JP2016223294A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively eliminate NOx exhausted from a NOx occlusion reduction type catalyst 32.SOLUTION: An exhaust emission control system includes the NOx occlusion reduction type catalyst 32 provided in an exhaust passage 13 of an engine 10 for occluding NOx in exhaust gas while reducing and eliminating it, and a control part 50 for performing purge control including at least injection system control to increase a fuel injection amount so that the air-fuel ratio of the exhaust gas is switched from a lean state into a rich state to recover the NOx eliminating capability of the NOx occlusion reduction type catalyst 32. In the exhaust passage 13 at its exhaust downstream side further than the NOx occlusion reduction type catalyst 32, a zeolite supporting catalyst 33 is arranged for trapping NOx exhausted from the NOx occlusion reduction type catalyst 32 and hydrocarbon passing through the NOx occlusion reduction type catalyst 32 in the rich state.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification system.

  Conventionally, NOx occlusion reduction type catalysts are known as catalysts for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from internal combustion engines such as diesel engines. 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. For this reason, 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 SOx 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

  The NOx occlusion reduction type catalyst has a characteristic that the NOx occlusion efficiency decreases in a high temperature range. The decrease in NOx occlusion efficiency in the high temperature range becomes more prominent as poisoning deterioration due to SOx progresses. As the NOx occlusion efficiency decreases, NOx occluded in the NOx occlusion reduction type catalyst is exhausted, or NOx is occluded without being occluded in the NOx occlusion reduction type catalyst.

  An object of the disclosed system is to effectively purify NOx discharged from a NOx storage reduction catalyst.

  The disclosed system includes an NOx occlusion reduction catalyst that is provided in an exhaust passage of an internal combustion engine to occlude and reduce NOx in exhaust gas, and at least an injection system control that increases a fuel injection amount, thereby reducing an exhaust air-fuel ratio. A control unit that performs a catalyst regeneration process for recovering the NOx purification ability of the NOx reduction catalyst by switching from the lean state to the rich state, wherein the NOx reduction catalyst in the exhaust passage Further, a collection member that collects NOx discharged from the NOx reduction catalyst and hydrocarbons that have passed through the NOx reduction catalyst in the rich state is disposed downstream of the exhaust.

  According to the disclosed system, NOx discharged from the NOx storage reduction catalyst can be effectively purified.

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. NOx concentration at the NOx purge rich control according to this embodiment, NH ₃ concentration, and a diagram illustrating the change with time of the NOx purification rate in the zeolite-supported catalysts. It is a block diagram which shows the process of the injection amount learning correction | amendment of the in-cylinder injector which concerns on this embodiment. It is a flowchart explaining the calculation process of the learning correction coefficient which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF correction coefficient which concerns on this embodiment.

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

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

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

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

  The exhaust aftertreatment device 30 is configured by arranging an oxidation catalyst 31, a NOx occlusion reduction type catalyst 32, a zeolite supported catalyst 33, and a particulate filter (hereinafter simply referred to as a filter) 34 in order from the exhaust upstream side in a case 30A. Yes. The exhaust passage 13 upstream of the oxidation catalyst 31 is provided with an exhaust pipe injection device 35 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 injection device 35 or the in-cylinder injector 11, the oxidation catalyst 31 oxidizes this and raises the exhaust temperature.

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

The zeolite-supported catalyst 33 is formed, for example, by supporting zeolite, such as β zeolite or ZSM-5 type zeolite, on the surface of a ceramic carrier such as a honeycomb structure. This zeolite-supported catalyst 33 is an example of a collecting member according to the present invention. NOx discharged from the NOx storage reduction catalyst 32, hydrocarbons slipped (passed) through the NOx storage reduction catalyst 32 in a rich state (HC) ) And ammonia (NH ₃ ) discharged from the NOx occlusion reduction catalyst 32 is collected. Further, the zeolite-supported catalyst 33 reduces and purifies the collected NOx by the NH ₃ -SCR (selective catalytic reduction) effect and the HC-SCR effect using NH ₃ or HC as a reducing agent.

