JP2003049629A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology capable of uniforming exhaust amount passing through a filter and suppressing degradation of a filter function in an exhaust emission control device of an internal combustion engine. SOLUTION: In the exhaust emission control device 20 of the internal combustion engine, a plurality of filters 201, 202, and 203 are disposed in parallel in an exhaust passage, the flow direction of the exhaust passing through the filters 201, 202, and 203 can be reversed by an exhaust passage separating means 211. Flow rates of exhaust gas flowing through respective filters 201, 202, and 203 are substantially uniformed by making formations of respective filters 201, 202, and 203 different.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust emission control device for an internal combustion engine.

[0002]

2. Description of the Related Art Diesel engines are excellent in economic efficiency, but on the other hand, particulate matter represented by soot, which is a suspended particulate matter contained in exhaust gas, is used.
Hereinafter, unless otherwise specified, it is referred to as “PM”. ) Is an important issue. Therefore, a technique is known in which a particulate filter (hereinafter, simply referred to as “filter”) that traps PM is provided in an exhaust system of a diesel engine so that PM is not released into the atmosphere.

This filter can prevent the PM in the exhaust gas from being once collected and released into the atmosphere. However, if the PM collected by the filter accumulates on the filter, the filter may be clogged. If this clogging occurs, the pressure of the exhaust gas upstream of the filter may increase, which may lead to a decrease in the output of the internal combustion engine or damage to the filter. In such a case, the PM accumulated on the filter can be removed by igniting and burning the PM. PM deposited on the filter in this way
Removing the filter is called filter regeneration.

However, in order to ignite and burn the PM collected in the filter, the temperature of the filter is set to, for example, 60.
Although it is necessary to raise the temperature to 0 ° C. or higher, the temperature of the exhaust gas of the diesel engine is usually lower than this temperature, so it was difficult to burn off PM.

Therefore, it is conceivable to heat and raise the temperature of the filter to a temperature at which the ignition and combustion of PM collected by using an electric heater, a burner or the like occurs, but this requires a large amount of energy to be supplied from the outside. There is. For this problem,
For example, according to Japanese Patent Laid-Open No. 6-159037, NOx
Using a filter that supports a catalyst and a device that supplies hydrocarbons that are reducing agents into the exhaust gas, the heat generated when the hydrocarbons that are supplied into the exhaust gas are burned by the NOx catalyst is used to easily PM. It is possible to burn.

[0006]

However, since the exhaust gas passing through the filter does not always flow uniformly over the entire filter, a large amount of PM is trapped in a portion having a large exhaust gas flow amount. There is a risk that clogging may occur early. Further, even when the reducing agent is supplied, a large amount of the reducing agent is supplied to a portion where the exhaust gas flow amount is large, so that the effect of supplying the reducing agent may not be uniform. Furthermore, in order to remove the sulfur component absorbed in the filter, a sulfur poisoning recovery control may be performed in which a reducing agent is supplied to raise the filter temperature to a high temperature. Therefore, since the catalyst bed temperature is also different, it becomes difficult to recover the sulfur poisoning at the low temperature portion while preventing the thermal deterioration at the high temperature portion.

On the other hand, if a plurality of small-diameter filters are provided in parallel along the flow of exhaust gas in order to improve the mountability of the vehicle, the exhaust gas flowing through the exhaust pipe receives inertial force and flows more to the downstream filter. There is. In this case, a large amount of PM and reducing agent in the exhaust gas also flow to the downstream filter. Therefore, the temperature increase due to the heat of the oxidation reaction of the reducing agent and the heat of combustion of PM becomes large in the downstream filter.
In such a state, if the reducing agent supply amount is adjusted according to the downstream filter, sufficient amount of reducing agent is not supplied to the upstream filter and PM is removed or nitrogen oxides (NOx) are not supplied. There is a risk that purification and release of sulfur oxides (SOx) will not be performed sufficiently. Therefore, in the filter having such a structure, the amount capable of absorbing NOx is small relative to the amount of the carried catalyst.

The present invention has been made to solve the above problems, and the problem to be solved by the present invention is to reduce the amount of exhaust gas passing through a filter in an exhaust gas purification apparatus for an internal combustion engine having a filter. It is an object of the present invention to provide a technique capable of making uniform and suppressing the deterioration of the filter function.

[0009]

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means. That is, a filter capable of temporarily capturing fine particles in exhaust gas of an internal combustion engine and carrying a catalyst, a first exhaust passage connected to one end side of the filter, and a second exhaust gas connected to the other end side of the filter. A passage, an exhaust passage selecting means for selecting one of the first exhaust passage and the second exhaust passage, and one end of the filter when the exhaust passage selecting means selects the first exhaust passage And a third exhaust passage connected to the side and the other end of which is open to the atmosphere, and one end of which is connected to one end of the filter and the other end of which is open to the atmosphere when the exhaust passage selecting means selects the second exhaust passage. An exhaust gas purification apparatus for an internal combustion engine, comprising: a plurality of filters arranged in parallel; Characterized in that is substantially uniform.

The greatest feature of the present invention is that in an exhaust gas purification apparatus for an internal combustion engine in which a plurality of filters are provided in parallel, the flow rate of exhaust gas passing through each filter is made uniform, and the temperature of the filter and the amount of trapped PM are made uniform. It is to try to realize

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, when the exhaust passage selecting means is circulating the exhaust gas to the first exhaust passage, the exhaust gas is introduced into the filter from one end side of the filter, After passing, it flows out from the other end side of the filter and is discharged into the atmosphere through the third exhaust passage. On the other hand, when the exhaust passage selecting means is circulating the exhaust gas to the second exhaust passage selecting means, the exhaust gas is introduced into the filter from the other end side of the filter, passes through the filter, and then flows out from the one end side of the filter. 4 It is released into the atmosphere through the exhaust passage.

Further, by making the flow rate of the exhaust gas flowing through the respective filters substantially uniform, it is possible to suppress the occurrence of a temperature difference between the filters.

When the temperature difference between the filters is reduced as described above, some of the filters become hot due to the above-mentioned sulfur poisoning recovery and are thermally deteriorated. On the other hand, some of the filters become low temperature and the sulfur poisoning is recovered. It is possible to avoid the situation where the work is not sufficiently done.

In the present invention, the size of each filter can be determined so that the flow rate of exhaust gas per unit volume is substantially uniform among the filters.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the size of the filter can be determined based on the flow rate of the exhaust gas flowing through the filter, and the flow rate of the exhaust gas passing through each filter can be adjusted.

In the present invention, when the size of each filter is the same, if there is a difference in the amount of exhaust gas flowing between the filters, the filter having the larger amount of exhaust gas flow has a larger size. Can be large.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, when a large amount of exhaust gas is about to flow through a certain filter, the diameter of the filter is increased according to the flow rate thereof,
The throughput of exhaust gas per unit volume can be made uniform.

