JP3912001B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust purification device that purifies exhaust gas from an internal combustion engine.
[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 an exhaust gas purification device that purifies harmful components in exhaust gas, lean NOx catalysts such as a selective reduction type NOx catalyst and an occlusion reduction type NOx catalyst are known.
[0004]
The selective reduction type NOx catalyst is a catalyst that reduces or decomposes NOx in the presence of hydrocarbon (HC) in an oxygen-excess atmosphere. In order to purify NOx with this selective reduction type NOx catalyst, an appropriate amount of HC component ( Reducing agent) is required. When this selective reduction type NOx catalyst is used for exhaust purification of the internal combustion engine, the amount of HC components in the exhaust during normal operation of the internal combustion engine is extremely small. Therefore, in order to purify NOx during normal operation, selective reduction It is necessary to supply the HC component to the type NOx catalyst.
[0005]
On the other hand, the NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases,₂It is a catalyst that reduces to
[0006]
When this storage reduction type NOx catalyst is arranged in the exhaust system of the internal combustion engine, when the internal combustion engine is operated with lean combustion and the air-fuel ratio of the exhaust gas becomes high, nitrogen oxides (NOx) in the exhaust gas are stored in the NOx storage reduction catalyst. When the air-fuel ratio of the exhaust gas absorbed into the NOx storage reduction catalyst becomes low, nitrogen oxide (NOx) absorbed in the NOx storage reduction catalyst is released while nitrogen (N₂).
[0007]
In the exhaust purification system using these lean NOx catalysts, it is very important to manage the catalyst bed temperature of the lean NOx catalyst.
[0008]
For example, the lean NOx catalyst has an activation temperature, and if the catalyst bed temperature is out of this activation temperature range, the purification capacity is extremely reduced.
[0009]
In order to solve such a problem, an exhaust gas purification apparatus for an internal combustion engine as described in Japanese Patent No. 2845056 has been proposed. 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, thereby reducing the temperature of the NOx storage material. It tries to solve the problem of decline.
[0010]
Further, as a method of reducing the amount of nitrogen oxide (NOx) discharged from the internal combustion engine, exhaust gas recirculation (EGR) in which a part of the exhaust gas flowing through the exhaust passage of the internal combustion engine is recirculated to the intake passage of the internal combustion engine. : Exhaust Gas Recirculation) is proposed.
[0011]
The EGR device uses water vapor (H₂O), carbon monoxide (CO), carbon dioxide (CO₂), Etc., to reduce the combustion speed and temperature of the air-fuel mixture in the combustion chamber of the internal combustion engine, thereby reducing the nitrogen oxide (NOx) generated during combustion. The amount is reduced.
[0012]
The above-described EGR device includes an EGR passage that communicates an exhaust passage and an intake passage of an internal combustion engine, and an EGR valve that adjusts the flow rate of exhaust gas (EGR gas) flowing through the EGR passage. In addition to the EGR passage and the EGR valve, devices having various configurations such as a device configured by providing an EGR cooler for cooling EGR gas in the middle of the EGR passage have been proposed.
[0013]
[Problems to be solved by the invention]
However, since the lean NOx catalyst does not reach the activation temperature immediately after the internal combustion engine is started, the catalyst does not function, and NOx in the exhaust gas passes through the NOx catalyst without being purified and is released into the atmosphere. Therefore, it is important to raise the temperature of the NOx catalyst at an early stage immediately after starting the internal combustion engine.
[0014]
As a means for increasing the temperature of the NOx catalyst at an early stage, the sub-injection of fuel is performed again at a time (for example, expansion stroke) that does not become the engine output after the main injection for injecting the fuel for engine output into the cylinder of the internal combustion engine. Examples of the injection (also referred to as post injection) can be given. The fuel injected by the sub-injection burns in the cylinder of the internal combustion engine and raises the temperature of the exhaust. If this sub-injection is used, the temperature of the NOx catalyst can be raised at an early stage, but even in this case, a certain amount of time is required until the NOx catalyst reaches the activation temperature.
[0015]
Therefore, it is also important to suppress NOx emission during the period until the NOx catalyst reaches the activation temperature. If EGR is used in such a case, it becomes possible to reduce NOx emissions. However, in order to extract a part of the exhaust energy as EGR gas, for example, when the EGR cooler is installed, the exhaust gas energy is supplied to the EGR cooler. On the contrary, since the temperature of the recirculated exhaust gas is lowered, the time until the NOx catalyst reaches the activation temperature becomes longer. Moreover, if the EGR gas ratio increases, it causes misfire and HC emission increases. However, conversely, if the EGR amount is decreased, not only the exhaust amount of NOx increases, but also when the intake throttle valve is used, the intake pressure of the internal combustion engine decreases, so the compression pressure decreases, and misfires occur. This causes HC emissions to increase.
