JP2019065826A - Exhaust emission control device for engine - Google Patents

Abstract

To suppress the pass-through of NHto the downstream side of an SCR catalyst while properly eliminating NOx.SOLUTION: In an engine having an exhaust passage 40 where an NOx catalyst 41 and an SCR catalyst 46 are provided, there are provided excess air ratio change means 10 for changing an excess air ratio λ of exhaust gas, and SCR reductant supply means 45 for supplying SCR reductant formed of a raw material for NHor the NHinto the exhaust passage 40 between the NOx catalyst 41 and the SCR catalyst 46. Regeneration control is performed to regenerate the NOx catalyst 41, and the SCR reductant is less supplied from the SCR reductant supply means 45 to the exhaust passage 40 when the temperature of the NOx catalyst 41 at the time of the regeneration control is high, than when it is low.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust gas purification control device for an engine provided with an NOx catalyst and an SCR catalyst in an exhaust passage.

  Conventionally, it is known to provide a catalyst or the like in an exhaust passage in order to purify NOx exhausted from an engine.

For example, according to Patent Document 1, when the air excess ratio of the exhaust gas is larger than 1, that is, when the air-fuel ratio of the exhaust gas is in a lean state larger than the theoretical air-fuel ratio, NOx in the exhaust gas is stored. An NOx storage reduction type NOx catalyst is provided in the exhaust passage, which reduces NOx stored when the air excess ratio of gas is 1 or less, and NH ₃ (ammonia) downstream of the NOx catalyst in the exhaust passage. Discloses an engine provided with an SCR catalyst that purifies NOx in exhaust gas by reaction with the catalyst. In this engine, an ammonia compound injection device for injecting an ammonia compound to be a raw material of NH ₃ is provided on the upstream side of the SCR catalyst in the exhaust passage, and NH ₃ is generated from the ammonia compound injected by this device. , NOx is purified in the SCR catalyst.

Patent No. 3518398 gazette

Here, in the NOx storage reduction type NOx catalyst as described above, when the NOx stored in the NOx catalyst is reduced, “N” in the stored NOx and H as the reducing agent introduced are NH ₃ is generated by combining with each other.

Therefore, as in Patent Document 1, an SCR catalyst is provided downstream of the NOx catalyst, and an engine provided with a device for supplying a substance to be an NH ₃ or NH ₃ raw material in the exhaust passage is simply provided with a fixed amount. If a substance to be a raw material of NH ₃ or NH ₃ is supplied to the exhaust passage, when the NOx is reduced by the NOx catalyst, the amount of NH ₃ supplied to the SCR catalyst becomes excessive, and many NH ₃ may slip to the downstream side of the SCR catalyst.

On the other hand, it is conceivable to reduce the amount of substances such as NH ₃ supplied from the device to the exhaust passage when NOx is reduced by the NOx catalyst. However, if this amount of reduction is not properly controlled, there is again the problem that NH ₃ slips downstream than the SCR catalyst. Alternatively, the lack of NH ₃ supplied to the SCR catalyst, a problem that NOx can not be properly purified by the SCR catalyst occurs.

The present invention has been made in view of the circumstances described above, to provide an exhaust gas purification control apparatus for an engine slipping possible suppression of the downstream side of the SCR catalyst NH ₃ while appropriately purify NOx To aim.

In order to solve the above problems, the inventors of the present invention, as a result of earnest research, when using a NOx storage reduction type NOx catalyst having an oxygen storage capacity, an exhaust gas for reducing NOx stored in the NOx catalyst excess air rate with 1 or less immediately be carried out playback control for playing the NOx catalyst without being released NH ₃ from NOx catalyst, the NH ₃ from the NOx catalyst since the start of the regeneration control start to be released It was determined that there was a predetermined delay time between Furthermore, the inventors of the present invention have a high correlation with the storage oxygen reduction rate, which is the reduction rate of oxygen stored in the NOx catalyst, and the delay time is longer when the storage oxygen reduction rate is smaller. I found out. Here, when the delay time is shorter, after the regeneration control is started, the amount of NH ₃ which is released from the NOx catalyst and supplied to the SCR catalyst and stored (stored) in the SCR catalyst becomes larger than that of the longer one. . Therefore, temporarily supplying a fixed amount of NH ₃ or its raw material to the exhaust passage independently of the delay time at the time of regeneration control may result in excessive or insufficient NH ₃ in the SCR catalyst.

The present invention has been made based on this finding, and includes an engine body in which cylinders are formed, an exhaust passage through which exhaust gas discharged from the engine body flows, and an NOx catalyst provided in the exhaust passage. An exhaust gas purification control apparatus for an engine, comprising: an SCR catalyst provided downstream of the NOx catalyst, the excess air ratio changing means for changing an excess air ratio of exhaust gas, and the NOx in the exhaust passage. A SCR reducing agent supply means for supplying a raw material of NH ₃ or a reducing agent for SCR consisting of NH ₃ between the catalyst and the SCR catalyst, the air excess ratio changing means, and the reducing agent supply means for the SCR Control means for performing regeneration control to regenerate the NOx catalyst by controlling the excess air ratio of the exhaust gas to 1 or less by the excess air ratio changing means while controlling When the temperature of the NOx catalyst at the time of the regeneration control is high, the control means is configured so that the amount of the SCR reducing agent supplied from the SCR reducing agent supply means to the exhaust passage is smaller than when the temperature is low. Controlling the reducing agent supply means for SCR (claim 1).

  According to the findings of the inventors of the present invention, the rate of decrease in stored oxygen increases as the temperature of the NOx catalyst increases.

On the other hand, in this device, the higher the temperature of the NOx catalyst at the time of regeneration control, the smaller the amount of the SCR reducing agent supplied from the SCR reducing agent supply means to the exhaust passage. That is, in this device, when the storage oxygen reduction rate increases with the temperature of the NOx catalyst and the delay time is short, furthermore, the NOx catalyst is released from the NOx catalyst and the SCR catalyst is short When the total amount of NH ₃ supplied to the exhaust gas increases, the amount of the SCR reducing agent supplied to the exhaust passage is reduced.

Therefore, the amount is the sum of NH ₃ supplied from the NOx catalyst to the SCR catalyst and the amount of NH ₃ supplied to the SCR catalyst by the SCR reducing agent supply means during regeneration control, and is supplied to the SCR catalyst. The total amount of NH ₃ can be maintained at an appropriate amount, and the NOx can be appropriately purified in the SCR catalyst, and the slip-through of NH ₃ to the downstream side of the SCR catalyst can be suppressed.

  Further, according to the findings of the present inventors, the lower the temperature of the NOx catalyst, the larger the rate of change of the rate of decrease in stored oxygen with respect to the temperature of the NOx catalyst.

  Therefore, in the above-mentioned configuration, the SCR performs the SCR so that the rate of change of the supply amount of the SCR reducing agent with respect to the temperature of the NOx catalyst increases as the temperature of the NOx catalyst at the time of the regeneration control decreases. It is preferable to control the reducing agent supply means (claim 2).

In this way, the combined amount of NH ₃ supplied from the NOx catalyst to the SCR catalyst and the amount of NH ₃ supplied to the SCR catalyst by the reducing agent supply means for SCR can be more reliably made appropriate. Can be maintained.

  In the above configuration, it is preferable that the control means controls the excess air ratio changing means so that the excess air ratio of the exhaust gas becomes larger than 0.9 at the time of the regeneration control (claim 3).

In this way, by suppressing the variation width of the amount of reducing agent in the exhaust gas decreases, since it is possible to supply stably reducing agent to the NOx catalyst, thus the SCR catalyst 46 of NH ₃ released from the NOx catalyst 41 The amount of NH ₃ can be more reliably maintained in an appropriate amount.

  In the above configuration, the excess air ratio changing means is slower than the main injection in addition to the main injection for injecting the fuel for obtaining the engine torque introduced into the cylinder into the cylinder during the regeneration control. It is preferable to perform post injection for injecting fuel into the cylinder at a corner timing, and change the injection amount of the post injection to change the excess air ratio of the exhaust gas (claim 4).

  In this way, the excess air ratio of the exhaust gas can be stabilized as compared with the case where the excess air ratio of the exhaust gas is changed by changing the amount of air introduced to the cylinder and the exhaust passage. And, the excess air ratio of the exhaust gas can be more reliably maintained at a value larger than 0.9.

In the above-mentioned configuration, the control means may reduce the SCR reducing agent before the predetermined period elapses after the end of the regeneration control until the predetermined period elapses after the end of the regeneration control. The reducing agent supplying means for SCR is controlled so that the amount of the reducing agent for SCR supplied from the supplying means to the exhaust passage is reduced, and NH ₃ is supplied from the NOx catalyst with the start of the regeneration control. It is estimated by estimating the total amount of NH ₃ released from the NOx catalyst from this NH ₃ release start time to the end time of the regeneration control while estimating the NH ₃ release start time which is the release time. the person total emission amount of the NH ₃ is large, subjected to the exhaust passage from the SCR for reducing agent supply means during the period from the reproduction control is finished until the predetermined period elapses Wherein as the amount of SCR reducing agent for less is to control the SCR for reducing agent supply means, it is preferably (claim 5).

