JP6230010B1 - Engine exhaust purification system - Google Patents

Abstract

Even if unburned fuel is contained in the exhaust gas existing in the exhaust passage upstream of the EGR, the internal components of the EGR caused by the flow of unburned fuel HC into the passage in the EGR Prevent the occurrence of failure. In an exhaust purification device for an engine, an EGR control means closes an EGR valve 43c when a first NOx reduction control is performed by a first NOx reduction control means and when a second NOx reduction control is executed by a second NOx reduction control means. The EGR control means limits the introduction of exhaust gas into the EGR passage, and the EGR control means delays until the EGR valves 43c and 43e are started to open from the closed state after the execution of the second NOx reduction control by the second NOx reduction control means. However, after the execution of the first NOx reduction control by the first NOx reduction control means, the EGR valves 43c and 43e are controlled to be shorter than the delay time until the opening operation is started from the closed state. [Selection] Figure 12

Description

  The present invention relates to an exhaust emission control device for an engine, and more particularly, to an exhaust emission control device for an engine provided with an NOx catalyst for purifying NOx in exhaust gas on an exhaust passage.

  Conventionally, NOx in the exhaust gas is occluded in a lean state (λ> 1) where the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio, and this occluded NOx is stored in the vicinity of the stoichiometric air-fuel ratio. NOx occlusion reduction type NOx catalysts that reduce in a certain state (λ≈1) or a rich state (λ <1) smaller than the stoichiometric air-fuel ratio are known. In the normal operating range, from the viewpoint of improving fuel efficiency, the engine is operated with the air-fuel ratio set to a lean state (λ> 1). If this lean operating state continues, the NOx storage of the NOx catalyst is continued. When the amount reaches the limit, the NOx catalyst cannot store NOx in the exhaust gas (in this case, NOx is released). Therefore, the air-fuel ratio is appropriately set to a stoichiometric air-fuel ratio or a richer state (λ ≦ 1) than the stoichiometric air-fuel ratio, so that NOx occluded in the NOx catalyst is reduced. “Λ” is an index indicating the air-fuel ratio expressed with the theoretical air-fuel ratio as a reference, and corresponds to a so-called excess air ratio.

  For example, in Patent Document 1, when the NOx occlusion amount of the NOx catalyst is a predetermined amount or more, fuel injection control is performed so as to enrich the air-fuel ratio of the exhaust gas so as to reduce NOx occluded in the NOx catalyst. Techniques to do are disclosed.

JP 2004-360593 A

  As one of control methods for setting the air-fuel ratio of the exhaust gas to an air-fuel ratio that can reduce NOx occluded in the NOx catalyst (hereinafter referred to as “target air-fuel ratio”), in order to output a desired engine torque A method of performing post-injection in which fuel is injected at a timing that does not contribute to the output of engine torque (typically an expansion stroke) after main injection in which fuel is injected into the cylinder can be considered. Basically, it is desirable to combust the post-injected fuel in the cylinder in order to reduce the NOx catalyst. This is because if the post-injected fuel is not combusted in the cylinder, unburned fuel is discharged and the emission of HC (hydrocarbon) or the like may deteriorate.

  Here, in Patent Document 1 described above, when NOx stored in the NOx catalyst is reduced, control is performed to increase the amount of EGR gas recirculated to the intake system, thereby reducing the amount of fresh air introduced into the engine. It is suggested that the air-fuel ratio of the exhaust gas is enriched by doing so. However, when the control for increasing the amount of EGR gas suggested in Patent Document 1 is applied to the configuration in which the post-injection is performed at the time of reduction of the NOx catalyst and the post-injected fuel is combusted in the cylinder as described above. In some cases, post-injected fuel may not be properly burned in the cylinder due to a decrease in combustion stability. In this case, HC corresponding to unburned fuel is generated. When the unburned fuel generated in this way is supplied to the EGR device, there arises a problem that the EGR device may cause a blockage.

In addition, in NOx reduction control, in order to suppress the generation of smoke (soot), when the oxygen concentration in the engine cylinder is controlled to further improve fuel efficiency, unburned fuel is discharged into the waste passage. There was a problem that there was a risk of it.
As described above, there is a problem that unburned fuel is discharged into the exhaust passage and supplied to the EGR device in the NOx reduction control.

  The present invention has been made to solve the above-described problems of the prior art, and even if unburned fuel is contained in the exhaust gas existing in the exhaust passage on the upstream side of the EGR, It is an object of the present invention to provide an engine exhaust purification device capable of preventing the occurrence of failure of internal components of the EGR due to the flow of unburned fuel HC or the like through a passage in the EGR.

  In order to achieve the above object, the present invention is provided on an exhaust passage of an engine, and stores NOx in exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. An engine exhaust purification device that includes an NOx catalyst that reduces the stored NOx when the air-fuel ratio of the exhaust gas is in the vicinity of the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and is stored in the NOx catalyst NOx reduction control means for performing NOx reduction control for post-injecting from the fuel injection valve so as to set the air-fuel ratio of the exhaust gas to a target air-fuel ratio capable of reducing NOx stored in the NOx catalyst in order to reduce NOx; Through the EGR passage connected to the exhaust passage and the intake passage of the engine, the exhaust gas having a flow rate corresponding to the operating state of the engine is recirculated from the exhaust passage to the intake passage. An EGR control means for controlling an EGR valve provided on the EGR passage, and the NOx reduction control means is in a state in which a relatively large amount of unburned fuel is contained in the exhaust gas in an operating state of a high engine load. The first NOx reduction control means for executing the first NOx reduction control and the second NOx in a state where the amount of unburned fuel in the exhaust gas is smaller than the first NOx reduction control executed by the first NOx reduction control means in the low engine load operation state. A second NOx reduction control means for executing reduction control, and the EGR control means is configured to execute the first NOx reduction control by the first NOx reduction control means and the second NOx reduction control by the second NOx reduction control means. The EGR valve is closed to restrict the introduction of exhaust gas into the EGR passage, and the EGR control means further includes a second NOx After the execution of the second NOx reduction control by the original control means, the delay time from when the EGR valve is closed until the start of the opening operation is started. After the execution of the first NOx reduction control by the first NOx reduction control means, the EGR valve is opened from the closed state. Control is performed so as to be shorter than the delay time until the operation is started.

  In the present invention configured as described above, the EGR control means has the first NOx reduction control after the execution of the second NOx reduction control by the second NOx reduction control means until the EGR valve starts to open from the closed state. After the execution of the first NOx reduction control by the means, the EGR valve is controlled so as to be shorter than the delay time from the closed state until the opening operation is started, so there is less unburned fuel in the exhaust gas than the first NOx reduction control The delay time after the end of execution of the second NOx reduction control executed in the state is made shorter than the delay time after the end of execution of the first NOx reduction control executed in a state where a large amount of unburned fuel is contained in the exhaust gas. Can do. Therefore, after the execution of the second NOx reduction control that is executed in a state where there is little unburned fuel, the EGR valve opening operation can be started with a relatively short delay time to return to the normal control of the EGR and the inside of the EGR. Occurrence of failure due to adhesion of unburned fuel to parts can be suppressed.

In the present invention, preferably, the second NOx reduction control by the second NOx reduction control means is NOx reduction control that is set so that the post-injected fuel is combusted in the cylinder of the engine.
According to the present invention configured as described above, the second NOx reduction control by the second NOx reduction control means is the NOx reduction control set so that the fuel injected by the post injection is burned in the cylinder of the engine. The injected fuel can be prevented from being discharged as unburned fuel as it is, and after the execution of the second NOx reduction control, the EGR valve opening operation is started with a relatively short delay time, and the normal control of EGR is performed. It can be restored and the occurrence of failure due to the unburned fuel adhering to the internal parts of the EGR can be suppressed.

In the present invention, preferably, the first NOx reduction control by the first NOx reduction control means is the NOx reduction set to enrich the air-fuel ratio by discharging at least a part of the post-injected fuel as unburned fuel. Control.
According to the present invention configured as described above, the first NOx reduction control by the first NOx reduction control means enriches the air-fuel ratio by discharging at least part of the post-injected fuel as unburned fuel. Since the NOx reduction control is set to, the delay time from when the EGR valve is closed to when the opening operation is started after the first NOx reduction control for discharging at least a part of the post-injected fuel as unburned fuel is completed. Is made longer than the delay time after the end of execution of the second NOx reduction control. After the end of execution of the first NOx reduction control, the opening operation of the EGR valve is started with a relatively long delay time, and the normal control of EGR is restored. And the occurrence of failure due to unburned fuel adhering to the internal parts of the EGR can be suppressed.

In the present invention, preferably, the EGR passage includes a cooler side EGR passage in which an EGR cooler is provided on the passage, and a bypass side EGR passage that bypasses the EGR cooler, and the EGR valve passes through the cooler side EGR passage. And a second EGR valve that adjusts the flow rate of the exhaust gas that passes through the bypass side EGR passage, and the EGR control means includes a second NOx reduction control by the second NOx reduction control means. During execution, control is performed such that the second EGR valve is opened and the first EGR valve is closed.
According to the present invention configured as described above, the EGR control unit causes the exhaust gas to flow through the bypass side EGR passage and not to the cooler side EGR passage side when the second NOx reduction control is performed by the second NOx reduction control unit. Therefore, HC generated by post injection at the time of execution of the second NOx reduction control flows into the cooler side EGR passage and is cooled by the EGR cooler, thereby preventing the occurrence of a failure that closes the EGR cooler. be able to.

In the present invention, preferably, the EGR passage includes a cooler-side EGR passage in which an EGR cooler is provided on the passage, and a bypass-side EGR passage that bypasses the EGR cooler, and the EGR valve passes the cooler-side EGR passage. A first EGR valve that adjusts the flow rate of the exhaust gas, and a second EGR valve that adjusts the flow rate of the exhaust gas that passes through the bypass-side EGR passage. The EGR control means performs the first NOx reduction control by the first NOx reduction control means. At the time of execution, control is performed so that the first EGR valve is closed and the second EGR valve is closed.
According to the present invention configured as described above, the EGR control means closes the first EGR valve and closes the second EGR valve when the first NOx reduction control is executed by the first NOx reduction control means. Therefore, when performing the first NOx reduction control in which the post-injected fuel is discharged as unburned fuel, HC of unburned fuel flows into the cooler side EGR passage and is cooled by the EGR cooler, thereby reducing the EGR cooler. Occurrence of a failure that can be blocked can be prevented. Further, when the first NOx reduction control is executed, it is possible to prevent the occurrence of a failure in which unburned fuel HC or the like flows into the bypass EGR passage and closes the bypass EGR passage.

In the present invention, it is preferable that the EGR control means closes the first EGR valve after the second NOx reduction control by the second NOx reduction control means until the second EGR valve is started after the second EGR valve is closed. Control is performed so as to be shorter than the delay time from the start to the start of the opening operation.
According to the present invention configured as described above, the EGR control unit has a delay time from the closed state of the first EGR valve to the start of the opening operation after the execution of the first NOx reduction control by the first NOx reduction control unit being the second EGR. Since the valve is controlled to be longer than the delay time from when the valve is closed to when the opening operation is started, HC generated by post injection at the time of executing the second NOx reduction control is opened after a longer delay time elapses. It is more difficult to enter the cooler-side EGR passage, and HC or the like flows into the cooler-side EGR passage and is cooled by the EGR cooler, so that it is possible to prevent a failure that blocks the EGR cooler.

In the present invention, it is preferable that the EGR control unit delays the second EGR valve from the closed state to the start of the opening operation after the execution of the first NOx reduction control by the first NOx reduction control unit, and the first EGR valve is closed. The delay time from the start to the opening operation is controlled so as to be a relatively long delay time so that the unburned fuel hardly flows into the EGR passage.
According to the present invention configured as described above, the EGR control means has a delay time until the second EGR valve starts to open from the closed state after the execution of the first NOx reduction control by the first NOx reduction control means, and Since the delay time from when the first EGR valve is closed to when the opening operation is started is controlled to be a relatively long time so that the unburned fuel hardly flows into the EGR passage, the first NOx reduction control is executed. The occurrence of a failure that closes the EGR cooler can be prevented by the HC generated by the post-injection flowing through the cooler side EGR passage and being cooled by the EGR cooler.

In the present invention, preferably, the EGR control means sets a delay time until the second EGR valve starts to open from the closed state and / or a delay time until the first EGR valve starts to open from the closed state. It is set according to the time until the exhaust amount of exhaust gas discharged from the engine to the exhaust passage reaches a predetermined amount.
According to the present invention configured as described above, the EGR control means delays until the second EGR valve starts to open from the closed state and / or until the first EGR valve starts to open from the closed state. The delay time is set by the time until the exhaust amount of exhaust gas discharged from the engine to the exhaust passage reaches a predetermined amount, so that the exhaust gas discharged from the engine to the exhaust passage passes through the delay time, Since the exhaust gas already existing in the exhaust passage upstream of the EGR is replaced by pushing it downstream, the unburned fuel is compared with the exhaust gas already existing in the exhaust passage upstream of the EGR. Even if a large amount is contained, the exhaust gas containing the unburned fuel can be pushed downstream. Therefore, the occurrence of a failure that closes the EGR cooler can be prevented by causing the unburned fuel HC or the like to flow into the cooler-side EGR passage and be cooled by the EGR cooler. It is also possible to prevent the occurrence of a failure in which unburned fuel HC or the like flows into the bypass side EGR passage and closes the bypass side EGR passage.

