JP2016142174A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent deterioration of drivability due to MAF follow-up control.SOLUTION: An exhaust emission control system includes: an NOx reduction type catalyst 32; an intake air amount sensor 40 for acquiring intake air amount; catalyst regeneration control sections 60, 70 for performing catalyst regeneration processing for recovering purification capacity of the NOx reduction type catalyst 32 by switching exhaust gas to a rich state by using both of air system control for reducing intake air amount and injection system control for increasing fuel injection amount; a follow-up control section 80 for performing follow-up control for changing at least one of fuel injection timing and fuel injection amount of an internal combustion engine 10 in accordance with the intake air amount acquired by the intake air amount sensor 40 for a switching period from a lean state to the rich state and a switching period from the rich state to the lean state; and a prohibition section 81 for prohibiting the performance of the follow-up control in the case where the internal combustion engine 10 is in a motoring state when the follow-up control is performed.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 (hereinafter referred to as NOx) in exhaust gas discharged from an internal combustion engine. The NOx occlusion reduction catalyst occludes NOx contained in the exhaust when the exhaust is in a lean atmosphere, and harmless NOx occluded by hydrocarbons contained in the exhaust when the exhaust is in a rich atmosphere. And release. For this reason, when the NOx occlusion amount of the catalyst reaches a predetermined amount, so-called NOx purge that makes the exhaust rich by post injection or exhaust pipe injection needs to be performed periodically to restore the NOx occlusion capacity ( For example, see Patent Document 1).

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

JP 2008-202425 A JP 2009-47086 A

  As this type of device, when performing SOx purge or NOx purge (hereinafter also simply referred to as catalyst regeneration processing), the intake system is controlled by increasing the fuel injection amount and adjusting the opening of the intake throttle valve or EGR valve. One that uses air system control to reduce the amount of air is known. When a large amount of EGR gas is introduced into the combustion chamber by the air system control at the start of the catalyst regeneration process using both the air system control and the injection system control, the ignition delay is delayed at the same injection timing as the normal lean state. It can happen. For this reason, when the exhaust gas is switched to the rich state, it is necessary to advance the injection timing as the injection amount increases.

  In order to appropriately control the increase in the injection amount and the advance angle of the injection timing, in order to synchronize the instantaneously reacting injection system with the air system with a delayed response, the increase or advance in accordance with the actual change in the intake air amount. It is preferable to implement MAF tracking control for adjusting the angular amount.

  However, when performing the MAF follow-up control, if the air system enters a motoring state in which the air system is switched to open loop control, the intake air amount does not change, and the increase in the injection amount and the advance angle of the injection timing do not advance. This may cause the combustion of the fuel to become unstable and cause drivability to deteriorate. In addition, when the idle operation is performed in a state where the intake air amount does not change during MAF tracking control, a state where the actual injection amount is small is maintained, and there is a problem that hinders acceleration of the vehicle and the like.

  An object of the disclosed system is to effectively prevent the drivability from being deteriorated by MAF tracking control during catalyst regeneration processing.

  The disclosed system is provided in an exhaust system of an internal combustion engine to reduce and purify NOx in the exhaust, a NOx reduction type catalyst, intake air amount acquisition means for acquiring the intake air amount of the internal combustion engine, and a reduction in the intake air amount The catalyst which performs the catalyst regeneration process which recovers the NOx purification ability of the NOx reduction catalyst by switching the exhaust gas from the lean state to the rich state in combination with the air system control to be performed and the injection system control to increase the fuel injection amount The intake air amount acquisition means in at least one of a regeneration means, a switching period from the lean state to start the catalyst regeneration process to the rich state, and a switching period from the rich state to the lean state to end the catalyst regeneration process In accordance with the intake air amount acquired in step 1, the at least one of the fuel injection timing and the fuel injection amount of the internal combustion engine is changed. To include a follow-up control unit, and a prohibiting means for prohibiting the implementation of the following control when the internal combustion engine in carrying out the follow-up control is in a motoring state to stop the fuel injection.

  According to the disclosed system, it is possible to effectively prevent the drivability from being deteriorated by the MAF tracking control during the catalyst regeneration process.

