JP6610628B2 - Engine control device - Google Patents

Description

  The present invention relates to an engine control device including an engine in which a cylinder is formed and a NOx catalyst provided in an exhaust passage through which exhaust of the engine flows.

  Conventionally, NOx in the exhaust gas is occluded in a lean state where the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio (that is, a state where the excess air ratio λ is λ> 1). As a result, a NOx occlusion reduction type NOx catalyst that reduces in a state where the air-fuel ratio of the air-fuel mixture in the cylinder is close to the stoichiometric air-fuel ratio (λ≈1) or in a rich state smaller than the stoichiometric air-fuel ratio (λ <1) is known It has been.

  In an engine equipped with such a NOx catalyst, from the viewpoint of improving fuel efficiency, the air-fuel ratio of the air-fuel mixture in the cylinder is normally set to a lean state (λ> 1), and the NOx occlusion amount of the NOx catalyst increases. When the amount of NOx that can be stored by the NOx catalyst decreases (for example, when the NOx catalyst cannot be stored), the air-fuel ratio of the air-fuel mixture is made richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio (λ ≦ 1). The stored NOx is reduced.

  For example, in Patent Document 1, when the NOx occlusion amount of the NOx catalyst becomes a predetermined amount or more, the amount of EGR gas that is part of the exhaust gas recirculated to the intake air is increased in order to reduce NOx occluded in the NOx catalyst. What to do is disclosed. In this apparatus, the amount of fresh air introduced into the cylinder is reduced by increasing the amount of EGR gas, thereby enriching the air-fuel ratio of the mixture in the cylinder and the air-fuel ratio of the exhaust.

JP 2004-360593 A

  In the apparatus of Patent Document 1, the amount of fresh air introduced into the cylinder when reducing NOx stored in the NOx catalyst is reduced. Therefore, there is a possibility that sufficient engine torque cannot be obtained. In particular, if control for reducing this NOx during acceleration is performed, the acceleration performance deteriorates.

  The present invention has been made in view of the above circumstances, and in an engine equipped with a NOx catalyst, an engine control apparatus capable of improving acceleration while reducing NOx stored in the NOx catalyst. The purpose is to provide.

In order to solve the above problems, the present invention is provided in an engine main body in which a cylinder is formed and an exhaust passage through which exhaust discharged from the engine main body circulates. NOx catalyst that stores NOx in the exhaust when it is in a lean state, and reduces and releases the stored NOx when the air-fuel ratio of the exhaust is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio And a post-injection for injecting fuel into the cylinder at a timing retarded from the main injection. preparative a fuel injection device capable of carrying out, the air-fuel ratio of the exhaust gas is post-injection in the manner and within the cylinder becomes richer than the stoichiometric air-fuel ratio near or stoichiometric fuel within the cylinder A NOx reduction control for causing said main injection to the fuel injection device so as to burn and the post injection, the normal control not to perform the post injection in the fuel injection device is switched according to the operating condition performed Control means for controlling the fuel injection device so that the injection amount of the main injection becomes equal to or less than a predetermined upper limit value when the normal control and the NOx reduction control are executed. At the same time, when the NOx reduction control is performed, the upper limit value is set to a correction upper limit value that is larger than when the normal control is performed under the same operating conditions, and the control means is configured to perform the normal control. until the predetermined period after the NOx reduction control is terminated even if there is passed, setting the upper limit on the maximum correction value, it provides an engine control apparatus wherein the That.

  According to this device, the NOx reduction control is performed so that the air-fuel ratio of the exhaust is made close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio by performing post injection, so that NOx stored in the NOx catalyst is reduced. It is configured. Therefore, the amount of fresh air introduced into the cylinder can be reduced or reduced, and the acceleration performance during NOx reduction can be improved. In addition, in this device, during the NOx reduction control, the upper limit value of the injection amount of the main injection is increased so that more fuel can be injected in the main injection. Therefore, acceleration can be further enhanced.

Here, if the amount of main injection is simply increased, the amount of soot discharged from the engine may increase. However, in this device, post-injection is performed during NOx reduction control as described above, and the main injection amount is increased. Even if the amount of soot generated by the injection is increased, the soot can be burned during the subsequent post-injection fuel combustion. Therefore, according to this device, the amount of soot discharged from the engine can be kept small while enhancing the acceleration.
Further, in this apparatus, even when the normal control is performed, the upper limit value is the same large value (corrected upper limit value) as in the NOx reduction control until a predetermined period elapses after the NOx reduction control ends. Therefore, it is possible to prevent the upper limit from changing suddenly with the end of the NOx reduction control. Therefore, when the injection amount of the main injection is controlled to the upper limit value, it is possible to suppress a sudden change in the injection amount of the main injection and a sudden change in engine torque.

  In the above configuration, it is preferable that an upper limit value of the injection amount of the main injection is set based on an oxygen state in the cylinder.

  According to this configuration, since the upper limit value of the injection amount of the main injection is set based on the oxygen state in the cylinder having a high correlation with the generation amount of soot, the generation amount of soot can be reliably suppressed.

  In the above configuration, it is preferable that the control means sets an upper limit value of the injection amount of the main injection based on the oxygen concentration in the cylinder and before the combustion starts in the cylinder. Item 3).

  According to this configuration, since the upper limit value of the injection amount of the main injection is set based on the oxygen concentration of the cylinder that has a particularly high correlation with the amount of soot generation, the amount of soot generation can be more reliably suppressed. .

In the above configuration, the turbocharger is provided in the exhaust passage and supercharges intake air flowing into the cylinder, and the control means is configured to increase the supercharging pressure of the supercharger when the NOx reduction control is performed. It is preferable that the pressure is lower than the pressure during the normal control.

  According to this configuration, the air-fuel ratio of the exhaust can be more reliably made rich when performing the NOx reduction control. Further, as described above, when the injection amount of the main injection is increased and the exhaust energy is increased when the NOx reduction control is performed, it is possible to prevent the supercharging force and the engine torque from becoming excessively high.

In the above configuration, when the NOx reduction control is started immediately after the normal control is performed in a state where the injection amount of the main injection is smaller than the upper limit value, the control unit is configured to inject the main injection amount. Is preferably reduced (Claim 5).

  In this way, it is possible to prevent the engine torque from becoming excessively large by converting the combustion energy of the post-injected fuel into the engine torque.

