JP6508264B2 - Engine control device - Google Patents

Description

  The present invention relates to a control device for an engine including an engine body in which cylinders are formed, and an NOx catalyst provided in an exhaust passage through which the exhaust gas discharged from the engine body flows.

  Conventionally, NOx is stored in exhaust gas in a lean state where the air-fuel ratio of the exhaust gas is larger than the theoretical air-fuel ratio (that is, the excess air ratio λ is λ> 1), and the stored NOx is A NOx storage reduction type NOx catalyst is known that reduces in a state where the air-fuel ratio of air-fuel mixture in the cylinder is near the theoretical air-fuel ratio (λ ≒ 1) or in a rich state smaller than the theoretical air-fuel ratio (λ <1). ing.

  Here, in the NOx catalyst as described above, SOx in the exhaust gas is adsorbed in addition to NOx, and so-called S poisoning occurs. Therefore, in order to maintain the purification function of the NOx catalyst, it is necessary to release SOx from the NOx catalyst to eliminate the S poisoning.

  On the other hand, for example, in Patent Document 1, an oxygen storage agent that generates heat by storing oxygen together with the NOx catalyst is provided in the exhaust passage, and the air-fuel ratio of the mixture in the cylinder is alternately rich for a predetermined time (the theory It is disclosed to switch between richer than air-fuel ratio and lean (leaner than stoichiometric air-fuel ratio). Specifically, in this configuration, the air-fuel ratio in the cylinder is made rich, so that the exhaust gas contains a large amount of unburned fuel and carbon monoxide to expose the NOx catalyst to a reducing atmosphere to enable the reduction of SOx, and then By making the air-fuel ratio in the cylinder lean, a large amount of oxygen is contained in the exhaust to heat the oxygen storage agent to raise the temperature of the NOx catalyst to a temperature at which the SOx can be reduced, thereby separating the SOx from the NOx catalyst. It is like that.

JP, 2016-109041, A

  Here, since there is a possibility that the exhaust performance may deteriorate at the time of implementation of the control for reducing SOx as described above and leaving it from the NOx catalyst, it may be considered to limit the implementation of this control outside the predetermined operation range. I see. However, in this case, there is a problem that the time required for the reduction process of SOx becomes long.

  Specifically, when the control for the reduction process of SOx is interrupted in response to the shift to the operation range for making the air-fuel ratio of the mixture in the cylinder lean, the reduction process of SOx is simply resumed. The time required for the reduction process of SOx becomes longer due to the time during which the air fuel ratio is made lean being excessively long or the temperature of the NOx catalyst decreasing. Specifically, if the air-fuel ratio of the mixture is made lean simply by resuming the control for the reduction process of SOx after the operation in the operating region where the air-fuel ratio of the mixture is lean, the air-fuel ratio of the mixture becomes The time for being leaned becomes excessively long, resulting in a time when SOx is not properly reduced.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a control device of an engine capable of reducing SOx adsorbed to a NOx catalyst in a shorter time.

  In order to solve the above problems, the present invention is provided in an engine body in which a cylinder is formed and an exhaust passage through which exhaust gas discharged from the engine body flows, and the air-fuel ratio of the exhaust is leaner than the theoretical air-fuel ratio Engine including a NOx catalyst which occludes NOx in the exhaust when the engine is in the normal state and reduces the occluded NOx when the air-fuel ratio of the exhaust gas is near the theoretical air-fuel ratio or richer than the theoretical air-fuel ratio A fuel supply device for supplying fuel into the cylinder, and only a basic rich time set in advance in a specific operation area set in advance in order to eliminate S poisoning of the NOx catalyst. A rich step of driving the fuel supply device so that the air-fuel ratio of the exhaust gas becomes near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio; Control means for alternately performing air-fuel ratio control for driving the fuel supply device so that unburned fuel is discharged to the passage and the air-fuel ratio of the exhaust gas becomes leaner than the stoichiometric air-fuel ratio; The control means limits the air-fuel ratio control when the operating range of the engine shifts from the specific operating range to another range during execution of the air-fuel ratio control, and the operating range of the engine is specified again after the transition. When returning to the operating range, the air-fuel ratio control is restored, and when the air-fuel ratio control is restored, the rich step is first returned from the rich step, and the operating range of the engine is changed from the specific operating range to the other range. The shorter the air-fuel ratio control limit time that has restricted the air-fuel ratio control since the transition, the shorter the execution time of the rich step to be performed first after the air-fuel ratio control returns. To provide a control apparatus for an engine, characterized in that as to set the execution time of the rich performing this first.

  According to this device, the SOx adsorbed to the NOx catalyst is appropriately reduced and desorbed (S poisoning is eliminated by performing air-fuel ratio control that alternately performs rich step and lean step in the specific operation region. And the air-fuel ratio control is stopped in other areas (areas other than the specific operation area), the exhaust gas performance is deteriorated, for example, the temperature in the cylinder tends to be high. By performing the air-fuel ratio control in the region, the temperature in the cylinder becomes excessively high and the generation amount of soot increases, or the unburned fuel by performing the air-fuel ratio control in the region where the temperature in the cylinder is low It can be prevented from being discharged in large quantities.

  Moreover, in this device, the rich step is performed first when the air-fuel ratio control is restored after the operating region of the engine shifts to the region other than the specific operating region (region excluding the specific operating region). Therefore, it can be avoided that the time during which the air-fuel ratio of the mixture in the cylinder and hence the exhaust gas is made leaner than the air-fuel ratio at the rich step becomes excessively long, and SOx from the NOx catalyst earlier after the return of air-fuel ratio control. Can be removed.

  In addition, if the air-fuel ratio control is limited as the time to shift to a region other than the specific region is shorter, the time for performing the rich step to be performed first when the air-fuel ratio control is restored becomes shorter. The execution time of the rich step is set. Therefore, the ratio between the rich step time and the time during which the air-fuel ratio of the exhaust gas is made leaner than the air-fuel ratio at the rich step is made appropriate, and SOx is released from the NOx catalyst earlier after the return of air-fuel ratio control. It can be done.

  In the above-mentioned configuration, the control means controls the engine in a state in which the time from the transition of the operating range of the engine to the other range from the specific operating range to the return to the specific operating range is less than a predetermined determination time. When the operating range returns to the specific operating range, it is preferable to restore the air-fuel ratio control after continuing the restriction of the air-fuel ratio control for a predetermined time after the return to the specific operating range (claim 2).

  According to this configuration, the execution time of the rich step performed first at the time of return of the air-fuel ratio control is set excessively short according to the time when it has shifted to another region, whereby the air-fuel ratio of the exhaust gas is sufficiently rich It is possible to prevent the shift to the lean step before becoming

  In the above configuration, the exhaust passage is provided with a PM filter provided downstream of the NOx catalyst and capable of collecting particulate matter in the exhaust, and the air-fuel ratio of the exhaust at the time of the lean step execution is the inside of the PM filter. Preferably, the particulate matter is set to a flammable air-fuel ratio (claim 3).

