JP2002122019A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Problem] To supply a reducing agent based on the bed temperature of a NOx catalyst and prevent deterioration of the catalyst and deterioration of exhaust emission. An NOx catalyst, operating state detecting means for detecting an operating state of an internal combustion engine, input gas temperature measuring means for measuring a temperature of exhaust gas flowing into the NOx catalyst,
An outlet gas temperature measuring means 24 for measuring the temperature of the exhaust gas flowing out of the NOx catalyst 20, a catalyst bed temperature estimating means 35 for estimating the bed temperature of the NOx catalyst 20 based on the temperature of the exhaust gas and the operating state; A reducing agent supply means 28 for supplying a reducing agent based on the bed temperature of the catalyst, a catalyst bed temperature detecting means 35 for detecting the bed temperature of the NOx catalyst 20 based on the temperature of exhaust gas, Abnormality judgment means for judging whether or not there is an error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for purifying exhaust gas of an internal combustion engine.

[0002]

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

In response to such demands, a technique has been proposed in which a lean NOx catalyst is disposed in an exhaust system of an internal combustion engine.
Lean N such as a selective reduction type NOx catalyst or a storage reduction type NOx catalyst as an exhaust purification device for purifying harmful components in exhaust gas.
Ox catalysts are known.

A selective reduction type NOx catalyst is a catalyst that reduces or decomposes NOx in the presence of hydrocarbons (HC) in an oxygen-excess atmosphere. To purify NOx with this selective reduction type NOx catalyst, an appropriate amount is used. An HC component (reducing agent) is required. When this selective reduction type NOx catalyst is used for purifying the exhaust gas of the internal combustion engine, the amount of the HC component in the exhaust gas during the normal operation of the internal combustion engine is extremely small.
It is necessary to supply the HC component to the NOx selective reduction catalyst in order to purify the NOx.

On the other hand, the NOx storage reduction catalyst absorbs NOx when the air-fuel ratio of the inflow exhaust gas is lean, and releases the absorbed NOx when the oxygen concentration of the inflow exhaust gas decreases.
A catalyst for reducing the N _2.

When the NOx storage reduction catalyst is disposed in the exhaust system of an internal combustion engine, when the internal combustion engine is operated in a lean burn mode and the air-fuel ratio of the exhaust gas becomes high, nitrogen oxide (NOx) in the exhaust gas is increased.
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 decreases, nitrogen (NOx) absorbed by the NOx storage reduction catalyst is released while nitrogen (NOx) is released. N ₂ ).

However, since the NOx absorption capacity of the NOx storage reduction catalyst is limited, when the internal combustion engine is operated in lean combustion for a long period of time, the NOx absorption capacity of the NOx storage reduction catalyst is saturated and the NOx in the exhaust gas is saturated. Oxides (NOx) are released to the atmosphere without being removed by the NOx storage reduction catalyst.

Therefore, when the NOx storage reduction catalyst is applied to a lean burn internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst before the NOx absorption capacity of the NOx storage reduction catalyst is saturated. It is necessary to release and reduce the nitrogen oxides (NOx) absorbed in the NOx storage reduction catalyst by executing the so-called rich spike control for reducing the NOx.

[0009] As a specific method of the rich spike control, a method of adding a fuel as a reducing agent to exhaust gas flowing upstream of the NOx storage reduction catalyst can be exemplified.

On the other hand, a sulfur oxide (SO 2) generated by combustion of sulfur contained in fuel is stored in the NOx storage reduction catalyst.
x) is also absorbed by the same mechanism as NOx. The absorbed SOx forms a stable sulfate over time and is therefore less likely to be released than NOx, and is accumulated in the NOx catalyst. This is called SOx poisoning, and as SOx poisoning progresses, N
When the accumulated amount of SOx in the Ox catalyst increases, the Nx of the NOx catalyst increases.
Since the Ox absorption amount decreases, the NOx purification rate decreases. Therefore, it is necessary to perform poisoning elimination processing for recovering from SOx poisoning at an appropriate time. This poisoning elimination process is performed by NOx
The exhaust gas having a stoichiometric air-fuel ratio or a rich air-fuel ratio must be flowed through the NOx catalyst while the temperature of the catalyst is raised (for example, about 600 to 700 ° C.).

In the exhaust gas purification system using the lean NOx catalyst, it is very important to control the catalyst bed temperature of the lean NOx catalyst.

For example, a lean NOx catalyst has an activation temperature, and if the catalyst bed temperature falls outside this activation temperature range, the purification capacity is extremely reduced. Further, as described above, it is necessary to maintain a predetermined temperature in order to eliminate SOx poisoning. Further, if the temperature of the NOx catalyst rises excessively at the time of SOx poisoning elimination, thermal degradation of the NOx catalyst may be induced.

Here, the thermal deterioration of the NOx storage reduction catalyst will be described. The NOx is absorbed by the NOx catalyst at the interface between platinum Pt (catalytic substance) and potassium K (NOx absorbent). It is known that sintering occurs and grows to increase the particle size. In purifying exhaust gas discharged from a vehicle internal combustion engine, the heat load applied to the NOx catalyst is large, and platinum Pt
Sintering cannot be avoided. When platinum Pt causes sintering, the contact area between platinum Pt and potassium K decreases, that is, the interface between platinum Pt and potassium K decreases. As a result, the NOx of the NOx catalyst
The absorption capacity decreases, and the NOx purification ability decreases.

To solve such a problem, Japanese Patent No. 28450
An exhaust gas purifying apparatus for an internal combustion engine as described in Japanese Patent Publication No. 56 has been proposed. The exhaust gas purifying apparatus for an internal combustion engine described in this publication discloses the amount of a reducing agent consumed by reacting with oxygen in exhaust gas in an NOx storage reduction catalyst and the amount of NO stored and reduced.
x The amount of the reducing agent to be added is determined in consideration of the amount of the reducing agent required to reduce the nitrogen oxides (NOx) absorbed by the catalyst. Therefore, the problem of lowering the temperature of the NOx storage material is to be solved.

[0015]

However, even if the required amount of the reducing agent can be accurately determined, if the added reducing agent adheres to the exhaust passage, it evaporates and NO
It takes time to reach the x catalyst, and it becomes difficult to accurately obtain the air-fuel ratio required for maintaining the temperature of the NOx catalyst.

Further, there is a concern that the reducing agent adhering to the exhaust passage may flow into the NOx catalyst at a stretch when the vehicle is accelerating, and the catalyst bed temperature may rise excessively.

As described above, since the temperature of the catalyst becomes unstable when the reducing agent adheres to the exhaust passage, it is necessary to supply an appropriate amount of the reducing agent to the NOx catalyst according to the temperature of the catalyst. It is also necessary to monitor for an excessive rise in catalyst bed temperature in order to prevent thermal degradation of the catalyst.

To solve such a problem, it is conceivable to directly obtain the catalyst bed temperature by installing a temperature sensor in the catalyst carrier, but it is actually difficult because the reliability of the carrier is reduced.
In addition, a technology is known in which a temperature sensor is installed in an exhaust passage of an internal combustion engine to perform a temporary delay process on the temperature of exhaust gas to estimate a catalyst bed temperature. And it is difficult to obtain the required estimation accuracy.

The present invention has been made in view of such problems of the prior art, and the problem to be solved by the present invention is to accurately estimate the bed temperature of the NOx catalyst and to determine the appropriate reducing agent. The purpose is to prevent the deterioration of the catalyst and the exhaust emission by performing the addition.

[0020]

The present invention employs the following means to solve the above-mentioned problems.

That is, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention comprises: a NOx catalyst provided in an exhaust passage of a lean-burn internal combustion engine capable of burning an air-fuel mixture in an excess oxygen state; Operating state detecting means for detecting a state, incoming gas temperature measuring means for measuring the temperature of exhaust gas flowing into the NOx catalyst, outgoing gas temperature measuring means for measuring the temperature of exhaust gas flowing out of the NOx catalyst; Gas inlet catalyst bed temperature estimating means for estimating the bed temperature of the NOx catalyst based on the exhaust gas temperature measured by the gas temperature measuring means and the operating state detected by the operating state detecting means; The NOx estimated by the estimation means
Reducing agent supply means for supplying a reducing agent to the NOx catalyst based on the bed temperature of the catalyst; and an outgassing catalyst for detecting the bed temperature of the NOx catalyst based on the temperature of the exhaust gas measured by the outgassing temperature measuring means. A bed temperature detecting unit; and an abnormality determining unit that determines whether the NOx catalyst is abnormal based on the bed temperature of the NOx catalyst estimated by the outgassing catalyst bed temperature estimating unit.

