JP2016169622A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent the excessive temperature rise of a catalyst and the deterioration of fuel efficiency during restarting SOx purge.SOLUTION: An exhaust emission control system includes a NOx reduction type catalyst 32 provided in an exhaust passage 13 of an internal combustion engine 10, a SOx purge control part 60 for performing SOx purge control such that injection system control to increase a fuel injection amount raises an exhaust temperature up to a first target temperature where SOx desorbs to recover the NOx reduction type catalyst 32 from sulfur poisoning, a prohibition processing part 70 for prohibiting the performance of the SOx purge control depending on the operating condition of the internal combustion engine 10, and a temperature retaining mode control part 71 for performing temperature retaining mode control such that a fuel injection amount is controlled during a period for prohibiting the SOx purge control to keep the exhaust temperature as a second target temperature lower than the first target temperature.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust purification system.

  Conventionally, a NOx occlusion reduction type catalyst is known as a catalyst for reducing and purifying nitrogen compounds (NOx) in exhaust gas discharged from an internal combustion engine. 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.

  The NOx occlusion reduction type catalyst also occludes sulfur oxide (hereinafter referred to as SOx) contained in the exhaust gas. When the SOx occlusion amount increases, there is a problem that the NOx purification ability of the NOx occlusion reduction type catalyst is lowered. Therefore, when the SOx occlusion amount reaches a predetermined amount, unburned fuel is added to the upstream oxidation catalyst by post injection or exhaust pipe injection so that SOx is released from the NOx occlusion reduction type catalyst and recovered from S poisoning. So as to raise the exhaust temperature to the SOx separation temperature, so-called SOx purge must be performed periodically (see, for example, Patent Document 1).

JP 2009-47086 A JP 2008-64063 A

  If the SOx purge is performed in a state where the engine speed is very high or the fuel injection amount is very large, there is a possibility that the engine temperature will rise rapidly. In such a state, it is preferable to prohibit or interrupt the execution of the SOx purge.

  However, if post injection or exhaust pipe injection is completely stopped, the catalyst temperature decreases, so that the amount of fuel consumption becomes excessive when the SOx purge is restarted thereafter, causing a problem of excessive catalyst temperature rise and fuel consumption deterioration.

  It is an object of the disclosed system to effectively prevent catalyst overheating and fuel consumption deterioration when resuming SOx purge.

  The disclosed system is provided with a NOx reduction type catalyst that is provided in an exhaust passage of an internal combustion engine for reducing and purifying NOx in exhaust gas, and at least a predetermined temperature at which the sulfur oxide is removed from the exhaust temperature by injection system control that increases the fuel injection amount. The catalyst regeneration means for performing catalyst regeneration control for recovering the NOx reduction type catalyst from sulfur poisoning by raising the temperature to the first target temperature, and prohibiting the execution of the catalyst regeneration control according to the operating state of the internal combustion engine And a catalyst heat retention control for controlling the fuel injection amount and maintaining the exhaust gas temperature at a predetermined second target temperature lower than the first target temperature during the prohibition period of the catalyst regeneration control by the prohibiting means. Thermal insulation control means.

  According to the disclosed system, it is possible to effectively prevent excessive catalyst temperature rise and fuel consumption deterioration when SOx purge is restarted.

1 is an overall configuration diagram showing an exhaust purification system according to an embodiment. It is a timing chart explaining SOx purge control concerning this embodiment. It is a functional block diagram which shows the SOx purge control part which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF target value at the time of SOx purge lean control which concerns on this embodiment. It is a block diagram which shows the setting process of the target injection amount at the time of SOx purge rich control which concerns on this embodiment. It is a timing chart explaining catalyst temperature adjustment control of SOx purge control concerning this embodiment. It is a figure explaining the prohibition process of SOx purge control concerning this embodiment. It is a figure explaining the completion | finish process of the heat retention mode control which concerns on this embodiment, and SOx purge control. It is a flowchart explaining switching from the lean state of the MAF tracking control which concerns on this embodiment to a rich state. It is a flowchart explaining switching from the rich state of the MAF tracking control which concerns on this embodiment to a lean state. It is a block diagram which shows the process of the injection amount learning correction | amendment of the injector which concerns on this embodiment. It is a flowchart explaining the calculation process of the learning correction coefficient which concerns on this embodiment. It is a block diagram which shows the setting process of the MAF correction coefficient which concerns on this embodiment.