  According to this configuration, the reduction treatment of SOx adsorbed to the NOx catalyst and the treatment of burning and removing the particulate matter from the PM filter can be simultaneously performed, and the unburned fuel is compared to the case where these are individually performed. The fuel consumption performance can be enhanced by shortening the period in which the exhaust gas must be introduced into the exhaust passage.

  In the above-mentioned configuration, it is preferable that the ratio of the basic lean time to the basic rich time be smaller as the engine speed is higher (claim 4).

  In this way, heat damage to various devices in the exhaust passage can be suppressed.

  Specifically, the higher the engine speed is, the larger the flow rate of the exhaust gas is, and the various devices provided in the exhaust passage and the exhaust passage are likely to be at high temperature, and the exhaust gas air fuel ratio leans for a longer time The exhaust gas tends to be hot due to the oxidation reaction in the passage. Therefore, if configured as described above, it is possible that the temperature of the exhaust and thus the temperature of various devices provided in the exhaust passage and the exhaust passage become excessively high with the execution of the lean step under the operating condition where the engine rotational speed is high. It can be suppressed.

  In the above-mentioned configuration, it is preferable that the ratio of the basic lean time to the basic rich time be smaller as the engine load is higher (claim 5).

  In this way, heat damage to various devices in the exhaust passage can be suppressed.

  Specifically, when the engine load is high, various devices provided in the exhaust passage and the exhaust passage tend to be high temperature, and the longer the time to make the air-fuel ratio of the exhaust lean, the oxidation reaction in the exhaust passage The exhaust is likely to get hot. Therefore, if configured as described above, under the operating conditions where the engine load is high, the time during which the air-fuel ratio of the exhaust gas is leaned is relatively shortened, and various devices provided in the exhaust and exhaust passages and exhaust passages are excessive. High temperature can be suppressed.

  In the above-mentioned configuration, it is preferable that the control means sets the execution time of the rich step performed first after the return of the air-fuel ratio control to be equal to or less than the basic rich time (claim 6).

  According to this configuration, the execution time of the rich step can be made appropriate.

FIG. 1 is a schematic configuration diagram of an engine system to which a control device for an engine according to an embodiment of the present invention is applied. It is a block diagram showing a control system of an engine system. It is a figure showing a control map of passive DeNOx control and active DeNOx control. It is a figure showing the relation between the ratio of the implementation time of the lean step to the implementation time of the rich step and the engine speed. It is a figure showing the relation between the ratio of the lean step execution time to the rich step execution time and the engine load. It is the flowchart which showed the setting procedure of the DeSOx basic execution flag. It is the flowchart which showed the first half part of the control procedure of DeSOx control. It is the flowchart which showed the first half part of the control procedure of DeSOx control. It is the figure which showed typically the time change of each parameter when the control which concerns on this embodiment is implemented. It is a figure for demonstrating an effect | action when the control which concerns on this embodiment is implemented. It is a figure for demonstrating an effect | action when the control which concerns on this embodiment is implemented.

  Hereinafter, an engine control device 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 a control device of an engine of the present embodiment is applied.

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

  The engine body 1 has 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 reciprocably inserted in the cylinder 2 There is. A combustion chamber 6 is formed above the piston 5.

  The piston 5 is connected to the crankshaft 7, and in response to the reciprocation of the piston 5, the crankshaft 7 rotates about its central axis.

  The cylinder head 4 includes an injector (fuel supply device) 10 for injecting fuel into the combustion chamber 6 (in the cylinder 2), and a glow plug 11 for heating the mixture of fuel and air in the combustion chamber 6 Are provided for each cylinder 2 one by one.

  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. Also, the glow plug 11 has a heat generating portion at its tip that generates heat when energized, and the heat generating portion is attached to the ceiling surface of the combustion chamber 6 so as to be located near the tip portion of the injector 10 ing. For example, the injector 10 has a plurality of injection holes at its tip, and the glow plug 11 is positioned so that its heat generating portion is located between the plurality of sprays from the plurality of injection holes of the injector 10 and does not directly contact the fuel spray. Is arranged.

  The injector 10 is an injection that is mainly performed to obtain an engine torque, and is a main injection that injects a fuel that burns near the compression top dead center into the combustion chamber 6, and a retarded side of the main injection and a combustion. However, it is possible to carry out post injection that injects the fuel into the combustion chamber 6 at a time when the combustion energy hardly contributes to the engine torque.

  In the cylinder head 4, an intake port for introducing air supplied from the intake passage 20 into the combustion chamber 6 of each cylinder 2, an intake valve 12 for opening and closing the intake port, and a combustion chamber 6 of each cylinder 2 An exhaust port for leading out the exhaust 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 51a of the first turbocharger 51 (hereinafter referred to as appropriate as the first compressor 51a), and the compressor 52a of the second turbocharger 52 (hereinafter referred to as appropriate) from the upstream side. , The second compressor 52a), the intercooler 22, the throttle valve 23, and the surge tank 24 are provided. Further, the intake passage 20 is provided with an intake side bypass passage 25 that bypasses the second compressor 52 a and an intake side bypass valve 26 that opens and closes the second compressor 52 a. The intake side bypass valve 26 is switched between a fully closed state and a fully open state by a drive device (not shown).

  In the exhaust passage 40, in order from the upstream side, a turbine 52b of the second turbocharger 52 (hereinafter, appropriately referred to as a second turbine 52b), a turbine 51b of the first turbocharger 51 (hereinafter, appropriately, a first). Using a turbine 51b), a first catalyst 43, a DPF (Diesel particulate filter (PMF) 44), a urea injector 45 for injecting urea into the exhaust passage 40 on the downstream side of the DPF 44, and urea injected from the urea injector 45 A selective catalytic induction (SCR) catalyst 46 for purifying NOx and a slip catalyst 47 for oxidizing and purifying unreacted ammonia discharged from the SCR catalyst 46 are provided.

  The SCR catalyst 46 hydrolyzes the urea injected from the urea injector 45 to generate ammonia, and reacts (reduces) the ammonia with NOx in the exhaust to purify the ammonia.

  The DPF 44 collects particulate matter (PM: Particulate Matter) in the exhaust gas. The PM collected in the DPF 44 burns by being exposed to high temperature and supplied with oxygen, and is removed from the DPF 44. The temperature at which the PM burns and removes is a relatively high temperature of about 600 ° C. Therefore, to burn PM and remove it from the DPF 44, the temperature of the DPF 44 needs to be relatively high.

  The first catalyst 43 includes an NOx catalyst 41 that purifies NOx, and an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 42.

  The oxidation catalyst 42 oxidizes hydrocarbon (HC), that is, unburned fuel, carbon monoxide (CO), etc. using oxygen in the exhaust gas to convert it into water and carbon dioxide. Here, this oxidation reaction which occurs in the oxidation catalyst 42 is an exothermic reaction, and when the oxidation reaction occurs in the oxidation catalyst 42, the temperature of the exhaust gas is raised.