1 is an overall configuration diagram showing an exhaust purification system according to an embodiment. It is a timing chart explaining SOx purge control concerning this embodiment. It is a block diagram which shows the setting process of the MAF target value at the time of SOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection amount at the time of SOx purge rich control which concerns on this embodiment. It is a timing chart explaining catalyst temperature adjustment control of SOx purge control concerning this embodiment. It is a timing chart figure explaining NOx purge control concerning this embodiment. It is a block diagram which shows the setting process of the MAF target value at the time of NOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection quantity at the time of NOx purge rich control which concerns on this embodiment. It is a block diagram which shows the process of the catalyst heat retention control which concerns on this embodiment. It is a flowchart explaining switching from the lean state of MAF tracking control which concerns on this embodiment to the rich state by SOx purge control. It is a flowchart explaining switching from the lean state of MAF follow-up control which concerns on this embodiment to the rich state by NOx purge control. It is a flowchart explaining switching from the rich state to the lean state by the SOx purge control of the MAF follow-up control according to the present embodiment. It is a flowchart explaining switching from the rich state to the lean state by the NOx purge control of the MAF follow-up control according to the present embodiment. It is a figure explaining the shift | offset | difference of the actual MAF value and MAF target value at the time of shifting from a lean state to a rich state or from a rich state to a lean state. It is a block diagram which shows the process of the injection amount learning correction | amendment of the injector which concerns on this embodiment. It is a flowchart explaining the calculation process of the learning correction coefficient which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF correction coefficient which concerns on this embodiment.

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

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

  An intake passage 12 for introducing fresh air is connected to the intake manifold 10A of the engine 10, and an exhaust passage 13 for leading the exhaust to the outside is connected to the exhaust manifold 10B. In the intake passage 12, an air cleaner 14, an intake air amount sensor (hereinafter referred to as MAF sensor) 40, a compressor 20A of the variable displacement supercharger 20, an intercooler 15, an intake throttle valve 16 and the like are provided in order from the intake upstream side. ing. The exhaust passage 13 is provided with a turbine 20B of the variable displacement supercharger 20, an exhaust aftertreatment device 30 and the like in order from the exhaust upstream side. In FIG. 1, reference numeral 41 denotes an engine speed sensor, reference numeral 42 denotes an accelerator opening sensor, reference numeral 46 denotes a boost pressure sensor, and reference numeral 47 denotes a vehicle speed sensor.

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

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

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

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

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

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

  The ECU 50 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, sensor values of the sensors 40 to 47 are input to the ECU 50. Further, the ECU 50 includes a filter regeneration control unit 51, a SOx purge control unit 60, a NOx purge control unit 70, a catalyst heat retention control unit 52, a MAF follow-up control unit 80, a MAF follow-up control prohibition unit 81, an injection amount. The learning correction unit 90 and the MAF correction coefficient calculation unit 95 are included as some functional elements. Each of these functional elements will be described as being included in the ECU 50 which is an integral hardware, but any one of these may be provided in separate hardware.

[Filter forced 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 forced regeneration flag F _DPF is turned on (see time t _{1 in} FIG. 2). When the forced regeneration flag F _DPF is turned on, an instruction signal for executing exhaust pipe injection is transmitted to the exhaust pipe injection device 34, or an instruction signal for executing post injection to each injector 11 is transmitted. The exhaust temperature is raised to the PM combustion temperature (for example, about 550 ° C.). The forced 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 forced 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 forced filter regeneration (F _DPF = 1).

[SOx purge control]
The SOx purge control unit 60 is an example of the catalyst regeneration means of the present invention, and makes the exhaust gas rich and raises the exhaust gas temperature to a sulfur desorption temperature (for example, about 600 ° C.). Control to recover from SOx poisoning (hereinafter, this control is referred to as SOx purge control) is executed.

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 off and on at the same time forced 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 forced regeneration of the filter 33, and the fuel consumption can be effectively reduced.

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

[Air system control for SOx purge lean control]
FIG. 3 is a block diagram illustrating a process for setting the MAF target value MAF _{SPL_Trgt} during the SOx purge lean control. The first target excess air ratio setting map 61 is a map that is referred to based on the engine speed Ne and the accelerator opening Q (the fuel injection amount of the engine 10), and the engine speed Ne, the accelerator opening Q, The excess air ratio target value λ _{SPL_Trgt} (first target excess air ratio) at the time of SOx purge lean control corresponding to is preset based on experiments or the like.

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

MAF _{SPL_Trgt} = λ _{SPL_Trgt} × Q _{fnl_corrd} × Ro _Fuel × AFR _sto / _{Maf_corr} (1)
In Equation (1), Q _{fnl_cord} represents a learning-corrected fuel injection amount (excluding post-injection) described later, Ro _Fuel represents fuel specific gravity, AFR _sto represents a theoretical air-fuel ratio, and _{Maf_corr} represents a MAF correction coefficient described later. Yes.

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

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

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

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each injector 11, the MAF target value MAF _{SPL_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. The influence of individual differences can be effectively eliminated.

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

[Fuel injection amount setting for SOx purge rich control]
FIG. 4 is a block diagram showing processing for setting the target injection amount Q _{SPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in SOx purge rich control. The second target excess air ratio setting map 65 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and at the time of SOx purge rich control corresponding to the engine speed Ne and the accelerator opening Q. Of the excess air ratio target value λ _{SPR_Trgt} (second target excess air ratio) is set in advance based on experiments or the like.

