JP3798623B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology for purifying exhaust gas from an internal combustion engine, and more particularly to a technology for purifying harmful gas components in exhaust gas by supplying a reducing agent to an exhaust gas purification catalyst.
[0002]
[Prior art]
In recent years, lean NOx catalysts such as a selective reduction type NOx catalyst and an occlusion reduction type NOx catalyst have been known as one means for reducing nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine capable of lean combustion. .
[0003]
The selective reduction type NOx catalyst is a catalyst that reduces or decomposes nitrogen oxides (NOx) when a reducing agent such as hydrocarbon (HC) is present in an oxygen-excess atmosphere. Examples include a catalyst formed by supporting a transition metal such as Cu by ion exchange, a catalyst formed by supporting a noble metal on a support made of zeolite or alumina, and the like.
[0004]
In order to purify nitrogen oxide (NOx) using this selective reduction type NOx catalyst, an appropriate amount of HC component (reducing agent) is required. However, when the internal combustion engine is in a lean burn operation, the HC in the exhaust gas is exhausted. Since the amount of the component becomes extremely small, it is necessary to separately supply an HC component to the selective reduction type NOx catalyst in order to purify NOx in the exhaust during the lean combustion operation.
[0005]
On the other hand, the NOx storage reduction catalyst absorbs nitrogen oxides (NOx) in the exhaust when the inflowing exhaust is in an oxygen excess state, the oxygen concentration in the inflowing exhaust is reduced, and a reducing agent such as hydrocarbon (HC) is added. When present, it is a catalyst that reduces nitrogen oxides (NOx) while absorbing them.
[0006]
When this NOx storage reduction catalyst is applied to a lean combustion internal combustion engine, the exhaust gas air-fuel ratio becomes lean during the lean combustion operation of the internal combustion engine, so that nitrogen oxides (NOx) in the exhaust are stored and reduced. It will be absorbed by the NOx catalyst. However, if the lean air-fuel ratio exhaust gas continues to be supplied to the NOx storage reduction catalyst over a long period of time, the NOx absorption capacity of the NOx storage reduction catalyst becomes saturated, and nitrogen oxides (NOx) are absorbed by the NOx storage reduction catalyst. Without leaking. Therefore, when purifying nitrogen oxide (NOx) using a NOx storage reduction catalyst, the oxygen concentration of the inflowing exhaust gas is reduced at a predetermined timing before the NOx absorption capacity of the NOx storage reduction catalyst is saturated. While increasing the amount of HC component in the exhaust gas, releasing nitrogen oxide (NOx) absorbed by the NOx storage reduction catalyst, nitrogen (N₂Therefore, it is necessary to restore the NOx absorption capacity of the NOx storage reduction catalyst.
[0007]
As described above, the lean NOx catalyst such as the selective reduction type NOx catalyst or the occlusion reduction type NOx catalyst can uniformly purify the nitrogen oxide (NOx) in the exhaust gas in the presence of the reducing agent. When purifying nitrogen oxides (NOx) in the exhaust gas using an exhaust gas, it is necessary to supply an appropriate amount of reducing agent to the lean NOx catalyst.
[0008]
In response to such a demand, conventionally, an “exhaust gas purification device for an internal combustion engine” as described in JP-A-11-93641 is known.
[0009]
In the “exhaust gas purification device for an internal combustion engine” described in Japanese Patent Application Laid-Open No. 11-93641, the exhaust pipe of the internal combustion engine is branched into a first exhaust pipe and a second exhaust pipe, and the first exhaust pipe has an occlusion reduction A first catalytic converter containing a type NOx catalyst is provided, and a second catalytic converter containing a selective reduction type NOx catalyst is provided in the second exhaust pipe. Further, a switching valve is installed at a branch portion between the first exhaust pipe and the second exhaust pipe.