[0016]
Therefore, it is important to obtain an optimum EGR amount for realizing a reduction in NOx emission amount and an early temperature increase of the NOx catalyst.
[0017]
The present invention has been made in view of the various problems as described above, and in an exhaust gas purification apparatus for an internal combustion engine, by adjusting the EGR gas ratio in the intake air, the temperature of the catalyst can be increased quickly, and An object of the present invention is to provide a technique for reducing NOx emission during that period, and to prevent deterioration of exhaust emissions such as when the catalyst is cold immediately after starting.
[0018]
[Means for Solving the Problems]
  The present invention employs the following means in order to solve the above problems. That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention is
  A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture.
  An exhaust purification catalyst provided in an exhaust passage of the internal combustion engine for purifying harmful components in the exhaust;
  Driving state detecting means for detecting the driving state of the vehicle;
  At a time when the engine output does not become the engine output after the fuel for engine output is injected into the internal combustion engine.
Sub-injection means for injecting fuel again;
  A fuel addition determination unit that determines whether or not the sub-injection unit can be executed based on a driving state of the vehicle detected by the driving state detection unit;
  An EGR device that recirculates part of the exhaust gas to the intake system of the internal combustion engine;
An intake throttle valve for adjusting the amount of fresh air sucked into the internal combustion engine;
  Comprising
  The EGR device includes an EGR cooler that cools EGR gas, and when the exhaust purification catalyst has not reached the activation temperature and the internal combustion engine is not warmed up, sub-injection is performed and the EGR gas ratio is 10%. Restrict toFurthermore, the intake throttle valve is controlled to the valve closing side.Thus, a decrease in the temperature of the exhaust gas reaching the exhaust purification catalyst is suppressed.
[0020]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, harmful components in the exhaust gas are purified by the catalyst of the exhaust gas purification apparatus. Further, when the exhaust gas purification apparatus immediately after the internal combustion engine is started does not reach the activation temperature, the fuel for generating the engine output is mainly injected into the cylinder of the internal combustion engine and then again, for example, in the expansion stroke that does not affect the engine output. Sub-injection for injecting fuel is performed. The fuel injected by this sub-injection burns in the cylinder and the exhaust temperature rises. In this way, when the exhaust gas having a higher temperature than usual reaches the exhaust purification catalyst, the temperature of the exhaust purification catalyst rises early.
[0021]
Further, a part of the exhaust discharged from the internal combustion engine is recirculated to the intake system to be recirculated gas (EGR gas) and taken into the combustion chamber together with fresh air. The EGR gas does not burn by itself but serves to lower the combustion temperature, thereby suppressing the amount of nitrogen oxide (NOx) generated.
[0022]
Here, in terms of suppressing the generation of NOx, the larger the EGR gas ratio in the intake air, the better. However, in terms of the early temperature rise of the exhaust purification catalyst, the smaller the EGR gas ratio, the better.
[0023]
Further, when the intake throttle valve is used, the amount of fresh air taken into the internal combustion engine can be adjusted, and air-fuel ratio control can be easily performed. However, since the amount of fresh air taken into the internal combustion engine by the intake throttle valve is limited and the pressure in the cylinder is lowered, the compression pressure in the compression stroke of the internal combustion engine does not increase, and there is a risk of misfire. In such a case, the compression pressure can be increased by inhaling EGR gas, and misfire can be suppressed.
[0024]
In this case, the compression pressure increases as the EGR gas ratio increases. However, when the EGR gas ratio exceeds a predetermined ratio, the amount of unburned hydrocarbons in the exhaust (hereinafter referred to as THC: Total Hydorocarbons) due to misfiring due to a decrease in the amount of fresh air. Increase).
[0025]
Further, if the EGR gas is less than a predetermined ratio, THC increases due to misfire caused by the compression pressure not increasing.
[0026]
Thus, the EGR gas ratio in the intake air sucked into the internal combustion engine affects the gas component in the exhaust gas and the temperature increase of the exhaust purification catalyst.
