JP2019132165A - Exhaust emission control device for engine - Google Patents

Abstract

To provide an exhaust emission control device for an engine including a NOx catalyst, for suppressing the deterioration of the catalyst due to turbo lag.SOLUTION: When predetermined first conditions are established, an ECU 100 outputs a control signal to an injector 10 to perform NOx catalyst regeneration control so that performing post injection after fuel injection corresponding to the operating condition of an engine 1 makes an air-fuel ratio richer than before the first conditions are established. Even when the first conditions are established, the ECU 100 also restricts the execution of the post injection during the time before predetermined second conditions are established showing that turbosuperchargers 51, 52 are kept stable.SELECTED DRAWING: Figure 5

Description

  The technology disclosed herein relates to an exhaust purification control device for an engine.

  In an engine having a so-called NOx catalyst such as a NOx storage catalyst, it is known to control the fuel injection amount (so-called DeNOx control) in order to remove NOx stored in the NOx catalyst.

  For example, Patent Document 1 describes performing rich spike control for temporarily controlling the air-fuel ratio to the rich side during vehicle acceleration as an example of DeNOx control. In order to realize such DeNOx control, it is conceivable to perform additional fuel injection as in post injection in a diesel engine and burn it in a cylinder.

Japanese Patent Application Laid-Open No. 2005-291098

  By the way, in addition to the NOx catalyst as described in Patent Document 1, there is a case where a catalyst having a hydrocarbon (HC) adsorption function configured by adding an HC adsorbent to an oxidation catalyst, for example, may be provided. In this case, for example, when the catalyst temperature is low, HC is trapped by the HC adsorbent, whereas when the catalyst temperature is high, HC is released from the HC adsorbent.

  Here, when the engine provided with the NOx catalyst and the oxidation catalyst as described above is further provided with a turbocharger, a delay (so-called turbo lag) is caused in the increase of the supercharging pressure as in acceleration of the vehicle. As a result, the amount of intake air introduced into the combustion chamber is insufficient. Then, a relatively large amount of unburned fuel is generated, and a large amount of HC is adsorbed by the HC adsorbent of the oxidation catalyst.

  After a large amount of HC has been adsorbed, if DeNOx control as described in Patent Document 1 is started, it is discharged into the exhaust passage due to the influence of in-cylinder combustion due to post injection. Exhaust gas becomes hot. Thereby, a large amount of HC may be released at once from the HC adsorbent in a short period of time. In this case, the released HC excessively causes an oxidation reaction in the oxidation catalyst, and the oxidation heat or the NOx catalyst may be excessively heated by the reaction heat. An excessive temperature rise of the catalyst is not desirable from the viewpoint of suppressing deterioration thereof.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to suppress deterioration of a catalyst in an exhaust purification control device for an engine provided with a turbocharger.

  The technology disclosed herein is an engine exhaust gas purification control device that includes a combustion chamber, a turbocharger provided in an exhaust passage leading to the combustion chamber, and a NOx catalyst provided in the exhaust passage. Related. The exhaust purification control apparatus includes an injector that injects fuel into the combustion chamber, a catalyst that is provided in the exhaust passage and has a hydrocarbon adsorption function, and a controller that is connected to the injector.

  The controller makes the air-fuel ratio richer than before the first condition is satisfied by performing additional fuel injection after the fuel injection corresponding to the operating state of the engine when the predetermined first condition is satisfied. A control signal is output to the injector so as to perform NOx catalyst regeneration control.

  The controller further executes the additional injection until a predetermined second condition indicating that the turbocharger is stable, even when the first condition is satisfied. Restrict.

  According to this configuration, when the predetermined first condition is satisfied, the controller removes NOx from the NOx catalyst by executing NOx catalyst regeneration control by additional injection such as so-called post-injection, and as a result, removes the NOx catalyst. Can be purified.

  However, the controller does not only make a determination based on the first condition, but even when the first condition is satisfied, the additional injection is performed until a second condition different from the first condition is satisfied. Is configured to restrict execution. This second condition indicates that the turbocharger is stable, such as a situation where the actual supercharging pressure reaches near the target supercharging pressure.

  That is, when the second condition is satisfied, the intake air is sufficiently supplied to the combustion chamber. When additional injection is performed in such a situation, generation of unburned fuel due to the turbo lag can be suppressed as compared to before the second condition is satisfied. As a result, the amount of HC adsorbed to the HC adsorbent can be reduced, so that it is possible to suppress the excessive temperature rise of the catalyst and thus the deterioration of the catalyst performance caused by the release of the adsorbed HC. Is possible.

  The controller may determine that the second condition is satisfied when the amount of change in the accelerator opening is equal to or less than a predetermined first threshold value.

  In general, turbo lag occurs when the accelerator pedal is depressed, that is, when the accelerator opening, and thus the target boost pressure, changes greatly. In other words, when the change in the accelerator opening is small, the target boost pressure also changes accordingly, so that the actual boost pressure is sufficiently higher than the target boost pressure thus changing. Can be followed. This suggests that the amount of change in the accelerator opening can be used as an index for determining that the turbocharger is operating stably.

  Therefore, as described above, the turbocharger is operating stably by determining that the second condition is satisfied when the amount of change in the accelerator opening is equal to or less than a predetermined value. It becomes possible to determine more accurately.

  The controller may determine a target torque of the engine based on the accelerator opening.

  Generally, if additional injection such as post-injection is executed when the accelerator opening changes greatly, the air supply cannot catch up as described above, and the air-fuel ratio becomes excessively rich, and torque fluctuations can occur in the engine. There is sex. Such torque fluctuation is not preferable because it can give the passenger an uncomfortable feeling.

  On the other hand, according to the above-described configuration, by restricting the execution of additional injection until the second condition is satisfied, it is possible to suppress as much as possible the possibility of causing engine torque fluctuations and, consequently, a sense of discomfort to the passengers. It becomes possible.

  In particular, according to the above configuration, the target torque of the engine is based on the accelerator opening, while the amount of change in the accelerator opening satisfies the second condition. Since the amount of change in the accelerator opening is strongly related to the target torque of the engine, it is possible to more accurately and effectively determine when to start additional injection by setting such amount of change as the second condition. can do.

  Further, the controller may set the first threshold value lower when the accelerator opening is large than when the accelerator opening is small.

  In general, when the accelerator opening is large, the engine load, and hence the amount of fuel supplied to the combustion chamber, increases compared to when the accelerator opening is small. If it does so, since the room | chamber interior of a combustion chamber will become high temperature, it will become difficult to discharge | emit unburned fuel. Therefore, even if the additional injection is started at an earlier timing, the problem related to the excessive temperature rise of the catalyst is less likely to occur as described above.

  Therefore, according to the above configuration, when the accelerator opening is large, the first threshold value is set low. Since the second condition is established earlier as much as the first threshold is set lower, the additional injection can be started earlier.

  The controller may determine that the second condition is satisfied when the amount of change in the engine speed is equal to or less than a predetermined second threshold value.

  If only the amount of change in the accelerator opening is monitored, there is a possibility of overlooking the situation where unburned fuel can be discharged, such as when the engine speed fluctuates relatively large.

  Therefore, according to the above configuration, not only the amount of change in the accelerator opening but also the amount of change in the engine speed can be monitored, so that the timing at which additional injection should be started can be determined more accurately. .

  In particular, if the determination based on the change amount of the engine speed is performed simultaneously with the determination based on the change amount of the accelerator opening, it becomes more advantageous. That is, as described above, monitoring only the amount of change in the accelerator opening may be insufficient to determine the timing for starting the additional injection.

  On the other hand, if only the amount of change in engine speed is monitored, the effect of depression of the accelerator pedal is not yet reflected in the magnitude of the engine speed, just after the accelerator pedal is depressed greatly. The situation may be overlooked.

  Therefore, by monitoring the amount of change in the accelerator opening and the engine speed, it is possible to perform additional injection at a more accurate timing.

  Further, the controller may set the second threshold value lower when the engine speed is large than when the engine speed is small.

  In general, when the engine speed is high, the amount of heat generated per unit time by combustion of the air-fuel mixture increases as compared with when the engine speed is low. If it does so, since the room | chamber interior of a combustion chamber will become high temperature, it will become difficult to discharge | emit unburned fuel. Therefore, even if the additional injection is started at an earlier timing, the problem related to the excessive temperature rise of the catalyst is less likely to occur as described above.

  Therefore, according to the above configuration, when the engine speed is large, the second threshold value is set lower. Since the second condition is established earlier as much as the second threshold is set lower, the additional injection can be performed earlier.

  In addition, when the predetermined third condition is satisfied, the controller performs an additional fuel injection after the fuel injection corresponding to the operating state of the engine, thereby making the air-fuel ratio richer than before the third condition is satisfied. It is also possible to execute the second regeneration control in which the rich step to be changed and the lean step to make the air-fuel ratio leaner than the rich step are alternately performed.

  The NOx catalyst can adsorb not only NOx but also so-called SOx. Therefore, as in the second regeneration control, the SOx adsorbed on the NOx catalyst can be desorbed by alternately executing the rich step and the lean step.

  By the way, if the temperature of the NOx catalyst rises excessively, SOx adsorbed on the NOx catalyst may aggregate and it may be difficult to desorb from the NOx catalyst.

