JP3620446B2 - 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, and in particular, a particulate matter represented by soot, which is a suspended particulate matter contained in the exhaust of a diesel engine (hereinafter referred to as “PM” unless otherwise specified). The present invention relates to an exhaust emission control device having a means for collecting gas.
[0002]
[Prior art]
Diesel engines are excellent in economy, but removal of PM contained in exhaust gas is an important issue. For this reason, a technique of providing a particulate filter (hereinafter simply referred to as “filter”) for collecting PM in an exhaust system of a diesel engine so that PM is not released into the atmosphere is well known.
[0003]
This filter can prevent PM in the exhaust gas from being collected once and released into the atmosphere. However, the collected PM accumulates on the filter and causes clogging of the filter. This clogging causes the exhaust pressure upstream of the filter to rise, leading to a reduction in the output of the internal combustion engine and filter damage. Therefore, it is necessary to remove PM by igniting and burning PM accumulated on the filter. The removal of PM deposited on the filter in this way is called filter regeneration.
[0004]
However, in order to ignite and combust PM collected by the filter, it is necessary to set the temperature of the filter to a high temperature of, for example, 500 ° C. or more. However, since the temperature of exhaust gas from a diesel engine is usually lower than this temperature, PM It was difficult to burn off.
[0005]
Therefore, it is conceivable to heat and raise the temperature of the filter up to a temperature at which PM collected by an electric heater, burner or the like is generated, but this requires a large amount of energy to be supplied from the outside. To solve this problem, for example, according to Japanese Patent Laid-Open No. 6-1559037, a filter carrying a NOx catalyst and a device for supplying hydrocarbons into exhaust gas are used, and the hydrocarbons supplied into the exhaust gas are converted into NOx catalyst. PM can be easily burned using the heat generated when burned.
[0006]
[Problems to be solved by the invention]
In the exhaust gas purification apparatus for an internal combustion engine having such a configuration, it is important to appropriately set an execution condition for supplying the reducing agent to the NOx catalyst and an execution condition for reducing the combustion of PM.
[0007]
For example, if the operating condition of the vehicle, the NOx catalyst temperature, and the elapsed time from the previous execution of PM combustion control are the execution conditions of PM combustion control, PM combustion control is not performed unless this condition is satisfied. More PM may accumulate on the filter than the amount of deposition that needs to be removed. After this state continues for a long time, when reducing agent is supplied into the exhaust gas to reduce NOx absorbed by the NOx catalyst, the reducing agent adheres to the PM deposited on the filter before reaching the NOx catalyst, and is similar to PM. The filter accumulates on the filter and clogs the filter.
[0008]
The present invention has been made to solve the above problems, and an object of the present invention is to remove particulate matter in an exhaust gas purification apparatus for an internal combustion engine including a filter and a nitrogen oxide absorbent. It is another object of the present invention to provide a technique capable of reducing nitrogen oxides at an appropriate time to prevent the reducing agent from accumulating on the filter and thereby preventing the filter function from deteriorating.
[0009]
[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.
[0010]
That is, a filter provided in the exhaust passage of the internal combustion engine for collecting particulate matter contained in the exhaust,
A nitrogen oxide absorbent that is provided in the exhaust passage of the internal combustion engine and absorbs nitrogen oxide contained in the exhaust; and
Reducing agent supply means for supplying a reducing agent to the nitrogen oxide absorbent;
Deposition state estimation means for estimating the amount of particulate matter deposited on the filter;
An operating state detecting means for detecting an operating state of the internal combustion engine;
The particulate matter deposited when the accumulation state estimation means estimates that a predetermined amount or more of particulate matter has accumulated and the operation state of the internal combustion engine detected by the operation state detection means satisfies a predetermined condition. Filter regeneration means for removing and regenerating the filter;
Comprising
The operation state detected by the operation state detection unit does not satisfy the predetermined condition even though the accumulation state estimation unit estimates that a predetermined amount or more of the particulate matter that is the filter regeneration condition is accumulated on the filter. Therefore, when the filter is not regenerated for a predetermined period or longer, the reducing agent is not supplied by the reducing agent supply means until the removal of the particulate matter deposited on the filter is completed.
[0011]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, particulate matter contained in the exhaust gas is collected by a filter provided in the exhaust passage.
[0012]
The particulate matter collected by the filter is deposited on the filter and induces clogging of the filter, so that it is removed by the filter regeneration means.
[0013]
Further, nitrogen oxide (NOx) contained in the exhaust is absorbed by the nitrogen oxide absorbent provided in the exhaust passage.
[0014]
Then, when it becomes necessary to supply the reducing agent to the nitrogen oxide absorbent, the reducing agent supply means supplies the reducing agent to the exhaust passage upstream of the nitrogen oxide absorbent.
[0015]
The reducing agent supplied to the exhaust passage flows into the nitrogen oxide absorbent together with the exhaust flowing from the upstream of the exhaust passage. The nitrogen oxide absorbent reduces and purifies harmful gas components in the exhaust using a reducing agent.
[0016]
By the way, the effects when the filter is regenerated and the nitrogen oxides are reduced greatly differ depending on the operating state of the internal combustion engine.
