JPH06272541A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To simply perform operation of detoxication of an NOX absorbent caused by SOX. CONSTITUTION:A particulate filter 10 is disposed in an exhaust path 6 of a diesel engine body 2 and constituted to carry an NOX absorbent. After particulates collected in the particulate filter are burnt, a throttle valve 8 is closed and a reducing agent is supplied from a reducing agent supply device 12 to the particulate filter. Since the NOX absorbent is heated by heat generated in the burning of the particulates to a high temperature, the NOX absorbent is placed under the high temperature and rich atmosphere to rapidly dissolve damages poisened by SOX.

Description

Detailed Description of the Invention

[0001]

Relates to an exhaust purifying apparatus of the present invention is an internal combustion engine BACKGROUND OF THE relates effectively removable exhaust purification apparatus NO _X components contained in the exhaust of diesel engines in particular.

[0002]

2. Description of the Related Art Japanese Unexamined Patent Publication No. 62-106826 discloses
Air-fuel ratio of the exhaust gas is arranged _the NO _X absorbent to the oxygen concentration in the exhaust gas absorbs the NO _X when the lean releasing NO _X absorbed and reduced in the exhaust passage of the diesel engine, the _the NO _X absorbent Absorbs NO _x in the exhaust gas,
O absorption efficiency of _X absorbent shut off the flow of exhaust when the reduced supply the reducing agent to the NO _X absorbent was released with the release of NO _X absorbed from _the NO _X absorbent NO
An exhaust gas purification device for an internal combustion engine that performs reduction purification of _X is disclosed.

Further, in order to prevent the exhaust particulates (particulates) contained in the exhaust of the diesel engine from being released into the atmosphere, a particulate filter is arranged in the exhaust passage of the diesel engine to collect the particulates in the exhaust. It is known.

[0004]

SUMMARY OF THE INVENTION An object of _the NO _X absorbent absorbs NO _X in the exhaust gas of a lean air-fuel ratio as described above, the oxygen concentration in the exhaust gas to release NO _X absorbed and reduced N
It acts to absorb and release O _X. Although this absorption and desorption action will be described in detail later, when sulfur oxide (SO _x ) is present in the exhaust gas, the NO _x absorbent absorbs the SO _x in the exhaust gas by the same mechanism as the absorption action of the NO _x. I do.

However, NO_XSO absorbed by absorbent
_XIs generally decomposed and released to form a stable sulfate.
Difficult, NO_XIt tends to accumulate in the absorbent.
NO _XSO in absorbent_XWhen the accumulated amount increases, NO_XSucking
NO of collecting agent_XNO in exhaust gas due to reduced absorption capacity_XRemoval of
Can not be performed sufficiently, so NO_XPurifying effect of
So-called SO whose rate decreases_XThere is a problem of poisoning.
In particular, light oil containing a relatively large amount of sulfur is used as fuel
This diesel engine has a SO_XQuestion of poisoning
Subject is likely to occur.

On the other hand, it is known that SO _X absorbed in a NO _X absorbent can be released and reduced and purified by the same mechanism as NO _X is released and reduced and purified. However, since the sulfate accumulated in the NO _X absorbent is relatively stable as described above, normal NO _X release and reduction purification operations (hereinafter referred to as “NO _X absorbent regeneration operation”) are performed. It is difficult to release the SO _X absorbed in the NO _X absorbent at a temperature (for example, about 250 ° C. or higher). Therefore, in order to eliminate SO _X poisoning, NO _X
The absorbent should be heated to a higher temperature (eg 500
It is necessary to periodically perform a poisoning elimination operation for increasing the air-fuel ratio of the inflowing exhaust gas to a high temperature (C or more).

Therefore, in a diesel engine or the like having a relatively low exhaust temperature, heating means such as an electric heater and a burner are provided for SO _X poisoning elimination operation, and the NO _X absorbent is heated to a temperature higher than usual at regular intervals. Therefore, there has been a problem that the installation of the heating means increases the cost of the apparatus and increases the fuel consumption due to the energy required for heating. In view of the above problems, it is an object of the present invention to provide an exhaust gas purification device for an internal combustion engine, which can easily perform SO _X poisoning elimination operation of a NO _X absorbent without providing special heating means.

