JP3487269B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for purifying exhaust gas of an internal combustion engine, and more particularly to a technique for eliminating poisoning of an exhaust purification catalyst provided in an exhaust system of the internal combustion engine.

[0002]

2. Description of the Related Art Generally, in a lean-burn internal combustion engine mounted on an automobile or the like, NOx absorption represented by an NOx storage reduction catalyst is used as a technology for purifying nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine. Wood is proposed.

The NOx absorbent absorbs nitrogen oxides (NOx) in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is high, and absorbs the nitrogen oxides (NOx) when the oxygen concentration of the inflowing exhaust gas decreases. Is to be released.

A storage-reduction type NOx catalyst, which is one of such NOx absorbents, absorbs nitrogen oxides (NOx) in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is high, and lowers the oxygen concentration of the inflowing exhaust gas. In the presence of a reducing agent, it is a catalyst that reduces the absorbed nitrogen oxides (NOx) to nitrogen (N ₂ ).

When the NOx storage reduction catalyst is arranged in the exhaust system of the lean-burn internal combustion engine, when the lean air-fuel ratio exhaust gas flows into the NOx storage reduction catalyst, the nitrogen oxides (NOx) in the exhaust gas are reduced. Absorbed by the NOx storage reduction catalyst,
When exhaust gas having a stoichiometric air-fuel ratio or a rich air-fuel ratio flows into the NOx storage reduction catalyst, the nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst are released as nitrogen dioxide (NO ₂ ) and released. Nitrogen dioxide (N
O ₂ ) is a hydrocarbon (HC) or carbon monoxide (C) in the exhaust gas.
It reacts with a reducing component such as O) to be reduced to nitrogen (N ₂ ).

On the other hand, the fuel of the internal combustion engine may contain a sulfur (S) component, and when such a fuel is burned in the internal combustion engine, the sulfur (S) component in the fuel is oxidized. S
It forms sulfur oxides (SOx) such as O ₂ and SO ₃ . Since the storage reduction type NOx catalyst absorbs sulfur oxide (SOx) in the exhaust gas by the same mechanism as the nitrogen oxide (NOx), when the storage reduction type NOx catalyst is arranged in the exhaust passage of the internal combustion engine, The NOx storage reduction catalyst absorbs not only nitrogen oxides (NOx) but also sulfur oxides (SOx).

However, since the sulfur oxide (SOx) absorbed by the NOx storage reduction catalyst forms stable barium sulfate (BaSO ₄ ) with the passage of time, nitrogen oxides (NOx) are generated from the NOx storage reduction catalyst. Under conditions that release and reduce NOx, it is difficult to decompose and release NOx
Accumulates easily in the catalyst.

When the amount of SOx accumulated in the NOx storage reduction catalyst increases, the NOx absorption capacity of the NOx storage reduction catalyst decreases and it becomes difficult to sufficiently purify nitrogen oxides (NOx) in the exhaust gas. So-called SOx poisoning occurs.

As a technique for eliminating such poisoning by the oxide of the exhaust purification catalyst, an exhaust purification device for an internal combustion engine as disclosed in Japanese Patent Laid-Open No. 8-170558 has been proposed.

The exhaust gas purifying apparatus for an internal combustion engine described in the above publication heats the catalyst and controls the air-fuel ratio of the exhaust gas flowing into the catalyst to be richer than the theoretical air-fuel ratio during idle operation when the exhaust gas flow rate is small. Thus, it is intended to eliminate the poisoning of the catalyst while suppressing the unnecessary cooling of the catalyst by the exhaust gas and the increase of the fuel consumption amount due to the enrichment of the exhaust gas.

[0011]

By the way, when the internal combustion engine is in the idle operation state, the flow rate of the exhaust gas discharged from the internal combustion engine per unit time decreases, and accordingly, the exhaust gas flows into the catalyst per unit time. Since the flow rate of the exhaust gas also decreases, the amount of the reducing agent that flows into the catalyst per unit time when the air-fuel ratio of the exhaust gas becomes the rich air-fuel ratio decreases.

Therefore, in the exhaust gas purification apparatus in which the catalyst poisoning elimination processing is executed only during the idle operation like the above-described conventional exhaust gas purification apparatus, the internal combustion engine is idle for a long time in order to eliminate the catalyst poisoning. It is necessary to operate the engine, and when the idle operation of the internal combustion engine is not continued for a long time, it is difficult to sufficiently eliminate the poisoning of the catalyst.
On the other hand, if the idle operation of the internal combustion engine is continued for a long period of time and the air-fuel ratio of the exhaust gas is continuously set to the rich air-fuel ratio,
The amount of reducing agent that adheres to the wall surface of the exhaust passage upstream of the exhaust purification catalyst may increase excessively.

When a large amount of reducing agent adheres to the wall surface of the exhaust passage and the operating state of the internal combustion engine shifts from the idle operation state to the accelerated operation state, the exhaust pressure rises to adhere to the wall surface of the exhaust passage. There is a possibility that an extremely large amount of reducing agent will be simultaneously released from the wall surface of the exhaust passage and flow into the catalyst.

