WO2017047678A1

WO2017047678A1 - Catalyst deterioration degree estimation device

Info

Publication number: WO2017047678A1
Application number: PCT/JP2016/077205
Authority: WO
Inventors: 輝男中田; 隆行坂本; 長岡　大治
Original assignee: いすゞ自動車株式会社
Priority date: 2015-09-18
Filing date: 2016-09-15
Publication date: 2017-03-23
Also published as: JP2017057842A

Abstract

This catalyst deterioration degree estimation device for an exhaust purification system provided with a NOx occlusion/reduction catalyst (32), and a NOx sensor (45) provided further downstream an exhaust passage than the NOx occlusion/reduction catalyst (32), is provided with: a calculation unit (120) which estimates, on the basis of the operation state of an internal combustion engine (10), the NOx amount included in exhaust that has passed through the NOx reduction catalyst (32), and calculates, on the basis of the difference between the estimated NOx amount and the actual NOx amount detected by the NOx sensor (45), the deterioration degree of the NOx occlusion/reduction catalyst (32); and a calculation control unit (121) which controls the calculation of the deterioration degree by the calculation unit (120) on the basis of the operation state of the internal combustion engine (10) and/or the state of the exhaust passage of the internal combustion engine (10).

Description

Catalyst degradation degree estimation device

This disclosure relates to a catalyst deterioration degree estimation device.

Conventionally, a NOx occlusion reduction type catalyst is known as a catalyst for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from an internal combustion engine. 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, etc., a recovery process is periodically performed to restore the NOx occlusion capacity of the NOx occlusion reduction type catalyst by making exhaust rich by exhaust pipe injection or post injection. It is necessary to execute (see, for example, Patent Documents 1 and 2).

Since the NOx occlusion reduction type catalyst tends to deteriorate the NOx occlusion performance by continuous use, a deterioration correction coefficient for correcting the deterioration is acquired. In order to increase the accuracy of correction, a technique for executing acquisition of a deterioration correction coefficient under a specific condition is disclosed. For example, Patent Document 3 discloses a method of executing correction parameter calculation during lean operation and not executing correction parameter calculation during rich operation. Patent Document 4 discloses a system that calculates a correction coefficient when the catalyst temperature is lower than a predetermined value. Patent Document 5 discloses a control device that calculates a NOx correction coefficient when the engine is in steady operation and the NOx sensor value is stable.

Japanese Unexamined Patent Publication No. 2008-202425 Japanese Unexamined Patent Publication No. 2007-16713 Japanese Unexamined Patent Publication No. 2004-270469 Japanese Unexamined Patent Publication No. 2007-162603 International Publication No. 2014/083626

The deterioration correction coefficient can be calculated by integrating the difference between the estimated value and the detected value of the NOx amount on the exhaust downstream side of the NOx storage reduction catalyst. In order to improve the accuracy of correction using the deterioration correction coefficient, it is desirable to take the integration time as long as possible.

The technique of the present disclosure aims to increase the accuracy of correction using a deterioration correction coefficient.

The technology of the present disclosure is provided in an exhaust passage of an internal combustion engine, stores NOx in exhaust in an exhaust lean state, and reduces and purifies NOx stored in an exhaust rich state, and the NOx And a NOx sensor provided downstream of the exhaust passage relative to the storage reduction catalyst, and a catalyst deterioration degree estimation device for an exhaust purification system, the NOx reduction catalyst based on an operating state of the internal combustion engine. A calculation unit that estimates the amount of NOx contained in the exhaust gas that has passed, and calculates the degree of deterioration of the NOx storage reduction catalyst based on the difference between the estimated amount of NOx and the actual amount of NOx detected by the NOx sensor; A calculation control unit that controls the calculation of the degree of deterioration of the calculation unit based on at least one of the operating state of the internal combustion engine and the state of the exhaust passage of the internal combustion engine; Equipped with a.

According to the technique of the present disclosure, it is possible to improve the accuracy of correction using the deterioration correction coefficient.

FIG. 1 is an overall configuration diagram showing an exhaust purification system according to the present embodiment. FIG. 2 is a timing chart for explaining the SOx purge control according to the present embodiment. FIG. 3 is a block diagram showing the MAF target value setting process during SOx purge lean control according to the present embodiment. FIG. 4 is a block diagram showing a target injection amount setting process during SOx purge rich control according to the present embodiment. FIG. 5 is a timing chart illustrating the catalyst temperature adjustment control of the SOx purge control according to the present embodiment. FIG. 6 is a timing chart for explaining the NOx purge control according to the present embodiment. FIG. 7 is a block diagram showing a start process of NOx purge control according to the present embodiment. FIG. 8 is a block diagram for explaining deterioration correction coefficient calculation processing according to the present embodiment. FIG. 9 is a diagram schematically illustrating the calculation start condition. FIG. 10 is a block diagram showing the MAF target value setting process during NOx purge lean control according to the present embodiment. FIG. 11 is a block diagram illustrating a target injection amount setting process during NOx purge rich control according to the present embodiment.

Hereinafter, an exhaust purification system according to an embodiment of the present disclosure will be described based on the accompanying drawings.

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

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

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 the 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 injector 34 that injects unburned fuel (mainly HC) into the exhaust passage 13 in accordance with an instruction signal input from the ECU 50. Yes.

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

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

The filter 33 is formed, for example, by arranging a large number of cells partitioned by porous partition walls along the flow direction of the exhaust gas and alternately plugging the upstream side and the downstream side of these cells. . The filter 33 collects PM in the exhaust gas in the pores and surfaces of the partition walls, and when the estimated amount of PM deposition reaches a predetermined amount, so-called filter 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 upstream of the oxidation catalyst 31 and detects the exhaust temperature (catalyst inlet temperature) flowing into the oxidation catalyst 31. The second exhaust temperature sensor 44 is provided between the NOx storage reduction catalyst 32 and the filter 33 and detects the exhaust temperature flowing into the filter 33. The NOx / lambda sensor 45 is an example of a NOx sensor according to the present disclosure. In the present embodiment, the NOx / lambda sensor 45 is provided on the downstream side of the filter 33, and 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. To detect.

The ECU 50 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, the sensor values of the sensors 40 to 46 are input to the ECU 50. In addition, the ECU 50 includes the filter regeneration control unit 51, the SOx purge control unit 60, and the NOx purge control unit 70 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 regeneration control]
The filter regeneration control unit 51 estimates the PM accumulation amount of the filter 33 from the travel distance of the vehicle or the differential pressure across the filter detected by a differential pressure sensor (not shown), and the estimated PM accumulation amount exceeds a predetermined upper limit threshold. And the regeneration flag F _DPF is turned on (see time t _{1 in} FIG. 2). When the regeneration flag F _DPF is turned on, an instruction signal for performing exhaust pipe injection is transmitted to the exhaust injector 34, or an instruction signal for performing post injection is transmitted to each in-cylinder injector 11, and the exhaust gas is exhausted. The temperature is raised to the PM combustion temperature (for example, about 550 ° C.). The regeneration flag F _DPF is, PM deposition estimation amount is turned off drops to a predetermined lower limit threshold indicating the burn off (determination threshold value) (see time t ₂ in FIG. 2). The determination threshold value for turning off the regeneration flag F _DPF may be based on, for example, the upper limit elapsed time or the upper limit cumulative injection amount from the start of filter regeneration (F _DPF = 1).

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

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

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

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

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

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

The MAF correction coefficient _{Maf_corr} is read from a correction coefficient setting map (not shown) using the engine speed Ne and the accelerator opening Q as input signals. In the correction coefficient setting map, a MAF correction coefficient _{Maf_corr} indicating the sensor characteristics of the MAF sensor 40 corresponding to the engine speed Ne and the accelerator opening Q is set in advance based on experiments or the like.

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 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} represents the fuel injection amount (excluding post injection) before application of MAF tracking control, Ro _Fuel represents fuel specific gravity, AFR _sto represents the theoretical air-fuel ratio, and _{Maf_corr} represents the MAF correction coefficient.

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 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.

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

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

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

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

Then, when the SOx purge rich flag _{F SPR} is turned off with the passage of the injection period _{T F_INJ_1,} until interval _{T F_INT_1} set by PID control has elapsed, SOx purge rich flag _{F SPR} is turned off (time in FIG. 5 t ₂ to t ₃ ). Further, when the SOx purge rich flag F _SPR is turned on as the interval _{TF_INT_1} elapses, the exhaust pipe injection or the post injection according to the injection period _{TF_INJ_2} is executed again (see times 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.

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]
FIG. 6 shows a timing chart of the NOx purge control of this embodiment. The NOx purge control unit 70 restores the NOx storage capability of the NOx storage reduction catalyst 32 by making the exhaust atmosphere rich and detoxifying and releasing NOx stored in the NOx storage reduction catalyst 32 by reduction purification. Execute control.