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

Q _{SPR_Trgt} = MAF _{SPL_Trgt} × _{Maf_corr} / (λ _{SPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (2)
In Expression (2), MAF _{SPL_Trgt} is the MAF target value at the SOx purge _{lean, and} is input from the above-described MAF target value calculation unit 62. Q _{fnl_cord} is a fuel injection amount (excluding post-injection) before application of learning corrected MAF tracking control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, and _{Maf_corr} is a MAF correction coefficient described later. Show.

The target injection amount Q _{SPR_Trgt} calculated by the injection amount target value calculation unit 66 is transmitted as an injection instruction signal to the exhaust pipe injector 34 or each injector 11 when a SOx purge rich flag F _SPR described later is turned on.

As described above, in this embodiment, the target injection amount Q _{SPR_Trgt} is set based on the air excess rate target value λ _{SPR_Trgt} read from the second target air excess rate setting map 65 and the fuel injection amount of each injector 11. It has become. Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. The exhaust can be effectively reduced to a desired excess air ratio required for SOx purge rich control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each injector 11, the target injection amount Q _{SPR_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. Etc. can be effectively eliminated.

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

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

The interval T _{F_INT} is set by feedback control when the SOx purge rich flag F _{SPR at} which the catalyst temperature is highest is switched from on to off. Specifically, the proportional control for changing the input signal in proportion to the deviation ΔT between the target catalyst temperature and the estimated catalyst temperature when the SOx purge rich flag _FSPR is turned off, and the time integral value of the deviation ΔT are proportional. This is processed by PID control constituted by integral control for changing the input signal and differential control for changing the input signal in proportion to the time differential value of the deviation ΔT. The target catalyst temperature is set at a temperature at which SOx can be removed from the NOx storage reduction catalyst 32. The estimated catalyst temperature is, for example, the inlet temperature of the oxidation catalyst 31 detected by the first exhaust temperature sensor 43, and the oxidation catalyst 31. It may be estimated based on the exothermic reaction in the NOx occlusion reduction type catalyst 32 or 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 forced regeneration is turned on, SOx purge rich flag _{F SPR} also turned on, further previous SOx purge control The interval _{TF_INT} that is sometimes feedback calculated is also reset. That is, for the first time immediately after the forced filter regeneration, exhaust pipe injection or 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. 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 fuel gas consumption is promptly shifted to the SOx purge control without lowering the exhaust temperature that has been raised by the forced filter regeneration. Can be reduced.

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

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

[Determining completion of SOx purge control]
SOx purge control, (1) SOx purge flag F from on the _SP injection quantity of the exhaust pipe injection or post injection accumulated, when the amount of the cumulative injected has reached the predetermined upper limit threshold amount, of (2) SOx purge control When the elapsed time counted from the start reaches a predetermined upper threshold time, (3) calculation is performed based on a predetermined model formula including the operating state of the engine 10 and the sensor value of the NOx / lambda sensor 45 as input signals. If any of the conditions in the case of SOx adsorption amount of NOx occlusion-reduction catalyst 32 has decreased to a predetermined threshold value indicating a SOx removal success is established, SOx purge flag F _SP is terminated by turning off the (time t ₄ in FIG. 2 , reference time _{t n} in FIG. 5).

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

[NOx purge control]
The NOx purge control unit 70 is an example of the catalyst regeneration means of the present invention. The NOx stored in the NOx occlusion reduction type catalyst 32 is made harmless by reduction purification and released by making the exhaust atmosphere rich and reducing NOx. Control for recovering the NOx storage capacity of the storage reduction catalyst 32 (hereinafter, this control is referred to as NOx purge control) is executed.

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

  In the present embodiment, the enrichment by the NOx purge control is performed on the lean side of the excess air ratio from the stoichiometric air-fuel ratio equivalent value (about 1.0) from the time of steady operation (for example, about 1.5) by the air system control. NOx purge lean control for reducing to 3 target excess air ratio (for example, about 1.3) and injection system control to reduce the excess air ratio from the third target excess air ratio to the fourth target excess air ratio on the rich side (for example, about 0) .9) and NOx purge rich control for reducing the pressure to 9). The details of the NOx purge lean control and the NOx purge rich control will be described below.

[NOF purge lean control MAF target value setting]
FIG. 7 is a block diagram showing a process for setting the MAF target value MAF _{NPL_Trgt} during the NOx purge lean control. The third target excess air ratio setting map 71 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge lean control corresponding to the engine speed Ne and the accelerator opening Q. The excess air ratio target value λ _{NPL_Trgt} (third excess air ratio) is set in advance based on experiments or the like.

