JP2003065042A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of increasing opportunities to carry out the control for regeneration of an NOx catalyst poisoned by sulfur and also suppressing the deterioration of the catalyst caused by sulfur poisoning. SOLUTION: This exhaust emission control device is provided with an NOx absorbent which absorbs NOx in an exhaust gas when the air/fuel ratio of the inflowing exhaust gas is lean and releases the absorbed NOx when the above air/fuel ratio is theoretical or rich, and a control means for carrying out the temperature elevation control of the NOx absorbent and the control of regenerating the catalyst poisoned by sulfur. Since the control means releases oxygen (O2 ) stored in the NOx absorbent by lowering the air/fuel ratio in the exhaust gas when the temperature elevation control is carried out before the start of regeneration control of the poisoned NOx absorbent, the delay thereof is eliminated. The NOx absorbent may be carried on a filter capable of temporarily capturing particulates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly to an exhaust gas purification device capable of recovering sulfur poisoning of a NOx absorbent in a short time.

[0002]

2. Description of the Related Art In an internal combustion engine mounted on an automobile or the like, particularly a diesel engine or a lean burn gasoline engine capable of burning an air-fuel mixture in an oxygen excess state (so-called lean air-fuel mixture), A technique for purifying nitrogen oxides (NOx) contained in exhaust gas is desired.

In response to such demands, a technique for arranging a NOx absorbent in the exhaust system of an internal combustion engine has been proposed. As one of the NOx absorbents, it absorbs nitrogen oxides (NOx) in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and absorbs when the oxygen concentration of the inflowing exhaust gas is low and a reducing agent is present. An occlusion reduction type NOx catalyst is known that reduces nitrogen oxide (NOx) to nitrogen (N ₂ ) while releasing it.

When the NOx storage reduction catalyst is arranged in the exhaust system of the internal combustion engine, nitrogen oxide (NOx) in the exhaust gas is generated when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high.
Is absorbed by the NOx storage reduction catalyst, and when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst becomes low, the nitrogen oxide (NOx) absorbed by the NOx storage reduction catalyst is released and nitrogen ( N ₂ ).

By the way, the NOx storage reduction catalyst is a sulfur oxide (S) produced by combustion of sulfur contained in fuel.
Ox) is also absorbed by the same mechanism as NOx. Since this sulfur oxide (SOx) is not released during normal release and reduction of nitrogen oxide (NOx), when its accumulation exceeds a predetermined amount, a saturated state is brought about and the NOx catalyst becomes unable to absorb NOx. This is called sulfur poisoning (SOx poisoning),
Since the NOx purification rate decreases, it is necessary to perform a poisoning recovery process for recovering the NOx catalyst from SOx poisoning at an appropriate time. In this poisoning recovery process, the NOx catalyst is heated to a high temperature (for example, 6
The temperature is set to about 00 to 650 ° C.) and the exhaust gas having a reduced oxygen concentration is passed through the NOx catalyst.

However, since the exhaust gas during lean burn operation is lower than the above-mentioned temperature, it is difficult to raise the bed temperature of the NOx catalyst to a temperature required for recovery of sulfur poisoning under normal operating conditions. In such a case, by adding fuel to the exhaust passage, the temperature of the catalyst can be raised and the oxygen concentration of the exhaust can be lowered.

As a method for raising the temperature of the NOx catalyst, an exhaust gas purifying apparatus for an internal combustion engine is proposed in Japanese Patent No. 2845056. In the exhaust gas purification device for an internal combustion engine described in this publication, the amount of the reducing agent consumed by reacting with oxygen in the exhaust gas in the NOx storage reduction catalyst and the nitrogen oxides absorbed in the NOx storage reduction catalyst ( By determining the addition amount of the reducing agent in consideration of the amount of the reducing agent necessary for reducing NOx), it is possible to prevent the excessive supply or the insufficient supply of the reducing agent, and to reduce the reducing agent or the nitrogen oxide ( It is intended to suppress the deterioration of exhaust emission due to the release of (NOx) into the atmosphere.

[0008]

As described above, the sulfur poisoning recovery is executed by lowering the oxygen concentration in the exhaust gas. However, if the reducing agent is added during high load operation of the internal combustion engine, the reducing agent will occlude and reduce. The NOx catalyst burns and the temperature of the NOx storage reduction catalyst rises, which may cause thermal deterioration of the NOx storage reduction catalyst. Therefore, it is preferable to perform the sulfur poisoning recovery in the light load region.

On the other hand, since the NOx storage reduction catalyst has a so-called O ₂ storage capacity that absorbs oxygen (O ₂ ) in the exhaust gas together with NOx and accumulates the NOx when it absorbs NOx, the NOx storage reduction catalyst cannot discharge the exhaust gas. When operating lean, it absorbs NOx and stores oxygen (O ₂ ).

Therefore, in order to execute the sulfur poisoning regeneration, NOx
Even if the temperature of the catalyst is raised to a predetermined temperature and the air-fuel ratio of the exhaust flowing into the NOx catalyst is adjusted to be rich, the sulfur poisoning recovery does not start immediately. That is, as shown in FIG. 8, when rich exhaust gas flows into the NOx catalyst, oxygen (O ₂ ) stored in the NOx catalyst is released into the exhaust gas for a while, so that the air-fuel ratio of the exhaust gas immediately increases. Does not become rich and remains near the stoichiometric air-fuel ratio, and shifts to rich after such release of oxygen (O ₂ ) is completed. Along with this, the release of sulfur oxide (SOx) in the NOx catalyst is not started until it becomes rich.

