JP4867655B2 - 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.

  Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-89246, an exhaust gas purification device having a NOx trapping catalyst is known. In the above-described conventional technique, a substance capable of adsorbing NOx (hereinafter also referred to as NOx adsorbing substance) and a substance capable of being occluded (hereinafter also referred to as NOx occlusion substance) are provided in the exhaust passage of the internal combustion engine together with the catalyst. ing. In such a configuration, NOx in the exhaust gas is trapped by the NOx trapping catalyst in a lean atmosphere. In the rich atmosphere, the trapped NOx is reduced and decomposed.

In order for the above reaction to be carried out smoothly, it is desirable that the catalyst reaches the activation temperature and sufficiently exhibits its activity function. However, when the internal combustion engine is started, the catalyst temperature is low. Therefore, in the conventional exhaust gas purification device, ozone (O ₃ ) is added to the exhaust gas when the internal combustion engine is started in order to cope with this.

The NOx trapping reaction occurs more actively in an atmosphere rich in NO ₂ than in an atmosphere rich in NO. By adding ozone, NO in the exhaust gas can be oxidized, and the amount of NO ₂ can be increased. Thus, according to the above-described conventional technique, even when the catalyst is not in a sufficiently active state, such as when the internal combustion engine is started, NO ₂ flowing into the NOx trapping catalyst is increased to efficiently capture NOx, and exhaust gas Gas purification can be performed effectively.

JP 2002-89246 A JP-A-5-192535 JP 2005-538295 A JP-A-6-185343 JP-A-10-169434 Japanese Patent No. 3551346

  The conventional NOx trapping catalyst includes a catalyst and a NOx occlusion material, and these are integrally formed. Such a NOx trapping catalyst tends to have a lower exhaust gas purification capacity (capability to purify NOx, HC, CO) of the catalyst than a conventional three-way catalyst that does not contain NOx occlusion substances. There is a problem that the function is hindered.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an exhaust gas purification device for an internal combustion engine that can perform NOx occlusion reduction without interfering with the exhaust gas purification function of the catalyst. And

In order to achieve the above object, a first invention is an exhaust gas purification apparatus for an internal combustion engine,
A NOx holding material disposed in an exhaust passage of the internal combustion engine;
A three-way catalyst disposed downstream of the NOx holding material;
Ozone supply means for supplying ozone (O ₃ ) so as to be mixed with the exhaust gas flowing into the NOx holding material;
Ozone supply control means for suppressing or stopping ozone supply by the ozone supply means when the temperature of the three-way catalyst is equal to or higher than an activation temperature capable of purifying exhaust gas;
It is characterized by providing.

The second invention is the first invention, wherein
An ozone decomposition catalyst containing an ozone decomposition substance is provided downstream of the NOx holding material and upstream of the three-way catalyst.

The third invention is the second invention, wherein
The ozonolysis material includes palladium (Pd).

The fourth invention is the first to third invention,
The three-way catalyst includes platinum (Pt) or rhodium (Rh).

The fifth invention is the first to fourth inventions,
An exhaust gas sensor disposed downstream of the three-way catalyst;
The first injection amount control means for controlling the fuel injection amount of the internal combustion engine by open loop control and the output of the exhaust gas sensor is fed back to the fuel injection amount so that the exhaust gas flowing out from the three-way catalyst becomes the stoichiometric air-fuel ratio. A second injection amount control means for controlling the fuel injection amount by closed loop control;
The fuel injection amount control by the first injection amount control means is executed during the ozone supply by the ozone supply means, and when the ozone supply by the ozone supply means is stopped, the fuel injection amount control of the internal combustion engine is controlled by the first injection amount. Injection amount control switching means for switching from control by the control means to control by the second injection amount control means;
It is characterized by providing.

According to the first aspect of the present invention, the NOx holding material and the three-way catalyst are individually arranged, so that the exhaust gas purification function can be satisfactorily exhibited. The NOx occlusion substance is considered to be a catalyst poison for the catalyst (noble metal element), and is a factor that lowers the exhaust gas purification ability of the catalyst in the NOx trapping catalyst. According to the first invention, the NOx holding material and the catalyst are arranged separately, and the NOx occlusion reaction is promoted without relying on the catalyst by the ozone supply means, so that the NOx occlusion substance becomes a catalyst poison. The NOx occlusion and reduction can be performed while avoiding the exhaust gas purification function of the catalyst sufficiently. In addition, ozone can be used efficiently by reducing or reducing the amount of ozone used when the temperature at which the purification ability of the catalyst is exhibited.

  According to the second invention, after decomposing ozone in the gas downstream of the NOx holding material, the gas can be flowed into the three-way catalyst. When ozone flows into the catalyst, it is considered that the noble metal used in the catalyst is oxidized by ozone, which may affect its active function. According to the second invention, since ozone can be decomposed upstream of the catalyst, the influence of ozone on the exhaust gas purification capacity of the catalyst can be suppressed.

  According to 3rd invention, the fall of the exhaust gas purification ability resulting from ozone can be prevented more effectively by including palladium in an ozonolysis catalyst.

  According to the fourth aspect of the invention, Pt or Rh, which has a relatively high NOx purification capacity but is affected by oxidation by ozone, can be included in the three-way catalyst while avoiding the influence.

According to the fifth aspect of the present invention, it is possible to appropriately adjust the air-fuel ratio of the exhaust gas and maintain good emission characteristics even under the situation where the NOx occluded in the NOx holding material is affected.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram for explaining an exhaust gas purification apparatus according to Embodiment 1 of the present invention. As shown in FIG. 1, the exhaust gas purification apparatus of Embodiment 1 has a catalyst device 20 in the exhaust passage 12 of the internal combustion engine 10. The catalyst device 20 houses a NOx holding material 24 therein.

The NOx holding material 24 is configured by supporting BaCO ₃ as a NOx storage material on a ceramic carrier. BaCO ₃ has a function of storing NOx in the exhaust gas as nitrate, that is, Ba (NO ₃ ) ₂ . According to such a configuration, when the exhaust gas is in a lean atmosphere, the exhaust gas is occluded when passing through the NOx holding material 24 and then flows downstream. In addition, when the exhaust gas is rich or at a high temperature, the stored Ba (NO ₃ ) ₂ release reaction becomes active, and NOx flows out downstream of the NOx holding material 24.

  A three-way catalyst 26 is further provided downstream of the NOx holding material 24 in the catalyst device 20. According to such a configuration, the exhaust gas flowing into the catalyst device 20 from the exhaust passage 12 sequentially passes through the NOx holding material 24 and the three-way catalyst 26. The three-way catalyst 26 contains a noble metal such as platinum (Pt), rhodium (Rh) and palladium (Pd). These noble metals function as active sites that simultaneously activate the oxidation reaction of CO and HC and the reduction reaction of NOx. In addition, many techniques are already known regarding specific configurations and functions of NOx storage substances, noble metals used as active sites, carriers, and the like (see, for example, Japanese Patent No. 3551346). Therefore, detailed description thereof will be omitted.

In the following description, the noble metal (Pt or the like in the first embodiment) and the portion of the carrier on which the noble metal is supported are collectively referred to as “catalyst”. Further, the NOx storage material (BaCO _{3 in the} first embodiment) and the portion of the carrier on which the NOx storage material is supported are collectively referred to as “NOx holding material”.

