JP2002195025A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

(57) [Summary] (Problem corrected) [Problem] To prevent deterioration of exhaust emission caused by a shortage of supply of a reducing agent by providing a technique capable of adding a reducing agent in consideration of a NOx storage amount. The purpose is to: A lean-burn internal combustion engine (1) and NO in exhaust gas are provided.
a NOx purification catalyst 20 for purifying the x component, a reducing agent supply mechanism 28 for supplying a reducing agent to exhaust gas flowing through an exhaust passage,
Elapsed time detecting means 35 for detecting an elapsed time after the reducing agent supply mechanism 28 stops supplying the reducing agent, and a supply amount increasing means for increasing the supply amount of the reducing agent based on the elapsed time detected by the elapsed time detecting means 35 Means.

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 an internal combustion engine that purifies NOx in exhaust gas discharged from the 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.
As one of lean NOx catalysts, it absorbs nitrogen oxides (NOx) in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is high, and absorbs it when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present. A storage-reduction NOx catalyst that reduces nitrogen oxides (NOx) to nitrogen (N ₂ ) while releasing the same is known.

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 oxides (NOx) in the exhaust gas are 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 for 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.

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.

When the reducing agent is added to the exhaust gas upstream of the NOx storage reduction catalyst, the amount of the reducing agent to be added must be accurately determined according to the nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst. It is also important to control

This is because if the amount of the reducing agent added to the nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst is excessively increased, the excess reducing agent is released into the atmosphere. If the amount of the reducing agent added is insufficient for the nitrogen oxides (NOx) absorbed by the NOx storage reduction catalyst, the NOx absorption capacity of the NOx storage reduction catalyst is saturated, and the nitrogen oxides (NOx ) Will be released into the atmosphere without purification.

In order to solve such a problem, an exhaust gas purifying apparatus for an internal combustion engine as disclosed in Japanese Patent No. 2845056 has been proposed. The exhaust gas purifying apparatus for an internal combustion engine described in this publication discloses an amount of a reducing agent consumed by reacting with oxygen in exhaust gas in an NOx storage reduction catalyst and an amount of nitrogen oxides absorbed in the NOx storage reduction catalyst. NOx)
Taking into account the amount of reducing agent required to reduce
By determining the amount of the reducing agent to be added, it is possible to prevent an excessive supply or a shortage of the reducing agent.
x) to reduce the deterioration of exhaust emissions due to release into the atmosphere.

[0011]

However, the addition of the reducing agent to the NOx catalyst is performed only when the temperature of the NOx catalyst or the operating condition of the internal combustion engine satisfies predetermined conditions due to emission requirements. is there. Therefore, if the state where the predetermined condition is not satisfied continues, NOx is continuously stored in the NOx catalyst.

[0012] In this way, the N that has been continuously storing NOx is N.
When a reducing agent is added to the Ox catalyst, a large amount of the stored NOx is released immediately after the addition of the reducing agent is started. For this reason, a large amount of reducing agent is required as compared with the case where the NOx catalyst having a small NOx storage amount is reduced. If the reducing agent is insufficient at this time, unreduced NOx may be released to the atmosphere.

Therefore, it is important to change the amount of the reducing agent added based on the amount of NOx stored in the NOx catalyst, and to add a reducing agent corresponding to the amount of released NOx.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described various problems, and combines nitrogen oxide (NO) in exhaust gas with a combination of a lean NOx catalyst and rich spike control.
x) in an exhaust gas purification device for an internal combustion engine that purifies NOx
An object of the present invention is to provide a technique capable of adding a reducing agent in consideration of an occlusion amount, thereby preventing deterioration of exhaust emission due to a shortage of the reducing agent.

[0015]

The present invention has the following features to attain the object mentioned above. That is, the exhaust gas purifying apparatus for an internal combustion engine according to the first invention is provided with a lean-burn internal combustion engine capable of burning an air-fuel mixture in an excess oxygen state, and an exhaust gas purification apparatus provided in an exhaust passage of the internal combustion engine, in the presence of a reducing agent A NOx purification catalyst for purifying NOx components in the exhaust gas, a reducing agent supply mechanism for supplying the reducing agent to the exhaust gas flowing through the exhaust passage, and an elapsed time after the reducing agent supply mechanism stops the reducing agent supply. , And supply amount increasing means for increasing the supply amount of the reducing agent based on the elapsed time detected by the elapsed time detecting means.

The supply amount increasing means increases the supply amount of the reducing agent as the elapsed time detected by the elapsed time detecting means increases.

The supply amount increasing means does not increase the amount by more than a predetermined amount.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, when it becomes necessary to supply the reducing agent to the NOx purification catalyst, the reducing agent supply mechanism supplies the reducing agent to the exhaust passage upstream of the NOx purification catalyst. Supply.

The reducing agent supplied to the exhaust passage flows into the NOx purification catalyst together with the exhaust gas flowing from the upstream of the exhaust passage. In this case, the NOx purification catalyst reduces and purifies the harmful gas components in the exhaust using the reducing agent.