[NOx purge control start processing]
FIG. 7 is a block diagram showing a start process of NOx purge control by the NOx purge control unit 70. The NOx purge control unit 70 includes a NOx purge start determination unit 111, a NOx occlusion amount estimation unit 113, an occlusion amount threshold map 114, a catalyst temperature estimation unit 115, an occlusion amount threshold correction unit 116, a purification rate calculation unit 117, and an interval target value map. 118, an interval target value correction unit 119, and a deterioration degree estimation unit 120 are included as some functional elements.

The NOx purge start determination unit 111 receives the interval target value Int in which the elapsed time _{Int_Time} from the end of the previous NOx purge control is input from the interval target value correction unit 119 when any of the predetermined start conditions is satisfied. _It is determined that the NOx purge is started on the condition that _{_tgr} has elapsed, the NOx purge flag F _NP is set to ON (F _NP = 1), and the NOx purge control is started (see time t _{1 in} FIG. 6).

As the start condition determined by the NOx purge start determination unit 111, for example, (1) when an operation signal is input from a forced rich switch (not shown), (2) NOx occlusion amount estimation of the NOx occlusion reduction type catalyst 32 is estimated. When the value _{m_NOx} increases to a value _{equal to} or greater than the predetermined storage amount threshold value _{STR_thr_NOx} , (3) When the NOx purification rate _{NOx_pur%} in the NOx storage reduction type catalyst 32 decreases below the predetermined purification rate threshold value, (4) Idling (5) When the engine 10 rotates at a predetermined rotation speed threshold value or higher and the load on the engine 10 is equal to or higher than the predetermined load threshold value, (6) the estimated catalyst temperature _{Temp_LNT} is Although the case where the low temperature state which is less than a predetermined catalyst temperature threshold is continuing over predetermined time is mentioned, it is not limited to these.

The NOx occlusion amount estimated value _{m_NOx} used for the determination of the start condition is estimated by the NOx occlusion amount estimation unit 113. The NOx occlusion amount estimated value _{m_NOx} is calculated based on the following formula (3), for example.

NOx occlusion amount estimated value _{m_NOx} = engine-out NOx amount x occlusion efficiency based on catalyst temperature x occlusion efficiency based on NOx accumulation rate (3)
The engine-out NOx amount is acquired from an engine-out NOx map using the engine speed Ne and the accelerator opening Q as input signals. The engine-out NOx map is created in advance by experiments or the like. Further, the engine-out NOx amount can be obtained by other methods such as a NOx sensor or a model formula.

The storage efficiency (0 <C ≦ 1) based on the catalyst temperature is acquired from a T_STR map _{using the} estimated catalyst temperature _{Temp_LNT} estimated by the catalyst temperature estimation unit 115 as an input signal. The T_STR map is created in advance by experiments or the like.

The storage efficiency (0 <C ≦ 1) based on the NOx accumulation rate is acquired from the Fill_STR map _using the NOx accumulation rate _{NOx_LEV} as an input signal. The Fill_STR map is created in advance by experiments or the like. The NOx accumulation rate _{NOx_LEV} is a ratio of the NOx accumulation amount _{NOx_STR} accumulated in the NOx occlusion reduction type catalyst 32 at that time to the maximum NOx occlusion amount. The NOx accumulation _{amount_STR} is obtained by subtracting the NOx reduction amount from the immediately preceding NOx storage amount. In these maps, correction can be made as appropriate using MAF, engine-out NOx, or the like.

NOx storage amount threshold _{STR _Thr_NOx} used for determining the start conditions are set by the storage amount threshold value map 114 referenced based on the estimated catalyst temperature _{Temp _LNT} the NOx occlusion-reduction catalyst 32. The estimated catalyst temperature _{Temp_LNT} is estimated by the catalyst temperature estimation unit 115. The estimated catalyst temperature _{Temp_LNT} is estimated _based on, for example, the inlet temperature of the oxidation catalyst 31 detected by the first exhaust temperature sensor 43, the HC / CO heat generation amount inside the oxidation catalyst 31 and the NOx storage reduction catalyst 32, and the like. Is done.

The NOx storage amount threshold value _{STR_thr_NOx} set based on the storage amount threshold map 114 is corrected by the storage amount threshold value correcting unit 116. The occlusion amount threshold value correction unit 116 _{multiplies the} NOx occlusion amount threshold value _{STR_thr_NOx} by a deterioration correction coefficient (deterioration degree) obtained by the deterioration degree estimation unit 120. The calculation of the deterioration correction coefficient will be described later.