The exhaust gas purification apparatus of the first embodiment includes an ozone supply device 30. The ozone supply device 30 can obtain air from the air inlet 34 and generate ozone (O ₃ ). In addition, since various techniques are already publicly known regarding the configuration, function, and the like of the ozone supply device, detailed description thereof is omitted.

  The ozone supply device 30 has an ozone injection port 32 that injects ozone in the catalyst device 20. The ozone injection port 32 is disposed upstream of the NOx holding material 24 in the catalyst device 20. According to such a configuration, ozone can be added to the exhaust gas flowing through the exhaust passage 12 by injecting ozone from the ozone injection port 32. Then, the added ozone and the exhaust gas are mixed, and the mixed gas flows into the NOx holding material 24.

  From the viewpoint of efficiently performing the NOx occlusion reaction described above, it is desirable that the NOx in the exhaust gas exists in a more oxidized state. In the first embodiment, ozone can be appropriately supplied to the exhaust gas using the NOx oxidizing gas supply device 30. Thereby, NOx in exhaust gas can be oxidized and exhaust gas can be effectively purified.

  The exhaust gas purification apparatus of the first embodiment has an ECU (Electronic Control Unit) 50. The ECU 50 is connected to the ozone supply device 30. When the ECU 50 transmits a control signal to the ozone supply device 30, the ozone injection timing and the injection amount are controlled. With such a configuration, ozone can be supplied at a desired timing, and the ozone amount in the mixed gas flowing into the NOx holding material 24 can be adjusted to a desired value.

  The ECU 50 is connected to various sensors provided in the internal combustion engine 10. Thus, the ECU 50 can acquire information such as the temperature of the internal combustion engine 10, the engine speed Ne, the air-fuel ratio A / F, the load, and the intake air amount in order to grasp the operation state of the internal combustion engine 10. .

[Operation of Embodiment 1]
As described above, the NOx storage material (BaCO _{3 in the} first embodiment) contained in the NOx holding material has a function of storing NOx in the exhaust gas. Further, the noble metals (Pt, Rh, Pd in the first embodiment) contained in the catalyst function as active points when purifying the exhaust gas. Effective use of these functions together is extremely important for efficiently performing NOx occlusion reduction and exhaust gas purification.

  Conventionally, various catalysts in which these NOx holding materials and catalysts are integrated are also known (also referred to as “NOx occlusion reduction catalyst” and “NSR catalyst”, for example, disclosed in Japanese Patent No. 3551346). . The NOx occlusion reduction catalyst has the feature that the NOx occlusion reaction can be promoted by accelerating the oxidation of NOx by the catalyst, and the exhaust gas can be purified by the catalyst when NOx is released.

  However, when the NOx holding material is integrated with the catalyst in this way, the exhaust gas purification ability of the catalyst (the ability to purify NOx, HC, and CO) is lower than that of a conventional three-way catalyst that does not contain NOx storage materials. turn into. It is considered that this is because the NOx occlusion material becomes a catalyst poison with respect to the catalyst (noble metal element), and the NOx occlusion material reduces the activity capacity of the catalyst. From the viewpoint of performing efficient exhaust gas purification, it is preferable to avoid such harmful effects and maximize the ability of the catalyst.

  Therefore, in the exhaust gas purifying apparatus of the first embodiment, the NOx holding material 24 and the three-way catalyst 26 are individually arranged in the exhaust passage 12 and the NOx occlusion reaction is required, for example, when the internal combustion engine is started. In particular, at the time of cold start, ozone is added to the exhaust gas by the ozone supply device 30. According to such a configuration, since the NOx holding material and the three-way catalyst are individually arranged, it is possible to prevent the exhaust gas purification function from being hindered by the catalyst poison. Then, NOx is oxidized by adding ozone to the exhaust gas, and the NOx occlusion reaction to the NOx holding material 24 can be promoted without depending on the catalyst.

  In the first embodiment, the supply of ozone is stopped when a sufficient time has elapsed after the start of the internal combustion engine, for example, sufficient time has elapsed to stop NOx storage. When the supply of ozone is stopped, NOx emission is activated, and the exhaust gas containing the released NOx flows out downstream of the NOx holding material 24. In the first embodiment, since the three-way catalyst 26 is disposed downstream of the NOx holding material 24, the exhaust gas flowing out from the NOx holding material 24 flows into the three-way catalyst 26. Therefore, the exhaust gas is purified in the process of passing through the three-way catalyst 26, and the gas flowing out downstream of the catalyst device 20 can be reliably purified.

  As described above, according to the exhaust gas purification apparatus of the first embodiment, the NOx holding material 24 and the three-way catalyst 26 are separated and arranged, and the NOx occlusion reaction is performed by the ozone supply device 30 without depending on the catalyst. Therefore, the NOx occlusion reaction can be realized while avoiding the influence of the catalyst poison. As a result, the catalyst exhibits its exhaust gas purification capacity to the maximum, and good emission characteristics can be obtained.

  By using the ozone supply method, it is possible to reliably oxidize NOx under a low temperature condition such as when the internal combustion engine is started, and promote NOx occlusion. Further, according to the NOx oxidation method using ozone, NOx can be oxidized by a gas phase reaction, and if water vapor is present, nitric acid is generated and easily reacts with the NOx storage material, so that NOx can be stored efficiently.

  In the first embodiment described above, the NOx holding material 24 is the “NOx holding material” in the first invention, the three-way catalyst 26 is the “three-way catalyst” in the first invention, and the ozone supply device 30. Respectively correspond to the “ozone supply means” in the first invention.

[Experimental result of Embodiment 1]
Hereinafter, the results of experiments performed on the first embodiment of the present invention will be described with reference to FIGS.

(Configuration of measurement system)
FIG. 2 is a diagram showing a measurement system used in this experiment. This measurement system includes a model gas generator 230 and a plurality of gas cylinders 232 in order to generate a model gas imitating the exhaust gas of an internal combustion engine. The model gas generator 230 can create a simulated gas having the following composition by mixing the gas in the gas cylinder 232.
Simulated gas composition: C ₃ H ₆ 1000 ppm,
CO 7000 ppm,
NO 1500ppm,
O ₂ 7000 ppm
CO ₂ 10%,
H ₂ O 3%
Remaining N ₂

  The model gas generator 230 communicates with an electric furnace in which the test body 222 is installed. FIG. 3 is an enlarged view of the test body 222 and its vicinity. As shown in FIG. 3, the test body 222 contains a NOx holding material sample 224 and a three-way catalyst sample 226 in a quartz tube (hereinafter, these are collectively referred to as “first embodiment sample”). ). In this experiment, as a comparative example, the first example sample is replaced with a comparative example sample to be described later, and the same experiment as in the case of the first example sample is performed.

  The measurement system in FIG. 3 has an oxygen cylinder 240. The oxygen cylinder 240 communicates with the flow rate control units 242, 244 on the downstream side. The flow rate control unit 242 communicates with the ozone generator 246. The ozone generator 246 can generate ozone in response to oxygen supply from the oxygen cylinder 240. The ozone generator 246 communicates with the downstream position of the model gas generator 230 and the upstream position of the test body 222 via the ozone analyzer 248 and the flow rate control unit 250.

On the other hand, the flow rate control unit 244 communicates directly with the ozone analyzer downstream thereof. According to such a configuration, a mixed gas of O ₃ and O ₂ when the power to the ozone generator 246 is turned ON is only O ₂ if the power is turned OFF is supplied to the upstream position of the test body 222 .

