JP2003041930A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique for recovering functions of a NOx catalyst by controlling opening of a nozzle vane of a variable displacement type turbo charger to adjust temperature of exhaust or an air-fuel ratio in exhaust in an exhaust emission control device for an internal combustion engine. SOLUTION: This device is provided with the variable displacement type turbo charger 15, the NOx catalyst 20, a toxicity eliminating control means 35 for detoxification, an NOx catalyst condition detection means 38 to detect a condition of the NOx catalyst 20, and a variable displacement type turbo charger control means 35 to open/close the nozzle vane 74 of the variable displacement type turbo charger 15 based on the condition of the NOx catalyst 20 detected by the NOx catalyst condition detecting means 38.

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 In an internal combustion engine, if a variable displacement turbocharger driven by utilizing the energy of exhaust gas discharged from the internal combustion engine is provided, the efficiency of filling the combustion chamber is improved and the engine output is improved. be able to.

A variable capacity turbocharger is, for example,
Even when the displacement is small, such as in the low rotation speed region of the internal combustion engine, by rotating the nozzle vanes in the closing direction, the flow velocity of exhaust gas can be increased and the rotational speed and rotational force of the turbine wheel can be increased. As a result, the rotational speed and rotational force of the compressor wheel are increased, the density of intake air is increased, and the efficiency of filling the combustion chamber can be improved.

On the other hand, by controlling the opening of the nozzle vane, the EGR gas flow rate can be obtained according to the engine operating condition at that time.

For example, in Japanese Unexamined Patent Publication No. 8-270454, the opening of the nozzle vane is determined based on the pressure difference generated at both ends of the EGR gas passage and the exhaust pressure. Here, if the operating state of the internal combustion engine is determined, the EGR gas amount and the nozzle vane opening degree have a unique relationship. Therefore, if the EGR gas amount for the operating state of the internal combustion engine is determined, the nozzle vane that realizes the EGR gas amount is determined. The opening is uniquely determined with respect to the operating state of the internal combustion engine. Therefore, another mechanism for adjusting the EGR gas flow rate is not required.

[0006]

When the opening of the nozzle vane is controlled, the EGR gas flow rate and the amount of fresh air drawn into the internal combustion engine change. Therefore, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine also changes.

By the way, in the exhaust purification catalyst for purifying the exhaust and the filter for trapping the particulates in the exhaust, it is necessary to set the air-fuel ratio of the exhaust, the temperature of the exhaust purification catalyst or the temperature of the filter to a predetermined state.

For example, the NOx storage reduction catalyst (hereinafter simply referred to as NOx catalyst) is, for example, alumina (Al ₂ O ₃ )
Is used as a carrier, and potassium (K), sodium (Na), lithium (Li), and cesium (Cs) are used on the carrier.
Alkali metals such as barium (Ba), calcium (Ca), lanthanum (L)
a) At least one selected from rare earths such as yttrium (Y) and a noble metal such as platinum (Pt) are supported.

The NOx catalyst absorbs NOx when the oxygen concentration of the inflowing exhaust gas is high, and releases the absorbed NOx when the oxygen concentration of the inflowing exhaust gas decreases, and reduces it to N _2.
It acts to absorb and release Ox.

In the case of this storage reduction type NOx catalyst, the air-fuel ratio of the exhaust gas in the normal operation of the internal combustion engine becomes lean, so that the NOx in the exhaust gas is absorbed by the NOx catalyst. However, if the lean air-fuel ratio exhaust gas is continuously supplied to the NOx catalyst, the NOx absorption capacity of the NOx catalyst becomes saturated, NOx cannot be absorbed any more, and NOx is leaked. Therefore, in the NOx catalyst, the oxygen concentration of the inflowing exhaust gas is reduced and the amount of HC component in the exhaust gas is increased at a predetermined timing before the NOx absorbing capacity is saturated, and the NOx absorbed in the NOx catalyst is released while Nx is released. ₂
To recover the NOx absorption capacity of the NOx catalyst.

As described above, in the exhaust gas purification apparatus using the lean NOx catalyst, it is necessary to intermittently reduce the oxygen concentration of the exhaust gas in order to purify NOx.

[0012] On the other hand, the NOx storage reduction catalyst is a sulfur oxide (SO
x) is also absorbed by the same mechanism as NOx. SOx absorbed in this way is less likely to be released than NOx, and NOx
Accumulates in the catalyst. This is called SOx poisoning, and since the NOx purification rate decreases, it is necessary to perform poisoning recovery processing for recovering from SOx poisoning at an appropriate time. This poisoning recovery process is performed by passing exhaust gas, which has a reduced oxygen concentration while the NOx catalyst has a high temperature (for example, about 600 to 650 ° C.), to the NOx catalyst.

However, since the temperature of the exhaust gas during the lean burn operation is low, it is difficult to raise the temperature of the catalyst to the temperature required to recover SOx poisoning. In such a case, by adding fuel to the exhaust passage, it is possible to raise the temperature of the catalyst and reduce the oxygen concentration of the exhaust.

By the way, while the diesel engine is excellent in economy, it is a particulate matter (Particulat) represented by soot which is a suspended particulate matter contained in exhaust gas.
e Matter Hereinafter referred to as "PM" unless otherwise specified. ) Is an important issue. Therefore, PM in the atmosphere
P is added to the exhaust system of the diesel engine to prevent
A technique of providing a particulate filter (hereinafter, simply referred to as “filter”) for collecting M is well known.

By providing this filter, PM in the exhaust gas can be temporarily collected and PM can be prevented from being released into the atmosphere. However, if the amount of PM trapped in the filter increases and accumulates on the filter, clogging of the filter may occur.
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 it. The removal of PM deposited on the filter in this way is called filter regeneration. The filter not only removes soot and other fine particles, it also removes harmful components (H
Some catalysts (three-way catalysts and lean NOx catalysts) are supported so that C, CO, and NOx) can be simultaneously purified. Also in this case, for the same reason as described above, it is often the case that the oxygen concentration of the exhaust gas is reduced to reduce NOx.

Here, in the invention described in the above-mentioned Japanese Patent Laid-Open No. 8-270454, the purpose is simply to control the EGR gas flow rate, and therefore the Nx absorbed by the NOx catalyst is used.
The air-fuel ratio of the exhaust gas and the temperature of the exhaust gas, which are necessary for the reduction of Ox, the recovery of SOx poisoning and the regeneration of the filter, have not been taken into consideration. At this time, if the nozzle vanes are used for improving the output and controlling the EGR gas flow rate as described above, there is a possibility that the required air-fuel ratio or temperature cannot be obtained.