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means as another means. That is, a filter capable of temporarily capturing fine particles in exhaust gas of an internal combustion engine and carrying a catalyst, a first exhaust passage connected to one end side of the filter, and a second exhaust gas connected to the other end side of the filter. A passage, an exhaust passage selecting means for selecting one of the first exhaust passage and the second exhaust passage, and one end of the filter when the exhaust passage selecting means selects the first exhaust passage And a third exhaust passage connected to the side and the other end of which is open to the atmosphere, and one end of which is connected to one end of the filter and the other end of which is open to the atmosphere when the exhaust passage selecting means selects the second exhaust passage. An exhaust gas purifying apparatus for an internal combustion engine, comprising a plurality of filters arranged in parallel, and when the filters have the same size, When there is a difference in quantity Is characterized in that is substantially uniform across the filter the flow rate of the exhaust gas that flows by reducing the size of the filter as flow amount of the exhaust is larger filter.

The greatest feature of the present invention is that in an exhaust gas purification apparatus for an internal combustion engine, the filter having a larger exhaust gas flow amount has a smaller size, and the temperature in the filter and the amount of trapped PM are made uniform. Especially.

In the exhaust gas purifying apparatus for an internal combustion engine having such a structure, even if a large amount of exhaust gas flows through a certain filter, the size of the filter is reduced according to the flow rate of the exhaust gas. Distribution volume decreases.
On the other hand, in other filters, the flow amount increases by the amount of exhaust gas that cannot pass through the filter having the reduced size. In this way, the throughput of exhaust gas per unit volume between the filters can be made uniform.

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means as another means. That is, a filter capable of temporarily capturing fine particles in exhaust gas of an internal combustion engine and carrying a catalyst, a first exhaust passage connected to one end side of the filter, and a second exhaust gas connected to the other end side of the filter. A passage, an exhaust passage selecting means for selecting one of the first exhaust passage and the second exhaust passage, and one end of the filter when the exhaust passage selecting means selects the first exhaust passage And a third exhaust passage connected to the side and the other end of which is open to the atmosphere, and one end of which is connected to one end of the filter and the other end of which is open to the atmosphere when the exhaust passage selecting means selects the second exhaust passage. An exhaust gas purification device for an internal combustion engine, the filter having a plurality of filters, the filters having substantially the same size, and the exhaust flow resistance of each filter. When the same When there is a difference in the amount of exhaust gas that flows between the filters, the larger the amount of exhaust gas that flows, the greater the flow resistance of the filter and the smaller the amount of exhaust gas that flows through the filter. It is characterized in that the amount is made substantially uniform among the filters.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the flow resistance of the filter, which tends to flow a large amount of exhaust gas, is increased to reduce the flow rate of the exhaust gas, and the reduced amount is circulated to another filter. The flow rate can be made uniform.

In order to achieve the above object, the exhaust gas purifying apparatus for an internal combustion engine of the present invention employs the following means as another means. That is, an exhaust passage which is an exhaust passage of an internal combustion engine and which is branched in parallel, and a filter which is provided in each of the branched exhaust passages and is capable of temporarily capturing fine particles in exhaust gas and carrying a catalyst, Exhaust passage selecting means for selecting at least one of the plurality of exhaust passages to circulate exhaust gas, wherein at least one passage length of the plurality of exhaust passages is different, and at least one form of the filter is different. It is characterized in that the flow rate of the exhaust gas that flows in this way is made substantially uniform between the filters.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, it is possible to suppress the occurrence of a temperature difference or the like between the filters by making the flow rates of the exhaust gas flowing through the filters substantially uniform. Become.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Specific embodiments of an exhaust gas purification apparatus for an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example. <First Embodiment> FIG. 1 is a diagram showing a schematic configuration of an engine 1 to which an exhaust emission control device according to the present embodiment is applied and an intake / exhaust system thereof.

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

The engine 1 is equipped with 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 accumulator (common rail) 4 that accumulates fuel to a predetermined pressure. A common rail pressure sensor 4a that outputs an electric signal corresponding to the pressure of the fuel in the common rail 4 is attached to the common rail 4.

The common rail 4 communicates with a fuel pump 6 via a fuel supply pipe 5. This fuel pump 6
Is a pump that operates using the rotational torque of the output shaft (crankshaft) of the engine 1 as a drive source. A pump pulley 6a attached to the input shaft of the fuel pump 6 is attached to the output shaft (crankshaft) of the engine 1. The crank pulley 1a is connected to the crank pulley 1a via a belt 7.

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

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

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

The intake branch pipe 8 is connected to the intake pipe 9,
The intake pipe 9 is connected to the air cleaner box 10. An air flow meter 11 for outputting an electric signal corresponding to the mass of the intake air flowing through the intake pipe 9 and an intake air temperature flowing through the intake pipe 9 are provided in the intake pipe 9 downstream of the air cleaner box 10. The intake air temperature sensor 12 that outputs the electric signal is attached.

An intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 13 is provided with an intake throttle actuator 14 configured by a step motor or the like for driving 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 by using heat energy of exhaust gas as a drive source. The
An intercooler 16 for cooling the intake air that has become hot due to being compressed in the compressor housing 15a is provided in the intake pipe 9 downstream of the compressor housing 15a.
Is provided.

In the intake system configured as described above, the intake air that has flowed into the air cleaner box 10 is passed through the intake pipe 9 after dust and the like in the intake air have been removed by an air cleaner (not shown) in the air cleaner box 10. Flow into the compressor housing 15a.

The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel installed in the compressor housing 15a. The intake air, which has been compressed in the compressor housing 15a and has reached a high temperature, is cooled by the intercooler 16 and then flows into the intake branch pipe 8 with its flow rate adjusted by the intake throttle valve 13 if necessary. The intake air that has flowed into the intake branch pipe 8 is distributed to the combustion chamber of each cylinder 2 through 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 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 serves as the centrifugal supercharger 15.
Is connected to the turbine housing 15b. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected downstream to a muffler (not shown).

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

Exhaust pipe 1 downstream of the filter 20 described above
An exhaust throttle valve 21 for adjusting the flow rate of the exhaust gas flowing through the exhaust pipe 19 is provided in the valve 9. This exhaust throttle valve 2
1, an exhaust throttle valve 2 which is composed of a step motor or the like
An exhaust throttle actuator 22 for driving to open and close 1 is attached.

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

The exhaust gas discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19, PM in the exhaust gas is collected, and harmful gas components are removed or purified. The exhaust gas, in which the PM is collected by the filter 20 and the harmful gas component is removed or purified, is discharged into the atmosphere through the muffler after the flow rate is adjusted by the exhaust throttle valve 21 as necessary.

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

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

In the exhaust gas recirculation mechanism constructed as described above, when the EGR valve 26 is opened, the EGR passage 25 is brought into conduction, and a part of the exhaust gas flowing through the exhaust branch pipe 18 is part of the EGR passage 25. To the intake branch pipe 8 via the EGR cooler 27.