  The filter 34 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 34 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 34 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 zeolite-supported catalyst 33 and the filter 34 and detects the exhaust temperature flowing into the filter 34. The NOx / lambda sensor 45 is provided on the downstream side of the filter 34, and the NOx value and the lambda value (hereinafter also referred to as excess air ratio) of the exhaust gas that has passed through the NOx storage reduction catalyst 32 and the zeolite-supported catalyst 33. To detect.

  The ECU 50 performs various controls of the engine 10 and the like, and is an example of a control unit according to the present invention. The ECU 50 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 34 from the travel distance of the vehicle or the differential pressure across the filter detected by a differential pressure sensor (not shown), and this PM accumulation estimation amount exceeds a predetermined upper limit threshold value. 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 35 to execute exhaust pipe injection is transmitted, or an instruction signal for causing the in-cylinder injector 11 to perform post injection is transmitted. The exhaust 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). By the recovery from the SOx poisoning, the NOx purification ability of the NOx storage reduction catalyst 32 is also recovered. For this reason, the SOx purge in which the exhaust is made rich and the exhaust temperature is raised to the sulfur desorption temperature is an example of the catalyst regeneration process according to the present invention.

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 where the exhaust gas temperature has been raised by the regeneration of the filter 34, 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 this 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 the in-cylinder 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 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.

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} at the time of SOx purge rich control based on the following formulas (2) and (2) ′.

Q _{SPR_Trgt} = MAF _{SPL_Trgt} × _{Maf_corr} / (λ _{SPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (2)
Q _{SPR_Trgt} = (MAF _{SPL_Trgt} × _{Maf_corr} / (λ _{SPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_cord} ) × F _{Inc_coe} (2) ′
In Expressions (2) and (2) ′, MAF _{SPL_Trgt} is the MAF target value at the SOx purge _{lean, and} is input from the MAF target value calculation unit 62 described above. Further, Q _{fnl_corrd} is a fuel injection amount (excluding post injection) after learning corrected MAF follow-up control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, _{Maf_corr} is a MAF correction coefficient described later, F _{Inc_coe} indicates an increase coefficient.

Equation (2) calculates a target injection amount Q _{SPR_Trgt} necessary for SOx purge (catalyst regeneration process), and Equation (2) ′ is a target injection amount Q that is set larger than the amount necessary for SOx purge. _{SPR_Trgt} is calculated.

The increase coefficient F _{Inc_coe} is a coefficient used to increase the target injection amount Q _{SPR_Trgt} at the beginning of SOx purge rich control more than the amount necessary for SOx purge, and is set to a number larger than “1”. In the equation (2) ′, the portion (MAF _{SPL_Trgt} × _{Maf_corr} / (λ _{SPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_cord} ) multiplied by the increase coefficient F _{Inc_coe} has the same content as the equation (2). Increasing coefficient _{F Inc_coe} since is greater than 1, the target injection amount _{Q SPR_Trgt} calculated by Equation (2) 'is larger than the target injection amount _{Q SPR_Trgt} calculated by Equation (2).

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 35 or the in-cylinder injector 11 when a SOx purge rich flag F _SPR described later is turned on. .

  The increase timer 66a measures time over the beginning of SOx purge rich control, starts counting from the start timing of SOx purge rich control, and ends counting when a predetermined period elapses. The increase timer 66a turns on the time measurement flag during the time measurement. The injection amount target value calculation unit 66 recognizes whether or not the SOx purge rich control is in the initial stage based on the time counting flag from the increase timer 66a.

The injection amount target value calculation unit 66 transmits the target injection amount Q _{SPR_Trgt} calculated by Expression (2) ′ as an injection instruction signal at the beginning of the start of the SOx purge rich control, and then calculated by Expression (2). The target injection amount Q _{SPR_Trgt} thus transmitted is transmitted as an injection instruction signal. As a result, at the beginning of the SOx purge rich control, the fuel injection amount is increased from the amount necessary for the SOx purge.

  Part of the injected fuel is oxidized by the oxidation catalyst 31 and the exhaust temperature is raised. As the exhaust gas temperature rises, the NOx occlusion reduction type catalyst 32 also rises in temperature, but the NOx occlusion reduction type catalyst 32 has a reduced NOx occlusion efficiency in a high temperature range where SOx purge and DPF regeneration are performed.

