JPH11257051A - Device for reclaiming catalyst poisoning in internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent SOx released from SOx absorbent from being absorbed into NOx absorbent. SOLUTION: A NOx absorbent 17 is disposed within an exhaust passage for absorbing NOx when the air/fuel ratio of inflowing exhaust gas is lean, and for releasing the absorbed NOx when the concentration COX of oxygen in the exhaust gas becomes lower. A SOx absorbent 14 is disposed upstream of the NOx absorbent 17 within the exhaust passage for absorbing SOx when the air-fuel ratio of inflowing exhaust gas is lean, and for releasing the absorbed SOx when the oxygen concentration of the exhaust gas becomes lower and the temperature becomes higher than the temperature at the start of releasing. In order to release SOx from the SOx absorbent 14, the temperature of SOx absorbent 14 is maintained to be lower than the temperature at the start of releasing while making the oxygen concentration COX lower than the non- absorption concentration. Then the temperature of the SOx absorbent 14 is made higher than the temperature at the start of releasing while keeping the oxygen concentration COX to be lower than the non-absorption concentration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst poisoning regeneration apparatus for an internal combustion engine.

[0002]

2. Description of the Related Art The ratio of the total amount of air to the total amount of fuel and the total amount of reducing agent supplied into an exhaust passage, a combustion chamber, and an intake passage upstream of a certain position in an exhaust passage flows through the position. when referred to as air-fuel ratio of the exhaust gas, conventionally, in an internal combustion engine which is adapted allowed to combust a lean air-fuel mixture, air-fuel ratio of the exhaust flowing absorbs NO _X when the lean,
N that is absorbed when the oxygen concentration in the inflowing exhaust gas decreases
The _the NO _X absorbent to release the O _X disposed engine exhaust passage, NO _X absorbing temporary air-fuel ratio of the exhaust gas flowing into the agent release the NO _X that is absorbed from _the NO _X absorbent to a rich 2. Description of the Related Art An internal combustion engine is known which reduces the released NO _X while causing the exhaust gas to be reduced.

[0003] However since in the lubricating oil of the fuel and the engine contains sulfur content, the exhaust contains sulfur component, NO _X with NO _X in the sulfur also eg SO ₄ ^2-form Absorbed by absorbent. However not released from _the NO _X absorbent even if the air-fuel ratio of exhaust gas flowing into the sulfur content is _the NO _X absorbent simply rich, therefore the amount of sulfur in _the NO _X absorbent to be increased gradually Become. However the amount of the NO _X when the amount of sulfur in the absorbent increases _the NO _X absorbent can absorb NO _X is reduced gradually, finally _the NO _X absorbent can hardly be absorbed NO _X.

[0004] Therefore, when the air-fuel ratio of the exhaust gas flowing into the the SO _X absorbent absorbs SO _X arranged in the NO _X absorbent in the engine exhaust passage upstream of the time of lean, the lean air-fuel mixture has been burned an internal combustion engine of the sO _X in the exhaust gas was set to absorb the sO _X absorbent are known (JP-a-6-173
652). SO _X discharged from the engine in this engine is that only NO _X is absorbed in _the NO _X absorbent is absorbed in SO _X absorbent.

However, NO_XNO from absorbent_XRelease
SO to make_XAbsorbent and NO _XFlows into the absorbent
Even if the air-fuel ratio of exhaust gas is simply rich, SO_XAbsorbent or
SO_XIs not released. Therefore SO_XAbsorbed by absorbent
SO being collected_XThe amount gradually increases and SO_XAbsorbent
SO_XWhen the absorption capacity is saturated, SO_XIs SO_XThrough the absorbent
NO_XIt will be absorbed by the absorbent.

In [0006] Therefore the above-described internal combustion engine, so that to release SO _X which brought temporarily SO _X release state SO _X absorbent is absorbed from the SO _X absorbent.

[0007]

SUMMARY OF THE INVENTION SO_XSO absorbent_X
When it is to be released, for example, SO_XFlows into the absorbent
The exhaust gas air-fuel ratio is made rich. SO_XFlow into absorbent
NO when the air-fuel ratio of the exhaust_XAbsorbent
The air-fuel ratio of the exhaust gas flowing into the
O_XSO released from the absorbent_XIs NO_XAbsorbed by absorbent
NO without being done_XIt is thought to pass through the absorbent.
However, according to the present inventor, NO_XFlow into absorbent
If the exhaust gas contains a certain concentration of oxygen,
Even if no _XThe air-fuel ratio of the exhaust flowing into the absorbent is rich
Even if SO_XIs NO_XNO absorbed by the absorbent_Xabsorption
Oxygen concentration in exhaust gas entering the agent is below a certain threshold
SO_XIs NO_XWithout being absorbed by the absorbent
NO_XIt has been found to pass through the absorbent. But
Therefore, this threshold is set to NO_XAbsorbent SO_XNon-absorbed concentration
First, NO_XAcids in the exhaust flowing into the absorbent
NO concentration_XAbsorbent SO_XLower than non-absorbed concentration
And then NO_XThe oxygen concentration in the exhaust gas flowing into the absorbent
SO_XSO while maintaining lower than non-absorbed concentration_XAbsorbent or
SO_XRelease SO_XIs NO_XAbsorbed by absorbent
NO without being_XWill pass through the absorbent. the above
The gazette does not suggest anything about this.

[0008]

[MEANS FOR SOLVING THE PROBLEMS]
According to the first aspect, the air-fuel ratio of the inflowing exhaust gas is low.
NO when_XOxygen concentration in the exhaust gas
NO becomes low when_XReleases NO_Xabsorption
The agent is placed in the engine exhaust passage and the exhaust
SO when the air-fuel ratio is lean_XAbsorbs SO_XRelease
SO that is absorbed when it is in a state_XReleases SO
_XNO absorbent_XLocated in the engine exhaust passage upstream of the absorbent
When the lean mixture is burned, the engine exhaust
SO in exhaust gas discharged into road_XTo SO_XAbsorbed by absorbent
And the NO in this exhaust_XNO_XAbsorbed by absorbent
And NO_XTemporary oxygen concentration in exhaust gas flowing into the absorbent
NO when reduced to_XAbsorbed from the absorbent
NO_XTo release SO_XAbsorbent is temporarily SO_XRelease
SO when it is put out_XAbsorbed by the absorbent
SO_XPoisoning of an internal combustion engine designed to emit gas
In the playback device, SO _XAbsorbent to SO_XRelease
NO when to_XOxygen concentration in exhaust gas flowing into the absorbent
NO_XAbsorbent SO_XOxygen lower than non-absorbed concentration
Concentration reduction means, NO_XOxygen in exhaust gas flowing into the absorbent
Oxygen concentration sensor for detecting concentration and oxygen concentration lowering means
More NO_XThe oxygen concentration in the exhaust gas flowing into the absorbent decreases.
After being squeezed, the oxygen concentration becomes SO_XHigher than non-absorbed concentration
SO_XAbsorbent is SO_XForbidden to release
Stop and this oxygen concentration becomes SO_XLower than the non-absorbed concentration
SO when_XSO absorbent_XSO to release state
_XRelease control means. That is, the first departure
In the Ming, NO_XThe oxygen concentration in the exhaust gas flowing into the absorbent is S
O_XSO until the concentration becomes lower than the non-absorbed concentration_XFrom the absorbent
SO_XIs not released and the oxygen concentration is SO_XFrom non-absorbed concentration
SO also becomes lower_XIs released, so SO_XFrom the absorbent
Released SO_XIs NO_XWithout being absorbed by the absorbent
NO_XPass through absorbent.

[0009] In the second first aspect according to the invention, the oxygen concentration lowered means comprises a hydrogenation unit for adding hydrogen to SO _X absorbent, reacting oxygen and hydrogen in the SO _X absorbent and so as to reduce the oxygen concentration in the exhaust gas flowing to the NO _X absorbent by. That is, in the second invention, hydrogen is used as a reducing agent for consuming oxygen in the exhaust gas.

[0010] In the third first aspect according to the invention, it is made to mix an oxidation catalyst in _the NO _X absorbent. That is, in the third invention, the amount of oxygen deposited on the surface of the NO _X absorbent is reduction.