In the above-described configuration, the control means, when stopping the post-injection with the termination of the NOx reduction control, it is preferable to increase the injection quantity of the main injection (claim 6).
In this way, when post-injection is stopped, the combustion energy of the post-injected fuel is eliminated, so that sudden changes in engine torque can be prevented.

Further, the present invention is provided in an engine main body in which a cylinder is formed and an exhaust passage through which exhaust discharged from the engine main body flows, and the air-fuel ratio of the exhaust is leaner than the stoichiometric air-fuel ratio. Control of an engine equipped with a NOx catalyst that stores NOx in the exhaust gas and reduces and releases the stored NOx when the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio A fuel capable of performing main injection for injecting fuel for obtaining engine torque into the cylinder and post-injection for injecting fuel into the cylinder at a timing retarded from the main injection The injector and the exhaust gas so that the air-fuel ratio of the exhaust is in the vicinity of the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and so that the fuel post-injected into the cylinder burns in the cylinder A control means for switching between NOx reduction control for causing the fuel injection device to perform the main injection and the post injection, and normal control for preventing the fuel injection device from performing the post injection according to operating conditions. The control means controls the fuel injection device so that the injection amount of the main injection is equal to or less than a predetermined upper limit value when the normal control is performed and when the NOx reduction control is performed, and the NOx reduction is performed. When the control is performed, the upper limit value is set to a correction upper limit value that is larger than that when the normal control is performed under the same operating conditions, and the control unit is configured so that the injection amount of the main injection is greater than the upper limit value. when the NOx reduction control immediately after the normal control is performed in a small state is started, the decrease the fuel injection amount of main injection, the engine control instrumentation of, characterized in that Providing (claim 7).

1 is a schematic configuration diagram of an engine system to which an engine control device according to an embodiment of the present invention is applied. It is the figure which showed control maps, such as an intake side bypass valve. It is a block diagram which shows the control system of an engine system. It is the figure which showed the control map of passive DeNOx control and active DeNOx control. It is the flowchart which showed the switching procedure of passive DeNOx control, active DeNOx control, and normal control. It is the flowchart which showed the first half part of the control procedure of fuel injection. It is the flowchart which showed the second half part of the control procedure of fuel injection. It is a time chart which showed the time change of each parameter typically.

  Hereinafter, an engine control apparatus according to an embodiment of the present invention will be described with reference to the drawings.

(1) Overall Configuration FIG. 1 is a schematic configuration diagram of an engine system 100 to which an engine control device of this embodiment is applied.

  The engine system 100 includes a four-stroke engine main body 1, an intake passage 20 for introducing air (intake air) into the engine main body 1, an exhaust passage 40 for discharging exhaust from the engine main body 1 to the outside, a first A turbocharger (supercharger) 51 and a second turbocharger (supercharger) 52 are provided. The engine system 100 is provided in a vehicle, and the engine body 1 is used as a drive source for the vehicle. The engine body 1 is a diesel engine, for example, and has four cylinders 2 arranged in a direction orthogonal to the paper surface of FIG.

  The engine body 1 includes a cylinder block 3 in which a cylinder 2 is formed, a cylinder head 4 provided on the upper surface of the cylinder block 3, and a piston 5 that is slidably inserted into the cylinder 2. Yes. A combustion chamber 6 is formed above the piston 5.

  The piston 5 is connected to the crankshaft 7, and the crankshaft 7 rotates about its central axis in accordance with the reciprocating motion of the piston 5.

  The cylinder head 4 includes an injector (fuel injection device) 10 that injects fuel into the combustion chamber 6 (inside the cylinder 2), and a glow plug 11 that raises the temperature of the fuel / air mixture in the combustion chamber 6. However, one set is provided for each cylinder 2. In the example shown in FIG. 1, the injector 10 is provided in the center of the ceiling surface of the combustion chamber 6 so as to face the combustion chamber 6 from above. The glow plug 11 has a heat generating portion that generates heat when energized, and is attached to the ceiling surface of the combustion chamber 6 so that the heat generating portion is located in the vicinity of the front end portion of the injector 10. ing. For example, the injector 10 is provided with a plurality of nozzle holes at its tip, and the glow plug 11 is located between the plurality of sprays from the plurality of nozzles of the injector 10 so that the heat generating portion is not in direct contact with the fuel spray. Have been placed.

  The injector 10 is an injection that is performed to obtain engine torque and injects fuel that burns in the vicinity of the compression top dead center into the combustion chamber 6, and is a retarded side of the main injection and combustion energy. It is possible to carry out post-injection in which fuel is injected into the combustion chamber 6 at a time when the ratio of conversion to engine torque is much smaller than that of main injection.

  The cylinder head 4 is generated in the intake port for introducing the air supplied from the intake passage 20 into the combustion chamber 6 of each cylinder 2, the intake valve 12 for opening and closing the intake port, and the combustion chamber 6 of each cylinder 2. An exhaust port for leading the exhausted gas to the exhaust passage 40 and an exhaust valve 13 for opening and closing the exhaust port are provided.

  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, a throttle valve 23, and a surge tank 24. The intake passage 20 is provided with an intake side bypass passage 25 that bypasses the second compressor 52a and an intake side bypass valve 26 that opens and closes the intake side bypass passage 25. The intake-side bypass valve 26 is switched between a fully closed state and a fully open state by a driving device (not shown).

  In the exhaust passage 40, in order from the upstream side, the turbine 52b of the second turbocharger 52 (hereinafter referred to as the second turbine 52b as appropriate) and the turbine 51b of the first turbocharger 51 (hereinafter referred to as the first of the first as appropriate). Turbine 51 b), first catalyst 43, PM filter (hereinafter referred to as DPF (Diesel particulate filter)) 44 that collects particulate matter (PM) in the exhaust, and exhaust passage 40 downstream of the DPF 44. The urea injector 45 for injecting urea into the SCR, the SCR (Selective Catalytic Education) catalyst 46 for purifying NOx using urea injected from the urea injector 45, and the unreacted ammonia discharged from the SCR catalyst 46 are oxidized and purified. Slip catalyst 47 is provided. It is

  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 first catalyst 43 includes a NOx catalyst 41 that purifies NOx, and an oxidation catalyst (hereinafter referred to as “oxidation catalyst”) that oxidizes hydrocarbons (HC), carbon monoxide (CO), and the like using oxygen in the exhaust gas to convert them into water and carbon dioxide. DOC (referred to as Diesel 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 (a state where λ> 1 where λ is the excess air ratio of the exhaust). This is a NOx storage reduction catalyst (NSC) that reduces in a state where the air-fuel ratio of exhaust is close to 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). . The first catalyst 43 is formed, for example, by coating the surface of a DOC catalyst material layer with an NSC catalyst material.

