JP3791312B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology for purifying exhaust gas from an internal combustion engine, and more particularly to an exhaust gas purification device that purifies nitrogen oxides in the exhaust gas.
[0002]
[Prior art]
In recent years, in an internal combustion engine mounted on an automobile or the like, particularly a diesel engine or lean burn gasoline engine that can burn an oxygen-rich mixture (so-called lean air-fuel mixture), the exhaust gas from the internal combustion engine A technique for purifying contained nitrogen oxide (NOx) is desired.
[0003]
In response to such demands, a technique for arranging a lean NOx catalyst in the exhaust system of an internal combustion engine has been proposed. As one of the lean NOx catalysts, it absorbs nitrogen oxides (NOx) in the exhaust when the oxygen concentration in the inflowing exhaust is high, and absorbs when the oxygen concentration in the inflowing exhaust is low and a reducing agent is present. Nitrogen (Nx) while releasing nitrogen oxides (NOx)₂The NOx storage reduction catalyst is known to reduce to (3).
[0004]
When the NOx storage reduction catalyst is arranged in the exhaust system of the internal combustion engine, when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high, nitrogen oxide (NOx) in the exhaust gas becomes the NOx storage reduction catalyst. When the air-fuel ratio of the exhaust gas that has been absorbed and flows into the NOx storage reduction catalyst becomes low, nitrogen oxide (NOx) that has been absorbed by the NOx storage reduction catalyst is released while nitrogen (N₂).
[0005]
By the way, since the NOx absorption capacity of the NOx storage reduction catalyst is limited, when the internal combustion engine is operated for lean combustion over a long period of time, the NOx absorption capacity of the NOx storage reduction catalyst is saturated, and the nitrogen oxide ( NOx) is released into the atmosphere without being removed by the NOx storage reduction catalyst.
[0006]
Therefore, when the NOx storage reduction catalyst is applied to a lean combustion internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is reduced before the NOx absorption capacity of the NOx storage reduction catalyst is saturated. It is necessary to release and reduce nitrogen oxide (NOx) absorbed in the NOx storage reduction catalyst by performing so-called rich spike control.
[0007]
As a specific method of the rich spike control, a method of adding fuel as a reducing agent into the exhaust gas flowing upstream from the NOx storage reduction catalyst can be exemplified.
[0008]
When a reducing agent is added to the exhaust gas upstream of the NOx storage reduction catalyst, the amount of reducing agent added is accurately controlled according to the nitrogen oxide (NOx) absorbed in the NOx storage reduction catalyst. It is also important.
[0009]
This is because if the amount of reducing agent added is excessively increased relative to nitrogen oxide (NOx) absorbed in the NOx storage reduction catalyst, excess reducing agent will be released into the atmosphere. If the amount of reducing agent added is insufficient with respect to nitrogen oxide (NOx) absorbed in the reduced NOx catalyst, the NOx absorption capacity of the NOx storage reduction catalyst will be saturated, and the nitrogen oxide (NOx) in the exhaust will be purified. This is because they are released into the atmosphere without being used.
[0010]
Conventionally, an exhaust emission control device for an internal combustion engine as described in Japanese Patent No. 2845056 has been proposed for such a problem. The exhaust gas purification apparatus for an internal combustion engine described in this publication includes an amount of reducing agent consumed by reacting with oxygen in exhaust gas in the NOx storage reduction catalyst and nitrogen oxides absorbed in the NOx storage reduction catalyst ( In consideration of the amount of reducing agent required to reduce (NOx), the amount of reducing agent added is determined to prevent excessive supply or supply shortage of the reducing agent. It is intended to suppress the deterioration of exhaust emission due to the release of (NOx) into the atmosphere.
[0011]
[Problems to be solved by the invention]
The conventional exhaust purification apparatus described above reduces the amount of reducing agent consumed by reacting with oxygen in the exhaust in the NOx storage reduction catalyst and nitrogen oxides (NOx) absorbed in the NOx storage reduction catalyst. Therefore, when determining the amount of reducing agent required for this purpose, the amount of oxygen in the exhaust and the amount of NOx absorbed by the NOx storage reduction catalyst are required.
[0012]
As a method for obtaining the amount of oxygen in the exhaust, an oxygen sensor or an air-fuel ratio sensor is provided in the exhaust passage downstream of the NOx storage reduction catalyst, and the output signal value of the oxygen sensor or air-fuel ratio sensor (actual exhaust gas when the rich spike control is executed) A method of feedback control of the amount of reducing agent added based on the air / fuel ratio) is conceivable.
[0013]
However, the output signal of the oxygen sensor or air-fuel ratio sensor may be shifted due to aging or deterioration. If a deviation occurs between the amount of oxygen or reducing agent output from the sensor and the actual amount of oxygen or reducing agent, it becomes difficult to accurately control the amount of reducing agent added. Deterioration of exhaust emissions due to supply shortage may be induced.
[0014]
The present invention has been made in view of the various problems described above, and is an exhaust gas purification apparatus for an internal combustion engine that purifies nitrogen oxides (NOx) in exhaust gas by combining a lean NOx catalyst and rich spike control. An object of the present invention is to provide a technique capable of correcting an output value of an air-fuel ratio sensor provided in an exhaust passage, thereby enabling feedback control of an appropriate air-fuel ratio and preventing deterioration of exhaust emission.
[0015]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above-described problems.
[0016]
That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in a lean combustion type internal combustion engine capable of combusting an air-fuel mixture in an oxygen-excess state, and an exhaust passage of the internal combustion engine when the air-fuel ratio of the exhaust gas is high. NOx catalyst that absorbs nitrogen oxides in the exhaust and reduces the exhausted nitrogen oxides when the air-fuel ratio of the exhaust is low, and releases and reduces the nitrogen oxides absorbed by the NOx catalyst NOx purification control means for performing NOx purification processing as much as possible, and poisoning by at least making the air-fuel ratio of the exhaust gas flowing into the NOx catalyst a rich air-fuel ratio in order to eliminate poisoning due to oxides of the NOx catalyst Poisoning elimination control means for executing elimination processing, air-fuel ratio measuring means provided in the exhaust passage downstream of the NOx catalyst, for measuring the air-fuel ratio of the exhaust,When the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst at the initial stage of execution of the poisoning elimination processing becomes an air-fuel ratio in the vicinity of the theoretical air-fuel ratio,The output signal of the air-fuel ratio measuring means is compared with a predetermined value, and if there is a deviation in the output signal, the air-fuel ratio for correcting the output signal of the subsequent air-fuel ratio measuring means based on the deviation value And a correcting means.
[0017]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the internal combustion engine is in a lean combustion operation, the air-fuel ratio of the exhaust gas becomes high, so that nitrogen oxides contained in the exhaust gas are absorbed by the NOx catalyst. . When it is necessary to release and reduce the nitrogen oxides absorbed by the NOx catalyst, the NOx purification control means executes a NOx purification process to release and reduce the nitrogen oxides absorbed by the NOx catalyst. .
