JP4952645B2 - 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.

  In order to purify harmful components in the exhaust gas of an internal combustion engine, a technique of installing a catalyst in the exhaust passage is widely used. The activity of the exhaust purification catalyst does not appear unless it exceeds a certain temperature. That is, when the temperature of the catalyst is low, the exhaust gas cannot be sufficiently purified by the catalyst. For this reason, suppressing the discharge | emission of a harmful | toxic component at the time of catalyst low temperature, such as immediately after engine starting, remains as an important subject.

  Japanese Patent Application Laid-Open No. 2007-289844 discloses an oxidation catalyst disposed in an exhaust passage, a filter disposed downstream of the oxidation catalyst and collecting PM (Particulate Matter), and a downstream of the PM filter. An exhaust purification device is disclosed that includes a NOx catalyst disposed in an exhaust passage and ozone supply means capable of supplying ozone between the PM filter and the NOx catalyst. According to this apparatus, it is said that ozone can be used efficiently when oxidizing and removing PM using ozone.

JP 2007-289844 A JP 2005-538295 A

  Active oxygen such as ozone has a very high oxidizing power. By using this active oxygen, it is conceivable to suppress emission of harmful components at a low catalyst temperature. However, electric power is required to generate active oxygen. For this reason, in order to suppress deterioration of fuel consumption, it is important to use active oxygen efficiently without waste.

  The technique described in the above-mentioned conventional publication focuses on efficiently using ozone for the purpose of oxidizing and removing PM accumulated in the PM filter. On the other hand, it is not considered enough about suppression of the discharge | emission of a harmful | toxic component at the time of catalyst low temperature.

  The present invention has been made in view of the above points, and in an exhaust gas purification apparatus for an internal combustion engine that can purify harmful components in exhaust gas using active oxygen, while reducing the amount of active oxygen used, It is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine that can obtain excellent purification performance.

In order to achieve the above object, a first invention is an exhaust gas purification apparatus for an internal combustion engine,
An oxidation catalyst disposed in the exhaust passage of the internal combustion engine and having a function of oxidizing unburned components in the exhaust gas;
A NOx catalyst installed downstream of the oxidation catalyst and having a function of purifying NOx in exhaust gas;
An active oxygen supply device for supplying active oxygen between the oxidation catalyst and the NOx catalyst;
Temperature information acquisition means for acquiring information relating to temperatures of the oxidation catalyst and the NOx catalyst;
Control means for controlling the supply of active oxygen by the active oxygen supply device based on the information;
With
The control means includes
Catalyst temperature determination means for determining whether the temperature of the oxidation catalyst and the NOx catalyst is in a predetermined low temperature region, medium temperature region, or high temperature region based on the information;
The HC concentration in the exhaust gas flowing into the NOx catalyst when determined to be in the intermediate temperature region is higher than the HC concentration in the exhaust gas flowing into the NOx catalyst when determined to be in the low temperature region. Active oxygen amount control means for controlling the amount of active oxygen supply,
It is characterized by including.

The second invention is the first invention, wherein
The control means includes
When it is determined that the temperature is in the low temperature region, an amount of active oxygen necessary for purifying NOx in exhaust gas and an amount of active oxygen necessary for purifying HC in exhaust gas are Low temperature active oxygen amount control means to be supplied by the active oxygen supply device;
An active oxygen in an amount necessary to purify NOx in the exhaust gas and an active oxygen in an amount necessary to purify a part of the HC in the exhaust gas when it is determined that the temperature is in the intermediate temperature range; Medium temperature active oxygen amount control means to be supplied by the active oxygen supply device,
It is characterized by including.

The third invention is the first or second invention, wherein
The control means includes supply suppression means for suppressing supply of active oxygen when it is determined that the temperature is in the high temperature region.

According to a fourth invention, in any one of the first to third inventions,
The low temperature region corresponds to a temperature region in which the activities of the oxidation catalyst and the NOx catalyst are not expressed, and the intermediate temperature region is from a temperature at which the activities of the oxidation catalyst and the NOx catalyst start to be expressed. Corresponding to the temperature until activation, the high temperature region corresponds to a temperature region exceeding the intermediate temperature region.

According to a fifth invention, in any one of the first to fourth inventions,
Exhaust gas flow velocity calculating means for calculating the flow velocity of the exhaust gas flowing through the exhaust passage;
Means for suppressing the supply of active oxygen when the exhaust gas flow rate exceeds a predetermined value;
It is characterized by providing.