[0008]

According to the present invention, inflow and outflow
NO when the air-fuel ratio is lean_XAbsorbs the
NO absorbed when the oxygen concentration decreased_XReleasing N
O_XPlace the absorbent in the exhaust passage of the diesel engine
NO in the exhaust_XAbsorbed, NO_XNO after absorption_X
When the exhaust air-fuel ratio flowing into the absorbent is made rich, the NO_X
NO absorbed from the absorbent_XIs released and released
NO_XIn the exhaust purification device for reducing and purifying
NO_XParticulates that collect particulates in the absorbent and exhaust
The heat filter and the heat
O_XThe exhaust air-fuel ratio flowing into the absorbent is made rich and the N
O_XRelease and reduction purification, and then the particulate
Burns the particulates collected by the air filter.
After the particulate burning operation is completed, the N
O_XThe exhaust air-fuel ratio flowing into the absorbent is made rich and NO _X
Absorbent SO_XInternal combustion engine characterized by eliminating poisoning
An exhaust purification device of Seki is provided.

[0009]

When the exhaust air-fuel ratio flowing into _the NO _X absorbent [action] becomes rich, the absorbed NO _X is released oxygen concentration in the exhaust gas decreases rapidly in the NO _X absorbent, unburned HC components in the exhaust Reacts with and is purified by reduction. Next, the exhaust air-fuel ratio is made lean, and the particulate matter collected by the particulate filter is burned, and the particulate filter becomes high in temperature. Since the NO _x absorbent and the particulate filter are arranged at positions where heat can be mutually transferred,
In this case _the NO _X absorbent becomes high. Generally the NO _X absorbent becomes so NO _X is released from _the NO _X absorbent in lean atmosphere becomes a high temperature, the combustion of the particulates is performed after completion of NO _X release of the NO _X absorbent, particulate during combustion NO _X is NO _X unpurified not released is prevented from being released into the atmosphere.

Next, when the combustion of particulates is completed, the exhaust air-fuel ratio is made rich again. Therefore, NO
_{The X} absorbent becomes a high temperature and rich atmosphere condition, SO _X is released from the NO _X absorbent, and SO _X poisoning is eliminated.

[0011]

FIG. 1 shows a first embodiment of the present invention. In FIG. 1, 2 is a diesel engine, 4 is an intake passage, and 6 is an exhaust passage. An intake throttle valve 8 is provided in the intake passage 4, and the intake throttle valve 8 is normally fully opened. The intake throttle valve 8 is closed when the NO _x absorbent is regenerated as described later, and The intake air amount is throttled to reduce the exhaust flow rate flowing into the NO _X absorbent. This reduces the amount of reducing agent required to consume oxygen in the exhaust gas and reduce the oxygen concentration in the NO _x absorbent atmosphere. Reference numeral 16 in the drawing denotes an actuator of an appropriate type such as a solenoid for driving the intake throttle valve 8 or a negative pressure actuator.

A particulate filter 10 is arranged in the exhaust passage 6. Reference numeral 12 is a NO to supply the reducing agent to the exhaust passage 6 on the upstream side of the particulate filter 10.
_{This is} a reducing agent supply device for making the exhaust air-fuel ratio flowing into the _X absorbent rich. In this embodiment, the fuel of the diesel engine 2 is used as the reducing agent, and the reducing agent supply device 12 is provided with a nozzle that atomizes the fuel supplied from the engine fuel system into the exhaust passage 6.

The particulate filter 10 and the reducing agent are used together.
An exhaust gas temperature sensor 14 is provided in the exhaust passage 6 between the supply device 12.
The detection signal of the exhaust temperature sensor 14 is electronically controlled.
It is input to the unit (ECU) 30. The ECU 30
CPU (central processing unit), RAM (random access memory)
Memory), ROM (Read Only Memory), I / O port
A digital computer of a known type in which
The basic control system of the engine such as fuel injection amount control.
In addition to the control, in this embodiment, NO_XRegeneration of absorbent, patty
Curate burning, NO _XAbsorbent SO_XSuch as elimination of poisoning
It also controls. For these controls, the ECU 30
Is an actuator 16 that drives the intake throttle valve 8, and
And the reducing agent supply device 12 are controlled to open / close the intake throttle valve 8.
And adjusting the supply of the reducing agent from the reducing agent supply device 12.
U