The inlet gas catalyst bed temperature estimating means includes: an amount of air taken into the internal combustion engine, an amount of HC exhausted from the internal combustion engine, and an amount of reducing agent supplied by the reducing agent supply means. And the exhaust gas temperature measured by the incoming gas temperature measuring means, to calculate the amount of the reducing agent attached and the amount of evaporation in the exhaust passage and the NOx catalyst, and based on the calculated values, the NOx catalyst Bed temperature can be estimated.

In the exhaust gas purifying apparatus for an internal combustion engine constructed as described above, the amount of the reducing agent attached to the exhaust passage and the amount of the reducing agent attached to the exhaust passage are determined based on the exhaust gas temperature measured by the input gas temperature measuring means and the operating state of the internal combustion engine. The bed temperature of the NOx catalyst can be estimated in consideration of the amount of evaporation of the reducing agent. Since the estimated catalyst bed temperature is estimated based on the temperature of the exhaust gas flowing into the catalyst, there is no delay from the actual catalyst bed temperature. Therefore, the reducing agent supply means determines the estimated NO.
x The reducing agent can be supplied without delay based on the bed temperature of the catalyst.

If the input gas temperature measuring means fails to output an accurate temperature due to failure or deterioration, etc., the bed temperature of the NOx catalyst cannot be estimated correctly, so that the reducing agent is supplied excessively and the temperature of the NOx catalyst becomes excessive. May rise.

Therefore, the safety can be improved by using the temperature of the exhaust gas measured by the outlet gas temperature measuring means for abnormality determination such as overheating of the catalyst. When overheating or the like of the NOx catalyst is detected, the reducing agent supply means stops the supply of the reducing agent and can prevent the catalyst from being thermally degraded. For this reason, it is desirable that the outlet gas temperature measuring means be installed as close as possible to the NOx catalyst.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, a case where the exhaust gas purification apparatus 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 internal combustion engine to which an exhaust gas purifying apparatus according to the present invention is applied and an intake / exhaust system thereof.

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

The internal combustion engine 1 has a fuel injection valve 3 for directly injecting fuel into the combustion chamber of each cylinder 2. Each fuel injection valve 3 is connected to a pressure accumulation chamber (common rail) 4 for accumulating fuel up to a predetermined pressure. The common rail 4 is provided with a common rail pressure sensor 4a that outputs an electric signal corresponding to the pressure of the fuel in 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 internal combustion engine 1 as a drive source. The pump pulley 6 attached to the input shaft of the fuel pump 6 is connected to the output shaft (crankshaft) of the internal combustion engine 1. It is connected to the attached crank pulley 1a via a belt 7.

In the fuel injection system configured as described above, when the rotation 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 corresponding to the rotating torque.

The fuel discharged from the fuel pump 6 is
The fuel is supplied to the common rail 4 via the fuel supply pipe 5, accumulated in the common rail 4 to a predetermined pressure, and distributed to the fuel injection valves 3 of each cylinder 2. When a drive current is applied to the fuel injection valve 3, the fuel injection valve 3 opens, and as a result, fuel is injected from the fuel injection valve 3 into the cylinder 2.

Next, an intake branch pipe 8 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 8 communicates with a combustion chamber of each cylinder 2 via an intake port (not shown). .

The intake branch pipe 8 is connected to an intake pipe 9.
This intake pipe 9 is connected to an air cleaner box 10. An air flow meter 11 that outputs an electric signal corresponding to the mass of the intake air flowing through the intake pipe 9 and an electric current corresponding to the temperature of the intake air flowing through the intake pipe 9 are provided at an intake pipe 9 downstream of the air cleaner box 10. An intake air temperature sensor 12 that outputs a 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 position of the intake pipe 9 immediately upstream of the intake branch pipe 8. The intake throttle valve 13 has an intake throttle actuator 1 that includes a stepper motor or the like and drives the intake throttle valve 13 to open and close.
4 is attached.

A compressor housing 15a of a centrifugal supercharger (turbocharger) 15 which operates using heat energy of exhaust gas as a drive source is provided in an intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13. And
An intercooler 16 for cooling intake air, which has been compressed in the compressor housing 15a and has become high temperature, 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 passes through the intake pipe 9 after dust and the like in the intake are removed by an air cleaner (not shown) in the air cleaner box 10. And flows into the compressor housing 15a.

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

On the other hand, an exhaust branch pipe 18 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 18 communicates with a combustion chamber of each cylinder 2 via an exhaust port (not shown).

The exhaust branch pipe 18 is connected to the centrifugal turbocharger 15.
Of 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 exhaust gas purifying catalyst 20 for purifying harmful gas components in exhaust gas is disposed in the exhaust pipe 19. The exhaust pipe 19 downstream of the exhaust purification catalyst 20 includes:
An air-fuel ratio sensor 23 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust flowing through the exhaust pipe 19; and an outgoing gas that outputs an electric signal corresponding to the temperature of the exhaust flowing through the exhaust pipe 19 and flowing into the catalyst 20. A temperature sensor 24 and an incoming gas temperature sensor 37 that outputs an electric signal corresponding to the temperature of exhaust gas flowing through the exhaust pipe 19 and flowing out of the catalyst 20 are attached.

The exhaust pipe 19 downstream of the air-fuel ratio sensor 23 and the outlet gas temperature sensor 24 is provided with an exhaust throttle valve 21 for adjusting the flow rate of exhaust flowing through the exhaust pipe 19. The exhaust throttle valve 21 is provided with an exhaust throttle actuator 22 configured by a stepper motor or the like and driving the exhaust throttle valve 21 to open and close.

In the exhaust system configured as described above, the air-fuel mixture (burned gas) burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust branch pipe 18 through the exhaust port, and then to the exhaust branch pipe 18. To the turbine housing 15b of the centrifugal supercharger 15
Flows into The exhaust gas flowing into the turbine housing 15b rotates a turbine wheel rotatably supported in the turbine housing 15b by using thermal energy of the exhaust gas. At this 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 an exhaust gas purifying catalyst 20 through an exhaust pipe 19, and harmful gas components in the exhaust gas are removed or purified. The exhaust gas from which the harmful gas components have been removed or purified by the exhaust purification catalyst 20 is discharged into the atmosphere via a muffler after the flow rate is adjusted by an exhaust throttle valve 21 as necessary.

The exhaust branch pipe 18 and the intake branch pipe 8 communicate with each other via an exhaust gas recirculation passage (EGR passage) 25 for recirculating a part of the exhaust gas flowing through the exhaust branch pipe 18 to the intake branch pipe 8. Have been. In the middle of the EGR passage 25, a flow rate adjusting valve (EGR) configured by an electromagnetic valve or the like to change the flow rate of exhaust gas (hereinafter, referred to as EGR gas) flowing in the EGR passage 25 according to the magnitude of the applied electric power. (Valve) 26 is provided.

In the EGR passage 25, an EGR valve 26
The EG flowing in the EGR passage 25 is located at a more upstream portion.
An EGR cooler 27 for cooling the R gas is provided.

In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe 18 flows to the EGR passage 25. It flows into the intake branch pipe 8 through 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 a predetermined refrigerant, and the EGR gas is cooled.

The EGR gas recirculated from the exhaust branch pipe 18 to the intake branch pipe 8 through the EGR passage 25 is guided to the combustion chamber of each cylinder 2 while mixing with fresh air flowing from the upstream of the intake branch pipe 8. Then, the fuel injected from the fuel injection valve 3 is burned using the ignition source.

Here, the EGR gas contains an inert gas component such as water (H ₂ O) or carbon dioxide (CO ₂ ) which does not burn itself and has endothermic properties, such as water (H ₂ O). Therefore, if EGR gas is contained in the air-fuel mixture,
The combustion temperature of the air-fuel mixture is lowered, so that nitrogen oxides (NO
x) is suppressed.

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

Next, the exhaust purification catalyst 2 according to the present embodiment
0 will be specifically described.