  Both the SCR catalyst 46 and the NOx catalyst 41 can purify NOx, but they have different temperatures at which the purification rate (NOx storage rate) increases, and the SCR catalyst 46 and the NOx storage rate (NOx storage rate). ) Increases when the temperature of the exhaust gas is relatively high, and the NOx purification rate of the NOx catalyst 41 increases when the temperature of the exhaust gas is relatively low.

  The exhaust passage 40 includes an exhaust-side bypass passage 48 that bypasses the second turbine 52b, an exhaust-side 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 that opens and closes the exhaust passage. A valve 54 is provided. The exhaust side bypass valve 49 and the waste gate valve 54 are switched between a fully closed state and a fully opened state by a driving device (not shown), respectively, and are changed to an arbitrary opening degree therebetween.

  FIG. 2 is a diagram showing a control map of these valves 49, 54 and 25. In the present embodiment, as shown in FIG. 2, the open / close states of the valves 49, 54, and 25 are determined in accordance with the engine speed and the engine load. Specifically, in the first rotation region A1 where the engine speed is low, the intake side bypass valve 25 is fully closed, and the openings of the exhaust side bypass valve 49 and the waste gate valve 54 depend on the engine speed and the engine load. Be changed. In the second rotation region A2 where the engine speed is higher than that in the first rotation region A1, the intake bypass valve and the exhaust side bypass valve 49 are fully opened, the supercharging by the second turbocharger 52 is stopped, and the waist Only the opening degree of the gate valve 54 is changed by the engine speed and the engine load.

  The engine system 100 according to the present embodiment includes an EGR device 55 that recirculates a part of exhaust gas to intake air. The EGR device 55 connects the portion of the exhaust passage 40 upstream of the upstream end of the exhaust-side bypass passage 49 and the portion of the intake passage 20 between the throttle 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.

(2) Control system The control system of an engine system is demonstrated using FIG. The engine system 100 of the present embodiment is controlled mainly by a PCM (control means, powertrain control module) 200 mounted on a vehicle. The PCM 200 is a microprocessor including a CPU, a ROM, a RAM, an I / F, and the like, and corresponds to a control unit according to the present invention.

  Information from various sensors is input to the PCM 200. For example, the PCM 200 detects a rotation speed sensor SN1 that detects the rotation speed of the crankshaft 7, that is, the engine rotation speed, and an intake air amount that is provided near the air cleaner 21 and that is the amount of fresh air (air) that flows through the intake passage 20. An air flow sensor SN3, an intake pressure sensor SN3 for detecting the pressure of intake air in the surge tank 24 after being supercharged by the turbochargers 51 and 52, that is, the supercharging pressure, provided in the surge tank 24, and the oxygen concentration of the exhaust gas The exhaust passage 40 is electrically connected to an exhaust O2 sensor SN4 or the like that detects the oxygen concentration of exhaust that passes through a portion between the first turbocharger 51 and the first catalyst 43, and these Input signals from the sensors SN1 to SN4 are received. Further, the vehicle is provided with an accelerator opening sensor SN5 that detects an accelerator opening that is an opening of an accelerator pedal (not shown) operated by a driver, a vehicle speed sensor SN6 that detects a vehicle speed, and the like. Detection signals from these sensors SN5 and SN6 are also input to the PCM 200. The PCM 200 controls the injector 10 and the like by executing various calculations and the like based on input signals from the sensors (SN1 to SN6 and the like).

(2-1) Normal Control In the present embodiment, during normal operation in which DeNOx control, DPF regeneration control, and DeSOx control, which will be described later, are not performed, the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 and the exhaust gas are improved in order to improve fuel efficiency. Normal control is performed so that the air-fuel ratio of the engine is leaner than the theoretical air-fuel ratio (λ> 1). In this normal control, the post injection is stopped. In the present embodiment, only the main injection is performed in the normal control.

(2-2) DeNOx Control DeNOx control, which is control for reducing NOx occluded in the NOx catalyst 41 (hereinafter referred to as occluded NOx as appropriate) and releasing it from the NOx catalyst 41, will be described.

  As described above, in the NOx catalyst 41, the stored NOx is reduced in a state where the air-fuel ratio of the exhaust is close to 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 exhaust as compared with the normal control.

  As one method for reducing the air-fuel ratio of the exhaust, it is conceivable to reduce the amount of fresh air (air) introduced into the combustion chamber 6. However, if the amount of fresh air is simply reduced, the engine torque may not be obtained properly. In particular, if the amount of fresh air is reduced during acceleration, the acceleration performance may deteriorate.

  Therefore, in this embodiment, post-injection is performed to reduce the stored NOx so as to reduce the air-fuel ratio of the exhaust gas while suppressing the amount of fresh air to be reduced. That is, in DeNOx control, the PCM 200 causes the injector 10 to perform post injection in addition to main injection, thereby reducing the air-fuel ratio of the exhaust. In the present embodiment, the amount of fresh air is slightly reduced during DeNOx control. Specifically, the throttle valve 23 is closed from the normal control, and at least one of the exhaust-side bypass valve 49 and the wastegate valve 54 is opened from the normal control so that the boost pressure is higher than that from the normal control. Is also reduced.

  In the present embodiment, this DeNOx control is performed only in the first region R1 and the second region R2 shown in FIG. In the first region R1, the engine speed is equal to or higher than a first reference speed N1 set in advance and equal to or lower than a second reference speed N2 set in advance. The engine load is equal to or higher than a first reference load Tq1 set in advance. This is an area below the set second reference load Tq2. The second region R2 is a region where the engine load is higher than that of the first region R1, and the engine load is equal to or higher than a preset third reference load Tq3.

  In the first region R1, active DeNOx control (NOx) that performs post-injection at the timing at which post-injected fuel burns in the combustion chamber 6 (the first half of the expansion stroke, for example, 30 to 70 ° CA after compression top dead center). Reduce control). When the active DeNOx control is performed, the air-fuel mixture is heated by energizing the glow plug 11 in order to promote the combustion of the post-injected fuel.