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

MAF _{NPL_Trgt} = λ _{NPL_Trgt} × Q _{fnl_corrd} × Ro _Fuel × AFR _sto / _{Maf_corr} (3)
In Equation (3), Q _{fnl_cord} represents a learning-corrected fuel injection amount (excluding post-injection) described later, Ro _Fuel represents fuel specific gravity, AFR _sto represents a theoretical air-fuel ratio, and _{Maf_corr} represents a MAF correction coefficient described later. Yes.

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

The valve control unit 74 is an example of an air system control unit of the present invention, and _closes the intake throttle valve 16 so that the actual MAF value MAF _Act input from the MAF sensor 40 becomes the MAF target ramp value MAF _{NPL_Trgt_Ramp.} At the same time, feedback control is performed to open the EGR valve 24 to the open side.

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

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each injector 11, the MAF target value MAF _{NPL_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. Etc. can be effectively eliminated.

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

[NOx purge rich control fuel injection amount setting]
FIG. 8 is a block diagram showing processing for setting the target injection amount Q _{NPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in NOx purge rich control. The fourth target excess air ratio setting map 75 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge rich control corresponding to the engine speed Ne and the accelerator opening Q. The air excess rate target value λ _{NPR_Trgt} (fourth target air excess rate) is set in advance based on experiments or the like.

First, the excess air ratio target value λ _{NPR_Trgt} at the time of NOx purge rich control is read from the fourth target excess air ratio setting map 75 using the engine speed Ne and the accelerator opening Q as input signals, and the injection amount target value calculation section 76 is performed. Is input. Further, the injection amount target value calculation unit 76 calculates the target injection amount Q _{NPR_Trgt} at the time of NOx purge rich control based on the following formula (4).

Q _{NPR_Trgt} = MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Target} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (4)
In Expression (4), MAF _{NPL_Trgt} is a NOx purge lean MAF target value, and is input from the MAF target value calculation unit 72 described above. Q _{fnl_cord} is a fuel injection amount (excluding post-injection) before application of learning corrected MAF tracking control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, and _{Maf_corr} is a MAF correction coefficient described later. Show.

The target injection amount Q _{NPR_Trgt} calculated by the injection amount target value calculation unit 76 is transmitted as an injection instruction signal to the exhaust pipe injector 34 or each injector 11 when the NOx purge flag F _NP is turned on (time t in FIG. 6). ₁ ). The transmission of this injection instruction signal is continued until the NOx purge flag F _NP is turned off (time t _{2 in} FIG. 6) by the end determination of NOx purge control described later.

As described above, in this embodiment, the target injection amount Q _{NPR_Trgt} is set based on the air excess rate target value λ _{NPR_Trgt} read from the fourth target air excess rate setting map 75 and the fuel injection amount of each injector 11. It has become. Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge rich control.

_Further, by using the fuel injection amount Q _{fnl_corrd} after learning correction as the fuel injection amount of each injector 11, the target injection amount Q _{NPR_Trgt} can be set by feedforward control, and the aging deterioration and characteristic change of each injector 11 can be _achieved. Etc. can be effectively eliminated.

[Determining completion of NOx purge control]
In the NOx purge control, (1) when the NOx purge flag F _NP is turned on, the amount of exhaust pipe injection or post injection is accumulated, and when this cumulative injection amount reaches a predetermined upper limit threshold amount, (2) NOx purge control When the elapsed time counted from the start reaches a predetermined upper threshold time, (3) calculation is performed based on a predetermined model formula including the operating state of the engine 10 and the sensor value of the NOx / lambda sensor 45 as input signals. If any of the conditions in the case where the NOx occlusion amount of the NOx occlusion reduction type catalyst 32 decreases to a predetermined threshold value indicating successful removal of NOx is satisfied, the NOx purge flag F _NP is turned off and the process ends (time t _{2 in} FIG. 6). reference).

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

[Catalyst heat retention control (MAF throttle control)]
FIG. 9 is a block diagram showing a catalyst heat retention control process by the catalyst heat retention control unit 52.

  The idle operation detection unit 53 detects whether or not the engine 10 is in an idle operation state based on sensor values input from the various sensors 41, 42, and 47.

  The motoring detection unit 54 detects whether or not the engine 10 is in a motoring state in which the fuel injection of the injector 11 is stopped at a predetermined rotation speed or higher based on sensor values input from the various sensors 41, 42 and 47. To do.

  The MAF throttle control unit 57 is the catalyst heat retention control means of the present invention, and throttles the opening of the intake throttle valve 16 (or at least one of the exhaust throttle valves) to the closed side when the following conditions are satisfied. By reducing the amount of intake air, catalyst heat retention control (hereinafter also referred to as MAF throttling control) that suppresses the inflow of low-temperature exhaust gas to the catalysts 31 and 32 is executed. (1) When the idle operation state of the engine 10 is detected by the idle operation detection unit 53. (2) When the motoring detection unit 54 detects the motoring state of the engine 10. Even when the condition (1) for detecting the idle operation state of the engine 10 is satisfied, the execution of the MAF throttle control is prohibited when the SOx purge control is performed.