The exhaust purification catalyst 20 is a NOx catalyst that purifies nitrogen oxides (NOx) in exhaust gas in the presence of a reducing agent. Examples of such a NOx catalyst include a selective reduction type NOx catalyst and a storage reduction type NOx catalyst. Here, the storage reduction type NOx catalyst will be described as an example. Hereinafter, the exhaust purification catalyst 20 is replaced with the NOx storage reduction catalyst 2.
It shall be referred to as 0.

The storage-reduction type NOx catalyst 20 uses, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li) or cesium (Cs) and barium on the carrier. (Ba) or at least one selected from alkaline earths such as calcium (Ca) and lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). ing. In the present embodiment,
Barium (Ba) and platinum (P) on a support made of alumina
t) will be described as an example.

When the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 is high, nitrogen oxides (NOx) in the exhaust gas are stored in the NOx storage reduction catalyst 20 configured as described above.
Absorb.

On the other hand, the NOx storage reduction catalyst 20 releases nitrogen oxides (NOx) absorbed when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 decreases. At this time, if reducing components such as hydrocarbons (HC) and carbon monoxide (CO) are present in the exhaust gas, the storage-reduction type N
The Ox catalyst 20 can reduce nitrogen oxides (NOx) released from the storage reduction type NOx catalyst 20 to nitrogen (N ₂ ).

Incidentally, although there is no clear explanation of the NOx absorbing / releasing action of the NOx storage reduction catalyst 20,
It is thought that this is done by the following mechanism.

First, in the NOx storage reduction catalyst 20, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes a lean air-fuel ratio and the oxygen concentration in the exhaust gas increases, FIG.
As shown in (A), the oxygen (O ₂ ) in the exhaust gas becomes O ₂ ⁻
Or adheres to the surface of platinum (Pt) in the form of O ²⁻ . Nitric oxide (NO) in the exhaust reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum (Pt) to form nitrogen dioxide (NO ₂ ) (2NO + O ₂ → 2NO ₂ ). Nitrogen dioxide (NO ₂ )
Is further oxidized on the surface of platinum (Pt) and absorbed by the NOx storage reduction catalyst 20 in the form of nitrate ions (NO ₃₋ ). The nitrate ions (NO ₃₋ ) absorbed by the NOx storage reduction catalyst 20 combine with barium oxide (BaO) to form barium nitrate (Ba (NO ₃ ) ₂ ).

When the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is the lean air-fuel ratio, the nitrogen oxides (NOx) in the exhaust gas are converted into nitrate ions (NO ₃₋ ) as the NOx storage-reduction type. It is absorbed by the catalyst 20.

In the NOx absorbing operation as described above, the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio, and the NOx storage-reduction type
The operation is continued as long as the NOx absorption capacity of the x catalyst 20 is not saturated. Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is the lean air-fuel ratio, the NOx storage-reduction NOx
As long as the NOx absorption capacity of the x catalyst 20 is not saturated, nitrogen oxides (NOx) in the exhaust gas are absorbed by the NOx storage reduction catalyst 20, and nitrogen oxides (NOx) are removed from the exhaust gas.

On the other hand, the storage reduction type NOx catalyst 20
Then, when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 20 decreases, the amount of nitrogen dioxide (NO ₂ ) generated on the surface of platinum (Pt) decreases, so that it is combined with barium oxide (BaO). The nitrate ions (NO ₃₋ ) that have been conversely turn into nitrogen dioxide (NO ₂ ) or nitrogen monoxide (NO) and are released from the NOx storage reduction catalyst 20.

At this time, if reducing components such as hydrocarbons (HC) and carbon monoxide (CO) are present in the exhaust gas, those reducing components are converted to oxygen (O ₂₋ or O ₂ ) on platinum (Pt). ^2- )
Reacts to form active species. This active species
Nitrogen dioxide (NO ₂ ) and nitric oxide (NO) released from the NOx storage reduction catalyst 20 are reduced to nitrogen (N ₂ ).

Accordingly, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, the oxygen concentration in the exhaust decreases and the concentration of the reducing agent increases, the NOx storage-reduction NOx increases. The nitrogen oxides (NOx) absorbed by the catalyst 20 are released and reduced, whereby the NOx absorption capacity of the NOx storage reduction catalyst 20 is regenerated.

When the internal combustion engine 1 is operating in the lean burn operation, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust gas becomes high.
Nitrogen oxides (NOx) contained in exhaust gas are stored and reduced N
Although it is absorbed by the Ox catalyst 20, if the lean burn operation of the internal combustion engine 1 is continued for a long time, the NOx stored and reduced
The NOx absorption capacity of the catalyst 20 is saturated, and nitrogen oxides (NOx) in the exhaust gas are released to the atmosphere without being removed by the NOx storage reduction catalyst 20.

In particular, in a diesel engine such as the internal combustion engine 1, a mixture having a lean air-fuel ratio is burned in most of the operating region, and the air-fuel ratio of exhaust gas becomes a lean air-fuel ratio in most of the operating region. Therefore, the storage reduction type NO
The NOx absorption capacity of the x catalyst 20 is likely to be saturated.

Therefore, when the internal combustion engine 1 is operating in the lean burn operation, the oxygen concentration in the exhaust gas flowing into the NOx storage reduction catalyst 20 is reduced before the NOx absorption capacity of the NOx storage reduction catalyst 20 is saturated. At the same time, it is necessary to increase the concentration of the reducing agent to release and reduce nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst 20.

On the other hand, the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment supplies a reducing agent (light oil) as a reducing agent to exhaust gas flowing through an exhaust passage upstream of the NOx storage reduction catalyst 20. Mechanism, and by adding fuel from the reducing agent supply mechanism to the exhaust gas, the storage reduction NO
The x concentration of the exhaust gas flowing into the catalyst 20 was reduced, and the concentration of the reducing agent was increased.

As shown in FIG. 1, the reducing agent supply mechanism is mounted on the cylinder head of the internal combustion engine 1 so that the injection hole faces the exhaust branch pipe 18, and the fuel having a predetermined valve opening pressure or higher is applied. A reducing agent injection valve 28 that opens and injects fuel when the fuel is discharged; a reducing agent supply passage 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28; A flow control valve 30 provided in the middle of the flow passage for adjusting the flow rate of the fuel flowing through the reducing agent supply passage 29
A shutoff valve 31 provided in the reducing agent supply passage 29 upstream of the flow control valve 30 to shut off the flow of fuel in the reducing agent supply passage 29; and a reducing agent supply passage upstream of the flow control valve 30. A reducing agent pressure sensor 32 that is attached to and outputs an electric signal corresponding to the pressure in the reducing agent supply passage 29;
And

The reducing agent injection valve 28 has an injection hole of the reducing agent injection valve 28 located downstream from a connection portion of the exhaust branch pipe 18 with the EGR passage 25, and is connected to four branch pipes of the exhaust branch pipe 18. It is preferable that the projection is protruded to the exhaust port of the cylinder 2 closest to the collecting portion and is attached to the cylinder head so as to face the collecting portion of the exhaust branch pipe 18.

This prevents the reducing agent (unburned fuel component) injected from the reducing agent injection valve 28 from flowing into the EGR passage 25 and suppresses the reducing agent from remaining in the exhaust branch pipe 18. To do that.

In the example shown in FIG. 1, the first (# 1) cylinder 2 of the four cylinders 2 of the internal combustion engine 1 is located closest to the collecting portion of the exhaust branch pipe 18, so that the first (# 1) cylinder 2 1) Although the reducing agent injection valve 28 is attached to the exhaust port of the cylinder 2, when the cylinder 2 other than the first (# 1) cylinder 2 is located closest to the gathering portion of the exhaust branch pipe 18, The reducing agent injection valve 28 is attached to the exhaust port of the cylinder 2.

Further, the reducing agent injection valve 28 is designed to penetrate a water jacket (not shown) formed in the cylinder head or to be mounted close to the water jacket, and to reduce the water using cooling water flowing through the water jacket. The agent injection valve 28 may be cooled.

In such a reducing agent supply mechanism, when the flow control valve 30 is opened, the high-pressure fuel discharged from the fuel pump 6 is supplied through the reducing agent supply passage 29 to the reducing agent injection valve 28.
Is applied. When the pressure of the fuel applied to the reducing agent injection valve 28 reaches or exceeds the valve opening pressure, the reducing agent injection valve 2
8 is opened, 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 flows into the turbine housing 15b together with the exhaust gas flowing from the upstream of the exhaust branch pipe 18. The exhaust gas and the reducing agent that have flowed into the turbine housing 15b are agitated and uniformly mixed by the rotation of the turbine wheel to form an exhaust gas having a rich air-fuel ratio.