At this time, in the EGR cooler 27, heat exchange is performed between the EGR gas flowing in the EGR passage 25 and the cooling water of the engine 1 to cool the EGR gas.

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

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

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

In this embodiment, low temperature combustion is performed to increase the EGR gas amount more than usual at a light load, and P
Removal of M, purification of NOx, maintenance of the temperature of the filter 20 and the like are performed.

Here, the low temperature combustion will be described.

As described above, conventionally, EGR has been used to suppress the generation of NOx. Since the EGR gas has a relatively high specific heat ratio and a large amount of heat required to raise the temperature, the combustion temperature in the cylinder 2 decreases as the EGR gas ratio in the intake air increases. Since the amount of NOx generated decreases as the combustion temperature decreases, the NOx emission amount can be decreased as the EGR gas ratio increases.

However, if the EGR gas ratio is increased, the soot generation amount starts to increase rapidly at a certain ratio or higher. Normal EGR control is lower than the soot that starts to increase rapidly
It is done at the R gas rate.

However, if the EGR gas ratio is further increased, the soot increases sharply as described above, but there is a peak in the amount of soot generated, and the EGR gas ratio is further exceeded beyond this peak. If you raise it, then the soot will start to decrease sharply until it almost never occurs.

This is because when the temperature of the fuel and the gas around it during combustion in the combustion chamber is below a certain temperature, the growth of hydrocarbons (HC) stops in the middle of the process before it reaches soot,
This is because if the temperature of the fuel and the gas around it rises above a certain temperature, hydrocarbons (HC) will grow to soot all at once.

Therefore, if the temperature of combustion during combustion in the combustion chamber and the gas temperature around it are suppressed below the temperature at which the growth of hydrocarbons (HC) stops halfway, soot will not be generated.
In this case, the temperature of the fuel and the gas around it is greatly affected by the endothermic action of the gas around the fuel when the fuel burns, and the endothermic amount of the gas around the fuel, that is, EGR It is possible to suppress the generation of soot by adjusting the gas ratio.

The EGR gas ratio when performing low temperature combustion is
ECUs that have been obtained in advance by experiments and are mapped
It is stored in the ROM (352 in FIG. 5) in the memory 35. Feedback control of the EGR gas amount is performed based on this map.

On the other hand, the hydrocarbon (HC), the growth of which has stopped before reaching soot, is NOx carried by the filter 20.
It can be burned with an absorbent or the like.

As described above, in the low temperature combustion, the hydrocarbon (HC), the growth of which has stopped halfway before reaching the soot, is basically purified by the NOx absorbent or the like. Therefore NOx
When the absorbent is not activated, hydrocarbons (H
It is difficult to use low temperature combustion because C) is not purified but is released into the atmosphere.

Further, the temperature of the fuel and the gas around it during combustion in the cylinder 2 can be controlled below the temperature at which the growth of hydrocarbons (HC) stops midway. When is low.

Therefore, in the present embodiment, the low temperature combustion control is performed when the engine 1 is operated at low rotation and low load and when the NOx storage reduction catalyst carried on the filter 20 reaches the active region. Done.

Whether or not it is within the active region can be determined based on the output signal of the exhaust temperature sensor 24 and the like.

Thus, in low temperature combustion, hydrocarbons (HC) as reducing agents can be supplied to the NOx storage reduction catalyst while suppressing the emission of PM represented by soot, and NOx can be reduced and purified. . In addition, since heat is generated at this time, it becomes possible to maintain the temperature of the filter 20 which has been raised.

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

FIG. 2 is a sectional view of the filter 20. 2A is a horizontal sectional view, FIG. 2B is a vertical sectional view, and FIG. 2C is a lateral sectional view. The filter 20 has a case 212. Both ends of the case 212 are formed in a truncated cone shape, and the ends are connected to the exhaust pipe 19. The inside of the case 212 is divided into three in the longitudinal direction by two walls 204 and 205 extending in the longitudinal direction and parallel to each other. The first channel 206 and the second channel 207 are located on both sides, and the first channel 206 is located in the center. Three flow paths 208 are formed. All the exhaust gas flowing out from the exhaust pipe 19 is adapted to flow out from the third flow path 208. Case 2
A first filter 20 having a circular cross-section
A first filter 202, a second filter 202, and a third filter 203 penetrate through both wall portions 204 and 205, and each filter 20
The central axes of 1, 202 and 203 are arranged so as to be orthogonal to the central axis of the case 212. Here, the cross-sectional area of the first filter 201 is the smallest and the second filter 202,
The filter size increases in the order of the third filter 203. The sizes of the filters 201, 202 and 203 are set in advance by experiments or the like so that the flow rates of the exhaust gas passing through the filters 201, 202 and 203 become substantially equal.

Each of the filters 201, 202 and 203 has a first opening 209 and a second opening 210 for inflow and outflow of exhaust gas, and the first opening 209 is the first flow path 20.
6 and the second opening 210 communicates with the second flow path 207. The central axis of the filter 20 is
It means a central axis passing through the centers of the first opening 209 and the second opening 210. In addition, each filter 201,
First opening 209 and second opening 210 of 202, 203
Between and, a part of the third flow path 208 is vertically divided,
Exhaust gas flowing through the third flow path 208 is filtered by the filters 201, 20.
It is designed to be distributed while being in contact with 2,203.

Further, the ECU 3 is provided upstream of the filter 20.
The filters 201, 202,
Switching valve 2 for switching the flow direction of exhaust gas passing through 203
11 is provided. The switching valve 21 shown in FIG.
At the position 1, the third flow passage 208 is connected to the second flow passage 207 and the first flow passage 206 is connected to the exhaust pipe 19 on the upstream side of the filter 20. As a result, the exhaust gas is
It flows through the first flow path 206 as indicated by the arrow in (a), and the first opening 2 of each of the filters 201, 202, 203.
09, passes through the second opening 210, flows out into the second flow path 207, and flows out through the third flow path 208 into the exhaust pipe 19 on the downstream side of the filter 20.

On the other hand, FIG. 3 is a diagram showing the flow direction of exhaust gas after the switching valve 211 rotates from the position of FIG.

At the position of the switching valve 211 shown in FIG. 3, the third flow passage 208 is connected to the second flow passage 207 and the first flow passage 206 is connected to the exhaust pipe 19 on the upstream side of the filter 20. As a result, the exhaust gas flows from the second flow path 207 to the filters 201, 202, 20 as shown by the arrows in FIG.
3 through the second opening 210 to the first opening 209,
Filter 2 from the first flow path 206 through the third flow path 208
0 flows to the exhaust pipe 19 on the downstream side.

In this way, the switching valve 211 can reverse the flow direction of the exhaust gas passing through the filters 201, 202, 203.

