JP5845906B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas recirculation device for an internal combustion engine that recirculates part of exhaust gas to an intake passage, and more particularly to an exhaust gas recirculation device for an internal combustion engine in which hydrogen generated by fuel reforming is added to exhaust gas recirculation gas that recirculates in an intake passage. .

  2. Description of the Related Art EGR systems that take out part of exhaust gas from an internal combustion engine, recirculate it to an intake system, mix it with intake air, lower the maximum temperature during combustion, and reduce Nox in exhaust gas have been widely known.

  Further, in Patent Document 1, based on such an EGR system, fuel is supplied to the recirculated exhaust gas, and the reforming reaction (endothermic reaction) is performed on the reforming catalyst using the heat of the exhaust gas. The exhaust gas containing carbon monoxide is recirculated to the intake system to recover exhaust heat and improve the fuel efficiency of the internal combustion engine EGR reforming system. An EGR reforming system for an internal combustion engine that prevents fluctuations is disclosed.

  As the reforming reaction, a steam reforming reaction using steam in exhaust gas and dry reforming using carbon dioxide are assumed, but in order to perform a sufficient reaction, a relatively high temperature ( In general, for example, a temperature of 600 ° C. or higher is necessary. On the other hand, exhaust gas temperature has been decreasing in recent engine developments, and the operating range with a high load such that the exhaust temperature exceeds 600 ° C. is about 20% of the whole. If hydrogen can be obtained by the reforming reaction even in an operation region where the exhaust temperature is 400 to 600 ° C., the operation region in which hydrogen can be introduced into the intake passage can be expanded. Can be improved. That is, if hydrogen can be obtained by reforming even at an exhaust temperature of 600 ° C. or lower, fuel efficiency can be further improved.

Japanese Patent No. 4013704

  However, in the EGR reforming system as disclosed in Patent Document 1, when the exhaust gas temperature is high, hydrogen is generated by the reforming catalyst, and only in a limited operating region where the exhaust gas temperature becomes high, There is a problem that the effect of improving fuel consumption cannot be obtained by adding hydrogen.

Therefore, an exhaust gas recirculation apparatus for an internal combustion engine according to the present invention injects reforming fuel into the exhaust gas recirculation passage, and an exhaust gas recirculation passage capable of recirculating exhaust gas from the upstream side of the exhaust purification catalyst provided in the exhaust passage to the intake air passage. The reforming fuel injection means, the reforming catalyst provided in the exhaust gas recirculation passage and generating hydrogen from the reforming fuel, and the amount of exhaust gas recirculation gas recirculating to the intake passage according to the operating state of the internal combustion engine are adjusted. And when the load on the internal combustion engine is low, the exhaust on the upstream side of the exhaust purification catalyst is recirculated to the intake passage, the load on the internal combustion engine is high, and the upstream side of the exhaust purification catalyst When the oxygen concentration of the exhaust gas is low, the exhaust gas upstream of the exhaust purification catalyst is recirculated to the intake passage . The lower the load on the internal combustion engine, the lower the temperature of the exhaust discharged from the internal combustion engine. Further, since the exhaust gas discharged from the internal combustion engine contains oxygen, the exhaust gas containing oxygen flows into the reforming catalyst by introducing the exhaust gas upstream of the exhaust purification catalyst into the exhaust gas recirculation passage. Become.

  According to the present invention, even when the exhaust temperature is low, hydrogen can be generated by the reforming catalyst by the reforming reaction utilizing oxidation of oxygen contained in the exhaust. As compared with the case where only the reforming catalyst generates hydrogen, the operating range in which hydrogen can be introduced into the intake passage can be expanded.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which showed typically the whole structure of the exhaust gas recirculation apparatus of the internal combustion engine in 1st Example of this invention. The flowchart which shows the flow of control of the EGR control valve in 1st Example. Explanatory drawing which showed typically the whole structure of the exhaust gas recirculation apparatus of the internal combustion engine in 2nd Example of this invention. The flowchart which shows the flow of control of the upstream control valve and downstream control valve in 2nd Example. Explanatory drawing which showed typically the whole structure of the exhaust gas recirculation apparatus of the internal combustion engine in 3rd Example of this invention. The flowchart which shows the flow of control of the upstream control valve and downstream control valve in 3rd Example.

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

  FIG. 1 is an explanatory view schematically showing the overall configuration of an exhaust gas recirculation device for an internal combustion engine in a first embodiment of the present invention.

  The internal combustion engine 1 is mounted as a drive source in a vehicle such as an automobile. An intake passage 4 is connected to the combustion chamber 2 of the internal combustion engine 1 via an intake valve 3 and an exhaust passage 6 is connected via an exhaust valve 5. A spark plug 7 for spark-igniting the air-fuel mixture in the combustion chamber 2 is provided at the central top of the combustion chamber 2.