  The NOx catalyst 41 occludes NOx in the exhaust in a lean state (excess air ratio λ of λ> 1) where the air-fuel ratio of the exhaust is larger than the theoretical air-fuel ratio, and stores the occluded NOx into the air-fuel ratio of the exhaust Is close to the theoretical air fuel ratio (.lambda..apprxeq.1) or a rich state (.lambda. <1) smaller than the theoretical air fuel ratio, that is, the exhaust gas passing through the NOx catalyst 41 contains a large amount of unburned HC. NOx storage reduction type catalyst (NSC: NOx Storage Catalyst) which is reduced in The first catalyst 43 is formed, for example, by coating the surface of the catalyst material layer of DOC with the catalyst material of NSC.

  In the present embodiment, a device for separately supplying air or fuel to the exhaust passage is not provided, and the air-fuel ratio of the exhaust gas corresponds to the air-fuel ratio of the air-fuel mixture in the combustion chamber 6. 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 also becomes lean, and the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is near the stoichiometric air-fuel ratio (λ ≒ 1) or rich state smaller than the theoretical air fuel ratio (λ <1) is also close to the theoretical air fuel ratio (λ 1 1) or rich state smaller than the theoretical air fuel ratio (λ It becomes <1).

  Here, SOx is also stored (adsorbed) in the NOx catalyst 41 in addition to NOx. Specifically, the NOx catalyst 41 stores SOx in exhaust gas in a lean state (λ> 1) in which the air-fuel ratio of the exhaust gas is larger than the stoichiometric air-fuel ratio. The SOx stored in the NOx catalyst 41 is reduced in a state where the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio (λ ≒ 1) or in a rich state (λ <1) smaller than the theoretical air-fuel ratio.

  Although both the SCR catalyst 46 and the NOx catalyst 41 can purify NOx, the temperatures at which the purification rate (NOx storage rate) becomes high are different from each other, and the NOx purification rate of the SCR catalyst 46 (NOx storage rate) ) Becomes high when the temperature of the exhaust is relatively high, and the NOx purification rate of the NOx catalyst 41 becomes high when the temperature of the exhaust is relatively low.

  In the exhaust passage 40, an exhaust side bypass passage 48 for bypassing the second turbine 52b, an exhaust side bypass valve 49 for opening and closing the same, a waste gate passage 53 for bypassing the first turbine 51b, and a waste gate for opening and closing the same A valve 54 is provided. The exhaust side bypass valve 49 and the waste gate valve 54 are respectively switched to the fully closed state and the fully open state by the drive device (not shown), and are changed to any opening degree therebetween.

  The engine system 100 according to the present embodiment includes an EGR device 55 that recirculates part of the exhaust gas to the intake air. The EGR device 55 connects the portion of the exhaust passage 40 upstream of the upstream end of the exhaust side bypass passage 49 and the portion of the intake passage 20 between the throttle valve 23 and the surge tank 24. , A first EGR valve 57 for opening and closing the valve, and an EGR cooler 58 for cooling the exhaust gas passing through the EGR passage 56. The EGR device 55 also has 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.

(2) Control System The control system of the engine system will be described with reference to FIG. The engine system 100 according to this embodiment is mainly controlled by a PCM (power train 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 control means according to the present invention.

  Information from various sensors is input to the PCM 200. For example, the PCM 200 detects the rotational speed of the crankshaft 7, that is, the rotational speed sensor SN1 for detecting the engine rotational speed, detects the amount of fresh air (air) flowing in the intake passage 20 provided near the air cleaner 21 Air flow sensor SN2, an intake pressure sensor SN3 provided in the surge tank 24 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, Among them, it is electrically connected to an exhaust O2 sensor SN4 or the like for detecting the oxygen concentration of a portion between the first turbocharger 51 and the first catalyst 43, and receives input signals from these sensors SN1 to SN4. . Also, the vehicle is provided with an accelerator opening sensor SN5 for detecting an accelerator opening which is an opening of an accelerator pedal (not shown) operated by the driver, a vehicle speed sensor SN6 for detecting a vehicle speed, etc. Detection signals from these sensors SN5 and SN6 are also input to the PCM 200. The PCM 200 executes various calculations and the like based on input signals from the respective sensors (SN1 to SN6 and the like) to control the injectors 10 and the like.

(2-1) Normal control In normal control performed during normal operation in which DeNOx control, DeSOx control, and DPF regeneration control (filter regeneration control) described later are not performed, air mixture in the combustion chamber 6 is empty to improve fuel efficiency performance. The fuel ratio (hereinafter sometimes simply referred to as the air-fuel ratio of the air-fuel mixture) is made leaner (λ> 1, for example, λ = about 1.7) than the stoichiometric air-fuel ratio. For example, in normal control, the excess air ratio λ of the mixture is about λ = 1.7. Further, in the normal control, the post injection is stopped and only the main injection is performed. In the normal control, the operation of the glow plug 11 is stopped. Further, in the normal control, the first EGR valve 57, the second EGR valve 60, the intake side bypass valve 26, the exhaust side bypass valve 49, and the waste gate valve 54 respectively operate the operating state of the engine body 1, for example, the engine speed and the engine The EGR rate and the supercharging pressure are controlled to be respectively appropriate values according to the load and the like.

(2-2) DeNOx Control DeNOx control which is control for releasing (detaching) NOx stored in the NOx catalyst 41 (hereinafter referred to as stored NOx as appropriate) from the reduced NOx catalyst 41 will be described.

  As described above, in the NOx catalyst 41, the stored NOx is reduced in the state where the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio (λ ≒ 1) or in the rich state (λ <1) smaller than the theoretical air-fuel ratio. . Therefore, in the present embodiment, in order to reduce the stored NOx, it is necessary to reduce the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 more than in the normal operation.

  One way to reduce the air-fuel ratio of the mixture is to reduce the amount of fresh air introduced into the combustion chamber 6. However, if the amount of fresh air is simply reduced, engine torque may not be obtained properly. In particular, if the amount of fresh air is reduced during acceleration, the acceleration may be deteriorated.

  Therefore, in the present embodiment, the post injection is performed to reduce the air-fuel ratio of the air-fuel mixture without reducing the amount of fresh air or suppressing the amount of reduction of the amount of fresh air to a small amount. That is, the PCM 200 reduces the air-fuel ratio of the exhaust gas by causing the injector 10 to perform the post injection in addition to the main injection. For example, in the DeNOx control, the excess air ratio λ of the mixture and the exhaust gas is set to about λ = 0.94 to 1.06.