When a large amount of reducing agent separated from the wall surface of the exhaust passage flows into the catalyst, the reducing agent may rapidly burn in the catalyst and the catalyst may be deteriorated due to overheating. The present invention has been made in view of the above-mentioned various problems, and in an exhaust emission control device in which an NOx absorbent is arranged in the exhaust system of an internal combustion engine, NOx absorption while preventing unnecessary deterioration of the NOx absorbent. It is an object of the present invention to provide a technique capable of reliably eliminating poisoning caused by oxides of materials.

[0015]

The present invention adopts the following means in order to solve the above problems.
That is, the exhaust gas purification apparatus for an internal combustion engine according to the present invention,
An NOx absorbent that is provided in the exhaust passage of the internal combustion engine and that stores nitrogen oxides when the oxygen concentration of the inflowing exhaust gas is high and releases the stored nitrogen oxides when the oxygen concentration of the inflowing exhaust gas is low; When it becomes necessary to eliminate the poisoning due to the oxide of the absorber, when the internal combustion engine is in the deceleration operation state and the idle operation state, poisoning elimination means for executing the poisoning elimination process of the NOx absorber, It is characterized by having.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, when it is necessary to eliminate the poisoning caused by the oxide of the NOx absorbent, the poisoning eliminating means changes the operating state of the internal combustion engine to the idle operating state. Under the condition that the NOx absorbent is poisoned or the operating condition of the internal combustion engine is in the decelerating operating condition, the NOx absorbent poisoning elimination process is executed.

That is, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, when it is necessary to eliminate the poisoning due to the oxide of the NOx absorbent, the internal combustion engine is operated in the idling operation state. Even when the operating state of the engine is in the decelerating operating state, the NOx absorbent poisoning elimination processing is executed.

As a result, the execution area of the poisoning elimination process is expanded, and it becomes easy to secure the execution time of the poisoning process. In the poisoning elimination process, the poisoning elimination means may set the air-fuel ratio of the exhaust gas flowing into the NOx absorbent to the stoichiometric air-fuel ratio or the rich air-fuel ratio.

Next, the exhaust gas purification catalyst for an internal combustion engine according to the present invention is provided in the exhaust passage of the internal combustion engine, and when the oxygen concentration of the inflowing exhaust gas is high, it occludes nitrogen oxides to lower the oxygen concentration of the inflowing exhaust gas. When a reducing agent is present, a NOx catalyst that reduces and purifies while releasing the stored nitrogen oxides, a reducing agent adding unit that adds the reducing agent to the exhaust passage upstream of the NOx catalyst, and the NOx catalyst When it becomes necessary to eliminate poisoning due to oxides, when the internal combustion engine is in the decelerating operation state and the idle operation state, the poisoning elimination for controlling the reducing agent addition means to eliminate the poisoning of the NOx catalyst Means may be provided.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, when the poisoning eliminating means needs to eliminate the poisoning due to the oxide of the NOx catalyst, the operating state of the internal combustion engine is in the idle operating state. That is, or the operating state of the internal combustion engine is in the decelerating operating state, the reducing agent adding means is controlled to execute the NOx catalyst poisoning elimination processing.

In this case, since the NOx catalyst poisoning elimination processing is executed when the operating state of the internal combustion engine is in the decelerating operating state in addition to when the operating state of the internal combustion engine is in the idling operating state, poisoning is performed. The execution area of the elimination process is expanded, and as a result, it becomes easy to secure the execution time of the poisoning elimination process.

The poisoning elimination means is designed to eliminate the exhaust gas flowing into the NOx catalyst when the internal combustion engine is in the deceleration operation state or the idle operation state under the condition that it is necessary to eliminate the poisoning by the oxide of the NOx catalyst. The reducing agent addition means is controlled so that the air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, and when the internal combustion engine is not in the deceleration operation state and the idle operation state, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes the lean air-fuel ratio. Thus, the reducing agent addition means may be controlled.

This is based on the assumption of an exhaust purification catalyst configured to add a reducing agent to the exhaust passage upstream of the NOx catalyst. During the execution of the poisoning elimination process, the operating state of the internal combustion engine will be When the execution of the poisoning elimination processing is interrupted by shifting to an operation state other than the deceleration operation state, N
When the reducing agent is added to the exhaust passage upstream of the Ox catalyst and the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the reducing agent becomes N
This is because there is a possibility that the temperature of the NOx catalyst may drop instead of the reducing agent receiving heat from the NOx catalyst and being vaporized when passing through the Ox catalyst.

Further, the poisoning elimination means, when the internal combustion engine is idled continuously for a predetermined time or longer during the poisoning elimination process and then accelerated, is operated for a predetermined period from the start of the acceleration operation for a predetermined period. The reducing agent adding means may be controlled so as to prohibit the addition of.

Here, when the internal combustion engine is in the idle operation state, the flow rate of exhaust gas is low and the pressure of exhaust gas is low,
The reducing agent added from the reducing agent adding means to the exhaust passage is NO
x Easily adheres to the wall surface of the exhaust passage upstream of the catalyst.