In the measurement system of FIG. 3, by using the flow rate control units 242 and 244 and the ozone generator 246 as appropriate, gases having the following two types of compositions can be created. This gas is a gas to be injected into the test body 222, and will be simply referred to as “injected gas” hereinafter.
Injection gas composition: (1) 30000 ppm of O ₃ , balance O ₂
(2) Only O ₂ and the flow rate control unit 250 can supply the injection gas at a desired flow rate.

  Downstream of the test body 222, exhaust gas analyzers 260 and 262 and an ozone analyzer 264 are provided. With these analyzers, the component of the gas flowing out from the test body 222 can be measured.

The measurement equipment used in this experiment is shown below.
Ozone generator 246: Iwasaki Electric OP100W
Ozone analyzer 248 (upstream side): Sugawara Jigyo EG600
Ozone analyzer 264 (downstream): Sugawara Jigyo EG2001B
Exhaust gas analyzers 260 and 262:
HORIBA, Ltd. MEXA9100D (HC, CO, NOx measurement)
HORIBA, Ltd. VAI-510 (measures CO ₂ )

(How to create a sample)
FIG. 4 is a diagram for explaining the first example sample and the comparative example sample used in this experiment. FIG. 4A shows the NOx holding material sample 224 and the three-way catalyst sample 226 (that is, the first embodiment sample) also shown in FIG. The NOx holding material sample 224 was prepared by the following procedure. A cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount was 120 g / L. To this, barium acetate was supported by water absorption and calcined at 500 ° C. for 2 hours. The supported amount of barium acetate was 0.2 mol / L. The catalyst thus prepared was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C.

The three-way catalyst sample 226 was prepared by the following procedure. A cordierite honeycomb of φ30 mm × L50 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount was 120 g / L. Furthermore, Pt was supported using an aqueous solution containing dinitrodiammine platinum, dried, and then fired at 450 ° C. for 1 hour. The amount of platinum supported was 2 g / L. Therefore, the amount of Pt and Ba in the NOx holding material sample 224 and the three-way catalyst sample 226 is 0.07 g for Pt and 0.0035 mol for Ba.

On the other hand, the comparative sample 280 shown in FIG. 4B was prepared by the following procedure. A cordierite honeycomb of φ30 mm × L50 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount was 120 g / L. To this, barium acetate was supported by water absorption and calcined at 500 ° C. for 2 hours. The supported amount of barium acetate was 0.1 mol / L.

  The catalyst thus prepared was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C. Furthermore, Pt was supported using an aqueous solution containing dinitrodiammine platinum, dried, and then fired at 450 ° C. for 1 hour. The amount of platinum supported was 2 g / L. That is, the amounts of Pt and Ba contained in the comparative sample 280 are 0.07 g for Pt and 0.0035 mol for Ba, which are equal to the combined amounts of the NOx holding material sample 224 and the three-way catalyst sample 226.

(Experiment contents)
In the measurement system as described above, the simulated gas having various compositions described above and the injected gas were combined and supplied to the test body 222 under the following conditions. Then, the electric furnace was controlled so that the catalyst temperature increased at the following temperature increase rate, and the concentration of NOx flowing out downstream was investigated.
Temperature: 30 ° C to 500 ° C
Temperature increase rate: 10 ° C / min (constant)
Simulated gas flow rate: 15 L / min
Injection gas flow rate: 3 L / min
The injection gas was supplied in the range of 30 ° C. to 300 ° C., and in the range of 300 ° C. to 500 ° C., the injection gas was not supplied and only the simulation gas was circulated.

(Calculation method of purification rate)

  FIG. 5 is an image diagram of calculation of the exhaust gas purification rate in this experiment. FIG. 5A is an image of the component amount in the supplied exhaust gas, which is obtained by multiplying the simulated gas concentration by the test time. In this experiment, based on such an image, specifically, the component amount in the exhaust gas supplied within the measurement time was calculated by the equation of the concentration of the component in the simulated gas × simulated gas flow rate × test time.

  FIG. 5B is an image of the downstream exhaust gas component amount obtained by multiplying the concentration of gas flowing out downstream of the test body 222 by the test time. Based on this image, the amount of component flowing out downstream was calculated by the equation of component concentration detected by exhaust gas analyzer × gas flow rate × test time.

  Then, using these calculated values, as shown in FIG. 5 (c), the amount of the component flowing out downstream from the amount of gas supplied within the measurement time (FIG. 5 (a)) (FIG. 5 (b)). ) Was subtracted, and this was divided by the amount of gas supplied within the measurement time (FIG. 5 (a)) and calculated at a rate of 100 minutes.

(Experimental result 1)
FIG. 6 is a diagram for explaining a first experimental result of the above-described experiment. As shown in the graph of FIG. 6, all of the NOx, HC, and CO in the case of using the first example sample (NOx holding material sample 224, three-way catalyst sample 226) is more than in the case of the comparative example sample 280. As can be seen from FIG.

  From this result, according to the first embodiment, the NOx occlusion reaction is realized while avoiding the influence of the catalyst poison. Therefore, the catalyst exhibits its exhaust gas purification ability to the maximum, and good emission is achieved. It can be seen that characteristics can be obtained. As described above, the amounts of barium and platinum contained in the first example sample are the same as those contained in the comparative example sample. That is, according to the present embodiment, the NOx storage material and the noble metal can be used efficiently.

(Experimental result 2)
FIG. 7 is a diagram for explaining a second experimental result of the above-described experiment. FIG. 7 shows a NOx holding material sample 224 which has been tested by adding ozone (hereinafter also referred to as “sample A”). The coating layer is scraped off and the NOx occlusion state is confirmed using the IR spectrum. went. For comparison, the NOx holding material sample 224 has a simulated gas distributed without adding ozone (that is, an environment in which the ozone generator 246 is turned off and air addition is simulated) (hereinafter, “ The same measurement was performed for sample B).

The experimental state of IR spectrum measurement is as follows.
Device type: Nicolet Magna IR550
Atmosphere: Dry Air
Temperature: 25 ° C
Number of scans: 128
Resolution: 8cm ^-1
Detector: DTGS-KBr
Sample dilution: Sample / KBr = 1/99 and tablet format

The solid line in [A] in FIG. 7 is the measurement result for sample A, and the solid line in [B] is the measurement result for sample B. As shown in FIG. 7, the NO ₃ ²⁻ peak is observed in the result of sample A to which ozone is added, and NOx occlusion occurs even in the NOx holding material sample 224 that does not contain a noble metal. It could be confirmed. On the other hand, in the result of Sample B to which ozone was not added, only the peak of CO ₃ ²⁻ was detected, and it was confirmed that NOx occlusion did not occur. Thus, it was confirmed that by supplying ozone to the NOx holding material, NOx in the exhaust gas can be occluded without depending on the catalyst.

[Modification of Embodiment 1]
(First modification)
In the first embodiment, the NOx holding material 24 is configured by supporting BaCO ₃ on a ceramic carrier. However, the material constituting the “NOx holding material” in the present invention is not limited to the material specified in the above description. That is, the NOx occlusion substance constituting the NOx holding material is not limited to BaCO ₃ , and for example, as disclosed in Japanese Patent No. 3551346, alkali metals such as Na, K, Cs, and Rb, Ba, Ca, Sr Alkaline earth metals such as Y, Ce, La and Pr can be used as necessary.

