JP2009270549A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of materializing rich operation reducing NOx contained in exhaust gas from an engine 1 by using EGR introduction, and inhibiting emission of unburned fuel and soot by securing combustion stability right after engine start or under low temperature environment. <P>SOLUTION: This device is provided with a fuel reformer 50 separately from an exhaust passage 4 of the engine 1, a first introduction passage 57 for introducing gas having reduction properties formed by a fuel reformer 50 into the exhaust passage 4 from an upstream side of an NOx elimination catalyst 32 in the exhaust passage 4, and a second introduction passage 58 for introducing the gas into an intake passage 2. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine. Specifically, the present invention relates to an exhaust gas purification apparatus for an internal combustion engine that includes a NOx purification catalyst that adsorbs or occludes NOx in exhaust gas and reduces the adsorbed or occluded NOx.

  In the present invention, the term “rich” indicates that the air / fuel ratio of the fuel in question (hereinafter referred to as “air-fuel ratio”) is smaller than the stoichiometric air-fuel ratio, and is referred to as “lean”. The term indicates that the air / fuel ratio of the fuel in question is greater than the stoichiometric air / fuel ratio described above. In the following description, the mass ratio of air to fuel in the air-fuel mixture flowing into the internal combustion engine (hereinafter also referred to as engine) is referred to as the engine air-fuel ratio, and the mass ratio of air to combustible gas in the exhaust passage is defined as the exhaust gas. It is called air-fuel ratio.

Conventionally, a technique for purifying nitrogen oxide (hereinafter referred to as “NOx”) contained in exhaust gas is known.
For example, in Patent Documents 1 and 2 and Non-Patent Document 1, a NOx occlusion reduction catalyst (hereinafter referred to as “LNT”) is provided in the exhaust passage, and the exhaust gas is passed through the oxidation catalyst during the lean operation in which the exhaust gas has excessive oxygen. There is shown an exhaust purification device that stores NOx by reacting with alkali metal or alkaline earth metal and stores it, and reduces the stored NOx during a rich operation in which the oxygen concentration of the exhaust gas becomes low. In this exhaust purification apparatus, NOx occlusion and NOx reduction can be performed periodically by repeating the lean operation and the rich operation.

  Further, for example, in Non-Patent Document 2, NOx is adsorbed on the catalyst during a lean operation in which the exhaust gas has excess oxygen, and then a lean operation is performed to periodically form a state where the oxygen concentration in the exhaust gas is low. A method is shown in which NOx adsorbed during lean operation is periodically reduced by periodically synthesizing and supplying carbon oxide.

More specifically, in the method shown in Non-Patent Document 2, first, during the lean operation in which the exhaust gas is excessive in oxygen, the following formulas (1) to (3) indicate that nitrogen monoxide present in the exhaust gas and Nitrogen dioxide is adsorbed on the catalyst.
NO → NO (adsorption) (1)
2NO + O ₂ → 2NO ₂ (2)
NO ₂ → NO ₂ (Adsorption) (3)
Next, rich operation is performed and carbon monoxide is synthesized. The carbon monoxide synthesized here produces hydrogen by an aqueous gas shift reaction represented by the following formula (4) in an environment where the oxygen partial pressure is low.
CO + H ₂ O → H ₂ + CO ₂ (4)
Further, this hydrogen reacts with nitric oxide in a reducing atmosphere to generate ammonia, and this ammonia is adsorbed on the catalyst by the following formula (5).
5H ₂ + 2NO → 2NH ₃ (adsorption) + 2H ₂ O (5)
As described above, NOx in the exhaust gas or NOx adsorbed on the catalyst is reduced by the following formulas (6) to (8) using ammonia generated from carbon monoxide as a final reducing agent.
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (6)
2NH ₃ + NO ₂ + NO → 2N ₂ + 3H ₂ O (7)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (8)

  In addition, for example, Patent Documents 3 and 4 provide a fuel reformer in which an LNT is provided in the exhaust passage, and further, a hydrocarbon gas is reformed upstream of the LNT to produce a reducing gas containing hydrogen and carbon monoxide. An exhaust purification system provided with a vacuum vessel is shown. In particular, this exhaust purification system uses a fuel reformer that produces a reducing gas such that hydrogen is larger than carbon monoxide by volume ratio. According to this system, it is possible to selectively reduce NOx in the exhaust gas by adding a reducing gas containing hydrogen from the upstream side of the LNT into the exhaust gas.

Here, as a method for producing a reducing gas from a hydrocarbon fuel, for example, a partial oxidation reaction using oxygen as an oxidant is known as shown in the following formula (9).
_{C n H m + 1 / 2nO} 2 → nCO + 1 / 2mH 2 (9)
This partial oxidation reaction is an exothermic reaction using fuel and oxygen, and the reaction proceeds spontaneously. For this reason, once reaction starts, it can continue producing hydrogen, without supplying heat from the outside. Further, in such a partial oxidation reaction, when a fuel and oxygen coexist at a high temperature, a combustion reaction as shown in the following formula (10) also proceeds.
_{C n H m + (n +} 1 / 4m) O 2 → nCO 2 + 1 / 2mH 2 O (10)
Further, a steam reforming reaction represented by the following formula (11) using steam as an oxidant is known.
_{C n H m + nH 2 O} → nCO + (n + 1 / 2m) H 2 (11)
This steam reforming reaction is an endothermic reaction using fuel and steam, and is not a reaction that proceeds spontaneously. For this reason, the steam reforming reaction is easily controlled with respect to the partial oxidation reaction described above.

  For example, Patent Document 5 discloses a technique (hereinafter also referred to as EGR) that recirculates part of the exhaust gas to the intake passage as a technique for reducing NOx contained in the exhaust gas from the engine. In this technique, if a large amount of EGR is recirculated when the engine is in a low temperature state, the combustion stability is greatly impaired. For this reason, in order to prevent this, the EGR gas temperature is raised by separately providing a combustion heater and a heat exchanger.

Further, for example, in Patent Document 6, as a technique for reducing NOx contained in exhaust from an engine, a hydrogen injection device is installed in the combustion chamber of the engine, and hydrogen is added to the combustion chamber, so that the complete fuel can be obtained. Techniques that promote combustion, reduce NOx, and suppress the generation of soot have been shown.
Japanese Patent No. 2,586,738 Japanese Patent No. 2600492 Japanese Patent No. 3642273 JP 2002-89240 A JP 2000-186630 A Japanese Patent Laying-Open No. 2005-291107 “Development of NOx occlusion reduction type three-way catalyst system” Proceedings of Automobile Engineering Society Vol. 26, no. 4, October 1995 "A NOx Reduction System Using Ammonia Storage- Selective Catalytic Reduction in Rich and Lean Poorations", 15 Achener Koloquanchuen Mohrent 259-270

However, for example, when the engine lean operation and rich operation are repeated as in the techniques disclosed in Patent Documents 1 and 2 and Non-Patent Documents 1 and 2 described above, there are the following problems.
That is, when the exhaust air-fuel ratio is made rich by performing rich operation, NOx stored in the LNT is desorbed, but if the NOx stored in the LNT is large, the NOx is not reduced and flows out downstream of the LNT. As a result, the NOx purification performance may be reduced.
Therefore, it is conceivable to increase the frequency of rich operation and reduce NOx frequently so that the NOx storage amount in the LNT does not increase. However, the region where the rich operation can be performed is limited depending on the operation state of the engine such as the rotation speed and the torque. For this reason, it is difficult to reduce NOx frequently regardless of the operating state of the engine.

In addition, the exhaust gas purification systems of Patent Documents 3 and 4 are different from the techniques shown in Patent Documents 1 and 2 described above, basically, hydrogen is not contained in exhaust gas with excess oxygen, regardless of lean operation and rich operation. This is a technique of adding carbon monoxide and hydrocarbons.
However, in the case where LNT is purified by adding a reducing agent such as hydrogen or carbon monoxide into the exhaust gas containing excess oxygen, NOx can be purified only at about 200 ° C. For example, if the temperature of the LNT is 200 ° C. or higher, the added hydrogen and carbon monoxide will burn on the catalyst. For this reason, under such a temperature, the amount of reducing agent added is insufficient, and the progress of the NOx reduction reaction is not sufficient.

Further, in the case where a fuel reformer is provided in an exhaust passage in which the exhaust amount constantly varies, as in the exhaust purification systems of Patent Documents 3 and 4, in order to produce hydrogen effectively with the fuel reformer. Therefore, it is necessary to increase the time during which the reforming catalyst of the fuel reformer and the exhaust gas are in contact with each other. Thus, in order to increase the reaction time, it is necessary to enlarge the reforming catalyst, which leads to an increase in cost.
Further, in order to operate the fuel reformer in a stable state, it is necessary to keep the reaction temperature in the reforming catalyst of the fuel reformer constant. However, when the fuel reformer is provided in the exhaust passage in which the oxygen amount, the water vapor amount, and the temperature constantly change as in the above-described exhaust purification systems of Patent Documents 3 and 4, the fuel reformer is stabilized. It is difficult to drive in a state.

  Further, in the technique of Patent Document 5, in the case of an engine that repeats the lean operation and the rich operation as described above, in order to improve the purification rate of NOx contained in the exhaust gas, more EGR is taken into the intake air. It is possible to introduce into the passage. However, if a large amount of EGR is introduced for the purpose of reducing NOx even during lean operation, the combustion stability deteriorates and the generation of unburned fuel and soot increases. This tendency is conspicuous when the temperature of the gas sucked into the combustion chamber of the engine is low, for example, immediately after starting the engine or in a low temperature environment.

