JP2003041929A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide technique for recovering functions of a filter carrying catalyst while preventing fixing of a nozzle vane in a variable displacement type turbo charger 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 filter 20 carrying occlusion-reduction type NOx catalyst provided in to downstream side of the variable displacement type turbo charger 15 to be capable of temporarily catching particles in exhaust, and a reducer adding means 28 provided between the variable displacement type turbo charger 15 and the filter 20 to add a reducer to exhaust.

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 As an exhaust gas purification device for purifying exhaust gas from an internal combustion engine such as a diesel engine or a gasoline engine, a technique of arranging a lean NOx catalyst in an exhaust passage of the internal combustion engine is known.

The lean NOx catalyst is a catalyst capable of purifying exhaust gas emitted from a lean-burn internal combustion engine such as a diesel engine or a lean burn gasoline engine, and includes a selective reduction type NOx catalyst and a storage reduction type NOx catalyst. Is mentioned.

The NOx storage reduction catalyst uses, for example, alumina (Al ₂ O ₃ ) as a carrier, and an alkali such as potassium (K), sodium (Na), lithium (Li) or cesium (Cs) is used on the carrier. Metal and barium (B
a), alkaline earths such as calcium (Ca),
It is configured to carry at least one selected from rare earths such as lanthanum (La) yttrium (Y) and a noble metal such as platinum (Pt).

This NOx storage reduction 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 is low, and reduces it to N _2. Performs release action.

In the case of this NOx storage reduction 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. Then, as one of the methods of intermittently reducing the oxygen concentration of the exhaust gas, there is addition of fuel in the exhaust gas.

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

The 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.

By the way, in general, a turbocharger is often provided immediately after an exhaust manifold because the charging efficiency can be improved as higher energy is obtained from exhaust gas. Therefore, the exhaust gas purification catalyst and the like are provided downstream of the turbocharger, and the exhaust gas whose energy has been lowered by supplying energy to the turbocharger flows through the exhaust gas purification catalyst and the like.

Here, when fuel is added to the lean NOx catalyst to reduce NOx, hydrocarbons (HC) adhere to the periphery of the nozzle vanes of the variable displacement turbocharger, and the operation of the nozzle vanes is restricted. There is.

To solve such a problem, Japanese Patent Laid-Open No. 2000-
In JP-A-220445, a nozzle for supplying a reducing agent into exhaust gas is provided with a variable capacity turbocharger and a lean NO.
It is provided between the catalyst and the x-catalyst so that the reducing agent does not pass through the variable capacity turbocharger to prevent the operation of the nozzle vanes from being restricted.

[0013]

By the way, while the diesel engine is excellent in economical efficiency, it is a particulate matter (hereinafter referred to as "PM") represented by soot which is a suspended particulate matter contained in exhaust gas. That is the important issue. For this reason, there is known a technique of providing a particulate filter (hereinafter, simply referred to as “filter”) for collecting PM in an exhaust system of a diesel engine so that PM is not released into the atmosphere.

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 may occur in the filter.
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 fine particles such as soot, but also contains harmful components (HC, CO, NOx) in the exhaust gas.
The catalyst (three-way catalyst or lean N
Some have Ox catalyst). Also in this case, for the same reason as described above, the oxygen concentration in the exhaust gas is reduced to reduce NO.
There are many ways to reduce x.

Further, the storage reduction type NOx catalyst is a sulfur oxide (SO
x) is also absorbed by the same mechanism as NOx. The absorbed SOx is less likely to be released than NOx, and is accumulated in the NOx 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
The NOx catalyst is heated at a high temperature (for example, about 600 to 650 ° C.) and the exhaust gas having a reduced oxygen concentration is passed through the NOx catalyst.

However, since the temperature of the exhaust gas during the lean burn operation is low, it is difficult to recover the SOx poisoning or raise the temperature of the catalyst to a temperature at which the accumulated fine particles burn.
In such a case, the temperature of the catalyst can be raised by adding fuel to the exhaust passage.