In this manner, a large amount of NH ₃ in the SCR catalyst increases after the regeneration control ends and the predetermined period elapses and the regeneration control is performed. It is possible to prevent the SCR reducing agent from being supplied to the SCR catalyst, and it is possible to suppress the slipping of a large amount of the SCR reducing agent downstream of the SCR catalyst.

According to the control device for an engine according to the present invention, it is possible to suppress passage of NH ₃ to the downstream side of the SCR catalyst while appropriately purifying NOx.

FIG. 1 is a schematic configuration diagram of an engine system to which an engine exhaust gas purification control device 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 field of passive DeNOx control and active DeNOx control. It is the flowchart which showed the control procedure of fuel injection. It is the graph which showed the relationship between the excess air ratio of exhaust gas, and the density | concentration of each substance contained in exhaust gas. It is the graph which showed the relationship between the lack of air of exhaust gas and the density | concentration of each substance contained in exhaust gas. It is the graph which showed the relationship between excess air ratio and the 1st correction coefficient. It is a graph showing the relationship between the temperature of the NOx catalyst, the exhaust flow rate, and the ratio of the reducing agent to be oxidized. It is a diagram for explaining the NH ₃ amount estimation procedure emitted from the NOx catalyst. It is a graph showing the relationship between the temperature of the NOx catalyst and the first temperature coefficient. It is the graph which showed the relationship between the exhaust flow rate and the 1st flow coefficient. It is the graph which showed the relationship between the air fuel ratio of exhaust gas, and the 1st A / F coefficient. It is the graph which showed the relationship between the exhaust gas flow rate and the 2nd flow rate coefficient. It is the graph which showed the relationship between the air fuel ratio of exhaust gas and the 2nd A / F coefficient. It is the flowchart which showed the control procedure of the urea injection quantity.

  Hereinafter, an exhaust gas purification control device for an engine 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 exhaust gas purification control device for 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, A first 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 (air excess ratio changing means) 10 for injecting fuel into the combustion chamber 6 (inside the cylinder 2), and a glow plug for heating the mixture of fuel and air in the combustion chamber 6 One set 11 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. 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 carried out to obtain an engine torque, and is a main injection that injects fuel burning in the vicinity of the compression top dead center into the combustion chamber 6, and is on the retard side of the main injection and burns. However, it is possible to carry out post injection in which the fuel is injected 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, an air cleaner 21, a compressor 51a of a first turbocharger 51, a compressor 52a of a second turbocharger 52, an intercooler 22, a throttle valve 23, and a surge tank 24 are provided in this order from the upstream side. ing. 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, the turbine 52b of the second turbocharger 52, the turbine 51b of the first turbocharger 51, the first catalyst 43, and particulate matter in the exhaust gas (PM: Particulate Matter) Are provided, a urea injector (reductant supply means for SCR) 45, a selective catalytic reduction (SCR) catalyst 46, and a slip catalyst 47.

  The first catalyst 43 comprises an NOx catalyst 41 for purifying NOx, and DOC (diesel for oxidizing hydrocarbons (HC) and carbon monoxide (CO) and the like into water and carbon dioxide using oxygen in exhaust gas. And an oxidation catalyst (diesel oxidation catalyst) 42.

  The NOx catalyst 41 is a NOx storage reduction catalyst (NSC: NOx Storage Catalyst). That is, the NOx catalyst 41 occludes NOx in the exhaust gas in a lean state where the excess air ratio λ of the exhaust gas is larger than 1 (the exhaust gas air-fuel ratio is larger than the theoretical air-fuel ratio). Then, the NOx catalyst 41 stores the stored NOx in a rich state in which the excess air ratio λ of the exhaust gas is near 1 or less than 1 (a state where the air-fuel ratio of the exhaust gas is near the theoretical air-fuel ratio or In the small state, that is, the exhaust gas passing through the NOx catalyst 41 is reduced in a reducing atmosphere containing a large amount of unburned HC.

In detail, the NOx catalyst 41 is configured to be able to store oxygen contained in the exhaust gas in a lean state where the excess air ratio λ of the exhaust gas is larger than one. For example, the NOx catalyst 41 includes ceria having an oxygen storage capacity. Then, the NOx catalyst 41 oxidizes (NO ₂ ) NO in the exhaust gas using oxygen contained in the exhaust gas and occluded oxygen, and occludes this.

Further, the NOx catalyst 41 generates and releases NH ₃ (ammonia) when reducing the stored NOx. Specifically, at the time of NOx reduction, “N” in NOx stored in the NOx catalyst 41 and NOx passing through the NOx catalyst 41 combine with H as a reducing agent introduced to the NOx catalyst 41 and the like. , NH3 is generated.

  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 and fuel to the exhaust passage is not provided, and the excess air ratio λ of the exhaust gas corresponds to the excess air ratio λ of the mixture in the combustion chamber 6. That is, when the excess air ratio λ of the mixture in the combustion chamber 6 is larger than 1, the excess air ratio λ of the exhaust gas also becomes larger than 1 and the excess air ratio λ of the mixture in the combustion chamber 6 is 1 or less Also, the excess air ratio λ of the exhaust gas becomes 1 or less.

  The urea injector 45 injects urea into the exhaust passage 40 downstream of the DPF 44. The urea injector 45 is connected to the urea tank 45c via the urea supply path 45a and the urea delivery pump 45b, and injects urea pressure-fed from the urea tank 45c into the exhaust passage 40 by the urea delivery pump 45b. In the present embodiment, a heater 45 d for preventing freezing of urea is provided. The urea injected from the urea injector 45 is introduced into the SCR catalyst 46.

The SCR catalyst 46 purifies NH ₃ (ammonia) by reacting (reducing) with NOx in the exhaust gas. The SCR catalyst 46 hydrolyzes the urea injected from the urea injector 45 to generate NH ₃ (CO (NH ₂ ) ₂ + H ₂ O → CO ₂ + 2NH ₃ ), and the generated NH ₃ is contained in the exhaust gas. It is reacted (reduced) with NOx to purify NOx.

Thus, in the present embodiment, the urea injected (supplied) to the exhaust passage 40 by the urea injector 45 functions as the NH ₃ raw material and the SCR reducing agent in the claims.

In detail, the SCR catalyst 46 adsorbs the introduced NH ₃ , and the adsorbed NH ₃ reacts with the NOx to reduce the NOx. Further, as described above, at the time of reduction of NOx in the NOx catalyst 41, NH ₃ is also released from the NOx catalyst 41, and the SCR catalyst 46 exhausts NH ₃ released from the NOx catalyst 41. NOx is also purified by reacting (reducing) it with NOx contained in it.

For example, the SCR catalyst 46 supports a catalyst metal (Fe, Ti, Ce, W, etc.) having a function of reducing NOx by NH ₃ on a zeolite having a function of trapping NH ₃ as a catalyst component, and this catalyst It is produced by supporting the components on the cell walls of the honeycomb carrier.

  Although both the SCR catalyst 46 and the NOx catalyst 41 can purify NOx, the temperatures at which the purification rates become high are different from each other, and the NOx purification rate of the SCR catalyst 46 is that the exhaust temperature is relatively high. Sometimes it is high, and the NOx purification rate of the NOx catalyst 41 becomes high when the temperature of the exhaust is relatively low.

  That is, in the present embodiment, purification of NOx is performed using both the NOx catalyst 41 and the SCR catalyst 46. Specifically, when the temperature of the SCR catalyst 46 is lower than the first temperature and the NOx purification rate by the SCR catalyst 46 is low, NOx purification is performed only by the NOx catalyst 41, and the temperature of the SCR catalyst 46 is higher than the second temperature When (the second temperature is higher than the first temperature) and the NOx purification rate by the SCR catalyst 46 is high, the NOx purification is performed only by the SCR catalyst 46. Then, when the temperature of the SCR catalyst 46 is between the first temperature and the second temperature, NOx purification is performed by both the NOx catalyst 41 and the SCR catalyst 46. Further, even when the exhaust gas flow rate is large and the NOx purification rate by the SCR catalyst 46 becomes low, NOx purification is performed by both the NOx catalyst 41 and the SCR catalyst 46.

The slip catalyst 47 oxidizes and purifies unreacted NH ₃ discharged from the SCR catalyst 46.

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

  Engine system 100 further 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 vehicle is provided with a DCU (Dosing Control Unit) 300 mainly for controlling the urea injector 45, and a Power-train Control Module (PCM) 200 for controlling the other components. Each of the PCM 200 and the DCU 300 is a microprocessor configured of a CPU, a ROM, a RAM, an I / F, and the like. In the present embodiment, the PCM 200 and the DCU 300 constitute the control means in the claims.