Therefore, when NOx is stored as a nitrate in the NOx storage material, the composition of the nitrate is not limited to Ba (NO ₃ ) ₂ described in the first embodiment. As for Ba, it is possible to occlude 3 mol of NO ₃ with respect to 1 mol of Ba, and the feature is that the occlusion amount is large, and the thermal stability is higher than other materials, and as an NOx occlusion substance used in the exhaust gas purification device. Is suitable.

In addition, the material constituting the “catalyst” in the present invention is not limited to the material such as Pt specified in the above description. Various catalyst materials known as noble metal materials constituting the catalyst can be used in the present invention. Furthermore, a suitable material such as alumina (Al ₂ O ₃ ) can be used as a material for the carrier of the noble metal or NOx storage substance.

(Second modification)
In the first embodiment, ozone is added to the exhaust gas by the ozone supply device 30. This ozone addition may more preferably be performed in the following manner. It is known that when ozone (O ₃ ) is added to exhaust gas, NOx in the exhaust gas is oxidized by a gas phase reaction. Specifically, NOx reacts with ozone and the following reaction occurs.
NO + O ₃ → NO ₂ + O ₂ [1]
NO ₂ + O ₃ → NO ₃ + O ₂ ... [2]
NO ₂ + NO ₃ → N ₂ O ₅ [3]
In the following description, the reaction formula [1] is also called “first formula”, the reaction formula [2] is called “second formula”, and the reaction formula [3] is also called “third formula”. . In addition, although only the arrow which shows the reaction to the right direction is described in the 3rd type | formula, the reaction to the left direction may also arise.

The NOx occlusion produced by the NOx occlusion material is realized by occlusion of higher-order nitrogen oxides produced by the oxidation of NOx in the NOx occlusion material. For example, NO ₃ is stored in the NOx storage material by becoming a nitrate such as Ba (NO ₃ ) ₂ . In the NOx occlusion reaction, occlusion is possible in the form of NO _2, NO ₃ , or N ₂ O ₅ . However, there is a limit to the NOx occlusion amount by the form NO _2. For this reason, if a large amount of NO ₂ can be converted into higher-order nitrogen oxides such as NO ₃ and N ₂ O ₅ by actively carrying out the reactions of the above-mentioned second and third formulas, NOx occlusion is possible. The amount can be increased dramatically.

Therefore, in the second modification, ozone is added so that the molar ratio of ozone to NO in the mixed gas is larger than 1, so that the reaction of the second formula occurs. That is, the ratio of mol (O ₃ ) in which the amount of ozone in the mixed gas is converted to mol and mol (NO) in which the amount of nitric oxide in the mixed gas is converted into mol also satisfies the following relational expression. Thus, ozone is added.
mol (O ₃ ) / mol (NO)> 1 ... [4]
In the following description, the equation [4] is also referred to as “fourth equation”.

In the state where the molar ratio of ozone to NO in the mixed gas is 1 or less (mol (O ₃ ) / mol (NO) ≦ 1), NO ₂ is generated by the reaction of the above-mentioned first formula, but the second formula The production of NO ₃ and N ₂ O ₅ is not achieved by this reaction. In the second modification, the amount of ozone added in consideration of this point is made larger than the amount of NO in the exhaust gas, so NO is oxidized to NO ₃ and N ₂ O ₅ . A sufficient amount of ozone can be supplied (to cause the reactions of formulas 2 and 3). As a result, the amount of higher-order nitrogen oxides in the exhaust gas can be reliably increased, and NOx occlusion can be performed effectively.

  In this process, the ECU 50 performs “a process of adjusting the ozone supply amount so that the molar ratio of ozone to nitrogen monoxide (NO) in the mixed gas flowing into the NOx holding material 24 is greater than 1” ( This is realized by executing ozone supply amount adjustment processing. This process can be performed, for example, before step S100 of the routine of FIG. In addition, the ozone supply amount that satisfies the above-described molar ratio is included in the exhaust gas based on, for example, the operating state of the internal combustion engine 10 (engine speed Ne, air-fuel ratio A / F, load, intake air amount, etc.). It can be determined by estimating the molar amount of NOx and calculating the flow rate of ozone supplied in accordance with the estimated molar amount of NOx.

(Third Modification)
Further, the ozone supply amount may be further increased so that the molar ratio of ozone to nitrogen monoxide in the mixed gas is 2 or more (mol (O ₃ ) / mol (NO) ≧ 2). If the molar ratio of ozone (O ₃ ) to nitrogen monoxide (NO) in the mixed gas is greater than 1, ozone is still in the mixed gas even after NO is oxidized to NO ₂ by the above-described first equation. Since it remains, the reactions of the second and third formulas occur to generate NO ₃ and N ₂ O ₅ . However, when the amount of ozone remaining after the reaction of the first formula is very small, the amounts of NO ₃ and N ₂ O ₅ produced by the reactions of the second and third formulas are also reduced.

Therefore, in the third modification, the supply amount of ozone is adjusted so that the molar ratio of ozone to NO in the mixed gas is mol (O ₃ ) / mol (NO) ≧ 2. As a result, after the reaction of the first formula, a sufficient amount of ozone that contributes to the reaction during the reactions of the second formula and the third formula remains, and the amount of higher-order nitrogen oxides can be increased reliably. it can. As described above, according to the sixth modification, it is possible to supply a sufficient amount of ozone to oxidize NO into NO ₃ and N ₂ O ₅ , effectively promoting the NOx occlusion reaction. can do.

In this process, the ECU 50 adjusts the ozone supply amount so that the molar ratio of ozone (O ₃ ) to nitrogen monoxide (NO) in the mixed gas flowing into the NOx holding material 24 becomes 2 or more. This is realized by executing “processing”.

(4th modification "ozone supply form")
In Embodiment 1, the ozone supply device 30 was provided outside the catalyst device 20, and ozone was supplied in a configuration in which the ozone injection port 32 was disposed in the catalyst device 20. However, the present invention is not limited to this. Ozone can be added to the exhaust gas using various known ozone generators and ozone generation methods. For example, the configuration may be such that ozone is directly generated in the exhaust passage 12 or the catalyst device 20 by plasma discharge.

Embodiment 2. FIG.
[Configuration of Embodiment 2]
FIG. 8 is a diagram for explaining the apparatus according to the second embodiment. The apparatus of the second embodiment is different from the first embodiment in that the exhaust passage 12 has a catalyst device 40 instead of the catalyst device 20. Other configurations similar to those of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  Similar to the catalyst device 20 of the first embodiment, the catalyst device 40 of the second embodiment has a NOx holding material 24 inside thereof. The catalyst device 40 includes an ozone decomposition catalyst 46 and a three-way catalyst 48 sequentially downstream of the NOx holding material 24. The ozonolysis catalyst 46 contains Pd. Further, the three-way catalyst 46 includes Pd, Pt, and Rh similarly to the three-way catalyst 26 of Embodiment 1, and exhibits the same exhaust gas purification ability.

[Operation of Embodiment 2]
Similarly to the first embodiment, the exhaust gas purifying apparatus according to the second embodiment also promotes the NOx occlusion reaction without relying on the catalyst by supplying ozone to the exhaust gas. By the way, when ozone is supplied to the exhaust gas, NOx in the exhaust gas is oxidized and ozone flowing into the catalyst device may oxidize the internal structure. Specifically, when ozone flows into the catalyst, the noble metal contained in the catalyst can be poisoned (oxidized).