Therefore, when the temperature rise control is started in a light load state, and after the temperature rise of the NOx storage reduction catalyst, a rich spike for adding fuel to the exhaust passage to make the air-fuel ratio of the exhaust rich is performed, It suffices if the sulfur release time, that is, the execution time of sulfur poisoning regeneration is sufficiently long, but depending on the operating conditions, the case where the execution time of sulfur poisoning regeneration is short, such as the light load state does not last long, may be repeated. . In such a case, sulfur poisoning regeneration of the NOx catalyst becomes impossible due to the above-mentioned O ₂ storage, NOx cannot be absorbed, and the exhaust gas may not be sufficiently purified.

The present invention has been made to solve the above problems, and it is possible to increase the chances of executing the sulfur poisoning regeneration control of the NOx catalyst and suppress the sulfur poisoning deterioration of the NOx catalyst. The purpose is to provide.

[0013]

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means. That is, when the air-fuel ratio of the inflowing exhaust gas is lean, the NOx in the exhaust gas is absorbed, and when the air-fuel ratio of the inflowing exhaust gas becomes the theoretical air-fuel ratio or rich, the absorbed NOx is released N.
An Ox absorbent, and sulfur poisoning recovery control means for executing temperature rise control and sulfur poisoning recovery control of the NOx absorbent,
The sulfur poisoning recovery control means reduces the air-fuel ratio of the exhaust gas to release the oxygen stored in the NOx absorbent when executing the temperature increase control before starting the sulfur poisoning recovery control of the NOx absorbent. It is characterized by

The most important feature of the present invention is that when the temperature rising control before the start of the sulfur poisoning recovery control of the NOx absorbent is executed, the air-fuel ratio is reduced and the oxygen (O 2) stored in the NOx absorbent in advance is reduced. By releasing ₂ ), the time required for sulfur release during sulfur poisoning recovery control is shortened. Here, the execution of the temperature increase control includes during the temperature increase control and immediately after the temperature increase control is completed before the sulfur poisoning recovery control is started.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, sulfur poisoning recovery control for releasing the sulfur oxide (SOx) absorbed and accumulated in the NOx absorbent is carried out. , N by making the exhaust rich
In order to avoid an excessive temperature rise of the Ox absorbent, it is preferable to perform it in the light load region of the internal combustion engine.

Further, in the present invention, the exhaust gas purification apparatus for an internal combustion engine may include a filter capable of temporarily trapping fine particles in exhaust gas, and the NOx absorbent may be carried by this filter.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the air-fuel ratio of the exhaust gas is set to the stoichiometric air-fuel ratio or rich by a method such as adding fuel to the exhaust system while the temperature of the NOx absorbent is rising. The temperature raising control may be performed, for example, by delaying the fuel injection timing in the combustion chamber of the internal combustion engine until after compression top dead center, by performing auxiliary injection during the expansion stroke or exhaust stroke in addition to the main injection, or by exhausting It is implemented by injecting fuel into the road. By these controls, the exhaust temperature rises, and the temperature of the NOx absorbent or the filter carrying the NOx absorbent can be raised.

In order to reduce the air-fuel ratio of the exhaust gas, a method of injecting fuel into the exhaust passage, in particular, a so-called rich spike control for reducing the oxygen concentration in the exhaust gas in a short cycle in a spike-like (short time) manner is executed. can do. This rich spike can be executed, for example, a plurality of times during the temperature increase control.

Next, when the air-fuel ratio is made rich when it becomes possible to recover from sulfur poisoning, the release of sulfur from the NOx absorbent is immediately started. This can be done by adding internal combustion engine fuel to the exhaust system.

In this exhaust gas purification apparatus for an internal combustion engine, although air is added to the exhaust system for sulfur poisoning recovery control, the air-fuel ratio is rich due to oxygen (O ₂ ) released from the NOx absorbent. Most of the time that is not reached can be eliminated. Therefore, it is possible to recover the sulfur poisoning of the NOx absorbent in a short time. In addition, since recovery can be performed in a short time, the chances of implementing sulfur poisoning recovery control will increase significantly. Therefore, by reducing the degree of sulfur poisoning, the sulfur poisoning deterioration of the NOx absorbent can be suppressed.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below 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.

FIG. 1 is a diagram showing a schematic configuration of an engine 1 and an intake / exhaust system for the engine 1 to which an exhaust purification system according to the present embodiment is applied.

The engine 1 shown in FIG. 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

The engine 1 has a fuel injection valve 3 for injecting fuel directly into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulator (common rail) 4 that accumulates fuel to a predetermined pressure. A common rail pressure sensor 4a that outputs an electric signal corresponding to the pressure of the fuel in the common rail 4 is attached to the common rail 4.

The common rail 4 communicates with a fuel pump 6 via 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. A pump pulley 6a attached to the input shaft of the fuel pump 6 is attached to the output shaft (crankshaft) of the engine 1. The crank pulley 1a is connected to the crank pulley 1a via a belt 7.

In the fuel injection system thus constructed, when the rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 is transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure according to the rotating torque.

The fuel discharged from the fuel pump 6 is
It is supplied to the common rail 4 through the fuel supply pipe 5, accumulated in the common rail 4 up to a predetermined pressure, and distributed to the fuel injection valve 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.

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 through an intake port (not shown). There is.

The intake branch pipe 8 is connected to the intake pipe 9,
The intake pipe 9 is connected to the 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 to the intake pipe 9 downstream of the air cleaner box 10 and a temperature of the intake air flowing through the intake pipe 9 are provided. The intake air temperature sensor 12 that outputs the electric signal is attached.

An intake throttle valve 13 for adjusting the flow rate of 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 configured by a step motor or the like to open and close the intake throttle valve 13.

