JP6515577B2 - Exhaust purification system - Google Patents

Description

  The present invention relates to an exhaust gas purification system.

  Conventionally, NOx storage reduction 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 storage reduction type catalyst stores NOx contained in the exhaust when the exhaust atmosphere is lean atmosphere, and harmless by reducing and purifying NOx stored by the hydrocarbon contained in the exhaust when the exhaust atmosphere is rich atmosphere And release. For this reason, when the NOx storage amount of the catalyst reaches a predetermined amount, it is necessary to periodically perform so-called NOx purge in which the exhaust is made rich by post injection or exhaust pipe injection in order to restore the NOx storage capacity. For example, refer to Patent Document 1).

  Further, sulfur oxides (hereinafter referred to as SOx) contained in the exhaust gas are also stored in the NOx storage reduction type catalyst. When the SOx storage amount increases, there is a problem of reducing the NOx purification capacity of the NOx storage reduction catalyst. Therefore, when the SOx storage amount reaches a predetermined amount, the upstream oxidation catalyst is left unburned by the post injection or exhaust pipe injection in order to desorb the SOx from the NOx storage reduction type catalyst and recover from S poisoning. It is necessary to periodically perform a so-called SOx purge to supply the exhaust gas to raise the exhaust temperature to the SOx separation temperature (see, for example, Patent Document 2).

JP, 2008-202425, A JP, 2009-47086, A

  Generally, in this type of device, when performing catalyst regeneration processing such as NOx purge, feedback control of the exhaust pipe injection amount and the post injection amount is performed based on the deviation between the target temperature and the catalyst temperature. For this reason, if the catalyst temperature estimation accuracy at the time of the catalyst regeneration process can not be ensured, controllability of exhaust pipe injection and post injection is deteriorated, and there is a problem of causing excessive temperature rise of the catalyst and deterioration of fuel efficiency.

  The disclosed system aims to effectively improve the catalyst temperature estimation accuracy during the catalyst regeneration process.

  The disclosed system is provided with an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine to reduce and purify NOx in the exhaust, and a reduction exhaust purification catalyst for reducing NOx stored in the NOx storage reduction catalyst by making exhaust gas rich. Catalyst regeneration means for executing a catalyst regeneration process, and first emission amount storage means for acquiring and storing in advance at least one of the amount of hydrocarbon and the amount of carbon monoxide exhausted from the internal combustion engine at the time of execution of the catalyst regeneration process And the amount of heat generated by the hydrocarbon and the amount of carbon monoxide generated by the NOx storage reduction catalyst based on at least one of the amount of hydrocarbon and the amount of carbon monoxide read from the first emission storage means at the time of execution of the catalyst regeneration process. A first calorific value estimating means for estimating at least one of the amounts; and a small amount of hydrocarbon calorific value and carbon monoxide calorific value estimated by the first calorific value estimating means It is based on one, and a first catalyst temperature estimating means for estimating the catalyst temperature of the NOx storage reduction catalyst during the execution of the catalyst regeneration process.

  According to the disclosed system, it is possible to effectively improve the catalyst temperature estimation accuracy during the catalyst regeneration process.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram which shows the exhaust gas purification system which concerns on this embodiment. It is a timing chart figure explaining SOx purge control concerning this embodiment. It is a block diagram which shows the setting process of MAF target value at the time of SOx purge lean control which concerns on this embodiment. It is a block diagram showing setting processing of a target injection quantity at the time of SOx purge rich control concerning 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. FIG. 6 is a block diagram showing a setting process of the MAF target value at the time of NOx purge lean control according to the present embodiment. It is a block diagram showing setting processing of a target injection quantity at the time of NOx purge rich control concerning this embodiment. It is a block diagram showing processing of catalyst heat retention control concerning this embodiment. It is a block diagram which shows the catalyst temperature estimation process which concerns on this embodiment. It is a block diagram which shows the process of injection quantity learning correction | amendment of the injector which concerns on this embodiment. It is a flow figure explaining operation processing of a learning amendment coefficient concerning 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 gas purification system according to an embodiment of the present invention will be described based on the attached 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 for directly injecting high-pressure fuel stored in a common rail (not shown) into each cylinder. There is. The fuel injection amount and fuel injection timing of each of the in-cylinder injectors 11 are controlled in accordance with an instruction signal input from an electronic control unit (hereinafter referred to as an ECU) 50.

  An intake passage 12 for introducing fresh air is connected to an intake manifold 10A of the engine 10, and an exhaust passage 13 for leading the exhaust gas to the outside is connected to an exhaust manifold 10B. In the intake passage 12, sequentially from the intake upstream side, an air cleaner 14, an intake air amount sensor (hereinafter referred to as MAF sensor) 40, an intake temperature sensor 48, a compressor 20A of the variable displacement supercharger 20, an intercooler 15, an intake throttle valve 16 mag is provided. In the exhaust passage 13, a turbine 20B of the variable displacement turbocharger 20, an exhaust brake valve 17 which constitutes a part of an exhaust brake device, an exhaust post-treatment device 30, and the like are provided in this order from the exhaust upstream side. In FIG. 1, reference numeral 41 denotes an engine speed sensor, 42 denotes an accelerator opening sensor, 46 denotes a boost pressure sensor, 47 denotes an outside air temperature sensor, and 49 denotes a vehicle speed sensor.

  The EGR device 21 includes an EGR passage 22 connecting the exhaust manifold 10B and the intake manifold 10A, an EGR cooler 23 for cooling EGR gas, and an EGR valve 24 for adjusting the amount of EGR.

  The exhaust post-treatment device 30 is configured by arranging an oxidation catalyst 31, a NOx storage 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. Further, an exhaust injector 34 for injecting unburned fuel (mainly HC) into the exhaust passage 13 according to an instruction signal input from the ECU 50 is provided in the exhaust passage 13 on the upstream side of the oxidation catalyst 31. There is.

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

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

  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, and alternately sealing upstream and downstream sides of these cells. . The filter 33 collects the PM in the exhaust gas on the pores and surfaces of the partition walls, and when the estimated PM deposition amount reaches a predetermined amount, so-called filter forced regeneration is performed to burn and remove this. The filter forced regeneration is performed by supplying unburned fuel to the oxidation catalyst 31 on the upstream side by exhaust pipe injection or post injection, and raising the temperature of the exhaust flowing into the filter 33 to the PM combustion temperature.