  In the present embodiment, DeNOx control for implementing post injection to reduce stored NOx as described above is performed only in the first region R1 and the second region R2 shown in FIG. The first region R1 has an engine speed equal to or higher than a predetermined first reference rotational speed N1 and equal to or lower than a predetermined second reference rotational speed N2, and has an engine load predetermined to be equal to or higher than the first reference load Tq1. This is an area equal to or less than 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 is a region where the engine load is equal to or higher than a predetermined third reference load Tq3.

  Further, the PCM 200 performs active DeNOx control in which post injection is performed at timing when the post-injected fuel burns in the combustion chamber 6 in the first region R1. The injection timing of the post injection is set in advance, for example, in the first half of the expansion stroke and at a time between 30 and 70 ° CA after compression top dead center. In the present embodiment, in the active DeNOx control, the glow plug 11 is energized to heat the air-fuel mixture in order to promote the combustion of the post-injected fuel. Further, in the active DeNOx control, although the first EGR valve 60 is fully closed and the second EGR valve 57 is opened, the opening degree thereof is smaller than that in the normal operation.

  On the other hand, in the second region R2, the PCM 200 performs passive injection in which post injection is performed at timing when the post-injected fuel does not burn in the combustion chamber 6 (the latter half of the expansion stroke, for example, 110 ° CA after compression top dead center) Implement control. Further, in the passive DeNOx control, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent the EGR cooler 58 and the like from being blocked by the deposit caused by the post-injected unburned fuel.

  As described above, the control content of the DeNOx control is changed in the first region R1 and the second region R2 for the following reason.

  In a region where the engine load is low or the engine load is relatively high but the engine rotational 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 due to the low temperature of the exhaust gas. So, in this embodiment, DeNOx control is stopped in this area.

  Also, as described above, although post injection is performed in DeNOx control, if the post-injected fuel is discharged to the exhaust passage 40 without being burned, the EGR cooler 58 etc. There is a risk of blocking. Therefore, it is preferable to burn the post-injected fuel 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, the combustion within the combustion chamber 6 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 before the gas in the chamber 6 is exhausted, and there is a possibility that the post-injected fuel can not be sufficiently burned in the combustion chamber 6 is there. In addition, the insufficient mixing may increase wrinkles. Therefore, 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 mixture is 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). Be Therefore, in the second region R2, the post injection injection amount required to reduce stored NOx (hereinafter referred to as a post injection amount as appropriate) is reduced, and unburned fuel is discharged to the exhaust passage 40. The said influence can be restrained small.

  Therefore, in the present embodiment, active DeNOx control is performed in which post-injected fuel is burned in the combustion chamber 6 in the first region R1 in which neither the engine load nor the engine speed is too low and too high. 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 exhaust temperature is sufficiently high and the DOC catalyst 42 is sufficiently activated. Therefore, the unburned fuel discharged to the exhaust passage 40 is purified by the DOC catalyst 42. Further, by permitting DeNOx control only in the middle rotation and middle load region as described above, it is possible to secure the combustion stability of post injection at the time of implementation of DeNOx control, and to suppress the deterioration of exhaust performance.

  In the active DeNOx control and the passive DeNOx control, the NOx storage amount is the NOx amount at which the temperature of the SCR catalyst 46 is lower than a predetermined temperature, the temperature of the NOx catalyst 41 is higher than a predetermined temperature, and the NOx catalyst 41 is storing If the amount is equal to or more than a predetermined amount, implementation is permitted. However, as described above, the active DeNOx control is performed only when the engine body 1 is operated in the first region R1, and the passive DeNOx control is performed when the engine body 1 is operated in the second region R2. To be implemented only in Further, in the present embodiment, the minimum value of the NOx storage amount permitted to be implemented is set to a value smaller in the passive DeNOx control than in the active DeNOx control.

(2-3) DPF Regeneration Control In this embodiment, DPF regeneration control, which is control for removing the PM collected by the DPF 44 to regenerate the purification capacity of the DPF 44, is performed.

  In the DPF regeneration control, the oxidation catalyst 42 reaches a predetermined temperature and the oxidation reaction becomes possible, and the amount of PM collected in the DPF 44 (hereinafter simply referred to as the PM deposition amount) is equal to or more than the regeneration start amount preset. When the PM accumulation amount becomes equal to or less than the regeneration end amount set to a value smaller than the regeneration start amount, the processing is ended. The PM deposition amount is calculated from, for example, the differential pressure across DPF 44 (the difference between the pressure upstream of DPF 44 and the pressure downstream) calculated from pressure sensors provided upstream and downstream of DPF 44, etc. Ru.

  The PM collected in the DPF 44 can be removed from the DPF 44 by burning under high temperature. On the other hand, if the oxidation catalyst 42 contained in the first catalyst 43 provided upstream of the DPF 44 causes an oxidation reaction of HC or the like, that is, unburned fuel, the temperature of the exhaust flowing into the DPF 44 can be increased. .

  Therefore, in the present embodiment, as DPF regeneration control, post injection is performed while making the air-fuel ratio of the air-fuel mixture leaner than the theoretical air-fuel ratio, air and unburned fuel are made to flow into the oxidation catalyst 42, and these are oxidized catalyst Control to oxidize at 42 is implemented. 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 (at the second half of the expansion stroke, for example, 110 ° CA after compression top dead center) . For example, in DPF regeneration control, the excess air ratio λ of the mixture gas and the exhaust gas is about λ = 1.2-1.4.

  In DPF regeneration control, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent unburned fuel from flowing into the EGR passage 56 and the EGR cooler 58 and being blocked. Further, in the DPF regeneration control, since it is not necessary to burn the post injection, the energization of the glow plug 11 is stopped.

(2-4) DeSOx Control Next, DeSOx control (air-fuel ratio control) which is control for reducing and removing SOx stored in the NOx catalyst 41 (hereinafter referred to as stored SOx as appropriate) will be described.

  As described above, in the NOx catalyst 41, the stored SOx is reduced in the state where the air-fuel ratio of the exhaust gas is near the stoichiometric air-fuel ratio (λ ≒ 1) or in the rich state (λ <1) smaller than the theoretical air-fuel ratio. . Along with this, even in DeSOx control, in order to make the air-fuel ratio of the air-fuel mixture close to the theoretical air-fuel ratio (λ ≒ 1) or to make the rich state smaller than the theoretical air-fuel ratio (λ <1), Implement post injection.

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

  Therefore, in the present embodiment, as the DeSOx control, post injection is performed similarly to the DeNOx control, and the air-fuel ratio of the exhaust is made richer than in the normal operation to make it close to or smaller than the stoichiometric air-fuel ratio. Make the air and unburned fuel into the oxidation catalyst 42 by performing the rich injection and the post injection while making the air-fuel ratio of the exhaust gas leaner than the theoretical air-fuel ratio (hereinafter referred to simply as being lean). The step of supplying and oxidizing these with the oxidation catalyst 42 is alternately performed.

