WO2016133026A1

WO2016133026A1 - Exhaust purification system and control method therefor

Info

Publication number: WO2016133026A1
Application number: PCT/JP2016/054200
Authority: WO
Inventors: 輝男中田; 隆行坂本; 長岡　大治; 裕之遊座
Original assignee: いすゞ自動車株式会社
Priority date: 2015-02-16
Filing date: 2016-02-12
Publication date: 2016-08-25
Also published as: JP6492733B2; JP2016151197A

Abstract

This exhaust purification system is provided with: a NOx reduction catalyst 32 which is provided to an exhaust passage of an engine 10, and which occludes NOx in exhaust when the exhaust air-fuel ratio is in a lean state; a MAF sensor 40 for detecting the intake air amount of the engine 10; and an ECU 50 which switches the lean state to a rich state using both air-system control for reducing the intake air amount, and injection-system control for increasing the fuel injection amount, to reduce and purify occluded NOx and cause the occluded NOx to be released from the NOx reduction catalyst 32. The ECU 50 determines the start time of the injection-system control on the basis of the ratio (the actual MAF change ratio ∆MAF_Ratio) of the actual MAF change amount ∆MAF_Act, i.e. the value of the difference between a first MAF target value MAF_{L_Trgt} and the actual MAF value MAF_Act, to the MAF target value change amount ∆MAF_Trgt, i.e. the value of the difference between the first MAF target value MAF_{L_Trgt} and a second MAF target value MAF_{NPL_Trgt}.

Description

Exhaust gas purification system and control method thereof

The present invention relates to an exhaust purification system and a control method thereof.

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. This NOx occlusion reduction type catalyst occludes NOx contained in the exhaust when the exhaust is in a lean atmosphere, and reduces and purifies NOx occluded by hydrocarbons contained in the exhaust when the exhaust is in a rich atmosphere. Detoxify and release. For this reason, when the NOx occlusion amount of the catalyst reaches a predetermined amount, so-called NOx purge that makes the exhaust rich by post injection or exhaust pipe injection needs to be performed periodically to restore the NOx occlusion capacity ( For example, see Patent Document 1).

Japanese Unexamined Patent Publication No. 2008-202425

If the above-mentioned NOx purge is performed only by injection system control by post injection or exhaust pipe injection, the fuel consumption becomes excessive and the fuel efficiency is deteriorated. For this reason, it is preferable to use both the injection system control and the air system control for reducing the intake air amount by adjusting the opening of the intake throttle valve and the EGR valve.

When using injection system control and air system control together, it is desirable to perform injection system control after sufficiently reducing the amount of intake air by air system control. This is because the excess air ratio of the exhaust gas can be sufficiently reduced and NOx can be reliably reduced and purified by the NOx storage reduction catalyst. However, there are variations in the time taken to reduce the intake air amount to a desired amount by air system control. For this reason, there is a possibility that the injection system control is performed in a state where the intake air amount is not sufficiently lowered, and there are problems such as an increase in fuel discharge amount and an increase in fuel consumption accompanying an increase in the injection system control time.

An object of the present disclosure is to make it possible to perform injection system control in a state in which the amount of intake air is sufficiently reduced.

An exhaust purification system of the present disclosure includes a NOx reduction catalyst that is provided in an exhaust passage of an internal combustion engine and stores NOx in exhaust when the exhaust air-fuel ratio is lean, and an intake air amount that detects an intake air amount of the internal combustion engine The exhaust air-fuel ratio is switched from the lean state to the rich state by using a sensor, air system control for reducing the intake air amount, and injection system control for increasing the fuel injection amount, thereby reducing and purifying the stored NOx. And a controller that releases the NOx reduction catalyst from the NOx reduction catalyst, wherein the controller includes a first difference value between the lean target first target intake air amount and the rich target second target intake air amount; The start timing of the injection system control is determined based on the ratio of the second difference value between the first target intake air amount and the intake air amount.