  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.

  The DCU 70 and the PCM 60 are communicably connected in both directions. The DCU 70 controls the urea injector 45 by calculating the amount of urea injected into the exhaust passage 40 by the urea injector 45 using the calculation result of the PCM 200 and the like. The DCU 70 also controls the urea delivery pump 45 b and the heater 45 d.

(2-1) DeNOx Control DeNOx, which is control for reducing NOx stored in the NOx catalyst 41 (hereinafter referred to as stored NOx as appropriate) and releasing it from the NOx catalyst 41 (removing it) to regenerate the NOx catalyst 41. Control (reproduction control) will be described.

  In the present embodiment, DeNOx control, control for reducing SOx stored in the NOx catalyst 41 (so-called DeSOx control), control for regenerating the DPF 44 (control for burning and removing particulate matter from the DPF 44) In normal operation without performing), the excess air ratio λ of the mixture in the combustion chamber 6 and hence the excess air ratio λ of the exhaust gas are set to λ> 1 (eg, about λ = 1.7) in order to improve the fuel efficiency. Ru. Hereinafter, the excess air ratio λ of the mixture in the combustion chamber 6 will be referred to simply as the excess air ratio λ of the mixture.

  On the other hand, as described above, in the NOx catalyst 41, the stored NOx is reduced and NOx is released from the NOx catalyst 41 in the rich state where the excess air ratio λ of the exhaust gas is near 1 or less than 1. ing. Therefore, in order to reduce the stored NOx, it is necessary to reduce the excess air ratio λ of the exhaust gas and the excess air ratio λ of the air-fuel mixture than in the normal operation.

  One way to reduce the excess air ratio λ of the mixture (the excess air ratio λ of the exhaust gas) is to reduce the amount of fresh air (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. In addition, when adjusting the amount of fresh air, it is relatively difficult to control the excess air ratio λ of the mixture accurately.

  Therefore, in the present embodiment, post injection is performed as DeNOx control, thereby reducing the excess air ratio of the air-fuel mixture while suppressing the amount of reduction of the amount of fresh air small. That is, the PCM 200 performs control to cause the injector 10 to perform post injection in addition to main injection as DeNOx control. In the normal operation, post injection is stopped.

  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.

  In the first region R1, the PCM 200 is at a timing at which post-injected fuel burns in the combustion chamber 6 (first half of the expansion stroke, specifically, from compression top dead center to 90 ° CA after compression top dead center, For example, active DeNOx control is performed in which post injection is performed at 30 to 70 ° CA after compression top dead center. In addition, at the time of implementation of active DeNOx control, in order to accelerate | stimulate combustion of the fuel by which post injection was carried out, electricity supply of the glow plug 11 is carried out, and air-fuel mixture is heated.

  On the other hand, in the second region R2, the PCM 200 performs passive injection in the second period R2 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) Conduct.

  This is due to the following reason.

  In a region where the engine load is low or 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 as the temperature of the exhaust gas is low. 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 speed is high, the gas in the combustion chamber 6 is exhausted 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 fuel is injected, and there is a possibility that the post-injected fuel can not be burned sufficiently in the combustion chamber 6. 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 excess amount of air-fuel mixture is small even in the normal operation because the injection amount of the main injection (hereinafter referred to as the main injection amount as appropriate) is large. It is suppressed. 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.

(2-2) Fuel Injection Control A control procedure of fuel injection will be described using the flowchart of FIG.

  First, in step S1, the PCM 200 acquires various information of the vehicle including the accelerator opening degree, the engine speed, the value of the active DeNOx control execution flag, and the passive DeNOx control execution flag.

  The active DeNOx control execution flag is a flag that is “1” when a basic condition for implementing the active DeNOx control is satisfied, and is “0” otherwise. In the present embodiment, the NOx storage amount, which is the amount of NOx stored in the NOx catalyst 41, is equal to or greater than a first reference amount set in advance, and the temperature of the SCR catalyst 46 is set near the second temperature. If the temperature is lower than the determination temperature and the temperature of the NOx catalyst 41 is equal to or higher than a preset NOx reduction possible temperature, the active DeNOx control execution flag is set to "1". The first reference amount is set near the maximum amount of NOx that can be stored by the NOx catalyst 41 when the active DeNOx control is performed for the first time after engine start, and in other cases, it is a value somewhat lower than this maximum amount. Be done. The NOx reducible temperature is the minimum value of the temperature at which the NOx catalyst 41 can reduce NOx, and is set in advance.

  The passive DeNOx control execution flag is a flag that is “1” when a basic condition for implementing the passive DeNOx control is satisfied, and is “0” otherwise. In the present embodiment, when the NOx storage amount is equal to or greater than the third reference amount set in advance, the temperature of the SCR catalyst 46 is less than the SCR determination temperature, and the temperature of the NOx catalyst 41 is equal to or higher than the NOx reducible temperature. The passive DeNOx control execution flag is set to 1. The third reference amount is set to a value smaller than the first storage amount determination value. For example, the third storage amount determination value is set to about half the maximum value of the amount of NOx that can be stored by the NOx catalyst 41.

  As described above, although the purification rate of NOx by the SCR catalyst 46 is relatively low and it is necessary to purify the NOx by the NOx catalyst 41, the amount of NOx stored in the NOx catalyst 41 is large. When the NOx catalyst 41 can reduce NOx, the active DeNOx control execution flag and the passive DeNOx control execution flag become 1.

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

  After step S1, the process proceeds to step S2. In step S2, the PCM 200 determines whether the active DeNOx control execution flag is "1". If the determination in step S2 is NO, the process proceeds to step S10. On the other hand, if the determination in step S2 is YES, the process proceeds to step S3.

  In step S3, the PCM 200 determines whether the engine is operated in the first region R1. If the determination in step S3 is NO, the process proceeds to step S10.

  On the other hand, if the determination in step S3 is YES, the process proceeds to step S4. In step S4, the PCM 200 determines the injection amount and injection timing of post injection in active DeNOx control.

  Specifically, the PCM 200 calculates, as a main injection amount, a fuel injection amount corresponding to the required torque calculated from the accelerator opening degree and the like. Next, the excess air ratio λ of the mixture gas and the exhaust gas is determined by the total injection amount obtained by combining the calculated main injection amount and the post injection amount and the air amount introduced into the cylinder 2 for air for active DeNOx control. The post injection amount is determined based on the main injection and the air amount so as to achieve the target value of the excess rate λ. The amount of air introduced into the cylinder 2 is estimated using a value or the like detected by the air flow sensor SN2. As described above, in the present embodiment, the excess air ratio λ of the exhaust gas is changed by changing the injection amount of the post injection.

  Further, the PCM 200 sets the injection timing of post injection for active DeNOx control to the timing of the first half of the expansion stroke as described above. Here, if the post injection timing is advanced too much, this air-fuel mixture starts combustion in a state where air and fuel are not sufficiently mixed. As a result, the amount of smoke generation increases. So, in this embodiment, based on the amount of air etc. which are introduced into cylinder 2, a post injection timing is adjusted within the range of the first half of an expansion stroke so that the generation amount of smoke does not exceed a predetermined amount. In the present embodiment, at the time of active DeNOx control, an appropriate amount of EGR gas is introduced into the cylinder 2 to delay the ignition of the post-injected fuel and thereby suppress the generation of smoke.

  After step S4, the process proceeds to step S5. In step S5, the PCM 200 causes the injector 10 to perform main injection of the fuel of the main injection amount and post-inject the fuel of the post injection amount for active DeNOx control determined in step S4 at the timing determined in step S4. . After step S5, the process ends (return to step S1). When the post injection amount is small, the amount of air introduced into the cylinder 2 may be reduced by controlling the throttle valve 23 to the closing side or the like.

  On the other hand, in step S10, which proceeds when the determination in step S2 is NO or the determination in step S3 is NO, PCM 200 determines whether the passive DeNOx control execution flag is "1". If the determination in step S10 is NO, the process proceeds to step S11.

  In step S11, the PCM 200 performs normal control without performing active DeNOx control and passive DeNOx control. That is, the PCM 200 stops the post injection and makes the main injection a fuel injection amount corresponding to the required torque calculated from the accelerator opening degree and the like. After step S11, the process ends (return to step S1). On the other hand, if the determination in step S10 is YES, the process proceeds to step S12.

  In step S12, the PCM 200 determines whether the engine is operated in the second region R21. If the determination in step S12 is NO, the process proceeds to step S11.

  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 the injection amount and injection timing of post injection in passive DeNOx control.

  Specifically, the PCM 200 calculates, as a main injection amount, a fuel injection amount corresponding to the required torque calculated from the accelerator opening degree and the like. Next, the excess air ratio λ of the mixture gas and the exhaust gas is the air for passive DeNOx control according to the total injection amount obtained by combining the main injection amount and the post injection amount calculated and the air amount introduced into the cylinder 2 The post injection amount is determined based on the main injection and the air amount so as to achieve the target value of the excess rate λ. In the present embodiment, the PCM 200 sets the injection timing of post injection for passive DeNOx control to the timing of the first half of the expansion stroke as described above.