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

  According to the first invention, active oxygen can be supplied between the oxidation catalyst and the NOx catalyst. Thereby, purification of HC and NOx can be promoted using active oxygen. For this reason, it is possible to reliably suppress the release of HC and NOx into the atmosphere even at a low catalyst temperature. Further, according to the first invention, the supply of active oxygen can be controlled according to the temperatures of the oxidation catalyst and the NOx catalyst. Thereby, excess and deficiency of active oxygen can be prevented. For this reason, since the amount of active oxygen used can be reduced while realizing excellent purification performance, the power required for generating active oxygen can be reduced. Furthermore, according to the first aspect of the invention, the active oxygen supply amount is set such that the HC concentration in the exhaust gas flowing into the NOx catalyst in the intermediate temperature region is higher than the HC concentration in the exhaust gas flowing into the NOx catalyst in the low temperature region. Can be controlled. In the low temperature region, the NOx purification rate increases as the HC flowing into the NOx catalyst approaches zero. On the other hand, in the intermediate temperature region, there exists an optimum value of the HC inflow amount to the NOx catalyst so that the NOx purification rate becomes maximum. Therefore, according to the first invention, by controlling the HC concentration in the exhaust gas flowing into the NOx catalyst as described above, the NOx purification rate can be further increased in both the low temperature region and the intermediate temperature region. In addition, active oxygen can be used more efficiently.

  According to the second invention, in the low temperature region, an amount of active oxygen necessary for purifying NOx in the exhaust gas and an amount of active oxygen necessary for purifying HC in the exhaust gas are supplied. In the intermediate temperature range, an amount of active oxygen necessary for purifying NOx in the exhaust gas and an amount of active oxygen necessary for purifying a part of the HC in the exhaust gas can be supplied. . In the low temperature region, the NOx purification rate increases as the HC flowing into the NOx catalyst approaches zero. On the other hand, in the intermediate temperature region, there exists an optimum value of the HC inflow amount to the NOx catalyst so that the NOx purification rate becomes maximum. According to the control of the second invention as described above, the HC concentration in the exhaust gas flowing into the NOx catalyst in the intermediate temperature region can be made higher than the HC concentration in the exhaust gas flowing into the NOx catalyst in the low temperature region. . Therefore, the NOx purification rate can be further increased in both the low temperature region and the intermediate temperature region, and active oxygen can be used more efficiently.

  According to the third aspect of the invention, the supply of active oxygen can be suppressed when in the high temperature region. In the high temperature region, active oxygen is easily decomposed. For this reason, even if active oxygen is supplied, the effect of improving purification performance is small. Further, since the oxidation catalyst and the NOx catalyst are sufficiently activated in the high temperature region, HC and NOx can be sufficiently purified without supplying active oxygen. According to the third invention, the amount of active oxygen used can be reduced by suppressing the supply of active oxygen in such a case. For this reason, fuel consumption can be improved.

  According to the fourth invention, the low temperature region corresponds to a temperature region where the activities of the oxidation catalyst and the NOx catalyst are not expressed, and the intermediate temperature region is from the temperature at which the activities of the oxidation catalyst and the NOx catalyst start to appear. Corresponding to the temperature until full activation, the high temperature region corresponds to a temperature region exceeding the intermediate temperature region. Thereby, since each temperature area | region can be set appropriately, active oxygen can be used more efficiently.

  According to the fifth invention, when the exhaust gas flow rate exceeds a predetermined value, the supply of active oxygen can be suppressed. In a state where the exhaust gas flow rate is increased during acceleration or the like, there is no sufficient time for active oxygen to react with NO until the active oxygen reaches the NOx catalyst. For this reason, the NOx purification promotion effect by active oxygen becomes thin. In such a case, the supply of active oxygen can be prevented from being wasted by suppressing the supply of active oxygen. Therefore, the electric power consumed for the production of active oxygen can be reduced, and the fuel consumption can be improved.

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

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is common in each figure, and the overlapping description is abbreviate | omitted.