  On the other hand, in the second region R2, the passive DeNOx control is performed in which the post-injected fuel is not burned in the combustion chamber 6 (second half of the expansion stroke, for example, 110 ° CA after compression top dead center). To do.

  This is due to the following reason.

  In a region where the engine load is low or the engine load is relatively high but the engine speed is low, the temperature of the NOx catalyst 41 tends to be lower than the temperature at which the stored NOx can be reduced as the exhaust gas temperature is low. Therefore, in this embodiment, DeNOx control is stopped in this region.

  In addition, as described above, post injection is performed in the DeNOx control. If 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, the post-injected fuel is preferably 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. It is difficult to sufficiently mix the post-injected fuel and air until the gas in the chamber 6 is exhausted, and the post-injected fuel may not be sufficiently combusted in the combustion chamber 6. is there. Moreover, there exists a possibility that wrinkles may increase when the said mixing is inadequate. Accordingly, the DeNOx control is basically stopped in such a region.

  However, in the second region R2 where the engine load is very high, the air-fuel ratio of the exhaust gas can be kept small even during normal operation due to the large injection amount of the main injection (hereinafter referred to as the main injection amount as appropriate). . Therefore, in the second region R2, the amount of post-injection necessary for reducing the stored NOx (hereinafter referred to as post-injection amount as appropriate) is reduced, and unburned fuel is discharged into the exhaust passage 40. The influence can be suppressed small.

  Therefore, in the present embodiment, as described above, in the first region R1, active DeNOx control is performed in which the post-injected fuel burns in the combustion chamber 6, and in the second region R2, the post-injected fuel is Passive DeNOx control that does not cause combustion in the combustion chamber 6 is performed. The second region R2 is a region where the temperature of the exhaust is sufficiently high and the DOC catalyst 42 is sufficiently activated. Therefore, unburned fuel discharged to the exhaust passage 40 is purified by the DOC catalyst 42.

  Here, the NOx reduction control in the claims refers to active DeNOx control.

(2-3) Switching Procedure Next, a switching procedure between normal control, active DeNOx control, and passive DeNOx control will be described with reference to the flowchart of FIG. In this embodiment, a switching flag is set as a flag representing these switching. When the switching flag is 0, normal control is performed, and when the switching flag is 1, active DeNOx control is performed, and the switching flag is set. In the case of 2, passive DeNOx control is implemented.

  First, the PCM 200 reads various types of vehicle information in step S10. For example, the PCM 200 acquires the NOx catalyst temperature that is the temperature of the NOx catalyst 41, the SCR temperature that is the temperature of the SCR catalyst 46, and the NOx occlusion amount that is the amount of NOx occluded in the NOx catalyst 41.

  The NOx catalyst temperature is estimated based on, for example, a temperature detected by a temperature sensor provided immediately upstream of the NOx catalyst 41. The SCR temperature is estimated based on, for example, a temperature detected by a temperature sensor provided immediately upstream of the SCR catalyst 46. Further, the NOx occlusion amount is obtained, for example, by accumulating the NOx amount in the exhaust estimated based on the operating state of the engine body 1, the exhaust flow rate, the temperature, and the like.

  Next, in step S11, the PCM 200 determines whether or not the SCR temperature is lower than a preset SCR determination temperature. The SCR determination temperature is the minimum value of the SCR catalyst temperature at which NOx can be purified by the SCR catalyst 46.

  When the determination in step S11 is NO and the SCR temperature is equal to or higher than the SCR determination temperature and NOx can be appropriately purified by the SCR catalyst 46, the process proceeds to step S31, and the PCM 200 sets the switching flag to 0. Normal control. On the other hand, if the determination in step S11 is yes, the process proceeds to step S12.

  In step S12, the PCM 200 determines whether or not the NOx catalyst temperature is equal to or higher than a preset NOx reducible temperature. The NOx reducible temperature is the minimum value of the NOx catalyst temperature at which the NOx catalyst 41 can reduce the stored NOx.

  If the determination in step S12 is NO and the NOx catalyst temperature is less than the NOx reducible temperature, the process proceeds to step S31, and the PCM 200 sets the switching flag to 0 and performs normal control. On the other hand, if the determination in step S12 is yes, the process proceeds to step S13.

  In step S13, the PCM 200 determines whether or not the engine body 1 is operated in the first region R1. If this determination is NO, the process proceeds to step S21. On the other hand, if this determination is YES, the process proceeds to step S14.

  In step S14, the PCM 200 determines whether or not active DeNOx control has never been executed after the engine is started. If this determination is YES, the process proceeds to step S15. On the other hand, if this determination is NO, the process proceeds to step S16.

  In step S15, the PCM 200 determines whether or not the NOx occlusion amount is equal to or greater than a preset first occlusion amount determination value. The first storage amount determination value is set to a value that is somewhat lower than the maximum value of the amount of NOx that can be stored by the NOx catalyst 41, for example.

  If the determination in step S15 is NO and the NOx storage amount is less than the first storage amount determination value, it is not necessary to perform the reduction process of the NOx catalyst 41, so the PCM 200 proceeds to step S31 and sets the switching flag to 0. Set and perform normal control. On the other hand, if the determination in step S15 is yes, the process proceeds to step S17. In step S17, the PCM 200 sets the switching flag to 1 and performs active DeNOx control.

  On the other hand, in step S16 which proceeds when the determination in step S14 is NO, the PCM 200 determines whether or not the NOx occlusion amount is equal to or greater than a preset second occlusion amount determination value. The second storage amount determination value is set to a value larger than the first storage amount determination value. For example, the second storage amount determination value is set to a value near the maximum value of the amount of NOx that can be stored by the NOx catalyst 41. If the determination in step S16 is NO and the NOx storage amount is less than the second storage amount determination value, the PCM 200 proceeds to step S31, sets the switching flag to 0, and performs normal control. On the other hand, if the determination in step S16 is YES, the PCM 200 proceeds to step S17, sets the switching flag to 1, and performs active DeNOx control.

  In step S21 that proceeds when the determination in step S13 is NO, the PCM 200 determines whether or not the engine body 1 is operated in the second region R2. If this determination is NO, the PCM 200 proceeds to step S31, sets the switching flag to 0, and performs normal control. On the other hand, if this determination is YES, the process proceeds to step S22.