[0011]

FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can also be applied to a spark ignition type internal combustion engine. Referring to FIG. 1, 1 is a diesel engine main body, 2 is a piston, 3 is a combustion chamber, 4 is an intake valve, 5 is an intake port, 6 is an exhaust valve, 7 is an exhaust port, and 8 is fuel in the combustion chamber 3. Each of the fuel injection valves for direct injection is shown. Each intake port 5 is connected to a surge tank 10 via a corresponding branch pipe 9, and the surge tank 10 is connected to an air cleaner 12 via an intake duct 11. On the other hand, the exhaust port 7 is connected via an exhaust manifold 13 to a casing 15 containing a SO _X absorbent 14. The casing 15 is connected via an exhaust pipe 16 to a casing 18 containing a NO _X absorbent 17.

The exhaust manifold 13 is provided with a reducing agent injection valve 20 for adding a reducing agent to the exhaust gas flowing through the exhaust manifold. As the reducing agent, for example, hydrocarbons such as gasoline, isooctane, hexane, heptane, light oil and kerosene, or hydrocarbons such as butane and propane which can be stored in a liquid state can be used. However, the diesel engine shown in FIG. 1 uses hydrogen as a reducing agent, and the reducing agent injection valve 20 is hereinafter referred to as a hydrogen injection valve. The hydrogen injection valve 20 is connected to a cylinder 21 mounted on a vehicle. The fuel injection valve 8 and the hydrogen injection valve 20 are controlled based on an output signal from the electronic control unit 30.

The electronic control unit 30 is composed of a digital computer, and is connected to a ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a backup RAM 34 which is always supplied with power, and which are interconnected by a bidirectional bus 31. It has a CPU (microprocessor) 35, an input port 36 and an output port 37. A temperature sensor 38 that generates an output voltage proportional to the temperature of exhaust flowing through the exhaust pipe 16 is provided in the exhaust pipe 16.
And an oxygen concentration sensor 39 that generates an output voltage proportional to the oxygen concentration in the exhaust gas flowing through the exhaust pipe 16. The output voltages of the sensors 38 and 39 are input to the input port 36 via the corresponding AD converters 40, respectively. Incidentally, exhaust flowing through the exhaust pipe 16, i.e. the temperature of the exhaust gas flowing out from the SO _X absorbent 14 represents the temperature of the SO _X absorbent 14. The output voltage of the depression amount sensor 41 that generates an output voltage proportional to the depression amount of an accelerator pedal (not shown) is input to the input port 36 via the corresponding AD converter 40. Further, the input port 36 is connected to a rotation speed sensor 42 that generates an output pulse representing the engine rotation speed. On the other hand, output port 3
7 is connected to the fuel injection valve 8 and the hydrogen injection valve 20 via a corresponding drive circuit 43, respectively.

NO _X contained in casing 18
The absorbent 17 is made of, for example, alumina as a carrier. On this carrier, for example, alkali metals such as potassium K, sodium Na, lithium Li, and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, and yttrium Y are used. At least one selected from such rare earths and a noble metal such as platinum Pt are supported. This _the NO _X absorbent 17 absorbs NO _X when the air-fuel ratio of the exhaust gas flowing is lean, perform absorption and release action of the NO _X that releases NO _X to the oxygen concentration in the exhaust gas absorbed and reduced flowing.

If the above-mentioned NO _X absorbent 17 is disposed in the engine exhaust passage, the NO _X absorbent 17 actually performs the NO _X absorption / release operation, but the detailed mechanism of this absorption / release operation is not clear. There is also. However, it is considered that this absorption / release action is performed by a mechanism as shown in FIG. Next, this mechanism will be described by taking as an example a case where platinum Pt and barium Ba are supported on a carrier, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths and rare earths.

[0016] That is, the oxygen concentration in the exhaust gas exhaust gas flowing into _the NO _X absorbent 17 flows considerably becomes lean is increased by a large margin, Figure 2 these oxygen O ₂ as shown in (A) is O ₂ ^- or it is deposited on the surface of the platinum Pt in the O ^2- shape. On the other hand, NO in the flowing exhaust gas reacts with O ₂ ⁻ or O ²⁻ on the surface of platinum Pt to become NO ₂ (2NO + O 2).
₂ → 2NO ₂ ). Then part of the produced NO ₂ while bonding with the barium oxide BaO is absorbed into the absorbent while being further oxidized on the platinum Pt, 2 nitrate ions NO ₃ as shown in (A) ^- of It diffuses into the absorbent in form. In this way, NO _X is absorbed in the NO _X absorbent 17.

The NO ₂ is produced on the surface of the oxygen concentration is as high as platinum Pt in the inflowing exhaust gas, as long as NO ₂ to NO _X absorbing capacity of the absorbent is not saturated is absorbed in the absorbent and nitrate ions NO ₃ ^- Is generated. On the other hand, when the oxygen concentration in the exhaust gas flowing into the NO _X absorbent 17 decreases and the amount of generated NO ₂ decreases, the reaction proceeds in the opposite direction (NO ₃ ⁻ → NO ₂ ).
Advances to, thus to nitrate ions in the absorbent NO ₃ ^- is NO
It is released from the absorbent in the form of ₂ . That is, when the oxygen concentration in the exhaust gas flowing into the NO _X absorbent 17 decreases, the NO _X
NO _X will be released from the absorbent 17. The oxygen concentration in the exhaust degree of lean of the exhaust gas flowing to flow the lower the decrease, therefore _the NO _X absorbent 1 if low degree of lean of the exhaust gas flowing to the NO _X absorbent 17
NO _X is to be released from the 7.

At this time, NO_XFlows into absorbent 17
When the air-fuel ratio of exhaust gas becomes rich, a large amount of
Base agents such as HC, H_TwoAnd a large amount of HC and H
_TwoIs oxygen O on platinum Pt_Two ^-Or O^2-Reacts with and oxidizes
I'm sullen. In addition, the air-fuel ratio of the exhaust
If this happens, the oxygen concentration in the inflowing exhaust gas will drop extremely
NO from absorbent_TwoIs released and this NO_TwoFigure 2
As shown in (B), HC, H_TwoReact with and reduce
Can be In this way, NO on the surface of platinum Pt _TwoBut
When it is no longer present, NO will change from one absorbent to the next_TwoIs released
Is done. Therefore NO_XOf the exhaust gas flowing into the absorbent 17
If the air-fuel ratio is made rich, NO _XAbsorbent 1
7 to NO_XWill be released.

In a diesel engine, the excess air ratio is usually maintained at 1.0 or more in all operating states, that is, the average air-fuel ratio of the air-fuel mixture burned in the combustion chamber 3 is kept lean. Therefore, at this time, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 17 becomes lean. As a result, NO _X discharged from the combustion chamber 3 at this time is absorbed in the NO _X absorbent 17 is prevented from NO _X is discharged from _the NO _X absorbent 17 and thus.

Thus, during normal operation, the engine discharges
NO_XIs NO_XAbsorbed by the absorbent 17. But
NO_XNO of absorbent 17_XThe absorption capacity is limited,
NO _XNO of absorbent 17_XNO if absorption capacity is saturated_X
Absorbent 17 is no longer NO_XCan not be absorbed. But
NO_XNO of absorbent 17_XBefore the absorption capacity is saturated
NO_XNO from absorbent 17_XMust be released.
Therefore, in this embodiment, NO_XAbsorbed by the absorbent 17
NO_XFind the quantity and use this NO_XThe amount is more than a certain value
NO when it becomes_XAir-fuel ratio of exhaust gas flowing into absorbent 17
Is temporarily rich, so that NO_XAbsorbent 17
NO_XTo release NO_XNO of absorbent 17_XAbsorption capacity
Restores power and releases NO_XI will reduce
I'm trying.

[0021] Incidentally, in the lubricating oil of the fuel and the engine SO _X is discharged from the combustion chamber 3 because it contains sulfur, the SO _X is absorbed in the NO _X absorbent 17 with NO _X. It is considered that the absorption mechanism of SO _X into the NO _X absorbent 17 is the same as the absorption mechanism of NO _X. That is, taking as an example the case where platinum Pt and barium Ba are carried on the carrier in the same manner as when the NO _X absorption mechanism is described, as described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen O ₂ is O
₂ ^- or it is deposited on the surface of the platinum Pt in the O ^2- form,
O ₂ SO ₂ in the exhaust gas flowing on the surface of the platinum Pt ^{-
Alternatively,} it reacts with O ²⁻ to form SO ₃ . Next, the generated SO ₃ is further oxidized on the platinum Pt, is absorbed in the absorbent, and is bonded to barium oxide BaO, and diffuses into the absorbent in the form of sulfate ion SO ₄ ^2- . Next, this sulfate ion SO ₄ ^2- is combined with barium ion Ba ²⁺ to form sulfate BaSO ₄ .

