JP2016123909A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent combustion of an engine from becoming unstable when starting and after finishing catalyst regeneration.SOLUTION: An exhaust emission control system comprises an NOx reduction type catalyst 32 provided in an exhaust passage of an internal combustion engine 10, an intake air quantity sensor 40 and a control unitt 50 for executing regeneration processing of the NOx reduction type catalyst 32 by switching exhaust gas to a rich state from a lean state by simultaneously using air system control for reducing an intake air quantity and injection system control for increasing a fuel injection quantity, and the control unit 50 executes first follow-up control for changing the fuel injection timing of the internal combustion engine in response to a detection value of the intake air quantity sensor 40 in a switching period to the rich state from the lean state, and stops the first follow-up control by advancing the fuel injection timing of the internal combustion engine 10 to the target fuel injection timing corresponding to the rich state when the intake air quantity detected in the switching period is separated by a predetermined threshold value or more from a target intake air quantity in the switching period.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. This NOx occlusion reduction type catalyst occludes NOx contained in the exhaust when the exhaust is in a lean atmosphere, and reduces and purifies NOx occluded by hydrocarbons contained in the exhaust when the exhaust is in a rich atmosphere. Detoxify 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).

  The NOx occlusion reduction type catalyst also occludes sulfur oxide (hereinafter referred to as SOx) contained in the exhaust gas. When this SOx occlusion amount increases, there is a problem that the NOx purification ability of the NOx occlusion reduction type catalyst is lowered. Therefore, when the SOx occlusion amount reaches a predetermined amount, unburned fuel is added to the upstream oxidation catalyst by post injection or exhaust pipe injection so that SOx is released from the NOx occlusion reduction type catalyst and recovered from S poisoning. Therefore, it is necessary to periodically perform a so-called SOx purge for raising the exhaust temperature to the SOx separation temperature (see, for example, Patent Document 2).

JP 2008-202425 A JP 2009-47086 A

  If the above-mentioned NOx purge or SOx purge is performed only by injection system control by post injection or exhaust pipe injection, the fuel consumption becomes excessive and fuel efficiency is deteriorated. For this reason, it is preferable to use both the injection system control and the air system control for reducing the intake air amount by adjusting the opening of the intake throttle valve and the EGR valve.

  When a large amount of EGR gas is introduced into the combustion chamber by air system control, an ignition delay occurs at the same injection timing as in the normal lean state. Therefore, when switching from the lean state to the rich state, the injection timing is advanced, and when switching from the rich state to the lean state, it is necessary to return the advanced injection timing to the original injection timing by delaying. .

  In order to appropriately advance and retard these injection timings, advance and retard amounts corresponding to changes in the actual intake air amount are required to synchronize the instantaneously reacting injection system with the air system that is delayed in response. It is preferable to control by. However, when such a control method is used, when the intake air amount does not change due to a valve control delay or the like, the advance timing or delay angle of the injection timing does not advance, and there is a risk of destabilizing engine combustion. .

  An object of the disclosed system is to effectively prevent engine combustion from becoming unstable at the start or end of catalyst regeneration.

  The disclosed system is provided in an exhaust passage of an internal combustion engine to reduce and purify NOx in exhaust gas, an intake air amount sensor that detects an intake air amount of the internal combustion engine, and an intake air amount. Control for executing regeneration processing for recovering the NOx purification ability of the NOx reduction catalyst by switching the exhaust air-fuel ratio from the lean state to the rich state by using both the air system control and the injection system control for increasing the fuel injection amount. An exhaust purification system comprising: an internal combustion engine according to a detected value of the intake air amount sensor in a first switching period from a lean state to a rich state in which the regeneration process is started. The first follow-up control is executed to advance the fuel injection timing of the first fuel injection timing toward the first target fuel injection timing in the rich state, and is detected during the first switching period. When the intake air amount deviates from the target intake air amount during the first switching period by a predetermined threshold or more, the fuel injection timing of the internal combustion engine is advanced to the first target fuel injection timing to perform the first follow-up control. Cancel.

  According to the disclosed system, it is possible to effectively prevent engine combustion from becoming unstable at the start or end of catalyst regeneration.