[0018]
Further, when it becomes necessary to eliminate the poisoning due to the oxide of the NOx catalyst, the poisoning elimination control means executes a NOx catalyst poisoning elimination process. In order to eliminate the NOx catalyst oxide poisoning, it is necessary to make the inside of the NOx catalyst a reducing atmosphere.NO x The air / fuel ratio of the exhaust gas flowing into the catalyst will be reduced to the rich air / fuel ratio..
[0019]
When nitrogen oxides are released from the NOx catalyst at the initial stage of the poisoning elimination process, the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst changes to a predetermined air-fuel ratio in the vicinity of the theoretical air-fuel ratio.
[0020]
That is, when the output value of the air-fuel ratio measuring means at the initial stage of the poisoning elimination process is not at the predetermined air-fuel ratio, the air-fuel ratio control means may be deteriorated.
[0021]
Furthermore, since the poisoning elimination process is performed for a longer period of time than the NOx purification process, a change in the exhaust air-fuel ratio due to the nitrogen oxides released from the NOx catalyst tends to appear clearly.
[0022]
Then, the output value of the air-fuel ratio measuring means at the initial stage of the poisoning elimination process is compared with a predetermined value (the output value when the air-fuel ratio measuring means is new), and if there is a difference between the two, the calculated value is calculated. Based on the deviation value, the output value of the air-fuel ratio measuring means can be corrected.
[0023]
As a result, an accurate air-fuel ratio can be measured, and the reducing agent addition control to the NOx catalyst and the fuel injection amount control to the internal combustion engine can be performed based on the measured value.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the exhaust emission control device according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
[0025]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus according to the present invention is applied and its intake and exhaust system.
[0026]
An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having four cylinders 2.
[0027]
The internal combustion engine 1 includes a fuel injection valve 3 that injects fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 that accumulates fuel to a predetermined pressure. A common rail pressure sensor 4 a that outputs an electrical signal corresponding to the fuel pressure in the common rail 4 is attached to the common rail 4.
[0028]
The common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5. The fuel pump 6 is a pump that operates using the rotational torque of the output shaft (crankshaft) of the internal combustion engine 1 as a drive source. A pump pulley 6 attached to the input shaft of the fuel pump 6 is connected to the output shaft of the internal combustion engine 1 ( And a crank pulley 1a attached to the crankshaft) via a belt 7.
[0029]
In the fuel injection system configured as described above, when the rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 transmits the rotational torque transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure according to the pressure.
[0030]
The fuel discharged from the fuel pump 6 is supplied to the common rail 4 via the fuel supply pipe 5, accumulated in the common rail 4 up to a predetermined pressure, and distributed to the fuel injection valves 3 of each cylinder 2. When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2.
[0031]
Next, an intake branch pipe 8 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown).
[0032]
The intake branch pipe 8 is connected to an intake pipe 9, and the intake pipe 9 is connected to an air cleaner box 10. An air flow meter 11 that outputs an electric signal corresponding to the mass of the intake air flowing in the intake pipe 9 and an electric current corresponding to the temperature of the intake air flowing in the intake pipe 9 are provided in the intake pipe 9 downstream of the air cleaner box 10. An intake air temperature sensor 12 that outputs a signal is attached.
[0033]
An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided in a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 13 is provided with an intake throttle actuator 14 that is configured by a stepper motor or the like and that drives the intake throttle valve 13 to open and close.
[0034]
The intake pipe 9 positioned between the air flow meter 11 and the intake throttle valve 13 is provided with a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using the thermal energy of exhaust as a drive source. The intake pipe 9 downstream of the housing 15a is provided with an intercooler 16 for cooling the intake air that has been compressed in the compressor housing 15a and has reached a high temperature.
[0035]
In the intake system configured as described above, the intake air that has flowed into the air cleaner box 10 is removed from dust, dust, and the like in the intake air by an air cleaner (not shown) in the air cleaner box 10, and then is connected to the compressor housing via the intake pipe 9. Flows into 15a.
[0036]
The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel built in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has reached a high temperature is cooled by the intercooler 16, and then the flow rate is adjusted by the intake throttle valve 13 as necessary to flow into the intake branch pipe 8. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chambers of the respective cylinders 2 through the respective branch pipes, and is burned using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0037]
On the other hand, an exhaust branch pipe 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with the combustion chamber of each cylinder 2 via an exhaust port (not shown).
[0038]
The exhaust branch pipe 18 is connected to the turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, and this exhaust pipe 19 is connected downstream to a muffler (not shown).
[0039]
An exhaust gas purification catalyst 20 for purifying harmful gas components in the exhaust gas is disposed in the middle of the exhaust pipe 19. The exhaust pipe 19 downstream of the exhaust purification catalyst 20 corresponds to the air-fuel ratio sensor 23 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust flowing in the exhaust pipe 19 and the temperature of the exhaust flowing in the exhaust pipe 19. An exhaust temperature sensor 24 for outputting the electrical signal is attached.
[0040]
The exhaust pipe 19 downstream of the air-fuel ratio sensor 23 and the exhaust temperature sensor 24 is provided with an exhaust throttle valve 21 for adjusting the flow rate of the exhaust gas flowing through the exhaust pipe 19. The exhaust throttle valve 21 is provided with an exhaust throttle actuator 22 that is configured by a stepper motor or the like and that drives the exhaust throttle valve 21 to open and close.
[0041]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then is centrifuged from the exhaust branch pipe 18. It flows into the turbine housing 15b of the feeder 15. The exhaust gas flowing into the turbine housing 15b rotates a turbine wheel that is rotatably supported in the turbine housing 15b using the thermal energy of the exhaust gas. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.
[0042]
The exhaust discharged from the turbine housing 15b flows into the exhaust purification catalyst 20 through the exhaust pipe 19, and harmful gas components in the exhaust are removed or purified. The exhaust gas from which harmful gas components have been removed or purified by the exhaust purification catalyst 20 is discharged into the atmosphere through the muffler after the flow rate is adjusted by the exhaust throttle valve 21 as necessary.
[0043]
Further, the exhaust branch pipe 18 and the intake branch pipe 8 communicate with each other via an exhaust gas recirculation passage (EGR passage) 25 that recirculates a part of the exhaust gas flowing in the exhaust branch pipe 18 to the intake branch pipe 8. . In the middle of the EGR passage 25, a flow rate adjusting valve (EGR) configured by an electromagnetic valve or the like that changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) flowing in the EGR passage 25 according to the magnitude of applied power. Valve) 26 is provided.
[0044]
An EGR cooler 27 that cools the EGR gas flowing in the EGR passage 25 is provided at a position upstream of the EGR valve 26 in the EGR passage 25.