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

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

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

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

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

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

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

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

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

  The ECU 50 performs various controls of the engine 10 and the like, and includes a known CPU, ROM, RAM, input port, output port, and the like. In order to perform these various controls, 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, the MAF follow-up control unit 80, the injection amount learning correction unit 90, and the MAF correction coefficient calculation unit 95 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. Then, the forced regeneration flag F _DPF is turned on (F _DPF = 1) and the filter regeneration control is started (see time t _{1 in} FIG. 2). The filter regeneration control is performed by feedback-controlling the exhaust pipe injection amount and the post injection amount based on a predetermined PM combustion temperature (for example, about 550 ° C.). Filter regeneration control, when the PM deposition amount estimated value is reduced to a predetermined lower threshold (determination threshold value) and the PM combustion removal, (see time t ₂ in FIG. 2) which is terminated by turning off the forced regeneration flag F _DPF. 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 filter forced regeneration start (F _DPF = 1) or the upper limit cumulative injection amount.

[SOx purge control]
The SOx purge control unit 60 is a catalyst regeneration unit according to the present invention, which makes the exhaust gas rich and raises the exhaust gas temperature to the SOx removal temperature (for example, about 600 ° C.). Control to recover from poison (hereinafter, this control is referred to as SOx purge control) is executed. The SOx purge control is started when the filter regeneration flag F _DPF is turned off upon completion of the filter regeneration control, and when the SOx purge flag F _SP is turned on while a heat retention mode flag F _SPK described later is turned off (FIG. 2). see time _{t 2).}

  In the present embodiment, as shown in FIG. 3, the SOx purge control unit 60 includes an SOx purge lean control unit 60A, an SOx purge rich control unit 60B, an SOx purge prohibition processing unit 70, a heat retention mode control unit 71, and an SOx. A purge / heat retention mode end processing unit 72 is provided as a part of functional elements. Details of each of these functional elements will be described below.

[SOx purge lean control]
The SOx purge lean control unit 60A sets a first target air excess ratio (for example, a leaner side than a theoretical air-fuel ratio equivalent value (about 1.0) from the time of steady operation (for example, about 1.5) as the exhaust air excess ratio. The SOx purge lean control is performed to reduce the pressure to about 1.3). Details of the SOx purge lean control will be described below.

FIG. 4 is a block diagram showing a process for setting the MAF target value MAF _{SPL_Trgt} during SOx purge lean control. The first target excess air ratio setting map 61 is a map that is referred to based on the engine speed Ne and the accelerator opening Q (the fuel injection amount of the engine 10), and the engine speed Ne, the accelerator opening Q, The excess air ratio target value λ _{SPL_Trgt} (first target excess air ratio) at the time of SOx purge lean control corresponding to is preset based on experiments or the like.

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

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

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

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

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

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

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

[SOx purge rich control]
The SOx purge rich control unit 60B performs SOx purge rich control for further reducing the excess air ratio of the exhaust gas from the first target excess air ratio to the second target excess air ratio on the rich side (for example, about 0.9). Details of the SOx purge rich control will be described below.

FIG. 5 is a block diagram showing processing for setting the target injection amount Q _{SPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in SOx purge rich control. The second target excess air ratio setting map 65 is a map that is referred to based on the engine speed Ne and the accelerator opening Q, and at the time of SOx purge rich control corresponding to the engine speed Ne and the accelerator opening Q. Of the excess air ratio target value λ _{SPR_Trgt} (second target excess air ratio) is set in advance based on experiments or the like.