FIG. 4 shows the structure of the filters 201, 202 and 203. In FIG. 4, (A) is the filter 20.
1 shows a transverse cross section of 1, 202, 203, (B)
Shows a longitudinal sectional view of the filters 201, 202, 203. As shown in FIGS. 4A and 4B, the filters 201, 202 and 203 are so-called wall flow type filters having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages are composed of an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. The hatched portion in FIG. 4A indicates the plug 53. Therefore, the exhaust inflow passage 50
The exhaust gas outflow passages 51 are alternately arranged via the thin partition walls 54. 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. Here, since the filters 201, 202 and 203 have different diameters, respectively, the number of the exhaust passages 50 and 51 arranged is different.

The filters 201, 202 and 203 are made of a porous material such as cordierite, and therefore the exhaust gas flowing into the exhaust gas inflow passage 50 is shown in FIG.
As shown by the arrow in (B), it passes through the surrounding partition wall 54 and flows into the adjacent exhaust outflow passage 51.

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

Next, each filter 20 according to the present embodiment
The function of the NOx storage reduction catalyst carried by Nos. 1, 202 and 203 will be described.

The filters 201, 202 and 203 are, for example,
For example, alumina is used as a carrier, and potassium is placed on the carrier.
(K), sodium (Na), lithium (Li), if
Alkali metals such as cesium (Cs) and barium
Alkaline earth such as (Ba) or calcium (Ca)
And lantern (La) or yttrium (Y)
At least one selected from rare earths and platinum (P
and a precious metal such as t) are supported. In addition,
In the embodiment, barium (B
a) and platinum (Pt) are supported, and further O₂Storage capacity
Powerful ceria (Ce₂O ₃))
A reduction type NOx catalyst was adopted.

The NOx catalyst thus constructed is
When the exhaust gas flowing into the Ox catalyst has a high oxygen concentration, it absorbs nitrogen oxides (NOx) in the exhaust gas.

On the other hand, the NOx catalyst releases the nitrogen oxides (NOx) absorbed when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust gas, the NOx catalyst converts the nitrogen oxide (NOx) released from the NOx catalyst into nitrogen (N). It can be reduced to ₂ ).

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

Particularly, in a diesel engine such as the engine 1, a lean air-fuel ratio mixture is burned in most operating regions, and accordingly, the exhaust air-fuel ratio becomes lean air-fuel ratio in most operating regions. , N of NOx catalyst
Ox absorption capacity is easily saturated.

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

The exhaust gas purification apparatus for an internal combustion engine according to the present embodiment is provided with a reducing agent supply mechanism for adding a fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust pipe 19 upstream of the filter 20. By adding fuel from the agent supply mechanism into the exhaust gas, the oxygen concentration of the exhaust gas flowing into the filter 20 is reduced and the concentration of the reducing agent is increased.

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

It should be noted that the reducing agent injection valve 28 has four injection pipes in which the injection holes of the reducing agent injection valve 28 are located downstream of the connection 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. The cylinder head is preferably attached to the cylinder head so as to project to the exhaust port of the cylinder 2 closest to the collecting portion and 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 centrifuges the reducing agent in the exhaust branch pipe 18 without stagnation. This is so that the turbine housing 15b of the supercharger can be reached.

In the example shown in FIG. 1, the fourth (# 4) cylinder 2 among the four cylinders 2 of the engine 1 is located closest to the collecting portion of the exhaust branch pipe 18, and thus the fourth (# 4) ) A reducing agent injection valve 28 is attached in the vicinity of the cylinder 2, but when the cylinders 2 other than the fourth (# 4) cylinder 2 are located closest to the collecting portion of the exhaust branch pipe 18, the cylinder 2 The reducing agent injection valve 28 is mounted in the vicinity of.

Further, the reducing agent injection valve 28 penetrates a water jacket (not shown) formed in the cylinder head or is attached in the vicinity of the water jacket, and uses the cooling water flowing through the water jacket. The reducing agent injection valve 28 may be cooled.

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

The reducing agent injected from the reducing agent injection valve 28 into the exhaust branch pipe 18 flows into the turbine housing 15b together with the exhaust gas flowing from the upstream side of the exhaust branch pipe 18.
The exhaust gas flowing into the turbine housing 15b and the reducing agent are agitated by the rotation of the turbine wheel and mixed homogeneously to form exhaust gas having a low oxygen concentration.

The thus formed exhaust gas having a low oxygen concentration flows into the filter 20 from the turbine housing 15b through the exhaust pipe 19 and releases the nitrogen oxides (NOx) absorbed in the filter 20. It will be reduced to nitrogen (N ₂ ).

After that, the reducing agent injection valve 28 is closed by a signal from the ECU 35, and the addition of the reducing agent into the exhaust branch pipe 18 is stopped.

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

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

On the other hand, the ECU 35 is connected to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the cutoff valve 31 and the like through electrical wiring, and the ECU 35 controls the above-mentioned respective parts. It is possible to do.

Here, the ECU 35, as shown in FIG. 5, is connected to each other by a bidirectional bus 350, C,
The input port 356 includes a PU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357.
And an A / D converter (A / D) 355 connected to.

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

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

The output port 357 is connected to the fuel injection valve 3,
The control signal output from the CPU 351 is connected to the intake throttle actuator 14, the exhaust throttle actuator 22, the EGR valve 26, the cutoff valve 31 and the like via electrical wiring, and the control signal output from the CPU 351 is used as described above. , Exhaust throttle actuator 22, EGR valve 26,
Alternatively, it is transmitted to the shutoff valve 31.

The ROM 352 has 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, an EGR. EGR control routine for controlling the valve 26, NOx purification control routine for adding a reducing agent to the filter 20 to release the absorbed NOx, Sx for eliminating SOx poisoning of the filter 20
Application programs such as an Ox poisoning elimination control routine and a PM combustion control routine for burning and removing the PM collected in the filter 20 are stored.

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

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

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

The CPU 351 operates according to the application program stored in the ROM 352 to control the fuel injection valve, intake throttle control, exhaust throttle control, E
GR control, reducing agent addition control, PM combustion control, etc. are executed.

For example, in the NOx purification control, the CPU 35
1 executes so-called rich spike control in which the oxygen concentration in the exhaust gas flowing into the filter 20 is reduced in a spike-like (short time) manner in a relatively short cycle.

In rich spike control, the CPU 351
Determines whether the rich spike control execution condition is satisfied every predetermined period. As the rich spike control execution condition, for example, the filter 20 is in an active state, the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value, poisoning elimination control is not executed, Examples of such conditions are as follows.

If it is determined that the rich spike control execution condition as described above is satisfied, the CPU 351
Controls the reducing agent injection valve 28 so that the reducing agent injection valve 28 injects fuel as the reducing agent in a spike manner to temporarily change the air-fuel ratio of the exhaust gas flowing into the filter 20 to a predetermined target rich air-fuel ratio. And

Specifically, the CPU 351 has the RAM 35.
Engine speed, accelerator opening sensor 3 stored in 3
6 output signal (accelerator opening), air flow meter 11
Output signal value (intake air amount), output signal of the air-fuel ratio sensor, fuel injection amount, and the like. The CPU 351 accesses the reducing agent addition amount control map of the ROM 352 using the engine speed, the accelerator opening, the intake air amount, and the fuel injection amount as parameters, and sets the exhaust air-fuel ratio to the preset target air-fuel ratio. The addition amount of the reducing agent (target addition amount) required above is calculated.