[0010]
In the above-described exhaust gas purification apparatus for an internal combustion engine, when the exhaust gas is changing from a high temperature to a low temperature, the exhaust gas is caused to flow through the second exhaust passage by the switching valve, thereby selectively reducing nitrogen oxide (NOx) in the exhaust gas. Reduction with catalyst. Further, the exhaust gas purification apparatus for an internal combustion engine described above allows nitrogen oxide (NOx) in the exhaust gas to flow by flowing the exhaust gas through the first exhaust passage by the switching valve when the exhaust gas is not changing from high temperature to low temperature. The NOx storage reduction catalyst absorbs the nitrogen oxide (NOx) absorbed by the NOx storage reduction catalyst by appropriately supplying a reducing agent from the reducing agent addition means to the NOx storage reduction catalyst. . That is, the above-described exhaust gas purification apparatus for an internal combustion engine uses a selective reduction type NOx catalyst and an occlusion reduction type NOx catalyst in accordance with the respective characteristics, thereby improving the nitrogen oxide (NOx) purification rate. Is.
[0011]
[Problems to be solved by the invention]
By the way, in the conventional technique described in the above-mentioned JP-A-11-93641, it is also important to detect leakage of the reducing agent in the reducing agent supply mechanism.
[0012]
For example, if the reducing agent leaks from the reducing agent supply mechanism, it becomes difficult to supply a desired amount of the reducing agent to the lean NOx catalyst, leading to deterioration of exhaust emission and the possibility of unnecessary consumption of the reducing agent. There is.
[0013]
The present invention has been made in view of various circumstances as described above, and an internal combustion engine that purifies harmful gas components in exhaust gas by supplying a reducing agent to an exhaust gas purification catalyst provided in an exhaust passage of the internal combustion engine. An object of the present invention is to detect leakage of a reducing agent in a mechanism for supplying a reducing agent in an exhaust emission control device of an engine, thereby preventing unnecessary consumption of the reducing agent.
[0014]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems. That is, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is a lean combustion type internal combustion engine capable of combusting an air-fuel mixture in an oxygen excess state,
An exhaust purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies harmful gas components in the exhaust in the presence of a reducing agent;
Reducing agent discharge means for discharging the reducing agent at a predetermined pressure;
A reducing agent addition nozzle that is provided in an exhaust passage upstream from the exhaust purification catalyst and opens when a reducing agent having a predetermined valve opening pressure or higher is applied, and adds the reducing agent into the exhaust passage;
A reducing agent supply passage for guiding the reducing agent discharged from the reducing agent discharge means to the reducing agent addition nozzle;
A reducing agent metering valve which is provided in the middle of the reducing agent supply passage and adjusts the amount of reducing agent supplied from the reducing agent discharge means to the reducing agent addition nozzle;
A shutoff valve that is provided upstream of the reducing agent metering valve in the reducing agent supply passage and shuts off the reducing agent supply passage;
A reducing agent pressure detecting means provided between the shutoff valve and the reducing agent metering valve in the reducing agent supply passage for detecting the pressure of the reducing agent in the reducing agent supply passage;
Whether the reducing agent has leaked based on the pressure of the reducing agent detected by the reducing agent pressure detecting means when the shut-off valve is open or closed and the reducing agent metering valve is in the closed state Leakage determination means for determining whether or not,
It is characterized by providing.
[0015]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the reducing agent needs to be supplied to the exhaust gas purification catalyst, the reducing agent metering valve is opened under the condition that the shutoff valve is opened, and the reduction is performed. The reducing agent discharged from the agent discharging means is applied to the reducing agent addition nozzle. When the reducing agent pressure applied to the reducing agent addition nozzle reaches or exceeds the opening pressure of the reducing agent addition nozzle, the reducing agent addition nozzle opens and the reducing agent is added to the exhaust passage upstream of the exhaust purification catalyst. Is done.
[0016]
The reducing agent supplied to the exhaust passage flows into the exhaust purification catalyst together with the exhaust flowing from the upstream of the exhaust passage. In this case, the exhaust purification catalyst uses a reducing agent to reduce and purify harmful gas components in the exhaust.
[0017]
On the other hand, the leakage occurrence determining means detects that the reducing agent leaks based on the reducing agent pressure detected by the reducing agent pressure detecting means when the shut-off valve is opened and the reducing agent metering valve is opened. It is determined whether or not.
[0018]
At that time, if leakage of the reducing agent has occurred, the pressure detected by the reducing agent pressure detecting means is lower than the pressure when no leakage of the reducing agent has occurred.