The present invention has been made to solve the above problems, and in an exhaust gas purification apparatus for an internal combustion engine,
An object of the present invention is to provide a technique capable of recovering the function of a NOx catalyst by controlling the opening of a nozzle vane of a variable displacement turbocharger to adjust the temperature of exhaust gas or the air-fuel ratio of exhaust gas.

[0018]

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 variable capacity turbocharger that varies the flow velocity of the exhaust gas blown to the turbine wheel so that the supercharging pressure of the intake air becomes a desired pressure, and a variable capacity turbocharger provided in the exhaust passage of the internal combustion engine when the air-fuel ratio of the exhaust gas is high. Is a NOx catalyst that absorbs the nitrogen oxides in the exhaust gas and reduces the nitrogen oxides that have been absorbed when the air-fuel ratio of the exhaust gas is low, and to eliminate the poisoning of the NOx catalyst by the sulfur oxides. SOx poisoning elimination control means for executing poisoning elimination processing, and the NOx
NOx catalyst state detection means for detecting the state of the catalyst, based on the state of the NOx catalyst detected by the NOx catalyst state detection means, a variable capacity turbocharger control means for opening and closing the nozzle vanes of the variable capacity turbocharger,
It is characterized by having.

The greatest feature of the present invention is that in an exhaust gas purifying apparatus for an internal combustion engine equipped with a variable capacity turbocharger and a NOx catalyst, the opening of the nozzle vane of the variable capacity turbocharger is controlled to reduce NOx and sulfur. To obtain the optimum air-fuel ratio, temperature, etc. for poison recovery.

In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when it is necessary to recover the SOx poisoning of the NOx catalyst, the variable displacement turbocharger control is performed based on the detection result of the NOx catalyst state detecting means. The SOx poisoning recovery means performs SOx poisoning recovery while the means opens and closes the nozzle vane. For example, when the variable displacement turbocharger control means rotates the nozzle vane in the opening direction, the intake air amount is reduced and the air-fuel ratio of the exhaust gas can be reduced, and at the same time, the intake air cooled to the intercooler becomes an internal combustion engine. It is possible to increase the temperature of exhaust gas by reducing the introduction amount of.

In the present invention, the NOx catalyst state detecting means may detect the bed temperature of the NOx catalyst. In the exhaust gas purification device for an internal combustion engine configured in this way, the nozzle vanes are opened and closed based on the bed temperature of the NOx catalyst to generate NOx.
It becomes possible to control the temperature of the catalyst to a desired temperature.

In the present invention, the NOx catalyst state detecting means may detect the air-fuel ratio of the exhaust gas flowing through the NOx catalyst. In the exhaust gas purification device for an internal combustion engine configured as described above, the nozzle vanes are opened and closed based on the air-fuel ratio of the exhaust flowing through the NOx catalyst, and the air-fuel ratio of the exhaust flowing through the NOx catalyst is controlled to a desired air-fuel ratio. Is possible.

In the present invention, the variable displacement turbocharger control means may rotate the nozzle vane to the closing side when the bed temperature of the NOx catalyst is higher than a predetermined value.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, if the nozzle vane is turned to the valve closing side to increase the intake air amount, the intake amount of the intake air cooled by the intercooler into the internal combustion engine is increased. Is increased, and as a result, the temperature of exhaust gas can be lowered.

In the present invention, the variable displacement turbocharger control means may rotate the nozzle vane to the closing side when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is larger than a predetermined value.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, when the nozzle vane is turned to the valve closing side to increase the intake air amount, the intake amount of the intake air cooled by the intercooler is introduced into the internal combustion engine. However, the air-fuel ratio of the exhaust gas can be reduced by further increasing the fuel injection amount.

[0027]

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,
A compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using heat energy of exhaust gas as a drive source is provided in the middle of the intake pipe 9, and the intake pipe 9 downstream of the compressor housing 15a is provided with the compressor housing 15a. An intercooler 16 is provided to cool the intake air that has been compressed in the housing 15a and has a high temperature.

In the intake system thus constructed, the intake air flows into the compressor housing 15a via the intake pipe 9.

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 that has been compressed in the compressor housing 15 a and has a high temperature is cooled by the intercooler 16 and then flows into the intake branch pipe 8. 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 temperature sensor 24 that outputs an electric signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 to the exhaust pipe 19 downstream of the turbocharger 15 and upstream of the filter 20.
Further, an air-fuel ratio sensor 38 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust pipe 19 is attached.

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 addition, the filter 20 and the exhaust throttle valve 21
An air-fuel ratio sensor 39 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas that flows through the exhaust pipe 19 is attached to the exhaust pipe 19 between and.

The air-fuel ratio sensor 38 can detect the air-fuel ratio actually introduced into the filter 20. Therefore, at the time of NOx reduction of the filter 20 and recovery of SOx poisoning, P
The fuel amount and the air amount can be feedback-controlled so that the air-fuel ratio is required when M is removed. Also,
The deterioration determination of the filter 20 can be performed by the air-fuel ratio sensor 38 and the air-fuel ratio sensor 39. When the filter 20 deteriorates and the catalyst ability decreases, the amount of hydrocarbons (HC) and the like oxidized in the filter 20 decreases, and thus the difference in the air-fuel ratio before and after the filter 20 decreases as the deterioration progresses. Therefore, the air-fuel ratio sensor 38 and the air-fuel ratio sensor 3
It can be determined that the catalyst has deteriorated when the difference between the output signals of 9 becomes smaller than a predetermined value.

In this embodiment, a variable capacity turbocharger is used as the turbocharger 15.

Next, a specific structure of the variable capacity turbocharger 15 will be described with reference to FIGS.

FIG. 2 is a sectional view showing the structure of the variable capacity turbocharger.

FIG. 3 is a diagram showing a variable nozzle mechanism of a variable capacity turbocharger.

As shown in FIG. 2, the variable displacement turbocharger (hereinafter, simply referred to as a turbocharger) 15 is constituted by connecting a compressor housing 15a and a turbine housing 15b via a center housing 15c.

In the center housing 15c, one end of the rotor shaft 48 projects into the compressor housing 15a, and a compressor wheel 46 having a plurality of compressor impellers 46a is attached to the projecting portion.

The other end of the rotor shaft 48 projects into the turbine housing 15b, and the projecting portion has a turbine wheel 47 having a plurality of turbine impellers 47a.
Is attached.

