JP2016133048A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent deterioration of fuel economy by prohibiting execution of NOx purge in a state where an exhaust lambda value is hard to lower.SOLUTION: An exhaust emission control system includes: an NOx occlusion and reduction type catalyst 32 that occludes NOx in exhaust gas in an exhaust lean state and reduces the occluded NOx for purification in an exhaust rich state; an NOx purge control section 60 for executing NOx purge for reducing the NOx occluded in the NOx occlusion and reduction type catalyst 32 for purification by causing exhaust gas to become a rich state; and an NOx purge prohibiting processing section 70 for prohibiting the execution of the NOx purge by the NOx purge control section 60 when fuel injection amount of an internal combustion engine 10 is smaller than a predetermined lower limit injection amount threshold value.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification system.

  Conventionally, a NOx occlusion reduction type catalyst is known as a catalyst for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from an internal combustion engine. The NOx occlusion reduction catalyst occludes NOx contained in the exhaust when the exhaust is in a lean atmosphere, and harmless NOx occluded by hydrocarbons contained in the exhaust when the exhaust is in a rich atmosphere. And release. For this reason, when the NOx occlusion amount of the catalyst reaches a predetermined amount, so-called NOx purging that makes the exhaust gas rich by exhaust pipe injection or post injection needs to be performed periodically in order to recover the NOx occlusion capacity ( For example, see Patent Documents 1 and 2).

JP 2008-202425 A JP 2007-16713 A

  By the way, when the fuel injection amount of the engine is small, the exhaust lambda is kept high. Even if the NOx purge is performed in such a state that the exhaust lambda is not easily lowered, the exhaust lambda cannot be lowered to a desired lambda required for the NOx purge, and the fuel consumption is deteriorated due to wasteful exhaust rich injection. There is.

  An object of the disclosed system is to effectively prevent deterioration of fuel consumption by prohibiting the execution of NOx purge in a state where the exhaust lambda is hardly lowered.

  The disclosed system is provided in an exhaust system of an internal combustion engine, stores NOx in exhaust gas in an exhaust lean state, and reduces and purifies NOx stored in an exhaust rich state, and a rich exhaust gas. In this state, the catalyst regeneration means for performing catalyst regeneration processing for reducing and purifying NOx stored in the NOx storage reduction catalyst, and the fuel injection amount of the internal combustion engine is smaller than a predetermined lower limit injection amount threshold value. And a prohibiting means for prohibiting the catalyst regeneration process from being performed by the catalyst regeneration means.

  According to the disclosed system, it is possible to effectively prevent the deterioration of fuel consumption by prohibiting the execution of the NOx purge in a state where the exhaust lambda is hardly lowered.

1 is an overall configuration diagram showing an exhaust purification system according to an embodiment. It is a timing chart figure explaining NOx purge control concerning this embodiment. It is a block diagram which shows the setting process of the MAF target value used for NOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection amount used for NOx purge rich control which concerns on this embodiment. It is a block diagram which shows the prohibition process of NOx purge control which concerns on this embodiment. It is a figure which shows an example of the prohibition determination map which concerns on this embodiment. It is a block diagram which shows the process of the injection amount learning correction | amendment of the in-cylinder injector which concerns on this embodiment. It is a flowchart explaining the calculation process of the learning correction coefficient which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF correction coefficient which concerns on this embodiment.

  Hereinafter, an exhaust purification system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, each cylinder of a diesel engine (hereinafter simply referred to as “engine”) 10 is provided with an in-cylinder injector 11 that directly injects high-pressure fuel that is stored in a common rail (not shown) into each cylinder. Yes. The fuel injection amount and fuel injection timing of each in-cylinder injector 11 are controlled according to an instruction signal input from an electronic control unit (hereinafter referred to as ECU) 50.