[0017]
Therefore, regeneration of the filter or nitrogen oxidation based on the detection result of the operating state detection means while taking into account the state in which particulate matter is deposited on the filter or the amount of nitrogen oxide absorbed in the nitrogen oxide absorbent The timing for supplying the reducing agent to the material absorbent is determined.
[0018]
If such conditions are set, even if a predetermined amount or more of the particulate matter is accumulated on the filter and regeneration is required, the filter is not regenerated when a predetermined condition such as an operating state is not satisfied. When such a state continues and a particulate matter of a predetermined amount or more is deposited on the filter, if the condition for supplying the reducing agent to the nitrogen oxide absorbent is satisfied and the reducing agent is supplied, Before the reducing agent reaches the material absorbent, the reducing agent adheres to the particulate matter deposited on the filter and is deposited on the filter together with the particulate matter.
[0019]
Therefore, the amount of particulate matter deposited on the filter is estimated by the accumulation state estimation means, and when the accumulation of particulate matter exceeding a predetermined amount is estimated, the supply of the reducing agent is not performed until the regeneration of the filter is completed. Do not do so to prevent the filter from clogging.
[0020]
The accumulation state estimation means can estimate the accumulation amount of the particulate matter by using a numerical map obtained in advance based on, for example, the differential pressure before and after the filter. There are other conditions such as the filter is not regenerated for a predetermined period, the filter is not regenerated while traveling a predetermined distance, and the operation of the internal combustion engine is stopped before the filter is regenerated. When established, the reducing agent may not be supplied to the nitrogen oxide absorbent until the regeneration of the filter is completed.
[0021]
In the present invention, when the internal combustion engine is in a high load state when the regeneration of the filter is not performed because the operation state detected by the operation state detection means does not satisfy a predetermined condition, The amount of fuel supplied to the internal combustion engine may be reduced.
[0022]
When the amount of fuel supplied at the time of high load is large, high temperature combustion is performed in a state where the oxygen concentration is low, so that a large amount of particulate matter is generated. Therefore, the particulate matter discharged from the internal combustion engine can be reduced by reducing the amount of fuel when the load is high, and the clogging of the filter can be prevented from proceeding.
[0023]
In the present invention, an EGR device that recirculates a part of the exhaust gas to the intake system of the internal combustion engine is provided, and the filter is regenerated because the operation state detected by the operation state detection means does not satisfy the predetermined condition. When not noticed, the amount of EGR gas may be reduced.
[0024]
When the amount of EGR gas is large at high load, a high amount of particulate matter is generated because of high temperature combustion with a low oxygen concentration. Thus, by reducing the amount of EGR gas at the time of high load, particulate matter discharged from the internal combustion engine can be reduced, and the progress of clogging of the filter can be prevented.
[0025]
In the present invention, the reducing agent supply means is a reducing agent addition nozzle for adding a reducing agent to an exhaust passage of the internal combustion engine, and the filter regeneration means injects fuel for engine output to the internal combustion engine. It may be a sub-injection in which fuel is injected again at a time when the engine output does not become after the main injection.
[0026]
When the sub-injection is performed, the injected fuel is burned before being discharged from the internal combustion engine, and the temperature of the exhaust is increased. When the exhaust gas having reached a high temperature reaches the filter, the particulate matter deposited on the filter is ignited and removed by combustion.
[0027]
Moreover, the hydrocarbons discharged at this time are sufficiently gasified and are not easily caused by clogging by being collected by the filter.
[0028]
In the present invention, the nitrogen oxide absorbent may be supported on the filter.
[0029]
In the present invention, the filter may be installed upstream of the nitrogen oxide absorbent in the exhaust passage.
[0030]
Filters loaded with nitrogen oxide absorbent and filters installed upstream of the exhaust passage from nitrogen oxide absorbent are particulate matter deposited on the filter before the reducing agent reaches the nitrogen oxide absorbent. Especially effective because it adheres to the surface.
[0031]
In the present invention, when the internal combustion engine is operating at a low rotation and a low load and the internal combustion engine is in a warm state, the EGR gas amount is increased more than usual, and the internal combustion engine is cooled. When the engine is in the intermediate state, the temperature of the filter or the nitrogen oxide absorbent is increased by performing the sub-injection to inject the fuel again at the time when the engine output after the main injection for injecting the fuel for engine output to the internal combustion engine is not reached. Can be raised.
[0032]
When the sub-injection is performed, the injected fuel is burned before being discharged from the internal combustion engine, and the temperature of the exhaust is increased. This sub-injection makes it possible to increase the temperature of the nitrogen oxide absorbent and the filter early. Here, the nitrogen oxide absorbent also has a function of oxidizing hydrocarbons, but during cold, the temperature of the nitrogen oxide absorbent does not reach the activation temperature, so the hydrocarbon is not oxidized and carbonized. Sub-injection with low hydrogen emissions.
[0033]
Further, the hydrocarbons discharged at this time are sufficiently gasified due to the high temperature, and are not easily caused by clogging by being collected by the filter.
[0034]
The sub-injection is effective in raising the temperature of the filter and the nitrogen oxide absorbent because the fuel is burned to bring the exhaust gas into a high temperature state, but it is mainly performed in the cold because it consumes a lot of fuel. However, in the region where low-temperature combustion described below cannot be achieved, it can be used even when warm.