[0019]
For example, if the shutoff valve is closed and the reducing agent metering valve is closed when the reducing agent discharge means is in an operating state or immediately before the reducing agent discharge means stops operating, it is detected by the reducing agent pressure detection means. The pressure that should be approximately approximate to the discharge pressure of the reducing agent discharge means should be approximately the same as the discharge pressure of the reducing agent discharge means. The pressure is lower than the discharge pressure.
[0020]
Therefore, the leakage determination means can determine the leakage abnormality of the reducing agent supply mechanism based on the pressure detected by the reducing agent pressure detection means.
[0021]
Examples of the timing at which the leakage determining unit determines whether or not the reducing agent has leaked include when the reducing agent discharging unit is in an operating state or immediately after the reducing agent discharging unit stops operating. However, when the discharge capacity of the reducing agent discharge means is high, the amount of reducing agent discharged from the reducing agent discharge means is very large compared to the amount of reducing agent leaking per unit time, and leakage of the reducing agent is detected. Therefore, it is preferable that the reducing agent leakage determination be performed immediately after the operation of the reducing agent discharge unit is stopped.
[0022]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the leakage determining means closes the shutoff valve while holding the reducing agent metering valve in a closed state when it is determined that leakage of the reducing agent has occurred. The leakage site of the reducing agent may be specified based on the reducing agent pressure detected by the reducing agent pressure detecting means after the shut-off valve is closed.
[0023]
In this case, since the inside of the reducing agent supply passage from the shutoff valve to the reducing agent metering valve becomes a closed space, if there is no leakage of the reducing agent from the closed space, the reducing agent in the closed space closes the shutoff valve. It will be stored while maintaining the pressure when it was valved.
[0024]
On the other hand, when the reducing agent leaks from the closed space, the reducing agent in the closed space leaks out of the closed space, so the pressure of the reducing agent in the closed space decreases. become.
[0025]
Accordingly, if the reducing agent pressure in the closed space is maintained at a predetermined pressure after the shut-off valve is closed, the reducing agent leaks in the reducing agent supply passage from the shut-off valve to the reducing agent metering valve. If the reducing agent leaks upstream from the shut-off valve, and the pressure of the reducing agent in the closed space is lower than the predetermined pressure after the shut-off valve is closed, the reducing agent is reduced from the shut-off valve. Leakage of the reducing agent has occurred in the reducing agent supply passage leading to the agent metering valve.
[0026]
As a result, when the leakage determination means determines that leakage of the reducing agent has occurred under the condition that the shutoff valve is open and the reducing agent metering valve is closed, In addition, the shut-off valve is also closed, and thereafter, the reducing agent leakage occurrence site can be determined based on the reducing agent pressure detected by the reducing agent pressure detecting means.
[0027]
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the abnormality determining means may hold the shutoff valve closed after determining that leakage of the reducing agent has occurred.
[0028]
This is because when reducing agent leakage occurs, it becomes difficult to add a desired amount of reducing agent into the exhaust, or when reducing agent leakage occurs downstream from the shutoff valve. For example, unnecessary consumption of the reducing agent is suppressed.
[0029]
In the present invention, the lean burn internal combustion engine can be exemplified by an in-cylinder direct injection type lean burn gasoline engine or a diesel engine.
[0030]
In the present invention, as the lean NOx catalyst, an NOx storage reduction catalyst or a selective reduction NOx catalyst can be exemplified.
[0031]
In the present invention, as the reducing agent, those containing hydrocarbon (HC) such as light oil and gasoline are suitable.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
<First Embodiment>
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.
[0033]
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.
[0034]
An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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.
[0039]
On the other hand, since the amount of fuel injected into the cylinder 2 is smaller than the amount of fuel discharged from the fuel pump 6, the fuel pressure rises because the fuel is supplied excessively into the fuel supply pipe. When the fuel in the fuel supply pipe 5 reaches a predetermined pressure or higher, a relief valve (not shown) that opens at a predetermined pressure or higher opens, and the fuel is discharged upstream of the fuel pump 6 via a return pipe (not shown). The In this way, the fuel pressure is prevented from rising above a predetermined pressure.
[0040]
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).
[0041]
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 corresponds to 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.
[0042]
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.
[0043]
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.
[0044]
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.
[0045]
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.
[0046]
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).
[0047]
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).
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
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.
[0052]
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.
[0053]
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.
[0054]
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.
[0055]
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.
[0056]
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.