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

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

To avoid this phenomenon, MAF tracking control unit 80, as shown in the flow chart of FIG. _10-14, advancing or retarding the injection timing in accordance with the MAF changes, MAF follow-up control to increase or decrease correcting the injection amount Execute.

  First, the MAF follow-up control during the switching period from the exhaust lean state to the exhaust rich state by the SOx purge control will be described with reference to FIG.

In step S100A, the SOx purge flag _{F SP} is turned on, in step S110A, the engine 10 whether the motoring state is determined. When it is determined that the motoring state is not established (No), the process proceeds to step S120A, and time measurement by a timer is started to measure the elapsed time of MAF tracking control. On the other hand, when it is determined that the motoring state is set (Yes), the process proceeds to step S190A to perform the prohibiting process by the MAF follow-up control prohibiting unit 81 (shown only in FIG. 1).

  When the engine 10 is in a motoring state, the air system is switched to open loop control (MAF throttle control). Since the MAF follow-up control controls the advance angle of the injection timing and the increase in the injection amount according to the rate of change of the intake air amount, there is a problem that accurate control cannot be performed when the air system becomes open loop control.

Therefore, if the MAF follow-up control prohibition unit 81 (see FIG. 1) determines that the motoring state is set in step S110A, the MAF follow-up control prohibition unit 81 proceeds to step S190A, and the MAF follow-up coefficient Comp ₁ , set in step S150A described later in detail. by the force the ₂ "1" to prohibit the implementation of MAF follow-up control. As a result, it is possible to effectively prevent instability of combustion of the engine 10 and deterioration of drivability caused by inaccurate MAF tracking control.

In step S120A, subtraction when measurement of the elapsed time of MAF following control is started, in step S130A, the MAF target value _{MAF L_Trgt} after switching before switching from MAF target value _{MAF SPL_Trgt} of (rich state) (lean state) Thus, the MAF target value change amount ΔMAF _Trgt (= MAF _{SPL_Trgt} −MAF _{L_Trgt} ) before and after switching is calculated.

In step S140A, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{L_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{L_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S150A, in accordance with the current actual MAF change rate ΔMAF _Ratio , a coefficient for advancing or retarding the injection timing of each injector 11 (hereinafter referred to as an injection timing tracking coefficient Comp ₁ ) and the injection amount of each injector 11 Is set to increase or decrease (hereinafter referred to as injection amount tracking coefficient Comp ₂ ). More specifically, the storage unit (not shown) of the ECU 50 stores an injection timing follow-up coefficient setting map M1 that defines the relationship between the actual MAF change rate MAF _Ratio and the injection timing follow-up coefficient Comp ₁ created in advance by experiments and the like, and the actual MAF change. An injection amount follow-up coefficient setting map M2 that defines the relationship between the rate MAF _Ratio and the injection amount follow-up coefficient Comp ₂ is stored. The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are set by reading values corresponding to the actual MAF change rate ΔMAF _Ratio calculated in step S130A from these maps M1 and M2.

In step S160A, the injection timing of each injector 11 is advanced by the amount obtained by multiplying the target advance amount by the injection timing follow-up coefficient Comp _1, and each time by the amount obtained by multiplying the target injection increase amount by the injection amount follow-up coefficient Comp _2. The injector 11 also increases the fuel injection amount.

Thereafter, in step S170A, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{SPL_Trgt} after switching (rich state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{SPL_Trgt} (No), the process returns to step S140A via step S180A. That is, by repeating the processing of steps S140A to S160A until the actual MAF value MAF _Act becomes the MAF target value MAF _{SPL_Trgt} , the advance angle of the injection timing corresponding to the actual MAF change rate MAF _Ratio that changes every moment, and the injection The increase in quantity continues. Details of the processing in step S180A will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{SPL_Trgt} in the determination in step S170A (Yes), this control ends.

In step S180A, it is determined whether or not the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max .

As shown in FIG. 14A, when shifting from the lean state to the rich state, the actual MAF value MAF _Ref cannot catch up with the MAF target value MAF _{L-R_Trgt} during the transition period due to the influence of valve control delay, etc. The MAF value MAF _Ref may be maintained in a state lower than the MAF target value MAF _{L-R_Trgt} (see times t _{1 to} t ₂ ). If MAF follow-up control is continued in such a state, particularly during idle operation, the actual injection amount is maintained in a small state, and acceleration of the vehicle is hindered.