[0035]
When warm, the temperature of the nitrogen oxide absorbent has reached the activation temperature, so hydrocarbon purification by the nitrogen oxide absorbent can be expected. At this time, the internal combustion engine is operated with the EGR gas amount increased more than usual. In this method, the fuel is burned by adding more EGR gas than the amount of EGR gas at which the generation amount of particulate matter peaks. This is called low-temperature combustion, and almost no particulate matter is generated. Instead, a lot of unburned hydrocarbons are discharged. The discharged unburned hydrocarbon is oxidized by the nitrogen oxide absorbent, and the temperature of the nitrogen oxide absorbent rises. This low temperature combustion discharges a lot of unburned hydrocarbons, so if the nitrogen oxide absorbent does not reach the activation temperature, the unburned hydrocarbons will be released into the atmosphere without being oxidized by the nitrogen oxide absorbent. . Therefore, it was decided to perform low-temperature combustion only when warm.
[0036]
In the present invention, a particulate filter can be exemplified as the filter.
[0037]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the exhaust emission control device according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
<First Embodiment>
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.
[0038]
An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.
[0039]
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.
[0040]
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 ( It is connected to a crank pulley 1a attached to the crankshaft) via a belt 7.
[0041]
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.
[0042]
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.
[0043]
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).
[0044]
The intake branch pipe 8 is connected to an intake pipe 9, and the intake pipe 9 is connected to an air cleaner box 10. The intake pipe 9 downstream of the air cleaner box 10 has an air flow meter 11 for outputting an electric signal corresponding to the mass of the intake air flowing through the intake pipe 9 and the temperature of the intake air flowing through the intake pipe 9. An intake air temperature sensor 12 for outputting the electrical signal is attached.
[0045]
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.
[0046]
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.
[0047]
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.
[0048]
The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel built in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15 a and has reached a high temperature is cooled by the intercooler 16, and then the flow rate is adjusted by the intake throttle valve 13 as necessary to flow into the intake branch pipe 8. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chambers of the respective cylinders 2 through the respective branch pipes, and is burned using the fuel injected from the fuel injection valves 3 of the respective cylinders 2 as an ignition source.
[0049]
On the other hand, an exhaust branch pipe 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with a combustion chamber of each cylinder 2 via an exhaust port (not shown).
[0050]
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).
[0051]
In the middle of the exhaust pipe 19, a particulate filter 20 carrying an NOx storage reduction catalyst is disposed. A filter upstream pressure sensor 38 that outputs an electrical signal corresponding to the pressure of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20. In the exhaust pipe 19 downstream of the filter 20, an air-fuel ratio sensor 23 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust flowing in the exhaust pipe 19, and the temperature of the exhaust flowing in the exhaust pipe 19 are supported. An exhaust temperature sensor 24 for outputting the electrical signal and a filter downstream pressure sensor 39 for outputting an electrical signal corresponding to the pressure of the exhaust gas flowing through the exhaust pipe 19 are attached.
[0052]
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.
[0053]
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.
[0054]
Exhaust gas discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19, PM in the exhaust gas is collected, and harmful gas components are removed or purified. The exhaust gas from which PM has been collected by the filter 20 and from which harmful gas components have been 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.
[0055]
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.
[0056]
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.
[0057]
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.
[0058]
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.
[0059]
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.
[0060]
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.
[0061]
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.
[0062]
Next, the filter 20 according to the present embodiment will be described.
[0063]
FIG. 4 shows the structure of the filter 20. 4A shows a cross section in the horizontal direction of the filter 20, and FIG. 4B shows a cross section in the vertical direction of the filter 20. As shown in FIGS. 4A and 4B, 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. Note that the hatched portion in FIG. 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.
[0064]
The filter 20 is formed of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust inflow passage 50 passes through the surrounding partition wall 54 as indicated by an arrow in FIG. To the exhaust outlet passage 51.
[0065]
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 this carrier.
[0066]
Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to the present embodiment will be described.
[0067]
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, an occlusion reduction type NOx catalyst configured by supporting barium (Ba) and platinum (Pt) on a support made of alumina will be described as an example.
[0068]
The NOx catalyst configured in this way absorbs nitrogen oxide (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high.
[0069]
On the other hand, the NOx catalyst releases the absorbed 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 (N₂).
[0070]
In addition, although there is a part which is not clarified about the NOx absorption / release action of the NOx catalyst, it is considered that it is performed by the following mechanism.
[0071]
First, in the NOx catalyst, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes a lean air-fuel ratio and the oxygen concentration in the exhaust gas increases, as shown in FIG.₂) Is O₂ ⁻Or O^2-It adheres on the surface of platinum (Pt) in the form of Nitric oxide (NO) in the exhaust is O on the surface of platinum (Pt).₂ ⁻Or O^2-Reacts with nitrogen dioxide (NO₂) (2NO + O)₂→ 2NO₂). Nitrogen dioxide (NO₂) Is further oxidized on the surface of platinum (Pt), and nitrate ions (NO)₃ ⁻) Is absorbed by the NOx catalyst. Nitrate ions absorbed by the NOx catalyst (NO₃ ⁻) Combines with barium oxide (BaO) to form barium nitrate (Ba (NO₃)₂).
[0072]
Thus, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is a lean air-fuel ratio, nitrogen oxides (NOx) in the exhaust gas are nitrate ions (NO_3-) Is absorbed by the NOx catalyst.