The NOx purification rate _{NOx_pur%} used for the determination of the start condition is calculated by the purification rate calculation unit 117. The NOx purification rate _{NOx_pur%} is obtained, for example, by _dividing the NOx amount on the downstream side of the catalyst detected by the NOx / lambda sensor 45 by the NOx emission amount on the upstream side of the catalyst estimated from the operating state of the engine 10 or the like. It is done.

The interval target value _{Int_tgr} used for the start determination is set in an interval target value map 118 that is referred to based on the engine speed Ne and the accelerator opening Q. The interval target value _{Int_tgr} is corrected by the interval target value correction unit 119. The interval target value correction unit 119 performs a shortening correction that shortens as the degree of deterioration of the NOx storage reduction catalyst 32 increases. This shortening correction is performed by multiplying the NOx occlusion amount threshold value _{STR_thr_NOx} by a deterioration correction coefficient (deterioration degree) obtained by the deterioration degree estimation unit 120.

[Calculation of deterioration correction coefficient]
FIG. 8 is a block diagram for explaining the calculation process of the deterioration correction coefficient. As shown in the figure, the degradation degree estimation unit 120 includes a calculation start condition determination unit 121, an engine-out NOxs acquisition unit 122, an exit NOx estimation unit 123, and a correction coefficient calculation unit 124 as some functional elements.

The calculation start condition determining unit 121 determines whether or not the deterioration correction coefficient calculation start condition is satisfied. If the condition is satisfied, the engine out NOx calculating unit 122, the outlet NOx estimating unit 123, and the correction coefficient calculating unit. A permission signal for permitting execution of the calculation process is output to 124. For example, the voltage of the permission signal is set to H level. Each of the

units

122, 123, and 124 starts the process on the condition that the output of the permission signal is started, and executes the process over the output period of the permission signal. Each

unit

122, 123, and 124 stops processing in a period during which the permission signal is not output (for example, a period in which the signal is at the L level). The determination of the calculation start condition by the calculation start condition determination unit 121 will be described later.

The engine-out NOx acquisition unit 122 acquires the NOx amount (engine-out NOx amount) contained in the exhaust discharged from the engine 10 based on the operating state of the engine 10. In the present embodiment, the engine-out NOx amount is acquired from an engine-out NOx amount map using the engine speed Ne and the accelerator opening Q as input signals. The engine-out NOx amount map is prepared in advance by experiments or the like. The engine-out NOx amount may be obtained from a model formula or may be obtained by other methods.

The outlet NOx estimating unit 123 estimates the NOx amount (exit NOx estimated amount) contained in the exhaust gas that has passed through the NOx storage reduction catalyst 32. In the present embodiment, the estimated outlet NOx amount is calculated by subtracting the NOx storage amount estimated by the NOx storage amount estimation unit 113 from the engine out NOx amount acquired by the engine out NOx acquisition unit 122.

The correction coefficient calculation unit 124 calculates a deterioration correction coefficient for correcting the estimated value to the detected value with respect to the NOx amount contained in the exhaust gas that has passed through the NOx storage reduction catalyst 32. The deterioration correction coefficient in the present embodiment is calculated by time-integrating a difference obtained by subtracting the actual NOx amount based on the detected value of the NOx / lambda sensor 45 from the exit NOx estimated amount estimated by the exit NOx estimating unit 123. The As described above, the calculated deterioration correction coefficient is used for threshold correction in the occlusion amount threshold correction unit 116 or used for target value correction in the interval target value correction unit 119.

[Judgment of calculation start condition]
FIG. 9 is a diagram schematically illustrating the calculation start condition by the calculation start condition determining unit (calculation control unit) 121. In the figure, a solid line of code _{m _NOx} is NOx occlusion amount estimation value, dotted line code _{NOx _Act} is actual NOx amount based on the detected value of the NOx / lambda sensors 45, dashed line code _{NOx _Est} exit NOx estimated The amount of NOx estimated by the unit 123, and the two-dot chain line of the symbol _{NOx_Err} is an error between the actual NOx amount and the estimated NOx amount. An arrow with a symbol _{T_AL} is a permission period for the deterioration correction calculation.

