JP3651382B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine mounted on an automobile or the like, and more particularly to a technique for purifying harmful gas components contained in exhaust gas by supplying a reducing agent to an exhaust gas purification catalyst.
[0001]
[Prior art]
In recent years, an internal combustion engine mounted on an automobile or the like, particularly a diesel engine or a lean-burn gasoline engine that can burn an oxygen-rich mixture (so-called lean air-fuel mixture), A technique for efficiently purifying nitrogen oxides (NOx) contained in the gas is desired.
[0002]
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. While releasing nitrogen oxide (NOx), nitrogen (N₂The NOx storage reduction catalyst is known to reduce to (3).
[0003]
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).
[0004]
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.
[0005]
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 execute so-called rich spike control to release and reduce nitrogen oxide (NOx) absorbed in the NOx storage reduction catalyst.
[0006]
As a specific method of the rich spike control, as described in Japanese Patent No. 2845056, a reducing agent supply device that supplies a reducing agent to the exhaust passage upstream of the NOx storage reduction catalyst is provided, and the storage reduction type Reducing agent concentration while reducing the oxygen concentration of exhaust gas flowing into the NOx storage reduction catalyst by supplying the reducing agent from the reducing agent supply device to the exhaust passage at a predetermined time before the NOx absorption capacity of the NOx catalyst is saturated. A method has been proposed for enhancing the above.
[0007]
[Problems to be solved by the invention]
By the way, an exhaust purification catalyst such as a NOx storage reduction catalyst is uniformly activated at a predetermined temperature or more to be able to purify harmful gas components in the exhaust, so that the internal combustion engine is cold-started. In addition, when the temperature of the exhaust purification catalyst is lower than the predetermined temperature, it becomes inactive, and the harmful gas component in the exhaust cannot be sufficiently purified.
[0008]
When the rich spike control as described above is executed when the NOx storage reduction catalyst is in an inactive state, not only the nitrogen oxide (NOx) in the exhaust gas can be reduced and purified, but also the reducing agent It is released into the atmosphere as it is, or the reducing agent liquefies in the low-temperature storage-reduction NOx catalyst and adheres to the storage-reduction NOx catalyst, and the reducing agent burns after the activation of the storage-reduction NOx catalyst to generate soot And overheating of the NOx storage reduction catalyst may occur.
[0009]
On the other hand, a method of directly detecting the bed temperature of the NOx storage reduction catalyst and determining whether the NOx storage reduction catalyst is in an active state is also conceivable. However, a new dedicated temperature is added to the NOx storage reduction catalyst. A sensor needs to be installed.
[0010]
The present invention has been made in view of the various circumstances as described above, and is an exhaust purification device for an internal combustion engine that purifies harmful gas components in exhaust gas by supplying a reducing agent to an exhaust purification catalyst. An object of the present invention is to provide a technique capable of determining the active state of a catalyst, and to prevent deterioration of exhaust emission, overheating of an exhaust purification catalyst, and the like.
[0011]
[Means for Solving the Problems]
  The present invention employs the following means in order to solve the above-described problems. That is, an exhaust gas purification apparatus for an internal combustion engine according to the present invention includes an exhaust gas purification catalyst that is provided in an exhaust passage of the internal combustion engine to reduce and purify a predetermined component contained in exhaust gas, and a reduction agent that supplies a reducing agent to the exhaust gas purification catalyst. Agent supply means and exhaust gas flowing out from the exhaust purification catalystCheck the air-fuel ratio ofWhen the exhaust state detection means to be discharged and the reducing agent supply means supply the reducing agent to the exhaust purification catalystWhen the air-fuel ratio of the exhaust gas detected by the exhaust gas state detecting means changes, the catalyst for determining that the exhaust gas purification catalyst is active.Medium active state determination means.
[0012]
  In the exhaust gas purification apparatus for an internal combustion engine configured as described above, the catalyst activation state determining means includes the exhaust gas detected by the exhaust gas state detecting means when the reducing agent is supplied to the exhaust gas purification catalyst by the reducing agent supply means.Air / fuel ratioBased on this, it is determined whether or not the exhaust purification catalyst is active.