An exhaust purification system of the present disclosure includes a NOx reduction catalyst that is disposed in an exhaust passage of an internal combustion engine, and stores NOx contained in the exhaust when the exhaust discharged from the internal combustion engine is in a lean state. The air-fuel ratio of the exhaust gas is controlled by using an intake air amount sensor for detecting the intake air amount of the internal combustion engine, an air system control for controlling the intake air amount, and an injection system control for controlling the fuel injection amount. An exhaust purification system comprising: a control unit that operates to perform the following process:
Catalyst regeneration that switches the air-fuel ratio of the exhaust gas from a lean state to a rich state by executing the air system control and the injection system control, and releases NOx stored in the NOx reduction catalyst from the NOx reduction catalyst processing;
A calculation process for calculating a second difference value that is a difference between a first target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust gas is in a lean state and an intake air amount of the internal combustion engine; A ratio between a first difference value that is a difference between one target intake air amount and a second target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust gas is in a rich state, and the second difference value The determination process which determines the start time of the said injection system control based on this.

An exhaust purification system control method according to an embodiment of the present disclosure is provided in an exhaust passage of an internal combustion engine, and stores NOx contained in the exhaust when the exhaust discharged from the internal combustion engine is in a lean state. A control method for an exhaust purification system comprising: an air system control for controlling an intake air amount and an injection system control for controlling a fuel injection amount to change the air-fuel ratio of the exhaust from a lean state to a rich state A catalyst regeneration process for switching and releasing NOx stored in the NOx reduction catalyst from the NOx reduction catalyst; a first target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust is in a lean state And a calculation process for calculating a second difference value, which is a difference between the intake air amount of the internal combustion engine and the first target intake air amount and the air-fuel ratio of the exhaust is in a rich state A first difference value that is the difference between the second target intake air amount is an intake air quantity, on the basis of a ratio between the second difference value, including the determination process determines the start timing of the injection system control.

According to the exhaust purification system and its control method of the present disclosure, the injection system control can be performed in a state where the intake air amount is sufficiently reduced.

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 NOx purge control according to the present embodiment. FIG. 3 is a block diagram showing a MAF target value setting process during NOx purge lean control according to the present embodiment. FIG. 4 is a block diagram showing a target injection amount setting process during NOx purge rich control according to the present embodiment. FIG. 5 is a diagram schematically illustrating the processing of the injection system control start determination unit according to the present embodiment. FIG. 6 is a flowchart for explaining the switching from the lean state to the rich state of the MAF tracking control according to the present embodiment. FIG. 7 is a flowchart for explaining switching from the rich state to the lean state of the MAF tracking control according to the present embodiment. FIG. 8 is a diagram for explaining the difference between the actual MAF value and the MAF target value when shifting from the lean state to the rich state or from the rich state to the lean state. FIG. 9 is a block diagram showing the injection amount learning correction processing of the injector according to the present embodiment. FIG. 10 is a flowchart for explaining the learning correction coefficient calculation processing according to the present embodiment. FIG. 11 is a block diagram showing the MAF correction coefficient setting process 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 is provided with an injector 11 that directly injects high-pressure fuel accumulated 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 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. An engine speed sensor 41, an accelerator opening sensor 42, and a boost pressure sensor 46 are attached to the engine 10.

In the description of the present embodiment, the MAF sensor 40 that measures and detects the mass flow rate (Mass Air Flow) is used as an intake air amount sensor that measures and detects the intake air amount (intake flow rate (Suction Air Flow)) of the engine. As long as the intake flow rate of the engine can be measured and detected, a different type of flow rate (Air Flow) sensor from the MAF sensor 40 or a means in place of the flow rate sensor may be used.

The EGR (Exhaust Gas Recirculation) 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. Further, exhaust pipe injection for injecting unburned fuel (mainly hydrocarbon (HC)) into the exhaust passage 13 in the exhaust passage 13 upstream of the oxidation catalyst 31 in response to an instruction signal input from the ECU 50. A device 34 is provided.

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 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 particulate matter (hereinafter also referred to as PM) in the exhaust gas in the pores and surfaces of the partition walls, and performs so-called filter regeneration that burns and removes the estimated PM deposition amount when it reaches a predetermined amount. Executed. Filter regeneration is performed by supplying unburned fuel to the upstream oxidation catalyst 31 by exhaust pipe injection or post injection, and raising the exhaust temperature flowing into the filter 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.