[0057]
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.
[0058]
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.
[0059]
Next, the exhaust purification catalyst 20 according to the present embodiment will be specifically described.
[0060]
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.
[0061]
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.
[0062]
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.
[0063]
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).
[0064]
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.
[0065]
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).
[0066]
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_Three ^-) Is absorbed by the NOx storage reduction catalyst 20.
[0067]
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.
[0068]
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.
[0069]
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).
[0070]
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.
[0071]
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 Will be absorbed by the NOx storage reduction catalyst 20, but 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 will be saturated, and the nitrogen oxidation in the exhaust will occur. Things (NOx) are not removed by the NOx storage reduction catalyst 20 but are released into the atmosphere.
[0072]
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.
[0073]
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.
[0074]
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 that flows 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.
[0075]
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 of the flow rate 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.
[0076]
The reducing agent injection valve 28 described above corresponds to the reducing agent addition nozzle according to the present invention, the reducing agent supply passage 29 corresponds to the reducing agent supply passage according to the present invention, and the flow rate adjusting valve 30 corresponds to the reducing agent adjustment according to the present invention. It corresponds to a quantity valve, and the reducing agent pressure sensor 32 corresponds to a reducing agent pressure detecting means according to the present invention.
[0077]
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.
[0078]
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.
[0079]
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.
[0080]
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.
[0081]
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.
[0082]
The reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 flows into the turbine housing 15 b together with the exhaust gas flowing from the upstream side of the exhaust branch pipe 18. The exhaust gas flowing into the turbine housing 15b and the reducing agent are agitated and uniformly mixed by the rotation of the turbine wheel to form a rich air-fuel ratio exhaust gas.
[0083]
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).
[0084]
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.
[0085]
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.
[0086]
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.
[0087]
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.
[0088]
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.
[0089]
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.
[0090]
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.
[0091]
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.
[0092]
The ROM 352 includes a fuel injection control routine for controlling the fuel injection valve 3, an intake throttle control routine for controlling the intake throttle valve 13, an exhaust throttle control routine for controlling the exhaust throttle valve 21, and an EGR valve 26. EGR control routine for controlling, NOx purification control routine for purifying nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst 20, and elimination of poisoning of the NOx storage reduction catalyst 20 due to oxides Application programs such as a poisoning elimination control routine and a leakage abnormality determination control routine for determining a leakage abnormality of the reducing agent are stored.
[0093]
The ROM 352 stores various control maps in addition to the application programs described above. The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection amount (basic fuel injection time), and the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection timing. The fuel injection timing control map shown, the intake throttle valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the intake throttle valve 13, the operating state of the internal combustion engine 1 and the target opening of the exhaust throttle valve 21 Exhaust throttle valve opening control map showing the relationship between the EGR valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the EGR valve 26, the operating state of the internal combustion engine 1 and the reducing agent target A reducing agent addition amount control map showing the relationship with the addition amount (or the target air-fuel ratio of the exhaust), a flow rate adjustment valve control map showing the relationship between the target addition amount of the reducing agent and the valve opening time of the flow rate adjustment valve 30, etc. is there.
[0094]
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.
[0095]
The backup RAM 354 is a nonvolatile memory capable of storing data even after the internal combustion engine 1 is stopped.
[0096]
The CPU 351 operates according to the application program stored in the ROM 352, and in addition to the fuel injection valve control, the intake throttle control, the exhaust throttle control, the EGR control, the NOx purification control, the poison elimination control, etc. The leakage abnormality determination control is executed.
[0097]
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.
[0098]
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.
[0099]
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.
[0100]
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 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.
[0101]
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.
[0102]
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.
[0103]
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.
[0104]
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.
[0105]
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.
[0106]
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.
[0107]
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.
[0108]
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.
[0109]
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. .
[0110]
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
[0111]
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.
[0112]
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.
[0113]
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 changed to a rich air-fuel ratio in a spike manner (short time) in a relatively short cycle. .
[0114]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. As the rich spike control execution condition, for example, poisoning elimination control in which the NOx storage reduction catalyst 20 is in an active state and the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value is executed. The conditions such as not being performed can be exemplified.
[0115]
When it is determined that the rich spike control execution condition as described above is established, 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.
[0116]
Specifically, the CPU 351 displays 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, etc. 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.