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

  An oxidation catalyst 20 and a NOx catalyst 21 are installed in this order from the side close to the internal combustion engine 10 in the exhaust passage 15. An ozone supply nozzle 22 is installed between the oxidation catalyst 20 and the NOx catalyst 21. The ozone supply nozzle 22 is provided with a plurality of ozone supply ports 23. An ozone generator 25 is connected to the ozone supply nozzle 22 via an ozone supply passage 24. In the configuration shown in the drawing, the ozone supply nozzle 22 is disposed inside the casing 26 common to the NOx catalyst 21 and on the front side (upstream side) of the NOx catalyst 21. In the present embodiment, the ozone generator 25, the ozone supply passage 24, and the ozone supply nozzle 22 constitute an ozone supply device 27.

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

According to the ozone supply device 27 as described above, ozone (O ₃ ) can be generated by the ozone generator 25, and this ozone can be injected from the ozone supply port 23 of the ozone supply nozzle 22. Thereby, ozone can be added to the exhaust gas between the oxidation catalyst 20 and the NOx catalyst 21.

The oxidation catalyst 20 has a function of purifying HC by reacting hydrocarbons (hereinafter referred to as “HC”), which are unburned fuel components in the exhaust gas, with O ₂ to form CO ₂ , H ₂ O, and the like. Have. As the catalyst component of the oxidation catalyst 20, for example, Pt / CeO ₂ , Mn / CeO ₂ , Fe / CeO ₂ , Ni / CeO ₂ , Cu / CeO ₂ or the like can be used.

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

  In the present embodiment, no other catalyst or the like is provided between the oxidation catalyst 20 and the NOx catalyst 21, and they are arranged at a distance close to each other. For this reason, the temperature of the oxidation catalyst 20 and the temperature of the NOx catalyst 21 are approximately the same. In the illustrated configuration, the oxidation catalyst 20 and the NOx catalyst 21 are housed in separate casings, but may be housed in a common casing.

  The system of this embodiment includes a temperature sensor 28 that detects the temperature (bed temperature) of the oxidation catalyst 20, a temperature sensor 29 that detects the temperature (bed temperature) of the NOx catalyst 21, and an ECU (Electronic Control Unit) 50. In addition. The ECU 50 includes various sensors for controlling the internal combustion engine 10 such as the fuel injector 14, the ozone generator 25, the temperature sensors 28 and 29, the crank angle sensor 46, the air flow meter 47, and the accelerator position sensor 48. And the actuator is electrically connected.

The storage material of the NOx catalyst 21 absorbs NOx (nitrogen oxide) by forming a nitrate (Ba (NO ₃ ) _{2 in} this embodiment). The occlusion material can absorb NO ₂ and NO ₃ well among 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, usually, the NOx catalyst 21, by a noble metal (platinum Pt in this embodiment) as a catalyst, NO ₂ is produced and NO in exhaust gas and oxygen O ₂ reacts, the NO ₂ It is made to absorb in the occlusion material.

However, the activity of the noble metal catalyst does not appear unless it reaches a certain temperature or higher (for example, 200 ° C. or higher). Therefore, when the temperature of the NOx catalyst 21 is low, such as immediately after the internal combustion engine 10 is started, NO is not oxidized to NO ₂ by the noble metal catalyst, so that NOx cannot be stored.

  Further, if the oxidation catalyst 20 does not reach a certain temperature or higher (for example, 200 ° C. or higher), its activity does not appear, and HC cannot be oxidized and purified.

In this embodiment, when the temperature of the oxidation catalyst 20 or the NOx catalyst 21 is low, ozone is supplied by the ozone supply device 27 and exhausted in order to suppress the release of HC and NOx into the atmosphere. It was decided to add it to the gas. Ozone has a high oxidizing power. For this reason, NOx, HC, and ozone can react in the gas phase from a low temperature of about room temperature. HC is purified to CO ₂ or H ₂ O by reacting with ozone.

FIG. 2 is a diagram showing how NOx is purified (absorbed) when ozone is supplied when the NOx catalyst 21 is in a low temperature state. When ozone is supplied, NO in the exhaust gas is converted into NO ₂ and NO ₃ by reacting with ozone. The occlusion material Ba can sufficiently absorb NO ₂ and NO ₃ from a low temperature of about room temperature to form nitrate. For this reason, even if the activity of the NOx catalyst 21 is not expressed, by supplying ozone, the NOx can be absorbed by the storage material and the release of NOx into the atmosphere can be suppressed. .

