JP3512064B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to a storage reduction type NOx
The present invention relates to an exhaust purification device for an internal combustion engine equipped with a catalyst.
You. [0002] 2. Description of the Related Art From an internal combustion engine that performs combustion at a lean air-fuel ratio
An exhaust gas purification device that purifies NOx in exhaust gas
There is a storage reduction type NOx catalyst. This storage reduction type NOx
The catalyst absorbs NOx when the air-fuel ratio of the inflow exhaust gas is lean.
And absorbed when the oxygen concentration in the inflow exhaust decreased
It is a catalyst that releases NOx.
Nitrogen oxidation from lean air-fuel ratio exhaust with Ox catalyst
Absorb substances (NOx) and supply to internal combustion engine after NOx absorption
Increase the amount of fuel flowing into the NOx storage reduction catalyst
The exhaust air-fuel ratio to be rich or stoichiometric
Thus, the NOx absorbed from the NOx storage reduction catalyst is released.
And release the released NOx into the unburned H
It is reduced and purified by reducing components such as C and CO. [0003] In general, sulfuric acid is used as fuel for internal combustion engines.
It contains yellow matter, and when burning fuel in an internal combustion engine,
Sulfur in the fuel burns to produce sulfur oxides (SOx)
You. The NOx storage reduction catalyst performs an NOx absorbing action.
It absorbs SOx in exhaust by the same mechanism as
The storage reduction type NOx catalyst is placed in the exhaust passage of the internal combustion engine.
Then, not only NOx but also SOx is stored in the NOx storage reduction catalyst.
x is also absorbed. However, the NOx storage-reduction type NOx catalyst
SOx forms stable sulfate over time
Therefore, release of NOx from a normal NOx storage reduction catalyst,
Under the conditions for reduction purification (hereinafter referred to as regeneration), decomposition,
Not easily released and easily accumulated in the NOx storage reduction catalyst
Tend. The amount of SOx stored in the NOx storage reduction catalyst increases.
When it increases, the NOx absorption capacity of the NOx storage reduction catalyst decreases.
To remove NOx from exhaust gas
NOx purification efficiency decreases, so-called SOx poisoning occurs
I will. Therefore, the NOx purification ability of the NOx storage reduction catalyst is extended.
In order to maintain a high NOx over
SOx absorbed in the medium is released at appropriate timing.
Need to be done. [0005] The SOx absorbed by the NOx storage reduction catalyst is
To release it, make the intake air / fuel ratio rich or stoichiometric.
Irritating, and the NOx stored and reduced compared to normal regeneration
It has been found that the medium needs to be at a high temperature. Further, according to recent studies, these conditions
Reaction between the reducing agent and oxygen near the catalyst surface
Releases SOx absorbed by the NOx storage reduction catalyst.
Has proved to be very important. [0007] By the way, the SOx in the NOx storage reduction catalyst
The distribution of the absorption amount of
The closer to the inlet side, the more (hereinafter, this SOx absorption
The region where the yield is high is called the SOx absorption region).
When releasing SOx absorbed by the NOx storage reduction catalyst
In addition, the rich or stoichiometric air-fuel ratio exhaust is
If flowed in the same direction as the exhaust flow direction during Ox absorption,
Absorbed at the exhaust inlet side in the NOx storage reduction catalyst
Even if the released SOx is released, the released SOx is stored and reduced.
Occlusion and recovery by simply moving to the exhaust outlet side in the type NOx catalyst
Is absorbed by the primary NOx catalyst, and is stored and reduced.
There is a problem that it cannot be discharged from the catalyst. Therefore, Japanese Patent Application Laid-Open No. 7-259542 discloses
As disclosed, the absorption reduction NOx catalyst
When releasing concentrated SOx, rich or
Storage and return of Iki's air-fuel ratio exhaust in the opposite direction to that during NOx absorption
A technique of flowing over an original NOx catalyst has been proposed. this is,
If SOx is released by reversing the flow of exhaust,
SOx released from the catalytic NOx catalyst is stored and reduced NOx
Immediately after reducing the movement distance in the catalyst, NO
x is released outside the catalyst, and the released SOx
Considering that it will not be re-absorbed by the NOx storage reduction catalyst
Based on [0009] However, this is not the case.