However, the sulfate BaSO ₄ is hard to be decomposed, and SO _X is hardly released from the NO _X absorbent 17 even if the air-fuel ratio of the inflowing exhaust gas is made rich.
Thus will be sulfates BaSO ₄ increases as time in _the NO _X absorbent 17 has elapsed, that the amount of NO _{X the} NO _X absorbent 17 can absorb as thus to time has elapsed is reduced Become.

[0023] Therefore, in the diesel engine of FIG. 1 absorb SO _X when the air-fuel ratio of the exhaust gas flowing to not SO _X flows into _the NO _X absorbent 17 is lean, to absorb the caused to the SO _X release state SO _X that releases SO _X
The absorbent 14 is placed upstream _the NO _X absorbent 17. As a result, SO _X discharged from the engine during normal operation is
Is absorbed in the _X absorbent 14, is the NO _X absorbent 17 NO _X
Only will be absorbed.

[0024] However there is a limit to the SO _X absorbing capacity of the SO _X absorbent 14, it is necessary to release the NO _X from the SO _X absorbent 14 before the SO _X absorbing capacity of the SO _X absorbent 14 becomes saturated. Therefore, in this embodiment, the SO _X absorbent 1
4 obtains the SO _X amount absorbed in the, allowed temporarily SO _X release state SO _X absorbent 14 when the amount of the SO _X becomes larger than a predetermined value, whereby SO _X absorbent 1
And to release SO _X and so as to restore the SO _X absorbing capacity of the SO _X absorbent 14 from 4.

That is, the SO _X absorbent 14 absorbs the SO _X when the oxygen concentration in the exhaust gas flowing in decreases and the temperature of the SO _X absorbent 14 is higher than the SO _X release start temperature.
Temporarily the temperature of the vital SO _X absorbent 14 rich SO _X release initiation temperature the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 14 when the SO _X absorbent 14 to be released the SO _X will release _X Higher than that.

SO_XAbsorbent 14 is the oxygen in the inflowing exhaust
SO absorbed when the concentration decreases _XIt's easy to release
SO absorbed_XThe sulfate ion SO_Four ^2-Absorbent in the form of
Present in the sulphate BaSO_FourWas generated
Also sulfate BaSO_FourIs not stable in the absorbent
It is necessary to make it exist. Make this possible
SO_XThe absorbent 14 is made of, for example, alumina.
Iron Fe, manganese Mn, nickel Ni, tin Sn on carrier
Selected from transition metals such as lithium and lithium Li
An absorbent carrying at least one can be used.

This SO_XIn the absorbent 14, SO_XAbsorbent 1
4 when the air-fuel ratio of the exhaust gas flowing into it is lean.
SO_TwoIs oxidized on the surface of the absorbent while sulfate ions
SO _Four ^2-Absorbed into the absorbent in the form of
Spread. In this case SO_XPlatinum on the carrier of absorbent 14
When Pt is supported, SO_TwoIs SO_Three ^2-In the form of platinum P
t on the surface of the substrate and thus the SO_TwoIs sulfate ion S
O_Four ^2-It is easy to be absorbed in the absorbent in the form of. Accordingly
SO_TwoSO to promote absorption of SO_XOf absorbent 14
It is preferable to carry platinum Pt on a carrier.

[0028] Since the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 when the air-fuel ratio of the exhaust gas flowing from the SO _X absorbent 14 in the SO _X absorbent 14 so as to release the SO _X is rich also rich SO _X released from the time SO _X absorbent 14 is believed to pass through _the NO _X absorbent 17 without being absorbed in the NO _X absorbent 17. However, according to the present inventor, if the exhaust gas flowing into the NO _X absorbent 17 contains a certain concentration of oxygen, the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 17 is rich. However, SO _X is absorbed by the NO _X absorbent 17 and NO
The oxygen concentration in the exhaust gas flowing into the _X absorbent 17 is _the NO _X absorbent 17 of SO _X nonabsorbable is lower than the concentration in without SO _X is absorbed in the NO _X absorbent 17 is _the NO _X absorbent 1
7 has been confirmed. Therefore, NO
_While maintaining the oxygen concentration in the exhaust gas flowing into the _X absorbent 17 lower than the SO _X non-absorbing concentration of the NO _X absorbent 17, the SO _X
If ask from the absorbent 14 release SO _X SO _X will pass through the _the NO _X absorbent 17 without being absorbed in the NO _X absorbent 17.

Therefore, in this embodiment, the SO_XAbsorbent 14
SO_XFirst to release SO_XAbsorbent
14 temperature SO_XWhile keeping it below the release starting temperature
NO _XThe oxygen concentration in the exhaust gas flowing into the absorbent 17 is_X
Lower than the non-absorbed concentration and then NO_XFlow to absorbent 17
The oxygen concentration in the incoming exhaust_XLower than non-absorbed concentration
SO while maintaining_XThe temperature of the absorbent 14 is set to SO_XRelease start temperature
The degree is higher than the degree. As a result, SO_XSucking
NO released from collector 14_XIs NO_XAbsorbed by absorbent 17
NO without being collected_XWill pass through the absorbent 17
You. That is, NO_XSO in absorbent 17_XIs absorbed
NO_XNO of absorbent 17_XPrevents reduction in absorption capacity
Is done.

[0030] As described above, NO _X in the air-fuel ratio of the exhaust gas flowing into the absorbent 17 is a richer in the NO _X absorbent 17 when the oxygen concentration in the exhaust is higher than the SO _X nonabsorbable concentration SO _X Is absorbed. NO _X is released which is absorbed from _the NO _X absorbent 17 to thus when the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 is the concentration of oxygen is and in the exhaust rich is higher than the SO _X nonabsorbable concentration At the same time, SO _X is absorbed by the NO _X absorbent 17. This is considered for the following reasons. In other words, even if the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 17 is rich, if a certain amount of oxygen is contained in the exhaust gas, oxygen is accumulated on the NO _X absorbent 17 such as platinum Pt. attached, whereby the _the NO _X absorbent 17 NO _X and S
O _X is absorbed. However NO fuel ratio of the exhaust gas flowing into the _X absorbent 17 is NO _X release rate when the rich overwhelmingly higher than NO _X absorbing rate, thus the NO _X is released from the NO _X absorbent 17 at this time Become. In contrast, SO _X release speed air-fuel ratio is a rich exhaust gas flowing to the NO _X absorbent 17 is considerably smaller than the SO _X absorbing rate, therefore this case NO _X
SO _X is absorbed by the absorbent 17.

Next, first, N in _the NO _X absorbent 17
It will be described in detail O _X release control. NO In this embodiment as described above, which is absorbed in the NO _X absorbent 17
Seeking _X amount, the amount of NO _X is temporarily rich air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 when it becomes more than a certain value, NO _X thereby from _the NO _X absorbent 17
Is to be released. NO of _the NO _X absorbent 17
_Since it is difficult to directly determine the _X absorption amount, the present embodiment estimates the NO _X absorption amount based on the engine operating state. That, NO _X absorption of the NO _X absorbent 17 is substantially equal to the NO _X amount flowing into _the NO _X absorbent 17 when the lean air-fuel mixture has been burned, _the amount of NO _X that is flowing into _the NO _X absorbent 17 The NO _X amount discharged from the engine is proportional to the engine speed N. Therefore, in the present embodiment calculates the integrated value SN of the engine speed from the previous of the NO _X release action of hydrogen by a set time PN1 from the hydrogen injection valve 20 when the integrated value SN is larger than a predetermined value SN1 H ₂ is injected to thereby temporarily make the air-fuel ratio of the exhaust gas flowing into the NO _X absorbent 17 rich. Incidentally, the constant value SN1 is _the NO _X absorbent 17 is equivalent to, for example, 30% of the absorption maximum possible amount.

