WO2017010550A1

WO2017010550A1 - Exhaust gas purification system

Info

Publication number: WO2017010550A1
Application number: PCT/JP2016/070852
Authority: WO
Inventors: 輝男中田; 隆行坂本; 長岡　大治
Original assignee: いすゞ自動車株式会社
Priority date: 2015-07-16
Filing date: 2016-07-14
Publication date: 2017-01-19
Also published as: JP2017025718A

Abstract

An exhaust gas purification system is provided with: a NOx reduction-type catalyst 32 that is disposed in an exhaust gas passage of an engine 10; an intake throttle valve 16 that regulates the amount of air sucked into the engine 10; an EGR valve 24 that regulates the amount of exhaust gas recirculated to the engine 10; and an ECU 50 that carries out a regeneration treatment in which the purification capacity of the NOx reduction-type catalyst 32 is recovered by jointly using an air system control for reducing the amount of sucked-in air, and an injection system control for increasing the amount of fuel injection. When the exhaust air-fuel ratio switches from a lean state to a rich state, the ECU 50 fixes the EGR valve 24 in a closed state or at a designated opening degree, and regulates the amount of sucked-in air via the intake throttle valve 16.

Description

Exhaust purification system

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).

Further, 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).

Japanese Unexamined Patent Publication No. 2008-202425 Japanese Unexamined Patent Publication No. 2009-47086

If the above-mentioned NOx purge and SOx purge are performed only by injection system control by post injection or exhaust pipe injection, the fuel consumption becomes excessive and the 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 an intake throttle valve or an EGR (Exhaust gas Recirculation) valve.

If the recirculation amount of the EGR gas is increased to reduce the intake air amount, the EGR cooler and the EGR flow path may be fouled, and measures such as adding an EGR catalyst are required to suppress this fouling. . Further, when the fuel injection amount in the injection system control is increased and the intake air amount is decreased, the fuel consumption becomes excessive as described above, and the fuel efficiency is deteriorated.

The exhaust purification system of the present disclosure is intended to improve fuel efficiency while suppressing fouling of a flow path for recirculating exhaust gas.

An exhaust purification system of the present disclosure includes a NOx reduction catalyst that is provided in an exhaust passage of an internal combustion engine to reduce and purify NOx in exhaust, an intake air amount adjustment valve that adjusts an amount of air sucked into the internal combustion engine, The exhaust air-fuel ratio is changed from a lean state by using a recirculation amount adjustment valve that adjusts the amount of exhaust gas recirculated to the internal combustion engine, an air system control that decreases the intake air amount, and an injection system control that increases the fuel injection amount. A control unit that executes a regeneration process for recovering the purification ability of the NOx reduction catalyst by switching to the rich state, wherein the control unit richly changes the exhaust air-fuel ratio from the lean state. When switching to a state, the recirculation amount adjustment valve is closed or fixed at a specified opening, and the amount of air taken into the internal combustion engine by the intake amount adjustment valve Adjust to.

According to the exhaust purification system of the present disclosure, fuel efficiency can be improved while suppressing fouling of the flow path for recirculating exhaust gas.