On the other hand, the elapsed time detecting means detects an elapsed time from when the reducing agent supply mechanism supplies the previous reducing agent and stops the supply thereafter. The longer the elapsed time, the more NOx is stored in the NOx purification catalyst.

Therefore, the supply amount increasing means increases the supply amount of the reducing agent based on the elapsed time detected by the elapsed time detecting means, and the reducing agent supply mechanism matches the NOx amount stored in the NOx purification catalyst. The reducing agent can be supplied into the exhaust gas.

Examples of the method of increasing the supply amount of the reducing agent include a method of increasing the supply amount at one time and a method of narrowing the supply interval.

If a predetermined amount or more of the reducing agent is supplied to the NOx purification catalyst, a part of the reducing agent may pass through the NOx purification catalyst and be released to the atmosphere without being used for NOx reduction. For this reason, it was decided not to supply a reducing agent of a predetermined amount or more.

According to a second aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine, which is capable of burning an air-fuel mixture in an excess oxygen state, and an exhaust passage of the internal combustion engine. In the exhaust gas in the presence of a reducing agent.
A NOx purification catalyst that purifies the Ox component, a reducing agent supply mechanism that supplies the reducing agent into the exhaust gas flowing through the exhaust passage, and occlusion in the NOx purification catalyst after the reducing agent supply mechanism stops the supply of the reducing agent. NOx for calculating the amount of NOx
It is characterized by comprising storage amount calculating means and supply amount increasing means for increasing the supply amount of the reducing agent based on the stored NOx amount calculated by the NOx storage amount calculating means.

The supply amount increasing means can increase the supply amount of the reducing agent as the NOx storage amount calculated by the NOx storage amount calculation means increases.

The supply amount increasing means may not increase the supply amount of the reducing agent beyond a predetermined amount.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, the criterion for increasing the NOx supply amount is different from that of the first invention. In the first invention, the supply amount of the reducing agent is increased based on the elapsed time from the previous supply of the reducing agent. In the second invention, however, the supply amount of the reducing agent is increased based on the amount of NOx stored in the NOx purification catalyst. Increase the supply of reducing agent.

Here, the NOx stored in the NOx purification catalyst
Can be calculated, for example, by a numerical map obtained in advance based on the load and the rotation speed of the internal combustion engine.

The supply amount increasing means reduces the supply amount of the reducing agent as a whole by shortening the supply interval when the reducing agent is supplied a plurality of times and increasing the number of times the reducing agent is supplied. It can be increased.

Since the supply of the reducing agent may be carried out in a plurality of times, the supply amount of the reducing agent can be increased without increasing the supply amount per time.
If the supply interval is shortened and the number of times of supply is increased, the supply amount of the reducing agent can be increased as a whole.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment 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 the 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 thus configured, when the rotational torque of the crankshaft is transmitted to the input shaft of the fuel pump 6, the fuel pump 6 is transmitted from the crankshaft to the input shaft of the fuel pump 6. The fuel is discharged at a pressure 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 a mass of the intake air flowing through the intake pipe 9 is provided in an intake pipe 9 downstream of the air cleaner box 10 and a temperature corresponding to the temperature of the intake air flowing through the intake pipe 9. And an intake air temperature sensor 12 that outputs a detected electric signal.

At a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8, an intake throttle valve 13 for adjusting the flow rate of intake air flowing through the intake pipe 9 is provided. The intake throttle valve 13 is provided with an intake throttle actuator 14 that is configured by a stepper motor or the like and drives the intake throttle valve 13 to open and close.

The intake pipe 9 located between the air flow meter 11 and the intake throttle valve 13 is provided with a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 which operates using heat energy of exhaust gas as a driving source. 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 inside 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 the 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 exhaust temperature sensor 24 that outputs an electric signal corresponding to the temperature of the exhaust flowing through the exhaust pipe 19. Is attached.

The exhaust pipe 19 downstream of the air-fuel ratio sensor 23 and the exhaust temperature sensor 24 is provided with an exhaust throttle valve 21 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 are connected via an exhaust gas recirculation passage (EGR passage) 25 for recirculating a part of the exhaust flowing through the exhaust branch pipe 18 to the intake branch pipe 8. Are in communication. In the middle of the EGR passage 25, a solenoid valve or the like is provided.
A flow control valve (EGR valve) 26 for changing the flow rate of exhaust gas (hereinafter, referred to as EGR gas) flowing through the passage 25 is provided.

In the EGR passage 25, an EGR valve 26
A portion upstream of the EGR passage 25
An EGR cooler 27 for cooling the GR gas is provided.

In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 is brought into a conductive state, and a part of the exhaust flowing through the exhaust branch pipe 18 is partially discharged. And is guided to the intake branch pipe 8 through the EGR cooler 27.

