JP6579165B2 - Control device for turbocharged engine - Google Patents

Description

  The present invention includes an engine body in which a cylinder in which a mixture of air and fuel burns is formed, and a turbine provided in an exhaust passage through which exhaust discharged from the engine body flows, and intake air flowing into the cylinder And a supercharger that supercharges the exhaust gas, and stores NOx in the exhaust when the air-fuel ratio of the exhaust is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust is theoretically The present invention relates to a control device for a supercharged engine comprising a NOx catalyst that reduces and releases NOx occluded when the air-fuel ratio is near or richer than the stoichiometric air-fuel ratio.

  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). NOx storage-reduction type NOx catalysts are known that reduce NOx occluded in a state where the air-fuel ratio 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). Yes.

  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), while the NOx occlusion amount of the NOx catalyst increases. Then, 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), and NOx occluded in the NOx catalyst is reduced.

  For example, in Patent Document 1, when the NOx occlusion amount of the NOx catalyst becomes a predetermined amount or more, in order to reduce NOx occluded in the NOx catalyst, in addition to the main injection for injecting the main fuel into the cylinder, A technique is disclosed in which post-injection for injecting fuel on the retard side is performed to enrich the air-fuel ratio in the cylinder and the exhaust.

JP 2002-295242 A

  Here, in an engine provided with a supercharger for the purpose of improving acceleration performance, as described above, if post injection is simply performed to reduce NOx, NOx reduction processing cannot be started early. There is a fear.

  Specifically, as described above, in order to reduce NOx stored in the NOx catalyst, it is necessary to make the air-fuel ratio of the exhaust richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. However, when the post injection is simply performed in addition to the main injection, a part of the post-injected fuel is combusted, so that the energy of the exhaust gas is increased and the supercharging power of the supercharger is increased. As a result, the introduction of fresh air into the cylinder is promoted, the exhaust air-fuel ratio cannot be made richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio at an early stage, and NOx reduction processing cannot be started early. There is.

  The present invention has been made in view of the circumstances as described above, and in an engine equipped with a NOx catalyst and a supercharger, an engine capable of starting reduction processing of NOx occluded in the NOx catalyst earlier. An object of the present invention is to provide a control device.

In order to solve the above-described problems, the present invention provides an engine body in which a cylinder in which an air-fuel mixture burns is formed, and a turbine provided in an exhaust passage through which exhaust discharged from the engine body flows. And a supercharger that supercharges the intake air flowing into the cylinder, and is provided in the exhaust passage to store NOx in the exhaust when the air-fuel ratio of the exhaust is leaner than the stoichiometric air-fuel ratio, And a control device for a supercharged engine comprising a NOx catalyst that reduces and releases NOx occluded when the air-fuel ratio of exhaust is close to or richer than the stoichiometric air-fuel ratio, the engine torque A fuel injection device capable of performing main injection for injecting fuel into the cylinder to obtain fuel and post injection for injecting fuel into the cylinder at a timing retarded from the main injection, and the supercharging By machine An intake pressure sensor for detecting a boost pressure which is a pressure of the intake air after being supercharged, before SL and boost pressure changing device capable of changing the charging pressure, the air-fuel ratio is near stoichiometric air-fuel ratio or stoichiometric air-fuel ratio of the exhaust It is possible to implement DeNOx control that causes the fuel injection device to perform the main injection and the post injection so that at least a part of the fuel supplied to the cylinder by the post injection is burned in the cylinder. Control means, and when the DeNOx control is performed, the control means reduces the target boost pressure, which is a target value of the boost pressure, and toward the target boost pressure after the decrease. The supercharging pressure changing device is controlled so that the supply pressure decreases , and the difference between the target boost pressure after the decrease and the actual boost pressure that is the boost pressure detected by the intake pressure sensor is set in advance. Reference amount Controlling said fuel injection device such that the post injection when it becomes lower is started, to provide a control apparatus for an engine with a supercharger, characterized in that (claim 1).

  According to this apparatus, by performing post injection, the NOx stored in the NOx catalyst can be reduced by making the air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. Then, the post-injected fuel is performed at the timing when the fuel is burned in the cylinder, and the post-injected fuel is compared with the case where the post-injection is performed at the retarded timing at which the fuel is not burned in the cylinder. As a result, unburned fuel is discharged into the exhaust passage and deposits resulting from the unburned fuel can prevent the various devices provided in the exhaust passage from being blocked. .

  In addition, in this apparatus, since the amount of air introduced into the cylinder is reduced by lowering the supercharging pressure when performing DeNOx control, the injection amount of post injection necessary to make the air-fuel ratio of the exhaust rich. This can reduce fuel consumption and improve fuel efficiency.

However, as described above, when the fuel related to the post injection is burned in the cylinder, the energy of the exhaust gas is increased and the supercharging force is increased. As a result, the supercharging pressure and the amount of air introduced into the cylinder are sufficiently reduced. There is a possibility that the air-fuel ratio of the exhaust gas cannot be made sufficiently rich with a small amount of post-injection. On the other hand, in this device, the target supercharging pressure is first lowered, and the post-injection is performed when the difference between the target supercharging pressure after the decrease and the actual supercharging pressure becomes equal to or less than a preset reference amount. Is started. Therefore, it is possible to suppress the delay in the decrease in the supercharging pressure and the amount of air introduced into the cylinder due to the increase in the exhaust energy accompanying the combustion of fuel related to the post injection, and the amount of post injection is suppressed to a small level. Meanwhile, the air-fuel ratio of the exhaust can be made rich early. Therefore, NOx reduction can be started early and appropriately while improving fuel efficiency as described above.

  In the above configuration, it is preferable that the control means controls the injection amount of the post injection so that the air-fuel ratio of the exhaust gas becomes a preset reference air-fuel ratio when the DeNOx control is performed. .