[0045]
In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing in the exhaust branch pipe 18 flows into the EGR passage 25, It is guided to the intake branch pipe 8 through the EGR cooler 27.
[0046]
At that time, in the EGR cooler 27, heat exchange is performed between the EGR gas flowing in the EGR passage 25 and a predetermined refrigerant, thereby cooling the EGR gas.
[0047]
The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 through the EGR passage 25 is guided to the combustion chamber of each cylinder 2 while being mixed with fresh air flowing from the upstream side of the intake branch pipe 8. The fuel injected from the injection valve 3 is burned using an ignition source.
[0048]
Here, the EGR gas contains water (H₂O) and carbon dioxide (CO₂) And the like, and an inert gas component having endothermic properties is contained in the mixture, so if EGR gas is contained in the mixture, the combustion temperature of the mixture is lowered. Therefore, the amount of nitrogen oxide (NOx) generated is suppressed.
[0049]
Further, when the EGR gas is cooled in the EGR cooler 27, the temperature of the EGR gas itself is reduced and the volume of the EGR gas is reduced. Therefore, when the EGR gas is supplied into the combustion chamber, the atmospheric temperature in the combustion chamber is reduced. Is not increased unnecessarily, and the amount of fresh air (volume of fresh air) supplied into the combustion chamber is not unnecessarily reduced.
[0050]
Next, the exhaust purification catalyst 20 according to the present embodiment will be specifically described.
[0051]
The exhaust purification catalyst 20 is a NOx catalyst that purifies nitrogen oxides (NOx) in the exhaust in the presence of a reducing agent. Examples of such a NOx catalyst include a selective reduction type NOx catalyst, a storage reduction type NOx catalyst, and the like. Here, the storage reduction type NOx catalyst will be described as an example. Hereinafter, the exhaust purification catalyst 20 will be referred to as an NOx storage reduction catalyst 20.
[0052]
The NOx storage reduction catalyst 20 uses, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs) on the carrier, and barium (Ba). Or at least 1 selected from alkaline earths, such as calcium (Ca), rare earths, such as lanthanum (La) or yttrium (Y), and noble metals, such as platinum (Pt), are comprised. In this embodiment, an occlusion reduction type NOx catalyst constituted by supporting barium (Ba) and platinum (Pt) on a support made of alumina will be described as an example.
[0053]
The NOx storage reduction catalyst 20 thus configured absorbs nitrogen oxide (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx storage reduction catalyst 20 is high.
[0054]
On the other hand, the NOx storage reduction catalyst 20 releases the absorbed nitrogen oxides (NOx) when the oxygen concentration in the exhaust gas flowing into the NOx storage reduction catalyst 20 decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, the NOx storage reduction catalyst 20 oxidizes the nitrogen released from the NOx storage reduction catalyst 20. Things (NOx) to nitrogen (N₂).
[0055]
In addition, although there is a part which is not clarified about the NOx absorption / release action of the NOx storage reduction catalyst 20, it is considered that it is performed by the following mechanism.
[0056]
First, in the NOx storage reduction catalyst 20, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes a lean air-fuel ratio and the oxygen concentration in the exhaust gas increases, as shown in FIG. , Oxygen in the exhaust (O₂) Is O₂ ^-Or O^2-It adheres on the surface of platinum (Pt) in the form of Nitric oxide (NO) in the exhaust is O on the surface of platinum (Pt).₂ ^-Or O^2-Reacts with nitrogen dioxide (NO₂) (2NO + O)₂→ 2NO₂). Nitrogen dioxide (NO₂) Is further oxidized on the surface of platinum (Pt), and nitrate ions (NO)_3-) Is absorbed by the NOx storage reduction catalyst 20. The nitrate ions (NO) absorbed in the NOx storage reduction catalyst 20_3-) Combines with barium oxide (BaO) to form barium nitrate (Ba (NO_Three)₂).
[0057]
Thus, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is a lean air-fuel ratio, nitrogen oxides (NOx) in the exhaust gas are nitrate ions (NO_3-) Is absorbed by the NOx storage reduction catalyst 20.
[0058]
The above-described NOx absorption action is continued unless the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio and the NOx absorption capacity of the NOx storage reduction catalyst 20 is saturated. Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is a lean air-fuel ratio, nitrogen oxides (NOx) in the exhaust gas are stored unless the NOx absorption capacity of the NOx storage reduction catalyst 20 is saturated. It is absorbed by the reduced NOx catalyst 20 and nitrogen oxide (NOx) is removed from the exhaust.
[0059]
On the other hand, in the NOx storage reduction catalyst 20, when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 decreases, nitrogen dioxide (NO) on the surface of platinum (Pt).₂Nitrate ions (NO) bound to barium oxide (BaO)._3-) On the contrary, nitrogen dioxide (NO₂) And nitrogen monoxide (NO), and desorbs from the NOx storage reduction catalyst 20.
[0060]
At that time, if reducing components such as hydrocarbon (HC) and carbon monoxide (CO) are present in the exhaust, these reducing components are converted into oxygen (O) on platinum (Pt)._2-Or O^2-) To form an active species. This active species is nitrogen dioxide (NO) released from the NOx storage reduction catalyst 20.₂) Or nitric oxide (NO) to nitrogen (N₂).
[0061]
Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes the stoichiometric air-fuel ratio or rich air-fuel ratio, the oxygen concentration in the exhaust gas decreases and the concentration of the reducing agent increases, the NOx storage reduction catalyst 20 The absorbed nitrogen oxide (NOx) is released and reduced, so that the NOx absorption capacity of the NOx storage reduction catalyst 20 is regenerated.
[0062]
By the way, when the internal combustion engine 1 is in a lean combustion operation, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high. Therefore, nitrogen oxides (NOx) contained in the exhaust Is absorbed by the NOx storage reduction catalyst 20. However, if the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx absorption capacity of the NOx storage reduction catalyst 20 is saturated, and nitrogen oxidation in the exhaust gas is performed. Things (NOx) are not removed by the NOx storage reduction catalyst 20 but are released into the atmosphere.
[0063]
In particular, in a diesel engine such as the internal combustion engine 1, the lean air-fuel ratio mixture is combusted in most of the operating region, and the exhaust air-fuel ratio becomes the lean air-fuel ratio in most of the operating region accordingly. The NOx absorption capacity of the reduced NOx catalyst 20 is easily saturated.
[0064]
Therefore, when the internal combustion engine 1 is operated in lean combustion, the oxygen concentration in the exhaust gas flowing into the NOx storage reduction catalyst 20 is reduced and the reducing agent before the NOx absorption capacity of the NOx storage reduction catalyst 20 is saturated. Therefore, it is necessary to release and reduce nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst 20.
[0065]
In contrast, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment includes a reducing agent supply mechanism that adds fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust passage upstream of the NOx storage reduction catalyst 20. By adding fuel from the reducing agent supply mechanism into the exhaust gas, the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 is reduced and the concentration of the reducing agent is increased.