At this time, in the EGR cooler 27, heat is exchanged between the EGR gas flowing through 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 via 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) and carbon dioxide (CO ₂ ). 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 NOx catalyst 20 has, 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, the NOx storage reduction catalyst 20 having the above-described structure can reduce the nitrogen oxides (NOx) in the exhaust gas.
Absorb.

On the other hand, the NOx storage reduction catalyst 20 releases the absorbed nitrogen oxides (NOx) 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, there is a portion where the NOx absorbing / releasing action of the NOx storage reduction catalyst 20 has not been clarified.
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 is 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 ).

As described above, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is the lean air-fuel ratio, nitrogen oxides (NOx) in the exhaust gas are converted into nitrate ions (NO ₃₋ ) as NOx storage-reduction NOx. 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 NO
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 NOx storage reduction 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 nitric oxide (NO) and desorb 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 operated 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.

Accordingly, when the internal combustion engine 1 is operating in the lean burn mode, 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, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, fuel (light oil) as a reducing agent is contained in exhaust gas flowing through an exhaust passage upstream of the NOx storage reduction catalyst 20.
Is added to the exhaust gas from the reducing agent supply mechanism, whereby the occlusion reduction type N is added.
The oxygen concentration of the exhaust gas flowing into the Ox catalyst 20 is reduced and the concentration of the reducing agent is increased.

As shown in FIG. 1, the reducing agent supply mechanism is attached to the cylinder head of the internal combustion engine 1 so that its injection hole faces the exhaust branch pipe 18, and fuel at 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 to adjust 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 regulating valve 30 to block the flow of fuel in the reducing agent supply passage 29; and a reducing agent supply passage upstream of the flow regulating 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 is configured such that the injection hole of the reducing agent injection valve 28 is located downstream of the connecting portion of the exhaust branch pipe 18 with the EGR passage 25 and the four branch pipes of the exhaust branch pipe 18 are connected to each other. 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 also prevents the reducing agent from being centrifuged in the exhaust branch pipe 18 without centrifugation. This is to reach the turbine housing 15b of the supercharger.

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 is 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 configured to penetrate a water jacket (not shown) formed in the cylinder head or to be mounted close to the water jacket, and to utilize cooling water flowing through the water jacket. The reducing 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 into the exhaust branch pipe 18 from the reducing agent injection valve 28 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 to 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 has a common rail pressure sensor 4
a, various types of air flow meter 11, intake air temperature sensor 12, intake pipe pressure sensor 17, air-fuel ratio sensor 23, exhaust gas temperature sensor 24, reducing agent pressure sensor 32, crank position sensor 33, water temperature sensor 34, accelerator opening degree sensor 36, etc. The sensors are connected via electric wiring, and output signals of the various sensors described above are input to 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 outputs those signals to the C port.
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, exhaust temperature sensor 24, reducing agent pressure sensor 32, water temperature sensor 3.
4, an accelerator opening sensor 36, etc., which are input through an A / D 355 of a sensor that outputs a signal in the form of an analog signal, and output those signals to the CPU 351 or the RAM 35.
Send to 3.

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 showing the relationship between the target addition amount of the reducing agent and the opening time of the flow control valve 30, and a NOx storage amount calculation showing the relationship between the elapsed time after the supply of the reducing agent is stopped and the NOx storage amount The map includes a reducing agent supply amount correction coefficient calculation map showing a relationship between a NOx occlusion amount and a correction coefficient for increasing the reducing agent supply amount.

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 in accordance with an application program stored in the ROM 352, and controls fuel injection valve control, intake throttle control, exhaust throttle control, E
GR control, NOx purification control, poisoning elimination control, and the like 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 the output signal of the crank position sensor 33 starts the fuel injection. 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 this 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 increases accordingly. 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 the 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.

When it is determined that the EGR control execution condition described above is satisfied, the CPU 351 accesses the EGR valve opening control map using the engine speed and the accelerator opening as parameters, and 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 rich spike control in which the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 20 is spiked (short-time) to a rich air-fuel ratio in 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, whether the NOx storage reduction catalyst 20 is in an active state, whether the output signal value (exhaust gas temperature) of the exhaust gas temperature sensor 24 is equal to or lower than a predetermined upper limit value, or the poisoning elimination control. Is not executed, or the like.

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 that the reducing agent injection valve 28 injects the fuel as the reducing agent in a spike manner. 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 (intake air amount), fuel injection amount, and the like are read out. Further, 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 air-fuel ratio of the exhaust gas to a preset target rich air-fuel ratio. The addition amount (target addition amount) of the reducing agent required for obtaining the fuel ratio is calculated.

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 the 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 time when 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.

In the present embodiment, the amount of fuel is increased by extending the opening time of the flow control valve 30. However, the same effect can be obtained by shortening the opening interval of the flow control valve 30 without changing the opening time of the flow control valve 30 per one time. The valve opening interval of the flow control valve 30 may be mapped in advance and stored in the ROM 352.

Next, a method for increasing the supply amount of the reducing agent in the present embodiment will be described.

FIG. 4 is a flowchart showing a method for increasing the amount of reducing agent supplied according to the present invention.