  The first exhaust temperature sensor 43 is provided upstream of the oxidation catalyst 31 and detects the temperature of exhaust 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 temperature of the exhaust flowing into the NOx storage reduction catalyst 32. The NOx / lambda sensor 45 is provided downstream of the filter 33, and detects the NOx value and the lambda value (hereinafter also referred to as the excess air ratio) of the exhaust 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, a ROM, a RAM, an input port, an output port, and the like. In order to perform these various controls, sensor values of the sensors 40 to 48 are input to the ECU 50. Further, the ECU 50 includes the filter regeneration control unit 51, the SOx purge control unit 60, the NOx purge control unit 70, the catalyst heat retention control unit 52, the catalyst temperature estimation unit 80, the MAF follow control unit 98, and the injection amount learning The correction unit 90 and the MAF correction coefficient calculation unit 95 are included as a part of functional elements. Although each of these functional elements is described as being included in the ECU 50 which is an integral hardware, any part of these may be provided in a separate hardware.

[Filter regeneration control]
The filter regeneration control unit 51 estimates the PM deposition amount of the filter 33 from the traveling distance of the vehicle or the differential pressure across the filter detected by a differential pressure sensor (not shown), and the PM deposition estimated amount exceeds a predetermined upper threshold. Turn on forced regeneration flag _{F DPF} (see time _{t 1} in FIG. 2). When the forced regeneration flag F _DPF is turned on, an instruction signal for performing exhaust pipe injection to the exhaust injector 34 is transmitted, or an instruction signal for performing post injection to each in-cylinder injector 11 is transmitted. The exhaust temperature is raised to the PM combustion temperature (eg, 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 from the start of filter forced regeneration (F _DPF = 1) or the upper limit accumulated injection amount.

  In the present embodiment, the fuel injection amount at the time of filter forced regeneration is feedback control based on either the oxidation catalyst temperature or the NOx catalyst temperature appropriately selected by the reference temperature selection unit 89 (see FIG. 10) described later in detail. It is supposed to be

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

FIG. 2 shows a timing chart of SOx purge control according to the present 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 becomes possible to efficiently shift to the SOx purge control from the state in which the exhaust gas temperature is 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 using the air system control to set the excess air ratio between steady operation (for example, about 1.5) to the lean side of the stoichiometric air fuel ratio equivalent value (about 1.0). 1 SOx purge lean control to reduce the target excess air ratio (for example, about 1.3), and the excess air ratio from the first target excess air ratio to the second target excess air ratio for rich side (for example, about 0) by injection system control .9) It is realized by using in combination with SOx purge rich control to reduce to .9). Hereinafter, the details of the SOx purge lean control and the SOx purge rich control will be described.

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

First, from the first target excess air ratio setting map 61, the excess air ratio target value λ _{SPL_Trgt} at the time of SOx purge lean control is read using the engine speed Ne and the accelerator opening Q as input signals, and the MAF target value calculation unit 62 It is input. Furthermore, the MAF target value calculation unit 62 calculates the MAF target value MAF _{SPL_Trgt} at the time of 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_corrd} is a learning-corrected fuel injection amount (except post injection) described later, Ro _Fuel is a fuel specific gravity, AFR _sto is a theoretical air fuel ratio, and Maf _{_ corr} is a MAF correction coefficient described later. There is.

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 lamp processing unit 63 reads a lamp coefficient from each of the lamp coefficient maps 63A, B using the engine rotational speed Ne and the accelerator opening Q as input signals, and the MAF target lamp value MAF _{SPL_Trgt_Ramp} to which the lamp coefficient is added as a valve control unit 64. Enter in

The valve control unit 64 is a _feedback that throttles the intake throttle valve 16 to the closing side and opens the EGR valve 24 to the opening side so that the actual MAF value MAF _Act input from the MAF sensor 40 becomes the MAF target lamp value MAF _{SPL_Trgt_Ramp.} Execute control.

As described above, 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 air excess ratio setting map 61 and the fuel injection amount of each in-cylinder injector 11 The air system operation is feedback controlled based on the MAF target value MAF _{SPL_Trgt} . As a result, the lambda sensor is not provided 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 to the desired excess air 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 in-cylinder injector 11, it becomes possible to set the MAF target value MAF _{SPL_Trgt} by feed forward control, and aging of each in-cylinder injector 11 The effects of deterioration, characteristic change, individual differences and the like can be effectively eliminated.

In addition, by adding a ramp coefficient set according to the operating state of the engine 10 to the MAF target value MAF _{SPL_Trgt} , the engine 10 misfires due to a rapid change in the amount of intake air, deterioration of drivability due to torque fluctuation, etc. It can be effectively prevented.

[Set fuel injection amount for SOx purge rich control]
FIG. 4 is a block diagram showing processing for setting a target injection amount Q _{SPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in the SOx purge rich control. The second target excess air ratio setting map 65 is a map that is referred to based on the engine rotational speed Ne and the accelerator opening degree Q, and at the time of SOx purge rich control corresponding to the engine rotational speed Ne and the accelerator opening degree Q. The excess air ratio target value λ _{SPR_Trgt} (second target excess air ratio) is set in advance based on experiments and 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 with the engine speed Ne and the accelerator opening Q as input signals, and the injection amount target value calculation unit Input to 66 Further, in the injection amount target value calculation unit 66, the target injection amount Q _{SPR_Trgt} at the time of the SOx purge rich control is calculated 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 Equation (2), MAF _{SPL_Trgt} is the MAF target value at the time of SOx purge _{lean, and} is input from the above-described MAF target value calculation unit 62. Also, Q _{fnl_corrd} is the fuel injection amount before application of the learning corrected MAF (except for post injection), Ro _Fuel is the fuel specific gravity, AFR _sto is the theoretical air fuel ratio, and Maf _{_ corr} is the MAF correction coefficient described later. It shows.

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 injector 34 or each in-cylinder injector 11 when an SOx purge rich flag F _SPR described later is turned on.

