JP3800065B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[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 capable of combusting an oxygen-rich mixture (so-called lean air-fuel mixture) is used in the exhaust system of the internal combustion engine. Techniques for arranging NOx catalysts have been proposed. As one of the NOx catalysts, nitrogen oxide (NOx) in the exhaust gas is occluded when the oxygen concentration of the inflowing exhaust gas is high, and occluded when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. An NOx storage reduction catalyst that reduces nitrogen oxide (NOx) to nitrogen (N ₂ ) while releasing the nitrogen oxide is known.
[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 occluded and flows into the occlusion reduction type NOx catalyst becomes low, the nitrogen oxide (NOx) occluded in the occlusion reduction type NOx catalyst is released and reduced to nitrogen (N ₂ ). .
[0004]
By the way, in the NOx storage reduction catalyst, sulfur oxide (SOx) generated by combustion of sulfur contained in the fuel is also stored by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning (SOx poisoning), and the NOx purification rate decreases. Therefore, it is necessary to perform poisoning recovery processing for recovering from SOx poisoning at an appropriate time. This poisoning recovery process is performed by circulating exhaust gas having a reduced oxygen concentration while the NOx catalyst is at a high temperature (for example, about 600 to 650 ° C.) to the NOx catalyst.
[0005]
However, since the temperature of the exhaust gas during the lean combustion operation is low, it is difficult to raise the temperature of the catalyst to the temperature required for recovery from SOx poisoning. In such a case, by supplying a reducing agent (fuel) into the exhaust, it is possible to reduce the oxygen concentration of the exhaust while increasing the temperature of the catalyst.
[0006]
For example, in the exhaust gas purification apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. 11-343836, when it is necessary to recover the poisoning of the NOx storage reduction catalyst, the exhaust gas flowing into the NOx storage reduction catalyst is required. While maintaining the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio, the air-fuel ratio is intermittently made smaller than the stoichiometric air-fuel ratio. As a result, most of the time during the recovery from poisoning is maintained at an air-fuel ratio in the vicinity of the theoretical air-fuel ratio, so that generation of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust can be suppressed. Become. Further, by intermittently making the air-fuel ratio smaller than the stoichiometric air-fuel ratio, the average air-fuel ratio during poisoning recovery becomes richer than the stoichiometric air-fuel ratio. For this reason, it is possible to recover the sulfur poisoning of the NOx storage reduction catalyst in a relatively short time. According to the publication, the poisoning recovery control is executed when the temperature of the NOx storage reduction catalyst is, for example, 300 ° C. or more and the stored sulfur oxide is a predetermined amount or more.
[0007]
[Problems to be solved by the invention]
By the way, as described above, the sulfur poisoning recovery is performed by lowering the air-fuel ratio in the exhaust gas. However, if the air-fuel ratio is lowered while the internal combustion engine is operating at a high load, the temperature of the NOx storage reduction catalyst is reduced. May rise excessively and induce thermal degradation of the NOx storage reduction catalyst.
[0008]
Here, in the above publication, if the temperature of the NOx storage reduction catalyst and the storage amount of the sulfur oxide satisfy the start conditions for the poisoning recovery control, the temperature increase control of the NOx storage reduction catalyst is performed. However, if the operation in the light load region is not performed thereafter, the catalyst is maintained in a high temperature state for a long period of time, which leads to deterioration of fuel consumption.
[0009]
In addition, although sulfur poisoning recovery is usually performed in the light load region, if the temperature increase control is started after shifting to the light load region, it takes time to raise the temperature of the NOx storage reduction catalyst to the required temperature. In the meantime, if the operating state of the internal combustion engine shifts to a high load region, the opportunity for recovery from sulfur poisoning is lost.
[0010]
The present invention has been made to solve the above problems, and the problem to be solved by the present invention is required for recovery of sulfur poisoning while suppressing deterioration of fuel consumption in an exhaust gas purification apparatus for an internal combustion engine. An object of the present invention is to provide a technique capable of increasing the temperature of the NOx catalyst to a temperature at which sulfur poisoning can be recovered at an early stage when the conditions are satisfied.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine of the present invention is
A NOx catalyst that stores NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich;
A temperature raising means for performing temperature rise control of the NOx catalyst when it is necessary to remove the sulfur oxide stored in the NOx catalyst;
An operating state detecting means for detecting an operating state of the internal combustion engine;
With
Said heating means, when the internal combustion engine is in a low load state to a temperature required target temperature of the NO x catalyst for the removal of sulfur oxides, when the internal combustion engine is in an intermediate load state of the NO x catalyst closer to low load the target temperature is increased, or, characterized in that it does not perform the temperature increase of N Ox catalyst when the internal combustion engine is in the operating state which is not suitable to perform the heating of a to the NOx catalyst in a high load state.