  In order to avoid this, the temperature of the exhaust gas passing through the EGR passage is increased for the purpose of increasing the temperature of the gas sucked into the combustion chamber, or hydrogen having a remarkably high flame propagation speed as in Patent Document 6 is introduced into the combustion chamber. Although it has been devised such as direct injection and uniform combustion from low temperature, it is necessary to separately install equipment such as a combustion heater, heat exchanger, hydrogen injector, etc., which is expensive, large equipment, There is a problem in reality from the viewpoint of control difficulty.

  The present invention has been made in view of the problems as described above. The purpose of the present invention is to introduce EGR to realize rich operation in which NOx contained in exhaust from the engine is reduced, An object of the present invention is to provide an exhaust emission control device that ensures combustion stability in a low-temperature environment and can suppress the discharge amount of unburned fuel and soot.

  The inventors of the present invention have made extensive studies to solve the above problems. As a result, a fuel reformer is provided separately from the exhaust passage of the internal combustion engine, and reducing gas produced by the fuel reformer is introduced into the exhaust passage from the upstream side of the NOx purification catalyst in the exhaust passage. It has been found that the above problem can be solved by providing the first introduction passage and the second introduction passage for introduction into the intake passage, and the present invention has been completed. More specifically, the present invention provides the following.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 1 is provided in an exhaust passage of the internal combustion engine in which periodic lean and rich control is performed, and an exhaust air / fuel ratio of the exhaust gas flowing through the exhaust passage is used as the exhaust air / fuel ratio. An exhaust purification device for an internal combustion engine comprising a NOx purification catalyst that adsorbs or occludes NOx in exhaust when the air-fuel ratio is made lean and reduces the adsorbed or occluded NOx when the exhaust air-fuel ratio is made rich In the above, the enrichment means for enriching the exhaust air-fuel ratio, the recirculation passage for recirculating part of the exhaust gas into the intake air recirculation passage of the internal combustion engine, and the exhaust passage are provided separately to reform the fuel. A fuel reformer for producing a reducing gas and a reducing gas produced by the fuel reformer are introduced into the exhaust passage from the upstream side of the NOx purification catalyst in the exhaust passage. A first introduction passage of the reducing gas produced by the fuel reformer, and further comprising a second introduction passage for introducing into the intake passage of the internal combustion engine.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 2 is the exhaust gas purification apparatus for the internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus for the internal combustion engine measures or estimates a water temperature of the internal combustion engine; An introduction passage switching means for switching between the first introduction passage and the second introduction passage, wherein the introduction passage switching means is configured such that the water temperature of the internal combustion engine estimated by the water temperature estimation means is a predetermined water temperature determination value. In the above case, the first introduction passage is switched, and when the water temperature of the internal combustion engine estimated by the water temperature estimation means is lower than a predetermined water temperature determination value, the second introduction passage is switched. First switching means for performing the above is provided.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 3 is the exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the first switching means sets the predetermined water temperature determination value in accordance with an operating state of the internal combustion engine. A water temperature determination value determining means for determining is provided.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 4 is the exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the first switching means further comprises an outside air temperature estimating means for measuring or estimating the temperature of the outside air, The water temperature determination value determining means determines the predetermined water temperature determination value according to the temperature of the outside air estimated by the outside air temperature estimating means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 5 is the exhaust gas purification apparatus for an internal combustion engine according to claim 3 or 4, wherein the first switching means corrects the water temperature determination value determined by the water temperature determination value determination means. And a water temperature judgment value correcting means, and an intake air temperature estimating means for measuring or estimating the temperature of the intake air sucked into the combustion chamber of the internal combustion engine, wherein the water temperature judgment value correcting means is provided by the intake air temperature estimating means. The predetermined water temperature determination value is corrected in accordance with the measured or estimated intake air temperature.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 6 is the exhaust gas purification apparatus for an internal combustion engine according to claim 3 or 4, wherein the first switching means corrects the water temperature determination value determined by the water temperature determination value determination means. And a cetane number estimation means for measuring or estimating the cetane number of the fuel of the internal combustion engine, wherein the water temperature determination value correction means is a cetane number estimated by the cetane number estimation means. The predetermined water temperature determination value is corrected according to the above.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 7 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 2 to 6, wherein the exhaust gas purification apparatus for the internal combustion engine has a flow rate of a recirculation gas flowing through the recirculation passage. A recirculation gas flow rate estimating means for measuring or estimating the recirculation gas flow rate estimating means, and when the flow rate of the recirculation gas estimated by the recirculation gas flow rate estimation means is greater than or equal to a predetermined recirculation gas flow rate determination value, Switching to the second introduction passage, and when the flow rate of the recirculation gas estimated by the recirculation gas flow rate estimating means is less than a predetermined recirculation gas flow rate judgment value, the second introduction passage is switched to the second introduction passage. It further comprises a switching means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 8 is the exhaust gas purification apparatus for an internal combustion engine according to claim 7, wherein the second switching means is based on the rotational speed of the internal combustion engine and the required torque of the internal combustion engine. Determined by a reflux gas flow rate target value determining means for determining a target value of the flow rate of the reflux gas flowing through the reflux passage, an outside air temperature estimating means for measuring or estimating the temperature of the outside air, and the reflux gas flow rate target value determining means. And a recirculation gas flow rate determination value determining means for determining the predetermined recirculation gas flow rate determination value based on the target value of the recirculated gas flow rate and the outside air temperature estimated by the outside air temperature estimation means. Features.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 9 is the exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein the second switching means measures or estimates the cetane number of the fuel of the internal combustion engine. And a recirculation gas flow rate determination value correction unit that corrects the recirculation gas flow rate determination value determined by the recirculation gas flow rate determination value determination unit according to the cetane number estimated by the cetane number estimation unit. It is characterized by.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 10 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 9, wherein the exhaust gas purification apparatus for the internal combustion engine includes the number of rotations of the internal combustion engine and the internal combustion engine. NOx emission amount estimating means for estimating NOx emission amount based on generated torque, NOx emission amount estimated by the NOx emission amount estimating means, intake air amount of the internal combustion engine, fuel consumption amount of the internal combustion engine, the internal combustion engine Adsorbing NOx amount estimating means for estimating the adsorbed NOx amount of the NOx purification catalyst based on at least one of the engine operating time and the oxygen concentration in the exhaust, and the enrichment means comprises the adsorption The exhaust air / fuel ratio is enriched when the adsorbed NOx amount estimated by the NOx amount estimating means is greater than or equal to a predetermined adsorbed NOx amount determination value.

  12. The exhaust gas purification apparatus for an internal combustion engine according to claim 11, wherein the exhaust gas purification apparatus for the internal combustion engine estimates or detects the temperature of the NOx purification catalyst. And an adsorption NOx amount determination value determining means for determining the predetermined adsorption NOx amount determination value based on the catalyst temperature estimated by the catalyst temperature estimation means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 12 is the exhaust gas purification apparatus for an internal combustion engine according to claim 11, wherein the enrichment means is a first rich gas by introducing a reducing gas produced by the fuel reformer. And the second enrichment control means by post combustion or rich combustion, and the exhaust air / fuel ratio is enriched by the first enrichment control means in accordance with the operating state of the internal combustion engine. Or whether to enrich by the second enrichment control means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 13 is the exhaust gas purification apparatus for an internal combustion engine according to claim 12, wherein the enrichment means includes the temperature of the NOx purification catalyst estimated by the catalyst temperature estimation means, and the adsorption. The exhaust air / fuel ratio is enriched by the first enrichment control means according to at least one of the adsorbed NOx quantity estimated by the NOx quantity estimation means, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. Or whether to enrich by the second enrichment control means.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 14 is the exhaust gas purification apparatus for an internal combustion engine according to any one of claims 11 to 13, wherein the enrichment means has an exhaust air / fuel ratio when enriching the exhaust air / fuel ratio. The main injection amount of the internal combustion engine, the sub injection amount of the internal combustion engine, the intake air amount of the internal combustion engine, and the introduction amount of reducing gas produced by the fuel reformer so as to coincide with a predetermined target value And adjusting at least one of them.

  16. The exhaust gas purification apparatus for an internal combustion engine according to claim 15, wherein the exhaust gas purification apparatus for the internal combustion engine uses the predetermined target value of the exhaust air-fuel ratio as the catalyst temperature estimate. At least among the temperature of the NOx purification catalyst estimated by the means, the adsorption NOx amount estimated by the adsorption NOx amount estimation means, the duration of the enrichment means, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine An exhaust air / fuel ratio target value determining means for determining based on one is further provided.

  The exhaust gas purification apparatus for an internal combustion engine according to claim 16, wherein the reducing gas produced by the fuel reformer is carbon monoxide, hydrogen, Among these, carbon monoxide has the largest volume fraction, and hydrocarbon has the smallest volume fraction.

  18. The exhaust gas purification apparatus for an internal combustion engine according to claim 17, wherein the internal combustion engine is a compression ignition type internal combustion engine, and the fuel used is light oil. It is characterized by being.