ECU50 is an example of the control part and control unit of this indication, and performs various control of engine 10 grade. The ECU 50 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. Further, the ECU 50 includes a filter regeneration control unit 51, a NOx purge control unit 70, a MAF follow-up control unit 80, an injection amount learning correction unit 90, and a MAF correction coefficient calculation unit 95 as 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, an instruction signal for executing exhaust pipe injection is transmitted to the exhaust pipe injection device 34, or an instruction signal for executing post injection is transmitted to each injector 11, and the exhaust temperature is set to the PM combustion temperature (for example, about 550 ° C.). This filter regeneration process is terminated when the PM accumulation estimated amount falls to a predetermined lower threshold (determination threshold) indicating combustion removal. The end determination may be based on the upper limit elapsed time from the start of filter regeneration or the upper limit cumulative injection amount.

[NOx purge control]
The NOx purge control unit 70 restores the NOx storage capability of the NOx storage reduction catalyst 32 by making the exhaust atmosphere rich and detoxifying and releasing NOx stored in the NOx storage reduction catalyst 32 by reduction purification. Control (hereinafter, this control is referred to as NOx purge control) is executed.

As shown in FIG. 2, the NOx purge flag F _NP for starting the NOx purge control estimates the NOx emission amount per unit time from the operating state of the engine 10, and the estimated cumulative value ΣNOx obtained by accumulating the NOx purge flag FNP has a predetermined threshold value. It is turned on when exceeding (see time t ₁ in FIG. 2). Alternatively, the NOx purification rate by the NOx occlusion reduction type catalyst 32 is calculated from the NOx emission amount upstream of the catalyst estimated from the operating state of the engine 10 and the NOx amount downstream of the catalyst detected by the NOx / lambda sensor 45. When the NOx purification rate becomes lower than a predetermined determination threshold, the NOx purge flag F _NP is turned on.

In the present embodiment, the enrichment by the NOx purge control is performed on the lean side of the excess air ratio from the stoichiometric air-fuel ratio equivalent value (about 1.0) from the time of steady operation (for example, about 1.5) by the air system control. NOx purge lean control for reducing to 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) .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. 3 is a block diagram showing a process for setting the MAF target value MAF _{NPL_Trgt} during the NOx purge lean control. The first 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. An excess air ratio target value λ _{NPL_Trgt} (first 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 first 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} during NOx purge lean control based on the following formula (1).

MAF _{NPL_Trgt} = λ _{NPL_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 _{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. 2). The ramp processing unit 73 reads the ramp coefficient from the + ramp coefficient map 73A and the −ramp coefficient map 73B using the engine speed Ne and the accelerator opening Q as input signals, and obtains the MAF target ramp value MAF _{NPL_Trgt_Ramp} to which the ramp coefficient is added. Input to the valve control unit 74.

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

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

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

[NOx purge rich control fuel injection amount setting]
FIG. 4 is a block diagram showing processing for setting the target injection amount Q _{NPR_Trgt} (injection amount per unit time) of exhaust pipe injection or post injection in NOx purge rich control.

The injection system control start determination unit 75 determines the start timing of the injection system control by the NOx purge control unit 70. A detection signal of the MAF sensor 40 is input to the injection system control start determination unit 75, and the first MAF target value MAF _{L_Trgt} that is the MAF target value before switching from the lean state to the rich state (lean state) is switched. The second MAF target value MAF _{NPL_Trgt} , which is the later (rich state) MAF target value, and the determination threshold for determining the arrival of the start timing of the injection system control are referred to. The determination threshold in the present embodiment is stored in a storage unit (not shown) of the ECU 50, and can be changed within the range from the maximum value to the minimum value.

As shown at time t ₁ in FIG. 5, when the NOx purge flag F _NP is turned on (F _NP = 1), the injection system control start determination unit 75 determines from the second MAF target value MAF _{NPL_Trgt} to the first MAF target value MAF _{L_Trgt.} Is _subtracted to calculate the MAF target value change amount ΔMAF _Trgt (= MAF _{NPL_Trgt} −MAF _{L_Trgt} ) before and after switching. This MAF target value change amount ΔMAF _Trgt is an example of the first difference value of the present disclosure.