  In this way, the air / fuel ratio of the exhaust gas can be more reliably set to an appropriate air / fuel ratio. Here, if the post-injection injection amount is controlled in this way, if the supercharging pressure and the amount of air introduced into the cylinder are not reduced early, the post-injection injection amount is adjusted according to this air amount. As a result, the amount of post injection may be excessive. However, in the present invention, as described above, the boost pressure and the amount of air introduced into the cylinder are reduced early, so that the post-injection injection amount is reliably reduced while appropriately controlling the air-fuel ratio of the exhaust gas. Can be suppressed.

In the above-described configuration, the control means is configured 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 the fuel supplied into the cylinder by the post injection does not burn in the cylinder. The second DeNOx control that causes the injection device to perform the main injection and the post injection can be performed, and when the second DeNOx control is performed, the target supercharging pressure is reduced and the target supercharging pressure after the reduction is reduced. The supercharging pressure changing device is controlled so that the supercharging pressure decreases toward the target, and the difference between the target supercharging pressure and the actual supercharging pressure after the decrease or simultaneously with the decrease in the supercharging pressure is preferably controls the fuel injection device such that the post injection when it becomes less than the second reference amount larger than the reference amount is started (claim 3).

  According to this configuration, it is possible to increase the chances of reducing the NOx stored in the NOx catalyst, and it is possible to maintain the purification performance of the NOx catalyst high.

Here, in the second DeNOx control, the post-injected fuel is not combusted in the cylinder, so there is no possibility that the reduction of the supercharging pressure is limited by the post-injection. On the other hand, in this configuration, when the second DeNOx control is performed, post-injection is started at a timing at which the difference between the target boost pressure after the decrease and the actual boost pressure is greater than when the DeNOx control is performed. Therefore, when the second DeNOx control is performed, the exhaust air-fuel ratio can be made richer at an earlier stage, and the reduction of NOx can be started earlier.

In the above configuration, the NOx catalyst occludes SOx in the exhaust when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the exhaust air-fuel ratio is near the stoichiometric air-fuel ratio or more than the stoichiometric air-fuel ratio. The control means is configured to reduce and release the stored SOx when the engine is rich, and the control means is configured such that the air-fuel ratio of the exhaust becomes richer than the theoretical air-fuel ratio or near the stoichiometric air-fuel ratio, and the post-injection causes the A rich step for causing the fuel injection device to perform the main injection and the post injection so that at least a part of the fuel supplied into the cylinder burns in the cylinder, and the air-fuel ratio of the exhaust is higher than the stoichiometric air-fuel ratio. The main injection and the post injection are made to the fuel injection device so that the fuel that is lean and is supplied into the cylinder by the post injection does not burn in the cylinder. DeSOx control that alternately performs lean steps for performing the control can be performed, and when the DeSOx control is performed, the supercharging pressure changing device is controlled so that the supercharging pressure decreases, and preferably controls the fuel injection device such that the post injection after the decrease in Kyu圧has started is started (claim 4).

According to this configuration, the SOx occluded in the NOx catalyst by performing DeSOx control can be appropriately released from the NOx catalyst.
In addition, in this configuration, as in the DeNOx control, the exhaust air-fuel ratio is made close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and when the rich step is performed in which the post-injected fuel is burned in the cylinder, The post-injection is performed after the supply pressure is reduced and the reduction of the supercharging pressure is started. Therefore, even when the DeSOx control is performed, the same effect as that obtained by the DeNOx control, that is, the effect that the reduction of SOx can be started early and appropriately while improving the fuel efficiency. it can.

The present invention also includes an engine body in which a cylinder in which a mixture of air and fuel burns is formed, and a turbine provided in an exhaust passage through which exhaust gas discharged from the engine body flows. A supercharger that supercharges the intake air, and is provided in the exhaust passage to store NOx in the exhaust when the air-fuel ratio of the exhaust is leaner than the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust Is a control device for an engine with a supercharger comprising a NOx catalyst that reduces and releases NOx occluded when it is near or richer than the stoichiometric air-fuel ratio, the fuel for obtaining engine torque A fuel injection device capable of performing main injection injected into the cylinder and post injection for injecting fuel into the cylinder at a timing retarded from the main injection; and a supercharging pressure of the supercharger Changeable supercharging The fuel injection system so that the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and at least a part of the fuel supplied into the cylinder by the post-injection burns in the cylinder. DeNOx control for causing the apparatus to perform the main injection and the post-injection, and the air-fuel ratio of the exhaust gas near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and the fuel supplied into the cylinder by the post-injection is in the cylinder Control means capable of performing the second DeNOx control for causing the fuel injection device to perform the main injection and the post injection so that the fuel injection device does not burn at the time of the deNOx control. The supercharging pressure changing device is controlled so that the supply pressure decreases, and the amount of decrease in the supercharging pressure is set to a predetermined reference amount. In other words, the fuel injection device is controlled so that the post-injection is started, and when the second DeNOx control is performed, the supercharging pressure changing device is controlled so that the supercharging pressure decreases, and The fuel injection device is controlled so that the post-injection is started simultaneously with a decrease in the supply pressure or after a decrease amount of the supercharging pressure exceeds a second reference amount that is smaller than the reference amount. A control device for a supercharged engine is provided.

  According to the supercharger-equipped engine control apparatus according to the present invention, the reduction process of NOx stored in the NOx catalyst can be started earlier.

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 control procedure of active DeNOx control. It is the figure which showed the time change of each parameter when active DeNOx control is implemented. It is the flowchart which showed the control procedure of passive DeNOx control. It is the figure which showed the time change of each parameter when passive DeNOx control is implemented. It is the figure which showed the time change of each parameter when DeSOx control is implemented. It is the figure which showed the time change of each parameter when DPF regeneration control is implemented.