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

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

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

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

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

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

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

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

As shown at time _{t 1} in FIG. 6, the filter regeneration flag _{F DPF} and, when SOx purge flag _{F SP} is turned on by the off warmth mode flag _{F SPK,} SOx purge rich flag _{F SPR} also turned on, further feedback calculation Is also reset once. That is, for the first time immediately after the forced filter regeneration, exhaust pipe injection or post injection is executed according to the injection period _{TF_INJ_1} set in the injection period setting map (see times t _{1 to} t _{2 in} FIG. 6). Thereby, without reducing the exhaust temperature that has risen due to the forced filter regeneration, it is possible to promptly shift to the SOx purge control and reduce the fuel consumption.

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. 6 t see ₂ ~t _3). Further, when the SOx purge rich flag _{F SPR} is turned on by the lapse of the interval _{T F_INT_1,} injection period _{T F_INJ_2} exhaust pipe injection or post injection according to is performed again (see time _t 3 ~t ₄ in FIG. 6 ). 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. 6) 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.

[SOx purge control prohibition judgment]
If the SOx purge control is performed in a state where the engine speed Ne is very high or the fuel injection amount of the injector 11 is very large, there is a possibility that the engine temperature rapidly increases. Further, when unburned fuel is supplied in a state where the temperature of the NOx storage reduction catalyst 32 is lowered, there is a problem that white smoke or the like is generated due to an increase in HC slip.

  In order to prevent these phenomena, the SOx purge prohibition processing unit 70 (1) When the engine speed Ne exceeds a predetermined rotation speed upper limit threshold value indicating, for example, a rotation abnormality, (2) The fuel injection amount of the injector 11 However, for example, when a predetermined injection amount upper limit threshold value indicating injection abnormality is exceeded, or (3) a predetermined threshold value where the catalyst temperature of the NOx storage reduction catalyst 32 is lower than the target temperature (PM combustion temperature) of the filter regeneration control If any prohibition condition when the temperature drops to about 500 degrees (for example, about 500 degrees) is satisfied, it is determined that “outside the SOx purge possible region” and the execution of the SOx purge control is prohibited. More specifically, when any of these prohibition conditions (1) to (3) is satisfied at the start or during execution of the SOx purge control, and it is determined that “outside the SOx purgeable region”, a heat retention described later is performed. On the other hand, when none of these prohibition conditions (1) to (3) is satisfied while the mode control is performed, it is determined as “in the SOx purgeable region” and the execution of the SOx purge control is permitted. ing.

  The prohibition conditions are not limited to these three conditions, and other prohibition conditions that are not suitable for performing SOx purge, such as a system failure, can be added.

[Insulation mode control]
The heat retention mode control unit 71 is a heat retention control unit of the present invention, and is configured to perform the above-described prohibition conditions (1) to (1) at the end of filter regeneration control (at the start of SOx purge control) or during the execution of SOx purge control. If any one of (3) is established, the heat retention mode flag F _SPK is turned on and the heat retention mode control is started. The heat retention mode control is performed by feedback control of the exhaust pipe injection amount and the post injection amount based on a predetermined heat retention target temperature (second target temperature) lower than the SOx separation temperature. In this embodiment, the heat retention target temperature is set to, for example, the target temperature (PM combustion temperature) for filter regeneration control.

  Hereinafter, based on FIG. 7, the details of the switching process of the filter regeneration control, the heat retention mode control, and the SOx purge control will be described.

When any of the prohibition conditions (1) to (3) is satisfied at the end of the filter regeneration control (F _DPF = 0) and it is determined that “outside the SOx purgeable region”, a pattern A in FIG. As described above, the heat mode control is performed without starting the SOx purge control (F _SPK = 1).

On the other hand, when the prohibition conditions (1) to (3) are not satisfied at the end of the filter regeneration control (F _DPF = 0) and it is determined that “in the SOx purgeable region”, the pattern B in FIG. Thus, the SOx purge control is started without shifting to the heat retention mode control (F _SP = 1).

