JP2009264320A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To activate an exhaust emission control catalyst at an early stage in an exhaust emission control device for an internal combustion engine. <P>SOLUTION: This exhaust emission control device for the internal combustion engine is disposed in an exhaust passage 15 of the internal combustion engine 10, and is provided with an NOx catalyst 21 eliminating noxious components in exhaust gas, an ozone supply device 27 supplying ozone as activated oxygen at an upstream of the NOx catalyst 21, and an unburned fuel component supply means increasing HC concentration (unburned fuel component concentration) in exhaust gas at an upstream of the NOx catalyst 21 more than that in normal time. ECU 50 executes catalyst temperature raising control supplying ozone at the upstream of the NOx catalyst 21 by the ozone supply device 27 and increasing HC concentration in exhaust gas at the upstream of the NOx catalyst 21 by the unburned fuel component supply means when raise of temperature of the NOx catalyst 21 is demanded. <P>COPYRIGHT: (C)2010,JPO&INPIT

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, in order to suppress the release of harmful components into the atmosphere, it is important to raise the temperature of the catalyst to the activation temperature or more as soon as possible when the catalyst is in a low temperature state, such as immediately after the engine is started. In order to solve this problem, an electric heating catalyst or the like has been proposed. However, there are disadvantages such as an increase in cost, an increase in power consumption, and an increase in weight.

Japanese Patent Application Laid-Open No. 2007-16635 discloses a PM collection device, a selective reduction type NOx catalyst provided downstream thereof, and a first oxidation for supplying an oxidizing agent such as ozone immediately before the PM collection device. Disclosed is an exhaust emission control device comprising an agent supply means, a second oxidant supply means for supplying an oxidant immediately before the NOx catalyst, and a reducing agent supply means for supplying a reducing agent such as ammonia immediately before the NOx catalyst. Has been. In this apparatus, a sufficient amount of NO ₂ is supplied to the NOx catalyst by making the oxidant supply amount by the second oxidant supply means larger than the oxidant supply amount by the first oxidant supply means. It aims to promote the purification of NOx by the NOx catalyst.

JP 2007-16635 A JP 2007-152336 A

  The technique described in the above-mentioned conventional publication does not sufficiently consider raising the catalyst temperature early, and has not yet solved the problem of early activation of the catalyst.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine capable of early activation of an exhaust purification catalyst.

In order to achieve the above object, a first invention is an exhaust gas purification apparatus for an internal combustion engine,
A catalyst disposed in the exhaust passage of the internal combustion engine for purifying harmful components in the exhaust gas;
An active oxygen supply device for supplying active oxygen to the upstream side of the catalyst;
Unburned fuel component supply means for increasing the unburned fuel component concentration in the exhaust gas upstream of the catalyst from the normal time;
When it is required to increase the temperature of the catalyst, active oxygen is supplied to the upstream side of the catalyst by the active oxygen supply device, and the concentration of unburned fuel components in the exhaust gas upstream of the catalyst is A catalyst temperature raising means for performing catalyst temperature raising control, which is increased by the unburned fuel component supply means;
It is characterized by providing.

The second invention is the first invention, wherein
The catalyst includes Ag as a catalyst component.

The third invention is the first or second invention, wherein
A flow rate index value calculating means for calculating an index value of the exhaust gas flow rate;
A catalyst temperature increase control suppressing means for suppressing execution of the catalyst temperature increase control when the index value exceeds a predetermined value;
It is characterized by providing.

According to a fourth invention, in any one of the first to third inventions,
The catalyst temperature raising means includes addition ratio control means for increasing the ratio of the amount of unburned fuel component added to the amount of active oxygen added to the exhaust gas as the temperature of the catalyst rises.

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

  According to the first invention, when it is required to increase the temperature of the catalyst, the catalyst temperature increase control for adding the active oxygen and the unburned fuel component to the exhaust gas upstream of the catalyst can be executed. it can. Since active oxygen has a strong oxidizing power, the added active oxygen and the unburned fuel component can react efficiently even at low temperatures. For this reason, the temperature of a catalyst can be raised rapidly using the reaction heat. According to the first invention, since the catalyst can be activated at an early stage, for example, at a low temperature of the catalyst such as immediately after the start of the internal combustion engine, the release of harmful components into the atmosphere can be sufficiently reduced.