In this embodiment, in order to avoid such a phenomenon, when it is determined in step S180A that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, the actual MAF value MAF _Ref continues for a predetermined time. If it has not changed more than the predetermined value, the process proceeds to step S190A, and the injection timing tracking coefficient Comp ₁ and the injection amount tracking coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control at the start of SOx purge is forcibly stopped, and torque fluctuation and drivability deterioration can be effectively prevented.

  Next, the MAF follow-up control during the switching period from the exhaust lean state to the exhaust rich state by the NOx purge control will be described based on FIG.

When the NOx purge flag F _NP is turned on in step S100B, it is determined in step S110B whether or not the engine 10 is in a motoring state or an idle operation state. When it is determined that neither the motoring state nor the idle operation state is present (No), the process proceeds to step S120B, and the timer is started to measure the elapsed time of the MAF follow-up control. On the other hand, if it is determined that the motoring state or the idling operation state is present (Yes), the process proceeds to step S190B to perform the prohibiting process by the MAF follow-up control prohibiting unit 81 (FIG. 1).

  When the engine 10 is in a motoring state or an idle operation state, the air system is switched to open loop control (MAF throttle control). Since the MAF follow-up control controls the advance angle of the injection timing and the increase in the injection amount according to the rate of change of the intake air amount, there is a problem that accurate control cannot be performed when the air system becomes open loop control.

Therefore, if the MAF follow-up control prohibition unit 81 (see FIG. 1) determines that the motoring state or the idle operation state is determined in step S110B, the process proceeds to step S190B, and the details are set in step S150B described later. By forcibly setting the MAF tracking coefficients Comp ₁ and ₂ to “1”, the execution of the MAF tracking control is prohibited. As a result, it is possible to effectively prevent instability of combustion of the engine 10 and deterioration of drivability caused by inaccurate MAF tracking control.

In step S120b, subtraction when measurement of the elapsed time of MAF following control is started, in step S130b, the MAF target value _{MAF L_Trgt} after switching before switching from MAF target value _{MAF NPL_Trgt} of (rich state) (lean state) Thus, the MAF target value change amount ΔMAF _Trgt (= MAF _{NPL_Trgt} −MAF _{L_Trgt} ) before and after switching is calculated.

In step S140B, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{L_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{L_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S150B, the values corresponding to the actual MAF change rate ΔMAF _Ratio calculated in step S130B are read from the maps M1 and M2 to set the injection timing tracking coefficient Comp ₁ and the injection amount tracking coefficient Comp ₂ .

In step S160B, the injection timing of each injector 11 is advanced by an amount obtained by multiplying the target advance amount by the injection timing follow-up coefficient Comp _1, and at the same time each amount obtained by multiplying the target injection increase amount by the injection amount follow-up coefficient Comp _2. The injector 11 also increases the fuel injection amount.

Thereafter, in step S170B, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{NPL_Trgt} after switching (rich state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{NPL_Trgt} (No), the process returns to step S140B via step S180B. That is, by repeating the processing of steps S140B to S160B until the actual MAF value MAF _Act becomes the MAF target value MAF _{NPL_Trgt} , the advance angle of the injection timing corresponding to the actual MAF change rate MAF _Ratio that changes every moment, and the injection The increase in quantity continues. Details of the processing in step S180B will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{NPL_Trgt} in the determination in step S170B (Yes), this control ends.

In step S180B, it is determined whether or not the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max . If it is determined in step S180B that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, if the actual MAF value MAF _Ref has not changed more than the predetermined value for a predetermined time, step S190B The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. As a result, MAF follow-up control at the start of NOx purge is forcibly stopped, and torque fluctuation and drivability deterioration can be effectively prevented.

  Next, MAF follow-up control at the time of switching from the exhaust rich state to the exhaust lean state by the SOx purge control will be described based on FIG.

In step S200A, the SOx purge flag _{F SP} is turned off, at step S210, the engine 10 whether the motoring state is determined. If it is determined that the motoring state is not established (No), the process proceeds to step S220A, and the timer is started to measure the elapsed time of the MAF follow-up control. On the other hand, if it is determined that the motoring state is set (Yes), the process proceeds to step S290A to perform the prohibiting process by the MAF follow-up control prohibiting unit 81 (see FIG. 1).

  As described above, since the air system is switched to open loop control in the motoring state, the MAF follow-up control for controlling the retard of the injection timing and the decrease in the injection amount according to the change rate of the intake air amount is accurately performed. There is a problem that can not be done.

Therefore, if the MAF follow-up control prohibition unit 81 (see FIG. 1) determines that the motoring state is set in step S210A, the process proceeds to step S290A to forcibly use the MAF follow-up coefficients Comp ₁ and ₂ set in step S250A. By setting “1” to “1”, execution of MAF tracking control is prohibited. As a result, it is possible to effectively prevent instability of combustion of the engine 10 and deterioration of drivability caused by inaccurate MAF tracking control.