The intake pipe 9 located 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 which operates by using heat energy of exhaust gas as a drive source. The
An intercooler 16 for cooling the intake air that has become hot due to being compressed in the compressor housing 15a is provided in the intake pipe 9 downstream of the compressor housing 15a.
Is provided.

In the intake system configured as described above, the intake air flowing into the air cleaner box 10 is cleaned by the air cleaner (not shown) in the air cleaner box 10 to remove dust and dirt from the intake air, and then the intake pipe 9 Through the compressor housing 15a.

The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel installed in the compressor housing 15a. The intake air that has been compressed in the compressor housing 15a and has a high temperature is cooled by the intercooler 16,
If necessary, the flow rate is adjusted by the intake throttle valve 13 and flows into the intake branch pipe 8. The intake air flowing into the intake branch pipe 8 is
It is distributed to the combustion chamber of each cylinder 2 via each branch pipe,
The fuel injected from the fuel injection valve 3 is used as an ignition source for combustion.

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 through an exhaust port (not shown).

The exhaust branch pipe 18 serves as the centrifugal supercharger 15.
Is connected to the turbine housing 15b. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected downstream to a muffler (not shown).

An occlusion reduction type N is provided in the middle of the exhaust pipe 19.
A particulate filter carrying an Ox catalyst (hereinafter,
Simply called a filter. ) 20 are provided. An exhaust temperature sensor 24 that outputs an electric 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.

Exhaust pipe 1 downstream of the above-mentioned filter 20
An exhaust throttle valve 21 that adjusts the flow rate of the exhaust gas flowing through the exhaust pipe 19 is provided in the valve 9. The exhaust throttle valve 21 is provided with an exhaust throttle actuator 22 configured by a step motor or the like for opening and closing the exhaust throttle valve 21.

In the exhaust system configured as described above, the air-fuel mixture (burnt gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then from the exhaust branch pipe 18. Turbine housing 15b of centrifugal supercharger 15
Flow into. The exhaust gas flowing into the turbine housing 15b uses the thermal energy of the exhaust gas to rotate the turbine wheel rotatably supported in the turbine housing 15b. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.

The exhaust 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. PM is collected by the filter 20,
The exhaust gas from which harmful gas components have been removed or purified is discharged into the atmosphere via the muffler after the flow rate is adjusted by the exhaust throttle valve 21 as necessary.

The exhaust branch pipe 18 and the intake branch pipe 8 are exhaust gas recirculation passages (hereinafter referred to as EGR passages) for recirculating a part of the exhaust gas flowing in the exhaust branch pipe 18 to the intake branch pipe 8. )
25 are communicated with each other. In the middle of the EGR passage 25, an exhaust valve (hereinafter, referred to as EG, which is composed of a solenoid valve or the like, flows through the EGR passage 25 according to the magnitude of the applied power.
R gas. ) Flow rate adjustment valve (hereinafter,
Use EGR valve. ) 26 are provided.

In the middle of the EGR passage 25, the EGR valve 26
Further upstream, the EGR flowing in the EGR passage 25
An EGR cooler 27 that cools the gas is provided. A cooling water passage (not shown) is provided in the EGR cooler 27, and a part of the cooling water for cooling the engine 1 circulates.

In the exhaust gas recirculation mechanism thus constructed, 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 is part of the EGR passage 25. To the intake branch pipe 8 via the EGR cooler 27.

At this 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.

The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 through the EGR passage 25 is introduced into the combustion chamber of each cylinder 2 while being mixed with the fresh air flowing from the upstream side of the intake branch pipe 8. Get burned.

Here, the EGR gas contains an inert gas component such as water (H ₂ O) and carbon dioxide (CO ₂ ) that does not burn by itself and has a high heat capacity. Therefore, when EGR gas is contained in the air-fuel mixture, the combustion temperature of the air-fuel mixture is lowered, and thus nitrogen oxide (NOx)
Is suppressed.

Further, when the EGR gas is cooled in the EGR cooler 27, the temperature of the EGR gas itself is lowered and the volume of the EGR gas is reduced, so that when the EGR gas is supplied into the combustion chamber, the EGR gas is reduced. The ambient temperature of 1 is not unnecessarily increased, and the amount of fresh air (volume of fresh air) supplied into the combustion chamber is not unnecessarily reduced.

Next, the filter 20 according to this embodiment will be described.

FIG. 2 is a sectional view of the filter 20. FIG. 2A is a view showing a cross section in the lateral direction of the filter 20. FIG. 2B is a diagram showing a vertical cross section of the filter 20.

As shown in FIGS. 2A and 2B, the filter 20 is of 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 are composed of 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. The hatched portion in FIG. 2A indicates the plug 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, in the exhaust inflow passage 50 and the exhaust outflow passage 51, each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51, and each exhaust outflow passage 51 includes four exhaust inflow passages 50.
It is arranged to be surrounded by.

The filter 20 is made of, for example, a porous material such as cordierite, so that the exhaust gas flowing into the exhaust gas inflow passage 50 flows in the surrounding partition wall 54 as shown by the arrow in FIG. 2B. It flows out into the adjacent exhaust outflow passage 51.

In the embodiment according to the present invention, each exhaust inflow passage 5
0 and the peripheral wall surface of each exhaust outflow passage 51, that is, each partition wall 54
A carrier layer made of, for example, alumina is formed on both side surfaces of the above and on the inner wall surface of the pores in the partition wall 54, and the occlusion reduction type NOx catalyst is carried on this carrier.

Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to this embodiment will be described.