Here, the above-mentioned Japanese Patent Laid-Open No. 2000-220445.
In the invention described in the publication, the temperature of the exhaust gas flowing into the NOx catalyst is simply raised to reduce the NOx, and the SOx is reduced.
The air-fuel ratio and exhaust temperature during poisoning recovery and filter regeneration were not considered. NOx reduction, SOx poisoning recovery, and filter regeneration are common in that they can be performed by adding a reducing agent to the exhaust gas, but the conditions such as the temperature and oxygen concentration necessary for these executions are the same. Since they are different, even if they are all controlled by common control, a sufficient effect 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 exhaust gas purification function of a particulate filter carrying a NOx storage reduction catalyst while preventing the nozzle vanes of a variable capacity turbocharger from sticking.

[0020]

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 rate of the exhaust gas blown to the turbine wheel so that the supercharging pressure of intake air becomes a desired pressure, and a variable capacity turbocharger that is provided downstream of the variable capacity turbocharger and is discharged from the combustion chamber. On the particulate filter for removing particulates in the exhaust gas, if excess oxygen exists in the surroundings, it takes in oxygen and retains it, and when the surrounding oxygen concentration decreases, the retained oxygen is released in the form of active oxygen. In addition, when the air-fuel ratio of the exhaust gas flowing into the particulate filter is lean, it absorbs NOx in the exhaust gas, and when the air-fuel ratio of the exhaust gas flowing into the particulate filter becomes the stoichiometric air-fuel ratio or rich, it releases the absorbed NOx. It supports the active oxygen release and NOx absorbent, and changes the air-fuel ratio of the exhaust gas flowing into the particulate filter. Normal active oxygen release · NOx when the air-fuel ratio of the exhaust gas is switched occasionally temporarily rich while maintaining lean switched to rich
The active oxygen released from the absorbent accelerates the oxidation reaction of the particulates on the particulate filter and reduces the active oxygen release / NOx released from the NOx absorbent, which causes the particulates on the particulate filter to shine. Is provided between the variable-capacity turbocharger and the particulate filter, which is capable of oxidizing and removing NOx in the exhaust gas at the same time, and reducing the NOx in the exhaust gas. And an agent adding means.

The greatest feature of the present invention is that it is provided with a variable capacity turbocharger and a particulate filter carrying a NOx storage reduction catalyst, and a reducing agent addition means is provided between the variable capacity turbocharger and the filter. This is to prevent the reducing agent from flowing through the variable capacity turbocharger, thereby preventing the nozzle vanes from sticking due to the reducing agent.

In the exhaust gas purification apparatus for an internal combustion engine configured as described above, when the air-fuel ratio of the exhaust gas is lean, the NOx contained in the exhaust gas is absorbed by the NOx storage reduction catalyst carried by the filter. . Then, when the reducing agent adding means adds the reducing agent to the exhaust gas downstream of the variable capacity turbocharger and the oxygen concentration in the exhaust gas decreases, the storage reduction type NOx.
The NOx absorbed by the catalyst is released and reduced from the NOx storage reduction catalyst.

On the other hand, as described above, oxygen is generated when NOx is absorbed by the NOx storage reduction catalyst and when NOx is released. This oxygen is active oxygen and can oxidize and remove fine particles.

Further, since the reducing agent adding means adds the reducing agent downstream of the variable capacity turbocharger, it is possible to prevent the reducing agent from adhering to the variable capacity turbocharger.

In the present invention, a NOx catalyst for purifying nitrogen oxides in exhaust gas may be provided between the reducing agent adding means and the particulate filter.

In the exhaust gas purifying apparatus for an internal combustion engine thus configured, the temperature of the exhaust gas is raised by the catalyst for purifying nitrogen oxides, and the temperature of the downstream filter can be raised.
In addition, it is possible to maintain the increased filter temperature. Here, since the catalyst has a temperature range where exhaust gas can be effectively purified, it is necessary to raise the temperature early. If the reducing agent is added to the upstream catalyst when the temperature of the particulate filter is low such as when the engine is started, the reducing agent reacts with the upstream catalyst and the temperature of the exhaust gas rises. Thus, the temperature of the downstream filter can be raised early by the exhaust gas whose temperature has risen.

In the present invention, an oxidation catalyst may be provided downstream of the particulate filter.

In this way, even if the reducing agent added to the particulate filter is not oxidized by the particulate filter, it can be purified by the oxidation catalyst provided downstream.