In this case, the hydrogen injection time QH of the hydrogen injection valve 20 is set to QN. The QN is needed to a rich air-fuel ratio required for reducing the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17, and promptly release the NO _X that is absorbed from _the NO _X absorbent 17 The hydrogen injection time, which is obtained in advance by an experiment. QN is a function of the depression amount DEP of the accelerator pedal representing the engine load and the engine speed N and is stored in advance in the ROM 32 in the form of a map shown in FIG.
Is stored within.

By the way, hydrogen H is supplied from the hydrogen injection valve 20._TwoSpout
This hydrogen H_TwoIs SO first _XFlow into absorbent 14
And then NO_XIt flows into the absorbent 17. That is, N
O_XThe air-fuel ratio of the exhaust gas flowing into the absorbent 17 should be rich.
SO when_XThe air-fuel ratio of the exhaust gas flowing into the absorbent 14 is also
Be rich. However, at this time SO_XAbsorbent 14 temperature
Degree is SO_XIf the temperature is higher than the release start temperature, SO_XAbsorbent 14
SO absorbed from_XIs released, and NO
_XThe oxygen concentration in the exhaust gas flowing into the absorbent 17 is not necessarily S
O_XSince it is not lower than the non-absorbed concentration, SO_XIs NO_Xabsorption
It may be absorbed in the agent 17. Also, SO_XAbsorbent
The temperature of 14 is SO_XEven if the temperature is lower than the release start temperature
Hydrogen H_TwoIs in exhaust or SO_XOf the surface of the absorbent 14
Oxygen O_TwoAnd SO_XBy reacting with absorbent 14, SO
_XThe temperature of the absorbent 14 rises and SO_XFrom release start temperature
May also be higher.

On the other hand, NO_XOf the exhaust gas flowing into the absorbent 17
NO when temperature is low_XThe temperature of the absorbent 17 is also low.
As a result, the decomposition rate of nitrate decreases,
_XThe release rate decreases. On the other hand, SO_XAbsorbent 14 temperature
SO for degree_XTemperature TS of exhaust gas flowing out of absorbent 14
Is lower than the upper threshold temperature UTN, NO_XSucking
NO from collector 17 _XTo release hydrogen from the hydrogen injection valve 20
Hydrogen H_TwoSupply SO_XThe temperature of the absorbent 14 is SO
_XIt will not be higher than the release start temperature. Also exhaust
When the temperature TS is higher than the lower threshold temperature LTN, N
O_XNO from absorbent 17_XCan be released quickly. So
In this embodiment, the engine speed integrated value SN is a constant value S
The exhaust temperature TS has an upper limit when it becomes larger than N1.
Higher or lower limit temperature LTN
Lower than hydrogen H_TwoSupply of exhaust gas and exhaust temperature
TS is lower than upper threshold temperature UTN and lower threshold
When the temperature is higher than the temperature LTN, hydrogen H_TwoSupply it to
More NO_XNO from absorbent 17_XTo release
ing. The upper threshold temperature UTN is, for example, about 350
° C and the lower threshold temperature LTN is, for example, about 200 ° C.
is there.

By the way described above set time PN1 is the time required to release substantially all of the NO _X that is absorbed in the NO _X absorbent 17. However, in this embodiment, NO _X
When the NO _X releasing action of the absorbent 17 should be started, NO _X
The amount of NO _X absorbed in the absorbent 17 is a not necessarily constant, proportional to the engine speed integrated value SN at this point. Therefore, in this embodiment, the set time PN1 is calculated according to the engine speed integrated value SN.

That is, as shown at time a in FIG. 3, the engine speed integrated value SN becomes larger than the constant value SN1,
At this time, when the exhaust gas temperature TS is between the lower threshold temperature LTN and the upper threshold temperature UTN, the hydrogen injection time QH
Is QN, that is, hydrogen H ₂ is supplied. Next, when the set time PN1 elapses after the supply of the hydrogen H ₂ is started as in the time b, the supply of the hydrogen H ₂ is stopped, and at this time, the engine speed integrated value SN is reset.
On the other hand, the engine speed integrated value S
N supply of hydrogen H ₂ is stopped when higher than the exhaust temperature TS, for example, the upper limit threshold temperature UTN even this time is larger than a predetermined value SN1. Therefore, the engine speed integrated value SN increases beyond the fixed value SN1. Then, as at time d, the exhaust gas temperature TS rises to the upper threshold temperature U
Hydrogen H ₂ is supplied by the set time PN1 becomes lower than TN. The set time PN1 in this case corresponds to the engine speed integrated value SN at time d, and is longer than the set time (ba) in the previous hydrogen supply operation. In FIG. 3, the SRT is the S of the SO _X absorbent 14.
It indicates the _OX release start temperature, for example, about 450 ° C. In addition, the set time PN1 is set to about 1 to 5 seconds.

Next, the SO _X release control in the SO _X absorbent 14 will be described in detail. Determine the SO _X amount absorbed in the SO _X absorbent 14 in this embodiment as described above, temporarily SO _X absorbent 14 when the amount of the SO _X becomes larger than a predetermined value set in advance and to perform the sO _X release action on. Since determining the SO _X amount of absorption of SO _X absorbent 14 directly is difficult in the present embodiment is to estimate the SO _X absorbing amount based on the engine operating state. That, SO _X absorbed amount of SO _X absorbent 14 is substantially equal to the SO _X amount flowing into the SO _X absorbent 14 when the lean air-fuel mixture has been burned, SO _X absorbent 1
4, the amount of SO _X flowing into the engine 4
_{The X} amount is proportional to the engine speed N. Therefore, in this embodiment, the integrated value S of the engine speed from the previous SO _X release operation is calculated.
S is calculated, and when the integrated value SS becomes larger than the fixed value SS1, the SO _X releasing action is performed.
That is, when the engine speed integrated value SS becomes larger than the fixed value SS1, first, the temperature TS of the exhaust gas flowing out of the SO _X absorbent 14 is kept lower than the SO _X release start temperature SRT while the NO _X absorbent 17 is maintained. oxygen concentration COX in the inflowing exhaust gas is made to be lower than the sO _X unabsorbed concentration COX1 on. Note that this constant value SS1 corresponds to, for example, 30% of the maximum amount that the SO _X absorbent 14 can absorb.

In this embodiment, the hydrogen H
₂ and reacts the hydrogen H ₂ with oxygen O ₂ in the exhaust gas in the SO _X absorbent 14, thereby reducing the oxygen concentration COX in the exhaust gas flowing into the NO _X absorbent 17 from the SO _X non-absorbing concentration COX 1. Also try to lower. However, as described above, the temperature of the SO _X absorbent 14 increases due to the reaction between the hydrogen H ₂ and the oxygen O _2, and the SO _X absorbent 1
Is a possibility that the temperature of the 4 SO _X fuel ratio of the exhaust gas flowing at this time SO _X absorbent 14 becomes higher than the SO _X release initiation temperature, which is absorbed from the SO _X absorbent 14 since it is rich is released is there. Further, when the temperature of the SO _X absorbent 14 is low, hydrogen H ₂ and oxygen O ₂ do not react quickly in the SO _X absorbent 14, and it takes a long time to lower the oxygen concentration COX.

On the other hand, the exhaust temperature TS is equal to the upper threshold temperature UT.
When the oxygen concentration COX is lower than S_XNon-absorbent
Hydrogen H until the temperature becomes lower than COX1_TwoS
O_XThe temperature of the absorbent 14 is SO_XFrom release start temperature SRT
Can never be higher. Also, SO_XAbsorbent 14 temperature
That is, the exhaust gas temperature TS is higher than the lower threshold temperature LTS.
SO_XHydrogen H in the absorbent 14_TwoAnd oxygen O
_TwoAnd react quickly. Therefore, in this embodiment, the engine
When the rotation speed integrated value SS becomes larger than the constant value SS1
The exhaust gas temperature TS is higher than the upper threshold temperature UTS?
Alternatively, when the temperature is lower than the lower threshold temperature LTS, hydrogen H
_TwoSupply is prohibited, and the exhaust temperature TS becomes the upper threshold temperature UT
When the temperature is lower than S and higher than the lower limit threshold temperature LTS
Hydrogen H _TwoSo that the SO_XFrom absorbent 14
SO_XWhile the oxygen concentration COX is S
O_XIt should be lower than the non-absorbed concentration COX1
You. The upper limit threshold temperature UTS is, for example, about 300 ° C.
The lower limit threshold temperature LTS is, for example, about 200 ° C.
You. Also, SO_XThe non-absorbed concentration COX1 is, for example, about 0.3
%.

In this case, the hydrogen injection time QH of the hydrogen injection valve 20 is set to QOX. This QOX is _the NO _X absorbent 17
It has been previously determined by experimentation a hydrogen injection time required to lower than promptly SO _X nonabsorbable concentration COX1 oxygen concentration COX in the exhaust gas flowing into the. The QOX is stored in advance in the ROM 32 in the form of a map shown in FIG. 5B as a function of the accelerator pedal depression amount DEP and the engine speed N.
Is stored within.

When the oxygen concentration COX in the exhaust gas flowing into the NO _X absorbent 17 becomes lower than the SO _X non-absorbing concentration COX1, the oxygen concentration COX is then reduced to the SO _X non-absorbing concentration CX1.
Maintaining while SO _X absorbent 14 is heated to the exhaust gas temperature TS is set to be higher than the SO _X release initiation temperature SRT lower than OX1. Hydrogen injection valve in order to maintain the oxygen concentration COX SO _X nonabsorbable concentration COX1 lower than 20
May be set to at least the above-described QOX. Further, hydrogen H ₂ and oxygen O ₂ in the SO _X absorbent 14 as described above SO _X absorbent 14 is heated by the reaction. Therefore, in this embodiment, the oxygen concentration C
When the OX becomes lower than the SO _X non-absorption concentration COX1, then the hydrogen injection time QH is set to QO for the set time PS1.
QS longer than X, that is, the supply amount of hydrogen H ₂ is increased, so that the oxygen concentration COX is reduced to the SO _X non-absorbed concentration CO
The exhaust temperature TS is set to be higher than the SO _X release start temperature SRT while maintaining the temperature lower than X1.

[0042] The air-fuel ratio of the exhaust the hydrogen injection time QS in this case is flowing into the SO _X absorbent 14, the rich air-fuel ratio required to quickly release the SO _X being absorbed from the SO _X absorbent 14 This is the hydrogen injection time required to perform this, and is obtained in advance by experiments. QS is a function of the accelerator pedal depression amount DEP and the engine speed N as shown in FIG.
It is stored in the ROM 32 in advance in the form of a map shown in FIG.

When the exhaust temperature TS is SO_XRelease start temperature SRT
Higher than SO_XAbsorbed from absorbent 14
SO_XIs released. At this time, the oxygen concentration COX becomes SO
_XSO released since it is lower than the non-absorbed concentration COX1_X
Is NO_XNO without being absorbed by the absorbent 17_XAbsorbent
Pass through 17. That is, NO_XSO in absorbent 17 _X
Is prevented from being absorbed and therefore NO_XAbsorbent 1
7 NO_XA reduction in absorption capacity is prevented.

The above-mentioned set time PS1 is equal to the SO _X absorbent 14
This is the time required to release almost all of the SO _X that has been absorbed into the air. However, in this embodiment, the SO _X absorbent 1
4 of SO _X absorbent 1 when should start SO _X release action
The SO _X amount absorbed by the engine 4 is not necessarily constant, and is proportional to the engine speed integrated value SS at this time. Therefore, in the present embodiment, the set time PS1 is calculated according to the engine speed integrated value SS. That is, as shown at time a in FIG.
At this time, when the exhaust temperature TS is between the lower threshold temperature LTS and the upper threshold temperature UTS, the hydrogen injection time QH is set to QOX. Then, as at time b, the oxygen concentration COX becomes the SO _X non-absorption concentration C
When it becomes lower than OX1, the hydrogen injection time QH is set to QS. Then, as at time c, the exhaust temperature TS becomes SO _X
When the temperature becomes higher than the release start temperature SRT, SO _X release is started. Then, as at time d, hydrogen injection time QH
, The supply of hydrogen H ₂ is stopped when the set time PS1 elapses, and at this time, the integrated engine speed value SS
Is reset. The set time PS1 is set to about 5 to 20 seconds.

[0045] Incidentally, rich of the air-fuel ratio of the exhaust gas flowing to the NO _X absorbent 17 when that the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 14 to release the SO _X from the SO _X absorbent 14 rich It has become. Therefore NO
_The NO _X absorbed by the _X absorbent 17 is released, and the NO _X is reduced by H ₂ in the inflowing exhaust gas. Also, significantly than the time PN1 hydrogen H ₂ is supplied to the time PS1 hydrogen H ₂ is supplied in order to release the SO _X from the SO _X absorbent 14 to release NO _X from _the NO _X absorbent 17 long. When the SO _X release action of SO _X absorbent 14 has been completed thus it has been completed also NO _X release action of _the NO _X absorbent 17.

FIGS. 6 and 7 show the above-mentioned NO _X and S
Absorbing the O _X is a routine for exiting control action. This routine is executed by interruption every predetermined set time. Referring to FIGS. 6 and 7, first, at step 50, the amount of sulfur absorbed from the SO _X absorbent 14 is determined.
It is determined whether an SO _X release flag is set when O _X is to be released and reset otherwise. Since usually SO _X release flag is reset and then proceeds to step 51, it is set to when releasing the NO _X that is absorbed from _the NO _X absorbent 17, otherwise NO _X release flag is set to be reset It is determined whether or not it has been performed. Since the NO _X release flag is normally reset, the routine proceeds to step 52, where the current engine speed N is added to the engine speed integrated value SN for the NO _X release action. In the following step 53, it is determined whether or not the engine speed integrated value SN is larger than a fixed value SN1. When SN ≦ SN1, the process jumps to step 56. In contrast SN> routine goes to step 54 when the SN1, whether NO _X release conditions are satisfied or not is judged. In the present embodiment, when the temperature TS of the exhaust gas flowing out of the SO _X absorbent 14 is between the lower threshold temperature LTN and the upper threshold temperature UTN, NO is determined.
It is determined that the _X release condition is satisfied. When the NO _X release condition is not satisfied, the process jumps to step 56. When the NO _X release condition is satisfied, the process proceeds to step 55, where the NO _X release flag is set, and then the process proceeds to step 56.

In step 56, SO_XFor release action
The current engine speed N is added to the engine speed integrated value SS.
You. In the following step 57, the engine speed integrated value SS is constant.
It is determined whether the value is larger than the value SS1. SS ≦ SS
If it is 1, the processing cycle ends. SS
If> SS1, then the routine proceeds to step 58, where SO _X
It is determined whether the release condition is satisfied. This embodiment
The exhaust gas temperature TS is lower than the lower threshold temperature LTS and the upper
SO when the temperature is between_XRelease condition satisfied
It is determined that you are. SO_XRelease condition not satisfied
If not, the processing cycle is terminated and SO_XRelease conditions are met
If it is standing, the process then proceeds to step 59 where SO_X
After setting the release flag, the processing cycle ends.

The SO _X release flag is reset while NO
When _{the X} release flag is set the process proceeds from step 51 to step 60, the count value CN representing the time of hydrogen H ₂ is supplied in order to release NO _X from _the NO _X absorbent 17 is incremented by 1. In the following step 61, based on the present engine speed integrated value SN, FIG.
The set value CN1 is calculated using the map shown in FIG. This set value CN1 corresponds to the above set time PN1, and is stored in the ROM 32 in advance in the form of a map shown in FIG. In the following step 62, the count value CN
Is larger than the set value CN1. CN
When ≤CN1, the processing cycle ends. On the other hand, when CN> CN1, the routine proceeds to step 63,
NO _X releasing flag is reset. Next step 64
Then, the count value CN is cleared, and in the following step 65, the engine speed integrated value SN is cleared.

When the SO _X release flag is set, the process proceeds from step 51 to step 66, where the SO _X absorbent 1
From 4, the count value CS representing the time during which the hydrogen H ₂ is being supplied to release SO _X is incremented by one. In the following step 67, the set value C is set using the map shown in FIG.
S1 is calculated. This set value CS1 corresponds to the above set time PS1, and is set in advance in the form of a map shown in FIG.
It is stored in the OM32. In the following step 68, it is determined whether or not the count value CS is larger than the set value CS1. When CS ≦ CS1, the processing cycle ends. On the other hand, when CS> CS1, the routine proceeds to step 69, where the SO _X release flag is reset. In the following step 70, the count value CS is cleared, and in the following step 71, the engine speed integrated value SS is cleared.
In the following step 72, the NO _X release flag is reset or maintained in a reset state, and in the following step 73, the engine speed integrated value SN is cleared.