[0012]
The most important feature of the present invention is that, in an exhaust purification system for an internal combustion engine, when it is necessary to remove sulfur oxide from the NOx catalyst, a target temperature of the NOx catalyst is determined according to the operating state of the internal combustion engine, and the NOx catalyst On the other hand, when the sulfur poisoning recovery cannot be performed in the high load range, the NOx catalyst is not heated so that the deterioration of fuel consumption is suppressed and the sulfur poisoning recovery can be performed. It is to make it possible to raise the temperature of the NOx catalyst to a temperature necessary for recovery of sulfur poisoning at an early stage when the state is reached.
[0013]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, the temperature of the NOx catalyst is not increased when the operation state of the internal combustion engine cannot recover sulfur poisoning, for example, in a high load operation region. . In a high-load operation state, if the sulfur poisoning is recovered, the temperature of the NOx catalyst excessively increases, and there is a risk of inducing thermal deterioration of the NOx catalyst. Therefore, in a high load region, even if the temperature of the NOx catalyst is raised, it may not be possible to recover sulfur poisoning thereafter. Further, in the high load region, the temperature of the NOx catalyst rises to some extent due to the heat of the exhaust. Therefore, it is possible to raise the temperature of the NOx catalyst in a short period of time to a temperature required for sulfur poisoning recovery. Furthermore, the high-load region continues often when, for example, the vehicle is traveling on a highway. In such a case, it is necessary to recover sulfur poisoning even if the temperature of the NOx catalyst is increased. It may take a considerable amount of time to shift to the operating state. For this reason, in the present invention, the temperature of the NOx catalyst is not increased in the high load operation region. Thereby, consumption of fuel is suppressed and it becomes possible to suppress deterioration of fuel consumption.
[0014]
On the other hand, for example, in an intermediate load region, there is a high possibility of shifting to an operating state in which sulfur poisoning recovery can be performed. Further, since the temperature of the NOx catalyst is not sufficiently raised at the exhaust temperature at this time, the temperature of the NOx catalyst needs to be raised when the sulfur poisoning is recovered. Here, the closer to the low load region, the higher the temperature of the NOx catalyst cannot be expected, and the closer to the low load region, the higher the possibility of shifting to an operating state in which sulfur poisoning recovery can be performed. Therefore, it is necessary to increase the temperature of the NOx catalyst. Therefore, in the medium load region, if the set temperature of the NOx catalyst is determined so that the NOx catalyst becomes higher as it approaches the low load region, the operation region can be recovered from sulfur poisoning. It is possible to raise the temperature of the NOx catalyst to a temperature necessary for recovery from sulfur poisoning in a short period of time, and to reduce the amount of fuel consumed until recovery from sulfur poisoning is performed.
[0015]
Further, for example, in a low load region, the sulfur poisoning can be immediately recovered if the temperature of the NOx catalyst is a temperature suitable for the sulfur poisoning recovery. Therefore, it is possible to immediately recover the sulfur poisoning by raising the temperature of the NOx catalyst to a temperature required for the sulfur poisoning recovery.
[0016]
In this way, by changing the target temperature of the NOx catalyst based on the operating region of the internal combustion engine, the NOx catalyst can be brought to the required temperature at an early stage when the sulfur poisoning recovery can be achieved while suppressing the deterioration of fuel consumption. It is possible to raise the temperature.
[0017]
In the present invention, when the temperature raising means is raising the temperature of the NOx catalyst and the operation state in which the sulfur oxide cannot be removed continues for a predetermined time or longer, the temperature raising means The temperature increase of the NOx catalyst can be stopped.
[0018]
If such an operating state continues and sulfur poisoning recovery is not performed, the NOx catalyst is maintained in a high temperature state, so that fuel consumption is deteriorated. Therefore, in such an operating state, it is possible to suppress the deterioration of fuel consumption by stopping the temperature increase of the NOx catalyst.
[0019]
In the present invention, the temperature raising means once raises the temperature of the NOx catalyst to a temperature required for recovery of sulfur poisoning when it becomes necessary to remove the sulfur oxide stored in the NOx catalyst. If the sulfur poisoning recovery is not performed for a predetermined period after that, when the internal combustion engine is in a low load state, the target temperature of the NO x catalyst is set to a temperature necessary for removing sulfur oxides, and the internal combustion engine when the state to increase the target temperature of the nO x catalyst closer to low load, or, N Ox catalyst when the internal combustion engine is in the operating state which is not suitable to perform the heating of a to the NOx catalyst in a high load state It is not possible to raise the temperature.
[0020]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when it becomes necessary to recover the sulfur poisoning of the NOx catalyst, the temperature of the NOx catalyst is raised to a temperature required for the sulfur poisoning recovery. Thereafter, when the operating state of the internal combustion engine shifts to the light load region, the sulfur poisoning is recovered. However, if the operation is continued without shifting to such an operating region, the temperature of the NOx catalyst is maintained. Fuel is consumed. Therefore, when recovery from sulfur poisoning is not performed for a predetermined period, it is possible to suppress deterioration in fuel consumption by performing temperature increase control of the NOx catalyst in accordance with the operation region.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
<First Embodiment>
FIG. 1 is a diagram showing a schematic configuration of an engine 1 and an intake / exhaust system to which the exhaust purification apparatus according to the present embodiment is applied.
