JP2016160857A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent deterioration of exhaust emissions at restart of an engine.SOLUTION: An exhaust emission control system includes: an NOx purge control section 100 for performing NOx purge control of recovering an NOx occlusion capacity of an NOx occlusion reduction type catalyst 32 by making exhaust gas rich; and an NOx purge start processing section 110 for causing the NOx purge control section 100 to perform next NOx purge control when NOx occlusion amount exceeds a predetermined upper limit threshold value and lapsed time after completion of previous NOx purge control reaches a first target interval time. The NOx purge start processing section 110 also starts the NOx purge control when the NOx occlusion amount does not exceed the upper limit threshold value and the lapsed time after the completion of the previous NOx purge control reaches a second target interval time.SELECTED DRAWING: Figure 4

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 purge that makes the exhaust rich by post injection or exhaust pipe injection needs to be performed periodically to restore the NOx occlusion capacity ( For example, see Patent Document 1).

JP 2008-202425 A JP 2014-125975 A JP 2006-336518 A

  In general, the NOx purge is performed when the NOx occlusion amount of the NOx occlusion reduction catalyst exceeds a predetermined upper limit threshold or when the NOx purification rate falls to a predetermined lower limit threshold. However, if the engine is turned off (stopped) without the NOx occlusion amount exceeding the upper limit threshold for a long period of time or the NOx purification rate falling to the lower limit threshold, the catalyst temperature will be reduced when the engine is restarted thereafter. When it falls, there is a possibility that the NOx occlusion ability is already in a saturated state, and there is a problem that causes deterioration of exhaust emission.

  An object of the disclosed system is to effectively prevent deterioration of exhaust emission when the engine is restarted.

  A disclosed system is provided in an exhaust system of an internal combustion engine, and stores NOx in exhaust gas in an exhaust lean state and reduces and purifies NOx stored in an exhaust rich state, and the NOx storage catalyst. NOx occlusion amount estimation means for estimating the NOx occlusion amount of the reduction catalyst, catalyst regeneration control means for performing catalyst regeneration processing for recovering the NOx occlusion capacity of the NOx occlusion reduction catalyst by setting the exhaust to a rich state, and the NOx When the NOx occlusion amount estimated by the occlusion amount estimation means exceeds a predetermined upper limit threshold and the elapsed time from the end of the previous catalyst regeneration process reaches a predetermined first target interval time, the catalyst regeneration control means is Regeneration start processing means for starting the catalyst regeneration processing, and the regeneration start processing means is estimated by the NOx occlusion amount estimation means N Even when the amount of occlusion does not exceed the upper limit threshold and the elapsed time from the end of the previous catalyst regeneration process reaches a predetermined second target interval time, the catalyst regeneration control means starts the next catalyst regeneration process. .

  According to the disclosed system, exhaust emission deterioration at the time of engine restart can be effectively prevented.

1 is an overall configuration diagram showing an exhaust purification system according to an embodiment. It is a functional block diagram which shows the NOx purge control part which concerns on this embodiment. It is a timing chart figure explaining NOx purge control concerning this embodiment. It is a block diagram which shows the starting process of NOx purge control which concerns on this embodiment. It is a flowchart which shows the start process of NOx purge control which concerns on this embodiment. It is a block diagram which shows the completion | finish process of NOx purge control which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF target value at the time of NOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection quantity at the time of NOx purge rich control which concerns on this embodiment. It is a block diagram which shows the process of the injection amount learning correction | amendment of the 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 an engine) 10 is provided with an injector 11 that directly injects high-pressure fuel stored in a common rail (not shown) into each cylinder. The fuel injection amount and fuel injection timing of each injector 11 are controlled in accordance with 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 pipe injection device 34 that injects unburned fuel (mainly HC) into the exhaust passage 13 in accordance with an instruction signal input from the ECU 50. It has been.

  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 post-injection of the exhaust pipe injector 34 or the 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. Further, the ECU 50 includes the NOx purge control unit 100, the MAF follow-up control unit 200, the injection amount learning correction unit 300, and the MAF correction coefficient calculation unit 400 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 100 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 atmosphere by reduction purification. Regeneration processing control (hereinafter, this control is referred to as NOx purge control) for recovering the NOx storage capacity of the type catalyst 32 is executed. In the present embodiment, the NOx purge control unit 100 includes a NOx purge start processing unit 110, an air system control unit 130, an injection system control unit 140, and a NOx purge end processing unit 150, as shown in FIG. It is provided as a functional element. Details of each of these functional elements will be described below.