  Various precious metals are used as the catalyst, and some of them include elements such as Pt and Rh whose activity ability decreases due to oxidation reaction. Therefore, when the NOx occlusion reaction is promoted by supplying ozone, it is desirable to prevent ozone from flowing into the catalyst and avoid a decrease in catalyst function.

  Therefore, in the second embodiment, the ozone decomposition catalyst 46 is provided in the catalyst device 40 at a position downstream of the NOx holding material 24 and upstream of the three-way catalyst 48. Pd contained in the ozone decomposition catalyst 46 has a function of decomposing ozone. With such a configuration, first, NOx in the exhaust gas is occluded in the process of flowing through the NOx holding material 24 after being oxidized by ozone supply. Of the ozone mixed with the exhaust gas, the ozone that does not contribute to the oxidation of NOx and flows out downstream of the NOx holding material 24 is decomposed by the ozone decomposition catalyst 46. As a result, the influence of ozone on the exhaust gas purification capacity of the three-way catalyst 48 can be suppressed.

  As described above, according to the second embodiment, after the ozone in the gas downstream of the NOx holding material 24 is decomposed, the gas can flow into the three-way catalyst 48. Thereby, it is possible to prevent ozone from flowing into the three-way catalyst 48, and it is possible to prevent noble metals such as Pt and Rh used in the catalyst from being oxidized by ozone. As a result, it is possible to avoid an influence on the active function of the noble metal, to suppress the influence on the exhaust gas purification capacity of the three-way catalyst 48, and to ensure good emission characteristics.

  Further, according to Embodiment 2, palladium (Pd) is included in the ozone decomposition catalyst 46. Pd has the function of decomposing ozone, and its active function is not easily lowered even when oxidized, and the exhaust gas purification ability is relatively easy to maintain (rather, oxidized Pd is more active). Yes. For this reason, according to Embodiment 2, the fall of the exhaust gas purification capability resulting from ozone can be prevented more effectively.

  Further, according to the second embodiment, Pt and Rh are included in the three-way catalyst 48 downstream of the ozone decomposition catalyst 46. Pt and Rh have a relatively high NOx purification capability, but their activity capability is reduced by oxidation with ozone. According to the second embodiment, ozone can be reliably prevented from flowing into the three-way catalyst 48 by the ozone decomposition catalyst 46, so that Pt and Rh can be included in the three-way catalyst 48 while avoiding the influence.

  In the second embodiment described above, the ozone decomposition catalyst 46 corresponds to the “ozone decomposition catalyst” in the second invention.

In Embodiment 2, palladium (Pd) is included in the ozone decomposition catalyst 46 as an ozone decomposition substance. However, the present invention is not limited to this. Various substances that decompose ozone, known ozone decomposing substances, and ozone decomposing agents may be appropriately included in the ozone decomposing catalyst 46. Specifically, silver (Ag) or manganese dioxide (MnO ₂ ) can be included as a material exhibiting ozonolysis characteristics.

[Experimental result of Embodiment 2]
In the second embodiment, an experiment was performed using the same measurement system as in the first embodiment. The results will be described below.

(Measurement configuration)
The measurement system used in the experiment of the second embodiment has the same configuration as that of the first embodiment except that the test body 222 of the first embodiment is replaced with the test body 322 shown in FIG. In the following description, except for the configuration of the test body 322, the description of the measurement system in the experiment of the first embodiment described above will be referred to, and the detailed description is omitted here.

  FIG. 9 is an enlarged view of the test body 322 and the vicinity thereof. As shown in FIG. 3, the test body 322 sequentially stores a NOx holding material sample 324, an ozone decomposition catalyst sample 326, and a three-way catalyst sample 328 in a quartz tube (hereinafter referred to as “second”. Also referred to as “Example Sample”). In this experiment, as a comparative example, the inside of the test body 322 is replaced with a comparative example sample to be described later, and the same experiment is performed.

(How to create a sample)
FIG. 10 is a diagram for explaining an example sample and a comparative example sample used in this experiment. FIG. 10A shows the NOx holding material sample 324, the ozone decomposition catalyst sample 326, and the three-way catalyst sample 328 (that is, the second embodiment sample) shown in FIG.

The NOx holding material sample 324 was prepared by the following procedure. A cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount was 120 g / L. To this, barium acetate was supported by water absorption and calcined at 500 ° C. for 2 hours. The supported amount of barium acetate was 0.2 mol / L. The catalyst thus prepared was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C.

Further, the ozone decomposition catalyst sample 326 was prepared by the following procedure. A cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi was coated with CeO ₂ —ZrO ₂ composite oxide. The coating amount was 100 g / L. Furthermore, Pd was supported using a palladium nitrate solution, dried, and calcined at 450 ° C. for 1 hour. The amount of Pd supported was 1 g / L.

A three-way catalyst sample 328 was prepared by the following procedure. A cordierite honeycomb of φ30 mm × L50 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ . The coating amount was 120 g / L. Furthermore, Pt and Rh were supported using an aqueous solution containing dinitrodiammine platinum and rhodium nitrate, dried, and then fired at 450 ° C. for 1 hour. The supported amount of platinum was 1 g / L, and the supported amount of rhodium was 0.5 g / L. Accordingly, as shown in the figure, the content of each component of the ozone decomposition catalyst 326 and the three-way catalyst sample 328 is 0.035 g for Pt, 0.0175 g for Rh, 0.0175 g for Pd, Al ₂ O ₃ is 4.2 g, and CeO ₂ —ZrO ₂ is 1.75 g.

On the other hand, comparative example samples 380 and 382 are shown in FIG. The comparative example sample 380 is a sample as a NOx holding material, and the comparative example sample 382 is a sample as a three-way catalyst. For Comparative Sample 380, γ-Al ₂ O ₃ was coated on a cordierite honeycomb of φ30 mm × L25 mm, 4 mil / 400 cpsi. The coating amount was 120 g / L. To this, barium acetate was supported by water absorption and calcined at 500 ° C. for 2 hours. The supported amount of barium acetate was 0.2 mol / L. The catalyst thus prepared was immersed in a solution containing ammonium hydrogen carbonate and dried at 250 ° C.

For Comparative Sample 382, a cordierite honeycomb of φ30 mm × L50 mm, 4 mil / 400 cpsi was coated with γ-Al ₂ O ₃ and CeO ₂ —ZrO ₂ composite oxide. The coating amount was 120 g / L for γ-Al ₂ O ₃ and 50 g / L for CeO ₂ —ZrO ₂ . Furthermore, Pt, Rh and Pd were supported using an aqueous solution containing dinitrodiammine platinum, rhodium nitrate and palladium nitrate, dried, and then fired at 450 ° C. for 1 hour. The supported amount of platinum was 1 g / L, the supported amount of rhodium was 0.5 g / L, and the supported amount of Pd was 0.5 g / L. Therefore, as shown in the figure, the content of each component of the comparative sample 382 is 0.035 g for Pt, 0.0175 g for Rh, 0.0175 g for Pd, 4.2 g for Al ₂ O ₃ , CeO ₂ −. ZrO ₂ is 1.75 g, which matches the content of each component of the ozone decomposition catalyst 326 and the three-way catalyst sample 328.