When the temperature of the NOx catalyst 21 is higher than a certain temperature (for example, 200 ° C. or higher), the catalytic activity starts to be expressed, so that NO in the exhaust gas and oxygen O ₂ can be reacted and converted to NO _2. Become. However, until the temperature of the NOx catalyst 21 reaches a sufficiently high temperature (for example, 300 ° C.), the catalytic activity is not sufficient, so that all of the NO in the exhaust gas cannot be converted to NO ₂ by the catalyst. For this reason, if ozone is not supplied, a part of NO passes through the NOx catalyst 21. Therefore, in the present embodiment, even after the temperature of the NOx catalyst 21 exceeds the activation expression temperature (for example, 200 ° C.), the supply of ozone is continued until the temperature reaches a sufficiently activated temperature (for example, 300 ° C.). It was decided to.

FIG. 3 is a diagram showing a state in which NOx is purified when ozone is supplied when the NOx catalyst 21 is in an intermediate temperature state (a state where the catalytic activity is expressed but the activation is not sufficient). When the NOx catalyst 21 is in an intermediate temperature state, the activity of the Pt catalyst is partially expressed. Therefore, as shown in FIG. 3, some of the NO in the exhaust gas can be converted to NO ₂ by being reacted with oxygen O ₂ by the Pt catalyst and absorbed by the storage material. On the other hand, the amount of NO that cannot be treated with the Pt catalyst can be absorbed by the occlusion material by reacting with ozone in the gas phase and converting it to NO ₂ or NO ₃ .

Further, according to the knowledge of the present inventors, when NOx occlusion is promoted by supplying ozone when the NOx catalyst 21 is in an intermediate temperature state, if HC coexists, selective reduction of NOx by HC. It has been confirmed that reactions occur in parallel. That is, as shown in FIG. 3, when HC coexists, a reaction in which NOx is reduced by HC and purified to N ₂ , CO ₂ , H ₂ O occurs in parallel with the NOx occlusion reaction. . For this reason, the NOx purification rate can be further increased.

  On the other hand, according to the knowledge of the present inventors, when NOx occlusion is promoted by supplying ozone when the NOx catalyst 21 is in a low temperature state, it is better that HC does not coexist. FIG. 4 is a graph showing the relationship between the HC coexistence amount and the NOx purification rate when the NOx catalyst 21 is in a low temperature state. As shown in FIG. 4, when the NOx catalyst 21 is in a low temperature state, the NOx purification rate becomes maximum when the HC coexistence amount is zero. The NOx purification rate decreases as the HC coexistence amount increases. The reason is considered as follows. When the NOx catalyst 21 is in a low temperature state, that is, in a state where the activity is not expressed, even if HC exists, the selective reduction reaction as described above does not occur. On the other hand, if HC is present, ozone is consumed by reacting with HC, and the amount of reaction between ozone and NO is reduced accordingly. As a result, it is considered that the amount of NOx absorbed decreases and the NOx purification rate decreases.

  On the other hand, when the NOx catalyst 21 is in an intermediate temperature state, the NOx purification rate can be increased when a certain amount of HC coexists. FIG. 5 is a graph showing the relationship between the HC coexistence amount and the NOx purification rate when the NOx catalyst 21 is in an intermediate temperature state. As shown in FIG. 5, when the NOx catalyst 21 is in an intermediate temperature state, there exists an optimum value of the HC coexistence amount that maximizes the NOx purification rate. As described above, this is considered to be because when HC is present, the selective reduction reaction of NOx by HC occurs in parallel with the NOx occlusion reaction. When the HC coexistence amount becomes larger than the optimum value, the NOx purification rate gradually decreases. This is considered to be because the amount of NOx absorbed decreases as a result of the consumption of ozone by HC as in the case of the low temperature state.

  In view of the matters described above, in the present system, the amount of ozone added to the exhaust gas by the ozone supply device 27 is controlled as follows. FIG. 6 is a diagram showing the relationship between the temperature of the oxidation catalyst 20 and the NOx catalyst 21 and the amount of ozone added. Hereinafter, the ozone supply control in this embodiment will be described with reference to FIG.

(Low temperature region)
When the temperature of the oxidation catalyst 20 and the NOx catalyst 21 is in a low temperature region (region where the catalytic activity does not appear), it is necessary to purify (absorb) NOx in an amount necessary for purifying HC and NOx. A quantity of ozone is supplied by an ozone supply device 27. In the low temperature region where the activity of the oxidation catalyst 20 is not expressed, the oxidation catalyst 20 cannot purify HC. On the other hand, the NOx purification rate increases as the amount of HC in the NOx catalyst 21 approaches zero. Therefore, the “amount of ozone necessary for purifying HC” is preferably set to an ozone amount that can remove almost all of the HC.