[0022]
An engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0023]
The 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.
[0024]
The common rail 4 communicates with a fuel pump 6 through a fuel supply pipe 5. This fuel pump 6 is a pump that operates using the rotational torque of the output shaft (crankshaft) of the engine 1 as a drive source, and a pump pulley 6 a attached to the input shaft of the fuel pump 6 is connected to the output shaft (crankshaft) of the engine 1. ) And the belt pulley 7 are connected to each other.
[0025]
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.
[0026]
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.
[0027]
Next, an intake branch pipe 8 is connected to the 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).
[0028]
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 through the intake pipe 9 is attached to the intake pipe 9 downstream of the air cleaner box 10.
[0029]
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 step motor or the like and that drives the intake throttle valve 13 to open and close.
[0030]
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.
[0031]
In the intake system configured as described above, the intake air that has flowed into the air cleaner box 10 is removed through the intake pipe 9 after dust or dust in the intake air is removed by an air cleaner (not shown) in the air cleaner box 10. It flows into the compressor housing 15a.
[0032]
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.
[0033]
On the other hand, an exhaust branch pipe 18 is connected to the 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).
[0034]
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 the exhaust pipe 19 is connected to a muffler (not shown) downstream.
[0035]
In the middle of the exhaust pipe 19, a particulate filter (hereinafter simply referred to as a filter) 20 carrying a NOx catalyst is provided. An exhaust gas temperature sensor 24 that outputs an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20.
[0036]
In the present embodiment, NOx in the exhaust flowing in when the air-fuel ratio of the exhaust is lean is occluded, and when the air-fuel ratio of the inflowing exhaust becomes rich, the stored NOx is released and reduced. An example of a particulate filter carrying a NOx storage reduction catalyst will be described.
[0037]
Here, the lean air-fuel ratio means an area where the exhaust air-fuel ratio during normal operation is, for example, 20 to 50 in the case of a diesel engine, and NOx cannot be reduced by a three-way catalyst.
[0038]
The exhaust pipe 19 downstream of the filter 20 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 step motor or the like and that drives the exhaust throttle valve 21 to open and close.
[0039]
In the exhaust system configured as described above, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then centrifugally supercharged from the exhaust branch pipe 18. Flows into the turbine housing 15b of the machine 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.
[0040]
Exhaust gas discharged from the turbine housing 15b flows into the filter 20 via the exhaust pipe 19, and exhaust particulates (hereinafter referred to as PM) are collected and harmful gas components are removed or purified. The exhaust gas from which PM is collected by the filter 20 and from which harmful gas components are removed or purified is discharged to the atmosphere through the muffler after the flow rate is adjusted by the exhaust throttle valve 21 as necessary.
[0041]
Further, the exhaust branch pipe 18 and the intake branch pipe 8 have an exhaust recirculation passage (hereinafter referred to as an EGR passage) 25 that recirculates a part of the exhaust gas flowing through the exhaust branch pipe 18 to the intake branch pipe 8. It is communicated through. In the middle of the EGR passage 25, a flow rate adjusting valve is configured with an electromagnetic valve or the like, and changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) flowing through the EGR passage 25 in accordance with the magnitude of applied power. (Hereinafter referred to as an EGR valve) 26 is provided.
[0042]
An EGR cooler 27 that cools the EGR gas flowing in the EGR passage 25 is provided in the middle of the EGR passage 25 and upstream of the EGR valve 26. The EGR cooler 27 is provided with a cooling water passage (not shown), and a part of the cooling water for cooling the engine 1 circulates.
[0043]
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.
[0044]
At that time, in the EGR cooler 27, heat exchange is performed between the EGR gas flowing in the EGR passage 25 and the cooling water of the engine 1 to cool the EGR gas.
[0045]
The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 via 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.
[0046]
Here, the EGR gas contains an inert gas component that does not burn itself and has a high heat capacity, such as water (H ₂ O) and carbon dioxide (CO ₂ ). When the EGR gas is contained in the air-fuel mixture, the combustion temperature of the air-fuel mixture is lowered, and the amount of nitrogen oxide (NOx) generated is suppressed.
[0047]
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.
[0048]
Next, the filter 20 according to the present embodiment will be described.
[0049]
FIG. 2 is a cross-sectional view of the filter 20. FIG. 2A is a diagram illustrating a cross-section in the horizontal direction of the filter 20. FIG. 2B is a view showing a longitudinal section of the filter 20.