Even if the flow of exhaust gas is reversed in the direction opposite to NOx absorption,
Couldn't get the effect of SOx release as much as
Was. The cause is considered as follows. [0010] In the NOx storage reduction catalyst during SOx release
Even if the flow of exhaust gas
Alternatively, the stoichiometric air-fuel ratio exhaust gas is
Return in the exhaust before reaching the SOx absorption region in the medium
Since the base agent component reacts with oxygen, the SOx absorption region
When it reaches, the amount of reducing agent in the exhaust
There is almost no element, and SOx absorption region can be released SOx
I can't create a working atmosphere. As a result, occlusion reduction
The SOx can be released sufficiently from the type NOx catalyst?
It is inferred that The present invention addresses such problems of the prior art.
The present invention has been made in view of the above, and is intended to be solved by the present invention.
The challenge is to efficiently convert SOx absorbed by the NOx storage reduction catalyst
By releasing well, the NOx of the NOx storage reduction catalyst
The aim is to achieve a sufficient recovery of absorption capacity. [0012] The present invention solves the above-mentioned problems.
In order to do so, the following means were adopted. That is, the present invention
The air-fuel ratio of the exhaust gas flowing in the exhaust passage of the internal combustion engine
When lean, it absorbs NOx in the exhaust and
The absorption that releases the absorbed NOx when the oxygen concentration falls
The storage reduction type NOx catalyst and the storage reduction type NOx catalyst
SOx in exhaust gas absorbed at the time of x absorption is stored and reduced NOx catalyst
Rich air-fuel ratio of exhaust gas flowing in when discharging from medium
Or a stoichiometric regeneration means to lower the oxygen concentration
The exhaust gas purifying apparatus for an internal combustion engine, comprising:
NOx absorption in the direction of exhaust gas flowing through the NOx storage reduction catalyst
In the same direction as the time (called the forward flow direction) or when NOx is absorbed
Exhaust flow direction switch to reverse direction (called reverse flow direction)
Exhaust gas flow direction switching means.
During the regeneration period by the means, the NOx storage reduction type
Change the flow direction of the exhaust gas flowing through the medium at least once
It is characterized by that. In this exhaust gas purifying apparatus for an internal combustion engine, the regenerator
Flow through the NOx storage reduction catalyst
The exhaust gas flow is divided into forward flow direction and reverse flow direction,
Ox release is performed. In this way, occlusion return
Low-concentration oxygen at one end and the other end of the primary NOx catalyst.
Supply rich or stoichiometric air-fuel ratio exhaust
Can be absorbed by the NOx storage reduction catalyst.
Can release SOx reliably and sufficiently
You. The first exhaust flow during the regeneration period
The direction may be a forward flow direction or a backward flow direction.
In short, regeneration is performed by exhaust gas flow in both directions.
It just needs to be done. The internal combustion engine according to the present invention is a lean engine.
Illustrates burn gasoline and diesel engines
Can be [0016] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of an internal combustion engine according to the present invention.
An embodiment of a gas purifying device will be described with reference to FIGS.
explain. The embodiments described below are not limited to the present invention.
Diesel for vehicles using such an exhaust gas purification device as an internal combustion engine
This is a form applied to an engine. FIG. 1 shows an exhaust gas purifying apparatus for an internal combustion engine according to the present invention.
FIG. 1 is a diagram illustrating an overall configuration according to an embodiment of the present invention. This
In the figure, the diesel engine (hereinafter referred to as the engine)
Abbreviated) 1 is an in-line four-cylinder engine, and an intake pipe 2 and an intake manifold
The intake air is supplied to each cylinder via a fuel tank 3. The discharge pressure of the fuel (light oil) in the fuel tank 4 is controlled.
Pumped by common fuel supply pump 5 and common
It is supplied to the rail 6. Electronic system for engine control
The control unit (ECU) 50 controls the fuel in the common rail 6.
The pressure becomes a predetermined pressure value according to the operation state of the engine 1
In this way, the operation of the fuel supply pump 5 is controlled. The engine 1 has a common rail 6
Fuel injection valve 7 that injects fuel supplied from each cylinder into each cylinder
The opening timing and the opening period of the fuel injection valve 7 are provided.