In the present invention, preferably, the EGR control means sets the opening of the EGR valve based on the target in-cylinder oxygen concentration that should be set during the NOx reduction control by the NOx reduction control means.
According to the present invention configured as described above, since the opening degree of the EGR valve is controlled based on the target in-cylinder oxygen concentration to be set at the time of NOx reduction control, a desired amount of exhaust gas is introduced into the engine, The inside of the engine cylinder can be appropriately set to a desired oxygen concentration.

  According to the exhaust emission control device for an engine of the present invention, even if unburned fuel is contained in the exhaust gas existing in the exhaust passage upstream of the EGR, HC of unburned fuel is contained in the EGR. It is possible to prevent the failure of the internal parts of the EGR caused by flowing in the passage.

1 is a schematic configuration diagram of an engine system to which an engine exhaust gas purification apparatus according to an embodiment of the present invention is applied. 1 is a block diagram showing an electrical configuration of an engine exhaust gas purification apparatus according to an embodiment of the present invention. It is a flowchart which shows the fuel-injection control by one Embodiment of this invention. It is a flowchart which shows the post injection amount calculation process for DeNOx by one Embodiment of this invention. It is explanatory drawing about the driving | operation area | region of the engine which performs each of passive DeNOx control and active DeNOx control in one Embodiment of this invention. It is a flowchart which shows the setting process of the active DeNOx control execution flag by one Embodiment of this invention. It is a flowchart which shows the setting process of the passive DeNOx control execution flag by one Embodiment of this invention. 4 is a flowchart illustrating active DeNOx control according to an embodiment of the present invention. It is a flowchart which shows the passive DeNOx control by one Embodiment of this invention. It is explanatory drawing about the setting method of the post injection timing of active DeNOx control by one Embodiment of this invention. It is a flowchart which shows EGR control by one Embodiment of this invention. It is a flowchart which shows EGR return control by one Embodiment of this invention. Regarding EGR control of the exhaust purification device for engine E according to one embodiment of the present invention, in the complete warm-up state of engine E, the EGR control region is changed according to the operating state of engine E, the EGR bypass side control region, the cooler side control region, It is a figure which shows the EGR control map set to any of a bypass side and cooler side combined use control area, and an EGR cut control area. Regarding EGR control of an engine exhaust gas purification apparatus according to an embodiment of the present invention, when the engine E is in a semi-warm-up state, the EGR control region is changed into an EGR bypass side control region, a cooler side control region, and a bypass according to the operating state of the engine E. It is a figure which shows the EGR control map set to any of a side and cooler side combined use control area | region, and an EGR cut control area | region.

  Hereinafter, an exhaust emission control device for an engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<System configuration>
First, an engine system to which an exhaust emission control device for an engine according to an embodiment of the present invention is applied will be described with reference to FIG. FIG. 1 is a schematic configuration diagram of an engine system to which an engine exhaust gas purification apparatus according to an embodiment of the present invention is applied.

  As shown in FIG. 1, the engine system 200 mainly includes an engine E as a diesel engine, an intake system IN that supplies intake air to the engine E, a fuel supply system FS that supplies fuel to the engine E, An exhaust system EX that exhausts exhaust gas from the engine E, sensors 100 to 119 that detect various states relating to the engine system 200, a PCM (Power-train Control Module) 60 that controls the engine system 200, and an SCR catalyst 47 And a DCU (Dosing Control Unit) 70 for performing control related to the above.

First, the intake system IN has an intake passage 1 through which intake air passes, and an air cleaner 3 that purifies air introduced from the outside in order from the upstream side, and intake air that passes through the intake passage 1. The compressor of the turbocharger 5 that compresses and raises the intake pressure, the intercooler 8 that cools the intake air by outside air or cooling water, and the intake shutter valve 7 that adjusts the intake air flow rate (corresponding to a throttle valve) And a surge tank 12 for temporarily storing the intake air supplied to the engine E.
In the intake system IN, an air flow sensor 101 for detecting the intake air amount and a temperature sensor 102 for detecting the intake air temperature are provided on the intake passage 1 immediately downstream of the air cleaner 3. A pressure sensor 103 for detecting the pressure of the intake air is provided. A temperature sensor 106 for detecting the intake air temperature is provided on the intake passage 1 immediately downstream of the intercooler 8. A position sensor 105 for detecting the opening degree is provided, and the surge tank 12 is provided with a pressure sensor 108 for detecting the pressure of intake air in the intake manifold. Various sensors 101 to 108 provided in the intake system IN output detection signals S101 to S108 corresponding to the detected parameters to the PCM 60, respectively.

  Next, the engine E includes an intake valve 15 for introducing the intake air supplied from the intake passage 1 (specifically, an intake manifold) into the combustion chamber 17, a fuel injection valve 20 for injecting fuel toward the combustion chamber 17, A glow plug 21 provided with a heat generating portion (hereinafter referred to as “21a”) in the combustion chamber 17, a piston 23 reciprocating by combustion of the air-fuel mixture in the combustion chamber 17, and a piston 23 A crankshaft 25 that is rotated by the reciprocating motion of the exhaust gas, and an exhaust valve 27 that discharges exhaust gas generated by combustion of the air-fuel mixture in the combustion chamber 17 to the exhaust passage 41. Further, the engine E is provided with a crank angle sensor 100 that detects a crank angle as a rotation angle with respect to a top dead center in the crankshaft 25, and the crank angle sensor 100 is provided at the detected crank angle. The corresponding detection signal S100 is output to the PCM 60, and the PCM 60 acquires the engine speed based on the detection signal S100.

  The fuel supply system FS includes a fuel tank 30 that stores fuel, and a fuel supply passage 38 that supplies fuel from the fuel tank 30 to the fuel injection valve 20. In the fuel supply passage 38, a low-pressure fuel pump 31, a high-pressure fuel pump 33, and a common rail 35 are provided in order from the upstream side.

  Next, the exhaust system EX has an exhaust passage 41 through which exhaust gas passes. A turbo that is rotated by the exhaust gas passing through the exhaust passage 41 and drives the compressor as described above by this rotation. A turbine of the supercharger 5 is provided. Further, on the exhaust passage 41 on the downstream side of the turbine, NOx catalyst 45 for purifying NOx in the exhaust gas and particulate matter (PM) in the exhaust gas are collected in order from the upstream side. A diesel particulate filter (DPF) 46, a urea injector 51 for injecting urea into the exhaust passage 41 downstream of the DPF 46, and urea injected from the urea injector 51 are hydrolyzed to generate ammonia. SCR (Selective Catalytic Reduction) catalyst 47 for purifying NOx by reacting (reducing) this NOx with NOx in the exhaust gas, and slip catalyst 48 for oxidizing and purifying unreacted ammonia discharged from SCR catalyst 47 And are provided. The urea injector 51 is controlled to inject urea into the exhaust passage 41 by a control signal S51 supplied from the DCU 70.

  Here, the NOx catalyst 45 will be described more specifically. The NOx catalyst 45 occludes NOx in the exhaust gas in a lean state (λ> 1) in which the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio. This is a NOx storage reduction catalyst (NSC) that reduces in the vicinity (λ≈1) or in a rich state (λ <1) smaller than the stoichiometric air-fuel ratio. The NOx catalyst 45 not only functions as this NSC, but also oxidizes hydrocarbons (HC), carbon monoxide (CO), etc. using oxygen in the exhaust gas to change them into water and carbon dioxide. It is comprised so that it may also have a function as a catalyst (DOC: Diesel Oxidation Catalyst). Specifically, the NOx catalyst 45 is made by coating the surface of a DOC catalyst material layer with an NSC catalyst material.

In the exhaust system EX, a pressure sensor 109 for detecting the pressure of the exhaust gas and a temperature sensor 110 for detecting the temperature of the exhaust gas are provided on the exhaust passage 41 upstream of the turbine of the turbocharger 5. An O ₂ sensor 111 for detecting the oxygen concentration is provided on the exhaust passage 41 immediately downstream of the turbine of the turbocharger 5. Further, the exhaust system EX includes a temperature sensor 112 for detecting the temperature of the exhaust gas immediately upstream of the NOx catalyst 45, a temperature sensor 113 for detecting the temperature of the exhaust gas between the NOx catalyst 45 and the DPF 46, and the DPF 46. Differential pressure sensor 114 for detecting the pressure difference between the exhaust gas immediately upstream and the downstream side, a temperature sensor 115 for detecting the temperature of the exhaust gas immediately downstream of the DPF 46, and the exhaust gas immediately downstream of the DPF 46 NOx sensor 116 for detecting the concentration of NOx in the exhaust gas, temperature sensor 117 for detecting the temperature of the exhaust gas immediately upstream of the SCR catalyst 47, and the concentration of NOx in the exhaust gas immediately downstream of the SCR catalyst 47 And a PM sensor 119 for detecting PM in the exhaust gas immediately upstream of the slip catalyst 48. Various sensor sensors 109 to 119 provided in the exhaust system EX output detection signals S109 to S119 corresponding to the detected parameters to the PCM 60, respectively.

  Further, in the present embodiment, the turbocharger 5 is configured as a two-stage supercharging system that can efficiently obtain high supercharging throughout the entire range from a low rotation range to a high rotation range where the exhaust energy is low. That is, the turbocharger 5 includes a large turbocharger 5a for supercharging a large amount of air in a high rotation range, a small turbocharger 5b capable of efficiently supercharging with low exhaust energy, and a compressor of the small turbocharger 5b. A compressor bypass valve 5c for controlling the flow of intake air to the turbine, a regulator valve 5d for controlling the flow of exhaust gas to the turbine of the small turbocharger 5b, and a waste gate for controlling the flow of exhaust gas to the turbine of the large turbocharger 5a A valve 5e is provided, and the supercharging by the large turbocharger 5a and the small turbocharger 5b is switched by driving each valve according to the operating state (engine speed and load) of the engine E.

  The engine system 200 according to the present embodiment further includes an EGR device 43. The EGR device 43 connects the exhaust passage 41 upstream of the turbine of the turbocharger 5 and the intake passage 1 downstream of the compressor of the turbocharger 5 (specifically, downstream of the intercooler 8). The passage 43a, the EGR cooler 43b that cools the exhaust gas that passes through the EGR passage 43a, the first EGR valve 43c that adjusts the flow rate of the exhaust gas that passes through the EGR passage 43a, and the EGR cooler 43b are bypassed to flow the exhaust gas. The EGR cooler bypass passage 43d and the second EGR valve 43e for adjusting the flow rate of the exhaust gas passing through the EGR cooler bypass passage 43d are provided.

  Next, with reference to FIG. 2, an electrical configuration of an engine exhaust gas purification apparatus according to an embodiment of the present invention will be described. FIG. 2 is a block diagram showing an electrical configuration of an engine exhaust gas purification apparatus according to an embodiment of the present invention.

  In addition to the detection signals S100 to S119 of the various sensors 100 to 119 described above, the PCM 60 according to the embodiment of the present invention detects an accelerator opening sensor 150 that detects an accelerator pedal opening (accelerator opening), and a vehicle speed. Based on the detection signals S150 and S151 output from the vehicle speed sensors 151, the control signal S20 is mainly output to control the fuel injection valve 20, and the control signal S7 is output to control the intake shutter valve 7. Then, a control signal S21 is output to control the glow plug 21, and control signals S431 and S432 are output to control each of the first and second EGR valves 43c and 43e.

  In particular, in the present embodiment, the PCM 60 sets the air-fuel ratio of the exhaust gas from the fuel injection valve 20 so as to set the target air-fuel ratio (specifically, near the stoichiometric air-fuel ratio or a predetermined air-fuel ratio smaller than the stoichiometric air-fuel ratio). Control (NOx reduction control) is performed to reduce the NOx occluded in the NOx catalyst 45 by post injection. That is, the PCM 60 adds to the main injection that injects fuel into the cylinders in order to output the engine torque according to the driver's accelerator operation (basically, the air-fuel ratio of the exhaust gas becomes lean in the main injection). After this main injection, post injection is performed to inject fuel at a timing that does not contribute to engine torque output (specifically, an expansion stroke), and the air-fuel ratio of the exhaust gas is reduced. The NOx occluded in the NOx catalyst 45 is reduced so as to be set to a state close to the theoretical air-fuel ratio (λ≈1) or a rich state smaller than the theoretical air-fuel ratio (λ <1). Hereinafter, such control for reducing the NOx stored in the NOx catalyst 45 is referred to as “DeNOx control”. Note that “De” in the word “DeNOx” is a prefix meaning separation or removal.

  Although details will be described later, the PCM 60 functions as “NOx reduction control means”, “EGR control means”, and the like.

  The PCM 60 stores a CPU, various programs interpreted and executed on the CPU (including a basic control program such as an OS and an application program that is activated on the OS and realizes a specific function), programs, and various data. It is configured by a computer having an internal memory such as a ROM or RAM for storing.

<Fuel injection control>
Next, the fuel injection control according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a flowchart (fuel injection control flow) showing the fuel injection control according to the embodiment of the present invention. This fuel injection control flow is started when the ignition of the vehicle is turned on and the PCM 60 is turned on, and is repeatedly executed at a predetermined cycle.

  First, in step S101, the PCM 60 acquires the driving state of the vehicle. Specifically, the PCM 60 is currently set to at least the accelerator opening detected by the accelerator opening sensor 150, the vehicle speed detected by the vehicle speed sensor 151, the crank angle detected by the crank angle sensor 100, and the transmission of the vehicle. Get the gear position.