1 is an overall configuration diagram showing an exhaust purification system according to an embodiment. It is a timing chart explaining SOx purge control concerning this embodiment. It is a block diagram which shows the setting process of the MAF target value at the time of SOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection amount at the time of SOx purge rich control which concerns on this embodiment. It is a timing chart explaining catalyst temperature adjustment control of SOx purge control concerning this 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 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 flowchart explaining switching from the lean state of the MAF tracking control which concerns on this embodiment to a rich state. It is a flowchart explaining switching from the rich state of the MAF tracking control which concerns on this embodiment to a lean state. It is a figure explaining the shift | offset | difference of the actual MAF value and MAF target value at the time of shifting to a lean state from a lean state or a rich state. It is a figure explaining the shift | offset | difference of the actual MAF value and MAF target value at the time of shifting from a lean state to a rich state or a rich state, and a target injection amount and a fuel injection amount. 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 regeneration is performed to remove the combustion. Filter regeneration is performed by supplying unburned fuel to the upstream 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 partially includes a filter regeneration control unit 51, a SOx purge control unit 60, a NOx purge control 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 a functional element. 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.

[Filter regeneration control]
The filter regeneration control unit 51 estimates the PM accumulation amount of the filter 33 from the travel distance of the vehicle or the differential pressure across the filter detected by a differential pressure sensor (not shown), and the estimated PM accumulation amount exceeds a predetermined upper limit threshold. And the regeneration flag F _DPF is turned on (see time t _{1 in} FIG. 2). When the regeneration flag F _DPF is turned on, an instruction signal for causing the exhaust pipe injection device 34 to execute exhaust pipe injection is transmitted, or an instruction signal for causing each injector 11 to execute post injection is transmitted. The temperature is raised to the PM combustion temperature (for example, about 550 ° C.). The regeneration flag F _DPF is, PM deposition estimation amount is turned off drops to a predetermined lower limit threshold indicating the burn off (determination threshold value) (see time t ₂ in FIG. 2). The determination threshold value for turning off the regeneration flag F _DPF may be based on, for example, the upper limit elapsed time or the upper limit cumulative injection amount from the start of filter regeneration (F _DPF = 1).

[SOx purge control]
The SOx purge control unit 60 makes the exhaust rich and raises the exhaust temperature to a sulfur desorption temperature (for example, about 600 ° C.) to recover the NOx occlusion reduction type catalyst 32 from SOx poisoning (hereinafter, this control). (Referred to as SOx purge control).

FIG. 2 shows a timing chart of the SOx purge control of this embodiment. As shown in FIG. 2, SOx purge flag _{F SP} to start SOx purge control is turned on at the same time off the regeneration flag _{F DPF} (see time _{t 2} in FIG. 2). As a result, it is possible to efficiently shift to the SOx purge control from the state in which the exhaust gas temperature has been raised by the regeneration of the filter 33, and the fuel consumption can be effectively reduced.

  In the present embodiment, the enrichment by the SOx purge control is performed by adjusting the excess air ratio to the lean side from the theoretical air-fuel ratio equivalent value (about 1.0) from the steady operation (for example, about 1.5) by the air system control. SOx purge lean control for reducing to 1 target excess air ratio (for example, about 1.3) and injection system control to reduce the excess air ratio from the first target excess air ratio to the second target excess air ratio on the rich side (for example, about 0) This is realized by using together with the SOx purge rich control that lowers to .9). Details of the SOx purge lean control and the SOx purge rich control will be described below.

[Air system control for SOx purge lean control]
FIG. 3 is a block diagram illustrating a process for setting the MAF target value MAF _{SPL_Trgt} during the SOx purge lean control. 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 (the fuel injection amount of the engine 10), and the engine speed Ne, the accelerator opening Q, The excess air ratio target value λ _{SPL_Trgt} (first target excess air ratio) at the time of SOx purge lean control corresponding to is preset based on experiments or the like.

First, the excess air ratio target value λ _{SPL_Trgt} at the time of SOx 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 _{SPL_Trgt} during the SOx purge lean control based on the following formula (1).

MAF _{SPL_Trgt} = λ _{SPL_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.

MAF target value _{MAF SPL_Trgt} calculated by the MAF target value calculation unit 62, when the SOx purge flag _{F SP} is turned on (see time _{t 2} in FIG. 2) is input to the lamp unit 63. 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 _{SPL_Trgt_Ramp} to which the ramp coefficient is added as the 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 _{SPL_Trgt_Ramp.} Execute control.

Thus, in the present embodiment, the MAF target value MAF _{SPL_Trgt} is set based on the excess air ratio target value λ _{SPL_Trgt} read from the first target excess air ratio setting map 61 and the fuel injection amount of each injector 11, The air system operation is feedback-controlled based on the MAF target value MAF _{SPL_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. The exhaust can be effectively reduced to a desired excess air ratio required for SOx 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 _{SPL_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. The influence of individual differences 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 _{SPL_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.