An intake port 62a for taking intake air into the compressor housing 15a is formed in a portion of the compressor housing 15a located on the opposite side of the center housing 15c. In the compressor housing 15a, a spiral compressor passage 64 that surrounds the outer periphery of the compressor wheel 46 is formed, and an annular delivery passage 65 that connects the interior portion of the compressor wheel 46 and the compressor passage 64 is formed. There is. At the end of the compressor passage 64,
An intake air exhaust port (not shown) for exhausting the intake air compressed in the compressor housing 15a is formed.

On the other hand, in the turbine housing 15b,
A spiral scroll passage 66 that surrounds the outer periphery of the turbine wheel 47 is formed, and an annular nozzle passage 67 that connects the interior portion of the turbine wheel 47 and the scroll passage 66 is formed. Scroll passage 6
An exhaust inlet (not shown) for taking in the exhaust gas into the turbine housing 15b is formed at the base end of 6. An exhaust gas exhaust port 63 for exhausting exhaust gas in the turbine housing 15b is provided in a portion of the turbine housing 15b located on the opposite side of the center housing 15c.
a is provided.

Further, a variable nozzle mechanism 71 is installed inside the turbine housing 15b on the side of the center housing 15c. This variable nozzle mechanism 71 is shown in FIG.
As shown in (b), the nozzle back plate 72 formed in a ring shape is provided. The nozzle back plate 72 is fixed to the turbine housing 15b by bolts (not shown). Subsequently, the nozzle back plate 72 is provided with a plurality of shafts 73 at equal angles centered on the circle center of the plate 72.

Each shaft 73 is rotatably supported by penetrating the nozzle back plate 72 in its thickness direction. A nozzle vane 74 is fixed to one end portion (the left end portion in FIG. 3A) of each shaft 73. On the other hand, the other end of the shaft 73 (the right end in FIG. 3A) has an opening / closing lever 75 that extends orthogonally to the shaft 73 and extends to the outer edge of the nozzle back plate 72.
Is fixed, and the shaft 73 and the opening / closing lever 75 are integrally rotatable. At the tip of the opening / closing lever 75, a pair of holding portions 75a that are bifurcated are provided.

An annular ring plate 76 is provided between each opening / closing lever 75 and the nozzle back plate 72 so as to overlap with the nozzle back plate 72.
The ring plate 76 is rotatable in the circumferential direction around its center. In addition, the ring plate 76,
A plurality of pins 77 are provided at equal angles around the center of the circle, and the pins 77 are rotatably held between the holding portions 75 a of the opening / closing levers 75.

The variable nozzle mechanism 71 configured as described above
Then, when the above-mentioned ring plate 76 is rotated about its center, each pin 77 pushes the sandwiching portion 75a of each opening / closing lever 75 in the same direction as the rotation direction of the ring plate 76. As a result, the opening / closing lever 75 rotates the shaft 73, and in synchronization with the rotation of the shaft 73, the nozzle vane 74 is rotated by the shaft 7.
It will rotate about 3.

For example, when the ring vanes 74 rotate to move the end of the nozzle vanes 74 located on the circular center side of the ring vanes in a direction to separate from the circular centroid, the gap between the adjacent nozzle vanes 74 becomes narrow. The flow path between the nozzle vanes 74 is closed.

On the other hand, when the ring plate 76 is rotated so as to rotate the end portion of the nozzle vane 74, which is located on the side of the center of the circle of the ring plate 76, toward the center of the circle, the gap between the adjacent nozzle vanes 74 becomes wide. Becomes
The flow path between the nozzle vanes 74 will be opened.

Next, the variable nozzle mechanism 71 is driven, that is,
A mechanism for rotationally driving the ring plate 76 will be described. As shown in FIGS. 2 and 3, a pin 86 extending in the same direction as the axis L is attached to a part of the outer edge of the ring plate 76, and the drive mechanism 82 is connected to the pin 86.

The drive mechanism 82 includes a center housing 15c.
Further, a support shaft 83 rotatably supported in a state of extending to the compressor housing 15a side in parallel with the pin 86 is provided. A drive lever 84 rotatably connected to a pin 86 is fixed to an end of the support shaft 83 on the turbine housing 15b side (left end in FIG. 2). Support shaft 8
An operation piece 85 rotatable about the support shaft 83 is attached to the end of the compressor 3 on the compressor housing 15a side (the right end in FIG. 2). The operation piece 85 is connected to a negative pressure type VNT actuator 87.

As shown in FIG. 4, the VNT actuator 87 is divided by a diaphragm 88 into a negative pressure chamber 87a and an atmosphere chamber 87b. The negative pressure chamber 87a is internally provided with a coil spring 88a which expands and contracts in a direction orthogonal to the diaphragm 88. Further, a negative pressure passage 89 is connected to the negative pressure chamber 87a, and the negative pressure passage 89 is
It is connected to a vacuum pump 91 which is drivingly connected to the crankshaft of the engine 1. An electric vacuum regulating valve (EVRV) 90 is provided in the middle of the negative pressure passage 89.

The EVRV90 is equipped with an air inlet (not shown) that is open to the atmosphere.
It connects between the negative pressure passage 89a located on the NT actuator 87 side and the atmosphere introduction port, and the negative pressure passage 89b located on the vacuum pump 91 side of the EVRV 90 and the negative pressure passage 89a on the VNT actuator 87 side.

The EVRV 90 is equipped with an electromagnetic solenoid, and when the electromagnetic solenoid is in a non-excited state,
The negative pressure passage 89a and the atmosphere introduction port are held in a conductive state, and when the electromagnetic solenoid is in an excited state, the negative pressure passage 89a and the negative pressure passage 89b are held in a conducting state. On the other hand, VN
The atmosphere chamber 87b of the T actuator 87 communicates with the outside (in the atmosphere) of the VNT actuator 87, and the atmosphere chamber 87b
The pressure inside is always atmospheric pressure.

On the atmosphere chamber 87b side of the diaphragm 88,
The rod 8 extending in the extension direction of the coil spring 88a
8b is projected. This rod 88b is used in the atmosphere chamber 8
It penetrates through 7b and protrudes to the outside of the VNT actuator 87, and its tip is connected to the operation piece 85.

In the VNT actuator 87 having such a structure, when the electromagnetic solenoid of the EVRV 90 is in the non-excited state, the negative pressure passage 89a and the atmosphere introduction port are in a conductive state and the negative pressure chamber 87a is at atmospheric pressure. . in this case,
The rod 88b of the VNT actuator 87 is held in the most advanced state by the biasing force of the coil spring 88a.