FIG. 2 shows an enlarged sectional view of the particulate filter 10. Referring to FIG. 2, the particulate filter 10 is made of a porous ceramic, and exhaust gas flows from left to right in the figure as indicated by an arrow. Inside the particulate filter 10, the first passages 22 having the plugs 18 on the upstream side and the second passages 24 having the plugs 20 on the downstream side are alternately arranged to form a honeycomb shape. When the exhaust gas flows from the left to the right in the figure, the exhaust gas passes from the second passage 24 through the flow passage wall surface of the porous ceramic, flows into the first passage 22, and flows downstream. At this time, the particulates in the exhaust gas are captured by the porous ceramic, and the particulates are prevented from being released to the atmosphere.

A NO _x absorbent 26 is carried on the wall surfaces of the first and second passages 22 and 24. The NO _x absorbent 26 is, for example, potassium K, sodium Na, lithium Li, an alkali metal such as cesium Cs, or barium B.
a, alkaline earth such as calcium Ca, lanthanum L
a, at least one selected from rare earths such as yttrium Y, and a noble metal such as platinum Pt. NO
_X absorbent 26 absorbs NO _X when the air-fuel ratio of the inflowing exhaust gas is lean, perform absorption and release action of the NO _X that releases NO _X concentration of oxygen absorbed to decrease in the inflowing exhaust gas.

Since a diesel engine is used in this embodiment, the exhaust air-fuel ratio at normal times is lean and NO.
_{The X} absorbent 26 absorbs NO _{X in} the exhaust gas. Further, when the reducing agent is supplied from the reducing agent device 12 to the exhaust passage on the upstream side of the particulate filter 10 and the air-fuel ratio of the inflowing exhaust gas becomes rich, the NO _X absorbent 26 releases the absorbed NO _X.

The detailed mechanism of this absorption / release action is not clear in some parts. However, it is considered that this absorbing and releasing action is performed by the mechanism shown in FIG. Next, this mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

That is, the inflowing exhaust gas becomes considerably lean.
And the oxygen concentration in the inflowing exhaust gas increased significantly,
As shown in (A), these oxygen O₂Is O₂ ^-Or
O^2-It adheres to the surface of platinum Pt in the form of. On the other hand, inflow exhaust
NO in the gas is O on the surface of platinum Pt.₂ ^-Or O^2-When
Reacts, NO₂Becomes (2NO + O₂→ 2 NO₂). Next
NO generated by₂Is partially oxidized on platinum Pt.
While being NO_XBarium oxide B absorbed in the absorbent 26
As shown in FIG. 3 (A), nitric acid binds with aO.
Ionic NO₃ ^-In the form of NO_XIt diffuses into the absorbent 26.
NO in this way _XIs NO_XAbsorbed in the absorbent 26
It

Platinum as long as the oxygen concentration in the inflowing exhaust gas is high
NO on the surface of Pt₂Is generated and NO_XAbsorbent 26 N
O_XNO unless the absorption capacity is saturated₂Is NO_XAbsorbent 2
Nitrate ion NO absorbed in 6₃ ^-Is generated. This
On the other hand, the oxygen concentration in the inflowing exhaust gas decreases and NO₂
If the production amount of₃ ^-→ N
O ₂), And thus NO_XIo nitrate in the absorbent 26
No₃ ^-Is NO₂Is released from the absorbent in the form of. Immediately
If the oxygen concentration in the inflowing exhaust gas decreases, NO_Xabsorption
Agent 26 to NO_XWill be released. Inflow exhaust gas
If the leanness of the air becomes low, the oxygen in the inflowing exhaust gas
The concentration is reduced and therefore the leanness of the incoming exhaust gas
NO if lowered_XAbsorbent 26 to NO_XIs released
Becomes

On the other hand, at this time, the air-fuel ratio of the inflowing exhaust gas is
HC and CO are oxygen O on platinum Pt.₂ ^-Well
Or O^2-It reacts with and is oxidized. Also the inflow exhaust
When the air-fuel ratio of the gas is made rich, the oxygen concentration in the inflowing exhaust gas is increased.
NO because the degree is extremely low_XAbsorbent 26 to NO₂
Is released and this NO₂As shown in FIG.
It reacts with unburned HC and CO and is reduced and purified. this
NO on the surface of platinum Pt₂Disappears
And NO_XNO one after another from the absorbent 26₂Is released
It Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, it will be
NO in the meantime _XAbsorbent 26 to NO_XIs released and returned
The original will be purified.