While the SOx purge control is being performed (F _SP = 1), the prohibition conditions (1) to (3) are not satisfied, and while it is determined “in the SOx purgeable region”, the pattern C in FIG. Further, the catalyst temperature adjustment control (see FIG. 6) for alternately switching on / off (rich / lean) of the SOx purge rich flag _FSPR is performed.

On the other hand, if any of the prohibition conditions (1) to (3) is satisfied during the execution of the SOx purge control and it is determined that “outside the SOx purgeable region”, as shown in the pattern D of FIG. In order to interrupt the purge control, the mode is shifted to the heat retention mode control (F _SPK = 1).

  As described above, in the present embodiment, when it is determined that the SOx purge control starts or is “out of the SOx purgeable region”, the SOx purge control is prohibited and the heat retention mode control is performed. ing. As a result, useless SOx purge control is reliably suppressed, and it is possible to effectively prevent deterioration in fuel consumption, rapid increase in engine temperature, generation of white smoke, and the like. Further, during the prohibition (interruption) of the SOx purge control, the catalyst temperature is maintained at the PM combustion temperature by the heat retention mode control, so that it is possible to effectively reduce the fuel consumption when restarting the SOx purge control thereafter. .

[Determining SOx purge control / heat retention mode control end]
The SOx purge / heat retention mode end processing unit 72 is an end processing means of the present invention, and is based on the SOx storage amount of the NOx storage reduction catalyst 32, the heat retention mode control, the cumulative execution time of the SOx purge control, and the like. A termination process for terminating the control and the SOx purge control is executed. The details of each end processing pattern will be described below with reference to FIG.

[End pattern A]
A pattern A shown in FIG. 8 is an example in which the SOx purge control is ended by SOx poisoning recovery of the NOx storage reduction catalyst 32. When the SOx purge control performs the SOx purge control, the SOx occlusion amount SA of the NOx occlusion reduction type catalyst 32 is lowered to a predetermined first occlusion amount threshold value SA ₁ indicating SOx poisoning recovery, and the SOx purge rich flag F _SPR is turned off (F _SPR = 0), and the SOx purge control is terminated without shifting to the heat retention mode control. The SOx occlusion amount SA of the NOx occlusion reduction type catalyst 32 may be estimated based on, for example, a model formula or a map including the operation state of the engine 10 and the sensor value of the NOx / lambda sensor 45 as an input signal. First storage amount threshold SA ₁ is stored in the memory of the ECU50 obtains in advance by experiments or the like.

[End pattern B]
Pattern B shown in FIG. 8 is an example in which the SOx purge control is terminated by time limitation regardless of SOx poisoning recovery. When the cumulative execution time T _{SPR_sum} measured by the timer from the start of the SOx purge control reaches a predetermined first upper limit threshold time T _{SPR_Lim} , the SOx purge rich flag F _SPR is turned off (F) without performing the heat retention mode control. _SP , F _SPR = 0) and SOx purge control is terminated. The first upper limit threshold time T _{SPR_Lim1} is acquired in advance by experiments or the like and stored in the memory of the ECU 50.

[End pattern C]
The pattern C shown in FIG. 8 is an example in which the heat retention mode control is ended in the upper limit time when the heat retention mode control is continued by the determination “out of SOx purgeable region”. When the cumulative execution time T _{SPK_sum} measured by the timer from the start of the heat retention mode control reaches a predetermined second upper limit threshold time T _{SPK_Lim2} , the heat retention mode flag F _SPK is turned off (F _SPK without shifting to the SOx purge control). = 0) to end the heat retention mode control. The second upper limit threshold time T _{SPK_Lim2} is shorter than the first upper limit threshold time T _{SPR_Lim1} , and is acquired in advance through experiments or the like and stored in the memory of the ECU 50 (T _{SPK_Lim2} <T _{SPR_Lim1} ).