The rich air-fuel ratio exhaust gas thus formed flows from the turbine housing 15b into the NOx storage reduction catalyst 20 via the exhaust pipe 19, and is stored in the NOx storage reduction catalyst.
While releasing nitrogen oxides are absorbed in Ox catalyst 20 (NOx) will be reduced to nitrogen (N _2).

Thereafter, when the flow control valve 30 is closed and the supply of the reducing agent from the fuel pump 6 to the reducing agent injection valve 28 is interrupted, the pressure of the fuel applied to the reducing agent injection valve 28 is increased. As a result, the reducing agent injection valve 28 closes, and the addition of the reducing agent into the exhaust branch pipe 18 is stopped.

The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the internal combustion engine 1. The ECU 35 is a unit that controls the operating state of the internal combustion engine 1 according to the operating conditions of the internal combustion engine 1 and the driver's requirements.

The ECU 35 includes a common rail pressure sensor 4
a, air flow meter 11, intake air temperature sensor 12, intake pipe pressure sensor 17, air-fuel ratio sensor 23, outgoing gas temperature sensor 24, incoming gas temperature sensor 37, reducing agent pressure sensor 3
2, crank position sensor 33, water temperature sensor 34,
Various sensors such as an accelerator opening sensor 36 are connected via electric wiring, and output signals of the various sensors described above are output from the ECU.
35.

On the other hand, the ECU 35 is connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the flow control valve 30, the shutoff valve 31 and the like via electric wiring. Each part is ECU3
5 can be controlled.

Here, as shown in FIG. 3, the ECU 35 is connected to a C
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, such as the crank position sensor 33, and converts those output signals to C.
The data is transmitted to the PU 351 and the RAM 353.

The input port 356 is connected to the common rail pressure sensor 4a, the air flow meter 11, the intake air temperature sensor 1
2, intake pipe pressure sensor 17, air-fuel ratio sensor 23, outlet gas temperature sensor 24, inlet gas temperature sensor 37, reducing agent pressure sensor 32, water temperature sensor 34, accelerator opening sensor 36,
And the like, input through an A / D 355 of a sensor that outputs a signal in the form of an analog signal, and output these signals to C
The data is transmitted to the PU 351 and the RAM 353.

The output port 357 is connected to the fuel injection valve 3,
Intake throttle actuator 14, exhaust throttle actuator 22, EGR valve 26, flow control valve 30, shut-off valve 31
Control signals output from the CPU 351 are connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22,
The signal is transmitted to the EGR valve 26, the flow control valve 30, 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 EGR. EGR control routine for controlling valve 26, storage reduction type NOx
NOx purification control routine for purifying nitrogen oxides (NOx) absorbed by the catalyst 20, NOx storage-reduction type NOx catalyst 2
An application program such as a poisoning elimination control routine for eliminating poisoning caused by the oxide of 0 is stored.

The ROM 352 stores various control maps in addition to the application programs described above. The control map includes, for example, a fuel injection amount control map indicating a relationship between an operation state of the internal combustion engine 1 and a basic fuel injection amount (basic fuel injection time), and a relation between the operation state of the internal combustion engine 1 and the basic fuel injection timing. Fuel injection timing control map,
An intake throttle valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the intake throttle valve 13, and the exhaust throttle showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the exhaust throttle valve 21. Valve opening control map, operating state of internal combustion engine 1 and EGR
EGR valve opening control map showing the relationship with the target opening of the valve 26, reducing agent addition control showing the relationship between the operating state of the internal combustion engine 1 and the target adding amount of the reducing agent (or the target air-fuel ratio of the exhaust). A map, a flow control valve control map, and the like showing a relationship between a target addition amount of the reducing agent and a valve opening time of the flow control valve 30.

The RAM 353 stores an output signal from each sensor, a calculation result of the CPU 351 and the like. The calculation result is, for example, an engine speed calculated based on a time interval at which the crank position sensor 33 outputs a pulse signal. These data are rewritten to the latest data each time the crank position sensor 33 outputs a pulse signal.

The backup RAM 354 is a nonvolatile memory capable of storing data even after the operation of the internal combustion engine 1 is stopped.

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

For example, in the fuel injection valve control, the CPU 35
1 first determines the amount of fuel injected from the fuel injection valve 3 and then determines the timing for injecting fuel from the fuel injection valve 3.

When determining the fuel injection amount, the CPU 35
1 reads the engine speed and the output signal (accelerator opening) of the accelerator opening sensor 36 stored in the RAM 353. The CPU 351 accesses the fuel injection amount control map, and calculates a basic fuel injection amount (basic fuel injection time) corresponding to the engine speed and the accelerator opening. The CPU 351 corrects the basic fuel injection time based on output signal values of the air flow meter 11, the intake air temperature sensor 12, the water temperature sensor 34, and the like, and determines a final fuel injection time.

When determining the fuel injection timing, the CPU 3
51 accesses a fuel injection start timing control map and calculates a basic fuel injection timing corresponding to the engine speed and the accelerator opening. The CPU 351 corrects the basic fuel injection timing by using output signal values of the air flow meter 11, the intake air temperature sensor 12, the water temperature sensor 34, and the like as parameters, and determines the final fuel injection timing.

When the fuel injection time and the fuel injection timing are determined, the CPU 351 compares the fuel injection timing with the output signal of the crank position sensor 33, and determines that the output signal of the crank position sensor 33 is the fuel injection start time. At the time coincident with the timing, application of drive power to the fuel injection valve 3 is started. The CPU 351 stops applying the driving power to the fuel injection valve 3 when the elapsed time from the start of the application of the driving power to the fuel injection valve 3 reaches the fuel injection time.

In the fuel injection control, when the operating state of the internal combustion engine 1 is an idle operating state, the CPU 351
Is a target idle speed of the internal combustion engine 1 using parameters such as the output signal value of the water temperature sensor 34 and the operating state of accessories that operate using the rotational force of a crankshaft, such as a compressor of a vehicle interior air conditioner. Is calculated. And
The CPU 351 performs feedback control of the fuel injection amount so that the actual idle speed matches the target idle speed.

In the intake throttle control, the CPU 351
Reads the engine speed and the accelerator opening stored in the RAM 353, for example. The CPU 351 accesses the intake throttle valve opening control map, and calculates a target intake throttle valve opening corresponding to the engine speed and the accelerator opening. C
The PU 351 applies drive power corresponding to the target intake throttle valve opening to the intake throttle actuator 14. At that time, the CPU 351 detects the actual opening of the intake throttle valve 13 and feeds back the intake throttle actuator 14 based on the difference between the actual opening of the intake throttle valve 13 and the target intake throttle valve opening. You may make it control.

In the exhaust throttle control, the CPU 351
For example, when the internal combustion engine 1 is in a warm-up operation state after a cold start, or when a vehicle interior heater is in an operating state, the exhaust throttle actuator is driven to close the exhaust throttle valve 21 in the valve closing direction. 22 is controlled.

In this case, the load on the internal combustion engine 1 increases, and the fuel injection amount is correspondingly increased. As a result, the calorific value of the internal combustion engine 1 increases, the warm-up of the internal combustion engine 1 is promoted, and the heat source of the vehicle interior heater is secured.

In EGR control, the CPU 351
The engine speed stored in the RAM 353, the output signal of the water temperature sensor 34 (cooling water temperature), the accelerator opening sensor 3
The output signal of 6 (accelerator opening) and the like are read, and it is determined whether or not the execution condition of the EGR control is satisfied.

The above-mentioned EGR control execution conditions are as follows: the coolant temperature is equal to or higher than a predetermined temperature, the internal combustion engine 1 has been continuously operated for a predetermined time or more from the start, and the change amount of the accelerator opening is a positive value. Conditions such as certain conditions can be exemplified.

If it is determined that the above-described EGR control execution condition is satisfied, the CPU 351 accesses the EGR valve opening control map using the engine speed and the accelerator opening as parameters, and And a target EGR valve opening corresponding to the accelerator opening. CPU
351 applies the drive power corresponding to the target EGR valve opening to the EGR valve 26. On the other hand, EGR as described above
If it is determined that the control execution condition is not satisfied,
U351 controls to keep the EGR valve 26 in the fully closed state.