  A throttle valve 8 that controls the amount of intake air and a fuel injection valve 9 that is located downstream of the throttle valve 8 and injects fuel into the intake passage 4 are disposed in the intake passage 4.

  An exhaust purification catalyst 10 is provided in the exhaust passage 6. The exhaust purification catalyst 10 is located upstream of the exhaust passage 6 and is disposed in the engine room of a vehicle on which the internal combustion engine 1 is mounted, and is disposed immediately downstream of the exhaust manifold of the internal combustion engine 1. This is a so-called manifold catalyst. The exhaust purification catalyst 10 purifies exhaust using oxygen in the exhaust, and is, for example, a three-way catalyst that simultaneously purifies NOx, HC, and CO in the exhaust.

  Between the exhaust passage 6 and the intake passage 4, an EGR passage 11 is provided as an exhaust recirculation passage for returning a part of the exhaust gas to the intake passage 4. One end of the EGR passage 11 is connected to the exhaust passage 6 on the upstream side of the exhaust purification catalyst 10, and the other end is connected to the collector portion 4 a of the intake passage 4 located between the throttle valve 8 and the fuel injection valve 9. ing. The EGR passage 11 includes, in order from the exhaust passage 6 side, a reforming fuel injection valve 12 as a reforming fuel injection means, a reforming catalyst 13, an EGR cooler 14, and an EGR control valve 15 as an exhaust recirculation valve. Is arranged.

  The reforming fuel injection valve 12 injects the same fuel as the fuel injected by the fuel injection valve 9 into the EGR passage 11 as a reforming fuel. The reforming fuel is supplied to the reforming catalyst 13 together with the exhaust gas introduced into the EGR passage 11.

  The reforming catalyst 13 is formed by supporting rhodium on a honeycomb carrier made of, for example, cordierite, and generates hydrogen using the exhaust gas introduced into the EGR passage 11 and the reforming fuel. Here, the reforming reaction in the reforming catalyst 13 is roughly classified into a reforming reaction using steam and carbon dioxide in exhaust gas and a reforming reaction using oxidation of oxygen in exhaust gas. The reforming reaction using water vapor and carbon dioxide in the exhaust gas is a reaction that hardly proceeds unless the temperature is relatively high. For example, the reforming reaction proceeds in a temperature atmosphere of 600 ° C. or higher to generate hydrogen. On the other hand, the reforming reaction using oxidation of oxygen in the exhaust gas proceeds even when the temperature is relatively low. For example, the reforming reaction proceeds from a temperature atmosphere of about 300 ° C. to 350 ° C. to generate hydrogen. The hydrogen produced by the reforming catalyst 13 burns in the combustion chamber 2 through the intake passage 4 and contributes to an improvement in fuel consumption of the internal combustion engine 1.

  The EGR cooler 14 cools the EGR gas (exhaust gas recirculation gas) that recirculates to the intake passage 4.

  The EGR control valve 15 adjusts the amount of EGR gas (exhaust gas recirculation gas) recirculated to the intake passage 4 according to the operating state of the internal combustion engine 1. The opening degree of the EGR control valve 15 is controlled by an ECU (engine control unit) 16.

  The ECU 16 includes an oxygen sensor 17 serving as an oxygen concentration detection unit that is disposed upstream of the exhaust purification catalyst 10 and detects the oxygen concentration of the exhaust discharged from the combustion chamber 2, and the degree of opening of the accelerator pedal operated by the driver. Signals from various sensors such as the accelerator opening sensor 18 to be detected are input. In addition to the EGR control valve 15 described above, the ECU 16 performs various types of internal combustion engine 1 such as the fuel injection amount from the fuel injection valve 9 and the fuel injection amount from the reforming fuel injection valve 12 according to the operating state. Control is in progress.

  Here, in the first embodiment, basically, a part of the exhaust discharged when stoichiometric combustion (combustion at the stoichiometric air-fuel ratio) is performed in the combustion chamber 2 on the upstream side of the exhaust purification catalyst 10. The hydrogen is introduced into the passage 11 and the reforming catalyst 13 is added to generate hydrogen by the reforming catalyst 13, and the exhaust gas containing the hydrogen is recirculated to the intake passage 4 as EGR gas (exhaust gas recirculation gas). Exhaust gas when stoichiometric combustion (combustion at the stoichiometric air-fuel ratio) in the combustion chamber 2 actually contains unburned hydrocarbons and carbon monoxide, and these emissions are used as exhaust purification catalyst 10. About 1% oxygen is also included for purification.

  In the first embodiment, basically, the reforming catalyst 13 generates hydrogen using the exhaust having an oxygen concentration of about 1%. Therefore, in the reforming catalyst 13, the water vapor and carbon dioxide in the exhaust are used. The reforming reaction utilizing oxygen proceeds and the reforming reaction utilizing oxidation of oxygen in the exhaust proceeds.