  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 at 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 carried out to obtain engine torque, and injects fuel that burns near the compression top dead center into the combustion chamber 6, and burns on the retard side of the main injection. However, post-injection in which fuel is injected into the combustion chamber 6 when the combustion energy hardly contributes to the engine torque can be performed.

  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, DPF (Diesel particulate filter) 44 that collects particulate matter (PM) in the exhaust, and urea injector that injects urea into the exhaust passage 40 on the downstream side of the DPF 44. 45, an SCR (Selective Catalytic Education) 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. ing.

  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 is a NOx catalyst 41 that purifies NOx, and a DOC (diesel oxidation) that oxidizes hydrocarbons (HC), carbon monoxide (CO), and the like using oxygen in the exhaust gas to convert them into water and carbon dioxide. Catalyst, 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 the excess air ratio λ> 1), and this occluded NOx is stored in the exhaust air. A state where the fuel ratio is in the vicinity of the stoichiometric air-fuel ratio (λ≈1) or a rich state (λ <1) smaller than the stoichiometric air-fuel ratio, that is, a reducing atmosphere in which the exhaust gas passing through the NOx catalyst 41 contains a large amount of unburned HC It is a NOx storage reduction catalyst (NSC: NOx Storage Catalyst) that reduces below. The first catalyst 43 is formed, for example, by coating the surface of a DOC catalyst material layer with an NSC catalyst material. In the present embodiment, there is no separate device for supplying air or fuel to the exhaust passage, and the air-fuel ratio of the exhaust and the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 correspond. That is, when the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio of the exhaust gas becomes lean, and the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is in the vicinity of the stoichiometric air-fuel ratio (λ ≈1) or rich state smaller than the stoichiometric air-fuel ratio (λ <1), the exhaust air-fuel ratio is also in the vicinity of the stoichiometric air-fuel ratio (λ≈1), or the rich state smaller than the stoichiometric air-fuel ratio (λ <1).

  The NOx catalyst 41 also stores SOx in addition to NOx. Specifically, the NOx catalyst 41 occludes SOx in the exhaust in a lean state (λ> 1) where the air-fuel ratio of the exhaust is larger than the stoichiometric air-fuel ratio. Reduction is performed in a state near the air-fuel ratio (λ≈1) or a rich state smaller than the stoichiometric air-fuel ratio (λ <1).

  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.

  The exhaust side bypass valve 49, the waste gate valve 54, and the intake side bypass valve 25 are controlled based on the engine speed and the engine load.

  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 the intake air in the surge tank 24 after being supercharged by the turbochargers 51, 52, that is, the supercharging pressure, provided in the surge tank 24, and the exhaust passage 40 Of these, it is electrically connected to an exhaust O2 sensor SN4 or the like that detects the oxygen concentration in the portion between the first turbocharger 51 and the first catalyst 43, and receives input signals from these sensors SN1 to SN4. . 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) 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 (leaving) it from the NOx catalyst 41, will be described.

  In the present embodiment, during normal operation in which DeNOx control, DeSOx control and DPF regeneration control, which will be described later, are not performed, the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 and thus the air-fuel ratio of the exhaust are higher than the stoichiometric air-fuel ratio in order to improve fuel efficiency. Is also made lean (λ> 1, for example, λ = 1.7). Hereinafter, as appropriate, the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is simply referred to as the air-fuel ratio of the air-fuel mixture.

  On the other hand, as described above, in the NOx catalyst 41, the air-fuel ratio of the exhaust gas, and thus 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). , The stored NOx is reduced and NOx is released from the NOx catalyst 41. Therefore, in order to reduce the stored NOx, it is necessary to reduce the air-fuel ratio of the exhaust gas and the air-fuel ratio of the air-fuel mixture as compared with the normal operation.

  As one method for reducing the air-fuel ratio of the air-fuel mixture (exhaust air-fuel ratio), 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 the present embodiment, post-injection is performed as DeNOx control, thereby reducing the air-fuel ratio of the air-fuel mixture while suppressing the amount of reduction in the amount of fresh air. That is, the PCM 200 performs control for causing the injector 10 to perform post injection in addition to main injection as DeNOx control. For example, in DeNOx control, the excess air ratio λ of the air-fuel mixture and exhaust is set to about λ = 0.94 to 1.06. Note that post-injection is stopped during normal operation.

  In the present embodiment, DeNOx control for performing post injection to reduce the stored NOx in this way 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, the PCM 200 performs active DeNOx control in which post-injection is performed 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). To implement. 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 PCM 200 performs the passive DeNOx control in which the post-injected fuel performs the post-injection at a timing at which the 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). To implement.

  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 air-fuel mixture is kept small even during normal operation due to a large amount of main injection (hereinafter referred to as “main injection amount” where appropriate). It is done. 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, in the first region R1 in which neither the engine load nor the engine speed is neither too low nor too high, active DeNOx control is performed in which the post-injected fuel burns in the combustion chamber 6, In the second region R2, passive DeNOx control is performed in which the post-injected fuel is not burned in the combustion chamber 6. 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 DeNOx control in the claims refers to active DeNOx control, and the second DeNOx control in the claims refers to passive DeNOx control.

(I) Switching Procedure Next, a switching procedure among normal control, active DeNOx control, and passive DeNOx control performed during normal operation 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, in step S10, the PCM 200 reads various types of vehicle information. 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. The NOx occlusion amount is estimated by, for example, integrating 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 SCR 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. . 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.