[0050]
As shown in FIGS. 2A and 2B, the filter 20 is a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. In FIG. 2A, hatched portions indicate plugs 53. Therefore, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by four exhaust inflow passages 50.
[0051]
The filter 20 is made of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust inflow passage 50 is adjacent to the surrounding partition wall 54 as shown by an arrow in FIG. To the exhaust outlet passage 51.
[0052]
In the embodiment according to the present invention, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of each exhaust inflow passage 50 and each exhaust outflow passage 51, that is, on both side surfaces of each partition wall 54 and on the pore inner wall surface in each partition wall 54. The NOx storage reduction catalyst is supported on the carrier.
[0053]
Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to the present embodiment will be described.
[0054]
The filter 20 uses, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), and barium (Ba) or calcium (Ca). ), An alkaline earth such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). In the present embodiment, occlusion configured by supporting barium (Ba) and platinum (Pt) on a support made of alumina and further adding ceria (Ce ₂ O ₃ ) having O ₂ storage capability. A reduced NOx catalyst was employed.
[0055]
The thus configured NOx catalyst occludes nitrogen oxide (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high.
[0056]
On the other hand, the NOx catalyst releases the stored nitrogen oxide (NOx) when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, the NOx catalyst converts nitrogen oxide (NOx) released from the NOx catalyst to nitrogen (N ₂ ) can be reduced.
[0057]
By the way, when the engine 1 is operated with lean combustion, the air-fuel ratio of the exhaust discharged from the engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high, so that nitrogen oxide (NOx) contained in the exhaust is NOx. When the lean combustion operation of the engine 1 is continued for a long period of time, the NOx storage capacity of the NOx catalyst is saturated, and nitrogen oxides (NOx) in the exhaust gas are removed by the NOx catalyst. Without being released into the atmosphere.
[0058]
In particular, in a diesel engine such as the 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 occlusion capacity is easily saturated.
[0059]
Therefore, when the engine 1 is in lean burn operation, before the NOx occlusion capacity of the NOx catalyst is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is lowered and the concentration of the reducing agent is increased and occluded in the NOx catalyst. The released nitrogen oxide (NOx) needs to be released and reduced.
[0060]
As a method for reducing the oxygen concentration in this way, methods such as fuel addition in exhaust, low-temperature combustion, and fuel injection during the expansion stroke into the cylinder 2 can be considered. In this embodiment, a filter is used. 20 is provided with a reducing agent supply mechanism for adding fuel (diesel oil) as a reducing agent to the exhaust gas flowing through the exhaust pipe 19 upstream from the exhaust gas 20, and flows into the filter 20 by adding fuel from the reducing agent supply mechanism into the exhaust gas. The exhaust gas oxygen concentration was lowered and the reducing agent concentration was increased.
[0061]
As shown in FIG. 1, the reducing agent supply mechanism is attached so that its injection hole faces the exhaust branch pipe 18, and is opened by a signal from the ECU 35 to inject fuel and a reducing agent injection valve 28. A reducing agent supply path 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and a shutoff that is provided in the reducing agent supply path 29 and blocks the flow of fuel in the reducing agent supply path 29. And a valve 31.
[0062]
In such a reducing agent supply mechanism, 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. Then, the reducing agent injection valve 28 is opened by a signal from the ECU 35 and fuel as a reducing agent is injected into the exhaust branch pipe 18.
[0063]
The reducing agent injected into the exhaust branch pipe 18 from the reducing agent injection valve 28 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust branch pipe 18.
[0064]
The exhaust gas having a low oxygen concentration thus formed flows into the filter 20 and is reduced to nitrogen (N ₂ ) while releasing nitrogen oxides (NOx) stored in the filter 20.
[0065]
Thereafter, the reducing agent injection valve 28 is closed by a signal from the ECU 35, and the addition of the reducing agent into the exhaust branch pipe 18 is stopped.
[0066]
In this embodiment, the fuel is added by injecting the fuel into the exhaust gas. Instead, the amount of soot is increased by increasing the amount of recirculated EGR gas and becomes the maximum. After that, low-temperature combustion for further increasing the EGR gas amount may be performed, or fuel may be injected from the fuel injection valve 3 during the expansion stroke or exhaust stroke of the engine 1.
[0067]
The engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the engine 1. The ECU 35 is a unit that controls the operating state of the engine 1 in accordance with the operating conditions of the engine 1 and the driver's request.
[0068]
Various sensors such as the common rail pressure sensor 4a, the air flow meter 11, the exhaust temperature sensor 24, the crank position sensor 33, the accelerator opening sensor 36, and the like are connected to the ECU 35 through electric wiring, and output signals from the various sensors described above are transmitted to the ECU 35. To be input.
[0069]
On the other hand, the ECU 35 is connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the reducing agent injection valve 28, the EGR valve 26, the shutoff valve 31 and the like via electrical wiring, The ECU 35 can be controlled.
[0070]
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.
