JP2010209789A - Control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine suppressing deterioration in conversion performance when NOx stored in a catalyst is removed by rich combustion. <P>SOLUTION: When the amount of NOx stored in the catalyst 50 is larger than the upper limit of the amount of NOx, NOx stored in the catalyst 50 is removed by performing fuel rich injection, and the amount of LPL-EGR gas flowing from an LPL-EGR passage 70 to an intake passage 15 is increased. Since HC in exhaust gas is changed into CO, NOx is reduced with CO and temperature rise of the catalyst 50 is suppressed. When catalyst bed temperature is higher than a threshold during the fuel rich injection, the amount of LPL-EGR gas circulated is increased. Thereby, it is possible to more certainly change HC generated by the rich combustion into CO. As a result, it is possible to suppress the deterioration in the conversion performance when NOx stored in the catalyst 50 is removed by the rich combustion. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine. In particular, the present invention relates to a control device for an internal combustion engine that performs rich combustion for the purpose of removing NOx from a catalyst.

  An internal combustion engine burns fuel in a combustion chamber and is operated by the energy at the time of combustion of the fuel. At the time of combustion of the fuel, air pollutants such as NOx (nitrogen oxide) are generated. For this reason, when an internal combustion engine is mounted on a vehicle as a power source, a catalyst for storing air pollutants in exhaust gas discharged from the internal combustion engine is often used. In this case, the exhaust gas is purified by storing air pollutants with the catalyst, and the purified exhaust gas is released to the atmosphere. However, if the air pollutant continues to be occluded by the catalyst, the air pollutant accumulates in the catalyst. Therefore, the control device for the conventional internal combustion engine performs control to remove the air pollutant accumulated in the catalyst. There is.

  For example, in the control device for an internal combustion engine described in Patent Document 1, when a regeneration process for removing sulfur oxides and the like deposited on the NOx purification catalyst is executed, the fuel injection amount is increased or the intake air flow rate is used as a raw material. As a result, air-fuel ratio enrichment control is performed to remove sulfur oxides and the like deposited on the NOx purification catalyst.

JP 2008-232092 A

However, when the air-fuel ratio is enriched in this way, part of the fuel may not be combusted in the combustion chamber and may be exhausted without being burned. Since this unburned fuel contains a lot of HC (hydrocarbon), when this exhaust gas is discharged to the atmosphere, the emission performance may be lowered. In addition, when HC flows through the catalyst on which NOx is deposited, NOx is reduced and released as N ₂ (nitrogen). However, when a large amount of HC flows through the catalyst, heat from this reaction is reduced. Many occur. For this reason, the temperature of the catalyst has risen too much, and the function of the catalyst may be reduced.

  The present invention has been made in view of the above, and an object of the present invention is to provide a control device for an internal combustion engine that can suppress a decrease in purification performance when NOx occluded by a catalyst is removed by rich combustion.

  In order to solve the above-described problems and achieve the object, an internal combustion engine control device according to the present invention performs NOx storage reduction in exhaust gas discharged from a combustion chamber that burns fuel during operation of the internal combustion engine. A catalyst temperature obtaining means for obtaining a temperature of the catalyst, an EGR passage which is a passage for flowing the exhaust gas flowing downstream of the catalyst in a flow direction of the exhaust gas to an intake passage of the internal combustion engine, The stored NOx amount estimating means for estimating the NOx amount stored by the catalyst, and the ratio of the air supplied to the combustion chamber and the fuel when the NOx amount estimated by the stored NOx amount estimating means is greater than a predetermined value Fuel ratio increasing means for performing control to increase the ratio of the fuel in the air-fuel ratio, and the flow rate of the exhaust gas flowing through the EGR passage is adjustable, and When performing control to increase the ratio of the fuel at the air-fuel ratio by the fuel ratio increasing means, the amount of the exhaust gas flowing from the EGR passage to the intake passage is increased and acquired by the catalyst temperature acquiring means. And an EGR amount adjusting means for increasing the amount of the exhaust gas flowing from the EGR passage to the intake passage when the temperature of the catalyst is higher than a predetermined temperature.

  In this invention, when the estimated value of the amount of NOx occluded by the catalyst is larger than a predetermined value, the ratio of fuel at the air-fuel ratio is increased, so-called rich combustion is performed to remove NOx, and rich combustion Is performed, the amount of exhaust gas flowing from the EGR passage to the intake passage is increased. In the EGR passage, exhaust gas that has become hot due to a reaction of occlusion and reduction by the catalyst flows through the catalyst, and thus the exhaust gas flowing from the EGR passage to the intake passage during rich combustion in this way. By increasing the amount, a large amount of high-temperature exhaust gas can flow into the combustion chamber, and the temperature at which fuel is burned in the combustion chamber can be increased. As a result, unburned fuel is generated by performing rich combustion, and even in a situation where the exhaust gas contains a lot of HC contained in the unburned fuel, HC becomes CO (carbon monoxide) due to the high combustion temperature. It becomes easy to change. When CO flows through the catalyst, the NOx stored in the catalyst can be reduced in the same manner as when HC flows through the catalyst, and moreover during the reduction reaction than when NOx is reduced by HC. Since temperature becomes low, it can suppress that the temperature of a catalyst rises too much. Thereby, the temperature of the catalyst can be maintained at an appropriate temperature when purifying the exhaust gas, and the exhaust gas can be continuously purified.

  Further, when the temperature of the catalyst is higher than a predetermined temperature during the control of rich combustion, the amount of exhaust gas flowing from the EGR passage to the intake passage is increased, so that HC generated by rich combustion is more reliably converted to CO. Can be changed. That is, when rich combustion is performed by increasing the fuel ratio in the air-fuel ratio, the exhaust gas is likely to contain a lot of HC, and the temperature of the catalyst is likely to rise due to this HC, so the temperature of the catalyst is high. In this case, it can be estimated that a lot of HC is generated. Therefore, the amount of exhaust gas flowing from the EGR passage to the intake passage is adjusted based on the temperature of the catalyst, and when the temperature of the catalyst is higher than a predetermined temperature during the rich combustion control, the exhaust gas flows from the EGR passage to the intake passage. By increasing the amount of exhaust gas, it is possible to change HC, which can be estimated to be generated, to CO. As a result, HC generated by rich combustion can be more reliably changed to CO, so that the increase in the temperature of the catalyst can be more reliably suppressed, and the temperature of the catalyst can be set to an appropriate temperature for purifying the exhaust gas. Can be maintained. As a result, it is possible to suppress a decrease in purification performance when the NOx stored by the catalyst is removed by rich combustion.

  Further, in the control apparatus for an internal combustion engine according to the present invention, in the above invention, the EGR amount adjusting means is the catalyst temperature acquiring means during the control for increasing the fuel ratio in the air-fuel ratio by the fuel ratio increasing means. When the acquired temperature of the catalyst is equal to or lower than the predetermined temperature, the amount of the exhaust gas flowing from the EGR passage to the intake passage is reduced.