The air-fuel ratio of exhaust gas referred to here is NO _x.
It means the ratio of the air and the fuel supplied to the exhaust passage 6 on the upstream side of the absorbent 26 and the engine combustion chamber or the intake passage. Therefore, when air or a reducing agent is not supplied to the exhaust passage 6, the exhaust air-fuel ratio becomes equal to the operating air-fuel ratio of the engine (the combustion air-fuel ratio in the engine combustion chamber). Further, the reducing agent used in the present invention may be one that generates a reducing component such as hydrocarbon or carbon monoxide in the exhaust gas, and a gas such as hydrogen or carbon monoxide, propane, propylene, butane or the like. Liquid or gaseous hydrocarbons, liquid fuels such as gasoline, light oil, kerosene, etc. can be used, but in the present embodiment, as described above, light oil, which is the fuel of the diesel engine 2, is used to avoid complexity during storage, replenishment, etc. Is used as a reducing agent.

Next, NO_XAbsorbent SO_XPoisoned mechanics
I will explain about. SO during exhaust _XContains ingredients
Then NO_XAbsorbent is NO above_XSame mechanism as absorption of
SO in the exhaust_XAbsorbs. That is, exhaust air-fuel
SO in the exhaust when the ratio is lean_X(Eg SO₂) Is
SO oxidized by platinum Pt₃ ^-, SO_Four ^-And then acid
BaSO combined with BaO_FourTo form. B
aSO_FourIs relatively stable, and the crystals become coarse.
Once produced, it is difficult to decompose and release due to rinsing. others
No_XBaSO in the absorbent_FourWhen the production of
NO_XThe amount of BaO that can be involved in the absorption of
NO_XAbsorbs less. This SO_XPoisoning
NO to solve_XBaS formed in the absorbent
O_FourGenerated at the same time as decomposing at high temperature
SO₃ ^-, SO_Four ^-Sulfate ions in a rich atmosphere
Original, gaseous SO₂Convert to NO_XRelease from absorbent
Need to let. Therefore SO_XTo eliminate poisoning
Is NO_XPut the absorbent in a high temperature and rich atmosphere
Is needed.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 4 is a flowchart showing a control routine for SO _X poisoning elimination operation of the NO _X absorbent 26. This routine is executed by the ECU 30 by interruption at regular intervals. Referring to FIG. 4, first, step 40
Then, it is determined whether or not the conditions for executing the release of NO _X from the NO _X absorbent 26 and the reduction purification operation (regeneration operation) are satisfied. The NO _X absorbent regeneration start condition is, for example, that the vehicle is decelerating, that the NO _X absorbent 26 is at the activation temperature or higher, and that a predetermined time or more has passed since the previous regeneration was executed. When it is determined that the NO _X absorbent regeneration start condition is not satisfied, the routine proceeds to step 42, where the intake throttle valve 8 is opened, and at step 44, the fuel supply from the reducing agent supply device 12 is prohibited.

On the other hand, when the NO _X absorbent regeneration start condition is satisfied in step 40, the routine proceeds to step 46, where N
Elapsed time T from when the conditions for starting regeneration of the O _X absorbent are satisfied
There is judged whether the first or the time T ₁ is less than a predetermined. The first time T ₁ is the time required to regenerate the NO _X absorbent 26. If T <T ₁ , step 4
8 and the intake throttle valve 8 is closed. As a result, the amount of air flowing into the particulate filter 10 is reduced. Next, at step 50, the fuel is supplied from the reducing agent supply device 12. The supplied fuel is NO _x absorbent 26
Oxygen in the exhaust gas is consumed by burning due to the catalytic action of. For this reason, the oxygen concentration in the exhaust gas in the particulate filter 10 is extremely reduced, and the air-fuel ratio of the exhaust gas becomes rich. Thereby, as described above, NO _X from _the NO _X absorbent 26 is released, the released NO _X
Will be reduced and purified.