[Fuel injection amount setting for SOx purge rich control]
FIG. 4 is a block diagram showing processing for setting the target injection amount Q _{SPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in SOx purge rich control. 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 at the time of SOx purge rich control corresponding to the engine speed Ne and the accelerator opening Q. Of the excess air ratio target value λ _{SPR_Trgt} (second target excess air ratio) is set in advance based on experiments or the like.

First, the excess air ratio target value λ _{SPR_Trgt} at the time of SOx 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 an injection quantity target value calculation unit 66. Further, the injection amount target value calculation unit 66 calculates the target injection amount Q _{SPR_Trgt} during the SOx purge rich control based on the following formula (2).

Q _{SPR_Trgt} = MAF _{SPL_Trgt} × _{Maf_corr} / (λ _{SPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (2)

In Expression (2), MAF _{SPL_Trgt} is the MAF target value at the SOx purge _{lean, and} is input from the above-described MAF target value calculation unit 62. 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 _{SPR_Trgt} calculated by the injection amount target value calculation unit 66 is transmitted as an injection instruction signal to the exhaust pipe injector 34 or each injector 11 when a SOx purge rich flag F _SPR described later is turned on.

As described above, in this embodiment, the target injection amount Q _{SPR_Trgt} is set based on the air excess rate target value λ _{SPR_Trgt} read from the second target air excess rate setting map 65 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. The exhaust can be effectively reduced to a desired excess air ratio required for SOx 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 _{SPR_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.

[Catalyst temperature adjustment control for SOx purge control]
The exhaust temperature (hereinafter also referred to as catalyst temperature) flowing into the NOx occlusion reduction type catalyst 32 during the SOx purge control is the SOx that performs exhaust pipe injection or post injection as shown at times t _{2 to} t ₄ in FIG. The purge rich flag F _SPR is controlled by alternately switching on / off (rich / lean). When the SOx purge rich flag F _SPR is turned on (F _SPR = 1), the catalyst temperature rises by exhaust pipe injection or post injection (hereinafter, this period is referred to as an injection period _{TF_INJ} ). On the other hand, when the SOx purge rich flag _FSPR is turned off, the catalyst temperature is lowered by stopping the exhaust pipe injection or the post injection (hereinafter, this period is referred to as an interval _{TF_INT} ).

In the present embodiment, the injection period _{TF_INJ} is set by reading values corresponding to the engine speed Ne and the accelerator opening Q from an injection period setting map (not shown) created in advance by experiments or the like. In this injection time setting map, an injection period required to reliably reduce the excess air ratio of exhaust gas obtained in advance through experiments or the like to the second target excess air ratio is set according to the operating state of the engine 10. ing.

The interval T _{F_INT} is set by feedback control when the SOx purge rich flag F _{SPR at} which the catalyst temperature is highest is switched from on to off. Specifically, the proportional control for changing the input signal in proportion to the deviation ΔT between the target catalyst temperature and the estimated catalyst temperature when the SOx purge rich flag _FSPR is turned off, and the time integral value of the deviation ΔT are proportional. This is processed by PID control constituted by integral control for changing the input signal and differential control for changing the input signal in proportion to the time differential value of the deviation ΔT. The target catalyst temperature is set at a temperature at which SOx can be removed from the NOx storage reduction catalyst 32. The estimated catalyst temperature is, for example, the inlet temperature of the oxidation catalyst 31 detected by the first exhaust temperature sensor 43, and the oxidation catalyst 31. Further, it may be estimated based on the amount of HC / CO heat generated inside the NOx storage reduction catalyst 32, the amount of heat released to the outside air, and the like.

As shown at time _{t 1} in FIG. 5, when the SOx purge flag _{F SP} by ends _{(F DPF} = 0) of the filter regeneration is turned on, SOx purge rich flag _{F SPR} also turned on, further in the previous SOx purge control The interval T _{F_INT} calculated by feedback is also reset once. That is, the first immediately after the filter regeneration, the exhaust pipe injection or post injection is executed in accordance with the injection period T _{F_INJ_1} set by the injection period setting map (see time t ₁ ~t ₂ in FIG. 5). As described above, since the SOx purge control is started from the SOx purge rich control without performing the SOx purge lean control, the SOx purge control is promptly transferred to the fuel consumption amount without lowering the exhaust temperature increased by the filter regeneration. Can be reduced.

Then, when the SOx purge rich flag _{F SPR} is turned off with the passage of the injection period _{T F_INJ_1,} until interval _{T F_INT_1} set by PID control has elapsed, SOx purge rich flag _{F SPR} is turned off (time in FIG. 5 t see ₂ ~t _3). Further, when the SOx purge rich flag _{F SPR} is turned on by the lapse of the interval _{T F_INT_1,} injection period _{T F_INJ_2} exhaust pipe injection or post injection according to is performed again (see time _t 3 ~t ₄ of 5 ). Thereafter, the switching on and off of these SOx purge rich flag _{F SPR} is repeatedly executed until the SOx the purge flag _{F SP} is turned off (see time _{t n} in FIG. 5) by the completion judgment of the SOx purge control described later.