  In the present invention, when the temperature of the catalyst is equal to or lower than a predetermined temperature during the rich combustion control, the amount of exhaust gas flowing from the EGR passage to the intake passage is reduced, so that hot exhaust gas is supplied from the EGR passage to the intake passage. By flowing, it can be suppressed that the temperature of the catalyst becomes too low and it becomes difficult to purify the exhaust gas. That is, the catalyst is activated when the temperature is within a predetermined temperature range, and the exhaust gas can be purified by, for example, storing and reducing NOx. Therefore, when the temperature of the catalyst becomes too low and falls below the activation temperature, the catalyst Makes it difficult to purify the exhaust gas. For this reason, when the temperature of the catalyst becomes equal to or lower than a predetermined temperature during the control of rich combustion, the amount of exhaust gas flowing from the EGR passage to the intake passage is reduced, so that HC generated more by rich combustion is reduced to CO. Therefore, the amount of HC flowing through the catalyst can be increased. As a result, the rate at which NOx stored in the catalyst is reduced by HC increases, so that the temperature of the catalyst can be increased by the heat during the reduction reaction. Therefore, when the HC is changed to CO by the high-temperature exhaust gas flowing from the EGR passage to the intake passage, it is possible to suppress the temperature of the catalyst from being excessively lowered and it becomes difficult to purify the exhaust gas. Gas purification can be performed. As a result, it is possible to more reliably suppress the reduction in purification performance when the NOx occluded by the catalyst is removed by rich combustion.

  The control apparatus for an internal combustion engine according to the present invention is characterized in that, in the above invention, the fuel is a GTL fuel.

  In this invention, since the GTL fuel is used as the fuel, it is possible to more reliably suppress the temperature of the catalyst from excessively rising during the rich combustion. That is, when the combustion temperature of the GTL fuel is increased at the time of rich combustion, HC is more likely to be changed to CO than light oil, so that the temperature of the catalyst can be more reliably prevented from rising excessively. Thereby, the temperature of the catalyst at the time of rich combustion can be maintained at an appropriate temperature for purifying the exhaust gas. As a result, it is possible to more reliably suppress the reduction in purification performance when the NOx occluded by the catalyst is removed by rich combustion.

  The control apparatus for an internal combustion engine according to the present invention has an effect that it is possible to suppress a decrease in purification performance when the catalyst is purified by rich combustion.

FIG. 1 is a schematic configuration diagram of an engine including an engine control apparatus according to an embodiment. FIG. 2 is a configuration diagram of a main part of the engine control apparatus shown in FIG. FIG. 3 is an explanatory diagram showing changes in the HC amount when rich combustion is performed. FIG. 4 is an explanatory diagram showing changes in the catalyst bed temperature when rich combustion is performed. FIG. 5 is a flowchart illustrating a processing procedure of the engine control apparatus according to the embodiment. FIG. 6 is a flowchart showing a processing procedure of LPL-EGR amount control. FIG. 7 is an explanatory diagram of the air-fuel ratio when rich combustion is performed by the engine control apparatus according to the embodiment. FIG. 8 is an explanatory diagram of the HC amount when the rich combustion is performed by the engine control apparatus according to the embodiment.

  Embodiments of an internal combustion engine control apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily replaced by those skilled in the art or those that are substantially the same.

  FIG. 1 is a schematic configuration diagram of an engine including an engine control apparatus according to an embodiment. A control device 1 for an engine 10 according to an embodiment which is an example of a control device for an internal combustion engine according to the present invention is mounted on a vehicle (not shown), for example, and operates an engine 10 provided as a power source when the vehicle travels. Is provided to be controllable. The engine 10 is a so-called diesel engine that burns fuel by supplying fuel to compressed air. The fuel is a GTL (Gas) that is a liquid fuel generated from gas fuel such as natural gas. To Liquids) fuel is used.

  The engine 10 has four cylinders (not shown) arranged in series, and each cylinder is connected to a combustion chamber 11 for burning fuel when the engine 10 is in operation. Further, the engine 10 communicates with the combustion chamber 11, and an intake passage 15 that is a passage through which air sucked into the combustion chamber 11 flows, and fuel is combusted in the combustion chamber 11, and then discharged from the combustion chamber 11. And an exhaust passage 16 through which exhaust gas flows. These intake passages 15 and exhaust passages 16 are branched into four passages according to the number of combustion chambers 11. The branched passages correspond to the four combustion chambers 11 and communicate with the combustion chambers 11. Connected to the engine 10.

  Each combustion chamber 11 is provided with a fuel injector 21 which is a fuel supply means capable of supplying fuel to the combustion chamber 11 during operation of the engine 10. The fuel injector 21 is provided so that fuel can be supplied to the combustion chamber 11 by injecting fuel into the combustion chamber 11 during operation of the engine 10.

  Thus, all the fuel injectors 21 disposed in the combustion chambers 11 are connected to the common rail 25. The common rail 25 is connected to a supply pump 26 that applies pressure to the fuel and supplies the fuel to the common rail 25 via an engine fuel passage 31. The supply pump 26 is a fuel storage unit that stores fuel. The fuel tank 35 is connected via the main fuel passage 30. A main fuel passage 30 that connects the supply pump 26 and the fuel tank 35 is provided with a fuel filter 36 that removes impurities contained in the fuel.

  The common rail 25 and the fuel tank 35 are passages for returning surplus fuel from the fuel supplied to the common rail 25 to the fuel tank 35, and one end is connected to the common rail 25 and the other end is connected to the fuel tank 35. A return passage 32, which is a separate passage, is connected.

  Further, the engine 10 includes a turbocharger 40 that is a supercharging unit that compresses air taken in the combustion chamber 11. A compressor 41 included in the turbocharger 40 is connected to the intake passage 15, and a turbine included in the turbocharger 40. 42 is connected to the exhaust passage 16. In the turbocharger 40, the turbine 42 is operated by the exhaust gas flowing through the exhaust passage 16 to which the turbine 42 is connected, and the operation force of the turbine 42 is transmitted to the compressor 41 to operate the compressor 41. The air flowing through the compressor 15 can be compressed by the compressor 41.

  The intake passage 15 to which the compressor 41 of the turbocharger 40 is connected is provided with an intercooler 45 that cools the air compressed by the compressor 41 on the downstream side of the compressor 41 in the flow direction of the air flowing through the intake passage 15. . Further, a throttle valve 46 that can open and close the intake passage 15 is disposed in the intake passage 15 downstream of the intercooler 45. The intake passage 15 is provided with an air flow meter 47 that is an intake air amount detection means capable of detecting the flow rate of the air flowing through the intake passage 15 on the upstream side of the compressor 41.

  Further, the exhaust passage 16 is provided with a catalyst 50, which is a means for purifying exhaust gas discharged from the combustion chamber 11 when the engine 10 is operating, on the downstream side of the turbine 42. This catalyst 50 is an NOx storage reduction catalyst capable of storing and reducing NOx (nitrogen oxide) contained in exhaust gas. For example, a known NSR (NOx Storage Reduction) catalyst or DPNR (Diesel Particulate NOx Reduction) is used. ) A catalyst is used. The catalyst 50 is provided with a catalyst bed temperature sensor 51 which is a catalyst bed temperature detection means capable of detecting the catalyst bed temperature which is the temperature of the catalyst 50.

  EGR (Exhaust Gas Recirculation) gas, which is a part of exhaust gas discharged from the engine 10 and is recirculated to the engine 10 again, flows through the exhaust passage 16 and the intake passage 15 provided as described above. An EGR passage which is a passage is connected, and two types of EGR passages are provided. Of the two types of EGR passages, one type of EGR passage 60 has one end connected to the upstream side of the turbine 42 in the exhaust passage 16 and the other end connected to the intake passage 15. Is connected to the downstream side of the throttle valve 46. As a result, the EGR passage 60 can cause a part of the exhaust gas flowing through the exhaust passage 16 to flow from the exhaust passage 16 to the intake passage 15 as EGR gas.

  The EGR passage 60 provided in this way is provided with an EGR cooler 62 that is a cooling means capable of cooling the EGR gas flowing through the EGR passage 60. The EGR cooler 62 is formed so that heat can be exchanged between cooling water (not shown) that is a cooling medium that cools the engine 10 during operation of the vehicle and EGR gas. The temperature of the EGR gas passing through the temperature decreases by exchanging heat with the cooling water.