[0027]
Therefore, in the present invention, the optimum EGR gas ratio is 10% or less based on the experimental results. By adjusting the EGR gas ratio sucked into the internal combustion engine, the exhaust purification catalyst is suppressed while suppressing the generation of harmful components. By raising the temperature early, harmful components in the exhaust are prevented from being released into the atmosphere.
[0028]
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.
[0029]
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.
[0030]
An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0031]
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.
[0032]
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 a 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.
[0033]
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.
[0034]
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.
[0035]
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).
[0036]
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. The intake pipe 9 downstream of the air cleaner box 10 has an air flow meter 11 for outputting an electric signal corresponding to the mass of the intake air flowing through the intake pipe 9, and the temperature of the intake air flowing through the intake pipe 9. An intake air temperature sensor 12 for outputting the electrical signal is attached.
[0037]
An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at 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.
[0038]
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.
[0039]
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.
[0040]
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.
[0041]
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).
[0042]
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).
[0043]
An exhaust purification catalyst 20 for purifying harmful gas components in the exhaust is disposed in the middle of the exhaust pipe 19. In the exhaust pipe 19 downstream of the exhaust purification catalyst 20, an air-fuel ratio sensor 23 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust gas that flows through the exhaust pipe 19, and the temperature of the exhaust gas that flows through the exhaust pipe 19 And an exhaust gas temperature sensor 24 for outputting an electrical signal corresponding to the above.
[0044]
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 that adjusts 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.
[0045]
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.
[0046]
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.
[0047]
The exhaust branch pipe 18 and the intake branch pipe 8 are communicated with each other via an exhaust gas recirculation passage (EGR passage) 25 that recirculates a part of the exhaust gas flowing through the exhaust branch pipe 18 to the intake branch pipe 8. Yes. A flow rate adjusting valve (hereinafter referred to as EGR gas) that is configured by an electromagnetic valve or the like in the middle of the EGR passage 25 and changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) that flows through the EGR passage 25 according to the magnitude of applied power. EGR valve) 26 is provided.
[0048]
An EGR cooler 27 that cools the EGR gas flowing through the EGR passage 25 is provided at a location upstream of the EGR valve 26 in the EGR passage 25.
[0049]
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 through the exhaust branch pipe 18 flows into the EGR passage 25. Then, it is guided to the intake branch pipe 8 through the EGR cooler 27.
[0050]
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, and the EGR gas is cooled.
[0051]
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.
[0052]
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.
[0053]
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.
[0054]
Next, the exhaust purification catalyst 20 according to the present embodiment will be specifically described.
[0055]
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.
[0056]
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 carry | supported and 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.
[0057]
The NOx storage reduction catalyst 20 configured as described above absorbs nitrogen oxide (NOx) in the exhaust gas when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 is high.
[0058]
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).
[0059]
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.
[0060]
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)_Three ^-) Is absorbed by the NOx storage reduction catalyst 20. The nitrate ions (NO) absorbed in the NOx storage reduction catalyst 20_Three ^-) Combines with barium oxide (BaO) to form barium nitrate (Ba (NO_Three)₂).
[0061]
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.
[0062]
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.
[0063]
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)._Three ^-) On the contrary, nitrogen dioxide (NO₂) And nitrogen monoxide (NO), and desorbs from the NOx storage reduction catalyst 20.
[0064]
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).
[0065]
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.
[0066]
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.
[0067]
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.
[0068]
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.
[0069]
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 into the exhaust gas flowing through the exhaust passage upstream of the NOx storage reduction catalyst 20. In addition, by adding fuel into the exhaust gas from the reducing agent supply mechanism, the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 is lowered and the concentration of the reducing agent is increased.
[0070]
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 fuel in the reducing agent supply passage 29 that is provided in the reducing agent supply passage 29 upstream from the flow amount adjusting valve 30. A shut-off valve 31 that shuts off the flow of the reductant, a reducing agent pressure sensor 32 that is attached to the reducing agent supply path 29 upstream of the flow rate adjusting valve 30 and outputs an electrical signal corresponding to the pressure in the reducing agent supply path 29, It has.
[0071]
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.
[0072]
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.
[0073]
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.
[0074]
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 the reducing agent injection is performed using the cooling water flowing through the water jacket. The valve 28 may be cooled.
[0075]
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.
[0076]
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 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.
[0077]
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).
[0078]
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.
[0079]
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.
[0080]
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.
[0081]
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.
[0082]
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.
[0083]
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.
[0084]
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.
[0085]
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.
[0086]
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 oxide (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.
[0087]
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 gas), 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.
[0088]
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.
