JP2003343245A - Exhaust purifying device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technology wherein a reducing agent and hydrogen sulfide flown on feeding the reducing agent to NOx catalyst are removed in an exhaust purifying device of an internal combustion engine. <P>SOLUTION: The exhaust gas purifying device is provided with: a NOx catalyst 14; a reducing agent feeding means 28; an oxidation catalyst 18 at the downstream side of the NOx catalyst 14; a supercharger 15; a secondary air intake pipe 24 communicating an exhaust system 13 from NOx catalyst 14 to the oxidation catalyst 18 with an intake system 9 from the supercharger 15 to the internal combustion engine 1; a secondary air quantity regulating valve 25 for regulating the secondary air quantity; a differential pressure detecting means 26 for detecting the differential pressure between the exhaust system 13 from the NOx catalyst 14 to the oxidation catalyst 18 and the intake system 9 from the supercharger 15 to the internal combustion engine 1; and a sulfur poison recovering means for recovering the sulfur poison only when the pressure of the exhaust system 13 is higher than that of the intake system 9. <P>COPYRIGHT: (C)2004,JPO

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 recent years, internal combustion engines mounted in automobiles,
In particular, diesel engines and lean burn engines that can burn an air-fuel mixture that is in an oxygen excess state (so-called lean air-fuel mixture)
In a gasoline engine, a technique for purifying nitrogen oxides (NOx) contained in exhaust gas of the internal combustion engine is desired.

In response to such demands, a technique for arranging a NOx storage agent in the exhaust system of an internal combustion engine has been proposed. As one of the NOx storage agents, when the oxygen concentration of the inflowing exhaust gas is high, nitrogen oxides (NOx) in the exhaust gas are stored (absorbed, adsorbed), the oxygen concentration of the inflowing exhaust gas decreases, and the reducing agent becomes Nitrogen oxides (NO when stored)
Storage-reduction type NOx catalysts that reduce x) are known.

When the NOx storage reduction catalyst is arranged in the exhaust system of the internal combustion engine, nitrogen oxide (NOx) in the exhaust gas is generated when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high.
Are stored in the NOx storage reduction catalyst, and when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst becomes low, the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst are reduced.

By the way, the NOx storage reduction catalyst is a sulfur oxide (S) produced by combustion of sulfur contained in fuel.
Ox) is also stored by the same mechanism as NOx. The SOx thus stored is less likely to be released than NOx, and is stored in the NOx storage reduction 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 carried out by flowing the exhaust gas whose oxygen concentration is lowered by adding fuel to the storage reduction type NOx catalyst while keeping the storage reduction type NOx catalyst at a high temperature (for example, about 600 to 650 ° C.).

In this way, when the reduction of NOx and the recovery of SOx poisoning are performed in a rich atmosphere, the storage reduction type NOx
A reducing agent or hydrogen sulfide (H ₂ S) may flow out downstream of the catalyst.

Here, in the invention described in Japanese Patent Application Laid-Open No. 2000-110552, an oxidation catalyst is provided in the downstream side, and further air is supplied to the oxidation catalyst to form an oxygen-excess atmosphere, and a reducing agent and hydrogen sulfide are formed. It is possible to oxidize.

[0008]

However, according to the above publication, since the air pump is provided for supplying air to the oxidation catalyst, the cost becomes high and the installation space is required.

The present invention has been made in view of the above problems, and it is possible to remove the reducing agent and hydrogen sulfide that flow out at the time of supplying the reducing agent to the NOx catalyst in the exhaust purification system of the internal combustion engine. The purpose is to provide technology that can.

[0010]

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 NOx catalyst provided in the exhaust system of an internal combustion engine to reduce NOx in the presence of a reducing agent, a reducing agent supply means for supplying the reducing agent to the NOx catalyst, and an oxidizing function provided downstream of the NOx catalyst. A catalyst having, a supercharger, a secondary air introducing pipe that communicates an exhaust system from the NOx catalyst to the catalyst having the oxidizing function and an intake system from the supercharger to an internal combustion engine, and the secondary air A secondary air amount adjusting valve that adjusts the flow area of the introduction pipe to adjust the amount of air flowing through the secondary air introduction pipe, an exhaust system from the NOx catalyst to the catalyst having the oxidizing function, and the supercharger. From the NOx catalyst to the catalyst having the oxidizing function, the pressure in the intake system from the supercharger to the internal combustion engine is the pressure in the exhaust system from the NOx catalyst to the catalyst having the oxidizing function. Is higher than the differential pressure detection means Sulfur poisoning recovery means for supplying a reducing agent to the NOx catalyst to recover from sulfur poisoning only when detected.

The most significant feature of the present invention is that in an exhaust gas purification apparatus for an internal combustion engine, sulfur poisoning recovery is performed only when supercharged air can be supplied to a catalyst having an oxidizing function.
This is to make it possible to oxidize the reducing agent and hydrogen sulfide flowing out from the Ox catalyst by the downstream oxidation catalyst.