  The EGR passage 60 includes a portion between a portion where the EGR cooler 62 is provided and a portion connected to the intake passage 15, that is, a portion connected to the intake passage 15 in the EGR passage 60. An EGR valve 63 capable of adjusting the opening degree in the EGR passage 60 is disposed in the vicinity.

  Of the two types of EGR passages, another type of EGR passage flows through a low pressure loop (LPL) -EGR gas that is a recirculation gas that causes the engine 10 to again intake a portion of the exhaust gas that has passed through the catalyst 50. It is an LPL-EGR passage 70 which is a passage. The LPL-EGR passage 70 is provided as an EGR passage that causes the exhaust gas flowing downstream of the catalyst 50 in the flow direction of the exhaust gas flowing through the exhaust passage 16 to flow into the intake passage 15 as LPL-EGR gas that is a high-temperature EGR gas. ing. Specifically, one end of the LPL-EGR passage 70 is connected to the downstream side of the catalyst 50 in the exhaust passage 16, and the other end is downstream of the throttle valve 46 in the intake passage 15. Connected to the side. Thereby, the LPL-EGR passage 70 can cause a part of the exhaust gas that has passed through the catalyst 50 provided in the exhaust passage 16 to flow from the exhaust passage 16 to the intake passage 15 as LPL-EGR gas.

  In the LPL-EGR passage 70 thus provided, a reflux side LPL-EGR valve 71 capable of adjusting the opening degree in the LPL-EGR passage 70 is disposed. Further, an exhaust side LPL-EGR valve 72 capable of adjusting the opening degree in the exhaust passage 16 is disposed in the exhaust passage 16 downstream of a portion to which the LPL-EGR passage 70 is connected.

  These fuel injector 21, supply pump 26, throttle valve 46, air flow meter 47, catalyst bed temperature sensor 51, EGR valve 63, recirculation side LPL-EGR valve 71, and exhaust side LPL-EGR valve 72 are mounted on the vehicle. At the same time, it is connected to an ECU (Electronic Control Unit) 80 that controls each part of the vehicle. Further, the ECU 80 includes an accelerator opening sensor 76 that is provided in the vicinity of an accelerator pedal 75 provided in the driver's seat of the vehicle and is an accelerator opening detecting means that can detect an accelerator opening that is an opening of the accelerator pedal 75. It is connected.

  FIG. 2 is a configuration diagram of a main part of the engine control apparatus shown in FIG. The ECU 80 is provided with a processing unit 81, a storage unit 100, and an input / output unit 101, which are connected to each other and can exchange signals with each other. The fuel injector 21, the supply pump 26, the throttle valve 46, the air flow meter 47, the catalyst bed temperature sensor 51, the EGR valve 63, the recirculation side LPL-EGR valve 71, and the exhaust side LPL-EGR valve 72 connected to the ECU 80 are The input / output unit 101 inputs / outputs signals to / from these fuel injectors 21 and the like. The storage unit 100 stores a computer program for controlling the engine 10. The storage unit 100 is a hard disk device, a magneto-optical disk device, a nonvolatile memory such as a flash memory (a storage medium that can be read only such as a CD-ROM), or a RAM (Random Access Memory). A volatile memory or a combination thereof can be used.

  The processing unit 81 includes a memory and a CPU (Central Processing Unit), and at least an accelerator opening that can acquire an accelerator opening degree that is an opening degree of the accelerator pedal 75 based on a detection result of the accelerator opening degree sensor 76. An accelerator opening degree obtaining unit 82 which is a degree obtaining unit, a throttle valve control unit 83 which is an intake air amount control unit capable of controlling the intake air amount of the engine 10 by controlling opening and closing of the throttle valve 46, an air flow By controlling the amount of fuel injected from the fuel injector 21 and the intake air amount acquisition unit 84 that is an intake air amount acquisition means capable of acquiring the intake air amount of the engine 10 during operation from the detection result of the meter 47 A fuel injection amount control unit 85 which is a fuel supply amount control means capable of controlling the amount of fuel supplied to the engine 10, and the EGR valve 6 Has an EGR valve control unit 86 is controllable EGR gas amount control means the flow rate of the EGR gas, a by controlling the opening and closing of the.

  Further, the processing unit 81 is a catalyst capable of acquiring the catalyst bed temperature from the detection result of the storage NOx amount estimation unit 87 which is a storage NOx amount estimation means for estimating the NOx amount stored by the catalyst 50 and the catalyst bed temperature sensor 51. Whether or not fuel-rich injection, which is fuel injection when the air-fuel ratio, which is the ratio of the air and fuel supplied to the combustion chamber 11, is made rich, can be executed. When the NOx amount estimated by the rich injection execution determining unit 89, which is a rich injection execution determining unit, and the occluded NOx amount estimating unit 87 is larger than a predetermined value, the control is performed to increase the fuel ratio in the air-fuel ratio. And a fuel rich injection control unit 90 which is a fuel ratio increasing means for controlling the fuel rich injection.

  Further, the processing unit 81 compares the NOx amount estimated by the occluded NOx amount estimating unit 87 with the threshold value of the NOx amount used when performing control of the fuel rich injection and the like, and the estimated NOx amount and the threshold value of the NOx amount The NOx storage determination unit 91 is a storage NOx amount determination means for determining the magnitude of the catalyst bed temperature, the catalyst bed temperature acquired by the catalyst bed temperature acquisition unit 88, the reflux side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72. A catalyst bed temperature determination unit 92 that is a catalyst bed temperature determination unit that compares the acquired catalyst bed temperature with a threshold value of the catalyst bed temperature and compares the acquired catalyst bed temperature with a threshold value of the catalyst bed temperature. The flow rate of the LPL-EGR gas flowing through the LPL-EGR passage 70 can be adjusted by controlling the opening and closing of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72, and the fuel lip is adjusted. When the NOx amount estimated by the injection control unit 90 is larger than a predetermined value, LPL-EGR valve control which is an EGR amount adjusting means for increasing the amount of LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15. Part 93.

  The control of the engine 10 controlled by the ECU 80 is, for example, based on the detection result of the catalyst bed temperature acquisition unit 88 or the like, the processing unit 81 reads the computer program into a memory incorporated in the processing unit 81 and performs calculation. Control is performed by operating the reflux side LPL-EGR valve 71, the exhaust side LPL-EGR valve 72, and the like according to the result of the calculation. At that time, the processing unit 81 appropriately stores a numerical value in the middle of the calculation in the storage unit 100, and takes out the stored numerical value and executes the calculation. When the engine 10 is controlled in this way, it may be controlled by dedicated hardware different from the ECU 80 instead of the computer program.

  The control device 1 for the engine 10 according to this embodiment is configured as described above, and the operation thereof will be described below. In the control apparatus 1 for the engine 10 according to the embodiment, since the engine 10 can be operated with GTL fuel, the fuel tank 35 that stores fuel used for operating the engine 10 stores GTL fuel.

  When a vehicle equipped with the engine 10 is running, an accelerator pedal 75 provided in the vehicle interior is operated with a foot, and the stroke amount of the accelerator pedal 75 or the accelerator opening is provided in the vicinity of the accelerator pedal 75. Detected by sensor 76. The detection result by the accelerator opening sensor 76 is transmitted to an accelerator opening acquiring unit 82 included in the processing unit 81 of the ECU 80 and acquired by the accelerator opening acquiring unit 82. The accelerator opening acquired by the accelerator opening acquisition unit 82 is transmitted to each part such as the throttle valve control unit 83 and the fuel injection amount control unit 85 of the processing unit 81 of the ECU 80, and the engine 10 operates according to the accelerator opening. To do.