Is determined by the ECU 50 according to the operating state of the engine 1.
Controlled. The combustion chamber of each cylinder contains compression in each cylinder.
In the vicinity of the top dead center, fuel mainly flows from the corresponding fuel injection valve 7.
The fuel is expelled and the exhaust generated by this fuel explosion
The gas is discharged to the exhaust pipe 9 via the manifold 8. In this engine 1, a predetermined
During the expansion or exhaust stroke of a given cylinder
Fuel is injected into the cylinder from the fuel injection valve 7 of the corresponding cylinder
Is being fired. HC component of sub-injected fuel
Is converted into light HC by the heat of the explosion process,
The air is discharged to the exhaust pipe 9 through the exhaust manifold 8 together with the air.
Then, it is supplied to a storage reduction type NOx catalyst 31 described later.
The predetermined timing at which the sub-injection is performed will be described later.
I do. The exhaust pipe 9 has four ports for exhaust switching.
Connected to the first port of the valve (exhaust flow direction switching means) 20
Have been. The second port of the exhaust switching valve 20 converts the exhaust to the atmosphere.
The third of the exhaust switching valve 20 is connected to the exhaust pipe 10 for discharging.
The port is the inlet of the catalytic converter 30 via the exhaust pipe 11
30a, and the fourth port of the exhaust switching valve 20 is an exhaust port.
Connected to outlet 30b of catalytic converter 30 via tube 12
Have been. The catalytic converter 30 has a storage reduction type NOx
A catalyst (hereinafter abbreviated as NOx catalyst) 31 is housed therein.
You. The NOx catalyst 31 will be described later in detail. The exhaust switching valve 20 is shown in FIG.
By switching between the forward flow position and the reverse flow position shown in FIG.
Change the flow direction of the exhaust gas flowing through the catalytic converter 30
Valve. The valve body is in the forward flow position shown in FIG.
, The exhaust switching valve 20 is connected to the exhaust pipe 9.
The exhaust pipe 10 and the exhaust pipe 12 are connected to the trachea 11.
And at this time, the exhaust gas is discharged from the exhaust pipe 9 → the exhaust pipe 11 →
Flow in the order of catalytic converter 30 → exhaust pipe 12 → exhaust pipe 10
And released to the atmosphere. In this way, the exhaust gas
Flows from the inlet 30a to the outlet 30b of the data 30
The flow direction is referred to as "forward flow" in the following description. Ma
In addition, the valve body of the exhaust switching valve 20 is located at the backflow position shown in FIG.
During the operation, the exhaust switching valve 20 is connected to the exhaust pipe 9 and the exhaust pipe 1.
2 and the exhaust pipe 10 and the exhaust pipe 11 are connected.
Then, at this time, the exhaust gas is changed from the exhaust pipe 9 to the exhaust pipe 12 to the catalyst core.
It flows in the order of inverter 30 → exhaust pipe 11 → exhaust pipe 10,
Released to the atmosphere. In this way, the exhaust gas is exhausted by the catalytic converter 3
0 Flow from the outlet 30b to the inlet 30a
The direction is referred to as “backflow” in the following description. This exhaust switching valve 20 is connected to an actuator 21
To switch the valve position, and the actuator
The ECU 21 is controlled by the ECU 50. Exhaust switching valve 20
The valve position control will be described later in detail. In the exhaust pipe 11, the catalytic converter 30
Near the inlet 30a, the temperature of the exhaust gas flowing through the exhaust pipe 11
The exhaust temperature sensor outputs an output signal corresponding to the temperature to the ECU 50.
The sensor 13 is attached. The ECU 50 is a digital computer.
ROMs (leads) interconnected by a bidirectional bus
Memory), RAM (random access memory),
CPU (central processor unit), input port
And an output port for controlling the fuel injection amount of the engine 1
In addition to performing basic control such as
The reproduction control of the inverter 30 is performed. For these controls, an input port of the ECU 50 is used.