  In this embodiment, a basic one cycle time, that is, a combination of one rich step execution time and one lean step execution time (the interruption time of the DeSOx control as described later and the first While the time (under conditions excluding the time of return to the region R1) is preset (for example, 60 to 80 seconds), the ratio of the lean step execution time to the rich step execution time is preset. In this embodiment, the ratio is set to increase as the engine speed decreases as shown in FIG. 4 and to increase as the engine load decreases as shown in FIG. And in connection with this, basic rich time which is basic implementation time of one rich step, and basic lean time which is basic implementation time of one lean step are determined.

  In the rich step, similarly to the active DeNOx control, the post injection is performed at the timing when the post-injected fuel burns in the combustion chamber 6 (in the first half of the expansion stroke, for example, 30 to 70 ° CA after compression top dead center) Conduct. Then, in the rich step, the excess air ratio λ of the mixture and the exhaust is set to about 1.0, and the air-fuel ratio of the mixture and the exhaust is made close to the theoretical air-fuel ratio. For example, in the rich step, the excess air ratio λ of the mixture and the exhaust gas is set to about λ = 0.94 to 1.06. In the rich step, the PCM 200 fully closes the first EGR valve 57 as in the active DeNOx control, while making the second EGR valve 60 open, but making its opening degree smaller than that in the normal operation. Further, in the rich step, the PCM 200 controls the throttle valve 23, the exhaust side bypass valve 49 and the waste gate valve 54 in such a direction that the amount of intake air is smaller than that in the normal operation.

  On the other hand, in the lean step, the post injection is performed at a timing at which the post-injected fuel does not burn in the combustion chamber 6 (at the second half of the expansion stroke, for example, 110 ° CA after compression top dead center). Then, the air-fuel ratio of the mixture and the exhaust gas is made leaner than the stoichiometric air-fuel ratio by setting the excess air ratio λ of the mixture and the exhaust gas to 1 or more. For example, in the lean step, the excess air ratio λ of the mixture and the exhaust gas is set to about λ = 1.2 to 1.4. Further, in the lean step, the first EGR valve 57 and the second EGR valve 60 are fully closed in order to prevent the EGR cooler or the like from being blocked by the deposit caused by the unburned fuel.

  As described above, in the DeSOx control, it is necessary to make the air-fuel ratio of the mixture in the combustion chamber 6 lean. Therefore, it is difficult to implement DeSOx control in the second region where the engine load is high and the air-fuel ratio of the air-fuel mixture can not be made sufficiently lean. On the other hand, as described above, the control for burning the post injection is preferably performed in the first region R1. Thus, in the present embodiment, the DeSOx control is performed only when the engine body 1 is operated in the first region (specific operation region) R1.

  The PCM 200 calculates the post injection amount as follows. First, the PCM 200 includes the oxygen concentration of the exhaust detected by the exhaust O2 sensor SN4 provided on the upstream side of the first catalyst 43 (NOx catalyst 41), the intake air amount detected by the air flow sensor SN2, and the combustion chamber 6 The oxygen concentration (oxygen concentration before combustion) in the combustion chamber 6 is estimated based on the amount of EGR gas introduced into the combustion chamber. Then, a basic value of the post injection amount is calculated based on the estimated oxygen concentration in the combustion chamber 6, that is, the oxygen concentration of the intake air. The amount of EGR gas is estimated from the operating state of the engine, the differential pressure between the EGR valves 57 and 60, and the like. Next, the PCM 200 corrects the basic post injection amount based on the oxygen concentration of the exhaust detected by the exhaust O2 sensor SN4, the amount of the main injection, and the like. That is, the PCM 200 performs feedback control of the post injection amount so that the air-fuel ratio of the exhaust gas corresponding to the detected oxygen concentration of the exhaust gas becomes the target air-fuel ratio, thereby setting the air-fuel ratio of the exhaust gas to an appropriate value.

  Here, as described above, if the air-fuel ratio of the air-fuel mixture in the combustion chamber 6 is made leaner than the theoretical air-fuel ratio and the post injection is performed without burning the fuel, the PM can be removed by burning. , PM can be removed by combustion when the lean step is performed. Then, in the present embodiment, as described above, the air-fuel ratio of the air-fuel mixture in the lean step becomes the same value as the air-fuel ratio at the DPF regeneration control so that the PM can be removed by combustion when the lean step is performed. (The excess air ratio λ is λ = 1.2 to 1.4).

(2-5) Flow of Control (i) DeSOx Basic Flag The procedure for setting the DeSOx basic flag will be described with reference to the flowchart of FIG.

  The DeSOx basic flag is a flag that is set to 1 when a basic condition for implementing DeSOx control is satisfied, and is set to 0 when a basic condition for stopping DeSOx control is satisfied.

  First, in step S11, the PCM 200 determines whether the SOx storage amount is equal to or more than the first SOx storage amount set in advance. The first SOx storage amount is the maximum value of the SOx storage amount that does not need to be controlled by DeSOx, and is set to a value near zero.

  If the determination in step S11 is NO and the SOx storage amount is less than the first SOx storage amount, it is not necessary to implement the DeSOx control, so the process proceeds to step S22 and the DeSOx basic flag is set to 0.

  On the other hand, if the determination in step S11 is YES, the process proceeds to step S12, and the PCM 200 determines whether the DPF regeneration control execution flag is 1. The DPF regeneration control execution flag is a flag indicating whether or not DPF regeneration control is being performed, and becomes 1 when DPF regeneration control is performed, and becomes 0 otherwise. As described above, the DPF regeneration control execution flag is set to 1 when the oxidation catalyst 42 reaches a predetermined temperature and the PM deposition amount exceeds the regeneration start amount, and then the PCM deposition amount falls below the regeneration end amount. It will be 0.

  If the determination in step S12 is NO, the process proceeds to step S22 and the DeSOx basic flag is set to 0. On the other hand, if the determination in step S12 is YES, the process proceeds to step S13, and the PCM 200 determines whether the PM deposition amount is less than or equal to the preset DeSOx start deposition amount. The DeSOx start deposition amount is set to a value smaller than the aforementioned regeneration start amount. For example, the DeSOx start permission amount is set to about half the regeneration start amount.

  If the determination in step S13 is NO, the PCM 200 proceeds to step S21 and maintains the value of the DeSOx basic flag at the current value. On the other hand, if the determination in step S13 is YES, the process proceeds to step S14, and the PCM 200 determines whether the SOx storage amount is greater than or equal to the second SOx storage amount set in advance. The second SOx storage amount is the minimum value of the SOx storage amount to start DeSOx control, and is set to, for example, a value slightly smaller than the SOx amount that can be stored by the NOx catalyst 41.

  If the determination in step S14 is NO, the PCM 200 proceeds to step S21 and maintains the value of the DeSOx basic flag at the current value. On the other hand, if the determination in step S14 is YES, the process proceeds to step S15, and the PCM 200 determines whether the engine body 1 is operated in the first region R1.