Further, in the EGR control, the CPU 351
EGR valve 2 using intake air amount of internal combustion engine 1 as a parameter
The so-called EGR valve feedback control for performing feedback control of the opening degree of the valve 6 may be performed.

In the EGR valve feedback control, for example, the CPU 351 determines the target intake air amount of the internal combustion engine 1 using the accelerator opening, the engine speed and the like as parameters. At this time, the relationship between the accelerator opening, the engine speed, and the target intake air amount may be mapped in advance, and the target intake air amount may be calculated from the map, the accelerator opening, and the engine speed. .

When the target intake air amount is determined by the above procedure, the CPU 351 reads out the output signal value (actual intake air amount) of the air flow meter 11 stored in the RAM 353, and reads the actual intake air amount and the target intake air amount. Compare with air volume.

When the actual intake air amount is smaller than the target intake air amount, the CPU 351 closes the EGR valve 26 by a predetermined amount. In this case, the amount of EGR gas flowing into the intake branch pipe 8 from the EGR passage 25 decreases, and accordingly, the amount of EGR gas drawn into the cylinder 2 of the internal combustion engine 1 decreases. As a result, the cylinder 2 of the internal combustion engine 1
The amount of fresh air sucked in increases by the amount of the decrease in the EGR gas.

On the other hand, when the actual intake air amount is larger than the target intake air amount, the CPU 351 opens the EGR valve 26 by a predetermined amount. In this case, the amount of EGR gas flowing into the intake branch pipe 8 from the EGR passage 25 increases, and accordingly, the amount of EGR gas drawn into the cylinder 2 of the internal combustion engine 1 increases. As a result, the amount of fresh air sucked into the cylinder 2 of the internal combustion engine 1 decreases by an amount corresponding to the increase in the EGR gas.

Next, in the NOx purification control, the CPU 351
Executes a so-called rich spike control in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is set to a rich air-fuel ratio in a spike-like (short-time) manner at a relatively short cycle.

In the rich spike control, the CPU 351
Determines whether the rich spike control execution condition is satisfied at predetermined intervals. The conditions for executing the rich spike control include, for example, poisoning elimination control in which the storage reduction type NOx catalyst 20 is in an active state, the output signal value (exhaust gas temperature) of the gas output temperature sensor 24 is equal to or lower than a predetermined upper limit value. Conditions such as not being executed can be exemplified.

When it is determined that the rich spike control execution condition described above is satisfied, the CPU 351
Is to temporarily control the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 to a predetermined target rich by controlling the flow control valve 30 so as to inject fuel as a reducing agent spikes from the reducing agent injection valve 28. Air-fuel ratio.

More specifically, the CPU 351
Engine speed, accelerator opening sensor 3 stored in
6 output signal (accelerator opening), air flow meter 11
, The output signal value of the air-fuel ratio sensor 23, the fuel injection amount, and the like. The CPU 351 accesses the reducing agent addition amount control map of the ROM 352 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 rich air-fuel ratio. Calculate the addition amount (target addition amount) of the reducing agent necessary for performing the above.

Subsequently, the CPU 351 accesses the flow control valve control map of the ROM 352 using the target addition amount as a parameter, and controls the flow control valve necessary for injecting the target addition amount of reducing agent from the reducing agent injection valve 28. The valve opening time of 30 (target valve opening time) is calculated.

When the target opening time of the flow control valve 30 is calculated, the CPU 351 opens the flow control valve 30.
In this case, since the high-pressure fuel discharged from the fuel pump 6 is supplied to the reducing agent injection valve 28 via the reducing agent supply path 29, the pressure of the fuel applied to the reducing agent injection valve 28 is equal to or higher than the valve opening pressure. , And the reducing agent injection valve 28 opens.

The CPU 351 closes the flow control valve 30 when the target valve opening time has elapsed since the flow control valve 30 was opened. In this case, since the supply of the reducing agent from the fuel pump 6 to the reducing agent injection valve 28 is shut off, the pressure of the fuel applied to the reducing agent injection valve 28 becomes lower than the valve opening pressure, and the reducing agent injection valve 28 is closed. Give a valve.

When the flow control valve 30 is opened for the target opening time in this manner, the target amount of fuel is supplied to the reducing agent injection valve 2.
8, the fuel is injected into the exhaust branch pipe 18. Then, the reducing agent injected from the reducing agent injection valve 28 is mixed with the exhaust gas flowing from the upstream of the exhaust branch pipe 18 to form an air-fuel mixture having a target rich air-fuel ratio, and the storage-reduction NOx catalyst 2
Flows into zero.

As a result, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes “lean” in a relatively short cycle.
And the "spike-like target rich air-fuel ratio" are alternately repeated, so that the NOx storage reduction catalyst 20 alternately repeats the absorption, release, and reduction of nitrogen oxides (NOx) in a short cycle. Will be.

Next, in the poisoning elimination control, the CPU 351
Means that the poisoning elimination process is performed to eliminate the poisoning of the NOx storage reduction catalyst 20 due to the oxide.

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

The sulfur oxides (SOx) flow into the NOx storage reduction catalyst 20 together with the exhaust gas, and the nitrogen oxides (NOx)
By the same mechanism as described above, the NOx storage reduction catalyst 20 is used.
Is absorbed by

Specifically, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is a lean air-fuel ratio,
As described in the above description of the NOx absorption mechanism,
Oxygen (O ₂₎ is O ₂ ^- or for adhering with O ^2- in the form on the surface of platinum (Pt), sulfur dioxide (S in the inflowing exhaust gas
O ₂₎ and sulfur trioxide (SO ₃₎ Sulfur oxides such as (SOx)
SO reacts or O ^2- and ^- but O ₂ on the surface of the platinum (Pt)
_3- or SO _4- .

[0118] SO_3-And SO_Four-Is on the surface of platinum (Pt)
Is further oxidized by sulfate ion (SO _Four ^2-Occlusion in the form of)
It is absorbed by the original NOx catalyst 20. In addition, the storage reduction type NOx
Sulfate ions (SO_Four ^2-) Oxidation
Combined with barium (BaO), sulfate (BaSO)_Four)
Form.

When the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is the lean air-fuel ratio, the sulfur oxides (SOx) in the exhaust gas are converted into sulfate ions (SO ₄ ²⁻ ) as the occlusion-reduction type NOx catalyst. It is absorbed by the NOx catalyst 20.

Sulfate (BaSO ₄ ) is more stable than barium nitrate (Ba (NO ₃ ) ₂ ) and is less likely to be decomposed, and the air-fuel ratio of exhaust gas flowing into the NOx storage reduction catalyst 20 is theoretically higher. Even when the air-fuel ratio or the rich air-fuel ratio is reached, the fuel is not decomposed and remains in the NOx storage reduction catalyst 20.

When the amount of sulfate (BaSO ₄ ) in the NOx storage reduction catalyst 20 increases, the amount of barium oxide (BaO) that can participate in the absorption of nitrogen oxide (NOx) decreases accordingly. , Storage reduction type NOx
So-called SOx poisoning occurs in which the NOx absorption capacity of the catalyst 20 decreases.

As a method for eliminating SOx poisoning of the NOx storage reduction catalyst 20, the ambient temperature of the NOx storage reduction catalyst 20 is raised to a high temperature range of about 500 ° C. to 700 ° C. By setting the air-fuel ratio of the exhaust gas flowing into the NOx 20 to the rich air-fuel ratio, the barium sulfate (Ba)
The SO ₄₎ is thermally decomposed into SO _3- and SO _4-, then SO _3- and SO _4-a in the exhaust hydrocarbons (HC) and carbon monoxide (C
O) to reduce to gaseous SO ₂₋ .

Therefore, in the poisoning elimination process according to the present embodiment, the CPU 351 firstly performs the storage reduction type NOx catalyst 20 operation.
After the catalyst temperature raising process for raising the bed temperature of the NOx catalyst is performed, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is set to the rich air-fuel ratio.