The input signal from the accelerator opening sensor 14 includes
An input signal from the crank angle sensor 15 is input. A
The accelerator opening sensor 14 outputs an output voltage proportional to the accelerator opening.
The ECU 50 outputs the pressure to the ECU 50, and the ECU 50
The engine load is calculated based on the output signal of the sensor 14.
You. The crank angle sensor 15 has a fixed angle of the crankshaft.
Output pulse to the ECU 50 every time the motor rotates
U50 determines the engine speed based on this output pulse.
Calculate. These engine loads and engine speeds
Thus, the engine operating state is determined. NO stored in catalytic converter 30
The x catalyst 31, that is, the NOx storage reduction catalyst, is made of, for example, aluminum.
Na as a carrier, for example, potassium K, sodium
Alkali such as Na, Li, Cs
Alkali such as metal, barium Ba, calcium Ca
Rare earths such as lithium earth, lanthanum La, yttrium Y
And at least one selected from platinum and precious gold such as platinum Pt
Genus is carried. This NOx catalyst provides an air-fuel ratio (hereinafter referred to as
NOx is absorbed when the exhaust air-fuel ratio is lean.
When the oxygen concentration in the inflow exhaust decreases, the absorbed NOx
Release. Here, the exhaust air-fuel ratio is the NOx catalyst here.
To the exhaust passage, engine combustion chamber, intake passage, etc.
The total amount of air supplied and the sum of fuel (hydrocarbon)
Shall mean the total ratio. Therefore, the NOx catalyst
Fuel, reducing agent or air is supplied into the exhaust passage upstream.
If not, the exhaust air-fuel ratio is supplied to the engine combustion chamber.
The air-fuel ratio of the air-fuel mixture to be used. Mechanism of NOx Absorption and Release Action of NOx Catalyst
Is not clear, but as shown in FIG.
It is thought to be done by a simple mechanism. This mechanic
Pt and barium Ba on the carrier
The following describes the case where the precious metal is
The same method is used when using alkali metals, alkaline earths, and rare earths.
It becomes canism. First, when the inflow exhaust gas becomes considerably lean,
Since the oxygen concentration in the intake and exhaust greatly increases, FIG.
Oxygen O as shown in_TwoIs O_Two ^-Or O^2-In the form of platinum Pt
Attaches to surface. Next, NO contained in the exhaust gas is white
O on the surface of gold Pt_Two ^-Or O ^2-Reacts with NO_TwoBecomes
(2NO + O_Two→ 2NO_Two). Thereafter, the generated NO_TwoIs the NOx catalyst
Unless the NOx absorption capacity is saturated, oxidation on platinum Pt
While moving to Ba and binding with barium oxide BaO,
Nitrate ion NO_Three ^-In the NOx catalyst. this
Thus, NOx is absorbed in the NOx catalyst. On the other hand, the oxygen concentration in the inflow exhaust gas decreases.
NO if_TwoProduction amount is reduced,
Reaction, nitrate ions NO in the NOx catalyst_Three ^-Is
NO_TwoAlternatively, it is released from the NOx catalyst in the form of NO. On the other hand, during the inflow exhaust gas, reduction products such as HC and CO
When these components are present, these components become oxygen O on platinum Pt._Two ^-
Or O^2-Reacts with and oxidizes and consumes oxygen in the exhaust
Reduce the oxygen concentration in the exhaust. Also, the oxygen concentration in the exhaust
NO released from the NOx catalyst_TwoOr N
O reacts with HC and CO as shown in FIG.
Reduced N_TwoBecomes Thus, NO on platinum Pt
_TwoOr, when NO is no longer present, the NOx catalyst
NO to next_TwoOr NO is released. That is, HC and CO in the inflowing exhaust gas are first white.
Oxygen O on gold Pt_Two ^-Or O^2-Reacts immediately with oxidized
And then oxygen O on platinum Pt_Two ^-Or O^2-Is consumed
If HC and CO still remain, this HC and CO
NOx released from the NOx catalyst and from the engine
Exhausted NOx is N_TwoIs reduced to Therefore, the air-fuel ratio of the inflow exhaust gas is
Or stoichiometric absorption into NOx catalyst in a short time
NOx is released, and this released
NOx is released into the atmosphere because NOx is reduced
Can be prevented. By the way, in the case of a diesel engine,
More than stoichiometric (stoichiometric air-fuel ratio, A / F = 13-14)
Normally engine operation because combustion is performed in the lean region
In this state, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is very low.