  An intake passage 12 for introducing fresh air is connected to the intake manifold 10A of the engine 10, and an exhaust passage 13 for leading the exhaust to the outside is connected to the exhaust manifold 10B. In the intake passage 12, an air cleaner 14, an intake air amount sensor (hereinafter referred to as MAF sensor) 40, a compressor 20A of the variable displacement supercharger 20, an intercooler 15, an intake throttle valve 16 and the like are provided in order from the intake upstream side. ing. The exhaust passage 13 is provided with a turbine 20B of the variable displacement supercharger 20, an exhaust aftertreatment device 30 and the like in order from the exhaust upstream side. In FIG. 1, reference numeral 41 denotes an engine speed sensor, reference numeral 42 denotes an accelerator opening sensor, and reference numeral 46 denotes a boost pressure sensor.

  The EGR device 21 includes an EGR passage 22 that connects the exhaust manifold 10B and the intake manifold 10A, an EGR cooler 23 that cools EGR gas, and an EGR valve 24 that adjusts the EGR amount.

  The exhaust aftertreatment device 30 is configured by arranging an oxidation catalyst 31, a NOx occlusion reduction type catalyst 32, and a particulate filter (hereinafter simply referred to as a filter) 33 in order from the exhaust upstream side in a case 30A. The exhaust passage 13 upstream of the oxidation catalyst 31 is provided with an exhaust injector 34 that injects unburned fuel (mainly HC) into the exhaust passage 13 in accordance with an instruction signal input from the ECU 50. Yes.

  The oxidation catalyst 31 is formed, for example, by carrying an oxidation catalyst component on the surface of a ceramic carrier such as a honeycomb structure. When the unburned fuel is supplied by the exhaust pipe injection of the exhaust injector 34 or the post injection of the in-cylinder injector 11, the oxidation catalyst 31 oxidizes this and raises the exhaust temperature.

  The NOx storage reduction catalyst 32 is formed, for example, by supporting an alkali metal or the like on the surface of a ceramic carrier such as a honeycomb structure. The NOx occlusion reduction type catalyst 32 occludes NOx in the exhaust when the exhaust air-fuel ratio is in a lean state, and occludes with a reducing agent (HC or the like) contained in the exhaust when the exhaust air-fuel ratio is in a rich state. NOx is reduced and purified.

  The filter 33 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. . The filter 33 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and when the estimated amount of PM deposition reaches a predetermined amount, so-called filter forced regeneration is performed in which the PM is burned and removed. Filter forced regeneration is performed by supplying unburned fuel to the upstream side oxidation catalyst 31 by exhaust pipe injection or post injection, and raising the exhaust temperature flowing into the filter 33 to the PM combustion temperature.

  The first exhaust temperature sensor 43 is provided on the upstream side of the oxidation catalyst 31 and detects the exhaust temperature flowing into the oxidation catalyst 31. The second exhaust temperature sensor 44 is provided between the NOx storage reduction catalyst 32 and the filter 33 and detects the exhaust temperature flowing into the filter 33. The NOx / lambda sensor 45 is provided on the downstream side of the filter 33, and detects the NOx value and lambda value (hereinafter also referred to as excess air ratio) of the exhaust gas that has passed through the NOx storage reduction catalyst 32.

  The ECU 50 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, sensor values of the sensors 40 to 46 are input to the ECU 50. The ECU 50 includes a NOx purge control unit 60, a NOx purge prohibition processing unit 70, a MAF follow-up control unit 80, an injection amount learning correction unit 90, and a MAF correction coefficient calculation unit 95 as some functional elements. . Each of these functional elements will be described as being included in the ECU 50 which is an integral hardware, but any one of these may be provided in separate hardware.

[NOx purge control]
The NOx purge control unit 60 is the catalyst regeneration means of the present invention, and makes NOx occluded and reduced by detoxifying and releasing NOx occluded in the NOx occlusion reduction type catalyst 32 in a rich state by reduction purification. A catalyst regeneration process for recovering the NOx occlusion capacity of the type catalyst 32 (hereinafter, this control is referred to as NOx purge control) is executed.

The “start request” of the NOx purge control is, for example, a case where the NOx emission amount per unit time is estimated from the operating state of the engine 10 and the estimated cumulative value ΣNOx obtained by accumulating this is over a predetermined threshold, or the engine The NOx purification rate by the NOx occlusion reduction type catalyst 32 is calculated from the NOx emission amount on the upstream side of the catalyst estimated from the ten operating states and the NOx amount on the downstream side of the catalyst detected by the NOx / lambda sensor 45, and this NOx. This is established when the purification rate is lower than a predetermined determination threshold. When the “start request” is established when the prohibition flag F _{Pro_NP} described later in detail is off, the NOx purge flag F _NP for performing the NOx purge control is turned on (F _NP = 1) (see time t _{1 in} FIG. 2). ).

  In the present embodiment, the exhaust gas enrichment by the NOx purge control is performed on the lean side from the theoretical air-fuel ratio equivalent value (about 1.0) from the time of steady operation (for example, about 1.5) by the air system control. NOx purge lean control to lower the first target excess air ratio (e.g., about 1.3) and the injection system control to reduce the excess air ratio from the first target excess air ratio to the rich second target excess air ratio (e.g., This is realized by using together with the NOx purge rich control for reducing to about 0.9). The details of the NOx purge lean control and the NOx purge rich control will be described below.

[NOx purge lean control]
FIG. 3 is a block diagram showing a setting process of the MAF target value MAF _{NPL_Trgt} by the NOx purge lean control unit 60A. The first target excess air ratio setting map 61 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge lean control corresponding to the engine speed Ne and the accelerator opening Q. An excess air ratio target value λ _{NPL_Trgt} (first excess air ratio) is set in advance based on experiments or the like.

First, the excess air ratio target value λ _{NPL_Trgt} at the time of NOx purge lean control is read from the first target excess air ratio setting map 61 using the engine speed Ne and the accelerator opening Q as input signals, and is sent to the MAF target value calculation unit 62. Entered. Further, the MAF target value calculation unit 62 calculates the MAF target value MAF _{NPL_Trgt} at the time of NOx purge lean control based on the following formula (1).

MAF _{NPL_Trgt} = λ _{NPL_Trgt} × Q _{fnl_corrd} × Ro _Fuel × AFR _sto / _{Maf_corr} (1)
In Equation (1), Q _{fnl_cord} is the fuel injection amount (excluding post-injection) of the in-cylinder injector 11 corrected later, Ro _Fuel is the fuel specific gravity, AFR _sto is the stoichiometric air-fuel ratio, and _{Maf_corr} is the MAF correction described later. Each coefficient is shown.

The MAF target value MAF _{NPL_Trgt} calculated by the MAF target value calculation unit 62 is input to the ramp processing unit 63 when the NOx purge flag F _NP is turned on (see time t _{1 in} FIG. 2). The ramp processing unit 63 reads the ramp coefficient from each of the ramp coefficient maps 63A and _63B using the engine speed Ne and the accelerator opening Q as input signals, and _{uses the} MAF target ramp value MAF _{NPL_Trgt_Ramp} to which the ramp coefficient is added as a valve control unit 64. To enter.

The valve control unit 64 throttles the intake throttle valve 16 to the _close side and opens the EGR valve 24 to the open side so that the actual MAF value MAF _Act input from the MAF sensor 40 becomes the MAF target ramp value MAF _{NPL_Trgt_Ramp.} Execute control.

Thus, in this embodiment, the MAF target value MAF _{NPL_Trgt} is set based on the excess air ratio target value λ _{NPL_Trgt} read from the first target excess air ratio setting map 61 and the fuel injection amount of each in-cylinder injector 11. The air system operation is feedback-controlled based on the MAF target value MAF _{NPL_Trgt} . Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge lean control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each in-cylinder injector 11, the MAF target value MAF _{NPL_Trgt} can be set by feedforward control. Effects such as deterioration and characteristic changes can be effectively eliminated.