In the exhaust gas purification apparatus for an internal combustion engine configured as above, when the reducing agent is supplied to the NOx catalyst, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst becomes a rich air-fuel ratio, and the sulfur oxide (SOx) is reduced. Is released. However, at this time, a part of the reducing agent such as hydrocarbon (HC) and carbon monoxide (CO) may flow out to the downstream. Further, when recovering from SOx poisoning, SOx released from the NOx catalyst easily becomes hydrogen sulfide. In this way, the hydrocarbon (HC), carbon monoxide (CO), and hydrogen sulfide that have flowed out from the NOx catalyst are oxidized by the downstream oxidation catalyst. Here, the catalyst having an oxidizing function has an effective oxidizing function in an atmosphere of excess oxygen, but at the time of SOx poisoning recovery, the oxygen concentration is lowered by the supply of the reducing agent, and the oxidizing ability of the oxidizing catalyst is also lowered. I will end up.
Even in such a state, by supplying air from the secondary air introducing pipe to the upstream of the catalyst having an oxidizing function, the oxidizing ability of the oxidizing catalyst can be improved. Here, in the intake system, since the pressure of the air downstream of the supercharger is increased by the supercharger, the air flows from the intake system to the exhaust system through the secondary air introducing pipe. This makes it possible to improve the oxidation ability of the oxidation catalyst. Further, when the supercharging pressure by the supercharger is not sufficient, it is possible to suppress the release of the reducing agent and hydrogen sulfide into the atmosphere by not performing SOx poisoning recovery.

When an intake throttle valve is provided in the intake system from the supercharger to the internal combustion engine, the secondary air introduction pipe is provided with an exhaust system from the NOx catalyst to the catalyst having an oxidizing function. It is desirable to communicate with the intake system from the supercharger to the intake throttle valve.

According to the present invention, the EGR passage for connecting the exhaust system and the intake system of the internal combustion engine to recirculate a part of the exhaust gas discharged from the internal combustion engine to the intake system of the internal combustion engine, and the EGR passage.
An EGR valve for adjusting the flow rate of EGR gas flowing in the passage, and when the secondary air is being supplied by the secondary air supply means, the EGR valve is controlled to be closed. be able to.

As described above, when the EGR valve is controlled to the closing side, the EGR gas amount decreases and the temperature of the exhaust gas rises. Therefore, in the supercharger that supercharges with the energy of the exhaust gas, the supercharging pressure is increased. It is possible to raise the temperature, and it becomes possible to supply a large amount of air to the catalyst having an oxidizing function.

In the present invention, the supercharger is a variable capacity type turbocharger that changes the flow velocity of the exhaust gas blown to the turbine wheel by opening and closing the nozzle vanes so that the supercharging pressure of the intake air becomes a desired pressure. When the secondary air is being supplied by the secondary air supply means, the nozzle vane can be controlled to the closing side.

As described above, when the nozzle vane is controlled to the closing side, the supercharging pressure rises, and it becomes possible to increase the supply amount of air to the catalyst having the oxidizing function.

In the present invention, an oxygen concentration detecting means for detecting the oxygen concentration of the exhaust gas flowing through the catalyst having the oxidizing function is further provided, and the sulfur poisoning recovery means is provided for the exhaust gas flowing through the catalyst having the oxidizing function. The secondary air amount adjusting valve can be controlled to the closing side within a range where the oxygen concentration is a concentration that activates the catalyst having an oxidizing function.

In the exhaust gas purifying apparatus for an internal combustion engine configured as described above, the required minimum amount of air can be supplied to the catalyst having an oxidizing function, so that the supercharging pressure can be prevented from decreasing early and the long-term operation can be prevented. It is possible to supply air to the catalyst having an oxidizing function over a period of time.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of an internal combustion engine according to the present invention will be described below with reference to the drawings. Here, a case where the internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.

FIG. 1 is a diagram showing a schematic configuration of an engine and its intake and exhaust system according to the present embodiment.

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.

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.

Further, 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). .

The intake branch pipe 8 is connected to the intake pipe 9,
In the middle of the intake pipe 9, a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates by using heat energy of exhaust gas as a drive source is provided.

An intake throttle valve 10 for adjusting the flow rate of intake air flowing through the intake pipe 9 is provided at a portion of the intake pipe 9 located immediately upstream of the intake branch pipe 8. The intake throttle valve 10 is provided with an intake throttle actuator 11 configured by a step motor or the like for driving the intake throttle valve 10 to open and close.

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

The intake air that has flowed into the compressor housing 15a is compressed by the rotation of the compressor wheel installed in the compressor housing 15a, 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 12 is connected to the engine 1, and each branch pipe of the exhaust branch pipe 12 communicates with a combustion chamber of each cylinder 2 via an exhaust port 1b.