[NOx purge control start processing]
FIG. 4 is a block diagram showing a start process by the NOx purge start processing unit 110.

The NOx purge start determination unit 111 is (1) a first condition in which the NOx occlusion amount estimated value _{m_NOx of the} NOx occlusion reduction catalyst 32 exceeds a predetermined NOx occlusion amount threshold _{STR_thr_NOx} , or (2) the NOx occlusion reduction type catalyst. A NOx purge start request that satisfies any of the second conditions in which the NOx purification rate _{Pur_NOx% of} 32 decreases to a predetermined purification rate threshold value _{Pur_thr_NOx%} , and (3) a timer built in the ECU from the end of the previous NOx purge control When the third condition in which the elapsed time _{Int_Time} timed by the above reaches the predetermined first interval target value _{Int_tgr_1} is satisfied, the NOx purge flag F _NP is turned on (F _NP = 1) to start the NOx purge control (FIG. 3). reference of time _{t 1).}

Furthermore, the above-described first condition and second condition are not satisfied, and (4) a fourth condition in which the elapsed time _{Int_Time} from the end of the previous NOx purge control reaches a predetermined second interval target value _{Int_tgr_2.} Also when NO is established, the NOx purge flag F _NP is turned on (F _NP = 1) to start the NOx purge control.

The NOx occlusion amount estimated value _{m_NOx} used for the determination of the first condition is estimated by the NOx occlusion amount estimation unit 113. The NOx occlusion amount estimated value _{m_NOx} may be calculated based on, for example, a map or a model formula that includes the operating state of the engine 10, the sensor value of the NOx / lambda sensor 45, and the like as input signals. NOx storage amount threshold _{STR _Thr_NOx} is set in storage amount threshold map 114 referenced based on the estimated catalyst temperature _{Temp _LNT} the NOx occlusion-reduction catalyst 32. The estimated catalyst temperature _{Temp_LNT} is estimated by the catalyst temperature estimation unit 115. The estimated catalyst temperature _{Temp_LNT} is, for example, the inlet temperature of the oxidation catalyst 31 detected by the first exhaust temperature sensor 43, the HC / CO heat generation amount inside the oxidation catalyst 31 and the NOx storage reduction catalyst 32, and the heat release amount to the outside air. It may be estimated based on the above. The NOx occlusion amount threshold value _{STR_thr_NOx} set based on the occlusion amount threshold value map 114 is corrected by an occlusion amount threshold value correction unit 116, which will be described in detail later.

The NOx purification rate _{NOx_pur%} used for the determination of the second condition is calculated by the purification rate calculation unit 117. The NOx purification rate _{NOx_pur%} is obtained, for example, by _dividing the NOx amount on the downstream side of the catalyst detected by the NOx / lambda sensor 45 by the NOx emission amount on the upstream side of the catalyst estimated from the operating state of the engine 10 or the like. That's fine.

The first interval target value _{Int_tgr_1} used for the determination of the third condition is set by the first interval target value map 118A that is referred to based on the engine speed Ne and the accelerator opening Q.

The second interval target value _{Int_tgr_2} used for determination of the fourth condition is set by the second interval target value map 118B that is referred to based on the engine speed Ne and the accelerator opening Q. The second interval target value _{Int_tgr_2} is set in a shorter time than the first interval target value _{Int_tgr_1} .

  The details of the NOx purge control start processing will be described below based on the flow shown in FIG. This control flow is started by starting the engine 10 or ending the NOx purge control.

In step S200, the first condition that NOx occluded amount estimation value _{m _NOx} exceeds NOx storage amount threshold _{STR _Thr_NOx,} or any of the second condition that NOx purifying ratio _{Pur _NOx%} is reduced to a predetermined purification rate threshold _{Pur _thr_NOx%} Whether or not is established is determined. If an affirmative determination is made in this step, the process proceeds to step S210, and if a negative determination is made, the process proceeds to step S250.