  For example, the throttle valve control unit 83 controls the opening degree of the throttle valve 46 in accordance with the accelerator opening degree transmitted from the accelerator opening degree obtaining unit 82. As a result, air corresponding to the opening of the throttle valve 46 flows through the intake passage 15. When air flows into the intake passage 15, the flow rate of the air is detected by the air flow meter 47, and the detection result of the air flow meter 47 is acquired by the intake air amount acquisition unit 84 included in the processing unit 81 of the ECU 80.

  Here, the compressor 41 of the turbocharger 40 is connected to the intake passage 15. The compressor 41 is provided so as to be operable by a force generated when the turbine 42 of the turbocharger 40 is operated by the exhaust gas discharged from the engine 10. When the compressor 41 is operated, the air on the upstream side of the compressor 41 in the flow direction of the air flowing through the intake passage 15 is sucked, compressed, and flowed downstream. As a result, air whose pressure is higher than atmospheric pressure flows through the intake passage 15 on the downstream side of the compressor 41 when the turbocharger 40 is in operation.

  The air whose pressure has increased flows through the intake passage 15 and flows into an intercooler 45 disposed on the downstream side of the compressor 41. When the pressure is increased by compressing air, the temperature rises, but the intercooler 45 performs heat exchange between the compressed air flowing in the intercooler 45 and the air flowing around the intercooler 45, The temperature of the air flowing through the intercooler 45 is lowered. Thereby, the density of the air which flows in the intercooler 45 becomes high.

  The air cooled by the intercooler 45 and having a higher density flows further downstream in the intake passage 15. The throttle valve 46 is disposed downstream of the intercooler 45, and the throttle valve 46 that adjusts the flow rate of the air flowing through the intake passage 15 is compressed by the compressor 41 of the turbocharger 40 and cooled by the intercooler 45. Adjust the air flow after The air whose flow rate is adjusted by the throttle valve 46 is supplied to the engine 10. That is, the engine 10 takes in air while being supercharged by the turbocharger 40.

  Further, when the engine 10 is in operation, the supply pump 26 operates to supply the fuel in the fuel tank 35 to the common rail 25. That is, when the supply pump 26 operates, the fuel in the fuel tank 35 is sucked into the supply pump 26 via the main fuel passage 30. At that time, the fuel sucked into the supply pump 26 flows into the supply pump 26 after impurities are removed by the fuel filter 36 disposed in the main fuel passage 30.

  The fuel sucked into the supply pump 26 is increased in pressure by the supply pump 26 and supplied to the common rail 25 through the engine fuel passage 31. For this reason, the fuel in the common rail 25 is in a high pressure state. Further, since the fuel injector 21 disposed in the combustion chamber 11 is connected to the common rail 25, high-pressure fuel is supplied to the fuel injector 21 from the common rail 25.

  Thus, the fuel injector 21 to which high-pressure fuel is supplied can be controlled by the fuel injection amount control unit 85 included in the processing unit 81 of the ECU 80. That is, the fuel injection amount control unit 85 is transmitted with information related to the operation state such as the accelerator opening acquired by the accelerator opening acquisition unit 82 and the intake air amount acquired by the intake air amount acquisition unit 84. The unit 85 controls and operates the fuel injector 21 according to the transmitted information on the operating state. As a result, the fuel injector 21 injects fuel into the combustion chamber 11 according to the control by the fuel injection amount control unit 85.

  Specifically, the fuel injection amount control unit 85 injects an amount of fuel suitable for the operating state from the fuel injector 21 into the combustion chamber 11 when the air in the combustion chamber 11 becomes high pressure during the compression stroke of the engine 10. Let The fuel injected into the combustion chamber 11 is combusted by the air heated to a high temperature by compression, and the exhaust gas after combustion is exhausted from the combustion chamber 11 to the exhaust passage 16 in the exhaust stroke. The exhaust gas exhausted to the exhaust passage 16 flows to the turbine 42 of the turbocharger 40 connected to the exhaust passage 16 to operate the turbocharger 40.

  The exhaust gas after operating the turbocharger 40 further flows through the exhaust passage 16 and passes through the catalyst 50. The catalyst 50 allows NOx in the exhaust gas to flow through the exhaust gas passing through the catalyst 50 by repeatedly changing the air-fuel ratio, which is the ratio of fuel and air combusted in the combustion chamber 11, between rich and lean. Purify (nitrogen oxides).

Specifically, when the air-fuel ratio is stoichiometric or lean, that is, when a large amount of oxygen is contained in the exhaust gas, the catalyst 50 stores NOx. In addition, when the air-fuel ratio is rich, that is, the oxygen concentration is low and the amount of fuel is large, unburned fuel is generated, and HC (hydrocarbon) and CO (carbon monoxide) contained in the unburned fuel. ) And the like are contained in the exhaust gas in a large amount, the catalyst 50 reduces NOx to NO ₂ (nitrogen dioxide) or NO (nitrogen monoxide) and releases it. NOx that has been released as NO ₂ or NO is further reduced by reacting with HC or CO in the exhaust gas, the _{N 2} (nitrogen). In this case, HC and CO are oxidized by reducing NO ₂ and NO, and most of them become H ₂ O (water) and CO ₂ (carbon dioxide). The catalyst 50 thus purifies the exhaust gas.

In this way, the catalyst 50 purifies the exhaust gas by changing the air-fuel ratio. However, during normal operation, the air-fuel ratio is stoichiometric with emphasis on driving performance, or the air-fuel ratio is made lean with emphasis on fuel efficiency. Or In this case, the catalyst 50 occludes NOx in the exhaust gas. When the air-fuel ratio is stoichiometric or lean and the operation is continued, the catalyst 50 continues to store NOx, so the amount of NOx stored by the catalyst 50 continues to increase, but the stored amount of NOx exceeds a predetermined amount. To make the air-fuel ratio rich. Thereby, NOx occluded by the catalyst 50 is reduced to N ₂ and released to the atmosphere.

  Here, normally, when the air-fuel ratio is made rich, the fuel rich injection control unit 90 of the processing unit 81 of the ECU 80 increases the injection amount of fuel injected from the fuel injector 21 or opens the throttle valve 46. The degree is decreased and the opening degree of the EGR valve 63 is increased. As a result, the injection amount of the fuel supplied to the combustion chamber 11 increases, or the flow rate of the outside air sucked into the combustion chamber 11, that is, the flow rate of fresh air decreases, and the flow rate of EGR gas increases. The ratio of fuel to fresh air to be inhaled is higher than the ratio of fuel during normal operation.

  On the other hand, when the air-fuel ratio is made rich for the purpose of reducing NOx occluded by the catalyst 50, the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 are controlled to control the catalyst 50. The exhaust gas that has passed through is returned from the LPL-EGR passage 70 to the intake passage 15 and is sucked into the combustion chamber 11. Specifically, the opening of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 is controlled by the LPL-EGR valve control unit 93 of the processing unit 81 of the ECU 80, and the exhaust side LPL-EGR valve 72. The opening degree of the reflux side LPL-EGR valve 71 is increased. As a result, the amount of the exhaust gas that has passed through the catalyst 50 is reduced to the atmosphere, and the amount that returns to the intake passage through the LPL-EGR passage 70 increases.