The exhaust branch pipe 12 is provided with the centrifugal supercharger 15.
Is connected to the turbine housing 15b. The turbine housing 15b is connected to an exhaust pipe 13, and the exhaust pipe 13 is connected downstream to a muffler (not shown).

In the middle of the exhaust pipe 13, a storage reduction type N
A particulate filter carrying an Ox catalyst (hereinafter,
Simply called a filter. ) 14 are provided. The filter 14 carries a storage-reduction type NOx catalyst, collects particulate matter (hereinafter referred to as PM) in the exhaust gas, and stores (absorbs, absorbs, NOx in the exhaust gas when the oxygen concentration of the inflowing exhaust gas is high). It has a function of reducing the stored NOx when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. A first oxidation catalyst 16 having an oxidation function is provided upstream of the filter 14. Further, a first exhaust gas temperature sensor 17 that outputs an electric signal corresponding to the temperature of the exhaust gas that flows is attached between the filter 14 and the first oxidation catalyst 16. Further, a second oxidation catalyst 18 having an oxidizing function is provided downstream of the filter 14. Between the filter 14 and the second oxidation catalyst 18, a second exhaust gas temperature sensor 19 for outputting an electric signal corresponding to the temperature of the exhaust gas flowing therethrough and a first output for outputting an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing therethrough The air-fuel ratio sensor 20 is attached. Further, downstream of the second oxidation catalyst 18, a second air-fuel ratio sensor 21 that outputs an electric signal corresponding to the air-fuel ratio of the flowing exhaust gas is attached.

In the exhaust system thus constructed, the air-fuel mixture (burnt gas) burned in each cylinder 2 of the engine 1 is discharged to the exhaust branch pipe 12 through the exhaust port 1b, and then the exhaust branch pipe 12 is exhausted. Flows into the first oxidation catalyst 16 upstream of the filter 14. In the first oxidation catalyst 16, part of the reducing agent is oxidized and the temperature of the exhaust gas can be raised, and the temperature of the NOx storage reduction catalyst can be raised at the time of SOx poisoning recovery described later. Further, it is possible to prevent the filter 14 from being clogged with the reducing agent. The exhaust gas that has passed through the first oxidation catalyst 16 flows into the filter 14, where PM in the exhaust gas is collected and NOx is stored. The exhaust gas flowing out from the filter 14 flows into the second oxidation catalyst 18 on the downstream side. In the second oxidation catalyst 18, hydrocarbons (H
C), carbon monoxide (CO), etc. can be oxidized.

The exhaust branch pipe 12 and the intake branch pipe 8 are provided with an EGR passage (hereinafter referred to as an EGR passage) 22 for recirculating a part of the exhaust gas flowing in the exhaust branch pipe 12 to the intake branch pipe 8. Are in communication. A solenoid valve or the like is provided in the middle of the EGR passage 22, and the E
A flow rate adjusting valve (hereinafter, referred to as an EGR valve) 23 that changes a flow rate of exhaust gas (hereinafter, referred to as an EGR gas) flowing in the GR passage 22 is provided.

In the EGR mechanism constructed as described above, E
When the GR valve 23 is opened, the EGR passage 22 is brought into a conductive state, and a part of the exhaust gas flowing through the exhaust branch pipe 12 becomes E.
It flows into the GR passage 22 and is guided to the intake branch pipe 8. The EGR gas recirculated to the intake branch pipe 8 is introduced into the combustion chamber of each cylinder 2 while being mixed with fresh air flowing from the upstream side of the intake branch pipe 8.

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

On the other hand, one end of a secondary air introducing pipe 24 is connected to the intake pipe 9 between the turbocharger 15 and the intake throttle valve 10. On the other hand, the other end of the secondary air introduction pipe 24 is connected to the exhaust pipe 13 between the filter 14 and the second oxidation catalyst 18. The intake system and the exhaust system are communicated with each other via the secondary air introduction pipe 24. A secondary air amount adjusting valve configured by a solenoid valve or the like in the middle of the secondary air introducing pipe 24 and changing the flow rate of the air flowing through the secondary air introducing pipe 24 according to the magnitude of the applied power. 25 are provided.

In the secondary air introducing mechanism constructed as described above, when the secondary air amount adjusting valve 25 is opened, the secondary air introducing pipe 24 becomes conductive. When the pressure of the intake system is higher than that of the exhaust system, part of the air flowing through the intake pipe 9 flows into the secondary air introduction pipe 24 and is introduced into the exhaust pipe 13. The air introduced into the exhaust pipe 13 mixes with the exhaust gas flowing from the upstream side of the exhaust pipe 13 while mixing with the second oxidation catalyst 18
Flow into.