  Next, in step S102, the PCM 60 sets a target acceleration based on the driving state of the vehicle including the operation of the accelerator pedal acquired in step S101. Specifically, the PCM 60 determines the acceleration corresponding to the current vehicle speed and gear stage from acceleration characteristic maps (created in advance and stored in a memory or the like) defined for various vehicle speeds and various gear stages. A characteristic map is selected, and a target acceleration corresponding to the current accelerator opening is determined with reference to the selected acceleration characteristic map.

  Next, in step S103, the PCM 60 determines a target torque of the engine E for realizing the target acceleration determined in step S102. In this case, the PCM 60 determines a target torque within the range of torque that can be output by the engine E based on the current vehicle speed, gear stage, road surface gradient, road surface μ, and the like.

  Next, in step S104, the PCM 60 calculates the fuel injection amount to be injected from the fuel injection valve 20 based on the target torque and the engine speed so as to output the target torque determined in step S103 from the engine E. . This fuel injection amount is a fuel injection amount (main injection amount) applied in main injection.

  On the other hand, in parallel with the processing of steps S102 to S104 described above, in step S105, the PCM 60 sets a fuel injection pattern according to the operating state of the engine E. Specifically, when performing the above-described DeNOx control, the PCM 60 sets a fuel injection pattern for performing at least post injection in addition to main injection. In this case, the PCM 60 also determines the fuel injection amount (post injection amount) applied in the post injection and the timing (post injection timing etc.) for performing the post injection. Details of these will be described later.

  After steps S104 and S105, the process proceeds to step S106, where the PCM 60 is based on the main injection amount calculated in step S104 and the fuel injection pattern set in step S105 (when post injection is performed, the post injection amount or post injection). The fuel injection valve 20 is controlled. That is, the PCM 60 controls the fuel injection valve 20 so that a desired amount of fuel is injected in a desired fuel injection pattern.

  Next, a method for calculating the post injection amount (hereinafter referred to as “DeNOx post injection amount”) applied during DeNOx control in the embodiment of the present invention will be described with reference to FIG. 4. FIG. 4 is a flowchart (DeNOx post injection amount calculation flow) showing the DeNOx post injection amount calculation processing according to the embodiment of the present invention. This DeNOx post-injection amount calculation flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG. That is, while the fuel injection control is being performed, the post injection amount for DeNOx is calculated as needed.

First, in step S201, the PCM 60 acquires the operating state of the engine E. Specifically, the PCM 60 determines at least the intake air amount (fresh air amount) detected by the air flow sensor 101, the oxygen concentration of the exhaust gas detected by the O ₂ sensor 111, and the main calculated in step S104 of FIG. Get the injection amount. In addition, the PCM 60 also obtains an exhaust gas amount (EGR gas amount) recirculated to the intake system IN by the EGR device 43, which is obtained by a predetermined model or the like.

  Next, in step S202, the PCM 60 calculates the amount of air (that is, the filling amount) introduced into the engine E based on the fresh air amount and the EGR gas amount acquired in step S201. In step S203, the PCM 60 calculates the oxygen concentration of the air introduced into the engine E from the filling amount calculated in step S202.

Next, in step S204, the PCM 60 performs post-injection in addition to main injection, so that the NOx occluded in the NOx catalyst 45 is reduced, so that the air-fuel ratio of the exhaust gas is near or below the stoichiometric air-fuel ratio. A post injection amount (DeNOx post injection amount) necessary to set the air-fuel ratio is calculated. That is, the PCM 60 determines how much post injection amount should be applied in addition to the main injection amount in order to set the air-fuel ratio of the exhaust gas to the target air-fuel ratio. In this case, the PCM 60 considers the difference between the oxygen concentration acquired in step S201 (the oxygen concentration detected by the O ₂ sensor 111) and the oxygen concentration calculated in step S203, and determines the post-injection amount for DeNOx. calculate. Specifically, the PCM 60 appropriately performs feedback processing according to the difference between the detected oxygen concentration and the calculated oxygen concentration from the air-fuel ratio of the exhaust gas generated when the main injected fuel is burned. Then, the post-injection amount for DeNOx for setting the air-fuel ratio of the exhaust gas to the target air-fuel ratio is calculated. By calculating the post-injection amount for DeNOx in this way, the air-fuel ratio of the exhaust gas is accurately set to the target air-fuel ratio by post-injection in DeNOx control, and NOx occluded in the NOx catalyst 45 is reliably reduced. I am doing so.

<DeNOx control>
Hereinafter, DeNOx control according to the embodiment of the present invention will be specifically described.

(Basic concept)
First, the basic concept of DeNOx control according to an embodiment of the present invention will be described.

  In this embodiment, the PCM 60 reduces the NOx occluded in the NOx catalyst 45 to approximately 0 when the NOx occlusion amount of the NOx catalyst 45 is equal to or greater than a predetermined amount, typically when the NOx occlusion amount is near the limit. DeNOx control in which post-injection is performed from the fuel injection valve 20 so as to continuously set the air-fuel ratio of the exhaust gas to a target air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio or lower than the stoichiometric air-fuel ratio (“second NOx reduction in the present invention”). In the following, it is referred to as “active DeNOx control” as appropriate). By so doing, NOx stored in the NOx catalyst 45 in a large amount is forcibly reduced, and the NOx purification performance of the NOx catalyst 45 is reliably ensured.

  Further, in this embodiment, even if the NOx occlusion amount of the NOx catalyst 45 is less than a predetermined amount, the PCM 60 is occluded in the NOx catalyst 45 when the air-fuel ratio of the exhaust gas changes to the rich side due to vehicle acceleration. In order to reduce the NOx, the DeNOx control (which corresponds to the “first NOx reduction control” in the present invention, which is post-injected from the fuel injection valve 20 so as to temporarily set the air-fuel ratio of the exhaust gas to the target air-fuel ratio, is described below. Appropriately called “passive DeNOx control”). In this passive DeNOx control, the air-fuel ratio is adjusted to a target air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio or below the stoichiometric air-fuel ratio by multiplying the situation where the main injection amount increases during acceleration and the air-fuel ratio of the exhaust gas decreases. Since the post-injection is performed so as to be set, the post-injection amount for setting the air-fuel ratio to the target air-fuel ratio is smaller than in the case where the DeNOx control is performed in a situation where the air-fuel ratio of the exhaust gas does not decrease (that is, during non-acceleration) Become. Further, since the passive DeNOx control is performed by taking advantage of acceleration of the vehicle, it is performed at a relatively high frequency.

  In the present embodiment, by applying such passive DeNOx control, DeNOx is performed at a high frequency while suppressing deterioration in fuel consumption due to DeNOx. Although the passive DeNOx control is performed only for a relatively short period, it is performed at a high frequency, so that the NOx occlusion amount of the NOx catalyst 45 can be efficiently reduced. As a result, the NOx occlusion amount of the NOx catalyst 45 is less likely to exceed a predetermined amount, so that the frequency of execution of active DeNOx control that requires a larger amount of post-injection than passive DeNOx control can be reduced, and fuel consumption deterioration due to DeNOx can be reduced. It becomes possible to improve effectively.

  Further, in the present embodiment, when the above-described active DeNOx control is executed, the post-injected fuel is burned in the cylinder of the engine E, so that the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio. In this case, the PCM 60 performs the post-injection at the timing when the post-injected fuel is combusted in the cylinder. Specifically, the PCM 60 sets a predetermined timing in the first half of the expansion stroke of the engine E as a post injection timing in the active DeNOx control. By applying such post injection timing in the active DeNOx control, the post-injected fuel is discharged as it is as unburned fuel (that is, HC) and the oil dilution by the post-injected fuel is suppressed. ing.

  On the other hand, in the present embodiment, when the above-described passive DeNOx control is performed, the PCM 60 causes the post-injected fuel to be discharged into the exhaust passage 41 as unburned fuel without burning in the cylinder of the engine E. Thus, the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio. In this case, the PCM 60 performs post-injection at a timing at which at least a part of the post-injected fuel is not burned in the cylinder and is discharged to the exhaust passage 41 as unburned fuel. Specifically, the PCM 60 sets a predetermined timing in the latter half of the expansion stroke of the engine E as a post injection timing in the passive DeNOx control. In principle, the post-injection timing in the passive DeNOx control is set to be retarded from the post-injection timing in the active DeNOx control. By applying such post-injection timing in passive DeNOx control, it is possible to prevent the post-injected fuel from burning in the cylinder and generating smoke.

  Here, with reference to FIG. 5, the operation area | region of the engine E which performs each of passive DeNOx control and active DeNOx control in embodiment of this invention is demonstrated. FIG. 5 shows the engine speed on the horizontal axis and the engine load on the vertical axis. In FIG. 5, a curve L1 indicates the maximum torque line of the engine E.

  As shown in FIG. 5, in the present embodiment, the PCM 60 is in an intermediate load range where the engine load is equal to or higher than the first predetermined load Lo1 and lower than the second predetermined load Lo2 (> first predetermined load Lo1), and When the engine speed is in the middle engine speed range that is greater than or equal to the first predetermined engine speed N1 and less than the second predetermined engine speed N2 (> the first predetermined engine speed N1), that is, the engine load and the engine engine speed are indicated by reference numeral R12 When included in the region (hereinafter referred to as “active DeNOx execution region R12”), the active DeNOx control is executed. The reason for adopting such an active DeNOx execution region R12 is as follows.

  As described above, when executing the active DeNOx control, the post-injected fuel is reduced from the viewpoint of suppressing the generation of HC due to the post-injected fuel being discharged as it is or the oil dilution by the post-injected fuel. Post injection is performed at the timing of combustion in the cylinder. In this case, in this embodiment, when the post-injected fuel is burned, the generation of smoke is suppressed and the generation of HC (that is, the discharge of unburned fuel due to incomplete combustion) is suppressed. Specifically, the generation of smoke and HC is suppressed by maximizing the time until the post-injected fuel burns as much as possible, that is, ignition occurs in a state where air and fuel are properly mixed. Yes. For this reason, the ignition of post-injected fuel is effectively delayed by introducing an appropriate amount of EGR gas during active DeNOx control.

The reason for suppressing the generation of HC during the active DeNOx control is that when EGR gas is introduced as described above, HC is also recirculated to the intake system IN as EGR gas, and this HC becomes a binder and is combined with soot. This is to prevent the gas passage from being blocked. In addition, when active DeNOx control is performed in an area where the temperature of the NOx catalyst 45 is low and HC purification performance (HC purification performance by DOC in the NOx catalyst 45) is not ensured, HC is not purified. This is to prevent discharge. Incidentally, the active DeNOx execution region R12 includes a region where the temperature of the NOx catalyst 45 where the HC purification performance is not ensured is relatively low.
The reason for suppressing the generation of smoke during active DeNOx control is that PM corresponding to the smoke is collected by the DPF 46, but DPF regeneration for burning and removing the PM collected by the DPF 46 (similar to DeNOx control). This is to prevent the fuel efficiency and the like from being deteriorated by frequently performing post-injection control).

By the way, when the engine load increases, the air introduced into the engine E in order to achieve the target air-fuel ratio is reduced, so that there is not enough oxygen necessary to properly burn the post-injected fuel, so that smoke and HC Tend to occur. In particular, when the engine load increases, the in-cylinder temperature rises and the time until the post-injected fuel is ignited cannot be properly secured, and ignition occurs midway, that is, the air and fuel are mixed properly. Combustion occurs in a state where it is not performed, and smoke and HC are generated. On the other hand, in a region where the engine load is considerably low, the temperature of the NOx catalyst 45 is low, and the NOx reduction function of the NOx catalyst 45 is not sufficiently exhibited. In addition, in this region, the post-injected fuel does not burn properly, that is, misfire occurs.
In addition, although the phenomenon regarding an engine load was described above, the same phenomenon arises also about an engine speed.

  From the above, in this embodiment, the operation region of the engine E corresponding to the medium load region and the medium rotation region is employed as the active DeNOx execution region R12 for executing the active DeNOx control. In other words, in this embodiment, the active DeNOx control is executed only in the active DeNOx execution region R12, and the execution of the active DeNOx control is prohibited in the operation region other than the active DeNOx execution region R12. Thus, in the operation region of the engine E for which execution of the active DeNOx control is prohibited, particularly in the region on the higher load side or the higher rotation side than the active DeNOx execution region R12 (region denoted by reference numeral R13), the SCR Since the NOx purification performance of the catalyst 47 is sufficiently secured, the SCR catalyst 47 purifies NOx, and NOx emission from the vehicle can be prevented without executing DeNOx control.

Further, in this embodiment, in the region on the higher load side than the region R13 in which the SCR catalyst 47 purifies NOx (the region denoted by reference numeral R11, hereinafter referred to as “passive DeNOx execution region R11”). Since the amount of exhaust gas increases and the SCR catalyst 47 cannot completely purify NOx, passive DeNOx control is executed. In this passive DeNOx control, as described above, post-injection is performed at a timing at which the post-injected fuel is discharged into the exhaust passage 41 as unburned fuel without being combusted in the cylinder. In the passive DeNOx execution region R11, the temperature of the NOx catalyst 45 is sufficiently high, and the HC purification performance (HC purification performance by DOC in the NOx catalyst 45) is ensured, so the unburned fuel discharged in this way Can be appropriately purified by the NOx catalyst 45.
In passive DeNOx control, smoke is generated when post-injected fuel is combusted in the cylinder as in active DeNOx control. As described above, the reason is the same as the reason why the execution of the active DeNOx control is prohibited when the engine load increases. Therefore, in passive DeNOx control, the post-injected fuel is discharged into the exhaust passage 41 as unburned fuel without burning in the cylinder.