  According to the second invention, Ag is contained in the catalyst. When active oxygen and unburned fuel components are added by the catalyst temperature increase control, CO is generated by the reaction thereof. Ag expresses the activity of efficiently oxidizing CO from a low temperature in the presence of active oxygen. For this reason, according to the second aspect of the invention, Ag generated by the reaction of the active oxygen and unburned fuel component added in the catalyst temperature increase control can be oxidized and purified using Ag as a catalyst. Moreover, according to 2nd invention, there exists an advantage that the temperature of a catalyst can be raised more rapidly. This is because the catalyst can be heated not only by the reaction heat between the active oxygen and the unburned fuel component but also by the reaction heat of the CO oxidation reaction.

  According to the third invention, when the index value of the exhaust gas flow rate exceeds a predetermined value, execution of the catalyst temperature increase control can be suppressed. If the index value of the exhaust gas flow rate exceeds a predetermined value due to sudden acceleration, etc., the reaction gas stays in the catalyst for a short time, so even if active oxygen and unburned fuel components are added, the catalyst temperature rises. It can be determined that the effect is difficult to obtain. According to the third invention, in such a case, the use of active oxygen or fuel can be saved by temporarily suppressing the execution of the catalyst temperature increase control. For this reason, active oxygen and fuel can be used more effectively, and fuel consumption performance can be improved.

  According to the fourth invention, as the temperature of the catalyst rises, the ratio of the unburned fuel component addition amount to the active oxygen addition amount in the exhaust gas can be increased. When the temperature of the catalyst is low, the oxidation rate of the added unburned fuel component is relatively low. For this reason, it can suppress reliably that the unburned fuel component which remains without being oxidized arises by making the ratio of the unburned fuel component addition amount with respect to the amount of active oxygen addition comparatively small. On the other hand, as the temperature of the catalyst increases, the oxidation rate of the unburned fuel component increases. For this reason, even if the ratio of the unburned fuel component addition amount to the active oxygen addition amount is increased, the unburned fuel component can be oxidized without remaining. Therefore, by controlling the addition amount of the active oxygen and the unburned fuel component as described above, the active oxygen and the unburned fuel component can be used more effectively, and the unburned fuel component can pass through the catalyst. It can be surely suppressed.

  According to 5th invention, the said effect can be exhibited more notably by using ozone as active oxygen.

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

A NOx catalyst 21 having a function of purifying NOx is installed in the exhaust passage 15. The NOx catalyst 21 of the present embodiment is an NOx storage reduction (NSR: NOx Storage Reduction) catalyst. That is, the NOx catalyst 21 has, for example, a catalyst component in which a noble metal such as platinum Pt and a NOx occlusion material are arranged 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 this specification, the term “occlusion” includes all concepts similar to “holding”, “adsorption”, “absorption”, and the like.

  An ozone supply nozzle 22 is installed on the upstream side of the NOx catalyst 21. The ozone supply nozzle 22 is provided with a plurality of ozone supply ports 23. An ozone generator 25 is connected to the ozone supply nozzle 22 via an ozone supply passage 24. In the illustrated configuration, the ozone supply nozzle 22 is disposed inside the casing 26 that houses the NOx catalyst 21 and on the front side (upstream side) of the NOx catalyst 21. In the present embodiment, the ozone generator 25, the ozone supply passage 24, and the ozone supply nozzle 22 constitute an ozone supply device 27.

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

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

  In the exhaust passage 15, a temperature sensor 28 that detects the temperature of exhaust gas flowing into the NOx catalyst 21 (hereinafter referred to as “gas temperature with catalyst”), and a temperature sensor that detects the temperature (bed temperature) of the NOx catalyst 21. 29 are installed.

  The system of the present embodiment further includes an ECU (Electronic Control Unit) 50. 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 by forming a nitrate such as Ba (NO ₃ ) ₂ , for example. The storage material can well absorb NO ₂ , NO ₃ or N ₂ O ₅ in NOx. On the other hand, most of NOx originally contained in the exhaust gas is NO (nitrogen monoxide). NO cannot be absorbed by the occlusion material as it is. Therefore, in the NOx catalyst 21, by a noble metal such as Pt is the catalyst, the NO in the exhaust gas and oxygen O ₂ reacted was converted to NO _2, so as to absorb the NO ₂ by the occluding material Yes.

However, the activity of the noble metal catalyst does not appear unless the temperature is higher than a certain temperature (for example, 200 ° C. or higher). Therefore, when the temperature of the NOx catalyst 21 is lower than that temperature, NO is not oxidized to NO ₂ by the noble metal catalyst, and therefore NOx cannot be occluded. Further, in order to sufficiently activate the noble metal catalyst, a higher temperature (for example, about 300 ° C.) is required. For this reason, when the temperature of the NOx catalyst 21 is lower than that temperature, the NOx cannot be sufficiently stored.