As described above, in the present embodiment, the injection period _{TF_INJ} for raising the catalyst temperature and lowering the excess air ratio to the second target excess air ratio is set from the map referred to based on the operating state of the engine 10, The interval _{TF_INT} for lowering the catalyst temperature is processed by PID control. This makes it possible to reliably reduce the excess air ratio to the target excess ratio while effectively maintaining the catalyst temperature during the SOx purge control within a desired temperature range necessary for the purge.

[Determining completion of SOx purge control]
SOx purge control, (1) SOx purge flag F from on the _SP injection quantity of the exhaust pipe injection or post injection accumulated, when the amount of the cumulative injected has reached the predetermined upper limit threshold amount, of (2) SOx 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 of SOx adsorption amount of NOx occlusion-reduction catalyst 32 has decreased to a predetermined threshold value indicating a SOx removal success is established, SOx purge flag F _SP is terminated by turning off the (time t ₄ in FIG. 2 , reference time _{t n} in FIG. 5).

  As described above, in this embodiment, when the SOx purge control end condition is provided with the upper limit of the cumulative injection amount and the elapsed time, the fuel consumption amount when the SOx purge does not progress due to a decrease in the exhaust temperature or the like. Can be effectively prevented from becoming excessive.

[NOx purge control]
The NOx purge control unit 70 restores the NOx storage capability of the NOx storage reduction catalyst 32 by making the exhaust atmosphere rich and detoxifying and releasing NOx stored in the NOx storage reduction catalyst 32 by reduction purification. Control (hereinafter, this control is referred to as NOx purge control) is executed.

The NOx purge flag F _NP for starting the NOx purge control is turned on when 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 exceeds a predetermined threshold value ( reference time _{t 1} of FIG. 6). Alternatively, the NOx purification rate by the NOx occlusion reduction type catalyst 32 is calculated from the NOx emission amount upstream of the catalyst estimated from the operating state of the engine 10 and the NOx amount downstream of the catalyst detected by the NOx / lambda sensor 45. When the NOx purification rate becomes lower than a predetermined determination threshold, the NOx purge flag F _NP is turned on.

  In the present embodiment, the enrichment by the NOx purge control is performed on the lean side of the excess air ratio from the stoichiometric 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 for reducing to 3 target excess air ratio (for example, about 1.3) and injection system control to reduce the excess air ratio from the third target excess air ratio to the fourth target excess air ratio on the rich side (for example, about 0) .9) and NOx purge rich control for reducing the pressure to 9). The details of the NOx purge lean control and the NOx purge rich control will be described below.

[NOF purge lean control MAF target value setting]
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 third target excess air ratio setting map 71 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. The excess air ratio target value λ _{NPL_Trgt} (third 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 third target excess air ratio setting map 71 using the engine speed Ne and the accelerator opening Q as input signals, and is sent to the MAF target value calculation unit 72. Entered. Further, the MAF target value calculation unit 72 calculates the MAF target value MAF _{NPL_Trgt} at the time of NOx purge lean control based on the following formula (3).

MAF _{NPL_Trgt} = λ _{NPL_Trgt} × Q _{fnl_corrd} × Ro _Fuel × AFR _sto / _{Maf_corr} (3)

In Equation (3), 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 72 is input to the ramp processing unit 73 when the NOx purge flag F _NP is turned on (see time t _{1 in} FIG. 6). The ramp processing unit 73 reads the ramp coefficient from the ramp coefficient maps 73A and _73B using the engine speed Ne and the accelerator opening Q as input signals, and _{calculates the} MAF target ramp value MAF _{NPL_Trgt_Ramp} to which the ramp coefficient is added as a valve control unit 74. To enter.

The valve control unit 74 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 third target excess air ratio setting map 71 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]
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 fourth target excess air ratio setting map 75 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} (fourth target air excess rate) is set in advance 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 fourth target excess air ratio setting map 75 using the engine speed Ne and the accelerator opening Q as input signals, and the injection amount target value calculation section 76 is performed. Is input. Further, the injection amount target value calculation unit 76 calculates the target injection amount Q _{NPR_Trgt} at the time of NOx purge rich control based on the following formula (4).