In step 101, it is determined whether or not to execute the rich spike control for adding the fuel as the reducing agent. The conditions for executing the rich spike control include, for example, whether the NOx storage reduction catalyst 20 is in an active state, whether the output signal value (exhaust gas temperature) of the exhaust gas temperature sensor 24 is equal to or lower than a predetermined upper limit value, or the poisoning elimination control. Is not executed, or the like. When it is determined that these execution conditions are satisfied, the process proceeds to step 102, and when it is determined that the execution conditions are not satisfied, the process proceeds to step 111.

In step 102, it is determined whether or not the elapsed time from the end of the previous rich spike control to the present is a predetermined time or more. The elapsed time from the end of the previous rich spike control is accumulated and stored in the RAM 353.

If the elapsed time is not longer than the predetermined time, N
Since the amount of NOx released from the Ox catalyst 20 is an amount that can be reduced by the normal fuel addition amount, the process proceeds to step 113 in order to determine whether to reduce the NOx with the normal fuel addition amount.

On the other hand, if the elapsed time from the end of the previous rich spike control is longer than the predetermined time, the NOx catalyst 2
Since a large amount of NOx is stored at 0, when the rich spike control is executed, a large amount of NOx is released from the NOx catalyst 20, which is insufficient with a normal fuel addition amount. Therefore, the process proceeds to step 103 to correct the amount of fuel to be added and to compensate for the shortage of fuel.

In step 113, it is determined whether or not the elapsed time has reached a predetermined time. If the predetermined time has elapsed, the routine proceeds to step 114 because NOx needs to be released from the NOx catalyst 20. In the case of a negative determination, the NOx catalyst 20 can still store NOx, so the process proceeds to step 111 without performing rich spike control.

In step 114, the normal rich spike control described above is executed to reduce NOx.
Proceed to step 109.

In step 103, the number of executions for increasing the fuel addition amount is calculated. If the elapsed time is long, the amount of NOx stored in the NOx catalyst 20 increases, and it becomes difficult to release all NOx by one rich spike control. Further, when a predetermined amount or more of fuel is added to the NOx catalyst 20, a part of the fuel may pass through the NOx catalyst 20 and be released to the atmosphere without being used for NOx reduction. Therefore, in the present embodiment, the amount of added fuel is increased in a plurality of times. The number of times of this increase is R
The elapsed time from the end of the previous rich spike control stored in the AM 353 is defined by a predetermined relationship between the elapsed time from the end of the previous rich spike control and the number of times of increasing the fuel addition amount shown in FIG. It is calculated by substituting. The increase number increases in accordance with the elapsed time when the elapsed time from the end of the previous rich spike control is equal to or longer than a predetermined time. However, if the number of times of increasing the added fuel is large, the operating state of the vehicle may deviate from the fuel addition execution condition during the fuel addition control. Therefore, the increase is not performed more than a predetermined number of times.

The calculated number of times the fuel addition amount is increased is stored in the RAM 353. In the present embodiment, the area of the RAM 353 in which the number of times of increase is stored is referred to as “counter”, and storing the number of times of increase in the RAM 353 is referred to as “set in the counter”.

In step 104, it is determined whether or not the number of times the fuel addition amount stored in the RAM 353 has been increased is greater than zero. If it is determined that the value is larger than 0, the process proceeds to step 105 to increase the amount of fuel.

If a negative determination is made, there is no need to increase the addition amount, so the routine proceeds to step 113.

In step 105, it is determined whether or not the elapsed time is equal to or longer than a predetermined time. Here, the predetermined time is shorter than the predetermined time used as the determination condition in step 102. The predetermined time is calculated by a predetermined map using the engine speed (output pulse from the crank position sensor 33), the engine load (output signal from the accelerator opening sensor 36) and the predetermined time as parameters. .

If the rich spike control is performed when the elapsed time is short, similar to the case where a predetermined amount or more of fuel is added to the NOx catalyst 20, a part of the fuel is not used for NOx reduction and the NOx catalyst 20 is not used. May be released into the atmosphere through the air. Therefore, the rich spike control is performed after the lapse of a predetermined time.

If the elapsed time is equal to or longer than the predetermined time, the process proceeds to step 106 to perform rich spike control.
If a negative determination is made, the process proceeds to step 111.

In step 106, a correction amount for correcting the fuel addition amount is calculated. By correcting and increasing the fuel addition amount based on the time during which the rich spike control has not been performed, the shortage of fuel with the normal fuel addition amount is compensated for. The amount of fuel actually added can be obtained by the following equation.

Corrected fuel addition amount = normal fuel addition amount × correction coefficient Here, the normal fuel addition amount is the same as the amount of fuel added by the rich spike control in step 114. Further, the correction coefficient of the fuel addition amount is obtained by calculating the elapsed time from the end of the previous rich spike control stored in the RAM 353 to the predetermined elapsed time from the end of the previous rich spike control shown in FIG. It is calculated by substituting it into the relationship with the correction coefficient of the fuel addition amount.