  Here, there is a correlation between the load of the internal combustion engine 1 and the temperature of the exhaust gas discharged from the combustion chamber 2, and the temperature of the exhaust gas discharged from the combustion chamber 2 when the load of the internal combustion engine 1 is low. Is also relatively low. Therefore, when the load of the internal combustion engine 1 is low, the reforming reaction using the steam and carbon dioxide in the exhaust gas may not proceed at the reforming catalyst 13. Even if the load of the internal combustion engine 1 is low, if the oxygen concentration of the exhaust gas discharged from the combustion chamber 2 is high to some extent (the oxygen concentration is about 1%), the reforming reaction utilizing the oxidation of oxygen in the exhaust gas proceeds. The reforming catalyst 13 can generate hydrogen.

  Further, when the load on the internal combustion engine 1 is high, the temperature of the exhaust gas discharged from the combustion chamber 2 also becomes relatively high. At this time, if the oxygen concentration in the exhaust gas discharged from the combustion chamber 2 is high, reforming is performed by heat generation due to the reforming reaction utilizing oxidation of oxygen in the exhaust gas and high-temperature exhaust gas introduced into the reforming catalyst 13. There is a possibility that the catalyst 13 becomes excessively hot and the reforming catalyst 13 is thermally deteriorated.

  Therefore, in the first embodiment, the EGR control valve 15 is opened and closed according to the load of the internal combustion engine 1 and the oxygen concentration of the exhaust gas exhausted from the combustion chamber 2 (the oxygen concentration upstream of the exhaust purification catalyst 10). Control is performed as follows.

  When the load of the internal combustion engine 1 is lower than a predetermined load set in advance, the EGR control valve 15 is opened, and the exhaust gas upstream of the exhaust purification catalyst 10 is introduced into the EGR passage 11. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 mainly from the reforming reaction utilizing oxidation of oxygen.

  Thereby, even if the temperature of the exhaust gas discharged from the combustion chamber 2 is low, hydrogen can be generated by the reforming catalyst 13 by the reforming reaction utilizing oxidation of oxygen contained in the exhaust gas. Therefore, compared with the case where hydrogen is generated by the reforming catalyst 13 only when the exhaust temperature is relatively high, the operating range in which hydrogen can be introduced into the intake passage 4 can be expanded.

  Further, the exhaust contains components derived from fuel and lubricating oil (engine oil). If these components adhere to the reforming catalyst 13, it becomes a catalyst poison, which may suppress the reforming reaction. However, since the catalyst poison adhering to the reforming catalyst 13 can be burned and removed using oxygen contained in the exhaust gas, it is possible to prevent the reforming reaction of the reforming catalyst 13 from deteriorating due to the catalyst poison. In other words, the regeneration process for removing the catalyst poison on the reforming catalyst 13 can be performed simultaneously with the generation of hydrogen by the reforming catalyst 13 using the oxygen contained in the exhaust gas.

  When the load of the internal combustion engine 1 is higher than the predetermined load set in advance and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10 is lower than the predetermined value set in advance, the EGR control valve 15 is opened and EGR is set. Exhaust gas upstream of the exhaust purification catalyst 10 is introduced into the passage 11. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 from the reforming reaction mainly using water vapor and carbon dioxide in the exhaust gas.

  If the oxygen concentration in the exhaust gas flowing into the reforming catalyst 13 is low, the reforming reaction in the reforming catalyst 13 utilizing oxidation of oxygen contained in the exhaust does not proceed, and the reforming catalyst 13 is generated by the heat generated by this reforming reaction. The temperature does not increase greatly. That is, the reforming catalyst 13 does not become higher than the temperature of the exhaust gas introduced into the EGR passage 11.

  Thereby, even if the temperature of the exhaust gas discharged from the combustion chamber 2 is high, the temperature of the reforming catalyst 13 does not become excessively high, so that the thermal deterioration of the reforming catalyst 13 can be prevented.

  When the load of the internal combustion engine 1 is higher than a predetermined load set in advance and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10 is higher than a predetermined value set in advance, the EGR control valve 15 is closed and the EGR passage is closed. The introduction of exhaust to 11 is stopped.

  If the concentration of oxygen in the exhaust gas flowing into the reforming catalyst 13 is high, the reforming reaction in the reforming catalyst 13 utilizing oxidation of oxygen contained in the exhaust proceeds. Therefore, the reforming catalyst 13 is generated by heat generated by the reforming reaction. The temperature may increase significantly. That is, the reforming catalyst 13 becomes excessively high due to the heat generated by the reforming reaction in the reforming catalyst 13 utilizing the oxidation of oxygen in the exhaust gas and the original temperature of the exhaust gas introduced into the EGR passage 11. There is a possibility.

  Therefore, when the load on the internal combustion engine 1 is high and the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is high, the introduction of the exhaust gas into the EGR passage 11 is stopped so that the high temperature exhausted from the combustion chamber 2 is increased. It is possible to prevent the reforming catalyst 13 from becoming further hotter than the exhaust, and to reliably prevent thermal degradation of the reforming catalyst 13.