  When the determination in step S12 is NO and the NOx catalyst temperature is lower than the NOx reducible temperature, the process proceeds to step S31, and the PCM 200 sets the switching flag to 0. 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. 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 and sets the switching flag to 0. 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 and sets the switching flag to 0. 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 storage amount is less than the third 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. 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 passive DeNOx control, post-injection is performed at a relatively retarded timing at which the fuel is not combusted in the combustion chamber 6, so that unburned fuel is likely to leak from the combustion chamber 6 to the crankcase. Fuel consumption deteriorates. Therefore, in the present embodiment, 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, or when the deterioration of fuel consumption can be suppressed to some extent. The determination in step S23 is performed.

  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 and sets the switching flag to 0.

  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 due to post injection, after the determination in step S16, it is determined whether the travel distance from the previous execution of the active DeNOx control is equal to or greater than a predetermined determination distance. When the determination is YES, the process proceeds to step S17 and the active DeNOx control is performed. When this determination is NO, the process proceeds to step S31 and the switching flag may be set to zero.

  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.

(Ii) Details of Active DeNOx Control Next, detailed control contents of the active DeNOx control will be described with reference to the flowchart of FIG.

  First, in step S50, the PCM 200 determines whether or not the switching flag is 1. If this determination is NO, the process ends without performing the subsequent processes. On the other hand, if this determination is YES, the PCM 200 proceeds to step S51.

  In step S51, the PCM 200 reads various types of vehicle information.

  Next, in step S52, the PCM 200 is a target value of the air-fuel ratio of the air-fuel mixture for setting the air-fuel ratio of the exhaust gas to a predetermined target value (reference air-fuel ratio), and reduces the stored NOx of the NOx catalyst 41. A target air-fuel ratio, which is an air-fuel ratio required for the operation, is set. As described above, this target air-fuel ratio is set so that the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio or set to a preset value (reference air-fuel ratio) smaller than the stoichiometric air-fuel ratio. It is set to a value close to or smaller than the theoretical air-fuel ratio. For example, the target air-fuel ratio is set so that the excess air ratio λ becomes a value between 0.94 and 1.06. After step S52, the process proceeds to step S53.

  In step S53, the PCM 200 sets a target boost pressure that is a target value of the boost pressure. In the present embodiment, in order to make the air-fuel ratio of the air-fuel mixture rich, the amount of fresh air introduced into the combustion chamber 6 is reduced in addition to the post injection. Correspondingly, in step S53, the target supercharging pressure is set to a value smaller than the value during normal operation.

  Specifically, the normal target boost pressure that is the target boost pressure during normal operation and the target boost pressure for active DeNOx that is the target boost pressure during active DeNOx control are the engine speed and engine load, respectively. And is stored in the PCM 200 as a map. These maps are set so that the target supercharging pressure value for active DeNOx is smaller than the normal target supercharging pressure value under the same engine speed and engine load. In step S53, the PCM 200 extracts a value corresponding to the current engine speed and engine load from the active DeNOx target supercharging pressure map, and sets the target supercharging pressure.

  Next, the PCM 200 proceeds to step S54, and changes the opening degree of the exhaust side bypass valve 49 or the opening degree of the waste gate valve 54 in addition to this so that the target boost pressure is realized. In this embodiment, the opening of the throttle valve 23 is also changed at this time. In the present embodiment, as described above, the pressure of the intake air in the surge tank 24 detected by the intake pressure sensor SN3 is used as a supercharging pressure, and the exhaust side bypass valve 49 is set so that this pressure becomes the target supercharging pressure. Etc. are controlled. Specifically, the opening degree of the exhaust side bypass valve 49 is feedback-corrected based on the difference between the boost pressure detected by the intake pressure sensor SN3 and the target boost pressure.

  Next, in step S55, the PCM 200 determines that the difference between the supercharging pressure detected by the intake pressure sensor SN3 (hereinafter referred to as an actual supercharging pressure as appropriate) and the target supercharging pressure is a first reference pressure set in advance. It is determined whether or not it is less than (reference amount). Specifically, it is determined whether or not a value obtained by subtracting the target boost pressure from the actual boost pressure is equal to or lower than the first reference pressure (> 0).

  If the determination in step S55 is NO and the difference between the actual boost pressure and the target boost pressure is greater than the first reference pressure and the actual boost pressure has not sufficiently decreased, the process proceeds to step S56. In step S56, the PCM 200 performs only main injection without performing post injection, and proceeds to step S60.

  On the other hand, if the determination in step S55 is YES and the actual boost pressure is sufficiently low, the process proceeds to step S57, and the PCM 200 realizes the target air-fuel ratio set in step S52 for the post-injection injection amount. Adjust to the amount to be. Specifically, the PCM 200 calculates a post-injection amount that can achieve the target air-fuel ratio, using a separately calculated main injection amount, intake oxygen concentration, and the like.

  The main injection amount is, for example, a target vehicle acceleration that is a target value of the acceleration of the vehicle based on the accelerator opening and the vehicle speed, and a target value of the engine torque based on this and the engine speed. After a certain target engine torque is calculated, it is calculated based on this target engine torque. Further, the intake oxygen concentration is the oxygen concentration in the combustion chamber 6 before combustion is performed, and the PCM 200 is, for example, the intake air amount, the exhaust oxygen concentration, the opening degrees of the EGR valves 57 and 60, the supercharging pressure, and the like. Estimate based on

  After step S57, the process proceeds to step S58, and the PCM 200 performs main injection and post injection. In step S58, the PCM 200 sets the post injection amount as the post injection amount calculated in step S57, and injects this amount of fuel by the post injection. After step S58, the process proceeds to step S59.

  In step S59, it is determined whether or not the switching flag has a value other than 1. If this determination is YES, the process ends (return to step S50). That is, the active DeNOx control is terminated. On the other hand, if this determination is NO, the process returns to step S51, and steps S51 to S59 are performed.

  Thus, in the present embodiment, when the active DeNOx control is performed (when the switching flag becomes 1), the supercharging pressure is first reduced, and then post injection is started. In the present embodiment, the exhaust-side bypass valve 49, the waste gate valve 54, the throttle valve 23, and the drive device that drives them function as a boost pressure change device that can reduce, that is, change the boost pressure.