Next, the injection system control start determination unit 75 subtracts the first MAF target value MAF _{L_Trgt} from the current actual MAF value MAF _Act detected by the MAF sensor 40 to thereby determine the actual MAF from the start of the MAF follow-up control to the present. A change amount ΔMAF _Act (= MAF _Act −MAF _{L_Trgt} ) is calculated. This actual MAF change amount ΔMAF _Act is an example of the second difference value of the present disclosure.

The injection system control start determination unit 75 calculates the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ) by dividing the actual MAF change amount ΔMAF _Act by the MAF target value change amount ΔMAF _Trgt before and after switching. To do. This actual MAF change rate ΔMAF _Ratio is an example of a ratio between the first difference value and the second difference value of the present disclosure.

Further, the injection system control start determination unit 75 calculates the actual MAF change rate ΔMAF _Ratio in real time and compares it with the determination threshold value. When the actual MAF change rate ΔMAF _Ratio becomes equal to or greater than the determination threshold value, the MAF is sufficient. As a result, a start signal is output to the injection amount target value calculation unit 77 to instruct the start of injection system control. In the example of FIG. 5, at time t ₂ is the actual MAF change rate DerutaMAF _Ratio since reaching the determination threshold value, the start of the injection system control is instructed to the injection amount target value computing unit 77. As a result, the post-injection and exhaust pipe injection is carried out in time t ₂ or later.

The second target excess air ratio setting map 76 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} (second target air excess rate) is preset based on experiments or the like.

First, from the second target excess air ratio setting map 76, the excess air ratio target value λ _{NPR_Trgt} at the time of NOx purge rich control is read using the engine speed Ne and the accelerator opening Q as input signals, and an injection amount target value calculation unit 77 is obtained. Is input.

The injection amount target value calculation unit 77 calculates a target injection amount Q _{NPR_Trgt} at the time of NOx purge rich control based on the following mathematical formula (2). This calculation is performed on condition that a start signal from the injection system control start determination unit 75 is input.

Q _{NPR_Trgt} = MAF _{NPL_Trgt} × _{Maf_corr} / (λ _{NPR_Trgt} × Ro _Fuel × AFR _sto ) −Q _{fnl_corrd} (2)
In Formula (2), 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_cord} is a fuel injection amount (excluding post-injection) before application of learning corrected MAF tracking control described later, Ro _Fuel is fuel specific gravity, AFR _sto is a theoretical air-fuel ratio, and _{Maf_corr} is a MAF correction coefficient described later. Show.

The target injection amount Q _{NPR_Trgt} calculated by the injection amount target value calculation unit 77 is transmitted as an injection instruction signal to each injector 11 or the exhaust pipe injection device 34 (time t _{2 in} FIGS. 2 and 5). The transmission of the injection instruction signal is continued until the NOx purge flag F _NP is turned off (time t _{4 in} FIG. 2) by the end determination of NOx purge control described later. Thus, post injection by each injector 11 and exhaust pipe injection by the exhaust pipe injection device 34 are performed.

Thus, in this embodiment, the target achievement level of the MAF value by air system control (NOx purge lean control) is determined based on the actual MAF change rate ΔMAF _Ratio calculated by the injection system control start determination unit 75. . The injection system control start determination unit 75 starts injection system control (post injection, exhaust pipe injection) when the actual MAF change rate ΔMAF _Ratio reaches a predetermined determination threshold. As a result, unburned fuel is supplied with the MAF sufficiently lowered. In other words, unburned fuel is supplied in a situation where the effect of NOx reduction by rich control can be expected. As a result, the injection system control time can be shortened and fuel consumption can be improved.

Further, since the ECU 50 stores the determination threshold value so that the numerical value can be changed within the range from the maximum value to the minimum value, the determination criterion suitable for the system can be easily set.