When the electromagnetic solenoid of the EVRV 90 is in the excited state, the negative pressure passage 89a and the negative pressure passage 89b are provided.
Are brought into conduction, and the inside of the negative pressure chamber 87a of the VNT actuator 87 becomes negative pressure. In this case, the diaphragm 88
Is displaced against the biasing force of the coil spring 88a, and accordingly, the rod 88b is held in the most retracted state.

Further, by controlling the duty of excitation and non-excitation of the electromagnetic solenoid of the EVRV 90, it is possible to adjust the amount of advance / retreat of the rod 88b.

VNT actuator 87 as described above
The operation piece 85 is rotated by the forward / backward movement of the rod 88b. When the operation piece 85 is rotated, the support shaft 83 rotates in synchronization with it, and the drive lever 84 rotates about the support shaft 83 as the support shaft 83 rotates. As a result, the drive lever 84 pushes the ring plate 76 in the circumferential direction via the pin 86 and rotates the ring plate 76 about the axis L.

Variable capacity type turbocharger 1 described above
In No. 5, the drive mechanism 82 adjusts the rotation direction and the rotation amount of the nozzle vane 74, so that the nozzle vane 7
It is possible to change the direction of the flow path between the nozzles 4 and the gap between the nozzle vanes 74. That is, by controlling the rotation direction and the rotation amount of the nozzle vane 74, the direction and flow velocity of the exhaust gas blown from the scroll passage 66 to the turbine wheel 47 are adjusted.

For example, when the amount of exhaust gas from the engine 1 is small, the drive mechanism 82 is operated to close the nozzle vanes 74 of the variable nozzle mechanism 71 so that the flow velocity of the exhaust gas blown to the turbine wheel 47 is increased and the exhaust gas is exhausted. Since the collision angle between the turbine impeller 47a and the turbine impeller 47a becomes more vertical, the rotational speed and rotational force of the turbine wheel 47 can be increased even with a small displacement.

On the contrary, when the amount of exhaust gas from the engine 1 is sufficiently large, the nozzle vane 74 of the variable nozzle mechanism 71 is used.
By operating the drive mechanism 82 to open the valve, the excessive increase in the flow velocity of the exhaust gas blown to the turbine wheel 47 is controlled, and it is possible to suppress the excessive increase in the rotational speed and the rotational force of the turbine wheel 47. .

In the present embodiment, when the electromagnetic solenoid of the EVRV 90 is in the non-excited state and the rod 88b of the VNT actuator 87 is in the most advanced state,
Nozzle vane 74 is held in the most open state, and EVR
It is assumed that when the electromagnetic solenoid of V90 is in the excited state and the rod 88b of the VNT actuator 87 is in the most retracted state, the nozzle vane 74 is kept in the most closed state.

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 47 that is rotatably supported in the turbine housing 15b. At that time, the rotational torque of the turbine wheel 47 is transmitted to the compressor wheel 46 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.

Next, 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 itself and has an endothermic property. Therefore, when EGR gas is contained in the air-fuel mixture,
The combustion temperature of the air-fuel mixture is lowered, so 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 is lowered and the volume of the EGR gas is reduced, so that 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.

Next, the filter 20 adopted in the present invention will be described.

FIG. 5 shows the structure of the filter 20. In addition,
In FIG. 5, (A) shows the cross section of the filter 20 in the horizontal direction, and (B) shows the cross section of the filter 20 in the vertical direction. As shown in FIGS. 5A and 5B, the filter 20 is a so-called wall flow type 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. Note that FIG.
The hatched portion in (A) shows the plug 53. Therefore, the exhaust inflow passages 50 and the exhaust 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.

The filter 20 is made of a porous material such as cordierite. Therefore, the exhaust gas flowing into the exhaust gas inflow passage 50 flows in the surrounding partition wall 54 as shown by the arrow in FIG. 5B. 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 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, the function of the NOx storage reduction catalyst carried by the filter 20 according to this embodiment will be described.

The filter 20 uses, for example, alumina as a carrier, and potassium (K) and sodium (N) are placed on the carrier.
a), an alkali metal such as lithium (Li) or cesium (Cs), an alkaline earth such as barium (Ba) or calcium (Ca), and a rare earth such as lanthanum (La) or yttrium (Y). And at least one of them is carried and a noble metal such as platinum (Pt). In the present embodiment, barium (Ba) and platinum (Pt) are supported on a carrier made of alumina, and ceria (Ce ₂ O ₃ ) having an O ₂ storage capacity is further supported.
An NOx storage reduction catalyst was added.

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 oxide (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 lowered 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 equipped with a reducing agent supply mechanism for adding 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 mounted 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. 28, a reducing agent supply path 29 that guides the fuel discharged from the fuel pump 6 to the reducing agent injection valve 28, and a distribution of the fuel in the reducing agent supply path 29 that is provided in the reducing agent supply path 29. And a shutoff valve 31 for shutting off.

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 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust branch pipe 18.

The thus formed exhaust gas having a low oxygen concentration flows into the filter 20 and releases nitrogen oxides (NOx) absorbed by the filter 20 while releasing nitrogen (N ₂ ).
Will be reduced to.

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, the air flow meter 11, the intake air temperature sensor 12, the intake pipe pressure sensor 17, the exhaust gas temperature sensor 24, the crank position sensor 33, the water temperature sensor 34, the accelerator opening sensor 36, the air-fuel ratio sensors 38 and 39, and other various electrical wiring. The output signals of the various sensors described above are input to the ECU 35.

On the other hand, the ECU 35 has a fuel injection valve 3, an intake throttle actuator 14, an exhaust throttle actuator 22, a reducing agent injection valve 28, an EGR valve 26, and a shutoff valve 31.
Etc. are connected via electrical wiring, and the above-mentioned parts are connected to the ECU.
35 can be controlled.

Here, the ECU 35, as shown in FIG. 6, 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 used for the common rail pressure sensor 4a, the air flow meter 11, the intake air temperature sensor 1
2, intake pipe pressure sensor 17, exhaust temperature sensor 24, water temperature sensor 34, accelerator opening sensor 36, air-fuel ratio sensor 3
As in 8 and 39, the signals are input through the A / D 355 of the sensor that outputs an analog signal format signal, and those output signals are transmitted to the CPU 351 and the RAM 353.