  FIG. 7 shows the switching flag, the supercharging pressure, the post injection amount, the opening degree of the exhaust side bypass valve 49, the opening degree of the throttle valve 23, when the active DeNOx control is performed according to the above-described procedure. FIG. 6 is a diagram schematically showing a change over time in the amount of intake air that is the amount of air introduced into the combustion chamber 6. In the graph of the supercharging pressure, the solid line is the actual supercharging pressure, and the broken line is the target supercharging pressure. FIG. 7 illustrates a case where the supercharging pressure is changed by changing the opening degree of the exhaust side bypass valve 49 and changing the opening degree of the throttle valve 23.

  As shown in FIG. 7, in the present embodiment, when the operation condition of the active DeNOx control is satisfied at time t1 and the switching flag becomes 1 at the time t1, the target boost pressure is set at the time of normal operation. It is changed to a value smaller than the target supercharging pressure. Here, the operating state of the engine is almost the same before and after the switching flag becomes 1. Therefore, when the switching flag becomes 1 during the normal operation, the target boost pressure is lowered. As the target boost pressure decreases, the opening of the exhaust side bypass valve 49 is increased at time t1 in order to decrease the actual boost pressure. Further, the opening degree of the throttle valve 23 is reduced (to the closed side). Specifically, after time t1, the opening degree of the throttle valve 23 is gradually reduced. On the other hand, in this embodiment, post injection is not started at time t1, and only main injection is performed.

  Thus, by changing the opening degree of the exhaust side bypass valve 49 and the throttle valve 23, the actual supercharging pressure and the intake air amount are reduced.

  Then, after a predetermined time has elapsed from time t1, post injection is started when the difference between the actual boost pressure and the target boost pressure becomes equal to or less than the first reference pressure at time t2.

  In the example of FIG. 7, the injection amount of the post injection is gradually increased from time t2 to time t3. Further, after the time t2, the opening degree of the throttle valve 23 is gradually reduced, whereby the intake air amount is gradually reduced. However, after time t2, the rate of decrease in the opening of the throttle valve 23 is made smaller than before. Further, in the example of FIG. 7, the opening degree of the throttle valve 23 is gradually reduced at a small speed even after time t3 in order to prevent undershoot of the supercharging pressure.

(Iii) Details of Passive DeNOx Control Next, the contents of the passive DeNOx control will be described. FIG. 8 is a flowchart showing a control procedure of passive DeNOx control. As is clear from the comparison between FIG. 6 and FIG. 8, the basic control procedure of the passive DeNOx control is almost the same as that of the active DeNOx control.

  Specifically, in the passive DeNOx control, the PCM 200 determines whether or not the switching flag is 2 (step S60), and executes the subsequent passive DeNOx control when this determination is YES. Also in the passive DeNOx control, the PCM 200 reads various information (step S61), and then sets the target air-fuel ratio and target supercharging pressure of the air-fuel mixture (steps S62 and S63) so that these are realized. In addition, the opening degree of the exhaust side bypass valve 49 and the opening degree of the throttle valve 23 (and / or the wastegate valve 54) are changed (step S64), and the post injection amount is adjusted (step S67).

  Also in the passive DeNOx control, the target boost pressure is set to a value smaller than the normal target boost pressure value. Specifically, the PCM 200 has a target boost pressure for passive DeNOx, which is a target boost pressure during passive DeNOx control, and a pressure set to a value smaller than the normal target boost pressure, and the engine speed. The PCM 200 extracts a value from this map and sets it to the target boost pressure.

  However, in passive DeNOx control, the determination in step S55 performed during active DeNOx control, that is, whether or not the difference between the actual boost pressure and the target boost pressure is equal to or lower than the first reference pressure is not performed. Further, in the passive DeNOx control, step S56 for stopping the post injection and performing only the main injection is not performed. That is, in the passive DeNOx control, after the post injection amount is adjusted in step S67, the process immediately proceeds to step S68 and the post injection is performed in addition to the main injection.

  After step S68, as in the case of active DeNOx control, the switching flag is determined in step S69 (however, in passive DeNOx control, it is determined whether or not the switching flag is 2), and the process ends. Alternatively, the process returns to step S60.

  FIG. 9 is a diagram corresponding to FIG. 7, and shows a switching flag, a supercharging pressure, a post injection amount, an opening of the exhaust side bypass valve, and an intake air amount when passive DeNOx control is performed. It is the figure which showed typically the time change of. In the graph of the supercharging pressure in FIG. 9, the solid line is the actual supercharging pressure, and the broken line is the target supercharging pressure (target supercharging pressure for passive DeNOx).

  As described above, also in the passive DeNOx control, when the switching flag becomes 2 at time t1 and the execution condition of the passive DeNOx control is satisfied, the target boost pressure and the target air-fuel ratio are reduced, and the exhaust side bypass valve 49 and the throttle valve 23 are The change of the opening degree is started, whereby the actual supercharging pressure and the intake air amount are reduced. On the other hand, unlike the active DeNOx control, in the passive DeNOx control, post injection is started almost simultaneously with the decrease in the actual supercharging pressure at time t1.

  Further, in the example of FIG. 9, until the time t12 when the intake air amount sufficiently decreases, the air-fuel ratio of the air-fuel mixture and the air-fuel ratio of the exhaust gas are set to predetermined values so that the intake air amount is adjusted to a relatively large amount. As a result, the amount of post-injection is increased. When the intake air amount decreases sufficiently at time t12, the post injection amount is reduced.