  When the exhaust gas passes through the catalyst 50, the exhaust gas undergoes a reaction such as occlusion reduction at the catalyst 50, so that the temperature rises. For this reason, the LPL-EGR gas, which is the exhaust gas recirculated to the intake passage 15 through the LPL-EGR passage 70 after passing through the catalyst 50, is a gas having a high temperature, and when the air-fuel ratio is made rich. When the LPL-EGR gas is refluxed, a high-temperature gas is sucked into the combustion chamber 11. Thereby, since the ignitability of fuel improves, the temperature at the time of combustion of the fuel in the combustion chamber 11 rises with LPL-EGR gas.

  FIG. 3 is an explanatory diagram showing changes in the HC amount when rich combustion is performed. When rich combustion is performed with the air-fuel ratio being rich, unburned fuel is generated because the ratio of fuel is large. However, when the temperature during combustion of the fuel is increased by LPL-EGR gas, unburned fuel is generated. Even the temperature rises. For this reason, HC contained in the unburned fuel undergoes a chemical change due to the combustion gas that is at a higher temperature than when the LPL-EGR gas is not recirculated, and changes to CO. As a result, the amount of HC in the exhaust gas decreases, and the amount of CO increases.

  That is, in the control apparatus 1 for the engine 10 according to the embodiment, since the LPL-EGR gas is recirculated at the time of rich combustion, as shown in FIG. 3, the LPL-EGR gas is recirculated when the rich combustion is started. The HC amount at the time of LPL-EGR, which is reduced by the LPL-EGR, is generated when the LPL-EGR gas is not recirculated as in the control of the conventional engine, and is compared with the conventional HC amount HCh that is the HC amount flowing to the catalyst 50 And greatly reduced.

FIG. 4 is an explanatory diagram showing changes in the catalyst bed temperature when rich combustion is performed. The exhaust gas flowing through the exhaust passage 16 flows to the catalyst 50 in a state where HC decreases and CO increases in this way, but CO reduces NOx occluded in the catalyst 50 to N ₂ in the same manner as HC. . Here, when CO reduces NOx occluded in the catalyst 50, the catalyst bed temperature is less likely to rise than when HC reduces NOx.

  For this reason, when the amount of HC flowing through the catalyst 50 is reduced by starting rich combustion and refluxing the LPL-EGR gas, the catalyst bed temperature is less likely to rise by refluxing the LPL-EGR gas. The catalyst bed temperature TCi at the time of LPL-EGR is compared with the conventional catalyst bed temperature TCh which is the catalyst bed temperature when NOx is reduced by HC without recirculating the LPL-EGR gas as in the control in the conventional engine. , Greatly reduced.

  In addition, the LPL-EGR valve control unit 93 controls the opening degree of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72, so that the catalyst bed temperature acquisition unit 88 included in the processing unit 81 of the ECU 80 is used. Control is performed based on the catalyst bed temperature obtained in (1). That is, when the amount of HC flowing through the catalyst 50 is large, the catalyst bed temperature easily rises. Therefore, when the catalyst bed temperature acquired by the catalyst bed temperature acquisition unit 88 is high, the opening degree of the reflux side LPL-EGR valve 71 is increased. Is increased and the opening degree with the exhaust side LPL-EGR valve 72 is decreased, thereby increasing the recirculation amount of the LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15. As a result, the combustion temperature easily rises and HC easily changes to CO, so that the rise in the catalyst bed temperature can be suppressed.

  On the other hand, when the catalyst bed temperature is low, the catalyst 50 is not activated and it is difficult to purify the exhaust gas. Therefore, when the catalyst bed temperature acquired by the catalyst bed temperature acquisition unit 88 is low, The opening degree of the reflux side LPL-EGR valve 71 is reduced, and the opening degree with the exhaust side LPL-EGR valve 72 is increased. As a result, the recirculation amount of the LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15 decreases, and the combustion temperature hardly rises, so the amount of HC flowing to the catalyst 50 increases and the catalyst bed temperature rises. It becomes easy to do. For this reason, the catalyst 50 is activated and it becomes easy to purify the exhaust gas.

  When rich combustion is performed for the purpose of reducing NOx stored in the catalyst 50, when the LPL-EGR gas is recirculated, the amount of HC decreases in this way, so that the catalyst bed temperature rises so much. Instead, the proper temperature is maintained. When the vehicle is driven in this state and it is determined that the NOx stored by the catalyst 50 has been reduced by a predetermined amount, the rich combustion is terminated and the recirculation of the LPL-EGR gas is also stopped, or the normal rich Recirculate at a flow rate other than during combustion.

  FIG. 5 is a flowchart illustrating a processing procedure of the engine control apparatus according to the embodiment. Next, a control method by the control device 1 of the engine 10 according to the embodiment, that is, a processing procedure by the control device 1 of the engine 10 will be described. In the processing procedure by the control device 1 of the engine 10 according to the embodiment, first, the NOx amount (NOx_est) occluded in the catalyst 50 is estimated (step ST101). This estimation is performed by the occluded NOx amount estimating unit 87 included in the processing unit 81 of the ECU 80. Although the amount of NOx flowing through the catalyst 50 varies depending on the operating state of the engine 10, that is, the accelerator opening state, the storage unit 100 of the ECU 80 stores in advance a map indicating the NOx emission amount with respect to the accelerator opening. ing. The stored NOx amount estimation unit 87 continues to estimate the NOx emission amount based on this map and the accelerator opening acquired by the accelerator opening acquisition unit 82 during the operation of the engine 10, and the estimated NOx emission amount Continue to accumulate. Since most of the NOx discharged from the engine 10 flows to the catalyst 50, the stored NOx amount estimating unit 87 estimates the amount of NOx stored in the catalyst 50 from the accumulated amount of NOx discharged.

  Further, the amount of NOx flowing through the catalyst 50 can be estimated by the catalyst bed temperature that changes due to the reaction heat when the exhaust gas reacts with the catalyst 50, and the storage unit 100 of the ECU 80 stores the change in the catalyst bed temperature. A map indicating the storage amount of NOx is stored in advance. The stored NOx amount estimation unit 87 continues to estimate the stored amount of NOx stored by the catalyst 50 based on this map and the catalyst bed temperature acquired by the catalyst bed temperature acquisition unit 88 while the engine 10 is operating. The accumulated NOx storage amount is continuously accumulated. As described above, the stored NOx amount estimating unit 87 accurately estimates the NOx amount (NOx_est) stored in the catalyst 50 based on the accelerator opening and the catalyst bed temperature.

  Next, it is determined whether or not the NOx amount (NOx_est) stored in the catalyst 50 is larger than the upper limit (NOx_max) of the NOx amount (step ST102). This determination is performed by the storage NOx amount determination unit 91 included in the processing unit 81 of the ECU 80. The upper limit value (NOx_max) of the NOx amount used for this determination is preset as a threshold value used for determining whether or not the NOx stored in the catalyst 50 needs to be removed, and is stored in the storage unit 100 of the ECU 80. . The storage NOx amount determination unit 91 compares the NOx amount (NOx_est) estimated by the storage NOx amount estimation unit 87 with the upper limit value (NOx_max) of the NOx amount stored in the storage unit 100, and (NOx_est> NOx_max). It is determined whether or not. If it is determined that there is no (NOx_est> NOx_max), that is, if it is determined that (NOx_est ≦ NOx_max), the processing procedure is exited.

  On the other hand, if it is determined that (NOx_est> NOx_max) by the determination in the storage NOx amount determination unit 91 (step ST102), it is next determined whether or not the fuel rich injection execution condition is satisfied. (Step ST103). This determination is performed by the rich injection execution determination unit 89 included in the processing unit 81 of the ECU 80. The rich injection execution determination unit 89 acquires the operation state of the engine 10 and determines whether or not the current operation state can execute fuel rich injection. For example, based on the accelerator opening obtained by the accelerator opening obtaining unit 82, a required torque that is a torque requested by the driver is estimated, and whether or not fuel-rich injection can be executed based on the requested torque. Determine. That is, when the required torque is large, the engine 10 needs to be operated with priority on the torque. In such a case, the rich injection execution determination unit 89 determines that the fuel rich injection cannot be executed. To do.