[0013]
  Here, when the reducing agent is supplied from the reducing agent supply means to the exhaust purification catalyst when the exhaust purification catalyst is in the inactive state, the reducing agent does not react with the predetermined component in the exhaust purification catalyst, and the reducing agent further Exhaust gas flowing out from the exhaust purification catalyst because it liquefies in the low temperature exhaust purification catalyst and adheres to the exhaust purification catalystThe air-fuel ratio ofAs compared with before and after the supply of the reducing agent, it hardly changes. On the other hand, if the reducing agent is supplied from the reducing agent supply means to the exhaust purification catalyst when the exhaust purification catalyst is in the active state, the atmosphere temperature in the exhaust purification catalyst becomes somewhat high, so that the reduction is performed in the exhaust purification catalyst. Since the agent no longer liquefies and adheres to the exhaust purification catalyst, the reducing agent and the predetermined component react with each other.The air-fuel ratio ofIt will change compared to before and after the supply of the reducing agent.
[0014]
  Therefore, the catalyst activation state determination means detects the exhaust state detection means when the reducing agent is supplied to the exhaust purification catalyst by the reducing agent supply means.The air-fuel ratio of the exhaustBased on this, it becomes possible to determine whether or not the exhaust purification catalyst is active.. In other words, the catalyst activation state determination means indicates that the exhaust purification catalyst is active when the exhaust air-fuel ratio detected by the exhaust state detection means changes due to the supply of the reducing agent, and the exhaust air condition detected by the exhaust state detection means. If the fuel ratio does not change due to the supply of reduction, it can be determined that the exhaust purification catalyst is not active.
[0015]
In addition, when the exhaust purification catalyst is in an inactive state, if the reducing agent is inadvertently supplied to the exhaust purification catalyst for the purpose of determining the activity of the exhaust purification catalyst, deterioration of exhaust emission or overheating of the exhaust purification catalyst will occur. Therefore, the exhaust gas purification apparatus for an internal combustion engine according to the present invention further comprises catalyst temperature estimation means for estimating the temperature of the exhaust gas purification catalyst based on the operating state of the internal combustion engine, The catalyst activity determining means may determine the activity of the exhaust purification catalyst by supplying the reducing agent from the reducing agent supply means to the exhaust purification catalyst on the condition that the estimated value by the catalyst temperature estimating means is equal to or higher than a predetermined temperature. Good.
[0016]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the parameter detected by the exhaust state detection means.As an example, instead of the air-fuel ratio of the exhaust,Concentration of predetermined components contained in exhaust, exhaust temperature, etc.May be used.
[0017]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the determination process by the catalyst activity determination means may be executed only during a period from the start of the internal combustion engine to the activation of the exhaust gas purification catalyst, or the exhaust gas purification device. As long as the internal combustion engine is in an operating state even after the catalyst is activated, it may be executed at a predetermined cycle.
[0018]
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.
[0019]
<Embodiment 1>
First, a first embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to FIGS.
[0020]
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. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-stroke cycle diesel engine having four cylinders 2.
[0021]
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.
[0022]
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 (crank) of the internal combustion engine 1. It is connected to a crank pulley 1a attached to a shaft) via a belt 7.
[0023]
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.
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 combustion chamber of each cylinder 2.
[0024]
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).
[0025]
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.
[0026]
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.
[0027]
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.
[0028]
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.
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 15 a 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.
[0029]
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 a combustion chamber of each cylinder 2 via an exhaust port (not shown).
[0030]
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).
[0031]
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. An air-fuel ratio sensor 23 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 downstream of the exhaust purification catalyst 20. The air-fuel ratio sensor 23 is an embodiment of the exhaust state detection means according to the present invention.
[0032]
The exhaust pipe 19 downstream of the air-fuel ratio sensor 23 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.
[0033]
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.
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.
[0034]
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. ing. In the middle of the EGR passage 25, a flow rate adjusting valve (EGR valve) that is constituted by an electromagnetic valve or the like and changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) flowing in the EGR passage 25 in accordance with the magnitude of applied power. ) 26 is provided.
[0035]
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.
[0036]
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.
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.
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.
[0037]
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.
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.
[0038]
Next, the exhaust purification catalyst 20 according to the present embodiment will be specifically described.
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 is referred to as a storage reduction type NOx catalyst 20.
[0039]
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 the present embodiment, an occlusion reduction type NOx catalyst configured by supporting barium (Ba) and platinum (Pt) on a support made of alumina will be described as an example.
[0040]
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.
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).
[0041]
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.
[0042]
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).
As described above, 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_Three ^-) Is absorbed by the NOx storage reduction catalyst 20.