If the idle operation state of the internal combustion engine is continued for a long period of time, a large amount of reducing agent will adhere to the wall surface of the exhaust passage upstream of the NOx catalyst. The reducing agent thus attached to the wall surface of the exhaust passage separates from the wall surface of the exhaust passage and flows into the NOx catalyst when the flow rate of the exhaust gas is large and the exhaust pressure is high, such as when the internal combustion engine is in the accelerated operation state. .

Therefore, when the internal combustion engine is idled continuously for a predetermined time or longer and then accelerated, a large amount of the reducing agent adhering to the wall surface of the exhaust passage during the idle operation of the internal combustion engine is simultaneously discharged during the accelerated operation of the internal combustion engine. Since it separates from the wall surface of the exhaust passage and flows into the NOx catalyst, when the reducing agent is added to the exhaust passage from the reducing agent adding means in such a situation, excess reducing agent is supplied to the NOx catalyst, The reducing agents burn rapidly at the NOx catalyst, and the NOx catalyst overheats.

On the other hand, when the internal combustion engine is idled continuously for a predetermined time or longer during the poisoning elimination process and then accelerated, the reducing agent is not added for a predetermined period from the start of the acceleration operation. If prohibited, only the reducing agent that has separated from the wall surface of the exhaust passage will flow into the NOx catalyst, and the reducing agent that has separated from the wall surface of the exhaust passage and the reducing agent that has been added to the exhaust passage from the reducing agent addition means will all be at once. To NOx
It does not flow into the catalyst. The above-mentioned predetermined period may be a fixed value or a variable value that is changed according to the idle operation duration of the internal combustion engine.

Further, the poisoning elimination means according to the present invention may prohibit the supply of the reducing agent when the idle operation duration of the internal combustion engine exceeds a preset upper limit value. An example of the NOx catalyst according to the present invention is a NOx storage reduction catalyst, and an example of the oxide according to the present invention is a sulfur oxide (SOx).

[0030]

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 with reference to the drawings.

FIG. 1 is a diagram showing a schematic construction of an internal combustion engine and an intake / exhaust system thereof to which an exhaust purification system according to the present invention is applied. An internal combustion engine 1 shown in FIG. 1 is a diesel engine for driving a vehicle, and an intake branch pipe 2 and an exhaust branch pipe 3 are connected to the internal combustion engine 1.

The intake branch pipe 2 is connected to the intake pipe 4,
The intake pipe 4 is connected upstream to an intake duct via an air cleaner box (not shown). An intake throttle valve 5 for adjusting the flow rate of intake air flowing through the intake pipe 4 is arranged in the middle of the intake pipe 4.

On the other hand, the exhaust branch pipe 3 is connected to an exhaust pipe 6, and the exhaust pipe 6 is connected downstream to a muffler (not shown). A casing 7 accommodating a NOx storage reduction catalyst according to the present invention as an NOx absorbent according to the present invention is arranged in the middle of the exhaust pipe 6, and the exhaust pipe 6 upstream of the casing 7 is provided with the inside of the exhaust pipe 6. A fuel addition nozzle 8 for adding fuel as a reducing agent to the flowing exhaust gas is attached.

The fuel addition nozzle 8 is connected to a fuel pump 10 via a fuel pipe 9 so that the fuel discharged from the fuel pump 10 can be injected into the exhaust pipe 6.

The NOx storage reduction catalyst 70 contained in the casing 7 has, for example, alumina as a carrier,
On this carrier, for example, potassium (K), sodium (N
a), alkali metals such as lithium (Li) and cesium (Cs), alkaline earths such as barium (Ba) and calcium (Ca), and rare earths such as lanthanum (La) and yttrium (Y). And at least one
It is configured to support a noble metal such as platinum (Pt).

Here, the ratio of air and fuel (hydrocarbon (HC)) supplied into the intake passage of the internal combustion engine 1 and the exhaust passage upstream of the NOx storage reduction catalyst 70 is stored in the NOx storage reduction catalyst 70. The air-fuel ratio of the inflowing exhaust gas (hereinafter abbreviated as the exhaust air-fuel ratio) and the NOx storage reduction catalyst 70 are
When the exhaust air-fuel ratio becomes a lean air-fuel ratio and the oxygen concentration in the exhaust gas is high, it absorbs nitrogen oxides (NOx) in the exhaust gas, and the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or rich air-fuel ratio and the oxygen content in the exhaust gas When the concentration decreases, the NOx absorption / release function of releasing the absorbed nitrogen oxides (NOx) is performed.

It is considered that the NOx absorbing / releasing action of the NOx storage reduction catalyst 70 is carried out by a mechanism roughly shown in FIG. Hereinafter, this mechanism will be described by taking as an example the case where platinum (Pt) and barium (Ba) are supported on a carrier made of alumina, but the same is true when other precious metals, alkali metals, alkaline earths and rare earths are used. It becomes a mechanism.