  In other words, the rich injection execution determination unit 89 performs the fuel rich injection when the operation state of the engine 10 is such that the required torque is small or the rotational speed of the engine 10 is low, or the output performance is not relatively required. Is determined to be executable. The required torque and the rotational speed used for this determination are set in advance as threshold values used for determining whether or not fuel-rich injection can be executed, and are stored in the storage unit 100 of the ECU 80. If it is determined by the rich injection execution determination unit 89 that the fuel rich injection execution condition is not satisfied, the processing procedure is exited.

  On the other hand, if it is determined by the rich injection execution determination unit 89 (step ST103) that the fuel rich injection execution condition is satisfied, the fuel rich injection is started (step ST104). This fuel-rich injection is performed by the fuel-rich injection control unit 90 included in the processing unit 81 of the ECU 80.

  The fuel rich injection control unit 90 transmits a control signal to the fuel injection amount control unit 85 to increase the injection amount of fuel injected from the fuel injector 21 to the fuel injection amount control unit 85, or to control the throttle. By transmitting a control signal to the valve control unit 83 and the LPL-EGR valve control unit 93, the opening degree of the throttle valve 46 is reduced, the opening degree of the recirculation side LPL-EGR valve 71 is increased, and the exhaust side LPL -Control by which the ratio of the fuel with respect to the air inhaled by the engine 10 is increased by decreasing the opening degree of the EGR valve 72 or the like. When it is determined that the NOx amount (NOx_est) stored in the catalyst 50 is larger than the upper limit value (NOx_max) of the NOx amount (NO in step ST102), the fuel-rich injection is started. Instead of the EGR gas flowing through 60, the LPL-EGR gas flowing through the LPL-EGR passage 70 is refluxed. Once the fuel rich injection is started, a routine for controlling the LPL-EGR amount is called (step ST105).

  FIG. 6 is a flowchart showing a processing procedure of LPL-EGR amount control. In the processing procedure for controlling the LPL-EGR amount, first, the catalyst bed temperature (Cat_mea) is acquired (step ST201). This acquisition is performed by the catalyst bed temperature acquisition unit 88 included in the processing unit 81 of the ECU 80. When the catalyst bed temperature is acquired by the catalyst bed temperature acquisition unit 88, the catalyst bed temperature detected by the catalyst bed temperature sensor 51 is transmitted to the catalyst bed temperature acquisition unit 88, and the detection result transmitted from the catalyst bed temperature sensor 51 is displayed. Get by getting.

  Next, it is determined whether or not the catalyst bed temperature (Cat_mea) acquired by the catalyst bed temperature acquisition unit 88 is higher than the catalyst bed temperature threshold (Cat_max) (step ST202). This determination is performed by the catalyst bed temperature determination unit 92 included in the processing unit 81 of the ECU 80. Here, as for the catalyst bed temperature, when the amount of HC flowing through the catalyst 50 is large, the reaction between NOx and HC stored in the catalyst 50 is promoted, and the temperature tends to increase. That is, when the catalyst bed temperature is high, it can be estimated that the exhaust gas contains a lot of HC. In this case, the amount of HC is decreased by increasing the LPL-EGR amount. On the other hand, when the catalyst bed temperature is low, it can be estimated that the amount of HC contained in the exhaust gas is small. In this case, the LPL-EGR amount can be reduced and the engine 10 can suck the outside air. .

  The threshold (Cat_max) of the catalyst bed temperature used for the determination in the catalyst bed temperature determination unit 92 is a determination whether to increase or decrease the LPL-EGR amount when the LPL-EGR amount is changed based on the catalyst bed temperature. Is set in advance as a threshold value used for the determination, and is stored in the storage unit 100 of the ECU 80. The catalyst bed temperature determination unit 92 compares the catalyst bed temperature (Cat_mea) acquired by the catalyst bed temperature acquisition unit 88 with the threshold (Cat_max) of the catalyst bed temperature stored in the storage unit 100, and (Cat_mea> Cat_max). ).

  If it is determined by the determination at the catalyst bed temperature determination unit 92 (step ST202) that (Cat_mea> Cat_max), the opening degree of the exhaust side LPL-EGR valve 72 is then decreased (step ST203). . This control is performed by the LPL-EGR valve control unit 93 included in the processing unit 81 of the ECU 80. The LPL-EGR valve control unit 93 transmits a control signal for reducing the opening degree by a predetermined control amount set in advance to the exhaust side LPL-EGR valve 72, thereby controlling the exhaust side LPL-EGR valve 72. Reduce the opening.

  Next, the opening degree of the reflux side LPL-EGR valve 71 is increased (step ST204). In this control, the opening degree of the exhaust side LPL-EGR valve 72 is increased from the LPL-EGR valve control unit 93 to the recirculation side LPL-EGR valve 71 by a predetermined control amount, as in the case of reducing the opening degree of the exhaust side LPL-EGR valve 72. By transmitting the control signal to be increased, the opening degree of the reflux side LPL-EGR valve 71 is increased.

  On the other hand, when it is determined that (Cat_mea> Cat_max) is not satisfied by the determination in the catalyst bed temperature determination unit 92 (step ST202), that is, when it is determined that (Cat_mea ≦ Cat_max), In addition, the opening degree of the exhaust side LPL-EGR valve 72 is increased (step ST205). That is, by transmitting a control signal for increasing the opening degree by a predetermined control amount from the LPL-EGR valve control unit 93 to the exhaust side LPL-EGR valve 72, the opening degree of the exhaust side LPL-EGR valve 72 is set. Enlarge.

  Furthermore, the opening degree of the reflux side LPL-EGR valve 71 is controlled by transmitting a control signal for reducing the opening degree by a predetermined control amount from the LPL-EGR valve control unit 93 to the reflux side LPL-EGR valve 71. Decrease (step ST206). After controlling the opening degrees of the exhaust side LPL-EGR valve 72 and the recirculation side LPL-EGR valve 71 as described above, the routine for controlling the LPL-EGR amount is exited, and the original control flow is restored. .

  When the routine for controlling the LPL-EGR amount returns to the original control flow, the NOx amount occluded in the catalyst 50 (NOx_est) is estimated by the occluded NOx amount estimation unit 87 (step ST106). When the LPL-EGR amount is controlled, the exhaust gas component flowing in the catalyst 50 changes, so the catalyst bed temperature also changes. However, the occluded NOx amount estimation unit 87 uses the catalyst acquired by the catalyst bed temperature acquisition unit 88. The amount of NOx occluded in the catalyst 50 is also estimated using the bed temperature. Therefore, the catalyst bed temperature changed by controlling the amount of LPL-EGR is acquired by the catalyst bed temperature acquisition unit 88, and the NOx amount (NOx_est) occluded in the catalyst 50 is estimated from the changed catalyst bed temperature. .

  Next, it is determined whether or not the NOx amount (NOx_est) stored in the catalyst 50 estimated by the stored NOx amount estimation unit 87 (step ST106) is equal to or lower than the lower limit (NOx_min) of the NOx amount (step ST107). This determination is performed by the storage NOx amount determination unit 91 as in the case of determining whether or not the NOx amount (NOx_est) stored in the catalyst 50 is larger than the upper limit (NOx_max) of the NOx amount (step ST102). The lower limit (NOx_min) of the NOx amount used for this determination is set in advance as a threshold used for determining whether or not the NOx stored in the catalyst 50 has been removed, and is stored in the storage unit 100 of the ECU 80. The storage NOx amount determination unit 91 compares the NOx amount (NOx_est) estimated by the storage NOx amount estimation unit 87 with the lower limit value (NOx_min) of the NOx amount stored in the storage unit 100, and (NOx_est ≦ NOx_min). It is determined whether or not.

  When it is determined that (NOx_est ≦ NOx_min) is not satisfied (NOx_est ≦ NOx_min) by the determination in the storage NOx amount determining unit 91 (step ST107), the process returns to step ST105. A routine for controlling the LPL-EGR amount is called again to control the opening degree of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72, and then the NOx amount (NOx_est) occluded in the catalyst 50 is estimated ( Step ST106). Thereafter, until it is determined by the storage NOx amount determination unit 91 that (NOx_est ≦ NOx_min), that is, the NOx amount stored in the catalyst 50 (NOx_est) is determined to be equal to or lower than the lower limit value (NOx_min) of the NOx amount. Until this time, a routine for controlling the LPL-EGR amount is called, and the opening degree control of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 is repeated.

  On the other hand, when it is determined that (NOx_est ≦ NOx_min) is determined by the stored NOx amount determining unit 91 (step ST107), the fuel rich injection is ended (step ST108). That is, the control of the fuel rich injection by the fuel rich injection control unit 90 is finished, and the fuel injection amount control unit 85 causes the fuel injector 21 to inject fuel suitable for the current operating state of the engine 10, and the throttle valve control unit 83. The throttle valve 46 is set to an opening suitable for the current operating state of the engine 10.

  Next, the LPL-EGR valve is returned to the initial value (step ST109). That is, the opening degree of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 whose opening degree is adjusted by the LPL-EGR valve control part 93 is again adjusted by the LPL-EGR valve control part 93, and fuel rich injection is performed. It returns to the initial value which is the opening when not performing. When the LPL-EGR valve is returned to the initial value in this way, the processing procedure is exited.

  When the NOx amount occluded in the catalyst 50 (NOx_est) estimated by the occlusion NOx amount estimation unit 87 is larger than the upper limit value (NOx_max) of the NOx amount, the control device 1 of the engine 10 described above stores the occlusion NOx amount determination unit 91. When the fuel rich injection control unit 90 performs the fuel rich injection, the NOx occluded in the catalyst 50 is removed, and when the fuel rich injection is performed, from the LPL-EGR passage 70. The amount of LPL-EGR gas that is exhaust gas flowing in the intake passage 15 is increased. Since the LPL-EGR gas flowing through the LPL-EGR passage 70 becomes exhaust gas that has become a high temperature due to the occlusion reduction reaction in the catalyst 50 when passing through the catalyst 50, fuel rich injection is performed in this way. When performing, by increasing the amount of LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15, a large amount of high-temperature LPL-EGR gas can flow through the combustion chamber 11, and fuel is burned in the combustion chamber 11. The temperature at the time of making can be made high. Thereby, rich combustion is performed in the combustion chamber 11 by performing fuel-rich injection, and even when a large amount of unburned fuel is generated by this rich combustion and a large amount of HC is contained in the exhaust gas, the temperature becomes high. HC easily changes to CO depending on the combustion temperature. When CO flows to the catalyst 50, the NOx stored in the catalyst 50 can be reduced in the same manner as when HC flows to the catalyst 50, and more reduced than when NOx is reduced by HC. Since the temperature at the time of reaction becomes low, it can suppress that the temperature of the catalyst 50 rises too much. Thereby, the temperature of the catalyst 50 can be maintained at an appropriate temperature when purifying the exhaust gas, and the exhaust gas can be continuously purified.

  FIG. 7 is an explanatory diagram of the air-fuel ratio when rich combustion is performed by the engine control apparatus according to the embodiment. FIG. 8 is an explanatory diagram of the HC amount when the rich combustion is performed by the engine control apparatus according to the embodiment. That is, in the control apparatus 1 for the engine 10 according to the embodiment, when removing NOx stored in the catalyst 50, fuel rich injection is performed, so that the amount of oxygen in the exhaust gas is reduced, but the LPL-EGR gas Even when the gas flows through the intake passage 15, the amount of oxygen in the exhaust gas does not change. Therefore, the LPL-EGR air-fuel ratio AFi, which is the air-fuel ratio at the entrance of the catalyst 50 when the LPL-EGR gas is flowed into the intake passage 15 in the control device 1 of the engine 10 according to the embodiment, is as in the conventional engine. This is equivalent to the conventional air-fuel ratio AFh that is the air-fuel ratio at the entrance of the catalyst 50 when fuel rich injection is performed without flowing the LPL-EGR gas into the intake passage 15. That is, when fuel rich injection is performed, as shown in FIG. 7, both the LPL-EGR air-fuel ratio AFi and the conventional air-fuel ratio AFh are smaller than when the air-fuel ratio is stoichiometric.

  On the other hand, when the fuel rich injection is being performed and the LPL-EGR gas is caused to flow into the intake passage 15, the amount of HC in the exhaust gas decreases, so as shown in FIG. 8, the LPL-EGR gas LPL-EGR HC amount HCi, which is the HC amount when the gas flows through the intake passage 15, is larger than the conventional HC amount HCh, which is the HC amount when the LPL-EGR gas does not flow through the intake passage 15 as in the conventional engine. Less. Thus, when the LPL-EGR gas is caused to flow into the intake passage 15 during the execution of the fuel rich injection, the HC amount in the exhaust gas is the difference D between the LPL-EGR HC amount HCi and the conventional HC amount HCh. And the temperature of the catalyst 50 is less likely to rise by the difference between the heat generated when NOx is reduced by HC corresponding to the difference D and the heat generated when NOx is reduced by CO. By these, it can suppress that the temperature of the catalyst 50 rises too much, and can maintain the temperature of the catalyst 50 at the appropriate temperature in purifying exhaust gas, and can continue purifying exhaust gas.

  Further, when the catalyst bed temperature determination unit 92 determines that the catalyst bed temperature (Cat_mea) acquired by the catalyst bed temperature acquisition unit 88 is higher than the catalyst bed temperature threshold (Cat_max) during execution of the fuel rich injection. The LPL-EGR valve control section 93 adjusts the opening degree of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72, thereby allowing the LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15 to flow. The amount is increasing. Thereby, HC generated by rich combustion can be changed to CO more reliably. That is, when rich combustion is performed by executing fuel-rich injection, a large amount of HC is easily contained in the exhaust gas, and the temperature of the catalyst 50 is likely to rise due to this HC, so that the catalyst bed temperature is high. It can be estimated that a lot of HC is generated. For this reason, the amount of LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15 is adjusted based on the catalyst bed temperature, and the catalyst bed temperature (Cat_mea) becomes the catalyst bed temperature threshold ( When it is determined that it is higher than (Cat_max), the amount of LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15 is increased, thereby changing the HC that can be estimated to be generated to CO. Can do. As a result, the HC generated by rich combustion can be changed to CO more reliably. Therefore, the increase in the temperature of the catalyst 50 can be more reliably suppressed, and the temperature of the catalyst 50 can be set appropriately when purifying the exhaust gas. Temperature can be maintained. As a result, it is possible to suppress a decrease in purification performance when the NOx occluded by the catalyst 50 is removed by rich combustion.