Further, in the present embodiment, the target injection amount Q _{NPR_Trgt} is set based on the excess air ratio target value λ _{NPR_Trgt} read from the second target excess air ratio setting map 76 and the fuel injection amount of each injector 11. ing. Thus, without providing a lambda sensor upstream of the NOx storage reduction catalyst 32, or even when a lambda sensor is provided upstream of the NOx storage reduction catalyst 32, the sensor value of the lambda sensor is not used. It is possible to effectively reduce the exhaust gas to a desired excess air ratio required for NOx purge rich control.

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

[No air system control for NOx purge control]
The ECU 50 feedback-controls the opening degree of the intake throttle valve 16 and the EGR valve 24 based on the sensor value of the MAF sensor 40 in the region where the operating state of the engine 10 is on the low load side. On the other hand, in the region where the operating state of the engine 10 is on the high load side, the ECU 50 feedback-controls the supercharging pressure by the variable displacement supercharger 20 based on the sensor value of the boost pressure sensor 46 (hereinafter, this region is referred to as “high”). (Referred to as boost pressure FB control region).

In such a boost pressure FB control region, a phenomenon occurs in which the control of the intake throttle valve 16 and the EGR valve 24 interferes with the control of the variable displacement supercharger 20. For this reason, there is a problem that the intake air amount cannot be maintained at the MAF target value MAF _{NPL_Trgt} even if the NOx purge lean control for performing feedback control of the air system based on the MAF target value MAF _{NPL_Trgt} set by the above formula (1) is executed. is there. As a result, even if the NOx purge rich control for executing the post injection or the exhaust pipe injection is started, the excess air ratio can be lowered to the second target excess air ratio (the excess air ratio target value λ _{NPR_Trgt} ) necessary for the NOx purge. There is no possibility.

In order to avoid such a phenomenon, the NOx purge control unit 70 of the present embodiment prohibits NOx purge lean control for adjusting the opening of the intake throttle valve 16 and the EGR valve 24 in the boost pressure FB control region, and The excess air ratio is decreased to the second target excess air ratio (the excess air ratio target value λ _{NPR_Trgt} ) only by injection or post injection. As a result, the NOx purge can be reliably performed even in the boost pressure FB control region. In this case, the MAF target value set based on the operating state of the engine 10 may be applied to the MAF target value MAF _{NPL_Trgt} of the above-described mathematical formula (2).

[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 of the NOx occlusion amount of the NOx occlusion-reduction catalyst 32 has decreased to a predetermined threshold value indicating a successful removal of NOx is satisfied, NOx purge flag F _NP is terminated by turning off the (time t ₄ in FIG. 2 reference).

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

[MAF tracking control]
The MAF follow-up control unit 80 includes (1) a switching period from the lean state in the normal operation to the rich state by the NOx purge control, and (2) a switching period from the rich state to the lean state in the normal operation by the NOx purge control. Control for correcting the fuel injection timing and the fuel injection amount of the injector 11 in accordance with 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 NOx purge lean control, an ignition delay occurs at the same fuel injection timing as in the lean state of normal operation. Therefore, when switching from the lean state to the rich state, it is necessary to advance the injection timing by a predetermined amount. Further, when switching from the rich state to the normal lean state, it is necessary to return the injection timing to the normal injection timing by retarding. However, the advance angle or retard angle of the injection timing is performed more rapidly than the air system operation. For this reason, the advance or retard of the injection timing is completed before the excess air ratio reaches the target excess air ratio due to the air system operation, and the drivability due to the sudden increase in NOx generation amount, combustion noise, torque, etc. There is a problem that causes deterioration.

In order to avoid such a phenomenon, the MAF follow-up control unit 80, as shown in the flowcharts of FIGS. 6 and 7, performs MAF follow-up control for correcting the advance / retard of the injection timing and the injection amount according to the change in MAF. Execute.

First, the MAF tracking control during the switching period from the lean state to the rich state will be described with reference to FIG.

In step S100, when the NOx purge flag F _NP is turned on (F _NP = 1), in step S110, a timer is started to measure the elapsed time of MAF follow-up control.

In step S120, before the switching from the MAF target value _{MAF NPL_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 NPL_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 _{NPL_Trgt} after switching (rich state). If the actual MAF value MAF _Act has not reached the MAF target value MAF _{NPL_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 _{NPL_Trgt} , the advance angle of the injection timing corresponding to the actual MAF change rate MAF _Ratio that changes from moment to 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 _Act reaches the MAF target value MAF _{NPL_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 .