FIG. 1 is an overall configuration diagram showing an exhaust purification system according to the present embodiment. FIG. 2 is a timing chart for explaining the SOx purge control according to the present embodiment. FIG. 3 is a block diagram showing the MAF target value setting process during SOx purge lean control according to the present embodiment. FIG. 4 is a block diagram showing a lamp application process for the MAF target value during SOx purge control according to the present embodiment. FIG. 5A is a diagram for explaining valve opening / closing control during SOx purge control according to the present embodiment, and shows the valve opening degree MAP of the intake throttle valve and the EGR valve during lean. FIG. 5B is a diagram for explaining the valve opening / closing control during the SOx purge control according to the present embodiment, and shows the valve opening degree MAP of the intake throttle valve in the rich state. FIG. 6A is a block diagram showing a lamp application process for an EGR target value during SOx purge control according to the present embodiment. FIG. 6B shows valve opening control of the EGR valve at the rich time. FIG. 7 is a block diagram showing a target injection amount setting process during SOx purge rich control according to the present embodiment. FIG. 8 is a timing chart for explaining the catalyst temperature adjustment control of the SOx purge control according to the present embodiment. FIG. 9 is a timing chart illustrating the NOx purge control according to this embodiment. FIG. 10 is a block diagram showing a MAF target value setting process during NOx purge control according to the present embodiment. FIG. 11 is a block diagram showing a lamp application process for the MAF target value during NOx purge control according to the present embodiment. FIG. 12A is a diagram for explaining valve opening / closing control during NOx purge control according to this embodiment, and shows the valve opening degree MAP of the intake throttle valve and the EGR valve during lean. FIG. 12B is a diagram for explaining valve opening / closing control during NOx purge control according to the present embodiment, and shows the valve opening degree MAP of the intake throttle valve when rich. FIG. 13A is a block diagram showing a lamp application process for an EGR target value during NOx purge control according to the present embodiment. FIG. 13B is a diagram illustrating valve opening degree control of the EGR valve at the rich time. FIG. 14 is a block diagram showing a target injection amount setting process during NOx purge rich control according to the present embodiment. FIG. 15 is a block diagram showing processing for correcting the injection amount of the in-cylinder injector according to the present embodiment. FIG. 16 is a flowchart for explaining the learning correction coefficient calculation processing according to the present embodiment. FIG. 17 is a block diagram showing MAF correction coefficient setting processing according to this embodiment.

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

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

An intake passage 12 for introducing fresh air is connected to the intake manifold 10A of the engine 10, and an exhaust passage 13 for connecting exhaust to the outside is connected to the exhaust manifold 10B.

The intake passage 12 is supplied with an air cleaner 14, an intake air amount sensor (hereinafter referred to as MAF sensor) 40 for detecting the amount of intake air, a compressor 20 </ b> A of the variable displacement supercharger 20, and the like. An intercooler 15 that cools the air, an intake throttle valve 16 that adjusts the amount of air taken into the engine 10 (an example of an intake air amount adjustment valve of the present invention), and the like are provided. 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 amount of exhaust gas recirculated to the engine 10). (An example of a recirculation amount adjusting valve of the present invention).

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

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

The NOx occlusion reduction type 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, the 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 performing exhaust pipe injection is transmitted to the exhaust injector 34, or an instruction signal for performing post injection is transmitted to the in-cylinder injector 11, and the exhaust temperature is increased. 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 uses the engine speed Ne and the accelerator opening Q as input signals, reads the increase change amount from the increase change amount MAP63A, and reads the decrease change amount from the decrease change amount MAP63B. The increasing amount of change is used when switching from the rich state to the lean state, and indicates the amount of addition per unit time to the MAF target value MAF. The change amount at the time of decrease is used when switching from the lean state to the rich state, and indicates a subtraction amount per unit time with respect to the MAF target value MAF.

As shown in FIG. 4, the ramp processing unit 63 includes a ramp start / end determination unit 63C, an increase target value calculation unit 63D, a decrease target value calculation unit 63E, a target value selection unit 63F, and an output switching unit 63G. .

A start instruction signal is input to the lamp start / end determination unit 63C. The start instruction signal indicates the start timing of the ramp process according to a change in the state of the signal, and identifies the switching from the lean state to the rich state and the switching from the rich state to the lean state. The lamp start / end determination unit 63C outputs a permission signal to the output switching unit 63G when it is determined that the lamp processing start timing is reached. This permission signal is output until the MAF target value MAF _{SPL_Trgt} from the MAF target value calculation unit 62 and the MAF target value (MAF target ramp value MAF _{SPL_Trgt_Ramp} ) output from the output switching unit _63G match.

The increase target value calculation unit 63D receives the increase change amount from the increase change amount MAP63A, the MAF target value MAF _{SPL_Trgt,} and the MAF target value (MAF target value immediately before the update) output from the output switching unit _63G. . In the increase target value calculation unit 63D, the section correction value obtained by multiplying the increase amount of change by the calculation clock is added to the MAF target value from the output switching unit 63G. Then, this added value is compared with the MAF target value MAF _{SPL_Trgt} from the MAF target value calculation unit 62, and the smaller one is output to the target value selection unit 63F as an increased provisional MAF target value.