The output port 357 is connected to the fuel injection valve 3,
Intake throttle actuator 14, exhaust throttle actuator 22, EGR valve 26, reducing agent injection valve 28, shutoff valve 3
1 and the like via electric wiring, and outputs control signals output from the CPU 351 to the fuel injection valve 3, the intake throttle actuator 14, the exhaust throttle actuator 2 described above.
2, to the EGR valve 26, the reducing agent injection valve 28, or 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, and an EGR. The EGR control routine for controlling the valve 26, the NOx purification control routine for adding the reducing agent to the filter 20 to release the absorbed NOx, the poisoning elimination control routine for eliminating the SOx poisoning of the filter 20, and the filter 20 Application programs such as a PM combustion control routine for burning and removing the collected PM and a nozzle opening control routine for opening and closing the nozzle vanes 74 of the turbocharger 15 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, NOx purification control, poisoning elimination 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 the 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 while rotating the nozzle vane 74 to the open side to reduce the intake air amount. The air-fuel ratio of the exhaust gas flowing into the engine is temporarily set to a predetermined target rich air-fuel ratio.

Specifically, the CPU 351 operates the drive mechanism 82 to rotate the nozzle vane 74 of the variable nozzle mechanism 71 to the open side. Then, turbine wheel 47
The flow velocity of the exhaust gas blown onto the engine 1 decreases, the rotational speed and the rotational force of the turbine wheel 47 decrease, and the amount of air taken into the engine 1 decreases.

Next, the CPU 351 controls the engine speed stored in the RAM 353, the output signal of the accelerator opening sensor 36 (accelerator opening), the output signal value of the air flow meter 11 (intake air amount), and the air-fuel ratio sensor. The output signal, fuel injection amount, etc. are read.

The CPU 351 accesses the reducing agent addition amount control map of the ROM 352 by 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 amount of addition of the reducing agent (target amount of addition) required to obtain the fuel ratio is calculated.

Subsequently, the CPU 351 accesses the reducing agent injection valve control map of the ROM 352 with 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.

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.

Here, since the nozzle vane 74 is rotated to the opening side, the intake air amount is smaller than usual, so that the oxygen concentration can be sufficiently reduced even if the amount of fuel added is small, and therefore It is possible to suppress deterioration of fuel efficiency.

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.

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 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 included.
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 and less likely to be decomposed than barium nitrate (Ba (NO ₃ ) ₂ ), and is decomposed even if 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 of eliminating SOx poisoning of the filter 20, the ambient temperature of the filter 20 is raised to a high temperature range of about 600 to 650 ° C. and the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered. ,
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 operates the drive mechanism 82 to fully open the nozzle vanes 74 of the variable nozzle mechanism 71. Then, turbine wheel 47
The flow velocity of the exhaust gas blown onto the engine 1 decreases, the rotational speed and the rotational force of the turbine wheel 47 decrease, and the amount of air taken into the engine 1 decreases. When the intake air amount decreases in this way, the amount of fresh air cooled by the intercooler 16 introduced into the engine 1 decreases, and as a result, the exhaust gas temperature rises. When the exhaust gas whose temperature has risen reaches the filter 20, the temperature of the filter 20 rises.

On the contrary, when the temperature of the exhaust gas rises excessively, the CPU 351 operates the drive mechanism 82 to close the nozzle vane 74 of the variable nozzle mechanism 71. Then, the flow velocity of the exhaust gas blown to the turbine wheel 47 increases, the rotational speed and the rotational force of the turbine wheel 47 increase, and the amount of air taken into the engine 1 increases.
When the intake air amount increases in this manner, the amount of fresh air cooled by the intercooler 16 introduced into the engine 1 increases, and as a result, the exhaust gas temperature decreases. When the exhaust gas whose temperature has dropped reaches the filter 20, the temperature of the filter 20 drops.

When the bed temperature of the filter 20 rises to a high temperature range of about 600 ° C. to 650 ° C. due to the catalyst temperature raising process as described above, the CPU 351 causes the reducing agent injection 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 38.

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 a long time to burn 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 may remain 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.

[0135] 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 rotates the nozzle vane 74 to the open side to decrease the intake air amount and reduce the amount of intake air from the reducing agent injection valve 28. By controlling the reducing agent injection valve 28 to inject the fuel that is the reducing agent in a spike manner, the air-fuel ratio of the exhaust gas flowing into the filter 20 is temporarily set to the predetermined target rich air-fuel ratio.

Specifically, the CPU 351 causes the drive mechanism 8 to fully open the nozzle vanes 74 of the variable nozzle mechanism 71.
2 is operated. Then, the flow velocity of the exhaust gas blown to the turbine wheel 47 decreases,
The rotation speed and the rotation force of the engine 1 decrease, and the amount of air taken into the engine 1 decreases. When the intake air amount decreases in this way, the amount of fresh air cooled by the intercooler 16 introduced into the engine 1 decreases, and as a result, the exhaust gas temperature rises. When the exhaust gas whose temperature has risen reaches the filter 20, the temperature of the filter 20 rises and the oxidation of PM is promoted. On the other hand, by fully opening the nozzle vanes 74, it is possible to suppress the exhaust energy from being lost in the turbocharger 15, and it is possible to prevent the exhaust temperature from decreasing.

Next, the CPU 351 controls the engine speed stored in the RAM 353, 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, The engine operating state such as fuel injection timing is read. Furthermore, the CPU 35
1 is R using the engine operating state as a parameter.
The reducing agent addition amount control map of the OM 352 is accessed to calculate the reducing agent addition amount (target addition amount) necessary for setting the exhaust air-fuel ratio to the preset target air-fuel ratio.

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 reduces the reducing agent required to inject 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.

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.

By the way, the temperature of the filter 20 may drop during the execution of the NOx purification control, the poisoning elimination control, the PM combustion control, etc., and the desired temperature may not be maintained. Even in such a case, if the temperature of the filter 20 is raised, it becomes possible to continue the NOx purification control, the poisoning elimination control, the PM combustion control and the like.

Next, the flow of temperature control of the filter 20 during the SOx poisoning recovery control according to this embodiment will be described.

FIG. 7 is a flow chart showing the flow of temperature control of the filter 20 during SOx poisoning recovery control according to this embodiment.

In step S101, it is determined whether or not SOx poisoning recovery control is in progress. If an affirmative decision is made, the operation proceeds to step S102. On the other hand, if a negative determination is made, the process proceeds to step S106, and normal engine operation control is performed.

In step S102, the nozzle vane 74
It is determined whether or not is the activation capacity. Here, the PM in the exhaust gas may adhere to the nozzle vanes 74 and its surroundings to restrict the operation of the nozzle vanes 74. In such a case, the effect is reduced even if the catalyst bed temperature is increased by operating the nozzle vanes 74. Therefore, the nozzle vane 7
If the operation of No. 4 is limited, normal SOx poisoning recovery control is performed to increase the catalyst bed temperature.
Whether or not the nozzle vanes 74 can be operated can be detected by monitoring the operation of the VNT actuator 87 by a sensor (not shown).

If an affirmative judgment is made in step S102, the routine proceeds to step S103, and if a negative judgment is made, this routine is ended.

On the other hand, when the vehicle is accelerated or the like, it is required to increase the output, and it is necessary to rotate the nozzle vane 74 to the closing side. In such a case, the nozzle vane 74 is controlled by giving priority to the output increase, and accordingly, step S102.
Then, the nozzle vane operation may be disabled and this routine may be ended.

In step S103, it is determined whether the bed temperature of the filter 20 is higher than the target bed temperature (for example, 600 to 650 ° C.). A high temperature is required for recovery from SOx poisoning, so if this temperature is not reached, the filter 2
Aim to raise the temperature to 0. On the other hand, if the temperature of the filter 20 becomes too high, the filter 20 may be thermally deteriorated. Therefore, at this time, the temperature of the filter 20 needs to be lowered. The temperature rise of the filter 20 is estimated from the output signal of the exhaust temperature sensor 24.

If an affirmative judgment is made in step S103, the routine proceeds to step S104, and if a negative judgment is made, the routine proceeds to step S105.

In step S104, the nozzle vane 74
Is rotated to the closing side to reduce the bed temperature of the filter 20. First, the CPU 351 operates the drive mechanism 82 to close the nozzle vane 74 of the variable nozzle mechanism 71.
Then, the flow velocity of the exhaust gas blown to the turbine wheel 47 increases, the rotational speed and the rotational force of the turbine wheel 47 increase, and the amount of air taken into the engine 1 increases. When the intake air amount increases in this manner, the amount of fresh air cooled by the intercooler 16 introduced into the engine 1 increases, and as a result, the exhaust gas temperature decreases. When the exhaust gas whose temperature has dropped reaches the filter 20, the temperature of the filter 20 drops.

In step S105, the nozzle vane 74
Is rotated to the open side to raise the bed temperature of the filter 20. First, the CPU 351 operates the drive mechanism 82 to open the nozzle vane 74 of the variable nozzle mechanism 71. Then, the flow velocity of the exhaust gas blown to the turbine wheel 47 decreases, the rotational speed and the rotational force of the turbine wheel 47 decrease, and the amount of air taken into the engine 1 decreases. When the intake air amount decreases in this way, the amount of fresh air cooled by the intercooler 16 introduced into the engine 1 decreases, and as a result, the exhaust gas temperature rises. When the exhaust gas whose temperature has risen reaches the filter 20, the temperature of the filter 20 will rise.

In this way, by controlling the opening and closing of the nozzle vanes 74 of the variable capacity turbocharger 15, S
It is possible to control the bed temperature of the filter 20 during the Ox poisoning recovery to an optimum temperature.

In this flow, the temperature control of the filter 20 during SOx poisoning recovery is described.
The same can be applied to NOx reduction, PM oxidation combustion removal, etc., which require temperature control. Further, the target temperatures at this time are different from each other.

On the other hand, if the air-fuel ratio of the exhaust gas flowing through the filter 20 fluctuates during execution of the NOx purification control, the poisoning elimination control, the PM combustion control, etc. as described above, the desired air-fuel ratio may not be maintained. . Even in such a case, if the air-fuel ratio of the exhaust gas flowing through the filter 20 is set to a desired air-fuel ratio by controlling the amount of fresh air drawn into the engine 1, the NOx purification control and poisoning elimination can be performed. Control, PM
It becomes possible to continue combustion control and the like.

Next, the flow of the air-fuel ratio control during the SOx poisoning recovery control according to this embodiment will be described.

FIG. 8 is a flow chart showing the flow of the air-fuel ratio control during the SOx poisoning recovery control according to this embodiment.

Steps S201 and S202
Is step S101 and step S10 in the flow of temperature control of the filter 20 during SOx poisoning recovery control of FIG.
The same control as in 2 is performed.

In step S203, it is determined whether the air-fuel ratio of the exhaust gas flowing through the filter 20 is larger than the target air-fuel ratio. The CPU 351 reads the output signal of the air-fuel ratio sensor 38 stored in the RAM 353 and compares it with a preset target air-fuel ratio.

Here, in order to recover from SOx poisoning, it is necessary to reduce the oxygen concentration in the exhaust gas. When the oxygen concentration in the exhaust gas decreases, barium sulfate absorbed in the filter 20 (BaSO ₄₎ is SO ₃ ^- and SO ₄ ^- are thermally decomposed, they SO ₃ ^- and SO ₄ ^- hydrocarbons in the exhaust gas ( HC) and carbon monoxide (CO) to be reduced.

At this time, even if the fuel injection amount from the reducing agent injection valve 28 is feedback-controlled based on the output signal of the air-fuel ratio sensor 38, the air-fuel ratio in the exhaust gas can be controlled, but the flow rate of the exhaust gas can be controlled. When there is a lot of fuel, a large amount of fuel is required, which causes deterioration of fuel efficiency. Therefore, if the amount of fresh air drawn into the engine 1 is reduced, the oxygen concentration in the exhaust gas can be sufficiently reduced even with the addition of a small amount of fuel, and the deterioration of fuel efficiency can be suppressed.

If an affirmative judgment is made in step S203, the routine proceeds to step S204, and if a negative judgment is made, the routine proceeds to step S205.

In step S204, the nozzle vane 74
Is rotated to the closing side. First, the CPU 351 operates the drive mechanism 82 to close the nozzle vane 74 of the variable nozzle mechanism 71. Then, the flow velocity of the exhaust gas blown to the turbine wheel 47 increases and the turbine wheel 4
The rotation speed and the rotation force of 7 increase, and the amount of air taken into the engine 1 increases. When the intake air amount increases in this way, the oxygen concentration in the exhaust gas can be increased. At this time, the intake throttle valve 13 may be operated to the open side and the EGR valve 26 may be operated to the close side. By doing so, the pressure in the intake branch pipe 8 rises and the pressure difference between both ends of the EGR passage 25 decreases, so that the EGR gas amount decreases and the air-fuel ratio can be further increased.