[0117]
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).
[0118]
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.
[0119]
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.
[0120]
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. .
[0121]
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, and thus the storage The reduced NOx catalyst 20 repeats absorption and release / reduction of nitrogen oxides (NOx) alternately in a short cycle.
[0122]
Next, the leakage abnormality determination control in the present embodiment will be described.
[0123]
In the leakage abnormality determination control, the CPU 351 sets the reducing agent pressure sensor 32 on the condition that the fuel pump 6 is in an operating state, the flow rate adjustment valve 30 is in a closed state, and the shutoff valve 31 is in an open state. An output signal value is input, and it is determined whether or not leakage of reducing agent (fuel) has occurred in the reducing agent supply mechanism based on the input reducing agent pressure.
[0124]
Here, if no fuel leakage occurs in the reducing agent supply mechanism, the fuel pump 6 is in an operating state, the flow rate adjusting valve 30 is in a closed state, and the shutoff valve 31 is in an open state. The pressure of the fuel in the reducing agent supply passage 29 upstream from the flow rate adjusting valve 30 substantially matches the discharge pressure of the fuel pump 6 (hereinafter referred to as “feed pressure”).
[0125]
On the other hand, when fuel leakage occurs in the reducing agent supply mechanism, the fuel pump 6 is in an operating state, the flow rate adjusting valve 30 is in a closed state, and the shutoff valve 31 is in an open state. The fuel pressure in the reducing agent supply passage 29 upstream from the flow rate adjustment valve 30 is lower than the feed pressure described above.
[0126]
Therefore, in the leakage abnormality determination control according to the present embodiment, the CPU 351 requires that the fuel pump 6 is in an operating state, the flow rate adjustment valve 30 is in a closed state, and the shutoff valve 31 is in an open state. Then, the output signal value (fuel pressure) of the reducing agent pressure sensor 32 is input to the fuel, and the input fuel pressure and the feed pressure of the fuel pump 6 are compared to determine whether or not fuel leakage has occurred. It becomes possible.
[0127]
When the fuel leakage in the reducing agent supply mechanism is determined in this way, the CPU 351 closes the shutoff valve 31 while holding the flow rate adjustment valve 30 in the closed state. Subsequently, the CPU 351 monitors the output signal value of the reducing agent pressure sensor 32 from the time when the shutoff valve 31 is closed.
[0128]
Here, when the flow rate adjusting valve 30 and the shutoff valve 31 are in the closed state, the reducing agent supply passage 29 from the shutoff valve 31 to the flow rate regulating valve 30 becomes a closed space. If no fuel leakage occurs in the reducing agent supply path 29 leading to the valve 30, the output signal value of the reducing agent pressure sensor 32 from the time when the shutoff valve 31 is closed maintains a substantially constant value.
[0129]
On the other hand, when fuel leakage occurs at a site downstream of the shutoff valve 31 in the reducing agent supply mechanism, the reducing agent supply path 29 from the shutoff valve 31 to the flow rate adjustment valve 30 does not become a closed space. The output signal value of the reducing agent pressure sensor 32 from the time when the valve 31 is closed decreases with time.
[0130]
Therefore, when the output signal value of the reducing agent pressure sensor 32 from the time when the shutoff valve 31 is closed maintains a substantially constant value, the CPU 351 causes fuel to flow to a site downstream of the shutoff valve 31 in the reducing agent supply mechanism. No leakage has occurred, and it can be considered that fuel has leaked in a region upstream of the shut-off valve 31, and the output of the reducing agent pressure sensor 32 from the time when the shut-off valve 31 is closed. When the signal value decreases with the passage of time, it can be considered that fuel leakage has occurred in a portion downstream of the shutoff valve 31 in the reducing agent supply mechanism.
[0131]
After determining that the leakage of fuel has occurred in the reducing agent supply mechanism by executing the leakage abnormality determination control as described above, the CPU 351 holds the shut-off valve 31 in the closed state and executes rich spike control. Is preferably prohibited.
[0132]
Further, when the CPU 351 determines that a fuel leak has occurred, it turns on a warning light (not shown) provided in the passenger compartment to notify the vehicle driver of the leak abnormality. May be.