Therefore, in order to suppress the release of NOx into the atmosphere, when the NOx catalyst 21 is at a low temperature, such as immediately after the start of the internal combustion engine 10, the temperature is raised to the above active temperature as early as possible. Is important. As a result of intensive studies to solve this problem, the present inventors have added unburned fuel components (hereinafter referred to as “HC”) and ozone into the exhaust gas upstream of the NOx catalyst 21. Thus, it has been found that the temperature of the NOx catalyst 21 can be rapidly increased. Ozone has a stronger oxidizing power than O ₂ . For this reason, ozone and HC can react efficiently in a gas phase or via a catalyst even in a low temperature range (normal temperature range). Therefore, by adding them into the exhaust gas upstream of the NOx catalyst 21, the temperature of the NOx catalyst 21 can be quickly raised using the reaction heat.

FIG. 2 is a diagram showing the results of tests conducted to verify the effectiveness of the above method. In this test, a 1 mm square pellet in which 1% of Pt was supported on γAl ₂ O ₃ was used as a catalyst. The catalyst was placed in a model gas stream at about 200 ° C., and the catalyst temperature was measured. The composition of the model gas is 1000 ppm for HC (here, C ₃ H ₆ ), 10% for O ₂ , 3% for H ₂ O, and the rest for N ₂ . The upper graph in FIG. 2 shows the measurement results of the temperature of the catalyst and the temperature of the model gas flowing into the catalyst (hereinafter referred to as “entering gas temperature”). In this test, a portion of O _{2 in} the model gas flowing into the catalyst was converted into ozone by discharge after 800 seconds from the start of measurement. The concentration of ozone was about 1000 ppm. The lower graph in FIG. 2 shows the measurement results of the ozone concentration in the model gas flowing into the catalyst and the HC concentration in the model gas passing through the catalyst.

  As shown in the lower graph of FIG. 2, when ozone starts to flow into the catalyst 800 seconds after the start of measurement, the HC concentration in the catalyst downstream suddenly decreases. This indicates that HC is consumed by reaction with ozone. As shown in the upper graph of FIG. 2, the catalyst temperature after the start of ozone inflow is higher than before. This is due to the reaction heat between HC and ozone.

  From the results of the above-mentioned test, when the catalyst activity is low, the catalyst temperature can be rapidly raised by supplying HC and ozone upstream of the catalyst. Has been demonstrated. Therefore, in the system of the present embodiment, when the NOx catalyst 21 is at a low temperature such as immediately after the start of the internal combustion engine 10 and it is required to quickly increase the temperature of the NOx catalyst 21, the upstream side of the NOx catalyst 21 is required. The control for adding ozone and HC to the exhaust gas was executed. This control is hereinafter referred to as “catalyst temperature rise control”.

In the catalyst temperature increase control, ozone added to the exhaust gas can be supplied by the ozone supply device 27 described above. Further, in this specification, “adding HC” means that the HC concentration in the exhaust gas upstream of the NOx catalyst 21 is increased as compared with that during normal operation (operation that optimizes fuel consumption). It means that The method for adding HC is not particularly limited, and for example, any of the following methods can be employed.
(1) A method of injecting fuel from the fuel injector 14 in the expansion stroke or exhaust stroke of the cylinder 13 of the internal combustion engine 10 (that is, post injection).
(2) A method of injecting fuel from a fuel addition valve (not shown) provided in the exhaust passage 15 upstream of the NOx catalyst 21 (that is, exhaust system fuel addition).
(3) A method in which a large amount of exhaust gas recirculation (EGR) is performed so that the air-fuel ratio in the cylinder is significantly richer than normal, and combustion is performed at a low temperature so as not to generate soot (that is, low temperature rich combustion).

  Further, in the case of a spark ignition internal combustion engine such as a gasoline engine, HC can be added by increasing the fuel injection amount.

[Specific Processing in Embodiment 1]
FIG. 3 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to realize the catalyst temperature raising control as described above. According to the routine shown in FIG. 3, first, it is determined whether or not the temperature of the NOx catalyst 21 detected by the temperature sensor 29 is lower than a predetermined determination value (300 ° C. in the present embodiment) ( Step 100). In the present embodiment, the temperature of the NOx catalyst 21 is directly detected by the temperature sensor 29. However, in the present invention, the temperature of the NOx catalyst 21 is based on the engine speed, the engine load, the exhaust gas temperature, and the like. May be estimated. In the present invention, the determination in step 100 may be performed based on the catalyst input gas temperature or the catalyst output gas temperature (the temperature of the exhaust gas that has exited the catalyst).