According to the first aspect of the present invention, the reducing gas produced by the fuel reformer can be introduced into the exhaust passage from the upstream side of the NOx purification catalyst through the first introduction passage, and the intake air is introduced through the second introduction passage. It can be introduced into the passage. For this reason, by introducing reducing gas into the exhaust passage, the engine air-fuel ratio is made lean, the combustion in the internal combustion engine is kept in an optimal state, and the exhaust air-fuel ratio of the exhaust flowing into the NOx purification catalyst is made rich. be able to. Therefore, the NOx purification performance can be improved regardless of the operating state of the internal combustion engine. Since the engine air-fuel ratio can be kept lean, oil dilution occurs as in the case of changing the exhaust air-fuel ratio by supplying fuel by post-injection, etc. Combustion does not become unstable.
Moreover, even when the engine is started or when a large amount of EGR is introduced, a high-temperature reducing gas containing hydrogen can be introduced into the intake passage, resulting in stable combustion of the engine without adding a special device. And the amount of unburned fuel and soot can be reduced.
In addition, by providing a fuel reformer that produces reducing gas separately from the exhaust passage, the reducing gas is always supplied with optimum efficiency regardless of the operating state of the internal combustion engine, the oxygen concentration and the water vapor concentration of the exhaust gas, etc. It can be manufactured and this reducing gas can be introduced into the intake passage or the exhaust passage. When the fuel reformer is provided in the exhaust passage, it is necessary to enlarge the fuel reformer so that the fuel reformer can be operated without affecting the exhaust component, temperature, and flow velocity. According to the invention, by providing the fuel reformer separately from the exhaust passage, it is not necessary to increase the size of the apparatus, and stable operation is possible. Furthermore, by providing the fuel reformer separately from the exhaust passage, it is possible to control the system separately from the control of the internal combustion engine, and to activate the reforming catalyst provided in the fuel reformer at an early stage.
Moreover, the reduction reaction rate in the NOx purification catalyst can be improved by introducing a reducing gas containing hydrogen. Thereby, when the exhaust air-fuel ratio is made rich, NOx adsorbed or stored in the NOx purification catalyst can be prevented from being desorbed without being reduced.

  According to the second aspect of the present invention, when the water temperature of the internal combustion engine estimated by the water temperature estimating means is equal to or higher than a predetermined water temperature judgment value, the first introduction passage is switched and estimated by the water temperature estimating means. When the water temperature of the internal combustion engine is lower than a predetermined water temperature determination value, the second introduction passage is switched. That is, when the estimated water temperature of the internal combustion engine is lower than the predetermined water temperature determination value, it is determined that the temperature of the intake air sucked into the combustion chamber of the engine is low, and therefore, a high temperature is generated in the intake passage. By introducing the reducing gas, combustion stability can be further secured, and generation of unburned fuel and soot can be more effectively suppressed.

According to the third aspect of the invention, since the predetermined water temperature determination value is corrected according to the operating state of the internal combustion engine, the introduction passage can be switched according to the operating state of the internal combustion engine.
Specifically, as in the invention described in claim 4, the outside air estimated by the outside air temperature estimating means as in the invention described in claim 5 according to the intake air temperature measured or estimated by the intake air temperature estimating means. The predetermined water temperature determination value is corrected according to the cetane number estimated by the cetane number estimating means, as in the invention according to claim 6.
In other words, the introduction of reducing gas into the intake passage is performed according to the intake air temperature, the outside air temperature, or the cetane number of the fuel, so that high robustness against disturbances that may impair combustion stability is maintained. it can.

  According to the seventh aspect of the present invention, when the flow rate of the recirculation gas estimated by the recirculation gas flow rate estimating means is equal to or higher than a predetermined recirculation gas flow rate determination value, the second introduction passage is switched to recirculation gas flow rate. When the flow rate of the recirculation gas estimated by the estimation means is less than a predetermined recirculation gas flow rate determination value, the flow is switched to the first introduction passage. That is, when the estimated recirculation gas flow rate is equal to or higher than the predetermined recirculation gas flow rate judgment value, it is determined that the combustion stability of the engine is likely to deteriorate, so that a high temperature reducing gas is introduced into the intake passage. By introducing, combustion stability can be further secured, and generation of unburned fuel and soot can be more effectively suppressed.

According to the eighth aspect of the present invention, the target value of the flow rate of the recirculation gas flowing through the recirculation passage is determined based on the rotation speed and the required torque of the internal combustion engine, and the determined recirculation gas flow rate target value and the outside air temperature estimation are determined. A predetermined recirculation gas flow rate determination value is determined based on the temperature of the outside air estimated by the means. In other words, by determining the recirculation gas flow rate judgment value according to the rotational speed of the internal combustion engine and the required torque in consideration of the temperature of the outside air, when the combustion stability is likely to deteriorate, a high-temperature reducing gas is introduced into the intake passage. As a result, the generation of unburned fuel and soot can be more effectively suppressed while further ensuring the combustion stability.
Furthermore, according to the ninth aspect of the present invention, in order to correct the recirculation gas flow rate determination value determined by the recirculation gas flow rate determination value determination unit according to the cetane number estimated by the cetane number estimation unit, it is further appropriate. As a result of being able to introduce the high-temperature reducing gas into the intake passage at an appropriate timing, it is possible to always ensure the combustion stability regardless of the properties of the fuel, and to more effectively suppress the generation of unburned fuel and soot.

  According to the tenth aspect of the invention, first, the NOx emission amount is estimated based on the rotational speed and the generated torque of the internal combustion engine, the estimated NOx emission amount, the intake air amount of the internal combustion engine, and the fuel consumption amount of the internal combustion engine. The amount of adsorbed NOx of the NOx purification catalyst is estimated based on at least one of the operation time of the internal combustion engine and the oxygen concentration in the exhaust gas. Next, when the estimated amount of adsorbed NOx is greater than or equal to a predetermined adsorbed NOx amount determination value, the exhaust air / fuel ratio is enriched. As a result, the amount of NOx adsorbed or occluded by the NOx purification catalyst increases too much, and the amount of NOx that flows out without being reduced when enriched can be reduced, and the fuel consumption due to excessive enrichment can be reduced. A great deterioration can be suppressed.

  According to the eleventh aspect of the present invention, since the predetermined adsorption NOx amount determination value is determined based on the temperature of the NOx purification catalyst, enrichment can always be performed at an effective timing. For this reason, the amount of NOx that flows out without being reduced can be effectively reduced.

According to the twelfth aspect of the present invention, the exhaust air-fuel ratio is enriched by introducing reducing gas produced by the fuel reformer, or the exhaust air is exhausted by post-combustion or rich combustion according to the operating state of the internal combustion engine. Whether to enrich the fuel ratio is selected.
According to the invention of claim 13, the fuel reformer is manufactured according to at least one of the temperature of the NOx purification catalyst, the amount of adsorbed NOx, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. It is selected whether to enrich the exhaust air-fuel ratio by introducing a reducing gas, or to enrich the exhaust air-fuel ratio by post-combustion or rich combustion.
That is, depending on the operating conditions such as the temperature of the NOx purification catalyst, the amount of adsorbed NOx, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine, enrichment by introduction of reducing gas, or enrichment by post-combustion or rich combustion may occur. Since it is selected, the optimum reduction process is always performed, and the amount of NOx can be reduced more effectively.

  According to the fourteenth aspect of the invention, the main injection amount of the internal combustion engine, the sub injection amount of the internal combustion engine, and the internal combustion engine of the internal combustion engine are adjusted so that the exhaust air / fuel ratio when enriching the exhaust air / fuel ratio matches a predetermined target value. At least one of the intake air amount and the introduction amount of the reducing gas produced by the fuel reformer is adjusted. Thereby, since the exhaust air-fuel ratio at the time of enrichment can be set to a desired value, NOx can be effectively prevented from flowing out without being reduced, and deterioration of fuel consumption due to excessive enrichment can be suppressed.

  According to the fifteenth aspect of the present invention, the predetermined target value of the exhaust air / fuel ratio is set such that the temperature of the NOx purification catalyst, the amount of adsorbed NOx, the duration of the enrichment control by the enrichment means, the rotational speed of the internal combustion engine, and the internal combustion engine. Is determined based on at least one of the generated torques. As a result, the exhaust gas having the optimum exhaust air / fuel ratio can always be caused to flow into the NOx purification catalyst.

According to the sixteenth aspect of the present invention, the reducing gas produced by the fuel reformer contains carbon monoxide, hydrogen, and hydrocarbons. Of these, carbon monoxide has the highest volume fraction, and hydrocarbon has the lowest volume fraction.
In a fuel reformer that reforms hydrocarbon fuel, a reducing gas containing carbon monoxide, hydrogen, and light hydrocarbons is produced only by a partial oxidation reaction using only hydrocarbon fuel and air as raw materials. In the exhaust gas purification apparatus according to the present invention, a reducing gas containing more carbon monoxide than hydrogen is preferably used. For this reason, in the present invention, a catalyst or system for concentrating hydrogen such as a shift reaction is unnecessary, and since the partial oxidation reaction is an exothermic reaction, it is not necessary to supply energy from the outside once the reaction starts. Therefore, a small and simple fuel reformer can be obtained. Since the fuel reformer can be downsized, the light-off time of the fuel reformer can be shortened, and the reducing gas can be quickly introduced into the exhaust passage and the intake passage as necessary.
In addition, light hydrocarbon components that are generated as a secondary component can also contribute to the reduction of NOx by being introduced into the NOx purification catalyst.

  According to the invention of claim 17, the applied internal combustion engine is a compression ignition type internal combustion engine, and the fuel to be used is light oil. In a compression ignition type internal combustion engine such as diesel, since operation is normally performed in a lean state, purification of NOx has been a problem in the past. However, by applying the exhaust purification device according to the present invention, it is efficient. NOx purification is possible.

  Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a configuration of an engine and an exhaust purification device thereof according to a first embodiment of the present invention. The engine 1 is a diesel engine that directly injects fuel into the combustion chamber of each cylinder 7, and each cylinder 7 is provided with a fuel injection valve (not shown). These fuel injection valves are electrically connected by an electronic control unit (hereinafter referred to as ECU) 40, and the valve opening time and valve closing time of the fuel injection valve are controlled by the ECU 40.

  The engine 1 includes an intake passage 2 through which intake air flows, an exhaust passage 4 through which exhaust flows, and a return passage (hereinafter referred to as an EGR passage) 6 that recirculates a part of the exhaust gas in the exhaust passage 4 to the intake passage 2. A supercharger 8 that pumps intake air into the intake passage 2 is provided.

  The intake passage 2 is connected to an intake port of each cylinder 7 of the engine 1 through a plurality of branch portions of an intake manifold 3 (also serving as a part of the intake passage 2). The exhaust passage 4 is connected to the exhaust port of each cylinder 7 of the engine 1 through a plurality of branch portions of the exhaust manifold 5. The EGR passage 6 branches from the exhaust manifold 5 and reaches the intake manifold 3.

  The supercharger 8 includes a turbine (not shown) provided in the exhaust passage 4 and a compressor (not shown) provided in the intake passage 2. The turbine is driven by the kinetic energy of the exhaust flowing through the exhaust passage 4. The compressor is rotationally driven by the turbine, pressurizes the intake air, and pumps it into the intake passage 2. The turbine includes a plurality of variable vanes (not shown), and is configured to change the turbine rotation speed (rotational speed) by changing the opening of the variable vanes. The vane opening degree of the turbine is electromagnetically controlled by the ECU 40.

  A throttle valve 9 for controlling the intake air amount of the engine 1 is provided on the upstream side of the supercharger 8 in the intake passage 2. The throttle valve 9 is connected to the ECU 40 via an actuator, and the opening degree is electromagnetically controlled by the ECU 40. An intercooler 15 for cooling the intake air pressurized by the supercharger 8 is provided on the downstream side of the supercharger 8 in the intake passage 2.

  The EGR passage 6 connects the exhaust manifold 5 and the intake manifold 3 and recirculates a part of the exhaust discharged from the engine 1. The EGR passage 6 includes an EGR cooler 12 that cools the exhaust gas that is recirculated, an EGR valve 13 that controls the flow rate of the recirculated exhaust gas, an EGR gas flow meter 14 that measures the flow rate of the EGR gas flowing into the intake manifold 3, An EGR catalyst 11 having oxidation performance is provided upstream of the EGR cooler 12. The EGR valve 13 is connected to the ECU 40 via an actuator (not shown), and the valve opening degree is electromagnetically controlled by the ECU 40. The EGR gas flow meter 14 is connected to the ECU 40, and the detection signal of the EGR gas flow meter 14 is supplied to the ECU 40.

The EGR catalyst 11 is not particularly limited as long as it has oxidation performance, and a conventionally known oxidation catalyst, three-way catalyst, or the like can be used. Hereinafter, an example of a method for preparing the EGR catalyst will be shown. For example, a material containing each of these components together with an aqueous medium so as to have a blending composition of Pt = 2.4 g / L, Pd = 6.0 g / L, Al ₂ O ₃ = 150 g / L, and binder = 10 g / L. A slurry is obtained by putting into a ball mill and stirring and mixing. An EGR catalyst can be prepared by coating the obtained slurry on a support made of Fe—Cr—Al alloy and drying and firing at 600 ° C. for 2 hours.

In the EGR passage 6, on the upstream side of the EGR catalyst 11, a fuel that reforms the fuel gas to produce a reducing gas containing carbon monoxide (CO), hydrogen (H ₂ ), and hydrocarbon (HC). The reformer 50 is connected via the second introduction passage 58. The reducing gas produced by the fuel reformer 50 is introduced into the EGR passage 6 from the upstream side of the EGR catalyst 11 and flows into the NOx purification catalyst 32.

A NOx purification catalyst 32 is provided on the downstream side of the exhaust passage 4, and the NOx purification catalyst 32 is provided with a catalyst temperature sensor (not shown). In addition to the NOx purification catalyst 32, a three-way catalyst (TWC) may be provided upstream (previous stage).
TWC can be prepared, for example, by the following preparation method. Pt = 2.4 g / L, Rh = 1.2 g / L, Pd = 6.0 g / L, CeO ₂ = 50 g / L, Al ₂ O ₃ = 150 g / L, binder = 10 g / L As described above, a material containing these components is put into a ball mill together with an aqueous medium, and a slurry is obtained by stirring and mixing. A TWC can be prepared by coating the obtained slurry on a support made of Fe—Cr—Al alloy, and drying and firing at 600 ° C. for 2 hours.

The NOx purification catalyst 32 preferably contains rhodium (Rh) in order to enhance the NOx reduction ability. In addition, even in a sudden change in oxygen concentration, it is necessary to enhance the oxygen storage capacity in order to exhibit stable catalytic action, and it is preferable that cerium (Ce) is contained as an element.
More specifically, the NOx purification catalyst 32 is a catalyst supported on a support of alumina (Al ₂ O ₃ ), ceria (CeO ₂ ), and a composite oxide of cerium and rare earth (hereinafter referred to as ceria composite oxide). Has the function of holding platinum (Pt) and rhodium (Rh) that act as ceria, ceria or ceria-based composite oxide having NOx adsorption ability, and the generated ammonia (NH ₃ ) as ammonium ions (NH ₄ ⁺ ) It is preferable to provide zeolite.

As the NOx purification catalyst 32, a NOx purification catalyst having a two-layer structure is more preferably used. Hereinafter, an example of a method for preparing a two-layer NOx purification catalyst will be described. For example, as a lower layer, Pt = 4.5 g / L, Rh = 1.0 g / L, CeO ₂ = 60 g / L, Al ₂ O ₃ = 30 g / L, Ce—Pr—La—Ox = 60 g / L, Nd A material containing these components is put into a ball mill together with an aqueous medium so as to obtain a blending composition of -Zr-Ox = 20 g / L, and a slurry is obtained by stirring and mixing. The resulting slurry is formed by coating a cordierite carrier.
In addition, as an upper layer, a material containing these components is ball milled together with an aqueous medium so as to have a composition of Fe · Ce ion exchange β zeolite = 75 g / L, Al ₂ O ₃ = 7 g / L, and binder = 8 g / L. The slurry is obtained by stirring and mixing. The obtained lower layer is coated on the above-mentioned lower layer, dried at 600 ° C. for 2 hours, and calcined, whereby the NOx purification catalyst 32 can be prepared.

When the amount of adsorbed ammonia in the NOx purification catalyst 32 decreases, the NOx purification capacity decreases, so that a reducing agent is supplied to the NOx purification catalyst 32 (hereinafter referred to as reduction) in order to reduce NOx as appropriate. In this reduction, for example, the air-fuel ratio (engine air-fuel ratio) of the air-fuel mixture in the combustion chamber of the engine 1 is stoichiometrically determined by increasing the amount of fuel injected from the fuel injection valve and decreasing the amount of intake air by the throttle valve 9. By making the ratio richer than the ratio, the reducing agent is supplied to the NOx purification catalyst 32.
Specifically, by reducing the air-fuel ratio (exhaust air-fuel ratio) of the exhaust discharged from the engine 1 by post combustion or rich combustion, the concentration of the reducing agent in the exhaust flowing into the NOx purification catalyst 32 becomes the oxygen concentration. It becomes higher and reduction is performed. Further, as will be described later, by introducing reducing gas produced by the fuel reformer into the exhaust passage 4 or the intake passage 2, the exhaust air-fuel ratio is enriched to perform reduction.

Hereinafter, NOx purification in the NOx purification catalyst 32 will be described.
First, when the engine air-fuel ratio is set leaner than the stoichiometric ratio and so-called lean burn operation is performed, the concentration of the reducing agent in the exhaust gas flowing into the NOx purification catalyst 32 becomes lower than the oxygen concentration. As a result, nitric oxide (NO) and oxygen (O ₂ ) in the exhaust gas react with each other by the action of the catalyst, and are adsorbed as NO ₂ on the ceria or ceria-based composite oxide. In addition, carbon monoxide (CO) that has not reacted with oxygen is also adsorbed to the ceria or the ceria-based composite oxide.

Next, so-called rich operation is performed in which the engine air-fuel ratio is set to be richer than the stoichiometric ratio, and the exhaust air-fuel ratio is enriched. That is, when reduction is performed to make the reducing agent concentration in the exhaust gas higher than the oxygen concentration, carbon monoxide (CO) in the exhaust gas reacts with water (H ₂ O), and carbon dioxide (CO ₂ ) and hydrogen ( H ₂ ) is generated, and the hydrocarbon (HC) in the exhaust gas reacts with water to generate hydrogen (H ₂ ) together with carbon monoxide (CO) and carbon dioxide (CO ₂ ). Furthermore, NOx contained in the exhaust gas, NOx (NO, NO ₂ ) adsorbed on ceria or ceria-based complex oxide (and platinum), and generated hydrogen (H ₂ ) act as a catalyst. To produce ammonia (NH ₃ ) and water (H ₂ O). The ammonia (NH ₃ ) produced here is adsorbed on the zeolite in the form of ammonium ions (NH ₄ ⁺ ).