(Medium temperature range)
When the temperature of the oxidation catalyst 20 and the NOx catalyst 21 is in an intermediate temperature range (a range from a temperature at which catalytic activity begins to appear to a temperature at which activation is sufficient), an amount necessary for partially purifying HC The ozone supply device 27 supplies ozone in an amount necessary for purifying (absorbing) NOx. In the intermediate temperature range where the activity of the oxidation catalyst 20 starts to be expressed, a part of HC is purified by the oxidation catalyst 20. On the other hand, as described above, in the NOx catalyst 21, there is an optimum value of the HC coexistence amount that maximizes the NOx purification rate. For this reason, it is most desirable to flow an optimal amount of HC into the NOx catalyst 21 instead of completely removing HC with ozone. Therefore, the above “amount of ozone necessary for partially purifying HC” excludes the amount of HC to be purified by the oxidation catalyst 20 and the optimum amount of HC that should flow into the NOx catalyst 21. The amount of ozone is set such that the remaining HC can be purified. Further, as described above, in the intermediate temperature region where the activity of the NOx catalyst 21 is partially expressed, a part of the NO can be converted to NO ₂ by the Pt catalyst and absorbed by the storage material. For this reason, the amount of ozone required to purify NOx is smaller than that in the low temperature region. In view of the above, in the intermediate temperature region, as shown in FIG. 6, the ozone supply amount is reduced compared to the low temperature region.

(High temperature region)
When the temperatures of the oxidation catalyst 20 and the NOx catalyst 21 are in a high temperature region (a region higher than the temperature at which activation of the catalyst is sufficient), supply of ozone by the ozone supply device 27 is stopped. In a high temperature region (for example, 300 ° C. or higher), ozone is easily decomposed. For this reason, even if ozone is supplied, the effect is thin. Further, in the high temperature region where the catalyst is sufficiently activated, HC and NOx can be sufficiently purified by the oxidation catalyst 20 and the NOx catalyst 21, respectively. Therefore, there is little need to supply ozone. Therefore, the supply of ozone was stopped in the high temperature region. As a result, in the high temperature region, power is not consumed by the ozone supply device 27, so that fuel efficiency can be improved.

[Specific Processing in Embodiment 1]
FIG. 7 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. 7, first, the temperatures of the oxidation catalyst 20 and the NOx catalyst 21 are a low temperature region (for example, less than 200 ° C.), a medium temperature region (for example, 200 ° C. to 300 ° C.), and a high temperature region (for example, 300 ° C. or more). Is determined (step 100). In this embodiment, the determination in step 100 is made based on the outputs of the temperature sensors 28 and 29. In this embodiment, temperature sensors are provided for both the oxidation catalyst 20 and the NOx catalyst 21, but in the present invention, this is based on the output of the temperature sensor provided for either the oxidation catalyst 20 or the NOx catalyst 21. The determination in step 100 may be made. Further, in the present invention, the temperature of the oxidation catalyst 20 and the NOx catalyst 21 is estimated based on the operation state (engine speed, load, exhaust gas temperature, etc.) of the internal combustion engine 10 without using the temperature sensor. You may make it judge.

  If it is determined in step 100 that the temperature is in the low temperature region, the amount of ozone necessary to purify HC is calculated (step 102). In the present embodiment, the ECU 50 stores an HC emission amount map created by examining the relationship between the operating state of the internal combustion engine 10 (engine speed, load, cooling water temperature, etc.) and the amount of HC in the exhaust gas in advance. Has been. In this step 102, first, the amount of HC discharged from the internal combustion engine 10 is calculated based on the HC emission map. Next, based on the amount of HC, the amount of ozone that needs to be added to react with this is calculated by a predetermined calculation method.

  Following the processing of step 102, the amount of ozone required to purify (absorb) NOx is calculated (step 104). In the present embodiment, the ECU 50 stores a NOx emission map created by examining the relationship between the operating state of the internal combustion engine 10 (engine speed, load, cooling water temperature, etc.) and the amount of NOx in the exhaust gas in advance. Has been. In this step 104, first, the amount of NOx discharged from the internal combustion engine 10 is calculated based on the NOx emission amount map. Next, based on the NOx amount, the amount of ozone that needs to be added to react with the NOx amount is calculated by a predetermined calculation method.