  Accordingly, in such a first embodiment, the EGR control valve 15 depends on the load of the internal combustion engine 1 and the oxygen concentration of the exhaust gas exhausted from the combustion chamber 2 (the oxygen concentration upstream of the exhaust purification catalyst 10). By controlling the opening and closing of the engine, the operating range in which the hydrogen produced by the reforming catalyst 13 is introduced into the intake passage 4 is expanded while preventing the thermal deterioration of the reforming catalyst 13, and the fuel efficiency of the internal combustion engine 1 is improved. It can be greatly improved.

  In addition, since the regeneration process of removing the catalyst poison component of the reforming catalyst 13 using oxygen contained in the exhaust gas can be performed, it is possible to prevent the reforming reaction of the reforming catalyst 13 from being deteriorated due to the catalyst poison.

  FIG. 2 is a flowchart showing a control flow of the EGR control valve 15 in the first embodiment. In S11, it is determined whether or not the load of the internal combustion engine 1 is high. If it is high, the process proceeds to S12, and if not, the process proceeds to 13. In S12, it is determined whether or not the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is high. If so, the process proceeds to S14, and if not, the process proceeds to S15. In S13, the EGR control valve 15 is controlled to a predetermined valve open state. In S14, the EGR control valve 15 is controlled to be closed. In S15, the EGR control valve 15 is controlled to a predetermined valve open state.

  In the first embodiment described above, the exhaust gas recirculation is performed when the load on the internal combustion engine 1 is high and the exhaust gas upstream of the exhaust purification catalyst 10 has a low oxygen concentration. If the estimated exhaust temperature is very high and the exhaust temperature immediately before flowing into the reforming catalyst 13 is predicted to exceed the heat resistance temperature of the reforming catalyst 13, the oxygen in the exhaust upstream of the exhaust purification catalyst 10 is predicted. Even when the concentration is low, the EGR control valve 15 may be controlled to be in a closed state to reliably prevent thermal deterioration of the reforming catalyst 13.

  In the first embodiment described above, the opening / closing control of the EGR control valve 15 is performed according to the load of the internal combustion engine 1 and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10. It is also possible to carry out the opening / closing control of the EGR control valve 15 only according to the above.

  In this case, if the load on the internal combustion engine 1 is high, the EGR control valve 15 is controlled to be closed, and if the load on the internal combustion engine 1 is not high, the EGR control valve 15 is opened to a predetermined value. Control to the state.

  When exhaust gas having a high exhaust temperature is introduced into the EGR passage 11, if the oxygen concentration of the exhaust gas is high, heat is generated by the reforming reaction in the reforming catalyst 13 using oxidation of oxygen in the exhaust gas and introduced into the EGR passage 11. There is a possibility that the reforming catalyst 13 becomes excessively high temperature due to the original temperature of the exhaust gas. Therefore, when performing the opening / closing control of the EGR control valve 15 according to only the load of the internal combustion engine 1, if the load of the internal combustion engine 1 is high, the EGR control valve 15 is controlled to be closed, Thermal deterioration of the reforming catalyst 13 can be reliably prevented.

  Hereinafter, other embodiments of the present invention will be described, but the same components as those in the first embodiment described above are denoted by the same reference numerals, and redundant description will be omitted.

  FIG. 3 is an explanatory view schematically showing the overall configuration of an exhaust gas recirculation device for an internal combustion engine in a second embodiment of the present invention. The second embodiment has substantially the same configuration as the first embodiment described above, but one end side of the EGR passage 21 is connected to the exhaust passage 6 on the upstream side of the exhaust purification catalyst 10. 22 and a downstream side exhaust introduction portion 23 connected to the exhaust passage 6 on the downstream side of the exhaust purification catalyst 10.

  The upstream side exhaust introduction part 22 is provided with an upstream side control valve 24 that can adjust the amount of exhaust introduced into the upstream side exhaust introduction part 22. The downstream side exhaust introduction part 23 is provided with a downstream side control valve 25 that can adjust the amount of exhaust introduced into the downstream side exhaust introduction part 23. The valve opening degree of the upstream control valve 24 and the downstream control valve 25 is controlled by the ECU 16.

  Here, the exhaust gas introduced from the downstream side exhaust gas introduction portion 25 is in a state in which almost all oxygen is consumed and hardly contains oxygen when passing through the exhaust purification catalyst 10.

  Accordingly, in the second embodiment, the upstream control valve 24 and the oxygen concentration of the exhaust gas exhausted from the combustion chamber 2 (the oxygen concentration upstream of the exhaust purification catalyst 10) and The opening / closing control of the downstream control valve 25 is performed as follows.