  Here, a specific example of active DeNOx control when the operating state of the engine E changes as indicated by an arrow A11 in FIG. 5 will be described. First, when the operating state of the engine E enters the active DeNOx execution region R12 (see A12), the PCM 60 executes active DeNOx control. When the operating state of the engine E deviates from the active DeNOx execution region R12 (see symbol A13), the PCM 60 temporarily stops the active DeNOx control. At this time, the SCR catalyst 47 purifies NOx. When the operating state of the engine E enters the active DeNOx execution region R12 again (see reference A14), the PCM 60 resumes active DeNOx control. By doing so, the active DeNOx control is not terminated until the NOx occluded in the NOx catalyst 45 drops to almost zero.

Hereinafter, the active DeNOx control and the passive DeNOx control according to the embodiment of the present invention will be specifically described.
First, with reference to FIG. 6, the setting process of the active DeNOx control execution flag used for determining whether or not to execute the active DeNOx control according to the embodiment of the present invention will be described. FIG. 6 is a flowchart showing an active DeNOx control execution flag setting process (active DeNOx control execution flag setting flow). This active DeNOx control execution flag setting flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG.

  First, in step S301, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 acquires at least the NOx catalyst temperature, the SCR temperature, and the NOx occlusion amount of the NOx catalyst 45. In this case, the NOx catalyst temperature is estimated based on, for example, the temperature detected by the temperature sensor 112 provided immediately upstream of the NOx catalyst 45 (a temperature sensor provided between the NOx catalyst 45 and the DPF 46). The temperature detected by 113 may also be used). The SCR temperature is estimated based on the temperature detected by the temperature sensor 117 provided immediately upstream of the SCR catalyst 47, for example. Further, the NOx occlusion amount is obtained by, for example, estimating the NOx amount in the exhaust gas based on the operating state of the engine E, the flow rate of the exhaust gas, the temperature of the exhaust gas, and the like, and integrating this NOx amount. It is done.

  Next, in step S302, the PCM 60 determines whether or not the SCR temperature acquired in step S301 is less than the SCR determination temperature. As a result of this determination, when the SCR temperature is lower than the SCR determination temperature (step S302: Yes), the process proceeds to step S303. On the other hand, when the SCR temperature is equal to or higher than the SCR determination temperature (step S302: No), the process proceeds to step S309. In this case, since NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47, the PCM 60 sets the active DeNOx control execution flag to “0” in order to prohibit the execution of the active DeNOx control ( Step S309). Then, the process ends.

  Next, in step S303, the PCM 60 determines whether or not the NOx catalyst temperature acquired in step S301 is equal to or higher than a predetermined temperature. When the NOx catalyst temperature is low, the NOx catalyst 45 hardly reduces the stored NOx even if the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio. Therefore, in step S303, it is determined whether or not the NOx stored in the NOx catalyst 45 can be reduced. Therefore, the predetermined temperature used in the determination in step S303 is set based on the NOx catalyst temperature that can reduce the NOx stored in the NOx catalyst 45. As a result of the determination in step S303, when the NOx catalyst temperature is equal to or higher than the predetermined temperature (step S303: Yes), the process proceeds to step S304. On the other hand, when the NOx catalyst temperature is lower than the predetermined temperature (step S303: No), the process proceeds to step S309. In this case, the PCM 60 sets an active DeNOx control execution flag to “0” in order to prohibit execution of active DeNOx control (step S309).

  Next, in step S304, the PCM 60 determines whether or not active DeNOx control has never been executed after engine startup. In the determination in step S304, if the active DeNOx control has never been executed after the engine has been started, the execution conditions for the active DeNOx control are relaxed compared to the case where the active DeNOx control has been executed after the engine has been started. The purpose is to preferentially execute the active DeNOx control. Specifically, when the active DeNOx control has been executed after the engine is started, the execution conditions of step S307 and the execution condition of step S308, which are relatively severe, are used, whereas the active DeNOx control is executed after the engine is started. Is never executed, only the execution condition of step S305, which is relatively mild, is used (details thereof will be described later). As a result of the determination in step S304, when the active DeNOx control is not executed after the engine is started (step S304: Yes), the process proceeds to step S305.

  Next, in step S305, the PCM 60 determines whether or not the NOx storage amount acquired in step S301 is greater than or equal to the first storage amount determination value. For example, the first storage amount determination value is set to a value that is somewhat lower than the limit value of the NOx storage amount. As a result of this determination, when the NOx storage amount is equal to or greater than the first storage amount determination value (step S305: Yes), the process proceeds to step S306. In this case, the PCM 60 sets the active DeNOx control execution flag to “1” in order to allow execution of the active DeNOx control (step S306). In this way, the active DeNOx control is executed after the engine is started to forcibly reduce NOx occluded in the NOx catalyst 45 to some extent, thereby ensuring the NOx purification performance of the NOx catalyst 45 reliably. On the other hand, when the NOx storage amount is less than the first storage amount determination value (step S305: No), the process proceeds to step S309. In this case, the PCM 60 sets the active DeNOx control execution flag to “0” in order to prohibit execution of useless active DeNOx control (step S309). Then, the process ends.

  On the other hand, if the result of determination in step S304 is that active DeNOx control has been executed after engine startup (step S304: No), the process proceeds to step S307. In step S307, the PCM 60 determines whether or not the NOx storage amount acquired in step S301 is greater than or equal to the second storage amount determination value. The second storage amount determination value is at least a value larger than the first storage amount determination value described above. For example, a value near the limit value of the NOx storage amount (in one example, a value about 2/3 of the limit value). ). As a result of this determination, when the NOx storage amount is equal to or greater than the second storage amount determination value (step S307: Yes), the process proceeds to step S308. On the other hand, when the NOx storage amount is less than the second storage amount determination value (step S307: No), the process proceeds to step S309. In this case, the PCM 60 sets the active DeNOx control execution flag to “0” in order to prohibit execution of useless active DeNOx control (step S309). Then, the process ends.

  Next, in step S308, the PCM 60 determines whether or not the travel distance from the previous execution time of the active DeNOx control is greater than or equal to a predetermined determination distance. As a result of the determination in step S308, when the travel distance from the previous execution time of the active DeNOx control is equal to or greater than the determination distance (step S308: Yes), the process proceeds to step S306. In this case, the PCM 60 sets the active DeNOx control execution flag to “1” in order to allow execution of the active DeNOx control (step S306). In this way, the active DeNOx control is executed to forcibly reduce the NOx occluded in a large amount in the NOx catalyst 45, thereby ensuring the NOx purification performance of the NOx catalyst 45 reliably. On the other hand, when the travel distance from the previous execution time of the active DeNOx control is less than the determination distance (step S308: No), the process proceeds to step S309. In this case, the PCM 60 sets an active DeNOx control execution flag to “0” in order to prohibit execution of active DeNOx control (step S309). Then, the process ends.

When the active DeNOx control is executed in a situation where the travel distance from the previous execution time of the active DeNOx control is short (that is, when the execution interval of the active DeNOx control is short), there is a high possibility that oil dilution due to post injection occurs. Therefore, in the present embodiment, when the travel distance from the previous execution time of the active DeNOx control is less than the determination distance (step S308: No), the execution of the active DeNOx control is prohibited and the post injection in the active DeNOx control. The oil dilution caused by this is suppressed. On the other hand, when the travel distance from the previous execution time of the active DeNOx control is long (that is, when the execution interval of the active DeNOx control is long), even if the active DeNOx control is executed from now on, the oil dilution caused by the post injection is not performed. It is unlikely to occur. Therefore, in this embodiment, when the travel distance from the previous execution time of the active DeNOx control is equal to or greater than the determination distance (step S308: Yes), the execution of the active DeNOx control is not prohibited.
Further, in the present embodiment, considering that the post-injected fuel is more vaporized and the oil dilution is less likely to occur when the in-cylinder temperature becomes higher, the determination distance used in step S308 becomes higher as the in-cylinder temperature becomes higher. The value is set to a small value, and the restriction on the control according to the travel distance from the previous execution time of the active DeNOx control is relaxed.

  Next, a passive DeNOx control execution flag setting process used to determine whether or not to execute passive DeNOx control according to the embodiment of the present invention will be described with reference to FIG. FIG. 7 is a flowchart (passive DeNOx control execution flag setting flow) showing the setting process of the passive DeNOx control execution flag according to the embodiment of the present invention. This passive DeNOx control execution flag setting flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG. 3, the active DeNOx control execution flag setting flow shown in FIG. Is done.

First, in step S401, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 calculates at least the NOx catalyst temperature, the SCR temperature, the target torque determined by the fuel injection control flow shown in FIG. 3, and the DeNOx post injection amount calculation flow shown in FIG. DeNOx post-injection amount (specifically, the DeNOx post-injection amount calculated as applied during passive DeNOx control), the NOx occlusion amount of the NOx catalyst 45, and the active DeNOx control execution flag shown in FIG. And the value of the active DeNOx control execution flag set in the setting flow. The method for obtaining the NOx catalyst temperature, the SCR temperature, and the NOx occlusion amount is as described above.
In addition, in step S401, the PCM 60 also acquires the execution frequency of passive DeNOx control within a predetermined period. Specifically, the PCM 60 acquires, as the execution frequency of the passive DeNOx control, the number of times that the passive DeNOx control has been executed during a predetermined period (for example, several seconds or several minutes).

  Next, in step S402, the PCM 60 determines whether or not the SCR temperature acquired in step S401 is lower than the SCR determination temperature. As a result of this determination, when the SCR temperature is lower than the SCR determination temperature (step S402: Yes), the process proceeds to step S403. On the other hand, when the SCR temperature is equal to or higher than the SCR determination temperature (step S402: No), the process proceeds to step S408. In this case, since NOx in the exhaust gas can be appropriately purified by the SCR catalyst 47, the PCM 60 sets the passive DeNOx control execution flag to “0” in order to prohibit the execution of the passive DeNOx control ( Step S408). Then, the process ends.

  Next, in step S403, the PCM 60 determines whether or not the execution frequency of the passive DeNOx control acquired in step S401 is less than a predetermined frequency determination value. As a result of the determination in step S403, when the execution frequency of the passive DeNOx control is less than the frequency determination value (step S403: Yes), the process proceeds to step S404. On the other hand, when the execution frequency of the passive DeNOx control is equal to or higher than the frequency determination value (step S403: No), the process proceeds to step S408. In this case, the PCM 60 sets the passive DeNOx control execution flag to “0” to prohibit the execution of the passive DeNOx control (step S408).

When the passive DeNOx control has been performed relatively frequently so far, when the passive DeNOx control is executed from now on, there is a high possibility that oil dilution due to post injection occurs. Therefore, in this embodiment, when the execution frequency of the passive DeNOx control is equal to or higher than the frequency determination value (step S403: No), the execution of the passive DeNOx control is prohibited and the oil resulting from the post injection in the passive DeNOx control. Dilution is controlled. On the other hand, when passive DeNOx control has hardly been performed so far (that is, when the frequency of passive DeNOx control is relatively low), even if passive DeNOx control is executed from now on, oil dilution caused by post-injection will occur. Is unlikely to occur. Therefore, in this embodiment, when the execution frequency of passive DeNOx control is less than the frequency determination value (step S403: Yes), execution of passive DeNOx control is not prohibited.
In the present embodiment, the frequency determination value used in step S403 is set to a larger value as the in-cylinder temperature becomes higher. When the frequency determination value is a large value, the possibility that the execution frequency of the passive DeNOx control is less than the frequency determination value (step S403: Yes) is higher than when the frequency determination value is a small value. Therefore, in this embodiment, as the in-cylinder temperature becomes higher, the restriction on the control according to the execution frequency of the passive DeNOx control is relaxed. This is because as the in-cylinder temperature increases, the post-injected fuel is more vaporized and oil dilution is less likely to occur.

  Next, in step S404, it is determined whether or not the NOx occlusion amount acquired in step S401 is greater than or equal to the third occlusion amount determination value. For example, the third storage amount determination value is set to a value that is about 1/3 of the limit value of the NOx storage amount. If the result of this determination is that the NOx storage amount is greater than or equal to the third storage amount determination value (step S404: Yes), the process proceeds to step S405. On the other hand, when the NOx storage amount is less than the third storage amount determination value (step S404: No), the process proceeds to step S408. In this case, the PCM 60 prohibits the execution of useless passive DeNOx control and sets the passive DeNOx control execution flag to “0” in order to suppress deterioration in fuel consumption caused by the execution of passive DeNOx control (step S408). ). Then, the process ends.

  Next, in step S405, the PCM 60 determines whether or not the active DeNOx control execution flag acquired in step S401 is “0”. That is, the PCM 60 determines whether or not the situation is that the active DeNOx control should be executed. As a result of this determination, when the active DeNOx control execution flag is “0” (step S405: Yes), the process proceeds to step S406. On the other hand, when the active DeNOx control execution flag is not “0”, that is, when it is “1” (step S405: No), the process proceeds to step S408. In this case, the PCM 60 prohibits the execution of the passive DeNOx control and sets the passive DeNOx control execution flag to “0” in order to preferentially execute the active DeNOx control (step S408). That is, even if the execution condition of the passive DeNOx control is satisfied, the active DeNOx control is preferentially executed when the execution condition of the active DeNOx control is satisfied. Then, the process ends.

