JP2002180816A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the functional deterioration of a filter over a long period by completely removing a particle-like substance accumulated in the filter while restraining the thermal deterioration of the particulate filter. SOLUTION: This exhaust emission control device is provided with the filter 20 for carrying a catalyst, and a filter temperature raising means 35 for raising a temperature of the filter. The filter temperature raising means 35 reduces a quantity of the particle-like substance by combustion by raising the temperature of the filter 20 up to a first prescribed temperature when a first prescribed condition is realized, raises the temperature of the filter 20 to a second prescribed temperature higher than the first prescribed temperature when a second prescribed condition is realized, and lengthens an interval for raising the temperature up to the second prescribed temperature more than the first temperature.

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 and, for example, to a particulate matter represented by soot, which is a suspended particulate matter contained in exhaust gas of a diesel engine. The present invention relates to an exhaust gas purification device having a means for trapping “PM”.

[0002]

2. Description of the Related Art While diesel engines are excellent in economical efficiency, removal of PM contained in exhaust gas is an important issue. For this reason, a particulate filter (hereinafter simply referred to as a “filter”) that traps PM in the exhaust system of a diesel engine so that PM is not released into the atmosphere.
The technique of providing is well known.

The PM in the exhaust gas is once collected by this filter. However, the trapped PM accumulates on the filter and causes clogging of the filter. Due to this clogging, the pressure of the exhaust gas upstream of the filter increases, causing a decrease in the output of the internal combustion engine and damage to the filter. Thus, it is necessary to prevent the clogging of the filter by removing the PM by igniting and burning the PM collected on the filter. Such removal of PM is called filter regeneration.

However, in order to ignite and burn the PM trapped in the filter, a high temperature of, for example, 500 ° C. or more is required. However, since the temperature of the exhaust gas of a diesel engine is usually lower than this temperature, the PM combustion Removal is difficult.

To solve such a problem, see, for example,
According to Japanese Patent No. 38230, a filter supporting a catalyst and a device for supplying hydrocarbons to the exhaust gas are used, and heat generated when the hydrocarbons supplied to the exhaust gas are burned by the catalyst is used. The PM can be burned, thereby preventing clogging.

[0006]

However, when hydrocarbons are supplied into the exhaust gas and the filter is brought to a high temperature state, thermal deterioration of the catalyst is induced, which causes a reduction in the catalyst performance.

[0007] Here, regarding the thermal degradation, the storage reduction type NOx
Taking the catalyst as an example, NOx absorption in the NOx catalyst is determined by platinum Pt (catalytic substance) and potassium K (NOx absorbent)
It is known that Pt causes sintering by heat 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 P
The sintering of t 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. It is impossible to return Pt that once sintered to the state before sintering, and therefore, the NOx catalyst cannot be recovered from thermal deterioration.

If the amount of hydrocarbons supplied to the exhaust gas is adjusted to suppress such a problem and the increase in the catalyst temperature is suppressed, PM combustion may not be promoted but remain unburned. In this case, thermal deterioration of the catalyst can be prevented, but on the other hand, the filter may be clogged.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a filter for an exhaust gas purifying apparatus for an internal combustion engine having a particulate filter carrying a catalyst. To completely remove particulate matter deposited on the filter while suppressing thermal degradation of
Accordingly, it is an object of the present invention to provide a technique capable of preventing the filter from functioning for a long time.

[0010]

Means for Solving the Problems To achieve the above object, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention employs the following means.

That is, a filter provided in an exhaust passage of an internal combustion engine and supporting a catalyst for collecting particulate matter contained in exhaust gas and promoting combustion of the collected particulate matter; Filter temperature raising means for raising the temperature of the filter to a first predetermined temperature when a first predetermined condition is satisfied, thereby burning and reducing the particulate matter. And
Further, when the second predetermined condition is satisfied, the temperature of the filter is raised to a second predetermined temperature higher than the first predetermined temperature, and the interval for raising the temperature to the second predetermined temperature is the third time. It is characterized in that it is longer than the interval for raising to one predetermined temperature.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the particulate matter contained in the exhaust gas is collected by the filter provided in the exhaust passage. Since the collected particulate matter accumulates in the filter and causes clogging of the filter, when the first predetermined condition is satisfied, the temperature of the filter is increased by the filter temperature increasing means, and the accumulated particulate matter is increased. Causes burning weight loss. At this time, if the temperature of the filter becomes high, the filter is thermally degraded and the catalytic function is deteriorated.

However, at this first predetermined temperature, the deposited particulate matter may remain unburned, and the amount of the remaining particulate matter gradually increases, which may cause clogging of the filter.

Therefore, in the present invention, when the second predetermined condition is satisfied, the temperature of the filter is raised to a second predetermined temperature higher than the first predetermined temperature, for example, about 700 ° C. The substance was to be completely burned off.