  After step S13, the process proceeds to step S14. In step S14, the PCM 200 causes the injector 10 to perform main injection of the fuel of the main injection amount and post-inject the fuel of the post injection amount for passive DeNOx control determined in step S13 at the timing determined in step S12. . After step S14, the process ends (return to step S1).

(3) Injection Control of Urea Solution Next, injection control of the urea injector 45 will be described. Hereinafter, the amount of urea injected from the urea injector 45 is referred to as a urea injection amount as appropriate. As described above, the injection control of the urea injector 45 is performed by the DCU 300 while obtaining information from the PCM 200.

(3-1) Outline of Urea Injection Control at DeNOx Control As described above, at the time of NOx reduction, that is, at the time of DeNOx control, NH ₃ is released from the NOx catalyst 41 and introduced into the SCR catalyst 46. Therefore, if the amount of urea injection during DeNOx control is the same as the amount of urea injection during non-DeNOx control (when DeNOx control is not performed), the amount of NH ₃ supplied to the SCR catalyst 46 Becomes excessive, and there is a risk that NH ₃ may slip off downstream of the SCR catalyst 46. Therefore, during the DeNOx control, the urea injection amount is made smaller than when the DeNOx control is not performed.

However, the amount of NH ₃ supplied to the SCR catalyst 46 becomes excessive if the urea injection amount during DeNOx control is simply controlled to a predetermined amount smaller than that during non-DeNOx control regardless of operating conditions. Alternatively, it has been found that there is a risk that more NH ₃ may pass downstream of the SCR catalyst 46 or NOx may not be properly purified in the SCR catalyst 46.

The inventors of the present invention conducted intensive studies, and as a result, the release of NH ₃ from the NOx catalyst 41 occurs only after a predetermined period has elapsed since De NOx control was started, and this predetermined period is an operating condition. It has been found that the problem arises due to differences in Hereinafter, a period from the start of the DeNOx control to the start of the release of NH ₃ from the NOx catalyst 41 is appropriately referred to as a delay period.

That is, even if the execution period of the DeNOx control is the same, NH ₃ is supplied from the NOx catalyst 41 to the SCR catalyst 46 for a longer period when the delay period is shorter. Therefore, if the total amount of urea injected into the exhaust passage 40 during the implementation period of DeNOx control is constant regardless of the delay period, the amount of NH ₃ supplied to the SCR catalyst 46 becomes excessive, and a large amount of NH ₃ is an SCR Otherwise, the amount of NH ₃ supplied to the SCR catalyst 46 may be insufficient and the purification rate of NOx in the SCR catalyst 46 may be degraded.

  Also, the inventors of the present invention have a correlation between the delay period and the amount of decrease of oxygen stored in the NOx catalyst 41 per unit time (hereinafter referred to as the rate of decrease in stored oxygen). It was found that the delay period became shorter as the oxygen reduction rate was higher.

  The reason why the delay period becomes shorter as the stored oxygen reduction rate increases is considered to be due to the following reason.

As described above, the reason why NH ₃ is generated by the NOx catalyst 41 is that the reducing agent is supplied to the NOx catalyst 41 along with the DeNOx control, so that “N” in the NOx stored in the NOx catalyst 41 The reason is that NOx passing through the NOx catalyst 41 is combined with H, which is a reducing agent introduced to the NOx catalyst 41, and the like. However, as described above, the NOx catalyst 41 has an oxygen storage capacity. Further, a large amount of oxygen is stored in the NOx catalyst 41 as the excess air ratio λ of the exhaust gas is made larger than 1 in the normal operation and the like. Therefore, immediately after DeNOx control is started and introduction of the reducing agent to the NOx catalyst 41 is started, the supplied reducing agent reacts with oxygen stored in the NOx catalyst 41 instead of “N”. And the reaction of producing NH ₃ are suppressed. From this, it is considered that the release of NH ₃ is started only when the oxygen stored in the NOx catalyst 41 disappears. Here, in the period from when DeNOx control is started to when the oxygen stored in the NOx catalyst 41 disappears, the larger the rate of decrease in stored oxygen, the larger. Therefore, it is considered that as the stored oxygen reduction rate increases, the timing at which release of NH ₃ starts is earlier, and the delay period becomes shorter.

  Therefore, in the present embodiment, the storage oxygen reduction rate is estimated, and the delay period is estimated based on this.

Specifically, the storage oxygen reduction rate is integrated, and the reduction per unit time of oxygen stored in the NOx catalyst 41 is integrated, and this integrated value is the storage oxygen maximum amount, and the NOx catalyst 41 The time when the maximum amount of occludable oxygen is exceeded is estimated as the time when release of NH ₃ from the NOx catalyst 41 is started (hereinafter referred to as NH ₃ release start time). Then, a period from the start timing of DeNOx control to the start timing of this NH ₃ release is estimated as a delay period. The procedure for estimating the stored oxygen reduction rate will be described later.

Then, until DeNOx control starts and until this delay period elapses, the urea injection amount is maintained at the same amount as before DeNOx control, that is, when DeNOx control is not performed, and only after the delay period has elapsed ₍₃ ) Only when the release start time is reached) Make the urea injection amount smaller than when not performing DeNOx control.

  Therefore, in the present embodiment, even if the execution period of DeNOx control is the same, the shorter the delay period, the longer the period during which the urea injection amount is smaller than that during the non-execution of DeNOx control. The total amount of urea injection during the period, that is, the total amount of urea supplied to the exhaust passage 40 during the implementation period of the DeNOx control decreases.

  Here, the larger the stored oxygen reduction rate, the shorter the delay period. Therefore, in the present embodiment, the larger the rate of decrease in stored oxygen, the smaller the total amount of urea injection during the implementation period of DeNOx control.

More specifically, in the present embodiment, the amount of NH ₃ released from the NOx catalyst 41 at each time (hereinafter referred to as “the amount of NH ₃ released at each time”) when the delay period elapses (at the NH ₃ release start timing) As appropriate, the amount of released NH ₃ is estimated. Also, (to calculate the minimum amount of urea required to produce a NH ₃ in NH ₃ emissions) that the estimated NH ₃ emissions the converted urea. Then, the urea conversion value of the NH ₃ release amount is subtracted from the urea injection amount at the time of non-execution of DeNOx control, and the obtained value is calculated as the urea injection amount.

Here, in the calculation procedure of the urea injection amount, the amount of the urea injection amount also changes depending on the NH ₃ release amount. However, the effect on the amount of total NH ₃ released from the NOx catalyst 41 during the implementation period of the DeNOx control, better oxygen reduction rate is greater than the NH ₃ emissions, as described above, the present embodiment Then, as the stored oxygen reduction rate increases, the total amount of urea injection during the implementation period of DeNOx control decreases.

As described later, when the exhaust gas is rich, the NH ₃ release amount is calculated to be a large value, and when the excess air ratio λ of the exhaust gas is small, that is, the rich exhaust gas reduces the stored oxygen rate Is calculated to be a large value. Therefore, with respect to the change in excess air ratio λ of the exhaust gas, the influence of the NH ₃ release amount on the total amount of urea injection and the influence of the storage oxygen reduction rate on the total amount of urea injection are on the same side The total amount increases or decreases). That is, when the excess air ratio λ of the exhaust gas is small, the total of the urea injection amount becomes smaller as the storage oxygen reduction rate becomes larger, and becomes smaller as the NH ₃ release amount becomes larger.

Similarly, the exhaust gas flow rate (hereinafter referred to as the exhaust gas flow rate) the larger is NH ₃ emissions is calculated to a large value, it exhaust flow rate is large is calculated for the stored oxygen reduction rate larger value With respect to changes in the exhaust flow rate, both the effect of the NH ₃ release amount on the total amount of urea injection and the effect of the rate of reduction of stored oxygen on the total amount of urea injection are on the same side ( The total amount increases (or decreases).

(3-2) so that the summary of the urea injection control after DeNOx control end, during DeNOx control NH ₃ is introduced from the NOx catalyst 41 in SCR catalyst 46. Therefore, a large amount of NH ₃ is adsorbed to the SCR catalyst 46 immediately after the DeNOx control ends. Therefore, if the amount of urea injection is increased significantly immediately after the end of DeNOx control, NH ₃ supplied to the SCR catalyst 46 may become excessive and NH ₃ may slip to the downstream side of the SCR catalyst 46. There is.

Therefore, in the present embodiment, the urea injection amount is made smaller for a predetermined period (hereinafter, appropriately referred to as a switching period) after the end of DeNOx control, even during the non-execution of DeNOx control than in other periods. . However, as described above, even during the switching period, the amount of NH ₃ released from the NOx catalyst 41, which is the amount of released NH ₃ from the NOx catalyst 41, becomes almost zero after the DeNOx control is completed. The urea injection amount is made larger than at the time of DeNOx control. The switching period is set in advance.