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

When the target valve opening time of the reducing agent injection valve 28 is calculated, the CPU 351 opens the reducing agent injection valve 28.

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

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

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

Next, in the poisoning elimination control, the CPU 351
Will perform a poisoning elimination process in order to eliminate the poisoning due to the oxide of the filter 20.

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

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

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

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

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

As a method for eliminating SOx poisoning of the filter 20, the ambient temperature of the filter 20 is set to about 500 ° C.
By raising the temperature to a high temperature range of up to 700 ° C. and lowering the oxygen concentration of the exhaust gas flowing into the filter 20,
Barium sulfate (BaSO) absorbed by the filter 20
₄₎ the SO ₃ ^- and SO ₄ ^- and pyrolyzed, followed by SO ₃ ^- and SO ₄
^- it can be exemplified a method of reducing the ^- is reacted with a hydrocarbon in the exhaust gas (HC) and carbon monoxide (CO) gaseous SO ₂ and.

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

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

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

When the bed temperature of the filter 20 rises to a high temperature range of about 500 ° C. to 700 ° C. by the catalyst temperature raising process as described above, the CPU 351 injects the reducing agent to reduce the oxygen concentration of the exhaust gas flowing into the filter 20. Fuel is injected from the valve 28.

When excessive fuel is injected from the reducing agent injection valve 28, those fuels burn rapidly in the filter 20 and the filter 20 overheats, or excessive fuel injected from the reducing agent injection valve 28 is injected. Since the filter 20 may be unnecessarily cooled by the fuel, the CPU 351 preferably feedback-controls the fuel injection amount from the reducing agent injection valve 28 based on the output signal of the air-fuel ratio sensor.

When the poisoning elimination processing is executed in this way,
When the bed temperature of the filter 20 is high, the oxygen concentration of the exhaust gas flowing into the filter 20 is low, so that barium sulfate (BaSO ₄ ) absorbed by the filter 20 is thermally decomposed into SO ₃ ⁻ and SO ₄ ^−. The SO ₃ ⁻ and SO ₄ ⁻ react with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and are reduced, whereby SOx poisoning of the filter 20 is eliminated.

By the way, in the exhaust gas purifying apparatus for an internal combustion engine equipped with the filter, the PM accumulated on the filter is burned and removed by the high temperature exhaust gas discharged when the engine is operated in the high rotation and high load region. However, since it takes time to burn the PM, if the operating region of the engine deviates from the high rotation and high load region before the PM is completely burned and removed, the PM remains unburned. It is difficult to maintain such an engine operating state suitable for burning PM for a long period of time. For this reason, unburned PM gradually accumulates on the filter, which causes the filter to be clogged.

[0126] One of the methods for effectively removing the PM that remains unburned in this way is to add fuel to the exhaust gas.

Next, PM combustion control by adding fuel to the exhaust will be described.

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

First, the CPU 351 determines whether or not the fuel addition control execution condition is satisfied every predetermined period. The fuel addition control execution condition is, for example, the filter 2
Conditions such as whether or not 0 is in an active state and whether or not the output signal value (exhaust temperature) of the exhaust temperature sensor 24 is equal to or lower than a predetermined upper limit value can be exemplified.

When it is determined that the fuel addition control execution condition as described above is satisfied, the CPU 351 controls the reducing agent injection valve 28 so that the reducing agent injection valve 28 injects the fuel serving as the reducing agent. As a result, the air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to the predetermined target air-fuel ratio.

Specifically, the CPU 351 has the RAM 35.
Engine speed, accelerator opening sensor 3 stored in 3
6 output signal (accelerator opening), air flow meter 11
Output signal value (intake air amount), fuel injection amount, fuel injection timing, and other engine operating states are read. Furthermore, CP
The U 351 accesses the reducing agent addition amount control map of the ROM 352 using the engine operating state as a parameter, and the reducing agent addition amount (target addition amount required to set the air-fuel ratio of the exhaust gas to the preset target air-fuel ratio (target addition). Amount).

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

When the target valve opening time of the reducing agent injection valve 28 is calculated, the CPU 351 opens the reducing agent injection valve 28.

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

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

As a result, the oxygen concentration of the exhaust gas flowing into the filter 20 changes in a relatively short cycle. Then, the active oxygen is released by the fuel that has flowed into the filter 20, so that the PM is transformed into a substance that is easily oxidized, and the amount that can be oxidized and removed per unit time is improved. Further, the addition of fuel removes oxygen poisoning of the catalyst and increases the activity of the catalyst, so that active oxygen is easily released. Then, PM is oxidatively burned and removed by the active oxygen.

In the present embodiment, fuel is injected into the exhaust gas to add the fuel to reduce the oxygen concentration in the exhaust gas. Alternatively, the above-described low temperature combustion may be performed, or the oxygen concentration in the exhaust gas may be reduced by injecting fuel from the fuel injection valve 3 during the expansion stroke, the exhaust stroke, etc. of the engine 1.

For example, in the case of low temperature combustion, the ECU 35
First obtains the target air-fuel ratio. The target air-fuel ratio can be obtained by predefining a map based on the operating state of the engine 1. Next, the ECU 35 calculates the target opening degree of the intake throttle valve 13 according to the target air-fuel ratio, and the intake throttle valve 13
Is controlled to the target opening. Next, the ECU 35
Calculates the target opening degree of the EGR valve 26 according to the target air-fuel ratio, and controls the EGR valve 26 to be the target opening degree.
Further, the ECU 35 calculates the fuel injection amount and the fuel injection start timing. The target opening amounts of the intake throttle valve 13 and the EGR valve 26, the fuel injection amount, and the fuel injection start timing are calculated based on a map obtained in advance.

Next, the ECU 35 determines whether the actual air-fuel ratio detected by the air-fuel ratio sensor (not shown) is larger than the target air-fuel ratio. This air-fuel ratio sensor is provided in the exhaust branch pipe 18. When the actual air-fuel ratio is larger than the target air-fuel ratio, a fixed value is added to the correction value for the opening of the EGR valve 26, while when the actual air-fuel ratio is less than the target air-fuel ratio, the opening of the EGR valve 26 is reduced. A constant value is subtracted from the correction value for. Next, the ECU 35
Controls the EGR valve 26 with a new target opening obtained by adding a correction value to the target opening of the EGR valve 26. That is,
The air-fuel ratio is controlled by controlling the opening degree of the EGR valve 26. Similarly, the air-fuel ratio control can be performed by controlling the opening degree of the intake throttle valve 13.
Further, the exhaust gas at this time contains a large amount of unburned hydrocarbons (HC) as a reducing agent as described above.