  When the load of the internal combustion engine 1 is lower than a predetermined load set in advance, the EGR control valve 15 and the upstream control valve 24 are opened, and the downstream control valve 25 is closed, so that the exhaust gas purification catalyst is provided in the EGR passage 21. 10 Introduce only upstream exhaust. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 mainly from the reforming reaction utilizing oxidation of oxygen.

  Thereby, even if the temperature of the exhaust gas discharged from the combustion chamber 2 is low, hydrogen can be generated by the reforming catalyst 13 by the reforming reaction utilizing oxidation of oxygen contained in the exhaust gas. Therefore, compared with the case where hydrogen is generated by the reforming catalyst 13 only when the exhaust temperature is relatively high, the operating range in which hydrogen can be introduced into the intake passage 4 can be expanded. If the exhaust gas is introduced into the EGR passage 11 from the downstream side of the exhaust purification catalyst 10 when the load of the internal combustion engine 1 is lower than a predetermined load set in advance, the temperature of the exhaust gas passes through the exhaust purification catalyst 10 and passes through the exhaust purification catalyst 10. When the temperature further decreases, the temperature of the exhaust gas flowing into the reforming catalyst 13 becomes excessively low, and the reforming reaction utilizing water vapor and carbon dioxide in the exhaust gas does not proceed, and hydrogen is not generated by the reforming catalyst 13. There is a fear.

  Further, since the catalyst poison adhering to the reforming catalyst 13 can be burned and removed using oxygen contained in the exhaust gas, it is possible to prevent the reforming reaction of the reforming catalyst 13 from deteriorating due to the catalyst poison. That is, the regeneration process for removing the catalyst poison component on the reforming catalyst 13 can be performed at the same time that hydrogen is generated by the reforming catalyst 13 using oxygen contained in the exhaust gas.

  When the load of the internal combustion engine 1 is higher than the predetermined load set in advance and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10 is lower than the predetermined value set in advance, the EGR control valve 15 and the upstream control are performed. By opening the valve 24 and closing the downstream control valve 25, only exhaust gas upstream of the exhaust purification catalyst 10 is introduced into the EGR passage 21. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 from the reforming reaction mainly using water vapor and carbon dioxide in the exhaust gas.

  Accordingly, even if the temperature of the exhaust gas discharged from the combustion chamber 2 is high, the oxygen concentration contained in the exhaust gas is low. Therefore, even if the exhaust gas is introduced from the upstream side of the exhaust purification catalyst 10 into the EGR passage 11, the reforming catalyst 13. Since the temperature does not become excessively high, thermal deterioration of the reforming catalyst 13 can be prevented. Note that when the load of the internal combustion engine 1 is higher than a predetermined load set in advance and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10 is lower than a predetermined value set in advance, the EGR passage from the downstream side of the exhaust purification catalyst 10 If exhaust gas is introduced into the exhaust gas 11, the temperature of the exhaust gas flowing into the reforming catalyst 13 becomes excessively low when the exhaust gas temperature is lowered by passing through the exhaust gas purification catalyst 10, and water vapor and carbon dioxide in the exhaust gas are reduced. There is a possibility that the used reforming reaction does not proceed and hydrogen is not generated by the reforming catalyst 13.

  Further, when the load of the internal combustion engine 1 is higher than a predetermined load set in advance and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10 is higher than a predetermined value set in advance, the EGR control valve 15 and the downstream control are performed. By opening the valve 25 and closing the upstream control valve 24, only the exhaust on the downstream side of the exhaust purification catalyst 10 is introduced into the EGR passage 21. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 from the reforming reaction mainly using water vapor and carbon dioxide in the exhaust gas.

  By introducing exhaust gas into the EGR passage 11 from the downstream side of the exhaust purification catalyst 10, exhaust gas containing almost no oxygen flows into the reforming catalyst 13, and reforming utilizing oxidation of oxygen in the exhaust gas. Since the reaction does not proceed, it is possible to prevent the reforming catalyst 13 from becoming excessively high in temperature and to prevent thermal degradation of the reforming catalyst. In addition, when exhaust is introduced into the EGR passage 11 from the exhaust purification catalyst 10 downstream side, the exhaust gas reaches the reforming catalyst 13 as compared with when exhaust is introduced into the EGR passage 11 from the exhaust purification catalyst 10 upstream side. The length of the path becomes longer, and the amount of heat radiation increases accordingly. Therefore, when the temperature of the exhaust gas exhausted from the combustion chamber 2 is high and the oxygen concentration is high, it is better to introduce the exhaust gas into the EGR passage 11 from the downstream side of the exhaust purification catalyst 10 to prevent thermal deterioration of the reforming catalyst 13. It is effective in doing.

  Therefore, in the second embodiment as well, as in the first embodiment described above, the operating range in which hydrogen can be introduced into the intake passage 4 while the thermal degradation of the reforming catalyst 13 is prevented is expanded. Thus, the fuel consumption of the internal combustion engine 1 can be greatly improved.