The filter 20 uses, for example, alumina as a carrier, and potassium (K) and sodium (N) are deposited on the carrier.
a), an alkali metal such as lithium (Li) or cesium (Cs), an alkaline earth such as barium (Ba) or calcium (Ca), and a rare earth such as lanthanum (La) or yttrium (Y). And at least one of them is carried and a noble metal such as platinum (Pt). In the present embodiment, barium (Ba) and platinum (Pt) are supported on a carrier made of alumina, and ceria (Ce) having an O ₂ storage capacity is supported on the carrier.
_A NOx storage reduction catalyst formed by adding ₂ O ₃ ) is used.

Such a NOx catalyst absorbs nitrogen oxides (NOx) in the exhaust gas when the oxygen concentration of the exhaust gas flowing into the NOx catalyst is high.

On the other hand, the NOx catalyst releases the nitrogen oxide (NOx) absorbed 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) exists in the exhaust gas, the NOx catalyst converts the nitrogen oxide (NOx) released from the NOx catalyst into nitrogen (N). It can be reduced to ₂ ).

By the way, when the engine 1 is in the lean burn operation, the air-fuel ratio of the exhaust gas discharged from the engine 1 becomes a lean atmosphere and the oxygen concentration of the exhaust gas becomes high.
Nitrogen oxides (NOx) contained in the exhaust gas will be absorbed by the NOx catalyst, but if the lean burn operation of the engine 1 is continued for a long period of time, the NOx absorption capacity of the NOx catalyst will be saturated, and Nitrogen oxides (NOx) remain in the exhaust gas without being removed by the NOx catalyst.

In particular, in the engine 1 which is a diesel engine, the lean air-fuel ratio mixture is burned in most operating regions, and the air-fuel ratio of the exhaust gas becomes lean air-fuel ratio in most operating regions accordingly. NOx of NOx catalyst
Absorption capacity is easily saturated.

Therefore, when the engine 1 is in the lean burn operation, the concentration of oxygen in the exhaust flowing into the NOx catalyst is reduced and the concentration of the reducing agent is increased before the NOx absorption capacity of the NOx catalyst is saturated, and the NOx concentration is increased. It is necessary to release and reduce nitrogen oxides (NOx) absorbed by the catalyst.

As a method of lowering the oxygen concentration in this way, fuel addition in the exhaust gas, low temperature combustion as described above, and the cylinder 2
A method of changing the fuel injection timing into the inside or the number of times may be considered, but in the present embodiment, a reducing agent that adds fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust pipe 19 upstream of the filter 20. A supply mechanism is provided, and by adding fuel from the reducing agent supply mechanism into the exhaust gas, the oxygen concentration of the exhaust gas flowing into the filter 20 is reduced and the concentration of the reducing agent is increased.

As shown in FIG. 1, the reducing agent supply mechanism is installed so that its injection hole faces the inside of the exhaust branch pipe 18, and is opened by a signal from the ECU 35 to inject fuel. 28, a reducing agent supply path 29 for guiding the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and a distribution of the fuel in the reducing agent supply path 29 provided in the reducing agent supply path 29. And a shutoff valve 31 for shutting off.

In such a reducing agent supply mechanism, the high-pressure fuel discharged from the fuel pump 6 is applied to the reducing agent injection valve 28 via the reducing agent supply passage 29. And ECU3
The reducing agent injection valve 28 is opened by a signal from 5 and fuel as a reducing agent is injected into the exhaust branch pipe 18.

The reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust branch pipe 18.

The exhaust gas having a low oxygen concentration formed in this way flows into the filter 20 and releases nitrogen oxides (NOx) absorbed by the filter 20 while releasing nitrogen (N ₂ ).
Will be reduced to.

After that, 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.

In the present embodiment, the fuel is injected into the exhaust gas to add the fuel, but instead of this, the amount of recirculated EGR gas is increased to increase the amount of soot generated. After reaching the maximum, low temperature combustion may be performed to further increase the EGR gas amount, and fuel may be injected from the fuel injection valve 3 in the expansion stroke, exhaust stroke, etc. of the engine 1.

The engine 1 configured as described above is provided with an electronic control unit (ECU: Electronic Control Unit) 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.

The ECU 35 includes the common rail pressure sensor 4
a, an air flow meter 11, an intake air temperature sensor 12, an intake pipe pressure sensor 17, an exhaust gas temperature sensor 24, a crank position sensor 33, a water temperature sensor 34, an accelerator opening sensor 36, and other various sensors are connected via electrical wiring. Output signals of the various sensors are input to the ECU 35.

On the other hand, the ECU 35 has a fuel injection valve 3, an intake throttle actuator 14, an exhaust throttle actuator 22, a reducing agent injection valve 28, an EGR valve 26, and a shutoff valve 31.
Etc. are connected via electrical wiring, and the above-mentioned parts are connected to the ECU.
35 can be controlled.

Here, the ECU 35, as shown in FIG. 3, is connected to each other by a bidirectional bus 350, C,
The input port 356 includes a PU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357.
And an A / D converter (A / D) 355 connected to.

The input port 356 inputs the output signals of a sensor that outputs a digital signal format signal such as the crank position sensor 33, and outputs those output signals to C
It is transmitted to the PU 351 and the RAM 353.

The input port 356 is used for the common rail pressure sensor 4a, the air flow meter 11, and the intake air temperature sensor 1.
2, such as the intake pipe pressure sensor 17, the exhaust gas temperature sensor 24, the water temperature sensor 34, the accelerator opening sensor 36, etc., which are input through the A / D 355 of a sensor that outputs a signal in an analog signal format, and output signals thereof CPU351 and RA
Send to M353.

The output port 357 is connected to the fuel injection valve 3,
Intake throttle actuator 14, exhaust throttle actuator 22, EGR valve 26, reducing agent injection valve 28, shutoff valve 3
1 and the like via electric wiring, and outputs control signals output from the CPU 351 to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 2 described above.
2, to the EGR valve 26, the reducing agent injection valve 28, or the shutoff valve 31.