By performing the low temperature combustion in this way, the concentration of oxygen in the exhaust gas flowing into the filter 20 is reduced, the concentration of the reducing agent is increased, and the nitrogen oxide (NOx) absorbed by the filter 20 is released. It is also possible to oxidize PM.

Here, FIG. 6 is a diagram showing the flow distribution of the exhaust gas passing through each filter and the temperature distribution of the filters when the diameters of all the filters provided in the case 212 are the same. 6 (a) is a horizontal sectional view, FIG.
6B is a vertical cross-sectional view, FIG. 6C is a diagram showing the exhaust gas flow distribution in the filter 20, and FIG.
It is a figure which shows the temperature distribution of.

In the filter having the structure as shown in FIG. 6 (a), since the exhaust gas flowing from the upstream flows largely into the third filter 203 on the most downstream side, there is a difference in the exhaust flow rate between the filters. In such a case, the amount of purification treatment per unit volume is not uniform among the filters, and the upstream first filter 201 does not exhibit its purification capacity sufficiently. Further, the reducing agent added to the exhaust gas and the hydrocarbon (HC) discharged from the internal combustion engine together with the exhaust gas also flow to the third filter 203 on the most downstream side, and the third filter 203 on the downstream side is on the upstream side. The temperature was higher than that of the first filter 201. In particular, when sulfur poisoning elimination control is performed,
Since the temperature of the filter becomes high (for example, 650 ° C. or higher), if the supply amount of the reducing agent or the like is adjusted in order to prevent thermal deterioration with the third filter 203 on the most downstream side, the first on the most upstream side
In the filter 201, a shortage of reducing agent or the like occurs. Therefore,
In the upstream side first filter 201, poisoning is not sufficiently eliminated and it becomes difficult to effectively purify NOx.

On the other hand, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, by increasing the diameter of the filter from the upstream side to provide a filter having a size corresponding to the flow rate of exhaust gas, the unit volume is increased. The amount of exhaust gas processed per unit can be made uniform among the filters. Further, since the supply of the reducing agent and the like becomes uniform and the temperature difference between the filters is eliminated, poisoning can be effectively eliminated in all the filters during the sulfur poisoning recovery control.

As described above, in the exhaust gas purification device for an internal combustion engine according to the present embodiment, the exhaust gas flow distribution among a plurality of filters can be made uniform.

In this embodiment, the case 212 has three
Although two filters are provided, the number may be two or four or more. Further, the diameters of all the filters 20 do not necessarily have to be different depending on the exhaust gas flow distribution, and filters having the same diameter may be provided. <Second Embodiment> This embodiment is different from the first embodiment in the following points.

In the first embodiment, the diameters of a plurality of filters provided are successively increased from the exhaust pipe upstream side to the downstream side. However, in the present embodiment, conversely, the filter diameter is reduced downstream. To do.

Here, FIG. 7 is a sectional view of the filter according to the present embodiment. 7A is a horizontal sectional view, and FIG. 7B is a vertical sectional view. Inside the filter 20, three filters 201, 202 and 203 are provided. Here, the cross-sectional area of the filter 201 is the largest,
The filter 202 and the filter 203 are smaller in this order. The size of the filters 201, 202, 203 is
The amount of exhaust gas passing through each of the filters 201, 202 and 203 is set in advance by experiments or the like so that the flow rates of the exhaust gas become substantially equal.

In this embodiment, although the structure of the filter 20 is different from that of the first embodiment,
The basic configuration of the engine 1 and other hardware to be used in common is the same as that of the first embodiment, and the description thereof will be omitted.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, most of the exhaust gas flowing through the exhaust pipe 19 and flowing into the filter 20 tries to pass through the third filter 203 on the most downstream side. Become. At this time, since the third filter 203 has a small diameter, a large amount of exhaust gas cannot pass through, and the flow rate of exhaust gas in the third filter 203 is smaller than that of the filter having the configuration of FIG.
Since the first filter 201 has a larger diameter than the other filters 202 and 203, it can pass the exhaust gas that cannot pass through the filters 202 and 203. Therefore, the flow rate of the exhaust gas that passes through the first filter 201 is as shown in FIG. It becomes many compared with the filter by.

As described above, in the present embodiment, in the filter having the configuration of FIG. 6, the diameter of the third filter 203 through which a large amount of exhaust gas passes is made small, and the diameter of the upstream filter is gradually increased so that a large amount of exhaust gas passes. As a result, the throughput of exhaust gas per unit volume of each filter 201, 202, 203 can be made uniform.

As described above, in the exhaust gas purification device for an internal combustion engine according to this embodiment, the exhaust gas flow distribution can be made uniform among the filters. <Third Embodiment> This embodiment is different from the first and second embodiments in the following points.

In the first embodiment and the second embodiment, it is possible to adjust the flow rate of exhaust gas by making the diameters of a plurality of filters different, but in this embodiment, the exhaust gas flow rate can be adjusted. The flow rate of exhaust gas between the filters is made uniform by adjusting the resistance when passing through each filter.

Here, FIG. 8 is a sectional view of the filter 20 according to the present embodiment. Inside the filter 20, three filters 201, 202 and 203 are provided. Here, the size of the cross-sectional area of the exhaust flow passages 50 and 51 of the first filter 201 is the largest and the size of the filter 202 and the filter 203 is smaller in this order. This filter 201,
The sizes of the cross-sectional areas of the exhaust flow passages 50, 51 of 202, 203 are set in advance by experiments or the like so that the flow rates of the exhaust gas passing through the filters 201, 202, 203 become substantially equal.

In this embodiment, although the structure of the filter 20 is different from that of the first embodiment,
The basic configuration of the engine 1 and other hardware to be used in common is the same as that of the first embodiment, and the description thereof will be omitted.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, most of the exhaust gas flowing through the exhaust pipe 19 and flowing into the filter 20 tries to pass through the third filter 203 on the most downstream side. Become. At this time, the filter 20
Since 3 has a small cross-sectional area of the exhaust flow passages 50 and 51, a large amount of exhaust gas cannot pass through, and the flow rate of exhaust gas in the third filter 203 is smaller than that of the filter having the configuration of FIG. The first filter 201 has a larger cross-sectional area of the exhaust flow passages 50 and 51 than the other filters 202 and 203, and therefore can pass the exhaust gas that cannot pass through the other filters 202 and 203. The flow rate of exhaust gas passing therethrough is larger than that of the filter having the configuration of FIG.

As described above, in the present embodiment, the cross-sectional area of the exhaust flow passages 50 and 51 of the third filter 203 through which a large amount of exhaust gas passes in the filter having the configuration of FIG. The cross-sectional areas of the passages 50 and 51 are sequentially increased to allow a large amount of exhaust gas to pass therethrough, and the throughput of exhaust gas per unit volume of each filter 201, 202, 203 can be made uniform.

As described above, in the exhaust gas purification apparatus for an internal combustion engine according to this embodiment, the exhaust gas flow distribution can be made uniform among the filters.