  FIG. 4 is a flowchart showing a flow of control of the upstream control valve 24 and the downstream control valve 25 in the second embodiment. In S21, it is determined whether or not the load of the internal combustion engine 1 is high. If it is high, the process proceeds to S22, and if not, the process proceeds to 23. In S22, it is determined whether or not the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is high. If so, the process proceeds to S24, and if not, the process proceeds to S25. In S23, the EGR control valve 15 and the upstream side control valve 24 are controlled to a predetermined valve open state, and the downstream side control valve 25 is controlled to be closed. In S14, the EGR control valve 15 and the downstream control valve 25 are controlled to a predetermined valve open state, and the upstream control valve 24 is controlled to a closed state. In S15, the EGR control valve 15 and the upstream side control valve 24 are controlled to a predetermined valve open state, and the downstream side control valve 25 is controlled to be closed.

  In the second embodiment described above, the exhaust gas on the downstream side of the exhaust purification catalyst 10 is introduced into the EGR passage 11 when the load on the internal combustion engine 1 is high and the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is high. However, when the exhaust temperature estimated from the load of the internal combustion engine 1 is very high and the exhaust temperature immediately before flowing into the reforming catalyst 13 is predicted to exceed the heat resistance temperature of the reforming catalyst 13, The EGR control valve 15, the upstream side control valve 24, and the downstream side control valve 25 may all be controlled to be closed to reliably prevent thermal deterioration of the reforming catalyst 13.

  Further, in the second embodiment described above, opening / closing control of the upstream control valve 24 and the downstream control valve 25 is performed according to the load of the internal combustion engine 1 and the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10. However, the opening / closing control of the upstream control valve 24 and the downstream control valve 25 can be performed only in accordance with the oxygen concentration of the exhaust gas upstream of the exhaust purification catalyst 10.

  In this case, if the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is low, the EGR control valve 15 and the upstream control valve 24 are opened, and the downstream control valve 25 is closed, so that the exhaust purification catalyst 21 enters the EGR passage 21. 10 Introduce only upstream exhaust. Also, if the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is high, the EGR control valve 15 and the downstream control valve 25 are opened and the upstream control valve 24 is closed, so that the EGR passage 21 is connected to the downstream side of the exhaust purification catalyst 10. Introduce exhaust only.

  When exhaust gas having a high oxygen concentration is introduced into the EGR passage 21, if the temperature of the exhaust gas is high, the heat generated by the reforming reaction utilizing oxidation of oxygen contained in the exhaust gas and the original exhaust gas introduced into the EGR passage 21. Depending on the temperature, the reforming catalyst 13 may become excessively hot. Further, since the exhaust gas downstream of the exhaust purification catalyst 10 hardly contains oxygen as described above, the reforming reaction utilizing oxidation of oxygen does not proceed in the reforming catalyst 13 even if it is introduced into the EGR passage 21. The reforming catalyst 13 does not become higher than the original temperature of the exhaust gas introduced into the EGR passage 21.

  Therefore, when the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 13 is low, the exhaust gas is introduced from the upstream side of the exhaust purification catalyst 10 to oxidize oxygen contained in the exhaust gas even if the exhaust temperature is high. The temperature of the reforming catalyst 13 does not rise excessively due to the heat generated by the reforming reaction utilizing the heat, and the thermal deterioration of the reforming catalyst 13 can be prevented.

  In addition, when the oxygen concentration in the exhaust gas upstream of the exhaust purification catalyst 10 is high, the exhaust gas is introduced from the downstream side of the exhaust purification catalyst 10 to generate heat due to the reforming reaction utilizing oxidation of oxygen contained in the exhaust gas. It is possible to prevent the temperature of the reforming catalyst 13 from rising excessively due to the influence, and to prevent thermal degradation of the reforming catalyst 13.

  Further, in the second embodiment described above, control is performed such that when one of the upstream control valve 24 and the downstream control valve 25 is opened, the other is closed, but the exhaust temperature (exhaust gas) discharged from the internal combustion engine 1 is controlled. The ratio of the exhaust amount introduced from the upstream exhaust introduction portion 22 and the exhaust amount introduced from the downstream exhaust introduction portion 23 is adjusted according to the exhaust temperature upstream of the purification catalyst 10), and the reforming catalyst 13 It is also possible to control the temperature and oxygen concentration of the exhaust gas introduced into the gas so as to have desired values.

  For example, when the internal combustion engine 1 has a low load and the exhaust temperature upstream of the exhaust purification catalyst 10 becomes a predetermined temperature or lower (for example, 600 ° C. or lower), the reforming catalyst 13 uses oxygen oxidation for reforming. In order to generate hydrogen by advancing the reaction, the exhaust amount introduced from the upstream side exhaust introduction unit 22 is made larger than the exhaust amount introduced from the downstream side exhaust introduction unit 23. Further, when the internal combustion engine 1 is heavily loaded and the exhaust temperature upstream of the exhaust purification catalyst 10 becomes higher than a predetermined temperature (for example, 650 ° C.), the reforming catalyst is formed by a reforming reaction utilizing oxygen oxidation. The amount of exhaust introduced from the downstream side exhaust introduction part 23 is made larger than the amount of exhaust introduced from the upstream side exhaust introduction part 22 so that the temperature of 13 does not become excessively high. The exhaust temperature upstream of the exhaust purification catalyst 10 may be calculated using, for example, a map that associates the load of the internal combustion engine and the exhaust temperature, or may be detected by a temperature sensor.