  When ozone reaches a high temperature of about 300 ° C. or higher, it is likely to be thermally decomposed. For this reason, when the temperature of the NOx catalyst 21 is 300 ° C. or higher, even if ozone is added from the ozone supply port 23, many of them are thermally decomposed. Therefore, the effect of increasing the temperature of the NOx catalyst 21 is reduced. When the temperature of the NOx catalyst 21 is 300 ° C. or higher, the noble metal catalyst in the NOx catalyst 21 is sufficiently activated, so that the NOx can be sufficiently absorbed by the storage material. For this reason, normally, there is no need to increase the temperature of the NOx catalyst 21. Therefore, in this embodiment, when the temperature of the NOx catalyst 21 becomes 300 ° C. or higher, the catalyst temperature increase control is stopped. Therefore, if it is determined in step 100 that the temperature of the NOx catalyst 21 is not lower than 300 ° C. (that is, 300 ° C. or higher), the addition of ozone and HC is stopped (step 102).

  On the other hand, if it is determined in step 100 that the temperature of the NOx catalyst 21 is less than 300 ° C., it is next determined whether or not the value of the space velocity SV of the NOx catalyst 21 is less than a predetermined value α. (Step 104). The space velocity SV is defined as a value obtained by dividing the exhaust gas flow rate passing through the catalyst by the catalyst volume. The smaller the space velocity SV, the longer the reaction gas stays in the NOx catalyst 21. In the present embodiment, the exhaust gas flow rate is calculated based on the intake air amount detected by the air flow meter 47, and the exhaust gas flow rate is divided by the volume (volume) of the NOx catalyst 21 stored in advance to obtain the space velocity. The SV value can be acquired.

  When the load on the internal combustion engine 10 increases due to sudden acceleration of the vehicle or the like, the exhaust gas flow rate increases, so the space velocity SV increases. That is, the time during which the reaction gas stays in the NOx catalyst 21 is shortened. As a result, the time for the reaction heat of ozone and HC to transfer to the NOx catalyst 21 becomes insufficient, and the efficiency of raising the temperature of the NOx catalyst 21 is reduced. Therefore, in this embodiment, when the space velocity SV is equal to or higher than the predetermined value α, the catalyst temperature increase control is stopped.

  That is, when it is determined in step 104 that the value of the space velocity SV is not less than the predetermined value α (greater than the predetermined value α), the reaction gas stays in the NOx catalyst 21 for a short time. Even if HC and HC are added, it can be determined that the effect of raising the temperature of the NOx catalyst 21 is difficult to obtain. Therefore, in this case, the addition of ozone and HC is stopped to save the use of ozone and fuel (step 102). As described above, according to the present embodiment, when the exhaust gas flow rate increases due to rapid acceleration or the like, and it is difficult to obtain the effect of increasing the catalyst temperature due to the addition of ozone and HC, the addition can be stopped (interrupted). it can. For this reason, ozone and fuel can be used more effectively, and fuel consumption performance can be improved.

  On the other hand, if it is determined in step 104 that the value of the space velocity SV is less than the predetermined value α, it can be determined that the catalyst temperature increasing effect by adding ozone and HC is sufficiently obtained. Therefore, in this case, catalyst temperature increase control, that is, addition of ozone and HC is executed (step 106). That is, by adding ozone to the exhaust gas by the ozone supply device 27 and executing a predetermined HC addition method (post injection, exhaust system fuel addition, low temperature rich combustion, fuel injection amount increase, etc.) HC is added to the exhaust gas.

  Ozone and HC added to the exhaust gas by the catalyst temperature rise control efficiently react from a low temperature through the noble metal catalyst in the gas phase or in the NOx catalyst 21 to generate reaction heat. For this reason, according to the present embodiment, when the NOx catalyst 21 is at a low temperature, such as immediately after the internal combustion engine 10 is started, the temperature of the NOx catalyst 21 can be rapidly increased to a temperature at which sufficient activity can be obtained. it can. Therefore, discharge of harmful substances into the atmosphere can be sufficiently suppressed.

  FIG. 4 is a diagram showing the relationship between the amounts of ozone and HC added to the exhaust gas and the temperature of the NOx catalyst 21 when the catalyst temperature raising control is executed. In step 106, it is preferable to control the addition amounts of ozone and HC in accordance with the temperature of the NOx catalyst 21 according to the map as shown in FIG. According to the map shown in FIG. 4, as the temperature of the NOx catalyst 21 rises, both addition amounts are controlled so that the ratio of the HC addition amount to the ozone addition amount increases. This has the following advantages. When the temperature of the NOx catalyst 21 is low, the oxidation rate of HC is relatively low. For this reason, by making the ratio of the HC addition amount with respect to the ozone addition amount relatively small, it is possible to reliably suppress the generation of HC that remains without being oxidized. On the other hand, as the temperature of the NOx catalyst 21 increases, the oxidation rate of HC increases. For this reason, even if the ratio of the HC addition amount to the ozone addition amount is increased, it is possible to oxidize without leaving HC. Therefore, by controlling the addition amounts of ozone and HC as described above, ozone and HC can be utilized more effectively, and HC can be reliably suppressed from passing through the NOx catalyst 21.

  FIG. 5 is a diagram showing data obtained by measuring the time passage of the temperature of the NOx catalyst 21 and the engine exhaust gas temperature (the temperature of exhaust gas leaving the internal combustion engine 10) after the internal combustion engine 10 is started. The catalyst temperature indicated by the broken line in FIG. 5 is measurement data when the catalyst temperature increase control by the routine shown in FIG. 3 described above is executed. In addition, the period shown by the upper arrow is a period when addition of ozone and HC was performed. On the other hand, the catalyst temperature indicated by the solid line in FIG. 5 is a comparative example, and is measured data when the catalyst temperature increase control is not executed, that is, when ozone and HC are not added.

  According to the measurement data shown in FIG. 5, when the catalyst temperature increase control is executed, the temperature of the NOx catalyst 21 is set to a temperature at which sufficient activity can be obtained (here, 300 ° C.) compared to the case where the catalyst temperature increase control is not executed. It was revealed that the temperature could be rapidly increased to the temperature and that the temperature could be reliably maintained.

  In the present embodiment, the addition of ozone and HC is stopped when the temperature of the NOx catalyst 21 is 300 ° C. or higher or when the space velocity SV is equal to or higher than the predetermined value α (step 102 above). However, in the present invention, the addition of ozone and HC may not be completely stopped, but may be suppressed only (that is, the addition amount is reduced).

  In the example shown in FIG. 5, the case where the catalyst temperature increase control is executed immediately after the start of the internal combustion engine 10 is shown. However, in the present invention, the execution timing of the catalyst temperature increase control is not limited to immediately after the start. Absent. For example, NOx reduction (a process for supplying a reducing agent to the NOx catalyst 21 to reduce and purify the stored NOx), sulfur poisoning regeneration, PM regeneration (a process for burning and removing the collected particulate matter), etc. In order to increase the catalyst temperature in order to perform it, the catalyst temperature increase control (addition of ozone and HC) may be executed.

  Further, in the present embodiment, the target of the catalyst temperature increase control is described as the NOx storage reduction catalyst, but the catalyst that is the target of the catalyst temperature increase control in the present invention is not limited to this, for example, Alternatively, a selective reduction type NOx catalyst, a three-way catalyst, an oxidation catalyst, or the like may be used.

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

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

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

  In the first embodiment described above, the ECU 50 adds HC as an unburned fuel component by a predetermined method such as post-injection or exhaust system fuel addition, whereby the “unburned fuel component supply means” in the first invention is applied. "By performing the processing of step 106, the" catalyst temperature raising means "in the first invention calculates the space velocity SV based on the output of the air flow meter 47, and" in the third invention " When the “flow rate index value calculating means” executes the processing of steps 104 and 102 described above, the “catalyst temperature rise control suppressing means” according to the third aspect of the present invention is based on the map shown in FIG. By controlling the “addition ratio control means” in the fourth aspect of the present invention, each is realized.

Embodiment 2. FIG.
Next, the second embodiment of the present invention will be described with reference to FIG. 6 and FIG. 7. 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 this embodiment is almost the same as the configuration shown in FIG. However, in this embodiment, it is assumed that Ag (silver) is further added to the NOx catalyst 21 as a catalyst component.