The decrease target value calculation unit 63E receives the decrease change amount from the decrease change amount MAP63B, the MAF target value MAF _{SPL_Trgt,} and the MAF target value (MAF target value immediately before the update) output from the output switching unit _63G. . In the decrease target value calculation unit 63E, the section correction value obtained by multiplying the decrease change amount by the calculation clock is subtracted from the MAF target value from the output switching unit 63G. Then, this subtraction value is compared with the MAF target value MAF _{SPL_Trgt} from the MAF target value calculation unit 62, and the larger one is output to the target value selection unit 63F as a reduced provisional MAF target value.

The target value selection unit 63F switches one of the increase temporary MAF target value output from the increase target value calculation unit 63D and the decrease temporary MAF target value output from the decrease target value calculation unit 63E between the rich state and the lean state. It selects according to this, and outputs it to the output switching part 63G. Specifically, the increase temporary MAF target value is selected and output when switching from the rich state to the lean state, and the decrease temporary MAF target value is selected and output when switching from the lean state to the rich state.

The output switching unit 63G outputs the increase temporary MAF target value or the decrease temporary MAF target value from the target value selection unit 63F as the MAF target ramp value MAF _{SPL_Trgt_Ramp over the} period when the permission signal is output from the lamp start / end determination unit 63C. Output as. In addition, the output switching unit _63G outputs the MAF target value MAF _{SPL_Trgt} from the MAF target value calculation unit 62 during a period when the permission signal is not output.

The valve control unit 64 shown in FIG. 3 obtains the intake throttle valve 16 from the MAF target values (MAF _{SPL_Trgt} , MAF _{SPL_Trgt_Ramp} ) output from the ramp processing unit 63 and the actual MAF value MAF _Act based on the detection result of the MAF sensor 40. And the EGR valve 24 is controlled.

When the exhaust air-fuel ratio is in a lean state, the MAF operation amount is determined by PID control so that the actual MAF value MAF _Act matches the MAF target value, and the intake throttle valve opening is determined from the lean valve opening MAP64A shown in FIG. 5A. The _{VO_ith_L} and the EGR valve opening _{VO_EGR_L} are read, and the intake throttle valve 16 and the EGR valve 24 are feedback-controlled.

When the exhaust air-fuel ratio is rich, the MAF operation amount is determined by PID control so that the actual MAF value MAF _Act matches the MAF target value, and the intake throttle valve opening is determined from the lean valve opening MAP64B shown in FIG. 5B. _{VO_ith_R} is read and the intake throttle valve 16 is feedback-controlled. In this embodiment, when switching from the lean state to the rich state, the feedback integral term is reset to an initial value (for example, 0). Thereby, when performing feedback control in a rich state, the influence resulting from feedback control in a lean state can be suppressed.

On the other hand, the EGR valve 24 is fixed in a closed state or a specified opening degree with a reduced flow rate. When the EGR valve 24 is closed, ramp control is performed to gradually change the valve opening so that the torque of the engine 10 does not fluctuate. For this reason, as shown in FIG. 6A, the valve control unit 64 includes the immediately preceding target value holding unit 64C, the first control amount calculation unit 64D, the second control amount calculation unit 64E, the output target value holding unit 64F, and the control. An amount selection unit 64G, a target value calculation unit 64H, and an output switching unit 64J are provided.

The immediately preceding target value holding unit 64C holds the EGR target value (the target value of the valve opening in the EGR valve 24) immediately before the change. The first control amount calculator 64D calculates the first control amount by multiplying the valve opening per unit time by the calculation clock. The second control amount calculation unit 64D has an EGR decrease reached value (final valve opening) and an output target value held in the output target value holding unit 64F (an EGR target value output immediately before from the output switching unit 64J). The second control amount is calculated from the difference.

The control amount selection unit 64G selects the smaller one of the first control amount calculated by the first control amount calculation unit 64D and the second control amount calculated by the second control amount calculation unit 64E as the control amount. The target value calculation unit 64H calculates the EGR target value by subtracting the control amount selected by the control amount selection unit 64G from the output target value held in the output target value holding unit 64F. The output switching unit 64J outputs the EGR target value calculated by the target value calculation unit 64H over the output period of the start instruction signal.

By executing the above control, the ramp process is applied to the EGR target value when the exhaust air-fuel ratio is switched from the lean state to the rich state, as shown by the symbol _{VO_EGR_R} in FIG. Can be closed.