Thus, in the present embodiment, the target injection amount Q _{SPR_Trgt} is set based on the air excess ratio target value λ _{SPR_Trgt} read from the second target air excess ratio setting map 65 and the fuel injection amount of each in-cylinder injector 11 It is supposed to As a result, the lambda sensor is not provided 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 to the 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 in-cylinder injector 11, it becomes possible to set the target injection amount Q _{SPR_Trgt} by feed forward control, and aging of each in-cylinder injector 11 Effects such as deterioration and characteristic change can be effectively eliminated.

[Catalyst temperature adjustment control of SOx purge control]
Exhaust gas temperature flowing into the NOx occlusion-reduction catalyst 32 during the SOx purge control (hereinafter, referred to as catalyst temperature), as shown at time t ₂ ~t ₄ in FIG. 2, performing the exhaust pipe injection or post injection SOx The purge rich flag F _SPR is controlled by alternately switching on and off (rich and 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 injection period _{TF_INJ} ). On the other hand, when the SOx purge rich flag F _SPR 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 rotational speed Ne and the accelerator opening degree Q from an injection period setting map (not shown) created in advance by experiment or the like. In this injection time setting map, the injection period required to reliably reduce the excess air ratio of the exhaust determined in advance by experiments etc. to the second target excess air ratio is set according to the operating state of 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 becomes the highest is switched from on to off. Specifically, the proportional control in which the input signal is changed in proportion to the deviation ΔT between the catalyst target temperature and the catalyst estimated temperature when the SOx purge rich flag F _SPR is turned off, and the time integral value of the deviation ΔT Processing is performed by PID control configured of integral control that changes the input signal and differential control that changes the input signal in proportion to the time differential value of the deviation ΔT. The catalyst target temperature is set to a temperature at which SOx can be desorbed from the NOx storage reduction type catalyst 32, and the estimated catalyst temperature is an oxidation catalyst temperature appropriately selected by a reference temperature selection unit 89 (see FIG. 10) described later in detail. And the NOx catalyst temperature.

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 feedback calculated interval _{TF_INT} is also reset once. That is, the first immediately after the filter forced 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 SOx purge control is started from SOx purge rich control without performing SOx purge lean control, SOx purge control is promptly transferred without decreasing the exhaust temperature raised by filter forced regeneration, and the fuel consumption amount 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 _{2 to} t ₃ ). Furthermore, when the SOx purge rich flag F _SPR is turned on by the passage of the interval T _{F_INT_1} , the exhaust pipe injection or the post injection is executed again according to the injection period T _{F_INJ_2} (see time t _{3 to} t _{4 in} FIG. 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.

Thus, in the present embodiment, the injection period _{TF_INJ} for increasing the catalyst temperature and decreasing 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, An 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 SOx purge control within the desired temperature range required for the purge.

[Stop determination 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 If the elapsed time measured from the start reaches a predetermined upper limit threshold time, (3) Calculation is performed based on a predetermined model equation including the operating state of engine 10, the sensor value of NOx / lambda sensor 45, etc. 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 , Time t _{n in} FIG. 5).

  As described above, in the present embodiment, the fuel consumption amount is obtained when the SOx purge does not progress due to a decrease in the exhaust temperature or the like by providing the cumulative injection amount and the upper limit of the elapsed time as the SOx purge control termination condition. Can be effectively prevented.

[NOx purge control]
The NOx purge control unit 70 is an example of the catalyst regeneration means of the present invention, and makes the exhaust gas rich and detoxifies and releases NOx stored in the NOx storage reduction catalyst 32 by reduction purification. 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.

NOx purge flag F _NP starting the NOx purge control estimates the NOx emission amount per unit time from the operation state of the engine 10, the cumulative calculated estimated cumulative value ΣNOx is turned on exceeds a predetermined threshold value so ( reference time _{t 1} of FIG. 6). Alternatively, the NOx purification rate by the NOx storage reduction catalyst 32 is calculated from the NOx emission amount on the catalyst upstream side estimated from the operating state of the engine 10 and the NOx amount on the catalyst downstream side detected by the NOx / lambda sensor 45 , if the NOx purification rate becomes lower than a predetermined judgment threshold, NOx purge flag F _NP is turned on.

  In the present embodiment, the enrichment by NOx purge control is performed by using the air system control to set the excess air ratio to a side closer to the lean side than the theoretical air fuel ratio equivalent value (about 1.0) from the steady operation time (for example, about 1.5). 3 Reduce the excess air ratio from the third excess air ratio to the fourth excess air ratio rich from the third excess air ratio (for example, approximately 0) This is realized by using in combination with NOx purge rich control to reduce to 9). The details of the NOx purge lean control and the NOx purge rich control will be described below.

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

First, from the third target excess air ratio setting map 71, the excess air ratio target value λ _{NPL_Trgt} at the time of NOx purge lean control is read using the engine rotational speed Ne and the accelerator opening Q as input signals, and the MAF target value calculation unit 72 It is input. 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_corrd} is a learning-corrected fuel injection amount (except post injection) described later, Ro _Fuel is a fuel specific gravity, AFR _sto is a theoretical air fuel ratio, and _{Maf_corr} is a MAF correction coefficient described later. There is.

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

The valve control unit 74 is a _feedback that throttles the intake throttle valve 16 to the closing side and opens the EGR valve 24 to the opening side so that the actual MAF value MAF _Act input from the MAF sensor 40 becomes the MAF target lamp value MAF _{NPL_Trgt_Ramp.} Execute control.

As described above, in the present embodiment, the MAF target value MAF _{NPL_Trgt} is set based on the air excess ratio target value λ _{NPL_Trgt} read from the third target air excess ratio setting map 71 and the fuel injection amount of each in-cylinder injector 11 The feedback control of the air system operation is performed based on the MAF target value MAF _{NPL_Trgt} . As a result, the lambda sensor is not provided 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 to the 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 in-cylinder injector 11, it becomes possible to set the MAF target value MAF _{NPL_Trgt} by feed forward control, and aging of each in-cylinder injector 11 Effects such as deterioration and characteristic change can be effectively eliminated.