The calculation start condition determination unit 121 starts calculating the deterioration correction coefficient on condition that the NOx occlusion amount estimated value _{m_NOx} is equal to or less than a predetermined threshold _{NOx_TH1} . The threshold value _{NOx_TH1} in the present embodiment is 20% of the occlusion amount threshold value _{STR_thr_NOx} , but is not limited to this value. In the example of FIG, NOx occlusion amount estimation value _{m _NOx} is time t3 to reach a predetermined threshold _{NOx _TH1.} For this reason, the calculation process of the deterioration correction coefficient is started in a period from time t0 to time t3 when the engine is started.

Thus, the deterioration correction coefficient calculation process is started on the condition that the NOx occlusion amount estimated value _{m_NOx} is equal to or less than the predetermined threshold _{NOx_TH1} (the NOx occlusion amount estimated value _{m_NOx} exceeds the predetermined threshold _{NOx_TH1)} . In such a case, the calculation process is not started until the NOx occlusion amount estimated value _{m_NOx} becomes equal to or less than the predetermined threshold _{NOx_TH1} ), thereby improving the accuracy of correction of the calculated deterioration correction coefficient. This is because the deterioration correction coefficient is calculated by integrating the difference between the estimated value and the detected value of the NOx amount contained in the exhaust gas that has passed through the NOx storage reduction catalyst 32. In this case, the lower the NOx occlusion amount estimated value _{m_NOx} at the start of calculation, the longer the period until the NOx occlusion amount estimated value _{m_NOx} reaches the occlusion amount threshold _{STR_thr_NOx} , and the difference between the estimated value and the detected value becomes clearer. Because it becomes.

The calculation start condition determination unit 121 prohibits the calculation of the deterioration correction coefficient for a predetermined period from when the engine 10 is started until the NOx / lambda sensor 45 can effectively detect the NOx amount. The NOx / lambda sensor 45 of this embodiment includes a heater (not shown), but energization of the heater is performed in a state where moisture adhering to the sensor is removed. For this reason, after the engine 10 is started, energization of the heater is started on the condition that the exhaust temperature has reached a predetermined drying temperature (for example, 100 ° C.). At the same time, detection of the NOx amount by the NOx / lambda sensor 45 is started. In the example of FIG. 9, energization of the heater and detection of the NOx amount are started at time t1. Here, as indicated by the dotted line with the symbol _{NOx_act} , the detected value of the amount of NOx is not stable immediately after the start of detection, so that the error becomes large when used for calculating the deterioration correction coefficient. Therefore, in the present embodiment, the calculation process of the deterioration correction coefficient is started on the condition that the time necessary for stabilizing the detected value has elapsed. In the example of the figure, the calculation process of the deterioration correction coefficient is started from time t2. As a result, the calculation accuracy of the deterioration correction coefficient can be increased.

Further, regarding the standby period from the start of energization to the heater (start of detection by the NOx / lambda sensor 45) to the start of the calculation process of the deterioration correction coefficient, it may be a predetermined period as described above, or may be NOx / lambda. A condition may be that the amount of change per unit time of the sensor 45 is equal to or less than a determination threshold value indicating a stable state of detection.

The calculation start condition determination unit 121 calculates the deterioration correction coefficient until a predetermined period elapses after the end of the above-described SOx purge rich control or until a predetermined period elapses after the end of NOx purge rich control described later. Is prohibited. This is because a large error occurs in the estimated value of the NOx discharge amount immediately after the end of each rich control. Therefore, in the present embodiment, the calculation process of the deterioration correction coefficient is started on the condition that the time necessary for stabilizing the detected value has elapsed. In the example of FIG. 9, the calculation of the deterioration correction coefficient is prohibited with the standby period from the end time t4 to the time t5 of the NOx purge rich control. Thereby, the calculation accuracy of the deterioration correction coefficient can be increased. In addition, regarding this waiting period, it is good also as a period until the variation _{| change_quantity} per unit time in NOx occlusion amount estimated value _{m_NOx} becomes below the determination threshold value which shows a stable state.

Thus, in this embodiment, since the calculation accuracy of the deterioration correction coefficient can be increased, the accuracy of correction using the deterioration correction coefficient for the NOx storage reduction catalyst 32 can be increased.

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

[NOF purge lean control MAF target value setting]
FIG. 10 is a block diagram showing a process for setting the MAF target value MAF _{NPL_Trgt} during the NOx purge lean control. The third target excess air ratio setting map 71 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and during NOx purge lean control corresponding to the engine speed Ne and the accelerator opening Q. The excess air ratio target value λ _{NPL_Trgt} (third excess air ratio) is set in advance based on experiments or the like.