[End pattern D]
Pattern D shown in FIG. 8 is an example in which when the heat retention mode control is continued by the determination “out of SOx purgeable region”, the heat retention mode control is terminated within the upper limit time although the SOx occlusion amount has decreased only to a predetermined amount. It is. Although the amount of SOx occlusion SA during the performance of thermal insulation mode control becomes lower than a predetermined second storage amount threshold SA _2, third upper threshold time accumulating execution times T _{SPK_sum} that clocking of predetermined by the timer from the start of the heat retention mode control When T _{SPK_Lim3} is reached, the heat retention mode flag F _SPK is turned off (F _SPK = 0) and the process is terminated without shifting to the SOx purge control. Second storage amount threshold SA ₂ is a more value than the first storage amount threshold SA _1, is stored in the memory of the ECU50 obtains in advance by experiments or the like _(SA 2> SA 1). The third upper limit threshold time T _{SPK_Lim3} is shorter than the second upper limit threshold time T _{SPK_Lim2} and is acquired in advance through experiments or the like and stored in advance in the memory of the ECU 50 (T _{SPK_Lim3} <T _{SPK_Lim2} <T _{SPR_Lim1} ). .

[End pattern E]
Pattern E shown in FIG. 8 is an example of termination when the sum of accumulated times of SOx purge lean control and SOx purge rich control (accumulated time of SOx purge control) reaches the upper limit time. When the cumulative execution time T _{SP_sum} of the SOx purge control _{reaches the} predetermined fourth upper limit threshold time _{T_Lim4} , the SOx purge flag F _SP is turned off (F _SP = 0), and the SOx purge control is ended. The fourth upper limit threshold time _{T_Lim4} is acquired in advance through experiments or the like and stored in the memory of the ECU 50.

[End pattern F]
The pattern F shown in FIG. 8 is an example that is terminated when the heat retention mode control implementation time reaches the upper limit time. When the accumulated execution time T _{SPK_sum} of the heat retention mode control _{reaches the} predetermined fifth upper limit threshold time _{T_Lim5} , the heat retention mode flag F _SPK is turned off (F _SP = 0, F _SPK = 0), and the heat retention mode control is performed. Terminate. The fifth upper threshold time _{T_Lim5} is acquired in advance through experiments or the like and stored in the memory of the ECU 50.

  As described above, in this embodiment, by setting the upper limit of the cumulative execution time in the end conditions of the SOx purge control and the heat retention mode control, an increase in fuel consumption and an exhaust overheating temperature due to continuous execution of these controls are provided. PM abnormal combustion, catalyst thermal deterioration, and the like can be effectively prevented.

[MAF tracking control]
The MAF follow-up control unit 80 (1) switches each injector 11 during the switching period from the end of the filter regeneration control to the rich state by the start of the SOx purge control and (2) the switching period from the rich state to the lean state by the end of the SOx purge control. The control for correcting the fuel injection timing and the fuel injection amount according to the MAF change (hereinafter, this control is referred to as MAF tracking control) is executed.

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

  In order to avoid such a phenomenon, as shown in the flowcharts of FIGS. 9 and 10, MAF follow-up control is executed to increase / decrease the advance / retard angle of the injection timing and the injection amount in accordance with the MAF change.

  First, based on FIG. 9, the MAF tracking control during the switching period from the lean state to the rich state will be described.

In step S100, the SOx purge flag _{F SP} is turned on, at step S110, time measurement by the timer in order to measure the elapsed time of MAF following control is started.

In step S120, before the switching from the MAF target value _{MAF SPL_Trgt} after switching (rich state) by subtracting the MAF target value _{MAF L_Trgt} of (lean state), before and after switching of the MAF target value change amount ΔMAF _{Trgt (= MAF SPL_Trgt} - MAF _{L_Trgt} ) is calculated.