(Experiment content and purification rate calculation method)
In the configuration as described above, the mixed gas of the injected gas was supplied to the test body 322 in the same manner as in the first embodiment. Thereafter, the purification rate was calculated by the same calculation method as in the first embodiment.

(Experimental result)
FIG. 11 is a diagram showing the results of the experiment conducted with the above-described contents, and is a diagram showing the NOx, HC, and CO purification rates when the temperature of the catalyst in the test body 322 is between 30 ° C. and 500 ° C. As shown in the graph of FIG. 11, the case of using the second example sample (NOx holding material sample 324, ozone decomposition catalyst 326, three-way catalyst sample 328) is more than the case of using comparative example samples 380 and 382. It can also be seen that NOx, HC and CO all show high purification rates.

  From this result, according to the second embodiment, it is possible to prevent the activation function of the noble metal due to ozone and to maximize the exhaust gas purifying ability of the catalyst, so that good emission characteristics can be obtained. Recognize. Further, as described above, the contents of the noble metal component and the like included in the second example sample are the same as those included in the comparative example. That is, according to the present embodiment, a noble metal component or the like can be used efficiently.

[Modification of Embodiment 2]
In the second embodiment, a three-way catalyst 46 containing Pt and Rh as a noble metal functioning as an active site is used. However, the present invention is not limited to this. If the three-way catalyst of the exhaust gas purifying apparatus contains various precious metals whose active function is reduced due to the influence (poisoning) of ozone, the idea of the present invention, that is, the ozone decomposition catalyst is placed upstream of the three-way catalyst. By using the idea of arranging in the above, the same effect as in the second embodiment can be obtained.

  In the second embodiment as well, as described in the modification of the first embodiment, the ozone supply mode, specifically, the ozone supply amount and the ozone generation method are appropriately changed to appropriate ones. May be.

Embodiment 3 FIG.
[Configuration of Embodiment 3]
FIG. 12 is a diagram for explaining the apparatus according to the third embodiment of the present invention. In the third embodiment, a temperature sensor 60 is added to the apparatus of the first embodiment. Hereinafter, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The temperature sensor 60 provided in the apparatus according to the third embodiment is connected to the three-way catalyst 26. Further, the temperature sensor 60 is connected to the ECU 50. According to such a configuration, the ECU 50 can detect the temperature of the three-way catalyst 26 based on the output of the temperature sensor 60.

[Operation of Embodiment 3]
In the third embodiment, as in the first embodiment, the NOx occlusion reaction is promoted by supplying ozone to the exhaust gas without depending on the catalyst. By using the ozone supply method, it is possible to reliably oxidize NOx and promote NOx occlusion even under low temperature conditions such as when the internal combustion engine is started.

  By the way, ozone requires a corresponding energy when it is generated. If the amount of ozone supplied to the exhaust gas is large, the energy required for ozone generation naturally increases. Therefore, it is not preferable to supply ozone to the exhaust gas more than necessary.

  The main reason for the need for ozone supply is that the three-way catalyst 26 is not at an activation temperature sufficient to purify the exhaust gas in a low temperature state such as when the internal combustion engine is started. In other words, if the temperature of the three-way catalyst 26 reaches the activation temperature, even if the NOx occlusion is not promoted and the occluded NOx starts to be released after the ozone supply is stopped, they can be purified reliably. .

  Therefore, in the third embodiment, the temperature of the three-way catalyst 46 is grasped by the temperature sensor 60, and when the temperature becomes equal to or higher than the activation temperature capable of purifying the exhaust gas, the supply of ozone by the ozone supply device 30 is stopped. And This makes it possible to obtain good emission characteristics while suppressing the amount of ozone used.

[Specific Processing of Embodiment 3]
Hereinafter, specific processing performed by the third embodiment will be described with reference to FIG. FIG. 13 is a flowchart of a routine executed by ECU 50 in the third embodiment. This routine is executed when the internal combustion engine 10 is started, particularly at a low temperature start (Cold Start). In the present embodiment, in advance by an experiment or the like, to understand the activity temperatures T ₁ the three-way catalyst 26 can exhibit a sufficient exhaust gas purification performance, and be stored in the ECU 50.

  In the routine shown in FIG. 13, first, the ECU 50 acquires the output of the temperature sensor 60, and based on this, detects the temperature of the three-way catalyst 26 (hereinafter referred to as catalyst temperature T) (step S300).

Subsequently, the catalyst temperature T is, whether it is in a state of less than _{T 1} is is determined (step S310). When the catalyst temperature T is judged to be less than T _1, the three-way catalyst 26 is judged not yet reached its activation temperature which can exhibit a sufficient exhaust gas purification performance. Therefore, in this case, an ozone supply command is issued to the NOx oxidizing gas supply device 30, and ozone is supplied to the exhaust gas (step S320). Thereafter, the processing is executed from step S300 again, until the catalyst temperature T is above T _1, the ozone supply is continued.

In step S310, the in the case where the catalyst temperature T is determined to above T ₁ is the three-way catalyst 26 is judged to have a state capable of exhibiting a sufficient exhaust gas purification performance. In this case, the ozone supply is stopped immediately (step S330), and then the fuel injection amount is set so that the air-fuel ratio of the exhaust gas becomes slightly rich (slight rich) for the purpose of reducing and releasing the stored NOx. Is controlled (step S340). Thereafter, the current routine ends.

  According to the above processing, when the internal combustion engine 10 is started, the NOx occlusion reaction can be promoted even when the three-way catalyst 26 is not in a sufficiently active state, and the temperature of the three-way catalyst 26 is equal to or higher than the activation temperature at which the exhaust gas can be purified. Then, the ozone supply can be stopped immediately. As a result, the NOx occlusion reaction can be realized while avoiding the influence of the catalyst poison as in the first embodiment, and the ozone is efficiently used while suppressing the amount of ozone used. Can be reduced.

In the third embodiment described above, the “ozone supply control means” according to the first aspect of the present invention is realized by executing the processing of steps S300 to S330.

[Modification of Embodiment 3]
(First modification)
In the third embodiment, the routine of FIG. 13 is executed for the configuration of the first embodiment. However, instead of the first embodiment, the routine of FIG. 13 may be similarly executed for the configuration of the second embodiment. That is, with respect to the configuration of the second embodiment, the temperature sensor 60 may be connected to the three-way catalyst 46 to execute the routine of FIG.

(Second modification)
In the third embodiment, the ozone supply is completely stopped when the three-way catalyst 26 reaches an activation temperature at which sufficient exhaust gas purification ability can be exhibited. However, the present invention is not limited to this. When the three-way catalyst 26 reaches the activation temperature, the amount of ozone used may be gradually reduced (suppressed), and then the supply may be stopped.

(Third Modification)
In the third embodiment, the temperature of the three-way catalyst 26 is detected based on the output of the temperature sensor 60, and the ozone supply is controlled. However, the present invention is not limited to this. For example, the three-way catalyst 26 has a sufficient exhaust gas purification capability depending on the operating state of the internal combustion engine 10, the temperature of the exhaust gas, and whether or not a sufficient time has elapsed after the start. It may be determined whether or not the activation temperature has been reached.

  In the third embodiment, the modifications described in the first or second embodiment can be used as appropriate.