  When the amount of ozone necessary to purify HC is calculated in step 102 and the amount of ozone necessary to purify NOx is calculated in step 104, the total amount of ozone is exhaust gas. Control for driving the ozone supply device 27 is performed so as to be added to the inside (step 106).

  On the other hand, if it is determined in step 100 that the temperature is in the middle temperature range, the amount of ozone necessary to partially purify HC is calculated (step 108). In the present embodiment, the ECU 50 provides the HC purification rate map created by examining the relationship between the temperature of the oxidation catalyst 20 and the HC purification rate in the oxidation catalyst 20 in advance, and the optimal HC inflow amount to the NOx catalyst 21. (HC inflow amount that maximizes the NOx purification rate) is stored. In this step 108, first, the HC emission amount from the internal combustion engine 10 is calculated based on the HC emission amount map described above. Next, the HC purification amount in the oxidation catalyst 20 calculated based on the HC purification rate map and the optimum HC inflow amount to the NOx catalyst 21 should be subtracted from the HC emission amount to be purified by ozone. The amount of HC is calculated. Then, the amount of ozone that needs to be added to react with that amount of HC is calculated by a predetermined calculation method.

  Subsequent to step 108, the amount of ozone required to purify (absorb) NOx is calculated (step 110). In the present embodiment, the ECU 50 stores a map created by examining in advance the relationship between the temperature of the NOx catalyst 21 and the NOx purification rate that can be purified without using ozone at that temperature. In step 110, first, the amount of NOx that can be purified without using ozone is calculated based on the map. Next, the amount of NOx to be purified by ozone is calculated by subtracting the amount of NOx that can be purified without using ozone from the NOx emission amount calculated based on the NOx emission amount map described above. Then, the amount of ozone that needs to be added to react with that amount of NOx is calculated by a predetermined calculation method.

  When the amount of ozone necessary for partially purifying HC is calculated in step 108 and the amount of ozone necessary for purifying NOx is calculated in step 110, the total amount of ozone is calculated. Control for driving the ozone supply device 27 is performed so as to be added to the exhaust gas (step 112).

  When it is determined in step 100 that the temperature is in the high temperature region, the ozone supply device 27 is stopped to stop the addition of ozone into the exhaust gas (step 114).

  As described above, according to the present embodiment, even if the temperature of the oxidation catalyst 20 or the NOx catalyst 21 is in a low temperature region where the activity is not expressed or in an intermediate temperature region where the activation is not sufficient, By adding ozone into the exhaust gas by the supply device 27, HC and NOx can be sufficiently purified. For this reason, even if the temperature of the oxidation catalyst 20 or the NOx catalyst 21 is not sufficiently increased, such as immediately after the start of the internal combustion engine 10, it is possible to reliably suppress the release of HC and NOx into the atmosphere. it can.

  Further, by controlling the ozone supply amount and supply stop according to the temperatures of the oxidation catalyst 20 and the NOx catalyst 21, ozone can be used efficiently without waste. For this reason, the electric power consumed for the production | generation of ozone can be suppressed, and a fuel consumption can be improved.

  Furthermore, in the present embodiment, the ozone amount (HC concentration) flowing into the NOx catalyst 21 in the intermediate temperature region is higher than the HC amount (HC concentration) flowing into the NOx catalyst 21 in the low temperature region. The supply is controlled. Thereby, the NOx purification rate can be further increased in each of the low temperature region and the medium temperature region.

  In the present embodiment, the internal combustion engine 10 is described as being of the compression ignition type, but the present invention can also be applied to a spark ignition type internal combustion engine.

  Further, the ozone supply device 27 of the present embodiment is configured to supply the ozone generated by the ozone generator 25 as it is into the exhaust passage 15, but in the present invention, ozone is generated and stored in advance. The stored ozone may be supplied into the exhaust passage 15 when necessary.

  Further, in the present embodiment, the supply of ozone is stopped in the high temperature region. However, in the present invention, the ozone supply may not be completely stopped in the high temperature region, and the ozone supply amount may only be reduced. .

In the present embodiment, ozone is added to the exhaust gas as active oxygen. However, in the present invention, other types of active oxygen (for example, O ⁻ , O ²⁻ , O ₂ ⁻⁾ are used instead of ozone. , O ₃ ⁻ , O _n ^−, etc.) may be added to the exhaust gas.