In step S130, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{L_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{L_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S140, in accordance with the current actual MAF change rate ΔMAF _Ratio , a coefficient for advancing or retarding the injection timing of each injector 11 (hereinafter referred to as an injection timing tracking coefficient Comp ₁ ) and the injection amount of each injector 11 Is set to increase or decrease (hereinafter referred to as injection amount tracking coefficient Comp ₂ ). More specifically, the storage unit (not shown) of the ECU 50 stores an injection timing follow-up coefficient setting map M1 that defines the relationship between the actual MAF change rate MAF _Ratio and the injection timing follow-up coefficient Comp ₁ created in advance by experiments and the like, and the actual MAF change. An injection amount follow-up coefficient setting map M2 that defines the relationship between the rate MAF _Ratio and the injection amount follow-up coefficient Comp ₂ is stored. The injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are set by reading values corresponding to the actual MAF change rate ΔMAF _Ratio calculated in step S130 from these maps M1 and M2.

In step S150, the injection timing of each injector 11 is advanced by the amount obtained by multiplying the target advance amount by the injection timing follow-up coefficient Comp _1, and each time by the amount obtained by multiplying the target injection increase amount by the injection amount follow-up coefficient Comp _2. The injector 11 also increases the fuel injection amount.

Thereafter, in step S160, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{SPL_Trgt} after switching (rich state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{SPL_Trgt} (No), the _{process returns} to step S130 via step S170. That is, by repeating the processing of steps S130 to _S150 until the actual MAF value MAF _Act becomes the MAF target value MAF _{SPL_Trgt} , the advance angle of the injection timing according to the actual MAF change rate MAF _Ratio that changes _every moment, and the injection The increase in quantity continues. Details of the processing in step S170 will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{SPL_Trgt} in the determination in step S160 (Yes), this control is finished.

In step S170, it is determined whether or not the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max .

When shifting from the lean state to the rich state, the actual MAF value MAF _Ref cannot catch up with the MAF target value MAF _{L-R_Trgt} during the transition period due to the influence of valve control delay or the like, and the actual MAF value MAF _Ref becomes the MAF target value MAF _L it may be maintained at lower than _{-R_Trgt} (see time _t 1 ~t _2). If the MAF follow-up control is continued in such a state, the actual fuel injection amount is not increased to the target injection amount, the combustion of the engine 10 becomes unstable, and there is a possibility that torque fluctuation or drivability deteriorates. is there.

In the present embodiment, in order to avoid such a phenomenon, when it is determined in step S170 that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, the actual MAF value MAF _Ref continues for a predetermined time. If it has not changed more than the predetermined value, the process proceeds to step S180, and the injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control is forcibly terminated, and torque fluctuation and drivability deterioration can be effectively prevented.

  Next, MAF tracking control at the time of switching from the rich state to the lean state will be described based on FIG.

In step S200, SOx purge flag _{F SP} is when turned off, at step S210, time measurement by the timer in order to measure the elapsed time of MAF following control is started.

In step S220, before the switching from the MAF target value _{MAF L_Trgt} after switching (lean state) by subtracting the MAF target value _{MAF SPL_Trgt} of (rich state), before and after switching of the MAF target value change amount ΔMAF _{Trgt (= MAF L_Trgt} - MAF _{SPL_Trgt} ) is calculated.

In step S230, the current actual MAF change rate ΔMAF _Ratio is calculated. More specifically, by subtracting the MAF target value MAF _{SPL_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{SPL_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step S240, a value corresponding to the actual MAF change rate ΔMAF _Ratio is read from the injection timing tracking coefficient setting map M1 as the injection timing tracking coefficient Comp ₁ , and also corresponds to the actual MAF change rate ΔMAF _Ratio from the injection amount tracking coefficient setting map M2. value is read as the injection quantity coefficient of following Comp _2.

In step S250, the injection timing of each injector 11 is retarded by the target delay amount multiplied by the injection timing follow-up coefficient Comp ₁ , and the target injection decrease amount is multiplied by the injection amount follow-up coefficient Comp _2. The fuel injection amount of the injector 11 is also reduced.