The intake pipe 9 between the turbocharger 15 and the intake throttle valve 10 is connected to one end of an intake introduction pipe 26a for introducing intake air, and the exhaust gas between the filter 14 and the second oxidation catalyst 18 is exhausted. One end of an exhaust introduction pipe 26b is connected to the pipe 13. The other end of the intake introduction pipe 26a and the other end of the exhaust introduction pipe 26b are connected to the differential pressure sensor 26. The differential pressure sensor 26 outputs an electric signal corresponding to the pressure difference between the intake air introduced through the intake introduction pipe 26a and the exhaust gas introduced through the exhaust introduction pipe 26b.

In the present embodiment, a reducing agent supply mechanism for adding fuel (light oil) as a reducing agent to the exhaust gas flowing through the exhaust branch pipe 12 upstream of the filter 14 is provided. By adding fuel into the exhaust gas, the oxygen concentration of the exhaust gas flowing into the filter 14 is reduced and the concentration of the reducing agent is increased.

As shown in FIG. 1, the reducing agent supply mechanism is installed so that its injection hole faces the inside of the exhaust branch pipe 12, and the reducing agent is opened by a signal from an ECU 27 described later to inject fuel. The injection valve 28 and the fuel pump 6 described above.
A reducing agent supply path 29 for guiding the fuel discharged from the reducing agent injection valve 28 to the reducing agent injection valve 28.

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 the ECU 2
The reducing agent injection valve 28 is opened by a signal from 7 and fuel as a reducing agent is injected into the exhaust branch pipe 12. The fuel injected from the reducing agent injection valve 28 into the exhaust branch pipe 12 reduces the oxygen concentration of the exhaust gas flowing from the upstream side of the exhaust branch pipe 12.

After that, the reducing agent injection valve 28 is closed by a signal from the ECU 27, and the addition of fuel into the exhaust branch pipe 12 is stopped.

As a result of the fuel being supplied to the filter 14 in this way, the oxygen concentration of the exhaust gas flowing into the filter 14 changes in a relatively short cycle. As a result, the nitrogen oxides (NO
x) is reduced.

The engine 1 configured as described above is provided with an electronic control unit (ECU) 27 for controlling the engine 1. The ECU 27 is a unit that controls the operating state of the engine 1 according to the operating conditions of the engine 1 and the driver's request.

Various sensors are connected to the ECU 27 through electrical wiring, and the output signals of the various sensors described above are EC.
It is designed to be input to U27. On the other hand, the ECU 2
7, a fuel injection valve 3 and an intake throttle actuator 1
1, the EGR valve 23, the secondary air amount adjusting valve 25, the reducing agent injection valve 28, etc. are connected via electric wiring, and these can be controlled. Further, the ECU 27 is
It stores various application programs and various control maps.

By the way, in the NOx storage reduction catalyst, sulfur oxides (S
Ox) is also stored by the same mechanism as NOx. The SOx thus stored is less likely to be released than NOx, and is stored in the NOx storage reduction 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 carried out by flowing the exhaust gas whose oxygen concentration is lowered by adding fuel to the storage reduction type NOx catalyst while keeping the storage reduction type NOx catalyst at a high temperature (for example, about 600 to 650 ° C.). Here, the first exhaust gas temperature sensor 17
Can be used to determine whether the temperature of the filter 14 is at a predetermined temperature (for example, 600 to 650 degrees) when SOx poisoning is recovered. Further, the second exhaust gas temperature sensor 19 can be used to detect that the temperature of the filter 14 excessively rises when the SOx poisoning is recovered.

FIG. 2 is a time chart diagram showing the concentration of SOx released from the filter and the time course of the air-fuel ratio in the filter when the SOx poisoning is recovered.

When recovering from SOx poisoning, the ECU 27 executes fuel addition control (so-called rich spike control) for reducing the oxygen concentration in the exhaust gas flowing into the filter 14 in a spike manner in a relatively short cycle.

In the fuel addition control, the ECU 27 controls the reducing agent injection valve 28 so that the reducing agent injection valve 28 injects the fuel serving as the reducing agent in a spike manner, thereby changing the air-fuel ratio of the exhaust gas flowing into the filter 14. The predetermined target rich air-fuel ratio is temporarily set.

Specifically, the ECU 27 controls the stored engine speed, engine load (accelerator opening), output signal value (intake air amount) of an air flow meter (not shown), first
The output signal of the air-fuel ratio sensor 20, the fuel injection amount, etc. are read.

The ECU 27 accesses the fuel addition amount control map using the engine speed, the engine load, 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. Calculate the fuel addition amount (target addition amount) required in.

Subsequently, the ECU 27 accesses the reducing agent injection valve control map using the target addition amount as a parameter, and the reducing agent injection valve 28 necessary for injecting the target addition amount of fuel from the reducing agent injection valve 28. The valve opening time of (target valve opening time) is calculated.