Further, in the present embodiment, the total amount of NH ₃ discharged from the NOx catalyst 41 is estimated in conjunction with the implementation of the DeNOx control, and during the switching period, the larger the total amount is, the smaller the urea injection amount becomes. decide.

Specifically, as described above, estimates the NH ₃ emissions each time after Ongoing and delay period of DeNOx control, will the release Nh3 amount by accumulating until DeNOx control ends, the integrated The value is calculated as the total amount (the total amount of NH ₃ emitted from the NOx catalyst 41 with the execution of the DeNOx control).

(3-3) Calculation Procedure of Storage Oxygen Deceleration Rate Next, a calculation procedure of the storage oxygen reduction velocity will be described.

  The inventors of the present application have found that the rate of decrease in stored oxygen can be accurately estimated by calculating it as MreO2 according to the following equation (2). Therefore, in the present embodiment, the stored oxygen reduction rate is calculated using this equation (2).

MreO2 = (1−λ) × K × Mex (2)
In equation (2), λ is the excess air ratio of the exhaust gas. In the present embodiment, as described above, the target value of the excess air ratio λ of the exhaust gas at the time of DeNOx control is set in advance, and the post injection is implemented so as to realize this. Therefore, although the excess air ratio λ in the equation (2) is almost this target value, in the present embodiment, the excess air ratio λ of the present exhaust gas is calculated from the fuel injection amount, the air amount introduced into the cylinder 2 and the like. Then, this calculated value is used in equation (2).

  Further, in the equation (2), Mex is the flow rate of the exhaust gas. In the present embodiment, the exhaust flow rate Mex is calculated using a value or the like detected by the air flow meter.

  Further, in the equation (2), K is a correction coefficient. The correction coefficient K is calculated by K = α1 × α2 × α3 where the first correction coefficient is α1, the second correction coefficient is α2, and the third correction coefficient is α3.

  The value calculated by the term (1−λ) × Mex included in the equation (2) is an exhaust gas when it is intended to oxidize all the unburned fuel flowing into the NOx catalyst 41 and thus the reducing agent. Insufficient amount of oxygen. Therefore, X1 obtained by the following equation (3) is considered to be a value close to the storage oxygen reduction rate. That is, at the start of the DeNOx control, the NOx catalyst 41 is considered to consume the storage oxygen of the amount calculated by the term (1−λ) × Mex.

X1 = (1−λ) × Mex (3)
However, there is a difference between the value X1 obtained by the equation (3) and the actual storage oxygen reduction rate, and the correction coefficients α1, α2 and α3 are coefficients for correcting this difference. In the following, the parameter represented by “1−λ” will be described as being referred to as an air shortage.

(First correction factor)
As a result of earnest research conducted to make the deviation smaller, the concentrations of CO, H ₂ and THC which are reducing agents exhausted from the engine main body 1 when the excess air ratio λ of the exhaust gas is made 1 or less, It turned out that it comes to show in 5. Further, as shown in FIG. 5, it was found that the exhaust gas discharged from the engine body 1 contains oxygen (O ₂ ) even if the excess air ratio λ of the exhaust gas is 1 or less.

Specifically, in FIG. 5, the horizontal axis represents the excess air ratio λ of the exhaust gas, and the vertical axis represents the concentration of each substance in the exhaust gas. As shown in FIG. 5, as the excess air ratio λ of the exhaust gas decreases, the concentrations of CO, H ₂ and THC contained in the exhaust gas increase, and as the excess air ratio λ of the exhaust gas increases, the concentration is included in the exhaust gas. The concentration of O ₂ decreases.

Also, the present inventors have found that the amount of H ₂ in addition to CO contained mainly in the exhaust gas affects the rate of oxygen storage reduction. It is considered that this is because H ₂ has a high reducing ability and easily reacts with oxygen stored in the NOx catalyst 41 (hereinafter referred to as stored oxygen as appropriate). Further, reduction of stored oxygen by O ₂ contained in the exhaust gas is suppressed, the amount of O ₂ contained in the exhaust gas was also discovered to affect the stored oxygen reduction rate.

From these findings, the amount of the reducing agent that actually reacts with the stored oxygen in the NOx catalyst 41 is the amount of O ₂ that reacts with these, from the total amount of CO and H ₂ contained in the exhaust gas, It was found to approximate to a value obtained by subtracting half of the amount of O ₂ contained in the gas.

Here, FIG. 6 is a value obtained by subtracting a half value of the concentration of O ₂ contained in the exhaust gas from the total value of the concentrations of CO and H ₂ contained in the exhaust gas, as described above, FIG. 7 is a graph in which the concentration of a reducing agent considered to react with stored oxygen in the NOx catalyst 41 (hereinafter referred to as the net reducing agent concentration) is plotted for each air shortage width (“1−λ”) of exhaust gas. In FIG. 6, a line L1 indicated by a solid line is a line connecting representative points of these plot points.

  As shown in FIG. 6, as the excess air ratio λ of the exhaust gas becomes smaller (more rich), the net concentration of the reducing agent becomes larger.

  However, as the air shortage width of the exhaust gas increases (as the excess air ratio λ of the exhaust gas decreases), the rate of change of the concentration of the net reductant relative to the insufficient air width of the exhaust gas and the excess air ratio λ of the exhaust gas increases. The net reductant concentration and the air shortage are not proportional. That is, there is a difference between a line L2 which is a line connecting points calculated by the equation (3) for each air shortage width and a line L1 connecting a point proportional to the air shortage width, the line L1 and the line L2 It is considered that the difference between the two and the third one constitutes at least a part of the difference between the value of X1 obtained by the equation (3) and the actual rate of decrease in stored oxygen.

  The first correction coefficient α1 is a coefficient for correcting this deviation, that is, a coefficient for correcting the point on the line L1 to a point on the line L2, and is set as shown in FIG. Specifically, the first correction coefficient α1 is set such that the value thereof increases as the excess air ratio λ of the exhaust gas decreases. Further, the first correction coefficient α1 is set such that the rate of change of the first correction coefficient α1 with respect to the excess air ratio λ of the exhaust gas increases as the excess air ratio λ of the exhaust gas increases.

(Second and third correction factors)
Furthermore, the inventors of the present invention have determined that all reducing agents introduced to the NOx catalyst 41 are not oxidized even during DeNOx control, depending on the temperature and exhaust flow rate of the NOx catalyst 41, and that the temperature of the NOx catalyst 41. It was found that the proportion of the reducing agent oxidized by the stored oxygen at the NOx catalyst 41 was different depending on the exhaust flow rate and the DeNOx control.

  FIG. 8 is a graph in which the horizontal axis represents the temperature of the NOx catalyst 41 and the vertical axis represents the rate at which the reducing agent introduced into the NOx catalyst 41 is oxidized during the DeNOx control. Three lines L11, L12 and L13 in the graph of FIG. 8 are lines when the exhaust flow rates are different from each other. The exhaust flow rate increases in the order of the lines L11, L12, and L13.

  As shown in FIG. 8, the lower the temperature of the NOx catalyst 41, the smaller the ratio. More specifically, when the temperature of the NOx catalyst 41 is higher than a predetermined temperature (for example, about 350 ° C.), the ratio is 100% and the reducing agent introduced into the NOx catalyst 41 is almost entirely oxidized. On the other hand, when the temperature of the NOx catalyst 41 is lower than a predetermined temperature, the ratio decreases as the temperature of the NOx catalyst 41 decreases. Also, the ratio decreases as the exhaust flow rate increases.

  Therefore, the amount of reductant that is actually oxidized by the stored oxygen in the NOx catalyst 41 and thus the amount of stored oxygen used for this oxidation is the value obtained by (1−λ) × Mex × α1 (NOx catalyst 41 The total amount of the reducing agent to be introduced and the value estimated to be the amount of stored oxygen corresponding to the total amount are multiplied by the above ratio.

  Therefore, in the present embodiment, the ratio that changes according to the temperature of the NOx catalyst 41 is set as the second correction coefficient α2, and the ratio that changes according to the exhaust gas flow is set as the third correction coefficient α3. By multiplying these α2 and α3 by (1−λ) × Mex × α1, it is possible to more accurately estimate the amount of reducing agent oxidized by the stored oxygen in the NOx catalyst 41 and hence the amount of stored oxygen used for this oxidation. .

  As described above, the second correction coefficient α 2, that is, the ratio that changes according to the temperature of the NOx catalyst 41, is a smaller value as the temperature of the NOx catalyst 41 is lower.

  As described above, the third correction coefficient α3, that is, the ratio that changes in accordance with the exhaust flow rate, is a smaller value as the exhaust flow rate is higher.