NOx in the exhaust gas is absorbed by the NOx catalyst,
The amount of NOx released from the Ox catalyst is extremely small. In the case of a gasoline engine, combustion
Make the mixture supplied to the room rich or stoichiometric.
To make the air-fuel ratio of exhaust gas rich or stoichiometric
And reduce the concentration of oxygen in the exhaust gas,
Can release and release absorbed NOx
However, in the case of a diesel engine, supply it to the combustion chamber.
If the mixture is rich or stoichiometric, soot will
Cannot be adopted due to problems such as the occurrence of Therefore, in a diesel engine, N
Before the NOx absorption capacity of the Ox catalyst is saturated,
Fuel directly as a reducing agent separately from the air-fuel mixture for combustion.
Contact with the NOx catalyst to release NOx.
You. Therefore, in this embodiment, the NOx catalyst 31
When the NOx is released, the expansion stroke of the engine 1
Alternatively, sub-inject fuel into the cylinder during the exhaust stroke.
With this, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 31 is reset.
Or stoichiometric. Next, the mechanism of SOx poisoning of the NOx catalyst
Will be described. Exhaust gas contains SOx components
And the NOx catalyst has the same mechanism as the NOx absorption described above.
Absorbs SOx in exhaust gas. That is, the exhaust air-fuel ratio is lean
In the case of oxygen O_TwoIs O_Two ^-Or O^2-NOx catalyst in the form of
SOx adhering to the surface of platinum Pt,
(Eg SO_Two) Is oxidized on the surface of platinum Pt to form SO_Three
Becomes Thereafter, the generated SO_ThreeIs the platinum Pt
Barium oxide moves to Ba while being further oxidized on the surface
Binds to BaO to form sulfate ion SO_Four ^2-In the form of NOx catalyst
To the sulfate BaSO_FourTo form BaSO_FourIs a crystal
Is easy to coarsen and relatively stable.
Is difficult to be decomposed and released. For this reason, over time
BaSO in NOx catalyst_FourNOx increases as the amount of
The amount of BaO that can contribute to the absorption of the catalyst decreases,
Absorption capacity is reduced. Therefore, the NOx catalyst
In order to maintain high NOx purification performance over a long period of time, N
SOx absorbed by the Ox catalyst is released at appropriate timing.
You need to get them out. The SOx absorbed by the NOx catalyst is released.
To achieve a rich or stoichiometric air-fuel ratio
Normal regeneration that releases NOx from the NOx catalyst
It is necessary to make the NOx catalyst temperature higher than
Requires the presence of oxygen. In this embodiment, the NOx catalyst converts SOx
When releasing NOx, similarly to NOx releasing,
In the expansion stroke or exhaust stroke of the engine 1
By sub-injecting the fuel, the fuel flows into the NOx catalyst 31.
The air-fuel ratio of exhaust gas is rich or stoichiometric,
In this embodiment, the fuel injection valve 7 and the sub injection control are performed.
The ECU 50 constitutes a reproducing means. Next, an exhaust gas purifying apparatus according to this embodiment will be described.
The operation of will be described. As described above, the engine 1
Is a diesel engine and has no exhaust air under normal operating conditions
The fuel ratio is lean and the oxygen concentration is high. So this
When the exhaust gas flows through the NOx catalyst 31, NOx in the exhaust gas becomes NO.
x is absorbed by the catalyst 31. Here, in this embodiment, the N
When Ox is absorbed by the NOx catalyst 31, the ECU 50
Executes the fuel injection valve 7 only for the main injection and executes the sub-injection
Control so that the actuator 21 does not
The valve body of the exhaust switching valve 20 is held at the forward flow position shown in FIG.
Control so that As a result, the exhaust of the engine 1 is empty.