[0071]
The input port 356 receives an output signal of a sensor that outputs a digital signal format signal like the crank position sensor 33 and transmits the output signal to the CPU 351 and the RAM 353.
[0072]
The input port 356 is input via an A / D 355 of a sensor that outputs an analog signal format signal such as the common rail pressure sensor 4a, the air flow meter 11, the exhaust gas temperature sensor 24, the accelerator opening sensor 36, and the like. Are output to the CPU 351 and the RAM 353.
[0073]
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 reducing agent injection valve 28, 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 reducing agent injection valve 28, or the shutoff valve 31.
[0074]
The ROM 352 controls 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. Trapped in the filter 20, a NOx purification control routine for releasing the stored NOx by adding a reducing agent to the filter 20, a poisoning recovery control routine for recovering SOx poisoning of the filter 20, An application program such as a PM combustion control routine for burning and removing PM is stored.
[0075]
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 indicating the relationship between the operating state of the engine 1 and the basic fuel injection amount (basic fuel injection time), and the fuel indicating the relationship between the operating state of the engine 1 and the basic fuel injection timing. The injection timing control map, the intake throttle valve opening control map showing the relationship between the operating state of the engine 1 and the target opening of the intake throttle valve 13, the relationship between the operating state of the engine 1 and the target opening of the exhaust throttle valve 21 Exhaust throttle valve opening control map, EGR valve opening control map showing the relationship between the operating state of the engine 1 and the target opening of the EGR valve 26, the operating state of the engine 1 and the target addition amount of reducing agent (or the exhaust gas A reducing agent addition amount control map showing the relationship with the target air-fuel ratio), a reducing agent injection valve control map showing the relationship between the target addition amount of the reducing agent and the opening time of the reducing agent injection valve 28, and the like.
[0076]
The RAM 353 stores output signals from the sensors, calculation results of the CPU 351, and the like. The calculation result is, for example, an engine speed calculated based on a 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.
[0077]
The backup RAM 354 is a non-volatile memory capable of storing data even after the engine 1 is stopped.
[0078]
The CPU 351 operates in accordance with an application program stored in the ROM 352, and executes fuel injection valve control, intake throttle control, exhaust throttle control, EGR control, NOx purification control, poisoning recovery control, PM combustion control, and the like.
[0079]
For example, in the NOx purification control, the CPU 351 executes so-called rich spike control in which the oxygen concentration in the exhaust gas flowing into the filter 20 is reduced in a spike manner (short time) in a relatively short cycle.
[0080]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. As this rich spike control execution condition, for example, the filter 20 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value, poisoning recovery control is not executed, Etc. can be exemplified.
[0081]
When it is determined that the rich spike control execution condition as described above is satisfied, the CPU 351 controls the reducing agent injection valve 28 to inject fuel as a reducing agent from the reducing agent injection valve 28 in a spike manner. As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to a predetermined target rich air-fuel ratio.
[0082]
Specifically, the CPU 351 stores the engine speed stored in the RAM 353, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), and the output of the air-fuel ratio sensor. Read signal, fuel injection amount, etc.
[0083]
The CPU 351 accesses the reducing agent addition amount control map in the ROM 352 using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the air-fuel ratio of the exhaust to a preset target air-fuel ratio. The amount of addition of the reducing agent (target addition amount) required above is calculated.
[0084]
Subsequently, the CPU 351 accesses the reducing agent injection valve control map of the ROM 352 using the target addition amount as a parameter, and the reducing agent injection valve 28 necessary for injecting the reducing agent with the target addition amount from the reducing agent injection valve 28. The valve opening time (target valve opening time) is calculated.
[0085]
When the target valve opening time of the reducing agent injection valve 28 is calculated, the CPU 351 opens the reducing agent injection valve 28.
[0086]
When the target valve opening time has elapsed from the time when the reducing agent injection valve 28 is opened, the CPU 351 closes the reducing agent injection valve 28.
[0087]
Thus, when the reducing agent injection valve 28 is opened for the target valve opening time, a 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 an air-fuel mixture having a target air-fuel ratio and flows into the filter 20.
[0088]
As a result, the oxygen concentration of the air-fuel ratio of the exhaust gas flowing into the filter 20 changes in a relatively short cycle, so that the filter 20 alternates between storing and releasing / reducing nitrogen oxide (NOx). Will be repeated in a short period.
[0089]
Next, in the poisoning recovery control, the CPU 351 performs a poisoning recovery process to recover the poisoning due to the oxide of the filter 20.
[0090]
Here, the fuel of the engine 1 may contain sulfur (S). When such fuel is burned in the engine 1, sulfur dioxide (SO ₂ ), sulfur trioxide (SO ₃ ), etc. Of sulfur oxide (SOx).
[0091]
Sulfur oxide (SOx) flows into the filter 20 together with the exhaust gas, and is stored in the filter 20 by the same mechanism as nitrogen oxide (NOx).
[0092]
Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 20 is high, sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) in the inflowing exhaust gas are platinum (Pt). Then, it is oxidized on the surface of the water and stored in the filter 20 in the form of sulfate ions (SO ₄ ²⁻ ). Further, the sulfate ions (SO ₄ ²⁻ ) occluded in the filter 20 are combined with barium oxide (BaO) to form sulfate (BaSO ₄ ).
[0093]
By the way, sulfate (BaSO ₄ ) is more stable and difficult to decompose than barium nitrate (Ba (NO ₃ ) ₂ ), and is not decomposed even if the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered. It remains in the filter 20.
[0094]
As the amount of sulfate (BaSO ₄ ) in the filter 20 increases, the amount of barium oxide (BaO) that can participate in the storage of nitrogen oxides (NOx) decreases accordingly. So-called SOx poisoning occurs.
[0095]
As a method for recovering SOx poisoning of the filter 20, the temperature of the atmosphere of the filter 20 is raised to a high temperature range of approximately 600 to 650 ° C., and the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered to reduce the filter 20. barium sulfate which is occluded (BaSO ₄₎ SO ₃ in ^- and SO ₄ ^- in pyrolyzing, then SO ₃ ^- and SO ₄ ^- hydrocarbons (HC) and carbon monoxide in the exhaust gas (CO) and reaction The method of reducing to gaseous SO ₂ ⁻ can be exemplified.
[0096]
Therefore, in the poisoning recovery process according to the present embodiment, the CPU 351 first performs the catalyst temperature increase control for increasing the bed temperature of the filter 20 and then reduces the oxygen concentration of the exhaust gas flowing into the filter 20. .
[0097]
In the catalyst temperature increase control, the CPU 351 injects fuel from the reducing agent injection valve 28 to oxidize the fuel in the filter 20 and increase the temperature increase of the filter 20 by heat generated at that time. At this time, the injection amount of the fuel injected from the reducing agent injection valve 28 is set so that the injection interval is shorter than the fuel injection performed at the time of NOx release / reduction and the air-fuel ratio at that time is higher.
[0098]
Further, in the catalyst temperature increase control, the CPU 351, for example, injects fuel from the fuel injection valve 3 at the time of the expansion stroke of each cylinder 2 and adds fuel from the reducing agent injection valve 28 into the exhaust. These unburned fuel components may be oxidized in the filter 20 and the bed temperature of the filter 20 may be increased by the heat generated during the oxidation.
[0099]
However, if the temperature of the filter 20 is excessively increased, thermal degradation of the filter 20 may be induced. Therefore, the secondary injected fuel amount and the added fuel amount are feedback controlled based on the output signal value of the exhaust temperature sensor 24. It is preferable to do so.
[0100]
When the bed temperature of the filter 20 rises to a high temperature range of, for example, 630 ° C. by the catalyst temperature raising process as described above, the CPU 351 injects fuel from the reducing agent injection valve 28 to reduce the oxygen concentration of the exhaust gas flowing into the filter 20. Let
[0101]
When excessive fuel is injected from the reducing agent injection valve 28, the fuel is burnt rapidly in the filter 20 and the filter 20 is overheated, or the excess fuel injected from the reducing agent injection valve 28 filters the fuel. Therefore, it is preferable that the CPU 351 feedback-controls the fuel injection amount from the reducing agent injection valve 28 based on an output signal of an air-fuel ratio sensor (not shown).
[0102]
When the poisoning recovery process is performed in this way, the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low under the condition where the bed temperature of the filter 20 is high, so that barium sulfate (BaSO ₄ ) contained in the filter 20 is reduced. ) is SO ₃ ^- and SO ₄ ^- are thermally decomposed, they SO ₃ ^- and SO ₄ ^- are reduced by reaction with hydrocarbons (HC) and carbon monoxide in the exhaust gas (CO), than Te filter 20 SOx poisoning will be restored.
[0103]
By the way, if fuel is added in order to recover SOx poisoning in the middle and high load region, the temperature of the filter 20 may rise excessively and may cause thermal degradation. However, if the engine 1 is not subsequently operated in the light load region, fuel addition for SOx poisoning recovery is not performed. If such a state continues, the temperature of the filter 20 will decrease, and it will be necessary to carry out temperature rise control again in order to recover SOx poisoning. .
[0104]
However, if fuel is not added to the filter 20 in order to suppress the deterioration of fuel consumption, the temperature of the filter 20 will be lowered this time, and SOx poisoning recovery will be performed immediately when shifting to a light load region. May not be possible, and there is a risk of losing the opportunity for SOx poisoning recovery.
[0105]
Therefore, in the present embodiment, the temperature of the filter 20 is maintained according to the operating state, so that both the temperature maintenance of the filter 20 and the suppression of deterioration of fuel consumption are achieved.
[0106]
Here, FIG. 4 is a diagram showing the relationship among the rotational speed, the load, and the target temperature of the filter 20. This map is stored in the ROM 352 in advance. The hatched region in the figure is, for example, a region of 630 ° C., and the target temperature gradually decreases as the distance from this region increases. In FIG. 4, an operation region in which the target temperature is 500 ° C. is representatively shown.
[0107]
Since the exhaust gas temperature is high and the exhaust gas flow rate is high in the high load region, the filter 20 is at a high temperature of, for example, 550 ° C. without adding fuel. When shifting from such a state to the light load region, it is possible to raise the temperature of the filter 20 in a short period of time, for example, to 630 ° C., which is necessary for SOx poisoning recovery. Until the fuel is added, fuel consumption is prevented from deteriorating.
[0108]
On the other hand, in the middle to high load region, the target temperature is determined according to the rotation speed and load, and the fuel addition is performed by feeding back the amount of fuel to be added.
[0109]
Here, the CPU 351 reads the output signal (rotation speed) of the crank position sensor 33 and the output signal (load) of the accelerator opening sensor 36, and substitutes this value in the map of FIG. calculate. Next, the CPU 351 reads the output signal of the exhaust temperature sensor 24 and estimates the temperature of the filter 20. The temperature of the filter 20 is estimated from the intake air amount (output signal of the air flow meter 11), the rotation speed, the load, the fuel injection amount, and the like. Alternatively, the temperature of the filter 20 may be obtained by mapping values obtained by experiments in advance. Further, a temperature sensor may be provided in the filter 20 to directly measure the temperature of the filter 20. In this way, the obtained actual temperature is compared with the target temperature. When the actual filter 20 temperature is higher than the target temperature, the fuel addition amount is decreased. On the other hand, when the actual filter 20 temperature is lower than the target temperature, the fuel addition amount is increased. . Examples of the method for increasing or decreasing the fuel include adjustment of the fuel injection interval, adjustment of the opening time of the reducing agent injection valve 28 at the time of one fuel injection, and the like.
[0110]
In the low load region, the temperature of the filter 20 is maintained at, for example, 630 ° C. necessary for SOx poisoning recovery so that SOx poisoning recovery can be started immediately. In such an operating region, the temperature is maintained at a temperature at which SOx poisoning recovery can be started immediately so as not to miss the opportunity for SOx poisoning recovery.
[0111]
In this way, in the high load region, the amount of fuel added is reduced to suppress the deterioration of fuel consumption. On the other hand, in the low load region, the temperature of the filter 20 is maintained at a high temperature to miss the opportunity for SOx poisoning recovery. In this way, it is possible to suppress the deterioration of exhaust emission.
[0112]
In the present embodiment, for the sake of convenience, the operation region has been described using the terms low load region, medium load region, and high load region. However, in actuality, the operation region is classified according to the rotation speed and load shown in FIG. Has been.
[0113]
On the other hand, in the present embodiment, when the operation region in which SOx poisoning recovery cannot be performed continues for a predetermined time (for example, 3 minutes), the fuel addition is stopped.
[0114]
As described above, the SOx poisoning recovery control is performed at a light load. Therefore, SOx poisoning recovery control is hardly performed during traveling on a suburb or highway. Even if the fuel is added and the temperature of the filter 20 is maintained at a high temperature in such an operation state, it takes a considerable time until the SOx poisoning recovery control is performed, so that the amount of fuel consumption increases. . Therefore, when such an operating state continues for a predetermined time (for example, 3 minutes), the fuel addition is stopped to suppress the deterioration of fuel consumption. Note that a predetermined time until the fuel addition is stopped may be determined depending on the operation state at this time.
[0115]
Here, the conventional temperature increase control is executed when a predetermined amount or more of SOx is occluded in the NOx catalyst. However, if the light load operation is not performed thereafter, the SOx poisoning recovery control is not performed, so that the temperature must be raised again, and the amount of fuel consumption increases.
[0116]
In that regard, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the fuel consumption is increased by setting the target temperature of the filter 20 to a higher temperature in the operation region where the possibility of SOx poisoning recovery is higher. And the opportunity for recovery from SOx poisoning can be effectively utilized.
[0117]
As described above, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the higher the possibility that SOx poisoning recovery is performed, the higher the temperature of the filter 20 is maintained and the opportunity for SOx poisoning recovery is missed. The target temperature of the filter 20 is lowered and the fuel consumption is improved as the possibility that the SOx poisoning recovery is performed is low, and the exhaust emission deterioration due to the SOx poisoning of the NOx storage reduction catalyst is suppressed. Can do.
<Second Embodiment>
This embodiment is different from the first embodiment in the following points.