  FIG. 5 is an explanatory view schematically showing the overall configuration of an exhaust gas recirculation device for an internal combustion engine in a third embodiment of the present invention. This third embodiment has substantially the same configuration as the second embodiment described above, but in this third embodiment, an oxygen sensor for detecting the oxygen concentration of the exhaust upstream of the exhaust purification catalyst 10 is omitted. It becomes the composition.

  In the third embodiment, the opening / closing control of the upstream control valve 24 and the downstream control valve 25 is performed as follows according to the load of the internal combustion engine 1.

  When the load of the internal combustion engine 1 is lower than a predetermined load set in advance, the EGR control valve 15 and the upstream control valve 24 are opened, and the downstream control valve 25 is closed, so that the exhaust gas purification catalyst is provided in the EGR passage 21. 10 Introduce only upstream exhaust. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 mainly from the reforming reaction utilizing oxidation of oxygen.

  Thereby, even if the temperature of the exhaust gas discharged from the combustion chamber 2 is low, hydrogen can be generated by the reforming catalyst 13 by the reforming reaction utilizing oxidation of oxygen contained in the exhaust gas. Therefore, compared with the case where hydrogen is generated by the reforming catalyst 13 only when the exhaust temperature is relatively high, the operating range in which hydrogen can be introduced into the intake passage 4 can be expanded. If the exhaust gas is introduced into the EGR passage 11 from the downstream side of the exhaust purification catalyst 10 when the load of the internal combustion engine 1 is lower than a predetermined load set in advance, the temperature of the exhaust gas passes through the exhaust purification catalyst 10 and passes through the exhaust purification catalyst 10. When the temperature further decreases, the temperature of the exhaust gas flowing into the reforming catalyst 13 becomes excessively low, and the reforming reaction utilizing water vapor and carbon dioxide in the exhaust gas does not proceed, and hydrogen is not generated by the reforming catalyst 13. There is a fear.

  Further, since the catalyst poison adhering to the reforming catalyst 13 can be burned and removed using oxygen contained in the exhaust gas, it is possible to prevent the reforming reaction of the reforming catalyst 13 from deteriorating due to the catalyst poison. That is, the regeneration process for removing the catalyst poison component on the reforming catalyst 13 can be performed at the same time that hydrogen is generated by the reforming catalyst 13 using oxygen contained in the exhaust gas.

  Further, when the load of the internal combustion engine 1 is higher than a predetermined load set in advance, the EGR control valve 15 and the downstream control valve 25 are opened, and the upstream control valve 24 is closed, whereby the exhaust gas purification is performed in the EGR passage 21. Only the exhaust on the downstream side of the catalyst 10 is introduced. If the reforming fuel is injected from the reforming fuel injection valve 12 at this time, hydrogen is generated in the reforming catalyst 13 from the reforming reaction mainly using water vapor and carbon dioxide in the exhaust gas.

  By introducing exhaust gas into the EGR passage 11 from the downstream side of the exhaust purification catalyst 10, exhaust gas containing almost no oxygen flows into the reforming catalyst 13, and reforming utilizing oxidation of oxygen in the exhaust gas. Since the reaction does not proceed, it is possible to prevent the reforming catalyst 13 from becoming excessively high in temperature and to prevent thermal degradation of the reforming catalyst. In addition, when exhaust is introduced into the EGR passage 11 from the exhaust purification catalyst 10 downstream side, the exhaust gas reaches the reforming catalyst 13 as compared with when exhaust is introduced into the EGR passage 11 from the exhaust purification catalyst 10 upstream side. The length of the path becomes longer, and the amount of heat radiation increases accordingly. Therefore, when the temperature of the exhaust gas exhausted from the combustion chamber 2 is high and the oxygen concentration is high, it is better to introduce the exhaust gas into the EGR passage 11 from the downstream side of the exhaust purification catalyst 10 to prevent thermal deterioration of the reforming catalyst 13. It is effective in doing.

  In the third embodiment as well, as in the first embodiment described above, the operating range in which hydrogen can be introduced into the intake passage 4 is expanded while preventing the thermal deterioration of the reforming catalyst 13, and the internal combustion engine is expanded. The fuel consumption of the engine 1 can be greatly improved.