When the target opening time of the reducing agent injection valve 28 is calculated, the ECU 27 opens the reducing agent injection valve 28.

The ECU 27 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 target valve opening time, the target addition amount of fuel is injected from the reducing agent injection valve 28 into the exhaust branch pipe 12. Then, the fuel injected from the reducing agent injection valve 28 mixes with the exhaust gas flowing from the upstream side of the exhaust branch pipe 12 to form the air-fuel mixture having the target air-fuel ratio to form the first oxidation catalyst 16 and the filter 1.
Inflow to 4.

In the first oxidation catalyst, the fuel is oxidized and heat is generated at that time. Due to this heat, the temperature of the exhaust gas rises and the temperature of the downstream filter 14 rises. This allows
The temperature of the filter 14 rises to the temperature required for SOx poisoning recovery.

On the other hand, in the air-fuel ratio of the exhaust gas flowing into the filter 14, the oxygen concentration changes in a relatively short cycle. In the filter 14, SOx is released from the NOx storage reduction catalyst as the temperature rises, so that SOx poisoning of the NOx storage reduction catalyst carried by the filter 14 can be recovered.

In the present embodiment, one rich spike may be formed by the fuel a plurality of times to prevent the air-fuel ratio from becoming excessively rich. Here, when a large amount of fuel is injected at one time, the air-fuel ratio becomes excessively rich, and there is a risk that the fuel will not fully react in the filter 14 and will flow out to the downstream side. Therefore, in the present embodiment, the fuel injection amount per injection is reduced and the fuel is injected a plurality of times to form the rich atmosphere while suppressing the excessive rich.

Here, FIG. 3 is a diagram showing an opening / closing signal of the reducing agent injection valve 28 corresponding to the portion indicated by A in FIG. The reducing agent injection valve 28 closes when the signal is OFF and opens when the signal is ON.

One rich spike is formed by, for example, 17 times of fuel injection. The valve opening time per time of the fuel injection valve 14 is, for example, 60 ms, and then 1
It is closed for 50 ms. By repeating this 17 times, one rich spike is formed as a whole. In this way, when one rich spike is formed by a plurality of fuel injections, it is possible to suppress the air-fuel ratio from becoming excessively rich. Therefore, the filter 14
It is possible to reduce the amount of fuel flowing downstream without reacting with. Further, the rich spike is formed, for example, at every rich rest period of 7.5 s. By this rich pause period, overheating of the filter 14 can be suppressed, and heat deterioration of the filter 14 can be suppressed.

By the way, when fuel is supplied to recover SOx poisoning of the NOx storage reduction catalyst, SOx is released from the NOx storage reduction catalyst as described above. Hydrogen sulfide (H
₂ S) tends to occur. In addition, reducing components such as hydrocarbons (HC) and carbon monoxide (CO) may pass through the NOx storage reduction catalyst and flow out downstream.

On the other hand, it is possible to oxidize hydrocarbons (HC) and the like by providing an oxidation catalyst on the downstream side.
When the Ox poisoning is recovered, a reducing atmosphere is created, so that the oxidizing ability of the oxidation catalyst is significantly reduced.

Here, in the conventional exhaust gas purifying apparatus for an internal combustion engine, an oxidation catalyst is provided downstream of the NOx storage reduction catalyst, and secondary air is supplied to the oxidation catalyst. This allows SO
x The oxidation ability of the oxidation catalyst could be increased even when the poisoning was recovered. However, the cost was high because an air pump was required to supply the secondary air.

Therefore, in the present embodiment, supercharged air whose pressure has been boosted by the turbocharger 15 is introduced upstream of the second oxidation catalyst 18, and the exhaust gas flowing into the second oxidation catalyst 18 is made into an oxidizing atmosphere, The oxidizing ability of the second oxidation catalyst 18 is increased. As a result, carbon monoxide (CO) and hydrocarbons (HC) and hydrogen sulfide (H) are generated in the second oxidation catalyst 18.
₂ S) etc. can be oxidized.

Here, the SOx poisoning recovery is performed by the intake throttle valve 1
In many cases, the air-fuel ratio is set to 20 or less by controlling 0 to the closing side to reduce the intake air amount. As described above, by reducing the intake air amount, the air-fuel ratio can be lowered by adding a small amount of fuel, and the fuel consumption can be improved. Then, in the operating state in which the intake air amount is reduced when SOx poisoning is recovered, supercharging by the supercharger is unnecessary. Therefore, the compressed air in the intake pipe can be supplied to the oxidation catalyst as secondary air with almost no influence on the operating state of the engine or recovery of SOx poisoning.

Further, since the air compressed by the turbocharger 15 is supplied to the oxidation catalyst, it is not necessary to provide a pump for supplying the air.