Next, when lean burn operation is performed in which the engine air-fuel ratio is set leaner than the stoichiometric ratio, and the reducing agent concentration in the exhaust gas flowing into the NOx purification catalyst 32 is set lower than the oxygen concentration, ceria or ceria NOx is adsorbed on the system complex oxide. Further, in the state where ammonium ions (NH ₄ ⁺ ) are adsorbed on the zeolite, NOx and oxygen (O ₂ ) in the exhaust gas react with ammonia (NH ₃ ) to react with nitrogen (N ₂ ) and water (H ₂ O). ) Is generated.

Thus, according to the NOx purification catalyst 32, ammonia (NH ₃ ) generated during the supply of the reducing agent is adsorbed on the zeolite, and ammonia (NH ₃ ) adsorbed during the lean burn operation reacts with NOx. It is possible to efficiently purify NOx.

Further, on the upstream side of the NOx purification catalyst 32 in the exhaust passage 4, a reducing gas containing carbon monoxide (CO), hydrogen (H ₂ ), and hydrocarbon (HC) is produced by reforming the fuel gas. A fuel reformer 50 is connected through the first introduction passage 57. The reducing gas produced by the fuel reformer 50 is introduced into the exhaust passage 4 from the upstream side of the NOx purification catalyst 32 and flows into the NOx purification catalyst 32.

  The fuel reformer 50 includes an introduction passage branched from an introduction passage switching valve 56 into a first introduction passage 57 connected at one end to the exhaust passage 4 and a second introduction passage 58 connected at one end to the intake passage 2. A fuel gas supply device 52 that supplies fuel gas, a fuel gas adjustment valve 51 that adjusts the amount of fuel gas supplied by the fuel gas supply device 52, a compressor 54, and an amount of air supplied by the compressor An air regulating valve 53 and a reforming catalyst 55 provided in the introduction passage are included. The introduction passage switching valve 56 is connected to the ECU 40.

  The fuel gas supply device 52 gasifies the fuel stored in the fuel tank, and supplies the fuel gas to the reforming catalyst 55 while adjusting the flow rate by the fuel gas adjustment valve 51. Further, the air supplied from the compressor is adjusted in its flow rate by the air adjusting valve 53, and then is uniformly mixed with the fuel gas and supplied to the reforming catalyst 55. The fuel reformer 50 is connected to the ECU 40, and the fuel gas supply amount and the air supply amount are controlled by the ECU 40. Further, the amount of reducing gas introduced into the exhaust passage 4 can be controlled by controlling the amount of fuel gas and air supplied.

  The reforming catalyst 55 contains rhodium and ceria. The reforming catalyst 55 reforms the fuel gas supplied from the fuel gas supply device 52 to produce a reducing gas containing hydrogen, carbon monoxide, and hydrocarbons. More specifically, the reforming catalyst 55 has a pressure higher than atmospheric pressure due to a partial oxidation reaction between the hydrocarbon fuel in the fuel gas and air, and has a volume fraction of carbon monoxide higher than that of hydrogen. A reducing gas containing a large amount of is produced. Further, as described above, the partial oxidation reaction is an exothermic reaction. As a result, the fuel reformer 50 can introduce reducing gas having a temperature higher than the temperature of the intake air flowing through the intake passage 2 into the intake passage 2. In addition, reducing gas having a temperature higher than that of the exhaust gas flowing upstream of the NOx purification catalyst 32 in the exhaust passage 4 can be introduced into the exhaust passage 4.

Hereinafter, an example of a method for preparing the reforming catalyst 55 will be described. For example, in order to obtain a blending composition of Pt = 0.8 g / L, Rh = 0.8 g / L, CeO ₂ = 150 g / L, and binder = 10 g / L, the materials containing these components are ball milled together with an aqueous medium. The slurry is obtained by adding, stirring and mixing. The reforming catalyst 55 can be prepared by coating the obtained slurry on a Fe—Cr—Al alloy carrier, and drying and firing at 600 ° C. for 2 hours.

  The reforming catalyst 55 is connected to a heater (not shown) that includes a glow plug, a spark plug, and the like, and the reforming catalyst 55 can be heated when the fuel reformer 50 is started. It is possible. The fuel reformer 50 is provided separately from the exhaust passage 4. That is, the fuel gas supply device 52 and the reforming catalyst 55 of the fuel reformer 50 are not provided in the exhaust passage 4.

The ECU 40 includes a crank angle position sensor (not shown) that detects the rotation angle of the crankshaft of the engine 1, an accelerator sensor (not shown) that detects the amount of depression of an accelerator pedal of a vehicle driven by the engine 1, and an engine An in-cylinder pressure sensor 10 provided in one cylinder, an engine water temperature sensor 16 that measures the water temperature of the engine 1, and an air flow that detects the intake air amount of the engine 1 (the amount of air newly sucked into the engine 1 per unit time). Meter 21, an outside air temperature sensor 22 that measures the temperature of the outside air, an exhaust temperature sensor 34 that detects the temperature of the exhaust gas flowing into the NOx purification catalyst 32, and an oxygen concentration of the exhaust gas that flows into the NOx purification catalyst 32, that is, an exhaust air-fuel ratio. UEGO sensors 33 are connected, and detection signals from these sensors are supplied to the ECU 40.
Here, the rotational speed of the engine 1 is calculated by the ECU 40 based on the output of the crank angle position sensor. The generated torque of the engine 1 is calculated by the ECU 40 based on the fuel injection amount of the fuel injection valve determined according to the depression amount of an accelerator pedal (not shown). The required torque of the engine 1 is calculated by the ECU 40 based on the number of revolutions of the engine 1 and the amount of depression of an accelerator pedal (not shown).

  The ECU 40 shapes an input signal waveform from various sensors, corrects a voltage level to a predetermined level, converts an analog signal value into a digital signal value, and a central processing unit (hereinafter, referred to as a central processing unit). CPU). In addition, the ECU 40 includes a storage circuit that stores various calculation programs executed by the CPU, calculation results, and the like, a fuel reformer 50, an introduction passage switching valve 56, a throttle valve 9, an EGR valve 13, a supercharger 8, And an output circuit for outputting a control signal to the fuel injection valve of the engine 1.

  The engine 1 is normally operated with the engine air-fuel ratio set to a lean side with respect to the stoichiometric ratio, and rich control for setting the engine air-fuel ratio to the rich side with respect to the stoichiometric ratio is periodically performed.

FIG. 2 is a flowchart showing an engine control procedure according to the embodiment of the present invention. First, when the engine 1 is started, in step S1, a water temperature lower limit value (determination value) of the engine 1 is determined based on the outside air temperature measured or estimated by the outside air temperature estimating means, and the process proceeds to step S2.
Here, the outside air temperature is measured by the outside air temperature sensor 22, and the water temperature lower limit value (determination value) of the engine 1 is determined based on the relationship between the outside air temperature and the water temperature lower limit value (determination value) of the engine 1 shown in FIG. To do.

In step S2, based on the cetane number estimated by the cetane number estimating means, the water temperature lower limit (determination value) of the engine 1 determined in step S1 is corrected, and the process proceeds to step S3.
Here, the cetane number of the fuel is estimated by monitoring the ignition timing of the fuel with the in-cylinder pressure sensor 10, and the water temperature correction coefficient is calculated based on the relationship between the cetane number and the water temperature correction coefficient shown in FIG. The water temperature lower limit value (determination value) of the engine 1 determined in step S1 is corrected. As shown in FIG. 4, the higher the cetane number of the fuel, the smaller the water temperature correction coefficient is determined in the direction of lowering the engine water temperature lower limit value.
Further, the water temperature lower limit (determination value) of the engine 1 may be corrected based on the intake air temperature estimated by the intake air temperature estimating means instead of the cetane number estimated by the cetane number estimating means.

In step S3, it is determined whether or not the water temperature of the engine 1 estimated by the engine water temperature estimating means is equal to or higher than the water temperature lower limit value (determination value) determined and corrected in steps S2 to S3. ) If YES in step S4, the process proceeds to step S4. If NO in step S4, the process proceeds to step S6.
Here, the water temperature of the engine 1 is measured by an engine water temperature sensor 16 provided in the engine 1.

In step S4, it is determined in step S3 that the water temperature of the engine 1 is equal to or higher than the water temperature lower limit (determination value), and it is determined that the warm-up of the engine 1 has been completed. And switch to the first introduction passage. Next, the process proceeds to step S5, and the addition of H ₂ gas (reducing gas) into the intake passage 2 is stopped.
Here, the switching to the first introduction passage is performed by the introduction passage switching valve 56.
After that, the process proceeds to the enrichment control by the enrichment means in step S21 described later.

In step S6, it is determined in step S3 that the water temperature of the engine 1 is lower than the lower limit value (determination value) of the water temperature, and it is determined that the engine 1 is warming up. And switch to the second introduction passage. Next, the process proceeds to step S7, and the addition of H ₂ gas (reducing gas) into the intake passage 2 is performed.
Here, the switching to the first introduction passage is performed by the introduction passage switching valve 56.
After that, the process proceeds to the enrichment control by the enrichment means in step S21 described later.

FIG. 5 is a flowchart showing a procedure of engine control in one embodiment of the present invention. First, in step S21, the adsorption NOx amount of the NOx purification catalyst 32 is estimated, and it is determined whether or not the estimated adsorption NOx amount is equal to or greater than a predetermined adsorption NOx amount determination value. If this determination is YES, the process proceeds to step S22, and if NO, the process proceeds to step S23.
Here, the amount of NOx adsorbed by the NOx purification catalyst 32 is estimated based on the rotational speed and generated torque of the engine 1, the estimated NOx emission amount, and the intake air of the engine 1 measured by the air flow meter 21. It is estimated based on at least one of the amount, the fuel consumption of the engine 1, the operating time of the engine 1, and the oxygen concentration in the exhaust gas measured by the UEGO sensor.
The adsorbed NOx amount determination value is determined based on the estimated catalyst temperature by estimating or detecting the temperature of the NOx purification catalyst 32. The estimation or detection of the catalyst temperature is estimated or detected by a catalyst temperature sensor provided in the NOx purification catalyst 32.