In addition, by adding a ramp coefficient set according to the operating state of the engine 10 to the MAF target value MAF _{NPL_Trgt} , the engine 10 misfires due to a rapid change in the amount of intake air, deterioration of drivability due to torque fluctuation, etc. It can be effectively prevented.

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

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

Q _{NPR_Trgt} = MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (4)
In Equation (4), MAF _{NPL_Trgt} is the NOx purge lean MAF target value, and is input from the above-described MAF target value calculation unit 72. Also, Q _{fnl_corrd} is the fuel injection amount before application of the learning corrected MAF (except for post injection), Ro _Fuel is the fuel specific gravity, AFR _sto is the theoretical air fuel ratio, and Maf _{_ corr} is the MAF correction coefficient described later. It shows.

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 injector 34 or each in-cylinder injector 11 when the NOx purge flag F _SP is turned on (time t in FIG. 6). ₁ ). Transmission of the injection instruction signal is continued until the NOx purge flag F _NP is turned off (time t ₂ in FIG. ₆₎ by the completion judgment of the NOx purge control described later.

Thus, in the present embodiment, the target injection amount Q _{NPR_Trgt} is set based on the air excess ratio target value λ _{NPR_Trgt} read from the fourth target air excess ratio setting map 75 and the fuel injection amount of each in-cylinder injector 11 It is supposed to As a result, the lambda sensor is not provided 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 to the 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 in-cylinder injector 11, it becomes possible to set the target injection amount Q _{NPR_Trgt} by feed forward control, and aging of each in-cylinder injector 11 Effects such as deterioration and characteristic change can be effectively eliminated.

[Determining the end of NOx purge control]
NOx purge control, (1) the injection amount of the exhaust pipe injection or post-injection from on the NOx purge flag F _NP accumulated, when the amount of the cumulative injected has reached the predetermined upper limit threshold amount, of (2) NOx purge control If the elapsed time measured from the start reaches a predetermined upper limit threshold time, (3) Calculation is performed based on a predetermined model equation including the operating state of engine 10, the sensor value of NOx / lambda sensor 45, etc. as input signals. The NOx purge flag F _NP is turned off and the process is terminated (time t _{2 in} FIG. 6) when any condition is satisfied when the NOx storage amount of the NOx storage reduction catalyst 32 decreases to a predetermined threshold value indicating successful NOx removal. reference).

  As described above, in the present embodiment, by providing the cumulative injection amount and the upper limit of the elapsed time as the termination condition of the NOx purge control, the fuel consumption amount is increased when the NOx purge does not succeed due to a decrease in the exhaust temperature or the like. It can be reliably prevented from becoming excessive.

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

  The idle operation detection unit 53 detects whether the engine 10 is in the idle operation state based on the sensor values input from the various sensors 41, 42, 49.

  The motoring detection unit 54 determines whether or not the engine 10 is in the motoring state to stop fuel injection of the in-cylinder injector 11 at a predetermined rotation speed or more based on sensor values input from the various sensors 41, 42, 49. To detect

  The exhaust brake operation detection unit 55 detects the operation of the exhaust brake device that reduces the rotational speed of the engine 10 by increasing the exhaust pressure by closing the exhaust brake valve 17. The presence or absence of the operation of the exhaust brake device may be detected based on the on / off operation of the exhaust brake switch 56 provided in the driver's cab (not shown).

  The MAF throttle control unit 57 reduces the intake air amount by squeezing the opening degree of the intake throttle valve 16 (or at least one of the exhaust throttle valves) to the close side when the following conditions are satisfied. Catalyst heat retention control (hereinafter, also referred to as MAF throttle control) for suppressing the inflow of low-temperature exhaust gas to 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 state of the engine 10 is detected by the motoring detection unit 54. In addition, the valve opening degree at the time of MAF throttle control is feedback-controlled based on the deviation of the predetermined target MAF value lower than that at the time of normal lean operation and the sensor value (actual MAF value) of the MAF sensor 40. The predetermined target MAF value is set, for example, by multiplying a base map (not shown) referenced based on the operating state of the engine 10 by a correction coefficient according to the intake air temperature and the atmospheric pressure. .

  Even if the motoring state is detected by the motoring detection unit 54, the MAF stop control prohibition unit 55A performs MAF stop control to ensure the braking force when the exhaust brake operation detection unit 55 detects the operation of the exhaust brake device. Prohibit the implementation of

  As described above, in the present embodiment, the catalyst heat retention control is performed to reduce the amount of intake air in a situation where the catalyst temperature can be cooled lower than the activation temperature due to the decrease of the exhaust temperature, such as idle operation and motoring. Thus, the catalysts 31 and 32 can be effectively maintained in the activated state. Further, even in the motoring state, the braking force can be effectively secured by prohibiting the catalyst heat retention control when the exhaust brake device is in operation.

[Catalyst temperature estimation]
FIG. 10 is a block diagram showing estimation processing of the oxidation catalyst temperature and the NOx catalyst temperature by the catalyst temperature estimation unit 80. As shown in FIG.

The lean-time HC map 81A (second emission amount storage means) is a map referred to based on the operating state of the engine 10, and the amount of HC exhausted from the engine 10 during lean operation (hereinafter referred to as lean-time HC emission amount Is set by experiments etc. in advance. The idle operation is not detected by the idle operation detection unit 53 (see FIG. 9), and all of the forced regeneration flag F _DPF , the SOx purge flag F _SP and the NOx purge flag F _NP are off (F _DPF = 0, F _SP = 0 , F _NP = 0), the lean HC emission amount read from the lean HC map 81A based on the engine speed Ne and the accelerator opening Q is transmitted to the respective calorific value estimation units 88A, B. It has become.

The lean time CO map 81B (second emission amount storage means) is a map that is referred to based on the operating state of the engine 10, and the amount of CO emitted from the engine 10 during lean operation (hereinafter referred to as lean time CO emission amount Is set by experiments etc. in advance. The idle operation is not detected by the idle operation detection unit 53 (see FIG. 9), and all of the forced regeneration flag F _DPF , the SOx purge flag F _SP and the NOx purge flag F _NP are off (F _DPF = 0, F _SP = 0 , F _NP = 0), the lean CO emissions read from the lean CO map 81B based on the engine speed Ne and the accelerator opening Q are transmitted to the respective calorific value estimation units 88A, B. It has become.