In this embodiment, the NOx catalyst 21 is described as an NOx storage reduction catalyst. However, in the present invention, the NOx catalyst 21 is a selective reduction NOx catalyst (SCR: Selective Catalytic Reduction). Applicable. As the selective reduction NOx catalyst, for example, a catalyst in which Fe is supported on the surface of zeolite can be preferably used. In the case of a selective reduction type NOx catalyst, a reducing agent such as urea is preferably used. In the selective reduction type NOx catalyst, the best purification rate is obtained when the ratio of the amount of NO to the amount of NO ₂ is 1: 1. Therefore, in the case of a selective reduction type NOx catalyst, the active oxygen supply amount is controlled so that the ratio of the amount of NO inside thereof to the amount of NO ₂ becomes 1: 1 in the low temperature region or the intermediate temperature region. Is preferred.

  In the first embodiment described above, the ozone supply device 27 corresponds to the “active oxygen supply device” in the first invention, and the temperature sensors 28 and 29 correspond to the “temperature information acquisition means” in the first invention. is doing. Further, when the ECU 50 executes the routine shown in FIG. 7, the “control means” in the first invention executes the process of the above step 100, thereby the “catalyst temperature determination means in the first invention”. "In the second invention, the" active oxygen amount control means "in the first invention is executed in the second invention by executing the processes in the steps 102, 104 and 106. The “low temperature active oxygen amount control means” executes the processing of steps 108, 110 and 112, so that the “medium temperature active oxygen amount control means” of the second invention executes the processing of step 114. Thus, the “supply suppression means” in the third aspect of the present invention is realized.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 8 and FIG. 9. The description will focus on the differences from the first embodiment described above, and the same matters will be described. Simplify or omit.

  The hardware configuration of the present embodiment is as shown in FIG. 1 as in the first embodiment. When the amount of exhaust gas of the internal combustion engine 10 increases, such as during acceleration, the exhaust gas flow rate in the exhaust passage increases. When the exhaust gas flow rate is fast, the time until the ozone added from the ozone supply port 23 reaches the NOx catalyst 21 is shortened. As a result, it is considered that sufficient time for ozone to react with NOx (NO) in the exhaust gas cannot be taken, and the NOx occlusion promoting effect is reduced.

In order to verify the above items, the following tests were conducted. As a catalyst, 3 g of 1 mm square pellets in which 1% of Pt was supported on Al ₂ O ₃ was used. With respect to this catalyst, the NOx occlusion amount in an air stream containing 10% O ₂ and 200 ppm NO in N ₂ was measured at room temperature. In the evaluation, the reaction time between ozone and NO was changed by changing the gas flow rate. When the gas flow rate changes, the amount of NOx passing through the catalyst per unit time changes. Therefore, the NOx occlusion time was changed for each evaluation so that the total amount of NOx passing through the catalyst was uniform. The conditions for each evaluation are shown in Table 1 below.

  The results of the above test are shown in FIG. As shown in FIG. 8, when the reaction time between ozone and NO is shortened, the NOx occlusion amount is decreased. Thus, it was demonstrated that the NOx occlusion promoting effect by ozone cannot be sufficiently obtained when the reaction time between ozone and NO is short. Such a phenomenon is the same not only in a temperature range near room temperature but also in a higher temperature range. Therefore, in the present embodiment, when the reaction time between ozone and NO cannot be secured, that is, when the exhaust gas flow rate is high at the time of acceleration or the like, supply of ozone by the ozone supply device 27 is prohibited.

  FIG. 9 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. 9, first, the exhaust gas flow velocity is calculated (step 120). In this case, the exhaust gas flow velocity can be calculated based on the intake air amount detected by the air flow meter 47. Next, it is determined whether or not the exhaust gas flow rate calculated in step 120 is greater than a predetermined determination value (step 122).

  If the exhaust gas flow rate exceeds the determination value in step 122, it can be determined that a sufficient NOx occlusion promoting effect cannot be obtained even if ozone is supplied. Therefore, in this case, the supply of ozone by the ozone supply device 27 is prohibited (step 124). Thereby, since ozone can be prevented from being supplied unnecessarily, power consumed for ozone generation can be reduced, and fuel consumption can be improved.