In this embodiment, the size of the passage areas of the exhaust flow passages 50 and 51 is used as the means for adjusting the resistance of the filter, but instead of this, the exhaust flow passages 50 and 51 are replaced.
Number, the thickness of the partition wall 54, the number of the plugs 52 and 53 to be filled (for example, a part or all of the plugs are omitted), the porosity of the partition wall 54, the pore diameter of the partition wall 54, and the method of filling the plugs 52 and 53 (eg, Use of filter without plugging), loading amount of catalyst and coat layer, method of loading catalyst and coat layer (for example, changing thickness of coat layer), material of base material (for example, cordierite, SiC, metal nonwoven fabric, etc.) It is also possible to adjust the resistance of each filter by changing the length of the base material and the like to make the exhaust flow distribution uniform.

Here, a filter that does not perform plugging will be described.

FIG. 9 is a cross-sectional view of a filter that does not plug according to the present embodiment.

As shown in FIG. 9, the filters 201, 2
Reference numerals 02 and 203 are so-called wall-flow type having a plurality of exhaust flow passages 500 and 501 extending in parallel with each other. These exhaust flow passages have a closed portion 50 at the downstream end.
The exhaust inflow passage 500 is closed by 2 and the exhaust outflow passage 501 whose upstream end is closed by the closing portion 503. Therefore, the exhaust inflow passages 500 and the exhaust outflow passages 501 are alternately arranged via the thin partition walls 504. In other words, in the exhaust inflow passage 500 and the exhaust outflow passage 501, each exhaust inflow passage 500 is surrounded by four exhaust outflow passages 501, and each exhaust outflow passage 501 is divided into four.
It is arranged so as to be surrounded by one exhaust inflow passage 500.

Here, the above-mentioned closing portions 502 and 503.
Is formed by bending both ends of the partition wall 504 by a molding die and closing the exhaust inflow passage 500 and the exhaust outflow passage 501. Therefore, it is not necessary to block the exhaust flow passage by plugging.

The filters 201, 202 and 203 are made of a porous material such as a ceramic material made of SiC, so that the exhaust gas which has flowed into the exhaust gas inflow passage 50 is surrounded by the surrounding air as shown by the arrow in FIG. Partition wall 5
04 and through the closed portions 502 and 503 to flow into the adjacent exhaust outflow passage 501. In this way, the blocking portion 50
Since the exhaust gas can also be circulated in 2, 503, the exhaust gas flow resistance in the filter can be reduced. <Fourth Embodiment> This embodiment differs from the third embodiment in the following points.

In the third embodiment, the exhaust is the case 21.
It is possible to equalize the flow rate of exhaust gas between the filters by adjusting the resistance when passing through each filter housed in No. 2, but in the present embodiment, they are connected to a plurality of exhaust pipes, respectively. By adjusting the resistance of the exhaust gas passing through the filter, the flow rate of the exhaust gas passing through the filters connected to the exhaust pipes is made uniform.

Here, FIG. 10 is a diagram showing a schematic structure of an intake and exhaust system of an engine to which the exhaust purification system according to the present embodiment is applied.

The exhaust pipe 19 is branched downstream of the turbocharger 15 into a first exhaust pipe 19a and a second exhaust pipe 19b. A first filter 20a is provided in the middle of the first exhaust pipe 19a.
On the other hand, a second filter 20b is provided in the middle of the second exhaust pipe 19b. In addition, the first filter 2
The first exhaust pipe 19a downstream of 0a is provided with a flow path switching valve 22a which is opened / closed by a signal from the ECU 35, while the second exhaust pipe 19b downstream of the second filter 20b is opened / closed by a signal from the ECU 35. Flow path switching valve 22
b is provided. Then, the flow path switching valves 22a and 2
After the first exhaust pipe 19a and the second exhaust pipe 19b join together downstream of 2b, they are connected to a muffler (not shown). ECs are provided upstream of the first filter 20a and the second filter 20b.
Reducing agent injection valves 28a and 28b that are opened by a signal from U35 and inject fuel that is a reducing agent are provided.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, a filter for circulating exhaust gas is selected, and the flow path switching valve 2 provided downstream of the selected filter 20a.
2a is opened. On the other hand, the flow path switching valve 22b provided downstream of the other unselected filter 20b is closed. By circulating the exhaust gas through the selected filter 20a, NOx in the exhaust gas is absorbed by the NOx storage reduction catalyst and PM is captured by the filter 20a. On the other hand, the reducing agent injection valve 28 is attached to the filter 20b in which exhaust gas does not flow.
By supplying the fuel from b, the NOx absorbed in the NOx storage reduction catalyst is released / reduced, and
It is possible to remove PM, etc.
It is possible to restore the function of 0b. That is, the absorption of NOx in the exhaust gas, the capture of PM, and the recovery processing of the function of the filter can be simultaneously executed in parallel.

In this embodiment, although the exhaust passage has a different structure as compared with the third embodiment, the basic structure of the engine 1 and other hardware to be used is the same as that of the first embodiment. The description is omitted because it is common to the embodiments.

By the way, in the case of providing two or more filters in parallel, there are cases where the filters have to be mounted back and forth due to a small vehicle mounting space, and the filters are connected to each filter. In some cases, the exhaust pipe must be bent. In the exhaust pipe configured in this manner, the flow resistance of the exhaust gas when passing through the exhaust pipe connected to each filter is different, and the flow rate of the exhaust gas flowing through each filter may be different. In such a case, operation of the flow path switching valve according to the flow rate of exhaust gas flowing through each filter,
If the reducing agent is not supplied according to the flow rate of exhaust gas, the effect commensurate with the capacity of the filter may not be obtained. However, if the above control is performed for each filter, the control becomes complicated.

Therefore, in the present embodiment, the length of the first exhaust pipe 19a from the branch of the exhaust pipe 19 to the first filter 20a and the length of the second exhaust pipe 19b from the branch of the exhaust pipe 19 to the second filter 20b. In an exhaust gas purification device in which both filters 20a and 20b are arranged so as to have different lengths, the flow resistance of the exhaust gas passing through both filters 20a and 20b is made substantially different by varying the flow resistance when the exhaust gas passes through both filters 20a and 20b. Adjusted to be equal. As a means for adjusting the resistance when the exhaust gas passes through the filters 20a and 20b in this manner, for example, the exhaust flow passage 5
Exhaust flow passage 5 for changing the size of the cross-sectional area of 0, 51
The number of 0, 51, the thickness of the partition wall 54, the number of plugs 52, 53 to be filled (for example, a part or all of plugging is omitted), the partition wall 5
4, porosity of partition wall 54, pore size of partition wall 54, method of filling plugs 52 and 53 (for example, use of filter without plugging), loading amount of catalyst and coat layer, loading method of catalyst and coat layer (for example, coat layer) The thickness of the base material), the material of the base material (for example, cordierite, SiC, metal nonwoven fabric, etc.),
Examples include changing the length of the base material. Then, the flow rate of the exhaust gas flowing through each filter is obtained by an experiment or the like, and the resistance of the exhaust gas flowing through each filter is adjusted by the above method, whereby the exhaust gas flow distribution between the filters can be made uniform.