  In step S22, the PCM 200 determines whether the NOx storage amount is equal to or greater than a preset third storage amount determination value. The third storage amount determination value is set to a value smaller than the first storage amount determination value. For example, the third storage amount determination value is set to a value that is about half the maximum value of the amount of NOx that can be stored by the NOx catalyst 41.

  If the determination in step S22 is NO and the NOx occlusion amount is less than the third occlusion amount determination value, the PCM 200 proceeds to step S31 and sets the switching flag to 0 because there is no need to perform a reduction process of the NOx catalyst. Then, normal control is performed. On the other hand, if the determination in step S22 is yes, the process proceeds to step S23.

  In step S23, it is determined whether or not the post injection amount calculated in the procedure described later is less than a preset reference post injection amount. The reference post-injection amount is set, for example, from the viewpoint of suppressing oil dilution, or in addition, from the viewpoint of suppressing fuel consumption deterioration due to the execution of passive DeNOx control. That is, in the passive DeNOx control, since the post-injected fuel is performed at a retarded timing at which the fuel is not burned in the combustion chamber 6, unburned fuel is likely to leak from the combustion chamber 6 to the crankcase. Therefore, in the present embodiment, the determination in step S23 is performed so that the passive DeNOx control is performed only when the post injection amount is less than the reference post injection amount and the leakage can be suppressed to some extent.

  That is, if the determination in step S23 is YES, the process proceeds to step S24, and the PCM 200 sets the switching flag to 2 and performs passive DeNOx control. On the other hand, if the determination in step S23 is NO, the PCM 200 proceeds to step S31, sets the switching flag to 0, and performs normal control.

  Thus, in the present embodiment, the SCR temperature is lower than the SCR determination temperature, the NOx catalyst temperature is equal to or higher than the NOx reducible temperature, the engine body 1 is operated in the first region R1, and the NOx occlusion amount is set. Active DeNOx control is performed when the amount is equal to or greater than the fixed amount. However, when the active DeNOx control has never been executed after the engine is started, the predetermined amount is set to a relatively small value in order to ensure the NOx purification performance of the NOx catalyst 41.

  In order to suppress oil dilution caused by post injection, it is determined after the determination in step S16 whether or not the travel distance from the previous execution time of the active DeNOx control is equal to or greater than a predetermined determination distance. If YES, the process proceeds to step S17 to perform active DeNOx control, while if this determination is NO, the process proceeds to step S31, and the normal control may be performed with the switching flag set to 0.

  In this embodiment, the SCR temperature is lower than the SCR determination temperature, the NOx catalyst temperature is equal to or higher than the NOx reducible temperature, the engine is operated in the second region R2, the NOx occlusion amount is equal to or greater than a predetermined amount, and the post Passive DeNOx control is performed when the injection amount of injection is less than a predetermined amount.

(2-4) Fuel Injection Control Next, the procedure of the fuel injection control procedure will be described using the flowcharts of FIGS. 6 and 7.

  First, the PCM 200 reads various types of vehicle information in step S51. For example, the PCM 200 detects the engine speed detected by the speed sensor SN1, the intake air amount detected by the air flow sensor SN2, the oxygen concentration of the exhaust gas detected by the exhaust O2 sensor SN4, and the accelerator opening sensor SN5. The accelerator opening, the vehicle speed detected by the vehicle speed sensor SN6, and the like are acquired.

  Next, in step S52, the PCM 200 estimates the intake oxygen concentration and the total intake gas amount. The intake oxygen concentration is an oxygen concentration in the combustion chamber 6 and is an oxygen concentration before combustion is performed. For example, the PCM 200 estimates the intake oxygen concentration based on the intake air amount, the exhaust oxygen concentration, the opening degree of the EGR valves 57 and 60, and the like. The total intake gas amount is the total amount of gas existing in the combustion chamber 6 (gas existing in the combustion chamber 6 immediately before the start of combustion). For example, the PCM 200 estimates the total intake gas amount based on the intake air amount, the opening degree of the EGR valves 57 and 60, and the like.

  Next, in step S53, the PCM 200 calculates a target vehicle acceleration that is a target value of the acceleration of the vehicle based on the accelerator opening and the vehicle speed.

  Next, in step S54, the PCM 200 sets a target engine torque that is a target value of the engine torque, that is, a requested engine torque, based on the target vehicle acceleration, the engine speed, and the like.

  Next, in step S55, the PCM 200 sets a basic main injection amount that is a basic value of the main injection amount based on the target engine torque, the engine speed, and the like.

  Here, in the active DeNOx control, the post-injected fuel burns in the combustion chamber 6. As a result, part of the combustion energy of the post-injected fuel is converted into engine torque. Therefore, the basic main injection amount at the time of active DeNOx control is the basic main injection amount at the time of other control (during normal control and passive DeNOx control) so that the target engine torque is realized by main injection and part of post injection. The amount is slightly smaller than the injection amount. That is, the basic main injection amount is reduced in the active DeNOx control so that the engine torque does not fluctuate greatly before and after the start and end of the active DeNOx control.

  Next, in step S56, the PCM 200 determines whether or not the switching flag is 1, that is, whether or not active DeNOx control is being performed.

  If the determination in step S61 is YES and the active DeNOx control is being performed, the process proceeds to step S63.

  On the other hand, if the determination in step S61 is NO and the active DeNOx control is not being performed, the PCM 200 proceeds to step S62, and after the switch flag changes from 1 to 0 or 2, a preset reference time (predetermined) It is determined whether or not (period) has elapsed. That is, it is determined whether or not the reference time has elapsed since the end of the active DeNOx control. If the determination in step S62 is no, the process proceeds to step S63. On the other hand, if the determination in step S62 is yes, the process proceeds to step S64.

  As described above, in the present embodiment, the process proceeds to step S63 during the execution of the active DeNOx control and from the end of the active DeNOx control until the reference time elapses, and in other cases, the process proceeds to step S64.

  In step S64, the PCM 200 sets the exhaust O2 guard value to the first exhaust O2 guard value. On the other hand, in step S63, the PCM 200 sets the exhaust O2 guard value to a value that is the second exhaust O2 guard value and smaller than the first exhaust O2 guard value.