Thereafter, in step S260, it is determined whether or not the current actual MAF value MAF _Act detected by the MAF sensor 40 has reached the MAF target value MAF _{L_Trgt} after switching (lean state). When the actual MAF value MAF _Act has not reached the MAF target value MAF _{L_Trgt} (No), the _{process returns} to step S230 via step S270. That is, by repeating the processing of steps S230 to S250 until the actual MAF value MAF _Act becomes the MAF target value MAF _{L_Trgt} , the delay of the injection timing according to the actual MAF change rate MAF _Ratio that changes every moment, and the injection The amount continues to decrease. Details of the processing in step S270 will be described later. On the other hand, when the actual MAF value MAF _Ref reaches the MAF target value MAF _{L_Trgt} in the determination in step S260 (Yes), this control ends.

In step S270, it is determined whether or not the accumulated time T _Sum measured by the timer from the start of the MAF follow-up control has exceeded a predetermined upper limit time T _Max .

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

In this embodiment, in order to avoid such a phenomenon, when it is determined in step S270 that the accumulated time T _Sum has exceeded the upper limit time T _Max (Yes), that is, the actual MAF value MAF _Ref continues for a predetermined time. If it has not changed more than the predetermined value, the process proceeds to step S280, and the injection timing follow-up coefficient Comp ₁ and the injection amount follow-up coefficient Comp ₂ are forcibly set to “1”. Thereby, MAF follow-up control is forcibly terminated, and torque fluctuation and drivability deterioration can be effectively prevented.

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

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

In step S310, an error Δλ obtained by subtracting the actual lambda value λ _Act detected by the NOx / lambda sensor 45 from the estimated lambda value λ _Est is multiplied by the learning value gain K ₁ and the correction sensitivity coefficient K ₂ to thereby obtain the learning value F _CorrAdpt is calculated (F _CorrAdpt = (λ _Est −λ _Act ) × K ₁ × K ₂ ). The estimated lambda value λ _Est is estimated and calculated from the operating state of the engine 10 according to the engine speed Ne and the accelerator opening Q. Further, the correction sensitivity coefficient _{K 2} is read the actual lambda value lambda _Act detected by the NOx / lambda sensor 45 from the correction sensitivity coefficient map 91A shown in FIG. 11 as an input signal.

In step S320, it is determined whether or not the absolute value | F _CorrAdpt | of the learning value F _CorrAdpt is within the range of the predetermined correction limit value A. If the absolute value | F _CorrAdpt | exceeds the correction limit value A, the present control is returned to stop the current learning.

In step S330, it is determined whether the learning prohibition flag _FPro is off. The learning prohibition flag F _Pro corresponds to, for example, the transient operation of the engine 10 or the SOx purge control (F _SP = 1). This is because when these conditions are satisfied, the error Δλ increases due to a change in the actual lambda value λ _Act , and accurate learning cannot be performed. Whether or not the engine 10 is in a transient operation state is determined based on, for example, the time change amount of the actual lambda value λ _Act detected by the NOx / lambda sensor 45 when the time change amount is larger than a predetermined threshold value. What is necessary is just to determine with a transient operation state.

In step S340, the learning value map 91B (see FIG. 11) referred to based on the engine speed Ne and the accelerator opening Q is updated to the learning value F _CorrAdpt calculated in step S310. More specifically, on the learning value map 91B, a plurality of learning areas divided according to the engine speed Ne and the accelerator opening Q are set. These learning regions are preferably set to have a narrower range as the region is used more frequently and to be wider as a region is used less frequently. As a result, learning accuracy is improved in regions where the usage frequency is high, and unlearning can be effectively prevented in regions where the usage frequency is low.

In step S350, the learning correction coefficient F _Corr is calculated by adding “1” to the learned value read from the learned value map 91B using the engine speed Ne and the accelerator opening Q as input signals (F _Corr = 1 + F). _CorrAdpt ). This learning correction coefficient F _Corr is input to the injection amount correction unit 92 shown in FIG.