[0073]
The above-described NOx absorption action is continued as long as the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio and the NOx absorption capacity of the NOx catalyst is not saturated. Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is a lean air-fuel ratio, nitrogen oxide (NOx) in the exhaust gas is absorbed by the NOx catalyst unless the NOx absorption capacity of the NOx catalyst is saturated. Nitrogen oxide (NOx) will be removed.
[0074]
On the other hand, in the NOx catalyst, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst is lowered, nitrogen dioxide (NOt) on the surface of platinum (Pt).₂Nitrate ions (NO) bound to barium oxide (BaO).₃ ⁻) On the contrary, nitrogen dioxide (NO₂) Or nitric oxide (NO) and is released from the NOx catalyst.
[0075]
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 catalyst.₂) Or nitric oxide (NO) to nitrogen (N₂).
[0076]
Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 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 nitrogen oxides absorbed by the NOx catalyst ( NOx) is released and reduced, so that the NOx absorption capacity of the NOx catalyst is regenerated.
[0077]
By the way, when the internal combustion engine 1 is operated in lean combustion, 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 oxide (NOx) contained in the exhaust However, if the lean combustion operation of the internal combustion engine 1 is continued for a long time, the NOx absorption capacity of the NOx catalyst is saturated, and nitrogen oxides (NOx) in the exhaust gas are absorbed into the NOx catalyst. Will be released to the atmosphere without being removed.
[0078]
In particular, in a diesel engine such as the internal combustion engine 1, the lean air-fuel ratio mixture is combusted in the most operating region, and the exhaust air-fuel ratio becomes the lean air-fuel ratio in the most operating region accordingly. The NOx absorption capacity of the catalyst is easily saturated.
[0079]
Therefore, when the internal combustion engine 1 is operated in lean combustion, before the NOx absorption capacity of the NOx catalyst is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is reduced and the concentration of the reducing agent is increased, so that the NOx catalyst It is necessary to release and reduce absorbed nitrogen oxides (NOx).
[0080]
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 filter 20, and from this reducing agent supply mechanism. By adding fuel into the exhaust gas, the oxygen concentration of the exhaust gas flowing into the filter 20 is decreased and the concentration of the reducing agent is increased.
[0081]
As shown in FIG. 1, the reducing agent supply mechanism is attached to the cylinder head of the internal combustion engine 1 so that its nozzle hole faces the exhaust branch pipe 18, and when a fuel having a predetermined valve opening pressure or higher is applied. A reducing agent injection valve 28 that opens and injects fuel, a reducing agent supply passage 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and in the middle of the reducing agent supply passage 29. A flow rate adjusting valve 30 that adjusts the flow rate of the fuel that is provided and flows through the reducing agent supply passage 29, and a fuel in the reducing agent supply passage 29 that is provided in the reducing agent supply passage 29 upstream from the flow amount adjusting valve 30. A shut-off valve 31 that shuts off the flow of the reductant, a reducing agent pressure sensor 32 that is attached to the reducing agent supply path 29 upstream of the flow rate adjusting valve 30 and outputs an electrical signal corresponding to the pressure in the reducing agent supply path 29, It has.
[0082]
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.
[0083]
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.
[0084]
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.
[0085]
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.
[0086]
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.
[0087]
The reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 flows into the turbine housing 15 b together with the exhaust flowing from the upstream side of the exhaust branch pipe 18. The exhaust gas flowing into the turbine housing 15b and the reducing agent are agitated and uniformly mixed by the rotation of the turbine wheel to form a rich air-fuel ratio exhaust gas.
[0088]
The rich air-fuel ratio exhaust gas thus formed flows into the filter 20 from the turbine housing 15b through the exhaust pipe 19, and releases nitrogen oxides (NOx) absorbed by the filter 20 to nitrogen (N₂).
[0089]
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.
[0090]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 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.
[0091]
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 an opening sensor 36, a filter upstream pressure sensor 38, and a filter downstream pressure sensor 39 are connected via electric wiring, and output signals of the various sensors described above are input to the ECU 35.
[0092]
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.
[0093]
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.
[0094]
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.
[0095]
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, the filter upstream pressure sensor 38, the filter downstream pressure sensor 39, and the like are input via an A / D 355 of a sensor that outputs an analog signal format signal, and the output signals are transmitted to the CPU 351 and the RAM 353.
[0096]
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.
[0097]
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. An EGR control routine for controlling, a PM combustion control routine for burning and removing PM trapped in the filter 20, a fuel addition control routine for reducing NOx stored in the NOx storage reduction catalyst, Application programs such as a poisoning elimination control routine for eliminating the poisoning caused by oxides are stored.
[0098]
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 They are a reducing agent addition amount control map showing the relationship with the addition amount (or the target air-fuel ratio of 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, and the like. .
[0099]
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.
[0100]
The backup RAM 354 is a nonvolatile memory capable of storing data even after the internal combustion engine 1 is stopped.
[0101]
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, PM combustion control, fuel addition control, poisoning elimination control, and the like.
[0102]
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.