Exhaust pipe 9 → exhaust pipe 11 → catalyst converter
Flow in the order of data 30 → exhaust pipe 12 → exhaust pipe 10
At the catalytic converter 30
Exhaust gas flows forward from the inlet 30a toward the outlet 30b
Becomes When the exhaust gas flows in the forward flow, NO
x is the NOx contact on the side near the inlet 30a of the catalytic converter 30.
NO that is absorbed from the medium 31 and is gradually closer to the outlet 30b
The absorption spreads to the x catalyst 31. <NOx Release Processing> The air-fuel ratio lean exhaust gas is
When flowing to the catalytic converter 30 in the forward flow, the catalytic converter
The amount of NOx absorbed by the motor 30 increases and continues as it is.
If so, the NOx absorption capacity is saturated. Therefore,
Before the NOx absorption capacity of the catalytic converter 30 is saturated
At a certain time, the NOx catalyst 31 of the catalytic converter 30
NOx release processing is performed. Here, the NOx release processing is executed.
The predetermined time at which the ECU 50 performs
The operating time of the engine 1 is integrated, and the integrated time
May be reached, or the ECU 50 may emit NOx.
The output amount is integrated, and this integrated discharge amount reaches a predetermined amount.
You may. When the NOx releasing process is executed, EC
U50 controls the fuel injection valve 7 to perform both main injection and sub-injection.
Control, the injection timing and injection period of the sub-injection,
The number of times of the sub injection is controlled. The emissions during this NOx release process
The flow direction of the gas is set to the same forward flow as when NOx is absorbed.
The ECU 50 sets the actuator 21 to the exhaust switching valve.
20 so as to be held at the downstream position shown in FIG.
Control. Sub-injection of fuel during expansion or exhaust stroke
The air-fuel ratio of the exhaust can be rich or stoichiometric.
And the exhaust of this rich or stoichiometric air-fuel ratio
By flowing through the catalytic converter 30, the NOx catalyst 3
The NOx released in the first step is released and reduced,_Twoage
Can be released to the atmosphere. <SOx release processing: poisoning regeneration processing>
At this time, as described above, the NOx catalyst 31
At the same time as absorbing Ox, SOx in the exhaust gas is also absorbed, and SOx
As the amount of absorbed NOx increases, the NOx absorption capacity of the NOx catalyst 31
If the power drops, even if the NOx release process is executed
Cannot recover the initial NOx absorption capacity
turn into. As described above, the NOx catalyst 31
In order to release SOx, a higher touch than when releasing NOx is required.
A medium temperature is required, and in the NOx releasing process, a NOx catalyst is used.
31 cannot release SOx. Therefore, the SOx poisoning of the NOx catalyst 31 is extremely high.
At a predetermined time when it does not go down, the NOx of the catalytic converter 30
A process for releasing SOx from the catalyst 31 is performed. Here, SOx release
The predetermined time for executing the output processing is, for example, ECU
50, the operation time of the engine 1 is integrated.
The time may be a time when a predetermined time is reached, or the ECU 50
SOx emission is integrated from the
It may be when it reaches. High catalyst temperature is required for SOx release treatment
Therefore, the acceleration operation of the engine 1 in which the exhaust gas temperature becomes high
SOx release processing is executed at the time of
Control by the ECU 50, or
Actively increases the exhaust temperature during SOx release processing
The operation state of the engine 1 is controlled by the ECU 50 as described above.
You may. In any case, the ECU 50 uses the NOx catalyst
31 becomes the temperature range suitable for SOx release processing.
The SOx release process is performed. When executing the SOx release process, the EC
U50 controls the fuel injection valve 7 to perform both main injection and sub-injection.
Control, the injection timing and injection period of the sub-injection,
The number of times of the sub injection is controlled. Expansion stroke or exhaust stroke
The air-fuel ratio of exhaust gas is rich
Or become stoichiometric, this rich or stoichiometric
By flowing the air-fuel ratio exhaust to the catalytic converter 30,
To release the SOx absorbed by the NOx catalyst 31,
Originally, SO_TwoTo the atmosphere. In addition, SOx release
When the process is executed, the N2 absorbed in the NOx catalyst 31
Ox is also released and reduced to N_TwoAnd is discharged. By the way, in this exhaust gas purification apparatus, SOx
During the discharge process, the flow of exhaust gas in the catalytic converter 30 is
By performing the flow in two directions, flow and reverse flow, SOx emission
In minutes. In this regard, FIGS. 4 and 5
This will be described with reference to FIG. Catalytic converter before execution of SOx release processing
The distribution state of SOx in the exhaust gas 30 during NOx absorption
Of the catalytic converter 30 because the flow of
The concentration is high at the side close to the mouth 30a (FIG. 4).