Embodiment 4 FIG.
[Configuration of Embodiment 4]
FIG. 12 is a diagram for explaining the apparatus according to the fourth embodiment of the present invention. In the fourth embodiment, the apparatus of the third embodiment is further provided with an air-fuel ratio sensor 70. Hereinafter, the same components as those in the third embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The air-fuel ratio sensor 70 provided in the apparatus of the fourth embodiment is disposed downstream of the three-way catalyst 26. The air-fuel ratio sensor 70 is a sensor that emits a substantially linear output with respect to the air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 26. The air-fuel ratio sensor 70 is connected to the ECU 50, and the ECU 50 can detect the atmosphere downstream of the three-way catalyst 26 based on the output of the air-fuel ratio sensor 70. Further, in the apparatus of the fourth embodiment, the ECU 50 is connected to the fuel injection valve of the internal combustion engine 10, and the fuel injection amount of the internal combustion engine 10 is appropriately adjusted by the ECU 50 issuing a control signal. ing.

[Operation of Embodiment 4]
In the fourth embodiment, as in the third embodiment, the NOx occlusion reaction is promoted by supplying ozone to the exhaust gas without depending on the catalyst. By using the ozone supply method, it is possible to reliably oxidize NOx and promote NOx occlusion even under low temperature conditions such as when the internal combustion engine is started.

  When the internal combustion engine 10 according to the fourth embodiment is started, while the supply of ozone to the exhaust gas as described above is being executed, the internal combustion engine 10 is operated so as to operate under stoichiometric conditions as in the first embodiment. The fuel injection amount is controlled by open loop. In the fourth embodiment, after that, when sufficient time has passed since the internal combustion engine 10 is started, the temperature of the three-way catalyst 26 also rises, and when the active function of the catalyst can be sufficiently exhibited, ozone supply is performed. To stop.

  When the supply of ozone is stopped, the reaction in which the stored NOx reacts with the reducing agent (HC, CO) in the exhaust gas to release NOx (NOx release reaction) becomes active. As a result, under the situation where the NOx releasing reaction occurs, if the composition of the exhaust gas is stoichiometric, the amount of released NOx becomes a lean atmosphere and the reducing material becomes insufficient.

  Therefore, in the fourth embodiment, in order to cope with this, when the supply of ozone is stopped, the fuel injection amount of the internal combustion engine 10 is controlled from the open loop control to the closed loop using the output of the air-fuel ratio sensor 70. Switch to control. Thus, the fuel injection amount can be corrected (riched) so as to cancel out the leaning caused by the NOx releasing reaction. As a result, even if the leaning effect is caused by the NOx releasing reaction, the fuel injection amount can be corrected and the composition of the exhaust gas can be maintained in an appropriate state.

  In the fourth embodiment, when the air-fuel ratio sensor 70 shows a rich output, the fuel injection amount is reduced and the air-fuel ratio is adjusted within the appropriate range. According to such a method, the above-described correction of the fuel injection amount can be performed without excess or deficiency. In addition, it is possible to prevent a situation in which the enrichment correction is continued even though the NOx emission has stopped after the enrichment correction of the air-fuel ratio.

  As described above, according to the fourth embodiment, the NOx occlusion reaction can be realized while avoiding the influence of the catalyst poison as in the first embodiment, and the NOx releasing reaction is occurring. However, it is possible to correct the fuel injection amount without excess or deficiency and maintain good emission characteristics.

[Specific processing of the fourth embodiment]
Hereinafter, specific processing performed by the apparatus according to the fourth embodiment will be described with reference to FIG. FIG. 15 is a flowchart of a routine executed in the fourth embodiment, which is executed when the internal combustion engine 10 is started and in a low temperature state (for example, at Cold Start). Note that the processing in steps S300 to S330 in the routine of FIG. 15 is the same as that in the third embodiment, and a description thereof will be omitted. During the execution of the above steps in the fourth embodiment, it is assumed that the fuel injection amount of the internal combustion engine 10 is controlled in an open loop so that the operation under the stoichiometric condition is performed.

  When the ozone supply is stopped in step S330, the NOx stored as nitrate reacts with the reducing agent in the exhaust gas, and the NOx release reaction is activated. Therefore, in the routine of FIG. 15, in the process of step S440, the control of the fuel injection amount is controlled by the closed loop control that feeds back the output of the exhaust gas sensor to the fuel injection amount from the control by the open loop control that has been executed so far. We are going to switch to control. Specifically, the open loop control that has been executed so far is stopped by the process of step S440, and the process executed by the ECU 50 proceeds to the following steps S450 to S490. As a result, the fuel injection amount control is switched to the closed loop control.

  In step S450, first, the ECU 50 acquires the output of the air-fuel ratio sensor 70, and it is determined whether or not the air-fuel ratio of the exhaust gas flowing out from the three-way catalyst 26 is lean. If the establishment of the condition in step S450 is confirmed, it is determined that the reducing agent in the exhaust gas is used for the NOx reduction reaction and the exhaust gas is lean. Therefore, in this case, the fuel injection amount is increased (step S460). When the process of step S460 ends, the process of S450 is executed again, and the fuel injection amount is corrected until the exhaust gas leaves the lean atmosphere.

  If it is determined in step S450 that the output of the air-fuel ratio sensor 70 is not lean, it is next determined whether or not the output of the air-fuel ratio sensor 70 is rich (step S470). If the establishment of this condition is confirmed, it is determined that the increase in the fuel injection amount in step S460 is excessive, and the fuel injection amount decrease correction is performed (step S480). After the reduction correction is performed, the process returns to step S450, and it is determined again whether or not the output of the air-fuel ratio sensor 70 is lean.

  As described above, by executing the processing of steps S450 to S480, the fuel injection amount can be corrected without excess or deficiency so as to offset the influence of leaning due to the NOx release reaction. As a result, even under a situation in which the NOx releasing reaction occurs, the composition of the exhaust gas can be maintained in an appropriate state, and good emission characteristics can be ensured.

  If it is determined in step S470 that the output of the air-fuel ratio sensor 70 is not rich, it is determined that the air-fuel ratio is in a stoichiometric atmosphere. In this case, it is determined whether or not a routine stop condition is satisfied (step S490). In the fourth embodiment, the time until the NOx occluded in the NOx holding material 24 is sufficiently released is measured in advance through experiments or the like, and whether or not the time has elapsed after the ozone supply is stopped in step S330. Is the routine stop condition.

  If the establishment of step S470 is not confirmed, it is determined that the NOx releasing reaction is still occurring, and the process of step S450 is executed again. If it is determined that the condition is satisfied, it is determined that the NOx releasing reaction has ended, the current routine ends, and the operating condition of the internal combustion engine 10 shifts to a normal operating condition.

  According to the above process, the NOx occlusion reaction can be realized while avoiding the influence of the catalyst poison as in the first embodiment, and ozone can be used efficiently as in the third embodiment. By correcting the fuel injection amount in consideration of the effect of the release reaction, even if there is an effect of leaning due to the NOx release reaction, the air-fuel ratio is corrected without excess or deficiency and the composition of the exhaust gas is maintained in an appropriate state. be able to. Furthermore, after the air-fuel ratio enrichment correction, it is possible to prevent a situation where the enrichment correction is continued even though the NOx release has stopped. As a result, good emission characteristics can be ensured.