  In addition, the second correction coefficient α2 and the third correction coefficient α3 are fixed values (for example, 1.0) regardless of the temperature of the NOx catalyst 41 and the exhaust flow rate when the temperature of the NOx catalyst 41 is equal to or higher than a predetermined temperature. Be done.

  The higher the temperature of the NOx catalyst 41, the higher the ratio, which is considered to be because the NOx catalyst 41 is more active when the temperature is higher and the oxidation reaction of the reducing agent is promoted. Further, the larger the exhaust gas flow rate, the smaller the ratio, which is considered to be because the larger the exhaust gas flow rate, the larger the amount of substances other than the reducing agent, and the smaller the chance of contact between the NOx catalyst 41 and the reducing agent.

  Thus, in the present embodiment, the stored oxygen reduction rate is accurately estimated by the equation (2).

Further, in the present embodiment, the NH ₃ release start timing is estimated using the storage oxygen reduction rate estimated in this manner. Specifically, as described above, the time when the integrated value of the estimated occluded oxygen reduction rate becomes equal to or more than the occluded oxygen maximum amount is estimated as the NH ₃ release start time.

(3-4) Target value of excess air ratio at the time of DeNOx control As described above, in the NOx catalyst 41, the excess air ratio λ of the introduced exhaust gas is made close to 1 or richer than 1 , NOx is reduced. Therefore, the excess air ratio λ of the exhaust gas may be close to 1 as long as NOx is only reduced in the NOx catalyst 41.

However, as described above, the NOx catalyst 41 has an oxygen storage capacity, and stores oxygen when the excess air ratio λ of the exhaust gas becomes 1 or more. Then, when oxygen is stored in the NOx catalyst 41, the release of NH ₃ from the NOx catalyst 41 is stopped until the stored oxygen disappears.

Therefore, in the present embodiment, the excess air ratio λ of the exhaust gas is set to less than 1 in order to supply NH ₃ efficiently to the SCR catalyst 46. That is, the excess air ratio λ of the exhaust gas is less than 1 in order to release NH ₃ from the NOx catalyst 41 and reduce the amount of urea injected from the urea injector 45 so as to suppress the reduction of urea in the urea tank 45 c. Make it In particular, it has been found that when the excess air ratio λ of the exhaust gas becomes 1 or more, a large amount of oxygen is stored in the NOx catalyst 41 in a short time, and the release of NH ₃ is interrupted for a relatively long time. In order to release a large amount of NH ₃ from the NOx catalyst 41, it is necessary to make the excess air ratio λ of the exhaust gas less than one.

However, the excess air ratio λ of the exhaust gas changes depending on the amount of air introduced into the cylinder 2 and the amount of fuel. Therefore, when the target value of the excess air ratio λ of the exhaust gas is set to a value very close to 1, the excess air ratio λ of the actual exhaust gas becomes 1 or more along with the fluctuation of the air amount and the fuel amount. Opportunities to become Further, as described above, when the excess air ratio λ of the exhaust gas becomes 1 or more, the release of NH ₃ is stopped, so when the excess air ratio λ of the exhaust gas fluctuates so as to cross one, the SCR catalyst 46 is supplied. Fluctuation of NH ₃ is increased. From this, in order to supply NH ₃ efficiently and stably to the SCR catalyst 46, in the present embodiment, the target value of the excess air ratio λ of the exhaust gas is made less than 0.98.

On the other hand, as shown by the arrows in FIG. 5, when the excess air ratio λ of the exhaust gas decreases, the amount of the reducing agent in the exhaust gas increases, and the variation in the amount of the reducing agent in the exhaust gas greatly varies. Become. Therefore, even if too small excess air ratio of the exhaust gas lambda, NH ₃ in turn in the SCR catalyst 46 of NH ₃ released from the NOx catalyst 41 becomes unstable. In particular, when the excess air ratio λ of the exhaust gas becomes 0.9 or more, the variation range of the amount of the reducing agent in the exhaust gas becomes a predetermined value or more. Therefore, in the present embodiment, the target value of the excess air ratio λ of the exhaust gas is made larger than 0.9. That is, in the present embodiment, the target value of the excess air ratio λ of the exhaust gas at the time of DeNOx control is set to a value larger than 0.9 and smaller than 0.98.

  For example, in the low load first region R1_L where the engine load is low in the first region R1, the target value of the air-fuel mixture and hence the excess air ratio λ of the exhaust gas is set to 0.98. Further, in the region other than the low load side first region R1_L of the first region R1 and the second region R2, the target value of the air-fuel mixture and hence the excess air ratio λ of the exhaust is set to 0.96.

(3-5) Estimation Procedure of NH ₃ Amount Released from NOx Catalyst Next, an estimation procedure of the NH ₃ amount released from the NOx catalyst 41 at the time of DeNOx control will be described. FIG. 9 is a diagram for explaining this procedure.

  In the present embodiment, the DCU 300 is functionally provided with a first estimation unit 301 and a second estimation unit 302.

First estimation unit 301, at the time DeNOx control, the NOx stored in the NOx catalyst 41, the reducing agent NH ₃ to H and the like are generated by combining (hereinafter referred to as a 1N H ₃₎ of Estimate the quantity.

The second estimation unit 302 is generated by combining NOx (hereinafter referred to as RawNOx as appropriate) generated by the engine main body 1 and flowing into the NOx catalyst 41 at the time of DeNOx control, H as a reducing agent, etc. by the NOx catalyst 41. The amount of NH ₃ (hereinafter referred to as second NH ₃ appropriately) is estimated.

The first estimation unit 301 first estimates the current NOx storage amount of the NOx catalyst 41. Next, the first estimation unit 301 multiplies the estimated value of the NOx storage amount by the first temperature coefficient β1, the first flow coefficient β2, the first A / F coefficient β3, and the first thermal deterioration coefficient β4. Then, the amount of first NH ₃ is calculated.

The first temperature coefficient β1 is a coefficient set based on the map shown in FIG. 10, and is set according to the temperature of the NOx catalyst 41. Specifically, the temperature coefficient β1 is set to a smaller value as the temperature of the NOx catalyst 41 is higher. That is, it is known that a reaction in which NOx stored in the NOx catalyst 41 is converted to HN ₃ is promoted as the temperature of the NOx catalyst 41 is higher, and the one where the temperature of the NOx catalyst 41 is higher is the first NH ₃ The first temperature coefficient β1 is set so that the amount can be calculated large.

The first flow coefficient β2 is a coefficient set based on the map shown in FIG. 11, and is set according to the exhaust flow rate. Specifically, the first flow coefficient β2 is set to a larger value as the exhaust flow rate increases. That is, the amount of reducing material flowing into the NOx catalyst 41 increases as the flow rate of exhaust gas increases, and the amount of HN ₃ released from the NOx catalyst 41 increases. Therefore, the larger the flow rate of exhaust gas, the more the first NH ₃ The first flow coefficient β2 is set so that the amount can be calculated large.

The first A / F coefficient β3 is a coefficient set based on the map shown in FIG. 12, and is set according to the air-fuel ratio (A / F) of the exhaust gas. Specifically, the A / F coefficient β3 is set to a larger value as the air-fuel ratio of the exhaust gas is smaller (rich). That is, as the air-fuel ratio of the exhaust gas becomes richer, the amount of reducing material flowing into the NOx catalyst 41 increases, and the amount of NH ₃ released from the NOx catalyst 41 increases, so the exhaust flow rate correspondingly increases. The first A / F coefficient β3 is set so that the first NH ₃ amount is calculated larger.

The first thermal deterioration coefficient β4 is a coefficient set in accordance with the degree of deterioration of the NOx catalyst 41. The PCM 200 estimates the deterioration degree of the NOx catalyst 41 based on the traveling time of the vehicle, the number of times of execution of DeNOx control, etc., and the thermal deterioration coefficient β 4 indicates that the higher the degree of this estimated deterioration ), It is considered a large value. That is, it is known that the higher the degree of deterioration of the NOx catalyst 41 is, the more the reaction of converting the NOx stored in the NOx catalyst 41 into NH ₃ is promoted, and the higher degree of deterioration corresponds to this. The thermal deterioration coefficient β4 is set so that the first NH ₃ amount is largely calculated.

The second estimation unit 302 first estimates the amount (flow rate) of RawNOx discharged from the engine body 1. In the present embodiment, the flow rate of RawNOx is estimated from the exhaust flow rate and the excess air ratio λ of the mixture. Next, the second estimation unit 302 calculates the amount of second NH _{3 by} multiplying the estimated value of the stored NOx amount by the second flow coefficient β22 and the second A / F coefficient β23.

  The second flow coefficient β22 is a coefficient set based on the map shown in FIG. 13, and is set according to the exhaust flow rate. Specifically, like the first flow coefficient β2, the second flow coefficient β22 is set to a larger value as the exhaust flow is larger. However, unlike NOx stored in the NOx catalyst 41, the influence of the temperature of the NOx catalyst 41 on RawNOx becomes equivalent when the temperature of the NOx catalyst 41 becomes equal to or higher than the predetermined temperature, and the second flow coefficient β22 is the NOx catalyst 41. When the temperature of the above is a predetermined temperature or more, it is a constant value.