At step 107, rich spike control is performed based on the corrected fuel addition amount.

The correction coefficient increases according to the elapsed time when the elapsed time from the end of the previous rich spike control is equal to or longer than a predetermined time. However, if a predetermined amount or more of fuel is added to the NOx catalyst 20, a part of the fuel may pass through the NOx catalyst 20 and be released to the atmosphere without being used for NOx reduction. And an upper limit is set so that the addition of a predetermined amount or more of fuel is not performed.

In step 108, the CPU 351 subtracts 1 from the counter, and newly sets this calculation result in the counter.

In step 109, the elapsed time stored in the RAM 353 is reset.

In step 110, the NOx occlusion is performed in order to perform the next rich spike control in consideration of the time required for the NOx occluded in the NOx catalyst 20 to be occluded during the current rich spike control. Calculate the time. At this time, simply measuring the time during which the rich spike control was being executed would cause the amount of NOx occluded to vary depending on the bed temperature of the NOx catalyst 20, so that the rich spike control execution time was corrected based on the exhaust gas temperature. did. By doing so, it is possible to calculate the NOx occlusion time corresponding to the actually stored NOx amount.

This time can be calculated by the following equation.

NOx occlusion time = rich spike control execution time × elapsed time correction coefficient Here, the rich spike control execution time is obtained by accumulating and storing the elapsed time since the execution of the rich spike control in the RAM 353 at the same time as the start of the rich spike control. Can be obtained by Further, the elapsed time correction coefficient is determined by the exhaust temperature sensor 2
4 is calculated by substituting the temperature detected in FIG. 4 into the relationship between the exhaust gas temperature and the elapsed time correction coefficient in FIG. Here, when the bed temperature of the NOx catalyst 20 is a predetermined temperature, the amount of stored NOx is the largest, and the stored amount decreases as the temperature increases or decreases from the predetermined temperature. As described above, during the rich spike control, the temperature of the NOx catalyst 20 rises, so that the NOx storage amount fluctuates.
The temperature of the exhaust gas flowing out of the NOx catalyst 20 is substituted for the bed temperature of the NOx catalyst 20, and correction is performed based on this temperature.

Here, the obtained NOx storage time is used for correcting a predetermined time used as a determination condition in another step. The newly set predetermined time can be calculated by the following equation.

Predetermined time = basic predetermined time + NOx occlusion time Here, the basic predetermined time is a predetermined time which is stored in the ROM 352 as a map.

[0146] Even if the elapsed time is the same, if the NOx occlusion time becomes longer, the amount of NOx occluded in the NOx catalyst 20 increases, so that the amount of released NOx at the time of fuel addition increases. Therefore,
As the NOx storage time became longer, the interval between fuel additions was lengthened by lengthening the predetermined time used for the determination condition. Thus, rich spike control can be performed at an addition interval commensurate with the increased NOx amount. The predetermined time corrected by this calculation is stored in the RAM 353 and used as a determination condition from the next time.

In the step 111, the RAM 353 is newly added.
Is calculated. This elapsed time is calculated by the following equation.

Elapsed time (i) = elapsed time (i-1) + fuel addition control execution interval Here, the fuel addition control execution interval is an interval at which rich spike control is performed.

In step 112, it is determined whether or not the counter indicating the number of times of increasing the fuel addition amount is 0, or whether or not the condition for executing the rich spike control for adding the fuel as the reducing agent is not satisfied.

When the rich spike control is performed with the normal addition amount, the routine is terminated because the counter is 0. If the fuel addition amount has been increased, step 1
When the rich spike control in which the addition amount is increased by the number calculated in 03 is performed, the counter becomes 0, and this routine ends.

If the fuel addition execution condition is not satisfied during the execution of this routine, the routine is temporarily terminated. The determination conditions at this time are the same as those determined in step 101.

As described above, the fuel addition amount is corrected based on the time during which the rich spike control has not been performed, and NOx
Fuel addition corresponding to the NOx emission amount of the catalyst 20 can be performed.

As a result, it is possible to prevent NOx from being released into the atmosphere due to a shortage of fuel to be added. <Second Embodiment> Hereinafter, a specific embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the second invention will be described.

This embodiment is different from the first embodiment in the following points.

In the first embodiment, the criterion for correcting the amount of added fuel is the time during which the rich spike control is not performed. However, in the present embodiment, NOx is used.
The fuel addition amount is corrected based on the amount of NOx stored in the catalyst 20.

The other configuration is the same as that of the first embodiment and will not be described.

FIG. 8 is a flowchart showing a method for increasing the amount of reducing agent supplied according to the present invention.

In step 201, it is determined whether or not the execution of the rich spike control for adding the fuel as the reducing agent can be performed. As the conditions for executing the rich spike control, for example, the poisoning elimination control is executed when the occlusion reduction type NOx catalyst 20 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value. Conditions such as not being performed. When these execution conditions are satisfied, the process proceeds to step 202, and when the execution conditions are not satisfied, the process proceeds to step 210.