First, when the exhaust air-fuel ratio becomes a lean air-fuel ratio and the oxygen concentration in the exhaust gas becomes high, the oxygen (O ₂ ) in the exhaust gas becomes O ₂ ^- or O ² as shown in FIG. 2 (A). ^- to form a deposition on the surface of the platinum (Pt). On the other hand, nitric oxide (NO) contained in the exhaust gas reacts with O ₂ ⁻ or O ^{2 −} on the surface of platinum (Pt) to become nitrogen dioxide (NO ₂ ) (2NO +
O ₂ → 2NO ₂ ).

Next, part of the nitrogen dioxide (NO ₂ ) is
Storage-reduction type NOx catalyst 7 while being oxidized on platinum (Pt)
Absorbed by barium oxide in the 0 (BaO) and bound with nitrate ions (NO ₃ ^-) storage in the form of a reduction NOx catalyst 7
Spread within 0.

In this way, the nitrogen oxides (N
Ox) is absorbed by the NOx storage reduction catalyst 70. The NOx absorbing action of the storage reduction type NOx catalyst 70 is continued unless the oxygen concentration of the exhaust gas flowing into the storage reduction type NOx catalyst 70 is high and the NOx absorption capacity of the storage reduction type NOx catalyst 70 is saturated.

On the other hand, when the exhaust air-fuel ratio becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio and the oxygen concentration in the exhaust decreases, as shown in FIG. 2 (B), on the surface of platinum (Pt). Since the amount of nitrogen dioxide (NO ₂ ) produced decreases, the nitrate ions (NO _{3 −} ) bound to barium oxide (BaO) become nitrogen dioxide (NO ₂ ) or nitric oxide (NO). It is released from the NOx storage reduction catalyst 70.

At this time, a part of the unburned fuel components (hydrocarbon (HC)) and carbon monoxide (CO) existing in the exhaust gas,
Platinum (Pt) reacts with oxygen (O ₂ ⁻ or O ^{2 −} ) to be oxidized, and the remaining hydrocarbons (HC) and carbon monoxide (C
O) reacts with nitrogen dioxide (NO ₂ ) and nitric oxide (NO) released from the NOx storage reduction catalyst 70,
Nitrogen dioxide (NO ₂ ) and nitric oxide (NO) will be reduced to nitrogen (N ₂ ).

That is, hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas are first reacted with oxygen (O ₂ ⁻ or O ²⁻ ) on platinum (Pt) to be oxidized. Then, platinum (P
t) If hydrocarbons (HC) and carbon monoxide (CO) remain in the exhaust gas after the oxygen (O ₂ ⁻ or O ²⁻ ) above is consumed, those hydrocarbons (HC) and Carbon oxide (C
O), (particularly active species of hydrocarbon (HC) and carbon monoxide (CO) partially oxidized by oxygen (O ₂ ⁻ or O ^{2 −} )) released from the NOx storage reduction catalyst 70 and oxidized by nitrogen. The substances (NOx) and nitrogen oxides (NOx) discharged from the internal combustion engine 1 are reduced to nitrogen (N ₂ ).

The storage reduction type NOx catalyst 70 as described above.
According to the above, when the exhaust air-fuel ratio is the lean air-fuel ratio, the nitrogen oxides (NOx) in the exhaust gas are stored / reduced NOx catalyst 70.
When the exhaust air-fuel ratio is the stoichiometric air-fuel ratio or the rich air-fuel ratio, the nitrogen oxides (NOx) absorbed in the NOx catalyst 70 are reduced. Is reduced to nitrogen (N ₂ ) while being released from the NOx storage reduction catalyst 70, and the nitrogen oxides (NOx) discharged from the internal combustion engine 1 are also stored reduction Nx.
The Ox catalyst 70 is reduced to nitrogen (N2) or the like.

An electronic control unit (ECU) 11 for controlling the operating state of the internal combustion engine 1 is attached to the internal combustion engine 1 thus constructed. The ECU 11 is composed of, for example, a CPU, a ROM, a RAM, a backup RAM, an input port, an output port, and the like, which are mutually connected by a bidirectional bus.

A crankshaft (not shown) of the internal combustion engine 1 has a predetermined angle (for example, 10 °) in the ECU 11.
A crank position sensor 12 that outputs a pulse signal each time it rotates, and an accelerator pedal 13 provided in the vehicle interior
In addition to various sensors such as the accelerator position sensor 14 which outputs an electric signal corresponding to the operation amount of the fuel addition nozzle 8, the fuel addition nozzle 8 is electrically connected, and the output signals of the crank position sensor 12 and the accelerator position sensor 14 described above are used as parameters. As a result, it is possible to control the fuel addition nozzle 8.

For example, in a diesel engine such as the internal combustion engine 1, since lean burn operation is performed in most operating regions, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 70 is also lean in most operating regions. The fuel ratio becomes the NOx with respect to the NOx absorbing action of the NOx storage reduction catalyst 70.
The release action is not in time, and the NOx storage reduction catalyst 7
It is assumed that the NOx absorption capacity of 0 is saturated.