When the filter temperature is raised to the second predetermined temperature in this manner, there is a possibility that the catalyst may be thermally degraded. Therefore, the period during which the temperature of the filter is raised to the second predetermined temperature is set shorter than the period during which the temperature is raised to the first predetermined temperature, and the temperature rise interval of the filter due to the establishment of the second predetermined condition is set to the first. By setting the first and second conditions so as to be longer than the case where one predetermined condition is satisfied, a decrease in the catalytic function is suppressed.

The first predetermined condition, which is a condition for raising the filter temperature to the first predetermined temperature, includes a condition that the vehicle has traveled a predetermined distance and a particle calculated from the load and the number of revolutions of the internal combustion engine. For example, it is possible to exemplify that the discharge amount of the particulate matter has reached a predetermined amount.

Further, as a second predetermined condition which is a condition for raising the filter temperature to the second predetermined temperature, the filter is raised to the first predetermined temperature and the amount of combustion of particulate matter is reduced by a predetermined number of times. For example, the fact that the vehicle has traveled a predetermined distance, that the amount of particulate matter calculated from the load and the rotation speed of the internal combustion engine has reached a predetermined amount, and the like can be exemplified.

As described above, normally, the particulate matter can be burned and reduced while preventing the heat deterioration by raising the filter temperature to the first predetermined temperature.

Further, since the temperature of the filter is raised to a second predetermined temperature higher than the first predetermined temperature at long intervals,
It is possible to prevent early deterioration of the function of the catalyst while completely burning and removing the remaining particulate matter.

The filter temperature increasing means includes a method of supplying a reducing agent upstream of the filter by a nozzle provided in an exhaust passage, and a method of increasing engine output after main injection for injecting fuel for engine output into a cylinder of an internal combustion engine. Examples of the method include a method using a sub-injection (also referred to as a post-injection) for re-injecting fuel at a time when the fuel injection does not occur (for example, an expansion stroke), and a method of directly heating the filter using an external heater.

Examples of the catalyst supported on the filter include a storage reduction type NOx catalyst, a selective reduction type NOx catalyst, and an oxidation catalyst.

As the filter, a particulate filter can be exemplified.

[0023]

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. A pump pulley 6 a 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 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.

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

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 supercharger 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).

In the middle of the exhaust pipe 19, a storage reduction type N
A particulate filter 20 supporting an Ox catalyst is provided. An exhaust pipe 19 downstream of the filter 20 includes an air-fuel ratio sensor 23 that outputs an electric signal corresponding to the air-fuel ratio of exhaust flowing through the exhaust pipe 19,
An exhaust temperature sensor 24 that outputs an electric signal corresponding to the temperature of exhaust gas flowing through the inside 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 via 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 a filter 20 via an exhaust pipe 19, where PM in the exhaust gas is collected and harmful gas components are removed or purified. The exhaust gas from which PM has been collected by the filter 20 and harmful gas components have been removed or purified is discharged to 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 gas 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 gas 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 ) that does not burn itself and has endothermic properties. 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 filter 20 according to the present embodiment will be described.

FIG. 4 shows the structure of the filter 20. In addition,
4A shows a cross section of the filter 20 in the horizontal direction, and FIG. 4B shows a cross section of the filter 20 in the vertical direction. As shown in FIGS. 4A and 4B, the filter 20 is a so-called wall flow type including a plurality of exhaust passages 50 and 51 extending parallel to each other. These exhaust passages are constituted by an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. FIG.
In FIG. 5A, the hatched portion indicates the plug 53. Accordingly, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged with the thin partition walls 54 interposed therebetween. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by the four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by the four exhaust inflow passages 50.

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

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

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

The filter 20 uses, for example, alumina as a carrier, and places potassium (K) and sodium (N) on the carrier.
a) Alkali metals such as lithium (Li) or cesium (Cs), alkaline earths such as barium (Ba) or calcium (Ca), and rare earths such as lanthanum (La) or yttrium (Y). And a noble metal such as platinum (Pt). In the present embodiment, a description will be given of an example of an occlusion reduction type NOx catalyst constituted by supporting barium (Ba) and platinum (Pt) on a carrier made of alumina.

The NOx catalyst configured as described above is used for the Nx catalyst.
When the oxygen concentration of exhaust gas flowing into the Ox catalyst is high, nitrogen oxide (NOx) in the exhaust gas is absorbed.

On the other hand, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases, the NOx catalyst releases the absorbed nitrogen oxides (NOx). At this time, if reducing components such as hydrocarbons (HC) and carbon monoxide (CO) are present in the exhaust gas, the NOx catalyst converts the nitrogen oxides (NOx) released from the NOx catalyst into nitrogen (N ₂ ) can be reduced.

Although the NOx absorption / release action of the NOx catalyst has not been clarified in some parts, it is considered that the action is performed by the following mechanism.