In the present invention, when it is necessary to remove the particulates captured by the particulate filter and the air-fuel ratio of the exhaust gas from the internal combustion engine is the lean air-fuel ratio,
The reducing agent adding means may add a reducing agent to the exhaust gas, and the variable capacity turbocharger may open and close the nozzle vanes to remove the particulates captured by the particulate filter.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the reducing agent added to the exhaust gas by the reducing agent adding means reduces the oxygen concentration in the exhaust gas. At this time, if the temperature in the exhaust gas becomes high, the oxidation of PM is promoted. Therefore, if the nozzle vane is opened to reduce the intake air amount, the intake amount of the intake air cooled by the intercooler into the internal combustion engine is increased. Is reduced, and as a result, the temperature of the exhaust gas rises and PM can be oxidized (burned).

In the present invention, the reducing agent adding means adds a reducing agent to the exhaust gas, and the variable capacity turbocharger opens and closes the nozzle vanes to store sulfur in the NOx storage reduction catalyst carried on the particulate filter. Can recover poisoning.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the reducing agent added by the reducing agent adding means can reduce the oxygen concentration in the exhaust gas. Further, since it is necessary to raise the temperature of the particulate filter when recovering from sulfur poisoning, if the nozzle vane is opened, for example, to reduce the intake air amount, the intake air cooled by the intercooler will be introduced into the internal combustion engine. The amount decreases. As a result, the temperature of the exhaust gas rises, and it becomes possible to raise the temperature of the particulate filter.

[0033]

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 is used for 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 air-fuel ratio sensor 37 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust branch pipe 18 is attached to the exhaust branch pipe 18 upstream of the turbine housing 15b. Further, a reducing agent injection valve 28 that is opened by a signal from the ECU 35 and injects fuel is provided in the exhaust pipe 19 downstream of the turbine housing 15b.

In the middle of the exhaust pipe 19, a storage reduction type N
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, and an exhaust pipe 19 that is downstream of the reducing agent injection valve 28 and upstream of the filter 20. An air-fuel ratio sensor 38 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing inside 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.

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

Next, a specific configuration of the variable capacity turbocharger 15 will be described with reference to FIGS. 2 and 3.

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

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

As shown in FIG. 2, the variable displacement turbocharger (hereinafter, simply referred to as a turbocharger) 15 is formed 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 provided with 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 circle center side in the direction of moving away from the circle center, 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 to rotate the end portion of the nozzle vane 74 located on the circle center side of the ring plate 76 in the direction of approaching the circle center, the gap between the adjacent nozzle vanes 74 is widened. 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 the 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 side of the atmosphere chamber 87b 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 a 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, the amount of advance / retreat of the rod 88b can be adjusted by duty-controlling the excitation and non-excitation of the electromagnetic solenoid of the EVRV 90.

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 this 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.

The air-fuel ratio sensor 37 can measure the air-fuel ratio of the exhaust gas discharged from the engine 1 regardless of the addition of fuel from the reducing agent injection valve 28. Therefore, the combustion state of the engine 1 can be detected from the output signal of the air-fuel ratio sensor 37. On the other hand, the air-fuel ratio sensor 38 can measure the air-fuel ratio after the fuel addition from the reducing agent injection valve 28,
The air-fuel ratio actually introduced into the filter 20 can be detected. Therefore, at the time of NOx reduction of the filter 20 and SOx
The fuel injection amount from the reducing agent injection valve 28 can be feedback-controlled so that the air-fuel ratio is required at the time of poisoning recovery, PM removal, or the like. In addition, 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 its catalytic ability decreases, the hydrocarbons (H
Since the amount of C) and the like decreases, the difference in the air-fuel ratio before and after the filter 20 becomes smaller as the deterioration progresses. Therefore,
It can be determined that the catalyst has deteriorated when the difference between the output signals of the air-fuel ratio sensor 38 and the air-fuel ratio sensor 39 becomes smaller than a predetermined value.

As described above, by providing the air-fuel ratio sensors 37, 38 and 39, the combustion state of the engine 1 and the state of the exhaust gas passing through the filter 20 can be detected independently, and the inside of the cylinder 2 is detected. It is possible to control the amount of fuel injected and the amount of fuel added to the exhaust gas independently.