[0103]
When determining the fuel injection amount, the CPU 351 reads the engine speed and the output signal (accelerator opening) of the accelerator opening sensor 36 stored in the RAM 353. The CPU 351 accesses the fuel injection amount control map and calculates a basic fuel injection amount (basic fuel injection time) corresponding to the engine speed and the accelerator opening. The CPU 351 corrects the basic fuel injection time based on output signal values from the air flow meter 11, the intake air temperature sensor 12, the water temperature sensor 34, etc., and determines the final fuel injection time.
[0104]
When determining the fuel injection timing, the CPU 351 accesses the fuel injection start timing control map and calculates a 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.
[0105]
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.
[0106]
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.
[0107]
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.
[0108]
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.
[0109]
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.
[0110]
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.
[0111]
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.
[0112]
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.
[0113]
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.
[0114]
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. .
[0115]
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
[0116]
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.
[0117]
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.
[0118]
Next, in the fuel addition 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 is changed to a rich air-fuel ratio in a spike-like (short time) manner with a relatively short cycle.
[0119]
In the rich spike control, the CPU 351 determines whether or not the rich spike control execution condition is satisfied every predetermined cycle. The rich spike control execution condition includes, for example, whether the NOx storage reduction catalyst is in an active state, whether the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit, or poisoning elimination control. A condition such as whether it is not executed can be exemplified.
[0120]
When it is determined that the rich spike control execution condition as described above is satisfied, the CPU 351 controls the flow rate adjustment valve 30 to inject fuel as a reducing agent from the reducing agent injection valve 28 in a spike manner. The air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is temporarily set to a predetermined target rich air-fuel ratio.
[0121]
Specifically, the CPU 351 determines the engine speed, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), the fuel injection amount, and the like stored in the RAM 353. read out. Further, the CPU 351 accesses the reducing agent addition amount control map in the ROM 352 using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the air-fuel ratio of the exhaust to a preset target rich air. The amount of addition of the reducing agent (target addition amount) necessary for obtaining the fuel ratio is calculated.
[0122]
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).
[0123]
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.
[0124]
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.
[0125]
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. Then, the reducing agent injected from the reducing agent injection valve 28 is mixed 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.
[0126]
As a result, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst repeats “lean” and “spike target rich air-fuel ratio” alternately in a relatively short cycle, and thus the storage reduction The type NOx catalyst repeats absorption and release / reduction of nitrogen oxides (NOx) alternately in a short cycle.
[0127]
Next, PM combustion control which is the gist of the present invention will be described.
[0128]
FIG. 5 is a flowchart of PM combustion control performed when the filter 20 is regenerated.
[0129]
In step 101, it is determined whether or not PM has accumulated on the filter 20 by a predetermined amount or more and regeneration is necessary.
[0130]
First, the CPU 351 calculates the differential pressure before and after the filter 20 based on the output signal of the filter upstream pressure sensor 38 installed on the upstream side of the filter 20 and the output signal of the filter downstream pressure sensor 39 installed on the downstream side. By substituting the calculated differential pressure into a numerical map indicating the relationship between the differential pressure before and after the filter 20 and the PM accumulation amount stored in the ROM 352, the amount of PM accumulated on the filter 20 can be obtained.
[0131]
Further, the PM accumulation amount may be estimated based on the time when the filter 20 is not regenerated, the distance traveled by the vehicle while the filter 20 is not regenerated, and the like.
[0132]
If the amount of accumulated PM estimated in this way is larger than a predetermined amount, a numerical value indicating that the filter needs to be regenerated is stored in the RAM 353. In this way, the state in which the numerical value indicating that the PM regeneration is necessary is stored in the RAM 353 is expressed as “PM regeneration flag ON” in FIG. Further, when the estimated amount of accumulated PM is equal to or smaller than a predetermined amount, a numerical value indicating that the regeneration of the filter is not necessary is stored in the RAM 353. In this way, the state in which the numerical value indicating that the filter regeneration is not necessary is stored in the RAM 353 is expressed as “PM regeneration flag OFF” in FIG.
[0133]
In step 102, it is determined whether or not a filter regeneration enabling condition is satisfied. Specifically, it is determined whether the numerical value stored in the RAM 353 is a numerical value indicating that the filter needs to be regenerated. If it is stored in the RAM 353 that the filter needs to be regenerated, the process proceeds to Step 103, and if it is stored in the RAM 353 that the filter need not be regenerated, the process proceeds to Step 105.
[0134]
In step 105, a numerical value indicating that the filter regeneration is not necessary is stored in the RAM 353.
[0135]
In step 103, it is determined whether or not PM combustion control can be executed. Examples of the PM combustion control execution condition include conditions such as whether the filter 20 is in an active state or whether the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value. it can. If the filter regeneration condition is satisfied, the routine proceeds to step 104.
[0136]
In step 104, sub-injection is performed to regenerate the filter 20. As means for increasing the temperature of the filter 20 at an early stage, it is effective to perform sub-injection in which fuel is sub-injected during the expansion stroke of the internal combustion engine 1. The reason why the fuel is injected in the expansion stroke is that fuel injection performed during the compression stroke increases the engine output and may deteriorate the operation state. The fuel injected by the sub-injection burns in the cylinder 2 and raises the gas temperature in the cylinder 2. The gas whose temperature has risen becomes exhaust gas, reaches the filter 20 through the exhaust pipe 19, raises the temperature of the filter 20, and PM burns.