Next, when it is judged at step 46 that T ≧ T ₁ , that is, when the regeneration of the NO _x absorbent 26 is completed, the routine proceeds to step 52, where the elapsed time T
There is judged whether or not the second or the time T ₂ is less than a predetermined. T ₂ is a value larger than T ₁ , and T ₂ −T
₁ is the time required to burn the particulates collected by the particulate filter 10. T
If <T ₂ , that is, if it is within the combustion time, the routine proceeds to step 54, where the intake throttle valve 8 is opened. As a result, a large amount of air flows into the particulate filter 10. Next, in step 56, the reducing agent supply device 1
Fuel for ignition is supplied from 2 and burned. As a result, the particulates collected by the particulate filter 10 are ignited and burned. Although not shown, if an auxiliary heating means such as an electric heater is provided on the upstream side of the particulate filter 10 and the particulate filter 10 is heated for a certain period of time after the completion of regeneration of the NO _X absorbent, the particulate filter 10 can be heated. Ignition is accelerated.

Next, at step 52, T ≧ T₂Is determined
If, i.e., the burning of particulates is completed
In this case, the process proceeds to step 58 where the elapsed time T is the third
Time T₃It is determined whether or not it is smaller. T₃Is T₂
Greater value, T₃-T₂Is NO_XAbsorbent 26
SO_XThis is the time required to eliminate poisoning. T <T
₃, Ie SO_XWithin the poisoning elimination operation time
Proceeds to step 60, the intake throttle valve 8 is closed again, and
From the reducing agent supply device 12 at step 62 to SO_XFor eliminating poisoning
Fuel is supplied. As a result, NO_XThe absorbent 26
NO in high temperature and rich atmosphere_XAbsorbent 26
Absorbed by SO_XIs SO₂In the form of NO _XRelease from absorbent
Will be issued.

When it is judged at step 58 that T ≧ T ₃ , that is, when the SO _X poisoning elimination operation is completed, the routine proceeds to step 42, where the intake throttle valve 8 is opened, and at step 44 the reduction is performed. Fuel supply from the agent supply device 12 is prohibited. As a result, the NO _X absorbent 26 absorbs the NO _{X in} the exhaust gas again. As described above, according to this embodiment,
The NO _X absorbent 26 is carried on the particulate filter, the NO _X absorbent is regenerated, the particulates are burned, and then the SO _X of the NO _X absorbent is burned.
Since the poisoning elimination operation is performed, the following effects can be obtained.

Collected by the particulate filter 10
By burning the particulates,
NO carried on the filter 10_XThe absorbent 26
NO due to high temperature_XSO of absorbent 26_XPoison elimination operation
No separate heating means for production_XAdd absorbent 26
No need to heat up heat easily_XAbsorbent SO _X
Poisoning elimination operation can be performed. Also, SO_XPoisoning
The heat generated by the burning of particulates during the extinguishing operation
Use NO_XNO to heat the absorbent_XAbsorbent
Significantly reduces energy supplied from the outside for heating
You can

Further, _the NO _X absorbent by heat during particulate combustion because it so as to burn the particulates after the regenerating operation of the NO _X absorbent 26 26
Absorbed NO _X can be prevented from being released into the atmosphere, further, NO _X fuel supplied to the playback operation of the absorbent 26 is of the particulate filter 10 is burned on _the NO _X absorbent 26 Since the temperature rises, the temperature of the particulates trapped in the particulate filter 10 rises, which facilitates the ignition and combustion of the particulates.

Although the NO _x absorbent is carried on the wall surface of the exhaust passage in the particulate filter in this embodiment, the NO _x absorbent and the particulate filter may be separately provided. In this case, a particulate filter is arranged on the upstream side of the NO _X absorbent so that the heat generated by the particulate filter at the time of particulate combustion can be efficiently transferred to the NO _X absorbent.

Next, a second embodiment of the present invention will be described with reference to FIG. In the embodiment of FIG. 1, the intake throttle valve 8 is closed to reduce the intake air amount of the engine at the time of regeneration of the NO _X absorbent and SO _X poisoning elimination operation, and the exhaust flow rate flowing into the NO _X absorbent (particulate filter) is controlled. The amount of the reducing agent required to consume the oxygen in the exhaust gas is reduced by decreasing the amount. For this reason, regeneration of NO _X absorbent, SO _X
The engine output will decrease during the poisoning elimination operation. For this reason, these operations must be performed under limited operating conditions (for example, conditions such as engine braking that do not affect the operation even when the engine output decreases), and NO _x absorbent regeneration at any time. And SO _X poisoning elimination operation cannot be performed.