As described above, in the present embodiment, the throughput of exhaust gas of both filters 20a and 20b can be made uniform. Therefore, the difference between the filters in the effect of supplying the reducing agent and the effect of recovering the SOx poisoning can be reduced, so that the performance of both filters 20a and 20b can be sufficiently exhibited. Further, various conditions at the time of supplying the reducing agent, for example, the opening degrees of the flow path switching valves 22a and 22b, the flow path switching valves 22a and 2b.
2b switching timing, reducing agent supply timing (for example, fuel addition timing), reducing agent addition amount and the like can be performed by common control without considering the difference in the amount of exhaust gas flowing through both filters 20a and 20b. Therefore, it becomes possible to simplify the control.

[0172]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the amount of exhaust gas flowing between a plurality of filters can be made substantially uniform. Therefore, the temperature difference between the filters can be reduced. Further, since it is possible to reduce the difference in effect between the filters when performing NOx absorption / release, SOx poisoning recovery, PM removal, etc., it is possible to fully utilize the capacity of the filter.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of the filter 20. 2A is a horizontal sectional view, FIG. 2B is a vertical sectional view, and FIG. 2C is a lateral sectional view.

FIG. 3 is a diagram showing a flow direction of exhaust gas after the switching valve rotates from the position of FIG.

FIG. 4 (A) is a lateral cross section of the filter, FIG.
(B) is a vertical cross-sectional view of the filter.

FIG. 5 is a block diagram showing an internal configuration of an ECU.

6 (a) is a horizontal sectional view when all filters have the same diameter, FIG. 6 (b) is a vertical sectional view, and FIG. 6 (c) is an exhaust flow distribution in the filter. FIG. 6D is a diagram showing the temperature distribution of the filter.

7A is a horizontal sectional view of a filter according to a second embodiment, and FIG. 7B is a vertical sectional view thereof.

FIG. 8 is a sectional view of a filter according to a third embodiment.

FIG. 9 is a sectional view of a filter without plugging according to a third embodiment.

FIG. 10 is a schematic configuration diagram showing an exhaust system of an engine to which an exhaust gas purification apparatus for an internal combustion engine according to a fourth embodiment is applied.

[Explanation of symbols]

1 ... Engine 1a: Crank pulley 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 4a ... Common rail pressure sensor 5 ... Fuel supply pipe 6 ... Fuel pump 6a ... Pump pulley 8 ... Intake branch pipe 9 ... Intake pipe 18 ... Exhaust branch pipe 19 ... Exhaust pipe 20 ... Particulate filter 21 ... Exhaust throttle valve 24 ... Exhaust gas temperature sensor 25 ... EGR passage 26 ... EGR valve 27 ... EGR cooler 28 ... Reducing agent injection valve 29 ... Reductant supply path 31 ... Shut-off valve 33 ... Crank position sensor 34 ... Water temperature sensor 35 ... ECU 36 ... Accelerator opening sensor

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Claims (6)

[Claims] 1. A filter capable of temporarily capturing fine particles in exhaust gas of an internal combustion engine and carrying a catalyst, a first exhaust passage connected to one end side of the filter, and connected to the other end side of the filter. A second exhaust passage, an exhaust passage selecting means for selecting either the first exhaust passage or the second exhaust passage, and one end of the filter when the exhaust passage selecting means selects the first exhaust passage A third exhaust passage connected to the other end side of the filter and the other end opened to the atmosphere; and one end connected to one end side of the filter and the other end connected to the filter when the exhaust passage selecting means selects the second exhaust passage. An exhaust gas purifying apparatus for an internal combustion engine, comprising: a fourth exhaust passage open to the atmosphere, wherein a plurality of the filters are provided in parallel, and the flow rate of the exhaust gas flowing by changing the form of at least one filter. To Exhaust purification system of an internal combustion engine, characterized in that is substantially uniform across filter. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the size of each filter is determined so that the flow rate of exhaust gas per unit volume is substantially uniform among the filters. 3. When each filter has the same size,
If there is a difference in the amount of exhaust gas that flows between the filters,
The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 or 2, wherein a filter having a larger exhaust gas flow amount has a larger size. 4. A filter capable of temporarily capturing fine particles in exhaust gas of an internal combustion engine and carrying a catalyst, a first exhaust passage connected to one end side of the filter, and connected to the other end side of the filter. A second exhaust passage, an exhaust passage selecting means for selecting either the first exhaust passage or the second exhaust passage, and one end of the filter when the exhaust passage selecting means selects the first exhaust passage A third exhaust passage connected to the other end side of the filter and the other end opened to the atmosphere; and one end connected to one end side of the filter and the other end connected to the filter when the exhaust passage selecting means selects the second exhaust passage. An exhaust gas purification device for an internal combustion engine, comprising: a fourth exhaust passage open to the atmosphere; wherein a plurality of the filters are provided in parallel, and when the size of each filter is the same, the filters flow between the filters. Difference in the amount of exhaust In some cases, the exhaust gas purifying apparatus for an internal combustion engine, characterized in that to substantially equalize the flow rate of the exhaust gas that flows across the filter by reducing the size of the filter as flow amount of the exhaust is larger filter. 5. A filter capable of temporarily capturing fine particles in exhaust gas of an internal combustion engine and carrying a catalyst, a first exhaust passage connected to one end side of the filter, and connected to the other end side of the filter. A second exhaust passage, an exhaust passage selecting means for selecting either the first exhaust passage or the second exhaust passage, and one end of the filter when the exhaust passage selecting means selects the first exhaust passage A third exhaust passage connected to the other end side of the filter and the other end opened to the atmosphere; and one end connected to one end side of the filter and the other end connected to the filter when the exhaust passage selecting means selects the second exhaust passage. An exhaust gas purification apparatus for an internal combustion engine, comprising: a fourth exhaust passage open to the atmosphere, wherein a plurality of the filters are provided, each filter has substantially the same size, and the exhaust gas of each filter is also provided. The same distribution resistance When there is a difference in the amount of exhaust gas that flows between the filters, the larger the amount of exhaust gas that flows, the greater the flow resistance of the filter and the smaller the amount of exhaust gas that flows to the filter. An exhaust emission control device for an internal combustion engine, wherein the flow rate of exhaust gas is substantially equalized between the filters. 6. An exhaust passage of an internal combustion engine which is branched in parallel, and a filter which is provided in each of the plurality of branched exhaust passages and is capable of temporarily capturing fine particles in exhaust gas and carrying a catalyst. And exhaust passage selecting means for selecting at least one of the plurality of exhaust passages to circulate exhaust gas, at least one passage length of the plurality of exhaust passages being different, and at least one of the filters. An exhaust gas purification device for an internal combustion engine, characterized in that the flow rate of exhaust gas flowing in different forms is made substantially uniform among filters.