[0066]
As shown in FIG. 1, the reducing agent supply mechanism is attached to the cylinder head of the internal combustion engine 1 so that its nozzle hole faces the exhaust branch pipe 18, and when a fuel having a predetermined valve opening pressure or higher is applied. A reducing agent injection valve 28 that opens and injects fuel, a reducing agent supply passage 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and in the middle of the reducing agent supply passage 29. A flow rate adjusting valve 30 that adjusts the flow rate of the fuel that is provided and flows through the reducing agent supply passage 29, and a reducing agent supply passage 29 that is provided upstream of the flow amount adjusting valve 30 and that is provided in the reducing agent supply passage 29. A shutoff valve 31 for shutting off the flow, and a reducing agent pressure sensor 32 that is attached to the reducing agent supply passage 29 upstream of the flow rate adjusting valve 30 and outputs an electrical signal corresponding to the pressure in the reducing agent supply passage 29. I have.
[0067]
The reducing agent injection valve 28 has an injection hole downstream of the connection portion of the exhaust branch pipe 18 with the EGR passage 25 and is formed at a collection portion of the four branch pipes in the exhaust branch pipe 18. The cylinder head is preferably attached to the cylinder head so as to project to the exhaust port of the nearest cylinder 2 and to face the collecting portion of the exhaust branch pipe 18.
[0068]
This prevents the reducing agent (unburned fuel component) injected from the reducing agent injection valve 28 from flowing into the EGR passage 25, and the centrifugal supercharger without the reducing agent remaining in the exhaust branch pipe 18. This is to reach the turbine housing 15b.
[0069]
In the example shown in FIG. 1, the first (# 1) cylinder 2 of the four cylinders 2 of the internal combustion engine 1 is located closest to the collecting portion of the exhaust branch pipe 18, so that the first (# 1) cylinder Although the reducing agent injection valve 28 is attached to the exhaust port of No. 2, when the cylinders 2 other than the first (# 1) cylinder 2 are located closest to the aggregate portion of the exhaust branch pipe 18, the cylinder 2 The reducing agent injection valve 28 is attached to the exhaust port.
[0070]
The reducing agent injection valve 28 is attached to a water jacket (not shown) formed in the cylinder head so as to penetrate or close to the water jacket, and using the cooling water flowing through the water jacket, the reducing agent injection valve. 28 may be cooled.
[0071]
In such a reducing agent supply mechanism, when the flow rate adjustment valve 30 is opened, high-pressure fuel discharged from the fuel pump 6 is applied to the reducing agent injection valve 28 via the reducing agent supply path 29. When the pressure of the fuel applied to the reducing agent injection valve 28 reaches a valve opening pressure or higher, the reducing agent injection valve 28 opens and fuel as a reducing agent is injected into the exhaust branch pipe 18.
[0072]
The reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 flows into the turbine housing 15 b together with the exhaust gas flowing from the upstream side of the exhaust branch pipe 18. The exhaust gas flowing into the turbine housing 15b and the reducing agent are agitated and uniformly mixed by the rotation of the turbine wheel to form a rich air-fuel ratio exhaust gas.
[0073]
The rich air-fuel ratio exhaust gas thus formed flows into the NOx storage reduction catalyst 20 from the turbine housing 15b through the exhaust pipe 19, and is absorbed by the NOx storage reduction catalyst 20 (NOx). ) While releasing nitrogen (N₂).
[0074]
Thereafter, when the flow rate adjustment valve 30 is closed and the supply of the reducing agent from the fuel pump 6 to the reducing agent injection valve 28 is shut off, the pressure of the fuel applied to the reducing agent injection valve 28 is less than the valve opening pressure. As a result, the reducing agent injection valve 28 is closed, and the addition of the reducing agent into the exhaust branch pipe 18 is stopped.
[0075]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the internal combustion engine 1. The ECU 35 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.
[0076]
The ECU 35 includes a common rail pressure sensor 4a, an air flow meter 11, an intake air temperature sensor 12, an intake pipe pressure sensor 17, an air-fuel ratio sensor 23, an exhaust gas temperature sensor 24, a reducing agent pressure sensor 32, a crank position sensor 33, a water temperature sensor 34, an accelerator. Various sensors such as the opening sensor 36 are connected via electric wiring, and output signals of the various sensors described above are input to the ECU 35.
[0077]
On the other hand, the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the flow rate adjustment valve 30, the shut-off valve 31, and the like are connected to the ECU 35 via electric wiring. Can be controlled.
[0078]
Here, as shown in FIG. 3, the ECU 35 includes a CPU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357, which are connected to each other by a bidirectional bus 350. , An A / D converter (A / D) 355 connected to the input port 356 is provided.
[0079]
The input port 356 receives an output signal from a sensor that outputs a digital signal format signal, such as the crank position sensor 33, and transmits the output signal to the CPU 351 and the RAM 353.
[0080]
The input port 356 includes a common rail pressure sensor 4a, an air flow meter 11, an intake air temperature sensor 12, an intake pipe pressure sensor 17, an air-fuel ratio sensor 23, an exhaust gas temperature sensor 24, a reducing agent pressure sensor 32, a water temperature sensor 34, an accelerator opening sensor. 36, etc., are input via the A / D 355 of the sensor that outputs signals in the analog signal format, and these output signals are transmitted to the CPU 351 and the RAM 353.
[0081]
The output port 357 is connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the flow rate adjustment valve 30, the shutoff valve 31, etc. via electrical wiring, and is output from the CPU 351. The control signal is transmitted to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the flow rate adjustment valve 30, or the cutoff valve 31.
[0082]
The ROM 352 includes a fuel injection control routine for controlling the fuel injection valve 3, an intake throttle control routine for controlling the intake throttle valve 13, an exhaust throttle control routine for controlling the exhaust throttle valve 21, and an EGR valve 26. EGR control routine for controlling, NOx purification control routine for purifying nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst 20, and elimination of poisoning of the NOx storage reduction catalyst 20 due to oxides Application programs such as a poisoning elimination control routine are stored.
[0083]
The ROM 352 stores various control maps in addition to the application programs described above. The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection amount (basic fuel injection time), and the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection timing. The fuel injection timing control map shown, the intake throttle valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the intake throttle valve 13, the operating state of the internal combustion engine 1 and the target opening of the exhaust throttle valve 21 Exhaust throttle valve opening control map showing the relationship between the EGR valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the EGR valve 26, the operating state of the internal combustion engine 1 and the reducing agent target A reducing agent addition amount control map showing the relationship with the addition amount (or the target air-fuel ratio of the exhaust), a flow rate adjustment valve control map showing the relationship between the target addition amount of the reducing agent and the valve opening time of the flow rate adjustment valve 30, etc. is there.