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

  FIG. 10 is a diagram schematically showing temporal changes in the DeSOx execution flag, the exhaust air-fuel ratio, the boost pressure, and the post injection amount when the DeSOx control is performed. In the graph of the supercharging pressure in FIG. 10, the solid line is the actual supercharging pressure, and the broken line is the target supercharging pressure during DeSOx control. The DeSOx execution flag is a flag set so that DeSOx control is started when its value becomes 1. The DeSOx execution flag becomes 1 when the amount of SOx stored in the NOx catalyst 41 exceeds a predetermined amount, and becomes 0 when the amount of SOx stored in the NOx catalyst 41 becomes less than a predetermined amount. For example, when the running time after the previous DeSOx control is performed is equal to or longer than a predetermined time, it is estimated that the amount of SOx stored in the NOx catalyst 41 is equal to or greater than a predetermined amount, and the DeSOx execution flag is set to 1. Then, DeSOx control is started. In addition, the DeSOx execution flag is set to 0 when a predetermined time has elapsed since the DeSox control was started. Then, DeSOx control is stopped.

  As described above, in the NOx catalyst 41, the stored SOx is reduced in a state where the air-fuel ratio of the exhaust 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 this embodiment, post-injection is performed in DeSOx control as well as main injection, in addition to DeNOx control. However, since SOx has a stronger binding force than NOx, in order to reduce the stored SOx, it is necessary to raise the temperature of the NOx catalyst 41 and thus the temperature of the exhaust gas that passes through the NOx catalyst 41 more than during DeNOx control. On the other hand, if the unburned HC is oxidized in the DOC 42 included in the first catalyst 43, the temperature of the exhaust gas passing through the first catalyst 43 and thus the NOx catalyst 41 can be increased.

  Therefore, in the present embodiment, as shown in FIG. 10, as the DeSOx control, the post-injection is performed similarly to the DeNOx control to make the exhaust air-fuel ratio richer than in normal operation, and the exhaust air-fuel ratio is Control is performed to alternately perform a lean step in which post-injection is performed while leaner than the stoichiometric air-fuel ratio, and air and unburned HC are supplied to the DOC 42 and these are oxidized by the DOC 42.

  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.

  On the other hand, in the lean step, 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). Then, the air / fuel ratio of the mixture and exhaust is set to 1 or more so that the air / fuel ratio of the mixture and exhaust becomes leaner than the stoichiometric air / fuel ratio. For example, in the lean step, the excess air ratio λ of the air-fuel mixture and exhaust is set to about λ = 1.2 to 1.4.

  Further, in the present embodiment, in the rich step of the DeSOx control, the boost pressure, the post injection amount, and the active DeNOx control are controlled.

  Specifically, even in the rich step in the DeSOx control, the target air-fuel ratio of the air-fuel mixture corresponding to the target value of the exhaust air-fuel ratio is set, the post-injection amount is set so as to be realized, and the target boost pressure is set. And the opening degree of the exhaust side bypass valve 49 is changed so that this is realized. Even in the rich step, the target boost pressure is set to a value smaller than the normal target boost pressure value. Specifically, the PCM 200 stores a target supercharging pressure at the time of rich step execution as a map for engine speed and engine load, and the PCM 200 extracts a value from this map and performs the target supercharging. Set to pressure.

  Further, as shown in FIG. 10, similarly to the active DeNOx control, even in the rich step, after the start of the rich step at time t1, t2, etc., first, the exhaust side bypass valve is set so that the boost pressure approaches the target boost pressure. After the opening degree of 49 is changed (not shown), the post-injection is started only when the difference between the actual boost pressure and the target boost pressure becomes a predetermined value or less.

(2-3) DPF regeneration control An outline of DPF regeneration control, which is control for regenerating the purification ability of the DPF 44 by removing PM collected by the DPF 44, will be described.

  FIG. 11 is a diagram schematically showing temporal changes in the DPF regeneration flag, the supercharging pressure, and the post injection amount when the DPF regeneration control is performed. In the graph of the supercharging pressure in FIG. 11, the solid line is the actual supercharging pressure, and the broken line is the target supercharging pressure.

  The DPF regeneration flag is a flag set so that DPF regeneration control is started when the value becomes 1. In the present embodiment, the DPF regeneration flag, which is estimated that the amount of PM collected in the DPF 44 has become equal to or greater than a predetermined amount, becomes 1, and DPF regeneration control is started. Further, when it is estimated that the amount of PM collected in the DPF 44 has become a predetermined amount or less, the DPF regeneration flag becomes 0, and the DPF regeneration control is stopped. The amount of PM trapped in the DPF 44 is, for example, the differential pressure across the DPF 44 calculated from pressure sensors provided on the upstream side and downstream side of the DPF 44 (the pressure on the upstream side and the pressure on the downstream side of the DPF 44). Etc.).

  The PM collected by the DPF 44 can be removed from the DPF 44 by burning it at a high temperature. Here, if the unburned HC is oxidized in the DOC 42, the temperature in the DPF 44 located on the downstream side can be increased.

  Therefore, in the present embodiment, as DPF regeneration control, post-injection is performed while the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, air and unburned HC are supplied to the DOC 42, and these are oxidized by the DOC 42. carry out. 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, the supercharging pressure and the post injection amount are controlled similarly to the passive DeNOx control.

  Specifically, even in the DPF regeneration control, the target air-fuel ratio of the exhaust is set, the post injection amount is set so as to be realized, and the target supercharging pressure is set, so that this is realized. The opening degree of the bypass valve 49 is changed. Also in the DPF regeneration control, the target boost pressure is set to a value smaller than the normal target boost pressure value. Specifically, the PCM 200 stores a DPF regeneration control target supercharging pressure, which is a target supercharging pressure at the time of DPF regeneration control, as a map of the engine speed and the engine load. The value is extracted from the map and set to the target boost pressure.