On the other hand, when the internal combustion engine 1 is in the lean burn operation, the ECU 11 theoretically makes the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 70 into a spike (short time) in a relatively short cycle. By executing the so-called rich spike control for controlling the reducing agent addition nozzle 8 so as to obtain the air-fuel ratio or the rich air-fuel ratio, the storage and reduction type NOx catalyst 70 releases and reduces nitrogen oxides (NOx) in a short cycle. I'm trying to do it.

On the other hand, the fuel of the internal combustion engine 1 may contain a sulfur (S) component, and when such a fuel is burned, the sulfur (S) component in the fuel is oxidized and SO ₂ and S
Sulfur oxides (SOx) such as O ₃ are produced.

When the above-mentioned sulfur oxide (SOx) flows into the storage reduction type NOx catalyst 70 together with the exhaust gas, the storage reduction type NOx catalyst 70 has a mechanism similar to that of the nitrogen oxide (NOx). Will be absorbed.

[0051] That is, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 70 is lean air-fuel ratio, as described in the explanation of the NOx absorption described above, oxygen (O ₂₎ O ₂ ^- or O Storage-reduction type NOx catalyst 70 in the form of ^2-
Since it adheres to the surface of platinum (Pt), the sulfur oxide (SOx) (for example, SO ₂ ) in the exhaust gas is oxidized on the surface of platinum (Pt) to become SO ₃ .

Subsequently, SO ₃ is further oxidized on the surface of platinum (Pt) and is absorbed in the NOx storage reduction catalyst 70 to be bonded to barium oxide (BaO) to form sulfate ions (SO ₄ ^{2 −} ). In the form, it is diffused into the NOx storage reduction catalyst 70 to produce barium sulfate (BaSO ₄ ).

By the way, the above barium sulfate (BaS)
O ₄ ) is stable and difficult to decompose, and is not decomposed even if the air-fuel ratio of the inflowing exhaust gas is made to be a rich air-fuel ratio and the storage reduction NO
x It remains in the catalyst 70. Therefore, when the production amount of barium sulfate (BaSO ₄ ) in the NOx storage reduction catalyst 70 increases with the lapse of time, barium oxide (BaO) that can participate in the absorption of the NOx storage reduction catalyst 70 increases.
The amount of O) is reduced, and as a result, so-called SOx poisoning occurs, which reduces the NOx absorption capacity of the NOx storage reduction catalyst 70.

Therefore, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the ECU 11 determines the amount of sulfur oxide (SOx) absorbed by the NOx storage reduction catalyst 70 using the operating history of the internal combustion engine 1 as a parameter. When the estimated amount reaches a predetermined upper limit value, the poisoning elimination process is executed to release the sulfur oxide (SOx) from the NOx storage reduction catalyst 70.

As a method for eliminating SOx poisoning of the storage reduction type NOx catalyst 70, the catalyst bed temperature of the storage reduction type NOx catalyst 70 is in a higher temperature range (for example, 600 to 650) than when the NOx releasing / reducing action is performed. It is considered that a method of raising the exhaust air-fuel ratio to the stoichiometric air-fuel ratio or the rich air-fuel ratio after raising the temperature to ℃) is effective.

According to such a method, the storage reduction type NO
x Barium sulfate (BaSO ₄ ) stored in the catalyst 70
Is decomposed into SO ₃ , and SO ₃ is reduced by hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and released as SO ₂ .

The poisoning elimination process will be specifically described below. <First Embodiment> First, SOx according to the first embodiment.
The poisoning elimination process will be described.

The SOx poisoning elimination processing according to the present embodiment is executed when the internal combustion engine 1 is in the idle operation state or the deceleration operation state. When the internal combustion engine 1 is in the idling operation state and when the internal combustion engine 1 is in the deceleration operation state, the exhaust gas flow rate is small, so even if the injection amount of the fuel addition nozzle 8 is made relatively small, the exhaust air-fuel ratio Can be the stoichiometric air-fuel ratio or the rich air-fuel ratio.

At this time, when the opening degree of the intake throttle valve 5 is reduced, the intake amount of the internal combustion engine 1 is reduced, and the exhaust flow rate is further reduced accordingly, so that the injection amount of the fuel addition nozzle 8 is further reduced. However, the exhaust air-fuel ratio can be made the stoichiometric air-fuel ratio or the rich air-fuel ratio.

The SOx poisoning elimination processing in this embodiment will be described below with reference to the flowchart of FIG. The flowchart shown in FIG. 3 is a flowchart showing a SOx poisoning elimination processing routine, and the SOx poisoning elimination processing routine is repeated by the ECU 11 every predetermined time (for example, every time the crank position sensor 12 outputs a pulse signal). It is a routine that is executed.

<Step 101> First, step 101
Then, the ECU 11 estimates the amount of sulfur oxide (SOx) absorbed by the NOx storage reduction catalyst 70. As a method for estimating the amount of absorption of sulfur oxide (SOx), the engine speed and the output signal value (accelerator opening) of the accelerator position sensor 14 are stored as parameters in the NOx storage reduction catalyst 70 per unit time. An example is a method of estimating the amount of sulfur oxide (SOx) absorbed by the NOx storage reduction catalyst 70 by calculating the amount of sulfur oxide (SOx) and accumulating it.