[0084]
The RAM 353 stores output signals from the sensors, calculation results of the CPU 351, and the like. The calculation result is, for example, the engine speed calculated based on the time interval at which the crank position sensor 33 outputs a pulse signal. These data are rewritten to the latest data every time the crank position sensor 33 outputs a pulse signal.
[0085]
The backup RAM 354 is a nonvolatile memory capable of storing data even after the internal combustion engine 1 is stopped.
[0086]
The CPU 351 operates in accordance with an application program stored in the ROM 352 and executes fuel injection valve control, intake throttle control, exhaust throttle control, EGR control, NOx purification control, and poisoning elimination control.
[0087]
For example, in the fuel injection valve control, the CPU 351 first determines the amount of fuel injected from the fuel injection valve 3 and then determines the timing for injecting fuel from the fuel injection valve 3.
[0088]
When determining the fuel injection amount, the CPU 351 reads the engine speed and the output signal (accelerator opening) of the accelerator opening sensor 36 stored in the RAM 353. The CPU 351 accesses the fuel injection amount control map and calculates a basic fuel fuel injection amount (basic fuel injection time) corresponding to the engine speed and the accelerator opening. The CPU 351 corrects the basic fuel injection time based on the output signal values of the air flow meter 11, the intake air temperature sensor 12, the water temperature sensor 34, etc., and determines the final fuel injection time.
[0089]
When determining the fuel injection timing, the CPU 351 accesses the fuel injection start timing control map, and calculates the basic fuel injection timing corresponding to the engine speed and the accelerator opening. The CPU 351 corrects the basic fuel injection timing using output signal values of the air flow meter 11, the intake air temperature sensor 12, the water temperature sensor 34, the air-fuel ratio sensor 23, etc. as parameters, and determines the final fuel injection timing.
[0090]
When the fuel injection time and the fuel injection timing are determined, the CPU 351 compares the fuel injection timing with the output signal of the crank position sensor 33, and the output signal of the crank position sensor 33 coincides with the fuel injection start timing. At that time, application of drive power to the fuel injection valve 3 is started. The CPU 351 stops applying the drive power to the fuel injection valve 3 when the elapsed time from the start of the application of the drive power to the fuel injection valve 3 reaches the fuel injection time.
[0091]
In the fuel injection control, when the operation state of the internal combustion engine 1 is an idle operation state, the CPU 351 uses the output signal value of the water temperature sensor 34 or the rotational force of the crankshaft as in the compressor of the air conditioner for the passenger compartment. Then, the target idle speed of the internal combustion engine 1 is calculated using the operating state of the auxiliary machinery operating as a parameter. Then, the CPU 351 feedback-controls the fuel injection amount so that the actual idle speed matches the target idle speed.
[0092]
In the intake throttle control, for example, the CPU 351 reads out the engine speed and the accelerator opening stored in the RAM 353. The CPU 351 accesses the intake throttle valve opening control map and calculates a target intake throttle valve opening corresponding to the engine speed and the accelerator opening. The CPU 351 applies drive power corresponding to the target intake throttle valve opening to the intake throttle actuator 14. At that time, the CPU 351 detects the actual opening of the intake throttle valve 13 and feeds back the intake throttle actuator 14 based on the difference between the actual opening of the intake throttle valve 13 and the target intake throttle valve opening. You may make it control.
[0093]
In the exhaust throttle control, the CPU 351 closes the exhaust throttle valve 21 in the valve closing direction, for example, when the internal combustion engine 1 is in a warm-up operation state after a cold start or when the vehicle interior heater is in an operating state. The exhaust throttle actuator 22 is controlled so as to be driven to the position.
[0094]
In this case, the load on the internal combustion engine 1 increases, and the fuel injection amount is increased correspondingly. As a result, the amount of heat generated by the internal combustion engine 1 increases, warming up of the internal combustion engine 1 is promoted, and a heat source for the vehicle interior heater is secured.
[0095]
In the EGR control, the CPU 351 reads out the engine speed, the output signal from the water temperature sensor 34 (cooling water temperature), the output signal from the accelerator opening sensor 36 (accelerator opening), etc. stored in the RAM 353, and the EGR control. It is determined whether or not the execution condition is satisfied.
[0096]
As the EGR control execution condition described above, the cooling water temperature is equal to or higher than a predetermined temperature, the internal combustion engine 1 is continuously operated for a predetermined time or more from the start, the amount of change in the accelerator opening is a positive value, etc. Conditions can be exemplified.
[0097]
If it is determined that the EGR control execution condition as described above is satisfied, the CPU 351 accesses the EGR valve opening control map using the engine speed and the accelerator opening as parameters, and the engine speed and the accelerator A target EGR valve opening corresponding to the opening is calculated. The CPU 351 applies drive power corresponding to the target EGR valve opening to the EGR valve 26. On the other hand, if it is determined that the EGR control execution condition as described above is not satisfied, the CPU 351 controls to keep the EGR valve 26 in a fully closed state.
[0098]
Further, in the EGR control, the CPU 351 may perform so-called EGR valve feedback control in which the opening degree of the EGR valve 26 is feedback-controlled using the intake air amount of the internal combustion engine 1 as a parameter.
[0099]
In the EGR valve feedback control, for example, the CPU 351 determines the target intake air amount of the internal combustion engine 1 using the accelerator opening, the engine speed, and the like as parameters. At that time, the relationship between the accelerator opening, the engine speed, and the target intake air amount may be mapped in advance, and the target intake air amount may be calculated from the map, the accelerator opening, and the engine speed. .
[0100]
When the target intake air amount is determined by the above-described procedure, the CPU 351 reads the output signal value (actual intake air amount) of the air flow meter 11 stored in the RAM 353, and determines the actual intake air amount and the target intake air amount. Compare
[0101]
When the actual intake air amount is smaller than the target intake air amount, the CPU 351 closes the EGR valve 26 by a predetermined amount. In this case, the amount of EGR gas flowing into the intake branch pipe 8 from the EGR passage 25 decreases, and the amount of EGR gas sucked into the cylinder 2 of the internal combustion engine 1 decreases accordingly. As a result, the amount of fresh air sucked into the cylinder 2 of the internal combustion engine 1 increases by the amount that the EGR gas has decreased.
[0102]
On the other hand, when the actual intake air amount is larger than the target intake air amount, the CPU 351 opens the EGR valve 26 by a predetermined amount. In this case, the amount of EGR gas flowing into the intake branch pipe 8 from the EGR passage 25 increases, and the amount of EGR gas sucked into the cylinder 2 of the internal combustion engine 1 increases accordingly. As a result, the amount of fresh air drawn into the cylinder 2 of the internal combustion engine 1 decreases by the amount of EGR gas that has increased.
[0103]
Next, in the NOx purification control, the CPU 351 executes so-called rich spike control in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is changed to a rich air-fuel ratio in a spike manner (short time) in a relatively short cycle. To do.