In step S210, the “start request” for NOx purge control is established, and the process proceeds to step S220. In step S220, the first interval target value _{Int_tgr_1} is set based on the first interval target value map 118A, and the process proceeds to step S230. In step S230, it is determined whether or not the first interval target value _{Int_tgr_1} has elapsed since the end of the previous NOx purge control. If an affirmative determination is made, the process proceeds to step S240. In step S240, NOx purge control is started, and this control is returned.

On the other hand, if a negative determination is made in step S200, the “start request” is not established in step S250, and the process proceeds to step S260. In step S260, a second interval target value _{Int_tgr_2} shorter than the first interval target value _{Int_tgr_1} is set based on the second interval target value map 118B, and the process proceeds to step S270. In step S270, it is determined whether or not the second interval target value _{Int_tgr_2} has elapsed since the end of the previous NOx purge control. If a negative determination is made, the process returns to step S200, and if an affirmative determination is made, the process proceeds to step S280. . In step S280, NOx purge control is started, and this control is returned.

  Here, when the engine 10 is turned off without performing the NOx purge in a high purification rate holding state where the “start request” is not established over a long period of time, the engine 10 is restarted with a large NOx occlusion amount. It will be. For this reason, when the catalyst temperature is lowered at the time of restart, the NOx occlusion ability of the catalyst is saturated, and exhaust emission may be deteriorated. Therefore, in this embodiment, when it is determined that the “start request” is in a high purification rate holding state that does not hold for a long time, NOx purge is forcibly performed. Thereby, it becomes possible to effectively prevent the exhaust emission from deteriorating when the engine is restarted.

  In the present embodiment, the interval is set with reference to the interval target value map, but the interval may be a fixed value set in advance.

[Occlusion amount threshold correction]
Returning to FIG. 4, the details of the occlusion amount threshold correction will be described. The NOx occlusion capacity of the NOx occlusion reduction type catalyst 32 decreases with the progress of aging degradation, thermal degradation, and the like. For this reason, if the NOx occlusion amount threshold value _{NOx_thr_val} is set to a fixed value, the execution frequency of NOx purge according to aging deterioration, thermal deterioration, etc. cannot be secured, and exhaust emission may be deteriorated.

The occlusion amount threshold value correction unit 116 _{decreases the} NOx occlusion amount threshold value _{NOx_thr_val} set by the occlusion amount threshold map 114 as the deterioration degree of the NOx occlusion reduction type catalyst 32 increases in order to prevent such deterioration of exhaust emission. Perform a decrease correction.

More specifically, this reduction correction is performed by multiplying the NOx occlusion amount threshold _{NOx_thr_val} by a deterioration correction coefficient (deterioration degree) obtained by the deterioration degree estimation unit 120. The deterioration correction coefficient includes, for example, a decrease in the HC / CO heat generation amount inside the NOx storage reduction catalyst 32, a heat history of the NOx storage reduction catalyst 32, a decrease in the NOx purification rate of the NOx storage reduction catalyst 32, a vehicle travel distance, and the like. Find it based on this.

[NOx purge control end processing]
FIG. 6 is a block diagram showing an end process by the NOx purge end processing unit 150. The NOx purge end determination unit 151 includes (1) a first end condition under which the NOx occlusion amount estimated value _{m_NOx} calculated by the NOx occlusion amount estimation unit 113 (see FIG. 4) decreases to a predetermined occlusion amount lower limit threshold, (2 ) A second end condition in which the total injection amount of exhaust pipe injection or post injection accumulated from the start of NOx purge control reaches a predetermined upper limit injection amount; and (3) an elapsed time measured from the start of NOx purge control is a predetermined upper limit time. NOx purge flag F _NP is satisfied when either the third end condition for reaching NO or the fourth end condition for (4) the elapsed time measured by the timer from the start of NOx purge control to reach the predetermined NOx purge target time _{NP_Time_trg} is satisfied. _Is turned off (F _NP = 0), and the NOx purge control is terminated (see time t _{1 in} FIG. 3).

The NOx purge target time _{NP_Time_trg} used for determination of the fourth end condition is set by a NOx purge target time map 153 that is referred to based on the engine speed Ne and the accelerator opening Q. The NOx purge target time _{NP_Time_trg} is corrected by a NOx purge target time correction unit 154 described later in detail.