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 26, a NOx purification control routine for adding a reducing agent to the filter 20 to release the absorbed NOx, a poisoning elimination control routine for eliminating SOx poisoning of the filter 20, and a trap for the filter 20. An application program such as a PM combustion control routine for burning and removing the collected PM is stored.

The ROM 352 stores various control maps in addition to the above application programs. The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the engine 1 and the basic fuel injection amount (basic fuel injection time), and the fuel showing the relationship between the operating state of the engine 1 and the basic fuel injection timing. Injection timing control map,
An intake throttle valve opening control map showing the relationship between the operating state of the engine 1 and the target opening degree of the intake throttle valve 13, and an exhaust throttle valve opening map showing the relationship between the operating state of the engine 1 and the target opening degree of the exhaust throttle valve 21. Control map, engine 1 operating status and EGR
An EGR valve opening control map showing the relationship with the target opening of the valve 26, a reducing agent addition control map showing the relationship between the operating state of the engine 1 and the target addition of the reducing agent (or the target air-fuel ratio of the exhaust gas), It is a reducing agent injection valve control map and the like showing the relationship between the target addition amount of the reducing agent and the valve opening time of the reducing agent injection valve 28.

The RAM 353 stores the output signal from each sensor, the calculation result 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 each time the crank position sensor 33 outputs a pulse signal.

The backup RAM 354 is a non-volatile memory capable of storing data even after the operation of the engine 1 is stopped.

The CPU 351 operates according to the application program stored in the ROM 352 to control the fuel injection valve, the intake throttle control, the exhaust throttle control, and the E throttle control.
GR control, NOx purification control, poisoning elimination control, PM combustion control, etc. are executed.

For example, in the NOx purification control, the CPU 35
1 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-like (short time) manner in a relatively short cycle.

In the rich spike control, the CPU 351
Determines whether the rich spike control execution condition is satisfied every predetermined period. As the 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 elimination control is not executed, Examples of such conditions are as follows.

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 so that the reducing agent injection valve 28 injects fuel as the reducing agent in a spike manner to temporarily change the air-fuel ratio of the exhaust gas flowing into the filter 20 to a predetermined target rich air-fuel ratio. And

Specifically, the CPU 351 has the RAM 35.
Engine speed, accelerator opening sensor 3 stored in 3
6 output signal (accelerator opening), air flow meter 11
Output signal value (intake air amount), output signal of the air-fuel ratio sensor, fuel injection amount, and the like.

The CPU 351 accesses the reducing agent addition amount control map of the ROM 352 by using the engine speed, the accelerator opening, the intake air amount and the fuel injection amount as parameters, and sets the exhaust air-fuel ratio to a preset target air-fuel ratio. The amount of addition of the reducing agent (target amount of addition) required to obtain the fuel ratio is calculated.

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 reduces the reducing agent required to inject the target addition amount of the reducing agent from the reducing agent injection valve 28. The valve opening time (target valve opening time) of the injection valve 28 is calculated.

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.

The CPU 351 closes the reducing agent injection valve 28 when the target opening time elapses from the time when the reducing agent injection valve 28 is opened.

When the reducing agent injection valve 28 is opened for the target opening time in this way, the target addition amount of fuel is injected from the reducing agent injection valve 28 into the exhaust branch pipe 18. Then, the reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust gas that has flowed from the upstream side of the exhaust branch pipe 18 to form an air-fuel mixture having a target air-fuel ratio, and then flows into the filter 20.

As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 is such that the oxygen concentration changes in a relatively short cycle, so that the filter 20 absorbs and releases / reduces nitrogen oxides (NOx). And will be repeated alternately in a short cycle.

Next, in the poisoning elimination control, the CPU 351
Performs the poisoning elimination processing to eliminate the poisoning caused by the oxide of the filter 20.

Here, sulfur (S) is used as the fuel for the engine 1.
When such fuel is burned in the engine 1, sulfur oxides (SOx) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) are generated.

Sulfur oxide (SOx) flows into the filter 20 together with the exhaust gas and is absorbed by the filter 20 by the same mechanism as nitrogen oxide (NOx).

Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 20 is high, the sulfur oxides (S) such as sulfur dioxide (SO ₂ ) and sulfur trioxide (SO ₃ ) in the inflowing exhaust gas are included.
Ox) is oxidized on the surface of platinum (Pt) and absorbed by the filter 20 in the form of sulfate ions (SO ₄ ²⁻ ). Furthermore,
The sulfate ions (SO ₄ ^2- ) absorbed by the filter 20 are
Sulfate (BaS) combined with barium oxide (BaO)
O ₄ ) is formed.

By the way, the sulfate (BaSO ₄ ) is more stable than barium nitrate (Ba (NO ₃ ) ₂ ) and hard to decompose, and is decomposed even when the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low. Instead, they remain in the filter 20.

Sulfate in the filter 20 (BaS
As the amount of O ₄ ) increases, the nitrogen oxides (N
Barium oxide (B) which can participate in the absorption of Ox)
Since the amount of aO) decreases, so-called sulfur poisoning occurs in which the NOx absorption capacity of the filter 20 decreases.

A method for eliminating sulfur poisoning of the filter 20 and
The ambient temperature of the filter 20 is about 600 to
While raising the temperature to a high temperature range of 650 ° C, the filter 2
By reducing the oxygen concentration of the exhaust gas flowing into
Barium sulfate (BaS) absorbed in the filter 20
O_Four) SO₃ ^-And SO_Four ^-Pyrolyzes into SO and then SO₃ ^-And S
O_Four ^-Hydrocarbons (HC) and carbon monoxide (CO) in the exhaust
Gaseous SO by reacting with₂ ^-Exemplifies how to reduce to
be able to.