  Next, in step S406, the PCM 60 determines whether or not the DeNOx post injection amount acquired in step S401 is less than the first post injection amount determination value. In this step S406, based on the post injection amount for DeNOx calculated as the fuel amount necessary for realizing the target air fuel ratio by post injection as described above, the air fuel ratio of the exhaust gas is reduced to a predetermined value or less on the rich side. It is determined whether or not the situation decreases, that is, whether the vehicle is in a predetermined acceleration state. By doing so, it is determined whether or not DeNOx control can be executed while suppressing deterioration in fuel consumption as much as possible, and whether or not there is a possibility of oil dilution by post injection is determined. Based on such a viewpoint, a first post injection amount determination value applied to the determination in step S406 is set.

  As a result of the determination in step S406, if the DeNOx post injection amount is less than the first post injection amount determination value (step S406: Yes), the process proceeds to step S407. In this case, since all the conditions of the above-described steps S402 to S406 are satisfied, the PCM 60 sets the passive DeNOx control execution flag to “1” in order to permit the execution of the passive DeNOx control (step S407). Then, the process ends. On the other hand, when the DeNOx post injection amount is equal to or greater than the first post injection amount determination value (step S406: No), the process proceeds to step S408. In this case, the PCM 60 prohibits the execution of the passive DeNOx control, and sets the passive DeNOx control execution flag to “0” in order to suppress the deterioration of fuel consumption and oil dilution due to the execution of the passive DeNOx control (step). S408). Then, the process ends.

  Next, with reference to FIG. 8, the active DeNOx control according to the embodiment of the present invention executed based on the active DeNOx control execution flag set as described above will be described. FIG. 8 is a flowchart (active DeNOx control flow) showing active DeNOx control according to the embodiment of the present invention. This active DeNOx control flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG. 3, the active DeNOx control execution flag setting flow shown in FIG.

  First, in step S501, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 determines at least the engine load, the engine speed, the NOx catalyst temperature, and the DeNOx post injection amount calculated by the DeNOx post injection amount calculation flow shown in FIG. And the value of the active DeNOx control execution flag set in the active DeNOx control execution flag setting flow shown in FIG. 6.

  Next, in step S502, the PCM 60 determines whether or not the active DeNOx control execution flag acquired in step S501 is “1”. That is, the PCM 60 determines whether or not it is a situation in which active DeNOx control should be executed. As a result of this determination, when the active DeNOx control execution flag is “1” (step S502: Yes), the process proceeds to step S503. On the other hand, when the active DeNOx control execution flag is “0” (step S502: No), the process ends without executing the active DeNOx control.

  Next, in step S503, the PCM 60 determines whether or not the operating state (engine load and engine speed) of the engine E is included in the active DeNOx execution region R12 (see FIG. 5). As a result of the determination in step S503, when the operation state of the engine E is included in the active DeNOx execution region R12 (step S503: Yes), the process proceeds to step S505. On the other hand, when the operating state of the engine is not included in the active DeNOx execution region R12 (step S503: No), the process proceeds to step S504.

  Next, in step S505, the PCM 60 sets a post injection timing (post injection timing) to be applied in the active DeNOx control. FIG. 10 is an explanatory diagram illustrating a method for setting the post injection timing of the active DeNOx control according to the embodiment of the present invention. FIG. 10 shows the engine load on the horizontal axis and the post injection timing on the vertical axis. Graphs G21, G22, and G23 indicate post injection timings that should be set according to the engine load for different engine speeds. Specifically, it is assumed that the engine speed increases in the order of graphs G21, G22, and G23.

  As described above, in the present embodiment, when executing the active DeNOx control, the air-fuel ratio of the exhaust gas is set to the target air-fuel ratio by burning the post-injected fuel in the cylinder. In order to burn the post-injected fuel in the cylinder, the post-injection may be performed at a relatively advanced timing in the expansion stroke. However, if the post injection timing is advanced too much, ignition occurs in a state where air and fuel are not properly mixed, and smoke is generated. Therefore, in the present embodiment, the post injection timing is appropriately set to the advance side, specifically, an appropriate timing in the first half of the expansion stroke is adopted as the post injection timing in the active DeNOx control, and an appropriate amount is set during the active DeNOx control. By introducing the EGR gas, the ignition of the post-injected fuel is delayed to suppress the occurrence of smoke and the like. In this embodiment, the post-injection timing at least in the first half of the expansion stroke is set to be more retarded as the engine load increases, as shown in FIG. This is because the amount of fuel injection increases as the engine load increases and smoke is likely to be generated, so that the post injection timing is retarded as much as possible. In this case, if the post injection timing is retarded too much, the post-injected fuel will not burn (misfire) and HC will be generated. Therefore, in this embodiment, the post injection timing is retarded appropriately. ing.

  Further, in this embodiment, as shown in graphs G21, G22, and G23 in FIG. 10, the post injection timing is set to the advance side as the engine speed increases, that is, the delay angle of the post injection timing is reduced. . If fuel is injected at the same crank angle as when the engine speed is low when the engine speed is high, misfire may occur due to a short time until the fuel ignites. In order to ensure combustion stability, the post injection timing is set to the advance side as the engine speed increases.

  Again, referring back to FIG. In step S504, the PCM 60 does not include the post injection without performing the active DeNOx control, that is, without performing the fuel injection control including the post injection for setting the air-fuel ratio of the exhaust gas to the target air-fuel ratio. The fuel injection control is performed (step S504). Basically, the PCM 60 performs only control for main injection of the fuel injection amount corresponding to the target torque. Actually, the PCM 60 executes the process of step S504 in step S106 of the fuel injection control flow shown in FIG. And a process returns to step S503 and performs determination of above-described step S503 again. That is, when the active DeNOx control execution flag is “1”, the PCM 60 performs normal fuel injection control while the operating state of the engine E is not included in the active DeNOx execution region R12. When the operation state E is included in the active DeNOx execution region R12, the normal fuel injection control is switched to the fuel injection control in the active DeNOx control. For example, when the operating state of the engine E is out of the active DeNOx execution region R12 during the fuel injection control in the active DeNOx control, the PCM 60 interrupts the fuel injection control and performs normal fuel injection control, and thereafter the engine E When the operating state enters the active DeNOx execution region R12, the fuel injection control in the active DeNOx control is resumed.

  Next, in step S506, the PCM 60 determines whether or not the DeNOx post injection amount acquired in step S501 is less than the second post injection amount determination value. The second post injection amount determination value is set to a value larger than the first post injection amount determination value (see step S406 in FIG. 7). In this way, it is possible to inject a larger amount of post-injection in the active DeNOx control than in the passive DeNOx control, regardless of the operating state of the engine E (for example, in a situation where the air-fuel ratio decreases during acceleration). If not), the air-fuel ratio of the exhaust gas can be reliably set to the target air-fuel ratio.

  As a result of the determination in step S506, when the DeNOx post injection amount is less than the second post injection amount determination value (step S506: Yes), the process proceeds to step S507. In step S507, the PCM 60 controls the fuel injection valve 20 so as to post-inject the post injection amount for DeNOx acquired in step S501. Actually, the PCM 60 executes the process of step S507 in step S106 of the fuel injection control flow shown in FIG. Then, the process proceeds to step S510.

On the other hand, when the DeNOx post injection amount is equal to or greater than the second post injection amount determination value (step S506: No), the process proceeds to step S508. In step S508, the PCM 60 sets the air-fuel ratio of the exhaust gas by the post injection amount that does not exceed the second post injection amount determination value (specifically, the second post injection amount determination value itself is applied as the DeNOx post injection amount). In order to set the target air-fuel ratio, control is performed to reduce the oxygen concentration of the air introduced into the engine E. In this case, the PCM 60 executes at least one of the control for driving the intake shutter valve 7 in the valve closing direction, the control for increasing the EGR gas amount, and the control for decreasing the supercharging pressure by the turbocharger 5. Thus, the oxygen concentration of the air introduced into the engine E is reduced, that is, the filling amount is reduced. For example, the PCM 60 obtains the supercharging pressure required to bring the air-fuel ratio of the exhaust gas to the target air-fuel ratio by the DeNOx post-injection amount to which the second post-injection amount determination value is applied, and realizes this supercharging pressure. In addition, the intake shutter valve 7 is controlled to a desired opening on the closing side based on the actual supercharging pressure (pressure detected by the pressure sensor 108) and the EGR gas amount. Then, the process proceeds to step S509.
Note that the intake shutter valve 7 is set to be fully open in the normal operation state of the engine E. On the other hand, at the time of DeNOx, DPF regeneration, idle operation, etc., the intake shutter valve 7 is basically set to a predetermined base opening. In the operation state where EGR gas is not introduced, the intake shutter valve 7 is feedback-controlled based on the supercharging pressure.

  In step S509, the PCM 60 applies the second post injection amount determination value to the DeNOx post injection amount, that is, sets the DeNOx post injection amount to the second post injection amount determination value, and this DeNOx post injection amount. The fuel injection valve 20 is controlled to post-inject fuel. Actually, the PCM 60 executes the process of step S509 in step S106 of the fuel injection control flow shown in FIG. Then, the process proceeds to step S510.

  In step S510, the PCM 60 determines whether or not the NOx occlusion amount of the NOx catalyst 45 has become substantially zero. Specifically, in the PCM 60, the NOx occlusion amount estimated based on the operating state of the engine E, the flow rate of exhaust gas, the temperature of exhaust gas, and the like is almost zero, and the NOx provided immediately downstream of the DPF 46 When the detection value of the sensor 116 changes, it is determined that the NOx occlusion amount of the NOx catalyst 45 has become almost zero. When the NOx occlusion amount of the NOx catalyst 45 becomes almost zero (step S510: Yes), the process ends. In this case, the PCM 60 ends the active DeNOx control. Further, the PCM 60 resets the NOx occlusion amount used in the active DeNOx control flow and the active DeNOx control execution flag setting flow of FIG.

  On the other hand, when the NOx occlusion amount of the NOx catalyst 45 is not substantially 0 (step S510: No), the process returns to step S503. In this case, the PCM 60 continues the active DeNOx control. That is, the PCM 60 continues the active DeNOx control until the NOx occlusion amount of the NOx catalyst 45 becomes substantially zero. In particular, the PCM 60 does not satisfy the execution condition of the active DeNOx control (specifically, the condition in step S503) during the active DeNOx control, and even if the active DeNOx control is stopped, the execution condition of the active DeNOx control is satisfied thereafter In this case, the active DeNOx control is promptly restarted so that the NOx occlusion amount of the NOx catalyst 45 becomes substantially zero.

  Here, the reason why it is possible to determine that the NOx occlusion amount of the NOx catalyst 45 has become substantially zero based on the detection value of the NOx sensor 116 is as follows. Since the NOx sensor 116 also has a function as an oxygen concentration sensor, the detected value of the NOx sensor 116 corresponds to the air-fuel ratio of the exhaust gas supplied to the NOx sensor 116. While the NOx catalyst 45 is being reduced, that is, when the NOx occlusion amount of the NOx catalyst 45 is not substantially zero, oxygen produced by the reduction of NOx is supplied to the NOx sensor 116. On the other hand, when the NOx occlusion amount of the NOx catalyst 45 becomes substantially zero, oxygen generated by such reduction is not supplied to the NOx sensor 116. Therefore, at the timing when the NOx occlusion amount of the NOx catalyst 45 becomes substantially zero, the detected value of the NOx sensor 116 changes as the air-fuel ratio of the exhaust gas supplied to the NOx sensor 116 decreases.

  Next, the passive DeNOx control according to the embodiment of the present invention executed based on the passive DeNOx control execution flag set as described above will be described with reference to FIG. FIG. 9 is a flowchart (passive DeNOx control flow) showing the passive DeNOx control according to the embodiment of the present invention. This passive DeNOx control flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the fuel injection control flow shown in FIG. 3 and the passive DeNOx control execution flag setting flow shown in FIG.

  First, in step S601, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 at least has a DeNOx post injection amount calculated in the DeNOx post injection amount calculation flow shown in FIG. 4 (specifically, a DeNOx post calculated as applied during passive DeNOx control). Injection amount) and the value of the passive DeNOx control execution flag set in the passive DeNOx control execution flag setting flow shown in FIG.

  Next, in step S602, the PCM 60 determines whether or not the passive DeNOx control execution flag acquired in step S601 is “1”. That is, the PCM 60 determines whether or not it is a situation where passive DeNOx control should be executed. As a result of this determination, when the passive DeNOx control execution flag is “1” (step S602: Yes), the process proceeds to step S603. On the other hand, when the passive DeNOx control execution flag is “0” (step S602: No), the process ends without executing the passive DeNOx control.

  Next, in step S603, the PCM 60 controls the fuel injection valve 20 to post-inject the DeNOx post injection amount acquired in step S601. That is, passive DeNOx control is executed. Actually, the PCM 60 executes the process of step S603 in step S106 of the fuel injection control flow shown in FIG. Then, the process proceeds to step S604.

  In step S604, the PCM 60 determines whether or not the passive DeNOx control execution flag has become “0”. As a result, when the passive DeNOx control execution flag becomes “0” (step S604: Yes), the process ends. In this case, the PCM 60 ends the passive DeNOx control. On the other hand, when the passive DeNOx control execution flag is not “0” (step S604: No), that is, when the passive DeNOx control execution flag is maintained at “1”, the process returns to step S603. In this case, the PCM 60 continues the passive DeNOx control. That is, the PCM 60 continues the passive DeNOx control until the passive DeNOx control execution flag is switched from “1” to “0”.

Returning to FIG. 8, the processing after step S504 will be described. In step S504, the PCM 60 controls the fuel injection valve 20 to inject the DeNOx post-injection amount acquired in step S501 at the post-injection timing set in step S503, and targets the air-fuel ratio of the exhaust gas. The air-fuel ratio is set so that the NOx stored in the NOx catalyst 45 is reduced. Specifically, the PCM 60 corresponds to the detection value of the O ₂ sensor 111 provided on the exhaust passage 41 in order to cope with detection variations of various sensors and variations in the fuel injection amount of the fuel injection valve 20. Based on the air-fuel ratio (actual air-fuel ratio) and the target air-fuel ratio, the post-injection amount injected from the fuel injection valve 20 is F / B controlled so that the actual air-fuel ratio matches the target air-fuel ratio. Hereinafter, the F / B control of the post injection amount performed during the passive DeNOx control is appropriately referred to as “first post injection F / B control”. In this first post-injection F / B control, not only F / B control but also F / F control is performed. However, because F / B control is mainly performed, the term “F / B control” is used for convenience of explanation. Is used.
Specifically, the PCM 60 first sets a relatively small air-fuel ratio (an air-fuel ratio with a relatively large rich degree) as a target value, and performs F / F control on the post-injection amount to be injected from the fuel injection valve 20, and thereafter Based on the actual air-fuel ratio and the target air-fuel ratio, the post-injection amount injected from the fuel injection valve 20 is F / B controlled using a relatively large F / B gain. In this way, the actual air-fuel ratio is made to quickly coincide with the target air-fuel ratio during passive DeNOx control that is performed for a relatively short time.
Actually, the PCM 60 executes the process of step S504 in step S106 of the fuel injection control flow shown in FIG.

  Next, in step S505, the PCM 60 determines whether or not the passive DeNOx control execution flag has become “0”. That is, the PCM 60 determines whether or not to end the passive DeNOx control. As a result of this determination, when the passive DeNOx control execution flag becomes “0” (step S505: Yes), the process ends. In this case, the PCM 60 ends the passive DeNOx control. On the other hand, when the passive DeNOx control execution flag is not “0” (step S505: No), that is, when the passive DeNOx control execution flag is maintained at “1”, the process returns to step S503. The processing after step S503 is performed again. In this case, the PCM 60 continues the passive DeNOx control. That is, the PCM 60 continues the passive DeNOx control until the passive DeNOx control execution flag is switched from “1” to “0”.

<EGR control>
Next, EGR control according to the embodiment of the present invention will be described with reference to FIG. FIG. 11 is a flowchart (EGR control flow) showing the EGR control according to the embodiment of the present invention. This EGR control flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the various control flows described above (particularly, the active DeNOx control flow and the glow control flow).

  First, in step S701, the PCM 60 acquires various information on the vehicle. Specifically, the PCM 60 at least sets the target torque determined in the fuel injection control flow shown in FIG. 3 and the value of the passive DeNOx control execution flag set in the passive DeNOx control execution flag setting flow shown in FIG. And the value of the active DeNOx control execution flag set in the active DeNOx control execution flag setting flow shown in FIG. Further, the PCM 60 acquires the in-cylinder oxygen concentration obtained by the estimation (details of the in-cylinder oxygen concentration estimation method will be described later).

  Next, in step S702, the PCM 60 determines whether or not the passive DeNOx control execution flag acquired in step S701 is “1”. As a result, when the passive DeNOx control execution flag is “1” (step S702: Yes), that is, when it is a situation where the passive DeNOx control should be executed, the process proceeds to step S703. In this case, the PCM 60 fully closes both the first EGR valve 43c provided on the EGR passage 43a and the second EGR valve 43e provided on the EGR cooler bypass passage 43d that bypasses the EGR cooler 43b. (Step S703). That is, the PCM 60 prohibits the recirculation of the EGR gas to the intake system IN when executing the passive DeNOx control. This is because, in passive DeNOx control, the post-injected fuel is discharged as unburned fuel without being burned. Therefore, when EGR gas is recirculated, unburned fuel (HC) is also recirculated. This is because it is possible to prevent the occurrence of a failure in which the gas passage (such as the EGR passages 43a and 44d and the intake passage 1) is blocked by the deposit.

  On the other hand, when the passive DeNOx control execution flag is “0” (step S702: No), the process proceeds to step S704. In step S704, the PCM 60 determines whether or not the active DeNOx control execution flag acquired in step S701 is “1”. As a result, when the active DeNOx control execution flag is “1” (step S704: Yes), that is, when it is a situation where the active DeNOx control should be executed, the process proceeds to step S705. In this case, the PCM 60 sets the target in-cylinder oxygen concentration to be applied during the active DeNOx control (step S705). Specifically, the PCM 60 suppresses the occurrence of smoke or the like when the post-injected fuel is burned while ensuring the combustion stability of the post-injected fuel by introducing EGR gas in the active DeNOx control. In this way, the target in-cylinder oxygen concentration to be applied at the time of active DeNOx control is set. As will be described later, the EGR cooler 43b is bypassed during the active DeNOx control so that the EGR gas flows. Therefore, the EGR gas becomes relatively high temperature, and it is difficult to take in the EGR gas. Also, the target in-cylinder oxygen concentration is set to a large value. For example, such a target in-cylinder oxygen concentration may be determined in advance according to the operating state of the engine E.

Next, in step S706, the PCM 60 controls the first EGR valve 43c provided on the EGR passage 43a to be fully closed (closed state) so that the target in-cylinder oxygen concentration set in step S705 is realized. The opening degree of the second EGR valve 43e provided on the EGR cooler bypass passage 43d is controlled. Specifically, the PCM 60 controls the opening degree of the second EGR valve 43e based on the estimated in-cylinder oxygen concentration and the target in-cylinder oxygen concentration. As described above, when executing the active DeNOx control, the PCM 60 recirculates the EGR gas to the intake system IN via the EGR cooler bypass passage 43d. By doing this, an appropriate amount of EGR gas is recirculated during the active DeNOx control, and the ignition of the post-injected fuel is delayed, thereby ensuring the combustion stability of the post-injected fuel and suppressing the occurrence of smoke. I am doing so. Further, the reason why the EGR gas is recirculated not through the EGR passage 43a but through the EGR cooler bypass passage 43d, that is, the EGR gas is recirculated without passing through the EGR cooler 43b is that post injection during active DeNOx control. This is because the HC generated by the above is taken in as EGR gas and cooled by the EGR cooler 43b, thereby preventing the EGR cooler 43b from being blocked due to deposits.
Basically, when the PCM 60 performs active DeNOx control when compared in the same operating state of the engine E, the EGR gas amount is greater than when the DeNOx control is not performed (that is, during normal operation of the engine E). The degree of opening of the second EGR valve 43e is controlled so that becomes smaller. This is because NOx is hardly generated during DeNOx control, and it is not necessary to introduce a large amount of EGR gas. In addition, if a large amount of EGR gas is introduced, the fuel post-injected in the active DeNOx control does not burn properly (misfire) and HC is generated.

  On the other hand, when the active DeNOx control execution flag is “0” (step S704: No), the process proceeds to step S707. In this case, the PCM 60 performs neither passive DeNOx control nor active DeNOx control, and thus sets a target in-cylinder oxygen concentration to be applied when EGR gas is introduced during normal operation of the engine E (step S707). Specifically, the PCM 60 suppresses the generation of smoke and NOx by appropriately reducing the in-cylinder oxygen concentration by introducing EGR gas, and controls the in-cylinder temperature by introducing EGR gas to stabilize combustion. The target in-cylinder oxygen concentration to be applied is set in accordance with the target torque so as to ensure the performance. For example, such a target in-cylinder oxygen concentration may be determined in advance according to the operating state of the engine E.

  Next, in step S708, the PCM 60 is provided on the first EGR valve 43c and the EGR cooler bypass passage 43d provided on the EGR passage 43a so that the target in-cylinder oxygen concentration set in step S707 is realized. The opening degree of both of the second EGR valves 43e is controlled. Specifically, the PCM 60 controls the opening degrees of the first EGR valve 43c and the second EGR valve 43e based on the estimated in-cylinder oxygen concentration and the target in-cylinder oxygen concentration. For example, a map that defines the opening degree of each of the first EGR valve 43c and the second EGR valve 43e to be set according to the target in-cylinder oxygen concentration is created in advance, and the PCM 60 refers to such a map. The opening degree of each of the first EGR valve 43c and the second EGR valve 43e is set.

<In-cylinder oxygen concentration estimation>
Next, a method for estimating the in-cylinder oxygen concentration according to the embodiment of the present invention will be described.

  In the present embodiment, the PCM 60 estimates the in-cylinder oxygen concentration by the following procedure in consideration of the transport delay of the intake / exhaust system. First, the PCM 60 calculates the in-cylinder gas concentration obtained from the previously estimated in-cylinder oxygen concentration (basically, the in-cylinder oxygen concentration is obtained by F / B calculation) and a statistical model when no EGR gas is introduced. The exhaust gas oxygen concentration is obtained based on the amount, the fuel injection amount, and the oxygen consumption rate in the cylinder. Specifically, the PCM 60 calculates “(cylinder oxygen concentration × cylinder gas amount−oxygen consumption ratio × fuel injection amount) / (cylinder gas amount + fuel injection amount)”. In this case, the PCM 60 obtains the exhaust gas oxygen concentration in consideration of the delay of about two strokes in the engine E and the learning result of the exhaust gas oxygen concentration.

  Next, the PCM 60 obtains the EGR gas oxygen concentration from the exhaust gas oxygen concentration obtained as described above in consideration of the gas transport delay in the EGR passage 43a (including the EGR cooler bypass passage 43d). Then, the PCM 60 uses the engine E based on the EGR gas oxygen concentration, the EGR gas amount, the intake shutter valve passage gas amount determined by another model (described later), and the intake shutter valve passage gas oxygen concentration. Obtain the oxygen concentration of gas passing through the intake port. Specifically, the PCM 60 calculates “(EGR gas oxygen concentration × EGR gas amount−intake shutter valve passage gas oxygen concentration × intake shutter valve passage gas amount) / (EGR gas amount + intake shutter valve passage gas amount)”. I do. Further, in this case, the PCM 60 obtains the intake port passage gas oxygen concentration in consideration of the gas transport delay in the intake manifold of the engine E.

  Next, the PCM 60 determines the intake port passage gas oxygen concentration obtained as described above, the intake port passage gas amount, the internal EGR gas amount, and the internal EGR corresponding to the exhaust gas oxygen concentration obtained as described above. The in-cylinder oxygen concentration is estimated based on the gas oxygen concentration. Specifically, the PCM 60 calculates “(intake port passage gas oxygen concentration × intake port passage gas amount−internal EGR gas oxygen concentration × internal EGR gas amount) / (intake port passage gas amount + internal EGR gas amount)”. I do.

  Here, the PCM 60 estimates the intake shutter valve passing gas amount according to the following procedure. First, the PCM 60 obtains the intake port passage gas amount by subtracting the internal EGR gas amount from the in-cylinder gas amount obtained by the statistical model when no EGR gas is introduced. In parallel with this calculation, the PCM 60 obtains the corrected airflow flow rate by subtracting the correction amount of the airflow flow rate considering the transition time from the flow rate (airflow flow rate) detected by the airflow sensor 101.

  Next, the PCM 60 obtains the EGR gas amount by subtracting the corrected airflow flow rate from the intake port passage gas amount obtained as described above. Then, the PCM 60 obtains the intake shutter valve passage gas amount by subtracting the EGR gas amount from the intake port passage gas amount obtained as described above. When the EGR gas is not introduced (that is, when the first EGR valve 43c and the second EGR valve 43e are fully closed), the PCM 60 determines the intake port passage gas amount as it is as the intake shutter valve passage gas amount.

<EGR return control>
Next, EGR return control according to an embodiment of the present invention will be described with reference to FIG. FIG. 12 is a flowchart (EGR return control flow) showing the EGR return control according to the embodiment of the present invention. The EGR return control flow is repeatedly executed by the PCM 60 at a predetermined cycle, and is executed in parallel with the various control flows described above (particularly, the active DeNOx control flow and the passive DeNOx control flow). EGR return control refers to normal operation after the end of these DeNOx controls from the EGR control state in which all or part of the EGR valve is closed while active DeNOx control or passive DeNOx control is being performed. This refers to control that returns to normal EGR control in an operating state in which no active DeNOx control or passive DeNOx control is performed.

  First, in step S801, the PCM 60 determines whether or not it is a return from active DeNOx control. As a result, if it is a return from the active DeNOx control (step S801: Yes), that is, if it is a situation where it is going to return to the normal control of the EGR in the normal operation state after the end of the active DeNOx control, the process proceeds to step S803. Proceed to On the other hand, when it is not return from the active DeNOx control (step S801: No), the process proceeds to step S802.

  Next, in step S803, the PCM 60 determines whether or not the operating state at the time of return is in a bypass side control region that controls only the second EGR valve 43e provided on the EGR cooler bypass passage 43d to an open state. . As a result, when the operating state at the time of return is in the bypass side control region in which only the second EGR valve 43e provided on the EGR cooler bypass passage 43d is controlled to be in an open state (step S803: Yes), the process proceeds to step S804. move on. On the other hand, when the operation state at the time of return is not in the bypass side control region that controls only the second EGR valve 43e provided on the EGR cooler bypass passage 43d to be in the open state (step S803: No), the process is step. The process proceeds to S805.

Here, referring to FIG. 13 and FIG. 14, the EGR control region is used in the determination of step S803 described above according to the operating state of the engine E. The EGR bypass side control region, the cooler side control region, the bypass side, and the cooler A method for setting either the side combination control region or the EGR cut control region will be described.
FIG. 13 shows the EGR control of the exhaust purification device for the engine E according to one embodiment of the present invention. The EGR control region is changed to the EGR bypass side control region, the cooler according to the operating state of the engine E in the complete warm-up state of the engine E. FIG. 14 is a diagram showing an EGR control map set in any of the side control region, the bypass side and cooler side combined control region, and the EGR cut control region, and FIG. 14 shows EGR control of the exhaust emission control device for an engine according to one embodiment of the present invention. In the semi-warm state of the engine E, the EGR control region is changed to any of the EGR bypass side control region, the cooler side control region, the bypass side and cooler side combined control region, and the EGR cut control region according to the operating state of the engine E. It is a figure which shows the EGR control map to set.
In FIGS. 13 and 14, the horizontal axis indicates the engine speed, and the vertical axis indicates the engine load. Here, the complete warm-up state of the engine E means that each part of the engine has reached an appropriate temperature or the like with respect to the temperature of the engine oil, the temperature of the cooling water, or a change in the engine speed during idling. The semi-warm state of the engine means a state in which the complete warm-up state has not been reached immediately after the engine is started.

As shown in FIG. 13, in the complete warm-up state of the engine E, when the engine speed is a relatively low speed and the engine load is also a relatively low load, the EGR bypass side control region is set. Yes. In the EGR bypass side control region, the second EGR valve 43e is opened to control the exhaust gas to pass through the EGR cooler bypass passage 43d.
Further, when the engine speed is higher than the bypass side control area (medium speed) and the engine load is higher than the bypass side control area (medium load), the EGR bypass is performed. Side and cooler side combined control areas are set. In the EGR bypass side and cooler side combined control region, the second EGR valve 43e is opened to allow exhaust gas to pass through the EGR cooler bypass passage 43d, and the first EGR valve 43c is opened to provide exhaust gas to the EGR cooler 43b. The EGR passage 43a is controlled to pass.
When the engine speed is higher than the bypass side and cooler side combined control area and the engine load is higher than the bypass side and cooler side combined control area, the EGR cooler side control area is set. Yes. In the EGR cooler-side control region, the first EGR valve 43c is opened to control the exhaust gas to pass through the EGR passage 43a provided with the EGR cooler 43b.
The EGR EGR cut control area is set when the engine speed is higher than the cooler side control area and the engine load is higher than the cooler side control area. In the EGR cut control region of EGR, the first EGR valve 43c is closed and the second EGR valve 43e is closed so that the exhaust gas does not flow into any of the EGR passage 43a and the EGR cooler bypass passage 43d.

  As shown in FIG. 14, in the semi-warm state of the engine, when the engine speed is relatively low to medium speed and the engine load is also relatively low to medium load, the EGR bypass side A control area is set. In the EGR bypass side control region, the second EGR valve 43e is opened to control the exhaust gas to pass through the EGR cooler bypass passage 43d. When the engine speed is higher than the bypass-side control area and the engine load is higher than the bypass-side control area, the EGR EGR cut control area is set. In the EGR cut control region of EGR, the first EGR valve 43c is closed and the second EGR valve 43e is closed so that exhaust gas does not flow into either the EGR passage 43a or the EGR cooler bypass passage 43d.

  Next, in step S804, the PCM 60 omits a delay time until the first EGR valve 43c and / or the second EGR valve 43e is opened from the closed state (for example, the delay time until the return is not set). The opening operation is immediately started to return to the normal control of the EGR in the normal operation state, and the process proceeds to the return process. In other words, it can be said that the PCM 60 sets the delay time until return to zero.

  Next, in step S805, the PCM 60 sets a delay time until the first EGR valve 43c and / or the second EGR valve 43e is opened from the closed state, and the process proceeds to step S807. The PCM 60 sends a delay time until the second EGR valve 43e is opened from the closed state and / or a delay time until the first EGR valve 43c is opened from the closed state to the exhaust passage 41 from the engine E. It is set according to the time until the exhaust gas exhaust amount reaches a predetermined amount. The time taken for the exhaust gas discharged from the engine E to the exhaust passage to reach a predetermined amount is an estimated integrated value of the exhaust gas discharged from the combustion chamber 17 of the engine E described later to the exhaust passage 41. Is calculated from the time required to reach the volume (predetermined amount) of the EGR upstream side exhaust passage 41a from the combustion chamber outlet 17a of the exhaust passage 41 to the EGR passage inlet 43f. The processes in steps S805 and S807 may be performed almost simultaneously as one step.

The delay time until the PCM 60 starts the opening operation of the second EGR valve 43e from the closed state after the execution of the active DeNOx control by the active DeNOx control means is until the first EGR valve 43c is started to open from the closed state. It is set to be shorter than the delay time. Therefore, HC generated by post injection at the time of execution of active DeNOx control is less likely to flow through the cooler-side EGR passage 43a that is opened after a longer delay time elapses, and HC or the like is less likely to flow into the cooler-side EGR passage 43a. Therefore, it is possible to prevent the occurrence of a failure that closes the EGR cooler.
If the operating state at the time of return is in the EGR cut control region in which the first EGR valve 43c and the second EGR valve 43e are controlled to be closed, the PCM 60 omits the processes in steps S805 and S807, Advances to step S809.

Next, in step S807, the PCM 60 determines that the estimated integrated value of the exhaust gas exhaust amount discharged from the combustion chamber 17 of the engine E to the exhaust passage 41, which is obtained according to the operating state of the engine E, is It is determined whether or not the volume (predetermined value) of the EGR upstream side exhaust passage 41a from 17a to the EGR passage inlet 43f is reached.
The estimated integrated value of the exhaust gas emission amount according to the operating state of the engine E is calculated during the period from the end of the active DeNOx control to the time of calculation (for example, the time of starting the opening operation of the target EGR valve). The exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 is estimated and calculated and integrated according to the operating state. The PCM 60 determines the amount of exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 based on the air flow rate, the air filling amount, the fuel injection amount corresponding to the air filling amount, the engine speed, the engine load, and the like. To estimate.

  When the estimated integrated exhaust amount of exhaust gas corresponding to the operating state of the engine E obtained as described above becomes equal to or larger than the volume value of the EGR upstream exhaust passage 41a, the exhaust gas is discharged from the combustion chamber 17 to the EGR upstream exhaust passage 41a. Since the exhaust gas to be discharged is replaced by pushing the exhaust gas already existing in the EGR upstream side exhaust passage 41a to the downstream side during the delay time, the exhaust gas already exists in the EGR upstream side exhaust passage 41a. Even if a relatively large amount of unburned fuel is contained in the exhaust gas, the exhaust gas containing the unburned fuel can be pushed downstream. Therefore, even in the case where the residual unburned fuel is discharged on the EGR upstream side exhaust passage 41a in the active DeNOx control, after the active DeNOx control is finished, the normal operation state (basically, it is injected by the fuel injection valve 20). The exhaust gas discharged from the combustion chamber 17 to the EGR upstream exhaust passage 41a in the operation state in which the fuel to be burned in the cylinder of the engine E) is already present in the EGR upstream exhaust passage 41a. The exhaust gas containing is replaced so as to push it downstream. Therefore, before starting the opening operation from the closed state of the first EGR valve 43c and / or the second EGR valve 43e, almost no HC due to residual unburned fuel is present or reduced in the EGR upstream exhaust passage 41a. It will be in the state. Therefore, HC or the like of unburned fuel flows into the EGR passage 43a on the cooler side and is cooled by the EGR cooler 43b, thereby preventing a failure that blocks the EGR cooler 43b. Further, it is possible to prevent the occurrence of a failure in which unburned fuel HC or the like flows into the EGR cooler bypass passage 43d and closes the EGR cooler bypass passage 43d.

As a result, the estimated integrated value of the exhaust amount of exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 determined by the operating state of the engine E is from the combustion chamber outlet 17a of the exhaust passage 41 to the EGR passage inlet 43f. If the EGR upstream exhaust passage 41a has a volume (predetermined value) or more (step S807: Yes), the process proceeds to step S809.
On the other hand, the estimated integrated value of the exhaust amount of exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 determined by the operating state of the engine E is calculated from the combustion chamber outlet 17a of the exhaust passage 41 to the EGR passage inlet If the volume of the EGR upstream exhaust passage 41a up to 43f is not reached, the process waits in step 807 until the estimated integrated value of the exhaust gas discharge amount becomes equal to or greater than the volume of the EGR upstream exhaust passage 41a.

  Next, in step S809, after the delay time until the PCM 60 starts the opening operation from the closed state of the first EGR valve 43c and / or the second EGR valve 43e set in step S805, the first EGR valve 43c and The second EGR valve 43e is started to open from the closed state to return to the normal control of the EGR in the normal operation state, and the process proceeds to the return process.

  In step S802, the PCM 60 determines whether the return from the passive DeNOx control is performed. As a result, when it is a return from the passive DeNOx control (step S802: Yes), that is, when the passive DeNOx control is finished, the process is to return to the normal control of the EGR in the normal operation state. Proceed to On the other hand, when it is not a return from the passive DeNOx control (step S802: No), the process proceeds to a return process.

Next, in step S806, the PCM 60 sets a delay time until the first EGR valve 43c and / or the second EGR valve 43e is opened from the closed state, and the process proceeds to step S808. The PCM 60 sends a delay time until the second EGR valve 43e is opened from the closed state and / or a delay time until the first EGR valve 43c is opened from the closed state to the exhaust passage 41 from the engine E. It is set according to the time until the exhaust gas exhaust amount reaches a predetermined amount. The time taken for the exhaust gas discharged from the engine E to the exhaust passage to reach a predetermined amount is an estimated integrated value of the exhaust gas discharged from the combustion chamber 17 of the engine E described later to the exhaust passage 41. Is calculated from the time required to reach the volume (predetermined amount) of the EGR upstream side exhaust passage 41a from the combustion chamber outlet 17a of the exhaust passage 41 to the EGR passage inlet 43f. The processes in step S806 and step S808 may be performed almost simultaneously as one step.
Here, the PCM 60 has a delay time until the second EGR valve 43e is started to open from the closed state after the execution of the passive DeNOx control, and a delay time until the first EGR valve 43c is started to open from the closed state. In addition, since the post-injected fuel in the passive DeNOx control is actively discharged to the exhaust passage 41 as unburned fuel, the exhaust gas containing unburned fuel is unlikely to flow into the EGR passage 43a and the EGR cooler bypass passage 43d. Control is performed so that the delay time is relatively long.
Note that the PCM 60 omits the processing in steps S806 and S808 when the operating state at the time of return is in the EGR cut control region in which the first EGR valve 43c and the second EGR valve 43e are closed. Advances to step S810.

  Note that the PCM 60 has a delay time until the first EGR valve 43c and / or the second EGR valve 43e is started to open from the closed state after the execution of the active DeNOx control by the active DeNOx control unit. After the execution of the control, the first EGR valve 43c and / or the second EGR valve 43e is set and controlled so as to be shorter than the delay time until the opening operation is started from the closed state. Therefore, the delay time after the end of the execution of the active DeNOx control executed in a state where the amount of unburned fuel in the exhaust gas is less than that in the passive DeNOx control is the passive time executed in a state where the exhaust gas contains a lot of unburned fuel. The delay time after completion of execution of DeNOx control can be made shorter. Accordingly, after the execution of the active DeNOx control that is executed in a state where there is little unburned fuel, the opening operation of the first EGR valve 43c and / or the second EGR valve 43e is started with a relatively short delay time, and the normal control of the EGR device 43 is performed. The occurrence of a failure due to the unburned fuel adhering to the internal parts of the EGR device 43 can be suppressed.

  Next, in step S808, the PCM 60 determines that the estimated integrated value of the exhaust gas discharged from the combustion chamber 17 of the engine E into the exhaust passage 41, which is obtained from the operating state of the engine E, is the combustion chamber outlet of the exhaust passage 41. It is determined whether or not the volume (predetermined value) of the EGR upstream side exhaust passage 41a from 17a to the EGR passage inlet 43f is reached. The estimated integrated value of the exhaust gas emission amount according to the operating state of the engine E is the value of the engine E during the period from the end of the passive DeNOx control to the calculation time (for example, the time when the target EGR valve opening operation is started). The exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 is estimated and calculated and integrated according to the operating state. The PCM 60 determines the amount of exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 based on the air flow rate, the air filling amount, the fuel injection amount corresponding to the air filling amount, the engine speed, the engine load, and the like. To estimate.

  When the estimated accumulated exhaust amount of exhaust gas corresponding to the engine operating state obtained as described above becomes equal to or larger than the volume value of the EGR upstream exhaust passage 41a, the exhaust gas is discharged from the combustion chamber 17 to the EGR upstream exhaust passage 41a. The exhaust gas that has already existed in the EGR upstream side exhaust passage 41a is replaced by pushing the exhaust gas downstream, so that the exhaust gas that has already existed in the EGR upstream side exhaust passage 41a is not burned. Even if a relatively large amount of fuel is contained, the exhaust gas containing the unburned fuel can be pushed downstream. Therefore, even in the case where the fuel post-injected onto the EGR upstream side exhaust passage 41a in the passive DeNOx control is discharged as unburned fuel as it is, after the passive DeNOx control is finished, the normal operation state (basically fuel condition) The exhaust gas discharged from the combustion chamber 17 into the EGR upstream exhaust passage 41a in the operation state in which the fuel injected by the injection valve 20 is combusted in the cylinder of the engine E) already exists in the EGR upstream exhaust passage 41a. The exhaust gas containing a relatively large amount of unburned fuel is exchanged by pushing it downstream. Therefore, before starting the opening operation from the closed state of the first EGR valve 43c and / or the second EGR valve 43e, almost no HC due to unburned fuel is present or reduced in the EGR upstream exhaust passage 41a. It becomes a state. Particularly, by opening the second EGR valve 43e, it is possible to suppress a failure in which exhaust gas containing HC resulting from unburned fuel passes through the EGR cooler bypass passage 43d and closes the EGR cooler 43b.

As a result, the estimated integrated value of the exhaust amount of exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 determined by the operating state of the engine E is from the combustion chamber outlet 17a of the exhaust passage 41 to the EGR passage inlet 43f. If the EGR upstream exhaust passage 41a has a volume (predetermined value) or more (step S808: Yes), the process proceeds to step S810.
On the other hand, the estimated integrated value of the exhaust amount of exhaust gas discharged from the combustion chamber 17 of the engine E to the exhaust passage 41 determined by the operating state of the engine E is calculated from the combustion chamber outlet 17a of the exhaust passage 41 to the EGR passage inlet If the capacity of the EGR upstream side exhaust passage 41a up to 43f is not reached, the process waits in step 808 until the estimated integrated value of the exhaust gas discharge amount becomes equal to or larger than the volume of the EGR upstream side exhaust passage 41a.

  Next, in step S810, the PCM 60 passes the delay time until the first EGR valve 43c and / or the second EGR valve 43e set in step S806 is started from the closed state, and then the first EGR valve 43c and The second EGR valve 43e is started to open from the closed state to return to the normal control of the EGR in the normal operation state, and the process proceeds to the return process.

  According to the engine exhaust gas purification apparatus according to the embodiment of the present invention described above, the EGR control means switches the first EGR valve 43c and / or the second EGR valve 43e from the closed state after the execution of the active DeNOx control by the active DeNOx control means. The delay time until the opening operation is started is shorter than the delay time until the first EGR valve 43c and / or the second EGR valve 43e is started from the closed state after the execution of the passive DeNOx control by the passive DeNOx control means. Therefore, the delay time after the execution of the active DeNOx control executed in a state where the amount of unburned fuel in the exhaust gas is smaller than that in the passive DeNOx control is a state in which the exhaust gas contains a large amount of unburned fuel. Delay time after the end of passive DeNOx control Remote can be shortened. Therefore, after the execution of the active DeNOx control executed in a state where there is little unburned fuel, the opening operation of the first EGR valve 43C and / or the second EGR valve 43E is started with a relatively short delay time, and the normal control of the EGR device 43 is performed. The occurrence of a failure due to the unburned fuel adhering to the internal parts of the EGR device 43 can be suppressed.

  Further, according to the engine exhaust gas purification apparatus of the present embodiment, the active DeNOx control by the active DeNOx control means is NOx reduction control that is set so that the post-injected fuel is combusted in the cylinder of the engine E. Therefore, the post-injected fuel can be prevented from being discharged as unburned fuel as it is, and the first EGR valve 43C and / or the second EGR valve 43E can be opened by a relatively short delay time after the execution of the active DeNOx control. The operation can be started, the normal control of the EGR device 43 can be restored, and the occurrence of failure due to the unburned fuel adhering to the internal parts of the EGR device 43 can be suppressed.

  Further, according to the engine exhaust gas purification apparatus according to the present embodiment, the passive DeNOx control by the passive DeNOx control means makes the air-fuel ratio rich by discharging at least part of the post-injected fuel as unburned fuel. Therefore, after the execution of the passive DeNOx control for discharging at least a part of the post-injected fuel as unburned fuel, the first EGR valve 43C and / or the second EGR valve 43E is opened from the closed state. The delay time until the operation is started is longer than the delay time after the execution of the active DeNOx control, and after the execution of the passive DeNOx control, the first EGR valve 43C and / or the second EGR valve due to a relatively long delay time. 43E is started and the EGR device 43 is turned on. The occurrence of a failure due to internal parts of and EGR device 43 causes it can to return the control to unburned fuel adhering can be suppressed.

  Further, according to the engine exhaust gas purification apparatus according to the present embodiment, the EGR control means causes the exhaust gas to flow into the EGR cooler bypass passage 43d and the cooler side EGR passage 43a side when the active DeNOx control is executed by the active DeNOx control means. Therefore, HC generated by post-injection during execution of active DeNOx control flows into the cooler-side EGR passage 43a and is cooled by the EGR cooler 43B, thereby blocking the EGR cooler 43B. Can be prevented.

  Further, according to the engine exhaust gas purification apparatus according to the present embodiment, the EGR control means closes the first EGR valve 43c and closes the second EGR valve 43e when the passive DeNOx control is executed by the passive DeNOx control means. Therefore, when performing passive DeNOx control for discharging post-injected fuel as unburned fuel, HC of unburned fuel flows into the cooler side EGR passage 43a and is cooled by the EGR cooler 43B. Occurrence of a failure that closes the EGR cooler 43B can be prevented. Further, when passive DeNOx control is performed, it is possible to prevent the occurrence of a failure in which HC or the like of unburned fuel flows into the EGR cooler bypass passage 43d and closes the EGR cooler bypass passage 43d.

  Further, according to the engine exhaust gas purification apparatus of the present embodiment, the delay time until the EGR control unit starts opening the first EGR valve 43c from the closed state after the execution of the passive DeNOx control by the passive DeNOx control unit is completed. Since the second EGR valve 43e is controlled to be longer than the delay time until the opening operation is started from the closed state, the HC generated by the post injection at the time of executing the active DeNOx control is opened after the longer delay time elapses. It becomes more difficult to enter the cooler-side EGR passage 43a to be valved, and HC or the like flows into the cooler-side EGR passage 43a and is cooled by the EGR cooler 43B, thereby preventing the occurrence of a failure that blocks the EGR cooler 43B. be able to.

  Further, according to the exhaust emission control device for an engine according to the present embodiment, the EGR control means delays until the second EGR valve 43e is started to open from the closed state after the execution of the passive DeNOx control by the passive DeNOx control means, In addition, since the delay time from when the first EGR valve 43c is closed to when the first EGR valve 43c is started to open is controlled to be a relatively long time so that the unburned fuel hardly flows into the EGR passage, the passive DeNOx control is executed. HC generated by the post-injection of the gas flows into the cooler-side EGR passage 43a and is cooled by the EGR cooler 43B, thereby preventing the occurrence of a failure that blocks the EGR cooler 43B.

  Further, according to the engine exhaust gas purification apparatus of the present embodiment, the EGR control means opens the delay time until the second EGR valve 43e is opened from the closed state and / or opens the first EGR valve 43c from the closed state. Since the delay time until the operation is started is set by the time until the exhaust amount of the exhaust gas discharged from the engine to the exhaust passage 41 reaches a predetermined amount, the exhaust gas discharged from the engine 41 to the exhaust passage 41 is set. However, since the exhaust gas already existing in the exhaust passage 41 on the upstream side of the EGR is replaced by pushing the exhaust gas downstream while the delay time elapses, the exhaust gas already exists in the exhaust passage 41 on the upstream side of the EGR device 43. Even if a relatively large amount of unburned fuel is contained in the exhaust gas, the exhaust gas containing the unburned fuel can be pushed downstream. Therefore, HC or the like of unburned fuel flows into the cooler side EGR passage 43a and is cooled by the EGR cooler 43B, thereby preventing a failure that blocks the EGR cooler 43B. Further, it is possible to prevent the occurrence of a failure in which unburned fuel HC or the like flows into the EGR cooler bypass passage 43d and closes the EGR cooler bypass passage 43d.

  Further, according to the engine exhaust gas purification apparatus according to the present embodiment, the opening degree of the first EGR valve 43C and / or the second EGR valve 43E is controlled based on the target in-cylinder oxygen concentration to be set during the NOx reduction control. This amount of exhaust gas can be introduced into the engine to appropriately set the inside of the cylinder of the engine to a desired oxygen concentration.

41 Exhaust passage 41a Upstream exhaust passage 43 EGR device 43a EGR passage 43b EGR cooler 43c First EGR valve 43d Cooler bypass passage 43e Second EGR valve 43f EGR passage inlet EX Exhaust system FS Fuel supply system IN Intake system

Claims (9)

NOx in the exhaust gas is occluded when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, provided on the exhaust passage of the engine. An engine exhaust purification device comprising a NOx catalyst that reduces when the fuel is in the vicinity of the fuel ratio or richer than the stoichiometric air-fuel ratio,
In order to reduce the NOx occluded in the NOx catalyst, NOx reduction control for post-injecting from the fuel injection valve so as to set the air-fuel ratio of the exhaust gas to a target air-fuel ratio capable of reducing NOx occluded in the NOx catalyst is performed. NOx reduction control means to be executed;
The EGR passage is provided on the EGR passage so that the exhaust gas having a flow rate corresponding to the operating state of the engine is recirculated from the exhaust passage to the intake passage through the EGR passage connected to the exhaust passage and the intake passage of the engine. EGR control means for controlling the EGR valve,
The NOx reduction control means includes:
A first NOx reduction control means for executing the first NOx reduction control in a state where a relatively large amount of unburned fuel is contained in the exhaust gas in an operating state under a high engine load;
Second NOx reduction control means for executing the second NOx reduction control in a state where the amount of unburned fuel in the exhaust gas is less than the first NOx reduction control executed by the first NOx reduction control means in an operating state at a low engine load. Prepared,
The EGR control means closes the EGR valve when the first NOx reduction control means executes the first NOx reduction control and the second NOx reduction control means executes the second NOx reduction control. Restrict the introduction to the EGR passage,
further,
The EGR control means has a delay time from when the second NOx reduction control means finishes executing the second NOx reduction control until the EGR valve starts to open from the closed state, and the first NOx reduction control means uses the first NOx reduction control means. An exhaust emission control device for an engine, characterized in that after the execution of the reduction control is completed, the EGR valve is controlled to be shorter than a delay time from the closed state to the start of the opening operation.   2. The engine exhaust gas purification apparatus according to claim 1, wherein the second NOx reduction control by the second NOx reduction control means is NOx reduction control that is set so that post-injected fuel is combusted in a cylinder of the engine.   The first NOx reduction control by the first NOx reduction control means is NOx reduction control that is set to enrich the air-fuel ratio by discharging at least part of the post-injected fuel as unburned fuel. Item 3. The exhaust emission control device for an engine according to Item 1 or 2. The EGR passage includes a cooler-side EGR passage provided with an EGR cooler on the passage, and a bypass-side EGR passage that bypasses the EGR cooler,
The EGR valve includes a first EGR valve that adjusts the flow rate of exhaust gas that passes through the cooler-side EGR passage, and a second EGR valve that adjusts the flow rate of exhaust gas that passes through the bypass-side EGR passage,
4. The control device according to claim 1, wherein the EGR control unit performs control to open the second EGR valve and close the first EGR valve when the second NOx reduction control is performed by the second NOx reduction control unit. 5. The engine exhaust gas purification apparatus according to claim 1. The EGR passage includes a cooler-side EGR passage provided with an EGR cooler on the passage, and a bypass-side EGR passage that bypasses the EGR cooler,
The EGR valve includes a first EGR valve that adjusts the flow rate of exhaust gas that passes through the cooler-side EGR passage, and a second EGR valve that adjusts the flow rate of exhaust gas that passes through the bypass-side EGR passage,
The EGR control means controls the first EGR valve to be closed and the second EGR valve to be closed when the first NOx reduction control is executed by the first NOx reduction control means. The engine exhaust gas purification apparatus according to claim 1.   The EGR control means opens the first EGR valve from the closed state after the execution of the second NOx reduction control by the second NOx reduction control means until the second EGR valve is started from the closed state to the opening operation. The exhaust emission control device for an engine according to claim 4, wherein control is performed so as to be shorter than a delay time until the operation is started.   The EGR control means opens the first EGR valve from the closed state after the end of the execution of the first NOx reduction control by the first NOx reduction control means until the second EGR valve is opened from the closed state, and the first EGR valve is opened from the closed state. 6. The engine exhaust gas purification apparatus according to claim 5, wherein the delay time until the operation is started is controlled so as to be a relatively long delay time so that unburned fuel hardly flows into the EGR passage.   The EGR control means sends a delay time from when the second EGR valve is closed to the start of the opening operation and / or delay time until the first EGR valve is started from the closed state to the opening operation. The engine exhaust gas purification device according to claim 6 or 7, wherein the exhaust gas exhaust gas discharged into the exhaust passage is set according to a time until the exhaust gas reaches a predetermined amount.   The said EGR control means sets the opening degree of the said EGR valve based on the target cylinder oxygen concentration which should be set at the time of the said NOx reduction | restoration control by the said NOx reduction | restoration control means, The any one of Claim 1 thru | or 8 The engine exhaust gas purification apparatus as described.

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