In step 202, it is determined whether or not the NOx occlusion amount since the end of the previous rich spike control is larger than a threshold value. The NOx occlusion amount from the end of the previous rich spike control is determined in advance in the ROM 3 based on the load of the internal combustion engine 1 (signal from the accelerator opening sensor 36) and the rotation speed (pulse generated from the crank position sensor 33).
It is calculated using the numerical map stored in 52.

When the NOx storage amount is equal to or less than the threshold value, the amount of NOx released from the NOx catalyst 20 is an amount that can be reduced by the normal fuel addition amount. Proceed to.

NO from the end of the previous rich spike control
If the x storage amount is larger than the threshold, the NOx amount released from the NOx catalyst 20 increases, and the normal fuel addition amount becomes insufficient. Therefore, the process proceeds to step 203 to correct the amount of fuel to be added and to compensate for the shortage of fuel.

In step 214, a numerical value indicating that rich spike control is to be performed with a normal addition amount is stored in the RAM 353.
353. In the present embodiment, this is referred to as “normal addition ON”.

At step 215, it is determined whether or not the NOx occlusion amount from the end of the previous rich spike control is equal to the threshold value. Here, the threshold used as the determination condition is the same as that used in step 202.

When the NOx storage amount is equal to the threshold value, the process proceeds to step 216 to perform the rich spike control with the normal fuel addition amount. In the case of a negative determination, the NOx catalyst 20
Proceeds to step 210 without performing rich spike control because NOx can still be stored.

At step 216, rich spike control is performed with a normal addition amount to reduce NOx, and thereafter, the routine proceeds to step 210.

At step 203, a numerical value indicating that rich spike control is not performed by increasing the amount of addition in RAM 353 is stored in RAM 353. In the present embodiment, this is referred to as “normal addition OFF”.

In step 204, it is determined whether the amount of NOx stored in the NOx catalyst 20 is larger than a threshold value. Here, the threshold value is smaller than the threshold value in step 202, and is a numerical value representing the NOx storage amount that can be reduced without increasing the fuel addition amount.

When the NOx storage amount is larger than the threshold value,
The process proceeds to step 205 to perform the rich spike control by increasing the fuel addition amount. In the case of a negative determination, since it is not necessary to increase the addition amount, the process proceeds to step 214 to perform the rich spike control with the normal addition amount.

In step 205, it is determined whether or not the elapsed time since the previous addition has reached a predetermined time. Here, the predetermined time is calculated by a predetermined map using the engine speed (output pulse from the crank position sensor 33), the engine load (output signal from the accelerator opening sensor 36) and the predetermined time as parameters. You. The elapsed time is accumulated and stored in the RAM 353.

If the rich spike control is performed when the elapsed time is short, similar to the case where a predetermined amount or more of fuel is added to the NOx catalyst 20, a part of the fuel is not used for NOx reduction and the NOx catalyst 20 is not used. May be released into the atmosphere through the air. Therefore, the rich spike control is performed after the lapse of a predetermined time.

If the elapsed time has reached the predetermined time,
The process proceeds to step 206 to perform the rich spike control. In the case of a negative determination, the process proceeds to step 209.

In step 206, the correction amount of the fuel addition amount is calculated. When fuel is added to the NOx catalyst 20, N
The amount of released Ox is large and the amount of added normal fuel is insufficient. Therefore, the fuel addition amount is corrected and increased based on the NOx storage amount of the NOx catalyst 20. The amount of fuel actually added can be obtained by the following equation.

Corrected fuel addition amount = Normal fuel addition amount × Correction coefficient Here, the normal fuel addition amount is the same as the amount of fuel added by the rich spike control in step 215. Further, the correction coefficient of the fuel addition amount is calculated by the N
The NOx storage amount of the Ox catalyst 20 is calculated by substituting it into a predetermined relationship between the NOx storage amount of the NOx catalyst 20 and the correction coefficient of the fuel addition amount shown in FIG.

On the basis of the corrected fuel addition amount, rich spike control is performed in step 207.

The correction coefficient increases in accordance with the amount of NOx stored when the amount of NOx stored in the NOx catalyst 20 is equal to or more than a predetermined amount. However, if a predetermined amount or more of fuel is added to the NOx catalyst 20, a part of the fuel may pass through the NOx catalyst 20 and be released to the atmosphere without being used for NOx reduction. And an upper limit is set so that the addition of a predetermined amount or more of fuel is not performed.

At step 208, the elapsed time stored in the RAM 353 is reset.

At step 209, the CPU 351 accumulates the elapsed time and stores it in the RAM 353.

In step 210, the NOx amount per unit time reduced in the current rich spike control is calculated by the following equation.