Therefore, in the poisoning elimination process according to the present embodiment, the CPU 351 first executes the catalyst temperature raising control for raising the bed temperature of the filter 20, and then lowers the oxygen concentration of the exhaust gas flowing into the filter 20. I did it.

In the catalyst temperature raising control, the CPU 351 may, for example, inject fuel secondarily from the fuel injection valve 3 and add fuel from the reducing agent injection valve 28 to the exhaust during the expansion stroke of each cylinder 2. Alternatively, those unburned fuel components may be oxidized in the filter 20, and the heat generated during the oxidation may raise the bed temperature of the filter 20.

However, if the temperature of the filter 20 rises excessively,
Since the heat deterioration of the filter 20 may be induced, it is preferable that the secondary injection fuel amount and the additional fuel amount be feedback-controlled based on the output signal value of the exhaust temperature sensor 24.

When the bed temperature of the filter 20 rises to a high temperature range of about 600 ° C. to 650 ° C. by the catalyst temperature raising process as described above, the CPU 351 causes the reducing agent injection to reduce the oxygen concentration of the exhaust gas flowing into the filter 20. Fuel is injected from the valve 28.

When excessive fuel is injected from the reducing agent injection valve 28, those fuels burn rapidly in the filter 20 and the filter 20 overheats, or excessive fuel injected from the reducing agent injection valve 28 is injected. Since the filter 20 may be unnecessarily cooled by the fuel, the CPU 351 controls the reducing agent injection valve 28 based on the output signal of the air-fuel ratio sensor (not shown).
It is preferable to feedback control the fuel injection amount from.

When the poisoning elimination processing is executed in this way,
When the bed temperature of the filter 20 is high, the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low. Then filter 2
Barium sulphate (BaSO ₄ ) absorbed at 0 is SO ₃
^- and SO ₄ ^- are thermally decomposed, these SO ₃ ^- and SO ₄ ^- so is reduced by reacting with hydrocarbons (HC) and carbon monoxide in the exhaust gas (CO), the filter 20 sulfur poisoning Will be resolved.

On the other hand, as described above, the filter 20 has
It contains ceria (Ce ₂ O ₃ ) having an O ₂ storage capacity, which releases active oxygen for oxidizing and purifying particulate matter PM (Particulate Matter) contained in the exhaust gas of the engine 1. . However, when the oxygen concentration of the exhaust gas decreases, the stored oxygen (O ₂ ) begins to be released from the above-mentioned ceria (Ce ₂ O ₃ ), etc. Therefore, while the release continues, the air-fuel ratio of the exhaust gas becomes Even if fuel is added to the exhaust system so that it is on the side, the air-fuel ratio actually does not easily become rich.

As shown in FIG. 4, this is a control in which the exhaust gas is suddenly made rich from a lean operating state (fuel addition, etc.).
Even if is performed, the air-fuel ratio stays near the stoichiometric air-fuel ratio for several tens of seconds, and does not immediately shift to rich. Therefore, not only may the sulfur poisoning of the NOx catalyst not be sufficiently recovered, but in FIG. 4, the bed temperature of the filter 20 starts to drop from 600 ° C. when the air-fuel ratio starts to shift to rich. Furthermore, there is a possibility that the sulfur poisoning recovery may not be sufficient.

In the sulfur poisoning recovery control according to the present embodiment, the air-fuel ratio of the exhaust gas is quickly changed to rich by executing the following control before executing this control.

In the sulfur poisoning recovery control illustrated in FIG. 5, rich spike is performed during the catalyst temperature raising control for raising the bed temperature of the filter 20. The rich spike is executed several times, but since the air-fuel ratio is lowered during the catalyst temperature increase control by this rich spike, the oxygen (O ₂₎ stored in the NOx catalyst while the exhaust gas is in the lean air-fuel ratio with excess air is used. ) Is released. Therefore, during the sulfur poisoning recovery control, almost no oxygen (O ₂ ) is released. Here, the rich spike interval can be executed every few seconds, for example, every 2.5 seconds, but the execution mode of the rich spike is not particularly limited.

In the example shown in FIG. 5, the bed temperature of the NOx catalyst is kept below 600 ° C. by executing the rich spike. Further, the output of the A / F sensor also quickly shifts to the rich side by the addition of fuel to the exhaust system, and the O ₂ storage state is almost eliminated.

FIG. 6 shows a case in which a predetermined amount of ceria (Ce ₂ O ₃ ) is contained in the catalyst carried on the filter, and the rich spike is executed even when the filter is in a lean atmosphere. This shows that the O ₂ storage time is shortened.

Here, depending on the amount of ceria (Ce ₂ O ₃ ) contained in 1 liter of the catalyst, Ce 20 g / L (20
Examples of filters containing g) and Ce6g / L (containing 6g) are shown.

The horizontal axis represents the duration of the state where the air-fuel ratio of the exhaust gas is lean, and the vertical axis represents the O ₂ storage time, that is, oxygen (O ₂ ) continued from the filter when the oxygen concentration of the exhaust gas decreased. The time is shown for a specific release.

Further, in the figure, a square (□) shows a change in O ₂ storage time with the passage of time of the Ce 20 g / L filter, and a triangle (△) shows a change in the case of the Ce 6 g / L filter as well. ing. Also, the thin wire is Ce 20 g / L
, The thick line represents the average of the transition of the O ₂ storage time of each of the Ce 6 g / L filters.

According to the example shown in FIG. 6, by performing the rich spike once every 2.5 seconds, the Ce 20 g / L filter can reduce the O ₂ storage time even when the excess air lean time continues for 60 seconds. It is reduced to 10 seconds or less. Similarly, in the Ce6g / L filter, the O ₂ storage time is reduced to about 5 seconds.

Here, the case where the rich spike is executed at a predetermined interval (2.5 seconds) is shown, but the execution interval may be lengthened to increase the amount of fuel added in one rich spike.

It should be noted that the rich spike is executed several times as described above during the temperature rise control, or the deceleration of the vehicle is started at the final stage of the temperature rise control or immediately after the end of the temperature rise control. It is also possible to intensively increase the addition amount when executing.

In this way, when the rich spike is executed during the temperature rise control or immediately after that, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst quickly shifts to the rich side by the sulfur poisoning control. That is, the CPU 351 uses the filter 2
Fuel is injected from the reducing agent injection valve 28 in order to reduce the oxygen concentration of the exhaust gas flowing into 0, but the sulfur poisoning recovery is started without delay from the injection of this fuel.

FIG. 7 shows an example in which the rich spike is executed during the temperature raising control. As shown in FIG.
The air-fuel ratio (air-fuel ratio of the exhaust gas flowing into the filter 20) indicated by the / F sensor output temporarily changes to the rich side with an interval, and the temperature rise control is performed by performing such rich spikes a plurality of times. The air-fuel ratio is falling inside.
In this state, oxygen (O ₂ ) is gradually released from the NOx catalyst, so that the change in the air-fuel ratio does not become stagnant during the sulfur poisoning recovery control due to the O ₂ storage effect, as shown in B. When the vehicle speed decreases and the sulfur recovery control is started, the air-fuel ratio becomes rich immediately. Along with this, as shown by C, the release of sulfur from the NOx catalyst is started quickly.

Next, as a comparative example, a case of the conventional method is shown in FIG. Without rich spikes like this,
When the normal temperature increase control is shifted to the sulfur poisoning recovery control, the air-fuel ratio remains near the stoichiometric air-fuel ratio for several tens of seconds and then shifts to rich, so the timing of sulfur release is delayed. Therefore, in such a conventional method,
It is highly possible that the sulfur poisoning recovery cannot be carried out during a short time such as waiting for a traffic light in the town, for example, a time of about 30 seconds to 1 minute.

However, according to the control of the present embodiment, the sulfur poisoning recovery control is executed and the sulfur can be released even in a short time of about 1 minute. In particular, when waiting for a signal several times, the sulfur poisoning recovery can be performed little by little, so that the opportunity to eliminate the accumulation of sulfur oxides on the NOx catalyst becomes extremely large. Along with this
The sulfur poisoning deterioration of the Ox catalyst can be suppressed.

Next, the flow of temperature raising control and sulfur poisoning recovery control according to this embodiment will be described.

FIG. 9 is a flow chart showing the flow of temperature raising control according to this embodiment.

In step S101, it is determined whether or not the sulfur poisoning recovery control needs to be performed. The determination condition can be determined based on the amount of fuel added, an output signal from a NOx sensor (not shown), the traveling distance of the vehicle, and the like.
Here, since the NOx storage reduction catalyst carried on the filter 20 is poisoned by the sulfur component in the fuel, the addition amount of the fuel is stored in the RAM 353, and when the addition amount of the fuel reaches the predetermined amount, the sulfur is stored. It may be used as a start condition for poisoning recovery control. Further, when sulfur poisoning progresses, the amount of NOx absorbed by the NOx storage reduction catalyst decreases, and the amount of NOx flowing downstream of the filter 20 increases. Therefore, a NOx sensor (not shown) may be provided downstream of the filter 20, the output signal thereof may be monitored, and the condition for starting the sulfur poisoning recovery control may be set when the NOx flow amount exceeds a predetermined amount. Furthermore, when the vehicle travel distance becomes equal to or greater than a predetermined value, it is necessary to recover from sulfur poisoning, and this time may be set as the start condition for the sulfur poisoning recovery control.

When the affirmative judgment is made in step S101, the routine proceeds to step S102, while when the negative judgment is made, this routine is ended.

In step S102, it is determined whether or not the temperature raising control of the filter 20 is started. The temperature rise control is started when the internal combustion engine is in the light load region.

If an affirmative decision is made in step S102, the operation proceeds to step S103.

If the load is not in the light load area, step S102
When the negative determination is made in step S <b> 103, the process proceeds to step S <b> 103 when the light load operation is performed.

In step S103, the addition of fuel to the exhaust system and the rich spike are executed together to raise the temperature of the filter 20.

Next, in step S104, the filter 20
It is determined whether or not the bed temperature of is above 600 ° C. If this is 600 ° C. or higher, the process proceeds to step S105.

If the bed temperature of the filter 20 is lower than 600 ° C., the process returns to step S103 to continue the temperature raising control, and if the bed temperature of the filter 20 is 600 ° C. or higher, step S1.
Go to 05.

In step S105, it is determined whether the internal combustion engine is in the light load region.

If it is in the light load region, step S1
In 06, the sulfur poisoning recovery control is executed.

When the vehicle is not in the light load region, the process proceeds to step S106 when the operation is shifted to the light load operation thereafter.
Sulfur poisoning recovery control is performed.

As described above, in the exhaust emission control system for the internal combustion engine according to the present embodiment, the oxygen released from the NOx absorbent is added even though the fuel is added to the exhaust system for the sulfur poisoning recovery control. (O ₂ ) can almost eliminate the existence of the time when the air-fuel ratio does not reach rich. Therefore, it is possible to recover the sulfur poisoning of the NOx absorbent in a short time.