In this embodiment, the pressure in the intake pipe 9 between the turbocharger 15 and the intake throttle valve 10 and the pressure in the exhaust pipe 13 between the filter 14 and the second oxidation catalyst 18 are , The secondary air amount adjusting valve 25 is opened to recover SOx poisoning only when the pressure in the intake pipe 9 is higher than the pressure in the exhaust pipe 13.

Here, FIG. 4 shows the air-fuel ratio, the amount of hydrocarbons (HC), carbon monoxide (CO), and hydrogen sulfide (H ₂ S) of the exhaust gas discharged from each catalyst at the time of SOx poisoning recovery. It is a figure.

The filter 14 needs a rich air-fuel ratio to recover SOx poisoning. In addition, at this time, the reducing agent passes through the filter 14 and the hydrocarbon (H
C), carbon monoxide (CO) is discharged. Further, although a small amount, SOx is released from the NOx storage reduction catalyst, and due to the rich atmosphere, it becomes hydrogen sulfide (H ₂ S) and flows out downstream.

In the second oxidation catalyst 18, the minimum air-fuel ratio rises due to the introduction of the secondary air, resulting in a weak lean. in this way,
In the second oxidation catalyst 18, since the air-fuel ratio of the exhaust gas becomes equal to or higher than the stoichiometric air-fuel ratio, it becomes possible to oxidize hydrocarbon (HC), carbon monoxide (CO) and hydrogen sulfide (H ₂ S).

As described above, the filter 14 carrying the NOx storage reduction catalyst and the second oxidation catalyst 18 are arranged in this order from the upstream side, and the secondary air is introduced from the upstream side of the second oxidation catalyst 18 to recover SOx poisoning. It is possible to oxidize hydrocarbon (HC), carbon monoxide (CO) and hydrogen sulfide (H ₂ S) flowing out from the NOx storage reduction catalyst.

In the present embodiment, during the SOx poisoning recovery control, the opening degree of the secondary air amount adjusting valve 25 is feedback controlled based on the output signals of the differential pressure sensor 26 and the second air-fuel ratio sensor 21. You may do it. Where SO
x Poisoning recovery is performed at light load, and the intake throttle valve 10 is controlled to the closing side. Therefore, the flow rate of exhaust gas is reduced, and the boost pressure is less likely to rise. When the secondary air amount adjusting valve 25 is fully opened in such a state, the pressure in the intake pipe 9 drops early, so the second oxidation catalyst 18
It becomes difficult to supply secondary air for a long time. Therefore, the secondary air amount adjusting valve 25 is controlled to the closing side within a range in which the air-fuel ratio obtained from the output signal of the second air-fuel ratio sensor 21 becomes larger than stoichiometry. In such a state, since the oxidizing atmosphere can be maintained, hydrocarbons (HC), carbon monoxide (CO) and hydrogen sulfide (H) are generated in the second oxidation catalyst 18.
It is possible to oxidize ₂ S). Moreover, since the necessary minimum amount of air is supplied, it is possible to prevent the supercharging pressure from decreasing early, and thus it is possible to supply the secondary air for a long period of time.

Further, in the present embodiment, when the pressure difference between the pressure in the intake pipe 9 and the pressure in the exhaust pipe 13 becomes a predetermined value or less, the secondary air amount adjusting valve 25 is controlled to the closing side. You may. In this way, it becomes possible to continuously supply the secondary air while suppressing the decrease in the supercharging pressure. Here, the predetermined value is the minimum pressure difference required to supply the secondary air to the second oxidation catalyst, and is determined in advance by experiments or the like.

In the present embodiment, the second oxidation catalyst 18
May be made to contain ceria (Ce) or the like to have an oxygen storage capacity. When the exhaust gas having a weak rich air-fuel ratio or the stoichiometric air-fuel ratio flows into the second oxidation catalyst 18 because the second oxidation catalyst 18 has an oxygen storage capacity, the stored oxygen is released and an oxidizing atmosphere is easily formed. Is possible. As described above, by providing the oxygen storage capacity, it is possible to easily form the oxidizing atmosphere, but since the oxygen storage amount is limited, the oxygen amount is increased when the SOx poisoning amount is large. I will run out. Even in this case,
By additionally using the supply of the secondary air according to the present embodiment, it becomes possible to form an oxidizing atmosphere for a long period of time.

In this embodiment, when SOx poisoning is recovered, E
The GR valve 23 may be controlled to the closing side. Thus, E
When the GR valve 23 is controlled to the closing side, the amount of fresh air drawn into the engine increases, so the temperature of the exhaust gas rises. As a result, the energy of the exhaust increases, so that the supercharging pressure of the turbocharger 15 can be increased, and the second oxidation catalyst 1
It is possible to supply more air to 8. Here, the EGR valve 23 may be fully closed.