  The second A / F coefficient β23 is a coefficient set based on the map shown in FIG. 14, and is set according to the air fuel ratio (A / F) of the exhaust gas. Specifically, similarly to the second A / F coefficient β3, the second A / F coefficient β23 is set to a larger value as the air-fuel ratio of the exhaust gas is smaller (rich). However, unlike NOx stored in the NOx catalyst 41, the influence of the air-fuel ratio of the exhaust gas on RawNOx becomes equivalent when the air-fuel ratio of the exhaust gas becomes equal to or less than a predetermined value, and the second A / F coefficient β23 is the exhaust gas When the air-fuel ratio is equal to or more than a predetermined value, the value is fixed.

In this manner, in the present embodiment, the amount and the amount of the 2NH ₃ of the 1N H ₃ is estimated. Then, DCU300 is the amount and the combined amount of the amount of the 2NH ₃ of the 1N H _3, during the DeNOx control (specifically, between the NH ₃ release start timing until the DeNOx control end) to, NOx Calculated as NH ₃ released from the catalyst 41.

(3-6) Control Flow of Urea Injection Amount FIG. 15 is a flow chart summarizing the control procedure of the urea injection amount. The overall flow of control of the urea injection amount will be described using this flowchart. FIG. 15 is a control flow when NOx purification is performed by both the SCR catalyst 46 and the NOx catalyst 41.

  First, in step S21, the DCU 300 acquires various information of various vehicles including the engine speed, the engine load, the excess air ratio λ of the mixture and the exhaust gas, the temperature of the NOx catalyst 41, and the exhaust flow rate.

Next, in step S22, as described later, the DCU 300 calculates a basic urea injection amount which is a value of the urea injection amount in the non-execution of DeNOx control and in the normal operation excluding the switching period, as described later. In the present embodiment, the basic urea injection amount is determined based on the operating conditions of the engine and the like so that the amount of NH ₃ adsorbed to the SCR catalyst 46 is maintained at a predetermined amount.

  Next, in step S23, the DCU 300 determines whether or not DeNOx control is in progress. In the present embodiment, a flag is set which is “1” during execution of active DeNOx control or passive DeNOx control, and is “0” otherwise, and in step S23, whether or not this flag is 1 Determine if

  If the determination in step S23 is YES, the process proceeds to step S24. In step S24, the value of the correction coefficient K is determined. Specifically, the value of the correction coefficient K is calculated by K = α1 × α2 × α3.

  Here, the first correction coefficient α1 is obtained from the map shown in FIG. 7 according to the excess air ratio λ of the exhaust gas. Specifically, the map shown in FIG. 7 is stored in the DCU 300, and the DCU 300 extracts a value corresponding to the current excess air ratio λ of the exhaust gas from this map.

  A map corresponding to FIG. 8 is stored in the DCU 300. The DCU 300 extracts a value corresponding to the current exhaust gas flow rate and the temperature of the NOx catalyst 41 from this map, and calculates a value of α2 × α3. Do.

  After step S24, the process proceeds to step S25. In step S25, the DCU 300 calculates the stored oxygen reduction rate MreO2. Specifically, the DCU 300 uses the correction coefficient K determined in step S24, the exhaust flow rate read in step S21, and the excess air ratio λ of the exhaust gas to calculate the stored oxygen reduction rate MreO2 according to equation (2). .

  After step S25, the process proceeds to step S26. In step S26, the stored oxygen decrease rate MreO2 calculated in step S25 is integrated. That is, ΣMreO2 is calculated, and the stored oxygen amount of the NOx catalyst 41, which has decreased up to the present with the start of the DeNOx control, is calculated.

After step S26, the process proceeds to step S27. In step S27, it is determined whether ΣMreO2 calculated in step S26 is equal to or larger than the stored oxygen maximum amount, that is, whether or not the NH ₃ release start time has arrived. As described above, the stored oxygen maximum amount is preset and stored in the DCU 300.

If the determination in step S27 is NO, that is, if it is estimated that ΣMreO2 is less than the stored maximum amount of oxygen and the NH ₃ release start time has not been reached yet, the process proceeds to step S28 and the NH ₃ released amount, ie, The amount of NH ₃ released from the NOx catalyst 41 is made zero. After step S28, the process proceeds to step S29, where the final (actually injected) urea injection amount is set to the basic value of the urea injection amount calculated in step S22. After step S29, the process ends (return to step S21).

On the other hand, if the determination in step S27 is YES and ΣMreO2 is greater than or equal to the storage oxygen maximum amount and it is estimated that the NH ₃ release start time has arrived or exceeded, the process proceeds to step S30. At step S30, it is calculated by the procedure described amount of released NH ₃ from NH ₃ emissions clogging NOx catalyst 41 in (3-5).

After step S30, the process proceeds to step S31. In step S31, the DCU 300 calculates, as a reduction amount, a value obtained by converting the amount of released NH ₃ calculated in step S30 into urea.

  After step S31, the process proceeds to step S32. In step S32, the DCU 300 subtracts the urea conversion value obtained in step S31 from the basic urea injection amount obtained in step S22, and sets the value as the final urea injection amount.

After step S32, the process proceeds to step S33. In step S33, the DCU 300 integrates the release amount of NH ₃ calculated in step S301 to calculate the total amount of NH ₃ released from the DeNOx catalyst 41 after the NH ₃ release start timing. After step S32, the process ends (return to step S21).

As described above, in the present embodiment, even during the implementation of DeNOx control, reduction of the urea injection amount from the basic urea injection amount only after the determination in step S27 becomes YES and the NH ₃ release start timing is reached. Is done. Therefore, the larger the storage oxygen reduction rate and the shorter the time from the start of DeNOx control to the arrival of the NH ₃ release start time, the longer the time for weight reduction is made. The total urea injection amount supplied is reduced.

As described above, the basic urea injection amount is appropriately adjusted so that the amount of NH ₃ adsorbed to the SCR catalyst 46 is maintained at a predetermined amount, but a reduction amount exceeding the basic urea injection amount is necessary. If this is the case, the amount of reduction that has been exceeded may be subtracted from the basic urea injection amount after the end of DeNOx control.

  On the other hand, if the determination in step S23 is NO, the process proceeds to step S40.

In step S40, the DCU 300 resets the integrated value (ΣMreO2) of the stored oxygen reduction rate to 0, and resets the NH ₃ release amount from the NOx catalyst 41 to 0. The total amount of NH ₃ emissions is stored.

  After step S40, the process proceeds to step S41. In step S41, the DCU 300 determines whether or not a switching period (previously set as described above) has not elapsed since the end of DeNOx control.

If the determination in step S41 is YES, the process proceeds to step S42. In step S42, a value calculated in step S32 at the time of execution of the DeNOx control just before, in accordance with the embodiment of the DeNOx control based on the total amount of NH ₃ released from the NOx catalyst 41, reducing the urea injection amount Determine the amount. As described above, in the present embodiment, this is determined such that the larger the total amount of NH ₃ , the larger the reduction amount. Further, as described above, the reduction amount (reduction amount in the switching period) calculated in step S42 is set to a value smaller than the reduction amount (reduction amount in DeNOx control) calculated in step S26. .

  After step S42, the process proceeds to step S43. In step S43, the DCU 300 determines a value obtained by subtracting the reduction amount calculated in step S42 from the basic urea injection amount calculated in step S22 as a final urea injection amount. After step S42, the process ends (return to step S21).

On the other hand, if the determination in step S41 is NO, that is, if the reduction of the urea injection amount corresponding to the total amount of NH ₃ emissions generated in the DeNOx control is completed, the process proceeds to step S51. In step S51, the final urea injection amount is set to the basic value of the urea injection amount calculated in step S22. After step S51, the process ends (return to step S21).

(4) Operation, Etc. As described above, in the present embodiment, during DeNOx control, the urea injection amount is reduced compared to the non-execution of DeNOx control. Therefore, at the time of DeNOx control, it can be suppressed that the NH ₃ supplied to the SCR catalyst 46 becomes excessive and this slips to the downstream side of the SCR catalyst 46.

Then, at the time of DeNOx control, the urea injection amount is changed according to the stored oxygen decrease rate. Specifically, the urea injection amount is reduced as the time (delay time) from the start of the DeNOx control to the start of the DeNOx control and the start of the release of NH ₃ from the NOx catalyst 41 becomes shorter. Ru.

Therefore, it is possible to ensure that the amount of NH ₃ supplied to the SCR catalyst 46 is an appropriate amount to prevent the NH ₃ from slipping to the downstream side of the SCR catalyst 46 and to purify NOx by the SCR catalyst 46 appropriately. it can.