  The exhaust O2 guard value is a gas after main combustion that can suppress the amount of soot generated by combustion of fuel injected into the combustion chamber 6 by main injection (hereinafter referred to as main combustion as appropriate) below a predetermined amount. Is the minimum value of the oxygen concentration (exhaust oxygen concentration when only main injection is performed). In other words, there is a high correlation between the amount of soot produced by the main combustion and the oxygen concentration of the gas after the main combustion, and if this oxygen concentration can be maintained above a predetermined value, the amount of soot produced by the main combustion is determined. The exhaust O2 guard value is a lower limit value of the oxygen concentration of the gas after the main combustion that can suppress the amount of soot generated due to the main combustion to a predetermined amount or less.

  Here, in the active DeNOx control, as described above, the post injection is performed in addition to the main injection, and the fuel injected into the combustion chamber 6 by the post injection is controlled to burn in the combustion chamber 6. . Therefore, when the active DeNOx control is performed, a part of the soot generated by the main combustion is combusted when the fuel injected into the combustion chamber 6 by the post injection is combusted. Therefore, when active DeNOx control is performed and when other operations are performed (when normal control or passive DeNOx control is performed), even when the amount of soot generated by the main combustion is the same, when active DeNOx control is performed However, the amount of soot discharged from the engine main body 1 is smaller than during other operations, and the exhaust O2 guard value can be made smaller than during other operations when active DeNOx control is performed.

  Therefore, in the present embodiment, the exhaust O2 guard value is set to the first exhaust O2 guard value during other operations, and the exhaust O2 guard value is set to a value smaller than the first exhaust O2 guard value during active DeNOx control. The second exhaust O2 guard value.

  Specifically, in the PCM 200, the values of the first exhaust O2 guard value and the second exhaust O2 guard value that are set in advance through experiments or the like are stored in a map for the engine speed and the engine torque. In these maps, even if the engine speed and the engine torque are the same, the second exhaust O2 guard value extracted from the map of the second exhaust O2 guard value is extracted from the first exhaust O2 guard map. It is set to be smaller than the O2 guard value. Further, in the present embodiment, under the operating conditions where the engine speed and the engine torque are the same, the amount of soot discharged from the engine main body 1 is the same during DeNOx control and during other operations. Value is set. In step S57, the PCM 200 extracts the exhaust O2 guard value from the map of the first exhaust O2 guard. In step S58, the PCM 200 extracts the exhaust O2 guard value from the map of the second exhaust O2 guard.

  After step S63 or step S64, the process proceeds to step S65. In step S65, the PCM 200 sets the main injection guard amount based on the intake oxygen concentration, the total intake gas amount, and the exhaust O2 guard value.

  The main injection guard amount is an upper limit value of the main injection amount, and is a value of the main injection amount when the oxygen concentration of the gas after main combustion becomes the exhaust O2 guard value. The main injection guard amount is calculated from the exhaust O2 guard value, the intake oxygen concentration and the total intake gas amount calculated in step S52.

  Specifically, the oxygen concentration of the gas after the main combustion is a value obtained by subtracting the oxygen concentration consumed by the main combustion from the intake oxygen concentration, and the amount of oxygen consumed by the main combustion is predetermined to the main injection amount. It is a value multiplied by a coefficient. Accordingly, assuming that the intake oxygen concentration is X_inO2, the total intake gas amount is Mtotal, the main injection amount is Qm, and the coefficient is K, the oxygen concentration X_exO2 of the gas after main combustion is X_exO2 = X_inO2- (K × Qm) / Mtotal Is calculated by Therefore, using this equation, the exhaust O2 guard value is applied to X_exO2, the intake oxygen concentration and total intake gas amount calculated in step S52 are applied to X_inO2 and Mtotal, respectively, and a preset value is applied to K. , Qm is calculated, and this Qm is calculated as the main injection guard amount.

  Thus, in the present embodiment, the main injection guard amount that is the upper limit value of the main injection amount is calculated based on the oxygen state in the combustion chamber 6 using the intake oxygen concentration and the total intake gas amount.

  Next, in step S66, the PCM 200 calculates whether or not the basic main injection amount calculated in step S55 is less than or equal to the main injection guard amount calculated in step S63 or step S64.

  If the determination in step S66 is YES, the PCM 200 proceeds to step S67 and sets the basic main injection amount to the final main injection amount. On the other hand, if the determination in step S66 is NO, the PCM 200 proceeds to step S68, and sets the main injection guard amount calculated in step S63 or step S64 as the final main injection amount. That is, in step S68, the PCM 200 limits the main injection amount to a main injection guard amount that is smaller than the basic main injection amount. After step S67 or S68, the process proceeds to step S69.

  In step S69, the PCM 200 determines whether or not the switching flag is 1 or 2, that is, whether or not the active DeNOx control is being performed or the passive DeNOx control is being performed. If this determination is NO and normal control is being performed, the PCM 200 proceeds to step S71, sets the post injection amount to 0, and proceeds to step S72.

  On the other hand, if the determination in step S69 is yes, the process proceeds to step S70. In step S70, the PCM 200 calculates the post injection amount from the final main injection amount set in step S63 or S64 and the preset DeNOx control air-fuel ratio. The DeNOx control air-fuel ratio is an air-fuel ratio of the air-fuel mixture in the cylinder necessary for reducing the stored NOx in the NOx catalyst 41, and is set in advance. As described above, this air-fuel ratio is set in the vicinity of the stoichiometric air-fuel ratio or a value smaller than the stoichiometric air-fuel ratio. For example, the DeNOx control air-fuel ratio is set so that the excess air ratio λ becomes a value between 0.94 and 1.06. After step S70, the process proceeds to step S72.

  In step S72, the PCM 200 causes the injector 10 to main-inject the fuel corresponding to the final main injection amount set in step S67 or S68, and posts the fuel corresponding to the post-injection amount set in step S70 or S71 to the injector 10. Let spray. When the post injection amount is set to 0 in step S71, the post injection is stopped. After step S72, the process ends (returns to step S51).

  Thus, in this embodiment, the injection amount of the main injection is suppressed to be equal to or less than the main injection guard amount so that the amount of soot discharged from the engine body 1 is equal to or less than a predetermined amount. Then, during the execution of the active DeNOx control and until the reference time elapses after the end of the active DeNOx control, the main injection guard amount is made larger than that during other operations.

(3) Action, etc. FIG. 8 schematically shows the time change of each parameter when the above control is performed. FIG. 8 shows that active DeNOx control is started at time t1 during steady running (running with a constant accelerator opening and a constant vehicle speed), and the accelerator opening is stepped on and acceleration is performed at time t2. It is a figure when active DeNOx control is complete | finished at the time t4 in the middle of acceleration.

In the graph of the main injection guard amount in FIG. 8, the first main injection guard amount is a main injection guard amount calculated when the exhaust O2 guard value is the first exhaust O2 guard value, and the second main injection guard amount. Is a main injection guard amount calculated when the exhaust O2 guard value is set to the second exhaust O2 guard value. Specifically, the first main injection guard amount is the first exhaust O2 guard value dispensed based on the current engine speed and engine torque, the current intake oxygen concentration, and the current total intake gas amount. And the second main injection guard amount is calculated based on the current engine speed and the engine torque, and the second exhaust O2 guard value that is dispensed based on the current engine speed and the engine torque. , And the current intake oxygen concentration and the current total intake gas amount, and the main injection guard amount calculated according to the procedure related to step S65. The second main injection guard amount corresponds to the “correction upper limit value” in the present invention.

  As described above, the second exhaust O2 guard value is set to be smaller than the first exhaust O2 guard value even at the same engine speed and engine torque. Therefore, since the current values are used for the engine speed, engine torque, intake oxygen concentration, and total intake gas amount, the first main injection guard amount is larger than the second main injection guard amount as shown in FIG. Small value.

  As described above with reference to steps S61 to S65 in FIG. 7, in this embodiment, the exhaust O2 guard value is switched between the first exhaust O2 guard value and the second exhaust O2 guard value according to the determination in step S62. In practice, only one value is calculated as the main injection guard amount, but here, in order to facilitate the explanation, the first main injection guard amount and the second main injection amount are calculated. The description will be made using the guard amount.

  As shown in FIG. 8, in steady running until time t1, normal control is performed as the switching flag is 0, post-injection is stopped (post-injection amount is set to 0), and the air-fuel mixture The excess air ratio λ is set to a value larger than 1.

  On the other hand, when the switching flag becomes 1 and active DeNOx control is started at time t1, post injection is started (the post injection amount is set to a value larger than 0). In the present embodiment, as described above, as the active DeNOx control starts, the throttle valve 23 is controlled to the closed side, and at least one of the exhaust side bypass valve 49 and the waste gate valve 54 is controlled to the open side. Is done. With these controls, the excess air ratio λ of the air-fuel mixture gradually decreases from time t1. Further, as shown in FIG. 8, the supercharging pressure is reduced as compared with the case where the normal control is continued. Moreover, although illustration is abbreviate | omitted, the air quantity and oxygen amount which are introduce | transduced in the cylinder 2 fall.

  In addition, at time t1, the actual main injection amount decreases as the post injection is started. The actual main injection amount is the main injection amount that is finally injected.

  Specifically, normal control is performed until time t1. Therefore, the final main injection guard amount that is the final main injection guard amount (the main injection guard amount actually calculated in step S65) is the first main injection guard amount calculated using the first exhaust O2 guard value. It is. In the example of FIG. 8, the actual main injection amount is set to the basic main injection amount as the basic main injection amount is less than the first main injection guard amount during the period up to time t1. Further, after time t1, the final main injection guard amount becomes the second main injection guard amount, but the second main injection guard amount is larger than the first main injection guard amount, and the actual main injection amount is also immediately after time t1. This is the basic main injection amount. Here, as described above, the basic main injection amount at the time of active DeNOx control is set to an amount smaller than the basic main injection amount at the time of other control (during normal control and passive DeNOx control). Accordingly, when post injection is started at time t1, the actual main injection amount is reduced. Note that the actual main injection amount is set to the first main injection guard amount immediately before time t1 (the actual main injection amount becomes the first main injection guard amount as the basic injection amount is larger than the first main injection guard amount). In other words, the basic main injection amount calculated with the start of the active DeNOx control at time t1 may be calculated to a value larger than the first main injection guard amount. When the final main injection guard amount becomes the second main injection guard amount larger than the first main injection guard amount at time t1, the actual main injection amount may increase. That is, in the present embodiment, when the active DeNOx control is started in a state where the main injection amount is the basic main injection amount and is smaller than the first main injection guard amount, the main injection amount is decreased. It has become.

  As described above, after time t1, as the active DeNOx control is performed, the final main injection guard amount is switched to the second main injection guard amount, and the value is increased.

  Specifically, as described above, the amount of air and the amount of oxygen introduced into the cylinder 2 decrease after time t1. Accordingly, after time t1, the first and second main injection guard amounts and the final main injection guard amount decrease.

  When acceleration is started at time t2 and the target engine torque is increased, the basic main injection amount, that is, the actual main injection amount is increased accordingly. Along with this, the supercharging pressure increases.

  Here, in the example of FIG. 8, the basic main injection amount (actual main injection amount) exceeds the first main injection guard amount at time t3. That is, the O2 concentration of the gas generated by the main combustion is reduced to less than the first exhaust O2 guard value. However, in this embodiment, the final main injection guard amount at this time is set to a second exhaust O2 guard amount that is larger than the first exhaust O2 guard amount. Accordingly, the actual main injection amount is a basic main injection amount that exceeds the first main injection guard amount, and an amount of fuel corresponding to the target engine torque is injected by the main injection.

  Thereafter, when the switching flag becomes 0 at time t4 and the active DeNOx control is terminated, the post injection is stopped (the post injection amount is set to 0). Then, the actual main injection amount (basic main injection amount) is increased. Further, the throttle valve 23 is controlled to the open side, and at least one of the exhaust side bypass valve 49 and the waste gate valve 54 is controlled to the closed side. With these controls, the excess air ratio λ of the air-fuel mixture gradually increases from time t1. Further, the supercharging pressure increases at a higher rate than the rate of increase up to time t4. Although illustration is omitted, the amount of air and the amount of oxygen introduced into the cylinder 2 increase at a higher rate than the rate of increase up to time t4.

  As described above, as the boost pressure, the amount of air introduced into the cylinder 2, and the amount of oxygen increase, the amount of each main injection guard also increases. Specifically, first, the amount of air and oxygen introduced into the cylinder 2 due to the change of the throttle valve 23 increases, so that each main injection guard amount increases until time t5. Thereafter, each main injection guard amount further increases as the supercharging pressure increases.

  Here, in the present embodiment, as described above, the second exhaust O2 guard value is set to the exhaust O2 guard value until the reference time elapses even after the active DeNOx control ends. Therefore, from time t4 to time t5 when the reference time has elapsed, the final main injection guard amount is set to the second main injection guard amount, and after time t5, the final main injection guard amount is switched to the first main injection guard amount. Then, after time t5, acceleration under normal control is continued. As shown in FIG. 8, time t5 is the time when the excess air ratio λ of the air-fuel mixture returns to about the value at the time of normal control, and in this embodiment, the active DeNOx control is finished with the reference time in this way. Then, the time until the time when the excess air ratio λ of the air-fuel mixture returns to about the value at the time of normal control is set.

  Thus, in the present embodiment, the actual main injection amount (basic main injection amount) exceeds the first main injection guard amount at time t3, but the final main injection guard amount at time t3 is the first main injection guard amount. By setting the second main injection guard amount to be higher, the actual main injection amount can be made the basic main injection amount corresponding to the target engine torque. Therefore, the target engine torque can be realized. That is, at time t3 (under operating conditions where the engine speed, target engine torque, total intake gas amount, and intake oxygen concentration have the values at time t3) and after time t3, normal control is temporarily performed. When post injection is stopped, the actual main injection amount is suppressed to a value smaller than the basic main injection amount, and therefore the engine torque cannot be increased to the target engine torque. This can be realized to increase acceleration.

  As described above, in the present embodiment, the post-injection is performed to reduce the stored NOx, which is NOx stored in the NOx catalyst 41, by setting the air-fuel ratio of the exhaust to be near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio of the exhaust gas can be brought into a rich state where the stored NOx can be reduced without reducing the amount of fresh air introduced into the combustion chamber 6 or while suppressing the amount of reduction. Therefore, occluded NOx can be appropriately reduced while avoiding the deterioration of acceleration associated with a reduction in the amount of fresh air.

  Moreover, in the present embodiment, the active DeNOx control is performed so that the post-injected fuel is burned in the combustion chamber 6, and the main injection guard amount (final main injection guard amount) at this time is set to be higher than that during other operations. It is getting bigger. Therefore, in order to suppress the amount of soot discharged from the engine main body 1 at the time of acceleration or the like when the intake oxygen concentration or the like becomes smaller than a desired value as the intake air delays, the main injection amount is set to the main injection amount. Even when the injection guard amount must be kept below, the soot generated by the main combustion is burned by the combustion of the post-injected fuel, thereby suppressing the amount of soot discharged from the engine body 1 and reducing the main injection. A large amount of injection can be secured. Therefore, acceleration performance can be further enhanced while maintaining good exhaust performance.

  In the present embodiment, after the end of the active DeNOx control, the final main injection guard amount is changed to the second main injection guard amount calculated using the second exhaust O2 guard value until the reference time elapses. It is set. Therefore, it is possible to suppress a sudden change in the main injection amount and a sudden change in the engine torque immediately after the end of the active DeNOx control.

1 Engine Body 2 Cylinder 6 Combustion Chamber 10 Injector (Fuel Injection Device)
41 NOx catalyst 200 PCM (control means)

Claims (7)

NOx in the exhaust when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, provided in the engine main body in which the cylinder is formed and the exhaust passage through which the exhaust discharged from the engine main body flows. And an NOx catalyst for reducing and releasing the stored NOx when the air-fuel ratio of the exhaust gas is close to or richer than the stoichiometric air-fuel ratio,
A fuel injection device capable of performing main injection for injecting fuel for obtaining engine torque into the cylinder, and post injection for injecting fuel into the cylinder at a timing retarded from the main injection;
The main injection and the fuel are injected into the fuel injection device so that 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 so that the fuel post-injected into the cylinder burns in the cylinder. Control means for switching between NOx reduction control for performing post-injection and normal control for preventing the fuel injection device from performing post-injection according to operating conditions;
The control means controls the fuel injection device so that the injection amount of the main injection becomes a predetermined upper limit value or less during the execution of the normal control and the NOx reduction control, and the NOx reduction control Is set to a correction upper limit value that is larger than when the normal control is performed under the same operating conditions,
The control means sets the upper limit value to the corrected upper limit value until a predetermined period elapses after the NOx reduction control ends even when the normal control is performed. Engine control device. The engine control device according to claim 1,
The engine control apparatus according to claim 1, wherein the control means sets an upper limit value of an injection amount of the main injection based on an oxygen state in the cylinder. The engine control device according to claim 2,
The engine control is characterized in that the control means sets the upper limit value of the injection amount of the main injection based on the oxygen concentration in the cylinder and before the combustion starts in the cylinder. apparatus. The engine control device according to any one of claims 1 to 3,
A supercharger that is provided in the exhaust passage and supercharges intake air flowing into the cylinder;
Wherein, when the implementation of the NOx reduction control, the lower than the pressure of the implementation time of the normal control a supercharging pressure of the supercharger, the engine control system, characterized in that. An engine control apparatus according to any one of claims 1 to 4,
The control means reduces the injection amount of the main injection when the NOx reduction control is started immediately after the normal control is performed with the injection amount of the main injection being smaller than the upper limit value. An engine control device. An engine control apparatus according to any one of claims 1 to 5,
The control device of the engine increases the injection amount of the main injection when stopping the post-injection as the NOx reduction control ends. NOx in the exhaust when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, provided in the engine main body in which the cylinder is formed and the exhaust passage through which the exhaust discharged from the engine main body flows. And an NOx catalyst for reducing and releasing the stored NOx when the air-fuel ratio of the exhaust gas is close to or richer than the stoichiometric air-fuel ratio,
A fuel injection device capable of performing main injection for injecting fuel for obtaining engine torque into the cylinder, and post injection for injecting fuel into the cylinder at a timing retarded from the main injection;
The main injection and the fuel are injected into the fuel injection device so that 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 so that the fuel post-injected into the cylinder burns in the cylinder. Control means for switching between NOx reduction control for performing post-injection and normal control for preventing the fuel injection device from performing post-injection according to operating conditions;
The control means controls the fuel injection device so that the injection amount of the main injection becomes a predetermined upper limit value or less during the execution of the normal control and the NOx reduction control, and the NOx reduction control Is set to a correction upper limit value that is larger than when the normal control is performed under the same operating conditions,
The control means reduces the injection amount of the main injection when the NOx reduction control is started immediately after the normal control is performed in a state where the injection amount of the main injection is smaller than the upper limit value. An engine control device.

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