[0118]
That is, in the first embodiment, the temperature of the filter 20 is set in consideration of the operating state of the engine 1 immediately after the SOx poisoning recovery is necessary. In this embodiment, the SOx poisoning recovery is performed. When necessary, first, the temperature of the filter 20 was raised to a temperature required for SOx poisoning recovery (for example, 630 ° C.), and then SOx poisoning recovery was not performed for a predetermined time (for example, 3 minutes). In this case, similarly to the first embodiment, the temperature rise control of the filter 20 according to the operating state of the engine 1 is performed.
[0119]
The present embodiment differs from the first embodiment in that the filter 20 is first raised to a predetermined temperature, but the basic configuration of the engine 1 and other hardware to be applied is different. Since this is common to the first embodiment, the description thereof is omitted.
[0120]
Here, since it is generally difficult to predict when the operating region of the engine 1 will shift to the light load region, in the exhaust gas purification apparatus for the internal combustion engine according to the first embodiment, a short period of time after shifting to the light load region. The target temperature of the filter 20 was set in accordance with the operating region of the engine 1 so that the temperature of the filter 20 could be increased.
[0121]
However, even during high-load driving, high-load driving may continue during highway driving or the like, or may immediately shift to low-load driving during urban driving.
[0122]
Therefore, in the present embodiment, when SOx poisoning recovery is required, first, the temperature of the filter 20 is increased to a temperature required for SOx poisoning recovery (for example, 630 ° C.). After that, in the case where it does not shift to an operation region in which SOx poisoning recovery can be performed for a predetermined period (for example, 3 minutes), in order to suppress the deterioration of fuel consumption, according to the operation region as in the first embodiment. The temperature of the filter 20 is controlled.
[0123]
In this way, when SOx poisoning recovery is required, the temperature of the filter 20 is raised so that SOx poisoning recovery can be performed immediately, so that the SOx poisoning recovery can be performed. In this case, the SOx poisoning can be recovered immediately, and when the operating state where the SOx poisoning cannot be recovered continues, the temperature of the filter 20 is controlled in accordance with the operating state, thereby reducing the fuel consumption. It is possible to raise the temperature of the filter 20 at an early stage when shifting to the light load region while suppressing the deterioration of.
[0124]
【The invention's effect】
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the target temperature of the NOx catalyst is set according to the operation state, the NOx is quickly recovered when the sulfur poisoning recovery is possible while suppressing the deterioration of fuel consumption. The catalyst can be heated to obtain many opportunities for SOx poisoning recovery.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.
FIG. 2A is a diagram showing a transverse cross section of a particulate filter. (B) is a figure which shows the longitudinal direction cross section of a particulate filter.
FIG. 3 is a block diagram showing an internal configuration of an ECU.
FIG. 4 is a diagram showing filter set temperatures according to the first embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine 1a ... Crank pulley 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 4a ... Common rail pressure sensor 5 ... Fuel supply pipe 6 ... .... Fuel pump 6a ... Pump pulley 8 ... Intake branch pipe 9 ... Intake pipe 18 ... Exhaust branch pipe 19 ... Exhaust pipe 20 ... Particulate filter 21 ... Exhaust throttle Valve 24 ... Exhaust temperature sensor 25 ... EGR passage 26 ... EGR valve 27 ... EGR cooler 28 ... Reducing agent injection valve 29 ... Reducing agent supply path 31 ... Shut-off valve 33 ..Crank position sensor 35 ECU
36 Accelerator opening sensor

Claims (3)

A NOx catalyst that stores NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich;
A temperature raising means for performing temperature rise control of the NOx catalyst when it is necessary to remove the sulfur oxide stored in the NOx catalyst;
An operating state detecting means for detecting an operating state of the internal combustion engine;
With
Said heating means, when the internal combustion engine is in a low load state to a temperature required target temperature of the NO x catalyst for the removal of sulfur oxides, when the internal combustion engine is in an intermediate load state of the NO x catalyst closer to low load the target temperature is increased, or, characterized in that it does not perform the temperature increase of N Ox catalyst when the internal combustion engine is in the operating state which is not suitable to perform the heating of a to the NOx catalyst in a high load state internal combustion Engine exhaust purification system.   When the temperature raising means is raising the temperature of the NOx catalyst and the operation state in which the sulfur oxide cannot be removed continues for a predetermined time or longer, the temperature raising means 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein The temperature raising means once raises the temperature of the NOx catalyst to a temperature required for recovery of sulfur poisoning when it becomes necessary to remove the sulfur oxides stored in the NOx catalyst, and then for a predetermined period of time. sulfur when poisoning recovery has not been performed, when the internal combustion engine is in the low load condition to a temperature required target temperature of the NO x catalyst for the removal of sulfur oxides, a low load when the internal combustion engine is in a middle load condition The target temperature of the NOx catalyst is increased as the value approaches N , or the temperature of the NOx catalyst is increased when the internal combustion engine is in a high load state and is not suitable for increasing the temperature of the NOx catalyst. The exhaust emission control device for an internal combustion engine according to claim 1, wherein there is no exhaust gas.

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