In the catalyst temperature increasing process, the CPU 351 performs, for example, post-injection of fuel from the fuel injection valve 3 and addition of fuel from the reducing agent injection valve 28 into exhaust gas during the expansion stroke of each cylinder 2. Thereby, those unburned fuel components are oxidized in the NOx storage reduction catalyst 20,
Oxidation-reduction type NOx catalyst 2 due to heat generated during oxidation
The floor temperature of 0 may be raised.

However, if the temperature of the NOx storage reduction catalyst 20 rises excessively, thermal deterioration of the NOx storage reduction catalyst 20 may be induced. It is preferable that the injected fuel amount and the added fuel amount are feedback-controlled.

When the bed temperature of the NOx storage reduction catalyst 20 rises to a high temperature range of about 500 ° C. to 700 ° C. by the above-described catalyst temperature raising processing, the CPU 351 starts the storage reduction type NOx catalyst.
Fuel is injected from the reducing agent injection valve 28 so that the air-fuel ratio of the exhaust gas flowing into the Ox catalyst 20 becomes a rich air-fuel ratio.

When excess fuel is injected from the reducing agent injection valve 28, the fuel is stored in the NOx storage reduction catalyst 20.
And the NOx storage reduction catalyst 20 is overheated,
Alternatively, the storage-reduction NOx catalyst 20 may be unnecessarily cooled by excessive fuel injected from the reducing agent injection valve 28. May be feedback controlled.

When the poisoning elimination process is executed as described above,
When the bed temperature of the NOx storage reduction catalyst 20 is high, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 becomes a rich air-fuel ratio. Therefore, the barium sulfate absorbed by the NOx storage reduction catalyst 20 ( BaSO ₄ ) is SO ₃₋ or SO ₄₋
Is thermally decomposed into SO ₃ and SO _4−, which react with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas to form gaseous sulfur.
It is reduced to O ₂₋ , so that the SOx of the NOx storage reduction catalyst 20 is reduced.
Poisoning will be eliminated.

In the NOx purification control described above, CP
The U351 executes the rich spike control at a predetermined cycle, so that the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is spiked to the target rich air-fuel ratio, and the nitrogen oxidation absorbed by the NOx storage reduction catalyst 20 is performed. The substance (NOx) is released and reduced.

In order to efficiently purify NOx and eliminate poisoning, it is necessary to accurately grasp the bed temperature of the NOx catalyst 20 and to perform rich spike control according to the bed temperature.

However, since the bed temperature of the NOx catalyst 20 rises due to the rich spike, the bed temperature of the NOx catalyst 20 may become higher than the exhaust gas temperature measured by the gas input temperature sensor 37 during the rich spike control. There is.

The temperature of the exhaust gas measured by the outlet gas temperature sensor 24 is lower than the bed temperature of the NOx catalyst 20 because it is installed downstream of the NOx catalyst 20.

Even if the bed temperature of the NOx catalyst 20 is simply estimated from the amount of fuel added to the exhaust branch 18, the fuel added to the exhaust branch 18 is immediately evaporated or atomized, and the NOx catalyst is added together with the exhaust gas. Some reach the NOx catalyst 20, while others take a long time to reach the NOx catalyst 20 as they adhere to the wall surface of the exhaust branch pipe 18 as liquid. As described above, since the entire amount of the added fuel does not immediately reach the NOx catalyst 20, it is difficult to accurately obtain the bed temperature of the NOx catalyst 20.

Therefore, in the present embodiment, N is taken into consideration in consideration of the attachment and evaporation of the fuel added as the reducing agent on the exhaust branch pipe 20.
The bed temperature of the Ox catalyst 20 was estimated.

Next, a method for estimating the bed temperature of the NOx catalyst 20 of the exhaust gas purifying apparatus for an internal combustion engine according to this embodiment will be described with reference to the flowchart of FIG.

In step 101, the operation status of the internal combustion engine 1 is determined.
Necessary for estimating the bed temperature of the NOx catalyst 20 based on the state
New volume G_a, Exhaust temperature T_ex, Emission HC amount M_HC, Emission CO
Quantity M_{C O}, The exhaust fuel injection pulse (or fuel injection amount) is R
AM 353.

[0137] intake fresh air amount G _a is calculated based on the output signal value of the airflow meter 11 stored in the RAM 353.

The temperature T _{ex of} the exhaust gas discharged from the internal combustion engine 1, the HC amount M _HC contained in the exhaust gas, and the CO amount M _CO contained in the exhaust gas are represented by an exhaust temperature map, an HC map, and a C map, respectively.
It is calculated with reference to the O map.

Here, the operating state of the internal combustion engine 1 includes the engine speed, the amount of intake air, the amount of fuel injected into the cylinder 2, and the like. The relationship between the amount of CO and the amount of CO is determined in advance and mapped.
352.

The CPU 351 determines the engine speed and accelerator opening.
RO, using the degree, intake air amount and fuel injection amount as parameters
Access the M352 reduction agent addition amount control map and exhaust
To make the air-fuel ratio of the target rich air-fuel ratio set in advance
Required fuel addition amount F_{in j}Is calculated.

In step 102, the amount M _WSUM and the amount of evaporation M _Y of the fuel added to the exhaust branch 18 on the wall surface of the exhaust branch 18 are calculated. This value is calculated by the following equation, for example.

M _WSUM = ΣM _{f (n)} M _Y = Y · M _{f (n)} M _{f (n)} = X · M _inj −Y · M _{f (n-1)} where M _f : one time The amount of fuel adhering to the wall surface during the fuel injection X: the fuel wall adhering rate Y: the evaporation rate of the wall adhering fuel _Minj : the amount of fuel (reducing agent) injected at one time.

It has been confirmed that the fuel wall deposition rate X and the wall deposition fuel evaporation rate Y change in accordance with the wall temperature of the exhaust branch pipe 18, the flow rate of the exhaust gas, and the temperature of the exhaust gas. The flow rate of the exhaust gas is expressed as a function of the fuel injection amount to the intake air amount and the cylinder 2, the wall surface temperature T _exm, the intake air amount G _a, fuel injection amount, the wall adhesion ratio X, the relationship of the evaporation rate Y Are determined in advance by experiments, etc.
352.

It is known that the wall surface temperature T _exm before fuel addition is obtained as, for example, a temporary delay of the exhaust gas temperature T _ex or a response delay required for heat transfer. After the fuel addition is started, the temperature T _exa of the exhaust branch pipe 18 obtained in step 104 of the previous routine is used.

In step 103, energy calculation in the exhaust branch pipe 18 is performed. This includes the amount of heat Q
_ex, the amount of heat Q _exm with the exhaust branch pipe 18, the amount of heat Q _ExmX included in the fuel adhering to the wall surface, fuel is required quantity of heat Q _ExmY required to evaporate.

The heat quantity Q _{ex of the} exhaust gas can be expressed by the following equation, for example.

Q _ex = M _ex · C _ex · T _ex where M _ex is the mass of the exhaust, C _ex is the specific heat of the exhaust, T _ex is the temperature of the exhaust, and the mass M _ex of the exhaust is calculated based on the fuel main injection amount to the output signal and the cylinder 2, the temperature T _ex of the exhaust is used as the temperature T _ex of the exhaust gas calculated in step 101. Incidentally, the specific heat C _ex of the exhaust is constant.

The heat quantity Q _exm of the exhaust branch pipe 18 can be expressed by the following equation, for example.

Q _exm = M _exm · C _exm · T _exm M _exm is the mass of the exhaust branch 18, C _exm is the specific heat of the exhaust branch 18, and T _exm is the temperature of the exhaust branch 18. Exhaust branch pipe 18
Is measured in advance and stored in the ROM 352.
As the temperature T _exm of the exhaust branch pipe 18, the value obtained in step 102 is used.

The heat quantity Q of the fuel attached to the wall surface
_exmX can be represented by the following equation, for example.

Q_exmX= M_WSUM・ C_exmX・ T_exmX M_WSUMAdheres to the exhaust branch pipe 18 calculated in step 102
Fuel mass, C_{ex mX}Is the fuel attached to the exhaust branch pipe 18.
Specific heat, T_exmXIs the temperature of the fuel attached to the exhaust branch pipe 18.
is there. The specific heat C of the fuel attached to the exhaust branch pipe 18_exmXIs
To be constant.

The fuel temperature T _exmX can be estimated based on the intake air temperature obtained by the intake air temperature sensor 12 or calculated by installing a fuel temperature sensor (not shown) in the reducing agent supply passage 29.