The long-time NOx purge HC map 82A (first emission storage means) is a map that is referred to based on the operating state of the engine 10, and is a long-time NOx where the target execution time of NOx purge control is longer than a predetermined time The amount of HC discharged from the engine 10 when the purge is performed (hereinafter, referred to as HC discharge amount during long-time NOx purge) is set in advance by experiment or the like. If the NOx purge flag F _NP is on (F _NP = 1) and the target execution time of NOx purge control is equal to or longer than a predetermined time, the long-term NOx purge HC map 82A is used based on the engine speed Ne and the accelerator opening Q. The long-time NOx purge HC discharge amount read out is multiplied by a predetermined correction coefficient according to the operation state of the engine 10, and is sent to the respective heat generation amount estimation units 88A and 88B.

The long-time NOx purge CO map 82B (first emission storage means) is a map that is referred to based on the operating state of the engine 10, and the long-term NOx for which the target execution time of NOx purge control is a predetermined time or more The amount of CO discharged from the engine 10 when the purge is performed (hereinafter, referred to as “long-time NOx purge CO emission amount”) is set in advance by experiment or the like. If the NOx purge flag F _NP is on (F _NP = 1) and the target execution time of NOx purge control is greater than or equal to a predetermined time, the long-term NOx purge CO map 82B is used based on the engine speed Ne and the accelerator opening Q. The long-time NOx purge CO emission amount read out is read by a predetermined correction coefficient according to the operating state of the engine 10, and is transmitted to the respective heat generation amount estimation units 88A and 88B.

The short time NOx purge HC estimation unit 83A performs the lean time HC map 81A (or the long time NOx purge time HC map 82A) when performing the short time NOx purge in which the target execution time of the NOx purge control is less than a predetermined time. By multiplying the HC discharge amount read based on the engine rotational speed Ne and the accelerator opening Q by a predetermined correction coefficient, the HC amount discharged from the engine 10 during the short time NOx purge control (hereinafter referred to as the short time NOx purge Estimate the HC emission). When the NOx purge flag F _NP is on (F _NP = 1) and the target execution time of the NOx purge control is less than a predetermined time, the calculated short-time NOx purge HC emissions are calculated as the respective heat generation amount estimation units 88A, B. To be sent to.

The short-time NOx purge CO estimation unit 83B performs the lean-time CO map 81B (or the long-time NOx purge CO map 82B when performing a short-time NOx purge in which the target execution time of NOx purge control is less than a predetermined time. By multiplying the CO emission amount read based on the engine speed Ne and the accelerator opening Q by a predetermined correction coefficient, the amount of CO emitted from the engine 10 at the time of short time NOx purge control (hereinafter, short time NOx purge Estimated CO2 emissions). The calculated short-time NOx purge CO emissions are as follows: when the NOx purge flag F _NP is on (F _NP = 1) and the target execution time of NOx purge control is less than a predetermined time, the respective heat generation amount estimation units 88A, B To be sent to.

The idle MAF throttle state HC map 84A is a map that is referred to based on the operating state of the engine 10, and the HC amount discharged from the engine 10 at the time of catalyst heat control (MAF throttle control) described above (hereinafter referred to as idle MAF throttle The hourly HC emission amount is set in advance by experiments and the like. The catalyst warm-up control is executed in the idle operation state, and all of the forced regeneration flag F _DPF , the SOx purge flag F _SP and the NOx purge flag F _NP are off (F _DPF = 0, F _SP = 0, F _NP = 0). In this case, the amount of HC emission at idle MAF throttle read based on the engine speed Ne and the MAF sensor value from the idle MAF throttle HC map 84A is transmitted to the respective calorific value estimation units 88A, B. .

The idle MAF throttle state HC map 84B is a map that is referred to based on the operating state of the engine 10, and the amount of CO discharged from the engine 10 at the time of the catalyst heat retention control (MAF throttle control) described above (hereinafter referred to as an idle MAF throttle The hourly CO emission amount is set in advance by experiments and the like. The catalyst warm-up control is executed in the idle operation state, and all of the forced regeneration flag F _DPF , the SOx purge flag F _SP and the NOx purge flag F _NP are off (F _DPF = 0, F _SP = 0, F _NP = 0). In this case, the CO emission amount at idle MAF throttle read based on the engine rotational speed Ne and the MAF sensor value from the idle MAF throttle CO map 84B is transmitted to the respective calorific value estimation units 88A and 88B. .

The filter forced regeneration HC map 85A is a map that is referred to based on the operating condition of the engine 10, and the amount of HC discharged from the engine 10 when the filter forced regeneration control is performed (hereinafter referred to as HC emission at the time of filter regeneration The amount is set in advance by experiment or the like. When the forced regeneration flag F _DPF is on (F _DPF = 1), the engine regeneration speed HC is read out based on the engine speed Ne and the accelerator opening degree Q from the filter forced regeneration HC map 85A. A predetermined correction coefficient according to the driving condition of the above is multiplied and transmitted to each of the calorific value estimation units 88A and 88B.

The filter forced regeneration CO map 85B is a map that is referred to based on the operating state of the engine 10, and the amount of CO emitted from the engine 10 when the filter forced regeneration control is performed (hereinafter referred to as CO emission at the time of filter regeneration The amount is set in advance by experiment or the like. When the forced regeneration flag F _DPF is on (F _DPF = 1), the engine 10 is set to the CO amount during filter regeneration read from the filter forced regeneration CO map 85B based on the engine rotational speed Ne and the accelerator opening Q. A predetermined correction coefficient according to the driving condition of the above is multiplied and transmitted to each of the calorific value estimation units 88A and 88B.