Q _{NPR_Trgt} = MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (4)

In Expression (4), MAF _{NPL_Trgt} is a NOx purge lean MAF target value, and is input from the MAF target value calculation unit 72 described above. 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} that is calculated by the injection amount target value computing unit 76, NOx purge flag _{F SP} When turned on, is sent as the injection instruction signal to the exhaust pipe injector 34 or the injectors 11 (time of FIG. 6 t ₁ ). The transmission of this injection instruction signal is continued until the NOx purge flag F _NP is turned off (time t _{2 in} FIG. 6) by the end determination of NOx purge control described later.

As described above, in this embodiment, the target injection amount Q _{NPR_Trgt} is set based on the air excess rate target value λ _{NPR_Trgt} read from the fourth target air excess rate setting map 75 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.

[No air system control for NOx purge control]
The ECU 50 feedback-controls the opening degree of the intake throttle valve 16 and the EGR valve 24 based on the sensor value of the MAF sensor 40 in the region where the operating state of the engine 10 is on the low load side. On the other hand, in the region where the operating state of the engine 10 is on the high load side, the ECU 50 feedback-controls the supercharging pressure by the variable displacement supercharger 20 based on the sensor value of the boost pressure sensor 46 (hereinafter, this region is referred to as “high”). (Referred to as boost pressure FB control region).

In such a boost pressure FB control region, a phenomenon occurs in which the control of the intake throttle valve 16 and the EGR valve 24 interferes with the control of the variable displacement supercharger 20. For this reason, there is a problem that the intake air amount cannot be maintained at the MAF target value MAF _{NPL_Trgt} even if the NOx purge lean control for performing feedback control of the air system based on the MAF target value MAF _{NPL_Trgt} set by the above equation (3) is executed. is there. As a result, even if the NOx purge rich control for executing the post injection or the exhaust pipe injection is started, the excess air ratio can be lowered to the fourth target excess air ratio (the excess air ratio target value λ _{NPR_Trgt} ) necessary for the NOx purge. There is no possibility.

In order to avoid such a phenomenon, the NOx purge control unit 70 of the present embodiment prohibits NOx purge lean control for adjusting the opening of the intake throttle valve 16 and the EGR valve 24 in the boost pressure FB control region, and The excess air ratio is reduced to the fourth target excess air ratio (the excess air ratio target value λ _{NPR_Trgt} ) only by injection or post injection. As a result, the NOx purge can be reliably performed even in the boost pressure FB control region. In this case, the MAF target value set based on the operating state of the engine 10 may be applied to the MAF target value MAF _{NPL_Trgt} of the above-described equation (4).

[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 decreases to a predetermined threshold value indicating successful removal of NOx is satisfied, the NOx purge flag F _NP is turned off and the process ends (time t _{2 in} FIG. 6). 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 period for switching from a lean state in normal operation to a rich state by SOx purge control or NOx purge control, and (2) lean in normal operation from a rich state by SOx purge control or NOx purge control. During the period of switching to the state, control for correcting the fuel injection timing and the fuel injection amount of each injector 11 according to the MAF change is executed. Hereinafter, control during the switching period from the lean state to the rich state is referred to as first MAF tracking control, and control during the switching period from the rich state to the lean state is referred to as second MAF tracking control.

  When a large amount of EGR gas is introduced into the combustion chamber of the engine 10 by the air system operation of SOx purge lean control or NOx purge lean control, an ignition delay occurs at the same fuel injection timing as in the lean state of normal operation. Therefore, when switching from the lean state to the rich state, it is necessary to advance the injection timing by a predetermined amount. Further, when switching from the rich state to the normal lean state, it is necessary to return the injection timing to the normal injection timing by retarding. However, the advance angle or retard angle of the injection timing is performed more rapidly than the air system operation. For this reason, the advance or retard of the injection timing is completed before the excess air ratio reaches the target excess air ratio due to the air system operation, and the drivability due to the sudden increase in NOx generation amount, combustion noise, torque, etc. There is a problem that causes deterioration.

  In order to avoid such a phenomenon, the MAF follow-up control unit 80, as shown in the flowcharts of FIGS. 9 and 10, performs MAF follow-up control for correcting the advance / retard of the injection timing and the injection amount in accordance with changes in MAF. Execute. Since both the SOx purge control and the NOx purge control are processed according to the same flow, only the SOx purge control will be described below, and the description of the NOx purge control will be omitted.

  First, based on FIG. 9, the first MAF follow-up control in the switching period (first switching period) from the lean state to the rich state will be described. In the first MAF follow-up control, the fuel injection timing of the engine 10 (internal combustion engine) is advanced toward the first target fuel injection timing in the rich state, and the fuel injection amount is changed to the first target fuel injection amount in the rich state. The first follow-up control to be increased is executed.