By performing the above-described control, when the exhaust air-fuel ratio is switched from the lean state to the rich state, the EGR valve 24 is closed or fixed at a specified opening degree, and the intake air is sucked into the engine 10 by the intake throttle valve 16. The amount is adjusted. Since the EGR valve 24 is closed or fixed at a specified opening degree, the EGR passage 22 and the EGR cooler 23 can be prevented from being contaminated. Further, since the intake air amount is adjusted by the intake throttle valve 16, it is possible to reduce the fuel injection amount by the exhaust pipe injection and the post injection for generating the rich condition. As a result, it is possible to improve fuel efficiency while suppressing contamination of the EGR passage 22 and the like.

Further, when the exhaust air-fuel ratio is switched from the lean state to the rich state, the EGR valve 24 is closed with a predetermined valve operation amount per unit time, so that the torque fluctuation of the engine 10 at the start of the SOx purge can be suppressed, and the driver It is possible to effectively suppress the deterioration of the ability.

Similarly, when the exhaust air-fuel ratio is switched between the lean state and the rich state, the intake throttle valve 16 is opened and closed at a predetermined valve operation amount per unit time, so that the engine at the start and end of the SOx purge The torque fluctuation of 10 can be suppressed, and the deterioration of drivability can be effectively suppressed.

Further, the valve opening of the intake throttle valve 16 is determined based on the MAF target values (MAF _{SPL_Trgt} , MAF _{SPL_Trgt_Ramp} ) based on the operating state of the engine 10 (engine speed Ne, accelerator opening Q) and the detected value of the MAF sensor 40. Control is performed by PID control based on the deviation of the actual intake air amount MAF _Act , and the integral term of PID control is initialized when switching from lean state control to rich state control, resulting in feedback control in the lean state Can be suppressed.

_Further , since the air system operation is feedback-controlled based on the MAF target value MAF _{SPL_Trgt} , the lambda sensor is not provided on the upstream side of the NOx storage reduction catalyst 32, or the NOx storage reduction catalyst 32 Even when a lambda sensor is provided on the upstream side, exhaust can be effectively reduced to a desired excess air ratio required for SOx purge lean control without using the sensor value of the lambda sensor.

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

[Fuel injection amount setting for SOx purge rich control]
FIG. 7 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 injection amount target value calculation unit 66 refers to the distribution MAP and reads out the distribution value. The distribution value indicates the ratio between the fuel injection amount by the exhaust injector 34 and the fuel injection amount by the in-cylinder injector 11. Injection amount target value computing unit 66, by multiplying the distribution value to the target injection amount _{Q SPR_Trgt,} calculates the fuel injection amount _{Q SPR_Trgt_Post} in the fuel injection amount _{Q SPR_Trgt_EXT-cylinder} injector 11 of the exhaust injector 34. These fuel injection amount, SOx purge rich flag F _SPR to be described later is turned on, is sent as the injection instruction signal to the exhaust injector 34 and cylinder injector 11.

Thus, in the present 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 the in-cylinder injector 11. It is like that. 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 the in-cylinder injector 11, the target injection amount Q _{SPR_Trgt} can be set by feedforward control. Effects such as characteristic changes 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. 8, when the SOx purge flag F _SP is turned on by the end of filter regeneration (F _DPF = 0), the SOx purge rich flag F _SPR is also turned on, and further during the previous SOx purge control. The interval T _{F_INT} calculated by feedback is also reset once. That is, the first time immediately after the regeneration of the filter, the exhaust pipe injection or the post injection is executed according to the injection period _{TF_INJ_1} set in the injection period setting map (see times t ₁ to t _{2 in} FIG. 8). 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. 8 t ₂ to t ₃ ). Further, when the SOx purge rich flag F _SPR is turned on as the interval _{TF_INT_1} has elapsed, the exhaust pipe injection or the post injection according to the injection period _{TF_INJ_2} is executed again (see time t ₃ to t _{4 in} FIG. 8). ). Thereafter, the switching on and off of these SOx purge rich flag _{F SPR} is repeatedly executed until the SOx purge flag _{F SP} is turned off (see time _{t n} in FIG. 8) 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. 8).

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} in FIG. 9). 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. 10 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. 9).