First, in the NOx catalyst, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes a lean air-fuel ratio and the oxygen concentration in the exhaust gas increases, as shown in FIG. (O ₂₎ is O ₂ ^- or O ^2- in the form deposited on the surface of the platinum (Pt). 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 catalyst in the form of nitrate ions (NO ₃ ⁻ ). Incidentally, nitrate ions (N
O ₃ ⁻ ) combines 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 catalyst is a lean air-fuel ratio, nitrogen oxides (NOx) in the exhaust gas are absorbed by the NOx catalyst as nitrate ions ( _NO3- ).

The NOx absorbing action as described above is based on the fact that the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio and the Nx of the NOx catalyst
It is continued as long as the Ox absorption capacity is not saturated. Therefore, N
When the air-fuel ratio of the exhaust gas flowing into the Ox catalyst is a lean air-fuel ratio, unless the NOx absorption capacity of the NOx catalyst is saturated,
Nitrogen oxides (NOx) in the exhaust are absorbed by the NOx catalyst,
Nitrogen oxides (NOx) are removed from the exhaust gas.

On the other hand, in the NOx catalyst, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases, platinum (P
Since the amount of generated nitrogen dioxide (NO ₂ ) on the surface of t) is reduced, nitrate ions (NO ₃ ⁻ ) bonded to barium oxide (BaO) are conversely changed to nitrogen dioxide (NO ₂ ) and nitric oxide. It becomes (NO) and separates from the NOx catalyst.

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 catalyst are reduced to nitrogen (N ₂ ).

Accordingly, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio and the oxygen concentration in the exhaust decreases and the concentration of the reducing agent increases, the NO
The nitrogen oxides (NOx) absorbed by the x catalyst are released and reduced, whereby the NOx absorption capacity of the NOx catalyst 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 the exhaust gas are absorbed by the NOx catalyst. However, if the lean burn operation of the internal combustion engine 1 is continued for a long time, the NOx absorption capacity of the NOx catalyst is saturated, and Of nitrogen oxides (NOx) are released to the atmosphere without being removed by the NOx catalyst.

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 Nx of the NOx catalyst
Ox absorption capacity is easily saturated.

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

The exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment includes a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to exhaust gas flowing through an exhaust passage upstream of the filter 20. By adding fuel from the supply mechanism into the exhaust gas, the concentration of oxygen in the exhaust gas flowing into the filter 20 is reduced and the concentration of the reducing agent is increased.

As shown in FIG. 1, the reducing agent supply mechanism is 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 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 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 prevents the reducing agent from being centrifuged in the exhaust branch pipe 18 without stagnation. 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 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 use 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 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 into the filter 20 from the turbine housing 15b via the exhaust pipe 19, and emits nitrogen oxides (NOx) absorbed by the filter 20. It 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, 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 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, 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. An EGR control routine for controlling the valve 26, a PM combustion control routine for burning and removing PM trapped in the filter 20, a poisoning elimination control routine for eliminating poisoning of the filter 20 by oxides, and the like. Stores application programs.

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, PM combustion 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 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 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 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.

Next, the PM combustion control which is the gist of the present invention will be described.

FIG. 5A is a diagram showing the passage area of the filter 20 which changes with time. FIG. 5B
FIG. 5 is a diagram showing the bed temperature of the filter 20 corresponding to FIG. Here, the passage area of the filter 20 is the area of the gap when the exhaust gas passes through the partition wall 54 shown in FIG. 4B.

In this embodiment, the first predetermined temperature is set to, for example, 600 ° C. or less, and the second predetermined temperature is set to, for example, 700 ° C.
As described above, the temperature rise control of the filter was performed. Further, raising the temperature of the filter 20 to the first predetermined temperature is referred to as “normal regeneration”.
Is called "strength regeneration".
It is called.

In normal regeneration, the CPU 351 executes fuel addition control for adding fuel to the exhaust gas flowing into the filter 20.

In the fuel addition control, the CPU 351 determines whether or not the fuel addition control execution condition is satisfied at predetermined intervals. As the fuel addition control execution conditions, for example, the filter 20 is in an active state, the output signal value (exhaust gas temperature) of the exhaust gas temperature sensor 24 is equal to or lower than a predetermined upper limit, or the poisoning elimination control is executed. For example, the conditions such as whether or not there is not.

If it is determined that the above-described fuel addition control execution condition is satisfied, the CPU 351 controls the flow control valve 30 so that the reducing agent injection valve 28 injects the fuel as the reducing agent. The air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to a predetermined target rich 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 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 normal target opening time in this manner, the fuel of the normal target addition amount is injected from the reducing agent injection valve 28 into the exhaust branch pipe 18. Then, the reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust gas flowing from the upstream of the exhaust branch pipe 18 to form an air-fuel mixture having a target rich air-fuel ratio, thereby forming a filter 20.
Flows into.