[0089]
The backup RAM 354 is a nonvolatile memory capable of storing data even after the internal combustion engine 1 is stopped.
[0090]
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, poisoning elimination control, and the like.
[0091]
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.
[0092]
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.
[0093]
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, etc. as parameters, and determines the final fuel injection timing.
[0094]
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.
[0095]
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.
[0096]
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.
[0097]
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.
[0098]
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.
[0099]
Next, in the NOx purification control, the CPU 351 executes rich spike control in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is spiked (short time) to a rich air-fuel ratio in a relatively short cycle. .
[0100]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. The rich spike control execution condition includes, for example, whether the NOx storage reduction catalyst 20 is in an active state, whether the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit, or poisoning elimination control. The conditions such as whether or not is executed can be exemplified.
[0101]
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.
[0102]
Specifically, the CPU 351 determines the engine speed, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), the fuel injection amount, and the like stored in the RAM 353. read out. Further, the CPU 351 accesses the reducing agent addition amount control map in the ROM 352 using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the air-fuel ratio of the exhaust to a preset target rich air. The amount of addition of the reducing agent (target addition amount) necessary for obtaining the fuel ratio is calculated.
[0103]
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).
[0104]
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.
[0105]
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.
[0106]
When the flow rate adjusting valve 30 is thus 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. .
[0107]
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 Reduced NOx catalyst 20 absorbs and releases nitrogen oxides (NOx)
The reduction is repeated alternately in a short cycle.
[0108]
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.
[0109]
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.
[0110]
When 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, when 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.
[0111]
Here, in the present invention, when the NOx catalyst 20 has not reached the activation temperature immediately after starting the internal combustion engine 1 or the like, the EGR gas ratio in the intake air is adjusted to reduce harmful substances in the exhaust, The temperature of the NOx catalyst 20 was raised early.
[0112]
Hereinafter, EGR control according to the present invention will be described.
[0113]
Immediately after the internal combustion engine 1 is started, the NOx catalyst 20 has not reached the activation temperature, so the NOx catalyst 20 is not functioning.
[0114]
In such a state, NOx in the exhaust gas passes through the NOx catalyst 20 without being purified and is released into the atmosphere.
[0115]
Here, as a means for increasing the temperature of the NOx catalyst 20 at an early stage, it is effective to perform sub-injection (post-injection) in which fuel is secondarily injected during the expansion stroke of the internal combustion engine 1. The reason why the fuel is injected in the expansion stroke is that fuel injection performed during the compression stroke increases the engine output and may deteriorate the operation state. The fuel injected by the sub-injection burns in the cylinder 2 and raises the gas temperature in the cylinder 2. The gas whose temperature has risen becomes exhaust gas, reaches the NOx catalyst 20 through the exhaust pipe 19, and raises the temperature of the NOx catalyst 20. If the sub-injection is used in this way, the temperature of the NOx catalyst can be raised early.
[0116]
If the relationship between the accelerator opening, the engine speed, the sub-injection amount or the sub-injection timing is mapped in advance and stored in the ROM 352, the map, the accelerator opening, and the engine rotation can be obtained. It can be calculated from the number. Further, the cooling water temperature of the internal combustion engine 1 may be added as a parameter.
[0117]
However, a certain amount of time is required until the temperature of the NOx catalyst 20 rises and reaches the activation temperature of the catalyst. The NOx discharged during this time passes through the NOx catalyst 20 without being purified and is released into the atmosphere. Therefore, it is necessary to reduce the NOx emission amount itself during this period.
[0118]
The use of EGR can be cited as a means for reducing NOx emissions. FIG. 4 is a graph showing the relationship between the EGR gas ratio during intake and the NOx emission amount. From this figure, it can be seen that the NOx emission decreases as the EGR gas ratio increases. However, the exhaust gas recirculated as EGR gas is sucked into the cylinder 2 without heating the NOx catalyst 20. During this time, the temperature of the EGR gas decreases, so that the larger the EGR gas ratio, the lower the temperature of the exhaust gas that reaches the NOx catalyst 20, which is contrary to the original purpose of raising the temperature of the NOx catalyst 20 at an early stage.
[0119]
Thus, in terms of reducing the NOx emission amount, the larger the EGR gas ratio in the intake air, the better. However, in terms of the early temperature rise of the NOx catalyst 20, the smaller the EGR gas ratio, the better.
[0120]
Further, when the intake throttle valve 13 is used, the amount of fresh air taken into the internal combustion engine 1 can be adjusted, and air-fuel ratio control can be easily performed, which is effective for exhaust purification. However, since the amount of fresh air drawn into the internal combustion engine 1 is limited by the intake throttle valve 13 and the pressure in the cylinder 2 is lowered, the compression pressure in the compression stroke of the internal combustion engine does not increase and there is a risk of misfire. . FIG. 5 shows the relationship between the EGR gas ratio during intake and the compression pressure in the cylinder 2. From this figure, it can be seen that the greater the EGR gas ratio, the higher the compression pressure. That is, when the EGR gas is sucked, the pressure drop in the cylinder 2 can be suppressed, the compression pressure can be increased, and misfire can be suppressed.
[0121]
On the other hand, FIG. 6 is a diagram showing the relationship between the EGR gas ratio in the intake air and the amount of unburned hydrocarbons (THC: Total Hydorocarbons). When the ratio of EGR gas in the intake air increases, the ratio of fresh air in the intake air decreases, causing a misfire and increasing the THC emission amount. On the other hand, if the EGR gas ratio in the exhaust gas is reduced, when the intake throttle valve 13 is used, the compression pressure decreases, causing a misfire and increasing the THC emission amount.
[0122]
Thus, the ratio of EGR gas in the intake air sucked into the internal combustion engine 1 affects the gas component in the exhaust gas and the temperature increase of the NOx catalyst 20.
[0123]
Therefore, it is important to obtain an optimum EGR gas ratio for realizing reduction of harmful components in the exhaust gas and early temperature increase of the NOx catalyst 20.
[0124]
In the present invention, an optimal EGR gas ratio is determined, and EGR control is performed to achieve the ratio, thereby solving the above problem.
[0125]
Here, based on FIG. 4 thru | or FIG. 6 calculated | required by experiment, it is preferable that an optimal EGR gas ratio shall be 10 percent or less in inhalation | air-intake. By setting such a ratio, NOx emission can be suppressed, a required compression pressure can be secured, and THC emission can be suppressed.
[0126]
In the EGR control according to the present embodiment, the CPU 351 feedback-controls the opening degree of the EGR valve 26 using the intake fresh air amount of the internal combustion engine 1 as a parameter, and adjusts the intake fresh air amount and the EGR gas amount.
[0127]
In the EGR valve feedback control, for example, the CPU 351 determines the target intake fresh 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 fresh air is mapped in advance, and the target intake fresh air amount is calculated from the map, the accelerator opening, and the engine rotational speed.
[0128]
Further, as described above, it is preferable to adjust the EGR gas amount and the intake fresh air amount so that the EGR gas ratio in the intake air is 10% or less from the request for emission. Therefore, the CPU 351 calculates a target EGR gas amount such that the ratio of EGR gas in the intake air is 10% or less based on the calculated target intake fresh air amount.
[0129]
Here, if the relationship between the opening change amount of the EGR valve 26 and the intake throttle valve 13 and the amount of EGR gas sucked into the internal combustion engine 1 is obtained in advance by experiment and mapped and stored in the ROM 352, the target EGR gas amount is obtained. Based on this, it is possible to calculate the valve opening correction amount for correcting the valve opening amounts of the EGR valve 26 and the intake throttle valve 13. Further, the cooling water temperature of the internal combustion engine 1 may be added as a parameter.
[0130]
The CPU 351 adjusts the EGR gas amount and the intake fresh air amount by changing the valve opening amounts of the EGR valve 26 and the intake throttle valve 13 based on the calculated valve opening correction amount.
[0131]
When the target intake fresh air amount and the target EGR gas amount are determined by the above-described procedure, the CPU 351 reads the output signal value (actual intake fresh air amount) of the air flow meter 11 stored in the RAM 353, and the actual intake fresh air amount. Compare air volume with target fresh air volume.
[0132]
When the actual intake fresh air amount is smaller than the target intake fresh air amount, the CPU 351 closes the EGR valve 26 by a predetermined amount and opens the intake throttle valve 13 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.
[0133]
On the other hand, when the actual intake fresh air amount is larger than the target intake fresh air amount, the CPU 351 opens the EGR valve 26 by a predetermined amount and closes the intake throttle valve 13 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 increase in EGR gas.
[0134]
As described above, the EGR gas ratio in the intake air can be adjusted to 10% or less by adjusting the EGR gas amount and the fresh intake air amount.
[0135]
Next, the control flow of this embodiment will be described.
[0136]
FIG. 7 is a flowchart of NOx catalyst temperature rise and EGR control according to the present embodiment.
[0137]
In step 101, the accelerator opening degree and engine speed data stored in the RAM 353 are read.
[0138]
In step 102, data such as cooling water temperature and exhaust temperature stored in the RAM 353 is read.
[0139]
In step 103, it is determined whether or not the bed temperature of the NOx catalyst 20 is not higher than a predetermined temperature (for example, 300 ° C.) and the cooling water temperature of the internal combustion engine 1 is not higher than a predetermined temperature (for example, 60 ° C.). Here, it is determined whether or not the temperature rise of the NOx catalyst 20 by the sub-injection and the EGR gas ratio need to be set to a predetermined ratio or less.
[0140]
Here, the output temperature of the exhaust temperature sensor 24 is substituted for the bed temperature of the NOx catalyst 20.
[0141]
If this condition is satisfied, the process proceeds to step 105. If not satisfied, the process proceeds to step 104.
[0142]
In step 104, since the NOx catalyst 20 has reached the activation temperature or the internal combustion engine 1 has been warmed up, normal fuel injection control and EGR control are performed. That is, control for raising the temperature of the NOx catalyst 20 early is not performed.
[0143]
In step 105, since the NOx catalyst 20 has not reached the activation temperature and the internal combustion engine 1 has not been warmed up, control for raising the temperature of the NOx catalyst 20 to the activation temperature early is started.
[0144]
In step 106, EGR control is performed so that the sub-injection and the EGR gas ratio are less than or equal to a predetermined ratio. The NOx catalyst 20 can be raised in temperature early, and generation of harmful gas components such as NOx and THC is suppressed.
[0145]
In this way, the EGR gas ratio can be changed based on the state of the NOx catalyst 20 and the internal combustion engine 1.
[0146]
Further, when the NOx catalyst 20 has not reached the activation temperature, the generation of harmful gas components such as NOx and THC can be suppressed by adjusting the EGR gas ratio to a predetermined value or less.
[0147]
Further, since the amount of EGR gas passing through the EGR cooler or the like is reduced, the NOx catalyst 20 can be warmed up early without unnecessary cooling of the EGR gas, so that the NOx can be quickly increased immediately after the internal combustion engine 1 is started. Can be purified.
[0148]
Thus, air-fuel ratio control corresponding to the EGR gas ratio can be performed, and deterioration of exhaust emission can be prevented.
[0149]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the EGR gas ratio in inhalation | air_intake can be adjusted to 10% or less, the exhaust gas temperature can be raised, and the exhaust gas purification apparatus can be raised in temperature early, and the harmful component in exhaust gas can be suppressed.
[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 an intake / exhaust system thereof.
FIG. 2 (A) is a view for explaining the NOx absorption mechanism of the NOx storage reduction catalyst. (B) is a diagram illustrating the NOx release mechanism of the NOx storage reduction catalyst.
FIG. 3 is a block diagram showing an internal configuration of an ECU.
FIG. 4 is a diagram showing a relationship between an EGR gas ratio in exhaust gas and NOx emission amount.
FIG. 5 is a diagram showing a relationship between an EGR gas ratio in exhaust gas and a compression pressure in a cylinder.
FIG. 6 is a graph showing the relationship between the ratio of EGR gas in exhaust gas and the amount of unburned hydrocarbons.
FIG. 7 is a flowchart of NOx catalyst temperature increase control and EGR control according to the present invention.
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 (1)

A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture.
An exhaust purification catalyst provided in an exhaust passage of the internal combustion engine for purifying harmful components in the exhaust;
Driving state detecting means for detecting the driving state of the vehicle;
Sub-injection means for injecting fuel again at a time when the engine output does not become the engine output after the main output of fuel for engine output to the internal combustion engine;
A fuel addition determination unit that determines whether or not the sub-injection unit can be executed based on a driving state of the vehicle detected by the driving state detection unit;
An EGR device that recirculates part of the exhaust gas to the intake system of the internal combustion engine;
An intake throttle valve for adjusting the amount of fresh air sucked into the internal combustion engine;
Comprising
The EGR device includes an EGR cooler that cools EGR gas, and when the exhaust purification catalyst has not reached the activation temperature and the internal combustion engine is not warmed up, sub-injection is performed and the EGR gas ratio is increased to 10%. An exhaust purification device for an internal combustion engine, characterized in that a reduction in the temperature of the exhaust gas reaching the exhaust purification catalyst is suppressed by controlling the intake throttle valve to the valve closing side in the following manner.

Images