  As shown in FIG. 1, in this embodiment, since the zeolite-supported catalyst 33 is disposed on the exhaust downstream side of the NOx occlusion reduction type catalyst 32, the NOx occlusion reduction type catalyst 32 is reduced as the NOx occlusion efficiency decreases. Even if part of the occluded NOx is exhausted, the exhausted NOx is collected (adsorbed) by the zeolite-supported catalyst 33. Similarly, NOx that cannot be stored due to saturation of the NOx storage-reduction catalyst 32 and is discharged is also collected (adsorbed) by the zeolite-supported catalyst 33.

In the NOx occlusion reduction type catalyst 32, water (H ₂ O) is decomposed by CO or HC to generate hydrogen (H ₂ ). Oxygen (O) constituting NOx is replaced with H ₂ to generate NH ₃ . This NH ₃ is discharged from the NOx occlusion reduction catalyst 32 and collected by the zeolite-supported catalyst 33.

Part of the injected fuel passes (slips) through the NOx storage reduction catalyst 32 and reaches the zeolite-supported catalyst 33. In the zeolite-supported catalyst 33, HC such as NH ₃ or fuel serves as a reducing agent, and the collected NOx is reduced and purified by the NH ₃ -SCR effect or the HC-SCR effect. Therefore, even if the NOx occlusion efficiency of the NOx occlusion reduction catalyst 32 decreases in the high temperature range, the NOx occluded from the NOx occlusion reduction catalyst 32 can be reduced and purified by the zeolite-supported catalyst 33.

  Further, since the fuel injection amount at the beginning of the SOx purge rich control is increased from the amount required for the SOx purge, the fuel can be slipped by the NOx occlusion reduction type catalyst 32, and the zeolite supported catalyst 33 It can be used reliably as a reducing agent.

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 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 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. 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 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. By the recovery of the NOx storage capacity, the NOx purification capacity of the NOx storage reduction catalyst 32 is also recovered. Therefore, the NOx purge for reducing and purifying NOx stored in the NOx storage reduction catalyst 32 by setting the exhaust to a rich state is an example of the catalyst regeneration process according to the present invention.

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 _{uses 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 this embodiment, the MAF target value MAF _{NPL_Trgt} is set based on the excess air ratio target value λ _{NPL_Trgt} read from the third target excess air ratio setting map 71 and the fuel injection amount of the in-cylinder injector 11. The air system operation is feedback-controlled based on the MAF target value MAF _{NPL_Trgt} . Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge lean control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of 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.

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_cord} ) × F _{Inc_coe} (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. Further, Q _{fnl_corrd} is a fuel injection amount (excluding post injection) after learning corrected MAF follow-up control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, _{Maf_corr} is a MAF correction coefficient described later, F _{Inc_coe} indicates an increase coefficient.

The increase coefficient F _{Inc_coe} is a coefficient used to increase the target injection amount Q _{NPR_Trgt} at the beginning of the start of the NOx purge rich control _{beyond the} amount _required for the NOx purge (catalyst regeneration process), and is larger than “1”. It is determined by the number. In Equation (4), the portion (MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} ) multiplied by the increase coefficient F _{Inc_coe} is calculated by calculating the target injection amount necessary for the NOx purge. Yes. For this reason, the target injection amount Q _{NPR_Trgt} calculated by Expression (4) is larger than the amount necessary for the NOx purge.

The target injection amount _{Q NPR_Trgt} that is calculated by the injection amount target value calculation unit 76, when the NOx purge flag _{F SP} is turned on, is sent as the injection instruction signal to the exhaust pipe injector 35 or in-cylinder injector 11 (in FIG. 6 Time 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.

The exhaust pipe injection device 35 and the in-cylinder injector 11 inject fuel with the reception of the injection instruction signal. As described above, since the increase coefficient is multiplied when the target injection amount Q _{NPR_Trgt} is calculated, an amount of fuel larger than that required for the NOx purge is injected. A part of the injected fuel is used for NOx purge in the NOx occlusion reduction type catalyst 32.