As shown in FIG. 8A, when shifting from the lean state to the rich state, the actual MAF value MAF _Act cannot catch up with the MAF target value MAF _{LR_Trgt} during the transition period due to the influence of valve control delay, etc. The MAF value MAF _Act may be maintained in a state higher than the MAF target value MAF _{LR_Trgt} (see times t ₁ to 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 this 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 _Act 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, based on FIG. 7, the MAF tracking control at the time of switching from the rich state to the lean state will be described.

When the NOx purge flag F _NP is turned off (F _NP = 0) in step S200, time measurement by a timer is started in step S210 to measure the elapsed time of MAF follow-up control.

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 NPL_Trgt} of (rich state), before and after switching of the MAF target value change amount ΔMAF _Trgt _{(= MAF L_Trgt} - MAF _{NPL_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 _{NPL_Trgt} before switching from the current actual MAF value MAF _Act detected by the MAF sensor 40, the actual MAF change amount ΔMAF _Act (= MAF _Act -MAF _{NPL_Trgt} ) is calculated. Then, the actual MAF change rate ΔMAF _Act is divided by the MAF target value change amount ΔMAF _Trgt before and after switching, _thereby calculating the actual MAF change rate ΔMAF _Ratio (= ΔMAF _Act / ΔMAF _Trgt ).

In step 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 processes 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 corresponding to the actual MAF change rate MAF _Ratio that changes from moment to moment, and the injection The amount continues to decrease. Details of the processing in step S270 will be described later. On the other hand, when the actual MAF value MAF _Act 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 .

As shown in FIG. 8B, when shifting from the lean state to the rich state, the actual MAF value MAF _Act cannot catch up with the MAF target value MAF _{LR_Trgt} during the transition period due to the influence of valve control delay, etc. The MAF value MAF _Act may be kept lower than the MAF target value MAF _{L-R_Trgt} (see times t ₁ to t ₂ ). If MAF follow-up control is continued in such a state, 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 _Act 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.

[Prohibition of MAF tracking control]
As described above, in the boost pressure FB control region, NOx purge lean control for feedback control of the air system based on the sensor value of the MAF sensor 40 is prohibited. Since MAF tracking control also controls the advance of the injection timing and the increase of the injection amount according to the rate of change of the intake air amount, there is a possibility that accurate control cannot be performed in the boost pressure FB control region.

Therefore, in the present embodiment, the MAF follow-up control is prohibited by setting the MAF follow-up coefficients Comp ₁ and ₂ to “1” in the boost pressure FB control region. Thereby, the torque fluctuation of the engine 10 and the deterioration of drivability caused by inaccurate MAF tracking control are effectively prevented.

[Injection amount learning correction]
As shown in FIG. 9, the injection amount learning correction unit 90 includes a learning correction coefficient calculation unit 91 and an injection amount correction unit 92.

The learning correction coefficient calculation unit 91 is based on the error Δλ between the actual lambda value λ _Act detected by the NOx / lambda sensor 45 during the lean operation of the engine 10 and the estimated lambda value λ _Est, and the learning correction coefficient F for the fuel injection amount. Calculate _Corr . When the exhaust gas is in a lean state, since the oxidation reaction of HC does not occur in the oxidation catalyst 31, the actual lambda value λ _Act in the exhaust gas that passes through the oxidation catalyst 31 and is detected by the downstream NOx / lambda sensor 45, It is considered that the estimated lambda value λ _Est in the exhaust discharged from the engine 10 coincides. Therefore, when an error Δλ occurs between the actual lambda value λ _Act and the estimated lambda value λ _Est , it can be assumed that the difference is between the commanded injection amount and the actual injection amount for each injector 11. Hereinafter, the learning correction coefficient calculation processing by the learning correction coefficient calculation unit 91 using the error Δλ will be described 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. 9 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, a transient operation of the engine 10 or a NOx purge control (F _NP = 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. 9) referred to based on the engine speed Ne and the accelerator opening Q is updated to the learning value F _CorrAdpt calculated in step S310. More specifically, on the learning value map 91B, a plurality of learning areas divided according to the engine speed Ne and the accelerator opening Q are set. These learning regions are preferably set to have a narrower range as the region is used more frequently and to be wider as a region is used less frequently. As a result, learning accuracy is improved in regions where the usage frequency is high, and unlearning can be effectively prevented in regions where the usage frequency is low.