In step S100, the SOx purge flag _{F SP} is turned on, at step S110, time measurement by the timer in order to measure the elapsed time of MAF following control is started.

In step S120, before the switching from the MAF target value _{MAF SPL_Trgt} after switching (rich state) by subtracting the MAF target value _{MAF L_Trgt} of (lean state), before and after switching of the MAF target value change amount ΔMAF _{Trgt (= MAF SPL_Trgt} - MAF _{L_Trgt} ) is calculated.

In step S130, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{L_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{L_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S140, the comparison current MAF target value _{MAF L-R_Trgt} in actual MAF value _{MAF Act} and the transition period greater than a predetermined threshold value than the MAF target value _{MAF L-R_Trgt} in actual MAF value _{MAF Act} transition period Alternatively, if it is smaller, that is, if it is more than the predetermined threshold (Yes), the process of step S190 is performed, and if not (No), the process of step S150 is performed. Details of the processing in step S140 will be described later.

In step S150, in accordance with the current actual MAF change rate ΔMAF _Ratio , a coefficient for advancing or retarding the injection timing of each injector 11 (hereinafter referred to as an injection timing tracking coefficient Comp ₁ ), and the injection amount of each injector 11 Is set to increase or decrease (hereinafter referred to as injection amount tracking coefficient Comp ₂ ). More specifically, in a storage unit (not shown) of the ECU 50, an injection timing tracking coefficient setting map M1 that defines a relationship between an actual MAF change rate ΔMAF _Ratio and an injection timing tracking coefficient Comp ₁ created in advance by experiments or the like, and an actual MAF change An injection amount follow-up coefficient setting map M2 that defines the relationship between the rate MAF _Ratio and the injection amount follow-up coefficient Comp ₂ is stored. The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are set by reading values corresponding to the actual MAF change rate ΔMAF _Ratio calculated in step S130 from these maps M1 and M2.

In step S160, the injection timing of each injector 11 is advanced by the amount obtained by multiplying the target advance amount by the injection timing follow-up coefficient Comp _1, and each time by the amount obtained by multiplying the target injection increase amount by the injection amount follow-up coefficient Comp _2. The injector 11 also increases the fuel injection amount.

Thereafter, in step S170, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{SPL_Trgt} after switching (rich state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{SPL_Trgt} (No), the _{process returns} to step S130 via step S180. That is, by repeating the processing of steps S130 to S160 until the actual MAF value MAF _Act becomes the MAF target value MAF _{SPL_Trgt} , the advance angle of the injection timing according to the actual MAF change rate MAF _Ratio that changes every moment, and the injection The increase in quantity continues. Details of the processing in step S180 will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{SPL_Trgt} in the determination in step S170 (Yes), this control is finished.

In step S140, the current actual MAF value MAF _Act is compared with the MAF target value MAF _{L-R_Trgt} during the transition period.

As shown in FIG. 11 (A), when switching from the lean state to the rich state, the actual MAF value MAF _Act may _deviate from the MAF target value MAF _{L-R_Trgt} during the transition period by a predetermined threshold or more (time t _1- reference numeral OV of t _2). For example, the actual MAF value MAF _Act is the MAF target value MAF _{L-R_Trgt} when the valve control is excessively effective, when a disturbance such as electric noise occurs, or when the engine 10 is in a motoring state where fuel injection is stopped. May be more than a predetermined threshold.

  In this case, since the advance angle is excessive, the injection timing is shifted. Further, the fuel injection amount is also greatly deviated. As a result, the combustion of the engine 10 becomes unstable, which may cause torque fluctuations, deterioration of drivability, and the like.

In the present embodiment, in order to avoid such a phenomenon, when the actual MAF value MAF _Act is _separated from the MAF target value MAF _{LR_Trgt} during the transition period by a predetermined threshold or more in step S140, the process proceeds to step S190. The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control is forcibly terminated (stopped), and torque fluctuations and drivability deterioration can be effectively prevented.

In step S180, it is determined whether or not the cumulative time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max .

As shown in FIG. 12A, when shifting from the lean state to the rich state, the actual MAF value MAF _Ref cannot catch up with the MAF target value MAF _{L-R_Trgt} during the transition period due to the influence of valve control delay, etc. The MAF value MAF _Ref may be maintained higher than the MAF target value MAF _{L-R_Trgt} (see times t _{1 to} t ₂ ). If the MAF follow-up control is continued in such a state, the actual fuel injection amount is not increased to the target injection amount, the combustion of the engine 10 becomes unstable, and there is a possibility that torque fluctuation or drivability deteriorates. is there.