[0104]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. As the rich spike control execution condition, for example, poisoning elimination control in which the NOx storage reduction catalyst 20 is in an active state and the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value is executed. The conditions such as not being performed can be exemplified.
[0105]
When it is determined that the rich spike control execution condition as described above is satisfied, the CPU 351 controls the flow rate adjustment valve 30 to inject fuel as a reducing agent from the reducing agent injection valve 28 in a spike manner. The air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is temporarily set to a predetermined target rich air-fuel ratio.
[0106]
Specifically, the CPU 351 stores the engine speed stored in the RAM 353, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), and the air-fuel ratio sensor 23. Read output signal, fuel injection amount, etc. The CPU 351 accesses the reducing agent addition amount control map in the ROM 352 using the engine speed, accelerator opening, intake air amount, and fuel injection amount as parameters, and sets the exhaust air / fuel ratio to a preset target rich air / fuel ratio. The amount of addition of the reducing agent (target addition amount) necessary for the calculation is calculated.
[0107]
Subsequently, the CPU 351 accesses the flow rate adjustment valve control map of the ROM 352 using the target addition amount as a parameter, and opens the flow rate adjustment valve 30 required for injecting the target addition amount of reducing agent from the reducing agent injection valve 28. Calculate the valve time (target valve opening time).
[0108]
When the target valve opening time of the flow rate adjustment valve 30 is calculated, the CPU 351 opens the flow rate adjustment valve 30. In this case, since the high-pressure fuel discharged from the fuel pump 6 is supplied to the reducing agent injection valve 28 via the reducing agent supply path 29, the pressure of the fuel applied to the reducing agent injection valve 28 is equal to or higher than the valve opening pressure. And the reducing agent injection valve 28 is opened.
[0109]
The CPU 351 closes the flow rate adjusting valve 30 when the target valve opening time has elapsed since the flow rate adjusting valve 30 was opened. In this case, since the supply of the reducing agent from the fuel pump 6 to the reducing agent injection valve 28 is interrupted, the fuel pressure applied to the reducing agent injection valve 28 becomes less than the valve opening pressure, and the reducing agent injection valve 28 is closed. I speak.
[0110]
Thus, when the flow rate adjusting valve 30 is opened for the target valve opening time, the target addition amount of fuel is injected into the exhaust branch pipe 18 from the reducing agent injection valve 28. The reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust gas flowing from the upstream side of the exhaust branch pipe 18 to form a target rich air-fuel ratio mixture and flows into the NOx storage reduction catalyst 20. .
[0111]
As a result, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 repeats “lean” and “spike target rich air-fuel ratio” alternately in a relatively short cycle, thereby The reduced NOx catalyst 20 repeats absorption and release / reduction of nitrogen oxides (NOx) alternately in a short cycle.
[0112]
Next, in the poisoning elimination control, the CPU 351 performs a poisoning elimination process to eliminate the poisoning due to the oxide of the NOx storage reduction catalyst 20.
[0113]
Here, the fuel of the internal combustion engine 1 may contain sulfur (S), and when such fuel is burned in the internal combustion engine 1, sulfur dioxide (SO₂) And sulfur trioxide (SO_Three) And other sulfur oxides (SOx).
[0114]
Sulfur oxide (SOx) flows into the NOx storage reduction catalyst 20 together with the exhaust gas, and is absorbed by the NOx storage reduction catalyst 20 by the same mechanism as nitrogen oxide (NOx).
[0115]
Specifically, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is a lean air-fuel ratio, as described in the explanation of the NOx absorption mechanism described above, oxygen (O₂) Is O₂ ^-Or O^2-It adheres to the surface of platinum (Pt) in the form of sulfur dioxide (SO₂) And sulfur trioxide (SO_Three) And other sulfur oxides (SOx) on the surface of platinum (Pt).₂ ^-Or O^2-Reacts with SO_3-And SO_Four-It becomes.
[0116]
SO_3-And SO_Four-Is further oxidized on the surface of platinum (Pt), and sulfate ions (SO_Four ^2-) Is absorbed by the NOx storage reduction catalyst 20. It should be noted that the sulfate ions (SO_Four ^2-) Combines with barium oxide (BaO) to form sulfate (BaSO)._Four).
[0117]
Thus, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is a lean air-fuel ratio, the sulfur oxide (SOx) in the exhaust gas is sulfate ions (SO_Four ^2-) Is absorbed by the NOx storage reduction catalyst 20.
[0118]
By the way, sulfate (BaSO_Four) Is barium nitrate (Ba (NO_Three)₂) Is stable and difficult to decompose, and even if the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes the stoichiometric or rich air-fuel ratio, it is not decomposed into the NOx storage reduction catalyst 20. It will remain.
[0119]
Sulfate (BaSO) in the NOx storage reduction catalyst 20_Four) Increases, the amount of barium oxide (BaO) that can participate in the absorption of nitrogen oxides (NOx) decreases accordingly, so the NOx absorption capacity of the NOx storage reduction catalyst 20 decreases. So-called SOx poisoning occurs.
[0120]
As a method for eliminating SOx poisoning of the NOx storage reduction catalyst 20, the ambient temperature of the NOx storage reduction catalyst 20 is raised to a high temperature range of about 500 ° C. to 700 ° C. and flows into the NOx storage reduction catalyst 20. By making the air-fuel ratio of the exhaust gas to be rich air-fuel ratio, barium sulfate (BaSO) absorbed in the NOx storage reduction catalyst 20_Four) SO_3-And SO_Four-Pyrolyzed, and then SO_3-And SO_Four-Reacts with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust to produce gaseous SO_2-An example of the method for reduction is shown.
[0121]
Therefore, in the poisoning elimination process according to the present embodiment, the CPU 351 first executes a catalyst temperature increasing process for increasing the bed temperature of the NOx storage reduction catalyst 20 and then the exhaust gas flowing into the NOx storage reduction catalyst 20. The air-fuel ratio was made rich.
[0122]
In the catalyst temperature raising process, the CPU 351, for example, performs post-injection of fuel from the fuel injection valve 3 during the expansion stroke of each cylinder 2 and adds the fuel from the reducing agent injection valve 28 into the exhaust gas. The unburned fuel component may be oxidized in the NOx storage reduction catalyst 20 and the bed temperature of the NOx storage reduction catalyst 20 may be increased by the heat generated during the oxidation.
[0123]
However, if the storage reduction type NOx catalyst 20 is excessively heated, thermal deterioration of the storage reduction type NOx catalyst 20 may be induced. Therefore, based on the output signal value of the exhaust temperature sensor 24, the post injection fuel amount and It is preferable that the amount of added fuel is feedback controlled.
[0124]
When the bed temperature of the NOx storage reduction catalyst 20 rises to a high temperature range of about 500 ° C. to 700 ° C. by the catalyst temperature increasing process as described above, the CPU 351 enriches the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20. Fuel is injected from the reducing agent injection valve 28 so as to obtain an air-fuel ratio.