In step S205, the nozzle vane 74
Is rotated to the open side. First, the CPU 351 causes the drive mechanism 8 to open the nozzle vane 74 of the variable nozzle mechanism 71.
2 is operated. Then, the flow velocity of the exhaust gas blown to the turbine wheel 47 decreases,
The rotation speed and the rotation force of the engine 1 decrease, and the amount of air taken into the engine 1 decreases. When the intake air amount is reduced in this way, the oxygen concentration in the exhaust gas can be reduced even if the amount of fuel added is small. At this time, the intake throttle valve 13 may be operated to the closing side and the EGR valve 26 may be operated to the opening side. By doing so, the pressure in the intake branch pipe 8 decreases, and the pressure difference between the both ends of the EGR passage 25 increases, so that a large amount of EGR gas recirculates to the intake side, and it is possible to further reduce the air-fuel ratio. Become.

In this way, by controlling the opening and closing of the nozzle vanes 74 of the variable capacity turbocharger 15, S
It becomes possible to control the air-fuel ratio of the exhaust gas flowing through the filter 20 to the optimum one during the recovery of Ox poisoning.

In this flow, the air-fuel ratio control of the exhaust gas flowing through the filter 20 during the SOx poisoning recovery is described, but the same applies to NOx reduction and PM oxidation combustion removal, which requires the air-fuel ratio control of the exhaust gas. Can be applied to.
The target air-fuel ratios at this time are different from each other.

A temperature sensor (not shown) for measuring the actual bed temperature of the filter 20 is provided to monitor the temperature of the filter 20 regardless of the control flow described above, and the temperature of the filter 20 rises above the allowable temperature. In that case, the nozzle vanes 74 may be controlled in the closing direction. By doing so, the amount of exhaust gas flowing into the filter 20 can be reduced, and the occurrence of heat deterioration of the filter 20 can be suppressed. Similarly, by providing a differential pressure sensor (not shown) for measuring the pressure difference between the exhaust gas before and after the filter 20,
When the pressure difference before and after the filter 20 rises abnormally by an allowable amount, the nozzle vanes 74 may be controlled to be closed. By doing so, the amount of exhaust gas flowing into the filter 20 can be reduced, and damage to the filter 20 can be prevented.

Here, in the conventional exhaust gas purifying apparatus for an internal combustion engine, the main purpose has been to control the EGR gas amount by a variable capacity turbocharger. However, depending on the type of catalyst that purifies the exhaust gas, reduction of NOx and recovery of SOx poisoning are required, and removal of PM is required by the filter. In such a case, even if the variable displacement turbocharger is controlled for the purpose of controlling the EGR gas amount, it is not possible to obtain the temperature and air-fuel ratio required for NOx reduction, SOx poisoning recovery and PM removal. .

In this respect, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the control of the variable capacity turbocharger makes it possible to control the catalyst bed temperature and the air-fuel ratio, thereby reducing NOx and reducing SOx. It is possible to obtain the temperature and air-fuel ratio required for poison recovery, PM removal, etc.

Therefore, NOx reduction, PM removal and S
It is possible to recover the Ox poisoning in the optimum condition. Here, when the nozzle vane 74 is rotated to the closing side and the fuel injection amount is increased, the air-fuel ratio becomes small (rich air-fuel ratio). In this case, the rich air-fuel ratio is not obtained unless the fuel injection amount is increased. Meanwhile, the nozzle vane 7
When 4 is rotated to the open side and the fuel injection amount is increased or maintained constant, the air-fuel ratio becomes small (rich air-fuel ratio). In this case, the rich air-fuel ratio can be achieved by increasing or maintaining the fuel injection amount constant. Therefore, for example, when the vehicle is accelerated, the nozzle vane 74 is rotated to the closed side and the fuel injection amount is increased to reduce the air-fuel ratio (to a rich air-fuel ratio), while the vehicle is decelerated, the nozzle vane 74 is rotated to the open side. Moreover, the fuel injection amount is increased or maintained constant to reduce the air-fuel ratio (to a rich air-fuel ratio).
NOx can be used when the vehicle is accelerated and when the vehicle is decelerated.
It is possible to perform reduction of PM, removal of PM, and recovery of SOx poisoning in optimum conditions. <Second Embodiment> In the first embodiment, the opening degree of the nozzle vane 74 is controlled based on the temperature of the filter 20 or the air-fuel ratio of the exhaust gas that is read. On the other hand, in the present embodiment, the opening degree of the nozzle vane 74 is controlled based on the bed temperature of the filter 20 and the engine speed or engine load. The engine speed and the engine load are represented by the output signal of the crank position sensor 33 and the opening time of the fuel injection valve 3, respectively.

Here, FIG. 9 is a control map for obtaining the nozzle vane opening degree according to the present embodiment. CPU 351
Reads the output signal of the exhaust gas temperature sensor 38 and the output signal of the crank position sensor 33 or the valve opening time of the fuel injection valve 3 from the RAM 353, and substitutes it into the map shown in FIG. 9 to calculate the opening degree of the nozzle vane 74. Based on the calculation result, the drive mechanism 82 is operated to adjust the opening degree of the nozzle vane 74.

By setting this control map for each of NOx reduction, SOx poisoning recovery and PM removal, these controls can be performed independently.

The present embodiment is different from the first embodiment in that the opening of the nozzle vane 74 is calculated by a map, but the basics of the engine 1 and other hardware to be applied are different. The configuration is the same as that of the first embodiment, so the description is omitted. <Third Embodiment> FIG. 10 is a view showing the opened / closed state of the nozzle vanes 74 according to the present embodiment. In the present embodiment, opening / closing of the nozzle vanes 74 is repeated at regular intervals according to the period during which the control of NOx reduction, SOx poisoning recovery, and PM removal is being performed.

Here, NOx reduction, SOx poisoning recovery and P
The time required for M removal is NO absorbed by the filter 20.
It depends on the amount of x and SOx and the amount of PM captured.
Since the amounts of NOx and SOx absorbed by the filter 20 and the amounts of PM trapped can be estimated from the history of the operating state of the engine 1, the period required for NOx reduction, SOx poisoning recovery and PM removal is , Determined by the operating time of the engine and the distance traveled. In the present embodiment, the nozzle vane 74 is fully opened and fully closed at regular intervals according to the periods required for NOx reduction, SOx poisoning recovery and PM removal thus obtained. By adjusting the opening / closing interval of the nozzle vanes 74, the temperature rise rate of the bed temperature of the filter 20 can be changed. That is, the longer the time the nozzle vanes 74 are open, the slower the temperature rise of the bed temperature of the filter 20 becomes.