  As shown in FIG. 11, in the DPF regeneration control, as in the case of the passive DeNOx control, when the execution condition for the DPF regeneration control is satisfied at time t1, the target supercharging pressure is lowered and the exhaust side bypass valve 49 and the like are At the same time as the control is started, the post injection is started at the same time.

(3) Operation, etc. As described above, in the present embodiment, the post-injection 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, and the NOx occluded in the NOx catalyst 41 is occluded. NOx is reduced. Therefore, the air-fuel ratio of the exhaust gas can be brought into a rich state in which the stored NOx can be reduced without reducing the amount of fresh air introduced into the combustion chamber 6 or while reducing the amount of this reduction. The occluded NOx can be appropriately reduced while avoiding the deterioration of acceleration due to the reduction in the amount.

  Moreover, in the active DeNOx control, the post-injected fuel is burned in the combustion chamber 6. Therefore, compared with the case where the post-injection is performed at the retarded timing at which the fuel does not burn in the combustion chamber 6, the post-injected fuel is prevented from leaking into the crankcase and being mixed into the engine oil. It is possible to prevent the exhaust passage 40 and the like from being blocked by deposits resulting from unburned fuel.

  Further, in the present embodiment, in the active DeNOx control, the supercharging pressure is lowered than that in the normal operation to reduce the amount of air introduced into the cylinder, so that it is necessary to make the air-fuel ratio of the exhaust rich. It is possible to improve fuel efficiency by reducing the amount of post-injection.

  However, if the post injection is burned in the combustion chamber 6, the energy of the exhaust increases and the supercharging force increases, and the amount of air introduced into the combustion chamber 6 may not be reduced early. In other words, the post-injected fuel burns in spite of trying to lower the supercharging pressure, so that the reduction of the supercharging pressure is inhibited, and the air-fuel ratio of the exhaust gas and the air-fuel mixture can reduce the stored NOx. There is a possibility that it takes a long time to reduce the amount to the minimum.

  On the other hand, in the present embodiment, in the active DeNOx control, post injection is started after the difference between the actual boost pressure and the target boost pressure falls below the reference pressure. For this reason, the increase in the supercharging force associated with the post injection is prevented from delaying the decrease in the supercharging pressure, thereby reducing the amount of air introduced into the combustion chamber 6 at an early stage, thereby reducing the air-fuel ratio of the exhaust. It can be rich early. Therefore, the reduction of NOx can be started early and appropriately while obtaining the effect of improving the fuel consumption performance due to the decrease in the supercharging pressure. Thus, if the reduction of NOx starts early, the total amount of post-injection necessary for reducing NOx can be kept small, so that the fuel efficiency can be further improved.

  Further, in the present embodiment, when the active DeNOx control is performed, the post-injection injection amount is adjusted so that the air-fuel ratio of the exhaust gas becomes the target air-fuel ratio at which the NOx catalyst 41 can reduce NOx. Therefore, occluded NOx can be reduced more appropriately.

  In addition, in the present embodiment, as described above, since the supercharging pressure is reduced earlier when the active DeNOx control is performed, the post-injection injection amount is set to the exhaust air-fuel ratio in this way. The amount of post-injection can be suppressed to a low level while changing the amount accordingly. In other words, if the supercharging pressure decreases slowly, the amount of air introduced into the combustion chamber 6 and the exhaust gas is increased over a relatively long period of time, so that the post air pressure is reduced to the target air fuel ratio. It becomes necessary to increase the injection amount. On the other hand, in the present embodiment, the supercharging pressure can be reduced earlier, so that the post-injection amount necessary for reducing the air-fuel ratio of the exhaust gas to the target air-fuel ratio can be reduced.

  In the present embodiment, also during the execution of the rich step of the DeSOx control, as in the active DeNOx control, the post injection is performed at the timing when the fuel burns in the combustion chamber 6 and the target boost pressure is lowered. The post injection is started after the supercharging pressure is lowered. Therefore, even when the DeSOx control rich step is performed, the supercharging pressure and the air-fuel ratio of the exhaust can be reduced early, fuel efficiency is improved, and SOx reduction is started early and appropriately. Can do.

  On the other hand, in the passive DeNOx control and the DPF control, the target supercharging pressure is reduced and post injection is performed. In these controls, the post-injected fuel is not burned in the combustion chamber 6 and is discharged into the exhaust passage 40. Discharged. Therefore, in these controls, the decrease in supercharging pressure is hardly inhibited by post injection. On the other hand, in the present embodiment, in passive DeNOx control and DPF control, the supercharging pressure is reduced (the opening degree of the exhaust-side bypass valve 49 and the like for reducing the supercharging pressure) and post-injection. Start at the same time. Therefore, it is possible to start post-injection at an early stage without waiting for a decrease in the supercharging pressure, shortening the time related to the NOx reduction process, and thus improving the fuel efficiency.

(4) Modification In the above embodiment, when the rich step of the active DeNOx control and the DeSOx control is performed, the post injection is started when the difference between the actual boost pressure and the target boost pressure is equal to or lower than the first reference pressure. However, it is only necessary that the post-injection is started after the supercharging pressure starts to decrease, and the specific setting procedure of the start timing is not limited to this. For example, post injection may be started after a predetermined time has elapsed after the start of control for reducing the supercharging pressure.

  However, as described above, when the difference between the actual supercharging pressure and the target supercharging pressure is equal to or lower than the first reference pressure, the post injection is started more reliably after the supercharging pressure is reduced if the post injection is started. Can be started.

Further, in the above-described embodiment, the case where the supercharging pressure reduction and the post injection are simultaneously started in the passive DeNOx control and the DPF control has been described. However, in these controls as well, the actual supercharging pressure and the target supercharging pressure The post injection may be started when the difference is equal to or less than a predetermined second reference pressure (second reference amount). However, as described above, in passive DeNOx control and DPF control, it is possible to start post-injection earlier, and this can improve fuel efficiency. also, the second reference pressure is preferably set larger than the first reference pressure.