In the present embodiment, in order to avoid such a phenomenon, when it is determined in step S180 that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, the actual MAF value MAF _Ref continues for a predetermined time. If it does not change more than the predetermined value, the process proceeds to step S190, and the injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control is forcibly terminated, and torque fluctuation and drivability deterioration can be effectively prevented.

  Next, the second MAF follow-up control in the switching period (second switching period) from the rich state to the lean state will be described based on FIG. In the second MAF follow-up control, the fuel injection timing of the engine 10 (internal combustion engine) is retarded toward the second target fuel injection timing in the lean state, and the fuel injection amount is changed to the second target fuel injection amount in the lean state. The second follow-up control that decreases toward is executed.

In step S200, SOx purge flag _{F SP} is when turned off, at step S210, time measurement by the timer in order to measure the elapsed time of MAF following control is started.

In step S220, before the switching from the MAF target value _{MAF L_Trgt} after switching (lean state) by subtracting the MAF target value _{MAF SPL_Trgt} of (rich state), before and after switching of the MAF target value change amount ΔMAF _{Trgt (= MAF L_Trgt} - MAF _{SPL_Trgt} ) is calculated.

In step S230, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{SPL_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{SPL_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S240, the current actual MAF value MAF _Act and the MAF target value MAF _{R-L_Trgt} during the transition period are compared, and the actual MAF value MAF _Act is greater than the MAF target value MAF _{R-L_Trgt} during the transition period by a predetermined threshold or more. Alternatively, if it is smaller, that is, if it is more than the predetermined threshold (Yes), the process of step S290 is performed, and if not (No), the process of step S250 is performed. Details of the process of step S240 will be described later.

In step S250, a value corresponding to the actual MAF change rate ΔMAF _Ratio is read from the injection timing follow-up coefficient setting map M1 as an injection timing follow-up coefficient Comp ₁ , and from the injection amount follow-up coefficient setting map M2, it corresponds to the actual MAF change rate ΔMAF _Ratio . value is read as the injection quantity coefficient of following Comp _2.

In step S260, the injection timing of each injector 11 is retarded by the target delay amount multiplied by the injection timing follow-up coefficient Comp ₁ , and the target injection decrease amount is multiplied by the injection amount follow-up coefficient Comp _2. The fuel injection amount of the injector 11 is also reduced.

Thereafter, in step S270, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{L_Trgt} after switching (lean state). If the actual MAF value MAF _Act has not reached the MAF target value MAF _{L_Trgt} (No), the _{process returns} to step S230 via step S280. That is, by repeating the processing of steps S230 to S260 until the actual MAF value MAF _Act becomes the MAF target value MAF _{L_Trgt} , the delay of the injection timing corresponding to the actual MAF change rate MAF _Ratio that changes every moment, and the injection The amount continues to decrease. Details of the processing in step S280 will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{L_Trgt} in the determination in step S270 (Yes), this control is finished.

In step S240, the current actual MAF value MAF _Act is compared with the MAF target value MAF _{R-L_Trgt} during the transition period.

As shown in FIG. 11B, when switching from the rich state to the lean state, the actual MAF value MAF _Act may be more than a predetermined threshold value away from the MAF target value MAF _{R-L_Trgt} during the transition period (time t ₁ reference numeral OV of ~t _2). For example, the actual MAF value MAF _Act is the MAF target value MAF _{R−L_Trgt} when the valve control is too effective, when disturbance such as electric noise occurs, or when the engine 10 is in a motoring state where fuel injection is stopped. May be more than a predetermined threshold.

  In this case, the injection timing is shifted because the angle is excessively retarded. Further, the fuel injection amount is also greatly deviated. As a result, the combustion of the engine 10 becomes unstable, which may cause torque fluctuations, deterioration of drivability, and the like.

In this embodiment, in order to avoid such a phenomenon, when the actual MAF value MAF _Act is _separated from the MAF target value MAF _{R-L_Trgt} during the transition period by a predetermined threshold or more in step S240, the process proceeds to step S290. The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control is forcibly terminated (stopped), and torque fluctuations and drivability deterioration can be effectively prevented.

In step S280, it is determined whether the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max .

As shown in FIG. 12B, when shifting from the rich state to the lean state, the actual MAF value MAF _Ref cannot catch up with the MAF target value MAF _{LR_Trgt} during the transition period due to the influence of valve control delay, etc. The MAF value MAF _Ref may be kept lower than the MAF target value MAF _{L-R_Trgt} (see times t _{1 to} t ₂ ). If MAF follow-up control is continued in such a state, the actual fuel injection amount becomes larger than the target injection amount, which may cause torque fluctuation, drivability deterioration, and the like.