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 pipes 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 a conductive state, 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 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 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, for example, 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 deposited 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 storage reduction catalyst thus constructed absorbs nitrogen oxides (NOx) in the exhaust gas when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst is high. At this time, active oxygen is released to accelerate the oxidation of PM.

On the other hand, the NOx storage reduction catalyst releases nitrogen oxides (NOx) absorbed when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst decreases. At that time, hydrocarbons (HC) and carbon monoxide (CO) are contained in the exhaust gas.
If a reducing component such as is present, the NOx storage reduction catalyst can reduce nitrogen oxides (NOx) released from the NOx storage reduction catalyst to nitrogen (N ₂ ).
At the same time, active oxygen is released and the oxidation of PM is promoted.

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 oxide (NOx) contained in exhaust gas is a storage reduction type N
Although it is absorbed by the Ox catalyst, when the lean burn operation of the engine 1 is continued for a long period of time, the NOx absorption capacity of the NOx storage reduction catalyst is saturated and the nitrogen oxides (NO
x) is not removed by the NOx storage reduction catalyst and is released into the atmosphere.

In particular, in a diesel engine such as the engine 1, the lean air-fuel mixture is burned in most operating regions, and the air-fuel ratio of the exhaust gas becomes lean air-fuel ratio in most operating regions accordingly. , Storage reduction type NO
The NOx absorption capacity of the x catalyst is easily saturated.

Therefore, when the engine 1 is in the lean burn operation, the oxygen concentration in the exhaust gas flowing into the NOx storage reduction catalyst is reduced before the NOx absorption capacity of the NOx storage reduction catalyst is saturated, and the reducing agent is reduced. It is necessary to increase the concentration of NOx and release and reduce the nitrogen oxides (NOx) absorbed by the NOx storage reduction 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 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 mounted between the turbocharger 15 and the filter 20 so that its injection hole faces the exhaust pipe 19, and the ECU 3
5, a reducing agent injection valve 28 that opens by a signal from 5 to inject fuel, 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 reducing agent supply path. And a shutoff valve 31 provided on the shutoff valve 29 for shutting off the flow of fuel in the reducing agent supply passage 29.

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 pipe 19.

The reducing agent injected from the reducing agent injection valve 28 into the exhaust pipe 19 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust pipe 19.

The thus formed exhaust gas having a low oxygen concentration flows into the filter 20 and releases nitrogen oxides (NOx) absorbed in 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 pipe 19 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 temperature sensor 24, a crank position sensor 33, a water temperature sensor 34, an accelerator opening sensor 36, various sensors such as air-fuel ratio sensors 37, 38 and 39. The output signals of the various sensors described above are connected to each other via electrical wiring and 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 receives 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, and 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
7, 38, 39 and the like are input via the A / D 355 of a sensor that outputs an analog signal type 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. An EGR control routine for controlling the valve 26, a fuel addition control routine for adding a reducing agent to the filter 20 to release the absorbed NOx, and burning and removing PM, the filter 2
Application programs such as a poisoning elimination control routine for eliminating SOx poisoning of 0 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 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, fuel addition control, poisoning elimination control, etc. are executed.

For example, in the fuel addition control, the CPU 351
Adds fuel to the exhaust flowing into the filter 20 to change the oxygen concentration in a relatively short cycle.

In the fuel addition control, the CPU 351 determines whether or not the fuel addition control execution condition is satisfied every predetermined period. As the fuel addition control execution condition, for example, the exhaust temperature sensor 2 in which the filter 20 is in the active state is used.
The output signal value of 4 (exhaust gas temperature) is equal to or lower than a predetermined upper limit value, the poisoning elimination control is not executed, or the like.

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 reduce the intake air amount and to reduce the intake air amount 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.

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 described above as parameters, and sets the air-fuel ratio of the exhaust gas 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 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 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 valve opening time in this way, the target addition amount of fuel is injected from the reducing agent injection valve 28 into the exhaust pipe 19. Then, the reducing agent injected from the reducing agent injection valve 28 mixes with the exhaust flowing from the upstream of the exhaust pipe 19 to form a 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 vanes 74 are fully opened, 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 the fuel consumption can be reduced. It is possible to suppress the deterioration.