  Here, if the NOx storage reduction catalyst 32 is heated to a high temperature range (for example, 400 ° C. or higher), the NOx storage efficiency of the NOx storage reduction catalyst 32 is lowered.

  As shown in FIG. 1, in this embodiment, since the zeolite-supported catalyst 33 is disposed on the exhaust downstream side of the NOx occlusion reduction type catalyst 32, the NOx occlusion reduction type catalyst 32 is reduced as the NOx occlusion efficiency decreases. Even if part of the occluded NOx is exhausted, the exhausted NOx is collected (adsorbed) by the zeolite-supported catalyst 33. Similarly, NOx that cannot be stored due to saturation of the NOx storage-reduction catalyst 32 and is discharged is also collected by the zeolite-supported catalyst 33.

In the NOx occlusion reduction type catalyst 32, H ₂ O is decomposed by CO or HC to generate H ₂ . This H ₂ is replaced with O constituting NOx, and NH ₃ is generated. The produced NH ₃ is discharged from the NOx occlusion reduction catalyst 32 and collected by the zeolite-supported catalyst 33.

  Further, a portion of the injected fuel passes through the NOx storage reduction catalyst 32 and reaches the zeolite-supported catalyst 33.

In the zeolite-supported catalyst 33, HC such as NH ₃ or fuel serves as a reducing agent, and the collected NOx is reduced and purified by the NH ₃ -SCR effect or the HC-SCR effect. Therefore, even if the NOx occlusion efficiency of the NOx occlusion reduction catalyst 32 decreases in a high temperature range, NOx discharged from the NOx occlusion reduction catalyst 32 can be collected by the zeolite-supported catalyst 33 and reduced and purified.

FIG. 9 is a diagram for explaining temporal changes in NOx concentration, NH ₃ concentration, and NOx purification rate during NOx purge rich control. Hereinafter, the reduction purification of NOx will be described with reference to FIG.

In FIG. 9, the uppermost stage on the vertical axis indicates the NOx concentration (LNT outlet NOx concentration) discharged from the downstream end of the NOx storage reduction catalyst 32, and the second stage from the uppermost stage is the downstream of the NOx storage reduction catalyst 32. The NH ₃ concentration discharged from the end (LNT outlet NH ₃ concentration) is shown. The third stage from the uppermost stage shows the NOx concentration (zeolite outlet NOx density) discharged from the downstream end of the zeolite-supported catalyst 33, and the fourth stage from the uppermost stage shows the NOx purification rate (zeolite catalyst) in the zeolite-supported catalyst 33. The purification rate). The bottom row shows the on timing of the rich flag.

When the rich flag is turned on at time _{t 1,} LNT outlet NOx concentration rises rapidly. This is because the NOx concentration contained in the exhaust gas from the engine 10 rapidly increases due to the rich control, and NOx is discharged from the NOx storage reduction catalyst 32.

Further, the LNT outlet NH ₃ concentration also rises rapidly together with the LNT outlet NOx concentration. This is because NH ₃ produced by the NOx storage reduction catalyst 32 is discharged from the NOx storage reduction catalyst 32.

Zeolite outlet NOx concentration over the time _{t 1} to time _{t 2} is sufficiently smaller than the LNT outlet NOx concentration. This, NOx was collected (adsorbed) by zeolite-supported catalyst 33 is, _NH 3 -SCR effect of the NH ₃ as a reducing agent, and, because that is reduced and purified by HC-SCR effect of the HC as a reducing agent. Accordingly, the zeolite catalyst purification rate at time t ₂ from time t _1, once with the spikes LNT outlet NOx concentration is reduced but recovered in a short period of time, generally a high purification rate is obtained.

From time t ₂ to time t ₃ , an upward trend is seen in the LNT outlet NOx concentration. This indicates that NOx that has not been occluded by the NOx occlusion reduction type catalyst 32 has increased. On the other hand, the LNT outlet NH ₃ concentration is sufficiently low. This indicates that H ₂ is not generated.