The ramp processing unit 73 uses the engine speed Ne and the accelerator opening Q as input signals, reads the change amount when increasing from the increase amount MAP 73A, and reads the change amount when decreasing from the decrease amount MAP 73B. The increasing amount of change is used when switching from the rich state to the lean state, and indicates the amount of addition per unit time to the MAF target value MAF. The change amount at the time of decrease is used when switching from the lean state to the rich state, and indicates a subtraction amount per unit time with respect to the MAF target value MAF.

As shown in FIG. 11, the ramp processing unit 73 includes a ramp start / end determination unit 73C, an increase target value calculation unit 73D, a decrease target value calculation unit 73E, a target value selection unit 73F, and an output switching unit 73G. .

The lamp start / end determination unit 73C receives a start instruction signal. The start instruction signal indicates the start timing of the ramp process according to a change in the state of the signal, and identifies the switching from the lean state to the rich state and the switching from the rich state to the lean state. The lamp start / end determination unit 73C outputs a permission signal to the output switching unit 73G when it is determined that the lamp processing start timing is reached. This permission signal is output until the MAF target value MAF _{NPL_Trgt} from the MAF target value calculation unit 72 and the MAF target value (MAF target ramp value MAF _{NPL_Trgt_Ramp} ) output from the output switching unit 73G match.

The increase target value calculation unit 73D receives the increase change amount from the increase change amount MAP 73A, the MAF target value MAF _{NPL_Trgt,} and the MAF target value (MAF target value immediately before the update) output from the output switching unit 73G. . In the increase target value calculation unit 73D, the section correction value obtained by multiplying the change amount during increase by the calculation clock is added to the MAF target value from the output switching unit 73G. Then, this added value is compared with the MAF target value MAF _{NPL_Trgt} from the MAF target value calculation unit 72, and the smaller one is output to the target value selection unit 73F as an increased provisional MAF target value.

The decrease target value calculation unit 73E receives the decrease change amount from the decrease change amount MAP 73B, the MAF target value MAF _{NPL_Trgt,} and the MAF target value (MAF target value immediately before the update) output from the output switching unit 73G. . In the decrease target value calculation unit 73E, the section correction value obtained by multiplying the decrease change amount by the calculation clock is subtracted from the MAF target value from the output switching unit 73G. Then, this subtraction value is compared with the MAF target value MAF _{NPL_Trgt} from the MAF target value calculation unit 72, and the larger one is output to the target value selection unit 73F as a reduced provisional MAF target value.

The target value selection unit 73F switches one of the increase temporary MAF target value output from the increase target value calculation unit 73D and the decrease temporary MAF target value output from the decrease target value calculation unit 73E between the rich state and the lean state. Depending on the selection, the output is output to the output switching unit 73G. Specifically, the increase temporary MAF target value is selected and output when switching from the rich state to the lean state, and the decrease temporary MAF target value is selected and output when switching from the lean state to the rich state.

The output switching unit 73G sets the increase temporary MAF target value or the decrease temporary MAF target value from the target value selection unit 73F as the MAF target ramp value MAF _{NPL_Trgt_Ramp over the} period when the permission signal is output from the lamp start / end determination unit _73C. Output as. Further, the output switching unit 73G outputs the MAF target value MAF _{NPL_Trgt} from the MAF target value calculation unit 72 during a period when the permission signal is not output.

The valve control unit 74 shown in FIG. 10 calculates the intake throttle valve 16 from the MAF target values (MAF _{NPL_Trgt} , MAF _{NPL_Trgt_Ramp} ) output from the ramp processing unit 73 and the actual MAF value MAF _Act based on the detection result of the MAF sensor 40. And the EGR valve 24 is controlled.

When the exhaust air-fuel ratio is in the lean state, the MAF operation amount is determined by PID control so that the actual MAF value MAF _Act matches the MAF target value, and the intake throttle valve opening is determined from the lean valve opening MAP74A shown in FIG. 12A. The _{VO_ith_L} and the EGR valve opening _{VO_EGR_L} are read, and the intake throttle valve 16 and the EGR valve 24 are feedback-controlled.

When the exhaust air-fuel ratio is in a rich state, the MAF operation amount is determined by PID control so that the actual MAF value MAF _Act matches the MAF target value, and the intake throttle valve opening from the lean valve opening MAP74B shown in FIG. 12B _{VO_ith_R} is read and the intake throttle valve 16 is feedback-controlled. In this embodiment, when switching from the lean state to the rich state, the feedback integral term is reset to an initial value (for example, 0). Thereby, when performing feedback control in a rich state, the influence resulting from feedback control in a lean state can be suppressed.