Further, in this embodiment, the flow velocity of the exhaust gas blown to the turbine wheel (not shown) in the turbocharger 15 so that the supercharging pressure of the intake air becomes a desired pressure can be changed by opening and closing the nozzle vane (not shown). Alternatively, the nozzle vane of the turbocharger may be controlled to the closing side when SOx poisoning is recovered.

The variable capacity turbocharger can change the direction of the flow path between the nozzle vanes and the gap between the nozzle vanes by adjusting the rotating direction and the rotating amount of the nozzle vanes. That is, by controlling the rotation direction and the rotation amount of the nozzle vane, the direction and flow velocity of the exhaust gas blown to the turbine wheel are adjusted.

For example, when the amount of exhaust gas from the engine 1 is small, the nozzle vane is closed to increase the flow velocity of the exhaust gas blown to the turbine wheel, and
Since the collision angle between the exhaust gas and the turbine impeller (not shown) becomes more vertical, the rotational speed and rotational force of the turbine wheel can be increased even with a small amount of exhaust gas.

On the other hand, when the amount of exhaust gas from the engine 1 is sufficiently large, the nozzle vane is opened to control an excessive increase in the flow velocity of the exhaust gas blown to the turbine wheel, and the rotational speed and rotational force of the turbine wheel are increased. It is possible to suppress an excessive rise.

Therefore, in this embodiment, the supercharging pressure can be increased by controlling the nozzle vanes to the closing side when the SOx poisoning is recovered, and more air can be supplied to the second oxidation catalyst 18. Is possible.

In the present embodiment, the addition of fuel into the exhaust gas is adopted as the method of supplying the reducing agent as described above, but in addition to this, the amount of recirculated EGR gas is increased to generate soot. Low temperature combustion that further increases the amount of EGR gas after increasing to the maximum (Patent No. 3116876)
No.), a method such as sub-injection in which fuel is injected again during the expansion stroke or the exhaust stroke after main injection for injecting fuel for engine output.

Further, in the present embodiment, the most downstream second oxidation catalyst 18 may be another catalyst having an oxidation function such as a three-way catalyst. Further, the filter 14 may simply be an occlusion reduction type NOx catalyst. Furthermore, the most upstream first oxidation catalyst 16 is not always necessary.

In the present embodiment, the supply of secondary air at the time of recovery from SOx poisoning has been described. Similarly, when the secondary air is supplied when reducing NOx stored in the NOx storage reduction catalyst, You may apply. That is, the rich spike control is performed only when the secondary air can be supplied, and N
Ox reduction may be performed.

As described above, according to the exhaust purification system of the internal combustion engine of the present embodiment, by supplying the boosted intake air to the oxidation catalyst, carbon monoxide (CO) flowing out at the time of SOx poisoning recovery. It is also possible to oxidize hydrocarbon (HC), further hydrogen sulfide (H ₂ S) and the like.

[0088]

In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the NOx catalyst and the oxidation catalyst are arranged in this order from the upstream side, and the air boosted by the supercharger can be supplied only to the oxidation catalyst. SOx poisoning recovery can be implemented only when air can be supplied. As a result, carbon monoxide (CO), hydrocarbons (H
C) can be oxidized and purified, and further hydrogen sulfide (H ₂ S) and the like can be oxidized to remove odorous components.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an engine and an intake / exhaust system thereof according to the present embodiment.

FIG. 2 is a time chart diagram showing the time transition of the concentration of SOx released from the filter and the air-fuel ratio in the filter at the time of SOx poisoning recovery.

FIG. 3 is a diagram showing an opening / closing signal of a reducing agent injection valve corresponding to a portion indicated by A in FIG.

FIG. 4 is a diagram showing the air-fuel ratio, the amount of hydrocarbons (HC), carbon monoxide (CO), and hydrogen sulfide (H ₂ S) of the exhaust gas discharged from each catalyst when recovering from SOx poisoning.

[Explanation of symbols]

1 ... Engine 1a: Crank pulley 1b ... Exhaust port 2 ... Cylinder 3 ... Fuel injection valve 4 ... Common rail 5 ... Fuel supply pipe 6a ... Pump pulley 6 ... Fuel pump 7 ... Belt 8 ... Intake branch pipe 9 ... Intake pipe 10 ... Intake throttle valve 11 ... Actuator for intake throttle 12 ... Exhaust branch pipe 13 ... Exhaust pipe 14 ... Particulate filter 15 ... Turbocharger 15a ... Compressor housing 15b · Turbine housing 16 ... First oxidation catalyst 17 ... First exhaust temperature sensor 18 ... Second oxidation catalyst 19 ... Second exhaust temperature sensor 20: First air-fuel ratio sensor 21 ... Second air-fuel ratio sensor 22 ... EGR passage 23 ... EGR valve 24 ... Secondary air inlet pipe 25 ... Secondary air amount adjusting valve 26 ... Differential pressure sensor 26a ... Intake pipe 26b ... Exhaust gas introduction pipe 27 ... ECU 28 ... Reducing agent injection valve 29 ... Reductant supply path