[0125]
When excessive fuel is injected from the reducing agent injection valve 28, the fuel is rapidly burned in the NOx storage reduction catalyst 20, and the NOx storage reduction catalyst 20 is overheated, or from the reducing agent injection valve 28. Since the NOx storage reduction catalyst 20 may be unnecessarily cooled by the excessive fuel injected, the CPU 351 feedback-controls the fuel injection amount from the reducing agent injection valve 28 based on the output signal of the air-fuel ratio sensor 23. It is preferable to do so.
[0126]
When the poisoning elimination process is executed in this way, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes a rich air-fuel ratio under a situation where the bed temperature of the NOx storage reduction catalyst 20 is high, so that the storage is performed. Barium sulfate (BaSO) absorbed in the reduced NOx catalyst 20_Four) Is SO_3-And SO_Four-They are pyrolyzed into SO_3-And SO_Four-Reacts with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust to produce gaseous SO_2-As a result, the SOx poisoning of the NOx storage reduction catalyst 20 is eliminated.
[0127]
In the above-described NOx purification control, the CPU 351 executes rich spike control at a predetermined cycle, so that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is spiked to the target rich air-fuel ratio, and the NOx storage reduction type is executed. Nitrogen oxide (NOx) absorbed by the NOx catalyst 20 is released and reduced.
[0128]
By the way, the target rich air-fuel ratio related to the rich spike control is a fixed value determined on the assumption that the reducing agent supply mechanism and the NOx storage reduction catalyst 20 are in a typical state. When the performance of the NOx storage reduction catalyst 20, the characteristics of the reducing agent supply mechanism, the characteristics of the fuel injection valve 3, and the like change due to changes in the environment or the like, nitrogen oxides absorbed in the NOx storage reduction catalyst 20 (NOx) ) The amount of reducing agent supplied may be excessive with respect to the amount, or the amount of reducing agent supplied may be insufficient with respect to the amount of nitrogen oxide (NOx) absorbed by the NOx storage reduction catalyst 20. .
[0129]
To solve this problem, the amount of nitrogen oxide (NOx) released from the NOx storage reduction catalyst 20 is detected based on the output signal of the air-fuel ratio sensor 23 during the execution of rich spike control, and the detected nitrogen oxidation. It is conceivable to perform feedback control of the target rich air-fuel ratio (in other words, the amount of reducing agent added) according to the amount of substances (NOx).
[0130]
Further, since the air-fuel ratio is calculated from the output signal of the air-fuel ratio sensor 23 that is new, if the output characteristics change due to aging or deterioration, the air-fuel ratio is misidentified, making it difficult to perform accurate feedback control. become.
[0131]
Therefore, in the present embodiment, the CPU 351 outputs the output signal of the air-fuel ratio sensor 23 when executing the poisoning elimination process in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is set to the rich air-fuel ratio for a relatively long period. The air-fuel ratio calculated from the above is compared with a predetermined value (the air-fuel ratio at the beginning of the poisoning elimination process when the air-fuel ratio sensor 23 is new), and the output signal of the air-fuel ratio sensor 23 is corrected based on the deviation. .
[0132]
That is, in the poisoning elimination process, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is made rich, so that it is absorbed by the NOx storage reduction catalyst 20 at the initial stage of the poisoning elimination process. Nitrogen oxide (NOx) is released. When nitrogen oxide (NOx) is released from the NOx storage reduction catalyst 20, the exhaust air-fuel ratio downstream of the NOx storage reduction catalyst 20 (hereinafter referred to as the downstream exhaust air-fuel ratio) is as shown in FIG. Oxygen contained in released nitrogen oxides (NOx) or stored oxygen (so-called O₂Due to storage, the air-fuel ratio becomes a predetermined air-fuel ratio in the vicinity of the theoretical air-fuel ratio.
[0133]
Therefore, by calculating how much the downstream exhaust air-fuel ratio deviates from the predetermined air-fuel ratio at the initial stage of execution of the poisoning elimination process, it is possible to calculate the deviation amount of the air-fuel ratio sensor 23, that is, the value to be corrected.
[0134]
When the output value of the air-fuel ratio sensor 23 is corrected in this way, the CPU 351 stores the correction value in a predetermined area of the RAM 353 or the backup RAM 354.
[0135]
When the NOx purification control is executed after the execution of the poisoning elimination control, the CPU 351 executes the rich spike control based on the correction value of the air-fuel ratio sensor 23 stored in the RAM 353 or the backup RAM 354.
[0136]
In this case, the amount of the reducing agent injected from the reducing agent injection valve 28 in the rich spike control is an amount reflecting the air-fuel ratio of the exhaust actually discharged from the NOx storage reduction catalyst 20, Even when the output characteristics of the air-fuel ratio sensor 23 change due to deterioration or the like, the amount of reducing agent added can be set to an optimum amount.
[0137]
As a result, there is no excessive supply or supply shortage of the reducing agent in the rich spike control during the elimination of poisoning or the NOx purification process, and the exhaust emission caused by the excessive supply or supply of the reducing agent is prevented.
[0138]
Further, even when the rich spike control is not performed, the amount of fuel supplied to the internal combustion engine can be feedback controlled from the air-fuel ratio of the exhaust, and similarly, the exhaust emission can be prevented from deteriorating.
[0139]
Hereinafter, the poisoning elimination control according to the present embodiment will be specifically described along the flowchart of FIG.
[0140]
The flowchart shown in FIG. 5 is a flowchart showing a poisoning elimination control routine. This poisoning elimination control routine is a routine that is repeatedly executed by the CPU 351 every predetermined time (for example, every time the crank position sensor 33 outputs a pulse signal), and is stored in the ROM 352 in advance.
[0141]
In the poisoning elimination control routine, first, in S501, the CPU 351 determines whether or not an execution condition for the poisoning elimination processing is satisfied. As an execution condition of the above-described poisoning elimination processing, for example, NOx purification control in which the NOx storage reduction catalyst 20 is in an active state and the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value. Are in the non-execution state, and the SOx poisoning degree of the NOx storage reduction catalyst 20 exceeds the allowable range.
[0142]
If it is determined in S501 that the execution condition of the poisoning elimination process is not satisfied, the CPU 351 once ends the execution of this routine.
[0143]
If it is determined in S501 that the condition for executing the poisoning elimination process is satisfied, the CPU 351 proceeds to S502, and from the RAM 353, the engine speed, the output signal value of the accelerator opening sensor 36 (accelerator opening), When the output signal from the air-fuel ratio sensor 23 is read and the engine speed, accelerator opening, and air-fuel ratio are used as parameters, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is set to a predetermined reference rich air-fuel ratio. Calculate the required amount of reducing agent (fuel) to be added.