The amount of heat Q _exmY required for the fuel to evaporate is
For example, it can be represented by the following equation.

Q_exmY= M_Y・ R_exmY M_YAdheres to the exhaust branch pipe 18 calculated in step 102.
Fuel evaporation, R_{exm Y}Evaporates fuel per unit mass
It is the heat of evaporation required to make Heat of evaporation R_exmYIs required in advance
It is stored in the ROM 352 in advance.

[0155] At step 104, the exhaust branch pipe after the fuel M _Y evaporated based on the calculation result of Step 103 1
8 to calculate the wall surface temperature T _exa of. Here, it is assumed that the temperature of the exhaust and the exhaust branch 18 become the same temperature T _exa , and that all the heat _absorbed by the evaporation of the fuel is consumed by the temperature drop between the exhaust and the exhaust branch 18. Then, the following equation is established.

Q _ex + Q _exm + Q _exmX -Q _exmY = M _ex · C
_ex・ T _exa + M _exm・ C _exm・ T _exa + (M _WSUM −M _Y ) ・
C _exmX · T _exmX Here, the left side of this equation represents the total amount of heat before fuel evaporation, and the right side represents the total amount of heat after fuel evaporation.

Accordingly, the wall surface temperature T _exa of the exhaust branch pipe 18 after fuel evaporation can be calculated by the following equation.

T _exa = ｛Q _ex + Q _exm + Q _exmX −Q _exmY −
(M _WSUM −M _Y ) · C _exmX · T _exmX ｝ / (M _ex · C _ex +
M _exm · C _exm ) In step 105, the amount of heat Q _HC generated when HC contained in the exhaust gas is burned by the NOx catalyst 20 is calculated.

Q _HC = R _HC · M _HC Here, R _HC is a reaction heat generated when unburned HC per unit mass in exhaust gas undergoes an oxidation reaction, and is a constant value. M
_HC is the exhaust HC amount calculated in step 101. In addition, the amount of heat Q _CO generated when CO is burned by the NOx catalyst 20 is calculated in the same manner.

Q _CO = R _CO · M _CO Here, R _CO is a reaction heat generated when unburned CO per unit mass in the exhaust gas undergoes an oxidation reaction, and is a constant value. M
_CO is the amount of emitted CO calculated in step 101.

In step 106, the NOx catalyst 20
Fuel adhesion M arrived as a body_{CSU M}And NOx catalyst 2
Evaporation amount of fuel at 0_CYIs calculated. This value is, for example,
It is calculated by the following equation.

M _CSUM = ΣM _{Cf (n)} M _CY = Y · M _{Cf (n)} M _{Cf (n)} = X _C · (M _inj −M _{f (n)} ) −Y _C · M _{Cf (n−1) )} in _{M f (n) = X ·} M inj -Y · M f (n-1) where, M _Cf: the amount of fuel adhering to the NOx catalyst 18 in a single fuel injection X _C: NOx catalyst adhering ratio of the fuel Y _C : Evaporation rate of fuel adhering to NOx catalyst, M _f : Amount of fuel adhering to wall surface in one fuel injection X: Adhesion ratio of fuel wall surface Y: Evaporation rate of fuel adhering to wall surface M _inj : One time fuel The injection amount of the (reducing agent) is the value calculated in step 102.

The fuel injected from the reducing agent injection valve 28 to the exhaust branch pipe 18 adheres to the wall surface of the exhaust branch pipe 18 or flows to the NOx catalyst 20 together with the exhaust gas. Fuel that has not adhered to the exhaust branch pipe 18 and that has not evaporated during reaching the NOx catalyst 20 will adhere to the NOx catalyst 20.

NOx catalyst adhesion rate X of fuel_CAnd NOx catalyst
Evaporation rate Y of attached fuel_CIs the bed temperature T of the NOx catalyst 20_C, Exhaust
It is confirmed that it changes according to the air flow rate and the exhaust temperature.
ing. The flow rate of exhaust gas depends on the amount of intake air and fuel injection into cylinder 2.
It is expressed as a function of the irradiation amount, so the catalyst bed temperature, intake air
Quantity G_a, Fuel injection amount, exhaust temperature T_exn, Catalyst adhesion rate
X _C, Evaporation rate Y_CIs determined in advance by experiments, etc.
These relationships are mapped and stored in the ROM 352.
Good.

The catalyst bed temperature T _C before the addition of the fuel is calculated based on, for example, the output signal of the input gas temperature sensor 37. After fuel addition has begun, step 10 of the previous routine
The catalyst bed temperature _TCa determined in 9 is used.

In step 107, steps 102 and
The fuel vapor calculated in step 106 is the NOx catalyst 20
Of heat generated when burning at_YIs calculated. this
Calorific value Q _YCan be expressed by the following equation, for example.

Q _Y = R _Y · (M _Y + M _CY ) Here, R _Y is a constant value of reaction heat generated when a unit mass of fuel vapor is burned.

In step 108, the energy of the NOx catalyst 20 is calculated. This is because the HC and CO contained in the exhaust gas calculated in step 105 are reduced by the NOx catalyst 20.
In addition to the heat _amounts Q _HC and Q _CO generated when the fuel is burned by the NOx catalyst 20 and the heat amount Q _Y generated when the evaporated fuel is burned by the NOx catalyst 20, the heat amount _{QexC of the} exhaust gas and the NOx catalyst 20
Heat Q _C with the amount of heat Q _CX having the fuel adhering to the NOx catalyst 20, the amount of heat Q _CY necessary fuel evaporation is required.

The heat quantity Q _{exC of the} exhaust gas can be expressed by the following equation, for example.

Q _exC = M _exC · C _exC · T _exC where M _exC is the mass of exhaust gas flowing into the NOx catalyst 20,
C _exC is the specific heat of the exhaust gas flowing into the NOx catalyst 20. The mass M _exC of the exhaust gas is calculated based on the output signal of the air flow meter 11 and the main fuel injection amount into the cylinder 2, and the specific heat C _exC of the exhaust gas is fixed. T _exC is the temperature of the exhaust gas obtained by the incoming gas temperature sensor 37.

[0171] amount of heat Q _C having the NOx catalyst 20 can be represented for example by the following equation.

Q _C = M _C · C _C · T _C where M _C is the mass of the NOx catalyst 20 and C _C is the NOx catalyst 2
The specific heat is 0, and the mass M _C and the specific heat C _C are constant. T _C is the catalyst bed temperature of the NOx catalyst 20 before the catalyst reaction occurs, using the values obtained in step 106.

The heat quantity Q _CX of the fuel attached to the NOx catalyst 20 can be expressed by the following equation, for example.

Q_CX= M_CSUM・ C_CX・ T_exmX M_CSUMIs attached to the NOx catalyst 20 calculated in step 106.
Mass of fuel deposited, C_{C X}Is the fuel adhering to the NOx catalyst 20
Heat of material, T_exmXIs the value of the fuel calculated in step 103.
Temperature.

The amount of heat Q _CY required for the fuel to evaporate can be expressed, for example, by the following equation.

Q_CY= M_CY・ R_exmY M_CYAdheres to the NOx catalyst 20 calculated in step 106
Fuel evaporation, R_{e xmY}Is the unit obtained in step 103
The amount of heat required to evaporate fuel per unit mass
You.

At step 109, the bed temperature of the NOx catalyst 20 is calculated based on the calculation result at step. Here, all the heat generated by the catalytic reaction in the NOx catalyst 20 is consumed for heating the exhaust gas and the NOx catalyst, and all the heat removed by the evaporation of the fuel is consumed for the temperature drop between the exhaust gas and the exhaust branch pipe 18. Assuming that the temperature of the exhaust gas and the temperature of the NOx catalyst 20 have reached the same temperature _TCa , the following equation holds.

[0178] _{Q exC + Q C + Q HC} + Q CO + Q Y + Q CX -Q
_CY = M _C · C _C · T _Ca + M _exC · C _exC · T _Ca + (M _CSUM −
M _CY ) · C _CX • T _CX Here, the left side of this equation represents the total amount of heat before the catalytic reaction, and the right side represents the total amount of heat after the catalytic reaction.

Therefore, the catalyst bed temperature _TCa of the NOx catalyst 20 after the catalytic reaction can be calculated by the following equation.