The above-described NOx absorption action is continued as long as 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 oxide (NOx) in the exhaust gas is 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.
[0043]
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.
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).
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.
[0044]
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. Substances (NOx) are not removed by the NOx storage reduction catalyst 20 but are released into the atmosphere.
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.
Therefore, when the internal combustion engine 1 is operated in lean combustion, before the NOx absorption capacity of the NOx storage reduction catalyst 20 is saturated, the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 is reduced and the reducing agent is used. It is necessary to increase the concentration and release and reduce nitrogen oxide (NOx) absorbed by the NOx storage reduction catalyst 20.
[0045]
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.
[0046]
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.
[0047]
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.
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.
[0048]
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.
[0049]
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 valve 28 is cooled by the cooling water flowing through the water jacket. You may be made to do.
[0050]
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.
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.
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).
[0051]
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.
[0052]
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.
[0053]
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, a reducing agent pressure sensor 32, a crank position sensor 33, a water temperature sensor 34, an accelerator opening sensor 36, and the like. These various sensors are connected via electrical wiring, and the output signals of the various sensors described above are input to the ECU 35.
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 shutoff valve 31 and the like are connected to the ECU 35 via electric wiring. Can be controlled.
[0054]
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.
[0055]
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.
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, a reducing agent pressure sensor 32, a water temperature sensor 34, an accelerator opening sensor 36, and the like. In addition, an output signal of a sensor that outputs a signal in an analog signal format is input via the A / D 355, and the output signal is transmitted to the CPU 351 and the RAM 353.
[0056]
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.
[0057]
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. In addition to application programs such as an EGR control routine for control and a NOx purification control routine for purifying nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst 20, the active state of the NOx storage reduction catalyst 20 is determined. A catalyst activity determination control routine for determination is stored.
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.
[0058]
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.
[0059]
The backup RAM 354 is a nonvolatile memory capable of storing data even after the internal combustion engine 1 is stopped.
[0060]
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 catalyst determination control.
[0061]
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.
[0062]
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 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 output signal values from the air flow meter 11, the intake air temperature sensor 12, the water temperature sensor 34, etc., and determines the final fuel injection time.
[0063]
When determining the fuel injection timing, the CPU 351 accesses the fuel injection 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.
[0064]
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 matches the fuel injection timing. At the time, application of drive power to the fuel injection valve 3 is started. The CPU 351 stops applying the driving power to the fuel injection valve 3 when the elapsed time from the time when the application of the driving power to the fuel injection valve 3 is started reaches the fuel injection time.
[0065]
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.
[0066]
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. 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.
[0067]
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.
As the EGR control execution condition described above, the coolant temperature is equal to or higher than a predetermined temperature, the internal combustion engine 1 is continuously operated for a predetermined time or longer from the start, the amount of change in the accelerator opening is a positive value, etc. Conditions can be exemplified.
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.
[0068]
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.
[0069]
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. .
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
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.
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.
[0070]
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.
[0071]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. Examples of the rich spike control execution condition include a condition that the NOx storage reduction catalyst 20 is in an active state and that poisoning elimination control is not executed.
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.
[0072]
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. 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.
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).
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.
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 pressure of the fuel applied to the reducing agent injection valve 28 becomes less than the valve opening pressure, and the reducing agent injection valve 28 is closed. To do.
[0073]
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. .
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.
[0074]
Next, in the catalyst activity determination control, the CPU 351 controls the flow rate adjustment valve 30 to temporarily reduce the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 at a predetermined time after the start of the internal combustion engine 1 is completed. The output signal of the air-fuel ratio sensor 23 at that time is monitored.
[0075]
Here, when the bed temperature of the NOx storage reduction catalyst 20 is lower than the activation temperature, the oxidation / reduction action of the NOx storage reduction catalyst 20 does not work, and oxygen in the exhaust is not consumed accordingly, and in the exhaust. Since the reducing agent liquefies in the low-temperature storage-reduction NOx catalyst 20 and adheres to the storage-reduction NOx catalyst 20, the output signal of the air-fuel ratio sensor 23 when the reducing agent is supplied to the storage-reduction NOx catalyst 20 As shown in FIG. 4, there is almost no change compared to before and after the reducing agent is supplied to the NOx storage reduction catalyst 20.