  Further, when the catalyst bed temperature determination unit 92 determines that the catalyst bed temperature (Cat_mea) acquired by the catalyst bed temperature acquisition unit 88 during execution of the fuel rich injection is equal to or less than the catalyst bed temperature threshold (Cat_max). Of the LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15 by adjusting the opening degree of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 by the LPL-EGR valve control unit 93. The amount is decreasing. As a result, it is possible to prevent the temperature of the catalyst 50 from becoming too low due to the flow of high-temperature LPL-EGR gas from the LPL-EGR passage 70 to the intake passage 15, making it difficult to purify the exhaust gas.

  That is, the catalyst 50 is activated when the temperature is within a predetermined temperature range, and the exhaust gas can be purified by, for example, storing and reducing NOx. Therefore, when the temperature of the catalyst 50 becomes too low and falls below the activation temperature. The catalyst 50 is difficult to purify the exhaust gas. Therefore, when the temperature of the catalyst 50 becomes equal to or lower than a predetermined temperature during the rich combustion control, the rich combustion is performed by reducing the amount of LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15. As a result, the ratio of the more HC generated to CO can be reduced, and the amount of HC flowing through the catalyst 50 can be increased. As a result, the rate at which NOx stored in the catalyst 50 is reduced by HC increases, so that the temperature of the catalyst 50 can be increased by the heat during the reduction reaction. Therefore, when the HC is changed to CO by the high-temperature LPL-EGR gas flowing from the LPL-EGR passage 70 to the intake passage 15, it is possible to prevent the exhaust gas from becoming difficult to purify because the temperature of the catalyst 50 is too low. Thus, the exhaust gas can be purified with the catalyst 50 more reliably. As a result, it is possible to more reliably suppress the reduction in purification performance when the NOx occluded by the catalyst 50 is removed by rich combustion.

  Further, when the NOx amount occluded in the catalyst 50 is larger than the upper limit value of the NOx amount, fuel rich injection is performed while the LPL-EGR gas is recirculated, and NOx is removed by CO. When the amount of NOx is removed, it can be removed without considering the emission. As a result, the NOx purification rate is improved, so that it is possible to suppress an increase in resistance when exhaust gas passes through the catalyst 50 due to NOx being deposited on the catalyst 50. As a result, the exhaust resistance is reduced, so that the fuel consumption can be improved.

  Further, since the GTL fuel is used as the fuel for operating the engine 10, it is possible to more reliably suppress the temperature of the catalyst 50 from excessively rising during the rich combustion. That is, when the combustion temperature of the GTL fuel is increased at the time of rich combustion, HC is more likely to change to CO than light oil, so that the temperature of the catalyst 50 can be more reliably prevented from rising excessively. Thereby, the temperature of the catalyst 50 at the time of rich combustion can be maintained at an appropriate temperature for purifying the exhaust gas. As a result, it is possible to more reliably suppress the reduction in purification performance when the NOx occluded by the catalyst 50 is removed by rich combustion.

  In the control device 1 for the engine 10 according to the embodiment, when the LPL-EGR amount is controlled, the opening degrees of the recirculation side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 are controlled in advance. The control amount may be preset as a constant value, or the catalyst bed temperature (Cat_mea) acquired by the catalyst bed temperature acquisition unit 88 and the catalyst bed temperature threshold value. The control amount may be set to increase as the difference from (Cat_max) increases. When the control amount is set to a constant value, the opening degree of the reflux side LPL-EGR valve 71 and the exhaust side LPL-EGR valve 72 can be easily controlled. When the control amount is set to increase as the difference between the catalyst bed temperature (Cat_mea) acquired by the catalyst bed temperature acquisition unit 88 and the catalyst bed temperature threshold (Cat_max) increases, the catalyst bed temperature Even when the temperature is far from the desired temperature, the catalyst bed temperature can be quickly brought close to the desired temperature, and the catalyst bed temperature can be more reliably maintained at the desired temperature.

  Further, in the control device 1 for the engine 10 according to the embodiment, the EGR passage 60 and the LPL-EGR passage 70 are provided as passages through which the exhaust gas to be recirculated, and are selectively used according to the operating conditions. The flowing passage may be only the LPL-EGR passage 70. When rich combustion is performed to remove NOx occluded in the catalyst 50 and the temperature of the catalyst 50 is prevented from rising at that time, the LPL-EGR gas can be suppressed by recirculation, so that the recirculation is performed. As a passage through which the exhaust gas flows, it is sufficient that at least the LPL-EGR passage 70 is provided.

  Further, in the control device 1 for the engine 10 according to the embodiment, the GTL fuel is used as the fuel, but the fuel may be other than the GTL fuel, for example, light oil may be used. Any fuel can be used as long as it generates HC when rich fuel is used and LPL-EGR gas recirculates, as long as HC changes to CO and flows into the exhaust passage 16. .

  As described above, the control device for an internal combustion engine according to the present invention is useful for an internal combustion engine having a storage reduction type NOx catalyst, and in particular, performs control to reduce NOx stored by the catalyst by performing rich combustion. Suitable for internal combustion engines.

DESCRIPTION OF SYMBOLS 1 Control apparatus 10 Engine 11 Combustion chamber 15 Intake passage 16 Exhaust passage 21 Fuel injector 35 Fuel tank 40 Turbocharger 46 Throttle valve 50 Catalyst 51 Catalyst bed temperature sensor 60 EGR passage 70 LPL-EGR passage 71 Reflux side LPL-EGR valve 72 Exhaust Side LPL-EGR valve 75 Accelerator pedal 80 ECU
DESCRIPTION OF SYMBOLS 81 Processing part 82 Accelerator opening degree acquisition part 83 Throttle valve control part 84 Intake air amount acquisition part 85 Fuel injection amount control part 86 EGR valve control part 87 Occlusion NOx amount estimation part 88 Catalyst bed temperature acquisition part 89 Rich injection execution determination part 90 Fuel rich injection control unit 91 NOx storage determination unit 92 Catalyst bed temperature determination unit 93 LPL-EGR valve control unit 100 Storage unit 101 Input / output unit

Claims (3)

A catalyst that occludes and reduces NOx contained in exhaust gas discharged from a combustion chamber that burns fuel during operation of the internal combustion engine;
Catalyst temperature acquisition means for acquiring the temperature of the catalyst;
An EGR passage which is a passage through which the exhaust gas flowing downstream of the catalyst in the flow direction of the exhaust gas flows into the intake passage of the internal combustion engine;
Occluded NOx amount estimating means for estimating the NOx amount occluded by the catalyst;
When the NOx amount estimated by the stored NOx amount estimating means is larger than a predetermined value, the fuel is controlled to increase the ratio of the fuel in the air-fuel ratio that is the ratio of the air supplied to the combustion chamber and the fuel. A rate increase means,
When the flow rate of the exhaust gas flowing through the EGR passage is adjustable and the control to increase the fuel ratio in the air-fuel ratio is performed by the fuel ratio increasing means, When the amount of the exhaust gas flowing into the intake passage is increased and the temperature of the catalyst acquired by the catalyst temperature acquisition means is higher than a predetermined temperature, the amount of the exhaust gas flowing from the EGR passage to the intake passage EGR amount adjusting means for increasing the amount,
A control device for an internal combustion engine, comprising:   The EGR amount adjusting means, when the temperature of the catalyst acquired by the catalyst temperature acquiring means during the control to increase the ratio of the fuel at the air-fuel ratio by the fuel ratio increasing means is equal to or lower than the predetermined temperature, 2. The control device for an internal combustion engine according to claim 1, wherein an amount of the exhaust gas flowing from the EGR passage to the intake passage is reduced.   The control device for an internal combustion engine according to claim 1, wherein the fuel is a GTL fuel.

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