T_Ca= ｛Q_exC+ Q_C+ Q_HC+ Q_CO+ Q_Y+
Q_CX−Q_CY− (M_CSUM-M_CY) ・ C_{C X}・ T_CX｝ / (M_C
・ C_C+ M_exC・ C_exCWhen the execution of step 109 is completed, the first
The second processing cycle is completed, and the ECU 35 returns to the second processing cycle.
The process returns to step 101 to execute the processing cycle. Soshi
Step 10 in the second and subsequent processing cycles
8, the catalyst bed calculated in step 107 of the previous cycle
Warm T_CUsing the heat quantity Q of the NOx catalyst before the catalytic reaction
_CIs calculated.

The ECU 35 repeatedly executes the processing from step 101 to step 109 to make the N
The catalyst bed temperature of the Ox catalyst is estimated and updated. And
The updated latest catalyst bed temperature is used as the catalyst bed temperature of the NOx catalyst 20 for various controls of the exhaust gas purification device.

Therefore, in the exhaust gas purifying apparatus according to this embodiment, the catalyst bed temperature of the NOx catalyst can be known without directly measuring the catalyst bed temperature of the NOx catalyst 20.

The estimated bed temperature of the NOx catalyst 20
Since the estimation is made based on the temperature of the exhaust gas flowing into zero, there is no problem such as a response delay to the actual catalyst bed temperature. Therefore, the engine operation control and the reducing agent addition control according to the catalyst bed temperature can be executed without delay with respect to the actual catalyst bed temperature, and the performance of the catalyst can be maximized.

As described above, in this exhaust gas purification apparatus, NOx
Since the catalyst bed temperature of the catalyst 20 can be estimated, the temperature detecting means for directly measuring the catalyst bed temperature is unnecessary,
In this embodiment, an outgassing temperature sensor 24 is provided downstream of the NOx catalyst 20 in order to realize fail-safe for the exhaust gas purification device. In the fail-safe system according to this embodiment, the outlet gas temperature measured by the outlet gas temperature sensor 24 is used as an actual measured value of the catalyst bed temperature (hereinafter, referred to as an actually measured catalyst bed temperature) _TC2 .

When the measured catalyst bed temperature T _C2 is significantly lower than the catalyst bed temperature of the NOx catalyst 20 (hereinafter referred to as estimated catalyst bed temperature) T _Ca estimated by executing the above-described catalyst bed temperature estimation processing. It is considered that the fuel (HC) supplied to the exhaust gas from the reducing agent injection valve 28 adheres to the NOx catalyst 20 without reacting with the NOx catalyst 20. HC thus adhering to the NOx catalyst 20 may start burning when a predetermined temperature condition is satisfied, abnormally increasing the catalyst bed temperature of the NOx catalyst 20, and promoting thermal deterioration of the NOx catalyst 20.

On the other hand, when the measured catalyst bed temperature T _C2 is significantly higher than the estimated catalyst bed temperature T _{Ca, the} amount of fuel (HC) supplied into the exhaust gas from the reducing agent injection valve 28 is smaller than the command supply amount. It is considered that there are many cases, and the cause may be a malfunction of the flow control valve 30 or the like.

If the temperature of the exhaust gas cannot be accurately obtained due to the change over time of the incoming gas temperature sensor 37, it becomes difficult to accurately control the bed temperature of the NOx catalyst 20.

Therefore, in the exhaust gas purifying apparatus of this embodiment, when the error Δt between the estimated catalyst bed temperature T _Ca and the actually measured catalyst bed temperature TC ₂ is out of the predetermined allowable error range, the exhaust gas purifying apparatus is operated. It was determined that the fuel injection was abnormal, and the execution of fuel addition from the reducing agent injection valve 28 was prohibited.

In this embodiment, when the ECU 35 executes the abnormality determination processing routine, the abnormality determination means of the present invention is realized.

The outlet gas temperature sensor 24 measures the temperature of the exhaust gas downstream of the NOx catalyst 20, and detects a value close to the actual catalyst bed temperature although there is a delay. By using this value, it is possible to detect overheating of the catalyst due to a failure of the device, which cannot be measured by the incoming gas temperature sensor 37, and to reliably realize fail-safe.

[0191]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the bed temperature of the catalyst can be known accurately and without delay, and the operation control of the internal combustion engine and the supply control of the reducing agent can be accurately performed. Can be. Further, by detecting overheating of the catalyst, thermal deterioration of the catalyst can be prevented.

As a result, it is possible to suppress the deterioration of the exhaust emission.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification device for an internal combustion engine according to the present invention is applied and an intake and exhaust system thereof.

FIG. 2 (A) illustrates the NOx absorption mechanism of a NOx storage reduction catalyst. (B) NOx of a NOx storage reduction catalyst.
Diagram explaining the release mechanism

FIG. 3 is a block diagram showing an internal configuration of an ECU.

FIG. 4 is a flowchart showing a catalyst bed temperature estimation method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 5 ... Fuel supply pipe 6 ... Fuel pump 18 ... Exhaust branch pipe 19 ... Exhaust pipe 20 ... NOx storage reduction catalyst 21 ... Exhaust throttle valve 23 ... Air-fuel ratio sensor 24 ... Outgassing temperature sensor 25 ... EGR passage 26 ... EGR valve 27 ... ..EGR cooler 28 ・ ・ ・ Reducing agent injection valve 29 ・ ・ ・ Reducing agent supply path 30 ・ ・ ・ Flow regulating valve 31 ・ ・ ・ Shutoff valve 32 ・ ・ ・ Reducing agent pressure sensor 33 ・ ・ ・ Crank position sensor 34 ・··· Water temperature sensor 35 · · · ECU 37 · · · Inlet gas temperature sensor 351 · · · CPU 352 · · · ROM 353 · · · RAM 354 · · · backup RAM

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisashi Ohki 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Kotaro Hayashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation ( 72) Inventor Shinobu Ishiyama 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Masaaki Kobayashi 1 Toyota Town Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Daisuke Shibata Aichi Prefecture 1 Toyota Town, Toyota City Inside Toyota Motor Co., Ltd. (72) Inventor Takashi Maguta 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yasuo Harada 1 Toyota Town, Toyota City, Aichi Prefecture Toyota (72) Inventor Akihiko Negami 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Stock In-company (72) Inventor Hiroki Matsuoka 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yasuhiko Otsubo 1 Toyota City Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Aoyama Taro 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Jun Tahara 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F term (reference) 3G091 AA10 AA11 AA18 AA28 AB06 BA11 BA14 BA33 CA18 CA27 CB03 DB13 DC01 DC06 EA05 EA08 EA17 EA22 EA33 FB12 FC08 GB02Y GB03Y GB04Y GB05W GB06W GB10X GB17X HA36 HA37

Claims (2)

[Claims] 1. A NOx catalyst provided in an exhaust passage of a lean-burn internal combustion engine capable of burning an air-fuel mixture in an excess oxygen state, an operating state detecting means for detecting an operating state of the internal combustion engine, and the NOx Inlet gas temperature measuring means for measuring the temperature of the exhaust gas flowing into the catalyst, outgoing gas temperature measuring means for measuring the temperature of the exhaust gas flowing out of the NOx catalyst, and the temperature of the exhaust gas measured by the incoming gas temperature measuring means. An inlet gas catalyst bed temperature estimating means for estimating a bed temperature of the NOx catalyst based on an operating state detected by the operating state detecting means; and a bed temperature of the NOx catalyst estimated by the incoming gas catalyst bed temperature estimating means. Reducing agent supply means for supplying a reducing agent to the NOx catalyst based on the temperature of the exhaust gas measured by the exhaust gas temperature measuring means. And abnormality determination means for determining whether or not the NOx catalyst is abnormal based on the bed temperature of the NOx catalyst estimated by the outgassing catalyst bed temperature estimation means. An exhaust gas purification device for an internal combustion engine. 2. The gas catalyst bed temperature estimating means includes an amount of air taken into the internal combustion engine, an amount of HC exhausted from the internal combustion engine, and a reducing agent supplied by the reducing agent supplying means. From the exhaust passage and the NOx from the exhaust gas temperature measured by the incoming gas temperature measuring means.
2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the amount of adhesion and evaporation of the reducing agent on the catalyst is calculated, and the bed temperature of the NOx catalyst is estimated based on the calculated values.