  If the determination in step S15 is NO, the PCM 200 proceeds to step S21 and maintains the value of the DeSOx basic flag at the current value. On the other hand, when the determination in step S15 is YES, the PCM 200 proceeds to step S16 and sets the DeSOx basic flag to 1.

  As described above, the SOx storage amount is the second SOx storage amount and the first SOx storage amount, the DPF regeneration execution flag is 1, the PM deposition amount is the DeSOx start deposition amount or less, and the engine main body 1 in the first region R1. Is being driven, the DeSOx basic flag is 1. Then, when the SOx storage amount falls below the first SOx storage amount or the DPF regeneration execution flag becomes 0, the DeSOx basic flag becomes 0.

(Ii) Control Procedure of DeSOx Control A control procedure of DeSOx control will be described using the flowcharts of FIGS. 7 and 8.

  The PCM 200 first determines whether the DeSOx basic flag has changed from 0 to 1 in step S31. And if this determination becomes YES, it will progress to step S32 and PCM200 will start DeSOx control. As shown in FIG. 6, when the DeSOx basic flag changes from 0 to 1, the engine is in the state of being operated in the first region R1.

  In the present embodiment, at the start of the DeSOx control, first, the rich step is started, and the PCM 200 performs post injection at the timing when the injected fuel burns in the combustion chamber 6 and mixes the mixture. Make air and exhaust air-fuel ratio rich.

  After step S32, the process proceeds to step S33, and the PCM 200 determines whether the engine is operated in the first region R1, that is, after the start of the DeSOx control, the operating region of the engine deviates from the first region R1 and shifts to another region. It is determined whether it has been done. If this determination is YES, the process proceeds to step S37. On the other hand, if the determination is NO, the process proceeds to step S34.

  In step S37, the PCM 200 has the rich continuation time which is the execution time of the rich step performed immediately before is equal to or greater than the basic rich time, or the lean continuation time which is the execution time of the lean step performed immediately before the basic lean time It is determined whether the That is, it is determined whether the duration of one step has become equal to or longer than a predetermined time set in advance. If this determination is YES, the PCM 200 proceeds to step 39 and switches between the rich step and the lean step. On the other hand, if this determination is NO, the PCM 200 proceeds to step S38 and maintains the current step. After step S38 or step S39, the process proceeds to step S40. Thus, when the engine is continuously operated in the first region R1, the rich step and the lean step are alternately performed for the basic rich time and the basic lean time, respectively.

  In step S40, the PCM 200 determines whether the DeSOx basic flag is 1 or not. If the determination is YES, the process returns to step S33. On the other hand, if the determination in step S40 is NO, the process ends as it is (return to step S31). That is, the DeSOx control ends.

  In step S34, which proceeds when the determination in step S33 is NO, the PCM 200 suspends DeSOx control (while the DeSOx control is suspended, the suspension is maintained). In the present embodiment, as described above, DeSOx control is performed during implementation of DPF regeneration control. Therefore, when the DeSOx control is interrupted, the control is switched to the DPF regeneration control, the air-fuel ratio of the air-fuel mixture is made lean, and the timing of post injection is made the timing when the fuel does not burn. However, in the present embodiment, since the control content of the lean step of the DPF regeneration control and the DeSOx control is the same, when this is interrupted at the time of performing the lean step, the specific control content does not change. After step S34, the process proceeds to step S35.

  In step S35, the PCM 200 determines whether or not it has returned to the first region R1. If this determination is NO, the PCM 200 returns to step S34. That is, step S34 is implemented and the DeSOx control is interrupted until the determination in step S35 is YES and the process returns to the first region R1. And if determination of step S35 becomes YES, it will progress to step S42 and will implement step S42-step S50.

  FIG. 8 is a flowchart showing the flow of control from step S42 to step S45.

  In step S42, the PCM 200 is the time spent in the other region, that is, the operation region other than the first region R1 (the period from the first region R1 to the other region and the return to the first region R1) It is determined whether or not the time of (1) is equal to or greater than a preset reference staying time (determination time). The reference stay time is set to a time shorter than the basic lean time, and is set to, for example, about 5 to 10 seconds.

  If the determination in step S42 is YES and the other area stay time is equal to or longer than the reference stay time, the process proceeds to step S46. In step S46, the PCM 200 sets the other area staying time as the interruption time. After step S46, the process proceeds to step S47.

  In step S47, the PCM 200 sets a target rich time based on the interruption time.

  The target rich time is set such that the shorter the pause time, the shorter the basic rich time. In the present embodiment, the target rich time is set based on the ratio of the basic lean time to the basic rich time determined from the current engine speed of the engine body 1 and the engine load as described above, and the interruption time. Specifically, the target rich time is set such that the ratio of the region staying time to the target rich time matches the ratio of the basic lean time to the basic rich time, and thereby the same operating conditions (engine speed, engine In the load), the shorter the interruption time, the shorter the target rich time. After step S47, the process proceeds to step S48.

  In step S48, the PCM 200 carries out rich step and resumes (returns) DeSOx control. After step S48, the process proceeds to step S49. In step S49, it is determined whether the rich continuation time which is the continuation time of the rich step performed immediately before is equal to or more than the target rich time set in step S47. If this determination is NO and the rich step has not been performed for the target rich time yet, the process returns to step S48. Thus, the PCM 200 continues the rich step until the rich continuation time becomes equal to or more than the target rich time.

  Then, if the determination in step S49 is YES, the PCM 200 proceeds to step S50 and switches to the lean step. After step S50, the process proceeds to step S37 shown in FIG. Then, the control returns to the normal DeSOx control (control for performing rich step and lean step at basic rich time and basic lean time).

  On the other hand, if the determination in step S42 is NO, and the other area stay time is less than the reference stay time, the PCM 200 proceeds to step S43. In step S43, the PCM 200 continues the suspension of the DeSOx control. In the present embodiment, DPF regeneration control is continued as described above.

  After step S43, the process proceeds to step S44. In step S44, the PCM 200 determines whether the time (return time to R1) after returning to the first region R1 is equal to or longer than a predetermined time. If the determination in step S44 is NO, the process returns to step S43 and the PCM 200 continues the suspension of the DeSOx control.

  As described above, even when the first region R1 is returned, if the time spent in the first region R1 (the other region staying time) is less than the reference stay time, the first region R1 is restored. The suspension of DeSOx control is continued until the time from when the predetermined time reaches or exceeds a predetermined time. In the present embodiment, the predetermined time is set to a value obtained by subtracting the stay time in the other area from the reference stay time, and at least after the operation area of the engine shifts from the first area R1 to the other area. The DeSOx control will be interrupted until the reference stay time passes. The predetermined time may be separately set to a preset constant value or the like.