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/22 F01N 3/24 T 4D048 3/24 3/28 301D F02B 37/00 302F 3/28 301 F02D 21/08 301F F02B 37/00 302 301H 37/24 311B F02D 21/08 301 23/00 J 43/00 301N 311 301R 23/00 301T 43/00 301 F02M 25/07 550C 550R F02B 37/12 301Q F02M 25/07 550 B01D 53/36 103B K 101A (72) Inventor Hisashi Oki 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. (72) Inventor, Daisuke Shibata 1 Toyota Town, Toyota City, Aichi Prefecture, Toyota Motor Co., Ltd. F Terms (reference) 3G005 DA02 EA15 EA16 FA35 GA04 GB25 GB26 HA12 HA18 3G062 AA01 AA05 AA06 BA02 BA07 GA14 GA22 3G084 AA01 AA03 BA05 BA07 BA08 BA09 BA13 BA15 BA20 BA24 BA25 DA10 DA22 DA27 EB11 EB22 FA07 FA12 FA 20 FA26 FA27 FA30 FA33 FA38 3G091 AA10 AA11 AA18 AA28 AB02 AB06 AB13 BA00 BA04 BA11 BA14 BA15 BA19 BA20 BA38 CA13 CA18 CA22 CB02 CB03 CB07 CB08 DA01 DA02 DA04 DB10 EA01 EA03 EA05 EA17 EA30 EA32 EA34 FB10 FB12 FC02 GA06 GB04W HA02 HA09 HA10 HA12 HA14 HA36 HA37 HA38 HA42 HA47 HB05 HB06 HB07 3G092 AA02 AA06 AA13 AA17 AA18 AB03 AB20 BA02 BA04 BB01 BB06 DB03 DC03 DC09 DC15 DC16 DE03S DF01 DF02 DF06 HAY HD16 HA01 HAZ HA16 HA01 HA01 HA01Y02 HD07Y HD07Z HD08Y HD08Z HE01Y HE01Z HE03Y HE03Z HE08Y HE08Z HF08Y HF08Z 4D048 AA06 AA13 AA14 AA18 AB01 AB02 AB05 AB07 AC02 AC10 BB01 BD03 CC32 CC46 CC61 DA01 DA02 DA06 DA07 DA10 EA04

Claims (4)

[Claims] 1. An NOx catalyst provided in an exhaust system of an internal combustion engine for reducing NOx in the presence of a reducing agent, a reducing agent supply means for supplying the reducing agent to the NOx catalyst, and a NOx catalyst provided downstream of the NOx catalyst. A catalyst having an oxidizing function, a supercharger, a secondary air introducing pipe that connects an exhaust system from the NOx catalyst to the catalyst having the oxidizing function and an intake system from the supercharger to an internal combustion engine, A secondary air amount adjusting valve that adjusts the amount of air flowing through the secondary air introducing pipe by varying the flow area of the secondary air introducing pipe, an exhaust system from the NOx catalyst to the catalyst having the oxidizing function, and Differential pressure detecting means for detecting a pressure difference between the supercharger and the internal combustion engine and the intake system; and
x Sulfur poisoning for recovering sulfur poisoning by supplying a reducing agent to the NOx catalyst only when it is detected by the differential pressure detection means as being higher than the pressure of the exhaust system from the catalyst to the catalyst having the oxidation function An exhaust emission control device for an internal combustion engine, comprising: a recovery means. 2. An EGR passage that connects the exhaust system and the intake system of the internal combustion engine to recirculate a part of the exhaust gas discharged from the internal combustion engine to the intake system of the internal combustion engine, and an EGR gas flowing in the EGR passage. An EGR valve for adjusting a flow rate is further provided, and when the secondary air is being supplied by the secondary air supply means, the EGR valve is controlled to a closing side. An exhaust emission control device for an internal combustion engine as set forth in. 3. The turbocharger is a variable capacity type turbocharger for varying the flow rate of exhaust gas blown to a turbine wheel by opening and closing a nozzle vane so that a supercharging pressure of intake air becomes a desired pressure. The exhaust gas purification device for an internal combustion engine according to claim 1 or 2, wherein when the secondary air is being supplied by the secondary air supply means, the nozzle vane is controlled to the closing side. 4. The oxygen concentration detecting means for detecting the oxygen concentration of the exhaust gas flowing through the catalyst having the oxidizing function, wherein the sulfur poisoning recovery means is configured to detect the oxygen concentration of the exhaust gas flowing through the catalyst having the oxidizing function. The exhaust gas purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the secondary air amount adjusting valve is controlled to a closing side within a range where a concentration having a catalyst having an oxidizing function is activated. .