By the way, when the engine output is required at the time of acceleration or the like, it is desirable to rotate the nozzle vanes 74 to the closing side to raise the supercharging pressure. However, when the nozzle vane 74 is rotated to the closing side, the temperature of exhaust gas is lowered as described above. Therefore, in the present embodiment, the nozzle vane 74 is repeatedly fully opened and fully closed to increase the supercharging pressure and suppress the temperature decrease of the filter 20.

In this way, the bed temperature of the filter 20 can be maintained without performing complicated control, and the oxygen concentration in the exhaust gas can be periodically changed. <Fourth Embodiment> In the present embodiment, NOx reduction,
The nozzle vane 74 is maintained at a predetermined opening while the SOx poisoning recovery and PM removal are being controlled.

Here, FIG. 11 is a view showing the opened / closed state of the nozzle vane 74 according to the present embodiment. By doing so, the bed temperature of the filter 20 can be raised without performing complicated control, and the oxygen concentration in the exhaust gas can be lowered.

[0183]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the control of the catalyst bed temperature and the air-fuel ratio can be performed by performing the nozzle vane opening / closing control of the variable capacity turbocharger, and the NOx reduction and SOx poisoning can be performed. It is possible to accurately obtain the temperature of the catalyst and the air-fuel ratio of the exhaust, which are required when performing recovery, PM removal, and the like.

Therefore, deterioration of exhaust emission can be suppressed, and fuel consumption can be improved.

[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 a first embodiment is applied and an intake / exhaust system thereof.

FIG. 2 is a diagram showing a configuration of a variable capacity turbocharger.

FIG. 3A is a side view of a variable nozzle mechanism of a variable capacity turbocharger. (B) is a figure showing the front view of the variable nozzle mechanism of a variable capacity type turbocharger.

FIG. 4 is a diagram showing a configuration of a VNT actuator of a variable displacement turbocharger.

FIG. 5A is a diagram showing a lateral cross section of a particulate filter. (B) is a figure which shows the longitudinal cross section of a particulate filter.

FIG. 6 is a block diagram showing an internal configuration of an ECU.

FIG. 7 is a flowchart showing a flow of temperature control of the filter 20 during SOx poisoning recovery control according to the first embodiment.

FIG. 8 is a flowchart showing a flow of air-fuel ratio control during SOx poisoning recovery control according to the first embodiment.

FIG. 9 is a control map for obtaining a nozzle vane opening degree according to the second embodiment.

FIG. 10 is a diagram showing an opened / closed state of a nozzle vane according to a third embodiment.

FIG. 11 is a diagram showing an opened / closed state of a nozzle vane according to a fourth embodiment.

[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 15 ... Turbocharger 15a ... Compressor housing 15b · Turbine housing 15c ... Center housing 16 ... Intercooler 17 ... Intake pipe pressure sensor 18 ... Exhaust branch pipe 19 ... Exhaust pipe 20 ... Particulate filter 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 38 ... Air-fuel ratio sensor 39 ... Air-fuel ratio sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/24 F01N 3/24 ET 3/36 3/36 B F02B 37/12 302 F02B 37/12 302Z 37/24 F02D 23/00 P F02D 23/00 41/02 301D 41/02 301 43/00 301R 43/00 301 301T 45/00 312R 45/00 312 312 312Z 314R 314 314Z 368G 368 F02B 37/12 301Q (72 ) Inventor Michio Furuhashi 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Takashi Yamamoto 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation (72) Inventor Shiro Tanno Toyota Motor Corporation, Aichi Prefecture 1 Toyota-cho, Toyota-shi Toyota Motor Corporation F-term (reference) 3G005 DA02 EA04 EA15 FA35 GA0 4 GB24 GC05 GD00 HA04 HA12 HA18 JA00 JA16 3G084 BA08 BA24 DA10 EA11 EB22 EC01 EC03 FA00 FA07 FA10 FA18 FA20 FA28 FA33 FA38 3G091 AA10 AA11 AA18 AA28 AB06 AB13 BA11 BA14 BA33 CA18 CA26 CA27 DA01 DA02 DB10 EA01 EA05 EA07 EA08 EA09 EA18 EA30 EA34 FB10 FB12 FC01 FC04 GB02Y GB03Y GB04Y GB06W GB17X HA18 HA36 HA37 HA42 HB05 HB06 3G092 AA02 AA06 AA17 AA18 AB03 BA06 BA07 DB03 DC12 DC15 DG06 EA01 EA02 EC08 EC21 FA01 NE011917170111 PA01Z PA11Z PA17Z PD01B PD09B PD12B PE01Z PE08Z PF03Z

Claims (5)

[Claims] 1. A variable displacement turbocharger for varying a flow rate of exhaust gas blown to a turbine wheel so that a supercharging pressure of intake air becomes a desired pressure, and an air-fuel ratio of exhaust gas provided in an exhaust passage of the internal combustion engine. When the NOx catalyst is high, the NOx catalyst absorbs nitrogen oxides in the exhaust gas, and when the air-fuel ratio of the exhaust gas is low, the NOx catalyst reduces the NOx catalyst while releasing the absorbed nitrogen oxides. Based on the state of the NOx catalyst detected by the NOx catalyst state detection means for detecting the state of the NOx catalyst, SOx poisoning elimination control means for executing the poisoning elimination processing to eliminate, An exhaust gas purifying apparatus for an internal combustion engine, comprising: a variable capacity turbocharger control means for opening and closing a nozzle vane of the variable capacity turbocharger. 2. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the NOx catalyst state detecting means detects a bed temperature of the NOx catalyst. 3. The exhaust gas purification device for an internal combustion engine according to claim 1, wherein the NOx catalyst state detection means detects an air-fuel ratio of exhaust gas flowing through the NOx catalyst. 4. The variable displacement turbocharger control means rotates the nozzle vane to the closing side when the bed temperature of the NOx catalyst is higher than a predetermined value. Exhaust gas purification device for internal combustion engine. 5. The variable displacement turbocharger control means rotates the nozzle vane to the closing side when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is larger than a predetermined value. 1. An exhaust gas purification device for an internal combustion engine according to 1.