NOx reduction amount = basic NOx reduction amount × temperature correction coefficient Here, the basic NOx reduction amount can be obtained from FIG. 10A showing the relationship between the fuel addition amount and the basic NOx reduction amount. This is because the reduced amount of NOx has a correlation with the amount of fuel added to the NOx catalyst 20. The fuel addition amount in FIG. 10A is the fuel addition amount in the rich spike control performed in step 204 or step 215.
This fuel addition amount is stored in the RAM 353 in advance in step 204 or step 215, and the basic correction elapsed time is calculated by substituting this numerical value into FIG.

On the other hand, as the temperature coefficient, the temperature of the exhaust gas detected by the exhaust gas temperature sensor 24 is stored in the RAM 353 in advance, and the relationship between the temperature of the exhaust gas and the temperature coefficient is shown in FIG.
It is calculated by substituting the stored numerical value into (b). Here, when the bed temperature of the NOx catalyst 20 is at a predetermined temperature, the amount of release / reduction of NOx is the largest, and the release / reduction amount decreases as the temperature increases or decreases from the predetermined temperature. Since the amount of NOx released and reduced varies depending on the bed temperature of the NOx catalyst 20, the temperature of the exhaust gas flowing out of the NOx catalyst 20 is substituted for the bed temperature of the NOx catalyst 20, and correction is performed based on this temperature. I decided to do.

In step 211, the amount of NOx stored in the NOx catalyst 20 per unit time is calculated regardless of whether the rich spike control is executed. This is because NOx in the exhaust gas flowing into the NOx catalyst 20 is stored in the NOx catalyst 20 even during execution of the rich spike control.

This NOx amount can be calculated by the following equation.

NOx storage amount = (input gas NOx amount per unit time) × (NOx storage coefficient) Here, the input gas NOx amount per unit time is determined by the load of the internal combustion engine 1 (the signal from the accelerator opening sensor 36). ) And the number of revolutions (pulses generated from the crank position sensor 33) using a numerical map stored in the ROM 352 in advance. The NOx storage coefficient is calculated by substituting the temperature detected by the exhaust gas temperature sensor 24 into FIG. 11 showing the relationship between the exhaust gas temperature and the NOx storage coefficient. Here, when the bed temperature of the NOx catalyst 20 is a predetermined temperature, the amount of stored NOx is the largest, and the stored amount decreases as the temperature increases or decreases from the predetermined temperature. As described above, during the rich spike control, the temperature of the NOx catalyst 20 rises, so that the NOx storage amount fluctuates.
The temperature of the exhaust gas flowing from zero is substituted for the bed temperature of the NOx catalyst 20, and correction is performed based on this temperature.

In step 212, the amount of NOx stored in the NOx catalyst 20 without being released after the execution of the current rich spike control is calculated. This is because the next rich spike control is performed in consideration of the amount of NOx not reduced in the current rich spike control. The amount of NOx stored in the catalyst per unit time is obtained by the following equation.

The catalyst NOx occlusion amount (i) = catalyst NOx occlusion amount (i-1) + NOx occlusion amount−NOx reduction amount The “catalyst NOx occlusion amount” thus obtained is stored in the RAM.
The RAM 353 stores the “catalyst NOx storage amount” stored in the RAM 353.

In step 213, it is determined whether or not the "normal addition ON" or not, or whether the condition for executing the rich spike control for adding the fuel as the reducing agent is not satisfied.

When the rich spike control is performed with the normal addition amount, the routine is ended because the normal addition is ON. When the fuel addition amount has been increased, if a negative determination is made in step 204, "normal addition ON" is set, and this routine ends.

If the fuel addition execution condition is not satisfied during execution of this routine, the routine is temporarily terminated. The determination conditions at this time are the same as those determined in step 201.

The fuel addition amount is corrected based on the NOx amount stored in the NOx catalyst 20 in this manner, and the NOx catalyst 2
The fuel addition corresponding to the NOx emission amount of 0 can be performed.

In this way, it is possible to prevent NOx from being released into the atmosphere without being reduced due to a shortage of fuel to be added.

[0191]

According to the present invention, it is possible to increase the supply amount of the reducing agent based on the time during which the reducing agent is not added to the NOx purification catalyst, and to supply the reducing agent in accordance with the NOx release amount.

Further, it is possible to increase the supply amount of the reducing agent based on the amount of NOx stored in the NOx purification catalyst, and to supply the reducing agent in accordance with the amount of released NOx.

Therefore, it is possible to prevent the exhaust emission from being deteriorated due to insufficient supply of the reducing agent.

[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. 2A is a diagram illustrating a NOx absorption mechanism of a storage reduction type NOx catalyst. (B) is a diagram for explaining the NOx release mechanism of the NOx storage reduction catalyst.

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

FIG. 4 is a flow chart illustrating a method for increasing a reducing agent supply amount according to the first invention.

FIG. 5 is a diagram showing a relationship between an elapsed time from the end of the previous rich spike control and a fuel addition amount correction coefficient.

FIG. 6 is a diagram illustrating a relationship between an elapsed time from the end of the previous rich spike control and the number of times of increasing the fuel addition amount.

FIG. 7 is a diagram showing a relationship between exhaust gas temperature and an elapsed time correction coefficient.