  After the determination in step S44 is YES, the process proceeds to step S45, and the PCM 200 performs the other area staying time (the time spent in the first area R1) and the predetermined time (the first area R1) after returning to the DeSOx. The time obtained by combining the time during which the suspension of control is continued) is calculated as the suspension time. After step S45, the process proceeds to step S47. In the present embodiment, as described above, the value of the interruption time is made the same as the value of the reference staying time in step S45.

  In step S47, the target rich time is set based on the interruption time as described above.

  As described above, in the present embodiment, when returning to the first region R1, if the other region staying time is equal to or longer than the reference staying time, the target rich time is set according to the other region staying time Is less than the reference time, the target rich time is set in accordance with the sum of the other area stay time and the predetermined time. However, even during the other region staying time, the DeSOx control is interrupted even during the predetermined time, and the air fuel ratio of the mixture and the exhaust gas is made lean. Therefore, in any of the above cases, the target rich time is set according to the time during which the DeSOx control is interrupted and the air-fuel ratio of the mixture is lean.

  FIG. 9 schematically shows the time change of various parameters when the above control is performed.

  In FIG. 9, the normal operation in which the air-fuel ratio of the air-fuel mixture (and the exhaust gas) is made leaner than the stoichiometric air-fuel ratio is implemented until time t1, and the DPF regeneration flag switches from 0 to 1 at time t1. There is. Further, the first region operation flag in FIG. 9 is 1 when the engine body 1 is operated in the first region R1 and 1 when the engine body 1 is operated in the other regions is 0. is there.

  When the DPF regeneration flag switches from 0 to 1 at time t1, the post injection is performed while the air-fuel ratio of the air-fuel mixture is made lean. As a result, the PM deposition amount is reduced. When the PM deposition amount decreases to the DeSOx start deposition amount at time t2, the DeSOx basic flag becomes 1. Along with this, DeSOx control is started. Specifically, after time t2, the rich step in which the air fuel ratio of the exhaust gas is made rich and post injection is performed, and the lean step in which the air fuel ratio of the exhaust gas is made lean and the post injection is performed are alternately performed. Ru. Then, the stored SOx is desorbed mainly at the time of implementation of the rich step, and the SOx storage amount decreases, and the PM is burned and removed mainly at the time of the implementation of the lean step, so that the PM deposition amount is reduced.

  Here, at time t4 in the middle of the rich step started at time t3, the operating region of the engine body 1 shifts to a region other than the first region R1 (for example, the operating region of the engine is as shown by arrow Y1 in FIG. 3). At time t4, DeSOx control is interrupted to shift to DPF regeneration control, and the air-fuel ratio of the exhaust gas is made lean accordingly.

  Thereafter, at time t5, the operating region of the engine body 1 returns to the first region R1 (for example, the operating region of the engine changes as indicated by the arrow Y2 in FIG. 3). In the example of FIG. 9, the time Δt2 from time t4 to time t5, which is the other area staying time, is equal to or longer than the reference staying time. Therefore, at time t5, DeSOx control is resumed along with the return to the first region R1. At this time, first, the rich step is performed, and the air-fuel ratio of the exhaust gas is made rich. Thereafter, the rich step is continued until time t6.

  Here, as described above, the rich step continuation time Δt3 from the time t5 to the time t6 and after the return to the first region R1 is set based on the other region staying time Δt2. Therefore, in the illustrated example, the rich step continuation time Δt3 is also shortened corresponding to the other area staying time Δt2 being relatively short.

  When the first rich step after returning to the first region R1 is completed at time t6, the normal (which is continued by the basic lean time and basic rich time) lean step and rich step are repeated again.

  Further, in the example of FIG. 9, the operating range of the engine body 1 again deviates from the first range R1 during execution of the lean step at time t8, and returns to the first range R1 at time t9. However, the other region staying time Δt4 at this time is longer than the basic rich time Δt1. Therefore, the duration Δt5 of the rich step when the rich step is resumed at time t9 is made the same as the basic rich time Δt1.

  In the example of FIG. 9, the DeSOx basic flag is set to 0 at time t10 as the SOx storage amount decreases to less than the first SOx storage amount at time t10 due to the execution of the rich step from time t9. Control is stopped. On the other hand, in the example of FIG. 9, the DPF regeneration control is performed until time t11 with the PM deposition amount not falling below the regeneration end amount at time t10. Then, at time t11 when the PM deposition amount falls below the regeneration end amount, the DPF regeneration flag is set to 0, the DPF regeneration control is stopped, and the normal control returns.

(3) Operation, Etc. As described above, in the present embodiment, the rich step is performed when the operating range of the engine shifts to a range other than the first range R1 and then returns to the first range R1 to resume DeSOx control. Let me start earlier. Therefore, it can be avoided that the time during which the air-fuel ratio of the exhaust gas is leaned becomes excessively long.

  This will be specifically described with reference to FIG. FIG. 10 is a view schematically showing temporal changes in the first region operation flag and the air-fuel ratio of the exhaust gas when the DeSOx control is performed. The air-fuel ratio of the exhaust shown by the second solid line from the top in FIG. 10 is the air-fuel ratio of the exhaust in the present embodiment. On the other hand, the air-fuel ratio of the exhaust gas indicated by the lowermost broken line in this figure is the air-fuel ratio when the lean step is first started at the restart of the DeSOx control in the comparative example.

  As shown in FIG. 10, after the operating range of the engine body 1 deviates from the first range R1 at time t10 and the air-fuel ratio of the exhaust gas becomes lean, when returning to the first range R1 at time t11, DeSOx from time t11 At this time, if the lean step is first resumed as shown by the broken line, the air-fuel ratio of the exhaust gas is made lean for a long time from the time t10 to the time t12 until the lean step ends. Ru. Therefore, from time t10 to time t12, the stored SOx can not be sufficiently reduced, and the time taken for the reduction of the stored SOx becomes long.

  On the other hand, in the present embodiment, since the rich step is resumed first when returning to the first region R1, the reduction of the stored SOx becomes possible from time t11, and the time taken for the reduction of the stored SOx is shortened. be able to.

  Further, in the present embodiment, the upper limit of the normal rich time is set so that the execution time of the rich step to be performed first when restarting the DeSOx control is shorter as the time during which the DeSOx control is interrupted is shorter. Therefore, in accordance with the time when the DeSOx control is interrupted and the air fuel ratio of the air fuel mixture and the exhaust gas is made lean, the time of the rich step at the time of restarting DeSOx can be appropriately shortened. Therefore, it is possible to avoid an increase in the time of the rich step and an excessive decrease in the temperature of the NOx catalyst, and to suppress an increase in the time required for the reduction process of SOx along with the temperature decrease.

  This will be specifically described with reference to FIG. Similarly to FIG. 10, FIG. 11 schematically shows the first region operation flag and the time change of the air fuel ratio of the exhaust (solid line: air fuel ratio of the exhaust according to the present embodiment, broken line: air fuel ratio of the exhaust according to the comparative example). FIG. The comparative example in this figure is an example in which the rich step is started first when returning to the first region R1 as in the present embodiment, while the duration of the rich step at this time is the basic rich time.