First, the excess air ratio target value λ _{NPL_Trgt} at the time of NOx purge lean control is read from the third target excess air ratio setting map 71 using the engine speed Ne and the accelerator opening Q as input signals, and is sent to the MAF target value calculation unit 72. Entered. Further, the MAF target value calculation unit 72 calculates the MAF target value MAF _{NPL_Trgt} at the time of NOx purge lean control based on the following formula (4).

MAF _{NPL_Trgt} = λ _{NPL_Trgt} × Q _{fnl_corrd} × Ro _Fuel × AFR _sto / _{Maf_corr} (4)
In Equation (4), Q _{fnl_cord} represents the fuel injection amount (excluding post injection), Ro _Fuel represents the fuel specific gravity, AFR _sto represents the stoichiometric air-fuel ratio, and _{Maf_corr} represents the MAF correction coefficient.

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

The valve control unit 74 throttles the intake throttle valve 16 to the _close side and opens the EGR valve 24 to the open side so that the actual MAF value MAF _Act input from the MAF sensor 40 becomes the MAF target ramp value MAF _{NPL_Trgt_Ramp.} Execute control.

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

Further, by 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. 11 is a block diagram showing processing for setting a target injection amount Q _{NPR_Trgt} (injection amount per unit time) for 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 a target injection amount Q _{NPR_Trgt} at the time of NOx purge rich control based on the following formula (5).

Q _{NPR_Trgt} = MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (5)
In Expression (5), MAF _{NPL_Trgt} is a NOx purge lean MAF target value, and is input from the above-described MAF target value calculation unit 72. Q _{fnl_corrd} represents the fuel injection amount (excluding post injection), Ro _Fuel represents the fuel specific gravity, AFR _sto represents the stoichiometric air-fuel ratio, and _{Maf_corr} represents the MAF correction coefficient.

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

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

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

As described above, in the present embodiment, the cumulative injection amount and the upper limit of the elapsed time are provided in the end condition of the NOx purge control, so that the fuel consumption amount is reduced when the NOx purge is not successful due to a decrease in the exhaust temperature or the like. It is possible to reliably prevent the excess.

[Others]
It should be noted that the present disclosure is not limited to the above-described embodiment, and can be appropriately modified and implemented without departing from the spirit of the present disclosure.

This application is based on a Japanese patent application (Japanese Patent Application No. 2015-185757) filed on September 18, 2015, the contents of which are incorporated herein by reference.

The catalyst deterioration degree estimation device of the present disclosure is useful in that the accuracy of correction using a deterioration correction coefficient can be increased.

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

Claims

More than the NOx occlusion reduction type catalyst provided in the exhaust passage of the internal combustion engine, which occludes NOx in the exhaust gas in the exhaust lean state and reduces and purifies NOx occluded in the exhaust rich state, and the NOx occlusion reduction type catalyst A NOx sensor provided downstream of the exhaust passage, and a catalyst deterioration degree estimating device for an exhaust purification system comprising:
Estimating the amount of NOx contained in the exhaust gas that has passed through the NOx reduction catalyst based on the operating state of the internal combustion engine, and based on the difference between the estimated NOx amount and the actual NOx amount detected by the NOx sensor, A calculation unit for calculating the degree of deterioration of the NOx storage reduction catalyst;
A catalyst deterioration degree estimation device, comprising: a calculation control unit that controls calculation of the deterioration degree of the calculation unit based on at least one of an operating state of the internal combustion engine and an exhaust passage state of the internal combustion engine.
2. The catalyst deterioration according to claim 1, wherein the calculation control unit prohibits the calculation of the deterioration degree for a predetermined period from when the internal combustion engine is started until the NOx amount can be effectively detected by the NOx sensor. Degree estimation device.
When the catalyst regeneration process is executed to restore the NOx purification ability of the NOx occlusion reduction catalyst by setting the exhaust to a rich state, the calculation control unit is configured to perform the predetermined period from the execution time of the catalyst regeneration process. The catalyst deterioration degree estimation apparatus according to claim 1 or 2, wherein calculation of the deterioration degree is prohibited.
An estimation unit for estimating the amount of NOx occluded in the NOx occlusion reduction catalyst based on the operating state of the internal combustion engine;
The calculation control unit, when the storage unit NOx amount estimated by the estimation unit exceeds a predetermined threshold when the calculation unit starts calculating the degree of deterioration as the predetermined period elapses, The catalyst deterioration degree estimation device according to any one of claims 1 to 3, wherein start of calculation of the deterioration degree is prohibited.