  Moreover, in the said embodiment, the case where the exhaust side bypass valve 49, the wastegate valve 54, the throttle valve 23, and the drive device which drives these function as a supercharging pressure change device which can change supercharging pressure is demonstrated. However, all of these do not have to function as a supercharging pressure changing device for reducing the supercharging pressure during DeNOx control, DeSOx control, and DPF control. For example, during DeNOx control, the opening of the waste gate valve 54 and the opening of the throttle valve 23 may be constant, and the supercharging pressure may be changed only by the exhaust side bypass valve 49.

1 Engine Body 2 Cylinder 6 Combustion Chamber 10 Injector (Fuel Injection Device)
23 Throttle valve (supercharging pressure changing device)
41 NOx catalyst 49 Exhaust-side bypass valve (supercharging pressure changing device)
51 1st turbocharger (supercharger)
51b 1st turbine (turbine)
52 Second turbocharger (supercharger)
52b Second turbine (turbine)
54 Wastegate valve (Supercharging pressure change device)
200 PCM (control means)

Claims (5)

An engine body in which a cylinder in which a mixture of air and fuel burns is formed, and a turbine provided in an exhaust passage through which exhaust gas discharged from the engine body flows, is supercharged with intake air flowing into the cylinder Provided in the supercharger and the exhaust passage, when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, occludes NOx in the exhaust gas, and the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio or A control device for a supercharged engine comprising a NOx catalyst that reduces and releases NOx occluded when richer than a theoretical 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;
An intake pressure sensor that detects a supercharging pressure that is a pressure of intake air after being supercharged by the supercharger;
And boost pressure changing device capable of changing the pre-Symbol charging pressure,
The main body of the fuel is injected into the cylinder so that at least a part of the fuel supplied into the cylinder by the post-injection burns in the cylinder. Control means capable of performing DeNOx control for performing injection and post-injection,
When the DeNOx control is performed, the control unit reduces the target boost pressure, which is a target value of the boost pressure, and decreases the boost pressure toward the target boost pressure after the decrease. controls the boost pressure changing device, falls below a reference amount difference is previously set between the actual supercharging pressure which is a boost pressure detected target supercharging pressure after said decreased by the intake pressure sensor The supercharger-equipped engine control device is characterized in that the fuel injection device is controlled so that the post-injection is started at a point in time . It is a control apparatus of the engine with a supercharger of Claim 1, Comprising:
The control means controls the injection amount of the post-injection so that the air-fuel ratio of exhaust becomes a preset reference air-fuel ratio when the DeNOx control is performed. Control device. A control device for a supercharged engine according to claim 1 or 2 ,
The control means includes
The main injection and the post are supplied to 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 the fuel supplied into the cylinder by the post-injection does not burn in the cylinder. The second DeNOx control to perform the injection,
At the time of performing the second DeNOx control, the supercharging pressure changing device is controlled so that the target supercharging pressure is decreased and the supercharging pressure is decreased toward the target supercharging pressure after the decrease. The post-injection is started at the time when the difference between the target boost pressure after the decrease of the supercharging pressure or the actual supercharging pressure becomes equal to or less than the second reference amount that is larger than the reference amount. And controlling the fuel injection device to a supercharged engine control device. It is a control apparatus of the engine with a supercharger in any one of Claims 1-3 ,
The NOx catalyst occludes SOx in the exhaust when the exhaust air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and the exhaust air-fuel ratio is close to the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio. The occluded SOx is reduced and released,
The control means includes
The main body of the fuel is injected into the cylinder so that at least a part of the fuel supplied into the cylinder by the post-injection burns in the cylinder. A rich step for performing the injection and the post-injection, and the fuel injection so that the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, and the fuel supplied into the cylinder by the post-injection does not burn in the cylinder DeSOx control can be performed in which a lean step for causing the apparatus to perform the main injection and the post injection is performed alternately.
When performing the DeSOx control, the supercharging pressure changing device is controlled so that the supercharging pressure decreases, and the fuel injection is performed so that the post injection is started after the supercharging pressure starts decreasing. A control device for an engine with a supercharger, characterized by controlling the device. An engine body in which a cylinder in which a mixture of air and fuel burns is formed, and a turbine provided in an exhaust passage through which exhaust gas discharged from the engine body flows, is supercharged with intake air flowing into the cylinder Provided in the supercharger and the exhaust passage, when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio, occludes NOx in the exhaust gas, and the air-fuel ratio of the exhaust gas is close to the stoichiometric air-fuel ratio or A control device for a supercharged engine comprising a NOx catalyst that reduces and releases NOx occluded when richer than a theoretical 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;
A supercharging pressure changing device capable of changing the supercharging pressure of the supercharger;
The main body of the fuel is injected into the cylinder so that at least a part of the fuel supplied into the cylinder by the post-injection burns in the cylinder. DeNOx control for performing injection and post-injection, and so that the air-fuel ratio of exhaust becomes near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio, and fuel supplied into the cylinder by the post-injection does not burn in the cylinder Control means capable of performing a second DeNOx control for causing the fuel injection device to perform the main injection and the post injection,
The control means includes
When the DeNOx control is performed, the supercharging pressure changing device is controlled so that the supercharging pressure decreases, and the post-injection starts when the amount of decrease in the supercharging pressure exceeds a predetermined reference amount. Controlling the fuel injection device to be
When the second DeNOx control is performed, the supercharging pressure changing device is controlled so that the supercharging pressure decreases, and at the same time as the supercharging pressure decreases or the supercharging pressure decreases from the reference amount. The supercharger-equipped engine control device is characterized in that the fuel injection device is controlled so that the post-injection is started after the second reference amount is exceeded.

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