On the other hand, when the bed temperature of the NOx storage reduction catalyst 20 is equal to or higher than the activation temperature, the oxidation / reduction action of the NOx storage reduction catalyst 20 works and oxygen in the exhaust is consumed accordingly, and in the exhaust. Therefore, the output signal of the air-fuel ratio sensor 23 when the reducing agent is supplied to the NOx storage reduction catalyst 20 is shown in FIG. As shown in the figure, it is lower than before and after the reducing agent is supplied to the NOx storage reduction catalyst 20.
Therefore, when the reducing agent is supplied from the reducing agent injection valve 28 to the NOx storage reduction catalyst 20, the CPU 351 stores the NOx storage reduction if the output signal of the air-fuel ratio sensor 23 changes corresponding to the supply of the reducing agent. If it is determined that the catalyst 20 is active and the output signal of the air-fuel ratio sensor 23 does not change, it can be determined that the NOx storage reduction catalyst 20 is in an inactive state.
[0076]
If the supply of the reducing agent to the NOx storage reduction catalyst 20 for the purpose of determining the activity of the NOx storage reduction catalyst 20 is inadvertently repeated, the amount of the reducing agent adhering to the NOx storage reduction catalyst 20 increases. The following problems may occur.
[0077]
Since the reducing agent attached to the NOx storage reduction catalyst 20 is assumed to vaporize as the storage reduction NOx catalyst 20 rises in temperature, the amount of reducing agent attached to the NOx storage reduction catalyst 20 increases. In the temperature increasing process of the NOx storage reduction catalyst 20, a relatively large amount of heat may be lost due to vaporization of the reducing agent, and a decrease in the bed temperature of the NOx storage reduction catalyst 20 may be induced.
In addition, since a part of the reducing agent attached to the NOx storage reduction catalyst 20 is assumed to burn after the activation of the NOx storage reduction catalyst 20, the amount of the reducing agent attached to the NOx storage reduction catalyst 20 is small. If increased, a relatively large amount of reducing agent burns simultaneously after the activation of the NOx storage reduction catalyst 20, and overheating of the NOx storage reduction catalyst 20 may be induced.
Further, it is assumed that a part of the reducing agent adhering to the NOx storage reduction catalyst 20 is separated from the NOx storage reduction catalyst 20 and released into the atmosphere during the temperature increase process of the NOx storage reduction catalyst 20. Therefore, when the amount of the reducing agent adhering to the NOx storage reduction catalyst 20 increases, a relatively large amount of the reducing agent is released into the atmosphere during the temperature rising process of the NOx storage reduction catalyst 20, and the exhaust emission may deteriorate. is there.
[0078]
Therefore, in the catalyst activity determination control according to the present embodiment, the CPU 351 estimates the approximate bed temperature of the NOx storage reduction catalyst 20 using the operation state of the internal combustion engine 1 as a parameter, and the estimated value is equal to or higher than the activation temperature. Under these conditions, a reducing agent is supplied to the NOx storage reduction catalyst 20 to determine whether the NOx storage reduction catalyst 20 is actually in an active state.
[0079]
Hereinafter, the catalyst activity determination control according to the present embodiment will be specifically described along the flowchart of FIG.
[0080]
The flowchart shown in FIG. 6 is a flowchart showing a catalyst activity determination control routine. The catalyst activity determination routine is a routine stored in advance in the ROM 352, and is a routine executed by the CPU 351 every predetermined time (for example, every time the crank position sensor 33 outputs a pulse signal).
[0081]
In the catalyst activation determination control routine, the CPU 351 first accesses the catalyst activation flag storage area preset in the RAM 353 in S601 and determines whether or not “1” is stored in the catalyst activation flag storage area. .
The catalyst activation flag storage area is set to “1” when it is determined that the NOx storage reduction catalyst 20 is in an active state, and is reset to “0” when the internal combustion engine 1 is stopped or started. It is. In the separate rich spike control, whether the rich spike control execution condition is satisfied or not is determined based on the value stored in the catalyst activation flag storage area. That is, execution of rich spike control is permitted when “1” is stored in the catalyst activation flag storage area, and execution of rich spike control is prohibited when “0” is stored in the catalyst activation flag storage area. Will be.
[0082]
If it is determined in S601 that “1” is stored in the catalyst activation flag storage area, the CPU 351 regards that the active state of the NOx storage reduction catalyst 20 has already been determined, and executes this routine. Exit once.