The first SOx purge HC map 86A is a map that is referred to based on the operating state of the engine 10, and the engine 10 performs the SOx purge control in a state where after injection is included in the injection pattern of the in-cylinder injector 11. The amount of HC discharged from the engine (hereinafter referred to as the first SOx purge HC discharge amount) is set in advance by experiment or the like. SOx purge flag _{F SP} is on _(F SP = 1) and, if the injection pattern of the in-cylinder injector 11 comprises after injection, reading on the basis of the first 1SOx purge during HC map 86A to the engine rotational speed Ne and the accelerator opening Q The first SOx purge HC discharge amount is multiplied by a predetermined correction coefficient, and is transmitted to the heat generation amount estimation units 88A and 88B.

The second SOx purge HC map 86B is a map that is referred to based on the operating state of the engine 10, and when the SOx purge control is performed in a state where the after injection is not included in the injection pattern of the in-cylinder injector 11. The amount of HC discharged from 10 (hereinafter referred to as the second SOx purge HC discharge amount) is set in advance by experiments and the like. SOx purge flag _{F SP} is on _(F SP = 1) and, if the injection pattern of the in-cylinder injector 11 does not include the after-injection, based on the first 2SOx purge during HC map 86B to the engine rotational speed Ne and the accelerator opening Q The second SOx purge HC discharge amount read is multiplied by a predetermined correction coefficient and transmitted to each of the heat generation amount estimation units 88A and 88B.

The first SOx purge CO map 87A is a map that is referred to based on the operating state of the engine 10, and when the SOx purge control is performed in a state where after injection is included in the injection pattern of the in-cylinder injector 11. The amount of CO (hereinafter referred to as the first SOx purge CO emission amount) emitted from the above is set in advance by experiments and the like. SOx purge flag _{F SP} is on _(F SP = 1) and, if the injection pattern of the in-cylinder injector 11 comprises after injection, reading on the basis of the first 1SOx purge during CO maps 87A to the engine rotational speed Ne and the accelerator opening Q The first SOx purge CO emission amount is multiplied by a predetermined correction coefficient, and is transmitted to the calorific value estimation units 88A and 88B.

The second SOx purge CO map 87B is a map that is referred to based on the operating state of the engine 10, and when the SOx purge control is performed in a state where the after injection is not included in the injection pattern of the in-cylinder injector 11. The amount of CO discharged from 10 (hereinafter referred to as the second SOx purge CO emission amount) is set in advance by experiments and the like. SOx purge flag _{F SP} is on _(F SP = 1) and, if the injection pattern of the in-cylinder injector 11 does not include the after-injection, based on the first 2SOx purge during CO map 87B to the engine rotational speed Ne and the accelerator opening Q The read-out second SOx purge CO emission amount is multiplied by a predetermined correction coefficient, and is transmitted to the calorific value estimation units 88A and 88B.

  The SOx purge HC / CO maps 86A to 87B are not limited to the two types of maps according to the presence or absence of after injection, but a plurality of the pilot injection or the pre-injection according to the presence or absence of each injection. It may be configured to provide a map.

The oxidation catalyst calorific value estimation unit 88A is a second calorific value estimation unit according to the present invention, and includes the NOx purge flag F _NP , the SOx purge flag F _SP , the forced regeneration flag F _DPF , presence or absence of MAF throttling at idle, execution of NOx purge Based on the HC / CO emissions input from each of the maps 81A to 87B and the estimation units 83A and B according to the time length, etc., the HC / CO calorific value inside the oxidation catalyst 31 (hereinafter, the oxidation catalyst HC / CO Estimate the calorific value). Oxidation catalyst HC · CO calorific value, for example, be estimated calculation based on the model equation or a map containing the map 81A~87B and estimator 8 3 A, the HC · CO emissions or the like transmitted from B as an input value Good.

The NOx catalyst heat generation amount estimation unit 88B is a first heat generation amount estimation unit of the present invention, and includes the NOx purge flag F _NP , the SOx purge flag F _SP , the forced regeneration flag F _DPF , presence or absence of MAF throttling at idle, execution of NOx purge time depending on the length or the like, each map 8 1 A~87B and estimator 83A, based on the HC · CO emissions inputted from B, HC · CO calorific value of the internal NOx occlusion reduction type catalyst 32 (hereinafter, NOx Catalyst HC · CO calorific value is estimated). The heat amount of NOx catalyst HC / CO may be estimated and calculated based on, for example, a model formula or a map including the amount of HC / CO emissions transmitted from each of the maps 81A to 87B and the estimation units 83A and B as input values.

  The oxidation catalyst temperature estimation unit 88C is a second catalyst temperature estimation unit of the present invention, and the oxidation catalyst inlet temperature detected by the first exhaust temperature sensor 43, the oxidation catalyst HC input from the oxidation catalyst heating value estimation unit 88A · An oxidation catalyst 31 based on a model formula or a map including, as input values, a CO heat generation amount, a sensor value of the MAF sensor 40, a heat release amount to the outside air estimated from the outside air temperature sensor 47 or the sensor value of the intake air temperature sensor 48, etc. The catalyst temperature (hereinafter referred to as the oxidation catalyst temperature) is estimated and calculated.

  In addition, at the time of the motoring which makes the engine 10 stop a fuel injection, the exothermic reaction of HC * CO in the inside of the oxidation catalyst 31 is lose | eliminated, or it falls so that it can disregard. Therefore, during motoring, oxidation is performed based on the oxidation catalyst inlet temperature, the MAF sensor value, and the heat release to the outside air without using the oxidation catalyst HC / CO calorific value input from the oxidation catalyst calorific value estimation unit 88A. The catalyst temperature is configured to be estimated and calculated.

  The NOx catalyst temperature estimation unit 88D is a first catalyst temperature estimation unit of the present invention, and estimates the oxidation catalyst temperature (hereinafter also referred to as the NOx catalyst inlet temperature) input from the oxidation catalyst temperature estimation unit 88A, and the NOx catalyst calorific value estimation. Based on a model formula or a map including, as input values, the NOx catalyst HC · CO heat generation amount input from the unit 88 B, the heat release amount to the outside air estimated from the outside air temperature sensor 47 or the sensor value of the intake air temperature sensor 48, etc. The catalyst temperature (hereinafter referred to as the NOx catalyst temperature) of the storage reduction catalyst 32 is estimated and calculated.