[0133]
According to the embodiment described above, the leakage determination means according to the present invention is realized by the CPU 351 executing the leakage abnormality determination control. As a result, according to the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the reduction is performed using the reducing agent pressure sensor 32 disposed between the shutoff valve 31 and the flow rate adjustment valve 30 in the reducing agent supply path 29. It becomes possible to detect the fuel leakage of the agent supply mechanism and to specify the occurrence location of the fuel leakage to some extent. Furthermore, according to the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, when the fuel leakage of the reducing agent supply mechanism is detected, the shutoff valve 31 is closed to prohibit the execution of the rich spike control. It is also possible to suppress unnecessary addition or leakage of fuel.
[0134]
<Second Embodiment>
Next, a second embodiment of the exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described. Here, a configuration different from that of the first embodiment will be described, and description of the same configuration will be omitted.
[0135]
In the above-described first embodiment, the example in which the reducing agent leakage abnormality determination control is executed while the fuel pump 6 is operating, in other words, during the operation of the internal combustion engine 1 has been described. An example in which the reducing agent leakage abnormality determination control is executed immediately after the operation of 6 is stopped, in other words, immediately after the operation of the internal combustion engine 1 is stopped will be described.
[0136]
In the reducing agent supply mechanism, when the fuel is not injected from the reducing agent injection valve 28, the flow rate adjusting valve 30 is closed, and the reducing agent supply path 29 upstream of the flow rate adjusting valve 30 has the fuel pump 6 in the reducing agent supply path 29. Feed pressure is applied.
[0137]
When the fuel pump 6 is in an operating state and the feed pressure of the fuel pump 6 is relatively high, even if a small amount of fuel leakage occurs in the reducing agent supply mechanism, leakage occurs from the reducing agent supply mechanism per unit time. Since the amount of fuel to be discharged is much smaller than the amount of fuel discharged from the fuel pump 6 per unit time, a small amount of fuel leakage is detected during operation of the fuel pump 6, in other words, during operation of the internal combustion engine 1. It is assumed that it will be difficult.
[0138]
Therefore, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the reducing agent leakage abnormality determination control is performed immediately after the operation of the fuel pump 6 is stopped, and it is accurate regardless of the feed pressure of the fuel pump 6. It was made possible to make a proper leakage abnormality determination.
[0139]
More specifically, when there is no fuel leakage in the reducing agent supply mechanism, the flow rate adjustment valve 30 is closed immediately before the fuel pump 6 stops operating, and the shutoff valve 31 is closed. The pressure of the fuel in the reducing agent supply passage 29 upstream from the valve 30 substantially matches the feed pressure immediately before the fuel pump 6 stops operating. On the other hand, if fuel leaks from the fuel pump 6 to the flow rate adjusting valve 30, the fuel pressure in the reducing agent supply path 29 becomes lower than the feed pressure.
[0140]
Therefore, the fuel in the reducing agent supply passage 29 detected by the reducing agent pressure sensor 32 when the adjustment valve 30 is closed and the shutoff valve 31 is closed immediately after the operation of the fuel pump 6 is stopped. The presence or absence of fuel leakage from the fuel pump 6 to the flow rate adjustment valve 30 can be determined based on the pressure of
[0141]
If fuel leakage has occurred, there is a risk of further fuel leakage if left as it is. Therefore, if it is determined that a fuel leak has occurred, considering the possibility of fuel leaking downstream from the shut-off valve 31, the shut-off valve 31 is closed to prevent subsequent fuel leaks. While preventing, it is discriminate | determined whether the leak generation | occurrence | production location is an upstream or the downstream from the cutoff valve 31. FIG. The method for determining the leakage location is the same as in the first embodiment described above.
[0142]
As described above, according to the present embodiment, since the reducing agent leakage abnormality determination control is executed immediately after the fuel pump 6 stops operating, the leakage abnormality determination is performed without being affected by the feed pressure from the fuel pump 6. It is possible to accurately detect even a small amount of fuel leakage.
[0143]
【The invention's effect】
According to the present invention, in the exhaust gas purification apparatus for an internal combustion engine that purifies harmful gas components in the exhaust gas by supplying the reducing agent to the exhaust gas purification catalyst provided in the exhaust passage of the internal combustion engine, from the mechanism for supplying the reducing agent. It becomes possible to detect leakage of the reducing agent.