In the embodiment shown in FIG. 5, NO_XCarrying absorbent
Place two particulate filters in parallel with the exhaust pipe.
Put, and NO one by one_XShut off the exhaust flowing into the absorbent
NO _XRegeneration of absorbent and SO_XPerform poisoning elimination operation. this
One of the NO_XThe other side during the regeneration operation of the absorbent
NO_XCan be operated by switching the exhaust flow to the absorbent
Therefore, it is not necessary to throttle the exhaust flow rate as a whole
It does not cause weakness. Therefore, it may depend on operating conditions.
NO at any time_XPerform operations such as regeneration of absorbent
It becomes possible.

In FIG. 5, 6 is an engine (not shown).
Exhaust pipes 6a, 6b are branch passages of the exhaust pipe 6, 10a,
10b is a particulate filter disposed in the branch passages 6a and 6b, and 9a and 9b are branch passages 6a and 6b, respectively.
b of the particulate filters 10a and 10b, cutoff valves provided on the upstream side, and 91a and 91b are cutoff valves 9a and 9b.
It is an actuator of an appropriate type such as a solenoid for driving a. Also in this embodiment, each of the particulate filters 10a and 10b has a structure in which the NO _x absorbent is carried similarly to the embodiment of FIG.

Further, in the present embodiment, the reducing agent supply device 12 is provided with the particulate filters 10a and 10 respectively.
Injection nozzles 12a and 12b for supplying a reducing agent (fuel) are provided in the branch passages 6a and 6b on the upstream side of b. Further, in this embodiment, a secondary air supply device 11 that supplies secondary air to the branch passages 6a and 6b between the shutoff valves 9a and 9b and the particulate filters 10a and 10b is provided. The secondary air supply device 11 is provided with an air supply source 11c such as an air pump and nozzles 11a and 11b for supplying air to the branch passages 6a and 6b, respectively, and a particulate filter 10a according to a control signal from an ECU 30 described later,
Supply secondary air to 10b.

Further, in the present embodiment, the branch passage 6a, for judging whether or not the regeneration operation of the particulate filter is necessary,
A back pressure sensor 21 that detects the exhaust pressure in the exhaust pipe 6 is provided in the exhaust pipe 6 on the upstream side of 6b. Further, an exhaust gas temperature sensor 2 for detecting the exhaust gas temperature is provided in the branch passages 6a, 6b on the downstream side of the particulate filters 10a, 10b.
3a and 23b, and an oxygen concentration sensor 2 that detects the oxygen concentration in the exhaust gas and generates a continuous output signal according to the oxygen concentration.
5a and 25b are arranged respectively.

The input port of the electronic control unit (ECU) 30 has a back pressure sensor 21 and an exhaust temperature sensor 23.
Output signals from the sensors a, 23b and the oxygen concentration sensors 25a, 25b are respectively input through an A / D converter (not shown), and signals such as engine speed are also input by a sensor (not shown). Further, the output port of the ECU 30 is connected to the actuators 91a and 91b of the shutoff valves 9a and 9b, the nozzles 12a and 12b of the reducing agent supply device 12, the air pump 11c and the nozzles 11a and 11b of the secondary air supply device 11 through a drive circuit (not shown). Each is connected and controls these operations.

In the present embodiment, one of the normal-time cutoff valves 9a and 9b (for example, the cutoff valve 9a) closes the branch passage (for example, the branch passage 6a), and substantially the entire amount of exhaust gas is discharged to the other particulate filter (10b). Then, the one particulate filter absorbs NO _X and collects the particulates. Further, NO in _the NO _X absorbent on the particulate filter are subjected to absorption of NO _X (10b)
_{When the} amount of absorbed _X increases, the shut-off valve is switched to guide almost all of the exhaust gas to the particulate filter (6a, 10a) in the other branch passage to absorb NO _X and collect the particulates. , The reducing agent is supplied to the particulate filter (10b) having increased NO _X absorption amount to regenerate the NO _X absorbent.