  In step S22, since it is determined in step S21 that the adsorbed NOx amount is equal to or greater than a predetermined adsorbed NOx amount determination value, the enrichment control is performed, which will be described later.

  In step S23, since it is determined in step S21 that the adsorbed NOx amount is less than the predetermined adsorbed NOx amount determination value, first, based on the rotational speed of the engine 1 and the required torque, the flow rate of the EGR gas flowing in the EGR passage The target value is determined, and the process proceeds to step S24.

In step S24, a predetermined EGR gas flow rate upper limit value (determination value) is determined based on the target value of the EGR gas flow rate determined by the EGR gas flow rate target value determination unit and the outside air temperature estimated by the outside air temperature estimation unit. Then, the process proceeds to step S25.
Here, the outside air temperature is measured by the outside air temperature sensor 22, and the EGR gas flow rate upper limit value (determination value) is determined based on the relationship between the outside air temperature and the EGR upper limit value (determination value) shown in FIG.

In step S25, the EGR gas flow rate upper limit value (determination value) determined in step S24 is corrected according to the cetane number estimated by the cetane number estimation means, and the process proceeds to step S26.
Here, the cetane number of the fuel is estimated by monitoring the ignition timing of the fuel by the in-cylinder pressure sensor 10, and the EGR correction coefficient is calculated based on the relationship between the cetane number and the EGR correction coefficient shown in FIG. The EGR gas flow rate upper limit value (determination value) determined in step S24 is corrected. As shown in FIG. 7, the higher the cetane number of the fuel, the larger the EGR correction coefficient, which is determined in the direction of increasing the EGR upper limit value.

In step S26, it is determined whether or not the flow rate of the EGR gas estimated by the EGR gas flow rate estimating means is equal to or larger than the EGR gas flow rate determination value determined and corrected in steps S23 to S25, and the estimated EGR gas flow rate is determined. When the flow rate is equal to or greater than the EGR gas flow rate determination value, the process proceeds to step S27, and when the estimated EGR gas flow rate is less than the EGR gas flow rate determination value, the process proceeds to step S29.
Here, the flow rate of EGR gas is measured by an EGR gas flow meter.

In step S27, it is determined in step S26 that the flow rate of the EGR gas is less than the EGR gas flow rate determination value and it is determined that a large amount of EGR is not being introduced. Switch. Next, the process proceeds to step S28, and the addition of H ₂ gas (reducing gas) into the intake passage 2 is stopped. Thereby, engine control is complete | finished.
Here, the switching to the first introduction passage is performed by the introduction passage switching valve 56.

In step S29, the flow rate of EGR gas is determined to be equal to or greater than the EGR gas flow rate determination value in step S26, and it is determined that a large amount of EGR is being introduced. Therefore, the second switching unit of the introduction channel switching unit switches to the second introduction channel. To do. Next, the process proceeds to step S30, and the addition of H ₂ gas (reducing gas) into the intake passage 2 is performed. Thereby, engine control is complete | finished.
Here, the switching to the second introduction passage is performed by the introduction passage switching valve 56.

  Next, returning to step S22, FIG. 8 shows a flowchart showing the enrichment control procedure in step S22.

In FIG. 8, in step S31, it is determined whether or not the temperature of the NOx purification catalyst 32 is not more than a certain value. If this determination is YES, the process proceeds to step S36, and if NO, the process proceeds to step S32.
Here, the temperature of the NOx purification catalyst 32 is estimated or detected by a catalyst temperature sensor. Further, in addition to the temperature of the NOx purification catalyst 32, it may be determined whether at least one of the adsorbed NOx amount, the rotation speed of the engine 1, and the generated torque is equal to or less than a certain value. The amount of adsorbed NOx is estimated by the same procedure as in step S21.

  In step S32, an exhaust air-fuel ratio target value for normal rich control (second rich control) is determined. The exhaust air / fuel ratio target value is determined based on at least one of the temperature of the NOx purification catalyst 32, the amount of adsorbed NOx, the duration of the enrichment control, the rotational speed of the engine 1, and the generated torque.

In step S33, normal enrichment control (second enrichment control) is performed. Here, as the normal enrichment control, post combustion or rich combustion is performed.
Further, the exhaust air-fuel ratio during the normal enrichment control is monitored by the UEGO sensor, and the normal enrichment control is performed so as to coincide with the target value of the exhaust air-fuel ratio determined in step S32. More specifically, the enrichment control is performed by adjusting at least one of the main injection amount, the sub injection amount, and the intake air amount of the engine 1.

  In step S34, it is determined whether or not the normal rich timer is zero. If this determination is YES, the process proceeds to step S35, the normal rich timer is started, and then the process proceeds to step S42. If the determination is NO, the process proceeds to step S42.

Returning to step S31, if the temperature of the NOx purification catalyst 32 is equal to or lower than a certain value, the process proceeds to step S36, and in step S36, an exhaust air-fuel ratio target value for H ₂ enrichment control (first enrichment control) is determined. To do. This exhaust air-fuel ratio target value is determined by the same procedure as in the normal enrichment control.

In step S37, H ₂ enrichment control (first enrichment control) is performed. Here, the H ₂ enrichment control is performed by introducing the reducing gas produced by the fuel reformer 50 into the exhaust passage 4. Specifically, by reducing the intake throttle 9, the intake air amount of the engine 1 is reduced, and the addition of reducing gas from the fuel reformer 50 into the exhaust passage 4 is started.
Further, the exhaust air / fuel ratio during the H ₂ enrichment control is monitored by the UEGO sensor, and the amount of reducing gas introduced is adjusted to match the target value of the exhaust air / fuel ratio determined in step S36 to enrich the H ₂ . Implement control.

In step S38, the H ₂ enrichment control timer and the normal rich timer are started, and the process proceeds to step S39. In step S39, it is determined whether or not the temperature of the NOx purification catalyst 32 is equal to or higher than a certain value.
If this determination is YES, the process proceeds to step S41, the H ₂ enrichment control is stopped, the H ₂ enrichment control timer is set, and the process proceeds to step S42.
If the determination is NO, the process moves to step S40, and it is determined whether or not the H ₂ enrichment control timer has passed a certain time. If this determination is YES, the process proceeds to step S41, the H ₂ enrichment control is stopped, the H ₂ enrichment control timer is set, and the process proceeds to step S42. If the determination is NO, the process proceeds to step S42.

  In step S42, it is determined whether or not the normal rich timer has passed a predetermined time. If this determination is YES, the process proceeds to step S43, the enrichment control is stopped, the normal rich timer is set, and the enrichment control is terminated. If the determination is NO, the enrichment control is terminated.

As described above in detail, according to this embodiment, the reducing gas produced by the fuel reformer 50 can be introduced into the exhaust passage 4 from the upstream side of the NOx purification catalyst 32 through the first introduction passage 57. In addition, the air can be introduced into the intake passage 2 through the second introduction passage 58. For this reason, a rich operation in which NOx contained in the exhaust from the engine 1 is reduced can be realized, and also when the engine is started or a large amount of EGR is introduced, a high-temperature reducing gas containing hydrogen is introduced into the intake passage 2. As a result, the combustion stability of the engine can be ensured and the amount of unburned fuel and soot can be reduced without adding a special device.
Further, by introducing the reducing gas into the exhaust passage 4, the engine air-fuel ratio is made lean, and the exhaust air-fuel ratio of the exhaust gas flowing into the NOx purification catalyst 32 is enriched while the combustion in the engine 1 is kept in an optimal state. be able to. Therefore, the NOx purification performance can be improved regardless of the operating state of the engine 1. Since the engine air-fuel ratio can be kept lean, oil dilution occurs or combustion of the engine 1 becomes unstable as in the case of changing the exhaust air-fuel ratio by supplying fuel by post injection or the like. There is nothing.
Further, by providing the fuel reformer 50 for producing reducing gas separately from the exhaust passage 4, the reducing performance is always reduced with optimum efficiency regardless of the operating state of the engine 1 and the oxygen concentration and water vapor concentration of the exhaust gas. Gas can be produced, and this reducing gas can be introduced into the intake passage 2 or the exhaust passage 4. When the fuel reformer 50 is provided in the exhaust passage 4, it is necessary to enlarge the fuel reformer 50 so that the fuel reformer 50 can be operated without affecting the exhaust components, temperature, and flow velocity. According to the embodiment, by providing the fuel reformer 50 separately from the exhaust passage 4, it is not necessary to increase the size of the apparatus, and stable operation is possible. Furthermore, by providing the fuel reformer 50 separately from the exhaust passage 4, it is possible to control the system different from the control of the engine 1, and to activate the reforming catalyst provided in the fuel reformer 50 at an early stage.
Moreover, the reduction reaction rate in the NOx purification catalyst 32 can be improved by introducing a reducing gas containing hydrogen. Thereby, when the exhaust air-fuel ratio is made rich, NOx adsorbed or stored in the NOx purification catalyst 32 can be prevented from being desorbed without being reduced.

  Further, according to the present embodiment, when the water temperature of the engine 1 estimated by the water temperature estimating means is equal to or higher than a predetermined water temperature determination value, the first introduction passage 57 is switched and the water temperature estimating means estimates the water temperature. When the water temperature of the engine 1 is lower than the predetermined water temperature determination value, the second introduction passage 58 is switched. That is, when the estimated water temperature of the engine 1 is less than a predetermined water temperature determination value, it is determined that the temperature of the intake air sucked into the combustion chamber of the engine 1 is low, so By introducing a high-temperature reducing gas, combustion stability can be further secured, and generation of unburned fuel and soot can be more effectively suppressed.

Further, according to the present embodiment, since the predetermined water temperature determination value is corrected according to the operating state of the engine 1, the introduction passage can be switched according to the operating state of the engine 1.
Specifically, according to the intake air temperature measured or estimated by the intake air temperature estimation means, according to the outside air temperature estimated by the outside air temperature estimation means, according to the cetane number estimated by the cetane number estimation means, A predetermined water temperature judgment value is corrected. That is, the introduction of the reducing gas into the intake passage 2 is performed according to the intake air temperature, the outside air temperature, or the cetane number of the fuel, so that it has high robustness against disturbances that may impair combustion stability. I can maintain.

  Further, according to the present embodiment, when the flow rate of the EGR gas estimated by the EGR gas flow rate estimation means is equal to or greater than a predetermined EGR gas flow rate determination value, the second introduction passage 58 is switched to provide the EGR gas flow rate. When the flow rate of the EGR gas estimated by the estimation means is less than a predetermined EGR gas flow rate determination value, the first introduction passage 57 is switched. That is, when the estimated EGR gas flow rate is equal to or higher than a predetermined EGR gas flow rate determination value, it is determined that the combustion stability of the engine 1 is likely to deteriorate, and therefore, a high-temperature reduction in the intake passage 2 By introducing the property gas, it is possible to more effectively suppress the generation of unburned fuel and soot while further ensuring the combustion stability.

Further, according to the present embodiment, the target value of the flow rate of the EGR gas flowing through the EGR passage 6 is determined based on the rotational speed of the engine 1 and the required torque, and the determined EGR gas flow rate target value and the outside air temperature estimation are determined. A predetermined EGR gas flow rate judgment value is determined based on the temperature of the outside air estimated by the means. That is, by taking the temperature of the outside air into consideration and determining the EGR gas flow rate judgment value according to the engine speed and the required torque, the hot reducing gas is introduced into the intake passage 2 at a more appropriate timing. As a result, it is possible to more effectively suppress the generation of unburned fuel and soot while always ensuring combustion stability.
Furthermore, according to the present embodiment, the EGR gas flow rate determination value determined by the EGR gas flow rate determination value determination unit is corrected according to the cetane number estimated by the cetane number estimation unit. As a result of the introduction of the high-temperature reducing gas into the intake passage 2, the generation of unburned fuel and soot can be more effectively suppressed while ensuring the combustion stability.

  Further, according to the present embodiment, first, the NOx emission amount is estimated based on the rotational speed and generated torque of the engine 1, the estimated NOx emission amount, the intake air amount of the engine 1, the fuel consumption amount of the engine 1, The adsorbed NOx amount of the NOx purification catalyst 32 is estimated based on at least one of the operation time of the engine 1 and the oxygen concentration in the exhaust. Next, when the estimated amount of adsorbed NOx is greater than or equal to a predetermined adsorbed NOx amount determination value, the exhaust air / fuel ratio is enriched. As a result, the amount of NOx adsorbed or occluded by the NOx purification catalyst 32 increases excessively, and the amount of NOx that flows out without being reduced when enriched can be reduced, and the fuel consumption due to excessive enrichment is reduced. Can be suppressed.

  Further, according to the present embodiment, since the predetermined adsorption NOx amount determination value is determined based on the temperature of the NOx purification catalyst 32, enrichment can be performed at a more effective timing. For this reason, the amount of NOx that flows out without being reduced can be more effectively reduced, and a significant deterioration in fuel consumption due to excessive enrichment can be suppressed.

Further, according to the present embodiment, the exhaust air / fuel ratio is enriched by introducing reducing gas produced by the fuel reformer 50 according to the operating state of the engine 1, or the exhaust air is exhausted by post combustion or rich combustion. Whether to enrich the fuel ratio is selected.
Further, according to the present embodiment, the fuel reformer 50 is manufactured according to at least one of the temperature of the NOx purification catalyst 32, the amount of adsorbed NOx, the rotational speed of the engine 1, and the generated torque of the engine 1. It is selected whether to enrich the exhaust air-fuel ratio by introducing reducing gas, or to enrich the exhaust air-fuel ratio by post-combustion or rich combustion.
That is, enrichment by introducing reducing gas, or enrichment by post-combustion or rich combustion, depending on operating conditions such as the temperature of the NOx purification catalyst 32, the amount of adsorbed NOx, the rotational speed of the engine 1, and the generated torque of the engine 1. Therefore, the optimal reduction process is always performed, and the amount of NOx can be reduced more effectively.

  Further, according to the present embodiment, the main injection amount of the engine 1, the sub-injection amount of the engine 1, and the engine 1 are related so that the exhaust air-fuel ratio when enriching the exhaust air-fuel ratio matches a predetermined target value. At least one of the intake air amount and the introduction amount of the reducing gas produced by the fuel reformer 50 is adjusted. As a result, the exhaust air-fuel ratio at the time of enrichment can be set to a desired value, so that NOx can be effectively prevented from flowing out without being reduced, and a significant deterioration in fuel consumption due to excessive enrichment can be suppressed. .

  Further, according to the present embodiment, the predetermined target value of the exhaust air / fuel ratio is set such that the temperature of the NOx purification catalyst 32, the amount of adsorbed NOx, the duration of the enrichment control by the enrichment means, the rotational speed of the engine 1, and the engine 1 Is determined based on at least one of the generated torques. As a result, the exhaust gas having the optimum exhaust air / fuel ratio can always flow into the NOx purification catalyst 32.

Further, according to the present embodiment, the reducing gas produced by the fuel reformer 50 includes carbon monoxide, hydrogen, and hydrocarbons. Of these, carbon monoxide has the highest volume fraction, and hydrocarbon has the lowest volume fraction.
In the fuel reformer 50 for reforming hydrocarbon fuel, a reducing gas containing carbon monoxide, hydrogen, and light hydrocarbons is produced only by a partial oxidation reaction using only hydrocarbon fuel and air as raw materials. However, in the exhaust gas purification apparatus according to the present invention, a reducing gas containing more carbon monoxide than hydrogen is preferably used. For this reason, in the present invention, a catalyst or system for concentrating hydrogen such as a shift reaction is unnecessary, and since the partial oxidation reaction is an exothermic reaction, it is not necessary to supply energy from the outside once the reaction starts. Therefore, a small and simple fuel reformer 50 can be obtained. Since the fuel reformer 50 can be downsized, the light-off time of the fuel reformer 50 can be shortened, and the reducing gas can be quickly introduced into the exhaust passage 4 and the intake passage 2 as necessary.
In addition, light hydrocarbon components that are generated as a secondary component can also contribute to the reduction of NOx by being introduced into the NOx purification catalyst 32.

  Moreover, according to this embodiment, the applied engine 1 is the compression ignition type engine 1, and the fuel to be used is light oil. In a compression ignition type internal combustion engine such as diesel, since operation is normally performed in a lean state, purification of NOx has been a problem in the past. However, by applying the exhaust purification device according to the present invention, it is efficient. NOx purification is possible.

  In this embodiment, the ECU 40 is a part of the enrichment means, a part of the water temperature estimation means, the introduction passage switching means, the water temperature judgment value determination means, a part of the outside air temperature estimation means, a part of the water temperature judgment value correction means, and a part of the intake air temperature estimation means. , Part of the cetane number estimation means, part of the EGR gas flow rate estimation means, part of the EGR gas flow rate target value determination means, EGR gas flow rate determination value determination means, EGR gas flow rate determination value correction means, part of the NOx emission amount estimation means A part of the adsorption NOx amount estimation means, a part of the catalyst temperature estimation means, an adsorption NOx amount determination value determination means, a first enrichment control means, a second enrichment control means, and an exhaust air / fuel ratio target value determination means. .

Specifically, the means according to step S1 in FIG. 2 corresponds to the water temperature determination value determination means, the means according to step S1 and the outside air temperature sensor 22 correspond to the outside air temperature estimation means, and the means according to step S2 corresponds to the water temperature determination. It corresponds to a value correction means, the means according to step S2 and the in-cylinder pressure sensor 10 correspond to a cetane number estimation means, the means according to steps S3 to 7 correspond to a first switching means of the introduction passage switching means, The means relating to S3 and the water temperature sensor 16 correspond to the water temperature estimating means.
5 corresponds to the enrichment means, the means related to step S23 corresponds to the EGR gas flow rate target value determination means, and the means related to step S24 corresponds to the EGR gas flow rate determination value determination means. The means according to step S24 and the outside temperature sensor 22 correspond to outside temperature estimation means, the means according to step S25 corresponds to EGR gas flow rate determination value correction means, and the means according to step S25 and the in-cylinder pressure sensor 10 Corresponds to the cetane number estimating means, the means according to steps S26-30 corresponds to the second switching means of the introduction passage switching means, and the means according to step S26 and the EGR gas flow meter 14 are the EGR gas flow rate estimating means. Equivalent to.
Further, the means according to steps S31 to S44 in FIG. 8 corresponds to the enrichment means, the means according to step S31 corresponds to the NOx emission amount estimation means and the adsorption NOx amount estimation means, and the means according to step S32 and the catalyst temperature sensor. Corresponds to the catalyst temperature estimating means, the means related to step S32 corresponds to the adsorption NOx amount determination value determining means, steps 32-44 correspond to the second enrichment control means, and steps S37-44 correspond to the first enrichment. It corresponds to the control means, and the means according to steps S33 and 37 corresponds to the exhaust air / fuel ratio target value determining means.

1 is a diagram illustrating a configuration of an engine and an exhaust purification device thereof according to an embodiment of the present invention. It is a flowchart which shows the procedure of the engine control which concerns on one Embodiment of this invention. It is a figure which shows the relationship between external temperature and a water temperature lower limit. It is a figure which shows the relationship between a cetane number and a water temperature correction coefficient. It is a flowchart which shows the procedure of the engine control which concerns on one Embodiment of this invention. It is a figure which shows the relationship between outside temperature and an EGR upper limit. It is a figure which shows the relationship between a cetane number and an EGR correction coefficient. It is a flowchart which shows the procedure of the engine control which concerns on one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 2 Intake passage 4 Exhaust passage 6 EGR passage 10 In-cylinder pressure sensor 11 EGR catalyst 14 EGR gas flow meter 16 Engine water temperature sensor 17 Intake temperature sensor 21 Air flow meter 22 Outside air temperature sensor 32 NOx purification catalyst 33 UEGO sensor 34 Exhaust temperature sensor 40 ECU
50 Fuel reformer 56 Introduction passage switching valve 57 First introduction passage 58 Second introduction passage

Claims (17)

NOx in the exhaust gas when the exhaust air-fuel ratio is made lean by setting the air-fuel ratio of the exhaust gas that is provided in the exhaust passage of the internal combustion engine where periodic lean and rich control are performed and the exhaust air flowing through the exhaust passage as the exhaust air-fuel ratio. In an exhaust gas purification apparatus for an internal combustion engine comprising a NOx purification catalyst that reduces the adsorbed or occluded NOx when the exhaust air-fuel ratio is made rich,
Enriching means for enriching the exhaust air-fuel ratio;
A recirculation passage for recirculating part of the exhaust gas into an intake recirculation passage of the internal combustion engine;
A fuel reformer that is provided separately from the exhaust passage and reforms the fuel to produce a reducing gas;
A first introduction passage for introducing the reducing gas produced by the fuel reformer into the exhaust passage from the upstream side of the NOx purification catalyst in the exhaust passage;
An exhaust purification device for an internal combustion engine, further comprising: a second introduction passage for introducing the reducing gas produced by the fuel reformer into the intake passage of the internal combustion engine. The exhaust gas purification device for the internal combustion engine includes:
Water temperature estimating means for measuring or estimating the water temperature of the internal combustion engine;
An introduction passage switching means for switching between the first introduction passage and the second introduction passage,
The introduction passage switching means is
When the water temperature of the internal combustion engine estimated by the water temperature estimation means is equal to or higher than a predetermined water temperature determination value, the water temperature of the internal combustion engine estimated by the water temperature estimation means is switched to the first introduction passage. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising first switching means for switching to the second introduction passage when the temperature is lower than a predetermined water temperature determination value.   3. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein the first switching unit includes a water temperature determination value determining unit that determines the predetermined water temperature determination value in accordance with an operating state of the internal combustion engine. The first switching means further includes outside air temperature estimating means for measuring or estimating the temperature of the outside air,
4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the water temperature determination value determination means determines the predetermined water temperature determination value according to the temperature of the outside air estimated by the outside air temperature estimation means. The first switching means includes
Water temperature determination value correction means for correcting the water temperature determination value determined by the water temperature determination value determination means;
An intake air temperature estimating means for measuring or estimating the temperature of intake air taken into the combustion chamber of the internal combustion engine,
The exhaust gas of an internal combustion engine according to claim 3 or 4, wherein the water temperature determination value correction means corrects the predetermined water temperature determination value according to the intake air temperature measured or estimated by the intake air temperature estimation means. Purification equipment. The first switching means includes
Water temperature determination value correction means for correcting the water temperature determination value determined by the water temperature determination value determination means;
Cetane number estimation means for measuring or estimating the cetane number of the fuel of the internal combustion engine,
5. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the water temperature determination value correction unit corrects the predetermined water temperature determination value according to the cetane number estimated by the cetane number estimation unit. . The exhaust gas purification device for the internal combustion engine includes:
A reflux gas flow rate estimating means for measuring or estimating a flow rate of the reflux gas flowing through the reflux passage;
The introduction passage switching means is
When the flow rate of the recirculation gas estimated by the recirculation gas flow rate estimation means is greater than or equal to a predetermined recirculation gas flow rate determination value, the recirculation gas flow rate estimation means switches to the second introduction passage and the recirculation gas flow estimated by the recirculation gas flow rate estimation means. The internal combustion engine according to any one of claims 2 to 6, further comprising a second switching means for switching to the first introduction passage when the gas flow rate is less than a predetermined recirculation gas flow rate judgment value. Exhaust purification equipment. The second switching means includes
Recirculation gas flow rate target value determining means for determining a target value of the flow rate of the recirculation gas flowing through the recirculation passage based on the rotational speed of the internal combustion engine and the required torque of the internal combustion engine;
An outside air temperature estimating means for measuring or estimating the temperature of the outside air;
The recirculation gas flow rate for determining the predetermined recirculation gas flow rate determination value based on the recirculation gas flow rate target value determined by the recirculation gas flow rate target value determination unit and the outside air temperature estimated by the outside air temperature estimation unit. An exhaust gas purification apparatus for an internal combustion engine according to claim 7, further comprising a determination value determining means. The second switching means includes
Cetane number estimating means for measuring or estimating the cetane number of the fuel of the internal combustion engine;
Recirculation gas flow rate determination value correction means for correcting the recirculation gas flow rate determination value determined by the recirculation gas flow rate determination value determination unit in accordance with the cetane number estimated by the cetane number estimation unit. An exhaust emission control device for an internal combustion engine according to claim 8. The exhaust gas purification device for the internal combustion engine includes:
NOx emission amount estimation means for estimating the NOx emission amount based on the rotational speed of the internal combustion engine and the generated torque of the internal combustion engine;
Based on at least one of the NOx emission amount estimated by the NOx emission amount estimating means, the intake air amount of the internal combustion engine, the fuel consumption amount of the internal combustion engine, the operating time of the internal combustion engine, and the oxygen concentration in the exhaust gas. And an adsorption NOx amount estimating means for estimating an adsorption NOx amount of the NOx purification catalyst,
2. The enrichment unit enriches the exhaust air-fuel ratio when the adsorption NOx amount estimated by the adsorption NOx amount estimation unit is equal to or greater than a predetermined adsorption NOx amount determination value. 9. An exhaust emission control device for an internal combustion engine according to any one of 9 above. The exhaust gas purification device for the internal combustion engine includes:
Catalyst temperature estimating means for estimating or detecting the temperature of the NOx purification catalyst;
11. The internal combustion engine according to claim 10, further comprising an adsorption NOx amount determination value determining unit that determines the predetermined adsorption NOx amount determination value based on the catalyst temperature estimated by the catalyst temperature estimation unit. Exhaust purification device.   The enrichment means includes first enrichment control means by introduction of reducing gas produced by the fuel reformer, and second enrichment control means by post-combustion or rich combustion, and 12. The method according to claim 11, wherein whether the exhaust air-fuel ratio is enriched by the first enrichment control means or the second enrichment control means is selected according to an operating state of the internal combustion engine. An exhaust gas purification apparatus for an internal combustion engine as described.   The enrichment means includes the temperature of the NOx purification catalyst estimated by the catalyst temperature estimation means, the adsorption NOx amount estimated by the adsorption NOx amount estimation means, the rotational speed of the internal combustion engine, and the generated torque of the internal combustion engine. 13. The method according to claim 12, wherein the exhaust air-fuel ratio is selected to be enriched by the first enrichment control means or enriched by the second enrichment control means according to at least one of them. An exhaust gas purification apparatus for an internal combustion engine as described.   The enrichment means is configured so that the exhaust air-fuel ratio when enriching the exhaust air-fuel ratio matches a predetermined target value, the main injection amount of the internal combustion engine, the sub-injection amount of the internal combustion engine, The exhaust emission control device for an internal combustion engine according to any one of claims 11 to 13, wherein at least one of an intake air amount and an introduction amount of reducing gas produced by the fuel reformer is adjusted. The exhaust gas purification device for the internal combustion engine includes:
The predetermined target value of the exhaust air-fuel ratio is set to the temperature of the NOx purification catalyst estimated by the catalyst temperature estimation means, the amount of adsorption NOx estimated by the adsorption NOx amount estimation means, the duration of the enrichment means, the internal combustion engine 15. The exhaust gas purification apparatus for an internal combustion engine according to claim 14, further comprising an exhaust air / fuel ratio target value determining means for determining based on at least one of an engine speed and a torque generated by the internal combustion engine.   The reducing gas produced by the fuel reformer contains carbon monoxide, hydrogen, and hydrocarbons. Of these, carbon monoxide has the highest volume fraction and has the lowest volume fraction. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 15, wherein is an hydrocarbon.   The exhaust purification device for an internal combustion engine according to any one of claims 1 to 16, wherein the internal combustion engine is a compression ignition type internal combustion engine, and a fuel to be used is light oil.

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