  FIG. 6 is a flowchart showing the flow of control of the upstream control valve 24 and the downstream control valve 25 in the third embodiment. In S31, it is determined whether or not the load of the internal combustion engine 1 is high. If so, the process proceeds to S32, and if not, the process proceeds to 33. In S32, the EGR control valve 15 and the downstream control valve 25 are controlled to be in a predetermined open state, and the upstream control valve 24 is controlled to be in a closed state. In S33, the EGR control valve 15 and the upstream control valve 24 are controlled to be in a predetermined open state, and the downstream control valve 25 is controlled to be in a closed state.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Combustion chamber 3 ... Intake valve 4 ... Intake passage 4a ... Collector part 5 ... Exhaust valve 6 ... Exhaust passage 7 ... Spark plug 8 ... Throttle valve 9 ... Fuel injection valve 10 ... Exhaust purification catalyst 11 ... EGR passage 12 ... Reforming fuel injection valve 13 ... Reforming catalyst 14 ... EGR cooler 15 ... EGR control valve 16 ... ECU
17 ... oxygen sensor 18 ... accelerator opening sensor 21 ... EGR passage 22 ... upstream exhaust introduction part 23 ... downstream exhaust introduction part 24 ... upstream control valve 25 ... downstream control valve

Claims (6)

An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
An exhaust gas recirculation passage capable of recirculating exhaust gas from the upstream side of the exhaust purification catalyst to the intake passage of the internal combustion engine;
Reforming fuel injection means for injecting reforming fuel into the exhaust gas recirculation passage;
A reforming catalyst that is provided in the exhaust gas recirculation passage and generates hydrogen from the reforming fuel;
An exhaust gas recirculation device for an internal combustion engine, comprising: an exhaust gas recirculation valve that adjusts an amount of exhaust gas recirculation gas that recirculates to the intake passage according to an operating state of the internal combustion engine.
Oxygen concentration detection means for detecting the oxygen concentration of the exhaust upstream of the exhaust purification catalyst,
When the load of the internal combustion engine is low, the exhaust gas upstream of the exhaust purification catalyst is recirculated to the intake passage ,
An exhaust gas recirculation device for an internal combustion engine, wherein when the load on the internal combustion engine is high and the oxygen concentration detected by the oxygen concentration detection means is low, the exhaust gas upstream of the exhaust purification catalyst is recirculated to the intake passage. . The internal combustion engine load is high and when the oxygen concentration of oxygen concentration detected by the detection means is high, according to claim 1, characterized in that to stop the reflux from the exhaust purification catalyst upstream of the exhaust gas into the intake passage 2. An exhaust gas recirculation device for an internal combustion engine according to 1. One end of the exhaust gas recirculation passage connected to the exhaust passage is connected to the upstream exhaust introduction portion connected to the exhaust passage on the upstream side of the exhaust purification catalyst and to the exhaust passage on the downstream side of the exhaust purification catalyst. Branching to the downstream exhaust introduction part
The exhaust gas recirculation apparatus for an internal combustion engine according to claim 1, wherein when the load on the internal combustion engine is low, exhaust gas is introduced from the upstream side exhaust gas introduction section. The exhaust of the internal combustion engine according to claim 3, wherein when the load on the internal combustion engine is high and the oxygen concentration detected by the oxygen concentration detection means is low, exhaust is introduced from the upstream side exhaust introduction section. Reflux apparatus. High load of the internal combustion engine, and when the oxygen concentration detected oxygen concentration detection means is high, an internal combustion engine according to claim 3 or 4, characterized in that introducing the exhaust from the downstream exhaust inlet portion Exhaust gas recirculation device. An exhaust purification catalyst provided in the exhaust passage of the internal combustion engine;
An exhaust gas recirculation passage for recirculating exhaust gas to the intake passage of the internal combustion engine;
Reforming fuel injection means for injecting reforming fuel into the exhaust gas recirculation passage;
A reforming catalyst that is provided in the exhaust gas recirculation passage and generates a gas containing hydrogen by the reforming fuel;
An exhaust gas recirculation valve that adjusts an amount of exhaust gas recirculation gas that recirculates to the intake passage according to the operating state of the internal combustion engine;
Oxygen concentration detection means for detecting the oxygen concentration of the exhaust upstream of the exhaust purification catalyst;
In an exhaust gas recirculation device for an internal combustion engine having
The exhaust gas recirculation passage includes an upstream side exhaust introduction part that introduces exhaust gas on the upstream side of the exhaust purification catalyst, and a downstream side exhaust introduction part that introduces exhaust gas on the downstream side of the exhaust purification catalyst,
When the oxygen concentration detected by the oxygen concentration detection means is low, the introduction of the exhaust gas from the upstream exhaust introduction part to the exhaust gas recirculation passage is permitted, and when the oxygen concentration detected by the oxygen concentration detection means is high, An exhaust gas recirculation apparatus for an internal combustion engine, which permits introduction of exhaust gas from the downstream exhaust gas introduction portion into the exhaust gas recirculation passage.

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