[0144]
As a result, it is possible to contribute to the prevention of the waste of the reducing agent.
[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. 2A is a diagram for explaining a NOx absorption mechanism of a NOx storage reduction catalyst. (B) is a diagram for explaining the NOx release mechanism of the NOx storage reduction catalyst.
FIG. 3 is a block diagram showing the internal configuration of the ECU
[Explanation of symbols]
1 ... Internal combustion engine
2. Cylinder
3. Fuel injection valve
4 ... Common rail
5. Fuel supply pipe
6. Fuel pump
18 ... Exhaust branch pipe
19 ... Exhaust pipe
20 ... NOx storage reduction catalyst
21 ... Exhaust throttle valve
23 ... Air-fuel ratio sensor
25 ... EGR passage
26 ... EGR valve
27 ... EGR cooler
28 ... Reducing agent injection valve
29 ... Reducing agent supply path
30 ... Flow control valve
31 ... Shut-off valve
32 ... Reducing agent pressure sensor
33 ... Crank position sensor
34 ... Water temperature sensor
35 ... ECU
351 ... CPU
352 ... ROM
353 ... RAM
354 ... Backup RAM

Claims (2)

A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture
An exhaust purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies harmful gas components in the exhaust in the presence of a reducing agent;
Reducing agent discharge means for discharging the reducing agent at a predetermined pressure;
A reducing agent addition nozzle that is provided in an exhaust passage upstream from the exhaust purification catalyst and opens when a reducing agent having a predetermined valve opening pressure or higher is applied, and adds the reducing agent into the exhaust passage;
A reducing agent supply passage for guiding the reducing agent discharged from the reducing agent discharge means to the reducing agent addition nozzle;
A reducing agent metering valve which is provided in the middle of the reducing agent supply passage and adjusts the amount of reducing agent supplied from the reducing agent discharge means to the reducing agent addition nozzle;
A shutoff valve that is provided upstream of the reducing agent metering valve in the reducing agent supply passage and shuts off the reducing agent supply passage;
A reducing agent pressure detecting means provided between the shutoff valve and the reducing agent metering valve in the reducing agent supply passage for detecting the pressure of the reducing agent in the reducing agent supply passage;
Whether the reducing agent has leaked based on the pressure of the reducing agent detected by the reducing agent pressure detecting means when the shut-off valve is in the open state and the reducing agent metering valve is in the closed state. Leakage determining means for determining;
Equipped with a,
The leakage determining means closes the shut-off valve when the leakage of the reducing agent is determined, and based on the pressure of the reducing agent detected by the reducing agent pressure detecting means after the shut-off valve is closed. exhaust purification system of an internal combustion engine, characterized that you identify the leakage site.   A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture.
  An exhaust purification catalyst that is provided in an exhaust passage of the internal combustion engine and purifies harmful gas components in the exhaust in the presence of a reducing agent;
  Reducing agent discharge means for discharging the reducing agent at a predetermined pressure;
  A reducing agent addition nozzle that is provided in an exhaust passage upstream from the exhaust purification catalyst and opens when a reducing agent having a predetermined valve opening pressure or higher is applied, and adds the reducing agent into the exhaust passage;
  A reducing agent supply passage for guiding the reducing agent discharged from the reducing agent discharge means to the reducing agent addition nozzle;
  A reducing agent metering valve which is provided in the middle of the reducing agent supply passage and adjusts the amount of reducing agent supplied from the reducing agent discharge means to the reducing agent addition nozzle;
  A shutoff valve that is provided upstream of the reducing agent metering valve in the reducing agent supply passage and shuts off the reducing agent supply passage;
  A reducing agent pressure detecting means provided between the shutoff valve and the reducing agent metering valve in the reducing agent supply passage for detecting the pressure of the reducing agent in the reducing agent supply passage;
  Whether the reducing agent has leaked based on the pressure of the reducing agent detected by the reducing agent pressure detecting means when the shut-off valve is in the open state and the reducing agent metering valve is in the closed state. Leakage determining means for determining;
With
  The leakage determining means closes the shut-off valve and closes the reducing agent metering valve immediately before the operation of the reducing agent discharge means stops, and performs leakage determination of the reducing agent. An exhaust purification device for an internal combustion engine.

Images