In step S220A, subtraction when measurement of the elapsed time of MAF following control is started, in step S230A, the MAF target value _{MAF SPL_Trgt} after switching before switching from MAF target value _{MAF L_Trgt} of (lean state) (rich state) Thus, the MAF target value change amount ΔMAF _Trgt (= MAF _{L_Trgt} −MAF _{SPL_Trgt} ) before and after switching is calculated.

In step S240A, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{SPL_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{SPL_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S250A, a value corresponding to the actual MAF change rate ΔMAF _Ratio is read from the injection timing follow-up coefficient setting map M1 as an injection timing follow-up coefficient Comp ₁ , and from the injection amount follow-up coefficient setting map M2, it corresponds to the actual MAF change rate ΔMAF _Ratio . value is read as the injection quantity coefficient of following Comp _2.

In step S260A, the injection timing of each injector 11 is retarded by the target delay amount multiplied by the injection timing follow-up coefficient Comp ₁ , and the target injection decrease amount is multiplied by the injection amount follow-up coefficient Comp _2. The fuel injection amount of the injector 11 is also reduced.

Thereafter, in step S270A, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{L_Trgt} after switching (lean state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{L_Trgt} (No), the process returns to step S240A via step S280A. That is, by repeating the processing of steps S240A to S260A until the actual MAF value MAF _Act becomes the MAF target value MAF _{L_Trgt} , the delay of the injection timing corresponding to the actual MAF change rate MAF _Ratio that changes every moment, and the injection The amount continues to decrease. Details of the processing in step S280A will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{L_Trgt} in the determination in step S270A (Yes), this control ends.

In step S280A, it is determined whether or not the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max .

As shown in FIG. 14B, when shifting from the lean state to the rich state, the actual MAF value MAF _Ref cannot catch up with the MAF target value MAF _{LR_Trgt} during the transition period due to the influence of valve control delay or the like. The MAF value MAF _Ref may remain higher than the MAF target value MAF _{L-R_Trgt} (see times t _{1 to} t ₂ ). If MAF follow-up control is continued in such a state, the actual fuel injection amount becomes larger than the target injection amount, which may cause torque fluctuation, drivability deterioration, and the like.

In this embodiment, in order to avoid such a phenomenon, when it is determined in step S280A that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, the actual MAF value MAF _Ref continues for a predetermined time. If it has not changed more than the predetermined value, the process proceeds to step S290A, and the injection timing tracking coefficient Comp ₁ and the injection amount tracking coefficient Comp ₂ are forcibly set to “1”. As a result, the MAF follow-up control at the end of the SOx purge is forcibly stopped, and torque fluctuation and drivability deterioration can be effectively prevented.

  Next, MAF follow-up control at the time of switching from the exhaust rich state to the exhaust lean state by NOx purge control will be described based on FIG.

When the NOx purge flag F _NP is turned off in step S200B, it is determined in step S210B whether the engine 10 is in a motoring state or an idle operation state. If it is determined that neither the motoring state nor the idle operation state is present (No), the process proceeds to step S220B, and time measurement by a timer is started to measure the elapsed time of MAF follow-up control. On the other hand, when it is determined that the motoring state or the idling operation state is present (Yes), the process proceeds to step S290B to perform the prohibiting process by the MAF follow-up control prohibiting unit 81 (see FIG. 1).

  As described above, in the motoring state or the idling operation state, the air system is switched to the open loop control, so the MAF that controls the retard of the injection timing and the decrease in the injection amount according to the change rate of the intake air amount. There is a problem that tracking control cannot be performed accurately.

Therefore, if the MAF follow-up control prohibition unit 81 (see FIG. 1) determines that the motoring state or the idle operation state is determined in step S210B, the process proceeds to step S290B, and the MAF follow-up coefficient Comp set in step S250B. By forcing ₁ and ₂ to “1”, execution of MAF tracking control is prohibited. As a result, it is possible to effectively prevent instability of combustion of the engine 10 and deterioration of drivability caused by inaccurate MAF tracking control.

In step S220b, subtraction when measurement of the elapsed time of MAF following control is started, in step S230B, the MAF target value _{MAF NPL_Trgt} after switching before switching from MAF target value _{MAF L_Trgt} of (lean state) (rich state) Thus, the MAF target value change amount ΔMAF _Trgt (= MAF _{L_Trgt} −MAF _{NPL_Trgt} ) before and after switching is calculated.

In step S240B, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{NPL_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{NPL_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S250B, the value corresponding to the actual MAF change rate ΔMAF _Ratio is read from the injection timing tracking coefficient setting map M1 as the injection timing tracking coefficient Comp ₁ , and also corresponds to the actual MAF change rate ΔMAF _Ratio from the injection amount tracking coefficient setting map M2. value is read as the injection quantity coefficient of following Comp _2.