When the ECU 30 detects from the output of the back pressure sensor 21 that the exhaust resistance of the particulate filter in use has increased, the shut-off valve is closed after the NO _x absorbent regeneration operation of this particulate filter is executed. As it is, the secondary air is supplied from the secondary air supply device 11 to the particulate filter, so that the particulates collected in the particulate filter are subsequently burned.

Further, when the combustion of particulates is completed, the shutoff valve is closed and the supply of the reducing agent is maintained, and the supply of the secondary air is stopped. Thus _the NO _X absorbent carried on the particulate filter SO _X is released from _the NO _X absorbent to be placed in a high temperature and rich atmosphere SO _X
Poisoning disappears. FIG. 6 is a flowchart showing the SO _X poisoning elimination operation of the NO _X absorbent. This routine is ECU
30 is executed at regular intervals.

When the routine starts in FIG. 6,
In step 601, it is judged whether or not the conditions for starting the regeneration operation of the NO _x absorbent of the particulate filter currently used are satisfied. Regeneration of _the NO _X absorbent engine exhaust temperature is equal to or higher than a predetermined value (i.e., _the NO _X absorbent is higher than a predetermined activation temperature) is, and _the NO _X absorbent usage time (NO _X absorption amount) exceeds a predetermined value (e.g. If reaches about 1 to 3 minutes) (i.e., NO _X absorption of the NO _X absorbent during use is executed when) that is a predetermined amount or more.

When the condition for starting the NO _x absorbent regeneration operation is satisfied in step 601, the shut-off valves 9a and 9b are switched in step 603 to close the branch passage of the particulate filter on the regeneration operation side. . This allows
Almost all of the exhaust gas flows to the other branch passage, and only the exhaust gas flow amount corresponding to the leak flow amount when the shutoff valve is fully closed flows to the particulate filter on the regeneration side. Next, at step 605, the reducing agent supply device 12 supplies the fuel to the particulate filter on the side where the regeneration operation is performed.
Thus, the fuel is combusted on _the NO _X absorbent carried on the particulate filter, it is consumed oxygen in the exhaust around of the NO _X absorbent, the reduction purification and release of the NO _X from _the NO _X absorbent As it is performed, the temperature of the particulate filter carrying the NO _X absorbent rises due to combustion.

Next, at step 607, the condition for ending the regeneration operation of the NO _X absorbent is judged. In the regeneration operation of the NO _x absorbent, the exhaust oxygen concentration detected by the oxygen concentration sensor (25a or 25b) on the downstream side of the particulate filter during the regeneration operation is equal to or lower than a predetermined value (approximately zero) (during exhaust). When a predetermined time (for example, several seconds to several tens of seconds) has passed from the state where all the oxygen was consumed), the process ends.

When it is determined in step 607 that the NO _X absorbent regeneration operation has ended, it is determined in step 609 whether or not the particulate filter regeneration operation must be performed simultaneously. The regeneration operation of the particulate filter is performed by the back pressure sensor 21 before starting the regeneration of the NO _X absorbent.
Exhaust pressure read from the specified value (engine speed,
It is determined by whether or not it is a value set in advance according to the load or the like.

When it is determined in step 609 that the particulate filter regeneration operation is not necessary, the fuel supply from the reducing agent supply device 12 is stopped in step 621, and the cutoff valves 9a and 9b are maintained as they are. After the regeneration, the NO _X absorbent is put on standby. Step 6
If it is judged at 09 that the particulate filter regeneration operation is necessary, then the particulate filter regeneration operation in steps 611 to 615 is performed. That is, in step 611, the amount of fuel supplied from the reducing agent supply device 12 is increased, and in step 613, a predetermined amount of secondary air (for example, about 50 liters / minute) is supplied from the secondary air supply device 11 to the particulate filter. Supplied. As a result, the particulates collected by the particulate filter are ignited and burned.