  The NOx purge end prohibiting unit 155 prohibits the NOx purge end determining unit 152 from ending the NOx purge control until the elapsed time counted from the start of the NOx purge control reaches a predetermined minimum required time. This necessary minimum time is set to a time that is longer than the time for completing the control operation by air system control and MAF follow-up control, which will be described later, and shorter than the upper limit time used in the determination of the end condition (3).

  As described above, in this embodiment, even if the end conditions (1) to (4) are satisfied, the execution of the NOx purge control is continued until the elapsed time from the start of the NOx purge control reaches the necessary minimum time. It has become. As a result, it is possible to reliably prevent malfunctions caused by stopping various control operations such as air system control, injection system control, and MAF follow-up control started for NOx purging in an incomplete state.

[NOx purge target time correction]
Since the NOx occlusion capacity of the NOx occlusion reduction type catalyst 32 decreases with the progress of aged deterioration, thermal deterioration, etc., if the NOx purge target time _{NP_Time_trg} does not reflect the degree of catalyst deterioration, the fuel supply amount becomes excessive, so-called. It may cause HC slip.

The NOx purge target time correction unit 154 _{shortens the} NOx purge target time _{NP_Time_trg} set by the NOx purge target time map 153 as the deterioration degree of the NOx occlusion reduction type catalyst 32 increases in order to prevent such HC slip. Perform shortening correction. More specifically, this shortening correction is performed by multiplying the NOx purge target time _{NP_Time_trg} by the deterioration correction coefficient obtained by the deterioration degree estimation unit 120 (see FIG. 4).

[NOx purge lean control]
When the NOx purge flag F _NP is turned on, the air system control unit 130 sets the excess air ratio to a leaner side than the theoretical air-fuel ratio equivalent value (about 1.0) from the steady operation (for example, about 1.5). The NOx purge lean control is performed to reduce the first target excess air ratio (for example, about 1.3). Details of the NOx purge lean control will be described below.

FIG. 7 is a block diagram showing a process for setting the MAF target value MAF _{NPL_Trgt} during the NOx purge lean control. The first target excess air ratio setting map 131 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, from the first target excess air ratio setting map 131, the excess air ratio target value λ _{NPL_Trgt} at the time of NOx purge lean control is read using the engine speed Ne and the accelerator opening Q as input signals, and the MAF target value calculation unit 132 reads it. Entered. Further, the MAF target value calculation unit 132 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} represents a learning-corrected fuel injection amount (excluding post-injection) described later, Ro _Fuel represents fuel specific gravity, AFR _sto represents a theoretical air-fuel ratio, and _{Maf_corr} represents a MAF correction coefficient described later. Yes.

The MAF target value MAF _{NPL_Trgt} calculated by the MAF target value calculation unit 132 is input to the ramp processing unit 133 when the NOx purge flag F _NP is turned on (see time t _{1 in} FIG. 3). The ramp processing unit 133 reads the ramp coefficient from the ramp coefficient maps 133A, _133B using the engine speed Ne and the accelerator opening Q as input signals, and _{sets the} MAF target ramp value MAF _{NPL_Trgt_Ramp} to which the ramp coefficient is added as a valve control unit 134. To enter.

The valve control unit 134 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 the present 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 131 and the fuel injection amount of each 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 injector 11, the MAF target value MAF _{NPL_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. Etc. 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]
When the NOx purge flag F _NP is turned on, the injection system control unit 140 reduces the excess air ratio from the first target excess air ratio to the rich second target excess air ratio (for example, about 0.9). Execute purge rich control. Details of the NOx purge rich control will be described below.

FIG. 8 is a block diagram showing processing for setting the target injection amount Q _{NPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in NOx purge rich control. The second target excess air ratio setting map 145 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 145 using the engine speed Ne and the accelerator opening Q as input signals, and the injection amount target value calculation unit 146 is read. Is input. Further, the injection amount target value calculation unit 146 calculates a 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 Formula (2), MAF _{NPL_Trgt} is a NOx purge lean MAF target value, and is input from the above-described MAF target value calculation unit 72. Q _{fnl_cord} is a fuel injection amount (excluding post-injection) before application of learning corrected MAF tracking control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, and _{Maf_corr} is a MAF correction coefficient described later. Show.