  During motoring in which the engine 10 stops fuel injection, the exothermic reaction of HC and CO inside the NOx storage reduction catalyst 32 disappears or drops to a negligible extent. Therefore, at the time of motoring, based on the NOx catalyst inlet temperature, the MAF sensor value, and the amount of heat released to the outside air, without using the NOx catalyst HC · CO heat value input from the NOx catalyst heat value estimation unit 88B. It is configured to estimate and calculate the NOx catalyst temperature.

  As described above, in this embodiment, during normal lean operation with different HC and CO emissions, during idle operation where catalyst heat retention control (MAF throttling) is performed, during filter forced regeneration, during SOx purge, during NOx purge By appropriately switching the HC / CO maps 81A to 87B according to the respective operating conditions such as, it becomes possible to calculate the HC / CO calorific value inside the catalyst according to these operating conditions with high accuracy. The 32 temperature estimation accuracy can be effectively improved.

  In addition, at the time of SOx purge, the multi-injection pattern in which in-cylinder injector 11 performs multiple injection, such as after injection implementation in which the HC and CO calorific value in each catalyst 31 and 32 increases, is appropriately switched It becomes possible to calculate the HC and CO calorific value accurately according to the injection pattern, and it is possible to effectively improve the catalyst temperature estimation accuracy at the time of SOx purge.

  During NOx purge, according to the execution time, for example, maps 82A and 82B are used during long-term NOx purge, and lean maps 81A and B during a short-term NOx purge where mapping is difficult. By using the method of multiplying the coefficient together, it is possible to calculate the HC / CO heat generation amount accurately according to the length of the NOx purge time, and it is possible to effectively improve the catalyst temperature estimation accuracy at the time of NOx purge .

  In addition, during motoring, each catalyst 31 can also be used during motoring by calculating the catalyst temperature based on the catalyst inlet temperature, the MAF value, and the amount of heat released to the outside without considering the HC and CO calorific value. It becomes possible to estimate 32 temperatures effectively.

[FB control reference temperature selection]
A reference temperature selection unit 89 shown in FIG. 10 selects a reference temperature used for the above-described filter forced regeneration and temperature feedback control of SOx purge.

  In the exhaust gas purification system provided with the oxidation catalyst 31 and the NOx storage reduction type catalyst 32, the HC · CO calorific value in each of the catalysts 31 and 32 becomes different according to the heat generation characteristic of the catalyst and the like. For this reason, as the reference temperature for temperature feedback control, it is preferable to select the catalyst temperature having the larger calorific value in order to improve the controllability.

  The reference temperature selection unit 89 selects one of the catalyst temperature among the oxidation catalyst temperature and the NOx catalyst temperature, which has a larger amount of heat generation estimated from the operating state of the engine 10 at that time, And the SOx purge control unit 60 as a reference temperature for temperature feedback control. More specifically, at the time of filter forced regeneration where the oxygen concentration in exhaust gas is relatively high and the HC · CO calorific value of the oxidation catalyst 31 increases, the temperature of the oxidation catalyst input from the oxidation catalyst temperature estimation unit 88A is temperature feedback control Selected as reference temperature. On the other hand, at the time of SOx purge rich control or NOx purge rich control in which the HC / CO calorific value of the NOx storage reduction catalyst 32 increases due to the decrease of the oxygen concentration in the exhaust, the NOx catalyst temperature input from the NOx catalyst temperature estimation unit 88B Is selected as a reference temperature for temperature feedback control.

  As described above, in the present embodiment, the controllability can be effectively improved by selecting the catalyst temperature at which the HC / CO heat generation amount increases as the reference temperature for temperature feedback control.

[MAF tracking control]
The MAF follow-up control unit 98 performs (1) a switching period from a lean state of normal operation to a rich state by SOx purge control or NOx purge control, and (2) a lean period from a rich state by SOx purge control or NOx purge control to normal operation. During the switching period to the state, control (referred to as MAF follow-up control) is performed to correct the fuel injection timing and fuel injection amount of each in-cylinder injector 11 according to the MAF change.

[Injection amount learning correction]
As shown in FIG. 11, 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 performs a learning correction coefficient F of the fuel injection amount based on an error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 during lean operation of the engine 10 and the estimated lambda value λ _Est. Calculate _Corr . When the exhaust is in a lean state, the HC concentration in the exhaust is very low, so the change of the exhaust lambda value due to the oxidation reaction of HC in the oxidation catalyst 31 is negligible. Therefore, it is assumed that the actual lambda value λ _Act in the exhaust gas detected by the NOx / lambda sensor 45 downstream of the oxidation catalyst 31 and the estimated lambda value λ _Est in the exhaust gas discharged from the engine 10 coincide with each other. 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 indicated injection amount and the actual injection amount for each in-cylinder injector 11. Hereinafter, calculation processing of the learning correction coefficient by the learning correction coefficient calculation unit 91 using the error Δλ will be described based on the flow of FIG.

  In step S300, it is determined based on the engine speed Ne and the accelerator opening degree Q 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 calculation of the learning correction coefficient.

At step S310, the the error Δλ obtained by subtracting the actual lambda value lambda _Act detected by the NOx / lambda sensor 45 from the estimated lambda value lambda _Est, by multiplying the learning value gain _{K 1} and the correction sensitivity coefficient _{K 2,} 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 from the operating state of the engine 10 according to the engine speed Ne and the accelerator opening degree 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. 11 as an input signal.

In step S320, it is determined whether 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, this control is returned to cancel the current learning.

In step S330, it is determined whether the learning prohibition flag F _Pro is off. As the learning inhibition flag _FPro , for example, during transient operation of the engine 10, during SOx purge control ( _FSP = 1), during NOx purge control ( _FNP = 1), etc. correspond. In the state where these conditions are satisfied, the change in the actual lambda value λ _Act increases the error Δλ, and accurate learning can not be performed. Whether or not the engine 10 is in the transient operation state is, for example, based on 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. It may be determined as a transient operation state.

In step S340, the learning value map 91B (see FIG. 11) referenced based on the engine rotational speed Ne and the accelerator opening degree 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 degree Q are set. These learning areas are preferably set so as to narrow the range as the area used more frequently, and the range as the area used less frequently. As a result, the learning accuracy is improved in the region where the frequency of use is high, and it is possible to effectively prevent unlearning in the region where the frequency of use is low.