(SOx absorption region shown in (A)), outlet 30b
SOx is hardly absorbed by the NOx catalyst 31 on the side. Therefore, in this embodiment, SOx release
At the beginning of the processing, the exhaust gas is caused to flow in a forward flow, and the ECU 50
Shows the actuator 21 and the valve body of the exhaust switching valve 20
Control is performed so as to be maintained at the downstream position shown in FIG. This
In the early stage of the SOx release process,
The reason is that rich or stoichiometric air-fuel containing oxygen
By flowing the exhaust gas of the specific ratio in the forward flow, the SOx absorption region
Reducing agents (HC, CO) and oxygen (O_Two)
In order to promote the release of SOx
You. Thereby, S absorbed in the SOx absorption region
Ox is released from the NOx catalyst 31 and reduced to form SOx._TwoTona
Flows through the catalytic converter 30 toward the outlet 30b.
To go. The SO generated here_TwoMost of the catalyst
It is discharged from the outlet 30a of the barter 30 to the exhaust pipe 12,
Through the air switching valve 20 and the exhaust pipe 10 and finally to the atmosphere.
Will be issued. However, in the catalytic converter 30
As the exhaust approaches the outlet 30b,
Due to the reduction of reducing agent and oxygen, some SO_TwoIs exit 3
NOa near the NOx catalyst 31_ThreeOr H_TwoIn the form of S
It will be reabsorbed. In FIG. 4B, and
The Ox re-absorption region is shown, and S
The SOx concentration is higher in the Ox reabsorption region. Therefore, SOx release processing by forward flow is prescribed.
After the execution of the time, the ECU 50
1 is held at the reverse flow position shown in FIG.
So that the exhaust gas in the catalytic converter 30 is
Reverse the flow direction and continue SOx release processing for a predetermined time
You. As a result, as shown in FIG.
Exhaust with rich or stoichiometric air-fuel ratio
Flow from the outlet 30b side of the
The reducing agent (HC,
CO) and oxygen (O_Two) Is supplied. As a result, the absorption in the SOx re-absorption region and
The collected SOx is released from the NOx catalyst 31 and reduced.
SO_TwoAnd the inside of the catalytic converter 30
Exhaust pipe 11, exhaust switching valve 20, exhaust pipe
And finally to the atmosphere. This regurgitation
SOx in the catalytic converter 30 is almost released and returned by the raw
The distribution of SOx absorption is shown in FIG. 5 (B).
As shown in FIG. As described above, according to this exhaust gas purification apparatus,
The SOx absorbed by the NOx catalyst 31 is reliably and sufficiently released.
Can be discharged and reduced, and as a result, the catalytic converter 3
The NOx absorption capacity of 0 can be sufficiently recovered. In this embodiment, only one
Only by switching the valve positions of the two exhaust switching valves 20,
The flow direction of the exhaust gas flowing through the medium converter 30 is a forward flow and a reverse flow.
Can be switched on, the structure is simple and cheap
You. <Other Embodiments> In the above embodiment,
Indicates that the flow of exhaust gas changes from forward flow to reverse flow during SOx release processing.
Only once, but then the exhaust flow
Switch direction and execute SOx release process by forward flow
Is also good. In this case, as shown in FIG.
SOx remaining in the region can also be released and reduced. Further, in the exhaust gas flow direction of the above-described embodiment,
The order is reversed, and the exhaust gas is discharged early in the SOx release process.
May be made a reverse flow, and then made a forward flow. The above
In this embodiment, the fuel is discharged by sub-injecting fuel into the cylinder.
Although the air-fuel ratio of the air is rich or stoichiometric,
The reducing agent is supplied to the exhaust pipe 9 located upstream of the air switching valve 20.
A device for adding a reducing agent to be added is provided to release NOx and SOx.