  On the other hand, when the exhaust gas flow rate is equal to or lower than the determination value in step 122, the supply of ozone by the ozone supply device 27 is not prohibited. In this case, the supply of ozone is controlled based on the routine process shown in FIG.

  In the present embodiment, the supply of ozone is prohibited when the exhaust gas flow rate is fast. However, in the present invention, the supply of ozone is suppressed (the supply amount is reduced) when the exhaust gas flow rate is fast. It may be only.

  In the second embodiment described above, the ECU 50 executes the process of step 120, so that the “exhaust gas flow rate calculating means” in the fifth aspect of the invention executes the processes of steps 122 and 124. The “means for suppressing the supply of active oxygen” in the fifth invention is realized.

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 purified when ozone is supplied when a NOx catalyst is in a low temperature state. It is a figure which shows a mode that NOx is purified when ozone is supplied when a NOx catalyst is in an intermediate temperature state. It is a graph which shows the relationship between HC coexistence amount and NOx purification rate when a NOx catalyst is a low temperature state. It is a graph which shows the relationship between HC coexistence amount and NOx purification rate when a NOx catalyst is an intermediate temperature state. It is a figure which shows the relationship between the temperature of an oxidation catalyst and a NOx catalyst, and ozone addition amount. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the test result in Embodiment 2 of this invention. It is a flowchart of the routine performed in Embodiment 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Intake manifold 12 Exhaust manifold 13 Cylinder 14 Fuel injector 15 Exhaust passage 17 Supply pump 18 Common rail 19 Turbocharger 20 Oxidation catalyst 21 NOx catalyst 22 Ozone supply nozzle 23 Ozone supply port 24 Ozone supply passage 25 Ozone generator 26 Casing 27 Ozone supply device 28, 29 Temperature sensor 50 ECU

Claims (6)

An oxidation catalyst disposed in the exhaust passage of the internal combustion engine and having a function of oxidizing unburned components in the exhaust gas;
A NOx catalyst installed downstream of the oxidation catalyst and having a function of purifying NOx in exhaust gas;
An active oxygen supply device for supplying active oxygen between the oxidation catalyst and the NOx catalyst;
Temperature information acquisition means for acquiring information relating to temperatures of the oxidation catalyst and the NOx catalyst;
Control means for controlling the supply of active oxygen by the active oxygen supply device based on the information;
With
The control means includes
Catalyst temperature determination means for determining whether the temperature of the oxidation catalyst and the NOx catalyst is in a predetermined low temperature region, medium temperature region, or high temperature region based on the information;
When it is determined that the temperature is in the low temperature region, an amount of active oxygen necessary for purifying NOx in exhaust gas and an amount of active oxygen necessary for purifying HC in exhaust gas are Low temperature active oxygen amount control means to be supplied by the active oxygen supply device;
An active oxygen in an amount necessary to purify NOx in the exhaust gas and an active oxygen in an amount necessary to purify a part of the HC in the exhaust gas when it is determined that the temperature is in the intermediate temperature range; Medium temperature active oxygen amount control means to be supplied by the active oxygen supply device,
And the HC concentration in the exhaust gas flowing into the NOx catalyst when it is determined to be in the intermediate temperature region, the HC in the exhaust gas flowing into the NOx catalyst when it is determined to be in the low temperature region An exhaust gas purification apparatus for an internal combustion engine, wherein the supply amount of active oxygen is controlled so as to be higher than the concentration . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein when the NOx catalyst is in the intermediate temperature range, a reaction in which NOx is reduced and purified by HC occurs in parallel with a NOx occlusion reaction. .
  3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the control means includes supply suppression means for suppressing supply of active oxygen when it is determined that the temperature is in the high temperature region.   The low temperature region corresponds to a temperature region in which the activities of the oxidation catalyst and the NOx catalyst are not expressed, and the intermediate temperature region is from a temperature at which the activities of the oxidation catalyst and the NOx catalyst start to be expressed. The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 3, wherein the high temperature region corresponds to a temperature region exceeding the intermediate temperature region, corresponding to a temperature until activation. Exhaust gas flow velocity calculating means for calculating the flow velocity of the exhaust gas flowing through the exhaust passage;
Means for suppressing the supply of active oxygen when the exhaust gas flow rate exceeds a predetermined value;
The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 4, further comprising:   The exhaust gas purifying device for an internal combustion engine according to any one of claims 1 to 5, wherein the active oxygen supply device supplies ozone as active oxygen.

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