[0137]
If the relationship between the accelerator opening, the engine speed, the sub-injection amount or the sub-injection timing is mapped in advance and stored in the ROM 352, the map, the accelerator opening, and the engine rotation can be obtained. It can be calculated from the number.
[0138]
On the other hand, if the filter regeneration condition is not satisfied in step 103, the process proceeds to step 106.
[0139]
In step 106, it is determined whether or not a predetermined time has elapsed since the PM regeneration flag was turned on. The CPU 351 calculates the time during which the PM regeneration flag is ON, and whether or not the elapsed time after the PM regeneration flag is ON is longer than the predetermined time compared with the predetermined time stored in the ROM 352. judge. If the predetermined time or more has elapsed, the process proceeds to step 108, and if the predetermined time or more has not elapsed, the process proceeds to step 107.
[0140]
In step 106, a numerical value for prohibiting the addition of fuel is stored in the RAM 353. In this manner, the state in which the numerical value for prohibiting the addition of fuel is stored in the RAM 353 is expressed as “fuel addition flag OFF” in FIG. In this state, since a predetermined amount or more of PM is accumulated on the filter 20, if fuel is added, the fuel adheres to the PM and clogging progresses. Therefore, addition of fuel is prohibited to prevent this. The
[0141]
In step 107, a numerical value for adding fuel is stored in the RAM 353. In this way, the state in which the numerical value for adding the fuel is stored in the RAM 353 is expressed as “fuel addition flag ON” in FIG. In this state, since a predetermined amount or more of PM has not accumulated on the filter 20, fuel is added and NOx stored in the NOx catalyst is reduced.
[0142]
In step 109, the fuel main injection amount into the cylinder 2 at the time of high load is reduced. Since a predetermined amount or more of PM is accumulated on the filter 20, the amount of PM discharged is reduced and the progress of clogging is suppressed.
[0143]
In general, when the load is high, the fuel injection amount is increased in order to increase the engine output. However, when the fuel injection amount is increased, an excessively concentrated portion of the fuel is locally generated, and the PM emission amount due to incomplete combustion. Will increase. Therefore, the amount of main injection of fuel for engine output is reduced to reduce PM emissions.
[0144]
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 a fuel injection amount reduction control map stored in advance in the ROM 352, and calculates a fuel injection amount (fuel injection time) corresponding to the engine speed and the accelerator opening. The CPU 351 corrects the 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.
[0145]
In step 110, the amount of EGR gas at the time of high load is decreased. Since a predetermined amount or more of PM is accumulated on the filter 20, the amount of PM discharged is reduced and the progress of clogging is suppressed.
[0146]
In general, when the load is high, the fuel injection amount is increased in order to increase the engine output. However, if the EGR gas amount is large, an excessively concentrated portion of the fuel is locally generated, and the PM emission amount is reduced due to incomplete combustion. To increase. Therefore, the amount of EGR gas is reduced to reduce PM emission.
[0147]
Here, the CPU 351 accesses the EGR reduction valve opening degree control map using the engine speed and the accelerator opening that are stored in advance in the ROM 352 as parameters, and the target EGR reduction corresponding to the engine speed and the accelerator opening. The valve opening is calculated and EGR valve feedback control is performed.
[0148]
In this way, execution or prohibition of regeneration of the filter 20 is selected based on the amount of PM accumulated on the filter 20, PM is combusted when regeneration is performed, and PM is further accumulated when regeneration is prohibited. Progressing clogging can be suppressed.
[0149]
Next, fuel addition control for reducing NOx stored in the NOx storage reduction catalyst will be described.
[0150]
FIG. 6 is a flowchart when NOx stored in the NOx storage reduction catalyst supported by the filter 20 is reduced.
[0151]
In step 201, it is determined whether or not a filter regeneration enabling condition is satisfied. Specifically, it is determined whether or not the numerical value stored in the RAM 353 is a numerical value indicating that it is necessary to add fuel as a reducing agent. If it is stored in the RAM 353 that fuel addition is necessary, the process proceeds to step 202. If it is stored in the RAM 353 that fuel addition is not necessary, the process proceeds to step 204. In step 204, a numerical value indicating that the addition of fuel is not necessary is stored in the RAM 353.
[0152]
In step 202, it is determined whether or not rich spike control for adding fuel from the reducing agent injection valve 28 can be executed. The rich spike control execution condition includes, for example, whether the NOx storage reduction catalyst is in an active state, whether the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit, or poisoning elimination control. A condition such as whether it is not executed can be exemplified. If the rich spike control execution condition is satisfied, the process proceeds to step 203; otherwise, the process proceeds to step 204.
[0153]
In step 203, the CPU 351 temporarily controls the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst by controlling the flow rate adjusting valve 30 to inject fuel as a reducing agent in a spike manner from the reducing agent injection valve 28. Rich spike control is performed to obtain a predetermined target rich air-fuel ratio.
[0154]
As a result, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst repeats “lean” and “spike target rich air-fuel ratio” alternately in a relatively short cycle, and thus the storage reduction The type NOx catalyst repeats absorption and release / reduction of nitrogen oxides (NOx) alternately in a short cycle.
[0155]
In this way, fuel addition control can be performed only when PM is not accumulated in the filter 20 in a predetermined amount or more, and the progress of clogging can be suppressed.
<Second Embodiment>
The second embodiment according to the present invention differs from the first embodiment in the means for raising the temperature of the filter 20 and the NOx catalyst.