FIG. 9 shows the hydrogen injection time QH of the hydrogen injection valve 20.
2 shows a routine for calculating. This routine is executed by interruption every predetermined set time. Referring to FIG. 9, first, at step 80, SO _X
It is determined whether the release flag is set. S
O _X release flag is because it is usually reset and then proceeds to step 81, NO _X releasing flag whether it is set or not. NO _X emission flag because it is normally reset and then proceeds to step 82, the hydrogen injection time QH is zero. That is, the SO _X release flag is also N
O _X release flag when also been reset hydrogen H ₂
Is not supplied.

The SO _X release flag is reset while NO
Step 8 when the _X release flag is reset
From 1, the process proceeds to step 83, and from the map of FIG.
N is calculated. In the following step 84, this QN is set as the hydrogen injection time QH. That is, when the NO _X release flag is set while the SO _X release flag is reset, hydrogen H ₂ is injected from the hydrogen injection valve 20 by QN.

When the SO _X release flag is set, the routine proceeds from step 80 to step 85, where the oxygen concentration C
OX whether low is determined than SO _X unabsorbed concentration COX1. When COX ≧ COX1, the routine proceeds to step 86, where the count value CS in the routine of FIGS. 6 and 7 is cleared. In the following step 87, FIG.
The QOX is calculated from the map shown in FIG. In the following step 88, this QOX is set as the hydrogen injection time QH. That is, after the SO _X release flag is set, the oxygen concentration COX
There SO _X when greater than non-absorption density COX1 is hydrogen H ₂ is injected only QOX from hydrogen injection valve 20, this time the count value CS is maintained at zero.

When COX <COX1, it proceeds from step 85 to step 89, and QS is calculated from the map shown in FIG. In the subsequent step 90, this QS is set as the hydrogen injection time QH. That oxygen concentration COX is SO _X nonabsorbable concentration COX1 is lower than the count of the count value CS is started, QS only hydrogen H ₂ from the hydrogen injection valve 20 to the SO _X release flag is reset is injected.

Next, another embodiment will be described with reference to the routines shown in FIGS. 10 and 11 show a routine for calculating the hydrogen injection time QH of the hydrogen injection valve 20. This routine is executed by interruption every predetermined set time. In this embodiment, the NO _X and SO _X absorption / release control routine shown in FIGS. 6 and 7 is also executed.

Referring to FIGS. 10 and 11, first, at step 180, it is determined whether or not the SO _X release flag is set. When the SO _X release flag has been reset, the routine proceeds to step 181, where it is determined whether the NO _X release flag has been set. NO
_{When the X} release flag has been reset, the routine proceeds to step 182, where the hydrogen injection time QH is set to zero. S
When the NO _X release flag is being reset while the O _X release flag is being reset, the process proceeds from step 181 to step 183, where QN is calculated from the map of FIG. In the following step 184, this QN is set as the hydrogen injection time QH.

If the SO _X release flag is set, the routine proceeds from step 180 to step 185, where it is determined whether the oxygen concentration COX is lower than the SO _X non-absorption concentration COX1. When COX ≧ COX1, the routine proceeds to step 186, where the count value CS counted up in the routine of FIGS. 6 and 7 is cleared.
In the following step 187, the count value CC is incremented by one. This count value CC is the oxygen concentration COX
Represents the time since hydrogen H ₂ was supplied to the SO _X absorbent 14 in order to reduce the H ₂ . When the process proceeds to step 188 for the first time after the SO _X release flag is set, C
Since C = 1, the process proceeds to step 189, and FIG.
The QOX is calculated from the map shown in FIG. In the following step 190, this QOX is set as the hydrogen injection time QH. That is, when the SO _X release flag is set as at time a in FIG.
OX only hydrogen H ₂ is injected, counts up the count value CC is started.

[0057] oxygen concentration COX is SO _X non-absorption concentration COX
Unless it becomes lower than 1, the count-up of the count value CC is continued. Next, when the count value CC becomes larger than the first set value CC1, then step 1 is executed.
Proceeding to 91, the count value CC becomes the second set value CC2 (>
It is determined whether it is larger than CC1). When the process proceeds to step 191 for the first time after the count up of the count value CC is started, since CC ≦ CC2, the process proceeds to step 192, and the QO is determined from the map of FIG.
X is calculated. In the following step 193, the product of this QOX and a constant K larger than 1 is set as the hydrogen injection time QH. That is, even when the time corresponding to the first set value CC1 has elapsed since the supply of the hydrogen H ₂ to the SO _X absorbent 14 started as in the time b in FIG.
Is not lower than the SO _X non-absorption concentration COX1, the amount of hydrogen supplied to the SO _X absorbent 14 is increased.

The reason why the amount of supplied hydrogen is increased is as follows.
For the following reasons. That is, the hydrogen injection time QOX is SO
_XThe temperature of the absorbent 14 is set to SO_XUp to the release starting temperature
Hydrogen injection time to provide the required amount of hydrogen
But hydrogen H_TwoTime since we started supplying
SO when it comes_XThe temperature of the absorbent 14 is SO_XRelease temperature
May be higher. Therefore, in this embodiment, water
Element H_TwoOxygen concentration even after a certain period of time
COX is SO_XWhen it does not become lower than the non-absorbed concentration
Increases the amount of supplied hydrogen, thereby increasing the oxygen concentration COX.
SO_XLower than the non-absorbed concentration
You. As described above, the hydrogen injection time QOX depends on the oxygen concentration.
Degree COX promptly SO_XLower than the non-absorbed concentration
Is the hydrogen injection time required for
The augmenting action takes place, for example, in _XAbsorbent 14 deteriorates
Or the hydrogen injection valve 20 or the depression amount sensor 41
Is when it breaks down.

On the other hand, in step 191, CC> CC
In the case of 2, the process then proceeds to step 194, where the hydrogen injection time QH is set to zero. In the following step 195, the count value CC is cleared, and in the following step 196, the count value CS is set to an extremely large CMX. That is, FIG.
Time constant supply amount of hydrogen from increasing elapsed oxygen concentration COX is SO _X nonabsorbable concentration C also, as in the second time c
If the temperature does not become lower than OX1, it is determined that the temperature of the SO _X absorbent 14 becomes higher than the SO _X release start temperature, and S
Supply of hydrogen of H ₂ to O _X absorbent 14 is stopped. In other words, the SO _X releasing action is stopped. Thus the oxygen concentration COX is SO _X is released from the SO _X absorbent 14 is higher than the SO _X unabsorbed concentration COX1 is prevented. Also, advances since the time count value CS is counted up in the routine of FIG. 6 and FIG. 7 is a very large CMX from routine in step 68 of FIG. 6 and 7 to step 69, SO _X release flag is reset You. The other configuration and operation of the catalyst poisoning regeneration device are the same as those of the embodiment described with reference to FIG.

FIG. 13 shows still another embodiment. FIG.
Referring to FIG. 3, in this embodiment, an additional hydrogen injection valve 22 is provided in the exhaust pipe 16. This additional hydrogen injection valve 2
2 is connected to the cylinder 21. Further, an alkali metal on a carrier consisting of, for example alumina in the NO _X absorbent 17a in this embodiment, the alkaline earth oxide catalyst carrying a noble metal, such as without the platinum Pt to contain rare earth are brought together. The output port 37 of the electronic control unit 30 is connected to the additional hydrogen injection valve 22 via the corresponding drive circuit 43, and the additional hydrogen injection valve 22 is controlled based on an output signal from the electronic control unit 30. You.

As described above, when the air-fuel ratio of the inflowing exhaust gas is lean, oxygen O _{2 is} deposited on the surface of the NO _x absorbent 17a.
Is attached. However, for a while even if the air-fuel ratio of the exhaust gas flowing becomes rich NO _X absorbent 17a
And oxygen O ₂ may remain on the surface of, there is a possibility that SO _X is absorbed in the NO _X absorbent 17a when flowing into this time _the NO _X absorbent 17a.