Specifically, with the delay time being short, a large amount of NH ₃ is released from the NOx catalyst 41 and a large amount of NH ₃ is accumulated (adsorbed) in the SCR catalyst 46. 46 it is possible to prevent the large amount of NH ₃ is supplied, NH ₃ can be prevented from slipping through the downstream side of the SCR catalyst 46 without being adsorbed by the SCR catalyst 46. Also, with the delay time being long, a small amount of NH ₃ introduced from the NOx catalyst 41 to the SCR catalyst 46 and a small amount of NH ₃ in the SCR catalyst 46 to the SCR catalyst 46 are obtained. It can be prevented that only NH ₃ is supplied, and the amount of NH ₃ in the SCR catalyst 46 can be secured to purify NOx appropriately.

  Here, as described above, the stored oxygen reduction rate is calculated by equation (2). The second correction coefficient α2 constituting the correction coefficient K in the equation (2) is set so that the lower the temperature of the NOx catalyst 41 becomes smaller (the higher the temperature of the NOx catalyst 41 becomes larger) ing. Therefore, the higher the temperature of the NOx catalyst 41, the larger the value of the stored oxygen reduction rate, and during DeNOx control, the higher the temperature of the NOx catalyst 41, the smaller the urea injection amount.

That is, in the present embodiment, at the time of DeNOx control, the urea injector 45 is controlled so that the urea injection amount is smaller when the temperature of the NOx catalyst 41 is higher, so that the stored oxygen reduction rate is smaller. Is controlled so that the amount of urea injection is appropriately changed according to the rate of decrease in stored oxygen, thereby obtaining the effect of efficiently purifying NOx while preventing the NH ₃ slipping through. be able to.

  Further, in the present embodiment, as shown in FIG. 8, the second correction coefficient α2 is set such that the rate of change of the second correction coefficient α2 with respect to the temperature of the NOx catalyst 41 increases as the temperature of the NOx catalyst 41 decreases. Is set. Therefore, in the present embodiment, the urea injection amount is controlled such that the change rate of the urea injection amount with respect to the temperature of the NOx catalyst 41 becomes larger as the temperature of the NOx catalyst 41 is lower.

  That is, in the present embodiment, at the time of DeNOx control, the urea injection amount is controlled by controlling the urea injection amount so that the change rate of the urea injection amount with respect to this temperature increases as the temperature of the NOx catalyst 41 decreases. The value is made more appropriate according to the oxygen reduction rate, whereby the effect can be obtained more reliably.

  Further, in the present embodiment, after the DeNOx control ends, the final (actually injected) urea injection amount is configured to be smaller than the basic urea injection amount until the switching period elapses. The urea injection amount is configured to be smaller than that during the non-execution of the DeNOx control.

Accordingly, in a state where a large amount of NH ₃ in the SCR catalyst 46 in accordance with the embodiment of the DeNOx control is adsorbed, can be prevented from the NH ₃ excess amounts from the urea injector 45 is supplied, the SCR catalyst 46 of the NH ₃ The NOx can be efficiently purified while preventing the slippage to the downstream side of the

Further, in the present embodiment, by calculating the storage oxygen reduction rate using the equation (2), it is possible to estimate this with high accuracy. Then, the storage oxygen reduction rate is accurately estimated, so that the urea injection amount adjusted according to the storage oxygen reduction rate is a more appropriate value, that is, the NH ₃ slips to the downstream side of the SCR catalyst 46. It can control to the value which can purify NOx efficiently, preventing.

Further, in the present embodiment, the target value of the excess air ratio λ of the exhaust gas at the time of DeNOx control is set to a value larger than 0.9, and control is performed such that this value is realized. Therefore, the variation range of the amount of the reducing agent in the exhaust gas can be suppressed small, and the reducing agent can be stably supplied to the NOx catalyst 41. Therefore, the NH ₃ released from the NOx catalyst 41 can eventually be supplied to the SCR catalyst 46. The amount of NH ₃ can be maintained more properly.

  And in this embodiment, the injection quantity of post injection is adjusted so that this air excess ratio (lambda) is implement | achieved. Therefore, the excess air ratio λ is controlled with high accuracy as compared to the case where the excess air ratio λ is changed by adjusting the amount of air introduced into the cylinder 2 and the exhaust passage 40 by changing the opening of the throttle valve 23 or the like. can do.

(5) Modification In the above embodiment, the case of controlling the excess air ratio λ of the exhaust gas to 0.96 or 0.98 at the time of DeNOx control has been described, but a specific example of the excess air ratio λ of the exhaust gas at the time of DeNOx control Values are not limited to this.

However, as described above, if the excess air ratio λ of the exhaust gas is controlled to a value larger than 0.9 and smaller than 1.0 during DeNOx control, NH ₃ is efficiently and stably added to the SCR catalyst 46. Can be supplied.

  Further, in the above embodiment, the case of adjusting the excess air ratio λ of the exhaust gas by performing the post injection during the DeNOx control has been described, but the exhaust amount can be changed by changing the amount of air introduced into the cylinder 2 The excess air ratio λ of the gas may be adjusted. However, as described above, when the amount of air is reduced, the acceleration may be deteriorated, and the control accuracy of the excess air ratio λ may be deteriorated. Therefore, as described above, at the time of DeNOx control, it is preferable to control the excess air ratio λ of the exhaust gas to a target value by changing the injection amount of the post injection.

  Further, although FIG. 15 illustrates the case where the urea injection amount is reduced in a state where purification of NOx is performed by both the SCR catalyst 41 and the NOx catalyst 46, NOx is purified only by the NOx catalyst 41. And when purification of NOx by the SCR catalyst 41 is started after DeNOx control is implemented, the urea injection amount after the start of NOx purification by the SCR catalyst 41 is calculated from the basic urea injection amount by the NH3 calculated in step S33. The total amount of released amount may be reduced.

10 Fuel injection valve (air excess ratio change means)
40 exhaust passage 41 NOx catalyst 45 urea injector (reductant supply means for SCR)
46 SCR catalyst 200 PCM (control means)
300 DCU (control means)

Claims (5)

An engine body in which cylinders are formed, an exhaust passage through which exhaust gas discharged from the engine body flows, an NOx catalyst provided in the exhaust passage, and an SCR catalyst provided on the downstream side of the NOx catalyst; An exhaust purification control device for an engine having
Excess air ratio change means for changing the excess air ratio of the exhaust gas,
A reducing agent supply unit for SCR, which supplies a raw material of NH ₃ or a reducing agent for SCR consisting of NH ₃ between the NOx catalyst and the SCR catalyst in the exhaust passage;
Control for performing the regeneration control to control the excess air ratio changing means and the reducing agent supply means for SCR and reduce the excess air ratio of exhaust gas to 1 or less by the excess air ratio changing means Equipped with
When the temperature of the NOx catalyst at the time of the regeneration control is high, the control means may reduce the amount of the SCR reducing agent supplied from the SCR reducing agent supply means to the exhaust passage compared to when the temperature is low. An exhaust gas purification control device for an engine, which controls the reducing agent supply means for SCR. The exhaust gas purification control device for an engine according to claim 1, wherein
The control means is configured to supply the reducing agent for SCR such that the rate of change of the supply amount of the reducing agent for SCR with respect to the temperature of the NOx catalyst is larger as the temperature of the NOx catalyst during the regeneration control is lower. An exhaust purification control device for an engine, characterized in that: In the engine exhaust gas purification control device according to claim 1 or 2,
The control device controls the excess air ratio changing means so that the excess air ratio of the exhaust gas becomes larger than 0.9 at the time of the regeneration control. In the engine exhaust gas purification control device according to any one of claims 1 to 3,
The excess air ratio changing means is added to the main injection for injecting the fuel for obtaining the engine torque introduced into the cylinder into the cylinder at the time of the regeneration control, and the timing on the retard side of the main injection An exhaust purification control system for an engine, comprising: performing post injection for injecting fuel into the cylinder and changing an injection amount of the post injection to change an excess air ratio of the exhaust gas. In the engine exhaust gas purification control device according to any one of claims 1 to 4,
The control means controls the SCR reducing agent supply means from after the regeneration control ends until the predetermined period elapses after the regeneration control ends, rather than after the predetermined period elapses after the regeneration control ends. The SCR reducing agent supply means is controlled to reduce the amount of the SCR reducing agent supplied to the exhaust passage.
The NOx during the period from the NOx catalyst with the start of the regeneration control with the NH ₃ estimates the NH ₃ release start timing is a timing that is released, until the end timing of the playback control from the NH ₃ release start timing The larger the total amount of NH ₃ released estimated from the total amount of NH ₃ released from the catalyst, the larger the amount of the NH ₃ released from the SCR when the predetermined period elapses from the end of the regeneration control. An exhaust gas purification control device for an engine, comprising: controlling the SCR reducing agent supply unit such that the amount of the SCR reducing agent supplied from the reducing agent supply unit to the exhaust passage decreases.

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