[0156]
In the first embodiment, the fuel injection from the sub-injection and the reducing agent injection valve 28 is used. However, in the present embodiment, the internal combustion engine 1 is particularly operated at a low rotation and a low load. Only when it is warm, low-temperature combustion is used, and when cold, secondary injection is used.
[0157]
Here, the low temperature combustion will be described.
[0158]
Conventionally, EGR has been used to suppress the generation of NOx in an internal combustion engine. Since the EGR gas has a relatively high specific heat ratio and can absorb a large amount of heat, the combustion temperature in the cylinder 2 decreases as the EGR gas ratio in the intake air increases. Since the amount of NOx generated decreases as the combustion temperature decreases, the NOx emissions can be reduced as the EGR gas ratio increases.
[0159]
However, as the EGR gas ratio is increased, the generation amount of soot begins to increase abruptly at a certain ratio or more. Normal EGR control is performed at a lower EGR gas ratio than when soot begins to increase rapidly.
[0160]
However, as the EGR gas ratio is further increased, soot rapidly increases as described above, but there is a peak in the generation amount of this soot, and when the EGR gas ratio is further increased beyond this peak, This time, wrinkles start to decrease rapidly, and finally it hardly occurs.
[0161]
This is because when the temperature of the fuel during combustion in the combustion chamber and the surrounding gas is below a certain temperature, the growth of hydrocarbons (HC) stops at an intermediate stage before reaching soot, and the temperature of the fuel and the surrounding gas is reduced. This is because the hydrocarbon (HC) grows to soot all at once when the temperature rises above a certain temperature.
[0162]
Therefore, no soot will be generated if the combustion during combustion in the combustion chamber and the gas temperature around it are controlled below the temperature at which hydrocarbon (HC) growth stops midway. In this case, the endothermic effect of the gas around the fuel when the fuel burns greatly affects the temperature of the fuel and the surrounding gas, and the endothermic amount of the gas around the fuel, that is, EGR, according to the amount of heat generated during fuel combustion. It is possible to suppress the generation of soot by adjusting the gas ratio.
[0163]
On the other hand, hydrocarbons (HC) that have stopped growing before reaching soot can be purified using a NOx absorbent or the like.
[0164]
Thus, low temperature combustion is based on purifying hydrocarbons (HC) whose growth has stopped halfway before reaching soot with a NOx absorbent or the like. Therefore, when the NOx absorbent or the like is not activated, hydrocarbons (HC) are not purified but are released into the atmosphere, so low temperature combustion cannot be used.
[0165]
Further, the temperature of the fuel during combustion in the cylinder 2 and the gas temperature around it can be controlled to a temperature below the temperature at which the growth of hydrocarbon (HC) stops halfway when the engine load is small and the amount of heat generated by combustion is small. Limited to.
[0166]
Therefore, in the present invention, the low-temperature combustion control is performed only when the internal combustion engine 1 is operated at a low rotation and low load and when the NOx catalyst supported on the filter 20 reaches the activation temperature. .
[0167]
Whether or not the NOx catalyst has reached the activation temperature can be determined based on the output signal of the exhaust temperature sensor 24.
[0168]
In this way, in low-temperature combustion, PM emission typified by soot is suppressed, so that HC can be supplied to the NOx catalyst without causing clogging of the filter 20. In the NOx catalyst, HC is combusted and the temperature of the filter 20 rises due to the heat.
[0169]
Further, when the NOx catalyst has not reached the activation temperature, the sub-injection is performed to raise the temperature of the filter 20 and the NOx catalyst. The fuel injected by the sub-injection burns in the cylinder 2 and raises the gas temperature in the cylinder 2. The gas whose temperature has increased becomes exhaust gas, reaches the filter 20 through the exhaust pipe 19, and increases the temperature of the filter 20. Further, the HC discharged at this time is sufficiently gasified, and is not easily caused by clogging by being collected by the filter 20.
[0170]
When the sub-injection is used in this way, the temperature of the NOx catalyst can be raised early, but a large amount of fuel is consumed. Therefore, when the internal combustion engine 1 is operated at a low rotation and low load for improving fuel efficiency, the NOx Sub-injection was performed only when the catalyst was cold when it did not reach the activation temperature.
[0171]
This sub-injection and low-temperature combustion are performed in step 104 during PM combustion control and step 203 during fuel addition control in the first embodiment of FIG. Further, when the internal combustion engine 1 is not operated at a low rotation and low load, normal PM combustion control and fuel addition control are performed.
[0172]
In this way, even when the internal combustion engine 1 is operating at a low rotation and a low load and the temperatures of the filter 20 and the NOx catalyst are difficult to rise, the temperature is raised early while suppressing the emission of HC, so that the combustion of PM and NOx Can be reduced.
<Third Embodiment>
In the third embodiment according to the present invention, the positional relationship between the filter 20 and the NOx storage reduction catalyst 37 is different from that in the first embodiment.
[0173]
In the first embodiment, the NOx storage reduction catalyst is supported by the filter 20, but in the third embodiment, the NOx storage reduction catalyst 37 is provided downstream of the filter 20 as shown in FIG. Arranged.