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 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 hard 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 (BaS in filter 20)
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 600.degree.
By raising the temperature to a high temperature range of ˜650 ° C. and reducing 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 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. by 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 excess fuel is injected from the reducing agent injection valve 28, those fuels burn rapidly in the filter 20 and the filter 20 overheats, or excess 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 deposited 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.

However, in the filter carrying the NOx storage reduction catalyst, it is possible to prevent the PM in the exhaust gas from burning by adding the reducing agent to the exhaust gas. One of the methods for adding the reducing agent in this way is to add the above-mentioned fuel into the exhaust gas.

As a result of the addition of fuel, 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 conventional exhaust gas purifying apparatus for an internal combustion engine, a fuel injection valve is provided downstream of the turbocharger to control the temperature of the NOx storage reduction catalyst while preventing the nozzle vanes from sticking. However, when it is necessary to raise the temperature of the NOx storage reduction catalyst, the required temperature differs depending on the purpose. In particular, when the particulate filter carrying the NOx storage reduction catalyst is provided, it is necessary to recover the SOx poisoning and remove PM in addition to the NOx purification. It needs to be done on the terms.

In this respect, in the present embodiment, a variable capacity turbocharger and a particulate filter are provided,
By adding a reducing agent between the variable capacity turbocharger and the particulate filter, the nozzle vanes are prevented from sticking and the nozzle vanes are operated to reduce NOx, remove PM and recover SOx poisoning under different conditions. Can be done at.

Therefore, NOx reduction, PM removal and S
It is possible to recover the Ox poisoning in the optimum condition. <Second Embodiment> FIG. 7 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 its intake and exhaust system. The exhaust gas purification apparatus for an internal combustion engine according to this embodiment differs from the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment in the following points.

That is, in the present embodiment, the reducing agent injection valve 2
The NOx catalyst 40 was provided downstream of 8 and upstream of the filter 20. Although the present embodiment is different from the first embodiment in that the NOx catalyst 40 is provided, the basic configuration of the engine 1 and other hardware to be applied is the same as that of the first embodiment. The explanation is omitted because it is the same as the form.

Incidentally, an internal combustion engine capable of lean burn may be operated near the stoichiometric air-fuel ratio depending on various conditions. In such a case, the exhaust gas near the stoichiometric air-fuel ratio is discharged, but the storage reduction type NOx catalyst carried on the filter 20 has the ability to purify nitrogen oxides (NOx) in the exhaust gas near the stoichiometric air-fuel ratio. Low. As described above, when the internal combustion engine is operated near the stoichiometric air-fuel ratio, it is effective to install the NOx catalyst in the exhaust passage.

This NOx catalyst is used for the hydrocarbons (H
C) and carbon monoxide (CO) oxidation, and nitrogen oxides (N
Ox) is simultaneously reduced to purify these harmful components in exhaust gas into harmless carbon dioxide (CO ₂ ), water (H ₂ O), and nitrogen (N ₂ ).

By the way, the above-mentioned NOx storage reduction catalyst and NOx catalyst have an active temperature range, and a high purification rate cannot be obtained unless the bed temperature of the catalyst is in this active temperature range. Therefore, when the capacity of the NOx catalyst 40 is set to be small, the temperature can be raised early even when the engine is started, etc., and the oxidation of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust gas and nitrogen oxides can be prevented. (NOx) can be reduced at an early stage. And the reaction heat at this time is N
When the temperature of the exhaust gas passing through the Ox catalyst 40 is increased and the exhaust gas having the increased temperature passes through the filter 20 provided downstream of the NOx catalyst 40, the temperature of the filter 20 is increased. In this way, it is possible to increase the temperature of the filter 20 at an early stage.

When the nozzle vane 74 is rotated to the open side, the temperature of the NOx catalyst 40 can be raised early. That is, when the CPU 351 rotates the nozzle vane 74 to the open side, the flow velocity of the exhaust gas blown to the turbine wheel 47 decreases, the rotational speed and rotational force of the turbine wheel 47 decrease, and the amount of air taken into the engine 1 decreases. Decrease. When the intake air amount decreases in this way, the fresh air engine 1 cooled by the intercooler 16
The amount of gas introduced into the exhaust gas decreases, and as a result, the temperature of the exhaust gas increases.
When the exhaust gas whose temperature has risen reaches the NOx catalyst 40, the N
The temperature of the Ox catalyst 40 rises.

As described above, according to the present embodiment, NOx reduction in the filter 20, oxidation of PM and SOx.
Poisoning recovery can be started early, and oxidation of hydrocarbons (HC) and carbon monoxide (CO) and reduction of nitrogen oxides (NOx) in exhaust gas can be started early. <Third Embodiment> FIG. 8 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 exhaust gas purification apparatus for an internal combustion engine according to the present embodiment differs from the exhaust gas purification apparatus for an internal combustion engine according to the second embodiment in the following points.

That is, in this embodiment, the oxidation catalyst 41 is provided downstream of the filter 20 and upstream of the air-fuel ratio sensor 39. The oxidation catalyst 41 has a function of oxidizing carbon monoxide (CO) and hydrocarbons (HC) contained in the exhaust gas. Although the present embodiment is different from the second embodiment in that the oxidation catalyst 41 is provided, the basic configuration of the engine 1 and other hardware to be applied is the same as that of the first embodiment. The explanation is omitted because it is the same as the form.

Fuel is added to the filter 20 from the reducing agent injection valve 28 when it is necessary to perform NOx reduction, PM removal, and SOx poisoning recovery. There is a possibility that a part of the fuel added at this time will pass through the filter 20 as it is without reacting and be released into the atmosphere.

By providing the oxidation catalyst 41 downstream of the filter 20, the fuel that has passed through the filter 20 can be oxidized and purified.

By the way, the oxidation catalyst 41 also has an active temperature region, and if the bed temperature of the catalyst is not within this active temperature region, a high purification rate cannot be obtained. In such a case, by rotating the nozzle vane 74 to the open side, the temperature of the oxidation catalyst 41 can be raised early. That is, when the CPU 351 rotates the nozzle vane 74 to the open side, the flow velocity of the exhaust blown to the turbine wheel 47 decreases, the rotation speed and the rotation force of the turbine wheel 47 decrease, and the amount of air taken into the engine 1 decreases. Decrease. 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 oxidation catalyst 41, the temperature of the oxidation catalyst 41 rises.

As described above, according to the exhaust purification system of the internal combustion engine of the present embodiment, it is possible to suppress the release of fuel into the atmosphere and prevent the deterioration of exhaust emission performance. .

[0158]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, since the reducing agent is added downstream of the turbocharger, it is possible to prevent the nozzle vanes from sticking to the reducing agent. Further, the temperature of the exhaust gas is raised by rotating the nozzle vane to the open side, and NOx reduction, PM removal and S
It is possible to raise the temperature of the filter when performing Ox poisoning recovery or the like. Further, it is possible to reduce the number of additions of the reducing agent for removing the PM deposited on the filter and the number of additions of the reducing agent for increasing the catalyst bed temperature.

Therefore, it is possible to prevent the exhaust emission from deteriorating while preventing the nozzle vanes from sticking.
Fuel efficiency 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 schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to a second embodiment.

FIG. 8 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to a third 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 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 37 ... Air-fuel ratio sensor 38 ... Air-fuel ratio sensor 39 ... Air-fuel ratio sensor 40 ... NOx catalyst 41 ... Oxidation catalyst