[0083]
On the other hand, if it is determined in S601 that "1" is not stored in the catalyst activation flag storage area, in other words, if it is determined that "0" is stored in the catalyst activation flag storage area, the CPU 351 Therefore, it is considered that the active state of the NOx storage reduction catalyst 20 has not yet been determined, and the process proceeds to S602.
In S602, the CPU 351 reads the engine speed, the output signal value of the air flow meter 11 (intake air amount), the output signal value of the accelerator opening sensor 36 (accelerator opening), the fuel injection time, and the like from the RAM 353.
[0084]
In S603, the CPU 351 estimates the bed temperature: TC of the NOx storage reduction catalyst 20 using the engine speed, intake air amount, accelerator opening, and fuel injection time read in S602 as parameters. At that time, the relationship between the engine speed, the intake air amount, the accelerator opening, the fuel injection time, and the bed temperature of the NOx storage reduction catalyst 20 is experimentally obtained in advance, and these relationships are mapped and stored in the ROM 352. It is good to leave.
[0085]
In S604, the CPU 351 reads the activation temperature: T of the NOx storage reduction catalyst 20 from the backup RAM 354, and whether the bed temperature: TC of the NOx storage reduction catalyst 20 estimated in S603 is equal to or higher than the activation temperature: T. Is determined.
[0086]
If it is determined in S604 that the bed temperature: TC is lower than the activation temperature: T, the CPU 351 proceeds to S609, maintains the value of the catalyst activation flag storage area of the RAM 353 at “0”, and executes this routine. End execution once.
[0087]
On the other hand, if it is determined in S604 that the bed temperature: TC is equal to or higher than the activation temperature: T, the CPU 351 proceeds to S605 to inject the reducing agent from the reducing agent injection valve 28 into the exhaust branch pipe 18. The flow regulating valve 30 is controlled.
[0088]
In S606, the CPU 351 inputs the output signal value of the air-fuel ratio sensor 23 (the air-fuel ratio of the exhaust gas flowing out from the NOx storage reduction catalyst 20) for a predetermined period. The predetermined period is a period determined in consideration of the time required for the reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 to reach the position of the air-fuel ratio sensor 23, so-called response delay time. is there.
[0089]
In S607, the CPU 351 determines whether or not the exhaust air-fuel ratio input in S606 has changed to the rich side in response to the addition of the reducing agent.
[0090]
If it is determined in S607 that the exhaust air-fuel ratio has not changed, the CPU 351 considers that the NOx storage reduction catalyst 20 has not yet been activated, and proceeds to S610.
In S610, the CPU 351 adds a predetermined temperature: α to the activation temperature: T of the NOx storage reduction catalyst 20 stored in the backup RAM 354, and stores the obtained value as the activation temperature: T in the backup RAM 354. .
[0091]
In S611, the CPU 351 determines whether or not the new activation temperature T updated in S610 is higher than a predetermined upper limit value TMAX.
[0092]
If it is determined in S611 that the activation temperature T is equal to or lower than the upper limit value TMAX, the CPU 351 proceeds to S609 and maintains the value of the catalyst activation flag storage area of the RAM 353 at “0”. The execution of is temporarily terminated.
[0093]
If it is determined in S611 that the activation temperature: T is higher than the upper limit value: TMAX, the CPU 351 proceeds to S612, determines that the NOx storage reduction catalyst 20 has deteriorated, and executes this routine. finish. In this case, the CPU 351 may prohibit the execution of the rich spike control, or turn on a warning lamp provided in the passenger compartment to notify the driver of the deterioration of the NOx storage reduction catalyst 20. May be.
[0094]
On the other hand, if it is determined in S607 that the exhaust air-fuel ratio has changed to the rich side in response to the addition of the reducing agent, the CPU 351 regards the NOx storage reduction catalyst 20 as active, and S608. , The value of the catalyst activation flag storage area of the RAM 353 is rewritten from “0” to “1”, and the execution of this routine is terminated.
[0095]
Thus, when the CPU 351 executes the catalyst activity determination control routine, the catalyst temperature estimation means and the catalyst activation state determination means according to the present invention are realized.
[0096]
Therefore, according to the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the occlusion is performed based on the output signal of the air-fuel ratio sensor 23 when the reducing agent is supplied from the reducing agent injection valve 28 to the NOx storage reduction catalyst 20. It becomes possible to determine the activity / inactivity of the reduced NOx catalyst 20. As a result, the rich spike control is not executed carelessly when the NOx storage reduction catalyst 20 is in an inactive state, the temperature rise of the NOx storage reduction catalyst 20 is not hindered, and exhaust emission is prevented. Deterioration and overheating of the NOx storage reduction catalyst 20 are prevented.