In step S260B, the injection timing of each injector 11 is retarded by the amount obtained by multiplying the target retard amount by the injection timing follow-up coefficient Comp _1, and the amount obtained by multiplying the target injection decrease amount by the injection amount follow-up coefficient Comp ₂ is set. The fuel injection amount of the injector 11 is also reduced.

Thereafter, in step S270B, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{L_Trgt} after switching (lean state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{L_Trgt} (No), the process returns to step S240B via step S280B. That is, by repeating the processing of steps S240B to S260B until the actual MAF value MAF _Act becomes the MAF target value MAF _{L_Trgt} , the delay of the injection timing corresponding to the actual MAF change rate MAF _Ratio that changes from moment to moment, and the injection The amount continues to decrease. Details of the processing in step S280B will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{L_Trgt} in the determination in step S270B (Yes), this control ends.

In step S280B, it is determined whether or not the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max . If it is determined in step S280B that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, if the actual MAF value MAF _Ref has not changed more than the predetermined value for a predetermined time, step S290B The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. As a result, the MAF follow-up control at the end of the NOx purge is forcibly stopped, and torque fluctuation and drivability deterioration can be effectively prevented.

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

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

In step S310, an error Δλ obtained by subtracting the actual lambda value λ _Act detected by the NOx / lambda sensor 45 from the estimated lambda value λ _Est is multiplied by the learning value gain K ₁ and the correction sensitivity coefficient K ₂ to thereby obtain the learning value F _CorrAdpt is calculated (F _CorrAdpt = (λ _Est −λ _Act ) × K ₁ × K ₂ ). The estimated lambda value λ _Est is estimated and calculated from the operating state of the engine 10 according to the engine speed Ne and the accelerator opening Q. Further, the correction sensitivity coefficient _{K 2} is read the actual lambda value lambda _Act detected by the NOx / lambda sensor 45 from the correction sensitivity coefficient map 91A shown in FIG. 15 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 each injector 11 with the learning value corresponding to the error Δλ between the estimated lambda value λ _Est and the actual lambda value λ _Act , the aging deterioration, characteristic change, individual difference of each injector 11 is corrected. It is possible to effectively eliminate such variations.

[MAF correction coefficient]
MAF correction coefficient calculating unit 95 MAF is used to set the MAF target value _{MAF SPL_Trgt} and the target injection amount _{Q SPR_Trgt} during SOx purge control and the setting of the MAF target value _{MAF NPL_Trgt} and the target injection amount _{Q NPR_Trgt} during NOx purge control A correction coefficient _{Maf_corr} is calculated.

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

FIG. 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.

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

Claims (5)

A NOx reduction catalyst provided in an exhaust system of an internal combustion engine for reducing and purifying NOx in the exhaust;
Intake air amount acquisition means for acquiring the intake air amount of the internal combustion engine;
Catalyst regeneration that restores the NOx purification ability of the NOx reduction catalyst by switching the exhaust 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 catalyst regeneration means for carrying out the treatment;
Acquired by the intake air amount acquisition means in at least one of the switching period from the lean state to the rich state for starting the catalyst regeneration process and the switching period from the rich state to the lean state for ending the catalyst regeneration process. Follow-up control means for performing follow-up control to change at least one of the fuel injection timing and the fuel injection amount of the internal combustion engine according to the intake air amount;
An exhaust purification system comprising: prohibiting means for prohibiting execution of the follow-up control when the internal combustion engine is in a motoring state that stops fuel injection when the follow-up control is performed. The catalyst regeneration means performs a NOx purge process for reducing and purifying NOx stored in the NOx reduction catalyst as the catalyst regeneration process,
The exhaust purification system according to claim 1, wherein the prohibiting unit prohibits the execution of the follow-up control even when the internal combustion engine is in an idle operation state when the follow-up control is performed. 2. The follow-up control unit stops the follow-up control when the intake air amount acquired by the intake air amount acquisition unit does not change more than a predetermined amount continuously for a predetermined time during the execution of the follow-up control. Or the exhaust gas purification system of 2. The follow-up control means, as the follow-up control, changes the intake air amount acquired by the intake air amount acquisition means during the switching period from the lean state to the rich state where the catalyst regeneration process is started. The exhaust gas purification system according to any one of claims 1 to 3, wherein the fuel injection timing of the engine is advanced and the fuel injection amount of the internal combustion engine is increased. The follow-up control means, as the follow-up control, changes the intake air amount acquired by the intake air amount acquisition means during the switching period from the rich state to the lean state where the catalyst regeneration process is finished, according to the change in the intake air amount. The exhaust gas purification system according to any one of claims 1 to 4, wherein a fuel injection timing is retarded and a fuel injection amount of the internal combustion engine is decreased.

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