In the fourth embodiment described above, the air-fuel ratio sensor 70 uses the “exhaust gas sensor” of the fifth aspect of the invention to perform fuel injection amount control by open loop control that is being executed during the processing of steps S300 to S330. It corresponds to “first injection amount control means”. In the specific processing described above, the “second injection amount control means” of the fifth aspect of the present invention is realized by executing steps S450 to S480. The ECU 50 executes Step S440, thereby realizing the “injection amount control switching means” according to the fifth aspect of the present invention.

[Modification of Embodiment 4]
(First modification)
In the fourth embodiment, the routine of FIG. 15 is executed for the configuration of the first embodiment. However, instead of the first embodiment, the routine of FIG. 15 may be similarly executed for the configuration of the second embodiment. That is, with respect to the configuration of the second embodiment, the temperature sensor 60 is connected to the three-way catalyst 46, the air-fuel ratio sensor 70 is arranged downstream of the three-way catalyst 46, and the routine of FIG. good.

(Second modification)
In the specific processing of the fourth embodiment, when the control of the fuel injection amount is switched from the open loop control to the closed loop control (feedback control) in step S440, and then the establishment of the routine stop condition in step S490 is recognized, Changed to normal operating state. However, the present invention is not limited to this. In the case where the normal operation state includes the feedback control of the fuel injection amount, unlike the fourth embodiment, the direct operation may be shifted from the open loop control to the normal operation state including the feedback control. Good.

  That is, as an air-fuel ratio control mechanism for an internal combustion engine, conventionally, for example, an air-fuel ratio sensor disposed upstream of the catalyst, a sub-oxygen sensor disposed downstream of the catalyst, and an air-fuel ratio of exhaust gas flowing into the catalyst are controlled. A main feedback mechanism that feeds back the output of the air-fuel ratio sensor to the fuel injection amount so that it matches the target air-fuel ratio, and the fuel injection of the output of the sub oxygen sensor so that the air-fuel ratio of the exhaust gas flowing out from the catalyst becomes the stoichiometric air-fuel ratio An air-fuel ratio feedback control mechanism including a sub-feedback mechanism that feeds back the amount is known (for example, JP-A-2005-48711).

  In step S440, the fuel injection amount control in the present invention may be realized by directly switching the fuel injection amount control to the air-fuel ratio feedback control.

  In the second modification described above, the “sub oxygen sensor” disposed downstream of the catalyst corresponds to the “exhaust gas sensor” of the third aspect of the invention, and the sub feedback control included in the normal operation control of the internal combustion engine is performed. This corresponds to the “second fuel injection amount control means” of the third aspect of the invention.

(Third Modification)
In the third embodiment, the idea of “switching ozone and air supply in accordance with the catalyst temperature” (specifically, this corresponds to the processing of steps S300 to S330 of the routine of FIG. 3) is also referred to. In the fourth embodiment, the idea of “correcting the fuel injection amount during the NOx releasing reaction” (specifically, this corresponds to the processing of steps S440 to S490 of the routine of FIG. Also referred to as “idea”.

  The specific process (routine in FIG. 15) of the fourth embodiment described above includes both the third idea and the fourth idea (steps S300 to S330 and S440 to S490 in FIG. 15). However, this does not necessarily mean that the fourth idea is used in combination with the third idea, and only the fourth idea can be used alone.

  That is, only the fourth idea can be applied to the first and second embodiments. Specifically, for example, by applying the routine of FIG. 15, “Start → Start ozone supply → Continue ozone supply until a predetermined ozone supply stop condition is reached → Stop ozone supply when the ozone stop condition is satisfied → Step S440 and after. It is sufficient to perform the process “execute the process.”

  In the fourth embodiment, an air-fuel ratio sensor is provided downstream of the three-way catalyst 26, and the fuel injection amount is feedback controlled based on the output. However, an oxygen sensor may be used instead of the air-fuel ratio sensor. Also in the fourth embodiment, it is possible to appropriately use the modifications described in the first to third embodiments.

  The NOx holding material may not only occlude NOx but also adsorb NOx. That is, the NOx occlusion reduction type catalyst 22 may not only occlude NOx but also adsorb it. For this reason, “holding” in the NOx holding material includes not only the meaning of “occluding” NOx but also the meaning of “adsorbing” NOx. That is, “NOx storage substance” in the above description may be read as “NOx retention substance”.

It is a figure for demonstrating the structure of the exhaust-gas purification apparatus of the internal combustion engine of Embodiment 1 of this invention. 6 is a diagram for explaining an experimental result regarding the first embodiment. FIG. 6 is a diagram for explaining an experimental result regarding the first embodiment. FIG. 6 is a diagram for explaining an experimental result regarding the first embodiment. FIG. 6 is a diagram for explaining an experimental result regarding the first embodiment. FIG. 6 is a diagram for explaining an experimental result regarding the first embodiment. FIG. 6 is a diagram for explaining an experimental result regarding the first embodiment. FIG. FIG. 6 is a diagram for illustrating a configuration of an exhaust gas purification apparatus for an internal combustion engine according to a second embodiment. FIG. 10 is a diagram for explaining an experimental result regarding the second embodiment. FIG. 10 is a diagram for explaining an experimental result regarding the second embodiment. FIG. 10 is a diagram for explaining an experimental result regarding the second embodiment. FIG. 6 is a diagram for illustrating a configuration of an exhaust gas purification device for an internal combustion engine according to a third embodiment. 12 is a flowchart of a routine executed in the third embodiment. FIG. 10 is a diagram for illustrating a configuration of an exhaust gas purification apparatus for an internal combustion engine according to a fourth embodiment. 12 is a flowchart of a routine executed in the fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Exhaust passage 20, 40 Catalytic device 24 NOx holding material 26, 48 Three-way catalyst 30 Ozone supply device 32 Ozone injection port 34 Air inlet 46 Ozone decomposition catalyst 50 ECU
60 Temperature sensor 70 Air-fuel ratio sensor

Claims (5)

A NOx holding material disposed in an exhaust passage of the internal combustion engine;
A three-way catalyst disposed downstream of the NOx holding material;
Ozone supply means for supplying ozone (O ₃ ) so as to be mixed with the exhaust gas flowing into the NOx holding material;
Ozone supply control means for suppressing or stopping ozone supply by the ozone supply means when the temperature of the three-way catalyst is equal to or higher than an activation temperature capable of purifying exhaust gas;
An exhaust gas purifying device for an internal combustion engine, comprising:   The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising an ozone decomposition catalyst containing an ozone decomposition substance downstream of the NOx holding material and upstream of the three-way catalyst. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the ozone decomposing substance includes palladium (Pd).   The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the three-way catalyst contains platinum (Pt) or rhodium (Rh). An exhaust gas sensor disposed downstream of the three-way catalyst;
The first injection amount control means for controlling the fuel injection amount of the internal combustion engine by open loop control and the output of the exhaust gas sensor is fed back to the fuel injection amount so that the exhaust gas flowing out from the three-way catalyst has a stoichiometric air-fuel ratio. A second injection amount control means for controlling the fuel injection amount by closed loop control;
The fuel injection amount control by the first injection amount control means is executed during the ozone supply by the ozone supply means, and when the ozone supply by the ozone supply means is stopped, the fuel injection amount control of the internal combustion engine is controlled by the first injection amount. Injection amount control switching means for switching from control by the control means to control by the second injection amount control means;
The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 4 , further comprising:

Images