[0097]
Furthermore, the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment estimates the approximate bed temperature of the NOx storage reduction catalyst 20 using the operating state of the internal combustion engine 1 as a parameter, and the estimated value is equal to or higher than the activation temperature. In order to determine whether the NOx storage reduction catalyst 20 is actually in an active state by supplying a reducing agent to the NOx storage reduction catalyst 20 on the condition of The addition of the reducing agent is not performed inadvertently.
[0098]
<Embodiment 2>
Next, a second embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described with reference to FIG. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.
[0099]
In the first embodiment described above, the activation determination control is executed only during the period from when the internal combustion engine 1 is started until the storage reduction type NOx catalyst 20 is activated, and after the storage reduction type NOx catalyst 20 is once activated. In the present embodiment, an example in which the activity determination control is executed every time the rich spike control is executed even after the NOx storage reduction catalyst 20 is activated will be described.
This is because if the internal combustion engine 1 is decelerated for a long time after the activation of the NOx storage reduction catalyst 20 or if the idle operation is continued for a long time, the NOx storage reduction catalyst 20 is cooled by the low-temperature exhaust gas, This is because the bed temperature of the NOx storage reduction catalyst 20 may drop to below the activation temperature.
[0100]
In the catalyst activity determination control according to the present embodiment, the CPU 351 executes a catalyst activity determination control routine as shown in FIG. The catalyst activity determination control routine shown in FIG. 7 is a routine stored in advance in the ROM 352, and is a routine that is repeatedly executed by the CPU 351 every predetermined time.
[0101]
In the catalyst activity determination control routine, the CPU 351 first determines in S701 whether or not it is time to execute rich spike control. As a method of determining the execution time of the rich spike control, a method of determining whether or not the elapsed time from the previous rich spike control execution time has reached the execution cycle of the rich spike control can be exemplified.
[0102]
If it is determined in S701 that it is not time to execute the rich spike control, the CPU 351 proceeds to S711, prohibits the execution of the rich spike control, and temporarily ends the execution of this routine.
[0103]
On the other hand, if it is determined in S701 that it is time to execute the rich spike control, the CPU 351 proceeds to S702, and from the RAM 353, the engine speed, the output signal value (intake air amount) of the air flow meter 11, the accelerator opening sensor. 36 output signal value (accelerator opening), fuel injection time, etc. are read out.
[0104]
In S703, the CPU 351 estimates the bed temperature: TC of the NOx storage reduction catalyst 20 using the engine speed, intake air amount, accelerator opening, and fuel injection time read in S702 as parameters.
[0105]
In S704, the CPU 351 reads the activation temperature: T of the NOx storage reduction catalyst 20 from the backup RAM 354, and determines whether the bed temperature: TC of the NOx storage reduction catalyst 20 estimated in S703 is equal to or higher than the activation temperature: T. Is determined.
[0106]
If it is determined in S704 that the bed temperature: TC is lower than the activation temperature: T, the CPU 351 proceeds to S711, prohibits execution of rich spike control, and temporarily ends execution of this routine.
[0107]
On the other hand, if it is determined in S704 that the bed temperature: TC is equal to or higher than the activation temperature: T, the CPU 351 proceeds to S705 and permits execution of rich spike control. In this case, the CPU 351 executes rich spike control according to a separate NOx purification control routine.
[0108]
In S706, the CPU 351 inputs the output signal value of the air-fuel ratio sensor 23 (the air-fuel ratio of the exhaust gas flowing out from the NOx storage reduction catalyst 20) for a predetermined period.
[0109]
In S707, the CPU 351 determines whether or not the exhaust air-fuel ratio input in S706 has changed to the rich side in response to the addition of the reducing agent.
[0110]
If it is determined in S707 that the exhaust air-fuel ratio has not changed, the CPU 351 considers that the NOx storage reduction catalyst 20 has not yet been activated, and proceeds to S708.
[0111]
In S708, the CPU 351 adds a predetermined temperature: α to the activation temperature: T of the NOx storage reduction catalyst 20 stored in the backup RAM 354, and stores the obtained value as the activation temperature: T in the backup RAM 354. .