During processing, a reducing agent is added to the exhaust gas from the reducing agent addition device.
To make the exhaust air-fuel ratio rich or stoichiometric
May be. In this case, the reducing agent addition device provides the regeneration means.
Constitute. In the above-described embodiment, the internal combustion engine is
Engine, the exhaust gas purification of the internal combustion engine according to the present invention.
The device also applies to lean burn gasoline engines
Can be. In that case, the suction is required to burn in the cylinder.
Make the air-fuel ratio of the incoming mixture rich or stoichiometric.
As a result, the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is reduced.
It can be rich or stoichiometric. [0066] According to the present invention, an exhaust passage of an internal combustion engine is provided.
Exhaust when the air-fuel ratio of the arranged and incoming exhaust is lean
NOx is absorbed and the oxygen concentration of the inflowing exhaust gas decreases.
A NOx storage-reduction catalyst that releases NOx absorbed during
Exhaust gas absorbed by the NOx storage reduction catalyst during NOx absorption
To release SOx in the NOx storage reduction catalyst
Make the air-fuel ratio of the inflowing exhaust rich or stoichiometric
Regeneration means for lowering the oxygen concentration;
In the exhaust gas purification device, the NOx storage reduction catalyst
The flow direction of the exhaust gas is set to the same
Exhaust flow direction switching means for switching in the opposite direction to that during Ox absorption
The exhaust flow direction switching means is provided in the regeneration means.
During the regeneration period, the NOx storage reduction catalyst
To change the flow direction of the exhaust air at least once.
With this configuration, the NOx storage reduction catalyst
To reliably and sufficiently release and reduce the released SOx
NOx absorption of the NOx storage reduction catalyst due to SOx poisoning
It is said that it is possible to surely recover the decline in yield capacity
Excellent effects are achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to an embodiment of the present invention, showing a state where an exhaust switching valve is positioned at a forward flow position. FIG. 2 is a view showing a main part when the exhaust gas switching device is located at a reverse flow position in the exhaust gas purification apparatus of the embodiment. FIG. 3 is a diagram illustrating the NOx absorption / release / reduction action of a storage reduction type NOx catalyst. FIG. 4 is a conceptual diagram when an SOx release process is performed with exhaust gas flowing forward in the exhaust gas purification apparatus of the embodiment. FIG. 5 is a conceptual diagram when SOx release processing is performed in the exhaust gas purifying apparatus of the embodiment with exhaust gas flowing backward. [Description of Signs] 1 Diesel engine (internal combustion engine) 7 Fuel injection valve (regeneration means) 9, 10, 11, 12 Exhaust pipe (exhaust passage) 20 Exhaust switching valve (exhaust flow direction switching means) 31 Storage-reduction NOx catalyst 50 ECU (regeneration means)

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI F01N 3/28 301 F01N 3/28 301C F02D 41/04 355 F02D 41/04 355 (56) References JP-A-7-259542 ( JP, A) JP-A-7-186785 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F01N 3/08-3/36 F02D 41/04

Claims (1)

(57) [Claim 1] When the air-fuel ratio of the inflowing exhaust gas disposed in the exhaust passage of the internal combustion engine is lean, NOx in the exhaust gas is absorbed and the oxygen concentration of the inflowing exhaust gas decreases. NO absorbed in
a NOx storage-reduction type NOx catalyst that releases x,
A regenerating means for reducing the oxygen concentration by enriching or stoichiometric the air-fuel ratio of the inflowing exhaust gas when the SOx in the exhaust gas absorbed by the Ox catalyst at the time of NOx absorption is released from the NOx storage reduction catalyst. In the exhaust gas purification apparatus, the flow direction of the exhaust gas flowing through the NOx storage reduction catalyst is set to N.
Exhaust flow direction switching means for switching in the same direction as when absorbing Ox or in the opposite direction when NOx is absorbed, and the exhaust flow direction switching means is configured to control the exhaust gas flowing through the NOx storage reduction catalyst during the regeneration period by the regeneration means. An exhaust gas purifying apparatus for an internal combustion engine, wherein the flow direction of the exhaust gas is changed at least once.