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01D 53/94 F01N 3/08 A B01J 38/04 G F01N 3/02 321 3/24 E 3/08 T 3/28 301C 3/24 301D F02D 41/04 355 3/28 301 43/00 301E 301R F02D 41/04 355 301T 43/00 301 45/00 310T 314Z B01D 53/36 103C 45/00 310 ZAB 314 103B 101B K (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 Bungo Kawaguchi Aichi Prefecture Toyota-cho, Toyota-shi 1 F-term in Toyota Motor Corporation (reference) 3G084 AA01 AA04 BA05 BA08 BA09 BA13 BA15 BA19 BA20 BA24 DA10 DA27 EB01 FA02 FA07 FA10 FA11 FA12 FA20 FA26 FA27 FA28 FA30 FA33 FA38 3G090 AA03 BA01 CA01 CA02 CB25 DA01 D A09 DA10 DA11 DA12 DA14 DA18 DA20 EA02 EA05 EA06 EA07 3G091 AA02 AA10 AA11 AA12 AA18 AA28 AB02 AB04 AB06 AB08 AB09 AB13 BA00 BA03 BA04 BA11 BA14 BA15 BA19 EA06 EA05 EA07 DB01 BA01 DC01 DB01 DB05 DB01 DB01 DB01 DA01 DA02 DA01 DA02 DA01 DA02 EA15 EA16 EA17 EA30 EA31 EA34 FA02 FA04 FA06 FA11 FB02 FB03 FB10 FB11 FB12 FC04 FC07 FC08 GA06 GB01X GB02W GB02Y GB03W GB03Y GB04W GB04Y GB05W GB06W GB10X GB16X HA08 HA09 HA12 HA14 HA15 HA16 HA18 HA21 HA36 HA37 HA42 HB05 HB06 3G301 HA02 HA04 HA06 HA11 HA13 HA15 JA15 JA24 JA25 JA26 JB09 LA03 LB11 MA01 MA11 MA18 NA07 NA08 ND01 NE01 NE06 NE13 NE14 NE15 PA01B PA01Z PA07B PA07Z PA10B PA10Z PD04B PD04Z PD08B PD08Z PD09B PD09Z PD11B PD11Z PE01B PE01Z PE03B PE03Z PE04B PE04Z PE08B PE08Z PF03B PF03Z 4D048 AA06 AA13 AA14 AA18 AB01 AB02 AB05 AB07 AC02 AC10 BA02X BA03X BA14X BA15X BA18X BA30X BA32X BA33X BA34X BA41X

Claims (5)

[Claims] 1. A variable capacity turbocharger for varying the flow velocity of exhaust gas blown to a turbine wheel so that a supercharging pressure of intake air becomes a desired pressure; and a combustion chamber provided downstream of the variable capacity turbocharger. On the particulate filter for removing the particulates in the exhaust gas discharged from, when excess oxygen exists in the surroundings, oxygen is taken in to retain oxygen and when the surrounding oxygen concentration decreases, the retained oxygen is converted into active oxygen. When the air-fuel ratio of the exhaust gas flowing into the particulate filter is lean, it absorbs NOx in the exhaust gas, and when the air-fuel ratio of the exhaust gas flowing into the particulate filter becomes the stoichiometric air-fuel ratio or rich The exhaust gas that flows into the particulate filter supports the active oxygen release and NOx absorbent that releases NOx. When the air-fuel ratio of the exhaust gas is switched to rich by maintaining the fuel ratio normally to lean and occasionally temporarily changing to rich, the active oxygen release ・ The active oxygen released from the NOx absorbent causes the particulates on the particulate filter to be separated. Along with promoting the oxidation reaction, NOx released from the active oxygen release / NOx absorbent is reduced, whereby the particulates on the particulate filter are oxidized and removed without emitting a bright flame, and at the same time NOx in the exhaust gas is removed. A particulate filter that can be removed, and a reducing agent addition unit that is provided between the variable capacity turbocharger and the particulate filter and that adds a reducing agent to the exhaust gas. Exhaust purification device. 2. NO for purifying nitrogen oxide in exhaust gas between the reducing agent adding means and the particulate filter.
The exhaust emission control device for an internal combustion engine according to claim 1, further comprising an x catalyst. 3. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, further comprising an oxidation catalyst downstream of the particulate filter. 4. The reducing agent addition means adds a reducing agent to the exhaust gas when it becomes necessary to remove the particulates captured by the particulate filter and the air-fuel ratio of the exhaust gas from the internal combustion engine is a lean air-fuel ratio. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the variable capacity turbocharger opens and closes a nozzle vane to remove particulates captured by the particulate filter. 5. The reducing agent addition means adds a reducing agent to the exhaust gas, and the variable capacity turbocharger opens and closes a nozzle vane to prevent sulfur poisoning of the storage reduction type NOx catalyst carried by the particulate filter. The exhaust emission control device for an internal combustion engine according to claim 1, which performs recovery.