The injection amount correction unit 92 multiplies each basic injection amount of pilot injection Q _Pilot , pre-injection Q _Pre , main injection Q _Main , after-injection Q _After , and post-injection Q _{Post by} a learning correction coefficient F _Corr. The injection amount is corrected.

In this way, by correcting the fuel injection amount to each injector 11 with the learning value corresponding to the error Δλ between the estimated lambda value λ _Est and the actual lambda value λ _Act , the aging deterioration, characteristic change, individual difference of each injector 11 is corrected. It is possible to effectively eliminate such variations.

[MAF correction coefficient]
MAF correction coefficient calculating unit 95 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 injector 11 is corrected based on the error Δλ between the actual lambda value λ _Act and the estimated lambda value λ _Est detected by the NOx / lambda sensor 45. However, since lambda is the ratio of air to fuel, the factor of error Δλ is not necessarily only the effect of the difference between the commanded injection amount and the actual injection amount for each injector 11. That is, there is a possibility that the error of not only each injector 11 but also the MAF sensor 40 affects the lambda error Δλ.

FIG. 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 speed Ne and the accelerator opening Q. The MAF indicating the sensor characteristics of the MAF sensor 40 corresponding to the engine speed Ne and the accelerator opening Q is shown in FIG. The correction coefficient _{Maf_corr} is set in advance based on experiments or the like.

The MAF correction coefficient calculation unit 95 reads the MAF correction coefficient _{Maf_corr} from the correction coefficient setting map 96 using the engine speed Ne and the accelerator opening Q as input signals, and _{uses the} MAF correction coefficient _{Maf_corr} as the MAF target value calculation unit 62 and It transmits to the injection quantity target value calculating part 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} during the SOx purge control.

[Others]
In addition, this invention is not limited to the above-mentioned embodiment, In the range which does not deviate from the meaning of this invention, it can change suitably and can implement.

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

Claims (5)

A NOx reduction catalyst provided in an exhaust passage of the internal combustion engine for reducing and purifying NOx in the exhaust;
Catalyst regeneration control for recovering the NOx reduction catalyst from sulfur poisoning is performed by raising the exhaust temperature to a predetermined first target temperature at which sulfur oxides are released by at least injection system control for increasing the fuel injection amount. Catalyst regeneration means;
Prohibiting means for prohibiting execution of the catalyst regeneration control in accordance with the operating state of the internal combustion engine;
Heat retention control means for performing catalyst heat retention control for controlling the fuel injection amount during the prohibition period of the catalyst regeneration control by the prohibition means to maintain the exhaust gas temperature at a predetermined second target temperature lower than the first target temperature; An exhaust purification system comprising. The exhaust purification system according to claim 1, wherein the prohibiting unit prohibits the execution of the catalyst regeneration control when the rotational speed of the internal combustion engine rises above a predetermined rotational speed upper limit threshold. 3. The exhaust purification system according to claim 1, wherein the prohibiting unit prohibits the catalyst regeneration control from being performed when a fuel injection amount of the injector of the internal combustion engine exceeds a predetermined injection amount upper limit threshold value. The exhaust purification system according to any one of claims 1 to 3, wherein when the catalyst temperature of the NOx reduction catalyst falls below the second target temperature, the prohibiting unit prohibits execution of the catalyst regeneration control. A filter provided in the exhaust passage to collect particulate matter in the exhaust;
Filter regeneration means for performing filter regeneration control for increasing the fuel injection amount to raise the exhaust gas temperature to the combustion temperature of the particulate matter deposited on the filter,
The catalyst regeneration means starts the catalyst regeneration control when the filter regeneration control by the filter regeneration means is completed, and the second target temperature used for the catalyst heat retention control is set to the combustion temperature of the particulate matter. Item 5. The exhaust gas purification system according to any one of Items 1 to 4.

Images