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

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

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

[MAF correction coefficient]
MAF correction coefficient calculating unit 95 calculates the MAF correction coefficient _{Maf _Corr} used to set the MAF target value _{MAF NPL_Trgt} and the target injection amount _{Q NPR_Trgt} during NOx 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. 11 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. 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 72 and It transmits to the injection quantity target value calculating part 77. As a result, the sensor characteristics of the MAF sensor 40 can be effectively reflected in the settings of the MAF target value MAF _{NPL_Trgt} and the target injection amount Q _{NPR_Trgt} during the NOx 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.

This application is based on a Japanese patent application (Japanese Patent Application No. 2015-027977) filed on February 16, 2015, the contents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY The exhaust purification system and the control method thereof according to the present invention have the effect that the injection system control can be performed in a state where the intake air amount is sufficiently lowered, and the fuel consumption can be improved by reducing the injection system control time It is useful in that respect.

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

A NOx reduction catalyst that is provided in the exhaust passage of the internal combustion engine and stores NOx in the exhaust when the exhaust air-fuel ratio is lean;
An intake air amount sensor for detecting an intake air amount of the internal combustion engine;
By switching the exhaust air / fuel ratio from the lean state to the rich state by using both the air system control for reducing the intake air amount and the injection system control for increasing the fuel injection amount, the stored NOx is reduced and purified. A control unit for releasing from the NOx reduction catalyst,
The control unit includes a first difference value between the first target intake air amount in the lean state and the second target intake air amount in the rich state, and a second difference between the first target intake air amount and the intake air amount. An exhaust purification system that determines a start time of the injection system control based on a ratio of the difference values.
The control unit compares the determination threshold value stored so that the numerical value can be changed with the ratio, and determines that it is the start timing of the injection system control when the ratio reaches the determination threshold value. The exhaust purification system according to claim 1.
A NOx reduction catalyst that is disposed in an exhaust passage of the internal combustion engine and occludes NOx contained in the exhaust when the exhaust discharged from the internal combustion engine is in a lean state;
An intake air amount sensor for detecting an intake air amount of the internal combustion engine;
An exhaust purification system comprising a control unit that controls an air-fuel ratio of the exhaust gas by using an air system control that controls an intake air amount and an injection system control that controls a fuel injection amount,
The control unit operates to perform the following process:
Catalyst regeneration that switches the air-fuel ratio of the exhaust gas from a lean state to a rich state by executing the air system control and the injection system control, and releases NOx stored in the NOx reduction catalyst from the NOx reduction catalyst processing;
A calculation process for calculating a second difference value that is a difference between a first target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust gas is in a lean state and an intake air amount of the internal combustion engine; A ratio between a first difference value that is a difference between one target intake air amount and a second target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust gas is in a rich state, and the second difference value The determination process which determines the start time of the said injection system control based on this.
A control method for an exhaust gas purification system including a NOx reduction catalyst that is disposed in an exhaust passage of an internal combustion engine and occludes NOx contained in the exhaust gas when the exhaust gas discharged from the internal combustion engine is in a lean state. ,
By executing air system control for controlling the intake air amount and injection system control for controlling the fuel injection amount, the air-fuel ratio of the exhaust gas is switched from the lean state to the rich state and stored in the NOx reduction type catalyst. Catalyst regeneration treatment for releasing NOx from the NOx reduction catalyst;
A calculation process for calculating a second difference value that is a difference between a first target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust gas is in a lean state and an intake air amount of the internal combustion engine; A ratio between a first difference value that is a difference between one target intake air amount and a second target intake air amount that is a target intake air amount when the air-fuel ratio of the exhaust gas is in a rich state, and the second difference value Determination processing for determining the start timing of the injection system control based on
A method for controlling an exhaust purification system.