Further, since the sulfur poisoning recovery can be carried out in a short time, the opportunity for carrying out the sulfur poisoning recovery control will be greatly increased. Therefore, by reducing the degree of sulfur poisoning, the sulfur poisoning deterioration of the NOx absorbent can be suppressed.

[0132]

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, before the start of the sulfur poisoning regeneration control of the NOx catalyst, N
Since the oxygen (O ₂ ) stored in the Ox absorbent can be released, the sulfur poisoning recovery control delay due to the O ₂ storage is eliminated, and the sulfur poisoning recovery time is shortened. Therefore, the chance of executing sulfur poisoning recovery control increases,
It is possible to effectively avoid the state where NOx in the exhaust gas is not absorbed by the NOx catalyst, and to suppress the sulfur poisoning deterioration of the NOx catalyst.

[Brief description of 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. 2 is a diagram showing an outline of a particulate filter, and FIG. 2 (A) is a diagram showing a lateral cross section of the particulate filter. (B) is a figure which shows the longitudinal 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 the influence of O ₂ storage when the exhaust air-fuel ratio shifts from a lean state to a rich state in the sulfur poisoning recovery control.

FIG. 5 is a diagram showing a change in exhaust air-fuel ratio when rich spike is executed in advance before sulfur poisoning recovery control.

FIG. 6 is a diagram showing that the stored oxygen is released and the O ₂ storage time is shortened by performing a rich spike.

FIG. 7 is a diagram showing a change in air-fuel ratio and a timing of releasing sulfur when a rich spike is executed in advance during temperature increase control.

FIG. 8 is a diagram showing changes in the air-fuel ratio and the timing of sulfur release in the case of temperature increase control by a conventional method.

FIG. 9 is a flowchart showing a temperature increase control execution flow according to the embodiment of the present invention.

[Explanation 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 gas temperature sensor 25 ... EGR passage 26 ... EGR valve 27 ... EGR cooler 28 ... Reducing agent injection valve 29 ... Reductant supply path 31 ... Shut-off valve 33 ... Crank position sensor 34 ... Water temperature sensor 35 ... ECU 36 ... Accelerator opening sensor

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI Theme Coat (Reference) F01N 3/02 F01N 3/08 A 3/08 G 3/24 E 3/24 R 3/28 301C 3 / 28 301 3/36 C 3/36 F02D 41/04 355 F02D 41/04 355 43/00 301E 43/00 301 301K 301N 301T 45/00 314Z 45/00 314 B01D 53/36 103C 103B (72) Inventor's song Naofumi Tada 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Masaaki Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Daisuke Shibata Toyota City, Aichi Prefecture Toyota City No. 1 Toyota Motor Co., Ltd. (72) Inventor Shinobu Ishiyama No. 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Akihiko Negami 1 Toyota Town, Toyota-shi, Aichi F-term in Toyota Motor Corporation (reference) 3G084 AA01 AA03 AA04 BA05 BA08 BA09 BA13 BA15 BA19 BA20 BA24 DA27 DA28 DA31 DA37 EA11 EB01 EB22 FA02 FA05 FA07 FA11 FA12 FA20 FA27 FA33 FA38 3G090 AA03 BA01 CA01 CA04 CB25 DA01 DA09 DA10 DA12 DA15 DA18 DA19 DA20 EA05 EA06 EA07 3G091 AA02 AA10 AA11 AA12 AA18 AA28 AB06 AB13 BA00 BA04 BA11 BA14 BA33 CA13 EA18 EA07 EA15 EA01 CB17 DC01 DB01 DA01 DA01 DA02 DA04 DB04 DB04 EA30 EA31 EA33 EA38 FA12 FA13 FB10 FB11 FB12 FC04 FC05 GA06 GA20 GA24 GB01X GB02W GB03W GB04W GB04Y GB05W GB06W GB10X GB10Y GB16X GB17X HA14 HA18 HA36 HB03 HB05 HB06 3G301 HA02 HA04 HA06 HA11 HA13 JA15 JA21 JA24 JA25 JB09 LA03 LB11 MA01 MA11 MA18 MA23 MA26 NA07 NA08 NE02 NE13 PA01B PA01Z PA07B PA07Z PA10B PA10Z PB08B PB08Z PD01B PD01Z PD11B PD11Z PE01B PE01Z PE03B PE03Z PE08B PE08Z PF01B PF01Z PF03B PF03Z 4D048 AA06 AA14 AB01 BA18 BAX BA17 BAX BAX BAD B02 BB14 BC01 BD03 CC27 CD05 DA01 DA02 DA03 DA06 DA10 DA13 DA20 EA04

Claims (3)

[Claims] 1. When the air-fuel ratio of the inflowing exhaust gas is lean, the NOx in the exhaust gas is absorbed, and when the air-fuel ratio of the inflowing exhaust gas becomes the stoichiometric air-fuel ratio or rich, the absorbed NOx is released N
An NOx absorbent and a sulfur poisoning recovery control means for executing temperature rise control and sulfur poisoning recovery control of the NOx absorbent, wherein the sulfur poisoning recovery control means is sulfur poisoning of the NOx absorbent. An exhaust emission control device for an internal combustion engine, which reduces an air-fuel ratio of exhaust gas to release oxygen stored in a NOx absorbent when a temperature rise control before starting recovery control is executed. 2. The exhaust emission control device for an internal combustion engine comprises a filter capable of temporarily trapping fine particles in exhaust gas, and the filter carries the NOx absorbent. Exhaust gas purification device for internal combustion engine. 3. The exhaust gas of an internal combustion engine according to claim 1, wherein the sulfur poisoning recovery control is performed by adding fuel of the internal combustion engine to an exhaust system during light load operation of the internal combustion engine. Purification device.