  However, according to the above configuration, it is possible to suppress the excessive temperature rise of the NOx catalyst by executing the additional injection of fuel at a more accurate timing. That is, such a configuration is effective not only for suppressing the performance deterioration of the NOx catalyst but also for smoothly desorbing SOx from the NOx catalyst.

  The exhaust passage is provided with an oxygen sensor that detects an oxygen concentration in exhaust gas flowing through the exhaust passage, and the controller is determined based on a detection result of the oxygen sensor and an operating state of the engine. The fuel injection amount in the additional injection may be feedback controlled based on the target air-fuel ratio.

  For example, immediately after acceleration of the vehicle, there is a possibility that a deviation occurs between the target air-fuel ratio and the actual air-fuel ratio. Here, even if it is attempted to perform feedback control on the fuel injection amount in the additional injection, it is controlled to the opposite side to the air-fuel ratio to be realized, and there is a possibility that the torque fluctuation will be prolonged.

  The above configuration is effective in that the occurrence of such torque fluctuation itself can be suppressed.

  As described above, according to the engine exhaust gas purification control apparatus, it is possible to suppress the deterioration of the catalyst due to the turbo lag.

FIG. 1 is a schematic view illustrating the configuration of an engine. FIG. 2 is a block diagram illustrating the configuration of the engine exhaust gas purification control apparatus. FIG. 3 is a flowchart illustrating the post-injection amount calculation process. FIG. 4 is a diagram illustrating an engine operating region. FIG. 5 is a flowchart illustrating a process for setting an execution flag for active DeNOx control. FIG. 6 is an explanatory diagram related to the setting of the first threshold value and the second threshold value. FIG. 7 is a flowchart illustrating the specific contents of the active DeNOx control. FIG. 8 is a flowchart illustrating the specific contents of the HC desorption promotion control. FIG. 9 is a time chart showing a specific example of active DeNOx control.

  Hereinafter, an embodiment of an engine exhaust gas purification control device will be described in detail with reference to the drawings. The following description is an example of an engine exhaust gas purification control device. FIG. 1 is a schematic diagram illustrating the configuration of the engine 1, and FIG. 2 is a block diagram illustrating the configuration of an exhaust purification control device of the engine 1.

  The engine 1 is a diesel engine to which a fuel mainly composed of light oil is supplied. The engine 1 is configured as a so-called four-stroke engine and is mounted on a four-wheeled automobile (vehicle). A crankshaft 7 that is an output shaft of the engine 1 is connected to a drive wheel of an automobile via a transmission (not shown), and when the engine 1 is operated, the output is transmitted to the drive wheel and the automobile travels. It is supposed to be.

  The engine 1 is a two-stage turbocharged engine. That is, as shown in FIG. 1, a first turbocharger 51 configured to supercharge the gas introduced into the combustion chamber 6 and the exhaust passage 40 leading to the combustion chamber 6 of the engine 1 and A second turbocharger 52 is provided. The exhaust passage 40 is also provided with a later-described NOx catalyst 41. The first turbocharger 51 and the second turbocharger 52 both exemplify “turbochargers”.

  Hereinafter, the overall configuration of the engine 1 will be described in detail.

(1) Overall Configuration The engine 1 includes a cylinder block 3 provided with a plurality of cylinders 2 (only one is shown in FIG. 1), a cylinder head 4 provided on the upper surface of the cylinder block 3, and each cylinder. And a piston 5 inserted into the inside. The piston 5 is connected to the crankshaft 7 via a connecting rod.

  A cavity is formed on the top surface of each piston 5. A combustion chamber 6 is defined for each cylinder 2 by the cavity, the inner wall surface of the cylinder 2, and the cylinder head 4.

  In the cylinder head 4, an intake port 16 for introducing intake air into the combustion chamber 6 and an exhaust port 17 for deriving exhaust gas from the combustion chamber 6 are formed for each cylinder 2. The intake port 16 is open to the combustion chamber 6, and an intake valve 12 for opening and closing the opening is provided. Similarly, the exhaust port 17 is also open to the combustion chamber 6, and an exhaust valve 13 for opening and closing the opening is provided.

  The cylinder head 4 is also provided with one set of injectors 10 for injecting fuel into the combustion chamber 6 and glow plugs 11 for raising the temperature of the gas in each cylinder 2 for each cylinder 2. .

  In the example shown in FIG. 1, the tip of the injector 10 is disposed so as to face the combustion chamber 6 from the ceiling surface of the combustion chamber 6 (specifically, the surface partitioned by the cylinder head 4). A plurality of injection ports are provided at the tip of the injector 10, and the opening degree of each injection port can be controlled.

  The ECU 100 described later inputs a pulse signal (control signal) to the injector 10 in order to control the fuel injection mode through the injector 10. The fuel injection mode can be controlled through the pulse width of the pulse signal, the input timing, the number of inputs, and the like.

  Specifically, the injector 10 can perform main injection that is mainly performed to obtain engine torque and post-injection in which the combustion energy hardly contributes to the engine torque. Here, the main injection is to inject the fuel before or near the compression top dead center so that the injected fuel starts to burn near the compression top dead center. On the other hand, post-injection is to inject fuel at a timing that is retarded from the main injection (specifically, timing during the expansion stroke).

  In addition, the glow plug 11 has a heat generating portion at the tip that generates heat according to the energized voltage when energized. Although illustration is omitted, the heat generating portion faces the inside of the combustion chamber 6 and is disposed so as to be positioned in the vicinity of the tip portion of the injector 10. For example, the heat generating portion of the glow plug 11 is located between the sprays ejected from the ejection ports of the injector 10 and is not in direct contact with those sprays.

  An intake passage 20 is connected to one side of the engine 1, while an exhaust passage 40 is connected to the other side. Here, the intake passage 20 communicates with the intake port 16 of each cylinder 2, and introduces fresh air into each combustion chamber 6. On the other hand, the exhaust passage 40 communicates with the exhaust port 17 of each cylinder 2 and discharges burned gas (exhaust gas) from each combustion chamber 6. In the intake passage 20 and the exhaust passage 40, the first turbocharger 51 and the second turbocharger 52 described above are disposed.

  In the intake passage 20, the air cleaner 21, the compressor 51 a of the first turbocharger 51 (hereinafter, appropriately referred to as the first compressor 51 a), and the compressor 52 a of the second turbocharger 52 (hereinafter, appropriately) from the upstream side. , A second compressor 52a), an intercooler 22, an intake shutter valve 23, and a surge tank 24. The intake shutter valve 23 is basically fully open, but is fully closed to prevent shock when the engine 1 is stopped, for example.

  The intake passage 20 is also provided with an intake bypass passage 25 that bypasses the second compressor 52a and an intake bypass valve 26 that opens and closes the intake compressor. The intake bypass valve 26 is switched between a fully closed state and a fully open state.

  In the exhaust passage 40, in order from the upstream side, a turbine 52b of the second turbocharger 52 (hereinafter referred to as a second turbine 52b as appropriate) and a turbine 51b of the first turbocharger 51 (hereinafter referred to as a first 1 turbine 51b), a first catalyst 43 including the aforementioned NOx catalyst 41, a DPF (Diesel Particulate Filter) 44, and a urea injector 45 for injecting urea into the exhaust passage 40 downstream of the DPF 44. An SCR (Selective Catalytic Reduction) catalyst 46 that purifies NOx using urea injected from the urea injector 45, and a slip catalyst 47 that oxidizes and purifies unreacted ammonia discharged from the SCR catalyst 46. Is provided.

  The first catalyst 43 includes a NOx catalyst 41 for purifying NOx and an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 42. Here, the oxidation catalyst 42 may be provided integrally with the NOx catalyst 41 or in the exhaust passage 40 upstream of the NOx catalyst 41. In this configuration example, the first catalyst 43 is configured by coating the surface of the catalyst material layer forming the NOx catalyst 41 with the catalyst material forming the oxidation catalyst 42.

  The NOx catalyst 41 occludes NOx in the exhaust in a lean state where the air-fuel ratio of the exhaust is larger than the stoichiometric air-fuel ratio (state where the excess air ratio λ is λ> 1), and this occluded NOx is stored in the air-fuel ratio of the exhaust. Is in the vicinity of the stoichiometric air-fuel ratio (λ≈1) or in a rich state smaller than the stoichiometric air-fuel ratio (λ <1), that is, in a reducing atmosphere in which the exhaust gas passing through the NOx catalyst 41 contains a large amount of unburned HC. NOx occlusion reduction type catalyst (NSC: NOx Storage Catalyst) that reduces at NO. Here, the term “exhaust air-fuel ratio” refers to the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 that can be estimated based on the oxygen concentration or the like in the exhaust gas.

  The oxidation catalyst 42 has a hydrocarbon (HC) adsorption function, and is configured to purify HC adsorbed by the function. Specifically, the oxidation catalyst 42 oxidizes HC, that is, unburned fuel, carbon monoxide (CO), and the like, using oxygen in the exhaust gas, and changes the water into carbon dioxide. Here, this oxidation reaction generated in the oxidation catalyst 42 is an exothermic reaction, and when the oxidation reaction occurs in the oxidation catalyst 42, the temperature of the exhaust is raised.