In the present embodiment, in order to avoid such a phenomenon, when it is determined in step S280 that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, the actual MAF value MAF _Ref continues for a predetermined time. If it has not changed more than the predetermined value, the process proceeds to step S280, and the injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control is forcibly terminated, and torque fluctuation and drivability deterioration can be effectively prevented.

[Prohibition of MAF tracking control]
As described above, in the boost pressure FB control region, NOx purge lean control for feedback control of the air system based on the sensor value of the MAF sensor 40 is prohibited. Since MAF tracking control also controls the advance of the injection timing and the increase of the injection amount according to the rate of change of the intake air amount, there is a possibility that accurate control cannot be performed in the boost pressure FB control region.

Therefore, in the present embodiment, the MAF follow-up control is prohibited by setting the MAF follow-up coefficients Comp ₁ and ₂ to “1” in the boost pressure FB control region. Thereby, the torque fluctuation of the engine 10 and the deterioration of drivability caused by inaccurate MAF tracking control are effectively prevented.

[Injection amount learning correction]
As shown in FIG. 13, 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 gas is in a lean state, since the oxidation reaction of HC does not occur in the oxidation catalyst 31, 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, It is considered that the estimated lambda value λ _Est in the exhaust discharged from the engine 10 coincides. Therefore, 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 and the actual injection amount for each injector 11. 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. 13 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, SOx purge control (F _SP = 1), NOx purge control (F _NP = 1), and the like. 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. 13) 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 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 calculating unit 95 MAF is used to set the MAF target value _{MAF SPL_Trgt} and the target injection amount _{Q SPR_Trgt} during SOx purge control and the setting of the MAF target value _{MAF NPL_Trgt} and the target injection amount _{Q NPR_Trgt} during NOx purge control A correction coefficient _{Maf_corr} is calculated.

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. 15 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 outputs the MAF correction coefficient _{Maf_corr} to the MAF target value calculation unit 62, 72 and the injection amount target value calculation units 66 and 76. Thus, SOx purge control when the MAF target value _{MAF SPL_Trgt} and the target injection amount _{Q SPR_Trgt,} the setting of the MAF target value _{MAF NPL_Trgt} and the target injection amount _{Q NPR_Trgt} during NOx purge control effectively the sensor characteristics of the MAF sensor 40 It becomes possible to reflect.

[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 (4)

NOx reduction catalyst provided in the exhaust passage of the internal combustion engine for reducing and purifying NOx in the exhaust, intake air amount sensor for detecting the intake air amount of the internal combustion engine, air system control and fuel for reducing the intake air amount And a control unit that executes a regeneration process for recovering the NOx purification ability of the NOx reduction catalyst by switching the exhaust air-fuel ratio from the lean state to the rich state in combination with the injection system control for increasing the injection amount. An exhaust purification system,
In the first switching period from the lean state to the rich state in which the regeneration process is started, the control unit sets the fuel injection timing of the internal combustion engine according to the detected value of the intake air amount sensor in the first state in the rich state. Execute first follow-up control to advance toward the target fuel injection timing,
When the intake air amount detected during the first switching period is more than a predetermined threshold from the target intake air amount during the first switching period, the fuel injection timing of the internal combustion engine is set to the first target fuel injection timing. An exhaust purification system that stops the first following control by advancing to. In the second switching period from the rich state to the lean state in which the regeneration process ends, the control unit sets the fuel injection timing of the internal combustion engine according to the detected value of the intake air amount sensor in the second state in the lean state. Execute second follow-up control to retard the target fuel injection timing,
When the intake air amount detected during the second switching period is more than a predetermined threshold from the target intake air amount during the second switching period, the fuel injection timing of the internal combustion engine is set to the second target fuel injection timing. The exhaust purification system according to claim 1, wherein the second follow-up control is stopped after being retarded. The control unit increases the fuel injection amount toward the first target fuel injection amount in the rich state in the first follow-up control,
When the intake air amount detected during the first switching period is more than a predetermined threshold from the target intake air amount during the first switching period, the fuel injection amount is increased to the first target fuel injection amount. The exhaust purification system according to claim 1 or 2, wherein the first tracking control is stopped. The control unit decreases the fuel injection amount toward the second target fuel injection amount in the lean state in the second follow-up control,
When the intake air amount detected during the second switching period is more than a predetermined threshold from the target intake air amount during the second switching period, the fuel injection amount is decreased to the second target fuel injection amount. The exhaust purification system according to claim 2 or 3, wherein the second follow-up control is stopped.

Images