Further, by adding a ramp coefficient that is set according to the operating state of the engine 10 to the MAF target value MAF _{NPL_Trgt} , it is possible to prevent misfire of the engine 10 due to a sudden change in the intake air amount, deterioration of drivability due to torque fluctuation, and the like. It can be effectively prevented.

[NOx purge rich control fuel injection amount setting]
FIG. 4 is a block diagram showing a setting process of the target injection amount Q _{NPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection by the NOx purge rich control unit 60B. The second target excess air ratio setting map 65 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge rich control corresponding to the engine speed Ne and the accelerator opening Q. The air excess rate target value λ _{NPR_Trgt} (second target air excess rate) is preset based on experiments or the like.

First, the excess air ratio target value λ _{NPR_Trgt} at the time of NOx purge rich control is read from the second target excess air ratio setting map 65 using the engine speed Ne and the accelerator opening Q as input signals, and the injection quantity target value calculation unit 66 is read. Is input. Further, the injection amount target value calculation unit 66 calculates the target injection amount Q _{NPR_Trgt} at the time of NOx purge rich control based on the following formula (2).

Q _{NPR_Trgt} = MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (2)
In Expression (2), MAF _{NPL_Trgt} is a NOx purge lean MAF target value, and is input from the MAF target value calculation unit 62 described above. Q _{fnl_cord} is the fuel injection amount (excluding post-injection) of the in-cylinder injector 11 before application of learning corrected MAF follow-up control, which will be described later, Ro _Fuel is fuel specific gravity, AFR _sto is the stoichiometric air-fuel ratio, and _{Maf_corr} is described later. MAF correction coefficients are shown respectively.

The target injection amount Q _{NPR_Trgt} calculated by the injection amount target value calculation unit 66 is transmitted as an injection instruction signal to the exhaust injector 34 or each in-cylinder injector 11 when the NOx purge flag F _NP is turned on (time t in FIG. 2). ₁ ). The transmission of the injection instruction signal is continued until the NOx purge flag F _NP is turned off (time t ₂ in FIG. ₂ ) by the end determination of NOx purge control described later.

Thus, in the present embodiment, the target injection amount Q _{NPR_Trgt} is set based on the excess air ratio target value λ _{NPR_Trgt} read from the second target excess air ratio setting map 65 and the fuel injection amount of each in-cylinder injector 11. It is supposed to be. Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge rich control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each in-cylinder injector 11, the target injection amount Q _{NPR_Trgt} can be set by feedforward control. Effects such as deterioration and characteristic changes can be effectively eliminated.

[NOx purge control prohibition process]
FIG. 5 is a block diagram showing prohibition processing by the NOx purge prohibition processing unit 70. The NOx purge prohibition processing unit 70 is a prohibition unit of the present invention, and when any of the following prohibition conditions (1) to (8) is satisfied, the NOx purge prohibition flag F _{Pro_NP} is turned on (F _{Pro_NP} = 1). Therefore, the execution of the NOx purge control is prohibited.
(1) The engine speed Ne is higher than a predetermined upper limit speed threshold value _{Ne_max} .
(2) The engine speed Ne is lower than a predetermined lower limit speed threshold value _{Ne_min} .
(3) (excluding post-injection) fuel injection quantity _{Q Fnl_corrd} in-cylinder injector 11 is often than a predetermined upper-limit injection amount threshold _{Q _max.}
(4) When the fuel injection amount _{Q Fnl_corrd} in-cylinder injector 11 (excluding post injection) is smaller than the predetermined lower limit injection amount threshold _{Q _min.}
(5) The engine 10 is in a predetermined high load operation state, and boost pressure feedback control (air system open loop control) is performed.
(6) When the engine 10 may enter a motoring state in which fuel injection is stopped immediately after the start of the NOx purge control.
(7) The reachable exhaust air excess rate estimated value λ _{est_max} estimated from the maximum limit injection amount Q _{exh_max of the} exhaust injector 34 is the excess air rate target value λ _{NPR_Trgt} set by the NOx purge rich control unit 60B. When it becomes higher than the second target excess air ratio).
(8) The catalyst temperature of the NOx occlusion reduction type catalyst 32 is lower than a predetermined catalyst activation temperature.

  Hereinafter, details of these prohibition conditions (1) to (8) will be described.

The prohibition conditions (1) to (4) are determined based on the prohibition determination map shown in FIG. 6 stored in the memory of the ECU 50 in advance. The prohibition determination map is a two-dimensional map to be referred to based on the engine speed Ne and fuel injection quantity Q (accelerator opening), advance the upper limit rotational speed threshold line Ne _{_Max_L} obtained by experiment or the _like, the lower limit engine speed The threshold line _{Ne_min_L} , the upper limit injection amount threshold line _{Q_max_L,} and the lower limit injection amount threshold line _{Q_min_L} are set as fixed values (constant values). That is, a substantially rectangular area surrounded by these four upper and lower limit lines is set as the NOx purge permission area α. When the engine speed Ne and the fuel injection amount Q are out of the NOx purge possible region α, the execution of the NOx purge control is prohibited.

In this embodiment, as described above, when the engine speed Ne is higher than the upper limit engine speed threshold value _{Ne_max} , or when the fuel injection amount of the in-cylinder injector 11 is larger than the upper limit injection amount threshold value _{Q_max} , the NOx purge control is performed. By prohibiting the implementation, a rapid increase in engine temperature can be effectively prevented. Further, by prohibiting the execution of NOx purge control when the engine speed Ne is lower than the lower limit speed threshold value _{Ne_min} , an increase in HC slip can be effectively prevented. Further, by prohibiting the NOx purge control when the fuel injection amount of the in-cylinder injector 11 is smaller than the lower limit injection amount threshold value _{Q_min,} it is possible to reliably prevent the wasteful NOx purge control from being performed in a state where the exhaust lambda is difficult to decrease. It is possible to effectively prevent deterioration of fuel consumption.

The prohibition condition (5) is also determined based on the prohibition determination map shown in FIG. 6 as in the prohibition conditions (1) to (4). In addition to the above four upper and lower limit lines, a boost pressure feedback control line _{FB_max_L} is set in the prohibition determination map. In the region where the fuel injection amount Q is _larger than the boost pressure feedback control line _{FB_max_L,} the booth pressure feedback control (air system) that feedback-controls the opening degree of the variable displacement supercharger 20 based on the sensor value of the boost pressure sensor 46. Open loop control).

The boost pressure feedback control line _{FB_max_L} is set so as to gradually decrease the fuel injection amount Q as the engine speed Ne increases on the high engine speed side, and at least part of the boost pressure feedback control line _{FB_max_L} is a high load within the NOx purge permission region α. It is included in the area. That is, the region β where the booth pressure feedback control is performed is set in the NOx purge permission region α _where the fuel injection amount Q is equal to or less than the upper limit injection amount threshold value _{Q_max} . When the NOx purge control is performed in this region β, the air system controls interfere with each other, the actual MAF cannot be matched with the target MAF value, and the exhaust rich injection amount may become inappropriate.

  In this embodiment, by setting the region β in which the actual MAF and the target MAF value do not coincide with each other as the NOx purge control prohibition region, the deterioration of fuel consumption caused by the inappropriate exhaust rich injection amount or the like. Exhaust overheating is reliably prevented.

The prohibition condition (6) is determined based on a change in the fuel injection amount of the in-cylinder injector 11 when the above-described “start request” for NOx purge control is satisfied. More specifically, when the “start request” for NOx purge control is established, the _sum of the fuel injection amount Q _{fnl_corrd} of the in-cylinder injector 11 and the value obtained by multiplying the injection amount differential value ΔQ by a predetermined time constant K is zero. When the following conditional expression (3) that is less than (a negative value) is satisfied, it is determined that the engine 10 is in a motoring state within a short time, and the execution of the NOx purge control is prohibited.

Q _{fnl_cord} −ΔQ × K <0 (3)
As described above, when there is a possibility that the engine 10 enters the motoring state immediately after the start of the NOx purge control, it is possible to effectively prevent wasteful fuel consumption by prohibiting the execution of the NOx purge control. .

The prohibition condition (7) is determined based on the maximum limit injection amount Q _{exh_max} of the exhaust injector 34 stored in advance in the memory of the ECU 50. More specifically, when the “start request” for NOx purge control is established, the exhaust air excess rate estimated value λ that can be reached when the NOx purge control is performed based on the maximum limit injection amount Q _{exh_max} of the exhaust injector 34. _{est_max} is calculated, and if this exhaust air excess rate estimated value λ _{est_max} is higher than the target value λ _{NPR_Trgt} (second target excess air rate) of NOx purge rich control (λ _{est_max} > λ _{NPR_Trgt} ), NOx Implementation of purge control is prohibited.

Thus, even if the NOx purge control is performed, if the exhaust gas cannot be reduced to the desired excess air ratio due to the limitation of the maximum limit injection amount Q _{exh_max} of the exhaust injector 34, the execution of the NOx purge control is prohibited. This makes it possible to effectively prevent wasteful fuel consumption.

  The prohibition condition (8) is determined based on the estimated catalyst temperature of the NOx storage reduction catalyst 32. The estimated catalyst temperature is estimated based on, for example, the inlet temperature of the oxidation catalyst 31 detected by the first exhaust temperature sensor 43, the exothermic reaction in the oxidation catalyst 31 and the NOx storage reduction catalyst 32, and the like. Is less than a predetermined catalyst activation temperature, NOx purge control is prohibited.

  As described above, when the catalyst temperature of the NOx storage reduction catalyst 32 is lower than the catalyst activation temperature, it is possible to effectively prevent the generation of white smoke and the like by prohibiting the NOx purge.

[Determining completion of NOx purge control]
In the NOx purge control, (1) when the NOx purge flag F _NP is turned on, the amount of exhaust pipe injection or post injection is accumulated, and when this cumulative injection amount reaches a predetermined upper limit threshold amount, (2) NOx purge control When the elapsed time counted from the start reaches a predetermined upper threshold time, (3) calculation is performed based on a predetermined model formula including the operating state of the engine 10 and the sensor value of the NOx / lambda sensor 45 as input signals. If any of the conditions in the case where the NOx occlusion amount of the NOx occlusion reduction type catalyst 32 falls to a predetermined threshold value indicating successful NOx removal is satisfied, the NOx purge flag F _NP is turned off and the process is terminated (time t _{2 in} FIG. 2). reference).

  As described above, in the present embodiment, the cumulative injection amount and the upper limit of the elapsed time are provided in the end condition of the NOx purge control. It is possible to reliably prevent the excess.

[MAF tracking control]
The MAF follow-up control unit 80 includes (1) a switching period from the lean state in the normal operation to the rich state by the NOx purge control, and (2) a switching period from the rich state to the lean state in the normal operation by the NOx purge control. MAF follow-up control for correcting the fuel injection timing and the fuel injection amount of the in-cylinder injector 11 according to the MAF change is executed.

[Injection amount learning correction]
As shown in FIG. 7, the injection amount learning correction unit 90 includes a learning correction coefficient calculation unit 91 and an injection amount correction unit 92.

The learning correction coefficient calculation unit 91 is based on the error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 during the lean operation of the engine 10 and the estimated lambda value λ _Est, and the learning correction coefficient F for the fuel injection amount. Calculate _Corr . When the exhaust is in a lean state, the HC concentration in the exhaust is very low, so that the change in the exhaust lambda value due to the oxidation reaction of HC at the oxidation catalyst 31 is negligibly small. Therefore, the actual lambda value λ _Act in the exhaust gas that passes through the oxidation catalyst 31 and is detected by the downstream NOx / lambda sensor 45 matches the estimated lambda value λ _Est in the exhaust gas discharged from the engine 10. Conceivable. That is, when an error Δλ occurs between the actual lambda value λ _Act and the estimated lambda value λ _Est , it can be assumed that the difference is between the instructed injection amount for each in-cylinder injector 11 and the actual injection amount. Hereinafter, the learning correction coefficient calculation processing by the learning correction coefficient calculation unit 91 using the error Δλ will be described with reference to the flow of FIG.

  In step S300, based on the engine speed Ne and the accelerator opening Q, it is determined whether or not the engine 10 is in a lean operation state. If it is in the lean operation state, the process proceeds to step S310 to start the calculation of the learning correction coefficient.

In step S310, an error Δλ obtained by subtracting the actual lambda value λ _Act detected by the NOx / lambda sensor 45 from the estimated lambda value λ _Est is multiplied by the learning value gain K ₁ and the correction sensitivity coefficient K ₂ to thereby obtain the learning value F _CorrAdpt is calculated (F _CorrAdpt = (λ _Est −λ _Act ) × K ₁ × K ₂ ). The estimated lambda value λ _Est is estimated and calculated from the operating state of the engine 10 according to the engine speed Ne and the accelerator opening Q. Further, the correction sensitivity coefficient _{K 2} is read the actual lambda value lambda _Act detected by the NOx / lambda sensor 45 from the correction sensitivity coefficient map 91A shown in FIG. 7 as the input signal.

In step S320, it is determined whether or not the absolute value | F _CorrAdpt | of the learning value F _CorrAdpt is within the range of the predetermined correction limit value A. If the absolute value | F _CorrAdpt | exceeds the correction limit value A, the present control is returned to stop the current learning.

In step S330, it is determined whether the learning prohibition flag _FPro is off. The learning prohibition flag F _Pro corresponds to, for example, a transient operation of the engine 10 or a NOx purge control (F _NP = 1). This is because when these conditions are satisfied, the error Δλ increases due to a change in the actual lambda value λ _Act , and accurate learning cannot be performed. Whether or not the engine 10 is in a transient operation state is determined based on, for example, the time change amount of the actual lambda value λ _Act detected by the NOx / lambda sensor 45 when the time change amount is larger than a predetermined threshold value. What is necessary is just to determine with a transient operation state.

In step S340, the learning value map 91B (see FIG. 7) referred to based on the engine speed Ne and the accelerator opening Q is updated to the learning value F _CorrAdpt calculated in step S310. More specifically, on the learning value map 91B, a plurality of learning areas divided according to the engine speed Ne and the accelerator opening Q are set. These learning regions are preferably set to have a narrower range as the region is used more frequently and to be wider as a region is used less frequently. As a result, learning accuracy is improved in regions where the usage frequency is high, and unlearning can be effectively prevented in regions where the usage frequency is low.

In step S350, the learning correction coefficient F _Corr is calculated by adding “1” to the learned value read from the learned value map 91B using the engine speed Ne and the accelerator opening Q as input signals (F _Corr = 1 + F). _CorrAdpt ). The learning correction coefficient F _Corr is input to the injection amount correction unit 92 shown in FIG.

The injection amount correction unit 92 multiplies each basic injection amount of pilot injection Q _Pilot , pre-injection Q _Pre , main injection Q _Main , after-injection Q _After , and post-injection Q _{Post by} a learning correction coefficient F _Corr. The injection amount is corrected.

In this way, by correcting the fuel injection amount to each in-cylinder injector 11 with a learning value corresponding to the error Δλ between the estimated lambda value λ _Est and the actual lambda value λ _Act , the aging deterioration and characteristics of each in-cylinder injector 11 are corrected. Variations such as changes and individual differences can be effectively eliminated.