FIG. 8 is a flowchart showing a reducing agent supply amount increasing method according to a second invention.

FIG. 9 is a diagram showing a relationship between a NOx storage amount of a NOx catalyst and a correction coefficient of a fuel addition amount.

FIG. 10A is a diagram showing a relationship between a fuel addition amount and a basic NOx reduction amount. (B) is a diagram showing the relationship between the temperature of the exhaust gas and the temperature coefficient.

FIG. 11 is a diagram showing a relationship between exhaust gas temperature and NOx storage coefficient.

[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 ... Storage reduction type NOx catalyst 21 ... Exhaust throttle valve 23 ... Air-fuel ratio sensor 25 ... EGR passage 26 ... EGR valve 27 ... EGR cooler 28 ... Reducing agent injection valve 29 ... Reducing agent supply path 30 ... Flow regulating valve 31 ... Shutoff valve 32 ... Reducing agent pressure sensor 33 ... Crank position sensor 34 ... Water temperature sensor 35 ... ECU 351, CPU 352, ROM 353, RAM 354, backup RAM

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) F01N 3/28 301 F02D 41/04 330A 3/36 41/14 310K F02D 41/04 330 B01D 53/36 ZAB 41/14 310 101A 101B (72) Inventor Shinobu Ishiyama 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Naofumi Matsuda 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Invention Person Masaaki Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Daisuke Shibata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Akihiko Negami Toyota Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Tomihisa Oda 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Yasuhiko 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation Within (7 2) Inventor Taro Aoyama 1 Toyota Town, Toyota City, Aichi Prefecture F-term in Toyota Motor Corporation (reference) 3G091 AA02 AA10 AA11 AA18 AA28 AB05 AB06 AB09 BA11 BA33 CA13 CA18 CB02 CB03 CB07 CB08 DA01 DA02 DB06 DB10 EA00 EA01 EA05 EA06 EA06 EA07 EA15 EA16 EA17 EA22 EA30 EA31 EA34 FB10 FC02 GB01X GB02W GB02Y GB03W GB03Y GB04W GB04Y GB05W GB06W GB10X GB16X HA18 HB03 HB05 HB06 3G301 HA02 HA04 HA06 HA11 HA13 JA21 JA01 LA07 NA18 PA01 NE01 PA01 PA10Z PA16B PA16Z PB08B PB08Z PD02B PD02Z PD11B PD11Z PE01B PE01Z PE03B PE03Z PE04B PE04Z PE05B PE05Z PE08B PE08Z PF03B PF03Z 4D048 AA06 AB02 AB07 AC02 BA03X BA15X BA30X BA41X CC61 DA01 DA02 DA02

Claims (7)

[Claims] 1. A lean-burn internal combustion engine capable of burning an air-fuel mixture in an excess oxygen state, and NOx provided in an exhaust passage of the internal combustion engine and purifying NOx components in exhaust gas in the presence of the reducing agent. A purifying catalyst; a reducing agent supply mechanism for supplying a reducing agent into the exhaust gas flowing through the exhaust passage; an elapsed time detecting means for detecting an elapsed time after the reducing agent supply mechanism stops supplying the reducing agent; An exhaust gas purification device for an internal combustion engine, comprising: a supply amount increasing unit that increases the supply amount of the reducing agent based on the elapsed time detected by the time detecting unit. 2. The exhaust gas purification system according to claim 1, wherein the supply amount increasing unit increases the supply amount of the reducing agent as the elapsed time detected by the elapsed time detection unit increases. apparatus. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the supply amount increasing unit does not increase the amount by a predetermined amount or more. 4. A lean-burn internal combustion engine capable of burning an air-fuel mixture in an excess oxygen state, and NOx purification provided in an exhaust passage of the internal combustion engine for purifying NOx components in exhaust gas in the presence of a reducing agent. A catalyst, a reducing agent supply mechanism for supplying the reducing agent into the exhaust gas flowing through the exhaust passage, and calculating an amount of NOx stored in the NOx purification catalyst after the reducing agent supply of the reducing agent supply mechanism is stopped. Exhaust gas of an internal combustion engine, comprising: a NOx storage amount calculating unit that performs the control; and a supply amount increasing unit that increases the supply amount of the reducing agent based on the stored NOx amount calculated by the NOx storage amount calculating unit. Purification device. 5. The internal combustion engine according to claim 4, wherein the supply amount increasing unit increases the supply amount of the reducing agent as the NOx storage amount calculated by the NOx storage amount calculation unit increases. Exhaust gas purification device. 6. The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, wherein the supply amount increasing unit does not increase the supply amount of the reducing agent beyond a predetermined amount. 7. The supply amount increasing means reduces the supply interval when the reducing agent is supplied a plurality of times and increases the number of times the reducing agent is supplied, so that the supply of the reducing agent as a whole is performed. The exhaust gas purifying apparatus for an internal combustion engine according to any one of claims 1 to 6, wherein the amount is increased.