[0112]
In S709, the CPU 351 determines whether or not the new activation temperature T updated in S708 is higher than a predetermined upper limit value TMAX.
[0113]
If the CPU 351 determines in S709 that the activation temperature T is equal to or lower than the upper limit value TMAX, the CPU 351 prohibits the execution of the rich spike control in S711 and temporarily terminates the execution of this routine.
[0114]
On the other hand, if it is determined in S709 that the activation temperature: T is higher than the upper limit value: TMAX, the CPU 351 proceeds to S710, determines that the NOx storage reduction catalyst 20 has deteriorated, and then in S711. The execution of the rich spike control is prohibited and the execution of this routine is terminated. At that time, the CPU 351 may turn on a warning lamp provided in the passenger compartment to notify the driver of the deterioration of the NOx storage reduction catalyst 20.
[0115]
On the other hand, if it is determined in S707 that the exhaust air-fuel ratio has changed to the rich side in response to the addition of the reducing agent, the CPU 351 regards the NOx storage reduction catalyst 20 as active. Routine execution is temporarily terminated.
[0116]
According to such a catalyst activity determination control routine, the active / inactive state of the NOx storage reduction catalyst 20 is determined every time the rich spike control is executed. Therefore, the NOx storage reduction catalyst 20 is once activated. If the inactive state is established after this, unnecessary rich spike control is not executed.
[0117]
In the first and second embodiments described above, the air-fuel ratio sensor 23 has been described as an example of the exhaust state detection means according to the present invention. However, the present invention is not limited to this, and instead of the air-fuel ratio sensor 23. A NOx sensor may be used.
[0118]
【The invention's effect】
In the exhaust purification device for an internal combustion engine according to the present invention, when the exhaust purification catalyst, the reducing agent supply means, the exhaust state detection means, and the catalyst activation state determination means are provided, the reducing agent is supplied to the exhaust purification catalyst. Sometimes it is possible to determine whether or not the exhaust purification catalyst is active based on the state of the exhaust gas flowing out from the exhaust purification catalyst, and it is not necessary to provide a dedicated temperature sensor for the exhaust purification catalyst.
[0119]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the temperature of the exhaust gas purification catalyst is estimated from the operating state of the internal combustion engine in addition to the exhaust gas purification catalyst, the reducing agent supply means, the exhaust gas state detection means, and the catalyst activation state determination means. When the catalyst temperature estimating means is provided, the activity determination of the exhaust purification catalyst is performed on the condition that the estimated value by the catalyst temperature estimating means is equal to or higher than a predetermined temperature, so the exhaust purification catalyst is in an inactive state. Sometimes the reducing agent is not inadvertently supplied to the exhaust purification catalyst, and the occurrence of problems such as deterioration of exhaust emission and overheating of the exhaust purification catalyst due to the supply of the reducing agent 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 aspect of the exhaust air-fuel ratio when the NOx storage reduction catalyst is in an inactive state.
FIG. 5 is a diagram showing an aspect of the exhaust air / fuel ratio when the NOx storage reduction catalyst is in an active state.
FIG. 6 is a flowchart showing a catalyst activity determination control routine according to the first embodiment.
FIG. 7 is a flowchart showing a catalyst activity determination control routine according to the second embodiment.
[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)

An exhaust purification catalyst provided in an exhaust passage of the internal combustion engine for reducing and purifying a predetermined component contained in the exhaust;
Reducing agent supply means for supplying a reducing agent to the exhaust purification catalyst;
An exhaust condition detecting means for detect the air-fuel ratio of the exhaust gas flowing out from the exhaust purification catalyst,
Wherein the reducing agent when the supply means the air-fuel ratio of the exhaust gas detected by the exhaust state detecting means when supplying reducing agent to the exhaust gas purifying catalyst changes, the touch exhaust purification catalyst is determined to be active medium activity State determination means;
An exhaust emission control device for an internal combustion engine, comprising: A catalyst temperature estimating means for estimating the temperature of the exhaust purification catalyst from the operating state of the internal combustion engine;
The catalyst activity determination means causes the reducing agent supply means to supply the reducing agent to the exhaust purification catalyst when the estimated value by the catalyst temperature estimation means is equal to or higher than a predetermined temperature, and at that time, the exhaust state detection means detects 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein it is determined whether or not the exhaust gas purification catalyst is active based on the state of the exhaust gas.
[0001]

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