At this time, the engine speed, accelerator opening and SO
The relationship with the x absorption amount may be experimentally obtained in advance, and the relationship may be mapped in advance. <Step 102> In step 102, the ECU 11
Determines whether or not the sulfur oxide (SOx) absorption amount calculated in step 101 is equal to or greater than a predetermined upper limit value. At this time, if it is determined that the amount of absorbed sulfur oxide (SOx) is less than the predetermined upper limit value, the ECU 11 once ends the execution of this routine. On the other hand, sulfur oxide (SO
x) When it is determined that the absorption amount is equal to or larger than the predetermined upper limit value,
The ECU 11 will proceed to step 103.

<Step 103> In Step 103,
The ECU 11 determines whether the internal combustion engine 1 is in the decelerating operation state. As a method for determining the decelerating operation state of the internal combustion engine 1, the accelerator opening is "zero", the traveling speed of the vehicle is not "0", or the operation amount of a brake pedal (not shown) is not "0". It is possible to exemplify a method of determining that the internal combustion engine 1 is in the decelerating operation state when the conditions such as, are satisfied.

If it is determined in step 103 that the internal combustion engine 1 is not in the decelerating operation state, the ECU 11
Proceeds to step 104. On the other hand, if it is determined in step 103 that the internal combustion engine 1 is in the decelerating operation state, the ECU 11 proceeds to step 105.

<Step 104> In Step 104,
The ECU 11 determines whether the internal combustion engine 1 is in the idle operation state. As a method of determining the idle operation state of the internal combustion engine 1, conditions such as the accelerator opening being "0", the engine speed being equal to or less than a predetermined speed, or the vehicle traveling speed being "0" A method of determining that the internal combustion engine 1 is in the idle operation state can be exemplified.

When it is determined in step 104 that the operating state of the internal combustion engine 1 is not the idle operating state, the ECU 11 once ends the execution of this routine.
On the other hand, if it is determined in step 104 that the operating state of the internal combustion engine 1 is the idle operating state, the ECU 1
1 proceeds to step 105.

<Step 105> In Step 105,
The ECU 11 executes poisoning elimination processing in order to recover SOx poisoning of the NOx storage reduction catalyst 70. In the poisoning elimination process, the ECU 11 adds the reducing agent from the reducing agent injection nozzle 8 into the exhaust pipe 6 to change the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 70 to the stoichiometric air-fuel ratio or the rich air-fuel ratio. As the fuel ratio, the NOx storage reduction catalyst 7
Sulfur oxides (SOx) are released from the NOx storage reduction catalyst 70 while increasing the bed temperature of zero.

The poisoning elimination means according to the present invention is realized by the ECU 11 thus executing the poisoning elimination processing routine. Therefore, according to the exhaust gas purification apparatus for the internal combustion engine according to the present embodiment, the poisoning elimination process is executed not only when the internal combustion engine 1 is in the idle operation state but also when the internal combustion engine 1 is in the deceleration operation state. Therefore, as compared with the case where the SOx poisoning elimination process is executed only when the internal combustion engine 1 is in the idle operation state,
It is possible to secure a sufficient execution time for the SOx poisoning elimination processing.

<Second Embodiment> Next, the SOx poisoning elimination process according to the second embodiment will be described. In the SOx poisoning elimination processing according to the present embodiment, the operating state of the internal combustion engine 1 during the execution of the SOx poisoning elimination processing is monitored, and the operating state of the internal combustion engine 1 is in the idle operation during the execution of the SOx poisoning elimination processing. When the state is changed to the accelerated operation state, the fuel addition nozzle 8
Prohibit fuel addition by.

Not all of the fuel added from the fuel addition nozzle 8 into the exhaust pipe 6 when the internal combustion engine 1 is in the idle operation state reaches the NOx storage reduction catalyst 70, but the NOx storage reduction type. It adheres to the wall surface and the like of the exhaust pipe 6 upstream of the catalyst 70 and stays there.

During execution of SOx poisoning elimination processing, the internal combustion engine 1
If the idle operation state of continues for a long time,
The amount of fuel retained in the exhaust pipe 6 upstream of the NOx storage reduction catalyst 70 increases. Under such circumstances, the internal combustion engine 1
When the operating state of NOx shifts from the idle operating state to the accelerated operating state, the exhaust pipe 6 upstream of the NOx storage reduction catalyst 70
A large amount of fuel that had accumulated inside was simultaneously stored and reduced NOx
There is a case where the fuel flows into the catalyst 70 and abruptly combusts the fuel in the NOx storage reduction catalyst 70.

When a large amount of fuel rapidly burns in the NOx storage reduction catalyst 70 in this way, the NOx storage reduction catalyst 70 is overheated by the heat generated when the fuel burns, and the NOx storage reduction catalyst 70 heats up. It may deteriorate.