The target injection amount Q _{NPR_Trgt} calculated by the injection amount target value calculation unit 146 is transmitted as an injection instruction signal to the exhaust pipe injection device 33 or each injector 11 when the NOx purge flag F _NP is turned on (time t in FIG. 3). 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. 3) due to 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 air excess rate target value λ _{NPR_Trgt} read from the second target air excess rate setting map 145 and the fuel injection amount of each injector 11. It has become. 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 injector 11, the target injection amount Q _{NPR_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. Etc. can be effectively eliminated.

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

[Injection amount learning correction]
As shown in FIG. 9, the injection amount learning correction unit 300 includes a learning correction coefficient calculation unit 310 and an injection amount correction unit 320.

The learning correction coefficient calculation unit 310 is a fuel injection amount learning correction coefficient F based on an error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 and the estimated lambda value λ _Est during the lean operation of the engine 10. 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 commanded injection amount for each injector 11 and the actual injection amount. Hereinafter, a learning correction coefficient calculation process by the learning correction coefficient calculation unit 310 using the error Δλ will be described with reference to the flowchart 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 310A shown in FIG. 9 as an 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, transient operation of the engine 10 or 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 310B (see FIG. 9) 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, a plurality of learning regions divided according to the engine speed Ne and the accelerator opening Q are set on the learning value map 310B. 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 310B using the engine speed Ne and the accelerator opening Q as input signals (F _Corr = 1 + F). _CorrAdpt ). This learning correction coefficient F _Corr is input to the injection amount correction unit 320 shown in FIG.

The injection amount correction unit 320 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 injector 11 with the learning value corresponding to the error Δλ between the estimated lambda value λ _Est and the actual lambda value λ _Act , the aging deterioration, characteristic change, individual difference of each injector 11 is corrected. It is possible to effectively eliminate such variations.

[MAF correction coefficient]
MAF correction coefficient calculation unit 400 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 injector 11 is corrected based on the error Δλ between the actual lambda value λ _Act and the estimated lambda value λ _Est detected by the NOx / lambda sensor 45. However, since lambda is the ratio of air to fuel, the factor of error Δλ is not necessarily only the effect of the difference between the commanded injection amount and the actual injection amount for each injector 11. That is, there is a possibility that the error of not only each injector 11 but also the MAF sensor 40 affects the lambda error Δλ.

FIG. 11 is a block diagram illustrating the setting process of the MAF correction coefficient _{Maf_corr} by the MAF correction coefficient calculation unit 400. The correction coefficient setting map 410 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and indicates a MAF that indicates the sensor characteristics of the MAF sensor 40 corresponding to the engine speed Ne and the accelerator opening Q. The correction coefficient _{Maf_corr} is set in advance based on experiments or the like.

The MAF correction coefficient calculation unit 400 reads the MAF correction coefficient _{Maf_corr} from the correction coefficient setting map 410 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 132 and It transmits to the injection quantity target value calculating part 146. 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 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 pipe injection device 40 MAF sensor 45 NOx / lambda sensor 50 ECU

Claims (3)

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;
NOx storage amount estimation means for estimating the NOx storage amount of the NOx storage reduction catalyst;
Catalyst regeneration control means for performing a catalyst regeneration process for recovering the NOx storage capacity of the NOx storage reduction catalyst by making the exhaust rich;
When the NOx occlusion amount estimated by the NOx occlusion amount estimation unit exceeds a predetermined upper limit threshold and the elapsed time from the end of the previous catalyst regeneration process reaches a predetermined first target interval time, the catalyst regeneration control unit And a regeneration start processing means for starting the next catalyst regeneration processing,
In the regeneration start processing means, the NOx storage amount estimated by the NOx storage amount estimation means does not exceed the upper limit threshold, and the elapsed time from the end of the previous catalyst regeneration processing has reached a predetermined second target interval time. Also in this case, an exhaust purification system in which the catalyst regeneration control means starts the next catalyst regeneration process. The exhaust purification system according to claim 1, wherein the second target interval time is set to be shorter than the first interval target time. The first target interval time is set by a first target interval map that is referred to based on the operating state of the internal combustion engine,
The exhaust purification system according to claim 1 or 2, wherein the second target interval time is set by a second target interval map referred to based on an operating state of the internal combustion engine.

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