On the other hand, the EGR valve 24 is closed or fixed at a specified opening degree with a reduced flow rate. When the EGR valve 24 is closed, ramp control is performed to gradually change the valve opening so that the torque of the engine 10 does not fluctuate. For this reason, as shown in FIG. 13A, the valve control unit 74 includes a previous target value holding unit 74C, a first control amount calculation unit 74D, a second control amount calculation unit 74E, an output target value holding unit 74F, and a control. An amount selection unit 74G, a target value calculation unit 74H, and an output switching unit 74J are provided.

The immediately preceding target value holding unit 74C holds the EGR target value (the target value of the valve opening in the EGR valve 24) immediately before the change. The first control amount calculation unit 74D calculates the first control amount by multiplying the valve opening per unit time by the calculation clock. The second control amount calculation unit 74E includes an EGR reduction reached value (final valve opening) and an output target value held in the output target value holding unit 74F (EGR target value output immediately before from the output switching unit 74J). The second control amount is calculated from the difference.

The control amount selection unit 74G selects the smaller one of the first control amount calculated by the first control amount calculation unit 74D and the second control amount calculated by the second control amount calculation unit 74E as the control amount. The target value calculation unit 74H calculates the EGR target value by subtracting the control amount selected by the control amount selection unit 74G from the output target value held in the output target value holding unit 74F. The output switching unit 74J outputs the EGR target value calculated by the target value calculation unit 74H over the output period of the start instruction signal.

By executing the above control, the ramp process is applied to the EGR target value when the exhaust air-fuel ratio is switched from the lean state to the rich state, as indicated by the symbol _{VO_EGR_R} in FIG. Can be closed.

Further, when the exhaust air-fuel ratio is switched from the lean state to the rich state, the EGR valve 24 is closed with a predetermined valve operation amount per unit time, so that the torque fluctuation of the engine 10 at the start of the NOx purge can be suppressed, and the driver It is possible to effectively suppress the deterioration of the ability.

Similarly, when the exhaust air-fuel ratio is switched between the lean state and the rich state, the intake throttle valve 16 is opened and closed at a predetermined valve operation amount per unit time, so that the engine at the start and end of the NOx purge The torque fluctuation of 10 can be suppressed, and the deterioration of drivability can be effectively suppressed.

Further, the valve opening of the intake throttle valve 16 is determined based on the MAF target values (MAF _{NPL_Trgt} , MAF _{NPL_Trgt_Ramp} ) based on the operating state of the engine 10 (engine speed Ne, accelerator opening Q) and the detection value of the MAF sensor 40. Control is performed by PID control based on the deviation of the actual intake air amount MAF _Act , and the integral term of PID control is initialized when switching from lean state control to rich state control, resulting in feedback control in the lean state Can be suppressed.

_Further , since the air system operation is feedback-controlled based on the MAF target value MAF _{NPL_Trgt} , the lambda sensor is not provided on the upstream side of the NOx storage reduction catalyst 32, or the NOx storage reduction catalyst 32 Even when a lambda sensor is provided on the upstream side, the exhaust can be effectively reduced to a desired excess air ratio required for NOx purge lean control without using the sensor value of the lambda sensor.

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

[NOx purge rich control fuel injection amount setting]
FIG. 14 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 injection amount target value calculation unit 76 refers to the distribution MAP and reads out the distribution value. The distribution value indicates the ratio between the fuel injection amount by the exhaust injector 34 and the fuel injection amount by the in-cylinder injector 11. Injection amount target value computing unit 66, by multiplying the distribution value to the target injection amount _{Q NPR_Trgt,} calculates the fuel injection amount _{Q NPR_Trgt_Post} in the fuel injection amount _{Q NPR_Trgt_EXT-cylinder} injector 11 of the exhaust injector 34. These fuel injection amounts are transmitted as injection instruction signals to the exhaust injector 34 and the in-cylinder injector 11 when the NOx purge flag F _NP is turned on (time t _{1 in} FIG. 9). The transmission of the injection instruction signal is continued until the NOx purge flag F _NP is turned off (time t _{2 in} FIG. 9) by the end determination of NOx purge control described later.