Therefore, in this embodiment, the SO _X absorbent 14
Prior to the SO _X released from the NO _X absorbent 17a flowing into the NO _X absorbent 17a, hydrogen H ₂ is temporarily supplied from the additional hydrogen injection valve 22 to the NO _X absorbent 17a, whereby the NO _X absorbent 17a The remaining oxygen on the surface is quickly removed. As a result, the possibility that SO _X released from SO _X absorbent 14 is absorbed by NO _X absorbent 17a is further reduced.

In this case, hydrogen may be supplied from the additional hydrogen injection valve 22 at any timing as long as SO _X released from the SO _X absorbent 14 flows into the NO _X absorbent 17a. . However after the hydrogen supply from the additional hydrogen injection valve 22 has been completed, NO _X absorbent 1
It is not preferable that exhaust gas containing a relatively high concentration of oxygen flows into 7a. Therefore, in this embodiment, the oxygen concentration COX
Is supplied from the additional hydrogen injection valve 22 for a certain period of time when the concentration becomes lower than the SO _X non-absorption concentration COX 1. As a result, hydrogen H ₂ can be effectively used for removing residual oxygen.

By the way, as described above, in this embodiment,
NO_XAn oxidation catalyst is mixed in the absorbent 17a.
ing. Therefore, NO_XWater in absorbent 17a
Element H _TwoWhen a reducing agent such as_TwoAnd the rest
The reaction with the stored oxygen proceeds quickly. That is, the residual acid
Element can be removed in a very short time. That
As a result, the hydrogen injection time from the additional hydrogen injection valve 22 is extremely short
And therefore hydrogen H_TwoThe residual oxygen
It can be used more effectively for removal.

FIG. 14 shows a routine for calculating the hydrogen injection time QHH of the additional hydrogen injection valve 22. This routine is executed by interruption every predetermined set time. Also in this embodiment, the NO _X and SO _X absorption / release control routine shown in FIGS. 6 and 7 and the calculation routine of the hydrogen injection time QH of the hydrogen injection valve 20 shown in FIG. 8 are executed.

Referring to FIG. 14, first, at step 200,
In the oxygen concentration COX whether lower than SO _X unabsorbed concentration COX1 is determined. When COX ≧ COX1, the routine proceeds to step 201, where the hydrogen injection time QHH is set to zero. That is, the hydrogen injection from the additional hydrogen injection valve 22 is stopped. In the following step 202, the count value CB indicating the time during which hydrogen is injected from the additional hydrogen injection valve 22 is cleared.

On the other hand, when COX <COX1, the routine proceeds from step 200 to step 203, where it is determined whether or not the count value CB is larger than the fixed value CB1.
When the process proceeds to step 203 for the first time after COX <COX1, the condition of CB ≦ CB1 is satisfied.
Proceeding to 04, the hydrogen injection time QHH is set to QXX. That is, hydrogen injection from the additional hydrogen injection valve 22 is performed. This QXX is the hydrogen injection time required to quickly remove the residual oxygen in the NO _X absorbent 17. In the following step 205, the count value CB is incremented by one.

Next, when CB> CB1, the routine proceeds from step 203 to step 201, in which hydrogen injection from the additional hydrogen injection valve 22 is stopped. The other configuration and operation of the catalyst poisoning regeneration device are the same as those of the embodiment described with reference to FIG. FIG.
Shows still another embodiment.

Referring to FIG. 15, in this embodiment, NO
_The exhaust pipe 16 bypasses the _X absorbent 17 and the NO _X absorbent 1
7 a bypass pipe 25 connecting the exhaust pipe 19 downstream of the
And a bypass valve 27 provided at the exhaust inflow end of the bypass pipe 25 and driven by the actuator 26. The bypass valve 27 is normally closed, and connects the exhaust pipe 16 and the casing 18 to each other and cuts off communication between the exhaust pipe 16 and the bypass pipe 25. When the bypass valve 27 is opened, the communication between the exhaust pipe 16 and the casing 18 is cut off, and the exhaust pipe 16 and the bypass pipe 25 are connected with each other. The output port 37 of the electronic control unit 30 is connected to the corresponding drive circuit 43
And the actuator 26 is controlled based on an output signal from the electronic control unit 30.

[0070] SO _X from SO _X absorbent 14 when the exhaust gas temperature TS is higher than the upper limit threshold temperature UTS when the engine rotational speed integrated value SS is larger than a predetermined value SS1 in embodiments described so far No release action takes place. However, the exhaust temperature TS, that is, the SO _X absorbent 1
It is preferable to perform the SO _X releasing action irrespective of the temperature of (4). On the other hand, NO _X concentration of oxygen in the exhaust gas flowing into the absorbent 17 i.e. SO _X absorbent 14 in the exhaust flowing out from the oxygen concentration COX is SO _X nonabsorbable concentration COX1 SO _X from SO _X absorbent 14 is higher than There the SO _X will not be SO _X is absorbed in the nO _X absorbent 17 unless directed to _the nO _X absorbent 17 even if they are released.

Therefore, in the present embodiment, when the engine speed integrated value SS becomes larger than the fixed value SS1, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 14 is made rich regardless of the exhaust gas temperature TS and the bypass valve is provided. Open valve 27 and S
The exhaust gas flowing out of the O _X absorbent 14 to guide the bypass pipe 25, whereby SO _X absorbent 14 SO _X released from is to be prevented from flowing into the _the NO _X absorbent 17.

In this case, the hydrogen injection time QH of the hydrogen injection valve 20 is set to QS. The QS is hydrogen injection time required to be higher than rapidly SO _X release initiation temperature SRT exhaust temperature TS as described above, to lower than the oxygen concentration COX promptly SO _X nonabsorbable concentration COX1 Hydrogen injection time. Therefore, SS> SS
When the hydrogen injection becomes 1 and the oxygen concentration COX becomes SO
_X lower than the non-absorbed concentration COX1, while the exhaust gas temperature T
S is higher than the SO _X release initiation temperature SRT, SO _X is released from the SO _X absorbent 14 and thus. When the hydrogen injection is to be started and the exhaust temperature TS is higher than the SO _X release start temperature SRT, the SO _X is immediately released from the SO _X absorbent 14 immediately after the hydrogen injection.

SO_XSO of absorbent 14_XRelease action completed
Until the bypass valve 27 is open.
You may. However, when the bypass valve 27 is opened,
NO emitted from Seki_XExhaust pipe 1 without reduction
9, the bypass valve 27 can be opened for a period of time.
Preferably, it is only short. On the other hand, when the oxygen concentration COX is SO _X
After the concentration becomes lower than the non-absorbed concentration COX1, SO_Xabsorption
Exhaust from the agent 14 is NO_XEven if it leads to absorbent 17,
SO_XIs NO_XIt is not absorbed by the absorbent 17. So
In this embodiment, the oxygen concentration COX is SO_XNon-absorbed concentration
When it becomes lower than COX1, the bypass valve 27 is reset.
And close the valve and SO_XThe exhaust gas flowing out of the absorbent 14 is NO_X
It leads to the absorbent 14. As a result, NO_XSucking
SO in absorbent 17_XIs reduced while preventing absorption
NO that flows into the exhaust pipe 19 without_XReduce volume
be able to.

When the engine is running at a low load or when the engine is running at a low speed.
NO emitted from the engine during operation _XBecause the amount is small
When SO_XSO of absorbent 14_XIf release action is performed, reduction
NO that flows into the exhaust pipe 19 without being_XFurther quantity
Can be reduced. Therefore, in this embodiment, the exhaust
The temperature TS is higher than the lower threshold temperature LTS and the engine
The depression amount DEP of the accelerator pedal that indicates the load is set
Smaller than the set-in amount or the engine speed N is the set speed
Lower than SO_XJudge that release condition is satisfied
Other than SO_XJudge that release condition is not satisfied
I am trying to do it.