[MAF correction coefficient]
MAF correction coefficient calculating unit 95 calculates the MAF correction coefficient _{Maf _Corr} used to set the MAF target value _{MAF NPL_Trgt} and the target injection amount _{Q NPR_Trgt} during NOx purge control.

In the present embodiment, the fuel injection amount of each in-cylinder injector 11 is corrected based on the error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 and the estimated lambda value λ _Est . However, since lambda is the ratio of air and fuel, the factor of error Δλ is not necessarily the only effect of the difference between the commanded injection amount and the actual injection amount for each in-cylinder injector 11. That is, there is a possibility that the error of the MAF sensor 40 as well as the in-cylinder injectors 11 affects the lambda error Δλ.

FIG. 9 is a block diagram showing the setting process of the MAF correction coefficient _{Maf_corr} by the MAF correction coefficient calculation unit 95. The correction coefficient setting map 96 is a map that is referred to based on the engine speed Ne and the accelerator opening Q. The MAF indicating the sensor characteristics of the MAF sensor 40 corresponding to the engine speed Ne and the accelerator opening Q is shown in FIG. The correction coefficient _{Maf_corr} is set in advance based on experiments or the like.

The MAF correction coefficient calculation unit 95 reads the MAF correction coefficient _{Maf_corr} from the correction coefficient setting map 96 using the engine speed Ne and the accelerator opening Q as input signals, and _{uses the} MAF correction coefficient _{Maf_corr} as the MAF target value calculation unit 62 and It transmits to the injection quantity target value calculating part 66. As a result, the sensor characteristics of the MAF sensor 40 can be effectively reflected in the settings of the MAF target value MAF _{NPL_Trgt} and the target injection amount Q _{NPR_Trgt} during the NOx purge control.

[Others]
In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

DESCRIPTION OF SYMBOLS 10 Engine 11 In-cylinder injector 12 Intake passage 13 Exhaust passage 16 Intake throttle valve 24 EGR valve 31 Oxidation catalyst 32 NOx occlusion reduction type catalyst 33 Filter 34 Exhaust injector 40 MAF sensor 45 NOx / lambda sensor 50 ECU

Claims (5)

A NOx occlusion reduction type catalyst that is provided in an exhaust system of an internal combustion engine and that occludes NOx in exhaust in an exhaust lean state and reduces and purifies NOx occluded in an exhaust rich state;
Catalyst regeneration means for performing catalyst regeneration processing for reducing and purifying NOx stored in the NOx storage reduction catalyst by making the exhaust rich;
An exhaust purification system comprising: prohibiting means for prohibiting execution of catalyst regeneration processing by the catalyst regeneration means when the fuel injection amount of the internal combustion engine is smaller than a predetermined lower limit injection amount threshold value. The exhaust purification system according to claim 1, wherein the prohibiting unit further prohibits the catalyst regeneration process from being performed by the catalyst regeneration unit even when the fuel injection amount of the internal combustion engine is greater than a predetermined upper limit injection amount threshold value. The exhaust purification system according to claim 1 or 2, wherein the prohibiting unit further prohibits the catalyst regeneration processing by the catalyst regeneration unit even when the rotational speed of the internal combustion engine is higher than a predetermined upper limit rotational speed threshold. 4. The prohibition unit further prohibits the catalyst regeneration process from being performed by the catalyst regeneration unit even when the rotational speed of the internal combustion engine is lower than a predetermined lower limit rotational speed threshold. 5. Exhaust purification system. The catalyst regeneration means performs the catalyst regeneration process by using both air system control for feedback control of the air flow rate of the internal combustion engine based on a predetermined target air flow rate and injection system control for increasing the fuel injection amount,
5. The prohibiting unit prohibits the catalyst regeneration process from being performed by the catalyst regeneration unit when the operating state of the internal combustion engine is in a high-load operation state in which boost pressure is feedback-controlled. 6. Exhaust purification system.