Thus, in this embodiment, the target injection amount Q _{NPR_Trgt} is set based on the excess air ratio target value λ _{NPR_Trgt} read from the fourth target excess air ratio setting map 75 and the fuel injection amount of the in-cylinder injector 11. It is like that. 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 the in-cylinder injector 11, the target injection amount Q _{NPR_Trgt} can be set by feedforward control. Effects such as characteristic changes 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 falls to a predetermined threshold value indicating successful NOx removal is satisfied, the NOx purge flag F _NP is turned off and the process is terminated (time t _{2 in} FIG. 9). 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, so that the fuel consumption amount is reduced when the NOx purge is not successful due to a decrease in the exhaust temperature or the like. 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 (MAF follow-up control) is performed to correct the fuel injection timing and the fuel injection amount of the in-cylinder injector 11 according to the MAF change.

[Injection amount learning correction]
As shown in FIG. 15, 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, if an error Δλ occurs between the actual lambda value λ _Act and the estimated lambda value λ _Est , it can be assumed that the difference is between the instructed injection amount for the in-cylinder injector 11 and the actual injection amount. Hereinafter, the learning correction coefficient calculation processing by the learning correction coefficient calculation unit 91 using the error Δλ will be described with reference to the flow of FIG.

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

In step S310, an error Δλ obtained by subtracting the actual lambda value λ _Act detected by the NOx / lambda sensor 45 from the estimated lambda value λ _Est is multiplied by the learning value gain K ₁ and the correction sensitivity coefficient K ₂ to thereby obtain the learning value F _CorrAdpt is calculated (F _CorrAdpt = (λ _Est −λ _Act ) × K ₁ × K ₂ ). The estimated lambda value λ _Est is estimated and calculated from the operating state of the engine 10 according to the engine speed Ne and the accelerator opening Q. Further, the correction sensitivity coefficient _{K 2} is read the actual lambda value lambda _Act detected by the NOx / lambda sensor 45 from the correction sensitivity coefficient map 91A shown in FIG. 12 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. 15) 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 the in-cylinder 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 , It becomes possible to effectively eliminate variations such as individual differences.

[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 the in-cylinder injector 11 is corrected 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 . However, since lambda is the ratio of air to fuel, the cause of the error Δλ is not necessarily only the influence of the difference between the command injection amount and the actual injection amount with respect to the in-cylinder injector 11. That is, there is a possibility that the error of the MAF sensor 40 as well as the in-cylinder injector 11 affects the lambda error Δλ.

FIG. 17 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.

This application is based on a Japanese patent application (Japanese Patent Application No. 2015-142036) filed on July 16, 2015, the contents of which are incorporated herein by reference.

The exhaust purification system of the present invention is useful in that fuel efficiency can be improved while suppressing fouling of a flow path for recirculating exhaust gas.

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

Claims

A NOx reduction catalyst provided in an exhaust passage of the internal combustion engine for reducing and purifying NOx in the exhaust;
An intake air amount adjustment valve for adjusting the amount of air taken into the internal combustion engine;
A recirculation amount adjusting valve for adjusting the amount of exhaust gas recirculated to the internal combustion engine;
Regeneration that restores the 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 for reducing the intake air amount and the injection system control for increasing the fuel injection amount. A control unit that executes processing;
An exhaust purification system comprising:
When the exhaust air-fuel ratio is switched from a lean state to a rich state, the control unit fixes the recirculation amount adjustment valve in a closed state or a specified opening, and is sucked into the internal combustion engine by the intake amount adjustment valve. An exhaust purification system that regulates the amount of air.
The exhaust purification system according to claim 1, wherein the control unit closes the recirculation amount adjusting valve by a predetermined valve operation amount per unit time when the exhaust air-fuel ratio is switched from a lean state to a rich state.
3. The exhaust gas purification according to claim 1, wherein the control unit opens and closes the intake air amount adjustment valve at a predetermined valve operation amount per unit time when the exhaust air-fuel ratio is switched between a lean state and a rich state. system.
The controller is
The valve opening degree of the intake air amount adjusting valve is controlled by PID control based on a deviation between a target intake air amount based on the operation state of the internal combustion engine and an actual intake air amount based on a detected value of the intake air amount sensor, and from the lean state control to the rich state The exhaust purification system according to any one of claims 1 to 3, wherein an integral term of the PID control is initialized when switching to state control.