Despite the sufficiently low concentration of NH _3, the NOx concentration at the zeolite outlet is low, indicating that NOx reduction and purification is being performed by the zeolite-supported catalyst 33. Therefore, at time _{t 3} from the time _{t 2,} HC passing through the NOx storage reduction catalyst 32 is trapped by the zeolite-supported catalyst 33, it can be understood that NOx is reduced and purified by HC-SCR effect .

The above has been described for the period from time t ₁ to time t _3, the period from time t ₃ to time t _5, and, for the period from time t ₅ to time t _7, the same tendency is confirmed it can.

Thus, also in the NOx purge rich control, in the zeolite-supported catalyst 33, HC such as NH ₃ or fuel serves as a reducing agent, and NOx collected by the NH ₃ -SCR effect or the HC-SCR effect is reduced and purified. Therefore, even if the NOx occlusion efficiency of the NOx occlusion reduction catalyst 32 decreases in the high temperature range, the NOx occluded from the NOx occlusion reduction catalyst 32 can be reduced and purified by the zeolite-supported catalyst 33.

  Further, since the fuel injection amount in the NOx purge rich control is increased more than the amount necessary for the NOx purge, the fuel can be slipped by the NOx occlusion reduction type catalyst 32 and used as a reducing agent in the zeolite supported catalyst 33. Can be used reliably.

In the present embodiment, the target injection amount Q _{NPR_Trgt} is set based on the excess air ratio target value λ _{NPR_Trgt} read from the fourth target excess air ratio setting map 75 and the fuel injection amount of the in-cylinder 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 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 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, 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 switching period to the state, MAF follow-up control for correcting the fuel injection timing and the fuel injection amount of each in-cylinder injector 11 according to the MAF change is executed.

[Injection amount learning correction]
As shown in FIG. 10, 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. 10 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. 10) 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. 12 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.

  For example, regarding the collection member, the zeolite-supported catalyst 33 is exemplified in the above-described embodiment, but the present invention is not limited to the zeolite-supported catalyst 33. If it is a member that collects NOx discharged from the NOx storage reduction catalyst 32 and hydrocarbons that have passed through the NOx storage reduction catalyst 32 in a rich state, downstream of the NOx storage reduction catalyst 32, it is collected. Can be used as a member.

Regarding the SOx purge control unit 60, in the above-described embodiment, the fuel injection amount at the beginning of SOx purge rich control is increased from the amount necessary for this rich control using the increase coefficient F _{Inc_coe} and the increase timer 66a. However, the present invention is not limited to this configuration. Other configurations may be used as long as the fuel injection amount at the beginning of the start can be increased.

Regarding the NOx purge control unit 70, in the above-described embodiment, the fuel injection amount in the NOx purge rich control is increased from the amount necessary for the rich control using the increase coefficient F _{Inc_coe} , but this configuration is limited. It is not a thing. Other configurations may be used as long as the fuel injection amount can be increased.

  Regarding the SOx purge control and the NOx purge control, the air system control and the injection system control are used together in the above-described embodiment, but the present invention can be applied to any system that performs at least the injection system control.

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 Zeolite carrying catalyst 34 Filter 35 Exhaust pipe injection device 40 MAF sensor 45 NOx / lambda sensor 50 ECU

Claims (3)

The exhaust air-fuel ratio is changed from a lean state to a rich state by performing at least an NOx occlusion reduction type catalyst that is provided in the exhaust passage of the internal combustion engine and stores and reduces and purifies NOx in the exhaust, and an injection system control that increases the fuel injection amount. An exhaust purification system comprising: a control unit that performs a catalyst regeneration process for recovering the NOx purification ability of the NOx reduction catalyst by switching to
A collection member that collects NOx discharged from the NOx reduction catalyst and hydrocarbons that have passed through the NOx reduction catalyst in the rich state on the exhaust gas downstream side of the NOx reduction catalyst in the exhaust passage. An exhaust purification system is located. The exhaust purification system according to claim 1, wherein the collection member is a zeolite-supported catalyst in which zeolite is supported on a carrier. The exhaust purification system according to claim 1 or 2, wherein the control unit injects an amount of fuel larger than an amount necessary for regeneration of the NOx reduction catalyst in the catalyst regeneration process.

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