  As shown in FIG. 11, the operating range of the engine body 1 deviates from the first range R1 at time t20 during execution of the rich step, and then the first range R1 occurs at time t21 where the elapsed time from time t20 is relatively short. When DeSOx control is resumed after returning to step 1, if the rich step is performed for the basic rich time Δt1 as in the comparative example, the exhaust air / fuel ratio is made rich relative to the time taken to be lean. Time will be too long. Therefore, in this case, the temperature raising effect of the exhaust gas due to the oxidation reaction in the oxidation catalyst 42 can not be appropriately obtained, and the temperature of the exhaust gas and the NOx catalyst 41 is greatly reduced. Then, along with this, the stored SOx can not be sufficiently reduced, and the time taken for the reduction of the stored SOx becomes long.

  On the other hand, in the present embodiment, the lean step is started early by suppressing the duration Δ10 of the rich step performed from time t21 to a short time corresponding to the time during which the air-fuel ratio of the exhaust gas is leaned. It can be done. Therefore, an oxidation reaction can be appropriately generated in the oxidation catalyst 42 to raise the temperature of exhaust gas earlier, and the temperature decrease of the exhaust gas and the NOx catalyst 41 can be suppressed. Therefore, the time taken for the reduction of the stored SOx can be shortened.

  Further, in the present embodiment, when the other area stay time is shorter than the reference stay time, even after returning to the first area R1, the time after the DeSOx control is interrupted and returned to the first area R1. DeSOx control is resumed after the predetermined time has passed. Therefore, it is possible to suppress that the execution time of the first rich step at the time of restarting DeSOx control becomes excessively short in accordance with the short other region staying time, and the lean step is performed before the exhaust air-fuel ratio becomes sufficiently rich. It can be prevented from being started.

  In particular, in the present embodiment, as described above, the post injection amount is feedback-controlled so that the air-fuel ratio of the exhaust gas corresponding to the detected oxygen concentration of the exhaust gas becomes the target air-fuel ratio. Therefore, even if the rich step is resumed, there is a possibility that the air-fuel ratio of the exhaust gas can not be made rich enough immediately. As mentioned above, if the execution time of the rich step is short Therefore, the temperature of the NOx catalyst 41 may be lowered. Therefore, if DeSOx control is resumed after the time since the return to the first area R1 after returning to the first area R1 when the other area stay time is less than the reference stay time as described above, the rich step time is Thus, the air-fuel ratio of the exhaust gas can be made sufficiently rich, and then the air-fuel ratio of the exhaust gas can be appropriately leaned.

(4) Modified Example Here, in the above embodiment, the DeSOx control is performed when performing the DPF regeneration control, but the DeSOx control may be performed regardless of whether the DPF regeneration control is being performed. You may configure it. However, as described above, if the reduction of the stored SOx and the combustion removal of PM are simultaneously performed with the air-fuel ratio of the exhaust at the lean step of DeSOx control as the air-fuel ratio capable of combustion removal of PM, NOx can be efficiently reduced. The purification performance of the catalyst 41 and the DPF 44 can be enhanced (restored). When the DeSOx control is performed regardless of the implementation state of the DPF regeneration control, the normal control is performed along with the interruption of the DeSOx control. Then, at step S48, the air fuel ratio is made lean by execution of the normal control.

  In the above embodiment, although the ratio of the basic lean time to the basic rich time is changed according to the engine speed and the engine load, the ratio is constant regardless of the engine speed or the engine load. It may be. However, when the engine speed is high and when the engine load is high, various devices provided in the exhaust passage and the exhaust passage are likely to become hot. Therefore, if the ratio of lean steps in which the exhaust gas temperature is likely to be high due to the oxidation reaction in the oxidation catalyst is reduced as the engine rotational speed is higher and the engine load is higher, it is provided in the exhaust and exhaust passages It is possible to suppress the excessively high temperatures of the various devices.

1 engine body 2 cylinders 6 combustion chamber 10 injector (fuel supply device)
40 exhaust passage 41 NOx catalyst 42 oxidation catalyst 44 DPF (PM filter)
200 PCM (control means)
R1 1st area (specific operation area)

Claims (6)

It is provided in an engine body in which a cylinder is formed and an exhaust passage through which exhaust gas discharged from the engine body flows, and occludes NOx in exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the theoretical air-fuel ratio And a NOx catalyst for reducing and releasing NOx stored when the air-fuel ratio of exhaust gas is near the stoichiometric air-fuel ratio or richer than the stoichiometric air-fuel ratio,
A fuel supply device for supplying fuel into the cylinder;
In order to eliminate S poisoning of the NOx catalyst, the air-fuel ratio of the exhaust gas is made to be closer to or richer than the theoretical air-fuel ratio for a preset basic rich time in a predetermined specific operation range. The fuel supply device so that the unburned fuel is discharged to the exhaust passage for a preset basic lean time and the air-fuel ratio of the exhaust gas becomes leaner than the stoichiometric air-fuel ratio for the rich step driving the fuel supply device Control means for alternately performing air-fuel ratio control for performing lean steps for driving
The control means limits the air-fuel ratio control when the operating range of the engine shifts from the specific operating range to another range during execution of the air-fuel ratio control, and after the transition, the operating range of the engine is again the specific operating range When the air-fuel ratio control is restored, when the air-fuel ratio control is restored, the rich step is first returned from the rich step and the operating range of the engine is shifted from the specific operating range to another range. And setting the execution time of the rich step to be performed first so that the execution time of the rich step to be performed first after the return of the air-fuel ratio control becomes shorter if the time for which the air-fuel ratio control is limited is shorter. The control device of the engine which makes it feature. In the engine control device according to claim 1,
The control means is configured such that the engine operating region is in a state in which the time from when the operating region of the engine shifts from the specific operating region to another region and before returning to the specific operating region is less than a predetermined determination time. When returning to the specific operating range, the control of the air-fuel ratio is restored after continuing the restriction of the air-fuel ratio control for a predetermined time after the return to the specific operating range. In the engine control device according to claim 1 or 2,
A PM filter provided downstream of the NOx catalyst in the exhaust passage and capable of collecting particulate matter in the exhaust gas;
An air-fuel ratio of exhaust gas at the time of implementation of the lean step is set to an air-fuel ratio at which the particulate matter can be combusted in the PM filter. In the engine control device according to any one of claims 1 to 3,
A control device for an engine, wherein the ratio of the basic lean time to the basic rich time is set smaller as the engine speed is higher. In the engine control device according to any one of claims 1 to 4,
A control device for an engine, wherein the ratio of the basic lean time to the basic rich time is set smaller as the engine load is higher. In the engine control device according to any one of claims 1 to 5,
A control device for an engine, wherein the control means sets an execution time of the rich step performed first after the return of the air-fuel ratio control to be equal to or less than the basic rich time.

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