In the present embodiment, as in the first embodiment, when it is required to increase the temperature of the NOx catalyst 21, the temperature of the NOx catalyst 21 is increased by adding ozone and HC to the upstream side of the NOx catalyst 21. Can be raised quickly. At that time, CO (carbon monoxide) is generated by the reaction of the added ozone and HC. Since CO is harmful, it is preferably oxidized and purified to CO ₂ . However, the reactivity between CO and ozone is lower than the reactivity between NO and HC and ozone. For this reason, it is difficult to oxidize CO by reacting ozone and CO in the gas phase.

As a result of intensive studies to sufficiently purify CO at a low temperature of the catalyst, the present inventors have found that a catalyst containing Ag (hereinafter referred to as “Ag catalyst”) efficiently oxidizes CO in the presence of ozone. It has been found that the activity is expressed from a low temperature of about 100 ° C. FIG. 6 is a diagram showing a mechanism by which an Ag catalyst oxidizes CO in the presence of ozone. As shown in this figure, when Ag reacts with ozone, it changes to Ag ₂ O or AgO, which is a stronger oxidizing agent. It is considered that CO is oxidized to CO ₂ by this Ag ₂ O or AgO.

  In the present embodiment, based on the above knowledge, the NOx catalyst 21 is made to contain Ag in order to purify CO generated by the reaction of ozone and HC added in the catalyst temperature increase control. Thereby, in this embodiment, even if CO is generated by the reaction of ozone and HC added in the catalyst temperature increase control, the CO is oxidized and purified by the Ag catalyst in the NOx catalyst 21. Can do. For this reason, it is possible to reliably suppress the flow of CO downstream of the NOx catalyst 21.

Further, since heat of reaction is generated by the oxidation reaction of CO, there is an advantage that the temperature of the NOx catalyst 21 can be increased more rapidly. In order to verify this point, the same test as in the first embodiment was performed. FIG. 7 is a diagram showing the results of the test. In this test, 1 mm square pellets in which 1% Pt and 10 wt% Ag were supported on γAl ₂ O ₃ were used as catalysts. Other test conditions are the same as in the test of the first embodiment.

  As is apparent from the test results shown in FIG. 7, when ozone and HC are added, the temperature of the catalyst containing Ag is higher than that of the catalyst not containing Ag. This is considered to be because the catalyst is heated by the heat of oxidation reaction of CO in addition to the heat of reaction of ozone and HC.

  As described above, according to the present embodiment, the catalyst temperature can be increased more quickly by adding Ag to the catalyst that is the target of the catalyst temperature increase control, thereby further improving the catalyst warm-up property. Can do.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a figure which shows the result of the catalyst temperature rising test by addition of ozone and HC. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a figure which shows the relationship between the addition amount of ozone and HC in exhaust gas, and the temperature of a NOx catalyst at the time of catalyst temperature rising control execution. It is a figure which shows the data which measured the time passage of the temperature of the NOx catalyst after the start of an internal combustion engine, and engine exhaust gas temperature. It is a figure which shows the mechanism in which Ag catalyst oxidizes CO in coexistence with ozone. It is a figure which shows the result of the catalyst temperature rising test by addition of ozone and HC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 11 Intake manifold 12 Exhaust manifold 13 Cylinder 14 Fuel injector 15 Exhaust passage 17 Supply pump 18 Common rail 19 Turbocharger 21 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 (5)

A catalyst disposed in the exhaust passage of the internal combustion engine for purifying harmful components in the exhaust gas;
An active oxygen supply device for supplying active oxygen to the upstream side of the catalyst;
Unburned fuel component supply means for increasing the unburned fuel component concentration in the exhaust gas upstream of the catalyst from the normal time;
When it is required to increase the temperature of the catalyst, active oxygen is supplied to the upstream side of the catalyst by the active oxygen supply device, and the concentration of unburned fuel components in the exhaust gas upstream of the catalyst is A catalyst temperature raising means for performing catalyst temperature raising control, which is increased by the unburned fuel component supply means;
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, wherein the catalyst contains Ag as a catalyst component. A flow rate index value calculating means for calculating an index value of the exhaust gas flow rate;
A catalyst temperature increase control suppressing means for suppressing execution of the catalyst temperature increase control when the index value exceeds a predetermined value;
The exhaust gas purifying device for an internal combustion engine according to claim 1 or 2, further comprising:   The catalyst temperature raising means includes addition ratio control means for increasing the ratio of the amount of unburned fuel component added to the amount of active oxygen added to the exhaust gas as the temperature of the catalyst rises. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 3.   The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 4, wherein the active oxygen supply device supplies ozone as active oxygen.

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