FIG. 16 shows the hydrogen injection time Q of the hydrogen injection valve 20.
A routine for calculating H and controlling the bypass valve 27 is shown. This routine is executed by interruption every predetermined set time. In this embodiment, the NO _X and SO _X absorption / release control routine shown in FIGS. 6 and 7 is also executed. Referring to FIG. 16, first, at step 280, it is determined whether or not the SO _X release flag is set. If the SO _X release flag has been reset, the process then proceeds to step 281 where it is determined whether the NO _X release flag has been set. NO
_{When the X} release flag has been reset, the routine proceeds to step 282, where the hydrogen injection time QH is set to zero. S
When the NO _X release flag is being reset while the O _X release flag is being reset, the process proceeds from step 281 to step 283, where QN is calculated from the map of FIG. In the following step 284, this QN is set as the hydrogen injection time QH.

When the SO _X release flag is set, the process proceeds from step 280 to step 285, where it is determined whether the oxygen concentration COX is lower than the SO _X non-absorption concentration COX1. When the process proceeds to step 285 for the first time after the SO _X release flag is set, COX ≧ COX1
Then, the process proceeds to step 286, where the bypass valve 2
7 is opened. Therefore, the exhaust gas flowing out of the SO _X absorbent 14 is guided into the bypass pipe 25, and the NO _X absorbent 1
7 is prevented from flowing. In the following step 287, QS is calculated from the map of FIG. In the following step 288, the hydrogen injection time QH is set to QS. That is, when the SO _X release flag is set, first,
The exhaust gas flowing out of the SO _X absorbent 14 becomes the NO _X absorbent 17
Hydrogen H ₂ is injected from the hydrogen injection valve 20 by QS while being prevented from flowing into the inside.

Next, when COX <COX1, it proceeds from step 285 to step 289, and the bypass valve 27 is closed. Next, the routine proceeds to steps 287 and 288, where the hydrogen injection time QH is set to QS. That is, CO
When X <COX1, the hydrogen injection time QH becomes QS
Exhausted from the SO _X absorbent 14 while maintaining
It is caused to flow into the O _X absorbent 17. The other configuration and operation of the catalyst poisoning regeneration device are the same as those of the embodiment described with reference to FIG.

In the embodiment described above, hydrogen H ₂ is injected from the hydrogen injection valve 20 in order to make the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 14 and the NO _X absorbent 17 rich. . However, when the present invention is applied to an in-cylinder direct injection internal combustion engine, the air-fuel ratio of the exhaust gas flowing into the SO _X absorbent 14 and the NO _X absorbent 17 by performing the secondary fuel injection during the engine expansion stroke or the exhaust stroke. Can be made rich. Alternatively, when the present invention is applied to a spark ignition type internal combustion engine, the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 3 is made rich to exhaust gas flowing into the SO _X absorbent 14 and the NO _X absorbent 17. Can also make the air-fuel ratio rich.

[0079] In addition, heat the SO _X absorbent 14 by the reaction heat of the reducing agent reducing agent supply such as hydrogen H ₂ to SO _X absorbent 14 in the time to heat the SO _X absorbent 14 in this embodiment I am trying to do it. However, SO _X
For example SO _X absorbent 14 to heat the absorbent 14 is heated directly, or can be provided an electric heater for heating the exhaust gas flowing into the SO _X absorbent 14. Alternatively, the present invention is applied to an in-cylinder direct injection internal combustion engine to perform secondary fuel injection during an engine expansion stroke or an exhaust stroke, thereby achieving SO _X
When the reducing agent (fuel) is supplied to the absorbent 14, the temperature of the exhaust gas discharged from the combustion chamber 3 is reduced by making the secondary fuel injection timing earlier than when the oxygen concentration COX should be reduced. Can be increased, thereby heating the SO _X absorbent 14. Further, when the present invention is applied to a spark ignition type internal combustion engine, the temperature of the exhaust gas discharged from the combustion chamber 3 can be increased by setting the ignition timing later than in the normal operation.

[0080]

Effect of the Invention NO_XOxygen concentration in exhaust gas flowing into the absorbent
Degree is SO_XSO until the concentration becomes lower than the non-absorbed concentration_Xabsorption
Agent to SO_XIs not released and the oxygen concentration is SO_XNon-absorbent
SO when the temperature is lower than_XIs released, so SO_Xabsorption
SO released from the agent_XIs NO _XIs absorbed by the absorbent
Can be prevented.

[Brief description of the drawings]

FIG. 1 is an overall view of a diesel engine.

FIG. 2 is a diagram for explaining the NO _X absorbing / releasing action of a NO _X absorbent.

FIG. 3 is a time chart for explaining NO _X absorption / release control.

FIG. 4 is a time chart for explaining SO _X absorption / release control.

FIG. 5 is a diagram showing hydrogen injection times QN, QOX, and QS.

FIG. 6 is a flowchart for executing NO _X and SO _X absorption / release control.

FIG. 7 is a flowchart for executing NO _X and SO _X absorption / release control.

FIG. 8 is a diagram showing set values CN1 and CS1.

FIG. 9 is a flowchart for calculating a hydrogen injection time QH.

FIG. 10 is a flowchart for calculating a hydrogen injection time QH according to another embodiment.

FIG. 11 is a flowchart for calculating a hydrogen injection time QH according to another embodiment.

FIG. 12 shows SO in the embodiment of FIGS. 10 and 11;
₆ is a time chart for explaining _X release control.

FIG. 13 is an overall view of a diesel engine according to still another embodiment.

FIG. 14 shows a hydrogen injection time QHH according to the embodiment of FIG.
Fig. 6 is a flowchart for calculating.

FIG. 15 is an overall view of a diesel engine according to still another embodiment.

FIG. 16 is a flowchart for calculating a hydrogen injection time QH and executing bypass control according to the embodiment of FIG. 13;

[Explanation of symbols]

1 ... engine body 13 ... exhaust manifold 14 ... SO _X absorbent 17 ... NO _X absorbent 20 ... hydrogen injection valves 22 ... additional hydrogen injection valve 25 ... bypass pipe 27 ... bypass valves 38 Temperature sensor 39 ... oxygen sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F01N 3/10 ZAB F01N 3/24 ZABE 3/20 ZAB B01D 53/34 132Z 3/24 53/36 103B ZAB

Claims (3)

[Claims] 1. A fuel ratio of the exhaust gas flowing absorbs NO _X when the lean, the oxygen concentration in the inflowing exhaust gas emits NO _X that is absorbed to be lower _the NO _X absorbent to the engine exhaust passage while disposed, the exhaust gas flowing into the air-fuel ratio is absorbed SO _X when the lean, the SO _X absorbent releases the SO _X being absorbed caused to the SO _X release state _the NO _X absorbent in the upstream placed in the engine exhaust passage, NO _X absorbing NO _X in the exhaust gas with a lean air-fuel mixture to absorb SO _X in the exhaust gas discharged into the engine exhaust passage when it is burned in the SO _X absorbent absorb the agent, releasing NO _X concentration of oxygen in the exhaust gas flowing to the NO _X absorbent is absorbed from _the NO _X absorbent when it is allowed to temporarily decrease, sO _X absorbent temporarily Absorbed from SO _X absorbent when exposed to SO _X release state In the catalyst poisoning regeneration apparatus for an internal combustion engine so as to release the SO _X being, N when it should emit SO _X from SO _X absorbent
The oxygen concentration in the exhaust gas flowing into the O _X absorbent and the oxygen concentration decreases means lower than SO _X nonabsorbable concentration of the NO _X absorbent, the oxygen concentration detecting the oxygen concentration in the exhaust gas flowing to the NO _X absorbent sensor and, when the oxygen concentration after the concentration of oxygen in the exhaust is caused to drop flowing into _the NO _X absorbent is higher than the SO _X nonabsorbable concentration by the oxygen concentration lowering means SO
_X absorbent is prohibited from becoming SO _X release state, and a SO _X release control means allowed to the SO _X absorbent SO _X release state when the oxygen concentration is lower than the SO _X nonabsorbable concentration Catalyst poisoning regeneration device for an internal combustion engine. Wherein the exhaust gas the oxygen concentration reducing means is provided with a hydrogenation means for adding hydrogen to SO _X absorbent, it flows into _the NO _X absorbent by reacting oxygen and hydrogen in the SO _X absorbent 2. The catalyst poisoning regeneration apparatus for an internal combustion engine according to claim 1, wherein the oxygen concentration of the catalyst is reduced. 3. A catalyst poisoning regeneration apparatus for an internal combustion engine according to claim 1, an oxidation catalyst was allowed mixed in _the NO _X absorbent.