In step S350, the learning correction coefficient F _Corr is calculated by adding “1” to the learning value read from the learning value map 91B using the engine rotational 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 the basic injection amounts of the pilot injection Q _Pilot , the pre injection Q _Pre , the main injection Q _Main , the after injection Q _After , and the post injection Q _{Post by} the learning correction coefficient F _Corr to obtain these fuels. Execute correction of injection quantity.

As described above, the fuel injection amount is corrected to each in-cylinder injector 11 by the learning value corresponding to the error Δλ between the estimated lambda value λ _Est and the actual lambda value λ _Act , so that the aged deterioration and characteristics of each in-cylinder injector 11 It is possible to effectively eliminate variations such as changes and individual differences.

[MAF correction factor]
MAF correction coefficient calculating unit 95 calculates the MAF correction coefficient _{Maf _Corr} used to set the MAF target value _{MAF SPL_Trgt} and the target injection amount _{Q SPR_Trgt} during SOx purge control.

In the present embodiment, the fuel injection amount of each in-cylinder injector 11 is corrected based on the 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 factor of the error Δλ is not necessarily the influence of the difference between the instructed injection amount and the actual injection amount for each in-cylinder injector 11. That is, not only the in-cylinder injectors 11 but also the errors of the MAF sensor 40 may affect the error λ of lambda.

FIG. 13 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 rotational speed Ne and the accelerator opening degree Q, and is a MAF indicating the sensor characteristics of the MAF sensor 40 corresponding to the engine rotational speed Ne and the accelerator opening degree Q. The correction coefficient _{Maf_corr} is set in advance based on experiments and 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 rotational speed Ne and the accelerator opening degree Q as input signals, and the MAF correction coefficient Maf _{_ corr} as the MAF target value calculation unit 62 It is transmitted to the injection amount target value calculation unit 66. As a result, the sensor characteristics of the MAF sensor 40 can be effectively reflected in the settings of the MAF target value MAF _{SPL_Trgt} and the target injection amount Q _{SPR_Trgt} at the time of SOx purge control.

[Others]
The present invention is not limited to the embodiments described above, and can be appropriately modified and implemented without departing from the spirit of the present invention.

Reference Signs List 10 engine 11 in-cylinder injector 12 intake passage 13 exhaust passage 16 intake throttle valve 24 EGR valve 31 oxidation catalyst 32 NOx storage reduction type catalyst 33 filter 34 exhaust injector 40 MAF sensor 45 NOx / lambda sensor 50 ECU

Claims (3)

A NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine to reduce and purify NOx in the exhaust;
Catalyst regeneration means for executing a catalyst regeneration process for reducing and purifying the NOx stored in the NOx storage reduction type catalyst while making the exhaust gas rich;
First emission storage means for acquiring and storing in advance at least one of the amount of hydrocarbon and the amount of carbon monoxide discharged from the internal combustion engine at the time of execution of the catalyst regeneration process;
At least one of the hydrocarbon calorific value and the carbon monoxide calorific value of the NOx storage reduction type catalyst based on at least one of the hydrocarbon quantity and the carbon monoxide quantity read from the first emission storage means at the time of execution of the catalyst regeneration process. A first heat generation amount estimation unit configured to estimate at least one of them;
First, the catalyst temperature of the NOx storage reduction type catalyst at the time of execution of the catalyst regeneration process is estimated based on at least one of a hydrocarbon calorific value and a carbon monoxide calorific value estimated by the first calorific value estimation means. Catalyst temperature estimation means ;
A second emission amount storage unit which acquires and stores in advance at least one of the amount of hydrocarbon and the amount of carbon monoxide exhausted from the internal combustion engine during lean operation of the internal combustion engine;
The first heat generation amount estimation means is executed based on at least one of the amount of hydrocarbon and the amount of carbon monoxide read from the second emission amount storage means when the execution time of the catalyst regeneration process is less than a predetermined time. At least one of the amount of hydrocarbon and the amount of carbon monoxide discharged from the internal combustion engine at the time of the catalyst regeneration process whose time is less than a predetermined time is estimated, and at the time of the catalyst regeneration process whose execution time is less than the predetermined time An exhaust gas purification system which estimates at least one of a hydrocarbon calorific value and a carbon monoxide calorific value in the NOx storage reduction type catalyst based on at least one of a hydrocarbon quantity and a carbon monoxide quantity discharged. The first calorific value estimation means determines that at least one of the hydrocarbon amount and the carbon monoxide amount read from the second emission amount storage means has a predetermined correction coefficient when the execution time of the catalyst regeneration process is less than a predetermined time. To multiply at least one of the hydrocarbon calorific value and the carbon monoxide calorific value of the NOx storage reduction type catalyst by multiplying the first emission quantity when the execution time of the catalyst regeneration process is a predetermined time or more. The exhaust gas according to claim 1, wherein at least one of a hydrocarbon calorific value and a carbon monoxide calorific value in the NOx storage reduction type catalyst is estimated based on at least one of a hydrocarbon amount and a carbon monoxide amount read from a storage means. Purification system. An oxidation catalyst provided in an exhaust passage upstream of the NOx storage reduction catalyst;
At the time of execution of the catalyst regeneration process, if the execution time of the catalyst regeneration process is less than a predetermined time, the oxidation is performed based on at least one of the amount of hydrocarbon and the amount of carbon monoxide read from the second emission storage means. At least one of a hydrocarbon calorific value and a carbon monoxide calorific value in the catalyst is estimated, and when the execution time of the catalyst regeneration process is equal to or longer than a predetermined time, the amount of hydrocarbons and the carbon monoxide read from the first emission storage means Second calorific value estimation means for estimating at least one of a hydrocarbon calorific value and a carbon monoxide calorific value in the oxidation catalyst based on at least one of carbon amounts;
Second catalyst temperature estimation for estimating the catalyst temperature of the oxidation catalyst during execution of the catalyst regeneration process based on at least one of hydrocarbon calorific value and carbon monoxide calorific value estimated by the second calorific value estimation means The exhaust gas purification system according to claim 2, further comprising:

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