As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 alternates between lean and rich alternately in a relatively short cycle. Then, the fuel flowing into the filter 20 is burned by the catalyst, and the temperature of the filter 20 rises.

As described above, in the normal regeneration, the temperature of the filter 20 is set to, for example, 60
Since the temperature is maintained at 0 ° C. or lower, PM can be reduced in combustion while preventing thermal degradation due to high temperature.

However, at the temperature for normal regeneration, PM may remain unburned due to the low temperature. Figure 5: PM after burning
(A), the passage area of the filter 20 is gradually reduced.

Therefore, when the condition for performing the intensity regeneration is satisfied, the intensity regeneration is performed to raise the temperature of the filter 20 as compared with the normal regeneration to remove the unburned PM.

The conditions for performing the intensity reproduction include, in addition to the conditions for performing the normal reproduction, for example, that the normal reproduction has been performed a predetermined number of times, that the vehicle has traveled a predetermined distance,
For example, a predetermined time has elapsed since the previous strength regeneration, and the PM emission amount calculated from the load and the rotation speed of the internal combustion engine has reached a predetermined amount.

When it is determined that the above-described strength regeneration execution condition is satisfied, the CPU 351 controls the flow control valve 30 so as to supply a larger amount of fuel to the filter 20 than during normal regeneration. The air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to a predetermined target rich air-fuel ratio.

Here, as a method of supplying a larger amount of fuel than at the time of normal regeneration, the valve opening time of the reducing agent injection valve 28 is lengthened, the valve opening interval is shortened, and the like.

Then, the CPU 351 stores the engine speed, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), the fuel injection amount, and the like stored in the RAM 353. read out. Further, the CPU 351 uses the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters as RO
The control unit accesses the reducing agent addition amount control map of M352, and calculates the addition amount (target addition amount) of the reducing agent necessary for setting the exhaust air-fuel ratio to the preset target rich air-fuel ratio.

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.

Thereafter, fuel is added in the same manner as in the normal regeneration, and the temperature of the filter 20 is raised to, for example, 700 ° C. or more as shown in FIG.

At this time, the feedback control of the fuel addition may be performed by estimating the bed temperature of the filter 20 from the output value of the exhaust gas temperature sensor 24.

In the filter 20 whose temperature has been raised in this way, PM that has remained unburned and accumulated in normal regeneration can be ignited and burned, and the filter 20 can be regenerated.

Further, since there is a possibility that the filter 20 may be thermally degraded when the intensity regeneration is performed, the execution time of the intensity regeneration is preferably shorter than the execution time of the normal regeneration.

[0121]

According to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, clogging of the filter can be eliminated while suppressing thermal deterioration of the catalyst.

Accordingly, the function of the filter can be maintained for a long time, and deterioration of exhaust emission can be prevented.

[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. 4A is a diagram showing a cross section of a particulate filter in a lateral direction. (B) is a figure which shows the longitudinal direction cross section of a particulate filter.

FIG. 5A is a diagram showing a change in a passage area of a filter. (B) is a figure which shows the change of the bed temperature of a filter.

[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 ... particulate filter 21 ... exhaust throttle valve 23 ... air-fuel ratio sensor 25 ... EGR passage 26 ... EGR valve 27 ... EGR cooler 28 ... reducing agent Injection valve 29 ... Reducing agent supply path 30 ... Flow 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 50 Exhaust inflow passage 51 Exhaust outflow passage 54 Partition wall

Continuing on the front page (72) Inventor Naofumi Matsuda 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Masaaki Kobayashi 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Daisuke Shibata 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Co., Ltd. (72) Inventor Akihiko Negami 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Tomiku Oda Toyota City, Aichi Prefecture 1st Toyota Town Inside Toyota Motor Corporation (72) Inventor Yasuo Harada 1st Toyota Town Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Yasuhiko Otsubo 1st Toyota Town Toyota City, Aichi Prefecture Toyota Motor Stock In-house (72) Inventor Taro Aoyama 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G090 AA03 BA01 DA00 DA12 DA18 DA20

Claims (1)

[Claims] 1. A filter provided in an exhaust passage of an internal combustion engine, the filter carrying a catalyst for collecting particulate matter contained in exhaust gas and promoting the combustion of the collected particulate matter, and a temperature of the filter. And a filter temperature raising means for raising the temperature of the filter to a first predetermined temperature when a first predetermined condition is satisfied, whereby the particulate matter is burned and reduced. When the second predetermined condition is satisfied, the temperature of the filter is raised to a second predetermined temperature higher than the first predetermined temperature, and the interval for raising the temperature to the second predetermined temperature is: An exhaust gas purification device for an internal combustion engine, wherein the interval is longer than the interval at which the temperature is raised to the first predetermined temperature.