  Specifically, an HC adsorbing portion 42 a having an HC adsorbing function is provided on the surface of the catalyst material forming the oxidation catalyst 42. The HC adsorbing part 42a is a crystal made of zeolite having a small diameter and a large number of pores, and adsorbs by trapping HC molecules in the exhaust gas in the pores of the zeolite at a low temperature such as during cold start. At high temperatures, the adsorbed HC molecules vibrate and are released by jumping out of the pores of the zeolite. On the other hand, the catalyst material forming the oxidation catalyst 42 is made of a catalyst metal such as platinum (Pt) or palladium (Pd), and is heated to a predetermined temperature and activated to activate HC in the exhaust gas discharged from the engine 1. In addition to oxidizing and purifying CO, it also has a function of oxidizing and purifying HC released from the HC adsorbing portion 42a.

  In this way, the oxidation catalyst 42 temporarily adsorbs HC when the oxidation catalyst 42 is not activated and cannot sufficiently purify HC, such as during cold start, and after the oxidation catalyst 42 is activated. It has a function to release and purify the adsorbed HC.

  On the other hand, the DPF 44 is located downstream of the first catalyst 43 in the exhaust passage 40 and collects particulate matter (PM) in the exhaust. The PM collected in the DPF 44 is exposed to a high temperature and burned by receiving supply of oxygen, and is removed from the DPF 44. The temperature at which PM is burned and removed is relatively high at about 600 ° C. Therefore, in order to burn PM and remove it from the DPF 44, the temperature of the DPF 44 needs to be relatively high.

  The SCR catalyst 46 hydrolyzes the urea injected from the urea injector 45 to generate ammonia, and purifies the ammonia by reacting (reducing) with NOx in the exhaust gas.

  The exhaust passage 40 also includes an exhaust bypass passage 48 that bypasses the second turbine 52b, an exhaust bypass valve 49 that opens and closes the exhaust passage, a waste gate passage 53 that bypasses the first turbine 51b, and a waste gate valve that opens and closes the exhaust passage. 54 is provided. The exhaust bypass valve 49 and the waste gate valve 54 are switched between a fully closed state and a fully opened state, respectively, and are changed to arbitrary opening degrees between these states.

  The engine 1 further includes an EGR device 55 that recirculates a part of the exhaust gas to the intake air. The EGR device 55 connects the portion of the exhaust passage 40 upstream of the upstream end of the exhaust bypass passage 48 and the portion of the intake passage 20 between the intake shutter valve 23 and the surge tank 24. And a first EGR valve 57 that opens and closes it, and an EGR cooler 58 that cools the exhaust gas that passes through the EGR passage 56. Further, the EGR device 55 includes an EGR cooler bypass passage 59 that bypasses the EGR cooler 58 and a second EGR valve 60 that opens and closes the EGR cooler bypass passage 59.

  Next, the control system of the engine 1 will be described in detail.

(2) Control System The engine exhaust gas purification control apparatus includes an ECU (Engine Control Unit) 100 for operating the engine 1. The ECU 100 is a controller based on a well-known microcomputer. The ECU 100 includes a central processing unit (CPU) that executes a program, a RAM (Random Access Memory) or a ROM (Read Only Memory), for example, and a memory that stores programs and data, and an electric signal And an input / output bus for input / output. The ECU 100 is an example of a controller.

  As shown in FIG. 2, various sensors SW <b> 1 to SW <b> 9 are connected to the ECU 100. Sensors SW1 to SW9 output detection signals to ECU 100. Such sensors include the following:

  That is, a water temperature sensor SW1 that is attached to the engine 1 and detects the temperature of the cooling water, and an airflow sensor SW2 that is disposed downstream of the air cleaner 21 in the intake passage 20 and detects the flow rate of fresh air flowing through the intake passage 20; And an intake air temperature sensor SW3 that detects the temperature of the fresh air, a crank angle sensor SW4 that is attached to the engine 1 and that detects the rotation angle of the crankshaft 7, an accelerator pedal mechanism (not shown), and an accelerator pedal An accelerator opening sensor SW5 for detecting the accelerator opening corresponding to the operation amount, an O2 sensor SW6 provided in the exhaust passage 40 for detecting the oxygen concentration in the exhaust gas, and a vehicle speed sensor SW7 for detecting the speed (vehicle speed) of the vehicle. The pressure of the air attached to the surge tank 24 and introduced into the combustion chamber 6 is detected. A supercharging pressure sensor SW8 is provided between the DPF 44 and the SCR catalyst 46 in the exhaust passage 40, and between the SCR catalyst 46 and the slip catalyst 47 in the passage, and detects the NOx concentration in the exhaust gas. This is the NOx sensor SW9. Here, the O2 sensor SW6 exemplifies an “oxygen sensor” in that the oxygen concentration in the exhaust gas flowing through the exhaust passage 40 is detected.

  The ECU 100 determines the operating state of the engine 1 and the vehicle based on these detection signals and calculates the control amount of each device. The ECU 100 sends control signals related to the calculated control amount to the injector 10, the glow plug 11, the intake shutter valve 23, the intake bypass valve 26, the exhaust bypass valve 49, the waste gate valve 54, the first EGR valve 57, and the second EGR. Output to valve 60.

  For example, the ECU 100 acquires an actual supercharging pressure (hereinafter also referred to as “actual supercharging pressure”) at the time of detection based on a detection signal from the supercharging pressure sensor SW8. In parallel with this, ECU 100 calculates a target value of the supercharging pressure (hereinafter also referred to as “target supercharging pressure”) based on detection signals from other sensors. Then, the ECU 100 adjusts the opening degrees of the intake bypass valve 26, the exhaust bypass valve 49, the waste gate valve 54, and the like so that the actual boost pressure becomes the target boost pressure.

  Then, the ECU 100 controls the operations of the first turbocharger 51 and the second turbocharger 52 through the opening adjustment of the intake bypass valve 26, the exhaust bypass valve 49, the wastegate valve 54, and the like.

  The ECU 100 performs DeNOx control (NOx catalyst regeneration control), DeSOx control (second regeneration control), and DPF regeneration in order to purify and regenerate various devices such as the first catalyst 43 and the DPF 44 provided in the exhaust passage 40. Control is to be executed.

  As an example, DeNOx control, which is control for reducing NOx stored in the NOx catalyst 41 (hereinafter also referred to as “storage NOx”) and releasing (leaving) it from the NOx catalyst 41, will be briefly described.

  As described above, the NOx catalyst 41 reduces the stored NOx when the air-fuel ratio of the air-fuel mixture is in the vicinity of the stoichiometric air-fuel ratio (λ≈1) or in a rich state where the stoichiometric air-fuel ratio is smaller (λ <1). . Therefore, in order to reduce the stored NOx, it is necessary to reduce the air-fuel ratio of the air-fuel mixture more than during normal operation (when normal control described later is performed).

  Therefore, when the predetermined first condition is satisfied (in this configuration example, when the NOx occlusion amount in the NOx catalyst 41 becomes equal to or greater than the DeNOx determination value described later), the ECU 100 enters the operating state of the engine 1. By performing additional fuel injection after the corresponding fuel injection (main injection), a control signal is output to the injector 10 so as to execute DeNOx control that makes the air-fuel ratio richer than before the first condition is satisfied. .

  Specifically, in this configuration example, the ECU 100 reduces post-injection as additional injection to reduce the stored NOx by reducing the air-fuel ratio of the air-fuel mixture. That is, the ECU 100 causes the injector 10 to perform post injection in addition to main injection. In such DeNOx control, for example, the excess air ratio λ of the mixture is set to about λ = 0.94 to 1.06. By doing so, NOx stored in the NOx catalyst 41 is reduced.

  Hereinafter, after describing the basic contents of the fuel injection control, details such as DeNOx control, DeSOx control, and DPF regeneration control will be described in order.

-Fuel injection control-
First, fuel injection control in this configuration example will be described. This fuel injection control is started when the ignition of the vehicle is turned on and the ECU 100 is turned on, and is repeatedly executed at a predetermined cycle.

  First, the ECU 100 determines the driving state of the vehicle. Specifically, the ECU 100 is currently set in at least the accelerator opening detected by the accelerator opening sensor SW5, the vehicle speed detected by the vehicle speed sensor SW7, the crank angle detected by the crank angle sensor SW4, and the transmission of the vehicle. Get the gear position.

  Next, ECU 100 determines a target acceleration of the vehicle based on the determined driving state of the vehicle. Specifically, an acceleration characteristic map defined for various vehicle speeds and various gear stages is stored in advance in the memory of the ECU 100 or the like. The ECU 100 selects an acceleration characteristic map corresponding to the current vehicle speed and gear position from such an acceleration characteristic map, and determines a target acceleration corresponding to the current accelerator opening by referring to the selected map. .

  Next, ECU 100 determines a target torque of engine 1 for realizing the determined target acceleration. In this case, the ECU 100 determines the target torque within the range of torque that can be output by the engine 1 based on the current vehicle speed, gear stage, road surface gradient, road surface μ, and the like.

  Next, the ECU 100 calculates the fuel injection amount to be injected from the injector 10 based on the target torque and the engine speed so as to output the determined target torque from the engine 1. This fuel injection amount is a fuel injection amount (main injection amount) to be injected in the main injection.

  On the other hand, in parallel with the processing described above, the ECU 100 sets a fuel injection pattern corresponding to the operating state of the engine 1. Specifically, when performing the aforementioned DeNOx control, the ECU 100 sets a fuel injection pattern that performs at least post injection in addition to main injection. In this case, the ECU 100 also determines the fuel injection amount (post injection amount) to be injected in the post injection, the injection timing (post injection timing), and the like. Details of these will be described later.

  Thereafter, ECU 100 outputs a control signal to injector 10 so as to realize the calculated main injection amount and the set injection pattern. Here, when post injection is performed, a control signal that realizes the above-described post injection amount and post injection timing is output. That is, ECU 100 controls injector 10 such that a desired amount of fuel is injected in a desired injection pattern.

  Next, a method for calculating the post injection amount to be injected during DeNOx control (hereinafter referred to as “DeNOx post injection amount”) will be described with reference to FIG. This calculation method is repeatedly executed by the ECU 100 at a predetermined cycle, and is executed in parallel with the above-described fuel injection control. That is, while the fuel injection control is being performed, the post injection amount for DeNOx is calculated as needed.

  First, the ECU 100 determines the operating state of the engine 1 (step S101). Specifically, the ECU 100 includes at least the amount of intake air (flow rate of fresh air) detected by the air flow sensor SW2, the oxygen concentration in the exhaust gas detected by the O2 sensor SW6, and the main calculated in the fuel injection control. Get the injection amount. In addition, the ECU 100 also acquires an exhaust gas amount (EGR gas amount) recirculated to the intake system (specifically, the intake passage 20) by the EGR device 55, which is obtained using a predetermined model or the like.

  Next, the ECU 100 calculates the amount of air introduced into the engine 1 (that is, the filling amount) based on the acquired fresh air amount and EGR gas amount (step S102). Then, ECU 100 calculates the oxygen concentration of the air introduced into engine 1 from the calculated filling amount (step S103).

  Next, the ECU 100 outputs a control signal to the injector 10 so that the injector 10 performs post injection in addition to main injection. Prior to performing such control, the ECU 100 is required to reduce the NOx stored in the NOx catalyst 41 so that the air-fuel ratio of the air-fuel mixture becomes the target air-fuel ratio near the stoichiometric air-fuel ratio or below the stoichiometric air-fuel ratio. A correct post injection amount (DeNOx post injection amount) is calculated (estimated) (step S104).

  That is, the ECU 100 determines how much post injection amount should be injected in addition to the main injection amount in order to realize the target air-fuel ratio. In this case, the ECU 100 determines the target air-fuel ratio in consideration of the difference between the oxygen concentration detection value (the oxygen concentration detected by the O2 sensor SW6) and the oxygen concentration calculation value (estimated value) based on the filling amount. The post injection amount for DeNO to be realized is calculated. Specifically, the ECU 100 calculates the post injection amount for DeNOx necessary for realizing the target air-fuel ratio by appropriately performing feedback processing according to the difference between the detected value of oxygen concentration and the calculated value.

  By calculating the post-injection amount for DeNOx in this way, the target air-fuel ratio can be realized with high accuracy by post-injection in DeNOx control, and thus NOx occluded in the NOx catalyst 41 can be more reliably reduced.

(2-1) Normal Control First, control (normal control) that is performed during normal steady operation in which DeNOx control, DeSOx control, and DPF regeneration control are not performed will be described.

  In this application control, the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is made leaner (λ> 1) than the stoichiometric air-fuel ratio in order to improve fuel efficiency. For example, in normal control, the excess air ratio λ of the air-fuel mixture is about λ = 1.7. In this normal control, post injection is limited and only main injection is performed. In normal control, the operation of the glow plug 11 is stopped. In the normal control, the first EGR valve 57, the second EGR valve 60, the intake bypass valve 26, the exhaust bypass valve 49, and the waste gate valve 54 are respectively set to the operating state of the engine 1, for example, the engine speed and the engine load. Accordingly, the EGR rate is controlled to an appropriate value. As described above, the supercharging pressure is also controlled so as to achieve the target supercharging pressure corresponding to the operating state of the engine 1.

(2-2) DeNOx Control Next, DeNOx control in this configuration example will be described.

  The ECU 100 performs, as DeNOx control, active DeNOx control that is performed when the engine load is in the middle load range (see the second region R12 in FIG. 4), and when the engine load is near the upper limit (first region R11 in FIG. 4). And the passive DeNOx control performed in FIG.

  For example, the ECU 100 performs active DeNOx control when the NOx occlusion amount in the NOx catalyst 41 (hereinafter, also simply referred to as “NOx occlusion amount”) is greater than or equal to a predetermined amount (typically when the NOx occlusion amount is near the limit). ), The post-injection from the injector 10 is continuously executed at an injection timing such that the fuel injected by the post-injection burns in the combustion chamber 6. By so doing, a large amount of occluded NOx can be forcibly reduced, so that the NOx purification performance of the NOx catalyst 41 can be ensured.

  The injection timing (post injection timing) of the post injection in the active DeNOx control is set in advance, for example, the first half of the expansion stroke and set to a timing between 30 and 70 ° CA after the compression top dead center. . By doing so, the fuel injected by the post injection is directly discharged as unburned fuel (that is, HC), and oil dilution by the post injected fuel is suppressed.

  Further, in this configuration example, the glow plug 11 is energized to heat the air-fuel mixture during the active DeNOx control in order to promote the combustion of the fuel injected by the post injection.

  On the other hand, even if the NOx occlusion amount is less than a predetermined amount as the passive DeNOx control, the ECU 100 causes the fuel injected by the post injection to be injected into the combustion chamber 6 when the air-fuel ratio changes to the rich side due to vehicle acceleration. The post-injection from the injector 10 is executed at an injection timing that does not cause combustion inside. In passive DeNOx control, post-injection is executed in a situation where the main injection amount increases and the air-fuel ratio of the air-fuel mixture decreases, such as during vehicle acceleration. The post injection amount for realizing the target air-fuel ratio is relatively small as compared with the case where the post injection is executed by multiplying by. This makes it possible to suppress deterioration in fuel consumption due to post injection while forcibly reducing the stored NOx.

  The injection timing of the post injection in the passive DeNOx control (post injection timing) is set to be retarded at least from the injection timing of the post injection in the active DeNOx control. For example, the injection timing of post-injection in the passive DeNOx control can be set in the second half of the expansion stroke and in the vicinity of 110 ° CA after the compression top dead center. By doing so, it is possible to suppress the generation of smoke (soot) due to the combustion of fuel injected by post injection.

  Here, with reference to FIG. 4, an operation region of the engine 1 that performs each of the passive DeNOx control and the active DeNOx control will be described. The horizontal axis in FIG. 4 indicates the engine speed, and the vertical axis in FIG. 4 indicates the engine load. In FIG. 4, a curve L1 indicates the maximum torque line of the engine 1.

  In this configuration example, the ECU 100 executes active DeNOx control when the engine load and the engine speed are included in the second region R12 shown in FIG. Here, in the second region R12, the engine load is not less than the first reference load Lo1 and less than the second reference load Lo2 (> the first reference load Lo1), and the engine speed is not less than the first reference speed N1. This is an operation region less than the second reference rotation speed (> first reference rotation speed N1).

  On the other hand, the ECU 100 executes the passive DeNOx control when the engine load and the engine speed are included in the first region R11 shown in FIG. Here, the first region R11 is a region where the engine load is higher than that of the second region R12, and the engine load is equal to or greater than a predetermined third reference load (> second reference load Lo2).

  As described above, the contents of DeNOx control are properly used in the first region R11 and the second region R12 for the following reason.

  In an operating region where the engine load is low or the engine load is relatively high but the engine speed is low, the exhaust temperature is low. Along with this, the temperature of the NOx catalyst 41 tends to be lower than the temperature at which the stored NOx can be reduced. Therefore, in this configuration example, DeNOx control is limited in such an operation region.

  In addition, as described above, post injection is performed in the DeNOx control. When the post-injected fuel is discharged without being burned into the exhaust passage 40, the EGR cooler 58 and the like are caused by deposits caused by the unburned fuel. There is a risk of blockage. Therefore, it is preferable that the fuel injected by the post injection is burned in the combustion chamber 6. However, in a region where the engine load is high or the engine load is relatively low but the engine speed is high, combustion occurs due to the high temperature in the combustion chamber 6 or the short time per crank angle. Until the gas in the chamber 6 is exhausted, it may be difficult to sufficiently mix the fuel and air injected by the post injection. In that case, there is a possibility that the fuel injected by the post injection cannot be sufficiently burned in the combustion chamber 6. Furthermore, there is a risk that soot will increase due to insufficient mixing of fuel and air. Therefore, in such an operation region, DeNOx control is basically stopped.

  However, in the first region R11 where the engine load is very high, the air-fuel ratio of the air-fuel mixture is kept small even during normal operation as the main injection amount is large. Therefore, in the first region R11, the post injection amount necessary for reducing the stored NOx can be reduced, and the influence caused by the unburned fuel being discharged to the exhaust passage 40 can be suppressed.

  Therefore, the ECU 100 performs active DeNOx control in which the post-injected fuel is burned in the combustion chamber 6 in the second region R12 where neither the engine load nor the engine speed is too low and too high. On the other hand, the ECU 100 performs passive DeNOx control in which the post-injected fuel is not burned in the combustion chamber 6 in the first region R11. The first region R11 is a region where the exhaust gas temperature is sufficiently high and the oxidation catalyst 42 is sufficiently activated. Therefore, unburned fuel discharged to the exhaust passage 40 is purified by the oxidation catalyst 42.

  Of the operating regions in which the DeNOx control is to be stopped, in particular, in the region on the higher load side than the second region R12 or the region on the higher rotation side (region R13 on the lower load side than the first region R11), the SCR Since the NOx purification performance by the catalyst 46 is sufficiently ensured, NOx emission from the vehicle can be reliably prevented without executing DeNOx control.

  In the first region R11 on the higher load side than the region R13 for purifying NOx by the SCR catalyst 46, the exhaust gas amount becomes large and the SCR catalyst 46 cannot completely purify NOx, but the passive DeNOx control is executed as described above. Thus, NOx can be purified by the NOx catalyst 41.

  Here, the control content when the operating state of the engine 1 changes as shown by the arrow in FIG. 4 will be specifically described. First, when the operating state of the engine 1 enters the second region R12 (see symbol A12), the ECU 100 executes active DeNOx control. When the operating state of the engine 1 deviates from the second region R12 (see reference A13), the ECU 100 temporarily stops the active DeNOx control. At this time, the SCR catalyst 46 purifies NOx. When the operating state of the engine 1 enters the second region R12 again (see reference A14), the ECU 100 resumes active DeNOx control. By doing so, the active DeNOx control is not terminated until the NOx stored in the NOx catalyst 41 falls to substantially zero.

  Next, a temperature range in which passive DeNOx control or active DeNOx control is performed in this configuration example will be described. In general, the NOx catalyst 41 exhibits NOx purification performance in a relatively low temperature range, while the SCR catalyst 46 has a relatively high temperature range, specifically, a temperature range in which the NOx catalyst 41 exhibits NOx purification performance. Demonstrates NOx purification performance in a high temperature range.

  In this configuration example, even when the operating state of the engine 1 is in the first operating region R1, if the temperature of the SCR catalyst 46 is increased to a temperature capable of purifying NOx, the SCR catalyst 46 Therefore, the active DeNOx control is not executed. By carrying out like this, the deterioration of the fuel consumption resulting from execution of DeNOx control can be suppressed.

  Specifically, ECU 100 allows execution of active DeNOx control only when the temperature of SCR catalyst 46 (hereinafter referred to as “SCR temperature”) is lower than a predetermined SCR determination temperature, and the SCR temperature is SCR. When the temperature is equal to or higher than the determination temperature, execution of active DeNOx control is prohibited. Here, the “SCR determination temperature” refers to a determination value set near the lower limit of the temperature range in which NOx can be purified (temperature range of the SCR catalyst 46).

  By the way, as described above, the ECU 100 is configured to additionally perform the post injection after the main injection corresponding to the operating state of the engine 1 when the predetermined first condition is satisfied. Specifically, the ECU 100 executes the active DeNOx control described so far.

  However, when the engine 1 including the NOx catalyst 41 and the oxidation catalyst 42 having the HC adsorption function as described above is provided with the turbochargers 51 and 52, the supercharging is performed as when the vehicle is accelerated. When a delay (so-called turbo lag) occurs in the pressure increase, the amount of intake air introduced into the combustion chamber 6 becomes insufficient. Then, a relatively large amount of unburned fuel is generated, and a large amount of HC may be adsorbed to the HC adsorption part 42a provided in the oxidation catalyst 42.

  If a large amount of HC is adsorbed to the HC adsorbing portion 42a and then in-cylinder combustion is caused by post injection, the exhaust discharged into the exhaust passage becomes high temperature. In this case, a large amount of HC may be released from the HC adsorbing portion 42a at a stretch within a short period. In this case, the released HC causes an excessive oxidation reaction in the oxidation catalyst 42, and the oxidation heat of the oxidation catalyst 42 and the NOx catalyst 41 may be excessively heated by the reaction heat. An excessive temperature rise of the catalyst is not desirable from the viewpoint of suppressing deterioration thereof.

  Therefore, in this configuration example, the ECU 100 predetermines that the turbochargers 51 and 52 are stable even when the first condition such as the NOx occlusion amount is satisfied. Until the two conditions are satisfied, execution of active DeNOx control (particularly, execution of post-injection) is restricted.

  Hereinafter, processing related to the second condition will be described with reference to FIG.

-Processing related to determination of active DeNOx flag-
Next, processing for determining an execution flag (active DeNOx flag) of active DeNOx control in this configuration example will be described with reference to the flowchart of FIG. The flow shown in FIG. 5 is repeatedly executed by the ECU 100 at a predetermined cycle, and is executed in parallel with the above-described fuel injection control, processing for calculating the DeNOx post injection amount, and the like.

  First, in step S501, the ECU 100 acquires various information based on the detection signals output from the various sensors SW1 to SW9, and determines the operating state of the engine 1 and the vehicle. In step S501, the ECU 100 acquires at least the engine load, the engine speed, the NOx catalyst temperature, the SCR temperature, and the NOx occlusion amount.

  Specifically, the NOx catalyst temperature is estimated based on, for example, a detection signal of a first exhaust temperature sensor (not shown) provided immediately upstream of the NOx catalyst 41. In addition to such a detection signal, a detection signal of a second exhaust temperature sensor (not shown) provided between the NOx catalyst 41 and the DPF 44 may be used. Similarly, the SCR temperature can be estimated based on a detection signal of a third exhaust temperature sensor (not shown) provided immediately upstream of the SCR catalyst 46.

  Further, the NOx occlusion amount is estimated based on, for example, the cumulative value of the difference between the amount of NOx contained in the exhaust gas and the detected value of the NOx sensor SW9, which is estimated based on the operating state of the engine 1. Can do.

  Next, in step S502, the ECU 100 determines whether or not the SCR temperature acquired in step S501 is less than a predetermined SCR determination value T1. Here, when the SCR temperature is lower than the SCR determination value T1 (step S502: YES), the control process proceeds to step S503. On the other hand, when the SCR temperature is equal to or higher than the SCR determination value T1 (step S502: NO), the control process proceeds to step S508. In the latter case, since the NOx in the exhaust gas can be appropriately purified by the SCR catalyst 46, the ECU 100 limits the execution of the active DeNOx control. Specifically, ECU 100 sets the active DeNOx flag to “0” in step S508, and ends the control process.

  Next, in step S503, the ECU 100 determines whether or not the NOx occlusion amount acquired in step S501 is greater than or equal to a predetermined DeNOx determination value. As described above, the determination in step S503 is equivalent to determining whether or not the first condition is satisfied.

  Here, the DeNOx determination value is set to a value that is somewhat lower than the limit value of the NO storage amount. If it is determined in step S503 that the NOx occlusion amount is greater than or equal to the DeNOx determination value (step S503: YES), it can be considered that the NOx catalyst 41 needs to be purified, and the control process proceeds to step S504. . On the other hand, when the NOx occlusion amount is less than the DeNOx determination value (step S503: NO), it can be considered that the NOx catalyst 41 does not need to be purified, so the control process proceeds to step S508 described above.

  Next, in step S504, the ECU 100 determines whether or not the NOx catalyst temperature is equal to or lower than a predetermined temperature in order to determine whether or not the NOx catalyst 41 acquired in step S501 is in a cold state. When the NOx catalyst temperature is low, the temperature of the HC adsorbing part 42a provided in the vicinity thereof is also low, so that HC contained in the unburned fuel is trapped by the HC adsorbing part 42a. That is, in this step S504, it is determined whether or not the HC adsorption unit 42a is in a state where HC can be trapped. Therefore, the predetermined temperature used in the determination in step S504 is set based on the temperature at which the HC adsorption unit 42a can trap HC.

  In step S504, when it is determined that the NOx catalyst temperature is equal to or lower than the predetermined temperature (step S504: YES), it is considered that the HC adsorption unit 42a can trap HC. In this case, as described above, there is a concern that the oxidation catalyst 42 may be excessively heated due to the release of HC trapped by the HC adsorption unit 42a. Therefore, in order to appropriately delay the timing at which the post injection is performed, the process proceeds to step S505 to determine whether the second condition is satisfied. On the other hand, when the NOx catalyst temperature is lower than the predetermined value (step S504: NO), there is no possibility of overheating of the oxidation catalyst 42, so the process skips steps S505 to S506 and proceeds to step S507. In this case, the ECU 100 allows execution of active DeNOx control. Specifically, the ECU 100 sets the active DeNOx flag to “1” in step S507 and ends the control process.

  In step S505, the ECU 100 determines whether or not the amount of change in the accelerator opening is equal to or less than a predetermined first threshold value. Here, the change amount of the accelerator opening is acquired based on a detection signal of the accelerator opening sensor SW5, for example. In step S505, when it is determined that the amount of change in the accelerator opening is equal to or less than the first threshold (step S505: YES), it is determined that the turbochargers 51 and 52 are operating stably, The control process proceeds to step S506. On the other hand, when the amount of change in the accelerator opening exceeds the first threshold (step S505: NO), at least one of the turbochargers 51 and 52 is not stable and post injection is performed. It is considered that there is a concern about overheating of the oxidation catalyst 42. Therefore, in the latter case, the ECU 100 sets the active DeNOx flag to “0” in step S508 so as to limit the execution of the active DeNOx control, and ends the control process.

  In step S506, the ECU 100 determines whether or not the amount of change in the engine speed is equal to or less than a predetermined second threshold value. Here, the amount of change in the engine speed is acquired based on, for example, a detection signal of the crank angle sensor SW4. If it is determined in step S506 that the amount of change in the engine speed is equal to or less than the second threshold value (step S506: YES), it is determined that the turbochargers 51 and 52 are operating stably, The control process proceeds to step S507. On the other hand, when the amount of change in the engine speed exceeds the second threshold (step S506: NO), at least one of the turbochargers 51 and 52 is not stable, and post injection is performed. It is considered that there is a concern about overheating of the oxidation catalyst 42. Therefore, in the latter case, the ECU 100 sets the active DeNOx flag to “0” in step S508 so as to limit the execution of the active DeNOx control, and ends the control process.

  That is, in this configuration example, when the NOx catalyst 41 is in the cold state, the ECU 100 sets the active DeNOx flag to “1” until both the condition shown in step S505 and the condition shown in step S506 are satisfied. It is not set. Both of these conditions exemplify the second condition.

  In addition, the 1st threshold value relevant to the variation | change_quantity of an accelerator opening is increased / decreased according to the magnitude | size of an engine speed and an engine load. Specifically, as shown in FIG. 6, when the engine speed is large, the first threshold value (simply referred to as “threshold value” in FIG. 6) is set smaller than when the engine speed is small. It is like that. Similarly, when the engine load is large, the first threshold is set smaller than when the engine load is small.

  This tendency is the same for the second threshold value related to the amount of change in the engine speed. That is, with respect to the second threshold, as shown in FIG. 6, when the engine speed is large, the second threshold (simply referred to as “threshold” in FIG. 6) is smaller than when the engine speed is small. It is designed to be set smaller. Similarly, when the engine load is large, the second threshold value is set smaller than when the engine load is small.

-Specific contents of active DeNOx control-
Next, specific contents of the active DeNOx control will be described with reference to the flowchart of FIG. The flow shown in FIG. 7 is repeatedly executed by the ECU 100 at a predetermined cycle, and is executed in parallel with the above-described fuel injection control, the process of calculating the DeNOx post injection amount, the flow shown in FIG. The

  First, in step S701, the ECU 100 acquires various information based on the detection signals output from the various sensors SW1 to SW9, and determines the operating state of the engine 1 and the vehicle. In step S701, the ECU 100 at least includes the engine load, the engine speed, the NOx catalyst temperature, the SCR temperature, the NOx occlusion amount, and the DeNOx post-injection amount set according to the control process shown in FIG. The value of the active DeNOx flag set according to the control process shown in FIG. 5 is acquired.

  Next, in step S702, the ECU 100 determines whether or not the active DeNOx flag acquired in step S701 is “1”. That is, the ECU 100 determines whether execution of the active DeNOx control is permitted or whether the control is restricted. If it is determined in step S702 that the active DeNOx flag is “1” (step S702: YES), the control process proceeds to step S703 in order to execute active DeNOx control. On the other hand, if the flag is “0” (step S701: NO), the process returns without executing active DeNOx control.

  Next, in step S703, the ECU 100 determines whether or not the operating state of the engine 1 (specifically, the engine load and the engine speed) is included in the second region R12 (see FIG. 4). If it is determined in step S703 that the operating state of the engine 1 is included in the second region R12 (step S703: YES), the control process proceeds to step S705. On the other hand, when the operation state of the engine 1 is not included in the second region R12 (step S703: NO), the control process proceeds to step S704.

  In step S704, the ECU 100 performs normal fuel injection control not including post-injection without executing active DeNOx, and then returns (step S704). In this case, the ECU 100 actually executes the process of step S704 in the above-described fuel injection control. Then, the control process returns to step S703, and the determination relating to step S703 is executed again.

  That is, when the active DeNOx flag is “1”, the ECU 100 performs normal fuel injection control while the operating state of the engine 1 is not included in the second region R12, while the engine 1 When the operation state is included in the second region R12, the normal fuel injection control is switched to the fuel injection control in the active DeNOx control. For example, if the operating state of the engine 1 is out of the second region R12 during the fuel injection control in the active DeNOx control, the ECU 100 interrupts the fuel injection control and performs normal fuel injection control. When the state enters the second region R12, the fuel injection control in the active DeNOx control is resumed.

  Next, in step S705, the ECU 100 energizes the glow plug 11 and determines whether or not a predetermined time has elapsed since the energization was started, that is, whether or not the energization time of the glow plug 11 has reached the predetermined time. Determine whether. The predetermined time used in step S705 is set based on the energization time required for the glow plug 11 to reach a desired temperature, for example. If it is determined in step S705 that the energization time of the glow plug 11 has reached the predetermined time (step S705: Yes), the control process proceeds to step S706. On the other hand, when the energization time of the glow plug 11 has not reached the predetermined time (step S705: No), the control process returns to step S703. In this case, it waits until the energization time of the glow plug 11 reaches a predetermined time.

  Next, in step S706, the ECU 100 sets the injection timing (post injection timing) of the post injection applied in the active DeNOx control. As described above, the post injection timing is set so that the fuel injected by the post injection burns in the combustion chamber 6.

  Next, in step S707, the ECU 100 feedback-controls the DeNOx post-injection amount so as to achieve the target air-fuel ratio based on the control process shown in FIG. In parallel with the feedback control, the ECU 100 performs post injection based on the set post injection timing and the DeNOx post injection amount.

  After step S707, the control process proceeds to step S708. In step S708, the ECU 100 determines whether or not the NOx occlusion amount in the NOx catalyst 41 has become substantially zero. If it is determined in step S708 that the NOx occlusion amount has become substantially zero (step S708: YES), the control process is returned. On the other hand, when it is not determined that the NOx occlusion amount has become substantially zero (step S708: NO), the control process returns to step S703. That is, the ECU 100 continues the active DeNOx control until the NOx occlusion amount reaches substantially zero.

  In particular, even if the condition shown in step S703 is no longer established during active DeNOx control and the active DeNOx control is interrupted, ECU 100 does not stop the active DeNOx control as long as the value of the active DeNOx flag is “1”. Resume active DeNOx control as soon as possible. Thus, the NOx occlusion amount is reduced to zero.

(2-3) DPF regeneration control The DPF regeneration control is a control for regenerating the purification ability of the DPF 44 by removing the PM collected by the DPF 44. The DPF regeneration control is started after, for example, the NOx occlusion amount reaches substantially zero by active DeNOx control.

  In the DPF regeneration control, an oxidation reaction is possible when the oxidation catalyst 42 reaches a predetermined temperature, and the amount of PM trapped in the DPF 44 (hereinafter simply referred to as “PM deposition amount”) is preset. This is started when the regeneration start amount is equal to or greater than the regeneration start amount, and is terminated when the PM accumulation amount is less than the regeneration end amount set smaller than the regeneration start amount. The PM accumulation amount is calculated from, for example, the differential pressure across the DPF 44 calculated from the pressure sensors provided on the upstream side and downstream side of the DPF 44 (the difference between the pressure upstream of the DPF 44 and the pressure downstream). Is done. The regeneration start amount is set to a value that is smaller by a predetermined amount than the PM accumulation amount that can be collected by the DPF 44.

  As described above, the PM collected in the DPF 44 can be burned and removed at a high temperature. On the other hand, if unburned fuel is supplied to the oxidation catalyst 42 provided on the upstream side of the DPF 44 to cause an oxidation reaction, the temperature of the exhaust gas flowing into the DPF 44 and thus the temperature of the DPF 44 can be increased.

  Therefore, in this configuration example, as DPF regeneration control, post-injection is performed while the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio, and air and unburned fuel are allowed to flow into the oxidation catalyst 42 to convert them into the oxidation catalyst. Control to oxidize at 42 is performed. Specifically, in DPF regeneration control, post-injection is performed at a timing at which post-injected fuel does not burn in the combustion chamber 6 (second half of the expansion stroke, for example, 110 ° CA after compression top dead center). .

  In the DPF regeneration control, energization to the glow plug 11 is stopped because there is no need to burn the post injection.

(2-4) DeSOx Control DeSOx control is control for reducing and removing SOx occluded in the NOx catalyst 41 (hereinafter referred to as occluded SOx as appropriate). The DeSOx control is started when a predetermined third condition is satisfied (for example, when a flag indicating that the DPF regeneration control is completed is satisfied).

  As described above, the stored SOx is reduced in a state where the air-fuel ratio is in the vicinity of the stoichiometric air-fuel ratio (λ≈1) or in a rich state where the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (λ <1). Accordingly, in DeSOx control, in addition to the main injection, the air-fuel ratio of the air-fuel mixture is in the vicinity of the stoichiometric air-fuel ratio (λ≈1) or in a rich state smaller than the stoichiometric air-fuel ratio (λ <1). Perform post-injection.

  However, since SOx has a stronger binding force than NOx, in order to reduce the stored SOx, the temperature of the NOx catalyst 41 and thus the temperature of the exhaust gas passing through the NOx catalyst 41 are made higher than that at the time of DeNOx control (about 600 ° C.). There is a need to. On the other hand, if the unburned fuel is oxidized in the oxidation catalyst 42 as described above, the temperature of the exhaust gas passing through the first catalyst 43 and thus the NOx catalyst 41 can be increased.

  Therefore, in this configuration example, as DeSOx control, post-injection is performed in the same manner as DeNOx control, and the air-fuel ratio is made richer than in normal operation to be close to or smaller than the theoretical air-fuel ratio (hereinafter simply referred to as simply rich). Rich step and post-injection while making the air-fuel ratio leaner than the stoichiometric air-fuel ratio (hereinafter simply referred to as “lean” as appropriate) to supply the oxidation catalyst 42 with air and unburned fuel. The lean step of oxidizing these with the oxidation catalyst 42 is performed alternately.

  In the rich step, as with the active DeNOx control, the post-injected fuel is combusted in the combustion chamber 6 (the first half of the expansion stroke, for example, 30 to 70 ° CA after compression top dead center). To implement. In the rich step, the excess air ratio λ of the mixture and exhaust is set to about 1.0, and the air-fuel ratio of the mixture and exhaust is made close to the theoretical air-fuel ratio. For example, in the rich step, the excess air ratio λ of the air-fuel mixture and the exhaust is set to about λ = 0.94 to 1.06.

  Further, in the rich step, the ECU 100 causes the intake shutter valve 23, the exhaust bypass valve 49, and the waste gate valve 54 to reduce the intake air amount from that during normal operation so that the air-fuel ratio of the air-fuel mixture becomes low. To control.

  On the other hand, in the lean step, post-injection is performed at a timing at which the fuel injected by post-injection does not burn in the combustion chamber 6 (second half of the expansion stroke, for example, 110 ° CA after compression top dead center). Then, the air excess ratio λ of the air-fuel mixture is set to 1 or more, and the air-fuel ratio of the air-fuel mixture is made leaner than the stoichiometric air-fuel ratio. For example, in the lean step, the air excess ratio λ of the air-fuel mixture is set to about λ = 1.2 to 1.4.

  In the lean step, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent the EGR cooler and the like from being blocked by deposits resulting from unburned fuel.

  Here, as described above, if the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is leaner than the stoichiometric air-fuel ratio and the post-injection is performed without burning the fuel, PM can be removed by combustion. The PM can be removed by combustion during the lean step.

(2-5) HC Desorption Promotion Control The HC desorption promotion control is a control for promoting the desorption of HC trapped in the HC adsorption unit 42a (hereinafter referred to as adsorbed HC as appropriate). The HC desorption promotion control is basically executed to suppress the temperature of the oxidation catalyst 42 from becoming a high temperature of about 700 ° C., for example, when the engine 1 is cold.

  Therefore, the specific contents of the HC desorption promotion control in this configuration example will be described using the flowchart of FIG. The flow shown in FIG. 8 is repeatedly executed by the ECU 100 at a predetermined cycle, and is executed in parallel with the fuel injection control described above.

  First, in step S801, the ECU 100 reads various information. In step S801, the ECU 100 acquires at least the engine speed and the engine load, the NOx catalyst temperature, and the HC adsorption amount.

  Here, the ECU 100 stores a map in which the engine speed and the engine load are associated with the amount of HC contained in the exhaust gas. Based on such a map, the engine speed and the engine load, the ECU 100 estimates the amount of HC. ECU 100 estimates the amount of HC adsorption by integrating the estimated values.

  In step S802 following step S801, the ECU 100 sets a third threshold value that is a criterion for determining the amount of HC adsorption. This third threshold value is at least lower than the upper limit of the HC adsorption amount in the HC adsorption unit 42a. Further, the third threshold value is set smaller when the NOx catalyst temperature is higher than when it is low.

  Next, in step S803, the ECU 100 determines whether or not the HC adsorption amount exceeds a third threshold value. Here, when the HC adsorption amount exceeds the third threshold value (step S803: YES), the process proceeds to step S804 and post injection is performed, whereas when the HC adsorption amount is equal to or less than the third threshold value (step S803: NO). ) Skips step S804 and the like and returns.

  In step S804, the ECU 100 sets the post injection timing based on the operating state of the engine 1 and performs post injection. The post injection timing is set so that the fuel injected by the post injection burns in the combustion chamber 6 as in the active DeNOx control. When such post injection is performed, the exhaust gas having a higher temperature is discharged into the exhaust passage 40. As a result, the first catalyst 43 and thus the HC adsorption part 42a are warmed, and as a result, the release of HC from the HC adsorption part 42a is promoted.

  Next, in step S805, the ECU 100 determines whether or not the HC adsorption amount has become substantially zero. If the HC adsorption amount is substantially zero (step S805: YES), the process proceeds to step S806. If the HC adsorption amount is not substantially zero (step S805: NO), the process proceeds to step S806. The determination in S805 is repeated. That is, the ECU 100 repeats the determination in step S805 until the HC adsorption amount becomes substantially zero.

  Next, in step S806, the ECU 100 stops post injection and returns.

(2-6) Control Example Next, a specific example of control (particularly, active DeNOx control) by the ECU 100 will be described with reference to FIG. FIG. 9 is a time chart illustrating changes in various parameters when active DeNOx control is executed in this configuration example.

  In (d), (e), and (f) of FIG. 9, the solid line indicates an example, while the thick broken line indicates a conventional example. On the other hand, in FIG. 9, the solid lines in (b) and (c) indicate the magnitude of the accelerator opening and the amount of change, respectively, while the thin broken lines indicate the engine speed and the amount of change, respectively. Yes. In FIG. 9G, the solid line indicates the target boost pressure, and the thin broken line indicates the actual boost pressure.

  When the accelerator pedal is depressed at time t1, the accelerator opening degree starts increasing. Then, the target boost pressure starts to increase in conjunction with the increase in the accelerator opening. In this case, the engine speed increases with a delay in the change in the accelerator opening. Thereafter, it is assumed that the accelerator opening is constant on the way from time t2 to time t3, and the engine speed is constant after time t3.

  Here, it is assumed that the NOx occlusion amount is equal to or greater than the DeNOx determination value from the beginning (that is, the first condition is satisfied), and the value of the active DeNOx flag is “1”. . In this case, in the conventional example, as soon as the operating state of the engine 1 reaches the second region R12, the value of the post injection flag is set to “1”, and the post injection is immediately performed. In this configuration example, post-injection is permitted when the value of the post-injection flag is “1”, while post-injection is restricted when the value of the flag is “0”.

  However, when such a configuration is adopted, as shown in FIG. 9 (g), the actual boost pressure rises behind the target boost pressure. That is, when the fuel injected by the post injection should be burned in the combustion chamber 6, the air introduced into the combustion chamber 6 is insufficient, and unburned fuel such as HC is introduced into the exhaust passage 40. Will be. As a result, the exhaust gas having a relatively low temperature is discharged into the exhaust passage 40 as compared with the case where the fuel injected by the post injection is sufficiently burned in the combustion chamber 6. As a result, the HC contained in the exhaust gas is trapped by the HC adsorbing portion 42a, and the amount of HC adsorbing increases steeply as shown in FIG. 9 (e) (see FIG. 9 (e)). (See dashed line). As a result, when the exhaust gas temperature increases, the HC adsorbed in this way is released all at once, and the oxidation catalyst 42 may overheat as shown by the thick broken line in FIG.

  However, in this configuration example, even if the NOx occlusion amount is equal to or greater than the DeNOx determination value, the change amount of the accelerator opening and the change amount of the engine speed do not fall below the first and second threshold values, respectively. As long as the operating state of the engine 1 reaches the second region R12, the value of the active DeNOx flag is not set to “1”. In other words, when the amount of change in the accelerator opening and the engine speed has become sufficiently small, that is, as a result of the actual supercharging pressure rising to near the target supercharging pressure, the turbochargers 51 and 52 operate stably. Until this happens, active DeNOx control is limited.

  For example, in the example shown in FIG. 9, the value of the Acty DeNOx flag is set to “1” at a timing after t1 to t3 (specifically, time t4). If it does so, the fuel injected by post injection will burn more fully in the combustion chamber 6 compared with a prior art example. As a result, the unburned fuel introduced into the exhaust passage 40 decreases, and as a result, HC adsorption by the HC adsorption portion 42a is suppressed. As a result, as shown by the solid line in FIG. 9 (f), the excessive temperature rise of the oxidation catalyst 42 can be suppressed.

(3) Summary As described above, when the first condition as shown in step S503 in FIG. 5 is satisfied, the ECU 100 performs NOx from the NOx catalyst 41 by executing active DeNOx control using so-called post injection. The NOx catalyst 41 can be purified by removing it.

  However, the ECU 100 does not merely make a determination based on the first condition, but even when the first condition is satisfied, the second condition as shown in steps S505 to S506 in FIG. Until it is established, post-injection execution is limited. This second condition indicates that the turbochargers 51 and 52 are stable, such as whether or not the actual supercharging pressure has reached the vicinity of the target supercharging pressure.

  That is, when the second condition is satisfied, the intake air is sufficiently supplied to the combustion chamber 6. When post-injection is performed under such circumstances, the generation of unburned fuel due to the turbo lag can be suppressed compared to before the second condition is satisfied. As a result, the amount of HC adsorbed to the HC adsorbing portion 42a can be reduced, so that the excessive temperature rise of the catalyst due to the release of the adsorbed HC and thus the deterioration of the catalyst performance can be suppressed. Is possible.

  In general, turbo lag occurs when the accelerator pedal is depressed, that is, when the accelerator opening, and thus the target boost pressure, changes greatly. In other words, when the change in the accelerator opening is small, the target boost pressure also changes accordingly, so that the actual boost pressure is sufficiently higher than the target boost pressure thus changing. Can be followed. This suggests that the change amount of the accelerator opening can be used as an index for determining that the turbochargers 51 and 52 are operating stably.

  Therefore, as shown in step S505 of FIG. 5, it is determined that the second condition is satisfied when the change amount of the accelerator opening is equal to or less than a predetermined value, so that the turbochargers 51 and 52 are stabilized. It is possible to more accurately determine that it is operating.

  Also, generally, if additional injection such as post injection is performed when the accelerator opening greatly changes, the air supply does not catch up as described above, the air-fuel ratio becomes excessively rich, and torque fluctuations occur in the engine 1. Can occur. Such torque fluctuation is not preferable because it can give the passenger an uncomfortable feeling.

  On the other hand, as shown in steps S505 to S506 in FIG. 5, by limiting the execution of the post-injection until the second condition is satisfied, there is a possibility that the torque fluctuation of the engine 1 and thus the occupant may feel uncomfortable. It becomes possible to suppress as much as possible.

  In particular, according to the above configuration, the target torque of the engine 1 is based on the accelerator opening, while the amount of change in the accelerator opening satisfies the second condition. Since the amount of change in the accelerator opening is strongly related to the target torque of the engine 1, setting the amount of change as the second condition makes it possible to more accurately and effectively determine the timing at which post injection should be started. Judgment can be made.

  In general, when the accelerator opening is large, the engine load, and thus, the amount of fuel supplied to the combustion chamber 6 increases compared to when the accelerator opening is small. If it does so, since the room | chamber interior of the combustion chamber 6 becomes higher temperature, it will become difficult to discharge | emit unburned fuel. Therefore, even if the post-injection is started at an earlier timing, the problem related to the excessive temperature rise of the catalyst is less likely to occur as described above.

  Therefore, as shown in FIG. 6, when the accelerator opening is large, the first threshold value (threshold value) is set smaller. Since the second condition is established earlier by the amount that the first threshold value is set smaller, post injection can be started earlier.

  Further, if only the amount of change in the accelerator opening is monitored, there is a possibility of overlooking the situation where unburned fuel can be discharged, such as when the engine speed fluctuates relatively large.

  Therefore, as shown in step S506 in FIG. 5, not only the amount of change in the accelerator opening but also the amount of change in the engine speed can be monitored to more accurately determine the timing at which post injection should be started. It becomes like this.

  In particular, as described above, the determination based on the amount of change in the engine speed is more advantageous if it is performed simultaneously with the determination based on the amount of change in the accelerator opening. That is, as described above, monitoring only the amount of change in the accelerator opening may be insufficient to determine the timing at which post injection should be started.

  On the other hand, if only the amount of change in engine speed is monitored, the effect of depression of the accelerator pedal is not yet reflected in the magnitude of the engine speed, just after the accelerator pedal is depressed greatly. The situation may be overlooked.

  Therefore, by monitoring the amount of change in the accelerator opening and the engine speed, post injection can be started at a more accurate timing.

  In general, when the engine speed is large, the amount of heat generated per unit time due to the combustion of the air-fuel mixture increases compared to when the engine speed is small. If it does so, since the room | chamber interior of the combustion chamber 6 becomes higher temperature, it will become difficult to discharge | emit unburned fuel. Therefore, even if the post-injection is started at an earlier timing, the problem related to the excessive temperature rise of the catalyst is less likely to occur as described above.

  Therefore, as shown in FIG. 6, when the engine speed is large, the second threshold value (threshold value) is set low. Since the second condition is established earlier as much as the second threshold is set lower, post-injection can be performed earlier.

  Further, the NOx catalyst 41 can adsorb not only NOx but also so-called SOx. Therefore, the SOx adsorbed on the NOx catalyst 41 can be desorbed by alternately executing the rich step and the lean step as in the DeSOx control.

  By the way, if the NOx catalyst 41 is excessively heated, the SOx adsorbed on the NOx catalyst 41 may be aggregated and may be difficult to desorb from the NOx catalyst 41.

  However, as shown in the flow of FIG. 5, the excessive temperature rise of the NOx catalyst 41 can be suppressed by performing the post injection at a more appropriate timing. That is, such a configuration is effective not only for suppressing performance deterioration of the NOx catalyst 41 but also for smoothly desorbing SOx from the NOx catalyst 41.

  Further, for example, immediately after acceleration of the vehicle, there is a possibility that a deviation occurs between the target air-fuel ratio and the actual air-fuel ratio. Here, even if feedback control is performed on the fuel injection amount in post-injection, control is performed on the opposite side to the air-fuel ratio to be realized, and torque fluctuation may be prolonged.

  The above configuration is effective in that the occurrence of such torque fluctuation itself can be suppressed.

  Further, as described above, the ECU 100 can execute HC desorption promotion control as well as DeNOx control and DeSOx control. Then, it seems that the adsorption of HC can be suppressed without referring to the second condition in the active DeNOx control.

  However, even if the amount of HC adsorbed at the time when the active DeNOx control is started by the HC desorption promotion control as described above (and just before the control is started), immediately after the start of the active DeNOx control. In addition, there is still a possibility that a large amount of HC is adsorbed to the HC adsorbing portion 42a. In this case, too, the catalyst excessively rises in temperature, and there is a possibility of hindering smooth execution of DeSOx control.

  Therefore, as in this configuration example, by performing a combination of the HC desorption promotion control and the process of referring to the second condition in the active DeNOx control, the excessive temperature rise of the catalyst due to the release of HC is sufficiently suppressed. As a result, it is effective in securing the purification performance of the catalyst.

<< Other embodiments >>
In the above-described embodiment, the first condition is configured to determine the magnitude of the NOx occlusion amount. However, the present invention is not limited to such a configuration. For example, when the operating state of the engine 1 is in the second region R12, it may be determined that the first condition is satisfied.

  In the above-described embodiment, the second condition is configured to determine the magnitudes of changes in the accelerator opening and the engine speed. However, the present invention is not limited to such a configuration. For example, the actual boost pressure may be directly determined by the boost pressure sensor SW8. In this case, it may be determined that the second condition is satisfied when the difference between the actual supercharging pressure and the target supercharging pressure falls within a predetermined range.

1 Engine 6 Combustion chamber 10 Injector 11 Glow plug 40 Exhaust passage 41 NOx catalyst 42 Oxidation catalyst (catalyst)
51 1st turbocharger (turbocharger)
52 2nd turbocharger (turbocharger)
100 ECU (controller)
SW6 O2 sensor (oxygen concentration)

Claims (8)

An exhaust purification control device for an engine comprising a combustion chamber, a turbocharger provided in an exhaust passage leading to the combustion chamber, and a NOx catalyst provided in the exhaust passage,
An injector for injecting fuel into the combustion chamber;
A catalyst provided in the exhaust passage and having a hydrocarbon adsorption function;
A controller connected to the injector,
The controller makes the air-fuel ratio richer than before the first condition is satisfied by performing additional fuel injection after the fuel injection corresponding to the operating state of the engine when the predetermined first condition is satisfied. A control signal is output to the injector so as to perform NOx catalyst regeneration control.
The controller further executes the additional injection until a predetermined second condition indicating that the turbocharger is stable, even when the first condition is satisfied. An exhaust emission control device for an engine characterized by limiting. The engine exhaust gas purification control device according to claim 1,
The controller determines that the second condition is satisfied when the change amount of the accelerator opening is equal to or less than a predetermined first threshold value. The engine exhaust gas purification control apparatus according to claim 2,
The controller determines an engine target torque based on the accelerator opening, and an engine exhaust gas purification control device. The engine exhaust gas purification control apparatus according to claim 2 or 3,
When the accelerator opening is large, the controller sets the first threshold value lower than when the accelerator opening is small. The engine exhaust gas purification control apparatus according to any one of claims 1 to 4,
The engine exhaust gas purification control apparatus, wherein the controller determines that the second condition is satisfied when the change amount of the engine speed is equal to or less than a predetermined second threshold value. The engine exhaust gas purification control apparatus according to claim 5,
When the engine speed is high, the controller sets the second threshold value to be lower than that when the engine speed is low. The engine exhaust gas purification control device according to any one of claims 1 to 6,
When the predetermined third condition is satisfied, the controller makes the air-fuel ratio richer than before the third condition is satisfied by performing additional fuel injection after fuel injection corresponding to the operating state of the engine. An engine exhaust gas purification control apparatus that executes a second regeneration control that alternately performs a rich step and a lean step that makes the air-fuel ratio leaner than the rich step. The engine exhaust gas purification control apparatus according to any one of claims 1 to 7,
The exhaust passage is provided with an oxygen sensor for detecting the oxygen concentration in the exhaust gas flowing through the exhaust passage,
The controller performs feedback control of a fuel injection amount in the additional injection based on a detection result by the oxygen sensor and a target air-fuel ratio determined based on an operating state of the engine. Control device.

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