[0144]
At this time, the relationship among the engine speed, the accelerator opening, and the amount of reducing agent added may be experimentally obtained in advance, and the relationship may be mapped and stored in the ROM 352 or the like.
[0145]
In S503, the CPU 351 controls the flow rate adjustment valve 30 according to the reducing agent addition amount determined in S502, and starts adding the reducing agent from the reducing agent injection valve 28 into the exhaust gas.
[0146]
In S504, the CPU 351 stores the output signal (downstream exhaust air-fuel ratio) of the air-fuel ratio sensor 23 in the RAM 353.
[0147]
In S505, the CPU 351 determines whether or not an execution end condition for the poisoning elimination process is satisfied. Examples of the condition for ending the poisoning elimination process include a condition that the execution time of the poisoning elimination process has reached a predetermined time or more.
[0148]
If it is determined in S505 that the condition for ending the poisoning elimination process is not satisfied, the CPU 351 repeatedly executes the processes after S504 described above.
[0149]
If it is determined in step 505 that the poisoning elimination process execution end condition is satisfied, the CPU 351 proceeds to step S506, and controls the flow rate adjustment valve 30 to end the addition of the reducing agent.
[0150]
In S507, it is determined whether or not the downstream exhaust air-fuel ratio in the initial poisoning elimination control is equal to the predetermined air-fuel ratio.
[0151]
When it is determined in S507 that the downstream exhaust air-fuel ratio is equal to the predetermined air-fuel ratio, the execution of this routine is temporarily terminated.
[0152]
If it is determined in S507 that the downstream exhaust air-fuel ratio is different from the predetermined air-fuel ratio, the process proceeds to S508.
[0153]
In S508, the deviation between the downstream exhaust air-fuel ratio during the poisoning elimination control stored in the RAM 353 in S504 and the predetermined air-fuel ratio is calculated, and the calculated value is stored as a correction value in a predetermined area of the backup RAM 354. The execution of is temporarily terminated.
[0154]
In the NOx purification control after the poisoning elimination control routine as described above is executed, the CPU 351 adds the correction value stored in the predetermined area of the backup RAM 354 to the air-fuel ratio obtained from the output signal of the air-fuel ratio sensor 23. The rich spike control is executed by regarding that as the actual downstream exhaust air-fuel ratio.
[0155]
Thus, when the CPU 351 executes the poisoning elimination control routine, the poisoning elimination control means, the NOx amount detection means, and the NOx purification process changing means according to the present invention are realized.
[0156]
Therefore, according to the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the amount of reducing agent injected from the reducing agent injection valve 28 in the rich spike control is the exhaust gas actually discharged from the NOx storage reduction catalyst 20. Therefore, even if the characteristics of the output signal of the air-fuel ratio sensor 23 change due to aging, deterioration, etc., the amount of reducing agent added is set to the optimum amount. It becomes possible to do.
[0157]
As a result, excessive supply or supply shortage of the reducing agent does not occur in the rich spike control, and it becomes possible to prevent the exhaust emission from being deteriorated due to excessive supply or supply of the reducing agent.
[0158]
【The invention's effect】
An exhaust gas purification apparatus for an internal combustion engine according to the present invention measures the air-fuel ratio of exhaust gas when NOx catalyst poisoning elimination processing is being executed, and based on the deviation between the measured air-fuel ratio and a predetermined value The output value of the measuring means is corrected.
[0159]
As a result, it is possible to accurately measure the air-fuel ratio, and it is possible to perform the optimum NOx purification process even when the output signal is deviated due to aging or deterioration of the air-fuel ratio measuring means.
[0160]
In particular, in an exhaust gas purification apparatus configured to add a reducing agent to the exhaust gas so that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst in the NOx purification process becomes a predetermined target exhaust air-fuel ratio, the reducing agent due to a misidentification of the air-fuel ratio. Exhaust emissions caused by excessive supply or supply shortage are prevented from deteriorating.
[0161]
In addition, when determining the fuel injection amount to the internal combustion engine other than the NOx purification process, accurate air-fuel ratio feedback control can be performed, and deterioration of exhaust emission is prevented.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied and its intake and exhaust system.
FIG. 2A is a view for explaining the NOx absorption mechanism of the NOx storage reduction catalyst.
(B) A diagram illustrating the NOx release mechanism of the NOx storage reduction catalyst
FIG. 3 is a block diagram showing the internal configuration of the ECU
FIG. 4 is a diagram showing an example of a predetermined value and an actual measurement value of a downstream exhaust air-fuel ratio in poisoning elimination processing
FIG. 5 is a flowchart showing a poisoning elimination control routine.
[Explanation of symbols]
1 ... Internal combustion engine
2. Cylinder
3. Fuel injection valve
4 ... Common rail
5. Fuel supply pipe
6. Fuel pump
18 ... Exhaust branch pipe
19 ... Exhaust pipe
20 ... NOx storage reduction catalyst
21 ... Exhaust throttle valve
23 ... Air-fuel ratio sensor
25 ... EGR passage
26 ... EGR valve
27 ... EGR cooler
28 ... Reducing agent injection valve
29 ... Reducing agent supply path
30 ... Flow control valve
31 ... Shut-off valve
32 ... Reducing agent pressure sensor
33 ... Crank position sensor
34 ... Water temperature sensor
35 ... ECU
351 ... CPU
352 ... ROM
353 ... RAM
354 ... Backup RAM

Claims (2)

A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture.
NOx that is provided in the exhaust passage of the internal combustion engine and absorbs nitrogen oxide in the exhaust when the air-fuel ratio of the exhaust is high, and reduces while releasing the nitrogen oxide that was absorbed when the air-fuel ratio of the exhaust is low A catalyst,
NOx purification control means for performing NOx purification processing to release and reduce nitrogen oxides absorbed by the NOx catalyst;
Poisoning elimination control means for performing poisoning elimination processing by setting the air-fuel ratio of exhaust flowing into the NOx catalyst to a rich air-fuel ratio in order to eliminate poisoning due to oxides of the NOx catalyst;
An air-fuel ratio measuring means that is provided in the exhaust passage downstream of the NOx catalyst and measures the air-fuel ratio of the exhaust;
When the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst at the initial stage of execution of the poisoning elimination process becomes an air-fuel ratio in the vicinity of the theoretical air-fuel ratio, the output signal of the air-fuel ratio measuring means is compared with a predetermined value and output When a deviation occurs in the signal, air-fuel ratio correction means for correcting the output signal of the subsequent air-fuel ratio measurement means based on the value of the deviation;
An exhaust emission control device for an internal combustion engine, comprising: The predetermined value is an output signal when the air-fuel ratio of the exhaust gas flowing out from the NOx catalyst becomes an air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio at the initial stage of the poisoning elimination process when the air-fuel ratio measuring means is new. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the exhaust gas purification device is an internal combustion engine.

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