On the other hand, in the SOx poisoning elimination processing according to the present embodiment, the ECU 11 monitors the duration of the idle operation, and when the duration becomes a predetermined time or longer, the fuel addition nozzle 8 moves into the exhaust pipe 6. Banned the addition of fuel.

Further, in the SOx poisoning elimination processing according to the present embodiment, when the internal combustion engine 1 is continuously idled for a predetermined time or longer and then is kept in the accelerated operation state, the acceleration operation is started from the time when the acceleration operation is started. The fuel addition from the fuel addition nozzle 8 into the exhaust pipe 6 is prevented for a predetermined period.

The above-mentioned predetermined period may be a preset fixed value or a variable value that is changed according to the duration of the idle operation state.
Hereinafter, the SOx poisoning elimination processing according to the present embodiment will be described with reference to the flowchart of FIG.

The flowchart shown in FIG. 4 is a flowchart showing a SOx poisoning elimination processing monitoring routine. The SOx poisoning elimination processing monitoring routine is executed by the ECU 11 at predetermined time intervals (for example, the crank position sensor 1).
2 is a routine that is repeatedly executed each time a pulse signal is output).

<Step 201> In Step 201,
The ECU 11 determines whether the SOx poisoning elimination process is being executed.

If it is determined in step 201 that the SOx poisoning elimination processing is not being executed, the ECU 1
1 temporarily ends the execution of this routine. On the other hand, when it is determined in step 201 that the SOx poisoning elimination process is being executed, the ECU 11 proceeds to step 202.

<Step 202> In Step 202,
The ECU 11 determines whether the duration of the idle operation state is less than a predetermined time, or whether the elapsed time from the time of shifting from the idle operation state to the acceleration operation state is longer than the predetermined time.

If it is determined in step 202 that the duration of the idle operation state is less than the predetermined time, or the elapsed time from the time of shifting from the idle operation state to the acceleration operation state is longer than the predetermined time, the ECU 11
Ends the execution of this routine once.

On the other hand, if it is determined in step 202 that the duration of the idle operation state is equal to or longer than the predetermined time and the elapsed time from the time when the idle operation state is changed to the acceleration operation state is equal to or shorter than the predetermined time, ECU1
1 proceeds to step 203.

<Step 203> In Step 203,
The ECU 11 prohibits fuel addition from the fuel addition nozzle 8 into the exhaust pipe 6.

According to the above-described embodiment, when the internal combustion engine 1 is idling continuously for a predetermined time or longer during execution of the SOx poisoning elimination processing, and then shifts to acceleration operation,
The fuel accumulated in the exhaust pipe 6 during the idle operation and the fuel added from the fuel addition nozzle 8 are simultaneously stored and reduced NO
Since it does not flow into the x-catalyst 70, excessive fuel does not burn rapidly in the NOx storage reduction catalyst 70, so that deterioration of the occlusion reduction NOx catalyst 70 due to overheating is prevented.

[0084]

In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when it is necessary to eliminate the poisoning due to the oxide of the NOx absorbent or the NOx catalyst, the internal combustion engine is not only added to the idle operation state, Since the poisoning elimination processing is executed even when the engine is in the deceleration operation state, the execution area of the poisoning elimination processing is expanded, and thus it is easy to secure sufficient execution time for the poisoning elimination processing. Becomes

As a result, the poisoning of the NOx absorbent or the NOx catalyst by the oxide can be eliminated in a short period of time.
Further, according to the exhaust gas purification device for an internal combustion engine according to the present invention,
Even if it is necessary to set the air-fuel ratio of the exhaust gas to the stoichiometric air-fuel ratio or the rich air-fuel ratio in the poisoning elimination processing, the flow rate of the exhaust gas is relatively low as when the internal combustion engine is in the idle operation state and the deceleration operation state. Since the poisoning elimination processing is executed when the amount is small, it is possible to make the exhaust air-fuel ratio the stoichiometric air-fuel ratio or the rich air-fuel ratio with a relatively small amount of fuel.

Further, when the exhaust gas purification apparatus for an internal combustion engine according to the present invention is equipped with a reducing agent addition means for adding a reducing agent to the exhaust passage upstream of the NOx catalyst, the poisoning elimination processing is being executed. If the internal combustion engine shifts to the acceleration operation state after continuing the idle operation state for a predetermined time or more below,
Since the addition of the reducing agent is prohibited for a predetermined period from the start of the acceleration operation, the reducing agent staying in the exhaust passage during the idle operation and the reducing agent added to the exhaust passage by the reducing agent addition means are simultaneously NOx catalyst. Never flow into.

As a result, the excessive reducing agent is not simultaneously oxidized (combusted) in the NOx catalyst, and the NOx catalyst is prevented from being overheated due to the combustion of the reducing agent.
It is possible to suppress the thermal deterioration of the Ox catalyst.

[Brief description of drawings]

FIG. 1 Overall view of internal combustion engine

FIG. 2 is a diagram for explaining a NOx absorption / release mechanism of an NOx storage reduction catalyst.

FIG. 3 is a flowchart showing a SOx poisoning elimination processing routine according to the first embodiment.