Next, at step 615, it is judged if the combustion of particulates has ended. In this embodiment, when steps 611 and 613 are started and a predetermined time (for example, about 8 minutes) has elapsed, it is determined that the particulates have been burned, and step 617 is continued.
To 619 SO _x poisoning elimination operation is executed. That is, in step 617, the secondary air supply from the secondary air supply device 11 is stopped while the fully closed state of the shutoff valve and the reducing agent supply amount from the reducing agent supply device 12 are maintained. As described above, in this state, the NO _x absorbent carried on the particulate filter is at a high temperature (500 ° C. or higher) due to the combustion of particulates, and the shutoff valve is fully closed and the reducing agent supply amount is maintained. temperature and _the NO _X absorbent than significantly during playback operation of normal of the NO _X absorbent by stopped while the supply of secondary air will be placed in a rich atmosphere. Therefore, SO _X absorbed by the NO _X absorbent is S
Is rapidly released from _the NO _X absorbent in the form of O _2, NO _X
SO _X poisoning of the absorbent is eliminated.

Next, at step 619, it is judged if the SO _X poisoning elimination operation is completed. In the present embodiment, it is determined that SO _X poisoning has been eliminated when a predetermined time (for example, several seconds to several tens of seconds) has elapsed since the poisoning elimination operation of step 617 was started, and in step 621 the shutoff valve 9a,
The supply of the reducing agent is stopped while maintaining the state of 9b.
As a result, the particulate filter that has completed the regeneration of the NO _X absorbent, the SO _X poisoning elimination, and the burning of the particulates is held in the standby state.

In the present embodiment, SO _X poisoning can be eliminated without throttling the exhaust flow rate of the engine itself, so the S of NO _X absorbent is not affected by operating conditions.
O _X poisoning elimination operation can be performed, and the absorption capacity of the NO _X absorbent can be constantly maintained at a high level. Also,
As in the embodiment of FIG. 1, since the SO _X poisoning elimination operation is performed after burning the particulates collected by the particulate filter, it is not necessary to provide a special heating means for SO _X poisoning elimination, and it is easy to perform. It is possible to obtain the same effect as that of the embodiment of FIG. 1 that can eliminate SO _X poisoning.

[0048]

According to the present invention, _the NO _X absorbent to be able to utilize the heat generated during the combustion of particulates trapped in the particulate filter in SO _X poisoning recovery of the NO _X absorbent and placing the particulate filter to another heat transfer possible positions, by which to perform the sO _X poisoning removing operation of the NO _X absorbent after the burning of particulates trapped in the particulate filter , it is possible to eliminate the sO _X poisoning simple in _the NO _X absorbent without providing any special heating means for sO _X poisoning recovery operation, heating _the NO _X absorbent when sO _X poisoning recovery operation Therefore, it is possible to significantly reduce the energy supplied from the outside.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of the particulate filter 10.

FIG. 3 is a diagram for explaining the action of NO _X absorption and release.

4 is a flow chart showing a SO _X poisoning elimination operation of the NO _X absorbent of the embodiment of FIG.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a flowchart showing a SO _X poisoning elimination operation of the NO _X absorbent of the embodiment of FIG.

[Explanation of symbols]

2 ... Diesel engine 6 ... Exhaust passage 8 ... Intake throttle valve 9a, 9b ... Exhaust cutoff valve 10 ... Particulate filter 11 ... Secondary air supply device 12 ... Reductant supply device 26 ... NO _X absorbent

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location F01N 3/24 ZAB ER F02D 41/04 305 Z 8011-3G 43/00 301 T 7536-3G E 7536-3G

Claims (1)

[Claims] 1. NO when the air-fuel ratio of the inflowing exhaust gas is lean
_XAbsorbed when the oxygen concentration in the exhaust gas decreases
NO_XReleases NO_XAbsorbent diesel engine
Placed in the exhaust passage of the NO in the exhaust_XAbsorbed, NO
_XNO after absorption_XThe exhaust air-fuel ratio flowing into the absorbent is
The above NO_XNO absorbed from the absorbent_XEmit
NO released_XExhaust purification to reduce and purify
In the gasification device, the NO_XAbsorbent and particulates in the exhaust
Heat transfer between the collecting particulate filter and each other
Place it in an effective position, NO_XExhaust air-fuel ratio flowing into the absorbent
Enriched with NO_XRelease and reduction purification,
After the particulates collected by the particulate filter
This particulate burning operation to burn the curate
After the end, the NO again_XThe exhaust air-fuel ratio flowing into the absorbent
Rich and NO _XAbsorbent SO_XEliminate poisoning
An exhaust emission control device for an internal combustion engine, characterized by: