx catalyst 21. Therefore, when the NOx catalyst 21 is normal (when HC is not poisoned), as shown in FIG. 9, when the rich operation is switched, the value of the oxygen sensor 29 is greatly reduced. On the other hand, when the noble metal catalyst of the NOx catalyst 21 is deactivated due to HC poisoning, oxygen does not sufficiently react with the reducing agent, and oxygen flows out downstream of the NOx catalyst 21. For this reason, as shown in FIG. 9, the value of the oxygen sensor 29 is larger than that in the normal state.

Therefore, in this embodiment, the deactivation of the NOx catalyst 21 is determined based on the value of the oxygen sensor 29 during the rich operation. The specific processing of this embodiment is almost the same as that of the first embodiment. That is, in the present embodiment, the ECU 50 stores the determination value O ₀ in advance. This determination value O ₀ is a value of the upper limit oxygen sensor 29 at which it can be determined that the NOx catalyst 21 is normal (not deactivated). In this embodiment, the value O of the oxygen sensor 29 is read at a position corresponding to step 102 of the routine shown in FIG. 8 described above, and the read sensor value O is compared with the determination value O ₀ . As a result, when O ≦ O _0, it is determined that the NOx catalyst 21 is not deactivated, and when O> O _0, it is determined that the NOx catalyst 21 is deactivated.

Since the specific processing of this embodiment is the same as that of Embodiment 1 except for the above points, further description is omitted. In the second embodiment described above, oxygen (O ₂ ) corresponds to the “predetermined component” in the second invention, and the oxygen sensor 29 corresponds to the “detecting means” in the second invention. In the present embodiment, an air-fuel ratio sensor can be used instead of the oxygen sensor 29.

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 absorbed by a NOx catalyst. It is a figure which shows the mechanism in the case of recovering HC poisoning by ozone addition. It is a figure which shows the result of HC poisoning test. It is a figure which shows the result of HC purification performance evaluation test. It is a figure which shows the result of HC purification performance evaluation test. It is a graph which shows the change of the value of a NOx sensor. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a graph which shows the change of the value of an oxygen sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Intake manifold 12 Exhaust manifold 14 Fuel injector 15 Exhaust passage 17 Supply pump 18 Common rail 19 Turbocharger 21 NOx catalyst 22 Ozone supply nozzle 23 Ozone supply port 24 Ozone supply passage 25 Ozone generator 26 Casing 28 Temperature sensor 29 NOx sensor (Oxygen sensor)
50 ECU

Claims (7)

An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine;
Deactivation determination means for determining deactivation of the catalyst;
Active oxygen supply means for supplying active oxygen for recovering the activity of the catalyst to the catalyst when the deactivation determination means determines that the catalyst is deactivated;
An exhaust gas purifying device for an internal combustion engine, comprising: A detecting means for detecting a concentration of a predetermined component in the exhaust gas flowing out from the catalyst;
2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the deactivation determination unit performs deactivation determination based on a detection result of the detection unit.   3. The exhaust gas purifying device for an internal combustion engine according to claim 2, wherein the detecting means is a NOx sensor that detects a NOx concentration.   The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the detecting means is an oxygen sensor for detecting an oxygen concentration. Switching means for switching between a lean operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is larger than the stoichiometric air-fuel ratio and a rich operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is less than the stoichiometric air-fuel ratio;
The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 4, wherein the deactivation determination means performs deactivation determination during execution of the rich operation. Switching means for switching between a lean operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is larger than the stoichiometric air-fuel ratio and a rich operation in which the air-fuel ratio of the exhaust gas flowing into the catalyst is less than the stoichiometric air-fuel ratio;
6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the active oxygen supply means supplies active oxygen to the catalyst during execution of the lean operation.   The exhaust gas purification device for an internal combustion engine according to claim 6, wherein the active oxygen supply means supplies active oxygen to the catalyst in the second half of the lean operation period.

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