FIG. 4 is a flowchart showing a SOx poisoning elimination processing monitoring routine according to a second embodiment.

[Explanation of symbols]

1 ... Internal combustion engine 2 ... Intake branch pipe 3 ... Exhaust branch pipe 4 ... Intake pipe 5 ... Intake throttle valve 6 ... Exhaust pipe 7 ... Casing 70 ··· NOx storage reduction catalyst 8 ... Fuel addition nozzle 9 ... Fuel piping 10 ... Fuel pump 11 ... ECU 12 ... Crank position sensor 13 ... Accelerator pedal 14 ... Accelerator position sensor

Continuation of front page (51) Int.Cl. ⁷ Identification code FI F01N 3/28 301 B01D 53/36 ZABK 3/36 101A 101B (72) Inventor Hiroki Matsuoka 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Kotaro Hayashi 1 Toyota-cho, Toyota-shi, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Shinobu Ishiyama 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Co., Ltd. (72) Inventor Yasuhiko Otsubo 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor Naofumi Kagata 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Company, Ltd. (72) Masaaki Kobayashi 1, Toyota Town, Toyota City, Aichi Prefecture Address Toyota Motor Co., Ltd. (72) Inventor Daisuke Shibata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Tomihisa Oda 1 Toyota Town, Aichi Prefecture Toyota Motor Co., Ltd. ( 72) Inventor Yasuo Harada Ai Toyota-cho, Toyota-shi, Japan (72) Inventor Tomoyuki Ono Tomo-cho, Toyota-shi, Aichi 1-cho, Toyota-cho, Toyota (56) Reference JP 2000-87732 (JP, A) Special Kaihei 6-307232 (JP, A) JP 2000-120428 (JP, A) JP 10-317946 (JP, A) JP 2000-73743 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/36 B01D 53/86 B01D 53/94

Claims (3)

(57) [Claims] 1. Inflow exhaust gas provided in an exhaust passage of an internal combustion engine
When the oxygen concentration in the
If the oxygen concentration is low and a reducing agent is present, store it
NOx catalyst that reduces and purifies existing nitrogen oxides
And adding a reducing agent to the exhaust passage upstream of the NOx catalyst
It is necessary to eliminate the poisoning by the reducing agent addition means and the oxide of the NOx catalyst.
If the internal combustion engine is in the decelerating operation state and the idle operation,
In order to eliminate poisoning of the NOx catalyst when in the state
Poisoning elimination means for controlling the reducing agent addition means , wherein the poisoning elimination means is exposed to oxides of the NOx catalyst.
Under the situation where it is necessary to eliminate the poison, the internal combustion engine is in the deceleration operation state or the idle operation state.
The air-fuel ratio of the exhaust gas flowing into the NOx catalyst is
The reducing agent is added to achieve the theoretical air-fuel ratio or the rich air-fuel ratio.
The internal combustion engine to the decelerating operating state and the idle operating state.
If the air-fuel ratio of the exhaust flowing into the NOx catalyst is
Controlling said reducing agent addition means so as to be over down air, further, the poisoning eliminating means during the execution of the poisoning recovery process
The internal combustion engine is idling continuously for a predetermined time or longer.
If acceleration is performed after
During the period, the above-mentioned reducing agent addition means is used to prohibit the addition of reducing agent.
An exhaust emission control device for an internal combustion engine, which is controlled. 2. The poisoning eliminating means is an engine of the internal combustion engine.
Determine the predetermined period based on the idle operation duration
Exhaust gas purification of an internal combustion engine according to claim 1, characterized in that
apparatus. 3. Inflow exhaust gas provided in an exhaust passage of an internal combustion engine
When the oxygen concentration in the
If the oxygen concentration is low and a reducing agent is present, store it
NOx catalyst that reduces and purifies existing nitrogen oxides
And adding a reducing agent to the exhaust passage upstream of the NOx catalyst
It is necessary to eliminate the poisoning by the reducing agent addition means and the oxide of the NOx catalyst.
If the internal combustion engine is in the decelerating operation state and the idle operation,
In order to eliminate poisoning of the NOx catalyst when in the state
Poisoning elimination means for controlling the reducing agent addition means , wherein the poisoning elimination means is exposed to oxides of the NOx catalyst.
Under the situation where it is necessary to eliminate the poison, the internal combustion engine is in the deceleration operation state or the idle operation state.
The air-fuel ratio of the exhaust gas flowing into the NOx catalyst is
The reducing agent is added to achieve the theoretical air-fuel ratio or the rich air-fuel ratio.
The internal combustion engine to the decelerating operating state and the idle operating state.
If the air-fuel ratio of the exhaust flowing into the NOx catalyst is
The reducing agent adding means is controlled so that the air-fuel ratio becomes equal to the engine air-fuel ratio, and the poisoning eliminating means is an idle engine of the internal combustion engine.
Operation duration returned to the wall of the exhaust passage upstream of the NOx catalyst
If the upper limit set by the amount of base agent is exceeded,
To control the reducing agent addition means to prohibit addition.
An exhaust purification device for an internal combustion engine.