[0174]
In the exhaust gas purification apparatus configured as described above, PM contained in the exhaust gas discharged from the internal combustion engine 1 is collected by the upstream filter 20, so that PM does not adhere to the downstream NOx catalyst 37. , NOx reduction ability is not reduced.
[0175]
However, the filter 20 installed upstream of the NOx catalyst 37 is attached with fuel as a reducing agent added to the exhaust gas to reduce NOx stored in the NOx catalyst 20. At this time, if PM is deposited on the filter 20, the fuel adheres to the deposited PM, and the fuel is also deposited on the filter 20 together with the PM. When clogging progresses in this way and the resistance of the filter 20 increases, the pressure of the exhaust gas upstream of the filter 20 increases, leading to damage to the filter 20 and a decrease in engine output.
[0176]
Therefore, when PM is accumulated on the filter 20 in a predetermined amount or more, the PM accumulated on the filter 20 is removed before the fuel is added to the NOx catalyst 37.
[0177]
Since the method for determining the amount of accumulated PM, PM combustion control, fuel addition control, and the like are the same as those in the first embodiment, description thereof will be omitted.
[0178]
【The invention's effect】
According to the exhaust gas purification apparatus for an internal combustion engine according to the present invention, it is possible to prevent the clogging from proceeding due to the reducing agent for reducing the nitrogen oxide absorbed by the nitrogen oxide absorbent adhering to the filter.
[0179]
Therefore, it is possible to prevent the filter from being damaged and the engine output from being reduced due to clogging, to maintain the function of the filter over a long period of time, and to prevent the exhaust emission from deteriorating.
[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 a first embodiment is applied and an intake / exhaust system thereof.
FIG. 2 (A) is a diagram illustrating a NOx absorption mechanism of a NOx storage reduction catalyst. (B) is a diagram illustrating the NOx release mechanism of the NOx storage reduction catalyst.
FIG. 3 is a block diagram showing an internal configuration of an ECU.
FIG. 4A 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. 5 is a flowchart of PM combustion control.
FIG. 6 is a flowchart of fuel addition control.
FIG. 7 is a diagram showing a positional relationship between a filter and an NOx storage reduction catalyst according to a third embodiment.
[Explanation of symbols]
1 ... Internal combustion engine
2. Cylinder
3. Fuel injection valve
4 ... Common rail
5. Fuel supply pipe
6. Fuel pump
18 ... Exhaust branch pipe
19 ... Exhaust pipe
20 ... Particulate filter
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
37 ... NOx storage reduction catalyst
38 ... Filter upstream pressure sensor
39 ... Filter downstream pressure sensor
351 ... CPU
352 ... ROM
353 ... RAM
354 ... Backup RAM
50 ... Exhaust inflow passage
51 ... Exhaust outlet passage
54 ... Bulkhead

Claims (7)

A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter contained in the exhaust;
A nitrogen oxide absorbent that is provided in the exhaust passage of the internal combustion engine and absorbs nitrogen oxide contained in the exhaust; and
Reducing agent supply means for supplying a reducing agent to the nitrogen oxide absorbent;
Deposition state estimation means for estimating the amount of particulate matter deposited on the filter;
An operating state detecting means for detecting an operating state of the internal combustion engine;
The particulate matter deposited when the accumulation state estimation means estimates that a predetermined amount or more of particulate matter has accumulated and the operation state of the internal combustion engine detected by the operation state detection means satisfies a predetermined condition. Filter regeneration means for removing and regenerating the filter;
Comprising
The operation state detected by the operation state detection unit does not satisfy the predetermined condition even though the accumulation state estimation unit estimates that a predetermined amount or more of the particulate matter that is the filter regeneration condition is accumulated on the filter. Therefore, when the filter is not regenerated for a predetermined period or longer, the reducing agent is not supplied by the reducing agent supply means until the removal of the particulate matter deposited on the filter is completed. Exhaust purification equipment. When the internal combustion engine is in a high load state when the regeneration of the filter is not performed because the operation state detected by the operation state detection means does not satisfy a predetermined condition, it is supplied to the internal combustion engine. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the amount of fuel to be reduced is reduced. An EGR device that recirculates part of the exhaust gas to the intake system of the internal combustion engine, and when the filter is not regenerated because the operating condition detected by the operating condition detection means does not satisfy a predetermined condition The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the EGR gas amount is reduced. The reducing agent supply means is a reducing agent addition nozzle for adding a reducing agent to an exhaust passage of the internal combustion engine, and the filter regeneration means is a main injection unit that injects fuel for engine output to the internal combustion engine. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the sub-injection is to inject fuel again at a time when the engine output is not reached. The exhaust purification device for an internal combustion engine according to claim 1, wherein the nitrogen oxide absorbent is carried on the filter. The exhaust purification device for an internal combustion engine according to claim 1, wherein the filter is installed upstream of the nitrogen oxide absorbent in the exhaust passage. When the internal combustion engine is operated at a low rotation and a low load and the internal combustion engine is in a warm state, the EGR gas amount is increased more than usual, and when the internal combustion engine is in a cold state Is characterized in that the temperature of the filter or the nitrogen oxide absorbent is increased by performing sub-injection for injecting fuel again at a time when the engine output does not become the engine output after main injection for injecting fuel for engine output to the internal combustion engine. The exhaust emission control device for an internal combustion engine according to claim 1.

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